604 research outputs found
Fast Differential Emission Measure Inversion of Solar Coronal Data
We present a fast method for reconstructing Differential Emission Measures
(DEMs) using solar coronal data. On average, the method computes over 1000 DEMs
per second for a sample active region observed by the Atmospheric Imaging
Assembly (AIA) on the Solar Dynamics Observatory (SDO), and achieves reduced
chi-squared of order unity with no negative emission in all but a few test
cases. The high performance of this method is especially relevant in the
context of AIA, which images of order one million solar pixels per second. This
paper describes the method, analyzes its fidelity, compares its performance and
results with other DEM methods, and applies it to an active region and loop
observed by AIA and by the Extreme-ultraviolet Imaging Spectrometer (EIS) on
Hinode.Comment: 22 Pages, 11 Figures; submitted to The Astrophysical Journal. This
version (2) includes clarifications in the text and reflects improvements to
the DEM cod
The QUEST Data Processing Software Pipeline
A program that we call the QUEST Data Processing Software Pipeline has been
written to process the large volumes of data produced by the QUEST camera on
the Samuel Oschin Schmidt Telescope at the Palomar Observatory. The program
carries out both aperture and PSF photometry, combines data from different
repeated observations of the same portion of sky, and produces a Master Object
Catalog. A rough calibration of the data is carried out. This program, as well
as the calibration procedures and quality checks on the output are described.Comment: 17 pages, 1 table, 8 figure
Vortices in attractive Bose-Einstein condensates in two dimensions
The form and stability of quantum vortices in Bose-Einstein condensates with
attractive atomic interactions is elucidated. They appear as ring bright
solitons, and are a generalization of the Townes soliton to nonzero winding
number . An infinite sequence of radially excited stationary states appear
for each value of , which are characterized by concentric matter-wave rings
separated by nodes, in contrast to repulsive condensates, where no such set of
states exists. It is shown that robustly stable as well as unstable regimes may
be achieved in confined geometries, thereby suggesting that vortices and their
radial excited states can be observed in experiments on attractive condensates
in two dimensions.Comment: 4 pages, 3 figure
Exciting dark matter in the galactic center
We reconsider the proposal of excited dark matter (DM) as an explanation for
excess 511 keV gamma rays from positrons in the galactic center. We
quantitatively compute the cross section for DM annihilation to nearby excited
states, mediated by exchange of a new light gauge boson with off-diagonal
couplings to the DM states. In models where both excited states must be heavy
enough to decay into e^+ e^- and the ground state, the predicted rate of
positron production is never large enough to agree with observations, unless
one makes extreme assumptions about the local circular velocity in the Milky
Way, or alternatively if there exists a metastable population of DM states
which can be excited through a mass gap of less than 650 keV, before decaying
into electrons and positrons.Comment: Dedicated to the memory of Lev Kofman; 16 pages, 9 figures; v3 added
refs, minor changes, accepted to PR
Development of Accessory Cells in B-Cell Compartments Is Retarted in B-Cell-Depleted Fetal Sheep
Accessory-cell populations in the lymphoid tissues of fetal sheep were investigated following depletion of
B cells. An intraperitoneal injection of an anti-IgM antibody early in gestation resulted in a marked depletion of IgM+
cells in lymphoid tissues. Immune and enzyme histochemical techniques were used to identify accessory-cell
populations in the ileal Peyer's patch, spleen, and lymph nodes of B-cell-depleted fetal sheep. The rudimentary
follicles in the ileal Peyer's patch showed strong enzyme reactivity for 5′ nucleotidase, indicating the presence
of follicular dendritic cells (FDCs). Enzyme reactivities for FDCs in primary follicles of the spleen and lymph nodes
were absent, as were reactivities for metallophilic macrophages in the marginal zone of the spleen. MgATPase
reactivity associated with dendritic-cell populations in the gut-associated lymphoid tissues was detected.
