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Paper Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets.Paper is a versatile material with many uses. Whilst the most common is for writing and printing upon, it is also widely used as a packaging material, in many cleaning products, in a number of industrial and construction processes, and even as a food ingredient – particularly in Asian cultures. SONY VGN-SZ780 Laptop CPU Cooling Fan Paper, and the pulp papermaking process, was said to be developed in China during the early 2nd century AD by the Han court eunuch Cai Lun, although the earliest archaeological fragments of paper derive from the 2nd century BC in China.[1] The oldest known archaeological fragments of the immediate precursor to modern paper date to 2nd century BC in China. The pulp papermaking process is ascribed to Cai Lun, a 2nd century AD Han court eunuch.[1] With paper an effective substitute for silk in many applications, China could export silk in greater quantity, contributing to a Golden Age. SONY Vaio VGN-CR290E/AW Laptop CPU Cooling Fan Paper spread from China through the Middle East to medieval Europe in the 13th century, where the first water-powered paper mills were built.[2] In the 19th century, industrial manufacture greatly lowered its cost, enabling mass exchange of information and contributing to significant cultural shifts. In 1844, Canadian inventor Charles Fenerty and German F.G. Keller independently developed processes for pulping wood fibers.[3] ACER TravelMate 4230 Laptop CPU Cooling Fan The word "paper" is etymologically derived from Latin papyrus, which comes from the Greek πάπυρος (papuros), the word for the Cyperus papyrus plant.[4][5] Papyrus is a thick, paper-like material produced from the pith of the Cyperus papyrus plant which was used in ancient Egypt and other Mediterranean cultures for writing before the introduction of paper into the Middle East and Europe.[6] Although paper is etymologically derived from papyrus, the two are produced very differently and the development of modern paper is separate from the development of papyrus. Papyrus is a "lamination of natural plants, while paper is manufactured from fibres whose properties have been changed by maceration or disintegration.[1]ACER 23.TB2V1.003 Laptop CPU Cooling Fan To make pulp from wood, a chemical pulping process separates lignin from cellulose fibers. This is accomplished by dissolving lignin in a cooking liquor, so that it may be washed from the cellulose fibers. This preserves the length of the cellulose fibers. Paper made from chemical pulps are also known as wood-free papers–not to be confused with tree-free paper. This is because they do not contain lignin, which deteriorates over time. The pulp can also be bleached to produce white paper, but this consumes 5% of the fibers. Chemical pulping processes are not used to make paper made from cotton, which is already 90% cellulose.  IBM Lenovo Thinkpad T410 Series Laptop CPU Cooling Fan There are three main chemical pulping processes. The sulfite process dates back to the 1840s, and it was the dominant process before the second world war. The kraft process, invented in the 1870s and first used in the 1890s, is now the most commonly practiced strategy. One advantage is a chemical reaction with lignin produces heat, which can be used to run a generator. Most pulping operations using the kraft process are net contributors to the electricity grid or use the electricity to run an adjacent paper-mill. Another advantage is the process recovers and reuses all inorganic chemical reagents. Soda pulping is a specialty process used to pulp straws,bagasse, and hardwoods with high silicate content. Toshiba Qosmio G30-219 Laptop CPU Cooling Fan Mechanical pulping There are two major mechanical pulps, thermo mechanical pulp (TMP) and groundwood pulp (GW). In the TMP process, wood is chipped and then fed into large steam-heated refiners where the chips are squeezed and made into fibres between two steel discs. In the groundwood process, debarked logs are fed into grinders where they are pressed against rotating stones and made into fibres. Mechanical pulping does not remove the lignin, so the yield is very high, >95%, but also causes paper made from this pulp to yellow and become brittle over time. Mechanical pulps have rather short fibre lengths and produce weak paper. Although large amounts of electrical energy are required to produce mechanical pulp, it costs less than chemical pulp.  HP COMPAQ 2510P Series Laptop CPU Cooling Fan The pulp is fed to a paper machine where it is formed as a paper web and the water is removed from it by pressing and drying. Pressing the sheet removes the water by force. Once the water is forced from the sheet, felt (not to be confused with the traditional felt) is used to collect the water. When making paper by hand, a blotter sheet is used.  HP 610774-001 Laptop CPU Cooling Fan Drying involves using air and or heat to remove water from the paper sheet. In the earliest days of papermaking this was done by hanging the paper sheets like laundry. In more modern times, various forms of heated drying mechanisms are used. On the paper machine, the most common is the steam-heated can dryer. These dryers can heat to temperatures above 200 °F (93 °C) and are used in long sequences of more than 40 cans. The heat produced by these can easily dry the paper to less than 6% moisture. HP 532141-001 Laptop CPU Cooling Fan The paper may then undergo sizing to alter its physical properties for use in various applications. Paper at this point is uncoated. Coated paper has a thin layer of material such as calcium carbonate or china clay applied to one or both sides in order to create a surface more suitable for high-resolution halftone screens. (Uncoated papers are rarely suitable for screens above 150 lpi.) Coated or uncoated papers may have their surfaces polished by calendering. Coated papers are divided into matte, semi-matte or silk, and gloss. Gloss papers give the highest optical density in the printed image. HP 3MLX8TATP20 Laptop CPU Cooling Fan The paper is then fed onto reels if it is to be used on web printing presses, or cut into sheets for other printing processes or other purposes. The fibres in the paper basically run in the machine direction. Sheets are usually cut "long-grain", i.e. with the grain parallel to the longer dimension of the sheet. HP 580718-001 Laptop CPU Cooling Fan All paper produced by paper machines as the Fourdrinier Machine are wove paper, i.e. the wire mesh that transports the web leaves a pattern that has the same density along the paper grain and across the grain. Textured finishes, watermarks and wire patterns imitating hand-made laid paper can be created by the use of appropriate rollers in the later stages of the machine.  Toshiba Tecra A2-S119 Laptop CPU Cooling Fan Wove paper does not exhibit "laidlines", which are small regular lines left behind on paper when it was handmade in a mould made from rows of metal wires or bamboo. Laidlines are very close together. They run perpendicular to the "chainlines", which are further apart. Handmade paper similarly exhibits "deckle edges", or rough and feathery borders.[8] HP Pavilion dv5-2074dx Laptop CPU Cooling Fan The thickness of paper is often measured by caliper, which is typically given in thousandths of an inch.[10] Paper may be between 0.07 millimetres (0.0028 in) and 0.18 millimetres (0.0071 in) thick.