A mandrel is one of the following: a round object against which material can be forged or shaped. A flanged mandrel is a parallel bar of a specific diameter with an integral flange towards one end, threaded at the opposite end. Work is gripped between a nut on the thread. A tapered mandrel has a taper of 0.005 inches per foot and is designed to hold work by being driven into an accurate hole on the work, gripping the work by friction. A threaded mandrel may have a male or female thread, work which has an identical thread is screwed onto the mandrel. On a lathe, mandrels are mounted between centres and driven by a lathe dog, but may be gripped in a chuck (typically the threaded mandrels, where the outer face of work is to be machined. Threaded mandrels may be mounted between centres. In addition to lathes, arbors are used to hold buffing wheels, circular saws, sanding discs; these mandrels consist of a cylinder, threaded on one end. There are many different types of mandrels for specialized applications.
Examples include live chuck mandrels, live bull ring mandrels, dead bull ring mandrels. A shaped bar of metal, placed inside a workpiece to be formed, e.g. arbors used to bend the exhaust pipes for automobiles and in the production of molten glass, metal rings, threaded rods, furniture legs. An example of one type of mandrel is a shaped bar of metal inserted in, or next to, an item to be machined or bent in a certain pattern, e.g. in tube drawing. Exhaust pipes for automobiles are bent using a mandrel during manufacture; the mandrel allows the exhaust pipes to be bent into smooth curves without undesirable creasing, kinking, or collapsing. Molten glass may be shaped in this way as well. Another example of this type of mandrel is found in jewelry manufacturing, where ring and bracelet mandrels are used to shape metal into a desired size and shape, using a tiny hammer to beat the metal against the mandrel. A type of mandrel is used in making reeds for double reed instruments such as the bassoon or oboe.
Another type of mandrel is the chuck that a lathe uses to hold pieces of wood, metal or plastic to be machined as they are turned. In this way, rods can be threaded, furniture legs are turned to have æsthetic patterns, irregularly-shaped objects can be given a round shape. There are several types of mandrels used with lathes. Original expanding mandrels have a tapered wedge that will expand to hold the item; the third type of mandrel discussed here is that, used to hold circular saw blades, buffing wheels, sanding discs onto drills, circular saws, similar power tools. A mandrel of this type consists of a cylinder, threaded on one end, with a washer brazed onto the threaded end and an accompanying screw and second washer used to clamp the circular saw blade, sanding media, or other rotary tool onto the mandrel. While most mandrels are driven by direct connection to an electric motor or engine, other mandrels are driven by attachment to a bearing-supported, pulley-driven shaft. Mandrels are used in industrial composite fabrication such as in filament winding.
During the manufacturing process, resin-impregnated filaments are wound around a mandrel to create a composite material structure or part. The structure is cured and the mandrel is removed. One problem with this type of process is that the mandrel can be difficult to remove once the part has been cured; as a result, engineers have created a new type of mandrel that has the ability to change shape and be extracted. When heated above a certain temperature, the mandrel becomes elastic and can be manipulated into the desired shape and cooled to become rigid again in the new shape, it can be used in the filament winding process. Once the composite part is cured, the mandrel can be reheated until elastic and removed from the cured part; these types of mandrels can be used repeatedly. In the production of steel core used for flexible drives, the centre wire upon which the subsequent layers are wound is referred to as a Mandrel; this "centre wire" may itself be composed of either a single wire or layers, depending on the sizing of the finished product.
A hole saw attaches to a mandrel, the latter being a drill bit with threads to secure the saw. Mandrels are not recent inventions. Metal machining utilizing the spinning process has been recorded as far back as ancient Egyptian times. In metal spinning, a wood or metal spinning mandrel is used, the form of which corresponds with the internal contour of the part to be produced; this method securely clamps the raw material and allows for accurate machining into the desired final form. Since the material is clamped internally, there is no interference to the operator from the lathe/mandrel assembly during production; the traversing mandrel was introduced around 1700, instantiated the design of a lathe mandrel able to slide axially in its bearings under the control of the operator, so that components having short lengths of thread could be produced, such as screws. The traversing mandrel was employed by clockmakers and ornamental turners during this era; the device was superseded by a mandrel-driven device called a leadscrew, which uses a train of gears that can be altered as required for the turning application.
