Zeravshan River, river rising in the eastern Turkistan Range and flowing 545 miles (877 km) west through Tajikistan and southeastern Uzbekistan to disappear in the desert north of Chärjew near the Amu Darya, of which it was at one time a tributary. The river supplies water to a vast irrigation

Zeravshan Range, mountain range in Tajikistan and Uzbekistan, forming a part of the Gissar–Alay system. It extends for more than 230 miles (370 km) east–west parallel to the Turkistan Range between the Zeravshan Valley on the north and the Yagnob and Iskanderdarya valleys on the south. The range is

Zeraʿim, (Hebrew: “Seeds”), the first of the six major divisions, or orders (sedarim), of the Mishna (codification of Jewish oral laws), which was completed early in the 3rd century ad by Judah ha-Nasi. Zeraʿim contains 11 tractates (treatises), the first of which (Berakhot, “Blessings”) deals with

Burkina Faso: Independence of Burkina Faso: Saye Zerbo.

Heinrich von Kleist: …verse, Der zerbrochene Krug (The Broken Pitcher), was unsuccessfully produced by Johann Wolfgang von Goethe in Weimar. The play employs vividly portrayed rustic characters, skillful dialogue, earthy humour, and subtle realism in its depiction of the fallibility of human feeling and the flaws inherent in human justice. It ranks…

Esterházy Family: Ferenc Zerházy (1563–94), deputy lord lieutenant of the county of Pozsony (now Bratislava, Slovakia), was the first family member of historical importance. He took the name Esterházy upon becoming baron of Galántha, an estate the family had acquired in 1421. With his sons the family…

Elias Zerhouni is an Algerian-born American radiologist who served as the 15th director of the U.S. National Institutes of Health (NIH) from 2002 to 2008. Zerhouni, who had seven siblings, was born in a small village in western Algeria. His father was a math professor. In 1953 the family moved to

Elias Zerhouni is an Algerian-born American radiologist who served as the 15th director of the U.S. National Institutes of Health (NIH) from 2002 to 2008. Zerhouni, who had seven siblings, was born in a small village in western Algeria. His father was a math professor. In 1953 the family moved to

Zarma, a people of westernmost Niger and adjacent areas of Burkina Faso and Nigeria. The Zarma speak a dialect of Songhai, a branch of the Nilo-Saharan language family, and are considered to be a branch of the Songhai people. The Zarma live in the arid lands of the Sahel. Many live in the Niger

Zermatt, town, Valais canton, southern Switzerland. It lies at the head of the Mattervisp Valley and at the foot of the Matterhorn (14,692 feet [4,478 m]), 23 miles (37 km) southeast of Sion. Its name is derived from its position Zur Matte (“in the Alpine meadow”) at an elevation of 5,302 feet

William Martin Conway, Baron Conway: …writer, he also authored The Zermatt Pocket Book (1881), a guide to climbing the Pennine Alps; Early Tuscan Art (1902); and Mountain Memoirs (1920).

axiom of choice, statement in the language of set theory that makes it possible to form sets by choosing an element simultaneously from each member of an infinite collection of sets even when no algorithm exists for the selection. The axiom of choice has many mathematically equivalent formulations,

axiom of choice: …1904 by the German mathematician Ernst Zermelo in order to prove the “well-ordering theorem” (every set can be given an order relationship, such as less than, under which it is well ordered; i.e., every subset has a first element [see set theory: Axioms for infinite and ordered sets]). Subsequently, it…

history of logic: Zermelo-Fraenkel set theory (ZF): Contradictions like Russell’s paradox arose from what was later called the unrestricted comprehension principle: the assumption that, for any property p, there is a set that contains all and only those sets that have p. In Zermelo’s system, the comprehension principle…

history of logic: Zermelo-Fraenkel set theory (ZF): Contradictions like Russell’s paradox arose from what was later called the unrestricted comprehension principle: the assumption that, for any property p, there is a set that contains all and only those sets that have p. In Zermelo’s system, the comprehension principle…

Abercrombie & Fitch: …opulence, inspiring the American humorist Ed Zern to lampoon a perfectly accoutred angler as an “Abercrombie and Fitcherman.”

