In materials science, a dislocation or Taylor's dislocation is a crystallographic defect or irregularity within a crystal structure. The presence of dislocations influences many of the properties of materials; the theory describing the elastic fields of the defects was developed by Vito Volterra in 1907. The term'dislocation' referring to a defect on the atomic scale was coined by G. I. Taylor in 1934; some types of dislocations can be visualized as being caused by the termination of a plane of atoms in the middle of a crystal. In such a case, the surrounding planes are not straight, but instead they bend around the edge of the terminating plane so that the crystal structure is ordered on either side; this phenomenon is analogous to the following situation related to a stack of paper: If half of a piece of paper is inserted into a stack of paper, the defect in the stack is noticeable only at the edge of the half sheet. The two primary types of dislocations are edge dislocations and screw dislocations.
Mixed dislocations are intermediate between these. Mathematically, dislocations are a type of topological defect, sometimes called a soliton. Dislocations behave as stable particles: they can move around, but maintain their identity. Two dislocations of opposite orientation can cancel when brought together, but a single dislocation cannot "disappear" on its own. Two main types of dislocations exist: screw. Dislocations found in real materials are mixed, meaning that they have characteristics of both. A crystalline material consists of a regular array of atoms, arranged into lattice planes. One approach is to begin by considering a 3D representation of a perfect crystal lattice, with the atoms represented by spheres; the viewer may start to simplify the representation by visualising planes of atoms instead of the atoms themselves. An edge dislocation is a defect where an extra half-plane of atoms is introduced midway through the crystal, distorting nearby planes of atoms; when enough force is applied from one side of the crystal structure, this extra plane passes through planes of atoms breaking and joining bonds with them until it reaches the grain boundary.
A simple schematic diagram of such atomic planes can be used to illustrate lattice defects such as dislocations.. The dislocation has two properties, a line direction, the direction running along the bottom of the extra half plane, the Burgers vector which describes the magnitude and direction of distortion to the lattice. In an edge dislocation, the Burgers vector is perpendicular to the line direction; the stresses caused by an edge dislocation are complex due to its inherent asymmetry. These stresses are described by three equations: σ x x = − μ b 2 π y 2 σ y y = μ b 2 π y 2 τ x y = μ b 2 π x 2 where μ is the shear modulus of the material, b is the Burgers vector, ν is Poisson's ratio and x and y are coordinates; these equations suggest a vertically oriented dumbbell of stresses surrounding the dislocation, with compression experienced by the atoms near the "extra" plane, tension experienced by those atoms near the "missing" plane. A screw dislocation is much harder to visualize. Imagine cutting a crystal along a plane and slipping one half across the other by a lattice vector, the halves fitting back together without leaving a defect.
This is similar to the Riemann surface of the complex logarithm. If the cut only goes part way through the crystal, slipped, the boundary of the cut is a screw dislocation, it comprises a structure in which a helical path is traced around the linear defect by the atomic planes in the crystal lattice. The closest analogy is a spiral-sliced ham. In pure screw dislocations, the Burgers vector is parallel to the line direction. Despite the difficulty in visualization, the stresses caused by a screw dislocation are less complex than those of an edge dislocation; these s
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists are interested in the root or ultimate causes of phenomena, frame their understanding in mathematical terms. Physicists work across a wide range of research fields, spanning all length scales: from sub-atomic and particle physics, through biological physics, to cosmological length scales encompassing the universe as a whole; the field includes two types of physicists: experimental physicists who specialize in the observation of physical phenomena and the analysis of experiments, theoretical physicists who specialize in mathematical modeling of physical systems to rationalize and predict natural phenomena. Physicists can apply their knowledge towards solving practical problems or to developing new technologies; the study and practice of physics is based on an intellectual ladder of discoveries and insights from ancient times to the present.
Many mathematical and physical ideas used today found their earliest expression in ancient Greek culture, for example in the work of Euclid, Thales of Miletus and Aristarchus. Roots emerged in ancient Asian culture and in the Islamic medieval period, for example the work of Alhazen in the 11th century; the modern scientific worldview and the bulk of physics education can be said to flow from the scientific revolution in Europe, starting with the work of Galileo Galilei and Johannes Kepler in the early 1600s. Newton's laws of motion and Newton's law of universal gravitation were formulated in the 17th century; the experimental discoveries of Faraday and the theory of Maxwell's equations of electromagnetism were developmental high points during the 19th century. Many physicists contributed to the development of quantum mechanics in the early-to-mid 20th century. New knowledge in the early 21st century includes a large increase in understanding physical cosmology; the broad and general study of nature, natural philosophy, was divided into several fields in the 19th century, when the concept of "science" received its modern shape.
