Issues of Interpreting the New Physics

六月 4, 2010 at 21:17 | 張貼於physics | 發表留言

Although quantum mechanics has been very successful, we must remember that quantum mechanics only describes and predicts observable physical phenomena; it does not describe the inner reality of physical matter. In fact, as quantum mechanics advanced, different and conflicting interpretations of quantum mechanics developed, even among eminent physicists.

One of the earliest interpretations of quantum mechanics is the Copenhagen interpretation, which was led by a Danish physicist, Dr. Niels Bohr. This interpretation states that “there is no deep reality,” and atoms, electrons, and photons do not exist like objects in our everyday experience. According to this interpretation, a phenomenon fully comes into existence only when it is observed. Bohr once described it this way: “There is no quantum world. There is only an abstract quantum description.”

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Willis E. Lamb Jr., a Nobel prize-winning physicist

五月 21, 2008 at 12:28 | 張貼於physics, USA | 發表留言
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TUCSON, Ariz. (AP) — Willis E. Lamb Jr., a Nobel prize-winning physicist whose work on the electron structure of the hydrogen atom revolutionized the quantum theory of matter, has died. He was 94.

Lamb died in a Tucson hospital from complications of a gallstone disorder on May 15, according to an announcement from the University of Arizona, where he was professor emeritus of physics and optical sciences.

Lamb worked as a physicist at various universities from the late 1930s until retiring from the University of Arizona in 2002.

Lamb was awarded the Nobel prize for physics in 1955 for research he conducted while working at Columbia University’s Columbia Radiation Laboratory. He was working on defense-related research into microwave sources for radar when he became interested in the properties of the hydrogen atom.

He designed and built a device in 1947 with Columbia graduate student R.C. Retherford to study the effect of microwave radiation on the hydrogen atom, according to a University of Arizona biography. That led to measurements that showed a change in the amount of energy emitted from the hydrogen atom in different states that became known as the “Lamb shift."

The discovery led to changes in the basic concepts behind the application of quantum theory to electromagnetism. His work became one of the foundations of quantum electrodynamics, a key aspect of modern elementary particle physics.

“Clearly he was a brilliant and serious scientist," his wife, Elsie Wattson Lamb, said in a statement released by the university. “But he was also deeply human."

Born July 12, 1913, in Los Angeles, Lamb attended the University of California, Berkeley as an undergraduate and graduate student. His doctoral thesis was overseen by J. Robert Oppenheimer, who went on to lead the U.S. effort to develop the atomic bomb during World War II.

Lamb joined the faculty at Columbia University in 1938 and rose to became a full professor of physics. He later worked at Stanford University and Harvard University before becoming a fellow of New College at the University of Oxford, England, from 1956 to 1962.

In 1962 he became Henry Ford II Professor of Physics at Yale University. He became professor of physics and optical sciences at the University of Arizona in 1974, a post he retained until retirement.

Lamb married his first wife, historian Ursula Schaefer, in 1939. She died in 1996. A second marriage ended in divorce. He married Elsie Wattson earlier this year, and is also survived by a brother, Perry.

Relativity in 9 minute

十一月 14, 2007 at 21:59 | 張貼於physics, video | 發表留言

Relativity in 9 minute

十一月 14, 2007 at 21:59 | 張貼於physics, video | 發表留言

Relativity in 9 minute

十一月 14, 2007 at 13:59 | 張貼於physics, video | 發表留言

Wing Morphing Of The Swift

十月 14, 2007 at 08:32 | 張貼於aircraft, physics | 發表留言

Wing Morphing Of The Swift Could Inspire New Aircraft Designs

Science Daily A swift adapts the shape of its wings to the immediate task at hand: folding them back to chase insects, or stretching them out to sleep in flight. Ten Dutch and Swedish scientists, based in Wageningen, Groningen, Delft, Leiden, and Lund, have shown how ‘wing morphing’ makes swifts such versatile flyers. Their study, published as cover story in Nature on April 26, proves that swifts can improve flight performance by up to three-fold, numbers that make ‘wing morphing’ the next big thing in aircraft engineering.


Turning swifts keep their head horizontal during a banked turn. (Credit: Copyright: Jean-Francois Cornuet)


Swifts spend almost their entire life in the air. During flight, they continually change the shape of their wings from spread wide to swept back. When they fly slowly and straight on, extended wings carry swifts 1.5 times farther and keep them airborne twice as long. To fly fast, swifts need to sweep back their wings to gain a similar advantage.

Swifts spend almost their entire life in the air. During flight, they continually change the shape of their wings from spread wide to swept back. When they fly slowly and straight on, extended wings carry swifts 1.5 times farther and keep them airborne twice as long. To fly fast, swifts need to sweep back their wings to gain a similar advantage.

Economic turns

During the summer, we can observe swifts circling above town squares, where they catch up to 20.000 insects a day. Swift can triple their efficiency by turning with their wings stretched out. When chasing rivals and flying insects, swifts also want to make their turns fast and tight. However, in fast and diving turns, the load on the wings easily reaches more than four times the swift’s body weight. So in extreme turns, swifts need to sweep back their wings or else risk breaking them.

