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Neurosis (: neuroses) is a term mainly used today by followers of Freudian thinking to describe mental disorders caused by past anxiety, often that has been repressed. In recent history, the term has been used to refer to anxiety-related conditions more generally.
The term "neurosis" is no longer used in condition names or categories by the World Health Organization's International Classification of Diseases (ICD) or the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM). According to the American Heritage Medical Dictionary of 2007, the term is "no longer used in psychiatric diagnosis".
Neurosis is distinguished from psychosis, which refers to a loss of touch with reality. Its descendant term, neuroticism, refers to a personality trait of being prone to anxiousness and mental collapse. The term "neuroticism" is also no longer used for DSM or ICD conditions; however, it is a common name for one of the Big Five personality traits. A similar concept is included in the ICD-11 as the condition "negative affectivity".
History
A broad condition (1769–1879)
The term neurosis was coined by Scottish doctor William Cullen to refer to "disorders of sense and motion" caused by a "general affection of the nervous system". The term is derived from the Greek word neuron (νεῦρον, 'nerve') and the suffix -osis (-ωσις, 'diseased' or 'abnormal condition'). It was first used in print in Cullen's System of Nosology, first published in Latin in 1769.
Cullen used the term to describe various nervous disorders and symptoms that could not be explained physiologically. Physical features, however, were almost inevitably present, and physical diagnostic tests, such as exaggerated knee-jerks, loss of the gag reflex and dermatographia, were used into the 20th century.
French psychiatrist Phillipe Pinnel's Nosographie philosophique ou La méthode de l'analyse appliquée à la médecine (1798) was greatly inspired by Cullen. It divided medical conditions into five categories, with one being "neurosis". This was divided into four basic types of mental disorder: melancholia, mania, dementia, and idiotism. | Neurosis | Wikipedia | 484 | 47588 | https://en.wikipedia.org/wiki/Neurosis | Biology and health sciences | Mental disorder | null |
Morphine was first isolated from opium in 1805, by German chemist Friedrich Sertürner. After the publication of his third paper on the topic in 1817, morphine became more widely known, and used to treat neuroses and other kinds of mental distress. After becoming addicted to this highly addictive substance, he warned "I consider it my duty to attract attention to the terrible effects of this new substance I called morphium in order that calamity may be averted."
German psychologist Johann Friedrich Herbart used the term repression in 1824, in a discussion of unconscious ideas competing to get into consciousness.
The tranquilising properties of potassium bromide were noted publicly by British doctor Charles Locock in 1857. Over the coming decades, this and other bromides were used in great quantities to calm people with neuroses. This led to many cases of bromism.
French psychiatrist Henri Legrand du Saulle used exposure therapy to treat phobias.
American doctor Weir Mitchell first published an account of his rest cure for non-psychotic mental disorders in 1875. His 1877 book "Fat and Blood: and how to make them" gave a fuller explanation. The cure originally involved women being isolated in bed, only communicating with a nurse trained to talk about unchallenging topics, a fattening diet of milk, plus massage and the application of electricity. Eventually, the cure advocated by the Mitchell family had less strict isolation and diet, and was followed by men as well as women. "Fat and Blood" was revised and reprinted for many decades.
Breuer, Freud and contemporaries (1880-1939)
Austrian psychiatrist Josef Breuer first used psychoanalysis to treat hysteria in 1880–1882. Bertha Pappenheim was treated for a variety of symptoms that began when her father suddenly fell seriously ill in mid-1880 during a family holiday in Ischl. His illness was a turning point in her life. While sitting up at night at his sickbed she was suddenly tormented by hallucinations and a state of anxiety. At first the family did not react to these symptoms, but in November 1880, Breuer, a friend of the family, began to treat her. He encouraged her, sometimes under light hypnosis, to narrate stories, which led to partial improvement of the clinical picture, although her overall condition continued to deteriorate. | Neurosis | Wikipedia | 479 | 47588 | https://en.wikipedia.org/wiki/Neurosis | Biology and health sciences | Mental disorder | null |
According to Breuer, the slow and laborious progress of her "remembering work" in which she recalled individual symptoms after they had occurred, thus "dissolving" them, came to a conclusion on 7 June 1882 after she had reconstructed the first night of hallucinations in Ischl. "She has fully recovered since that time" were the words with which Breuer concluded his case report. Accounts differ on the success of Pappenheim's treatment by Breuer. She did not speak about this episode in her later life, and vehemently opposed any attempts at psychoanalytic treatment of people in her care. Breuer was not quick to publish about this case.
(Subsequent research has suggested Pappenheim may have had one of a number of neurological illnesses. This includes temporal lobe epilepsy, tuberculous meningitis, and encephalitis. Whatever the nature of her condition, she went on to run an orphanage, and then found and lead the for twenty years.)
The term psychoneurosis was coined by Scottish psychiatrist Thomas Clouston for his 1883 book Clinical Lectures on Mental Diseases. He describes a condition that covers what is today considered the schizophrenia and autism spectrums (a combination of symptoms that would soon become better known as dementia praecox).
French neurologist Jean-Martin Charcot came to believe that psychological trauma was a cause of some cases of hysteria. He wrote in his book Leçons sur les maladies du système nerveux, (1885-1887) (and published in English as Clinical Lectures on the Diseases of the Nervous System):Quite recently male hysteria has been studied by Messrs. Putnam [1884] and Walton [1883] in America, principally as it occurs after injuries, and especially after railway accidents. They have recognised, like Mr. Page, [1885] who in England has also paid attention to this subject, that many of those nervous accidents described under the name of Railway-spine, and which according to them would be better described as Railway-brain, are in fact, whether occurring in man or woman, simply manifestations of hysteria.Charcot documented around two dozen cases where psychological trauma appears to have caused hysteria. In some cases, the results are described like the modern concept of PTSD. | Neurosis | Wikipedia | 472 | 47588 | https://en.wikipedia.org/wiki/Neurosis | Biology and health sciences | Mental disorder | null |
Austrian psychiatrist Sigmund Freud was a student of Charcot in 1885–6. In 1893 Freud credited Charcot with being the source of "all the modern advances made in the understanding and knowledge of hysteria."
French psychiatrist Pierre Janet released his book L'automatisme psychologique (Psychological automatism) in 1889, its third chapter detailing his understanding of hypnosis and the unconscious. At this time, he claimed that the main aspect of psychological trauma is dissociation (a disconnection of the conscious mind from reality). (Freud would later claim Janet as a major influence.)
In 1891, Thomas Clouston published Neuroses of Development, which covered a wide range of physical and mental developmental conditions.Breuer came to mentor Freud. The pair released the paper "Ueber den psychischen Mechanismus hysterischer Phänomene. (Vorläufige Mittheilung.)" (known in English as "On the physical mechanism of hysterical phenomena: preliminary communication") in January 1893. It opens with:A chance observation has led us, over a number of years, to investigate a great variety of different forms and symptoms of hysteria, with a view to discovering their precipitating cause the event which provoked the first occurrence, often many years earlier, of the phenomenon in question. In the great majority of cases it is not possible to establish the point of origin by a simple interrogation of the patient, however thoroughly it may be carried out. This is in part because what is in question is often some experience which the patient dislikes discussing; but principally because he is genuinely unable to recollect it and often has no suspicion of the causal connection between the precipitating event and the pathological phenomenon. As a rule it is necessary to hypnotize the patient and to arouse his memories under hypnosis of the time at which the symptom made its first appearance; when this has been done, it becomes possible to demonstrate the connection in the clearest and most convincing fashion...
It is of course obvious that in cases of 'traumatic' hysteria what provokes the symptoms is the accident. The causal connection is equally evident in hysterical attacks when it is possible to gather from the patient's utterances that in each attack he is hallucinating the same event which provoked the first one. The situation is more obscure in the case of other phenomena. | Neurosis | Wikipedia | 498 | 47588 | https://en.wikipedia.org/wiki/Neurosis | Biology and health sciences | Mental disorder | null |
Our experiences have shown us, however, that the most various symptoms, which are ostensibly spontaneous and, as one might say, idiopathic products of hysteria, are just as strictly related to the precipitating trauma as the phenomena to which we have just alluded and which exhibit the connection quite clearly.This paper was reprinted and supplemented with case studies in the pair's 1895 book Studien über Hysterie (Studies on Hysteria). Of the book's five case studies, the most famous became that of Breuer's patient Bertha Pappenheim (given the pseudonym "Anna O."). This book established the field of psychoanalysis.
French neurologist Paul Oulmont was mentored by Charcot. In his 1894 book Thérapeutique des névroses (Therapy of neuroses), he lists the neuroses as being hysteria, neurasthenia, exophthalmic goitre, epilepsy, migraine, Sydenham's chorea, Parkinson's disease and tetany.
The fifth edition of German psychiatrist Emil Kraepelin's popular psychiatry textbook in 1896 gave "neuroses" a well-accepted definition:In the following presentation we want to summarize a group of disease states as general neuroses, which are accompanied by more or less pronounced nervous dysfunctions. What is common to these manifestations of insanity is that we are constantly dealing with the morbid processing of vital stimuli; what they also have in common is the occurrence of more transitory, peculiar manifestations of illness, sometimes in the physical, sometimes in the psychic area. These attacks of fluctuations in mental balance are therefore not independent illnesses, but only the occasional increase in a persistent illness...
It seems useful to me, for the time being, to distinguish between two main forms of general neuroses, epileptic and hysterical insanity.Pierre Janet published the two volume work Névroses et Idées Fixes (Neuroses and Fixations) in 1898. According to Janet, neuroses could be usefully divided into hysterias and psychasthenias. Hysterias induced such symptoms as anaesthesia, visual field narrowing, paralyses, and unconscious acts. Psychasthenias involved the ability to adjust to one's surroundings, similar to the later concepts of adjustment disorder and executive functions. | Neurosis | Wikipedia | 491 | 47588 | https://en.wikipedia.org/wiki/Neurosis | Biology and health sciences | Mental disorder | null |
Janet founded the French "Société de psychologie" in 1901. This later became the "Société française de psychologie", and continues today as France's main psychology body.
Barbiturates are a class of highly addictive sedative drugs. The first barbiturate, barbital, was synthesized in 1902 by German chemists Emil Fischer and Joseph von Mering and was first marketed as "Veronal" in 1904. The similar barbiturate phenobarbital was brought to market in 1912 under the name "Luminal". Barbiturates became popular drugs in many countries to reduce neurotic anxiety and displaced the use of bromides.
Janet published the book Les Obsessions et la Psychasthénie (The Obsessions and the Psychasthenias) in 1903. Janet followed this with the books The Major Symptoms of Hysteria in 1907, and Les Névroses (The Neuroses) in 1909.
According to Janet, one cause of neurosis is when the mental force of a traumatic event is stronger than what someone can counter using their normal coping mechanisms.
The Swiss psychiatrist Paul Charles Dubois published the book Les psychonévroses et leur traitement moral in 1904, which was translated into English as "Psychic Treatment of Nervous Disorders (The Psychoneuroses and Their Moral Treatment)" in 1905. Dubois believed that neurosis could be successfully treated by listening carefully to patients, and rationally convincing them of the truth — what he called "rational psychotherapy". This was a form of cognitive behavioural therapy. He also followed Weir Mitchell's rest cure, though with a broad fattening diet and other modifications.
Meanwhile, Freud developed a number of different theories of neurosis. The most impactful one was that it referred to mental disorders caused by the brain's defence against past psychological trauma. This redefined the general understanding and use of the word. It came to replace the concept of "hysteria".
He held the First Congress for Freudian Psychology in Salzburg in April 1908. Subsequent Congresses continue today. | Neurosis | Wikipedia | 427 | 47588 | https://en.wikipedia.org/wiki/Neurosis | Biology and health sciences | Mental disorder | null |
Progressive muscle relaxation (PMR) was first developed by American psychiatrist and physiologist Edmund Jacobson. This began at Harvard University in 1908. PMR involves learning to relieve the tension in specific muscle groups by first tensing and then relaxing each muscle group. When the muscle tension is released, attention is directed towards the differences felt during tension and relaxation so that the patient learns to recognize the contrast between the states. This reduces anxiety and the effect of phobias.
Freud published the detailed case study "Bemerkungen über einen Fall von Zwangsneurose" ( | Neurosis | Wikipedia | 119 | 47588 | https://en.wikipedia.org/wiki/Neurosis | Biology and health sciences | Mental disorder | null |
In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time. Periodic waveforms repeat regularly at a constant period. The term can also be used for non-periodic or aperiodic signals, like chirps and pulses.
In electronics, the term is usually applied to time-varying voltages, currents, or electromagnetic fields. In acoustics, it is usually applied to steady periodic sounds — variations of pressure in air or other media. In these cases, the waveform is an attribute that is independent of the frequency, amplitude, or phase shift of the signal.
The waveform of an electrical signal can be visualized in an oscilloscope or any other device that can capture and plot its value at various times, with suitable scales in the time and value axes. The electrocardiograph is a medical device to record the waveform of the electric signals that are associated with the beating of the heart; that waveform has important diagnostic value. Waveform generators, that can output a periodic voltage or current with one of several waveforms, are a common tool in electronics laboratories and workshops.
The waveform of a steady periodic sound affects its timbre. Synthesizers and modern keyboards can generate sounds with many complicated waveforms.
Common periodic waveforms
Simple examples of periodic waveforms include the following, where is time, is wavelength, is amplitude and is phase:
Sine wave: The amplitude of the waveform follows a trigonometric sine function with respect to time.
Square wave: This waveform is commonly used to represent digital information. A square wave of constant period contains odd harmonics that decrease at −6 dB/octave.
Triangle wave: It contains odd harmonics that decrease at −12 dB/octave.
Sawtooth wave: This looks like the teeth of a saw. Found often in time bases for display scanning. It is used as the starting point for subtractive synthesis, as a sawtooth wave of constant period contains odd and even harmonics that decrease at −6 dB/octave.
The Fourier series describes the decomposition of periodic waveforms, such that any periodic waveform can be formed by the sum of a (possibly infinite) set of fundamental and harmonic components. Finite-energy non-periodic waveforms can be analyzed into sinusoids by the Fourier transform. | Waveform | Wikipedia | 491 | 47592 | https://en.wikipedia.org/wiki/Waveform | Physical sciences | Waves | Physics |
Other periodic waveforms are often called composite waveforms and can often be described as a combination of a number of sinusoidal waves or other basis functions added together. | Waveform | Wikipedia | 33 | 47592 | https://en.wikipedia.org/wiki/Waveform | Physical sciences | Waves | Physics |
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 1800s. Simple suspension bridges, which lack vertical suspenders, have a long history in many mountainous parts of the world.
Besides the bridge type most commonly called suspension bridges, covered in this article, there are other types of suspension bridges. The type covered here has cables suspended between towers, with vertical suspender cables that transfer the live and dead loads of the deck below, upon which traffic crosses. This arrangement allows the deck to be level or to arc upward for additional clearance. Like other suspension bridge types, this type often is constructed without the use of falsework.
The suspension cables must be anchored at each end of the bridge, since any load applied to the bridge is transformed into tension in these main cables. The main cables continue beyond the pillars to deck-level supports, and further continue to connections with anchors in the ground. The roadway is supported by vertical suspender cables or rods, called hangers. In some circumstances, the towers may sit on a bluff or canyon edge where the road may proceed directly to the main span. Otherwise, the bridge will typically have two smaller spans, running between either pair of pillars and the highway, which may be supported by suspender cables or their own trusswork. In cases where trusswork supports the spans, there will be very little arc in the outboard main cables.
History
The earliest suspension bridges were ropes slung across a chasm, with a deck possibly at the same level or hung below the ropes such that the rope had a catenary shape.
Precursors | Suspension bridge | Wikipedia | 338 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
The Tibetan siddha and bridge-builder Thangtong Gyalpo originated the use of iron chains in his version of simple suspension bridges. In 1433, Gyalpo built eight bridges in eastern Bhutan. The last surviving chain-linked bridge of Gyalpo's was the Thangtong Gyalpo Bridge in Duksum en route to Trashi Yangtse, which was finally washed away in 2004. Gyalpo's iron chain bridges did not include a suspended-deck bridge, which is the standard on all modern suspension bridges today. Instead, both the railing and the walking layer of Gyalpo's bridges used wires. The stress points that carried the screed were reinforced by the iron chains. Before the use of iron chains it is thought that Gyalpo used ropes from twisted willows or yak skins. He may have also used tightly bound cloth.
The Inca used rope bridges, documented as early as 1615. It is not known when they were first made. Queshuachaca is considered the last remaining Inca rope bridge and is rebuilt annually.
Chain bridges
The first iron chain suspension bridge in the Western world was the Jacob's Creek Bridge (1801) in Westmoreland County, Pennsylvania, designed by inventor James Finley. Finley's bridge was the first to incorporate all of the necessary components of a modern suspension bridge, including a suspended deck which hung by trusses. Finley patented his design in 1808, and published it in the Philadelphia journal, The Port Folio, in 1810. | Suspension bridge | Wikipedia | 310 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
Early British chain bridges included the Dryburgh Abbey Bridge (1817) and 137 m Union Bridge (1820), with spans rapidly increasing to 176 m with the Menai Bridge (1826), "the first important modern suspension bridge". The first chain bridge on the German speaking territories was the Chain Bridge in Nuremberg. The Sagar Iron Suspension Bridge with a 200 feet span (also termed Beose Bridge) was constructed near Sagar, India during 1828–1830 by Duncan Presgrave, Mint and Assay Master. The Clifton Suspension Bridge (designed in 1831, completed in 1864 with a 214 m central span), is similar to the Sagar bridge. It is one of the longest of the parabolic arc chain type. The current Marlow suspension bridge was designed by William Tierney Clark and was built between 1829 and 1832, replacing a wooden bridge further downstream which collapsed in 1828. It is the only suspension bridge across the non-tidal Thames. The Széchenyi Chain Bridge, (designed in 1840, opened in 1849), spanning the River Danube in Budapest, was also designed by William Clark and it is a larger-scale version of Marlow Bridge.
An interesting variation is Thornewill and Warham's Ferry Bridge in Burton-on-Trent, Staffordshire (1889), where the chains are not attached to abutments as is usual, but instead are attached to the main girders, which are thus in compression. Here, the chains are made from flat wrought iron plates, eight inches (203 mm) wide by an inch and a half (38 mm) thick, rivetted together.
Wire-cable
The first wire-cable suspension bridge was the Spider Bridge at Falls of Schuylkill (1816), a modest and temporary footbridge built following the collapse of James Finley's nearby Chain Bridge at Falls of Schuylkill (1808). The footbridge's span was 124 m, although its deck was only 0.45 m wide.
Development of wire-cable suspension bridges dates to the temporary simple suspension bridge at Annonay built by Marc Seguin and his brothers in 1822. It spanned only 18 m. The first permanent wire cable suspension bridge was Guillaume Henri Dufour's Saint Antoine Bridge in Geneva of 1823, with two 40 m spans. The first with cables assembled in mid-air in the modern method was Joseph Chaley's Grand Pont Suspendu in Fribourg, in 1834. | Suspension bridge | Wikipedia | 499 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
In the United States, the first major wire-cable suspension bridge was the Wire Bridge at Fairmount in Philadelphia, Pennsylvania. Designed by Charles Ellet Jr. and completed in 1842, it had a span of 109 m. Ellet's Niagara Falls suspension bridge (1847–48) was abandoned before completion. It was used as scaffolding for John A. Roebling's double decker railroad and carriage bridge (1855).
The Otto Beit Bridge (1938–1939) was the first modern suspension bridge outside the United States built with parallel wire cables.
Structure
Bridge main components
Two towers/pillars, two suspension cables, four suspension cable anchors, multiple suspender cables, the bridge deck.
Structural analysis
The main cables of a suspension bridge will form a catenary when hanging under their own weight only. When supporting the deck, the cables will instead form a parabola, assuming the weight of the cables is small compared to the weight of the deck. One can see the shape from the constant increase of the gradient of the cable with linear (deck) distance, this increase in gradient at each connection with the deck providing a net upward support force. Combined with the relatively simple constraints placed upon the actual deck, that makes the suspension bridge much simpler to design and analyze than a cable-stayed bridge in which the deck is in compression.
Comparison with cable-stayed bridge
Cable-stayed bridges and suspension bridges may appear to be similar, but are quite different in principle and in their construction.
In suspension bridges, large main cables (normally two) hang between the towers and are anchored at each end to the ground. The main cables, which are free to move on bearings in the towers, bear the load of the bridge deck. Before the deck is installed, the cables are under tension from their own weight. Along the main cables smaller cables or rods connect to the bridge deck, which is lifted in sections. As this is done, the tension in the cables increases, as it does with the live load of traffic crossing the bridge. The tension on the main cables is transferred to the ground at the anchorages and by downwards compression on the towers. | Suspension bridge | Wikipedia | 430 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
In cable-stayed bridges, the towers are the primary load-bearing structures that transmit the bridge loads to the ground. A cantilever approach is often used to support the bridge deck near the towers, but lengths further from them are supported by cables running directly to the towers. By design, all static horizontal forces of the cable-stayed bridge are balanced so that the supporting towers do not tend to tilt or slide and so must only resist horizontal forces from the live loads.
