1.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
2.
Membrane gas separation
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Gas mixtures can be effectively separated by synthetic membranes made from polymers such as polyamide or cellulose acetate, or from ceramic materials. Membranes can be used for separating gas mixtures where they act as a barrier through which different compounds move across at different rates or not move at all. The membranes can be nanoporous, polymer, etc. and the gas molecules penetrate according to their size, diffusivity, in these cases the movement of molecules is best described by pressure-driven convective flow through capillaries, which is quantified by Darcy’s Law. However, the general model in gas applications is the solution-diffusion where particles are first dissolved onto the membrane. This model is employed when the pores in the polymer membrane appear and disappear faster relative to the movement of the particles, in a typical membrane system the incoming feed stream is separated into two components, permeant and retentate. Permeant is the gas that travels across the membrane and the retentate is what is left of the feed, on both sides of the membrane, a gradient of chemical potential is maintained by a pressure difference which is the driving force for the gas molecules to pass through. The ease of transport of each species is quantified by the permeability, the product of DiKi is often expressed as the permeability of the species i, on the specific membrane being used. P i = D i K i The flow of a species, j, can be defined as, J = P j l With the expression above. It can be seen that the flow across the membrane is strongly dependent on the relation between the feed and permeate pressures. The ratio of feed pressure over permeate pressure is defined as the pressure ratio. If the gradient is positive, the flow will go from the feed to the permeate, α i j = P i P j This coefficient is used to indicate the level to which the membrane is able to separates species i from j. In the design of a process, normally the pressure ratio and the membrane selectivity are prescribed by the pressures of the system. The level of separation achieved by the needs to be evaluated based on the aforementioned design parameters in order to evaluate the cost effectiveness of the system. The concentration of species i and j across the membrane can be evaluated based on their respective diffusion flows across it, as a result, the total permeant flow results from the integration of the diffusion flow across the membrane from the feed inlet to feed outlet. It is optimal to have a membrane with a high permeability and sufficient selectivity, synthetic membranes are made from a variety of polymers including polyethylene, polyamides, polyimides, cellulose acetate, polysulphone and polydimethylsiloxan. Polymeric membranes are an option for use in the capture of CO2 from flue gas because of the maturity of the technology in a variety of industries. The ideal polymer membrane has both a high selectivity and permeability, polymer membranes are examples of systems that are dominated by the solution-diffusion mechanism. The membrane is considered to have holes which the gas can dissolve and it was discovered by Robeson in the early 1990s that polymers with a high selectivity have a low permeability and opposite is true, materials with a low selectivity have a high permeability
3.
Nitrogen generator
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Nitrogen generators and stations are stationary or mobile air-to-nitrogen production complexes. The adsorption gas separation process in nitrogen generators is based on the phenomenon of fixing various gas mixture components by a substance called an adsorbent. This phenomenon is brought about by the gas and adsorbent molecules interaction, among nitrogen adsorption plants of various types, pressure swing adsorption plants have found the broadest application world-wide. The systems design is based on the regulation of gas adsorption and this process requires constant temperature, close to ambient. With this process, nitrogen is produced by the plant at the above-atmospheric pressure, the swing adsorption process in each of the two adsorbers consists of two stages running for a few minutes. At the regeneration stage the adsorbed components are released from the adsorbent vented into the atmosphere, the process is then multiply repeated. PSA nitrogen generator plants allow production of high-purity nitrogen from air and this nitrogen purity may also be ensured by cryogenic systems, but they are considerably more complex and justified only by large consumption volumes. The nitrogen generators use CMS technology to produce a supply of ultra high purity nitrogen and are available with internal compressors or without. By substitution of out-of-date air separation plants nitrogen production savings largely exceed 50%, the net cost of nitrogen produced by nitrogen generators is significantly less than the cost of bottled or liquefied nitrogen. Generating nitrogen gas is a sustainable, environmentally friendly and energy efficient approach to providing pure, clean, the operation of membrane systems is based on the principle of differential velocity with which various gas mixture components permeate membrane substance. The driving force in the gas process is the difference in partial pressures on different membrane sides. Structurally, a hollow-fiber membrane represents a cylindrical cartridge functioning as a spool with specifically reeled polymer fibers, gas flow is supplied under pressure into a bundle of membrane fibers. Due to the difference in partial pressures on the external and internal membrane surface gas flow separation is accomplished, by substitution of out-of-date cryogenic or adsorption systems nitrogen production savings generally exceed 50%. The net cost of nitrogen produced by nitrogen complexes is significantly less than the cost of cylinder or liquefied nitrogen, with respect to the simplicity of the system, a nitrogen generator can be split into modules. This is in direct contrast to systems where the equipment is designed for a certain stage of the separation process. Using a modular system, the facility may be built from a selection of preexisting equipment and where necessary. Gas separation units have no moving component parts, thus ensuring exceptional reliability, membranes are highly resistant to vibration and shocks, chemically inert to greases, moisture-insensitive, and capable of operating over a wide temperature range of –40°С to +60°С. With appropriate maintenance, membrane unit useful life ranges between 130,000 and 180,000 hours and this is caused by bacteria and other organisms
4.
