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Articles 1 - 7 of 7
Full-Text Articles in Physics
Addendum: "Bethe Stopping-Power Theory For Heavy-Target Atoms", P.T. Leung
Addendum: "Bethe Stopping-Power Theory For Heavy-Target Atoms", P.T. Leung
Physics Faculty Publications and Presentations
Our previous result on the correction of the Bethe stopping power theory for heavy target elements is amended, with the application of a more consistent version of the semirelativistic Bethe sum rule worked out recently [Phys. Rev. A 57, 4994 (1998)]. This correction is found to be significant for high-Z target atoms and relatively high-energy incident particles.
Simple Model For Linear And Nonlinear Mixing At Unstable Fluid Interfaces In Spherical Geometry, John D. Ramshaw
Simple Model For Linear And Nonlinear Mixing At Unstable Fluid Interfaces In Spherical Geometry, John D. Ramshaw
Physics Faculty Publications and Presentations
A simple model was recently described for predicting linear and nonlinear mixing at an unstable planar fluid interface subjected to an arbitrary time-dependent variable acceleration history [J. D. Ramshaw, Phys. Rev. E 58, 5834 (1998)]. Here we present an analogous model for describing the mixing of two adjacent spherical fluid shells of different density resulting from an arbitrary time-dependent mean interface radius R(t). As in the planar case, the model is based on a heuristic expression for the kinetic energy of the system. This expression is based on that for the kinetic energy of a linearly perturbed interface, but with …
Comment On "Relativistic Correction Of The Generalized Oscillator Strength Sum Rules", P.T. Leung, Scott M. Cohen
Comment On "Relativistic Correction Of The Generalized Oscillator Strength Sum Rules", P.T. Leung, Scott M. Cohen
Physics Faculty Publications and Presentations
Romero and Aucar [Phys. Rev. A 57, 2212 (1998)] have found a vanishing result for the relativistic correction to the dipole sum rule ∆S1 for a one-electron system. They have given a result for the dipole sum rule ∆S2 as well. We argue that these results are both incorrect and show explicitly that their approach yields a nonvanishing result for ∆S1. The corrected result is in agreement with that which we have obtained in a recent paper, in which we present explicit expressions for ∆S1, ∆S2, and several other more general sum rules.
Near-Field Fluorescence Microscopy Based On Two-Photon Excitation With Metal Tips, Erik J. Sánchez, Lukas Novotny, X. Sunney Xie
Near-Field Fluorescence Microscopy Based On Two-Photon Excitation With Metal Tips, Erik J. Sánchez, Lukas Novotny, X. Sunney Xie
Physics Faculty Publications and Presentations
We present a new scheme for near-field fluorescence imaging using a metal tip illuminated with femtosecond laser pulses of proper polarization. The strongly enhanced electric field at the metal tip (ap15 nm end diameter) results in a localized excitation source for molecular fluorescence. Excitation of the sample via two-photon absorption provides good image contrast due to the quadratic intensity dependence. The spatial resolution is shown to be better than that of the conventional aperture technique. We used the technique to image fragments of photosynthetic membranes, as well as j-aggregates with spatial resolutions on the order of 20 nm.
Natural Emissions Of Chlorine-Containing Gases: Reactive Chlorine Emissions Inventory, M. A. K. Khalil, R. M. Moore, D. B. Harper, J. M. Lobert, D. J. Erickson, V. Koropalov, W. T. Sturges, W. C. Keene
Natural Emissions Of Chlorine-Containing Gases: Reactive Chlorine Emissions Inventory, M. A. K. Khalil, R. M. Moore, D. B. Harper, J. M. Lobert, D. J. Erickson, V. Koropalov, W. T. Sturges, W. C. Keene
Physics Faculty Publications and Presentations
Although there are many chlorine-containing trace gases in the atmosphere, only those with atmospheric lifetimes of 2 years or fewer appear to have significant natural sources. The most abundant of these gases are methyl chloride, chloroform, dichloromethane, perchloroethylene, and trichloroethylene. Methyl chloride represents about 540 parts per trillion by volume (pptv) Cl, while the others together amount to about 120 pptv Cl. For methyl chloride and chloroform, both oceanic and land-based natural emissions have been identified. For the other gases, there is evidence of oceanic emissions, but the roles of the soils and land are not known and have not …
Approaching Critical Thinking Through Science, Linda A. George, Jack C. Straton
Approaching Critical Thinking Through Science, Linda A. George, Jack C. Straton
Physics Faculty Publications and Presentations
One unanticipated development of University Studies is the degree to which it rapidly became seen not just as general education, but as the replacement for all generally re quired courses. Because the natural sciences had com prised one of the distribution areas of the old program, expectations that the new program would teach science quickly flowered, although exactly what faculty mean by that term has yet to be established. In fact, discussions of what we intend by science education have brought in creased attention to these expectations as we continually revisit the goals of University Studies. The matter is far …
Chlorine-Containing Gases In Antarctica, M. A. K. Khalil, R. A. Rasmussen
Chlorine-Containing Gases In Antarctica, M. A. K. Khalil, R. A. Rasmussen
Physics Faculty Publications and Presentations
In recent years, there has been considerable interest in chlorine-containing trace gases in the atmosphere, particularly in Antarctica because of the relationship between chlorofluorocarbons and the antarctic ozone hole. All chlorinecontaining trace gases, whether produced by human activities or by natural processes, have a potential for destroying ozone in the stratosphere. This is a complex environmental problem, but it is clear that manmade chlorine-containing gases are the driving force behind the antarctic ozone hole and, by extension, reductions of stratospheric ozone over other parts of the world [World Meteorological Organization (WMO) 1989, 1991, 1995]. We have taken measurements of the …