Specific categories emerged, such as "biology" and "biologist", "physics" and "physicist", "chemistry" and "chemist", among other technical fields and titles. The term physicist was coined by William Whewell in his 1840 book The Philosophy of the Inductive Sciences. A standard undergraduate physics curriculum consists of classical mechanics and magnetism, non-relativistic quantum mechanics, statistical mechanics and thermodynamics, laboratory experience. Physics students need training in mathematics, in computer science. Any physics-oriented career position requires at least an undergraduate degree in physics or applied physics, while career options widen with a Master's degree like MSc, MPhil, MPhys or MSci. For research-oriented careers, students work toward a doctoral degree specializing in a particular field. Fields of specialization include experimental and theoretical astrophysics, atomic physics, biological physics, chemical physics, condensed matter physics, geophysics, gravitational physics, material science, medical physics, molecular physics, nuclear physics, radiophysics, electromagnetic field and microwave physics, particle physics, plasma physics.
The highest honor awarded to physicists is the Nobel Prize in Physics, awarded since 1901 by the Royal Swedish Academy of Sciences. National physics professional societies have many awards for professional recognition. In the case of the American Physical Society, as of 2017, there are 33 separate prizes and 38 separate awards in the field; the three major employers of career physicists are academic institutions and private industries, with the largest employer being the last. Physicists in academia or government labs tend to have titles such as Assistants, Professors, Sr./Jr. Scientist, or postdocs; as per the American Institute of Physics, some 20% of new physics Ph. D.s holds jobs in engineering development programs, while 14% turn to computer software and about 11% are in business/education. A majority of physicists employed apply their skills and training to interdisciplinary sectors. Job titles for graduate physicists include Agricultural Scientist, Air Traffic Controller, Computer Programmer, Electrical Engineer, Environmental Analyst, Medical Physicist, Oceanographer, Physics Teacher/Professor/Researcher, Research Scientist, Reactor Physicist, Engineering Physicist, Satellite Missions Analyst, Science Writer, Software Engineer, Systems Engineer, Microelectronics Engineer, Radar Developer, Technical Consultant, etc.
A majority of Physics terminal bachelor's degree holders are employed in the private sector. Other fields are academia and military service, nonprofit entities and teaching. Typical duties of physicists with master's and doctoral degrees working in their domain involve research and analysis, data preparation, instrumentation and development of industrial or medical equipment and software development, etc. Chartered Physicist is a chartered status and a professional qualification awarded by the Institute of Physics, it is denoted by the postnominals "CPhys". Achieving chartered status in any profession denotes to the wider community a high level of specialised subject knowledge and professional competence. According to the Institute of Physics, holders of the award of the Chartered Physicist demonst
Mountaineering is the set of activities that involves ascending mountains. Mountaineering-related activities include traditional outdoor climbing, hiking and traversing via ferratas. Indoor climbing, sport climbing and bouldering are considered mountaineering as well. While mountaineering began as attempts to reach the highest point of unclimbed big mountains, it has branched into specializations that address different aspects of mountains, depending on whether the route chosen is over rock, snow, or ice or on level ground. All require various degrees of experience, athletic ability, technical knowledge to maintain safety, it is still common to seek the summits of peaks, whether unclimbed or not. Mountaineering is called alpinism, mountain climbers are sometimes called alpinists, although use of the term may vary between countries and eras; the word "alpinism" was born in the 19th century to refer to climbing for the purpose of enjoying climbing itself as a sport or recreation, distinct from climbing while hunting or as a religious pilgrimage, done at that time.
