Página 19 dos resultados de 179249 itens digitais encontrados em 0.211 segundos

## Probing relevant ingredients in mean-field approaches for the athermal rheology of yield stress materials

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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Although the notion of mechanical noise is expected to play a key role in the
non-linear rheology of athermally sheared amorphous systems, its
characterization has so far remained elusive. Here, we show using molecular
dynamic simulations that in spite of the presence of strong spatio-temporal
correlations in the system, the local stress exhibits normal diffusion under
the effect of the mechanical noise in the finite driving regime. The diffusion
constant appears to be proportional to the mean plastic activity. Our data
suggests that the corresponding proportionality constant is density
independent, and can be directly related to the specific form of the
rheological flow curve, pointing the way to a generic way of modeling
mechanical noise in mean-field equations.; Comment: 8 pages, 5 figures, 1 table in Soft Matter (2015)

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## Universal two-step crystallization of DNA-functionalized nanoparticles

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 12/08/2010

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We examine the crystallization dynamics of nanoparticles reversibly tethered
by DNA hybridization. We show that the crystallization happens readily only in
a narrow temperature "slot," and always proceeds via a two-step process,
mediated by a highly-connected amorphous intermediate. For lower temperature
quenches, the dynamics of unzipping strands in the amorphous state is
sufficiently slow that crystallization is kinetically hindered. This accounts
for the well-documented difficulty of forming crystals in these systems. The
strong parallel to the crystallization behavior of proteins and colloids
suggests that these disparate systems crystallize in an apparently universal
manner.; Comment: Accepted for publication in Soft Matter

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## Self-propelled particles with selective attraction-repulsion interaction - From microscopic dynamics to coarse-grained theories

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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In this work we derive and analyze coarse-grained descriptions of
self-propelled particles with selective attraction-repulsion interaction, where
individuals may respond differently to their neighbours depending on their
relative state of motion (approach versus movement away). Based on the
formulation of a nonlinear Fokker-Planck equation, we derive a kinetic
description of the system dynamics in terms of equations for the Fourier modes
of a one-particle density function. This approach allows effective numerical
investigation of the stability of possible solutions of the system. The
detailed analysis of the interaction integrals entering the equations
demonstrates that divergences at small wavelengths can appear at arbitrary
expansion orders.
Further on, we also derive a hydrodynamic theory by performing a closure at
the level of the second Fourier mode of the one-particle density function. We
show that the general form of equations is in agreement with the theory
formulated by Toner and Tu.
Finally, we compare our analytical predictions on the stability of the
disordered homogeneous solution with results of individual-based simulations.
They show good agreement for sufficiently large densities and non-negligible
short-ranged repulsion. Disagreements of numerical results and the hydrodynamic
theory for weak short-ranged repulsion reveal the existence of a previously
unknown phase of the model consisting of dense...

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## Numerical treatment of the Boltzmann equation for self-propelled particle systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 17/11/2014

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Kinetic theories constitute one of the most promising tools to decipher the
characteristic spatio-temporal dynamics in systems of actively propelled
particles. In this context, the Boltzmann equation plays a pivotal role, since
it provides a natural translation between a particle-level description of the
system's dynamics and the corresponding hydrodynamic fields. Yet, the intricate
mathematical structure of the Boltzmann equation substantially limits the
progress toward a full understanding of this equation by solely analytical
means. Here, we propose a general framework to numerically solve the Boltzmann
equation for self-propelled particle systems in two spatial dimensions and with
arbitrary boundary conditions. We discuss potential applications of this
numerical framework to active matter systems, and use the algorithm to give a
detailed analysis to a model system of self-propelled particles with polar
interactions. In accordance with previous studies, we find that spatially
homogeneous isotropic and broken symmetry states populate two distinct regions
in parameter space, which are separated by a narrow region of spatially
inhomogeneous, density-segregated moving patterns. We find clear evidence that
these three regions in parameter space are connected by first order phase
transitions...

