9,027 research outputs found
NASTRAN as a resource in code development
A case history is presented in which the NASTRAN system provided both guidelines and working software for use in the development of a discrete element program, PATCHES-111. To avoid duplication and to take advantage of the wide spread user familiarity with NASTRAN, the PATCHES-111 system uses NASTRAN bulk data syntax, NASTRAN matrix utilities, and the NASTRAN linkage editor. Problems in developing the program are discussed along with details on the architecture of the PATCHES-111 parametric cubic modeling system. The system includes model construction procedures, checkpoint/restart strategies, and other features
Domain structure of epitaxial Co films with perpendicular anisotropy
Epitaxial hcp Cobalt films with pronounced c-axis texture have been prepared
by pulsed lased deposition (PLD) either directly onto Al2O3 (0001) single
crystal substrates or with an intermediate Ruthenium buffer layer. The crystal
structure and epitaxial growth relation was studied by XRD, pole figure
measurements and reciprocal space mapping. Detailed VSM analysis shows that the
perpendicular anisotropy of these highly textured Co films reaches the
magnetocrystalline anisotropy of hcp-Co single crystal material. Films were
prepared with thickness t of 20 nm < t < 100 nm to study the crossover from
in-plane magnetization to out-of-plane magnetization in detail. The analysis of
the periodic domain pattern observed by magnetic force microscopy allows to
determine the critical minimum thickness below which the domains adopt a pure
in-plane orientation. Above the critical thickness the width of the stripe
domains is evaluated as a function of the film thickness and compared with
domain theory. Especially the discrepancies at smallest film thicknesses show
that the system is in an intermediate state between in-plane and out-of-plane
domains, which is not described by existing analytical domain models
Tunneling dynamics of side chains and defects in proteins, polymer glasses, and OH-doped network glasses
Simulations on a Lennard-Jones computer glass are performed to study effects
arising from defects in glasses at low temperatures. The numerical analysis
reveals that already a low concentration of defects may dramatically change the
low temperature properties by giving rise to extrinsic double-well potentials
(DWP's). The main characteristics of these extrinsic DWP's are (i) high barrier
heights, (ii) high probability that a defect is indeed connected with an
extrinsic DWP, (iii) highly localized dynamics around this defect, and (iv)
smaller deformation potential coupling to phonons. Designing an extension of
the Standard Tunneling Model (STM) which parametrizes this picture and
comparing with ultrasound experiments on the wet network glass -BO
shows that effects of OH-impurities are accurately accounted for. This model is
then applied to organic polymer glasses and proteins. It is suggested that side
groups may act similarly like doped impurities inasmuch as extrinsic DWP's are
induced, which possess a distribution of barriers peaked around a high barrier
height. This compares with the structurlessly distributed barrier heights of
the intrinsic DWP's, which are associated with the backbone dynamics. It is
shown that this picture is consistent with elastic measurements on polymers,
and can explain anomalous nonlogarithmic line broadening recently observed in
hole burning experiments in PMMA.Comment: 34 pages, Revtex, 9 eps-figures, accepted for publication in J. Chem.
Phy
SPARC CCMVal (2010), SPARC Report on the Evaluation of Chemistry-Climate Models: Chapter 5: Transport
Random matrix theory for CPA: Generalization of Wegner's --orbital model
We introduce a generalization of Wegner's -orbital model for the
description of randomly disordered systems by replacing his ensemble of
Gaussian random matrices by an ensemble of randomly rotated matrices. We
calculate the one- and two-particle Green's functions and the conductivity
exactly in the limit . Our solution solves the CPA-equation of the
-Anderson model for arbitrarily distributed disorder. We show how the
Lloyd model is included in our model.Comment: 3 pages, Rev-Te
Quantitative assessment of pinning forces and the superconducting gap in NbN thin films from complementary magnetic force microscopy and transport measurements
Epitaxial niobium-nitride thin films with a critical temperature of Tc=16K
and a thickness of 100nm were fabricated on MgO(100) substrates by pulsed laser
deposition. Low-temperature magnetic force microscopy (MFM) images of the
supercurrent vortices were measured after field cooling in a magnetic field of
3mT at various temperatures. Temperature dependence of the penetration depth
has been evaluated by a two-dimensional fitting of the vortex profiles in the
monopole-monopole model. Its subsequent fit to a single s-wave gap function
results in the superconducting gap amplitude Delta(0) = 2.9 meV = 2.1*kB*Tc, in
perfect agreement with previous reports. The pinning force has been
independently estimated from local depinning of individual vortices by lateral
forces exerted by the MFM tip and from transport measurements. A good
quantitative agreement between the two techniques shows that for low fields, B
<< Hc2, MFM is a powerful and reliable technique to probe the local variations
of the pinning landscape. We also demonstrate that the monopole model can be
successfully applied even for thin films with a thickness comparable to the
penetration depth.Comment: 6 pages, 6 figures, 2 table
Three eras of micellization
Micellization is the precipitation of lipids from aqueous solution into aggregates with a broad distribution of aggregation number. Three eras of micellization are characterized in a simple kinetic model of Becker-Döring type. The model asigns the same constant energy to the (k-1) monomer-monomer bonds in a linear chain of k particles. The number of monomers decreases sharply and many clusters of small size are produced during the first era. During the second era, nuclei are increasing steadily in size until their distribution becomes a self-similar solution of the diffusion equation. Lastly, when the average size of the nuclei becomes comparable to its equilibrium value, a simple mean-field Fokker-Planck equation describes the final era until the equilibrium distribution is reached
Practical management of heterogeneous neuroimaging metadata by global neuroimaging data repositories
Rapidly evolving neuroimaging techniques are producing unprecedented quantities of digital data at the same time that many research studies are evolving into global, multi-disciplinary collaborations between geographically distributed scientists. While networked computers have made it almost trivial to transmit data across long distances, collecting and analyzing this data requires extensive metadata if the data is to be maximally shared. Though it is typically straightforward to encode text and numerical values into files and send content between different locations, it is often difficult to attach context and implicit assumptions to the content. As the number of and geographic separation between data contributors grows to national and global scales, the heterogeneity of the collected metadata increases and conformance to a single standardization becomes implausible. Neuroimaging data repositories must then not only accumulate data but must also consolidate disparate metadata into an integrated view. In this article, using specific examples from our experiences, we demonstrate how standardization alone cannot achieve full integration of neuroimaging data from multiple heterogeneous sources and why a fundamental change in the architecture of neuroimaging data repositories is needed instead
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