NaAlSi: a self-doped semimetallic superconductor with free electrons and covalent holes

The layered ternary sp conductor NaAlSi, possessing the iron-pnictide "111" crystal structure, superconducts at 7 K. Using density functional methods, we show that this compound is an intrinsic (self-doped) low-carrier-density semimetal with a number of unusual features. Covalent Al-Si valence bands provide the holes, and free-electron-like Al 3s bands, which propagate in the channel between the neighboring Si layers, dip just below the Fermi level to create the electron carriers. The Fermi level (and therefore the superconducting carriers) lies in a narrow and sharp peak within a pseudogap in the density of states. The small peak arises from valence bands which are nearly of pure Si, quasi-two-dimensional, flat, and coupled to Al conduction bands. Isostructural NaAlGe, which is not superconducting above 1.6 K, has almost exactly the same band structure except for one missing piece of small Fermi surface. Certain deformation potentials induced by Si and Na displacements along the c-axis are calculated and discussed. It seems likely that the mechanism of pairing is related to that of several other lightly doped two-dimensional nonmagnetic semiconductors (TiNCl, ZrNCl, HfNCl), which is not well understood but apparently not of phonon origin.Comment: 9 pages, 7 figures, 1 tabl

Boundary effects on the scaling of the superfluid density

We study numerically the influence of the substrate (boundary conditions) on the finite--size scaling properties of the superfluid density $\rho_s$ in superfluid films of thickness $H$ within the XY model employing the Monte Carlo method. Our results suggest that the jump $\rho_s H/T_c$ at the Kosterlitz--Thouless transition temperature $T_c$ depends on the boundary conditions.Comment: 2 pages, 1 Latex file, 1 postscript figure, 2 style file

The Intracluster Light and its Link with the Dynamical State of the Host Group/Cluster: the Role of the Halo Concentration

We investigate on the role of the halo concentration in the formation of the intra-cluster light (ICL) in galaxy groups and clusters, as predicted by a state-of-art semi-analytic model of galaxy formation, coupled with a set of high-resolution dark matter only simulations. The analysis focuses on how the fraction of ICL correlates with halo mass, concentration and fraction of early-type galaxies (ETGs) in a large sample of groups and clusters with $13.0\leq \log M_{halo} \leq 15.0$. The fraction of ICL follows a normal distribution, a consequence of the stochastic nature of the physical processes responsible for the formation of the diffuse light. The fractional budget of ICL depends on both halo mass (very weakly) until group scales, and concentration (remarkably). More interestingly, the ICL fraction is higher in more concentrated objects, a result of the stronger tidal forces acting in the innermost regions of the haloes where the concentration is the quantity playing the most relevant role. Our model predictions do not show any dependence between the ICL and ETGs fractions and so, we instead suggest the concentration rather than the mass, as recently claimed, to be the main driver of the ICL formation. The diffuse light starts to form in groups via stellar stripping and mergers and later assembled in more massive objects. However, the formation and assembly keep going on group/cluster scales at lower redshift through the same processes, mainly via stellar stripping in the vicinity of the central regions where tidal forces are stronger.Comment: 16 pages, 6 figures, 1 table. Accepted for publication in ApJ, small correction

The Impact of Futures Trading on Cash Market Volatility: Evidence from the Tokyo Stock Exchange

This paper has examined Japanese stock market volatility using alternative estimates of volatility and several testing procedures to compare the time periods before and after the introduction of index futures contracts. On the basis of 100 randomly selected stocks, empirical evidence from these texts indicates that futures trading had an insignificant impact on prove volatility in the cash market. The results are generally consistent with what has been reported for the U.S. market

Sorting live stem cells based on Sox2 mRNA expression.

PMCID: PMC3507951This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.While cell sorting usually relies on cell-surface protein markers, molecular beacons (MBs) offer the potential to sort cells based on the presence of any expressed mRNA and in principle could be extremely useful to sort rare cell populations from primary isolates. We show here how stem cells can be purified from mixed cell populations by sorting based on MBs. Specifically, we designed molecular beacons targeting Sox2, a well-known stem cell marker for murine embryonic (mES) and neural stem cells (NSC). One of our designed molecular beacons displayed an increase in fluorescence compared to a nonspecific molecular beacon both in vitro and in vivo when tested in mES and NSCs. We sorted Sox2-MB(+)SSEA1(+) cells from a mixed population of 4-day retinoic acid-treated mES cells and effectively isolated live undifferentiated stem cells. Additionally, Sox2-MB(+) cells isolated from primary mouse brains were sorted and generated neurospheres with higher efficiency than Sox2-MB(-) cells. These results demonstrate the utility of MBs for stem cell sorting in an mRNA-specific manner

Scaling of the superfluid density in superfluid films

We study scaling of the superfluid density with respect to the film thickness by simulating the $x-y$ model on films of size $L \times L \times H$ ($L >> H$) using the cluster Monte Carlo. While periodic boundary conditions where used in the planar ($L$) directions, Dirichlet boundary conditions where used along the film thickness. We find that our results can be scaled on a universal curve by introducing an effective thickness. In the limit of large $H$ our scaling relations reduce to the conventional scaling forms. Using the same idea we find scaling in the experimental results using the same value of $\nu = 0.6705$.Comment: 4 pages, one postscript file replaced by one Latex file and 5 postscript figure

VE-cadherin and claudin-5: it takes two to tango

Endothelial barrier function requires the adhesive activity of VE-cadherin and claudin-5, which are key components of adherens and tight endothelial junctions, respectively. Emerging evidence suggests that VE-cadherin controls claudin-5 expression by preventing the nuclear accumulation of FoxO1 and -catenin, which repress the claudin-5 promoter. This indicates that a crosstalk mechanism operates between these junctional structures