The octet rule allows chemists to predict the placement of electrons around the nucleus (electron orbitals), the identification of electrons added or lost during chemical reactions, and the chemical reactivity of atoms based upon their particular electron configuration. The octet rule is used when drawing Lewis dot structures and disgraming electron configurations. The octet rule is used to descri…
The octopus is an invertebrate in the class Mollusca (the molluscs), which also includes snails, clams, and squid. Octopi are cephalopod molluscs which are generally considered to be the most advanced members of the class. There are about 220 species of octopus. Octopi are found in every ocean of the world, ranging in size from a tiny Philippine species barely an inch across to giant specimens tha…
Ohm's law is a relationship between the voltage across an electric circuit, the electrical resistance in the circuit, and the current in the circuit. This law is named after its discoverer, Georg Simon Ohm. Ohm found that for most electric circuits, the voltage across the circuit was equal to the current flowing through the circuit times the electrical resistance of the circuit. For the sam…
Petroleum is a critically important natural resource. However, petroleum is often mined in places that are far away from the regions where most of its consumption occurs. Accordingly, petroleum must therefore be transported in large quantities, mostly by oceanic tankers, barges on inland waters, and both subsea and overland pipelines. Any of these transportation systems can release pollution throu…
Oil and natural gas has been found in geologic strata of Earth from the surface to depths exceeding 30,000 ft (9,144 m). Bogs and seeps in the ancient world were the initial source of oil and gas. As advancing economic systems and industries emerged with the development of nations and expanding populations, the need for plentiful and more efficient sources of energy were required. Hydrocarbon base…
An omnivore is any animal that is a generalist feeder, consuming a wide variety of foods that can include both animal and plant matter. Because they have attributes of both carnivores and herbivores, omnivores have relatively diverse linkages within ecological food webs. Some examples of omnivorous animals are pig and bear, both of which will eat a remarkably wide range of plant and animal product…
In mathematics, one-to-one correspondence refers to a situation in which the members of one set (call it A) can be evenly matched with the members of a second set (call it B). Evenly matched means that each member of A is paired with one and only one member of B, each member of B is paired with one and only one member of A, and none of the members from either set are left unpaired. The result is t…
Many software programs must be purchased from a vendor. The purchase price entitles the buyer to the benefits of the functional software. The program code that makes these performance features possible (the source code), however, usually remains known only to the company that designed the software. Open source software runs counter to this philosophy. As its name implies, in open source software, …
The American or common opossum (Didelphis marsupialis) is the only member of the order Marsupialia to occur naturally in North America. The American opossum occurs from southern Ontario through to most of South America. The only other member of its genus is D. azarae, which occurs through much of South America. However, other genera and species of the family Didelphidae, the New World opossums, oc…
Opportunistic species of animals or plants are adapted to exploit newly available habitats or resources and are typically found in unpredictable, transient, and variable environments. For example, clear-cut forests create well-lit open areas which are colonized rapidly by the windbone seeds of opportunistic species of plants, many of which are regarded as weeds by farmers and gardeners. Besides pr…
Almost from the invention of the laser, researchers were considering the possibilities of optical data storage. Throughout the 1960s and 1970s, a number of companies were at work on optical data storage systems, held back in large part by the cost and performance level of available lasers. In 1982, Sony Corp. revolutionized the music industry with the introduction of the compact disc (CD). CD-ROM …
Optics is the branch of physics that is concerned with visible light and its properties. Physicists who focus on optics study the properties of light. They also apply these properties to phenomena such as color, mirrors, and lenses. Geometrical optics treats light phenomena (e.g., the determination of focal points, image characteristics, etc.) through calculations derived from the geometry of rays…
The challenge of reconstructing the history of nonliterate or preliterate societies makes necessary the study and interpretation of oral traditions. Many such societies have gone to great extents to preserve and transmit the knowledge of their past in oral forms. The phrase oral traditions refers to folklore, legends, tales, taboos, and stories through which knowledge of the past is preserved and …
For the vast majority of human history, the only way people could transmit information has been by speaking, listening, and remembering. Indeed, the capacity for speech and the connected capacities for learning and remembering might be thought of as the defining elements of human consciousness, shared perhaps with other, now extinct, members of the hominid lineage but not shared with any other exi…
