89-539: The Engadin Skimarathon is an annual cross-country skiing race ( ski marathon ) held on the second Sunday of March in the upper Engadine valley ( Switzerland ), between Maloja and S-chanf . It debuted in 1969 and has been a part of Worldloppet as long as Worldloppet has existed. It is one of the major cross-country skiing events in the Alps . Between 11,000 and 14,200 skiers participate each year. The total distance covered
178-412: A Relay for both men and women. The World Cup is organized every even year. Junior World Ski Orienteering Championships and World Masters Ski Orienteering Championships are organized annually. Biathlon combines cross-country skiing and rifle shooting . Depending on the shooting performance, extra distance or time is added to the contestant's total running distance/time. For each shooting round,
267-480: A carrier or by blending in extruders. Cyclic olefin copolymers are prepared by copolymerization of ethene and cycloolefins (usually norbornene ) produced by using metallocene catalysts. The resulting polymers are amorphous polymers and particularly transparent and heat resistant. The basic compounds used as polar comonomers are vinyl alcohol ( Ethenol , an unsaturated alcohol), acrylic acid ( propenoic acid , an unsaturated acid) and esters containing one of
356-580: A density range of 0.880–0.915 g/cm . VLDPE is a substantially linear polymer with high levels of short-chain branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1-hexene and 1-octene). VLDPE is most commonly produced using metallocene catalysts due to the greater co-monomer incorporation exhibited by these catalysts. VLDPEs are used for hose and tubing, ice and frozen food bags, food packaging and stretch wrap as well as impact modifiers when blended with other polymers. Much research activity has focused on
445-458: A few that could use plastic as their only carbon source. Not only could the bacteria from the guts of the Plodia interpunctella moth larvae metabolize polyethylene, they degraded it significantly, dropping its tensile strength by 50%, its mass by 10% and the molecular weights of its polymeric chains by 13%. The caterpillar of Galleria mellonella is claimed to consume polyethylene. The caterpillar
534-473: A long-lived and decomposition-resistant pollutant when disposed of improperly. Being a hydrocarbon , polyethylene is colorless to opaque (without impurities or colorants) and combustible. Polyethylene was first synthesized by the German chemist Hans von Pechmann , who prepared it by accident in 1898 while investigating diazomethane . When his colleagues Eugen Bamberger and Friedrich Tschirner characterized
623-501: A mixture of ethylene and benzaldehyde they again produced a white, waxy material. Because the reaction had been initiated by trace oxygen contamination in their apparatus, the experiment was difficult to reproduce at first. It was not until 1935 that another ICI chemist, Michael Perrin , developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial low-density polyethylene ( LDPE ) production beginning in 1939. Because polyethylene
712-517: A prologue of 15 km and La Sgambeda of 24 km: The Worldloppet Ski Federation recognizes twenty ski marathons including those in the Ski Classics series (except La Diagonala and Årefjällslopet). They recognize those athletes who complete Worldloppet races in 10 countries, at least one of which has to be on another continent, to qualify as a "Worldloppet Master". The organization, sanctioned by FIS, seeks to attract elite racers to its events with
801-507: A public ski competition was for an 1843 event in Tromsø . The announcement called the event a "wagering race on skis". A distinct alpine technique emerged around 1900 from how skiing was practiced up until then when Mathias Zdarsky advocated the "Lilienfelder Ski Method" as an alternative to the Norwegian technique. In Norwegian, langrenn refers to "competitive skiing where the goal is to complete
890-412: A relatively narrow molecular weight distribution , exceptionally high toughness, excellent optical properties and a uniform comonomer content. Because of the narrow molecular weight distribution it behaves less pseudoplastic (especially under larger shear rates). Metallocene polyethylene has a low proportion of low molecular weight (extractable) components and a low welding and sealing temperature. Thus, it
979-475: A seasonal schedule designed for the targeted events: marathon or mid-distance. Additional aspects of training address aerobic (low-intensity) exercise—especially for endurance—and strength to improve joint flexibility and to minimize the risk of injury. Cross-country ski training occurs throughout the year, including on dry land where athletes engage in roller skiing and ski striding to maintain ski-specific muscle fitness. In its "Organizing committee handbook",
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#17328523211201068-716: A specific distance in pre-set tracks in the shortest possible time". Alpine skiing competitions (known as hill races ) existed in Norway during the 18th and 19th centuries, but were discontinued when the main ski festival in Oslo focused on long races (competitive cross-country skiing) and ski jumping (now known as the Nordic disciplines). The alpine disciplines reemerged in Central Europe around 1920. Ski touring competitions ( Norwegian : turrenn ) are long-distance cross-country competitions open to
