Silicones known as polysiloxanes, are polymers that include any synthetic compound made up of repeating units of siloxane, a chain of alternating silicon atoms and oxygen atoms, combined with carbon and sometimes other elements. They are heat-resistant and either liquid or rubber-like, are used in sealants, lubricants, cooking utensils, thermal and electrical insulation; some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, silicone caulk. More called polymerized siloxanes or polysiloxanes, silicones consist of an inorganic silicon-oxygen backbone chain with organic side groups attached to the silicon atoms; these silicon atoms are tetravalent. So, silicones are polymers constructed from inorganic-organic monomers. Silicones have in general the chemical formula n, where R is an organic group such as an alkyl or phenyl group. In some cases, organic side groups can be used to link two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, crosslinking, silicones can be synthesized with a wide variety of properties and compositions.
They can vary in consistency from liquid to gel to rubber to hard plastic. The most common siloxane is a silicone oil; the second largest group of silicone materials is based on silicone resins, which are formed by branched and cage-like oligosiloxanes. F. S. Kipping coined the word silicone in 1901 to describe polydiphenylsiloxane by analogy of its formula, Ph2SiO, with the formula of the ketone benzophenone, Ph2CO. Kipping was well aware that polydiphenylsiloxane is polymeric whereas benzophenone is monomeric and noted that Ph2SiO and Ph2CO had different chemistry; the discovery of the structural differences between Kipping's molecules and the ketones means that silicone is no longer the correct term and that the term siloxanes is correct according to the nomenclature of modern chemistry. Silicone is confused with silicon, but they are distinct substances. Silicon is a chemical element, a hard dark-grey semiconducting metalloid which in its crystalline form is used to make integrated circuits and solar cells.
Silicones are compounds that contain silicon, hydrogen and other kinds of atoms as well, have different physical and chemical properties. Compounds containing silicon-oxygen double bonds, now called silanones but which could deserve the name "silicone", have long been identified as intermediates in gas-phase processes such as chemical vapor deposition in microelectronics production, in the formation of ceramics by combustion; however they have a strong tendency to polymerize into siloxanes. The first stable silanone was obtained in 2014 by others. Most common are materials based on polydimethylsiloxane, derived by hydrolysis of dimethyldichlorosilane; this dichloride reacts with water as follows: n Si2Cl2 + n H2O → n + 2n HClThe polymerization produces linear chains capped with Si-Cl or Si-OH groups. Under different conditions the polymer is a cyclic, not a chain. For consumer applications such as caulks silyl acetates are used instead of silyl chlorides; the hydrolysis of the acetates produce the less dangerous acetic acid as the reaction product of a much slower curing process.
This chemistry is used in many consumer applications, such as adhesives. Branches or cross-links in the polymer chain can be introduced by using organosilicone precursors with fewer alkyl groups, such as methyltrichlorosilane and methyltrimethoxysilane. Ideally, each molecule of such a compound becomes a branch point; this process can be used to produce hard silicone resins. Precursors with three methyl groups can be used to limit molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain; when silicone is burned in air or oxygen, it forms solid silica as a white powder and various gases. The dispersed powder is sometimes called silica fume. Silicones exhibit many useful characteristics, including: Low thermal conductivity Low chemical reactivity Low toxicity Thermal stability; the ability to repel water and form watertight seals. Does not stick to many substrates, but adheres well to others, e.g. glass. Does not support microbiological growth.
Resistance to oxygen and ultraviolet light. This property has led to widespread use of silicones in the construction industry and the automotive industry. Electrical insulation properties; because silicone can be formulated to be electrically insulative or conductive, it is suitable for a wide range of electrical applications. High gas permeability: at room temperature, the permeability of silicone rubber for such gases as oxygen is 400 times that of butyl rubber, making silicone useful for medical applications in which increased aeration is desired. Conversely, silicone rubbers can not be used. Silicone can be developed into rubber sheeting, where it has other properties, such as being FDA compliant; this extends the uses of silicone sheeting to industries that demand hygiene, for example and beverage and pharmaceutical. Silicones are used in many products. Ullmann's Encyclopedia of Industrial Chemistry lists the following major categories of application: Electrical, elec
Huddersfield is a large market and university town in West Yorkshire, England. It is the 11th largest town in the United Kingdom, with a population of 162,949 at the 2011 census, it lies 14 miles southwest of Leeds and 24 miles northeast of Manchester. Huddersfield is near the confluence of the River Holme. Within the historic county boundaries of the West Riding of Yorkshire, it is the largest urban area in the metropolitan borough of Kirklees and the administrative centre of the borough; the town is known for its role in the Industrial Revolution, for being the birthplaces of rugby league, Labour Prime Minister Harold Wilson, the film star James Mason. Huddersfield is home to rugby league team Huddersfield Giants, founded in 1895, who play in the Super League, Premier League football team Huddersfield Town A. F. C. Founded in 1908; the town is home to the University of Huddersfield and the sixth form colleges Greenhead College, Kirklees College and Huddersfield New College. Huddersfield is a town of Victorian architecture.
