1,460 research outputs found
Dynamics of the critical Casimir force for a conserved order parameter after a critical quench
Fluctuation-induced forces occur generically when long-ranged correlations
(e.g., in fluids) are confined by external bodies. In classical systems, such
correlations require specific conditions, e.g., a medium close to a critical
point. On the other hand, long-ranged correlations appear more commonly in
certain non-equilibrium systems with conservation laws. Consequently, a variety
of non-equilibrium fluctuation phenomena, including fluctuation-induced forces,
have been discovered and explored recently. Here, we address a long-standing
problem of non-equilibrium critical Casimir forces emerging after a quench to
the critical point in a confined fluid with order-parameter-conserving dynamics
and non-symmetry-breaking boundary conditions. The interplay of inherent
(critical) fluctuations and dynamical non-local effects (due to density
conservation) gives rise to striking features, including correlation functions
and forces exhibiting oscillatory time-dependences. Complex transient regimes
arise, depending on initial conditions and the geometry of the confinement. Our
findings pave the way for exploring a wealth of non-equilibrium processes in
critical fluids (e.g., fluctuation-mediated self-assembly or aggregation). In
certain regimes, our results are applicable to active matter.Comment: 38 pages, 11 figure
Ensemble dependence of Critical Casimir Forces in Films with Dirichlet Boundary Conditions
In a recent study [Phys. Rev. E \textbf{94}, 022103 (2016)] it has been shown
that, for a fluid film subject to critical adsorption, the resulting critical
Casimir force (CCF) may significantly depend on the thermodynamic ensemble.
Here, we extend that study by considering fluid films within the so-called
ordinary surface universality class. We focus on mean-field theory, within
which the OP profile satisfies Dirichlet boundary conditions and produces a
nontrivial CCF in the presence of external bulk fields or, respectively, a
nonzero total order parameter within the film. Our analytical results are
supported by Monte Carlo simulations of the three-dimensional Ising model. We
show that, in the canonical ensemble, i.e., when fixing the so-called total
mass within the film, the CCF is typically repulsive instead of attractive as
in the grand canonical ensemble. Based on the Landau-Ginzburg free energy, we
furthermore obtain analytic expressions for the order parameter profiles and
analyze the relation between the total mass in the film and the external bulk
field.Comment: 22 pages, 15 figures. Version 2: minor corrections; added Journal
referenc
Analyzing Laminated Structures from Fibre-Reinforced Composite Material: An Assessment
In the open literature there is available a tremendous number of models and methods for analyzing laminated structures. With respect to the assumptions across the laminate thickness, theories with Cz1-continuous functions are to be distinguished from layer-wise approaches, where for the latter the functional degrees of freedom can be dependent or independent of the number of layers. Transverse shear and normal stresses are more accurate when obtained by locally evaluating the equilibrium conditions. Guidelines are needed as to which model is suitable for what task. Especially for layer-wise models a fair judgment is missing. To ease up this deficiency two simple layer-wise models are evaluated and compared with models based on Cz1-continuous functions. It turns out that for standard application the FSDT with improved transverse shear stiffness is a good choice with respect to efficiency
Lectotypes of the Species of Hymenoptera (Except Apoidea) Described by Abbé Provancher
xBio:D Automated Uploa
The time dimension of neural network models
This review attempts to provide an insightful perspective on the role of time within neural network models and the use of neural networks for problems involving time. The most commonly used neural network models are defined and explained giving mention to important technical issues but avoiding great detail. The relationship between recurrent and feedforward networks is emphasised, along with the distinctions in their practical and theoretical abilities. Some practical examples are discussed to illustrate the major issues concerning the application of neural networks to data with various types of temporal structure, and finally some highlights of current research on the more difficult types of problems are presented
Correlations and forces in sheared fluids with or without quenching
Spatial correlations play an important role in characterizing material
properties related to non-local effects. Inter alia, they can give rise to
fluctuation-induced forces. Equilibrium correlations in fluids provide an
extensively studied paradigmatic case, in which their range is typically
bounded by the correlation length. Out of equilibrium, conservation laws have
been found to extend correlations beyond this length, leading, instead, to
algebraic decays. In this context, here we present a systematic study of the
correlations and forces in fluids driven out of equilibrium simultaneously by
quenching and shearing, both for non-conserved as well as for conserved
Langevin-type dynamics. We identify which aspects of the correlations are due
to shear, due to quenching, and due to simultaneously applying both, and how
these properties depend on the correlation length of the system and its
compressibility. Both shearing and quenching lead to long-ranged correlations,
which, however, differ in their nature as well as in their prefactors, and
which are mixed up by applying both perturbations. These correlations are
employed to compute non-equilibrium fluctuation-induced forces in the presence
of shear, with or without quenching, thereby generalizing the framework set out
by Dean and Gopinathan. These forces can be stronger or weaker compared to
their counterparts in unsheared systems. In general, they do not point along
the axis connecting the centers of the small inclusions considered to be
embedded in the fluctuating medium. Since quenches or shearing appear to be
realizable in a variety of systems with conserved particle number, including
active matter, we expect these findings to be relevant for experimental
investigations.Comment: 19 pgs (15 main text + 4 appendices); 7 figure
Self-motility of an active particle induced by correlations in the surrounding solution
Current models of phoretic transport rely on molecular forces creating a
"diffuse" particle-fluid interface. We investigate theoretically an alternative
mechanism, in which a diffuse interface emerges solely due to a non-vanishing
correlation length of the surrounding solution. This mechanism can drive
self-motility of a chemically active particle. Numerical estimates indicate
that the velocity can reach micrometers per second. The predicted phenomenology
includes a bilinear dependence of the velocity on the activity and a possible
double velocity reversal upon varying the correlation length.Comment: 6 pages, 2 figures, and 22 pages of supplemental material. To be
published as Phys. Rev. Let
A critical evaluation of Kenyonâs Shag (Phalacrocorax [Stictocarbo] kenyoni)
We examine the validity of Phalacrocorax [Stictocarbo] kenyoni, which was described by Siegel-Causey (1991) from the Aleutian Islands using midden remains and existing skeletal specimens. We emphasize a morphometric evaluation of the taxon using 224 skeletal specimens of North Pacific cormorants, but we also evaluate the qualitative characters originally used to characterize P. kenyoni. Principal components and discriminant function analyses of 14 skeletal characters failed to support the validity of the species. Similarly, all seven of the character states that Seigel-Causey described as unique to P. kenyoni also were found in P. pelagicus and P. urile. Thus, the three type specimens of P. kenyoni appear to be P. pelagicus. Although we could not confirm the validity of P. kenyoni, our morphometric analyses revealed that P. pelagicus individuals from the central Aleutians are smaller than those from surrounding populations
Self-Motility of an Active Particle Induced by Correlations in the Surrounding Solution
Current models of phoretic transport rely on molecular forces creating a âdiffuseâ particle-fluid interface. We investigate theoretically an alternative mechanism, in which a diffuse interface emerges solely due to a nonvanishing correlation length of the surrounding solution. This mechanism can drive self-motility of a chemically active particle. Numerical estimates indicate that the velocity can reach micrometers per second. The predicted phenomenology includes a bilinear dependence of the velocity on the activity and a possible double velocity reversal upon varying the correlation length.Spanish Government through Grant No. FIS2017-87117-P (partially financed by FEDER funds
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