200 research outputs found
Some properties of frustrated spin systems: extensions and applications of Lieb-Schupp approach
Lieb and Schupp have obtained, using certain version of ``spin-reflection
positivity'' method, a number of ground-state properties for frustrated
Heisenberg models. One group of these results is related to singlet nature of
ground state and it needs an assumption of reflection symmetry present in the
system. In this paper, it is shown that the result holds also for other
symmetries (inversion etc.). The second Lieb-Schupp result is relation between
ground-state energies of certain systems. In the paper, this relation is
applied to multidimensional models on various lattices.Comment: 15 pages, 8 eps figures, revtex
Influence of anisotropic next-nearest-neighbor hopping on diagonal charge-striped phases
We consider the model of strongly-correlated system of electrons described by
an extended Falicov-Kimball Hamiltonian where the stability of some axial and
diagonal striped phases was proved. Introducing a next-nearest-neighbor
hopping, small enough not to destroy the striped structure, we examine
rigorously how the presence of the next-nearest-neighbor hopping anisotropy
reduces the -rotation degeneracy of the diagonal-striped phase. The
effect appears to be similar to that in the case of anisotropy of the
nearest-neighbor hopping: the stripes are oriented in the direction of the
weaker next-nearest-neighbor hopping.Comment: 9 pages, 3 figures, 1 tabl
Particle Free Pump Down and Venting of UHV Vacuum Systems
Abstract Vacuum systems containing superconducting cavities which have to be operated at high gradients need to preserve the cleanliness of the superconducting cavity surfaces. In addition to an adequate preparation of the cavities and the neighbouring vacuum components special care needs to be taken during pump down and venting. Neither should be particles introduced into the vacuum system, nor should particles already present within the system be moved towards critical areas. For the superconducting linear accelerators of FLASH and the European XFEL at DESY a series of measurements have been performed to study the movement of particles in long tubes during pump down and venting. For this purpose an in-situ vacuum particle counter has been used. By reducing and varying the gas flow during these processes, it is possible to perform these actions without moving particles present inside such systems. Based on these measurements a set-up using various filters, flow controllers and a pressure gauge has been developed to avoid introducing particles into the vacuum system as well as moving existing particles. This set-up allows automated pump-down and venting of critical vacuum systems in a reliable and reproducible way, being much faster than the procedures used so far
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Early window of diabetes determinism in NOD mice, dependent on the complement receptor CRIg, identified by noninvasive imaging
All juvenile NOD mice exhibit insulitis, but there is substantial variation in their progression to diabetes. We demonstrate that a patient-validated magnetic-resonance-imaging (MRI) strategy to non-invasively visualize local effects of pancreatic-islet inflammation can predict diabetes onset in NOD mice. MRI signals acquired during a narrow early time-window allowed pre-sorting into disease-progressors and -nonprogressors and an estimate of time-to-diabetes. We exploited this capability to identify novel elements correlated with disease protection, including CRIg (complement receptor of the immunoglobulin superfamily), which marked a subset of macrophages associated with diabetes resistance. Administration of CRIg-Fc depressed MRI signals and diabetes incidence. In addition to identifying regulators of disease progression, this study shows that diabetes is set at an early age in NOD mice
Immunohistochemical characteristics of porcine intrahepatic nerves under physiological conditions and after bisphenol A administration
Background: The neurochemistry of hepatic nerve fibres was investigated in large animal models after dietary exposure to the endocrine disrupting compound known as bisphenol A (BPA).
Materials and methods: Antibodies against neuronal peptides were used to study changes in hepatic nerve fibres after exposure to BPA at varying concentrations using standard immunofluorescence techniques. The neuropeptides investigated were substance P (SP), galanin (GAL), pituitary adenylate cyclase activating polypeptide (PACAP), calcitonin gene regulated peptide (CGRP) and cocaine and amphetamine regulated transcript (CART). Immunoreactive nerve fibres were counted in multiple sections of the liver and among multiple animals at varying exposure levels. The data was pooled and presented as mean ± standard error of the mean.