Advantages
Longer main spans are achievable than with any other type of bridge.
Less material may be required than other bridge types, even at spans they can achieve, leading to a reduced construction cost.
Except for installation of the initial temporary cables, little or no access from below is required during construction and so a waterway can remain open while the bridge is built above.
They may be better able to withstand earthquake movements than heavier and more rigid bridges.
Bridge decks can have deck sections replaced in order to widen traffic lanes for larger vehicles or add additional width for separated cycling/pedestrian paths.
Disadvantages
Considerable stiffness or aerodynamic profiling may be required to prevent the bridge deck from vibrating under high winds.
The relatively low deck stiffness compared to other (non-suspension) types of bridges makes it more difficult to carry heavy rail traffic in which high concentrated live loads occur.
Some access below may be required during construction to lift the initial cables or to lift deck units. That access can often be avoided in cable-stayed bridge construction.
Variations
Underspanned
In an underspanned suspension bridge, also called under-deck cable-stayed bridge, the main cables hang entirely below the bridge deck, but are still anchored into the ground in a similar way to the conventional type. Very few bridges of this nature have been built, as the deck is inherently less stable than when suspended below the cables. Examples include the Pont des Bergues of 1834 designed by Guillaume Henri Dufour; James Smith's Micklewood Bridge; and a proposal by Robert Stevenson for a bridge over the River Almond near Edinburgh.
Roebling's Delaware Aqueduct (begun 1847) consists of three sections supported by cables. The timber structure essentially hides the cables; and from a quick view, it is not immediately apparent that it is even a suspension bridge.
Suspension cable types | Suspension bridge | Wikipedia | 464 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
The main suspension cables in older bridges were often made from a chain or linked bars, but modern bridge cables are made from multiple strands of wire. This not only adds strength but improves reliability (often called redundancy in engineering terms) because the failure of a few flawed strands in the hundreds used pose very little threat of failure, whereas a single bad link or eyebar can cause failure of an entire bridge. (The failure of a single eyebar was found to be the cause of the collapse of the Silver Bridge over the Ohio River.) Another reason is that as spans increased, engineers were unable to lift larger chains into position, whereas wire strand cables can be formulated one by one in mid-air from a temporary walkway.
Suspender-cable terminations
Poured sockets are used to make a high strength, permanent cable termination. They are created by inserting the suspender wire rope (at the bridge deck supports) into the narrow end of a conical cavity which is oriented in-line with the intended direction of strain. The individual wires are splayed out inside the cone or 'capel', and the cone is then filled with molten lead-antimony-tin (Pb80Sb15Sn5) solder.
Deck structure types
Most suspension bridges have open truss structures to support the roadbed, particularly owing to the unfavorable effects of using plate girders, discovered from the Tacoma Narrows Bridge (1940) bridge collapse. In the 1960s, developments in bridge aerodynamics allowed the re-introduction of plate structures as shallow box girders, first seen on the Severn bridge, built 1961–1966. In the picture of the Yichang Bridge, note the very sharp entry edge and sloping undergirders in the suspension bridge shown. This enables this type of construction to be used without the danger of vortex shedding and consequent aeroelastic effects, such as those that destroyed the original Tacoma Narrows bridge. | Suspension bridge | Wikipedia | 392 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
Forces
Three kinds of forces operate on any bridge: the dead load, the live load, and the dynamic load. Dead load refers to the weight of the bridge itself. Like any other structure, a bridge has a tendency to collapse simply because of the gravitational forces acting on the materials of which the bridge is made. Live load refers to traffic that moves across the bridge as well as normal environmental factors such as changes in temperature, precipitation, and winds. Dynamic load refers to environmental factors that go beyond normal weather conditions, factors such as sudden gusts of wind and earthquakes. All three factors must be taken into consideration when building a bridge.
Use other than road and rail
The principles of suspension used on a large scale also appear in contexts less dramatic than road or rail bridges. Light cable suspension may prove less expensive and seem more elegant for a cycle or footbridge than strong girder supports. An example of this is the Nescio Bridge in the Netherlands, and the Roebling designed 1904 Riegelsville suspension pedestrian bridge across the Delaware River in Pennsylvania. The longest pedestrian suspension bridge, which spans the River Paiva, Arouca Geopark, Portugal, opened in April 2021. The 516 metres bridge hangs 175 meters above the river.
Where such a bridge spans a gap between two buildings, there is no need to construct towers, as the buildings can anchor the cables. Cable suspension may also be augmented by the inherent stiffness of a structure that has much in common with a tubular bridge.
Construction sequence (wire strand cable type) | Suspension bridge | Wikipedia | 307 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
Typical suspension bridges are constructed using a sequence generally described as follows. Depending on length and size, construction may take anywhere between a year and a half (construction on the original Tacoma Narrows Bridge took only 19 months) up to as long as a decade (the Akashi-Kaikyō Bridge's construction began in May 1986 and was opened in May 1998 – a total of twelve years).
Where the towers are founded on underwater piers, caissons are sunk and any soft bottom is excavated for a foundation. If the bedrock is too deep to be exposed by excavation or the sinking of a caisson, pilings are driven to the bedrock or into overlying hard soil, or a large concrete pad to distribute the weight over less resistant soil may be constructed, first preparing the surface with a bed of compacted gravel. (Such a pad footing can also accommodate the movements of an active fault, and this has been implemented on the foundations of the cable-stayed Rio-Antirio bridge.) The piers are then extended above water level, where they are capped with pedestal bases for the towers.
Where the towers are founded on dry land, deep foundation excavation or pilings are used.
From the tower foundation, towers of single or multiple columns are erected using high-strength reinforced concrete, stonework, or steel. Concrete is used most frequently in modern suspension bridge construction due to the high cost of steel.
Large devices called saddles, which will carry the main suspension cables, are positioned atop the towers. Typically of cast steel, they can also be manufactured using riveted forms, and are equipped with rollers to allow the main cables to shift under construction and normal loads.
Anchorages are constructed, usually in tandem with the towers, to resist the tension of the cables and form as the main anchor system for the entire structure. These are usually anchored in good quality rock but may consist of massive reinforced concrete deadweights within an excavation. The anchorage structure will have multiple protruding open eyebolts enclosed within a secure space.
Temporary suspended walkways, called catwalks, are then erected using a set of guide wires hoisted into place via winches positioned atop the towers. These catwalks follow the curve set by bridge designers for the main cables, in a path mathematically described as a catenary arc. Typical catwalks are usually between eight and ten feet wide and are constructed using wire grate and wood slats. | Suspension bridge | Wikipedia | 489 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
Gantries are placed upon the catwalks, which will support the main cable spinning reels. Then, cables attached to winches are installed, and in turn, the main cable spinning devices are installed.
High strength wire (typically 4 or 6 gauge galvanized steel wire), is pulled in a loop by pulleys on the traveler, with one end affixed at an anchorage. When the traveler reaches the opposite anchorage the loop is placed over an open anchor eyebar. Along the catwalk, workers also pull the cable wires to their desired tension. This continues until a bundle, called a "cable strand" is completed, and temporarily bundled using stainless steel wire. This process is repeated until the final cable strand is completed. Workers then remove the individual wraps on the cable strands (during the spinning process, the shape of the main cable closely resembles a hexagon), and then the entire cable is then compressed by a traveling hydraulic press into a closely packed cylinder and tightly wrapped with additional wire to form the final circular cross-section. The wire used in suspension bridge construction is a galvanized steel wire that has been coated with corrosion inhibitors.
At specific points along the main cable (each being the exact distance horizontally in relation to the next) devices called "cable bands" are installed to carry steel wire ropes called Suspender cables. Each suspender cable is engineered and cut to precise lengths, and are looped over the cable bands. In some bridges, where the towers are close to or on the shore, the suspender cables may be applied only to the central span. Early suspender cables were fitted with zinc jewels and a set of steel washers, which formed the support for the deck. Modern suspender cables carry a shackle-type fitting. | Suspension bridge | Wikipedia | 358 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
Special lifting hoists attached to the suspenders or from the main cables are used to lift prefabricated sections of the bridge deck to the proper level, provided that the local conditions allow the sections to be carried below the bridge by barge or other means. Otherwise, a traveling cantilever derrick may be used to extend the deck one section at a time starting from the towers and working outward. If the addition of the deck structure extends from the towers the finished portions of the deck will pitch upward rather sharply, as there is no downward force in the center of the span. Upon completion of the deck, the added load will pull the main cables into an arc mathematically described as a parabola, while the arc of the deck will be as the designer intended – usually a gentle upward arc for added clearance if over a shipping channel, or flat in other cases such as a span over a canyon. Arched suspension spans also give the structure more rigidity and strength.
With the completion of the primary structure various details such as lighting, handrails, finish painting and paving is installed or completed. | Suspension bridge | Wikipedia | 220 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
Longest spans
Suspension bridges are typically ranked by the length of their main span. These are the ten bridges with the longest spans, followed by the length of the span and the year the bridge opened for traffic:
Other examples
(Chronological)
Union Bridge (England/Scotland, 1820), the longest span (137 m) from 1820 to 1826. The oldest suspension bridge in the world still carrying road traffic.
Roebling's Delaware Aqueduct (USA, 1847), the oldest wire suspension bridge still in service in the United States.
John A. Roebling Suspension Bridge (USA, 1866), then the longest wire suspension bridge in the world at 1,057 feet (322 m) main span.
Brooklyn Bridge (USA, 1883), the first steel-wire suspension bridge.
Bear Mountain Bridge (USA, 1924), the longest suspension span (497 m) from 1924 to 1926. The first suspension bridge to have a concrete deck. The construction methods pioneered in building it would make possible several much larger projects to follow.
Benjamin Franklin Bridge (USA, 1926), replaced Bear Mountain Bridge as the longest span at 1,750 feet between the towers. Includes an active subway line and never-used trolley stations on the span.
San Francisco–Oakland Bay Bridge eastern span (USA, 2013). The eastern portion is a self-anchored suspension bridge, the longest of its type in the world. It replaced a cantilever bridge.
Golden Gate Bridge (USA, 1937), the longest suspension bridge from 1937 to 1964. It was also the world's tallest bridge from 1937 to 1993, and remains the tallest bridge in the United States.
Mackinac Bridge (USA, 1957), the longest suspension bridge between anchorages in the Western hemisphere.
Si Du River Bridge (China, 2009), the highest bridge in the world, with its deck around 500 meters above the surface of the river.
Rod El Farag Axis Bridge (Egypt, 2019), a modern Egyptian steel wire-cables based suspension bridge crossing the river Nile, which was completed in 2019 and holds the Guinness World Record for the widest suspension bridge in the world with a width of 67.3 meters, and with a span of 540 meters.
Notable collapses | Suspension bridge | Wikipedia | 449 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
Broughton Suspension Bridge (England) was an iron chain bridge built in 1826. One of Europe's first suspension bridges, it collapsed in 1831 due to mechanical resonance induced by troops marching in step. As a result of the incident, the British Army issued an order that troops should "break step" when crossing a bridge.
Silver Bridge (USA) was an eyebar chain highway bridge, built in 1928, that collapsed in late 1967, killing forty-six people. The bridge had a low-redundancy design that was difficult to inspect. The collapse inspired legislation to ensure that older bridges were regularly inspected and maintained. Following the collapse a bridge of similar design was immediately closed and eventually demolished. A second similarly-designed bridge had been built with a higher margin of safety and remained in service until 1991.
The Tacoma Narrows Bridge, (USA), 1940, was vulnerable to structural vibration in sustained and moderately strong winds due to its plate-girder deck structure. Wind caused a phenomenon called aeroelastic fluttering that led to its collapse only months after completion. The collapse was captured on film. There were no human deaths in the collapse; several drivers escaped their cars on foot and reached the anchorages before the span dropped.
Yarmouth suspension bridge (England) was built in 1829 and collapsed in 1845, killing 79 people.
Peace River Suspension Bridge (Canada), which was completed in 1943, collapsed when the north anchor's soil support for the suspension bridge failed in October 1957. The entire bridge subsequently collapsed.
Kutai Kartanegara Bridge (Indonesia) over the Mahakam River, located in Kutai Kartanegara Regency, East Kalimantan district on the Indonesia island of Borneo, was built in 1995, completed in 2001 and collapsed in 2011. Dozens of vehicles on the bridge fell into the Mahakam River. As a result of this incident, 24 people died and dozens of others were injured and were treated at the Aji Muhammad Parikesit Regional Hospital. Meanwhile, 12 people were reported missing, 31 people were seriously injured, and 8 people had minor injuries. Research findings indicate that the collapse was largely caused by the construction failure of the vertical hanging clamp. It was also found that poor maintenance, fatigue in the cable hanger construction materials, material quality, and bridge loads that exceed vehicle capacity, can also have an impact on bridge collapse. In 2013 the Kutai Kartanegara Bridge rebuilt the same location and completed in 2015 with a Through arch bridge design. | Suspension bridge | Wikipedia | 499 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
On 30 October 2022, Jhulto Pul, a pedestrian suspension bridge over the Machchhu River in the city of Morbi, Gujarat, India collapsed, leading to the deaths of at least 141 people. | Suspension bridge | Wikipedia | 44 | 47607 | https://en.wikipedia.org/wiki/Suspension%20bridge | Technology | Transport infrastructure | null |
The Great Belt Bridge () or Great Belt fixed link () is a multi-element fixed link crossing the Great Belt strait between the Danish islands of Zealand and Funen. It consists of a road suspension bridge and a railway tunnel between Zealand and the small island Sprogø in the middle of the Great Belt, and a box-girder bridge for both road and rail traffic between Sprogø and Funen. The total length is .
The term Great Belt Bridge commonly refers to the suspension bridge, although it may also be used to mean the box-girder bridge or the link in its entirety. Officially named the East Bridge, the suspension bridge was designed by the Danish firms COWI and Ramboll, and the architecture firm Dissing+Weitling. It has the world's sixth-longest main span (). At the time of the opening of the bridge it was the second longest, beaten by the Akashi Kaikyō Bridge opened a few months previously.
Together with the New Little Belt Bridge, the Great Belt link provides a continuous road and rail connection between Copenhagen and the Danish mainland. The link replaced the Great Belt ferries service, which had been the primary means of crossing the Great Belt. After more than 50 years of debate, the Danish government decided in 1986 to construct a link; it opened to rail traffic in 1997 and to road traffic in 1998. At an estimated cost of DKK 21.4 billion (EUR 2.8 billion) (1988 prices), the link is the largest construction project in Danish history. It has reduced travel times significantly; previously taking one hour by ferry, the Great Belt can now be crossed in ten minutes. This link, together with the Øresund Bridge (built 1995–1999) and the Little Belt Bridge, have together enabled driving from mainland Europe to Sweden through Denmark.
Operation and maintenance are performed by A/S Storebælt under Sund & Bælt. Construction and maintenance are financed by tolls on vehicles and trains. Cyclists are not permitted to use the bridge, but bicycles may be transported by train or bus.
History
The Great Belt ferries entered service between the coastal towns of Korsør and Nyborg in 1883, connecting the railway lines on either side of the Belt. In 1957, road traffic was moved to the Halsskov–Knudshoved route, about 1.5 kilometres to the north and close to the fixed link. | Great Belt Bridge | Wikipedia | 494 | 47610 | https://en.wikipedia.org/wiki/Great%20Belt%20Bridge | Technology | Bridges | null |
Construction drafts for a fixed link were presented as early as the 1850s, with several suggestions appearing in the following decades. The Danish State Railways, responsible for the ferry service, presented plans for a bridge in 1934. The concepts of bridges over Øresund (152 million DKK) and Storebælt (257 million DKK) were calculated around 1936. In 1948, the Ministry for Public Works (now the Ministry of Transport) established a commission to investigate the implications of a fixed link.
The first law concerning a fixed link was enacted in 1973, but the project was put on hold in 1978 as the Venstre (Liberal) party demanded postponing public spending. Political agreement to restart work was reached in 1986, with a construction law () being passed in 1987.
The design was carried out by the engineering firms COWI and Ramboll together with Dissing+Weitling architecture practice.
Construction of the link commenced in 1988. In 1991, Finland sued Denmark at the International Court of Justice, on the grounds that Finnish-built mobile offshore drilling units would be unable to pass beneath the bridge. The two countries negotiated a financial compensation of 90 million Danish kroner, and Finland withdrew the lawsuit in 1992.
A European Court of Justice ruling in 1993 found that a contractual condition requiring use of local labour and local materials in constructing the bridge was incompatible with the principles of the EEC Treaty.
The link is estimated to have created a value of 379 billion DKK after 50 years of use.
In 2022, the bridge was crossed as part of the route of Stage 2 of the 2022 Tour de France.
Construction
The construction of the fixed link became the biggest building project in the history of Denmark. In order to connect Halsskov on Zealand with Knudshoved on Funen, to its west, a two-track railway and a four-lane motorway had to be built, via the small island of Sprogø in the middle of the Great Belt. The project comprised three different tasks: the East Bridge for road transport, the East Tunnel for rail transport and the West Bridge for road and rail transport combined. The construction work was carried out by Sundlink Contractors, a consortium of Skanska, Hochtief, Højgaard & Schultz (which built the West Bridge) and Monberg & Thorsen (which built the section under the Great Belt). The work of lifting and placing the elements was carried out by Ballast Nedam using a floating crane. | Great Belt Bridge | Wikipedia | 505 | 47610 | https://en.wikipedia.org/wiki/Great%20Belt%20Bridge | Technology | Bridges | null |
East Bridge
Built between 1991 and 1998 at a cost of US$950 million, the East Bridge (Østbroen) is a suspension bridge between Halsskov and Sprogø. It is long with a free span of ,. The East Bridge had been planned to be completed in time to be the longest bridge in the world, but there were delays in construction. Therefore, it happened that the Akashi-Kaikyo Bridge was opened two months earlier.
The vertical clearance for ships is , meaning the world's largest cruise ship, an Oasis-class cruise ship, just fits under with its smokestack folded. At above sea level, the two pylons of the East Bridge are the highest points on self-supporting structures in Denmark. Some radio masts, such as Tommerup transmitter, are taller.
To keep the main cables tensioned, an anchorage structure on each side of the span is placed below the road deck. After 15 years, the cables have no rust. They were scheduled for a 15 million DKK paint job, but due to corroding cables on other bridges, the decision was made to instead install a 70 million DKK sealed de-humidifying system in the cables. This was carried out by UK engineering firm Spencer Group, with help from Danish subcontractors Davai who provided the manpower, and Belvent A/S who provided the dehumidification system.
Nineteen concrete pillars (12 on the Zealand side, seven by Sprogø), apart, carry the road deck outside the span.
West Bridge
The West Bridge (Vestbroen) is a box girder bridge between Sprogø and Knudshoved. It is long, and has a vertical clearance for ships of . It is actually two separate, adjacent bridges: the northern one carries rail traffic and the southern one road traffic. The pillars of the two bridges rest on common foundations below sea level. The West Bridge was built between 1988 and 1994; its road/rail deck comprises 63 sections, supported by 62 pillars.
East Tunnel
The twin bored tunnel tubes of the East Tunnel (Østtunnelen) are each long. There are 31 connecting tunnels between the two main tunnels, at intervals. The equipment that is necessary for train operation in the tunnels is installed in the connecting tunnels, which also serve as emergency escape routes. | Great Belt Bridge | Wikipedia | 480 | 47610 | https://en.wikipedia.org/wiki/Great%20Belt%20Bridge | Technology | Bridges | null |
There were delays and cost overruns in the tunnel construction. The plan was to open it in 1993, giving the trains a head start of three years over road traffic, but train traffic started in 1997 and road traffic in 1998. During construction the sea bed gave way and one of the tunnels was flooded. The water continued to rise and reached the end at Sprogø, where it continued into the (still dry) other tunnel. The water damaged two of the four tunnel boring machines, but no workers were injured. Only by placing a clay blanket on the sea bed was it possible to dry out the tunnels. The two damaged machines were repaired and the majority of the tunnelling was undertaken from the Sprogø side. The machines on the Zealand side tunnelled through difficult ground and made little progress. A major fire on one of the Zealand machines in June 1994 stopped these drives and the tunnels were completed by the two Sprogø machines.
A total of 320 compressed air workers were involved in 9,018 pressure exposures in the four tunnel-boring machines. The project had a decompression sickness incidence of 0.14% with two workers having long-term residual symptoms.
Traffic implications
Prior to the opening of the link, an average of 8,000 cars used the ferries across the Great Belt every day. The traffic across the strait increased 127 percent over the first year after the link's opening due to the so-called traffic leap: new traffic generated by the improved ease, facility and lower price of crossing the Great Belt.
In 2021, an average of 34,100 vehicles used the link each day. On August 7, 2022 a record 61,528 vehicles passed the bridge in 24 hours. The increase in traffic is partly caused by the general growth of traffic, partly diversion of traffic volume from other services via ferry and services.
