Flight

Movement through the atmosphere or space, sustained by aerodynamic reaction or other forces. Animal flight includes gliding and flapping flight. Flapping flight in vertebrates was probably preceded by gliding; in insects it may have originated by leaping and gliding, by surface skimming on water, or (if small enough) by passive floating in the air. Flying insects show greater variation than flying vertebrates, and their flight spans a wider range of Reynolds numbers, which is the ratio of inertial forces to viscous forces in the flow. Flight of tiny insects is in the lower range of Reynolds numbers, where viscous forces are dominant, whereas large insects and vertebrates operate in the higher range, where inertial forces are important.

Flight is very expensive in terms of energy cost per unit time. However, flying animals can travel several times faster than nonflying ones, and the cost of carrying a unit of weight of an animal through a unit distance (cost of transport) is lower for flight than for running, but higher than for swimming.

The flight characteristics of large insects and vertebrates can be understood by aircraft aerodynamics. In steady level flight, an animal and an aircraft must generate forces that support weight against gravity and provide propulsive thrust against drag forces. The forces acting on an airfoil (the shape of the cross section of the wings) moving through the air depend upon the flow pattern around it. Because of the asymmetric profile on an airfoil, the air flowing over the upper surface travels farther and flows faster than air passing underneath. According to Bernoulli's principle, pressure falls when speed rises in a moving fluid, resulting in a pressure difference between the upper and lower sides of the airfoil (illus. a). This pressure difference has to disappear gradually toward the wingtips, and some air will flow upward around the wingtips. The air moves downward behind the wing as trailing vortices (illus. b), and the reaction of this momentum flow is experienced by the wing as lift. The stronger the vortex, the greater the lift generated, but with some energy loss to drag. The lift force is responsible for weight support (its vertical component) and thrust or drag (its horizontal component). See also Aerodynamic force; Airfoil; Bernoulli's theorem.

Aerodynamics of flight. (a) Airflow around a typical wing profile. (b) Pressure distribution around a typical wing profile. (c) The difference in pressure disappears toward the wingtips as trailing vortices in the wake. (After M. Brooke and T. Birkhead, eds., Cambridge Encyclopedia of Ornithology, Cambridge University Press, 1991)
Aerodynamics of flight. (a) Airflow around a typical wing profile. (b) Pressure distribution around a typical wing profile. (c) The difference in pressure disappears toward the wingtips as trailing vortices in the wake. (After M. Brooke and T. Birkhead, eds., Cambridge Encyclopedia of Ornithology, Cambridge University Press, 1991)

Energy must be expended to generate the trailing vortices in the wake and to overcome friction on the wing and body surfaces. These energy losses are experienced as drag forces, which act parallel to the direction of movement of the airfoil. Since drag is a retarding force, the animal must either descend (glide) through the air at such an angle that a component of its weight balances the drag, or do mechanical work with its flight muscles (flap its wings) to overcome it. The rate at which this work is done is the mechanical power required to fly, and it equals speed times drag (measured in watts). The flight muscles also produce heat when they contract, so the total metabolic power expenditure is the sum of this heat loss and the mechanical power. The metabolic power is estimated to be four to five times the mechanical power, and is dependent on the size of the animal. See also Work.

Compared with active flight, gliding flight is very inexpensive, and is found in a wide range of animals, such as squirrels, marsupials, lizards, frogs, fishes, and even one snake. It is the main component in soaring flight used by many birds and some bats, when the animals use thermals or updrafts. Gliding in birds costs only two to three times the basal metabolic rate, because the flight muscles do not perform any mechanical work other than for stability and control of movements, and produce mostly static forces to keep the wings down on the horizontal plane, opposing the aerodynamic force.

When gliding, the wings of the animal leave behind a continuous vortex sheet that rolls up into a pair of vortex tubes (wingtip vortices), as in fixed-wing airplanes (illus. b). The lift produced balances the animal's weight, but potential energy must be used to overcome the drag and the animal loses height. An animal gliding at steady speed descends at an angle to the horizontal (glide angle), established by the ratio of lift to drag (glide ratio). The best glide ratios in birds range from 10:1 to 15:1 for vultures and birds of prey and reach 23:1 in the wandering albatross, whereas modern gliders can achieve 45:1. An animal cannot glide more slowly than its stalling speed, which in birds can be reduced by splaying the wingtip primaries, or by spreading the alula (a digit of the wing) at the wrist, or both. An animal can increase its gliding speed by flexing the wings and reducing the wing area.

