A water wheel is a machine for converting the energy of flowing or falling water into useful forms of power in a watermill. A water wheel consists of a wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface. Water wheels were still in commercial use well into the 20th century but they are no longer in common use. Uses included milling flour in gristmills, grinding wood into pulp for papermaking, hammering wrought iron, ore crushing and pounding fiber for use in the manufacture of cloth; some water wheels are fed by water from a mill pond, formed when a flowing stream is dammed. A channel for the water flowing to or from a water wheel is called a mill race; the race bringing water from the mill pond to the water wheel is a headrace. In the mid to late 18th century John Smeaton's scientific investigation of the water wheel led to significant increases in efficiency supplying much needed power for the Industrial Revolution. Water wheels began being displaced by the smaller, less expensive and more efficient turbine, developed by Benoît Fourneyron, beginning with his first model in 1827.
Turbines are capable of handling high heads, or elevations, that exceed the capability of practical-sized waterwheels. The main difficulty of water wheels is their dependence on flowing water, which limits where they can be located. Modern hydroelectric dams can be viewed as the descendants of the water wheel, as they too take advantage of the movement of water downhill. Water wheels come in two basic designs: a horizontal wheel with a vertical axle; the latter can be subdivided according to where the water hits the wheel into backshot overshot, breastshot and stream-wheels. The term undershot can refer to any wheel where the water passes under the wheel but it implies that the water entry is low on the wheel. Most water wheels in the United Kingdom and the United States are vertical wheels rotating about a horizontal axle, but in the Scottish highlands and parts of Southern Europe mills had a horizontal wheel. Overshot and backshot water wheels are used where the available height difference is more than a couple of meters.
Breastshot wheels are more suited to large flows with a moderate head. Undershot and stream wheel use large flows at no head. There is an associated millpond, a reservoir for storing water and hence energy until it is needed. Larger heads store more potential energy for the same amount of water so the reservoirs for overshot and backshot wheels tend to be smaller than for breast shot wheels. Overshot and pitchback water wheels are suitable where there is a small stream with a height difference of more than 2 meters in association with a small reservoir. Breastshot and undershot wheels can be used on high volume flows with large reservoirs. A horizontal wheel with a vertical axle. Called a tub wheel, Norse mill or Greek mill, the horizontal wheel is a primitive and inefficient form of the modern turbine; however if it delivers the required power the efficiency is of secondary importance. It is mounted inside a mill building below the working floor. A jet of water is directed on to the paddles of the water wheel.
This is a simple system without gearing so that the vertical axle of the water wheel becomes the drive spindle of the mill. The earliest known reference to water wheels dates to about 400 BCE, the earliest horizontal axis wheels date to about 200 BCE, so vertical axis mills pre-date horizontal axis mills by about two centuries. A stream wheel is a vertically mounted water wheel, rotated by the water in a water course striking paddles or blades at the bottom of the wheel; this type of water wheel is the oldest type of horizontal axis wheel. They are known as free surface wheels because the water is not constrained by millraces or wheel pit. Stream wheels are cheaper and simpler to build, have less of an environmental impact, than other type of wheel, they do not constitute a major change of the river. Their disadvantages are their low efficiency, which means that they generate less power and can only be used where the flow rate is sufficient. A typical flat board undershot wheel uses about 20 percent of the energy in the flow of water striking the wheel as measured by English civil engineer John Smeaton in the 18th century.
More modern wheels have higher efficiencies. Stream wheels gain little or no advantage from head, a difference in water level. Stream wheels mounted on floating platforms are referred to as ship wheels and the mill as a ship mill; the earliest were constructed by the Byzantine general Belisarius during the siege of Rome in 537. They were sometimes mounted downstream from bridges where the flow restriction of the bridge piers increased the speed of the current, they were inefficient but major advances were made in the eighteenth century. An undershot wheel is a vertically mounted water wheel with a horizontal axle, rotated by the water from a low weir striking the wheel in the bottom quarter. Most of the energy gain comparatively little from the head, they are similar in design to stream wheels. The term undershot is sometimes used with related but different meanings: all wheels where the water passes under the wheel wheels where the water enters in the bottom quarter. Wheels where paddles are placed into the flow of a stream.
