Frequency is the number of occurrences of a repeating event per unit of time. It is referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency; the period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals, radio waves, light. For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics and radio, frequency is denoted by a Latin letter f or by the Greek letter ν or ν; the relation between the frequency and the period T of a repeating event or oscillation is given by f = 1 T.
The SI derived unit of frequency is the hertz, named after the German physicist Heinrich Hertz. One hertz means. If a TV has a refresh rate of 1 hertz the TV's screen will change its picture once a second. A previous name for this unit was cycles per second; the SI unit for period is the second. A traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. 60 rpm equals one hertz. As a matter of convenience and slower waves, such as ocean surface waves, tend to be described by wave period rather than frequency. Short and fast waves, like audio and radio, are described by their frequency instead of period; these used conversions are listed below: Angular frequency denoted by the Greek letter ω, is defined as the rate of change of angular displacement, θ, or the rate of change of the phase of a sinusoidal waveform, or as the rate of change of the argument to the sine function: y = sin = sin = sin d θ d t = ω = 2 π f Angular frequency is measured in radians per second but, for discrete-time signals, can be expressed as radians per sampling interval, a dimensionless quantity.
Angular frequency is larger than regular frequency by a factor of 2π. Spatial frequency is analogous to temporal frequency, but the time axis is replaced by one or more spatial displacement axes. E.g.: y = sin = sin d θ d x = k Wavenumber, k, is the spatial frequency analogue of angular temporal frequency and is measured in radians per meter. In the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has an inverse relationship to the wavelength, λ. In dispersive media, the frequency f of a sinusoidal wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave: f = v λ. In the special case of electromagnetic waves moving through a vacuum v = c, where c is the speed of light in a vacuum, this expression becomes: f = c λ; when waves from a monochrome source travel from one medium to another, their frequency remains the same—only their wavelength and speed change. Measurement of frequency can done in the following ways, Calculating the frequency of a repeating event is accomplished by counting the number of times that event occurs within a specific time period dividing the count by the length of the time period.
For example, if 71 events occur within 15 seconds the frequency is: f = 71 15 s ≈ 4.73 Hz If the number of counts is not large, it is more accurate to measure the time interval for a predetermined number of occurrences, rather than the number of occurrences within a specified time. The latter method introduces a random error into the count of between zero and one count, so on average half a count; this is called gating error and causes an average error in the calculated frequency of Δ f = 1 2 T
Brownsville is a city in Cameron County in the U. S. state of Texas. It located on the western Gulf Coast in South Texas, adjacent to the border with Mexico; the city covers 81.528 square miles and has a population of 183,299 as of 2017. It is 16th-largest in Texas, it is part of the Brownsville–Matamoros conurbation, with a population of 1,136,995 people. The city is known for deep-water seaport and Hispanic culture; the city was founded in 1848 by American entrepreneur Charles Stillman after he developed a successful river boat company nearby. It was named after Major Jacob Brown, who fought and died while serving as a U. S. Army soldier during the Mexican–American War; as the city is the seat of government for the county of Cameron, the city and county government are major employers. Other primary employers fall within the service and manufacturing industries, including a growing aerospace and space transportation sector, it operates international trading through the Port of Brownsville. The city experienced a population increase in the early 1900s.
Brownsville is cited as having one of the highest poverty rates in the United States. Due to significant historical events, the city has multiple houses and battle sites listed under the National Register of Historic Places, it was the scene of several key events of the American Civil War, such as the Battle of Brownsville and the Battle of Palmito Ranch. The city was involved in the Texas Revolution as well as the Mexican–American War. Brownsville's idiosyncratic geographic location has made it a wildlife refuge center. Several state parks and historical sites are protected by the Texas Parks and Wildlife Department. In 1781, Spanish government officials granted José Salvador de la Garza 59 leagues of land, he used the land to construct a ranch several miles northwest of the area. During the early 1800s, Brownsville was known to residents as los tejidos; the area was inhabited by a few settlers around 1836 when Texas declared its independence from Mexico. On February 4, 1846, President James K. Polk instructed American General Zachary Taylor and his troops to begin moving south towards Brownsville.
