Manchester

Manchester (/ˈmæntʃɪstər, -tʃɛs-/) is a city in Greater Manchester, England. 　It had a population of 552,000 in 2021. 　It is bordered by the Cheshire Plain to the south, the Pennines to the north and east, and the neighbouring city of Salford to the west. 　The two cities and the surrounding towns form one of the United Kingdom's most populous conurbations, the Greater Manchester Built-up Area, which has a population of 2.87 million. 　The history of Manchester began with the civilian settlement associated with the Roman fort (castra) of Mamucium or Mancunium, established in about AD 79 on a sandstone bluff near the confluence of the rivers Medlock and Irwell. 　Historically part of Lancashire, areas of Cheshire south of the River Mersey were incorporated into Manchester in the 20th century, including Wythenshawe in 1931. 　Throughout the Middle Ages Manchester remained a manorial township, but began to expand "at an astonishing rate" around the turn of the 19th century. 　Manchester's unplanned urbanisation was brought on by a boom in textile manufacture during the Industrial Revolution, and resulted in it becoming the world's first industrialised city. 　Manchester achieved city status in 1853. 　The Manchester Ship Canal opened in 1894, creating the Port of Manchester and linking the city to the Irish Sea, 36 miles (58 km) to the west. 　Its fortune declined after the Second World War, owing to deindustrialisation, and the IRA bombing in 1996 led to extensive investment and regeneration. 　Following considerable redevelopment, Manchester was the host city for the 2002 Commonwealth Games. 　The city is notable for its architecture, culture, musical exports, media links, scientific and engineering output, social impact, sports clubs and transport connections. 　Manchester Liverpool Road railway station was the world's first inter-city passenger railway station. 　At the University of Manchester, Ernest Rutherford first split the atom in 1917, Frederic C. Williams, Tom Kilburn and Geoff Tootill developed the world's first stored-program computer in 1948, and Andre Geim and Konstantin Novoselov isolated the first graphene in 2004.

Compact

Look up compact in Wiktionary, the free dictionary. 　Compact as used in politics may refer broadly to a pact or treaty; in more specific cases it may refer to: Interstate compact Blood compact, an ancient ritual of the Philippines Compact government, a type of colonial rule utilized in British North America Compact of Free Association whereby the sovereign states of the Federated States of Micronesia, the Republic of the Marshall Islands and the Republic of Palau have entered into as associated states with the United States. 　Mayflower Compact, the first governing document of Plymouth Colony United Nations Global Compact Global Compact for Migration, a UN non-binding intergovernmental agreement

Pi

The number π (/paɪ/; spelled out as "pi") is a mathematical constant that is the ratio of a circle's circumference to its diameter, approximately equal to 3.14159. 　The number π appears in many formulas across mathematics and physics. 　It is an irrational number, meaning that it cannot be expressed exactly as a ratio of two integers, although fractions such as 22 7 {\displaystyle {\tfrac {22}{7}}} are commonly used to approximate it. 　Consequently, its decimal representation never ends, nor enters a permanently repeating pattern. 　It is a transcendental number, meaning that it cannot be a solution of an equation involving only sums, products, powers, and integers. 　The transcendence of π implies that it is impossible to solve the ancient challenge of squaring the circle with a compass and straightedge. 　The decimal digits of π appear to be randomly distributed, but no proof of this conjecture has been found. 　For thousands of years, mathematicians have attempted to extend their understanding of π, sometimes by computing its value to a high degree of accuracy. 　Ancient civilizations, including the Egyptians and Babylonians, required fairly accurate approximations of π for practical computations. 　Around 250 BC, the Greek mathematician Archimedes created an algorithm to approximate π with arbitrary accuracy. 　In the 5th century AD, Chinese mathematicians approximated π to seven digits, while Indian mathematicians made a five-digit approximation, both using geometrical techniques. 　The first computational formula for π, based on infinite series, was discovered a millennium later. 　The earliest known use of the Greek letter π to represent the ratio of a circle's circumference to its diameter was by the Welsh mathematician William Jones in 1706. 　The invention of calculus soon led to the calculation of hundreds of digits of π, enough for all practical scientific computations. 　Nevertheless, in the 20th and 21st centuries, mathematicians and computer scientists have pursued new approaches that, when combined with increasing computational power, extended the decimal representation of π to many trillions of digits. 　These computations are motivated by the development of efficient algorithms to calculate numeric series, as well as the human quest to break records. 　The extensive computations involved have also been used to test supercomputers. 　Because its definition relates to the circle, π is found in many formulae in trigonometry and geometry, especially those concerning circles, ellipses and spheres. 　It is also found in formulae from other topics in science, such as cosmology, fractals, thermodynamics, mechanics, and electromagnetism. 　In modern mathematical analysis, it is often instead defined without any reference to geometry; therefore, it also appears in areas having little to do with geometry, such as number theory and statistics. 　The ubiquity of π makes it one of the most widely known mathematical constants inside and outside of science. 　Several books devoted to π have been published, and record-setting calculations of the digits of π often result in news headlines.