The UIAA, the International Climbing and Mountaineering Federation, is the International Olympic Committee-recognized world governing body for mountaineering and climbing, addressing issues like access, mountain protection, safety and ice climbing. Many cultures have harbored superstitions about mountains, which they regarded as sacred due to their perceived proximity with heaven, such as Mount Olympus for the Ancient Greeks. On April 26, 1336 famous Italian poet Petrarch climbed to the summit of 1,912 m Mount Ventoux overlooking the Bay of Marseilles, claiming to be inspired by Philip V of Macedon's ascent of Mount Haemo, making him the first known alpinist. One of the first European mountains visited by many tourists was Sněžka; this was due to the minor technical difficulties ascent and the fact that since the sixteenth century, many resort visitors flocked to the nearby Cieplice Śląskie-Zdrój and visible Sněžka, visually dominant over all Krkonoše was for them an important attraction. The first confirmed ascent took place in the year 1456.
In 1492 Antoine de Ville, lord of Domjulien and Beaupré, was the first to ascend the Mont Aiguille, in France, with a little team, using ladders and ropes. It appears to be the first recorded climb of any technical difficulty, has been said to mark the beginning of mountaineering. In 1573 Francesco De Marchi and Francesco Di Domenico ascended Corno Grande, the highest peak in the Apennine Mountains. During the Enlightenment, as a product of the new spirit of curiosity for the natural world, many mountain summits were surmounted for the first time.. In 1741 Richard Pococke and William Windham made a historic visit to Chamonix. In 1757 Swiss scientist Horace-Bénédict de Saussure made the first of several unsuccessful attempts on Mont Blanc in France offering a reward, claimed in 1786 by Jacques Balmat and Michel-Gabriel Paccard. By the early 19th century many of the alpine peaks were reached, including the Grossglockner in 1800, the Ortler in 1804, the Jungfrau in 1811, the Finsteraarhorn in 1812, the Breithorn in 1813.
In 1808 Marie Paradis became the first female to climb Mont Blanc, followed in 1838 by Henriette d'Angeville. The beginning of mountaineering as a sport in the UK is dated to the ascent of the Wetterhorn in 1854 by English mountaineer Sir Alfred Wills, who made mountaineering fashionable in Britain; this inaugurated what became known as the Golden age of alpinism, with the first mountaineering club - the Alpine Club - being founded in 1857. Prominent figures of the period include Lord Francis Douglas, Florence Crauford Grove, Charles Hudson, E. S. Kennedy, William Mathews, A. W. Moore, Leslie Stephen, Francis Fox Tuckett, John Tyndall, Horace Walker and Edward Whymper. Well-known guides of the era include Christian Almer, Jakob Anderegg, Melchior Anderegg, J. J. Bennen, Michel Croz, Johannes Zumtaugwald. In the early years of the "golden age", scientific pursuits were intermixed with the sport, such as by the physicist John Tyndall. In the years, it shifted to a more competitive orientation as pure sportsmen came to dominate the London-based Alpine Club and alpine mountaineering overall.
One of the most dramatic events was the spectacular first ascent of the Matterhorn in 1865 by a party led by English illustrator Edward Whymper, in which four of the party members fell to their deaths. This ascent is regarded as marking the end of the mountaineering golden age. By this point the sport of mountaineering had reached its modern form, with a body of professional guides and fixed guidelines. Mountaineering in the Americas became popular in the 1800s. In North America, Pikes Peak in the Colorado Rockies was first climbed by Edwin James and two others in 1820. Though lower than Pikes Peak, the glaciated Fremont Peak in Wyoming was thought to be the tallest mountain in the Rockies when it was first climbed by John C. Frémont and two others in 1842. Pico de Orizaba, the tallest peak in Mexico and third tallest in North America, was first climbed by U. S. military personnel which included William F. Raynolds and a half dozen other climbers in 1848. Glaciated and more technical climbs in North American were not achieved until the late 19th and early 20th centuries.
In 1897 Mount Saint Elias on the Alaska-Yukon border was summitted by the Duke of the Abruzzi and party. But it was not until 1913 that Denali, the tallest peak in North America, was climbed
University of Edinburgh
The University of Edinburgh, founded in 1582, is the sixth oldest university in the English-speaking world and one of Scotland's ancient universities. The university has five main campuses in the city of Edinburgh, with many of the buildings in the historic Old Town belonging to the university; the university played an important role in leading Edinburgh to its reputation as a chief intellectual centre during the Age of Enlightenment, helped give the city the nickname of the Athens of the North. The University of Edinburgh is ranked 18th in the world by the 2019 QS World University Rankings, it is ranked as the 6th best university in Europe by the U. S. News' Best Global Universities Ranking, 7th best in Europe by the Times Higher Education Ranking; the Research Excellence Framework, a research ranking used by the UK government to determine future research funding, ranked Edinburgh 4th in the UK for research power, 11th overall. It is ranked the 78th most employable university in the world by the 2017 Global Employability University Ranking.
