Plastic is material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and so can be molded into solid objects. Plasticity is the general property of all materials which can deform irreversibly without breaking but, in the class of moldable polymers, this occurs to such a degree that their actual name derives from this specific ability. Plastics are organic polymers of high molecular mass and contain other substances, they are synthetic, most derived from petrochemicals, however, an array of variants are made from renewable materials such as polylactic acid from corn or cellulosics from cotton linters. Due to their low cost, ease of manufacture and imperviousness to water, plastics are used in a multitude of products of different scale, including paper clips and spacecraft, they have prevailed over traditional materials, such as wood, stone and bone, metal and ceramic, in some products left to natural materials. In developed economies, about a third of plastic is used in packaging and the same in buildings in applications such as piping, plumbing or vinyl siding.
Other uses include automobiles and toys. In the developing world, the applications of plastic may differ—42% of India's consumption is used in packaging. Plastics have many uses in the medical field as well, with the introduction of polymer implants and other medical devices derived at least from plastic; the field of plastic surgery is not named for use of plastic materials, but rather the meaning of the word plasticity, with regard to the reshaping of flesh. The world's first synthetic plastic was bakelite, invented in New York in 1907 by Leo Baekeland who coined the term'plastics'. Many chemists have contributed to the materials science of plastics, including Nobel laureate Hermann Staudinger, called "the father of polymer chemistry" and Herman Mark, known as "the father of polymer physics"; the success and dominance of plastics starting in the early 20th century led to environmental concerns regarding its slow decomposition rate after being discarded as trash due to its composition of large molecules.
Toward the end of the century, one approach to this problem was met with wide efforts toward recycling. The word plastic derives from the Greek πλαστικός meaning "capable of being shaped or molded" and, in turn, from πλαστός meaning "molded"; the plasticity, or malleability, of the material during manufacture allows it to be cast, pressed, or extruded into a variety of shapes, such as: films, plates, bottles, amongst many others. The common noun plastic should not be confused with the technical adjective plastic; the adjective is applicable to any material which undergoes a plastic deformation, or permanent change of shape, when strained beyond a certain point. For example, aluminum, stamped or forged exhibits plasticity in this sense, but is not plastic in the common sense. By contrast, some plastics will, in their finished forms, break before deforming and therefore are not plastic in the technical sense. Most plastics contain organic polymers; the vast majority of these polymers are formed from chains of carbon atoms,'pure' or with the addition of: oxygen, nitrogen, or sulfur.
The chains comprise many repeat units, formed from monomers. Each polymer chain will have several thousand repeating units; the backbone is the part of the chain, on the "main path", linking together a large number of repeat units. To customize the properties of a plastic, different molecular groups "hang" from this backbone; these pendant units are "hung" on the monomers, before the monomers themselves are linked together to form the polymer chain. It is the structure of these side chains; the molecular structure of the repeating unit can be fine tuned to influence specific properties in the polymer. Plastics are classified by: the chemical structure of the polymer's backbone and side chains. Plastics can be classified by: the chemical process used in their synthesis, such as: condensation and cross-linking. Plastics can be classified by: their various physical properties, such as: hardness, tensile strength, resistance to heat and glass transition temperature, by their chemical properties, such as the organic chemistry of the polymer and its resistance and reaction to various chemical products and processes, such as: organic solvents and ionizing radiation.
In particular, most plastics will melt upon heating to a few hundred degrees celsius. Other classifications are based on qualities that are relevant for product design. Examples of such qualities and classes are: thermoplastics and thermosets, conductive polymers, biodegradable plastics and engineering plastics and other plastics with particular structures, such as elastomers. One important classification of plastics is by the permanence or impermanence of their form, or whether they are: thermoplastics or thermosetting polymers. Thermoplastics are the plastics that, when heated, do not undergo chemical change in their composition and so can be molded again and again. Examples include: polyethylene, polypropylene and polyvinyl chloride. Common thermoplastics range from 20,000 to 500,000 amu, while thermosets are assumed to have infinite molecular weight. Thermosets, or thermosetting polymers, can melt and take shape only once: after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs, irreversible.
