17,943 research outputs found
General Relativistic Description of the Observed Galaxy Power Spectrum: Do We Understand What We Measure?
We extend the general relativistic description of galaxy clustering developed
in Yoo, Fitzpatrick, and Zaldarriaga (2009). For the first time we provide a
fully general relativistic description of the observed matter power spectrum
and the observed galaxy power spectrum with the linear bias ansatz. It is
significantly different from the standard Newtonian description on large scales
and especially its measurements on large scales can be misinterpreted as the
detection of the primordial non-Gaussianity even in the absence thereof. The
key difference in the observed galaxy power spectrum arises from the real-space
matter fluctuation defined as the matter fluctuation at the hypersurface of the
observed redshift. As opposed to the standard description, the shape of the
observed galaxy power spectrum evolves in redshift, providing additional
cosmological information. While the systematic errors in the standard Newtonian
description are negligible in the current galaxy surveys at low redshift,
correct general relativistic description is essential for understanding the
galaxy power spectrum measurements on large scales in future surveys with
redshift depth z>3. We discuss ways to improve the detection significance in
the current galaxy surveys and comment on applications of our general
relativistic formalism in future surveys.Comment: accepted for publication in Physical Review
Young\u27s modulus of [111] germanium nanowires
This paper reports a diameter-independent Young’s modulus of 91.9 ± 8.2 GPa for [111] Germaniumnanowires (Ge NWs). When the surface oxide layer is accounted for using a core-shell NW approximation, the YM of the Ge core approaches a near theoretical value of 147.6 ± 23.4 GPa. The ultimate strength of a NW device was measured at 10.9 GPa, which represents a very high experimental-to-theoretical strength ratio of ∼75%. With increasing interest in this material system as a high-capacity lithium-ion battery anode, the presented data provide inputs that are essential in predicting its lithiation-induced stress fields and fracture behavior
Going beyond the Kaiser redshift-space distortion formula: a full general relativistic account of the effects and their detectability in galaxy clustering
Kaiser redshift-space distortion formula describes well the clustering of
galaxies in redshift surveys on small scales, but there are numerous additional
terms that arise on large scales. Some of these terms can be described using
Newtonian dynamics and have been discussed in the literature, while the others
require proper general relativistic description that was only recently
developed. Accounting for these terms in galaxy clustering is the first step
toward tests of general relativity on horizon scales. The effects can be
classified as two terms that represent the velocity and the gravitational
potential contributions. Their amplitude is determined by effects such as the
volume and luminosity distance fluctuation effects and the time evolution of
galaxy number density and Hubble parameter. We compare the Newtonian
approximation often used in the redshift-space distortion literature to the
fully general relativistic equation, and show that Newtonian approximation
accounts for most of the terms contributing to velocity effect. We perform a
Fisher matrix analysis of detectability of these terms and show that in a
single tracer survey they are completely undetectable. To detect these terms
one must resort to the recently developed methods to reduce sampling variance
and shot noise. We show that in an all-sky galaxy redshift survey at low
redshift the velocity term can be measured at a few sigma if one can utilize
halos of mass M>10^12 Msun (this can increase to 10-sigma or more in some more
optimistic scenarios), while the gravitational potential term itself can only
be marginally detected. We also demonstrate that the general relativistic
effect is not degenerate with the primordial non-Gaussian signature in galaxy
bias, and the ability to detect primordial non-Gaussianity is little
compromised.Comment: 13 pages, 5 figures, published in PR
A computationally efficient inorganic atmospheric aerosol phase equilibrium model (UHAERO)
A variety of thermodynamic models have been developed to predict inorganic gas-aerosol equilibrium. To achieve computational efficiency a number of the models rely on a priori specification of the phases present in certain relative humidity regimes. Presented here is a new computational model, named UHAERO, that is both efficient and rigorously computes phase behavior without any a priori specification. The computational implementation is based on minimization of the Gibbs free energy using a primal-dual method, coupled to a Newton iteration. The mathematical details of the solution are given elsewhere. The model also computes deliquescence and crystallization behavior without any a priori specification of the relative humidities of deliquescence or crystallization. Detailed phase diagrams of the sulfate/nitrate/ammonium/water system are presented as a function of relative humidity at 298.15 K over the complete space of composition
A new inorganic atmospheric aerosol phase equilibrium model (UHAERO)
A variety of thermodynamic models have been developed to predict inorganic gas-aerosol equilibrium. To achieve computational efficiency a number of the models rely on a priori specification of the phases present in certain relative humidity regimes. Presented here is a new computational model, named UHAERO, that is both efficient and rigorously computes phase behavior without any a priori specification. The computational implementation is based on minimization of the Gibbs free energy using a primal-dual method, coupled to a Newton iteration. The mathematical details of the solution are given elsewhere. The model computes deliquescence behavior without any a priori specification of the relative humidities of deliquescence. Also included in the model is a formulation based on classical theory of nucleation kinetics that predicts crystallization behavior. Detailed phase diagrams of the sulfate/nitrate/ammonium/water system are presented as a function of relative humidity at 298.15 K over the complete space of composition