Hovering flight represents the most expensive form of animal flapping flight. The essence of hovering is to produce a vertical force to balance body weight. The wake consists of a chain of vortex rings continuously shed during the wing strokes. In hummingbirds and insects, lift is produced during both the downstroke and upstroke of the wings (symmetrical hovering), and two vortex rings are produced during each wing stroke. In other hovering animals the wings are flexed during the upstroke (asymmetrical hovering), and the rings are produced during the downstrokes only. See also Aerodynamics; Aves.

Computer

A device that receives, processes, and presents information. The two basic types of computers are analog and digital. Although generally not regarded as such, the most prevalent computer is the simple mechanical analog computer, in which gears, levers, ratchets, and pawls perform mathematical operations—for example, the speedometer and the watt-hour meter (used to measure accumulated electrical usage). The general public has become much more aware of the digital computer with the rapid proliferation of the hand-held calculator and a large variety of intelligent devices and especially with exposure to the Internet and the World Wide Web. See also Calculators; Internet; World Wide Web.

An analog computer uses inputs that are proportional to the instantaneous value of variable quantities, combines these inputs in a predetermined way, and produces outputs that are a continuously varying function of the inputs and the processing. These outputs are then displayed or connected to another device to cause action, as in the case of a speed governor or other control device. Small electronic analog computers are frequently used as components in control systems. If the analog computer is built solely for one purpose, it is termed a special-purpose electronic analog computer. In any analog computer the key concepts involve special versus general-purpose computer designs, and the technology utilized to construct the computer itself, mechanical or electronic. See also Analog computer.

In contrast, a digital computer uses symbolic representations of its variables. The arithmetic unit is constructed to follow the rules of one (or more) number systems. Further, the digital computer uses individual discrete states to represent the digits of the number system chosen. A digital computer can easily store and manipulate numbers, letters, images, sounds, or graphical information represented by a symbolic code. Through the use of the stored program, the digital computer achieves a degree of flexibility unequaled by any other computing or data-processing device.

The advent of the relatively inexpensive and readily available personal computer, and the combination of the computer and communications, such as by the use of networks, have dramatically expanded computer applications. The most common application now is probably text and word processing, followed by electronic mail. See also Electronic mail; Local-area networks; Microcomputer; Word processing.

Computers have begun to meet the barrier imposed by the speed of light in achieving higher speeds. This has led to research and development in the areas of parallel computers (in order to accomplish more in parallel rather than by serial computation) and distributed computers (taking advantage of network connections to spread the work around, thus achieving more parallelism). Continuing demand for more processing power has led to significant changes in computer hardware and software architectures, both to increase the speed of basic operations and to reduce the overall processing time. See also Computer systems architecture; Concurrent processing; Distributed systems (computers); Multiprocessing; Supercomputer.

Society

Society

A society is a grouping of individuals, which is characterized by common interest and may have distinctive culture and institutions. In a society members can be from a different ethnic group. A "Society" may refer to a particular people, such as the Nuer, to a nation state, such as Switzerland, or to a broader cultural group, such as Western society. Society can also refer to an organized group of people associated together for religious, benevolent, cultural, scientific, political, patriotic, or other purposes.


Origin and usage

The English word society emerged in the 15th century and is derived from the French société. The French word, in turn, had its origin in the Latin societas, a "friendly association with others," from socius meaning "companion, associate, comrade or business partner." Implicit in the meaning of society is that its members share some mutual concern or interest, a common objective or common characteristics.

In political science, the term is often used to mean the totality of human relationships, generally in contrast to the State, i.e., the apparatus of rule or government within a territory :

I mean by it [the State] that summation of privileges and dominating positions which are brought into being by extra-economic power... I mean by Society, the totality of concepts of all purely natural relations and institutions between man and man...

