In chemistry and biology a cross-link is a bond that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural polymers. In polymer chemistry "cross-linking" refers to the use of cross-links to promote a change in the polymers' physical properties; when "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions, as well as other creative cross-linking methodologies. Although the term is used to refer to the "linking of polymer chains" for both sciences, the extent of crosslinking and specificities of the crosslinking agents vary greatly; as with all science, there are overlaps, the following delineations are a starting point to understanding the subtleties. Crosslinking is the general term for the process of forming covalent bonds or short sequences of chemical bonds to join two polymer chains together; the term curing refers to the crosslinking of thermosetting resins, such as unsaturated polyester and epoxy resin, the term vulcanization is characteristically used for rubbers.
When polymer chains are crosslinked, the material becomes more rigid. In polymer chemistry, when a synthetic polymer is said to be "cross-linked", it means that the entire bulk of the polymer has been exposed to the cross-linking method; the resulting modification of mechanical properties depends on the cross-link density. Low cross-link densities decrease the viscosities of polymer melts. Intermediate cross-link densities transform gummy polymers into materials that have elastomeric properties and high strengths. High cross-link densities can cause materials to become rigid or glassy, such as phenol-formaldehyde materials. Cross-links can be formed by chemical reactions that are initiated by heat, change in pH, or irradiation. For example, mixing of an unpolymerized or polymerized resin with specific chemicals called crosslinking reagents results in a chemical reaction that forms cross-links. Cross-linking can be induced in materials that are thermoplastic through exposure to a radiation source, such as electron beam exposure, gamma radiation, or UV light.
For example, electron beam processing is used to cross-link the C type of cross-linked polyethylene. Other types of cross-linked polyethylene are made by addition of peroxide during extruding or by addition of a cross-linking agent and a catalyst during extruding and performing a post-extrusion curing; the chemical process of vulcanization is a type of cross-linking that changes rubber to the hard, durable material associated with car and bike tires. This process is called sulfur curing; this is, however, a slower process. A typical car tire is cured for 15 minutes at 150 °C. However, the time can be reduced by the addition of accelerators such as 2-benzothiazolethiol or tetramethylthiuram disulfide. Both of these contain a sulfur atom in the molecule that initiates the reaction of the sulfur chains with the rubber. Accelerators increase the rate of cure by catalysing the addition of sulfur chains to the rubber molecules. Cross-links are the characteristic property of thermosetting plastic materials.
In most cases, cross-linking is irreversible, the resulting thermosetting material will degrade or burn if heated, without melting. In the case of commercially used plastics, once a substance is cross-linked, the product is hard or impossible to recycle. In some cases, though, if the cross-link bonds are sufficiently different, from the bonds forming the polymers, the process can be reversed. Permanent wave solutions, for example, break and re-form occurring cross-links between protein chains in hair. Where chemical cross-links are covalent bonds, physical cross-links are formed by weak interactions. For example, sodium alginate gels upon exposure to calcium ion, which allows it to form ionic bonds that bridge between alginate chains. Polyvinyl alcohol gels upon the addition of borax through hydrogen bonding between boric acid and the polymer's alcohol groups. Other examples of materials which form physically cross-linked gels include gelatin, collagen and agar agar. Chemical covalent cross-links are stable mechanically and thermally, so once formed are difficult to break.
Therefore, cross-linked products like car tires cannot be recycled easily. A class of polymers known as thermoplastic elastomers rely on physical cross-links in their microstructure to achieve stability, are used in non-tire applications, such as snowmobile tracks, catheters for medical use, they offer a much wider range of properties than conventional cross-linked elastomers because the domains that act as cross-links are reversible, so can be reformed by heat. The stabilizing domains may be crystalline as in thermoplastic copolyesters. Note: A rubber which cannot be reformed by heat or chemical treatment is called a thermoset elastomer. On the other hand, a thermoplastic elastomer can be recycled by heat. Many polymers undergo oxidative cross-linking when exposed to atmospheric oxygen. In some cases this is undesirable and thus polymerization reactions may involve the use of an antioxidant to slow the formation of oxidative cross-links. In other cases, when formation of cross-links by oxidation is desirable, an oxidizer such as hydrogen peroxide may be used to speed up the process.
