The Defense Advanced Research Projects Agency is an agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Known as the Advanced Research Projects Agency, the agency was created in February 1958 by President Dwight D. Eisenhower in response to the Soviet launching of Sputnik 1 in 1957. By collaborating with academic and government partners, DARPA formulates and executes research and development projects to expand the frontiers of technology and science beyond immediate U. S. military requirements. DARPA-funded projects have provided significant technologies that influenced many non-military fields, such as computer networking and the basis for the modern Internet, graphical user interfaces in information technology. DARPA is independent of other military research and development and reports directly to senior Department of Defense management. DARPA has about 220 employees, of whom 100 are in management; the name of the organization first changed from its founding name ARPA to DARPA in March 1972 changing back to ARPA in February 1993, only to revert to DARPA in March 1996.
Their mission statement is "to make pivotal investments in breakthrough technologies for national security". The creation of the Advanced Research Projects Agency was authorized by President Dwight D. Eisenhower in 1958 for the purpose of forming and executing research and development projects to expand the frontiers of technology and science, able to reach far beyond immediate military requirements, the two relevant acts being the Supplemental Military Construction Authorization and Department of Defense Directive 5105.15, in February 1958. Its creation was directly attributed to the launching of Sputnik and to U. S. realization that the Soviet Union had developed the capacity to exploit military technology. Initial funding of ARPA was $520 million. ARPA's first director, Roy Johnson, left a $160,000 management job at General Electric for an $18,000 job at ARPA. Herbert York from Lawrence Livermore National Laboratory was hired as his scientific assistant. Johnson and York were both keen on space projects, but when NASA was established in 1958 all space projects and most of ARPA's funding were transferred to it.
Johnson resigned and ARPA was repurposed to do "high-risk", "high-gain", "far out" basic research, a posture, enthusiastically embraced by the nation's scientists and research universities. ARPA's second director was Brigadier General Austin W. Betts, who resigned in early 1961, he was succeeded by Jack Ruina who served until 1963. Ruina, the first scientist to administer ARPA, managed to raise its budget to $250 million, it was Ruina who hired J. C. R. Licklider as the first administrator of the Information Processing Techniques Office, which played a vital role in creation of ARPANET, the basis for the future Internet. Additionally, the political and defense communities recognized the need for a high-level Department of Defense organization to formulate and execute R&D projects that would expand the frontiers of technology beyond the immediate and specific requirements of the Military Services and their laboratories. In pursuit of this mission, DARPA has developed and transferred technology programs encompassing a wide range of scientific disciplines that address the full spectrum of national security needs.
From 1958 to 1965, ARPA's emphasis centered on major national issues, including space, ballistic missile defense, nuclear test detection. During 1960, all of its civilian space programs were transferred to the National Aeronautics and Space Administration and the military space programs to the individual services; this allowed ARPA to concentrate its efforts on the Project Defender, Project Vela, Project AGILE programs, to begin work on computer processing, behavioral sciences, materials sciences. The DEFENDER and AGILE programs formed the foundation of DARPA sensor and directed energy R&D in the study of radar, infrared sensing, x-ray/gamma ray detection. ARPA at this point played an early role in Transit a predecessor to the Global Positioning System. "Fast-forward to 1959 when a joint effort between DARPA and the Johns Hopkins Applied Physics Laboratory began to fine-tune the early explorers’ discoveries. TRANSIT, sponsored by the Navy and developed under the leadership of Dr. Richard Kirschner at Johns Hopkins, was the first satellite positioning system."During the late 1960s, with the transfer of these mature programs to the Services, ARPA redefined its role and concentrated on a diverse set of small exploratory research programs.
