An ocean is a body of water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean; these are, in descending order by area, the Pacific, Indian and Arctic Oceans. The word "ocean" is used interchangeably with "sea" in American English. Speaking, a sea is a body of water or enclosed by land, though "the sea" refers to the oceans. Saline water covers 361,000,000 km2 and is customarily divided into several principal oceans and smaller seas, with the ocean covering 71% of Earth's surface and 90% of the Earth's biosphere; the ocean contains 97% of Earth's water, oceanographers have stated that less than 5% of the World Ocean has been explored. The total volume is 1.35 billion cubic kilometers with an average depth of nearly 3,700 meters. As the world ocean is the principal component of Earth's hydrosphere, it is integral to life, forms part of the carbon cycle, influences climate and weather patterns; the World Ocean is the habitat of 230,000 known species, but because much of it is unexplored, the number of species that exist in the ocean is much larger over two million.
The origin of Earth's oceans is unknown. Extraterrestrial oceans may be composed of water or other compounds; the only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their geologic histories and Venus are theorized to have had large water oceans; the Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, a runaway greenhouse effect may have boiled away the global ocean of Venus. Compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of natural satellites; the Solar System's giant planets are thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may exist on exoplanets and exomoons, including surface oceans of liquid water within a circumstellar habitable zone.
Ocean planets are a hypothetical type of planet with a surface covered with liquid. The word ocean comes from the figure in classical antiquity, the elder of the Titans in classical Greek mythology, believed by the ancient Greeks and Romans to be the divine personification of the sea, an enormous river encircling the world; the concept of Ōkeanós has an Indo-European connection. Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases. Though described as several separate oceans, the global, interconnected body of salt water is sometimes referred to as the World Ocean or global ocean; the concept of a continuous body of water with free interchange among its parts is of fundamental importance to oceanography. The major oceanic divisions – listed below in descending order of area and volume – are defined in part by the continents, various archipelagos, other criteria.
Oceans are fringed by smaller, adjoining bodies of water such as seas, bays and straits. The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system, part of every ocean and the longest mountain range in the world; the continuous mountain range is 65,000 km long. The total mass of the hydrosphere is about 1.4 quintillion metric tons, about 0.023% of Earth's total mass. Less than 3% is freshwater; the area of the World Ocean is about 361.9 million square kilometers, which covers about 70.9% of Earth's surface, its volume is 1.335 billion cubic kilometers. This can be thought of as a cube of water with an edge length of 1,101 kilometers, its average depth is about 3,688 meters, its maximum depth is 10,994 meters at the Mariana Trench. Nearly half of the world's marine waters are over 3,000 meters deep; the vast expanses of deep ocean cover about 66% of Earth's surface. This does not include seas not connected to the World Ocean, such as the Caspian Sea; the bluish ocean color is a composite of several contributing agents.
Prominent contributors include dissolved organic chlorophyll. Mariners and other seafarers have reported that the ocean emits a visible glow which extends for miles at night. In 2005, scientists announced that for the first time, they had obtained photographic evidence of this glow, it is most caused by bioluminescence. Oceanographers divide the ocean into different vertical zones defined by physical and biological conditions; the pelagic zone includes all open ocean regions, can be divided into further regions categorized by depth and light abundance. The photic zone includes the oceans from the surface to a depth of
A tile is a thin object square or rectangular in shape. Tile is a manufactured piece of hard-wearing material such as ceramic, metal, baked clay, or glass used for covering roofs, walls, or other objects such as tabletops. Alternatively, tile can sometimes refer to similar units made from lightweight materials such as perlite and mineral wool used for wall and ceiling applications. In another sense, a tile is a construction tile or similar object, such as rectangular counters used in playing games; the word is derived from the French word tuile, which is, in turn, from the Latin word tegula, meaning a roof tile composed of fired clay. Tiles are used to form wall and floor coverings, can range from simple square tiles to complex or mosaics. Tiles are most made of ceramic glazed for internal uses and unglazed for roofing, but other materials are commonly used, such as glass, cork and other composite materials, stone. Tiling stone is marble, granite or slate. Thinner tiles can be used on walls than on floors, which require more durable surfaces that will resist impacts.
