title: Laura Branigan

text: In 1972, Branigan met acoustic guitarist Walker Daniels and his future wife Sharon Storm, and acoustic guitarist Chris Van Cleave, forming the folk-rock band "Meadow". In 1973 the group, with bass player Bob Valdez, released their debut album "The Friend Ship", featuring the singles "When You Were Young", and "Cane and Able", which featured the hook line "Throw away your cane and you are able". The record was not properly promoted and never re-released. The band broke up, after which Walker Daniels committed suicide. Branigan preferred not to discuss her involvement with Meadow publicly.


title: Laura Branigan

text: During the years after Meadow broke up, Branigan had various jobs, including a stint as one of Leonard Cohen's backup singers for his European tour in April–August 1976.


title: Laura Branigan

text: Branigan met attorney Larry Ross Kruteck (1936–1996) at a party in Manhattan in 1978, and they married in December of that year. He died of colon cancer on June 15, 1996.


title: Laura Branigan

text: In 1979, after a chance meeting with manager Sid Bernstein on her return from Europe, Branigan was signed by Ahmet Ertegun to Atlantic Records. For several years Atlantic had difficulty classifying Branigan's powerful voice. Her pop single "Looking Out for Number One", from her unreleased album "Silver Dreams", made a brief appearance on the U.S. dance chart, reaching No. 60. Two other early Atlantic singles, "Tell Him" and "Fool's Affair", followed. None of these three singles (or the B-side, "When") were included on her first album, but all four songs were eventually released on CD over 30 years later in 2014 as bonus cuts on a U.S. CD reissue of Branigan's first album.


title: Laura Branigan

text: Branigan's 9-track debut album, "Branigan", was released in March 1982. The first single from the album was "All Night with Me", which reached No. 69 on the "Billboard" charts in early 1982. The album alternated four energetic up-tempo songs with five ballads, including one of the few songs written solely by Branigan, "I Wish We Could Be Alone". "Gloria", an Italian love song recorded in 1979 by Umberto Tozzi and successful in several European countries, was released as the album's second single. Branigan's version was reworked with Tozzi's own arranger, Greg Mathieson, who updated its production with fellow producer Jack White to give it what Branigan called "an American kick" to match the new English lyrics. U.S. radio stations were initially unreceptive to "Gloria", but after it was embraced by dance clubs it eventually won them over, becoming one of the biggest hits of the 1980s. The album went gold, and the single was eventually certified platinum (sales of more than two million U.S. copies). Branigan's performance of "Gloria" was nominated for a Grammy Award for Best Female Pop Vocal Performance alongside Linda Ronstadt, Olivia Newton-John, Juice Newton and that year's winner, Melissa Manchester, becoming her only solo nomination.


title: Laura Branigan

text: In the spring of 1983, Branigan released her second album "Branigan 2". Her vocals propelled her English-language version of the French song, "Solitaire" toward the top of the U.S. charts. The original "Solitaire" was written and recorded in 1981 by French singer-songwriter Martine Clemenceau. Two songs included on the album began the careers for two then-unknowns: the English translation of "Solitaire" was the first major hit for songwriter Diane Warren, while the ballad "How Am I Supposed to Live Without You" was the first major hit for its co-writer, Michael Bolton. Branigan's version reached No. 12 on the hot 100 and spent three weeks at No. 1 on the Billboard adult contemporary chart.


title: Laura Branigan

text: During the height of her career, Branigan also made acting appearances, first in 1981 in "An American Girl in Berlin" for West German television, and then after the success of "Gloria", guest appearances on American television series such as "CHiPs" ("Fox Trap", season 6, episode 16, in which she played Sarah, lead singer of the female rock band Cadillac Foxes), "Automan" and "Knight Rider". She would later appear in independent films including "Mugsy's Girls" (aka "Delta Pi", 1985) with Oscar-winner Ruth Gordon, and the Australian film "Backstage". She sang on major national television and radio campaigns for products including Dr Pepper, Coca-Cola and Chrysler, which sponsored her 1985–1986 "Hold Me" tour.


title: Laura Branigan

text: The year 1984, while she was working with German producer Jack White, was the height of the European synthpop era, and "Self Control", the title track of Branigan's third album, released in April 1984 became her biggest hit internationally, topping the charts in over six countries, most notably West Germany, where it spent six weeks at No. 1. The original version was recorded a few months earlier, still in 1984, under the name of one of the song's co-writers "Raf" (Raffaele Riefoli), and held the West German number 2 spot during this time period; Branigan's version enjoyed more success outside of Raf's native Italy, hitting No. 4 in the U.S. The song was featured on the eighth episode of the first season of the TV series, "Miami Vice", entitled "The Great McCarthy", which aired on November 16, 1984. Other pop, disco, and adult contemporary hits from the "Self Control" album include "The Lucky One" (which won her a Tokyo Music Festival prize), the continental ballad "Ti Amo" (another Umberto Tozzi hit, and a No. 2 hit in Australia for Branigan) and the dance hit "Satisfaction". The album also featured an understated version of Carole King's "Will You Still Love Me Tomorrow"; as a counterpoint to all the dance productions, it was a bare-bones piano version. (In concerts and television appearances throughout her career, Branigan accompanied herself on the piano for the song.)


title: Laura Branigan

text: Also during 1984, Branigan contributed the song "Hot Night" to the "Ghostbusters" soundtrack. The song was written by Diane Warren and The Doctor.


title: Laura Branigan

text: Branigan's vocal coach was Carlo Menotti, and she worked with Steve Lukather (Toto), Dann Huff (Giant) and Michael Landau; keyboardists Greg Mathieson, Harold Faltermeyer, Michael Boddicker and Robbie Buchanan; bassists Nathan East and Dennis Belfield (Rufus); drummers Carlos Vega and Doane Perry (Jethro Tull); percussionists Paulinho Da Costa and Lenny Castro; and guest vocalists including Joe "Bean" Esposito and background vocalists including The Waters Sisters (Maxine and Julia), James Ingram, and Richard Page and Stephen George (Mr. Mister). As her stature grew, she attracted Grammy-winning producers including Phil Ramone, Richard Perry and David Kershenbaum. She performed duets with John Farnham as well as Latin pop artist Luis Miguel.


title: Laura Branigan

text: In 1984, Branigan's live show was recorded twice, for a syndicated radio concert series and a concert video. Branigan was also nominated for an award at the American Music Awards of 1985 for favorite pop/rock female video artist, won by Cyndi Lauper. Also in 1985, Branigan performed the main theme song for the television mini-series "Hollywood Wives", based on the novel by Jackie Collins.


title: Laura Branigan

text: By the time Branigan's fourth album, "Hold Me" was released in July 1985, "Self Control" was a worldwide success. The hits continued with "Spanish Eddie", which was her sixth U.S. "Billboard" top 40 pop hit in two and a half years. The subsequent single release "Hold Me" was a U.S. top-40 dance hit, and Branigan's introduction of the rock ballad "I Found Someone" (co-written by Michael Bolton, a later hit for Cher) scored even higher on the adult contemporary chart. However, neither song was supported by a music video, and both stalled at the low end of the Hot 100 chart. On June 13, 1985, Branigan made her fourth appearance on legendary TV music show "American Bandstand", performing "Spanish Eddie" and "Hold Me".


title: Laura Branigan

text: In February 1986, Branigan was invited for the first time to XXVII Festival Internacional De La Canción De Viña Del Mar in Chile, having a successful performance on the main stage and by television and thus increasing its popularity both in Chile and in the rest of Latin America.


title: Laura Branigan

text: Branigan's fifth album, "Touch" (released July 7, 1987) marked a change in her career. Under new management and using different producers, Branigan took a more active role in her work and in the studio, seeing her return to dancefloors with the Stock-Aitken-Waterman-produced track "Shattered Glass", written by Bob Mitchell and Steve Coe, of the band Monsoon. "Shattered Glass" was performed by Branigan on the last episode of "American Bandstand" (hosted by Dick Clark) to be broadcast on ABC (the show would last for two more years, first in first-run syndication and finally on the USA Network) on September 5, 1987, becoming their last guest performer. The album also included a return to the Billboard top-40 with her cover of Jennifer Rush's "Power of Love", which was one of the 20 bestselling singles in the U.S. during the Christmas season. The album's third single, "Cry Wolf", a top-30 AC hit, did not capture the attention of pop radio stations and stalled; the ballad was recorded two years later by Stevie Nicks, and more recently by its writer Jude Johnstone.


title: Laura Branigan

text: Branigan's sixth album, "Laura Branigan" (1990), brought her back to the Hi-NRG charts and gay clubs with "Moonlight on Water", and she scored a top-30 adult contemporary hit with "Never in a Million Years". Branigan added production to her list of credits with her cover of Vicki Sue Robinson's disco-era "Turn the Beat Around" and the atmospheric "Let Me In", a cover of an Eddie Money song. The album also includes '"Unison", which was the title track for Céline Dion's English debut CD in the same year. The album's closing track, a cover of Bryan Adams' "The Best Was Yet to Come", was produced and arranged by Branigan. The 1990–1991 Laura Branigan Tour, which was kicked off with an appearance on "The Tonight Show Starring Johnny Carson" on July 13, 1990 was followed by a performance in the Trump Regency Showroom in Atlantic City, New Jersey on July 14, and filmed for a syndicated U.S. television show "SRO in Concert", which was released on videocassette and laserdisc; on July 15, 1990, she performed at the Warwick Musical Theatre in Rhode Island.


title: Laura Branigan

text: On Branigan's seventh and final studio album "Over My Heart" (August 17, 1993), the singer again produced (with Phil Ramone), and wrote and arranged. It included "Didn't We Almost Win It All" (by Branigan and Brian BecVar) (released as the first single), a cover of Cher's song "Hard Enough Getting Over You" (released as the second single), a cover of the Patty Loveless single "How Can I Help You Say Goodbye", a cover of Roxette's song "The Sweet Hello, The Sad Goodbye", and "Is There Anybody Here But Me?" (Pessis, Wells), a smooth mid-tempo number.


