In mathematics a quantity is said to be invariant if its value does not change following a given operation. For instance, multiplication of any real number by the identity element (1) leaves it unchanged. Thus, all real numbers are invariant under the operation of "multiplication by the identity element (1)." In some cases, mathematical operations leave certain properties unchanged. …
An exotic species is one that has been introduced into a habitat it would not normally populate. This introduction can be intentional or unintentional. Exotic species have also been called introduced, nonnative, nonindigenous, or alien species. An invasive species is an exotic species that thrives in its new environment, disrupting the natural ecosystem. The majority of exotic species have been in…
Invertebrates are animals without backbones. This simple definition hides the tremendous diversity found within this group which includes protozoa (single-celled animals), corals, sponges, sea urchins, starfish, sand dollars, worms, snails, clams, spiders, crabs, and insects. In fact, more than 98% of the nearly two million described species are invertebrates, ranging in size from less than a mill…
Ionization is the process in which one or more electrons are removed from an atom or molecule, thereby creating an ion. The word ionization is also used for the process in which an ionic solid, such as a salt, dissociates into its component ions upon solution. In order to remove an electron from an atom, enough energy must be supplied to break the bond between the negatively charged electron and t…
Ionizing radiation is any energy that causes the ionization of the substance through which it passes. As the radiation is emitted from a source, it detaches a charged particle from an atom or molecule, leaving the atom or molecule with an excess charge. This charged particle is called an ion. To remove an electron from an atom or molecule, the ionizing particles must have a kinetic energy exceedin…
The practice of diverting water from natural resources to crops has been practiced for at least 7,000 years. The earliest methods, as practiced in places like the areas surrounding the Nile river basin, included digging channels to allow water from the river during flood periods to reach cultivated fields along the river's banks. Ancient farmers also built dikes to help retain the water on …
After striking its roots in Egypt and in the far West, Islam was carried into the fringes of black Africa by indigenous tribesmen. Through the foundation of trading centers, the movement of populations, and the affiliation with local ruling elites, Muslim influence in the interior of the region was strongly felt. In their eleventh-century search for gold, Berber nomadic tribesmen reached the area …
A common misconception, based on the fact that Iran is today predominantly Shii, holds that Iran is the historic "homeland" of Shii Islam. However, the truth is that Medina and southern Iraq are the original centers of Shii Islam, which spread from there to other areas in the Muslim world. The heyday of the Shiis was in the tenth and eleventh centuries, when dynasties representing t…
The term Sunni is an adjective formed from the noun sunna (plural sunan), an ancient Arabic word meaning "customary practice." Although in the pre-Islamic world of tribal Arabia the word sunna referred generally to the time-tested and widely accepted customs of a tribe, in the Islamic period the term came to refer specifically to the customary practices or "way" of the …
Islam first developed and spread in a region of the world where urban civilizations had originated. Caravan routes crisscrossed the Fertile Crescent and the Arabian peninsula several millennia prior to the birth of Christianity, linking the urban-centered civilizations of Mesopotamia, the Nile Valley, and the Indian subcontinent. Overland routes were supplemented by water transit via the Red Sea a…
By contrast, the Shiite messianic vision was based upon the return of the Twelfth Imam (descended from the Prophet Muhammad), who went into occultation in 874. The Twelfth Imam will arise either in the east, as in the Sunni version, or in Mecca in some other versions and will similarly purify the Muslim world and take vengeance upon those who have oppressed the Shiites. However, in both the Sunni …
It was only in 661 at the accession of Mu'awiya that the Umayyad caliphate (661–750) became the first Islamic dynastic and caliphal monarchy. Knowledge of the Umayyad family is difficult to extract from the generally negative portrayal of them in later historical sources, but one criticism of them did highlight the fact that they were considered by some to be temporal kings (Ar., mul…
The mystical dimension of the Islamic religious tradition has roots in the divinely revealed text of the Koran. One passage often pointed to in this regard is the "Light Verse" (24:35), in which God is described as the Light of a blessed lamp, lit by a burning oil "neither of the East nor the West." One episode from the Koran, involving the prophet Moses, provided key e…
