Early life.

François René Jean Lucien Bayrou was born on 25 May 1951 in Bordères, Pyrénées-Atlantiques, a village located between Pau and Lourdes. The son of farmer Calixte Bayrou (1909-1974) and Emma Sarthou (1918-2009). Bayrou descends from an ancestry of primarily Occitans except from his maternal grandmother's side which is Irish.  When Bayrou was in his youth, he suffered from a stutter which led to him attending speech therapy for seven years. He first went to secondary school in Pau, before transferring to Bordeaux. He studied literature at university, and at the age of 23, sat the "agrégation", the highest qualifying level for teachers in senior high schools and universities in France. Around the same time, his father was killed in a tractor accident.  Bayrou was married in 1971 to Élisabeth Perlant also known as "Babette". He and Perlant have five children, Hélène, Marie, Dominique, Calixte and Agnes. The children were raised on the farm where Bayrou was born and Bayrou currently lives there with Perlant.  Prior to embarking on his political career, Bayrou taught history in Béarn in the French Pyrenees. He is the author of several books on politics and history, including one on King Henry IV of France. Bayrou's hobby is raising horses. Although a practising Roman Catholic, he strongly supports France's system of laïcité.

Political career.

First steps in politics: 1982–2002.

In Bayrou's youth, he was active in nonviolent movements and followed Gandhi disciple, Lanza del Vasto.  Bayrou, a member of the Centre of Social Democrats (CDS), the Christian-democratic wing of the Union for French Democracy (UDF) confederation, was elected to the General Council of the Pyrénées-Atlantiques department in 1982 in the canton of Pau-Sud, then the French National Assembly four years later. After the victory of the RPR/UDF coalition in the 1993 legislative election, he became Education Minister in the cabinet led by Edouard Balladur. In this post, he proposed a reform allowing local authorities to subsidise private schools, which caused massive protests and was quashed by the Constitutional Council.  In 1989, after poor results in both the municipal elections and the European Parliament elections, Bayrou and twelve other centre-right parliamentarians including Philippe Séguin, Michel Noir, Alain Carignon, Étienne Pinte, Michel Barnier, François Fillon, Charles Millon, Dominique Baudis, François d'Aubert, Philippe de Villiers and Bernard Bosson demanded reform of the system at the RPR and the UDF, criticising the most prominent politicians of these parties including former president Valéry Giscard d'Estaing and Prime Minister Jacques Chirac. They called for the formation of a new right-wing party to unite the UDF and the RPR into a single entity. Ideological differences between members of this group led to members leaving, though d'Estaing endorsed Bayrou to become UDF general secretary in 1991.  Despite supporting Édouard Balladur's candidacy in the 1995 presidential election, Bayrou remained Education Minister following Jacques Chirac's election and the formation of a new government headed by Alain Juppé. Following the majority for the Plural Left in the 1997 legislative election, Bayrou returned to opposition and became president of the UDF in 1998, transforming it into a unified party rather than a union of smaller parties.

Positioning of the UDF as a centrist party: 2002–2007.

In 2002 François Bayrou rejected proposals to merge the UDF with the Rally for the Republic (RPR), into a new entity that later became the Union for a Popular Movement (UMP). As a result, many UDF members left to join the UMP.  Bayrou was increasingly critical of the direction taken by the UMP-led government, which he described as out of touch with the average Frenchman. He denounced the "de facto" two-party system, in which the Socialist Party and the RPR (later UMP) alternate. Instead, Bayrou called for a pluralist system in which other parties would also contribute.  On 16 May 2006, Bayrou supported a motion of no confidence sponsored by Socialist deputies calling for the resignation of Prime Minister Dominique de Villepin's government following the Clearstream affair. As de Villepin's UMP had an absolute majority in the National Assembly, the motion failed. Following Bayrou's support for this measure, France's television authority classified him as a member of the parliamentary opposition for timing purposes. However, after Bayrou protested, he was classified as a member of neither the majority nor the opposition.

Second presidential campaign: 2007.

Bayrou contested the presidency again in 2007. Most commentators had expected the election to be fought primarily between Sarkozy and Ségolène Royal of the Parti Socialiste. However, Bayrou's increasing support in polls in February complicated the "Sarko-Ségo" scenario, and led to speculation that the Parti Socialiste candidate would fail to progress to the second round for a second consecutive election, following the defeat of former Prime Minister Lionel Jospin in 2002 by National Front leader Jean Marie Le Pen. Ultimately, Bayrou finished in third place in the election with 18.57% of the vote (6,820,119 votes), behind Sarkozy and Royal, the best performance by the UDF in a Presidential election since 1981. Bayrou declared that he could not endorse either Sarkozy or Royal in the second round, although he indicated that Sarkozy was the worse of the two.

Foundation of the Democratic Movement: 2007–2012.

After the 2007 election, Bayrou announced his intention to form a new centrist party, the Democratic Movement (MoDem). The majority of UDF politicians did not follow him, and instead formed a rival party, the New Centre, which pledged to support an alliance with the UMP. However, most of the UDF's grassroots membership remained with Bayrou and joined MoDem. In the subsequent legislative elections in June 2007, MoDem came third with 7.6% of the vote. Although an increase on the UDF share of the poll of 4.9% in the 2002 elections, MoDem won only four seats, including Bayrou's own seat. The other parliamentarians elected on the party's list were Jean Lasalle, Thierry Benoit (who has since left the party, to join the New Centre) and Abdoulatifou Aly. The establishment of MoDem led to the formal dismantling of the UDF alliance on 30 November.

Third presidential election: 2012.

18 August 2011, Bayrou released a book, "2012. Etat d'urgence", in which he discussed how and why the economic crisis happened, and outlined the top priorities of his next presidential program: production and education.  François Bayrou confirmed his candidacy for the 2012 presidential election on 25 November 2011, in an interview with journalist Laurence Ferrari on her show "Parole Directe" (TF1).  His supporters included:  Bayrou was eliminated in the first round, receiving around half of his vote share from 2007, and announced that he would be voting for François Hollande in the run-off.

2017 presidential election.

On 22 February 2017, Bayrou announced that he would not contest the 2017 presidential election, instead endorsing the centrist candidate Emmanuel Macron of En Marche!. The alliance surprised French political pundits and rival candidates. Part of the agreement was Macron's commitment to support a clean government law proposed by Bayrou. Bayrou said that France was "at extreme risk", requiring an "exceptional response", adding that the alliance did not mean that MoDem would be subsumed by En Marche!

Minister of Justice (2017).

On 17 May 2017, Bayrou was appointed as Minister of Justice in the first Philippe government.  "Le Canard enchaîné" published information that Democratic Movement politician Marielle de Sarnez had been paid for work she had not actually done, embroiling Bayrou in a fictitious jobs scandal. France Info later reported that MoDem had "over a dozen" fictitious jobs in the European Parliament.  Bayrou resigned several days before the 2017 legislative election, with Prime Minister Édouard Philippe announcing following the election that Bayrou would not be a part of the second Philippe government, only 35 days after he had taken the post.

Political views.

François Bayrou has been a vocal campaigner on a variety of issues, including reform of the political process, civil liberties, and free software (see DADVSI). During the 2007 presidential election campaign he described the European Union as "the most beautiful construction of all humanity". He called for France to play a greater role in the European Union's affairs, and supports the ratification of a European Constitution, in a more concise and readable form than the one voted down by the French electorate in 2005.  In an interview with "The New York Times" in 2007, Bayrou said: "I am a democrat, I am a Clintonian, I am a man of the 'third way'". He positioned himself as a centrist, although he has historic ties to the right. His platform emphasises job creation, improvement of educational standards, improved conditions in the troubled suburbs, reduced government spending, a balanced budget and a stronger European Union, with France as its "de facto" leader. He has also criticized China's protection of the Sudanese government from UN Security Council sanctions. Bayrou was highly critical of the American economic model under George Bush and of the unregulated free market in general. He described the United States economic model as a "survival of the fittest" system, where it was often stated that money was people's only motivation, where higher education was too expensive, and where the middle class was shrinking. Bayrou criticized the Iraq war, saying it was "the cause of chaos" in the region. He criticized Nicolas Sarkozy's foreign policy, including the invitation of Libyan leader Muammar Gaddafi for a week-long state visit to France and the signing of military cooperation agreements with Libya.  In 2009, he criticized statements by Pope Benedict XVI claiming that condoms promote AIDS. Bayrou called the remarks "unacceptable," adding that "the primary responsibility, particularly of Christians, is the defence of life...This is a continent in which tens of millions of women and men are dying."  He called for France to boycott the 2008 Summer Olympics, due to the poor human rights record in China and political unrest in Tibet. During a rally in Paris on 21 March he said that "if this drama does not stop, France would do itself credit by not coming to the Olympic Games", criticising China's opposition to sanctions against Sudan over its involvement in the humanitarian crisis in Darfur.  Bayrou is fluent in Béarnese and often expresses his support for regionalism.  European Parliament  National Assembly of France  General Council  Municipal Council

Bibliography.

Bayrou is the sole author unless other names are mentioned.

François Bayrou (, born 25 May 1951) is a French centrist politician and the president of the Democratic Movement (MoDem), who was a candidate in the 2002, 2007 and 2012 French presidential elections.

François Bayrou (* 25. května 1951 v Bordères u Lourdes) je jedním z předních francouzských politiků, předseda francouzské UDF, bývalý europoslanec a spolupředseda evropské EDS.


Format advantages.

