Optical properties of pyrochlore oxide Pb2Ru2O7−δPb_{2}Ru_{2}O_{7-{\delta}}

We present optical conductivity spectra for $Pb_{2}Ru_{2}O_{7-{\delta}}$ single crystal at different temperatures. Among reported pyrochlore ruthenates, this compound exhibits metallic behavior in a wide temperature range and has the least resistivity. At low frequencies, the optical spectra show typical Drude responses, but with a knee feature around 1000 \cm. Above 20000 \cm, a broad absorption feature is observed. Our analysis suggests that the low frequency responses can be understood from two Drude components arising from the partially filled Ru $t_{2g}$ bands with different plasma frequencies and scattering rates. The high frequency broad absorption may be contributed by two interband transitions: from occupied Ru $t_{2g}$ states to empty $e_{g}$ bands and from the fully filled O 2p bands to unoccupied Ru $t_{2g}$ states.Comment: 4 pages, 6 figure

Critical Exponents for Nuclear Multifragmentation: dynamical lattice model

We present a dynamical and dissipative lattice model, designed to mimic nuclear multifragmentation. Monte-Carlo simulations with this model show clear signature of critical behaviour and reproduce experimentally observed correlations. In particular, using techniques devised for finite systems, we could obtain two of its critical exponents, whose values are in agreement with those of the universality class to which nuclear multifragmentation is supposed to belong.Comment: 10 pages, 3 figures, to be published in Nuclear Physics

Non-Markovian dynamics for an open two-level system without rotating wave approximation: Indivisibility versus backflow of information

By use of the two measures presented recently, the indivisibility and the backflow of information, we study the non-Markovianity of the dynamics for a two-level system interacting with a zero-temperature structured environment without using rotating wave approximation (RWA). In the limit of weak coupling between the system and the reservoir, and by expanding the time-convolutionless (TCL) generator to the forth order with respect to the coupling strength, the time-local non-Markovian master equation for the reduced state of the system is derived. Under the secular approximation, the exact analytic solution is obtained and the sufficient and necessary conditions for the indivisibility and the backflow of information for the system dynamics are presented. In the more general case, we investigate numerically the properties of the two measures for the case of Lorentzian reservoir. Our results show the importance of the counter-rotating terms to the short-time-scale non-Markovian behavior of the system dynamics, further expose the relations between the two measures and their rationality as non-Markovian measures. Finally, the complete positivity of the dynamics of the considered system is discussed

The aminobisphosphonate pamidronate controls influenza pathogenesis by expanding a γδ T cell population in humanized mice

As shown in humanized mice, a population of Vγ9Vδ2 T cells can reduce the severity and mortality of disease caused by infection with human and avian influenza viruses

On the origin of the zero-resistance anomaly in heavy fermion superconducting Ir: a clue from magnetic field and Rh-doping studies

We present the results of the specific heat and AC magnetic susceptibility measurements of $CeIr_{1-x}Rh_xIn_5$ for x from 0 to 0.5. As x is increased from 0 both quantities reflect the competition between two effects. The first is a suppression of superconductivity below the bulk transition temperature of T$_c = 0.4$ K, which is due to the pair breaking effect of Rh impurities. The second is an increase in the volume fraction of the superconducting regions above T$_c$, which we attribute to defect-induced strain. Analysis of the H-T phase diagram for CeIrIn$_5$obtained from the bulk probes and resistance measurements points to the filamentary origin of the inhomogeneous superconductivity at T$_\rho \approx 1.2$ K, where the resistance drops to zero. The identical anisotropies in the magnetic field dependence of the specific heat and the resistance anomalies in CeIrIn$_5$ indicate that the filamentary superconductivity is intrinsic, involving electrons from the part of the Fermi surface responsible for bulk superconductivity.Comment: 4 page

High-Order Coupled Cluster Method (CCM) Calculations for Quantum Magnets with Valence-Bond Ground States

