Resolved -[RE-OPENED]Fiber optic (or "optical fiber")

[Basye98]

Fiber optic (or "optical fiber") refers to the medium and the technology associated with the transmission of information as light impulses along a glass or plastic wire or fiber. Fiber optic wire carries much more information than conventional copper wire and is far less subject to electromagnetic interference. Most telephone company long-distance lines are now fiber optic.

Transmission on fiber optic wire requires repeating at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have fiber optic wires or cables from the phone company's branch office to local customers (known as local loop).

VoIP (voice over IP - that is, voice delivered using the Internet Protocol) is a term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol (IP). In general, this means sending voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public switched telephone network (PSTN). A major advantage of VoIP and Internet telephony is that it avoids the tolls charged by ordinary telephone service.

In addition to IP, VoIP uses the real-time protocol (RTP) to help ensure that packets get delivered in a timely way. Using public networks, it is currently difficult to guarantee Quality of Service (QoS). Better service is possible with private networks managed by an enterprise or by an Internet telephony service provider (ITSP).

A technique used by at least one equipment manufacturer, Netspeak, to help ensure faster packet delivery is to Packet Internet or Inter-Network Groper (ping) all possible network gateway computers that have access to the public network and choose the fastest path before establishing a Transmission Control Protocol (TCP) sockets connection with the other end.

Using VoIP, an enterprise positions a "VoIP device" (such as Cisco's AS5300 access server with the VoIP feature) at a gateway. The gateway receives packetized voice transmissions from users within the company and then routes them to other parts of its intranet (local area or wide area network) or, using a T-carrier system or E-carrier interface, sends them over the public switched telephone network.

[catgate]

Well...yes.

[Hb_Kai]

Virgin Media offer this :)

[AlanHo]

I am on a high fibre diet so find this very useful.

Fiber optics, though used extensively in the modern world, is a fairly simple and old technology. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London a dozen years later.[1] Tyndall also wrote about the property of total internal reflection in an introductory book about the nature of light in 1870: "When the light passes from air into water, the refracted ray is bent towards the perpendicular... When the ray passes from water to air it is bent from the perpendicular... If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the ray will not quit the water at all: it will be totally reflected at the surface.... The angle which marks the limit where total reflexion begins is called the limiting angle of the medium. For water this angle is 48°27', for flint glass it is 38°41', while for diamond it is 23°42'."[2][3]

Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for internal medical examinations by Heinrich Lamm in the following decade. In 1952, physicist Narinder Singh Kapany conducted experiments that led to the invention of optical fiber. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade.[1] Development then focused on fiber bundles for image transmission. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material. A variety of other image transmission applications soon followed.

Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, was the first to propose the use of optical fibers for communications in 1963.[4] Nishizawa invented other technologies that contributed to the development of optical fiber communications as well.[5] Nishizawa invented the graded-index optical fiber in 1964 as a channel for transmitting light from semiconductor lasers over long distances with low loss.[6]

In 1965, Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), allowing fibers to be a practical medium for communication.[7] They proposed that the attenuation in fibers available at the time was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. The crucial attenuation level of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. A few years later they produced a fiber with only 4 dB/km attenuation using germanium dioxide as the core dopant. Such low attenuations ushered in optical fiber telecommunications and enabled the Internet. In 1981, General Electric produced fused quartz ingots that could be drawn into fiber optic strands 25 miles (40 km) long.[8]

Attenuations in modern optical cables are far less than those in electrical copper cables, leading to long-haul fiber connections with repeater distances of 50–80 kilometres (31–50 mi). The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by reducing or even in many cases eliminating the need for optical-electrical-optical repeaters, was co-developed by teams led by David N. Payne of the University of Southampton, and Emmanuel Desurvire at Bell Laboratories in 1986. The more robust optical fiber commonly used today utilizes glass for both core and sheath and is therefore less prone to aging processes. It was invented by Gerhard Bernsee in 1973 of Schott Glass in Germany.[9]

In 1991, the emerging field of photonic crystals led to the development of photonic-crystal fiber[10] which guides light by means of diffraction from a periodic structure, rather than total internal reflection. The first photonic crystal fibers became commercially available in 2000.[11] Photonic crystal fibers can be designed to carry higher power than conventional fiber, and their wavelength dependent properties can be manipulated to improve their performance in certain applications.