The aforementioned process of applying a permanent wave to hair is one example of oxidative cross-linking. In that process the disulfide bonds
Aerosol paint is a type of paint that comes in a sealed pressurized container and is released in an aerosol spray when depressing a valve button. A form of spray painting, aerosol paint leaves a smooth, evenly coated surface, unlike many traditional rolled or brushed paints. Standard sized cans are lightweight, portable and easy to store. Aerosol primer can be applied directly to many plastics. In 1949, Edward H. Seymour, of Sycamore, IL, added paint to existing spray can technology at his wife Bonnie's suggestion, it was designed to demonstrate an aluminum paint he developed. His patent was awarded in 1951. Most aerosol paints have a metal, glass or plastic ball called a pea inside of the can, used to mix the paint when the can is shaken. Acrylic-based craft primers and vinyl dye can be used on plastics like miniatures. Most brands include a wide variety of paints, including primers and traffic resistant enamels and matte finishes, metallic colors, textured paints for home decor. Aerosol paint is useful for semi-permanent marking on construction and surveying sites.
Inverted cans for street, utility or field marking can be used upside-down with an extension pole. APWA has standardized colors for excavation markings. Hiking trails can be marked with aerosol paint trail blazes. Small to medium-sized repairs to automobile bodywork can be completed by enthusiasts at home using aerosol paint, though to paint an entire vehicle in this manner would be difficult and expensive; the main disadvantages, compared to a professional spray gun, include the limited quality provided by the built-in nozzle and the lack of infrared baking after applying the paint, which indicates that the paint could take several months to obtain its final hardness. For a good finish it is essential to prepare the surface well, sanding to provide a key and degreasing with naptha. Areas not to be painted should be masked, although for repair work it is important to avoid spraying a full coat right up to the masking tape, which will leave a hard line; the flow of paint should be started or stopped on the masked area rather than over the area intended to be painted, as aerosols discharge "blobs" of paint under these conditions.
Coats should be built up enough to avoid runs, but a "dry" finish must be avoided by spraying too thinly or from too far away. The optimum distance between the can and workpiece is around one foot. Most automotive paints will require a clear lacquer after the color coat 24 hours later; the color coat should be well matted down with fine abrasive paper before applying the lacquer. There are a variety of tools to assist in the dispersal of paints including spray paint handles and attachments to equalize the pressure and secure hand grip. Other customized technology such as sprayprinter can be attached to aerosol cans to automate the process of spray painting and allow for images to be created in a manner similar to printing. Speed and permanence make aerosol paint a common graffiti medium. In the late 1970s, street graffiti writers' signatures and murals became more elaborate and a unique style developed as a factor of the aerosol medium and the speed required for illicit work. Many now recognize graffiti and street art as a unique art form and manufactured aerosol paints are made for the graffiti artist.
Graffiti artist paints tend to be more expensive, but have a wider selection of rich colors, are thicker and less to drip. They are produced in standard high pressure cans for fast, thick coverage and lower pressure cans for more control and flexibility. Most art brand paints have three mixing peas in a can. A wide array of actuators, or caps are available, from standard "skinny" caps to wider "fat" caps, as well as caps that control the softness or crispness of the spray. Calligraphy caps create fan spray instead of the standard round; when aerosol paint is used, care must be taken to mask areas where paint is not wanted. A stencil can be used to protect a surface except the specific shape, to be painted. Stencils can be purchased as movable letters, ordered as professionally cut logos, or hand-cut by artists. Stencils can be used multiple times for consistency. Official stencils can be used to and label objects, vehicles or locations. Graffiti writers can use stencils to mark in busy places or leave recognizable tags over a large area.
