Biochemistry, sometimes calledbiological chemistry, is the study of chemicalprocesses within and relating to living organisms. [ 1 ]By controlling information flow through biochemical signaling and the flow of chemical energy through metabolism, biochemical processes give rise to the complexity of life. Over the last 40 years, biochemistry has become so successful at explaining living processes that now almost all areas of the life sciencesfrom botanyto medicineare engaged in biochemical research. [ 2 ]Today, the main focus of pure biochemistry is in understanding how biological molecules give rise to the processes that occur within living cells, which in turn relates greatly to the study and understanding of whole organisms.
Biochemistry is closely related to molecular biology, the study of the molecular mechanisms by which geneticinformation encoded in DNAis able to result in the processes of life. Depending on the exact definition of the terms used, molecular biology can be thought of as a branch of biochemistry, or biochemistry as a tool with which to investigate and study molecular biology.
Much of biochemistry deals with the structures, functions and interactions of biological macromolecules, such as proteins, nucleic acids, carbohydratesand lipids, which provide the structure of cells and perform many of the functions associated with life. The chemistry of the cell also depends on the reactions of smaller moleculesand ions. These can be inorganic, for example waterand metalions, or organic, for example the amino acidswhich are used to synthesize proteins. The mechanisms by which cells harness energy from their environment via chemical reactions are known as metabolism. The findings of biochemistry are applied primarily in medicine, nutrition, and agriculture. In medicine, biochemists investigate the causes and cures of disease. In nutrition, they study how to maintain health and study the effects of nutritional deficiencies. In agriculture, biochemists investigate soil and fertilizers, and try to discover ways to improve crop cultivation, crop storage and pest control.
Biological warfare(BW)—also known asgerm warfare—is the use of biological toxinsor infectious agentssuch as bacteria, viruses, and fungiwith intent to kill or incapacitate humans, animals or plants as an act of war. Biological weapons(often termed "bio-weapons", "biological threat agents", or "bio-agents") are living organismsor replicating entities ( viruses, which are not universally considered "alive") that reproduce or replicate within their hostvictims. Entomological (insect) warfareis also considered a type of biological weapon. This type of warfare is distinct from nuclear warfareand chemical warfare, which together make up NBC, the military acronym for nuclear, biological, and chemical (warfare or weapons), all of which are considered " weapons of mass destruction" (WMDs). None of these fall under the term conventional weaponswhich are primarily effective due to their destructive potential.
Biological weapons may be employed in various ways to gain a strategic or tacticaladvantage over the enemy, either by threats or by actual deployments. Like some of the chemical weapons, biological weapons may also be useful as area denial weapons. These agents may be lethal or non-lethal, and may be targeted against a single individual, a group of people, or even an entire population. They may be developed, acquired, stockpiled or deployed by nation statesor by non-national groups. In the latter case, or if a nation-state uses it clandestinely, it may also be considered bioterrorism. [ 1 ]
There is an overlap between BW and chemical warfare, as the use of toxinsproduced by living organisms is considered under the provisions of both the Biological Weapons Conventionand the Chemical Weapons Convention. Toxins and psychochemical weaponsare often referred to asmidspectrum agents. Unlike bioweapons, these midspectrum agents do not reproduce in their host and are typically characterized by shorter incubation periods. [ 2 ]
Overview
Offensive biological warfare, including mass production, stockpiling and use of biological weapons, was outlawed by the 1972 Biological Weapons Convention (BWC). The rationalebehind this treaty, which has been ratifiedor acceded to by 165 countriesas of 2011, is to prevent a biological attack which could conceivably result in large numbers of civilian casualtiesand cause severe disruption to economicand societal infrastructure.[ citation needed]Many countries, including signatories of the BWC, currently pursue research into the defense or protection against BW, which is not prohibited by the BWC.
A nation or group that can pose a credible threat of mass casualty has the ability to alter the terms on which other nations or groups interact with it. Biological weapons allow for the potential to create a level of destruction and loss of life far in excess of nuclear, chemical or conventional weapons, relative to their mass and cost of development and storage. Therefore, biological agents may be useful as strategic deterrents in addition to their utility as offensive weapons on the battlefield.
