19,727 research outputs found
Pump power reduction by photodarkening in Yb-doped fibres
The influence of the photodarkening at a pump wavelength to envisage the direct impact of the photodarkening in the YDF based devices is reported. Results suggest that the photodarkening does not only induce excess background loss as commonly interpreted, but also influences pump efficiency
Nonlocal effects in the shot noise of diffusive superconductor - normal-metal systems
A cross-shaped diffusive system with two superconducting and two normal
electrodes is considered. A voltage is applied between the normal
leads. Even in the absence of average current through the superconducting
electrodes their presence increases the shot noise at the normal electrodes and
doubles it in the case of a strong coupling to the superconductors. The
nonequilibrium noise at the superconducting electrodes remains finite even in
the case of a vanishingly small transport current due to the absence of energy
transfer into the superconductors. This noise is suppressed by
electron-electron scattering at sufficiently high voltages.Comment: 4 pages, RevTeX, 2 eps figure
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
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
Dressage and the illusion of management control
A recent stream of information systems research emphasises the institutional or structural forces that can be embodied in an enterprise system. Other research focuses on the locally idiosyncratic adoption patterns of users after an enterprise systems implementation. To understand the tension that arises when these opposing views meet, we draw on Foucault’s notion of dressage. Dressage implies the exercise of total control by a governing body over the activities of its inhabitant population. In a context of enterprise systems, dressage is reflected in the control-rooted standardised rationality which is inherent in such systems, as well as in the ostensive compliance of individuals to such systems. Dressage highlights that enterprise systems may contain elements of non-productive control, and that responses to such control may appear to be compliant, whereas non-standardised locally idiosyncratic activities persist outside of the system’s gaze. These “organic” activities may be vital for organisational flexibility and for ongoing effective organisational performance
New Perspective on Galaxy Clustering as a Cosmological Probe: General Relativistic Effects
We present a general relativistic description of galaxy clustering in a FLRW
universe. The observed redshift and position of galaxies are affected by the
matter fluctuations and the gravity waves between the source galaxies and the
observer, and the volume element constructed by using the observables differs
from the physical volume occupied by the observed galaxies. Therefore, the
observed galaxy fluctuation field contains additional contributions arising
from the distortion in observable quantities and these include tensor
contributions as well as numerous scalar contributions. We generalize the
linear bias approximation to relate the observed galaxy fluctuation field to
the underlying matter distribution in a gauge-invariant way. Our full formalism
is essential for the consistency of theoretical predictions. As our first
application, we compute the angular auto correlation of large-scale structure
and its cross correlation with CMB temperature anisotropies. We comment on the
possibility of detecting primordial gravity waves using galaxy clustering and
discuss further applications of our formalism.Comment: 10 pages, 2 figures, accepted for publication in Physical Review
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
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