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October 15th, 2006 edit
A mirror neuron is a neuron which fires both when an animal performs an action and when the animal observes the same action performed by another (especially conspecific) animal. Thus, the neuron "mirrors" the behavior of another animal, as though the observer were himself performing the action. These neurons have been observed in primates, in some birds, and in humans. In humans, they have been found in Broca's area and the inferior parietal cortex of the brain. Some scientists consider mirror neurons one of the most important findings of neuroscience in the last decade. See for example this[1] essay by Ramachandran on their potential importance in imitation and language.
September 24th, 2006 edit
A comet is a small body in the solar system that orbits the Sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail — both due primarily to the effects of solar radiation upon the comet's nucleus, which itself is a minor planet composed of rock, dust, and ices. Due to their origins in the outer solar system and their propensity to be highly affected (or perturbed) by relatively close approaches to the major planets, comets' orbits are constantly changing. Some are moved into sungrazing orbits that destroy the comets when they near the Sun, while others are thrown out of the solar system forever.
August 27, 2006 edit
chicken (Gallus gallus domesticus) is a type of domesticated bird which is often raised as a type of poultry. It is believed to be descended from the wild Indian and south-east Asian Red Junglefowl.
With a population of more than 24 billion in 2003 (according to the Firefly Encyclopedia of Birds), there are more chickens in the world than any other bird. They provide two sources of food frequently consumed by humans: their meat, also known as chicken, and eggs.
August 13, 2006 edit
Erosion is the displacement of solids (soil, mud, rock and other particles) by the agents of wind, water or ice, by downward or down-slope movement in response to gravity or by living organisms (in the case of bioerosion). Erosion is distinguished from weathering, which is the decomposition of rock and particles through processes where no movement is involved, although the two processes may be concurrent.
Erosion is an intrinsic natural process but in many places it is increased by human land use. Poor land use practices include deforestation, overgrazing, unmanaged construction activity and road or trail building. However, improved land use practices can limit erosion, using techniques like terrace-building and tree planting.
A certain amount of erosion is natural and, in fact, healthy for the ecosystem. For example, gravels continually move downstream in watercourses. Excessive erosion, however, can cause problems, such as receiving water sedimentation, ecosystem damage (including fish kills) and outright loss of soil.
July 10, 2006 edit
The id, ego, and super-ego are the divisions of the psyche according to psychoanalyst Sigmund Freud's "structural theory". The id contains "primitive desires" (hunger, rage, and sex), the super-ego contains internalized norms, morality and taboos, and the ego mediates between the two and may include or give rise to the sense of self.
June 4, 2006 edit
Teflon is the brand name of the polymer polytetrafluoroethylene (PTFE) discovered by Roy J. Plunkett (1910–1994) of DuPont in 1938 and introduced as a commercial product in 1946. It is a fluoropolymer but not a thermoplastic in the true sense.
PTFE has the lowest coefficient of friction of any known solid material. It is used as a non-stick coating for pans and other cookware. PTFE is very non-reactive, and so is often used in containers and pipework for reactive chemicals. Its melting point is 327 °C, but its properties degrade above 260 °C.
May 14, 2006 edit
Nanotechnology comprises technological developments on the nanometer scale, usually 0.1 to 100 nm (1/1,000 µm, or 1/1,000,000 mm). A possible way to interpret this size is to take the width of a hair, and imagine something ten thousand times smaller. The term has sometimes been applied to microscopic technology. Nanotechnology is any technology which exploits phenomena and structures that can only occur at the nanometer scale, which is the scale of several atoms and small molecules. The United States's National Nanotechnology Initiative website [1] defines it as follows: "Nanotechnology is the understanding and control of matter at dimensions of roughly 1 to 100 nanometers, where unique phenomena enable novel applications."...
May 7, 2006 edit
Hydrogen chloride, also known under the name HCl, is a highly corrosive and toxic colorless gas that forms white fumes on contact with humidity. These fumes consist of hydrochloric acid which forms when hydrogen chloride dissolves in water. Hydrogen chloride gas as well as hydrochloric acid are important chemicals in chemistry, science, technology, and industry. The name HCl often refers somewhat misleadingly to hydrochloric acid instead of the gaseous hydrogen chloride.
Hydrogen chloride forms corrosive hydrochloric acid on contact with body tissue. Inhalation of the fumes can cause coughing, choking, inflammation of the nose, throat, and upper respiratory tract, and in severe cases, pulmonary edema, circulatory system failure, and death. Skin contact can cause redness, pain, and severe skin burns. Hydrogen chloride may cause severe burns to the eye and permanent eye damage.