Nitrogen
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Nitrogen is a chemical element with symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772, although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is generally accorded the credit because his work was published first. Nitrogen is the lightest member of group 15 of the periodic table, the name comes from the Greek πνίγειν to choke, directly referencing nitrogens asphyxiating properties. It is an element in the universe, estimated at about seventh in total abundance in the Milky Way. At standard temperature and pressure, two atoms of the element bind to form dinitrogen, a colourless and odorless diatomic gas with the formula N2, dinitrogen forms about 78% of Earths atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids, in the nucleic acids, the human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes movement of the element from the air, into the biosphere and organic compounds, many industrially important compounds, such as ammonia, nitric acid, organic nitrates, and cyanides, contain nitrogen. The extremely strong bond in elemental nitrogen, the second strongest bond in any diatomic molecule. Synthetically produced ammonia and nitrates are key industrial fertilisers, and fertiliser nitrates are key pollutants in the eutrophication of water systems. Apart from its use in fertilisers and energy-stores, nitrogen is a constituent of organic compounds as diverse as Kevlar used in high-strength fabric, Nitrogen is a constituent of every major pharmacological drug class, including antibiotics. Many notable nitrogen-containing drugs, such as the caffeine and morphine or the synthetic amphetamines. Nitrogen compounds have a long history, ammonium chloride having been known to Herodotus. They were well known by the Middle Ages, alchemists knew nitric acid as aqua fortis, as well as other nitrogen compounds such as ammonium salts and nitrate salts. The mixture of nitric and hydrochloric acids was known as aqua regia, celebrated for its ability to dissolve gold, the discovery of nitrogen is attributed to the Scottish physician Daniel Rutherford in 1772, who called it noxious air. Though he did not recognise it as a different chemical substance, he clearly distinguished it from Joseph Blacks fixed air. The fact that there was a component of air that does not support combustion was clear to Rutherford, Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as air or azote, from the Greek word άζωτικός. In an atmosphere of nitrogen, animals died and flames were extinguished
5.
Zeolite
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Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents and catalysts. Based on this, he called the material zeolite, from the Greek ζέω, meaning to boil and λίθος, the classic reference for the field has been Zeolite molecular sieves, structure, chemistry, and use by Donald W. Breck. Zeolites occur naturally but are produced industrially on a large scale. As of September 2016,232 unique zeolite frameworks have been identified, every new zeolite structure that is obtained has to be approved by the International Zeolite Association Structure Commission and receives a three letter designation. Zeolites have a structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+. These positive ions are rather loosely held and can readily be exchanged for others in a contact solution, some of the more common mineral zeolites are analcime, chabazite, clinoptilolite, heulandite, natrolite, phillipsite, and stilbite. An example of the formula of a zeolite is, Na2Al2Si3O10·2H2O. Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater, Zeolites also crystallize in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins. Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, metals, quartz, for this reason, naturally occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential. Zeolites are the members of the family of microporous solids known as molecular sieves mainly consisting of Si, Al, O, and metals including Ti, Sn, Zn. The term molecular sieve refers to a property of these materials. This is due to a very regular structure of molecular dimensions. The maximum size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the dimensions of the channels, therefore, the pores in many zeolites are not cylindrical. Zeolites transform to other minerals under weathering, hydrothermal alteration or metamorphic conditions, the sequence of silica-poor volcanic rocks commonly progresses from, Cowlesite → levyne–offretite → analcime → thomsonite–mesolite-scolecite → chabazite → calcite. Industrially important zeolites are produced synthetically, typical procedures entail heating aqueous solutions of alumina and silica with sodium hydroxide. Equivalent reagents include sodium aluminate and sodium silicate, further variations include changes in the cations to include quaternary ammonium cations. Synthetic zeolites hold some key advantages over their natural analogues, the synthetic materials are manufactured in a uniform, phase-pure state. It is also possible to produce zeolite structures that do not appear in nature, Zeolite A is a well-known example
6.
