Papermaking is the process of making paper, a substance which is used ubiquitously today for writing and packaging.
In papermaking a dilute suspension of fibers in water is drained through a screen, so that a mat of randomly interwoven fibers is laid down. Water is removed from this mat of fibers by pressing and drying to make paper. Most paper is made from wood pulp, but other fiber sources such as cotton and textiles may be used.
The history of papermaking can be traced to China about AD 105, when it was made by Cai Lun. Modern papermaking began in the early 1800s in Europe with the development of the Fourdrinier machine, which produces a continuous roll of paper rather than individual sheets. These machines have become very large, up to 500 feet (~150 m) in length, producing a sheet 400 inches (~10 m) wide, and operating at speeds of over 60 mph (100 km/h).
The technology was first transferred to Korea in 600 and then imported to Japan by a Buddhist priest, Dam Jing (曇徴) around 610 from Goguryeo, where bast fibers from the mulberry tree were used. Printing seems to have been invented in Japan, where 1000 prayers were printed for temples in 760 from stone 'blocks'. The idea went back to China, where the widespread use of paper also enhanced two innovations in the field of printing: woodblock printing by at least the 9th century (see the Diamond Sutra) and movable type printing, first invented by Bi Sheng (990-1051 AD) during the Song Dynasty.
Water was the problem for papermakers in the dry western part of China, and the slow westward progress of printing reflects experiments with different raw materials. Western paper was made from old clothes. In 751, the secret of papermaking reached Samarkand, in Central Asia, after papermakers were captured by the Arabs at the Battle of Talas. The method spread through the Arabic empire, and paper was first made in Baghdad during the time of Harun in 793.Soon after, the first paper mills were invented in Baghdad in 794, which transformed papermaking from an art into a major industry.
The secret of paper and silk manufacture had by then diffused to Damascus, and from there to the rest of the Muslim world, reaching India via Persia. It reached Western Europe via Islamic Spain: the earliest Christian book, or document, on paper was the 11th century Mozarab Missal of Silos, no doubt on Muslim-made paper. Production of paper moved to Italy in the 13th century. They used hemp and linen rags as a source of fiber. Rags from old clothing etc. were commonly bought by rag collectors and sold to paper makers. Bones were collected to make glue size to seal the paper.
The use of paper became increasingly common during the 14th century, and is documented as being manufactured in both Italy and Germany by 1400. Paper then spread rapidly, and was used for letters, records, old master prints, popular prints and manuscript books. Prints were initially in woodcut , and from the 1430s in engraving also.
A copy of the Gutenberg Bible, in the U.S. Library of Congress
But it was not until printing with movable type was invented that rag paper became more popular. Parchment was not ideal for printing, being expensive and susceptible to humidity. Paper on the other hand was ideal. But as the demand for books rose, the supply of rags became more and more inadequate and other sources of fiber were actively sought.
By the time of the invention of movable type printing in Germany about 1450, paper was readily available, although still expensive. Vellum remained in use as well, and it was on this that the most expensive copies of the Gutenberg Bible were first printed.
In America, archaeological evidence indicates that paper was invented by the Mayas no later than the 5th century AD.Called Amate, it was in widespread use among Mesoamerican cultures until the Spanish conquest. In small quantities, traditional Maya papermaking techniques are still practiced today.
The Bataks, living in Sumatra, sometimes use as writing material long strips of bamboo, welded by "beating" them together, then folded together, accordion-like, between wooden covers, and bound together with a string of woven rushes. Often long strips of the thin bark of trees -- such books being known as pustakas -- are used. Specimens of writing on bark from India are preserved in the British Museum. The people of the Malabar coast also frequently wrote upon bark with a stylus. Ancient books of the Bataks were written in ink on paper made of bark. The Lampong and Rendjang tribes, also inhabiting Sumatra, scratch their messages and books on bamboo, tree bark, or certain kinds of leaves.
2008年11月11日星期二
Die making
Die making is the process of creating a tool for the manufacturing of precisely shaped objects from a stock of workable material. Dies are typically made from steel, and are applied to a medium under pressure to cut out parts that are used in finished manufactured goods. For example, a die might be used to make many small metal parts for a mechanical assembly, to cut rubber parts in shoemaking, or to cut paper parts for stationery or box-board products. Die makers are skilled craftspeople who typically learn their trade through a combination of academic course-work, hands-on instruction and a substantial apprentice period.
In the common die cutting of materials like paper, cardboard and the like, the tool of choice is the steel rule die. The die maker creates a shape from a thin, blade-like steel strip with a sharpened edge which is attached to a high-density plywood base. The steel rule acts like a cookie-cutter to stamp out parts from the material of choice. Computerized machines can cut and form the steel rule to the specification of the design. The steel rule shape and height above the substrate can result in a cut, a crease-mark or a perforation.
Because making the Master Hub takes a lot of time and work, it is used very few times. When needed, it is put into a special hubbing press, which exerts a pressure of approximately 1500 short tons-force per square inch (21 GPa), forcing the image of the Master Hub into the Master Die. The Master Die is then used to form as many Working Hubs as needed through the same process, and then the Working Hubs are put through the same process to form the Working Dies. These Working Dies are the actual dies which will strike coins. The process of transferring the Hub to the Die can be repeated as many times as necessary in order to form the number of dies needed to make the amount of coins required. The difference between a Hub and a Die is that the Hub has a raised image and a Die has an incuse image, so one forms the other. When making Working Dies, the Mint has found that by using a lower amount of pressure in the hubbing press, they can prolong the life of the Hubs and Dies used. In between each hubbing, however, the die being made must be subjected to an annealing furnace to soften the steel, making it easier to push the image into the Die. As the Die is compressed in the hubbing press, the molecular structure of the steel changes. The large amount of pressure exerted on the steel forces the molecules of the steel to be compacted, making this hubbed die much stronger and denser. In the field of metallurgy this is called work hardening, and it is necessary to anneal the steel in order to get it malleable again. If, when the die is subjected to another hubbing, it is not lined up exactly with the hub, the result is a secondary image, or doubling. This is called hub doubling, and results in such spectacular coins as the famous 1955 doubled die cent.
Laser cutting
Laser cutters usually work much like a milling machine would for working a sheet in that the laser (equivalent to the mill) enters through the side of the sheet and cuts it through the axis of the beam. In order to be able to start cutting from somewhere else than the edge, a pierce is done before every cut. Piercing usually involves a high power pulsed laser beam which slowly (taking around 5-15 seconds for half-inch thick stainless steel, for example) makes a hole in the material.
There are many different methods in cutting using lasers, with different types used to cut different material. Some of the methods are vaporization, melt and blow, melt blow and burn, thermal stress cracking, scribing, cold cutting and burning stabilized laser cutting.
Vaporization cutting
In vaporization cutting the focused beam heats the surface of the material to boiling point and generates a keyhole. The keyhole leads to a sudden increase in absorptivity quickly deepening the hole. As the hole deepens and the material boils, vapor generated erodes the molten walls blowing ejecta out and further enlarging the hole. Non melting material such as wood, carbon and thermoset plastics are usually cut by this method.
Melt and blow
Melt and blow or fusion cutting uses high pressure gas to blow molten material from the cutting area, greatly decreasing the power requirement. First the material is heated to melting point then a gas jet blows the molten material out of the kerf avoiding the need to raise the temperature of the material any further. Materials cut with this process are usually metals.
Thermal stress cracking
Brittle materials are particularly sensitive to thermal fracture, a feature exploited in thermal stress cracking. A beam is focused on the surface causing localized heating and thermal expansion. This results in a crack that can then be guided by moving the beam. The crack can be moved in order of m/s. It is usually used in cutting of glass.
Burning stabilized laser gas cutting
Burning stabilized laser cutting is essentially oxygen cutting but with a laser beam as the ignition source. This process can be used to cut very thick steel plates with relatively little laser power.
Machine configurations
There are generally three different configurations of industrial laser cutting machines: Moving material, Hybrid, and Flying Optics systems. These refer to way that the laser beam is moved over the material to be cut or processed. For all of these, the axes of motion are typically designated X and Y. axis. If the cutting head may be controlled, it is designated as the Z-axis.
Moving material lasers have a stationary cutting head and move the material under it. This method provides a constant distance from the laser generator to the workpiece and a single point from which to remove cutting effluent. It requires fewer optics, but requires moving the workpiece.
Hybrid lasers provide a table which moves in one axis (usually the X-axis) and move the head along the shorter (Y) axis. This results in a more constant beam delivery path length than a flying optic machine and may permit a simpler beam delivery system. This can result in reduced power loss in the delivery system and more capacity per watt than flying optics machines.
Flying optics lasers feature a stationary table and a cutting head (with laser beam) that moves over the work piece in both of the horizontal dimensions. Flying-optics cutters keep the workpiece stationary during processing, and often don't require material clamping. The moving mass is constant, so dynamics aren't affected by varying size and thickness of workpiece. Flying optics machines are the fastest class of machines, with higher accelerations and peak velocities than hybrid or moving material systems.
Dual Pallet Flying Optics Laser
Flying optic machines must use some method to take into account the changing beam length from near field (close to resonator) cutting to far field (far away from resonator) cutting. Common methods for controlling this include collimation, adaptive optics or the use of a constant beam length axis.
The above is written about X-Y systems for cutting flat materials. The same discussion applies to five and six-axis machines, which permit cutting formed workpieces. In addition, there are various methods of orienting the laser beam to a shaped workpiece, maintaining a proper focus distance and nozzle standoff, etc.
There are many different methods in cutting using lasers, with different types used to cut different material. Some of the methods are vaporization, melt and blow, melt blow and burn, thermal stress cracking, scribing, cold cutting and burning stabilized laser cutting.