[11] Paper is often characterized by weight. In the United States, the weight assigned to a paper is the weight of a ream, 500 sheets, of varying "basic sizes", before the paper is cut into the size it is sold to end customers. For example, a ream of 20 lb, 8.5 in × 11 in (216 mm × 279 mm) paper weighs 5 pounds, because it has been cut from a larger sheet into four pieces.[12] In the United States, printing paper is generally 20 lb, 24 lb, or 32 lb at most. Cover stock is generally 68 lb, and 110 lb or more is considered card stock. Toshiba Satellite A105-S4094 Laptop CPU Cooling Fan In Europe, and other regions using the ISO 216 paper sizing system, the weight is expressed in grammes per square metre (g/m2or usually just g) of the paper. Printing paper is generally between 60 g and 120 g. Anything heavier than 160 g is considered card. The weight of a ream therefore depends on the dimensions of the paper and its thickness. HP G50-118NR Laptop CPU Cooling Fan Most commercial paper sold in North America is cut to standard paper sizes based on customary units and is defined by the length and width of a sheet of paper. The ISO 216 system used in most other countries is based on the surface area of a sheet of paper, not on a sheet's width and length. It was first adopted in Germany in 1922 and generally spread as nations adopted the metric system. The largest standard size paper is A0 (A zero), measuring one square meter (approx. 1189x841 mm). Two sheets of A1, placed upright side by side fit exactly into one sheet of A0 laid on its side. Similarly, two sheets of A2 fit into one sheet of A1 and so forth. Common sizes used in the office and the home are A4 and A3 (A3 is the size of two A4 sheets). Packard Bell NEW90 Laptop Keyboard The density of paper ranges from 250 kg/m3 (16 lb/cu ft) for tissue paper to 1,500 kg/m3 (94 lb/cu ft) for some speciality paper. Printing paper is about 800 kg/m3 (50 lb/cu ft).[13] Much of the early paper made from wood pulp contained significant amounts of alum, a variety of aluminium sulfate salts that are significantly acidic. Alum was added to paper to assist in sizing the paper,[15] making it somewhat water resistant so that inks did not "run" or spread uncontrollably.  Packard Bell PEW91 Laptop Keyboard The early papermakers did not realize that the alum they added liberally to cure almost every problem encountered in making their product would eventually be detrimental.[16] Thecellulose fibres which make up paper are hydrolyzed by acid, and the presence of alum would eventually degrade the fibres until the paper disintegrated in a process which has come to be known as "slow fire". Documents written on rag paper were significantly more stable. The use of non-acidic additives to make paper is becoming more prevalent and the stability of these papers is less of an issue. SONY VAIO VGN-CS11Z/T Laptop Keyboard Paper made from mechanical pulp contains significant amounts of lignin, a major component in wood. In the presence of light and oxygen lignin reacts to give yellow materials, which is why newsprint and other mechanical paper yellows with age. Paper made from bleached kraft or sulfite pulps does not contain significant amounts of lignin and is therefore better suited for books, documents and other applications where whiteness of the paper is essential. Acer eMachines E732 Laptop Keyboard It is important to note that just because a paper is made of wood pulp, does not necessarily mean it is any less durable than a rag paper. The factor that determines the ageing behavior of a paper is how it was manufactured, not the original source of the fibres.[17] Furthermore, tests sponsored by the Library of Congress prove that all paper is at risk of acid decay, because cellulose itself produces formic, acetic, lactic and oxalic acids.[18]Packard Bell NEW95 Laptop Keyboard Mechanical pulping yields almost a tonne of pulp per tonne of dry wood used (which is why mechanical pulps are sometimes referred to as "high yield" pulps), which is about twice as much as chemical pulping. Consequently, paper made with mechanical pulps is often cheaper than that made with bleached chemical pulps. Mass-market paperback books and newspapers use these mechanical papers. Book publishers tend to use acid-free paper, made from fully bleached chemical pulps forhardback and trade paperback books. Acer eMachines G640 Laptop Keyboard The production and use of paper has a number of adverse effects on the environment. Worldwide consumption of paper has risen by 400% in the past 40 years leading to increase in deforestation, with 35% of harvested trees being used for paper manufacture. Logging of old growth forests accounts for less than 10% of wood pulp,[19] but is one of the most controversial issues. HP Pavilion dv7-3000sl Laptop CPU Cooling Fan Paper waste accounts for up to 40% of total waste produced in the United States each year, which adds up to 71.6 million tons of paper waste per year in the United States alone.[20] Conventional bleaching of wood pulp using elemental chlorine produces and releases into the environment large amounts of chlorinated organic compounds, including chlorinated dioxins.[21] Dioxins are recognized as a persistent environmental pollutant, regulated internationally by the Stockholm Convention on Persistent Organic Pollutants. Dioxins are highly toxic, and health effects on humans include reproductive, developmental, immune and hormonal problems. They are known to be carcinogenic. Over 90% of human exposure is through food, primarily meat, dairy, fish and shellfish, as dioxins accumulate in the food chain in the fatty tissue of animals.[22]Toshiba Satellite L675D-S7104 Laptop CPU Cooling Fan Some manufacturers have started using a new, significantly more environmentally friendly alternative to expanded plastic packaging made out of paper, known commercially as paperfoam. The packaging has very similar mechanical properties to some expanded plastic packaging, but is biodegradable and can also be recycled with ordinary paper.[23]HP Pavilion dv7-6199us Laptop CPU Cooling Fan With increasing environmental concerns about synthetic coatings (such as PFOA) and the higher prices of hydrocarbon based petrochemicals, there is a focus onzein (corn protein) as a coating for paper in high grease applications such as popcorn bags.[24] Also, synthetics such as Tyvek and Teslin have been introduced as printing media as a more durable material than paper. HP Pavilion dv7-3165dx Laptop CPU Cooling Fan United States annual pulp paper goods comsumption exceeds 110,000,000 tons per year,[citation needed] consuming 1 billion trees annually, an area of approximately 12,400 square miles; US demand for paper is increasing notwithstanding the advent of the "digital age".HP Pavilion dv7-3060ca Laptop CPU Cooling Fan Paper manufacturing is highly competitive, with historically tight margins and small operating profits. As a result, the raw materials used to make paper have to be very cost effective using cheap scalable renewable resouces coupled with relatively inexpensive ways to deliver large quantities to market. Until recently,[when?] commercial tree farming, has been shaped to account for the these tight operating margins and supply cost limitations. Virtually all paper, however, requires massive cutting, replanting and re-cutting of wide swaths of forest. These limitations have made wood pulped farm grown supply stock the paper industry's overwhelming scalable raw material of choice.  HP Pavilion dv7-3190em Laptop CPU Cooling Fan The paper industry's answer to "tree free" paper has been focused on "recycled waste paper" as a tree free alternative even though the vast majority of "recycled waste paper" originally started its life cycle from tree grown pulp. Fiber dense agricultural residues, have been known as a pulp substitute for years.