AC power plugs and sockets
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AC power plugs and sockets are devices that allow electrically operated equipment to be connected to the primary alternating current power supply in a building. Electrical plugs and sockets differ in voltage and current rating, shape, size, Plugs and sockets for portable appliances started becoming available in the 1880s, to replace connections to light sockets with easier to use wall-mounted outlets. A proliferation of types developed to address the issues of convenience, today there are approximately 20 types in common use around the world, and many obsolete socket types are still found in older buildings. The International Electrotechnical Commission publishes IEC60050, the International Electrotechnical Vocabulary, the plug has protruding pins or, in US terminology, blades that fit into matching slots or holes in the sockets. In this article, the plug is used in the sense defined by IEC60050. Sockets are designed to prevent exposure of bare energised contacts, sockets may also have protruding exposed contacts, but these are used exclusively for grounding. These may include plugs with insulated sleeves, recessed sockets, sockets with blocking shutters, the term plug is in general and technical use in all forms of English, common alternatives being power plug, electric plug, and plug top. The normal technical term for an AC power socket is socket-outlet, in British English the general term is socket, but there are numerous common alternatives, including power point, plug socket, wall socket, and wall plug. In American English receptacle is used in official standards and codes such as the NEMA connector standard, there is also colloquial use of socket in American English. A socket may be surrounded by a decorative or protective cover called a plate, face plate, outlet cover, socket cover. In some designs this is a piece with the socket itself, bought. Electrical sockets for single phase domestic, commercial and light industrial purposes generally provide two or three electrical connections to the supply conductors. Two-pin sockets normally provide neutral and line connections, both of which carry current and are defined as live parts, Neutral is usually very near to earth potential, usually being earthed either at the distribution board or at the substation. Line carries the full supply voltage relative to the neutral, three-pin sockets provide, in addition, a protective earth connection for exposed metal parts of an appliance. An adaptor is defined in IEC60050 as a portable accessory constructed as an integral unit incorporating both a plug portion and one or more socket-outlet portions, when electricity was first introduced into houses, it was primarily used for lighting. At that time, many electricity companies operated a system where the cost of electricity for lighting was lower than that for other purposes. This led to portable appliances being connected to light bulb sockets using lampholder plugs, as electricity became a common method of operating labour-saving appliances, a safe means of connection to the electric system other than using a light socket was needed. Smith subsequently received US patent 311,616 for the device in 1885
7.
Cabin pressurization
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For aircraft, this air is usually bled off from the gas turbine engines at the compressor stage, and for spacecraft, it is carried in high-pressure, often cryogenic tanks. The air is cooled, humidified, and mixed with recirculated air if necessary, the cabin pressure is regulated by the outflow valve. It also serves to increase passenger comfort and is a regulatory requirement above 15,000 feet in the U. S. A. The principal physiological problems are listed below, Pressurization of the cargo hold is also required to prevent damage to pressure-sensitive goods that might leak, expand, burst or be crushed on re-pressurization. In some individuals, particularly those with heart or lung disease, symptoms may begin as low as 5,000 feet, at this altitude, there is about 25% less oxygen than there is at sea level. Hypoxia may be addressed by the administration of oxygen, either through an oxygen mask or through a nasal cannula. Without pressurization, sufficient oxygen can be delivered up to an altitude of about 40,000 feet. At 40,000 feet, the ambient air pressure falls to about 0.2 bar, emergency oxygen supply masks in the passenger compartment of airliners do not need to be pressure-demand masks because most flights stay below 40,000 feet. Above that altitude the pressure of oxygen will fall below 0.2 bar even at 100% oxygen. Passengers may experience fatigue, nausea, headaches, sleeplessness, and these are the same symptoms that mountain climbers experience, but the limited duration of powered flight makes the development of pulmonary oedema unlikely. The mechanism is the same as that of compressed-air divers on ascent from depth, symptoms may include the early symptoms of the bends—tiredness, forgetfulness, headache, stroke, thrombosis, and subcutaneous itching—but rarely the full symptoms thereof. Decompression sickness may also be controlled by a suit as for altitude sickness. Barotrauma As the aircraft climbs or descends, passengers may experience discomfort or acute pain as gases trapped within their bodies expand or contract, the most common problems occur with air trapped in the middle ear or paranasal sinuses by a blocked Eustachian tube or sinuses. Pain may also be experienced in the tract or even the teeth. The pressure inside the cabin is technically referred to as the equivalent effective cabin altitude or more commonly as the cabin altitude and this is defined as the equivalent altitude above mean sea level having the same atmospheric pressure according to a standard atmospheric model such as the International Standard Atmosphere. Thus a cabin altitude of zero would have the pressure found at sea level. Federal Aviation Administration regulations in the U. S. mandate that under normal operating conditions, the rate of change of cabin altitude strongly affects comfort as humans are sensitive to pressure changes in the inner ear and sinuses and this has to be managed carefully. The cabin altitude of the Boeing 767 is typically about 6,900 feet when cruising at 39,000 feet and this is typical for older jet airliners
8.
