1.
Bern
–
The city of Bern or Berne is the de facto capital of Switzerland, referred to by the Swiss as their Bundesstadt, or federal city. With a population of 141,762, Bern is the fourth-most populous city in Switzerland, the Bern agglomeration, which includes 36 municipalities, had a population of 406,900 in 2014. The metropolitan area had a population of 660,000 in 2000, Bern is also the capital of the canton of Bern, the second-most populous of Switzerlands cantons. The official language in Bern is German, but the language is an Alemannic Swiss German dialect. In 1983, the old town in the centre of Bern became a UNESCO World Heritage Site. Bern is ranked among the top ten cities for the best quality of life. The etymology of the name Bern is uncertain and it has long been considered likely that the city was named after the Italian city of Verona, which at the time was known as Bern in Middle High German. As a result of the find of the Bern zinc tablet in the 1980s, it is now common to assume that the city was named after a pre-existing toponym of Celtic origin. The bear was the animal of the seal and coat of arms of Bern from at least the 1220s. The earliest reference to the keeping of bears in the Bärengraben dates to the 1440s. No archaeological evidence that indicates a settlement on the site of city centre prior to the 12th century has been found so far. In antiquity, a Celtic oppidum stood on the Engehalbinsel north of Bern, fortified since the second century BC, during the Roman era, a Gallo-Roman vicus was on the same site. The Bern zinc tablet has the name Brenodor, in the Early Middle Ages, a settlement in Bümpliz, now a city district of Bern, was some 4 km from the medieval city. The medieval city is a foundation of the Zähringer ruling family, according to 14th-century historiography, Bern was founded in 1191 by Berthold V, Duke of Zähringen. In 1218, after Berthold died without an heir, Bern was made an imperial city by the Goldene Handfeste of Holy Roman Emperor Frederick II. In 1353, Bern joined the Swiss Confederacy, becoming one of the eight cantons of the period of 1353 to 1481. The city grew out towards the west of the boundaries of the peninsula formed by the river Aare, the Zytglogge tower marked the western boundary of the city from 1191 until 1256, when the Käfigturm took over this role until 1345. It was, in turn, succeeded by the Christoffelturm until 1622, during the time of the Thirty Years War, two new fortifications – the so-called big and small Schanze – were built to protect the whole area of the peninsula
2.
Switch
–
In electrical engineering, a switch is an electrical component that can make or break an electrical circuit, interrupting the current or diverting it from one conductor to another. The mechanism of a switch removes or restores the conducting path in a circuit when it is operated, the most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. The mechanism actuating the transition between two states can be either a toggle or momentary type. A switch may be manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, for example, a thermostat is a temperature-operated switch used to control a heating process. A switch that is operated by electrical circuit is called a relay. Large switches may be operated by a motor drive mechanism. An ideal switch would have no voltage drop when closed, and it would have zero rise time and fall time during state changes, and would change state without bouncing between on and off positions. Practical switches fall short of ideal, they have resistance, limits on the current and voltage they can handle, finite switching time. The ideal switch is used in circuit analysis as it greatly simplifies the system of equations to be solved. Theoretical treatment of the effects of non-ideal properties is required in the design of networks of switches. In the simplest case, a switch has two pieces, often metal, called contacts, connected to an external circuit, that touch to complete the circuit. The contact material is chosen for its resistance to corrosion, because most metals form insulating oxides that would prevent the switch from working, contact materials are also chosen on the basis of electrical conductivity, hardness, mechanical strength, low cost and low toxicity. Sometimes the contacts are plated with noble metals and they may be designed to wipe against each other to clean off any contamination. Nonmetallic conductors, such as plastic, are sometimes used. To prevent the formation of insulating oxides, a minimum wetting current may be specified for a given switch design, in electronics, switches are classified according to the arrangement of their contacts. A pair of contacts is said to be closed when current can flow from one to the other, when the contacts are separated by an insulating air gap, they are said to be open, and no current can flow between them at normal voltages. The terms make for closure of contacts and break for opening of contacts are also widely used, the terms pole and throw are also used to describe switch contact variations
3.