title: Laura Branigan

text: Branigan recorded a duet with David Hasselhoff which was hugely successful for being broadcast as the closing track of the "Baywatch" TV series. The single "I Believe" was originally released on CD album in 1994.


title: Laura Branigan

text: After 1990, Branigan's chart success cooled in the U.S., though she was still in demand around the world and went on several global tours. In 1994, not long after the release of "Over My Heart", Larry Kruteck, Branigan's husband (m. 1978), was diagnosed with colon cancer. Branigan refused to accept the medical prognosis, and left the music industry to devote her attention to him. Branigan put Kruteck on herbal treatments, eventually nursing him full-time. Kruteck survived for another two and a half years and died on June 15, 1996, after which Branigan stopped performing.


title: Laura Branigan

text: Branigan had official greatest hits collections released in South America, Japan, Germany, South Africa, and the U.S.; the U.S. collection was released in 1995. The 13-track "The Best of Branigan" included two newly recorded covers: "Show Me Heaven" (written by Maria McKee) and the Donna Summer hit "Dim All the Lights", which Branigan released in several remixes.


title: Laura Branigan

text: On August 15, 1995, Branigan was a guest on the TV show "Talking Food", hosted by Robin Leach and broadcast by the Food Network, and she promoted the album and sang "Dim All the Lights", before preparing her Summer Delight pasta dish on the show.


title: Laura Branigan

text: In February 1996, she was selected to be part of the international jury at the , in Chile. Besides her duties as a jury member of this international musical competition, Branigan performed on February 16 on the main stage for an audience who enthusiastically sang her greatest hits.


title: Laura Branigan

text: In early 2001, Branigan's return to the stage was postponed, when she broke both of her femurs in a 10-foot fall from a ladder while she was hanging wisteria outside her three-bedroom lakeside home in Westchester County, New York, resulting in physical therapy for six months. In 2002, she performed twice as the "singing" Janis Joplin in the off-Broadway musical "Love, Janis", before dropping out of the show. "I left "Janis" because the producers failed to file with Equity properly," she told the "Sunday News" in Lancaster, Pennsylvania. "I was sort of relieved. My voice isn't anything like Janis Joplin's, and there were 19 of her songs in the show." In later years she continued to record, and dated Tommy Bayiokos, the drummer in her band. Also in 2002, her second official US hits collection, "The Essentials", was released, including the long out-of-print hit "I Found Someone".


title: Laura Branigan

text: Branigan died in her sleep at her lodge in East Quogue, New York, on August 26, 2004, aged 52. The cause was attributed to a previously undiagnosed ventricular brain aneurysm. It was reported that she had been experiencing persistent headaches for several weeks before her death, but had sought no medical attention for them. At the time of her death, it was widely and erroneously reported that she was 47 years old, resulting from a technical error the Associated Press published after contacting Branigan's management company.


title: Laura Branigan

text: At Byram Hills High School in Armonk, New York, the Laura Branigan Memorial Scholarship is given annually to a senior for excellence in the performing arts.


title: Laura Branigan

text: On April 18, 2019, Jain debuted a single titled "Gloria" that is not a cover, but a tribute to Branigan.


title: Laura Branigan

text: The St. Louis Blues NHL team began using Branigan's version of "Gloria" as its unofficial victory song when they went on a franchise-record 11-game winning streak during the 2018–19 season. A few Blues players visited a bar in South Philadelphia called Jacks NYB to watch the NFL Wild Card game between the Philadelphia Eagles and Chicago Bears.


title: Laura Branigan

text: At the time, the Blues had the worst record in the league at 15–18–4, had fired head coach Mike Yeo, called up rookie goaltender Jordan Binnington from the minor leagues to replace struggling starter Jake Allen, and seemed bound for a lost season. Following their January 7 victory over the Flyers, which was Binnington's first NHL start, the Blues played "Gloria" in the locker room to celebrate their victory, with it then becoming a regular locker room ritual. When their stadium's DJ learned of it, he began playing the song in the stadium to rally the team. From January 2019 the Blues would post a 30-10-5 record in the remaining games to finish at 45-28-9 and qualify for a playoff spot, eventually advancing to the 2019 Stanley Cup Finals, the teams' first Stanley Cup Final since 1970, where they defeated the Boston Bruins in 7 games to win their first Stanley Cup in franchise history. The dramatic turnaround in the Blues' fortunes following their adoption of "Gloria" led to it being embraced as their new victory anthem. The song is played at Enterprise Center every time the Blues win a game, leading to "Play Gloria!" becoming both a meme and victory chant for Blues fans. Local radio station Y98 played the song for 24 hours following the Blues' Game 7 double-overtime 2–1 victory over the Dallas Stars on May 8 and again two weeks later on May 22 after its Game 6 5–1 win over the San Jose Sharks to win the Western Conference Championship and advance to the finals. After the Blues defeated the Boston Bruins in the Stanley Cup Finals, on June 12, Y98 played "Gloria" again for 24 hours. The bands Phish and Vampire Weekend, who were both holding concerts in St. Louis on the night of Game 7, performed covers of "Gloria" when they learned the Blues had won the Cup.


title: Laura Branigan

text: Branigan's legacy manager and representative Kathy Golik has embraced the trend, with Branigan's verified Twitter page frequently posting support for the Blues, especially during their 2019 playoff run. Branigan's official website also got updated with a new splash page which expressed support for the Blues and proclaimed Branigan as the "Original Play Gloria". Golik stayed in St. Louis and attended every game and watch party during the Blues' 2019 Stanley Cup run as Branigan's representative among the Blues fanbase while discussing the trend with media outlets. When fans of the Boston Bruins, the Blues' opponent in the 2019 Stanley Cup Finals, started re-purposing the "Play Gloria" meme it earned a rebuke from Branigan's Twitter page which went viral. Custom-made Blues jerseys with Branigan's name and the number 82 surged in popularity during the 2019 Stanley Cup playoffs, with one being displayed on Branigan's Twitter page, along with other Blues merchandise sent by fans. "Gloria" reappeared on the iTunes singles chart thanks to the trend, going to number 3 after the Blues won the Stanley Cup. "Gloria" would also re-enter the Billboard charts in the wake of the Blues' championship, landing at No. 46 on the Billboard Digital Song Sales chart for the week of June 22, 2019. Golik noted that streams of "Gloria" have surged across all platforms and this has had a "trickle down" effect to the rest of Branigan's catalog, with her other hit songs such as "Self Control", "Solitaire" and "How Am I Supposed to Live Without You" seeing significant upticks in streams and downloads during the 2019 Stanley Cup Playoffs. The song's resurgence in popularity has led to Branigan's management getting numerous requests for live performances and public appearances, leading them to release a statement reminding the public that Branigan is deceased, as well as adding a note about this to her social media accounts. "Forbes" described "Gloria" as an "unlikely championship anthem" and noted that the Blues' Stanley Cup victory could permanently alter the meaning and legacy of the song, with it becoming forever associated with the St. Louis Blues and ice hockey in general. Golik has also stated her belief that Branigan and "Gloria" "will forever be intertwined" with the Blues and the city of St. Louis. When asked how she thought Branigan would have reacted to the "Play Gloria" meme had she lived to see it, Golik said, "She was very sincere, very down to Earth, she would just have been very touched by it all. If she were here, I know she would have participated in a very big way. I know she's there in spirit. To see them win and to hear that song blaring and coming up in the arena and looking around and seeing people singing out as loud as they can, cheering and having a good time, it's indescribable what that's like."


title: Laura Branigan

text: In addition, Branigan's boyfriend at the time of her passing Tommy Bayiokos, who also was in her band, said "Laura would have gladly satisfied fans' desire to hear it live. She would have been humbled and performed with gusto. The "Play Gloria" wave started at the Jacks NYB bar and was totally UNSCRIPTED...it's been bittersweet and a testament of Laura's musical prowess."


title: 2013 NBA draft

text: The 2013 NBA draft was held on June 27, 2013, at the Barclays Center in Brooklyn, New York. National Basketball Association (NBA) teams took turns selecting amateur U.S. college basketball players and other eligible players, including international players. State Farm was the presenting sponsor. The lottery took place on May 21, 2013. This was the first draft for New Orleans under their new Pelicans name after playing as the New Orleans Hornets previously. It would also be the last draft for the Charlotte Bobcats under their old name, as they resumed playing under their old Hornets moniker that they last used in 2002 once the 2013–14 NBA season was over. Anthony Bennett, the first pick in the draft, had a very limited amount of media outlets considering him as a potential #1 pick in the draft. He bounced around the league and then was finally released by the Brooklyn Nets in January 2017 after averaging just 5.2 PPG.


title: 2013 NBA draft

text: Highlights of the draft included the first Canadian number one selection (Anthony Bennett). The draft also included the first Canadian pair of lottery picks (Bennett and Kelly Olynyk), the first Iranian draft choice (Arsalan Kazemi), the first New Zealander first round pick (Steven Adams) and the last first round draft selections announced by then-NBA commissioner David Stern, the last of which included a visit by Hakeem Olajuwon, Stern's first pick he ever announced back in 1984. He was replaced by current commissioner Adam Silver beginning with the 2014 NBA draft.


title: 2013 NBA draft

text: The draft is conducted under the eligibility rules established in the league's new 2011 collective bargaining agreement (CBA) with its players union. The CBA that ended the 2011 lockout instituted no immediate changes to the draft, but called for a committee of owners and players to discuss future changes. , the basic eligibility rules for the draft are listed below.


title: 2013 NBA draft

text: Player who are not automatically eligible must declare their eligibility for the draft by notifying the NBA offices in writing no later than 60 days before the draft. For the 2013 draft, this date fell on April 28. Under NCAA rules, players will only have until April 16 to withdraw from the draft and maintain their college eligibility.


title: 2013 NBA draft

text: A player who has hired an agent will forfeit his remaining college eligibility, regardless of whether he is drafted. Also, while the CBA allows a player to withdraw from the draft twice, the NCAA mandates that a player who has declared twice loses his college eligibility.


title: 2013 NBA draft

text: Fifteen players who did not attend college in the US or Canada between the ages of 18 and 22 declared for the draft.