Vaporization cutting
In vaporization cutting the focused beam heats the surface of the material to boiling point and generates a keyhole. The keyhole leads to a sudden increase in absorptivity quickly deepening the hole. As the hole deepens and the material boils, vapor generated erodes the molten walls blowing ejecta out and further enlarging the hole. Non melting material such as wood, carbon and thermoset plastics are usually cut by this method.
Melt and blow
Melt and blow or fusion cutting uses high pressure gas to blow molten material from the cutting area, greatly decreasing the power requirement. First the material is heated to melting point then a gas jet blows the molten material out of the kerf avoiding the need to raise the temperature of the material any further. Materials cut with this process are usually metals.
Thermal stress cracking
Brittle materials are particularly sensitive to thermal fracture, a feature exploited in thermal stress cracking. A beam is focused on the surface causing localized heating and thermal expansion. This results in a crack that can then be guided by moving the beam. The crack can be moved in order of m/s. It is usually used in cutting of glass.
Burning stabilized laser gas cutting
Burning stabilized laser cutting is essentially oxygen cutting but with a laser beam as the ignition source. This process can be used to cut very thick steel plates with relatively little laser power.
Machine configurations
There are generally three different configurations of industrial laser cutting machines: Moving material, Hybrid, and Flying Optics systems. These refer to way that the laser beam is moved over the material to be cut or processed. For all of these, the axes of motion are typically designated X and Y. axis. If the cutting head may be controlled, it is designated as the Z-axis.
Moving material lasers have a stationary cutting head and move the material under it. This method provides a constant distance from the laser generator to the workpiece and a single point from which to remove cutting effluent. It requires fewer optics, but requires moving the workpiece.
Hybrid lasers provide a table which moves in one axis (usually the X-axis) and move the head along the shorter (Y) axis. This results in a more constant beam delivery path length than a flying optic machine and may permit a simpler beam delivery system. This can result in reduced power loss in the delivery system and more capacity per watt than flying optics machines.
Flying optics lasers feature a stationary table and a cutting head (with laser beam) that moves over the work piece in both of the horizontal dimensions. Flying-optics cutters keep the workpiece stationary during processing, and often don't require material clamping. The moving mass is constant, so dynamics aren't affected by varying size and thickness of workpiece. Flying optics machines are the fastest class of machines, with higher accelerations and peak velocities than hybrid or moving material systems.
Dual Pallet Flying Optics Laser
Flying optic machines must use some method to take into account the changing beam length from near field (close to resonator) cutting to far field (far away from resonator) cutting. Common methods for controlling this include collimation, adaptive optics or the use of a constant beam length axis.
The above is written about X-Y systems for cutting flat materials. The same discussion applies to five and six-axis machines, which permit cutting formed workpieces. In addition, there are various methods of orienting the laser beam to a shaped workpiece, maintaining a proper focus distance and nozzle standoff, etc.
Steel engraving
Steel engraving, is a commercial engraving technique for printing illustrations, based on steel instead of copper. It has been rarely used in artistic printmaking, although was much used for reproductions in the 19th century. Steel engraving was introduced in 1792 by Jacob Perkins (1766-1849), an American Inventor, for the use of banknote printing. When Perkins moved to London in 1818, the technique in 1820 became adapted by Charles Warren and especially by Charles Heath (1785-1848) for Thomas Campbell's Pleasures of Hope with the first published plates engraved on steel. The new technique only partially replaced the other commercial techniques of that time as woodcut, wood engraving, and later lithography. All the illustrations of the Encyclopedia Britannica of 1911 are steel engravings.
Most engraving is done by laying out the broad, general outline onto the plate first. This is commonly referred to simply as etching. After this step is complete the artist can move to strictly engraving the work. The tool most commonly used for engraving is the burin, which is a small bar of hardened steel with a sharp point. This is pushed along the plate to produce thin strips of waste metal and thin furrows. This is followed by a scraper which removes any burs as they will be an impediment to the ink. It is important to note that engraving must be done in the reverse or mirror image, so that the image faces the correct way when the die prints. One trick of the trade was for engravers to look at the object that they were engraving through a mirror so that the image was naturally reversed and they would be less likely to engrave the image incorrectly. Steel plates can be case hardened to ensure that they can print thousands of times with little wear. Copper plates can not be case hardened but can be steel-faced or nickel-plated to increase their life expectancy.
Until around 1820 copper plates were the common medium used for engraving. Copper, being a soft metal, was easy to carve or engrave and would strike a few hundred copies before the image began to severely deteriorate from wear. Engravers would then rework a worn plate retracing the previous engraving to sharpen the image again. Another advantage to using copper is due simply to the fact that it is a soft metal and can be corrected or updated with a reasonable degree of ease. For this vary reason, copper plates were the preferred medium of printing for mapmakers who would have to change their maps with newly discovered, claimed land, or that which had changed hands.
During the 1820s steel began to replace copper as the preferred medium of commercial publishers for illustration, replacing etching but rivalled still by wood engraving and later lithography. This produced plates with shaper, harder, more distinct lines. Also, the harder steel plates produced much longer wearing dies that could strike thousands of copies before they would need any repair or refurbishing engraving. The hardness of steel also allowed for much finer detail than would have been possible under copper which would have quickly deteriorated under the stress. As the nineteenth century began to close, devices such as the ruling machine made even greater detail possible allowing for more exact parallel lines in a very close proximity. Commercial etching techniques also gradually replaced it.
Steel engraving is still done today but to a much lesser extent. Today, most printing is done using computerized stencils that transfer ink instead of a steel plate. The exception to this is currency which is still printed using steel dies. By using actual steel engraved dies, each bill has a character and feeling that is very difficult for counterfeiters to duplicate. An engraved plate allows the ink to be slightly raised and the paper to be slightly pressed that produces a different sensation that is felt with a stencil ink transfer.
Most engraving is done by laying out the broad, general outline onto the plate first. This is commonly referred to simply as etching. After this step is complete the artist can move to strictly engraving the work. The tool most commonly used for engraving is the burin, which is a small bar of hardened steel with a sharp point. This is pushed along the plate to produce thin strips of waste metal and thin furrows. This is followed by a scraper which removes any burs as they will be an impediment to the ink. It is important to note that engraving must be done in the reverse or mirror image, so that the image faces the correct way when the die prints. One trick of the trade was for engravers to look at the object that they were engraving through a mirror so that the image was naturally reversed and they would be less likely to engrave the image incorrectly. Steel plates can be case hardened to ensure that they can print thousands of times with little wear. Copper plates can not be case hardened but can be steel-faced or nickel-plated to increase their life expectancy.
Until around 1820 copper plates were the common medium used for engraving. Copper, being a soft metal, was easy to carve or engrave and would strike a few hundred copies before the image began to severely deteriorate from wear. Engravers would then rework a worn plate retracing the previous engraving to sharpen the image again. Another advantage to using copper is due simply to the fact that it is a soft metal and can be corrected or updated with a reasonable degree of ease. For this vary reason, copper plates were the preferred medium of printing for mapmakers who would have to change their maps with newly discovered, claimed land, or that which had changed hands.
During the 1820s steel began to replace copper as the preferred medium of commercial publishers for illustration, replacing etching but rivalled still by wood engraving and later lithography. This produced plates with shaper, harder, more distinct lines. Also, the harder steel plates produced much longer wearing dies that could strike thousands of copies before they would need any repair or refurbishing engraving. The hardness of steel also allowed for much finer detail than would have been possible under copper which would have quickly deteriorated under the stress. As the nineteenth century began to close, devices such as the ruling machine made even greater detail possible allowing for more exact parallel lines in a very close proximity. Commercial etching techniques also gradually replaced it.
Steel engraving is still done today but to a much lesser extent. Today, most printing is done using computerized stencils that transfer ink instead of a steel plate. The exception to this is currency which is still printed using steel dies. By using actual steel engraved dies, each bill has a character and feeling that is very difficult for counterfeiters to duplicate. An engraved plate allows the ink to be slightly raised and the paper to be slightly pressed that produces a different sensation that is felt with a stencil ink transfer.
Electronic waste
Electronic waste, "e-waste" or "Waste Electrical and Electronic Equipment" ("WEEE") is a waste type consisting of any broken or unwanted electrical or electronic device. Recyclable electronic waste is sometimes further categorized as a "commodity" while e-waste which cannot be reused is distinguished as "waste". Both types of e-waste have raised concern considering that many components of such equipment are considered toxic and are not biodegradable. Responding to these concerns, many European countries banned e-waste from landfills in the 1990s. As the price of gold, silver and copper continue to rise, e-waste has become more desirable. E-waste roundups can be used as fundraises in some communities.
The European Union would further advance e-waste policy in Europe by implementing the Waste Electrical and Electronic Equipment Directive in 2002 which holds manufacturers responsible for e-waste disposal at end-of-life. Similar legislation has been enacted in Asia, with e-waste legislation in the United States limited to the state level due to stalled efforts in the United States Congress regarding multiple e-waste legislation bills.
Due to the difficulty and cost of recycling used electronics as well as lacklustre enforcement of legislation regarding e-waste exports, large amounts of used electronics have been sent to countries such as China, India, and Kenya, where lower environmental standards and working conditions make processing e-waste more profitable.
Some activists define "Electronic waste" to include all secondary computers, entertainment devices electronics, mobile phones and other items, whether they have been sold, donated, or discarded by their original owner. This definition includes used electronics which are destined for reuse, resale, salvage, recycling or disposal. Others define the reusable (working and repairable electronics) and secondary scrap (copper, steel, plastic, etc.) to be "commodities", and reserve the use of the term "waste" for residue or material which was represented as working or repairable but which was discarded by the buyer.
Debate continues over the distinction between "commodity" and "waste" electronics definitions. Some exporters may deliberately leave obsolete or non-working equipment mixed in loads of working equipment (through ignorance, or to avoid more costly treatment processes for 'bad' equipment). On the other hand, some importing countries specifically seek to exclude working or repairable equipment in order to protect domestic manufacturing markets. "White box" computers ('off-brand' or 'no name' computers) are often assembled by smaller scale manufacturers utilizing refurbished components. These 'white box' sales accounted for approximately 45% of all computer sales worldwide by 2004, and are considered a threat to some large manufacturers, who therefore seek to classify used computers as 'waste'.
