Current-induced shuttlecock-like movement of non-axisymmetric chiral skyrmions

Current-induced motion of non-axisymmetric skyrmions within tilted ferromagnetic phases of polar helimagnets with the easy plane anisotropy is studied by micromagnetic simulations. Such non-axisymmetric skyrmions consist of a circular core and a crescent-shaped domain-wall region formed with respect to the tilted surrounding state. Current-driven motion of non-axisymmetric skyrmions exhibits two distinct time regimes: initially the skyrmions rotate towards the current flow direction and subsequently move along the current with the skyrmionic crescent first. According to the Thiele equation, the asymmetric distribution of the topological charge and the dissipative force tensor play an important role for giving the different velocities for the circular and the crescent-shaped constituent parts of the skyrmion what underlies such a shuttlecock-like movement. Moreover, the current-velocity relation depends on the angle of the tilted ferromagnetic phase what makes in particular the transverse velocity of skyrmions sensitive to their field-driven configurational transformation. We also argue the possibility of magnetic racetrack waveguides based on complex interplay of robust asymmetric skyrmions with multiple twisted edge states

The electronic state of vortices in YBa2Cu3Oy investigated by complex surface impedance measurement

The electromagnetic response to microwaves in the mixed state of YBa2Cu3Oy(YBCO) was measured in order to investigate the electronic state inside and outside the vortex core. The magnetic-field dependence of the complex surface impedance at low temperatures was in good agreement with a general vortex dynamics description assuming that the field-independent viscous damping force and the linear restoring force were acting on the vortices. In other words, both real and imaginary parts of the complex resistivity, \rho_1, and \rho_2, were linear in B. This is explained by theories for d-wave superconductors. Using analysis based on the Coffey-Clem description of the complex penetration depth, we estimated that the vortex viscosity \eta at 10 K was (4 \sim 5) \times 10^{-7} Ns/m^2. This value corresponds to \omega_0 \tau \sim 0.3 - 0.5, where \omega_0 and \tau are the minimal gap frequency and the quasiparticle lifetime in the vortex core, respectively. These results suggest that the vortex core in YBCO is in the moderately clean regime. Investigation of the moderately clean vortex core in high-temperature superconductors is significant because physically new effects may be expected due to d-wave characteristics and to the quantum nature of cuprate superconductors. The behavior of Z_s as a function of B across the first order transition (FOT) of the vortex lattice was also investigated. Unlike Bi2Sr2CaCu2Oy (BSCCO), no distinct anomaly was observed around the FOT in YBCO. Our results suggest that the rapid increase of X_s due to the change of superfluid density at the FOT would be observed only in highly anisotropic two-dimensional vortex systems like BSCCO. We discuss these results in terms of the difference of the interlayer coupling and the energy scale between the two materials.Comment: 10 pages, 6 figures, to be published in Phys. Rev. B, one reference adde

External rotation during elevation of the arm

Background Knowledge about the pattern of rotation during arm elevation is necessary for a full understanding of shoulder function, and it is also useful for planning of rehabilitation protocols to restore range of motion in shoulders in disorder. However, there are insufficient in vivo data available

Genetic Deficiency of Glycogen Synthase Kinase-3β Corrects Diabetes in Mouse Models of Insulin Resistance

Despite treatment with agents that enhance β-cell function and insulin action, reduction in β-cell mass is relentless in patients with insulin resistance and type 2 diabetes mellitus. Insulin resistance is characterized by impaired signaling through the insulin/insulin receptor/insulin receptor substrate/PI-3K/Akt pathway, leading to elevation of negatively regulated substrates such as glycogen synthase kinase-3β (Gsk-3β). When elevated, this enzyme has antiproliferative and proapoptotic properties. In these studies, we designed experiments to determine the contribution of Gsk-3β to regulation of β-cell mass in two mouse models of insulin resistance. Mice lacking one allele of the insulin receptor (Ir+/−) exhibit insulin resistance and a doubling of β-cell mass. Crossing these mice with those having haploinsufficiency for Gsk-3β (Gsk-3β+/−) reduced insulin resistance by augmenting whole-body glucose disposal, and significantly reduced β-cell mass. In the second model, mice missing two alleles of the insulin receptor substrate 2 (Irs2−/−), like the Ir+/− mice, are insulin resistant, but develop profound β-cell loss, resulting in early diabetes. We found that islets from these mice had a 4-fold elevation of Gsk-3β activity associated with a marked reduction of β-cell proliferation and increased apoptosis. Irs2−/− mice crossed with Gsk-3β+/− mice preserved β-cell mass by reversing the negative effects on proliferation and apoptosis, preventing onset of diabetes. Previous studies had shown that islets of Irs2−/− mice had increased cyclin-dependent kinase inhibitor p27kip1 that was limiting for β-cell replication, and reduced Pdx1 levels associated with increased cell death. Preservation of β-cell mass in Gsk-3β+/−Irs2−/− mice was accompanied by suppressed p27kip1 levels and increased Pdx1 levels. To separate peripheral versus β-cell–specific effects of reduction of Gsk3β activity on preservation of β-cell mass, mice homozygous for a floxed Gsk-3β allele (Gsk-3F/F) were then crossed with rat insulin promoter-Cre (RIP-Cre) mice to produce β-cell–specific knockout of Gsk-3β (βGsk-3β−/−). Like Gsk-3β+/− mice, βGsk-3β−/− mice also prevented the diabetes of the Irs2−/− mice. The results of these studies now define a new, negatively regulated substrate of the insulin signaling pathway specifically within β-cells that when elevated, can impair replication and increase apoptosis, resulting in loss of β-cells and diabetes. These results thus form the rationale for developing agents to inhibit this enzyme in obese insulin-resistant individuals to preserve β-cells and prevent diabetes onset