Arbor support Historical pictures of mandrels and leadscrews: http://www.historicgames.com/lathes/special.html http://www.mmsonline.com/articles/expanding-the-expanding-mandrel39s-usefulness
A laser diode, injection laser diode, or diode laser is a semiconductor device similar to a light-emitting diode in which the laser beam is created at the diode's junction. Laser diodes can directly convert electrical energy into light. Driven by voltage, the doped p-n-transition allows for recombination of an electron with a hole. Due to the drop of the electron from a higher energy level to a lower one, radiation, in the form of an emitted photon is generated; this is spontaneous emission. Stimulated emission can be produced when the process is continued and further generate light with the same phase and wavelength; the choice of the semiconductor material determines the wavelength of the emitted beam, which in today's laser diodes range from infra-red to the UV spectrum. Laser diodes are the most common type of lasers produced, with a wide range of uses that include fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray disc reading/recording, laser printing, laser scanning and light beam illumination.
A laser diode is electrically a PIN diode. The active region of the laser diode is in the intrinsic region, the carriers are pumped into that region from the N and P regions respectively. While initial diode laser research was conducted on simple P-N diodes, all modern lasers use the double-hetero-structure implementation, where the carriers and the photons are confined in order to maximize their chances for recombination and light generation. Unlike a regular diode, the goal for a laser diode is to recombine all carriers in the I region, produce light. Thus, laser diodes are fabricated using direct band-gap semiconductors; the laser diode epitaxial structure is grown using one of the crystal growth techniques starting from an N doped substrate, growing the I doped active layer, followed by the P doped cladding, a contact layer. The active layer most consists of quantum wells, which provide lower threshold current and higher efficiency. Laser diodes form a subset of the larger classification of semiconductor p-n junction diodes.
Forward electrical bias across the laser diode causes the two species of charge carrier – holes and electrons – to be "injected" from opposite sides of the p-n junction into the depletion region. Holes are injected from the p-doped, electrons from the n-doped, semiconductor. Due to the use of charge injection in powering most diode lasers, this class of lasers is sometimes termed "injection lasers," or "injection laser diode"; as diode lasers are semiconductor devices, they may be classified as semiconductor lasers. Either designation distinguishes diode lasers from solid-state lasers. Another method of powering some diode lasers is the use of optical pumping. Optically pumped semiconductor lasers use a III-V semiconductor chip as the gain medium, another laser as the pump source. OPSL offer several advantages over ILDs in wavelength selection and lack of interference from internal electrode structures. A further advantage of OPSLs is invariance of the beam parameters - divergence and pointing - as pump power is varied over a 10:1 output power ratio.
When an electron and a hole are present in the same region, they may recombine or "annihilate" producing a spontaneous emission — i.e. the electron may re-occupy the energy state of the hole, emitting a photon with energy equal to the difference between the electron's original state and hole's state. Spontaneous emission below the lasing threshold produces similar properties to an LED. Spontaneous emission is necessary to initiate laser oscillation, but it is one among several sources of inefficiency once the laser is oscillating; the difference between the photon-emitting semiconductor laser and a conventional phonon-emitting semiconductor junction diode lies in the type of semiconductor used, one whose physical and atomic structure confers the possibility for photon emission. These photon-emitting semiconductors are the so-called "direct bandgap" semiconductors; the properties of silicon and germanium, which are single-element semiconductors, have bandgaps that do not align in the way needed to allow photon emission and are not considered "direct."
