In zoology, an operculum is a lid or flap of skin covering an aperture, such as the gill slit cover of fish and larval amphibians and the horny calcareous operculum secreted by many gastropod molluscs, which closes the opening of the shell when the animal is inside. In botany an operculum is the cone-shaped lid of the capsule of mosses, which is forcibly detached to release the spores. Research Operculum
Paucituberculata is an order of Metatheria with just one family, Caenolestidae. The members are small, shrew-like animals with small eyes, and thick, grey or greyish-brown pelage. The margin of each upper lip is interrupted by a distinctive flap of skin. The tail is long but not prehensile, and the feet are not syndactylous. Females lack a pouch. Research Paucituberculata
The Abbe-Estlander operation is a type of skin graft which takes place on the mouth in the case of an injured lip. A flap of skin from the healthy lip is attached to the injured lip. Inside the flap of skin is a small artery that sends blood to the graft. After the graft has been accepted by the body the flap is removed. Research Abbe-Estlander Operation
A camera is a device used in photography for capturing photographic pictures or television pictures. The camera as we know it was originally known as the camera obscura, a device used for both projecting images on to paper for sketching, and on to sensitised paper for photography, in distinction from the camera lucida, which was a similar, portable device without an enclosed box, used solely for projecting an image on to paper for sketching.
Photographic cameras have been produced in a variety of forms, but the basic principal remains the same. A fast opening and closing flap, called a shutter, allows light to enter the body of the camera through a small hole, called the aperture, and fall upon a light sensitive medium; originally a paper, glass or plastic material impregnared with some chemical such as silver iodide, later an electronic light sensor.
Photographic cameras are divided into several types: compact, single lensreflex (SLR) and medium format being the most common. Compact cameras are generally simple to operate devices used to capture low quality, domestic photographs to serve as reminders of events. SLR cameras have lots of adjustable settings and detachable lenses to allow a multitude of different lenses to be fitted for long distance and close-up photography and are widely used by professional photographers. Medium format cameras use a relatively large light sensitive medium to produce very high quality large prints, and are sometimes used by portrait photographers. Research Camera
A clack valve or flap valve is a type of valve employed for pumps. It consists of a metal disk, or a weighted disk of leather or rubber, hinged at one side, making contact with a flat metal seat. Research Clack Valve
For a heavier-than-air aircraft to fly, it must generate a lifting force equal to or greater than its weight, and (for powered flights) sufficient power to overcome its drag. The aircraft must also be stable in flight, and for most purposes it must be possible to control direction and attitude of flight. Balloons and airships (lighter-than-air aircraft) exploit Archimedes' principle, whereby a body immersed in a fluid experiences a lifting force equal to the weight of fluid it displaces. The envelope of a balloon or air-ship displaces a large amount of air, but it is filled with a gas lighter than the surrounding air, so it experiences an appreciable lifting force. A heavier-than-air aeroplane obtains its lift from its wings. An aircraft wing is essentially a plate presented edgewise to a moving air-stream (produced by the aeroplane's forward motion), with the leading edge slightly higher than the trailing edge. A component of the air pressure on this inclined plate creates lift; the rest causes drag. The lift generated by such an inclined plate can be experienced by holding your hand out of the window of a moving vehicle. The upward force on the hand is intermittent and slight because the hand's poor aerodynamic shape causes air turbulence and large amounts of drag, but the air-flow around the streamlined, aerofoil cross-section of an aircraft wing is much smoother, drag is minimized, and lift maximized.
The lift-to-drag ratio is a measure of aerodynamic efficiency. The overall shape of an aircraft wing also affects its lifting capabilities. A convenient measure of a wing's shape is its aspect ratio, defined as the square of the wing span divided by wing area. Wings with a high aspect ratio (long and thin) produce more lift: they are used for long-range, high-altitude, relatively slow aircraft, and for sailplanes. Low aspect-ratio wings (short and broad) tend to be used in fast, highly manoeuvrable aircraft. The types of aerofoil used in aircraft wings are inherently unstable, in that the lifting force is produced behind the wing's centre of gravity. A turning effect is thus produced that tends to force the nose of the aircraft downwards. In most aircraft designs a small tail fin situated well back from the wing produces a negative lift to counteract this turning force. An alternative, recently used on some military aircraft, is a lifting surface (canard) forward of the wings. Aircraft with a canard are inherently unstable, and require advanced electronic control systems to confer artificial stability. In order to manoeuvre an aircraft and to maintain its stability in level flight it is necessary to be able to control pitch, yaw, and roll. Pitch is usually controlled by flaps (elevators) on the rear of the horizontal tail. Yaw is controlled by the rudder, a flap on the vertical tail fin. Roll is controlled by ailerons on the outer trailing edges of the wings - to produce or correct roll, one aileron is lowered while the other is lifted. The rudder and ailerons are used together when banking (turning). Spoilers, retractable flaps that 'spoil' the lift of the wing, may be used in combination with or instead of ailerons to control roll; they also increase drag.
The amount of lift generated by an aircraft is proportional to the square of air-speed, which means that at high speeds, wings generate much more lift than at the low speeds of take-off and landing. Extra lift can be generated by increasing the angle of incidence of the wing to the air-flow (by lifting the nose), but beyond a certain point the smooth flow of air across the wing breaks down, lift is lost and drag is increased, a phenomenon known as wing stall. The design of modern high-speed aircraft is such that they cannot be flown slowly. Various devices are needed to enable such aircraft to take off and land at speeds that do not require excessively long runways. Slats on the leading edge of the wing and various flaps on the trailing edge provide an optimised arrangement by which the lift of the wing is maximized without unacceptable increases in drag. A propulsive system is needed to produce forward motion in an aeroplane; this may be an engine- or turbine-driven propeller, or a jet engine. At take-off, the engine's thrust generates forward motion, and the resulting air-flow over the wings generates lift in excess of the total weight of the machine. Research Principles of Manned Flight
The 66 Pattern DPM Jacket is a British army, padded, camouflaged combatjacket with a front zip fastening and button own storm flap. The 66 Pattern DPM Jacket has a drawstring waist and hem, numerous pockets including poachers pockets, and a collar that can be worn down or standing up. A hood can also be fitted. Research 66 Pattern DPM Jacket
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Operculum