It is a member of both the Russell Group, the League of European Research Universities, a consortium of 21 research universities in Europe. It has the third largest endowment of any university in the United Kingdom, after the universities of Cambridge and Oxford; the annual income of the institution for 2017–18 was £949.0 million of which £279.7 million was from research grants and contracts, with an expenditure of £931.3 million. Alumni of the university include some of the major figures of modern history, including 3 signatories of the American declaration of independence and 9 heads of state; as of March 2019, Edinburgh's alumni, faculty members and researches include 19 Nobel laureates, 3 Turing Award laureates, 1 Fields Medalist, 1 Abel Prize winner, 2 Pulitzer Prize winners, 2 currently-sitting UK Supreme Court Justices, several Olympic gold medallists. It continues to have links to the British Royal Family, having had the Duke of Edinburgh as its Chancellor from 1953 to 2010 and Princess Anne since 2011.
Edinburgh receives 60,000 applications every year, making it the second most popular university in the UK by volume of applications. It has 4th highest average UCAS entry tariff in Scotland, 5th overall in the UK. Founded by the Edinburgh Town Council, the university began life as a college of law using part of a legacy left by a graduate of the University of St Andrews, Bishop Robert Reid of St Magnus Cathedral, Orkney. Through efforts by the Town Council and Ministers of the City the institution broadened in scope and became formally established as a college by a Royal Charter, granted by King James VI of Scotland on 14 April 1582 after the petitioning of the Council; this was unprecedented in newly Presbyterian Scotland, as older universities in Scotland had been established through Papal bulls. Established as the "Tounis College", it opened its doors to students in October 1583. Instruction began under the charge of another St Andrews graduate Robert Rollock, it was the fourth Scottish university in a period when the richer and much more populous England had only two.
It was renamed King James's College in 1617. By the 18th century, the university was a leading centre of the Scottish Enlightenment. In 1762, Reverend Hugh Blair was appointed by King George III as the first Regius Professor of Rhetoric and Belles-Lettres; this formalised literature as a subject at the university and the foundation of the English Literature department, making Edinburgh the oldest centre of literary education in Britain. Before the building of Old College to plans by Robert Adam implemented after the Napoleonic Wars by the architect William Henry Playfair, the University of Edinburgh existed in a hotchpotch of buildings from its establishment until the early 19th century; the university's first custom-built building was the Old College, now Edinburgh Law School, situated on South Bridge. Its first forte in teaching was anatomy and the developing science of surgery, from which it expanded into many other subjects. From the basement of a nearby house ran the anatomy tunnel corridor.
It went under what was North College Street, under the university buildings until it reached the university's anatomy lecture theatre, delivering bodies for dissection. It was from this tunnel. Towards the end of the 19th century, Old College was becoming overcrowded and Sir Robert Rowand Anderson was commissioned to design new Medical School premises in 1875; the design incorporated a Graduation Hall, but this was seen as too ambitious. A separate building was constructed for the purpose, the McEwan Hall designed by Anderson, after funds were donated by the brewer and politician Sir William McEwan in 1894, it was presented to the University in 1897. New College was opened in 1846 as a Free Church of Scotland college of the United Free Church of Scotland. Since the 1930s it has been the home of the School of Divinity. Prior to the 1929 reunion of the Church of Scotland, candidates for the ministry in the United Free Church studied at New College, whilst candidates for the old Church of Scotland studied in the Divinity Faculty of the University of Edinburgh.