Decorative tilework or tile art should be distinguished from mosaic, where forms are made of great numbers of tiny irregularly positioned tesserae, each of a single color of glass or sometimes ceramic or stone. The earliest evidence of glazed brick is the discovery of glazed bricks in the Elamite Temple at Chogha Zanbil, dated to the 13th century BC. Glazed and colored bricks were used to make low reliefs in Ancient Mesopotamia, most famously the Ishtar Gate of Babylon, now reconstructed in Berlin, with sections elsewhere. Mesopotamian craftsmen were imported for the palaces of the Persian Empire such as Persepolis; the use of sun-dried bricks or adobe was the main method of building in Mesopotamia where river mud was found in abundance along the Tigris and Euphrates. Here the scarcity of stone may have been an incentive to develop the technology of making kiln-fired bricks to use as an alternative. To strengthen walls made from sun-dried bricks, fired bricks began to be used as an outer protective skin for more important buildings like temples, city walls and gates.
Making fired. Fired bricks are solid masses of clay heated in kilns to temperatures of between 950° and 1,150°C, a well-made fired brick is an durable object. Like sun-dried bricks they were made in wooden molds but for bricks with relief decorations special molds had to be made. Rooms with tiled floors made of clay decorated with geometric circular patterns have been discovered from the ancient remains of Kalibangan and AhladinoTiling was used in the second century by the Sinhalese kings of ancient Sri Lanka, using smoothed and polished stone laid on floors and in swimming pools. Historians consider the techniques and tools for tiling as well advanced, evidenced by the fine workmanship and close fit of the tiles. Tiling from this period can be seen in Ruwanwelisaya and Kuttam Pokuna in the city of Anuradhapura; the Achaemenid Empire decorated buildings with glazed brick tiles, including Darius the Great's palace at Susa, buildings at Persepolis. The succeeding Sassanid Empire used tiles patterned with geometric designs, plants and human beings, glazed up to a centimeter thick.
Early Islamic mosaics in Iran consist of geometric decorations in mosques and mausoleums, made of glazed brick. Typical turquoise tiling becomes popular in 10th-11th century and is used for Kufic inscriptions on mosque walls. Seyyed Mosque in Isfahan, Dome of Maraqeh and the Jame Mosque of Gonabad are among the finest examples; the dome of Jame' Atiq Mosque of Qazvin is dated to this period. The golden age of Persian tilework began during the reign the Timurid Empire. In the moraq technique, single-color tiles were cut into small geometric pieces and assembled by pouring liquid plaster between them. After hardening, these panels were assembled on the walls of buildings, but the mosaic was not limited to flat areas. Tiles were used to cover both the exterior surfaces of domes. Prominent Timurid examples of this technique include the Jame Mosque of Yazd, Goharshad Mosque, the Madrassa of Khan in Shiraz, the Molana Mosque. Other important tile techniques of this time include girih tiles, with their characteristic white girih, or straps.
Mihrabs, being the focal points of mosques, were the places where most sophisticated tilework was placed. The 14th-century mihrab at Madrasa Imami in Isfahan is an outstanding example of aesthetic union between the Islamic calligrapher's art and abstract ornament; the pointed arch, framing the mihrab's niche, bears an inscription in Kufic script used in 9th-century Qur'an. One of the best known architectural masterpieces of Iran is the Shah Mosque in Isfahan, from the 17th century, its dome is a prime example of tile mosaic and its winter praying hall houses one of the finest ensembles of cuerda seca tiles in the world. A wide variety of tiles had to be manufactured in order to cover complex forms of the hall with consistent mosaic patterns; the result was a technological triumph as well as a dazzling display of abstract ornament. During the Safavid period, mosaic ornaments were replaced by a haft rang technique. Pictures were painted on plain rectangle tiles and fired afterwards. Besides economic reasons, the seven colors method gave more freedom to artists and was less time-consuming.
It was popular until the Qajar period, when the palette of colors was extended by orange. The seven colors of Haft Rang tiles were black, ultramarine
Los Angeles the City of Los Angeles and known by its initials L. A. is the most populous city in California, the second most populous city in the United States, after New York City, the third most populous city in North America. With an estimated population of four million, Los Angeles is the cultural and commercial center of Southern California; the city is known for its Mediterranean climate, ethnic diversity and the entertainment industry, its sprawling metropolis. Los Angeles is the largest city on the West Coast of North America. Los Angeles is in a large basin bounded by the Pacific Ocean on one side and by mountains as high as 10,000 feet on the other; the city proper, which covers about 469 square miles, is the seat of Los Angeles County, the most populated county in the country. Los Angeles is the principal city of the Los Angeles metropolitan area, the second largest in the United States after that of New York City, with a population of 13.1 million. It is part of the Los Angeles-Long Beach combined statistical area the nation's second most populous area with a 2015 estimated population of 18.7 million.