See stream above. This is the oldest type of vertical water wheel; the word breastshot is used in a variety o
Rosa × alba
Rosa × alba, the white rose of York, is a hybrid rose of unknown parentage, cultivated in Europe since ancient times. It may have been grown for the sweet scent of the flowers, but is now used as a winter-hardy garden shrub. Cultivated forms have white or pink flowers, most have many petals. Hybrid cultivars have been produced with red or yellow flowers. Rosa × alba plants are tall shrubs with arching bluish-green leaves, they bloom only in mid summer. They are cold hardy and disease resistant, hence they are used to create new varieties for subarctic climates like northern Scandinavia and Canada; these magnificent shrubs can withstand shade and semishade, are found abandoned in semi wild situations. In Sweden and Finland the French bred ` Minette' has been considered; the Mustiala rose belongs to the Finns' tradition of roses "and is unknown outside the Nordic countries, although in 1819 it was bred in France". Found alba roses are common in Germany. Rosa × alba is hexaploid, with six sets of chromosomes in each cell, which means that it interbreeds only with the more common diploid and pentaploid roses.
Maskew and Primavesi concluded in 2005 that a 1993 suggestion by Graham and Primavesi that it was derived by chromosome duplication from a triploid offspring of R. arvensis and R. gallica had been mistaken. R. alba shares some nuclear DNA sequences with R. canina and may be derived from hybridization between that species and R. gallica. Cultivars of Rosa × alba that are still grown include: Rosa'Alba Foliacea' Rosa'Alba Maxima' Rosa'Alba Semi-plena' Rosa'Alba' Suaveolens' Rosa'Amélia' Rosa'Belle Amour' Rosa'Blanche de Belgique' Rosa'Céleste' Rosa'Chloris' Rosa'Félicité Parmentier' Rosa'Great Maiden's Blush' Rosa'Jeanne d'Arc' Rosa'Königin von Dänemark' Rosa'Mme Legras de St Germain' Hybrid cultivars include: Rosa'Mme Plantier', an old rose with feathery sepals and cream flowers fading to white Rosa'Crimson Blush', with red flowers, introduced 1988 Rosa'Lemon Blush', with pale yellow flowers, introduced 1988 Rosa'Morning Blush', white with pink and red edges, introduced 1988 Rosa'Royal Blush', with pale pink flowers, introduced 1988 Rosa'Tender Blush', with pale apricot flowers, introduced 1988
1925 Santa Barbara earthquake
The 1925 Santa Barbara earthquake hit the area of Santa Barbara, California on June 29, with a moment magnitude between 6.5 and 6.8 and a maximum Mercalli Intensity of IX. It resulted in 13 casualties and destroyed the historic center of the city, with damage estimated at $8 million. Although no foreshocks were reported felt before the mainshock, a pressure gauge recording card at the local waterworks showed disturbances beginning at 3:27 a.m. which were caused by foreshocks. At 6:44 a.m. the mainshock occurred. The epicenter of the earthquake was located in the sea off the coast of Santa Barbara, in the Santa Barbara Channel; the fault on which it occurred appears to have been an extension of the Mesa fault or the Santa Ynez system. The earthquake was felt from Paso Robles to the north to Santa Ana to the south and to Mojave to the east. Major damage occurred in the city of Santa Barbara and along the coast, as well as north of Santa Ynez Mountains, including Santa Ynez and Santa Maria valleys.
Though thirteen people died, it may have been far worse without the actions of three heroes, who shut off the town gas and electricity preventing a catastrophic fire. Most homes survived the earthquake in good condition, although nearly every chimney in the city crumbled; the downtown of Santa Barbara was destroyed. Only a few buildings along State Street, the main commercial street, remained standing after the earthquake; the City Cab building and The Californian and Arlington garages, all large and occupied parking structures, collapsed full with cars. Many other vehicles were crushed in the downtown area. At least one death resulted when a driver near the San Marcos building was crushed as walls of buildings fell onto cars parked there. In the business district, an area of about 36 blocks, only a few structures were not damaged, many had to be demolished and rebuilt; the facade of the church of the Mission Santa Barbara was damaged and lost its statues. Many important buildings, including hotels and the Potter Theater, were lost.