The agency was renamed the Defense Advanced Research Projects Agency in 1972, during the early 1970s, it emphasized direct energy programs, information processing, tactical technologies. Concerning information processing, DARPA made great progress through its support of the development of time-sharing. DARPA supported the evolution of the ARPANET, Packet Radio Network, Packet Satellite Network and the Internet and research in the artificial intelligence fields of speech recognition and signal processing, including parts of Shakey the robot. DARPA funded the development of the Douglas Engelbart's NLS computer system and The Mother of
The Boeing Company is an American multinational corporation that designs and sells airplanes, rockets and missiles worldwide. The company provides leasing and product support services. Boeing is among the largest global aircraft manufacturers. Boeing stock is included in the Dow Jones Industrial Average. Boeing was founded by William Boeing on July 15, 1916, in Washington; the present corporation is the result of the merger of Boeing with McDonnell Douglas on August 1, 1997. Former Boeing's chair and CEO Philip M. Condit continued as the chair and CEO of the new Boeing, while Harry Stonecipher, former CEO of McDonnell Douglas, became the president and chief operating officer of the newly merged company; the Boeing Company has its corporate headquarters in Illinois. The company is led by CEO Dennis Muilenburg. Boeing is organized into five primary divisions: Boeing Commercial Airplanes. In 2017, Boeing recorded $93.3 billion in sales, ranked 24th on the Fortune magazine "Fortune 500" list, ranked 64th on the "Fortune Global 500" list, ranked 19th on the "World's Most Admired Companies" list.
In March 1910, William E. Boeing bought Heath's shipyard in Seattle on the Duwamish River, which became his first airplane factory. Boeing was incorporated in Seattle by William Boeing, on July 15, 1916, as "Pacific Aero Products Co". Boeing was incorporated in Delaware. Boeing, who studied at Yale University, worked in the timber industry, where he became wealthy and learned about wooden structures; this knowledge proved invaluable in his subsequent assembly of airplanes. The company stayed in Seattle to take advantage of the local supply of spruce wood. One of the two "B&W" seaplanes built with the assistance of George Conrad Westervelt, a U. S. Navy engineer, took its maiden flight on June 15, 1916. Boeing and Westervelt decided to build the B&W seaplane after having flown in a Curtiss aircraft. Boeing bought a Glenn Martin "Flying Birdcage" seaplane and was taught to fly by Glenn Martin himself. Boeing soon crashed the Birdcage and when Martin informed Boeing that replacement parts would not become available for months, Boeing realized he could build his own plane in that amount of time.
He and his friend Cdr. G. C. Westervelt soon produced the B&W Seaplane; this first Boeing airplane was assembled in a lakeside hangar located on the northeast shore of Seattle's Lake Union. Many of Boeing's early planes were seaplanes. On April 6, 1917, the U. S. declared war on Germany and entered World War I. On May 9, 1917, the company became the "Boeing Airplane Company". With the U. S. entering the war, Boeing knew that the U. S. Navy needed seaplanes for training. So Boeing shipped two new Model Cs to Pensacola, where the planes were flown for the Navy; the Navy ordered 50 more. The company moved its operations to a larger former shipbuilding facility known as Boeing Plant 1, located on the lower Duwamish River, Washington state; when World War I ended in 1918, a large surplus of cheap, used military planes flooded the commercial airplane market, preventing aircraft companies from selling any new airplanes, driving many out of business. Others, including Boeing, started selling other products. Boeing built dressers and furniture, along with flat-bottom boats called Sea Sleds.
In 1919 the Boeing B-1 flying boat made its first flight. It accommodated two passengers and some mail. Over the course of eight years, it made international airmail flights from Seattle to Victoria, British Columbia. On May 24, 1920, the Boeing Model 8 made its first flight, it was the first plane to fly over Mount Rainier. In 1923, Boeing entered competition against Curtiss to develop a pursuit fighter for the U. S. Army Air Service. Although Curtiss finished its design first and was awarded the contract, Boeing continued to develop its PW-9 fighter; that plane, along with the Boeing P-12/F4B fighter, made Boeing a leading manufacturer of fighters over the course of the next decade. In 1925, Boeing built its Model 40 mail plane for the U. S. government to use on airmail routes. In 1927, an improved version of this plane was built, the Model 40A which won the U. S. Post Office's contract to deliver mail between San Chicago; the 40A had a passenger cabin that accommodated two. That same year, Boeing created an airline named Boeing Air Transport, which merged a year with Pacific Air Transport and the Boeing Airplane Company.
