2,718 research outputs found
Magnification relations in gravitational lensing via multidimensional residue integrals
We investigate the so-called magnification relations of gravitational lensing
models. We show that multidimensional residue integrals provide a simple
explanation for the existence of these relations, and an effective method of
computation. We illustrate the method with several examples, thereby deriving
new magnification relations for galaxy lens models and microlensing (point mass
lensing).Comment: 16 pages, uses revtex4, submitted to Journal of Mathematical Physic
Automated data acquisition and reduction system for torsional braid analyzer
Automated Data Acquisition and Reduction System (ADAR) evaluates damping coefficient and relative rigidity by storing four successive peaks of waveform and time period between two successive peaks. Damping coefficient and relative rigidity are then calculated and plotted against temperature or time in real time
Study of the local field distribution on a single-molecule magnet-by a single paramagnetic crystal; a DPPH crystal on the surface of an Mn12-acetate crystal
The local magnetic field distribution on the subsurface of a single-molecule
magnet crystal, SMM, above blocking temperature (T >> Tb) detected for a very
short time interval (~ 10-10 s), has been investigated. Electron Paramagnetic
Resonance (EPR) spectroscopy using a local paramagnetic probe was employed as a
simple alternative detection method. An SMM crystal of
[Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O (Mn12-acetate) and a crystal of 2,2-
diphenyl-1-picrylhydrazyl (DPPH) as the paramagnetic probe were chosen for this
study. The EPR spectra of DPPH deposited on Mn12-acetate show additional
broadening and shifting in the magnetic field in comparison to the spectra of
the DPPH in the absence of the SMM crystal. The additional broadening of the
DPPH linewidth was considered in terms of the two dominant electron spin
interactions (dipolar and exchange) and the local magnetic field distribution
on the crystal surface. The temperature dependence of the linewidth of the
Gaussian distribution of local fields at the SMM surface was extrapolated for
the low temperature interval (70-5 K)
Astrometric Microlensing as a Method of Discovering and Characterizing Extra-Solar Planets
We introduce a new method of searching for and characterizing extra-solar
planets. We show that by monitoring the center-of-light motion of microlensing
alerts using the next generation of high precision astrometric instruments the
probability of detecting a planet orbiting the lens is high. We show that
adding astrometric information to the photometric microlensing lightcurve
greatly helps in determining the planetary mass and semi-major axis. We
introduce astrometric maps as a new way for calculating astrometric motion and
planet detection probabilities. Finite source effects are important for low
mass planets, but even Earth mass planets can give detectable signals.Comment: 9 pages includes 8 postscript figures, AAS Latex, submitted to Ap
Coherent manipulation of electron spins up to ambient temperatures in Cr(S=1/2) doped KNbO
We report coherent spin manipulation on Cr (\emph{S} = 1/2, \emph{I} =
0) doped KNbO, which constitutes a dilute two-level model relevant for
use as a spin qubit. Rabi oscillations are observed for the first time in a
spin system based on transition metal oxides up to room temperature. At liquid
helium temperature the phase coherence relaxation time \emph{} reaches
s and, with a Rabi frequency of 20 MHz, yields a single qubit
figure of merit \emph{} of about 500. This shows that a diluted ensemble
of Cr (\emph{S} = 1/2) doped KNbO is a potential candidate for
solid-state quantum information processing.Comment: 4 page
Links across disabilities:unveiling associations between functional domains
Background: Persons with disabilities experience higher risks of mortality as well as poorer health as compared to the general population. The aim of this study is to estimate the correlations between functional difficulties across several domains in six countries. Methods: National census data with questions on disability from six countries (Mauritius, Morocco, Senegal, Myanmar, Vietnam, and Uruguay) was used in this study. We performed logistic regressions to assess the extent to which having a functional difficulty in one domain is correlated with having a functional difficulty in each of the other domains and report weighted odds ratios (ORs) overall and within age-groups (‘18–44’ years and ‘45+’ years). Models adjust for age, sex, and location (rural or urban). Sensitivity analyses around different choices of predictors and response variables were conducted. Findings: For all countries, reporting a functional difficulty in one domain was consistently and significantly positively correlated with reporting a functional difficulty in other domains (overall) and for each of the two age-groups considered - ‘18–44’ years and ‘45+’ years. All ORs were greater than one. Cognition, mobility, and hearing were the domains that were the most correlated ones with other domains. The highest pairwise correlations were for i/ hearing and cognition; ii/ mobility and cognition. Results were robust to changing the severity thresholds for functional difficulties. Across countries, Uruguay, the only high-income country among the six countries under study, had the lowest correlations between functional domains. Conclusions: There are consistent positive associations in the experience of functional difficulties in various domains in the six countries under study. Such correlations may reflect barriers to social services including healthcare services and resources (e.g. assistive devices) that may lead to an avoidable deterioration of functioning across domains. Further research is needed on the trajectories of functional difficulties and on structural barriers that people with functional difficulties may experience in their communities and in healthcare settings in particular. This is important as some functional difficulties may be preventable.</p
The imprints of primordial non-gaussianities on large-scale structure: scale dependent bias and abundance of virialized objects
We study the effect of primordial nongaussianity on large-scale structure,
focusing upon the most massive virialized objects. Using analytic arguments and
N-body simulations, we calculate the mass function and clustering of dark
matter halos across a range of redshifts and levels of nongaussianity. We
propose a simple fitting function for the mass function valid across the entire
range of our simulations. We find pronounced effects of nongaussianity on the
clustering of dark matter halos, leading to strongly scale-dependent bias. This
suggests that the large-scale clustering of rare objects may provide a
sensitive probe of primordial nongaussianity. We very roughly estimate that
upcoming surveys can constrain nongaussianity at the level |fNL| <~ 10,
competitive with forecasted constraints from the microwave background.Comment: 16 pages, color figures, revtex4. v2: added references and an
equation. submitted to PRD. v3: simplified derivation, additional reference
Dark Matter Structures in the Universe: Prospects for Optical Astronomy in the Next Decade
The Cold Dark Matter theory of gravitationally-driven hierarchical structure
formation has earned its status as a paradigm by explaining the distribution of
matter over large spans of cosmic distance and time. However, its central
tenet, that most of the matter in the universe is dark and exotic, is still
unproven; the dark matter hypothesis is sufficiently audacious as to continue
to warrant a diverse battery of tests. While local searches for dark matter
particles or their annihilation signals could prove the existence of the
substance itself, studies of cosmological dark matter in situ are vital to
fully understand its role in structure formation and evolution. We argue that
gravitational lensing provides the cleanest and farthest-reaching probe of dark
matter in the universe, which can be combined with other observational
techniques to answer the most challenging and exciting questions that will
drive the subject in the next decade: What is the distribution of mass on
sub-galactic scales? How do galaxy disks form and bulges grow in dark matter
halos? How accurate are CDM predictions of halo structure? Can we distinguish
between a need for a new substance (dark matter) and a need for new physics
(departures from General Relativity)? What is the dark matter made of anyway?
We propose that the central tool in this program should be a wide-field optical
imaging survey, whose true value is realized with support in the form of
high-resolution, cadenced optical/infra-red imaging, and massive-throughput
optical spectroscopy.Comment: White paper submitted to the 2010 Astronomy & Astrophysics Decadal
Surve
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