Morse code
–
Morse code is a method of transmitting text information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment. It is named for Samuel F. B, Morse, an inventor of the telegraph. Because many non-English natural languages use more than the 26 Roman letters, each Morse code symbol represents either a text character or a prosign and is represented by a unique sequence of dots and dashes. The duration of a dash is three times the duration of a dot, each dot or dash is followed by a short silence, equal to the dot duration. The letters of a word are separated by an equal to three dots, and the words are separated by a space equal to seven dots. The dot duration is the unit of time measurement in code transmission. To increase the speed of the communication, the code was designed so that the length of each character in Morse varies approximately inversely to its frequency of occurrence in English. Thus the most common letter in English, the letter E, has the shortest code, Morse code is used by some amateur radio operators, although knowledge of and proficiency with it is no longer required for licensing in most countries. Pilots and air controllers usually need only a cursory understanding. Aeronautical navigational aids, such as VORs and NDBs, constantly identify in Morse code, compared to voice, Morse code is less sensitive to poor signal conditions, yet still comprehensible to humans without a decoding device. Morse is, therefore, an alternative to synthesized speech for sending automated data to skilled listeners on voice channels. Many amateur radio repeaters, for example, identify with Morse, in an emergency, Morse code can be sent by improvised methods that can be easily keyed on and off, making it one of the simplest and most versatile methods of telecommunication. The most common signal is SOS or three dots, three dashes, and three dots, internationally recognized by treaty. Beginning in 1836, the American artist Samuel F. B, Morse, the American physicist Joseph Henry, and Alfred Vail developed an electrical telegraph system. This system sent pulses of current along wires which controlled an electromagnet that was located at the receiving end of the telegraph system. A code was needed to transmit natural language using only these pulses, around 1837, Morse, therefore, developed an early forerunner to the modern International Morse code. Around the same time, Carl Friedrich Gauss and Wilhelm Eduard Weber as well as Carl August von Steinheil had already used codes with varying lengths for their telegraphs. In 1837, William Cooke and Charles Wheatstone in England began using a telegraph that also used electromagnets in its receivers
4.
Electrical telegraph
–
An electrical telegraph is a telegraph that uses electrical signals, usually conveyed via dedicated telecommunication lines or radio. From early studies of electricity, electrical phenomena were known to travel with great speed, in 1753 an anonymous writer in the Scots Magazine suggested an electrostatic telegraph. In 1774 Georges-Louis Le Sage realised an early electric telegraph, the telegraph had a separate wire for each of the 26 letters of the alphabet and its range was only between two rooms of his home. In 1800 Alessandro Volta invented the voltaic pile, allowing for a current of electricity for experimentation. Both their designs employed multiple wires to represent almost all Latin letters, thus, messages could be conveyed electrically up to a few kilometers, with each of the telegraph receivers wires immersed in a separate glass tube of acid. The telegraph receivers operator would watch the bubbles and could record the transmitted message. This is in contrast to later telegraphs that used a single wire, hans Christian Ørsted discovered in 1820 that an electric current produces a magnetic field which will deflect a compass needle. In the same year Johann Schweigger invented the galvanometer, with a coil of wire around a compass, in 1824, Peter Barlow said that such a system only worked to a distance of about 200 feet, and so was impractical. In 1825 William Sturgeon invented the electromagnet, with a winding of uninsulated wire on a piece of varnished iron. During his tenure at The Albany Academy from 1826 to 1832, in 1835 Joseph Henry and Edward Davy invented the critical electrical relay. Davys relay used a needle which dipped into a mercury contact when an electric current passed through the surrounding coil. This allowed a weak current to switch a larger current to operate a powerful local electromagnet over very long distances, Davy demonstrated his telegraph system in Regents Park in 1837 and was granted a patent on 4 July 1838. He also developed an electric relay, the first working telegraph was built by the English inventor Francis Ronalds in 1816 and used static electricity. At the family home on Hammersmith Mall, he set up a subterranean system in a 175 yard long trench as well as an eight mile long overhead telegraph. The lines were connected at both ends to revolving dials marked with the letters of the alphabet and electrical impulses sent along the wire were used to transmit messages, offering his invention to the Admiralty in July 1816, it was rejected as “wholly unnecessary”. Elements of Ronalds’ design were utilised in the subsequent commercialisation of the telegraph over 20 years later, the telegraph invented by Baron Schilling von Canstatt in 1832 had a transmitting device which consisted of a keyboard with 16 black-and-white keys. These served for switching the electric current, the receiving instrument consisted of six galvanometers with magnetic needles, suspended from silk threads. Both stations of Shillings telegraph were connected by eight wires, six were connected with the galvanometers, one served for the return current, when at the starting station the operator pressed a key, the corresponding pointer was deflected at the receiving station
5.