An orbit is the path followed by a celestial body moving in a gravitational field. When a single object, such as a planet, is moving freely in a gravitational field of a massive body, such as a star, the orbit is in the shape of a conic section, that is, elliptical, parabolic, or hyperbolic. Most orbits are elliptical. The exact path and position of an object in space can be determined by taking i…
The number 8 can be used in three ways: to tell "how many," to tell "where" in a ranking, and to name someone or something. The girl with the number 8 on her baseball uniform, who is 8th in the batting order, playing on a team that scores 8 runs, is using the same number in each of these ways. When she is 8th in the batting order, she is using the number as an ordinal n…
Ore is metalliferous rock that can be mined and processed at a profit. Although a broader definition includes nonmetallic rocks like rock salt and gypsum, most geologists classify these materials as industrial rocks and minerals. Unlike products from the forest and farm, ores are a nonrenewable resource. The economic survival of industrial societies is linked to the discovery of new supplies of me…
An organ is a functional structure of multicellular organisms which consists of a group of several different tissues. Many multicellular organisms have individual cells grouped together into tissues, a group of many associated cells with similar function; tissues grouped together into organs, a group of tissues interacting so as to form a functional unit; and organs grouped together into organ sys…
Organelles are internal cellular structures that perform dedicated functions. Oraganelles includes tructures such as ribosomes, mitochondria, chloroplasts (the site of photosynthesis in plants and other photosynthesizing organisms), endoplasmic reticulum (ER), Golgi apparatus, and lysosomes. The mitochondrion of all eukaryotes and the chloroplasts of plant cells are the only organelles that have t…
An organism is any individual living entity. Organisms range in size and complexity from microorganisms to multicellular plants and animals. Modern biologists classify Earth's organisms into five kingdoms on the basis of common patterns of the design of life, that is, in their cellular and sub-cellular organization, metabolism, reproduction, and behavior. Listed in order of their earliest a…
Organogensis refers to that period of time during development when the organs are being formed. After an egg has been fertilized, and has been implanted in the uterus, the developing form is known as the embryo. Organogenesis takes place during this embryonic phase. In fact, most organogenesis has begun as early as week five in humans (remember that a normal human pregnancy lasts an average of 40 …
In the human body an organ is composed of two or more different histological types of tissue that work together to carry out a complex function. An organ system consists of a group of organs that perform intricate functions necessary for the survival of an organism. Sometimes an organism can survive with an impaired or nonfunctioning organ. However, when a whole system of organs shuts down, the li…
The Arab-American political activist and professor of European literature Edward Said (1935–2003) durably redefined the term Orientalism with the publication in 1978 of his book by the same name. Before Said's book, Orientalism had two distinct meanings. Both were politically neutral and marginal to the central concerns of the humanities and social sciences. After Said's Orien…
There is not direct fossil-like evidence of how life originated on Earth, the molecular processes that preceded the appearance of cells do not leave such tangible evidence. However, fossils of single-celled microorganisms are present in rocks 3.0–3.5 billion years old (with some scientific controversy over which rocks contain the oldest true bacterial fossils), and chemical traces in Greenl…
The true or forest orioles include 28 species of medium-sized birds that make up the family Oriolidae. These birds occur in Africa, Europe, Asia, Southeast Asia, the Philippines, New Guinea, and Australia. Their usual habitats are forests, open woodlands, and savannas. Most species are tropical, but some migratory species occur in temperate regions. Orioles are jay-sized birds with long, pointed w…
Ornithology is the branch of zoology that deals with the study of birds. Birds are any organisms in the class Aves. They are warm-blooded (or homoiothermic) vertebrates that have feathers covering their body; forelimbs modified into wings; stouter hindlimbs used for walking, swimming, or perching; scaly legs and feet; jaws reduced to a toothless beak; and a four-chambered heart. Birds lay hard-she…
The very suggestion of a unified tradition implicit in the idea of the word orthodox renders its meaning problematic for the simple reason that conceptions of any religion's traditions are notoriously pluralist. Moreover, the term is hardly universal, since it is seldom applied to indigenous traditions around the world, even though there are some beliefs and practices within each aboriginal…
Orthopedics is the branch of medicine that specializes in diseases and injuries of bones. It is a specialty devoted to the diagnosis, treatment, rehabilitation and prevention of injuries and diseases of your body's musculoskeletal system. This complex system includes your bones, joints, ligaments, tendons, muscles, and nerves. Once devoted to the care of children with spine and limb deformi…
