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. 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. Because of the difficulty of building antennas that can radiate such long waves, ELF frequencies have been used in only a very few man-made communication systems. ELF waves can penetrate seawater, which makes them useful in communication with submarines. The US, Russia, India, and China are the only nations known to have constructed ELF communication facilities. The U.S. facilities were used between 1985 and 2004 but are now decommissioned.
|Extremely low frequency|
|3 to 30 Hz|
|100,000 to 10,000 km, respectively|
ELF is a subradio frequency. Some medical peer reviewed journal articles refer to ELF in the context of "extremely low frequency (ELF) magnetic fields (MF)" with frequencies of 50 Hz and 50–80 Hz. United States Government agencies, such as NASA, describe ELF as non-ionizing radiation with frequencies between 0 and 300 Hz. The World Health Organization (WHO) have used ELF to refer to the concept of "extremely low frequency (ELF) electric and magnetic fields (EMF)" The WHO also stated that at frequencies between 0 and 300 Hz, "the wavelengths in air are very long (6000 km at 50 Hz and 5000 km at 60 Hz), and, in practical situations, the electric and magnetic fields act independently of one another and are measured separately."
Due to their extremely long wavelength, ELF waves can diffract around large obstacles, and are not blocked by mountain ranges or the horizon and can travel around the curve of the Earth. ELF and VLF waves propagate long distances by an Earth-ionosphere waveguide mechanism. The Earth is surrounded by a layer of charged particles (ions) in the atmosphere at an altitude of about 60 km at the bottom of the ionosphere, called the D layer which reflects ELF waves. The space between the conductive Earth's surface and the conductive D layer acts as a parallel-plate waveguide which confines ELF waves, allowing them to propagate long distances without escaping into space. In contrast to VLF waves, the height of the layer is much less than one wavelength at ELF frequencies, so the only mode that can propagate at ELF frequencies is the TEM mode in vertical polarization, with the electric field vertical and the magnetic field horizontal. ELF waves have extremely low attenuation of 1–2 dB per 1000 km, giving a single transmitter the potential to communicate worldwide.
ELF waves can also travel considerable distances through "lossy" media like earth and seawater, which would absorb or reflect higher frequency radio waves.
The attenuation of ELF waves is so low that they can travel completely around the Earth several times before decaying to negligible amplitude, and thus waves radiated from a source in opposite directions circumnavigating the Earth on a great circle path interfere with each other. At certain frequencies these oppositely directed waves are in phase and add (reinforce), causing standing waves. In other words, the closed spherical Earth-ionosphere cavity acts as a huge cavity resonator, enhancing ELF radiation at its resonant frequencies. These are called Schumann resonances after German physicist Winfried Otto Schumann who predicted them in 1952, and were detected in the 1950s. Modeling the Earth-ionosphere cavity with perfectly conducting walls, Schumann calculated the resonances should occur at frequencies of
The actual frequencies differ slightly from this due to the conduction properties of the ionosphere. The fundamental Schumann resonance is at approximately 7.83 Hz, the frequency at which the wavelength equals the circumference of the Earth, and higher harmonics occur at 14.1, 20.3, 26.4, and 32.4 Hz, etc. Lightning strikes excite these resonances, causing the Earth-ionosphere cavity to "ring" like a bell, resulting in a peak in the noise spectrum at these frequencies, so the Schumann resonances can be used to monitor global thunderstorm activity.
Interest in Schumann resonances was renewed in 1993 when E. R. Williams showed a correlation between the resonance frequency and tropical air temperatures, suggesting the resonance could be used to monitor global warming.
The United States Navy utilized extremely low frequencies (ELFs) as radio band and radio communications. The Submarine Integrated Antenna System (SIAS) was a research and development effort to communicate with submerged submarines. The Soviet/Russian Navy also utilized ELFs for submarine communications system, ZEVS. The Indian Navy has an operational ELF communication facility at the INS Kattabomman naval base to communicate with its Arihant class and Akula class submarines.
Because of its electrical conductivity, seawater shields submarines from most higher frequency radio waves, making radio communication with submerged submarines at ordinary frequencies impossible. Signals in the ELF frequency range, however, can penetrate much deeper. Two factors limit the usefulness of ELF communications channels: the low data transmission rate of a few characters per minute and, to a lesser extent, the one-way nature due to the impracticality of installing an antenna of the required size on a submarine (the antenna needs to be of an exceptional size in order to achieve successful communication). Generally, ELF signals have been used to order a submarine to rise to a shallow depth where it could receive some other form of communication.