Stencil artists use multiple colors, or create elaborate stencils that are works of art in themselves. Unauthorized graffiti is considered to be vandalism in most jurisdictions because the work or display is done without permission of the property owner; the term'aerosol art' is used for displaying art form'with' permission of the property owner. The UK and many cities in the United States prohibit the sale of aerosol paint to minors as part of graffiti abatement programs. While major industrial and consumer aerosol paint companies like Krylon and Rust-Oleum participate in anti-graffiti programs, art-brand companies are supportive of writers and graffiti culture, though most do not endorse illegal writing. Like many household chemicals and aerosols, aerosol paint vapor and propellant can be misused as an inhalant. Graffiti Monstercolors Rust-Oleum Krylon Vanishing spray The Plain Man's Guide to Aerosols CAPCO is a non-profit organization dedicated to providing accurate information about aerosol products The Aerosol Products Division of the Consumer Specialty Products Association gives
Collage is a technique of an art production used in the visual arts, where the artwork is made from an assemblage of different forms, thus creating a new whole. A collage may sometimes include magazine and newspaper clippings, paint, bits of colored or handmade papers, portions of other artwork or texts and other found objects, glued to a piece of paper or canvas; the origins of collage can be traced back hundreds of years, but this technique made a dramatic reappearance in the early 20th century as an art form of novelty. The term collage was coined by both Georges Braque and Pablo Picasso in the beginning of the 20th century when collage became a distinctive part of modern art. Techniques of collage were first used at the time of the invention of paper in China, around 200 BC; the use of collage, wasn't used by many people until the 10th century in Japan, when calligraphers began to apply glued paper, using texts on surfaces, when writing their poems. The technique of collage appeared in medieval Europe during the 13th century.
Gold leaf panels started to be applied in Gothic cathedrals around the 16th centuries. Gemstones and other precious metals were applied to religious images, to coats of arms. An 18th-century example of collage art can be found in the work of Mary Delany. In the 19th century, collage methods were used among hobbyists for memorabilia and books. Many institutions have attributed the beginnings of the practice of collage to Picasso and Braque in 1912, early Victorian photocollage suggest collage techniques were practiced in the early 1860s. Many institutions recognize these works as memorabilia for hobbyists, though they functioned as a facilitator of Victorian aristocratic collective portraiture, proof of female erudition, presented a new mode of artistic representation that questioned the way in which photography is truthful. In 2009, curator Elizabeth Siegel organized the exhibition: Playing with Pictures at the Art Institute Chicago to acknowledge collage works by Alexandra of Denmark and Mary Georgina Filmer among others.
The exhibition traveled to The Metropolitan Museum of Art and The Art Gallery of Ontario. Despite the pre-twentieth-century use of collage-like application techniques, some art authorities argue that collage, properly speaking, did not emerge until after 1900, in conjunction with the early stages of modernism. For example, the Tate Gallery's online art glossary states that collage "was first used as an artists' technique in the twentieth century.". According to the Guggenheim Museum's online art glossary, collage is an artistic concept associated with the beginnings of modernism, entails much more than the idea of gluing something onto something else; the glued-on patches which Braque and Picasso added to their canvases offered a new perspective on painting when the patches "collided with the surface plane of the painting." In this perspective, collage was part of a methodical reexamination of the relation between painting and sculpture, these new works "gave each medium some of the characteristics of the other," according to the Guggenheim essay.
Furthermore, these chopped-up bits of newspaper introduced fragments of externally referenced meaning into the collision: "References to current events, such as the war in the Balkans, to popular culture enriched the content of their art." This juxtaposition of signifiers, "at once serious and tongue-in-cheek," was fundamental to the inspiration behind collage: "Emphasizing concept and process over end product, collage has brought the incongruous into meaningful congress with the ordinary." Collage in the modernist sense began with Cubist painters Georges Pablo Picasso. According to some sources, Picasso was the first to use the collage technique in oil paintings. According to the Guggenheim Museum's online article about collage, Braque took up the concept of collage itself before Picasso, applying it to charcoal drawings. Picasso adopted collage after: "It was Braque who purchased a roll of simulated oak-grain wallpaper and began cutting out pieces of the paper and attaching them to his charcoal drawings.
Picasso began to make his own experiments in the new medium."In 1912 for his Still Life with Chair Caning, Picasso pasted a patch of oilcloth with a chair-cane design onto the canvas of the piece. Surrealist artists have made extensive use of collage. Cubomania is a collage made by cutting an image into squares which are reassembled automatically or at random. Collages produced using a similar, or identical, method are called etrécissements by Marcel Mariën from a method first explored by Mariën. Surrealist games such as parallel collage use collective techniques of collage making; the Sidney Janis Gallery held an early Pop Art exhibit called the New Realist Exhibition in November 1962, which included works by the American artists Tom Wesselmann, Jim Dine, Robert Indiana, Roy Lichtenstein, Claes Oldenburg, James Rosenquist, George Segal, Andy Warhol. It followed the Nouveau Réalisme exhibition at the Galerie Rive Droite in Paris, marked the international debut of the artists who soon gave rise to what came to be called Pop Art in Britain and The United States and Nouveau Réalisme on the European continent.
