Dystopia is utopia's polarized mirror image. While utilizing many of the same concepts as utopia—for example, social stability created by authoritarian regimentation—dystopia reads these ideas pessimistically. Dystopia angrily challenges utopia's fundamental assumption of human perfectibility, arguing that humanity's inherent flaws negate the possibility of const…
Dystrophinopathies are progressive hereditary degenerative diseases (often called muscular dystrophies) of skeletal muscles due to an absence or deficiency of the protein dystrophin. Dystrophin and the associated proteins form a complex system that connects the intracellular cytoskeleton to the extracellular matrix. The normal operation of this system is critical for maintaining the integrity of t…
The number e, like the number pi, is a useful mathematical constant that is the basis of the system of natural logarithms. Its value correct to nine places is 2.718281828... The number e is used in complex equations to describe a process of growth or decay. It is therefore utilized in the biology, business, demographics, physics, and engineering fields. …
Eagles are large, diurnal birds of prey in the subfamily Buteonidae, which also includes buzzards and other broad-winged hawks. The buteonids are in the order Falconiformes, which also includes falcons, osprey, goshawks, and vultures. Like all of these predatory birds, eagles have strong, raptorial (or grasping) talons, a large hooked beak, and extremely acute vision. Eagles are broadly distinguis…
The human ear is the anatomical structure responsible for hearing and balance. The ear consists of three parts: the outer, middle, and inner ears. The outer ear collects sounds from the environment and funnels them through the auditory system. The outer ear is composed of three parts, the pinna (or auricle), the external auditory canal (or external auditory meatus), and the tympanic membrane (or e…
Earth is our home planet. Its surface is mostly water (about 70%), and it has a moderately dense nitrogen-and-oxygen atmosphere that supports life—the only known life in the Universe. Rich in iron and nickel, Earth is a dense, rocky ball orbiting the Sun with its only natural satellite, the Moon. A complete revolution of the earth around the Sun takes about one year, while a rotation on its…
It is approximately 3,950 mi (6,370 km) from Earth's surface to its center. Geologists understand the structure and composition of the surface by direct observation and by analysis of rock samples raised by drilling projects; however, the depth of drill holes and, therefore, the depth limit of scientists' ability to directly observe Earth's interior is severely limited. Even t…
Earth acts as a dipole magnet with the positive and negative magnetic poles near, but not aligned exactly with, the north and south geographic poles. Because of this difference, detailed maps commonly distinguish between true north and magnetic north. The difference, known as magnetic declination, must be taken into account when navigating with a magnetic compass. Its magnetic field also molds the…
All objects in the universe and our solar system move in space. The earth moves in two ways. It rotates like a top on its axis, an imaginary line through the north and south poles, and revolves in an orbit around the Sun. Centrifugal force results from the earth's rotation; without gravity, centrifugal force could cause objects to fly into space. Because the force of the earth's grav…
Befitting a dynamic Earth, the study of Earth science embraces a multitude of subdisciplines. At the heart of Earth science is the study of geology. Literally meaning "to study the Earth," traditional geological studies of rocks, minerals, and local formations have within the last century, especially in the light of the development of plate tectonic theory, broadened to include studi…
An earthquake is the shaking or vibration of Earth's surface as the result of sudden movement along a fault, the movement of molten rock within the Earth, or human activities. The terms temblor and seism are often used as synonyms for earthquake. The location of an earthquake source within the Earth is known as its focus, and the point on the Earth's surface directly above the focus …
Earwigs are long-bodied insects with chewing mouthparts and many-jointed antennae in the order Dermaptera. Earwigs have small, vestigial forewings modified into a wing case, but their membranous hind-wings are large, folded, and functional, although they are not often used for flying. Earwigs hatch into nymphs which closely resemble the adults, only they are much smaller. Metamorphosis in earwigs …
Eating disorders are psychological conditions that involve either overeating, voluntary starvation, or both. No one is sure what causes eating disorders, but researchers think that family dynamics, biochemical abnormalities, and society's preoccupation with thinness may all contribute. Eating disorders are virtually unknown in parts of the world where food is scarce and within less affluent…
The Ebola virus is one of a number of viruses that cause a devastating disease in humans and closely related species such as monkeys, gorillas, and chimpanzees. The disease is known as a hemorrhagic fever because of the massive internal bleeding caused by the viral infection. Most strains of Ebola hemorrhagic fever progresses quickly from the initial appearance of symptoms to resolution, which is …