Silicones known as polysiloxanes, are polymers that include any synthetic compound made up of repeating units of siloxane, a chain of alternating silicon atoms and oxygen atoms, combined with carbon and sometimes other elements. They are heat-resistant and either liquid or rubber-like, are used in sealants, lubricants, cooking utensils, thermal and electrical insulation; some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, silicone caulk. More called polymerized siloxanes or polysiloxanes, silicones consist of an inorganic silicon-oxygen backbone chain with organic side groups attached to the silicon atoms; these silicon atoms are tetravalent. So, silicones are polymers constructed from inorganic-organic monomers. Silicones have in general the chemical formula n, where R is an organic group such as an alkyl or phenyl group. In some cases, organic side groups can be used to link two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, crosslinking, silicones can be synthesized with a wide variety of properties and compositions.
They can vary in consistency from liquid to gel to rubber to hard plastic. The most common siloxane is a silicone oil; the second largest group of silicone materials is based on silicone resins, which are formed by branched and cage-like oligosiloxanes. F. S. Kipping coined the word silicone in 1901 to describe polydiphenylsiloxane by analogy of its formula, Ph2SiO, with the formula of the ketone benzophenone, Ph2CO. Kipping was well aware that polydiphenylsiloxane is polymeric whereas benzophenone is monomeric and noted that Ph2SiO and Ph2CO had different chemistry; the discovery of the structural differences between Kipping's molecules and the ketones means that silicone is no longer the correct term and that the term siloxanes is correct according to the nomenclature of modern chemistry. Silicone is confused with silicon, but they are distinct substances. Silicon is a chemical element, a hard dark-grey semiconducting metalloid which in its crystalline form is used to make integrated circuits and solar cells.
Silicones are compounds that contain silicon, hydrogen and other kinds of atoms as well, have different physical and chemical properties. Compounds containing silicon-oxygen double bonds, now called silanones but which could deserve the name "silicone", have long been identified as intermediates in gas-phase processes such as chemical vapor deposition in microelectronics production, in the formation of ceramics by combustion; however they have a strong tendency to polymerize into siloxanes. The first stable silanone was obtained in 2014 by others. Most common are materials based on polydimethylsiloxane, derived by hydrolysis of dimethyldichlorosilane; this dichloride reacts with water as follows: n Si2Cl2 + n H2O → n + 2n HClThe polymerization produces linear chains capped with Si-Cl or Si-OH groups. Under different conditions the polymer is a cyclic, not a chain. For consumer applications such as caulks silyl acetates are used instead of silyl chlorides; the hydrolysis of the acetates produce the less dangerous acetic acid as the reaction product of a much slower curing process.
This chemistry is used in many consumer applications, such as adhesives. Branches or cross-links in the polymer chain can be introduced by using organosilicone precursors with fewer alkyl groups, such as methyltrichlorosilane and methyltrimethoxysilane. Ideally, each molecule of such a compound becomes a branch point; this process can be used to produce hard silicone resins. Precursors with three methyl groups can be used to limit molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain; when silicone is burned in air or oxygen, it forms solid silica as a white powder and various gases. The dispersed powder is sometimes called silica fume. Silicones exhibit many useful characteristics, including: Low thermal conductivity Low chemical reactivity Low toxicity Thermal stability; the ability to repel water and form watertight seals. Does not stick to many substrates, but adheres well to others, e.g. glass. Does not support microbiological growth.
Resistance to oxygen and ultraviolet light. This property has led to widespread use of silicones in the construction industry and the automotive industry. Electrical insulation properties; because silicone can be formulated to be electrically insulative or conductive, it is suitable for a wide range of electrical applications. High gas permeability: at room temperature, the permeability of silicone rubber for such gases as oxygen is 400 times that of butyl rubber, making silicone useful for medical applications in which increased aeration is desired. Conversely, silicone rubbers can not be used. Silicone can be developed into rubber sheeting, where it has other properties, such as being FDA compliant; this extends the uses of silicone sheeting to industries that demand hygiene, for example and beverage and pharmaceutical. Silicones are used in many products. Ullmann's Encyclopedia of Industrial Chemistry lists the following major categories of application: Electrical, elec
A strap-on dildo is a dildo designed to be worn with a harness, during sexual activity. Harnesses and dildos are made in a wide variety of styles, with variations in how the harness fits the wearer, how the dildo attaches to the harness, as well as various features intended to facilitate stimulation of the wearer or a sexual partner. A strap-on dildo can be used for a wide variety of sexual activities, including vaginal sex, gay sex, oral sex, or solo or mutual masturbation. Sexual lubricant can be used to ease insertion, strap-on dildos can be used by people of any gender or sexuality. Due to the taboo nature of strap-on activities, information on their history is difficult to find. Many artifacts from the Upper Paleolithic have been found that appear to be dildos, including a double "baton" with a hole in the middle, theorized to be for a strap to hold it to a wearer. Female-female dildo usage in ancient China has been documented, but it is not clear if this was double-dildos, strap-on dildos, or just a simple dildo being used by one woman on another.
