Science & Philosophy: Laser - Background And History to Linear equation

Science Encyclopedia

Laser - Background And History, How It Works, Stimulated Emission, Oscillation, Solid State Lasers, Gas Lasers - Applications

The laser is a device that uses the principle of stimulated emission to produce light. The qualities of the light generated by a laser are significantly different from that generated by a conventional source such as an incandescent light bulb or fluorescent light tube. These major differences include: divergence: the laser generally emits a pencil thin beam of light whose divergent angle is closel…

1 minute read

Latitude and Longitude

The concepts of latitude and longitude create a grid system for the unique expression of any location on Earth's surface. Latitudes—also known as parallels—mark and measure distance north or south from the equator. Earth's equator (the great circle or middle circumference) is designated 0° latitude. The north and south geographic poles, respectively, measure 90&#…

3 minute read

Islamic Law - Legal Literature And Institutions, Jurisprudence: The "sources" Of The Law, The Modern Period

Islam, like Judaism and unlike Christianity, is a nomocracy, a religion of the law as opposed to theology. It is evident from the Koranic text that sacred law is a crucial feature of the covenants that God establishes, through prophets, with the various nations of mankind. Prophets are united by their main directive, to worship God alone, by their moral exhortations, and by accompanying miracles p…

6 minute read

LCD

LCD is short for liquid crystal display. LCDs are devices that use liquid crystals to create images. Liquid crystal images are being used in watch faces, laptop computer screens, camcorder viewers, virtual reality helmet displays, and television screens. The two main LCDs are passive and active. In passive LCDs, once the image has been made, it cannot be changed. In active LCDs, the image can be m…

2 minute read

Leaching

Leaching usually refers to the movement of dissolved substances with water percolating through soil. Sometimes, leaching may also refer to the movement of soluble chemicals out of biological tissues, as when rainfall causes potassium and other ions to be lost by foliage. Leaching occurs naturally in all soils, as long as the rate of water input through precipitation is greater than water losses by…

3 minute read

Lead - General Properties, Where It Comes From, How The Metal Is Obtained, How We Use It

A metallic element with atomic number 82. Symbol Pb, atomic weight 207.19, specific gravity 11.35, melting point 621.32°F (327.4°C), boiling point 3,191°F (1,755°C). Lead is in column IVA of the periodic table. It has four naturally occurring stable isotopes, lead-204, lead-206, lead-207, and lead-208. The last three of these are all end products of one or another radio…

1 minute read

Leaf - Blade, Venation, Anatomy, Epidermis, Mesophyll, Veins, Phyllotaxy, Evolution - Morphology

A leaf is a plant organ which is an outgrowth of the stem, and has three main parts: the blade, a flattened terminal portion; the petiole, a basal stalk which connects the blade to the stem; and the stipules, small appendages at the base of the petiole. However, the leaves of many species lack one or more of these three parts. Leaves function in photosynthesis, or the biological conversion of ligh…

1 minute read

Leafhoppers

Leafhoppers are a species of insects in the family Cicadellidae, order Homoptera, a group that also includes the cicadas, whiteflies, aphids, and scale insects. There are about 20,000 species of leafhoppers, including about 2,500 species in North America. Leafhoppers are leaf-feeding herbivores that use their sucking mouthparts to pierce the tissues of plants and feed on their juices, in some case…

2 minute read

Learning

Learning is the alteration of behavior as a result of experience. When an organism is observed to change its behavior, it is said to learn. Many theories have been formulated by psychologists to explain the process of learning. Early in the twentieth century, learning was primarily described through behaviorist principles that included associative, or conditioned response. Associative learning is …

3 minute read

Learning and Contemporary Views Memory - The Structuralist Approach, The Proceduralist Approach, Dynamic Memory, Bibliography

People have long wondered how best to characterize learning and memory. Most people typically conceive of memory as a place in which information is stored. As Henry Roediger has noted, this spatial metaphor has dominated the study of memory: "We speak of storing memories, of searching for and locating them. We organize our thoughts; we look for memories that have been lost, and if we are fo…

