1,128 research outputs found
Complex Langevin dynamics for dynamical QCD at nonzero chemical potential: a comparison with multi-parameter reweighting
We study lattice QCD at non-vanishing chemical potential using the complex
Langevin equation. We compare the results with multi-parameter reweighting both
from and phase quenched ensembles. We find a good agreement for lattice
spacings below 0.15 fm. On coarser lattices the complex Langevin
approach breaks down. Four flavors of staggered fermions are used on
and 8 lattices. For one ensemble we also use two flavors to investigate the
effects of rooting.Comment: 10 pages, 11 figures, PRD version, minor change
Quasiperiodic oscillations in a strong gravitational field around neutron stars testing braneworld models
The strong gravitational field of neutron stars in the brany universe could
be described by spherically symmetric solutions with a metric in the exterior
to the brany stars being of the Reissner-Nordstrom type containing a brany
tidal charge representing the tidal effect of the bulk spacetime onto the star
structure. We investigate the role of the tidal charge in orbital models of
high-frequency quasiperiodic oscillations (QPOs) observed in neutron star
binary systems. We focus on the relativistic precession model. We give the
radial profiles of frequencies of the Keplerian (vertical) and radial epicyclic
oscillations. We show how the standard relativistic precession model modified
by the tidal charge fits the observational data, giving estimates of the
allowed values of the tidal charge and the brane tension based on the processes
going in the vicinity of neutron stars. We compare the strong field regime
restrictions with those given in the weak-field limit of solar system
experiments.Comment: 26 pages, 6 figure
The Aschenbach effect: unexpected topology changes in motion of particles and fluids orbiting rapidly rotating Kerr black holes
Newton's theory predicts that the velocity of free test particles on
circular orbits around a spherical gravity center is a decreasing function of
the orbital radius , . Only very recently, Aschenbach (A&A 425,
p. 1075 (2004)) has shown that, unexpectedly, the same is not true for
particles orbiting black holes: for Kerr black holes with the spin parameter
, the velocity has a positive radial gradient for geodesic, stable,
circular orbits in a small radial range close to the black hole horizon. We
show here that the {\em Aschenbach effect} occurs also for non-geodesic
circular orbits with constant specific angular momentum . In Newton's theory it is , with being the cylindrical
radius. The equivelocity surfaces coincide with the surfaces which,
of course, are just co-axial cylinders. It was previously known that in the
black hole case this simple topology changes because one of the ``cylinders''
self-crosses. We show here that the Aschenbach effect is connected to a second
topology change that for the tori occurs only for very highly
spinning black holes, .Comment: 9 pages, 7 figure
Inflammatory bowel disease-specific autoantibodies in HLA-B27-associated spondyloarthropathies: Increased prevalence of ASCA and pANCA
Aims: An association between inflammatory bowel disease (IBD) and spondyloarthropathies (SpA) has repeatedly been reported. The aim of the present study was to investigate whether serologic markers of IBD, e. g. antibodies against Saccharomyces cerevisiae (ASCA), antibodies against exocrine pancreas (PAB) and perinuclear antineutrophil cytoplasmic antibodies (pANCA) are present in HLA-B27-associated SpA. Methods: 87 patients with HLA-B27-positive SpA and 145 controls were tested for ASCA, PAB and pANCA employing ELISA or indirect immunofluorescence, respectively. Antibody-positive patients were interviewed regarding IBD-related symptoms using a standardized questionnaire. Results/Conclusion: When compared to the controls, ASCA IgA but not ASCA IgG levels were significantly increased in patients with SpA, in particular in ankylosing spondylitis (AS) and undifferentiated SpA (uSpA). pANCA were found in increased frequency in patients with SpA whereas PAB were not detected. The existence of autoantibodies was not associated with gastrointestinal symptoms but sustains the presence of a pathophysiological link between bowel inflammation and SpA. Copyright (C) 2004 S. Karger AG, Basel
Initiation and Early Kinematic Evolution of Solar Eruptions
We investigate the initiation and early evolution of 12 solar eruptions,
including six active region hot channel and six quiescent filament eruptions,
which were well observed by the \textsl{Solar Dynamics Observatory}, as well as
by the \textsl{Solar TErrestrial RElations Observatory} for the latter. The
sample includes one failed eruption and 11 coronal mass ejections, with
velocities ranging from 493 to 2140~km~s. A detailed analysis of the
eruption kinematics yields the following main results. (1) The early evolution
of all events consists of a slow-rise phase followed by a main-acceleration
phase, the height-time profiles of which differ markedly and can be best fit,
respectively, by a linear and an exponential function. This indicates that
different physical processes dominate in these phases, which is at variance
with models that involve a single process. (2) The kinematic evolution of the
eruptions tends to be synchronized with the flare light curve in both phases.
