1.
Sedimentary rock
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Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earths surface and within bodies of water. Sedimentation is the name for processes that cause mineral and/or organic particles to settle in place. The particles that form a rock by accumulating are called sediment. Sedimentation may also occur as minerals precipitate from solution or shells of aquatic creatures settle out of suspension. The sedimentary rock cover of the continents of the Earths crust is extensive, sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding, sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores. The study of the sequence of rock strata is the main source for an understanding of the Earths history, including palaeogeography, paleoclimatology. The scientific discipline that studies the properties and origin of rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences, such as pedology, geomorphology, geochemistry, sedimentary rocks have also been found on Mars. Clastic sedimentary rocks are composed of rock fragments that were cemented by silicate minerals. Clastic rocks are composed largely of quartz, feldspar, rock fragments, clay minerals, and mica, any type of mineral may be present, clastic sedimentary rocks, are subdivided according to the dominant particle size. Most geologists use the Udden-Wentworth grain size scale and divide unconsolidated sediment into three fractions, gravel, sand, and mud and this tripartite subdivision is mirrored by the broad categories of rudites, arenites, and lutites, respectively, in older literature. The subdivision of these three categories is based on differences in clast shape, conglomerates and breccias), composition. Conglomerates are dominantly composed of rounded gravel, while breccias are composed of dominantly angular gravel, composition of framework grains The relative abundance of sand-sized framework grains determines the first word in a sandstone name. Naming depends on the dominance of the three most abundant components quartz, feldspar, or the lithic fragments that originated from other rocks, all other minerals are considered accessories and not used in the naming of the rock, regardless of abundance. Clean sandstones with open space are called arenites. Muddy sandstones with abundant muddy matrix are called wackes, six sandstone names are possible using the descriptors for grain composition and the amount of matrix. Mudrocks are sedimentary rocks composed of at least 50% silt- and clay-sized particles and these relatively fine-grained particles are commonly transported by turbulent flow in water or air, and deposited as the flow calms and the particles settle out of suspension
2.
Shades of white
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Shades of white are colors that differ only slightly from pure white. Variations of white include what are commonly termed off-white colors, which may be considered part of a color scheme. In color theory, a shade is a pure color mixed with black, strictly speaking, a “shade of white” would be a neutral gray. This article is also about off-white colors that vary from white in hue. Colors often considered shades of white include, cream, eggshell, ivory, Navajo white, even the lighting of a room, however, can cause a pure white to be perceived as off-white. Off-white colors were pervasively paired with beiges in the 1930s, whiteness measures the degree to which a surface is white in colorimetry. Below is a showing the computer web color shades of white. An achromatic white is a color in which the red, green. The web colors white and white smoke are achromatic colors, a chromatic shade of white is a white color in which the red, green, and blue codes are not exactly equal, but are close to each other, which is what makes it a shade of white. A white visual stimulation will be void of hue and grayness, white is the lightest possible color. The web color ghost white is a tint of white associated with what it is imagined the color of a ghost might be, there is no evidence that this color name was in use before the X11 color names were formulated in 1987. The web color white smoke is displayed on the left, there is no evidence that this color name was in use before the X11 color names were formulated in 1987. The Crayola crayon color baby powder was introduced in 1994 as part of its specialty Magic Scent crayon collection, the web color snow is displayed at left. The first recorded use of snow as a name in English was in 1000. The color snow was included as one of the X11 colors when they were formulated in 1987, ivory is an off-white color that resembles ivory, the material out of which the teeth and tusks of animals are made. It has a slight tint of yellow. The first recorded use of ivory as a name in English was in 1385. The color ivory was included as one of the X11 colors when they were formulated in 1987, the web color floral white is displayed at left
3.
Abrasive
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An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflective surface, in short, the Ceramics which are used to cut, grind and polish other softer materials are known as Abrasives. Abrasives are extremely commonplace and are used extensively in a wide variety of industrial, domestic. This gives rise to a variation in the physical and chemical composition of abrasives as well as the shape of the abrasive. Common uses for abrasives include grinding, polishing, buffing, honing, cutting, drilling, sharpening, lapping, and sanding. Files are not abrasives, they remove material not by scratching or rubbing, however, diamond files are a form of coated abrasive. Abrasives generally rely upon a difference in hardness between the abrasive and the material being worked upon, the abrasive being the harder of the two substances. Diamond, an abrasive, for instance occurs both naturally and is industrially produced, as is corundum which occurs naturally but which is nowadays more commonly manufactured from bauxite. However, even softer minerals like calcium carbonate are used as abrasives and these minerals are either crushed or are already of a sufficiently small size to permit their use as an abrasive. These grains, commonly called grit, have rough edges, often terminating in points which will decrease the area in contact. The abrasive and the material to be worked are brought into contact while in motion to each other. Abrasives may be classified as natural or synthetic. When discussing sharpening stones, natural stones have long been considered superior, many synthetic abrasives are effectively identical to a natural mineral, differing only in that the synthetic mineral has been manufactured rather than been mined. Impurities in the mineral may make it less effective. Natural abrasives are often sold as dressed stones, usually in the form of a rectangular block, a bonded abrasive is composed of an abrasive material contained within a matrix, although very fine aluminium oxide abrasive may comprise sintered material. This matrix is called a binder and is often a clay, a resin and this mixture of binder and abrasive is typically shaped into blocks, sticks, or wheels. The most usual abrasive used is aluminium oxide, also common are silicon carbide, tungsten carbide and garnet. Artificial sharpening stones are often a bonded abrasive and are available as a two sided block, each side being a different grade of grit
4.
Pumice
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Pumice, called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. Scoria is another vesicular volcanic rock that differs from pumice in having larger vesicles, thicker walls and being dark colored. Pumice is created when super-heated, highly pressurized rock is violently ejected from a volcano, the unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering the solubility of gases that are dissolved in the lava, the simultaneous cooling and depressurization freezes the bubbles in a matrix. Eruptions under water are cooled and the large volume of pumice created can be a shipping hazard for cargo ships. Pumice is composed of highly microvesicular glass pyroclastic with very thin and it is commonly, but not exclusively of silicic or felsic to intermediate in composition, but basaltic and other compositions are known. Pumice is commonly pale in color, ranging from white, cream, blue or grey and it forms when volcanic gases exsolving from viscous magma form bubbles that remain within the viscous magma as it cools to glass. Pumice is a product of explosive eruptions and commonly forms zones in upper parts of silicic lavas. Pumice has a porosity of 90%, and initially floats on water. Scoria differs from pumice in being denser, with larger vesicles and thicker vesicle walls, it sinks rapidly. The difference is the result of the viscosity of the magma that forms scoria. When larger amounts of gas are present, the result is a variety of pumice known as pumicite. Pumice is considered a glass because it has no crystal structure, pumice varies in density according to the thickness of the solid material between the bubbles, many samples float in water. After the explosion of Krakatoa, rafts of pumice drifted through the Pacific Ocean for up to 20 years, in fact, pumice rafts disperse and support several marine species. In 1979,1984 and 2006, underwater volcanic eruptions near Tonga created large pumice rafts, there are two main forms of vesicles. Most pumice contains tubular microvesicles that can impart a silky or fibrous fabric, the elongation of the microvesicles occurs due to ductile elongation in the volcanic conduit or, in the case of pumiceous lavas, during flow. The other form of vesicles are subspherical to spherical and result from high pressure during eruption. Pumice is widely used to make concrete or insulative low-density cinder blocks
5.
Density
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The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
6.
Porosity
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Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0 and 100%. Strictly speaking, some measure the accessible void, the total amount of void space accessible from the surface. There are many ways to test porosity in a substance or part, the term porosity is used in multiple fields including pharmaceutics, ceramics, metallurgy, materials, manufacturing, earth sciences, soil mechanics and engineering. Void fraction usually varies from location to location in the flow channel and it fluctuates with time and its value is usually time averaged. In separated flow, it is related to flow rates of the gas and the liquid phase. It is defined by the ratio, ϕ = V V V T where VV is the volume of void-space and VT is the total or bulk volume of material, both the mathematical symbols ϕ and n are used to denote porosity. Porosity is a fraction between 0 and 1, typically ranging from less than 0.01 for solid granite to more than 0.5 for peat and it may also be represented in percent terms by multiplying the fraction by 100. The porosity of a rock, or sedimentary layer, is an important consideration when attempting to evaluate the potential volume of water or hydrocarbons it may contain. Sedimentary porosity is a function of many factors, including but not limited to, rate of burial, depth of burial, the nature of the connate fluids. The principal complication is that there is not a direct proportionality between porosity and hydraulic conductivity but rather an inferred proportionality, there is a clear proportionality between pore throat radii and hydraulic conductivity. Also, there tends to be a proportionality between pore throat radii and pore volume, if the proportionality between pore throat radii and porosity exists then a proportionality between porosity and hydraulic conductivity may exist. Well sorted materials have higher porosity than similarly sized poorly sorted materials, for tables of common porosity values for earth materials, see the further reading section in the Hydrogeology article. Consolidated rocks potentially have more complex dual porosities, as compared with alluvial sediment and this can be split into connected and unconnected porosity. Connected porosity is more easily measured through the volume of gas or liquid that can flow into the rock, porosity is the ratio of pore volume to its total volume. Porosity is controlled by, rock type, pore distribution, cementation, diagenetic history, porosity is not controlled by grain size, as the volume of between-grain space is related only to the method of grain packing. Rocks normally decrease in porosity with age and depth of burial, tertiary age Gulf Coast sandstones are in general more porous than Cambrian age sandstones. There are exceptions to this rule, usually because of the depth of burial and thermal history, porosity of surface soil typically decreases as particle size increases. This is due to soil formation in finer textured surface soils when subject to soil biological processes
7.
