Do birds use magnetoreception?
Sense
Magnetoception (or magnetoreception) is the ability to detect the direction one is facing based on the Earth's magnetic field. Directional awareness is most commonly observed in birds, which rely on their magnetic sense to navigate during migration. It has also been observed in insects such as bees. Cattle make use of magnetoception to align themselves in a north-south direction. Magnetotactic bacteria build miniature magnets inside themselves and use them to determine their orientation relative to the Earth's magnetic field.
Bird
The ability of birds to return to precise locations across vast distances has been known for some time; in an experiment conducted in the 1950s, a Manx shearwater released in Boston in the United States returned to its colony in Skomer, in Wales within 13 days, a distance of . Birds navigate during migration using a variety of methods. For diurnal migrants, the sun is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an internal clock. Orientation with the stellar compass depends on the position of the constellations surrounding Polaris. These are backed up in some species by their ability to sense the Earth's geomagnetism through specialised photoreceptors.
Magnets (song)
Recording and management
Magnetic Joe
When Joe passes near a magnetic cell his magnetism activates. The player can see a lightning effect between Joe and the magnet, and Joe moves towards the magnet. As he moves closer to the magnet, his movement and rotation changes. The player can control the ball's movement by timing when the magnetism is activated. Different magnets push or pull the ball in different directions and are marked accordingly.
List of Dutch discoveries
A theory about the magnetic sense of birds assumes that a protein in the retina is changed due to the Zeeman effect.
Sensory systems in fish
Electroreception, or electroception, is the ability to detect electric fields or currents. Some fish, such as catfish and sharks, have organs that detect weak electric potentials on the order of millivolts. Other fish, like the South American electric fishes Gymnotiformes, can produce weak electric currents, which they use in navigation and social communication. In sharks, the ampullae of Lorenzini are electroreceptor organs. They number in the hundreds to thousands. Sharks use the ampullae of Lorenzini to detect the electromagnetic fields that all living things produce. This helps sharks (particularly the hammerhead shark) find prey. The shark has the greatest electrical sensitivity of any animal. Sharks find prey hidden in sand by detecting the electric fields they produce. Ocean currents moving in the magnetic field of the Earth also generate electric fields that sharks can use for orientation and possibly navigation.
Feather pecking
It has been shown that domestic hens have iron mineral deposits in the dendrites in the upper beak and are capable of magnetoreception. Because hens use directional information from the magnetic field of the earth to orient in relatively small areas, this raises the possibility that beak-trimming impairs the ability of hens to orient in extensive systems, or move in and out of buildings in free-range systems.
Magnetoreception
The nematode "Caenorhabditis elegans" was proposed to orient to the magnetic field of the Earth using the first described set of magnetosensory neurons. Worms appear to use the magnetic field to orient during vertical soil migrations that change in sign depending on their satiation state (with hungry worms burrowing down, and satiated worms burrowing up). However, recent evidence challenges these findings.
Charles F. Hockett
While there have been studies attempting to disprove Chomsky, Marcus states that, "An intriguing possibility is that the capacity to recognize recursion might be found only in species that can acquire new patterns of vocalization, for example, songbirds, humans and perhaps some cetaceans." This is in response to a study performed by psychologist Timothy Gentner of the University of California at San Diego. Gentner's study found that starling songbirds use recursive grammar to identify “odd” statements within a given “song.” However, the study does not necessarily debunk Chomsky's observation because it has not yet been proven that songbirds have the semantic ability to generalize from patterns.
Magnetoreception
Studies of magnetoreception in vertebrate fish have been conducted mainly with salmon. For instance, the presence of an internal magnetic compass has been discovered in Sockeye Salmon ("Oncorhynchus nerka"). Researchers made this discovery by first placing the young of this species in a symmetrical, circular tank and allowing them to pass through exits in the tank freely. A mean vector was then calculated to represent the directional preferences of these salmon in the natural magnetic field. Notably, when the magnetic field was experimentally rotated, the directional preferences of the young Sockeye Salmon changed accordingly. As such, researchers concluded that the orientation of swimming behaviour in Sockeye Salmon is influenced by magnetic field information.
Photoreceptor cell
The pineal and parapineal glands are photoreceptive in non-mammalian vertebrates, but not in mammals. Birds have photoactive cerebrospinal fluid (CSF)-contacting neurons within the paraventricular organ that respond to light in the absence of input from the eyes or neurotransmitters. Invertebrate photoreceptors in organisms such as insects and molluscs are different in both their morphological organization and their underlying biochemical pathways. Described here are human photoreceptors.
Magnetism
The explanation of the phenomena is thus essentially based on all subtleties of quantum mechanics, whereas the electrodynamics covers mainly the phenomenology.Some organisms can detect magnetic fields, a phenomenon known as magnetoception. In addition to detection, biomagnetic phenomena are utilized by organisms in a number of ways. For instance, chitons, a type of marine mollusk, produce magnetite to harden their teeth, and even humans produce magnetite in bodily tissue. Magnetobiology studies magnetic fields as a medical treatment; fields naturally produced by an organism are known as biomagnetism.
Magnetic field
Devices used to measure the local magnetic field are called magnetometers. Important classes of magnetometers include using induction magnetometer (or search-coil magnetometer) which measure only varying magnetic field, rotating coil magnetometer, Hall effect magnetometers, NMR magnetometers, SQUID magnetometers, and fluxgate magnetometers. The magnetic fields of distant astronomical objects are measured through their effects on local charged particles. For instance, electrons spiraling around a field line produce synchrotron radiation that is detectable in radio waves.
Magnetofection
The magnetic nanoparticles are made of iron oxide, which is fully biodegradable, coated with specific cationic proprietary molecules varying upon the applications. Their association with the gene vectors (DNA, siRNA, ODN, virus, etc.) is achieved by salt-induced colloidal aggregation and electrostatic interaction. The magnetic particles are then concentrated on the target cells by the influence of an external magnetic field generated by magnets. The cellular uptake of the genetic material is accomplished by endocytosis and pinocytosis, two natural biological processes. Consequently, membrane architecture and structure stays intact, in contrast to other physical transfection methods that damage the cell membrane.
Pygmy sperm whale
The rostroventral dura of the brain contains a significant concentration of magnetite crystals, which suggests that "K. breviceps" can navigate by magnetoreception.
Magnetic shark repellent
Magnetic shark repellents utilize permanent magnets, which exploit the sensitivity of the Ampullae of Lorenzini in sharks and rays (electrosense). This organ is not found on bony fishes (teleosts), therefore, this type of shark repellent is selective to sharks and rays. Permanent magnets do not require power input, making them ideal for use in fisheries and as bycatch reduction devices.
Nuclear magnetic resonance spectroscopy
When placed in a magnetic field, NMR active nuclei (such as H or C) absorb electromagnetic radiation at a frequency characteristic of the isotope. The resonant frequency, energy of the radiation absorbed, and the intensity of the signal are proportional to the strength of the magnetic field. For example, in a 21 Tesla magnetic field, hydrogen atoms (commonly referred to as protons) resonate at 900 MHz. It is common to refer to a 21 T magnet as a 900 MHz magnet since hydrogen is the most common nucleus detected, however different nuclei will resonate at different frequencies at this field strength in proportion to their nuclear magnetic moments.
