339 research outputs found
Visualizing Spacetime Curvature via Frame-Drag Vortexes and Tidal Tendexes II. Stationary Black Holes
When one splits spacetime into space plus time, the Weyl curvature tensor
(which equals the Riemann tensor in vacuum) splits into two spatial, symmetric,
traceless tensors: the tidal field , which produces tidal forces, and the
frame-drag field , which produces differential frame dragging. In recent
papers, we and colleagues have introduced ways to visualize these two fields:
tidal tendex lines (integral curves of the three eigenvector fields of ) and
their tendicities (eigenvalues of these eigenvector fields); and the
corresponding entities for the frame-drag field: frame-drag vortex lines and
their vorticities. These entities fully characterize the vacuum Riemann tensor.
In this paper, we compute and depict the tendex and vortex lines, and their
tendicities and vorticities, outside the horizons of stationary (Schwarzschild
and Kerr) black holes; and we introduce and depict the black holes' horizon
tendicity and vorticity (the normal-normal components of and on the
horizon). For Schwarzschild and Kerr black holes, the horizon tendicity is
proportional to the horizon's intrinsic scalar curvature, and the horizon
vorticity is proportional to an extrinsic scalar curvature. We show that, for
horizon-penetrating time slices, all these entities (, , the tendex lines
and vortex lines, the lines' tendicities and vorticities, and the horizon
tendicities and vorticities) are affected only weakly by changes of slicing and
changes of spatial coordinates, within those slicing and coordinate choices
that are commonly used for black holes. [Abstract is abbreviated.]Comment: 19 pages, 7 figures, v2: Changed to reflect published version
(changes made to color scales in Figs 5, 6, and 7 for consistent
conventions). v3: Fixed Ref
Frame-Dragging Vortexes and Tidal Tendexes Attached to Colliding Black Holes: Visualizing the Curvature of Spacetime
When one splits spacetime into space plus time, the spacetime curvature (Weyl
tensor) gets split into an "electric" part E_{jk} that describes tidal gravity
and a "magnetic" part B_{jk} that describes differential dragging of inertial
frames. We introduce tools for visualizing B_{jk} (frame-drag vortex lines,
their vorticity, and vortexes) and E_{jk} (tidal tendex lines, their tendicity,
and tendexes), and also visualizations of a black-hole horizon's (scalar)
vorticity and tendicity. We use these tools to elucidate the nonlinear dynamics
of curved spacetime in merging black-hole binaries.Comment: 4 pages, 5 figure
A habitat-use model to determine essential fish habitat for juvenile brown shrimp (Farfantepenaeus aztecus) in Galveston Bay, Texas
A density prediction model for juvenile brown shrimp (Farfantepenaeus aztecus) was developed by using three bottom types, five salinity zones, and four seasons to quantify patterns of habitat use in Galveston Bay, Texas. Sixteen years of quantitative density data were used. Bottom types were vegetated marsh edge, submerged aquatic vegetation, and shallow nonvegetated bottom. Multiple regression was used to develop density estimates, and the resultant formula was then coupled with a geographical information system (GIS) to provide a spatial mosaic (map) of predicted habitat use. Results indicated that juvenile brown shrimp (0.50. These results indicate that this model may have a broader geographic application and is a plausible approach in refining current EFH designations for all Gulf of Mexico estuaries with similar geomorphological and hydrological characteristics
Visualizing Spacetime Curvature via Frame-Drag Vortexes and Tidal Tendexes III. Quasinormal Pulsations of Schwarzschild and Kerr Black Holes
In recent papers, we and colleagues have introduced a way to visualize the
full vacuum Riemann curvature tensor using frame-drag vortex lines and their
vorticities, and tidal tendex lines and their tendicities. We have also
introduced the concepts of horizon vortexes and tendexes and 3-D vortexes and
tendexes (regions where vorticities or tendicities are large). Using these
concepts, we discover a number of previously unknown features of quasinormal
modes of Schwarzschild and Kerr black holes. These modes can be classified by
mode indexes (n,l,m), and parity, which can be electric [(-1)^l] or magnetic
[(-1)^(l+1)]. Among our discoveries are these: (i) There is a near duality
between modes of the same (n,l,m): a duality in which the tendex and vortex
structures of electric-parity modes are interchanged with the vortex and tendex
structures (respectively) of magnetic-parity modes. (ii) This near duality is
perfect for the modes' complex eigenfrequencies (which are well known to be
identical) and perfect on the horizon; it is slightly broken in the equatorial
plane of a non-spinning hole, and the breaking becomes greater out of the
equatorial plane, and greater as the hole is spun up; but even out of the plane
for fast-spinning holes, the duality is surprisingly good. (iii)
Electric-parity modes can be regarded as generated by 3-D tendexes that stick
