1,228 research outputs found
Response functions of an artificial Anderson atom in the atomic limit
We consider the spin and pseudospin (charge) response functions of the
exactly soluble Anderson atom model. We demonstrate, in particular, that a
deviation from the magnetic Curie-law behaviour, appropriate for a free spin
one-half, increases with increasing asymmetry and temperature. In general,
oscillator strength is transferred from the spin degrees of freedom to the
pseudospin modes. We also consider the negative-U Anderson atom and demonstrate
that the pseudospin modes are the relevant low-energy excitations in this case.
Especially, the roles of the spin and charge excitations are interchanged upon
reversal of the intrasite Coulomb repulsion, U.Comment: 23 pages, 12 figures. Accepted for publication in J. Low Temp. Phy
Use of near infrared reflectance spectroscopy to predict nitrogen uptake by winter wheat within fields with high variability in organic matter
In this study, the ability to predict N-uptake in winter wheat crops using NIR-spectroscopy on soil samples was evaluated. Soil samples were taken in unfertilized plots in one winter wheat field during three years (1997-1999) and in another winter wheat field nearby in one year (2000). Soil samples were analyzed for organic C content and their NIR-spectra. N-uptake was measured as total N-content in aboveground plant materials at harvest. Models calibrated to predict N-uptake were internally cross validated and validated across years and across fields. Cross-validated calibrations predicted N-uptake with an average error of 12.1 to 15.4 kg N ha-1. The standard deviation divided by this error (RPD) ranged between 1.9 and 2.5. In comparison, the corresponding calibrations based on organic C alone had an error from 11.7 to 28.2 kg N ha-1 and RPDs from 1.3 to 2.5. In three of four annual calibrations within a field, the NIR-based calibrations worked better than the organic C based calibrations. The prediction of N-uptake across years, but within a field, worked slightly better with an organic C based calibration than with a NIR based one, RPD = 1.9 and 1.7 respectively. Across fields, the corresponding difference was large in favour of the NIR-calibration, RPD = 2.5 for the NIR-calibration and 1.5 for the organic C calibration. It was concluded that NIR-spectroscopy integrates information about organic C with other relevant soil components and therefore has a good potential to predict complex functions of soils such as N-mineralization. A relatively good agreement of spectral relationships to parameters related to the N-mineralization of datasets across the world suggests that more general models can be calibrated
Are pinholes the cause of excess current in superconducting tunnel junctions? A study of Andreev current in highly resistive junctions
In highly resistive superconducting tunnel junctions, excess subgap current
is usually observed and is often attributed to microscopic "pinholes" in the
tunnel barrier. We have studied the subgap current in
superconductor-insulator-superconductor (SIS) and
superconductor-insulator-normal-metal (SIN) junctions. In Al/AlOx/Al junctions,
we observed a decrease of 2 orders of magnitude in the current upon the
transition from the SIS to the SIN regime, where it then matched theory. In
Al/AlOx/Cu junctions, we also observed generic features of coherent diffusive
Andreev transport in a junction with a homogenous barrier. We use the
quasiclassical Keldysh-Green function theory to quantify single- and
two-particle tunneling and find good agreement over 2 orders of magnitude in
transparency. We argue that our observations rule out pinholes as the origin of
the excess current.Comment: 4 pages, 4 figure
Higher-order mesoscopic fluctuations in quantum wires: Conductance and current cumulants
We study conductance cumulants and current cumulants
related to heat and electrical transport in coherent mesoscopic quantum wires
near the diffusive regime. We consider the asymptotic behavior in the limit
where the number of channels and the length of the wire in the units of the
mean free path are large but the bare conductance is fixed. A recursion
equation unifying the descriptions of the standard and Bogoliubov--de Gennes
(BdG) symmetry classes is presented. We give values and come up with a novel
scaling form for the higher-order conductance cumulants. In the BdG wires, in
the presence of time-reversal symmetry, for the cumulants higher than the
second it is found that there may be only contributions which depend
nonanalytically on the wire length. This indicates that diagrammatic or
semiclassical pictures do not adequately describe higher-order spectral
correlations. Moreover, we obtain the weak-localization corrections to
with .Comment: 7 page
Numerical Computations with H(div)-Finite Elements for the Brinkman Problem
The H(div)-conforming approach for the Brinkman equation is studied
numerically, verifying the theoretical a priori and a posteriori analysis in
previous work of the authors. Furthermore, the results are extended to cover a
non-constant permeability. A hybridization technique for the problem is
presented, complete with a convergence analysis and numerical verification.