Los Angeles is one of the most substantial economic engines within the United States, with a diverse economy in a broad range of professional and cultural fields. Los Angeles is famous as the home of Hollywood, a major center of the world entertainment industry. A global city, it has been ranked 6th in the Global Cities Index and 9th in the Global Economic Power Index; the Los Angeles metropolitan area has a gross metropolitan product of $1.044 trillion, making it the third-largest in the world, after the Tokyo and New York metropolitan areas. Los Angeles hosted the 1932 and 1984 Summer Olympics and will host the event for a third time in 2028; the city hosted the Miss Universe pageant twice, in 1990 and 2006, was one of 9 American cities to host the 1994 FIFA men's soccer World Cup and one of 8 to host the 1999 FIFA women's soccer World Cup, hosting the final match for both tournaments. Home to the Chumash and Tongva, Los Angeles was claimed by Juan Rodríguez Cabrillo for Spain in 1542 along with the rest of what would become Alta California.
The city was founded on September 4, 1781, by Spanish governor Felipe de Neve. It became a part of Mexico in 1821 following the Mexican War of Independence. In 1848, at the end of the Mexican–American War, Los Angeles and the rest of California were purchased as part of the Treaty of Guadalupe Hidalgo, becoming part of the United States. Los Angeles was incorporated as a municipality on April 4, 1850, five months before California achieved statehood; the discovery of oil in the 1890s brought rapid growth to the city. The completion of the Los Angeles Aqueduct in 1913, delivering water from Eastern California assured the city's continued rapid growth; the Los Angeles coastal area was settled by the Chumash tribes. A Gabrieleño settlement in the area was called iyáangẚ, meaning "poison oak place". Maritime explorer Juan Rodríguez Cabrillo claimed the area of southern California for the Spanish Empire in 1542 while on an official military exploring expedition moving north along the Pacific coast from earlier colonizing bases of New Spain in Central and South America.
Gaspar de Portolà and Franciscan missionary Juan Crespí, reached the present site of Los Angeles on August 2, 1769. In 1771, Franciscan friar Junípero Serra directed the building of the Mission San Gabriel Arcángel, the first mission in the area. On September 4, 1781, a group of forty-four settlers known as "Los Pobladores" founded the pueblo they called El Pueblo de Nuestra Señora la Reina de los Ángeles,'The Town of Our Lady the Queen of the Angels'; the present-day city has the largest Roman Catholic Archdiocese in the United States. Two-thirds of the Mexican or settlers were mestizo or mulatto, a mixture of African and European ancestry; the settlement remained a small ranch town for decades, but by 1820, the population had increased to about 650 residents. Today, the pueblo is commemorated in the historic district of Los Angeles Pueblo Plaza and Olvera Street, the oldest part of Los Angeles. New Spain achieved its independence from the Spanish Empire in 1821, the pueblo continued as a part of Mexico.
During Mexican rule, Governor Pío Pico made Los Angeles Alta California's regional capital. Mexican rule ended during the Mexican–American War: Americans took control from the Californios after a series of battles, culminating with the signing of the Treaty of Cahuenga on January 13, 1847. Railroads arrived with the completion of the transcontinental Southern Pacific line to Los Angeles in 1876 and the Santa Fe Railroad in 1885. Petroleum was discovered in the city and surrounding area in 1892, by 1923, the discoveries had helped California become the country's largest oil producer, accounting for about one-quarter of the world's petroleum output. By 1900, the population had grown to more than 102,000; the completion of the Los Angeles Aqueduct in 1913, under the supervision of William Mulholland, assured the continued growth of the city. Due to clauses in the city's charter that prevented the City of Los Angeles from selling or providing water from the aqueduct to any area outside its borders, many adjacent city and communities became compelled to annex themselves into Los Angeles.