title: 2013 NBA draft

text: Players who do not meet the criteria for "international" players are automatically eligible if they meet any of the following criteria:


title: 2013 NBA draft

text: Players who meet the criteria for "international" players are automatically eligible if they meet any of the following criteria:


title: 2013 NBA draft

text: In addition to every college players who has completed their college eligibility and every "international" players who was born on or before December 31, 1991, the following player would also be eligible for selection in the 2013 NBA draft:


title: 2013 NBA draft

text: The first 14 picks in the draft belong to teams that miss the playoffs; the order was determined through a lottery. The lottery determined the three teams that will obtain the first three picks on the draft. The remaining first-round picks and the second-round picks were assigned to teams in reverse order of their win–loss record in the previous season.


title: 2013 NBA draft

text: Below were the chances for each team to get specific picks in the 2013 draft lottery, rounded to three decimal places.


title: 2013 NBA draft

text: The NBA annually invites around 10–15 players to sit in the so-called "green room", a special room set aside at the draft site for the invited players plus their families and agents. The following 13 players were invited (listed alphabetically) to the 2013 NBA draft.


title: 2013 NBA draft

text: Prior to the day of the draft, the following trades were made and resulted in exchanges of draft picks between the teams.


title: Epstein–Barr virus

text: The Epstein–Barr virus (EBV), formally called Human gammaherpesvirus 4, is one of the nine known human herpesvirus types in the herpes family, and is one of the most common viruses in humans. EBV is a double-stranded DNA virus.


title: Epstein–Barr virus

text: It is best known as the cause of infectious mononucleosis ("mono" or "glandular fever"). It is also associated with various non-malignant, premalignant, and malignant Epstein–Barr virus-associated lymphoproliferative diseases such as Burkitt lymphoma, hemophagocytic lymphohistiocytosis, and Hodgkin's lymphoma; non-lymphoid malignancies such as gastric cancer and nasopharyngeal carcinoma; and conditions associated with human immunodeficiency virus such as hairy leukoplakia and central nervous system lymphomas. The virus is also associated with the childhood disorders of Alice in Wonderland syndrome and acute cerebellar ataxia and, by some evidence, higher risks of developing certain autoimmune diseases, especially dermatomyositis, systemic lupus erythematosus, rheumatoid arthritis, and Sjögren's syndrome. About 200,000 cancer cases globally per year are thought to be attributable to EBV. In 2022, a large study (population of 10 million over 20 years) suggested EBV as the leading cause of multiple sclerosis, with a recent EBV infection causing a 32-fold increase in the risk of developing multiple sclerosis.


title: Epstein–Barr virus

text: Most people become infected with EBV and gain adaptive immunity. In the United States, about half of all five-year-old children and about 90% of adults have evidence of previous infection. Infants become susceptible to EBV as soon as maternal antibody protection disappears. Many children become infected with EBV, and these infections usually cause no symptoms or are indistinguishable from the other mild, brief illnesses of childhood. In the United States and other developed countries, many people are not infected with EBV in their childhood years. When infection with EBV occurs during adolescence or young adulthood, it causes infectious mononucleosis 35 to 50% of the time.


title: Epstein–Barr virus

text: EBV infects B cells of the immune system and epithelial cells. Once EBV's initial lytic infection is brought under control, EBV latency persists in the individual's memory B cells for the rest of their life.


title: Epstein–Barr virus

text: The virus is about 122–180 nm in diameter and is composed of a double helix of deoxyribonucleic acid (DNA) which contains about 172,000 base pairs encoding 85 genes. The DNA is surrounded by a protein nucleocapsid, which is surrounded by a tegument made of protein, which in turn is surrounded by an envelope containing both lipids and surface projections of glycoproteins, which are essential to infection of the host cell. In July 2020, a team of researchers reported the first complete atomic model of the nucleocapsid of the virus. This "first complete atomic model [includes] the icosahedral capsid, the capsid-associated tegument complex (CATC) and the dodecameric portal--the viral genome translocation apparatus."


title: Epstein–Barr virus

text: The term viral tropism refers to which cell types that EBV infects. EBV can infect different cell types, including B cells and epithelial cells.


title: Epstein–Barr virus

text: The viral three-part glycoprotein complexes of gHgL gp42 mediate B cell membrane fusion; although the two-part complexes of gHgL mediate epithelial cell membrane fusion. EBV that are made in the B cells have low numbers of gHgLgp42 complexes, because these three-part complexes interact with Human-leukocyte-antigen class II molecules present in B cells in the endoplasmic reticulum and are degraded. In contrast, EBV from epithelial cells are rich in the three-part complexes because these cells do not normally contain HLA class II molecules. As a consequence, EBV made from B cells are more infectious to epithelial cells, and EBV made from epithelial cells are more infectious to B cells. Viruses lacking the gp42 portion are able to bind to human B cells, but unable to infect.


title: Epstein–Barr virus

text: EBV can infect both B cells and epithelial cells. The mechanisms for entering these two cells are different.


title: Epstein–Barr virus

text: To enter B cells, viral glycoprotein gp350 binds to cellular receptor CD21 (also known as CR2). Then, viral glycoprotein gp42 interacts with cellular MHC class II molecules. This triggers fusion of the viral envelope with the cell membrane, allowing EBV to enter the B cell. Human CD35, also known as complement receptor 1 (CR1), is an additional attachment factor for gp350/220, and can provide a route for entry of EBV into CD21-negative cells, including immature B-cells. EBV infection downregulates expression of CD35.


title: Epstein–Barr virus

text: To enter epithelial cells, viral protein BMRF-2 interacts with cellular β1 integrins. Then, viral protein gH/gL interacts with cellular αvβ6/αvβ8 integrins. This triggers fusion of the viral envelope with the epithelial cell membrane, allowing EBV to enter the epithelial cell. Unlike B-cell entry, epithelial-cell entry is actually impeded by viral glycoprotein gp42.


title: Epstein–Barr virus

text: Once EBV enters the cell, the viral capsid dissolves and the viral genome is transported to the cell nucleus.


title: Epstein–Barr virus

text: The lytic cycle, or productive infection, results in the production of infectious virions. EBV can undergo lytic replication in both B cells and epithelial cells. In B cells, lytic replication normally only takes place after reactivation from latency. In epithelial cells, lytic replication often directly follows viral entry.


title: Epstein–Barr virus

text: For lytic replication to occur, the viral genome must be linear. The latent EBV genome is circular, so it must linearize in the process of lytic reactivation. During lytic replication, viral DNA polymerase is responsible for copying the viral genome. This contrasts with latency, in which host-cell DNA polymerase copies the viral genome.


title: Epstein–Barr virus

text: Immediate-early lytic gene products act as transactivators, enhancing the expression of later lytic genes. Immediate-early lytic gene products include BZLF1 (also known as Zta, EB1, associated with its product gene "ZEBRA") and BRLF1 (associated with its product gene "Rta").


title: Epstein–Barr virus

text: Early lytic gene products have many more functions, such as replication, metabolism, and blockade of antigen processing. Early lytic gene products include BNLF2.


title: Epstein–Barr virus

text: Finally, late lytic gene products tend to be proteins with structural roles, such as VCA, which forms the viral capsid. Other late lytic gene products, such as BCRF1, help EBV evade the immune system.


title: Epstein–Barr virus

text: EGCG, a polyphenol in green tea, has shown in a study to inhibit EBV spontaneous lytic infection at the DNA, gene transcription, and protein levels in a time- and dose-dependent manner; the expression of EBV lytic genes" Zta, Rta", and early antigen complex EA-D (induced by "Rta"), however, the highly stable "EBNA-1" gene found across all stages of EBV infection is unaffected. Specific inhibitors (to the pathways) suggest that Ras/MEK/MAPK pathway contributes to EBV lytic infection though BZLF1 and PI3-K pathway through BRLF1, the latter completely abrogating the ability of a BRLF1 adenovirus vector to induce the lytic form of EBV infection. Additionally, the activation of some genes but not others is being studied to determine just how to induce immune destruction of latently infected B-cells by use of either TPA or sodium butyrate.


title: Epstein–Barr virus

text: Instead, the EBV genome circular DNA resides in the cell nucleus as an episome and is copied by cellular DNA polymerase.


title: Epstein–Barr virus

text: Latent EBV expresses its genes in one of three patterns, known as latency programs. EBV can latently persist within B cells and epithelial cells, but different latency programs are possible in the two types of cell.


title: Epstein–Barr virus

text: EBV can exhibit one of three latency programs: Latency I, Latency II, or Latency III. Each latency program leads to the production of a limited, distinct set of viral proteins and viral RNAs.


title: Epstein–Barr virus

text: EBV latency within B cells usually progresses from Latency III to Latency II to Latency I. Each stage of latency uniquely influences B cell behavior. Upon infecting a resting naive B cell, EBV enters Latency III. The set of proteins and RNAs produced in Latency III transforms the B cell into a proliferating blast (also known as B cell activation).


title: Epstein–Barr virus

text: Later, the virus restricts its gene expression and enters Latency II. The more limited set of proteins and RNAs produced in Latency II induces the B cell to differentiate into a memory B cell.


title: Epstein–Barr virus

text: Finally, EBV restricts gene expression even further and enters Latency I. Expression of EBNA-1 allows the EBV genome to replicate when the memory B cell divides.


title: Epstein–Barr virus

text: In primary infection, EBV replicates in oropharyngeal epithelial cells and establishes Latency III, II, and I infections in B-lymphocytes. EBV latent infection of B-lymphocytes is necessary for virus persistence, subsequent replication in epithelial cells, and release of infectious virus into saliva. EBV Latency III and II infections of B-lymphocytes, Latency II infection of oral epithelial cells, and Latency II infection of NK- or T-cell can result in malignancies, marked by uniform EBV genome presence and gene expression.


title: Epstein–Barr virus

text: Latent EBV in B cells can be reactivated to switch to lytic replication. This is known to happen "in vivo", but what triggers it is not known precisely. "In vitro", latent EBV in B cells can be reactivated by stimulating the B cell receptor, so it is likely reactivation "in vivo" takes place after latently infected B cells respond to unrelated infections.