Results: It was found that all of the nerve fibres investigated showed upregulation of these neural markers after BPA exposure, even at exposure levels currently considered to be safe. These results show very dramatic increases in nerve fibres containing the above-mentioned neuropeptides and the altered neurochemical levels may be causing a range of pathophysiological states if the trend of over-expression is extrapolated to developing humans.
Conclusions: This may have serious implications for children and young adults who are exposed to this very common plastic polymer, if the same trends are occurring in humans
A Monte Carlo study of the Falicov–Kimball model in the perturbative regime
Finite-temperature properties of the Falicov–Kimball model on the square lattice have been studied in
the perturbative regime, i.e. for t/U << 1, where t is the hopping constant and U denotes the Coulomb interaction
strength. In our study, we have determined the phase diagram of the model in the second-order of the
perturbation theory, where the antiferromagnetic Ising model in the magnetic field emerges. In the fourth-order,
where our model constitutes the Ising model with more complicated frustrated antiferromagnetic interactions,
the sketch of the phase diagram was established. The Monte Carlo method was employed and the behavior
of Binder cumulants based on the order parameters was analyzed to determine the type of ordering
and phase boundaries in the diagram
Ground-state properties of the Falicov-Kimball model with correlated hopping in two dimensions
A new numerical method, recently developed to study ground states of the
Falicov-Kimball model (FKM), is used to examine the effects of correlated
hopping on the ground-state properties of this model in two dimensions. It is
shown that the ground-state phase diagram as well as the picture of
metal-insulator transitions found for the conventional FKM (without correlated
hopping) are strongly changed when the correlated hopping term is added. The
effect of correlated hopping is so strong that it can induce the
insulator-metal transition, even in the strong-coupling limit, where the ground
states of the conventional FKM are insulating for all -electron densities.Comment: 11 pages, 2 figures, LaTe
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Measuring Myeloperoxidase Activity in Biological Samples
Background: Enzymatic activity measurements of the highly oxidative enzyme myeloperoxidase (MPO), which is implicated in many diseases, are widely used in the literature, but often suffer from nonspecificity and lack of uniformity. Thus, validation and standardization are needed to establish a robust method that is highly specific, sensitive, and reproducible for assaying MPO activity in biological samples. Principal findings We found conflicting results between in vivo molecular MR imaging of MPO, which measures extracellular activity, and commonly used in vitro MPO activity assays. Thus, we established and validated a protocol to obtain extra- and intracellular MPO from murine organs. To validate the MPO activity assays, three different classes of MPO activity assays were used in spike and recovery experiments. However, these assay methods yielded inconsistent results, likely because of interfering substances and other peroxidases present in tissue extracts. To circumvent this, we first captured MPO with an antibody. The MPO activity of the resultant samples was assessed by ADHP and validated against samples from MPO-knockout mice in murine disease models of multiple sclerosis, steatohepatitis, and myocardial infarction. We found the measurements performed using this protocol to be highly specific and reproducible, and when performed using ADHP, to be highly sensitive over a broad range. In addition, we found that intracellular MPO activity correlated well with tissue neutrophil content, and can be used as a marker to assess neutrophil infiltration in the tissue. Conclusion: We validated a highly specific and sensitive assay protocol that should be used as the standard method for all MPO activity assays in biological samples. We also established a method to obtain extra- and intracellular MPO from murine organs. Extracellular MPO activity gives an estimate of the oxidative stress in inflammatory diseases, while intracellular MPO activity correlates well with tissue neutrophil content. A detailed step-by-step protocol is provided
Phase transitions in the spinless Falicov-Kimball model with correlated hopping
The canonical Monte-Carlo is used to study the phase transitions from the
low-temperature ordered phase to the high-temperature disordered phase in the
two-dimensional Falicov-Kimball model with correlated hopping. As the
low-temperature ordered phase we consider the chessboard phase, the axial
striped phase and the segregated phase. It is shown that all three phases
persist also at finite temperatures (up to the critical temperature )
and that the phase transition at the critical point is of the first order for
the chessboard and axial striped phase and of the second order for the
segregated phase. In addition, it is found that the critical temperature is
reduced with the increasing amplitude of correlated hopping in the
chessboard phase and it is strongly enhanced by in the axial striped and
segregated phase.Comment: 17 pages, 6 figure
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