Military
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The armed forces of a country are its government-sponsored defense, fighting forces, and organizations. They exist to further the foreign and domestic policies of their body and to defend that body. Armed force is the use of armed forces to achieve political objectives, the study of the use of armed forces is called military science. Broadly speaking, this involves considering offense and defense at three levels, strategy, operational art, and tactics, all three levels study the application of the use of force in order to achieve a desired objective. In most countries the basis of the forces is the military. However, armed forces can include other paramilitary structures, the obvious benefit to a country in maintaining armed forces is in providing protection from foreign threats and from internal conflict. In recent decades armed forces personnel have also used as emergency civil support roles in post-disaster situations. On the other hand, they may harm a society by engaging in counter-productive warfare. Expenditure on science and technology to develop weapons and systems sometimes produces side benefits, although some claim that greater benefits could come from targeting the money directly
9.
Aquaculture
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Aquaculture, also known as aquafarming, is the farming of fish, crustaceans, molluscs, aquatic plants, algae, and other aquatic organisms. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, mariculture refers to aquaculture practiced in marine environments and in underwater habitats. According to the FAO, aquaculture Farming implies some form of intervention in the process to enhance production, such as regular stocking, feeding, protection from predators. Farming also implies individual or corporate ownership of the stock being cultivated, further, in current aquaculture practice, products from several pounds of wild fish are used to produce one pound of a piscivorous fish like salmon. Particular kinds of aquaculture include fish farming, shrimp farming, oyster farming, mariculture, algaculture, particular methods include aquaponics and integrated multi-trophic aquaculture, both of which integrate fish farming and plant farming. The indigenous Gunditjmara people in Victoria, Australia, may have raised eels as early as 6000 BC, Aquaculture was operating in China circa 2500 BC. When the waters subsided after river floods, some fish, mainly carp, were trapped in lakes, early aquaculturists fed their brood using nymphs and silkworm feces, and ate them. A fortunate genetic mutation of carp led to the emergence of goldfish during the Tang dynasty, japanese cultivated seaweed by providing bamboo poles and, later, nets and oyster shells to serve as anchoring surfaces for spores. Romans bred fish in ponds and farmed oysters in coastal lagoons before 100 CE, in central Europe, early Christian monasteries adopted Roman aquacultural practices. Aquaculture spread in Europe during the Middle Ages since away from the seacoasts, improvements in transportation during the 19th century made fresh fish easily available and inexpensive, even in inland areas, making aquaculture less popular. The 15th-century fishponds of the Trebon Basin in the Czech Republic are maintained as a UNESCO World Heritage Site, a remarkable example is a fish pond dating from at least 1,000 years ago, at Alekoko. Legend says that it was constructed by the mythical Menehune dwarf people, in first half of 18th century, German Stephan Ludwig Jacobi experimented with external fertilization of brown trouts and salmon. He wrote an article Von der künstlichen Erzeugung der Forellen und Lachse, by the latter decades of the 18th century, oyster farming had begun in estuaries along the Atlantic Coast of North America. The word aquaculture appeared in an 1855 newspaper article in reference to the harvesting of ice, in 1859, Stephen Ainsworth of West Bloomfield, New York, began experiments with brook trout. By 1864, Seth Green had established a commercial fish-hatching operation at Caledonia Springs, near Rochester, by 1866, with the involvement of Dr. W. W. Fletcher of Concord, Massachusetts, artificial fish hatcheries were under way in both Canada and the United States. When the Dildo Island fish hatchery opened in Newfoundland in 1889, the word aquaculture was used in descriptions of the hatcheries experiments with cod and lobster in 1890. By the 1920s, the American Fish Culture Company of Carolina, Rhode Island, during the 1940s, they had perfected the method of manipulating the day and night cycle of fish so that they could be artificially spawned year around. Californians harvested wild kelp and attempted to supply around 1900
10.
