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Seminars are held on Tuesdays, 3:45-4:45pm in SB 101, unless otherwise noted. Physics & Astronomy Seminar
Fall 2001
Meet at 3:30 in SB 157 (formerly known as SB 153) for refreshments.
See Calvin's Visitor Resources for maps and directions to the Science Building.
If you would like to receive regular email announcements for each week's seminar, or have other questions or comments, contact seminar chair Steve Steenwyk.Previous semesters: Fall 1999, Spring 2000, Fall 2000, Spring 2001.
Date Title Speaker September 18 in SB 110 Quantum Computing: Part I Prof. Alex Dragt THURSDAY, September 27, 12:30pm Classroom Demonstrations: More Than Just Entertainment? Dr. Catherine Crouch, Harvard University October 2 in SB 110 Quantum Computing: Part II Prof. Alex Dragt October 9 Summer Research: Time Delay Monitoring of Gravitational Lens 2016+112 Drew VandenHeuvel, sophomore October 16 Summer Research: Cold Avalanche Photodiodes and the Lifetime of a Neutron Josh Gabrielse, junior MONDAY October 29 Spinning Teenage Stars Dr. Luisa Rebull, NASA/Jet Propulsion Laboratory November 6 Double Ionization of Helium by Intense Lasers: Identifying the Mechanism Prof. Stanley Haan December 4 God's Holiday Lights: Northern Lights, Comets, Meteors and the Star of Bethlehem Profs. S. Steenwyk, L. Molnar, and D. Haarsma September 18 and October 2: Quantum Computing, Prof. Alex Dragt
Despite its great success, many find Quantum Mechanics hard to understand and some believe that it is not a complete theory. Until recently this has not caused too much concern since observable "quantum weirdness" has been confined to the microscopic world of atoms and elementary particles where one is perhaps not too alarmed to see apparent violations of "common sense" expectations. When logical/philosophical questions are raised about Quantum Mechanics, and since we know how to use it to make predictions, the general response has been to simply say, "Shut up, and calculate!"However, with modern experimental techniques and tools, it now appears to be in principle possible to produce quantum weirdness at the macroscopic level that may produce a conceptual revolution in our intuitive understanding of reality. One such possibility is a Quantum Computer. If it could be built, a Quantum Computer would be vastly more powerful (for some classes of problems) than a conventional computer. It could in principle solve some problems in seconds that it would take any conventional computer billions of years to solve. Such a quantum computer, it could lead to a technological revolution that would far surpass that already produced by present day electronics, communication, and computers! Indeed, because of this promise, the federal government is currently supporting some $50 million/year of research on the general subject of quantum information/computing. There are also active programs in Europe and Japan.
September 27: Classroom Demonstrations: More Than Just Entertainment?, Dr. Catherine Crouch
Classroom demonstrations in science courses are intended to serve two important purposes: to increase students' interest in the material being covered and to improve students' understanding of the underlying scientific concepts. Student end-of-semester evaluations typically praise demonstrations as one of the most interesting parts of a course, suggesting that demonstrations accomplish the first objective. What about the second? Do demonstrations effectively help students learn the underlying concepts? We examined whether the manner of presentation of demonstrations affects their effectiveness as teaching tools. Seven demonstrations were presented to different sections of an introductory physics course in different ways: (1) students were shown the demonstration and the outcome was explained (traditional style); (2) students were asked to predict the outcome before the demonstration; (3) students completed a brief worksheet predicting the outcome, discussing it with partners, and then comparing their prediction to the actual outcome; (4) no demonstration was shown. After the course, students completed a free-response test asking them to predict and explain the outcome of physical situations identical to the demonstrations. The results indicate that students who have to predict the outcome of a demonstration before seeing it, and especially those who then compare their prediction to the actual outcome, remember and understand the outcome at a much higher rate than those who saw the demonstration in traditional style.October 16: Cold Avalanche Photo Diodes and the Lifetime of a Neutron, Joshua Gabrielse
In isolation, the neutron is unstable and decays with a lifetime predicted by modern theories of elementary particles. Precise measurements of this lifetime can provide a test of the theory. Joshua Gabrielse will present results of his efforts to improve the signal obtained from a type of detector called an avalanche photo diode used in experiments to determine the neutron lifetime. An overview of these experiments will be given as well. Work presented was done as a summer 2001 research intern under the supervision of Professor John Doyle at Harvard University.October 29: Spinning Teenage Stars, Dr. Luisa Rebull
The cause of the rotation of young stars (stars less than 5 million years old) is a key element in our understanding of the formation of stars and planetary systems (including our own), but one about which there remain many questions. Stellar rotation also affects the structure and magnetic fields of stars. By studying 8000 young stars in two clusters, we have discovered about 300 periodic variable stars in Orion (roughly doubling the number previously known in that cluster) and about 200 periodic variable stars in NGC 2264 (six times the number previously known in that cluster). We find stars ranging in rotation rates from values comparable to the Sun (30 days/rotation, or about 2 km/s at equator) to 100 times faster (0.25 days/rotation, or about 200 km/s at equator!). In this context, I will give a brief overview of star formation and rotational evolution of low-mass stars. I will then review our most recent results; among other things, we find that stars apparently do not conserve stellar angular momentum and spin up over ages of at least 1-5 million years and maybe longer, a very surprising result.November 6: Prof. Stanley Haan
Double Ionization of Helium by Intense Lasers: Identifying the Mechanism
OR Why does zapping a helium atom with intense laser light liberate both electrons instead of just one of them?
The majority of this talk will be accessible to first-year physics students.
Experimental studies of helium and other atoms exposed to intense laser light reveal orders of magnitude more double ionization than would be expected for independently behaving electrons. This talk will describe some theoretical efforts to find what the mechanism is. We have employed a simple model of the helium atom, and performed numerical studies using both quantum mechanics and classical mechanics. We show the importance of processes in which one electron escapes the atom, but then comes back for another visit and cleverly helps the other electron use the laser force to escape the Coulombic clutches of the nucleus.December 4:
God's Holiday Lights: Northern Lights, Comets, Meteors and the Star of Bethlehem
Professors S. Steenwyk, L. Molnar, and D. Haarsma
Surely you have heard of some of the spectacular celestial events occurring recently. The Department of Physics and Astronomy will present a holiday seminar featuring some of God's celestial holiday decorations. Recently, we have had a spectacular display of the northern lights and a veritable storm of meteors has flashed through our skies. Meanwhile a comet named Linear has been captured by Calvin's telescope. Professor Larry Molnar will tell of the aurora and the comet. Professor Steve Steenwyk will give an eyewitness account of hundreds of meteors. Professor Debbie Haarsma will put these in perspective with an account of the first Christmas light-the Star of Bethlehem, including a simulation of the night sky back when Christ was born.