Scattering

Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including particles and radiation) in the medium through which they pass. 　In conventional use, this also includes deviation of reflected radiation from the angle predicted by the law of reflection. 　Reflections of radiation that undergo scattering are often called diffuse reflections and unscattered reflections are called specular (mirror-like) reflections. 　Originally, the term was confined to light scattering (going back at least as far as Isaac Newton in the 17th century). 　As more "ray"-like phenomena were discovered, the idea of scattering was extended to them, so that William Herschel could refer to the scattering of "heat rays" (not then recognized as electromagnetic in nature) in 1800. 　John Tyndall, a pioneer in light scattering research, noted the connection between light scattering and acoustic scattering in the 1870s. 　Near the end of the 19th century, the scattering of cathode rays (electron beams) and X-rays was observed and discussed. 　With the discovery of subatomic particles (e.g. Ernest Rutherford in 1911) and the development of quantum theory in the 20th century, the sense of the term became broader as it was recognized that the same mathematical frameworks used in light scattering could be applied to many other phenomena. 　Scattering can refer to the consequences of particle-particle collisions between molecules, atoms, electrons, photons and other particles. 　Examples include: cosmic ray scattering in the Earth's upper atmosphere; particle collisions inside particle accelerators; electron scattering by gas atoms in fluorescent lamps; and neutron scattering inside nuclear reactors. 　The types of non-uniformities which can cause scattering, sometimes known as scatterers or scattering centers, are too numerous to list, but a small sample includes particles, bubbles, droplets, density fluctuations in fluids, crystallites in polycrystalline solids, defects in monocrystalline solids, surface roughness, cells in organisms, and textile fibers in clothing. 　The effects of such features on the path of almost any type of propagating wave or moving particle can be described in the framework of scattering theory. 　Some areas where scattering and scattering theory are significant include radar sensing, medical ultrasound, semiconductor wafer inspection, polymerization process monitoring, acoustic tiling, free-space communications and computer-generated imagery. 　Particle-particle scattering theory is important in areas such as particle physics, atomic, molecular, and optical physics, nuclear physics and astrophysics. 　In Particle Physics the quantum interaction and scattering of fundamental particles is described by the Scattering Matrix or S-Matrix, introduced and developed by John Archibald Wheeler and Werner Heisenberg. 　Scattering is quantified using many different concepts, including scattering cross section (σ), attenuation coefficients, the bidirectional scattering distribution function (BSDF), S-matrices, and mean free path.

