Authority

In the fields of sociology and political science, authority is the legitimate power of a person or group over other people. 　In a civil state, authority is practiced in ways such a judicial branch or an executive branch of government. 　In the exercise of governance, the terms authority and power are inaccurate synonyms. 　The term authority identifies the political legitimacy, which grants and justifies the ruler's right to exercise the power of government; and the term power identifies the ability to accomplish an authorized goal, either by compliance or by obedience; hence, authority is the power to make decisions and the legitimacy to make such legal decisions and order their execution.

Authority (sociology)

In sociology, authority is the legitimate or socially approved power which one person or a group possesses and practices over another. 　The element of legitimacy is vital to the notion of authority and is the main means by which authority is distinguished from the more general concept of power. 　Power can be exerted by the use of force or violence. 　Authority, by contrast, depends on the acceptance by subordinates of the right of those above them to give them orders or directives.

Chair

A chair is a type of seat, typically designed for one person and consisting of one or more legs, a flat or slightly angled seat and a back-rest. 　They may be made of wood, metal, or synthetic materials, and may be padded or upholstered in various colors and fabrics. 　Chairs vary in design. 　An armchair has armrests fixed to the seat; a recliner is upholstered and features a mechanism that lowers the chair's back and raises into place a footrest; a rocking chair has legs fixed to two long curved slats; and a wheelchair has wheels fixed to an axis under the seat.

Eye

Eyes are organs of the visual system. 　They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. 　Eyes detect light and convert it into electro-chemical impulses in neurons (neurones). 　In higher organisms, the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. 　Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. 　Image-resolving eyes are present in molluscs, chordates and arthropods. 　The most simple eyes, pit eyes, are eye-spots which may be set into a pit to reduce the angle of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. 　From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex.

Hour

An hour (symbol: h; also abbreviated hr) is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned between 3,599 and 3,601 seconds, depending on the speed of Earth's rotation. 　There are 60 minutes in an hour, and 24 hours in a day. 　The hour was initially established in the ancient Near East as a variable measure of 1⁄12 of the night or daytime. 　Such seasonal, temporal, or unequal hours varied by season and latitude. 　Equal or equinoctial hours were taken as 1⁄24 of the day as measured from noon to noon; the minor seasonal variations of this unit were eventually smoothed by making it 1⁄24 of the mean solar day. 　Since this unit was not constant due to long term variations in the Earth's rotation, the hour was finally separated from the Earth's rotation and defined in terms of the atomic or physical second. 　In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds. 　However, on rare occasions an hour may incorporate a positive or negative leap second, making it last 3,599 or 3,601 seconds, in order to keep it within 0.9 seconds of UT1, which is based on measurements of the mean solar day.

Comes

Comes (/ˈkoʊmiːz/ KOH-meez), plural comites (/ˈkɒmɪtiːz/ KOM-i-teez), was a Roman title or office, and the origin Latin form of the medieval and modern title "count". 　Before becoming a word for various types of title or office, the word originally meant "companion", either individually or as a member of a collective denominated a "comitatus", especially the suite of a magnate, being in some instances sufficiently large and/or formal to justify specific denomination, e.g. a "cohors amicorum". 　"Comes" derives from "com-" ("with") and "ire" ("go").