Huddersfield railway station is a Grade I listed building described by John Betjeman as "the most splendid station façade in England", second only to St Pancras, London. The station in St George's Square was renovated at a cost of £4 million and subsequently won the Europa Nostra award for European architecture. There has been a settlement in the area for over 4,000 years; the remains of a Roman fort were unearthed in the mid 18th century at Slack near Outlane, west of the town. Castle Hill, a major landmark, was the site of an Iron Age hill fort. Huddersfield was recorded in the Domesday Book of 1086 as Odresfeld. Indeed, the modern name Huddersfield is pronounced without a word-initial /h/ in the local dialect, suggesting that the standard English pronunciation has influenced the accepted spelling. Huddersfield has been a market town since Anglo-Saxon times; the market cross is on Market Place. The manor of Huddersfield was owned by the de Lacy family until 1322, at which it reverted to royal ownership.
In 1599, William Ramsden bought the manor, the Ramsden family continued to own the manor, which came to be known as the'Ramsden Estate', until 1920. During their ownership they supported the development of the town, building the Huddersfield Cloth Hall in 1766 and the Sir John Ramsden's Canal in 1780, supporting the arrival of the railway in the 1840s. Huddersfield was a centre of civil unrest during the Industrial Revolution. In a period where Europe was experiencing frequent wars, where trade had slumped and the crops had failed, many local weavers faced losing their livelihood due to the introduction of machinery in factories. Luddites began destroying mills and machinery in response. In his book Rebels Against the Future, Kirkpatrick Sale describes how an army platoon was stationed at Huddersfield to deal with Luddites. In response, Luddites began to focus attacks on nearby towns and villages, which were less well-protected; the government campaign that crushed the movement was provoked by a murder that took place in Huddersfield.
William Horsfall, a mill-owner and a passionate prosecutor of Luddites, was killed in 1812. Although the movement faded out, Parliament began to increase welfare provision for those out of work, introduce regulations to improve conditions in the mills. Two Prime Ministers spent part of their childhood in Huddersfield: Harold Wilson and Herbert Asquith. Wilson is commemorated by a statue in front of the railway station; the Huddersfield constituency has been represented by Labour MP Barry Sheerman since its creation in 1983 and is considered a safe seat for Labour. Kirklees Council was the first in the UK to have a Green Party councillor, Nicholas Harvey, instrumental in protesting against the intended closure of the Settle and Carlisle Railway line; the town has Liberal Democrats and UKIP presences. Huddersfield was incorporated as a municipal borough in the ancient West Riding of Yorkshire in 1868; the borough comprised the parishes of Almondbury, Huddersfield, Lindley-cum-Quarmby and Lockwood.
When the West Riding County Council was formed in 1889, Huddersfield became a county borough, exempt from county council control. In 1920, the Corporation bought the Ramsden Estate from the Ramsden family, that had owned much of the town since 1599, for the sum of £1.3 million. As a result, the town became known for a time as'the town that bought itself'. To this day, much of the freehold of the town belongs to the local authority. Huddersfield expanded in 1937, assimilating parts of the Golcar and South Crosland urban districts; the county borough was abolished in 1974 and its former area was combined with that of other districts to form the Metropolitan Borough of Kirklees in West Yorkshire. Attempts by the council to gain support for city status were rejected by the population in an unofficial referendum held by the Huddersfield Daily Examiner; the council did not apply for that status in either 2002 competitions. Huddersfield had a strong liberal tradition up to the 1950s reflected in the number of liberal social clubs in the town.