Momentum

In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. 　It is a vector quantity, possessing a magnitude and a direction. 　If m is an object's mass and v is its velocity (also a vector quantity), then the object's momentum p is : p = m v . 　{\displaystyle \mathbf {p} =m\mathbf {v} .　} In the International System of Units (SI), the unit of measurement of momentum is the kilogram metre per second (kg⋅m/s), which is equivalent to the newton-second. 　Newton's second law of motion states that the rate of change of a body's momentum is equal to the net force acting on it. 　Momentum depends on the frame of reference, but in any inertial frame it is a conserved quantity, meaning that if a closed system is not affected by external forces, its total linear momentum does not change. 　Momentum is also conserved in special relativity (with a modified formula) and, in a modified form, in electrodynamics, quantum mechanics, quantum field theory, and general relativity. 　It is an expression of one of the fundamental symmetries of space and time: translational symmetry. 　Advanced formulations of classical mechanics, Lagrangian and Hamiltonian mechanics, allow one to choose coordinate systems that incorporate symmetries and constraints. 　In these systems the conserved quantity is generalized momentum, and in general this is different from the kinetic momentum defined above. 　The concept of generalized momentum is carried over into quantum mechanics, where it becomes an operator on a wave function. 　The momentum and position operators are related by the Heisenberg uncertainty principle. 　In continuous systems such as electromagnetic fields, fluid dynamics and deformable bodies, a momentum density can be defined, and a continuum version of the conservation of momentum leads to equations such as the Navier–Stokes equations for fluids or the Cauchy momentum equation for deformable solids or fluids.

Philip

Philip, also Phillip, is a male given name, derived from the Greek Φίλιππος (Philippos, lit. "horse-loving" or "fond of horses"), from a compound of φίλος (philos, "dear", "loved", "loving") and ἵππος (hippos, "horse"). 　Prominent Philips who popularized the name include kings of Macedonia and one of the apostles of early Christianity. 　Philip has many alternative spellings. 　One derivation often used as a surname is Phillips. 　It was also found during ancient Greek times with two Ps as Philippides and Philippos. 　It has many diminutive (or even hypocoristic) forms including Phil, Philly, Lip, Pip, Pep or Peps. 　There are also feminine forms such as Philippine and Philippa.

Construct (psychology)

Construct (psychology), also hypothetical construct or psychological construct, is a tool used to facilitate understanding of human behavior. 　A psychological construct is a label for a domain of behaviors. 　Behavioral sciences use constructs such as conscientiousness, intelligence, political power, self-esteem, and group culture. 　For example, if a student sees another sitting in a classroom before an examination biting her nails and fidgeting, the interpretation might be that she is experiencing anxiety. 　In that case, anxiety is a construct that underlies the behavior that is observed. 　Cognitive psychologists view constructs as hypothesized causes for certain behaviors, whereas behavioral psychologists view constructs as only descriptors of behaviors. 　A construct derives its name from the fact that it is a mental construction, derived from scientific process: observing natural phenomena, inferring the common features of those observations, and constructing a label for the commonality or the underlying cause. 　A construct derives its scientific value from the shared meaning it represents for different people. 　If a construct is clearly articulated and the phenomena it encompasses are clearly defined, it becomes a useful conceptual tool that facilitates communication. 　Once defined, constructs become objects of conceptual scrutiny in their own right. 　Constructs summarize behavioral domains. 　Constructs are the building blocks of scientific theories.

Construct

Look up construct in Wiktionary, the free dictionary. 　Construct, Constructs or constructs may refer to: Construct (information technology), a collection of logic components forming an interactive agent or environment Language construct Construct (album), a 2013 album by Dark Tranquillity Construct (philosophy), a hypothetical object whose phenomenal existence depends upon a subject's mind Construct (python library), a software library used for data-structuring Construct (software), an HTML5-based game creator Construct state, an Afro-Asiatic noun-form DNA construct, a segment of nucleic acid, created artificially, for transplantation into a target cell or tissue Social construct (disambiguation) Construct (psychology), a label used in behavioural sciences for a domain of behaviors an alternative name for a concrete category biological creations appearing in the Wheel of Time series of fantasy novels