Los Angeles created the first municipal zoning ordinance in the United States. On September 14, 1908, the Los Angeles City Council promulgated residential and industrial land use zones; the new ordinance established three residential zones of a single type, where industrial uses were
South Bay, Los Angeles
The South Bay is a region of the Los Angeles metropolitan area, located in the southwest corner of Los Angeles County. The name stems from its geographic location stretching along the southern shore of Santa Monica Bay; the South Bay contains fifteen cities plus portions of the City of Los Angeles and unincorporated portions of the county. The area is bounded by the Pacific Ocean on the south and west and by the City of Los Angeles on the north and east; the South Bay includes: The Beach Cities El Segundo Manhattan Beach Hermosa Beach Redondo Beach Torrance The Palos Verdes Peninsula Palos Verdes Estates Rolling Hills Rolling Hills Estates Rancho Palos Verdes The southernmost neighborhoods of the City of Los Angeles Harbor City Harbor Gateway San Pedro Wilmington Inland cities of the South Bay Inglewood Hawthorne Gardena Lawndale Lomita Carson And unincorporated areas of L. A. County including: Lennox Del Aire And other small unincorporated "county strip" areas of Los Angeles County; the region is bordered on the north by LAX, on the northeast by the South Los Angeles region, on the east by the Gateway Cities, on the southeast by Long Beach.
The Harbor, San Diego and Century Freeways provide the region with its principal transportation links. The Los Angeles MTA's Blue Line is a light rail line running between Downtown Los Angeles and Downtown Long Beach, it is the first of the MTA's modern rail lines since the 1961 demise of the Pacific Electric Railway's Red Car system. The Green Line, a freeway-median light rail line serves the South Bay, it runs between Redondo Beach and Norwalk in the median of the Century Freeway, providing indirect access to Los Angeles International Airport via a shuttle bus and future automated people mover. Several ports and harbors in the South Bay provide access to Santa Catalina Island, a popular resort. In addition, Los Angeles International Airport borders El Segundo to the north in the neighborhood of Westchester, Los Angeles; the South Bay is one of the most culturally and ethnically diverse areas in the United States, with a even distribution of the population across African, Asian/Pacific Islander, European and Latino ancestry.
However, the racial and economic makeup varies across the region. El Segundo, Hermosa Beach, Redondo Beach and Torrance have a mixture of middle-to-upper class residents, of which are White American and Asian American; the Palos Verdes Peninsula and Manhattan Beach are two of the wealthiest communities in the United States, with some of the most expensive real estate in the United States. The city of Carson has large populations of African Americans. Hawthorne, Inglewood and Lawndale are diverse communities with pluralities of blacks and White Americans. Gardena is home to one of America's oldest Japanese communities. In addition, San Pedro has a large community of Croatian immigrants; the Port of Los Angeles, sprawling across the shorelines of San Pedro and Wilmington, is the busiest in the United States. When combined with the Port of Long Beach, it is the fifth-busiest in the world. Traditionally, most of the populations of Wilmington and San Pedro have worked for the port in some capacity, it is the primary driver of the Southern California economy: industrial growth in the Inland Empire is entirely attributable to increased port traffic since the 1980s.
The massive increase in cargo volume has created significant air pollution in neighboring communities. The South Bay is the traditional home of Southern California's aerospace industry. While shrunken from its Cold War peak, it still represents a major economic force, employing thousands in high-skill, high-wage engineering positions and generating enormous amounts of tax revenue. Northrop Grumman has a major facility in El Segundo where the F/A-18 Hornet fuselage is manufactured, as well as the headquarters of the Space Technology division in Redondo Beach and a facility at the Hawthorne Municipal Airport. Alcoa Fastening Systems, a subsidiary of Alcoa Inc. which produces aerospace fasteners, has their corporate headquarters located in Torrance with manufacturing facilities in both Torrance and Carson. Boeing and Lockheed Martin maintain extensive production facilities throughout the South Bay, Raytheon's Space and Airborne Systems business unit is based in El Segundo; the Los Angeles Air Force Base, in El Segundo, is the locus of much of this aerospace research activity, as it is the primary development facility for military satellites and other space programs.