[citation needed] Commercial low cost production technology coupled with limited resource abundancy plus low cost transportion to commercial business markets had created a barrier, virtually relegating true "tree free" paper from developing into anything more than small niche markets with even smaller niche market players. HP Pavilion dv7-3165dx Laptop CPU Cooling Fan However, in early 2013, it appears that at least one or more corporations have overcome these barriers.[citation needed] These several entities have apparently developed the residue rich resource allocations, scalable low cost high quality manufacturing technology coupled with reasonably cheap transportation to produce "Xerox" identical, high quality true tree free paper on a price competitive basis with all recycled paper in the US markets. A proprietary formulation of sugar cane waste bagasse and bamboo residue appears to be the materials of choice.[citation needed] HP G62-340US Laptop CPU Cooling Fan By January 2013, at least one of the "big 3" U.S. office supply chains[who?] had satisfied itself that each of the commercial quality, quantity and competitive pricing barriers has been overcome sufficiently to begin offering, on a consistant basis, true "tree free" commercial copy paper at competitive or better pricing to all recycled paper. Toshiba Satellite P300-161 Laptop CPU Cooling Fan Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae (or Gramineae) family, as well as the sedges (Cyperaceae) and the rushes (Juncaceae). The true grasses include cereals, bamboo and the grasses of lawns (turf) and grassland. Sedges include many wild marshand grassland plants, and some cultivated ones such as water chestnut (Eleocharis dulcis) and papyrus sedge (Cyperus papyrus). HP G60-244DX Laptop CPU Cooling Fan Uses for graminoids Graminoids are among the most versatile life forms. They became widespread toward the end of the Cretaceous period, and fossilized dinosaur dung (coprolites) have been found containing phytoliths of a variety that include grasses that are related to modern rice and bamboo.[1] Grasses have adapted to conditions in lush rain forests, dry deserts, cold mountains and even intertidal habitats, and are now the most widespread plant type; grass is a valuable source of food and energy for all sorts of wildlife and organics. ACER TravelMate 243LC Laptop Keyboard Graminoids are the dominant vegetation in many habitats, including grassland, salt-marsh, reedswamp and steppes. They also occur as a smaller part of the vegetation in almost every other terrestrial habitat. There are some 3,500 species of graminoids.[2]ASUS X53S Laptop Keyboard Many types of animals eat grass as their main source of food, and are called graminivores – these include cattle, sheep,horses, rabbits and many invertebrates, such as grasshoppers and the caterpillars of many brown butterflies. Grasses are also eaten by omnivorous or even occasionally by primarily carnivorous animals. ACER Aspire 5742 Laptop Keyboard In cricket, the pitch is the strip of carefully mowed and rolled grass where the bowler bowls. In the days leading up to the match it is repeatedly mowed and rolled to produce a very hard, flat surface for the ball to bounce off. The quality of the preparation can have a considerable influence on the game; a relatively grassy pitch will favor bowlers and a hard and dryer pitch, with less grass remaining, will typically favor batsmen (at least initially). As the grass dries out and is damaged over the course of the match the pitch's characteristics will change, resulting in batting on the first day of a test match being vastly different to batting on the same pitch after several days of play. HP Pavilion dv6-3205tu Laptop Keyboard Golf is very dependent on a quality grass surface. Grass on golf courses is kept in three distinct conditions: that of therough, the fairway, and the putting green. Grass on the fairway is short and even, allowing the player to cleanly strike the ball. Playing from the rough is a disadvantage because the grass is generally much longer, which may affect the flight of the ball. Grass on the putting green is the shortest and most even, ideally allowing the ball to roll smoothly over the surface. An entire industry revolves around the development and marketing of grasses for golf courses. DELL Inspiron N4050 Laptop Keyboard SONY 147996611 Laptop Keyboard In tennis, grass is grown on very hard-packed soil, and the bounce of a tennis-ball may vary depending on the grass's health, how recently it has been mowed, and the wear and tear of recent play. The surface is softer than hard courts and clay (other tennis surfaces), so the ball bounces lower, and players must reach the ball faster resulting in a different style of play which may suit some players more than others. The most famous grass tennis court in the world is Centre Court at Wimbledon located in England, home of the Wimbledon Championship. This is considered the most expensive lawn in the world. DELL G238M Laptop Keyboard Grass plays a central role in two important science fiction catastrophe novels from the 1940s and 1950s, Ward Moore's Greener Than You Think, in which the world is slowly taken over by unstoppable Bermuda Grass, and John Christopher's The Death of Grass, in which a plague that kills off all forms of grass threatens the survival of the human species. TOSHIBA Satellite M645-S4080 Laptop Keyboard For each 10 tonnes of sugarcane crushed, a sugar factory produces nearly 3 tonnes of wet bagasse. Since bagasse is a by-product of the cane sugar industry, the quantity of production in each country is in line with the quantity of sugarcane produced.  SAMSUNG R520 Laptop Keyboard The high moisture content of bagasse, typically 40 to 50%, is detrimental to its use as a fuel. In general, bagasse is stored prior to further processing. For electricity production, it is stored under moist conditions, and the mild exothermic reaction that results from the degradation of residual sugars dries the bagasse pile slightly. For paper and pulp production, it is normally stored wet in order to assist in removal of the short pith fibres, which impede the papermaking process, as well as to remove any remaining sugar. SONY VAIO VGN-N31Z/W Laptop Keyboard Bagasse is often used as a primary fuel source for sugar mills; when burned in quantity, it produces sufficient heat energy to supply all the needs of a typical sugar mill, with energy to spare. To this end, a secondary use for this waste product is in cogeneration, the use of a fuel source to provide both heat energy, used in the mill, and electricity, which is typically sold on to the consumer electricity grid. ASUS X53S Laptop Keyboard The resulting CO2 emissions are equal to the amount of CO2 that the sugarcane plant absorbed from the atmosphere during its growing phase, which makes the process of cogeneration greenhouse gas-neutral[citation needed]. In many countries (such as Australia), sugar factories significantly contribute 'green' power to the electricity supply. For example, Florida Crystals Corporation, one of America's largest sugar companies, owns and operates the largest biomass power plant in North America. The 140 MW facility uses bagasse and urban wood waste as fuel to generate enough energy to power its large milling and refining operations as well as supply enough renewable electricity for nearly 60,000 homes. DELL Inspiron 1564 Laptop Keyboard Ethanol produced from the sugar in sugarcane is a popular fuel in Brazil. The cellulose-rich bagasse is being widely investigated for its potential for producing commercial quantities of cellulosic ethanol. For example, BP Biofuels is operating a cellulosic ethanol demonstration plant based on cellulosic materials in Jennings, Louisiana. HP Mini 110-1110SA Laptop Keyboard Around 5–10% of paper production worldwide is produced from agricultural crops, valuing agricultural paper production at between $5 and 10 billion.