7,251 research outputs found
Electronic structure and x-ray magnetic dichroism in random substitutional alloys of f-electron elements
The Koringa-Kohn-Rostoker —coherent-potential-approximation method combines multiple-scattering theory and the coherent-potential approximation to calculate the electronic structure of random substitutional alloys of transition metals. In this paper we describe the generalization of this theory to describe f-electron alloys. The theory is illustrated with a calculation of the electronic structure and magnetic dichroism curves for a random substitutional alloy containing rare-earth or actinide elements from first principles
Ab-initio calculation of the Gilbert damping parameter via linear response formalism
A Kubo-Greenwood-like equation for the Gilbert damping parameter is
presented that is based on the linear response formalism. Its implementation
using the fully relativistic Korringa-Kohn-Rostoker (KKR) band structure method
in combination with Coherent Potential Approximation (CPA) alloy theory allows
it to be applied to a wide range of situations. This is demonstrated with
results obtained for the bcc alloy system FeCo as well as for a
series of alloys of permalloy with 5d transition metals.
To account for the thermal displacements of atoms as a scattering mechanism,
an alloy-analogy model is introduced. The corresponding calculations for Ni
correctly describe the rapid change of when small amounts of
substitutional Cu are introduced
Effect of chemical disorder on NiMnSb investigated by Appearance Potential Spectroscopy: a theoretical study
The half-Heusler alloy NiMnSb is one of the local-moment ferromagnets with
unique properties for future applications. Band structure calculations predict
exclusively majority bands at the Fermi level, thus indicating {100%} spin
polarization there. As one thinks about applications and the design of
functional materials, the influence of chemical disorder in these materials
must be considered. The magnetization, spin polarization, and electronic
structure are expected to be sensitive to structural and stoichiometric
changes. In this contribution, we report on an investigation of the
spin-dependent electronic structure of NiMnSb. We studied the influence of
chemical disorder on the unoccupied electronic density of states by use of the
ab-initio Coherent Potential Approximation method. The theoretical analysis is
discussed along with corresponding spin-resolved Appearance Potential
Spectroscopy measurements. Our theoretical approach describes the spectra as
the fully-relativistic self-convolution of the matrix-element weighted,
orbitally resolved density of states.Comment: JPD submitte
Magneto-x-ray effects in transition-metal alloys
We present a theory that combines the relativistic spin-polarized version of the Koringa-Kohn-Rostoker coherent-potential approximation theory and the macroscopic theory of magneto-optical effects enabling us to calculate magneto-x-ray effects from first principles. The theory is illustrated by calculation of Faraday and Kerr rotations and ellipticities for transition-metal alloys
{BiQ} Analyzer {HiMod}: An Interactive Software Tool for High-throughput Locus-specific Analysis of 5-Methylcytosine and its Oxidized Derivatives
Recent data suggest important biological roles for oxidative modifications of methylated cytosines, specifically hydroxymethylation, formylation and carboxylation. Several assays are now available for profiling these DNA modifications genome-wide as well as in targeted, locus-specific settings. Here we present BiQ Analyzer HiMod, a user-friendly software tool for sequence alignment, quality control and initial analysis of locus-specific DNA modification data. The software supports four different assay types, and it leads the user from raw sequence reads to DNA modification statistics and publication-quality plots. BiQ Analyzer HiMod combines well-established graphical user interface of its predecessor tool, BiQ Analyzer HT, with new and extended analysis modes. BiQ Analyzer HiMod also includes updates of the analysis workspace, an intuitive interface, a custom vector graphics engine and support of additional input and output data formats. The tool is freely available as a stand-alone installation package from http://biq-analyzer-himod.bioinf.mpi-inf.mpg.de/
Chalcogen Height Dependence of Magnetism and Fermiology in FeTe_xSe_{1-x}
FeTexSe1-x (x=0, 0.25, 0.50, 0.75 and 1) system has been studied using
density functional theory. Our results show that for FeSe, LDA seems better
approximation in terms of magnitude of magnetic energy whereas GGA
overestimates it largely. On the other hand for FeTe, GGA is better
approximation that gives experimentally observed magnetic state. It has been
shown that the height of chalcogen atoms above Fe layers has significant effect
on band structure, electronic density of states (DOS) at Fermi level N(EF) and
Fermi surfaces. For FeSe the value of N(EF) is small so as to satisfy Stoner
criteria for ferromagnetism, (I\timesN(EF)\geq1) whereas for FeTe, since the
value of N(EF) is large, the same is close to be satisfied. Force minimization
done for FeTexSe1-x using supercell approach shows that in disordered system Se
and Te do not share same site and have two distinct z coordinates. This has
small effect on magnetic energy but no significant difference in band structure
and DOS near EF when calculated using either relaxed or average value of z for
chalcogen atoms. Thus substitution of Se at Te site decreases average value of
chalcogen height above Fe layers which in turn affect the magnetism and
Fermiology in the system. By using coherent-potential approximation for
disordered system we found that height of chalcogen atoms above Fe layer rather
than chalcogen species or disorder in the anion planes, affect magnetism and
shape of Fermi surfaces (FS), thus significantly altering nesting conditions,
which govern antiferromagnetic spin fluctuations in the system.Comment: 24 pages Text+Figs: comments/suggestions welcome
([email protected]
The diffusion coefficient of propagating fronts with multiplicative noise
Recent studies have shown that in the presence of noise both fronts
propagating into a metastable state and so-called pushed fronts propagating
into an unstable state, exhibit diffusive wandering about the average position.