While a protectionist may broaden the definition of "waste" electronics, the high value of working and reusable laptops, computers, and components (e.g. RAM), can help pay the cost of transportation for a large number of worthless "commodities". Broken monitors, obsolete circuit boards, short circuited transistors, and other junk are difficult to spot in a containerload of used electronics.
Until such time as equipment no longer contains such hazardous substances, the disposal and recycling operations must be undertaken with great care to avoid damaging pollution and workplace hazards, and exports need to be monitored to avoid "toxics along for the ride".
The European Union would further advance e-waste policy in Europe by implementing the Waste Electrical and Electronic Equipment Directive in 2002 which holds manufacturers responsible for e-waste disposal at end-of-life. Similar legislation has been enacted in Asia, with e-waste legislation in the United States limited to the state level due to stalled efforts in the United States Congress regarding multiple e-waste legislation bills.
Due to the difficulty and cost of recycling used electronics as well as lacklustre enforcement of legislation regarding e-waste exports, large amounts of used electronics have been sent to countries such as China, India, and Kenya, where lower environmental standards and working conditions make processing e-waste more profitable.
Some activists define "Electronic waste" to include all secondary computers, entertainment devices electronics, mobile phones and other items, whether they have been sold, donated, or discarded by their original owner. This definition includes used electronics which are destined for reuse, resale, salvage, recycling or disposal. Others define the reusable (working and repairable electronics) and secondary scrap (copper, steel, plastic, etc.) to be "commodities", and reserve the use of the term "waste" for residue or material which was represented as working or repairable but which was discarded by the buyer.
Debate continues over the distinction between "commodity" and "waste" electronics definitions. Some exporters may deliberately leave obsolete or non-working equipment mixed in loads of working equipment (through ignorance, or to avoid more costly treatment processes for 'bad' equipment). On the other hand, some importing countries specifically seek to exclude working or repairable equipment in order to protect domestic manufacturing markets. "White box" computers ('off-brand' or 'no name' computers) are often assembled by smaller scale manufacturers utilizing refurbished components. These 'white box' sales accounted for approximately 45% of all computer sales worldwide by 2004, and are considered a threat to some large manufacturers, who therefore seek to classify used computers as 'waste'.
While a protectionist may broaden the definition of "waste" electronics, the high value of working and reusable laptops, computers, and components (e.g. RAM), can help pay the cost of transportation for a large number of worthless "commodities". Broken monitors, obsolete circuit boards, short circuited transistors, and other junk are difficult to spot in a containerload of used electronics.
Until such time as equipment no longer contains such hazardous substances, the disposal and recycling operations must be undertaken with great care to avoid damaging pollution and workplace hazards, and exports need to be monitored to avoid "toxics along for the ride".
Relay
A simple electromagnetic relay, such as the one taken from a car in the first picture, is an adaptation of an electromechanical solenoid. It consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a moveable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energised there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the Printed Circuit Board (PCB) via the yoke, which is soldered to the PCB.
When an electric current is passed through the coil, the resulting magnetic field attracts the armature, and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. If the set of contacts was closed when the relay was de-energised, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.
If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to circuit components. Some automotive relays already include that diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle.
By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a thyristor or other solid-state switching device. To achieve electrical isolation an optocoupler can be used which is a light-emitting diode (LED) coupled with a photo transistor.
When an electric current is passed through the coil, the resulting magnetic field attracts the armature, and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. If the set of contacts was closed when the relay was de-energised, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.
If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to circuit components. Some automotive relays already include that diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle.
By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a thyristor or other solid-state switching device. To achieve electrical isolation an optocoupler can be used which is a light-emitting diode (LED) coupled with a photo transistor.
History of the battery
The first battery was invented in 1800 by Alessandro Volta. Although it was of great value for experimental purposes, its limitations made it impractical for large current drain. Later batteries, starting with John Frederic Daniell's wet cell in 1836, provided more reliable currents and were adopted by industry for use in stationary devices, particularly in telegraph networks where, in the days before electrical distribution networks, they were the only practical source of electricity.These so-called wet cells used liquid electrolytes, and were thus prone to leaks and spillage if not handled correctly. Some, like the gravity cell, could only function in a certain orientation. Many used glass jars to hold their components, which made them fragile. These practical flaws made them unsuitable for portable appliances. Near the end of the 19th century, the invention of dry cell batteries, which replaced liquid electrolyte with a paste, made portable electrical devices practical.
In 1780, Luigi Galvani was dissecting a frog affixed to a brass hook. When he touched its leg with his iron scalpel, the leg twitched. Galvani believed the energy that drove this contraction came from the leg itself, and called it "animal electricity".
However, Alessandro Volta, a friend and fellow scientist, disagreed, believing this phenomenon was actually caused by two different metals being joined together by a moist intermediary. He experimentally verified this hypothesis, and published it in 1791. In 1800 Volta invented the first true battery which came to be known as the Voltaic Pile. The Voltaic Pile consisted of pairs of copper and zinc discs piled on top of each other, separated by a layer of cloth or cardboard soaked in brine (i.e. the electrolyte). Unlike the Leyden jar, the Voltaic Pile produced a continuous and stable current, and lost little charge over time when not in use, though his early models could not produce a voltage strong enough to produce sparks.He experimented with various metals and found that zinc and silver gave the best results.
Volta believed the current was the result of two different materials simply touching each other—an obsolete scientific theory known as contact tension—and not the result of chemical reactions. Consequently, he regarded the corrosion of the zinc plates as an unrelated flaw that could perhaps be fixed by changing the materials somehow. However, no scientist ever succeeded in preventing this corrosion. In fact, it was observed that the corrosion was faster when a higher current was drawn. This suggested that the corrosion was actually integral the battery's ability to produce a current. This, in part, led to the rejection of Volta's contact tension theory in favor of electrochemical theory. Volta's illustrations of his Crown of Cups and Voltaic Pile (first figure, above), have extra metal disks, now know to be unnecessary, on both the top and the bottom. The figure associated with this section, of the zinc-copper voltaic pile, has the modern design, an indication that "contact tension" is not the source of electromotive force for the voltaic pile.
The trough battery, which was basically a Voltaic Pile laid down to prevent electrolyte leakage.
Volta's original pile models had some technical flaws, one of them involving the electrolyte leaking and causing short-circuits due to the weight of the discs compressing the brine-soaked cloth. An Englishman named William Cruickshank solved this problem by laying the elements in a box instead of piling them in a stack. This was known as the trough battery.Volta himself invented a variant which consisted of a chain of cups filled with a salt solution, linked together by metallic arcs dipped into the liquid. This was known as the Crown of Cups. These arcs were made of two different metals (eg zinc and copper) soldered together. This model also proved to be more efficient than his original piles,though it didn't prove as popular.
Another problem with Volta's batteries was short battery life (an hour's worth at best), which was caused by two phenomena. The first was that the current produced electrolysed the electrolyte solution, resulting in a film of hydrogen bubbles forming on the copper, which steadily increased the internal resistance of the battery (This effect, called polarization, is counteracted in modern cells by additional measures). The other was a phenomenon called local action, wherein minute short-circuits would form around impurities in the zinc, causing the zinc to degrade. The latter problem was solved in 1835 by William Sturgeon, who found that mixing some mercury into the zinc eliminated the local action.
In 1780, Luigi Galvani was dissecting a frog affixed to a brass hook. When he touched its leg with his iron scalpel, the leg twitched. Galvani believed the energy that drove this contraction came from the leg itself, and called it "animal electricity".
However, Alessandro Volta, a friend and fellow scientist, disagreed, believing this phenomenon was actually caused by two different metals being joined together by a moist intermediary. He experimentally verified this hypothesis, and published it in 1791. In 1800 Volta invented the first true battery which came to be known as the Voltaic Pile. The Voltaic Pile consisted of pairs of copper and zinc discs piled on top of each other, separated by a layer of cloth or cardboard soaked in brine (i.e. the electrolyte). Unlike the Leyden jar, the Voltaic Pile produced a continuous and stable current, and lost little charge over time when not in use, though his early models could not produce a voltage strong enough to produce sparks.He experimented with various metals and found that zinc and silver gave the best results.
Volta believed the current was the result of two different materials simply touching each other—an obsolete scientific theory known as contact tension—and not the result of chemical reactions. Consequently, he regarded the corrosion of the zinc plates as an unrelated flaw that could perhaps be fixed by changing the materials somehow. However, no scientist ever succeeded in preventing this corrosion. In fact, it was observed that the corrosion was faster when a higher current was drawn. This suggested that the corrosion was actually integral the battery's ability to produce a current. This, in part, led to the rejection of Volta's contact tension theory in favor of electrochemical theory. Volta's illustrations of his Crown of Cups and Voltaic Pile (first figure, above), have extra metal disks, now know to be unnecessary, on both the top and the bottom. The figure associated with this section, of the zinc-copper voltaic pile, has the modern design, an indication that "contact tension" is not the source of electromotive force for the voltaic pile.
The trough battery, which was basically a Voltaic Pile laid down to prevent electrolyte leakage.
Volta's original pile models had some technical flaws, one of them involving the electrolyte leaking and causing short-circuits due to the weight of the discs compressing the brine-soaked cloth. An Englishman named William Cruickshank solved this problem by laying the elements in a box instead of piling them in a stack. This was known as the trough battery.Volta himself invented a variant which consisted of a chain of cups filled with a salt solution, linked together by metallic arcs dipped into the liquid. This was known as the Crown of Cups. These arcs were made of two different metals (eg zinc and copper) soldered together. This model also proved to be more efficient than his original piles,though it didn't prove as popular.
