Major League Baseball
Major League Baseball is a professional baseball organization, the oldest of the four major professional sports leagues in the United States and Canada. A total of 30 teams play with 15 teams in each league; the NL and AL were formed as separate legal entities in 1901 respectively. After cooperating but remaining separate entities beginning in 1903, the leagues merged into a single organization led by the Commissioner of Baseball in 2000; the organization oversees Minor League Baseball, which comprises 256 teams affiliated with the Major League clubs. With the World Baseball Softball Confederation, MLB manages the international World Baseball Classic tournament. Baseball's first all-professional team was founded in Cincinnati in 1869; the first few decades of professional baseball were characterized by rivalries between leagues and by players who jumped from one team or league to another. The period before 1920 in baseball was known as the dead-ball era. Baseball survived a conspiracy to fix the 1919 World Series, which came to be known as the Black Sox Scandal.
The sport rose in popularity in the 1920s, survived potential downturns during the Great Depression and World War II. Shortly after the war, Jackie Robinson broke baseball's color barrier; the 1950s and 1960s were a time of expansion for the AL and NL new stadiums and artificial turf surfaces began to change the game in the 1970s and 1980s. Home runs dominated the game during the 1990s, media reports began to discuss the use of anabolic steroids among Major League players in the mid-2000s. In 2006, an investigation produced the Mitchell Report, which implicated many players in the use of performance-enhancing substances, including at least one player from each team. Today, MLB is composed of 1 in Canada. Teams play 162 games each season and five teams in each league advance to a four-round postseason tournament that culminates in the World Series, a best-of-seven championship series between the two league champions that dates to 1903. Baseball broadcasts are aired on television and the Internet throughout North America and in several other countries throughout the world.
MLB has the highest season attendance of any sports league in the world with more than 73 million spectators in 2015. MLB is governed by the Major League Baseball Constitution; this document has undergone several incarnations since its creation in 1876. Under the direction of the Commissioner of Baseball, MLB hires and maintains the sport's umpiring crews, negotiates marketing and television contracts. MLB maintains a unique, controlling relationship over the sport, including most aspects of Minor League Baseball; this is due in large part to the 1922 U. S. Supreme Court ruling in Federal Baseball Club v. National League, which held that baseball is not interstate commerce and therefore not subject to federal antitrust law; this ruling has been weakened only in subsequent years. The weakened ruling granted more stability to the owners of teams and has resulted in values increasing at double-digit rates. There were several challenges to MLB's primacy in the sport between the 1870s and the Federal League in 1916.
The chief executive of MLB is the commissioner Rob Manfred. The chief operating officer is Tony Petitti. There are five other executives: president, chief communications officer, chief legal officer, chief financial officer, chief baseball officer; the multimedia branch of MLB, based in Manhattan, is MLB Advanced Media. This branch oversees each of the 30 teams' websites, its charter states that MLB Advanced Media holds editorial independence from the league, but it is under the same ownership group and revenue-sharing plan. MLB Productions is a structured wing of the league, focusing on video and traditional broadcast media. MLB owns 67 percent of MLB Network, with the other 33 percent split between several cable operators and satellite provider DirecTV, it operates out of studios in Secaucus, New Jersey, has editorial independence from the league. In 1920, the weak National Commission, created to manage relationships between the two leagues, was replaced with the much more powerful Commissioner of Baseball, who had the power to make decisions for all of professional baseball unilaterally.
From 1901 to 1960, the American and National Leagues fielded eight teams apiece. In the 1960s, MLB expansion added eight teams, including the first non-U. S. Team. Two teams were added in the 1970s. From 1969 through 1993, each league consisted of an West Division. A third division, the Central Division, was formed in each league in 1994; until 1996, the two leagues met on the field only during the All-Star Game. Regular-season interleague play was introduced in 1997. In March 1995 two new franchises, the Arizona Diamondbacks and Tampa Bay Devil Rays, were awarded by MLB, to begin play in 1998; this addition brought the total number of franchises to 30. In early 1997, MLB decided to assign one new team to each league: Tampa Bay joined the AL and Arizona joined the NL; the original plan was to have an odd number of teams in each league, but in order for every team to be able to play daily, this would have required interleague play to be scheduled throughout the entire season. However, it
Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter. Different sources define different frequency ranges as microwaves. A more common definition in radio engineering is the range between 100 GHz. In all cases, microwaves include the entire SHF band at minimum. Frequencies in the microwave range are referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations; the prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range. Rather, it indicates that microwaves are "small", compared to the radio waves used prior to microwave technology; the boundaries between far infrared, terahertz radiation and ultra-high-frequency radio waves are arbitrary and are used variously between different fields of study. Microwaves travel by line-of-sight. At the high end of the band they are absorbed by gases in the atmosphere, limiting practical communication distances to around a kilometer.
