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53-583: Operation Zebra was a July 1945 major mine clearance operation by U.S. Navy minesweepers off Sakishima Gunto , in association with the invasion of Okinawa by Allied Forces in World War II . [REDACTED]   This article incorporates text from the public domain Dictionary of American Naval Fighting Ships . This World War II article is a stub . You can help Misplaced Pages by expanding it . Minesweeper (ship) The earliest known usage of

106-425: A magnetic force microscope to reveal magnetic domain boundaries that resemble white lines in the sketch. There are many scientific experiments that can physically show magnetic fields. When a domain contains too many molecules, it becomes unstable and divides into two domains aligned in opposite directions so that they stick together more stably. When exposed to a magnetic field, the domain boundaries move, so that

159-430: A crystalline solid. In an antiferromagnet , unlike a ferromagnet, there is a tendency for the intrinsic magnetic moments of neighboring valence electrons to point in opposite directions. When all atoms are arranged in a substance so that each neighbor is anti-parallel, the substance is antiferromagnetic . Antiferromagnets have a zero net magnetic moment because adjacent opposite moment cancels out, meaning that no field

212-569: A magnetic field, magnetism is one of two aspects of electromagnetism . The most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets , producing magnetic fields themselves. Demagnetizing a magnet is also possible. Only a few substances are ferromagnetic; the most common ones are iron , cobalt , nickel , and their alloys. All substances exhibit some type of magnetism. Magnetic materials are classified according to their bulk susceptibility. Ferromagnetism

265-463: A magnetic field. The force of a magnet on paramagnetic, diamagnetic, and antiferromagnetic materials is usually too weak to be felt and can be detected only by laboratory instruments, so in everyday life, these substances are often described as non-magnetic. The strength of a magnetic field always decreases with distance from the magnetic source, though the exact mathematical relationship between strength and distance varies. Many factors can influence

318-402: A material is put in a magnetic field, the electrons circling the nucleus will experience, in addition to their Coulomb attraction to the nucleus, a Lorentz force from the magnetic field. Depending on which direction the electron is orbiting, this force may increase the centripetal force on the electrons, pulling them in towards the nucleus, or it may decrease the force, pulling them away from

371-511: A needle." The 11th-century Chinese scientist Shen Kuo was the first person to write—in the Dream Pool Essays —of the magnetic needle compass and that it improved the accuracy of navigation by employing the astronomical concept of true north . By the 12th century, the Chinese were known to use the lodestone compass for navigation. They sculpted a directional spoon from lodestone in such

424-524: A paramagnetic substance, has unpaired electrons. However, in addition to the electrons' intrinsic magnetic moment's tendency to be parallel to an applied field, there is also in these materials a tendency for these magnetic moments to orient parallel to each other to maintain a lowered-energy state. Thus, even in the absence of an applied field, the magnetic moments of the electrons in the material spontaneously line up parallel to one another. Every ferromagnetic substance has its own individual temperature, called

477-502: A permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field. Electromagnets are widely used as components of other electrical devices, such as motors , generators , relays , solenoids, loudspeakers , hard disks , MRI machines , scientific instruments, and magnetic separation equipment. Electromagnets are also employed in industry for picking up and moving heavy iron objects such as scrap iron and steel. Electromagnetism

530-416: A person's body. In ancient China , the earliest literary reference to magnetism lies in a 4th-century BC book named after its author, Guiguzi . The 2nd-century BC annals, Lüshi Chunqiu , also notes: "The lodestone makes iron approach; some (force) is attracting it." The earliest mention of the attraction of a needle is in a 1st-century work Lunheng ( Balanced Inquiries ): "A lodestone attracts

583-577: A re-adjustment of Garzoni's work. Garzoni's treatise was known also to Giovanni Battista Della Porta . In 1600, William Gilbert published his De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure ( On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth ). In this work he describes many of his experiments with his model earth called the terrella . From his experiments, he concluded that