title: Epstein–Barr virus

text: When EBV infects B cells "in vitro", lymphoblastoid cell lines eventually emerge that are capable of indefinite growth. The growth transformation of these cell lines is the consequence of viral protein expression.


title: Epstein–Barr virus

text: Following natural infection with EBV, the virus is thought to execute some or all of its repertoire of gene expression programs to establish a persistent infection. Given the initial absence of host immunity, the lytic cycle produces large numbers of virions to infect other (presumably) B-lymphocytes within the host.


title: Epstein–Barr virus

text: The latent programs reprogram and subvert infected B-lymphocytes to proliferate and bring infected cells to the sites at which the virus presumably persists. Eventually, when host immunity develops, the virus persists by turning off most (or possibly all) of its genes, only occasionally reactivating to produce fresh virions. A balance is eventually struck between occasional viral reactivation and host immune surveillance removing cells that activate viral gene expression.


title: Epstein–Barr virus

text: The site of persistence of EBV may be bone marrow. EBV-positive patients who have had their own bone marrow replaced with bone marrow from an EBV-negative donor are found to be EBV-negative after transplantation.


title: Epstein–Barr virus

text: All EBV nuclear proteins are produced by alternative splicing of a transcript starting at either the Cp or Wp promoters at the left end of the genome (in the conventional nomenclature). The genes are ordered "EBNA-LP/EBNA-2/EBNA-3A/EBNA-3B/EBNA-3C/EBNA-1" within the genome.


title: Epstein–Barr virus

text: The initiation codon of the EBNA-LP coding region is created by an alternate splice of the nuclear protein transcript. In the absence of this initiation codon," EBNA-2/EBNA-3A/EBNA-3B/EBNA-3C/EBNA-1" will be expressed depending on which of these genes is alternatively spliced into the transcript.


title: Epstein–Barr virus

text: EBV can be divided into two major types, EBV type 1 and EBV type 2. These two subtypes have different EBNA-3 genes. As a result, the two subtypes differ in their transforming capabilities and reactivation ability. Type 1 is dominant throughout most of the world, but the two types are equally prevalent in Africa. One can distinguish EBV type 1 from EBV type 2 by cutting the viral genome with a restriction enzyme and comparing the resulting digestion patterns by gel electrophoresis.


title: Epstein–Barr virus

text: Epstein–Barr virus-encoded small RNAs (EBERs) are by far the most abundant EBV products transcribed in cells infected by EBV. They are commonly used as targets for the detection of EBV in histological tissues.


title: Epstein–Barr virus

text: EBV causes infectious mononucleosis. Children infected with EBV have few symptoms or can appear asymptomatic, but when infection is delayed to adolescence or adulthood, it can cause fatigue, fever, inflamed throat, swollen lymph nodes in the neck, enlarged spleen, swollen liver, or rash. Post-infectious chronic fatigue syndrome has also been associated with EBV infection.


title: Epstein–Barr virus

text: EBV has also been implicated in several other diseases, including Burkitt's lymphoma, hemophagocytic lymphohistiocytosis, Hodgkin's lymphoma, stomach cancer, nasopharyngeal carcinoma, multiple sclerosis, and lymphomatoid granulomatosis.


title: Epstein–Barr virus

text: Specifically, EBV infected B-cells have been shown to reside within the brain lesions of multiple sclerosis patients, and a 2022 study of 10 million soldiers' historical blood samples showed that "Individuals who were not infected with the Epstein-Barr virus virtually never get multiple sclerosis. It's only after Epstein-Barr virus infection that the risk of multiple sclerosis jumps up by over 30-fold," and that only EBV of many infections had such a clear connection with the disease.


title: Epstein–Barr virus

text: Additional diseases that have been linked to EBV include Gianotti–Crosti syndrome, erythema multiforme, acute genital ulcers, and oral hairy leukoplakia. The viral infection is also associated with, and often contributes to the development of, a wide range of non-malignant lymphoproliferative diseases such as severe hypersensitivity mosquito bite allergy reactions, Epstein-Barr virus-positive mucocutaneous ulcers, and hydroa vacciniforme as well as malignant lymphoproliferative diseases such as Epstein–Barr virus-positive Burkitt lymphoma, Epstein–Barr virus-positive Hodgkin lymphoma, and primary effusion lymphoma.


title: Epstein–Barr virus

text: The Epstein–Barr virus has been implicated in disorders related to alpha-synuclein aggregation (e.g. Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy).


title: Epstein–Barr virus

text: The Epstein–Barr virus was named after Michael Anthony Epstein, and Yvonne Barr, who discovered the virus together with Bert Achong. In 1961, Epstein, a pathologist and expert electron microscopist, attended a lecture on "The Commonest Children's Cancer in Tropical Africa—A Hitherto Unrecognised Syndrome" by Denis Parsons Burkitt, a surgeon practicing in Uganda, in which Burkitt described the "endemic variant" (pediatric form) of the disease that bears his name. In 1963, a specimen was sent from Uganda to Middlesex Hospital to be cultured. Virus particles were identified in the cultured cells, and the results were published in "The Lancet" in 1964 by Epstein, Achong, and Barr. Cell lines were sent to Werner and Gertrude Henle at the Children's Hospital of Philadelphia who developed serological markers. In 1967, a technician in their laboratory developed mononucleosis and they were able to compare a stored serum sample, showing that antibodies to the virus developed. In 1968, they discovered that EBV can directly immortalize B cells after infection, mimicking some forms of EBV-related infections, and confirmed the link between the virus and infectious mononucleosis.


title: Epstein–Barr virus

text: As a relatively complex virus, EBV is not yet fully understood. Laboratories around the world continue to study the virus and develop new ways to treat the diseases it causes. One popular way of studying EBV "in vitro" is to use bacterial artificial chromosomes. Epstein–Barr virus can be maintained and manipulated in the laboratory in continual latency (a property shared with Kaposi's sarcoma-associated herpesvirus, another of the eight human herpesviruses). Although many viruses are assumed to have this property during infection of their natural hosts, there is not an easily managed system for studying this part of the viral lifecycle. Genomic studies of EBV have been able to explore lytic reactivation and regulation of the latent viral episome.


title: Epstein–Barr virus

text: Although under active research, an Epstein–Barr virus vaccine is not yet available. The development of an effective vaccine could prevent up to 200,000 cancers globally per year. The absence of effective animal models is an obstacle to development of prophylactic and therapeutic vaccines against EBV.


title: Epstein–Barr virus

text: Like other human herpesviruses Epstein-Barr might allow eradication via a course of the pro-drug valaciclovir, but further research is needed to determine if eradication is actually achievable. Antiviral agents act by inhibiting viral DNA replication, but there is little evidence that they are effective against Epstein–Barr virus. Moreover, they are expensive, risk causing resistance to antiviral agents, and (in 1% to 10% of cases) can cause unpleasant side effects.


title: Atom

text: Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.


title: Atom

text: Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small, typically around 100 picometers across. They are so small that accurately predicting their behavior using classical physics, as if they were tennis balls for example, is not possible due to quantum effects.


title: Atom

text: More than 99.94% of an atom's mass is in the nucleus. The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge. If the number of protons and electrons are equal, then the atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively – such atoms are called ions.


title: Atom

text: The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force. The protons and neutrons in the nucleus are attracted to each other by the nuclear force. This force is usually stronger than the electromagnetic force that repels the positively charged protons from one another. Under certain circumstances, the repelling electromagnetic force becomes stronger than the nuclear force. In this case, the nucleus splits and leaves behind different elements. This is a form of nuclear decay.


title: Atom

text: The number of protons in the nucleus is the "atomic number" and it defines to which chemical element the atom belongs. For example, any atom that contains 29 protons is copper. The number of neutrons defines the isotope of the element. For example, a copper atom with 34 neutrons is copper-63 (29+34), and with 36 neutrons is copper-65; natural copper is about 70% Cu-63 and the rest is Cu-65.


title: Atom

text: Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules or crystals. For example, New York City's Statue of Liberty was originally made of pure copper, but over the years, the surface combined with oxygen, carbon and sulfur atoms to make a green patina on the copper. The ability of atoms to attach and detach is responsible for most of the physical changes observed in nature. Chemistry is the discipline that studies these changes.


title: Atom

text: The basic idea that matter is made up of tiny, indivisible particles is an old idea that appeared in many ancient cultures such as those of Greece and India. The word "atom" is derived from the ancient Greek word "atomos", which means "uncuttable". This ancient idea was based in philosophical reasoning rather than scientific reasoning. Modern atomic theory is not based on these old concepts. In the early 19th century, the scientist John Dalton noticed that chemical elements seemed to combine with each other by basic units of weight, and he decided to use the word "atom" to refer to these units because he assumed that these were the fundamental units of matter. About a century later it was discovered that Dalton's atoms are not actually indivisible, but the term stuck.


title: Atom

text: In the early 1800s, the English chemist John Dalton compiled experimental data gathered by himself and other scientists and discovered a pattern now known as the "law of multiple proportions". He noticed that in chemical compounds which contain a particular chemical element, the content of that element in these compounds will differ in weight by ratios of small whole numbers. This pattern suggested to Dalton that each chemical element combines with other elements by a basic and consistent unit of weight, and he decided to call these units "atoms".


title: Atom

text: For example, there are two types of tin oxide: one is a black powder that is 88.1% tin and 11.9% oxygen, and the other is a white powder that is 78.7% tin and 21.3% oxygen. Adjusting these figures, in the black oxide there is about 13.5 g of oxygen for every 100 g of tin, and in the white oxide there is about 27 g of oxygen for every 100 g of tin. 13.5 and 27 form a ratio of 1:2. Dalton concluded that in these oxides, for every tin atom there are one or two oxygen atoms respectively (SnO and SnO).