The first airmail flight for the airline was on July 1, 1927. In 1929 the company merged with Pratt & Whitney, Hamilton Aero Manufacturing Company, Chance Vought under the new title United Aircraft and Transport Corporation; the merge was followed by the acquisition of the Sikorsky Manufacturing Corporation, Stearman Aircraft Corporation, Standard Metal Propeller Company. United Aircraft purchased National Air Transport in 1930. On July 27, 1928, the 12-passenger Boeing 80 biplane made its first flight. With three engines, it was Boeing's first plane built with the sole intention of being a passenger transport. An upgraded version, the 80A, carrying eighteen passengers, made its first flight in September 1929. In the early 1930s Boeing became a leader in all-metal aircraft construction, in the design revolution t
Redondo Beach, California
Redondo Beach is coastal city in Los Angeles County, United States, located in the South Bay region of the Greater Los Angeles area. It is one of three adjacent beach cities along the southern portion of Santa Monica Bay; the population was 66,748 at the 2010 census, up from 63,261 at the 2000 census. Redondo Beach was part of the 1785 Rancho San Pedro Spanish land grant that became the South Redondo area; the city's territory has an unusual shape including an area along the beach and another strip inland from Manhattan Beach and Hermosa Beach. The primary attractions include Municipal Pier and the sandy beach, popular with tourists and a variety of sports enthusiasts; the western terminus of the Metro Rail Green Line is in North Redondo Beach. The Chowigna Indians used the site of today's Hopkins Wilderness Park Nike missile site LA-57 from 1956 to 1963, in Redondo Beach, California, as a lookout place; the wetlands located at the site of today's AES power plant in Redondo Beach were a source of foods including halibut and sea bass, of salt.
In the 1700s, the Chowigna bartered salt from the old Redondo Salt Lake, "a spring-fed salt lake about 200 yards wide and 600 yards long situated about 200 yards from the ocean", with other tribes. Their village by the lake was called "Onoova-nga", or "Place of Salt." The Chowigna were relocated to missions in 1854, when Manuel Dominguez sold 215 acres of Rancho San Pedro, including the lake, to Henry Allanson and William Johnson for the Pacific Salt Works. Moonstone Beach was a tourist attraction from the late 1880s to the early 1920s. Tourists gathered moonstones from the many mounds; the City of Redondo Beach is a Charter City in Southern California. Two thirds of the residents in LA County, the majority in Southern California, a plurality of Californians live in Charter Cities according to the 2010 US Census; as a Californian Charter City, Redondo Beach can adopt Amendments to the City Charter. In response to alleged overdevelopment, a group of Redondo’s residents formed a PAC called Building a Better Redondo and worked to place Measure DD on the ballot.
The City Council responded with Measure EE. Both measures are initiative petitions which would amend the Charter of the City of Redondo Beach by requiring both City Council approval and voter approval before a “major change in allowable land use” would become effective. However, the difference was in scope. Measure DD would apply to any zoning changes that would have the effect of converting any public land to private use. Measure DD was an initiative that earned a place on the ballot because its supporters collected over 6,000 signatures on petitions, while Measure EE was placed on the November ballot through the referral process by a vote of the Redondo Beach City Council. Out of Redondo’s 39,155 registered voters, 29,653 voted on Measure DD, 28,570 voted on Measure EE, with the turnout being 75.7 percent and 72.9 percent respectively. Measure DD passed 52.7 – 41.3 percent, Measure EE passed 50.9 – 49.1 percent. When two initiative measures conflict, the one with the greatest number of votes wins, since Measure DD defeated Measure EE by 2,884 votes, it was added to the Redondo Beach City Charter.