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636-565: A result of elementary point charges moving relative to each other. Wilhelm Eduard Weber advanced Gauss's theory to Weber electrodynamics . From around 1861, James Clerk Maxwell synthesized and expanded many of these insights into Maxwell's equations , unifying electricity, magnetism, and optics into the field of electromagnetism . However, Gauss's interpretation of magnetism is not fully compatible with Maxwell's electrodynamics. In 1905, Albert Einstein used Maxwell's equations in motivating his theory of special relativity , requiring that

689-592: A way that the handle of the spoon always pointed south. Alexander Neckam , by 1187, was the first in Europe to describe the compass and its use for navigation. In 1269, Peter Peregrinus de Maricourt wrote the Epistola de magnete , the first extant treatise describing the properties of magnets. In 1282, the properties of magnets and the dry compasses were discussed by Al-Ashraf Umar II , a Yemeni physicist , astronomer , and geographer . Leonardo Garzoni 's only extant work,

742-452: Is soundproofed to reduce its acoustic signature and often constructed using wood, fiberglass , or non-ferrous metal , or is degaussed to reduce its magnetic signature . Mechanical sweeps are devices designed to cut the anchoring cables of moored mines, and preferably attach a tag to help the subsequent localization and neutralization. They are towed behind the minesweeper and use a towed body (e.g., oropesa , paravane ) to maintain

795-416: Is anti-aligned. This is called a canted antiferromagnet or spin ice and is an example of geometrical frustration . Like ferromagnetism, ferrimagnets retain their magnetization in the absence of a field. However, like antiferromagnets, neighboring pairs of electron spins tend to point in opposite directions. These two properties are not contradictory, because in the optimal geometrical arrangement, there

848-497: Is impossible according to classical physics, and that a proper understanding requires a quantum-mechanical description. All materials undergo this orbital response. However, in paramagnetic and ferromagnetic substances, the diamagnetic effect is overwhelmed by the much stronger effects caused by the unpaired electrons. In a paramagnetic material there are unpaired electrons; i.e., atomic or molecular orbitals with exactly one electron in them. While paired electrons are required by

901-410: Is more magnetic moment from the sublattice of electrons that point in one direction, than from the sublattice that points in the opposite direction. Most ferrites are ferrimagnetic. The first discovered magnetic substance, magnetite , is a ferrite and was originally believed to be a ferromagnet; Louis Néel disproved this, however, after discovering ferrimagnetism. When a ferromagnet or ferrimagnet

954-403: Is produced by them. Antiferromagnets are less common compared to the other types of behaviors and are mostly observed at low temperatures. In varying temperatures, antiferromagnets can be seen to exhibit diamagnetic and ferromagnetic properties. In some materials, neighboring electrons prefer to point in opposite directions, but there is no geometrical arrangement in which each pair of neighbors

1007-417: Is responsible for most of the effects of magnetism encountered in everyday life, but there are actually several types of magnetism. Paramagnetic substances, such as aluminium and oxygen , are weakly attracted to an applied magnetic field; diamagnetic substances, such as copper and carbon , are weakly repelled; while antiferromagnetic materials, such as chromium , have a more complex relationship with

1060-408: Is sufficiently small, it acts like a single magnetic spin that is subject to Brownian motion . Its response to a magnetic field is qualitatively similar to the response of a paramagnet, but much larger. Japanese physicist Yosuke Nagaoka conceived of a type of magnetism in a square, two-dimensional lattice where every lattice node had one electron. If one electron was removed under specific conditions,

1113-494: Is unavailable, the TSM sweeping instead reproduces the influence of the friendly ship that is about to transit the area. TSM sweeping thus clears mines directed at this ship without knowledge of the mines. However, mines directed at other ships might remain. The minesweeper differs from a minehunter ; the minehunter actively detects and neutralizes individual mines. Minesweepers are in many cases complementary to minehunters, depending on