One of the difficulties posed when broadcasting in the ELF frequency range is antenna size, because the length of the antenna must be at least a substantial fraction of the length of the waves. Simply put, a 3 Hz (cycle per second) signal would have a wavelength equal to the distance EM waves travel through a given medium in one third of a second. Taking account of refractive index, ELF waves propagate slightly slower than the speed of light in a vacuum. As used in military applications, the wavelength is 299,792 km (186,282 mi) per second divided by 50–85 Hz, which equals around 3,500 to 6,000 km (2,200 to 3,700 mi) long. This is comparable to the Earth's diameter of around 12,742 km (7,918 mi). Because of this huge size requirement, to transmit internationally using ELF frequencies, the Earth itself forms a significant part of the antenna, and extremely long leads are necessary into the ground. Various means, such as electrical lengthening, are used to construct practical radio stations with smaller sizes.
The US maintained two sites, in the Chequamegon-Nicolet National Forest, Wisconsin and in the Escanaba River State Forest, Michigan (originally named Project Sanguine, then downsized and rechristened Project ELF prior to construction), until they were dismantled, beginning in late September 2004. Both sites used long power lines, so-called ground dipoles, as leads. These leads were in multiple strands ranging from 22.5 to 45 kilometres (14.0 to 28.0 mi) long. Because of the inefficiency of this method, considerable amounts of electrical power were required to operate the system.
There have been some concerns over the possible ecological impact of ELF signals. In 1984 a federal judge halted construction, requiring more environmental and health studies. This judgment was overruled by a federal appeals court on the basis that the US Navy claimed to have spent over $25 million studying the effects of the electromagnetic fields, with results indicating that they were similar to the effect produced by standard power distribution lines. The judgment was not accepted by everyone and, during the time that ELF was in use, some Wisconsin politicians such as Senators Herb Kohl, Russ Feingold and Congressman Dave Obey called for its closure. Similar concerns have, in the past, been raised about electromagnetic radiation and health.
Transmitters in the 22 Hz range are also used in pigging. The signal is generated as an alternating magnetic field, and the transmitter is mounted to, or to part of, the "pig". The pig is pushed through a pipeline mostly made of metal. The ELF signal can be detected through the metal allowing its location to be detected by receivers located outside of the pipe. It is needed to check if a pig has passed a certain location and to locate a stuck pig.
Some radio monitoring hobbyists record ELF signals using antennas ranging in size from eighteen inch active antennas up to several thousand feet in length taking advantage of fences, highway guard rails, and even decommissioned railroad tracks, and play them back at higher speeds to more easily observe natural low frequency fluctuations in the Earth's electromagnetic field. Increasing the playback speed increases the pitch, so that it can be brought into the audio frequency range for audibility.
Naturally occurring ELF waves are present on Earth, resonating in the region between ionosphere and surface seen in lightning strikes that make electrons in the atmosphere oscillate. Though VLF signals were predominantly generated from lightning discharges, it was found that an observable ELF component—slow tail—followed the VLF component in almost all cases. Also, the fundamental mode of the Earth-ionosphere cavity has the wavelength equal to the circumference of the Earth, which gives a resonance frequency of 7.8 Hz. This frequency, and higher resonance modes of 14, 20, 26 and 32 Hz appear as peaks in the ELF spectrum and are called Schumann resonance.
ELF waves have also been tentatively identified on Saturn's moon Titan. Titan's surface is thought to be a poor reflector of ELF waves, so the waves may instead be reflecting off the liquid-ice boundary of a subsurface ocean of water and ammonia, the existence of which is predicted by some theoretical models. Titan's ionosphere is also more complex than Earth's, with the main ionosphere at an altitude of 1,200 km (750 mi) but with an additional layer of charged particles at 63 km (39 mi). This splits Titan's atmosphere into two separate resonating chambers. The source of natural ELF waves on Titan is unclear as there does not appear to be extensive lightning activity.
Huge ELF radiation power outputs of 100,000 times the Sun's output in visible light may be radiated by magnetars. The pulsar in the Crab nebula radiates powers of this order at 30 Hz. Radiation of this frequency is below the plasma frequency of the interstellar medium, thus this medium is opaque to it, and it cannot be observed from Earth.
In electromagnetic therapy and electromagnetic radiation and health research, electromagnetic spectrum frequencies between 0 and 100 hertz are considered extremely low-frequency fields. A common source of exposure of the public to ELF fields is 60 Hz electric and magnetic fields from high-voltage electric power transmission lines and secondary distribution lines, such as those supplying electricity to residential neighborhoods.
