Physically Based Modeling Physically Based Modeling: Principles and Practice(Online Siggraph '97 Course notes) Please note: the lecture notes served from this page are copyright ©1997 by the authors (Andrew Witkin and David Baraff ). Chapters may be freely duplicated and distributed so long as no consideration is received in return, and this copyright notice remains intact. The slide sets are copyright ©1997 and may be neither distributed nor duplicated without permission of the authors. All documents on this page are in Adobe Acrobat format. Course Material
The 'Infinity Room': One of Many Ways to Imagine Infinity | Artists, Physicists, Mathematicians and Philosophers Contemplate Infinity As I stepped into the Infinity Environment on Wednesday morning (Feb. 1), I heard faint gasps from those around me. With apprehension, we entered a stark white, brilliantly lit room with no edges. The curved walls and angled lighting minimized shadows, giving the illusion that we were staring into a continuum. "There is no other time in your life when you will look out and see nothing at all," one young woman, an art student, whispered. The Infinity Environment, an art piece by Doug Wheeler, is currently on display at the David Zwirner Gallery in New York City. Art is one way to grapple with infinity. Andy Albrecht, a cosmologist and the chairman of the physics department at the University of California, Davis, has used the same analogy since he was a student. "In the case of the [art installation], the sense of it being infinite is just an optical illusion, because you could bring a ball and throw it against the wall and discover quite quickly that the room is finite," Albrecht said.
Technology Review: The Authority on the Future of Technology ScienceBlogs Science Daily: News & Articles in Science, Health, Environment & Technology Young's modulus Mechanical property that measures stiffness of a solid material Young's modulus is the slope of the linear part of the stress-strain curve for a material under tension or compression. Young's modulus (proportional deformation) in the linear elastic region of a material and is determined using the formula:[1] Example: Silly Putty (increasing pressure: length increases quickly, meaning low )Aluminum (increasing pressure: length increases slowly, meaning high ) Higher Young's modulus corresponds to greater (lengthwise) stiffness. Definition[edit] Linear elasticity[edit] A solid material will undergo elastic deformation when a small load is applied to it in compression or extension. At near-zero stress and strain, the stress–strain curve is linear, and the relationship between stress and strain is described by Hooke's law that states stress is proportional to strain. Not many materials are linear and elastic beyond a small amount of deformation. Not to be confused with[edit] Usage[edit] , bulk modulus
Researchers now able to stop, restart light By William J. Cromie Gazette Staff "Two years ago we slowed it down to 38 miles an hour; now we've been able to park it then bring it back up to full speed." Lene Hau isn't talking about a used motorbike, but about light – that ethereal, life-sustaining stuff that normally travels 93 million miles from the sun in about eight minutes. Less than five years ago, the speed of light was considered one of the universe's great constants. Hau, 41, a professor of physics at Harvard, admits that the famous genius would "probably be stunned" at the results of her experiments. "It's nifty to look into the chamber and see a clump of ultracold atoms floating there," Hau says. She and her team continued to tweak their system until they finally brought light to a complete stop. Inspired by Hau's success at slowing light, researchers working on a wooded hill a few miles away at the Harvard-Smithsonian Center for Astrophysics (CfA) used a similar technique to stop, then restart, a light beam.
The Tech Report - PC Hardware Explored Science" Poisson's ratio Measure of material deformation perpendicular to loading In materials science and solid mechanics, Poisson's ratio Origin[edit] Poisson's ratio is a measure of the Poisson effect, the phenomenon in which a material tends to expand in directions perpendicular to the direction of compression. Conversely, if the material is stretched rather than compressed, it usually tends to contract in the directions transverse to the direction of stretching. It is a common observation when a rubber band is stretched, it becomes noticeably thinner. Assuming that the material is stretched or compressed in only one direction (the x axis in the diagram below): where is the resulting Poisson's ratio, is transverse strain is axial strain and positive strain indicates extension and negative strain indicates contraction. Poisson's ratio from geometry changes[edit] Length change[edit] For a cube stretched in the x-direction (see Figure 1) with a length increase of in the x direction, and a length decrease of and is then .
Is Dark Energy Really "Repulsive Gravity"? In 1998 scientists discovered that the universe is not only expanding but that its expansion is accelerating. This totally unexpected behavior has been called the "most profound problem" in physics , because our current understanding of gravity says that attractions between mass in the universe should be causing the expansion to slow down. The leading theory to explain the accelerating expansion is the existence of a hypothetical repulsive force called dark energy. (Related: "New Galaxy Maps to Help Find Dark Energy Proof?" ) But in the new study, Massimo Villata , an astrophysicist at the Observatory of Turin in Italy, suggests the effects attributed to dark energy are actually due to a kind of "antigravity" created when normal matter and antimatter repel one another. "Usually this repulsion is ascribed to a mysterious dark energy that would uniformly permeate the cosmos, but nobody knows what it is nor why it behaves this way," Villata said in an email.
Observable Universe The surface of last scattering is the collection of points in space at the exact distance that photons from the time of photon decoupling just reach us today. These are the photons we detect today as cosmic microwave background radiation (CMBR). However, with future technology, it may be possible to observe the still older neutrino background, or even more distant events via gravitational waves (which also should move at the speed of light). Sometimes astrophysicists distinguish between the visible universe, which includes only signals emitted since recombination—and the observable universe, which includes signals since the beginning of the cosmological expansion (the Big Bang in traditional cosmology, the end of the inflationary epoch in modern cosmology). The universe versus the observable universe[edit] If the universe is finite but unbounded, it is also possible that the universe is smaller than the observable universe. Size[edit] Misconceptions[edit] 13.8 billion light-years
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