The fixed link has produced considerable savings in travel time between eastern and western Denmark. Previously, it took approximately 90 minutes on average to cross the Great Belt in a car with transfer by ferry, including the waiting time at the ports. It took considerably longer during peak periods, such as weekends and holidays. With the opening of the link, the journey is now between 10 and 15 minutes. | Great Belt Bridge | Wikipedia | 454 | 47610 | https://en.wikipedia.org/wiki/Great%20Belt%20Bridge | Technology | Bridges | null |
By train the time savings are significant as well. The journey has been reduced by 60 minutes, and there are many more seats available because more carriages may be added to a train that does not have to fit on a ferry. The seating capacity offered by DSB across the Great Belt on an ordinary Wednesday has risen from 11,060 seats to 37,490 seats. On Fridays the seating capacity exceeds 40,000 seats.
The shortest travel times are: Copenhagen–Odense 1 hour 15 minutes, Copenhagen–Aarhus 2 hours 30 minutes, Copenhagen–Aalborg 3 hours 55 minutes and Copenhagen–Esbjerg 2 hours 35 minutes.
Flights between Copenhagen and Odense, and between Copenhagen and Esbjerg have ceased, and the train now has the largest market share between Copenhagen and Aarhus.
Together with the Øresund Bridge, and the two Little Belt bridges, the link provides a direct fixed connection between western Continental Europe and northern Scandinavia, eventually connecting all parts of the European Union except Ireland, Malta, Cyprus, and outlying islands. Most people from Zealand still prefer to take the ferry between Puttgarden and Rødby, as it is a much shorter distance and provides a needed break for those travelling a long distance.
For freight trains, the fixed links are a large improvement between Sweden and Germany, and between Sweden and the UK. The Sweden-to-Germany ferry system is still used to some extent owing to limited rail capacity, with heavy passenger traffic over the bridges and some single track stretches in southern Denmark and northern Germany.
The Great Belt was used by now defunct night passenger trains between Copenhagen and Germany, which were too long to fit on the ferries. Day trains on the Copenhagen-Hamburg route first continued to use the Fehmarn Belt ferries, utilising short diesel trains, but now also use the Great Belt route, which potentially allows longer trains to be used, increasing capacity.
By 2028, the Fehmarn Belt Fixed Link is expected to be complete with much of the international traffic being shifted from the Great Belt Fixed Link. This more direct route will reduce the rail journey from Hamburg to Copenhagen from 4:45 to 3:30 hours.
Toll charge
In 2019, the vehicle tolls were:
Environmental effects | Great Belt Bridge | Wikipedia | 452 | 47610 | https://en.wikipedia.org/wiki/Great%20Belt%20Bridge | Technology | Bridges | null |
Environmental considerations have been an integral part of the project, and have been of decisive significance for the choice of alignment and determination of the design. Great Belt A/S established an environmental monitoring programme in 1988, and initiated co-operation with authorities and external consultants on the definition of environmental concerns during the construction work and the professional requirements to the monitoring programme. This co-operation issued in a report published at the beginning of 1997 on the state of the environment in the Great Belt. The conclusion of the report was that the marine environment was at least as good as before construction work began.
With regards to the water flow, the link must comply with the so-called zero-solution. This has been achieved by deepening parts of the Great Belt, so that the water flow cross section has been increased. This excavation compensates for the blocking effect caused by the bridge pylons and approach ramps. The conclusion of the report is that water flows are now almost at the level they were before the bridge was built.
The fixed link has generated increased road traffic volume, which has meant increased air pollution. However, there has been significant savings in the energy consumption by switching from ferries to the fixed link. Train and car ferries consume much energy for propulsion, high-speed ferries consume large amounts of energy at high speeds, and air transport is highly energy consuming. Domestic air travel over the Great Belt was greatly reduced after the opening of the bridge, with the former air travellers now using trains and private cars.
The larger energy consumption by ferries as opposed to via the fixed link is most clearly seen when comparing short driving distances from areas immediately east or west of the link. For more extended driving distances the difference in energy consumption is smaller, but any transport within Denmark across the link shows very clear energy savings.
During 2009, seven large wind turbines, likely Vestas 3MWs totalling 21MW capacity, were erected in the sea north of Sprogø to contribute to the electrical demand of the Great Belt Link. Their hub heights are about the same level as the road deck of the suspension bridge. Part of the project was to showcase sea wind at the December 2009 Copenhagen climate meeting.
Accidents
During construction 479 work-related accidents were reported, of which 53 resulted in serious injuries or death. Seven workers died as a result of work-related accidents. | Great Belt Bridge | Wikipedia | 470 | 47610 | https://en.wikipedia.org/wiki/Great%20Belt%20Bridge | Technology | Bridges | null |
The West Bridge has been struck by sea traffic twice. While the link was still under construction on 14 September 1993, the ferry M/F Romsø drifted off course in bad weather and hit the West Bridge. At 19:17 on 3 March 2005, the 3,500-ton freighter MV Karen Danielsen crashed into the West Bridge 800 metres from Funen. All traffic across the bridge was halted, effectively cutting Denmark in two. The bridge was re-opened shortly after midnight, after the freighter was pulled free and inspectors had found no structural damage to the bridge.
The East Bridge has so far been in the clear, although on 16 May 2001, the bridge was closed for 10 minutes as the Cambodian 27,000-ton bulk carrier Bella was heading straight for one of the anchorage structures. The ship was deflected by a swift response from the navy.
On 5 June 2006, a maintenance vehicle burst into flames in the east-bound railway tunnel at about 21:30. Nobody was hurt; its crew of three fled to the other tunnel and escaped. The fire was put out shortly before midnight, and the vehicle was removed from the tunnel the next day. Train service resumed on 6 June at reduced speed, and normal service was restored on 12 June.
On 2 January 2019, eight people were killed in a train accident on the West Bridge. A passenger train was hit by a semi-trailer that fell off a freight train travelling in the opposite direction.
In 2023, a 57-year-old truck driver was arrested by police after traffic on the bridge was disrupted due to spilled potatoes. Police stated that they were working on the hypothesis that the potatoes were either planted intentionally or as an accident.
Operations
In 2009, a study characterized the rail tunnel (together with other major projects like the Channel Tunnel between England and France) as financially non-viable.
Gallery | Great Belt Bridge | Wikipedia | 375 | 47610 | https://en.wikipedia.org/wiki/Great%20Belt%20Bridge | Technology | Bridges | null |
Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed siliceous spicules, often referred to as glass sponges. They are usually classified along with other sponges in the phylum Porifera, but some researchers consider them sufficiently distinct to deserve their own phylum, Symplasma. Some experts believe glass sponges are the longest-lived animals on earth; these scientists tentatively estimate a maximum age of up to 15,000 years.
Biology
Glass sponges are relatively uncommon and are mostly found at depths from below sea level. Although the species Oopsacas minuta has been found in shallow water, others have been found much deeper. They are found in all oceans of the world, although they are particularly common in Antarctic and Northern Pacific waters.
They are more-or-less cup-shaped animals, ranging from in height, with sturdy skeletons made of glass-like silica spicules, fused to form a lattice. In some glass sponges such as members of the genus Euplectela, these structures are aided by a protein called glassin. It helps accelerate the production of silicas from the silicic acid absorbed from the surrounding seawater. The body is relatively symmetrical, with a large central cavity that, in many species, opens to the outside through a sieve formed from the skeleton. Some species of glass sponges are capable of fusing together to create reefs or bioherms. They are generally pale in colour, ranging from white to orange.
Much of the body is composed of syncitial tissue, extensive regions of multinucleate cytoplasm. The epidermal cells characteristic of other sponges are absent, being replaced by a syncitial net of amoebocytes, through which the spicules penetrate. Unlike other sponges, they do not possess the ability to contract.
Their body comprises three parts: the inner and outer peripheral trabecular networks, and the choanosome, which is used for feeding purposes. The choanosome acts as the mouth for the sponge while the inner and outer canals that meet at the choanosome are passages for the food, creating a consumption path for the sponge. | Hexactinellid | Wikipedia | 459 | 47612 | https://en.wikipedia.org/wiki/Hexactinellid | Biology and health sciences | Porifera | Animals |
All hexactinellids have the potential to grow to different sizes, but the average maximum growth is estimated to be around 32 centimeters long. Some grow past that length and continue to extend their length up to 1 meter long. The estimated life expectancy for hexactinellids that grow around 1 meter is approximately 200 years (Plyes).
Glass sponges possess a unique system for rapidly conducting electrical impulses across their bodies, making it possible for them to respond quickly to external stimuli. In the case Rhabdocalyptus dawsoni, the sponge uses electrical neuron signaling to detect outside stimuli, such as sediments, and then send a signal through its body system to alert the organism to no longer be actively feeding. Another glass sponge species in the same experiment of R. dawsoni, showed that the electrical conduction system for this class of sponges all has its own threshold of how much outside stimuli, sediments, etc., it can endure before it will stop its feeding process. Species like "Venus' flower basket" have a tuft of fibers that extends outward like an inverted crown at the base of their skeleton. These fibers are long and about the thickness of a human hair.
Syncytia
Bodies of glass sponges are different from those other sponges in various other ways. For example, most of their cytoplasm is not divided into separate cells by membranes, but forms a syncytium or continuous mass of cytoplasm with many nuclei (e.g., Reiswig and Mackie, 1983); it is held suspended like a cobweb by a scaffolding-like framework made of silica spicules. The remaining cells are connected to the syncytium by bridges of cytoplasmic "rivers" that transport nuclei, organelles ("organs" within cells) and other substances. Instead of choanocytes, these bridges have further syncytia, known as choanosyncytia, which form bell-shaped chambers where water enters via perforations. The insides of these chambers are lined with "collar bodies", each consisting of a collar and flagellum but without a nucleus of its own. The motion of the flagella sucks water through passages in the "cobweb" and expels it via the open ends of the bell-shaped chambers. | Hexactinellid | Wikipedia | 480 | 47612 | https://en.wikipedia.org/wiki/Hexactinellid | Biology and health sciences | Porifera | Animals |
Some types of cells have a single nucleus and membrane each but are connected to other single-nucleus cells and to the main syncytium by "bridges" made of cytoplasm. The sclerocytes that build spicules have multiple nuclei, and in glass sponge larvae they are connected to other tissues by cytoplasm bridges; such connections between sclerocytes have not so far been found in adults, but this may simply reflect the difficulty of investigating such small-scale features. The bridges are controlled by "plugged junctions" that apparently permit some substances to pass while blocking others.
This physiology is what allows for a greater flow of ions and electrical signals to move throughout the organism, with around 75% of the sponge tissue being fused in this way. Another way is their role in the nutrient cycles of deep-sea environments. One species for example, Vazella pourtalesii, has an abundance of symbiotic microbes which aid in the nitrification and denitrification of the communities in which they are present. These interactions help the sponges survive in the low-oxygen conditions of the depths.
Longevity
These creatures are long-lived, but the exact age is hard to measure; one study based on modelling gave an estimated age of a specimen of Scolymastra joubini as 23,000 years (with a range from 13,000 to 40,000 years). However, due to changes in sea levels since the Last Glacial Maximum, its maximum age is thought to be no more than 15,000 years, hence its listing of c. 15,000 years in the AnAge Database. The shallow-water occurrence of hexactinellids is rare worldwide. In the Antarctic, two species occur as shallow as 33 meters under the ice. In the Mediterranean, one species occurs as shallow as in a cave with deep water upwelling (Boury-Esnault & Vacelet (1994)) | Hexactinellid | Wikipedia | 399 | 47612 | https://en.wikipedia.org/wiki/Hexactinellid | Biology and health sciences | Porifera | Animals |
Reefs
The sponges form reefs (called sponge reefs) off the coast of British Columbia, southeast Alaska and Washington state, which are studied in the Sponge Reef Project. In the case of Sarostegia oculata, this species almost always hosts symbiotic zoanthids, which cause the hexactinellid sponge to imitate the appearance and structure of coral reefs. Only 33 species of this sponge have ever been reported in the South Atlantic until 2017 when the Shinkai 6500 submersible went on an expedition through the Rio Grande Rise. Reefs discovered in Hecate Strait, British Columbia, have grown to up to 7 kilometres long and 20 metres high. Prior to these discoveries, sponge reefs were thought to have died out in the Jurassic period.
Reports of glass sponges have also been recorded on the HMCS Saskatchewan and HMCS Cape Breton wrecks off the coast of Vancouver Island. Species of zoantharin that rely on hexactinellid have also been found off the coast of the Japanese island of Minami-Torishima. Unidentified species of zoanthids have also been found in Australian waters, if these are identified as the same as the ones found in Minami-Torishima, this could potentially be proof of hexactinellids existing in all of the Pacific Ocean.
Conservation
Most hexactinellids live in deep waters that are not impacted by human activities. However, there are glass sponge reefs off the coast of British Columbia. The Canadian government designated 2140 km2 of the Hecate strait and Queen Charlotte sound as a marine protected area. This area contains four glass sponge reefs. The new regulations prohibit bottom contact fishing within 200 meters of the sponge reefs. Although human activities only affect a small portion of glass sponges, they are still subject to the threat of climate changes. Experiments using the species Aphrocallistes vastus have shown that increases in temperature and acidification can lead to weakened skeletal strength and stiffness. In 1995, an Antarctic ice shelf collapsed due to climate change. Since then, studies of the area have shown that hexactinellid reefs have been increasing in size despite the changes in climate. | Hexactinellid | Wikipedia | 448 | 47612 | https://en.wikipedia.org/wiki/Hexactinellid | Biology and health sciences | Porifera | Animals |
Evolution and taxonomy
The earliest known hexactinellids are from the earliest Cambrian or late Neoproterozoic eras; Helicolocellus is a possible hexactinellid relative from the late Ediacaran. They are fairly common relative to demosponges as fossils, but this is thought to be, at least in part, because their spicules are sturdier than spongin and fossilize better. Like almost all sponges, the hexactinellids draw water in through a series of small pores by the whip-like beating of a series of hairs or flagella in chambers which in this group line the sponge wall.
The class is divided into two subclasses and several orders:
Class Hexactinellida
Subclass Amphidiscophora
Order Amphidiscosida
Order †Hemidiscosa
Order †Reticulosa
Subclass Hexasterophora
Incertae sedis
Dactylocalycidae Gray, 1867
Order Lychniscosida
Order Lyssacinosida
Order Sceptrulophora | Hexactinellid | Wikipedia | 226 | 47612 | https://en.wikipedia.org/wiki/Hexactinellid | Biology and health sciences | Porifera | Animals |
A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanical stress, the impact and penetration of pressure-driven projectiles, pressure damage, and explosion-generated effects. Bombs have been utilized since the 11th century starting in East Asia.
The term bomb is not usually applied to explosive devices used for civilian purposes such as construction or mining, although the people using the devices may sometimes refer to them as a "bomb". The military use of the term "bomb", or more specifically aerial bomb action, typically refers to airdropped, unpowered explosive weapons most commonly used by air forces and naval aviation. Other military explosive weapons not classified as "bombs" include shells, depth charges (used in water), or land mines. In unconventional warfare, other names can refer to a range of offensive weaponry. For instance, in recent asymmetric conflicts, homemade bombs called "improvised explosive devices" (IEDs) have been employed by irregular forces to great effectiveness.
The word comes from the Latin , which in turn comes from the Greek romanized , an onomatopoetic term meaning 'booming', 'buzzing'.
History
Gunpowder bombs had been mentioned since the 11th century. In 1000 AD, a soldier by the name of Tang Fu (唐福) demonstrated a design of gunpowder pots (a proto-bomb which spews fire) and gunpowder caltrops, for which he was richly rewarded. In the same year, Xu Dong wrote that trebuchets used bombs that were like "flying fire", suggesting that they were incendiaries. In the military text Wujing Zongyao of 1044, bombs such as the "ten-thousand fire flying sand magic bomb", "burning heaven fierce fire unstoppable bomb", and "thunderclap bomb" (pilipao) were mentioned. However these were soft-shell bombs and did not use metal casings.
Bombs made of cast iron shells packed with explosive gunpowder date to 13th century China. Explosive bombs were used in East Asia in 1221, by a Jurchen Jin army against a Chinese Song city. The term for this explosive bomb seems to have been coined the "thunder crash bomb" during a Jin dynasty (1115–1234) naval battle in 1231 against the Mongols. | Bomb | Wikipedia | 494 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
The History of Jin (金史) (compiled by 1345) states that in 1232, as the Mongol general Subutai (1176–1248) descended on the Jin stronghold of Kaifeng, the defenders had a "thunder crash bomb" which "consisted of gunpowder put into an iron container ... then when the fuse was lit (and the projectile shot off) there was a great explosion the noise whereof was like thunder, audible for more than thirty miles, and the vegetation was scorched and blasted by the heat over an area of more than half a mou. When hit, even iron armour was quite pierced through."
The Song Dynasty (960–1279) official Li Zengbo wrote in 1257 that arsenals should have several hundred thousand iron bomb shells available and that when he was in Jingzhou, about one to two thousand were produced each month for dispatch of ten to twenty thousand at a time to Xiangyang and Yingzhou. The Ming Dynasty text Huolongjing describes the use of poisonous gunpowder bombs, including the "wind-and-dust" bomb.
During the Mongol invasions of Japan, the Mongols used the explosive "thunder-crash bombs" against the Japanese. Archaeological evidence of the "thunder-crash bombs" has been discovered in an underwater shipwreck off the shore of Japan by the Kyushu Okinawa Society for Underwater Archaeology. X-rays by Japanese scientists of the excavated shells confirmed that they contained gunpowder.
Shock
Explosive shock waves can cause situations such as body displacement (i.e., people being thrown through the air), dismemberment, internal bleeding and ruptured eardrums.
Shock waves produced by explosive events have two distinct components, the positive and negative wave. The positive wave shoves outward from the point of detonation, followed by the trailing vacuum space "sucking back" towards the point of origin as the shock bubble collapses. The greatest defense against shock injuries is distance from the source of shock. As a point of reference, the overpressure at the Oklahoma City bombing was estimated in the range of | Bomb | Wikipedia | 424 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
Heat
A thermal wave is created by the sudden release of heat caused by an explosion. Military bomb tests have documented temperatures of up to 2,480 °C (4,500 °F). While capable of inflicting severe to catastrophic burns and causing secondary fires, thermal wave effects are considered very limited in range compared to shock and fragmentation. This rule has been challenged, however, by military development of thermobaric weapons, which employ a combination of negative shock wave effects and extreme temperature to incinerate objects within the blast radius.
Fragmentation
Fragmentation is produced by the acceleration of shattered pieces of bomb casing and adjacent physical objects. The use of fragmentation in bombs dates to the 14th century, and appears in the Ming Dynasty text Huolongjing. The fragmentation bombs were filled with iron pellets and pieces of broken porcelain. Once the bomb explodes, the resulting fragments are capable of piercing the skin and blinding enemy soldiers.
While conventionally viewed as small metal shards moving at super-supersonic and hypersonic speeds, fragmentation can occur in epic proportions and travel for extensive distances. When the SS Grandcamp exploded in the Texas City Disaster on April 16, 1947, one fragment of that blast was a two-ton anchor which was hurled nearly two miles inland to embed itself in the parking lot of the Pan American refinery. | Bomb | Wikipedia | 266 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
Effects on living things
To people who are close to a blast incident, such as bomb disposal technicians, soldiers wearing body armor, deminers, or individuals wearing little to no protection, there are four types of blast effects on the human body: overpressure (shock), fragmentation, impact, and heat. Overpressure refers to the sudden and drastic rise in ambient pressure that can damage the internal organs, possibly leading to permanent damage or death. Fragmentation can also include sand, debris and vegetation from the area surrounding the blast source. This is very common in anti-personnel mine blasts. The projection of materials poses a potentially lethal threat caused by cuts in soft tissues, as well as infections, and injuries to the internal organs. When the overpressure wave impacts the body it can induce violent levels of blast-induced acceleration. Resulting injuries may range from minor to unsurvivable. Immediately following this initial acceleration, deceleration injuries can occur when a person impacts directly against a rigid surface or obstacle after being set in motion by the force of the blast. Finally, injury and fatality can result from the explosive fireball as well as incendiary agents projected onto the body. Personal protective equipment, such as a bomb suit or demining ensemble, as well as helmets, visors and foot protection, can dramatically reduce the four effects, depending upon the charge, proximity and other variables.
Types
Experts commonly distinguish between civilian and military bombs. The latter are almost always mass-produced weapons, developed and constructed to a standard design out of standard components and intended to be deployed in a standard explosive device. IEDs are divided into three basic categories by basic size and delivery. Type 76, IEDs are hand-carried parcel or suitcase bombs, type 80, are "suicide vests" worn by a bomber, and type 3 devices are vehicles laden with explosives to act as large-scale stationary or self-propelled bombs, also known as VBIED (vehicle-borne IEDs). | Bomb | Wikipedia | 400 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
Improvised explosive materials are typically unstable and subject to spontaneous, unintentional detonation triggered by a wide range of environmental effects, ranging from impact and friction to electrostatic shock. Even subtle motion, change in temperature, or the nearby use of cellphones or radios can trigger an unstable or remote-controlled device. Any interaction with explosive materials or devices by unqualified personnel should be considered a grave and immediate risk of death or dire injury. The safest response to finding an object believed to be an explosive device is to get as far away from it as possible.