title: Atom

text: Dalton also analyzed iron oxides. There is one type of iron oxide that is a black powder which is 78.1% iron and 21.9% oxygen; and there is another iron oxide that is a red powder which is 70.4% iron and 29.6% oxygen. Adjusting these figures, in the black oxide there is about 28 g of oxygen for every 100 g of iron, and in the red oxide there is about 42 g of oxygen for every 100 g of iron. 28 and 42 form a ratio of 2:3. In these respective oxides, for every two atoms of iron, there are two or three atoms of oxygen (FeO and FeO).


title: Atom

text: As a final example: nitrous oxide is 63.3% nitrogen and 36.7% oxygen, nitric oxide is 44.05% nitrogen and 55.95% oxygen, and nitrogen dioxide is 29.5% nitrogen and 70.5% oxygen. Adjusting these figures, in nitrous oxide there is 80 g of oxygen for every 140 g of nitrogen, in nitric oxide there is about 160 g of oxygen for every 140 g of nitrogen, and in nitrogen dioxide there is 320 g of oxygen for every 140 g of nitrogen. 80, 160, and 320 form a ratio of 1:2:4. The respective formulas for these oxides are NO, NO, and NO.


title: Atom

text: In 1827, botanist Robert Brown used a microscope to look at dust grains floating in water and discovered that they moved about erratically, a phenomenon that became known as "Brownian motion". This was thought to be caused by water molecules knocking the grains about. In 1905, Albert Einstein proved the reality of these molecules and their motions by producing the first statistical physics analysis of Brownian motion. French physicist Jean Perrin used Einstein's work to experimentally determine the mass and dimensions of molecules, thereby providing physical evidence for the particle nature of matter.


title: Atom

text: In 1897, J. J. Thomson discovered that cathode rays are not electromagnetic waves but made of particles that are 1,800 times lighter than hydrogen (the lightest atom). Thomson concluded that these particles came from the atoms within the cathode — they were "subatomic" particles. He called these new particles "corpuscles" but they were later renamed "electrons". Thomson also showed that electrons were identical to particles given off by photoelectric and radioactive materials. It was quickly recognized that electrons are the particles that carry electric currents in metal wires. Thomson concluded that these electrons emerged from the very atoms of the cathode in his instruments, which meant that atoms are not indivisible as Dalton thought.


title: Atom

text: J. J. Thomson thought that the negatively-charged electrons were distributed throughout the atom in a sea of positive charge that was distributed across the whole volume of the atom. This model is sometimes known as the plum pudding model.


title: Atom

text: Ernest Rutherford and his colleagues Hans Geiger and Ernest Marsden came to have doubts about the Thomson model after they encountered difficulties when they tried to build an instrument to measure the charge-to-mass ratio of alpha particles (these are positively-charged particles emitted by certain radioactive substances such as radium). The alpha particles were being scattered by the air in the detection chamber, which made the measurements unreliable. Thomson had encountered a similar problem in his work on cathode rays, which he solved by creating a near-perfect vacuum in his instruments. Rutherford didn't think he'd run into this same problem because alpha particles are much heavier than electrons. According to Thomson's model of the atom, the positive charge in the atom is not concentrated enough to produce an electric field strong enough to deflect an alpha particle, and the electrons are so lightweight they should be pushed aside effortlessly by the much heavier alpha particles. Yet there was scattering, so Rutherford and his colleagues decided to investigate this scattering carefully.


title: Atom

text: Between 1908 and 1913, Rutherford and his colleagues performed a series of experiments in which they bombarded thin foils of metal with alpha particles. They spotted alpha particles being deflected by angles greater than 90°. To explain this, Rutherford proposed that the positive charge of the atom is not distributed throughout the atom's volume as Thomson believed, but is concentrated in a tiny nucleus at the center. Only such an intense concentration of charge could produce an electric field strong enough to deflect the alpha particles as observed.


title: Atom

text: While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one type of atom at each position on the periodic table. The term isotope was coined by Margaret Todd as a suitable name for different atoms that belong to the same element. J. J. Thomson created a technique for isotope separation through his work on ionized gases, which subsequently led to the discovery of stable isotopes.


title: Atom

text: In 1913, the physicist Niels Bohr proposed a model in which the electrons of an atom were assumed to orbit the nucleus but could only do so in a finite set of orbits, and could jump between these orbits only in discrete changes of energy corresponding to absorption or radiation of a photon. This quantization was used to explain why the electrons' orbits are stable (given that normally, charges in acceleration, including circular motion, lose kinetic energy which is emitted as electromagnetic radiation, see "synchrotron radiation") and why elements absorb and emit electromagnetic radiation in discrete spectra.


title: Atom

text: Later in the same year Henry Moseley provided additional experimental evidence in favor of Niels Bohr's theory. These results refined Ernest Rutherford's and Antonius van den Broek's model, which proposed that the atom contains in its nucleus a number of positive nuclear charges that is equal to its (atomic) number in the periodic table. Until these experiments, atomic number was not known to be a physical and experimental quantity. That it is equal to the atomic nuclear charge remains the accepted atomic model today.


title: Atom

text: Chemical bonds between atoms were explained by Gilbert Newton Lewis in 1916, as the interactions between their constituent electrons. As the chemical properties of the elements were known to largely repeat themselves according to the periodic law, in 1919 the American chemist Irving Langmuir suggested that this could be explained if the electrons in an atom were connected or clustered in some manner. Groups of electrons were thought to occupy a set of electron shells about the nucleus.


title: Atom

text: The Bohr model of the atom was the first complete physical model of the atom. It described the overall structure of the atom, how atoms bond to each other, and predicted the spectral lines of hydrogen. Bohr's model was not perfect and was soon superseded by the more accurate Schrödinger model, but it was sufficient to evaporate any remaining doubts that matter is composed of atoms. For chemists, the idea of the atom had been a useful heuristic tool, but physicists had doubts as to whether matter really is made up of atoms as nobody had yet developed a complete physical model of the atom.


title: Atom

text: The Stern–Gerlach experiment of 1922 provided further evidence of the quantum nature of atomic properties. When a beam of silver atoms was passed through a specially shaped magnetic field, the beam was split in a way correlated with the direction of an atom's angular momentum, or spin. As this spin direction is initially random, the beam would be expected to deflect in a random direction. Instead, the beam was split into two directional components, corresponding to the atomic spin being oriented up or down with respect to the magnetic field.


title: Atom

text: In 1925, Werner Heisenberg published the first consistent mathematical formulation of quantum mechanics (matrix mechanics). One year earlier, Louis de Broglie had proposed the de Broglie hypothesis: that all particles behave like waves to some extent, and in 1926 Erwin Schrödinger used this idea to develop the Schrödinger equation, a mathematical model of the atom (wave mechanics) that described the electrons as three-dimensional waveforms rather than point particles.


title: Atom

text: A consequence of using waveforms to describe particles is that it is mathematically impossible to obtain precise values for both the position and momentum of a particle at a given point in time. This became known as the uncertainty principle, formulated by Werner Heisenberg in 1927. In this concept, for a given accuracy in measuring a position one could only obtain a range of probable values for momentum, and vice versa.


title: Atom

text: This model was able to explain observations of atomic behavior that previous models could not, such as certain structural and spectral patterns of atoms larger than hydrogen. Thus, the planetary model of the atom was discarded in favor of one that described atomic orbital zones around the nucleus where a given electron is most likely to be observed.


title: Atom

text: The development of the mass spectrometer allowed the mass of atoms to be measured with increased accuracy. The device uses a magnet to bend the trajectory of a beam of ions, and the amount of deflection is determined by the ratio of an atom's mass to its charge. The chemist Francis William Aston used this instrument to show that isotopes had different masses. The atomic mass of these isotopes varied by integer amounts, called the whole number rule. The explanation for these different isotopes awaited the discovery of the neutron, an uncharged particle with a mass similar to the proton, by the physicist James Chadwick in 1932. Isotopes were then explained as elements with the same number of protons, but different numbers of neutrons within the nucleus.


title: Atom

text: In 1938, the German chemist Otto Hahn, a student of Rutherford, directed neutrons onto uranium atoms expecting to get transuranium elements. Instead, his chemical experiments showed barium as a product. A year later, Lise Meitner and her nephew Otto Frisch verified that Hahn's result were the first experimental "nuclear fission". In 1944, Hahn received the Nobel Prize in Chemistry. Despite Hahn's efforts, the contributions of Meitner and Frisch were not recognized.


title: Atom

text: In the 1950s, the development of improved particle accelerators and particle detectors allowed scientists to study the impacts of atoms moving at high energies. Neutrons and protons were found to be hadrons, or composites of smaller particles called quarks. The standard model of particle physics was developed that so far has successfully explained the properties of the nucleus in terms of these sub-atomic particles and the forces that govern their interactions.


title: Atom

text: Though the word "atom" originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the atom is composed of various subatomic particles. The constituent particles of an atom are the electron, the proton and the neutron.


title: Atom

text: The electron is by far the least massive of these particles at , with a negative electrical charge and a size that is too small to be measured using available techniques. It was the lightest particle with a positive rest mass measured, until the discovery of neutrino mass. Under ordinary conditions, electrons are bound to the positively charged nucleus by the attraction created from opposite electric charges. If an atom has more or fewer electrons than its atomic number, then it becomes respectively negatively or positively charged as a whole; a charged atom is called an ion. Electrons have been known since the late 19th century, mostly thanks to J.J. Thomson; see history of subatomic physics for details.


title: Atom

text: Protons have a positive charge and a mass 1,836 times that of the electron, at . The number of protons in an atom is called its atomic number. Ernest Rutherford (1919) observed that nitrogen under alpha-particle bombardment ejects what appeared to be hydrogen nuclei. By 1920 he had accepted that the hydrogen nucleus is a distinct particle within the atom and named it proton.


title: Atom

text: Neutrons have no electrical charge and have a free mass of 1,839 times the mass of the electron, or . Neutrons are the heaviest of the three constituent particles, but their mass can be reduced by the nuclear binding energy. Neutrons and protons (collectively known as nucleons) have comparable dimensions—on the order of —although the 'surface' of these particles is not sharply defined. The neutron was discovered in 1932 by the English physicist James Chadwick.