The courthouse, library and churches were among the buildings sustaining serious damage. Concrete curbs buckled in every block in Santa Barbara. Pavement on the boulevard along the beach was displaced by about 20–36 centimeters, but the pavement in the downtown was not damaged; the earthen Sheffield Dam had been built near the city in 1917. It held 30 million US gallons of water; the soil under the dam liquefied during the earthquake and the dam collapsed. This was the only dam to fail during an earthquake in the US until the Lower San Fernando Dam failed in 1971; when it burst, a wall of water swept between Voluntario and Alisos Streets destroying trees, three houses and flooding the lower part of town to a depth of 2 feet. The Southern Pacific Company Railroad tracks were damaged in several places between Ventura and Gaviota. In particular, a portion between Naples and Santa Barbara was badly displaced. Seaside bluffs fell into the ocean, a slight tsunami was noted by offshore ships; the town was cut off from telephone and telegraph, news from the outside world arrived by shortwave radio.
The absence of post-earthquake fire permitted scientists to study earthquake damage to various types of construction. The American Legion and the Naval Reserves from the Naval Reserve Center Santa Barbara helped provide order amidst the chaos and manned posts and provided patrols throughout the town to inhibit looting of the damaged businesses and homes. Additional fire and police personnel arrived from as far as Los Angeles to assist the sailors and soldiers in maintaining order. Three strong aftershocks occurred in the next few hours, though none causing any additional damage, with events occurring at 8:08, 10:45, 10:57 am, many smaller shocks continued throughout the day. An aftershock on July 3 caused damaged chimneys. Since the downtown of Santa Barbara suffered irreparable damage, there was a large-scale construction effort in 1925 and 1926 aimed at removing or repairing damaged structures and constructing new buildings; this development altered the character of the city center. Before the earthquake, a considerable part of the center was built in the Moorish Revival style.
After the earthquake, the decision was made to rebuild it in the Spanish Colonial Revival style. This effort was undertaken by the Santa Barbara Community Arts Association, founded in the beginning of the 1920s and viewed the earthquake as the opportunity to rebuild the city center in the unified architectural style. Many architects were invited to design the building facades, among them James Osborne Craig, George Washington Smith, Carleton Winslow, Bertram Goodhue, Winsor Soule. Lionel Pries spent a year in Santa Barbara; as a result, many buildings listed on National Register of Historic Places were designed in the late 1920s, among them the Santa Barbara County Courthouse and the front of the Andalucia Building. Building codes in Santa Barbara were made more stringent after the earthquake demonstrated that traditional construction techniques of unreinforced concrete and masonry were unsafe and unlikely to survive strong temblors. List of earthquakes in 1925 List of earthquakes in California List of earthquakes in the United States Sources 1925 Santa Barbara Earthquake Survivor interview Views of Earthquake Damage in Santa Barbara, California 1925, finding aid and online photo collection, Bancroft Library, University of California, Berkeley M 6.8 - 14km SSE of Isla Vista, CA
National Park Service
The National Park Service is an agency of the United States federal government that manages all national parks, many national monuments, other conservation and historical properties with various title designations. It was created on August 25, 1916, by Congress through the National Park Service Organic Act and is an agency of the United States Department of the Interior; the NPS is charged with a dual role of preserving the ecological and historical integrity of the places entrusted to its management, while making them available and accessible for public use and enjoyment. As of 2018, the NPS employs 27,000 employees who oversee 419 units, of which 61 are designated national parks. National parks and national monuments in the United States were individually managed under the auspices of the Department of the Interior; the movement for an independent agency to oversee these federal lands was spearheaded by business magnate and conservationist Stephen Mather, as well as J. Horace McFarland. With the help of journalist Robert Sterling Yard, Mather ran a publicity campaign for the Department of the Interior.
They wrote numerous articles that praised the scenic and historic qualities of the parks and their possibilities for educational and recreational benefits. This campaign resulted in the creation of a National Park Service. On August 25, 1916, President Woodrow Wilson signed a bill that mandated the agency "to conserve the scenery and the natural and historic objects and wildlife therein, to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations." Mather became the first director of the newly formed NPS. On March 3, 1933, President Herbert Hoover signed the Reorganization Act of 1933; the act would allow the President to reorganize the executive branch of the United States government. It wasn't until that summer when the new President, Franklin D. Roosevelt, made use of this power. Deputy Director Horace M. Albright had suggested to President Roosevelt that the historic sites from the American Civil War should be managed by the National Park Service, rather than the War Department.