Since the late 1970s, questions have been raised whether exposure to ELF electric and magnetic fields (EMF) within this range of frequencies produces adverse health consequences. Some may think biological effects from acute exposure at high levels (well above 100 µT) that are explained by recognized biophysical mechanisms. External ELF magnetic fields induce electric fields and currents in the body which, at very high field strengths, cause nerve and muscle stimulation and changes in nerve cell excitability in the central nervous system. Health effects related to short-term, high-level exposure have been established and form the basis of two international exposure limit guidelines (ICNIRP, 1998; IEEE, 2002) such as 0.2-0.4 mA at 50/60 Hz. A study by Reilly in 1999 showed that the threshold for direct perception of exposure to ELF RF by human volunteer subjects started at around 2 to 5 kV/m at 60 Hz, with 10% of volunteers detecting the ELF exposure at this level. The percentage of detection increased to 50% of volunteers when the ELF level was raised from 7 to 20 kV/m. 5% of all test subjects considered the perception of ELF at these thresholds annoying. ELF at human perceivable kV/m levels was said to create an annoying tingling sensation in the areas of the body in contact with clothing, particularly the arms, due to the induction of a surface charge by the ELF. 7% of volunteers described the spark discharges as painful where the subject was well-insulated and touched a grounded object within a 5 kV/m field. 50% of volunteers described a similar spark discharge as painful in a 10 kV/m field.
There is some uncertainty regarding correlations between long-term, low-level exposure to ELF fields and a number of health effects, including leukemia in children. In October 2005, WHO convened a task group of scientific experts to assess any risks to health that might exist from "exposure to ELF electric and magnetic fields in the frequency range >0 to 100,000 Hz (100 kHz) in regards to childhood leukemia." The long-term, low-level exposure is evaluated as average exposure to residential power-frequency magnetic field above 0.3 to 0.4 µT, and it is estimated that only between 1% and 4% of children live in such conditions. Subsequently, in 2010, a pooled analysis of epidemiological evidence supported the hypothesis that exposure to power frequency magnetic fields is related to childhood leukemia. Other studies have found no evidence to support the hypothesis that ELF exposure is a contributing factor to leukemia in children.
A 2014 study estimated the cases of childhood leukemia attributable to exposure to ELF magnetic fields in the European Union (EU27), assuming that correlations seen in epidemiological studies were causal. It reported that around 50-60 cases of childhood leukemia might be attributable to ELF magnetic fields annually, corresponding to between ~1.5% and ~2.0% of all incident cases of childhood leukemia occurring in the EU27 each year. At present, however, ICNIRP and IEEE consider the scientific evidence related to possible health effects from long-term, low-level exposure to ELF fields insufficient to justify lowering these quantitative exposure limits. In summary, when all of the studies are evaluated together, the evidence suggesting that EMFs may contribute to an increased risk of cancer is very weak. Epidemiological studies suggest a possible association between long term occupational exposure to ELF and Alzheimer's disease.
Events from the year 1977 in Michigan.
The Associated Press (AP) selected Michigan's top stories of 1977 as follows:
The emergence of the Michigan PBB contamination scandal as a political issue and related medical investigation and legislative actions (the PBB scandal was one of the state's top stories for the fourth consecutive year dating back to 1974);
Cold weather through the winter of 1977 with many cities recording the coldest temperatures of the century, Lake Michigan frozen solid, several deaths due to exposure, closure of automobile plants due to natural gas shortages, and snow closing U.S. Route 131 between Grand Rapids and Kalamazoo for a week;
The Oakland County Child Killings involving the unsolved murders of at least four Oakland County youths reportedly tied to the driver of a blue Gremlin;
The 13-week trial, conviction, and subsequent new trial order in the prosecution of two Filipina nurses, Filipina Narciso and Leonora Perez, in the Ann Arbor Hospital Murders in which 10 patients at the Veterans Hospital in Ann Arbor died mysteriously from respiratory failure (the Ann Arbor Hospital Murders were one of the state's top stories for the third consecutive year dating back to 1975);
The case of Francine Hughes (subsequently the topic of The Burning Bed), a 29-year-old woman from Danville who killed her husband by setting his bed on fire in March after years of domestic abuse and was found not guilty in November by reason of temporary insanity;