In ancient Greece, dildos were made of stone or padded leather, some evidence shows aforementioned leather was used to make a harness as well, with olive oil used for anal penetration. The Kama Sutra includes mention of dildos made from a wide variety of materials, used by hand, with ties, or in a harness. A double-penetration dildo was found in ancient France. A 19th-century Chinese painting shows a woman using a dildo strapped to her shoe, showing that creative use of strap-ons was well under way. An 1899 report by Haberlandt documented current and historical use of double-ended dildos in Zanzibar, is one of the few historical documents of this kind, it is the history of the strap-on parallels the history of the dildo, given the age of many discoveries, is a rather long history. The first part of a strap-on setup is the harness, which connects the dildo to the wearer's body in a position similar to that of a male's genitals. A good harness should be sturdy yet comfortable, is designed to provide stimulation for the wearer.
Many types of harnesses are available, with different drawbacks. Some dildos are built onto one. A 2-strap harness, in its most basic form, is similar to a g-string. One strap goes around the wearer's waist, like a belt, while the other goes between the wearer's legs and connects to the other strap in the middle at the lower back. While these are simple, many people find them uncomfortable because the strap rubs against the anus and other areas, they sometimes do not hold the dildo firmly, causing it to sag, twist, or squeak. Three-strap harnesses have one strap around the wearer's waist, but instead of one strap between the legs, they have two straps, one around each thigh, rejoining the first strap near the front; this design leaves the genitals and anus uncovered, attaches the dildo more giving the wearer more control. Not all people find this design comfortable, sometimes they are difficult to fit properly, tend to slip. Strap-on harnesses built into various clothing items are available, most as a corset or other item of lingerie.
Some are designed to be worn underneath normal clothing for quick use, while others take advantage of the additional strength and sturdiness an item of clothing can provide over a few straps, or just to integrate the strap-on into an erotic outfit. Harnesses are not limited to the crotch, indeed many types are available for other body parts. A popular one is a thigh harness, which attaches a dildo to the wearer's thigh, allowing for many unique positions, as penetration is no longer limited to what could be done with a penis. Another unusual design attaches a dildo to the chin of the wearer, allowing vaginal penetration while performing anilingus or vice versa. An additional design is a gag-style harness, in which a gag is inserted into the wearer's mouth and a dildo protrudes at the other end. Harnesses are available to attach dildos to just about any household object, allowing for many creative uses. A dildo could be attached to a chair, bed, or any other item of furniture, penetrate someone during other activities, with or without a partner.
Another item, while not technically a harness, but worth mentioning, is an inflatable ball 9 to 18 inches diameter, made of sturdy rubber designed to support the weight of one or two people, with an attachment for a dildo on it. This allows many unique positions, such as double penetration for a woman by lying face down on the ball for vaginal penetration while her partner penetrates her anally doggy style, much more effective than a solid object due to the "bounce" of the ball; these inflatable balls are quite popular for solo use. Harnesses are available in many different materials, the choice of which to use depends on individual preference. Nylon webbing and soft foam-like synthetic leather are common affordable, durable. Synthetic harnesses are easy to clean and require little maintenance. Some, such as the Spare Parts harness, are machine-washable. Leather adjusts to the wearer's body, but still is strong. Leather requires more work to maintain than other materials. Cloth is used for clothing harnesses such as corsets and oth
Natural rubber called India rubber or caoutchouc, as produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds, plus water. Thailand and Indonesia are two of the leading rubber producers. Forms of polyisoprene that are used as natural rubbers are classified as elastomers. Rubber is harvested in the form of the latex from the rubber tree or others; the latex is a sticky, milky colloid drawn off by making incisions in the bark and collecting the fluid in vessels in a process called "tapping". The latex is refined into rubber ready for commercial processing. In major areas, latex is allowed to coagulate in the collection cup; the coagulated lumps are processed into dry forms for marketing. Natural rubber is used extensively in many applications and products, either alone or in combination with other materials. In most of its useful forms, it has a large stretch ratio and high resilience, is waterproof; the major commercial source of natural rubber latex is the Pará rubber tree, a member of the spurge family, Euphorbiaceae.