GaneshScience: Bacteria: Bacteria come in a wide variety of shapes Perhaps the most elemental structural property of bacteriais cell morphology(shape). Typical ...
GaneshScience: Google?What is it ?: Googleis an American multinational corporationspecializing in Internet-related services and products. These include online advert...
Bacteria come in a wide variety of shapes
Perhaps the most elemental structural property of bacteriais cell morphology(shape). Typical examples include:
*. coccus(spherical)
*. bacillus(rod-like)
*. spirillum(spiral)
*. filamentous(elongated)
Cell shape is generally characteristic of a given bacterial species, but can vary depending on growth conditions. Some bacteria have complex life cycles involving the production of stalks and appendages (e.g. Caulobacter) and some produce elaborate structures bearing reproductive spores (e.g. Myxococcus, Streptomyces). Bacteriagenerally form distinctive cell morphologies when examined by light microscopyand distinct colony morphologies when grown on Petri plates. These are often the first characteristics observed by a microbiologistto determine the identity of an unknown bacterial culture.
Perhaps the most obvious structural characteristic of bacteriais (with some exceptions) their small size. For example, Escherichia colicells, an "average" sized bacterium, are about 2 micrometres(μm) long and 0.5 μm in diameter, with a cell volume of 0.6 - 0.7 μm3. [ 1 ]This corresponds to a wet mass of about 1 picogram(pg), assuming that the cell consists mostly of water. The dry mass of a single cell can be estimated as 20% of the wet mass, amounting to 0.2 pg. About half of the dry mass of a bacterial cell consists of carbon, and also about half of it can be attributed to proteins. Therefore, a typical fully grown 1-liter culture of Escherichia coli(at an optical density of 1.0, corresponding to ca. 109cells/ml) yields about 1 g wet cell mass. [ 2 ]Small size is extremely important because it allows for a large surface area-to- volume ratiowhich allows for rapid uptake and intracellular distribution of nutrients and excretion of wastes. At low surface area-to-volume ratios the diffusion of nutrients and waste products across the bacterial cell membrane limits the rate at which microbial metabolism can occur, making the cell less evolutionarily fit. The reason for the existence of large cells is unknown, although it is speculated that the increased cell volume is used primarily for storage of excess nutrients.
Cell wall
The structure of peptidoglycan.
The cell envelopeis composed of the plasma membrane and cell wall. As in other organisms, the bacterial cell wallprovides structural integrity to the cell. In prokaryotes, the primary function of the cell wall is to protect the cell from internal turgor pressurecaused by the much higher concentrations of proteins and other molecules inside the cell compared to its external environment. The bacterial cell wall differs from that of all other organisms by the presence of peptidoglycanwhich is located immediately outside of the cytoplasmic membrane. Peptidoglycan is made up of a polysaccharide backbone consisting of alternating N-Acetylmuramic acid(NAM) and N-acetylglucosamine(NAG) residues in equal amounts. Peptidoglycanis responsible for the rigidity of the bacterial cell wall and for the determination of cell shape. It is relatively porous and is not considered to be a permeability barrier for small substrates. While all bacterial cell walls (with a few exceptions e.g. extracellular parasites such as Mycoplasma) contain peptidoglycan, not all cell walls have the same overall structures. Since the cell wall is required for bacterial survival, but is absent in eukaryotes, several antibioticsnotably the ( penicillinsand cephalosporins) stop bacterial infections by interfering with cell wall synthesis, while having no effects on human cellswhich have no cell wall only a cell membrane.
GaneshScience: Google?What is it ?: Googleis an American multinational corporationspecializing in Internet-related services and products. These include online advert...
