History.

The term "Algic" was first coined by Henry Schoolcraft in his "Algic Researches", published in 1839. Schoolcraft defined the term as "derived from the words Allegheny and Atlantic, in reference to the indigenous people anciently located in this geographical area." Schoolcraft's terminology was not retained. The peoples he called "Algic" were later included among the speakers of Algonquian languages. This language group is also referred to as "Algonquian-Ritwan" and "Wiyot-Yurok-Algonquian"  When Edward Sapir proposed that the well-established Algonquian family was genetically related to the Wiyot and Yurok languages of northern California, he applied the term "Algic" to this larger family. The Algic urheimat is thought to have been located in the Northwestern United States somewhere between the suspected homeland of the Algonquian branch (to the west of Lake Superior according to Goddard) and the earliest known location of the Wiyot and Yurok (along the middle Columbia River according to Whistler).

Classification of Algic.

The genetic relation of Wiyot and Yurok to Algonquian was first proposed by Edward Sapir (1913, 1915, 1923), and argued against by Algonquianist Truman Michelson (1914, 1914, 1935). According to Lyle Campbell (1997), the relationship "has subsequently been demonstrated to the satisfaction of all". This controversy in the early classification of North American languages was called the "Ritwan controversy" because Wiyot and Yurok were assigned to a genetic grouping called "Ritwan". Most specialists now reject the validity of the Ritwan genetic node. Berman (1982) suggested that Wiyot and Yurok share sound changes not shared by the rest of Algic (which would be explainable by either areal diffusion or genetic relatedness); Proulx (2004) argued against Berman's conclusion of common sound changes.  More recently, Sergei Nikolaev has argued in two papers for a systematic relationship between the Nivkh language of Sakhalin and the Amur river basin and the Algic languages, and a secondary relationship between these two together and the Wakashan languages.

The Algic (also Algonquian–Wiyot–Yurok or Algonquian–Ritwan) languages are an indigenous language family of North America. Most Algic languages belong to the Algonquian subfamily, dispersed over a broad area from the Rocky Mountains to Atlantic Canada. The other Algic languages are the Yurok and Wiyot of northwestern California, which, despite their geographic proximity, are not closely related. All these languages descend from Proto-Algic, a second-order proto-language estimated to have been spoken about 7,000 years ago and reconstructed using the reconstructed Proto-Algonquian language and the Wiyot and Yurok languages.

阿尔吉克语系(英:Algic languages)是北美洲原住民语言语系,主要使用在北美洲的北部地区,包括加拿大和美国的一些省份。语系内多数语言属于阿尔冈昆语族,分布在北美东岸至落基山脉的地区,此外还有尤罗克语和维约特语,分布在加州西北。


History.

Leonardo da Vinci's "Salvator Mundi" may have been painted for Louis XII of France and his consort, Anne of Brittany. It was probably commissioned around 1500, shortly after Louis conquered the Duchy of Milan and took control of Genoa in the Second Italian War. Leonardo himself moved from Milan to Florence in 1500. Various copies of the painting were made by followers of Leonardo including his pupil Salaì (1511). Some versions differ significantly from the original, with a few, including one by his pupil Marco d'Oggiono (c. 1500) and another by Salaì depicting a more youthful subject.  Leonardo's painting seems to have been at James Hamilton's Chelsea Manor in London from 1638 to 1641. After participating in the English Civil War, Hamilton was executed on 9 March 1649 and some of his possessions were taken to the Netherlands to be sold. Bohemian artist Wenceslaus Hollar could have made his engraved copy, dated 1650, in Antwerp at that time. It was also recorded in Henrietta Maria's possession in 1649, the same year her husband Charles I was executed, on 30 January. The painting was included in an inventory of the Royal Collection, valued at £30, and Charles' possessions were put up for sale under the English Commonwealth. The painting was sold to a creditor in 1651, returned to Charles II after the English Restoration in 1660, and included in an inventory of Charles' possessions at the Palace of Whitehall in 1666. It was inherited by James II, and may have remained with him until it passed to his mistress Catherine Sedley, whose illegitimate daughter with James became the third wife of John Sheffield, Duke of Buckingham. The duke's illegitimate son, Sir Charles Herbert Sheffield, auctioned the painting in 1763 along with other artworks from Buckingham House when the building was sold to George III.  The painting was likely placed in a gilded frame in the 19th century, which it remained in until 2005. It was bought by British collector Francis Cook in 1900 for his collection at Doughty House in Richmond. The painting had been damaged from previous restoration attempts and was attributed to Bernardino Luini, a follower of Leonardo. Cook's great-grandson sold it at auction in 1958 for £45 as a work by Leonardo's pupil Giovanni Antonio Boltraffio, whom the painting remained attributed to until 2011.

Rediscovery and restoration.

"Salvator Mundi" is one of Leonardo's most copied paintings, with about 12 known examples executed by his pupils and others. Leonardo's version was thought to have been lost after the mid-17th century. In 1978, Joanne Snow-Smith developed a compelling case that the located in the Marquis Jean-Louis de Ganay Collection, Paris, was the lost original based on its similarity to "Saint John the Baptist". Many art historians were convinced, as she was able to establish a direct historical connection between Leonardo da Vinci, the engraving by Wenceslaus Hollar and the painting in the Ganay collection.  In 2005, a "Salvator Mundi" was presented and acquired at an auction for less than $10,000 (€8,450) by a consortium of art dealers that included Alexander Parrish and Robert Simon, a specialist in Old Masters. It was sold from the estate of Baton Rouge businessman Basil Clovis Hendry Sr., at the St. Charles Gallery auction house in New Orleans. It had been heavily overpainted so it looked like a copy, and was, before restoration, described as "a wreck, dark and gloomy".  The consortium believed there was a possibility that this seemingly low-quality work might actually be the long-missing da Vinci original. They commissioned Dianne Dwyer Modestini at New York University to oversee the restoration. She began by removing the overpainting with acetone, leading her to discover that at some point, a stepped area of unevenness near Christ's face had been shaved down with a sharp object, and also leveled with a mixture of gesso, paint and glue. Using infrared photographs Simon had taken of the painting, Modestini discovered a pentimento (earlier draft) of the painting which had the blessing hand's thumb in a straight, rather than curved, position. The discovery that Christ had two thumbs on his right hand was crucial. This pentimento (literally'repent') showed the artist had a second thought about the positioning of the thumb. Such a second thought is considered evidence that this is not a copy but indeed an original, since copiers would have no doubts about composition.  Modestini proceeded to have panel specialist Monica Griesbach chisel off a marouflaged wood panel which had been tunnelled through by worms, causing the painting to break into seven pieces. Griesbach reassembled the painting with adhesive and wood slivers. In late 2006, Modestini began her restoration effort. Art historian Martin Kemp was critical of the result: "Both thumbs" of the painting's raw state "are rather better than the one painted by Dianne." The work was subsequently authenticated as a painting by Leonardo. From November 2011 through February 2012, the painting was exhibited at the National Gallery as a work by Leonardo da Vinci, after authentication by that facility. In 2012, it was also authenticated by the Dallas Museum of Art.  In May 2013, the Swiss dealer Yves Bouvier purchased the painting for just over US$75 million (in a private sale brokered by Sotheby's, New York). The painting was then sold to Russian collector Dmitry Rybolovlev for US$127.5 million. The price that Rybolovev paid was therefore significantly higher, well beyond the 2 percent commission Bouvier was supposed to receive, according to Dmitry Rybolovlev. Consequently, this sale—along with several other sales Bouvier made to Rybolovlev—created a legal dispute between Rybolovlev and Bouvier, as well as between the original dealers of the painting and Sotheby's. In 2016, the dealers sued Sotheby's for the difference of the sale, arguing they were shortchanged. The auction house has denied knowing that Rybolovlev was the intended buyer, and sought to dismiss the lawsuit. In 2018, Rybolovlev also sued Sotheby's for $380 million, alleging the auction house knowingly participated in a defrauding scheme by Bouvier, in which the painting played a part. Unearthed email exchanges between Bouvier and the auction house seem to confirm this, according to Rybolovlev's lawyers.  It was exhibited in Hong Kong, London, San Francisco and New York in 2017, and then sold at auction at Christie's in New York on 15 November 2017 for $450,312,500, a new record price for an artwork (hammer price $400 million plus $50.3 million in fees). The purchaser was identified as Saudi Arabian prince Badr bin Abdullah. In December 2017, the "Wall Street Journal" reported that Prince Badr was an intermediary for Crown Prince Mohammed bin Salman. However, Christie's confirmed that Prince Badr acted on behalf of Abu Dhabi's Department of Culture and Tourism for display at the Louvre Abu Dhabi. In September 2018, the exhibition was indefinitely postponed, and a January 2019 news report indicated that "no one knows where it is, and there are grave concerns for its physical safety." Georgina Adam, editor at large of "The Art Newspaper", dismissed these reports, stating that "We believe it's in storage in Geneva." It was later reported to be on a luxury yacht belonging to bin Salman, sailing on the Red Sea as of June 2019.  Just as the painting did not appear at the Abu Dhabi Louvre in 2018, it was not included in the Louvre's Paris exhibition of Leonardo works held from 24 October 2019 to 24 February 2020. A full 11 of the fewer than 20 paintings that da Vinci completed in his lifetime were displayed.

