3,821 research outputs found
Statistical Field Theory and Effective Action Method for scalar Active Matter
We employ Statistical Field Theory techniques for coarse-graining the
steady-state properties of Active Ornstein-Uhlenbeck particles. The computation
is carried on in the framework of the Unified Colored Noise approximation that
allows an effective equilibrium picture. We thus develop a mean-field theory
that allows to describe in a unified framework the phenomenology of scalar
Active Matter. In particular, we are able to describe through spontaneous
symmetry breaking mechanism two peculiar features of Active Systems that are
(i) The accumulation of active particles at the boundaries of a confining
container, and (ii) Motility-Induced Phase Separation (MIPS).
\textcolor{black}{We develop a mean-field theory for steric interacting active
particles undergoing to MIPS and for Active Lennard-Jones (ALJ) fluids.}
\textcolor{black}{Within this framework}, we discuss the universality class of
MIPS and ALJ \textcolor{black}{showing that it falls into Ising universality
class.} We \textcolor{black}{thus} compute analytically the critical line
for both models. In the case of MIPS, gives rise to a
reentrant phase diagram compatible with an inverse transition from liquid to
gas as the strength of the noise decreases. \textcolor{black}{However, in the
case of particles interacting through anisotropic potentials, } the field
theory acquires a term that, \textcolor{black}{in general, cannot
be canceled performing the expansion around the critical point.} In this case,
the \textcolor{black}{Ising} critical point might \textcolor{black}{be
replaced} by a first-order phase transition \textcolor{black}{region}
Effective equilibrium picture in model with exponentially correlated noise
We study the effect of exponentially correlated noise on model in the
limit of small correlation time discussing the order-disorder transition in
mean-field and the topological transition in two dimensions. We map the steady
states of the non-equilibrium dynamics into an effective equilibrium theory. In
mean-field, the critical temperature increases with the noise correlation time
indicating that memory effects promote ordering. This finding is
confirmed by numerical simulations. The topological transition temperature in
two dimensions remains untouched. However, finite size effects induce a
crossover in the vortices proliferation that is confirmed by numerical
simulations
Effective potential method for active particles
We investigate the steady state properties of an active fluid modeled as an
assembly of soft repulsive spheres subjected to Gaussian colored noise. Such a
noise captures one of the salient aspects of active particles, namely the
persistence of their motion and determines a variety of novel features with
respect to familiar passive fluids. We show that within the so-called
multidimensional unified colored noise approximation, recently introduced in
the field of active matter, the model can be treated by methods similar to
those employed in the study of standard molecular fluids. The system shows a
tendency of the particles to aggregate even in the presence of purely repulsive
forces because the combined action of colored noise and interactions enhances
the the effective friction between nearby particles. We also discuss whether an
effective two-body potential approach, which would allow to employ methods
similar to those of density functional theory, is appropriate. The limits of
such an approximation are discussed.Comment: 14 pages, 6 figures in Molecular Physics, 11 march 2016. arXiv admin
note: text overlap with arXiv:cond-mat/0605094 by other author
Rigidity and sharp stability estimates for hypersurfaces with constant and almost-constant nonlocal mean curvature
We prove that the boundary of a (not necessarily connected) bounded smooth
set with constant nonlocal mean curvature is a sphere. More generally, and in
contrast with what happens in the classical case, we show that the Lipschitz
constant of the nonlocal mean curvature of such a boundary controls its
-distance from a single sphere. The corresponding stability inequality is
obtained with a sharp decay rate.Comment: 17 page
Generalized energy equipartition in harmonic oscillators driven by active baths
We study experimentally and numerically the dynamics of colloidal beads
confined by a harmonic potential in a bath of swimming E. coli bacteria. The
resulting dynamics is well approximated by a Langevin equation for an
overdamped oscillator driven by the combination of a white thermal noise and an
exponentially correlated active noise. This scenario leads to a simple
generalization of the equipartition theorem resulting in the coexistence of two
different effective temperatures that govern dynamics along the flat and the
curved directions in the potential landscape.Comment: 4 pages, 3 figure
Pressure in an exactly solvable model of active fluid
We consider the pressure in the steady-state regime of three stochastic
models characterized by self-propulsion and persistent motion and widely
employed to describe the behavior of active particles, namely the Active
Brownian particle (ABP) model, the Gaussian colored noise (GCN) model and the
unified colored noise model (UCNA). Whereas in the limit of short but finite
persistence time the pressure in the UCNA model can be obtained by different
methods which have an analog in equilibrium systems, in the remaining two
models only the virial route is, in general, possible.
According to this method, notwithstanding each model obeys its own specific
microscopic law of evolution, the pressure displays a certain universal
behavior. For generic interparticle and confining potentials, we derive a
formula which establishes a correspondence between the GCN and the UCNA
pressures. In order to provide explicit formulas and examples, we specialize
the discussion to the case of an assembly of elastic dumbbells confined to a
parabolic well. By employing the UCNA we find that, for this model, the
pressure determined by the thermodynamic method coincides with the pressures
obtained by the virial and mechanical methods. The three methods when applied
to the GCN give a pressure identical to that obtained via the UCNA. Finally, we
find that the ABP virial pressure exactly agrees with the UCNA and GCN result.Comment: 12 pages, 1 figure Submitted for publication 23rd of January 2017 The
introduction has been modifie
Ambient Synthesis of Tricyclic Naphthalenes via Stepwise Styryl-yne Dearomative Diels{ extendash}Alder Cyclization
A cascade of styrylynols promoted by MnO2 allows the synthesis of fused tricycles with a naphthalene core. The reaction occurs under ambient conditions, offering a practical synthetic tool because of the inexpensive and abundant manganese species. The method affords products through the sequential oxidation of a propargyl alcohol, stepwise Diels-Alder cyclization, and finally rearomatization. According to density functional theory, the usually unfavorable stepwise Diels-Alder mechanism is instead a general tool for eliciting otherwise challenging dearomative annulation
Body mass index and age correlate with antioxidant supplementation effects on sperm quality: Post hoc analyses from a double-blind placebo-controlled trial
Spermatozoa are vulnerable to lack of energy and oxidative stress as a result of elevated levels of reactive oxygen species. Therefore, it is essential that appropriate nutrients are available during maturation. This randomised, double-blind, placebo-controlled trial investigated the effect of 6-month supplementation with carnitines and other micronutrients on sperm quality in 104 subjects with oligo- and/or astheno- and/or teratozoospermia with or without varicocele. Semen analyses were done at the beginning and end of the treatment. In addition to main analyses, post hoc analyses for age and body mass index (BMI) were carried out. Results were interpreted by dividing the population into two age and BMI classes. In 94 patients who completed the study, all sperm parameters increased in supplemented patients compared to the placebo group. A significant (p = .0272) difference in supplementation efficacy was observed for total motility on patients with varicocele and BMI < 25. In the same group, also the progressive motility was significantly superior (p = .0159). For Responder analysis, total motility results were confirmed in both the cited group (p = .0066) and in the varicocele group with BMI < 25 and age < 35 (p = .0078). This study suggests that supplementation is more effective in subjects with varicocele younger than 35 years with BMI < 25
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