Aluminium oxide
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Aluminium oxide or aluminum oxide is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. It is the most commonly occurring of several aluminium oxides, and it is commonly called alumina, and may also be called aloxide, aloxite, or alundum depending on particular forms or applications. It occurs naturally in its crystalline polymorphic phase α-Al2O3 as the mineral corundum, varieties of form the precious gemstones ruby. Al2O3 is significant in its use to produce metal, as an abrasive owing to its hardness. Corundum is the most common naturally occurring form of aluminium oxide. Rubies and sapphires are gem-quality forms of corundum, which owe their characteristic colors to trace impurities, rubies are given their characteristic deep red color and their laser qualities by traces of chromium. Sapphires come in different colors given by various other impurities, such as iron, Al2O3 is an electrical insulator but has a relatively high thermal conductivity for a ceramic material. Aluminium oxide is insoluble in water, in its most commonly occurring crystalline form, called corundum or α-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools. Aluminium oxide is responsible for the resistance of aluminium to weathering. Metallic aluminium is very reactive with oxygen, and a thin passivation layer of aluminium oxide forms on any exposed aluminium surface. This layer protects the metal from further oxidation, the thickness and properties of this oxide layer can be enhanced using a process called anodising. A number of alloys, such as bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. Aluminium oxide was taken off the United States Environmental Protection Agencys chemicals lists in 1988, aluminium oxide is on EPAs Toxics Release Inventory list if it is a fibrous form. Al2O3 +6 HF →2 AlF3 +3 H2O Al2O3 +2 NaOH +3 H2O →2 NaAl4 The most common form of aluminium oxide is known as corundum. The oxygen ions form a hexagonal close-packed structure with aluminium ions filling two-thirds of the octahedral interstices. In terms of its crystallography, corundum adopts a trigonal Bravais lattice with a group of R-3c. The primitive cell contains two units of aluminium oxide. Each has a crystal structure and properties
8.
Clay minerals
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Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals form in the presence of water and have been important to life and they are important constituents of soils, and have been useful to humans since ancient times in agriculture and manufacturing. Clays form flat hexagonal sheets similar to the micas, Clay minerals are common weathering products and low-temperature hydrothermal alteration products. Clay minerals are common in soils, in fine-grained sedimentary rocks such as shale, mudstone. Clay minerals are usually ultrafine-grained and so may require special techniques for their identification. These methods can be augmented by polarized light microscopy, a traditional technique establishing fundamental occurrences or petrologic relationships. Given the requirement of water, clay minerals are rare in the Solar System, though they occur extensively on Earth where water has interacted with other minerals. Clay minerals have been detected at several locations on Mars including Echus Chasma and Mawrth Vallis and the Memnonia quadrangle, spectrography has confirmed their presence on asteroids including the dwarf planet Ceres and Tempel 1 as well as Jupiters moon Europa. A1,1 clay would consist of one sheet and one octahedral sheet. A2,1 clay consists of an octahedral sheet sandwiched between two sheets, and examples are talc, vermiculite and montmorillonite. Smectite group which includes dioctahedral smectites such as montmorillonite, nontronite and beidellite, in 2013, analytical tests by the Curiosity rover found results consistent with the presence of smectite clay minerals on the planet Mars. Illite group which includes the clay-micas, illite is the only common mineral. Chlorite group includes a variety of similar minerals with considerable chemical variation. Other 2,1 clay types exist such as sepiolite or attapulgite, mixed layer clay variations exist for most of the above groups. Ordering is described as random or regular ordering, and is described by the term reichweite. Literature articles will refer to a R1 ordered illite-smectite, for example and this type would be ordered in an ISISIS fashion. R0 on the other hand describes random ordering, and other advanced ordering types are also found, mixed layer clay minerals which are perfect R1 types often get their own names. R1 ordered chlorite-smectite is known as corrensite, R1 illite-smectite is rectorite, knowledge of the nature of clay became better understood in the 1930s with advancements in x-ray diffraction technology necessary to analyze the molecular nature of clay particles
9.
Iron oxide
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Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides, common rust is a form of iron oxide. Iron oxides are used as inexpensive, durable pigments in paints, coatings. Colors commonly available are in the end of the yellow/orange/red/brown/black range. When used as a coloring, it has E number E172. Limonite Iron oxide nanoparticles List of inorganic pigments Information from Nano-Oxides, http, //chemed. chem. purdue. edu/demos/demosheets/12.3. html http, //minerals. usgs. gov/minerals/pubs/commodity/iron_oxide/ CDC - NIOSH Pocket Guide to Chemical Hazards de
10.
Fossil
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Fossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record. The study of fossils across geological time, how they were formed, such a preserved specimen is called a fossil if it is older than some minimum age, most often the arbitrary date of 10,000 years. The observation that fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century. The development of dating techniques in the early 20th century allowed geologists to determine the numerical or absolute age of the various strata. Like extant organisms, fossils vary in size from microscopic, even single bacterial cells one micrometer in diameter, to gigantic, such as dinosaurs, Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces. These types of fossil are called trace fossils, as opposed to body fossils, finally, past life leaves some markers that cannot be seen but can be detected in the form of biochemical signals, these are known as chemofossils or biosignatures. The process of fossilization varies according to type and external conditions. Permineralization is a process of fossilization that occurs when an organism is buried, the empty spaces within an organism become filled with mineral-rich groundwater. Minerals precipitate from the groundwater, occupying the empty spaces and this process can occur in very small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce very detailed fossils, for permineralization to occur, the organism must become covered by sediment soon after death or soon after the initial decay process. The degree to which the remains are decayed when covered determines the later details of the fossil, some fossils consist only of skeletal remains or teeth, other fossils contain traces of skin, feathers or even soft tissues. This is a form of diagenesis, in some cases the original remains of the organism completely dissolve or are otherwise destroyed. The remaining organism-shaped hole in the rock is called an external mold, if this hole is later filled with other minerals, it is a cast. An endocast or internal mold is formed when sediments or minerals fill the cavity of an organism. This is a form of cast and mold formation. If the chemistry is right, the organism can act as a nucleus for the precipitation of minerals such as siderite, if this happens rapidly before significant decay to the organic tissue, very fine three-dimensional morphological detail can be preserved. Nodules from the Carboniferous Mazon Creek fossil beds of Illinois, USA, are among the best documented examples of such mineralization, replacement occurs when the shell, bone or other tissue is replaced with another mineral
11.
Diatom
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Diatoms are a major group of algae, and are among the most common types of phytoplankton. Diatoms are unicellular, although they can form colonies in the shape of filaments or ribbons, fans, zigzags, the first diatom formally described in scientific literature, the colonial Bacillaria paradoxa, was found in 1783 by Danish naturalist Otto Friedrich Müller. Diatoms are producers within the food chain, a unique feature of diatom cells is that they are enclosed within a cell wall made of silica called a frustule. These frustules show a diversity in form, but are usually almost bilaterally symmetrical. The symmetry is not perfect since one of the valves is slightly larger than the other, fossil evidence suggests that they originated during, or before, the early Jurassic period. Only male gametes of centric diatoms are capable of movement by means of flagella, diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality. More than 200 genera of living diatoms are known, with an estimated 100,000 extant species, diatoms are a widespread group and can be found in the oceans, in fresh water, in soils, and on damp surfaces. They dominate over phytoplankton in nutrient-rich coastal waters and during oceanic spring blooms since they can more rapidly than phytoplankton. Most live pelagically in open water, although some live as surface films at the water-sediment interface and they are especially important in oceans, where they contribute an estimated 45% of the total oceanic primary production of organic material. Spatial distribution of phytoplankton species is restricted both horizontally and vertically. Though most are microscopic, some species of diatoms can reach up to 2 mm in length, diatoms belong to a large group called the heterokonts, including both autotrophs and heterotrophs. Their yellowish-brown chloroplasts are typical of heterokonts, having four membranes, individuals usually lack flagella, but they are present in male gametes of the centric diatoms and have the usual heterokont structure, except they lack the hairs characteristic in other groups. Most diatoms are nonmotile, as their relatively dense cell walls cause them to readily sink, planktonic forms in open water usually rely on turbulent mixing of the upper layers by the wind to keep them suspended in sunlit surface waters. Some species actively regulate their buoyancy with intracellular lipids to counter sinking, a feature of diatoms is the urea cycle, which links them evolutionarily to animals. This was discovered in research carried out by Andrew Allen, Chris Bowler and their study showed that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionally linked in such a way that animals and plants are not. Diatom cells are contained within a unique cell wall known as a frustule made up of two valves called thecae, that typically overlap one another. The biogenic silica composing the wall is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is extruded to the cell exterior and added to the wall
12.