Repetition priming
Research into repetition priming has been used to investigate the nature of mechanisms underlying the behavioural effects of rapid learning. In utilizing measures of "repetition suppression", the putative neural correlate of repetition priming, and measuring changes in the neural response associated with changing the presented stimuli, researchers are attempting to index regions and their processing biases along perceptual, conceptual and response dimensions. This area of research is based on multiple measurement methods from single cell recordings to multi-regional measurements using functional magnetic resonance imaging (fMRI), electroencephalography (EEG) and magnetoencephalography (MEG). Transcranial magnetic stimulation (TMS) has also been used to temporarily 'lesion' (inactivate) specific regions and so get an indication of the necessity of those regions in processing specific dimensions of the presented stimuli. Much of this research has been focused on the visual domain, however auditory and olfactory processes have also been investigated.
Magnetobiology
The magnetite model arose with the discovery of chains of single domain magnetite in certain bacteria in the 1970s. Histological evidence in a large number of species belonging to all major phyla. Honey bees have magnetic material in the front part of the abdomen while in vertebrates mostly in the ethmoid region of the head. Experiments prove that the input from magnetite-based receptors in birds and fish is sent over the ophthalmic nerve branch of the trigeminal nerve to the central nervous system.
Ferromagnetic resonance
FMR arises from the precessional motion of the (usually quite large) magnetization formula_1 of a ferromagnetic material in an external magnetic field formula_2. The magnetic field exerts a torque on the sample magnetization which causes the magnetic moments in the sample to precess. The precession frequency of the magnetization depends on the orientation of the material, the strength of the magnetic field, as well as the macroscopic magnetization of the sample; the effective precession frequency of the ferromagnet is much lower in value from the precession frequency observed for free electrons in EPR. Moreover, linewidths of absorption peaks can be greatly affected both by dipolar-narrowing and exchange-broadening (quantum) effects. Furthermore, not all absorption peaks observed in FMR are caused by the precession of the magnetic moments of electrons in the ferromagnet. Thus, the theoretical analysis of FMR spectra is far more complex than that of EPR or NMR spectra.
Sea turtle migration
The post-nesting migration of adult female green sea turtles from Ascension Island to Brazil has been recorded using satellite transmitters as part of an experiment into their navigation. In addition to the transmitters, some turtles were fitted with magnets which were expected to disrupt any ability to use the Earth's field for navigation. In fact there was no difference in migratory performance between these turtles and turtles which weren't carrying magnets, but the experimental design has been criticised. In fact there is strong evidence that green turtles are sensitive to magnetic cues. For example, juvenile green turtles exposed to fields north and south of a capture site (i.e. displaced in geomagnetic but not geographical space) oriented in a direction that would have led them back to the capture site, suggesting that they can use the earth's magnetic field to acquire positional information. Adult turtles also use magnetic cues. Whilst geomagnetic cues may guide navigation over long distances, close to the goal, it is thought that turtles use wind-borne cues emanating from the goal to home in on their target. Most recently, it has been shown that juvenile greens can orient using a 'sun compass' In other words, they can use directional information to determine their headings.
Magnetobiology
Magnetic intensity as a component of the navigational ‘map’ of pigeons had been discussed since the late nineteenth century. One of the earliest publications to prove that birds use magnetic information was a 1972 study on the compass of European robins by Wolfgang Wiltschko. A 2014 double blinded study showed that European robins exposed to low level electromagnetic noise between about 20 kHz and 20 MHz,could not orient themselves with their magnetic compass. When they entered aluminium-screened huts, which attenuated electromagnetic noise in the frequency range from 50 kHz to 5 MHz by approximately two orders of magnitude, their orientation reappeared.
Bar-Ilan University
The Gonda Multidisciplinary Brain Research Center hosts the only magnetoencephalography facility in Israel, operated by the Electromagnetic Brain Imaging Unit established in 2008. Magnetoencephalography is a brain imaging technique that allows studying human brain responses by measuring the magnetic fields produced by electrical brain activity at superb (millisecond) temporal resolution. The unit is headed by Professor Abraham Goldstein. It is equipped with a 248 magnetometer sensors whole-head system, positioned inside a double-wall magnetically shielded room by IMEDCO. Once a week, magnetoencephalography is dedicated to serving the community by providing clinical and diagnostic services, such as localization of epileptic foci, via BrainMap.
Magnetoencephalography
MEG has been used to study cognitive processes such as vision, audition, and language processing in fetuses and newborns.
Magnetic reconnection
Magnetic reconnection events that occur in the Earth's magnetosphere (in the dayside magnetopause and in the magnetotail) were observed by spacecrafts such as Cluster II and the Magnetospheric Multiscale Mission. Cluster II is a four-spacecraft mission, with the four spacecraft arranged in a tetrahedron to separate the spatial and temporal changes as the suite flies through space. It has observed numerous reconnection events in which the Earth's magnetic field reconnects with that of the Sun (i.e. the Interplanetary Magnetic Field). These include 'reverse reconnection' that causes sunward convection in the Earth's ionosphere near the polar cusps; 'dayside reconnection', which allows the transmission of particles and energy into the Earth's vicinity and 'tail reconnection', which causes auroral substorms by injecting particles deep into the magnetosphere and releasing the energy stored in the Earth's magnetotail. The Magnetospheric Multiscale Mission, launched on 13 March 2015, improved the spatial and temporal resolution of the Cluster II results by having a tighter constellation of spacecraft. This led to a better understanding of the behavior of the electrical currents in the electron diffusion region.
Airborne Interception radar
First introduced in March 1941, it was found that the ground reflection created a sort of artificial horizon on the bottom of the display, a surprising side-effect which proved very useful. However, the limited power of the magnetron, about 5 kW, provided range of about , not a great improvement over the Mk. IV. Performance of the system at low altitude was so improved over the Mk. IV that it was decided to make an initial run of 100 units out of what were essentially prototype systems as the Mk. VII, requiring very large amount of aircraft space for the install. Conversions on the Beaufighter began in December 1941.
Magnetoreception
In similar fashion, European ("Bufo bufo") and Natterjack ("Epidalea calamita)" toads appear to rely, at least somewhat, on magnetic information for certain orienting behaviours. These species of anurans are known to rely on vision and olfaction when locating and migrating to breeding sites, but it seems magnetic fields may also play a role. When randomly displaced from their breeding sites, these toads remain well-oriented, and are capable of navigating their way back, even when displaced by more than 150 meters. However, when this displacement is accompanied by the experimental attachment of small magnetic bars, toads fail to relocate breeding sites. Considering experimental attachment of non-magnetized bars of equal size and weight does not affect relocation, it seems that magnetism is responsible for the observed disorientation of these toads. Therefore, researchers have concluded that orientation toward breeding sites in these anurans is influenced by magnetic field information.
Bird vocalization
Research has indicated that birds' acquisition of song is a form of motor learning that involves regions of the basal ganglia. Further, the PDP (see "Neuroanatomy" below) has been considered homologous to a mammalian motor pathway originating in the cerebral cortex and descending through the brain stem, while the AFP has been considered homologous to the mammalian cortical pathway through the basal ganglia and thalamus. Models of bird-song motor learning can be useful in developing models for how humans learn speech. In some species such as zebra finches, learning of song is limited to the first year; they are termed "age-limited" or "close-ended" learners. Other species such as the canaries can develop new songs even as sexually mature adults; these are termed "open-ended" learners.
Magnetoreception
A number of amphibians and reptiles including salamanders, toads and turtles exhibit alignment behaviours with respect to the Earth's magnetic field.
Magnetite
Biomagnetism is usually related to the presence of biogenic crystals of magnetite, which occur widely in organisms. These organisms range from bacteria (e.g., "Magnetospirillum magnetotacticum") to animals, including humans, where magnetite crystals (and other magnetically-sensitive compounds) are found in different organs, depending on the species. Biomagnetites account for the effects of weak magnetic fields on biological systems. There is also a chemical basis for cellular sensitivity to electric and magnetic fields (galvanotaxis).