4 minute read

Least Common Denominator

A common denominator for a set of fractions is simply the same (common) lower symbol (denominator). In practice the common denominator is chosen to be a number that is divisible by all of the denominators in an addition or subtraction problem. Thus for the fractions 2/3, 1/10, and 7/15, a common denominator is 30. Other common denominators are 60, 90, etc. The smallest of the common denominators i…

less than 1 minute read

Lecithin - Structure And Properties, Dietary And Commercial Sources, Role In Health And Disease, Commercial Importance

Lecithin is a phospholipid which consists of glycerol, two fatty acids, a phosphate group and choline. Lecithin was first found in eggs in 1846, so its name was coined from the Greek word for egg yolk, lekithos. Though lecithin is its common name, chemists refer to it as phosphatidylcholine. It is a yellow-brown fatty substance. In contrast to fats, which function as fuel molecules, lecithin serve…

1 minute read

LED - The Solid-state Lamp, Convenient Uses And Ambitious Plans

A LED (light-emitting diode) converts electrical energy to light by means of a semiconductor, made of a solid material, such as silicon, whose electrical conductivity when hot is as great as that of metals and very low when cold. LEDs were commonly referred to early in their history as solid-state lamps. The light produced by LEDs is known as electroluminescence, distinguishing it from incandescen…

1 minute read

Ancient China Legalism - Shang Yang, Shen Buhai, Han Feizi, Later Legalism, Bibliography

Shang Yang aimed to turn Qin into a powerful state through two parallel and interconnected processes: encouraging agricultural production and strengthening military prowess. To achieve these goals he advocated a clear system of rewards and punishments, according to which aristocratic ranks would be granted for high grain yields and for military merits, while high taxation would be applied against …

1 minute read

Legionnaires' Disease - Causes And Symptoms, Diagnosis, Treatment, Prognosis, Prevention

Legionnaires' disease is a type of pneumonia caused by Legionella bacteria. The bacterial species re sponsible for Legionnaires' disease is L. pneumophila. Major symptoms include fever, chills, muscle aches, and a cough that is initially nonproductive. Definitive diagnosis relies on specific laboratory tests for the bacteria, bacterial antigens, or antibodies produced by the body�…

2 minute read

Legumes - Biology Of Legumes, Native Legumes Of North America, Legumes In Agriculture, Other Economic Products Obtained From Legumes

Legumes or beans are species of plants in the family Fabaceae (also known as Leguminoseae). The legume family is very large, containing about 12,000 species and 440 genera with species occurring on all of the habitable continents. The most species-rich groups in the legume family are the milk-vetches (Astragalus spp.) with 2,000 species, indigos (Indigoifera spp.; 500 species), clovers (Trifolium …

1 minute read

Lemmings

Lemmings are small mouselike rodents in the family Muridae, which also includes the voles, gerbils, hamsters, rats, and mice. Lemmings occur in open, northern habitats, especially in alpine and arctic tundra of North America and Eurasia. Lemmings are herbivores, feeding on sedges, grasses, berries, roots, and lichens. Lemmings are ecologically important in their habitat, in part because they are t…

2 minute read

Lemurs - Mouse And Dwarf Lemurs, True Lemurs, Indris Or Leaping Lemurs, Aye-aye, A Superfamily Of Its Own

Lemurs are primitive primates, or prosimians, found only on the island of Madagascar and nearby small islands off the eastern coast of Africa. Although lemurs, lorises, and tarsiers are all prosimians, or "premonkeys," only the lemurs and lorises have the typical prosimian snout that, like a dog's, remains moist. This wet snout, called a rhinarium, suggests that scent is a par…

2 minute read

Lens

In the field of optics, a lens is a device used for focusing or defocusing a beam of light. It is commonly formed from a disk-shaped blank of transparent material, such as glass, plastic, or fused quartz; both sides are ground and polished, with at least one surface being polished with a curve. The word lens is derived from the Latin word for lentil, since the shape of a lens resembles the curved …

7 minute read

Leukemia - History, Leukemia Types And Treatment

From the Greek words for white (leukos) and blood (hemia), leukemia refers to abnormally shaped and functioning leukocytes (white blood cells). Because the leukocytes multiply at an uncontrolled and rapid rate, leukemia is considered a cancer of the blood. Leukemia is neither contagious nor infectious, nor acquired from the mother prior to or during birth, but some researchers have suggested genet…

