An acid-base indicator is not always a synthetic chemical. It is often a complex organic dye that undergoes a change in color when the pH of a solution changes over a specific pH range. Many plant pigments and other natural products are good indicators, and synthetic ones like phenolphthalein and methyl red are also available and widely used. Paper dipped in a mixture of several indicators and the…
Indicator species are plants and animals that, by their presence, abundance, lack of abundance, or chemical composition, demonstrate some distinctive aspect of the character or quality of an environment. For example, in places where metal-rich minerals occur at the soil surface, indicator species of plants can be examined to understand the patterns of naturally occurring pollution, and they can ev…
The term indigenismo encompasses a diverse array of intellectual production concerning the indigenous peoples of Latin America. The twentieth century in particular witnessed an explosion of literary, critical, and visual work on the figure of the Indian. It should be made clear from the outset that the term, although most closely associated with Mexico and Guatemala and especially with the Andean …
Individualism endorses the principle that the ends or purposes of the human individual possess dignity and worth that take precedence over communal, metaphysical, cosmological, or religious priorities. While individualism may appeal to certain metaphysical or epistemological schools of thought such as nominalism or empiricism, it will be treated here as primarily a moral and/or political doctrine.…
Industrial minerals is a term used to describe naturally occurring non-metallic minerals that are used extensively in a variety of industrial operations. Some of the minerals commonly included in this category include asbestos, barite, boron compounds, clays, corundum, feldspar, fluorspar, phosphates, potassium salts, sodium chloride, and sulfur. Some of the mineral mixtures often considered as in…
Industrial Revolution is the name given by the German socialist author Friedrich Engels in 1844 to changes that took place in Great Britain during the period from roughly 1730 to 1850. In general, those changes involved the transformation of Great Britain from a largely agrarian society to one dominated by industry. In a broader context, the term has also been applied to the transformation of the …
Inertial guidance is a navigation technology that monitors changes in location by measuring cumulative acceleration. In inertial guidance, the motion of the object in three-dimensional space is measured continuously. This enables a special computer to provide related real-time information about velocity (speed) and location. An inertial-navigation system (INS) does not use information from an exte…
The term infection refers to the state where a host organism has been invaded by another organism, typically a microorganism such as a virus, bacterium, protozoa, algae, or fungus. The invader is able to elude the responses of the host that are designed to kill it. Strategies include rapid multiplication, which can overwhelm the host defenses, or escaping from the host's immune system by mu…
Infertility is a couple's inability to conceive a child after attempting to do so for at least one full year. Primary infertility refers to a situation in which pregnancy has never been achieved. Secondary infertility refers to a situation in which one or both members of the couple have previously conceived a child, but are unable to conceive again after a full year of trying. Currently, in…
The term infinity conveys the mathematical concept of large without bound, and is given the symbol ∞. As children, we learn to count, and are pleased when first we count to 10, then 100, and then 1,000. By the time we reach 1,000, we may realize that counting to 2,000, or certainly 100,000, is not worth the effort. This is partly because we have better things to do, and partly because we re…
Inflammation is a localized, defensive response of the body to injury, usually characterized by pain, redness, heat, swelling, and, depending on the extent of trauma, loss of function. The process of inflammation, called the inflammatory response, is a series of events, or stages, that the body performs to attain homeostasis (the body's effort to maintain stability). The body's infla…
Influenza ("the flu") is a disease caused by the influenza virus. The disease is easily spread from person to person, typically by inhaling virus that has been expelled into the air by coughing or sneezing. The virus can also be spread by touch. For example, if someone touches a doorknob that has influenza viruses clinging to it and then touches their mouth, the virus can pass into t…
Throughout most of history astronomers were confined to using optical light, the light we can detect with our eyes. The advent of electronic detectors has, in the past few decades, opened up new vistas to astronomers, allowing them to utilize the entire electromagnetic spectrum. Infrared astronomers use traditional optical telescopes equipped with special detectors that can detect infrared light. …
Heredity plays a part in almost all diseases. Recent advances in gene research have allowed a steadily increasing number of specific genes and genetic factors to be linked to a wide variety of medical complaints. There are currently approximately 6,000 known genetic diseases. Those that result from simple mutations of single genes are often referred to as hereditary diseases, and they exhibit dist…
Strictly speaking, insectivores are any predators that catch and eat insects. Often, however, insectivorous predators also eat other small invertebrates, such as spiders, millipedes, centipedes, and earthworms. Some insectivores specialize in catching and feeding upon flying insects, sometimes called aeroplankton. Some prominent examples of this insectivorous feeding strategy include dragonflies, …
Insects are invertebrates in the class Insecta, which contains 28 living orders. This class of the phylum Arthropoda is distinguished by a number of anatomical features, including an adult body that is typically divided into three parts (head, thorax, and abdomen), three pairs of segmented legs attached to the thorax, one pair of antennae, and ventilation of respiratory gases through pores called …
An instinct is a stereotyped, species-typical behavior that appears fully functional the first time it is performed, without the need for learning. Such behaviors are usually triggered by a particular stimulus or cue, and are not readily modified by subsequent experience. For instance, a kangaroo rat instantly performs an automatic escape jump maneuver when it hears the sound of a striking rattles…