Klaus Schulten
Schulten also began to explore the possibility that fast triplets could explain compass sensors in biological species such as migrating birds. That the European robin used some form of magnetoreception was demonstrated by Wolfgang Wiltschko and Fritz Merkel in 1965, and further studied by Wolfgang and Roswitha Wiltschko. Schulten proposed that quantum entanglement of a radical-pair system could underlie a biochemical compass. Schulten and others have since extended this early work, developing a model of the possible excitation of cryptochrome proteins in photoreceptors within the retina of the eye.
Manx shearwater
Manx shearwaters are able to fly directly back to their burrows when released hundreds of kilometres away, even inland. They are able to detect the Earth's magnetic field to navigate back to their colonies. The details of how birds interpret the magnetic data are not fully understood, but tiny crystals of magnetite around the eye are involved in detecting the field.
Manx shearwaters are long-lived birds. A Manx shearwater breeding on Copeland Island, Northern Ireland, was as of 2003/04, the oldest known living wild bird in the world: ringed as an adult (at least 5 years old) in July 1953, it was retrapped in July 2003, at least 55 years old.
Magnetotactic bacteria
Scientists have also proposed an extension of the described model of magneto-aerotaxis to a more complex redoxtaxis. In this case, the unidirectional movement of MTB in a drop of water would be only one aspect of a sophisticated redox-controlled response. One hint for the possible function of polar magnetotaxis could be that most of the representative microorganisms are characterised by possessing either large sulfur inclusions or magnetosomes consisting of iron-sulfides. Therefore, it may be speculated the metabolism of these bacteria, being either chemolithoautotrophic or mixotrophic, is strongly dependent on the uptake of reduced sulfur compounds, which occurs in many habitats only in deeper regions at or below the OATZ due to the rapid chemical oxidation of these reduced chemical species by oxygen or other oxidants in the upper layers.
Tape recorder
Magnetic recording was conceived as early as 1878 by the American engineer Oberlin Smith and demonstrated in practice in 1898 by Danish engineer Valdemar Poulsen. Analog magnetic wire recording, and its successor, magnetic tape recording, involve the use of a magnetizable medium which moves with a constant speed past a recording head. An electrical signal, which is analogous to the sound that is to be recorded, is fed to the recording head, inducing a pattern of magnetization similar to the signal. A playback head can then pick up the changes in magnetic field from the tape and convert it into an electrical signal to be amplified and played back through a loudspeaker.
Bird vocalization
Prather, et al. found that during the short period of time before and after the bird sings, his HVC neurons become insensitive to auditory input. In other words, the bird becomes "deaf" to his own song. This suggests that these neurons are producing a corollary discharge, which would allow for direct comparison of motor output and auditory input. This may be the mechanism underlying learning via auditory feedback. These findings are also in line with Leonardo's (2004) efference copy model of error correction in birdsong learning and production.
Magnetoreception
Red foxes ("Vulpes vulpes") may use magnetoreception when predating small rodents. When foxes perform their high-jumps onto small prey like mice and voles, they tend to jump in a north-eastern compass direction. In addition, successful attacks are "tightly clustered" to the north. One study has found that when domestic dogs are off the leash and the Earth's magnetic field is calm, they prefer to urinate and defecate with their bodies aligned on a north-south axis.
Magnetix
The leading American expert in the area of the effects of swallowed magnets on the human body is radiologist Dr. Alan Oestreich. As early as 2004 he warned the medical community about the dangers of "multiple magnet ingestion", but the case studies never made it into the popular press. A pediatric gastroenterologist, Dr. Marsha Kay of the Cleveland Clinic, is one of the first to write an article for health consumers on steps to take if a child is suspected of swallowing a magnet.
Magnetic storage
Magneto-optical recording writes/reads optically. When writing, the magnetic medium is heated locally by a laser, which induces a rapid decrease of coercive field. Then, a small magnetic field can be used to switch the magnetisation. The reading process is based on magneto-optical Kerr effect. The magnetic medium are typically amorphous R-FeCo thin film (R being a rare earth element). Magneto-optical recording is not very popular. One famous example is Minidisc developed by Sony.
European eel
Magnetoreception has also been reported in the European eel by at least one study, and may be used for navigation.
Magnet fishing
It is thought magnet fishing was initially started by boaters using magnets to recover fallen keys from the water. Today magnet retrieval tools are specially designed to retrieve items that are lost at the bottom of bodies of water. There are two main types of magnets used in the hobby: double sided and single sided.
Ethmoid bone
Some birds and other migratory animals have deposits of biological magnetite in their ethmoid bones which allow them to sense the direction of the Earth's magnetic field. Humans have a similar magnetite deposit, but it is believed to be vestigial.
Magnetoreception
Then there is the distinction of magnetic usage. Some species may only be able to sense a magnetic compass to find north and south, while others may only be able to discern between the equator and the pole. Although the ability to sense direction is important in migratory navigation, many animals also have the ability to sense small fluctuations in earth’s magnetic field to compute coordinate maps with a resolution of a few kilometers or better. For a magnetic map, the receptor system would have to be able to discern tiny differences in the surrounding magnetic field to develop a sufficiently detailed magnetic map. This is not out of the question, as many animals have the ability to sense small fluctuations in the earth's magnetic field. This is not out of the question biologically, but physically has yet to be explained. For example, birds such as the homing pigeon are believed to use the magnetite in their beaks to detect magnetic signposts and thus, the magnetic sense they gain from this pathway is a possible map. Yet, it has also been suggested that homing pigeons and other birds use the visually mediated cryptochrome receptor as a compass.
Electroreception
The electric field sensors of sharks are called the ampullae of Lorenzini. They consist of electroreceptor cells connected to the seawater by pores on their snouts and other zones of the head. A problem with the early submarine telegraph cables was the damage caused by sharks who sensed the electric fields produced by these cables. It is possible that sharks may use Earth's magnetic field to navigate the oceans using this sense.
Quantum biology
Experiments in the lab support the basic theory that radical-pair electrons can be significantly influenced by very weak magnetic fields, i.e. merely the direction of weak magnetic fields can affect radical-pair's reactivity and therefore can "catalyze" the formation of chemical products. Whether this mechanism applies to magnetoreception and/or quantum biology, that is, whether earth's magnetic field "catalyzes" the formation of "bio"chemical products by the aid of radical-pairs, is undetermined for two reasons. The first is that radical-pairs may need not be entangled, the key "quantum" feature of the radical-pair mechanism, to play a part in these processes. There are entangled and non-entangled radical-pairs. However, researchers found evidence for the radical-pair mechanism of magnetoreception when European robins, cockroaches, and garden warblers, could no longer navigate when exposed to a radio frequency that obstructs magnetic fields and radical-pair chemistry. To empirically suggest the involvement of entanglement, an experiment would need to be devised that could disturb entangled radical-pairs without disturbing other radical-pairs, or vice versa, which would first need to be demonstrated in a laboratory setting before being applied to in vivo radical-pairs.