Gov. William Milliken's veto of Project Seafarer, a proposed underground military extremely low frequency (ELF) network in the Upper Peninsula;
A civil lawsuit by farmers Roy and Marilyn Tacoma against several parties for the loss of cattle in connection with the Michigan PBB contamination scandal (See #1 above) and resulting in the longest court case in Michigan history;
The August 25 abduction of Evelyn Van Tassel from her Upper Peninsula home and the subsequent trial and conviction of her abductor, Douglas Henry, for kidnapping and rape;
The closure of Kincheloe Air Force Base in the eastern Upper Peninsula; and
The April announcement by U.S. Senator Robert P. Griffin that he would not run for reelection in 1978.The AP and the United Press International (UPI) each selected the state's top sports stories of 1977 as follows:
The second season of Detroit Tigers pitcher Mark Fidrych (2.89 ERA in 11 games) which was shortened by injuries (AP-1, UPI-1);
The 1977 Michigan Wolverines football team led by quarterback Rick Leach and running back Russell Davis compiling a 10–1 record in the regular season, including a victory over Ohio State (AP-3, UPI-3 [tie]);
The Detroit Red Wings' firing of Alex Delvecchio after the 1976–77 team compiled a 16–55–9 record, the hiring of Ted Lindsay as the team's general manager, and Lindsay's rebuilding program and promise to bring back aggressive hockey (AP-5, UPI-2);
The 1976–77 Detroit Titans men's basketball team led by John Long and Terry Tyler compiling a 25–4 record followed by Dick Vitale's resignation as head coach (AP-4 [season], AP-6 [resignation], UPI-5 [season]);
Magic Johnson's decision to attend Michigan State University after leading Lansing's Everett High School to the Michigan Class A high school basketball championship (AP-2, UPI-9);
The 1976–77 Michigan Wolverines men's basketball team led by Phil Hubbard and Rickey Green compiling a 26–4 record, receiving the No. 1 ranking at the end of the regular season, and advancing to the Elite Eight round in the NCAA tournament (AP-8, UPI-3 [tie])
The 1976 Michigan Wolverines football team's 14–6 loss to USC in the 1977 Rose Bowl (AP-7, UPI-7);
The performances of Detroit Tigers players Dave Rozema (15-7 record, 3.09 ERA), Ron LeFlore (.325 batting average, 212 hits), and Steve Kemp (18 home runs, 88 RBIs) (AP-9 [Rozema and LeFlore], UPI-8 [Rozema and Kemp]);
The trade of highly touted 1976 draft pick Marvin Barnes on November 23 after appearing in only 65 games for the Detroit Pistons to the Buffalo Braves in exchange for Gus Gerard, John Shumate and a 1979 first round draft pick (Roy Hamilton was selected) (UPI-6); and
The April 12 trade of designated hitter Willie Horton, who had played for the Detroit Tigers since 1963, to the Texas Rangers in exchange for pitcher Steve Foucault (UPI-10).Clam Lake, Wisconsin
Clam Lake is an unincorporated, census-designated place in the town of Gordon in Ashland County, Wisconsin, United States. It is located on Wisconsin Highway 77 near County Highway GG. The entire area lies within the Chequamegon National Forest, an 860,000 acre area spread across northern Wisconsin. As of the 2010 census, its population was 37.Situated near the headwaters of the Chippewa Flowage, the area encompasses several smaller lakes that host prime Musky fishing.
Clam Lake is well known as the site of the reintroduction of elk in Wisconsin with a herd of 25 in 1995 by the University of Wisconsin–Stevens Point, which has grown to an estimated 180.Clam Lake is the site of a U.S. Navy extremely low frequency (ELF) transmitter site, used to communicate with deeply submerged submarines. It was used between 1985 and 2004 but is now decommissioned.Communication with submarines
Communication with submarines is difficult because radio waves do not travel well through good electrical conductors like salt water.
The obvious solution is to surface and raise an antenna above the sea level, then use ordinary radio transmissions. However, a submarine is most vulnerable when on the surface. Early submarines mostly travelled on the surface because of their limited underwater speed and endurance; they dived mainly to evade immediate threats. During the Cold War, however, nuclear-powered submarines were developed that could stay submerged for months. To communicate with submerged submarines, several techniques are used.Earth–ionosphere waveguide
The Earth–ionosphere waveguide refers to the phenomenon in which certain radio waves can propagate in the space between the ground and the boundary of the ionosphere.
Because the ionosphere contains charged particles, it can behave as a conductor. The earth operates as a ground plane, and the resulting cavity behaves as a large waveguide.
Extremely low frequency (ELF) (< 3 kHz) and very low frequency (VLF)
(3–30 kHz) signals can propagate efficiently in this waveguide. For instance, lightning strikes launch a signal called radio atmospherics, which can travel many thousands of miles, because they are confined between the Earth and the ionosphere.