Frits Zernike was a Dutch physicist, winner of the Nobel Prize for Physics in 1953 for his invention of the phase-contrast microscope, an instrument that permits the study of internal cell structure without the need to stain and thus kill the cells. Zernike obtained a doctorate from the University

Zero, fighter aircraft, a single-seat, low-wing monoplane used with great effect by the Japanese during World War II. Designed by Horikoshi Jiro, it was the first carrier-based fighter capable of besting its land-based opponents. It was designed to specifications written in 1937, was first tested

abacus: …with its place value and zero, gradually replaced the abacus, though it was still widely used in Europe as late as the 17th century. The abacus survives today in the Middle East, China, and Japan, but it has been largely replaced by electronic calculators.

Fritz von Unruh: …in Monte Carlo (1931) and Zero (1932).

Edén Pastora was a Nicaraguan guerrilla leader and legendary fighter. A military commander of the Sandinista movement, Pastora led the assault on the national palace in Managua, Nicaragua, on August 22, 1978. Twenty-three men under his command took some 1,000 hostages, about half of them

Kathryn Bigelow: … screenwriter Mark Boal to make Zero Dark Thirty (2012), an unflinching account of the U.S. military and intelligence operation to capture Osama bin Laden. She also collaborated with Boal on Detroit (2017), about the city’s 1967 riot.

Jean Vigo: …directed Zéro de conduite (1933; Zero for Conduct), which was branded as “anti-French” by the censors, removed from the theatres after only a few months, and was not shown again in France until 1945. The moving story, set in a boy’s boarding school, explores the question of freedom versus authority…

Paraguay: Agriculture, forestry, and fishing: …the Paraguayan government passed the Zero Deforestation Law, which prohibits the conversion of forested area in Paraguay’s Eastern Region. Illegal logging in national parks, however, has remained a threat. Deforestation of the Gran Chaco increased dramatically from the beginning of the 21st century as Paraguayan Mennonites, Brazilian immigrants, and Uruguayan…

Hans Hellmut Kirst: …satiric trilogy Null-acht fünfzhen (1954–55; Zero Eight Fifteen), the continuing story of an army private, Gunner Asch, and his personal battle with the absurdities of the German military system. He was perhaps best known for Die Nacht der Generale (1962, The Night of the Generals), which was made into a…

Jean Vigo: …directed Zéro de conduite (1933; Zero for Conduct), which was branded as “anti-French” by the censors, removed from the theatres after only a few months, and was not shown again in France until 1945. The moving story, set in a boy’s boarding school, explores the question of freedom versus authority…

Caucasian languages: Proto-Kartvelian: …or without a vowel, called zero grade. (An asterisk [*] indicates that the following form is not attested but has been reconstructed as a hypothetical ancestral form.) In a sequence of word elements (called morphemes) only one element may occur in full grade, the others being in either zero or…

weightlessness, condition experienced while in free-fall, in which the effect of gravity is canceled by the inertial (e.g., centrifugal) force resulting from orbital flight. The term zero gravity is often used to describe such a condition. Excluding spaceflight, true weightlessness can be

William Gibson: Zero History (2010), which completed a trilogy that includes his previous two novels, reveals hidden governmental conspiracies through a search for a missing fashion designer. The Peripheral (2014) investigates the possibility of communication with future societies by way of computer technology. Its prequel/sequel, Agency, was…

German literature: The post-1945 period: Stunde Null: In the part of Germany that became West Germany in 1949, the immediate aftermath of World War II was known as the “Stunde Null,” or “zero hour.” Writers felt that the need to make a clean sweep after the defeat of Nazism had…

Ernesto Cardenal: La hora 0 (1960; Zero Hour, and Other Documentary Poems), a long documentary poem denouncing the effects of domestic tyranny and American imperialism in Central American history, is a masterpiece of protest poetry. In subsequent works Cardenal began to use empty phrases and commercial slogans as symbols of an…

Airplane!: …taken directly from the movie Zero Hour! (1957), and other elements were based on Airport 1975 (1974) and similar disaster films. The typical disaster film plot is satirized using a high saturation of humour, and the borrowed material is supplemented with a variety of comedic techniques including verbal humour and…

food insecurity: Solutions to food insecurity: …2012 the UN launched the Zero Hunger Challenge with the goal of eradicating hunger by 2030, as part of its global sustainable development objectives. In 2021 the UN held a summit to address hunger and consider the progress made by the Zero Hunger Challenge effort. While several UN organizations (including…

Don DeLillo: …a meditation on time; and Zero K (2016), an investigation of cryogenics and human immortality. The Silence (2020) follows several people who attend a Super Bowl party during a worldwide calamitous event.