Microwaves are used in modern technology, for example in point-to-point communication links, wireless networks, microwave radio relay networks, radar and spacecraft communication, medical diathermy and cancer treatment, remote sensing, radio astronomy, particle accelerators, industrial heating, collision avoidance systems, garage door openers and keyless entry systems, for cooking food in microwave ovens. Microwaves occupy a place in the electromagnetic spectrum with frequency above ordinary radio waves, below infrared light: In descriptions of the electromagnetic spectrum, some sources classify microwaves as radio waves, a subset of the radio wave band; this is an arbitrary distinction. Microwaves travel by line-of-sight paths. Although at the low end of the band they can pass through building walls enough for useful reception rights of way cleared to the first Fresnel zone are required. Therefore, on the surface of the Earth, microwave communication links are limited by the visual horizon to about 30–40 miles.
Microwaves are absorbed by moisture in the atmosphere, the attenuation increases with frequency, becoming a significant factor at the high end of the band. Beginning at about 40 GHz, atmospheric gases begin to absorb microwaves, so above this frequency microwave transmission is limited to a few kilometers. A spectral band structure causes absorption peaks at specific frequencies. Above 100 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is in effect opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges. In a microwave beam directed at an angle into the sky, a small amount of the power will be randomly scattered as the beam passes through the troposphere. A sensitive receiver beyond the horizon with a high gain antenna focused on that area of the troposphere can pick up the signal; this technique has been used at frequencies between 0.45 and 5 GHz in tropospheric scatter communication systems to communicate beyond the horizon, at distances up to 300 km.
The short wavelengths of microwaves allow omnidirectional antennas for portable devices to be made small, from 1 to 20 centimeters long, so microwave frequencies are used for wireless devices such as cell phones, cordless phones, wireless LANs access for laptops, Bluetooth earphones. Antennas used include short whip antennas, rubber ducky antennas, sleeve dipoles, patch antennas, the printed circuit inverted F antenna used in cell phones, their short wavelength allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter. Therefore, beams of microwaves are used for point-to-point communication links, for radar. An advantage of narrow beams is that they don't interfere with nearby equipment using the same frequency, allowing frequency reuse by nearby transmitters. Parabolic antennas are the most used directive antennas at microwave frequencies, but horn antennas, slot antennas and dielectric lens antennas are used. Flat microstrip antennas are being used in consumer devices.
Another directive antenna practical at microwave frequencies is the phased array, a computer-controlled array of antennas which produces a beam which can be electronically steered in different directions. At microwave frequencies, the transmission lines which are used to carry lower frequency radio waves to and from antennas, such as coaxial cable and parallel wire lines, have excessive power losses, so when low attenuation is required microwaves are carried by metal pipes called waveguides. Due to the high cost and maintenance requirements of waveguide runs, in many microwave antennas the output stage of the transmitter or the RF front end of the receiver is located at the antenna; the term microwave has a more technical meaning in electromagnetics and circuit theory. Apparatus and techniques may
Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, spacecraft, guided missiles, motor vehicles, weather formations, terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the object. Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed. Radar was developed secretly for military use by several nations in the period before and during World War II. A key development was the cavity magnetron in the UK, which allowed the creation of small systems with sub-meter resolution; the term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging The term radar has since entered English and other languages as a common noun, losing all capitalization.
The modern uses of radar are diverse, including air and terrestrial traffic control, radar astronomy, air-defense systems, antimissile systems, marine radars to locate landmarks and other ships, aircraft anticollision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring and flight control systems, guided missile target locating systems, ground-penetrating radar for geological observations, range-controlled radar for public health surveillance. High tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from high noise levels. Radar is a key technology that the self-driving systems are designed to use, along with sonar and other sensors. Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "lidar". With the emergence of driverless vehicles, Radar is expected to assist the automated platform to monitor its environment, thus preventing unwanted incidents.