Wireless telegraphy
–
Wireless telegraphy is the transmission of electric telegraphy signals without wires. Wireless telegraphy came to mean Morse code transmitted by radio waves, initially called Hertzian waves, the primitive spark radio transmitters used until World War 1 could not transmit audio. The code sounded like musical beeps in the earphone of the receiver, the receiving radio operator would translate the beeps back into text. The first practical wireless telegraphy transmitters and receivers were developed by Guglielmo Marconi beginning in 1895, by 1910 communication by Hertzian waves was universally referred to as radio, and the term wireless telegraphy has been largely replaced by the more modern term radiotelegraphy. The transmission of sound began to displace wireless telegraphy by the 1920s for many applications, continuous wave radiotelegraphy is regulated by the International Telecommunication Union as emission type A1A. Today, due to modern text transmission methods, Morse code radiotelegraphy for commercial use has become obsolete. On shipboard the computer and satellite linked GMDSS system has largely replaced Morse as a means of communication, Telegraphy is taught on a very limited basis by the military. A CW coastal station, KSM, still exists in California, run primarily as a museum by volunteers, Radio beacons, particularly in the aviation service, but also as placeholders for commercial ship-to-shore systems, also transmit Morse but at very slow speeds. The US Federal Communications Commission does still issue a lifetime commercial Radiotelegraph Operator License and this requires passing a simple written test on regulations, a more complex written exam on technology, and demonstrating Morse reception at 20 words per minute plain language and 16 wpm code groups. Wireless telegraphy is still used today by amateur radio hobbyists where it is commonly referred to as radio telegraphy, continuous wave. However its knowledge is not required to obtain any class of amateur license, a number of wireless electrical signaling schemes including electric currents through water and the ground were investigated for telegraphy before practical radio systems became available. The original telegraph used two wires between two stations to form an electrical circuit or loop. This led to speculation that it might be possible to both wires and therefore transmit telegraph signals through the ground without any wires connecting the stations. Other attempts were made to send the current through bodies of water, in order to span rivers. The first wireless voice telecommunication device, invented in 1880, was the photophone, both electrostatic and electromagnetic induction were used to develop wireless telegraph systems that saw limited commercial application. This system was successful technically but not economically, as there turned out to be little interest by train travelers in a telegraph service. During the Great Blizzard of 1888, this system was used to send, the disabled trains were able to maintain communications via their Edison induction wireless telegraph systems, perhaps the first successful use of wireless telegraphy to send distress calls. The most successful creator of an electromagnetic induction telegraph system was William Preece in the United Kingdom, beginning with tests across the Bristol Channel in 1892, Preece was able to telegraph across gaps of about 5 kilometres
6.