There are a number of mystical movements within Islam, but by far the dominant tradition is that of Sufism, one of the most dynamic and interesting dimensions of Islamic religious and cultural expression. Sufism is an umbrella term for a variety of philosophical, social, and literary phenomena occurring within the Islamic world. In its narrowest sense, the term refers to a number of schools of Isl…
All Muslims hold the Koran as the very word of God, who provides guidance and understanding of creation and proper human conduct by divine wisdom (hikma). This wisdom is also reflected in the oral statements of the prophet Muhammad collected in the Traditions (hadith) and in the reports of the life and deeds (sunna) of the Prophet. The study of these in the traditional Islamic religious sciences o…
Contemporary Islamic reform movements often trace their roots to the founding era of Islam. Several verses of the Koran encourage reform (islah), and a statement of the prophet Muhammad predicts that a renewer (mujaddid) will arise in each century to reform the community of Muslims. Among the scholars cited by various reform movements as fulfilling this prediction are Abu Hamid Muhammad al-Ghazali…
History of science in non-Western societies is often either disregarded—because it is not linked with that in Western societies—or disfigured into a member of a chain of transmission that links antiquity with Latin Christendom. Rather than attempt to fit Islamic science into the history or notions of Western science, this essay examines the relationships between various scientific di…
The Koran makes only passing reference to racial or ethnic categories. One verse refers to "the variety of your tongues and hues" as one of the many signs of God's divine power (30:22). Another proclaims the primacy of piety over racial or tribal distinction: "O mankind, we have created you male and female, and appointed you races and tribes, so that you may know one an…
An island is an area of land, smaller than a continent, that is entirely surrounded by water. That distinction, although somewhat artificial, suggests different geologic forces acting to create and maintain islands versus continents. Islands further differ from continents in their natural environments—in the biological systems they support, in their rate of response to change, in their abil…
Isobars are lines that connect points of equal atmospheric pressure on weather maps. Isobars are similar to height lines on a geographical map, and they are drawn so that they can never cross each other. Meteorologists use isobars on weather maps to depict atmospheric pressure changes over an area and to make predictions concerning wind flow. The term "isobar" originates from the Gre…
Isomer is the term used to describe two or more chemical compounds which can be represented by the same chemical formula. There are two main types of isomers: structural isomers which differ from one another by the attachment of atoms on the molecule; and stereoisomers which differ from on another by the location of the atoms in space. Chain isomerism, another type of structural isomerism, occurs …
An isotope is one of several kinds of atoms of the same element that have different masses. These atoms have the same number of protons in their nuclei, but different numbers of neutrons, and therefore different mass numbers. The term isotope comes from the Greek isos topos, which means same place, because isotopes of the same element have the same atomic number and therefore occupy the same place…
A narrow strip of land, an isthmus, connects two wider sections of land. The isthmus of Panama, which connects South America to Central/North America, and the Sinai peninsula, which connects Africa to Asia, illustrate better than any other examples. Moving plates create many isthmi (isthmuses). The earth's outer shell, the crust, breaks into sections, plates, that slowly slide around the ea…
Iteration consists of repeating an operation of a value obtained by the same operation. It is often used in making successive approximations, each one more accurate than the one that preceded it. One begins with an approximate solution and substitutes it into an appropriate formula to obtain a better approximation. This approximation is subsequently substituted into the same formula to arrive at a…
Jacanas are eight species of distinctive birds that inhabit the marshy edges of ponds, lakes, rivers, and swamps, and that make up the family Jacanidae. Jacanas are tropical birds, breeding in central and northern South America, sub-Saharan Africa, Madagascar, South and Southeast Asia, and Australasia. Jacanas do not migrate, but they may wander widely if their local aquatic habitats dry out. Jaca…
Jacks, also called scads, trevallys, and crevalles, are marine bony fishes living in open waters. Amberjacks, runners, and pompanos also belong to the same family Carangidae, order Perciformes. Jacks are swift, predatory fishes, found widely in warm and tropical seas. The younger fish tend to travel in vast schools, but the older ones may be solitary. Many jacks are valued for commercial and sport…
