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Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as temporal frequency to emphasize the contrast to spatial frequency, and ordinary frequency to emphasize the contrast to angular frequency. Frequency is expressed in units of hertz (Hz) which is equivalent to one (event) per second. The corresponding period is the time duration of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example, if a heart beats at a frequency of 120 times a minute, its period, T—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and periodic phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.
Maxwell's equations are a set of coupled partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits. The equations provide a mathematical model for electric, optical, and radio technologies, such as power generation, electric motors, wireless communication, lenses, radar etc. They describe how electric and magnetic fields are generated by charges, currents, and changes of the fields. The equations are named after the physicist and mathematician James Clerk Maxwell, who, in 1861 and 1862, published an early form of the equations that included the Lorentz force law. Maxwell first used the equations to propose that light is an electromagnetic phenomenon. The modern form of the equations in their most common formulation is credited to Oliver Heaviside.
Physical geography is one of the two fields of geography. Physical geography is the branch of natural science which deals with the processes and patterns in the natural environment such as the atmosphere, hydrosphere, biosphere, and geosphere, as opposed to the cultural or built environment, the domain of human geography.
Communications security is the discipline of preventing unauthorized interceptors from accessing telecommunications in an intelligible form, while still delivering content to the intended recipients.
In telecommunication, a cryptochannel is a complete system of crypto-communications between two or more holders. It includes: (a) the cryptographic aids prescribed; (b) the holders thereof; (c) the indicators or other means of identification; (d) the area or areas in which effective; (e) the special purpose, if any, for which provided; and (f) pertinent notes as to distribution, usage, etc. A cryptochannel is analogous to a radio circuit.
In metadata, the term data element is an atomic unit of data that has precise meaning or precise semantics. A data element has:
- An identification such as a data element name
- A clear data element definition
- One or more representation terms
- Optional enumerated values Code (metadata)
- A list of synonyms to data elements in other metadata registries Synonym ring
Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their electromagnetic environment, by limiting the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI) or even physical damage in operational equipment. The goal of EMC is the correct operation of different equipment in a common electromagnetic environment. It is also the name given to the associated branch of electrical engineering.
A nuclear electromagnetic pulse is a burst of electromagnetic radiation created by a nuclear explosion. The resulting rapidly varying electric and magnetic fields may couple with electrical and electronic systems to produce damaging current and voltage surges. The specific characteristics of a particular nuclear EMP event vary according to a number of factors, the most important of which is the altitude of the detonation.
Electro–optics is a branch of electrical engineering, electronic engineering, materials science, and material physics involving components, devices and systems which operate by the propagation and interaction of light with various tailored materials. It is essentially the same as what is popularly described today as photonics. It is not only concerned with the "electro–optic effect". Thus it concerns the interaction between the electromagnetic (optical) and the electrical (electronic) states of materials.
Foreign instrumentation signature intelligence, FISINT is intelligence from the interception of foreign electromagnetic emissions associated with the testing and operational deployment of foreign aerospace, surface, and subsurface systems. Since it deals with signals that have communicational content, it is a subset of Communications Intelligence (COMINT), which, in turn, is a subset of SIGINT. Unlike general COMINT signals, the content of FISINT signals is not in regular human language, but rather in machine to machine (instrumentation) language or in a combination of regular human language and instrumentation language. FISINT is also considered as a subset of MASINT.
In telecommunication, the term noise power has the following meanings:
- The measured total noise in a given bandwidth at the input or output of a device when the signal is not present; the integral of noise spectral density over the bandwidth
- The power generated by a random electromagnetic process.
- Interfering and unwanted power in an electrical device or system.
- In the acceptance testing of radio transmitters, the mean power supplied to the antenna transmission line by a radio transmitter when loaded with noise having a Gaussian amplitude-vs.-frequency distribution.
Electronic warfare (EW) is any action involving the use of the electromagnetic spectrum or directed energy to control the spectrum, attack an enemy, or impede enemy assaults. The purpose of electronic warfare is to deny the opponent the advantage of—and ensure friendly unimpeded access to—the EM spectrum. EW can be applied from air, sea, land, and/or space by crewed and uncrewed systems, and can target communication, radar, or other military and civilian assets.
The near field and far field are regions of the electromagnetic field (EM) around an object, such as a transmitting antenna, or the result of radiation scattering off an object. Non-radiative near-field behaviors dominate close to the antenna or scattering object, while electromagnetic radiation far-field behaviors dominate at greater distances.
In physics and engineering, surface power density is power per unit area.
The Fast Auroral SnapshoT Explorer was a NASA plasma physics satellite, and was the second spacecraft in the Small Explorer program (SMEX). It was launched on 21 August 1996, from Vandenberg Air Force Base aboard a Pegasus XL launch vehicle. The spacecraft was designed and built by NASA's Goddard Space Flight Center (GSFC). Flight operations were handled by GSFC for the first three years, and thereafter were transferred to the University of California, Berkeley's Space Sciences Laboratory.
Command and control is a "set of organizational and technical attributes and processes ... [that] employs human, physical, and information resources to solve problems and accomplish missions" to achieve the goals of an organization or enterprise, according to a 2015 definition by military scientists Marius Vassiliou, David S. Alberts, and Jonathan R. Agre. The term often refers to a military system.
The Electro-Magnetic Laboratory Rail Gun is a 32-megajoule electro-magnetic laboratory rail gun being evaluated by the US Office of Naval Research (ONR) Naval Air Warfare and Weapons Department. The US Navy is pursuing development of the launcher system through two industry teams -- General Atomics and BAE Systems - to reduce risk in the program and to foster innovation in next-generation shipboard weapons. The same amount of energy is released by the detonation of 4.8 kg (11 lb) of C4.
The ISEE-1 was a Explorer-class mother spacecraft, International Sun-Earth Explorer-1, was part of the mother/daughter/heliocentric mission. ISEE-1 was a 340.2 kg (750 lb) space probe used to study magnetic fields near the Earth. ISEE-1 was a spin-stabilized spacecraft and based on the design of the prior IMP series of spacecraft. ISEE-1 and ISEE-2 were launched on 22 October 1977, and they re-entered on 26 September 1987.
The ISEE-2 was a Explorer-class daughter spacecraft, International Sun-Earth Explorer-2, was part of the mother/daughter/heliocentric mission. ISEE-2 was a 165.78 kg (365.5 lb) space probe used to study magnetic fields near the Earth. ISEE-2 was a spin-stabilized spacecraft and based on the design of the prior IMP series of spacecraft. ISEE-1 and ISEE-2 were launched on 22 October 1977, and they re-entered on 26 September 1987.
EQUULEUS is a nanosatellite of the 6U CubeSat format that will measure the distribution of plasma that surrounds the Earth (plasmasphere) to help scientists understand the radiation environment in that region. It will also demonstrate low-thrust trajectory control techniques, such as multiple lunar flybys, within the Earth-Moon region using water steam as propellant. The spacecraft was designed and developed jointly by the Japan Aerospace Exploration Agency (JAXA) and the University of Tokyo.
References
- ↑ Directive 2014/30/EU of the European Parliament and of the Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to electromagnetic compatibility, Article 3 (Definitions), paragraph 8.