Another problem with Volta's batteries was short battery life (an hour's worth at best), which was caused by two phenomena. The first was that the current produced electrolysed the electrolyte solution, resulting in a film of hydrogen bubbles forming on the copper, which steadily increased the internal resistance of the battery (This effect, called polarization, is counteracted in modern cells by additional measures). The other was a phenomenon called local action, wherein minute short-circuits would form around impurities in the zinc, causing the zinc to degrade. The latter problem was solved in 1835 by William Sturgeon, who found that mixing some mercury into the zinc eliminated the local action.
Antique radio
Early transistor radios
The invention of the transistor made it possible to produce small portable radios that did not need a warm-up time, and ran on much smaller batteries. They were convenient and chic, though the prices were high and the sound quality not so good.
Transistor radios were available in many sizes from console to table-top to matchbox. Transistors are still used in today's radios, though the integrated circuit containing a large number of transistors has surpassed the use of singly packed transistors for the majority of radio circuitry.
Transistor radios appeared on the market in 1949, but at a high price. By the 1960s, reduced prices and the desire for portability made them very popular.
There was something of a marketing war over the number of transistors sets contained, with many models named after this number. Some sets even had non-functional reject transistors soldered to the circuit board, doing absolutely nothing, so the sales pitch could advertise a higher number of transistors.
Vacuum tube radios and early transistor radios were hand assembled. Today radios are designed with the assistance of computers and manufactured with much greater use of machinery.
Today's radios are usually uneconomic to repair because mass production and technological improvements in numerous areas have made them so cheap to buy, while the cost of human labour and workshop overheads have not fallen in real terms.
Early American sets - Regency, Motorola
Sony TR series like the TR-55
Typical insides of an antique radio, showing the vacuum tubes.
Car radios
Pre-war car radios were experimental only. They required a large aerial, reception was inconsistent, they required adjustment in use, which was not very practical. And they were of course not the most useful place to put an expensive radio.
All early car radios used a vibrator power supply to step up the low voltage to HT for the valves. Vibrator supplies are known for reliability issues, and produce radio interference and some mechanical noise.
Later car radios used valves that ran on 12v HT, eliminating the vibrator.
The 3rd generation of car radios were valve sets with a single output transistor, and makers were very keen to promote these as transistor sets. Some historic car radios badged as transistorised are in reality these hybrid valve sets.
All-transistor sets eventually took over from valves as prices fell.
The invention of the transistor made it possible to produce small portable radios that did not need a warm-up time, and ran on much smaller batteries. They were convenient and chic, though the prices were high and the sound quality not so good.
Transistor radios were available in many sizes from console to table-top to matchbox. Transistors are still used in today's radios, though the integrated circuit containing a large number of transistors has surpassed the use of singly packed transistors for the majority of radio circuitry.
Transistor radios appeared on the market in 1949, but at a high price. By the 1960s, reduced prices and the desire for portability made them very popular.
There was something of a marketing war over the number of transistors sets contained, with many models named after this number. Some sets even had non-functional reject transistors soldered to the circuit board, doing absolutely nothing, so the sales pitch could advertise a higher number of transistors.
Vacuum tube radios and early transistor radios were hand assembled. Today radios are designed with the assistance of computers and manufactured with much greater use of machinery.
Today's radios are usually uneconomic to repair because mass production and technological improvements in numerous areas have made them so cheap to buy, while the cost of human labour and workshop overheads have not fallen in real terms.
Early American sets - Regency, Motorola
Sony TR series like the TR-55
Typical insides of an antique radio, showing the vacuum tubes.
Car radios
Pre-war car radios were experimental only. They required a large aerial, reception was inconsistent, they required adjustment in use, which was not very practical. And they were of course not the most useful place to put an expensive radio.
All early car radios used a vibrator power supply to step up the low voltage to HT for the valves. Vibrator supplies are known for reliability issues, and produce radio interference and some mechanical noise.
Later car radios used valves that ran on 12v HT, eliminating the vibrator.
The 3rd generation of car radios were valve sets with a single output transistor, and makers were very keen to promote these as transistor sets. Some historic car radios badged as transistorised are in reality these hybrid valve sets.
All-transistor sets eventually took over from valves as prices fell.
Oxy-fuel welding and cutting
Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively.
Side of metal, cut by oxygen - propane cutting torch
In oxy-fuel welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal. The molten pool is generally supplied with additional metal called filler. Filler material depends upon the metals to be welded.
In oxy-fuel cutting, a cutting torch is used to heat metal to kindling temperature. A stream of oxygen then trained on the metal combines with the metal which then flows out of the cut (kerf) as an oxide slag .
Torches that do not mix fuel with oxygen (combining, instead, atmospheric air) are not considered oxy-fuel torches and can typically be identified by a single tank (Oxy-fuel welding/cutting generally requires two tanks, fuel and oxygen). Most metals cannot be melted with a single-tank torch. As such, single tank torches are typically used only for soldering and brazing, rather than welding.
Note: Sometimes a metal-cutting torch is colloquially called a "gas-axe", "smoke wrench", "hot wrench", "blue wrench" or "hot blue spanner" (in Britain). Colloquially, many people mistakenly call a welding torch a blowtorch. In the USA the word blowtorch is also used for what in Britain is called a blowlamp.
The apparatus used in gas welding consists basically of an oxygen source and a fuel gas source (usually cylinders), two pressure regulators and two flexible hoses (one of each for each cylinder), and a torch. This sort of torch can also be used for soldering and brazing. The cylinders are often carried in a special wheeled trolley.
There have been examples of oxyhydrogen cutting sets with small (scuba-sized) gas cylinders worn on the user's back in a backpack harness, for rescue work and similar.
There are also examples of pressurized liquid fuel cutting torches, usually using gasoline. These are used for their increased portability.
Regulator
Main article: Pressure regulator
The regulator is used to control pressure from the tanks by reducing pressure and regulating flow rate. Oxy-gas regulators usually have two stages: The first stage of the regulator releases the gas at a constant rate from the cylinder despite the pressure in the cylinder becoming less as the gas in the cylinder is used, as in the first stage of a scuba-diving regulator. The second stage of the regulator controls the pressure reduction from the intermediate pressure to low pressure. It is constant flow. The valve assembly has two pressure gauges, one indicating cylinder pressure, the other indicating hose pressure.
Some oxy-gas regulators only have one stage, and one pressure gauge. With those the gas flow gets less as the cylinder pressure drops.
Gas hoses
The hoses used are specifically designed for welding and cutting. The hose is usually a double-hose design, meaning that there are two hoses joined together. The oxygen hose is green and the fuel hose is red. The type of gas the hose will be carrying is important because the connections will have different threads for different types of gas. Fuel gases (red) will use left-hand threads and a groove cut into the nut, while the oxygen (green) will use right-hand threads. This is a safety precaution to prevent hoses from being hooked up the wrong way.
There are basically two types of connections that can be used. The first is using a jubilee clip. The second option is using a crimped connector. The second option is probably safer as it is harder for this type of connection to come loose. The hoses should also be clipped together at intervals approximately 3 feet apart.
Side of metal, cut by oxygen - propane cutting torch
In oxy-fuel welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal. The molten pool is generally supplied with additional metal called filler. Filler material depends upon the metals to be welded.
In oxy-fuel cutting, a cutting torch is used to heat metal to kindling temperature. A stream of oxygen then trained on the metal combines with the metal which then flows out of the cut (kerf) as an oxide slag .
Torches that do not mix fuel with oxygen (combining, instead, atmospheric air) are not considered oxy-fuel torches and can typically be identified by a single tank (Oxy-fuel welding/cutting generally requires two tanks, fuel and oxygen). Most metals cannot be melted with a single-tank torch. As such, single tank torches are typically used only for soldering and brazing, rather than welding.
Note: Sometimes a metal-cutting torch is colloquially called a "gas-axe", "smoke wrench", "hot wrench", "blue wrench" or "hot blue spanner" (in Britain). Colloquially, many people mistakenly call a welding torch a blowtorch. In the USA the word blowtorch is also used for what in Britain is called a blowlamp.
The apparatus used in gas welding consists basically of an oxygen source and a fuel gas source (usually cylinders), two pressure regulators and two flexible hoses (one of each for each cylinder), and a torch. This sort of torch can also be used for soldering and brazing. The cylinders are often carried in a special wheeled trolley.
There have been examples of oxyhydrogen cutting sets with small (scuba-sized) gas cylinders worn on the user's back in a backpack harness, for rescue work and similar.
There are also examples of pressurized liquid fuel cutting torches, usually using gasoline. These are used for their increased portability.
Regulator
Main article: Pressure regulator
The regulator is used to control pressure from the tanks by reducing pressure and regulating flow rate. Oxy-gas regulators usually have two stages: The first stage of the regulator releases the gas at a constant rate from the cylinder despite the pressure in the cylinder becoming less as the gas in the cylinder is used, as in the first stage of a scuba-diving regulator. The second stage of the regulator controls the pressure reduction from the intermediate pressure to low pressure. It is constant flow. The valve assembly has two pressure gauges, one indicating cylinder pressure, the other indicating hose pressure.
Some oxy-gas regulators only have one stage, and one pressure gauge. With those the gas flow gets less as the cylinder pressure drops.
Gas hoses
The hoses used are specifically designed for welding and cutting. The hose is usually a double-hose design, meaning that there are two hoses joined together. The oxygen hose is green and the fuel hose is red. The type of gas the hose will be carrying is important because the connections will have different threads for different types of gas. Fuel gases (red) will use left-hand threads and a groove cut into the nut, while the oxygen (green) will use right-hand threads. This is a safety precaution to prevent hoses from being hooked up the wrong way.
There are basically two types of connections that can be used. The first is using a jubilee clip. The second option is using a crimped connector. The second option is probably safer as it is harder for this type of connection to come loose. The hoses should also be clipped together at intervals approximately 3 feet apart.