At the time the LP was introduced, nearly all phonograph records for home use were made of an abrasive (and therefore noisy) shellac compound, employed a much larger groove, and played at approximately 78 revolutions per minute (rpm), limiting the playing time of a 12-inch diameter record to less than five minutes per side. The new product was a 12- or 10-inch (30 or 25 cm) fine-grooved disc made of PVC ("vinyl") and played with a smaller-tipped "microgroove" stylus at a speed of rpm. Each side of a 12-inch LP could play for about 22 minutes. Only the microgroove standard was new, as both vinyl and the rpm speed had been used for special purposes for many years, as well as in one unsuccessful earlier attempt (by RCA Victor) to introduce a long-playing record for home use.  Although the LP was suited to classical music because of its extended continuous playing time, it also allowed a collection of ten or more pop music recordings to be put on a single disc. Previously such collections, as well as longer classical music broken up into several parts, had been sold as sets of 78 rpm records in a specially imprinted "record album" consisting of individual record sleeves bound together in book form. The use of the word "album" persisted for the one-disc LP equivalent.

History.

Soundtrack discs.

The prototype of the LP was the soundtrack disc used by the Vitaphone motion picture sound system, developed by Western Electric and introduced in 1926. For soundtrack purposes, the less-than-five minutes of playing time of each side of a conventional 12-inch 78 rpm disc was not acceptable. The sound had to play continuously for at least 11 minutes, long enough to accompany a full reel of 35 mm film projected at 24 frames per second. The disc diameter was increased to 16 inches (40 cm) and the speed was reduced to revolutions per minute. Unlike their smaller LP descendants, they were made with the same large "standard groove" used by 78s.  Unlike conventional records, the groove started at the inside of the recorded area near the label and proceeded outward toward the edge. Like 78s, early soundtrack discs were pressed in an abrasive shellac compound and played with a single-use steel needle held in a massive electromagnetic pickup with a tracking force of five ounces (1.4 N).  By mid-1931 all motion picture studios were recording on optical soundtracks, but sets of soundtrack discs, mastered by dubbing from the optical tracks and scaled down to 12 inches to cut costs, were made as late as 1936 for distribution to theaters still equipped with disc-only sound projectors.

Radio transcription discs.

From 1928 onward, syndicated radio programming was distributed on 78 rpm discs. The desirability of longer continuous playing time soon led to the adoption of the Vitaphone soundtrack disc format. Beginning in about 1930, 16-inch rpm discs playing about 15 minutes per side were used for most of these "electrical transcriptions". Some transcriptions were, like soundtrack discs, pressed with the commencement at the center of the disc and the needle moving outward (in the era of shellac pressings and steel needles, needle wear considerations dictated an 'inside start' for such a long recording); conversely, some commenced at the edge.  Longer programs, which required several disc sides, pioneered the system of recording odd-numbered sides inside-out and even-numbered sides outside-in so that the sound quality would match from the end of one side to the start of the next. Although a pair of turntables was used, to avoid any pauses for disc-flipping, the sides had to be pressed in a hybrid of manual and automatic sequencing, arranged in such a manner that no disc being played had to be turned over to play the next side in the sequence. Instead of a three-disc set having the 1–2, 3–4 and 5–6 manual sequence, or the 1–6, 2–5 and 3–4 automatic sequence for use with a drop-type mechanical record changer, broadcast sequence would couple the sides as 1–4, 2–5 and 3–6.  Some transcriptions were recorded with a vertically modulated "hill and dale" groove. This was found to allow deeper bass (because turntable rumble was laterally modulated in early radio station turntables) and also an extension of the high-end frequency response. Neither of these was necessarily a great advantage in practice because of the limitations of AM broadcasting. Today we can enjoy the benefits of those higher-fidelity recordings, even if the original radio audiences could not.  Initially, transcription discs were pressed only in shellac, but by 1932 pressings in RCA Victor's vinyl-based "Victrolac" were appearing. Other plastics were sometimes used. By the late 1930s, vinyl was standard for nearly all kinds of pressed discs except ordinary commercial 78s, which continued to be made of shellac.  Beginning in the mid-1930s, one-off 16-inch rpm lacquer discs were used by radio networks to archive recordings of their live broadcasts, and by local stations to delay the broadcast of network programming or to prerecord their own productions.  In the late 1940s, magnetic tape recorders were adopted by the networks to pre-record shows or repeat them for airing in different time zones, but 16-inch vinyl pressings continued to be used into the early 1960s for non-network distribution of prerecorded programming. Use of the LP's microgroove standard began in the late 1950s, and in the 1960s the size of discs was reduced to 12 inches, becoming physically indistinguishable from ordinary LPs.  Unless the quantity required was very small, pressed discs were a more economical medium for distributing high-quality audio than tape, and CD mastering was, in the early years of that technology, very expensive, so the use of LP-format transcription discs continued into the 1990s. The "King Biscuit Flower Hour" is a late example, as are Westwood One's "The Beatle Years" and "Doctor Demento" programs, which were sent to stations on LP at least through 1992.

RCA Victor.

RCA Victor introduced an early version of a long-playing record for home use in September 1931. These "Program Transcription" discs, as Victor called them, played at rpm and used a somewhat finer and more closely spaced groove than typical 78s. They were to be played with a special "Chromium Orange" chrome-plated steel needle. The 10-inch discs, mostly used for popular and light classical music, were normally pressed in shellac, but the 12-inch discs, mostly used for "serious" classical music, were normally pressed in Victor's new vinyl-based Victrolac compound, which provided a much quieter playing surface. They could hold up to 15 minutes per side. Beethoven's Fifth Symphony, performed by the Philadelphia Orchestra under Leopold Stokowski, was the first 12-inch recording issued. "The New York Times" wrote, "What we were not prepared for was the quality of reproduction...incomparably fuller."  Unfortunately for Victor, it was downhill from there. Many of the subsequent issues were not new recordings but simply dubs made from existing 78 rpm record sets. The dubs were audibly inferior to the original 78s. Two-speed turntables with the rpm speed were included only on expensive high-end machines, which sold in small numbers, and people were not buying many records of any kind at the time. Record sales in the US had dropped from a high of 105.6 million records sold in 1921 to 5.5 million in 1933 because of competition from radio and the effects of the Great Depression. Few if any new Program Transcriptions were recorded after 1933, and two-speed turntables soon disappeared from consumer products. Except for a few recordings of background music for funeral parlors, the last of the issued titles had been purged from the company's record catalog by the end of the decade. The failure of the new product left RCA Victor with a low opinion of the prospects for any sort of long-playing record, influencing product development decisions during the coming decade.

Columbia.

CBS Laboratories head research scientist Peter Goldmark led Columbia's team to develop a phonograph record that would hold at least 20 minutes per side. Although Goldmark was the chief scientist who selected the team, he delegated most of the experimental work to William S. Bachman, whom Goldmark had lured from General Electric, and Howard H. Scott.  Research began in 1941, was suspended during World War II, and then resumed in 1945. Columbia Records unveiled the LP at a press conference in the Waldorf Astoria on June 18, 1948, in two formats: in diameter, matching that of 78 rpm singles, and in diameter. The initial release of 133 recordings were: 85 12-inch classical LPs (ML 4001 to 4085), 26 10-inch classics (ML 2001 to 2026), eighteen 10-inch popular numbers (CL 6001 to 6018), and four 10-inch juvenile records (JL 8001 to 8004). According to the 1949 Columbia catalog, issued September 1948, the first twelve-inch LP was Mendelssohn's Concerto in E Minor by Nathan Milstein on the violin with the New York Philharmonic, conducted by Bruno Walter (ML 4001). Three ten-inch series were released: 'popular', starting with the reissue of "The Voice of Frank Sinatra" (CL 6001); 'classical', numbering from Beethoven's 8th symphony (ML 2001), and 'juvenile', commencing with "Nursery Songs" by Gene Kelly (JL 8001). Also released at this time were a pair of 2-LP sets, Puccini's La Bohème (SL-1) and Humperdinck's Hansel & Gretel (SL-2). All 12-inch pressings were of 220 grams vinyl. Columbia may have planned for the Bach album ML 4002 to be the first since the releases came in alphabetical order by composer. (Bach, Beethoven, Brahms, Dvorak, Franck and Gershwin appear in order in the first 25 LPs) However Nathan Milstein was a hot property in the 1940s so his performance of the Mendelssohn concerto was moved to ML 4001. There have been two repressings of this LP, one from Classic Records to celebrate the 50th anniversary of the LP in 1998 and one from HMV (England) celebrating the 70th anniversary of the LP in 2018. There is also a CD of this album on the market.

Public reception.

When the LP was introduced in 1948, the 78 was the conventional format for phonograph records. By 1952, 78s still accounted for slightly more than half of the units sold in the United States, and just under half of the dollar sales. The 45, oriented toward the single song, accounted for just over 30% of unit sales and just over 25% of dollar sales. The LP represented not quite 17% of unit sales and just over 26% of dollar sales.  Ten years after their introduction, the share of unit sales for LPs in the US was almost 25%, and of dollar sales 58%. Most of the remainder was taken up by the 45; 78s accounted for only 2% of unit sales and 1% of dollar sales. For this reason, major labels in the United States ceased manufacturing of 78s for popular and classical releases in 1956 with the minor labels following suit, with the final US-made 78 being produced in 1959.  Canada and the UK continued production into 1960, while India, the Philippines, and South Africa produced 78s until 1965, with the last holdout, Argentina, continuing until 1970.  The popularity of the LP ushered in the "Album Era" of English-language popular music, beginning in the 1960s, as performers took advantage of the longer playing time to create coherent themes or concept albums. "The rise of the LP as a form—as an artistic entity, as they used to say—has complicated how we perceive and remember what was once the most evanescent of the arts", Robert Christgau wrote in "" (1981). "The album may prove a '70s totem—briefer configurations were making a comeback by decade's end. But for the '70s it will remain the basic musical unit, and that's OK with me. I've found over the years that the long-playing record, with its twenty-minute sides and four-to-six compositions/performances per side, suits my habits of concentration perfectly."  Although the popularity of LPs began to decline in the late 1970s with the advent of Compact Cassettes, and later compact discs, the LP survives as a format to the present day. Vinyl LP records enjoyed a resurgence in the early 2010s. Vinyl sales in the UK reached 2.8 million in 2012. US vinyl sales in 2017 reached 15.6 million and 16.7 million for 2018.