Quantum biology
Magnetoreception refers to the ability of animals to navigate using the inclination of the magnetic field of the earth. A possible explanation for magnetoreception is the entangled radical pair mechanism. The radical-pair mechanism is well-established in spin chemistry, and was speculated to apply to magnetoreception in 1978 by Schulten et al.. The ratio between singlet and triplet pairs is changed by the interaction of entangled electron pairs with the magnetic field of the earth. In 2000, cryptochrome was proposed as the "magnetic molecule" that could harbor magnetically sensitive radical-pairs. Cryptochrome, a flavoprotein found in the eyes of European robins and other animal species, is the only protein known to form photoinduced radical-pairs in animals. When it interacts with light particles, cryptochrome goes through a redox reaction, which yields radical pairs both during the photo-reduction and the oxidation. The function of cryptochrome is diverse across species, however, the photoinduction of radical-pairs occurs by exposure to blue light, which excites an electron in a chromophore. Magnetoreception is also possible in the dark, so the mechanism must rely more on the radical pairs generated during light-independent oxidation.
Vision in fishes
Cartilaginous fish (sharks, stingrays and chimaeras) use magnetoception. They possess special electroreceptors called the "ampullae of Lorenzini" which detect a slight variation in electric potential. These receptors, located along the mouth and nose of the fish, operate according to the principle that a time-varying magnetic field moving through a conductor induces an electric potential across the ends of the conductor. The ampullae may also allow the fish to detect changes in water temperature.
Nihoa millerbird
Using mist nets, 85 Nihoa millerbirds (60 males and 25 females) were captured and banded. Banding permits identification of previously captured birds and reduces stress that can be caused by multiple captures. Most importantly, however, banding allows individual birds to be identified in the field and enables biologists to identify pairs, map their territories, and track individual survival from year to year through repeat sightings. Photographs and measurements of wing and tail feathers were taken from each individual, as well as small feather samples for genetic analysis. Growth bars visible on the tail feathers can help scientists determine the age of the bird, and comparison of photographs and measurements with results of lab analyses will aid in finding a way to sex Nihoa millerbirds in the field. Development of these methods will ensure that the right numbers of male and female birds are moved to Laysan.
Several Nihoa millerbirds were placed in a temporary enclosure and presented with a selection of island insects. The purpose was to identify millerbird dietary preferences and see if the birds would eat in captivity. Preliminary results showed that the birds fed readily from a plastic container of prey items. Of the choices offered, they left behind only lady bugs, sow-bugs, and ants. One bird was quick to chase down fast-moving cockroaches before taking smaller, slower insects such as spiders and beetles. Another test with a male and female showed that, after a brief adjustment period, the pair fed together without hesitation.
Using an iPod and a speaker, the team played millerbird songs within the territories of all 60 banded males and recorded the responses with a microphone. These recordings were used to determine the territories of 20 males and will also be analyzed to determine if differences exist in millerbird songs across Nihoa. Preliminary spectrograph analysis of the recordings shows variety among the songs of male millerbirds, but more research is needed to determine if these differences are significant. Identifying millerbird dialects on such a small spatial scale would be a novel finding and a major accomplishment of the expedition.
Spin chemistry
Because the Zeeman Interaction is a function of magnetic field and Larmor frequency, it can be obstructed or amplified by altering the external magnetic or the Larmor frequency with experimental instruments that generate oscillating fields. This is interesting because migratory birds lose their navigational abilities in similar conditions where the Zeeman interaction is obstructed in radical-pairs, and researchers can control these conditions to probe the importance of Zeeman Interactions in Magnetoreception, implicating the presence of a radical-pair mechanism.
Neurotechnology
Magnetoencephalography is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers. Arrays of SQUIDs (superconducting quantum interference devices) are the most common magnetometer. Applications of MEG include basic research into perceptual and cognitive brain processes, localizing regions affected by pathology before surgical removal, determining the function of various parts of the brain, and neurofeedback. This can be applied in a clinical setting to find locations of abnormalities as well as in an experimental setting to simply measure brain activity.
Bioelectromagnetics
Some usually aquatic animals, such as sharks, have acute bioelectric sensors providing a sense known as electroreception, while migratory birds navigate in part by orienteering with respect to the Earth's magnetic field. In an extreme application of electromagnetism, the electric eel is able to generate a large electric field outside its body used for hunting and self-defense through a dedicated electric organ.
Animal navigation
Some animals, including mammals such as blind mole rats ("Spalax") and birds such as pigeons, are sensitive to the earth's magnetic field.
Solar wind Magnetosphere Ionosphere Link Explorer
SMILE will be equipped to simultaneously capture images and movies of the magnetopause, polar cusps, and aurora. Traditionally, satellites have taken local measurements of different regions to build up a global picture of the magnetosphere. However, a recent discovery that the magnetosphere emits X-rays will allow SMILE to capture more comprehensive data than previous missions did through the analysis of these X-rays.
Immunoprecipitation
As mentioned above, only standard laboratory equipment is required for the use of agarose beads in immunoprecipitation applications, while high-power magnets are required for magnetic bead-based IP reactions. While the magnetic capture equipment may be cost-prohibitive, the rapid completion of immunoprecipitations using magnetic beads may be a financially beneficial approach when grants are due, because a 30-minute protocol with magnetic beads compared to overnight incubation at 4 °C with agarose beads may result in more data generated in a shorter length of time.
Throttle position sensor
Non contact type TPS work on the principle of Hall effect or inductive sensors, or magnetoresistive technologies, wherein generally the magnet or inductive loop is the dynamic part which is mounted on the butterfly valve throttle spindle/shaft gear and the sensor & signal processing circuit board is mounted within the ETC gear box cover and is stationary. When the magnet/inductive loop mounted on the spindle which is rotated from the lower mechanical stop to WOT, there is a change in the magnetic field for the sensor. The change in the magnetic field is sensed by the sensor and the voltage generated is given as the input to the ECU. Normally a two pole rare-earth magnet is used for the TPS due to their high Curie temperatures required in the under-hood vehicle environment. The magnet may be of diametrical type, ring type, rectangular or segment type. The magnet is defined to have a certain magnetic field that does not vary significantly with time or temperature.
Magnetoelectric effect
Historically, the first and most studied example of this effect is the linear magnetoelectric effect. Mathematically, while the electric susceptibility formula_1 and magnetic susceptibility formula_2 describe the electric and magnetic polarization responses to an electric, resp. a magnetic field, there is also the possibility of a magnetoelectric susceptibility formula_3 which describes a linear response of the electric polarization to a magnetic field, and vice versa:
The tensor formula_6 must be the same in both equations. Here, P is the electric polarization, M the magnetization, E and H the electric and magnetic fields. The SI Unit of α is [s/m] which can be converted to the practical unit [V/(cm Oe)] by [s/m]=1.1 x10 ε [V/(cm Oe)]. For the CGS unit, [unitless] = 3 x 10 [s/m]/(4 x π)
Earth's magnetic field
Researchers found out that very weak electromagnetic fields disrupt the magnetic compass used by European robins and other songbirds to navigate using the Earth's magnetic field. Neither power lines nor cellphone signals are to blame for the electromagnetic field effect on the birds; instead, the culprits have frequencies between 2 kHz and 5 MHz. These include AM radio signals and ordinary electronic equipment that might be found in businesses or private homes.
Animal song
Birds are generally predisposed to favour learning of conspecific songs, and will typically preferentially learn the song form conspecific animals rather than heterospecifics. However, song learning is not completely restricted to within-species songs. If exposed to heterospecific birds of another species in absence of same-species birds, young birds will often adopt the song of the species to which it was exposed. Although birds are capable of learning song production purely from audio recordings of birdsong, tutor-student interaction may be important in some species. For example, white-crowned sparrows ("Zonotrichia leucophrys") preferentially learn the songs of song sparrows ("Melospiza melodia") when exposed to recordings of white-crowned sparrows and live song sparrows. In other words, the interactive nature of a live tutor seems to trump the familiarity of the recordings from conspecifics.
