23,988 research outputs found
Relativistic, QED, and finite nuclear mass corrections for low-lying states of Li and Be
Accurate results for nonrelativistic energy, relativistic, QED, and finite
nuclear mass corrections are obtained for , and
states of the Li atom and Be ion. Our computational approach
uses the Hylleraas basis set with the analytic integration and recursion
relations. From comparison of experimental results for the isotope shifts to
theoretical predictions including nuclear polarizabilities, we obtain nuclear
charge radii for Li and Be isotopes.Comment: 19 pages, 8 tables, Phys. Rev. A in prin
RR Lyrae Variables in the Globular Cluster M55. The First Evidence for Non Radial Pulsations in RR Lyr Stars
We present the results of a photometric study of RR Lyrae variables in the
field of the globular cluster M55. We have discovered nine new RR Lyrae stars,
increasing the number of known variables in this cluster to 15 objects. Five of
the newly discovered variables belong to Bailey type RRc and two to type RRab.
Two background RRab stars are probable members of the Sagittarius dwarf galaxy.
Fourier decomposition of the light curves was used to derive basic properties
of the present sample of RR Lyrae variables. From an analysis of the RRc
variables we obtain a mean mass of , luminosity , effective temperature K, and helium
abundance . Based on the colors, periods and metallicities
of the RRab stars we estimate the value of the color excess for M55 to be equal
to . Using this value we derive the colors of the blue and
red edges of the instability strip in M55. The blue edge lies at
mag and the red edge lies at mag. We estimate the values of the
visual apparent and dereddened distance moduli to be and
, respectively. The light curves of three of the RRc variables
exhibit changes in amplitude of over 0.1 mag on the time scale of less than a
week, rather short for the Blazhko effect, but with no evidence for another
radial pulsational frequency. However we do detect other periodicities which
are clearly visible in the light curve after removing variations with the first
overtone radial frequency. This is strong evidence for the presence of
non-radial pulsations, a behavior common for Scuti stars but not yet
observed among RR Lyr variables.Comment: submitted to Astronomical Journal, 33 pages with 11 figure
Stochastic Trends and Economic Fluctuations
Recent developments in macroeconomic theory emphasize that transient economic fluctuations can arise as responses to changes in long run factors -- in particular, technological improvements -- rather than short run factors. This contrasts with the view that short run fluctuations and shifts in long run trends are largely unrelated. We examine empirically the effect of shifts in stochastic trends that are common to several macroeconomic series. Using a linear time series model related to a VAR, we consider first a system with GNP, consumption and investment with a single common stochastic trend; we then examine this system augmented by money and prices and an additional stochastic trend. Our results suggest that movements in the "real" stochastic trend account for one-half to two-thirds of the variation in postwar U.S. GNP.
Nonlocality of Kohn-Sham exchange-correlation fields in dielectrics
The theory of the macroscopic field appearing in the Kohn-Sham
exchange-correlation potential for dielectric materials, as introduced by
Gonze, Ghosez and Godby, is reexamined. It is shown that this Kohn-Sham field
cannot be determined from a knowledge of the local state of the material (local
crystal potential, electric field, and polarization) alone. Instead, it has an
intrinsically nonlocal dependence on the global electrostatic configuration.