Many of these artists used collage techniques in their work. Wesselmann took part in the New Realist show with some reservations, exhibiting two 1962 works: Still life #17 and Still life
Activism consists of efforts to promote, direct, or intervene in social, economic, or environmental reform with the desire to make changes in society. Forms of activism range from mandate building in the community, petitioning elected officials, running or contributing to a political campaign, preferential patronage of businesses, demonstrative forms of activism like rallies, street marches, sit-ins, or hunger strikes. Activism may be performed on a day-to-day basis in a wide variety of ways, including through the creation of art, computer hacking, or in how one chooses to spend their money. For example, the refusal to buy clothes or other merchandise from a company as a protest against the exploitation of workers by that company could be considered an expression of activism. However, the most visible and impactful activism comes in the form of collective action, in which numerous individuals coordinate an act of protest together in order to make a bigger impact. Collective action, purposeful and sustained over a period of time becomes known as a social movement.
Activists have used literature, including pamphlets and books to disseminate their messages and attempt to persuade their readers of the justice of their cause. Research has now begun to explore how contemporary activist groups use social media to facilitate civic engagement and collective action combining politics with technology; the Online Etymology Dictionary records the English words "activism" and "activist" as in use in the political sense from the year 1920 or 1915 respectively. The history of the word activism traces back to earlier understandings of collective behavior and social action; as late as 1969 activism was defined as "the policy or practice of doing things with decision and energy", without regard to a political signification, whereas social action was defined as "organized action taken by a group to improve social conditions", without regard to normative status. Following the surge of so-called "new social movements" in the United States in the 1960's, a new understanding of activism emerged as a rational and acceptable democratic option of protest or appeal.
However, the history of the existence of revolt through organized or unified protest in recorded history dates back to the slave revolts of the 1st century BC in the Roman Empire, where under the leadership of former gladiator Spartacus 6,000 slaves rebelled and were crucified from Capua to Rome in what became known as the Third Servile War. In English history, the Peasant's Revolt erupted in response to the imposition of a poll tax, has been paralleled by other rebellions and revolutions in Hungary and more for example, Hong Kong. In 1930 under the leadership of Mahatma Gandhi thousands of protesting Indians participated in the Salt March as a protest against the oppressive taxes of their government, resulting in the imprisonment of 60,000 people and eventual independence for their nation. In nations throughout Asia and South America, the prominence of activism organized by social movements and under the leadership of civil activists or social revolutionaries has pushed for increasing national self-reliance or, in some parts of the developing world, collectivist communist or socialist organization and affiliation.
Activism has had major impacts on Western societies as well over the past century through social movements such as the Labour movement, the Women's Rights movement, the civil rights movement. Activists can function in a number of roles, including judicial, environmental and design. Most activism has focused on creating substantive changes in the policy or practice of a government or industry; some activists try to persuade people to change their behavior directly, rather than to persuade governments to change laws. For example, the cooperative movement seeks to build new institutions which conform to cooperative principles, does not lobby or protest politically. Other activists try to persuade people or government policy to remain the same, in an effort to counter change. Activism is not always an activity performed by those; the term activist may apply broadly to anyone who engages in activism, or be more narrowly limited to those who choose political or social activism as a vocation or characteristic practice.
Judicial activism involves the efforts of public officials. Arthur Schlesinger, Jr. - American historian, public intellectual, social critic - introduced the term "judicial activism" in a January 1946 Fortune magazine article titled "The Supreme Court: 1947". Activists can be public watchdogs and whistle blowers, attempting to understand all the actions of every form of government that acts in the name of the people and hold it accountable to oversight and transparency. Activism involves an engaged citizenry. Environmental activism takes quite a few forms: the protection of nature or the natural environment driven by a utilitarian conservation ethic or a nature oriented preservationist ethic the protection of the human environment (by pollution prevention or the protection of cultural heritage or quality of life the conservation of depletable natural resources the protection of the function of critical earth system elements or processes such as the climate; the power of Internet activism came into a global lens with the Arab Spring protests starting in late 2010.