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1166-696: The Curie temperature , or Curie point, above which it loses its ferromagnetic properties. This is because the thermal tendency to disorder overwhelms the energy-lowering due to ferromagnetic order. Ferromagnetism only occurs in a few substances; common ones are iron , nickel , cobalt , their alloys , and some alloys of rare-earth metals. The magnetic moments of atoms in a ferromagnetic material cause them to behave something like tiny permanent magnets. They stick together and align themselves into small regions of more or less uniform alignment called magnetic domains or Weiss domains . Magnetic domains can be observed with

1219-449: The Due trattati sopra la natura, e le qualità della calamita ( Two treatises on the nature and qualities of the magnet ), is the first known example of a modern treatment of magnetic phenomena. Written in years near 1580 and never published, the treatise had a wide diffusion. In particular, Garzoni is referred to as an expert in magnetism by Niccolò Cabeo, whose Philosophia Magnetica (1629) is just

1272-519: The Earth was itself magnetic and that this was the reason compasses pointed north whereas, previously, some believed that it was the pole star Polaris or a large magnetic island on the north pole that attracted the compass. An understanding of the relationship between electricity and magnetism began in 1819 with work by Hans Christian Ørsted , a professor at the University of Copenhagen, who discovered, by

1325-548: The English Channel clear of mines. A Trawler Section of the Royal Navy Reserve became the predecessor of the mine sweeping forces with specially designed ships and equipment to follow. These reserve Trawler Section fishermen and their trawlers were activated, supplied with mine gear, rifles, and uniforms, and paid as the first minesweepers. The dedicated, purpose-built minesweeper first appeared during World War I with

1378-549: The Flower-class minesweeping sloop . By the end of the War, naval mine technology had grown beyond the ability of minesweepers to detect and remove mines. Minesweeping made significant advancements during World War II . Combatant nations quickly adapted ships to the task of minesweeping, including Australia's 35 civilian ships that became auxiliary minesweepers . Both Allied and Axis countries made heavy use of minesweepers throughout

1431-506: The Greek term μαγνῆτις λίθος magnētis lithos , "the Magnesian stone, lodestone". In ancient Greece, Aristotle attributed the first of what could be called a scientific discussion of magnetism to the philosopher Thales of Miletus , who lived from about 625 BC to about 545 BC. The ancient Indian medical text Sushruta Samhita describes using magnetite to remove arrows embedded in

1484-466: The Pauli exclusion principle to have their intrinsic ('spin') magnetic moments pointing in opposite directions, causing their magnetic fields to cancel out, an unpaired electron is free to align its magnetic moment in any direction. When an external magnetic field is applied, these magnetic moments will tend to align themselves in the same direction as the applied field, thus reinforcing it. A ferromagnet, like

1537-481: The U.S. Navy had four minesweepers deployed to the Persian Gulf to address regional instabilities. The Royal Navy also has four minesweepers stationed in the Persian Gulf as part of the 9th Mine Counter-Measures Squadron . Minesweepers are equipped with mechanical or electrical devices, known as "sweeps", for disabling mines. The modern minesweeper is designed to reduce the chances of it detonating mines itself; it

1590-622: The naval mine dates to the Ming dynasty . Dedicated minesweepers, however, only appeared many centuries later during the Crimean War , when they were deployed by the British. The Crimean War minesweepers were rowboats trailing grapnels to snag mines. Minesweeping technology picked up in the Russo-Japanese War , using aging torpedo boats as minesweepers. In Britain, naval leaders recognized before

1643-569: The standard model . Magnetism, at its root, arises from three sources: The magnetic properties of materials are mainly due to the magnetic moments of their atoms ' orbiting electrons . The magnetic moments of the nuclei of atoms are typically thousands of times smaller than the electrons' magnetic moments, so they are negligible in the context of the magnetization of materials. Nuclear magnetic moments are nevertheless very important in other contexts, particularly in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). Ordinarily,

