952 research outputs found
Shining Light on Modifications of Gravity
Many modifications of gravity introduce new scalar degrees of freedom, and in
such theories matter fields typically couple to an effective metric that
depends on both the true metric of spacetime and on the scalar field and its
derivatives. Scalar field contributions to the effective metric can be
classified as conformal and disformal. Disformal terms introduce gradient
couplings between scalar fields and the energy momentum tensor of other matter
fields, and cannot be constrained by fifth force experiments because the
effects of these terms are trivial around static non-relativistic sources. The
use of high-precision, low-energy photon experiments to search for conformally
coupled scalar fields, called axion-like particles, is well known. In this
article we show that these experiments are also constraining for disformal
scalar field theories, and are particularly important because of the difficulty
of constraining these couplings with other laboratory experiments.Comment: 20 pages, 10 figures. v2: Matches version accepted by JCAP;
additional discussion of the strong coupling scale. Conclusions unchange
Superradiation from Crystals of High-Spin Molecular Nanomagnets
Phenomenological theory of superradiation from crystals of high-spin
molecules is suggested. We show that radiation friction can cause a
superradiation pulse and investigate the role of magnetic anisotropy, external
magnetic field and dipole-dipole interactions. Depending on the contribution of
all these factors at low temperature, several regimes of magnetization of
crystal sample are described. Very fast switch of magnetization's direction for
some sets of parameters is predicted.Comment: 10 pages, 3 figure
Inflation driven by scalar field with non-minimal kinetic coupling with Higgs and quadratic potentials
We study a scalar field with non-minimal kinetic coupling to itself and to
the curvature. The slow rolling conditions allowing an inflationary background
have been found. The quadratic and Higgs type potentials have been considered,
and the corresponding values for the scalar fields at the end of inflation
allows to recover the connection with particle physics.Comment: 16 pages, to appear in JCA
The Orbital and Absolute Magnitude Distributions of Main Belt Asteroids
We have developed a model-independent analytical method for debiasing the
four-dimensional (a,e,i,H) distribution obtained in any asteroid observation
program and have applied the technique to results obtained with the 0.9m
Spacewatch Telescope. From 1992 to 1995 Spacewatch observed ~3740 deg^2 near
the ecliptic and made observations of more than 60,000 asteroids to a limiting
magnitude of V~21. The debiased semi-major axis and inclination distributions
of Main Belt asteroids in this sample with 11.5<= H <16 match the distributions
of the known asteroids with H <11.5. The absolute magnitude distribution was
studied in the range 8< H <17.5. We have found that the set of known asteroids
is complete to about absolute magnitudes 12.75, 12.25 and 11.25 in the inner,
middle and outer regions of the belt respectively. The number distribution as a
function of absolute magnitude cannot be represented by a single power-law
(10^{alpha H}) in any region. We were able to define broad ranges in H in each
part of the belt where alpha was nearly constant. Within these ranges of H the
slope does not correspond to the value of 0.5 expected for an equilibrium
cascade in self-similar collisions (Dohnanyi, 1971). The value of alpha varies
with absolute magnitude and shows a `kink' in all regions of the belt for H~13.
This absolute magnitude corresponds to a diameter ranging from about 8.5 to
12.5 km depending on the albedo or region of the belt.Comment: 33 pages, 6 figures, 6 tables. published in Icaru
Smooth vortex precession in superfluid 4He
We have measured a precessing superfluid vortex line, stretched from a wire
to the wall of a cylindrical cell. By contrast to previous experiments with a
similar geometry, the motion along the wall is smooth. The key difference is
probably that our wire is substantially off center. We verify several numerical
predictions about the motion, including an asymmetry in the precession
signature, the behavior of pinning events, and the temperature dependence of
the precession.Comment: 8 pages, 8 figure
Isoscalar dipole strength in ^{208}_{82}Pb_{126}: the spurious mode and the strength in the continuum
Isoscalar dipole (compression) mode is studied first using schematic
harmonic-oscillator model and, then, the self-consistent Hartree-Fock (HF) and
random phase approximation (RPA) solved in coordinate space. Taking ^{208}Pb
and the SkM* interaction as a numerical example, the spurious component and the
strength in the continuum are carefully examined using the sum rules. It is
pointed out that in the continuum calculation one has to use an extremely fine
radial mesh in HF and RPA in order to separate, with good accuracy, the
spurious component from intrinsic excitations.Comment: 19 pages, 2 figure
Isoscalar Giant Dipole Resonance and Nuclear Matter Incompressibility Coefficient
We present results of microscopic calculations of the strength function,
S(E), and alpha-particle excitation cross sections sigma(E) for the isoscalar
giant dipole resonance (ISGDR). An accurate and a general method to eliminate
the contributions of spurious state mixing is presented and used in the
calculations. Our results provide a resolution to the long standing problem
that the nuclear matter incompressibility coefficient, K, deduced from sigma(E)
data for the ISGDR is significantly smaller than that deduced from data for the
isoscalar giant monopole resonance (ISGMR).Comment: 4 pages using revtex 3.0, 3 postscript figures created by Mathematica
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Enhancer deletion and allelic effects define a regulatory molecular mechanism at the VLDLR cholesterol GWAS locus
Total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) are heritable risk factors for cardiovascular disease, yet the molecular mechanisms underlying the majority of blood lipid-associated genome-wide association studies signals remain elusive. One association signal is located in intron 3 of VLDLR; rs3780181-A is a risk allele associated (P †2 à 10-9) with increased TC and LDL-C.We investigated variants, genes and mechanisms underlying this association signal.We used a functional genetic approach to show that the intronic region spanning rs3780181 exhibited 1.6-7.6-fold enhancer activity in human HepG2 hepatocyte, THP-1 monocyte and Simpson-Golabi-Behmel Syndrome (SGBS) preadipocyte cells and that the rs3780181-A risk allele showed significantly less enhancer activity compared with the G allele, consistent with the direction of an expression quantitative trait locus in liver. In addition, rs3780181 alleles showed differential binding to multiple nuclear proteins, including stronger IRF2 binding to the rs3780181 G allele.We used a CRISPR-cas9 approach to delete 475 and 663 bp of the putative enhancer element in HEK293T kidney cells; compared to expression of mock-edited cell lines, the homozygous enhancer deletion cell lines showed 1.2-fold significantly (P < 0.04) decreased expression of VLDLR, as well as 1.5-fold decreased expression of SMARCA2, located 388 kb away. Together, these results identify an enhancer of VLDLR expression and suggest that altered binding of one or more factors bound to rs3780181 alleles decreases enhancer activity and reduces at least VLDLR expression, leading to increased TC and LDL-C
EFFECTS OF CHANGE IN BODY POSTURE ON PLASMA AND SERUM ELECTROLYTES IN NORMAL SUBJECTS AND IN PRIMARY ALDOSTERONISM
We observed that change in body posture from the supine to the erect position in normal volunteers was associated with a rise in circulating potassium and a fall in sodium concentrations, irrespective of whether the electrolytes were measured in serum or plasma, or whether head-up tilt or ambulation was used. In patients with primary aldosteronism, the fall in serum sodium and rise in serum potassium with ambulation tended to obscure the characteristic electrolyte abnormalities of that syndrome. These changes in potassium and sodium could contribute to the rise in aldosterone secretion on orthostasis. The body posture of patients should be considered in the interpretation of plasma and serum electrolyte levels.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75439/1/j.1365-2265.1981.tb02972.x.pd
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