Atomic bombs are based on the theory of nuclear fission, that when a large atom splits, it releases a massive amount of energy. Thermonuclear weapons, (colloquially known as "hydrogen bombs") use the energy from an initial fission explosion to create an even more powerful fusion explosion.
The term "dirty bomb" refers to a specialized device that relies on a comparatively low explosive yield to scatter harmful material over a wide area. Most commonly associated with radiological or chemical materials, dirty bombs seek to kill or injure and then to deny access to a contaminated area until a thorough clean-up can be accomplished. In the case of urban settings, this clean-up may take extensive time, rendering the contaminated zone virtually uninhabitable in the interim.
The power of large bombs is typically measured in kilotons (kt) or megatons of TNT (Mt). The most powerful bombs ever used in combat were the two atomic bombs dropped by the United States to attack Hiroshima and Nagasaki, and the most powerful ever tested was the Tsar Bomba. The most powerful non-nuclear bomb is Russian "Father of All Bombs" (officially Aviation Thermobaric Bomb of Increased Power (ATBIP)) followed by the United States Air Force's MOAB (officially Massive Ordnance Air Blast, or more commonly known as the "Mother of All Bombs").
Below is a list of five different types of bombs based on the fundamental explosive mechanism they employ. | Bomb | Wikipedia | 417 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
Compressed gas
Relatively small explosions can be produced by pressurizing a container until catastrophic failure such as with a dry ice bomb. Technically, devices that create explosions of this type can not be classified as "bombs" by the definition presented at the top of this article. However, the explosions created by these devices can cause property damage, injury, or death. Flammable liquids, gasses and gas mixtures dispersed in these explosions may also ignite if exposed to a spark or flame.
Low explosive
The simplest and oldest bombs store energy in the form of a low explosive. Black powder is an example of a low explosive. Low explosives typically consist of a mixture of an oxidizing salt, such as potassium nitrate (saltpeter), with solid fuel, such as charcoal or aluminium powder. These compositions deflagrate upon ignition, producing hot gas. Under normal circumstances, this deflagration occurs too slowly to produce a significant pressure wave; low explosives, therefore, must generally be used in large quantities or confined in a container with a high burst pressure to be useful as a bomb.
High explosive
A high explosive bomb is one that employs a process called "detonation" to rapidly go from an initially high energy molecule to a very low energy molecule. Detonation is distinct from deflagration in that the chemical reaction propagates faster than the speed of sound (often many times faster) in an intense shock wave. Therefore, the pressure wave produced by a high explosive is not significantly increased by confinement as detonation occurs so quickly that the resulting plasma does not expand much before all the explosive material has reacted. This has led to the development of plastic explosive. A casing is still employed in some high explosive bombs, but with the purpose of fragmentation. Most high explosive bombs consist of an insensitive secondary explosive that must be detonated with a blasting cap containing a more sensitive primary explosive.
Thermobaric
A thermobaric bomb is a type of explosive that utilizes oxygen from the surrounding air to generate an intense, high-temperature explosion, and in practice the blast wave typically produced by such a weapon is of a significantly longer duration than that produced by a conventional condensed explosive. The fuel-air bomb is one of the best-known types of thermobaric weapons. | Bomb | Wikipedia | 465 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
Nuclear fission
Nuclear fission type atomic bombs utilize the energy present in very heavy atomic nuclei, such as U-235 or Pu-239. In order to release this energy rapidly, a certain amount of the fissile material must be very rapidly consolidated while being exposed to a neutron source. If consolidation occurs slowly, repulsive forces drive the material apart before a significant explosion can occur. Under the right circumstances, rapid consolidation can provoke a chain reaction that can proliferate and intensify by many orders of magnitude within microseconds. The energy released by a nuclear fission bomb may be tens of thousands of times greater than a chemical bomb of the same mass.
Nuclear fusion
A thermonuclear weapon is a type of nuclear bomb that releases energy through the combination of fission and fusion of the light atomic nuclei of deuterium and tritium. With this type of bomb, a thermonuclear detonation is triggered by the detonation of a fission type nuclear bomb contained within a material containing high concentrations of deuterium and tritium. Weapon yield is typically increased with a tamper that increases the duration and intensity of the reaction through inertial confinement and neutron reflection. Nuclear fusion bombs can have arbitrarily high yields making them hundreds or thousands of times more powerful than nuclear fission.
A pure fusion weapon is a hypothetical nuclear weapon that does not require a primary fission stage to start a fusion reaction.
Antimatter
Antimatter bombs can theoretically be constructed, but antimatter is very costly to produce and hard to store safely. | Bomb | Wikipedia | 317 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
Other
Aerial bomb – designed to be dropped from a military aircraft (or even any aircraft) and carried on hardpoints or in bomb bays
Delay-action bomb – explodes some time after impact, as opposed to before or on impact
Dummy bomb – harmless bomb that has been fully disabled or has had its explosive contents removed, often used for training or display
Glide bomb – features flight control surfaces, allowing it to glide fairly long distances to its target
General-purpose bomb – aerial bomb dropped for multiple purposes, and thus designed to suit multiple purposes
Incendiary bomb – designed to set targets ablaze
Cluster bomb – releases additional submunitions, often smaller bombs, upon detonation
Anti-runway penetration bomb – designed to destroy runways and aprons
Bunker buster – capable of penetrating hardened or fortified surfaces before detonating
Concrete bomb – contains dense, inert material (typically concrete) instead of explosives, using the kinetic energy of the falling bomb to destroy target
Improvised explosive device – classification of bombs produced in unconventional ways or using unconventional materials; includes explosives such as the barrel bomb, nail bomb, pipe bomb, pressure cooker bomb, fertilizer bomb, and Molotov cocktail
Delivery
The first air-dropped bombs were used by the Austrians in the 1849 siege of Venice. Two hundred unmanned balloons carried small bombs, although few bombs actually hit the city.
The first bombing from a fixed-wing aircraft took place in 1911 when the Italians dropped bombs by hand on the Turkish lines in what is now Libya, during the Italo-Turkish War. The first large scale dropping of bombs took place during World War I starting in 1915 with the German Zeppelin airship raids on London, England, and the same war saw the invention of the first heavy bombers. One Zeppelin raid on 8 September 1915 dropped of high explosives and incendiary bombs, including one bomb that weighed . | Bomb | Wikipedia | 371 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
During World War II bombing became a major military feature, and a number of novel delivery methods were introduced. These included Barnes Wallis's bouncing bomb, designed to bounce across water, avoiding torpedo nets and other underwater defenses, until it reached a dam, ship, or other destination, where it would sink and explode. By the end of the war, planes such as the allied forces' Avro Lancaster were delivering with accuracy from , ten ton earthquake bombs (also invented by Barnes Wallis) named "Grand Slam", which, unusually for the time, were delivered from high altitude in order to gain high speed, and would, upon impact, penetrate and explode deep underground ("camouflet"), causing massive caverns or craters, and affecting targets too large or difficult to be affected by other types of bomb.
Modern military bomber aircraft are designed around a large-capacity internal bomb bay, while fighter-bombers usually carry bombs externally on pylons or bomb racks or on multiple ejection racks, which enable mounting several bombs on a single pylon. Some bombs are equipped with a parachute, such as the World War II "parafrag" (an fragmentation bomb), the Vietnam War-era daisy cutters, and the bomblets of some modern cluster bombs. Parachutes slow the bomb's descent, giving the dropping aircraft time to get to a safe distance from the explosion. This is especially important with air-burst nuclear weapons (especially those dropped from slower aircraft or with very high yields), and in situations where the aircraft releases a bomb at low altitude. A number of modern bombs are also precision-guided munitions, and may be guided after they leave an aircraft by remote control, or by autonomous guidance.
Aircraft may also deliver bombs in the form of warheads on guided missiles, such as long-range cruise missiles, which can also be launched from warships.
A hand grenade is delivered by being thrown. Grenades can also be projected by other means, such as being launched from the muzzle of a rifle (as in the rifle grenade), using a grenade launcher (such as the M203), or by attaching a rocket to the explosive grenade (as in a rocket-propelled grenade (RPG)).
A bomb may also be positioned in advance and concealed. | Bomb | Wikipedia | 464 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
A bomb destroying a rail track just before a train arrives will usually cause the train to derail. In addition to the damage to vehicles and people, a bomb exploding in a transport network often damages, and is sometimes mainly intended to damage, the network itself. This applies to railways, bridges, runways, and ports, and, to a lesser extent (depending on circumstances), to roads.
In the case of suicide bombing, the bomb is often carried by the attacker on their body, or in a vehicle driven to the target.
The Blue Peacock nuclear mines, which were also termed "bombs", were planned to be positioned during wartime and be constructed such that, if disturbed, they would explode within ten seconds.
The explosion of a bomb may be triggered by a detonator or a fuse. Detonators are triggered by clocks, remote controls like cell phones or some kind of sensor, such as pressure (altitude), radar, vibration or contact. Detonators vary in ways they work, they can be electrical, fire fuze or blast initiated detonators and others,
Blast seat
In forensic science, the point of detonation of a bomb is referred to as its blast seat, seat of explosion, blast hole or epicenter. Depending on the type, quantity and placement of explosives, the blast seat may be either spread out or concentrated (i.e., an explosion crater).
Other types of explosions, such as dust or vapor explosions, do not cause craters or even have definitive blast seats. | Bomb | Wikipedia | 307 | 47628 | https://en.wikipedia.org/wiki/Bomb | Technology | Weapons | null |
The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetic, weak and strong interactions – excluding gravity) in the universe and classifying all known elementary particles. It was developed in stages throughout the latter half of the 20th century, through the work of many scientists worldwide, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks. Since then, proof of the top quark (1995), the tau neutrino (2000), and the Higgs boson (2012) have added further credence to the Standard Model. In addition, the Standard Model has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy.
Although the Standard Model is believed to be theoretically self-consistent and has demonstrated some success in providing experimental predictions, it leaves some physical phenomena unexplained and so falls short of being a complete theory of fundamental interactions. For example, it does not fully explain why there is more matter than anti-matter, incorporate the full theory of gravitation as described by general relativity, or account for the universe's accelerating expansion as possibly described by dark energy. The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology. It also does not incorporate neutrino oscillations and their non-zero masses.
The development of the Standard Model was driven by theoretical and experimental particle physicists alike. The Standard Model is a paradigm of a quantum field theory for theorists, exhibiting a wide range of phenomena, including spontaneous symmetry breaking, anomalies, and non-perturbative behavior. It is used as a basis for building more exotic models that incorporate hypothetical particles, extra dimensions, and elaborate symmetries (such as supersymmetry) to explain experimental results at variance with the Standard Model, such as the existence of dark matter and neutrino oscillations.
Historical background
In 1928, Paul Dirac introduced the Dirac equation, which implied the existence of antimatter.
In 1954, Yang Chen-Ning and Robert Mills extended the concept of gauge theory for abelian groups, e.g. quantum electrodynamics, to nonabelian groups to provide an explanation for strong interactions. In 1957, Chien-Shiung Wu demonstrated parity was not conserved in the weak interaction. | Standard Model | Wikipedia | 491 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
In 1961, Sheldon Glashow combined the electromagnetic and weak interactions. In 1964, Murray Gell-Mann and George Zweig introduced quarks and that same year Oscar W. Greenberg implicitly introduced color charge of quarks. In 1967 Steven Weinberg and Abdus Salam incorporated the Higgs mechanism into Glashow's electroweak interaction, giving it its modern form.
In 1970, Sheldon Glashow, John Iliopoulos, and Luciano Maiani introduced the GIM mechanism, predicting the charm quark. In 1973 Gross and Wilczek and Politzer independently discovered that non-Abelian gauge theories, like the color theory of the strong force, have asymptotic freedom. In 1976, Martin Perl discovered the tau lepton at the SLAC. In 1977, a team led by Leon Lederman at Fermilab discovered the bottom quark.
The Higgs mechanism is believed to give rise to the masses of all the elementary particles in the Standard Model. This includes the masses of the W and Z bosons, and the masses of the fermions, i.e. the quarks and leptons.
After the neutral weak currents caused by Z boson exchange were discovered at CERN in 1973, the electroweak theory became widely accepted and Glashow, Salam, and Weinberg shared the 1979 Nobel Prize in Physics for discovering it. The W± and Z0 bosons were discovered experimentally in 1983; and the ratio of their masses was found to be as the Standard Model predicted.
The theory of the strong interaction (i.e. quantum chromodynamics, QCD), to which many contributed, acquired its modern form in 1973–74 when asymptotic freedom was proposed (a development that made QCD the main focus of theoretical research) and experiments confirmed that the hadrons were composed of fractionally charged quarks.
The term "Standard Model" was introduced by Abraham Pais and Sam Treiman in 1975, with reference to the electroweak theory with four quarks. Steven Weinberg, has since claimed priority, explaining that he chose the term Standard Model out of a sense of modesty and used it in 1973 during a talk in Aix-en-Provence in France.
Particle content
The Standard Model includes members of several classes of elementary particles, which in turn can be distinguished by other characteristics, such as color charge.
All particles can be summarized as follows:
Fermions | Standard Model | Wikipedia | 505 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
The Standard Model includes 12 elementary particles of spin , known as fermions. Fermions respect the Pauli exclusion principle, meaning that two identical fermions cannot simultaneously occupy the same quantum state in the same atom. Each fermion has a corresponding antiparticle, which are particles that have corresponding properties with the exception of opposite charges. Fermions are classified based on how they interact, which is determined by the charges they carry, into two groups: quarks and leptons. Within each group, pairs of particles that exhibit similar physical behaviors are then grouped into generations (see the table). Each member of a generation has a greater mass than the corresponding particle of generations prior. Thus, there are three generations of quarks and leptons. As first-generation particles do not decay, they comprise all of ordinary (baryonic) matter. Specifically, all atoms consist of electrons orbiting around the atomic nucleus, ultimately constituted of up and down quarks. On the other hand, second- and third-generation charged particles decay with very short half-lives and can only be observed in high-energy environments. Neutrinos of all generations also do not decay, and pervade the universe, but rarely interact with baryonic matter. | Standard Model | Wikipedia | 261 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
There are six quarks: up, down, charm, strange, top, and bottom. Quarks carry color charge, and hence interact via the strong interaction. The color confinement phenomenon results in quarks being strongly bound together such that they form color-neutral composite particles called hadrons; quarks cannot individually exist and must always bind with other quarks. Hadrons can contain either a quark-antiquark pair (mesons) or three quarks (baryons). The lightest baryons are the nucleons: the proton and neutron. Quarks also carry electric charge and weak isospin, and thus interact with other fermions through electromagnetism and weak interaction. The six leptons consist of the electron, electron neutrino, muon, muon neutrino, tau, and tau neutrino. The leptons do not carry color charge, and do not respond to strong interaction. The charged leptons carry an electric charge of −1 e, while the three neutrinos carry zero electric charge. Thus, the neutrinos' motions are influenced by only the weak interaction and gravity, making them difficult to observe.
Gauge bosons | Standard Model | Wikipedia | 256 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
The Standard Model includes 4 kinds of gauge bosons of spin 1, with bosons being quantum particles containing an integer spin. The gauge bosons are defined as force carriers, as they are responsible for mediating the fundamental interactions. The Standard Model explains the four fundamental forces as arising from the interactions, with fermions exchanging virtual force carrier particles, thus mediating the forces. At a macroscopic scale, this manifests as a force. As a result, they do not follow the Pauli exclusion principle that constrains fermions; bosons do not have a theoretical limit on their spatial density. The types of gauge bosons are described below.
Electromagnetism: Photons mediate the electromagnetic force, responsible for interactions between electrically charged particles. The photon is massless and is described by the theory of quantum electrodynamics (QED).
Strong Interactions: Gluons mediate the strong interactions, which binds quarks to each other by influencing the color charge, with the interactions being described in the theory of quantum chromodynamics (QCD). They have no mass, and there are eight distinct gluons, with each being denoted through a color-anticolor charge combination (e.g. red–antigreen). As gluons have an effective color charge, they can also interact amongst themselves.
Weak Interactions: The , , and gauge bosons mediate the weak interactions between all fermions, being responsible for radioactivity. They contain mass, with the having more mass than the . The weak interactions involving the act only on left-handed particles and right-handed antiparticles. The carries an electric charge of +1 and −1 and couples to the electromagnetic interaction. The electrically neutral boson interacts with both left-handed particles and right-handed antiparticles. These three gauge bosons along with the photons are grouped together, as collectively mediating the electroweak interaction.
Gravity: It is currently unexplained in the Standard Model, as the hypothetical mediating particle graviton has been proposed, but not observed. This is due to the incompatibility of quantum mechanics and Einstein's theory of general relativity, regarded as being the best explanation for gravity. In general relativity, gravity is explained as being the geometric curving of spacetime. | Standard Model | Wikipedia | 480 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
The Feynman diagram calculations, which are a graphical representation of the perturbation theory approximation, invoke "force mediating particles", and when applied to analyze high-energy scattering experiments are in reasonable agreement with the data. However, perturbation theory (and with it the concept of a "force-mediating particle") fails in other situations. These include low-energy quantum chromodynamics, bound states, and solitons. The interactions between all the particles described by the Standard Model are summarized by the diagrams on the right of this section. | Standard Model | Wikipedia | 118 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
Higgs boson
The Higgs particle is a massive scalar elementary particle theorized by Peter Higgs (and others) in 1964, when he showed that Goldstone's 1962 theorem (generic continuous symmetry, which is spontaneously broken) provides a third polarisation of a massive vector field. Hence, Goldstone's original scalar doublet, the massive spin-zero particle, was proposed as the Higgs boson, and is a key building block in the Standard Model. It has no intrinsic spin, and for that reason is classified as a boson with spin-0.
The Higgs boson plays a unique role in the Standard Model, by explaining why the other elementary particles, except the photon and gluon, are massive. In particular, the Higgs boson explains why the photon has no mass, while the W and Z bosons are very heavy. Elementary-particle masses and the differences between electromagnetism (mediated by the photon) and the weak force (mediated by the W and Z bosons) are critical to many aspects of the structure of microscopic (and hence macroscopic) matter. In electroweak theory, the Higgs boson generates the masses of the leptons (electron, muon, and tau) and quarks. As the Higgs boson is massive, it must interact with itself.
Because the Higgs boson is a very massive particle and also decays almost immediately when created, only a very high-energy particle accelerator can observe and record it. Experiments to confirm and determine the nature of the Higgs boson using the Large Hadron Collider (LHC) at CERN began in early 2010 and were performed at Fermilab's Tevatron until its closure in late 2011. Mathematical consistency of the Standard Model requires that any mechanism capable of generating the masses of elementary particles must become visible at energies above ; therefore, the LHC (designed to collide two proton beams) was built to answer the question of whether the Higgs boson actually exists.
On 4 July 2012, two of the experiments at the LHC (ATLAS and CMS) both reported independently that they had found a new particle with a mass of about (about 133 proton masses, on the order of ), which is "consistent with the Higgs boson". On 13 March 2013, it was confirmed to be the searched-for Higgs boson.
Theoretical aspects
Construction of the Standard Model Lagrangian | Standard Model | Wikipedia | 505 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
Technically, quantum field theory provides the mathematical framework for the Standard Model, in which a Lagrangian controls the dynamics and kinematics of the theory. Each kind of particle is described in terms of a dynamical field that pervades space-time.
The construction of the Standard Model proceeds following the modern method of constructing most field theories: by first postulating a set of symmetries of the system, and then by writing down the most general renormalizable Lagrangian from its particle (field) content that observes these symmetries.
The global Poincaré symmetry is postulated for all relativistic quantum field theories. It consists of the familiar translational symmetry, rotational symmetry and the inertial reference frame invariance central to the theory of special relativity. The local SU(3) × SU(2) × U(1) gauge symmetry is an internal symmetry that essentially defines the Standard Model. Roughly, the three factors of the gauge symmetry give rise to the three fundamental interactions. The fields fall into different representations of the various symmetry groups of the Standard Model (see table). Upon writing the most general Lagrangian, one finds that the dynamics depends on 19 parameters, whose numerical values are established by experiment. The parameters are summarized in the table (made visible by clicking "show") above.
Quantum chromodynamics sector
The quantum chromodynamics (QCD) sector defines the interactions between quarks and gluons, which is a Yang–Mills gauge theory with SU(3) symmetry, generated by . Since leptons do not interact with gluons, they are not affected by this sector. The Dirac Lagrangian of the quarks coupled to the gluon fields is given by
where is a three component column vector of Dirac spinors, each element of which refers to a quark field with a specific color charge (i.e. red, blue, and green) and summation over flavor (i.e. up, down, strange, etc.) is implied.