In this article, we prove that exact representations of dimer and plaquette valence-bond ket ground states for quantum Heisenberg antiferromagnets may be formed via the usual coupled cluster method (CCM) from independent-spin product (e.g. N\'eel) model states. We show that we are able to provide good results for both the ground-state energy and the sublattice magnetization for dimer and plaquette valence-bond phases within the CCM. As a first example, we investigate the spin-half $J_1$--$J_2$ model for the linear chain, and we show that we are able to reproduce exactly the dimerized ground (ket) state at $J_2/J_1=0.5$. The dimerized phase is stable over a range of values for $J_2/J_1$ around 0.5. We present evidence of symmetry breaking by considering the ket- and bra-state correlation coefficients as a function of $J_2/J_1$. We then consider the Shastry-Sutherland model and demonstrate that the CCM can span the correct ground states in both the N\'eel and the dimerized phases. Finally, we consider a spin-half system with nearest-neighbor bonds for an underlying lattice corresponding to the magnetic material CaV$_4$O$_9$ (CAVO). We show that we are able to provide excellent results for the ground-state energy in each of the plaquette-ordered, N\'eel-ordered, and dimerized regimes of this model. The exact plaquette and dimer ground states are reproduced by the CCM ket state in their relevant limits.Comment: 34 pages, 13 figures, 2 table

The Chromatin Remodeler BPTF Activates a Stemness Gene-Expression Program Essential for the Maintenance of Adult Hematopoietic Stem Cells

Self-renewal and differentiation of adult stem cells are tightly regulated partly through configuration of chromatin structure by chromatin remodelers. Using knockout mice, we here demonstrate that bromodomain PHD finger transcription factor (BPTF), a component of the nucleosome remodeling factor (NURF) chromatin-remodeling complex, is essential for maintaining the population size of hematopoietic stem/progenitor cells (HSPCs), including long-term hematopoietic stem cells (HSCs). Bptf-deficient HSCs are defective in reconstituted hematopoiesis, and hematopoietic-specific knockout of Bptf caused profound defects including bone marrow failure and anemia. Genome-wide transcriptome profiling revealed that BPTF loss caused downregulation of HSC-specific gene-expression programs, which contain several master transcription factors (Meis1, Pbx1, Mn1, and Lmo2) required for HSC maintenance and self-renewal. Furthermore, we show that BPTF potentiates the chromatin accessibility of key HSC “stemness” genes. These results demonstrate an essential requirement of the chromatin remodeler BPTF and NURF for activation of “stemness” gene-expression programs and proper function of adult HSCs. Wang and colleagues show that a chromatin remodeler, BPTF, sustains appropriate functions of hematopoietic stem/progenitor cells (HSPCs). BPTF loss causes bone marrow failure and anemia. The authors further define a BPTF-dependent gene-expression program in HSPCs, which contains key HSC stemness factors. These results demonstrate an essential requirement of the BPTF-associated chromatin remodelers for HSC functionality and adult hematopoiesis

Magnetotunneling spectroscopy of mesoscopic correlations in two-dimensional electron systems

An approach to experimentally exploring electronic correlation functions in mesoscopic regimes is proposed. The idea is to monitor the mesoscopic fluctuations of a tunneling current flowing between the two layers of a semiconductor double-quantum-well structure. From the dependence of these fluctuations on external parameters, such as in-plane or perpendicular magnetic fields, external bias voltages, etc., the temporal and spatial dependence of various prominent correlation functions of mesoscopic physics can be determined. Due to the absence of spatially localized external probes, the method provides a way to explore the interplay of interaction and localization effects in two-dimensional systems within a relatively unperturbed environment. We describe the theoretical background of the approach and quantitatively discuss the behavior of the current fluctuations in diffusive and ergodic regimes. The influence of both various interaction mechanisms and localization effects on the current is discussed. Finally a proposal is made on how, at least in principle, the method may be used to experimentally determine the relevant critical exponents of localization-delocalization transitions.Comment: 15 pages, 3 figures include

Time-Dependent Spintronic Transport and Current-Induced Spin Transfer Torque in Magnetic Tunnel Junctions

The responses of the electrical current and the current-induced spin transfer torque (CISTT) to an ac bias in addition to a dc bias in a magnetic tunnel junction are investigated by means of the time-dependent nonquilibrium Green function technique. The time-averaged current (time-averaged CISTT) is formulated in the form of a summation of dc current (dc CISTT) multiplied by products of Bessel functions with the energy levels shifted by $m\hbar \omega _{0}$. The tunneling current can be viewed as to happen between the photonic sidebands of the two ferromagnets. The electrons can pass through the barrier easily under high frequencies but difficultly under low frequencies. The tunnel magnetoresistance almost does not vary with an ac field. It is found that the spin transfer torque, still being proportional to the electrical current under an ac bias, can be changed by varying frequency. Low frequencies could yield a rapid decrease of the spin transfer torque, while a large ac signal leads to both decrease of the electrical current and the spin torque. If only an ac bias is present, the spin transfer torque is sharply enhanced at the particular amplitude and frequency of the ac bias. A nearly linear relation between such an amplitude and frequency is observed.Comment: 13 pages,8 figure