Competing formats.

The LP was soon confronted by the "45", a diameter fine-grooved vinyl record playing at 45 rpm. It was introduced by RCA Victor in 1949. To compete with the LP, boxed albums of 45s were issued, along with EP (extended play) 45s, which squeezed two or even three selections onto each side. Despite these efforts, the 45 succeeded only in replacing the 78 as the format for singles.  The "last hurrah" for the 78 rpm record in the US was the microgroove 78 series pressed for the Audiophile label (Ewing Nunn, Saukville, Wis.) in the early 1950s. This series was labeled AP-1 through about AP-40, pressed on grainless red vinyl. Today AP-1 through AP-5 are very scarce. By very tightly packing the fine groove, a playing time of 17 minutes per side was achieved. Within a couple of years Audiophile switched to.  Reel-to-reel magnetic tape recorders posed a new challenge to the LP in the 1950s, but the higher cost of pre-recorded tapes was one of several factors that confined tape to a niche market. Cartridge and cassette tapes were more convenient and less expensive than reel-to-reel tapes, and they became popular for use in automobiles beginning in the mid-1960s. However, the LP was not seriously challenged as the primary medium for listening to recorded music at home until the 1970s, when the audio quality of the cassette was greatly improved by better tape formulations and noise-reduction systems. By 1983, cassettes were outselling LPs in the US.  The Compact Disc (CD) was introduced in 1982. It offered a recording that was, theoretically, completely noiseless and not audibly degraded by repeated playing or slight scuffs and scratches. At first, the much higher prices of CDs and CD players limited their target market to affluent early adopters and audiophiles; but prices came down, and by 1988 CDs outsold LPs. The CD became the top-selling format, over cassettes, in 1992.  Along with phonograph records in other formats, some of which were made of other materials, LPs are now widely referred to simply as "vinyl". Since the late 1990s there has been a vinyl revival. Demand has increased in niche markets, particularly among audiophiles, DJs, and fans of indie music, but most music sales as of 2018 came from CDs, online downloads, and online streaming, because of their availability, convenience, and price.

Playing time.

With the advent of sound film or "talkies", the need for greater storage space made rpm records more appealing. Soundtracks – played on records synchronized to movie projectors in theatres – could not fit onto the mere five minutes per side that 78s offered. When initially introduced, 12-inch LPs played for a maximum of about 23 minutes per side, 10-inchers for around 15. They were not an immediate success, however, as they were released during the height of the Great Depression, and seemed frivolous to the many impoverished of the time. It wasn't until "microgroove" was developed by Columbia Records in 1948 that Long Players (LPs) reached their maximum playtime, which has continued to modern times.  Economics and tastes initially determined which kind of music was available on each format. Recording company executives believed upscale classical music fans would be eager to hear a Beethoven symphony or a Mozart concerto without having to flip over multiple, four-minute-per-side 78s, and that pop music fans, who were used to listening to one song at a time, would find the shorter time of the 10-inch LP sufficient. As a result, the 12-inch format was reserved solely for higher-priced classical recordings and Broadway shows. Popular music continued to appear only on 10-inch records.  Their beliefs were wrong. By the mid-1950s, the 10-inch LP, like its similarly sized 78 rpm cousin, would lose the format war and be discontinued. Ten-inch records briefly reappeared as mini-LPs in the late 1970s and early 1980s in the United States and Australia as a marketing alternative.

Exceptions.

In 1952, Columbia Records introduced "extended-play" LPs that played for as long as 52 minutes, or 26 minutes per side. These were used mainly for the original cast albums of Broadway musicals, such as "Kiss Me, Kate" and "My Fair Lady", or to fit an entire play, such as the 1950 production of "Don Juan in Hell", onto two LPs. The 52-minute playing time remained rare, however, because of mastering limitations, and most LPs continued to be issued with a 30- to 45-minute playing time.  A small number of albums exceeded the 52-minute limit. These records had to be cut with much narrower spacing between the grooves, which allowed for a smaller dynamic range on the records, and meant that playing the record with a worn needle could damage the record. It also resulted in a much quieter sound. The list of long-playing vinyl records includes the 90-minute 1976 LP "90 Minutes with Arthur Fiedler and the Boston Pops", made by Radio Shack; Genesis' "Duke", with each side exceeding 27 minutes; Bob Dylan's 1976 album "Desire", with side two lasting almost thirty minutes; Def Leppard's 1987 album "Hysteria", with each side exceeding 30 minutes; Todd Rundgren's 1975 album "Initiation", totaling 67 min 32 s over two sides; and André Previn's "Previn Plays Gershwin,", with the London Symphony Orchestra, whose sides each exceeded 30 minutes. Finally, several recordings of Beethoven's Ninth Symphony were reissued on single discs; these LPs contained about 35 minutes on each side, with the third movement split into two parts.  Spoken word and comedy albums require a smaller dynamic range compared to musical records. Therefore, they can be cut with narrower spaces between the grooves. "The Comic Strip", released by Springtime Records in 1981, has a side A lasting 38 min 4 s, and a side B lasting 31 min 8 s, for a total of 69 min 12 s.

Changers.

Turntables called record changers could play records stacked vertically on a spindle. This arrangement encouraged the production of multiple-record sets in automatic sequence. A two-record set had Side 1 and Side 4 on one record, and Side 2 and Side 3 on the other, so the first two sides could play in a changer without the listener's intervention. Then the stack was flipped over. Larger boxed sets used appropriate automatic sequencing (1–8, 2–7, 3–6, 4–5) to allow continuous playback, but this created difficulties when searching for an individual track.

Disadvantages.

Vinyl records are vulnerable to dust, heat warping, scuffs, and scratches. Dust in the groove is usually heard as noise and may be ground into the vinyl by the passing stylus, causing lasting damage. A warp can cause a regular "wow" or fluctuation of musical pitch, and if substantial it can make a record physically unplayable. A scuff will be heard as a swishing sound. A scratch will create an audible tick or pop once each revolution when the stylus encounters it. A deep scratch can throw the stylus out of the groove; if it jumps to a place farther inward, part of the recording is skipped; if it jumps outward to a part of the groove it just finished playing, it can get stuck in an infinite loop, playing the same bit over and over until someone stops it. This last type of mishap, which in the era of brittle shellac records was more commonly caused by a crack, spawned the simile "like a broken record" to refer to annoying and seemingly endless repetition.  Records used in radio stations can suffer cue burn, which results from disc jockeys placing the needle at the beginning of a track, turning the record back and forth to find the exact start of the music, then backing up about a quarter turn, so that when it is released the music will start immediately after the fraction of a second needed for the disc to come up to full speed. When this is done repeatedly, the affected part of the groove is heavily worn and a hissing sound will be noticeable at the start of the track.  The process of playing a vinyl record with a stylus is by its very nature to some degree a destructive process. Wear to either the stylus or the vinyl results in diminished sound quality. Record wear can be reduced to virtual insignificance, however, by the use of a high-quality, correctly adjusted turntable and tonearm, a high-compliance magnetic cartridge with a high-end stylus in good condition, and careful record handling, with non-abrasive removal of dust before playing and other cleaning if necessary.

Groove.

The average LP has about of groove on each side. The average tangential needle speed relative to the disc surface is approximately. It travels fastest on the outside edge, unlike audio CDs, which change their speed of rotation to provide constant linear velocity (CLV). (By contrast, CDs play from the inner radius outward, the reverse of phonograph records.)  Thin, closely spaced spiral grooves that allowed for increased playing time on a rpm microgroove LP led to a faint pre-echo warning of upcoming loud sounds. The cutting stylus unavoidably transferred some of the subsequent groove wall's impulse signal into the previous groove wall. It was discernible by some listeners throughout certain recordings but a quiet passage followed by a loud sound would allow anyone to hear a faint pre-echo of the loud sound occurring 1.8 seconds ahead of time. This problem could also appear as post-echo, with a ghost of the sound arriving 1.8 seconds after its main impulse. Pre- and post-echo can be avoided by the use of direct metal mastering.  The first LP records introduced used fixed pitch grooves just like their 78 predecessors. The use of magnetic tape for the production of the master recordings allowed the introduction of variable pitch grooves. The magnetic tape reproducer used to transfer the recording to the master disc was equipped with an auxiliary playback head positioned ahead of the main head by a distance equal to one revolution of the disc. The sole purpose of this head was to monitor the amplitude of the recording. If the sound level from both the auxiliary and main magnetic heads was loud, the cutting head on the disc recording lathe was driven at its normal speed. However, if the sound level from both magnetic heads was quieter, then the disc cutting head could be driven at a lower speed reducing the groove pitch with no danger of the adjacent grooves colliding with each other. The playing time of the disc was therefore increased by an amount dependent on the duration of quieter passages.  The record manufacturers had also realised that by reducing the amplitude of the lower frequencies recorded in the groove, it was possible to decrease the spacing between the grooves and further increase the playing time. These low frequencies were then restored to their original level on playback. Furthermore, if the amplitude of the high frequencies was artificially boosted on recording the disc and then subsequently reduced to their original level on playback, the noise introduced by the disc would be reduced by a similar amount. This gave rise to an equalization frequency response applied during record coupled with an inverse of the response applied on playback. Each disc manufacturer applied their own version of an equalization curve (mostly because each manufacturer's equalization curve was protected by interlocking patents). Low-end reproduction equipment applied a compromise playback equalization that reproduced most discs reasonably well. However, amplifiers for audiophile equipment were equipped with an equalization selector with a position for most, if not all, disc manufacturers. The net effect of equalization is to allow longer playing time and lower background noise while maintaining full fidelity of music or other content.  In 1954, the Recording Industry Association of America (RIAA) introduced a standard equalization curve to be used by all record manufacturers. Consequently, both low-quality and audiophile reproducers alike could replay any recording with the correct equalization. There are two versions of the reproduction RIAA equalization curve. The first, is simply the inverse of the recording curve designed for cheaper equipment using crystal or ceramic reproduction cartridges. The second curve is intended for equipment fitted with magnetic reproduction cartridges where the output voltage is dependent on the frequency of the recorded signal (the voltage output is directly proportional to the frequency of the recorded signal; that is: the voltage doubles as the recorded frequency doubles).

