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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Helium-3 density measurements using atomic pressure broadening /

Mohon, Sara Elizabeth. January 2009 (has links)
Thesis (Honors)--College of William and Mary, 2009. / Includes bibliographical references (leaf 31). Also available via the World Wide Web.

A helium II rotation experiment

Turkington, Ralph Robert January 1962 (has links)
In this thesis a rotating helium experiment is described. A special dewar featuring a separate experimental chamber and optical windows was constructed and operated satisfactorily. A small helium bucket was rotated using a magnetic coupling to the outside driving mechanism. Observations of the free helium surface were made using monochromatic parallel light incident to the surface at an oblique angle. By observing the astigmatic images it was possible to calculate the curvature of the helium surface. Detecting the presence of angular momentum in this way we had hoped to elucidate the findings of Hall (1957) and Walmsey and Lane (1958). Their results suggest a "disappearance" or non-conservation of angular momentum at low angular velocities. The angular velocities in our experiment ranged from 1.58 to 13.7 radians per second, the lower value being limited by surface disturbances. Over this range classical behaviour of the helium surface was observed, so we conclude that the "disappearing" angular momentum phenomenon is confined to angular speeds lower than 1.58 radians per second. The effect of surface tension upon the shape of the rotating helium surface was considered at the lower angular velocities. An argument is advanced which shows that if certain scaling conditions are satisfied a helium model may be constructed. This entails choosing another liquid with suitable density and surface tension and matching, by calculation, the diameter of the container. In this way the curvature of the model is related to the helium surface curvature for both stationary and rotational states. From this we calculate the curvature-angular velocity relationship, which is shown to be in agreement with the observed helium data. It appears that there need be no lower angular velocity limitation due to surface tension in wide bucket rotating helium experiments. The rate of formation of curvature was also examined in a few instances. A review of the general properties of liquid Helium II and some of the hydrodynamical aspects are also presented. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Some dynamic properties of liquid helium

Chopra, Kasturi Lal January 1957 (has links)
This thesis describes three independent investigations of the dynamic properties of the superfluid He II film flow and the viscous flow of liquid helium in acoustic streams generated by the gradient of the radiation pressure occuring due to attenuation of sound propagating in liquid helium. The non-isothermal He II film flow induced gravitationally is studied for the covered (Cu-Ni cover of the wire-filled-tube superleak intact) and the uncovered film (Cu-Ni cover peeled off) flowing through a superleak when subjected to a thermal plus gravitational potential at a point midway between the two transfer points. It is found that the critical transfer rate of the covered film is not affected by the nature and magnitude of this potential. For the case of uncovered film warmed in the middle, in contrast to that of the covered film, the transfer can be reversed by a suitable thermal potential, the maximum rate being the same in either direction. In the case of cooling by direct pumping over the uncovered film, however, film flow stops either way; in the light of other results, we have given an explanation to this controversial observation in terms of thinning down of the film to its non-superfluid layers, a conclusion possibly equivalent to a shift of λ-point for thinner films. A closed glass capsule, sealed off at room temperature with 750 psig of He gas, sufficient to provide enough liquid at helium temperatures, is used to measure the gravitationally induced transfer rates of He II film at temperatures between 0.3°K and the λ-point. Like Ambler and Kurti, we find that the transfer rate rises by 25% above the flat minimum near 1°K though, in contrast to the steady rise observed by these authors, our results indicate slight flattening near 0.3°K. This confirms that, like thermal properties, the film flow property of He II also undergoes a radical change below 1°K. A technique is developed whereby fine particles of a suitable mixture of solid H₂ plus D₂ are suspended in liquid helium. A number of experiments are suggested to study flow properties of liquid He visually by using these particles as indicators. We have used these particles as indicators in acoustic streaming experiments designed to measure the ratio of the second to the first coefficient of viscosity. These two coefficients occur in the expression for absorption coefficient of sound and are calculated by Khalatnikov for He II. The streaming is observed to be turbulent to the lowest possible ultrasonic intensity. Thus, such determination is not feasible. The streaming in He II is found to obey the classical equation of turbulence. It is independent of temperature and shows no anomaly at or above the λ-point, possibly due to complete absorption of sound in the turbulent medium. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A rotation experiment with liquid helium II

Crooks, Michael John Chamberlain January 1957 (has links)
The thesis contains a brief introduction to the problem of He II, including mention of the salient experimental work, of the last fifty years. The treatment of He II in rotating systems is then discussed in more detail and a review of the previous rotation experiments is presented. In a rotating mass of He II, it has been shown by Osborne that the parabolic rise of the liquid surface should be proportional to the amount of normal fluid present and that a radial temperature gradient should be set up. For reasonable angular velocities (on the order of 3 rev/sec.) and for beakers of about 2 cm. radius, the temperature difference between the axis and the periphery would be on the order of 10⁻⁴°K . It can be shown that this temperature would lead to an effective distillation of liquid from the warmer to the cooler regions which it was thought might be the mechanism leading to the known result that the whole mass of liquid partakes of the rotary motion. An experiment was designed whereby a volume of helium might be rotated but the possibility of such a distillation process was eliminated. Measurements of the surface shape during rotation showed that even in this case the whole fluid rotated at all angular velocities and temperatures used. Finally, further experiments which might shed further light on this problem are proposed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Zero field level crossing in the helium atom

Bardsley, Robert Eckardt January 1970 (has links)
Zero-field level crossing techniques have been used to measure some upper state lifetimes of the helium atom. The upper states of the atom were excited in a discharge between two capacitor plates. A radio frequency voltage was applied to these plates by a 450 MHz source. The emitted light was modulated by rotating a quarter-wave plate in front of a polaroid in the beam of emitted light. The polarization, which is directly related to this modulation, was measured by a phase sensitive lock-in amplifier. The halfwidths of curves obtained by plotting the polarization against the magnetic field strength for the n¹D - 2¹P transitions yielded lifetimes of; 2.71 x 10(-8) sec. for the 3¹D state, 3.97 x 10(-8) sec. for the 4¹D state and 4.48 x 10(-8) sec. for the 5¹D state. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The influence of crossed electric and magnetic fields on the spectrum of helium

Pounder, Elton Roy January 1937 (has links)

The production of doubly charged helium ions and a study of their elastic scattering by carbon /

Bittner, John W. January 1954 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1954. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The scattering of low energy helium atoms at the surface of liquid helium /

Mrozinski, Peter M. January 1974 (has links)
No description available.

Migro-gas analysis in relation to radiochemical problems

Wilson, Edward James January 1950 (has links)
No description available.

Positronium ionisation in collision with He atoms

Armitage, Simon Peter January 2002 (has links)
No description available.

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