47 résultats pour "properties"
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Thermodynamics
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INTRODUCTION
Thermodynamics, field of physics that describes and correlates the physical properties of macroscopic systems of matter and energy.
Carnot EngineThe idealized Carnot engine was envisioned by the French physicist Nicolas Léonard Sadi Carnot, who lived during theearly 19th century. The Carnot engine is theoretically perfect, that is, it converts the maximum amount of energy intomechanical work. Carnot showed that the efficiency of any engine depends on the difference between the highest andlowest temperatures reached during one cycle. The greater the difference, the greater the efficiency. An automobileengine, for example, wou...
- Topology I INTRODUCTION Topology, branch of mathematics that explores certain properties of geometrical figures.
- Number Theory I INTRODUCTION Number Theory, branch of mathematics that deals with the properties and relationships of numbers (see Number).
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Physical Chemistry - chemistry.
by the system in the form of the flow of electrical currents, formation of surfaces and changes in surface tension, changes in volume or pressure, and formation ordisappearance of chemical species. B Chemical Kinetics This field studies the rates of chemical processes as a function of the concentration of the reacting species, of the products of the reaction, of catalysts and inhibitors, ofvarious solvent media, of temperature, and of all other variables that can affect the reaction rate. It is...
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Colour and qualia
Faced with the dilemmas posed by subjective colour for physicalist doctrine, some philosophers opt for eliminativism, the doctrine that subjective colour is not a genuine, or real, phenomenon after all. On this view the source of the puzzle is a conceptual confusion; a tendency to extend our judgments concerning objective colour, what appear to be intrinsic properties of the surfaces of physical objects, onto the properties of our mental states. Once we see that all that is happening ‘inside'...
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Magnetism
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INTRODUCTION
Magnetism, an aspect of electromagnetism, one of the fundamental forces of nature.
the French physicist Paul Langevin produced a theory regarding the temperature dependence of the magnetic properties of paramagnets (discussed below), which wasbased on the atomic structure of matter. This theory is an early example of the description of large-scale properties in terms of the properties of electrons and atoms.Langevin's theory was subsequently expanded by the French physicist Pierre Ernst Weiss, who postulated the existence of an internal, “molecular” magnetic field inmaterials...
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Organic Chemistry - chemistry.
B Alkenes and Alkynes Isomeric with the cyclanes, or cycloalkanes as they are sometimes called, is the family of alkenes, also represented by the general formula C nH2n. This family of hydrocarbons is characterized by one or more double bonds between carbon atoms. Propene and cyclopropane, for example, are isomers, as are 1,3-dimethylcyclohexane and 3,4-dimethyl-2-hexene. (The location of the double bond is indicated by the 2-hexene part of the name.) Double bonds may also occur incyclic compou...
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Periodic Law - chemistry.
VI QUANTUM THEORY With the development of the quantum theory and its application to atomic structure by the Danish physicist Niels Bohr and other scientists, most of the detailedfeatures of the periodic table have found a ready explanation. Every electron is characterized by four quantum numbers that designate its orbital motion in space. Bymeans of the selection rules governing these quantum numbers and the exclusion principle of Wolfgang Pauli, which states that two electrons in the same ato...
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Atom
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INTRODUCTION
Water Molecule
A water molecule consists of an oxygen atom and two hydrogen atoms, which are attached at an angle of 105°.
spontaneously break apart and change, or decay, into other atoms. Unlike electrons, which are fundamental particles, protons and neutrons are made up of other, smaller particles called quarks. Physicists know of six different quarks.Neutrons and protons are made up of up quarks and down quarks —two of the six different kinds of quarks. The fanciful names of quarks have nothing to do with their properties; the names are simply labels to distinguish one quark from another. Quarks are unique amo...
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Atom - chemistry.
Atoms have several properties that help distinguish one type of atom from another and determine how atoms change under certain conditions. A Atomic Number Each element has a unique number of protons in its atoms. This number is called the atomic number (abbreviated Z). Because atoms are normally electrically neutral,the atomic number also specifies how many electrons an atom will have. The number of electrons, in turn, determines many of the chemical and physical properties ofthe atom. The ligh...