The current Member of Parliament for the Huddersfield constituency is Barry Sheerman, a Labour Co-operative member. According to the United Kingdom Census 2001 the population of the Huddersfield urban sub-area of the West Yorkshire Urban Area was 146,234, the populatio
Nordic skiing encompasses the various types of skiing in which the toe of the ski boot is fixed to the binding in a manner that allows the heel to rise off the ski, unlike Alpine skiing, where the boot is attached to the ski from toe to heel. Recreational disciplines include Telemark skiing. Olympic events are cross-country skiing, ski jumping and nordic combined—competition in which athletes both cross-country ski and ski jump; the FIS Nordic World Ski Championships host these sports, plus Telemark skiing, at the championship level in the winter of every odd numbered year. Biathlon combines cross-country skiing and rifle shooting, but is not included as a Nordic discipline under FIS rules. Instead, it is under the jurisdiction of the International Biathlon Union; the biomechanics of competitive cross-country skiing and ski jumping have been the subject of serious study. Cross-country skiing requires strength and endurance and ski jumping requires aerodynamic efficiency, both of which requirements translate into specific skills to be optimized in training and competition
Tubing is a recreational activity where an individual rides on top of an inner tube, either on water, snow, or through the air. The tubes themselves are known as "donuts" or "biscuits" due to their shape. Tubing on water consists of two forms: towed and free-floating known as river tubing. According to Time Magazine, tubing was purportedly invented in Thailand by Princess Chumbhot of Nagar Svarga sometime in the middle of the 20th century, but examples of the practice were published as early as 1916, when the popularization of the automobile meant a large supply of rubber inner tubes was available to the general public. Towed tubing takes place on a large body of water such as a lake or river. One or more tube riders tether their tubes to a powered watercraft such as a motor boat or a personal watercraft; the riders are towed through the water by the watercraft. In free-floating tubing, the tube riders are untethered and conveyed by the current of a waterway. Tubers paddle with their hands and used webbed gloves to steer.
Tubes can be outfitted with tube covers or'skins'. These covers are fabric, cover the bottom of the tube, the sides, have a skirt that covers the inner diameter, while leaving room for the tuber to sit. Covers can have handles for the tuber to hold on to, it is discouraged to tie anything to the tube or use ropes of any kind as a tuber can get bound or wrapped in them and drown. The Esopus Creek in the Catskill Mountains, New York is a common place for tubing, starting in Phoenicia and proceeding eastward; as in all watersports tubers should wear appropriate safety gear such as life vests, protective water shoes and helmets. Whitewater tubing can be fun and exhilarating, the size of the tube allows a tuber to ride the river in an unencumbered manner not found in rafting or kayaking. Tubers can employ the use of such items as dry boxes and mesh bags to carry small personal items and pack out trash and bottles from their trip. Popular riverside tube rentals warn against glass due to riverside dangers.
Some law enforcement offices have prohibited kegs which were popularly chilled in metal tubs harnessed within larger tubes. Major water parks have specially designed courses for tubing called lazy rivers; these may consist of a circular, artificial river on which riders are conveyed or a linear course such as a water slide. Snow tubing is rumored to have begun as far back as the 1820s in the Alpine Mountains. Tubing on snow is a wintertime activity, similar to sledding; this kind of tubing is always performed on a hill or slope, using gravity to propel the rider to the bottom of the grade. The rider returns to the top of the slope with the tube to repeat the process; the low amount of friction between most tubes and snow allows tubers to reach considerable speeds while riding on steep slopes. Because of the circular shape of snow tubes, controlling the course and speed of a tube while riding on snow is difficult. While a sled rider can drag their arms on the snow to brake or steer to a degree, attempting this on a tube will cause the tube to spin.
This lack of control has led to injuries, some serious, when riders have struck obstacles such as trees while tubing on snow. Some ski resorts offer courses devoted to tubing; such courses have slopes or barriers on the periphery to guide the tubes along a safe course. Motorized pulley towlines are used to tow riders and their tube back to the top of the course after riding to the bottom. Adventure Point At Keystone Resort in Colorado offers snow tubing late into the summer, their elevation has been known to provide enough snow to last through the month of July. Steamboat Springs, Colorado ski mountain offers night snow tubing in ski season, it is possible to tow a tube through the snow behind a snowmobile. This is similar to towed tubing on water, only the watercraft is replaced by a snowmobile and the water with snow-covered ground. A variant of towed tubing dubbed "kite tubing" has begun to emerge; when tubes being towed on water reach high speeds, they may take flight. This is because the body of the tube creates lift.