President Roosevelt issued two Executive orders to make it happen. These two executive orders not only transferred to the National Park Service all the War Department historic sites, but the national monuments managed by the Department of Agriculture and the parks in and around the capital, run by an independent office. In 1951, Conrad Wirth became director of the National Park Service and went to work on bringing park facilities up to the standards that the public expected; the demand for parks after the end of the World War II had left the parks overburdened with demands that could not be met. In 1952, with the support of President Dwight D. Eisenhower, he began Mission 66, a ten-year effort to upgrade and expand park facilities for the 50th anniversary of the Park Service. New parks were added to preserve unique resources and existing park facilities were upgraded and expanded. In 1966, as the Park Service turned 50 years old, emphasis began to turn from just saving great and wonderful scenery and unique natural features to making parks accessible to the public.
Director George Hartzog began the process with the creation of the National Lakeshores and National Recreation Areas. Since its inception in 1916, the National Park Service has managed each of the United States' national parks, which have grown in number over the years to 60. Yellowstone National Park was the first national park in the United States. In 1872, there was no state government to manage it, so the federal government assumed direct control. Yosemite National Park began as a state park. Yosemite was returned to federal ownership. At first, each national park was managed independently, with varying degrees of success. In Yellowstone, the civilian staff was replaced by the U. S. Army in 1886. Due to the irregularities in managing these national treasures, Stephen Mather petitioned the federal government to improve the situation. In response, Secretary of the Interior Franklin K. Lane challenged him to lobby for creating a new agency, the National Park Service, to manage all national parks and some national monuments.
Mather was successful with the ratification of the National Park Service Organic Act in 1916. The agency was given authority over other protected areas, many with varying designations as Congress created them; the National Park System includes. The title or designation of a unit need not include the term park; the System as a whole is considered to be a national treasure of the United States, some of the more famous national parks and monuments are sometimes referred to metaphorically as "crown jewels". The system encompasses 84.4 million acres, of which more than 4.3 million acres remain in private ownership. The largest unit is Wrangell-St. Elias National Park and Preserve, Alaska. At 13,200,000 acres, it is over 16 percent of the entire system; the smallest unit in the system is Thaddeus Kosciuszko National Memorial, Pennsylvania, at 0.02 acre. In addition to administering its units and other properties, the National Park Service provides technical and financial assistance to several "affiliated areas" authorized by Congress.
The largest affiliated area is New Jersey Pinelands National Reserve at 1,164,025 acres. The smallest is Benjamin Franklin National Memorial at less than 0.01 acres. Although all units of the Nat
Santa Ynez Mountains
The Santa Ynez Mountains are a portion of the Transverse Ranges, part of the Pacific Coast Ranges of the west coast of North America. It is the westernmost range in the Transverse Ranges; the range is a large fault block of Cenozoic age created by the movements of the Santa Ynez Fault. A narrow range, the Santa Ynez Mountains rise on its north side and drops off dramatically along the range's south face; the Santa Ynez Mountains begin as a series of volcanic hills near Point Arguello, transitions eastward into a single, well-defined ridge extending from Gaviota Peak to Matilija Creek. The range is somewhat contiguous with the Topatopa Mountains beyond to the east, which terminates abruptly at Sespe Creek; the climate of the range is Mediterranean with semi-arid characteristics. Most of the range lies in the California chaparral and woodlands ecoregion. At the crest, rainier regions support large groves of conifers Coulter pines, they are principally in Santa Barbara County, with an eastward extension into Ventura County, are unusual in being an east-west trending mountain range—one of the few in the United States.
The range is within Los Padres National Forest. The northern boundary of the range is marked by the Santa Ynez Fault, the massive thrust fault that uplifted the mountains 5 million years ago. Notable features along the fault which mark the boundary of the range include Jalama Creek and the Santa Ynez River to the west and Matilija Creek in the far east. To the north of the range are the San Rafael Mountains; the southern slopes of the range drop off into a series of alluvial plains adjoining the Santa Barbara Channel. They tend to be made up of unconsolidated riverine deposits overlying shale bedrock. Laterally, the mountains extend from an eastern terminus at the canyon of the Ventura River and Matilija Creek, north of Ojai, west across the Santa Barbara County line, to north of the city of Santa Barbara, west, paralleling the coast, to the city of Lompoc and Vandenberg Air Force Base; the Santa Ynez River flows just north of the mountains. Before reaching Lompoc the mountain range diverges into two low ridges, separated by Jalama Creek, which vanish into the Pacific Ocean.