In the social sciences such as sociology society has been used[citation needed]to mean a group of people that form a semi-closed social system, in which most interactions are with other individuals belonging to the group.

According sociologist Richard Jenkins, the term addresses a number of important existential issues facing people:

1. How humans think and exchange information – the sensory world makes up only a fraction of human experience. In order to understand the world, we have to conceive of human interaction in the abstract (i.e., society). 2. Many phenomena cannot be reduced to individual behavior – to explain certain conditions, a view of something "greater than the sum of its parts" is needed. 3. Collectives often endure beyond the lifespan of individual members. 4. The human condition has always meant going beyond the evidence of our senses; every aspect of our lives is tied to the collective.


Evolution of societies

Gerhard Lenski, a sociologist, differentiates societies based on their level of technology, communication and economy: (1) hunters and gatherers, (2) simple agricultural, (3) advanced agricultural, (4) industrial.[3] This is somewhat similar to the system earlier developed by anthropologists Morton H. Fried, a conflict theorist, and Elman Service, an integration theorist, who have produced a system of classification for societies in all human cultures based on the evolution of social inequality and the role of the state. This system of classification contains four categories:

* Hunter-gatherer bands, which are generally egalitarian.
* Tribal societies in which there are some limited instances of social rank and prestige.
* Stratified structures led by chieftains.
* Civilizations, with complex social hierarchies and organized, institutional governments.
* Humanity, mankind, that upon which rest all the elements of society, including society's beliefs.

Over time, some cultures have progressed toward more-complex forms of organization and control. This cultural evolution has a profound effect on patterns of community. Hunter-gatherer tribes settled around seasonal foodstocks to become agrarian villages. Villages grew to become towns and cities. Cities turned into city-states and nation-states.


Characteristics of society

The following three components are common to all definitions of society:

* Social networks
* Criteria for membership, and
* Characteristic patterns of organization

Each of these will be explored further in the following sections.


Social networks

Social networks are maps of the relationships between people. Structural features such as proximity, frequency of contact and type of relationship (e.g., relative, friend, colleague) define various social networks.


Organization of society

Human societies are often organized according to their primary means of subsistence. As noted in the section on "Evolution of societies", above, social scientists identify hunter-gatherer societies, nomadic pastoral societies, horticulturalist or simple farming societies, and intensive agricultural societies, also called civilizations. Some consider industrial and post-industrial societies to be qualitatively different from traditional agricultural societies.

One common theme for societies in general is that they serve to aid individuals in a time of crisis. Traditionally, when an individual requires aid, for example at birth, death, sickness, or disaster, members of that society will rally others to render aid, in some form—symbolic, linguistic, physical, mental, emotional, financial, medical, or religious. Many societies will distribute largess, at the behest of some individual or some larger group of people. This type of generosity can be seen in all known cultures; typically, prestige accrues to the generous individual or group. Conversely, members of a society may also shun or scapegoat members of the society who violate its norms. Mechanisms such as gift-giving and scapegoating, which may be seen in various types of human groupings, tend to be institutionalized within a society.

Some societies will bestow status on an individual or group of people, when that individual or group performs an admired or desired action. This type of recognition is bestowed by members of that society on the individual or group in the form of a name, title, manner of dress, or monetary reward. Males, in many societies, are particularly susceptible to this type of action and subsequent reward, even at the risk of their lives. Action by an individual or larger group in behalf of some cultural ideal is seen in all societies. The phenomena of community action, shunning, scapegoating, generosity, and shared risk and reward occur in subsistence-based societies and in more technology-based civilizations.

Societies may also be organized according to their political structure. In order of increasing size and complexity, there are bands, tribes, chiefdoms, and state societies. These structures may have varying degrees of political power, depending on the cultural geographical, and historical environments that these societies must contend with. Thus, a more isolated society with the same level of technology and culture as other societies is more likely to survive than one in closer proximity to others that may encroach on their resources (see history for examples}. A society that is unable to offer an effective response to other societies it competes with will usually be subsumed into the culture of the competing society (see technology for examples).


