Friday, July 27, 2007
In geography
Geographical space is called land, and has a relation to ownership. While some cultures assert the rights of the individual in terms of ownership, other cultures will identify with a communal approach to land ownership, while still other cultures, rather than asserting ownership rights to land, invert the relationship and consider that they are in fact owned by the land. Spatial planning is a method of regulating the use of space at land-level, with decisions made at regional, national and international levels. Space can also impact on human and cultural behaviour, being an important factor in architecture, where it will impact on the design of buildings and structures, and on farming.
Ownership of space is not restricted to land. Ownership of airspace and of waters is decided internationally. Other forms of ownership have been recently asserted to other spaces — for example to the radio bands of the electromagnetic spectrum or to cyberspace.
Public space is a term used to define areas of land is collectively owned by the community, and managed in their name by delegated authorities. Such spaces are open to all, while private property is the land owned by an individual or company, for their own use and pleasure.
Abstract space is a term used in geography to refer to a hypothetical space characterized by complete homogeneity. When modeling activity or behavior, it is a conceptual tool used to limit extraneous variables such as terrain.
Ownership of space is not restricted to land. Ownership of airspace and of waters is decided internationally. Other forms of ownership have been recently asserted to other spaces — for example to the radio bands of the electromagnetic spectrum or to cyberspace.
Public space is a term used to define areas of land is collectively owned by the community, and managed in their name by delegated authorities. Such spaces are open to all, while private property is the land owned by an individual or company, for their own use and pleasure.
Abstract space is a term used in geography to refer to a hypothetical space characterized by complete homogeneity. When modeling activity or behavior, it is a conceptual tool used to limit extraneous variables such as terrain.
Sunday, July 22, 2007
Rod cells
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of photoreceptor, cone cells. Since they are more light-sensitive, rods are responsible for night vision. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. There are about 100 million rod cells in the human retina.
A rod cell is sensitive enough to respond to a single photon of light, and is about 100 times more sensitive to a single photon than cones. Since rods require less light to function than cones, they are therefore the primary source of visual information at night . Cone cells, on the other hand, require tens to hundreds of photons to become activated. Additionally, multiple rod cells converge on a single interneuron, collecting and amplifying the signals. However, this convergence comes at a cost to visual acuity since the pooled information from multiple cells is less distinct than it would be if the visual system received information from each rod cell individually. The convergence of rod cells also tends to make peripheral vision very sensitive to movement, and is responsible for the phenomenon of individuals seeing something vague occur out of the corner of his or her eye.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.
Rod cells also respond more slowly to light than cones do, so stimuli they receive are added over about 100 milliseconds. While this makes rods more sensitive to smaller amounts of light, it also means that their ability to sense temporal changes, such as quickly changing images is less accurate than that of cones However, if multiple flashes of sub-threshold light occurs during the 100 millisecond period, the energy of the flashes of light would summate to produce a light which will reach threshold and send a signal to the brain.
Experiments by George Wald and others showed that rods are more sensitive to the blue area of the spectrum, and are completely insensitive to wavelengths above about 640 nm . This fact is responsible for the Purkinje effect, in which blue colors appear more intense relative to reds in darker light, when rods take over as the cells responsible for vision.
Like cones, rod cells have a synaptic terminal, an inner segment, and an outer segment. The synaptic terminal forms a synapse with another neuron, for example a bipolar cell. The inner and outer segments are connected by a cilium. The inner segment contains organelles and the cell's nucleus, while the outer segment, which is pointed toward the front of the eye, contains the light-absorbing materials.
A rod cell is sensitive enough to respond to a single photon of light, and is about 100 times more sensitive to a single photon than cones. Since rods require less light to function than cones, they are therefore the primary source of visual information at night . Cone cells, on the other hand, require tens to hundreds of photons to become activated. Additionally, multiple rod cells converge on a single interneuron, collecting and amplifying the signals. However, this convergence comes at a cost to visual acuity since the pooled information from multiple cells is less distinct than it would be if the visual system received information from each rod cell individually. The convergence of rod cells also tends to make peripheral vision very sensitive to movement, and is responsible for the phenomenon of individuals seeing something vague occur out of the corner of his or her eye.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.
Rod cells also respond more slowly to light than cones do, so stimuli they receive are added over about 100 milliseconds. While this makes rods more sensitive to smaller amounts of light, it also means that their ability to sense temporal changes, such as quickly changing images is less accurate than that of cones However, if multiple flashes of sub-threshold light occurs during the 100 millisecond period, the energy of the flashes of light would summate to produce a light which will reach threshold and send a signal to the brain.
