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Ultra Low Frequency
Ultra low frequency (ULF) is the ITU designation for the frequency range of electromagnetic waves between 300 hertz and 3 kilohertz, corresponding to wavelengths between 1,000 and 100 km. In magnetosphere science and seismology, alternative definitions are usually given, including ranges from 1 mHz to 100 Hz, 1 mHz to 1 Hz, and 10 mHz to 10 Hz. Many types of waves in the ULF frequency band can be observed in the magnetosphere and on the ground. These waves represent important physical processes in the near-Earth plasma environment. The speed of the ULF waves is often associated with the Alfvén velocity that depends on the ambient magnetic field and plasma mass density. This band is used for communications in mines, as it can penetrate the earth. Earthquakes Some monitoring stations have reported that earthquakes are sometimes preceded by a spike in ULF activity. A remarkable example of this occurred before the 1989 Loma Prieta earthquake in California, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kilohertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base units is 1/s or s−1, meaning that one hertz is one per second or the reciprocal of one second. It is used only in the case of periodic events. It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. For high frequencies, the unit is commonly expressed in multiples: kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz). Some of the unit's most common uses are in the description of periodic waveforms and musical tones, particularly those used in radio- and audio-related applications. It is also used to describe the clock speeds at which computers and other electronics are driven. The units are sometimes also used as a representation o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Demeter (satellite)
DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) was a French micro-satellite operated by CNES devoted to the investigation of the ionospheric disturbances due to seismic and volcanic activity. It was launched on June 29, 2004, on a quasi Sun-synchronous circular orbit with an inclination of about 98.23° and an altitude of about 710 km. The altitude was changed to about 660 km in December 2005. Due to the specific orbit, DEMETER was always located either shortly before the local noon (10:30 local time) or local midnight (22:30 local time). The satellite performs 14 orbits per day and measures continuously between -65° and +65° of invariant latitude. DEMETER observed an increase in ultra low frequency radio waves in the month before the 2010 Haiti earthquake. During the 2010 eruption of Mount Merapi, DEMETER noted anomalies in the ionosphere. Scientific operations ended December 9, 2010. Scientific Objectives * To study ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electric Current
An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge carriers, which may be one of several types of particles, depending on the Electrical conductor, conductor. In electric circuits the charge carriers are often electrons moving through a wire. In semiconductors they can be electrons or Electron hole, holes. In an Electrolyte#Electrochemistry, electrolyte the charge carriers are ions, while in Plasma (physics), plasma, an Ionization, ionized gas, they are ions and electrons. In the International System of Units (SI), electric current is expressed in Unit of measurement, units of ampere (sometimes called an "amp", symbol A), which is equivalent to one coulomb per second. The ampere is an SI base unit and electric current is a ISQ base quantity, base quantity in the International System of Qua ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a variety of materials (chemicals) depending on the type of cell. An electrode may be called either a cathode or anode according to the direction of the electric current, unrelated to the potential difference between electrodes. Michael Faraday coined the term "" in 1833; the word recalls the Greek ἤλεκτρον (, "amber") and ὁδός (, "path, way"). The electrophore, invented by Johan Wilcke in 1762, was an early version of an electrode used to study static electricity. Anode and cathode in electrochemical cells Electrodes are an essential part of any battery. The first electrochemical battery was devised by Alessandro Volta and was aptly named the Voltaic cell. This battery consisted of a stack of copper and zinc electrodes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radio Amateurs
An amateur radio operator is someone who uses equipment at an amateur radio station to engage in two-way personal communications with other amateur operators on radio frequencies assigned to the amateur radio service. Amateur radio operators have been granted an amateur radio license by a governmental regulatory authority after passing an examination on applicable regulations, electronics, radio theory, and radio operation. As a component of their license, amateur radio operators are assigned a call sign that they use to identify themselves during communication. About three million amateur radio operators are currently active worldwide. Amateur radio operators are also known as radio amateurs or hams. The term "ham" as a nickname for amateur radio operators originated in a pejorative usage (like "ham actor") by operators in commercial and professional radio communities, and dates to wired telegraphy. The word was subsequently adopted by amateur radio operators. Demographic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
World War I
World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting took place mainly in European theatre of World War I, Europe and the Middle Eastern theatre of World War I, Middle East, as well as in parts of African theatre of World War I, Africa and the Asian and Pacific theatre of World War I, Asia-Pacific, and in Europe was characterised by trench warfare; the widespread use of Artillery of World War I, artillery, machine guns, and Chemical weapons in World War I, chemical weapons (gas); and the introductions of Tanks in World War I, tanks and Aviation in World War I, aircraft. World War I was one of the List of wars by death toll, deadliest conflicts in history, resulting in an estimated World War I casualties, 10 million military dead and more than 20 million wounded, plus some 10 million civilian de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Classified Information
