4,542 research outputs found
Expandable Factor Analysis
Bayesian sparse factor models have proven useful for characterizing
dependence in multivariate data, but scaling computation to large numbers of
samples and dimensions is problematic. We propose expandable factor analysis
for scalable inference in factor models when the number of factors is unknown.
The method relies on a continuous shrinkage prior for efficient maximum a
posteriori estimation of a low-rank and sparse loadings matrix. The structure
of the prior leads to an estimation algorithm that accommodates uncertainty in
the number of factors. We propose an information criterion to select the
hyperparameters of the prior. Expandable factor analysis has better false
discovery rates and true positive rates than its competitors across diverse
simulations. We apply the proposed approach to a gene expression study of aging
in mice, illustrating superior results relative to four competing methods.Comment: 28 pages, 4 figure
Molecular mechanisms involved in T cell migration across the blood-brain barrier
In the healthy individuum lymphocyte traffic into the central nervous system (CNS) is very low and tightly controlled by the highly specialized blood-brain barrier (BBB). In contrast, under inflammatory conditions of the CNS such as in multiple sclerosis or in its animal model experimental autoimmune encephalomyelitis (EAE) circulating lymphocytes and monocytes/macrophages readily cross the BBB and gain access to the CNS leading to edema, inflammation and demyelination. Interaction of circulating leukocytes with the endothelium of the blood-spinal cord and blood-brain barrier therefore is a critical step in the pathogenesis of inflammatory diseases of the CNS. Leukocyte/endothelial interactions are mediated by adhesion molecules and chemokines and their respective chemokine receptors. We have developed a novel spinal cord window preparation, which enables us to directly visualize CNS white matter microcirculation by intravital fluorescence videomicroscopy. Applying this technique of intravital fluorescence videomicroscopy we could provide direct in vivo evidence that encephalitogenic T cell blasts interact with the spinal cord white matter microvasculature without rolling and that alpha4-integrin mediates the G-protein independent capture and subsequently the G-protein dependent adhesion strengthening of T cell blasts to microvascular VCAM-1. LFA-1 was found to neither mediate the G-protein independent capture nor the G- protein dependent initial adhesion strengthening of encephalitogenic T cell blasts within spinal cord microvessel, but was rather involved in T cell extravasation across the vascular wall into the spinal cord parenchyme. Our observation that G-protein mediated signalling is required to promote adhesion strengthening of encephalitogenic T cells on BBB endothelium in vivo suggested the involvement of chemokines in this process. We found functional expression of the lymphoid chemokines CCL19/ELC and CCL21/SLC in CNS venules surrounded by inflammatory cells in brain and spinal cord sections of mice afflicted with EAE suggesting that the lymphoid chemokines CCL19 and CCL21 besides regulating lymphocyte homing to secondary lymphoid tissue might be involved in T lymphocyte migration into the immuneprivileged CNS during immunosurveillance and chronic inflammation. Here, I summarize our current knowledge on the sequence of traffic signals involved in T lymphocyte recruitment across the healthy and inflamed blood-brain and blood-spinal cord barrier based on our in vitro and in vivo investigations
Lattice QCD study of the Boer-Mulders effect in a pion
The three-dimensional momenta of quarks inside a hadron are encoded in
transverse momentum-dependent parton distribution functions (TMDs). This work
presents an exploratory lattice QCD study of a TMD observable in the pion
describing the Boer-Mulders effect, which is related to polarized quark
transverse momentum in an unpolarized hadron. Particular emphasis is placed on
the behavior as a function of a Collins-Soper evolution parameter quantifying
the relative rapidity of the struck quark and the initial hadron, e.g., in a
semi-inclusive deep inelastic scattering (SIDIS) process. The lattice
calculation, performed at the pion mass m_pi = 518 MeV, utilizes a definition
of TMDs via hadronic matrix elements of a quark bilocal operator with a
staple-shaped gauge connection; in this context, the evolution parameter is
related to the staple direction. By parametrizing the aforementioned matrix
elements in terms of invariant amplitudes, the problem can be cast in a Lorentz