Naseeruddin Shah: …starring roles in the series Zero KMS (2018) and Bandish Bandits (2020– ).

matrix: …elements 0 is called a zero, or null, matrix. A square matrix A with 1s on the main diagonal (upper left to lower right) and 0s everywhere else is called an identity, or unit, matrix. It is denoted by I or In to show that its order is n. If…

nuclear strategy: Limited nuclear war: That “zero option” was rejected by Soviet leader Leonid Brezhnev, and, despite warnings from the Soviet Union that deployment of a modernized INF would mean the end of negotiations, the first Tomahawk and Pershing II missiles were delivered in late 1983. Brezhnev’s successor Yury Andropov promptly…

Kingsley Davis: …the terms population explosion and zero population growth. His specific studies of American society led him to work on a general science of world society, based on empirical analysis of each society in its habitat.

Matt Damon: Later credits: …itself in Terry Gilliam’s atmospheric The Zero Theorem (2013), and a desperate space explorer in Christopher Nolan’s Interstellar (2014).

transfer of training: Kinds of transfer: can occur: positive, negative, and zero. The following examples from hypothetical experiments, purposely uncomplicated by distracting detail, illustrate each. Suppose a group of students learn a task, B, in 10 practice sessions. Another group of equivalent students, who previously had learned another task, A, is found to reach the same…

star: Subsequent development on the main sequence: …the Hertzsprung-Russell diagram called the zero-age main sequence. Without differences in initial chemical composition or in rotational velocity, all the stars would start exactly from this unique line. As the stars evolve, they adjust to the increase in the helium-to-hydrogen ratio in their cores and gradually move away from the…

government budget: Program budgeting and zero-base budgeting: …introduce the concept of “zero-base budgeting,” whereby the entire government program, not just its incremental parts, was to be evaluated each year. This idea, which involved considerable changes to existing procedures, was applied to some programs on a selective basis but never had the impact its designers envisaged. A…

China: COVID-19 outbreak: …spreading, China implemented strict “zero-COVID” policies aimed at keeping the number of cases as close to zero as possible through measures including strict lockdowns, quarantines, and mass testing. As a result, infection cases and deaths were relatively lower in China compared with other wealthy countries. Despite residents’ initial support…

advanced persistent threat: …and the distribution of “zero-day malware.” Spear phishing uses e-mails sent to selected employees within an organization. The e-mails appear to come from trusted or known sources. Either by clicking on links within the e-mail or by being persuaded by the e-mail’s seeming legitimacy to let their guard down,…

zero-energy building (ZEB), any building or construction characterized by zero net energy consumption and zero carbon emissions calculated over a period of time. Zero-energy buildings (ZEBs) usually use less energy than traditional buildings as well as generate their own energy on-site to use in

nuclear reactor: The first atomic piles: …reactor, the so-called ZEEP (Zero-Energy Experimental Pile), at Chalk River, Ontario.

organometallic compound: Zero-oxidation-state metal carbonyls: The central metal in a neutral metal carbonyl, such as those described above, is assigned an oxidation state of zero, quite unlike the case in simple inorganic compounds in which positive oxidation states are the norm, as, for example, Fe3+ in FeCl3…

zero-point energy, vibrational energy that molecules retain even at the absolute zero of temperature. Temperature in physics has been found to be a measure of the intensity of random molecular motion, and it might be expected that, as temperature is reduced to absolute zero, all motion ceases and

game theory: Classification of games: Constant-sum games are games of total conflict, which are also called games of pure competition. Poker, for example, is a constant-sum game because the combined wealth of the players remains constant, though its distribution shifts in the course of play.

no-till agriculture, cultivation technique in which the soil is disturbed only along the slit or in the hole into which the seeds are planted; reserved detritus from previous crops covers and protects the seedbed. The practice is one of several so-called “primitive farming” methods that have been

celestial mechanics: The restricted three-body problem: If such a zero-velocity curve is closed, the particle cannot escape from the interior of the closed zero-velocity curve if placed there with the constant of the motion equal to the value used to construct the curve. These zero-velocity curves can be used to show that the three…

telescope: Evolution of the optical telescope: …in the Canary Islands, and Zerodur was used for the 10.4-metre (410-inch) reflector at the Gran Telescopio Canarias in the Canary Islands.