This species is preferred. A properly managed tree responds to wounding by producing more latex for several years. Congo rubber a major source of rubber, came from vines in the genus Landolphia. Dandelion milk contains latex; the latex exhibits the same quality as the natural rubber from rubber trees. In the wild types of dandelion, latex content varies greatly. In Nazi Germany, research projects tried to use dandelions as a base for rubber production, but failed. In 2013, by inhibiting one key enzyme and using modern cultivation methods and optimization techniques, scientists in the Fraunhofer Institute for Molecular Biology and Applied Ecology in Germany developed a cultivar, suitable for commercial production of natural rubber. In collaboration with Continental Tires, IME began a pilot facility. Many other plants produce forms of latex rich in isoprene polymers, though not all produce usable forms of polymer as as the Pará; some of them require more elaborate processing to produce anything like usable rubber, most are more difficult to tap.
Some produce other desirable materials, for example chicle from Manilkara species. Others that have been commercially exploited, or at least showed promise as rubber sources, include the rubber fig, Panama rubber tree, various spurges, the related Scorzonera tau-saghyz, various Taraxacum species, including common dandelion and Russian dandelion, most for its hypoallergenic properties, guayule; the term gum rubber is sometimes applied to the tree-obtained version of natural rubber in order to distinguish it from the synthetic version. The first use of rubber was by the indigenous cultures of Mesoamerica; the earliest archeological evidence of the use of natural latex from the Hevea tree comes from the Olmec culture, in which rubber was first used for making balls for the Mesoamerican ballgame. Rubber was used by the Maya and Aztec cultures – in addition to making balls Aztecs used rubber for other purposes such as making containers and to make textiles waterproof by impregnating them with the latex sap.
The Pará rubber tree is indigenous to South America. Charles Marie de La Condamine is credited with introducing samples of rubber to the Académie Royale des Sciences of France in 1736. In 1751, he presented a paper by François Fresneau to the Académie that described many of rubber's properties; this has been referred to as the first scientific paper on rubber. In England, Joseph Priestley, in 1770, observed that a piece of the material was good for rubbing off pencil marks on paper, hence the name "rubber", it made its way around England. In 1764 François Fresnau discovered. Giovanni Fabbroni is credited with the discovery of naphtha as a rubber solvent in 1779. South America remained the main source of latex rubber used during much of the 19th century; the rubber trade was controlled by business interests but no laws expressly prohibited the export of seeds or plants. In 1876, Henry Wickham smuggled 70,000 Pará rubber tree seeds from Brazil and delivered them to Kew Gardens, England. Only 2,400 of these germinated.
Seedlings were sent to India, British Ceylon, Dutch East Indies and British Malaya. Malaya was to become the biggest producer of rubber. In the early 1900s, the Congo Free State in Africa was a significant source of natural rubber latex gathered by forced labor. King Leopold II's colonial state brutally enforced production quotas. Tactics to enforce the rubber quotas included removing the hands of victims to prove they had been killed. Soldiers came back from raids with baskets full of chopped-off hands. Villages that resisted were razed to encourage better compliance locally. See Atrocities in the Congo Free State for more information on the rubber trade in the Congo Free State in the late 1800s and early 1900s. Liberia and Nigeria started production. In India, commercial cultivation was introduced by British planters, although the experimental efforts to grow rubber on a commercial scale were initiated as early as 1873 at the Calcutta Botanical Gardens; the first commercial Hevea plantations were established at Thattekadu in Kerala in 1902.