Ebony (Diospyros spp., family Ebenaceae) are species of tropical hardwood trees favored for their hard and beautiful wood. Only the black or brown heartwood is used commercially. There are more than 300 species of ebony, ranging in size from shrubs to trees taller than 100 ft (30 m). The best commercial ebony comes from India, Madagascar, Nigeria, Zaire, and the Celebes Islands. Most species of eb…
Echiuroid worms, or echiurans, commonly called spoon worms, are soft-bodied, unsegmented, marine animals of worldwide distribution. The approximately 125 species in the phylum Echiura occur mostly in the shallow intertidal zone of oceans. Most burrow or form tubes in sand or mud. Some live in discarded shells of sea urchins and sand dollars. Others inhabit cracks and crevices in rocks or coral fra…
In the animal kingdom, echolocation is an animal's determination of the position of an object by the interpretation of echoes of sounds produced by the animal. Echolocation is an elegant evolutionary adaptation to a low-light niche. The only animals that have come to exploit this unique sense ability are mammals—bats, dolphins, porpoises, and toothed whales. It is now believed that t…
If the locus classicus of eclecticism was Diogenes Laertius' Lives of the Eminent Philosophers, the locus modernus was the Introduction to Stoic Philosophy (1604) of Justus Lipsius (1547–1606), who argued that the method of critical choosing or "election" was superior to the dogmas of particular schools and represented the true road to truth. From the second quarter of …
It is a coincidence of nature that the apparent size of the Sun and the Moon in the sky are about the same. Thus on those rare occasions when the orbital motion of Earth and Moon cause them to align with the sun, as seen from points on Earth, the Moon will just cover the surface of the Sun and day will suddenly become night. Those who are located in the converging lunar shadow that just reaches Ea…
Ecological integrity is a relatively new concept that is being actively discussed by ecologists. However, a consensus has not yet emerged as to the definition of ecological integrity. Clearly, human activities result in many environmental changes that enhance some species, ecosystems, and ecological processes, while at the same time causing important damage to others. The challenge for the concept…
Governments everywhere are increasingly recognizing the fact that human activities are causing serious environmental and ecological damage. To effectively deal with this environmental crisis, it is important to understand its dimensions and dynamics. What, specifically, are the damages, how are they changing over time, and what are the best means of prevention or mitigation? To develop answers to …
Ecological productivity refers to the primary fixation of solar energy by plants and the subsequent use of that fixed energy by plant-eating herbivores, animal-eating carnivores, and the detritivores that feed upon dead biomass. This complex of energy fixation and utilization is called a food web. Ecologists refer to the productivity of green plants as primary productivity. Gross primary productiv…
Ecological pyramids are graphical representations of the trophic structure of ecosystems. Ecological pyramids are organized with the productivity of plants on the bottom, that of herbivores above the plants, and carnivores above the herbivores. If the ecosystem sustains top carnivores, they are represented at the apex of the ecological pyramid of productivity. A fact of ecological energetics is th…
Ecology is commonly seen as a lineal descendant of traditional natural history extending back to such classical figures as Aristotle, Theophrastus, and Pliny. Notable persons in this tradition include the Swedish botanist, Carl von Linné (Carolus Linnaeus; 1707–1778), who coined the phrase "economy of nature" in 1749. Gilbert White (1720–1793), a British cleric, ma…
Ecology can be defined as the study of the relationships of organisms with their living and nonliving environment. Most ecologists are interested in questions involving the natural environment. Increasingly, however, ecologists are concerned about degradation associated with the ecological effects of humans and their activities. Ultimately, ecological knowledge will prove to be fundamental to the …
The term economics, from the Greek oikonomika, means a science or art of managing the household. In modern usage, it refers to the efficient allocation of scarce resources in the production, distribution, and consumption of goods and services to satisfy various desires. As a branch of knowledge, economics or economic science is the study of how to efficiently use limited resources—natural r…
The notion of ecosystem (or ecological system) refers to indeterminate ecological assemblages, consisting of communities of organisms and their environment. Ecosystems can vary greatly in size. Small ecosystems can be considered to occur in tidal pools, in a back yard, or in the rumen of an individual cow. Larger ecosystems might encompass lakes or stands of forest. Landscape-scale ecosystems comp…
An ecotone is a zone of transition between distinct ecological communities or habitats. Usually, the word is used to refer to relatively sharp, local transitions, also known as edges. Because many physical and chemical changes in the environment tend to be continuous, ecological transitions are often similarly gradual. For example, climate and precipitation change steadily across continents and up…