During the 1930s the two institutions came together. By the end of the 1950s, there were around 7,000 students matriculating annually. An Edinburgh Students' Representative Council was founded in 1884 by student Robert Fitzroy Bell. In 1889, the SRC voted to be housed in Teviot Row House; the Edinburgh University Sports Union, founded in 1866. The Edinburgh
Prof Henry Charles Fleeming Jenkin FRS FRSE LLD was Regius Professor of Engineering at the University of Edinburgh, remarkable for his versatility. Known to the world as the inventor of the cable car or telpherage, he was an electrician and cable engineer, lecturer, critic, actor and artist, his descendants include the engineer Charles Frewen Jenkin and through him the Conservative MPs Patrick, Lord Jenkin of Roding and Bernard Jenkin. Called Fleeming Jenkin, after Admiral Fleeming, one of his father's patrons, he was born to an old and eccentric family in a government building near Dungeness, England, his father, Captain Charles Jenkin, at that time being in the coast-guard service, his mother, Henrietta Camilla Jenkin was a published author. His mother was responsible for Fleeming's education, she took him to the south of Scotland, chiefly at Barjarg, she taught him drawing and allowed him to ride his pony on the moors. He went to school at Jedburgh and afterwards to the Edinburgh Academy, where he won many prizes.
Among his school fellows were Peter Guthrie Tait. On his father's retirement in 1847, the family moved to Frankfurt from motives of economy and for the boy's education. Here Jenkin and his father spent a pleasant time together, sketching old castles, observing the customs of the peasantry. At thirteen, Jenkin had produced a romance of three hundred lines in heroic couplets, a novel, innumerable poems, none of which are now extant, he learned German in Frankfurt and, on the family migrating to Paris the following year, he studied French and mathematics under a M. Deluc. While there, Jenkin witnessed the outbreak of the Revolution of 1848 and heard the first shot, describing the action in a letter written to an old schoolfellow; the Jenkins left Paris, went to Genoa, where they experienced another revolution, Mrs. Jenkin, with her son and sister-in-law, had to seek the protection of a British vessel in the harbour, leaving their house stored with the property of their friends, guarded by Captain Jenkin.
At Genoa, Jenkin attended the university. Father Bancalari, the professor of natural philosophy, lectured on electromagnetism, his physical laboratory being the best in Italy. Jenkin took the degree of M. A. with first-class honours, his special subject having been electromagnetism. The questions in the examinations were in Latin, had to be answered in Italian. Fleeming attended an art school in the city, gained a silver medal for a drawing from one of Raphael's cartoons, his holidays were spent in sketching, his evenings in learning to play the piano or, when permissible, at the theatre or opera-house. He had conceived a taste for acting. In 1850, Jenkin spent some time in a Genoese locomotive shop under Philip Taylor of Marseille but on the death of his Aunt Anna, who lived with them, Captain Jenkin took his family back to England, settled in Manchester, where the lad, in 1851, was apprenticed to mechanical engineering at the works of William Fairbairn, from half-past eight in the morning till six at night had, as he says, "to file and chip vigorously, in a moleskin suit, infernally dirty."At home he pursued his studies, was for a time engaged with Dr. Bell in working out a geometrical method of arriving at the proportions of Ancient Greek architecture.
His stay in Manchester, though in striking contrast to his life in Genoa, was agreeable. He liked his work, had the good spirits of youth, made some pleasant friends, one of them the author, Elizabeth Gaskell, he was argumentative, his mother tells of his having overcome a consul at Genoa in a political discussion when he was only sixteen'simply from being well-informed on the subject, honest. He is as true as steel,' she writes,'and for no one will he bend right or left... Do not fancy him a Bobadil. I am so glad he remains in all respects but information a great child.'""On leaving Fairbairn's he was engaged for a time on a survey for the proposed Lukmanier Railway in Switzerland, in 1856 he entered Penn's engineering works at Greenwich as a draughtsman, being occupied on the plans of a vessel designed for the Crimean War. He complained about the late hours, his rough comrades, his humble lodgings,'across a dirty green and through some half-built streets of two-storied houses.... Luckily,' he adds,'I am fond of my profession, or I could not stand this life.'
Jenkin had been his mother's pet until and felt the change from home more keenly for that reason. At night he read engineering and mathematics, or Thomas Carlyle and the poets, cheered his drooping spirits with frequent trips to London to see his mother.""Another social pleasure was his visits to the house of Alfred Austin, a barrister, who became permanent secretary to Her Majesty's Office of Works and Public Buildings, retired in 1868 with the title of CB. His wife, Eliza Barron, was the youngest daughter of a gentleman of Norwich who, when a child, had been patted on the head, in his father's shop, by Dr Samuel Johnson, while canvassing for Mr. Thrale. Jenkin had been introduced to the Austins by a letter from Mrs. Gaskell, was charmed with the atmosphere of their choice home, where intellectual conversation was united with kind and courteous manners, without any pretence or affectation. "Each of the Austins," says Stevenson in his memoir of Jenkin, "was full of high spirits. The Austins were hospitable and cultured, not so in form and appearance.