Googleis an American multinational corporationspecializing in Internet-related services and products. These include online advertisingtechnologies, search, cloud computing, and software. [ 7 ]Most of its profits are derived from AdWords. [ 8 ] [ 9 ]
Google was founded by Larry Pageand Sergey Brinwhile they were Ph.D.students at Stanford University. Together they own about 14 percent of its shares but control 56 of the stockholder voting power through supervoting stock. They incorporated Google as a privately held company on September 4, 1998. An initial public offeringfollowed on August 19, 2004. Its mission statementfrom the outset was "to organize the world's information and make it universally accessible and useful," [ 10 ]and its unofficial slogan was " Don't be evil." [ 11 ] [ 12 ]In 2006 Google moved to headquarters in Mountain View, California, nicknamed the Googleplex.
Rapid growth since incorporation has triggered a chain of products, acquisitionsand partnerships beyond Google's core search engine. It offers online productivity softwareincluding email( Gmail), a cloud storage service( Google Drive), an office suite( Google Docs) and a social networking service( Google+). Desktopproducts include applications for web browsing, organizing and editing photos, and instant messaging. The company leads the development of the Androidmobile operating systemand the browser-only Chrome OS [ 13 ]for a netbookknown as a Chromebook. Google has moved increasingly into communications hardware: it partners with major electronics manufacturers in production of its high-end Nexusdevices and acquired Motorola Mobilityin May 2012. [ 14 ]In 2012, a fiber-optic infrastructure was installed in Kansas Cityto facilitate a Google Fiberbroadband service. [ 15
Model of hydrogen bonds(1) between molecules of water
Impact from a water drop causes an upward "rebound" jet surrounded by circular capillary waves.
Snowflakesby Wilson Bentley, 1902
Dewdrops adhering to a spider web
Capillary actionof water compared to mercury
Water is the chemical substancewith chemical formulaH
2O: one moleculeof water has two hydrogen atoms covalently bondedto a single oxygenatom.
Water appears in nature in all three common states of matter (solid, liquid, and gas) and may take many different forms on Earth: water vapor and cloudsin the sky, seawaterin the oceans, icebergsin the polar oceans, glaciersin the mountains, fresh and salt water lakes, rivers, and aquifersin the ground.
The major chemical and physical properties of water are:
*.Water is a liquid at standard temperature and pressure. It is tasteless and odorless. The intrinsic colour of waterand ice is a very slight blue hue, although both appear colorless in small quantities. Water vapour is essentially invisible as a gas. [ 9 ]
*.Water is transparentin the visible electromagnetic spectrum. Thus aquatic plantscan live in water because sunlightcan reach them. Infrared light is strongly absorbedby the hydrogen-oxygen or OH bonds.
*.Since the water molecule is not linear and the oxygen atom has a higher electronegativitythan hydrogen atoms, the oxygen atom carries a slight negative charge, whereas the hydrogen atoms are slightly positive. As a result, water is a polar moleculewith an electrical dipole moment. Water also can form an unusually large number of intermolecular hydrogen bonds(four) for a molecule of its size. These factors lead to strong attractive forces between molecules of water, giving rise to water's high surface tension [ 10 ]and capillary forces. The capillary actionrefers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees. [ 11 ]
*.Water is a good polar solventand is often referred to asthe universal solvent. Substances that dissolve in water, e.g., salts, sugars, acids, alkalis, and some gases– especially oxygen and carbon dioxide( carbonation) – are known as hydrophilic(water-loving) substances, while those that are immisciblewith water (e.g., fats and oils), are known as hydrophobic(water-fearing) substances.
*.All of the components in cells ( proteins, DNAand polysaccharides) are dissolved in water, deriving their structure and activity from their interactions with the water.
*.Pure water has a low electrical conductivity, but this increases with the dissolutionof a small amount of ionic material such as sodium chloride.
*.The boiling pointof water (and all other liquids) is dependent on the barometric pressure. For example, on the top of Mt. Everestwater boils at 68 °C (154 °F), compared to 100 °C (212 °F) at sea levelat a similar latitude (since latitude modifies atmospheric pressure slightly). Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.
*.At 4181.3 J/(kg·K), water has a high specific heat capacity, as well as a high heat of vaporization(40.65 kJ·mol−1), both of which are a result of the extensive hydrogen bondingbetween its molecules. These two unusual properties allow water to moderate Earth's climateby buffering large fluctuations in temperature.