Shared belief or common goal

Peoples of many nations united by common political and cultural traditions, beliefs, or values are sometimes also said to be a society (such as Judeo-Christian, Eastern, and Western). When used in this context, the term is employed as a means of contrasting two or more "societies" whose members represent alternative conflicting and competing worldviews (see Secret Societies).

Some academic, learned and scholarly associations describe themselves as societies (for example, the American Society of Mathematics. More commonly, professional organizations often refer to themselves as societies (e.g., the American Society of Civil Engineers, American Chemical Society). In the United Kingdom and the United States, learned societies are normally nonprofit and have charitable status. In science, they range in size to include national scientific societies (i.e., the Royal Society) to regional natural history societies. Academic societies may have interest in a wide range of subjects, including the arts, humanities and science.

In some countries (for example the United States and France), the term "society" is used in commerce to denote a partnership between investors or to start a business. In the United Kingdom, partnerships are not called societies, but cooperatives or mutuals are often known as societies (such as friendly societies and building societies). In Latin America, the term society may also be used in commerce denoting a partnership between investors, or anonymous investors; for example: "Proveedor Industrial Anahuac S.A." where S.A. stands for Anonymous Society (Sociedad Anónima); however in Mexico in other type of partnership it would be declared as S.A. de C.V.


Ontology

As a related note, there is still an ongoing debate in sociological and anthropological circles as to whether there exists an entity we could call society. Some Marxist theorists, like Louis Althusser, Ernesto Laclau and Slavoj Zizek, have argued that society is nothing more than an effect of the ruling ideology of a certain class system, and shouldn't be used as a sociological notion. Marx's concept of society as the sum total of social relations among members of a community contrasts with interpretations from the perspective of methodological individualism where society is simply the sum total of individuals in a territory.

Alternate Perspective

Although the discrepancy model has dominated the school system for many years, there has been substantial criticism of this approach (eg, Aaron, 1995, Flanagan and Mascolo, 2005) among researchers. One reason for this has been that diagnosing on the basis of the discrepancy does not predict the effectiveness of treatment. Low academic achievers who do not have a discrepancy with IQ (ie their IQ scores are also low) appear to benefit from treatment just as much as low academic achievers who do have a discrepancy with IQ. An alternative approach has been proposed, which is known as Responsiveness to Intervention. Under this model, children who are having difficulties in school are identified early - in their first or second year after starting school. They then receive additional assistance such as participating in a reading remediation program. The response of the children to this intervention then determines whether they are designated as having a learning disability. Those few who still have trouble may then receive designation and further assistance. Sternberg (1999) has argued that early remediation can greatly reduce the number of children meeting diagnostic criteria for learning disabilities. He has also suggested that the focus on learning disabilities and the provision of accommodations in school fails to acknowledge that people have a range of strengths and weaknesses and places undue emphasis on academics by insisting that people should be propped up in this arena and not in music or sports

Learning disability

In the United States and Canada, the term learning disability (LD) is used to refer to a range of neurological conditions that affect one or more of the ways that a person takes in, stores, or uses information. Learning disabilities are specific, not global, impairments. For example, a person could have an LD which inhibits her ability to understand written information though the same information, delivered orally, might present no problem. People with learning disabilities often have trouble processing information. Therefore, when asked a question, they cannot produce a quick response because it takes them more time to process the question, then find the answer.

The term includes such conditions as dysgraphia (writing disorder), dyslexia (reading disorder), dyscalculia (mathematics disorder) and developmental aphasia.

In the United Kingdom, the term learning disability is used more generally to refer to developmental disability.

Learning disabilities affect all areas of life to the extent that the affected mode is used in that area. They are most often noticed in school settings, where certain learning modes are employed more than others, causing the weaknesses caused by the LD to stand out. Learning disabilities are usually identified by school psychologists through testing of intelligence, academics and processes of learning.

Burial

Burial, also called interment and (when applied to human burial) inhumation, is the act of placing a person or object into the ground. Usually, this is accomplished by digging a pit or trench, placing the person or object in it, and refilling it with the soil that was dug out of it.
Objects are sometimes buried in order to hide them against removal or tampering. For cables and pipelines, burial provides protection and allows the convenience of walking or driving over them.
People are often buried after they die, for a variety of reasons. The rest of this article discusses human burial.