2,779 research outputs found
Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds
Recently, the LIGO-Virgo collaboration discovered gravitational waves and in
their first publication on the subject the authors also presented a graviton
mass constraint as eV (Abbott et al., 2016).
In the paper we analyze a potential to reduce upper bounds for graviton mass
with future observational data on trajectories of bright stars near the
Galactic Center. Since gravitational potentials are different for these two
cases, expressions for relativistic advance for general relativity and Yukawa
potential are different functions on eccentricity and semimajor axis, it gives
an opportunity to improve current estimates of graviton mass with future
observational facilities. In our considerations of an improvement potential for
a graviton mass estimate we adopt a conservative strategy and assume that
trajectories of bright stars and their apocenter advance will be described with
general relativity expressions and it gives opportunities to improve graviton
mass constraints. In contrast with our previous studies, where we present
current constraints on parameters of Yukawa gravity (Borka et al., 2013) and
graviton mass (Zakharov et al., 2016) from observations of S2 star, in the
paper we express expectations to improve current constraints for graviton mass,
assuming the GR predictions about apocenter shifts will be confirmed with
future observations. We concluded that if future observations of bright star
orbits during around fifty years will confirm GR predictions about apocenter
shifts of bright star orbits it give an opportunity to constrain a graviton
mass at a level around eV or slightly better than current
estimates obtained with LIGO observations.Comment: 16 pages, 1 Figure, 1 Table, corrected minor typo
Maximum likelihood estimation of cloud height from multi-angle satellite imagery
We develop a new estimation technique for recovering depth-of-field from
multiple stereo images. Depth-of-field is estimated by determining the shift in
image location resulting from different camera viewpoints. When this shift is
not divisible by pixel width, the multiple stereo images can be combined to
form a super-resolution image. By modeling this super-resolution image as a
realization of a random field, one can view the recovery of depth as a
likelihood estimation problem. We apply these modeling techniques to the
recovery of cloud height from multiple viewing angles provided by the MISR
instrument on the Terra Satellite. Our efforts are focused on a two layer cloud
ensemble where both layers are relatively planar, the bottom layer is optically
thick and textured, and the top layer is optically thin. Our results
demonstrate that with relative ease, we get comparable estimates to the M2
stereo matcher which is the same algorithm used in the current MISR standard
product (details can be found in [IEEE Transactions on Geoscience and Remote
Sensing 40 (2002) 1547--1559]). Moreover, our techniques provide the
possibility of modeling all of the MISR data in a unified way for cloud height
estimation. Research is underway to extend this framework for fast, quality
global estimates of cloud height.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS243 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle Spectropolarimetric Imager
Accurate characterization of surface reflection is essential for retrieval of aerosols using downward-looking remote sensors. In this paper, observations from the Ground-based Multiangle SpectroPolarimetric Imager (GroundMSPI) are used to evaluate a surface polarized bidirectional reflectance distribution function (PBRDF) model. GroundMSPI is an eight-band spectropolarimetric camera mounted on a rotating gimbal to acquire pushbroom imagery of outdoor landscapes. The camera uses a very accurate photoelastic-modulator-based polarimetric imaging technique to acquire Stokes vector measurements in three of the instrument's bands (470, 660, and 865 nm). A description of the instrument is presented, and observations of selected targets within a scene acquired on 6 January 2010 are analyzed. Data collected during the course of the day as the Sun moved across the sky provided a range of illumination geometries that facilitated evaluation of the surface model, which is comprised of a volumetric reflection term represented by the modified Rahman-Pinty-Verstraete function plus a specular reflection term generated by a randomly oriented array of Fresnel-reflecting microfacets. While the model is fairly successful in predicting the polarized reflection from two grass targets in the scene, it does a poorer job for two manmade targets (a parking lot and a truck roof), possibly due to their greater degree of geometric organization. Several empirical adjustments to the model are explored and lead to improved fits to the data. For all targets, the data support the notion of spectral invariance in the angular shape of the unpolarized and polarized surface reflection. As noted by others, this behavior provides valuable constraints on the aerosol retrieval problem, and highlights the importance of multiangle observations.NASAJPLCenter for Space Researc
Integrable Euler top and nonholonomic Chaplygin ball