In years the plantation expanded to Karnataka, Tamil Nadu and the Andaman and Nicobar Islands of India. India today is the
Hitachi Magic Wand
The Hitachi Magic Wand is an electrical, AC-powered wand vibrator manufactured for relieving tension and relaxing sore muscles, but most famous for its use as a sex toy. Japanese company Hitachi listed the device for business in the United States in 1968. Sex educator Betty Dodson popularized its use as a vibrator and masturbation aid for women during the sex-positive movement in the late 1960s, it functions as a clitoral vibrator and is able to bring many women to orgasm. The wand is 12 inches long and weighs 1.2 pounds with stimulation provided by its rubberized 2.5-inch head. Hitachi executives assisted financing the production of chocolates in the shape of the massager in 1992, in honor of the 15-year anniversary of the sex shop Good Vibrations. Subsequently, the company asserted. Hitachi had a conflict with its U. S. distributor in 2000 and stopped selling the device until it reached a new deal with distributor Vibratex. The Magic Wand sold out after being featured in a 2002 episode of the City.
Hitachi decided to cease production of the device in 2013 because of concerns about having the company name attached to a sex toy. Vibratex persuaded the company to continue manufacturing it under the name "Original Magic Wand", omitting the Hitachi name. In 2014, the company used the name "Magic Wand Original". Academics have researched its use for treatment of female sexual arousal disorder and chronic anorgasmia—a sexual dysfunction in which a person cannot achieve orgasm; the Journal of Consulting and Clinical Psychology published a 1979 study which found self-administered treatment and use of the Magic Wand to be the best method to achieve orgasm. In 2008, The Scientific World Journal published research finding over 93% of a group of 500 chronic anorgasmic women could reach orgasm using the Magic Wand and the Betty Dodson Method; the device was used in studies in many applications, including articles published in Dermatology Online Journal, Journal of Applied Physiology, Experimental Brain Research, Neuroscience Letters, Journal of Perinatal & Neonatal Nursing.
The Magic Wand has alternatively been referred to as the Cadillac of vibrators, the Rolls-Royce of vibrators, the mother of all vibrators. Counselors Bettina Arndt, Laura Berman, Gloria Brame, Ruth Westheimer recommended the device to women, Cosmopolitan magazine reported the Magic Wand was the vibrator most suggested by sex therapists. Mobile Magazine readers in 2005 voted the Magic Wand "the No. 1 greatest gadget of all time". Tanya Wexler's film Hysteria featured the device while showing the evolution of the vibrator. Engadget called the Magic Wand "the most recognizable sex toy on Earth"; the device is 30 cm long and it weighs 540 g. Muscle and nerve stimulation is provided by the device's rubberised, 6.4 cm head, attached to the main body of the massager via a flexible neck. A 1.8 m cord is attached to the device to provide power from mains electricity with alternating current, requires 110 Volts. It does not take batteries; the massager provides two vibration rates—5,000 and 6,000 rpm, which are equivalent to 83 Hz and 100 Hz—that are controlled by a switch on its body.
Research published in the journal Sexual and Relationship Therapy determined that the Magic Wand operated on its low setting at a frequency of 89 Hz and at 101 Hz on its high setting. Its displacement was measured with an acceleration of 185.7 μg. Because the device was not designed as a sexual stimulation aid, it exhibits some deficiencies when used for this purpose. Apart from its size and its reliance on a mains power supply that limits its portability, it is not waterproof or water-resistant, it overheats when used for more than 25 minutes, it does not work well in electrical outlets in all countries internationally. Because of the Magic Wand's popularity, various aftermarket attachments with differences in colour, pattern of studs, material, became available to purchase; such attachments have been produced by many companies without ties to Hitachi. Without attachments, the device functions as a clitoral vibrator, able to bring women to orgasm. Add-ons that are fitted over the top of the device and are used to excite the clitoris are available.
An attachment called. According to an article in the Dermatology Online Journal, "The Wonder Wand" is created from a plastic material, in consistency and may be cleansed after use. Attachments made of silicone designed to aid with penetrative sensations or to modify texture of the device are available. An add-on called the "G-Spotter" fits over the device in the same fashion and turns the device into a G-spot vibrator; the "Gee-Whiz" is a similar type of attachment used to stimulate the G-spot. The "Fluffer Tip Wand Attachment" may be placed over the device and can be used to mimic the sensation of cunnilingus. "Liberator Axis" is a booster pillow that stabilizes the Magic Wand so the user does not have to hold it with her hands during use. Attachments have been sold by Betty Dodson on her website, which provides pictorial instructions on their use with the Magic Wand; the massager may be used with the "G-Whiz" attachment. An attachment made by an unaffiliated company provides a cap that fits over the top of the device so it can function as a male masturbation sleeve.