1157-516: A strategy for developing promising athletes and programs to encourage participation in the sport, starting at a young age. One example is Cross-Country Ski Canada's "Long-Term Athlete Development" program. The program encompasses youth development, training, introduction to competition and improvement of promising athletes with an emphasis on "stamina (endurance), strength, speed, skill and suppleness (flexibility)". It covers age groups from toddlers to mature adults, who are able to enjoy and participate in
1246-715: A variety of race formats and course lengths. Rules of cross-country skiing are sanctioned by the International Ski Federation and by various national organizations. International competitions include the FIS Nordic World Ski Championships , the FIS Cross-Country World Cup , and at the Winter Olympic Games . Such races occur over homologated , groomed courses designed to support classic (in-track) and freestyle events, where
1335-487: Is ethylene-vinyl acetate copolymer , or EVA, widely used in athletic-shoe sole foams) and a variety of acrylates . Applications of acrylic copolymer include packaging and sporting goods, and superplasticizer , used in cement production. The particular material properties of "polyethylene" depend on its molecular structure. Molecular weight and crystallinity are the most significant factors; crystallinity in turn depends on molecular weight and degree of branching. The less
1424-438: Is grooming the course to provide a surface for skate-skiing and setting tracks for classic events. This takes into account snow physics, methods for packing snow and surface shaping, and the equipment used for these functions. Also key is the layout of grooming and track setting in the stadium with various formats for starts, finishes and intermediate functions for relays and pursuits. In its "Cross-country homologation manual",
1513-480: Is 42 km, although it is also possible to complete the half-marathon of 21 km (finishing in Pontresina ) or the 17 km Women's Race (Samedan to S-chanf) . While it is a freestyle race, there are separate tracks for skiers practicing classic style for all but the narrowest parts of the race. Participation is open to anyone from the age of 16, and no licence is required to sign up. The track record of 1:16:10h
1602-743: Is a forested climb in the Stazerwald . The proceeding descent to Pontresina is regarded by many as the most spectacular part of the race for spectators, due to the high number of falls and crashes by skiers. The race then follows the runway of Samedan Airport and afterwards continues on the right side of the Engadin valley, passing several small communities before reaching the Finish in S-chanf at an elevation of 1,670 metres (5,480 ft). Cross-country skiing (sport) Competitive cross-country skiing encompasses
1691-410: Is a good electrical insulator . It offers good electrical treeing resistance; however, it becomes easily electrostatically charged (which can be reduced by additions of graphite , carbon black or antistatic agents ). When pure, the dielectric constant is in the range 2.2 to 2.4 depending on the density and the loss tangent is very low, making it a good dielectric for building capacitors . For
1780-651: Is able to digest polyethylene due to a combination of its gut microbiota and its saliva containing enzymes that oxidise and depolymerise the plastic. When exposed to ambient solar radiation the plastic produces trace amounts of two greenhouse gases , methane and ethylene . The plastic type which releases gases at the highest rate is low-density polyethylene (LDPE). Due to its low density it breaks down more easily over time, leading to higher surface areas. When incubated in air, LDPE emits gases at rates ~2 times and ~76 times higher in comparison to incubation in water for methane and ethylene, respectively. However, based on
1869-462: Is defined by a density of greater or equal to 0.941 g/cm . HDPE has a low degree of branching. The mostly linear molecules pack together well, so intermolecular forces are stronger than in highly branched polymers. HDPE can be produced by chromium /silica catalysts, Ziegler–Natta catalysts or metallocene catalysts; by choosing catalysts and reaction conditions, the small amount of branching that does occur can be controlled. These catalysts prefer
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#17328523211201958-538: Is defined by a density range of 0.910–0.940 g/cm . LDPE has a high degree of short- and long-chain branching, which means that the chains do not pack into the crystal structure as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility . LDPE is created by free-radical polymerization . The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE
2047-551: Is defined by a density range of 0.915–0.925 g/cm . LLDPE is a substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene , 1-hexene , and 1-octene ). LLDPE has higher tensile strength than LDPE, and it exhibits higher impact and puncture resistance than LDPE. Lower-thickness (gauge) films can be blown, compared with LDPE, with better environmental stress cracking resistance, but they are not as easy to process. LLDPE
