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An inflammation of the vermiform appendix. Acute appendicitis is the most common cause of emergency abdominal surgery, occurring in 5–6% of the population of the United States. Although about 80% of the individuals are between 5 and 35 years of age, the disease does occur in the very young as well as in the elderly. In the latter groups, the clinical picture is atypical, and frequently results in a significant delay in diagnosis with a higher incidence of complications. Acute appendicitis is rare in children less than 1 year of age.
Industry:Science
An informal assemblage of predominantly aquatic organisms that carry out oxygen-evolving photosynthesis but lack specialized water-conducting and food-conducting tissues. They may be either prokaryotic (lacking an organized nucleus) and therefore members of the kingdom Monera, or eukaryotic (with an organized nucleus) and therefore members of the kingdom Plantae, constituting with fungi the subkingdom Thallobionta. They differ from the next most advanced group of plants, Bryophyta, by their lack of multicellular sex organs sheathed with sterile cells and by their failure to retain an embryo within the female organ. Many colorless organisms are referable to the algae on the basis of their similarity to photosynthetic forms with respect to structure, life history, cell wall composition, and storage products. The study of algae is called algology (from the Latin <i>alga</i>, meaning sea wrack) or phycology (from the Greek <i>phykos</i>, seaweed).
Industry:Science
An informal group of Late Paleozoic and Early Mesozoic calcareous fossils of laminar, bulbous, and cabbagelike form and layered internal structure that formed reeflike bodies. The disjectoporids have been considered to be either hydrozoans or sponges and are similar in form, structure, and habitat to the Paleozoic stromatoporoids; however, they are separated from them and the “Mesozoic stromatoporoids” (sphaeractinids) by both time and basic structure. The typical genera <i>Disjectopora</i>, <i>Arduorhiza</i>(as <i>Carterina</i>) and <i>Irregulopora</i> were established by Waagen and Wentzel from Late Permian rocks of the Salt Range of Pakistan. Although some specimens of disjectoporids have been identified from Jurassic rocks, the youngest certain disjectoporids occur in Late Triassic beds.
Industry:Science
An informal set of flowering plant orders that contains Laurales, Magnoliales, Piperales, and Winterales, plus the monocotyledons, and in total contains roughly one-third of angiosperm species. Formerly, many have equated this group (minus the monocotyledons) to the subclass Magnoliidae, but studies of sequences of deoxyribonucleic acid (DNA) have demonstrated that orders such as Nymphaeales and Ranunculales are distantly related to the others and that the monocotyledons are much closer. A formal taxonomy for this group is not yet feasible because until more data are collected the exact relationships of the eumagnoliids to the eudicots are not clear, and before formal names are proposed it is preferable to understand these taxa better. The eumagnoliids, including the monocotyledons, exhibit a set of characteristics that reflect their relatively close relationships; these include a tendency to trimerous flowers and a suite of chemical compounds restricted to the group. They also have a set of traits that are “primitive” by most estimations; these include vesselless wood, laminar stamens, and laminar placentation. It now seems quite clear that although the eumagnoliids exhibit some primitive traits they are neither the most archaic nor the earliest of angiosperms, and they contain some of the most advanced taxa, such as many of the monocotyledons (grasses, palms, and orchids).
Industry:Science
An information-processing device that consists of a large number of simple nonlinear processing modules, connected by elements that have information storage and programming functions. The field of neural networks is an emerging technology in the area of machine information processing and decision making. This technology makes extensive use of the terminology and methods of artificial intelligence. The main thrusts are toward highly innovative machine and algorithmic architectures, radically different from those that have been employed in conventional digital computers, and toward overcoming the major technological shortcomings and inherent limitations imposed by the traditional information-processing machines. The information-processing elements and components of neural networks, inspired by neuroscientific studies of the structure and function of the human brain, are conceptually simple. Three broad categories of neural-network architectures have been formulated which exhibit highly complex information-processing capabilities. Several generic models have been advanced which offer distinct advantages over traditional digital-computer implementation. Neural networks have created an unusual amount of interest in the engineering and industrial communities by opening up new research directions and commercial and military applications.
Industry:Science
An infraclass of Mesozoic reptiles that are, without exception, adapted to the marine environment. The infraclass includes the nothosaurs, plesiosaurs, and placodonts. These reptiles, along with the ichthyosaurs, played a significant role as predators within the marine animal community of the Mesozoic Era.
Industry:Science
An infraclass of therian mammals including a single order, the Marsupialia. The Metatheria are distinguished from the Eutheria (the placental mammals) by numerous characters. The full metatherian dentition is I 5/4 C 1/1 Pm 3/3 M 4/4, for a total of 50 teeth. The braincase is small, the angular process of the mandible is inflected, and a pair of marsupial bones articulates with the pelvis. Almost all living marsupials have a pouch on the belly of the female in which the young are carried after birth. The Metatheria arose from unknown therians in the Cretaceous or earlier at about the same time as eutherian mammals. For a time the two groups evolved side by side, but the marsupials were unable to compete with the more progressive later placental forms and died out except in South America and Australia, where they were isolated by water barriers.
Industry:Science
An inherited disorder of red blood cells characterized by lifelong anemia and recurrent painful episodes. The sickle cell mutation is caused by a single nucleotide effecting a change in the β-globin gene, resulting in the substitution of valine for glutamic acid as the sixth amino acid of β-globin. The short circulatory survival of red blood cells that contain sickle cell hemoglobin S results in anemia, and their abnormal rigidity contributes to painful obstruction of small blood vessels.
Industry:Science
An instrument consisting of two thermometers which is used in the measurement of the moisture content of air or other gases. The bulb or sensing area of one of the thermometers either is covered by a thin piece of clean muslin cloth wetted uniformly with distilled water or is otherwise coated with a film of distilled water. The temperatures of both the bulb and the air contacting the bulb are lowered by the evaporation which takes place when unsaturated air moves past the wetted bulb. An equilibrium temperature, termed the wet-bulb temperature (<i>T</i><sub><i>W</i></sub>), will be reached; it closely approaches the lowest temperature to which air can be cooled by the evaporation of water into that air. The water-vapor content of the air surrounding the wet bulb can be determined from this wet-bulb temperature and from the air temperature measured by the thermometer with the dry bulb (<i>T</i><sub><i>D</i></sub>) by using an expression of the form <i>e</i> = <i>e</i><sub><i>SW</i></sub> − <i>aP</i> (<i>T</i><sub><i>D</i></sub> − <i>T</i><sub><i>W</i></sub>). Here <i>e</i> is the water-vapor pressure of the air, <i>e</i><sub><i>SW</i></sub> is the saturation water-vapor pressure at the wet-bulb temperature, <i>P</i> is atmospheric pressure, and <i>a</i> is the psychrometric constant, which depends upon properties of air and water, as well as on speed of ventilation of air passing the wet bulb.
Industry:Science
An instrument containing a transmitter for converting the acoustic signals of a person's voice to electrical signals, a receiver for reconverting electrical signals to acoustic signals, and associated signaling devices (the dial and alerter) for communicating with other persons using similar instruments connected to a network. The term “telephone” also refers to the complicated system of transmission paths and switching points, called the Public Switched Network (PSN), connected to this instrument. This article discusses only the instrument (also called a set); for a discussion of the telephone system .
Industry:Science