In Japan, an attachment is sold for men to stimulat
In electronics, a remote control is a component of an electronic device used to operate the device from a distance wirelessly. For example, in consumer electronics, a remote control can be used to operate devices such as a television set, DVD player, or other home appliance, from a short distance. A remote control is a convenience feature for the user, can allow operation of devices that are out of convenient reach for direct operation of controls. In some cases, remote controls allow a person to operate a device that they otherwise would not be able to reach, as when a garage door opener is triggered from outside or when a Digital Light Processing projector, mounted on a high ceiling is controlled by a person from the floor level. Early television remote controls used ultrasonic tones. Present-day remote controls are consumer infrared devices which send digitally-coded pulses of infrared radiation to control functions such as power, channels, track change, fan speed, or other features varying from device to device.
Remote controls for these devices are small wireless handheld objects with an array of buttons for adjusting various settings such as television channel, track number, volume. For many devices, the remote control contains all the function controls while the controlled device itself has only a handful of essential primary controls; the remote control code, thus the required remote control device, is specific to a product line, but there are universal remotes, which emulate the remote control made for most major brand devices. Remote control has continually evolved and advanced in the 2000s to include Bluetooth connectivity, motion sensor-enabled capabilities and voice control. In 1894, the first example of wirelessly controlling at a distance was during a demonstration by the British physicist Oliver Lodge, in which he made use of a Branly's coherer to make a mirror galvanometer move a beam of light when an electromagnetic wave was artificially generated; this was further refined by radio innovators Guglielmo Marconi and William Preece, at a demonstration that took place on December 12, 1896, at Toynbee Hall in London, in which they made a bell ring by pushing a button in a box, not connected by any wires.
In 1898 Nikola Tesla filed his patent, U. S. Patent 613,809, named Method of an Apparatus for Controlling Mechanism of Moving Vehicle or Vehicles, which he publicly demonstrated by radio-controlling a boat during an electrical exhibition at Madison Square Garden. Tesla called his boat a "teleautomaton". In 1903, Leonardo Torres Quevedo presented the Telekino at the Paris Academy of Science, accompanied by a brief, making an experimental demonstration. At the same time, he obtained a patent in France, Great Britain, the United States; the Telekino consisted of a robot. With the Telekino, Torres-Quevedo laid down modern wireless remote-control operation principles and was a pioneer in the field of remote control. In 1906, in the presence of the king and before a great crowd, Torres demonstrated the invention in the port of Bilbao, guiding a boat from the shore, he would try to apply the Telekino to projectiles and torpedoes but had to abandon the project for lack of financing. The first remote-controlled model airplane flew in 1932, the use of remote control technology for military purposes was worked intensively during the Second World War, one result of this being the German Wasserfall missile.
By the late 1930s, several radio manufacturers offered remote controls for some of their higher-end models. Most of these were connected to the set being controlled by wires, but the Philco Mystery Control was a battery-operated low-frequency radio transmitter, thus making it the first wireless remote control for a consumer electronics device. Using pulse-count modulation, this was the first digital wireless remote control; the first remote intended to control a television was developed by Zenith Radio Corporation in 1950. The remote, called "Lazy Bones," was connected to the television by a wire. A wireless remote control, the "Flashmatic," was developed in 1955 by Eugene Polley, it worked by shining a beam of light onto one of four photoelectric cells, but the cell did not distinguish between light from the remote and light from other sources. The Flashmatic had to be pointed precisely at one of the sensors in order to work. In 1956, Robert Adler developed "Zenith Space Command," a wireless remote.
It was mechanical and used ultrasound to change the volume. When the user pushed a button on the remote control, it struck a bar and clicked, hence they were called a "clicker," but it sounded like a "clink" and the mechanics were similar to a pluck; each of the four bars emitted a different fundamental frequency with ultrasonic harmonics, circuits in the television detected these sounds and interpreted them as channel-up, channel-down, sound-on/off, power-on/off. The rapid decrease in price of transistors made possible cheaper electronic remotes that contained a piezoelectric crystal, fed by an oscillating electric current at a frequency near or above the upper threshold of human hearing, though still audible to dogs; the receiver contained a microphone attached to a circuit, tuned to the same frequency. Some problems with this method were that the receiver could be triggered accidentally by occurring noises or deliberately by metal against glass, for example, some people could hear the lower ultrasonic harmonics.
