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Studies of the surface of liquid 4He /Mantz, Ira Bernard January 1980 (has links)
No description available.
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The infrared spectrum of the helium molecular ion helium-3 positive helium-4.Yu, Nan. January 1988 (has links)
This dissertation is concerned with the first experimental observation of the vibration-rotation spectrum of the helium molecular ion, ³He⁴He⁺. The Doppler-tuned fast-beam laser-resonance technique has been used. The ions produced in an electron-impact ion source form an ion beam of a few KeV and then intersect nearly colinearly with a CO IR laser beam of fixed frequency. The velocity of the ions is scanned to tune the ions into resonance with the laser frequency. Subsequent resonance detection is realized by using charge exchange processes of the ion with a target gas. Twelve spectral lines have been measured which correspond to nine different vibration-rotation transitions of the R branch in the fundamental band of the ground state of ³He⁴He⁺. The combination of the kinematic compression of the fast-beam method and the special frequency stabilization of the CO laser render an experimental accuracy of 0.0006 cm⁻¹ or 0.4 ppm. The accuracy exceeds that of the available theory by three orders of magnitude. The narrow spectral linewidth also allows partial resolution of the magnetic hyperfine structure due to helium-3. A hyperfine structure calculation has been carried out using a numerical multi-configuration self-consistent-field method. The agreement between the calculation and the observation is very satisfying.
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Helium Assisted Sand Casting of Aluminum AlloysSaleem, Muhammad Qaiser 28 April 2011 (has links)
Sand casting is the most widely used casting process for both ferrous and non-ferrous alloys; however, the process is marred by large grain size structures and long solidification times. The coarser microstructure has a negative effect on the mechanical properties of the cast components and the long processing time affects the overall productivity of the process. The research reported herein addresses these problems for aluminum sand castings by enhancing the rate of heat extraction from the casting by replacing air, which is typically present in the pores of the sand mold and has a relatively low thermal conductivity by helium which has a thermal conductivity that is at least five times that of air in the temperature range of interest. The effect of (1) the flow rate of helium, (2) the way in which it is introduced into the mold, and (3) the mold design on (a) the average grain size, (b) the secondary dendrite arm spacing, and (c) the room temperature tensile properties of castings is investigated and compared to their counterparts produced in a typical sand casting process. In addition, a cost analysis of the helium-assisted sand casting process is performed and an optimum set of parameters are identified. It is found that when the helium-assisted sand casting process is performed with close to the optimum parameters it produces castings that exhibit a 22 percent increase in ultimate tensile strength and a 34 percent increase in yield strength with no significant loss of ductility, no degradation in the quality of the as-cast surfaces, and no significant increase in the overall cost.
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Studies of homogeneous nucleation and transient heat transfer in cryogenic liquidsSinha, Dipen N. 01 January 1980 (has links)
We report the results of a series of experimental studies in two interrelated areas: homogeneous nucleation and transient heat transfer in cryogenic liquids. We report the first determination of the homogeneous nucleation temperature of liquid helium I and liquid nitrogen employing a transient superheating technique. This technique in liquid helium involved the development of a new transient magnetoresistive thermometer which relies on the strong temperaure dependence of magnetoresistance in bismuth as a thermometric property. Our measurements of the homogeneous nucleation temperature for both liquid helium I and nitrogen are in good agreement with the predictions from the Becker-Doring Volmer-Zel'dovich-Frenkel nucleation theory. On the basis of such agreement between theory and experiment in both liquid helium and liquid nitrogen we have developed a corresponding state analysis applicable to the case of homogeneous nucleation in liquid noble gases, both quantum and classical. Predictions of the homogeneous nucleation temperature and surface tension of several hydrogen isotopes are made from such a quantum mechanical law of corresponding states. We also comment on the limiting superheat temperature of liquid helium I. It is suggested that a comparison between the limiting superheat temperaure and the peak nucleate boiling temperature is meaningless and that the reported agreement between the two is largely fortuitous. In the studies of transient heat transfer in helium we find that the heat transfer from a solid into liquid helium is markedly enhanced by the application of a visible pulse of light. In liquid nitrogen we find that a transition to stable film boiling can be observed for power values as low as 40 per cent of the steady-state peak heat flux.
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A source and detector for coherent helium atom scattering /Deponte, Daniel Paul, January 2004 (has links)
Thesis (Ph. D.)--University of Oregon, 2004. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 69-70). Also available for download via the World Wide Web; free to University of Oregon users.
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Helium atom scattering as a probe of hydrogen adsorption and dynamicsTuddenham, Fay Elizabeth January 2011 (has links)
No description available.
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Vapor-liquid phase equilibria of the binary system argon-heliumMcCain, William David 05 1900 (has links)
No description available.
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Helium speech enhancement using the short-time fourier transformRichards, Mark Andrew 05 1900 (has links)
No description available.
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High energy pulses in liquid helium-4Ashworth, S. P. January 1998 (has links)
No description available.
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A physical interpretation of the He-He interaction by partitioning of the associated density matricesFrystak, Ronald Wayne January 1968 (has links)
Typescript. / Thesis (Ph. D.)--University of Hawaii, 1968. / Bibliography: leaves 142-143. / vi, 143 l graphs, tables
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