Protist
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Protist is an informal term for any eukaryotic organism that is not an animal, plant or fungus. The protists do not form a group, or clade. Besides their relatively simple levels of organization, protists do not necessarily have much in common, others use the term protist more broadly, to encompass both microbial eukaryotes and macroscopic organisms that do not fit into the other traditional kingdoms. In cladistic systems, there are no equivalents to the taxa Protista or Protoctista, in cladistic classification, the contents of Protista are distributed among various supergroups and Protista, Protoctista and Protozoa are considered obsolete. However, the term protist continues to be used informally as a term for eukaryotic microorganisms. For example, the phrase protist pathogen may be used to denote any disease-causing microbe which is not bacteria, virus, the term protista was first used by Ernst Haeckel in 1866. Some protists, sometimes called ambiregnal protists, have considered to be both protozoa and algae or fungi, and names for these have been published under either or both of the ICN and the ICZN. Conflicts, such as these – for example the dual-classification of Euglenids and Dinobryons and these traditional subdivisions, largely based on superficial commonalities, have been replaced by classifications based on phylogenetics. Molecular analyses in modern taxonomy have been used to redistribute former members of this group into diverse, however, the older terms are still used as informal names to describe the morphology and ecology of various protists. For example, the term protozoa is used to refer to species of protists that do not form filaments. Among the pioneers in the study of the protists, which were almost ignored by Linnaeus except for some genera were Leeuwenhoek, O. F. Müller, C. G. Ehrenberg, the first groups used to classify microscopic organism were the Animalcules and the Infusoria. In 1817, the German naturalist Georg August Goldfuss introduced the word Protozoa to refer to such as ciliates. After the cell theory of Schwann and Schleiden, this group was modified in 1848 by Carl von Siebold to include only animal-like unicellular organisms, such as foraminifera and amoebae. He defined the Protoctista as a kingdom of nature, in addition to the then-traditional kingdoms of plants. The kingdom of minerals was later removed from taxonomy in 1866 by Ernst Haeckel, leaving plants, animals, in 1938, Herbert Copeland resurrected Hoggs label, arguing that Haeckels term Protista included anucleated microbes such as bacteria, which the term Protoctista did not. In contrast, Copelands term included nucleated eukaryotes such as diatoms, green algae and this classification was the basis for Whittakers later definition of Fungi, Animalia, Plantae and Protista as the four kingdoms of life. The kingdom Protista was later modified to separate prokaryotes into the kingdom of Monera. Many systematists today do not treat Protista as a formal taxon, some systematists judge paraphyletic taxa acceptable, and use Protista in this sense as a formal taxon
13.
Golden algae
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The Chrysophyceae, usually called chrysophytes, chrysomonads, golden-brown algae or golden algae are a large group of algae, found mostly in freshwater. Golden algae is also used to refer to a single species, Prymnesium parvum. The Chrysophyceae should not be confused with the Chrysophyta, which is a more ambiguous taxon, although chrysophytes is the anglicization of Chrysophyta, it generally refers to the Chrysophyceae. Some heterotrophic flagellates as the bicosoecids and choanoflagellates were sometimes seen as related to golden algae too and they are now usually restricted to a core group of closely related forms, distinguished primarily by the structure of the flagella in motile cells, also treated as an order Chromulinales. It is possible membership will be revised further as more species are studied in detail, the primary cell of chrysophytes contains two specialized flagella. The active, feathered flagellum is oriented toward the moving direction, the smooth passive flagellum, oriented toward the opposite direction, may be present only in rudimentary form in some species. An important characteristic used to identify members of the class Chrysophyceae is the presence of a siliceous cyst that is formed endogenously, called statospore, stomatocyst or statocyst, this structure is usually globose and contains a single pore. The surface of mature cysts may be ornamented with different structural elements and are useful to distinguish species, most members are unicellular flagellates, with either two visible flagella, as in Ochromonas, or sometimes one, as in Chromulina. The Chromulinales as first defined by Pascher in 1910 included only the latter type, however, structural studies have revealed that a short second flagellum, or at least a second basal body, is always present, so this is no longer considered a valid distinction. Most of these have no cell covering, some have loricae or shells, such as Dinobryon, which is sessile and grows in branched colonies. Most forms with silicaceous scales are now considered a group, the synurids. Some members are generally amoeboid, with long branching cell extensions, chrysamoeba and Rhizochrysis are typical of these. There is also one species, Myxochrysis paradoxa, which has a life cycle involving a multinucleate plasmodial stage. These were originally treated as the order Chrysamoebales, the superficially similar Rhizochromulina was once included here, but is now given its own order based on differences in the structure of the flagellate stage. Cells may be naked and embedded in mucilage, such as Chrysosaccus, or coccoid and surrounded by a cell wall, a few are filamentous or even parenchymatous in organization, such as Phaeoplaca. These were included in various orders, most of the members of which are now included in separate groups. Hydrurus and its allies, freshwater genera which form branched gelatinous filaments, are placed in the separate order Hydrurales. Because of this, they were considered to be a specialized form of cyanobacteria
14.
Filtration
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Filtration is any of various mechanical, physical or biological operations that separate solids from fluids by adding a medium through which only the fluid can pass. The fluid that passes through is called the filtrate, in physical filters oversize solids in the fluid are retained and in biological filters particulates are trapped and ingested and metabolites are retained and removed. However, the separation is not complete, solids will be contaminated with some fluid, Filtration occurs both in nature and in engineered systems, there are biologic, geologic, and industrial forms. Filtration is used to separate particles and fluid in a suspension, where the fluid can be a liquid, depending on the application, either one or both of the components may be isolated. Filtration, as an operation is very important in chemistry for the separation of materials of different chemical composition. A solvent is chosen which dissolves one component, while not dissolving the other, by dissolving the mixture in the chosen solvent, one component will go into the solution and pass through the filter, while the other will be retained. This is one of the most important techniques used by chemists to purify compounds, Filtration is also important and widely used as one of the unit operations of chemical engineering. It may be combined with other unit operations to process the feed stream, as in the biofilter. Filtration differs from sieving, where separation occurs at a single perforated layer, in sieving, particles that are too big to pass through the holes of the sieve are retained. In filtration, a multilayer lattice retains those particles that are unable to follow the tortuous channels of the filter, oversize particles may form a cake layer on top of the filter and may also block the filter lattice, preventing the fluid phase from crossing the filter. Filtration differs from adsorption, where it is not the size of particles that causes separation. Some adsorption devices containing activated charcoal and ion exchange resin are commercially called filters, Filtration differs from removal of magnetic contaminants from fluids with magnets, because there is no filter medium. Commercial devices called magnetic filters are sold, but the name reflects their use, the remainder of this article focuses primarily on liquid filtration. There are many different methods of filtration, all aim to attain the separation of substances, separation is achieved by some form of interaction between the substance or objects to be removed and the filter. The substance that is to pass through the filter must be a fluid, methods of filtration vary depending on the location of the targeted material, i. e. whether it is dissolved in the fluid phase or suspended as a solid. There are several filtration techniques depending on the desired outcome namely, hot, cold, some of the major purposes of getting a desired outcome are, for the removal of impurities from a mixture or, for the isolation of solids from a mixture. Hot filtration method is used to separate solids from a hot solution. This is done in order to prevent crystal formation in the filter funnel, one of the most important measure to prevent the formation of crystals in the funnel and to undergo effective hot filtration is the use stemless filter funnel
15.
Toothpaste
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Toothpaste is a paste or gel dentifrice used with a toothbrush as an accessory to clean and maintain the aesthetics and health of teeth. Salt and sodium bicarbonate are among materials that can be substituted for commercial toothpaste, in addition to 20–42% water, toothpastes are derived from a variety of components, the three main ones being abrasives, fluoride, and detergents. Abrasives constitute at least 50% of a typical toothpaste and these insoluble particles help remove plaque from the teeth. The removal of plaque and calculus helps minimize cavities and periodontal disease, representative abrasives include particles of aluminum hydroxide, calcium carbonate, various calcium hydrogen phosphates, various silicas and zeolites, and hydroxyapatite. Abrasives, like the dental polishing agents used in dentists offices, some brands contain powdered white mica, which acts as a mild abrasive, and also adds a cosmetically pleasing glittery shimmer to the paste. The polishing of teeth removes stains from tooth surfaces, but has not been shown to improve dental health over and above the effects of the removal of plaque, the abrasive effect of toothpaste is indicated by its RDA value. Too high RDA values should be considered critical, and some dentists recommend toothpaste of an RDA value no higher than 50 for daily use, Fluoride in various forms is the most popular active ingredient in toothpaste to prevent cavities. Fluoride occurs in small amounts in plants, animals, and some water sources. The additional fluoride in toothpaste has beneficial effects on the formation of dental enamel, sodium fluoride is the most common source of fluoride, but stannous fluoride, olaflur, and sodium monofluorophosphate are also used. Stannous fluoride has been shown to be effective than sodium fluoride in reducing the incidence of dental caries and controlling gingivitis. Much of the toothpaste sold in the United States has 1,000 to 1,100 parts per million fluoride, in European countries, such as the UK or Greece, the fluoride content is often higher, a NaF content of 0. 312% w/w is common. Many, although not all, toothpastes contain sodium lauryl sulfate or related surfactants, SLS is found in many other personal care products, as well, such as shampoo, and is mainly a foaming agent, which enables uniform distribution of toothpaste, improving its cleansing power. Despite the different ingredients included in the toothpaste, recent study indicates that brushing with or without toothpaste has no impact on the level of plaque removal, triclosan, an antibacterial agent, is a common toothpaste ingredient in the United Kingdom. Triclosan or zinc chloride prevent gingivitis and, according to the American Dental Association, helps reduce tartar, a 2006 review of clinical research concluded there was evidence for the effectiveness of 0. 30% triclosan in reducing plaque and gingivitis. Toothpaste comes in a variety of colors, and flavors intended to use of the product. Three most common flavorants are peppermint, spearmint, and wintergreen, Toothpaste flavored with peppermint-anise oil is popular in the Mediterranean region. These flavors are provided by the oils, e. g. peppermint oil. More exotic flavors include Anethole anise, apricot, bubblegum, cinnamon, fennel, lavender, neem, ginger, vanilla, lemon, orange, hydroxyapatite nanocrystals and a variety of calcium phosphates are included in formulations for remineralization, i. e. the reformation of enamel
16.