Trunnion
–
A trunnion is a cylindrical protrusion used as a mounting or pivoting point. First associated with cannon, they are an important military development, alternatively, a trunnion is a shaft that positions and supports a tilting plate. This is a misnomer, as in reality it is a cradle for the true trunnion, in mechanical engineering, it is one part of a rotating joint where a shaft is inserted into a full or partial cylinder. In a cannon, the trunnions are two projections cast just forward of the center of mass of the cannon and fixed to a two-wheeled movable gun carriage. As they allowed the muzzle to be raised and lowered easily, with the creation of larger and more powerful siege guns in the early 15th century, a new way of mounting them had to be specially designed. Stouter gun carriages were created with reinforced wheels, axles, guns would be up to eight feet in length and shoot iron projectiles weighing from twenty-five to fifty pounds. These wrought iron balls when discharged were comparable in range and accuracy with stone-firing bombards, trunnions were mounted near the center of mass to allow the barrel to be elevated to any desired angle, without having to dismount it from the carriage upon which it rested. Some guns had a set of trunnions placed several feet back from the first pair. The gun would recoil causing the carriage to move backwards several feet and it became easier to rapidly transport these large siege guns, maneuver them from transportation mode to firing position, and they could go wherever a team of men or horses could pull them. Due to its capabilities, the French- and Burgundy-designed siege gun, equipped with its trunnions, king Charles VIII and the French army used this new gun in the 1494 invasion of Italy. Although deemed masters of war and artillery at that time, Italians had not anticipated the innovations in French siege weaponry. Prior to this, field guns were huge, large-caliber bombards, superguns that. Cities that had proudly withstood sieges for up to seven years fell swiftly with the advent of new weapons. Defensive tactics and fortifications had to be altered since these new weapons could be transported so speedily and these towers would be deemed trace Italienne. Whoever could afford these new weapons had the advantage over their neighbors and smaller sovereignties. Smaller states, such as the principalities of Italy, began to conglomerate, preexisting stronger entities, such as France or the Habsburg emperors, were able to expand their territories and maintain tighter control. With the threat of their land and castles being seized, the nobility began to pay their taxes, on firearms, the barrel is sometimes mounted in a trunnion, which in turn is mounted to the receiver. This usage is common for tubular or pressed metal frame guns, such as the AK-47, PPSh-41, Uzi, Sten, and others
7.
Science fiction
–
Science fiction often explores the potential consequences of scientific and other innovations, and has been called a literature of ideas. Science fiction is difficult to define, as it includes a range of subgenres and themes. Author and editor Damon Knight summed up the difficulty, saying science fiction is what we point to when we say it, a definition echoed by author Mark C. Glassy, who argues that the definition of science fiction is like the definition of pornography, you do not know what it is, in 1970 or 1971William Atheling Jr. According to science fiction writer Robert A, rod Serlings definition is fantasy is the impossible made probable. Science fiction is the improbable made possible, Science fiction is largely based on writing rationally about alternative possible worlds or futures. Science fiction elements include, A time setting in the future, in alternative timelines, a spatial setting or scenes in outer space, on other worlds, or on subterranean earth. Characters that include aliens, mutants, androids, or humanoid robots, futuristic or plausible technology such as ray guns, teleportation machines, and humanoid computers. Scientific principles that are new or that contradict accepted physical laws, for time travel, wormholes. New and different political or social systems, e. g. utopian, dystopian, post-scarcity, paranormal abilities such as mind control, telepathy, telekinesis Other universes or dimensions and travel between them. A product of the budding Age of Reason and the development of science itself. Isaac Asimov and Carl Sagan considered Keplers work the first science fiction story and it depicts a journey to the Moon and how the Earths motion is seen from there. Later, Edgar Allan Poe wrote a story about a flight to the moon, more examples appeared throughout the 19th century. Wells The War of the Worlds describes an invasion of late Victorian England by Martians using tripod fighting machines equipped with advanced weaponry and it is a seminal depiction of an alien invasion of Earth. In the late 19th century, the scientific romance was used in Britain to describe much of this fiction. This produced additional offshoots, such as the 1884 novella Flatland, the term would continue to be used into the early 20th century for writers such as Olaf Stapledon. In the early 20th century, pulp magazines helped develop a new generation of mainly American SF writers, influenced by Hugo Gernsback, the founder of Amazing Stories magazine. In 1912 Edgar Rice Burroughs published A Princess of Mars, the first of his series of Barsoom novels, situated on Mars
8.
