8,913 research outputs found
Concentration dependence of the exchange interaction in Pb1-xEuxTe
[[abstract]]From low-field measurements of the susceptibility at temperatures up to 385 K, fitted to the Curie-Weiss expression, the exchange constant J/kB of Pb1-xEuxTe has been obtained for different values of x. It has been observed that J/kB decreases with increasing x. Reasons for this decrease are proposed. Measurements of the low-temperature magnetization at fields up to 23 T yield a value of the pair exchange constant Jp/kB, which is somewhat larger than the values from the susceptibility measurements and is nearly independent of x. This result seems to be due to the clustering of Eu atoms.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子
Experiments with mixing in stratified flow over a topographic ridge
The interaction of quasi-steady abyssal ocean flow with submarine topography is expected to generate turbulent mixing in the ocean. This mixing may occur locally, close to topography, or via breaking quasi-steady lee waves that can carry energy into the ocean interior. There is currently no theoretical, or empirically derived, prediction for the relative amounts of local and interior mixing. We report measurements of the mixing rate in laboratory experiments with a topographic ridge towed through a density stratification. The experiments span three parameter regimes including linear lee waves, nonlinear flow and an evanescent regime in which wave radiation is weak. Full field density measurements provide the depth-dependence of energy loss to turbulent mixing, allowing separation of the local mixing in the turbulent wake and remote mixing by wave radiation. Remote mixing is significant only for a narrow band of forcing parameters where the flow speed is resonant with internal waves; in all other parameter regimes local mixing close to the topography is dominant. The results suggest that mixing by local nonlinear mechanisms close to abyssal ocean topography may be much greater than the remote mixing by quasi-steady lee waves
Laser-induced charge and spin photocurrents at BiAg surface: a first principles benchmark
Here, we report first principles calculations and analysis of laser-induced
photocurrents at the surface of a prototype Rashba system. By referring to
Keldysh non-equilibrium formalism combined with the Wannier interpolation
scheme we perform first-principles electronic structure calculations of a
prototype BiAg surface alloy, which is a well-known material realization of
the Rashba model. In addition to non-magnetic ground state situation we also
study the case of in-plane magnetized BiAg. We calculate the laser-induced
charge photocurrents for the ferromagnetic case and the laser-induced spin
photocurrents for both the non-magnetic and the ferromagnetic cases. Our
results confirm the emergence of very large in-plane photocurrents as predicted
by the Rashba model. The resulting photocurrents satisfy all the symmetry
restrictions with respect to the light helicity and the magnetization
direction. We provide microscopic insights into the symmetry and magnitude of
the computed currents based on the ab-initio multi-band electronic structure of
the system, and scrutinize the importance of resonant two-band and three-band
transitions for driven currents, thereby establishing a benchmark picture of
photocurrents at Rashba-like surfaces and interfaces. Our work contributes to
the study of the role of the interfacial Rashba spin-orbit interaction as a
mechanism for the generation of in-plane photocurrents, which are of great
interest in the field of ultrafast and terahertz spintronics
Antigenic Change in Human Influenza A(H2N2) Viruses Detected by Using Human Plasma from Aged and Younger Adult Individuals
The size-Ramsey number of powers of paths
Given graphs and and a positive integer , say that
\emph{is -Ramsey for} , denoted
, if every -colouring of the edges of
contains a monochromatic copy of . The \emph{size-Ramsey number} \sr(H) of
a graph is defined to be
\sr(H)=\min\{|E(G)|\colon G\rightarrow (H)_2\}. Answering a
question of Conlon, we prove that, for every fixed~, we have
\sr(P_n^k)=O(n), where~ is the th power of the
-vertex path (i.e., the graph with vertex set and
all edges such that the distance between and in
is at most ). Our proof is probabilistic, but can also be made constructive.Most of the work for this paper was done during my PhD, which was half funded by EPSRC grant reference 1360036, and half by Merton College Oxford.
The third author was partially supported by FAPESP
(Proc.~2013/03447-6) and by CNPq (Proc.~459335/2014-6,
310974/2013-5). The fifth author was
supported by FAPESP (Proc.~2013/11431-2, Proc.~2013/03447-6 and
Proc.~2018/04876-1) and partially by CNPq (Proc.~459335/2014-6).
This research was supported in part by CAPES (Finance Code 001).