The gauge covariant derivative of QCD is defined by , where
are the Dirac matrices,
is the 8-component () SU(3) gauge field,
are the 3 × 3 Gell-Mann matrices, generators of the SU(3) color group,
represents the gluon field strength tensor, and
is the strong coupling constant. | Standard Model | Wikipedia | 500 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
The QCD Lagrangian is invariant under local SU(3) gauge transformations; i.e., transformations of the form , where is 3 × 3 unitary matrix with determinant 1, making it a member of the group SU(3), and is an arbitrary function of spacetime.
Electroweak sector
The electroweak sector is a Yang–Mills gauge theory with the symmetry group ,
where the subscript sums over the three generations of fermions; , and are the left-handed doublet, right-handed singlet up type, and right handed singlet down type quark fields; and and are the left-handed doublet and right-handed singlet lepton fields.
The electroweak gauge covariant derivative is defined as , where
is the U(1) gauge field,
is the weak hypercharge – the generator of the U(1) group,
is the 3-component SU(2) gauge field,
are the Pauli matrices – infinitesimal generators of the SU(2) group – with subscript L to indicate that they only act on left-chiral fermions,
and are the U(1) and SU(2) coupling constants respectively,
() and are the field strength tensors for the weak isospin and weak hypercharge fields.
Notice that the addition of fermion mass terms into the electroweak Lagrangian is forbidden, since terms of the form do not respect gauge invariance. Neither is it possible to add explicit mass terms for the U(1) and SU(2) gauge fields. The Higgs mechanism is responsible for the generation of the gauge boson masses, and the fermion masses result from Yukawa-type interactions with the Higgs field.
Higgs sector
In the Standard Model, the Higgs field is an SU(2) doublet of complex scalar fields with four degrees of freedom:
where the superscripts + and 0 indicate the electric charge of the components. The weak hypercharge of both components is 1. Before symmetry breaking, the Higgs Lagrangian is
where is the electroweak gauge covariant derivative defined above and is the potential of the Higgs field. The square of the covariant derivative leads to three and four point interactions between the electroweak gauge fields and and the scalar field . The scalar potential is given by | Standard Model | Wikipedia | 498 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
where , so that acquires a non-zero Vacuum expectation value, which generates masses for the Electroweak gauge fields (the Higgs mechanism), and , so that the potential is bounded from below. The quartic term describes self-interactions of the scalar field .
The minimum of the potential is degenerate with an infinite number of equivalent ground state solutions, which occurs when . It is possible to perform a gauge transformation on such that the ground state is transformed to a basis where and . This breaks the symmetry of the ground state. The expectation value of now becomes
where has units of mass and sets the scale of electroweak physics. This is the only dimensional parameter of the Standard Model and has a measured value of ~.
After symmetry breaking, the masses of the W and Z are given by and , which can be viewed as predictions of the theory. The photon remains massless. The mass of the Higgs boson is . Since and are free parameters, the Higgs's mass could not be predicted beforehand and had to be determined experimentally.
Yukawa sector
The Yukawa interaction terms are:
where , , and are matrices of Yukawa couplings, with the term giving the coupling of the generations and , and h.c. means Hermitian conjugate of preceding terms. The fields and are left-handed quark and lepton doublets. Likewise, and are right-handed up-type quark, down-type quark, and lepton singlets. Finally is the Higgs doublet and is its charge conjugate state.
The Yukawa terms are invariant under the SU(2) × U(1) gauge symmetry of the Standard Model and generate masses for all fermions after spontaneous symmetry breaking.
Fundamental interactions
The Standard Model describes three of the four fundamental interactions in nature; only gravity remains unexplained. In the Standard Model, such an interaction is described as an exchange of bosons between the objects affected, such as a photon for the electromagnetic force and a gluon for the strong interaction. Those particles are called force carriers or messenger particles.
Gravity
Despite being perhaps the most familiar fundamental interaction, gravity is not described by the Standard Model, due to contradictions that arise when combining general relativity, the modern theory of gravity, and quantum mechanics. However, gravity is so weak at microscopic scales, that it is essentially unmeasurable. The graviton is postulated to be the mediating particle, but has not yet been proved to exist. | Standard Model | Wikipedia | 511 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
Electromagnetism
Electromagnetism is the only long-range force in the Standard Model. It is mediated by photons and couples to electric charge. Electromagnetism is responsible for a wide range of phenomena including atomic electron shell structure, chemical bonds, electric circuits and electronics. Electromagnetic interactions in the Standard Model are described by quantum electrodynamics.
Weak nuclear force
The weak interaction is responsible for various forms of particle decay, such as beta decay. It is weak and short-range, due to the fact that the weak mediating particles, W and Z bosons, have mass. W bosons have electric charge and mediate interactions that change the particle type (referred to as flavor) and charge. Interactions mediated by W bosons are charged current interactions. Z bosons are neutral and mediate neutral current interactions, which do not change particle flavor. Thus Z bosons are similar to the photon, aside from them being massive and interacting with the neutrino. The weak interaction is also the only interaction to violate parity and CP. Parity violation is maximal for charged current interactions, since the W boson interacts exclusively with left-handed fermions and right-handed antifermions.
In the Standard Model, the weak force is understood in terms of the electroweak theory, which states that the weak and electromagnetic interactions become united into a single electroweak interaction at high energies.
Strong nuclear force
The strong nuclear force is responsible for hadronic and nuclear binding. It is mediated by gluons, which couple to color charge. Since gluons themselves have color charge, the strong force exhibits confinement and asymptotic freedom. Confinement means that only color-neutral particles can exist in isolation, therefore quarks can only exist in hadrons and never in isolation, at low energies. Asymptotic freedom means that the strong force becomes weaker, as the energy scale increases. The strong force overpowers the electrostatic repulsion of protons and quarks in nuclei and hadrons respectively, at their respective scales. | Standard Model | Wikipedia | 420 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
While quarks are bound in hadrons by the fundamental strong interaction, which is mediated by gluons, nucleons are bound by an emergent phenomenon termed the residual strong force or nuclear force. This interaction is mediated by mesons, such as the pion. The color charges inside the nucleon cancel out, meaning most of the gluon and quark fields cancel out outside of the nucleon. However, some residue is "leaked", which appears as the exchange of virtual mesons, that causes the attractive force between nucleons. The (fundamental) strong interaction is described by quantum chromodynamics, which is a component of the Standard Model.
Tests and predictions
The Standard Model predicted the existence of the W and Z bosons, gluon, top quark and charm quark, and predicted many of their properties before these particles were observed. The predictions were experimentally confirmed with good precision.
The Standard Model also predicted the existence of the Higgs boson, which was found in 2012 at the Large Hadron Collider, the final fundamental particle predicted by the Standard Model to be experimentally confirmed.
Challenges
Self-consistency of the Standard Model (currently formulated as a non-abelian gauge theory quantized through path-integrals) has not been mathematically proved. While regularized versions useful for approximate computations (for example lattice gauge theory) exist, it is not known whether they converge (in the sense of S-matrix elements) in the limit that the regulator is removed. A key question related to the consistency is the Yang–Mills existence and mass gap problem.
Experiments indicate that neutrinos have mass, which the classic Standard Model did not allow. To accommodate this finding, the classic Standard Model can be modified to include neutrino mass, although it is not obvious exactly how this should be done.
If one insists on using only Standard Model particles, this can be achieved by adding a non-renormalizable interaction of leptons with the Higgs boson. On a fundamental level, such an interaction emerges in the seesaw mechanism where heavy right-handed neutrinos are added to the theory.
This is natural in the left-right symmetric extension of the Standard Model and in certain grand unified theories. As long as new physics appears below or around 1014 GeV, the neutrino masses can be of the right order of magnitude. | Standard Model | Wikipedia | 495 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
Theoretical and experimental research has attempted to extend the Standard Model into a unified field theory or a theory of everything, a complete theory explaining all physical phenomena including constants. Inadequacies of the Standard Model that motivate such research include:
The model does not explain gravitation, although physical confirmation of a theoretical particle known as a graviton would account for it to a degree. Though it addresses strong and electroweak interactions, the Standard Model does not consistently explain the canonical theory of gravitation, general relativity, in terms of quantum field theory. The reason for this is, among other things, that quantum field theories of gravity generally break down before reaching the Planck scale. As a consequence, we have no reliable theory for the very early universe.
Some physicists consider it to be ad hoc and inelegant, requiring 19 numerical constants whose values are unrelated and arbitrary. Although the Standard Model, as it now stands, can explain why neutrinos have masses, the specifics of neutrino mass are still unclear. It is believed that explaining neutrino mass will require an additional 7 or 8 constants, which are also arbitrary parameters.
The Higgs mechanism gives rise to the hierarchy problem if some new physics (coupled to the Higgs) is present at high energy scales. In these cases, in order for the weak scale to be much smaller than the Planck scale, severe fine tuning of the parameters is required; there are, however, other scenarios that include quantum gravity in which such fine tuning can be avoided. There are also issues of quantum triviality, which suggests that it may not be possible to create a consistent quantum field theory involving elementary scalar particles.
The model is inconsistent with the emerging Lambda-CDM model of cosmology. Contentions include the absence of an explanation in the Standard Model of particle physics for the observed amount of cold dark matter (CDM) and its contributions to dark energy, which are many orders of magnitude too large. It is also difficult to accommodate the observed predominance of matter over antimatter (matter/antimatter asymmetry). The isotropy and homogeneity of the visible universe over large distances seems to require a mechanism like cosmic inflation, which would also constitute an extension of the Standard Model.
Currently, no proposed theory of everything has been widely accepted or verified. | Standard Model | Wikipedia | 483 | 47641 | https://en.wikipedia.org/wiki/Standard%20Model | Physical sciences | Physics | null |
Reproducibility, closely related to replicability and repeatability, is a major principle underpinning the scientific method. For the findings of a study to be reproducible means that results obtained by an experiment or an observational study or in a statistical analysis of a data set should be achieved again with a high degree of reliability when the study is replicated. There are different kinds of replication but typically replication studies involve different researchers using the same methodology. Only after one or several such successful replications should a result be recognized as scientific knowledge.
With a narrower scope, reproducibility has been defined in computational sciences as having the following quality: the results should be documented by making all data and code available in such a way that the computations can be executed again with identical results.
In recent decades, there has been a rising concern that many published scientific results fail the test of reproducibility, evoking a reproducibility or replication crisis.
History
The first to stress the importance of reproducibility in science was the Anglo-Irish chemist Robert Boyle, in England in the 17th century. Boyle's air pump was designed to generate and study vacuum, which at the time was a very controversial concept. Indeed, distinguished philosophers such as René Descartes and Thomas Hobbes denied the very possibility of vacuum existence. Historians of science Steven Shapin and Simon Schaffer, in their 1985 book Leviathan and the Air-Pump, describe the debate between Boyle and Hobbes, ostensibly over the nature of vacuum, as fundamentally an argument about how useful knowledge should be gained. Boyle, a pioneer of the experimental method, maintained that the foundations of knowledge should be constituted by experimentally produced facts, which can be made believable to a scientific community by their reproducibility. By repeating the same experiment over and over again, Boyle argued, the certainty of fact will emerge. | Reproducibility | Wikipedia | 386 | 47651 | https://en.wikipedia.org/wiki/Reproducibility | Physical sciences | Science basics | Basics and measurement |
The air pump, which in the 17th century was a complicated and expensive apparatus to build, also led to one of the first documented disputes over the reproducibility of a particular scientific phenomenon. In the 1660s, the Dutch scientist Christiaan Huygens built his own air pump in Amsterdam, the first one outside the direct management of Boyle and his assistant at the time Robert Hooke. Huygens reported an effect he termed "anomalous suspension", in which water appeared to levitate in a glass jar inside his air pump (in fact suspended over an air bubble), but Boyle and Hooke could not replicate this phenomenon in their own pumps. As Shapin and Schaffer describe, "it became clear that unless the phenomenon could be produced in England with one of the two pumps available, then no one in England would accept the claims Huygens had made, or his competence in working the pump". Huygens was finally invited to England in 1663, and under his personal guidance Hooke was able to replicate anomalous suspension of water. Following this Huygens was elected a Foreign Member of the Royal Society. However, Shapin and Schaffer also note that "the accomplishment of replication was dependent on contingent acts of judgment. One cannot write down a formula saying when replication was or was not achieved".
The philosopher of science Karl Popper noted briefly in his famous 1934 book The Logic of Scientific Discovery that "non-reproducible single occurrences are of no significance to science". The statistician Ronald Fisher wrote in his 1935 book The Design of Experiments, which set the foundations for the modern scientific practice of hypothesis testing and statistical significance, that "we may say that a phenomenon is experimentally demonstrable when we know how to conduct an experiment which will rarely fail to give us statistically significant results". Such assertions express a common dogma in modern science that reproducibility is a necessary condition (although not necessarily sufficient) for establishing a scientific fact, and in practice for establishing scientific authority in any field of knowledge. However, as noted above by Shapin and Schaffer, this dogma is not well-formulated quantitatively, such as statistical significance for instance, and therefore it is not explicitly established how many times must a fact be replicated to be considered reproducible. | Reproducibility | Wikipedia | 474 | 47651 | https://en.wikipedia.org/wiki/Reproducibility | Physical sciences | Science basics | Basics and measurement |
Terminology
Replicability and repeatability are related terms broadly or loosely synonymous with reproducibility (for example, among the general public), but they are often usefully differentiated in more precise senses, as follows.
Two major steps are naturally distinguished in connection with reproducibility of experimental or observational studies:
When new data is obtained in the attempt to achieve it, the term replicability is often used, and the new study is a replication or replicate of the original one. Obtaining the same results when analyzing the data set of the original study again with the same procedures, many authors use the term reproducibility in a narrow, technical sense coming from its use in computational research.
Repeatability is related to the repetition of the experiment within the same study by the same researchers.
Reproducibility in the original, wide sense is only acknowledged if a replication performed by an independent researcher team is successful.
The terms reproducibility and replicability sometimes appear even in the scientific literature with reversed meaning, as different research fields settled on their own definitions for the same terms.
Measures of reproducibility and repeatability
In chemistry, the terms reproducibility and repeatability are used with a specific quantitative meaning. In inter-laboratory experiments, a concentration or other quantity of a chemical substance is measured repeatedly in different laboratories to assess the variability of the measurements. Then, the standard deviation of the difference between two values obtained within the same laboratory is called repeatability. The standard deviation for the difference between two measurement from different laboratories is called reproducibility.
These measures are related to the more general concept of variance components in metrology.
Reproducible research
Reproducible research method
The term reproducible research refers to the idea that scientific results should be documented in such a way that their deduction is fully transparent. This requires a detailed description of the methods used to obtain the data
and making the full dataset and the code to calculate the results easily accessible.
This is the essential part of open science. | Reproducibility | Wikipedia | 406 | 47651 | https://en.wikipedia.org/wiki/Reproducibility | Physical sciences | Science basics | Basics and measurement |
To make any research project computationally reproducible, general practice involves all data and files being clearly separated, labelled, and documented. All operations should be fully documented and automated as much as practicable, avoiding manual intervention where feasible. The workflow should be designed as a sequence of smaller steps that are combined so that the intermediate outputs from one step directly feed as inputs into the next step. Version control should be used as it lets the history of the project be easily reviewed and allows for the documenting and tracking of changes in a transparent manner.
A basic workflow for reproducible research involves data acquisition, data processing and data analysis. Data acquisition primarily consists of obtaining primary data from a primary source such as surveys, field observations, experimental research, or obtaining data from an existing source. Data processing involves the processing and review of the raw data collected in the first stage, and includes data entry, data manipulation and filtering and may be done using software. The data should be digitized and prepared for data analysis. Data may be analysed with the use of software to interpret or visualise statistics or data to produce the desired results of the research such as quantitative results including figures and tables. The use of software and automation enhances the reproducibility of research methods.
There are systems that facilitate such documentation, like the R Markdown language
or the Jupyter notebook.
The Open Science Framework provides a platform and useful tools to support reproducible research.
Reproducible research in practice
Psychology has seen a renewal of internal concerns about irreproducible results (see the entry on replicability crisis for empirical results on success rates of replications). Researchers showed in a 2006 study that, of 141 authors of a publication from the American Psychological Association (APA) empirical articles, 103 (73%) did not respond with their data over a six-month period. In a follow-up study published in 2015, it was found that 246 out of 394 contacted authors of papers in APA journals did not share their data upon request (62%). In a 2012 paper, it was suggested that researchers should publish data along with their works, and a dataset was released alongside as a demonstration. In 2017, an article published in Scientific Data suggested that this may not be sufficient and that the whole analysis context should be disclosed. | Reproducibility | Wikipedia | 474 | 47651 | https://en.wikipedia.org/wiki/Reproducibility | Physical sciences | Science basics | Basics and measurement |
In economics, concerns have been raised in relation to the credibility and reliability of published research. In other sciences, reproducibility is regarded as fundamental and is often a prerequisite to research being published, however in economic sciences it is not seen as a priority of the greatest importance. Most peer-reviewed economic journals do not take any substantive measures to ensure that published results are reproducible, however, the top economics journals have been moving to adopt mandatory data and code archives. There is low or no incentives for researchers to share their data, and authors would have to bear the costs of compiling data into reusable forms. Economic research is often not reproducible as only a portion of journals have adequate disclosure policies for datasets and program code, and even if they do, authors frequently do not comply with them or they are not enforced by the publisher. A Study of 599 articles published in 37 peer-reviewed journals revealed that while some journals have achieved significant compliance rates, significant portion have only partially complied, or not complied at all. On an article level, the average compliance rate was 47.5%; and on a journal level, the average compliance rate was 38%, ranging from 13% to 99%.
A 2018 study published in the journal PLOS ONE found that 14.4% of a sample of public health statistics researchers had shared their data or code or both.
There have been initiatives to improve reporting and hence reproducibility in the medical literature for many years, beginning with the CONSORT initiative, which is now part of a wider initiative, the EQUATOR Network.
This group has recently turned its attention to how better reporting might reduce waste in research, especially biomedical research.
Reproducible research is key to new discoveries in pharmacology. A Phase I discovery will be followed by Phase II reproductions as a drug develops towards commercial production. In recent decades Phase II success has fallen from 28% to 18%. A 2011 study found that 65% of medical studies were inconsistent when re-tested, and only 6% were completely reproducible.
Noteworthy irreproducible results
Hideyo Noguchi became famous for correctly identifying the bacterial agent of syphilis, but also claimed that he could culture this agent in his laboratory. Nobody else has been able to produce this latter result. | Reproducibility | Wikipedia | 469 | 47651 | https://en.wikipedia.org/wiki/Reproducibility | Physical sciences | Science basics | Basics and measurement |
In March 1989, University of Utah chemists Stanley Pons and Martin Fleischmann reported the production of excess heat that could only be explained by a nuclear process ("cold fusion"). The report was astounding given the simplicity of the equipment: it was essentially an electrolysis cell containing heavy water and a palladium cathode which rapidly absorbed the deuterium produced during electrolysis. The news media reported on the experiments widely, and it was a front-page item on many newspapers around the world (see science by press conference). Over the next several months others tried to replicate the experiment, but were unsuccessful.
Nikola Tesla claimed as early as 1899 to have used a high frequency current to light gas-filled lamps from over away without using wires. In 1904 he built Wardenclyffe Tower on Long Island to demonstrate means to send and receive power without connecting wires. The facility was never fully operational and was not completed due to economic problems, so no attempt to reproduce his first result was ever carried out.
Other examples which contrary evidence has refuted the original claim:
N-rays, a hypothesized form of radiation subsequently found to be illusory
Polywater, a hypothesized polymerized form of water found to be just water with common contaminations
Stimulus-triggered acquisition of pluripotency, revealed to be the result of fraud
GFAJ-1, a bacterium that could purportedly incorporate arsenic into its DNA in place of phosphorus
MMR vaccine controversy — a study in The Lancet claiming the MMR vaccine caused autism was revealed to be fraudulent
Schön scandal — semiconductor "breakthroughs" revealed to be fraudulent
Power posing — a social psychology phenomenon that went viral after being the subject of a very popular TED talk, but was unable to be replicated in dozens of studies | Reproducibility | Wikipedia | 370 | 47651 | https://en.wikipedia.org/wiki/Reproducibility | Physical sciences | Science basics | Basics and measurement |
A toxic heavy metal is a common but misleading term for a metal-like element noted for its potential toxicity. Not all heavy metals are toxic and some toxic metals are not heavy. Elements often discussed as toxic include cadmium, mercury and lead, all of which appear in the World Health Organization's list of 10 chemicals of major public concern. Other examples include chromium and nickel, thallium, bismuth, arsenic, antimony and tin.
These toxic elements are found naturally in the earth. They become concentrated as a result of human caused activities and can enter plant and animal (including human) tissues via inhalation, diet, and manual handling. Then, they can bind to and interfere with the functioning of vital cellular components. The toxic effects of arsenic, mercury, and lead were known to the ancients, but methodical studies of the toxicity of some heavy metals appear to date from only 1868. In humans, heavy metal poisoning is generally treated by the administration of chelating agents. Some elements otherwise regarded as toxic heavy metals are essential, in small quantities, for human health.