In this way, the tube becomes a kite. A tube's ability to achieve and maintain flight depends on a number of factors including the speed at which the tube is traveling, the shape and size of the tube, the weight of the rider, how the tube itself is oriented; as most tubes are not designed for flight, the rider has little or no control over a tube after it takes to the air. This can lead to a violent crash as the rider, with or without the tube, falls back to the surface of the water. To address the poor flight characteristics of most tubes and to target thrill seekers, tubes specially designed for kite tubing have been introduced; these tubes may feature channels to allow air to flow through the tube's body, a transparent "window" for the rider to signal the boat operator, as well as more streamlined, aerodynamic designs. As of July 2006, 39 injuries and two deaths from kite tubing have been reported. Injuries have included a broken neck, punctured lung, cracked ribs, a concussion and injuries to the chest and face.
Some accidents have been linked to gusts of wind that unexpectedly altered the flight characteristics and ejected the riders. In cooperation with the U. S. Consumer Product Safety Commission, Sportsstuff Inc. voluntarily withdrew the Wego Kite Tube from the market on July 13, 2006. Related to kite tubing is the kited inflated wing, a stiffened, flexible wing or gas-inflated bladder wing, where a control bar is affixed for the kited person to direct the inflated wing s
A bristle is a stiff hair or feather, either on an animal, such as a pig, a plant, or on a tool such as a brush or broom. Synthetic materials such as nylon are used to make bristles in items such as brooms and sweepers. Bristles are used to make brushes for cleaning purposes, as they are abrasive; the bristle brush and the scrub brush are common household cleaning tools used to remove dirt or grease from pots and pans. Bristles are used on brushes other than for cleaning, notably paintbrushes. Bristles are distinguished as unflagged. In cleaning applications, flagged bristles are suited for dry cleaning, unflagged suited for wet cleaning. In painting, flagged bristles yield more application. Bristles are found on pig breeds, instead of fur; because the density is less than with fur, pigs are vulnerable to sunburn. One breed, the Tamworth pig, is endowed with a dense bristle structure such that sunburn damage to skin is minimized. Animals named for their bristles include bristlebirds, the bristle-thighed curlew, the bristle-spined porcupine, the Trinity bristle snail.
Bristles anchor worms to the soil to help them move. Paint Brush Types of Bristle Materials Used for Brushes
Water is a transparent, tasteless and nearly colorless chemical substance, the main constituent of Earth's streams and oceans, the fluids of most living organisms. It is vital for all known forms of life though it provides no calories or organic nutrients, its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient pressure, it forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of its solid state; when finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is water vapor. Water moves continually through the water cycle of evaporation, condensation and runoff reaching the sea. Water covers 71% of the Earth's surface in seas and oceans. Small portions of water occur as groundwater, in the glaciers and the ice caps of Antarctica and Greenland, in the air as vapor and precipitation.
Water plays an important role in the world economy. 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a major source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers and canals. Large quantities of water and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a wide variety of chemical substances. Water is central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, sport fishing, diving; the word water comes from Old English wæter, from Proto-Germanic *watar, from Proto-Indo-European *wod-or, suffixed form of root *wed-. Cognate, through the Indo-European root, with Greek ύδωρ, Russian вода́, Irish uisce, Albanian ujë; the identification of water as a substance Water is a polar inorganic compound, at room temperature a tasteless and odorless liquid, nearly colorless with a hint of blue.
This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the "universal solvent" for its ability to dissolve many substances. This allows it to be the "solvent of life", it is the only common substance to exist as a solid and gas in normal terrestrial conditions. Water is a liquid at the pressures that are most adequate for life. At a standard pressure of 1 atm, water is a liquid between 0 and 100 °C. Increasing the pressure lowers the melting point, about −5 °C at 600 atm and −22 °C at 2100 atm; this effect is relevant, for example, to ice skating, to the buried lakes of Antarctica, to the movement of glaciers. Increasing the pressure has a more dramatic effect on the boiling point, about 374 °C at 220 atm; this effect is important in, among other things, deep-sea hydrothermal vents and geysers, pressure cooking, steam engine design. At the top of Mount Everest, where the atmospheric pressure is about 0.34 atm, water boils at 68 °C. At low pressures, water cannot exist in the liquid state and passes directly from solid to gas by sublimation—a phenomenon exploited in the freeze drying of food.