[catgate]

A rope is a bundle of flexible fibres twisted or braided together to increase its overall length and tensile strength. The use of ropes for hunting, carrying, lifting, and climbing dates back to prehistoric times. Ropes were originally made by hand using natural fibres. Modern ropes are made by machines and utilize many newer synthetic materials to give them improved strength, lighter weight, and better resistance to rotting. More than half of the rope manufactured today is used in the fishing and maritime industries.

Although the origin of rope is unknown, the Egyptians were the first people to develop special tools to make rope. Egyptian rope dates back to 4000 to 3500 B.C. and was generally made of water reed fibres. Other Egyptian rope was made from the fibres of date palms, flax, grass, papyrus, leather, or camel hair. The use of such ropes pulled by thousands of slaves allowed the Egyptians to move the heavy stones required to build the pyramids. By about 2800 B.C., rope made of hemp fibres was in use in China. Rope and the craft of rope making spread throughout Asia, India, and Europe over the next several thousand years. By the fourth century, rope making in India had become so specialized that some makers produced rope intended only for use with elephants. Leonardo da Vinci (1452-1519) drew sketches of a concept for a ropemaking machine, and by the late 1700s several working machines had been built and patented. Rope continued to be made from natural fibres until the 1950s when synthetic materials such as nylon became popular. Despite the changes in materials and technology, rope making today remains little changed since the time of the ancient Egyptians.

Rope is sometimes generally referred to as cordage and can be divided into four categories based on its diameter. Cordage under 0.1875 inches (0.5 cm) in diameter includes twine, clothesline, sash cord, and a tar-covered hemp line called marline. These are not considered to be true rope. Cordage with a diameter of 0.1875 to 0.5 inches (0.5-1.3 cm) is a light-duty rope and is some-times referred to as "small stuff." Cordage with a diameter of 0.5 to about 1.5 inches (1.3-3.8 cm) is considered to be true rope. Cordage over about 1.5 inches (3.8 cm) in diameter is generally called a hawser and is used for mooring large ships.

Rope construction involves twisting fibres together to form yarn. For twisted rope, the yarn is then twisted into strands, and the strands twisted into rope. Three-strand twisted rope is the most common construction. For braided rope, the yarn is braided rather than being twisted into strands. Double-braided rope has a braided core with a braided cover. Plaited rope is made by braiding twisted strands. Other rope construction includes combinations of these three techniques such as a three-strand twisted core with a braided cover. The concept of forming fibres or filaments into yarn and yarn into strands or

Rope may be made either from natural fibres, which have been processed to allow them to be easily formed into yarn, or from synthetic materials, which have been spun into fibres or extruded into long filaments.

Natural fibres include hemp, sisal, cotton, flax, and jute. Another natural material is called manila hemp, but it is actually the fibres from a banana plant. Sisal was used extensively to make twine, but synthetic materials are replacing it. Manila rope is still used by traditionalists, but it can rot from the inside, thus losing its strength without giving any outward indication.

Synthetic fibres include nylon, polyester, polypropylene and aramid. Polypropylene costs the least, floats on water, and does not stretch appreciably. For these reasons it makes a good water ski tow rope. Nylon is moderately expensive, fairly strong, and has quite a bit of stretch. It makes a good mooring and docking line for boats because of its ability to give slightly, yet hold. Aramid is the strongest, but is also very expensive. Nylon and polyester may be spun into fibres about 4-10 inches (10-25 cm) long. Ropes made from spun synthetic fibres feel fuzzy and are not as strong as ropes made from long, continuous filaments. Some ropes use two different synthetic materials to achieve a combination of high strength and low cost or high strength and smooth surface finish.