2136-429: Is defined by a density range of 0.926–0.940 g/cm . MDPE can be produced by chromium/silica catalysts, Ziegler–Natta catalysts, or metallocene catalysts. MDPE has good shock and drop resistance properties. It also is less notch-sensitive than HDPE; stress-cracking resistance is better than HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags, and screw closures. LLDPE
2225-412: Is likened to paddling or dancing, depending on the tempo. The primary turns used for racing, are the parallel turn , which is used while descending and can provide braking, and the step turn, which is used for maintaining speed during descents or out of track on flats. The wedge turn (or "snowplow turn"), is sometimes used for braking and turning. Countries with cross-country ski teams usually have
2314-416: Is much less than for producing hydrogen by electrolysis. Several experiments have been conducted aimed at discovering enzyme or organisms that will degrade polyethylene. Several plastics - polyesters, polycarbonates, polyamides - degrade either by hydrolysis or air oxidation. In some cases the degradation is increased by bacteria or various enzyme cocktails. The situation is very different polymers where
2403-766: Is particularly suitable for the food industry. Polyethylene with multimodal molecular weight distribution consists of several polymer fractions, which are homogeneously mixed. Such polyethylene types offer extremely high stiffness, toughness, strength, stress crack resistance and an increased crack propagation resistance. They consist of equal proportions higher and lower molecular polymer fractions. The lower molecular weight units crystallize easier and relax faster. The higher molecular weight fractions form linking molecules between crystallites, thereby increasing toughness and stress crack resistance. Polyethylene with multimodal molecular weight distribution can be prepared either in two-stage reactors, by catalysts with two active centers on
2492-400: Is the most commonly produced plastic . It is a polymer , primarily used for packaging ( plastic bags , plastic films , geomembranes and containers including bottles , cups , jars , etc.). As of 2017 , over 100 million tonnes of polyethylene resins are being produced annually, accounting for 34% of the total plastics market. Many kinds of polyethylene are known, with most having
2581-448: Is used for both rigid containers and plastic film applications such as plastic bags and film wrap. The radical polymerization process used to make LDPE does not include a catalyst that "supervises" the radical sites on the growing PE chains. (In HDPE synthesis, the radical sites are at the ends of the PE chains, because the catalyst stabilizes their formation at the ends.) Secondary radicals (in
2670-451: Is used in a diverse range of applications. These include can- and bottle -handling machine parts, moving parts on weaving machines, bearings, gears, artificial joints, edge protection on ice rinks, steel cable replacements on ships, and butchers' chopping boards. It is commonly used for the construction of articular portions of implants used for hip and knee replacements . As fiber , it competes with aramid in bulletproof vests . HDPE
2759-450: Is used in packaging, particularly film for bags and sheets. Lower thickness may be used compared to LDPE. It is used for cable coverings, toys, lids, buckets, containers, and pipe. While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility, and relative transparency. Product examples range from agricultural films, Saran wrap, and bubble wrap to multilayer and composite films. LDPE
Engadin Skimarathon - Misplaced Pages Continue
2848-455: Is useful on level ground and on gentle downhill slopes. On steep uphills fishbone technique can be used. While skate skiing, the skier provides propulsion on a firm snow surface by pushing alternating skis away from one another at an angle, in a manner similar to ice skating . Skis are waxed with a glide wax over their entire length, making them faster than classic skis. Freestyle events take place on smooth, wide, specially groomed courses. With
2937-446: Is usually open to the public. In Norwegian, such a race is called turrenn ("ski touring race"). Major events have more than 10,000 participants where mass starts often have a modified starting order by groupings of participants—who have been judged to be of similar ability, beginning with the elite skiers group and ending with a group of the least experienced skiers. Skiers can use either classic or skate-skiing techniques, depending on
3026-501: Is usually produced from petrochemical sources, but also is generated by dehydration of ethanol. Polymerization of ethylene to polyethylene is described by the following chemical equation : Ethylene is a stable molecule that polymerizes only upon contact with catalysts. The conversion is highly exothermic . Coordination polymerization is the most pervasive technology, which means that metal chlorides or metal oxides are used. The most common catalysts consist of titanium(III) chloride ,
3115-611: The 1924 Winter Olympics , was held in Chamonix , France and included Nordic skiing (which includes cross-country skiing ) among the five principal disciplines. Cross-country events have evolved in the Winter Olympics since 1924, as seen in the following timeline: At the 2022 Olympics in Beijing , cross-country skiing will feature events in both classic cross-country and skate skiing (also called free technique). The two styles alternate at