The mountains parallel the Channel Islands to the south, another east-west trending range, a geologic extension of the Santa Monica Mountains. Principal summits in the Santa Ynez range include Divide Peak, 4,707 ft, La Cumbre Peak, 3,985 ft, Santa Ynez Peak, 4,298 ft. There are several important passes, including Gaviota Pass in the western portion of the range, through which runs U. S. Highway 101 via the Gaviota Tunnel; the highest point, an unnamed and unmarked crest colloquially called Peak 4864, is located right above the eastern terminus of the range, near Lake Casitas and Matilija Canyon. Geologically the mountains are young and of sedimentary origin; the most common rock types in the range are sandstones and shales, with some limestone in the western portion of the range. Volcanic rocks can be found at the western extremity of the range, near Point Arguello, while some schists of the Franciscan Assemblage are exposed in a number of locations; the Santa Ynez Mountains were uplifted in the late Miocene Epoch, about five million years ago, along the Santa Ynez Fault, a feature, considered to be active.
Being young, the slopes are steep and the topography is rugged. Dramatic sandstone formations, including outcrops of the resistant Coldwater and Matilija formations, are visible at many locations in the range; the predominant ground cover is chaparral, with coastal sage scrub, oak woodland and grasslands at lower elevations. Isolated stands of conifers and other evergreen trees such as bay laurel, tanbark oak and madrone grow on the higher parts of the northern slopes, which are cooler and have a somewhat higher annual rainfall than the southern slopes. At lower elevations on the southern side of the range, a frost-free zone, avocados are grown in considerable quantity. Early inhabitants included the Chumash people who left behind many examples of rock art including those at Painted Cave SHP. Large portions of the mountain range are now in the Los Padres National Forest, although there are private inholdings, including some substantial communities, such as the Painted Cave community where Jane Fonda owned the ridgetop Laurel Springs Ranch into the late 1990s.
Other famous residents have included Ronald Reagan, whose Rancho del Cielo is at the top of the range west of Santa Barbara. The Cold Spring Tavern is a popular local gathering place beneath the Cold Spring Bridge; the climate of the mountain range is Mediterranean. Summers are warm and entirely rainless, save for occasional monsoonal showers in August and September, though in most years there is no rain between May and October. Most of the higher coastal slopes of the range average between 30 inches to 40 inches of precipitation per year, about twice the total of the coastal plain below. About one year in three snow falls on the higher peaks in the mountains, but it stays for longer than a few days. In the late spring and early summer the mountains and areas below to the south are subject to occasional intense sundowner winds, a type of foehn wind in which the air is
Santa Barbara, California
Santa Barbara is the county seat of Santa Barbara County in the U. S. state of California. Situated on a south-facing section of coastline, the longest such section on the West Coast of the United States, the city lies between the steeply rising Santa Ynez Mountains and the Pacific Ocean. Santa Barbara's climate is described as Mediterranean, the city has been promoted as the "American Riviera"; as of 2014, the city had an estimated population of 91,196, up from 88,410 in 2010, making it the second most populous city in the county after Santa Maria. The contiguous urban area, which includes the cities of Goleta and Carpinteria, along with the unincorporated regions of Isla Vista, Mission Canyon, Hope Ranch and others, has an approximate population of 220,000; the population of the entire county in 2010 was 423,895. In addition to being a popular tourist and resort destination, the city economy includes a large service sector, technology, health care, agriculture and local government. In 2004, the service sector accounted for 35% of local employment.
Education in particular is well represented, with four institutions of higher learning on the south coast. The Santa Barbara Airport serves the city, Santa Barbara Aviation provides jet charter aircraft and train service is provided by Amtrak the Pacific Surfliner which runs from San Diego to San Luis Obispo). U. S. Highway 101 connects the Santa Barbara area with Los Angeles to the southeast and San Francisco to the northwest. Behind the city, in and beyond the Santa Ynez Mountains, is the Los Padres National Forest, which contains several remote wilderness areas. Channel Islands National Park and Channel Islands National Marine Sanctuary are located 20 miles offshore. Evidence of human habitation of the area begins at least 13,000 years ago. Evidence for a Paleoindian presence includes a fluted Clovis-like point found in the 1980s along the western Santa Barbara County coast, as well as the remains of Arlington Springs Man, found on Santa Rosa Island in the 1960s. An estimated 8,000 to 10,000 Chumash lived on the south coast of Santa Barbara County at the time of the first European explorations.
