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Blackboard
A blackboard or a chalkboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate, better known as chalk. Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone. Design A blackboard can simply be a board painted with a dark matte (surface), matte paint (usually black, occasionally dark green). Matte black plastic sign material (known as closed-cell PVC foamboard) is also used to create custom chalkboard art. Blackboards on an A-frame are used by restaurants and bars to advertise daily specials. Adhesive chalkboard surface is also available in stores as rolls of textured black plastic shelf covering, which is applied to the desired wall, door or other surface. A more modern variation consists of a coiled sheet of plastic drawn across two parallel rollers, which can be scrolled to create additional writing space while saving what has been written. The highest grade blackboards ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chalk
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Chalk is common throughout Western Europe, where deposits underlie parts of France, and steep cliffs are often seen where they meet the sea in places such as the Dover cliffs on the Kent coast of the English Channel. Chalk is mined for use in industry, such as for quicklime, bricks and builder's putty, and in agriculture, for raising pH in soils with high acidity. It is also used for " blackboard chalk" for writing and drawing on various types of surfaces, although these can also be manufactured from other carbonate-based minerals, or gypsum. Description Chalk is a fine-textured, earthy type of limestone distinguished by its light colour, softness, and high porosity. It is composed mostly of tiny fragments of the calcite shells or sk ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Writing
Writing is the act of creating a persistent representation of language. A writing system includes a particular set of symbols called a ''script'', as well as the rules by which they encode a particular spoken language. Every written language arises from a corresponding spoken language; while the use of language is universal across human societies, most spoken languages are not written. Writing is a cognitive and social activity involving neuropsychological and physical processes. The outcome of this activity, also called ''writing'' (or a ''text'') is a series of physically inscribed, mechanically transferred, or digitally represented symbols. Reading is the corresponding process of interpreting a written text, with the interpreter referred to as a ''reader''. In general, writing systems do not constitute languages in and of themselves, but rather a means of encoding language such that it can be read by others across time and space. While not all languages use a writ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chalkboard Art
Chalkboard art or chalk art is the use of chalk on a blackboard as a visual art. It is similar to art using pastels and related to sidewalk art that often uses chalk. Chalkboard art is often used in restaurants, shops or walls. Chalkboard art has also been done on large boards while storytelling on beaches and in churches. Characteristics Chalkboard art is ephemeral. Chalkboard artists Chalkboard artists include Catherine Owens, Chris Yoon, Maggie Choate, Bryce Wisdom, C. J. Hughes, and Scrojo. References Visual arts media Chalk {{art-technique-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
WebMD
WebMD is an American corporation which publishes online news and information about human health and well-being. The WebMD website also includes information about drugs and is an important healthcare information website and the most popular consumer-oriented health site. WebMD was started in 1998 by internet entrepreneur Jeff Arnold. In early 1999, it was part of a three-way merger with Sapient Health Network (SHN) and Direct Medical Knowledge (DMK). SHN began in Portland, Oregon, in 1996 by Jim Kean, Bill Kelly, and Kris Nybakken, who worked together at a CD-ROM publishing firm, Creative Multimedia. Later, in 1999, WebMD merged with Healtheon, founded by Netscape Communications founder James H. Clark. History WebMD is best known as a health information services website, which publishes content regarding health and health care topics, including a symptom checklist, pharmacy information, drugs information, and blogs of physicians with specific topics, and provides a place t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk chalk. Gypsum also Crystallization, crystallizes as translucent crystals of selenite (mineral), selenite. It forms as an evaporite mineral and as a Mineral hydration, hydration product of anhydrite. The Mohs scale of mineral hardness defines gypsum as hardness value 2 based on Scratch hardness, scratch hardness comparison. Fine-grained white or lightly tinted forms of gypsum known as alabaster have been used for sculpture by many cultures including Ancient Egypt, Mesopotamia, Ancient Rome, the Byzantine Empire, and the Nottingham alabasters of Medieval England. Etymology and history The word ''wikt:gypsum, gypsum'' is derived from the Greek language, Greek word (), "plaster". Because the quarry, quarries of the Montmartre district of P ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on Scratch hardness, scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed mostly of calcite has numerous uses. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite. Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, and vaterite is even less stable. Etymology Calcite is derived from the German , a term from the 19th century that came from the Latin word for Lime (material), lime, (genitive ) with the suffix ''-ite'' used to name minerals. It is thus a Doublet (linguistics), doublet of the word ''wikt:chalk, chalk''. When applied by archaeology, archaeologists and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allergic
Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, sneezing, coughing, a runny nose, shortness of breath, or swelling. Note that food intolerances and food poisoning are separate conditions. Common allergens include pollen and certain foods. Metals and other substances may also cause such problems. Food, insect stings, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body's immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine. Diagnosis is typical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
American Academy Of Allergy, Asthma And Immunology
Founded in 1943, the American Academy of Allergy, Asthma & Immunology (AAAAI) is a professional medical membership organization of more than 7,000 allergists/ immunologists and related professionals around the world with advanced training and experience in allergy, asthma and other immunologic diseases. The Academy is dedicated to the advancement of the knowledge and practice of allergy, asthma and immunology for optimal patient care. Most members of the AAAAI are board-certified allergist/immunologists. A select group of the membership are elected as Fellows and carry the title FAAAAI. The organization, headquartered in Milwaukee, Wisconsin, hosts a website for patients and healthcare professionals that includes a physician referral directory for patients. Mission The AAAAI is dedicated to the advancement of the knowledge and practice of allergy, asthma, and immunology for optimal patient care. History The American Academy of Allergy, Asthma, and Immunology (AAAAI) dates back t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homer E
Homer (; , ; possibly born ) was an Ancient Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Despite doubts about his authorship, Homer is considered one of the most revered and influential authors in history. The ''Iliad'' centers on a quarrel between King Agamemnon and the warrior Achilles during the last year of the Trojan War. The ''Odyssey'' chronicles the ten-year journey of Odysseus, king of Ithaca, back to his home after the fall of Troy. The epics depict man's struggle, the ''Odyssey'' especially so, as Odysseus perseveres through the punishment of the gods. The poems are in Homeric Greek, also known as Epic Greek, a literary language that shows a mixture of features of the Ionic and Aeolic dialects from different centuries; the predominant influence is Eastern Ionic. Most researchers believe that the poems were originally transmitted orally. Despite being predomi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computers
A computer is a machine that can be programmed to automatically carry out sequences of arithmetic or logical operations ('' computation''). Modern digital electronic computers can perform generic sets of operations known as ''programs'', which enable computers to perform a wide range of tasks. The term computer system may refer to a nominally complete computer that includes the hardware, operating system, software, and peripheral equipment needed and used for full operation; or to a group of computers that are linked and function together, such as a computer network or computer cluster. A broad range of industrial and consumer products use computers as control systems, including simple special-purpose devices like microwave ovens and remote controls, and factory devices like industrial robots. Computers are at the core of general-purpose devices such as personal computers and mobile devices such as smartphones. Computers power the Internet, which links billions o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dihydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understood. Chemical nature Inorganic chemistry Hydrates are not inorganic salts "containing water molecules combined in a definite ratio as an integral part of the crystal" that are either bound to a metal center or that have crystallized with the metal complex. Such hydrates are also said to contain ''water of crystallization'' or ''water of hydration''. If the water is heavy water in which the constituent hydrogen is the isotope deuterium, then the term ''deuterate'' may be used in place of ''hydrate''. A colorful example is cobalt(II) chloride, which turns from blue to red upon hydration, and can therefore be used as a water indicator. The notation "''hydrated compound''⋅''n''", where ''n'' is the number of water molecules per formu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
