Magnetic field dependence of the temperature derivative of resistivity: a probe for distinguishing the effects of pseudogap and superconducting fluctuations in cuprates

We have studied the magnetic field dependence of the temperature derivative of the resistivity, dr(H,T)/dT, of a number of Y1-xCaxBa2(Cu1-yZny)3O7-d crystalline thin films over a wide range of sample compositions. From the analysis of the temperature derivative data we have been able to distinguish quite clearly between two characteristic temperature scales, (a) the onset of strong superconducting fluctuation temperature, Tscf and (b) the pseudogap temperature, TPG. Significantly different characteristic features of dr(H,T)/dT at Tscf and at TPG imply that Tscf and TPG have different physical origins.Comment: Submitted to Physica C (M2S-HTSC 2006 Proceedings

Economic Aspects of the Palestinian-Israeli Conflict: The Collapse of the Oslo Accord

conflict, Middle East, Israel, Palestine

Effects of Zn on the grain boundary properties of La2-xSrxCu1-yZnyO4 superconductors

The properties of the grain boundaries (GBs) are of significant importance in high-Tc cuprates. Most large scale applications of cuprate superconductors involve usage of sintered compounds. The critical current density and the ability to trap high magnetic flux inside the sample depend largely on the quality of the GBs. Zn has the ability to pin vortices but it also degrades superconductivity. In this study we have investigated the effect of Zn impurity on the intergrain coupling properties in high-quality La2-xSrxCu1-yZnyO4 sintered samples with different hole concentrations, p (\equiv x), over a wide range of Zn contents (y) using field-dependent ac susceptibility (ACS) measurements. The ACS results enabled us to determine the superconducting transition temperature Tc, and the temperature Tgcp, at which the randomly oriented superconducting grains become coupled as a function of hole and disorder contents. We have analyzed the behavior of the GBs from the systematic evolution of the values of Tgcp(p, y), Tc(p, y), and from the contribution to the field-dependent ACS signal coming from the intergrain shielding current. Zn suppresses both Tc and Tgcp in a similar fashion. The hole content and the carrier localization due to Zn substitution seem to have significant effect on the coupling properties of the GBs. We have discussed the possible implications of these findings in detail in this article. PACS: 74.72.Dn; 74.62.Dh; 74.25.Sv Keywords: Zn doped La214; Critical current density; Grain boundaryComment: To appear in Physica

The Isotope Effect in Superconductors

We review some aspects of the isotope effect (IE) in superconductors. Our focus is on the influence of factors not related to the pairing mechanism. After summarizing the main results obtained for conventional superconductors, we review the effect of magnetic impurities, the proximity effect and non-adiabaticity on the value of the isotope coefficient (IC). We discuss the isotope effect of $T_c$ and of the penetration depth $\delta$. The theory is applied to conventional and high-$T_c$ superconductors. Experimental results obtained for YBa$_2$Cu$_3$O$_{7-\delta}$ related materials (Zn and Pr-substituted as well as oxygen-depleted systems) and for La$_{2-x}$Sr$_x$CuO$_4$ are discussed.Comment: 31 pages, 10 figures. Review article to appear in "Pair Correlation in Many Fermions Systems", Plenum Press 199

Effect of Medicaid/SCHIP and WIC on Oral Health of Low-Income Children

Oral caries is the most prevalent chronic disease among US children, and disproportionately impacts those of low socioeconomic status. Studies have shown that the Special Supplemental Nutrition Program for Women Infants and Children (WIC) improves access to dental care among Medicaid children. This study investigated the impact of WIC, Medicaid, and the State Children\u27s Health Insurance Program (SCHIP) on the prevalence of dental caries among low-income children. The 1999-2000 and 2001-2002 NHANES data were utilized for this analysis. Children 2-4 years old who participated in WIC, Medicaid, or SCHIP, or who were uninsured, and for whom both interview and complete oral health exam data were available (n = 597) were included in the study. Multivariate logistic regression modeling was conducted to examine the effects of program participation on caries. There was no statistically significant association between dental caries and participation in public assistance programs. The risk of dental caries for children in MedicaidSCHIP only was comparable to the risk for children in WIC and MedicaidSCHIP (OR = 1.04; 95%CI = 0.622, 1.745) and also to uninsured children (OR = 0.96; 95%CI = 0.523, 1.773). Dental caries were not impacted if the child did not have a preventive dental visit in the past 6 months (OR = 0.68; 95% CI = 0.436, 1.063) or did not have a regular dental care provider (OR = 1.15; 95% CI = 0.646, 2.044). Participation in WIC and MedicaidSCHIP does not improve the oral health of low-income children. Because this population is a high-risk group requiring more specialized efforts, improving access to care is not sufficient to improve oral health. In addition to increased utilization of services, the program partnership between WIC and MedicaidSCHIP must provide targeted, educational interventions to prevent dental caries. It may also be necessary to increase the recommended number of preventive visits for low-income children