Insecticide
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An insecticide is a substance used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to be a factor behind the increase in agricultural 20th centurys productivity. Nearly all insecticides have the potential to significantly alter ecosystems, many are toxic to humans, Insecticides can be classified in two major groups, systemic insecticides, which have residual or long term activity, and contact insecticides, which have no residual activity. Furthermore, one can distinguish three types of insecticide, natural insecticides, such as nicotine, pyrethrum and neem extracts, made by plants as defenses against insects. Organic insecticides, which are chemical compounds, mostly working by contact. The mode of action describes how the pesticide kills or inactivates a pest and it provides another way of classifying insecticides. Mode of action is important in understanding whether an insecticide will be toxic to unrelated species, such as fish, birds, Insecticides are distinct from insect repellents, which do not kill. Systemic insecticides become incorporated and distributed throughout the whole plant. When insects feed on the plant, they ingest the insecticide, systemic insecticides produced by transgenic plants are called plant-incorporated protectants. For instance, a gene that codes for a specific Bacillus thuringiensis biocidal protein was introduced into corn, the plant manufactures the protein, which kills the insect when consumed. Contact insecticides are toxic to insects upon direct contact and these can be inorganic insecticides, which are metals and include arsenates, copper and fluorine compounds, which are less commonly used, and the commonly used sulfur. Contact insecticides can be organic insecticides, i. e. organic chemical compounds, synthetically produced, or they can be natural compounds like pyrethrum, neem oil etc. Contact insecticides usually have no residual activity, efficacy can be related to the quality of pesticide application, with small droplets, such as aerosols often improving performance. Many organic compounds are produced by plants for the purpose of defending the host plant from predation, a trivial case is tree rosin, which is a natural insecticide. Specific, the production of oleoresin by conifer species is a component of the response against insect attack. Many fragrances, e. g. oil of wintergreen, are in fact antifeedants, the technique has been expanded to include the use of RNA interference RNAi that fatally silences crucial insect genes. RNAi likely evolved as a defense against viruses, midgut cells in many larvae take up the molecules and help spread the signal
17.
Absorption (chemistry)
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In chemistry, absorption is a physical or chemical phenomenon or a process in which atoms, molecules or ions enter some bulk phase – gas, liquid or solid material. This is a different process from adsorption, since molecules undergoing absorption are taken up by the volume, a more general term is sorption, which covers absorption, adsorption, and ion exchange. Absorption is a condition in which something takes in another substance, for some examples of this effect, see liquid-liquid extraction. It is possible to extract from one phase to another a solute without a chemical reaction. Examples of such solutes are noble gases and osmium tetroxide, the process of absorption means that a substance captures and transforms energy. The absorbent distributes the material it captures throughout whole and adsorbent only distributes it through the surface and this equation is valid if concentrations are not too large and if the species x does not change its form in any of the two phases 1 or 2. In the case of gas absorption, one may calculate its concentration by using, e. g. the Ideal gas law, in alternative fashion, one may use partial pressures instead of concentrations. Absorption is a process that may be chemical or physical, chemical absorption or reactive absorption is a chemical reaction between the absorbed and the absorbing substances. Sometimes it combines with physical absorption and this type of absorption depends upon the stoichiometry of the reaction and the concentration of its reactants
18.
Litter box
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Many owners of these animals prefer not to let them roam outside for fear that they might succumb to outdoor dangers, such as weather, wildlife or traffic. A litter box makes it possible to shelter pets from these risks, in the wild, cats naturally excrete in soft or sandy soil for easy burial. They use their paws in a sweeping motion to cover their feces. To stimulate this instinctive desire, a litter boxs bottom is filled typically with an inch or more of cat litter, Litter box filler is a loose, granular material that absorbs moisture and odors such as ammonia. Some litter brands contain baking soda to absorb such odors, the litter material also satisfies a cats instinctive desire to use an easily dug material. The most common material is clay, although recycled paper pellets, sometimes, when an owner wishes to stimulate the cats natural instincts, natural dirt is used. One of the first commercially available cat litters in the United States of America was Kitty Litter, available in 1947 and this was the first large-scale use of clay in litter boxes, previously sand was used. Clay litter is much more absorbent than sand and is manufactured into large grains or clumps of clay to make it likely to be tracked from the litter box. The brand name Kitty Litter has become a trademark, used by many to denote any type of cat litter. Today, cat litter can be obtained quite economically at a variety of retail stores, conventional clay litter is indistinguishable from clay-based oil absorbent, as the latter is far less expensive, it is often used as a substitute. Non-clumping cat litter is made of zeolite, diatomite and sepiolite. The cat-box that the litter is poured into can give off a strong odor and it is recommended that it is kept in an area in the home that is not often used, such as a basement or laundry room. There are special types of litter to cover or lessen the odor and they contain baking soda and/or odorized crystals. If kept in room with a vent, an air freshener may be added on the furnace filter to isolate the odor from the rest of the house. Litter clumps were first developed in the UK in the 1950s by the Fullers Earth Union, the type of clumping litter developed by the FEU was calcium bentonite, a less swelling and less sticky type than American bentonite. Subsequently in America, clumping bentonite was developed in 1984 by biochemist Thomas Nelson, most are made from granulated bentonite clay which clumps together when wet and forms a solid mass separate from the other litter in the box. This solid clumped material can be scooped out and disposed of without changing the contents of the litter box. Clumping litter usually also contains quartz or diatomaceous earth, because of the clumping effect, the manufacturers usually instruct not to flush clumping litters down the toilet, because it could clog it
19.
Dynamite
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Dynamite is an explosive made of nitroglycerin, sorbents and stabilizers. It was invented by the Swedish chemist and engineer Alfred Nobel in Geesthacht and it rapidly gained wide-scale use as a safer alternative to gun powder and nitroglycerin. Dynamite was invented by Alfred Nobel and was the first safely manageable explosive stronger than black powder, Nobel obtained patents for his invention in England on 7 May 1867, in Sweden on 19 October 1867. After its introduction, dynamite rapidly gained wide-scale use as an alternative to black powder. Nobel tightly controlled the patents, and unlicensed duplicating companies were shut down. However, a few American businessmen got around the patent by using a different formula. Nobel originally sold dynamite as Nobels Blasting Powder but decided to change the name to dynamite, from the Ancient Greek word δύναμις dýnamis, an industrialist, engineer, and inventor, Alfred Nobels father, Immanuel Nobel, built bridges and buildings in Stockholm. His construction work inspired him to new methods of blasting rock. Immanuels work with later on inspired Alfred to make explosives safer. Today dynamite is used in the mining, quarrying, construction. Dynamite is still the product of choice for trenching applications, Dynamite is occasionally used as an initiator or booster for AN and ANFO explosive charges. Nitroglycerin by itself is a strong explosive, but is extremely shock-sensitive, and degrades over time to even more unstable forms. Dynamite combines nitroglycerin with absorbents and stabilizers, rendering it safe to use, the original composition of dynamite consisted of three parts Explosive Oil, one part diatomaceous earth as the absorbent, and a small admixture of sodium carbonate antacid as the stabilizer. Diatomaceous earth is not usually used today as an absorbent medium and it has replaced by cheaper media like sawdust, wood pulp, flour. Other stabilizers like calcium carbonate or zinc oxide can be used in the place of sodium carbonate, sodium nitrate is added to the medium as an oxidizer that improves the dynamites brisance. Dynamite is usually sold in the form of cardboard cylinders about 20 cm long and about 3.2 cm in diameter, a stick of dynamite thus produced contains roughly 1 MJ of energy. Other sizes also exist, rated by either portion or by weight, Dynamite is usually rated by weight strength, usually from 20% to 60%. For example, 40% dynamite is composed of 40% nitroglycerin and 60% dope, the maximum shelf life of nitroglycerin-based dynamite is recommended as one year from the date of manufacture under good storage conditions
20.