People living in the Middle East and North African countries that were experiencing revolutions used social networking to communicate information about protests, including videos recorded on smart phones
Bookbinding is the process of physically assembling a book of codex format from an ordered stack of paper sheets that are folded together into sections or sometimes left as a stack of individual sheets. The stack is bound together along one edge by either sewing with thread through the folds or by a layer of flexible adhesive. Alternative methods of binding that are cheaper but less permanent include loose-leaf rings, individual screw posts or binding posts, twin loop spine coils, plastic spiral coils, plastic spine combs. For protection, the bound stack is either attached to stiff boards. An attractive cover is adhered to the boards, including identifying information and decoration. Book artists or specialists in book decoration can greatly enhance a book's content by creating book-like objects with artistic merit of exceptional quality. Before the computer age, the bookbinding trade involved two divisions. First, there was Stationery binding that deals with books intended for handwritten entries such as accounting ledgers, business journals, blank books, guest log books, along with other general office stationery such as note books, manifold books, day books, portfolios, etc.
Computers have now replaced the pen and paper based accounting that constituted most of the stationery binding industry. Second was Letterpress binding which deals with making books intended for reading, including library binding, fine binding, edition binding, publisher's bindings. A third division deals with the repair and conservation of old used bindings. Today, modern bookbinding is divided between hand binding by individual craftsmen working in a shop and commercial bindings mass-produced by high-speed machines in a factory. There is a broad grey area between the two divisions; the size and complexity of a bindery shop varies with job types, for example, from one-of-a-kind custom jobs, to repair/restoration work, to library rebinding, to preservation binding, to small edition binding, to extra binding, to large-run publisher's binding. There are cases where binding jobs are combined in one shop. For the largest numbers of copies, commercial binding is effected by production runs of ten thousand copies or more in a factory.
Bookbinding is a specialized trade that relies on basic operations of measuring and gluing. A finished book might need dozens of operations to complete, according to the specific style and materials. Bookbinding combines skills from other trades such as paper and fabric crafts, leather work, model making, graphic arts, it requires knowledge about numerous varieties of book structures along with all the internal and external details of assembly. A working knowledge of the materials involved is required. A book craftsman needs a minimum set of hand tools but with experience will find an extensive collection of secondary hand tools and items of heavy equipment that are valuable for greater speed and efficiency. Bookbinding is an artistic craft of great antiquity, at the same time, a mechanized industry; the division between craft and industry is not so wide. It is interesting to observe that the main problems faced by the mass-production bookbinder are the same as those that confronted the medieval craftsman or the modern hand binder.
The first problem is still. The craft of bookbinding originated in India, where religious sutras were copied on to palm leaves with a metal stylus; the leaf was dried and rubbed with ink, which would form a stain in the wound. The finished leaves were given numbers, two long twines were threaded through each end through wooden boards, making a palm-leaf book; when the book was closed, the excess twine would be wrapped around the boards to protect the manuscript leaves. Buddhist monks took the idea through Afghanistan to China in the first century BC. Similar techniques can be found in ancient Egypt where priestly texts were compiled on scrolls and books of papyrus. Another version of bookmaking can be seen through the ancient Mayan codex. Writers in the Hellenistic-Roman culture wrote longer texts as scrolls. Court records and notes were written on wax tablets, while important documents were written on papyrus or parchment; the modern English word book comes from the Proto-Germanic *bokiz, referring to the beechwood on which early written works were recorded.
The book was not needed in ancient times, as many early Greek texts—scrolls—were 30 pages long, which were customarily folded accordion-fashion to fit into the hand. Roman works were longer, running to hundreds of pages; the Greeks used to call their books tome, meaning "to cut". The Egyptian Book of the Dead was a massive 200 pages long and was used in funerary services for the deceased. Torah scrolls, editions of the Jewish holy book, were—and still are—also held in special holders when read. Scrolls can be rolled in one of two ways; the first method is to wrap the scroll around a single core, similar to a modern roll of paper towels. While simple to construct, a single core scroll has a major disadvantage: in order to read text at the end of the scroll, the entire scroll must be unwound; this is overcome in the second method, to wrap the scroll around two cores, as in a Torah. With a double scroll, the text can be accessed from both beginning and end, th
Starch or amylum is a polymeric carbohydrate consisting of a large number of glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants as energy storage, it is the most common carbohydrate in human diets and is contained in large amounts in staple foods like potatoes, maize and cassava. Pure starch is a white and odorless powder, insoluble in cold water or alcohol, it consists of two types of molecules: the branched amylopectin. Depending on the plant, starch contains 20 to 25% amylose and 75 to 80% amylopectin by weight. Glycogen, the glucose store of animals, is a more branched version of amylopectin. In industry, starch is converted into sugars, for example by malting, fermented to produce ethanol in the manufacture of beer and biofuel, it is processed to produce many of the sugars used in processed foods. Mixing most starches in warm water produces a paste, such as wheatpaste, which can be used as a thickening, stiffening or gluing agent; the biggest industrial non-food use of starch is as an adhesive in the papermaking process.