The collaboration of part of the authors was supported by a
CAPES/DAAD PROBRAL grant (Proc.~430/15)
Sampling constrained probability distributions using Spherical Augmentation
Statistical models with constrained probability distributions are abundant in
machine learning. Some examples include regression models with norm constraints
(e.g., Lasso), probit, many copula models, and latent Dirichlet allocation
(LDA). Bayesian inference involving probability distributions confined to
constrained domains could be quite challenging for commonly used sampling
algorithms. In this paper, we propose a novel augmentation technique that
handles a wide range of constraints by mapping the constrained domain to a
sphere in the augmented space. By moving freely on the surface of this sphere,
sampling algorithms handle constraints implicitly and generate proposals that
remain within boundaries when mapped back to the original space. Our proposed
method, called {Spherical Augmentation}, provides a mathematically natural and
computationally efficient framework for sampling from constrained probability
distributions. We show the advantages of our method over state-of-the-art
sampling algorithms, such as exact Hamiltonian Monte Carlo, using several
examples including truncated Gaussian distributions, Bayesian Lasso, Bayesian
bridge regression, reconstruction of quantized stationary Gaussian process, and
LDA for topic modeling.Comment: 41 pages, 13 figure
Regularizing effect and local existence for non-cutoff Boltzmann equation
The Boltzmann equation without Grad's angular cutoff assumption is believed
to have regularizing effect on the solution because of the non-integrable
angular singularity of the cross-section. However, even though so far this has
been justified satisfactorily for the spatially homogeneous Boltzmann equation,
it is still basically unsolved for the spatially inhomogeneous Boltzmann
equation. In this paper, by sharpening the coercivity and upper bound estimates
for the collision operator, establishing the hypo-ellipticity of the Boltzmann
operator based on a generalized version of the uncertainty principle, and
analyzing the commutators between the collision operator and some weighted
pseudo differential operators, we prove the regularizing effect in all (time,
space and velocity) variables on solutions when some mild regularity is imposed
on these solutions. For completeness, we also show that when the initial data
has this mild regularity and Maxwellian type decay in velocity variable, there
exists a unique local solution with the same regularity, so that this solution
enjoys the regularity for positive time
Integration of GOCI and AHI Yonsei aerosol optical depth products during the 2016 KORUS-AQ and 2018 EMeRGe campaigns
The Yonsei Aerosol Retrieval (YAER) algorithm for the Geostationary Ocean Color Imager (GOCI) retrieves aerosol optical properties only over dark surfaces, so it is important to mask pixels with bright surfaces. The Advanced Himawari Imager (AHI) is equipped with three shortwave-infrared and nine infrared channels, which is advantageous for bright-pixel masking. In addition, multiple visible and near-infrared channels provide a great advantage in aerosol property retrieval from the AHI and GOCI. By applying the YAER algorithm to 10 min AHI or 1 h GOCI data at 6km x 6km resolution, diurnal variations and aerosol transport can be observed, which has not previously been possible from low-Earth-orbit satellites. This study attempted to estimate the optimal aerosol optical depth (AOD) for East Asia by data fusion, taking into account satellite retrieval uncertainty. The data fusion involved two steps: (1) analysis of error characteristics of each retrieved result with respect to the ground-based Aerosol Robotic Network (AERONET), as well as bias correction based on normalized difference vegetation indexes, and (2) compilation of the fused product using ensemble-mean and maximum-likelihood estimation (MLE) methods. Fused results show a better statistics in terms of fraction within the expected error, correlation coefficient, root-mean-square error (RMSE), and median bias error than the retrieved result for each product. If the RMSE and mean AOD bias values used for MLE fusion are correct, the MLE fused products show better accuracy, but the ensemble-mean products can still be useful as MLE
Extracting the Redox Orbitals in Li Battery Materials with High-Resolution X-Ray Compton Scattering Spectroscopy
We present an incisive spectroscopic technique for directly probing redox
orbitals based on bulk electron momentum density measurements via
high-resolution x-ray Compton scattering. Application of our method to spinel
LixMn2O4, a lithium ion battery cathode material, is discussed. The orbital
involved in the lithium insertion and extraction process is shown to mainly be
the oxygen 2p orbital. Moreover, the manganese 3d states are shown to
experience spatial delocalization involving 0.16 electrons per Mn site during
the battery operation. Our analysis provides a clear understanding of the
fundamental redox process involved in the working of a lithium ion battery.Comment: 24 pages, 3 figure
Evidence for CP Violation in B0 -> D+D- Decays
We report measurements of the branching fraction and CP violation parameters
in B0 -> D+D- decays. The results are based on a data sample that contains 535
x 10^6 BBbar pairs collected at the Upsilon(4S) resonance, with the Belle
detector at the KEKB asymmetric-energy e+e- collider. We obtain [1.97 +- 0.20
(stat) +- 0.20 (syst)] x 10^(-4) for the branching fraction of B0 -> D+D-. The
measured values of the CP violation parameters are: S = -1.13 +- 0.37 +- 0.09,
A = 0.91 +- 0.23 +- 0.06, where the first error is statistical and the second
is systematic. We find evidence of CP violation in B0 -> D+D- at the 4.1 sigma
confidence level. While the value of S is consistent with expectations from
other measurements, the value of the parameter A favors large direct CP
violation at the 3.2 sigma confidence level, in contradiction to Standard Model
expectations.Comment: 12 pages, 3 figures, submitted to PR
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