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1696-500: The accidental twitching of a compass needle near a wire, that an electric current could create a magnetic field. This landmark experiment is known as Ørsted's Experiment. Jean-Baptiste Biot and Félix Savart , both of whom in 1820 came up with the Biot–Savart law giving an equation for the magnetic field from a current-carrying wire. Around the same time, André-Marie Ampère carried out numerous systematic experiments and discovered that

1749-420: The domains aligned with the magnetic field grow and dominate the structure (dotted yellow area), as shown at the left. When the magnetizing field is removed, the domains may not return to an unmagnetized state. This results in the ferromagnetic material's being magnetized, forming a permanent magnet. When magnetized strongly enough that the prevailing domain overruns all others to result in only one single domain,

1802-416: The electrons preferentially adopt arrangements in which the magnetic moment of each electron is canceled by the opposite moment of another electron. Moreover, even when the electron configuration is such that there are unpaired electrons and/or non-filled subshells, it is often the case that the various electrons in the solid will contribute magnetic moments that point in different, random directions so that

1855-401: The enormous number of electrons in a material are arranged such that their magnetic moments (both orbital and intrinsic) cancel out. This is due, to some extent, to electrons combining into pairs with opposite intrinsic magnetic moments as a result of the Pauli exclusion principle (see electron configuration ), and combining into filled subshells with zero net orbital motion. In both cases,

1908-488: The lattice's energy would be minimal only when all electrons' spins were parallel. A variation on this was achieved experimentally by arranging the atoms in a triangular moiré lattice of molybdenum diselenide and tungsten disulfide monolayers. Applying a weak magnetic field and a voltage led to ferromagnetic behavior when 100-150% more electrons than lattice nodes were present. The extra electrons delocalized and paired with lattice electrons to form doublons. Delocalization

1961-408: The laws held true in all inertial reference frames . Gauss's approach of interpreting the magnetic force as a mere effect of relative velocities thus found its way back into electrodynamics to some extent. Electromagnetism has continued to develop into the 21st century, being incorporated into the more fundamental theories of gauge theory , quantum electrodynamics , electroweak theory , and finally

2014-434: The magnetic field are necessarily accompanied by a nonzero electric field, and propagate at the speed of light . In vacuum, where μ 0 is the vacuum permeability . In a material, The quantity μ 0 M is called magnetic polarization . If the field H is small, the response of the magnetization M in a diamagnet or paramagnet is approximately linear: the constant of proportionality being called

2067-430: The magnetic field of an object including the magnetic moment of the material, the physical shape of the object, both the magnitude and direction of any electric current present within the object, and the temperature of the object. Magnetism was first discovered in the ancient world when people noticed that lodestones , naturally magnetized pieces of the mineral magnetite , could attract iron. The word magnet comes from

2120-427: The magnetic field. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron ; the magnetic core concentrates the magnetic flux and makes a more powerful magnet. The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike

2173-453: The magnetic force between two DC current loops of any shape is equal to the sum of the individual forces that each current element of one circuit exerts on each other current element of the other circuit. In 1831, Michael Faraday discovered that a time-varying magnetic flux induces a voltage through a wire loop. In 1835, Carl Friedrich Gauss hypothesized, based on Ampère's force law in its original form, that all forms of magnetism arise as

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2226-409: The material is magnetically saturated . When a magnetized ferromagnetic material is heated to the Curie point temperature, the molecules are agitated to the point that the magnetic domains lose the organization, and the magnetic properties they cause cease. When the material is cooled, this domain alignment structure spontaneously returns, in a manner roughly analogous to how a liquid can freeze into

2279-402: The material will not be magnetic. Sometimes—either spontaneously, or owing to an applied external magnetic field—each of the electron magnetic moments will be, on average, lined up. A suitable material can then produce a strong net magnetic field. The magnetic behavior of a material depends on its structure, particularly its electron configuration , for the reasons mentioned above, and also on