DirecTV, a former subsidiary of Hughes Aircraft, is headquartered in El Segundo for this reason. SpaceX headquartered in the South Bay, is located in Hawthorne. Petroleum refining is another important component of the South Bay's economy. Major South Bay refiners include Tesoro, Phillips 66, PBF Energy and Valero; these refiners supply the lion's share of petroleum products for Southern California, as well as for Nevada and Arizona. As the Los Angeles region's oil fields are exhausted, most of the crude oil that feeds the refineries is brought in from terminals at the port. Local politicians and activists have long denounced the refineries for the amount of air pollution they generate, but in recent years these protests have been muted as the Port of Los Angeles has become the region's dominant polluter; the controversial practice of residue flaring returned to the forefront during the Sep
Asphalt known as bitumen, is a sticky and viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, is classed as a pitch. Before the 20th century, the term asphaltum was used; the word is derived from the Ancient Greek ἄσφαλτος ásphaltos. The primary use of asphalt is in road construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete, its other main uses are for bituminous waterproofing products, including production of roofing felt and for sealing flat roofs. The terms "asphalt" and "bitumen" are used interchangeably to mean both natural and manufactured forms of the substance. In American English, "asphalt" is used for a refined residue from the distillation process of selected crude oils. Outside the United States, the product is called "bitumen", geologists worldwide prefer the term for the occurring variety. Common colloquial usage refers to various forms of asphalt as "tar", as in the name of the La Brea Tar Pits.
Occurring asphalt is sometimes specified by the term "crude bitumen". Its viscosity is similar to that of cold molasses while the material obtained from the fractional distillation of crude oil boiling at 525 °C is sometimes referred to as "refined bitumen"; the Canadian province of Alberta has most of the world's reserves of natural asphalt in the Athabasca oil sands, which cover 142,000 square kilometres, an area larger than England. The word "asphalt" is derived from the late Middle English, in turn from French asphalte, based on Late Latin asphalton, the latinisation of the Greek ἄσφαλτος, a word meaning "asphalt/bitumen/pitch", which derives from ἀ-, "without" and σφάλλω, "make fall"; the first use of asphalt by the ancients was in the nature of a cement for securing or joining together various objects, it thus seems that the name itself was expressive of this application. Herodotus mentioned that bitumen was brought to Babylon to build its gigantic fortification wall. From the Greek, the word passed into late Latin, thence into French and English.
In French, the term asphalte is used for occurring asphalt-soaked limestone deposits, for specialised manufactured products with fewer voids or greater bitumen content than the "asphaltic concrete" used to pave roads. The expression "bitumen" originated in the Sanskrit words jatu, meaning "pitch", jatu-krit, meaning "pitch creating" or "pitch producing"; the Latin equivalent is claimed by some to be gwitu-men, by others, subsequently shortened to bitumen, thence passing via French into English. From the same root is derived the Anglo-Saxon word cwidu, the German word Kitt and the old Norse word kvada. In British English, "bitumen" is used instead of "asphalt"; the word "asphalt" is instead used to refer to asphalt concrete, a mixture of construction aggregate and asphalt itself. Bitumen mixed with clay was called "asphaltum", but the term is less used today. In Australian English, the word "asphalt" is used to describe a mix of construction aggregate. "Bitumen" refers to the liquid derived from the heavy-residues from crude oil distillation.
In American English, "asphalt" is equivalent to the British "bitumen". However, "asphalt" is commonly used as a shortened form of "asphalt concrete". In Canadian English, the word "bitumen" is used to refer to the vast Canadian deposits of heavy crude oil, while "asphalt" is used for the oil refinery product. Diluted bitumen is known as "dilbit" in the Canadian petroleum industry, while bitumen "upgraded" to synthetic crude oil is known as "syncrude", syncrude blended with bitumen is called "synbit"."Bitumen" is still the preferred geological term for occurring deposits of the solid or semi-solid form of petroleum. "Bituminous rock" is a form of sandstone impregnated with bitumen. The oil sands of Alberta, Canada are a similar material. Neither of the terms "asphalt" or "bitumen" should be confused with coal tars. Tar is the thick liquid product of the dry distillation and pyrolysis of organic hydrocarbons sourced from vegetation masses, whether fossilized as with coal, or freshly harvested; the majority of bitumen, on the other hand, was formed when vast quantities of organic animal materials were deposited by water and buried hundreds of metres deep at the diagenetic point, where the disorganized fatty hydrocarbon molecules joined together in long chains in the absence of oxygen.