Other materials, the so-called compound semiconductors, have identical crystalline structures as silicon or germanium but use alternating arrangements of two different atomic species in a checkerboard-like pattern to break the symmetry. The transition between the materials in the alternating pattern creates the critical "direct bandgap" property. Gallium arsenide, indium phosphide, gallium antimonide, gallium nitride are all examples of compound semiconductor materials that can be used to create junction diodes that emit light. In the absence of stimulated emission conditions and holes may coexist in proximity to one another, without recombining, for a certain time, termed the "upper-state lifetime" or "recombination time", before they recombine. A nearby photon with energy equal to the recombination energy can cause recombination by stimulated emission; this generates another photon of the same frequency and phase, travelling in the same direction as the first photon. This means that stimulated emission will cause gain in an optical wave (of the correct wavele
In telecommunications, transmission is the process of sending and propagating an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless. One example of transmission is the sending of a signal with limited duration, for example a block or packet of data, a phone call, or an email. Transmission technologies and schemes refer to physical layer protocol duties such as modulation, line coding, error control, bit synchronization and multiplexing, but the term may involve higher-layer protocol duties, for example, digitizing an analog message signal, data compression. Transmission of a digital message, or of a digitized analog signal, is known as digital communication
General Services Administration
The General Services Administration, an independent agency of the United States government, was established in 1949 to help manage and support the basic functioning of federal agencies. GSA supplies products and communications for U. S. government offices, provides transportation and office space to federal employees, develops government-wide cost-minimizing policies and other management tasks. GSA employs about 12,000 federal workers and has an annual operating budget of $20.9 billion. GSA oversees $66 billion of procurement annually, it contributes to the management of about $500 billion in U. S. federal property, divided chiefly among 8,700 owned and leased buildings and a 215,000 vehicle motor pool. Among the real estate assets managed by GSA are the Ronald Reagan Building and International Trade Center in Washington, D. C. – the largest U. S. federal building after the Pentagon – and the Hart-Dole-Inouye Federal Center. GSA's business lines include the Federal Acquisition Service and the Public Buildings Service, as well as several Staff Offices including the Office of Government-wide Policy, the Office of Small Business Utilization, the Office of Mission Assurance.
As part of FAS, GSA's Technology Transformation Services helps federal agencies improve delivery of information and services to the public. Key initiatives include FedRAMP, Cloud.gov, the USAGov platform, Data.gov, Performance.gov, Challenge.gov. GSA is a member of the Procurement G6, an informal group leading the use of framework agreements and e-procurement instruments in public procurement. In 1947 President Harry Truman asked former President Herbert Hoover to lead what became known as the Hoover Commission to make recommendations to reorganize the operations of the federal government. One of the recommendations of the commission was the establishment of an "Office of the General Services." This proposed office would combine the responsibilities of the following organizations: U. S. Treasury Department's Bureau of Federal Supply U. S. Treasury Department's Office of Contract Settlement National Archives Establishment All functions of the Federal Works Agency, including the Public Buildings Administration and the Public Roads Administration War Assets AdministrationGSA became an independent agency on July 1, 1949, after the passage of the Federal Property and Administrative Services Act.
General Jess Larson, Administrator of the War Assets Administration, was named GSA's first Administrator. The first job awaiting Administrator Larson and the newly formed GSA was a complete renovation of the White House; the structure had fallen into such a state of disrepair by 1949 that one inspector of the time said the historic structure was standing "purely from habit." Larson explained the nature of the total renovation in depth by saying, "In order to make the White House structurally sound, it was necessary to dismantle, I mean dismantle, everything from the White House except the four walls, which were constructed of stone. Everything, except the four walls without a roof, was stripped down, that's where the work started." GSA worked with President Truman and First Lady Bess Truman to ensure that the new agency's first major project would be a success. GSA completed the renovation in 1952. In 1986 GSA headquarters, U. S. General Services Administration Building, located at Eighteenth and F Streets, NW, was listed on the National Register of Historic Places, at the time serving as Interior Department offices.