In this paper we derive an expression for the effective diffusion coefficient
of such fronts, which was motivated before on the basis of a multiple scale
ansatz. Our systematic derivation is based on the decomposition of the
fluctuating front into a suitably positioned average profile plus fluctuating
eigenmodes of the stability operator. While the fluctuations of the front
position in this particular decomposition are a Wiener process on all time
scales, the fluctuations about the time averaged front profile relax
exponentially.Comment: 4 page
Positive and negative streamers in ambient air: measuring diameter, velocity and dissipated energy
Positive and negative streamers are studied in ambient air at 1 bar; they
emerge from a needle electrode placed 40 mm above a planar electrode. The
amplitudes of the applied voltage pulses range from 5 to 96 kV; most pulses
have rise times of 30 ns or shorter. Diameters, velocities and energies of the
streamers are measured. Two regimes are identified; a low voltage regime where
only positive streamers appear and a high voltage regime where both positive
and negative streamers exist. Below 5 kV, no streamers emerge. In the range
from 5 to 40 kV, positive streamers form, while the negative discharges only
form a glowing cloud at the electrode tip, but no streamers. For 5 to 20 kV,
diameters and velocities of the positive streamers have the minimal values of
d=0.2 mm and v \approx 10^5 m/s. For 20 to 40 kV, their diameters increase by a
factor 6 while the voltage increases only by a factor 2. Above the transition
value of 40 kV, streamers of both polarities form; they strongly resemble each
other, though the positive ones propagate further; their diameters continue to
increase with applied voltage. For 96 kV, positive streamers attain diameters
of 3 mm and velocities of 4*10^6 m/s, negative streamers are about 20 % slower
and thinner. An empirical fit formula for the relation between velocity v and
diameter d is v=0.5 d^2/(mm ns) for both polarities. Streamers of both
polarities dissipate energies of the order of several mJ per streamer while
crossing the gap.Comment: 20 pages, 9 figures, accepted for J. Phys.
DevOps in Practice -- A preliminary Analysis of two Multinational Companies
DevOps is a cultural movement that aims the collaboration of all the
stakeholders involved in the development, deployment and operation of soft-ware
to deliver a quality product or service in the shortest possible time. DevOps
is relatively recent, and companies have developed their DevOps prac-tices
largely from scratch. Our research aims to conduct an analysis on practic-ing
DevOps in +20 software-intensive companies to provide patterns of DevOps
practices and identify their benefits and barriers. This paper presents the
preliminary analysis of an exploratory case study based on the interviews to
relevant stakeholders of two (multinational) companies. The results show the
benefits (software delivery performance) and barriers that these companies are
dealing with, as well as DevOps team topology they approached during their
DevOps transformation. This study aims to help practitioners and researchers to
better understand DevOps transformations and the contexts where the practices
worked. This, hopefully, will contribute to strengthening the evidence
regarding DevOps and supporting practitioners in making better informed
decisions about the return of investment when adopting DevOps.Comment: 8 pages, 1 figure, 2 tables, conferenc
Finite-temperature magnetism of FePd and CoPt alloys
The finite-temperature magnetic properties of FePd and
CoPt alloys have been investigated. It is shown that the
temperature-dependent magnetic behaviour of alloys, composed of originally
magnetic and non-magnetic elements, cannot be described properly unless the
coupling between magnetic moments at magnetic atoms (Fe,Co) mediated through
the interactions with induced magnetic moments of non-magnetic atoms (Pd,Pt) is
included. A scheme for the calculation of the Curie temperature () for
this type of systems is presented which is based on the extended Heisenberg
Hamiltonian with the appropriate exchange parameters obtained from
{\em ab-initio} electronic structure calculations. Within the present study the
KKR Green's function method has been used to calculate the parameters.
A comparison of the obtained Curie temperatures for FePd and
CoPt alloys with experimental data shows rather good agreement.Comment: 10 pages, 12 figure
- …