4,812 research outputs found
Photoelectron diffraction investigation of the structure of the clean TiO2(110)(1×1) surface
The surface relaxations of the rutile TiO2(110)(1×1) clean surface have been determined by O 1 s and Ti 2p3∕2 scanned-energy mode photoelectron diffraction. The results are in excellent agreement with recent low-energy electron diffraction (LEED) and medium energy ion scattering (MEIS) results, but in conflict with the results of some earlier investigations including one by surface x-ray diffraction. In particular, the bridging O atoms at the surface are found to relax outward, rather than inward, relative to the underlying bulk. Combined with the recent LEED and MEIS results, a consistent picture of the structure of this surface is provided. While the results of the most recent theoretical total-energy calculations are qualitatively consistent with this experimental consensus, significant quantitative differences remain
Femtolensing and Picolensing by Axion Miniclusters
Non-linear effects in the evolution of the axion field in the early Universe
may lead to the formation of gravitationally bound clumps of axions, known as
``miniclusters.'' Minicluster masses and radii should be in the range and cm, and in plausible
early-Universe scenarios a significant fraction of the mass density of the
Universe may be in the form of axion miniclusters. If such axion miniclusters
exist, they would have the physical properties required to be detected by
``femtolensing.''Comment: 7 pages plus 2 figures (Fig.1 avalible upon request), LaTe
Gravitational Waves from Light Cosmic Strings: Backgrounds and Bursts with Large Loops
The mean spectrum and burst statistics of gravitational waves produced by a
cosmological population of cosmic string loops are estimated using analytic
approximations, calibrated with earlier simulations. Formulas are derived
showing the dependence of observables on the string tension, in the regime
where newly-formed loops are relatively large, not very much smaller than the
horizon. Large loops form earlier, are more abundant, and generate a more
intense stochastic background and more frequent bursts than assumed in earlier
background estimates, enabling experiments to probe lighter cosmic strings of
interest to string theory. Predictions are compared with instrument noise from
current and future experiments, and with confusion noise from known
astrophysical gravitational wave sources such as stellar and massive black hole
binaries. In these large-loop models, current data from millisecond pulsar
timing already suggests that the tension is less than about , a
typical value expected in strings from brane inflation. LISA will be sensitive
to stochastic backgrounds created by strings as light as , at frequencies where it is limited by confusion noise of Galactic
stellar populations; however, for those lightest detectable strings, bursts are
rarely detectable.Comment: 22 pages, Latex, 1 figure, submitted to Phys Rev D; minor corrections
and clarifications adde
Relativistic Magnetic Monopole Flux Constraints from RICE
We report an upper limit on the flux of relativistic monopoles based on the
non-observation of in-ice showers by the Radio Ice Cherenkov Experiment (RICE)
at the South Pole. We obtain a 95% C.L. limit of order 10^{-18}/(cm^2-s-sr) for
intermediate mass monopoles of 10^7<gamma<10^{12} at the anticipated energy
E=10^{16} GeV. This bound is over an order of magnitude stronger than all
previously published experimental limits for this range of boost parameters
gamma, and exceeds two orders of magnitude improvement over most of the range.
We review the physics of radio detection, describe a Monte Carlo simulation
including continuous and stochastic energy losses, and compare to previous
experimental limits.Comment: 16 pages, 6 figures. Accepted for publication in Phys. Rev. D. Minor
revisions, including expanded discussion of monopole energy uncertaint
DEPTOR Expression Correlates with Muscle Protein Synthesis
Mammalian target of rapamycin (mTOR) has long been declared a focal point of muscle protein synthesis. mTORC1 (an mTOR complex consisting of mTOR, raptor, PRAS40, and mLST8) has been associated with regulation of protein translation in muscle, altering expression and activity levels of key downstream targets S6K1 and eIF-4E-BP1. mTORC1 has been shown to be affected by various stimuli, including nutritional status, growth factors, and mechanical loading. But in past incidents we have found disconnects in muscle protein synthesis and mTOR signaling, stimulating discussions that mTOR content and activation alone may not be able to fully account for muscle protein synthesis. Gaining popularity as a target for anti-cancer therapies, we became interested in DEPTOR, an endogenous inhibitor of mTORC1. Pharmacological inhibition of DEPTOR in cell culture and mouse studies has displayed increases of anabolic signaling in response to atrophic circumstances. We present two unique catabolic conditions in which we explore DEPTOR expression and muscle protein synthesis and demonstrate the first known data proposing that DEPTOR expression is not only influenced by physiological stimuli, including mechanical loading and insulin sensitivity, but that DEPTOR expression strongly correlates with 24-hr cumulative muscle protein synthesis rates.