title: Atom

text: In the Standard Model of physics, electrons are truly elementary particles with no internal structure, whereas protons and neutrons are composite particles composed of elementary particles called quarks. There are two types of quarks in atoms, each having a fractional electric charge. Protons are composed of two up quarks (each with charge +) and one down quark (with a charge of −). Neutrons consist of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles.


title: Atom

text: The quarks are held together by the strong interaction (or strong force), which is mediated by gluons. The protons and neutrons, in turn, are held to each other in the nucleus by the nuclear force, which is a residuum of the strong force that has somewhat different range-properties (see the article on the nuclear force for more). The gluon is a member of the family of gauge bosons, which are elementary particles that mediate physical forces.


title: Atom

text: All the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to formula_1 femtometres, where formula_2 is the total number of nucleons. This is much smaller than the radius of the atom, which is on the order of 10 fm. The nucleons are bound together by a short-ranged attractive potential called the residual strong force. At distances smaller than 2.5 fm this force is much more powerful than the electrostatic force that causes positively charged protons to repel each other.


title: Atom

text: Atoms of the same element have the same number of protons, called the atomic number. Within a single element, the number of neutrons may vary, determining the isotope of that element. The total number of protons and neutrons determine the nuclide. The number of neutrons relative to the protons determines the stability of the nucleus, with certain isotopes undergoing radioactive decay.


title: Atom

text: The proton, the electron, and the neutron are classified as fermions. Fermions obey the Pauli exclusion principle which prohibits "identical" fermions, such as multiple protons, from occupying the same quantum state at the same time. Thus, every proton in the nucleus must occupy a quantum state different from all other protons, and the same applies to all neutrons of the nucleus and to all electrons of the electron cloud.


title: Atom

text: A nucleus that has a different number of protons than neutrons can potentially drop to a lower energy state through a radioactive decay that causes the number of protons and neutrons to more closely match. As a result, atoms with matching numbers of protons and neutrons are more stable against decay, but with increasing atomic number, the mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus.


title: Atom

text: The number of protons and neutrons in the atomic nucleus can be modified, although this can require very high energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at the core of the Sun protons require energies of 3 to 10 keV to overcome their mutual repulsion—the coulomb barrier—and fuse together into a single nucleus. Nuclear fission is the opposite process, causing a nucleus to split into two smaller nuclei—usually through radioactive decay. The nucleus can also be modified through bombardment by high energy subatomic particles or photons. If this modifies the number of protons in a nucleus, the atom changes to a different chemical element.


title: Atom

text: If the mass of the nucleus following a fusion reaction is less than the sum of the masses of the separate particles, then the difference between these two values can be emitted as a type of usable energy (such as a gamma ray, or the kinetic energy of a beta particle), as described by Albert Einstein's mass-energy equivalence formula, formula_3, where formula_4 is the mass loss and formula_5 is the speed of light. This deficit is part of the binding energy of the new nucleus, and it is the non-recoverable loss of the energy that causes the fused particles to remain together in a state that requires this energy to separate.


title: Atom

text: The fusion of two nuclei that create larger nuclei with lower atomic numbers than iron and nickel—a total nucleon number of about 60—is usually an exothermic process that releases more energy than is required to bring them together. It is this energy-releasing process that makes nuclear fusion in stars a self-sustaining reaction. For heavier nuclei, the binding energy per nucleon in the nucleus begins to decrease. That means fusion processes producing nuclei that have atomic numbers higher than about 26, and atomic masses higher than about 60, is an endothermic process. These more massive nuclei can not undergo an energy-producing fusion reaction that can sustain the hydrostatic equilibrium of a star.


title: Atom

text: The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed for the electron to escape. The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near the center of the potential well require more energy to escape than those at greater separations.


title: Atom

text: Electrons, like other particles, have properties of both a particle and a wave. The electron cloud is a region inside the potential well where each electron forms a type of three-dimensional standing wave—a wave form that does not move relative to the nucleus. This behavior is defined by an atomic orbital, a mathematical function that characterises the probability that an electron appears to be at a particular location when its position is measured. Only a discrete (or quantized) set of these orbitals exist around the nucleus, as other possible wave patterns rapidly decay into a more stable form. Orbitals can have one or more ring or node structures, and differ from each other in size, shape and orientation.


title: Atom

text: Each atomic orbital corresponds to a particular energy level of the electron. The electron can change its state to a higher energy level by absorbing a photon with sufficient energy to boost it into the new quantum state. Likewise, through spontaneous emission, an electron in a higher energy state can drop to a lower energy state while radiating the excess energy as a photon. These characteristic energy values, defined by the differences in the energies of the quantum states, are responsible for atomic spectral lines.


title: Atom

text: The amount of energy needed to remove or add an electron—the electron binding energy—is far less than the binding energy of nucleons. For example, it requires only 13.6 eV to strip a ground-state electron from a hydrogen atom, compared to 2.23 "million" eV for splitting a deuterium nucleus. Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either a deficit or a surplus of electrons are called ions. Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism, atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals.


title: Atom

text: By definition, any two atoms with an identical number of "protons" in their nuclei belong to the same chemical element. Atoms with equal numbers of protons but a different number of "neutrons" are different isotopes of the same element. For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no neutrons (hydrogen-1, by far the most common form, also called protium), one neutron (deuterium), two neutrons (tritium) and more than two neutrons. The known elements form a set of atomic numbers, from the single-proton element hydrogen up to the 118-proton element oganesson. All known isotopes of elements with atomic numbers greater than 82 are radioactive, although the radioactivity of element 83 (bismuth) is so slight as to be practically negligible.


title: Atom

text: About 339 nuclides occur naturally on Earth, of which 251 (about 74%) have not been observed to decay, and are referred to as "stable isotopes". Only 90 nuclides are stable theoretically, while another 161 (bringing the total to 251) have not been observed to decay, even though in theory it is energetically possible. These are also formally classified as "stable". An additional 35 radioactive nuclides have half-lives longer than 100 million years, and are long-lived enough to have been present since the birth of the Solar System. This collection of 286 nuclides are known as primordial nuclides. Finally, an additional 53 short-lived nuclides are known to occur naturally, as daughter products of primordial nuclide decay (such as radium from uranium), or as products of natural energetic processes on Earth, such as cosmic ray bombardment (for example, carbon-14).


title: Atom

text: For 80 of the chemical elements, at least one stable isotope exists. As a rule, there is only a handful of stable isotopes for each of these elements, the average being 3.1 stable isotopes per element. Twenty-six "monoisotopic elements" have only a single stable isotope, while the largest number of stable isotopes observed for any element is ten, for the element tin. Elements 43, 61, and all elements numbered 83 or higher have no stable isotopes.


title: Atom

text: Stability of isotopes is affected by the ratio of protons to neutrons, and also by the presence of certain "magic numbers" of neutrons or protons that represent closed and filled quantum shells. These quantum shells correspond to a set of energy levels within the shell model of the nucleus; filled shells, such as the filled shell of 50 protons for tin, confers unusual stability on the nuclide. Of the 251 known stable nuclides, only four have both an odd number of protons "and" odd number of neutrons: hydrogen-2 (deuterium), lithium-6, boron-10, and nitrogen-14. (Tantalum-180m is odd-odd and observationally stable, but is predicted to decay with a very long half-life.) Also, only four naturally occurring, radioactive odd-odd nuclides have a half-life over a billion years: potassium-40, vanadium-50, lanthanum-138, and lutetium-176. Most odd-odd nuclei are highly unstable with respect to beta decay, because the decay products are even-even, and are therefore more strongly bound, due to nuclear pairing effects.


title: Atom

text: The large majority of an atom's mass comes from the protons and neutrons that make it up. The total number of these particles (called "nucleons") in a given atom is called the mass number. It is a positive integer and dimensionless (instead of having dimension of mass), because it expresses a count. An example of use of a mass number is "carbon-12," which has 12 nucleons (six protons and six neutrons).


title: Atom

text: The actual mass of an atom at rest is often expressed in daltons (Da), also called the unified atomic mass unit (u). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately . Hydrogen-1 (the lightest isotope of hydrogen which is also the nuclide with the lowest mass) has an atomic weight of 1.007825 Da. The value of this number is called the atomic mass. A given atom has an atomic mass approximately equal (within 1%) to its mass number times the atomic mass unit (for example the mass of a nitrogen-14 is roughly 14 Da), but this number will not be exactly an integer except (by definition) in the case of carbon-12. The heaviest stable atom is lead-208, with a mass of .


title: Atom

text: As even the most massive atoms are far too light to work with directly, chemists instead use the unit of moles. One mole of atoms of any element always has the same number of atoms (about ). This number was chosen so that if an element has an atomic mass of 1 u, a mole of atoms of that element has a mass close to one gram. Because of the definition of the unified atomic mass unit, each carbon-12 atom has an atomic mass of exactly 12 Da, and so a mole of carbon-12 atoms weighs exactly 0.012 kg.


title: Atom

text: Atoms lack a well-defined outer boundary, so their dimensions are usually described in terms of an atomic radius. This is a measure of the distance out to which the electron cloud extends from the nucleus. This assumes the atom to exhibit a spherical shape, which is only obeyed for atoms in vacuum or free space. Atomic radii may be derived from the distances between two nuclei when the two atoms are joined in a chemical bond. The radius varies with the location of an atom on the atomic chart, the type of chemical bond, the number of neighboring atoms (coordination number) and a quantum mechanical property known as spin. On the periodic table of the elements, atom size tends to increase when moving down columns, but decrease when moving across rows (left to right). Consequently, the smallest atom is helium with a radius of 32 pm, while one of the largest is caesium at 225 pm.


title: Atom

text: When subjected to external forces, like electrical fields, the shape of an atom may deviate from spherical symmetry. The deformation depends on the field magnitude and the orbital type of outer shell electrons, as shown by group-theoretical considerations. Aspherical deviations might be elicited for instance in crystals, where large crystal-electrical fields may occur at low-symmetry lattice sites. Significant ellipsoidal deformations have been shown to occur for sulfur ions and chalcogen ions in pyrite-type compounds.