[2] One of the most notable of these is bagasse. Paper production is the second-largest revenue stream from bagasse; the largest is electricity cogeneration. Using the by-products of agricultural crops for paper production, rather than wood, does offset commercial forestry practices. This is believed beneficial because the conversion of the rainforest to commercial tree stock and common forestry practices destroys a majority of the indigenous rainforest life forms. Packard Bell Easynote LM82 Laptop Keyboard For example, the most common commercial tree stock for short fiber pulp for paper is eucalyptus, which is considered an invasive species due to compounds in the leaves that can be toxic in large quantities (i.e. on a tree farm), and because it is considered a fire hazard.[3] A secondary benefit of substituting agricultural by-products for commercial forestry practices is the reduction of the number of farmers following logging roads into the rainforest for the purpose of burning pristine rainforests to convert to farming.[4][5]Packard Bell Easynote TK85 Laptop Keyboard It is thought that bagasse has the added advantage over other forms of papermaking feedstock in that it requires fewer greenhouse gases to collect, compared to harvesting of wood chips, as the fibre has already been transported to the factory for extracting the sugar. However, a full lifecycle analysis should be performed before using this claim commercially. Due to the ease with which bagasse can be chemically pulped, bagasse requires less bleaching chemicals than wood pulp to achieve a bright, white sheet of paper. The fibers vary in length depending on the country and cane variety but are typically about 1.3 to 1.7 mm long. Bagasse fibers are well suited for tissue, corrugating medium, newsprint, and writing paper.[6][7]Lenovo ThinkPad Edge E520 Laptop Keyboard Bagasse pulp and paper mills tend to be smaller than wood-based mills, although many world-scale factories exist. TNPL is the Largest bagasse-based Paper Mill in the world, consuming about one million tones of bagasse every year.  HP 640436-001 Laptop Keyboard Most chemical bagasse pulp mills concentrate the spent reaction chemicals and combust them to power the paper mills and to recover the reaction chemicals. Common wood chips used in pulp production are 12–25 millimetres (0.47–0.98 in) long and 2–10 millimetres (0.079–0.39 in) thick. The chips normally first enter the presteaming where they are wetted and preheated with steam. Cavities inside fresh wood chips are partly filled with liquid and partly with air. The steam treatment causes the air to expand and about 25% of the air to be expelled from the chips.  DELL Latitude D830 Laptop Keyboard FUJITSU Lifebook E8310 Laptop Keyboard The next step is to impregnate the chips with black and white liquor. Air remaining in chips at the beginning of liquor impregnation is trapped within the chips. The impregnation can be done before or after the chips enters the digester and is normally done below 100 °C (212 °F). The cooking liquors consist of a mixture of white liquor, water in chips, condensed steam and weak black liquor. In the impregnation, cooking liquor penetrates into the capillary structure of the chips and low temperature chemical reactions with the wood begin. A good impregnation is important to get a homogeneous cook and low rejects. About 40–60% of all alkali consumption in the continuous process occurs in the impregnation zone. IBM Lenovo ThinkPad R52 1870 Laptop Keyboard The wood chips are then cooked in huge pressurized vessels called digesters. Some digesters operate in batch manner and some in continuous processes. There are several variations of the cooking processes both for the batch and the continuous digesters. Digesters producing 1,000 tonnes of pulp per day and more are common with the largest producing more than 3,500 tonnes of pulp per day.[4] In a continuous digester the materials are fed at a rate which allows the pulping reaction to be complete by the time the materials exit the reactor. HP 550 Laptop Keyboard Typically delignification requires several hours at 170 to 176 °C (338 to 349 °F). Under these conditions lignin and hemicellulose degrade to give fragments that are soluble in the strongly basic liquid. The solid pulp (about 50% by weight based on the dry wood chips) is collected and washed. At this point the pulp is quite brown and is known as brown stock. The combined liquids, known as black liquor (so called because of its color), contain lignin fragments, carbohydrates from the breakdown of hemicellulose, sodium carbonate, sodium sulfate and other inorganic salts. DELL G238M Laptop Keyboard The excess black liquor is at about 15% solids and is concentrated in a multiple effect evaporator. After the first step the black liquor is about 20 - 30% solids. At this concentration the rosin soap rises to the surface and is skimmed off. The collected soap is further processed to tall oil. Removal of the soap improves the evaporation operation of the later effects. HP Mini 110-1110SA Laptop Keyboard The weak black liquor is further evaporated to 65% or even 80% solids ("heavy black liquor"[5]) and burned in therecovery boiler to recover the inorganic chemicals for reuse in the pulping process. Higher solids in the concentrated black liquor increases the energy and chemical efficiency of the recovery cycle, but also gives higher viscosity and precipitation of solids (plugging and fouling of equipment).[6][7] The combustion is carried out such that sodium sulfate is reduced to sodium sulfide by the organic carbon in the mixture: SONY VAIO VGN NR100 Laptop Keyboard 1. Na2SO4 + 2 C → Na2S + 2 CO2 This reaction is similar to thermochemical sulfate reduction in geochemistry. The molten salts ("smelt") from the recovery boiler are dissolved in a process water known as "weak wash". This process water, also known as "weak white liquor" is composed of all liquors used to wash lime mud and green liquor precipitates. The resulting solution of sodium carbonate and sodium sulfide is known as "green liquor", although it is not known exactly what causes the liquor to be green. This liquid is mixed with calcium oxide, which becomes calcium hydroxide in solution, to regenerate the white liquor used in the pulping process through an equilibrium reaction (Na2S is shown since it is part of the green liquor, but does not participate in the reaction): HP Pavilion DV7-4053 Laptop Keyboard The combination of reactions 1 through 4 form a closed cycle with respect to sodium, sulfur and calcium and is the main concept of the so-called recausticizing process where sodium carbonate is reacted to regenerate sodium hydroxide. Compaq Presario CQ57 Series Laptop Keyboard The recovery boiler also generates high pressure steam which is fed to turbogenerators, reducing the steam pressure for the mill use and generating electricity. A modern kraft pulp mill is more than self-sufficient in its electrical generation and normally will provide a net flow of energy which can be used by an associated paper mill or sold to neighboring industries or communities through to the local electrical grid.