Insurance

Insurance is a means of protection from financial loss in which, in exchange for a fee, a party agrees to compensate another party in the event of a certain loss, damage, or injury. 　It is a form of risk management, primarily used to hedge against the risk of a contingent or uncertain loss. 　An entity which provides insurance is known as an insurer, insurance company, insurance carrier, or underwriter. 　A person or entity who buys insurance is known as a policyholder, while a person or entity covered under the policy is called an insured. 　The insurance transaction involves the policyholder assuming a guaranteed, known, and relatively small loss in the form of a payment to the insurer (a premium) in exchange for the insurer's promise to compensate the insured in the event of a covered loss. 　The loss may or may not be financial, but it must be reducible to financial terms. 　Furthermore, it usually involves something in which the insured has an insurable interest established by ownership, possession, or pre-existing relationship. 　The insured receives a contract, called the insurance policy, which details the conditions and circumstances under which the insurer will compensate the insured, or their designated beneficiary or assignee. 　The amount of money charged by the insurer to the policyholder for the coverage set forth in the insurance policy is called the premium. 　If the insured experiences a loss which is potentially covered by the insurance policy, the insured submits a claim to the insurer for processing by a claims adjuster. 　A mandatory out-of-pocket expense required by an insurance policy before an insurer will pay a claim is called a deductible (or if required by a health insurance policy, a copayment). 　The insurer may hedge its own risk by taking out reinsurance, whereby another insurance company agrees to carry some of the risks, especially if the primary insurer deems the risk too large for it to carry.

Cat

The cat (Felis catus) is a domestic species of small carnivorous mammal. 　It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of the family. 　Cats are commonly kept as house pets but can also be farm cats or feral cats; the feral cat ranges freely and avoids human contact. 　Domestic cats are valued by humans for companionship and their ability to kill rodents. 　About 60 cat breeds are recognized by various cat registries. 　The cat is similar in anatomy to the other felid species: it has a strong flexible body, quick reflexes, sharp teeth, and retractable claws adapted to killing small prey. 　Its night vision and sense of smell are well developed. 　Cat communication includes vocalizations like meowing, purring, trilling, hissing, growling, and grunting as well as cat-specific body language. 　Although the cat is a social species, it is a solitary hunter. 　As a predator, it is crepuscular, i.e. most active at dawn and dusk. 　It can hear sounds too faint or too high in frequency for human ears, such as those made by mice and other small mammals. 　It also secretes and perceives pheromones. 　Female domestic cats can have kittens from spring to late autumn, with litter sizes often ranging from two to five kittens. 　Domestic cats are bred and shown at events as registered pedigreed cats, a hobby known as cat fancy. 　Population control of cats may be achieved by spaying and neutering, but their proliferation and the abandonment of pets has resulted in large numbers of feral cats worldwide, contributing to the extinction of entire bird, mammal, and reptile species. 　It was long thought that cat domestication began in ancient Egypt, where cats were venerated from around 3100 BC, but recent advances in archaeology and genetics have shown that their domestication occurred in Western Asia around 7500 BC. 　As of 2021,[update] there were an estimated 220 million owned and 480 million stray cats in the world. 　As of 2017,[update] the domestic cat was the second most popular pet in the United States, with 95.6 million cats owned and around 42 million households owning at least one cat. 　In the United Kingdom, 26% of adults have a cat, with an estimated population of 10.9 million pet cats as of 2020.[update]

Matt

Look up matt, Matt, or Matt. 　in Wiktionary, the free dictionary. 　Look up mAtt, mätt, or mått in Wiktionary, the free dictionary. 　Matt may refer to: Matt (name), people with the given name Matt or Matthew, meaning "gift from God", or the surname Matt In British English, of a surface: having a non-glossy finish, see gloss (material appearance) Matt, Switzerland, a municipality "Matt", the cartoon by Matthew Pritchett in the UK Telegraph newspapers