Insect migration
Recent studies suggest that migratory butterflies may be sensitive to the Earth's magnetic field on the basis of the presence of magnetite particles. In an experiment on the monarch butterfly, it was shown that a magnet changed the direction of initial flight of migrating monarch butterflies. However this result was not a strong demonstration since the directions of the experimental butterflies and the controls did not differ significantly in the direction of flight.
Electroreception
Bees collect a positive static charge while flying through the air. When a bee visits a flower, the charge deposited on the flower takes a while to leak away into the ground. Bees can detect both the presence and the pattern of electric fields on flowers, and use this information to know if a flower has been recently visited by another bee and is therefore likely to have a reduced concentration of nectar.
Animals detect electric fields through insulating air by mechano-reception, not electroreception. Bees sense the electric field changes via the Johnston's organs in their antennae and possibly other mechano-receptors. They distinguish different temporal patterns and learn them. During the waggle dance, honeybees appear to use the electric field emanating from the dancing bee for distance communication.
Reverse migration (birds)
This is a technique used to track animals with a transmitter and receivers. A miniature transmitter is attached to the subject animal and this transmitter emits a very high frequency (30-300 MHz) which can be picked up with one or more receivers. For studying the moment behaviour of birds in a migration hotspot south-west of Sweden called Falsterbo near Falsterbo bird observatory three receivers were used to triangulate and track the birds.
Ringing birds is when a light weight metal band is attach to the foot to not impair movement but stay on the bird with a identification number. This identification number can provide people catching and these birds movement and history with information such as how old they are and where they have been. At the Falsterbo bird observatory these birds are caught with a mist net measured and banded.
Magnetotactic bacteria
Magnetotactic bacteria (or MTB) are a polyphyletic group of bacteria that orient themselves along the magnetic field lines of Earth's magnetic field. Discovered in 1963 by Salvatore Bellini and rediscovered in 1975 by Richard Blakmore, this alignment is believed to aid these organisms in reaching regions of optimal oxygen concentration. To perform this task, these bacteria have organelles called magnetosomes that contain magnetic crystals. The biological phenomenon of microorganisms tending to move in response to the environment's magnetic characteristics is known as magnetotaxis. (However, this term is misleading in that every other application of the term taxis involves a stimulus-response mechanism.) In contrast to the magnetoreception of animals, the bacteria contain fixed magnets that force the bacteria into alignment—even dead cells are dragged into alignment, just like a compass needle.
Snow bunting
The migration of this bird is nocturnal and they are able to detect the geomagnetic field of the earth in order to guide themselves to their breeding and overwinter territory. The orientation of the snow bunting during migration is independent of any type of visual cue. Furthermore, studies have shown that only those individuals with adequate energy storage will be able to select seasonally appropriate directions during their migration.
Electron magnetic circular dichroism
In the case of transition metals such as iron, cobalt, and nickel, the absorption spectra for EMCD are usually measured at the L-edge. This corresponds to the excitation of a 2p electron to a 3d state by the absorption of a virtual photon providing the ionisation energy. The absorption is visible as a spectral feature in the electron energy loss spectrum (EELS). Because the 3d electron states are the origin of the magnetic properties of the elements, the spectra contain information on the magnetic properties. Moreover, since the energy of each transition depends on the atomic number, the information obtained is element specific, that is, it is possible to distinguish the magnetic properties of a given element by examining the EMCD spectrum at its characteristic energy (708 eV for iron).
Bird migration
Navigation is based on a variety of senses. Many birds have been shown to use a sun compass. Using the sun for direction involves the need for making compensation based on the time. Navigation has also been shown to be based on a combination of other abilities including the ability to detect magnetic fields (magnetoception), use visual landmarks as well as olfactory cues.
Functional integration (neurobiology)
Magnetoencephalography (MEG) is an imaging modality that uses very sensitive magnetometers to measure the magnetic fields resulting from ionic currents flowing through neurons in the brain. High-quality MEG machines allow for sub-millisecond sampling rates.
History of electromagnetic theory
The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying phenomenon, without a theory to explain its behavior and often confused with magnetism. The ancients were acquainted with rather curious properties possessed by two minerals, amber (, "ēlektron") and magnetic iron ore (μαγνῆτις λίθος "magnētis lithos", "the Magnesian stone, lodestone"). Amber, when rubbed, attracts lightweight objects, such as feathers; magnetic iron ore has the power of attracting iron.
Based on his find of an Olmec hematite artifact in Central America, the American astronomer John Carlson has suggested that "the Olmec may have discovered and used the geomagnetic lodestone compass earlier than 1000 BC". If true, this "predates the Chinese discovery of the geomagnetic lodestone compass by more than a millennium". Carlson speculates that the Olmecs may have used similar artifacts as a directional device for astrological or geomantic purposes, or to orient their temples, the dwellings of the living or the interments of the dead. The earliest Chinese literature reference to magnetism lies in a 4th-century BC book called "Book of the Devil Valley Master" (鬼谷子): "The lodestone makes iron come or it attracts it."
Long before any knowledge of electromagnetism existed, people were aware of the effects of electricity. Lightning and other manifestations of electricity such as St. Elmo's fire were known in ancient times, but it was not understood that these phenomena had a common origin. Ancient Egyptians were aware of shocks when interacting with electric fish (such as the electric catfish) or other animals (such as electric eels). The shocks from animals were apparent to observers since pre-history by a variety of peoples that came into contact with them. Texts from 2750 BC by the ancient Egyptians referred to these fish as "thunderer of the Nile" and saw them as the "protectors" of all the other fish. Another possible approach to the discovery of the identity of lightning and electricity from any other source, is to be attributed to the Arabs, who before the 15th century used the same Arabic word for lightning ("barq") and the electric ray.
History of sound recording
Magnetic recording was demonstrated in principle as early as 1898 by Valdemar Poulsen in his telegraphone. Magnetic wire recording, and its successor, magnetic tape recording, involve the use of a magnetized medium which moves with a constant speed past a recording head. An electrical signal, which is analogous to the sound that is to be recorded, is fed to the recording head, inducing a pattern of magnetization similar to the signal. A playback head can then pick up the changes in magnetic field from the tape and convert it into an electrical signal.
Electrocommunication
All organisms respond to sufficiently strong electric shocks, but only some aquatic vertebrates can detect and utilize weak electric fields such as those that occur naturally. These aquatic organisms are therefore called electroreceptive. (For an example, human-beings react to strong electric currents with a sense of pain and sometimes a mixture of other senses; however, we cannot detect weakly electric fields and therefore are not electroreceptive.) The ability to sense and utilize electric fields was found almost solely in lower, aquatic vertebrates (fishes and some amphibians). Terrestrial animals, with very few exceptions, lack this electric sensing channel due to low conductivity of air, soil, or media other than aqueous environment. Exceptions include the Australian monotremes, i.e. the echidna which eats mainly ants and termites, and the semi-aquatic platypus that hunts by utilizing electric fields generated by invertebrate prey.