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## Rotational Diffusion in a Chain of Particles

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 24/10/2005

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We study the coupled rotational diffusion in a two-particle chain on the
basis of a Smoluchowski equation and calculate time-correlation functions that
are measurable in an experiment. This might be used to explore hydrodynamic
interactions in the limit where lubrication theory is valid.; Comment: 7 pages, 2 figures, to be published in J. Phys.: Condens. Matter

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## Geometric partition functions of cellular systems: Explicit calculation of the entropy in two and three dimensions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 22/11/2005

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A method is proposed for the characterisation of the entropy of cellular
structures, based on the compactivity concept for granular packings.
Hamiltonian-like volume functions are constructed both in two and in three
dimensions, enabling the identification of a phase space and making it possible
to take account of geometrical correlations systematically. Case studies are
presented for which explicit calculations of the mean vertex density and
porosity fluctuations are given as functions of compactivity. The formalism
applies equally well to two- and three-dimensional granular assemblies.; Comment: 14 pages, 4 figures, to appear in The European Physical Journal E -
Soft Matter

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## Salt-Induced Counterion-Mobility Anomaly in Polyelectrolyte Electrophoresis

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 23/05/2009

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We study the electrokinetics of a single polyelectrolyte chain in salt
solution using hydrodynamic simulations. The salt-dependent chain mobility
compares well with experimental DNA data. The mobility of condensed counterions
exhibits a salt-dependent change of sign, an anomaly that is also reflected in
the counterion excess conductivity. Using Green's function techniques this
anomaly is explained by electrostatic screening of the hydrodynamic
interactions between chain and counterions.; Comment: 4 pages, 3 figures

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## DNA toroid condensation as analytic solutions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/01/2007

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#Condensed Matter - Soft Condensed Matter#Condensed Matter - Statistical Mechanics#Quantitative Biology - Biomolecules

It now becomes apparent that condensed DNA toroid which emerges in a poor
solvent condition can be realised in the framework of the non-linear sigma
model on a line segment. In fact, the classical solutions of the model, i.e.,
of the bending potential exhibit toroidal forms, and fit well with the
delta-function term of the attractive interaction. The proposed theory is in
good agreement with experimental observations that the toroid is the ground
state. In this paper, we give a rigorous proof that the solutions are indeed
the exact solutions of the equations of motion with the first derivatives of
the attractive interaction term. We also show a refined mapping to experimental
data, considering the finite size effects of the cross section and of the chain
length.; Comment: 11 pages, 3 figures (colour)

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## Condensate localization in a quasi-periodic structure

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/05/2004

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We propose a set-up of optical laser beams by which one may realize a
quasi-one-dimensional Fibonacci array of potential wells for a Bose-Einstein
condensate. We use a Bose-Hubbard tight-binding model to evaluate the transport
of superfluid Rb87 atoms driven by a constant force through such an array. We
show that the minigaps that are generated in the spectral density-of-states by
the quasi-periodic disorder give rise to prominent localization effects, which
can be observed by measuring the tunnel output of matter into vacuum as a
function of the intensity of the applied force.; Comment: 9 pages, 4 figures

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## Nucleation of colloids and macromolecules: does the nucleation pathway matter?

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 06/02/2012

Relevância na Pesquisa

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#Condensed Matter - Soft Condensed Matter#Condensed Matter - Statistical Mechanics#Physics - Chemical Physics

A recent description of diffusion-limited nucleation based on fluctuating
hydrodynamics that extends classical nucleation theory predicts a very
non-classical two-step scenario whereby nucleation is most likely to occur in
spatially-extended, low-amplitude density fluctuations. In this paper, it is
shown how the formalism can be used to determine the maximum probability of
observing \emph{any} proposed nucleation pathway, thus allowing one to address
the question as to their relative likelihood, including of the newly proposed
pathway compared to classical scenarios. Calculations are presented for the
nucleation of high-concentration bubbles in a low-concentration solution of
globular proteins and it is found that the relative probabilities (new theory
compared to classical result) for reaching a critical nucleus containing $N_c$
molecules scales as $e^{-N_c/3}$ thus indicating that for all but the smallest
nuclei, the classical scenario is extremely unlikely.; Comment: 7 pages, 5 figures

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## Controlled self-assembly of periodic and aperiodic cluster crystals

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 17/01/2014

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#Condensed Matter - Soft Condensed Matter#Condensed Matter - Materials Science#Nonlinear Sciences - Pattern Formation and Solitons