3204-589: The Black Forest in 1900, the Norwegian Bjarne Nilssen won the 23 km cross-country race and was observed using a skating motion while skiing—a technique unknown to the spectators. Johan Grøttumsbråten used the skating technique at the 1931 World Championship in Oberhof , one of the earliest recorded use of skating in competitive cross-country skiing. This technique was later used in ski orienteering in
3293-463: The chemical formula (C 2 H 4 ) n . PE is usually a mixture of similar polymers of ethylene , with various values of n . It can be low-density or high-density and many variations thereof. Its properties can be modified further by crosslinking or copolymerization. All forms are nontoxic as well as chemically resilient, contributing to polyethylene's popularity as a multi-use plastic. However, polyethylene's chemical resilience also makes it
3382-401: The metallocenes , were reported in 1976 by Walter Kaminsky and Hansjörg Sinn . The Ziegler- and metallocene-based catalysts families have proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including very-low-density polyethylene and linear low-density polyethylene . Such resins, in
3471-1079: The 18th century. Starting in the latter part of the 20th century, technique evolved from the striding in-track classic technique to include skate-skiing, which occurs on courses that have been groomed with wide lanes for those using the technique. At the same time, equipment evolved from skis and poles that were made of wood and other natural materials to comprising such man-made materials as fiberglass , carbon fiber , and polyethylene plastics . Athletes train to achieve endurance, strength, speed, skill and flexibility at different levels of intensity. Off-season training often occurs on dry land, sometimes on roller skis . The organization of cross-country ski competitions aims to make those events accessible both to spectators and television audiences. As with other sports that require endurance, strength and speed, some athletes have chosen to use banned performance-enhancing drugs . In 1767 Danish-Norwegian general, Schack Carl Rantzau , codified four classes of military skiing contests and established prizes for each: An early record of
3560-444: The 1960s on roads and other firm surfaces. Finnish skier Pauli Siitonen developed a variant of the style for marathon or other endurance events in the 1970s by leaving one ski in the track while skating outwards to the side with the other ski (one-sided skating); this became known as the "marathon skate". American skier Bill Koch further developed the marathon skate technique in the late 1970s. Skate skiing became widespread during
3649-416: The 1980s after Koch's success with it in the 1982 Cross-country Skiing Championships drew more attention to the technique. Norwegian skier, Ove Aunli , started using the technique in 1984, when he found it to be much faster than classic style. Skating is most effective on wide, smooth, groomed trails, using fiberglass skis that glide well; it also benefits a stronger athlete—which, according to Olav Bø, are
Engadin Skimarathon - Misplaced Pages Continue
3738-485: The 2001 World Nordic skiing championships in Lahti, Finland revealed that Jari Isometsä , Janne Immonen and two other skiers from Finland's gold-medal relay team, Mika Myllylä and Harri Kirvesniemi , and two female skiers tested positive for hydroxyethyl starch (HES), a blood plasma expander usually used to cover up the use of erythropoietin (EPO). EPO boosts the oxygen-carrying capability of hemoglobin . In addition,
3827-558: The FIS Worldloppet Cup and aims thereby to "increase media and spectator interest in long distance racing". Notable races, other than the Ski Classics series include: Ski orienteering is an orienteering discipline recognized by the International Orienteering Federation . The World Ski Orienteering Championships is organized every odd year and includes sprint, middle and long distance competitions, and
3916-504: The FIS covers aspects of race management, including the layout of the competition venue, organization of the events (including scheduling, officiating, and awards), and addressing ancillary factors, such as the role of the media. National handbooks, such as the "USSA Cross-Country Technical Handbook" and the "Cross Country Canada officials manual", provide further guidance, sometimes specific to their venues. An important aspect of race preparation
4005-416: The FIS recognizes that fans of the sport wish to follow it on television. With this in mind, the manual addresses how to design the race course and the stadium in a manner that not only enhances the experience of spectators, but of viewers, as well—not just to show the athletes in action, but to show the ways in which fans enjoy the action. The manual includes considerations of: A course is expected to test
4094-571: The Phillips catalyst. The Phillips catalyst is less expensive and easier to work with, however, and both methods are heavily used industrially. By the end of the 1950s both the Phillips- and Ziegler -type catalysts were being used for high-density polyethylene (HDPE) production. In the 1970s, the Ziegler system was improved by the incorporation of magnesium chloride . Catalytic systems based on soluble catalysts,