Magnetic shark repellent
Several species of sharks have demonstrated the ability to sense magnetic fields (Kalmijn, 1978; Ryan, 1980; Klimley, 1993; 2002). The Ampullae of Lorenzini organ within sharks is used to detect weak electrical fields at short ranges. The detection range of this organ is effective only within inches, as sharks sense bioelectrical fields in the final stages of prey capture. The flux per unit area of certain permanent magnets, particularly Neodymium-Iron-Boride and Barium-Ferrite magnets, corresponds closely with the detection range of the Ampullae of Lorenzini. The fields generated by these permanent magnets (ferrite and rare-earth types) decrease at the inverse cube of the distance from the magnet to sharks and rays. Therefore, at distances of a few meters from the magnet, the field exerted is less than the Earth's magnetic field. Animals which lack that Ampullae of Lorenzini organ do not display aversive behavior in close proximity to the magnetic field, making this technology selective.
Magnetometer
Inductive pickup coils (also referred as inductive sensor) measure the magnetization by detecting the current induced in a coil due to the changing magnetic moment of the sample. The sample's magnetization can be changed by applying a small ac magnetic field (or a rapidly changing dc field), as occurs in capacitor-driven pulsed magnets. These measurements require differentiating between the magnetic field produced by the sample and that from the external applied field. Often a special arrangement of cancellation coils is used. For example, half of the pickup coil is wound in one direction, and the other half in the other direction, and the sample is placed in only one half. The external uniform magnetic field is detected by both halves of the coil, and since they are counter-wound, the external magnetic field produces no net signal.
Magnetoreception
For animals the mechanism for magnetoreception is unknown, but there exist two main hypotheses to explain the phenomenon.
According to one model, magnetoreception is possible via the radical pair mechanism. The radical-pair mechanism is well-established in spin chemistry, and was speculated to apply to magnetoreception in 1978 by Schulten et al.. In 2000, cryptochrome was proposed as the "magnetic molecule", so to speak, that could harbor magnetically sensitive radical-pairs. Cryptochrome, a flavoprotein found in the eyes of European robins and other animal species, is the only protein known to form photoinduced radical-pairs in animals. The function of cryptochrome is diverse across species, however, the photoinduction of radical-pairs occurs by exposure to blue light, which excites an electron in a chromophore. The Earth's magnetic field is only 0.5 gauss and so it is difficult to conceive of a mechanism, other than phase shift, by which such a field could lead to any chemical changes other than those affecting the weak magnetic fields between radical pairs. Cryptochromes are therefore thought to be essential for the light-dependent ability of the fruit fly "Drosophila melanogaster" to sense magnetic fields.
Magnetoreception
Subsequent research has examined magnetoreception in a more natural setting. Under typical circumstances, red-spotted newts ("Notophthalmus viridescens)" respond to drastic increases in water temperature (which tend to indicate environmental deterioration) by orienting themselves toward the shoreline and heading for land. However, when magnetic fields are experimentally altered, this behaviour is disrupted, and assumed orientations fail to direct the newts to the shoreline. Moreover, the change in orientation corresponds to the degree by which the magnetic field is shifted. In other words, inversion of the magnetic poles (a 180° shift) results in inversion of the typical orientation (a 180° shift). Further research has shown that magnetic information is not only used by red-spotted newts for orientation toward the shoreline, but also in orientation toward their home pools. Ultimately, it seems as though red-spotted newts rely on information regarding the Earth’s magnetic field for navigation within their environment, in particular when orienting toward the shoreline or toward home.
Long delayed echo
Shlionskiy lists 15 possible "natural" explanations in two groups: reflections in outer space, and reflections within the Earth's magnetosphere. Vidmar and Crawford suggest five of them are the most likely. Sverre Holm, professor of signal processing at the University of Oslo details those five; in summary,Radio waves of frequency less than about 7 MHz can become trapped in magnetic field-aligned ionization ducts with L values (distance from the center of the earth to the field line at the magnetic equator) less than about 4. These waves after being trapped can propagate to the opposite hemisphere where they become reflected in the topside ionosphere. They can return along the duct, leave it, and propagate to the receiver.
The signals from two separated transmitters T1 and T2, T2 transmitting CW or quasi-CW signals, interact nonlinearly in the ionosphere or magnetosphere. If the wave vector and frequency of the forced oscillation at the difference frequency of the two signals satisfies the dispersion relation for electrostatic waves, such waves would exist and begin to propagate. This wave could grow in amplitude due to wave-particle interaction. At a later time it could interact with the CW signal and propagate to T1.
None of these hypotheses can explain everything. Only the first mechanism is well established, and none of the other four are well-established enough to deserve the term "theory". The phenomena are often fleeting and non-repeatable. Our understanding of how the magnetosphere interacts with the solar wind is still evolving.
Magnetospheric Multiscale Mission
Magnetic reconnection in Earth's magnetosphere is one of the mechanisms responsible for the aurora, and it is important to the science of controlled nuclear fusion because it is one mechanism preventing magnetic confinement of the fusion fuel. These mechanisms are studied in outer space by the measurement of motions of matter in stellar atmospheres, like that of the Sun. Magnetic reconnection is a phenomenon in which energy may be efficiently transferred from a magnetic field to the motion of charged particles.
Amelia Earhart
It is unknown whether the model 20B receiver had a beat frequency oscillator that would enable the detection of continuous wave transmissions such as Morse code and radiolocation beacons. Neither Earhart nor Noonan were capable of using Morse code. They relied on voice communications. Manning, who was on the first world flight attempt but not the second, was skilled at Morse and had acquired an FCC aircraft radiotelegraph license for 15 words per minute in March 1937, just prior to the start of the first flight.
Olfactory navigation
The Earth’s magnetic field is a potential map cue as the field varies in both strength and direction over the Earth’s surface Manipulations of the ambient magnetic field are rather difficult, although Keeton (1971) and Ioalé (1984) did report that magnets caused disorientation in pigeons when they were released under total overcast. This first indication for magnetic compass orientation in homing was later supported by other studies, which reversed the field around the head of the pigeon using battery operated coils. Though the coils had little effect in clear conditions, their effect under overcast conditions was dependent on the direction of the current. Another observation consistent with the idea of a geomagnetic map is the shift in the initial bearings of pigeons that occurs when the field increases during magnetic storms. In magnetic anomalies too, pigeons are disoriented, even under sunny conditions.
Motion capture
Magnetic systems calculate position and orientation by the relative magnetic flux of three orthogonal coils on both the transmitter and each receiver. The relative intensity of the voltage or current of the three coils allows these systems to calculate both range and orientation by meticulously mapping the tracking volume. The sensor output is 6DOF, which provides useful results obtained with two-thirds the number of markers required in optical systems; one on upper arm and one on lower arm for elbow position and angle. The markers are not occluded by nonmetallic objects but are susceptible to magnetic and electrical interference from metal objects in the environment, like rebar (steel reinforcing bars in concrete) or wiring, which affect the magnetic field, and electrical sources such as monitors, lights, cables and computers. The sensor response is nonlinear, especially toward edges of the capture area. The wiring from the sensors tends to preclude extreme performance movements. With magnetic systems, it is possible to monitor the results of a motion capture session in real time. The capture volumes for magnetic systems are dramatically smaller than they are for optical systems. With the magnetic systems, there is a distinction between “AC” and “DC” systems: one uses square pulses, the other uses sine wave pulse.
Magnetoreception
Furthermore, orientation toward the sea, a behaviour commonly seen in hatchlings of a number of turtle species, may rely, in part, on magnetoreception.  In Loggerhead and Leatherback turtles, breeding takes place on beaches, and, after hatching, offspring crawl rapidly to the sea. Although differences in light density seem to drive this behaviour, magnetic alignment may also play a part. For instance, the natural directional preferences held by these hatchlings (which lead them from beaches to the sea) reverse upon experimental inversion of the magnetic poles, suggesting the Earth’s magnetic field serves as a reference for proper orientation.