In 1960 GSA created the Federal Telecommunications System, a government-wide intercity telephone system. In 1962 the Ad Hoc Committee on Federal Office Space created a new building program to address obsolete office buildings in Washington, D. C. resulting in the construction of many of the offices that now line Independence Avenue. In 1970 the Nixon administration created the Consumer Product Information Coordinating Center, now part of USAGov. In 1974 the Federal Buildings Fund was initiated, allowing GSA to issue rent bills to federal agencies. In 1972 GSA established the Automated Data and Telecommunications Service, which became the Office of Information Resources Management. In 1973 GSA created the Office of Federal Management Policy. GSA's Office of Acquisition Policy centralized procurement policy in 1978. GSA was responsible for emergency preparedness and stockpiling strategic materials to be used in wartime until these functions were transferred to the newly-created Federal Emergency Management Agency in 1979.
In 1984 GSA introduced the federal government to the use of charge cards, known as the GMA SmartPay system. The National Archives and Records Administration was spun off into an independent agency in 1985; the same year, GSA began to provide governmentwide policy oversight and guidance for federal real property management as a result of an Executive Order signed by President Ronald Reagan. In 2003 the Federal Protective Service was moved to the Department of Homeland Security. In 2005 GSA reorganized to merge the Federal Supply Service and Federal Technology Service business lines into the Federal Acquisition Service. On April 3, 2009, President Barack Obama nominated Martha N. Johnson to serve as GSA Administrator. After a nine-month delay, the United States Senate confirmed her nomination on February 4, 2010. On April 2, 2012, Johnson resigned in the wake of a management-deficiency report that detailed improper payments for a 2010 "Western Regions" training conference put on by the Public Buildings Service in Las Vegas.
In July 1991 GSA contractors began the excavation of what is now the Ted Weiss Federal Building in New York City. The planning for that buildin
An optical fiber is a flexible, transparent fiber made by drawing glass or plastic to a diameter thicker than that of a human hair. Optical fibers are used most as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths than electrical cables. Fibers are used instead of metal wires. Fibers are used for illumination and imaging, are wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are used for a variety of other applications, some of them being fiber optic sensors and fiber lasers. Optical fibers include a core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by the phenomenon of total internal reflection which causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers, while those that support a single mode are called single-mode fibers.
Multi-mode fibers have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters. Being able to join optical fibers with low loss is important in fiber optic communication; this is more complex than joining electrical wire or cable and involves careful cleaving of the fibers, precise alignment of the fiber cores, the coupling of these aligned cores. For applications that demand a permanent connection a fusion splice is common. In this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a mechanical splice, where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors; the field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics.
The term was coined by Indian physicist Narinder Singh Kapany, acknowledged as the father of fiber optics. 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, 12 years later. Tyndall 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 reflected at the surface.... The angle which marks the limit where total reflection 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′.
In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities. 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. In the 1930s, Heinrich Lamm showed that one could transmit images through a bundle of unclad optical fibers and used it for internal medical examinations, but his work was forgotten. In 1953, Dutch scientist Bram van Heel first demonstrated image transmission through bundles of optical fibers with a transparent cladding; that same year, Harold Hopkins and Narinder Singh Kapany at Imperial College in London succeeded in making image-transmitting bundles with over 10,000 fibers, subsequently achieved image transmission through a 75 cm long bundle which combined several thousand fibers. Their article titled "A flexible fibrescope, using static scanning" was published in the journal Nature in 1954.
The first practical fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, 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. A variety of other image transmission applications soon followed. Kapany coined the term fiber optics, wrote a 1960 article in Scientific American that introduced the topic to a wide audience, wrote the first book about the new field; the first working fiber-optical data transmission system was demonstrated by German physicist Manfred Börner at Telefunken Research Labs in Ulm in 1965, followed by the first patent application for this technology in 1966. NASA used fiber optics in the television cameras. At the time, the use in the cameras was classified confidential, employees handling the cameras had to be supervised by someone with an appropriate security clearance. Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables were the first, in 1965, to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer, making fibers a practical communication medium.
They proposed th