*.The densityof liquid water is 1,000 kg/m3(62.43 lb/cu ft) at 4 °C. Ice has a density of 917 kg/m3(57.25 lb/cu ft).
ADR labelfor transporting goods dangerously reactive with water
*.The maximum densityof water occurs at 3.98 °C (39.16 °F). [ 12 ]Most known pure substances become more dense as they cool, however water has the anomalous property of becoming less dense when it is cooled to its solid form, ice. During cooling water becomes more dense until reaching 3.98 °C. Below this temperature, the open structure of ice is gradually formed in the low temperature water; the random orientations of the water molecules in the liquid are maintained by the thermal motion, and below 3.98 °C
"H2O" and "HOH" redirect here. For other uses, see H2O (disambiguation)and HOH (disambiguation).
This article is about general aspects of water. For a detailed discussion of its physical and chemical properties, see Properties of water. For other uses, see Water (disambiguation).
Water in three states: liquid, solid ( ice), and gas (invisible water vaporin the air). Cloudsare accumulations of water droplets, condensedfrom vapor-saturated air.
Play media
Video demonstrating states of water present in domestic life.
Wateris a transparent fluid which forms the world's streams, lakes, oceans and rain, and is the major constituent of the fluids of living things. As a chemical compound, a water moleculecontains one oxygenand two hydrogen atomsthat are connected by covalent bonds. Water is a liquidat standard ambient temperature and pressure, but it often co-exists on Earthwith its solidstate, ice; and gaseousstate, steam( water vapor).
Water covers 71% of the Earth's surface. [ 1 ]It is vital for all known forms of life. On Earth, 96.5% of the planet's water is found in seas and oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the airas vapor, clouds(formed of solid and liquid water particles suspended in air), and precipitation. [ 2 ] [ 3 ]Only 2.5% of the Earth's water is freshwater, and 98.8% of that water is in ice and groundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an even smaller amount of the Earth's freshwater (0.003%) is contained within biological bodies and manufactured products. [ 2 ]
Water on Earth moves continually through the water cycleof evaporationand transpiration( evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea. Evaporation and transpiration contribute to the precipitation over land. Water used in the production of a good or service is known as virtual water.
Safe drinking wateris essential to humans and other lifeforms even though it provides no caloriesororganic nutrients . ... organic nutrients. Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation. [ 4 ]There is a clear correlation between access to safe water and gross domestic product per capita. [ 5 ]However, some observers have estimated that by 2025 more than half of the world populationwill be facing water-based vulnerability. [ 6 ]A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%. [ 7 ]Water plays an important role in the world economy, as it functions as a solventfor a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of the fresh water used by humans goes to agriculture. [ 8
Radiation pattern
Three-dimensional antenna radiation patterns. The radial distance from the origin in any direction represents the strength of radiation emitted in that direction. The top shows the directivepattern of a horn antenna, the bottom shows the omnidirectionalpattern of a dipole antenna.
In the field of antennadesign the termradiation pattern(orantenna patternorfar-field pattern) refers to thedirectional(angular) dependence of the strength of the radio wavesfrom the antenna or other source. [ 1 ] [ 2 ] [ 3 ]
Particularly in the fields of fiber optics, lasers, and integrated optics, the term radiation pattern may also be used as a synonym for the near-fieldpatternorFresnel pattern. [ 4 ]This refers to thepositionaldependence of the electromagnetic fieldin the near-field, or Fresnel region of the source. The near-field pattern is most commonly defined over a plane placed in front of the source, or over a cylindrical or spherical surface enclosing it. [ 1 ] [ 4 ]
The far-field pattern of an antenna may be determined experimentally at an antenna range, or alternatively, the near-field pattern may be found using a near-field scanner, and the radiation pattern deduced from it by computation. [ 1 ]The far-field radiation pattern can also be calculated from the antenna shape by computer programs such as NEC. Other software, like HFSScan also compute the near field.