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Artistic taste
objects of nature. Later he turns to the consideration of the exercise of taste in judgments of works of art,developing an elaborate theory of such judgments, but declaring that judgments of beauty made about works of artare inevitably 'impure', because the judge is implicitly aware that the the object was made . Kant's argument for the impurity of such judgments is elliptical. It turns on his conviction that a pure judgment of taste does not involve theapplication of a predicate conce...
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Chemistry - chemistry.
parts of oxygen by weight, which is a ratio of about 1 to 8, regardless of whether the water came from the Mississippi River or the ice of Antarctica. In other words, acompound has a definite, invariable composition, always containing the same elements in the same proportions by weight; this is the law of definite proportions. Many elements combine in more than one ratio, giving different compounds. In addition to forming water, hydrogen and oxygen also form hydrogen peroxide.Hydrogen peroxide h...
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Physics
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INTRODUCTION
Physics, major science, dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces.
Starting about 1665, at the age of 23, Newton enunciated the principles of mechanics, formulated the law of universal gravitation, separated white light into colors,proposed a theory for the propagation of light, and invented differential and integral calculus. Newton's contributions covered an enormous range of naturalphenomena: He was thus able to show that not only Kepler's laws of planetary motion but also Galileo's discoveries of falling bodies follow a combination of his ownsecond law of m...
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Quantum Theory
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INTRODUCTION
Quantum Theory, in physics, description of the particles that make up matter and how they interact with each other and with energy.
electron in the same way a particle with momentum would: It bumps the electron and changes the electron’s path. The light is also affected by the collision as though itwere a particle, in that its energy and momentum changes. Momentum is a quantity that can be defined for all particles. For light particles, or photons, momentum depends on the frequency, or color, of the photon, which in turndepends on the photon’s energy. The energy of a photon is equal to a constant number, called Planck’s cons...
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History of Chemistry - chemistry.
even better distillation apparatus than the Arabs had made and to condense the more volatile products of distillation. Among the important products obtained in thisway were alcohol and the mineral acids: nitric, aqua regia (a mixture of nitric and hydrochloric), sulfuric, and hydrochloric. Many new reactions could be carried outusing these powerful reagents. Word of the Chinese discovery of nitrates and the manufacture of gunpowder also came to the West through the Arabs. The Chinese atfirst use...
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Theater
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INTRODUCTION
The Art of Theater
BBC Worldwide Americas, Inc.
Theater at EpidaurusAncient Greek dramas were performed in open-air theaters like this one in Epidaurus, Greece, which was designed byPolyclitus the Younger in 350 bc. A festival of ancient Greek drama is still held in the summer in this 14,000-seat theater.Roger Wood/Corbis Fundamental to the theater experience is the act of seeing and being seen; in fact, the word theater comes from the Greek word theatron , meaning 'seeing place.' Throughout the history of world cultures, actors have used...
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Change
shape of a thing does not count as intrinsic on the above criterion since having shape is, arguably, not logically independent of the existence of the containing space. An alternative means of strengthening the Cambridge criterion employs the notion of causality. A genuine change in an object must, on this account, involve causal consequences contiguous to the object. This is not true of, for example, becoming an aunt or becoming famous - the effects of such 'changes' need not be near the obje...
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Inorganic Chemistry - chemistry.
two electrically charged plates (positively charged top plate and negatively charged bottom plate). By measuring the difference in how fast these electron-laden oildrops fell when the metal plates were charged and uncharged, Millikan was able to calculate the total charge on each oil drop. Because each measurement was a wholenumber multiple of -1.60 × 10 -19 coulombs, Millikan concluded this was the charge carried by a single electron. Using Thomson’s electron charge-to-mass ratio, Millikan then...
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Molecule - chemistry.
attracted to the negatively charged electrons between them. The electrons belong to the molecule as a whole. However, each hydrogen atom now has a complete outershell of two electrons. The formula H 2 describes a hydrogen molecule, a discrete unit. When a molecule contains just two atoms, such as the hydrogen molecule does, it is called a diatomic molecule. Some atoms can form covalent bonds with more than one other atom and thus create a larger molecule. Atoms form molecules with covalent bo...