Thermal insulation
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Thermal insulation is the reduction of heat transfer between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with specially engineered methods or processes, as well as with suitable object shapes, heat flow is an inevitable consequence of contact between objects of differing temperature. Thermal insulation provides a region of insulation in which thermal conduction is reduced or thermal radiation is reflected rather than absorbed by the lower-temperature body, the insulating capability of a material is measured with thermal conductivity. Low thermal conductivity is equivalent to high insulating capability, in thermal engineering, other important properties of insulating materials are product density and specific heat capacity. Solid materials chosen for insulation have a low thermal conductivity k, as the thickness of insulation is increased, the thermal resistance also increases. For insulated cylinders, a critical radius must be reached, before the critical radius is reached any added insulation increases heat transfer. If the outside radius of a cylinder is increased by applying insulation, however, at the same time, the convective resistance is reduced. This implies that adding insulation below a critical radius actually increases the heat transfer. If the radius of the cylinder is smaller than the critical radius for insulation. Gases possess poor thermal conduction properties compared to liquids and solids, in order to further augment the effectiveness of a gas it may be disrupted into small cells which cannot effectively transfer heat by natural convection. Convection involves a larger flow of gas driven by buoyancy and temperature differences. In order to accomplish gas cell formation in man-made thermal insulation, glass and this principle is used industrially in building and piping insulation such as, cellulose, rock wool, polystyrene foam, urethane foam, vermiculite, perlite, and cork. Trapping air is also the principle in all highly insulating clothing materials such as wool, down feathers, the air-trapping property is also the insulation principle employed by homeothermic animals to stay warm, for example down feathers, and insulating hair such as natural sheeps wool. In both cases the primary insulating material is air, and the used for trapping the air is natural keratin protein. Maintaining acceptable temperatures in buildings uses a proportion of global energy consumption. For a period of time, Asbestos was also used, however, when well insulated, a building, is energy-efficient, thus saving the owner money. Provides more uniform throughout the space. Unlike heating and cooling equipment, insulation is permanent and does not require maintenance, upkeep, lowers the carbon footprint of a building
21.
Bright-field microscopy
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Bright-field microscopy is the simplest of all the optical microscopy illumination techniques. Sample illumination is transmitted white light, and contrast in the sample is caused by attenuation of the light in dense areas of the sample. Bright-field microscopy is the simplest of a range of used for illumination of samples in light microscopes. The typical appearance of a bright-field microscopy image is a sample on a bright background. The light path of a microscope is extremely simple, no additional components are required beyond the normal light-microscope setup. Bright-field microscopy may use critical or Köhler illumination to illuminate the sample, bright-field microscopy typically has low contrast with most biological samples, as few absorb light to a great extent. Staining is often required to increase contrast, which prevents use on live cells in many situations, bright-field illumination is useful for samples that have an intrinsic color, for example chloroplasts in plant cells. Simplicity of setup with only basic equipment required, very low contrast of most biological samples. Low apparent optical resolution due to the blur of out-of-focus material, samples that are naturally colorless and transparent cannot be seen well, e. g. many types of mammalian cells. These samples often have to be stained before viewing, samples that do have their own color can be seen without preparation, e. g. the observation of cytoplasmic streaming in Chara cells. Reducing or increasing the amount of the source by the iris diaphragm. Use of an objective lens and a special immersion oil placed on a glass cover over the specimen. Immersion oil has the same refraction as glass and improves the resolution of the observed specimen, use of sample-staining methods for use in microbiology, such as simple stains and differential stains. Use of a colored or polarizing filter on the source to highlight features not visible under white light. The use of filters is especially useful with mineral samples, bracegirdle, BIOS Scientific Publishers Microbiology, Principles and Explorations by Jacquelyn G. Black, John Wiley & Sons, Inc
22.
Optical microscope
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The optical microscope, often referred to as light microscope, is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were invented in their present compound form in the 17th century. Basic optical microscopes can be simple, although there are many complex designs which aim to improve resolution. The image from a microscope can be captured by normal light-sensitive cameras to generate a micrograph. Originally images were captured by photographic film but modern developments in CMOS, purely digital microscopes are now available which use a CCD camera to examine a sample, showing the resulting image directly on a computer screen without the need for eyepieces. Alternatives to optical microscopy which do not use visible light include scanning electron microscopy, there are two basic types of optical microscopes, simple microscopes and compound microscopes. A simple microscope is one which uses a lens for magnification. A compound microscope uses several lenses to enhance the magnification of an object, the vast majority of modern research microscopes are compound microscopes while some cheaper commercial digital microscopes are simple single lens microscopes. Compound microscopes can be divided into a variety of other types of microscopes which differ in their optical configurations, cost. A simple microscope uses a lens or set of lenses to enlarge an object through angular magnification alone, the use of a single convex lens or groups of lenses are still found in simple magnification devices such as the magnifying glass, loupes, and eyepieces for telescopes and microscopes. A compound microscope uses a close to the object being viewed to collect light which focuses a real image of the object inside the microscope. That image is magnified by a second lens or group of lenses that gives the viewer an enlarged inverted virtual image of the object. The use of a compound objective/eyepiece combination allows for higher magnification. Common compound microscopes often feature exchangeable objective lenses, allowing the user to quickly adjust the magnification, a compound microscope also enables more advanced illumination setups, such as phase contrast. There are many variants of the optical microscope design for specialized purposes. Comparison microscope, which has two light paths allowing direct comparison of two samples via one image in each eye. Inverted microscope, for studying samples from below, useful for cell cultures in liquid, student microscope, designed for low cost, durability, and ease of use. Polarizing microscope, similar to the petrographic microscope, phase contrast microscope, which applies the phase contrast illumination method
23.
Cell wall
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A cell wall is a structural layer surrounding some types of cells, situated outside the cell membrane. It can be tough, flexible, and sometimes rigid and it provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae, plants and fungi, a major function is to act as pressure vessels, preventing over-expansion of the cell when water enters. The composition of cell walls varies between species and may depend on type and developmental stage. The primary cell wall of plants is composed of the polysaccharides cellulose, hemicellulose. Often, other such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess walls made of glycoproteins and polysaccharides such as carrageenan, in bacteria, the cell wall is composed of peptidoglycan. The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers, pseudopeptidoglycan, Fungi possess cell walls made of the glucosamine polymer chitin. Unusually, diatoms have a wall composed of biogenic silica. A plant cell wall was first observed and named by Robert Hooke in 1665, in 1804, Karl Rudolphi and J. H. F. Link proved that cells had independent cell walls, before, it had been thought that cells shared walls and that fluid passed between them this way. The mode of formation of the wall was controversial in the 19th century. Hugo von Mohl advocated the idea that the wall grows by apposition. Carl Nägeli believed that the growth of the wall in thickness, each theory was improved in the following decades, the apposition theory by Eduard Strasburger, and the intussusception theory by Julius Wiesner. In 1930, Ernst Münch coined the term apoplast in order to separate the living symplast from the dead plant region, Cell walls serve similar purposes in those organisms that possess them. They may give cells rigidity and strength, offering protection against mechanical stress, in multicellular organisms, they permit the organism to build and hold a definite shape. Cell walls also limit the entry of large molecules that may be toxic to the cell and they further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition, properties, and form may change during the cell cycle, in most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength
24.
Exoskeleton
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An exoskeleton is the external skeleton that supports and protects an animals body, in contrast to the internal skeleton of, for example, a human. In usage, some of the kinds of exoskeletons are known as shells. Examples of animals with exoskeletons include insects such as grasshoppers and cockroaches, the shells of certain sponges and the various groups of shelled molluscs, including those of snails, clams, tusk shells, chitons and nautilus, are also exoskeletons. Some animals, such as the tortoise, have both an endoskeleton and an exoskeleton, exoskeletons have a role in defense from pests and predators, support, and in providing an attachment framework for musculature. Exoskeletons contain chitin, the addition of calcium carbonate makes them harder and stronger, ingrowths of the arthropod exoskeleton known as apodemes serve as attachment sites for muscles. These structures are composed of chitin, and are six times as strong. Similar to tendons, apodemes can stretch to store energy for jumping. Many different species produce exoskeletons, which are composed of a range of materials, bone, cartilage, or dentine is used in the Ostracoderm fish and turtles. Chitin forms the exoskeleton in arthropods including insects, arachnids such as spiders, crustaceans such as crabs and lobsters, calcium carbonates constitute the shells of molluscs, brachiopods, and some tube-building polychaete worms. Silica forms the exoskeleton in the microscopic diatoms and radiolaria, one species of mollusc, the scaly-foot gastropod, even makes use of the iron sulfides greigite and pyrite. Some organisms, such as some foraminifera, agglutinate exoskeletons by sticking grains of sand, contrary to a common misconception, echinoderms do not possess an exoskeleton, as their test is always contained within a layer of living tissue. Exoskeletons have evolved many times,18 lineages evolved calcified exoskeletons alone. Further, other lineages have produced tough outer coatings analogous to an exoskeleton and this coating is constructed from bone in the armadillo, and hair in the pangolin. The armor of reptiles like turtles and Ankylosaurs is constructed of bone, crocodiles have bony scutes, since exoskeletons are rigid, they present some limits to growth. Organisms with open shells can grow by adding new material to the aperture of their shell, as is the case in snails, bivalves, a true exoskeleton, like that found in arthropods, must be shed when it is outgrown. A new exoskeleton is produced beneath the old one, as the old one is shed, the new skeleton is soft and pliable. The animal will pump itself up to expand the new shell to maximal size, when the shell has set, the empty space inside the new skeleton can be filled up as the animal eats. Failure to shed the exoskeleton once outgrown can result in the animal being suffocated within its own shell and this is the mechanism behind some insect pesticides, such as Azadirachtin
25.
