A Small-Sample Overlapping Variance-Ratio Test

The null distribution of the overlapping variance-ratio (OVR) test of the random-walk hypothesis is known to be downward biased and skewed to the right in small samples. As shown by Lo and MacKinlay (1989), the test under-rejects the null on the left tail seriously when the sample size is small. This property adversely affects the applicability of the OVR test to macroeconomic time series, which usually have rather small samples. In this paper, we propose a modified overlapping variance-ratio statistic and derive its exact mean under the normality assumption. We propose to approximate the small-sample distribution of the modified statistic using a beta distribution that matches the (exact) mean and the (asymptotic) variance. A Monte Carlo experiment shows that the beta approximation performs well in small samples.link_to_subscribed_fulltex

Gpr124 is essential for blood-brain barrier integrity in central nervous system disease

Although blood-brain barrier (BBB) compromise is central to the etiology of diverse central nervous system (CNS) disorders, endothelial receptor proteins that control BBB function are poorly defined. The endothelial G-protein-coupled receptor (GPCR) Gpr124 has been reported to be required for normal forebrain angiogenesis and BBB function in mouse embryos, but the role of this receptor in adult animals is unknown. Here Gpr124 conditional knockout (CKO) in the endothelia of adult mice did not affect homeostatic BBB integrity, but resulted in BBB disruption and microvascular hemorrhage in mouse models of both ischemic stroke and glioblastoma, accompanied by reduced cerebrovascular canonical Wnt-β-catenin signaling. Constitutive activation of Wnt-β-catenin signaling fully corrected the BBB disruption and hemorrhage defects of Gpr124-CKO mice, with rescue of the endothelial gene tight junction, pericyte coverage and extracellular-matrix deficits. We thus identify Gpr124 as an endothelial GPCR specifically required for endothelial Wnt signaling and BBB integrity under pathological conditions in adult mice. This finding implicates Gpr124 as a potential therapeutic target for human CNS disorders characterized by BBB disruption

Step phenomenon of vortices flow in superconductor

We investigate numerically the transport of vortices in superconductors under a driving force by using Langevin dynamics. The velocity-driving force characteristic (Vx–FL curve) of superconductors includes a region with series of stages. The impact of the initial states was investigated and there is a dramatic difference between the initial state produced by the current annealing process (CAP) and the well pinned state (WPS)

Residential Environment, Diet and Risk of Stomach Cancer: a Case-control Study in Linzhou, China.

A case-control study was conducted to investigate risk factors for stomach cancer in a rural population in China. Linzhou Cancer Registry was used to identify cases of stomach cancer, aged between 30 and 75 years, diagnosed between January 1998 and April 1999. Three neighbourhood controls were selected for each case, matched according to age, sex and village of residence. A total of 210 cases and 630 controls were interviewed. Conditional logistic regression was used to estimate odds ratios (OR) for factors associated with the risk of cancer. Among characteristics of the residential environment, significantly increased risk was found for: frequent irritation on eyes or throat by soot (OR 5.54, 95% CI 1.42-21.65, p for trend <0.01). This effect was particularly strong in women (OR 19.5, 95% CI 1.28-297.09, p for trend =0.01). Dietary factors that were significantly associated with an increased risk were food grains other than rice, wheat and maize (OR 2.93, 95% 1.16-7.38), pickled or salted vegetables (OR 3.99, 95% CI 1.63-9.75) and preference for a high salt diet (OR 2.58, 95% CI 1.56-4.26). The consumption of vegetables showed a protective effect with an odds ratio of 0.27 (95% CI 0.11-0.61). It follows that a developing economy and improvement in living standards, with associated increased intake of fruit and vegetables and reduced consumption of salt, can contribute to a reduction in the incidence of stomach cancer in the Linzhou population

Signaling via the prostaglandin E2 receptor EP4 exerts neuronal and vascular protection in a mouse model of cerebral ischemia

Stroke is the third leading cause of death in the United States. Fewer than 5% of patients benefit from the only intervention approved to treat stroke. Thus, there is an enormous need to identify new therapeutic targets. The role of inducible cyclooxygenase (COX-2) activity in stroke and other neurologic diseases is complex, as both activation and sustained inhibition can engender cerebral injury. Whether COX-2 induces cerebroprotective or injurious effects is probably dependent on which downstream prostaglandin receptors are activated. Here, we investigated the function of the PGE2 receptor EP4 in a mouse model of cerebral ischemia. Systemic administration of a selective EP4 agonist after ischemia reduced infarct volume and ameliorated long-term behavioral deficits. Expression of EP4 was robust in neurons and markedly induced in endothelial cells after ischemia-reperfusion, suggesting that neuronal and/or endothelial EP4 signaling imparts cerebroprotection. Conditional genetic inactivation of neuronal EP4 worsened stroke outcome, consistent with an endogenous protective role of neuronal EP4 signaling in vivo. However, endothelial deletion of EP4 also worsened stroke injury and decreased cerebral reperfusion. Systemic administration of an EP4 agonist increased levels of activated eNOS in cerebral microvessels, an effect that was abolished with conditional deletion of endothelial EP4. Thus, our data support the concept of targeting protective prostaglandin receptors therapeutically after stroke