Fidelity and formats.

The audio quality of LPs has increased greatly since their 1948 inception. While early LP recordings were monophonic, stereophony had been demonstrated in 1881 and Alan Blumlein had patented Stereophonic sound in 1931. Unsuccessful attempts were made to create stereophonic records starting in the 1920s, including Emory Cook's 1952 "binaural" LPs using two precisely spaced tracks on the record (one track for each channel) which had to be played with two monaural pick-ups on a tuning-fork-shaped tonearm. The modern system ultimately released by Audio Fidelity Records in November 1957 uses two modulation angles, equal and opposite 45 degrees from vertical (and so perpendicular to each other.) It can also be thought of as using traditional horizontal modulation for the sum of left and right channels (mono), making it essentially compatible with simple mono recordings, and vertical-plane modulation for the "difference" of the two channels.  The following are some significant advances in the format:  The composition of vinyl used to press records (a blend of polyvinyl chloride and polyvinyl acetate) has varied considerably over the years. Virgin vinyl is preferred, but during the 1970s energy crisis, it became commonplace to use recycled vinyl. Sound quality suffered, with increased ticks, pops, and other surface noises. Other experiments included reducing the thickness of LPs, leading to warping and increased susceptibility to damage. Using a biscuit of 130 grams of vinyl had been the standard. Compare these to the original Columbia 12-inch LPs (ML 4001) at around 220 grams each. Besides the standard black vinyl, specialty records are also pressed on different colors of PVC/A or picture discs with a card picture sandwiched between two clear sides. Records in different novelty shapes have also been produced.  In 2018, an Austrian startup, Rebeat Innovation GmBH, received 4.8 million in funding to develop high definition vinyl records that purport to contain longer play times, louder volumes and higher fidelity than conventional vinyl LPs. Rebeat Innovation, headed by CEO Günter Loibl, has called the format 'HD Vinyl'. The HD process works by converting audio to a digital 3D topography map which is then inscribed onto the vinyl stamper via lasers, resulting in less loss of information. Many critics have expressed skepticism regarding the cost and quality of HD records.  In May 2019, at the Making Vinyl conference in Berlin, Loibl unveiled the Perfect Groove software for creating 3D topographic audio data files. This is a critical step in the production of HD Vinyl stampers, as they provide the map for subsequent laser-engraving. The audio engineering software was created with mastering engineers Scott Hull and Darcy Proper, a four-time Grammy winner. The demonstration offered the first simulations of what HD Vinyl records are likely to sound like, ahead of actual HD vinyl physical record production. Loibl discussed the Perfect Groove software at a presentation titled "Vinyl 4.0 The next generation of making records" before offering demonstrations to attendees.

Use by disc jockeys.

Disc jockeys (or DJs) in clubs still frequently use vinyl records, as cueing tracks from cassette tapes is too slow and CDs did not allow creative playback options until 2001. The term "DJ", which had always meant a person who played various pieces of music on the radio (originally 78s, then 45s, then tape cartridges and reels; now cuts from CDs or tracks on a computer) – a play on the horse-racing term "jockey" – has also come to encompass all kinds of skills in "scratching" (record playback manipulation) and mixing dance music, rapping over the music or even playing musical instruments, but the original dance club (non-radio) definition was simply somebody who played records, alternating between two turntables. The skill came in subtly matching beats or instruments from one song to the next, providing a consistent dance tempo. DJs also made occasional announcements and chatted on the side with patrons while songs were playing to take requests, similar to what radio disc jockeys have been doing since the 1940s.

The LP (from "long playing" or "long play") is an analog sound storage medium, a phonograph record format characterized by a speed of rpm, a 12- or 10-inch (30- or 25-cm) diameter, and use of the "microgroove" groove specification. Introduced by Columbia in 1948, it was soon adopted as a new standard by the entire record industry. Apart from a few relatively minor refinements and the important later addition of stereophonic sound, it remained the standard format for record albums until its gradual replacement from the 1980s to the early 21st century, first by compact discs and then by streaming media.

Dlouhohrající deska (zkratka LP vlastní termín pochází z anglického "long play", lidově zvaná elpíčko nebo také slangově "elpé" či "elpí") je jeden z typů gramofonové desky.


History.

The earliest ovens were found in Central Europe, and date back to 29,000 BC. They were roasting and boiling pits inside yurts used to cook mammoth. In Ukraine from 20,000 BC they used pits with hot coals covered in ashes. The food was wrapped in leaves and set on top, then covered with earth. In camps found in Mezhirich, each mammoth bone house had a hearth used for heating and cooking. Ovens were used by cultures who lived in the Indus Valley and in pre-dynastic Egypt. By 3200 BC, each mud-brick house had an oven in settlements across the Indus Valley. Ovens were used to cook food and to make bricks. Pre-dynastic civilizations in Egypt used kilns around 5000–4000 BC to make pottery.  During the Middle Ages, instead of earth and ceramic ovens, Europeans used fireplaces in conjunction with large cauldrons. These were similar to the Dutch oven. Following the Middle-Ages, ovens underwent many changes over time from wood, iron, coal, gas, and even electric. Each design had its own motivation and purpose. The wood-burning stoves saw improvement through the addition of fire chambers that allowed better containment and release of smoke. Another recognizable oven would be the cast-iron stove. These were first used around the early 1700s when they themselves underwent several variations including the Stewart Oberlin iron stove that was smaller and had its own chimney.  In the early part of the 19th century, the coal oven was developed. It was cylindrical in shape and made of heavy cast iron. The gas oven saw its first use as early as the beginning of the 19th century as well. Gas stoves became very common household ovens once gas lines were available to most houses and neighborhoods. James Sharp patented one of the first gas stoves in 1826. Other various improvements to the gas stove included the AGA cooker invented in 1922 by Gustaf Dalén. The first electric ovens were invented in the very late 19th century, however, like many electrical inventions destined for commercial use, mass ownership of electrical ovens could not be a reality until better and more efficient use of electricity was available.  More recently, ovens have become slightly more high-tech in terms of cooking strategy. The microwave as a cooking tool was discovered by Percy Spencer in 1946, and with the help from engineers, the microwave oven was patented. The microwave oven uses microwave radiation to excite the molecules in food causing friction, thus producing heat.  <br>

Cooking.

In cooking, the conventional oven is a kitchen appliance used for roasting and heating. Foods normally cooked in this manner include meat, casseroles and baked goods such as bread, cake and other desserts. In modern times, the oven is used to cook and heat food in many households across the globe.  Modern ovens are typically fueled by either natural gas or electricity, with bottle gas models available but not common. When an oven is contained in a complete stove, the fuel used for the oven may be the same as or different from the fuel used for the burners on top of the stove.  Ovens usually can use a variety of methods to cook. The most common may be to heat the oven from below. This is commonly used for baking and roasting. The oven may also be able to heat from the top to provide broiling (US) or grilling (UK/Commonwealth). A fan-assisted oven that uses a small fan to circulate the air in the cooking chamber, can be used. Both are also known as convection ovens. An oven may also provide an integrated rotisserie.  Ovens also vary in the way that they are controlled. The simplest ovens (for example, the AGA cooker) may not have any controls at all; the ovens simply run continuously at various temperatures. More conventional ovens have a simple thermostat which turns the oven on and off and selects the temperature at which it will operate. Set to the highest setting, this may also enable the broiler element. A timer may allow the oven to be turned on and off automatically at pre-set times. More sophisticated ovens may have complex, computer-based controls allowing a wide variety of operating modes and special features including the use of a temperature probe to automatically shut the oven off when the food is completely cooked to the desired degree.

Cleaning.

Some ovens provide various aids to cleaning. "Continuous cleaning" ovens have the oven chamber coated with a catalytic surface that helps break down (oxidize) food splatters and spills over time. "Self-cleaning" ovens use pyrolytic decomposition (extreme heat) to oxidize dirt. Steam ovens may provide a wet-soak cycle to loosen dirt, allowing easier manual removal. In the absence of any special methods, chemical "oven cleaners" are sometimes used or just scrubbing.

Industrial, scientific, and artisanal use.

Outside the culinary world, ovens are used for a number of purposes.

An oven is a thermally insulated chamber used for the heating, baking, or drying of a substance, and most commonly used for cooking. Kilns and furnaces are special-purpose ovens used in pottery and metalworking, respectively.

Pec je zařízení pro tepelné zpracování surovin i výrobků (keramických, kovových, plastových, skleněných, textilních atd.), pro pečení potravin (např. pečiva), tepelnou přípravu jídel, případně vytápění chalupy. Průmyslové pece jsou zařízení či stavby, sloužící ke zpracovávání materiálů za vysokých teplot. Teplo pro provoz pece se získává obvykle spalováním, ale existují například i elektrické pece (odporové, indukční, obloukové).


Components.