The term orthopraxy means "right practice," and stands as a contrast term for orthodoxy "right belief." It is often said of Asian traditions generally that—in contrast to most Western traditions—right practice is of more importance that right belief, and to a certain extent this is true. For instance, Confucianism is primarily concerned with the rituals an…
The oryx (Oryx gazella) is a species of antelope in the family Bovidae. Oryx are native to a rather wide range, extending from the Middle East through much of Africa. There are eight recognized subspecies of oryx, which vary greatly in body and horn shape, and in habitat A herd of scimitar-horned oryx. Photograph by Yav Levy. Phototake. Reproduced by permission. requirements. In some tax…
In an oscillating chemical reaction, the concentrations of the reactants and products change with time in a periodic or quasi-periodic manner (i.e., they do not move directly or evenly toward their final concentrations). Chemical oscillators exhibit chaotic behavior, in which concentrations of products and the course of a reaction depend on the initial conditions of the reaction. Oscillating react…
An oscillation is a particular kind of motion in which an object repeats the same movement over and over. It is easy to see that a child on a swing and the pendulum on a grandfather clock both oscillate when they move back and forth along an arc. A small weight hanging from a rubber band or a spring can also oscillate if pulled slightly to start its motion, but this repeated motion is now linear (…
An oscilloscope is an instrument that provides a graphical display of electrical signals. It presents a considerable amount of information about the operation of a circuit almost instantly, and the visual nature of the display provides insights that tables of numbers do not offer. Oscilloscopes are extremely useful for monitoring and diagnosing electrical circuits or devices. Though it can plot an…
Osmosis is the movement of solvent, such as water, through a barrier from a less concentrated solution into a more concentrated solution. It occurs when two solutions are separated by a semipermeable membrane which allows only the solvent to pass through. Osmosis plays a major role in the chemistry of living things and also has applications in medicine and technology. Osmosis was first described i…
Osmosis is the movement of water across a membrane which is selectively permeable. In osmosis, water moves across a membrane from a region with low solute concentration to a region with high solute concentration. Thus, osmosis tends to equalize the solute concentrations in two separate membrane-enclosed regions. In living cells, water moves by osmosis across membranes between cells or between memb…
Ossification is the process of the synthesis of bone from cartilage. There are two types of ossification—intramembranous and endochondral ossification. Bone may be synthesized by intramembranous ossification, endochondral ossification, or a combination of the two. Intramembranous ossification is the transformation of the mesenchyme, cells of an embryo into bone. During early development of …
All epistemological and hermeneutical investigations are predicated on the observation that the human self, like all objects around a person, gains an understanding of its identity through the binary opposition of self and other. No value can be established for any element in the material and abstract world without the differentiation from "the Other." The famous linguist Ferdinand …
Otter shrews are small otter-like aquatic mammals in the family Tenrecidae, with silvery fur. The three species of otter shrews belong to the order Insectivora, and all live in west and central Africa near the equator. The Potamogalidae family includes two genera—Micropotamogale and Potamogale. These genera contain a total of three distinctive species of otter shrew—the giant African…
Otters are small to medium-sized mammals with a long body, flattened head, broad muzzle, and long stiff whiskers. Their tail is strong, long, flattened, and somewhat tapered. Otters have short legs and webbed toes; they are well adapted to a semi-aquatic existence and are skilled swimmers. The outer fur of otters is short, very dense, and highly water resistant. They also have a layer of soft unde…
When weathering and erosion expose part of a rock layer or formation, an outcrop appears. An outcrop is the exposed rock, so named because the exposed rock "crops out." Outcrops provide opportunities for field geologists to sample the local geology—photograph it, hold, touch, climb, hammer, map, sniff, lick, chew, and carry it home. Classes often visit outcrops to see illustra…
The ovarian cycle is a series of events in the ovaries that occur during and after the maturation of the oocyte (egg or ovum). During their reproductive years, nonpregnant females usually experience a cyclical sequence of changes in their ovaries and uterus. Each cycle takes about one month and involves both oogenesis, the process of formation and development of oocyte, and preparation of the uter…
Ovenbirds are 200 species of birds that compose the rather large family Furnariidae, occurring from southern Mexico through Central and all of South America. Ovenbirds occur in a wide variety of habitats, ranging from mature tropical forests to semi-desert, and from coastal lowlands to alpine tundra. In other words, the ovenbird family is very rich in species, and these birds successfully exploit …