Experiments by George Wald and others showed that rods are more sensitive to the blue area of the spectrum, and are completely insensitive to wavelengths above about 640 nm . This fact is responsible for the Purkinje effect, in which blue colors appear more intense relative to reds in darker light, when rods take over as the cells responsible for vision.
Like cones, rod cells have a synaptic terminal, an inner segment, and an outer segment. The synaptic terminal forms a synapse with another neuron, for example a bipolar cell. The inner and outer segments are connected by a cilium. The inner segment contains organelles and the cell's nucleus, while the outer segment, which is pointed toward the front of the eye, contains the light-absorbing materials.
Monday, July 16, 2007
Thunderbolt
A thunderbolt is a conventional expression for a release of lightning or a emblematic representation thereof. As a heavenly manifestation it has been a powerful symbol throughout history, and has appeared in many mythologies. Drawing from this influential association, the thunderbolt is often found in military symbolism and semiotic representations of electricity.Lightning plays a role in many mythologies, often as the stick of a sky and storm god. As such, it is an unsurpassed method of dramatic instantaneous retributive devastation: thunderbolts as divine weapons can be found in most mythologies. The most well-known thunderbolt weapon in the West was that of Zeus or Jupiter. His thunderbolts were manufactured by Hephaestus/Vulcan Jupiter used his thunderbolts to strike down impious criminals and divine opponents.
Wednesday, July 11, 2007
In Astronomy
Space refers collectively to the relatively empty parts of the universe. Any area outside the atmospheres of any celestial body can be considered 'space'. Although space is certainly spacious, it is not always empty, but can be filled with matter — say a tenuous plasma. In particular, the boundary between space and Earth's atmosphere is conventionally set at the Karman line.
Thursday, July 05, 2007
Jewellery and society
Jewellery is factually any piece of fine material used to decorate oneself. Although in earlier times jewellery was created for more convenient uses, such as wealth storage and pinning clothes together, in recent times it has been used almost completely for beautification. The first pieces of jewellery were made from likely materials, such as bone and animal teeth, shell, wood and engraved stone. Jewellery was often made for people of high importance to show their status and, in many cases, they were covered with it.Jewellery is made out of almost every material recognized and has been made to garnish nearly every body part, from hairpins to toe rings and many more types of jewellery. While high-quality and artistic pieces are made with gemstones and valuable metals, less pricey costume jewellery is made from less-valuable materials and is mass-produced.Form and function Kenyan man exhausting tribal beads.Over time, jewellery has been used for a number of reasons: Currency, wealth display and storage, purposeful Symbolism Protection and Artistic display Most cultures have at some point had a practice of observance large amounts of wealth stored in the form of jewellery. Numerous cultures move wedding dowries in the form of jewelry, or create jewelry as a means to store or display coins. on the other hand, jewellery has been used as a currency or trade good; a mostly poignant example being the use of slave beads.
In creating jewellery, a variety of gemstones, coins, or other valuable items can be used, often set into precious metals. Common expensive metals used for modern jewellery include gold, platinum or silver, although alloys of nearly every metal known can be encountered in jewellery -- bronze, for example, was common in Roman times. Most gold jewellery is made of an alloy of gold, the purity of which is affirmed in karats, indicated by a number followed by the letter K. For example, ordinary gold jewellery ranges from 10K (41.7% pure gold) to 22K (91.6% pure gold), while 24K (99.9% pure gold) is considered too soft for jewellery use.
Platinum alloys variety from 900 (90% pure) to 950 (95.0% pure). The silver used in jewellery is usually sterling silver, or 92.5% fine silver.Other generally used materials include glass, such as merged glass or enamel; wood, often carved or turned; shells and other natural animal substances such as bone and ivory; natural clay, polymer clay, and even plastics.
In creating jewellery, a variety of gemstones, coins, or other valuable items can be used, often set into precious metals. Common expensive metals used for modern jewellery include gold, platinum or silver, although alloys of nearly every metal known can be encountered in jewellery -- bronze, for example, was common in Roman times. Most gold jewellery is made of an alloy of gold, the purity of which is affirmed in karats, indicated by a number followed by the letter K. For example, ordinary gold jewellery ranges from 10K (41.7% pure gold) to 22K (91.6% pure gold), while 24K (99.9% pure gold) is considered too soft for jewellery use.
Platinum alloys variety from 900 (90% pure) to 950 (95.0% pure). The silver used in jewellery is usually sterling silver, or 92.5% fine silver.Other generally used materials include glass, such as merged glass or enamel; wood, often carved or turned; shells and other natural animal substances such as bone and ivory; natural clay, polymer clay, and even plastics.