The RS-25 engine consists of various pumps, valves, and other components which work in concert to produce thrust. Fuel (liquid hydrogen) and oxidizer (liquid oxygen) from the Space Shuttle's external tank entered the orbiter at the umbilical disconnect valves and from there flowed through the orbiter's main propulsion system (MPS) feed lines; whereas in the Space Launch System (SLS), fuel and oxidizer from the rocket's core stage will flow directly into the MPS lines. Once in the MPS lines, the fuel and oxidizer each branch out into separate paths to each engine (three on the Space Shuttle, four on the SLS). In each branch, prevalves then allow the propellants to enter the engine.  Once in the engine, the propellants flow through low-pressure fuel and oxidizer turbopumps (LPFTP and LPOTP), and from there into high-pressure turbopumps (HPFTP and HPOTP). From these HPTPs the propellants take different routes through the engine. The oxidizer is split into four separate paths: to the oxidizer heat exchanger, which then splits into the oxidizer tank pressurization and pogo suppression systems; to the low pressure oxidizer turbopump (LPOTP); to the high pressure oxidizer preburner, from which it is split into the HPFTP turbine and HPOTP before being reunited in the hot gas manifold and sent on to the main combustion chamber (MCC); or directly into the main combustion chamber (MCC) injectors.  Meanwhile, fuel flows through the main fuel valve into regenerative cooling systems for the nozzle and MCC, or through the chamber coolant valve. Fuel passing through the MCC cooling system then passes back through the LPFTP turbine before being routed either to the fuel tank pressurization system or to the hot gas manifold cooling system (from where it passes into the MCC). Fuel in the nozzle cooling and chamber coolant valve systems is then sent via pre-burners into the HPFTP turbine and HPOTP before being reunited again in the hot gas manifold, from where it passes into the MCC injectors. Once in the injectors, the propellants are mixed and injected into the main combustion chamber where they are ignited. The burning propellant mixture is then ejected through the throat and bell of the engine's nozzle, the pressure of which creates the thrust.

Turbopumps.

Oxidizer system.

The low-pressure oxidizer turbopump (LPOTP) is an axial-flow pump which operates at approximately 5,150 rpm driven by a six-stage turbine powered by high-pressure liquid oxygen from the high-pressure oxidizer turbopump (HPOTP). It boosts the liquid oxygen's pressure from, with the flow from the LPOTP then being supplied to the HPOTP. During engine operation, the pressure boost permits the high-pressure oxidizer turbine to operate at high speeds without cavitating. The LPOTP, which measures approximately, is connected to the vehicle propellant ducting and supported in a fixed position by being mounted on the launch vehicle's structure.  Then, mounted before the HPOTP, is the pogo oscillation suppression system accumulator. For use, it is pre- and post-charged with and charged with gaseous from the heat exchanger, and, not having any membrane, it operates by continuously recirculating the charge gas. A number of baffles of various types are present inside the accumulator to control sloshing and turbulence, which is useful of itself and also to prevent escape of gas into the low-pressure oxidizer duct to be ingested in the HPOTP.  The HPOTP consists of two single-stage centrifugal pumps (a main pump and a preburner pump) mounted on a

Fuel system.

The low-pressure fuel turbopump (LPFTP) is an axial-flow pump driven by a two-stage turbine powered by gaseous hydrogen. It boosts the pressure of the liquid hydrogen from 30 to 276 psia (0.2 to 1.9 MPa) and supplies it to the high-pressure fuel turbopump (HPFTP). During engine operation, the pressure boost provided by the LPFTP permits the HPFTP to operate at high speeds without cavitating. The LPFTP operates at around 16,185 rpm, and is approximately in size. It is connected to the vehicle propellant ducting and is supported in a fixed position by being mounted to the launch vehicle's structure.  The HPFTP is a three-stage centrifugal pump driven by a two-stage hot-gas turbine. It boosts the pressure of the liquid hydrogen from 1.9 to 45 MPa (276 to 6,515

Powerhead.

Preburners.

The oxidizer and fuel preburners are welded to the hot-gas manifold. The fuel and oxidizer enter the preburners and are mixed so that efficient combustion can occur. The augmented spark igniter is a small combination chamber located in the center of the injector of each preburner. Two dual-redundant spark igniters are activated by the engine controller, and are used during the engine start sequence to initiate combustion in each preburner. They are turned off after approximately three seconds because the combustion process is then self-sustaining. The preburners produce the fuel-rich hot gases that pass through the turbines to generate the power needed to operate the high-pressure turbopumps. The oxidizer preburner's outflow drives a turbine that is

Main combustion chamber.

The engine's main combustion chamber (MCC) receives fuel-rich hot gas from a hot-gas manifold cooling circuit. The gaseous hydrogen and liquid oxygen enter the chamber at the injector, which mixes the propellants. The mixture is ignited by the "Augmented Spark Igniter", an H/O flame at the center of the injector head. The main injector and dome assembly are welded to the hot-gas manifold, and the MCC is also bolted to the hot-gas manifold. The MCC comprises a structural shell made of Inconel 718 which is lined with a copper-silver-zirconium alloy called NARloy-Z, developed specifically for the RS-25 in the 1970s. Around 390 channels are machined into the liner wall to carry liquid hydrogen through

Nozzle.

The engine's nozzle is long with a diameter of at its throat and at its exit. The nozzle is a bell-shaped extension bolted to the main combustion chamber, referred to as a de Laval nozzle. The RS-25 nozzle has an unusually large expansion ratio (about 77.5:1) for the chamber pressure. At sea level, a nozzle of this ratio would normally undergo flow separation of the jet from the nozzle, which would cause control difficulties and could even mechanically damage the vehicle. However, to aid the engine's operation Rocketdyne engineers varied

Controller.

Each engine is equipped with a main engine controller (MEC), an integrated computer which controls all of the engine's functions (through the use of valves) and monitors its performance. Built by Honeywell Aerospace, each MEC originally comprised two redundant Honeywell HDC-601 computers, later upgraded to a system composed of two doubly redundant Motorola 68000 (M68000) processors (for a total of four M68000s per controller). Having the controller installed on the engine itself greatly simplifies the wiring between the engine and the launch vehicle, because all the sensors and actuators are connected directly to only the controller, each MEC then being connected to the orbiter's general purpose computers (GPCs) or the SLS's avionics suite via its own engine interface unit (EIU). Using a dedicated system also simplifies the software and thus improves its reliability.  Two independent dual-CPU computers, A and B, form the controller; giving redundancy to the system. The failure of controller system A automatically leads to a switch-over to controller system B without impeding

Gimbal.

Each engine is installed with a gimbal bearing, a universal ball and socket joint which is bolted to the launch vehicle by its upper flange and to the engine by its lower flange. It represents the thrust interface between the engine and the launch vehicle, supporting of engine weight and withstanding over of thrust. As well as providing a means to attach the engine to the launch vehicle, the gimbal bearing allows the engine to be pivoted (or "gimballed") around two axes of

Helium system.

In addition to fuel and oxidizer systems, the launch vehicle's main propulsion system is also equipped with a helium system consisting of ten storage tanks in addition to various regulators, check valves, distribution

History.

Development.

The history of the RS-25 traces back to the 1960s when NASA's Marshall Space Flight Center and Rocketdyne were conducting a series of studies on high-pressure engines, developed from the successful J-2 engine used on the S-II and S-IVB upper stages of the Saturn V rocket during the Apollo program. The studies were conducted under a program to upgrade the Saturn V engines, which produced a design for a upper-stage engine known as the HG-3. As funding levels for Apollo wound down the HG-3 was cancelled as well as the upgraded F-1 engines already being tested. It was the design for the HG-3 that would form the basis for the RS-25.  Meanwhile, in 1967, the US Air Force funded a study into advanced rocket propulsion systems for use during Project Isinglass, with Rocketdyne asked to investigate aerospike engines and Pratt & Whitney (P&W) to research more efficient conventional de Laval nozzle-type engines. At the conclusion of the study, P&W put forward a proposal for a 250,000 lb engine called the XLR-129, which used a two-position expanding nozzle to provide increased efficiency over a wide range of altitudes.  In January 1969 NASA awarded contracts to General Dynamics, Lockheed, McDonnell Douglas, and North American Rockwell to initiate early development of the Space Shuttle. As part of these 'Phase A' studies, the involved companies selected an upgraded version of the XLR-129, developing, as the baseline engine for their designs. This design can be found on many of the planned Shuttle versions right up to the final decision. However, since NASA was interested in pushing the state of the art in every way they decided to select a much more advanced design in order to "force an advancement of rocket engine technology". They called for a new design based on a high-pressure combustion chamber running around, which increases the performance of the engine.  Development began in 1970, when NASA released a request for proposal for 'Phase B' main engine concept studies, requiring development of a

Space Shuttle program.

Each Space Shuttle had three RS-25 engines, installed in the aft structure of the Space Shuttle orbiter in the Orbiter Processing Facility prior to the orbiter being transferred to the Vehicle Assembly Building. If necessary the engines could be changed on the pad. The engines, drawing propellant from the Space Shuttle external tank (ET) via the orbiter's main propulsion system (MPS), were ignited at T−6.6 seconds prior to liftoff (with each ignition staggered by 120 ms), which allowed their performance to be checked prior to ignition of the Space Shuttle Solid Rocket Boosters (SRBs), which committed the shuttle to the launch. At launch, the engines would be operating at 100% RPL, throttling up to 104.5% immediately following liftoff. The engines would maintain this power level until around T+40 seconds, where they would be throttled back to around 70% to reduce aerodynamic loads on the shuttle stack as it passed through the region of maximum dynamic pressure, or max. "q". The engines would then be throttled back up until around T+8 minutes, at which point they would be gradually throttled back down to 67% to prevent the stack exceeding 3 g of acceleration as it became progressively lighter due to propellant consumption. The engines were then shut down, a procedure known as main engine cutoff (MECO), at around T+8.5 minutes.  After each flight the engines would be removed from the orbiter and transferred to the Space Shuttle Main Engine Processing Facility (SSMEPF), where they would be inspected and refurbished in preparation for reuse on a subsequent flight. A total of 46 reusable RS-25 engines, each costing around US$40 million, were flown during the Space Shuttle program, with each new or overhauled engine entering the flight inventory requiring flight qualification on one of the test stands at Stennis Space Center prior to flight.

Upgrades.

Over the course of the Space Shuttle program, the RS-25 went through a series of upgrades, including combustion chamber changes, improved welds and

Engine throttle/output.

