Nuclear physics

Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions. Other forms of nuclear matter are studied. Nuclear physics should not be confused with atomic physics, which studies the atom as a whole, including its electrons. Discoveries in nuclear physics have led to applications in many fields; this includes nuclear power, nuclear weapons, nuclear medicine and magnetic resonance imaging and agricultural isotopes, ion implantation in materials engineering, radiocarbon dating in geology and archaeology. Such applications are studied in the field of nuclear engineering. Particle physics evolved out of nuclear physics and the two fields are taught in close association. Nuclear astrophysics, the application of nuclear physics to astrophysics, is crucial in explaining the inner workings of stars and the origin of the chemical elements; the history of nuclear physics as a discipline distinct from atomic physics starts with the discovery of radioactivity by Henri Becquerel in 1896 while investigating phosphorescence in uranium salts.

The discovery of the electron by J. J. Thomson a year was an indication that the atom had internal structure. At the beginning of the 20th century the accepted model of the atom was J. J. Thomson's "plum pudding" model in which the atom was a positively charged ball with smaller negatively charged electrons embedded inside it. In the years that followed, radioactivity was extensively investigated, notably by Marie Curie, Pierre Curie, Ernest Rutherford and others. By the turn of the century physicists had discovered three types of radiation emanating from atoms, which they named alpha and gamma radiation. Experiments by Otto Hahn in 1911 and by James Chadwick in 1914 discovered that the beta decay spectrum was continuous rather than discrete; that is, electrons were ejected from the atom with a continuous range of energies, rather than the discrete amounts of energy that were observed in gamma and alpha decays. This was a problem for nuclear physics at the time, because it seemed to indicate that energy was not conserved in these decays.

The 1903 Nobel Prize in Physics was awarded jointly to Becquerel for his discovery and to Marie and Pierre Curie for their subsequent research into radioactivity. Rutherford was awarded the Nobel Prize in Chemistry in 1908 for his "investigations into the disintegration of the elements and the chemistry of radioactive substances". In 1905 Albert Einstein formulated the idea of mass–energy equivalence. While the work on radioactivity by Becquerel and Marie Curie predates this, an explanation of the source of the energy of radioactivity would have to wait for the discovery that the nucleus itself was composed of smaller constituents, the nucleons. In 1906 Ernest Rutherford published "Retardation of the α Particle from Radium in passing through matter." Hans Geiger expanded on this work in a communication to the Royal Society with experiments he and Rutherford had done, passing alpha particles through air, aluminum foil and gold leaf. More work was published in 1909 by Geiger and Ernest Marsden, further expanded work was published in 1910 by Geiger.

In 1911–1912 Rutherford went before the Royal Society to explain the experiments and propound the new theory of the atomic nucleus as we now understand it. The key experiment behind this announcement was performed in 1910 at the University of Manchester: Ernest Rutherford's team performed a remarkable experiment in which Geiger and Marsden under Rutherford's supervision fired alpha particles at a thin film of gold foil; the plum pudding model had predicted that the alpha particles should come out of the foil with their trajectories being at most bent. But Rutherford instructed his team to look for something that shocked him to observe: a few particles were scattered through large angles completely backwards in some cases, he likened it to firing a bullet at tissue paper and having it bounce off. The discovery, with Rutherford's analysis of the data in 1911, led to the Rutherford model of the atom, in which the atom had a small dense nucleus containing most of its mass, consisting of heavy positively charged particles with embedded electrons in order to balance out the charge.

As an example, in this model nitrogen-14 consisted of a nucleus with 14 protons and 7 electrons and the nucleus was surrounded by 7 more orbiting electrons. Around 1920, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars. At that time, the source of stellar energy was a complete mystery; this was a remarkable development since at that time fusion and thermonuclear energy, that stars are composed of hydrogen, had not yet been discovered. The Rutherford model worked quite well until studies of nuclear spin were carried out by Franco Rasetti at the California Institute of Technology in 1929. By 1925 it was known that protons and electrons each had a spin of ​± 1⁄2. In the Rutherford model of nitrogen-14, 20 of the total 21 nuclear particles should have paired up to cancel each other's spin, the final odd particle should have left the nucleus with a net spin of ​1⁄2. Rasetti discovered, that nitrogen-14 had a spin of 1.

In 1932 Chadwick realized that radiation, observed by Walther Bothe, Herbert Becker, Irène and Frédéric Joliot-Curie was due to a neutral particle of about the same mass as the proton, that he called the neutron (following a suggestion from Rutherfor

2013 ITF Men's Circuit (October–December)

The 2013 ITF Men's Circuit is the 2013 edition of the entry level tour for men's professional tennis, is the third tier tennis tour below the Association of Tennis Professionals, World Tour and Challenger Tour. It is organised by the International Tennis Federation who additionally organizes the ITF Women's Circuit, an entry level tour for women's professional tennis. Future tournaments are organized to offer either $10,000 or $15,000 in prize money and tournaments which offering hospitality to players competing in the main draw give additional ranking points which are valid under the ATP ranking system, are to be organized by a national association or approved by the ITF Men's Circuit Committee; the tournaments are played on a rectangular flat surface referred to as a tennis court. The dimenstion of a tennis court are defined and regulated by the ITF and the court is 23.78 meters long, 10.97 meters wide. Its width is 8.23 meters for singles matches and 10.97 meters for doubles matches. Tennis is played on a variety of surfaces and each surface has its own characteristics which affect the playing style of the game.