Stefan Żeromski was a Polish novelist admired for the deep compassion about social problems that he expressed in naturalistic, yet lyrical, novels. Belonging to a family of impoverished gentry, Żeromski was born in the aftermath of the tragic 1863 January Insurrection against Russian rule, and that

Ethan Hawke: …2021 included the political thriller Zeros and Ones and an adaptation of Samuel Beckett’s play Waiting for Godot. He continued to demonstrate his versatility the following year, appearing in the Viking epic The Northman and the miniseries Moon Knight, part of the Marvel Cinematic Universe.

thermodynamics: laws of thermodynamics are:

telecommunications media: Optical fibres: …by what is called the zeroth order mode; other light rays propagate by higher-order modes. It is the simultaneous presence of many modes of propagation within a single fibre that creates multimode dispersion. Multimode dispersion causes a signal of uniform transmitted intensity to arrive at the far end of the…

Liamine Zeroual was the president of Algeria (1994–99). Zeroual joined the Algerian army at age 16 and fought against France during Algeria’s War of Independence. In 1965 Zeroual went to the Soviet Union for military training, after which he was posted to Sidi Bel Abbès, Algeria, to head an

Liamine Zeroual was the president of Algeria (1994–99). Zeroual joined the Algerian army at age 16 and fought against France during Algeria’s War of Independence. In 1965 Zeroual went to the Soviet Union for military training, after which he was posted to Sidi Bel Abbès, Algeria, to head an

Megan Fox: …movie credits from 2019 included Zeroville, a mystery dramedy that was directed by and starred James Franco. In 2020 she appeared in the family film Think Like a Dog and the action thriller Rogue. In Till Death (2021), Fox was cast as a woman trying to evade two killers after…

Milan Kundera: …his greatest works, Žert (1967; The Joke), a comic, ironic view of the private lives and destinies of various Czechs during the years of Stalinism; translated into several languages, it achieved great international acclaim. His second novel, Život je jinde (1969; Life Is Elsewhere), about a hapless, romantic-minded hero who…

Zerubbabel was the governor of Judaea under whom the rebuilding of the Jewish Temple at Jerusalem took place. Of Davidic origin, Zerubbabel is thought to have originally been a Babylonian Jew who returned to Jerusalem at the head of a band of Jewish exiles and became governor of Judaea under the

Temple of Jerusalem, either of two temples that were the centre of worship and national identity in ancient Israel. In the early years of the Israelite kingdom, the Ark of the Covenant was periodically moved about among several sanctuaries, especially those of Shechem and Shiloh. After King David’s

Zurvanism, modified form of Zoroastrianism that appeared in Persia during the Sāsānian period (3rd–7th century ad). It was opposed to orthodox Zoroastrianism, which by that time had become dualistic in doctrine. According to Zurvanism, time alone—limitless, eternal, and uncreated—is the source of

EDES: Napoleon Zervas, EDES was originally liberal and antimonarchist, but it moved steadily to the political right. It cooperated with ELAS for a time in operations against the Germans and Italians, but, between October 1943 and February 1944, the two guerrilla groups fought each other. The…

eclipse: Eclipsing binary stars: Zeta Aurigae is the prototype of a class of eclipsing binaries composed of a cool supergiant star and a hot blue star. Although the supergiant’s atmosphere is large enough to reach to the orbit of Venus were the star to replace the Sun in the…

zeta function, in number theory, an infinite series given by where z and w are complex numbers and the real part of z is greater than zero. For w = 0, the function reduces to the Riemann zeta function, named for the 19th-century German mathematician Bernhard Riemann, whose study of its properties

star: Stellar atmospheres: , Zeta Puppis), strong, relatively narrow emission lines can be seen; however, in the ultraviolet, observations from rockets and spacecraft show strong emission lines with distinct absorption components on the shorter wavelength side. These absorption features are produced by rapidly outflowing atoms that absorb the radiation…

Mizar, first star found (by the Italian astronomer Giovanni Battista Riccioli in 1650) to be a visual binary—i.e., to consist of two optically distinguishable components revolving around each other. Later, each of the visual components was determined to be a spectroscopic binary; Mizar is actually