Bitumen occurs as a solid or viscous liquid. It may be mixed in with coal deposits. Bitumen, coal using the Bergius process, can be refined into petrols such as gasoline, bitumen may be distilled into tar, not the other way around; the components of asphalt include four main classes of compounds: Naphthene aromatics, consisting of hydrogenated polycyclic aromatic compounds Polar aromatics, consisting of high molecular weight phenols and carboxylic acids produced by partial oxidation of the material Saturated hydrocarbons. Most natural bitumens a
Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic material, a natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin that resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees, or it is defined more broadly to include the same type of tissue elsewhere such as in the roots of trees or shrubs. In a living tree it performs a support function, enabling woody plants to grow large or to stand up by themselves, it conveys water and nutrients between the leaves, other growing tissues, the roots. Wood may refer to other plant materials with comparable properties, to material engineered from wood, or wood chips or fiber. Wood has been used for thousands of years for fuel, as a construction material, for making tools and weapons and paper. More it emerged as a feedstock for the production of purified cellulose and its derivatives, such as cellophane and cellulose acetate.
As of 2005, the growing stock of forests worldwide was about 434 billion cubic meters, 47% of, commercial. As an abundant, carbon-neutral renewable resource, woody materials have been of intense interest as a source of renewable energy. In 1991 3.5 billion cubic meters of wood were harvested. Dominant uses were for building construction. A 2011 discovery in the Canadian province of New Brunswick yielded the earliest known plants to have grown wood 395 to 400 million years ago. Wood can be dated by carbon dating and in some species by dendrochronology to determine when a wooden object was created. People have used wood for thousands of years for many purposes, including as a fuel or as a construction material for making houses, weapons, packaging and paper. Known constructions using wood date back ten thousand years. Buildings like the European Neolithic long house were made of wood. Recent use of wood has been enhanced by the addition of bronze into construction; the year-to-year variation in tree-ring widths and isotopic abundances gives clues to the prevailing climate at the time a tree was cut.
Wood, in the strict sense, is yielded by trees, which increase in diameter by the formation, between the existing wood and the inner bark, of new woody layers which envelop the entire stem, living branches, roots. This process is known as secondary growth; these cells go on to form thickened secondary cell walls, composed of cellulose and lignin. Where the differences between the four seasons are distinct, e.g. New Zealand, growth can occur in a discrete annual or seasonal pattern, leading to growth rings. If the distinctiveness between seasons is annual, these growth rings are referred to as annual rings. Where there is little seasonal difference growth rings are to be indistinct or absent. If the bark of the tree has been removed in a particular area, the rings will be deformed as the plant overgrows the scar. If there are differences within a growth ring the part of a growth ring nearest the center of the tree, formed early in the growing season when growth is rapid, is composed of wider elements.
It is lighter in color than that near the outer portion of the ring, is known as earlywood or springwood. The outer portion formed in the season is known as the latewood or summerwood. However, there are major differences, depending on the kind of wood; as a tree grows, lower branches die, their bases may become overgrown and enclosed by subsequent layers of trunk wood, forming a type of imperfection known as a knot. The dead branch may not be attached to the trunk wood except at its base, can drop out after the tree has been sawn into boards. Knots affect the technical properties of the wood reducing the local strength and increasing the tendency for splitting along the wood grain, but may be exploited for visual effect. In a longitudinally sawn plank, a knot will appear as a circular "solid" piece of wood around which the grain of the rest of the wood "flows". Within a knot, the direction of the wood is up to 90 degrees different from the grain direction of the regular wood. In the tree a knot is either the base of a dormant bud.