radially out of the horizon. As these "longitudinal," near-zone tendexes rotate
or oscillate, they generate longitudinal-transverse near-zone vortexes and
tendexes, and outgoing and ingoing gravitational waves. The ingoing waves act
back on the longitudinal tendexes, driving them to slide off the horizon, which
results in decay of the mode's strength. (iv) By duality, magnetic-parity modes
are driven in this same manner by longitudinal, near-zone vortexes that stick
out of the horizon. [Abstract abridged.]Comment: 53 pages with an overview of major results in the first 11 pages, 26
figures. v2: Very minor changes to reflect published version. v3: Fixed Ref
Frame-Dragging Vortexes and Tidal Tendexes Attached to Colliding Black Holes: Visualizing the Curvature of Spacetime
When one splits spacetime into space plus time, the spacetime curvature (Weyl
tensor) gets split into an "electric" part E_{jk} that describes tidal gravity
and a "magnetic" part B_{jk} that describes differential dragging of inertial
frames. We introduce tools for visualizing B_{jk} (frame-drag vortex lines,
their vorticity, and vortexes) and E_{jk} (tidal tendex lines, their tendicity,
and tendexes), and also visualizations of a black-hole horizon's (scalar)
vorticity and tendicity. We use these tools to elucidate the nonlinear dynamics
of curved spacetime in merging black-hole binaries.Comment: 4 pages, 5 figure
Momentum flow in black-hole binaries: II. Numerical simulations of equal-mass, head-on mergers with antiparallel spins
Research on extracting science from binary-black-hole (BBH) simulations has
often adopted a "scattering matrix" perspective: given the binary's initial
parameters, what are the final hole's parameters and the emitted gravitational
waveform? In contrast, we are using BBH simulations to explore the nonlinear
dynamics of curved spacetime. Focusing on the head-on plunge, merger, and
ringdown of a BBH with transverse, antiparallel spins, we explore numerically
the momentum flow between the holes and the surrounding spacetime. We use the
Landau-Lifshitz field-theory-in-flat-spacetime formulation of general
relativity to define and compute the density of field energy and field momentum
outside horizons and the energy and momentum contained within horizons, and we
define the effective velocity of each apparent and event horizon as the ratio
of its enclosed momentum to its enclosed mass-energy. We find surprisingly good
agreement between the horizons' effective and coordinate velocities. To
investigate the gauge dependence of our results, we compare pseudospectral and
moving-puncture evolutions of physically similar initial data; although
spectral and puncture simulations use different gauge conditions, we find
remarkably good agreement for our results in these two cases. We also compare
our simulations with the post-Newtonian trajectories and near-field
energy-momentum. [Abstract abbreviated; full abstract also mentions additional
results.]Comment: Submitted to Phys. Rev.
Visualizing Spacetime Curvature via Frame-Drag Vortexes and Tidal Tendexes I. General Theory and Weak-Gravity Applications
When one splits spacetime into space plus time, the Weyl curvature tensor
(vacuum Riemann tensor) gets split into two spatial, symmetric, and trace-free
(STF) tensors: (i) the Weyl tensor's so-called "electric" part or tidal field,
and (ii) the Weyl tensor's so-called "magnetic" part or frame-drag field. Being
STF, the tidal field and frame-drag field each have three orthogonal
eigenvector fields which can be depicted by their integral curves. We call the
integral curves of the tidal field's eigenvectors tendex lines, we call each
tendex line's eigenvalue its tendicity, and we give the name tendex to a
collection of tendex lines with large tendicity. The analogous quantities for
the frame-drag field are vortex lines, their vorticities, and vortexes. We
build up physical intuition into these concepts by applying them to a variety
of weak-gravity phenomena: a spinning, gravitating point particle, two such
particles side by side, a plane gravitational wave, a point particle with a
dynamical current-quadrupole moment or dynamical mass-quadrupole moment, and a
slow-motion binary system made of nonspinning point particles. [Abstract is
abbreviated; full abstract also mentions additional results.]Comment: 25 pages, 20 figures, matches the published versio
Association between intrarenal arterial resistance and diastolic dysfunction in type 2 diabetes