It was a rare privilege and preservative for a solitary young man in Jenkin's position to have
Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments; the most familiar effects occur in ferromagnetic materials, which are attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Only a few substances are ferromagnetic; the prefix ferro- refers to iron, because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, Fe3O4. Although ferromagnetism is responsible for most of the effects of magnetism encountered in everyday life, all other materials are influenced to some extent by a magnetic field, by several other types of magnetism. Paramagnetic substances such as aluminum and oxygen are weakly attracted to an applied magnetic field; the force of a magnet on paramagnetic and antiferromagnetic materials is too weak to be felt, can be detected only by laboratory instruments, so in everyday life these substances are described as non-magnetic.
The magnetic state of a material depends on temperature and other variables such as pressure and the applied magnetic field. A material may exhibit more than one form of magnetism as these variables change; as with magnetising a magnet, demagnetising a magnet is possible. "Passing an alternate current, or hitting a heated magnet in an east west direction are ways of demagnetising a magnet", quotes Sreekethav. Magnetism was first discovered in the ancient world, when people noticed that lodestones magnetized pieces of the mineral magnetite, could attract iron; the word magnet comes from the Greek term μαγνῆτις λίθος magnētis lithos, "the Magnesian stone, lodestone." In ancient Greece, Aristotle attributed the first of what could be called a scientific discussion of magnetism to the philosopher Thales of Miletus, who lived from about 625 BC to about 545 BC. The ancient Indian medical text Sushruta Samhita describes using magnetite to remove arrows embedded in a person's body. In ancient China, the earliest literary reference to magnetism lies in a 4th-century BC book named after its author, The Sage of Ghost Valley.
The 2nd-century BC annals, Lüshi Chunqiu notes: "The lodestone makes iron approach, or it attracts it." The earliest mention of the attraction of a needle is in a 1st-century work Lunheng: "A lodestone attracts a needle." The 11th-century Chinese scientist Shen Kuo was the first person to write—in the Dream Pool Essays—of the magnetic needle compass and that it improved the accuracy of navigation by employing the astronomical concept of true north. By the 12th century the Chinese were known to use the lodestone compass for navigation, they sculpted a directional spoon from lodestone in such a way that the handle of the spoon always pointed south. Alexander Neckam, by 1187, was the first in Europe to describe the compass and its use for navigation. In 1269, Peter Peregrinus de Maricourt wrote the Epistola de magnete, the first extant treatise describing the properties of magnets. In 1282, the properties of magnets and the dry compasses were discussed by Al-Ashraf, a Yemeni physicist and geographer.
In 1600, William Gilbert published his De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure. In this work he describes many of his experiments with his model earth called the terrella. From his experiments, he concluded that the Earth was itself magnetic and that this was the reason compasses pointed north. An understanding of the relationship between electricity and magnetism began in 1819 with work by Hans Christian Ørsted, a professor at the University of Copenhagen, who discovered by the accidental twitching of a compass needle near a wire that an electric current could create a magnetic field; this landmark experiment is known as Ørsted's Experiment. Several other experiments followed, with André-Marie Ampère, who in 1820 discovered that the magnetic field circulating in a closed-path was related to the current flowing through the perimeter of the path. James Clerk Maxwell synthesized and expanded these insights into Maxwell's equations, unifying electricity and optics into the field of electromagnetism.