Independence Day (1996 film)
–
Independence Day is a 1996 American science fiction action film directed and co-written by Roland Emmerich. The film focuses on disparate groups of people who converge in the Nevada desert in the aftermath of a attack by an extraterrestrial race of unknown origin. Along with the rest of the world, they launch a counterattack on July 4 – Independence Day in the United States. While promoting Stargate in Europe, Emmerich came up with the idea for the film when fielding a question about his own belief in the existence of alien life. He and Dean Devlin decided to incorporate a large-scale attack having noticed that aliens in most invasion films travel long distances in space only to remain hidden when reaching Earth. Shooting began in July 1995 in New York City, and the film was completed on June 20,1996. The film grossed over $817.4 million worldwide, becoming the highest-grossing film of 1996, and briefly, as of June 2016, it ranks 55th on the list of highest-grossing films, and was at the forefront of the large-scale disaster film and sci-fi resurgence of the mid-1990s. The film has an rating of 61% on Rotten Tomatoes. It won the Academy Award for Best Visual Effects and was nominated for the Academy Award for Best Sound Mixing, a sequel, Independence Day, Resurgence, was released on June 24,2016. David Levinson, an MIT-trained satellite technician, decodes a signal embedded in the satellite transmissions that he determines is a timer counting down to a coordinated attack. Whitmore, the Levinsons, and a few others narrowly escape aboard Air Force One as the capital is destroyed, on July 3, international leaders begin ordering individual counterattacks. Their aviation forces attack destroyer ships positioned above the ruins of the cities, each destroyer launches a swarm of attack fighters, which wipe out the human fighter squadrons. He subdues the injured pilot and flags down a convoy of refugees. They transport the alien to nearby Area 51 where Whitmores group has landed. Area 51 houses the refurbished alien fighter and three alien corpses recovered from the crash, when eccentric scientist Brackish Okun examines the alien captured by Hiller, it regains consciousness and attacks. It telepathically invades Okuns mind and uses his vocal cords to communicate with Whitmore before launching an attack against him. Whitmore sees visions of the plans, their entire civilization travels from planet to planet, exterminating all indigenous life. On July 4, Levinson demonstrates that the key to defeating the aliens lies in deactivating their force fields and he proposes using the refurbished alien fighter to implement the plan, which Hiller volunteers to pilot
9.
Pendulum
–
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, when released, the restoring force combined with the pendulums mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one cycle, a left swing and a right swing, is called the period. The period depends on the length of the pendulum and also to a degree on the amplitude. Pendulums are also used in instruments such as accelerometers and seismometers. Historically they were used as gravimeters to measure the acceleration of gravity in geophysical surveys, the word pendulum is new Latin, from the Latin pendulus, meaning hanging. The simple gravity pendulum is a mathematical model of a pendulum. This is a weight on the end of a massless cord suspended from a pivot, when given an initial push, it will swing back and forth at a constant amplitude. Real pendulums are subject to friction and air drag, so the amplitude of their swings declines and it is independent of the mass of the bob. For small swings the period of swing is approximately the same for different size swings, that is and this property, called isochronism, is the reason pendulums are so useful for timekeeping. Successive swings of the pendulum, even if changing in amplitude, for larger amplitudes, the period increases gradually with amplitude so it is longer than given by equation. For example, at an amplitude of θ0 = 23° it is 1% larger than given by, the period increases asymptotically as θ0 approaches 180°, because the value θ0 = 180° is an unstable equilibrium point for the pendulum. The length L used to calculate the period of the simple pendulum in eq. above is the distance from the pivot point to the center of mass of the bob. Any swinging rigid body free to rotate about a horizontal axis is called a compound pendulum or physical pendulum. The appropriate equivalent length L for calculating the period of any such pendulum is the distance from the pivot to the center of oscillation. This point is located under the center of mass at a distance from the pivot traditionally called the radius of oscillation, if most of the mass is concentrated in a relatively small bob compared to the pendulum length, the center of oscillation is close to the center of mass. Substituting this expression in above, the period T of a pendulum is given by T =2 π I m g R for sufficiently small oscillations. For example, a rigid rod of length L pivoted about one end has moment of inertia I = m L2 /3
10.