Edema is the accumulation of fluid in any given location in the body. Edema can result from trauma, as in a sprained ankle, or from a chronic condition such as heart or kidney failure. The word edema is from the Greek and means "swelling." The presence of edema can be an important diagnostic tool for the physician. A patient who is developing congestive heart failure often will devel…
A middle region, Southeast Asia, was influenced by Buddhism and Confucianism, resulting in a unique blended educational experience. From the eighteenth century on, as Western culture came into the region, Asia's educational practices in general underwent a sea change that resulted in a previously unknown level of uniformity. Regional diversity, however, remains visible, reflecting the diff…
The imperial state increased its expenditures on education during the Tang (618–906) and Song (960–1280) dynasties, when it created the first examination system for selecting officials. In addition, the rise of Buddhism in medieval China created charitable institutions for the common people, which included temple schools and monasteries, where many commoners—male and female&#x…
Global education, or global studies, is an interdisciplinary approach to learning concepts and skills necessary to function in a world that is increasingly interconnected and multicultural. The curricula based on this approach are grounded in traditional academic disciplines but are taught in the context of project-and problem-based inquiries. The learner examines issues from the vantage point of …
The shoen system declined due to the failure of the court nobility in the capitol to retain strong ties with outlying estates, and led to bushi (warrior) rule. Primarily, the warrior and the monk supported medieval education (1192–1603). In 1177, the daigakuryo burned and was not rebuilt. Because the Kamakura regime (1192–1333) was established upon a warrior code, despite the relativ…
What distinguishes the development of education in North America has been its cautious, halting, but nevertheless relentless movement toward universality and inclusivity, an impulse that owes much to the progressive ideals of the eighteenth-century Enlightenment and to the consequent development of liberal democracy on the continent. In the early twenty-first-century Canada and in the United State…
Eel grasses (or eelgrasses) are 18 species of herbaceous aquatic plants in the family Zosteraceae, 12 species of which are in the genus Zostera. However, some plant systematists have treated the eel grasses as a component of a much larger family, the pondweeds or Potamogetonaceae. Eel grasses have long, strap-like leaves that emerge from a thin rhizome growing in the surface sediment of the shallo…
El Niño and La Niña are disruptions of the oceanic and atmospheric systems of the equatorial Pacific Ocean that have far reaching effects on Earth's weather patterns. El Niño and La Niña do not change with the regularity of the seasons; instead, they repeat about every two to seven years. They are the extremes in an aperiodic, or irregular, cycle called the El Ni…
Elasticity is the ability of a material to return to its original shape and size after being stretched, compressed, twisted or bent. Elastic deformation (change of shape or size) lasts only as long as a deforming force is applied to the object, and disappears once the force is removed. Greater forces may cause permanent changes of shape or size, called plastic deformation. In ordinary language, a …
Rub a balloon or styrofoam drinking cup against a wool sweater. It will then stick to a wall (at least on a dry day) or pick up small bits of paper. Why? The answer leads to the concept of electric charge. Electromagnetic forces are one of the four fundamental forces in nature. The other three are gravitational, strong nuclear, and weak nuclear forces. The electromagnetic force unifies both electr…
An electric circuit is a system of conducting elements designed to control the path of electric current for a particular purpose. Circuits consist of sources of electric energy, like generators and batteries; elements that transform, dissipate, or store this energy, such as resistors, capacitors, and inductors; and connecting wires. Circuits often include a fuse or circuit breaker to prevent a pow…
Electric current is the result of the relative motion of net electric charge. In metals, the charges in motion are electrons. The magnitude of an electric current depends upon the quantity of charge that passes a chosen reference point during a specified time interval. Electric current is measured in amperes, with one ampere equal to a charge-flow of one coulomb per second. A current as small as a…
An electric motor is a machine used to convert electrical energy to mechanical energy. Electric motors are extremely important to modern-day life, being used in many different places, e.g., vacuum cleaners, dishwashers, computer printers, fax machines, video cassette recorders, machine tools, printing presses, automobiles, subway systems, sewage treatment plants and water pumping stations. The maj…
Electric vehicles (EV), vehicles whose wheels are turned by electric motors rather than by a mechanical gasoline-powered drivetrain, have been long touted as saviors of the environment due to their low pollution and high fuel efficiency. However, they have yet to take over the highways and byways. Thomas Davenport is credited with building the first practical EV in 1834, which was quickly followed…
