Structural and doping effects in the half-metallic double perovskite A2A_2CrWO6_6

he structural, transport, magnetic and optical properties of the double perovskite $A_2$CrWO$_6$ with $A=\text{Sr, Ba, Ca}$ have been studied. By varying the alkaline earth ion on the $A$ site, the influence of steric effects on the Curie temperature $T_C$ and the saturation magnetization has been determined. A maximum $T_C=458$ K was found for Sr$_2$CrWO$_6$ having an almost undistorted perovskite structure with a tolerance factor $f\simeq 1$. For Ca$_2$CrWO$_6$ and Ba$_2$CrWO$_6$ structural changes result in a strong reduction of $T_C$. Our study strongly suggests that for the double perovskites in general an optimum $T_C$ is achieved only for $f \simeq 1$, that is, for an undistorted perovskite structure. Electron doping in Sr$_2$CrWO$_6$ by a partial substitution of Sr$^{2+}$ by La$^{3+}$ was found to reduce both $T_C$ and the saturation magnetization $M_s$. The reduction of $M_s$ could be attributed both to band structure effects and the Cr/W antisites induced by doping. Band structure calculations for Sr$_2$CrWO$_6$ predict an energy gap in the spin-up band, but a finite density of states for the spin-down band. The predictions of the band structure calculation are consistent with our optical measurements. Our experimental results support the presence of a kinetic energy driven mechanism in $A_2$CrWO$_6$, where ferromagnetism is stabilized by a hybridization of states of the nonmagnetic W-site positioned in between the high spin Cr-sites.Comment: 14 pages, 10 figure

Equity, efficiency and inequality traps: A research agenda

This paper discusses a research agenda that arises from unanswered questions and unresolved issues considered in the World Bank’s World Development Report 2006: Equity and Development. After formalizing the key concepts of equity; equality of opportunity; and efficiency, and proposing a definition for an equitable development policy, the paper discusses the concept of inequality traps, around which the research agenda is structured. Four broad groups of research questions are highlighted: those revolving around the measurement of inequality of opportunity and the diagnostics for the existence of an inequality trap; those dealing with the causes of inequality traps; the quantification of their efficiency costs; and those related to how institutions (including governments) evolve to overcome inequality traps. Copyright Springer Science+Business Media, Inc. 2007equity, equality of opportunity, inequality traps.,

Tumor necrosis factor (TNF)-alpha, soluble TNF receptors and endometrial cancer risk: The EPIC study

Chronic inflammation has been hypothesized to play a role in endometrial cancer development. Tumor necrosis factor-alpha (TNF-alpha), one of the major pro-inflammatory cytokines, has also been implicated in endometrial physiology. We conducted a case-control study nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) to examine the association of TNF-alpha and its two soluble receptors (sTNFR1 and sTNFR2) with endometrial cancer risk. Two-hundred-seventy cases and 518 matched controls were analyzed using conditional logistic regression. All statistical tests were two-sided. We observed an increased risk of endometrial cancer among women in the highest versus lowest quartile of TNF-alpha (odds ratio [OR]: 1.73, 95% CI: 1.09-2.73, P(trend)=0.01), sTNFR1 (OR: 1.68, 95% CI: 0.99-2.86, P(trend)=0.07), and sTNFR2 (OR: 1.53, 95%CI: 0.92-2.55, P(trend)=0.03) after adjustment for body-mass-index, parity, age at menopause and previous postmenopausal hormone therapy use. Further adjustments for estrogens and C-peptide had minor effect on risk estimates. Our data show that elevated pre-diagnostic concentrations of TNF-alpha and its soluble receptors are related to a higher risk of endometrial cancer, particularly strong in women diagnosed within 2 years of blood donation. This is the first study of its kind and therefore deserves replication in further prospective studies