Classified information is confidential material that a government deems to be sensitive information which must be protected from unauthorized disclosure that requires special handling and dissemination controls. Access is restricted by law or regulation to particular groups of individuals with the necessary security clearance with a need to know. A formal security clearance is required to view or handle classified material. The clearance process requires a satisfactory background investigation. Documents and other information must be properly marked "by the author" with one of several (hierarchical) levels of sensitivity—e.g. Confidential (C), Secret (S), and Top Secret (S). All classified documents require designation markings on the technical file which is usually located either on the cover sheet, header and footer of page. The choice of level is based on an impact assessment; governments have their own criteria, including how to determine the classification of an inf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AGARD
The Advisory Group for Aerospace Research and Development (AGARD) was an agency of NATO that existed from 1952 to 1996. AGARD was founded as an Agency of the NATO Military Committee. It was set up in May 1952 with headquarters in Neuilly sur Seine, France. In a mission statement in the 1982 ''History'' it published, the purpose involved "bringing together the leading personalities of the NATO nations in the fields of science and technology relating to aerospace". Frank Wattendorf & Rolland A. Willaume editors (1982) ''The AGARD History 1952 — 1981'', AGARD Publishing The Advisory Group was organized by panels: :Aerospace medical, avionics, electromagnetic wave propagation, flight mechanics, fluid dynamics, guidance and control, propulsion and energetics, structures and materials, and technical information. In 1958 Theodore von Kármán hired Moe Berg to accompany him to the AGARD conference in Paris. "AGARD's aim was to encourage European countries to develop weapons technolo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Secure Communications
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 the North Atlantic Treaty Organization culture, including United States Department of Defense culture, it is often referred to by the abbreviation COMSEC. The field includes cryptographic security, transmission security, emissions security and physical security of COMSEC equipment and associated keying material. COMSEC is used to protect both classified and unclassified traffic on military communications networks, including voice, video, and data. It is used for both analog and digital applications, and both wired and wireless links. Voice over secure internet protocol VOSIP has become the de facto standard for securing voice communication, replacing the need for Secure Terminal Equipment (STE) in much of NATO, including the U.S.A. USCENTCOM moved entirely to VOSIP in 2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Massachusetts
Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode Island to its south, New Hampshire and Vermont to its north, and New York (state), New York to its west. Massachusetts is the List of U.S. states and territories by area, sixth-smallest state by land area. With a 2024 U.S. Census Bureau-estimated population of 7,136,171, its highest estimated count ever, Massachusetts is the most populous state in New England, the List of U.S. states and territories by population, 16th-most-populous in the United States, and the List of states and territories of the United States by population density, third-most densely populated U.S. state, after New Jersey and Rhode Island. Massachusetts was a site of early British colonization of the Americas, English colonization. The Plymouth Colony was founded in 16 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cambridge, Massachusetts
Cambridge ( ) is a city in Middlesex County, Massachusetts, United States. It is a suburb in the Greater Boston metropolitan area, located directly across the Charles River from Boston. The city's population as of the 2020 United States census, 2020 U.S. census was 118,403, making it the most populous city in the county, the List of municipalities in Massachusetts, fourth-largest in Massachusetts behind Boston, Worcester, Massachusetts, Worcester, and Springfield, Massachusetts, Springfield, and List of cities in New England by population, ninth-most populous in New England. The city was named in honor of the University of Cambridge in Cambridge, England, which was an important center of the Puritans, Puritan theology that was embraced by the town's founders. Harvard University, an Ivy League university founded in Cambridge in 1636, is the oldest institution of higher learning in the United States. The Massachusetts Institute of Technology (MIT), Lesley University, and Hult Inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MIT Technology Review
''MIT Technology Review'' is a bimonthly magazine wholly owned by the Massachusetts Institute of Technology. It was founded in 1899 as ''The Technology Review'', and was re-launched without "''The''" in its name on April 23, 1998, under then publisher R. Bruce Journey. In September 2005, it was changed, under its then editor-in-chief and publisher, Jason Pontin, to a form resembling the historical magazine. Before the 1998 re-launch, the editor stated that "nothing will be left of the old magazine except the name." It was therefore necessary to distinguish between the modern and the historical ''Technology Review''. The historical magazine had been published by the MIT Alumni Association, was more closely aligned with the interests of MIT alumni, and had a more intellectual tone and much smaller public circulation. The magazine, billed from 1998 to 2005 as "MIT's Magazine of Innovation", and from 2005 onwards as simply "published by MIT", focused on new technology and how it is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
