1,881 research outputs found
Pressure-dependent 13C chemical shifts in proteins: Origins and applications
Pressure-dependent (13)C chemical shifts have been measured for aliphatic carbons in barnase and Protein G. Up to 200 MPa (2 kbar), most shift changes are linear, demonstrating pressure-independent compressibilities. CH(3), CH(2) and CH carbon shifts change on average by +0.23, -0.09 and -0.18 ppm, respectively, due to a combination of bond shortening and changes in bond angles, the latter matching one explanation for the gamma-gauche effect. In addition, there is a residue-specific component, arising from both local compression and conformational change. To assess the relative magnitudes of these effects, residue-specific shift changes for protein G were converted into structural restraints and used to calculate the change in structure with pressure, using a genetic algorithm to convert shift changes into dihedral angle restraints. The results demonstrate that residual (13)C alpha shifts are dominated by dihedral angle changes and can be used to calculate structural change, whereas (13)C beta shifts retain significant dependence on local compression, making them less useful as structural restraints
Comparison of electric dipole moments and the Large Hadron Collider for probing CP violation in triple boson vertices
CP violation from physics beyond the Standard Model may reside in triple
boson vertices of the electroweak theory. We review the effective theory
description and discuss how CP violating contributions to these vertices might
be discerned by electric dipole moments (EDM) or diboson production at the
Large Hadron Collider (LHC). Despite triple boson CP violating interactions
entering EDMs only at the two-loop level, we find that EDM experiments are
generally more powerful than the diboson processes. To give example to these
general considerations we perform the comparison between EDMs and collider
observables within supersymmetric theories that have heavy sfermions, such that
substantive EDMs at the one-loop level are disallowed. EDMs generally remain
more powerful probes, and next-generation EDM experiments may surpass even the
most optimistic assumptions for LHC sensitivities.Comment: 26 pages, 14 figures, published version with more argument
Overview: Computer vision and machine learning for microstructural characterization and analysis
The characterization and analysis of microstructure is the foundation of
microstructural science, connecting the materials structure to its composition,
process history, and properties. Microstructural quantification traditionally
involves a human deciding a priori what to measure and then devising a
purpose-built method for doing so. However, recent advances in data science,
including computer vision (CV) and machine learning (ML) offer new approaches
to extracting information from microstructural images. This overview surveys CV
approaches to numerically encode the visual information contained in a
microstructural image, which then provides input to supervised or unsupervised
ML algorithms that find associations and trends in the high-dimensional image
representation. CV/ML systems for microstructural characterization and analysis
span the taxonomy of image analysis tasks, including image classification,
semantic segmentation, object detection, and instance segmentation. These tools
enable new approaches to microstructural analysis, including the development of
new, rich visual metrics and the discovery of
processing-microstructure-property relationships.Comment: submitted to Materials and Metallurgical Transactions
Lamellae Stability in Confined Systems with Gravity
The microphase separation of a diblock copolymer melt confined by hard walls
and in the presence of a gravitational field is simulated by means of a cell
dynamical system model. It is found that the presence of hard walls normal to
the gravitational field are key ingredients to the formation of well ordered
lamellae in BCP melts. To this effect the currents in the directions normal and
parallel to the field are calculated along the interface of a lamellar domain,
showing that the formation of lamellae parallel to the hard boundaries and
normal to the field correspond to the stable configuration. Also, it is found
thet the field increases the interface width.Comment: 4 pages, 2 figures, submitted to Physical Review
An Update-and-Stabilize Framework for the Minimum-Norm-Point Problem
We consider the minimum-norm-point (MNP) problem over zonotopes, a
well-studied problem that encompasses linear programming. Inspired by Wolfe's
classical MNP algorithm, we present a general algorithmic framework that
performs first order update steps, combined with iterations that aim to
`stabilize' the current iterate with additional projections, i.e., finding a
locally optimal solution whilst keeping the current tight inequalities. We
bound on the number of iterations polynomially in the dimension and in the
associated circuit imbalance measure. In particular, the algorithm is strongly
polynomial for network flow instances. The conic version of Wolfe's algorithm
is a special instantiation of our framework; as a consequence, we obtain
convergence bounds for this algorithm. Our preliminary computational
experiments show a significant improvement over standard first-order methods
Lifshitz-Slyozov Scaling For Late-Stage Coarsening With An Order-Parameter-Dependent Mobility
The coarsening dynamics of the Cahn-Hilliard equation with order-parameter
dependent mobility, , is addressed at
zero temperature in the Lifshitz-Slyozov limit where the minority phase
occupies a vanishingly small volume fraction. Despite the absence of bulk
diffusion for , the mean domain size is found to grow as , due to subdiffusive transport of the order parameter
through the majority phase. The domain-size distribution is determined
explicitly for the physically relevant case .Comment: 4 pages, Revtex, no figure
Evidence of Strong Correlation between Instanton and QCD-monopole on SU(2) Lattice
The correlation between instantons and QCD-monopoles is studied both in the
lattice gauge theory and in the continuum theory. An analytical study in the
Polyakov-like gauge, where is diagonalized, shows that the
QCD-monopole trajectory penetrates the center of each instanton, and becomes
complicated in the multi-instanton system. Using the SU(2) lattice with ,
the instanton number is measured in the singular (monopole-dominating) and
regular (photon-dominating) parts, respectively. The monopole dominance for the
topological charge is found both in the maximally abelian gauge and in the
Polyakov gauge.Comment: 4 pages, Latex, 3 figures. Talk presented by H. Suganuma at
International Symposium on 'Lattice Field Theory', July 11 - 15, 1995,
Melbourne, Australi
The Effect of Shear on Phase-Ordering Dynamics with Order-Parameter-Dependent Mobility: The Large-n Limit
The effect of shear on the ordering-kinetics of a conserved order-parameter
system with O(n) symmetry and order-parameter-dependent mobility
\Gamma({\vec\phi}) \propto (1- {\vec\phi} ^2/n)^\alpha is studied analytically
within the large-n limit. In the late stage, the structure factor becomes
anisotropic and exhibits multiscaling behavior with characteristic length
scales (t^{2\alpha+5}/\ln t)^{1/2(\alpha+2)} in the flow direction and (t/\ln
t)^{1/2(\alpha+2)} in directions perpendicular to the flow. As in the \alpha=0
case, the structure factor in the shear-flow plane has two parallel ridges.Comment: 6 pages, 2 figure
Critical dynamics of phase transition driven by dichotomous Markov noise
An Ising spin system under the critical temperature driven by a dichotomous
Markov noise (magnetic field) with a finite correlation time is studied both
numerically and theoretically. The order parameter exhibits a transition
between two kinds of qualitatively different dynamics, symmetry-restoring and
symmetry-breaking motions, as the noise intensity is changed.
There exist regions called channels where the order parameter stays for a
long time slightly above its critical noise intensity. Developing a
phenomenological analysis of the dynamics, we investigate the distribution of
the passage time through the channels and the power spectrum of the order
parameter evolution. The results based on the phenomenological analysis turn
out to be in quite good agreement with those of the numerical simulation.Comment: 27 pages, 12 figure
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