The far field radiation pattern may be represented graphically as a plot of one of a number of related variables, including; the field strengthat a constant (large) radius (anamplitude patternorfield pattern), the power per unit solid angle (power pattern) and the directive gain. Very often, only the relative amplitude is plotted, normalized either to the amplitude on the antenna boresight, or to the total radiated power. The plotted quantity may be shown on a linear scale, or in dB. The plot is typically represented as a three-dimensional graph (as at right), or as separate graphs in the vertical planeand horizontal plane. This is often known as apolar diagram.
GaneshScience: LIST OF HEAVY ELEMENTS.: custom toolbar custom toolbar Thetransuranium elements(also known astransuranic elements) are the chemical elementswith atomic ...
Thetransuranium elements(also known astransuranic elements) are the chemical elementswith atomic numbersgreater than 92 (the atomic number of uranium). All of these elements are unstable and decay radioactivelyinto other elements.
Overview
Periodic table with elements colored according to the half-life of their most stable isotope.
Elements which contain at least one stable isotope.
Slightly radioactive elements: the most stable isotope is very long-lived, with a half-life of over four million years.
Significantly radioactive elements: the most stable isotope has half-life between 800 and 34,000 years.
Radioactive elements: the most stable isotope has half-life between one day and 103 years.
Highly radioactive elements: the most stable isotope has half-life between several minutes and one day.
Extremely radioactive elements: the most stable isotope has half-life less than several minutes.
Of the elements with atomic numbers 1 to 92, all can be found in nature, having stable (such as hydrogen), or very long half-life(such as uranium) isotopes, or are created as common products of the decay of uranium and thorium (such as radon) — only technetium, of the elements below uranium, was man-made for its discoveryin 1936.
All of the elements with higher atomic numbers, however, have been first discovered in the laboratory, with neptunium, plutonium, americium, curium, berkeliumand californiumlater also discovered in nature. They are all radioactive, with a half-lifemuch shorter than the age of the Earth, so any atoms of these elements, if they ever were present at the Earth's formation, have long since decayed. Trace amounts of these six elements form in some uranium-rich rock, and small amounts are produced during atmospheric tests of atomic weapons. The Np, Pu, Am, Cm, Bk, and Cf are generated from neutron capturein uranium ore with subsequent beta decays(e.g. 238 U+ n→ 239 U→ 239 Np→ 239 Pu).
Transuranic elements can be artificially generated synthetic elements, via nuclear reactorsor particle accelerators. The half lives of these elements show a general trend of decreasing as atomic numbers increase. There are exceptions, however, including dubniumand several isotopes of curium. Further anomalous elements in this series have been predicted by Glenn T. Seaborg, and are categorised as the “ island of stability.” [ 1 ]
Heavy transuranic elements are difficult and expensive to produce, and their prices increase rapidly with atomic number. As of 2008, weapons-grade plutonium cost around $4,000/gram, [ 2 ]and californiumcost $60,000,000/gram. [ 3 ]Due to production difficulties, none of the elements beyond californium have industrial applications,[ citation needed]and of them, only einsteiniumhas ever been produced in macroscopic quantities. [ 4 ]
Transuranic elements that have not been discovered, or have been discovered but are not yet officially named, use IUPAC's systematic element names. The naming of transuranic elements may be a source of controversy.
Discovery and naming of transuranium elements
So far, essentially all the transuranium elements have been produced at three laboratories:
*.The Radiation Laboratory (now Lawrence Berkeley National Laboratory) at the University of California, Berkeley, led principally by Edwin McMillan, Glenn Seaborg, and Albert Ghiorso, during 1945-1974:
*.93. neptunium, Np, named after the planet Neptune, as it follows uraniumand Neptune follows Uranusin the planetary sequence(1940).
*.94. plutonium, Pu, named after the dwarf planet Pluto, following the same naming rule as it follows neptunium and Pluto follows Neptune in the pre-2006 planetary sequence (1940).
*.95. americium, Am, named because it is an analog to europium, and so was named after the continent where it was first produced (1944).
*.96. curium, Cm, named after Pierreand Marie Curie, famous scientists who separated out the first radioactiveelements (1944).
GaneshScience: Feedbacks to blogger.: custom toolbar custom toolbar I like blogging very much thanks to blogger. I really want to appriciete blogger. Thank you very ...
