Issued as a Part of Progress Report No. 13 of The Investigation of Prestressed Reinforced Concrete for Highway Bridges; Project IHR-10, Illinois Cooperative Highway Research Program

The Division of Highways. State of Illinois.The Bureau of Public Roads. U.S. Department of Commerc

Group expansions for impurities in superconductors

A new method is proposed for practical calculation of the effective interaction between impurity scatterers in superconductors, based on algebraic properties of related Nambu matrices for Green functions. In particular, we show that the density of states within the s-wave gap can have a non-zero contribution (impossible either in Born and in T-matrix approximation) from non-magnetic impurities with concentration $c \ll 1$, beginning from $\sim c^{3}$ order.Comment: 5 pages, 1 figur

Cooper pairs as resonances

Using the Bethe-Salpeter (BS) equation, Cooper pairing can be generalized to include contributions from holes as well as particles from the ground state of either an ideal Fermi gas (IFG) or of a BCS many-fermion state. The BCS model interfermion interaction is employed throughout. In contrast to the better-known original Cooper pair problem for either two particles or two holes, the generalized Cooper equation in the IFG case has no real-energy solutions. Rather, it possesses two complex-conjugate solutions with purely imaginary energies. This implies that the IFG ground state is unstable when an attractive interaction is switched on. However, solving the BS equation for the BCS ground state reveals two types of {\it real} solutions: one describing moving (i.e., having nonzero total, or center-of-mass, momenta) Cooper pairs as resonances (or bound composite particles with a {\it finite} lifetime), and another exhibiting superconducting collective excitations sometimes known as Anderson-Bogoliubov-Higgs (ABH) modes. A Bose-Einstein-condensation-based picture of superconductivity is addressed.Comment: 5 pages in PS, including 3 figures. In press Physica

Superfluid Spin-down, with Random Unpinning of the Vortices

The so-called ``creeping'' motion of the pinned vortices in a rotating superfluid involves ``random unpinning'' and ``vortex motion'' as two physically separate processes. We argue that such a creeping motion of the vortices need not be (biased) in the direction of an existing radial Magnus force, nor should a constant microscopic radial velocity be assigned to the vortex motion, in contradiction with the basic assumptions of the ``vortex creep'' model. We point out internal inconsistencies in the predictions of this model which arise due to this unjustified foundation that ignores the role of the actual torque on the superfluid. The proper spin-down rate of a pinned superfluid is then calculated and turns out to be much less than that suggested in the vortex creep model, hence being of even less observational significance for its possible application in explaining the post-glitch relaxations of the radio pulsars.Comment: To be published in J. Low Temp. Phys., Vol. 139, May 2005 [Eqs 11, 15-17 here, have been revised and, may be substituted for the corresponding ones in that paper

Examining the Link Between Pledging, Hazing, and Organizational Commitment Among Members of a Black Greek Fraternity

Black Greek-Letter Organization (BGLO) members hold strong opinions about the purposes and efficacy of pledging and hazing as a means of member initiation. Those who argue in favor of the pledge process claim it is needed to help remove those not genuinely interested in membership, develop appreciation for and pride in the organization, and generate longterm organizational commitment and sustained participation. Those who call for an end to pledging argue that whatever benefit might be gained from such bonding experiences is overshadowed by the mortal, legal, reputational, emotional, and financial risks posed for both the associations and the individuals involved. Despite decades of conjectural debate on the efficacy of pledging and hazing, to the authors’ knowledge, no empirical study has examined its impact on BGLO alumni-level membership continuance. To address this deficiency, the researchers conducted a logistic regression analysis of survey responses from alumni members of a BGLO fraternity (n = 285). Results revealed no statistically significant relationship between participation in a pledge process and alumni level membership. The implication of these findings for BGLOs and their members and leaders are discussed

Contact symmetry of time-dependent Schr\"odinger equation for a two-particle system: symmetry classification of two-body central potentials

Symmetry classification of two-body central potentials in a two-particle Schr\"{o}dinger equation in terms of contact transformations of the equation has been investigated. Explicit calculation has shown that they are of the same four different classes as for the point transformations. Thus in this problem contact transformations are not essentially different from point transformations. We have also obtained the detailed algebraic structures of the corresponding Lie algebras and the functional bases of invariants for the transformation groups in all the four classes