4183-497: The World Championships were held annually, including years with Winter Olympic Games . After World War II, the World Championships were held every four years from 1950 to 1982. Since 1985, the World Championships have been held in odd-numbered years. FIS events include: A ski marathon is a long-distance, usually point-to-point race, of more than 40 kilometers; some are held concurrent with shorter races and participation
4272-414: The backbone consists solely of C-C bonds. These polymers include polyethylene, but also polypropylene, polystyrene and acrylates. At best, these polymers degrade very slowly, but these experiments are difficult because yields and rates are very slow. Further confusing the situation, even preliminary successes are greeted with enthusiasm by the popular press. Some technical challenges in this area include
4361-492: The biathlete must hit five targets; the skier receives a penalty for each missed target, which varies according to the competition rules; in any given competition one of the following penalties would apply: Paralympic cross-country skiing is an adaptation of cross-country skiing for athletes with disabilities. Paralympic cross-country skiing is one of two Nordic skiing disciplines in the Winter Paralympic Games ;
4450-446: The case of classic skis, traction when striding forward. Racing ski boots are also lighter than recreational ones and are attached at the toe only to bindings that are specialized for classic or skate skiing. Racing ski poles are usually made from carbon fiber and feature smaller, lighter baskets than recreational poles . Poles designed for skating are longer than those designed for classic skiing. In classic cross-country skiing
4539-474: The commercial production of polyethylene began with the development of catalysts that promoted the polymerization at mild temperatures and pressures. The first of these was a catalyst based on chromium trioxide discovered in 1951 by Robert Banks and J. Paul Hogan at Phillips Petroleum . In 1953 the German chemist Karl Ziegler developed a catalytic system based on titanium halides and organoaluminium compounds that worked at even milder conditions than
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#17328523211204628-519: The event: classic and skating (in freestyle races, where all techniques are allowed). Skiathlon combines the two techniques in one race. Skis are lighter, narrower and designed to be faster than those used in recreational cross-country skiing and made of composite materials . For classic events, typical ski lengths are between 195 and 210 centimetres, while ski lengths for skating are 170 to 200 cm. Skis for skating are also more rigid than skis for classical. Skis are waxed for speed and, in
4717-466: The failure to identify enzymes responsible for the proposed degradation. Another issue is that organisms are incapable of importing hydrocarbons of molecular weight greater than 500. The Indian mealmoth larvae are claimed to metabolize polyethylene based on observing that plastic bags at a researcher's home had small holes in them. Deducing that the hungry larvae must have digested the plastic somehow, he and his team analyzed their gut bacteria and found
4806-466: The form of UHMWPE fibers , have (as of 2005) begun to replace aramids in many high-strength applications. The properties of polyethylene depend strongly on type. The molecular weight, crosslinking, and presence of comonomers all strongly affect its properties. It is for this structure-property relation that intense effort has been invested into diverse kinds of PE. LDPE is softer and more transparent than HDPE. For medium- and high-density polyethylene
4895-476: The formation of free radicals at the ends of the growing polyethylene molecules. They cause new ethylene monomers to add to the ends of the molecules, rather than along the middle, causing the growth of a linear chain. HDPE has high tensile strength. It is used in products and packaging such as milk jugs, detergent bottles, butter tubs, garbage containers, and water pipes . PEX is a medium- to high-density polyethylene containing cross-link bonds introduced into
4984-550: The gas and water vapour permeability (only polar gases) is lower than for most plastics. Oxygen , carbon dioxide and flavorings , on the other hand, can pass it easily. Polyethylene burns slowly with a blue flame having a yellow tip and gives off an odour of paraffin (similar to candle flame). The material continues burning on removal of the flame source and produces a drip. Polyethylene cannot be imprinted or bonded with adhesives without pretreatment. High-strength joints are readily achieved with plastic welding . Polyethylene
5073-549: The grooming surface on the race course. Such snow tends to be denser and icier than natural snow, which increases the speed of skiers, especially on downhills. With the increase of speed and a harder surface, comes the increased risk of injuries from falls. The FIS claims to be compiling data on the comparative frequency and severity of falls, but wasn't sharing the information, as of January 2022. As with other sports, some competitors in cross-country skiing have chosen to enhance their performance through doping . Anti-doping tests at