Controversial terminology
The International Union of Pure and Applied Chemistry (IUPAC), which standardizes nomenclature, says the term “heavy metals” is both meaningless and misleading". The IUPAC report focuses on the legal and toxicological implications of describing "heavy metals" as toxins when there is no scientific evidence to support a connection. The density implied by the adjective "heavy" has almost no biological consequences and pure metals are rarely the biologically active substance.
This characterization has been echoed by numerous reviews. The most widely used toxicology textbook, Casarett and Doull’s toxicology uses "toxic metal" not "heavy metals". Nevertheless many scientific and science related articles continue to use "heavy metal" as a term for toxic substances.
Major and minor metal toxins
Metals with multiple toxic effects include arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and nickel (Ni).
Elements that are nutritionally essential for animal or plant life but which are considered toxic metals in high doses or other forms include cobalt (Co), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), selenium (Se), and zinc (Zn).
Contamination sources | Toxic heavy metal | Wikipedia | 504 | 47671 | https://en.wikipedia.org/wiki/Toxic%20heavy%20metal | Physical sciences | Periodic table | Chemistry |
Toxic metals are found naturally in the earth, and become concentrated as a result of human activities, or, in some cases geochemical processes, such as accumulation in peat soils that are then released when drained for agriculture. Common sources include fertilisers; aging water supply infrastructure; and microplastics floating in the world's oceans. Arsenic is thought to be used in connection with coloring dyes. Rat poison used in grain and mash stores may be another source of the arsenic.
The geographical extent of sources may be very large. For example, up to one-sixth of China's arable land might be affected by heavy metal contamination.
Lead is the most prevalent heavy metal contaminant. As a component of tetraethyl lead, , it was used extensively in gasoline during the 1930s–1970s. Lead levels in the aquatic environments of industrialised societies have been estimated to be two to three times those of pre-industrial levels. Although the use of leaded gasoline was largely phased out in North America by 1996, soils next to roads built before this time retain high lead concentrations. Lead (from lead(II) azide or lead styphnate used in firearms) gradually accumulates at firearms training grounds, contaminating the local environment and exposing range employees to a risk of lead poisoning.
Entry routes | Toxic heavy metal | Wikipedia | 269 | 47671 | https://en.wikipedia.org/wiki/Toxic%20heavy%20metal | Physical sciences | Periodic table | Chemistry |
Toxic metals enter plant, animal and human tissues via air inhalation, diet, and manual handling. Welding, galvanizing, brazing, and soldering exposes workers to fumes that may be inhaled and result in metal fume fever. Motor vehicle emissions are a major source of airborne contaminants including arsenic, cadmium, cobalt, nickel, lead, antimony, vanadium, zinc, platinum, palladium and rhodium. Water sources (groundwater, lakes, streams and rivers) can be polluted by toxic metals leaching from industrial and consumer waste; acid rain can exacerbate this process by releasing toxic metals trapped in soils. Transport through soil can be facilitated by the presence of preferential flow paths (macropores) and dissolved organic compounds. Plants are exposed to toxic metals through the uptake of water; animals eat these plants; ingestion of plant- and animal-based foods are the largest sources of toxic metals in humans. Absorption through skin contact, for example from contact with soil, or metal containing toys and jewelry, is another potential source of toxic metal contamination. Toxic metals can bioaccumulate in organisms as they are hard to metabolize.
Detrimental effects
Toxic metals "can bind to vital cellular components, such as structural proteins, enzymes, and nucleic acids, and interfere with their functioning". Symptoms and effects can vary according to the metal or metal compound, and the dose involved. Broadly, long-term exposure to toxic heavy metals can have carcinogenic, central and peripheral nervous system, and circulatory effects. For humans, typical presentations associated with exposure to any of the "classical" toxic heavy metals, or chromium (another toxic heavy metal) or arsenic (a metalloid), are shown in the table.
History | Toxic heavy metal | Wikipedia | 369 | 47671 | https://en.wikipedia.org/wiki/Toxic%20heavy%20metal | Physical sciences | Periodic table | Chemistry |
The toxic effects of arsenic, mercury and lead were known to the ancients but methodical studies of the overall toxicity of heavy metals appear to date from only 1868. In that year, Wanklyn and Chapman speculated on the adverse effects of the heavy metals "arsenic, lead, copper, zinc, iron and manganese" in drinking water. They noted an "absence of investigation" and were reduced to "the necessity of pleading for the collection of data". In 1884, Blake described an apparent connection between toxicity and the atomic weight of an element. The following sections provide historical thumbnails for the "classical" toxic heavy metals (arsenic, mercury and lead) and some more recent examples (chromium and cadmium).
Arsenic
Arsenic, as realgar () and orpiment (), was known in ancient times. Strabo (64–50 BCE – c. AD 24?), a Greek geographer and historian, wrote that only slaves were employed in realgar and orpiment mines since they would inevitably die from the toxic effects of the fumes given off from the ores. Arsenic-contaminated beer poisoned over 6,000 people in the Manchester area of England in 1900, and is thought to have killed at least 70 victims. Clare Luce, American ambassador to Italy from 1953 to 1956, suffered from arsenic poisoning. Its source was traced to flaking arsenic-laden paint on the ceiling of her bedroom. She may also have eaten food contaminated by arsenic in flaking ceiling paint in the embassy dining room. Ground water contaminated by arsenic, as of 2014, "is still poisoning millions of people in Asia".
Mercury | Toxic heavy metal | Wikipedia | 333 | 47671 | https://en.wikipedia.org/wiki/Toxic%20heavy%20metal | Physical sciences | Periodic table | Chemistry |
The first emperor of unified China, Qin Shi Huang, it is reported, died of ingesting mercury pills that were intended to give him eternal life. The phrase "mad as a hatter" is likely a reference to mercury poisoning among milliners (so-called "mad hatter disease"), as mercury-based compounds were once used in the manufacture of felt hats in the 18th and 19th century. Historically, gold amalgam (an alloy with mercury) was widely used in gilding, leading to numerous casualties among the workers. It is estimated that during the construction of Saint Isaac's Cathedral alone, 60 workers died from the gilding of the main dome. Outbreaks of methylmercury poisoning occurred in several places in Japan during the 1950s due to industrial discharges of mercury into rivers and coastal waters. The best-known instances were in Minamata and Niigata. In Minamata alone, more than 600 people died due to what became known as Minamata disease. More than 21,000 people filed claims with the Japanese government, of which almost 3000 became certified as having the disease. In 22 documented cases, pregnant women who consumed contaminated fish showed mild or no symptoms but gave birth to infants with severe developmental disabilities. Since the Industrial Revolution, mercury levels have tripled in many near-surface seawaters, especially around Iceland and Antarctica.
Lead | Toxic heavy metal | Wikipedia | 278 | 47671 | https://en.wikipedia.org/wiki/Toxic%20heavy%20metal | Physical sciences | Periodic table | Chemistry |
The adverse effects of lead were known to the ancients. In the 2nd century BC the Greek botanist Nicander described the colic and paralysis seen in lead-poisoned people. Dioscorides, a Greek physician who is thought to have lived in the 1st century CE, wrote that lead "makes the mind give way". Lead was used extensively in Roman aqueducts from about 500 BC to 300 AD. Julius Caesar's engineer, Vitruvius, reported, "water is much more wholesome from earthenware pipes than from lead pipes. For it seems to be made injurious by lead, because white lead is produced by it, and this is said to be harmful to the human body." During the Mongol period in China (1271−1368 AD), lead pollution due to silver smelting in the Yunnan region exceeded contamination levels from modern mining activities by nearly four times. In the 17th and 18th centuries, people in Devon were afflicted by a condition referred to as Devon colic; this was discovered to be due to the imbibing of lead-contaminated cider. In 2013, the World Health Organization estimated that lead poisoning resulted in 143,000 deaths, and "contribute[d] to 600,000 new cases of children with intellectual disabilities", each year. In the U.S. city of Flint, Michigan, lead contamination in drinking water has been an issue since 2014. The source of the contamination has been attributed to "corrosion in the lead and iron pipes that distribute water to city residents". In 2015, the lead concentration of drinking water in north-eastern Tasmania, Australia, reached a level over 50 times the prescribed national drinking water guidelines. The source of the contamination was attributed to "a combination of dilapidated drinking water infrastructure, including lead jointed pipelines, end-of-life polyvinyl chloride pipes and household plumbing".
Chromium | Toxic heavy metal | Wikipedia | 388 | 47671 | https://en.wikipedia.org/wiki/Toxic%20heavy%20metal | Physical sciences | Periodic table | Chemistry |
Chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known since at least the late 19th century. In 1890, Newman described the elevated cancer risk of workers in a chromate dye company. Chromate-induced dermatitis was reported in aircraft workers during World War II. In 1963, an outbreak of dermatitis, ranging from erythema to exudative eczema, occurred amongst 60 automobile factory workers in England. The workers had been wet-sanding chromate-based primer paint that had been applied to car bodies. In Australia, chromium was released from the Newcastle Orica explosives plant on August 8, 2011. Up to 20 workers at the plant were exposed as were 70 nearby homes in Stockton. The town was only notified three days after the release and the accident sparked a major public controversy, with Orica criticised for playing down the extent and possible risks of the leak, and the state Government attacked for their slow response to the incident.
Cadmium
Cadmium exposure is a phenomenon of the early 20th century, and onwards. In Japan in 1910, the Mitsui Mining & Smelting Company began discharging cadmium into the Jinzū River, as a byproduct of mining operations. Residents in the surrounding area subsequently consumed rice grown in cadmium-contaminated irrigation water. They experienced softening of the bones and kidney failure. The origin of these symptoms was not clear; possibilities raised at the time included "a regional or bacterial disease or lead poisoning". In 1955, cadmium was identified as the likely cause and in 1961 the source was directly linked to mining operations in the area. In February 2010, cadmium was found in Walmart exclusive Miley Cyrus jewelry. Wal-Mart continued to sell the jewelry until May, when covert testing organised by Associated Press confirmed the original results. In June 2010 cadmium was detected in the paint used on promotional drinking glasses for the movie Shrek Forever After, sold by McDonald's Restaurants, triggering a recall of 12 million glasses.
Remediation
Human | Toxic heavy metal | Wikipedia | 440 | 47671 | https://en.wikipedia.org/wiki/Toxic%20heavy%20metal | Physical sciences | Periodic table | Chemistry |
In humans, heavy metal poisoning is generally treated by the administration of chelating agents. These are chemical compounds, such as (calcium disodium ethylenediaminetetraacetate) that convert heavy metals to chemically inert forms that can be excreted without further interaction with the body. Chelates are not without side effects and can also remove beneficial metals from the body. Vitamin and mineral supplements are sometimes co-administered for this reason
Environment
Soils contaminated by heavy metals can be remediated by one or more of the following technologies: isolation; immobilization; toxicity reduction; physical separation; or extraction. Isolation involves the use of caps, membranes or below-ground barriers in an attempt to quarantine the contaminated soil. Immobilization aims to alter the properties of the soil so as to hinder the mobility of the heavy contaminants. Toxicity reduction attempts to oxidise or reduce the toxic heavy metal ions, via chemical or biological means into less toxic or mobile forms. Physical separation involves the removal of the contaminated soil and the separation of the metal contaminants by mechanical means. Extraction is an on or off-site process that uses chemicals, high-temperature volatization, or electrolysis to extract contaminants from soils. The process or processes used will vary according to contaminant and the characteristics of the site.
Benefits
Some elements otherwise regarded as toxic heavy metals are essential, in small quantities, for human health. These elements include vanadium, manganese, iron, cobalt, copper, zinc, selenium, strontium and molybdenum. A deficiency of these essential metals may increase susceptibility to heavy metal poisoning.
Selenium is the most toxic of the heavy metals that are essential for mammals. Selenium is normally excreted and only becomes toxic when the intake exceeds the excretory capacity. | Toxic heavy metal | Wikipedia | 388 | 47671 | https://en.wikipedia.org/wiki/Toxic%20heavy%20metal | Physical sciences | Periodic table | Chemistry |
Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own galaxy, and from distant galaxies. Upon impact with Earth's atmosphere, cosmic rays produce showers of secondary particles, some of which reach the surface, although the bulk are deflected off into space by the magnetosphere or the heliosphere.
Cosmic rays were discovered by Victor Hess in 1912 in balloon experiments, for which he was awarded the 1936 Nobel Prize in Physics.
Direct measurement of cosmic rays, especially at lower energies, has been possible since the launch of the first satellites in the late 1950s. Particle detectors similar to those used in nuclear and high-energy physics are used on satellites and space probes for research into cosmic rays.
Data from the Fermi Space Telescope (2013) have been interpreted as evidence that a significant fraction of primary cosmic rays originate from the supernova explosions of stars. Based on observations of neutrinos and gamma rays from blazar TXS 0506+056 in 2018, active galactic nuclei also appear to produce cosmic rays.
Etymology
The term ray (as in optical ray) seems to have arisen from an initial belief, due to their penetrating power, that cosmic rays were mostly electromagnetic radiation. Nevertheless, following wider recognition of cosmic rays as being various high-energy particles with intrinsic mass, the term "rays" was still consistent with then known particles such as cathode rays, canal rays, alpha rays, and beta rays. Meanwhile "cosmic" ray photons, which are quanta of electromagnetic radiation (and so have no intrinsic mass) are known by their common names, such as gamma rays or X-rays, depending on their photon energy. | Cosmic ray | Wikipedia | 374 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
Composition
Of primary cosmic rays, which originate outside of Earth's atmosphere, about 99% are the bare nuclei of common atoms (stripped of their electron shells), and about 1% are solitary electrons (that is, one type of beta particle). Of the nuclei, about 90% are simple protons (i.e., hydrogen nuclei); 9% are alpha particles, identical to helium nuclei; and 1% are the nuclei of heavier elements, called HZE ions. These fractions vary highly over the energy range of cosmic rays. A very small fraction are stable particles of antimatter, such as positrons or antiprotons. The precise nature of this remaining fraction is an area of active research. An active search from Earth orbit for anti-alpha particles as of 2019 had found no unequivocal evidence.
Upon striking the atmosphere, cosmic rays violently burst atoms into other bits of matter, producing large amounts of pions and muons (produced from the decay of charged pions, which have a short half-life) as well as neutrinos. The neutron composition of the particle cascade increases at lower elevations, reaching between 40% and 80% of the radiation at aircraft altitudes.
Of secondary cosmic rays, the charged pions produced by primary cosmic rays in the atmosphere swiftly decay, emitting muons. Unlike pions, these muons do not interact strongly with matter, and can travel through the atmosphere to penetrate even below ground level. The rate of muons arriving at the surface of the Earth is such that about one per second passes through a volume the size of a person's head. Together with natural local radioactivity, these muons are a significant cause of the ground level atmospheric ionisation that first attracted the attention of scientists, leading to the eventual discovery of the primary cosmic rays arriving from beyond our atmosphere. | Cosmic ray | Wikipedia | 378 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
Energy
Cosmic rays attract great interest practically, due to the damage they inflict on microelectronics and life outside the protection of an atmosphere and magnetic field, and scientifically, because the energies of the most energetic ultra-high-energy cosmic rays have been observed to approach (This is slightly greater than 21 million times the design energy of particles accelerated by the Large Hadron Collider, .) One can show that such enormous energies might be achieved by means of the centrifugal mechanism of acceleration in active galactic nuclei. At , the highest-energy ultra-high-energy cosmic rays (such as the OMG particle recorded in 1991) have energies comparable to the kinetic energy of a baseball. As a result of these discoveries, there has been interest in investigating cosmic rays of even greater energies. Most cosmic rays, however, do not have such extreme energies; the energy distribution of cosmic rays peaks at .
History
After the discovery of radioactivity by Henri Becquerel in 1896, it was generally believed that atmospheric electricity, ionization of the air, was caused only by radiation from radioactive elements in the ground or the radioactive gases or isotopes of radon they produce. Measurements of increasing ionization rates at increasing heights above the ground during the decade from 1900 to 1910 could be explained as due to absorption of the ionizing radiation by the intervening air.
Discovery
In 1909, Theodor Wulf developed an electrometer, a device to measure the rate of ion production inside a hermetically sealed container, and used it to show higher levels of radiation at the top of the Eiffel Tower than at its base. However, his paper published in Physikalische Zeitschrift was not widely accepted. In 1911, Domenico Pacini observed simultaneous variations of the rate of ionization over a lake, over the sea, and at a depth of 3 metres from the surface. Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth. | Cosmic ray | Wikipedia | 416 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
In 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers to an altitude of 5,300 metres in a free balloon flight. He found the ionization rate increased to twice the rate at ground level. Hess ruled out the Sun as the radiation's source by making a balloon ascent during a near-total eclipse. With the moon blocking much of the Sun's visible radiation, Hess still measured rising radiation at rising altitudes. He concluded that "The results of the observations seem most likely to be explained by the assumption that radiation of very high penetrating power enters from above into our atmosphere." In 1913–1914, Werner Kolhörster confirmed Victor Hess's earlier results by measuring the increased ionization enthalpy rate at an altitude of 9 km. Hess received the Nobel Prize in Physics in 1936 for his discovery.
Identification
Bruno Rossi wrote in 1964:
In the late 1920s and early 1930s the technique of self-recording electroscopes carried by balloons into the highest layers of the atmosphere or sunk to great depths under water was brought to an unprecedented degree of perfection by the German physicist Erich Regener and his group. To these scientists we owe some of the most accurate measurements ever made of cosmic-ray ionization as a function of altitude and depth.
Ernest Rutherford stated in 1931 that "thanks to the fine experiments of Professor Millikan and the even more far-reaching experiments of Professor Regener, we have now got for the first time, a curve of absorption of these radiations in water which we may safely rely upon". | Cosmic ray | Wikipedia | 312 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
In the 1920s, the term cosmic ray was coined by Robert Millikan who made measurements of ionization due to cosmic rays from deep under water to high altitudes and around the globe. Millikan believed that his measurements proved that the primary cosmic rays were gamma rays; i.e., energetic photons. And he proposed a theory that they were produced in interstellar space as by-products of the fusion of hydrogen atoms into the heavier elements, and that secondary electrons were produced in the atmosphere by Compton scattering of gamma rays. In 1927, while sailing from Java to the Netherlands, Jacob Clay found evidence, later confirmed in many experiments, that cosmic ray intensity increases from the tropics to mid-latitudes, which indicated that the primary cosmic rays are deflected by the geomagnetic field and must therefore be charged particles, not photons. In 1929, Bothe and Kolhörster discovered charged cosmic-ray particles that could penetrate 4.1 cm of gold. Charged particles of such high energy could not possibly be produced by photons from Millikan's proposed interstellar fusion process.
In 1930, Bruno Rossi predicted a difference between the intensities of cosmic rays arriving from the east and the west that depends upon the charge of the primary particles—the so-called "east–west effect". Three independent experiments found that the intensity is, in fact, greater from the west, proving that most primaries are positive. During the years from 1930 to 1945, a wide variety of investigations confirmed that the primary cosmic rays are mostly protons, and the secondary radiation produced in the atmosphere is primarily electrons, photons and muons. In 1948, observations with nuclear emulsions carried by balloons to near the top of the atmosphere showed that approximately 10% of the primaries are helium nuclei (alpha particles) and 1% are nuclei of heavier elements such as carbon, iron, and lead. | Cosmic ray | Wikipedia | 387 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
During a test of his equipment for measuring the east–west effect, Rossi observed that the rate of near-simultaneous discharges of two widely separated Geiger counters was larger than the expected accidental rate. In his report on the experiment, Rossi wrote "... it seems that once in a while the recording equipment is struck by very extensive showers of particles, which causes coincidences between the counters, even placed at large distances from one another." In 1937, Pierre Auger, unaware of Rossi's earlier report, detected the same phenomenon and investigated it in some detail. He concluded that high-energy primary cosmic-ray particles interact with air nuclei high in the atmosphere, initiating a cascade of secondary interactions that ultimately yield a shower of electrons, and photons that reach ground level.
Soviet physicist Sergei Vernov was the first to use radiosondes to perform cosmic ray readings with an instrument carried to high altitude by a balloon. On 1 April 1935, he took measurements at heights up to 13.6 kilometres using a pair of Geiger counters in an anti-coincidence circuit to avoid counting secondary ray showers.