Attribution.

About a year into her restoration effort, Dianne Dwyer Modestini noted that color transitions in the subject's lips were "perfect" and that "no other artist could have done that." Upon studying the "Mona Lisa" for comparison, she concluded that "The artist who painted her was the same hand that had painted the "Salvator Mundi"."  In 2006, National Gallery director Nicholas Penny wrote that he and some of his colleagues considered the work a Leonardo original, but that "some of us consider that there may be [parts] which are by the workshop." Penny conducted a side-by-side study of the "Salvator Mundi" and "Virgin of the Rocks" in 2008. Martin Kemp later said of the meeting, "I left the studio thinking Leonardo must be heavily involved," and that "No one in the assembly was openly expressing doubt that Leonardo was responsible for the painting." In a 2011 consensus decision facilitated by Penny, the attribution to Leonardo da Vinci was agreed upon unequivocally. By July 2011, separate press release documents were issued by the owners' publicity representative and the National Gallery, officially announcing the "new discovery". Once it was cleaned and restored, the painting was compared with, and found superior to, twenty other versions of "Salvator Mundi". It was exhibited by London's National Gallery during the "Leonardo da Vinci: Painter at the Court of Milan" from November 2011 to February 2012. Several features in the painting have led to the positive attribution: a number of "pentimenti" are evident, most notably the position of the right thumb. The sfumato effect of the face—evidently achieved in part by manipulating the paint using the heel of the hand—is typical of many Leonardo works. The way the ringlets of hair and the knotwork across the stole have been handled is also seen as indicative of Leonardo's style. Furthermore, the pigments and the walnut panel upon which the work was executed are consistent with other Leonardo paintings. Additionally, the hands in the painting are very detailed, something that Leonardo is known for: he would dissect the limbs of the deceased in order to study them and render body parts in an extremely lifelike manner.  One of the world's leading Leonardo experts, Martin Kemp, who helped authenticate the work, said that he knew immediately upon first viewing the restored painting that it was the work of Leonardo: "It had that kind of presence that Leonardos have... that uncanny strangeness that the later Leonardo paintings manifest." Of the better-preserved parts, such as the hair, Kemp notes: "It's got that kind of uncanny vortex, as if the hair is a living, moving substance, or like water, which is what Leonardo said hair was like." Kemp also states: However skilled Leonardo's followers and imitators might have been, none of them reached out into such realms of "philosophical and subtle speculation". We cannot reasonably doubt that here, we are in the presence of the painter from Vinci. Walter Isaacson in his biography of Leonardo wrote that the orb that Christ is holding does not correspond to the way an orb would realistically look: In one respect, it is rendered with beautiful scientific precision, but Leonardo failed to paint the distortion that would occur when looking through a solid clear orb at objects that are not touching the orb. Solid glass or crystal, whether shaped like an orb or a lens, produces magnified, inverted, and reversed images. Instead, Leonardo painted the orb as if it were a hollow glass bubble that does not refract or distort the light passing through it. Isaacson believes that this was "a conscious decision on Leonardo's part", and speculates that either Leonardo felt a more accurate portrayal would be distracting, or that "he was subtly trying to impart a miraculous quality to Christ and his orb." Kemp, on the other hand, says that the doubled outline of the heel of the hand holding the sphere—which the restorer described as a pentimento—is an accurate rendering of the refraction produced by a calcite (or rock crystal) sphere. Kemp notes that the double refraction is typical of the type produced by a transparent calcite sphere. Kemp further notes that the orb "sparkles with a series of internal inclusions (or pockets of air)"—evidence supporting its solid nature.. More recently, the globe has been also interpreted as a magnifying instrument consisting of a vitreous globe filled with water.  Other versions or copies of "Salvator Mundi" often portray a brass, solid spherical orb, terrestrial globe, or globus cruciger; occasionally, they appear to be made of translucent glass, or show landscapes within them. The orb in Leonardo's painting, Kemp says, has "an amazing series of glistening little apertures—they're like bubbles, but they're not round—painted very delicately, with just a touch of impasto, a touch of dark, and these little sort of glistening things, particularly around the part where you get the back reflections." These are the characteristic features of rock crystal, which Leonardo was an avid expert on. He had been asked to evaluate vases that Isabella d'Este had thought of purchasing, and greatly admired the properties of the mineral.  Iconographically, the crystal sphere relates to the heavens. In Ptolemaic cosmology, the stars were embedded in a fixed celestial crystalline sphere (composed of aether), with the spherical Earth at the center of the universe. "So what you've got in the "Salvator Mundi"", Kemp states, "is really 'a savior of the cosmos', and this is a very Leonardesque transformation." Another aspect of Leonardo's painting Kemp studied was depth of field, or shallow focus. Christ's blessing hand appears to be in sharp focus, whereas his face—though altered or damaged to some extent—is in soft focus. Leonardo's Manuscript D of 1508–1509, explored theories of vision, optics of the eye, and theories relating to shadow, light and color. In "Salvator Mundi", the artist deliberately placed an emphasis on parts of the picture over others. Elements in the foreground are seen with a sense of focus, while elements further removed are barely in focus, such as the subject's face. Manuscript D shows Leonardo was investigating this particular phenomenon around the turn of the century. Combined, the intellectual aspects, optical aspects, and the use of semi-precious minerals, are distinctive of Leonardo's oeuvre. "There is extraordinary consensus it is by Leonardo," said the former co-chairman of old master paintings at Christie's, Nicholas Hall: "This is the most important old master painting to have been sold at auction in my lifetime." Christie's lists the ways scholars confirmed the attribution to Leonardo da Vinci:  The reasons for the unusually uniform scholarly consensus that the painting is an autograph work by Leonardo are several, including the previously mentioned relationship of the painting to the two autograph preparatory drawings in Windsor Castle; its correspondence to the composition of the 'Salvator Mundi' documented in Wenceslaus Hollar's etching of 1650; and its manifest superiority to the more than 20 known painted versions of the composition.Furthermore, the extraordinary quality of the picture, especially evident in its best-preserved areas, and its close adherence in style to Leonardo's known paintings from circa 1500, solidifies this consensus.  According to Robert Simon, "Leonardo painted the "Salvator Mundi" with walnut oil rather than linseed oil, as all the other artists in that period did.... In fact, he wrote about using walnut oil, as it was a new advanced technique." Simon also says that ultraviolet imaging reveals that the restoration mostly accounts for darker areas of the painting; the rest is original paint.  Author Ben Lewis, who disputes complete attribution to Leonardo, admits its possibility, owing to the originality of the face, which has "something modern about it." Kemp says: I don't rule out the possibility of studio participation.... But I cannot define any areas that I would say are studio work.

Partial attribution.