GaneshScience: Do u know ?: custom toolbar custom toolbar ¤The harrier jump jet can take off vertically (i.e without needing a runway) ¤The fuel in a jumbo ...
Biology deals with the study of the many varieties of living organisms. Clockwise from top left: Salmonella typhimurium(a type of bacteria), Phascolarctos cinereus(koala), Athyrium filix-femina(common lady-fern), Amanita muscaria(fly agaric, a toxic toadstool), Agalychnis callidryas(red-eyed tree frog) and Brachypelma smithi(Mexican Red-kneed Tarantula)
Biologyis a natural scienceconcerned with the study of lifeand living organisms, including their structure, function, growth, evolution, distribution, and taxonomy. [ 1 ]Modern biology is a vast and eclectic field, composed of many branches and subdisciplines. However, despite the broad scope of biology, there are certain general and unifying concepts within it that govern all study and research, consolidating it into single, coherent fields. In general, biology recognizes the cellas the basic unit of life, genesas the basic unit of heredity, and evolutionas the engine that propels the synthesis and creation of new species. It is also understood today that all organisms survive by consuming and transforming energyand by regulatingtheir internal environment to maintain a stable and vital condition.
Subdisciplines of biology are defined by the scale at which organisms are studied, the kinds of organisms studied, and the methods used to study them: Biochemistryexamines the rudimentary chemistry of life; molecular biologystudies the complex interactions among biological molecules; botanystudies the biology of plants; cellular biologyexamines the basic building-block of all life, the cell; physiologyexamines the physical and chemical functions of tissues, organs, and organ systemsof an organism; evolutionary biologyexamines the processesthat produced the diversity of life; and ecologyexamines how organisms interact in their environment.
GaneshScience: Genes: Ageneis the molecular unit of heredityof a living organism. It is used extensively by the scientific community as a name given to some str...
Ageneis the molecular unit of heredityof a living organism. It is used extensively by the scientific community as a name given to some stretches of deoxyribonucleic acids(DNA) and ribonucleic acids(RNA) that code for a polypeptideor for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains. Genes hold the information to build and maintain an organism's cellsand pass genetic traitsto offspring. All organisms have genes corresponding to various biological traits, some of which are instantly visible, such as eye coloror number of limbs, and some of which are not, such as blood type, increased risk for specific diseases, or the thousands of basic biochemicalprocesses that comprise life. The wordgeneis derived from the Greekwordgenesismeaning "birth", orgenosmeaning "origin" (see pangenesis).
The chemical structure of a four-base fragment of a DNA double helix.
A modern working definition of a gene is "a locatable regionof genomicsequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions, and or other functional sequence regions". [ 1 ] [ 2 ]Colloquial usage of the termgene(e.g. "good genes", "hair color gene") may actually refer to an allele: ageneis the basic instruction— a sequence of nucleic acids (DNA or, in the case of certain virusesRNA), while analleleis one variant of that gene. Thus, when the mainstream press refers to "having" a "gene" for a specific trait, this is customarily inaccurate. In most cases, all people would have a gene for the trait in question, although certain people will have a specific allele of that gene, which results in the trait variant. Further, genes code for proteins, which might result in identifiable traits, but it is the gene ( genotype), not the trait ( phenotype), which is inherited.
Big genes are a class of genes whose nuclear transcriptspans 500 kb (1kb = 1,000 base pairs) or more of chromosomal DNA. The largest of the big genes is the gene for dystrophin, which spans 2.3 Mb. Many big genes have modestly sized mRNAs; the exons encodingthese RNAstypically encompass about 1% of the total chromosomal gene region in which they occur.
GaneshScience: Nuclear power: Nuclear power, ornuclear energy, is the use of exothermic nuclear processes, [ 1 ]to generate useful heatand electricity. The term inclu...