Ian

Ian or Iain is a name of Scottish Gaelic origin, derived from the Hebrew given name יוֹחָנָן‎ (Yohanan, Yôḥānān) and corresponding to the English name John. 　The spelling Ian is an Anglicization of the Scottish Gaelic forename Iain. 　It is a popular name in Scotland, where it originated, as well as other English-speaking countries. 　The name has fallen out of the top 100 male baby names in the United Kingdom, having peaked in popularity as one of the top 10 names throughout the 1960s. 　In 1900, Ian was the 180th most popular male baby name in England and Wales. 　As of 2019[update], the name has been in the top 100 in the United States every year since 1982, peaking at 65 in 2003. 　Other Gaelic forms of "John" include "Seonaidh" ("Johnny" from Lowland Scots), "Seon" (from English), "Seathan", and "Seán" and "Eoin" (from Irish). 　Its Welsh counterpart is Ioan, its Cornish equivalent is Yowan and Breton equivalent is Yann.

Earl

Earl (/ɜːrl, ɜːrəl/) is a rank of the nobility in the United Kingdom. 　The title originates in the Old English word eorl, meaning "a man of noble birth or rank". 　The word is cognate with the Scandinavian form jarl, and meant "chieftain", particularly a chieftain set to rule a territory in a king's stead. 　After the Norman Conquest, it became the equivalent of the continental count (in England in the earlier period, it was more akin to a duke; in Scotland, it assimilated the concept of mormaer). 　Alternative names for the rank equivalent to "earl" or "count" in the nobility structure are used in other countries, such as the hakushaku (伯爵) of the post-restoration Japanese Imperial era. 　In modern Britain, an earl is a member of the peerage, ranking below a marquess and above a viscount. 　A feminine form of earl never developed; instead, countess is used.

Plain

In geography, a plain, commonly known as flatland, is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. 　Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands. 　Plains are one of the major landforms on earth, being present on all continents and covering more than one-third of the world's land area. 　Plains in many areas are important for agriculture. 　There are various types of plains and biomes on them.

Shed

A shed is typically a simple, single-story roofed structure that is used for hobbies, or as a workshop in a back garden or on an allotment. 　Sheds vary considerably in their size and complexity of construction, from simple open-sided ones designed to cover bicycles or garden items to large wood-framed structures with shingled roofs, windows, and electrical outlets. 　Sheds used on farms or in the industry can be large structures. 　The main types of shed construction are metal sheathing over a metal frame, plastic sheathing and frame, all-wood construction (the roof may be asphalt shingled or sheathed in tin), and vinyl-sided sheds built over a wooden frame. 　Small sheds may include a wooden or plastic floor, while more permanent ones may be built on a concrete pad or foundation. 　Sheds may be lockable to deter theft or entry by children, domestic animals, wildlife, etc.

Lawyer

A lawyer is a person who practices law. 　The role of a lawyer varies greatly across different legal jurisdictions. 　A lawyer can be classified as an advocate, attorney, barrister, canon lawyer, civil law notary, counsel, counselor, solicitor, legal executive, or public servant — with each role having different functions and privileges. 　Working as a lawyer generally involves the practical application of abstract legal theories and knowledge to solve specific problems. 　Some lawyers also work primarily in advancing the interests of the law and legal profession.

Indiana

Indiana (/ˌɪndiˈænə/ (listen)) is a U.S. state in the Midwestern United States. 　It is the 38th-largest by area and the 17th-most populous of the 50 States. 　Its capital and largest city is Indianapolis. 　Indiana was admitted to the United States as the 19th state on December 11, 1816. 　It is bordered by Lake Michigan to the northwest, Michigan to the north and northeast, Ohio to the east, the Ohio River and Kentucky to the south and southeast, and the Wabash River and Illinois to the west. 　Various indigenous peoples inhabited what would become Indiana for thousands of years, some of whom the U.S. government expelled between 1800 and 1836. 　Indiana received its name because the state was largely possessed by native tribes even after it was granted statehood. 　Since then, settlement patterns in Indiana have reflected regional cultural segmentation present in the Eastern United States; the state's northernmost tier was settled primarily by people from New England and New York, Central Indiana by migrants from the Mid-Atlantic states and adjacent Ohio, and Southern Indiana by settlers from the Upland South, particularly Kentucky and Tennessee. 　Indiana has a diverse economy with a gross state product of $352.62 billion in 2021. 　It has several metropolitan areas with populations greater than 100,000 and a number of smaller cities and towns. 　Indiana is home to professional sports teams, including the NFL's Indianapolis Colts and the NBA's Indiana Pacers. 　The state also hosts several notable competitive events, such as the Indianapolis 500, held at Indianapolis Motor Speedway.