The round-the-world nature of the waveguide produces resonances, like a cavity, which are at ~7 Hz.Electrical phenomena
Electrical phenomena are commonplace and unusual events that can be observed and that illuminate the principles of the physics of electricity and are explained by them.
Electrical phenomena are a somewhat arbitrary division of
Some examples are
Biefeld–Brown effect — Thought by the person who coined the name, Thomas Townsend Brown, to be an anti-gravity effect, it is generally attributed to electrohydrodynamics (EHD) or sometimes electro-fluid-dynamics, a counterpart to the well-known magneto-hydrodynamics.
Bioelectrogenesis — The generation of electricity by living organisms.
Contact electrification — The phenomenon of electrification by contact. When two objects were touched together, sometimes the objects became spontaneously charged (οne negative charge, one positive charge).
Direct Current — (old: Galvanic Current) or "continuous current"; The continuous flow of electricity through a conductor such as a wire from high to low potential.
Electroluminescence — The phenomenon wherein a material emits light in response to an electric current passed through it, or to a strong electric field.
Electrical conduction — The movement of electrically charged particles through transmission medium.
Electric shock — Physiological reaction of a biological organism to the passage of electric current through its body.
Ferroelectric effect — The phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment.
Inductance — The phenomenon whereby the property of a circuit by which energy is stored in the form of an electromagnetic field.
Lightning — powerful natural electrostatic discharge produced during a thunderstorm. Lightning's abrupt electric discharge is accompanied by the emission of light.
Photoconductivity — The phenomenon in which a material becomes more conductive due to the absorption of electro-magnetic radiation such as visible light, ultraviolet light, or gamma radiation.
Photoelectric effect — Emission of electrons from a surface (usually metallic) upon exposure to, and absorption of, electromagnetic radiation (such as visible light and ultraviolet radiation).
Piezoelectric effect — Ability of certain crystals to generate a voltage in response to applied mechanical stress.
Plasma — Plasma occur when gas is heated to very high temperatures and it disassociates into positive and negative charges.
Pyroelectric effect — The potential created in certain materials when they are heated.
Redox — (short for reduction-oxidation reaction) A chemical reaction in which the oxidation states of atoms are changed.
Static electricity — Class of phenomena involving the imbalanced charge present on an object, typically referring to charge with voltages of sufficient magnitude to produce visible attraction (e.g., static cling), repulsion, and sparks.
Sparks — Electrical breakdown of a medium that produces an ongoing plasma discharge, similar to the instant spark, resulting from a current flowing through normally nonconductive media such as air.
Telluric currents — Extremely low frequency electric current that occurs naturally over large underground areas at or near the surface of the Earth.
Thermionic emission — the emission of electrons from a heated electrode, usually the cathode, the principle underlying most vacuum tubes.
Thermoelectric effect — the Seebeck effect, the Peltier effect, and the Thomson effect
Thunderstorm — also electrical storm, form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder.
Triboelectric effect — Type of contact electrification in which objects become electrically charged after coming into contact and are then separated.
Whistlers — Very low frequency radio wave generated by lightningElectromagnetic radiation and health
At sufficiently high flux levels, various bands of electromagnetic radiation have been found to cause deleterious health effects in people. Electromagnetic radiation can be classified into two types: ionizing radiation and non-ionizing radiation, based on the capability of a single photon with more than 10 eV energy to ionize oxygen or break chemical bonds. Extreme ultraviolet and higher frequencies, such as X-rays or gamma rays are ionizing, and these pose their own special hazards: see radiation and radiation poisoning. The last quarter of the twentieth century saw a dramatic increase in the number of devices emitting non-ionizing radiation in all segments of society, which resulted in an elevation of health concerns by researchers and clinicians, and an associated interest in government regulation for safety purposes. In the United States, this has resulted in legislation such as the Radiation Control for Health and Safety Act of 1968 and the Occupational Safety and Health Act of 1970. By far the most common health hazard of radiation is sunburn, which causes over one million new skin cancers annually in United States.Environmental Health Criteria (WHO)
Environmental Health Criteria (EHC) is a series of monographs prepared by the International Programme on Chemical Safety (IPCS) and published by the World Health Organization (WHO). They aim to give "comprehensive data from scientific sources for the establishment of safety standards and regulations." More than 230 EHCs have been published.