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Geometry
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INTRODUCTION
Geometry, branch of mathematics that deals with shapes and sizes.
Conic sections, a commonly studied topic of geometry, are two-dimensional curves created by slicing a plane through a three-dimensional hollow cone. A Euclid’s Postulates Euclid, who lived about 300 BC, realized that only a small number of postulates underlay the various geometric theorems known at the time. He determined that these theorems could be deduced from just five postulates. 1. A straight line may be drawn through any two given points. 2. A straight line may be drawn infinitely or be...
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Trigonometry
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INTRODUCTION
Trigonometry, branch of mathematics that deals with the relationships between the sides and angles of triangles and with the properties and applications of the
trigonometric functions of angles.
If point P, in the definition of the general trigonometric function, is on the y-axis, x is 0; therefore, because division by zero is inadmissible in mathematics, the tangent and secant of such angles as 90°, 270°, and -270° do not exist. If P is on the x-axis, y is 0; in this case, the cotangent and cosecant of such angles as 0°, 180°, and - 180° do not exist. All angles have sines and cosines, because r is never equal to 0. Since r is greater than or equal to x or y, the values of si...
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Encyclopedia of Philosophy: Aesthetic attitude
there are some features that everyone with normal eyes, ears and intelligence perceives - shape or loudness, forexample. But there are also features that are perceived only by people with a special sensitivity - balance or unity,for example. These latter people are the ones who have taste. If a vase is gracefully curved, either one sees thegracefulness or one does not. Sibley believes that this explains why aesthetic concepts are not condition-governed.That is, no list of non-aesthetic features...
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Chemical Elements - chemistry.
Transition elements (also called transition metals) are a series of 30 chemical elements that share similar chemical properties. They have atomic numbers 21 to 30, 39to 48, and 71 to 80, and include titanium, iron, copper, zinc, gold, and mercury. The rare earth elements series (or rare earth metals) include the elements with atomic numbers 57 through 71, and include lanthanum, cerium, promethium, samarium,europium, gadolinium, ytterbium, and lutetium. (Yttrium [atomic no. 39] and scandium [ato...
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Electron
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INTRODUCTION
Models of the Atom
Once scientists discovered the electron, they set out to explain how electrons behave in atoms.
Electron Density and Orbital ShapesAtomic orbitals are mathematical descriptions of where the electrons in an atom (or molecule) are most likely to be found.These descriptions are obtained by solving an equation known as the Schrödinger equation, which expresses ourknowledge of the atomic world. As the angular momentum and energy of an electron increases, it tends to reside indifferently shaped orbitals. The orbitals corresponding to the three lowest energy states are s, p, and d, respectively....
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Sound
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INTRODUCTION
Sound, physical phenomenon that stimulates the sense of hearing.
A fundamental law of harmony states that two notes an octave apart, when sounded together, produce a pleasant-sounding combination. Other combinations of notescan also be pleasing. Physically, an interval of a fifth consists of two notes, the frequencies of which bear the arithmetical ratio 3 to 2, and a major third, the ratio 5 to4. Fundamentally, the law of harmony states that two or more notes sound pleasant when played together if their frequencies bear small, whole number ratios; if thefreq...
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Carbon - chemistry.
Graphite is black and slippery and conducts electricity. In graphite, the atoms form planar, or flat, layers. Each layer is made up of rings containing six carbon atoms.The rings are linked to each other in a structure that resembles the hexagonal mesh of chicken wire. Each atom has three sigma bonds (with 120° between any two ofthe bonds) and belongs to three neighboring rings. The fourth electron of each atom becomes part of an extensive pi bond system. Graphite conducts electricity,because th...
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Star (astronomy) - astronomy.
absorbing the missing colors of light. For example, the set of dark lines made by hydrogen includes a dark red line, the set of dark lines made by sodium includes a pairof dark yellow lines, and the set of dark lines made by iron includes lines of nearly every color. Each element in the gaseous outer layer of a star produces its ownparticular pattern of dark spectrum lines, depending on the temperature and pressure of the gas. Astronomers have observed spectrum lines, or spectra, for hundredsof...