As early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes; the next year, he added a spark-gap transmitter. In 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation; the German inventor Christian Hülsmeyer was the first to use radio waves to detect "the presence of distant metallic objects". In 1904, he demonstrated the feasibility of detecting a ship in dense fog, but not its distance from the transmitter, he obtained a patent for his detection device in April 1904 and a patent for a related amendment for estimating the distance to the ship.
He got a British patent on September 23, 1904 for a full radar system, that he called a telemobiloscope. It operated on a 50 cm wavelength and the pulsed radar signal was created via a spark-gap, his system used the classic antenna setup of horn antenna with parabolic reflector and was presented to German military officials in practical tests in Cologne and Rotterdam harbour but was rejected. In 1915, Robert Watson-Watt used radio technology to provide advance warning to airmen and during the 1920s went on to lead the U. K. research establishment to make many advances using radio techniques, including the probing of the ionosphere and the detection of lightning at long distances. Through his lightning experiments, Watson-Watt became an expert on the use of radio direction finding before turning his inquiry to shortwave transmission. Requiring a suitable receiver for such studies, he told the "new boy" Arnold Frederic Wilkins to conduct an extensive review of available shortwave units. Wilkins would select a General Post Office model after noting its manual's description of a "fading" effect when aircraft flew overhead.
Across the Atlantic in 1922, after placing a transmitter and receiver on opposite sides of the Potomac River, U. S. Navy researchers A. Hoyt Taylor and Leo C. Young discovered that ships passing through the beam path caused the received signal to fade in and out. Taylor submitted a report, suggesting that this phenomenon might be used to detect the presence of ships in low visibility, but the Navy did not continue the work. Eight years Lawrence A. Hyland at the Naval Research Laboratory observed similar fading effects from passing aircraft. Before the Second World War, researchers in the United Kingdom, Germany, Japan, the Netherlands, the Soviet Union, the United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, New Zealand, South Africa followed prewar Great Britain's radar development, Hungary generated its radar technology during the war. In France in 1934, following systematic studies on the split-anode magnetron, the research branch of the Compagnie Générale de Télégraphie Sans Fil headed by Maurice Ponte with Henri Gutton, Sylvain Berline and M. Hugon, began developing an obstacle-locatin
A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, uses the Doppler effect of the returned signal to determine the target object's velocity. It combines the features of pulse radars and continuous-wave radars, which were separate due to the complexity of the electronics. Pulse-Doppler systems were first used on fighter aircraft starting in the 1960s. Earlier radars had used pulse-timing in order to determine range and the angle of the antenna to determine the bearing. However, this only worked; as the ground moves at the same speed but opposite direction of the aircraft, Doppler techniques allow the ground return to be filtered out, revealing aircraft and vehicles. This gives pulse-Doppler radars "look-down/shoot-down" capability. A secondary advantage in military radar is to reduce the transmitted power while achieving acceptable performance for improved safety of stealthy radar. Pulse-Doppler techniques find widespread use in meteorological radars, allowing the radar to determine wind speed from the velocity of any precipitation in the air.
Pulse-Doppler radar is the basis of synthetic aperture radar used in radar astronomy, remote sensing and mapping. In air traffic control, they are used for discriminating aircraft from clutter. Besides the above conventional surveillance applications, pulse-Doppler radar has been applied in healthcare, such as fall risk assessment and fall detection, for nursing or clinical purposes; the earliest radar systems failed to operate. The reason was traced to Doppler effects that degrade performance of systems not designed to account for moving objects. Fast-moving objects cause a phase-shift on the transmit pulse. Doppler has maximum detrimental effect on moving target indicator systems, which must use reverse phase shift for Doppler compensation in the detector. Doppler weather effects were found to degrade conventional radar and moving target indicator radar, which can mask aircraft reflections; this phenomenon was adapted for use with weather radar in the 1950s after declassification of some World War II systems.
Pulse-Doppler radar was developed during World War II to overcome limitations by increasing pulse repetition frequency. This required the development of the klystron, the traveling wave tube, solid state devices. Pulse-Doppler is incompatible with other high power microwave amplification devices that are not coherent. Early examples of military systems include the AN/SPG-51B developed during the 1950s for the purpose of operating in hurricane conditions with no performance degradation; the Hughes AN/ASG-18 Fire Control System was a prototype airborne radar/combination system for the planned North American XF-108 Rapier interceptor aircraft for the United States Air Force, for the Lockheed YF-12. The US's first pulse-Doppler radar, the system had look-down/shoot-down capability and could track one target at a time. Weather, terrain, flying techniques, stealth are common tactics used to hide aircraft from radar. Pulse-Doppler radar eliminates these weaknesses, it became possible to use pulse-Doppler radar on aircraft after digital computers were incorporated in the design.