We discuss the Poisson structures, Lax matrices, -matrices, bi-hamiltonian
structures, the variables of separation and other attributes of the modern
theory of dynamical systems in application to the integrable Euler top and to
the nonholonomic Chaplygin ball.Comment: 25 pages, LaTeX with AMS fonts, final versio
Power Law Scaling for a System of Interacting Units with Complex Internal Structure
We study the dynamics of a system composed of interacting units each with a
complex internal structure comprising many subunits. We consider the case in
which each subunit grows in a multiplicative manner. We propose a model for
such systems in which the interaction among the units is treated in a mean
field approximation and the interaction among subunits is nonlinear. To test
the model, we identify a large data base spanning 20 years, and find that the
model correctly predicts a variety of empirical results.Comment: 4 pages with 4 postscript figures (uses Revtex 3.1, Latex2e,
multicol.sty, epsf.sty and rotate.sty). Submitted to PR
Epigenetic and genetic variation at SKA2 predict suicidal behavior and post-traumatic stress disorder
Traumatic stress results in hypothalamic pituitary adrenal (HPA) axis abnormalities and an increased risk to both suicidal behaviors and post-traumatic stress disorder (PTSD). Previous work out of our laboratory identified SKA2 DNA methylation associations with suicidal behavior in the blood and brain of multiple cohorts. Interaction of SKA2 with stress predicted suicidal behavior with ~80% accuracy. SKA2 is hypothesized to reduce the ability to suppress cortisol following stress, which is of potentially high relevance in traumatized populations. Our objective was to investigate the interaction of SKA2 and trauma exposure on HPA axis function, suicide attempt and PTSD. SKA2 DNA methylation at Illumina HM450 probe cg13989295 was assessed for association with suicidal behavior and PTSD metrics in the context of Child Trauma Questionnaire (CTQ) scores in 421 blood and 61 saliva samples from the Grady Trauma Project (GTP) cohort. Dexamethasone suppression test (DST) data were evaluated for a subset of 209 GTP subjects. SKA2 methylation interacted with CTQ scores to predict lifetime suicide attempt in saliva and blood with areas under the receiver operator characteristic curve (AUCs) of 0.76 and 0.73 (95% confidence interval (CI): 0.6–0.92, P=0.003, and CI: 0.65–0.78, P<0.0001) and to mediate the suppression of cortisol following DST (β=0.5±0.19, F=1.51, degrees of freedom (df)=12/167, P=0.0096). Cumulatively, the data suggest that epigenetic variation at SKA2 mediates vulnerability to suicidal behaviors and PTSD through dysregulation of the HPA axis in response to stress
Multifrequency Photo-polarimetric WEBT Observation Campaign on the Blazar S5 0716+714: Source Microvariability and Search for Characteristic Timescales
Here we report on the results of the WEBT photo-polarimetric campaign
targeting the blazar S5~0716+71, organized in March 2014 to monitor the source
simultaneously in BVRI and near IR filters. The campaign resulted in an
unprecedented dataset spanning \,h of nearly continuous, multi-band
observations, including two sets of densely sampled polarimetric data mainly in
R filter. During the campaign, the source displayed pronounced variability with
peak-to-peak variations of about and "bluer-when-brighter" spectral
evolution, consisting of a day-timescale modulation with superimposed hourlong
microflares characterized by \,mag flux changes. We performed an
in-depth search for quasi-periodicities in the source light curve; hints for
the presence of oscillations on timescales of \,h and \,h do
not represent highly significant departures from a pure red-noise power
spectrum. We observed that, at a certain configuration of the optical
polarization angle relative to the positional angle of the innermost radio jet
in the source, changes in the polarization degree led the total flux
variability by about 2\,h; meanwhile, when the relative configuration of the
polarization and jet angles altered, no such lag could be noted. The
microflaring events, when analyzed as separate pulse emission components, were
found to be characterized by a very high polarization degree () and
polarization angles which differed substantially from the polarization angle of
the underlying background component, or from the radio jet positional angle. We
discuss the results in the general context of blazar emission and energy
dissipation models.Comment: 16 pages, 17 Figures; ApJ accepte
`One-sided' log-normal distribution of conductances of a disordered quantum wire
We develop a simple systematic method, valid for all strengths of disorder,
to obtain analytically for the first time the full distribution of conductance
P(g) for a quasi one dimensional wire in the absence of electron-electron
interaction. We show that in the crossover region between the metallic and
insulating regimes, P(g) is highly asymmetric, given by an essentially `one
sided' log-normal distribution. For larger disorder, the tail of the log-normal
distribution for g > 1 is cut off by a Gaussian.Comment: 7 pages, 2 figures. Summary and new references added. Final version,
published in Phys. Rev. Let
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