A monoclonal antibody against complement receptor-2 (CD21) reacted with FDCs in the rudimentary follicles of
the ileal Peyer's patch and immature FDCs in lymph nodes. The results suggest that the development of accessory-cell
populations in B-cell compartments of peripheral but not central lymphoid tissues is dependent on the presence of B cells
Vortices in Thin, Compressible, Unmagnetized Disks
We consider the formation and evolution of vortices in a hydrodynamic
shearing-sheet model. The evolution is done numerically using a version of the
ZEUS code. Consistent with earlier results, an injected vorticity field evolves
into a set of long-lived vortices, each of which has a radial extent comparable
to the local scale height. But we also find that the resulting velocity field
has a positive shear stress, . This effect appears
only at high resolution. The transport, which decays with time as t^-1/2,
arises primarily because the vortices drive compressive motions. This result
suggests a possible mechanism for angular momentum transport in low-ionization
disks, with two important caveats: a mechanism must be found to inject
vorticity into the disk, and the vortices must not decay rapidly due to
three-dimensional instabilities.Comment: 8 pages, 10 figures (high resolution figures available in ApJ
electronic edition
Rectified Asteroid Albedos and Diameters from IRAS and MSX
Rectified diameters and albedo estimates of 1517 main belt asteroid selected
from the IRAS and MSX asteroid photometry catalogues are derived from updated
infrared thermal models, the Standard Thermal Model (STM) and the Near Earth
Asteroid Thermal Model (NEATM), and Monte Carlo simulations, using new Minor
Planet Center (MPC) compilations of absolute magnitudes (H-values) constrained
by occultation and radar derived parameters. The NEATM approach produces a more
robust estimate of albedos and diameters, yielding albedos of (NEATM
mean). The asteroid beaming parameter () for the
selected asteroids has a mean value of , and the smooth
distribution of suggests that this parameter is independent of asteroid
properties such as composition. No trends in due to size-dependent
rotation rates are evident. Comparison of derived 's as a function of
taxonomic type indicates the beaming parameter values for S-type and C-type
asteroids are identical within the standard deviation of the population of
beaming parameters.Comment: 43 pages in manuscript layout, 9 figures. Submitted to The
Astronomical Journa
Recent Fluid Deformation closure for velocity gradient tensor dynamics in turbulence: time-scale effects and expansions
In order to model pressure and viscous terms in the equation for the
Lagrangian dynamics of the velocity gradient tensor in turbulent flows,
Chevillard & Meneveau (Phys. Rev. Lett. 97, 174501, 2006) introduced the Recent
Fluid Deformation closure. Using matrix exponentials, the closure allows to
overcome the unphysical finite-time blow-up of the well-known Restricted Euler
model. However, it also requires the specification of a decorrelation time
scale of the velocity gradient along the Lagrangian evolution, and when the
latter is chosen too short (or, equivalently, the Reynolds number is too high),
the model leads to unphysical statistics. In the present paper, we explore the
limitations of this closure by means of numerical experiments and analytical
considerations. We also study the possible effects of using time-correlated
stochastic forcing instead of the previously employed white-noise forcing.
Numerical experiments show that reducing the correlation time scale specified
in the closure and in the forcing does not lead to a commensurate reduction of
the autocorrelation time scale of the predicted evolution of the velocity
gradient tensor. This observed inconsistency could explain the unrealistic
predictions at increasing Reynolds numbers.We perform a series expansion of the
matrix exponentials in powers of the decorrelation time scale, and we compare
the full original model with a linearized version. The latter is not able to
extend the limits of applicability of the former but allows the model to be
cast in terms of a damping term whose sign gives additional information about
the stability of the model as function of the second invariant of the velocity
gradient tensor.Comment: 11 pages, 14 figures, submitted to the special issue "Fluids and
Turbulence" of Physica
Immunopathological characterization of red focal changes in Atlantic salmon (Salmo salar) white muscle
Farmed Atlantic salmon (Salmo salar) are prone to various conditions affecting the quality of the fillet. A well-known but so far poorly understood condition is the focal red changes in muscle, often referred to as haemorrhages. Such changes are characterized by muscle necrosis, haemorrhages and acute inflammation. They can progress into focal melanised changes, a chronic inflammatory condition with melanin-producing leukocytes. The initial cause of intramuscular haemorrhages is unknown. In this study, we aimed to reveal some of their key immunological features. Samples of red focal changes were investigated by immunohistochemistry (IHC), in situ hybridization (ISH) and RT-qPCR for various immune markers. The results were compared with samples of melanised changes and control muscle, subjected to the same analyses. In all red changes, infiltrates with mononuclear cells were detected, consisting mostly of MHC class I/II+ cells, but also of CD3+ and CD8+ cells. ISH studies on IgM showed few to moderate amounts of B-cells in red focal changes. Trends in the RT-qPCR showed upregulation of genes related to innate immunity in the red changes, whereas genes related to adaptive immunity were upregulated in the melanised changes. An important result was the significant downregulation of the anti-inflammatory cytokine IL10 in all red changes. Our findings indicate that we can rule out an auto invasive nature of the changes. The downregulation of IL10 at an early phase is a trait for the condition.publishedVersio
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