Vintage amateur radio
Vintage amateur radio is a subset of the amateur radio hobby, considered a form of nostalgia much like antique car collecting, where enthusiasts collect, restore, preserve, build, and operate amateur radio equipment from bygone years, most notably those using vacuum tube technology.
Vintage radio enthusiasts contend that while modern, state-of-the-art, microprocessor based amateur radios are extremely good at what they are designed to do, they lack the aesthetic appeal and "soul" of amateur electronic gear from the vacuum tube era. Additionally, many find satisfaction in taking commercially-made amateur equipment from the 1930s - 1970s (affectionately called boat anchors by US/Canadian amateurs because of their relatively large size and weight) and carefully restoring it back to health.
Hallicrafters SX-28 tuning dial
The simple, roomy electrical and mechanical designs of boat anchor radios are more easily worked on, modified, and tinkered with than their modern Japanese counterparts. In an age where fixing a transceiver is accomplished by boxing it up to send to the manufacturer for a custom VLSI chip replacement, devotees think of boat anchors as "real radio". According to these hobbyists, a hot soldering iron is almost a requirement for operating a vintage station. Other enthusiasts claim that boat anchors sound better than their silicon descendants, saying that the tube audio from vintage gear is "warmer" and more aesthetically pleasing than the audio produced by the typical modern transceiver.Some hobbyists see vintage radio operation as a valuable asset to help preserve the history and heritage of radio for future generations, and may assist in the restoration and operation of vintage radio equipment for historical exhibits, museums and museum ships.
AM activity
"AM'er" Joe Walsh WB6ACU on the air
Amplitude modulation (AM) was once the main voice mode in amateur radio before being superseded by Single-sideband modulation (SSB). But AM has recently become a nostalgic specialty interest on the shortwave ham bands. Vintage radio operation has drawn a wide range of amateur radio enthusiasts from rock star Joe Walsh, WB6ACU, to Federal Communications Commission attorney Riley Hollingsworth, K4ZDH.
A majority of "AM'ers" stations consist of vintage transmitters and receivers housed in separate cabinets. Some operators have even obtained retired AM broadcast transmitters, donated or sold cheaply to hobbyists by radio stations with no further need for them. Others build their equipment from scratch (called homebrewing) using combinations of modern and vintage-era parts.
In the United States, shortwave HF frequencies (in MHz) on which amateur radio AM activity can be found include 1.885, 1.930, 1.985, 3.870--3.885, 7.285, 14.286, 21.425, and 29.010, and sometimes feature "special event" stations using unique call signs. In the United Kingdom, AM activity can be found almost every day on frequencies between 3.615 and 3.625 MHz.
Sound
LISTEN TO A SAMPLE of the "broadcast quality" sound exhibited by some vacuum tube-based vintage amateur stations. This example features "AM'er" N3WWL.
Conversations (QSO's in ham slang) are typically configured as "roundtables" where several participants take turns developing and presenting their thoughts in a storytelling fashion. Often the conversation revolves around do-it-yourself experimentation, repairs, and restoration of vintage vacuum-tube equipment, which has been rising in value because of nostalgic demand. Interested newcomers are usually encouraged to switch their modern transceivers to AM mode, introduce themselves, and join the conversation.
Vintage radio enthusiasts contend that while modern, state-of-the-art, microprocessor based amateur radios are extremely good at what they are designed to do, they lack the aesthetic appeal and "soul" of amateur electronic gear from the vacuum tube era. Additionally, many find satisfaction in taking commercially-made amateur equipment from the 1930s - 1970s (affectionately called boat anchors by US/Canadian amateurs because of their relatively large size and weight) and carefully restoring it back to health.
Hallicrafters SX-28 tuning dial
The simple, roomy electrical and mechanical designs of boat anchor radios are more easily worked on, modified, and tinkered with than their modern Japanese counterparts. In an age where fixing a transceiver is accomplished by boxing it up to send to the manufacturer for a custom VLSI chip replacement, devotees think of boat anchors as "real radio". According to these hobbyists, a hot soldering iron is almost a requirement for operating a vintage station. Other enthusiasts claim that boat anchors sound better than their silicon descendants, saying that the tube audio from vintage gear is "warmer" and more aesthetically pleasing than the audio produced by the typical modern transceiver.Some hobbyists see vintage radio operation as a valuable asset to help preserve the history and heritage of radio for future generations, and may assist in the restoration and operation of vintage radio equipment for historical exhibits, museums and museum ships.
AM activity
"AM'er" Joe Walsh WB6ACU on the air
Amplitude modulation (AM) was once the main voice mode in amateur radio before being superseded by Single-sideband modulation (SSB). But AM has recently become a nostalgic specialty interest on the shortwave ham bands. Vintage radio operation has drawn a wide range of amateur radio enthusiasts from rock star Joe Walsh, WB6ACU, to Federal Communications Commission attorney Riley Hollingsworth, K4ZDH.
A majority of "AM'ers" stations consist of vintage transmitters and receivers housed in separate cabinets. Some operators have even obtained retired AM broadcast transmitters, donated or sold cheaply to hobbyists by radio stations with no further need for them. Others build their equipment from scratch (called homebrewing) using combinations of modern and vintage-era parts.
In the United States, shortwave HF frequencies (in MHz) on which amateur radio AM activity can be found include 1.885, 1.930, 1.985, 3.870--3.885, 7.285, 14.286, 21.425, and 29.010, and sometimes feature "special event" stations using unique call signs. In the United Kingdom, AM activity can be found almost every day on frequencies between 3.615 and 3.625 MHz.
Sound
LISTEN TO A SAMPLE of the "broadcast quality" sound exhibited by some vacuum tube-based vintage amateur stations. This example features "AM'er" N3WWL.
Conversations (QSO's in ham slang) are typically configured as "roundtables" where several participants take turns developing and presenting their thoughts in a storytelling fashion. Often the conversation revolves around do-it-yourself experimentation, repairs, and restoration of vintage vacuum-tube equipment, which has been rising in value because of nostalgic demand. Interested newcomers are usually encouraged to switch their modern transceivers to AM mode, introduce themselves, and join the conversation.
2008年11月5日星期三
polonium
210Po is an alpha emitter that has a half-life of 138.376 days; it decays directly to its daughter isotope 206Pb. A milligram of 210Po emits about as many alpha particles per second as 4.5 grams of 226Ra. A few curies (1 curie equals 37 gigabecquerels) of 210Po emit a blue glow which is caused by excitation of surrounding air. A single gram of 210Po generates 140 watts of power.Because it emits many alpha particles, which are stopped within a very short distance in dense media and release their energy, 210Po has been used as a lightweight heat source to power thermoelectric cells in artificial satellites; for instance, 210Po heat source was also used in each of the Lunokhod rovers deployed on the surface of the Moon, to keep their internal components warm during the lunar nights.[ Some anti-static brushes contain up to 500 microcuries (20 MBq) of 210Po as a source of charged particles for neutralizing static electricity in materials like photographic film.210Po was also used as a murder weapon in the Alexander Litvinenko poisoning.
The majority of the time 210Po decays by emission of an alpha particle only, not by emission of an alpha particle and a gamma ray. About one in 100,000 alpha emissions causes an excitation in the nucleus which then results in the emission of a gamma ray.This low gamma ray production rate (and the short range of alpha particles) makes it difficult to find and identify this isotope. Rather than gamma ray spectroscopy, alpha spectroscopy is the best method of measuring this isotope.
Solid state form
The alpha form of solid polonium has a simple cubic crystal structure with an edge length of 335.2 picometres.
The beta form of polonium is rhombohedral; it has been reported in the chemical literature, along with the alpha form, several times. A picture of it is present on the web.
Two papers report X-ray diffraction experiments on polonium metal.The first report of the crystal structure of polonium was done using electron diffraction.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
The majority of the time 210Po decays by emission of an alpha particle only, not by emission of an alpha particle and a gamma ray. About one in 100,000 alpha emissions causes an excitation in the nucleus which then results in the emission of a gamma ray.This low gamma ray production rate (and the short range of alpha particles) makes it difficult to find and identify this isotope. Rather than gamma ray spectroscopy, alpha spectroscopy is the best method of measuring this isotope.
Solid state form
The alpha form of solid polonium has a simple cubic crystal structure with an edge length of 335.2 picometres.
The beta form of polonium is rhombohedral; it has been reported in the chemical literature, along with the alpha form, several times. A picture of it is present on the web.
Two papers report X-ray diffraction experiments on polonium metal.The first report of the crystal structure of polonium was done using electron diffraction.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
Switched video
Switched Video, also called Switched Digital Video or SDV, is a telecommunications industry term for a network scheme for distributing digital video via a cable. Switched video sends the digital video in a more efficient manner so that additional uses may be made of the freed up bandwidth. The scheme applies to digital video distribution both on typical cable TV systems using QAM channels, or on IPTV systems. Users of analog video transmitted on the cable are unaffected. See diagram below for an illustration of how Switched Video saves bandwidth on a cable company's cables in the last mile where channels are transmitted via coaxial cable.
In current Hybrid fibre-coaxial systems, a fiber optic network extending from the operator's central office carries all video channels out to a fiber optic node which services any number of homes ranging from 1 to 2000 homes. From this point, all channels are sent via coaxial cable to each of the homes. Note that only a percentage of these homes are actively watching channels at a given time. Rarely are all channels being accessed by the homes in the service group.In a Switched Video system, the unwatched channels do not need to be sent.
In cable TV systems in the United States, equipment in the home sends a channel request signal back to the distribution hub. If a channel is not currently being transmitted on the coaxial line, the distribution hub allocates a new QAM channel and transmits the new channel to the coaxial cable via the fiber optic node. For this to work, the equipment in the home must have two-way communication ability. Switched video uses the same mechanisms as Video on Demand and may be viewed as a non-ending video on demand show that any number of users may share.