Starch can be applied to parts of some garments before ironing. The word "starch" is from a Germanic root with the meanings "strong, strengthen, stiffen". Modern German Stärke is related; the Greek term for starch, "amylon", is related. It provides the root amyl, used as a prefix for several 5-carbon compounds related to or derived from starch. Starch grains from the rhizomes of Typha as flour have been identified from grinding stones in Europe dating back to 30,000 years ago. Starch grains from sorghum were found on grind stones in caves in Ngalue, Mozambique dating up to 100,000 years ago. Pure extracted wheat starch paste was used in Ancient Egypt to glue papyrus; the extraction of starch is first described in the Natural History of Pliny the Elder around AD 77–79. Romans used it in cosmetic creams, to powder the hair and to thicken sauces. Persians and Indians used it to make dishes similar to gothumai wheat halva. Rice starch as surface treatment of paper has been used in paper production in China since 700 CE.
In addition to starchy plants consumed directly, by 2008 66 million tonnes of starch were being produced per year worldwide. In 2011 production was increased to 73 million ton. In the EU the starch industry produced about 8.5 million tonnes in 2008, with around 40% being used for industrial applications and 60% for food uses, most of the latter as glucose syrups. In 2017 EU production was 11 million ton of which 9,4 million ton was consumed in the EU and of which 54% were starch sweeteners. US produced about 27,5 million ton starch in 2017 of which about 8,2 million ton high fructose syrup and 6,2 million ton glucose syrups and 2,5 million ton starch products, the rest of the starch was used for producing ethanol. Most green plants use starch as their energy store; the extra glucose is changed into starch, more complex than glucose. An exception is the family Asteraceae. Inulin-like fructans are present in grasses such as wheat, in onions and garlic and asparagus. In photosynthesis, plants use light energy to produce glucose from carbon dioxide.
The glucose is used to generate the chemical energy required for general metabolism, to make organic compounds such as nucleic acids, lipids and structural polysaccharides such as cellulose, or is stored in the form of starch granules, in amyloplasts. Toward the end of the growing season, starch accumulates in twigs of trees near the buds. Fruit, seeds and tubers store starch to prepare for the next growing season. Glucose is soluble in water, binds with water and takes up much space and is osmotically active. Glucose molecules are bound in starch by the hydrolyzed alpha bonds; the same type of bond is found in the animal reserve polysaccharide glycogen. This is in contrast to many structural polysaccharides such as chitin and peptidoglycan, which are bound by beta bonds and are much more resistant to hydrolysis. Plants produce starch by first converting glucose 1-phosphate to ADP-glucose using the enzyme glucose-1-phosphate adenylyltransferase; this step requires energy in the form of ATP. The enzyme starch synthase adds the ADP-glucose via a 1,4-alpha glycosidic bond to a growing chain of glucose residues, liberating ADP and creating amylose.
The ADP-glucose is certainly added to the non-reducing end of the amylose polymer, as the UDP-glucose is added to the non-reducing end of glycogen during glycogen synthesis. Starch branching enzyme introduces 1,6-alpha glycosidic bonds between the amylose chains, creating the branched amylopectin; the starch debranching enzyme isoamylase removes some of these branches. Several isoforms of these enzymes exist, leading to a complex synthesis process. Glycogen and amylopectin have similar structure, but the former has about one branch point per ten 1,4-alpha bonds, compared to about one branch point per thirty 1,4-alpha bonds in amylopectin. Amylopectin is synthesized from ADP-glucose while mammals and fungi synthesize glycogen from UDP-glucose. In addition to starch synthesis in plants, starch can be synthesized from non-food starch mediated by an enzyme cocktail. In this cell-free biosystem, beta-1,4-glycosidic bond-linked cellulose is hydrolyzed to cello
Graffiti is writing or drawings made on a wall or other surface without permission and within public view. Graffiti ranges from simple written words to elaborate wall paintings, it has existed since ancient times, with examples dating back to ancient Egypt, ancient Greece, the Roman Empire. In modern times and marker pens have become the most used graffiti materials. In most countries, marking or painting property without the property owner's permission is considered defacement and vandalism, a punishable crime. Unrelated to hip-hop graffiti, gangs use their own form of graffiti to mark territory or to serve as an indicator of gang-related activities. Controversies that surround graffiti continue to create disagreement amongst city officials, law enforcement, writers who wish to display and appreciate work in public locations. There are many different styles of graffiti. Both "graffiti" and its occasional singular form "graffito" are from the Italian word graffiato. "Graffiti" is applied in art history to works of art produced by scratching a design into a surface.