Train

A train (from Old French trahiner, from Latin trahere, "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. 　Trains are typically pulled or pushed by locomotives (often known simply as "engines"), though some are self-propelled, such as multiple units. 　Passengers and cargo are carried in railroad cars, also known as wagons. 　Trains are designed to a certain gauge, or distance between rails. 　Most trains operate on steel tracks with steel wheels, the low friction of which makes them more efficient than other forms of transport. 　Trains have their roots in wagonways, which used railway tracks and were powered by horses or pulled by cables. 　Following the invention of the steam locomotive in the United Kingdom in 1804, trains rapidly spread around the world, allowing freight and passengers to move over land faster and cheaper than ever possible before. 　Rapid transit and trams were first built in the late 1800s to transport large numbers of people in and around cities. 　Beginning in the 1920s, and accelerating following World War II, diesel and electric locomotives replaced steam as the means of motive power. 　Following the development of cars, trucks, and extensive networks of highways which offered greater mobility, as well as faster airplanes, trains declined in importance and market share, and many rail lines were abandoned. 　The spread of buses led to the closure of many rapid transit and tram systems during this time as well. 　Since the 1970s, governments, environmentalists, and train advocates have promoted increased use of trains due to their greater fuel efficiency and lower greenhouse gas emissions compared to other modes of land transport. 　High-speed rail, first built in the 1960s, has proven competitive with cars and planes over short to medium distances. 　Commuter rail has grown in importance since the 1970s as an alternative to congested highways and a means to promote development, as has light rail in the 21st century. 　Freight trains remain important for the transport of bulk commodities such as coal and grain, as well as being a means of reducing road traffic congestion by freight trucks. 　While conventional trains operate on relatively flat tracks with two rails, a number of specialized trains exist which are significantly different in their mode of operation. 　Monorails operate on a single rail, while funiculars and rack railways are uniquely designed to traverse steep slopes. 　Experimental trains such as high speed maglevs, which use magnetic levitation to float above a guideway, are under development in the 2020s and offer higher speeds than even the fastest conventional trains. 　Development of trains which use alternative fuels such as natural gas and hydrogen is another 21st century development.

Necessary

Look up necessary or necessity in Wiktionary, the free dictionary. 　Necessary or necessity may refer to: Need An action somebody may feel they must do An important task or essential thing to do at a particular time or by a particular moment Necessary and sufficient condition, in logic, something that is a required condition for something else to be the case Necessary proposition, in logic, a statement about facts that is either unassailably true (tautology) or obviously false (contradiction) Metaphysical necessity, in philosophy, a truth which is true in all possible worlds Necessity in modal logic Necessity good in economics Law Doctrine of necessity, a concept in constitutional law Military necessity, a concept in international law Necessity (criminal law), a defence in criminal law Necessity (tort), a concept in the law of tort A necessity in contract law Other Necessity.　, a poem by Letitia Elizabeth Landon being part of Three Extracts from the Diary of a Week, 1837. 　"Necessary" (song), by Every Little Thing, 1998 A bathroom or toilet, in some languages (in English this is an archaic usage) An economic need enunciated by US President Franklin D. Roosevelt in his 1944 Second Bill of Rights Necessity (novel), of 2016 by Jo Walton Necessary Records, UK record label

Metal

A metal (from Greek μέταλλον métallon, "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. 　Metals are typically ductile (can be drawn into wires) and malleable (they can be hammered into thin sheets). 　These properties are the result of the metallic bond between the atoms or molecules of the metal. 　A metal may be a chemical element such as iron; an alloy such as stainless steel; or a molecular compound such as polymeric sulfur nitride. 　In physics, a metal is generally regarded as any substance capable of conducting electricity at a temperature of absolute zero. 　Many elements and compounds that are not normally classified as metals become metallic under high pressures. 　For example, the nonmetal iodine gradually becomes a metal at a pressure of between 40 and 170 thousand times atmospheric pressure. 　Equally, some materials regarded as metals can become nonmetals. 　Sodium, for example, becomes a nonmetal at pressure of just under two million times atmospheric pressure. 　In chemistry, two elements that would otherwise qualify (in physics) as brittle metals—arsenic and antimony—are commonly instead recognised as metalloids due to their chemistry (predominantly non-metallic for arsenic, and balanced between metallicity and nonmetallicity for antimony). 　Around 95 of the 118 elements in the periodic table are metals (or are likely to be such). 　The number is inexact as the boundaries between metals, nonmetals, and metalloids fluctuate slightly due to a lack of universally accepted definitions of the categories involved. 　In astrophysics the term "metal" is cast more widely to refer to all chemical elements in a star that are heavier than helium, and not just traditional metals. 　In this sense the first four "metals" collecting in stellar cores through nucleosynthesis are carbon, nitrogen, oxygen, and neon, all of which are strictly non-metals in chemistry. 　A star fuses lighter atoms, mostly hydrogen and helium, into heavier atoms over its lifetime. 　Used in that sense, the metallicity of an astronomical object is the proportion of its matter made up of the heavier chemical elements. 　Metals, as chemical elements, comprise 25% of the Earth's crust and are present in many aspects of modern life. 　The strength and resilience of some metals has led to their frequent use in, for example, high-rise building and bridge construction, as well as most vehicles, many home appliances, tools, pipes, and railroad tracks. 　Precious metals were historically used as coinage, but in the modern era, coinage metals have extended to at least 23 of the chemical elements. 　The history of refined metals is thought to begin with the use of copper about 11,000 years ago. 　Gold, silver, iron (as meteoric iron), lead, and brass were likewise in use before the first known appearance of bronze in the fifth millennium BCE. 　Subsequent developments include the production of early forms of steel; the discovery of sodium—the first light metal—in 1809; the rise of modern alloy steels; and, since the end of World War II, the development of more sophisticated alloys.