The most obvious effects of the upgrades the RS-25 received through the Space Shuttle program were the improvements in engine throttle. Whilst the FMOF engine had a maximum output of 100% RPL, Block II engines could throttle as high as 109% or 111% in an emergency, with usual flight performance being 104.5%. These increases in throttle level made a significant difference to the thrust produced by the engine:  Specifying power levels over 100% may seem nonsensical, but there was a logic behind it. The 100% level does not mean the maximum physical power level

Incidents.

During the course of the Space Shuttle program, a total of 46 RS-25 engines were used (with one extra RS-25D being built but never used). During the 135 missions, for a total of 405 individual engine-missions, Pratt & Whitney Rocketdyne reports a 99.95% reliability rate, with the only in-flight SSME failure occurring during's STS-51-F mission. The engines, however, did suffer from a number of pad failures (redundant set launch sequencer aborts, or RSLSs) and other issues during the course of the program:

Constellation.

During the period preceding final Space Shuttle retirement, various plans for the remaining engines were proposed, ranging from them all being kept by NASA, to them all being given away (or sold for US$400,000–800,000 each) to various institutions such as museums and universities. This policy followed changes to the planned configurations of the Constellation program's Ares V cargo-launch vehicle and Ares I crew-launch vehicle rockets, which had been planned to use the RS-25 in their first and second stages respectively.

Space Launch System.

Following the retirement of the Space Shuttle, NASA announced on September 14, 2011, that it would be developing a new launch vehicle, known as the Space Launch System (SLS), to replace the shuttle fleet. The design for the SLS features the RS-25 on its core stage, with different versions of the rocket being installed with between three and five engines. The initial flights of the new launch vehicle will make use of flown Block II RS-25D engines, with NASA keeping the remaining such engines in a "purged safe" environment at Stennis Space Center, "along with all of the ground systems required to maintain them." In addition to the RS-25Ds, the SLS program will make use of the Main Propulsion Systems from the three remaining orbiters for testing purposes (having been removed as part of the orbiters' decommissioning), with the first two launches (Artemis 1 and Artemis 2) possibly making use of the MPS hardware from Space Shuttles and in their core stages. The SLS's propellants will be supplied to the engines from the rocket's core stage, which will consist of a modified Space Shuttle external tank with the MPS plumbing and engines at its aft, and an interstage structure at the top. Once the remaining RS-25Ds are used up, they are to be replaced with a cheaper, expendable version, currently designated the RS-25E. This engine may be based on one or both of two single-use variants which were studied in 2005, the RS-25E (referred to as the 'Minimal Change Expendable SSME') and the even more simplified RS-25F (referred to as the 'Low Cost Manufacture Expendable SSME'), both of which were under consideration in 2011 and are currently under development by Aerojet Rocketdyne.  On May 1, 2020, NASA awarded a contract extension to manufacture 18 additional RS-25 engines with associated services for $1.79 billion, bringing the total SLS contract value to almost $3.5 billion.

Engine tests.

In 2015, a test campaign was conducted to determine RS-25 engine performance with: the new engine controller unit; lower liquid oxygen temperatures; greater inlet pressure due to the taller SLS core stage liquid oxygen tank and higher vehicle acceleration; and, more nozzle heating due to the four-engine configuration and its position in-plane with the SLS booster exhaust nozzles. New ablative insulation and heaters were to be tested during the series. Test occurred on January 9, May 28, June 11 (500 seconds), July 17 (535 seconds), August 13 and August 27.  Following these tests, four more engines were scheduled to enter a new test cycle. A new series of tests designed to evaluate performance in SLS use cases was initiated in 2017.  On February 28, 2019, NASA conducted a 510 seconds burn test of a developmental RS-25 powered to 113 percent of its original design thrust for more than 430 seconds, about four times longer than any prior test.

XS-1.

On May 24, 2017, DARPA announced that they had selected The Boeing Company to complete design work on the XS-1 program. The

The Aerojet Rocketdyne RS-25, also known as the Space Shuttle main engine (SSME), is a liquid-fuel cryogenic rocket engine that was used on NASA's Space Shuttle. NASA is planning to continue using the RS-25 on the Space Shuttle's successor, the Space Launch System (SLS).

Space Shuttle Main Engine, zkráceně SSME ( hlavní motor raketoplánu), je raketový motor na kapalné pohonné látky používaný na amerických raketoplánech Space Shuttle. Motory jsou umístěny na zádi družicového stupně ve svazku po třech. Jako jedny z mála motorů jsou SSME znovupoužitelné. Cena jednoho se pohybuje kolem 50 milionů amerických dolarů.


In 2 dimensions.

In two-dimensional space, there are 5 Bravais lattices, grouped into four crystal families.  The unit cells are specified according to the relative lengths of the cell edges ("a" and "b") and the angle between them ("θ"). The area of the unit cell can be calculated by evaluating the norm, where a and b are the lattice vectors. The properties of the crystal families are given below:

In 3 dimensions.

In three-dimensional space, there are 14 Bravais lattices. These are obtained by combining one of the seven lattice systems with one of the centering types. The centering types identify the locations of the lattice points in the unit cell as follows:  Not all combinations of lattice systems and centering types are needed to describe all of the possible lattices, as it can be shown that several of these are in fact equivalent to each other. For example, the monoclinic I lattice can be described by a monoclinic C lattice by different choice of crystal axes. Similarly, all A- or B-centred lattices can be described either by a C- or P-centering. This reduces the number of combinations to 14 conventional Bravais lattices, shown in the table below. Below each diagram is the Pearson symbol for that Bravais lattice.  The unit cells are specified according to the relative lengths of the cell edges ("a", "b", "c") and the angles between them ("α", "β", "γ"). The volume of the unit cell can be calculated by evaluating the triple product, where a, b, and c are the lattice vectors. The properties of the lattice systems are given below:

In 4 dimensions.

In four dimensions, there are 64 Bravais lattices. Of these, 23 are primitive and 41 are centered. Ten Bravais lattices split into enantiomorphic pairs.

In geometry and crystallography, a Bravais lattice, named after, is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by:

Krystalová mřížka je množina určitých myšlených abstraktních bodů, pomocí nichž se popisuje struktury krystalu, neboli vzájemná poloha částic v krystalu. Podobně jako u krystalu i zde zatím není možné dosáhnout tzv. ideální krystalové mřížky, jejíž struktura je zcela pravidelná a bez jakýchkoliv poruch.


History.

Background.

Following the success of Japan's newly inaugurated Shinkansen network, the High Speed Ground Transportation Act of 1965 authorized the U.S. government to explore the creation of high-speed rail, which resulted in the introduction of "Metroliner" trains, the predecessor to "Acela". During the 1980s the U.S. Federal Railroad Administration explored the possibilities of high-speed rail in the United States. On December 18, 1991, five potential high speed rail corridors were authorized ("Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) (PL 102-240)") including the Northeast Corridor.  Amtrak asked railway equipment manufacturers to submit proposals. An X 2000 train was leased from Sweden for test runs from October 1992 to January 1993. It was operated from Washington, D.C. to New York City from February to May and August to September 1993. Siemens showed the ICE 1 train from Germany, organizing the ICE Train North America Tour which started to operate on the Northeast Corridor on July 3, 1993. This testing allowed Amtrak to define a set of specifications that went into a public tender in October 1994.

Building and development.

On March 9, 1999, Amtrak unveiled its plan for a high-speed train, the "Acela Express". Twenty new trains were to run on the Northeast Corridor. Several changes were made to the corridor to make it suitable for the "Acela". The Northend Electrification Project extended existing electrification from New Haven to Boston to complete the overhead power supply along the route, and several grade crossings were improved or removed. Prior to 2000, all trains bound for Boston had to switch to diesel power at New Haven.  In October 1994, Amtrak requested bids from train manufacturers for a trainset that could reach. A joint project of Bombardier (75%) and GEC Alsthom (now Alstom) (25%) was selected in March 1996. An inaugural VIP run of the "Acela" occurred on November 16, 2000, with the VIP train being led by power car number 2020 with no. 2009 at the opposite end, followed by the first revenue run on December 11, 2000, a few months after the intended date. By 2005, Amtrak's share of the common-carrier market between New York and Boston had reached 40%, from 18% pre-"Acela". With the increasing popularity of the faster, modern "Acela Express", "Metroliner" service was phased out in late 2006. To meet the demand, more "Acela" services were added in September 2005. By August 2008 crowding had become noticeable.  By 2011, the "Acela" fleet had reached half of its designed service life. Amtrak proposed several replacement options, including one as part of its "A Vision for High-Speed Rail in the Northeast Corridor". In 2011, Amtrak announced that forty new "Acela" coaches would be ordered in 2012 to increase capacity on existing trainsets. The existing trains would have received two more coaches, lengthening the trainsets from a 1-6-1 configuration to 1-8-1 (power car — passenger cars — power car). The longer trainsets would have required the modifications of the "Acela" maintenance facilities in Boston, New York and Washington. The first of the stretched trainsets was to have entered service in fiscal year 2014. This plan was cancelled in 2012 in favor of replacing, rather than refurbishing, the "Acela" fleet.  In January 2014, Amtrak issued a request for proposals on 28 or more new model "Acela" trainsets, in a combined order with the California High-Speed Rail Authority. These bids were due May 17, 2014. After discussions with manufacturers, Amtrak and the California High Speed Rail Authority concluded their needs were too disparate for common rolling stock and decided not to pursue the joint option.

Cost.

Amtrak's original contract with the Bombardier-Alstom consortium was for the delivery of 20 trainsets (6 coaches each, with power cars at front and rear) for $800 million. By 2004, Amtrak had settled contract disputes with the consortium, paying a total of $1.2 billion for the 20 trainsets plus 15 extra high-speed locomotives and the construction of maintenance facilities in Boston, New York, and Washington.

Branding.