Wire rope may be made from iron or steel wires. This is commonly referred to as cable and is used in bridges, elevators, and cranes. It is made by a different process than fiber or filament ropes.

Fibres and filaments are first formed into yarn. The yarn is then twisted, braided, or plaited according to the type of rope being made. The diameter of the rope is determined by the diameter of the yarn, the number.

Rope can get knotted.

[Gandalph]

Glass ingredients

Quartz sand (silica) as main raw material for commercial glass production

Oldest mouth-blown window-glass in Sweden (Kosta Glasbruk, Småland, 1742). In the middle is the mark from the glass blower's pipe.

Pure silica (SiO2) has a "glass melting point"— at a viscosity of 10 Pa·s (100 P)— of over 2300 °C (4200 °F). While pure silica can be made into glass for special applications (see fused quartz), other substances are added to common glass to simplify processing. One is sodium carbonate (Na2CO3), which lowers the melting point to about 1500 °C (2700 °F) in soda-lime glass; "soda" refers to the original source of sodium carbonate in the soda ash obtained from certain plants. However, the soda makes the glass water soluble, which is usually undesirable, so lime (calcium oxide (CaO), generally obtained from limestone), some magnesium oxide (MgO) and aluminium oxide are added to provide for a better chemical durability. The resulting glass contains about 70 to 74 percent silica by weight and is called a soda-lime glass.[8] Soda-lime glasses account for about 90 percent of manufactured glass.

As well as soda and lime, most common glass has other ingredients added to change its properties. Lead glass, such as lead crystal or flint glass, is more 'brilliant' because the increased refractive index causes noticeably more "sparkles", while boron may be added to change the thermal and electrical properties, as in Pyrex. Adding barium also increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion, and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eye glasses. Large amounts of iron are used in glass that absorbs infrared energy, such as heat absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs UV wavelengths (biologically damaging ionizing radiation).

Two other common glass ingredients are calumite (an iron industry by-product) and "cullet" (recycled glass). The recycled glass saves on raw materials and energy. However, impurities in the cullet can lead to product and equipment failure.

Finally, fining agents such as sodium sulfate, sodium chloride, or antimony oxide are added to reduce the bubble content in the glass.[8] Glass batch calculation is the method by which the correct raw material mixture is determined to achieve the desired glass composition.

[edit] Contemporary glass production

Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda-lime glass for mass production is melted in gas fired units. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks.[8]

After melting, homogenization and refining (removal of bubbles), the glass is formed. Flat glass for windows and similar applications is formed by the float glass process, developed between 1953 and 1957 by Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish.[9] Container glass for common bottles and jars is formed by blowing and pressing methods. Further glass forming techniques are summarized in the table Glass forming techniques.

Once the desired form is obtained, glass is usually annealed for the removal of stresses. Surface treatments, coatings or lamination may follow to improve the chemical durability (glass container coatings, glass container internal treatment), strength (toughened glass, bulletproof glass, windshields), or optical properties (insulated glazing, anti-reflective coating).

[edit] Glassmaking in the laboratory

A vitrification experiment for the study of nuclear waste disposal at Pacific Northwest National Laboratory.

Failed laboratory glass melting test. The striations must be avoided through good homogenization.

New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali oxides and hydroxides, alkaline earth oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition).[10] Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating SeO2. Also, more readily reacting raw materials may be preferred over relatively inert ones, such as Al(OH)3 over Al2O3. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually annealed to prevent breakage during processing.[10][11]

See also: Optical lens design, Fabrication and testing of optical components

[deuces wild]

Injection molding (British English: moulding) is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the mold cavity. [1] After a product is designed, usually by an industrial designer or an engineer, molds are made by a moldmaker (or toolmaker) from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars.