Some respected experts on Renaissance art question the full attribution of the painting to Leonardo. Jacques Franck, a Paris-based art historian and Leonardo specialist who has studied the "Mona Lisa" out of the frame multiple times, stated: "The composition doesn't come from Leonardo, he preferred twisted movement. It's a good studio work with a little Leonardo at best, and it's very damaged. It's been called 'the male Mona Lisa', but it doesn't look like it at all."  Michael Daley, the director of ArtWatch UK, doubts the "Salvator Mundi"s authenticity and theorizes that it may be the prototype of a subject painted by Leonardo: "This quest for an autograph prototype Leonardo painting might seem moot or vain: not only do the two drapery studies comprise the only accepted Leonardo material that might be associated with the group, but within the Leonardo literature there is no documentary record of the artist ever having been involved in such a painting project."  Carmen Bambach, Italian Renaissance art specialist at the Metropolitan Museum of Art, questioned full attribution to Leonardo: "having studied and followed the picture during its conservation treatment, and seeing it in context in the National Gallery exhibition, much of the original painting surface may be by Boltraffio, but with passages done by Leonardo himself, namely Christ's proper right blessing hand, portions of the sleeve, his left hand and the crystal orb he holds." In 2019, Dr. Bambach criticised Christie's for its claim that she was one of the experts who had attributed the painting to Leonardo. In her forthcoming book "Leonardo da Vinci Rediscovered", she is even more specific, attributing most of the work to Boltraffio, "with only'small retouchings' by the master himself".  Matthew Landrus, an art historian at the University of Oxford agreed with the concept of parts of the painting being executed by Leonardo ("between 5 and 20%"), but attributes the painting to Leonardo's studio assistant Bernardino Luini, noting Luini's ability in painting gold tracery.  Frank Zöllner, the author of the catalogue raisonné "Leonardo da Vinci. The Complete Paintings and Drawings". writes: This attribution is controversial primarily on two grounds. Firstly, the badly damaged painting had to undergo very extensive restoration, which makes its original quality extremely difficult to assess. Secondly, the "Salvator Mundi" in its present state exhibits a strongly developed "sfumato" technique that corresponds more closely to the manner of a talented Leonardo pupil active in the 1520s than to the style of the master himself. The way in which the painting was placed on the market also gave rise to concern.  Zöllner also explains that the quality of "Salvator Mundi" surpasses other known versions, however,  [it] also exhibits a number of weaknesses. The flesh tones of the blessing hand, for example, appear pallid and waxen as in a number of workshop paintings. Christ's ringlets also seem to me too schematic in their execution, the larger drapery folds too undifferentiated, especially on the right-hand side.... It will probably only be possible to arrive at a more informed verdict on this question after the results of the painting's technical analyses have been published in full (Dalivalle/Kemp/Simon 2017).  In Paris, the Louvre's request for "Salvator Mundi" to be exhibited in the 2019–20 Leonardo de Vinci exhibition was reportedly met without response, leading some to speculate that its non-presence was due to doubts over its full attribution to the artist. Kemp disputes this reasoning, saying: It's simply untrue... because even if the Louvre was persuaded that there was studio participation in the picture, which would be feasible and not unknown after all, it wouldn't stop them from showing it. It's a major picture, an important thing. The story is sensationalized and inaccurate.

Rejection of attribution.

British art historian Charles Hope dismissed the attribution to Leonardo entirely in a 2020 analysis of the painting's quality and provenance. He doubted that Leonardo would have painted a work where the eyes were not level and the drapery undistorted by a crystal orb. He added, "The picture itself is a ruin, with the face much restored to make it reminiscent of the Mona Lisa." Hope condemned the National Gallery's involvement in Simon's "astute" marketing campaign.

Reception.

The rediscovered painting by Leonardo generated considerable interest within the media and general public amid its pre-auction viewings in Hong Kong, London, San Francisco and New York. Over 27,000 people saw the work in person before the auction: the highest number of pre-sale viewers for an individual work of art, according to Christie's. Never before had Christie’s used an outside agency to advertise an artwork. Around 4,500 stood in line to preview the work in New York the weekend prior to the sale.  Referred to as the "Last da Vinci", "Salvator Mundi" was the only known painting by Leonardo still in private hands. Fewer than twenty other known works by Leonardo are held in museums around the world, including the "Mona Lisa" and "The Last Supper". The only work by Leonardo in North America, "Ginevra de' Benci", is held at the National Gallery of Art in Washington, D.C. The museum purchased "Ginevra" in 1967 for $5 million in a private sale (equivalent to approximately $36.4 million in 2017), a world record at the time. "Salvator Mundi" is the first painting by the artist to appear in a public sale for 100 years.

References.

Footnotes Citations

Salvator Mundi is a painting by Italian Renaissance artist Leonardo da Vinci dated to 1500. Long thought to be a copy of a lost original veiled with overpainting, it was rediscovered, restored, and included in a major Leonardo exhibition at the National Gallery, London, in 2011–12. Although most leading scholars have considered it to be an original work by Leonardo, this attribution has been disputed by other specialists, some of whom posit that he only contributed certain elements.

《救世主》()是列奥纳多·达·芬奇的其中一幅画作。过去它曾隐没很长一段时间,甚至一度被认为只是达芬奇弟子的作品。2004年,纽约的罗伯·赛门(Robert Simon)以低价买下该画作。并交由专家修复与鉴定后,2011年终于重现在世人面前。是一模拟肖像画制作的空想作品。


Boundaries.

The southern boundary with the Cocos Plate to the west and the Caribbean Plate to the east is a transform fault, represented by the Swan Islands Transform Fault under the Caribbean Sea and the Motagua Fault through Guatemala. The parallel Septentrional and Enriquillo–Plantain Garden faults, which run through the island of Hispaniola and bound the Gonâve Microplate, are also a part of the boundary. The rest of the southerly margin which extends east to the Mid Atlantic Ridge and marks the boundary between the North American Plate and the South American Plate is vague but located near the Fifteen-Twenty Fracture Zone around 16°N.  On the northerly boundary is a continuation of the Mid-Atlantic ridge called the Gakkel Ridge. The rest of the boundary in the far northwestern part of the plate extends into Siberia. This boundary continues from the end of the Gakkel Ridge as the Laptev Sea Rift, on to a transitional deformation zone in the Chersky Range, then the Ulakhan Fault between it and the Okhotsk Plate, and finally the Aleutian Trench to the end of the Queen Charlotte Fault system.  The westerly boundary is the Queen Charlotte Fault running offshore along the coast of Alaska and the Cascadia subduction zone to the north, the San Andreas Fault through California, the East Pacific Rise in the Gulf of California, and the Middle America Trench to the south.  On its western edge, the Farallon Plate has been subducting under the North American Plate since the Jurassic Period. The Farallon Plate has almost completely subducted beneath the western portion of the North American Plate leaving that part of the North American Plate in contact with the Pacific Plate as the San Andreas Fault. The Juan de Fuca, Explorer, Gorda, Rivera, Cocos and Nazca plates are remnants of the Farallon Plate.  The boundary along the Gulf of California is complex. The Gulf is underlain by the Gulf of California Rift Zone, a series of rift basins and transform fault segments between the northern end of the East Pacific Rise in the mouth of the gulf to the San Andreas Fault system in the vicinity of the Salton Trough rift/Brawley seismic zone.  It is generally accepted that a piece of the North American Plate was broken off and transported north as the East Pacific Rise propagated northward, creating the Gulf of California. However, it is as yet unclear whether the oceanic crust east of the Rise and west of the mainland coast of Mexico is actually a new plate beginning to converge with the North American Plate, consistent with the standard model of rift zone spreading centers generally.

Hotspots.

A few hotspots are thought to exist below the North American Plate. The most notable hotspots are the Yellowstone (Wyoming), Jemez Lineament (New Mexico), and Anahim (British Columbia) hotspots. These are thought to be caused by a narrow stream of hot mantle convecting up from the Earth's core–mantle boundary called a mantle plume, although some geologists think that upper mantle convection is a more likely cause. The Yellowstone and Anahim hotspots are thought to have first arrived during the Miocene period and are still geologically active, creating earthquakes and volcanoes. The Yellowstone hotspot is most notable for the Yellowstone Caldera and the many calderas that lie in the Snake River Plain while the Anahim hotspot is most notable for the Anahim Volcanic Belt, currently found in the Nazko Cone area.

Plate motion.

For the most part, the North American Plate moves in roughly a southwest direction away from the Mid-Atlantic Ridge at a rate of about 2.3 centimeters (~1 inch) per year. At the same time, the Pacific Plate is moving to the northwest at a speed of between 7 and 11 centimeters (~3-4 inches) a year.  The motion of the plate cannot be driven by subduction as no part of the North American Plate is being subducted, except for a small section comprising part of the Puerto Rico Trench; thus other mechanisms continue to be investigated.  One recent study suggests that a mantle convective current is propelling the plate.

The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of, it is the Earth's second largest tectonic plate, behind the Pacific Plate (which borders the plate to the west).

北美洲板块,或简称北美板块,是一个较大的板块,它的范围覆盖了北美洲的大部,向东延伸至中大西洋海岭,向西延伸至东西伯利亚的切尔斯基山脉。它是1968年勒皮雄首次提出的六大板块中美洲板块的一部分。后来,美洲板块又被细分为北部的北美洲板块、南部的南美洲板块和周围的一些小板块。由于不同的板块划分方案中承认的小板块数目不同,因此北美洲板块的边界随各家观点不同而不同。例如早先多把鄂霍次克板块(在勒皮雄的六大板块划分中,这一地区属于欧亚板块)也作为北美洲板块的一部分,这样北美洲板块就向西一直延伸到鄂霍次克海和日本东北部。但最新研究表明,鄂霍次克板块应该是一个独立的板块。


History.