Catherine Zeta-Jones is a Welsh-born actress who demonstrated her versatility in a wide range of films, most notably the musical Chicago (2002), for which she won the Academy Award for best supporting actress. Jones (Zeta was her middle name; she added the hyphen later) was the daughter of Irish

Los Zetas, Mexican crime syndicate formed in 1997 as the enforcement arm of the drug-trafficking Gulf Cartel; it broke away as an independent organized criminal enterprise in 2010. The group was known for its violent tactics and tight organizational structure. Osiel Cárdenas Guillén was competing

Panamanian golden toad: …a potent water-soluble toxin called zetekitoxin, which affects nerve cells and protects the toad from most predators. However, if minor precautions are taken, these toads can be safely handled.

Calais and Zetes: Zetes, in Greek mythology, the winged twin sons of Boreas and Oreithyia. On their arrival with the Argonauts at Salmydessus in Thrace, they liberated their sister Cleopatra, who had been thrown into prison by her husband, Phineus, the king of the country. According to Apollonius…

Amphion and Zethus: Zethus, in Greek mythology, the twin sons of Zeus by Antiope. When children, they were left to die on Mount Cithaeron but were found and brought up by a shepherd. Amphion became a great singer and musician, Zethus a hunter and herdsman. (In Euripides’ lost…

Mount of Olives, multi-summit limestone ridge just east of the Old City of Jerusalem and separated from it by the Kidron Valley. Frequently mentioned in the Bible and later religious literature, it is holy to Judaism, Christianity, and Islam. The peak usually regarded as the Mount of Olives proper

Clara Zetkin was a German feminist, Socialist, and Communist leader, who after World War I played a leading role in the new Communist Party of Germany (Kommunistische Partei Deutschlands; KPD) and the Comintern (Third International). Clara Eissner was educated at the Leipzig Teachers’ College for

Shetland Islands, group of about 100 islands, fewer than 20 of them inhabited, in Scotland, 130 miles (210 km) north of the Scottish mainland, at the northern extremity of the United Kingdom. They constitute the Shetland Islands council area and the historic county of Shetland. Among the

stadium: Design innovations: …baseball stadium was developed by Lev Zetlin, an American engineer.

Arno Schmidt: …especially, in Zettels Traum (1970; Bottom’s Dream)—a three-columned, more than 1,300-page, photo-offset typescript, centring on the mind and works of Poe. It was then that Schmidt developed his theory of “etyms,” the morphemes of language that betray subconscious desires. Two further works on the same grand scale are the “novella-comedy”…

Detroit Red Wings: …Chris Osgood, and left wing Henrik Zetterberg were star players on the team that won the 2007–08 Stanley Cup against the Pittsburgh Penguins. The following season Lidstrom, Osgood, and Zetterberg, along with centre Pavel Datsyuk (who finished fourth in the league with 97 points), helped lead the Red Wings to…

Mai Zetterling was a Swedish actress, director, and novelist. As a director, she imbued her work with a passionate feminism. Zetterling was trained for the stage and made both her stage and screen debut in 1941 when she was 16 years of age. In 1944 she appeared in Alf Sjöberg’s film Hets (Torment,

Mai Zetterling was a Swedish actress, director, and novelist. As a director, she imbued her work with a passionate feminism. Zetterling was trained for the stage and made both her stage and screen debut in 1941 when she was 16 years of age. In 1944 she appeared in Alf Sjöberg’s film Hets (Torment,

Cologne: Architecture of Cologne: …festival hall, and the 16th-century Arsenal, which contains a historical museum, were both restored to their medieval form only on the outside.

ancient Greek civilization: Political reforms: …was formally opened to the zeugitai (the hoplite class) only in 457. But despite the great increase in work for the big popular juries and the granting to the courts of the right (which may go back to Ephialtes) to quash or uphold allegedly unconstitutional proposals, it is not likely…