A knot is conical in shape with the inner tip at the point in stem diameter at which the plant's vascular cambium was located when the branch formed as a bud. In grading lumber and structural timber, knots are classified according to their form, size and the firmness with which they are held in place; this firmness is affected by, among other factors, the length of time for which the branch was dead while the attaching stem continued to grow. Knots materially affect cracking and warping, ease in working, cleavability of timber, they are defects which weaken timber and lower its value for structural purposes where strength is an important consideration. The weakening effect is much more serious when timber is subjected to forces perpendicular to the grain and/or tension than when under load along the grain and/or compression; the extent to which knots affect the strength of a beam depends upon their position, size and condition. A knot on the upper side is compressed. If there is a season check
Southern California is a geographic and cultural region that comprises California's southernmost counties, is the second most populous urban agglomeration in the United States. The region is traditionally described as eight counties, based on demographics and economic ties: Imperial, Los Angeles, Riverside, San Bernardino, San Diego, Santa Barbara, Ventura; the more extensive 10-county definition, which includes Kern and San Luis Obispo counties, is used and is based on historical political divisions. The Colorado Desert and the Colorado River are located on southern California's eastern border with Arizona, the Mojave Desert is located north on California's Nevada border. Southern California's southern border is part of the Mexico–United States border. Southern California includes the built-up urban area which stretches along the Pacific coast from Ventura through Greater Los Angeles down to Greater San Diego, inland to the Inland Empire and Coachella Valley, it encompasses eight metropolitan areas, three of which together form the Greater Los Angeles Combined Statistical Area with over 18 million people, the second-biggest CSA after the New York CSA.
These three MSAs are: the Los Angeles metropolitan area, the Inland Empire (, the Oxnard–Thousand Oaks–Ventura metropolitan area. In addition, Southern California contains the San Diego metropolitan area with 3.3 million people, Bakersfield metro area with 0.9 million, the Santa Barbara, San Luis Obispo, El Centro metropolitan areas. The Southern California Megaregion is larger still, extending east into Las Vegas and south across the Mexican border into Tijuana. Within southern California are two major cities, Los Angeles and San Diego, as well as three of the country's largest metropolitan areas. With a population of 4,042,000, Los Angeles is the most populous city in California and the second most populous in the United States. South of Los Angeles and with a population of 1,307,402 is San Diego, the second most populous city in the state and the eighth most populous in the nation; the counties of Los Angeles, San Diego, San Bernardino, Riverside are the five most populous in the state, are in the top 15 most populous counties in the United States.
The motion picture and music industry are centered in the Los Angeles area in southern California. Hollywood, a district of Los Angeles, gives its name to the American motion picture industry, synonymous with the neighborhood name. Headquartered in southern California are The Walt Disney Company, Sony Pictures, Universal Pictures, MGM, Paramount Pictures, 20th Century Fox, Warner Bros. Universal, Warner Bros. and Sony run major record companies. Southern California is home to a large homegrown surf and skateboard culture. Companies such as Vans, Quiksilver, No Fear, RVCA, Body Glove are all headquartered here. Skateboarder Tony Hawk; some of the most famous surf locations are in southern California as well, including Trestles, The Wedge, Huntington Beach, Malibu. Some of the world's largest action sports events, including the X Games, Boost Mobile Pro, the U. S. Open of Surfing, are held in southern California; the region is important to the world of yachting with premier events including the annual Transpacific Yacht Race, or Transpac, from Los Angeles to Hawaii.
The San Diego Yacht Club held the America's Cup, the most prestigious prize in yachting, from 1988 to 1995 and hosted three America's Cup races during that time. The first modern era triathlon was held in Mission Bay, San Diego, California in 1974. Since southern California, San Diego in particular have become a mecca for triathlon and multi-sport racing and culture. Southern California is home to many sports sports networks such as Fox Sports Net. Many locals and tourists frequent the southern California coast for its beaches; the inland desert city of Palm Springs is popular. Southern California is not a formal geographic designation and definitions of what constitutes southern California vary. Geographically, California's North-South midway point lies at 37° 9' 58.23" latitude, around 11 miles south of San Jose. When the state is divided into two areas, the term southern California refers to the 10 southernmost counties of the state; this definition coincides neatly with the county lines at 35° 47′ 28″ North latitude, which form the northern borders of San Luis Obispo and San Bernardino counties.
Another definition for southern California uses Point Conception and the Tehachapi Mountains as the northern boundary. Though there is no official definition for the northern boundary of southern California, such a division has existed from the time when Mexico ruled California and political disputes raged between the Californios of Monterey in the upper part and Los Angeles in the lower part of Alta California. Following the acquisition of California by the United States, the division continued as part of the attempt by several pro-slavery politicians to arrange the division of Alta California at 36 degrees, 30 minutes, the line of the Missouri Compromise. Instead, the passing of the Compromise of 1850 enabled California to be a