Historically a "Colonel-in-Chief" was the ceremonial head of a regiment, usually a member of a European country's royal family. The practice extends at least back to 1740 in Prussia when Frederick II held that position in the newly created Garde du Corps, an elite heavy cavalry regiment.  By the late 19th Century the designation could be given to the children of royalty; pictures exist of the daughters of Russian Czar Nicholas II in the uniforms of their regiments. The German Kaiser Wilhelm II carried the title to an extreme, holding it in literally dozens of German and (by diplomatic courtesy) Austro-Hungarian, British, Russian, and Portuguese regiments. In addition, his mother, wife, son, and daughters were also full or deputy Colonels-in-Chief of various units.

Role.

In modern usage, the Colonel-in-Chief of a regiment is its (usually royal) patron, who has a ceremonial role in the life of the regiment. They do not have an operational role, or the right to issue orders, but are kept informed of all important activities of the regiment and pay occasional visits to its units. The chief purpose of the Colonel-in-Chief is to maintain a direct link between the regiment and the royal family. Some artillery regiments have a Captain-General instead of a Colonel-in-Chief, but the posts are essentially the same.  The position of Colonel-in-Chief is distinct from the other ceremonial regimental posts of Colonel of the Regiment and Honorary Colonel, which are usually retired military officers or public figures with ties to the regiment.  Colonels-in-Chief are appointed at the invitation of the regiment. While it is traditional for a royal personage to hold the position, it is at the discretion of the regiment or corps whom they invite. , most Colonels-in-Chief in the British Army are members of the British royal family. However, two foreign monarchs hold the position: In the past non-royal persons have held, or been invited to hold, the post of Colonel-in-Chief. The Duke of Wellington was Colonel-in-Chief of the regiment that bore his name, whilst Winston Churchill was Honorary Colonel of the 4th Queen's Own Hussars, the regiment he served in before entering politics. The Governor General of Canada Adrienne Clarkson was invited to be Colonel-in-Chief of Princess Patricia's Canadian Light Infantry, while the Royal Australian Army Medical Corps decided to ask the Governor-General of Australia to serve as its Colonel-in-Chief. These exceptions, however, do not change the raison d'être of the post, which is to serve as a personal link between regiment and Monarch.  The role has spread to other armies in the Commonwealth of Nations, at least in countries which have royal families.

Colonel-in-Chief is a ceremonial position in a military regiment. It is in common use in several Commonwealth armies, where it is held by the regiment's patron, usually a member of the royal family. The position was formerly used in the armies of several European monarchies. A Colonel-in-Chief has a purely ceremonial role in their regiment.

名誉上校或荣誉上校(英语:Colonel-in-Chief)在英联邦国家军队是指一个军团的守护人,传统上是由皇室成员来担任。 名誉上校不需要像正式的上校一样负责团内的职务,但是他有必要了解团内正在进行的重要活动,并不定时到团内巡视,维持军队与皇室之间的联系。目前的英国陆军,有两位外国君主在英国的团内担任这个职位:


Example.

A typical example of vulnerable application in PHP code is: <?php $template ='red.php'; if (isset($_COOKIE['TEMPLATE'])) { include ("/home/users/phpguru/templates/". $template);  An attack against this system could be to send the following HTTP request:  GET /vulnerable.php HTTP/1.0 Cookie: TEMPLATE=../../../../../../../../../etc/passwd Generating a server response such as:  HTTP/1.0 200 OK Content-Type: text/html Server: Apache  root:fi3sED95ibqR6:0:1:System Operator:/:/bin/ksh daemon:*:1:1::/tmp: phpguru:f8fk3j1OIf31.:182:100:Developer:/home/users/phpguru/:/bin/csh The repeated codice_1 characters after codice_3 has caused codice_4 to traverse to the root directory, and then include the Unix password file codice_5.  Unix codice_5 is a common file used to demonstrate directory traversal, as it is often used by crackers to try cracking the passwords.  However, in more recent Unix systems, the passwd file does not contain the hashed passwords. They are, instead, located in the shadow file which cannot be read by unprivileged users on the machine. It is however, still useful for account enumeration on the machine, as it still displays the user accounts on the system.

Variations of directory traversal.

Listed below are some known directory traversal attack strings:

Directory traversal on Unix.

Common Unix-like directory traversal uses the codice_1 characters. Sudo, a privilege management program ubiquitous in Unix is vulnerable to this attack when users use the glob wildcard (e.g. chown /opt/myapp/myconfig/* could be exploited with the command sudo chown baduser /opt/myapp/myconfig/../../../etc/passwd).

Directory traversal on Microsoft Windows.

Microsoft Windows and DOS directory traversal uses the codice_8 or codice_1 character sequences.  Each partition has a separate root directory (labeled codice_10 for a particular partition C) and there is no common root directory above that. This means that for most directory vulnerabilities on Windows, the attack is limited to a single partition.  This kind of attack has been the cause of numerous Microsoft vulnerabilities.

URI encoded directory traversal.

Canonicalization problem.  Some web applications scan query string for dangerous characters such as: to prevent directory traversal. However, the query string is usually URI decoded before use. Therefore, these applications are vulnerable to percent encoded directory traversal such as:

Unicode / UTF-8 encoded directory traversal.

Canonicalization problem.  UTF-8 was noted as a source of vulnerabilities and attack vectors by Bruce Schneier and Jeffrey Streifling.  When Microsoft added Unicode support to their Web server, a new way of encoding codice_1 was introduced into their code, causing their attempts at directory traversal prevention to be circumvented.  Multiple percent encodings, such as translated into codice_25 or codice_26 characters.  Percent encodings were decoded into the corresponding 8-bit characters by Microsoft webserver. This has historically been correct behavior as Windows and DOS traditionally used canonical 8-bit characters sets based upon ASCII.  However, the original UTF-8 was not canonical, and several strings were now string encodings translatable into the same string. Microsoft performed the anti-traversal checks without UTF-8 canonicalization, and therefore not noticing that (HEX) codice_27 and (HEX) codice_28 were the same character when doing string comparisons. Malformed percent encodings, such as codice_29 was also utilized.

Zip/archive traversal attacks.

The use of archive formats like zip allows for directory traversal attacks: files in the archive can be written such that they overwrite files on the filesystem by backtracking. Code that uncompresses archive files can be written to check that the paths of the files in the archive do not engage in path traversal.

Possible methods to prevent directory traversal.

A possible algorithm for preventing directory traversal would be to:  <?php include($_GET['file']. '.html'); The user can use the NULL character (indicating the end of the string) in order to bypass everything after the $_GET. (This is PHP-specific.)

A directory traversal (or path traversal) consists in exploiting insufficient security validation / sanitization of user-supplied input file names, such that characters representing "traverse to parent directory" are passed through to the file APIs.

目录遍历(英文:),又名路径遍历(英文:)是一种利用网站的安全验证缺陷或用户请求验证缺陷(如传递特定字符串至文件应用程序接口)来列出服务器目录的漏洞利用方式。


Education and outreach programs.

The ASP's mission is to promote public interest in and awareness of astronomy (and increase scientific literacy) through its publications, web site, and many educational and outreach programs.  The ASP assists with astronomy education and outreach by partnering with other organizations both in the United States and internationally, and organizes an annual meeting to promote the appreciation and understanding of astronomy.

Publications.

The society promotes astronomy education through several publications. The Universe in the Classroom, a free electronic educational newsletter for teachers and other educators around the world who help students of all ages learn more about the wonders of the universe through astronomy.  Mercury, the ASP's quarterly on-line membership magazine, covers a wide range of astronomy topics, from history and archaeoastronomy to cutting-edge developments. First published in 1925 as the "Leaflets of the ASP", "Mercury" is now disseminated to thousands of ASP members and schools, universities, libraries, observatories, and institutions around the world. Mercury Online, a publicly accessible companion blog for "Mercury", was established in 2019 ""to showcase articles by our expert columnists after they've been published in Mercury magazine.""  The ASP also publishes the journal Publications of the Astronomical Society of the Pacific (PASP) aimed at professional astronomers. The "PASP" is a technical journal of refereed papers on astronomical research covering all wavelengths and distance scales as well as papers on the latest innovations in astronomical instrumentation and software, and has been publishing journals since 1889.  The Astronomical Society of the Pacific Conference Series (ASPCS) is a series of over 400 volumes of professional astronomy conference proceedings. Started in 1988, the Conference Series has grown to become a prominent publication series in the world of professional astronomy publications, and has published over 500 volumes. Volumes are sold to the attendees of the conferences of which the proceedings are published, as well as being offered through the Astronomical Society of the Pacific's AstroShop, and can be found in the libraries of major universities and research institutions worldwide. In 2004, the ASPCS stepped into electronic publishing, offering electronic access subscriptions for libraries and institutions, as well as individual access to volumes which they have purchased in hard copy form.  AstroBeat is an on-line ASP-membership column, which comes out every other week, and features a behind-the-scenes report on some aspect of astronomical discovery, astronomy education, or astronomy as a hobby, written by a key participant. Authors have included:

Awards.