Electrons in Dry DNA from Density Functional Calculations
The electronic structure of an infinite poly-guanine - poly-cytosine DNA
molecule in its dry A-helix structure is studied by means of density-functional
calculations. An extensive study of 30 nucleic base pairs is performed to
validate the method. The electronic energy bands of DNA close to the Fermi
level are then analyzed in order to clarify the electron transport properties
in this particularly simple DNA realization, probably the best suited candidate
for conduction. The energy scale found for the relevant band widths, as
compared with the energy fluctuations of vibrational or genetic-sequence
origin, makes highly implausible the coherent transport of electrons in this
system. The possibility of diffusive transport with sub-nanometer mean free
paths is, however, still open. Information for model Hamiltonians for
conduction is provided.Comment: 8 pages, 4 figure
Brain amyloid in preclinical Alzheimer\u27s disease is associated with increased driving risk
INTRODUCTION: Postmortem studies suggest that fibrillar brain amyloid places people at higher risk for hazardous driving in the preclinical stage of Alzheimer's disease (AD). METHODS: We administered driving questionnaires to 104 older drivers (19 AD, 24 mild cognitive impairment, and 61 cognitive normal) who had a recent (18)F-florbetapir positron emission tomography scan. We examined associations of amyloid standardized uptake value ratios with driving behaviors: traffic violations or accidents in the past 3 years. RESULTS: The frequency of violations or accidents was curvilinear with respect to standardized uptake value ratios, peaking around a value of 1.1 (model r(2) = 0.10, P = .002); moreover, this relationship was evident for the cognitively normal participants. DISCUSSION: We found that driving risk is strongly related to accumulating amyloid on positron emission tomography, and that this trend is evident in the preclinical stage of AD. Brain amyloid burden may in part explain the increased crash risk reported in older adults
Ultramafic xenoliths from the Bearpaw Mountains, Montana, USA: evidence for multiple metasomatic events in the lithospheric mantle beneath the Wyoming craton
Ultramafic xenoliths in Eocene minettes of the Bearpaw Mountains volcanic field (Montana, USA), derived from the lower lithosphere of the Wyoming craton, can be divided based on textural criteria into tectonite and cumulate groups. The tectonites consist of strongly depleted spinel lherzolites, harzburgites and dunites. Although their mineralogical compositions are generally similar to those of spinel peridotites in off-craton settings, some contain pyroxenes and spinels that have unusually low Al2O3 contents more akin to those found in cratonic spinel peridotites. Furthermore, the tectonite peridotites have whole-rock major element compositions that tend to be significantly more depleted than non-cratonic mantle spinel peridotites (high MgO, low CaO, Al2O3 and TiO2) and resemble those of cratonic mantle. These compositions could have been generated by up to 30% partial melting of an undepleted mantle source. Petrographic evidence suggests that the mantle beneath the Wyoming craton was re-enriched in three ways: (1) by silicate melts that formed mica websterite and clinopyroxenite veins; (2) by growth of phlogopite from K-rich hydrous fluids; (3) by interaction with aqueous fluids to form orthopyroxene porphyroblasts and orthopyroxenite veins. In contrast to their depleted major element compositions, the tectonite peridotites are mostly light rare earth element (LREE)-enriched and show enrichment in fluid-mobile elements such as Cs, Rb, U and Pb on mantle-normalized diagrams. Lack of enrichment in high field strength elements (HFSE; e.g. Nb, Ta, Zr and Hf) suggests that the tectonite peridotites have been metasomatized by a subduction-related fluid. Clinopyroxenes from the tectonite peridotites have distinct U-shaped REE patterns with strong LREE enrichment. They have 143Nd/144Nd values that range from 0·5121 (close to the host minette values) to 0·5107, similar to those of xenoliths from the nearby Highwood Mountains. Foliated mica websterites also have low 143Nd/144Nd values (0·5113) and extremely high 87Sr/86Sr ratios in their constituent phlogopite, indicating an ancient (probably mid-Proterozoic) enrichment. This enriched mantle lithosphere later contributed to the formation of the high-K Eocene host magmas. The cumulate group ranges from clinopyroxene-rich mica peridotites (including abundant mica wehrlites) to mica clinopyroxenites. Most contain >30% phlogopite. Their mineral compositions are similar to those of phenocrysts in the host minettes. Their whole-rock compositions are generally poorer in MgO but richer in incompatible trace elements than those of the tectonite peridotites. Whole-rock trace element patterns are enriched in large ion lithophile elements (LILE; Rb, Cs, U and Pb) and depleted in HFSE (Nb, Ta Zr and Hf) as in the host minettes, and their Sr–Nd isotopic compositions are also identical to those of the minettes. Their clinopyroxenes are LREE-enriched and formed in equilibrium with a LREE-enriched melt closely resembling the minettes. The cumulates therefore represent a much younger magmatic event, related to crystallization at mantle depths of minette magmas in Eocene times, that caused further metasomatic enrichment of the lithosphere
Isocurvature Perturbations and Non-Gaussianity of Gravitationally Produced Nonthermal Dark Matter
Gravitational particle production naturally occurs during the transition from
the inflationary phase to the non-inflationary phase. If the particles are
stable and very weakly interacting, they are natural nonthermal dark matter
candidates. We show that such nonthermal dark matter particles can produce
local non-Gaussianities large enough to be observed by ongoing and near future
experiments without being in conflict with the existing isocurvature bounds. Of
particular interest is the fact that these particles can be observable through
local non-Gaussianities even when they form a very small fraction of the total
dark matter content.Comment: 18 pages, 4 figures, version accepted by PR
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