Soft particles are known to overlap and form stable clusters that
self-assemble into periodic crystalline phases with density-independent lattice
constants. We use molecular dynamics simulations in two dimensions to
demonstrate that, through a judicious design of an isotropic pair potential,
one can control the ordering of the clusters and generate a variety of phases,
including decagonal and dodecagonal quasicrystals. Our results confirm
analytical predictions based on a mean-field approximation, providing insight
into the stabilization of quasicrystals in soft macromolecular systems, and
suggesting a practical approach for their controlled self-assembly in
laboratory realizations using synthesized soft-matter particles.; Comment: Supplemental Material can be obtained through the author's website
at: http://www.tau.ac.il/~ronlif/pubs/ClusterCrystals-Supp.pdf

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## Shear Banding and Spatiotemporal Oscillations in Vortex Matter in Nanostructured Superconductors

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 16/12/2009

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We propose a simple nanostructured pinning array geometry where a rich
variety of complex vortex shear banding phenomena can be realized. A single row
of pinning sites is removed from a square pinning array. Shear banding effects
arise when vortex motion in the pin-free channel nucleates motion of vortices
in the surrounding pinned regions, creating discrete steps in the vortex
velocity profile away from the channel. Near the global depinning transition,
the width of the band of moving vortices undergoes oscillations or fluctuations
that can span the entire system. We use simulations to show that these effects
should be observable in the transport properties of the system. Similar large
oscillations and shear banding effects are known to occur for sheared complex
fluids in which different dynamical phases coexist.; Comment: 4 pages, 4 postscript figures

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## Effects of particle-size ratio on jamming of binary mixtures

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 17/12/2009

Relevância na Pesquisa

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We perform a systematic numerical study of the effects of the particle-size
ratio $R \ge 1$ on the properties of jammed binary mixtures. We find that
changing $R$ does not qualitatively affect the critical scaling of the pressure
and coordination number with the compression near the jamming transition, but
the critical volume fraction at the jamming transition varies with $R$.
Moreover, the static structure factor (density correlation) $S(k)$ strongly
depends on $R$ and shows distinct long wave-length behaviors between large and
small particles. Thus the previously reported behavior of $S(k)\sim k$ in the
long wave-length limit is only a special case in the $R\to 1$ limit, and cannot
be simply generalized to jammed systems with $R>1$.; Comment: 5 pages and 4 figures, submitted to Soft Matter, special issue on
Granular and Jammed Materials

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## Slow relaxation and aging phenomena at nano-scale in granular materials

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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#Condensed Matter - Soft Condensed Matter#Condensed Matter - Mesoscale and Nanoscale Physics#Physics - Geophysics

Complex systems having metastable elements often demonstrate nearly log-time
relaxations and a kind of aging: repeated stimuli weaken the system's
relaxational response. Granular matter is known to exhibit a wealth of such
behaviors, for which the role of thermal fluctuations is usually ignored.
However, we demonstrate that the latter can pronouncedly affect contacting
mesoscopic-scale asperities and be macroscopically observed via appropriate
acoustic effects. We also propose a mechanism comprising slow relaxations and
aging as intrinsic properties of a wide class of systems with metastable
states.; Comment: 5 pages, 4 figures

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## Excitation energy after a smooth quench in a Luttinger liquid

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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#Condensed Matter - Superconductivity#Condensed Matter - Quantum Gases#Condensed Matter - Statistical Mechanics#Quantum Physics

Low energy physics of quasi-one-dimensional ultracold atomic gases is often
described by a gapless Luttinger liquid (LL). It is nowadays routine to
manipulate these systems by changing their parameters in time but, no matter
how slow the manipulation is, it must excite a gapless system. We study a
smooth change of parameters of the LL (a smooth "quench") with a variable
quench time and find that the excitation energy decays with an inverse power of
the quench time. This universal exponent is -2 at zero temperature, and -1 for
slow enough quenches at finite temperature. The smooth quench does not excite
beyond the range of validity of the low energy LL description.; Comment: 5 pages, 2 figures; minor changes, version published in Phys. Rev. B

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## Ejection dynamics of a ring polymer out of a nanochannel

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 18/09/2011

Relevância na Pesquisa

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#Condensed Matter - Soft Condensed Matter#Condensed Matter - Statistical Mechanics#Quantitative Biology - Biomolecules

We investigate the ejection dynamics of a ring polymer out of a cylindrical
nanochannel using both theoretical analysis and three dimensional Langevin
dynamics simulations. The ejection dynamics for ring polymers shows two regimes
like for linear polymers, depending on the relative length of the chain
compared with the channel. For long chains with length $N$ larger than the
critical chain length $N_{c}$, at which the chain just fully occupies the
nanochannel, the ejection for ring polymers is faster compared with linear
chains of identical length due to a larger entropic pulling force; while for
short chains ($N

