6,696 research outputs found
Atomistic spin-model based on a new spin-cluster expansion technique: Application to the IrMn3/Co interface
In order to derive tensorial exchange interactions and local magnetic
anisotropies in itinerant magnetic systems, an approach combining the
Spin-Cluster Expansion with the Relativistic Disordered Local Moment scheme is
introduced. The theoretical background and computational aspects of the method
are described in detail. The exchange interactions and site resolved anisotropy
contributions for the IrMn3/Co(111) interface, a prototype for an exchange bias
system, are calculated including a large number of magnetic sites from both the
antiferromagnet and ferromagnet. Our calculations reveal that the coupling
between the two subsystems is fairly limited to the vicinity of the interface.
The magnetic anisotropy of the interface system is discussed, including effects
of the Dzyaloshinskii-Moriya interactions that appear due to symmetry breaking
at the interface.Comment: 10 pages, 6 figure
Structure and electronic properties of the quasi-one-dimensional Ba₂Co₁₋ₓZnₓS₃ series
This work focuses on the structure and physical properties of the solid solution Ba₂Co₁₋ₓZnₓS₃ (0 ≤ x ≤ 1), a family of quasi-one-dimensional sulfides with end members Ba₂CoS₃ and Ba₂ZnS₃. The structure of selected compounds with increasing Zn²⁺ content has been analysed using, neutron diffraction, TEM and EXAFS and the physical properties via magnetic susceptibility and resistivity measurements. The progressive substitution of the non-magnetic Zn²⁺ cation for Co²⁺ rapidly destroys the antiferromagnetic transition present at 46 K in the quasi one-dimensional Ba₂CoS₃, leading to paramagnetic behaviour down to the lowest investigated temperature (5K) for compounds with x > 0.25. For compounds with x ≥ 0.4, a pure CW regime is recovered around 300 K, yielding effective moments consistent with the g factor of the tetrahedrally coordinated Co²⁺ previously determined for Ba₂CoS₃. The Zn²⁺/Co²⁺ substitution also removes the metallic-like behaviour of Ba₂CoS₃ causing an increase in the value of the resistivity with all the Ba₂Co₁₋ₓZnₓS₃ compounds showing semiconducting behaviour. The negative magnetoresistance of Ba₂CoS₃ is improved by the Zn²⁺/Co²⁺ substitution, with values of – 6% for Ba₂Co₀.₇₅Zn₀.₂₅S₃, – 9% for Ba₂Co₀.₅Zn₀.₅S₃ and – 8% for Ba₂Co₀.₂₅Zn₀.₇₅S₃. However, there does not seem to be a correlation between the values of the resistivity and the magnetoresistance and the content of Zn²⁺, leading to the hypothesis that transport properties may be linked more closely to extrinsic properties
Dynamics of Two-Level System Interacting with Random Classical Field
The dynamics of a particle interacting with random classical field in a
two-well potential is studied by the functional integration method. The
probability of particle localization in either of the wells is studied in
detail. Certain field-averaged correlation functions for quantum-mechanical
probabilities and the distribution function for the probabilities of final
states (which can be considered as random variables in the presence of a random
field) are calculated. The calculated correlators are used to discuss the
dependence of the final state on the initial state. One of the main results of
this work is that, although the off-diagonal elements of density matrix
disappear with time, a particle in the system is localized incompletely
(wave-packet reduction does not occur), and the distribution function for the
probability of finding particle in one of the wells is a constant at infinite
time.Comment: 5 page
Wave-packet Formalism of Full Counting Statistics
We make use of the first-quantized wave-packet formulation of the full
counting statistics to describe charge transport of noninteracting electrons in
a mesoscopic device. We derive various expressions for the characteristic
function generating the full counting statistics, accounting for both energy
and time dependence in the scattering process and including exchange effects
due to finite overlap of the incoming wave packets. We apply our results to
describe the generic statistical properties of a two-fermion scattering event
and find, among other features, sub-binomial statistics for nonentangled
incoming states (Slater rank 1), while entangled states (Slater rank 2) may
generate super-binomial (and even super-Poissonian) noise, a feature that can
be used as a spin singlet-triplet detector. Another application is concerned
with the constant-voltage case, where we generalize the original result of
Levitov-Lesovik to account for energy-dependent scattering and finite
measurement time, including short time measurements, where Pauli blocking
becomes important.Comment: 20 pages, 5 figures; major update, new figures and explanations
included as well as a discussion about finite temperatures and subleading
logarithmic term
ALTICORE: an initiative for coastal altimetry
ALTICORE (value-added ALTImetry for COastal REgions) is an international initiative whose main objective is to encourage the operational use of altimetry over coastal areas, by improving the quality and availability of coastal altimetry data. The ALTICORE proposal has recently been submitted for funding to the INTAS scheme (www.intas.be) by a consortium of partners from Italy, France, UK, Russia and Azerbaijan. ALTICORE is also meant as a contribution to the ongoing International Altimeter Service effort.