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Caffeine
The technique used to separate an organic compound from a mixture of compounds is called Extraction. Extraction process selectively dissolves one or more of the mixture compounds into a suitable solvent. The solution of these dissolved compounds is referred to as the Extract. Extractions of certain solids can be performed by utilizing the different chemical properties of various solvents. The initial solvent used in the extraction of caffeine is water. Caffeine is sparingly soluble...
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Soil.
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INTRODUCTION
Soil, the loose material that covers the land surfaces of
an exchange between plants and the atmosphere, as oxygen diffuses into the soil and is used by roots for respiration. In turn, the resulting carbon dioxide diffusesthrough pore spaces and returns to the atmosphere. This exchange is most efficient in soils with a high degree of porosity. For farmers, gardeners, landscapers, andothers with a professional interest in soil health, the process of aeration—making holes in the soil surface to permit the exchange of air—is a crucial activity. Theburrowi...
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Light - astronomy.
Each different frequency or wavelength of visible light causes our eye to see a slightly different color. The longest wavelength we can see is deep red at about 700 nm.The shortest wavelength humans can detect is deep blue or violet at about 400 nm. Most light sources do not radiate monochromatic light. What we call white light,such as light from the Sun, is a mixture of all the colors in the visible spectrum, with some represented more strongly than others. Human eyes respond best to greenlight...
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Electricity
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INTRODUCTION
Electricity, one of the basic forms of energy.
electrons in the neutral object are attracted to the positive object. Some of these electrons flow to the side of the neutral object that is nearest to the positive object.This side of the neutral object accumulates electrons and becomes negatively charged. Because electrons leave the far side of the neutral object while its protonsremain stationary, that side becomes positively charged. Since the negatively charged side of the neutral object is closest to the positive object, the attraction bet...
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Western Philosophy.
the popular belief in personal deities, but he failed to explain the way in which the familiar objects of experience could develop out of elements that are totally differentfrom them. Anaxagoras therefore suggested that all things are composed of very small particles, or “seeds,” which exist in infinite variety. To explain the way in whichthese particles combine to form the objects that constitute the familiar world, Anaxagoras developed a theory of cosmic evolution. He maintained that the activ...
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Compositionality
sentence construction, an operation on meanings, such that the meaning of any sentence is mechanically determined by applying the operations on meanings (given by the rules used in constructing the sentence) to the meanings of the simple parts. (Often a host of extra restrictions are incorporated. For example: the operations may be limited to applying function to argument; the order in which operations are applied may be settled by the structure of the sentence.) Some see such principles as prov...
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Programming Language.
Logic languages use logic as their mathematical base. A logic program consists of sets of facts and if-then rules, which specify how one set of facts may be deducedfrom others, for example: If the statement X is true, then the statement Y is false. In the execution of such a program, an input statement can be logically deduced from other statements in the program. Many artificial intelligence programs are writtenin such languages. IV LANGUAGE STRUCTURE AND COMPONENTS Programming languages use...
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Antibiotics.
In some species of bacteria the cell wall consists primarily of a thick layer of peptidoglycan. Other species have a much thinner layer of peptidoglycan and an outer aswell as an inner membrane. When bacteria are subjected to Gram's stain, these differences in structure affect the differential staining of the bacteria with a dye calledgentian violet. The differences in staining coloration (gram-positive bacteria appear purple and gram-negative bacteria appear colorless or reddish, depending on t...
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Computer Science.
theoretical research is called algorithmic complexity. Computer scientists in this field seek to develop techniques for determining the inherent efficiency of algorithmswith respect to one another. Another area of theoretical research called computability theory seeks to identify the inherent limits of computation. Software engineers use programming languages to communicate algorithms to a computer. Natural languages such as English are ambiguous—meaning that theirgrammatical structure and vocab...
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Museum.
History museums are dedicated to promoting a greater appreciation and knowledge of history and its importance to understanding the present and anticipating thefuture. They range from historic sites and small historic house museums to large, encyclopedic institutions such as the Smithsonian’s National Museum of AmericanHistory in Washington, D.C. Many cities and states have historical societies that operate museums or historic sites. History museums usually collect a wide range ofobjects, includi...