Pulse-Doppler provided look-down/shoot-down capability to support air-to-air missile systems in most modern military aircraft by the mid 1970s. Pulse-Doppler systems measure the range to objects by measuring the elapsed time between sending a pulse of radio energy and receiving a reflection of the object. Radio waves travel at the speed of light, so the distance to the object is the elapsed time multiplied by the speed of light, divided by two - there and back. Pulse-Doppler radar is based on the Doppler effect, where movement in range produces frequency shift on the signal reflected from the target. Doppler frequency = 2 × transmit frequency × range velocity C. Radial velocity is essential for pulse-Doppler radar operation; as the reflector moves between each transmit pulse, the returned signal has a phase difference, or phase shift, from pulse to pulse. This causes the reflector to produce Doppler modulation on the reflected signal. Pulse-Doppler radars exploit this phenomenon to improve performance.
The amplitude of the successively returning pulse from the same scanned volume is I = I 0 sin = I 0 sin , where x 0 is the distance radar to target, λ is the radar wavelength, t it the time between two pulses. So Δ Θ = 4 π v Δ t λ; this allows the radar to separate the reflections from multiple objects located in the same volume of space by separating
Weather radar called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type. Modern weather radars are pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather. During World War II, radar operators discovered that weather was causing echoes on their screen, masking potential enemy targets. Techniques were developed to filter them. Soon after the war, surplus radars were used to detect precipitation. Since weather radar has evolved on its own and is now used by national weather services, research departments in universities, in television stations' weather departments. Raw images are used and specialized software can take radar data to make short term forecasts of future positions and intensities of rain, snow and other weather phenomena.
Radar output is incorporated into numerical weather prediction models to improve analyses and forecasts. During World War II, military radar operators noticed noise in returned echoes due to rain and sleet. After the war, military scientists returned to civilian life or continued in the Armed Forces and pursued their work in developing a use for those echoes. In the United States, David Atlas at first working for the Air Force and for MIT, developed the first operational weather radars. In Canada, J. S. Marshall and R. H. Douglas formed the "Stormy Weather Group" in Montreal. Marshall and his doctoral student Walter Palmer are well known for their work on the drop size distribution in mid-latitude rain that led to understanding of the Z-R relation, which correlates a given radar reflectivity with the rate at which rainwater is falling. In the United Kingdom, research continued to study the radar echo patterns and weather elements such as stratiform rain and convective clouds, experiments were done to evaluate the potential of different wavelengths from 1 to 10 centimeters.
By 1950 the UK company EKCO was demonstrating its airborne'cloud and collision warning search radar equipment'. In 1953 Donald Staggs, an electrical engineer working for the Illinois State Water Survey, made the first recorded radar observation of a "hook echo" associated with a tornadic thunderstorm. Between 1950 and 1980, reflectivity radars, which measure position and intensity of precipitation, were incorporated by weather services around the world; the early meteorologists had to watch a cathode ray tube. During the 1970s, radars began to be organized into networks; the first devices to capture radar images were developed. The number of scanned angles was increased to get a three-dimensional view of the precipitation, so that horizontal cross-sections and vertical cross-sections could be performed. Studies of the organization of thunderstorms were possible for the Alberta Hail Project in Canada and National Severe Storms Laboratory in the US in particular; the NSSL, created in 1964, began experimentation on dual polarization signals and on Doppler effect uses.
In May 1973, a tornado devastated Union City, just west of Oklahoma City. For the first time, a Dopplerized 10 cm wavelength radar from NSSL documented the entire life cycle of the tornado; the researchers discovered a mesoscale rotation in the cloud aloft before the tornado touched the ground – the tornadic vortex signature. NSSL's research helped convince the National Weather Service that Doppler radar was a crucial forecasting tool; the Super Outbreak of tornadoes on 3–4 April 1974 and their devastating destruction might have helped to get funding for further developments. Between 1980 and 2000, weather radar networks became the norm in North America, Europe and other developed countries. Conventional radars were replaced by Doppler radars, which in addition to position and intensity could track the relative velocity of the particles in the air. In the United States, the construction of a network consisting of 10 cm radars, called NEXRAD or WSR-88D, was started in 1988 following NSSL's research.