title: Atom

text: Atomic dimensions are thousands of times smaller than the wavelengths of light (400–700 nm) so they cannot be viewed using an optical microscope, although individual atoms can be observed using a scanning tunneling microscope. To visualize the minuteness of the atom, consider that a typical human hair is about 1 million carbon atoms in width. A single drop of water contains about 2 sextillion () atoms of oxygen, and twice the number of hydrogen atoms. A single carat diamond with a mass of contains about 10 sextillion (10) atoms of carbon. If an apple were magnified to the size of the Earth, then the atoms in the apple would be approximately the size of the original apple.


title: Atom

text: Every element has one or more isotopes that have unstable nuclei that are subject to radioactive decay, causing the nucleus to emit particles or electromagnetic radiation. Radioactivity can occur when the radius of a nucleus is large compared with the radius of the strong force, which only acts over distances on the order of 1 fm.


title: Atom

text: Other more rare types of radioactive decay include ejection of neutrons or protons or clusters of nucleons from a nucleus, or more than one beta particle. An analog of gamma emission which allows excited nuclei to lose energy in a different way, is internal conversion—a process that produces high-speed electrons that are not beta rays, followed by production of high-energy photons that are not gamma rays. A few large nuclei explode into two or more charged fragments of varying masses plus several neutrons, in a decay called spontaneous nuclear fission.


title: Atom

text: Each radioactive isotope has a characteristic decay time period—the half-life—that is determined by the amount of time needed for half of a sample to decay. This is an exponential decay process that steadily decreases the proportion of the remaining isotope by 50% every half-life. Hence after two half-lives have passed only 25% of the isotope is present, and so forth.


title: Atom

text: Elementary particles possess an intrinsic quantum mechanical property known as spin. This is analogous to the angular momentum of an object that is spinning around its center of mass, although strictly speaking these particles are believed to be point-like and cannot be said to be rotating. Spin is measured in units of the reduced Planck constant (ħ), with electrons, protons and neutrons all having spin  ħ, or "spin-". In an atom, electrons in motion around the nucleus possess orbital angular momentum in addition to their spin, while the nucleus itself possesses angular momentum due to its nuclear spin.


title: Atom

text: The magnetic field produced by an atom—its magnetic moment—is determined by these various forms of angular momentum, just as a rotating charged object classically produces a magnetic field, but the most dominant contribution comes from electron spin. Due to the nature of electrons to obey the Pauli exclusion principle, in which no two electrons may be found in the same quantum state, bound electrons pair up with each other, with one member of each pair in a spin up state and the other in the opposite, spin down state. Thus these spins cancel each other out, reducing the total magnetic dipole moment to zero in some atoms with even number of electrons.


title: Atom

text: In ferromagnetic elements such as iron, cobalt and nickel, an odd number of electrons leads to an unpaired electron and a net overall magnetic moment. The orbitals of neighboring atoms overlap and a lower energy state is achieved when the spins of unpaired electrons are aligned with each other, a spontaneous process known as an exchange interaction. When the magnetic moments of ferromagnetic atoms are lined up, the material can produce a measurable macroscopic field. Paramagnetic materials have atoms with magnetic moments that line up in random directions when no magnetic field is present, but the magnetic moments of the individual atoms line up in the presence of a field.


title: Atom

text: The nucleus of an atom will have no spin when it has even numbers of both neutrons and protons, but for other cases of odd numbers, the nucleus may have a spin. Normally nuclei with spin are aligned in random directions because of thermal equilibrium, but for certain elements (such as xenon-129) it is possible to polarize a significant proportion of the nuclear spin states so that they are aligned in the same direction—a condition called hyperpolarization. This has important applications in magnetic resonance imaging.


title: Atom

text: The potential energy of an electron in an atom is negative relative to when the distance from the nucleus goes to infinity; its dependence on the electron's position reaches the minimum inside the nucleus, roughly in inverse proportion to the distance. In the quantum-mechanical model, a bound electron can occupy only a set of states centered on the nucleus, and each state corresponds to a specific energy level; see time-independent Schrödinger equation for a theoretical explanation. An energy level can be measured by the amount of energy needed to unbind the electron from the atom, and is usually given in units of electronvolts (eV). The lowest energy state of a bound electron is called the ground state, i.e. stationary state, while an electron transition to a higher level results in an excited state. The electron's energy increases along with "n" because the (average) distance to the nucleus increases. Dependence of the energy on is caused not by the electrostatic potential of the nucleus, but by interaction between electrons.


title: Atom

text: For an electron to transition between two different states, e.g. ground state to first excited state, it must absorb or emit a photon at an energy matching the difference in the potential energy of those levels, according to the Niels Bohr model, what can be precisely calculated by the Schrödinger equation.


title: Atom

text: Electrons jump between orbitals in a particle-like fashion. For example, if a single photon strikes the electrons, only a single electron changes states in response to the photon; see Electron properties.


title: Atom

text: The energy of an emitted photon is proportional to its frequency, so these specific energy levels appear as distinct bands in the electromagnetic spectrum. Each element has a characteristic spectrum that can depend on the nuclear charge, subshells filled by electrons, the electromagnetic interactions between the electrons and other factors.


title: Atom

text: When a continuous spectrum of energy is passed through a gas or plasma, some of the photons are absorbed by atoms, causing electrons to change their energy level. Those excited electrons that remain bound to their atom spontaneously emit this energy as a photon, traveling in a random direction, and so drop back to lower energy levels. Thus the atoms behave like a filter that forms a series of dark absorption bands in the energy output. (An observer viewing the atoms from a view that does not include the continuous spectrum in the background, instead sees a series of emission lines from the photons emitted by the atoms.) Spectroscopic measurements of the strength and width of atomic spectral lines allow the composition and physical properties of a substance to be determined.


title: Atom

text: Close examination of the spectral lines reveals that some display a fine structure splitting. This occurs because of spin–orbit coupling, which is an interaction between the spin and motion of the outermost electron. When an atom is in an external magnetic field, spectral lines become split into three or more components; a phenomenon called the Zeeman effect. This is caused by the interaction of the magnetic field with the magnetic moment of the atom and its electrons. Some atoms can have multiple electron configurations with the same energy level, which thus appear as a single spectral line. The interaction of the magnetic field with the atom shifts these electron configurations to slightly different energy levels, resulting in multiple spectral lines. The presence of an external electric field can cause a comparable splitting and shifting of spectral lines by modifying the electron energy levels, a phenomenon called the Stark effect.


title: Atom

text: If a bound electron is in an excited state, an interacting photon with the proper energy can cause stimulated emission of a photon with a matching energy level. For this to occur, the electron must drop to a lower energy state that has an energy difference matching the energy of the interacting photon. The emitted photon and the interacting photon then move off in parallel and with matching phases. That is, the wave patterns of the two photons are synchronized. This physical property is used to make lasers, which can emit a coherent beam of light energy in a narrow frequency band.


title: Atom

text: Valency is the combining power of an element. It is determined by the number of bonds it can form to other atoms or groups. The outermost electron shell of an atom in its uncombined state is known as the valence shell, and the electrons in


title: Atom

text: behavior with other atoms. Atoms tend to chemically react with each other in a manner that fills (or empties) their outer valence shells. For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts. Many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. Thus, chemical bonding between these elements takes many forms of electron-sharing that are more than simple electron transfers. Examples include the element carbon and the organic compounds.


title: Atom

text: The chemical elements are often displayed in a periodic table that is laid out to display recurring chemical properties, and elements with the same number of valence electrons form a group that is aligned in the same column of the table. (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the noble gases.


title: Atom

text: Quantities of atoms are found in different states of matter that depend on the physical conditions, such as temperature and pressure. By varying the conditions, materials can transition between solids, liquids, gases and plasmas. Within a state, a material can also exist in different allotropes. An example of this is solid carbon, which can exist as graphite or diamond. Gaseous allotropes exist as well, such as dioxygen and ozone.


title: Atom

text: At temperatures close to absolute zero, atoms can form a Bose–Einstein condensate, at which point quantum mechanical effects, which are normally only observed at the atomic scale, become apparent on a macroscopic scale. This super-cooled collection of atoms


title: Atom

text: then behaves as a single super atom, which may allow fundamental checks of quantum mechanical behavior.


title: Atom

text: While atoms are too small to be seen, devices such as the scanning tunneling microscope (STM) enable their visualization at the surfaces of solids. The microscope uses the quantum tunneling phenomenon, which allows particles to pass through a barrier that would be insurmountable in the classical perspective. Electrons tunnel through the vacuum between two biased electrodes, providing a tunneling current that is exponentially dependent on their separation. One electrode is a sharp tip ideally ending with a single atom. At each point of the scan of the surface the tip's height is adjusted so as to keep the tunneling current at a set value. How much the tip moves to and away from the surface is interpreted as the height profile. For low bias, the microscope images the averaged electron orbitals across closely packed energy levels—the local density of the electronic states near the Fermi level. Because of the distances involved, both electrodes need to be extremely stable; only then periodicities can be observed that correspond to individual atoms. The method alone is not chemically specific, and cannot identify the atomic species present at the surface.


title: Atom

text: Atoms can be easily identified by their mass. If an atom is ionized by removing one of its electrons, its trajectory when it passes through a magnetic field will bend. The radius by which the trajectory of a moving ion is turned by the magnetic field is determined by the mass of the atom. The mass spectrometer uses this principle to measure the mass-to-charge ratio of ions. If a sample contains multiple isotopes, the mass spectrometer can determine the proportion of each isotope in the sample by measuring the intensity of the different beams of ions. Techniques to vaporize atoms include inductively coupled plasma atomic emission spectroscopy and inductively coupled plasma mass spectrometry, both of which use a plasma to vaporize samples for analysis.


title: Atom

text: The atom-probe tomograph has sub-nanometer resolution in 3-D and can chemically identify individual atoms using time-of-flight mass spectrometry.


title: Atom

text: Electron emission techniques such as X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), which measure the binding energies of the core electrons, are used to identify the atomic species present in a sample in a non-destructive way. With proper focusing both can be made area-specific. Another such method is electron energy loss spectroscopy (EELS), which measures the energy loss of an electron beam within a transmission electron microscope when it interacts with a portion of a sample.


