Effects of diagonal disorder on Charge Density Wave and Superconductivity in local pair systems

We analyse the influence of diagonal disorder (random site energy) on Charge Density Wave (CDW) and Superconductivity (SS) in local pair systems which are described by the model of hard core charged bosons on a lattice. This problem was previously studied within the mean field approximation for the case of half filled band (n = 1). Here we extend that investigation to the case of arbitrary particle concentration (0 < n < 2) and examine the phase diagrams of the model and the behaviour of superfluid density as a function of n and the increasing disorder. Depending on the strength of random on-site energies, the intersite density-density repulsion and the concentration the model can exhibit several various phases, including homogeneous phases: CDW, SS and Bose-glass (NO) as well as the phase separated states: CDW-SS, CDW-NO and particle droplets. The obtained results for SS phase are in qualitative agreement with the available Monte Carlo calculations for two dimensional lattice. Also, in a definite range of parameters the system exhibits the phenomena which we call a disorder induced superconductivity and a disorder induced charge ordering.Comment: 21 pages, 8 figure

Cooh-Terminal Truncated Alpha1S Subunits Conduct Current Better than Full-Length Dihydropyridine Receptors

Skeletal muscle dihydropyridine (DHP) receptors function both as voltage-activated Ca2+ channels and as voltage sensors for coupling membrane depolarization to release of Ca2+ from the sarcoplasmic reticulum. In skeletal muscle, the principal or α1S subunit occurs in full-length (∼10% of total) and post-transcriptionally truncated (∼90%) forms, which has raised the possibility that the two functional roles are subserved by DHP receptors comprised of different sized α1S subunits. We tested the functional properties of each form by injecting oocytes with cRNAs coding for full-length (α1S) or truncated (α1SΔC) α subunits. Both translation products were expressed in the membrane, as evidenced by increases in the gating charge (Qmax 80–150 pC). Thus, oocytes provide a robust expression system for the study of gating charge movement in α1S, unencumbered by contributions from other voltage-gated channels or the complexities of the transverse tubules. As in recordings from skeletal muscle, for heterologously expressed channels the peak inward Ba2+ currents were small relative to Qmax. The truncated α1SΔC protein, however, supported much larger ionic currents than the full-length product. These data raise the possibility that DHP receptors containing the more abundant, truncated form of the α1S subunit conduct the majority of the L-type Ca2+ current in skeletal muscle. Our data also suggest that the carboxyl terminus of the α1S subunit modulates the coupling between charge movement and channel opening

Saddlepoint tests for quantile regression

Quantile regression is a flexible and powerful technique which allows us to model the quantiles of the conditional distribution of a response variable given a set of covariates. Regression quantile estimators can be viewed as M-estimators and standard asymptotic inference is readily available based on likelihood-ratio, Wald, and score-type test statistics. However these statistics require the estimation of the sparsity function s(α) = [g(G−1(α))]−1, where G and g are the cumulative distribution function and the density of the regression errors, respectively, and this can lead to nonparametric density estimation. Moreover the asymptotic χ2 distribution for these statistics can provide an inaccurate approximation of tail probabilities and this can lead to inaccurate P-values, especially for moderate sample sizes. Alternative methods which do not require the estimation of the sparsity function include rank techniques and resampling methods to obtain confidence intervals, which can be inverted to test hypotheses. These are typically more accurate than the standard M-tests. In this article we show how accurate tests can be obtained by using a nonparametric saddlepoint test statistic. The proposed statistic is asymptotically χ2 distributed, does not require the specification of the error distribution, and does not require the estimation of the sparsity function. The validity of the method is demonstrated through a simulation study, which shows both the robustness and the accuracy of the new test compared to the best available alternatives

Frustrated 3-Dimensional Quantum Spin Liquid in CuHpCl

Inelastic neutron scattering measurements are reported for the quantum antiferromagnetic material Cu_2(C_5H_12N_2)_2Cl_4 (CuHpCl). The magnetic excitation spectrum forms a band extending from 0.9 meV to 1.4 meV. The spectrum contains two modes that disperse throughout the a-c plane of the monoclinic unit cell with less dispersion along the unique b-axis. Simple arguments based on the measured dispersion relations and the crystal structure show that a spin ladder model is inappropriate for describing CuHpCl. Instead, it is proposed that hydrogen bond mediated exchange interactions between the bi-nuclear molecular units yield a three-dimensional interacting spin system with a recurrent triangular motif similar to the Shastry-Sutherland Model (SSM). Model independent analysis based on the first moment sum rule shows that at least four distinct spin pairs are strongly correlated and that two of these, including the dimer bond of the corresponding SSM, are magnetically frustrated. These results show that CuHpCl should be classified as a frustration induced three dimensional quantum spin liquid.Comment: 13 pages, 17 figures (Color) ReSubmitted to Phys. Rev. B 9/21/2001 resubmission has new content email comments to [email protected] or [email protected]