In Canada, Environment Canada constructed the King City station, with a 5 cm research Doppler radar, by 1985. This led to a complete Canadian Doppler network between 1998 and 2004. France and other European countries had switched to Doppler networks by the early 2000s. Meanwhile, rapid advances in computer technology led to algorithms to detect signs of severe weather, many applications for media outlets and researchers. After 2000, research on dual polarization technology moved into operational use, increasing the amount of information available on precipitation type. "Dual polarization" means that microwave radiation, polarized both horizontally and vertically is emitted. Wide-scale deployment was done by the end of the decade or the beginning of the next in some countries such as the United States and Canada. In April 2013, all United States National Weather Service NEXRADs were dual-polarized. Since 2003, the U. S. National Oceanic and Atmospheric Administration has been experimenting with phased-array radar as a replacement for conventional parabolic antenna to provide more time resolution in atmospheric sounding.
This could be significant with severe thunderstorms, as their evolution can be better evaluated with more timely data. In 2003, the National Science Foundation established the Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere
A circulator is a passive non-reciprocal three- or four-port device, in which a microwave or radio frequency signal entering any port is transmitted to the next port in rotation. A port in this context is a point where an external waveguide or transmission line, connects to the device. For a three-port circulator, a signal applied to port 1 only comes out of port 2. Depending on the materials involved, circulators fall into two main categories: ferrite circulators and nonferrite circulators. Ferrite circulators are radio frequency circulators which are composed of magnetised ferrite materials, they fall into two main classes: 4-port waveguide circulators based on Faraday rotation of waves propagating in a magnetised material, 3-port "Y-junction" circulators based on cancellation of waves propagating over two different paths near a magnetised material. Waveguide circulators may be of either type, while more compact devices based on stripline are of the 3-port type. Two or more Y-junctions can be combined in a single component to give four or more ports, but these differ in behaviour from a true 4-port circulator.
A permanent magnet produces the magnetic flux through the waveguide. Ferrimagnetic garnet crystal is used in optical circulators. Though ferrite circulators can provide good'forward' signal circulation while suppressing the'reverse' circulation, their major shortcomings at low frequencies, are the bulky sizes and the narrow bandwidths. Early work on nonferrite circulators includes active circulators using transistors that are non-reciprocal in nature. In contrast to ferrite circulators which are passive devices, active circulators require power. Major issues associated with transistor-based active circulators are the power limitation and the signal-to-noise degradation, which are critical when it is used as a duplexer for sustaining the strong transmit power and clean reception of the signal from the antenna. Varactors offer one solution. One study employed a structure similar to a time-varying transmission line with the effective nonreciprocity triggered by a one-direction propagating carrier pump.
This is like an AC-powered active circulator. The research claimed to be able to achieve positive gain and low noise for receiving path and broadband nonreciprocity. Another study used resonance with nonreciprocity triggered by angular-momentum biasing, which more mimics the way that signals passively circulate in a ferrite circulator. In 1964, Mohr presented and experimentally demonstrated a circulator based on transmission lines and switches. In April, 2016 a research team extended this concept, presenting an integrated circuit circulator based on N-path filter concepts, it offers the potential for full duplex communication. The device is much smaller than conventional devices; when one port of a three-port circulator is terminated in a matched load, it can be used as an isolator, since a signal can travel in only one direction between the remaining ports. An isolator is used to shield equipment on its input side from the effects of conditions on its output side. In radar, circulators are used as a type of duplexer, to route signals from the transmitter to the antenna and from the antenna to the receiver, without allowing signals to pass directly from transmitter to receiver.
The alternative type of duplexer is a transmit-receive switch that alternates between connecting the antenna to the transmitter and to the receiver. The use of chirped pulses and a high dynamic range may lead to temporal overlap of the sent and received pulses, requiring a circulator for this function. In the future-generation cellular communication, people talk about full-duplex radios, where signals can be transmitted and received at the same frequency. Given the limited, crowded spectrum resource, full-duplexing can directly benefit the wireless communication by twice of the data throughput speed; the wireless communication is still performed with "half-duplex", where either the signals are transmitted or received at different time frames, if at the same frequency, or the signals are transmitted and received at different frequencies. A reflection amplifier is a type of microwave amplifier circuit utilizing negative differential resistance diodes such as tunnel diodes and Gunn diodes. Negative differential resistance diodes can amplify signals, perform better at microwave frequencies than two-port devices.
