Browsing by Author "Houston, William V."
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Item A calculation of the distribution of normal vibrations and the specific heat of a body-centered cubic lattice(1949) Fischer, Mary Jane; Houston, William V.Item A measurement of resistance noise(1954) Dalrymple, George Frank; Houston, William V.Item A study of mechanical forces on Type I superconductors in a magnetic field(1966) Smith, David Robert, 1939-; Houston, William V.An investigation of the mechanical forces on superconducting strips of indium about 10-1 cm in thickness and strips of vacuum deposited tin about 8 x 10°5 cm thick due to their passage through magnetic fields has been made with a torsion pendulum. At 4.2°K the thin films showed no observable eddy current damping, while the indium strips showed damping which increased with the magnetic field intensity. At temperatures corresponding to critical fields of about 50 gauss both materials showed damping which increased with the magnetic field intensity. This damping is clearly not due to eddy currents in the normal regions in the case of the tin films, since no eddy current damping was observed at 4.2°K. It is believed to be associated with the motion of normal superconducting boundaries and to the motion of flux lines against a resistive pinning force. An analysis of the data, assuming the dissipative force to be made up of a constant force plus a force proportional to the first power of the velocity with which the samples pass through the field regions, indicates that the constant force is about the same for the films and the strips for corresponding degrees of flux penetration. There was also evidence of a conservative force which tended to expel the samples from the field regions and produced a flux penetration barrier opposing the entrance of the samples into the field regions.Item A study of the Meissner effect in type I superconductors(1966) Liu, Yu; Houston, William V.This report includes an analysis of the flux penetration and expulsion from a normal conducting cylinder and then an account of the observed results of a superconducting ellipsoid. The penetration and expulsion of magnetic flux during the normal to superconducting transition was governed principally by the eddy current shielding. There was au initial rapid penetration and expulsion of flux as the external magnetic field became equal to the critical field.Item ac-Induced voltages in superconducting wires(1965) Taylor, Henry Fuller; Houston, William V.The purpose of this work is to attempt an explanation of the energy loss in superconducting wires carrying varying current in terms of some theoretical model. In particular the model developed independently by Bean and by H. London (and henceforth referred to as the Bean model, since he published it first) is applied to predict voltages induced in a wire carrying alternating current. Bean's model, which prescribes the distribution of current in a sample as a function of present conditions and history, has been applied by other experimenters to accurately forecast the magnetization behavior of various non-ideal Type II superconductors. A basic premiss of the model is that the magnitude of the current density J is determined only by the magnitude of the local magnetic induction B. We have taken J(B) to be of the form deduced by Kim from magnetization measurements: We have also assumed that the depth of current penetration is much less than the wire's radius. Relations for voltage as a function of current are derived for ac and ac superimposed dc. Theoretical V vs. I curves are found to agree fairly well with oscilloscope tracings obtained for a defectsaturated Nb wire. Before each observation a canceling coil was set to make the measured voltage V= 0 for small alternating currents. We assume that these small currents are confined to the wire's surface, so that B 0 within the wire. If this is correct, then for large ac amplitude where wire is the flux contained within the material of the wire. The relation V has been assumed for the theoretical derivations.Item Alternating currents in superconducting wires(1964) Birchak, J. Robert; Houston, William V.The transition currents and the power losses were observed for superconducting wires that were carrying 60 cps. currents. The wires were made of niobium, niobium alloyed with 10%, 25% and 33% zirconium, and PbBi 18%. The wire diameters ranged from 10 mils to 62.5 mils. Near 4.2°K all the wires containing niobium remained superconducting until the peak value of the 60 cps. magnetic field at some point on the wire surface had reached or exceeded the bulk critical field of niobium. For the lead alloy the peak value was higher than expected for pure lead. The d.c. transition currents were also measured and were usually greater than the peak a.c. values. In addition, the experiment showed that alternating current power losses occurred while the peak field was far below the transition field. For any given wire, the losses were observed to increase as In. The magnitude of these power losses also varied with the material and the diameter of the wire. The results agreed reasonably well with data from other experiments. To study the results a model was used which had a superconducting cylinder surrounded by a shell of normal material. Maxwell's and London's equations were solved for this situation. The solutions did not predict the obsered relation between the current and the power loss, but they suggested that some form of flux trapping or hysteresis behavior-should have been included in the model.Item An initial study of the normal vibrations of white tin(1955) Dempesy, Colby Wilson; Houston, William V.Item An investigation of flux trapping in a superconducting tin sphere(1963) McAshan, Michael Sanford; Houston, William V.Measurements have been made of magnetic dipole moments trapped in a superconducting tin sphere by transition at constant temperature and at constant field. These measurements were made by suspending the sphere in a torsion pendulum and observing the interaction of the grozen-in moment with a uniform magnetic field. The magnetic moment of the sphere was found to be the same roughly reproducible