On July 30th, 2010 the Los Angeles Superior Court Judge Robert O’Brien confirmed that Measure DD was broad in scope, as intended by the voters. Measure DD led to the passage of Measure G, it passed, 12,622 votes to 11,422 votes. Building a Better Redondo proposed Measure A in November of 2013, which would have zoned 60 percent of the AES property as parkland and the rest – commercial. AES spent over $650K on the campaign promising everything from power failures to huge lawsuits if Measure A won. Measure A failed, with 6,553 "no" 6,295 "yes" votes. Buoyed by Measure A’s failure, AES, the operator of the powerplant and owner of the property, proposed Measure B, a mixed use development with residential and commercial components, poured over $1M into the campaign. Measure B failed, with 6,684 "no" 6,072 "yes" votes. In 2017 another activist group, Rescue Our Waterfront, which had quite a few crossover members from Building a Better Redondo, proposed Measure C; this was in reaction to a project called "The Waterfront", which moved the required boat ramp to Mole B, which would impact outrigger canoe clubs and was deemed dangerous by Harbor Patrol staff.
Measure C, or the King Harbor CARE Act, would tighten up the zoning passed in Measure G. It was designed to ensure long established recreational uses and views of the harbor were protected in future development and prevent the impacts of the proposed "Waterfront" project; the measure passed, with 9,229 “yes” votes and 6,925 “no” votes, swept Mayor Bill Brand, Councilmembers Todd Lowenstein and Nils Nehrenheim into office. The developer responded with a lawsuit. On August 9th, 2018, the California Coastal Commission certified Measure C, as is, without the additions that were suggested by its own staff, thus ending the ten year old saga. According to the United States Census Bureau, the city has a total area of 6.2 square miles, over 99% of it land. Redondo Beach was part of the 1784 Rancho San Pedro Sp
Fast Fourier transform
A fast Fourier transform is an algorithm that computes the discrete Fourier transform of a sequence, or its inverse. Fourier analysis converts a signal from its original domain to a representation in the frequency domain and vice versa; the DFT is obtained by decomposing a sequence of values into components of different frequencies. This operation is useful in many fields, but computing it directly from the definition is too slow to be practical. An FFT computes such transformations by factorizing the DFT matrix into a product of sparse factors; as a result, it manages to reduce the complexity of computing the DFT from O, which arises if one applies the definition of DFT, to O, where n is the data size. The difference in speed can be enormous for long data sets where N may be in the thousands or millions. In the presence of round-off error, many FFT algorithms are much more accurate than evaluating the DFT definition directly. There are many different FFT algorithms based on a wide range of published theories, from simple complex-number arithmetic to group theory and number theory.
Fast Fourier transforms are used for applications in engineering and mathematics. The basic ideas were popularized in 1965, but some algorithms had been derived as early as 1805. In 1994, Gilbert Strang described the FFT as "the most important numerical algorithm of our lifetime", it was included in Top 10 Algorithms of 20th Century by the IEEE journal Computing in Science & Engineering; the best-known FFT algorithms depend upon the factorization of N, but there are FFTs with O complexity for all N for prime N. Many FFT algorithms only depend on the fact that e − 2 π i / N is an N-th primitive root of unity, thus can be applied to analogous transforms over any finite field, such as number-theoretic transforms. Since the inverse DFT is the same as the DFT, but with the opposite sign in the exponent and a 1/N factor, any FFT algorithm can be adapted for it; the development of fast algorithms for DFT can be traced to Gauss's unpublished work in 1805 when he needed it to interpolate the orbit of asteroids Pallas and Juno from sample observations.
His method was similar to the one published in 1965 by Cooley and Tukey, who are credited for the invention of the modern generic FFT algorithm. While Gauss's work predated Fourier's results in 1822, he did not analyze the computation time and used other methods to achieve his goal. Between 1805 and 1965, some versions of FFT were published by other authors. Frank Yates in 1932 published his version called interaction algorithm, which provided efficient computation of Hadamard and Walsh transforms. Yates' algorithm is still used in the field of statistical analysis of experiments. In 1942, G. C. Danielson and Cornelius Lanczos published their version to compute DFT for x-ray crystallography, a field where calculation of Fourier transforms presented a formidable bottleneck. While many methods in the past had focused on reducing the constant factor for O computation by taking advantage of "symmetries", Danielson and Lanczos realized that one could use the "periodicity" and apply a "doubling trick" to get O runtime.