Process Characteristics

* Utilizes a ram or screw-type plunger to force molten plastic material into a mold cavity

* Produces a solid or open-ended shape which has conformed to the contour of the mold

* Uses thermoplastic or thermoset materials

* Produces a parting line, sprue, and gate marks

* Ejector pin marks are usually present

In 1868 John Wesley Hyatt developed a plastic material he named Celluloid which had been invented in 1851 by Alexander Parks. Hyatt improved it so that it could be processed into finished form. In 1872 John, with his brother Isaiah, patented the first injection molding machine.[3] This machine was relatively simple compared to the machines we use today. It basically worked like a large hypodermic needle injecting plastic through a heated cylinder into a mold. The industry progressed slowly over the years producing products such as collar stays, buttons, and hair combs until it exploded in the 1940s because World War 2 created a huge demand for inexpensive, mass-produced products. In 1946 James Hendry built the first screw injection machine. This machine allowed material to be mixed before injection, which meant colored plastic or recycled plastic could be added to the virgin material and mixed thoroughly before being injected. Today screw injection machines account for 95% of all injection machines. The industry has evolved over the years from producing combs and buttons to producing a vast array of products for many industries including automotive, medical, aerospace, consumer, toys, plumbing, packaging, and construction.[4]

Injection molding is used to create many things such as milk cartons, containers, bottle caps, automotive dashboards, pocket combs, and most other plastic products available today. Injection molding is the most common method of part manufacturing. It is ideal for producing high volumes of the same object.[5] Some advantages of injection molding are high production rates, high tolerances are repeatable, wide range of materials can be used, low labour cost, minimal scrap losses, and little need to finish parts after molding. Some disadvantages of this process are expensive equipment investment, running costs may be high, and parts must be designed with molding consideration.[6]

Most polymers may be used, including all thermoplastics, some thermosets, and some elastomers.[7] In 1995 there were approximately 18,000 different materials available for injection molding and that number was increasing at an average rate of 750 per year. The available materials are alloys or blends of previously developed materials meaning that product designers can choose from a vast selection of materials, one that has exactly the right properties. Materials are chosen based on the strength and function required for the final part but also each material has different parrameters for molding that must be taken into account.[8] Common polymers like Epoxy and phenolic are examples of thermosetting plastics while nylon, polyethylene, and polystyrene are thermoplastic.[9]

It is important when designing products for injection molding that you consider how they will be formed in the machine, how they will be taken out of the machine, and the structure of the final product. Some important guidelines are:

1. Use approximately uniform wall thicknesses throughout your designs.

2. Keep walls thin - typically between 1/32" and 1/10". This allows for proper cooling and reduces cost by minimizing use of material. Thin walls also reduce problems with material shrinkage. Although some unevenness will occur due to shrinkage, walls as thick as 1/5" can be used. Keep wall thickness at least wall length / 50. Keep 90 deg walls under 0.25" high. Keep thickness of ejection pin surface wall at least .07".

3. To strengthen parts, instead of using thicker walls, use additional structures such as ribs. Use fillets at the base of ribs.

4. When using a rib make it about half the main wall thickness.

5. Round corners and edges wherever possible.

6. For easy release of the part from the mold, add a slight taper to the sides (typically ~ 2 deg) - especially for textured walls and walls higher than 0.25".

7. Avoid undercuts that are impossible to remove from the mold.

8. Lighter colors hide flow patterns better than dark colors.

9. Where walls meet at a 90 angle, round inside and outside to at least .05" radius - sharper outside corners can create molding problems and sharper inside corners will increase tooling cost.

