Cylinder (geometry)
A cylinder (from Greek κύλινδρος – kulindros, "roller, tumbler") is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given straight line, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder. The surface area and the volume of a cylinder have been known since deep antiquity.
Common use
In common use a cylinder is taken to mean a finite section of a right circular cylinder, i.e., the cylinder with the generating lines perpendicular to the bases, with its ends closed to form two circular surfaces, as in the figure (right). If the ends are not closed, one obtains an open cylinder, whose surface is topologically equivalent to an open annulus.
Volume
If the cylinder has a radius r and length (height) h, then its volume is given by
Having a right circular cylinder with a height h units and a base of radius r units with the coordinate axes chosen so that the origin is at the center of one base and the height is measured along the positive x-axis. A plane section at a distance of x units from the origin has an area of A(x) square units where
Geometry (Ivo Perelman album)
Geometry is an album by Brazilian jazz saxophonist Ivo Perelman featuring American pianist Borah Bergman, which was recorded in 1996 and released on the English Leo label.
Reception
In his review for AllMusic, Alex Henderson says that "this CD doesn't quite fall into the 'essential' category... Nonetheless, Geometry is an enjoyable release that Perelman's more-devoted followers will want."
The Penguin Guide to Jazz notes that "Bergman is wily enough to find ways of both supporting and undercutting the mighty sound of the tenor."
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References
Geometric group action
In mathematics, specifically geometric group theory, a geometric group action is a certain type of action of a discrete group on a metric space.
Definition
In geometric group theory, a geometry is any proper, geodesic metric space. An action of a finitely-generated group G on a geometry X is geometric if it satisfies the following conditions:
Uniqueness
If a group G acts geometrically upon two geometries X and Y, then X and Y are quasi-isometric. Since any group acts geometrically on its own Cayley graph, any space on which G acts geometrically is quasi-isometric to the Cayley graph of G.
Examples
Cannon's conjecture states that any hyperbolic group with a 2-sphere at infinity acts geometrically on hyperbolic 3-space.
References
Geometry (Jega album)
Geometry is the second album by electronic musician Jega, released in 2000 on the Planet Mu label.
Track listing
External links
Rod (optics)
"Rods" (sometimes known as "skyfish", "air rods", or "solar entities") is a term used in cryptozoology, ufology, and outdoor photography to refer to elongated artifacts in the form of light-rods produced by cameras. Videos of rod-shaped objects moving quickly through the air were claimed by some ufologists and cryptozoologists to be alien life forms, "extradimensional" creatures, or very small UFOs. Subsequent experiments showed that these rods appear in film because of an optical illusion/collusion (especially in interlaced video recording), and are typically traces of a flying insect's wingbeats.
Optical analysis
Various paranormal interpretations appeared in the popular culture, and one of the more outspoken proponents of rods as alien life forms is Jose Escamilla, who claims to have been the first to film them on March 19, 1994 at Roswell, New Mexico, while attempting to film a UFO. Since then, Escamilla has made additional videos and embarked on lecture tours to promote his claims.
Rod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells. Rods are concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 90 million rod cells in the human retina. More sensitive than cone cells, rod cells are almost entirely responsible for night vision. However, because they have only one type of light-sensitive pigment, rather than the three types that human cone cells have, rods have little, if any, role in color vision (which is why colors are much less apparent in darkness).
Structure
Rods are a little longer and leaner than cones but have the same structural basis. The opsin or pigment is on the outer side, lying on the Retinal pigment epithelium, completing the cell's homeostasis. This epithelium end contains many stacked disks. Rods have a high area for visual pigment and thus substantial efficiency of light absorption.
Corporal punishment
Corporal punishment or physical punishment is punishment intended to cause physical pain on a person.
Common methods include spanking, paddling, caning and also bastinado. It can occur on minors but also on other individuals subjected to a right of corporal punishment such as prisoners in several countries or slaves in former times.
Official punishment for crime by inflicting pain or injury, including flogging, branding and even mutilation, was practised in most civilisations since ancient times. However, with the growth of humanitarian ideals since the Enlightenment, such punishments were increasingly viewed as inhumane. By the late 20th century, corporal punishment had been eliminated from the legal systems of most developed countries.
The legality in the 21st century of corporal punishment in various settings differs by jurisdiction. Internationally, the late 20th century and early 21st century saw the application of human rights law to the question of corporal punishment in a number of contexts:
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