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Extremely Low Frequency
Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation ( radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively. In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz.Liemohn, Michael W. and A. A. CHAN,Unraveling the Causes of Radiation Belt Enhancements". EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION, Volume 88, Number 42, 16 October 2007, pages 427-440. Republished by NASA and accessed online, 8 February 2010. Adobe File, page 2. In the related magnetosphere science, the lower frequency electromagnetic oscillations (pulsations occurring below ~3 Hz) are considered to lie in the ULF range, which is thus also defined differently from the ITU radio bands. ELF radio waves are generated by lightning and natural disturbances in Earth's magnetic field, so they are a subject of research by atmospheric scientists. B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one hertz is the reciprocal of one second. It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are 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 of the energy of a photon, via the Planck relation ''E'' = ''hν'', where ''E'' is the photon's energy, ''ν'' is its freq ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Communication With Submarines
Communication with submarines is a field within military communications that presents technical challenges and requires specialized technology. Because radio waves do not travel well through good electrical conductors like salt water, submerged submarines are cut off from radio communication with their command authorities at ordinary radio frequencies. Submarines can surface and raise an antenna above the sea level, or float a tethered buoy carrying an antenna, then use ordinary radio transmissions, however this makes them vulnerable to detection by anti-submarine warfare forces. Early submarines during World War II mostly traveled on the surface because of their limited underwater speed and endurance, and dove mainly to evade immediate threats or for stealthy approach to their targets. During the Cold War, however, nuclear-powered submarines were developed that could stay submerged for months. In the event of a nuclear war, submerged ballistic missile submarines have to be order ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charged Particle
In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary particle, which are all believed to have the same charge (except antimatter). Another charged particle may be an atomic nucleus devoid of electrons, such as an alpha particle. A plasma is a collection of charged particles, atomic nuclei and separated electrons, but can also be a gas containing a significant proportion of charged particles. Charges are arbitrarily labeled as ''positive''(+) or ''negative''(-). Only the existence of two 'types' of charges is known, there isn't anything inherent about positive charges that makes them positive, and the same goes for the negative charge. Examples Positively charged particles * protons and atomic nuclei * positrons (antielectrons) * alpha particles * positive charged pions * cations Negatively c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Very Low Frequency
Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave as the wavelengths range from one to ten myriameters (an obsolete metric unit equal to 10 kilometers). Due to its limited bandwidth, audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations (broadcasting time signals to set radio clocks) and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines. Propagation characteristics Because of their long wavelengths, VLF radio waves can diffract around large obstacles and so are not blocked by mountain ranges, and can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Curvature Of The Earth
Spherical Earth or Earth's curvature refers to the approximation of figure of the Earth as a sphere. The earliest documented mention of the concept dates from around the 5th century BC, when it appears in the writings of Greek philosophers. In the 3rd century BC, Hellenistic astronomy established the roughly spherical shape of Earth as a physical fact and calculated the Earth's circumference. This knowledge was gradually adopted throughout the Old World during Late Antiquity and the Middle Ages.Continuation into Roman and medieval thought: Reinhard Krüger:Materialien und Dokumente zur mittelalterlichen Erdkugeltheorie von der Spätantike bis zur Kolumbusfahrt (1492)Direct adoption by India: D. Pingree: "History of Mathematical Astronomy in India", ''Dictionary of Scientific Biography'', Vol. 15 (1978), pp. 533–633 (554f.); Glick, Thomas F., Livesey, Steven John, Wallis, Faith (eds.): "Medieval Science, Technology, and Medicine: An Encyclopedia", Routledge, New York 20 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffraction
Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi coined the word ''diffraction'' and was the first to record accurate observations of the phenomenon in 1660. In classical physics, the diffraction phenomenon is described by the Huygens–Fresnel principle that treats each point in a propagating wavefront as a collection of individual spherical wavelets. The characteristic bending pattern is most pronounced when a wave from a coherent source (such as a laser) encounters a slit/aperture that is comparable in size to its wavelength, as shown in the inserted image. This is due to the addition, or interference, of different points on the wavefront (or, equivalently, each wavelet) that travel by paths of d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schumann Resonance Spectrum