1 minute read

Lewis Structure

Lewis structures (also called electron-dot structures) are formed when Lewis symbols (also called electron-dot symbols) are combined. Lewis symbols are a simple way of visualizing the valence electrons in an atom. In a Lewis symbol, the symbol for the element is used to represent the atom and its core electrons. Dots placed around the atom are used to indicate the valence electrons. When combined …

10 minute read

Liberalism - Liberal Practice, Liberal Theories, The Historical Development Of The Liberal Idea, Some Issues In Liberal Theory And Practice

It is widely agreed that fundamental to liberalism is a concern to protect and promote individual liberty. This means that individuals can decide for themselves what to do or believe with respect to particular areas of human activity such as religion or economics. The contrast is with a society in which the society decides what the individual is to do or believe. In those areas of a society in whi…

less than 1 minute read

Liberation Theology - Latin American Liberation Theology, Black Theology, Feminist Theologies, Bibliography

The broad definition of liberation theology stresses the interrelatedness of differing structures of oppression and domination. Liberation from oppressive structures necessarily involves political, economic, social, racial, ethnic, and sexual aspects. As a paradigm, liberation theology today places explicit emphasis on assessing different forms of human oppression and suffering, and liberation fro…

4 minute read

Liberty - Ancient Conceptions, Medieval Conceptions, Modern Conceptions, Contemporary Conceptions, Islamic World, India, China

Liberty is an integral concept in Western political and social thought. Liberty as an inalienable social and political attribute of individuals emerged in the formation of the modern political discourse in the West. Since Georg Wilhelm Friedrich Hegel (1770–1831) the concept has often been categorized in a threefold manner: moral liberties (freedom of moral choice, such as freedom of consci…

less than 1 minute read

Lice - Lice On Humans, Lice On Other Animals

Lice are small, wingless, biting or sucking insects, many of which are ecto-parasites. There are about 3,000 species of lice in the orders Mallophaga and Anopleura. The Anopleura are sucking lice, which are parasites of mammals, and which feed only on blood. The Mallophaga are chewing or biting lice, and are primarily pests of birds, feeding on skin and feathers. Most species of lice are specific …

less than 1 minute read

Life - Idealist Versus Materialist Conceptions Of Life, Methodological Debates About The Study Of Life, Unity And Diversity In Living Organisms

Throughout recorded history human beings have recognized the qualitative difference between the living and non-living worlds, the animate and inanimate. Placing that recognition on solid, rational footing or giving it a quantitative basis has remained a major challenge, however. What exactly makes a living being so different from one that is nonliving? Living organisms carry out oxidation, for exa…

1 minute read

Life Cycle

The Sphinx, according to an ancient Greek tale, was a monster with the face of a woman, the body of a lion, and gigantic wings. Sent by the goddess Hera to punish the city of Thebes, she sat on a hilltop and stopped passersby, posing them a riddle: "What has one voice, and is four-footed, two-footed, and three-footed?" Every time the Thebans gave a wrong answer, she devoured one of t…

6 minute read

Life Cycle - Adolescence - Conceptualizing Adolescence, Anthropological Critique, Contemporary Perspectives, Bibliography

Many social historians have argued that adolescence emerged as a distinct life stage only with the advent of industrialization. Using case studies from regions where the historical record is plentiful, such as France, England, and the United States, scholars contend that prior to the industrial revolution, the physical processes of maturity did not necessarily signal a change in life status for th…

1 minute read

Life Cycle - Elders/Old Age - Social Theories Of Aging, Aging As Stigma, Critical And Constructionist Perspectives On Aging, Geroanthropology: A Cross-cultural And Holistic Inquiry

The study of the human life cycle is primarily a study of the aging process. The question of why humans age has long intrigued social and biological scientists. While a fountain of youth has yet to be discovered, public health and hygiene interventions have lengthened the human life expectancy greatly over the course of the past hundred years. And yet life expectancy varies greatly within and betw…