Finally, the numerical convergence studies are complemented with numerical
examples of applications to domain decomposition and adaptive mesh refinement.Comment: Minor clarifications, added references. Reordering of some figures.
To appear in Computational Geosciences, final article available at
http://www.springerlink.co
Nonreciprocal Directional Dichroism and Toroidalmagnons in Helical Magnets
We investigate a dynamical magnetoelectric effect due to a magnetic resonance
in helical spin structures through the coupling between magnetization and
electric polarization via a spin current mechanism. We show that the magnon has
both the dynamical magnetic moment and the electric moment
(), i.e., a dynamical toroidal moment,
under external magnetic fields, and thus it is named the {\em toroidalmagnon}.
The toroidalmagnon exists in most conical spin structures owing to the
generality of the spin current mechanism. In the absorption of electromagnetic
waves, the toroidalmagnon excitation process generally induces a nonreciprocal
directional dichroism as a consequence of an interference of the magnetic and
electric responses.Comment: 5 pages, 2 figure
Microservice Transition and its Granularity Problem: A Systematic Mapping Study
Microservices have gained wide recognition and acceptance in software
industries as an emerging architectural style for autonomic, scalable, and more
reliable computing. The transition to microservices has been highly motivated
by the need for better alignment of technical design decisions with improving
value potentials of architectures. Despite microservices' popularity, research
still lacks disciplined understanding of transition and consensus on the
principles and activities underlying "micro-ing" architectures. In this paper,
we report on a systematic mapping study that consolidates various views,
approaches and activities that commonly assist in the transition to
microservices. The study aims to provide a better understanding of the
transition; it also contributes a working definition of the transition and
technical activities underlying it. We term the transition and technical
activities leading to microservice architectures as microservitization. We then
shed light on a fundamental problem of microservitization: microservice
granularity and reasoning about its adaptation as first-class entities. This
study reviews state-of-the-art and -practice related to reasoning about
microservice granularity; it reviews modelling approaches, aspects considered,
guidelines and processes used to reason about microservice granularity. This
study identifies opportunities for future research and development related to
reasoning about microservice granularity.Comment: 36 pages including references, 6 figures, and 3 table
ILEEMS of thin α-Fe2O3 films prepared by RF sputtering
Thin α-Fe2O3 films on semi-quartz substrates have been prepared by radio frequency (RF) sputtering of a magnetite target in a pure argon gas flow with a bias power applied. The films were studied by X-ray diffraction and Integral Low-Energy Electron Mössbauer Spectroscopy (ILEEMS), the latter in the temperature range of 80 to 330 K. In ILEEMS electrons of ∼10 eV are detected and therefore it is an ideal instrument to study thin films with thicknesses below 500 nm. The first ILEEMS measurements on α-Fe2O3 films are reported and focus on the behaviour of the Morin transition, i.e., the reorientation of Fe3+ spins from the [111] crystallographic direction at low temperature, to the (111) basal plane at high temperature. Some films (∼400 nm) show the presence of both a weak- and antiferromagnetic hematite phase for all temperatures between 140 and 330 K. Others of about ∼100 nm thick only have a weak ferromagnetic phase for temperatures between 140 and 330 K of which the hyperfine field distribution shows two maxima, related to two distinct phases. Both phases stay in some films almost equal in intensity in the spectrum for the whole measured temperature range. In others a significant evolution in the spectral areas of both weak ferromagnetic phases as function of the temperature is observed
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