- Periodic Table - chemistry.
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Concepts
suggested that concept possession need not consist in knowing a definition, but in appreciating the role of a concept in thought and practice. Moreover, he claimed, a concept need not apply to things by virtue of some closed set of features captured by a definition, but rather by virtue of ‘family resemblances' among the things, a suggestion that has given rise in psychology to ‘prototype' theories of concepts. Most traditional approaches to possession conditions have been concerned with t...
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Consciousness
view faces several serious objections. Rival views of introspective consciousness fall into three categories, according to whether they treat introspective access (1) as epistemically looser or less direct than inner perception, (2) as tighter or more direct, or (3) as fundamentally non-epistemic or nonrepresentational. Theories in category (1) explain introspection as always retrospective, or as typically based on self-directed theoretical inferences. Rivals from category (2) maintain that an i...
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Elementary Particles
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INTRODUCTION
Structure of Matter
Modern physics has revealed successively deeper layers of structure in ordinary matter.
The most fundamental particles that make up matter fall into the fermion category. These fermions cannot be split into anything smaller. The particles that carry theforces acting on matter and antimatter are bosons called force carriers. Force carriers are also fundamental particles, so they cannot be split into anything smaller.These bosons carry the four basic forces in the universe: the electromagnetic, the gravitational, the strong (force that holds the nuclei of atoms together), and the wea...
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Nanotechnology.
ever-finer method of reducing material to the nanoscale size. Instead, nanostructures would be assembled atom by atom and molecule by molecule, from the atomiclevel up, just as occurs in nature. However, assembly at this scale has its own challenges. In school, children learn about some of these challenges when they study the random Brownian motion seen in particles suspended in liquids such as water. Theparticles themselves are not moving. Rather, the water molecules that surround the particles...
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Air - chemistry.
lighting systems, fertilizers, and semiconductors (substances used to make the chips in computers, calculators, televisions, microwave ovens, and many other electronicdevices). A Oxygen More than half of the oxygen produced in the United States is used by the steel industry, which injects the gas into basic oxygen furnaces to heat and produce steel(see Iron and Steel Manufacture: Basic Oxygen Process ). Metalworkers also combine oxygen with acetylene to produce high-temperature torch flames th...
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Radioactivity
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INTRODUCTION
Marie Curie
Working with her husband, Pierre Curie, French physicist Marie Curie discovered the radioactive elements polonium and
radium in 1898.
Rutherford when he allowed an alpha-emitting substance to decay near an evacuated thin-glass vessel. The alpha particles were able to penetrate the glass and werethen trapped in the vessel, and within a few days the presence of elemental helium was demonstrated by use of a spectroscope. Beta particles were subsequentlyshown to be electrons, and gamma rays to consist of electromagnetic radiation of the same nature as X rays but of considerably greater energy. A The Nuclear Hypothesis Rutherford...
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Fidel Castro.
result, Castro formed a radical branch of the Ortodoxo Party called the Radical Action Orthodox wing. This organization supported Chibás in the 1948 election. PrioSocarrás won the election, despite Castro’s efforts. After Chibás committed suicide in 1951, Castro believed he should become the leader of the Ortodoxo Party and ran for a seat in the Cuban House of Representatives inthe 1952 election. Before that election could occur, however, General Fulgencio Batista staged a bloodless coup d’etat...
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Radar.
gathers the weak returning radar signals and converts them into an electric current. Because a radar antenna may both transmit and receive signals, the duplexerdetermines whether the antenna is connected to the receiver or the transmitter. The receiver determines whether the signal should be reported and often does furtheranalysis before sending the results to the display. The display conveys the results to the human operator through a visual display or an audible signal. B1 The Antenna The rec...
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Albania - country.
Joining the international community in its concern over the degradation of the environment, Albania is party to international agreements concerning biodiversity, climatechange, and wetlands. III THE PEOPLE OF ALBANIA In 2008 Albania’s population estimate was 3,619,778, resulting in an average density of 132 persons per sq km (342 per sq mi). More and more people have left ruralareas for urban ones, particularly in the northern districts, such that in 2005 some 45 percent of the population live...