Dimension

In physics and mathematics, the dimension of a mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any point within it. 　Thus, a line has a dimension of one (1D) because only one coordinate is needed to specify a point on it – for example, the point at 5 on a number line. 　A surface, such as the boundary of a cylinder or sphere, has a dimension of two (2D) because two coordinates are needed to specify a point on it – for example, both a latitude and longitude are required to locate a point on the surface of a sphere. 　A two-dimensional Euclidean space is a two-dimensional space on the plane. 　The inside of a cube, a cylinder or a sphere is three-dimensional (3D) because three coordinates are needed to locate a point within these spaces. 　In classical mechanics, space and time are different categories and refer to absolute space and time. 　That conception of the world is a four-dimensional space but not the one that was found necessary to describe electromagnetism. 　The four dimensions (4D) of spacetime consist of events that are not absolutely defined spatially and temporally, but rather are known relative to the motion of an observer. 　Minkowski space first approximates the universe without gravity; the pseudo-Riemannian manifolds of general relativity describe spacetime with matter and gravity. 　10 dimensions are used to describe superstring theory (6D hyperspace + 4D), 11 dimensions can describe supergravity and M-theory (7D hyperspace + 4D), and the state-space of quantum mechanics is an infinite-dimensional function space. 　The concept of dimension is not restricted to physical objects. 　High-dimensional spaces frequently occur in mathematics and the sciences. 　They may be Euclidean spaces or more general parameter spaces or configuration spaces such as in Lagrangian or Hamiltonian mechanics; these are abstract spaces, independent of the physical space in which we live.

Tied

Look up tied in Wiktionary, the free dictionary. 　Tied may mean: of a game, with the score equal or inconclusive, see Tie (draw) of goods, sold as a mandatory addition to another purchase, see Tying (commerce) of foreign aid, granted on the condition that it is spent in a given country, see Tied aid of a dwelling, rented in exchange for work, see Tied cottage of a pub, required to source from a given brewery, see Tied house of two musical notes, played as a single note, see Tie (music) of a knot, fastened of a person, wearing a necktie

Gravity

In physics, gravity (from Latin gravitas 'weight') is a fundamental interaction which causes mutual attraction between all things with mass or energy. 　Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. 　As a result, it has no significant influence at the level of subatomic particles. 　However, gravity is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light. 　On Earth, gravity gives weight to physical objects, and the Moon's gravity is responsible for sublunar tides in the oceans (the corresponding antipodal tide is caused by the inertia of the Earth and Moon orbiting one another). 　Gravity also has many important biological functions, helping to guide the growth of plants through the process of gravitropism and influencing the circulation of fluids in multicellular organisms. 　Investigation into the effects of weightlessness has shown that gravity may play a role in immune system function and cell differentiation within the human body. 　The gravitational attraction between the original gaseous matter in the universe allowed it to coalesce and form stars which eventually condensed into galaxies, so gravity is responsible for many of the large-scale structures in the universe. 　Gravity has an infinite range, although its effects become weaker as objects get farther away. 　Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915), which describes gravity not as a force, but as the curvature of spacetime, caused by the uneven distribution of mass, and causing masses to move along geodesic lines. 　The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon. 　However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them: F = G m 1 m 2 r 2 , {\displaystyle F=G{\frac {m_{1}m_{2}}{r^{2}}},} where F is the force, m1 and m2 are the masses of the objects interacting, r is the distance between the centers of the masses and G is the gravitational constant. 　Current models of particle physics imply that the earliest instance of gravity in the universe, possibly in the form of quantum gravity, supergravity or a gravitational singularity, along with ordinary space and time, developed during the Planck epoch (up to 10−43 seconds after the birth of the universe), possibly from a primeval state, such as a false vacuum, quantum vacuum or virtual particle, in a currently unknown manner. 　Scientists are currently working to develop a theory of gravity consistent with quantum mechanics, a quantum gravity theory, which would allow gravity to be united in a common mathematical framework (a theory of everything) with the other three fundamental interactions of physics.