Polymerization
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In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them, in chemical compounds, polymerization occurs via a variety of reaction mechanisms that vary in complexity due to functional groups present in reacting compounds and their inherent steric effects. Alkanes can also be polymerized, but only with the help of strong acids, further compounds either being referred to as oligomers in smaller molecules. Polymerization that is not sufficiently moderated and proceeds at a fast rate can be very hazardous and this phenomenon is known as hazardous polymerization and can cause fires and explosions. Step-growth polymers are defined as polymers formed by the reaction between functional groups of monomers, usually containing heteroatoms such as nitrogen or oxygen. Most step-growth polymers are classified as condensation polymers, but not all step-growth polymers release condensates, in this case. Step-growth polymers increase in weight at a very slow rate at lower conversions. To alleviate inconsistencies in these methods, adjusted definition for condensation and addition polymers have been developed. Chain-growth polymerization involves the linking together of molecules incorporating double or triple carbon-carbon bonds and these unsaturated monomers have extra internal bonds that are able to break and link up with other monomers to form a repeating chain, whose backbone typically contains only carbon atoms. Chain-growth polymerization is involved in the manufacture of such as polyethylene, polypropylene. A special case of chain-growth polymerization leads to living polymerization, in the radical polymerization of ethylene, its π bond is broken, and the two electrons rearrange to create a new propagating center like the one that attacked it. The form this propagating center takes depends on the type of addition mechanism. There are several mechanisms through which this can be initiated, the free radical mechanism is one of the first methods to be used. Free radicals are very reactive atoms or molecules that have unpaired electrons, taking the polymerization of ethylene as an example, the free radical mechanism can be divided into three stages, chain initiation, chain propagation, and chain termination. Free radical addition polymerization of ethylene must take place at temperatures and pressures. While most other free radical polymerizations do not require such extreme temperatures and pressures, one effect of this lack of control is a high degree of branching. Also, as termination occurs randomly, when two chains collide, it is impossible to control the length of individual chains, a newer method of polymerization similar to free radical, but allowing more control involves the Ziegler-Natta catalyst, especially with respect to polymer branching. Other forms of chain growth polymerization include cationic addition polymerization and anionic addition polymerization, cationic and anionic mechanisms are also more ideally suited for living polymerizations, although free radical living polymerizations have also been developed
26.
Silicic acid
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Silicic acid /sɪˈlɪsɪk ˌæsɪd/ is a chemical compound. Silicic acid is the name for a family of chemical compounds containing the element silicon attached to oxide. This family of compounds have the formula n. In general, silicic acid reactions are difficult to control, partial dehydration to metasilicic acid, for example, is challenging because the reaction typically progresses all the way to silicon dioxide and water. Like other silanols, silicic acid is a weak acid and it can be deprotonated in solution, the conjugate base silicate is known. Silicic acid was discovered by Jöns Jacob Berzelius between 1810 and 1836 when studying silicon generated by his experiments, however, he failed to recognise it as distinct from silicon dioxide. Naturally occurring silicic acid is produced by a process called hydration involving water, and quartz. The reaction producing silicic acid from quartz can be written as, if the products are left in air dry products are formed. Silicic acid can be produced by the acidification of sodium silicate in aqueous solution, the main problem in using silicic acids in chemical synthesis is that silicic acids readily lose water to form randomly polymeric silica gel, a form of silicon dioxide. Dissolved silica is a used in the field of oceanography to describe the form of water-soluble silica as silicon hydroxide which can be measured by standard analyses. However, the dissolved silica excludes silicate occurring as silicate minerals, which is a class of minerals forming rings, sheets, chains. Likewise, the dissolved silica is different from the term silicone. There exist three different species of DSi in natural waters, SiO222− SiO3− Si4 DSi is created near the oceans surface and it is carried into the abyssopelagic zone by falling water in the poles. Uncontrolled build-up of silicic acid in the ocean is naturally checked – although human influence can upset this natural regulation and it is primarily removed by conversion to silicon dioxide and water. In the oceans, silicon exists primarily as orthosilicic acid, and these algae polymerise the silicic acid to so-called biogenic silica, used to construct their cell walls. In the uppermost water column the surface ocean is undersaturated with respect to DSi, DSi is regenerated with increasing water depth, and DSi values increase along the conveyor belt from the Atlantic over the Indian into the Pacific Ocean. Study has shown that physiological concentration of orthosilicic acid stimulates collagen type 1 synthesis, choline-stabilized orthosilicic acid is a bioavailable nutritional supplement. Bioinorganic Chemistry of Aluminium and Silicon research group website
27.
Miocene
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The Miocene is the first geological epoch of the Neogene Period and extends from about 23.03 to 5.333 million years ago. The Miocene was named by Sir Charles Lyell and its name comes from the Greek words μείων and καινός and means less recent because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene Epoch and is followed by the Pliocene Epoch, the earth went from the Oligocene through the Miocene and into the Pliocene, with the climate slowly cooling towards a series of ice ages. The Miocene boundaries are not marked by a single distinct global event, the apes arose and diversified during the Miocene, becoming widespread in the Old World. By the end of this epoch, the ancestors of humans had split away from the ancestors of the chimpanzees to follow their own evolutionary path, as in the Oligocene before it, grasslands continued to expand and forests to dwindle in extent. In the Miocene seas, kelp forests made their first appearance, the plants and animals of the Miocene were fairly modern. The Miocene faunal stages from youngest to oldest are typically named according to the International Commission on Stratigraphy, Two subdivisions each form the lower, middle, continents continued to drift toward their present positions. Mountain building took place in western North America, Europe, both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in the North American Great Plains, India continued to collide with Asia, creating dramatic new mountain ranges. The Tethys Seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish–Arabian region between 19 and 12 Ma. The subsequent uplift of mountains in the western Mediterranean region and a fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea near the end of the Miocene. The global trend was towards increasing aridity caused primarily by global cooling reducing the ability of the atmosphere to absorb moisture, climates remained moderately warm, although the slow global cooling that eventually led to the Pleistocene glaciations continued. Although a long-term cooling trend was well underway, there is evidence of a period during the Miocene when the global climate rivalled that of the Oligocene. The Miocene warming began 21 million years ago and continued until 14 million years ago, by 8 million years ago, temperatures dropped sharply once again, and the Antarctic ice sheet was already approaching its present-day size and thickness. Greenland may have begun to have large glaciers as early as 7 to 8 million years ago, life during the Miocene Epoch was mostly supported by the two newly formed biomes, kelp forests and grasslands. This allows for more grazers, such as horses, rhinoceroses, ninety five percent of modern plants existed by the end of this epoch. The higher organic content and water retention of the deeper and richer grassland soils, with long term burial of carbon in sediments, produced a carbon and this, combined with higher surface albedo and lower evapotranspiration of grassland, contributed to a cooler, drier climate. The expansion of grasslands and radiations among terrestrial herbivores correlates to fluctuations in CO2
28.
Eocene
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The Eocene Epoch, lasting from 56 to 33.9 million years ago, is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by a period in which the concentration of the carbon isotope 13C in the atmosphere was exceptionally low in comparison with the more common isotope 12C. As with other periods, the strata that define the start and end of the epoch are well identified. The name Eocene comes from the Ancient Greek ἠώς and καινός, the Eocene epoch is conventionally divided into early, middle, and late subdivisions. The corresponding rocks are referred to as lower, middle, the Ypresian stage constitutes the lower, the Priabonian stage the upper, and the Lutetian and Bartonian stages are united as the middle Eocene. The Eocene Epoch contained a variety of different climate conditions that includes the warmest climate in the Cenozoic Era. During this period of time, little to no ice was present on Earth with a difference in temperature from the equator to the poles. Following the maximum was a descent into an icehouse climate from the Eocene Optimum to the Eocene-Oligocene transition at 34 million years ago. During this decrease ice began to reappear at the poles, greenhouse gases, in particular carbon dioxide and methane, played a significant role during the Eocene in controlling the surface temperature. For the early Eocene there is discussion on how much carbon dioxide was in the atmosphere. This is due to numerous proxies representing different atmospheric carbon dioxide content, for contrast, today the carbon dioxide levels are at 400 ppm or 0. 04%. At about the beginning of the Eocene Epoch the amount of oxygen in the atmosphere more or less doubled. During the early Eocene, methane was another gas that had a drastic effect on the climate. In comparison to carbon dioxide, methane has much effect on temperature as methane is ~34 times more effective per molecule than carbon dioxide on a 100-year scale. Most of the methane released to the atmosphere during this period of time would have been from wetlands, swamps, the atmospheric methane concentration today is 0. 000179% or 1.79 ppmv. Due to the climate and sea level rise associated with the early Eocene, more wetlands, more forests. Comparing the early Eocene production of methane to current levels of atmospheric methane, biogenic production of methane produces carbon dioxide and water vapor along with the methane, as well as yielding infrared radiation
29.