From the short-term horizon of the Heisei era (the name Heisei, meaning "peace everywhere," was introduced in 1989 by the emperor Akihito after the death of his father, the emperor Showa [Hirohito]), the other is still the West and more precisely the West as an idealized United States. However, a strong conviction that it is time for Japan to establish a new order has surfaced in the…
Jaundice is not a disease but a symptom of an underlying disease or condition. It is caused by too much bilirubin in the blood stream, and is characterized by yellowness of skin, sclera (white of eyes), mucous membranes, and of body fluids such urine and blood plasma. The resulting yellow color (jaune means yellow in French) is also described by the Latin term icterus. Most bilirubin, which is a r…
Jellyfish, also called medusae, are free-swimming, marine invertebrates in the class Scyphozoa (phylum Coelenterata). They have a gelatinous, translucent, dome-shaped body and occur most commonly in warm, tropical seas, although they are found in all the world's oceans. Jellyfish feed on small planktonic animals or fish which they sting and paralyze with special cells called nematocysts loc…
Jerboas are small kangaroo-like rodents with large hind legs that make up the family Dipodidae. Three species of jerboas occur in North Africa, and a number of other species occur in Asia. Jerboas are typically pale-colored, with large eyes, immense ears, a long tail, small front legs and paws, and distinctively large hind legs and feet, which are used for jumping. Although the body length of a ty…
The jet stream is a narrow, fast, upper atmospheric wind current, flowing at high altitudes around Earth. Although often erroneously applied to all upper-level winds, by definition jet stream wind speeds are in excess of 57 MPH (92 km/h). The jet stream may extend for thousands of miles around the world, but it is only a few hundred miles wide, and usually less than a mile thick. Undulating jet st…
Jihad, in Islam, is an idea of action. The Arabic word literally means "striving." When followed by the modifying phrase fisabil Allah, "in the path of God," or when this phrase is absent but assumed to be in force, jihad has the specific sense of fighting for the sake of God and religion. Other Arabic words are closely related in meaning and usage, including ribat, wh…
As a religion developing over three millennia, Judaism changed, diversified, and acculturated to many cultural and spiritual environments, while maintaining at the same time some basic characteristics. In the following, an attempt is made to describe both the continuities and the variations characteristic of the various forms of Judaism up to 1800. Four main concepts organize the majority of the d…
Juniper is the common name for a large group of evergreen shrubs and trees belonging to genus Juniperus, in the family Cupressaceae (Cypress), order Pinales (pine). There are more than 50 species of Juniperus. They can be low creeping ground cover, broad spreading shrubs, or tall narrow trees. Both low growing and tall varieties are cultivated for ornamental purposes. Junipers have thick, dense fo…
Jupiter, the fifth planet from the Sun, is the largest and most massive planet in our solar system. One of the gas giants, it is composed of mostly hydrogen and helium. The Jovian atmosphere provides a rich laboratory for the study of planetary atmospheres. Its most famous feature, the Great Red Spot, has been visible for hundreds of years, and many smaller features are visible in its atmosphere. …
Virtually everyone becomes involved in disputes about justice at some point. Sometimes our involvement in such disputes is rooted in the fact that we believe ourselves to be victims of some form of injustice, such as job discrimination; sometimes our involvement is rooted in the fact that others believe us to be the perpetrators or at least the beneficiaries of some form of injustice affecting the…
Justice appears as a paradoxical concept in the history of the United States. On the one hand, it has been absent as a rallying cry in the major struggles that have shaped, and continue to shape, the plurality of identities of the American nation. The concept "justice" is not prominent in the Declaration of Independence or in the Constitution. It was not the cornerstone of the abolit…
In what follows, central themes and institutions related to justice that appeared within Confucian and Daoist teachings in preimperial China will be explained and evaluated, followed by brief comments about later developments. …
The K-T event (Cretaceous-Tertiary event) refers to the mass extinction of the dinosaurs that took place approximately 65 million years ago (mya). In addition to the dinosaurs, most large land animals perished and an estimated 70% of species became extinct. In the early 1980s, a team of physicists and geologists documented a band sedimentary rock in Italy that contained an unusually high level of …