Radiation

In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. 　This includes: electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ) particle radiation, such as alpha radiation (α), beta radiation (β), proton radiation and neutron radiation (particles of non-zero rest energy) acoustic radiation, such as ultrasound, sound, and seismic waves (dependent on a physical transmission medium) gravitational radiation, that takes the form of gravitational waves, or ripples in the curvature of spacetime Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. 　Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules and break chemical bonds. 　This is an important distinction due to the large difference in harmfulness to living organisms. 　A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, and photons, respectively. 　Other sources include X-rays from medical radiography examinations and muons, mesons, positrons, neutrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere. 　Gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. 　The word "ionize" refers to the breaking of one or more electrons away from an atom, an action that requires the relatively high energies that these electromagnetic waves supply. 　Further down the spectrum, the non-ionizing lower energies of the lower ultraviolet spectrum cannot ionize atoms, but can disrupt the inter-atomic bonds which form molecules, thereby breaking down molecules rather than atoms; a good example of this is sunburn caused by long-wavelength solar ultraviolet. 　The waves of longer wavelength than UV in visible light, infrared and microwave frequencies cannot break bonds but can cause vibrations in the bonds which are sensed as heat. 　Radio wavelengths and below generally are not regarded as harmful to biological systems. 　These are not sharp delineations of the energies; there is some overlap in the effects of specific frequencies. 　The word "radiation" arises from the phenomenon of waves radiating (i.e., traveling outward in all directions) from a source. 　This aspect leads to a system of measurements and physical units that are applicable to all types of radiation. 　Because such radiation expands as it passes through space, and as its energy is conserved (in vacuum), the intensity of all types of radiation from a point source follows an inverse-square law in relation to the distance from its source. 　Like any ideal law, the inverse-square law approximates a measured radiation intensity to the extent that the source approximates a geometric point.

Austria

Coordinates: 47°20′N 13°20′E / 47.333°N 13.333°E / 47.333; 13.333 Austria, formally the Republic of Austria, is a landlocked country in the southern part of Central Europe, lying in the Eastern Alps. 　It is a federation of nine states, one of which is the capital, Vienna, the most populous city and state. 　A landlocked country, Austria is bordered by Germany to the northwest, the Czech Republic to the north, Slovakia to the northeast, Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the west. 　The country occupies an area of 83,871 km2 (32,383 sq mi) and has a population of 9 million. 　Austria emerged from the remnants of the Eastern and Hungarian March at the end of the first millennium. 　Originally a margraviate of Bavaria, it developed into a duchy of the Holy Roman Empire in 1156 and was later made an archduchy in 1453. 　In the 16th century, Vienna began serving as the empire's administrative capital and Austria thus became the heartland of the Habsburg monarchy. 　After the dissolution of the Holy Roman Empire in 1806, Austria established its own empire, which became a great power and the dominant member of the German Confederation. 　The empire's defeat in the Austro-Prussian War of 1866 led to the end of the Confederation and paved the way for the establishment of Austria-Hungary a year later. 　After the assassination of Archduke Franz Ferdinand in 1914, Emperor Franz Joseph declared war on Serbia, which ultimately escalated into World War I. 　The empire's defeat and subsequent collapse led to the proclamation of the Republic of German-Austria in 1918 and the First Austrian Republic in 1919. 　During the interwar period, anti-parliamentarian sentiments culminated in the formation of an Austrofascist dictatorship under Engelbert Dollfuss in 1934. 　A year before the outbreak of World War II, Austria was annexed into Nazi Germany by Adolf Hitler, and it became a sub-national division. 　After its liberation in 1945 and a decade of Allied occupation, the country regained its sovereignty and declared its perpetual neutrality in 1955. 　Austria is a parliamentary representative democracy with a popularly elected president as head of state and a chancellor as head of government and chief executive. 　Major cities include Vienna, Graz, Linz, Salzburg, and Innsbruck. 　Austria is consistently listed as one of the richest countries in the world by GDP per capita and one of the countries with the highest standard of living; it was ranked 25th in the world for its Human Development Index in 2021. 　Austria has been a member of the United Nations since 1955 and of the European Union since 1995. 　It hosts the OSCE and OPEC and is a founding member of the OECD and Interpol. 　It also signed the Schengen Agreement in 1995, and adopted the euro currency in 1999.

