Oval

An oval (from Latin ovum, "egg") is a closed curve in a plane which "loosely" resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition, which may include either one or two axes of symmetry. In common English, the term is used in a broader sense: any shape which reminds one of an egg.

The 3-dimensional version of an oval is called an ovoid.

Oval in geometry

The term oval when used to describe curves in geometry is not well-defined, except in the context of projective geometry. Many distinct curves are commonly called ovals or are said to have an "oval shape". Generally, to be called an oval, a plane curve should resemble the outline of an egg or an ellipse. In particular, the common traits that these curves have are:

Oval, London

Coordinates: 51°28′53″N 0°07′11″W / 51.4813°N 0.1197°W / 51.4813; -0.1197

Oval is a geographically small area of Kennington, south London, in the London Borough of Lambeth. It is situated 2.1 miles (3.38 km) to the south-east of Charing Cross. Oval straddles the border of south-west London and south-east London, and is where the postcode SE11 converges with the postcodes SW8 and SW9. Oval is best known for The Oval cricket ground, the home-ground of Surrey County Cricket Club.

Oval is within the borough constituency of Vauxhall. The Member of Parliament for the area is Kate Hoey of the Labour Party.

History

The land here was, from the seventeenth century, used for a market garden. The name "Oval" emerged from a street layout which was originated in 1790 but never completely built. The Montpelier Cricket Club leased ten acres of land from the Duchy of Cornwall in 1844, and Surrey County Cricket Club was formed soon thereafter at a meeting at the Horns Tavern (since demolished) on Kennington Park Road.

Oval (projective plane)

In mathematics, an oval in a projective plane is a set of points, no three collinear, such that there is a unique tangent line at each point (a tangent line is defined as a line meeting the point set at only one point, also known as a 1-secant). If the projective plane is finite of order q, then the tangent condition can be replaced by the condition that the set contains q+1 points. In other words, an oval in a finite projective plane of order q is a (q+1,2)-arc, or a set of q+1 points, no three collinear. Ovals in the Desarguesian projective plane PG(2,q) for q odd are just the nonsingular conics. Ovals in PG(2,q) for q even have not yet been classified. Ovals may exist in non-Desarguesian planes, and even more abstract ovals are defined which cannot be embedded in any projective plane.

Odd q

In a finite projective plane of odd order q, no sets with more points than q + 1, no three of which are collinear, exist, as first pointed out by Bose in a 1947 paper on applications of this sort of mathematics to statistical design of experiments.

Habitat

A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant, or other type of organism.A place where a living thing lives is its habitat. It is a place where it can find food, shelter, protection and mates for reproduction. It is the natural environment in which an organism lives, or the physical environment that surrounds a species population.

A habitat is made up of physical factors such as soil, moisture, range of temperature, and availability of light as well as biotic factors such as the availability of food and the presence of predators. A habitat is not necessarily a geographic area—for a parasitic organism it is the body of its host, part of the host's body such as the digestive tract, or a cell within the host's body.

Microhabitat

A microhabitat is the small-scale physical requirements of a particular organism or population.

Monotypic habitat

The monotypic habitat occurs in botanical and zoological contexts, and is a component of conservation biology. In restoration ecology of native plant communities or habitats, some invasive species create monotypic stands that replace and/or prevent other species, especially indigenous ones, from growing there. A dominant colonization can occur from retardant chemicals exuded, nutrient monopolization, or from lack of natural controls such as herbivores or climate, that keep them in balance with their native habitats. The yellow starthistle, Centaurea solstitialis, is a botanical monotypic-habitat example of this, currently dominating over 15,000,000 acres (61,000 km²) in California alone. The non-native freshwater zebra mussel, Dreissena polymorpha, that colonizes areas of the Great Lakes and the Mississippi River watershed, without its home-range predator control, is a zoological monotypic-habitat example. Even though its name may seem to imply simplicity as compared with polytypic habitats, the monotypic habitat can be complex.

Habitat (magazine)

Habitat is an American real estate magazine founded in 1982 and aimed at co-op boards, condominium associations, and related professionals such as attorneys and managing agents. The print magazine concentrates on the greater New York City metropolitan area while its Web site contains features for general-interest co-op/condo directors, residents, and buyers/sellers.

Publication history

Journalist Carol J. Ott founded what was then titled N.Y. Habitat in New York City in 1982, for a primary audience of co-op and loft owners/renters. The magazine had evolved from Ott's 1980-82 newspaper, The Loft Letter. Originally bimonthly, in 1997 the publication schedule increased to 11 times yearly, with one double-issue. As of 2011, Ott remains publisher and editor-in-chief. The operations manager is Jennifer Wu.

Editorial and art

Habitat publishes both human-interest feature stories, such as how a co-op board avoided a financial collapse, and how a motivated board put through an environmentally friendly initiative; service articles, such as those detailing guidelines for hiring a property management firm, illuminating group decision-making dynamics, studying implementation of solar or geothermal power, and reviewing methods of increasing building revenue; and advocacy journalism, such as stories about shoddy new construction and poor enforcement of building codes. Shorter pieces provide updates on co-op/condo legislation, judicial decisions, and policy trends.

Positive pressure enclosure

A positive pressure enclosure, also known as an isolation chamber, is a chamber used to provide a safe work environment for performing hot work in the presence of explosive gases or vapours. They are used most often in conjunction with the need for welding, and are often associated with the offshore oil industry.

A positive pressure enclosure works by providing a constant inflow of breathable atmosphere, which in turn causes gas to continuously leak out of the chamber. This outflow of gases prevents the ingress of explosive gases or vapours which are often present in such work locations. This constant outflow of gases from the chamber also serves to cleanse the air within of the undesirable gaseous by-products of the welding process. Most commercial versions of positive pressure enclosures are referred to by their manufacturers as habitats.

Operating principles

Flammability limits

Flammable gases are not generally explosive under all conditions, and indeed, must be present within specific ranges in order to be explosive, or flammable. Additionally, oxygen must be present. The flammability limits of gases are expressed in proportions to the other gases present. For example, for methane, the lower explosive limit (LEL) is 4.4% and the upper explosive limit (UEL) is 17%. A positive pressure enclosure works by making sure that the methane present in the work area never approaches the 4.4% LEL.