Code

In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communication channel or storage in a storage medium. 　An early example is an invention of language, which enabled a person, through speech, to communicate what they thought, saw, heard, or felt to others. 　But speech limits the range of communication to the distance a voice can carry and limits the audience to those present when the speech is uttered. 　The invention of writing, which converted spoken language into visual symbols, extended the range of communication across space and time. 　The process of encoding converts information from a source into symbols for communication or storage. 　Decoding is the reverse process, converting code symbols back into a form that the recipient understands, such as English or/and Spanish. 　One reason for coding is to enable communication in places where ordinary plain language, spoken or written, is difficult or impossible. 　For example, semaphore, where the configuration of flags held by a signaler or the arms of a semaphore tower encodes parts of the message, typically individual letters, and numbers. 　Another person standing a great distance away can interpret the flags and reproduce the words sent.

Ice

Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or 32 °F (0 °C; 273 K) Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color. 　In the Solar System, ice is abundant and occurs naturally from as close to the Sun as Mercury to as far away as the Oort cloud objects. 　Beyond the Solar System, it occurs as interstellar ice. 　It is abundant on Earth's surface – particularly in the polar regions and above the snow line – and, as a common form of precipitation and deposition, plays a key role in Earth's water cycle and climate. 　It falls as snowflakes and hail or occurs as frost, icicles or ice spikes and aggregates from snow as glaciers and ice sheets. 　Ice exhibits at least eighteen phases (packing geometries), depending on temperature and pressure. 　When water is cooled rapidly (quenching), up to three types of amorphous ice can form depending on its history of pressure and temperature. 　When cooled slowly, correlated proton tunneling occurs below −253.15 °C (20 K, −423.67 °F) giving rise to macroscopic quantum phenomena. 　Virtually all ice on Earth's surface and in its atmosphere is of a hexagonal crystalline structure denoted as ice Ih (spoken as "ice one h") with minute traces of cubic ice, denoted as ice Ic and, more recently found, Ice VII inclusions in diamonds. 　The most common phase transition to ice Ih occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. 　It may also be deposited directly by water vapor, as happens in the formation of frost. 　The transition from ice to water is melting and from ice directly to water vapor is sublimation. 　Ice is used in a variety of ways, including for cooling, for winter sports, and ice sculpting.

Majority

Look up majority in Wiktionary, the free dictionary. 　A majority, also called a simple majority or absolute majority to distinguish it from related terms, is more than half of the total. 　It is a subset of a set consisting of more than half of the set's elements. 　For example, if a group consists of 20 individuals, a majority would be 11 or more individuals, while having 10 or fewer individuals would not constitute a majority. 　"Majority" can be used to specify the voting requirement, as in a "majority vote", which means more than half of the votes cast. 　A majority can be compared to a plurality (sometimes called relative majority), which is a subset larger than any other subset but not necessarily larger than all other subsets combined, and not necessarily greater than half of the set. 　For example, if there is a group with 20 members which is divided into subgroups with 9, 6, and 5 members, then the 9-member group would be the plurality. 　A plurality is not necessarily a majority as the largest subset considered may consist of less than half the set's elements. 　This can occur when there are three or more possible choices. 　The (absolute) majority is sometimes referred to as a "simple" majority, compared to a supermajority (a majority requirement above 50%, like a 2/3 requirement), however use of this term is inconsistent as it sometimes refers to a mere plurality (as opposed to an absolute majority). 　In British English the term "majority" is also alternatively used to refer to the winning margin, i.e., the number of votes separating the first-place finisher from the second-place finisher. 　Other related terms containing the word "majority" have their own meanings, which may sometimes be inconsistent in usage.