Electroreception
Active electroreception relies upon tuberous electroreceptors which are sensitive to high frequency (20-20,000 Hz) stimuli. These receptors have a loose plug of epithelial cells which capacitively couples the sensory receptor cells to the external environment. Passive electroreception however, relies upon ampullary receptors which are sensitive to low frequency stimuli (below 50 Hz). These receptors have a jelly-filled canal leading from the sensory receptors to the skin surface. Mormyrid electric fish from Africa use tuberous receptors known as Knollenorgans to sense electric communication signals.
Magnetoreception
Magnetoreception has also been reported in the European eel by at least one study.
Magnetoreception
Some of the earliest studies of amphibian magnetoreception were conducted with cave salamanders ("Eurycea lucifuga)". Researchers housed groups of cave salamanders in corridors aligned with either magnetic North-South, or magnetic East-West. In ensuing tests, the magnetic field was experimentally rotated by 90°, and salamanders were placed in cross-shaped structures (one corridor along the new North-South axis, one along the new East-West axis). Considering these salamanders showed a significant preference for test corridors which matched the magnetic alignment of their housing corridors, researchers concluded that cave salamanders have the capacity to detect the Earth’s magnetic field, and have a preference for movement along learned magnetic axes.
Sea turtle migration
In regards to the magnetic field hypothesis, there are three main concepts that should be considered. The concepts include electromagnetic induction, magnetic field chemical reactions, and magnetite. In regards to electromagnetic induction, it is assumed that the sea turtles have electroreceptors. Although evidence has been found in other species such as rays and sharks, no evidence has shown that there are electroreceptors in sea turtles making this hypothesis invalid. A second concept from the experimentation by Irwin involves chemical reactions which is commonly found in a variety of species of newts and birds. The strength of the magnetic field affects the chemical reactions within the bodies of the newts and birds. The final concept includes the magnetic crystals that form during the magnetic pulses from the earth’s magnetic fields. These magnetic crystals formed by magnetite give the turtles directional information and guides in migration. The magnetite affects the cells of the nervous system of the sea turtle by producing a signal that references the forces of the magnetic field and the direction and magnitude that is applied. If this magnetite is used in the migration, when the earth’s magnetic poles reverse at the dipole moment, the signal that the sea turtle nervous system receives will change the migration direction. Regardless of the hypothesis, hatchling turtles have the ability to determine the direction and inclination angle of which they are swimming with aide from magnetic fields.
Airborne Interception radar
In February 1940, John Randall and Harry Boot at Birmingham University successfully ran the first cavity magnetron, eventually generating 1 kW at 9.8 cm (3,060 MHz). Supported by GEC, the device quickly developed into a practical 10 kW system, and several test units were available by May 1940. Microwave wavelengths are so much shorter than the Mk. IV's 1.5 m, fifteen times, that the dipole antennas required for reasonable gain were only a few inches long. This dramatically reduced the size of the system, allowing it to fit entirely in the nose of the aircraft.
Magnetic field
Magnetic fields are widely used throughout modern technology, particularly in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric motors and generators. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits. Magnetic forces give information about the charge carriers in a material through the Hall effect. The Earth produces its own magnetic field, which shields the Earth's ozone layer from the solar wind and is important in navigation using a compass.
Although magnets and magnetism were studied much earlier, the research of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field on the surface of a spherical magnet using iron needles. Noting that the resulting field lines crossed at two points he named those points 'poles' in analogy to Earth's poles. He also clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them.
Thomas Gold
Immediately after the war, Hoyle and Bondi returned to Cambridge, while Gold stayed with naval research until 1947. He then began working at Cambridge's Cavendish Laboratory to help construct the world's largest magnetron, a device invented by two British scientists in 1940 that generated intense microwaves for radar. Soon after, Gold joined R. J. Pumphrey, a zoologist at the Cambridge Zoology Laboratory who had served as the deputy head of radar naval research during the war, to study the effect of resonance on the human ear. He found that the degree of resonance observed in the cochlea was not in accordance with the level of damping that would be expected from the viscosity of the watery liquid that fills the inner ear. In 1948, Gold hypothesized that the ear operates by "regeneration", in that electromechanical action occurs when electrical energy is used to counteract the effects of damping. Although Gold won a prize fellowship from Trinity College for his thesis on the regeneration and obtained a junior lectureship at the Cavendish Laboratory, his theory was widely ignored by ear specialists and physiologists, such as future Nobel Prize winner Georg von Békésy, who did not believe the cochlea operated under a feedback system. In the 1970s, researchers discovered that Gold's hypothesis had been correct – the ear contained microscopic hair cells that operated on a feedback mechanism to generate resonance.
Animal navigation
Homing pigeons use magnetic field information with other navigational cues. Pioneering researcher William Keeton showed that time-shifted homing pigeons could not orient themselves correctly on a clear sunny day, but could do so on an overcast day, suggesting that the birds prefer to rely on the direction of the sun, but switch to using a magnetic field cue when the sun is not visible. This was confirmed by experiments with magnets: the pigeons could not orient correctly on an overcast day when the magnetic field was disrupted.
Magnetophon
Magnetophon recorders were widely used in German radio broadcasts during World War II, although they were a closely guarded secret at the time. The Allies were aware of the existence of the pre-war Magnetophon recorders, but not of the introduction of high-frequency bias and PVC-backed tape.) their intelligence experts knew that the Germans had some new form of recording system but they did not know the full details of its construction and operation until working models of the Magnetophon were discovered during the Allied invasion of Germany during 1944-45.
American audio engineer Jack Mullin acquired two Magnetophon recorders and fifty reels of magnetic tape from a German radio station at Bad Nauheim near Frankfurt in 1945. The allied forces were traveling through Germany during WWII when they first discovered the device. The Allies then handed the Magnetophon over to Mullin. Over the next two years Mullin modified and developed these machines, hoping to create a commercial recording system that could be used by movie studios. American popular vocalist Bing Crosby, dissatisfied with the quality of existing radio network recordings was prevailed upon to invest in this development and would use the technology, as modified by Mullin and the fledgling Ampex company, to record his radio broadcasts in the more relaxed atmosphere of the recording studio, which was a significant break from the then-norm of live studio audience broadcasts. In 2008, at the 50th Annual Grammy Awards Ceremony, Ampex received the company's first Grammy Award for Technical Achievement, to honor their contribution sixty years earlier of the Ampex 200, which "revolutionized the radio and recording industries". Ampex 200 co-designer Myron Stolaroff was among the company's employees representing Ampex who accepted the award.
Magnetospirillum
Probably the most peculiar characteristic of "Magnetospirillum" species is their capacity to orient themselves according to Earth's magnetic field, magnetotaxis. This is achieved through the presence in the bacterium's cytoplasm of special organelles called magnetosomes. "Magnetospirillum" species also resort to aerotaxis, to remain in favorable O concentration conditions. When the bacteria ingest iron, proteins inside their cells interact with it to produce tiny crystals of the mineral magnetite, the most magnetic mineral on Earth.
Magnetoreception
Maghemite has been observed in platelets concentrated along the dendrites of the upper beak, consistently in the nanoscale. When in the nanoscale, iron oxides will remain permanently magnetized at lengths greater than 50 nm and will become magnetized at lengths smaller than 50 nm. Since these platelets have been observed in collections of 5-10, they are thought to form dipoles local to the dendrite they are present in. These local magnetic changes then cause a mechanical response along the membrane of the nerve cell, leading to a change in ion concentrations. This ion concentration, with respect to the other dendrite clusters is believed to form the magnetic sense.
