3,298 research outputs found
Quantum oscillations in the kinetic energy density: Gradient corrections from the Airy gas
We derive a closed form expression for the quantum corrections to the kinetic
energy density (KED) in the Thomas-Fermi (TF) limit of a linear potential model
system in three dimensions (the Airy gas). The universality of the expression
is tested numerically in a number of three dimensional model systems: (i)
jellium surfaces, (ii) hydrogen-like potentials, (iii) systems confined by an
harmonic potential in one and (iv) all three dimensions, and (v) a system with
a cosine potential (the Mathieu gas). Our results confirm that the usual
gradient expansion of extended Thomas-Fermi theory (ETF) does not describe the
quantum oscillations for systems that incorporate surface regions where the
electron density drops off to zero. We find that the correction derived from
the Airy gas is universally applicable to relevant spatial regions of systems
of type (i), (ii), and (iv), but somewhat surprisingly not (iii). We discuss
possible implications of our findings to the development of functionals for the
kinetic energy density.Comment: 15 pages, 9 figure
The role of airborne EM methods for environmental applications in different geological terrains
This paper reviews the increasing role of Airborne EM (AEM) methods for environmental purposes in a
variety of geological contexts. The ability of AEM data to differentiate geological, cultural and
environmental influences is considered using fixed-wing survey examples from Finland and the UK. The
provision of AEM subsurface resistivity information constitutes a unique capability in relation to general
remote-sensing information to which it is allied. To be fully exploited, the results of AEM surveys require
both ground calibration and integration (e.g. through GIS techniques) with existing geological,
hydrogeological and environmental databases
Monte Carlo Simulation of Ising Models with Dipole Interaction
Recently, a new memory effect was found in the metamagnetic domain structure
of the diluted Ising antiferromagnet by domain imaging
with Faraday contrast. Essential for this effect is the dipole interaction. We
simulate the low temperature behavior of diluted Ising-antiferromagnets by a
Monte Carlo simulation considering long range interaction. The metamagnetic
domain structure occurring due to the dipole interaction is investigated by
graphical representation. In the model considered the antiferromagnetic state
is stable for an external magnetic field smaller than a lower boundary
while for fields larger than an upper boundary the system is in the
saturated paramagnetic phase, where the spins are ferromagnetically polarized.
For magnetic fields in between these two boundaries a mixed phase occurs
consisting of ferromagnetic domains in an antiferromagnetic background. The
position of these ferromagnetic domains is stored in the system: after a cycle
in which the field is first removed and afterwards applied again the domains
reappear at their original positions. The reason for this effect can be found
in the frozen antiferromagnetic domain state which occurs after removing the
field.Comment: Latex, 10 pages; 3 postsript-figures, compressed tar-file, uuencoded,
report 10109
Supernovae data and perturbative deviation from homogeneity
We show that a spherically symmetric perturbation of a dust dominated
FRW universe in the Newtonian gauge can lead to an apparent
acceleration of standard candles and provide a fit to the magnitude-redshift
relation inferred from the supernovae data, while the perturbation in the
gravitational potential remains small at all scales. We also demonstrate that
the supernovae data does not necessarily imply the presence of some additional
non-perturbative contribution by showing that any Lemaitre-Tolman-Bondi model
fitting the supernovae data (with appropriate initial conditions) will be
equivalent to a perturbed FRW spacetime along the past light cone.Comment: 8 pages, 3 figures; v2: 1 figure added, references added/updated,
minor modifications and clarifications, matches published versio
European Community Multi-Center Trial "Fetal ECG Analysis During Labor": ST plus CTG analysis
This report form part of the European Community Multi-Center Trial "Fetal ECG Analysis during Labor". Aim of this prospective trial was to identify changes in the fetal ECG waveform with cases of verified fetal hypoxia. In this paper we also report on the use of a newly developed automatic system for identification of ST waveform changes (ST Log). All ECG were recorded with the STAN recorder (Neoventa Medical AB, Gothenburg, Sweden). The ECG information was not displayed during labor in order not to influence the clinical management. This report includes data from 320 cases and include six cases of fetal intrapartum hypoxia. Twenty seven cases showed changes in ST waveform. All five cases with the most marked ST change (a rise in T/QRS of >0.10 units and lasting more then 10 minutes) had signs of ongoing intrapartum hypoxia. Six out of six cases with evidence of intrapartum asphyxia, showed ST changes. On the basis of our multi-center trial it appears that the combined analysis of CTG and ST waveform changes provides an accurate way to identify adverse events during labor. The work is continuing with a new STAN recorder developed by Neoventa Medical in Goteborg and currently being tested in a Swedish randomized, controlled multi-center trial
Relativistic materials from an alternative viewpoint
Electrons in materials containing heavy elements are fundamentally
relativistic and should in principle be described using the Dirac equation.
However, the current standard for treatment of electrons in such materials
involves density functional theory methods originally formulated from the
Schr\"{o}dinger equation. While some extensions of the Schr\"{o}dinger-based
formulation have been explored, such as the scalar relativistic approximation
with or without spin-orbit coupling, these solutions do not provide a way to
fully account for all relativistic effects of electrons, and the language used
to describe such solutions are still based in the language of the
Schr\"{o}dinger equation. In this article, we provide a different method for
translating between the Dirac and Schr\"{o}dinger viewpoints in the context of
a Coulomb potential. By retaining the Dirac four-vector notation and
terminology in taking the non-relativistic limit, we see a much deeper
connection between the Dirac and Schr\"{o}dinger equation solutions that allow
us to more directly compare the effects of relativity in the angular and radial
functions. Through this viewpoint, we introduce the concepts of densitals and
Dirac spherical harmonics that allow us to translate more easily between the
Dirac and Schr\"{o}dinger solutions. These concepts allow us to establish a
useful language for discussing relativistic effects in materials containing
elements throughout the full periodic table and thereby enable a more
fundamental understanding of the effects of relativity on electronic structure
Quantum molecular dynamics simulations for the nonmetal-to-metal transition in fluid helium
We have performed quantum molecular dynamics simulations for dense helium to
study the nonmetal-to-metal transition at high pressures. We present new
results for the equation of state and the Hugoniot curve in the warm dense
matter region. The optical conductivity is calculated via the Kubo-Greenwood
formula from which the dc conductivity is derived. The nonmetal-to-metal
transition is identified at about 1 g/ccm. We compare with experimental results
as well as with other theoretical approaches, especially with predictions of
chemical models.Comment: 4 pages, 5 figure
Strain-Rate Frequency Superposition (SRFS) - A rheological probe of structural relaxation in soft materials
The rheological properties of soft materials often exhibit surprisingly
universal linear and non-linear features. Here we show that these properties
can be unified by considering the effect of the strain-rate amplitude on the
structural relaxation of the material. We present a new form of oscillatory
rheology, Strain-Rate Frequency Superposition (SRFS), where the strain-rate
amplitude is fixed as the frequency is varied. We show that SRFS can isolate
the response due to structural relaxation, even when it occurs at frequencies
too low to be accessible with standard techniques.Comment: 4 pages, 4 figure
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