[8] Additionally, bark and wood residues are often burned in a separate power boiler to generate steam. DELL Inspiron 1750 Laptop Keyboard Although recovery boilers using G.H. Tomlinson's invention have been in general use since the early 1930s attempts have been made to find a more efficient process for the recovery of cooking chemicals. Weyerhaeuser has operated a Chemrec first generation black liquor entrained flow gasifier successfully at its New Bern plant in North Carolina, while a second generation plant is run in pilot scale at Smurfit Kappa's plant in Piteå, Sweden.[9] Screening of the pulp after pulping is a process whereby the pulp is separated from large shives, knots, dirt and other debris. The accept is the pulp. The material separated from the pulp is called reject. HP Envy 15 Laptop Keyboard The screening section consists of different types of sieves (screens) and centrifugal cleaning. The sieves are normally set up in a multistage cascade operation because considerable amounts of good fibres can go to the reject stream when trying to achieve maximum purity in the accept flow. SONY VAIO VGN-CR520E Laptop Keyboard The fiber containing shives and knots are separated from the rest of the reject and reprocessed either in a refiner and/or is sent back to the digester. The content of knots is typically 0.5 - 3.0% of the digester output, while the shives content is about 0.1- 1.0%. In a modern mill, brownstock (cellulose fibers containing approximately 5% residual lignin) produced by the pulping is first washed to remove some of the dissolved organic material and then further delignified by a variety of bleaching stages.[10]Compaq Presario CQ57 Series Laptop Keyboard In the case of a plant designed to produce pulp to make brown sack paper or linerboard for boxes and packaging, the pulp does not always need to be bleached to a high brightness. Bleaching decreases the mass of pulp produced by about 5%, decreases the strength of the fibers and adds to the cost of manufacture. TOSHIBA NB100-11G Laptop Keyboard Pulp produced by the kraft process is stronger than that made by other pulping processes and maintaining a high effective sulfur ratio or sulfidity is important for the highest possible strength. Acidic sulfite processes degrade cellulose more than the kraft process, which leads to weaker fibers. Kraft pulping removes most of the lignin present originally in the wood whereas mechanical pulping processes leave most of the lignin in the fibers. The hydrophobic nature of lignin[13] interferes with the formation of the hydrogen bonds between cellulose (and hemicellulose) in the fibers needed for the strength of paper[2] (strength refers to tensile strength and resistance to tearing). HP Envy 15 Laptop Keyboard Kraft pulp is darker than other wood pulps, but it can be bleached to make very white pulp. Fully bleached kraft pulp is used to make high quality paper where strength, whiteness and resistance to yellowing are important. The kraft process can use a wider range of fiber sources than most other pulping processes. All types of wood, including very resinous types like southernpine,[14] and non-wood species like bamboo and kenaf can be used in the kraft process. HP 634139-001 Laptop Keyboard The main byproducts of kraft pulping are crude sulfate turpentine and tall oil soap. The availability of these is strongly dependent on wood species, growth conditions, storage time of logs and chips, and the mill's process.[15] Pines are the most extractive rich woods. The raw turpentine is volatile and is distilled of the digester, while the raw soap is separated from the spent black liquor by decantation of the soap layer formed on top of the liquor storage tanks. From pines the average yield of turpentine is 5–10 kg/t pulp and of crude tall oil is 30–50 kg/t pulp.[15]HP G72-b50US Laptop Keyboard Various byproducts containing hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, and other volatile sulfur compounds are the cause of the malodorous air emissions characteristic for pulp mills utilizing the kraft process. Outside the modern mills the odour is perceivable only during disturbance situations, for example when shutting the mill down for maintenance break. SAMSUNG N140 Laptop Keyboard This is due to practiced collection and burning of these odorous gases in the recovery boiler along with black liquor. The sulfur dioxide emissions of the kraft pulp mills are much lower than sulfur dioxide emissions from sulfite mills. In modern mills where high dry solids are burned in the recovery boiler hardly any sulfur dioxide leaves the boiler. This is mainly due to higher lower furnace temperature which leads to higher sodium release from the black liquor droplets that can react with sulfur dioxide forming sodium sulfate. SONY VAIO VGN-SZ790N Laptop Keyboard Pulp mills are almost always located near large bodies of water due to their former substantial demands. Delignification of chemical pulps released considerable amounts of organic material into the environment, particularly into rivers or lakes. The wastewater effluent can also be a major source of pollution, containing lignins from the trees, high biological oxygen demand (BOD) and dissolved organic carbon (DOC), along with alcohols, chlorates, heavy metals, and chelatingagents. Reducing the environmental impact of this effluent is accomplished by closing the loop and recycling the effluent where possible, as well as employing less damaging agents in the pulping and bleaching processes. The process effluents are treated in a biological effluent treatment plant, which guarantees that the effluents are not toxic in the recipient. Lenovo ThinkPad Edge E520 Laptop Keyboard Brightness is a measure of how much light is reflected by paper under specified conditions[2] and is usually reported as a percentage of how much light is reflected, so a higher number represents a brighter or whiter paper. In the US, the TAPPI T 452 [4] or T 525 standards are used. The international community uses ISO standards. The following table shows how the two systems rate high brightness papers, but there is no simple way to convert between the two systems because the test methods are so different.[3] Note that the ISO rating is higher and can go above 100. This is because today’s white paper manufacturing usesfluorescent whitening agents (FWA). Because the ISO standard only measures a narrow range of blue light, it is not an adequate measure for the actual whiteness or brightness.[4] HP 597635-001 Laptop Keyboard Newsprint ranges from 55-75 ISO brightness.[5] Writing and printer paper would typically be as bright as 104 ISO. While the results are the same, the processes and fundamental chemistry involved in bleaching chemical pulps (like kraft or sulfite) are very different from those involved in bleaching mechanical pulps (like stoneground, thermomechanical or chemithermomechanical). Chemical pulps contain very little lignin while mechanical pulps contain most of the lignin that was present in the wood used to make the pulp. Lignin is the main source of color in pulp due to the presence of a variety of chromophores naturally present in the wood or created in the pulp mill.  