James Cooley and John Tukey published a more general version of FFT in 1965, applicable when N is composite and not a power of 2. Tukey came up with the idea during a meeting of President Kennedy's Science Advisory Committee where a discussion topic involved detecting nuclear tests by the Soviet Union by setting up sensors to surround the country from outside. To analyze the output of these sensors, a fast Fourier transform algorithm would be needed. In discussion with Tukey, Richard Garwin recognized the general applicability of the algorithm not just to national security problems, but to a wide range of problems including one of immediate interest to him, determining the periodicities of the spin orientations in a 3-D crystal of Helium-3. Garwin gave Tukey's idea to Cooley for implementation. Cooley and Tukey published the paper in a short time of six months; as Tukey did not work at IBM, the patentability of the idea was doubted and the algorithm went into the public domain, through the computing revolution of the next decade, made FFT one of the indispensable algorithms in digital signal processing.
Let x0.... XN−1 be complex numbers; the DFT is defined by the formula X k = ∑ n = 0 N − 1 x n e − i 2 π k n / N = ∑ n = 0 N − 1 x n w − k n k = 0, …, N − 1. Where w = e i 2 π / N
El Segundo, California
El Segundo is a city located in Los Angeles County, United States. El Segundo, from Spanish, means "The Second" in English. Located on the Santa Monica Bay, it was incorporated on January 18, 1917, part of the South Bay Cities Council of Governments; the population was 16,654 at the 2010 census up from 16,033 at the 2000 census. The El Segundo and Los Angeles coastal area was first settled by the Tongva Native American tribes thousands of years ago; the area was once a part of Rancho Sausal Redondo. Rancho Sausal Redondo extended from Playa Del Rey in the North to Redondo Beach in the South. A Mexican land grant owned by Antonio Ygnacio Avila, the rancho was purchased by a Scottish baronet named Sir Robert Burnett. After his return to Scotland, the property was purchased by current manager of the rancho, Daniel Freeman. Daniel Freeman sold portions of the rancho to several persons. George H. Peck owned the 840 acres of land. Peck developed land in neighboring El Porto where a street still bears his name.
The city earned its name as it was the site of the second Standard Oil refinery on the West Coast, when Standard Oil of California purchased the 840 acres of farm land in 1911. The city was incorporated in 1917; the Standard Oil Company was renamed Chevron in 1984. The El Segundo refinery entered its second century of operation in 2011; the Douglas Aircraft Company plant in El Segundo was one of the major aircraft manufacturing facilities in California during World War II. It was one of the major producers of SBD Dauntless dive bombers, which achieved fame in the Battle of Midway; the facility, now operated by Northrop Grumman, is still an aircraft plant. The north and south boundaries of the town are Los Angeles International Airport and Manhattan Beach, with the Pacific Ocean as the western boundary, its eastern boundary is Aviation Blvd. El Segundo is located at 33°55′17″N 118°24′22″W. According to the United States Census Bureau, the city has a total area of 5.5 square miles, over 99% of, land.
Guinness World Records has listed El Segundo as having the most roads with a grade. The 2010 United States Census reported that El Segundo had a population of 16,654; the population density was 3,047.9 people per square mile. The racial makeup of El Segundo was 12,997 White, 337 African American, 68 Native American, 1,458 Asian, 38 Pacific Islander, 799 from other races, 957 from two or more races. Hispanic or Latino people of any race were 2,609 persons; the Census reported that 16,578 people lived in households, 66 lived in non-institutionalized group quarters, 10 were institutionalized. There were 7,085 households, out of which 2,183 had children under the age of 18 living in them, 3,050 were opposite-sex married couples living together, 729 had a female householder with no husband present, 326 had a male householder with no wife present. There were 369 unmarried opposite-sex partnerships. 2,254 households were made up of individuals and 570 had someone living alone, 65 years of age or older.