function of temperature for both types of transition, and it remained constant with time as long as the temperature was not changed. However, if the temperature was changed so as to make it possible, the moment would decrease toward the value given by this measured function. The angle between the direction at which the magnetic moment was trapped in the sphere and the direction of the applied magnetic field as also found to be a rough function of the temperature, the angle being greatest (about 45°) when the measured moment was smallest. The percentage of flux trapped was found to be constant (at about .05%) for low temperatures but to rise sharply near the critical temperature. Also noted near the critical temperature were some sort of electromagnetic losses in the superconducting sphere as evidenced by a greatly increased damping of the pendulum.Item Elastic constants and thermal expansion of niobium as a function of temperature(1962) Carroll, Keith James; Houston, William V.The three Independent elastic constants of the bcc niobium structure have been determined as a function of temperature over the range 4.2°-300°K, using an ultrasonic pulse technique - the propagation of 10 Me waves in preferred directions in the crystal specimen. Values obtained at 4.2°K are, in units of 10 dyne/cm2, c11 = 25.27 +/- 0.6%, c44 = 3.10 +/- 0.6%, c12 = 13.32 +/- 3.3%. A few measurements were also carried out on the thermal expansion of niobium, from 140°-280°K, and this quantity determined at a function of the temperature. The average expansion coefficient over the whole range studied was 6.24x10 to the -6th deg -1, which agreed moderately well with earlier work by other investigators.Item Forces on a superconducting disc rotating in a magnetic field(1967) Hardy, Rodger Willard; Houston, William V.This thesis describes experiments performed on a system consisting of a superconducting tin disc suspended to oscillate about its axis as a torsion pendulum. This disc is made to oscillate in a uniform magnetic field directed normal to its surface. Some nonuniformity is introduced in the field by having the disc oscillate above and parallel to a superconducting tin plate of the same diameter as the disc. Regularly spaced holes drilled in the plate trapped flux which also penetrated the pendulum, producing intermediate-state regions. The resulting motion was damped harmonic motion with the damping torque proportional to the angular velocity. This was indicated by graphs of the logarithm of the amplitude against time giving straight lines. This was true for nonuniform fields produced by plates having many holes, few holes, or no holes. The conclusion was that the damping torque is proportional to the angular velocity regardless of how the nonuniformity in the field is produced. Damping in the normal state in a uniform field without any plate was explained as being due to a small horizontal component of the magnetic field which was due partly to the coils and partly to the earth's field.Item Multiplicity of states in a many-body system(1965) Lee, Ching-Tsung; Houston, William V.In this thesis, a certain theorem in the representation theory of symmetric group is presented in a more detailed and precise form. The possibility of its application to a many-body system is pointed out. Specifically, its application to a system of N electrons has been worked out in some detail. Thus, the formulae for the number of possible states corresponding to a given spin value and for the total sum of these numbers over all possible spin values are presented.Item On the diamagnetism of free electrons(1963) Lane, Eric Trent; Houston, William V.The effect of proximity to an infinite potential wall boundary on the elgenvalues of single particle free electron states in a magnetic field is calculated. A general method for calculating the number of states below a specified energy is described and the diamagnetic susceptibility is calculated for three approximations, It is found that the Landau approximation gives surprisingly good results considering its simplicity. A classification of much of the important work in this subject is presented in the introduction, and a possible discrepancy in the usual applications of the WKB approximation is discussed in an appendix.Item Preliminary investigation of the normal vibrations of white tin(1953) Summers, Thomas W; Houston, William V.This paper has as its object the preliminary work required for a proposed investigation of the vibrational spectra. The main body of the paper is divided into three sections. The first is an outline of the theory of normal vibrations. The second is the application of the theory to tetragonal white tin. The third is a summary of results. In its most modern form, the theory is to be found in a paper of Born and Begbie, Applications of the theory to various solids are to be found in papers of Eellermann, Smith and Curien. Other papers of particular interest include those of Blackman, Montroll, Houston and Kroll. The series of papers by Blackman deserve special study since his work provided the first quantitative measure of the defect in the Debeye continuum theory. Houston's paper proposed a method of approximating the frequency distribution. The interesting work of Montroll and of Kroll treat the problem by taking the specific heat as a given function and solving an integral equation for the frequency distribution.Item Table of Contents for the Rice Institute Pamphlet, Volume Forty-five, No. 1, April 1958: Program in Celebration of the Opening of the M.D. Anderson Biological Laboratories and Welcome Remarks(Rice University, 1958-04) Houston, William V.; Chandler, Asa C.; Electronic version made possible with funding from the Rice Historical Society and Thomas R. Williams, Ph.D., class of 2000.Item The frequency spectrum of lithium fluoride(1957) Oliphint, George Clark; Houston, William V.Item Torsion pendulum studies on a superconducting sphere(1950) Muench, Nils Lilienberg; Houston, William V.Item Understanding the Physical World(Rice University, 1962-07) Houston, William V.; Electronic version made possible with funding from the Rice Historical Society and Thomas R. Williams, Ph.D., class of 2000.