Basilosaurus, extinct genus of primitive whales of the family Basilosauridae (suborder Archaeoceti) found in Middle and Late Eocene rocks in North America and northern Africa (the Eocene Epoch lasted from 55.8 million to 33.9 million years ago). Basilosaurus had primitive dentition and skull

cetacean: Paleontology: …whether the first cetaceans (archaeocetes) descended from an extinct group of large carnivores called mesonychids or from a group of hoofed herbivores (artiodactyls). The earliest archaeocetes were huge dolphinlike creatures 6 to 10 metres long. Basilosaurus (Zeuglodon) was an unusual genus that was up to 34 metres long, but…

gastropod: Classification: Superfamily Zeugobranchia (Pleurotomariacea) Slit shells (Pleurotomariidae) in deep ocean waters; abalones (Haliotidae) in shallow waters along rocky shores of western North America, Japan, Australia, and South Africa; keyhole limpets (Fissurellidae) in intertidal rocky areas. Superfamily Patellacea

Zeus, in ancient Greek religion, chief deity of the pantheon, a sky and weather god who was identical with the Roman god Jupiter. His name may be related to that of the sky god Dyaus of the ancient Hindu Rigveda. Zeus was regarded as the sender of thunder and lightning, rain, and winds, and his

Lucian: …of the Gods, and in Zeus Confuted and Tragic Zeus the leader of the gods is powerless to intervene on earth and prove his omnipotence to coldly skeptical Cynic and Epicurean philosophers. Lucian’s interest in philosophy was basically superficial, however, and his attitude to philosophical studies is best seen in…

Jupiter Dolichenus, god of a Roman mystery cult, originally a local Hittite-Hurrian god of fertility and thunder worshiped at Doliche (modern Dülük), in southeastern Turkey. Later the deity was given a Semitic character, but, under Achaemenid rule (6th–4th century bc), he was identified with the

architecture: Places of worship: …focus, while the altar of Pergamum and the Ara Pacis (Augustan Altar of Peace) in Rome are evidences of the open-air religious observances of the classical world. The atrium of early Christian architecture and the cloister were isolated areas for prayer.

Náxos: The island’s highest point is Mount Zeus (Zía Óros), which is about 3,290 feet (1,003 metres) in elevation. The 165-square-mile (428-square-kilometre) island forms an eparkhía (“eparchy”). The chief port, Náxos, on the west coast, is on the site of ancient and medieval capitals.

Statue of Zeus, at Olympia, Greece, one of the Seven Wonders of the World. The statue was one of two masterpieces by the Greek sculptor Phidias (the other being the statue of Athena in the Parthenon) and was placed in the huge Temple of Zeus at Olympia in western Greece. The statue, almost 12 m (40

Western architecture: Early Classical (c. 500–450 bce): …at Olympia, where a great Temple of Zeus was built in about 460. This temple was the first statement of Classical Doric in its canonical form and one of the largest Doric temples of the Greek mainland.

atlas: …colossal scale in the Greek temple of Zeus (c. 500 bc) at Agrigentum (Agrigento), Sicily. Atlantes were used only rarely in the Middle Ages but reappeared in the Mannerist and Baroque periods.

Zeuxis was one of the best-known painters of ancient Greece, who seems to have carried a trend toward illusionism to an unprecedented level. Zeuxis was, in one ancient account, a pupil of Demophilus of Himera in Sicily; other sources refer to him as a pupil of Neseus of Thasos (an island in the

leopard moth, (Zeuzera pyrina), widely distributed insect of the family Cossidae (order Lepidoptera), known particularly for its destructive larva. The adult moth has a fluffy white body and pale wings (span about four to six centimetres) with numerous black or blue spots and blotches. They fly at

zāwiyah, generally, in the Muslim world, a monastic complex, usually the centre or a settlement of a Sufi (mystical) brotherhood. In some Arabic countries the Arabic term zāwiyah is also used for any small private oratory not paid for by community funds. The first North African zāwiyah, dating from

Warren Zevon was an American singer-songwriter whose poetic rock songs—by turns hard-boiled, humorous, tough, and tender—were acclaimed by critics and much admired by other songwriters. Zevon studied classical piano before taking up songwriting. In the 1960s he wrote songs that were recorded by the

Ahmed H. Zewail was an Egyptian-born chemist who won the Nobel Prize for Chemistry in 1999 for developing a rapid laser technique that enabled scientists to study the action of atoms during chemical reactions. The breakthrough created a new field of physical chemistry known as femtochemistry.

Ahmed H. Zewail was an Egyptian-born chemist who won the Nobel Prize for Chemistry in 1999 for developing a rapid laser technique that enabled scientists to study the action of atoms during chemical reactions. The breakthrough created a new field of physical chemistry known as femtochemistry.