Once Taylor arrived, he built Fort Texas. It was renamed Fort Brown in honor of American General Jacob Brown, one of two deceased soldiers during the Siege of Fort Texas. Charles Stillman arrived in Matamoros in 1828 from Connecticut to help his father in the mercantile business. Brownsville became part of Texas after the signing of the Treaty of Guadalupe Hidalgo in 1848. During that year, Stillman formed a partnership with Samuel Belden and Simon Mussina to form the Brownsville Town Company, they sold lots valued at $1,500. The city of Brownsville was established in late 1848 by Stillman, was made the county seat of Cameron County on January 13, 1849; the state incorporated the city on January 24, 1850. This was repealed on April 1, 1852, because of a land-ownership dispute between Stillman and its former owners; the state reincorporated the city on February 7, 1853. The issue of ownership was not decided until 1879 when the United States Supreme Court ruled in favor of Stillman. On April 25, 1846, Captain Seth B.
Thornton received reports of Mexican troops crossing the Rio Grande river. Thornton and 63 U. S. Dragoons discovered several houses in the area. Mexican General Anastasio Torrejón crossed the Rio Grande the previous day, he commanded 1,600 cavalry and infantry troops to surround Thornton's troops in fractions. Due to heavy force from Torrejón's troops, Thornton's troops surrendered. 11 American casualties were reported. Reports of the incident were sent to President James K. Polk who announced that "American blood has been spilled upon the American territory". On May 13, the United States Congress declared war against Mexico. American General Zachary Taylor retreated from Fort Brown on May 1, 1846. On May 3, Arista and the Mexican Army began the Siege of Fort Texas, during the first active campaign in the Mexican–American War; this was counteracted by the United States 7th Infantry Regiment. Despite heavy strikes, Mexican General Pedro de Ampudia outlined a traditional siege to move forward. General Zachary Taylor began moving towards Fort Brown.
Mexican troops intercepted them near Palo Alto 5 miles north of present-day Brownsville, resulting in the first battle of the war. The following day, Mexican troops had retreated. Taylor's troops charged up to them resulting in the Battle of Resaca de la Palma, which took place within the present city limits; when Taylor arrived at the besieged Fort Texas, he found that two soldiers including the fort's commander Major Jacob Brown, had died. Brown, who suffered an injury when a cannonball hit his leg, died three days after his injury on May 9. In his honor, General Taylor renamed the facility as Fort Brown. An old cannon at the University of Texas at Brownsville and Texas Southmost College marks the spot where Major Brown received his fatal wound. On July 13, 1859, Juan Cortina saw Brownsville city Marshal Robert Sheers arrest and beat an elderly man, a ranch hand at his mother's ranch. Cortina approached the marshal, questioning his motives, before shooting him twice after he refused to release the man.
The first shot missed Sheers, but the second struck his shoulder causing him to fall t
The Rio Grande is one of the principal rivers in the southwest United States and northern Mexico. The Rio Grande begins in south-central Colorado in the United States and flows to the Gulf of Mexico. Along the way, it forms part of the Mexico–United States border. According to the International Boundary and Water Commission, its total length was 1,896 miles in the late 1980s, though course shifts result in length changes. Depending on how it is measured, the Rio Grande is either the fourth- or fifth-longest river system in North America; the river serves as part of the natural border between the U. S. state of Texas and the Mexican states of Chihuahua, Nuevo León, Tamaulipas. A short stretch of the river serves as part of the boundary between the U. S. states of New Mexico. Since the mid–20th century, heavy water consumption by farms and cities along with many large diversion dams on the river has left only 20% of its natural discharge to flow to the Gulf. Near the river's mouth, the irrigated lower Rio Grande Valley is an important agricultural region.