title: Atom

text: Spectra of excited states can be used to analyze the atomic composition of distant stars. Specific light wavelengths contained in the observed light from stars can be separated out and related to the quantized transitions in free gas atoms. These colors can be replicated using a gas-discharge lamp containing the same element. Helium was discovered in this way in the spectrum of the Sun 23 years before it was found on Earth.


title: Atom

text: Baryonic matter forms about 4% of the total energy density of the observable universe, with an average density of about 0.25 particles/m (mostly protons and electrons). Within a galaxy such as the Milky Way, particles have a much higher concentration, with the density of matter in the interstellar medium (ISM) ranging from 10 to 10 atoms/m. The Sun is believed to be inside the Local Bubble, so the density in the solar neighborhood is only about 10 atoms/m. Stars form from dense clouds in the ISM, and the evolutionary processes of stars result in the steady enrichment of the ISM with elements more massive than hydrogen and helium.


title: Atom

text: Up to 95% of the Milky Way's baryonic matter are concentrated inside stars, where conditions are unfavorable for atomic matter. The total baryonic mass is about 10% of the mass of the galaxy; the remainder of the mass is an unknown dark matter. High temperature inside stars makes most "atoms" fully ionized, that is, separates "all" electrons from the nuclei. In stellar remnants—with exception of their surface layers—an immense pressure make electron shells impossible.


title: Atom

text: Electrons are thought to exist in the Universe since early stages of the Big Bang. Atomic nuclei forms in nucleosynthesis reactions. In about three minutes Big Bang nucleosynthesis produced most of the helium, lithium, and deuterium in the Universe, and perhaps some of the beryllium and boron.


title: Atom

text: Ubiquitousness and stability of atoms relies on their binding energy, which means that an atom has a lower energy than an unbound system of the nucleus and electrons. Where the temperature is much higher than ionization potential, the matter exists in the form of plasma—a gas of positively charged ions (possibly, bare nuclei) and electrons. When the temperature drops below the ionization potential, atoms become statistically favorable. Atoms (complete with bound electrons) became to dominate over charged particles 380,000 years after the Big Bang—an epoch called recombination, when the expanding Universe cooled enough to allow electrons to become attached to nuclei.


title: Atom

text: Since the Big Bang, which produced no carbon or heavier elements, atomic nuclei have been combined in stars through the process of nuclear fusion to produce more of the element helium, and (via the triple alpha process) the sequence of elements from carbon up to iron; see stellar nucleosynthesis for details.


title: Atom

text: Isotopes such as lithium-6, as well as some beryllium and boron are generated in space through cosmic ray spallation. This occurs when a high-energy proton strikes an atomic nucleus, causing large numbers of nucleons to be ejected.


title: Atom

text: Elements heavier than iron were produced in supernovae and colliding neutron stars through the r-process, and in AGB stars through the s-process, both of which involve the capture of neutrons by atomic nuclei. Elements such as lead formed largely through the radioactive decay of heavier elements.


title: Atom

text: Most of the atoms that make up the Earth and its inhabitants were present in their current form in the nebula that collapsed out of a molecular cloud to form the Solar System. The rest are the result of radioactive decay, and their relative proportion can be used to determine the age of the Earth through radiometric dating. Most of the helium in the crust of the Earth (about 99% of the helium from gas wells, as shown by its lower abundance of helium-3) is a product of alpha decay.


title: Atom

text: There are a few trace atoms on Earth that were not present at the beginning (i.e., not "primordial"), nor are results of radioactive decay. Carbon-14 is continuously generated by cosmic rays in the atmosphere. Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors or explosions. Of the transuranic elements—those with atomic numbers greater than 92—only plutonium and neptunium occur naturally on Earth. Transuranic elements have radioactive lifetimes shorter than the current age of the Earth and thus identifiable quantities of these elements have long since decayed, with the exception of traces of plutonium-244 possibly deposited by cosmic dust. Natural deposits of plutonium and neptunium are produced by neutron capture in uranium ore.


title: Atom

text: The Earth contains approximately atoms. Although small numbers of independent atoms of noble gases exist, such as argon, neon, and helium, 99% of the atmosphere is bound in the form of molecules, including carbon dioxide and diatomic oxygen and nitrogen. At the surface of the Earth, an overwhelming majority of atoms combine to form various compounds, including water, salt, silicates and oxides. Atoms can also combine to create materials that do not consist of discrete molecules, including crystals and liquid or solid metals. This atomic matter forms networked arrangements that lack the particular type of small-scale interrupted order associated with molecular matter.


title: Atom

text: All nuclides with atomic numbers higher than 82 (lead) are known to be radioactive. No nuclide with an atomic number exceeding 92 (uranium) exists on Earth as a primordial nuclide, and heavier elements generally have shorter half-lives. Nevertheless, an "island of stability" encompassing relatively long-lived isotopes of superheavy elements with atomic numbers 110 to 114 might exist. Predictions for the half-life of the most stable nuclide on the island range from a few minutes to millions of years. In any case, superheavy elements (with "Z" > 104) would not exist due to increasing Coulomb repulsion (which results in spontaneous fission with increasingly short half-lives) in the absence of any stabilizing effects.


title: Atom

text: Each particle of matter has a corresponding antimatter particle with the opposite electrical charge. Thus, the positron is a positively charged antielectron and the antiproton is a negatively charged equivalent of a proton. When a matter and corresponding antimatter particle meet, they annihilate each other. Because of this, along with an imbalance between the number of matter and antimatter particles, the latter are rare in the universe. The first causes of this imbalance are not yet fully understood, although theories of baryogenesis may offer an explanation. As a result, no antimatter atoms have been discovered in nature. In 1996, the antimatter counterpart of the hydrogen atom (antihydrogen) was synthesized at the CERN laboratory in Geneva.


title: Atom

text: Other exotic atoms have been created by replacing one of the protons, neutrons or electrons with other particles that have the same charge. For example, an electron can be replaced by a more massive muon, forming a muonic atom. These types of atoms can be used to test fundamental predictions of physics.


title: M2 Browning

text: The M2 machine gun or Browning .50 caliber machine gun (informally, "Ma Deuce") is a heavy machine gun that was designed towards the end of World War I by John Browning. Its design is similar to Browning's earlier M1919 Browning machine gun, which was chambered for the .30-06 cartridge. The M2 uses Browning's larger and more powerful .50 BMG (12.7 mm) cartridge. The design has had many designations; the official U.S. military designation for the current infantry type is Browning Machine Gun, Cal. .50, M2, HB, Flexible. It is effective against infantry, unarmored or lightly armored vehicles and boats, light fortifications, and low-flying aircraft.


title: M2 Browning

text: The gun has been used extensively as a vehicle weapon and for aircraft armament by the United States since the 1930s. It was heavily used during World War II, the Korean War, the Vietnam War, the Falklands War, the Soviet–Afghan War, the Gulf War, the Iraq War, and the War in Afghanistan. It is the primary heavy machine gun of NATO countries and has been used by many other countries as well. U.S. forces have used the M2 longer than any other firearm except the .45 ACP M1911 pistol, which was also designed by John Browning.


title: M2 Browning

text: The current M2HB (heavy barrel) is manufactured in the U.S. by General Dynamics Ohio Ordnance Works, and U.S. Ordnance for use by the U.S. government, and for allies via Foreign Military Sales, as well as by foreign manufacturers such as FN Herstal.


title: M2 Browning

text: Machine guns were heavily used in World War I, and weapons of larger than rifle caliber began appearing on both sides of the conflict. The larger rounds were needed to defeat the armor that was being introduced to the battlefield, both on the ground and in the air. During the war, the Germans introduced a heavily armored airplane, the Junkers J.I. The armor made aircraft machine guns using conventional rifle ammunition (such as the .30-06) ineffective. Consequently, the American Expeditionary Force's commander General John J. Pershing asked for a larger caliber machine gun. Pershing asked the Army Ordnance Department to develop a machine gun with a caliber of at least and a muzzle velocity of at least .


title: M2 Browning

text: Around July 1917, John M. Browning started redesigning his .30-06 M1917 machine gun for a larger and more powerful round. Winchester worked on the cartridge, which was a scaled-up version of the .30-06. Winchester initially added a rim to the cartridge because the company wanted to use the cartridge in an anti-tank rifle, but Pershing insisted the cartridge be rimless. The first .50 caliber machine gun underwent trials on 15 October 1918. It fired at less than 500 rounds per minute, and the muzzle velocity was only . Cartridge improvements were promised. The gun was heavy, difficult to control, fired too slowly for the anti-personnel role, and was not powerful enough against armor.


title: M2 Browning

text: While the .50 caliber was being developed, some German T Gewehr 1918 anti-tank rifles and ammunition were seized. The German rounds had a muzzle velocity of , an bullet, and could penetrate armor thick at a range of . Winchester improved the .50 caliber round to have similar performance. Ultimately, the muzzle velocity was .


title: M2 Browning

text: Efforts by John M. Browning and Fred T. Moore resulted in the water-cooled, .50 caliber M1921 Browning machine gun and an aircraft version. These guns were used experimentally from 1921 until 1937. They had light-weight barrels and the ammunition fed only from the left side. Service trials raised doubts about whether the guns would be suitable for aircraft or for anti-aircraft use. A heavy barrel M1921 was considered for ground vehicles.


title: M2 Browning

text: John M. Browning died in 1926. Between 1927 and 1932, S.H. Green studied the design problems of the M1921 and the needs of the armed services. The result was a single receiver design that could be turned into seven types of .50 caliber machine guns by using different jackets, barrels, and other components. The new receiver allowed right or left side feed. In 1933, Colt manufactured several prototype Browning machine guns (including what would be known as the M1921A1 and M1921E2). With support from the Navy, Colt started manufacturing the M2 in 1933. FN Herstal (Fabrique Nationale) has manufactured the M2 machine gun since the 1930s. General Dynamics, U.S. Ordnance and Ohio Ordnance Works Inc. are other current manufacturers.