The average household size was 2.34. There were 4,105 families; the population was spread out with 3,719 people under the age of 18, 1,120 people aged 18 to 24, 5,182 people aged 25 to 44, 4,955 people aged 45 to 64, 1,678 people who were 65 years of age or older. The median age was 39.2 years. For every 100 females, there were 99.4 males. For every 100 females age 18 and over, there were 98.8 males. There were 7,410 housing units at an average density of 1,356.1 per square mile, of which 3,034 were owner-occupied, 4,051 were occupied by renters. The homeowner vacancy rate was 0.4%. 8,177 people lived in owner-occupied housing units and 8,401 people lived in rental housing units. According to the 2010 United States Census, El Segundo had a median household income of $84,341, with 4.8% of the population living below the federal poverty line. As of the 2000 Census, the population density was 2,894.6 inhabitants per square mile. There were 7,261 housing units at an average density of 1,310.9 per square mile.
The racial makeup of the city was 83.61% White, 1.17% Black or African American, 0.47% Native American, 6.41% Asian, 0.29% Pacific Islander, 3.51% from other races, 4.55% from two or more races. 11.01% of the population were Hispanic or Latino of any race. There were 7,060 households out of which 28.1% had children under the age of 18 living with them, 41.5% were married couples living together, 10.0% had a female householder with no husband present, 44.6% were non-families. 34.3% of all households were made up of individuals and 7.5% had someone living alone, 65 years of age or older. The average household size was 2.27 and the average family size was 3.00. In the city, the population was spread out with 22.7% under the age of 18, 6.2% from 18 to 24, 38.7% from 25 to 44, 22.9% from 45 to 64, 9.5% who were 65 years of age or older. The median age was 36 years. For every 100 females, there were 98.7 males. For every 100 females age 18 and over, there were 96.0 males. The median income for a household in the city was $61,341, the median income for a family was $74,007.
Males had a median income of $52,486 versus $41,682 for females. The per capita income for
California is a state in the Pacific Region of the United States. With 39.6 million residents, California is the most populous U. S. the third-largest by area. The state capital is Sacramento; the Greater Los Angeles Area and the San Francisco Bay Area are the nation's second and fifth most populous urban regions, with 18.7 million and 9.7 million residents respectively. Los Angeles is California's most populous city, the country's second most populous, after New York City. California has the nation's most populous county, Los Angeles County, its largest county by area, San Bernardino County; the City and County of San Francisco is both the country's second-most densely populated major city after New York City and the fifth-most densely populated county, behind only four of the five New York City boroughs. California's $3.0 trillion economy is larger than that of any other state, larger than those of Texas and Florida combined, the largest sub-national economy in the world. If it were a country, California would be the 5th largest economy in the world, the 36th most populous as of 2017.
The Greater Los Angeles Area and the San Francisco Bay Area are the nation's second- and third-largest urban economies, after the New York metropolitan area. The San Francisco Bay Area PSA had the nation's highest GDP per capita in 2017 among large PSAs, is home to three of the world's ten largest companies by market capitalization and four of the world's ten richest people. California is considered a global trendsetter in popular culture, innovation and politics, it is considered the origin of the American film industry, the hippie counterculture, fast food, the Internet, the personal computer, among others. The San Francisco Bay Area and the Greater Los Angeles Area are seen as global centers of the technology and entertainment industries, respectively. California has a diverse economy: 58% of the state's economy is centered on finance, real estate services and professional, scientific and technical business services. Although it accounts for only 1.5% of the state's economy, California's agriculture industry has the highest output of any U.
S. state. California is bordered by Oregon to the north and Arizona to the east, the Mexican state of Baja California to the south; the state's diverse geography ranges from the Pacific Coast in the west to the Sierra Nevada mountain range in the east, from the redwood–Douglas fir forests in the northwest to the Mojave Desert in the southeast. The Central Valley, a major agricultural area, dominates the state's center. Although California is well-known for its warm Mediterranean climate, the large size of the state results in climates that vary from moist temperate rainforest in the north to arid desert in the interior, as well as snowy alpine in the mountains. Over time and wildfires have become more pervasive features. What is now California was first settled by various Native Californian tribes before being explored by a number of European expeditions during the 16th and 17th centuries; the Spanish Empire claimed it as part of Alta California in their New Spain colony. The area became a part of Mexico in 1821 following its successful war for independence but was ceded to the United States in 1848 after the Mexican–American War.