The Rio Grande's watershed covers 182,200 square miles. Many endorheic basins are situated within, or adjacent to, the Rio Grande's basin, these are sometimes included in the river basin's total area, increasing its size to about 336,000 square miles; the Rio Grande rises in the western part of the Rio Grande National Forest in the U. S. state of Colorado. The river is formed by the joining of several streams at the base of Canby Mountain in the San Juan Mountains, just east of the Continental Divide. From there, it flows through the San Luis Valley south into the Middle Rio Grande Valley in New Mexico, passing through the Rio Grande Gorge near Taos toward Española, picking up additional water from the San Juan-Chama Diversion Project from the Rio Chama, it continues on a southerly route through the desert cities of Albuquerque and Las Cruces to El Paso and Ciudad Juárez, Chihuahua. In the Albuquerque area, the river flows past a number of historic Pueblo villages, including Sandia Pueblo and Isleta Pueblo.
Below El Paso, it serves as part of the border between the United States and Mexico. The official river border measurement ranges from 889 miles to 1,248 miles, depending on how the river is measured. A major tributary, the Rio Conchos, enters at Ojinaga, below El Paso, supplies most of the water in the border segment. Other tributaries include the Pecos and the smaller Devils, which join the Rio Grande on the site of Amistad Dam. Despite its name and length, the Rio Grande is not navigable by ocean-going ships, nor do smaller passenger boats or cargo barges use it as a route, it is navigable at all, except by small boats in a few places. The Rio Grande rises in high flows for much of its length at high elevation. In New Mexico, the river flows through the Rio Grande rift from one sediment-filled basin to another, cutting canyons between the basins and supporting a fragile bosque ecosystem on its flood plain. From El Paso eastward, the river flows through desert. Although irrigated agriculture exists throughout most of its stretch, it is extensive in the subtropical Lower Rio Grande Valley.
The river ends in a sandy delta at the Gulf of Mexico. During portions of 2001 and 2002, the mouth of the Rio Grande was blocked by a sandbar. In the fall of 2003, the sandbar was cleared by high river flows around 7,063 cubic feet per second. Navigation was active during much of the 19th century, with over 200 different steamboats operating between the river's mouth close to Brownsville and Rio Grande City, Texas. Many steamboats from the Ohio and Mississippi Rivers were requisitioned by the U. S. government and moved to the Rio Grande during the Mexican–American War in 1846. They provided transport for the U. S. Army, under General Zachary Taylor, to invade Monterrey, Nuevo León, via Camargo Municipality, Tamaulipas. Army engineers recommended that with small improvements, the river could be made navigable as far north as El Paso; those recommendations were never acted upon. The Brownsville & Matamoros International Bridge, a large swing bridge, dates back to 1910 and is still in use today by automobiles connecting Brownsville with Matamoros, Tamaulipas.
The swing mechanism has not been used since the early 1900s, when the last of the big steamboats disappeared. At one point, the bridge had rail traffic. Railroad trains no longer use this bridge. A new rail bridge connecting the U. S. and Mexico was built about 15 miles west of the Matamoros International Bridge. It was inaugurated in August 2015, it moved all rail operations out of downtown Matamoros. The West Rail International Crossing is the first new international rail crossing between the U. S. and Mexico in 105 years. The Brownsville & Matamoros International Bridge is now operated by the Brownsville and Matamoros Bridge Company, a joint venture between the Mexican government and the Union Pacific Railroad. At the mouth of the Rio Grande, on the Mexican side, was the large commercial port of Bagdad, Tamaulipas. During the American Civil War, this was the only legitimate port of the Confederacy. European warships anchored offshore to maintain the port's neutrality, managed to do so throughout that conflict, despite occasional stare-downs with blockading ships from the US Navy.
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Del Rio, Texas
Del Rio is a city in and the county seat of Val Verde County, Texas. It is 152 miles west of San Antonio; as of 2015, the city had a population of 40,549. Del Rio is connected to Ciudad Acuña by the Lake Amistad Dam International Crossing and Del Río – Ciudad Acuña International Bridge, it is home to Laughlin Air Force Base, the busiest United States Air Force pilot-training complex in the world. The Spanish established a small settlement south of the Rio Grande in present-day Mexico, some Spaniards settled on what became the United States side of the Rio Grande as early as the 18th century. Paula Losoya Taylor built the first hacienda in the area in 1862. U. S. development on the north shore of the Rio Grande did not begin until after the American Civil War. The San Felipe Springs, about 8 mi east of the Rio Grande on the U. S. side of the border, produces 90×10^6 US gal of water a day. Developers acquired several thousand acres of land adjacent to the springs, to San Felipe Creek formed by the springs, from the state of Texas in exchange for building a canal system to irrigate the area.