Nuclear power, ornuclear energy, is the use of exothermic nuclear processes, [ 1 ]to generate useful heatand electricity. The term includes nuclear fission, nuclear decayand nuclear fusion. Presently the nuclear fissionof elements in the actinideseries of the periodic tableproduce the vast majority of nuclear energy in the direct service of humankind, with nuclear decayprocesses, primarily in the form of geothermal energy, and radioisotope thermoelectric generators, in niche uses making up the rest. Nuclear (fission) power stations, excluding the contribution from naval nuclear fission reactors, provided about 5.7% of the world's energyand 13% of the world's electricity in 2012. [ 2 ]In 2013, the IAEAreport that there are 437 operational nuclear power reactors, [ 3 ]in 31 countries, [ 4 ]although not every reactor is producing electricity. [ 5 ]In addition, there are approximately 140 naval vessels using nuclear propulsionin operation, powered by some 180 reactors. [ 6 ] [ 7 ] [ 8 ]As of 2013, attaining a net energy gainfrom sustained nuclear fusionreactions, excluding natural fusion power sources such as the Sun, remains an ongoing area of international physicsand engineering research. More than 60 years after the first attempts, commercial fusion power production remains unlikely before 2050. [ 9 ]
There is an ongoing debate about nuclear power. [ 10 ] [ 11 ] [ 12 ]Proponents, such as the World Nuclear Association, the IAEAand Environmentalists for Nuclear Energycontend that nuclear power is a safe, sustainableenergy source that reduces carbon emissions. [ 13 ] Opponents, such as Greenpeace Internationaland NIRS, contend that nuclear power poses many threats to people and the environment. [ 14 ] [ 15 ] [ 16 ]
Nuclear power plant accidentsinclude the Chernobyl disaster(1986), Fukushima Daiichi nuclear disaster(2011), and the Three Mile Island accident(1979). [ 17 ]There have also been some nuclear submarine accidents. [ 17 ] [ 18 ] [ 19 ]In terms of lives lost per unit of energy generated, analysis has determined that nuclear power has caused less fatalities per unit of energy generated than the other major sources of energy generation. Energy production from coal, petroleum, natural gasand hydropowerhas caused a greater number of fatalities per unit of energy generated due to air pollutionand energy accidenteffects. [ 20 ] [ 21 ] [ 22 ] [ 23 ] [ 24 ]However, the economic costs of nuclear power accidents is high, and meltdowns can take decades to clean up. The human costs of evacuations of affected populations and lost livelihoods is also significant. [ 25 ] [ 26 ]
Along with other sustainable energy sources, nuclear power is a low carbon power generationmethod of producing electricity, with an analysis of the literature on its total life cycle emission intensityfinding that it is similar to other renewable sources in a comparison of greenhouse gas(GHG) emissions per unit of energy generated. [ 27 ]With this translating into, from the beginning of nuclear power stationcommercialization in the 1970s, having prevented the emission of approximately 64 gigatonnesof carbon dioxide equivalent(GtCO2-eq) greenhouse gases, gases that would have otherwise resulted from the burning of fossil fuelsin thermal power stations.
GaneshScience: ursa major: Ursa Major( Latin: "Larger Bear"; also known as theGreat BearandCharles' Wain [ 1 ]) is a constellationvisible throughout t...
Ursa Major( Latin: "Larger Bear"; also known as theGreat BearandCharles' Wain [ 1 ]) is a constellationvisible throughout the year in most of the northern hemisphere. It can be seen best in the month of April. It is dominated by the widely recognized asterismknown as the Big Dipperor the Plough, which is a useful pointer towards the north, and it has mythological significance in numerous world cultures.
Asterisms
Main article: Big Dipper
The seven brightest starsof Ursa Major form the asterismknown as theBig Dipperin the USA and Canada, thePloughin the United Kingdom, theGroßer Wagenin Germany & Austria and theSaptarshiin India.
Six of these seven stars are of 2nd magnitude, just the central star is of 3rdmagnitude.
Another asterism known as the "Three Leaps of Gazelle" [ 2 ]is recognized in Arab culture, a series of three pairs of stars:
*. νand ξUrsae Majoris, Alula Borealisand Australis, the "first leap";
*. λand μUrsae Majoris, Tania Borealisand Australis, the "second leap";
*. ιand κUrsae Majoris, Talitha Borealisand Australis, the "third leap".