Two-way communication is handled differently between cable and IPTV schemes. IPTV use communication protocols used on the Internet but requires entirely new video distribution infrastructure. Cable companies in the United States elected the less costly approach of upgrading existing infrastructure, and European operators may well take the same approach. In the upgrade approach, various proprietary schemes use specific frequencies for passing messages back to the distribution hub. In the United States, there is a recent standard for two-way communications from consumer electronics devices using CableCARDs, such as digital video recorders, high-definition televisions and home theater computers known as OpenCable which require three things to work: hardware that implements these three standards which allow the cable receiver to communicate with the cable head end: SCTE 55-1 which is the ALOHA protocol-based standard used by General Instrument and Motorola equipment, SCTE 55-2 a.k.a. DAVIC which is a slotted ALOHA-based standard used by Scientific Atlanta and Cisco cable boxes, and DOCSIS Set-top Gateway, an extension to the DOCSIS cable modem standard to make it degrade gracefully under adverse conditions and still provide as much functionality as possible; a CableCARD that decrypts the channel for the cable receiver; and a Java-based OpenCable Application Platform (abbreviated as OCAP) stack that allows the cable company to download an application written in OCAP to run on any cable receiver which contains an OCAP stack. This application programs the cable receiver on how to communicate with the switched video server, and does other tasks like running an interactive program guide and programming the receiver on how to perform video on demand. The cable company could choose whichever two-way communication standard it wants out of the three. It could choose the standard that its pre-OCAP hardware used in order to preserve its investment in legacy hardware, or could deploy DOCSIS Set-top Gateway in order to provide much more capacity and efficiency than either of the other two protocols.
For a switched video system to work on cable systems, all digital television users in a subscription group must have devices capable of communicating to the distribution hub in a compatible manner. Unlike other features dependent on two-way communication such as Video on Demand, the requirement to upgrade all digital set-top boxes within a group makes conversion to switched video extremely expensive. CableLabs proposed in the CableCARD 2.0 specification that two-way communication be supported with a scheme which required more powerful hardware capable of running Java programs. Many cable companies have indicated they will build lower cost devices that do not require this OCAP programing environment, so that upgrading to a switched video system would not be as costly. Consumer electronics companies also prefer a more light weight solution for two-way communication, and so absent a standard for two-way communication, the conversion to switched video may require many years to complete.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
In current Hybrid fibre-coaxial systems, a fiber optic network extending from the operator's central office carries all video channels out to a fiber optic node which services any number of homes ranging from 1 to 2000 homes. From this point, all channels are sent via coaxial cable to each of the homes. Note that only a percentage of these homes are actively watching channels at a given time. Rarely are all channels being accessed by the homes in the service group.In a Switched Video system, the unwatched channels do not need to be sent.
In cable TV systems in the United States, equipment in the home sends a channel request signal back to the distribution hub. If a channel is not currently being transmitted on the coaxial line, the distribution hub allocates a new QAM channel and transmits the new channel to the coaxial cable via the fiber optic node. For this to work, the equipment in the home must have two-way communication ability. Switched video uses the same mechanisms as Video on Demand and may be viewed as a non-ending video on demand show that any number of users may share.
Two-way communication is handled differently between cable and IPTV schemes. IPTV use communication protocols used on the Internet but requires entirely new video distribution infrastructure. Cable companies in the United States elected the less costly approach of upgrading existing infrastructure, and European operators may well take the same approach. In the upgrade approach, various proprietary schemes use specific frequencies for passing messages back to the distribution hub. In the United States, there is a recent standard for two-way communications from consumer electronics devices using CableCARDs, such as digital video recorders, high-definition televisions and home theater computers known as OpenCable which require three things to work: hardware that implements these three standards which allow the cable receiver to communicate with the cable head end: SCTE 55-1 which is the ALOHA protocol-based standard used by General Instrument and Motorola equipment, SCTE 55-2 a.k.a. DAVIC which is a slotted ALOHA-based standard used by Scientific Atlanta and Cisco cable boxes, and DOCSIS Set-top Gateway, an extension to the DOCSIS cable modem standard to make it degrade gracefully under adverse conditions and still provide as much functionality as possible; a CableCARD that decrypts the channel for the cable receiver; and a Java-based OpenCable Application Platform (abbreviated as OCAP) stack that allows the cable company to download an application written in OCAP to run on any cable receiver which contains an OCAP stack. This application programs the cable receiver on how to communicate with the switched video server, and does other tasks like running an interactive program guide and programming the receiver on how to perform video on demand. The cable company could choose whichever two-way communication standard it wants out of the three. It could choose the standard that its pre-OCAP hardware used in order to preserve its investment in legacy hardware, or could deploy DOCSIS Set-top Gateway in order to provide much more capacity and efficiency than either of the other two protocols.
For a switched video system to work on cable systems, all digital television users in a subscription group must have devices capable of communicating to the distribution hub in a compatible manner. Unlike other features dependent on two-way communication such as Video on Demand, the requirement to upgrade all digital set-top boxes within a group makes conversion to switched video extremely expensive. CableLabs proposed in the CableCARD 2.0 specification that two-way communication be supported with a scheme which required more powerful hardware capable of running Java programs. Many cable companies have indicated they will build lower cost devices that do not require this OCAP programing environment, so that upgrading to a switched video system would not be as costly. Consumer electronics companies also prefer a more light weight solution for two-way communication, and so absent a standard for two-way communication, the conversion to switched video may require many years to complete.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
lighting technology
Light-emitting diode (LED) Christmas lights are quickly gaining popularity in many places due to their low energy usage (about one tenth the energy used by incandescent bulbs), very long lifetimes, and associated low maintenance. Colored LEDs are also far more efficient at producing light than their colored incandescent counterparts.
There are two types of LEDs: colored LEDs and white LEDs. Colored LEDs emit a specific color light (monochromatic light), regardless of the color of the transparent plastic lens that encases the LED's chip. The plastic may be colored for cosmetic reasons, but does not substantially affect the color of the light emitted. Because the light is determined by the LED's chip rather than the plastic lens, Christmas lights of this type do not suffer from color fading. In addition, the plastic lens is much more durable than the glass envelope of incandescent bulbs.
White LEDs are similar to colored LEDs in most respects such as power and durability, but utilize a two-stage process to create the white (polychromatic, or broad spectrum) light. In the first stage, the LED actually only produces one color of light, similar to any other LED. In the second stage, some of the blue or violet-blue is absorbed by a phosphor which fluoresces yellow, imitating the broad spectrum of colors which our eyes perceive as "white". This is essentially the same process used in fluorescent lamps, except for the use of an LED to create blue light rather than excited gas plasma to create ultraviolet.
White LEDs can be used as white Christmas lights, or can be used to create any other color through the use of colored refractors and lenses, similar to the more commonly used incandescent bulbs. Color fading may therefore occur due to the exposure of colored plastics to sunlight or heat, as with ordinary Christmas lights. Yellowing may also occur in the epoxy "bulb" in which the LED is encased if left in the sun consistently.
LEDs use much less electricity (only 4 watts for a 70-light string) and have a much greater lifespan than incandescent lamps. Since they are constructed from solid state materials and have no metallic filaments to burn out or break, LEDs are also much less susceptible to breakage from impact or rough handling.
Although LEDs themselves are long-life devices, older or lower-quality strands of LED-based Christmas lights can suffer from early failure. This is particularly so with blue ones, which are the newest and most expensive, and therefore prone to cost-cutting; in addition, spares are rarely included with sets. Most LED-based Christmas lights use copper wire which connects to the aluminum-based wires of the LEDs. Exposing this combination of metals to moisture can result in galvanic corrosion inside of the lamps' sockets, causing them to stop working. Many other sets use cheaper steel leads on the LEDs, which instead rust, leading to the same result. Some newer and higher-quality sets of LED Christmas lights have each LED permanently mounted in a non-removable weathertight base to keep out rain and other moisture, helping to prevent such corrosion; however, this prevents the user from replacing defective bulbs.
Most common consumer LED lamps produce intense, deep, pure colours, versus incandescent bulbs which generally have subtler, yellow-tinted colours, often somewhat faded especially if used outside. Blue tends to be the dimmest incandescent color, but the brightest in LED, while yellow is just the opposite. Very early strings of LED lights were noticeably dimmer than incandescent bulbs, but now are often noticeably brighter. These factors combine to give LED lamps a distinct aesthetic from older incandescent strings, although white LEDs behind coloured lenses do offer the ability to provide a more incandescent-type appearance with most of the benefits of energy efficiency. However, most use coloured-chip type LEDs that produce the intense colours. This is largely due to the maturity of coloured LED versus newer white LED technology, and as the technology improves so will the ability to change the aesthetics of the lamps, at lower cost than at present. As of 2007, "warm white" LED sets are common for the first time in U.S. stores, having a color similar to a compact fluorescent light. However, this color needs to be more of an orange tint to match the color of such small bulbs, because they burn at a lower temperature. Still, this is a significant improvement from the very cold-white (and often irregularly-tinted) color of early white sets.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
There are two types of LEDs: colored LEDs and white LEDs. Colored LEDs emit a specific color light (monochromatic light), regardless of the color of the transparent plastic lens that encases the LED's chip. The plastic may be colored for cosmetic reasons, but does not substantially affect the color of the light emitted. Because the light is determined by the LED's chip rather than the plastic lens, Christmas lights of this type do not suffer from color fading. In addition, the plastic lens is much more durable than the glass envelope of incandescent bulbs.
White LEDs are similar to colored LEDs in most respects such as power and durability, but utilize a two-stage process to create the white (polychromatic, or broad spectrum) light. In the first stage, the LED actually only produces one color of light, similar to any other LED. In the second stage, some of the blue or violet-blue is absorbed by a phosphor which fluoresces yellow, imitating the broad spectrum of colors which our eyes perceive as "white". This is essentially the same process used in fluorescent lamps, except for the use of an LED to create blue light rather than excited gas plasma to create ultraviolet.