The ASP makes several different awards annually:

Affiliations.

The Astronomical Society of the Pacific is an affiliate of the American Association for the Advancement of Science.

Recent presidents.

Presidents of the ASP have included such notable astronomers as Edwin Hubble, George O. Abell, and Frank Drake. George Pardee, who later became Governor of the State of California, served as president in 1899.

Sources.

History of the Astronomical Society of the Pacific

The Astronomical Society of the Pacific (ASP) is an American scientific and educational organization, founded in San Francisco on February 7, 1889. Its name derives from its origins on the Pacific Coast, but today it has members all over the country and the world. It has the legal status of a nonprofit organization.

太平洋天文学会 (Astronomical Society of the Pacific)简称ASP,成立于1889年,具备法定身份的非营利组织。总部在旧金山。


Name.

The name is archaically spelled as "Widdin" in English. Old name "Dunonia" itself meant "fortified hill" in Celtic with the typically "dun" found frequently in Celtic place names.  A historical Romanian name of the city is "Diiu".

Geography.

Vidin is the westernmost important Bulgarian Danube port and is situated on one of the southernmost sections of the river. The New Europe Bridge, completed in 2013, connects Vidin to the Romanian town of Calafat on the opposite bank of the Danube. Previously, a ferry located from the town was in use for that purpose.

History.

Vidin emerged at the place of an old Celtic settlement known as "Dunonia". The settlement evolved into a Roman fortified town called "Bononia". The town grew into one of the important centres of the province of Upper Moesia, encompassing the territory of modern north-western Bulgaria and eastern Serbia.  When Slavs settled in the area, they called the town "Badin" or "Bdin", where the modern name comes from. Similarly, Anna Komnene refers to it as "Vidynē" (Βιδύνη) in the Alexiad.  Vidin's main landmark, the Baba Vida fortress, was built in the period from the 10th to the 14th century. In the Middle Ages Vidin used to be an important Bulgarian city, a bishop seat and capital of a large province. Between 971 and 976 the town was the center of Samuil's possessions while his brothers ruled to the south. In 1003 Vidin was seized by Basil II after an eight-month siege because of the betrayal of the local bishop. Its importance once again rose during the Second Bulgarian Empire (1185–1422) and its "despots" were influential figures in the Empire and were on several occasions chosen for Emperors. From the mid 13th century it was ruled by the Shishman family.  By early 1290s Serbia expanded towards the vicinity of Vidin. Threatened by Serbian expansion, Shishman failed to repel the brothers forces, and accepted Serbian suzerainty. In practice, Shishman continued to be largely independent and dealt mainly with Bulgaria. Serbian suzerainty lasted until Serbian king Stefan Milutin ́s death, in 1321. As Milutin left no testament, after his death, in Serbia occurred a period of civil war with Stefan Dečanski, Stefan Konstantin and Stefan Vladislav II fighting for power. Shishman took advantage of this situation, set free from Serbian rule, and returned to the Bulgarian sphere. In 1323 Shishman was chosen to be the Bulgarian tsar. Shishman made an anti-Serbian treaty with the Byzantines, however, after Serbian victory over Bulgarians in the Battle of Velbazhd in 1330, Bulgaria lay militarily crippled and politically subordinated to Serbia's interests.  In 1356, Bulgarian Tsar Ivan Alexander isolated Vidin from the Bulgarian monarchy and appointed his son Ivan Stratsimir (1356–1396) as absolute ruler of Vidin's new city-state - the Tsardom of Vidin (Bdin / Badin).

Hungarian occupation of Vidin.

In 1365, the Tsardom of Vidin was occupied by Magyar crusaders. Under Hungarian rule, the city became known as "Bodony", but the occupation was short-lived. In 1369, the Second Bulgarian empire drove out the Hungarian military, but in 1396 Vidin was occupied by a foreign force again.

The Ottomans.

The Ottomans went on to conquer the despotates of Dobrudzha, Prilep and Velbazhd as well. Vidin's independence did not last long. In 1396, the Ottomans invaded and turned Vidin into a sanjdak.  In the late years of Ottoman rule, Vidin was the centre of Turkish rebel Osman Pazvantoğlu's breakaway state.  In 1853, "The Times" of London reported that Widdin, as it was called, was  a considerable town, with a population of about 26,000, and a garrison of 8,000 to 10,000 men. Widdin is one of the important fortified places of the military line of the Danube. It covers the approaches of Servia, commands Little Wallachia, the defiles of Transylvania, and, above all, the opening of the road which leads through Nissia and Sophia on to Adrianople. Its form is an irregular pentagon; it is strongly bastioned, possesses a fortified castle, with two redoubts in the islands, and its defences are completed by an extensive marsh.  In 1859 the English traveler Samuel Baker happened to visit Vidin and spotted the 14-year old Romanian Florence Barbara Maria von Sass being sold into slavery, by some accounts destined to be owned by the Pasha of Vidin. Baker redeemed her and took her with him, she eventually became Florence Baker, his wife and partner in the exploration of Africa

Modern rule.

During the Serbo-Bulgarian War (1885), the town was besieged by a Serbian army.

Climate.

Vidin has a humid subtropical climate transforming to temperate continental climate. In the winter months, inversions are very common. The average annual temperature is.

Population.

Vidin is the 20th town by population in Bulgaria, but serious demographic problems have been experienced in the area during the last two decades. The number of the residents of the city reached its peak between 1988 and 1991 when the population exceeded 65,000. As of 2011, the town had a population of 48,071 inhabitants. The following table presents the change of the population after 1887.

Ethnic, linguistic and religious composition.

According to the latest 2011 census data, the individuals declared their ethnic identity were distributed as follows: Total: 48,071

Tourism.

Vidin maintains two well-preserved medieval fortresses, Baba Vida and Kaleto, as well as many old Orthodox churches such as St Pantaleimon, St Petka (both 17th century), and St Dimitar (Demetrius of Thessaloniki) (19th century), the Vidin Synagogue (1894), the Osman Pazvantoğlu Mosque and library, the late 18th-century Turkish ruler of north-western Bulgaria, the Krastata Kazarma of 1798, and a number of old Renaissance buildings. Also remarkable is the theatre building which was the first Bulgarian theatre in "European model" and was built in 1891.  Another tourist attraction in the Vidin area is the town of Belogradchik, famous for its unique and impressive rock formations, the Belogradchik Rocks and the medieval Belogradchik Fortress and also the nearby Magura Cave with its beautiful prehistoric cave paintings.

Transportation.

In Vidin is a border-station to neighbouring Romania via the Danube river. It was operated by ferryboats only until 14 June 2013 when the Vidin–Calafat Bridge opened. Crossing by ferry was possible only every 1⁄2 hour with just five trucks per ferry. Ticket prices were €50 per truck and €12 per car.  The city has an airport (ICAO code "LBVD") a few kilometres to the north-west;, there is no scheduled service, and the buildings are in a state of disrepair.

Landmarks.

Close to the town lies a powerful medium wave broadcasting station (since 1973) whose signals can be easily received throughout Europe. It works on 576 kHz and on 1224 kHz with a power of 500 kW each. For transmission on 576 kHz a guyed mast equipped with a cage antenna at its lower part is used. The transmission of 576 kHz Radio Hristo Botev is on hold for now, because of the world financial crisis and it is unknown when it will resume broadcasting. A powerful FM transmitter on 88.2 MHz provides good coverage for Hristo Botev radio. Only 1224 kHz Radio Bulgaria remains atm. For the transmission on 1224 kHz four guyed masts, insulated against ground, which are each equipped with a cage antenna are used, which allows a switchable directional pattern.

Honour.

Vidin Heights on Livingston Island in the South Shetland Islands, Antarctica is named after Vidin.

International relations.

Twin towns — sister cities.

Vidin is twinned with:

Partner towns.

Partner towns of Vidin:

Sports.

The football team of the town - FC Bdin was established in 1923.

Vidin (, ) is a port town on the southern bank of the Danube in north-western Bulgaria. It is close to the borders with Romania and Serbia, and is also the administrative centre of Vidin Province, as well as of the Metropolitan of Vidin (since 870).

维丁 (保加利亚语:Видин)是位于保加利亚西北部的一个城市。处多瑙河南岸。靠近塞尔维亚与罗马尼亚两国边境。维丁是维丁州的首府所在地。2011年2月,维丁有人口47,138人。维丁是一个农业和贸易中心,并且以葡萄酒著称。南极南设德兰群岛的利文斯顿岛上的维丁高地就得名自维丁。


Overview.