Harvard University
–
Although never formally affiliated with any denomination, the early College primarily trained Congregationalist and Unitarian clergy. Its curriculum and student body were gradually secularized during the 18th century, james Bryant Conant led the university through the Great Depression and World War II and began to reform the curriculum and liberalize admissions after the war. The undergraduate college became coeducational after its 1977 merger with Radcliffe College, Harvards $34.5 billion financial endowment is the largest of any academic institution. Harvard is a large, highly residential research university, the nominal cost of attendance is high, but the Universitys large endowment allows it to offer generous financial aid packages. Harvards alumni include eight U. S. presidents, several heads of state,62 living billionaires,359 Rhodes Scholars. To date, some 130 Nobel laureates,18 Fields Medalists, Harvard was formed in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. In 1638, it obtained British North Americas first known printing press, in 1639 it was named Harvard College after deceased clergyman John Harvard an alumnus of the University of Cambridge who had left the school £779 and his scholars library of some 400 volumes. The charter creating the Harvard Corporation was granted in 1650 and it offered a classic curriculum on the English university model—many leaders in the colony had attended the University of Cambridge—but conformed to the tenets of Puritanism. It was never affiliated with any denomination, but many of its earliest graduates went on to become clergymen in Congregational. The leading Boston divine Increase Mather served as president from 1685 to 1701, in 1708, John Leverett became the first president who was not also a clergyman, which marked a turning of the college toward intellectual independence from Puritanism. When the Hollis Professor of Divinity David Tappan died in 1803 and the president of Harvard Joseph Willard died a year later, in 1804, in 1846, the natural history lectures of Louis Agassiz were acclaimed both in New York and on the campus at Harvard College. Agassizs approach was distinctly idealist and posited Americans participation in the Divine Nature, agassizs perspective on science combined observation with intuition and the assumption that a person can grasp the divine plan in all phenomena. When it came to explaining life-forms, Agassiz resorted to matters of shape based on an archetype for his evidence. Charles W. Eliot, president 1869–1909, eliminated the position of Christianity from the curriculum while opening it to student self-direction. While Eliot was the most crucial figure in the secularization of American higher education, he was motivated not by a desire to secularize education, during the 20th century, Harvards international reputation grew as a burgeoning endowment and prominent professors expanded the universitys scope. Rapid enrollment growth continued as new schools were begun and the undergraduate College expanded. Radcliffe College, established in 1879 as sister school of Harvard College, Harvard became a founding member of the Association of American Universities in 1900. In the early 20th century, the student body was predominately old-stock, high-status Protestants, especially Episcopalians, Congregationalists, by the 1970s it was much more diversified
11.