For example, it vanishes in simple transverse configurations of a polarized
dielectric, but not in longitudinal ones.Comment: 4 pages, two-column style with 2 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#dv_gg
External Shear in Quadruply Imaged Lens Systems
We use publicly available N-body simulations and semi-analytic models of
galaxy formation to estimate the levels of external shear due to structure near
the lens in gravitational lens systems. We also describe two selection effects,
specific to four-image systems, that enhance the probability of observing
systems to have higher external shear. Ignoring additional contributions from
"cosmic shear" and assuming that lens galaxies are not significantly flattened,
we find that the mean shear at the position of a quadruple lens galaxy is 0.11,
the rms shear is roughly 0.15, and there is roughly a 45% likelihood of
external shear greater than 0.1. This is much larger than previous estimates
and in good agreement with typical measured external shear. The higher shear
primarily stems from the tendency of early-type galaxies, which are the
majority of lenses, to reside in overdense regions.Comment: 5 pages, 2 figures, ApJ in press, minor revision
LRG-BEASTS III: Ground-based transmission spectrum of the gas giant orbiting the cool dwarf WASP-80
We have performed ground-based transmission spectroscopy of the hot Jupiter
orbiting the cool dwarf WASP-80 using the ACAM instrument on the William
Herschel Telescope (WHT) as part of the LRG-BEASTS programme. This is the third
paper of a ground-based transmission spectroscopy survey of hot Jupiters using
low-resolution grism spectrographs. We observed two transits of the planet and
have constructed transmission spectra spanning a wavelength range of
4640-8840A. Our transmission spectrum is inconsistent with a previously claimed
detection of potassium in WASP-80b's atmosphere, and is instead most consistent
with a haze. We also do not see evidence for sodium absorption at a resolution
of 100A.Comment: 11 pages, 9 figures. Accepted for publication in MNRA
Isotope shifts and hyperfine structure of the Fe I 372 nm resonance line
We report measurements of the isotope shifts of the Fe I resonance line at 372 nm between all four stable
isotopes Fe, Fe, Fe, and Fe, as well as the
complete hyperfine structure of that line for Fe, the only stable
isotope having a non-zero nuclear spin. The field and specific mass shift
coefficients of the transition have been derived from the data, as well as the
experimental value for the hyperfine structure magnetic dipole coupling
constant of the excited state of the transition in Fe: MHz. The measurements were done by means of Doppler-free
laser saturated-absorption spectroscopy in a Fe-Ar hollow cathode using both
natural and enriched iron samples. The measured isotope shifts and hyperfine
constants are reported with uncertainties at the percent level.Comment: 5 pages, 5 figure
Insulin resistance induced by antiretroviral drugs: Current understanding of molecular mechanisms
The increase in incidence of HIV infection continues to be a major public health problem across the world, but more especially in sub-Saharan Africa. Treatment with highly active antiretroviral therapy (HAART) has improved the prognosis of patients with AIDS, but it has also increased the incidence of various metabolic disorders, in particular insulin resistance accompanied by dyslipidaemia, hyperglycaemia and lipodystrophy. This is often accompanied by frank type 2 diabetes and increased mortality from cardiovascular disease. It is important to understand the mechanistic basis for these side-effects as the incidence of these is likely to increase as the rollout of antiretroviral drugs continues
Quantifying Hydrologic Pathway and Source Connectivity Dynamics in Tile Drainage: Implications for Phosphorus Concentrations
Flowpathways and source water connectivity dynamics are widely recognized to affect tile-drainage water quality. In this study, we developed and evaluated a framework that couples event-based hydrograph recession and specific conductance end-member mixing analysis (SC-EMMA) to provide a more robust framework for quantifying both flow pathway dynamics and source connectivity of drainage water in tile-drained landscapes. High-frequency (30-min) flow and conductivity data were collected from an edge-of-field tile main located in northwestern Ohio, and the newly developed framework was applied for data collected in water year 2019. Multiple linear regression (MLR) analysis was used to evaluate the impact of pathway-connectivity dynamics on flow-weighted mean dissolved reactive P (DRP) concentrations, which were collected as part of the USDA-ARS edge-of-field monitoring network. The hydrograph recession and SC-EMMA results highlighted intra- and interevent differences between quick (preferential) flow and new (precipitation) water transported during events, challenging a common assumption that new water reflects drainage through preferential flow paths. The analysis of hydrologic flow pathways demonstrated matrix–macropore exchange (Qquick-old), preferential flow of new water (Qquick-new), slow flow of old water (Qslow-old), and slow flow of new water (Qslow-new) contributed 9, 39, 42, and 10% to tile discharge, on average, with interevent variability. Matrix water that is transported to tile drains via macropore flowpaths was found to be activated throughout the year, even under drier antecedent conditions, suggesting that matrix–macropore exchange was more sensitive to within-event hydrological processes as compared with antecedent conditions. The MLR results highlighted that pathway-connectivity hydrograph fractions improved prediction of DRP concentrations, although improvement may be more pronounced in landscapes with higher rates of matrix–macropore exchange
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