White LEDs can be used as white Christmas lights, or can be used to create any other color through the use of colored refractors and lenses, similar to the more commonly used incandescent bulbs. Color fading may therefore occur due to the exposure of colored plastics to sunlight or heat, as with ordinary Christmas lights. Yellowing may also occur in the epoxy "bulb" in which the LED is encased if left in the sun consistently.
LEDs use much less electricity (only 4 watts for a 70-light string) and have a much greater lifespan than incandescent lamps. Since they are constructed from solid state materials and have no metallic filaments to burn out or break, LEDs are also much less susceptible to breakage from impact or rough handling.
Although LEDs themselves are long-life devices, older or lower-quality strands of LED-based Christmas lights can suffer from early failure. This is particularly so with blue ones, which are the newest and most expensive, and therefore prone to cost-cutting; in addition, spares are rarely included with sets. Most LED-based Christmas lights use copper wire which connects to the aluminum-based wires of the LEDs. Exposing this combination of metals to moisture can result in galvanic corrosion inside of the lamps' sockets, causing them to stop working. Many other sets use cheaper steel leads on the LEDs, which instead rust, leading to the same result. Some newer and higher-quality sets of LED Christmas lights have each LED permanently mounted in a non-removable weathertight base to keep out rain and other moisture, helping to prevent such corrosion; however, this prevents the user from replacing defective bulbs.
Most common consumer LED lamps produce intense, deep, pure colours, versus incandescent bulbs which generally have subtler, yellow-tinted colours, often somewhat faded especially if used outside. Blue tends to be the dimmest incandescent color, but the brightest in LED, while yellow is just the opposite. Very early strings of LED lights were noticeably dimmer than incandescent bulbs, but now are often noticeably brighter. These factors combine to give LED lamps a distinct aesthetic from older incandescent strings, although white LEDs behind coloured lenses do offer the ability to provide a more incandescent-type appearance with most of the benefits of energy efficiency. However, most use coloured-chip type LEDs that produce the intense colours. This is largely due to the maturity of coloured LED versus newer white LED technology, and as the technology improves so will the ability to change the aesthetics of the lamps, at lower cost than at present. As of 2007, "warm white" LED sets are common for the first time in U.S. stores, having a color similar to a compact fluorescent light. However, this color needs to be more of an orange tint to match the color of such small bulbs, because they burn at a lower temperature. Still, this is a significant improvement from the very cold-white (and often irregularly-tinted) color of early white sets.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
Digital cinema
Digital cinema refers to the use of digital technology to distribute and project motion pictures. The final movie can be distributed via hard drives, DVDs or satellite and projected using a digital projector instead of a conventional film projector. Digital cinema is distinct from high-definition television and in particular, is not dependent on using television or HDTV standards, aspect ratios, or frame rates. Digital projectors capable of 2K resolution began deploying in 2005, and since 2006, the pace has accelerated. HDTV and pre-recorded HD disks could put pressure on movie theaters to offer something to compete with the home HD experience.
To match or improve the theater experience of movie audiences, a digital cinema system must provide high quality image, sound, subtitles, and captions. Theater managers require server controls for managing and displaying content in multiple theaters, and studios want their content encrypted with secure delivery, playback, and reporting of play times to the distribution company.
Digital Cinema Initiatives (DCI), a joint venture of the six major studios, published a system specification for digital cinema.Briefly, the specification calls for picture encoding using the ISO/IEC 15444-1 "JPEG2000" (.jp2) standard and use of the CIE XYZ color space at 12 bits per component encoded with a 2.6 gamma applied at projection, and audio using the "Broadcast Wave" (.wav) format at 24 bits and 48 kHz or 96 kHz sampling, controlled by an XML-format Composition Playlist, into an MXF-compliant file at a maximum data rate of 250 Mbit/s. Details about encryption, key management, and logging are all discussed in the specification as are the minimum specifications for the projectors employed including the color gamut, the contrast ratio and the brightness of the image. While much of the specification codifies work that had already been ongoing in the Society of Motion Picture and Television Engineers (SMPTE), the specification is important in establishing a content owner framework for the distribution and security of first-release motion picture content.
Digital cinema conforming to the DCI Standard is referred to within the film industry as D-Cinema while all other forms of digital cinema are referred to as E-Cinema. Thus, while D-Cinema is a defined standard, though one that is still partly being framed by SMPTE as of 2007, E-Cinema may be anything, ranging from a DVD player connected to a consumer projector to something that approaches the quality of D-Cinema without conforming to some of the standards. Even D-Cinema itself has evolved over time before the DCI standards were framed. However, the current DCI standards were made with the intention of standing the test of time, much like 35 mm film which has evolved but still retained compatibility over a substantial part of a century.
In addition to DCI's work, the National Association of Theatre Owners (NATO) released its Digital Cinema System Requirements.The document addresses the requirements of digital cinema systems from the operational needs of the exhibitor, focusing on areas not addressed by DCI, including access for the visually impaired and hearing impaired, workflow inside the cinema, and equipment interoperability. In particular, NATO's document details requirements for the Theatre Management System (TMS), the governing software for digital cinema systems within a theatre complex, and provides direction for the development of security key management systems. As with DCI's document, NATO's document is also important to the SMPTE standards effort.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
To match or improve the theater experience of movie audiences, a digital cinema system must provide high quality image, sound, subtitles, and captions. Theater managers require server controls for managing and displaying content in multiple theaters, and studios want their content encrypted with secure delivery, playback, and reporting of play times to the distribution company.
Digital Cinema Initiatives (DCI), a joint venture of the six major studios, published a system specification for digital cinema.Briefly, the specification calls for picture encoding using the ISO/IEC 15444-1 "JPEG2000" (.jp2) standard and use of the CIE XYZ color space at 12 bits per component encoded with a 2.6 gamma applied at projection, and audio using the "Broadcast Wave" (.wav) format at 24 bits and 48 kHz or 96 kHz sampling, controlled by an XML-format Composition Playlist, into an MXF-compliant file at a maximum data rate of 250 Mbit/s. Details about encryption, key management, and logging are all discussed in the specification as are the minimum specifications for the projectors employed including the color gamut, the contrast ratio and the brightness of the image. While much of the specification codifies work that had already been ongoing in the Society of Motion Picture and Television Engineers (SMPTE), the specification is important in establishing a content owner framework for the distribution and security of first-release motion picture content.
Digital cinema conforming to the DCI Standard is referred to within the film industry as D-Cinema while all other forms of digital cinema are referred to as E-Cinema. Thus, while D-Cinema is a defined standard, though one that is still partly being framed by SMPTE as of 2007, E-Cinema may be anything, ranging from a DVD player connected to a consumer projector to something that approaches the quality of D-Cinema without conforming to some of the standards. Even D-Cinema itself has evolved over time before the DCI standards were framed. However, the current DCI standards were made with the intention of standing the test of time, much like 35 mm film which has evolved but still retained compatibility over a substantial part of a century.
In addition to DCI's work, the National Association of Theatre Owners (NATO) released its Digital Cinema System Requirements.The document addresses the requirements of digital cinema systems from the operational needs of the exhibitor, focusing on areas not addressed by DCI, including access for the visually impaired and hearing impaired, workflow inside the cinema, and equipment interoperability. In particular, NATO's document details requirements for the Theatre Management System (TMS), the governing software for digital cinema systems within a theatre complex, and provides direction for the development of security key management systems. As with DCI's document, NATO's document is also important to the SMPTE standards effort.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
Ballistic vest
A ballistic vest is an item of protective clothing that absorbs the impact from gun-fired projectiles, and shrapnel fragments from explosion. This protection is for the torso. Soft vests are made from many layers of woven or laminated fibers and protect wearers from projectiles fired from handguns, shotguns, and small fragments from explosives such as hand grenades. When metal or ceramic plates are used with a soft vest, it can also protect wearers from shots fired from rifles. In combination with metallic components or tightly-woven fiber layers, soft armor can offer some protection to the wearer from stab and slash from a knife. Soft vests are commonly worn by police forces, private citizens and private security guards, and hard-plate reinforced vests are mainly worn by combat soldiers in the armies of various nations as well as police armed response units.
Modern body armor may combine a ballistic vest with other items of protective clothing, such as a helmet. Vests intended for police and military use may also include ballistic shoulder, and side protection armor components.
Ballistic vests use layers of very strong fiber to catch and deform a bullet and spread its force over a larger portion of the vest fiber. A deformable handgun bullet mushrooms into a dished plate on impact with a well designed textile vest. The vest absorbs the energy from the deforming bullet, bringing it to a stop before it can penetrate the overall matrix. Some layers may be penetrated but as the bullet deforms, the energy is absorbed by a larger and larger fiber area. While a vest can prevent bullet penetration, the vest and wearer still absorb the bullet's energy. Even without penetration, modern pistol bullets contain enough energy to cause blunt force trauma under the impact point. Vests' specifications include both penetration resistance requirements and limits on the amount of impact energy that is delivered to the body. Vests designed for bullets offer little protection against blows from sharp implements, such as knives, arrows or ice picks, or from bullets manufactured of non-deformable materials i.e. steel core instead of lead. The force of the impact of these objects is concentrated in a relatively small area, allowing them to puncture the fiber layers of most bullet-resistant fabrics. Textile vests may be augmented with metal (steel or titanium), ceramic or polyethylene plates that provide extra protection to vital areas. These hard armor plates have proven effective against all handgun bullets and a range of rifles. These upgraded ballistic vests have become standard in military use, as soft body armor vests are ineffective against military rifle rounds. Corrections officers and other law enforcement officers often wear vests which are designed specifically against bladed weapons and sharp objects. These vests may incorporate coated and laminated para-aramid textiles or metallic components.
