3D computer graphics

With the birth of workstation computers came 3D computer graphics, based on vector graphics. Instead of the computer storing information about points, lines, and curves on a 2-dimensional plane, the computer stores the location of points, lines, and, typically, faces in 3-dimensional space.

3-dimensional polygons are the lifeblood of virtually all 3D computer graphics. As a result, most 3D graphics engines are based around storing points, lines that connect those points together, faces defined by the lines, and then a sequence of faces to create 3D polygons.Modern-day computer graphics software goes far beyond just the simple storage of polygons in computer memory. Today's graphics are not only the product of massive collections of polygons into identifiable shapes, but they also result from techniques in shading, texturing, and rasterization.

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Biodiversity

Biodiversity or biological diversity is the diversity of life. There are a number of definitions and a measure of biodiversity.Biodiversity has no single standard definition. The most basic definition is "variation of life at all level of biological organization". Another definition holds that biodiversity is a measure of the relative diversity among organisms present in diverse ecosystems. "Diversity" in this definition includes diversity within a species and among species, and comparative diversity among ecosystems.

A third definition that is often used by ecologists is the "totality of genes, species, and ecosystems of a region". An advantage of this description is that it seems to describe most circumstances and present a unified view of the traditional three levels at which biodiversity has been identified:The 1992 United Nations Earth Summit in Rio de Janeiro defined "biodiversity" as "the changeability among living organisms from all sources, including, 'inter alia', terrestrial, marine, and other aquatic ecosystems, and the ecological complexes of which they are part: this includes diversity within species, between species and of ecosystems".

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Perception of sound

Sound is perceived through the sense of hearing. Humans and many animals use their ears to hear sound, but loud sounds and low frequency sounds can be supposed by other parts of the body through the sense of touch. Sounds are used in several ways, most notably for announcement through speech or, for example, music. Sound can also be used to acquire information about properties of the neighboring environment such as spatial characteristics and presence of other animals or objects. For example, bats use echolocation, ships and submarines use sonar, and humans can determine spatial information by the way in which they perceive sounds.

The range of frequencies that humans can hear well is between about 20 Hz and 16,000 Hz. This is by description the hearing range, but most people can hear above 16,000 Hz provided the sound pressure level is above the hearing threshold level. At 40,000 Hz and higher frequencies, for instance, this level is about 140 dB. The audible range varies by individual and, mostly in the upper part of the range, hearing damage accumulates with age. The ear is most sensitive to frequencies around 3,500 Hz. Sound above the hearing range is known as ultrasound and that below the hearing range as infrasound.

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