Perivascular Fat and the Microcirculation: Relevance to Insulin Resistance, Diabetes, and Cardiovascular Disease

Type 2 diabetes and its major risk factor, obesity, are a growing burden for public health. The mechanisms that connect obesity and its related disorders, such as insulin resistance, type 2 diabetes, and hypertension, are still undefined. Microvascular dysfunction may be a pathophysiologic link between insulin resistance and hypertension in obesity. Many studies have shown that adipose tissue-derived substances (adipokines) interact with (micro)vascular function and influence insulin sensitivity. In the past, research focused on adipokines from perivascular adipose tissue (PVAT). In this review, we focus on the interactions between adipokines, predominantly from PVAT, and microvascular function in relation to the development of insulin resistance, diabetes, and cardiovascular disease

Quantum phases and phase transitions of Mott insulators

This article contains a theoretical overview of the physical properties of antiferromagnetic Mott insulators in spatial dimensions greater than one. Many such materials have been experimentally studied in the past decade and a half, and we make contact with these studies. The simplest class of Mott insulators have an even number of S=1/2 spins per unit cell, and these can be described with quantitative accuracy by the bond operator method: we discuss their spin gap and magnetically ordered states, and the transitions between them driven by pressure or an applied magnetic field. The case of an odd number of S=1/2 spins per unit cell is more subtle: here the spin gap state can spontaneously develop bond order (so the ground state again has an even number of S=1/2 spins per unit cell), and/or acquire topological order and fractionalized excitations. We describe the conditions under which such spin gap states can form, and survey recent theories (T. Senthil et al., cond-mat/0312617) of the quantum phase transitions among these states and magnetically ordered states. We describe the breakdown of the Landau-Ginzburg-Wilson paradigm at these quantum critical points, accompanied by the appearance of emergent gauge excitations.Comment: 51 pages, 13 figure

Modulation of calcium-binding proteins expression and cisplatin chemosensitivity by calcium chelation in human breast cancer MCF-7 cells

© 2021 The Author(s).Cisplatin (CDDP) is currently one of the most effective FDA-approved treatments for breast cancer. Previous studies have shown that CDDP-induced cell death in human breast cancer (MCF-7) cells is associated with disruption of calcium homeostasis. However, whether the sensitivity of breast cancer cells to cisplatin is associated with dysregulation of the expression of calcium-binding proteins (CaBPs) remains unknown. In this study, we evaluated the effect of the intracellular calcium chelator (BAPTA-AM) on viability of MCF-7 cells in the presence of toxic and sub-toxic doses of cisplatin. Furthermore, this study assessed the expression of CaBPs, calmodulin, S100A8, and S100A14 in MCF-7 cells treated with cisplatin. Cell viability was determined using MTT-based in vitro toxicity assay. Intracellular calcium imaging was done using Fluo-4 AM, a cell-permeant fluorescent calcium indicator. Expression of CaBPs was tested using real-time quantitative PCR. Exposure of cells to increasing amounts of CDDP correlated with increasing fluorescence of the intracellular calcium indicator, Fluo-4 AM. Conversely, treating cells with cisplatin significantly decreased mRNA levels of calmodulin, S100A8, and S100A14. Treatment of the cells with calcium chelator, BAPTA-AM, significantly enhanced the cytotoxic effects of sub-toxic dose of cisplatin. Our results indicated a statistically significant negative correlation between calmodulin, S100A8, and S100A14 expression and sensitivity of breast cancer cells to a sub-toxic dose of cisplatin. We propose that modulating the activity of calcium-binding proteins, calmodulin, S100A8, and S100A14, could be used to increase cisplatin efficacy, lowering its treatment dosage while maintaining its chemotherapeutic value.Peer reviewedFinal Published versio