1 minute read

Life History

Life history is an ecological term that refers to the significant features of the life cycle of organisms and their relationships with environmental conditions. Life cycle refers to the sequence of discrete developmental stages of an organism from their origin as gametes to their eventual death. Life cycle also refers to the stages through which generations of organisms pass from their own origin …

2 minute read

Ligand - Structure And Bonding, Chelating Agents, Metal-ligand Bonds In Biological Chemistry - Other uses

In inorganic chemistry, ligands are molecules or electrically charged atoms (ions) which are bonded to metal atoms or ions. The ligand changes the metal's ability to dissolve in or react with its surroundings. In biochemistry, ligands are defined as molecules, usually Figure 1. Two ligands (ammonia) each donate a pair of electrons to bond with a silver ion. (N = nitrogen, H = hydrogen, A…

2 minute read

Light

Light can be narrowly defined as the visible portion of the electromagnetic spectrum. A broader definition would include infrared, ultraviolet, and x-ray wavelengths, which are not visible to the eye. The nature of light has been the subject of controversy for thousands of years. Even today, while scientists know how light behaves, they do not always know why light behaves as it does. The next con…

7 minute read

Light-Year

A light-year is the distance that light (or any other form of electromagnetic radiation, such as radio waves) travels in a vacuum in one year. Since light travels at a velocity of 186,171.1 mi/s (299,792.5 km/s), one light-year equals 5,878,489,000,000 miles (9,460,530,000,000 km). The light-year is a convenient unit of measurement to use when discussing distances to the stars in the Milky Way gal…

1 minute read

Lightning

Lightning is an electrical discharge usually, but not always, produced by well-developed thunderstorms. Although there is a clear-air lightening phenomena,lightning most frequently occurs within a cloud (intra-cloud), between two clouds (inter-cloud), or from the cloud to the ground. A lightning discharge can heat the air as much as five times hotter than the surface temperature of the Sun (about …

3 minute read

Lilac

Lilacs (Syringa spp.) are about 10 species of shrubs and small trees in the olive family (Oleaceae). Lilacs are native to Eurasia but have been widely planted elsewhere as ornamental shrubs. The common lilac (Syringa vulgaris) is the most familiar species to most people. The common lilac has shiny green wedge-shaped leaves without teeth on the margins which are arranged alternately on the twigs. …

1 minute read

Lily Family (Liliaceae)

Lilies are the classic representatives of the monocotyledons—those plants with only one seed leaf. Lilies are mostly perennial, erect herbs arising from a bulb. Some climb, a few are woody, but most arise from underground stems or other structures. The leaves vary in number from one to many, and are arranged on the stem alternately or in whorls. The leaves are flat, linear to lance-shaped, …

7 minute read

Limiting Factor

Limiting factors are environmental influences that constrain the productivity of organisms, populations, or communities and thereby prevent them from achieving their full biological potential which could be realized under optimal conditions. Limiting factors can be single elements or a group of related factors. The environment of organisms must be suitable in many respects. Environmental factors m…

2 minute read

Limpets

Limpets are a common mollusk of the class Gastropoda. Its shell is generally low, flat, oval, and more bilaterally symmetrical than coiled (like a snail's), and it covers the entire soft body, so that the living animal inside is rarely visible. Limpets adhere strongly to rocks by means of a broad muscular foot. It is important for their survival that they are not dislodged easily, since the…

3 minute read

Equations of Line

There are many different ways of writing the equation of a line in a coordinate plane. They all stem from the form ax + by + c = 0. Thus 2x + 3y - 5 = 0 is an equation of a line, with a = 2, b = 3, and c = -5. When the equation is written in the form y = mx + b we have slope-intercept form: m is the slope of the line and b is the y-intercept. The equation 2x + 3y - 5 = 0 becomes So the line h…

1 minute read

Linear Algebra - Historical Background, Fundamental Principles, Matrices, Applications - Vectors

Two important concepts emerge in linear algebra to help facilitate the expression and solution of systems of simultaneous linear equations. They are the vector and the matrix. Vectors correspond to directed line segments. They have both magnitude (length) and direction. Matrices are rectangular arrays of numbers. They are used in dealing with the coefficients of simultaneous equations. Using vecto…

1 minute read