<p>Abstract</p> <p>Background</p> <p>In comparison to the well established changes in compliance that occur at the large vessel level in diabetes, much less is known about the changes in compliance of the cardiovascular system at the end-organ level. The aim of this study was therefore to examine whether there was a correlation between resistance of the intrarenal arteries of the kidney and compliance of the left ventricle, as estimated by measurements of diastolic function, in subjects with type 2 diabetes.</p> <p>Methods</p> <p>We studied 167 unselected clinic patients with type 2 diabetes with a kidney duplex scan to estimate intrarenal vascular resistance, i.e. the resistance index (RI = peak systolic velocity-minimum diastolic velocity/peak systolic velocity) and a transthoracic echocardiogram (TTE) employing tissue doppler studies to document diastolic and systolic ventricular function.</p> <p>Results</p> <p>Renal RI was significantly higher in subjects with diastolic dysfunction (0.72 ± 0.05) when compared with those who had a normal TTE examination (0.66 ± 0.06, p < 0.01). Renal RI values were correlated with markers of diastolic dysfunction including the E/Vp ratio (r = 0.41, p < 0.001), left atrial area (r = 0.36, p < 0.001), the E/A ratio (r = 0.36, p < 0.001) and the E/E' ratio (r = 0.31, p < 0.001). These associations were independent of systolic function, hypertension, the presence and severity of chronic kidney disease, the use of renin-angiotensin inhibitors and other potentially confounding variables.</p> <p>Conclusion</p> <p>Increasing vascular resistance of the intrarenal arteries was associated with markers of diastolic dysfunction in subjects with type 2 diabetes. These findings are consistent with the hypothesis that vascular and cardiac stiffening in diabetes are manifestations of common pathophysiological mechanisms.</p
TADPOL: A 1.3 mm Survey of Dust Polarization in Star-forming Cores and Regions
We present {\lambda}1.3 mm CARMA observations of dust polarization toward 30
star-forming cores and 8 star-forming regions from the TADPOL survey. We show
maps of all sources, and compare the ~2.5" resolution TADPOL maps with ~20"
resolution polarization maps from single-dish submillimeter telescopes. Here we
do not attempt to interpret the detailed B-field morphology of each object.
Rather, we use average B-field orientations to derive conclusions in a
statistical sense from the ensemble of sources, bearing in mind that these
average orientations can be quite uncertain. We discuss three main findings:
(1) A subset of the sources have consistent magnetic field (B-field)
orientations between large (~20") and small (~2.5") scales. Those same sources
also tend to have higher fractional polarizations than the sources with
inconsistent large-to-small-scale fields. We interpret this to mean that in at
least some cases B-fields play a role in regulating the infall of material all
the way down to the ~1000 AU scales of protostellar envelopes. (2) Outflows
appear to be randomly aligned with B-fields; although, in sources with low
polarization fractions there is a hint that outflows are preferentially
perpendicular to small-scale B-fields, which suggests that in these sources the
fields have been wrapped up by envelope rotation. (3) Finally, even at ~2.5"
resolution we see the so-called "polarization hole" effect, where the
fractional polarization drops significantly near the total intensity peak. All
data are publicly available in the electronic edition of this article.Comment: 53 pages, 37 figures -- main body (13 pp., 3 figures), source maps
(32 pp., 34 figures), source descriptions (8 pp.). Accepted by the
Astrophysical Journal Supplemen
Viral Hepatitis and Rapid Diagnostic Test Based Screening for HBsAg in HIV-infected Patients in Rural Tanzania.
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Co-infection with hepatitis B virus (HBV) is highly prevalent in people living with HIV in Sub-Saharan Africa. Screening for HBV surface antigen (HBsAg) before initiation of combination antiretroviral therapy (cART) is recommended. However, it is not part of diagnostic routines in HIV programs in many resource-limited countries although patients could benefit from optimized antiretroviral therapy covering both infections. Screening could be facilitated by rapid diagnostic tests for HBsAg. Operating experience with these point of care devices in HIV-positive patients in Sub-Saharan Africa is largely lacking. We determined the prevalence of HBV and Hepatitis C virus (HCV) infection as well as the diagnostic accuracy of the rapid test device Determine HBsAg in an HIV cohort in rural Tanzania. Prospectively collected blood samples from adult, HIV-1 positive and antiretroviral treatment-naïve patients in the Kilombero and Ulanga antiretroviral cohort (KIULARCO) in rural Tanzania were analyzed at the point of care with Determine HBsAg, a reference HBsAg EIA and an anti-HCV EIA. Samples of 272 patients were included. Median age was 38 years (interquartile range [IQR] 32-47), 169/272 (63%) subjects were females and median CD4+ count was 250 cells/µL (IQR 97-439). HBsAg was detected in 25/272 (9.2%, 95% confidence interval [CI] 6.2-13.0%) subjects. Of these, 7/25 (28%) were positive for HBeAg. Sensitivity of Determine HBsAg was rated at 96% (95% CI 82.8-99.6%) and specificity at 100% (95% CI, 98.9-100%). Antibodies to HCV (anti-HCV) were found in 10/272 (3.7%, 95% CI 2.0-6.4%) of patients. This study reports a high prevalence of HBV in HIV-positive patients in a rural Tanzanian setting. The rapid diagnostic test Determine HBsAg is an accurate assay for screening for HBsAg in HIV-1 infected patients at the point of care and may further help to guide cART in Sub-Saharan Africa
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