These stars are found along the southwest border of the constellation.
Notable features
The constellation Ursa Major as it can be seen by the unaided eye.
Stars
The " Big Dipper" (or "Plough") asterismwithin Ursa Major is made up of seven bright stars that together comprise one of the best-known patterns in the sky, while also forming the hindquarters and tail of the Great Bear. Starting with the "ladle" portion of the dipper and extending clockwise through the handle, these stars are the following:
*. α Ursae Majoris, known by the Arabic name Dubhe("the bear"), which at a magnitude of 1.79 is the 35th brightest star in the sky and the second brightest of Ursa Major.
*. β Ursae Majoris, called Merak ("the loins of the bear"), with a magnitude of 2.37.
*. γ Ursae Majoris, or Phecda("thigh"), with a magnitude of 2.44.
*. δ Ursae Majoris, or Megrez, meaning "root of the tail," an appropriate name given its location as the intersection of the body and tail of the bear (or the ladle and handle of the dipper).
*. ε Ursae Majoris, known as Alioth, a name which refers not to a bear but to a "black horse," the name corrupted from the original and mis-assigned to the similarly named Alcor, the naked-eye binary companion of Mizar. [ 3 ]Alioth is the brightest star of Ursa Major and the 33rd brightest in the sky, with a magnitude of 1.76. It is also the brightest of the "peculiar A (Ap) stars," magnetic stars whose chemical elements are either depleted or enhanced, and appear to change as the star rotates. [ 4 ]
*. ζ Ursae Majoris, Mizar, the second star in from the end of the handle of the Big Dipper, and the constellation's fourth brightest star. Mizar, which means "girdle," forms a famous double star, with its optical companion Alcor(80 Ursae Majoris), the two of which were termed the "horse and rider" by the Arabs.
*. η Ursae Majoris, known as either Alkaidor Benetnash, both meaning the "end of the tail." With a magnitude of 1.85, Alkaid is the third-brightest star of Ursa Major.
High-speed railis a type of rail transportthat operates significantly faster than traditional rail traffic, using an integrated system of specialized rolling stockand dedicated tracks. The first such system began operations in Japan in 1964 and was widely known as the bullet train. High-speed trains normally operate on standard gaugetracks of continuously welded railon grade- separated right-of-waythat incorporates a large turning radiusin its design.
Many countries have developed high-speed rail to connect major cities, including China, France, Germany, Italy, Taiwan, Turkey, South Korea and Spain.
While high-speed rail is usually designed for passenger travel, some high-speed systems also offer freightservice. For instance, the French mail service La Posteowns a few special TGV trainsfor carrying postal freight.
Definitions
See also: Passenger rail terminology
Multiple definitions for high-speed rail are in use worldwide.
*.The European Union Directive 96/48/EC, Annex 1defines high-speed rail as a set of three elements with precise criteria:
1.Infrastructure:track built specially for high-speed travel or specially upgraded for high-speed travel.
2.Maximum Speed Limit:Minimum speed of 200 km/h (124 mph) on lines specially built for high speedand250 km/h (155 mph) on existing lines which have been specially upgraded. This must apply to at least one section of the line. Rolling stock must have a maximum speed of at least 200 km/h to be considered high speed.
3.Operating conditions:Rolling stock must be designed alongside its infrastructure for complete compatibility, safety and quality of service. [ 1 ]
*.The International Union of Railways(UIC) prefers to use "definitions" (plural) because they consider that there is no single standard definition of high-speed rail, nor even standard usage of the terms ("high speed", or "very high speed"). They make use of the European EC Directive 96/48, stating that high speed is a combination of all the elements which constitute the system: infrastructure, rolling stock and operating conditions. [ 1 ]
*.Some nations[ which?]have domestic standards which may vary from the international ones.
Early Flight
¤Early attempts at flight involved men trying to Beat gravity by strapping wings to their arms,but gravity always won.
¤george cayley Built a glider in which his poor butler beame the first aviates,flying assor the yorkship Dales in 1853. ¤Americon orville and wilbur wright made the successful powered flight in 1903