HP Pavilion dv6-2112sa Laptop Keyboard Mechanical pulp retains most of the lignin present in the wood used to make the pulp and thus contain almost as much lignin as they do cellulose and hemicellulose. It would be impractical to remove this much lignin by bleaching, and undesirable since one of the big advantages of mechanical pulp is the high yield of pulp based on wood used. Therefore the objective of bleaching mechanical pulp (also referred to as brightening) is to remove only the chromophores (color-causing groups). This is possible because the structures responsible for color are also more susceptible to oxidation or reduction. HP Pavilion dv4-1319tu Laptop Keyboard Alkaline hydrogen peroxide is the most commonly used bleaching agent for mechanical pulp. The amount of base such as sodium hydroxide is less than that used in bleaching chemical pulps and the temperatures are lower. These conditions allow alkaline peroxide to selectively oxidize non-aromatic conjugated groups responsible for absorbing visible light. The decomposition of hydrogen peroxide is catalyzed by transition metals, and iron, manganese and copper are of particular importance in pulp bleaching. The use of chelating agents like EDTA to remove some of these metal ions from the pulp prior to adding peroxide allows the peroxide to be used more efficiently. Magnesium salts and sodium silicate are also added to improve bleaching with alkaline peroxide.[6]HP 508112-001 Laptop Keyboard Sodium dithionite (Na2S2O4), also known as sodium hydrosulfite, is the other main reagent used to brighten mechanical pulps. In contrast to hydrogen peroxide, which oxidizes the chromophores, dithionite reduces these color-causing groups. Dithionite reacts with oxygen, so efficient use of dithionite requires that oxygen exposure be minimized during its use.[2]HP Pavilion dv2-1003ax Laptop Keyboard Chelating agents can contribute to brightness gain by sequestering iron ions, for example as EDTA complexes, which are less colored than the complexes formed between iron and lignin.[2] The brightness gains achieved in bleaching mechanical pulps are temporary since almost all of the lignin present in the wood is still present in the pulp. Exposure to air and light can produce new chromophores from this residual lignin.[7] This is why newspaper yellows as it ages. yellowing also occurs due to the acidic sizing HP G61-336NR Laptop Keyboard Chemical pulps, such as those from the kraft process or sulfite pulping, contain much less lignin than mechanical pulps, (<5% compared to approximately 40%). The goal in bleaching chemical pulps is to remove essentially all of the residual lignin, hence the process is often referred to as delignification. Sodium hypochlorite (household bleach) was initially used to bleach chemical pulps, but was largely replaced in the 1930s by chlorine. Concerns about the release oforganochlorine compounds into the environment prompted the development of Elemental Chlorine Free (ECF) and Totally Chlorine Free (TCF) bleaching processes. HP G61-336NR Laptop Keyboard Delignification of chemical pulps is rarely a single step process and is frequently composed of four or more discrete steps. These steps are given a letter designation,[8] and these are given in the following table: Chlorine dioxide, ClO2 is an unstable gas with moderate solubility in water. It is usually generated in an aqueous solution and used immediately because it decomposes and is explosive in higher concentrations. It is produced by reacting sodium chlorate with a reducing agent like sulfur dioxide. HP Pavilion dv6-2112sa Laptop Keyboard Chlorine dioxide is sometimes used in combination with chlorine, but it is used alone in ECF (elemental chlorine-free) bleaching sequences. It is used at moderately acidic pH (3.5 to 6). The use of chlorine dioxide minimizes the amount of organochlorine compounds produced.[7] Chlorine dioxide (ECF technology) currently is the most important bleaching method world wide. About 95% of all bleached Kraft pulp is made using chlorine dioxide in ECF bleaching sequences.[10] Oxygen exists as a ground state triplet state, SAMSUNG Q330-JS02 Laptop Keyboard which is relatively unreactive and needs free radicals or very electron-rich substrates such as deprotonatedlignin phenolic groups. The production of these phenoxide groups requires that delignification with oxygen be carried out under very basic conditions (pH >12). The reactions involved are primarily single electron (radical) reactions.[12][13] Oxygen opens rings and cleaves sidechains giving a complex mixture of small oxygenated molecules. Transition metal compounds, particularly those of iron, manganese and copper, which have multiple oxidation states, facilitate many radical reactions and impact oxygen delignification.[14][15] Compaq Presario CQ57 Series Laptop Keyboard While the radical reactions are largely responsible for delignification, they are detrimental to cellulose. Oxygen-based radicals, especially hydroxyl radicals, HO•, can oxidize hydroxyl groups in the cellulose chains to ketones, and under the strongly basic conditions used in oxygen delignification, these compounds undergo reverse aldol reactions leading to cleavage of cellulose chains. Magnesium salts are added to oxygen delignification to help preserve the cellulose chains,[14] but mechanism of this protection has not been confirmed. HP G62-a50SM Laptop Keyboard Using hydrogen peroxide to delignify chemical pulp requires more vigorous conditions than for brightening mechanical pulp. Both pH and temperature are higher when treating chemical pulp. The chemistry is very similar to that involved in oxygen delignification, in terms of the radical species involved and the products produced.[16] Hydrogen peroxide is sometimes used with oxygen in the same bleaching stage and this is give the letter designation Op in bleaching sequences. Metal ions, particularly manganese catalyze the decomposition of hydrogen peroxide, so some improvement in the efficiency of peroxide bleaching can be achieved if the metal levels are controlled.[17]TOSHIBA Mini NB 505-SP0160 Laptop Keyboard Ozone is a very powerful oxidizing agent and the biggest challenge in using it to bleach wood pulp is to get sufficient selectivity so that the desirable cellulose is not degraded. Ozone reacts with the carbon carbon double bonds in lignin, including those within aromatic rings. In the 1990s ozone was touted as good reagent to allow pulp to be bleached without any chlorine-containing chemicals (totally chlorine-free, TCF). The emphasis has changed and ozone is seen as an adjunct to chlorine dioxide in bleaching sequences not using any elemental chlorine (elemental chlorine-free, ECF). Over twenty-five pulp mills worldwide have installed equipment to generate and use ozone.[18]HP Pavilion G6-1223TX Laptop Keyboard The effect of transition metals on some of the bleaching stages has already been mentioned. Sometimes it is beneficial to remove some of these metal ions from the pulp by washing the pulp with a chelating agent such as EDTA or DTPA. This is more common in TCF bleaching sequences for two reasons: the acidic chlorine or chlorine dioxide stages tend to remove metal ions (metal ions usually being more soluble at lower pH) and TCF stages rely more heavily on oxygen-based bleaching agents, which are more susceptible to the detrimental effects of these metal ions. Chelant washes are usually carried out at or near pH 7. Lower pH solutions are more effective at removing transition metals, but also remove more of the beneficial metal ions, especially magnesium[19]TOSHIBA Satellite A300 Laptop Keyboard A variety of more exotic bleaching agents have been used on chemical pulps. They include peroxyacetic acid,[20] peroxyformic acid,[20] potassium peroxymonosulfate (Oxone),[20] dimethyldioxirane,[21] which is generated in situ from acetone and potassium peroxymonosulfate, and peroxymonophosphoric acid[22]DELL Vostro 1510 Laptop Keyboard Enzymes like xylanase have been used in pulp bleaching[20] to increase the efficiency of other bleaching chemicals. It is believed that xylanase does this by cleaving lignin-xylan bonds to make lignin more accessible to other reagents.