The developers sold tracts of land surrounding the canals to recover their investment and show a profit. The initial investors formed the San Felipe Agricultural and Irrigation Company in 1868; the organization completed construction of a network of irrigation canals in 1871. Residents referred to the developing town as San Felipe Del Rio because local lore said the name came from early Spanish explorers who offered a mass at the site on St. Philip's Day, 1635. In 1883, local residents requested a post office be established; the United States Postal Department shortened "San Felipe del Rio" to "Del Rio" to avoid confusion with San Felipe de Austin. In 1885, Val Verde County was organized and Del Rio became the county seat; the City of Del Rio was incorporated on November 15, 1911. The San Felipe community was started by the Arteaga family. Arteaga Street and Arteaga Park are named after them. Many historical artifacts from Del Rio from the 19th century, are preserved at the Whitehead Memorial Museum downtown.
Del Rio is known as the American address of legendary Mexican radio stations XERA and XERF just over the U. S.-Mexico border in Ciudad Acuña. Legendary deejay Wolfman Jack operated XERF in the 1960s, using a Del Rio address to sell various products advertised on the station. In 1942, the Army Air Corps opened Laughlin Field 9 mi east of Del Rio, as a training base for the Martin B-26, but the base was deactivated in 1945; as the Cold War pressures built, along with new border-control issues, Laughlin Field was rebuilt and renamed Laughlin Air Force Base and was again used as a home for flight training. In the mid-1950s, the Strategic Air Command noted that Laughlin's remoteness allowed for secret operations, opened its strategic reconnaissance program there with the RB-57, a bomber modified for high-altitude reconnaissance. SAC soon transitioned to the high-altitude U-2 Dragonlady and based all of them in Laughlin AFB. In 1962, Laughlin-based U-2s took the first photographs of land-based medium-range ballistic missile sites being constructed in Cuba.
The presence of these missiles precipitated what became known as "the Cuban Missile Crisis". In July 1963, the U-2s were relocated to Davis–Monthan Air Force Base near Tucson and Laughlin's mission transitioned to the Undergraduate Pilot Training mission in the T-37 and T-38 aircraft. Laughlin AFB provides training in the T-1A Jayhawk, the T-6A Texan II, the T-38 aircraft. Laughlin plays a large part in the Del Rio community as the area's largest employer; the United States Border Patrol is the city's second-largest employer. At one time, Del Rio was in the running to become the home of the Federal Law Enforcement Training Center for agents of the U. S. Border Patrol and Federal Air Marshal Service, but lost to the current site in New Mexico; the proposed site was located on property belonging to Laughlin AFB. Since the base has unused land, the Air Force is able to lease it to other federal law enforcement agencies for such projects; this benefits the city of Del Rio both financially and economically.
For example, Del Rio was one of five cities in the United States selected for an FBI regional headquarters' office, that building is adjacent to the six-story Roswell Hotel in downtown Del Rio. According to the United States Census Bureau, the city has a total area of 52.3 km2, of which 52.2 km2 are land and 0.1 km2, or 0.24%, is covered by water. Del Rio lies on the northwestern edges of the Tamaulipan mezquital called the South Texas brush country, it is near the southwestern corner of the Edwards Plateau, the western fringe of the famous, oak savanna-covered Texas Hill Country. The creek supplied fresh water for drinking and irrigation to early settlers of Del Rio, the springs are still the town's water supply; the Del Rio region, west to about the Pecos River, has a mix of desert shrub and steppe vegetation, depending on soil type, with the gray-leafed cenizo, several different acacias and grama grasses dominant members of local flora. The terrain is level, but some areas are dissected with substantial canyons and drainages, though none of the upland areas is high or large enough to be considered a mountain
A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing increased performance and reduced interference from unwanted sources. Directional antennas provide increased performance over dipole antennas—or omnidirectional antennas in general—when greater concentration of radiation in a certain direction is desired. A high-gain antenna is a directional antenna with a narrow radiowave beam width; this narrow beam width allows more precise targeting of the radio signals. Most referred to during space missions, these antennas are in use all over Earth, most in flat, open areas where no mountains lie to disrupt radiowaves. By contrast, a low-gain antenna is an omnidirectional antenna with a broad radiowave beam width, that allows the signal to propagate reasonably well in mountainous regions and is thus more reliable regardless of terrain. Low-gain antennas are used in spacecraft as a backup to the high-gain antenna, which transmits a much narrower beam and is therefore susceptible to loss of signal.