Homi J. Bhabha derived an expression for the probability of scattering positrons by electrons, a process now known as Bhabha scattering. His classic paper, jointly with Walter Heitler, published in 1937 described how primary cosmic rays from space interact with the upper atmosphere to produce particles observed at the ground level. Bhabha and Heitler explained the cosmic ray shower formation by the cascade production of gamma rays and positive and negative electron pairs. | Cosmic ray | Wikipedia | 317 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
Energy distribution
Measurements of the energy and arrival directions of the ultra-high-energy primary cosmic rays by the techniques of density sampling and fast timing of extensive air showers were first carried out in 1954 by members of the Rossi Cosmic Ray Group at the Massachusetts Institute of Technology. The experiment employed eleven scintillation detectors arranged within a circle 460 metres in diameter on the grounds of the Agassiz Station of the Harvard College Observatory. From that work, and from many other experiments carried out all over the world, the energy spectrum of the primary cosmic rays is now known to extend beyond 1020 eV. A huge air shower experiment called the Auger Project is currently operated at a site on the Pampas of Argentina by an international consortium of physicists. The project was first led by James Cronin, winner of the 1980 Nobel Prize in Physics from the University of Chicago, and Alan Watson of the University of Leeds, and later by scientists of the international Pierre Auger Collaboration. Their aim is to explore the properties and arrival directions of the very highest-energy primary cosmic rays. The results are expected to have important implications for particle physics and cosmology, due to a theoretical Greisen–Zatsepin–Kuzmin limit to the energies of cosmic rays from long distances (about 160 million light years) which occurs above 1020 eV because of interactions with the remnant photons from the Big Bang origin of the universe. Currently the Pierre Auger Observatory is undergoing an upgrade to improve its accuracy and find evidence for the yet unconfirmed origin of the most energetic cosmic rays.
High-energy gamma rays (>50MeV photons) were finally discovered in the primary cosmic radiation by an MIT experiment carried on the OSO-3 satellite in 1967. Components of both galactic and extra-galactic origins were separately identified at intensities much less than 1% of the primary charged particles. Since then, numerous satellite gamma-ray observatories have mapped the gamma-ray sky. The most recent is the Fermi Observatory, which has produced a map showing a narrow band of gamma ray intensity produced in discrete and diffuse sources in our galaxy, and numerous point-like extra-galactic sources distributed over the celestial sphere.
Modulation
The solar cycle causes variations in the magnetic field of the solar wind through which cosmic rays propagate to Earth.
This results in a modulation of the arriving fluxes at lower energies, as detected indirectly by the globally distributed neutron monitor network. | Cosmic ray | Wikipedia | 496 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
Sources
Early speculation on the sources of cosmic rays included a 1934 proposal by Baade and Zwicky suggesting cosmic rays originated from supernovae. A 1948 proposal by Horace W. Babcock suggested that magnetic variable stars could be a source of cosmic rays. Subsequently, Sekido et al. (1951) identified the Crab Nebula as a source of cosmic rays. Since then, a wide variety of potential sources for cosmic rays began to surface, including supernovae, active galactic nuclei, quasars, and gamma-ray bursts.
Later experiments have helped to identify the sources of cosmic rays with greater certainty. In 2009, a paper presented at the International Cosmic Ray Conference by scientists at the Pierre Auger Observatory in Argentina showed ultra-high energy cosmic rays originating from a location in the sky very close to the radio galaxy Centaurus A, although the authors specifically stated that further investigation would be required to confirm Centaurus A as a source of cosmic rays. However, no correlation was found between the incidence of gamma-ray bursts and cosmic rays, causing the authors to set upper limits as low as 3.4 × 10−6× erg·cm−2 on the flux of cosmic rays from gamma-ray bursts.
In 2009, supernovae were said to have been "pinned down" as a source of cosmic rays, a discovery made by a group using data from the Very Large Telescope. This analysis, however, was disputed in 2011 with data from PAMELA, which revealed that "spectral shapes of [hydrogen and helium nuclei] are different and cannot be described well by a single power law", suggesting a more complex process of cosmic ray formation. In February 2013, though, research analyzing data from Fermi revealed through an observation of neutral pion decay that supernovae were indeed a source of cosmic rays, with each explosion producing roughly 3 × 1042 – 3 × 1043J of cosmic rays.
Supernovae do not produce all cosmic rays, however, and the proportion of cosmic rays that they do produce is a question which cannot be answered without deeper investigation. To explain the actual process in supernovae and active galactic nuclei that accelerates the stripped atoms, physicists use shock front acceleration as a plausibility argument (see picture at right). | Cosmic ray | Wikipedia | 458 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
In 2017, the Pierre Auger Collaboration published the observation of a weak anisotropy in the arrival directions of the highest energy cosmic rays. Since the Galactic Center is in the deficit region, this anisotropy can be interpreted as evidence for the extragalactic origin of cosmic rays at the highest energies. This implies that there must be a transition energy from galactic to extragalactic sources, and there may be different types of cosmic-ray sources contributing to different energy ranges.
Types
Cosmic rays can be divided into two types:
galactic cosmic rays (GCR) and extragalactic cosmic rays, i.e., high-energy particles originating outside the solar system, and
solar energetic particles, high-energy particles (predominantly protons) emitted by the sun, primarily in solar eruptions.
However, the term "cosmic ray" is often used to refer to only the extrasolar flux.
Cosmic rays originate as primary cosmic rays, which are those originally produced in various astrophysical processes. Primary cosmic rays are composed mainly of protons and alpha particles (99%), with a small amount of heavier nuclei (≈1%) and an extremely minute proportion of positrons and antiprotons. Secondary cosmic rays, caused by a decay of primary cosmic rays as they impact an atmosphere, include photons, hadrons, and leptons, such as electrons, positrons, muons, and pions. The latter three of these were first detected in cosmic rays.
Primary cosmic rays
Primary cosmic rays mostly originate from outside the Solar System and sometimes even outside the Milky Way. When they interact with Earth's atmosphere, they are converted to secondary particles. The mass ratio of helium to hydrogen nuclei, 28%, is similar to the primordial elemental abundance ratio of these elements, 24%. The remaining fraction is made up of the other heavier nuclei that are typical nucleosynthesis end products, primarily lithium, beryllium, and boron. These nuclei appear in cosmic rays in greater abundance (≈1%) than in the solar atmosphere, where they are only about 10 as abundant (by number) as helium. Cosmic rays composed of charged nuclei heavier than helium are called HZE ions. Due to the high charge and heavy nature of HZE ions, their contribution to an astronaut's radiation dose in space is significant even though they are relatively scarce. | Cosmic ray | Wikipedia | 482 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
This abundance difference is a result of the way in which secondary cosmic rays are formed. Carbon and oxygen nuclei collide with interstellar matter to form lithium, beryllium, and boron, an example of cosmic ray spallation. Spallation is also responsible for the abundances of scandium, titanium, vanadium, and manganese ions in cosmic rays produced by collisions of iron and nickel nuclei with interstellar matter.
At high energies the composition changes and heavier nuclei have larger abundances in some energy ranges. Current experiments aim at more accurate measurements of the composition at high energies.
Primary cosmic ray antimatter
Satellite experiments have found evidence of positrons and a few antiprotons in primary cosmic rays, amounting to less than 1% of the particles in primary cosmic rays. These do not appear to be the products of large amounts of antimatter from the Big Bang, or indeed complex antimatter in the universe. Rather, they appear to consist of only these two elementary particles, newly made in energetic processes.
Preliminary results from the presently operating Alpha Magnetic Spectrometer (AMS-02) on board the International Space Station show that positrons in the cosmic rays arrive with no directionality. In September 2014, new results with almost twice as much data were presented in a talk at CERN and published in Physical Review Letters. A new measurement of positron fraction up to 500 GeV was reported, showing that positron fraction peaks at a maximum of about 16% of total electron+positron events, around an energy of . At higher energies, up to 500 GeV, the ratio of positrons to electrons begins to fall again. The absolute flux of positrons also begins to fall before 500 GeV, but peaks at energies far higher than electron energies, which peak about 10 GeV. These results on interpretation have been suggested to be due to positron production in annihilation events of massive dark matter particles.
Cosmic ray antiprotons also have a much higher average energy than their normal-matter counterparts (protons). They arrive at Earth with a characteristic energy maximum of 2 GeV, indicating their production in a fundamentally different process from cosmic ray protons, which on average have only one-sixth of the energy. | Cosmic ray | Wikipedia | 464 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
There is no evidence of complex antimatter atomic nuclei, such as antihelium nuclei (i.e., anti-alpha particles), in cosmic rays. These are actively being searched for. A prototype of the AMS-02 designated AMS-01, was flown into space aboard the on STS-91 in June 1998. By not detecting any antihelium at all, the AMS-01 established an upper limit of for the antihelium to helium flux ratio.
Secondary cosmic rays
When cosmic rays enter the Earth's atmosphere, they collide with atoms and molecules, mainly oxygen and nitrogen. The interaction produces a cascade of lighter particles, a so-called air shower secondary radiation that rains down, including x-rays, protons, alpha particles, pions, muons, electrons, neutrinos, and neutrons. All of the secondary particles produced by the collision continue onward on paths within about one degree of the primary particle's original path.
Typical particles produced in such collisions are neutrons and charged mesons such as positive or negative pions and kaons. Some of these subsequently decay into muons and neutrinos, which are able to reach the surface of the Earth. Some high-energy muons even penetrate for some distance into shallow mines, and most neutrinos traverse the Earth without further interaction. Others decay into photons, subsequently producing electromagnetic cascades. Hence, next to photons, electrons and positrons usually dominate in air showers. These particles as well as muons can be easily detected by many types of particle detectors, such as cloud chambers, bubble chambers, water-Cherenkov, or scintillation detectors. The observation of a secondary shower of particles in multiple detectors at the same time is an indication that all of the particles came from that event.
Cosmic rays impacting other planetary bodies in the Solar System are detected indirectly by observing high-energy gamma ray emissions by gamma-ray telescope. These are distinguished from radioactive decay processes by their higher energies above about 10 MeV.
Cosmic-ray flux | Cosmic ray | Wikipedia | 422 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
The flux of incoming cosmic rays at the upper atmosphere is dependent on the solar wind, the Earth's magnetic field, and the energy of the cosmic rays. At distances of ≈94 AU from the Sun, the solar wind undergoes a transition, called the termination shock, from supersonic to subsonic speeds. The region between the termination shock and the heliopause acts as a barrier to cosmic rays, decreasing the flux at lower energies (≤ 1 GeV) by about 90%. However, the strength of the solar wind is not constant, and hence it has been observed that cosmic ray flux is correlated with solar activity.
In addition, the Earth's magnetic field acts to deflect cosmic rays from its surface, giving rise to the observation that the flux is apparently dependent on latitude, longitude, and azimuth angle.
The combined effects of all of the factors mentioned contribute to the flux of cosmic rays at Earth's surface. The following table of participial frequencies reach the planet and are inferred from lower-energy radiation reaching the ground.
{| class="wikitable"
|+Relative particle energies and rates of cosmic rays
|-
!scope="col"| Particle energy (eV)
!scope="col"| Particle rate (ms)
|-
!scope="row"| (GeV)
|
|-
!scope="row"| (TeV)
| 1
|-
!scope="row"| (10 PeV)
| (a few times a year)
|-
!scope="row"| (100 EeV)
| (once a century)
|-
|}
In the past, it was believed that the cosmic ray flux remained fairly constant over time. However, recent research suggests one-and-a-half- to two-fold millennium-timescale changes in the cosmic ray flux in the past forty thousand years.
The magnitude of the energy of cosmic ray flux in interstellar space is very comparable to that of other deep space energies: cosmic ray energy density averages about one electron-volt per cubic centimetre of interstellar space, or ≈1 eV/cm3, which is comparable to the energy density of visible starlight at 0.3 eV/cm3, the galactic magnetic field energy density (assumed 3 microgauss) which is ≈0.25 eV/cm3, or the cosmic microwave background (CMB) radiation energy density at ≈0.25 eV/cm3.
Detection methods | Cosmic ray | Wikipedia | 512 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
There are two main classes of detection methods. First, the direct detection of the primary cosmic rays in space or at high altitude by balloon-borne instruments. Second, the indirect detection of secondary particle, i.e., extensive air showers at higher energies. While there have been proposals and prototypes for space and balloon-borne detection of air showers, currently operating experiments for high-energy cosmic rays are ground based. Generally direct detection is more accurate than indirect detection. However the flux of cosmic rays decreases with energy, which hampers direct detection for the energy range above 1 PeV. Both direct and indirect detection are realized by several techniques.
Direct detection
Direct detection is possible by all kinds of particle detectors at the ISS, on satellites, or high-altitude balloons. However, there are constraints in weight and size limiting the choices of detectors.
An example for the direct detection technique is a method based on nuclear tracks developed by Robert Fleischer, P. Buford Price, and Robert M. Walker for use in high-altitude balloons. In this method, sheets of clear plastic, like 0.25 mm Lexan polycarbonate, are stacked together and exposed directly to cosmic rays in space or high altitude. The nuclear charge causes chemical bond breaking or ionization in the plastic. At the top of the plastic stack the ionization is less, due to the high cosmic ray speed. As the cosmic ray speed decreases due to deceleration in the stack, the ionization increases along the path. The resulting plastic sheets are "etched" or slowly dissolved in warm caustic sodium hydroxide solution, that removes the surface material at a slow, known rate. The caustic sodium hydroxide dissolves the plastic at a faster rate along the path of the ionized plastic. The net result is a conical etch pit in the plastic. The etch pits are measured under a high-power microscope (typically 1600× oil-immersion), and the etch rate is plotted as a function of the depth in the stacked plastic.
This technique yields a unique curve for each atomic nucleus from 1 to 92, allowing identification of both the charge and energy of the cosmic ray that traverses the plastic stack. The more extensive the ionization along the path, the higher the charge. In addition to its uses for cosmic-ray detection, the technique is also used to detect nuclei created as products of nuclear fission. | Cosmic ray | Wikipedia | 485 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
Indirect detection
There are several ground-based methods of detecting cosmic rays currently in use, which can be divided in two main categories: the detection of secondary particles forming extensive air showers (EAS) by various types of particle detectors, and the detection of electromagnetic radiation emitted by EAS in the atmosphere.
Extensive air shower arrays made of particle detectors measure the charged particles which pass through them. EAS arrays can observe a broad area of the sky and can be active more than 90% of the time. However, they are less able to segregate background effects from cosmic rays than can air Cherenkov telescopes. Most state-of-the-art EAS arrays employ plastic scintillators. Also water (liquid or frozen) is used as a detection medium through which particles pass and produce Cherenkov radiation to make them detectable. Therefore, several arrays use water/ice-Cherenkov detectors as alternative or in addition to scintillators.
By the combination of several detectors, some EAS arrays have the capability to distinguish muons from lighter secondary particles (photons, electrons, positrons). The fraction of muons among the secondary particles is one traditional way to estimate the mass composition of the primary cosmic rays.
An historic method of secondary particle detection still used for demonstration purposes involves the use of cloud chambers to detect the secondary muons created when a pion decays. Cloud chambers in particular can be built from widely available materials and can be constructed even in a high-school laboratory. A fifth method, involving bubble chambers, can be used to detect cosmic ray particles.
More recently, the CMOS devices in pervasive smartphone cameras have been proposed as a practical distributed network to detect air showers from ultra-high-energy cosmic rays. The first app to exploit this proposition was the CRAYFIS (Cosmic RAYs Found in Smartphones) experiment. In 2017, the CREDO (Cosmic-Ray Extremely Distributed Observatory) Collaboration released the first version of its completely open source app for Android devices. Since then the collaboration has attracted the interest and support of many scientific institutions, educational institutions, and members of the public around the world. Future research has to show in what aspects this new technique can compete with dedicated EAS arrays. | Cosmic ray | Wikipedia | 455 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
The first detection method in the second category is called the air Cherenkov telescope, designed to detect low-energy (<200 GeV) cosmic rays by means of analyzing their Cherenkov radiation, which for cosmic rays are gamma rays emitted as they travel faster than the speed of light in their medium, the atmosphere. While these telescopes are extremely good at distinguishing between background radiation and that of cosmic-ray origin, they can only function well on clear nights without the Moon shining, have very small fields of view, and are only active for a few percent of the time.
A second method detects the light from nitrogen fluorescence caused by the excitation of nitrogen in the atmosphere by particles moving through the atmosphere. This method is the most accurate for cosmic rays at highest energies, in particular when combined with EAS arrays of particle detectors. Similar to the detection of Cherenkov-light, this method is restricted to clear nights.
Another method detects radio waves emitted by air showers. This technique has a high duty cycle similar to that of particle detectors. The accuracy of this technique was improved in the last years as shown by various prototype experiments, and may become an alternative to the detection of atmospheric Cherenkov-light and fluorescence light, at least at high energies.
Effects
Changes in atmospheric chemistry
Cosmic rays ionize nitrogen and oxygen molecules in the atmosphere, which leads to a number of chemical reactions. Cosmic rays are also responsible for the continuous production of a number of unstable isotopes, such as carbon-14, in the Earth's atmosphere through the reaction:
Cosmic rays kept the level of carbon-14 in the atmosphere roughly constant (70 tons) for at least the past 100,000 years, until the beginning of above-ground nuclear weapons testing in the early 1950s. This fact is used in radiocarbon dating.
Reaction products of primary cosmic rays, radioisotope half-lifetime, and production reaction | Cosmic ray | Wikipedia | 387 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
Role in ambient radiation
Cosmic rays constitute a fraction of the annual radiation exposure of human beings on the Earth, averaging 0.39mSv out of a total of 3mSv per year (13% of total background) for the Earth's population. However, the background radiation from cosmic rays increases with altitude, from 0.3mSv per year for sea-level areas to 1.0mSv per year for higher-altitude cities, raising cosmic radiation exposure to a quarter of total background radiation exposure for populations of said cities. Airline crews flying long-distance high-altitude routes can be exposed to 2.2mSv of extra radiation each year due to cosmic rays, nearly doubling their total exposure to ionizing radiation.
Figures are for the time before the Fukushima Daiichi nuclear disaster. Human-made values by UNSCEAR are from the Japanese National Institute of Radiological Sciences, which summarized the UNSCEAR data.
Effect on electronics
Cosmic rays have sufficient energy to alter the states of circuit components in electronic integrated circuits, causing transient errors to occur (such as corrupted data in electronic memory devices or incorrect performance of CPUs) often referred to as "soft errors". This has been a problem in electronics at extremely high-altitude, such as in satellites, but with transistors becoming smaller and smaller, this is becoming an increasing concern in ground-level electronics as well. Studies by IBM in the 1990s suggest that computers typically experience about one cosmic-ray-induced error per 256 megabytes of RAM per month. To alleviate this problem, the Intel Corporation has proposed a cosmic ray detector that could be integrated into future high-density microprocessors, allowing the processor to repeat the last command following a cosmic-ray event. ECC memory is used to protect data against data corruption caused by cosmic rays.
In 2008, data corruption in a flight control system caused an Airbus A330 airliner to twice plunge hundreds of feet, resulting in injuries to multiple passengers and crew members. Cosmic rays were investigated among other possible causes of the data corruption, but were ultimately ruled out as being very unlikely.
In August 2020, scientists reported that ionizing radiation from environmental radioactive materials and cosmic rays may substantially limit the coherence times of qubits if they are not shielded adequately which may be critical for realizing fault-tolerant superconducting quantum computers in the future.
Significance to aerospace travel | Cosmic ray | Wikipedia | 485 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
Galactic cosmic rays are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft. Cosmic rays also pose a threat to electronics placed aboard outgoing probes. In 2010, a malfunction aboard the Voyager 2 space probe was credited to a single flipped bit, probably caused by a cosmic ray. Strategies such as physical or magnetic shielding for spacecraft have been considered in order to minimize the damage to electronics and human beings caused by cosmic rays.
On 31 May 2013, NASA scientists reported that a possible crewed mission to Mars may involve a greater radiation risk than previously believed, based on the amount of energetic particle radiation detected by the RAD on the Mars Science Laboratory while traveling from the Earth to Mars in 2011–2012.
Flying high, passengers and crews of jet airliners are exposed to at least 10 times the cosmic ray dose that people at sea level receive. Aircraft flying polar routes near the geomagnetic poles are at particular risk.
Role in lightning
Cosmic rays have been implicated in the triggering of electrical breakdown in lightning. It has been proposed that essentially all lightning is triggered through a relativistic process, or "runaway breakdown", seeded by cosmic ray secondaries. Subsequent development of the lightning discharge then occurs through "conventional breakdown" mechanisms.
Postulated role in climate change
A role for cosmic rays in climate was suggested by Edward P. Ney in 1959 and by Robert E. Dickinson in 1975. It has been postulated that cosmic rays may have been responsible for major climatic change and mass extinction in the past. According to Adrian Mellott and Mikhail Medvedev, 62-million-year cycles in biological marine populations correlate with the motion of the Earth relative to the galactic plane and increases in exposure to cosmic rays. The researchers suggest that this and gamma ray bombardments deriving from local supernovae could have affected cancer and mutation rates, and might be linked to decisive alterations in the Earth's climate, and to the mass extinctions of the Ordovician. | Cosmic ray | Wikipedia | 410 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
Danish physicist Henrik Svensmark has controversially argued that because solar variation modulates the cosmic ray flux on Earth, it would consequently affect the rate of cloud formation and hence be an indirect cause of global warming. Svensmark is one of several scientists outspokenly opposed to the mainstream scientific assessment of global warming, leading to concerns that the proposition that cosmic rays are connected to global warming could be ideologically biased rather than scientifically based. Other scientists have vigorously criticized Svensmark for sloppy and inconsistent work: one example is adjustment of cloud data that understates error in lower cloud data, but not in high cloud data; another example is "incorrect handling of the physical data" resulting in graphs that do not show the correlations they claim to show. Despite Svensmark's assertions, galactic cosmic rays have shown no statistically significant influence on changes in cloud cover, and have been demonstrated in studies to have no causal relationship to changes in global temperature.
