25/04/2008 by admin.

In information science

In information science irrelevant or meaningless data is considered to be noise. Noise consists of a large number of transient disturbances with a statistically randomized time distribution.

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25/04/2008 by admin.

Gyrotrons are high powered vacuum tubes which emit millimeter wavelength beams by bunching electrons with cyclotron motion in a strong magnetic field. Output frequencies range from about 20 to 250 GHz, covering wavelengths from microwave to the edge of the terahertz gap. Typical output powers range from tens of kilowatts to 1-2 megawatts. Gyrotrons can be designed for pulsed or continuous operation

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25/04/2008 by admin.

Many Pencils

across the world and almost all in Europe are graded on the European system using a continuüm from “H” (for hardness) to “B” (for blackness), as well as “F” (for fine point). The standard writing Pencils
 are graded HB. According to Petroski this system might have been developed in the early 1900s by Brookman, an English pencil maker. It used “B” for black and “H” for hard; a Pencils
 grade was described by a sequence or successive Hs or Bs such as BB and BBB for successively softer leads, and HH and HHH for successively harder ones.

Today a set of Pencils
 ranging from a very hard, light-marking pencil to a very soft, black-marking Pencils
 usually ranges from hardest to softest as follows.

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25/04/2008 by admin.

While terahertz radiation is emitted as part of the black body radiation from anything with temperatures greater than about 10 kelvin, this thermal emission is very weak. As of 2004 the only viable sources of terahertz radiation were the gyrotron, the backward wave oscillator (”BWO”), the far infrared laser (”FIR laser”), quantum cascade laser, the free electron laser (FEL), synchrotron light sources, photomixing sources, and single-cycle sources used in Terahertz time domain spectroscopy. The first images generated using terahertz radiation date from the 1960’s; however, in 1995, images generated using terahertz time-domain spectroscopy generated a great deal of interest, and sparked a rapid growth in the field of terahertz science and technology. This excitement, along with the associated coining of the term “T-rays”, even showed up in a contemporary novel by Tom Clancy.

There have also been solid-state sources of millimeter and submillimeter waves for many years. AB Millimeter in Paris, for instance, produces a system that covers the entire range from 8 GHz to 1000 GHz with solid state sources and detectors. Nowadays, most time-domain work is done via ultrafast lasers.

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25/04/2008 by admin.

Electromagnetic (EM) radiation, also called light even though it is not always visible, is a self-propagating wave in space with electric and magnetic components. These components oscillate at right angles to each other and to the direction of propagation, and are in phase with each other. Electromagnetic radiation is classified into types according to the frequency of the wave: these types include, in order of increasing frequency, radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.

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25/04/2008 by admin.

In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field (that can also be equated to electric flux density). This electric field exerts a force on other electrically charged objects. The concept of electric field was introduced by Michael Faraday.

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25/04/2008 by admin.

In classical statistical mechanics, the equipartition theorem is a general formula that relates the temperature of a system with its average energies. The equipartition theorem is also known as the law of equipartition, equipartition of energy, or simply equipartition. The original idea of equipartition was that, in thermal equilibrium, energy is shared equally among its various forms; for example, the average kinetic energy in the translational motion of a molecule should equal the average kinetic energy in its rotational motion.

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25/04/2008 by admin.

Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the object’s temperature. Infrared radiation from a common household radiator or electric heater is an example of thermal radiation, as is the light emitted by a glowing incandescent light bulb. Thermal radiation is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation. The emitted wave frequency of the thermal radiation is a probability distribution depending only on temperature, and for a genuine black body is given by Planck’s law of radiation. Wien’s law gives the most likely frequency of the emitted radiation, and the Stefan–Boltzmann law gives the heat intensity.

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25/04/2008 by admin.

Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide. For example: a carbon-14 atom (the “parent”) emits radiation and transforms to a nitrogen-14 atom (the “daughter”). This is a random process on the atomic level, in that it is impossible to predict when a particular atom will decay, but given a large number of similar atoms, the decay rate, on average, is predictable

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25/04/2008 by admin.

Electromagnetic (EM) radiation, also called light even though it is not always visible, is a self-propagating wave in space with electric and magnetic components. These components oscillate at right angles to each other and to the direction of propagation, and are in phase with each other. Electromagnetic radiation is classified into types according to the frequency of the wave: these types include, in order of increasing frequency, radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.

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