Bird vocalization
The songs of different species of birds vary and are generally typical of the species. Species vary greatly in the complexity of their songs and in the number of distinct kinds of song they sing (up to 3000 in the brown thrasher); individuals within some species vary in the same way. In a few species, such as lyrebirds and mockingbirds, songs imbed arbitrary elements learned in the individual's lifetime, a form of mimicry (though maybe better called "appropriation" [Ehrlich et al.], as the bird does not pass for another species). As early as 1773, it was established that birds learned calls, and cross-fostering experiments succeeded in making linnet "Acanthis cannabina" learn the song of a skylark, "Alauda arvensis". In many species, it appears that although the basic song is the same for all members of the species, young birds learn some details of their songs from their fathers, and these variations build up over generations to form dialects.
Venus Express
MAG: The magnetometer is designed to measure the strength of Venus's magnetic field and the direction of it as affected by the solar wind and Venus itself. It mapped the magnetosheath, magnetotail, ionosphere, and magnetic barrier in high resolution in three-dimensions, aid ASPERA-4 in the study of the interaction of the solar wind with the atmosphere of Venus, identify the boundaries between plasma regions, and carry planetary observations as well (such as the search for and characterization of Venus lightning). MAG is derived from the "Rosetta" lander's ROMAP instrument.
Magnetoreception
Aside from the sensory receptor for magnetic reception in homing pigeons there has been work on neural regions that are possibly involved in the processing of magnetic information within the brain. Areas of the brain that have shown increases in activity in response to magnetic fields with a strength of 50 or 150 microtesla are the posterior vestibular nuclei, dorsal thalamus, hippocampus, and visual hyperpallium.
Magnetic storage
A write head magnetises a region by generating a strong local magnetic field, and a read head detects the magnetisation of the regions. Early HDDs used an electromagnet both to magnetise the region and to then read its magnetic field by using electromagnetic induction. Later versions of inductive heads included Metal In Gap (MIG) heads and thin film heads. As data density increased, read heads using magnetoresistance (MR) came into use; the electrical resistance of the head changed according to the strength of the magnetism from the platter. Later development made use of spintronics; in read heads, the magnetoresistive effect was much greater than in earlier types, and was dubbed "giant" magnetoresistance (GMR). In today's heads, the read and write elements are separate, but in close proximity, on the head portion of an actuator arm. The read element is typically magneto-resistive while the write element is typically thin-film inductive.
Zebra finch
Because zebra finch males learn their songs from their surroundings, they are often used as avian model organisms to investigate the neural bases of learning, memory, and sensorimotor integration. For example, studies have investigated the role of FoxP2 in song learning and have found that in young finches both knockdown and overexpression of FoxP2 in the striatal song control nucleus, Area X, prevents accurate song learning and tutor imitation. These studies also have implications for human speech. Individuals heterozygous for a point mutation in FOXP2 manifest a speech disorder. Because of similar expression patterns between humans and songbirds, the zebra finch is used as a model to study FoxP2 expression and function. The zebra finch genome was the second bird genome to be sequenced, in 2008, after that of the chicken.
Magnetoreception
For a long time the trigeminal system was the suggested location for a magnetite-based magnetoreceptor in the pigeon. This was based on two findings: First, magnetite-containing cells were reported in specific locations in the upper beak. Subsequent studies, however, revealed that these cells were macrophages, not magnetosensitive neurons. Second, pigeon magnetic field detection is impaired by sectioning the trigeminal nerve and by application of lidocaine, an anesthetic, to the olfactory mucosa. However, lidocaine treatment might lead to unspecific effects and not represent a direct interference with potential magnetoreceptors. Therefore, an involvment of the trigeminal system is still debated. In the search for magnetite receptors a large iron containing organelle (the cuticulosome) in the inner ear of pigeons was discovered. This organelle might represent part of an alternative magnetosensitive system. Taken together the receptor responsible for magnetosensitivity in homing pigeons remains uncertain.
Valdemar Poulsen
The magnetic recording was demonstrated in principle as early as 1898 by Poulsen in his telegraphone. Magnetic wire recording, and its successor, magnetic tape recording, involve the use of a magnetizable medium which moves past a recording head. An electrical signal, which is analogous to the sound that is to be recorded, is fed to the recording head, inducing a pattern of magnetization similar to the signal. A playback head (which may be the same as the recording head) can then pick up the changes in the magnetic field from the tape and convert them into an electrical signal.
Poulsen obtained a Telegraphone Patent in 1898, and with his assistant, Peder O. Pedersen, later developed other magnetic recorders that recorded on steel wire, tape, or disks. None of these devices had electronic amplification, but the recorded signal was easily strong enough to be heard through a headset or even transmitted on telephone wires. At the 1900 World's Fair in Paris, Poulsen had the chance to record the voice of Emperor Franz Josef of Austria which is believed to be the oldest surviving magnetic audio recording today.
Poulsen developed an arc converter in 1908, referred to as the "Poulsen Arc Transmitter", which was widely used in radio before the advent of vacuum tube technology. The system was able to communicate between Lyngby and Newcastle with a 100-foot mast.
Magnetoresistance
The AMR effect is used in a wide array of sensors for measurement of Earth's magnetic field (electronic compass), for electric current measuring (by measuring the magnetic field created around the conductor), for traffic detection and for linear position and angle sensing. The biggest AMR sensor manufacturers are Honeywell, NXP Semiconductors, STMicroelectronics, and Sensitec GmbH.
Electroreception
The monotremes are the only group of land mammals known to have evolved electroreception. While the electroreceptors in fish and amphibians evolved from mechanosensory lateral line organs, those of monotremes are based on cutaneous glands innervated by trigeminal nerves. The electroreceptors of monotremes consist of free nerve endings located in the mucous glands of the snout. Among the monotremes, the platypus ("Ornithorhynchus anatinus") has the most acute electric sense. The platypus has almost 40,000 electroreceptors arranged in a series of stripes along the bill, which probably aids the localisation of prey. The platypus electroreceptive system is highly directional, with the axis of greatest sensitivity pointing outwards and downwards. By making short-latency head movements called "saccades" when swimming, platypuses constantly expose the most sensitive part of their bill to the stimulus to localise prey as accurately as possible. The platypus appears to use electroreception along with pressure sensors to determine the distance to prey from the delay between the arrival of electrical signals and pressure changes in the water.
Sense
Body modification enthusiasts have experimented with magnetic implants to attempt to replicate this sense. However, in general humans (and it is presumed other mammals) can detect electric fields only indirectly by detecting the effect they have on hairs. An electrically charged balloon, for instance, will exert a force on human arm hairs, which can be felt through tactition and identified as coming from a static charge (and not from wind or the like). This is not electroreception, as it is a post-sensory cognitive action.
Lepidoptera migration
Earth's magnetic field: A number of moths use the Earth's magnetic field to navigate, as a study of the stray heart and dart suggests. Another study, this time of the migratory behaviour of the silver Y, showed that this species, even at high altitudes, can correct its course with changing winds, and prefers flying with favourable winds, which suggests a great sense of direction. A study in Panama of "Aphrissa statira," which migrate in large groups annually, found that this species loses its navigational capacity when exposed to a magnetic field, suggesting they use the Earth's magnetic field to determine their direction of flight in migration.
Magnetobiology
Magnetobiology is a subset of bioelectromagnetics. Bioelectromagnetism and biomagnetism are the study of the "production" of electromagnetic and magnetic fields by biological organisms. The "sensing" of magnetic fields by organisms is known as magnetoreception.