The first "soft" ballistic armor known is Myunjebaegab, invented in Korea in the 1860s. It was invented right after the French Campaign against Korea, 1866. Heungseon Daewongun ordered development of bullet-proof armor because of increasing threats from western armies. Kim Gi-Doo and Gang Yoon found that cotton could protect against bullets if thick enough, and devised bullet-proof vests made of 30 layers of cotton. The vests were used in battle when the US Navy attacked Ganghwa Island in Korea in 1871 (United States expedition to Korea). The US army captured one of the vests and took it to the US, where it was stored at the Smithsonian Museum until 2007. The vest has since been sent back to Korea and is currently on display to the public.
One of the early instances of ballistic armor being used was in Australia in 1879, when Ned Kelly's "Kelly Gang" made armor from scrap metals which covered their torsos, upper arms, and upper legs. Along with the helmet, the home-made suit weighed 44kg (96lbs), which made Kelly clumsy and unwieldy when he wore the armor during a police raid at Glenrowan in 1880. Its use proved futile as the suit lacked protection for the legs.
During the early 1880s, Dr. George Emery Goodfellow of Arizona began investigating silk vests resembling medieval padded jacks, which used 18 to 30 layers of cloth to protect the wearers from arrow penetration. Dr. Goodfellow's interest in silk bulletproof vests arose after he learned about several cases where silk fabric slowed the impact of bullets in the bodies of people who were shot.
Casimir Zeglen of Chicago, Illinois used Goodfellow's findings to develop a bulletproof vest made of silk fabric at the end of the 1800s which could stop the relatively slow rounds from black powder handguns. The vests cost $800 USD each in 1914, which is equivalent to about $16,886 in 2008 dollars. On June 28, 1914, Franz Ferdinand, Archduke of Austria, heir to the Austro-Hungarian throne was wearing a silk bulletproof vest when he was attacked by a gun-wielding assassin. However, the vest did not protect him, because he was shot in the neck above the vest. A similar vest, made by Jan Szczepanik in 1901, saved the life of Alfonso XIII of Spain when he was shot at by an attacker.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
Modern body armor may combine a ballistic vest with other items of protective clothing, such as a helmet. Vests intended for police and military use may also include ballistic shoulder, and side protection armor components.
Ballistic vests use layers of very strong fiber to catch and deform a bullet and spread its force over a larger portion of the vest fiber. A deformable handgun bullet mushrooms into a dished plate on impact with a well designed textile vest. The vest absorbs the energy from the deforming bullet, bringing it to a stop before it can penetrate the overall matrix. Some layers may be penetrated but as the bullet deforms, the energy is absorbed by a larger and larger fiber area. While a vest can prevent bullet penetration, the vest and wearer still absorb the bullet's energy. Even without penetration, modern pistol bullets contain enough energy to cause blunt force trauma under the impact point. Vests' specifications include both penetration resistance requirements and limits on the amount of impact energy that is delivered to the body. Vests designed for bullets offer little protection against blows from sharp implements, such as knives, arrows or ice picks, or from bullets manufactured of non-deformable materials i.e. steel core instead of lead. The force of the impact of these objects is concentrated in a relatively small area, allowing them to puncture the fiber layers of most bullet-resistant fabrics. Textile vests may be augmented with metal (steel or titanium), ceramic or polyethylene plates that provide extra protection to vital areas. These hard armor plates have proven effective against all handgun bullets and a range of rifles. These upgraded ballistic vests have become standard in military use, as soft body armor vests are ineffective against military rifle rounds. Corrections officers and other law enforcement officers often wear vests which are designed specifically against bladed weapons and sharp objects. These vests may incorporate coated and laminated para-aramid textiles or metallic components.
The first "soft" ballistic armor known is Myunjebaegab, invented in Korea in the 1860s. It was invented right after the French Campaign against Korea, 1866. Heungseon Daewongun ordered development of bullet-proof armor because of increasing threats from western armies. Kim Gi-Doo and Gang Yoon found that cotton could protect against bullets if thick enough, and devised bullet-proof vests made of 30 layers of cotton. The vests were used in battle when the US Navy attacked Ganghwa Island in Korea in 1871 (United States expedition to Korea). The US army captured one of the vests and took it to the US, where it was stored at the Smithsonian Museum until 2007. The vest has since been sent back to Korea and is currently on display to the public.
One of the early instances of ballistic armor being used was in Australia in 1879, when Ned Kelly's "Kelly Gang" made armor from scrap metals which covered their torsos, upper arms, and upper legs. Along with the helmet, the home-made suit weighed 44kg (96lbs), which made Kelly clumsy and unwieldy when he wore the armor during a police raid at Glenrowan in 1880. Its use proved futile as the suit lacked protection for the legs.
During the early 1880s, Dr. George Emery Goodfellow of Arizona began investigating silk vests resembling medieval padded jacks, which used 18 to 30 layers of cloth to protect the wearers from arrow penetration. Dr. Goodfellow's interest in silk bulletproof vests arose after he learned about several cases where silk fabric slowed the impact of bullets in the bodies of people who were shot.
Casimir Zeglen of Chicago, Illinois used Goodfellow's findings to develop a bulletproof vest made of silk fabric at the end of the 1800s which could stop the relatively slow rounds from black powder handguns. The vests cost $800 USD each in 1914, which is equivalent to about $16,886 in 2008 dollars. On June 28, 1914, Franz Ferdinand, Archduke of Austria, heir to the Austro-Hungarian throne was wearing a silk bulletproof vest when he was attacked by a gun-wielding assassin. However, the vest did not protect him, because he was shot in the neck above the vest. A similar vest, made by Jan Szczepanik in 1901, saved the life of Alfonso XIII of Spain when he was shot at by an attacker.
Animal Print Rug
in wall aquarium
Wallets And Purses
Cummins Engine Parts
nut bolt washer
Men's Outdoor Jacket
microscope cover glass
Boat trailer hardware
non-stick dutch oven
industrial coffee machine
vibration exercise machines
folding silk screen
jet fuel a1
latex bed sheets
automotive water pump
portable handsfree kit
diamond emerald necklace
Welding And Soldering
musical water globe
motorcycle wheel weights
Mini LED Torch
baby knee socks
av cables rca
ladies leather sandals
Plastic Pill Boxes
2008年11月4日星期二
Overlock
An overlock stitch sews over the edge of one or two pieces of cloth for edging, hemming or seaming. Usually an overlock sewing machine will cut the edges of the cloth as they are fed through (such machines are called ‘sergers’), though some are made without cutters. The inclusion of automated cutters allows overlock machines to create finished seams easily and quickly. An overlock sewing machine differs from a lockstitch sewing machine in that it utilizes loopers fed by multiple thread cones rather than a bobbin. Loopers serve to create thread loops that pass from the needle thread to the edges of the fabric so that the edges of the fabric are contained within the seam. Overlock sewing machines usually run at high speeds, from 1000 to 9000 rpm, and most are used in industrial setting for edging, hemming and seaming a variety of fabrics and products. Overlock stitches are extremely versatile, as they can be used for decoration, reinforcement, or construction.
Overlock stitching was invented by the Merrow Machine Company in 1881.
J. Makens Merrow and his son Joseph Merrow, who owned a knitting mill established in Connecticut in 1838, developed a number of technological advancements to be used in the mill’s operations. Merrow's first patent was a machine for crochet stitching. Merrow still produces crochet machines based on this original model. This technology was a starting point for the development of the overlock machine, patented by Joseph Merrow in 1889. Unlike standard lockstitching, which uses a bobbin, overlock sewing machines utilize loopers to create thread loops for the needle to pass through, in a manner similar to crocheting. Merrow's original three-thread overedge sewing machine is the forerunner of contemporary overlocking machines. Over time, the Merrow Machine Company pioneered the design of new machines to create a variety of overlock stitches, such as two, and four-thread machines, the one-thread butted seam, and the cutterless emblem edger.
A landmark lawsuit between Wilkox & Gibbs and the Merrow Machine Company in 1905 established the ownership and rights to the early mechanical development of overlocking to the Merrow Machine Company.
Throughout the early 19th Century the areas of Connecticut, USA and New York USA were the centers of textile manufacturing and machine production. Consequently many overlock machine companies established themselves in the Northeastern United States.
In 1964 Juki Corporation was formed; a precursor of the modern industrial overlock sewing machine company. Throughout the 1980s Japanese and Chinese sewing machine production came to dominate the industry.
In the United States the term "overlocker" has largely been replaced by "serger" but in other parts of the world (Australia, UK) the term "overlocker" is still in use.
Overlock stitching was invented by the Merrow Machine Company in 1881.
J. Makens Merrow and his son Joseph Merrow, who owned a knitting mill established in Connecticut in 1838, developed a number of technological advancements to be used in the mill’s operations. Merrow's first patent was a machine for crochet stitching. Merrow still produces crochet machines based on this original model. This technology was a starting point for the development of the overlock machine, patented by Joseph Merrow in 1889. Unlike standard lockstitching, which uses a bobbin, overlock sewing machines utilize loopers to create thread loops for the needle to pass through, in a manner similar to crocheting. Merrow's original three-thread overedge sewing machine is the forerunner of contemporary overlocking machines. Over time, the Merrow Machine Company pioneered the design of new machines to create a variety of overlock stitches, such as two, and four-thread machines, the one-thread butted seam, and the cutterless emblem edger.
A landmark lawsuit between Wilkox & Gibbs and the Merrow Machine Company in 1905 established the ownership and rights to the early mechanical development of overlocking to the Merrow Machine Company.
Throughout the early 19th Century the areas of Connecticut, USA and New York USA were the centers of textile manufacturing and machine production. Consequently many overlock machine companies established themselves in the Northeastern United States.
In 1964 Juki Corporation was formed; a precursor of the modern industrial overlock sewing machine company. Throughout the 1980s Japanese and Chinese sewing machine production came to dominate the industry.
In the United States the term "overlocker" has largely been replaced by "serger" but in other parts of the world (Australia, UK) the term "overlocker" is still in use.
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