[2] It is possible that other enzymes such as those found in fungi that degrade lignin may be useful in pulp bleaching.[23]HP Pavilion dv6-2112sa Laptop Keyboard Bleaching mechanical pulp is not a major cause for environmental concern since most of the organic material is retained in the pulp, and the chemicals used (hydrogen peroxide and sodium dithionite) produce benign byproducts (water and sodium sulfate (finally), respectively). SAMSUNG Q330-JS02 Laptop Keyboard However, the bleaching of chemical pulps has the potential to cause significant environmental damage, primarily through the release of organic materials into waterways. Pulp mills are almost always located near large bodies of water because they require substantial quantities of water for their processes. An increased public awareness of environmental issues from the 1970s and 1980s, as evidenced by the formation of organizations like Greenpeace, influenced the pulping industry and governments to address the release of these materials into the environment.[24]Compaq Presario CQ57 Series Laptop Keyboard Conventional bleaching using elemental chlorine produces and releases into the environment large amounts of chlorinated organic compounds, including chlorinated dioxins.[25] Dioxins are recognized as a persistent environmental pollutant, regulated internationally by the Stockholm Convention on Persistent Organic Pollutants. TOSHIBA Satellite L655-S5071 Laptop Keyboard Dioxins are highly toxic, and health effects on humans include reproductive, developmental, immune and hormonal problems. They are known to be carcinogenic. Over 90% of human exposure is through food, primarily meat, dairy, fish and shellfish, as dioxins accumulate in the food chain in the fatty tissue of animals.[26]HP Envy 15-1050nr Laptop Keyboard As a result, from the 1990 onwards the use of elemental chlorine in the delignification process was substantially reduced and replaced with ECF (Elemental Chlorine Free) and TCF (Totally Chlorine Free) bleaching processes. In 2005, elemental chlorine was used in 19-20% of kraft pulp production globally, down from over 90% in 1990. 75% of kraft pulp used ECF, with the remaining 5-6% using TCF.[27] Most TCF pulp is produced in Sweden and Finland for sale in Germany,[27] all markets with a high level of environmental awareness. In 1999, TCF pulp represented 25% of the European market.[28]HP 636191-001 Laptop Keyboard TCF bleaching, by removing chlorine from the process, reduces chlorinated organic compounds to background levels in pulp mill effluent.[29] ECF bleaching can substantially reduce but not fully eliminate chlorinated organic compounds, including dioxins, from effluent. While modern ECF plants can achieve chlorinated organic compounds (AOX) emissions of less than 0.05 kg per tonne of pulp produced, most do not achieve this level of emissions. Within the EU, the average chlorinated organic compound emissions for ECF plants is 0.15 kg per tonne.[30]DELL Latitude E5500 Laptop Keyboard However, there has been disagreement about the comparative environmental effects of ECF and TCF bleaching. Some researchers found that there is no environmental difference between ECF and TCF[31] while others concluded that among ECF and TCF effluents before and after secondary treatment, TCF effluents are the least toxic.[32]SONY VAIO VGN-N11M Laptop Keyboard Hydrogen sulfide (British English: hydrogen sulphide, but this spelling is not recommended by International Union of Pure and Applied Chemistry and the Royal Society of Chemistry) is the chemical compound with the formula H2S. It is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable and explosive. Packard Bell NEW95 Laptop Keyboard Hydrogen sulfide often results from the bacterial breakdown of organic matter in the absence of oxygen, such as in swampsand sewers; this process is commonly known as anaerobic digestion. H2S also occurs in volcanic gases, natural gas, and some well waters. The human body produce

s small amounts of H2S and uses it as a signaling molecule.  Packard Bell EasyNote TJ61 Laptop Keyboard Hydrogen sulfide is slightly heavier than air; a mixture of H2S and air is explosive. Hydrogen sulfide and oxygen burn with a blue flame to form sulfur dioxide (SO2) and water. In general, hydrogen sulfide acts as a reducing agent. At high temperature or in the presence of catalysts, sulfur dioxide can be made to react with hydrogen sulfide to form elemental sulfur and water. This is exploited in the Claus process, the main way to convert hydrogen sulfide into elemental sulfur. Packard Bell NEW90 Laptop Keyboard Hydrogen sulfide is slightly soluble in water and acts as a weak acid, giving the hydrosulfide ion HS (pKa = 6.9 in 0.01-0.1 mol/litre solutions at 18 °C). A solution of hydrogen sulfide in water, known as sulfhydric acid orhydrosulfuric acid, is initially clear but over time turns cloudy. This is due to the slow reaction of hydrogen sulfide with the oxygen dissolved in water, yielding elemental sulfur, which precipitates out. The sulfide dianion S2− exists only in strongly alkaline aqueous solutions; it is exceptionally basic with a pKa > 14. Compaq Presario CQ71-401SA Laptop Keyboard Hydrogen sulfide reacts with metal ions to form metal sulfides, which may be considered the salts of hydrogen sulfide. Some ores are sulfides. Metal sulfides often have a dark color. Lead(II) acetate paper is used to detect hydrogen sulfide because it turns grey in the presence of the gas as lead(II) sulfide is produced. Reacting metal sulfides with strong acid liberates hydrogen sulfide. HP Pavilion dv6-2173cl Laptop Keyboard Small amounts of hydrogen sulfide occur in crude petroleum, but natural gas can contain up to 90%.[7] Volcanoes and somehot springs (as well as cold springs) emit some H2S, where it probably arises via the hydrolysis of sulfide minerals, i.e. MS + H2O → MO + H2S.[citation needed] Hydrogen sulfide can be present naturally in well water, often as a result of the action of sulfate-reducing bacteria. DELL Inspiron N4050 Laptop Keyboard About 10% of total global emissions of H2S is due to human activity. By far the largest industrial route to H2S occurs inpetroleum refineries: The hydrodesulfurization process liberates sulfur from petroleum by the action of hydrogen. The resulting H2S is converted to elemental sulfur by partial combustion via the Claus process, which is a major source of elemental sulfur. Other anthropogenic sources of hydrogen sulfide include coke ovens, paper mills (using the sulfate method), and tanneries. H2S arises from virtually anywhere where elemental sulfur comes in contact with organic material, especially at high temperatures. SONY VAIO VGN-FS415S Laptop Keyboard As indicated above, many metal ions react with hydrogen sulfide to give the corresponding metal sulfides. This conversion is widely exploited. For example, gases or waters contaminated by hydrogen sulfide can be cleaned with metal sulfides. In the purification of metal ores by flotation, mineral powders are often treated with hydrogen sulfide to enhance the separation. Metal parts are sometimes passivated with hydrogen sulfide. Catalysts used in hydrodesulfurization are routinely activated with hydrogen sulfide, and the behavior of metallic catalysts used in other parts of a refinery is also modified using hydrogen sulfide. HP Probook 4320s Laptop Keyboard Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected. The toxicity of H2S is comparable with that of hydrogen cyanide. It forms a complex bond with iron in the mitochondrial cytochrome enzymes, thus preventing cellular respiration. Since hydrogen sulfide occurs naturally in the body, the environment and the gut, enzymes exist in the body capable of detoxifying it by oxidation to (harmless) sulfate.