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## Surveying the Free Energy Landscapes of Continuum Models: Application to Soft Matter Systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 13/02/2015

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#Condensed Matter - Soft Condensed Matter#Condensed Matter - Materials Science#Physics - Chemical Physics#Physics - Computational Physics

A variety of methods are developed for characterising the free energy
landscapes of continuum, Landau-type free energy models. Using morphologies of
lipid vesicles and a multistable liquid crystal device as examples, I show that
the methods allow systematic study of not only the most relevant minimum energy
configurations, but also the transition pathways between any two minima, as
well as their corresponding energy barriers and transition state
configurations. A global view of the free energy landscapes can then be
visualized using either a disconnectivity graph or a network representation.
Different forms of free energy functionals and boundary conditions can be
readily implemented, thus allowing these tools to be utilised for a broad range
of problems.

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## Effective non-additive pair potential for lock-and-key interacting particles: the role of the limited valence

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/03/2007

Relevância na Pesquisa

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#Condensed Matter - Soft Condensed Matter#Condensed Matter - Statistical Mechanics#Mathematics - Probability

Theoretical studies of self-assembly processes and condensed phases in
colloidal systems are often based on effective inter-particle potentials. Here
we show that developing an effective potential for particles interacting with a
limited number of ``lock-and-key'' selective bonds (due to the specificity of
bio-molecular interactions) requires -- beside the non-sphericity of the
potential -- a (many body) constraint that prevent multiple bonding on the same
site. We show the importance of retaining both valence and bond-selectivity by
developing, as a case study, a simple effective potential describing the
interaction between colloidal particles coated by four single-strand DNA
chains.; Comment: 4 pages, 5 figures

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## Phase Separation of Charge-Stabilized Colloids: A Gibbs Ensemble Monte Carlo Simulation Study

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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Fluid phase behavior of charge-stabilized colloidal suspensions is explored
by applying a new variant of the Gibbs ensemble Monte Carlo simulation method
to a coarse-grained one-component model with implicit microions and solvent.
The simulations take as input linear-response approximations for effective
electrostatic interactions -- hard-sphere-Yukawa pair potential and one-body
volume energy. The conventional Gibbs ensemble trial moves are supplemented by
exchange of (implicit) salt between coexisting phases, with acceptance
probabilities influenced by the state dependence of the effective interactions.
Compared with large-scale simulations of the primitive model, with explicit
microions, our computationally practical simulations of the one-component model
closely match the pressures and pair distribution functions at moderate
electrostatic couplings. For macroion valences and couplings within the
linear-response regime, deionized aqueous suspensions with monovalent microions
exhibit separation into macroion-rich and macroion-poor fluid phases below a
critical salt concentration. The resulting pressures and phase diagrams are in
excellent agreement with predictions of a variational free energy theory based
on the same model.; Comment: 11 pages...

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## Local origin of global contact numbers in frictional ellipsoid packings

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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In particulate soft matter systems the average number of contacts $Z$ of a
particle is an important predictor of the mechanical properties of the system.
Using X-ray tomography, we analyze packings of frictional, oblate ellipsoids of
various aspect ratios $\alpha$, prepared at different global volume fractions
$\phi_g$. We find that $Z$ is a monotonously increasing function of $\phi_g$
for all $\alpha$. We demonstrate that this functional dependence can be
explained by a local analysis where each particle is described by its local
volume fraction $\phi_l$ computed from a Voronoi tessellation. $Z$ can be
expressed as an integral over all values of $\phi_l$: $Z(\phi_g, \alpha, X) =
\int Z_l (\phi_l, \alpha, X) \; P(\phi_l | \phi_g) \; d\phi_l$. The local
contact number function $ Z_l (\phi_l, \alpha, X)$ describes the relevant
physics in term of locally defined variables only, including possible higher
order terms $X$. The conditional probability $P(\phi_l | \phi_g)$ to find a
specific value of $\phi_l$ given a global packing fraction $\phi_g$ is found to
be independent of $\alpha$ and $X$. Our results demonstrate that for frictional
particles a local approach is not only a theoretical requirement but also
feasible.; Comment: more revisions...

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