frame suited for the lattice calculation. In contrast to an earlier nucleon
study, due to the lower mass of the pion, the calculated data enable
quantitative statements about the physically interesting limit of large
relative rapidity. In passing, the similarity between the Boer-Mulders effects
extracted in the pion and the nucleon is noted.Comment: 16 pages, 9 figures, 3 table
An accuracy assessment of Magellan Very Long Baseline Interferometry (VLBI)
Very Long Baseline Interferometry (VLBI) measurements of the Magellan spacecraft's angular position and velocity were made during July through September, 1989, during the spacecraft's heliocentric flight to Venus. The purpose of this data acquisition and reduction was to verify this data type for operational use before Magellan is inserted into Venus orbit, in August, 1990. The accuracy of these measurements are shown to be within 20 nanoradians in angular position, and within 5 picoradians/sec in angular velocity. The media effects and their calibrations are quantified; the wet fluctuating troposphere is the dominant source of measurement error for angular velocity. The charged particle effect is completely calibrated with S- and X-Band dual-frequency calibrations. Increasing the accuracy of the Earth platform model parameters, by using VLBI-derived tracking station locations consistent with the planetary ephemeris frame, and by including high frequency Earth tidal terms in the Earth rotation model, add a few nanoradians improvement to the angular position measurements. Angular velocity measurements were insensitive to these Earth platform modelling improvements
Sivers and Boer-Mulders observables from lattice QCD
We present a first calculation of transverse momentum dependent nucleon
observables in dynamical lattice QCD employing non-local operators with
staple-shaped, "process-dependent" Wilson lines. The use of staple-shaped
Wilson lines allows us to link lattice simulations to TMD effects determined
from experiment, and in particular to access non-universal, naively
time-reversal odd TMD observables. We present and discuss results for the
generalized Sivers and Boer-Mulders transverse momentum shifts for the SIDIS
and DY cases. The effect of staple-shaped Wilson lines on T-even observables is
studied for the generalized tensor charge and a generalized transverse shift
related to the worm gear function g_1T. We emphasize the dependence of these
observables on the staple extent and the Collins-Soper evolution parameter. Our
numerical calculations use an n_f = 2+1 mixed action scheme with domain wall
valence fermions on an Asqtad sea and pion masses 369 MeV as well as 518 MeV.Comment: 25 pages, 13 figures; version accepted by journal. Contains
additional section explaining and summarizing the methodolog
A hot-water ice-coring drill
A new method of ice-core drilling uses an annulus of hot-water jets to melt out a cylindrical ice core. This lightweight device used in combination with a fast hot-water drill can quickly obtain ice cores from any depth
Nomenclature of structural and compositional characteristics of ordered microporous and mesoporous materials with inorganic hosts(IUPAC Recommendations 2001)
A system of terms applicable to ordered microporous and mesoporous materials is proposed, and rules for writing a standardized crystal chemical formula for such materials are presented. The recommendations are based both on common usage and on a systematic classification scheme. The nomenclature has been developed to encompass all inorganic materials with ordered, accessible pores with free diameters of less than 50 nm. The crystal chemical formula describes the chemical composition of both the guest species and the host, the structure of the host, the structure of the pore system, and the symmetry of the material. This formula can be simplified or expanded to suit the user's requirement
The Ice-Rock Interface and Basal Sliding Process as Revealed by Direct Observation in Bore Holes and Tunnels
The glacier bed, where basal sliding occurs, was reached by cable-tool drilling and sand-pump bailing in seven bore holes in Blue Glacier, Olympic National Park, Washington. Basal sliding velocities measured by bore-hole photography and confirmed by inclinometry are unexpectedly low, ranging from 0.3 to 3.0 cm/day and averaging 1.0 cm/day. This is much less than about half the surface velocity of 15 cm/day, which was the sliding-rate expected from earlier deformation measurements in bore holes made by thermal drilling alone
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