Appears

"Appears" is a song recorded by Japanese recording artist Ayumi Hamasaki. 　It was released by Avex Trax on November 10, 1999 as the sixth single from her second studio album Loveppears (1999), which was released on the same day. 　Alongside this, it has been released in several other territories with different release dates under her Western alias Ayu. 　It also served as Hamasaki's first limited edition single, limiting physical sales to 300,000 copies. 　The track was written by Hamasaki herself, while production was handled by long-time collaborator Max Matsuura. 　Musically, "Appears" is a dance song written in third person perspective, and is about the third person watching what appears to be a happy and loving relationship. 　Upon its release, "Appears" received positive reviews from music critics. 　Alexey Eremenko, writing for AllMusic, selected the track as the best song from the album and her career. 　However, an editor from CD Journal criticized the amount of remixes on the CD single. 　Commercially, the single was a success in Japan, peaking at number two on the Oricon Singles Chart and TBS' Count Down TV chart. 　It sold just below its restricted 300,000 units, and was certified Gold by the Recording Industry Association of Japan (RIAJ) for shipments of 200,000 units. 　An accompanying music video was directed by Wataru Takeishi, which displays Hamasaki walking around New York City and observing people. 　To promote the single, it appeared on several remix and greatest hits compilation albums conducted by Hamasaki, and has been included on some of her concert tours, including part two of her 2000 concert tour and the 2007 Secret Tour.

Engineering

Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. 　The discipline of engineering encompasses a broad range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied mathematics, applied science, and types of application. 　See glossary of engineering. 　The term engineering is derived from the Latin ingenium, meaning "cleverness" and ingeniare, meaning "to contrive, devise".

Purpose

Look up purpose, intention, intentional, intentionally, or purport in Wiktionary, the free dictionary. 　Purpose is the end for which something is done, created or for which it exists. 　It is part of the topic of intentionality and goal-seeking behavior. 　Related concepts and subjects: Goal, a desired result or possible outcome Intention, the state of intending something or the action intended Motivation, a driving factor for actions, willingness, and goals Determination or resolve Purpose clause, in grammar a dependent adverbial clause expressing purpose Purpose of life, questions regarding the significance of living or existence in general Teleology, the philosophical attempt to describe things in terms of their apparent purpose or goal Teleonomy, the apparent purposefulness of structures and functions in living organisms

Writer

A writer is a person who uses written words in different writing styles and techniques to communicate ideas. 　Writers produce different forms of literary art and creative writing such as novels, short stories, books, poetry, travelogues, plays, screenplays, teleplays, songs, and essays as well as other reports and news articles that may be of interest to the general public. 　Writers' texts are published across a wide range of media. 　Skilled writers who are able to use language to express ideas well, often contribute significantly to the cultural content of a society. 　The term "writer" is also used elsewhere in the arts and music, such as songwriter or a screenwriter, but also a stand-alone "writer" typically refers to the creation of written language. 　Some writers work from an oral tradition. 　Writers can produce material across a number of genres, fictional or non-fictional. 　Other writers use multiple media such as graphics or illustration to enhance the communication of their ideas. 　Another recent demand has been created by civil and government readers for the work of non-fictional technical writers, whose skills create understandable, interpretive documents of a practical or scientific kind. 　Some writers may use images (drawing, painting, graphics) or multimedia to augment their writing. 　In rare instances, creative writers are able to communicate their ideas via music as well as words. 　As well as producing their own written works, writers often write about how they write (their writing process); why they write (that is, their motivation); and also comment on the work of other writers (criticism). 　Writers work professionally or non-professionally, that is, for payment or without payment and may be paid either in advance, or on acceptance, or only after their work is published. 　Payment is only one of the motivations of writers and many are not paid for their work.　[citation needed] The term writer has been used as a synonym of author, although the latter term has a somewhat broader meaning and is used to convey legal responsibility for a piece of writing, even if its composition is anonymous, unknown or collaborative. 　Author most often refers to the writer of a book.

