8,173 research outputs found
Diffusion and Atomic Mobilities in fcc Ni-Sn Alloys
The composition-distance profiles in face-centered cubic (fcc) Ni-Sn alloys at 1173, 1223, 1273, and 1323K were measured by means of electronic probe microanalysis (EPMA) using Ni/Ni-7.3at.%Sn diffusion couples. Based on the available thermodynamic information and various experimental diffusion coefficients, the atomic mobilities of Ni and Sn in fcc Ni-Sn alloys were assessed as a function of temperature and composition in terms of the CALPHAD method using the DICTRA® software package. Optimized mobility parameters are presented. Comparisons between the calculated and measured diffusion coefficients show that most of the experimental information can be reproduced reasonably. The obtained mobility parameters can also predict satisfactorily the composition-distance profiles of the Ni/Ni-7.3at.%Sn diffusion couples determined in the present wor
Threshold Corrections in Precision LHC Physics: QED otimes QCD
With an eye toward LHC processes in which theoretical precisions of 1 percent
are desired, we introduce the theory of the simultaneous YFS resummation of QED
and QCD to compute the size of the expected resummed soft radiative threshold
effects in precision studies of heavy particle production at the LHC. Our
results show that both QED and QCD soft threshold effects must be controlled to
be on the conservative side to achieve such precision goals.Comment: 4 pages, no figures; presented by B.F.L. Ward in DPF200
Upper limit on spontaneous supercurrents in SrRuO
It is widely believed that the perovskite SrRuO is an unconventional
superconductor with broken time reversal symmetry. It has been predicted that
superconductors with broken time reversal symmetry should have spontaneously
generated supercurrents at edges and domain walls. We have done careful imaging
of the magnetic fields above SrRuO single crystals using scanning Hall
bar and SQUID microscopies, and see no evidence for such spontaneously
generated supercurrents. We use the results from our magnetic imaging to place
upper limits on the spontaneously generated supercurrents at edges and domain
walls as a function of domain size. For a single domain, this upper limit is
below the predicted signal by two orders of magnitude. We speculate on the
causes and implications of the lack of large spontaneous supercurrents in this
very interesting superconducting system.Comment: 9 page
Trend and variability in ozone in the tropical lower stratosphere over 2.5 solar cycles observed by SAGE II and OSIRIS
We have extended the satellite-based ozone anomaly time series to the
present (December 2012) by merging SAGE II (Stratospheric Aerosol and Gas Experiment
II) with OSIRIS (Optical Spectrograph and Infrared Imager System)
and correcting for the small bias (~0.5%) between them,
determined using their temporal overlap of 4 years. Analysis of the merged
data set (1984–2012) shows a statistically significant negative trend at all
altitudes in the 18–25 km range, including a trend of (−4.6 ± 2.6)% decade<sup>−1</sup>
at 19.5 km where the relative standard error is a minimum. We are
also able to replicate previously reported decadal trends in the tropical
lower-stratospheric ozone anomaly based on SAGE II observations.
Uncertainties are smaller on the merged trend than the SAGE II trend at all
altitudes. Underlying strong fluctuations in ozone anomaly due to El Niño–Southern Oscillation (ENSO), the altitude-dependent quasi-biennial
oscillation, and tropopause pressure need to be taken into account to reduce
trend uncertainties and, in the case of ENSO, to accurately determine the
linear trend just above the tropopause. We also compare the observed ozone
trend with a calculated trend that uses information on tropical upwelling
and its temporal trend from model simulations, tropopause pressure trend
information derived from reanalysis data, and vertical profiles from SAGE II
and OSIRIS to determine the vertical gradient of ozone and its trend. We
show that the observed trend agrees with the calculated trend and that the
magnitude of the calculated trend is dominated by increased tropical
upwelling, with minor but increasing contribution from the vertical ozone
gradient trend as the tropical tropopause is approached. Improvements are
suggested for future regression modelling efforts which could reduce trend
uncertainties and biases in trend magnitudes, thereby allowing accurate
trend detection to extend below 18 km
Effective forces in colloidal mixtures: from depletion attraction to accumulation repulsion
Computer simulations and theory are used to systematically investigate how
the effective force between two big colloidal spheres in a sea of small spheres
depends on the basic (big-small and small-small) interactions. The latter are
modeled as hard-core pair potentials with a Yukawa tail which can be both
repulsive or attractive. For a repulsive small-small interaction, the effective
force follows the trends as predicted by a mapping onto an effective
non-additive hard-core mixture: both a depletion attraction and an accumulation
repulsion caused by small spheres adsorbing onto the big ones can be obtained
depending on the sign of the big-small interaction. For repulsive big-small
interactions, the effect of adding a small-small attraction also follows the
trends predicted by the mapping. But a more subtle ``repulsion through
attraction'' effect arises when both big-small and small-small attractions
occur: upon increasing the strength of the small-small interaction, the
effective potential becomes more repulsive. We have further tested several
theoretical methods against our computer simulations: The superposition
approximation works best for an added big-small repulsion, and breaks down for
a strong big-small attraction, while density functional theory is very accurate
for any big-small interaction when the small particles are pure hard-spheres.