A related term is "sgraffito", which involves scratching through one layer of pigment to reveal another beneath it. This technique was used by potters who would glaze their wares and scratch a design into it. In ancient times graffiti were carved on walls with a sharp object, although sometimes chalk or coal were used; the word originates from Greek γράφειν—graphein—meaning "to write". The term graffiti referred to the inscriptions, figure drawings, such, found on the walls of ancient sepulchres or ruins, as in the Catacombs of Rome or at Pompeii. Use of the word has evolved to include any graphics applied to surfaces in a manner that constitutes vandalism; the only known source of the Safaitic language, a form of proto-Arabic, is from graffiti: inscriptions scratched on to the surface of rocks and boulders in the predominantly basalt desert of southern Syria, eastern Jordan and northern Saudi Arabia. Safaitic dates from the first century BC to the fourth century AD; the first known example of "modern style" graffiti survives in the ancient Greek city of Ephesus.
Local guides say. Located near a mosaic and stone walkway, the graffiti shows a handprint that vaguely resembles a heart, along with a footprint, a number, a carved image of a woman's head; the ancient Romans carved graffiti on walls and monuments, examples of which survive in Egypt. Graffiti in the classical world had different connotations than they carry in today's society concerning content. Ancient graffiti displayed phrases of love declarations, political rhetoric, simple words of thought, compared to today's popular messages of social and political ideals The eruption of Vesuvius preserved graffiti in Pompeii, which includes Latin curses, magic spells, declarations of love, political slogans, famous literary quotes, providing insight into ancient Roman street life. One inscription gives the address of a woman named Novellia Primigenia of Nuceria, a prostitute of great beauty, whose services were much in demand. Another shows a phallus accompanied by mansueta tene. Disappointed love found its way onto walls in antiquity: Ancient tourists visiting the 5th-century citadel at Sigiriya in Sri Lanka scribbled over 1800 individual graffiti there between the 6th and 18th centuries.
Etched on the surface of the Mirror Wall, they contain pieces of prose and commentary. The majority of these visitors appear to have been from the elite of society: royalty, officials and clergy. There were soldiers and some metalworkers; the topics range from love to satire, curses and lament. Many demonstrate a high level of literacy and a deep appreciation of art and poetry. Most of the graffiti refer to the frescoes of semi-nude females found there. One reads: Among the ancient political graffiti examples were Arab satirist poems. Yazid al-Himyari, an Umayyad Arab and Persian poet, was most known for writing his political poetry on the walls between Sajistan and Basra, manifesting a strong hatred towards the Umayyad regime and its walis, people used to read and circulate them widely. Historic forms of graffiti have helped gain understanding into the lifestyles and languages of past cultures. Errors in spelling and grammar in these graffiti offer insight into the degree of literacy in Roman times and provide clues on the pronunciation of spoken Latin.
Examples are 7838: Vettium Firmum / aed quactiliar rog. Here, "qu" is pronounced "co"; the 83 pieces of graffiti found at CIL IV, 4706-85 are evidence of the ability to read and write at levels of society where literacy might not be expected. The graffiti appear on a peristyle, being remodeled at the time of the eruption of Vesuvius by the architect Crescens; the graffiti were left by his workers. The brothel at CIL VII, 12, 18–20 contains more than 120 pieces of graffiti, some of which were the work of the prostitutes and their clients; the gladiatorial academy at CIL IV, 4397 was scrawled with graffiti left by the gladiator Celadus Crescens Another piece from Pompeii, written on a tavern wall about the owner of the establishment and his questionable wine: It was not only the Greeks and Romans who produced graffiti: the Maya s