Robert Schumann (; 8 June 181029 July 1856) was a German composer, pianist, and influential music critic. He is widely regarded as one of the greatest composers of the Romantic era. Schumann left the study of law, intending to pursue a career as a virtuoso pianist. His teacher, Friedrich Wieck, a German pianist, had assured him that he could become the finest pianist in Europe, but a hand injury ended this dream. Schumann then focused his musical energies on composing. In 1840, Schumann married Friedrich Wieck's daughter Clara Wieck, after a long and acrimonious legal battle with Friedrich, who opposed the marriage. A lifelong partnership in music began, as Clara herself was an established pianist and music prodigy. Clara and Robert also maintained a close relationship with German composer Johannes Brahms. Until 1840, Schumann wrote exclusively for the piano. Later, he composed piano and orchestral works, and many Lieder (songs for voice and piano). He composed four symphonies ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of health". Headquartered in Geneva, Switzerland, it has six regional offices and 150 field offices worldwide. The WHO was established on 7 April 1948. The first meeting of the World Health Assembly (WHA), the agency's governing body, took place on 24 July of that year. The WHO incorporated the assets, personnel, and duties of the League of Nations' Health Organization and the , including the International Classification of Diseases (ICD). Its work began in earnest in 1951 after a significant infusion of financial and technical resources. The WHO's mandate seeks and includes: working worldwide to promote health, keeping the world safe, and serve the vulnerable. It advocates that a billion more people should have: universal health care coverag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NeuroToxicology (journal)
''NeuroToxicology'' is a peer-reviewed scientific journal covering research on the toxicology of the nervous system. It was established in 1979 and originally published by Intox Press, until it was acquired by Elsevier in 2001. The editor-in-chief is Joan Marie Cranmer (University of Arkansas for Medical Sciences). Abstracting and indexing The journal is abstracted and indexed in: According to the ''Journal Citation Reports'', the journal has a 2014 impact factor The impact factor (IF) or journal impact factor (JIF) of an academic journal is a scientometric index calculated by Clarivate that reflects the yearly mean number of citations of articles published in the last two years in a given journal, as i ... of 3.379, ranking it 20th out of 87 journals in the category "Toxicology". References External links * Elsevier academic journals Publications established in 1979 Toxicology journals Bimonthly journals Neuroscience journals English-language journals ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peer Review
Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work (peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer review methods are used to maintain quality standards, improve performance, and provide credibility. In academia, scholarly peer review is often used to determine an academic paper's suitability for publication. Peer review can be categorized by the type of activity and by the field or profession in which the activity occurs, e.g., medical peer review. It can also be used as a teaching tool to help students improve writing assignments. Henry Oldenburg (1619–1677) was a German-born British philosopher who is seen as the 'father' of modern scientific peer review. Professional Professional peer review focuses on the performance of professionals, with a view to improving quality, upholding standards, or providing certification. In academia, peer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Times Of India
''The Times of India'', also known by its abbreviation ''TOI'', is an Indian English-language daily newspaper and digital news media owned and managed by The Times Group. It is the third-largest newspaper in India by circulation and largest selling English-language daily in the world. It is the oldest English-language newspaper in India, and the second-oldest Indian newspaper still in circulation, with its first edition published in 1838. It is nicknamed as "The Old Lady of Bori Bunder", and is an Indian " newspaper of record". Near the beginning of the 20th century, Lord Curzon, the Viceroy of India, called ''TOI'' "the leading paper in Asia". In 1991, the BBC ranked ''TOI'' among the world's six best newspapers. It is owned and published by Bennett, Coleman & Co. Ltd. (B.C.C.L.), which is owned by the Sahu Jain family. In the Brand Trust Report India study 2019, ''TOI'' was rated as the most trusted English newspaper in India. Reuters rated ''TOI'' as India's most trus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jane's Information Group
Jane's Information Group, now styled Janes, is a global open-source intelligence company specialising in military, national security, aerospace and transport topics, whose name derives from British author Fred T. Jane. History Jane's Information Group was founded in 1898 by Fred T. Jane, who had begun sketching ships as an enthusiast naval artist while living in Portsmouth. This gradually developed into an encyclopedic knowledge, culminating in the publishing of ''All the World's Fighting Ships'' (1898). The company then gradually branched out into other areas of military expertise. The books and trade magazines published by the company are often considered the ''de facto'' public source of information on warfare and transportation systems. Based in Greater London for most of its existence, the group was owned by the Thomson Corporation, The Woodbridge Company, then IHS Markit, before being acquired by Montagu Private Equity in 2019. Description The company name is officially ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