All practical antennas are at least somewhat directional, although only the direction in the plane parallel to the earth is considered, practical antennas can be omnidirectional in one plane. The most common types are the Yagi antenna, the log-periodic antenna, the corner reflector antenna, which are combined and commercially sold as residential TV antennas. Cellular repeaters make use of external directional antennas to give a far greater signal than can be obtained on a standard cell phone. Satellite Television receivers use parabolic antennas. For long and medium wavelength frequencies, tower arrays are used in most cases as directional antennas; when transmitting, a high-gain antenna allows more of the transmitted power to be sent in the direction of the receiver, increasing the received signal strength. When receiving, a high gain antenna captures more of the signal, again increasing signal strength. Due to reciprocity, these two effects are equal—an antenna that makes a transmitted signal 100 times stronger will capture 100 times as much energy as the isotropic antenna when used as a receiving antenna.
As a consequence of their directivity, directional antennas send less signal from directions other than the main beam. This property may be used to reduce interference. There are many ways to make a high-gain antenna. Horn antennas can be constructed with high gain, but are less seen. Still other configurations are possible—the Arecibo Observatory uses a combination of a line feed with an enormous spherical reflector, to achieve high gains at specific frequencies. Antenna gain is quoted with respect to a hypothetical antenna that radiates in all directions, an isotropic radiator; this gain, when measured in decibels, is called dBi. Conservation of energy dictates. For example, if a high gain antenna makes a 1 watt transmitter look like a 100 watt transmitter the beam can cover at most 1⁄100 of the sky. In turn this implies that high-gain antennas must be physically large, since according to the diffraction limit, the narrower the beam desired, the larger the antenna must be. Antenna gain can be measured in dBd, gain in Decibels compared to the maximum intensity direction of a half wave dipole.
In the case of Yagi type aerials this more or less equates to the gain one would expect from the aerial under test minus all its directors and reflector. It is important not to confuse dBd. Gain is dependent on the number of elements and the tuning of those elements. Antennas can be tuned to be resonant over a wider spread of frequencies but, all other things being equal, this will mean the gain of the aerial is lower than one tuned for a single frequency or a group of frequencies. For example, in the case of wideband TV antennas the fall off in gain is large at the bottom of the TV transmitting band. In the UK this bottom third of the TV band is known as group A. Other factors may affect gain such as aperture, efficiency; these factors are easy to improve without adjusting other features of the antennas or coincidentally improved by the same factors that increase directivity, so are not emphasized. High gain antennas are the largest component of deep space probes, the highest gain radio antennas are physically enormous structures, such as the Arecibo Observatory.
The Deep Space Network uses 35 m dishes at about 1 cm wavelengths. This combination gives the antenna gain of about 100,000,000, making the transmitter appear about 100 million times stronger, a receiver about 100 million times more sensitive, provided the target is within the beam; this beam can cover at most one hundred millionth of the sky, so accurate pointing is required. Use of high gain and Millimeter-
Pentecostalism or Classical Pentecostalism is a renewal movement within Protestant Christianity that places special emphasis on a direct personal experience of God through baptism with the Holy Spirit. The term Pentecostal is derived from the Greek name for the Jewish Feast of Weeks. For Christians, this event commemorates the descent of the Holy Spirit upon the followers of Jesus Christ, as described in the second chapter of the Acts of the Apostles. Like other forms of evangelical Protestantism, Pentecostalism adheres to the inerrancy of the Bible and the necessity of accepting Jesus Christ as personal Lord and Savior, it is distinguished by belief in the baptism in the Holy Spirit that enables a Christian to live a Spirit-filled and empowered life. This empowerment includes the use of spiritual gifts such as speaking in tongues and divine healing—two other defining characteristics of Pentecostalism; because of their commitment to biblical authority, spiritual gifts, the miraculous, Pentecostals tend to see their movement as reflecting the same kind of spiritual power and teachings that were found in the Apostolic Age of the early church.
