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Full-Text Articles in Physics

Cooperative Effects Among Partial Waves In Mie Scattering, James A. Lock Dec 1988

Cooperative Effects Among Partial Waves In Mie Scattering, James A. Lock

Physics Faculty Publications

Observations of an illuminated water droplet at a close distance are described mathematically by the Fourier transform of the Mie-scattering amplitude convolved with the aperture function of the observer’s eye. Most of the sharp enhancements found in the Fourier transform correspond to geometrical rays associated with the various terms in the Debye-series expansion of the Mie amplitude. However, there are some enhancements that cannot be ascribed to any individual Debye-series term. Instead, they arise from a constructive interference cooperation of the phase of a scattering resonance in a single partial wave with the region of the stationary phase corresponding to …


Transport Critical Current And Magnetization Measurements Of Melt-Processed Yba2cu3o7-X, A. H. Hermann, Z. Z. Sheng, W. Kiehl, D. Marsh, A. Elali, Paul D. Hambourger, C. Almasan, J. Estrada, T. Datta Nov 1988

Transport Critical Current And Magnetization Measurements Of Melt-Processed Yba2cu3o7-X, A. H. Hermann, Z. Z. Sheng, W. Kiehl, D. Marsh, A. Elali, Paul D. Hambourger, C. Almasan, J. Estrada, T. Datta

Physics Faculty Publications

We report magnetic field dependence of the transport critical current and dc magnetic susceptibility measurements on YBa2Cu3O7−x superconductors formed by melt-solid reactions at 950 °C between Ba-Cu-O (or Tb-Ba-Cu-O) and solid nonstoichiometric Y-Ba-Cu-oxide. Four-probe dc critical current measurements at 77, 64, and 4.2 K show strong depression of the critical current density with increasing magnetic field in agreement with a model of weakly linked superconducting regions. Diamagnetic shielding and Meissner flux expulsion measurements in the temperature range 10–300 K show about one third volume fraction of perfect superconductivity. Both shielding and flux expulsion were observed to be approximately temperature independent …


Possible Origins Of High-Tc, Superconductivity, John R. Hardy, John W. Flocken May 1988

Possible Origins Of High-Tc, Superconductivity, John R. Hardy, John W. Flocken

Physics Faculty Publications

A new mechanism is proposed to explain high-T, superconductivity in copper-oxide-based, open perovskitelike systems. It is shown that, should the oxygen ions be moving in a double-well potential, an order-of-magnitude enhancement of the electron-lattice coupling follows automatically from a consistent treatment of this motion. Both theoretical and experimental evidence for the presence of such double wells is cited.


Cayley-Tree Ising Model With Antiferromagnetic Nearest-Neighbor And Ferromagnetic Equivalent-Neighbor Interactions, Miron Kaufman, M. Kahana May 1988

Cayley-Tree Ising Model With Antiferromagnetic Nearest-Neighbor And Ferromagnetic Equivalent-Neighbor Interactions, Miron Kaufman, M. Kahana

Physics Faculty Publications

The phase diagram of the Ising model with antiferromagnetic nearest-neighbor interactions and ferromagnetic equivalent-neighbor interactions on the Cayley tree is determined exactly. A nonuniversal critical line separates the disordered and the ordered phases. A line of first-order transitions separating ferromagnetic order from antiferromagnetic order ends in the midst of the ordered phase at a classical ordered critical point. For a small range of values of the ratio of the two couplings, two transitions occur as the temperature is varied. In this case the uniform magnetization is not a monotonic function of the temperature.


A New Search For Interstellar C3, Charles L. Joseph, Theodore P. Snow, C Gregory Seab Jan 1988

A New Search For Interstellar C3, Charles L. Joseph, Theodore P. Snow, C Gregory Seab

Physics Faculty Publications

A new, very sensitive search for interstellar triatomic carbon has resulted in upper limits for a few diffuse clouds of order 1010 cm – 2, or about 10 – 11 with respect to hydrogen. These limits are consistent with recent cold diffuse cloud chemistry models, but may be in conflict with shocked cloud models such as those invoked to explain CH + abundances. Our results may also be argue against linear carbon-chain molecules as carriers of the diffuse interstellar bands.


Contact Resistance Measurements In Gaas Mesfet's And Modfet's By The Magneto‐Tlm Technique, David C. Look Jan 1988

Contact Resistance Measurements In Gaas Mesfet's And Modfet's By The Magneto‐Tlm Technique, David C. Look

Physics Faculty Publications

The standard transmission‐line model (TLM) for specific contact resistivity measurements of planar contacts is improved in two ways: (i) the addition of a magnetic field, which gives the mobility and carrier concentration of the bulk material, and the mobility of the material under the contact; and (ii) an extension to two layers, which makes the model applicable to MODFET structures. The results are applied to MESFET material, and MODFET material. One conclusion concerning the latter material is that the electrons directly beneath the annealed Au/Ge/Ni contacts have lower mobility than those in the bulk, but still …


The Energy-Dependence Of Polarization Observables In The ²H(D,Γ)⁴He Reaction, H. R. Weller, R. M. Whitton, J. Langenbrunner, Evans Hayward, W. R. Dodge, S. Kuhn, D. R. Tilley Jan 1988

The Energy-Dependence Of Polarization Observables In The ²H(D,Γ)⁴He Reaction, H. R. Weller, R. M. Whitton, J. Langenbrunner, Evans Hayward, W. R. Dodge, S. Kuhn, D. R. Tilley

Physics Faculty Publications

Measurements of the tensor and vector analyzing powers, Ayy(130°) and Ay(130°), have been obtained for the 2H(d,γ )4He reaction for energies ranging from Ed(lab) = 0.3 MeV to Ed(lab) = 50 MeV. The Ayy(130°) data are sensitive to the D-state present in the ground state of 4He and are observed to have their maximum value near Ed = 30 MeV. The vector analyzing power data show a maximum near Ed = 3 MeV. The data are compared to the results of a microscopic …