Christo orig. Christo Javacheff (b. June 13, 1935, Gabrovo, Bulg.) Bulgarian-born U.S. environmental artist. After attending Sofia’s Fine Arts Academy, he moved to Paris in 1958, where he invented empaque- tage, the wrapping of objects in various materials as art. He began with cans and bottles, and eventually his projects expanded to buildings and landscapes. In 1964 he moved to New York City. He is noted for such monumental outdoor projects as Valley Curtain (1970-72) in Rifle Gap, Colo., and Running Fence (1972—76) in Marin and Sonoma counties, Calif. In 1995 he wrapped the Berlin Reichstag in metallic silver fabric. Though his displays, which are temporary and involve hundreds of work¬ ers, are controversial among environmentalists, they have been critically well received. Since 1961 most have been collaborative efforts with his wife, Jeanne-Claude (b. 1935).
Christopher, Saint (fl. 3rd century; Western feast day July 25; East¬ ern feast day May 9) Patron saint of travelers and motorists. He is said to have been martyred in Lycia under the Roman emperor Decius (c. 250). Legends depict him as a giant who devoted his life to carrying travelers across a river. One day a small child asked to be transported, and in the middle of the river the child became so heavy that Christopher staggered under the burden. The child revealed that the saint had been carrying Christ and the sins of the world, thus giving rise to Christopher’s name (Greek: “Christ-Bearer”). His historicity is doubtful.
Agatha Christie, 1946.
UPI/CORBIS-BETTMANN
Christina, engraving by Cornelis Viss- cher, 1650.
COURTESY OF THE SVENSKA PORTRATTARKIVET, STOCKHOLM
© 2006 Encyclopaedia Britannica, Inc.
402 I Christus ► chronicle play
Christus Vkris-tiBsV Petrus (b. c. 1420, Baerle, Brabant—d. 1472/73, Bruges) Flemish painter. He is documented as working in Bruges (1444), where he was influenced by the work of Jan van Eyck. Christus is known for his sensitive portraits, but his most important contributions were the introduction of geometric perspective to Netherlandish painting, and his genrelike treatment of religious subjects, seen in works such as St. Eligius as a Goldsmith (1449) and Virgin and Child in a Domestic Interior (c.
1450-60).
chromaticism \kro-'ma-t9- l si-z9m\ In music, the use of all 12 tones, especially for heightened expressivity. A standard key or mode principally employs 7 tones, leaving 5 tones for discretionary use. Use of all 12 tones in a given piece increased in the 18th and 19th centuries. Strictly con¬ trolled chromaticism, as in the ornamentation of Frederic Chopin, did not threaten the perception of tonality. However, from the mid-19th century on, complaints were heard with ever greater frequency that it was difficult to perceive what a given piece’s tonal centre was, the chromaticism in the works of Richard Wagner being the most notorious. The virtual breakdown in tonality in the works of advanced composers led to the free atonality of Arnold Schoenberg and his followers in the early 20th century.
chromatography V.kro-mo-'ta-gro-feN Method first described in 1903 by Mikhail S. Tsvet for separating mixed chemical substances. Tsvet’s neglected work, rediscovered in the 1930s, uses the different affinities of substances in a solution in a mobile phase (a moving stream of gas or liq¬ uid) for adsorption onto a stationary phase (a fine-grained solid, a sheet of filtering material, or a thin film of a liquid on a solid surface). Choices of materials for these phases allow enormous versatility for separating substances including biological fluids (e.g., amino acids, steroids, carbo¬ hydrates, pigments), chemical mixtures, and forensic samples. In the origi¬ nal technique, an organic solvent flowed through a column of powdered alumina (see aluminum), sodium carbonate, or even powdered sugar to separate mixed plant pigments. Among current adaptations are paper chro¬ matography (PC), THIN-LAYER chromatography (TLC), liquid chromatography (LC, including high-performance liquid chromatography, or HPLC), and gas chromatography (GC). Some remain laboratory techniques, but oth¬ ers (especially HPLC) can be used on an industrial scale. They require different methods for detecting and identifying the separated components, including colorimetry, spectrophotometry, mass spectrometry, and measure¬ ment of fluorescence, ionization potential, or thermal conductivity. A.J.P. Martin shared a 1952 Nobel Prize for developing LC and PC, and in his Nobel lecture announced the development (with his cowinner R.L.M. Synge and other colleagues) of GC.
chromite Relatively hard, metallic, black oxide mineral of chromium and iron (FeCr 2 0 4 ) that is the chief commercial source of chromium. Chromite is commonly found as brittle masses in peridotites, serpentines, and other basic igneous and metamorphic rocks. The principal producing areas are South Africa, Russia, Albania, the Philippines, Zimbabwe, Tur¬ key, Brazil, India, and Finland.
chromium Metallic chemical element, one of the transition elements, chemical symbol Cr, atomic number 24. A hard, steel-gray metal that takes a high polish, it is used in alloys (e.g., ferrochromium, steel, stainless steel) to increase strength and corrosion resistance. It usually has valence 2, 3, or 6 and always occurs combined with other elements, especially oxygen; chromite is its only commercial source. Various coloured gem¬ stones (e.g., ruby, emerald, serpentine) owe their colour to chromium. Sodium chromate and dichromate are used in leather tanning, in metal surface treatment, and as catalysts. Chromium trioxide is used in chrome plating and as a colorant for ceramics. Chromium oxide, lead chromate, and various other chromium compounds are used as pigments. Chromium dioxide, strongly magnetic, is used in recording tapes and as a catalyst.
chromodynamics See quantum chromodynamics
chromosomal disorder Syndrome caused by chromosome abnormal¬ ity. Normally, humans have 23 pairs of chromosomes, including one pair of sex chromosomes. Any variation from this pattern causes abnormalities. A chromosome may be duplicated (trisomy) or absent (monosomy); one or more extra full sets of chromosomes can be present (see ploidy); or part of a chromosome may be missing (deletion) or transferred to another (translocation). Resulting disorders include Down's syndrome, mental retardation, heart malformation, abnormal sexual development, malignan¬ cies, and sex-chromosome disorders (e.g., Turner's syndrome, Klinefelter's syndrome). Chromosomal disorders occur in 0.5% of births; many can now be diagnosed before birth by amniocentesis.
chromosome Microscopic, threadlike part of a cell that carries heredi¬ tary information in the form of genes. The structure and location of chro¬ mosomes differentiate prokaryotic cells from eukaryotic cells (see prokaryote, eukaryote). Every species has a characteristic number of chro¬ mosomes; humans have 23 pairs (22 pairs of autosomal, or nonsex, chro¬ mosomes and one pair of sex chromosomes). Human chromosomes consist primarily of DNA. During cell division (see meiosis, mitosis), chro¬ mosomes are distributed evenly among daughter cells. In sexually repro¬ ducing organisms, the number of chromosomes in somatic (nonsex) cells is diploid, while gametes or sex cells (egg and sperm) produced by mei¬ osis are haploid (see ploidy). Fertilization restores the diploid set of chro¬ mosomes in the zygote.
duplicated
centromere
chromatin
dividing chromosome
chromatid
histones
DNA
nucleosome
During the first stages of cell division, the recognizable double-stranded chromo¬ some is formed by two tightly coiled DNA strands (chromatids) joined at a point called the centromere. During the middle stage of cell division, the centromere duplicates, and the chromatid pair separates. Following cell division, the separated chromatids uncoil; the loosely coiled DNA, wrapped around its associated proteins (histones) to form beaded structures called nucleosomes, is termed chromatin.