5162-528: The low pressure process α-olefins (e.g. 1-butene or 1-hexene ) may be added, which are incorporated in the polymer chain during polymerization. These copolymers introduce short side chains, thus crystallinity and density are reduced. As explained above, mechanical and thermal properties are changed thereby. In particular, PE-LLD is produced this way. Metallocene polyethylene (PE-M) is prepared by means of metallocene catalysts , usually including copolymers (z. B. ethene / hexene). Metallocene polyethylene has
5251-466: The major events (Olympic Games, World Championships). For example, at the 2018 Winter Olympics in Pyeongchang, the 15 km men's individual race was a skate skiing event. Therefore, at the 2022 Olympics, this event will be skied in classic style. The FIS Nordic World Ski Championships have been held in various numbers and types of events since 1925 for men and since 1954 for women. From 1924 to 1939,
5340-985: The melting point is typically in the range 120 to 130 °C (248 to 266 °F). The melting point for average commercial low-density polyethylene is typically 105 to 115 °C (221 to 239 °F). These temperatures vary strongly with the type of polyethylene, but the theoretical upper limit of melting of polyethylene is reported to be 144 to 146 °C (291 to 295 °F). Combustion typically occurs above 349 °C (660 °F). Most LDPE , MDPE , and HDPE grades have excellent chemical resistance, meaning that they are not attacked by strong acids or strong bases and are resistant to gentle oxidants and reducing agents. Crystalline samples do not dissolve at room temperature. Polyethylene (other than cross-linked polyethylene) usually can be dissolved at elevated temperatures in aromatic hydrocarbons such as toluene or xylene , or in chlorinated solvents such as trichloroethane or trichlorobenzene . Polyethylene absorbs almost no water ;
5429-409: The middle of a chain) are more stable than primary radicals (at the end of the chain), and tertiary radicals (at a branch point) are more stable yet. Each time an ethylene monomer is added, it creates a primary radical, but often these will rearrange to form more stable secondary or tertiary radicals. Addition of ethylene monomers to the secondary or tertiary sites creates branching. VLDPE is defined by
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#17328523211205518-624: The most important polyethylene grades are HDPE, LLDPE, and LDPE. UHMWPE is polyethylene with a molecular weight numbering in the millions, usually between 3.5 and 7.5 million amu . The high molecular weight makes it a very tough material, but results in less efficient packing of the chains into the crystal structure as evidenced by densities of less than high-density polyethylene (for example, 0.930–0.935 g/cm ). UHMWPE can be made through any catalyst technology, although Ziegler catalysts are most common. Because of its outstanding toughness and its cut, wear, and excellent chemical resistance, UHMWPE
5607-492: The nature and distribution of long chain branches in polyethylene. In HDPE, a relatively small number of these branches, perhaps one in 100 or 1,000 branches per backbone carbon, can significantly affect the rheological properties of the polymer. In addition to copolymerization with alpha-olefins, ethylene can be copolymerized with a wide range of other monomers and ionic composition that creates ionized free radicals. Common examples include vinyl acetate (the resulting product
5696-724: The other is biathlon . Competition is governed by the International Paralympic Committee (IPC). Paralympic cross-country skiing includes standing events, sitting events (for wheelchair users), and events for visually impaired athletes under the rules of the International Paralympic Committee. These are divided into several categories for people who are missing limbs, have amputations, are blind, or have any other physical disability, to continue their sport. The classifications are for: Cross-country ski competitors employ one of two techniques, according to
5785-507: The pole pushing on the side opposite of the extended, sliding ski. In classic skiing the alternating technique is used for the "diagonal stride"—the predominant classic sub-technique. In diagonal-stride legs move like in ordinary walking, but with longer and more powerful steps. Diagonal is useful on level ground and on gentle uphill slopes. Uphill steps are shorter and more frequent. With double-poling both poles are used simultaneously for thrust, which may be augmented with striding. Double-poling
5874-751: The polymer chains are branched, and the lower the molecular weight, the higher the crystallinity of polyethylene. Crystallinity ranges from 35% (PE-LD/PE-LLD) to 80% (PE-HD). Polyethylene has a density of 1.0 g/cm in crystalline regions and 0.86 g/cm in amorphous regions. An almost linear relationship exists between density and crystallinity. The degree of branching of the different types of polyethylene can be schematically represented as follows: [REDACTED] The figure shows polyethylene backbones, short-chain branches and side-chain branches. The polymer chains are represented linearly. The properties of polyethylene are highly dependent on type and number of chain branches. The chain branches in turn depend on
5963-422: The polymer structure, changing the thermoplastic into a thermoset . The high-temperature properties of the polymer are improved, its flow is reduced, and its chemical resistance is enhanced. PEX is used in some potable-water plumbing systems because tubes made of the material can be expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water-tight connection. MDPE