Possible mass extinction factor
A handful of studies conclude that a nearby supernova or series of supernovas caused the Pliocene marine megafauna extinction event by substantially increasing radiation levels to hazardous amounts for large seafaring animals.
Research and experiments
There are a number of cosmic-ray research initiatives, listed below.
Ground-based
Akeno Giant Air Shower Array
Chicago Air Shower Array
CHICOS
CLOUD
CRIPT
GAMMA
GRAPES-3
HAWC
HEGRA
High Energy Stereoscopic System
High Resolution Fly's Eye Cosmic Ray Detector
IceCube
KASCADE
MAGIC
MARIACHI
Milagro
NMDB
Pierre Auger Observatory
QuarkNet
Spaceship Earth
Telescope Array Project
Tunka experiment
VERITAS
Washington Large Area Time Coincidence Array
Satellite
ACE (Advanced Composition Explorer)
Alpha Magnetic Spectrometer
Cassini–Huygens
Fermi Gamma-ray Space Telescope
HEAO 1, HEAO 2, HEAO 3
Interstellar Boundary Explorer
Langton Ultimate Cosmic-Ray Intensity Detector
PAMELA
Solar and Heliospheric Observatory
Voyager 1 and Voyager 2
Balloon-borne
Advanced Thin Ionization Calorimeter
BESS
Cosmic Ray Energetics and Mass (CREAM)
HEAT (High Energy Antimatter Telescope)
PERDaix
TIGER
TRACER (cosmic ray detector) | Cosmic ray | Wikipedia | 438 | 47687 | https://en.wikipedia.org/wiki/Cosmic%20ray | Physical sciences | Basics_3 | null |
Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.
A coral "group" is a colony of very many genetically identical polyps. Each polyp is a sac-like animal typically only a few millimeters in diameter and a few centimeters in height. A set of tentacles surround a central mouth opening. Each polyp excretes an exoskeleton near the base. Over many generations, the colony thus creates a skeleton characteristic of the species which can measure up to several meters in size. Individual colonies grow by asexual reproduction of polyps. Corals also breed sexually by spawning: polyps of the same species release gametes simultaneously overnight, often around a full moon. Fertilized eggs form planulae, a mobile early form of the coral polyp which, when mature, settles to form a new colony.
Although some corals are able to catch plankton and small fish using stinging cells on their tentacles, most corals obtain the majority of their energy and nutrients from photosynthetic unicellular dinoflagellates of the genus Symbiodinium that live within their tissues. These are commonly known as zooxanthellae and give the coral color. Such corals require sunlight and grow in clear, shallow water, typically at depths less than , but corals in the genus Leptoseris have been found as deep as . Corals are major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the Great Barrier Reef off the coast of Australia. These corals are increasingly at risk of bleaching events where polyps expel the zooxanthellae in response to stress such as high water temperature or toxins.
Other corals do not rely on zooxanthellae and can live globally in much deeper water, such as the cold-water genus Lophelia which can survive as deep as . Some have been found as far north as the Darwin Mounds, northwest of Cape Wrath, Scotland, and others off the coast of Washington state and the Aleutian Islands. | Coral | Wikipedia | 468 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Taxonomy
The classification of corals has been discussed for millennia, owing to having similarities to both plants and animals. Aristotle's pupil Theophrastus described the red coral, korallion, in his book on stones, implying it was a mineral, but he described it as a deep-sea plant in his Enquiries on Plants, where he also mentions large stony plants that reveal bright flowers when under water in the Gulf of Heroes. Pliny the Elder stated boldly that several sea creatures including sea nettles and sponges "are neither animals nor plants, but are possessed of a third nature (tertia natura)". Petrus Gyllius copied Pliny, introducing the term zoophyta for this third group in his 1535 book On the French and Latin Names of the Fishes of the Marseilles Region; it is popularly but wrongly supposed that Aristotle created the term. Gyllius further noted, following Aristotle, how hard it was to define what was a plant and what was an animal. The Babylonian Talmud refers to coral among a list of types of trees, and the 11th-century French commentator Rashi describes it as "a type of tree (מין עץ) that grows underwater that goes by the (French) name 'coral'."
The Persian polymath Al-Biruni (d.1048) classified sponges and corals as animals, arguing that they respond to touch. Nevertheless, people believed corals to be plants until the eighteenth century when William Herschel used a microscope to establish that coral had the characteristic thin cell membranes of an animal.
Presently, corals are classified as species of animals within the sub-classes Hexacorallia and Octocorallia of the class Anthozoa in the phylum Cnidaria. Hexacorallia includes the stony corals and these groups have polyps that generally have a 6-fold symmetry. Octocorallia includes blue coral and soft corals and species of Octocorallia have polyps with an eightfold symmetry, each polyp having eight tentacles and eight mesenteries. The group of corals is paraphyletic because the sea anemones are also in the sub-class Hexacorallia.
Systematics | Coral | Wikipedia | 463 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
The delineation of coral species is challenging as hypotheses based on morphological traits contradict hypotheses formed via molecular tree-based processes. As of 2020, there are 2175 identified separate coral species, 237 of which are currently endangered, making distinguishing corals to be the utmost of importance in efforts to curb extinction. Adaptation and delineation continues to occur in species of coral in order to combat the dangers posed by the climate crisis. Corals are colonial modular organisms formed by asexually produced and genetically identical modules called polyps. Polyps are connected by living tissue to produce the full organism. The living tissue allows for inter module communication (interaction between each polyp), which appears in colony morphologies produced by corals, and is one of the main identifying characteristics for a species of coral.
There are two main classifications for corals: hard coral (scleractinian and stony coral) which form reefs by a calcium carbonate base, with polyps that bear six stiff tentacles, and soft coral (Alcyonacea and ahermatypic coral) which are pliable and formed by a colony of polyps with eight feather-like tentacles. These two classifications arose from differentiation in gene expressions in their branch tips and bases that arose through developmental signaling pathways such as Hox, Hedgehog, Wnt, BMP etc.
Scientists typically select Acropora as research models since they are the most diverse genus of hard coral, having over 120 species. Most species within this genus have polyps which are dimorphic: axial polyps grow rapidly and have lighter coloration, while radial polyps are small and are darker in coloration. In the Acropora genus, gamete synthesis and photosynthesis occur at the basal polyps, growth occurs mainly at the radial polyps. Growth at the site of the radial polyps encompasses two processes: asexual reproduction via mitotic cell proliferation, and skeleton deposition of the calcium carbonate via extra cellular matrix (EMC) proteins acting as differentially expressed (DE) signaling genes between both branch tips and bases. These processes lead to colony differentiation, which is the most accurate distinguisher between coral species. In the Acropora genus, colony differentiation through up-regulation and down-regulation of DEs.
Systematic studies of soft coral species have faced challenges due to a lack of taxonomic knowledge. Researchers have not found enough variability within the genus to confidently delineate similar species, due to a low rate in mutation of mitochondrial DNA. | Coral | Wikipedia | 506 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Environmental factors, such as the rise of temperatures and acid levels in our oceans account for some speciation of corals in the form of species lost. Various coral species have heat shock proteins (HSP) that are also in the category of DE across species. These HSPs help corals combat the increased temperatures they are facing which lead to protein denaturing, growth loss, and eventually coral death. Approximately 33% of coral species are on the International Union for Conservation of Nature's endangered species list and at risk of species loss. Ocean acidification (falling pH levels in the oceans) is threatening the continued species growth and differentiation of corals. Mutation rates of Vibrio shilonii, the reef pathogen responsible for coral bleaching, heavily outweigh the typical reproduction rates of coral colonies when pH levels fall. Thus, corals are unable to mutate their HSPs and other climate change preventative genes to combat the increase in temperature and decrease in pH at a competitive rate to these pathogens responsible for coral bleaching, resulting in species loss.
Anatomy
For most of their life corals are sessile animals of colonies of genetically identical polyps. Each polyp varies from millimeters to centimeters in diameter, and colonies can be formed from many millions of individual polyps. Stony coral, also known as hard coral, polyps produce a skeleton composed of calcium carbonate to strengthen and protect the organism. This is deposited by the polyps and by the coenosarc, the living tissue that connects them. The polyps sit in cup-shaped depressions in the skeleton known as corallites. Colonies of stony coral are markedly variable in appearance; a single species may adopt an encrusting, plate-like, bushy, columnar or massive solid structure, the various forms often being linked to different types of habitat, with variations in light level and water movement being significant.
The body of the polyp may be roughly compared in a structure to a sac, the wall of which is composed of two layers of cells. The outer layer is known technically as the ectoderm, the inner layer as the endoderm. Between ectoderm and endoderm is a supporting layer of gelatinous substance termed mesoglea, secreted by the cell layers of the body wall. The mesoglea can contain skeletal elements derived from cells migrated from the ectoderm. | Coral | Wikipedia | 492 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
The sac-like body built up in this way is attached to a hard surface, which in hard corals are cup-shaped depressions in the skeleton known as corallites. At the center of the upper end of the sac lies the only opening called the mouth, surrounded by a circle of tentacles which resemble glove fingers. The tentacles are organs which serve both for tactile sense and for the capture of food. Polyps extend their tentacles, particularly at night, often containing coiled stinging cells (cnidocytes) which pierce, poison and firmly hold living prey paralyzing or killing them. Polyp prey includes plankton such as copepods and fish larvae. Longitudinal muscular fibers formed from the cells of the ectoderm allow tentacles to contract to convey the food to the mouth. Similarly, circularly disposed muscular fibres formed from the endoderm permit tentacles to be protracted or thrust out once they are contracted. In both stony and soft corals, the polyps can be retracted by contracting muscle fibres, with stony corals relying on their hard skeleton and cnidocytes for defense. Soft corals generally secrete terpenoid toxins to ward off predators.
In most corals, the tentacles are retracted by day and spread out at night to catch plankton and other small organisms. Shallow-water species of both stony and soft corals can be zooxanthellate, the corals supplementing their plankton diet with the products of photosynthesis produced by these symbionts. The polyps interconnect by a complex and well-developed system of gastrovascular canals, allowing significant sharing of nutrients and symbionts.
The external form of the polyp varies greatly. The column may be long and slender, or may be so short in the axial direction that the body becomes disk-like. The tentacles may number many hundreds or may be very few, in rare cases only one or two. They may be simple and unbranched, or feathery in pattern. The mouth may be level with the surface of the peristome, or may be projecting and trumpet-shaped.
Soft corals
Soft corals have no solid exoskeleton as such. However, their tissues are often reinforced by small supportive elements known as sclerites made of calcium carbonate. The polyps of soft corals have eight-fold symmetry, which is reflected in the Octo in Octocorallia. | Coral | Wikipedia | 498 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Soft corals vary considerably in form, and most are colonial. A few soft corals are stolonate, but the polyps of most are connected by sheets of tissue called coenosarc, and in some species these sheets are thick and the polyps deeply embedded in them. Some soft corals encrust other sea objects or form lobes. Others are tree-like or whip-like and have a central axial skeleton embedded at their base in the matrix of the supporting branch. These branches are composed of a fibrous protein called gorgonin or of a calcified material.
Stony corals
The polyps of stony corals have six-fold symmetry. In stony corals, the tentacles are cylindrical and taper to a point, but in soft corals they are pinnate with side branches known as pinnules. In some tropical species, these are reduced to mere stubs and in some, they are fused to give a paddle-like appearance.
Coral skeletons are biocomposites (mineral + organics) of calcium carbonate, in the form of calcite or aragonite. In scleractinian corals, "centers of calcification" and fibers are clearly distinct structures differing with respect to both morphology and chemical compositions of the crystalline units. The organic matrices extracted from diverse species are acidic, and comprise proteins, sulphated sugars and lipids; they are species specific. The soluble organic matrices of the skeletons allow to differentiate zooxanthellae and non-zooxanthellae specimens.
Ecology
Feeding
Polyps feed on a variety of small organisms, from microscopic zooplankton to small fish. The polyp's tentacles immobilize or kill prey using stinging cells called nematocysts. These cells carry venom which they rapidly release in response to contact with another organism. A dormant nematocyst discharges in response to nearby prey touching the trigger (Cnidocil). A flap (operculum) opens and its stinging apparatus fires the barb into the prey. The venom is injected through the hollow filament to immobilise the prey; the tentacles then manoeuvre the prey into the stomach. Once the prey is digested the stomach reopens allowing the elimination of waste products and the beginning of the next hunting cycle. | Coral | Wikipedia | 477 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Intracellular symbionts
Many corals, as well as other cnidarian groups such as sea anemones form a symbiotic relationship with a class of dinoflagellate algae, zooxanthellae of the genus Symbiodinium, which can form as much as 30% of the tissue of a polyp. Typically, each polyp harbors one species of alga, and coral species show a preference for Symbiodinium. Young corals are not born with zooxanthellae, but acquire the algae from the surrounding environment, including the water column and local sediment. The main benefit of the zooxanthellae is their ability to photosynthesize which supplies corals with the products of photosynthesis, including glucose, glycerol, also amino acids, which the corals can use for energy. Zooxanthellae also benefit corals by aiding in calcification, for the coral skeleton, and waste removal. In addition to the soft tissue, microbiomes are also found in the coral's mucus and (in stony corals) the skeleton, with the latter showing the greatest microbial richness. | Coral | Wikipedia | 245 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
The zooxanthellae benefit from a safe place to live and consume the polyp's carbon dioxide, phosphate and nitrogenous waste. Stressed corals will eject their zooxanthellae, a process that is becoming increasingly common due to strain placed on coral by rising ocean temperatures. Mass ejections are known as coral bleaching because the algae contribute to coral coloration; some colors, however, are due to host coral pigments, such as green fluorescent proteins (GFPs). Ejection increases the polyp's chance of surviving short-term stress and if the stress subsides they can regain algae, possibly of a different species, at a later time. If the stressful conditions persist, the polyp eventually dies. Zooxanthellae are located within the coral cytoplasm and due to the algae's photosynthetic activity the internal pH of the coral can be raised; this behavior indicates that the zooxanthellae are responsible to some extent for the metabolism of their host corals. Stony Coral Tissue Loss Disease has been associated with the breakdown of host-zooxanthellae physiology. Moreover, Vibrio bacterium are known to have virulence traits used for host coral tissue damage and photoinhibition of algal symbionts. Therefore, both coral and their symbiotic microorganisms could have evolved to harbour traits resistant to disease and transmission.
Reproduction
Corals can be both gonochoristic (unisexual) and hermaphroditic, each of which can reproduce sexually and asexually. Reproduction also allows coral to settle in new areas. Reproduction is coordinated by chemical communication.
Sexual
Corals predominantly reproduce sexually. About 25% of hermatypic corals (reef-building stony corals) form single-sex (gonochoristic) colonies, while the rest are hermaphroditic. It is estimated more than 67% of coral are simultaneous hermaphrodites.
Broadcasters | Coral | Wikipedia | 414 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
About 75% of all hermatypic corals "broadcast spawn" by releasing gametes—eggs and sperm—into the water where they meet and fertilize to spread offspring. Corals often synchronize their time of spawning. This reproductive synchrony is essential so that male and female gametes can meet. Spawning frequently takes place in the evening or at night, and can occur as infrequently as once a year, and within a window of 10–30 minutes.
Synchronous spawning is very typical on the coral reef, and often, all corals spawn on the same night even when multiple species are present. Synchronous spawning may form hybrids and is perhaps involved in coral speciation.
Environmental cues that influence the release of gametes into the water vary from species to species. The cues involve temperature change, lunar cycle, day length, and possibly chemical signalling.
Other factors that affect the rhythmicity of organisms in marine habitats include salinity, mechanical forces, and pressure or magnetic field changes.
Mass coral spawning often occurs at night on days following a full moon. A full moon is equivalent to four to six hours of continuous dim light exposure, which can cause light-dependent reactions in protein. Corals contain light-sensitive cryptochromes, proteins whose light-absorbing flavin structures are sensitive to different types of light. This allows corals such as Dipsastraea speciosa to detect and respond to changes in sunlight and moonlight.
Moonlight itself may actually suppress coral spawning. The most immediate cue to cause spawning appears to be the dark portion of the night between sunset and moonrise.
Over the lunar cycle, moonrise shifts progressively later, occurring after sunset on the day of the full moon. The resulting dark period between day-light and night-light removes the suppressive effect of moonlight and enables coral to spawn.
The spawning event can be visually dramatic, clouding the usually clear water with gametes. Once released, gametes fertilize at the water's surface and form a microscopic larva called a planula, typically pink and elliptical in shape. A typical coral colony needs to release several thousand larvae per year to overcome the odds against formation of a new colony. | Coral | Wikipedia | 456 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Studies suggest that light pollution desynchronizes spawning in some coral species.
In areas such as the Red Sea, as many as 10 out of 50 species may be showing spawning asynchrony, compared to 30 years ago. The establishment of new corals in the area has decreased and in some cases ceased. The area was previously considered a refuge for corals because mass bleaching events due to climate change had not been observed there. Coral restoration techniques for coral reef management are being developed to increase fertilization rates, larval development, and settlement of new corals.
Brooders
Brooding species are most often ahermatypic (not reef-building) in areas of high current or wave action. Brooders release only sperm, which is negatively buoyant, sinking onto the waiting egg carriers that harbor unfertilized eggs for weeks. Synchronous spawning events sometimes occur even with these species. After fertilization, the corals release planula that are ready to settle.
Planulae
The time from spawning to larval settlement is usually two to three days but can occur immediately or up to two months. Broadcast-spawned planula larvae develop at the water's surface before descending to seek a hard surface on the benthos to which they can attach and begin a new colony. The larvae often need a biological cue to induce settlement such as specific crustose coralline algae species or microbial biofilms. High failure rates afflict many stages of this process, and even though thousands of eggs are released by each colony, few new colonies form. During settlement, larvae are inhibited by physical barriers such as sediment, as well as chemical (allelopathic) barriers. The larvae metamorphose into a single polyp and eventually develops into a juvenile and then adult by asexual budding and growth.
Asexual
Within a coral head, the genetically identical polyps reproduce asexually, either by budding (gemmation) or by dividing, whether longitudinally or transversely.
Budding involves splitting a smaller polyp from an adult. As the new polyp grows, it forms its body parts. The distance between the new and adult polyps grows, and with it, the coenosarc (the common body of the colony). Budding can be intratentacular, from its oral discs, producing same-sized polyps within the ring of tentacles, or extratentacular, from its base, producing a smaller polyp. | Coral | Wikipedia | 509 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
Division forms two polyps that each become as large as the original. Longitudinal division begins when a polyp broadens and then divides its coelenteron (body), effectively splitting along its length. The mouth divides and new tentacles form. The two polyps thus created then generate their missing body parts and exoskeleton. Transversal division occurs when polyps and the exoskeleton divide transversally into two parts. This means one has the basal disc (bottom) and the other has the oral disc (top); the new polyps must separately generate the missing pieces.
Asexual reproduction offers the benefits of high reproductive rate, delaying senescence, and replacement of dead modules, as well as geographical distribution.
Colony division
Whole colonies can reproduce asexually, forming two colonies with the same genotype. The possible mechanisms include fission, bailout and fragmentation. Fission occurs in some corals, especially among the family Fungiidae, where the colony splits into two or more colonies during early developmental stages. Bailout occurs when a single polyp abandons the colony and settles on a different substrate to create a new colony. Fragmentation involves individuals broken from the colony during storms or other disruptions. The separated individuals can start new colonies.
Coral microbiomes
Corals are one of the more common examples of an animal host whose symbiosis with microalgae can turn to dysbiosis, and is visibly detected as bleaching. Coral microbiomes have been examined in a variety of studies, which demonstrate how oceanic environmental variations, most notably temperature, light, and inorganic nutrients, affect the abundance and performance of the microalgal symbionts, as well as calcification and physiology of the host.
Studies have also suggested that resident bacteria, archaea, and fungi additionally contribute to nutrient and organic matter cycling within the coral, with viruses also possibly playing a role in structuring the composition of these members, thus providing one of the first glimpses at a multi-domain marine animal symbiosis. The gammaproteobacterium Endozoicomonas is emerging as a central member of the coral's microbiome, with flexibility in its lifestyle. Given the recent mass bleaching occurring on reefs, corals will likely continue to be a useful and popular system for symbiosis and dysbiosis research. | Coral | Wikipedia | 486 | 47700 | https://en.wikipedia.org/wiki/Coral | Biology and health sciences | Cnidarians | null |
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