The "Acela" name was announced on March 9, 1999, as a part of the original announcement of the service itself. Amtrak originally intended for this move to be part of a rebranding of the majority of their Northeast services, forming three levels: "Acela Express", "Acela Regional", and "Acela Commuter". The branding team based the name ""Acela"" on the ideas of acceleration and excellence.  There were then three classes of trains on the Northeast Corridor (and its extension south to Newport News, Virginia)— Philadelphia-New York "Clockers", the express "Metroliners", and the umbrella term "NortheastDirect", applied to other trains on the corridor (in addition to unique names assigned to each departure). "Empire Service" trains used the Empire Corridor from New York City to Niagara Falls, and "Keystone Service" ran along the Keystone Corridor from Philadelphia to Harrisburg.  The "Acela Regional" name was first applied to "NortheastDirect" trains 130–133 on January 31, 2000. Those trains, 130 and 131 running weekdays only and 132 and 133 running every day, were the first electrified trains to run on the full Northeast Corridor. As more trains were electrified, they too were rebranded. In 2003, due to confusion between the lower-speed "Acela Regional" trains and the "Acela Express", the "Acela" branding was removed from the "NortheastDirect" service (now the "Northeast Regional") and the "Acela Commuter" had its name changed back to the "Clocker" for a similar reason; the "Clocker" was ultimately discontinued on October 28, 2005.

Engineering.

First-generation train design.

The first-generation "Acela" trainset is a unique set of vehicles designed specifically to satisfy governmental rolling stock requirements established primarily by the Federal Railroad Administration (FRA). This includes the ability to withstand a collision with a freight train at speed without collapsing. Most manufacturers which bid on the "Acela" were unable to meet the structural requirements, due to increased costs and complications for the manufacture of the trains, and the need for manufacturers to make significant engineering changes to their standard designs. In the end, only three qualified bidders remained: ABB (Swedish-Swiss manufacturer of the X 2000 train), Siemens (manufacturer of the German ICE), and a consortium of Bombardier (manufacturer of the LRC trains) and Alstom (manufacturer of the French TGV).  The design, using identical 6,200 horsepower (4,600 kW) power cars at each end which operate on a voltage of 11,000 volts AC, and either 25 or 60 Hz frequency, derives several components from the TGV, such as the third-generation TGV's traction system (including the four asynchronous AC motors per power car, rectifiers, inverters, and regenerative braking), the trucks/bogies structure (a long wheelbase dual transom H frame welded steel with outboard mounted tapered roller bearings), the brake discs (although there are only three per axle, versus four on the TGV), and crash energy management techniques to control structural deformation in the event of an accident.  The tilting carriages are based upon Bombardier's earlier LRC trains used on Via Rail rather than the TGV's non-tilting articulated trailers. "Acela" power cars and passenger cars are much heavier than those of the TGV in order to meet the FRA's crash standards. French and Canadian crews testing the "Acela" referred to it as "the pig" due to its weight. The extra weight leads to the "Acela"'s power-to-weight ratio being about 22.4 hp per tonne, compared to 30.8 hp for a SNCF TGV Reseau trainset. The Tier II crash standards, adopted in 1999, have also resulted in the passenger cars being designed without steps and trapdoors, which means that the trainsets can only serve lines with high-level platforms such as the Northeast Corridor. "Acela" trains are semi-permanently coupled (but not articulated as in the TGV) and are referred to as trainsets. Bombardier later used the "Acela" carriage design and a diesel/gas turbine variant of the power car for its experimental JetTrain.

Operating speeds.

With a 71:23 gear ratio, the "Acela" is designed with a top speed of and reaches a maximum speed of in regular service on three sections of track totaling in Rhode Island and Massachusetts. The "Acela" achieves an average speed (including stops) of between Washington and New York, and an average speed of from New York to Boston. The average speed over the entire route is a slightly faster.  In practice, the "Acela"'s speed depends more on local restrictions along its corridor than on its trainset. In addition to speed restrictions through urban areas, the "Acela"'s corridor includes several speed restrictions below over older bridges, or through tunnels a century old or more. Altogether, Amtrak has identified 224 bridges along "Acela"'s route that are beyond their design life.  To prepare for the "Acela" launch, Amtrak upgraded the track along the Connecticut shoreline east of New Haven to allow maximum speeds in excess of. West of New York City, the "Acela"'s top speed is. One limiting factor is the overhead catenary support system which was constructed before 1935 and lacks the constant-tension features of the new catenary east of New Haven. The Pennsylvania Railroad ran "Metroliner" test trains in the late 1960s as fast as and briefly intended to run the "Metroliner" service at speeds reaching. Certification testing for commercial operation at involving test runs at up to began between Trenton and New Brunswick in September 2012.  The slowest section of the electrified NEC is the portion owned by Metro-North Railroad and the Connecticut Department of Transportation between New Haven, Connecticut and New Rochelle, New York and is heavily used by commuter trains. Amtrak's trains here achieve only on a limited stretch in New York State and rarely exceed at any time eastbound through Connecticut until reaching New Haven. In 1992, ConnDOT began plans to upgrade the catenary system, replace outdated bridges, and straighten certain sections of the New Haven Line to enable the "Acela" to run slightly faster. Curve straightening was later deemed too expensive. the catenary replacement and bridge work were under way and expected to be completed by mid-2018.  On July 9, 2007, Amtrak introduced a limited-stop round trip, with trains stopping only at Philadelphia between New York and Washington. This shortened the trip between the two cities to 2 hours 35 minutes, making the trip roughly an hour faster than some of the "Northeast Regional" train services. These trains were an experiment to find ways to expedite travel time on the "Acela"; Amtrak has since dropped them.  "Acela Express"'s fastest schedule between New York and Washington, DC was 2 hours and 45 minutes in 2012. $450 million was allotted by President Barack Obama's administration to replace catenary and upgrade signals between Trenton and New Brunswick, which will allow speeds of over a stretch. The improvements were scheduled to be completed in 2016, but have been delayed; the project is now scheduled to be finished in 2020. This section of track holds the record for the highest speed by a train in the US, which is, achieved in a test run by the U.S./Canada-built UAC TurboTrain on December 20, 1967.

High speed infrastructure.

The dense population of the northeastern United States makes the Northeast Corridor the most heavily traveled portion of the American passenger rail system. Two-thirds of rail passengers in the United States live in or near New York City, also home to the nation's busiest passenger rail station, Penn Station. In order to compete with airliners, Amtrak needed to increase the speed of trains in the region. The former Shore Line from New Haven to Boston is burdened by sharp turns and grade crossings, the crossings being of special concern.  Tilting enables passengers to ride more comfortably on curved sections of track faster than would otherwise be possible, by leaning into the bend. "Acela" trainsets tilt above on most of the system, but some segments of track in the Northeast Corridor are too close together for the cars to safely tilt while maintaining FRA minimum space between trains on parallel tracks. Metro-North Railroad restricts tilting on the segment of track north of New York which it owns. The system was originally designed for a 6.8° tilt, but the cars were redesigned wider to accommodate wider seats and aisles that reduced allowable tilt to 4.2° to fit within the clearance constraints of the existing tracks. Traveling at higher than also requires constant-tension catenary, which is only implemented on the more modern catenary system north of New York City. South of New York City, the trains are restricted to. By comparison, the "Northeast Regional" and the now-defunct "Metroliner" service reached.  "Acela" service was originally expected to begin in late 1999 but was delayed. The catenary system could not support the intended speeds between Washington DC and New York City, but the newer system between New York City and Boston allows the higher speeds. Attention was drawn to the decreased 4.2° tilt, but this was not the root of the speed problem, as the tracks from New York to Boston are similar to those between New York and Washington, and the tilt mechanism is not the factor enabling higher speeds. Following repairs, the first "Acela" service began on December 11, 2000, a year behind schedule.  "Acela" travels between Boston and New York in about three and a half hours (an improvement of half an hour); New York to Washington runs take a minimum two hours and forty-five minutes. These schedules, as well as the relative convenience of direct downtown-to-downtown rail service as opposed to air travel, especially after the September 11 attacks, have made the "Acela Express" more competitive with the air shuttles. Due to this competition, Southwest Airlines canceled service between Washington and New York.

Platform track speeds.

Due to the high speed at which "Acela" trains bypass platforms of local stations, concerns have mounted in some communities over inadequate warnings and safeguards for passengers waiting for other trains, including that the two-foot wide yellow platform markings may not keep people at a safe distance. At Kingston station in Rhode Island and Mansfield station in Massachusetts, "Acela" trains pass by at. Suggestions include platform safety barriers, or use of different announcements for approaching "Acela" trains versus slower ones. In 2011, federal transportation grants were awarded to improve Kingston station, including the construction of a third track to be used by the "Acela" as a through track to bypass the station, helping to alleviate safety concerns. Renovations were officially completed on October 30, 2017.

Outages.

In August 2002, shortly after their introduction, "Acela" trainsets were briefly removed from service when the brackets that connected truck (bogie) dampers (shocks) to the powerunit carbodies ("yaw dampers") were found to be cracking. The "Acela" returned to service when a program of frequent inspections was instituted. The damper brackets have since been redesigned and old brackets replaced by the newer design.  On April 15, 2005, the "Acela" was removed from service when cracks were found in the disc brakes of many passenger coaches. The Bombardier-Alstom consortium replaced the discs under warranty. Limited service resumed in July 2005, as a portion of the fleet operated with new brake discs. "Metroliner" trains, which the "Acela Express" was intended to replace, filled in during the outage. Amtrak announced on September 21, 2005, that all 20 trainsets had been returned to full operation.  In March 2020, all "Acela" trips were suspended as part of a round of service reduction in response to the ongoing COVID-19 pandemic. Amtrak resumed "Acela" service on June 1, 2020.

Future Acela trains.