6052-426: The process used: either the high-pressure process (only PE-LD) or the low-pressure process (all other PE grades). Low-density polyethylene is produced by the high-pressure process by radical polymerization, thereby numerous short chain branches as well as long chain branches are formed. Short chain branches are formed by intramolecular chain transfer reactions, they are always butyl or ethyl chain branches because
6141-424: The public, competition is usually within age categories. In the 1800s racers used a single, wooden pole, which was longer and stronger than modern poles, and could be used for braking downhill, as well. In Norway, racing with two poles ("Finland style") met with resistance, starting in the 1880s, when some race rules forbade them; objections included issues of aesthetics—how they made skiers "[waddle] like geese". As
6230-415: The rates measured in the study methane production by plastics is presently an insignificant component of the global methane budget. Polyethylene may either be modified in the polymerization by polar or non-polar comonomers or after polymerization through polymer-analogous reactions. Common polymer-analogous reactions are in case of polyethylene crosslinking , chlorination and sulfochlorination . In
6319-529: The reaction proceeds after the following mechanism: The widespread usage of polyethylene poses potential difficulties for waste management because it is not readily biodegradable. Since 2008, Japan has increased plastic recycling, but still has a large amount of plastic wrapping which goes to waste. Plastic recycling in Japan is a potential US$ 90 billion market. It is possible to rapidly convert polyethylene to hydrogen and graphene by heating. The energy needed
6408-524: The reasons that the technique made a breakthrough in the early 1980s. Athletes widely adopted skating to both sides by the time of the 1985 world championship and it was formally adopted by the FIS in 1986 —despite initial opposition from Norway , the Soviet Union and Finland —while preserving events using only classic technique. The Winter Olympic Games are a major international sporting event that occurs once every four years. The first Winter Olympics,
6497-660: The rules of the race. Awards are usually based on overall placement, placement by sex of athlete, and by age category. There are two major series in this category, the Ski Classics and the Worldloppet . Ski Classics is a commercially sponsored international long-distance cross-country skiing cup competition, held in Europe. It originated in January 2011. As of the winter of 2015–6, the tour consisted of eight long-distance events, preceded by
6586-401: The same reason it is commonly used as the insulation material for high-frequency coaxial and twisted pair cables. Depending on thermal history and film thickness, PE can vary between almost clear ( transparent ), milky-opaque ( translucent ) and opaque . LDPE has the greatest, LLDPE slightly less, and HDPE the least transparency. Transparency is reduced by crystallites if they are larger than
6675-491: The skating technique double-poling is usually employed with alternating skating strides or with every skate stride. The following table puts these poling sequences into order according to the speed achieved as a progression of "gears". In the lowest gear (rarely used in racing), one is poling on the side of the sliding ski, similar to diagonal stride. In the highest gear, the athlete skates without poles. There are equivalent terms in other languages; for example in Norwegian, skating
6764-405: The skier's technical and physical abilities, to be laid out in a manner that takes advantage of the natural terrain, and to provide smooth transitions among uphills, downhills and "undulating" terrain—distributed approximately evenly among the three. The manual advocates that courses present a variety of uphills, varying in lengths and gradients between 6% and 12%, which are arrayed efficiently within
6853-646: The skiers may employ skate skiing . It also encompasses cross-country ski marathon events, sanctioned by the Worldloppet Ski Federation , and cross-country ski orienteering events, sanctioned by the International Orienteering Federation . Related forms of competition are biathlon , where competitors race on cross-country skis and stop to shoot at targets with rifles, and paralympic cross-country skiing that allows athletes with disabilities to compete at cross-country skiing with adaptive equipment. Norwegian army units were skiing for sport (and prizes) in
6942-555: The skis remain parallel, as the skier strides straight ahead. The undersides of the skis have a grip section in the middle treated with a special ski wax that provides friction when the foot is still, yet glides when the foot is in motion, while the rest of the ski bottom has a glide wax . Classic events occur on courses with tracks set by a grooming machine at precise intervals and with carefully planned curvature. Both poles may be used simultaneously ("double-poling") or with alternating foot and arm extended (as with running or walking) with
7031-478: The so-called Ziegler–Natta catalysts . Another common catalyst is the Phillips catalyst , prepared by depositing chromium(VI) oxide on silica. Polyethylene can be produced through radical polymerization , but this route has only limited utility and typically requires high-pressure apparatus. Commonly used methods for joining polyethylene parts together include: Pressure-sensitive adhesives (PSA) are feasible if