2332-461: The nucleus. This effect systematically increases the orbital magnetic moments that were aligned opposite the field and decreases the ones aligned parallel to the field (in accordance with Lenz's law ). This results in a small bulk magnetic moment, with an opposite direction to the applied field. This description is meant only as a heuristic ; the Bohr–Van Leeuwen theorem shows that diamagnetism

2385-535: The operation and the environment; a minesweeper is, in particular, better suited to clearing open-water areas with large numbers of mines. Both kinds of ships are collectively called mine countermeasure vessels (MCMV), a term also applied to a vessel that combines both roles. Magnetism Magnetism is the class of physical attributes that occur through a magnetic field , which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to

2438-432: The outbreak of World War I that the development of sea mines was a threat to the nation's shipping and began efforts to counter the threat. Sir Arthur Wilson noted the real threat of the time was a blockade aided by mines and not an invasion. The function of the fishing fleet's trawlers with their trawl gear was recognized as having a natural connection with mine clearance and, among other things, trawlers were used to keep

2491-419: The paramagnetic behavior dominates. Thus, despite its universal occurrence, diamagnetic behavior is observed only in a purely diamagnetic material. In a diamagnetic material, there are no unpaired electrons, so the intrinsic electron magnetic moments cannot produce any bulk effect. In these cases, the magnetization arises from the electrons' orbital motions, which can be understood classically as follows: When

2544-653: The resulting theory ( electromagnetism ) is fully consistent with special relativity. In particular, a phenomenon that appears purely electric or purely magnetic to one observer may be a mix of both to another, or more generally the relative contributions of electricity and magnetism are dependent on the frame of reference. Thus, special relativity "mixes" electricity and magnetism into a single, inseparable phenomenon called electromagnetism , analogous to how general relativity "mixes" space and time into spacetime . All observations on electromagnetism apply to what might be considered to be primarily magnetism, e.g. perturbations in

2597-452: The sweep at the desired depth and position. Influence sweeps are equipment, often towed, that emulate a particular ship signature, thereby causing a mine to detonate. There are two modes of operating an influence sweep: MSM (mine setting mode) and TSM (target simulation mode or target setting mode). MSM sweeping is founded on intelligence on a given type of mine, and produces the output required for detonation of this mine. If such intelligence

2650-407: The temperature. At high temperatures, random thermal motion makes it more difficult for the electrons to maintain alignment. Diamagnetism appears in all materials and is the tendency of a material to oppose an applied magnetic field, and therefore, to be repelled by a magnetic field. However, in a material with paramagnetic properties (that is, with a tendency to enhance an external magnetic field),

2703-742: The war. Historian Gordon Williamson wrote that "Germany's minesweepers alone formed a massive proportion of its total strength, and are very much the unsung heroes of the Kriegsmarine ." Naval mines remained a threat even after the war ended, and minesweeping crews were still active after VJ Day . After the Second World War, Allied countries worked on new classes of minesweepers ranging from 120-ton designs for clearing estuaries to 735-ton oceangoing vessels. The United States Navy even used specialized mechanized landing craft to sweep shallow harbors in and around North Korea . As of June 2012 ,

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2756-452: Was discovered in 1820. As a consequence of Einstein's theory of special relativity , electricity and magnetism are fundamentally interlinked. Both magnetism lacking electricity, and electricity without magnetism, are inconsistent with special relativity, due to such effects as length contraction , time dilation , and the fact that the magnetic force is velocity-dependent. However, when both electricity and magnetism are taken into account,

2809-435: Was prevented unless the lattice electrons had aligned spins. The doublons thus created localized ferromagnetic regions. The phenomenon took place at 140 millikelvins. An electromagnet is a type of magnet in which the magnetic field is produced by an electric current . The magnetic field disappears when the current is turned off. Electromagnets usually consist of a large number of closely spaced turns of wire that create

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