However, since the diode is a one-port device, a nonreciprocal component is needed to separate the outgoing amplified signal from the incoming input signal. By using a 3-port circulator with the signal input connected to one port, the biased diode connected to a second, the output load connected to the third, the output and input can be uncoupled. Chait, H. N..
Health care or healthcare is the maintenance or improvement of health via the prevention and treatment of disease, illness and other physical and mental impairments in people. Health care is delivered by health professionals in allied health fields. Physicians and physician associates are a part of these health professionals. Dentistry, nursing, optometry, pharmacy, occupational therapy, physical therapy and other health professions are all part of health care, it includes work done in providing primary care, secondary care, tertiary care, as well as in public health. Access to health care may vary across countries and individuals influenced by social and economic conditions as well as health policies. Health care systems are organizations established to meet the health needs of targeted populations. According to the World Health Organization, a well-functioning health care system requires a financing mechanism, a well-trained and adequately paid workforce, reliable information on which to base decisions and policies, well maintained health facilities to deliver quality medicines and technologies.
An efficient health care system can contribute to a significant part of a country's economy and industrialization. Health care is conventionally regarded as an important determinant in promoting the general physical and mental health and well-being of people around the world. An example of this was the worldwide eradication of smallpox in 1980, declared by the WHO as the first disease in human history to be eliminated by deliberate health care interventions; the delivery of modern health care depends on groups of trained professionals and paraprofessionals coming together as interdisciplinary teams. This includes professionals in medicine, physiotherapy, dentistry and allied health, along with many others such as public health practitioners, community health workers and assistive personnel, who systematically provide personal and population-based preventive and rehabilitative care services. While the definitions of the various types of health care vary depending on the different cultural, political and disciplinary perspectives, there appears to be some consensus that primary care constitutes the first element of a continuing health care process and may include the provision of secondary and tertiary levels of care.
Health care can be defined as either private. Primary care refers to the work of health professionals who act as a first point of consultation for all patients within the health care system; such a professional would be a primary care physician, such as a general practitioner or family physician. Another professional would be a licensed independent practitioner such as a physiotherapist, or a non-physician primary care provider such as a physician assistant or nurse practitioner. Depending on the locality, health system organization the patient may see another health care professional first, such as a pharmacist or nurse. Depending on the nature of the health condition, patients may be referred for secondary or tertiary care. Primary care is used as the term for the health care services that play a role in the local community, it can be provided in different settings, such as Urgent care centers which provide same day appointments or services on a walk-in basis. Primary care involves the widest scope of health care, including all ages of patients, patients of all socioeconomic and geographic origins, patients seeking to maintain optimal health, patients with all types of acute and chronic physical and social health issues, including multiple chronic diseases.
A primary care practitioner must possess a wide breadth of knowledge in many areas. Continuity is a key characteristic of primary care, as patients prefer to consult the same practitioner for routine check-ups and preventive care, health education, every time they require an initial consultation about a new health problem; the International Classification of Primary Care is a standardized tool for understanding and analyzing information on interventions in primary care based on the reason for the patient's visit. Common chronic illnesses treated in primary care may include, for example: hypertension, asthma, COPD, depression and anxiety, back pain, arthritis or thyroid dysfunction. Primary care includes many basic maternal and child health care services, such as family planning services and vaccinations. In the United States, the 2013 National Health Interview Survey found that skin disorders and joint disorders, back problems, disorders of lipid metabolism, upper respiratory tract disease were the most common reasons for accessing a physician.
In the United States, primary care physicians have begun to deliver primary care outside of the managed care system through direct primary care, a subset of the more familiar concierge medicine. Physicians in this model bill patients directly for services, either on a pre-paid monthly, quarterly, or annual basis, or bill for each service in the office. Examples of direct primary care practices include Foundation Health in Colorado and Qliance in Washington. In context of global population aging, with increasing numbers of older adults at greater risk of chronic non-communicable diseases increasing demand for primary care services is expected in both developed and developing countries; the World Health Organization attributes the provision of essential primary care as an integral component of an inclusive primary health care strategy. Secondary care includes acute care: nec