3,926 research outputs found
On some geometric features of the Kramer interior solution for a rotating perfect fluid
Geometric features (including convexity properties) of an exact interior
gravitational field due to a self-gravitating axisymmetric body of perfect
fluid in stationary, rigid rotation are studied. In spite of the seemingly
non-Newtonian features of the bounding surface for some rotation rates, we
show, by means of a detailed analysis of the three-dimensional spatial
geodesics, that the standard Newtonian convexity properties do hold. A central
role is played by a family of geodesics that are introduced here, and provide a
generalization of the Newtonian straight lines parallel to the axis of
rotation.Comment: LaTeX, 15 pages with 4 Poscript figures. To be published in Classical
and Quantum Gravit
Electronic structure and spectral properties of Am, Cm and Bk: Charge density self-consistent LDA+HIA calculations in FP-LAPW basis
We provide a straightforward and numerically efficient procedure to perform
local density approximation + Hubbard I (LDA+HIA) calculations, including
self-consistency over the charge density, within the full potential linearized
augmented plane wave (FP-LAPW) method. This implementation is all-electron,
includes spin-orbit interaction, and makes no shape approximations for the
charge density. The method is applied to calculate selected heavy actinides in
the paramagnetic phase. The electronic structure and spectral properties of Am
and Cm metals obtained are in agreement with previous dynamical mean-field
theory (LDA+DMFT) calculations and with available experimental data. We point
out that the charge density self-consistent LDA+HIA calculations predict the
charge on Bk to exceed the atomic integer value by 0.22.Comment: 8 pages, 1 figur
Multiple scattering formalism for correlated systems: A KKR+DMFT approach
We present a charge and self-energy self-consistent computational scheme for
correlated systems based on the Korringa-Kohn-Rostoker (KKR) multiple
scattering theory with the many-body effects described by the means of
dynamical mean field theory (DMFT). The corresponding local multi-orbital and
energy dependent self-energy is included into the set of radial differential
equations for the single-site wave functions. The KKR Green's function is
written in terms of the multiple scattering path operator, the later one being
evaluated using the single-site solution for the -matrix that in turn is
determined by the wave functions. An appealing feature of this approach is that
it allows to consider local quantum and disorder fluctuations on the same
footing. Within the Coherent Potential Approximation (CPA) the correlated atoms
are placed into a combined effective medium determined by the dynamical mean
field theory (DMFT) self-consistency condition. Results of corresponding
calculations for pure Fe, Ni and FeNi alloys are presented.Comment: 25 pages, 5 fig. acepted PR
Existence of axially symmetric static solutions of the Einstein-Vlasov system
We prove the existence of static, asymptotically flat non-vacuum spacetimes
with axial symmetry where the matter is modeled as a collisionless gas. The
axially symmetric solutions of the resulting Einstein-Vlasov system are
obtained via the implicit function theorem by perturbing off a suitable
spherically symmetric steady state of the Vlasov-Poisson system.Comment: 32 page
Functional renormalization group study of an eight-band model for the iron arsenides
We investigate the superconducting pairing instabilities of eight-band models
for the iron arsenides. Using a functional renormalization group treatment, we
determine how the critical energy scale for superconductivity depends on the
electronic band structure. Most importantly, if we vary the parameters from
values corresponding to LaFeAsO to SmFeAsO, the pairing scale is strongly
enhanced, in accordance with the experimental observation. We analyze the
reasons for this trend and compare the results of the eight-band approach to
those found using five-band models.Comment: 11 pages, 10 figure
Frequency-dependent local interactions and low-energy effective models from electronic structure calculations
We propose a systematic procedure for constructing effective models of
strongly correlated materials. The parameters, in particular the on-site
screened Coulomb interaction U, are calculated from first principles, using the
GW approximation. We derive an expression for the frequency-dependent U and
show that its high frequency part has significant influence on the spectral
functions. We propose a scheme for taking into account the energy dependence of
U, so that a model with an energy-independent local interaction can still be
used for low-energy properties.Comment: 16 pages, 5 figure
Incorporating neurological and behavioral mechanisms of sociality into predator-prey models
Consumer-resource population models drive progress in predicting and understanding predation. However, they are often built by averaging the foraging outcomes of individuals to estimate per capita functional responses (functions that describe predation rate). Reliance on per-capita functional responses rests on the assumption that that individuals forage independently without affecting each other. Undermining this assumption, extensive behavioral neuroscience research has made clear that facilitative and antagonistic interactions among conspecifics frequently alter foraging through interference competition and persistent neurophysiological changes. For example, repeated social defeats dysregulates rodent hypothalamic signaling, modulating appetite. In behavioral ecology, similar mechanisms are studied under the concept of dominance hierarchies. Neurological and behavioral changes in response to conspecifics undoubtedly play some sort of role in the foraging of populations, but modern predator-prey theory does not explicitly include them. Here we describe how some modern approaches to population modeling might account for this. Further, we propose that spatial predator-prey models can be modified to describe plastic changes in foraging behavior driven by intraspecific interaction, namely individuals switching between patches or plastic strategies to avoid competition. Extensive neurological and behavioral ecology research suggests that interactions among conspecifics help shape populations’ functional responses. Modeling interdependent functional responses woven together by behavioral and neurological mechanisms may thus be indispensable in predicting the outcome of consumer–resource interactions across systems
Continuous Time Quantum Monte Carlo method for fermions
We present numerically exact continuous-time Quantum Monte Carlo algorithm
for fermions with a general non-local in space-time interaction. The new
determinantal grand-canonical scheme is based on a stochastic series expansion
for the partition function in the interaction representation. The method is
particularly applicable for multi-band time-dependent correlations since it
does not invoke the Hubbard-Stratonovich transformation. The test calculations
for exactly solvable models as well results for the Green function and for the
time-dependent susceptibility of the multi-band super-symmetric model with a
spin-flip interaction are discussed.Comment: 10 pages, 7 Figure
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Method for Measuring Architectural Test Coverage for Design Verification
A technique that applies the task coverage exercised within a behavioral model of the design to the design itself, while simulating one or more test sequences. Since the behavior model is an accurate and complete program representation of the architectural specification of the hardware design, the test case coverage of the architecture is implied by the measurement of how well the behavioral model code has been exercised. The completeness of the coverage is determined by the test coverage criteria selected, including, for example, statement coverage, branch coverage, or path coverage. The more detailed the criteria, the greater the number of tests
Development of a National Survey to Assess Student Learning Outcomes of Community-Based Research
With the goal of codifying student learning outcomes of commu- nity-based research (CBR), the authors created a conceptually valid and statistically reliable CBR Student Learning Outcomes Survey. The project began with individual interviews and focus groups with 70 undergraduates and faculty at six colleges and universities nationwide discussing perceived benefits of CBR. Based on analyses of these interviews, five CBR outcome con- structs were derived: academic skills, educational experience, civic engagement, professional skills, and personal growth. The survey was piloted online in spring 2009 to students who had experienced CBR from 15 colleges and universities (N = 166). Factor analyses revealed strong statistical reliability across survey constructs. The authors invite faculty to use the instrument to assess CBR courses and invite students who have experienced CBR to complete the survey online through spring 2012, as part of a national study of CBR outcomes
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