In 1905, Einstein used these laws in motivating his theory of special relativity, requiring that the laws held true in all inertial reference frames. Electromagnetism has continued to develop into the 21st century, being incorporated into the more fundamental theories of gauge theory, quantum electrodynamics, electroweak theory, the standard model. Magnetism, at its root, arises from two sources: Electric current. Spin magnetic moments of elementary particles; the magnetic properties of materials are due to the magnetic moments of their atoms' orbiting electrons. The magnetic moments of the nuclei of atoms are thousands of times smaller than the electro
A sanitary sewer or foul sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings to treatment facilities or disposal. Sanitary sewers are part of an overall system called sewerage. Sewage may be treated to control water pollution before discharge to surface waters. Sanitary sewers serving industrial areas carry industrial wastewater. Separate sanitary sewer systems are designed to transport sewage alone. In municipalities served by sanitary sewers, separate storm drains may convey surface runoff directly to surface waters. Sanitary sewers are distinguished from combined sewers, which combine sewage with stormwater runoff in one pipe. Sanitary sewer systems are beneficial. Sewage treatment is less effective when sanitary waste is diluted with stormwater, combined sewer overflows occur when runoff from heavy rainfall or snowmelt exceeds the hydraulic capacity of sewage treatment plants. To overcome these disadvantages, some cities built separate sanitary sewers to collect only municipal wastewater and exclude stormwater runoff collected in separate storm drains.
The decision between a combined sewer system or two separate systems is based on need for sewage treatment and cost of providing treatment during heavy rain events. Many cities with combined sewer systems built prior to installing sewage treatment have not replaced those sewer systems. In the developed world, sewers are pipes from buildings to one or more levels of larger underground trunk mains, which transport the sewage to sewage treatment facilities. Vertical pipes made of precast concrete, called manholes, connect the mains to the surface. Depending upon site application and use, these vertical pipes can be cylindrical, eccentric, or concentric; the manholes are used for access to the sewer pipes for inspection and maintenance, as a means to vent sewer gases. They facilitate vertical and horizontal angles in otherwise straight pipelines. Pipes conveying sewage from an individual building to a common gravity sewer line are called laterals. Branch sewers run under streets receiving laterals from buildings along that street and discharge by gravity into trunk sewers at manholes.
Larger cities may have sewers called interceptors. Design and sizing of sanitary sewers considers the population to be served over the anticipated life of the sewer, per capita wastewater production, flow peaking from timing of daily routines. Minimum sewer diameters are specified to prevent blockage by solid materials flushed down toilets. Commercial and industrial wastewater flows are considered, but diversion of surface runoff to storm drains eliminates wet weather flow peaks of inefficient combined sewers. Pumps may be necessary where gravity sewers serve areas at lower elevations than the sewage treatment plant, or distant areas at similar elevations. A lift station is a sewer sump; the pump may discharge to another gravity sewer at that location or may discharge through a pressurized force main to some distant location. Effluent sewer systems called septic tank effluent drainage or solids-free sewer systems, have septic tanks that collect sewage from residences and businesses, the effluent that comes out of the tank is sent to either a centralized sewage treatment plant or a distributed treatment system for further treatment.
Most of the solids are removed by the septic tanks, so the treatment plant can be much smaller than a typical plant. In addition, because of the vast reduction in solid waste, a pumping system can be used to move the wastewater rather than a gravity system; the pipes have small diameters 1.5 to 4 inches. Because the waste stream is pressurized, they can be laid just below the ground surface along the land's contour. Simplified sanitary sewers consist of small-diameter pipes around 100 millimetres laid at flat gradients. Although the investment cost for simplified sanitary sewers can be about half the cost of conventional sewers, the requirements for operation and maintenance are higher. Simplified sewers are most common in Brazil and are used in a number of other developing countries. In low-lying communities, wastewater is conveyed by vacuum sewer. Pipelines range in size from pipes of 6 inches in diameter to concrete-lined tunnels of up to 30 feet in diameter. A low pressure system uses a small grinder pump located at each point of connection a house or business.
Vacuum sewer systems use differential atmospheric pressure to move the liquid to a central vacuum station. Sanitary sewer overflow can occur due to blocked or broken sewer lines, infiltration of excessive stormwater or malfunction of pumps. In these cases untreated sewage is discharged from a sanitary sewer into the environment prior to reaching sewage treatment facilities. To avoid this, maintenance is required; the maintenance requirements vary with the type of sanitary sewer. In general, all sewers deteriorate with age, but infiltration and inflow are problems unique to sanitary sewers, since both combined sewers and storm drains are sized to carry these contributions. Holding infiltration to acceptable levels requires a higher standard of maintenance than necessary for structural integrity considerations of combined sewers. A comprehensive construction inspection program is required to prevent inappropriate connection of cellar and roof drains to sanitary sewers; the probability of inappropriate connecti