Strong-coupling effects in high-T c superconductors

It is conceivable that the high-T _c superconducting perovskites are conventional electronphonon superconductors. In this case one expects significant strong-coupling effects because of the unusually high ratiok _B T _c / of the order 0.1 and greater. We use a set of reasonable models for the Eliashberg function ² F() (which takes into account available information on the phonon spectra and which fit the measuredT _c 's) and calculate strong-coupling effects in the specific heatc _s (T)/T _c , the ratio ₀/k _B T _c , the critical fieldsH _c (T) andH _c2 (T) including Pauli limiting, and other measurable quantities. Strongcoupling corrections turn out to be in the range of 0 to about 100%, depending on the quantity of interest. We discuss the perspectives of using strong-coupling effects as indicators for conventional electron-phonon superconductivity in the new materials.     

Evaluating dredging and offshore loading locations for U.S. coal exports using the local logistics system

The formulation and use of a mixed integer mathematical programming location-allocation model, the Coal Logistics System (COLS), is presented in this study. COLS is used to evaluate the potential for reducing water-borne coal transportation costs, and concomitantly the costs of delivering coal to European markets. This cost reduction is accomplished through the use of supercolliers which would require the dredging of channels at selected ports or the use of offshore loading sites at East and Gulf Coast ports or both. The model developed and the analysis presented in this paper are intended to aid in the determination of the location and extent of these activities, and to indicate the size of the potential reduction in the costs of U.S. export coal. In order to be able to accommodate these deeper draft vessels at East and Gulf Coast ports, expensive improvements would need to be undertaken which may include the deepening of harbor channels to the depths required for 120 000 dead weight ton (dwt) or larger supercolliers. Since dredging requires large initial investments and has significant long-term maintenance costs, excess capacity could represent an inefficient use of both U.S. revenues and the ports' own funds. The use of offshore loading moorings to permit the topping off of supercolliers by self-unloading colliers at the deepwater sections of harbor channels has been proposed as a way of reducing trans-ocean transportation costs and avoiding the large investments and time delays associated with dredging activities. The Coal Logistics System was modified and extended to enable the evaluation of these two port improvement options to be undertaken in a consistent and realistic manner.     

The general three-vertex,BRS identities and renormalizability of the light-cone gauge

The general one-loop three-vertexГ _μeλ ^abc (p, q, r) in the four-component formulation of the Yang-Mills theory is calculated in the light-cone gauge. The nonvanishing counter Lagrangian constructed from this three-vertex and the self-energy is proportional to the original Lagrangian, the single renormalization constant being -11g² C _YM Г(2?ω)/48π². Gauge dependent and nonlocal counterterms do not contribute to the renormalization constant, but are needed to verify the appropriate Slavnov-Taylor (ST) and Becchi-Rouet-Stora (BRS) identities.