For a given context-free grammar, the parser attempts to find the leftmost derivation. Given an example grammar formula_1:  the leftmost derivation for formula_5 is:  Generally, there are multiple possibilities when selecting a rule to expand the leftmost non-terminal. In step 2 of the previous example, the parser must choose whether to apply rule 2 or rule 3:  To be efficient, the parser must be able to make this choice deterministically when possible, without backtracking. For some grammars, it can do this by peeking on the unread input (without reading). In our example, if the parser knows that the next unread symbol is formula_8, the only correct rule that can be used is 2.  Generally, an formula_9 parser can look ahead at formula_10 symbols. However, given a grammar, the problem of determining if there exists a formula_9 parser for some formula_10 that recognizes it is undecidable. For each formula_10, there is a language that cannot be recognized by an formula_9 parser, but can be by an formula_15.  We can use the above analysis to give the following formal definition:  Let formula_1 be a context-free grammar and formula_17. We say that formula_1 is formula_9, if and only if for any two leftmost derivations:  the following condition holds: the prefix of the string formula_22 of length formula_10 equals the prefix of the string formula_24 of length formula_10 implies formula_26.  In this definition, formula_27 is the start symbol and formula_28 any non-terminal. The already derived input formula_29, and yet unread formula_22 and formula_31 are strings of terminals. The Greek letters formula_32, formula_33 and formula_34 represent any string of both terminals and non-terminals (possibly empty). The prefix length corresponds to the lookahead buffer size, and the definition says that this buffer is enough to distinguish between any two derivations of different words.

Parser.

The formula_9 parser is a deterministic pushdown automaton with the ability to peek on the next formula_10 input symbols without reading. This peek capability can be emulated by storing the lookahead buffer contents in the finite state space, since both buffer and input alphabet are finite in size. As a result, this does not make the automaton more powerful, but is a convenient abstraction.  The stack alphabet is formula_37, where: The parser stack initially contains the starting symbol above the EOI: formula_41. During operation, the parser repeatedly replaces the symbol formula_42 on top of the stack: If the last symbol to be removed from the stack is the EOI, the parsing is successful; the automaton accepts via an empty stack.  The states and the transition function are not explicitly given; they are specified (generated) using a more convenient "parse table" instead. The table provides the following mapping: If the parser cannot perform a valid transition, the input is rejected (empty cells). To make the table more compact, only the non-terminal rows are commonly displayed, since the action is the same for terminals.

Concrete example.

Set up.

To explain an LL(1) parser's workings we will consider the following small LL(1) grammar:  and parse the following input:  An LL(1) parsing table for a grammar has a row for each of the non-terminals and a column for each terminal (including the special terminal, represented here as $, that is used to indicate the end of the input stream).  Each cell of the table may point to at most one rule of the grammar (identified by its number). For example, in the parsing table for the above grammar, the cell for the non-terminal 'S' and terminal '(' points to the rule number 2:  The algorithm to construct a parsing table is described in a later section, but first let's see how the parser uses the parsing table to process its input.

Parsing procedure.

In each step, the parser reads the next-available symbol from the input stream, and the top-most symbol from the stack. If the input symbol and the stack-top symbol match, the parser discards them both, leaving only the unmatched symbols in the input stream and on the stack.  Thus, in its first step, the parser reads the input symbol '(' and the stack-top symbol 'S'. The parsing table instruction comes from the column headed by the input symbol '(' and the row headed by the stack-top symbol 'S'; this cell contains '2', which instructs the parser to apply rule (2). The parser has to rewrite 'S' to '( S + F )' on the stack by removing 'S' from stack and pushing ')', 'F', '+', 'S', '(' onto the stack, and this writes the rule number 2 to the output. The stack then becomes:  In the second step, the parser removes the '(' from its input stream and from its stack, since they now match. The stack now becomes:  Now the parser has an 'a' on its input stream and an 'S' as its stack top. The parsing table instructs it to apply rule (1) from the grammar and write the rule number 1 to the output stream. The stack becomes:  The parser now has an 'a' on its input stream and an 'F' as its stack top. The parsing table instructs it to apply rule (3) from the grammar and write the rule number 3 to the output stream. The stack becomes:  The parser now has an 'a' on the input stream and an 'a' at its stack top. Because they are the same, it removes it from the input stream and pops it from the top of the stack. The parser then has an '+' on the input stream and '+' is at the top of the stack meaning, like with 'a', it is popped from the stack and removed from the input stream. This results in:  In the next three steps the parser will replace 'F' on the stack by 'a', write the rule number 3 to the output stream and remove the 'a' and ')' from both the stack and the input stream. The parser thus ends with '$' on both its stack and its input stream.  In this case the parser will report that it has accepted the input string and write the following list of rule numbers to the output stream:  This is indeed a list of rules for a leftmost derivation of the input string, which is:

Parser implementation in C++.

Below follows a C++ implementation of a table-based LL parser for the example language:  enum Symbols {  Converts a valid token to the corresponding terminal symbol Symbols lexer(char c)  int main(int argc, char **argv)  TERM = 0

Parser implementation in Python.

RULE = 1  T_LPAR = 0 T_RPAR = 1 T_A = 2 T_PLUS = 3 T_END = 4 T_INVALID = 5  N_S = 0 N_F = 1  table = 1, -1, 0, -1, -1, -1],  RULES = (RULE, N_F)],  stack = [(TERM, T_END), (RULE, N_S)]  def lexical_analysis(inputstring):  def syntactic_analysis(tokens):  inputstring = '(a+a)' syntactic_analysis(lexical_analysis(inputstring))

Remarks.

As can be seen from the example, the parser performs three types of steps depending on whether the top of the stack is a nonterminal, a terminal or the special symbol $: These steps are repeated until the parser stops, and then it will have either completely parsed the input and written a leftmost derivation to the output stream or it will have reported an error.

Constructing an LL(1) parsing table.

In order to fill the parsing table, we have to establish what grammar rule the parser should choose if it sees a nonterminal "A" on the top of its stack and a symbol "a" on its input stream. It is easy to see that such a rule should be of the form "A" → "w" and that the language corresponding to "w" should have at least one string starting with "a". For this purpose we define the "First-set" of "w", written here as Fi("w"), as the set of terminals that can be found at the start of some string in "w", plus ε if the empty string also belongs to "w". Given a grammar with the rules "A" → "w",..., "A" → "w", we can compute the Fi("w") and Fi("A") for every rule as follows: The result is the least fixed point solution to the following system: where, for sets of words U and V, the truncated product is defined by U·V = { (uv):1: u ∈ U, v ∈ V }, and w:1 denotes the initial length-1 prefix of words w of length 2 or more, or w, itself, if w has length 0 or 1.  Unfortunately, the First-sets are not sufficient to compute the parsing table. This is because a right-hand side "w" of a rule might ultimately be rewritten to the empty string. So the parser should also use the rule "A" → "w" if ε is in Fi("w") and it sees on the input stream a symbol that could follow "A". Therefore, we also need the "Follow-set" of "A", written as Fo("A") here, which is defined as the set of terminals "a" such that there is a string of symbols "αAaβ" that can be derived from the start symbol. We use $ as a special terminal indicating end of input stream, and "S" as start symbol.  Computing the Follow-sets for the nonterminals in a grammar can be done as follows: This provides the least fixed point solution to the following system: Now we can define exactly which rules will appear where in the parsing table. If "T"["A", "a"] denotes the entry in the table for nonterminal "A" and terminal "a", then Equivalently: "T"["A", "a"] contains the rule "A" → "w" for each "a" ∈ Fi("w")·Fo("A").  If the table contains at most one rule in every one of its cells, then the parser will always know which rule it has to use and can therefore parse strings without backtracking. It is in precisely this case that the grammar is called an "LL(1) grammar".

Constructing an LL("k") parsing table.

The construction for LL(1) parsers can be adapted to LL("k") for "k" > 1 with the following modifications: where an input is suffixed by k end-markers $, to fully account for the k lookahead context.  Until the mid-1990s, it was widely believed that LL("k") parsing (for "k" > 1) was impractical, since the parser table would have exponential size in "k" in the worst case. This perception changed gradually after the release of the Purdue Compiler Construction Tool Set around 1992, when it was demonstrated that many programming languages can be parsed efficiently by an LL("k") parser without triggering the worst-case behavior of the parser. Moreover, in certain cases LL parsing is feasible even with unlimited lookahead. By contrast, traditional parser generators like yacc use LALR(1) parser tables to construct a restricted LR parser with a fixed one-token lookahead.