On August 26, 2016, Vice President Joe Biden announced a $2.45 billion federal loan package to pay for new equipment for the "Acela Express" service, as well as upgrades to the NEC. The loans will finance 28 trainsets, named the Avelia Liberty, that will be built by Alstom in Hornell and Rochester, New York and will replace the existing fleet of twenty trainsets.  The fleet expansion will allow for hourly New York-Boston service all day and half-hourly New York-Washington service at peak hours. The new trainsets will be longer, offering 30% greater seating capacity and will feature active tilt technology that would allow service to operate at if infrastructure improvements were completed to allow the higher speeds.  The new trains will be phased in between 2021 and 2022, after which the current fleet is to be retired. Amtrak will pay off the loans from increased NEC passenger revenue.

Service.

Composition.

The production sets are formed as follows:  The "Acela Express" trainset consists of two power cars, a café car, a First Class car, and four Business Class cars, semi-permanently coupled together. It has fewer seats than regional service counterparts. The First Class car has 44 seats, being three seats across (one on one side, two on the other side), four seat tables and assigned seating. There are 260 Business Class seats on each trainset; these cars have four seats across (two on each side) and four-seat tables. Reservations guarantee seating in Business Class, but seats are not assigned. Baggage may be stowed in overhead compartments or underneath seats. Trains are wheelchair-accessible. Each car has or two toilets, with one being ADA compliant.  The Business Class car adjacent to First Class is designated as the quiet car, where passengers are asked to refrain from loud talking and phone conversations. Automatic sliding doors between cars reduce noise.

Operations and staffing.

"Acela" offers two classes of seating, Business Class and First Class. Unlike most other Amtrak trains, Business Class is the "de facto" standard class on "Acela" trains; there is no coach service.  "Acela" maintenance is generally taken care of at the Ivy City facility in Washington, DC; Sunnyside Yard in Queens, New York; or Southampton Street Yard in Boston.  The "Acela" trainsets underwent minor refurbishments between mid-2009 and 2010 at Penn Coach Yard, next to 30th Street Station in Philadelphia, Pennsylvania. These refurbishments included new blue leather seats throughout the trainset.  In May 2018, Amtrak announced a 14-month program to refresh the interiors of the "Acela" trainsets, including new seat cushions and covers, new aisle carpeting, and a deep clean. This refurbishment program has been completed as of June 2019.

Wi-Fi service.

Wireless Internet station service began in 2004. In 2010, with services provided by The GBS Group, all "Acela" trains began offering "AmtrakConnect" supporting IEEE 802.11a/b/g/n, 2.4 GHz and 5 GHz and standard VPN connections. In 2016, Amtrak made a successful effort to upgrade to a faster wifi service.

Staffing.

Generally Amtrak train crews consist of an engineer, a conductor, and at least one assistant conductor. "Acela" trains also have an On-Board Service crew consisting of two First Class attendants and a Cafe Car attendant. In addition to the food service provided in the Cafe Car, on most trains an attendant will also provide at seat cart service, serving refreshments throughout the train. First Class passengers are served meals at their seats on all services. At Amtrak, the On-Board Service crew is considered separate and subordinate to the Train and Engine crews.

The Acela Express ( ; abbreviated to Acela) is Amtrak's flagship service along the Northeast Corridor (NEC) in the Northeastern United States between Washington, D.C. and Boston via 16 intermediate stops, including Providence, Baltimore, Philadelphia, and New York City. The route contains segments of high-speed rail, and "Acela Express" trains are the fastest trainsets in the Americas; they attain on of the route.

Acela Express je americký vysokorychlostní vlak provozovaný národní železniční společností Amtrak. Jednotky jsou nasazovány na tzv. Severovýchodním koridoru mezi městy Washington, D.C. a Boston. Jsou vyráběny ve spolupráci kanadské společnosti Bombardier Inc. a francouzské Alstom. Vyráběn byl v letech 1996–2000.


Solving techniques.

Combinatoric techniques.

Although brute-force guessing is possible, a more efficient approach is the understanding of the various combinatorial forms that entries can take for various pairings of clues and entry lengths. The solution space can be reduced by resolving allowable intersections of horizontal and vertical sums, or by considering necessary or missing values.  Those entries with sufficiently large or small clues for their length will have fewer possible combinations to consider, and by comparing them with entries that cross them, the proper permutation—or part of it—can be derived. The simplest example is where a 3-in-two crosses a 4-in-two: the 3-in-two must consist of "1" and "2" in some order; the 4-in-two (since "2" cannot be duplicated) must consist of "1" and "3" in some order. Therefore, their intersection must be "1", the only digit they have in common.  When solving longer sums there are additional ways to find clues to locating the correct digits. One such method would be to note where a few squares together share possible values thereby eliminating the possibility that other squares in that sum could have those values. For instance, if two 4-in-two clues cross with a longer sum, then the 1 and 3 in the solution must be in those two squares and those digits cannot be used elsewhere in that sum.  When solving sums which have a limited number of solution sets then that can lead to useful clues. For instance, a 30-in-seven sum only has two solution sets: {1,2,3,4,5,6,9} and {1,2,3,4,5,7,8}. If one of the squares in that sum can only take on the values of {8,9} (if the crossing clue is a 17-in-two sum, for example) then that not only becomes an indicator of which solution set fits this sum, it eliminates the possibility of any other digit in the sum being either of those two values, even before determining which of the two values fits in that square.  Another useful approach in more complex puzzles is to identify which square a digit goes in by eliminating other locations within the sum. If all of the crossing clues of a sum have many possible values, but it can be determined that there is only one square which could have a particular value which the sum in question must have, then whatever other possible values the crossing sum would allow, that intersection must be the isolated value. For example, a 36-in-eight sum must contain all digits except 9. If only one of the squares could take on the value of 2 then that must be the answer for that square.

Box technique.

A "box technique" can also be applied on occasion, when the geometry of the unfilled white cells at any given stage of solving lends itself to it: by summing the clues for a series of horizontal entries (subtracting out the values of any digits already added to those entries) and subtracting the clues for a mostly overlapping series of vertical entries, the difference can reveal the value of a partial entry, often a single cell. This technique works because addition is both associative and commutative.  It is common practice to mark potential values for cells in the cell corners until all but one have been proven impossible; for particularly challenging puzzles, sometimes entire ranges of values for cells are noted by solvers in the hope of eventually finding sufficient constraints to those ranges from crossing entries to be able to narrow the ranges to single values. Because of space constraints, instead of digits some solvers use a positional notation, where a potential numerical value is represented by a mark in a particular part of the cell, which makes it easy to place several potential values into a single cell. This also makes it easier to distinguish potential values from solution values.  Some solvers also use graph paper to try various digit combinations before writing them into the puzzle grids.  As in the Sudoku case, only relatively easy Kakuro puzzles can be solved with the above-mentioned techniques. Harder ones require the use of various types of chain patterns, the same kinds as appear in Sudoku (see "Pattern-Based Constraint Satisfaction and Logic Puzzles").

Mathematics of Kakuro.

Mathematically, Kakuro puzzles can be represented as integer programming problems, and are NP-complete. See also Yato and Seta, 2004.  There are two kinds of mathematical symmetry readily identifiable in Kakuro puzzles: minimum and maximum constraints are duals, as are missing and required values.  All sum combinations can be represented using a bitmapped representation. This representation is useful for determining missing and required values using bitwise logic operations.

Popularity.

Kakuro puzzles appear in nearly 100 Japanese magazines and newspapers. Kakuro remained the most popular logic puzzle in Japanese printed press until 1992, when Sudoku took the top spot. In the UK, they first appeared in "The Guardian" with "The Telegraph" and the "Daily Mail" following.

Variants.

A relatively common variant of Kakuro is "Cross Products" (or "Cross Multiplication"), where the clues are the product of the digits in the entries rather than the sum. Dell Magazines has produced such puzzles but also allowed repeating of digits aside from 1 because of space limitations in the number of digits in each product in a puzzle. Puzzles by Games Magazines are more like crossword puzzles, allowing the implementation of the no-repeating digits rule.  Another variant is having a different range of values that are inserted in the cells, such as 1 to 12, instead of the standard 1 to 9.  A genuine combination of Sudoku and Kakuro is the so-called "Cross Sums Sudoku" in which clues are given as cross sums on a standard 9 x 9 Sudoku grid. A relevant variant is the so-called "Cryptic Kakuro" where the clues are given in terms of alphametics and each number represents a digit from 1 to 9.  The final puzzle of the 2004 United States qualifier for the World Puzzle Championship is titled "Cross Number Sums Place": it is a "Cross Sums" where every row and column of the grid (except the top row and leftmost column as usual) contains exactly nine white cells, none of which—even across multiple entries—are allowed to use the same digit twice, like a "Number Place" ("Sudoku"); in addition, small circles are printed on the borders between some white cells; numerically adjacent digits must be placed astride those circles, and may not appear orthogonally adjacent when not astride a circle.

Kakuro or Kakkuro () is a kind of logic puzzle that is often referred to as a mathematical transliteration of the crossword. Kakuro puzzles are regular features in many math-and-logic puzzle publications across the world. In 1966, Canadian Jacob E. Funk, an employee of Dell Magazines, came up with the original English name "Cross Sums" and other names such as "Cross Addition" have also been used, but the Japanese name "Kakuro," abbreviation of Japanese "kasan kurosu" (加算クロス, "addition cross"), seems to have gained general acceptance and the puzzles appear to be titled this way now in most publications. The popularity of Kakuro in Japan is immense, second only to Sudoku among Nikoli's famed logic-puzzle offerings.

Kakuro je logická číselná hra. Kakuro je hra podobná sudoku či klasické křížovce, která spočívá v doplňování čísel do prázdných políček. Do dané části řádku či sloupce je třeba doplnit různá (tj. neopakující se) čísla 1 až 9 tak, aby jejich součet vždy odpovídal číslu zadanému vlevo od této části řádku (resp. nad touto částí sloupce).