Night’s rest

Swifts do not land to roost, but spend the night at 1.5 km above the ground. To measure their flight speed, Swedish scientists used radar. They found that swifts let the air blow past their wings at 8 to 10 m/s (29-36 km/h). At these air speeds, swift wings deliver maximum flight efficiency. For the swift that means more gliding and less flapping to maintain altitude.

The scientists figured all this out when they measured just how much lift and drag a swift wing generates. The wings were tested to their limit in a windtunnel at speeds of up to 108 km/h (30 metres per second).Scientists compared extended and swept wings, and learnt that flying slowly with extended wings gives swifts maximum flight efficiency. But swept wings deliver a better aerodynamic performance for flying fast and straight. Swept wings are also better for fast and tight turns; but this time swept wings are better because they do not break as easily as extended wings.

Airplanes

Morphing wings are the latest trend in aviation. The best wing shape to save fuel costs depends on flight speed. In 2003, birds inspired NASA to design a revolutionary “morphing wing" aircraft. Also so-called micro-aircraft, which are the size of a bird, begin to exploit the benefits of varying wing shape. These tiny flyers, equipped with cameras and sensors to assist in surveillance and espionage, imitate faithfully the flight behaviour and appearance of birds. In an ongoing project, students at Delft University cooperate with scientist at Wageningen, to make such a small airplane fly like a swift.

The swifts for this study had been brought in dead or dying to seven Dutch bird sanctuaries. Swifts, when forced to land on the ground, cannot take off by themselves and will starve unless a kind and timely passer-by throws them in the air. Swifts are the most aerial of birds. They migrate annually from South Africa to Europe. Over their lifetime, swifts cover 4.5 million kilometres, a distance equal to six round trips to the moon or 100 times around the Earth. At day, swifts hunt insects; at night they ‘roost’ in flight. Swifts even mate in the air and land only lay their eggs, in nests tucked away into crevices of walls and cliffs. Swifts are not related to swallows. They are family of another well-known aerial acrobat, the hummingbird.

Note: This story has been adapted from material provided by Wageningen University and Research

Keel Lift- a misnomer

九月 22, 2007 at 12:28 | 張貼於physics, sail | 發表留言
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Catamaran VEGA Sailing School Chapter 11: “Water flowing past the hull, keel, and rudder of a sailboat is subject to the same basic rules as air flowing past the sails. The only difference between the sails and underwater appendages is that the latter are symmetrical while the former are asymmetrical. But the angle of attack (which we call ‘angle of incidence’ for wind hitting the sails and ‘yaw angle’ for water hitting the keel) solves the problem of getting ‘lift’ from the keel. Due to the pressure of the wind in the sails, a sailboat sideslips a little as it goes forward. This is called ‘making leeway.’ Thus the angle between the direction that the boat is heading and an imaginary line indicating its ‘track’ through the water is the ‘leeway angle’ as shown in Figure 1. Since the water has to travel a greater distance on the windward side of the keel, an area of reduced pressure produces ‘lift’ to windward. The more lift from the underwater surfaces, the less leeway the boat makes. In other words, it slips sideways less. Obviously, when sailing to windward we are trying to reach a destination upwind, and any sideslipping that pushes us downwind is undesirable. The slower the velocity of the fluid flowing past the ‘airfoil,’ the less efficiency it has as a lifting surface. So when the boat is going slowly, it sideslips more. This increases the leeway angle and, up to a point, increases the efficiency of the keel. Past that point, though, the water becomes turbulent on the windward side of the keel and a stall results. A good example of this situation is a sailboat sitting on the starting line before a race in a close-hauled pointing angle but with sails luffing, waiting for the starting gun. At the gun, the crew trims in the sails to get the boat moving forward. Instead, the boat goes almost as fast sideways as she goes forward because the velocity of the water flowing past the keel is not sufficient to counteract the sideways push of the sails. Instead, the helmsman should have sailed on a slight reach, where the force of the sails is more in the direction of the boat’s heading, in order to pick up speed and then harden up to close-hauled.


Fig 1: The more lift generated on the keel, the less leeway, or sideslipping.

All the above should not be taken seriously because the force come form the wind above. Below water only drag can be found, not lift.

 


Wind Tunnel movies

九月 9, 2007 at 15:41 | 張貼於physics, sailing | 發表留言


WB-Sails Ltd: Good windtunnel movies showing seperation. Both the jib and the mail should be eased out to rettach the airflow

http://www.wb-sails.fi/news/99_4_WindTunnelMovies/Movies.htm#

Wind Tunnel movies

九月 9, 2007 at 07:41 | 張貼於physics, sailing | 發表留言


WB-Sails Ltd: Good windtunnel movies showing seperation. Both the jib and the mail should be eased out to rettach the airflow

http://www.wb-sails.fi/news/99_4_WindTunnelMovies/Movies.htm#

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