Navy

A navy, naval force, or maritime force is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake-borne, riverine, littoral, or ocean-borne combat operations and related functions. 　It includes anything conducted by surface ships, amphibious ships, submarines, and seaborne aviation, as well as ancillary support, communications, training, and other fields. 　The strategic offensive role of a navy is projection of force into areas beyond a country's shores (for example, to protect sea-lanes, deter or confront piracy, ferry troops, or attack other navies, ports, or shore installations). 　The strategic defensive purpose of a navy is to frustrate seaborne projection-of-force by enemies. 　The strategic task of the navy also may incorporate nuclear deterrence by use of submarine-launched ballistic missiles. 　Naval operations can be broadly divided between riverine and littoral applications (brown-water navy), open-ocean applications (blue-water navy), and something in between (green-water navy), although these distinctions are more about strategic scope than tactical or operational division.

Density

Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. 　The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used. 　Mathematically, density is defined as mass divided by volume: ρ = m V {\displaystyle \rho ={\frac {m}{V}}} where ρ is the density, m is the mass, and V is the volume. 　In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more specifically called specific weight. 　For a pure substance the density has the same numerical value as its mass concentration. 　Different materials usually have different densities, and density may be relevant to buoyancy, purity and packaging. 　Osmium and iridium are the densest known elements at standard conditions for temperature and pressure. 　To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material, usually water. 　Thus a relative density less than one relative to water means that the substance floats in water. 　The density of a material varies with temperature and pressure. 　This variation is typically small for solids and liquids but much greater for gases. 　Increasing the pressure on an object decreases the volume of the object and thus increases its density. 　Increasing the temperature of a substance (with a few exceptions) decreases its density by increasing its volume. 　In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid, which causes it to rise relative to denser unheated material. 　The reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. 　Density is an intensive property in that increasing the amount of a substance does not increase its density; rather it increases its mass. 　Other conceptually comparable quantities or ratios include specific density, relative density (specific gravity), and specific weight.

Silver

Silver is a chemical element with the symbol Ag (from the Latin argentum, derived from the Proto-Indo-European h₂erǵ: "shiny" or "white") and atomic number 47. 　A soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. 　The metal is found in the Earth's crust in the pure, free elemental form ("native silver"), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. 　Most silver is produced as a byproduct of copper, gold, lead, and zinc refining. 　Silver has long been valued as a precious metal. 　Silver metal is used in many bullion coins, sometimes alongside gold: while it is more abundant than gold, it is much less abundant as a native metal. 　Its purity is typically measured on a per-mille basis; a 94%-pure alloy is described as "0.940 fine". 　As one of the seven metals of antiquity, silver has had an enduring role in most human cultures. 　Other than in currency and as an investment medium (coins and bullion), silver is used in solar panels, water filtration, jewellery, ornaments, high-value tableware and utensils (hence the term "silverware"), in electrical contacts and conductors, in specialized mirrors, window coatings, in catalysis of chemical reactions, as a colorant in stained glass, and in specialized confectionery. 　Its compounds are used in photographic and X-ray film. 　Dilute solutions of silver nitrate and other silver compounds are used as disinfectants and microbiocides (oligodynamic effect), added to bandages, wound-dressings, catheters, and other medical instruments.