The impetus for a more complex type of television remote control came in 1973, with the development of the Ceefax teletext service by the BBC. Most commercial remote controls at that tim
A metal is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, conducts electricity and heat well. Metals are malleable or ductile. A metal may be an alloy such as stainless steel. In physics, a metal is regarded as any substance capable of conducting electricity at a temperature of absolute zero. Many elements and compounds that are not classified as metals become metallic under high pressures. For example, the nonmetal iodine becomes a metal at a pressure of between 40 and 170 thousand times atmospheric pressure; some materials regarded as metals can become nonmetals. Sodium, for example, becomes a nonmetal at pressure of just under two million times atmospheric pressure. In chemistry, two elements that would otherwise qualify as brittle metals—arsenic and antimony—are instead recognised as metalloids, on account of their predominately non-metallic chemistry. Around 95 of the 118 elements in the periodic table are metals; the number is inexact as the boundaries between metals and metalloids fluctuate due to a lack of universally accepted definitions of the categories involved.
In astrophysics the term "metal" is cast more to refer to all chemical elements in a star that are heavier than the lightest two and helium, not just traditional metals. A star fuses lighter atoms hydrogen and helium, into heavier atoms over its lifetime. Used in that sense, the metallicity of an astronomical object is the proportion of its matter made up of the heavier chemical elements. Metals are present in many aspects of modern life; the strength and resilience of some metals has led to their frequent use in, for example, high-rise building and bridge construction, as well as most vehicles, many home appliances, tools and railroad tracks. Precious metals were used as coinage, but in the modern era, coinage metals have extended to at least 23 of the chemical elements; the history of metals is thought to begin with the use of copper about 11,000 years ago. Gold, iron and brass were in use before the first known appearance of bronze in the 5th millennium BCE. Subsequent developments include the production of early forms of steel.
Metals are lustrous, at least when freshly prepared, polished, or fractured. Sheets of metal thicker than a few micrometres appear opaque; the solid or liquid state of metals originates in the capacity of the metal atoms involved to lose their outer shell electrons. Broadly, the forces holding an individual atom’s outer shell electrons in place are weaker than the attractive forces on the same electrons arising from interactions between the atoms in the solid or liquid metal; the electrons involved become delocalised and the atomic structure of a metal can be visualised as a collection of atoms embedded in a cloud of mobile electrons. This type of interaction is called a metallic bond; the strength of metallic bonds for different elemental metals reaches a maximum around the center of the transition metal series, as these elements have large numbers of delocalized electrons. Although most elemental metals have higher densities than most nonmetals, there is a wide variation in their densities, lithium being the least dense and osmium the most dense.
Magnesium and titanium are light metals of significant commercial importance. Their respective densities of 1.7, 2.7 and 4.5 g/cm3 can be compared to those of the older structural metals, like iron at 7.9 and copper at 8.9 g/cm3. An iron ball would thus weigh about as much as three aluminium balls. Metals are malleable and ductile, deforming under stress without cleaving; the nondirectional nature of metallic bonding is thought to contribute to the ductility of most metallic solids. In contrast, in an ionic compound like table salt, when the planes of an ionic bond slide past one another, the resultant change in location shifts ions of the same charge into close proximity, resulting in the cleavage of the crystal; such a shift is not observed in a covalently bonded crystal, such as a diamond, where fracture and crystal fragmentation occurs. Reversible elastic deformation in metals can be described by Hooke's Law for restoring forces, where the stress is linearly proportional to the strain. Heat or forces larger than a metal's elastic limit may cause a permanent deformation, known as plastic deformation or plasticity.
An applied force may be a compressive force, or a shear, bending or torsion force. A temperature change may affect the movement or displacement of structural defects in the metal such as grain boundaries, point vacancies and screw dislocations, stacking faults and twins in both crystalline and non-crystalline metals. Internal slip and metal fatigue may ensue; the atoms of metallic substances are arranged in one of three common crystal structures, namely body-centered cubic, face-centered cubic, hexagonal close-packed. In bcc, each atom is positioned at the center of a cube of eight others. In fcc and hcp, each atom is surrounded by twelve others; some metals adopt different structures depending on the temperature. The