For this reason, some Pentecostals use the term Apostolic or Full Gospel to describe their movement. Pentecostalism emerged in the early 20th century among radical adherents of the Holiness movement who were energized by revivalism and expectation for the imminent Second Coming of Christ. Believing that they were living in the end times, they expected God to spiritually renew the Christian Church thereby bringing to pass the restoration of spiritual gifts and the evangelization of the world. In 1900, Charles Parham, an American evangelist and faith healer, began teaching that speaking in tongues was the Bible evidence of Spirit baptism and along with William J. Seymour, a Wesleyan-Holiness preacher, he taught that this was the third work of grace; the three-year-long Azusa Street Revival and led by Seymour in Los Angeles, resulted in the spread of Pentecostalism throughout the United States and the rest of the world as visitors carried the Pentecostal experience back to their home churches or felt called to the mission field.
While all Pentecostal denominations trace their origins to Azusa Street, the movement has experienced a variety of divisions and controversies. An early dispute centered on challenges to the doctrine of the Trinity; as a result, the Pentecostal movement is divided between trinitarian and non-trinitarian branches, resulting in the emergence of Oneness Pentecostals. Comprising over 700 denominations and a large number of independent churches, there is no central authority governing Pentecostalism. There are over 279 million Pentecostals worldwide, the movement is growing in many parts of the world the global South. Since the 1960s, Pentecostalism has gained acceptance from other Christian traditions, Pentecostal beliefs concerning Spirit baptism and spiritual gifts have been embraced by non-Pentecostal Christians in Protestant and Catholic churches through the Charismatic Movement. Together and Charismatic Christianity numbers over 500 million adherents. While the movement attracted lower classes in the global South, there is an increasing appeal to middle classes.
Middle class congregations tend to be more adapted to society and withdraw strong spiritual practices such as divine healing. Pentecostalism is an evangelical faith, emphasizing the reliability of the Bible and the need for the transformation of an individual's life through faith in Jesus. Like other evangelicals, Pentecostals adhere to the Bible's divine inspiration and inerrancy—the belief that the Bible, in the original manuscripts in which it was written, is without error. Pentecostals emphasize the teaching of the "full gospel" or "foursquare gospel"; the term foursquare refers to the four fundamental beliefs of Pentecostalism: Jesus saves according to John 3:16. The central belief of classical Pentecostalism is that through the death and resurrection of Jesus Christ, sins can be forgiven and humanity reconciled with God; this is the Gospel or "good news". The fundamental requirement of Pentecostalism is; the new birth is received by the grace of God through faith in Christ as Savior. In being born again, the believer is regenerated, adopted into the family of God, the Holy Spirit's work of sanctification is initiated.
Classical Pentecostal soteriology is Arminian rather than Calvinist. The security of the believer is a doctrine held within Pentecostalism. Pentecostals believe in both a literal heaven and hell, the former for those who have accepted God's gift of salvation and the latter for those who have rejected it. For most Pentecostals there is no other requirement to receive salvation. Baptism with the Holy Spirit and speaking in tongues are not required, though Pentecostal converts are encouraged to seek these experiences. A notable exception is Jesus' Name Pentecostalism, most adherents of which believe both water baptism and Spirit baptism are integral components of salvation. Pentecostals identify three distinct uses of the word "baptism" in the New Testament: Baptism into the body of Christ: This refers to salvation; every believer in Christ is made a part of the Church, through baptism. The Holy Spirit is the agent, the body of Christ is the medium. Water baptism: Symbolic of dying to the world and liv