The integers are the positive and negative whole numbers... -4, -3, -2, -1, 0, 1, 2,.... The name "integer" comes directly from the Latin word for "whole." The set of integers can be generated from the set of natural numbers by adding zero and the negatives of the natural numbers. To do this, one defines zero to be a number which, added to any number, equals the same nu…
The integral is one of two main concepts embodied in the branch of mathematics known as calculus, and it corresponds to the area under the graph of a function. The area under a curve is approximated by a series of rectangles. As the number of these rectangles approaches infinity, the approximation approaches a limiting value, called the value of the integral. In this sense, the integral gives mean…
An integrated circuit (IC) is a single semiconducting chip that contains transistors and sometimes, capacitors, resistors, and diodes. These components are connected to create an electrical circuit. Integrated circuits can be found in almost all electronic devices today, including those in automobiles, microwave ovens, traffic lights, and watches. Just a few years ago, the circuits required to ope…
The integumentary system includes the skin and the related structures that cover and protect the bodies of plants and animals. The integumentary system of plants includes the epidermis, cuticle, plant hairs, and glands. The integumentary system of invertebrates includes shells and exoskeletons as body covering. The integumentary system of vertebrates comprises skin, scales, feathers, hair and glan…
An abundance of studies on the subject of intellectuals has focused on societal differences and disparate issues, and featured a wide array of eras, cultures, and practices. A comparison by Raymond Williams between the French tradition of the intellectual engaged in public issues and the more reserved role ascribed to his or her English counterpart attests to this difference among societies. It ha…
The notion of intercession (shafa'a) is present within Muslim religious tradition as well as Muslim and Middle Eastern social and political culture. Intercession implies a special intervention or act of patronage providing favors, power, victory, or, in the religious variety, redemption from the terrible fate of sinners. Although there have been some objections, historic and modern, to this…
The development of innovative and creative ideas in the academy is taking place in the early 2000s largely across departmental and disciplinary divides. Intradisciplinary practice tends to be microfocused and piecemeal. Innovation proceeds intradisciplinarily, where it proceeds at all, mostly in small if not minute increments. Departmental institutionalization itself has been transforming, prompte…
Interference is the interaction of two or more waves. Waves move along their direction of propagation characterized by crests and troughs. Wherever two or more waves, either from one source by different paths or from different sources, reach the same point in space at the same time, interference occurs. When the waves arrive in-phase (the crests arrive together), constructive interference occurs. …
Interferometry uses the principles of interference to determine properties about waves, their sources, or the wave propagation medium. Acoustic interferometry has been applied to study the velocity of sound in a fluid. Radio astronomers use interferometry to get accurate measurements of the position and properties of stellar Figure 1. The Michelson interferometer. Illustration by Hans & …
Interferons are species-specific proteins that induce antiviral and antiproliferative responses in animal cells. They are a major defense against viral infections and abnormal growths (neoplasms). Interferons are produced in response to penetration of animal cells by viral (or synthetic) nucleic acid and then leave the infected cell to confer resistance on other cells of the organism. Interferons …
The term internal colonialism defines a condition of oppression or subordination, often of one ethnic group over another (as in the subordination of Mexicans in the United States at the conclusion of the U.S.-Mexican War of 1846–1848). Some view the term as a contraposition to the claim that all people in the United States "are immigrants." For example, immigrant does not desc…
The invention and development of the internal combustion engine in the nineteenth century has had a profound impact on human life. The internal combustion engine offers a relatively small, lightweight source for the amount of power it produces. Harnessing that power has made possible practical machines ranging from the smallest model airplane to the largest truck. Electricity is often generated by…
The image of a peaceful, orderly world where men and nations resolve their differences without war, where the lion lies down with the lamb, has haunted humankind for millennia. Roman law expressed the gulf between the ideal and the reality concisely by contrasting the condition of man living under the ius naturale, the natural law, a world of peace and harmony, with the human condition as it actua…
The International Ultraviolet Explorer satellite (IUE) was a joint project of the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), and the Planetary Plasma and Atmospheric Research Center (PPARC) in the United Kingdom. NASA provided the spacecraft, telescope, spectrographs, and one ground observatory facility. ESA created the solar panels for powering the craf…
Internet messages (e-mail, instant messages, etc.) and file transfers leave an electronic trail that can be traced. Tracing is a process that follows the Internet activity backwards, from the recipient to the user. As well, a users Internet activity on web sites can also be tracked on the recipient site (i.e., what sites are visited and how often, the activity at a particular site). Sometimes this…
The problem of interpretation is as old as the written record, even as old as the capacity for human beings to disagree fundamentally. It was raised by Plato. It marked many a conflict in early Christendom. From the Middle Ages to early modernity, cultural texts proliferated. Interpretation was the task of those who were in charge of biblical exegeses and of those who judged a text's origin…
On a clear winter night go outside to a dark location and look for the constellation Orion, the hunter. A row of three stars makes up his belt. Hanging from his belt is his sword, a smaller row of three fainter stars. If you look at the center star in the sword with a pair of binoculars or a small telescope, you will see a small fuzzy patch of interstellar gas and dust, called the Orion Nebula. Sp…
Some species of plants, animals, and microorganisms have been spread by humans over much wider ranges than they occupied naturally. Some of these introductions have been deliberate and were intended to improve conditions for some human activity, for example, in agriculture, or to achieve aesthetics that were not naturally available in some place. Other introductions have been accidental, as when p…