The M235T Polymorphism in the AGT Gene and CHD Risk: Evidence of a Hardy-Weinberg Equilibrium Violation and Publication Bias in a Meta-Analysis

BACKGROUND: The M235T polymorphism in the AGT gene has been related to an increased risk of hypertension. This finding may also suggest an increased risk of coronary heart disease (CHD). METHODOLOGY/PRINCIPAL FINDINGS: A case-cohort study was conducted in 1,732 unrelated middle-age women (210 CHD cases and 1,522 controls) from a prospective cohort of 15,236 initially healthy Dutch women. We applied a Cox proportional hazards model to study the association of the polymorphism with acute myocardial infarction (AMI) (n = 71) and CHD. In the case-cohort study, no increased risk for CHD was found under the additive genetic model (hazard ratio [HR] = 1.20; 95% confidence interval [CI], 0.86 to 1.68; P = 0.28). This result was not changed by adjustment (HR = 1.17; 95% CI, 0.83 to 1.64; P = 0.38) nor by using dominant, recessive and pairwise genetic models. Analyses for AMI risk under the additive genetic model also did not show any statistically significant association (crude HR = 1.14; 95% CI, 0.93 to 1.39; P = 0.20). To evaluate the association, a comprehensive systematic review and meta-analysis were undertaken of all studies published up to February 2007 (searched through PubMed/MEDLINE, Web of Science and EMBASE). The meta-analysis (38 studies with 13284 cases and 18722 controls) showed a per-allele odds ratio (OR) of 1.08 (95% CI, 1.01 to 1.15; P = 0.02). Moderate to large levels of heterogeneity were identified between studies. Hardy-Weinberg equilibrium (HWE) violation and the mean age of cases were statistically significant sources of the observed variation. In a stratum of non-HWE violation studies, there was no effect. An asymmetric funnel plot, the Egger's test (P = 0.066), and the Begg-Mazumdar test (P = 0.074) were all suggestive of the presence of publication bias. CONCLUSIONS/SIGNIFICANCE: The pooled OR of the present meta-analysis, including our own data, presented evidence that there is an increase in the risk of CHD conferred by the M235T variant of the AGT gene. However, the relevance of this weakly positive overall association remains uncertain because it may be due to various residual biases, including HWE-violation and publication biases

Contrasting patterns of the 5S and 45S rDNA evolutions in the Byblis liniflora complex (Byblidaceae)

To clarify the evolutionary dynamics of ribosomal RNA genes (rDNAs) in the Byblis liniflora complex (Byblidaceae), we investigated the 5S and 45S rDNA genes through (1) chromosomal physical mapping by fluorescence in situ hybridization (FISH) and (2) phylogenetic analyses using the nontranscribed spacer of 5S rDNA (5S-NTS) and the internal transcribed spacer of 45S rDNA (ITS). In addition, we performed phylogenetic analyses based on rbcL and trnK intron. The complex was divided into 2 clades: B. aquatica–B. filifolia and B. guehoi–B. liniflora–B. rorida. Although members of the complex had conservative symmetric karyotypes, they were clearly differentiated on chromosomal rDNA distribution patterns. The sequence data indicated that ITS was almost homogeneous in all taxa in which two or four 45S rDNA arrays were frequently found at distal regions of chromosomes in the somatic karyotype. ITS homogenization could have been prompted by relatively distal 45S rDNA positions. In contrast, 2–12 5S rDNA arrays were mapped onto proximal/interstitial regions of chromosomes, and some paralogous 5S-NTS were found in the genomes harboring 4 or more arrays. 5S-NTS sequence type-specific FISH analysis showed sequence heterogeneity within and between some 5S rDNA arrays. Interlocus homogenization may have been hampered by their proximal location on chromosomes. Chromosomal location may have affected the contrasting evolutionary dynamics of rDNAs in the B. liniflora complex