Amorphous solid
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In condensed matter physics and materials science, an amorphous or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal. In some older books, the term has been used synonymously with glass, nowadays, glassy solid or amorphous solid is considered to be the overarching concept, and glass the more special case, A glass is an amorphous solid that exhibits a glass transition. Other types of solids include gels, thin films. Amorphous materials have a structure made of interconnected structural blocks. Even amorphous materials have some shortrange order at the length scale due to the nature of chemical bonding. Furthermore, in small crystals a large fraction of the atoms are the crystal, relaxation of the surface and interfacial effects distort the atomic positions. Amorphous phases are important constituents of thin films, which are layers of a few nm to some tens of µm thickness deposited upon a substrate. For higher values, the diffusion of deposited atomic species would allow for the formation of crystallites with long range atomic order. Regarding their applications, amorphous metallic layers played an important role in the discussion of a suspected superconductivity in amorphous metals, today, optical coatings made from TiO2, SiO2, Ta2O5 etc. and combinations of them in most cases consist of amorphous phases of these compounds. Much research is carried out into thin films as a gas separating membrane layer. Also, hydrogenated amorphous silicon, a-Si, H in short, is of significance for thin film solar cells. In case of a-Si, H the missing long-range order between silicon atoms is partly induced by the presence by hydrogen in the percent range, the occurrence of amorphous phases turned out as a phenomenon of particular interest for studying thin film growth. Remarkably, the growth of polycrystalline films is used and preceded by an initial amorphous layer. The most investigated example is represented by thin multicrystalline silicon films, an initial amorphous layer was observed in many studies. The phenomenon has been interpreted in the framework of Ostwalds rule of stages that predicts the formation of phases to proceed with increasing condensation time towards increasing stability. Experimental studies of the phenomenon require a clearly defined state of the substrate surface, the Physics of Structurally Disordered Matter, An Introduction. Amorphous Solids and the Liquid State
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Opal
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Opal is a hydrated amorphous form of silica, its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals. It is deposited at a low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl. Opal is the gemstone of Australia. The internal structure of precious opal makes it diffract light, depending on the conditions in which it formed, it can take on many colors. Precious opal ranges from clear white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown. Of these hues, the black opals are the most rare, whereas white, opals vary in optical density from opaque to semitransparent. Precious opal shows a variable interplay of colors, and though it is a mineraloid. At microscopic scales, precious opal is composed of silica spheres some 150 to 300 nm in diameter in a hexagonal or cubic close-packed lattice, the regularity of the sizes and the packing of these spheres determines the quality of precious opal. The colors that are observed are determined by the spacing between the planes and the orientation of planes with respect to the incident light, the process can be described by Braggs law of diffraction. Visible light of diffracted wavelengths cannot pass through large thicknesses of the opal and this is the basis of the optical band gap in a photonic crystal. The notion that opals are photonic crystals for visible light was expressed in 1995 by Vasily Astratovs group, in addition, microfractures may be filled with secondary silica and form thin lamellae inside the opal during solidification. The term opalescence is commonly and erroneously used to describe this unique and beautiful phenomenon, contrarily, opalescence is correctly applied to the milky, turbid appearance of common or potch opal. Potch does not show a play of color, for gemstone use, most opal is cut and polished to form a cabochon. Solid opal refers to polished stones consisting wholly of precious opal, opals too thin to produce a solid may be combined with other materials to form attractive gems. An opal doublet consists of a thin layer of precious opal, backed by a layer of dark-colored material, most commonly ironstone, dark or black common opal, onyx. The darker backing emphasizes the play of color, and results in an attractive display than a lighter potch. An opal triplet is similar to a doublet, but has a third layer, the cap takes a high polish and acts as a protective layer for the opal
31.
Algae
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Algae is an informal term for a large, diverse group of photosynthetic organisms which are not necessarily closely related, and is thus polyphyletic. Included organisms range from unicellular genera, such as Chlorella and the diatoms, to forms, such as the giant kelp. Most are aquatic and autotrophic and lack many of the cell and tissue types, such as stomata, xylem, and phloem. No definition of algae is generally accepted, one definition is that algae have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells. Some authors exclude all prokaryotes thus do not consider cyanobacteria as algae, Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria, diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, and the roots, leaves, and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago, the singular alga is the Latin word for seaweed and retains that meaning in English. Although some speculate that it is related to Latin algēre, be cold, a more likely source is alliga, binding, entwining. The Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it, the Latinization, fūcus, meant primarily the cosmetic rouge. It could be any color, black, red, green, accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name Fucus appears in a number of taxa, most algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and presumably represent reduced endosymbiotic cyanobacteria, however, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three groups of algae. Their lineage relationships are shown in the figure in the upper right, many of these groups contain some members that are no longer photosynthetic
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Lake
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A lake is an area of variable size filled with water, localized in a basin, that is surrounded by land, apart from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, and therefore are distinct from lagoons, Lakes can be contrasted with rivers or streams, which are usually flowing. Most lakes are fed and drained by rivers and streams, natural lakes are generally found in mountainous areas, rift zones, and areas with ongoing glaciation. Other lakes are found in endorheic basins or along the courses of mature rivers, in some parts of the world there are many lakes because of chaotic drainage patterns left over from the last Ice Age. All lakes are temporary over geologic time scales, as they will fill in with sediments or spill out of the basin containing them. The word lake comes from Middle English lake, from Old English lacu, from Proto-Germanic *lakō, cognates include Dutch laak, Middle Low German lāke as in, de, Moorlake, de, Wolfslake, de, Butterlake, German Lache, and Icelandic lækur. Also related are the English words leak and leach, none of these definitions completely excludes ponds and all are difficult to measure. For this reason, simple size-based definitions are used to separate ponds. One definition of lake is a body of water of 2 hectares or more in area, however, others have defined lakes as waterbodies of 5 hectares and above, or 8 hectares and above. Charles Elton, one of the founders of ecology, regarded lakes as waterbodies of 40 hectares or more. The term lake is used to describe a feature such as Lake Eyre. In common usage, many bear names ending with the word pond. One textbook illustrates this point with the following, In Newfoundland, for example, almost every lake is called a pond, whereas in Wisconsin, the majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere at higher latitudes. Canada, with a drainage system has an estimated 31,752 lakes larger than 3 square kilometres and an unknown total number of lakes. Finland has 187,888 lakes 500 square metres or larger, most lakes have at least one natural outflow in the form of a river or stream, which maintain a lakes average level by allowing the drainage of excess water. Some lakes do not have an outflow and lose water solely by evaporation or underground seepage or both. Many lakes are artificial and are constructed for power generation, aesthetic purposes, recreational purposes, industrial use. Globally, lakes are greatly outnumbered by ponds, of an estimated 304 million standing water bodies worldwide, 91% are 1 hectare or less in area
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Ocean
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An ocean is a body of saline water that composes much of a planets hydrosphere. On Earth, an ocean is one of the major divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern, the word sea is often used interchangeably with ocean in American English but, strictly speaking, a sea is a body of saline water partly or fully enclosed by land. The ocean contains 97% of Earths water, and oceanographers have stated that less than 5% of the World Ocean has been explored, the total volume is approximately 1.35 billion cubic kilometers with an average depth of nearly 3,700 meters. As the world ocean is the component of Earths hydrosphere, it is integral to all known life, forms part of the carbon cycle. The world ocean is the habitat of 230,000 known species, but because much of it is unexplored, the origin of Earths oceans remains unknown, oceans are thought to have formed in the Hadean period and may have been the impetus for the emergence of life. Extraterrestrial oceans may be composed of water or other elements and compounds, the only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their histories, Mars and Venus are theorized to have had large water oceans. The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of many planets and natural satellites, notably. The Solar Systems giant planets are thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may also exist on exoplanets and exomoons, including surface oceans of water within a circumstellar habitable zone. Ocean planets are a type of planet with a surface completely covered with liquid. The concept of Ōkeanós has an Indo-European connection, Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases, though generally described as several separate oceans, these waters comprise one global, interconnected body of salt water sometimes referred to as the World Ocean or global ocean. This concept of a body of water with relatively free interchange among its parts is of fundamental importance to oceanography. The major oceanic divisions – listed below in descending order of area and volume – are defined in part by the continents, various archipelagos, Oceans are fringed by smaller, adjoining bodies of water such as seas, gulfs, bays, bights, and straits. The Mid-Oceanic Ridge of the World are connected and form the Ocean Ridge, the continuous mountain range is 65,000 km long, and the total length of the oceanic ridge system is 80,000 km long
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Sediment
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For sediment in beverages, see dregs. For example, sand and silt can be carried in suspension in water and on reaching the sea be deposited by sedimentation. Sediments are most often transported by water, but also wind, beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of transport and deposition. Glacial moraine deposits and till are ice-transported sediments, sediment can be classified based on its grain size and/or its composition. Sediment size is measured on a log base 2 scale, called the Phi scale, composition of sediment can be measured in terms of, parent rock lithology mineral composition chemical make-up. This leads to an ambiguity in which clay can be used as both a size-range and a composition, sediment is transported based on the strength of the flow that carries it and its own size, volume, density, and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise, rivers and streams carry sediment in their flows. This sediment can be in a variety of locations within the flow and these relationships are shown in the following table for the Rouse number, which is a ratio of sediment fall velocity to upwards velocity. If the upwards velocity is less than the settling velocity, but still high enough for the sediment to move, it will move along the bed as bed load by rolling, sliding. If the upwards velocity is higher than the velocity, the sediment will be transported high in the flow as wash load. As there are generally a range of different particle sizes in the flow, sediment motion can create self-organized structures such as ripples, dunes, antidunes on the river or stream bed. These bedforms are often preserved in rocks and can be used to estimate the direction. Overland flow can erode soil particles and transport them downslope, the erosion associated with overland flow may occur through different methods depending on meteorological and flow conditions. If the initial impact of rain droplets dislodges soil, the phenomenon is called rainsplash erosion, if overland flow is directly responsible for sediment entrainment but does not form gullies, it is called sheet erosion. If the flow and the substrate permit channelization, gullies may form, glaciers carry a wide range of sediment sizes, and deposit it in moraines. The overall balance between sediment in transport and sediment being deposited on the bed is given by the Exner equation and this expression states that the rate of increase in bed elevation due to deposition is proportional to the amount of sediment that falls out of the flow. This can be localized, and simply due to obstacles, examples are scour holes behind boulders, where flow accelerates