Many EHCs cover the properties of individual chemicals or of groups of related chemicals (see, e.g., EHC 65: Butanols). Since 1998, this role has mostly been taken over by the related Concise International Chemical Assessment Documents (CICADs), also prepared by the IPCS and published by the WHO. EHCs can also cover non-chemical (potential) hazards (see, e.g., EHC 35: Extremely low frequency (ELF) fields) and methodology (see, e.g., EHC 144: Aged Population, principles for evaluating the effects of chemicals).EHCs are based on a search of the scientific literature, and do not include new experimentation (unlike, e.g., SIDS or EU-RARs) although they may contain recommendations for further studies. A typical monograph on a chemical substance would include:
the physical and chemical properties of the substance and analytical methods for determining concentrations and exposure;
sources of environmental and industrial exposure and environmental transport;
chemobiokinetics and metabolism including absorption, distribution, transformation and elimination;
short- and long-term effects on animals, including carcinogenicity, mutagenicity, and teratogenicity;
an evaluation of risks for human health and of the effects on the environment.Monographs do not contain specific guidelines for regulations (although they might contain examples of national exposure limits, for example), and they do not constitute an official position of the WHO or of any of the other organizations participating in the IPCS.Ground dipole
In radio communication, a ground dipole, also referred to as an earth dipole antenna, transmission line antenna, and in technical literature as a horizontal electric dipole (HED), is a huge, specialized type of radio antenna that radiates extremely low frequency (ELF) electromagnetic waves. It is the only type of transmitting antenna that can radiate practical amounts of power in the frequency range of 3 Hz to 3 kHz, commonly called ELF waves A ground dipole consists of two ground electrodes buried in the earth, separated by tens to hundreds of kilometers, linked by overhead transmission lines to a power plant transmitter located between them. Alternating current electricity flows in a giant loop between the electrodes through the ground, radiating ELF waves, so the ground is part of the antenna. To be most effective, ground dipoles must be located over certain types of underground rock formations. The idea was proposed by U.S. Dept. of Defense physicist Nicholas Christofilos in 1959.Although small ground dipoles have been used for years as sensors in geological and geophysical research, their only use as antennas has been in a few military ELF transmitter facilities to communicate with submerged submarines. Besides small research and experimental antennas, four full-scale ground dipole installations are known to have been constructed; two by the U.S. Navy at Republic, Michigan and Clam Lake, Wisconsin, one by the Russian Navy on the Kola peninsula near Murmansk, Russia. and one in India at the INS Kattabomman naval base. The U.S. facilities were used between 1985 and 2004 but are now decommissioned.Haplogroup G-FGC7535
Haplogroup G-FGC7535, also known as Haplogroup G2a1 (and formerly G-L293), is a Y-chromosome haplogroup. It is an immediate descendant of G2a (G-P15), which is a primary branch of haplogroup G2 (P287).
G2a1 has an extremely low frequency in almost all populations except parts of the Caucasus Mountains.
In 2017, the SNP L293 was replaced by FGC7535, SK1106 and Z6552 as the defining SNPs of G2a1, due to the technical difficulty in testing for L293.Hiss (electromagnetic)
Electromagnetic hiss is a naturally occurring Extremely Low Frequency/Very Low Frequency electromagnetic wave (i.e., 300 Hz – 10 kHz) that is generated in the plasma of either the Earth's ionosphere or magnetosphere. Its name is derived from its incoherent, structureless spectral properties which, when played through an audio system, sound like white noise (hence the onomatopoetic name, "hiss").Maxime de la Rochefoucauld
Maxime Rioux (born October 29, 1959) known by his stage name Maxime De La Rochefoucauld is a Montreal-based musician and performance artist.
Rioux is best known for his compositions produced on musical instruments that are homemade and often built specifically for a single live performance. Most instruments (usually string or percussion) of his Système Ki, as Rioux calls it, are not played directly by a musician. Instead they are mechanically linked to a woofer that is driven by an inaudible, extremely low frequency electrical signal. The signal, in the range of 1-10 Hz, is most often generated on a synthesizer and prerecorded, but may be played live or be generated from other electrical sources.
The name "Ki" refers to the Japanese translation of Qi, the notion of a vital energy that animates all things.
Rioux is the brother of French-Canadian stage and film actress Geneviève Rioux.Non-ionizing radiation
Non-ionizing (or non-ionising) radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum (photon energy) to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule. Instead of producing charged
ions when passing through matter, non-ionizing electromagnetic radiation has sufficient energy only for excitation, the movement of an electron to a higher energy state. Ionizing radiation which has a higher frequency and shorter wavelength than nonionizing radiation, has many uses but can be a health hazard; exposure to it can cause burns, radiation sickness, cancer, and genetic damage. Using ionizing radiation requires elaborate radiological protection measures which in general are not required with nonionizing radiation.