10. Keep holes at least .015" from edges.[10]

Paper clip mold opened in molding machine; the nozzle is visible at right

Main article: Injection molding machine

Injection molding machines consist of a material hopper, an injection ram or screw-type plunger, and a heating unit.[11] They are also known as presses, they hold the molds in which the components are shaped. Presses are rated by tonnage, which expresses the amount of clamping force that the machine can exert. This force keeps the mold closed during the injection process. Tonnage can vary from less than 5 tons to 6000 tons, with the higher figures used in comparatively few manufacturing operations. The total clamp force needed is determined by the projected area of the part being molded. This projected area is multiplied by a clamp force of from 2 to 8 tons for each square inch of the projected areas. As a rule of thumb, 4 or 5 tons/in2 can be used for most products. If the plastic material is very stiff, it will require more injection pressure to fill the mold, thus more clamp tonnage to hold the mold closed.[12] The required force can also be determined by the material used and the size of the part, larger parts require higher clamping force.[13]

Mold or die are the common terms used to describe the tooling used to produce plastic parts in molding.

Traditionally, molds have been expensive to manufacture. They were usually only used in mass production where thousands of parts were being produced. Molds are typically constructed from hardened steel, pre-hardened steel, aluminium, and/or beryllium-copper alloy. The choice of material to build a mold from is primarily one of economics, steel molds generally cost more to construct, but their longer lifespan will offset the higher initial cost over a higher number of parts made before wearing out. Pre-hardened steel molds are less wear resistant and are used for lower volume requirements or larger components. The steel hardness is typically 38-45 on the Rockwell-C scale. Hardened steel molds are heat treated after machining. These are by far the superior in terms of wear resistance and lifespan. Typical hardness ranges between 50 and 60 Rockwell-C (HRC). Aluminium molds can cost substantially less, and when designed and machined with modern computerized equipment, can be economical for molding tens or even hundreds of thousands of parts. Beryllium copper is used in areas of the mold which require fast heat removal or areas that see the most shear heat generated.[14] The molds can be manufactured by either CNC machining or by using Electrical Discharge Machining processes.

More at http://en.wikipedia.org/wiki/Injection_molding

[Hb_Kai]

Scientists' 'perfect' bacon butty

Bacon sandwich

Experts spent 1,000 hours testing different bacon variations

Scientists have created a mathematical formula of how to make the perfect bacon butty.

Experts at Leeds University discovered the secret to the ideal sandwich lay in how crispy and crunchy rashers were.

They found that two or three back bacon rashers should be cooked under a preheated oven grill for seven minutes at about 240C (475F).

The bacon should then be placed between two slices of farmhouse bread, 1cm to 2cm thick.

Cooking times

Four researchers at the Department of Food Science spent more than 1,000 hours testing 700 variations on the traditional bacon sandwich.

They tried different types and cuts of bacon, cooking techniques, types of oil and a range of cooking times at different temperatures.

A shortlist was then tested with computers to measure the texture of each sandwich.

Fifty volunteers also judged each sandwich according to its taste, texture and flavour.

'Turn-off'

Dr Graham Clayton, who led the research, said: "We often think it's the taste and smell of bacon that consumers find most attractive.

"But our research proves that texture and the crunching sound is just - if not more - important.

"While there was much debate within our taste panels on the smoked or unsmoked decision, everyone agreed that tough or chewy bacon is a turn-off."

The formula is: N = C + {fb (cm) . fb (tc)} + fb (Ts) + fc . ta, where N=force in Newtons required to break the cooked bacon, fb=function of the bacon type, fc=function of the condiment/filling effect, Ts=serving temperature, tc=cooking time, ta=time or duration of application of condiment/filling, cm=cooking method, C=Newtons required to break uncooked bacon.

This is my area of expertise...

[-pops-]

Blimey! This is turning into Wikipedia.

The original post was a disguised advertisement for something (can't remember what) and I removed the advertising links as per Forum rules.

I think it has run its course with these snippets of vital information so I'll lock the thread.

[doug]

This topic has been reopened due to a member request.

Meany, I was enjoying that little bit of hedification!

Relocking it.

[doug]

This topic has now been resolved and subsequently closed.

If you wish to add a reply, please contact an administrator or moderator to reopen the topic.