7120-649: The sport. Similarly, the USSA has an outline of "Cross Country Athlete Competencies" that has four phases beginning at 12 years old and under and addressing the 21 and older phase at the top. The program encompasses six "domains:" Ski training for the athlete depends on whether the desired specialty emphasizes endurance (marathon) or intensity (mid-distance events). The "intensity" theory of ski training uses stress to break down muscles and recovery to build them up stronger than before. In this theory, there are five levels of intensity for training: Athletes train for each level on
7209-399: The surface chemistry or charge is modified with plasma activation , flame treatment , or corona treatment . Polyethylene is classified by its density and branching . Its mechanical properties depend significantly on variables such as the extent and type of branching, the crystal structure, and the molecular weight . There are several types of polyethylene: With regard to sold volumes,
7298-984: The team head coach left needles and drip bags at a public location near the Helsinki airport . At the Sochi Winter Olympic Games , Austrian cross-country skier Johannes Dürr was ejected from competition after testing positive for the blood booster EPO. In 2007, The International Olympic Committee banned biathletes, Wolfgang Perner and Wolfgang Rottmann , and the cross-country skiers, Martin Tauber , Jürgen Pinter , Johannes Eder, Roland Diethart and Christian Hoffmann, from all future Olympic competition. An Italian court found Tauber and Pinter not guilty in 2012. Skiers, who have tested positive for EPO or other performance-enhancing drugs, include (date of sanction): Polyethylene Polyethylene or polythene (abbreviated PE ; IUPAC name polyethene or poly(methylene) )
7387-466: The two compounds. Ethylene/vinyl alcohol copolymer (EVOH) is (formally) a copolymer of PE and vinyl alcohol (ethenol), which is prepared by (partial) hydrolysis of ethylene-vinyl acetate copolymer (as vinyl alcohol itself is not stable). However, typically EVOH has a higher comonomer content than the VAC commonly used. EVOH is used in multilayer films for packaging as a barrier layer (barrier plastic). As EVOH
7476-453: The use of pairs of pole became the norm, materials favored lightness and strength, starting with bamboo , which gave way to fiberglass, used at the 1968 Winter Olympics , aluminum , used at the 1972 Winter Olympics , and ultimately carbon fiber, introduced in 1975. Skate skiing was introduced to competition in the 20th Century. At the first German ski championship, held at the Feldberg in
7565-472: The venue. It cites two types of stadium, the horseshoe (preferred for television) and the "ski in, ski out" layout. It emphasizes the importance of accommodating television coverage at the start, finish, and exchange zones for equipment or relays. In addition, television coverage requires a variety of facilities to support the activities of the press. Climate change is causing venues, accustomed to natural snow, to rely increasingly on man-made snow to provide
7654-458: The wavelength of visible light. The ingredient or monomer is ethylene ( IUPAC name ethene), a gaseous hydrocarbon with the formula C 2 H 4 , which can be viewed as a pair of methylene groups (− CH 2 −) connected to each other. Typical specifications for PE purity are <5 ppm for water, oxygen, and other alkenes contents. Acceptable contaminants include N 2 , ethane (common precursor to ethylene), and methane. Ethylene
7743-643: The white, waxy substance that he had created, they recognized that it contained long −CH 2 − chains and termed it polymethylene . The first industrially practical polyethylene synthesis (diazomethane is a notoriously unstable substance that is generally avoided in industrial syntheses) was again accidentally discovered in 1933 by Eric Fawcett and Reginald Gibson at the Imperial Chemical Industries (ICI) works in Northwich , England . Upon applying extremely high pressure (several hundred atmospheres ) to
7832-661: Was found to have very low-loss properties at very high frequency radio waves, commercial distribution in Britain was suspended on the outbreak of World War II, secrecy imposed, and the new process was used to produce insulation for UHF and SHF coaxial cables of radar sets. During World War II, further research was done on the ICI process and in 1944, DuPont at Sabine River, Texas, and Union Carbide Corporation at South Charleston, West Virginia, began large-scale commercial production under license from ICI. The landmark breakthrough in
7921-724: Was set by Hervé Balland in 1994. In the same year, Silvia Honegger completed the race with the female track record of 1:22:08. As the race was extended by 2 km in 1998 to match the distance of a full marathon and the track was changed slightly in the Stazerwald section, resulting in a more difficult topography, longer racetimes are now standard. The start of the race takes place at the Maloja Palace Hotel with an elevation of 1,820 metres (5,970 ft). The track then leads over both Lake Sils and Lake Silvaplana (which are frozen at this time of year). After passing St. Moritz there
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