In one study, male Sprague Dawley rats were subjected to various conditions of musculoskeletal unloading, reloading, and overload, in which hindlimb unloading (HU) was utilized to mimic chronic disuse atrophy (28-d), followed by ambulatory reloading (56-d post HU) with and without the addition of resistance exercise prescribed to assist in recovery (3 sessions/wk for 7-wks; progressive increases in added resistance up to ~60% BW). DEPTOR expression was assessed via Immunoblotting. 24-hr cumulative muscle protein synthesis (FSR) was measured via stable isotope labeling and quantified by gas chromatogram/mass spectrometry. DEPTOR demonstrated a strong negative correlation with FSR in the gastrocnemius (r = - 0.93261; p \u3c0.01). In our second study, male obese Zucker rats were divided into their lean and obese phenotypes, as well as placed into sedentary and resistance exercised groups. DEPTOR and FSR were assessed as described above following operant conditioning and four progressive exercise sessions over 9-d. Gastrocnemius DEPTOR/FSR was again significant (r = - 0.75723; p\u3c0.01). Collectively, these results are the first to associate physiologic changes in DEPTOR expression with alterations of FSR, which may have important implications towards the design of therapeutic targets for the control of muscle mass or in evaluating muscle anabolism
The secondary infall model of galactic halo formation and the spectrum of cold dark matter particles on Earth
The spectrum of cold dark matter particles on Earth is expected to have peaks
in velocity space associated with particles which are falling onto the Galaxy
for the first time and with particles which have fallen in and out of the
Galaxy only a small number of times in the past. We obtain estimates for the
velocity magnitudes and the local densities of the particles in these peaks. To
this end we use the secondary infall model of galactic halo formation which we
have generalized to take account of the angular momentum of the dark matter
particles. The new model is still spherically symmetric and it admits
self-similar solutions. In the absence of angular momentum, the model produces
flat rotation curves for a large range of values of a parameter
which is related to the spectrum of primordial density perturbations. We find
that the presence of angular momentum produces an effective core radius, i.e.
it makes the contribution of the halo to the rotation curve go to zero at zero
radius. The model provides a detailed description of the large scale properties
of galactic halos including their density profiles, their extent and total
mass. We obtain predictions for the kinetic energies of the particles in the
velocity peaks and estimates for their local densities as functions of the
amount of angular momentum, the age of the universe and .Comment: LaTeX, 39 pages including 18 figure
Back reaction of a long range force on a Friedmann-Robertson-Walker background
It is possible that there may exist long-range forces in addition to gravity.
In this paper we construct a simple model for such a force based on exchange of
a massless scalar field and analyze its effect on the evolution of a
homogeneous Friedmann-Robertson-Walker cosmology. The presence of such an
interaction leads to an equation of state characterized by positive pressure
and to resonant particle production similar to that observed in preheating
scenarios.Comment: 14 pages, 6 color Postscript figures, LaTe
From colloidal CdSe quantum dots to microscale optically anisotropic supercrystals through bottom-up self-assembly
This is the author accepted manuscript. The final version is available on open access from Royal Society of Chemistry via the DOI in this recordThe development of fabrication techniques for novel nanostructured materials is one of the key tasks of modern materials science. One pathway to successfully complete this task is the bottom-up assembly of colloidal nanoparticles into ordered superstructures, possessing both the properties of individual nanoparticles and further novel properties resulting from their interactions. However, nanoparticle self-assembly depends on a variety of parameters, which makes the precise control of this process a complicated problem. Here, the time course of quantum dot (QD) self-assembly into ordered superstructures has been analyzed, along with the evolution of their morphological and optical properties. QD self-assembly occurs through two distinct stages (homo- and hetero-geneous), leading to the formation of supercrystals with a layered morphology. Analysis of the optical properties throughout the superstructures’ growth has shown that the absorption and photoluminescence (PL) bands are blue shifted, retaining almost the same PL lifetimes as in the initial QD solution. The supercrystals formed possess a further unique optical property caused by their layered morphology; namely, a four-fold symmetry characterized by strong birefringence. Such supercrystals may be used for the fabrication of microscale optical paths with high extinction coefficients and specific polarization properties for novel optoelectronic devices.This study was supported by the Ministry of Education and
Science of the Russian Federation through the grant No.
14.584.21.0032 (ID RFMEFI58417X0032), the Engineering
and Physical Sciences Research Council (EPSRC) of the United
Kingdom via the EPSRC Centre for Doctoral Training in Electromagnetic
Metamaterials (Grant No. EP/L015331/1) and
via EP/N035569/1, and the Royal Society via International
Exchange Grant No. 2016/R1
Equation of State of Oscillating Brans-Dicke Scalar and Extra Dimensions
We consider a Brans-Dicke scalar field stabilized by a general power law
potential with power index at a finite equilibrium value. Redshifting
matter induces oscillations of the scalar field around its equilibrium due to
the scalar field coupling to the trace of the energy momentum tensor. If the
stabilizing potential is sufficiently steep these high frequency oscillations
are consistent with observational and experimental constraints for arbitrary
value of the Brans-Dicke parameter . We study analytically and
numerically the equation of state of these high frequency oscillations in terms
of the parameters and and find the corresponding evolution of the
universe scale factor. We find that the equation of state parameter can be
negative and less than -1 but it is not related to the evolution of the scale
factor in the usual way. Nevertheless, accelerating expansion is found for a
certain parameter range. Our analysis applies also to oscillations of the size
of extra dimensions (the radion field) around an equilibrium value. This
duality between self-coupled Brans-Dicke and radion dynamics is applicable for
where D is the number of extra dimensions.Comment: 10 two-column pages, RevTex4, 8 figures. Added clarifying
discussions, new references. Accepted in Phys. Rev. D (to appear
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