Five Chumash villages flourished in the area. The present-day area of Santa Barbara City College was the village of Mispu. Portuguese explorer João Cabrilho, sailing for the Kingdom of Spain, sailed through what is now called the Santa Barbara Channel in 1542, anchoring in the area. In 1602, Spanish maritime explorer Sebastián Vizcaíno gave the name "Santa Barbara" to the channel and to one of the Channel Islands. A land expedition led by Gaspar de Portolà visited around 1769, Franciscan missionary Juan Crespi, who accompanied the expedition, named a large native town "Laguna de la Concepcion". Cabrillo's earlier name, however, is the one; the first permanent European residents were Spanish missionaries and soldiers under Felipe de Neve, who came in 1782 to build the Presidio. They were sent both to fortify the region against expansion by other powers such as England and Russia, to convert the natives to Christianity. Many of the Spaniards brought their families with them, those formed the nucleus of the small town – at first just a cluster of adobes – that surrounded the Presidio of Santa Barbara.
The Santa Barbara Mission was established on the Feast of Saint Barbara, December 4, 1786. It was the tenth of the California Missions to be founded by the Spanish Franciscans, it was dedicated by Padre Fermín Lasuén, who succeeded Padre Junipero Serra as the second president and founder of the California Franciscan Mission Chain. The Mission fathers began the slow work of converting the native Chumash to Christianity, building a village for them on the Mission grounds; the Chumash laborers built a connection between the canyon creek and the Santa Barbara Mission water system through the use of a dam and an aqueduct. During the following decades, many of the natives died of diseases such as smallpox, against which they had no natural immunity; the most dramatic event of the Spanish period was the powerful 1812 earthquake, tsunami, with an estimated magnitude of 7.1, which destroyed the Mission as well as the rest of the town. The Mission was rebuilt by 1820 after the earthquake. Following the earthquake, the Mission fathers chose to rebuild in a grander manner, it is this construction that survives to the present day, the best-preserved of the California Missions, still functioning as an active church by the Franciscans.
After the Mexican government secularized the missions in the 1830s, the baptismal and burial records of other missions were transferred to Santa Barbara, now found in the Santa Barbara Mission Archive-Library. C-SPAN has produced a program on the mission archive-library; the Spanish period ended in 1822 with the end of the Mexican War of Independence, which terminated 300 years of colonial rule. The flag of Mexico went up the flagpole at the Presidio, but only for 24 years. Santa Barbara street names reflect this time period as well; the names de le Guerra and Carrillo come from citizens of the town of this time. They were instrumental in building up the town, so they were honored by having streets after them. After the forced secularization of the Missions in 1833
Rosa chinensis, known as the China rose or Chinese rose, is a member of the genus Rosa native to Southwest China in Guizhou and Sichuan Provinces. The species is extensively cultivated as an ornamental plant in China, numerous cultivars have been selected which are known as the China roses, it has been extensively interbred with Rosa gigantea to produce Rosa × odorata and by further hybridization the tea roses and hybrid tea roses. It is a shrub growing to 1–2 m tall; the leaves are pinnate, have 3–5 leaflets, each leaflet 2.5–6 cm long and 1–3 cm broad. In the wild species, the flowers have five pink to red petals; the fruit is a red hip 1–2 cm diameter. Three varieties of the species are recognized in the Flora of China: R. chinensis var. chinensis, originated in cultivation, with red petals R. chinensis var. spontanea, native to Guizhou and Sichuan, with red petals R. chinensis var. semperflorens Koehne, originated in cultivation, with dark red or purple petals Cultivars developed from Rosa chinensis have been important in the breeding of many modern garden roses by providing the repeat-blooming characteristic, although this is not a feature of the wild species.
Garden roses Media related to Rosa chinensis at Wikimedia Commons Plants for a Future: Rosa chinensis