We devise an inverse statistical-mechanical methodology to find optimized interaction potentials that lead spontaneously to a target many-particle configuration. Target structures can possess varying degrees of disord...
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We devise an inverse statistical-mechanical methodology to find optimized interaction potentials that lead spontaneously to a target many-particle configuration. Target structures can possess varying degrees of disorder, thus extending the traditional idea of self-assembly to incorporate both amorphous and crystalline structures as well as quasicrystals. For illustration purposes, our computational technique is applied to yield an optimized isotropic (nondirectional) pair potential that spontaneously yields the three-coordinated honeycomb lattice as the ground state structure in two dimensions. This target choice is motivated by its three-dimensional analog, the diamond lattice, which is known to possess desirable photonic band gap properties.
The growth dynamics of filamentary microbial colonies is investigated. Fractality of the fungal or actinomycetes colonies is shown both theoretically and in numerical experiments to play an important role. The growth ...
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The growth dynamics of filamentary microbial colonies is investigated. Fractality of the fungal or actinomycetes colonies is shown both theoretically and in numerical experiments to play an important role. The growth observed in real colonies is described by the assumption of time-dependent fractality related to the different ages of various parts of the colony. The theoretical results are compared to a simulation based on branching random walks.
We present MEDUSA, an integrative method for learning motif models of transcription factor binding sites by incorporating promoter sequence and gene expression data. We use a modern large-margin machine learning appro...
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From algal suspensions to magma upwellings, one finds jets which exhibit complex symmetry-breaking instabilities as they are decelerated by their surroundings. We consider here a model system—a saline jet descending ...
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From algal suspensions to magma upwellings, one finds jets which exhibit complex symmetry-breaking instabilities as they are decelerated by their surroundings. We consider here a model system—a saline jet descending through a salinity gradient—which produces dynamics unlike those of standard momentum jets or plumes. The jet coils like a corkscrew within a conduit of viscously entrained fluid, whose upward recirculation braids the jet, and nearly confines transverse mixing to the narrow conduit. We show that the underlying jet structure and certain scaling relations follow from similarity solutions to the fluid equations and the physics of Kelvin-Helmholtz instabilities.
Current-induced switching in Py∕Cu∕Py spin valves with the Cu spacer thickness varying between 20 and 30 monolayers is described theoretically in terms of a multiscale approach based on ab initio calculations using ...
Current-induced switching in Py∕Cu∕Py spin valves with the Cu spacer thickness varying between 20 and 30 monolayers is described theoretically in terms of a multiscale approach based on ab initio calculations using the fully relativistic screened Korringa-Kohn-Rostoker method and the Landau-Lifshitz-Gilbert equation. It is found that in all investigated cases a perpendicular arrangement of the magnetic slabs is lowest in energy and that therefore the critical current refers to a switching from this initial magnetic configuration to a collinear magnetic configuration, the switching time being about 30ps. Because the twisting energy as well as the corresponding sheet resistance, both of them entering as key quantities the expression for the current, can be viewed layer resolved, very clear conclusions can be drawn with respect to possible reductions of the critical current.
We examine resonant interactions of optical pulses with nanostructured materials in the case of the electric field interacting with plasmonic oscillations in metallic nanospheres and double resonance including the mag...
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We study the approach to jamming in hard-sphere packings and, in particular, the pair correlation function g2(r) around contact, both theoretically and computationally. Our computational data unambiguously separate th...
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We study the approach to jamming in hard-sphere packings and, in particular, the pair correlation function g2(r) around contact, both theoretically and computationally. Our computational data unambiguously separate the narrowing δ-function contribution to g2 due to emerging interparticle contacts from the background contribution due to near contacts. The data also show with unprecedented accuracy that disordered hard-sphere packings are strictly isostatic: i.e., the number of exact contacts in the jamming limit is exactly equal to the number of degrees of freedom, once rattlers are removed. For such isostatic packings, we derive a theoretical connection between the probability distribution of interparticle forces Pf(f), which we measure computationally, and the contact contribution to g2. We verify this relation for computationally generated isostatic packings that are representative of the maximally random jammed state. We clearly observe a maximum in Pf and a nonzero probability of zero force, shedding light on long-standing questions in the granular-media literature. We computationally observe an unusual power-law divergence in the near-contact contribution to g2, persistent even in the jamming limit, with exponent −0.4 clearly distinguishable from previously proposed inverse-square-root divergence. Additionally, we present high-quality numerical data on the two discontinuities in the split-second peak of g2 and use a shared-neighbor analysis of the graph representing the contact network to study the local particle clusters responsible for the peculiar features. Finally, we present the computational data on the contact contribution to g2 for vacancy-diluted fcc crystal packings and also investigate partially crystallized packings along the transition from maximally disordered to fully ordered packings. We find that the contact network remains isostatic even when ordering is present. Unlike previous studies, we find that ordering has a significant impact on the sh
We computationally study jammed disordered hard-sphere packings as large as a million particles. We show that the packings are saturated and hyperuniform, i.e., that local density fluctuations grow only as a logarithm...
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We computationally study jammed disordered hard-sphere packings as large as a million particles. We show that the packings are saturated and hyperuniform, i.e., that local density fluctuations grow only as a logarithmically augmented surface area rather than the volume of the window. The structure factor shows an unusual nonanalytic linear dependence near the origin, S(k)∼|k|. In addition to exponentially damped oscillations seen in liquids, this implies a weak power-law tail in the total correlation function, h(r)∼−r−4, and a long-ranged direct correlation function c(r).
The mechanical properties of a model of Y-doped intergranular glassy film in silicon nitride ceramics are studied by large-scale ab initio modeling. By linking directly to its electronic structure, it is shown that th...
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The mechanical properties of a model of Y-doped intergranular glassy film in silicon nitride ceramics are studied by large-scale ab initio modeling. By linking directly to its electronic structure, it is shown that this microstructure has a complex nonlinear deformation under stress and Y doping significantly enhances the mechanical properties. The calculation of the electrostatic potential across the film supports the space charge model in ceramic microstructures.
Carbon nanotubes were catalytically grown by negative bias-enhanced hot filament chemical vapor deposition at low substrate temperature (550°C) and their growth was investigated by scanning electron microscopy. I...
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Carbon nanotubes were catalytically grown by negative bias-enhanced hot filament chemical vapor deposition at low substrate temperature (550°C) and their growth was investigated by scanning electron microscopy. It is found whether the carbon nanotubes could be orientationally grown at low temperature depended on the plasma power and carbon nanotubes could not be grown if the pressure was too low. The analysis results by the related theory indicate that the interaction of the strong electrical field formed by plasma with the catalyst particles resulted in the orientation growth of carbon nanotubes when the plasma power was large and the diffusion of the particles containing carbon at low pressure was too fast to grow the carbon nanotubes.
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