Chicago

Chicago (/ʃɪˈkɑːɡoʊ/ (listen) shih-KAH-goh, locally also /ʃɪˈkɔːɡoʊ/ shih-KAW-goh; Miami-Illinois: Shikaakwa; Ojibwe: Zhigaagong) is the most populous city in the U.S. state of Illinois and the third most populous in the United States after New York City and Los Angeles. 　With a population of 2,746,388 in the 2020 census, it is also the most populous city in the Midwest. 　As the seat of Cook County (the second-most populous U.S. county), the city is the center of the Chicago metropolitan area, one of the largest in the world. 　On the shore of Lake Michigan, Chicago was incorporated as a city in 1837 near a portage between the Great Lakes and the Mississippi River watershed. 　It grew rapidly in the mid-19th century; by 1860, Chicago was the youngest U.S. city to exceed a population of 100,000. 　The Great Chicago Fire in 1871 destroyed several square miles and left more than 100,000 homeless, but Chicago's population continued to grow to 503,000 by 1880 and then doubled to more than a million within the decade. 　The construction boom accelerated population growth throughout the following decades, and by 1900, less than 30 years after the fire, Chicago was the fifth-largest city in the world. 　Chicago made noted contributions to urban planning and zoning standards, including new construction styles (such as Chicago School architecture, the development of the City Beautiful Movement, and the steel-framed skyscraper). 　Chicago is an international hub for finance, culture, commerce, industry, education, technology, telecommunications, and transportation. 　It is the site of the creation of the first standardized futures contracts, issued by the Chicago Board of Trade, which today is part of the largest and most diverse derivatives market in the world, generating 20% of all volume in commodities and financial futures alone. 　O'Hare International Airport is routinely ranked among the world's top six busiest airports according to tracked data by the Airports Council International. 　The region also has the largest number of federal highways and is the nation's railroad hub. 　The Chicago area has one of the highest gross domestic products (GDP) in the world, generating $689 billion in 2018. 　The economy of Chicago is diverse, with no single industry employing more than 14% of the workforce. 　It is home to several Fortune 500 companies, including Archer-Daniels-Midland, Conagra Brands, Exelon, JLL, Kraft Heinz, McDonald's, Mondelez International, Motorola Solutions, Sears, and United Airlines Holdings. 　Chicago's 58 million tourist visitors in 2018 set a new record. 　Landmarks in the city include Millennium Park, Navy Pier, the Magnificent Mile, Art Institute of Chicago, Museum Campus, Willis (Sears) Tower, Grant Park, Museum of Science and Industry, and Lincoln Park Zoo. 　Chicago is also home to the Barack Obama Presidential Center being built in Hyde Park on the city's South Side. 　Chicago's culture includes the visual arts, literature, film, theater, comedy (especially improvisational comedy), food, dance (including modern dance and jazz troupes and the Joffrey Ballet), and music (particularly jazz, blues, soul, hip-hop, gospel, and electronic dance music, including house music). 　Chicago is also the location of the Chicago Symphony Orchestra and the Lyric Opera of Chicago. 　Of the area's colleges and universities, the University of Chicago, Northwestern University, and the University of Illinois Chicago are classified as "highest research" doctoral universities. 　Chicago has professional sports teams in each of the major professional leagues, including two Major League Baseball teams.

Peace

Peace is a concept of societal friendship and harmony in the absence of hostility and violence. 　In a social sense, peace is commonly used to mean a lack of conflict (such as war) and freedom from fear of violence between individuals or groups. 　"Psychological peace" (such as peaceful thinking and emotions) is perhaps less well defined, yet often a necessary precursor to establishing "behavioural peace." 　Peaceful behaviour sometimes results from a "peaceful inner disposition." 　Some have expressed the belief that peace can be initiated with a certain quality of inner tranquility that does not depend upon the uncertainties of daily life. 　The acquisition of such a "peaceful internal disposition" for oneself and others can contribute to resolving otherwise seemingly irreconcilable competing interests. 　Peace is not a state of excitement although we are happy when excited, but peace is when one's mind is quiet and satisfied.

Youth

Youth is the time of life when one is young. 　The word, youth, can also mean the time between childhood and adulthood (maturity), but it can also refer to one's peak, in terms of health or the period of life known as being a young adult. 　Youth is also defined as "the appearance, freshness, vigor, spirit, etc., characteristic of one, who is young". 　Its definitions of a specific age range varies, as youth is not defined chronologically as a stage that can be tied to specific age ranges; nor can its end point be linked to specific activities, such as taking unpaid work, or having sexual relations. 　Youth is an experience that may shape an individual's level of dependency, which can be marked in various ways according to different cultural perspectives. 　Personal experience is marked by an individual's cultural norms or traditions, while a youth's level of dependency means the extent to which they still rely on their family emotionally and economically.