The theoretical methods perform most poorly for small-small attractions.Comment: submitted to PRE; New version includes an important quantitative
correction to several of the simulations. The main conclusions remain
unchanged thoug
Determination of the orbital moment and crystal field splitting in LaTiO
Utilizing a sum-rule in a spin-resolved photoelectron spectroscopic
experiment with circularly polarized light, we show that the orbital moment in
LaTiO is strongly reduced both below and above the N\'{e}el temperature.
Using Ti x-ray absorption spectroscopy as a local probe, we found
that the crystal field splitting in the subshell is about 0.12-0.30
eV. This large splitting does not facilitate the formation of an orbital
liquid
KH 15D: Gradual Occultation of a Pre-Main-Sequence Binary
We propose that the extraordinary ``winking star'' KH 15D is an eccentric
pre-main-sequence binary that is gradually being occulted by an opaque screen.
This model accounts for the periodicity, depth, duration, and rate of growth of
the modern eclipses; the historical light curve from photographic plates; and
the existing radial velocity measurements. It also explains the re-brightening
events that were previously observed during eclipses, and the subsequent
disappearance of these events. We predict the future evolution of the system
and its full radial velocity curve. Given the small velocity of the occulting
screen relative to the center of mass of the binary, the screen is probably
associated with the binary, and may be the edge of a precessing circumbinary
disk.Comment: ApJ Letters, in press [11 pp., 5 figs]. Revision is shorter and
incorporates suggestions from the referee and other colleague
Recommended from our members
Turbulent flow at 190 m height above London during 2006-2008: A climatology and the applicability of similarity theory
Flow and turbulence above urban terrain is more complex than above rural terrain, due to the different momentum and heat transfer characteristics that are affected by the presence of buildings (e.g. pressure variations around buildings). The applicability of similarity theory (as developed over rural terrain) is tested using observations of flow from a sonic anemometer located at 190.3 m height in London, U.K. using about 6500 h of data. Turbulence statistics—dimensionless wind speed and temperature, standard deviations and correlation coefficients for momentum and heat transfer—were analysed in three ways. First, turbulence statistics were plotted as a function only of a local stability parameter z/Λ (where Λ is the local Obukhov length and z is the height above ground); the σ_i/u_* values (i = u, v, w) for neutral conditions are 2.3, 1.85 and 1.35 respectively, similar to canonical values. Second, analysis of urban mixed-layer formulations during daytime convective conditions over London was undertaken, showing that atmospheric turbulence at high altitude over large cities might not behave dissimilarly from that over rural terrain. Third, correlation coefficients for heat and momentum were analyzed with respect to local stability. The results give confidence in using the framework of local similarity for turbulence measured over London, and perhaps other cities. However, the following caveats for our data are worth noting: (i) the terrain is reasonably flat, (ii) building heights vary little over a large area, and (iii) the sensor height is above the mean roughness sublayer depth
Firm-Specific Assets, Multinationality, and Financial Performance: A Meta-Analytic Review and Theoretical Integration
Through a meta-analysis of 120 independent samples reported in 111 studies, we test the predictions of internalization theory in the context of the multinationality-performance relationship. Findings indicate that multinationality provides an efficient organizational form that enables firms to transfer their firm-specific assets to generate higher returns in international markets. In addition, the results delineate the conditions under which firm-specific assets have the strongest impact on the multinationality-performance relationship. Meta-analytic evidence also suggests that multinationality has intrinsic value above and beyond the intangible assets that firms possess, given analyses controlling for firms\u27 international experience, age, size, and product diversification
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