2,689 research outputs found
“Now Boarding: The Flight from Physics” David Goodstein’s acceptance speech for the 1999 Oersted Medal presented by the American Association of Physics Teachers, 11 January 1999
All across the country, the number of students majoring in physics is said to be at its lowest point since Sputnik, 40 years ago. The most important role of the college physics course today seems to be to weed out a few poor souls who might otherwise make it to medical school or some other kind of quasi-scientific training. If the profession of teaching physics were a business, we would be filing for bankruptcy. On the other hand, our assets include nothing less than the wisdom of the ages, the most important part of the body of human knowledge. Mastery of that knowledge, a fundamental grasp of how the world works, ought to be the best possible preparation for the coming century. Rather than being an endangered species, the physics major should be the wave of the future, but it isn’t, at least not yet. This talk will analyze how we got ourselves into this fix, and suggest what is needed to get ourselves out of it
Filming seismograms and related materials at the California Institute of Technology
As part of a world-wide effort to create an international earthquake data bank, Caltech's seismology archive has been organized, labeled, described, and microfilmed. It includes a wide variety of original records, documents, and printed materials relating to local and distant earthquakes. At present, we are filming significant seismograms prior to 1963; more than 50,000 records written between 1924 and 1935 have been filmed to date. Seismograms are the principal source of
information about earthquakes and the earth's interior. These records, housed at Kresge Laboratory, the headquarters for Caltech's seismological network of stations, are important because they span so much of the period for which instrumental data exists. The early history of the Laboratory points up the role technology has played in the advancement of the science
Viscosity, ion mobility, and the λ transition
A model is presented of the λ transition in superfluid helium in which fluctuations near the transition are approximated by distinct regions of normal fluid and superfluid. The macroscopic viscosity of such a medium is computed. The ion mobility is also computed, taking into account a region of normal fluid around the ion induced by electrostriction. The results are, for the viscosity, ηλ-η∼t^0.67 and for the mobility μ-μλ∼t^0.92 both in excellent agreement with recent experiments. The model suggests that the λ transition itself is the point at which superfluid regions become macroscopically connected
Control of ultralow pressures: an absolute thermodynamic manometer
A method of accurately manipulating the pressure of helium gas in the range P=10^–1 to 10^–20 Torr, T<5 K is presented. The method requires only a very modest apparatus and makes use of thermodynamic measurements on the 4He–Grafoil system. A calibration curve and a pressure scale for the manometer are developed which will allow convenient application in other laboratories. An experiment which utilizes the technique is briefly disscussed
A dynamic new look at the lambda transition
We discuss aspects of the theory of critical phenomena and explore the superfluid transition in 4He. We review some of the recent experimental and theoretical work on helium in nonequilibrium conditions and summarize some future space experiments that might shed light on disagreements between theory and experiment
Theory and Observation of Displacement Phenomena in Coadsorbed Films
Displacement refers to a surprising phenomenon observed in a number of adsorption systems. At low temperatures, some relatively inert gases, such as krypton (Kr) or methane ( CH4), are found to displace molecules from preadsorbed monolayer films of a more condensable species, such as carbon tetrachloride ( CCl4), from a graphite substrate. We present a simple thermodynamic model to explain displacement and make a prediction applicable to both first-order and continuous displacement processes. We also present measurements on CH4/CCl4 and Kr/CCl4 coadsorbed films from 77–112 K that verify our prediction and yield the CCl4 film spreading pressure
Superfluidity Without Superflow in Unsaturated Helium Films
It is shown experimentally that the superfluid fraction ρs/ρ is continuous and finite at the point at which superflow vanishes in unsaturated helium films. It follows that there is a region of superfluidity without superflow. In addition it is shown that the behavior of the partial molar entropy may account for the disappearance of superflow without requiring that ρs/ρ vanish
Critical behavior of ion mobilities near the superfluid transition
Measurements are reported of the mobilities of helium ions in superfluid helium very close to the λ transition. The mobilities of both positive and negative ions appear to be singular in the sense of having infinite slope at the transition. The measurements are made by a new differential technique, based on the space-charge-limited method, which makes possible a sensitivity to changes in mobility of the order of parts in 104. This allows mobility measurements into the range |ε|<10-4, where ε=(T/Tλ)-1. Most of the reported measurements are taken along isotherms which cross the λ line at elevated pressures, although a series at saturated vapor pressure is also reported. Means of transforming the data between various thermodynamic paths are discussed. Uncertainty as to which thermodynamic path should be considered fundamental together with experimental problems in the technique at this stage in its development make quantitative assessment of the singularity difficult. However, if we assume a limiting form (μ-μλ)/μλ∼(-ε)ρ′, where μ is the mobility and μλ its value at the transition, we find for the exponent ρ′=0.94±0.02
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