Wave

In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. 　Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (resting) value at some frequency. 　When the entire waveform moves in one direction, it is said to be a traveling wave; by contrast, a pair of superimposed periodic waves traveling in opposite directions makes a standing wave. 　In a standing wave, the amplitude of vibration has nulls at some positions where the wave amplitude appears smaller or even zero. 　Waves are often described by a wave equation (standing wave field of two opposite waves) or a one-way wave equation for single wave propagation in a defined direction. 　Two types of waves are most commonly studied in classical physics. 　In a mechanical wave, stress and strain fields oscillate about a mechanical equilibrium. 　A mechanical wave is a local deformation (strain) in some physical medium that propagates from particle to particle by creating local stresses that cause strain in neighboring particles too. 　For example, sound waves are variations of the local pressure and particle motion that propagate through the medium. 　Other examples of mechanical waves are seismic waves, gravity waves, surface waves, string vibrations, and vortices. 　In an electromagnetic wave (such as light), coupling between the electric and magnetic fields which sustains propagation of a wave involving these fields according to Maxwell's equations. 　Electromagnetic waves can travel through a vacuum and through some dielectric media (at wavelengths where they are considered transparent). 　Electromagnetic waves, according to their frequencies (or wavelengths) have more specific designations including radio waves, infrared radiation, terahertz waves, visible light, ultraviolet radiation, X-rays and gamma rays. 　Other types of waves include gravitational waves, which are disturbances in spacetime that propagate according to general relativity; heat diffusion waves; plasma waves that combine mechanical deformations and electromagnetic fields; reaction–diffusion waves, such as in the Belousov–Zhabotinsky reaction; and many more. 　Mechanical and electromagnetic waves transfer energy, momentum, and information, but they do not transfer particles in the medium. 　In mathematics and electronics waves are studied as signals. 　On the other hand, some waves have envelopes which do not move at all such as standing waves (which are fundamental to music) and hydraulic jumps. 　Some, like the probability waves of quantum mechanics, may be completely static[dubious – discuss]. 　A physical wave field is almost always confined to some finite region of space, called its domain. 　For example, the seismic waves generated by earthquakes are significant only in the interior and surface of the planet, so they can be ignored outside it. 　However, waves with infinite domain, that extend over the whole space, are commonly studied in mathematics, and are very valuable tools for understanding physical waves in finite domains. 　A plane wave is an important mathematical idealization where the disturbance is identical along any (infinite) plane normal to a specific direction of travel. 　Mathematically, the simplest wave is a sinusoidal plane wave in which at any point the field experiences simple harmonic motion at one frequency. 　In linear media, complicated waves can generally be decomposed as the sum of many sinusoidal plane waves having different directions of propagation and/or different frequencies. 　A plane wave is classified as a transverse wave if the field disturbance at each point is described by a vector perpendicular to the direction of propagation (also the direction of energy transfer); or longitudinal wave if those vectors are aligned with the propagation direction. 　Mechanical waves include both transverse and longitudinal waves; on the other hand electromagnetic plane waves are strictly transverse while sound waves in fluids (such as air) can only be longitudinal. 　That physical direction of an oscillating field relative to the propagation direction is also referred to as the wave's polarization, which can be an important attribute.

Municipality

A municipality is usually a single administrative division having corporate status and powers of self-government or jurisdiction as granted by national and regional laws to which it is subordinate. 　The term municipality may also mean the governing body of a given municipality. 　A municipality is a general-purpose administrative subdivision, as opposed to a special-purpose district. 　The term is derived from French municipalitécode: fra promoted to code: fr and Latin municipaliscode: lat promoted to code: la . 　The English word municipality derives from the Latin social contract municipiumcode: lat promoted to code: la (derived from a word meaning "duty holders"), referring to the Latin communities that supplied Rome with troops in exchange for their own incorporation into the Roman state (granting Roman citizenship to the inhabitants) while permitting the communities to retain their own local governments (a limited autonomy). 　A municipality can be any political jurisdiction, from a sovereign state such as the Principality of Monaco, to a small village such as West Hampton Dunes, New York. 　The territory over which a municipality has jurisdiction may encompass only one populated place such as a city, town, or village several such places (e.g., early jurisdictions in the U.S. state of New Jersey (1798–1899) as townships governing several villages, municipalities of Mexico, municipalities of Colombia) only parts of such places, sometimes boroughs of a city, such as the 34 municipalities of Santiago, Chile.