Sigma

Sigma (/ˈsɪɡmə/; uppercase Σ, lowercase σ, lowercase in word-final position ς; Greek: σίγμα) is the eighteenth letter of the Greek alphabet. 　In the system of Greek numerals, it has a value of 200. 　In general mathematics, uppercase Σ is used as an operator for summation. 　When used at the end of a letter-case word (one that does not use all caps), the final form (ς) is used. 　In Ὀδυσσεύς (Odysseus), for example, the two lowercase sigmas (σ) in the center of the name are distinct from the word-final sigma (ς) at the end. 　The Latin letter S derives from sigma while the Cyrillic letter Es derives from a lunate form of this letter.

Satellite

A satellite or artificial satellite is an object intentionally placed into orbit in outer space. 　Satellites have a variety of uses, including communication relay, weather forecasting, navigation (GPS), broadcasting, scientific research, and Earth observation. 　Additional military uses are reconnaissance, early warning, signals intelligence and, potentially, weapon delivery. 　Other satellites include the final rocket stages that placed satellites in orbit and formerly useful satellites that are now defunct. 　Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope thermoelectric generators (RTGs). 　Most satellites also have a method of communication to ground stations, called transponders. 　Many satellites use a standardized bus to save cost and work, the most popular of which is small CubeSats. 　Similar satellites can work together as a group, forming constellations. 　Because of the high launch cost to space, satellites are designed to be as lightweight and robust as possible. 　Most communication satellites are radio relay stations in orbit and carry dozens of transponders, each with a bandwidth of tens of megahertz. 　Satellites are placed from the surface to orbit by launch vehicles, high enough to avoid orbital decay by the atmosphere. 　Satellites can then change or maintain the orbit by propulsion, usually by chemical or ion thrusters. 　In 2018, about 90% of satellites orbiting Earth are in low Earth orbit or geostationary orbit; geostationary means the satellites stay still at the sky. 　Some imaging satellites chose a Sun-synchronous orbit because they can scan the entire globe with similar lighting. 　As the number of satellites and space debris around Earth increases, the threat of collision has become more severe. 　A small number of satellites orbit other bodies (such as the Moon, Mars, and the Sun) or many bodies at once (two for a halo orbit, three for a Lissajous orbit). 　Earth observation satellites gather information for reconnaissance, mapping, monitoring the weather, ocean, forest, etc. 　Space telescopes take advantage of outer space's near perfect vacuum to observe objects with the entire electromagnetic spectrum. 　Because satellites can see a large portion of the Earth at once, communications satellites can relay information to remote places. 　The signal delay from satellites and their orbit's predictability are used in satellite navigation systems, such as GPS. 　Space probes are satellites designed for robotic space exploration outside of Earth, and space stations are in essence crewed satellites. 　The first artificial satellite to be launched into the Earth's orbit was the Soviet Union's Sputnik 1, on 4 October 1957.