[10] Hence, low levels of hydrogen sulfide may be tolerated indefinitely. SONY VAIO PCG-FR285M Laptop Keyboard At some threshold level, believed to average around 300–350 ppm, the oxidative enzymes become overwhelmed. Many personal safety gas detectors, such as those used by utility, sewage and petrochemical workers, are set to alarm at as low as 5 to 10 ppm and to go into high alarm at 15 ppm. HP Pavilion dv6-2173cl Laptop Keyboard A diagnostic clue of extreme poisoning by H2S is the discoloration of copper coins in the pockets of the victim. Treatment involves immediate inhalation of amyl nitrite, injections of sodium nitrite, inhalation of pure oxygen, administration of bronchodilators to overcome eventual bronchospasm, and in some caseshyperbaric oxygen therapy (HBO). HBO therapy has anecdotal support and remains controversial.[11][12][13]HP Pavilion dv6-2170us Laptop Keyboard Exposure to lower concentrations can result in eye irritation, a sore throat and cough, nausea, shortness of breath, and fluid in the lungs (pulmonary edema). These effects are believed to be due to the fact that hydrogen sulfide combines with alkali present in moist surface tissues to form sodium sulfide, acaustic.[14] These symptoms usually go away in a few weeks. Lenovo 45N2240 Laptop Keyboard Long-term, low-level exposure may result in fatigue, loss of appetite, headaches, irritability, poor memory, and dizziness. Chronic exposure to low level H2S(around 2 ppm) has been implicated in increased miscarriage and reproductive health issues among Russian and Finnish wood pulp workers,[15] but the reports have not (as of circa 1995) been replicated. HP Pavilion G6-1223TX Laptop Keyboard Hydrogen sulfide was used by the British Army as a chemical weapon during World War I. It was not considered to be an ideal war gas, but, while other gases were in short supply, it was used on two occasions in 1916.[21] In 1975, a hydrogen sulfide release from an oil drilling operation in Denver City, Texas killed nine people and caused the state legislature to focus on the deadly hazards of the gas. State Representative E L Short took the lead in endorsing an investigation by the Texas Railroad Commission and urged that residents be warned "by knocking on doors if necessary" of the imminent danger stemming from the gas. One may die from the second inhalation of the gas, and a warning itself may be too late.[22]HP G62-b60SI Laptop CPU Cooling Fan A dump of toxic waste containing hydrogen sulfide is believed to have caused 17 deaths and thousands of illnesses in Abidjan, on the West Africa coast, in the2006 Côte d'Ivoire toxic waste dump. Three members of one family were killed in a slurry tank in Northern Ireland in September 2012 after one member entered the tank in an attempt to rescue a dog. He was quickly rendered unconscious by the gas (and other toxic gasses), at which point his younger brother entered the tank in an effort to rescue him. He too succumbed to the fumes, and in an attempt to save both sons, the father then entered the tank, and also perished.[23]ACER Aspire 1356LMI Laptop CPU Cooling Fan The gas, produced by mixing certain household ingredients, was used in a suicide wave in 2008 in Japan.[24] The wave prompted staff at Tokyo's suicide preventioncenter to set up a special hot line during "Golden Week", as they received an increase in calls from people wanting to kill themselves during the annual May holiday.[25]HP Pavilion dv7-6143cl Laptop CPU Cooling Fan As of 2010, this phenomenon has occurred in a number of US cities (and in Putney, West London, England), prompting warnings to those arriving at the site of the suicide.[26] These first responders, such as emergency services workers or family members are at risk of death from inhaling lethal quantities of the gas, or by fire.[27][28] Local governments have also initiated campaigns to prevent such suicides. HP Pavilion dv5-1203ax Laptop CPU Cooling Fan Hydrogen sulfide is produced in small amounts by some cells of the mammalian body and has a number of biological signaling functions. (Only two other such gases are currently known: nitric oxide (NO) and carbon monoxide (CO).) The gas is produced from cysteine by the enzymes cystathionine beta-synthase and cystathionine gamma-lyase. It acts as a relaxant of smooth muscle and as avasodilator[29] and is also active in the brain, where it increases the response of the NMDA receptor and facilitates long term potentiation,[30] which is involved in the formation of memory. ACER eMachines E525 Laptop CPU Cooling Fan Eventually the gas is converted to sulfite in the mitochondria by thiosulfate reductase, and the sulfite is further oxidized to thiosulfate and sulfate bysulfite oxidase. The sulfates are excreted in the urine.[31] Due to its effects similar to nitric oxide (without its potential to form peroxides by interacting with superoxide), hydrogen sulfide is now recognized as potentially protecting against cardiovascular disease.[29] The cardioprotective role effect of garlic is caused by catabolism of the polysulfide group in allicinto H2S, a reaction that could depend on reduction mediated by glutathione.[32]Toshiba Satellite M305D-S4829 Laptop CPU Cooling Fan Though both nitric oxide (NO) and hydrogen sulfide have been shown to relax blood vessels, their mechanisms of action are different: while NO activates the enzyme guanylyl cyclase, H2S activates ATP-sensitive potassium channels in smooth muscle cells. Researchers are not clear how the vessel-relaxing responsibilities are shared between nitric oxide and hydrogen sulfide. However there exists some evidence to suggest that nitric oxide does most of the vessel-relaxing work in large vessels and hydrogen sulfide is responsible for similar action in smaller blood vessels.[33]MSI E32-0800110-MC2 Laptop CPU Cooling Fan Recent findings suggest strong cellular crosstalk of NO and H2S,[34] demonstrating that the vasodilatatory effects of these two gases are mutually dependent. Additionally, H2S reacts with intracellular S-nitrosothiols to form the smallest S-nitrosothiol (HSNO), and a role of hydrogen sulfide in controlling the intracellular S-nitrosothiol pool has been suggested.[35]HP Pavilion dv9723cl Laptop CPU Cooling Fan Like nitric oxide, hydrogen sulfide is involved in the relaxation of smooth muscle that causes erection of the penis, presenting possible new therapy opportunities for erectile dysfunction.[36][37]SONY Vaio VPC-EE3E1E/WI Laptop CPU Cooling Fan In Alzheimer's disease the brain's hydrogen sulfide concentration is severely decreased.[38] In a certain rat model of Parkinson's disease, the brain's hydrogen sulfide concentration was found to be reduced, and administering hydrogen sulfide alleviated the condition.[39] In trisomy 21 (Down syndrome) the body produces an excess of hydrogen sulfide.[31] Hydrogen sulfide is also involved in the disease process of type 1 diabetes. The beta cells of the pancreas in type 1 diabetes produce an excess of the gas, leading to the death of these cells and to a reduced production of insulin by those that remain.[33] FUJITSU LifeBook E8210 Laptop CPU Cooling Fan IBM ThinkPad T42 2378 Laptop CPU Cooling Fan

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