The western portion of Alta California was organized and admitted as the 31st state on September 9, 1850. The California Gold Rush starting in 1848 led to dramatic social and demographic changes, with large-scale emigration from the east and abroad with an accompanying economic boom; the word California referred to the Baja California Peninsula of Mexico. The name derived from the mythical island California in the fictional story of Queen Calafia, as recorded in a 1510 work The Adventures of Esplandián by Garci Rodríguez de Montalvo; this work was the fifth in a popular Spanish chivalric romance series that began with Amadis de Gaula. Queen Calafia's kingdom was said to be a remote land rich in gold and pearls, inhabited by beautiful black women who wore gold armor and lived like Amazons, as well as griffins and other strange beasts. In the fictional paradise, the ruler Queen Calafia fought alongside Muslims and her name may have been chosen to echo the title of a Muslim leader, the Caliph. It's possible.
Know ye that at the right hand of the Indies there is an island called California close to that part of the Terrestrial Paradise, inhabited by black women without a single man among them, they lived in the manner of Amazons. They were robust of body with great virtue; the island itself is one of the wildest in the world on account of the craggy rocks. Shortened forms of the state's name include CA, Cal. Calif. and US-CA. Settled by successive waves of arrivals during the last 10,000 years, California was one of the most culturally and linguistically diverse areas in pre-Columbian North America. Various estimates of the native population range from 100,000 to 300,000; the Indigenous peoples of California included more than 70 distinct groups of Native Americans, ranging from large, settled populations living on the coast to groups in the interior. California groups were diverse in their political organization with bands, villages, on the resource-rich coasts, large chiefdoms, such as the Chumash and Salinan.
Trade, intermarriage a
Active laser medium
The active laser medium is the source of optical gain within a laser. The gain results from the stimulated emission of electronic or molecular transitions to a lower energy state from a higher energy state populated by a pump source. Examples of active laser media include: Certain crystals doped with rare-earth ions or transition metal ions. Liquids, in the form of dye solutions as used in dye lasers. In order to fire a laser, the active gain medium must be in a nonthermal energy distribution known as a population inversion; the preparation of this state is known as laser pumping. Pumping may be achieved with electrical currents or with light, generated by discharge lamps or by other lasers. More exotic gain media can be pumped by chemical reactions, nuclear fission, or with high-energy electron beams. A universal model valid for all laser types does not exist; the simplest model includes two systems of sub-levels: lower. Within each sub-level system, the fast transitions ensure that thermal equilibrium is reached leading to the Maxwell–Boltzmann statistics of excitations among sub-levels in each system.
The upper level is assumed to be metastable. Gain and refractive index are assumed independent of a particular way of excitation. For good performance of the gain medium, the separation between sub-levels should be larger than working temperature. In the case of amplification of optical signals, the lasing frequency is called signal frequency. However, the same term is used in the laser oscillators, when amplified radiation is used to transfer energy rather than information; the model below seems to work well for most optically-pumped solid-state lasers. The simple medium can be characterized with effective cross-sections of absorption and emission at frequencies ω p and ω s. Have N be concentration of active centers in the solid-state lasers. Have N 1 be concentration of active centers in the ground state. Have N 2 be concentration of excited centers. Have N 1 + N 2 = N; the relative concentrations can be defined as n 1 = N 1 / N and n 2 = N 2 / N. The rate of transitions of an active center from ground state to the excited state can be expressed with W u = I p σ a p ℏ ω p + I s σ a s ℏ ω s and The rate of transitions back to the ground state can be expressed with W d = I p σ e p ℏ ω p + I s σ e s ℏ ω s + 1 τ, where σ a s and σ a p are effective cross-sections of absorption at the frequencies of the signal and the pump.
Σ e s and σ e p are the same for stimulated emission. The kinetic equation for relative populations can be written as follows: d n 2 d t = W u n 1 − W d n 2, d n 1 d t = − W