Conflicts.

As described in the introduction, LL(1) parsers recognize languages that have LL(1) grammars, which are a special case of context-free grammars; LL(1) parsers cannot recognize all context-free languages. The LL(1) languages are a proper subset of the LR(1) languages, which in turn are a proper subset of all context-free languages. In order for a context-free grammar to be an LL(1) grammar, certain conflicts must not arise, which we describe in this section.

Terminology.

Let "A" be a non-terminal. FIRST("A") is (defined to be) the set of terminals that can appear in the first position of any string derived from "A". FOLLOW("A") is the union over: (1) FIRST("B") where "B" is any non-terminal that immediately follows "A" in the right-hand side of a production rule, and (2) FOLLOW("B") where "B" is any head of a rule of the form "B" → "wA".

LL(1) Conflicts.

There are two main types of LL(1) conflicts:

FIRST/FIRST Conflict.

The FIRST sets of two different grammar rules for the same non-terminal intersect. An example of an LL(1) FIRST/FIRST conflict: FIRST("E") = {"b", ε} and FIRST("E" "a") = {"b", "a"}, so when the table is drawn, there is conflict under terminal "b" of production rule "S".

Special Case: Left Recursion.

Left recursion will cause a FIRST/FIRST conflict with all alternatives.

FIRST/FOLLOW Conflict.

The FIRST and FOLLOW set of a grammar rule overlap. With an empty string (ε) in the FIRST set it is unknown which alternative to select. An example of an LL(1) conflict: The FIRST set of "A" now is {"a", ε} and the FOLLOW set {"a"}.

Solutions to LL(1) Conflicts.

Left Factoring.

A common left-factor is "factored out". becomes Can be applied when two alternatives start with the same symbol like a FIRST/FIRST conflict.  Another example (more complex) using above FIRST/FIRST conflict example: becomes (merging into a single non-terminal) then through left-factoring, becomes

Substitution.

Substituting a rule into another rule to remove indirect or FIRST/FOLLOW conflicts. Note that this may cause a FIRST/FIRST conflict.

Left recursion removal.

For a general method, see removing left recursion. A simple example for left recursion removal: The following production rule has left recursion on E This rule is nothing but list of Ts separated by '+'. In a regular expression form T ('+' T)*. So the rule could be rewritten as Now there is no left recursion and no conflicts on either of the rules.  However, not all context-free grammars have an equivalent LL(k)-grammar, e.g.: It can be shown that there does not exist any LL(k)-grammar accepting the language generated by this grammar.

In computer science, an LL parser (Left-to-right, Leftmost derivation) is a top-down parser for a subset of context-free languages. It parses the input from Left to right, performing Leftmost derivation of the sentence.

LL分析器是一种处理某些上下文无关文法的自顶向下分析器。因为它从左(Left)到右处理输入,再对句型执行最左推导出语法树(Left derivation,相对于LR分析器)。能以此方法分析的文法称为LL 文法。


Mechanics.

CAPE exists within the conditionally unstable layer of the troposphere, the free convective layer (FCL), where an ascending air parcel is warmer than the ambient air. CAPE is measured in joules per kilogram of air (J/kg). Any value greater than 0 J/kg indicates instability and an increasing possibility of thunderstorms and hail. Generic CAPE is calculated by integrating vertically the local buoyancy of a parcel from the level of free convection (LFC) to the equilibrium level (EL):  formula_1  Where formula_2 is the height of the level of free convection and formula_3 is the height of the equilibrium level (neutral buoyancy), where formula_4 is the virtual temperature of the specific parcel, where formula_5 is the virtual temperature of the environment (note that temperatures must be in the Kelvin scale), and where formula_6 is the acceleration due to gravity. This integral is the work done by the buoyant force minus the work done against gravity, hence it's the excess energy that can become kinetic energy.  CAPE for a given region is most often calculated from a thermodynamic or sounding diagram (e.g., a Skew-T log-P diagram) using air temperature and dew point data usually measured by a weather balloon.  CAPE is effectively positive buoyancy, expressed "B+" or simply "B"; the opposite of convective inhibition (CIN), which is expressed as "B-", and can be thought of as "negative CAPE". As with CIN, CAPE is usually expressed in J/kg but may also be expressed as m/s, as the values are equivalent. In fact, CAPE is sometimes referred to as "positive buoyant energy" ("PBE"). This type of CAPE is the maximum energy available to an ascending parcel and to moist convection. When a layer of CIN is present, the layer must be eroded by surface heating or mechanical lifting, so that convective boundary layer parcels may reach their level of free convection (LFC).  On a sounding diagram, CAPE is the "positive area" above the LFC, the area between the parcel's virtual temperature line and the environmental virtual temperature line where the ascending parcel is warmer than the environment. Neglecting the virtual temperature correction may result in substantial relative errors in the calculated value of CAPE for small CAPE values. CAPE may also exist below the LFC, but if a layer of CIN (subsidence) is present, it is unavailable to deep, moist convection until CIN is exhausted. When there is mechanical lift to saturation, cloud base begins at the lifted condensation level (LCL); absent forcing, cloud base begins at the convective condensation level (CCL) where heating from below causes spontaneous buoyant lifting to the point of condensation when the convective temperature is reached. When CIN is absent or is overcome, saturated parcels at the LCL or CCL, which had been small cumulus clouds, will rise to the LFC, and then spontaneously rise until hitting the stable layer of the equilibrium level. The result is deep, moist convection (DMC), or simply, a thunderstorm.  When a parcel is unstable, it will continue to move vertically, in either direction, dependent on whether it receives upward or downward forcing, until it reaches a stable layer (though momentum, gravity, and other forcing may cause the parcel to continue). There are multiple types of CAPE, "downdraft CAPE" ("DCAPE"), estimates the potential strength of rain and evaporatively cooled downdrafts. Other types of CAPE may depend on the depth being considered. Other examples are "surface based CAPE" ("SBCAPE"), "mixed layer" or "mean layer CAPE" ("MLCAPE"), "most unstable" or "maximum usable CAPE" ("MUCAPE"), and "normalized CAPE" ("NCAPE").  Fluid elements displaced upwards or downwards in such an atmosphere expand or compress adiabatically in order to remain in pressure equilibrium with their surroundings, and in this manner become less or more dense.  If the adiabatic decrease or increase in density is "less" than the decrease or increase in the density of the ambient (not moved) medium, then the displaced fluid element will be subject to downwards or upwards pressure, which will function to restore it to its original position. Hence, there will be a counteracting force to the initial displacement. Such a condition is referred to as "convective stability".  On the other hand, if adiabatic decrease or increase in density is "greater" than in the ambient fluid, the upwards or downwards displacement will be met with an additional force in the same direction exerted by the ambient fluid. In these circumstances, small deviations from the initial state will become amplified. This condition is referred to as "convective instability".  Convective instability is also termed "static instability", because the instability does not depend on the existing motion of the air; this contrasts with dynamic instability where instability is dependent on the motion of air and its associated effects such as dynamic lifting.

Significance to thunderstorms.

Thunderstorms form when air parcels are lifted vertically. Deep, moist convection requires a parcel to be lifted to the LFC where it then rises spontaneously until reaching a layer of non-positive buoyancy. The atmosphere is warm at the surface and lower levels of the troposphere where there is mixing (the planetary boundary layer (PBL)), but becomes substantially cooler with height. The temperature profile of the atmosphere, the change in temperature, the degree that it cools with height, is the lapse rate. When the rising air parcel cools more slowly than the surrounding atmosphere, it remains warmer and less dense. The parcel continues to rise freely (convectively; without mechanical lift) through the atmosphere until it reaches an area of air less dense (warmer) than itself.  The amount, and shape, of the positive-buoyancy area modulates the speed of updrafts, thus extreme CAPE can result in explosive thunderstorm development; such rapid development usually occurs when CAPE stored by a capping inversion is released when the "lid" is broken by heating or mechanical lift. The amount of CAPE also modulates how low-level vorticity is entrained and then stretched in the updraft, with importance to tornadogenesis. The most important CAPE for tornadoes is within the lowest 1 to 3 km (0.6 to 1.9 mi) of the atmosphere, whilst deep layer CAPE and the width of CAPE at mid-levels is important for supercells. Tornado outbreaks tend to occur within high CAPE environments. Large CAPE is required for the production of very large hail, owing to updraft strength, although a rotating updraft may be stronger with less CAPE. Large CAPE also promotes lightning activity.  Two notable days for severe weather exhibited CAPE values over 5 kJ/kg. Two hours before the 1999 Oklahoma tornado outbreak occurred on May 3, 1999, the CAPE value sounding at Oklahoma City was at 5.89 kJ/kg. A few hours later, an F5 tornado ripped through the southern suburbs of the city. Also on May 4, 2007 CAPE values of 5.5 kJ/kg were reached and an EF5 tornado tore through Greensburg, Kansas. On these days, it was apparent that conditions were ripe for tornadoes and CAPE wasn't a crucial factor. However, extreme CAPE, by modulating the updraft (and downdraft), can allow for exceptional events, such as the deadly F5 tornadoes that hit Plainfield, Illinois on August 28, 1990 and Jarrell, Texas on May 27, 1997 on days which weren't readily apparent as conducive to large tornadoes. CAPE was estimated to exceed 8 kJ/kg in the environment of the Plainfield storm and was around 7 kJ/kg for the Jarrell storm.  Severe weather and tornadoes can develop in an area of low CAPE values. The surprise severe weather event that occurred in Illinois and Indiana on April 20, 2004 is a good example. Importantly in that case, was that although overall CAPE was weak, there was strong CAPE in the lowest levels of the troposphere which enabled an outbreak of minisupercells producing large, long-track, intense tornadoes.