At high pressures, the liquid and gas states are no longer distinguishable, a state called supercritical steam. Water differs from most liquids in that it becomes less dense as it freezes; the maximum density of water in its liquid form is 1,000 kg/m3. The density of ice is 917 kg/m3. Thus, water expands 9% in volume as it freezes, which accounts for the fact that ice floats on liquid water; the details of the exact chemical nature of liquid water are not well understood. Pure water is described as tasteless and odorless, although humans have specific sensors that can feel the presence of water in their mouths, frogs are known to be able to smell it. However, water from ordinary sources has many dissolved substances, that may give it varying tastes and odors. Humans and other animals have developed senses that enable them to evaluate the potability of water by avoiding water, too salty or putrid; the apparent color of natural bodies of water is determined more by dissolved and suspended solids, or by reflection of the sky, than by water itself.
Light in the visible electromagnetic spectrum can traverse a couple meters of pure water without significant absorption, so that it looks transparent and colorless. Thus aquatic plants and other photosynthetic organisms can live in water up to hundreds of meters deep, because sunlight can reach them. Water vapour is invisible as a gas. Through a thickness of 10 meters or more, the intrinsic color of water is visibly turquoise, as its absorption spectrum has
In geometry, a hexagon is a six-sided polygon or 6-gon. The total of the internal angles of any simple hexagon is 720°. A regular hexagon has Schläfli symbol and can be constructed as a truncated equilateral triangle, t, which alternates two types of edges. A regular hexagon is defined as a hexagon, both equilateral and equiangular, it is bicentric, meaning that it is both tangential. The common length of the sides equals the radius of the circumscribed circle, which equals 2 3 times the apothem. All internal angles are 120 degrees. A regular hexagon has 6 rotational symmetries and 6 reflection symmetries, making up the dihedral group D6; the longest diagonals of a regular hexagon, connecting diametrically opposite vertices, are twice the length of one side. From this it can be seen that a triangle with a vertex at the center of the regular hexagon and sharing one side with the hexagon is equilateral, that the regular hexagon can be partitioned into six equilateral triangles. Like squares and equilateral triangles, regular hexagons fit together without any gaps to tile the plane, so are useful for constructing tessellations.
The cells of a beehive honeycomb are hexagonal for this reason and because the shape makes efficient use of space and building materials. The Voronoi diagram of a regular triangular lattice is the honeycomb tessellation of hexagons, it is not considered a triambus, although it is equilateral. The maximal diameter, D, is twice the maximal radius or circumradius, R, which equals the side length, t; the minimal diameter or the diameter of the inscribed circle, d, is twice the minimal radius or inradius, r. The maxima and minima are related by the same factor: 1 2 d = r = cos R = 3 2 R = 3 2 t and d = 3 2 D; the area of a regular hexagon A = 3 3 2 R 2 = 3 R r = 2 3 r 2 = 3 3 8 D 2 = 3 4 D d = 3 2 d 2 ≈ 2.598 R 2 ≈ 3.464 r 2 ≈ 0.6495 D 2 ≈ 0.866 d 2. For any regular polygon, the area can be expressed in terms of the apothem a and the perimeter p. For the regular hexagon these are given by a = r, p = 6 R = 4 r 3, so A = a p 2 = r ⋅ 4 r 3 2 = 2 r 2 3 ≈ 3.464 r 2. The regular hexagon fills the fraction 3 3 2 π ≈ 0.8270 of its circumscribed circle.
If a regular hexagon has successive vertices A, B, C, D, E, F and if P is any point on the circumscribing circle between B and C PE + PF = PA + PB + PC + PD. The regular hexagon has Dih6 symmetry, order 12. There are 3 dihedral subgroups: Dih3, Dih2, Dih1, 4 cyclic subgroups: Z6, Z3, Z2, Z1; these symmetries express 9 distinct symmetries of a regular hexagon. John Conway labels these by a group order. R12 is full symmetry, a1 is no symmetry. P6, an isogonal hexagon constructed by three mirrors can alternate long and short edges, d6, an isotoxal hexagon constructed with equal edge lengths, but vertices alternating two different internal angles; these two forms have half the symmetry order of the regular hexagon. The