The region at which radiation becomes considered as "ionizing" is not well defined, since different molecules and atoms ionize at different energies. The usual definitions have suggested that radiation with particle or photon energies less than 10 electronvolts (eV) be considered non-ionizing. Another suggested threshold is 33 electronvolts, which is the energy needed to ionize water molecules. The light from the Sun that reaches the earth is largely composed of non-ionizing radiation, since the ionizing far-ultraviolet rays have been filtered out by the gases in the atmosphere, particularly oxygen. The remaining ultraviolet radiation from the Sun causes molecular damage (for example, sunburn) by photochemical and free-radical-producing means.Different biological effects are observed for different types of non-ionizing radiation. The upper frequencies of non-ionizing radiation near these energies (much of the spectrum of UV light and some visible light) are capable of non-thermal biological damage, similar to ionizing radiation. Health debate therefore centers on the non-thermal effects of radiation of much lower frequencies (microwave, millimeter and radiowave radiation). The International Agency for Research on Cancer recently stated that there could be some risk from non-ionizing radiation to humans. But a subsequent study reported that the basis of the IARC evaluation was not consistent with observed incidence trends. This and other reports suggest that there is virtually no way that results on which the IARC based its conclusions are correct. The Bioinitiative Report 2012 makes the claim that there are significant health risk associated with low frequency non-ionizing electromagnetic radiation. This report claims that statistically significant increases in cancer among those exposed to even low power levels, low frequency, non-ionizing radiation. There is considerable debate on this matter. Currently regulatory bodies around the world have not seen the need to change current safety standards.Project Sanguine
Project Sanguine was a U.S. Navy project, proposed in 1968 for communication with submerged submarines using extremely low frequency (ELF) radio waves. The originally proposed system, hardened to survive a nuclear attack, would have required a giant antenna covering two fifths of the state of Wisconsin. Because of protests and potential environmental impact, the proposed system was never implemented. A smaller, less hardened system consisting of two linked ELF transmitters located at Clam Lake, Wisconsin and Republic, Michigan was built beginning in 1982 and operated from 1989 until 2004. The system transmitted at a frequency of 76 Hz. At ELF frequencies the bandwidth of the transmission is very small, so the system could only send short coded text messages at a very low data rate. These signals were used to summon specific vessels to the surface to receive longer operational orders by ordinary radio or satellite communication.Radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ)
particle radiation, such as alpha radiation (α), beta radiation (β), and neutron radiation (particles of non-zero rest energy)
acoustic radiation, such as ultrasound, sound, and seismic waves (dependent on a physical transmission medium)
gravitational radiation, radiation that takes the form of gravitational waves, or ripples in the curvature of spacetime.Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules, and break chemical bonds. This is an important distinction due to the large difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, and photons, respectively. Other sources include X-rays from medical radiography examinations and muons, mesons, positrons, neutrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere.
Gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. The word "ionize" refers to the breaking of one or more electrons away from an atom, an action that requires the relatively high energies that these electromagnetic waves supply. Further down the spectrum, the non-ionizing lower energies of the lower ultraviolet spectrum cannot ionize atoms, but can disrupt the inter-atomic bonds which form molecules, thereby breaking down molecules rather than atoms; a good example of this is sunburn caused by long-wavelength solar ultraviolet. The waves of longer wavelength than UV in visible light, infrared and microwave frequencies cannot break bonds but can cause vibrations in the bonds which are sensed as heat. Radio wavelengths and below generally are not regarded as harmful to biological systems. These are not sharp delineations of the energies; there is some overlap in the effects of specific frequencies.The word radiation arises from the phenomenon of waves radiating (i.e., traveling outward in all directions) from a source. This aspect leads to a system of measurements and physical units that are applicable to all types of radiation. Because such radiation expands as it passes through space, and as its energy is conserved (in vacuum), the intensity of all types of radiation from a point source follows an inverse-square law in relation to the distance from its source. Like any ideal law, the inverse-square law approximates a measured radiation intensity to the extent that the source approximates a geometric point.Radio propagation
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for international shortwave broadcasters, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems.
Several different types of propagation are used in practical radio transmission systems. Line-of-sight propagation means radio waves which travel in a straight line from the transmitting antenna to the receiving antenna. Line of sight transmission is used to medium range radio transmission such as cell phones, cordless phones, walkie-talkies, wireless networks, FM radio and television broadcasting and radar, and satellite communication, such as satellite television. Line-of-sight transmission on the surface of the Earth is limited to the distance to the visual horizon, which depends on the height of transmitting and receiving antennas. It is the only propagation method possible at microwave frequencies and above. At microwave frequencies, moisture in the atmosphere (rain fade) can degrade transmission.