Example from meteorology.

A good example of convective instability can be found in our own atmosphere. If dry mid-level air is drawn over very warm, moist air in the lower troposphere, a hydrolapse (an area of rapidly decreasing dew point temperatures with height) results in the region where the moist boundary layer and mid-level air meet. As daytime heating increases mixing within the moist boundary layer, some of the moist air will begin to interact with the dry mid-level air above it. Owing to thermodynamic processes, as the dry mid-level air is slowly saturated its temperature begins to drop, increasing the adiabatic lapse rate. Under certain conditions, the lapse rate can increase significantly in a short amount of time, resulting in convection. High convective instability can lead to severe thunderstorms and tornadoes as moist air which is trapped in the boundary layer eventually becomes highly negatively buoyant relative to the adiabatic lapse rate and escapes as a rapidly rising bubble of humid air triggering the development of a cumulus or cumulonimbus cloud.

In meteorology, convective available potential energy (commonly abbreviated as CAPE), is the integrated amount of work that the upward (positive) buoyancy force would perform on a given mass of air (called an air parcel) if it rose vertically through the entire atmosphere. Positive CAPE will cause the air parcel to rise, while negative CAPE will cause the air parcel to sink. Nonzero CAPE is an indicator of atmospheric instability in any given atmospheric sounding, a necessary condition for the development of cumulus and cumulonimbus clouds with attendant severe weather hazards.

对流可用位能(英语:Convective available potential energy)是大气科学当中使用的名词,为评估垂直大气是否稳定、对流是否容易发展的指标之一。近地面的空气块受垂直风切扰动或地形等其他因素而沿着绝热线上升时,在一定高度以上其温度若比周围环境温度高,意味着气块密度较周围环境空气小,则周围环境将给予气块向上的浮力。周围环境对空气块的作用力与空气块位移相乘,而得到周围环境对气块所做的功,这部分的能量在理想状态下将会储存在空气块中,使其具有向上发展的动能。一般对流可用位能的计算范围,是以自由对流高度以上到平衡高度为止,周围环境所能提供的浮力对高度积分而得。


Hinduism.

Amrita is repeatedly referred to as the drink of the devas, which grants them immortality. Despite this, the nectar does not actually offer true immortality. Instead, by partaking it, the devas were able to attain a higher level of knowledge and power, which they had lost due to the curse of Sage Durvasa, as described in the samudra manthana legend. It tells how the devas, after the curse, begin to lose their immortality. Assisted by their rivals, the asuras, the devas begin to churn the ocean, releasing (among other extraordinary objects and beings) the amrita.  Amrita is sometimes said to miraculously form on, or flow from, statues of Hindu gods. The substance is consumed by worshippers and is alleged to be sweet-tasting and not at all similar to honey or sugar water. Amrita was the last of the fourteen treasures that emerged from the churning of the ocean and contained in a pot borne by Dhanvantari, the physician of the devas.

Sikhism.

In Sikhism, amrit () is the name of the holy water used in Amrit Sanchar, a ceremony which resembles baptism. This ceremony is observed to initiate the Sikhs into the Khalsa and requires drinking amrit. This is created by mixing a number of soluble ingredients, including sugar, and is then rolled with a khanda with the accompaniment of scriptural recitation of five sacred verses.  Metaphorically, God's name is also referred to as a nectar: <poem>ਅੰਮ੍ਰਿਤ ਸਬਦੁ ਅੰਮ੍ਰਿਤ ਹਰਿ ਬਾਣੀ ॥  The Shabda is Amrit; the Lord's "bani" is Amrit. ਸਤਿਗੁਰਿ ਸੇਵਿਐ ਰਿਦੈ ਸਮਾਣੀ ॥  Serving the True Guru, it permeates the heart. ਨਾਨਕ ਅੰਮ੍ਰਿਤ ਨਾਮੁ ਸਦਾ ਸੁਖਦਾਤਾ ਪੀ ਅੰਮ੍ਰਿਤੁ ਸਭ ਭੁਖ ਲਹਿ ਜਾਵਣਿਆ  O Nanak, the Ambrosial Naam is forever the Giver of peace; drinking in this Amrit, all hunger is satisfied.</poem>

Theravada Buddhism.

According to Thanissaro Bhikkhu, "the deathless" refers to the deathless dimension of the mind which is dwelled in permanently after nibbana.  In the Amata Sutta, the Buddha advises monks to stay with the four Satipatthana: "Monks, remain with your minds well-established in these four establishings of mindfulness. Don't let the deathless be lost to you."  In the questions for Nagasena, King Milinda asks for evidence that the Buddha once lived, wherein Nagasena describes evidence of the Dhamma in a simile:

Vajrayana Buddhism.

Amrita () also plays a significant role in Vajrayana Buddhism as a sacramental drink which is consumed at the beginning of all important rituals such as the abhisheka, ganachakra, and homa. In the Tibetan tradition, "dütsi" is made during - lengthy ceremonies involving many high lamas. It usually takes the form of small, dark-brown grains that are taken with water, or dissolved in very weak solutions of alcohol and is said to improve physical and spiritual well-being.  The foundational text of traditional Tibetan medicine, the Four Tantras, is also known by the name "The Heart of Amrita" ().  "The Immaculate Crystal Garland" () describes the origin of amrita in a version of the samudra manthana legend retold in Buddhist terms. In this Vajrayana version, the monster Rahu steals the amrita and is blasted by Vajrapani's thunderbolt. As Rahu has already drunk the amrita he cannot die, but his blood, dripping onto the surface of this earth, causes all kinds of medicinal plants to grow. At the behest of all the Buddhas, Vajrapani reassembles Rahu who eventually becomes a protector of Buddhism according to the Nyingma school of Tibetan Buddhism.  "Inner Offering" (, ) is the most symbolic amrita offering assembly, and the "Inner Offering Nectar Pill" (, ) is a precious and secret medicine of Tibetan Buddhism, which are only used internally for higher ranking monks in Nyingma school. Its ingredients including Five Amrita and Five Meat, which represents five buddha, and five elements respectively. According to "Tantras of Chakravarti", and "Tantras of Vajravārāhī", a ceremony needs to be hold for melting and blessing the Inner Offering Nectar. Five Nectar needs to be arranged in four directions: yellow excrement in the east, green bone marrow in the north, white semen in the west and red blood in the south, blue urine is placed in the center. Four Nectar should come from wise monks and the ova should be collected from the first menstruation of a blessed woman. The Five Meats are arranged similarly, meat of black bull in the southeast, the meat of the blue dog in the southwest, the meat of the white elephant in the northwest, the meat of the green horse in the northeast, and the meat of a red human corpse in the center. After the ceremony, these ingredients will transform into an "one taste" ("ekarasa") elixir, which bestows bliss, vitality, immortality and wisdom. Actual modern practitioner will take a'synthesized essence' of the Nectar Pill and combined it with black tea or alcohol, but mostly the "Nectar Pill" are derived from plants.  Chinese Buddhism describes Amrita () as blessed water, food, or other consumable objects often produced through merits of chanting mantras.

Amrita (, IAST: "amṛta"), Amrit or Amata (also called Sudha, Amiy, Ami) literally means "immortality" and is often referred to in ancient Indian texts as nectar. "Amṛta" is etymologically related to the Greek "ambrosia" and carries the same meaning. Its first occurrence is in the Rigveda, where it is considered one of several synonyms for "soma", the drink of the devas.

甘露(,IAST: amṛta,音译阿密哩多,意为永生)是印度神话中出现的长生不老药。