An electrical power supply is a device that provides the energy needed by electrical or electronic equipment to perform their functions. Often, that energy originates from a source with inappropriate electrical characteristics, and a power supply is needed to change the power to meet the equipment's requirements. Power supplies usually change alternating current into direct current, raise o…
The electrical resistance of a wire or circuit is a way of measuring the resistance to the flow of an electrical current. A good electrical conductor, such as a copper wire, will have a very low resistance. Good insulators, such as rubber or glass insulators, have a very high resistance. The resistance is measured in ohms, and is related to the current in the circuit and voltage across the circuit…
Electricity is a natural phenomenon resulting from one of the most basic properties of matter, electrical charge. Our understanding of electrical principles has developed from a long history of experimentation. Electrical technology, essential to modern society for energy transmission and information processing, is the result of our knowledge about electrical charge at rest and electrical charge i…
The electrocardiogram, ECG or EKG, directly measures microvoltages in the heart muscle (myocardium) occurring over specific periods of time in a cardiac, i.e., a heartbeat, otherwise known as a cardiac impulse. With each heartbeat, electrical currents called action potentials, measured in millivolts (mV), travel at predictable velocities through a conducting system in the heart. The potentials ori…
An electroencephalogram, usually abbreviated EEG, is a medical test that records electrical activity in the brain. During the test, the brain's spontaneous electrical signals are traced onto paper. The electroencephalograph is the machine that amplifies and records the electrical signals from the brain. The electroencephalogram is the paper strip the machine produces. The EEG changes with d…
Electrolysis is the process of causing a chemical reaction to occur by passing an electric current through a substance or mixture of substances, most often in liquid form. Electrolysis frequently results in the decomposition of a compound into its elements. To carry out an electrolysis, two electrodes, a positive electrode (anode) and a negative electrode (cathode), are immersed into the material …
An electrolyte is a substance that will allow current to flow through the solution when dissolved in water. Electrolytes promote this current flow because they produce positive and negative ions when dissolved. The current flows through the solution in the form of positive ions (cations) moving toward the negative electrode and negative ion (anions) moving the positive electrode. Electrolytes can …
An electromagnetic field is an area in which electric and magnetic forces are interacting. It arises from electric charges in motion. Electromagnetic fields are directly related to the strength and direction of the force that a charged particle, called the "test" charge, would be subject to under the electromagnetic force caused by another charged particle or group of particles, call…
Electromagnetism is a branch of physical science that involves all the phenomena in which electricity and magnetism interact. This field is especially important to electronics because a magnetic field is created by an electric current. The rules of electromagnetism are responsible for the way charged particles of atoms interact. Some of the rules of electrostatics, the study of electric charges at…
In an electric circuit, electromotive force is the work done by a source on an electrical charge. Because it is not really a force, the term is actually a misnomer; it is more commonly referred to by the initials EMF. EMF is another term for electrical potential, or the difference in charge across a battery or voltage source. For a circuit with no current flowing, the potential difference is calle…
All atoms found in nature have a positively charged nucleus about which the negatively charged electrons move. The atom is electrically neutral and thus the positive electrical charge on the nucleus has the same magnitude as the negative charge due to all the electrons. The electrons are held in the atom by the attractive force exerted on them by the positively charged nucleus. They move very rapi…
The term electron cloud is used to describe the area around an atomic nucleus where an electron will probably be. It is also described as the "fuzzy" orbit of an atomic electron. An electron bound to the nucleus of an atom is often thought of as orbiting the nucleus in much the same manner that a planet orbits a sun, but this is not a valid visualization. An electron is not bound by …
Electronics is a field of engineering and applied physics that grew out of the study and application of electricity. Electricity concerns the generation and transmission of power and uses metal conductors. Electronics manipulates the flow of electrons in a variety of ways and accomplishes this by using gases, materials like silicon and germanium that are semiconductors, and other devices like sola…
Electrophoresis is a technique used for the separation of biological molecules based on their movement due to the influence of a direct electric current. The technique was pioneered in 1937 by the Swedish chemist Arne Tiselius for the separation of proteins. It has now been extended to the separation of many other different classes of biomolecules including nucleic acids, carbohydrates and amino a…