At lower frequencies in the MF, LF, and VLF bands, due to diffraction radio waves can bend over obstacles like hills, and travel beyond the horizon as surface waves which follow the contour of the Earth. These are called ground waves. AM broadcasting stations use ground waves to cover their listening areas. As the frequency gets lower, the attenuation with distance decreases, so very low frequency (VLF) and extremely low frequency (ELF) ground waves can be used to communicate worldwide. VLF and ELF waves can penetrate significant distances through water and earth, and these frequencies are used for mine communication and military communication with submerged submarines.
At medium wave and shortwave frequencies (MF and HF bands) radio waves can refract from a layer of charged particles (ions) high in the atmosphere, called the ionosphere. This means that radio waves transmitted at an angle into the sky can be reflected back to Earth beyond the horizon, at great distances, even transcontinental distances. This is called skywave propagation. It is used by amateur radio operators to talk to other countries, and shortwave broadcasting stations that broadcast internationally. Skywave communication is variable, dependent on conditions in the upper atmosphere; it is most reliable at night and in the winter. Due to its unreliability, since the advent of communication satellites in the 1960s, many long range communication needs that previously used skywaves now use satellites.
In addition, there are several less common radio propagation mechanisms, such as tropospheric scattering (troposcatter) and near vertical incidence skywave (NVIS) which are used in specialized communication systems.Republic, Michigan
Republic is an unincorporated community in Marquette County in the U.S. state of Michigan. It is also a census-designated place (CDP) for statistical purposes, covering a narrow, roughly crescent-shaped area along several miles of M-95. Most of the CDP is within Republic Township, although a small portion of the CDP extends north into Humboldt TownshipRepublic is also the name of the post office for ZIP code 49879, which includes the CDP as well as most of the rest of Republic Township and a small portion of Mansfield Township in Iron County.The population of the CDP was 614 at the 2000 census. The population of the 49879 ZCTA in 2000 was 996.Super low frequency
Super low frequency (SLF) is the ITU designation for electromagnetic waves (radio waves) in the frequency range between 30 hertz and 300 hertz. They have corresponding wavelengths of 10,000 to 1,000 kilometers. This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz). Another conflicting designation which includes this frequency range is Extremely Low Frequency (ELF), which in some contexts refers to all frequencies up to 300 hertz.
Because of the extreme difficulty of building transmitters that can generate such long waves, frequencies in this range have been used in very few artificial communication systems. However, SLF waves can penetrate seawater to a depth of hundreds of meters. Therefore, in recent decades the U.S., Russian and Indian military have built huge radio transmitters using SLF frequencies to communicate with their submarines. The U.S. naval service is called Seafarer and operates at 76 hertz. It became operational in 1989 but was discontinued in 2004 due to advances in VLF communication systems. The Russian service is called ZEVS and operates at 82 hertz. The Indian Navy has an operational ELF communication facility at the INS Kattabomman naval base to communicate with its Arihant class and Akula class submarines.The requirements for receivers at SLF frequencies is less stringent than transmitters, because the signal strength (set by atmospheric noise) is far above the noise floor of the receiver, so small, inefficient antennas can be used. Radio amateurs have received signals in this range using simple receivers built around personal computers, with coil or loop antennas connected to the PCs sound card. Signals are analysed by a software fast Fourier transform algorithm and converted into audible sound.TACAMO
TACAMO (TAke Charge And Move Out) is a United States military system of survivable communications links designed to be used in nuclear warfare to maintain communications between the decision-makers (the National Command Authority) and the triad of strategic nuclear weapon nuclear weapons delivery systems. Its primary mission is serving as a signals relay, where it receives orders from a command plane such as Operation Looking Glass, and verifies and retransmits their Emergency Action Messages (EAMs) to US strategic forces. As it is a dedicated communications post, it features the ability to communicate on virtually every radio frequency band from very low frequency (VLF) up through super high frequency (SHF) using a variety of modulations, encryptions and networks, minimizing the likelihood an emergency message will be jammed by the enemy. This airborne communications capability largely replaced the land-based extremely low frequency (ELF) broadcast sites which became vulnerable to nuclear strike.Telluric current
A telluric current (from Latin tellūs, "earth"), or Earth current, is an electric current which moves underground or through the sea. Telluric currents result from both natural causes and human activity, and the discrete currents interact in a complex pattern. The currents are extremely low frequency and travel over large areas at or near the surface of the Earth.
Radio spectrum (ITU)