Food and Drug Administration
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The Food and Drug Administration is a federal agency of the United States Department of Health and Human Services, one of the United States federal executive departments. As of 2017, 3/4th of the FDA budget is funded by the pharmaceutical companies due to the Prescription drug user fee act and these include regulating lasers, cellular phones, condoms and control of disease on products ranging from certain household pets to sperm donation for assisted reproduction. The FDA is led by the Commissioner of Food and Drugs, appointed by the President with the advice, the Commissioner reports to the Secretary of Health and Human Services. Dr. Robert M. Califf, MD is the current commissioner, who took over in February 2016 for Dr. Stephen Ostroff, the FDA has its headquarters in unincorporated White Oak, Maryland. The agency also has 223 field offices and 13 laboratories located throughout the 50 states, the United States Virgin Islands, in 2008, the FDA began to post employees to foreign countries, including China, India, Costa Rica, Chile, Belgium, and the United Kingdom. The site was renamed from the White Oak Naval Surface Warfare Center to the Federal Research Center at White Oak, the first building, the Life Sciences Laboratory, was dedicated and opened with 104 employees on the campus in December 2003. Only one original building from the facility was kept. All other buildings are new construction, the project is slated to be completed by 2017, assuming future Congressional funding While most of the Centers are located in the Washington, D. C. The Office of Regulatory Affairs is considered the eyes and ears of the agency, the Office of Regulatory Affairs is divided into five regions, which are further divided into 20 districts. Districts are based roughly on the divisions of the federal court system. Each district comprises a main office and a number of Resident Posts. ORA also includes the Agencys network of laboratories, which analyze any physical samples taken. Though samples are usually food-related, some laboratories are equipped to analyze drugs, cosmetics, the Office of Criminal Investigations was established in 1991 to investigate criminal cases. Unlike ORA Investigators, OCI Special Agents are armed, and dont focus on aspects of the regulated industries. In many cases, OCI pursues cases involving Title 18 violations, OCI Special Agents often come from other criminal investigations backgrounds, and work closely with the Federal Bureau of Investigation, Assistant Attorney General, and even Interpol. OCI receives cases from a variety of sources—including ORA, local agencies, OCI is a smaller branch, comprising about 200 agents nationwide. The FDA frequently works with federal agencies, including the Department of Agriculture, Drug Enforcement Administration, Customs and Border Protection. Often local and state government agencies also work with the FDA to provide regulatory inspections, the FDA regulates more than US$1 trillion worth of consumer goods, about 25% of consumer expenditures in the United States
11.
Hospital
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A hospital is a health care institution providing patient treatment with specialized medical and nursing staff and medical equipment. The best-known type of hospital is the hospital, which typically has an emergency department to treat urgent health problems ranging from fire. A district hospital typically is the health care facility in its region, with large numbers of beds for intensive care. Specialised hospitals can help reduce health care costs compared to general hospitals, a teaching hospital combines assistance to people with teaching to medical students and nurses. The medical facility smaller than a hospital is called a clinic. Hospitals have a range of departments and specialist units such as cardiology, some hospitals have outpatient departments and some have chronic treatment units. Common support units include a pharmacy, pathology, and radiology, Hospitals are usually funded by the public sector, by health organisations, by health insurance companies, or by charities, including direct charitable donations. Historically, hospitals were founded and funded by religious orders, or by charitable individuals. During the Middle Ages, hospitals served different functions from modern institutions, Middle Ages hospitals were almshouses for the poor, hostels for pilgrims, or hospital schools. The word hospital comes from the Latin hospes, signifying a stranger or foreigner, another noun derived from this, hospitium came to signify hospitality, that is the relation between guest and shelterer, hospitality, friendliness, and hospitable reception. By metonymy the Latin word then came to mean a guest-chamber, guests lodging, hospes is thus the root for the English words host hospitality, hospice, hostel and hotel. The German word Spital shares similar roots, the grammar of the word differs slightly depending on the dialect. Some patients go to a hospital just for diagnosis, treatment, or therapy and then leave without staying overnight, while others are admitted and stay overnight or for several days or weeks or months. Hospitals usually are distinguished from other types of facilities by their ability to admit and care for inpatients whilst the others. Larger cities may have several hospitals of varying sizes and facilities, some hospitals, especially in the United States and Canada, have their own ambulance service. A district hospital typically is the health care facility in its region, with large numbers of beds for intensive care. In California, district hospital refers specifically to a class of healthcare facility created shortly after World War II to address a shortage of beds in many local communities. Twenty-eight of Californias rural hospitals and 20 of its critical-access hospitals are District hospitals, Californias District hospitals are formed by local municipalities, have Boards that are individually elected by their local communities, and exist to serve local needs
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