April 23, 2006 edit
A quantum dot is a semiconducting crystal nanotechnology. Quantum dots confine electrons, holes, electron-hole pairs, or excitons to zero dimensions to a region on the order of the electrons' Compton wavelength. This confinement leads to discrete quantized energy levels and to the quantization of charge in units of the elementary electric charge e. Quantum dots are particularly significant for optical applications due to their theoretically high quantum yield. Quantum dots have also been suggested as implementations of a qubit for quantum information processing.
Because the quantum dot has discrete energy levels, much like an atom, they are sometimes called artificial atoms. The energy levels can be controlled by changing the size and shape of the quantum dot, and the depth of the potential. Like in atoms, the energy levels of small quantum dots can be probed by optical spectroscopy techniques. In contrast to atoms it is relatively easy to connect quantum dots by tunnel barriers to conducting leads, which allows the application of the techniques of tunneling spectroscopy for their investigation.
February 12, 2006 edit
A quantum computer is any device for computation that makes direct use of distinctively quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. In a classical (or conventional) computer, the amount of data is measured by bits; in a quantum computer, it is measured by qubits. The basic principle of quantum computation is that the quantum properties of particles can be used to represent and structure data, and that devised quantum mechanisms can be used to perform operations with this data. For a generally accessible overview of quantum computing, see Quantum Computing with Molecules, an article in Scientific American by Neil Gershenfeld and Isaac L. Chuang.
Experiments have already been carried out in which quantum computational operations were executed on a very small number of qubits. Research in both theoretical and practical areas continues at a frantic pace; see Quantum Information Science and Technology Roadmap for a sense of where the research is heading. Many national government and military funding agencies support quantum computing research, to develop quantum computers for both civilian and national security purposes, such as cryptanalysis.
January 15, 2006 edit
New Horizons is a NASA unmanned spacecraft designed to fly by Pluto and its moons (including Charon) and transmit images and data back to Earth. Mission planners hope that NASA will approve plans to continue the mission with a fly-by of a Kuiper Belt Object and return further data. A consortium of organizations, led by Southwest Research Institute and the Johns Hopkins Applied Physics Laboratory, has built the craft. The mission's principal investigator is S. Alan Stern of Southwest Research. The probe successfully launched from Cape Canaveral, Florida at 14:00 EST January 19, 2006 and is now en route to Jupiter for a gravity assist.
The primary scientific objectives are to characterize the global geology and morphology and map the surface composition of Pluto and Charon, and study the neutral atmosphere of Pluto and its escape rate. Other objectives include studying time variability of Pluto's surface and atmosphere; imaging and mapping areas of Pluto and Charon at high-resolution; characterizing Pluto's upper atmosphere, ionosphere, and energetic particle environment; searching for an atmosphere around Charon; refining bulk parameters of Pluto and Charon; and searching for additional satellites and rings.
January 8, 2006 edit
A space elevator is a hypothetical structure designed to transport material from a planet's surface into space. Many different types of space elevator structures have been proposed. They all share the goal of replacing rocket propulsion with the traversal of a fixed structure via a mechanism not unlike an elevator, hence its name, in order to move material into or beyond orbit. Space elevators have also sometimes been referred to as space bridges, beanstalks, space ladders or space lifts. The most common proposal is a tether (usually a cable or ribbon) that spans from the surface to a point beyond geosynchronous orbit. As the planet rotates, the inertia at the end of the tether counteracts gravity and keeps the tether taut. Vehicles can then climb the tether and escape the planet's gravity without the use of rockets. Such a structure could eventually permit delivery of great quantities of cargo and people to orbit, and at costs only a fraction of those associated with current means.
December 25, 2005 edit
Evolution is a change in the genetic makeup of a population within a species. Since the emergence of modern genetics in the 1940s, evolution has been defined more specifically as a change in the frequency of alleles from one generation to the next. The word "evolution" is often used as a shorthand for the modern theory of evolution of species based upon Charles Darwin's theory of natural selection, which states that all modern species are the products of an extensive process that began over three billion years ago with simple single-celled organisms, and Gregor Mendel's theory of genetics. As the theory of evolution by natural selection and genetics has become universally accepted in the scientific community, it has replaced other explanations including creationism and Lamarckism. Skeptics, often creationists, sometimes deride evolution as "just a theory" in an attempt to characterize it as an arbitrary choice and degrade its claims to truth. Such criticism overlooks the scientifically-accepted use of the word "theory" to mean a falsifiable and well-supported hypothesis.