There are four main types of courts depending on the materials used for the court surface, hard and carpet courts with the ITF classifying five different pace settings ranging from slow to fast. International Tennis Federation official website ITF Futures tournaments ITF Futures results archive

Sunset District, San Francisco

The Sunset District is a neighborhood located in the west-central area of San Francisco, United States. The Sunset District is the largest neighborhood within the city and county of San Francisco, with a population of over 85,000 it is the most populous. Golden Gate Park forms the neighborhood's northern border, the Pacific Ocean forms its western border. A section of the Sunset District towards its southeastern end is known as the Parkside neighborhood. Prior to the residential and commercial development of the Sunset District, much of the area was covered by sand dunes and was referred to by 19th century San Franciscans as the "Outside Lands."The Sunset District and the neighboring Richmond District are collectively known as The Avenues, because the majority of both neighborhoods are spanned by numbered north-south avenues. When the city was laid out, the avenues were numbered from 1st to 49th, the east-west streets were lettered A to X. In 1909, to reduce confusion for mail carriers, the east-west streets and 1st Avenue and 49th Avenue were renamed.

The east-west streets were named in ascending alphabetical order in a southward direction after prominent 19th-century American politicians, military leaders, or explorers. 1st Avenue was renamed Arguello Boulevard, 49th Avenue was renamed La Playa Street. Today, the first numbered avenue is 2nd Avenue, starting one block west of Arguello Boulevard, the last is 48th Avenue near Ocean Beach; the avenue numbers increase incrementally, with one exception: what would be 13th Avenue is known as Funston Avenue, named after Frederick Funston, a U. S. Army general known for his exploits during the Spanish–American War and Philippine–American War, for directing the U. S. Army response to the 1906 earthquake; the east-west streets in the Sunset appear in alphabetical order. These streets are: Lincoln Way, Irving, Kirkham, Moraga, Ortega, Quintara, Santiago, Ulloa, Wawona and Sloat Boulevard. "X" was proposed to be Xavier, but was changed to Yorba due to a pronunciation controversy. The origin of the "Sunset" name is not clear.

One claim indicates that Aurelius Buckingham, a developer who owned property in the area, coined the term in 1886. Another claim comes from the California Midwinter Exposition, held in Golden Gate Park in 1894 and known as "The Sunset City." Before construction of the Twin Peaks Tunnel in 1917, the Sunset was a vast, sparsely inhabited area of large sand dunes and coastal scrub land known as the "Outside Lands." Development was initiated in the 1870s and 1880s with construction of Golden Gate Park, but it did not reach a full scale until after the 1906 San Francisco earthquake, when small lots of tract homes and row homes now characteristic of the neighborhood were built into the sand dunes. These tract homes would displace a smaller original settlement built into the dunes called Carville, so named for squatters that lived in abandoned horsecars and cable cars that were dumped in the sand dunes. Development increased by the 1930s, as the Sunset was developed into a streetcar suburb; the post–World War II baby boom in the 1950s saw the last of the sand dunes leveled down and replaced with more single- and multifamily homes.

In these developments, built by Henry Doelger, entire blocks consist of houses of the same general character, differentiated by variations in their stucco facades and mirrored floorplans, with most built upon 25-foot-wide lots with no free space between houses. Oliver Rousseau built more individualistic homes in the district; the Sunset's demographics were consisted of European Americans Irish and Italian. Beginning in the late 1960s the neighborhood saw a steady influx of Asian immigrants following the Immigration and Nationality Act of 1965 which lifted racial quotas allowing for more non-European nationals to immigrate to the United States. Additionally, the Handover of Hong Kong motivated many Chinese to immigrate to the U. S. due to the economic uncertainties. Today, the vast majority of the neighborhood's population is Asian, with Chinese as the dominant ethnic group. There are still some small Irish enclaves however. For most of its history, the Sunset existed as a large individual area.

In recent years, the neighborhood has been popularly divided into three parts with sometimes vague borders. The Inner Sunset is bordered by Lincoln Way to the north, 2nd Ave to the east, Quintara Street to the south, 19th Avenue to the west; this far-east section of the Sunset is located just west of Mount Sutro. The main commercial area is along Irving Street from 5th Avenue to 12th Avenue, along 9th Avenue from Lincoln Way to Judah Street, much of, dotted with a variety of restaurants and shops; the Inner Sunset hosts a variety of local businesses, including restaurants, breweries, book stores, coffee shops, ice cream parlors and shoe stores, a tattoo parlor, a wine bar. All these establishments are clustered around the intersection of Irving Street. Food offered by the restaurants located in the Inner Sunset includes pizza, Thai, Korean, Hawaiian, Ethiopian, Cajun/Creole, Dim Sum, Peruvian, Vietnamese, California Cuisine, Indian, Vegetarian; the Central Sunset is bounded by Lincoln Way