The synchronization is often but not always close. A delayed onset of the
impulsive flare phase is found in the majority of the filament eruptions (5 out
of 6). This delay, and its trend to be larger for slower eruptions, favor ideal
MHD instability models. (3) The average decay index at the onset heights of the
main acceleration is close to the threshold of the torus instability for both
groups of events (although based on a tentative coronal field model for the hot
channels), suggesting that this instability initiates and possibly drives the
main acceleration.Comment: Accepted for publication in ApJ; 24 pages, 12 figures, 3 table
Fiber-integrated Brillouin microspectroscopy: Towards Brillouin endoscopy
© 2017 The Author(s). Brillouin imaging (BI) for micromechanical characterization of tissues and biomaterials is a fast-developing field of research with a strong potential for medical diagnosis of disease-modified tissues and cells. Although the principles of BI imply its compatibility with in vivo and in situ measurements, the integration of BI with a flexible catheter, capable of reaching the region of interest within the body, is yet to be reported. Here, for the first time, we experimentally investigate integration of the Brillouin spectroscope with standard optical fiber components to achieve a Brillouin endoscope. The performance of single-fiber and dual-fiber endoscopes are demonstrated and analyzed. We show that a major challenge in construction of Brillouin endoscopes is the strong backward Brillouin scattering in the optical fiber and we present a dual-fiber geometry as a possible solution. Measurements of Brillouin spectra in test liquids (water, ethanol and glycerol) are demonstrated using the dual-fiber endoscope and its performance is analyzed numerically with the help of a beam propagation model
The kinetic mechanisms of fast-decay red-fluorescent genetically encoded calcium indicators.
Genetically encoded calcium indicators (GECIs) are useful reporters of cell-signaling, neuronal, and network activities. We have generated novel fast variants and investigated the kinetic mechanisms of two recently developed red-fluorescent GECIs (RGECIs), mApple-based jRGECO1a and mRuby-based jRCaMP1a. In the formation of fluorescent jRGECO1a and jRCaMP1a complexes, calcium binding is followed by rate-limiting isomerization. However, fluorescence decay of calcium-bound jRGECO1a follows a different pathway from its formation: dissociation of calcium occurs first, followed by the peptide, similarly to GCaMP-s. In contrast, fluorescence decay of calcium-bound jRCaMP1a occurs by the reversal of the on-pathway: peptide dissociation is followed by calcium. The mechanistic differences explain the generally slower off-kinetics of jRCaMP1a-type indicators compared with GCaMP-s and jRGECO1a-type GECI: the fluorescence decay rate of f-RCaMP1 was 21 sâ1, compared with 109 sâ1 for f-RGECO1 and f-RGECO2 (37 °C). Thus, the CaMâpeptide interface is an important determinant of the kinetic responses of GECIs; however, the topology of the structural link to the fluorescent protein demonstrably affects the internal dynamics of the CaMâpeptide complex. In the dendrites of hippocampal CA3 neurons, f-RGECO1 indicates calcium elevation in response to a 100 action potential train in a linear fashion, making the probe particularly useful for monitoring large-amplitude, fast signals, e.g. those in dendrites, muscle cells, and immune cells
Multivariate analysis of Brillouin imaging data by supervised and unsupervised learning
Brillouin imaging relies on the reliable extraction of subtle spectral
information from hyperspectral datasets. To date, the mainstream practice has
been using line fitting of spectral features to retrieve the average peak shift
and linewidth parameters. Good results, however, depend heavily on sufficient
SNR and may not be applicable in complex samples that consist of spectral
mixtures. In this work, we thus propose the use of various multivariate
algorithms that can be used to perform supervised or unsupervised analysis of
the hyperspectral data, with which we explore advanced image analysis
applications, namely unmixing, classification and segmentation in a phantom and
live cells. The resulting images are shown to provide more contrast and detail,
and obtained on a timescale faster than fitting. The estimated spectral
parameters are consistent with those calculated from pure fitting
High affinity binding of amyloid ÎČ-peptide to calmodulin: Structural and functional implications.
Amyloid ÎČ-peptides (AÎČ) are a major hallmark of Alzheimer's disease (AD) and their neurotoxicity develop with cytosolic calcium dysregulation. On the other hand, calmodulin (CaM), a protein which plays a major multifunctional role in neuronal calcium signaling, has been shown to be involved in the regulation of non-amyloidogenic processing of amyloid ÎČ precursor protein (APP). Using fluorescent 6-bromoacetyl-2-dimethylaminonaphthalene derivatives of CaM, Badan-CaM, and human amyloid ÎČ(1-42) HiLyteâą-Fluor555, we show in this work that AÎČ binds with high affinity to CaM through the neurotoxic AÎČ25-35 domain. In addition, the affinity of AÎČ for calcium-saturated CaM conformation is approximately 20-fold higher than for CaM conformation in the absence of calcium (apo-CaM). Moreover, the value of Kd of 0.98 ± 0.11 nM obtained for AÎČ1-42 dissociation from CaM saturated by calcium point out that CaM is one of the cellular targets with highest affinity for neurotoxic AÎČ peptides. A major functional consequence of AÎČ-CaM interaction is that it slowdowns AÎČ fibrillation. The novel and high affinity interaction between calmodulin and AÎČ shown in this work opens a yet-unexplored gateway to further understand the neurotoxic effect of AÎČ in different neural cells and also to address the potential of calmodulin and calmodulin-derived peptides as therapeutic agents in AD
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