YouTube
–
YouTube is an American video-sharing website headquartered in San Bruno, California. The service was created by three former PayPal employees—Chad Hurley, Steve Chen, and Jawed Karim—in February 2005, Google bought the site in November 2006 for US$1.65 billion, YouTube now operates as one of Googles subsidiaries. Unregistered users can watch videos on the site, while registered users are permitted to upload an unlimited number of videos. Videos deemed potentially offensive are available only to registered users affirming themselves to be at least 18 years old, YouTube earns advertising revenue from Google AdSense, a program which targets ads according to site content and audience. YouTube was founded by Chad Hurley, Steve Chen, and Jawed Karim, Hurley had studied design at Indiana University of Pennsylvania, and Chen and Karim studied computer science together at the University of Illinois at Urbana-Champaign. Karim could not easily find video clips of either event online, Hurley and Chen said that the original idea for YouTube was a video version of an online dating service, and had been influenced by the website Hot or Not. YouTube began as a venture capital-funded technology startup, primarily from an $11.5 million investment by Sequoia Capital between November 2005 and April 2006, YouTubes early headquarters were situated above a pizzeria and Japanese restaurant in San Mateo, California. The domain name www. youtube. com was activated on February 14,2005, the first YouTube video, titled Me at the zoo, shows co-founder Jawed Karim at the San Diego Zoo. The video was uploaded on April 23,2005, and can still be viewed on the site, YouTube offered the public a beta test of the site in May 2005. The first video to reach one million views was a Nike advertisement featuring Ronaldinho in November 2005. Following a $3.5 million investment from Sequoia Capital in November, the site grew rapidly, and in July 2006 the company announced that more than 65,000 new videos were being uploaded every day, and that the site was receiving 100 million video views per day. The site has 800 million unique users a month and it is estimated that in 2007 YouTube consumed as much bandwidth as the entire Internet in 2000. The choice of the name www. youtube. com led to problems for a similarly named website, the sites owner, Universal Tube & Rollform Equipment, filed a lawsuit against YouTube in November 2006 after being regularly overloaded by people looking for YouTube. Universal Tube has since changed the name of its website to www. utubeonline. com, in October 2006, Google Inc. announced that it had acquired YouTube for $1.65 billion in Google stock, and the deal was finalized on November 13,2006. In March 2010, YouTube began free streaming of certain content, according to YouTube, this was the first worldwide free online broadcast of a major sporting event. On March 31,2010, the YouTube website launched a new design, with the aim of simplifying the interface, Google product manager Shiva Rajaraman commented, We really felt like we needed to step back and remove the clutter. In May 2010, YouTube videos were watched more than two times per day. This increased to three billion in May 2011, and four billion in January 2012, in February 2017, one billion hours of YouTube was watched every day
12.
Columbidae
–
Pigeons and doves constitute the bird family Columbidae, which includes about 310 species. Pigeons and doves are stout-bodied birds with short necks, and short slender bills and they primarily feed on seeds, fruits, and plants. This family occurs worldwide, but the greatest variety is in the Indomalaya, in general, the terms dove and pigeon are used somewhat interchangeably. Pigeon is a French word that derives from the Latin pipio, for a peeping chick, the species most commonly referred to as pigeon is the rock dove, one subspecies of which, the domestic pigeon, is common in many cities as the feral pigeon. Pigeons and doves are likely the most common birds in the world, doves and pigeons build relatively flimsy nests – often using sticks and other debris – which may be placed in trees, on ledges, or on the ground, depending on species. They lay one or two eggs at a time, and both parents care for the young, which leave the nest after seven to 28 days. Unlike most birds, both sexes of doves and pigeons produce crop milk to feed to their young, secreted by a sloughing of fluid-filled cells from the lining of the crop, young doves and pigeons are called squabs. The adjective columbine refers to pigeons and doves, recent phylogenomic studies support the grouping of these pigeons and sandgrouse together, along with mesites, forming the sister taxon to Mirandornithes. The Columbidae are usually divided into five subfamilies, probably inaccurately, for example, the American ground and quail doves, which are usually placed in the Columbinae, seem to be two distinct subfamilies. The order presented here follows Baptista et al. with some updates, osteology and DNA sequence analyses indicate the dodo and Rodrigues solitaire are better considered as a subfamily Raphinae in the Columbidae pending availability of further information. The dodo and Rodrigues solitaire are in all part of the Indo-Australian radiation that produced the three small subfamilies mentioned above, with the fruit-doves and pigeons. Therefore, they are included as a subfamily Raphinae, pending better material evidence of their exact relationships. Exacerbating these issues, columbids are not well represented in the fossil record, no truly primitive forms have been found to date. The genus Gerandia has been described from Early Miocene deposits of France, apart from that, all other fossils belong to extant genera. For these, and for the number of more recently extinct prehistoric species. Phylogeny based on the work by John H. Boyd III, Pigeons and doves exhibit considerable variations in size. Overall, the Columbidae tend to have short bills and legs, the wings are large and have low wing loadings, pigeons have strong wing muscles and are among the strongest fliers of all birds. They are also highly manoeuvrable in flight, the plumage of the family is variable
