7,635 research outputs found
Longitudinal variations, the opposition effect and monochromatic albedos for Mars
Magnitude at zero phase, phase coefficient, and monochromatic albedo computed for Mars as function of wavelengt
Truncated unity functional renormalization group for multiband systems with spin-orbit coupling
Although the functional renormalization group (fRG) is by now a
well-established method for investigating correlated electron systems, it is
still undergoing significant technical and conceptual improvements. In
particular, the motivation to optimally exploit the parallelism of modern
computing platforms has recently led to the development of the
"truncated-unity" functional renormalization group (TU-fRG). Here, we review
this fRG variant, and we provide its extension to multiband systems with
spin-orbit coupling. Furthermore, we discuss some aspects of the implementation
and outline opportunities and challenges ahead for predicting the ground-state
ordering and emergent energy scales for a wide class of quantum materials.Comment: consistent with published version in Frontiers in Physics (2018
Using molecular mechanics to predict bulk material properties of fibronectin fibers
The structural proteins of the extracellular matrix (ECM) form fibers with finely tuned mechanical properties matched to the time scales of cell traction forces. Several proteins such as fibronectin (Fn) and fibrin undergo molecular conformational changes that extend the proteins and are believed to be a major contributor to the extensibility of bulk fibers. The dynamics of these conformational changes have been thoroughly explored since the advent of single molecule force spectroscopy and molecular dynamics simulations but remarkably, these data have not been rigorously applied to the understanding of the time dependent mechanics of bulk ECM fibers. Using measurements of protein density within fibers, we have examined the influence of dynamic molecular conformational changes and the intermolecular arrangement of Fn within fibers on the bulk mechanical properties of Fn fibers. Fibers were simulated as molecular strands with architectures that promote either equal or disparate molecular loading under conditions of constant extension rate. Measurements of protein concentration within micron scale fibers using deep ultraviolet transmission microscopy allowed the simulations to be scaled appropriately for comparison to in vitro measurements of fiber mechanics as well as providing estimates of fiber porosity and water content, suggesting Fn fibers are approximately 75% solute. Comparing the properties predicted by single molecule measurements to in vitro measurements of Fn fibers showed that domain unfolding is sufficient to predict the high extensibility and nonlinear stiffness of Fn fibers with surprising accuracy, with disparately loaded fibers providing the best fit to experiment. This work shows the promise of this microstructural modeling approach for understanding Fn fiber properties, which is generally applicable to other ECM fibers, and could be further expanded to tissue scale by incorporating these simulated fibers into three dimensional network models
Truncated-Unity Parquet Equations: Application to the Repulsive Hubbard Model
The parquet equations are a self-consistent set of equations for the
effective two-particle vertex of an interacting many-fermion system. The
application of these equations to bulk models is, however, demanding due to the
complex emergent momentum and frequency structure of the vertex. Here, we show
how a channel-decomposition by means of truncated unities, which was developed
in the context of the functional renormalization group to efficiently treat the
momentum dependence, can be transferred to the parquet equations. This leads to
a significantly reduced numerical effort scaling only linearly with the number
of discrete momenta. We apply this technique to the half-filled repulsive
Hubbard model on the square lattice and present approximate solutions for the
channel-projected vertices and the full reducible vertex.Comment: Consistent with published version in Phys. Rev.
The MAHB, the Culture Gap, and Some Really Inconvenient Truths
Humanity's failure to take adequate actions to stem a likely environmental collapse calls for extraordinary measures to understand and alter human behavior, argues Paul Ehrlich. His Millennium Assessment of Human Behavior (MAHB) aims to chart the path to a sustainable future
The process of irreversible nucleation in multilayer growth. II. Exact results in one and two dimensions
We study irreversible dimer nucleation on top of terraces during epitaxial
growth in one and two dimensions, for all values of the step-edge barrier. The
problem is solved exactly by transforming it into a first passage problem for a
random walker in a higher-dimensional space. The spatial distribution of
nucleation events is shown to differ markedly from the mean-field estimate
except in the limit of very weak step-edge barriers. The nucleation rate is
computed exactly, including numerical prefactors.Comment: 22 pages, 10 figures. To appear in Phys. Rev.
Lattice Effects in Crystal Evaporation
We study the dynamics of a stepped crystal surface during evaporation, using
the classical model of Burton, Cabrera and Frank, in which the dynamics of the
surface is represented as a motion of parallel, monoatomic steps. The validity
of the continuum approximation treated by Frank is checked against numerical
calculations and simple, qualitative arguments. The continuum approximation is
found to suffer from limitations related, in particular, to the existence of
angular points. These limitations are often related to an adatom detachment
rate of adatoms which is higher on the lower side of each step than on the
upper side ("Schwoebel effect").Comment: DRFMC/SPSMS/MDN, Centre d'Etudes Nucleaires de Grenoble, 25 pages,
LaTex, revtex style. 8 Figures, available upon request, report# UBFF30119
Gravitational Waves: Just Plane Symmetry
We present some remarkable properties of the symmetry group for gravitational
plane waves. Our main observation is that metrics with plane wave symmetry
satisfy every system of generally covariant vacuum field equations except the
Einstein equations. The proof uses the homothety admitted by metrics with plane
wave symmetry and the scaling behavior of generally covariant field equations.
We also discuss a mini-superspace description of spacetimes with plane wave
symmetry.Comment: 10 pages, TeX, uses IOP style file
Book Reviews
Book 1 Book Title: Basic EpidemiologyBook Authors: R. Beaglehole, R. Bonita & T. KjellströmPp. viii + 174. (in English, French and Spanish in preparation). 20,50. Geneva: WHO. 1993. Order No. 1160144. ISBN 92-4-1571446.Book 6Book Title: The Guide to Heart Sounds: Normal and AbnormalBook Authors: Donald W. Novey, Marcia Pencak & John M. StangAudio-cassette narrated by: Donald W. Novey. pp. xi + 74. Illustrated. Florida: CRC Press. 1988. ISB J 0-8493-0153X.Book 7Book Title: Propachlor. Enviromnental Health Criteria. No. 147Book Author: W.H.O.Pp. 110. (English, French and Spanish summaries). $17,30. Geneva: WHO. 1993. Order TO. 1160147. ISBN 92-4-157147-0.Book 8Book Title: Quality Assurance in Health Care: A HandbookBook Authors: Roger Ellis & Dorothy WhittingronLondon: Edward Arnold. 1993. ISBN 0-340-55273-5.Book 9Book Title:  Rehabilitation after Cardiovascular Diseases, with Special Emphasis on Developing CountriesReport of a WHO expert committee. Technical Report Series No 831. Pp. viii + 122 (available in English, French and Spanish in preparation). Geneva: WHO. 1993. ISBN 92-4-120831-7
Rigid Singularity Theorem in Globally Hyperbolic Spacetimes
We show the rigid singularity theorem, that is, a globally hyperbolic
spacetime satisfying the strong energy condition and containing past trapped
sets, either is timelike geodesically incomplete or splits isometrically as
space time. This result is related to Yau's Lorentzian splitting
conjecture.Comment: 3 pages, uses revtex.sty, to appear in Physical Review
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