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Frustule
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A frustule is the hard and porous cell wall or external layer of diatoms. This layer is composed of several types of polysaccharides. The frustules structure is composed of two overlapping sections known as thecae. The join between the two thecae is supported by bands of silica that hold them together and this overlapping allows for some internal expansion room and is essential during the reproduction process. The frustule also contains many pores and slits that provide the access to the external environment for processes such as waste removal. A frustule is usually composed of two identically shaped but slightly differently sized thecae, the theca which is a bit smaller has an edge which fits slightly inside the corresponding edge of the larger theca. This overlapping region is reinforced with silica girdle bands, and constitutes an expansion joint. The larger theca is usually thought of as upper, and is termed the epitheca. The smaller theca is usually thought of as lower, and is called the hypotheca. As the diatom divides, each daughter retains one theca of the original frustule, diatoms have varied life strategies including floating in the water column, colonising submerged surfaces and living within the surface of deposited sediments. Some cells are essentially cylindrical while others have an elongated boat-like shape, since they are algae belonging to the division Bacillariophyta they require light for photosynthesis. Perhaps the most studied group of diatoms belong to the phytoplankton, phytoplanktonic diatoms rely on ocean currents and wind to keep them in the upper oceanic levels as their cell wall is denser than water around them. When diatoms die and their organic material decomposes, the sink to the bottom of the aquatic environment. There is also research underway regarding the use of diatom frustules and their properties for the field of optics, along with other cells, as the diatom prepares to separate it undergoes several processes in order to start the production of either a new hypotheca or new epitheca. Once each cell is completely separate they then have similar protection, a brief and extremely simplified version can be explained as, The newly formed nucleus and the pre-existing nucleus each move to the side of the diatom where the new hypotheca will be formed. A vesicle known as the silica deposition vesicle forms near the plasma membrane and this forms the center of the pattern and silica deposition can continue outward from that point, till the frustule is produced
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Peasant
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A peasant is a member of a traditional class of farmers, either laborers or owners of small farms, especially in the Middle Ages under feudalism, or more generally, in any pre-industrial society. In Europe, peasants were divided into three classes according to their status, slave, serf, and free tenant. Peasants either hold title to land in fee simple, or hold land by any of several forms of tenure, among them socage, quit-rent, leasehold. The implication of the term is that the peasant is uneducated, ignorant, the word peasant is also commonly used in a non-pejorative sense as a collective noun for the rural population in the poor and under-developed countries of the world. The word peasant is derived from the 15th century French word païsant, meaning one from the pays, or countryside, ultimately from the Latin pagus, Peasants typically made up the majority of the agricultural labour force in a pre-industrial society. The majority of the people in the Middle Ages were peasants, more generally, the word peasant is sometimes used to refer pejoratively to those considered to be lower class, perhaps defined by poorer education and/or a lower income. The open field system of agriculture dominated most of northern Europe during medieval times, under this system, peasants lived on a manor presided over by a lord or a bishop of the church. Peasants paid rent or labor services to the lord in exchange for their right to cultivate the land, fallowed land, pastures, forests, and wasteland were held in common. The open field system required cooperation among the peasants of the manor and it was gradually replaced by individual ownership and management of land. This process happened in a pronounced and truncated way in Eastern Europe. Lacking any catalysts for change in the 14th century, Eastern European peasants largely continued upon the original medieval path until the 18th and 19th centuries, even before emancipation in 1861, serfdom was on the wane in Russia. The proportion of serfs within the empire had decreased from 45-50 percent at the end of the eighteenth century. In Germany, peasants continued to center their lives in the well into the 19th century. They belonged to a body and helped to manage the community resources. In the East they had the status of serfs bound permanently to parcels of land, a peasant is called a Bauer in German and Bur in Low German. In most of Germany, farming was handled by tenant farmers who paid rents, Peasant leaders supervised the fields and ditches and grazing rights, maintained public order and morals, and supported a village court which handled minor offenses. Inside the family the patriarch made all the decisions, and tried to arrange marriages for his children. Much of the communal life centered on church services and holy days
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Limestone
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Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate, about 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, most cave systems are through limestone bedrock. The first geologist to distinguish limestone from dolomite was Belsazar Hacquet in 1778, like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts and these organisms secrete shells made of aragonite or calcite, and leave these shells behind when they die. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragment, some limestones do not consist of grains at all, and are formed completely by the chemical precipitation of calcite or aragonite, i. e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters and this produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance, the primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone typically does not form in deeper waters. Limestones may also form in lacustrine and evaporite depositional environments, calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, and dissolved ion concentrations. Calcite exhibits a characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors, especially with weathered surfaces, Limestone may be crystalline, clastic, granular, or massive, depending on the method of formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock, when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams, particularly there are waterfalls. Calcium carbonate is deposited where evaporation of the leaves a solution supersaturated with the chemical constituents of calcite. Tufa, a porous or cellular variety of travertine, is found near waterfalls, coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the building process, limestone recrystallizes into marble
38.
World War I
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World War I, also known as the First World War, the Great War, or the War to End All Wars, was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918. More than 70 million military personnel, including 60 million Europeans, were mobilised in one of the largest wars in history and it was one of the deadliest conflicts in history, and paved the way for major political changes, including revolutions in many of the nations involved. The war drew in all the worlds great powers, assembled in two opposing alliances, the Allies versus the Central Powers of Germany and Austria-Hungary. These alliances were reorganised and expanded as more nations entered the war, Italy, Japan, the trigger for the war was the assassination of Archduke Franz Ferdinand of Austria, heir to the throne of Austria-Hungary, by Yugoslav nationalist Gavrilo Princip in Sarajevo on 28 June 1914. This set off a crisis when Austria-Hungary delivered an ultimatum to the Kingdom of Serbia. Within weeks, the powers were at war and the conflict soon spread around the world. On 25 July Russia began mobilisation and on 28 July, the Austro-Hungarians declared war on Serbia, Germany presented an ultimatum to Russia to demobilise, and when this was refused, declared war on Russia on 1 August. Germany then invaded neutral Belgium and Luxembourg before moving towards France, after the German march on Paris was halted, what became known as the Western Front settled into a battle of attrition, with a trench line that changed little until 1917. On the Eastern Front, the Russian army was successful against the Austro-Hungarians, in November 1914, the Ottoman Empire joined the Central Powers, opening fronts in the Caucasus, Mesopotamia and the Sinai. In 1915, Italy joined the Allies and Bulgaria joined the Central Powers, Romania joined the Allies in 1916, after a stunning German offensive along the Western Front in the spring of 1918, the Allies rallied and drove back the Germans in a series of successful offensives. By the end of the war or soon after, the German Empire, Russian Empire, Austro-Hungarian Empire, national borders were redrawn, with several independent nations restored or created, and Germanys colonies were parceled out among the victors. During the Paris Peace Conference of 1919, the Big Four imposed their terms in a series of treaties, the League of Nations was formed with the aim of preventing any repetition of such a conflict. This effort failed, and economic depression, renewed nationalism, weakened successor states, and feelings of humiliation eventually contributed to World War II. From the time of its start until the approach of World War II, at the time, it was also sometimes called the war to end war or the war to end all wars due to its then-unparalleled scale and devastation. In Canada, Macleans magazine in October 1914 wrote, Some wars name themselves, during the interwar period, the war was most often called the World War and the Great War in English-speaking countries. Will become the first world war in the sense of the word. These began in 1815, with the Holy Alliance between Prussia, Russia, and Austria, when Germany was united in 1871, Prussia became part of the new German nation. Soon after, in October 1873, German Chancellor Otto von Bismarck negotiated the League of the Three Emperors between the monarchs of Austria-Hungary, Russia and Germany
39.
Vogelsberg
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The Vogelsberg Mountains or Vogelsberg are a large volcanic massif in eastern Upper Hesse separated from the Rhön Mountains by the Fulda River and its valley. The main peaks of the Vogelsberg are Taufstein,773 meters, in recent years the Eurasian lynx has returned. There are rumors about wolves being sighted in the region, sightings have been confirmed in an area north of the Vogelsberg. Wildcats are also said to exist in the region, although they, as in most of Hessen, wild boar are present in large numbers. In German, return of the Eurasian Lynx
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Upper Hesse
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The province of Upper Hesse was one of three provinces in the Grand Duchy of Hesse and later the Peoples State of Hesse. Its territory covers the area of north of the River Main in the historic region of Upper Hesse. The provincial capital and largest town of the provinces was the university town of Gießen. The province emerged as part of the new order in Germany after the Vienna Congress of 1815, the other two provinces in Hess were Starkenburg and Rhenish Hesse. The provinces of the Grand Duchy were wound up on 31 Juli 1848 and replaced by administrative regions, this was reversed again on 12 May 1852