In this work we will describe the anticipated project stages, namely: 1) improvement of the most widely distributed, 1 Hz, data by analyzing the corrective terms and providing the best solutions, including those derived from appropriate local modelling; 2) development of a set of algorithms to automate quality control and gap-filling functions for the coastal regions; 3) development of testing strategies to ensure a thorough validation of the data.
The improved products will be delivered to ALTICORE users via Grid-compliant technology; this makes it easier to integrate the local data holdings, allows access from a range of services, e.g. directly into model assimilation or GIS systems and should therefore facilitate a widespread and complete assessment of the 1Hz data performance and limitations. We will also outline the design and implementation of the Grid-compliant system for efficient access to distributed archives of data; this consists of regional data centres, each having primary responsibility for regional archives, local corrections and quality control, and operating a set of web-services allowing access to the full functionality of data extraction.
We will conclude by discussing a follow-on phase of the project; this will investigate further improvements on the processing strategy, including the use of higher frequency (10 or 20 Hz) data. Phenomena happen at smaller spatial scales near the coast, so this approach is necessary to match the required resolution. The whole project will hopefully promote the 15-year sea surface height from altimetry to the rank of operational record for the coastal areas
Transport on weighted Networks: when correlations are independent of degree
Most real-world networks are weighted graphs with the weight of the edges
reflecting the relative importance of the connections. In this work, we study
non degree dependent correlations between edge weights, generalizing thus the
correlations beyond the degree dependent case. We propose a simple method to
introduce weight-weight correlations in topologically uncorrelated graphs. This
allows us to test different measures to discriminate between the different
correlation types and to quantify their intensity. We also discuss here the
effect of weight correlations on the transport properties of the networks,
showing that positive correlations dramatically improve transport. Finally, we
give two examples of real-world networks (social and transport graphs) in which
weight-weight correlations are present.Comment: 8 pages, 8 figure
Decay of scalar turbulence revisited
We demonstrate that at long times the rate of passive scalar decay in a
turbulent, or simply chaotic, flow is dominated by regions (in real space or in
inverse space) where mixing is less efficient. We examine two situations. The
first is of a spatially homogeneous stationary turbulent flow with both viscous
and inertial scales present. It is shown that at large times scalar
fluctuations decay algebraically in time at all spatial scales (particularly in
the viscous range, where the velocity is smooth). The second example explains
chaotic stationary flow in a disk/pipe. The boundary region of the flow
controls the long-time decay, which is algebraic at some transient times, but
becomes exponential, with the decay rate dependent on the scalar diffusion
coefficient, at longer times.Comment: 4 pages, no figure
N-particle scattering matrix for electrons interacting on a quantum dot
We present a non-perturbative expression for the scattering matrix of
particles interacting inside a quantum dot. Characterizing the dot by its
resonances, we find a compact form for the scattering matrix in a real-time
representation. We study the transmission probabilities and interaction-induced
orbital entanglement of two electrons incident on the dot in a spin-singlet
state.Comment: 4 page
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