78 research outputs found
Anomalous Diffusion In Microrheology: A Comparative Study
We present a comparative study on two theoretical descriptions of
microrheological experiments. Using a generalized Langevin equation (GLE), we
analyze the origin of the power-law behavior of the main properties of a
viscoelastic medium. Then, we discuss the equivalence of the GLE with a
generalized Fokker-Planck equation (GFPE), and how more general GFPE's can be
derived from a thermo-kinetic formalism. These complementary theories lead to a
justification for the physical nature of the Hurst exponent of fractional
kinetics. Theory is compared with experiments.Comment: 7 pages, 3 figure
A FDR-preserving field theory for interacting Brownian particles: one-loop theory and MCT
We develop a field theoretical treatment of a model of interacting Brownian
particles. We pay particular attention to the requirement of the time reversal
invariance and the fluctuation-dissipation relationship (FDR). The method used
is a modified version of the auxiliary field method due originally to
Andreanov, Biroli and Lefevre [J. Stat. Mech. P07008 (2006)]. We recover the
correct diffusion law when the interaction is dropped as well as the standard
mode coupling equation in the one-loop order calculation for interacting
Brownian particle systems.Comment: 66 pages, 8 figures, submitted to J. Stat. Mec
Critical fluctuations of time-dependent magnetization in a random-field Ising model
Cooperative behaviors near the disorder-induced critical point in a random
field Ising model are numerically investigated by analyzing time-dependent
magnetization in ordering processes from a special initial condition. We find
that the intensity of fluctuations of time-dependent magnetization, ,
attains a maximum value at a time in a normal phase and that
and exhibit divergences near the disorder-induced critical
point. Furthermore, spin configurations around the time are
characterized by a length scale, which also exhibits a divergence near the
critical point. We estimate the critical exponents that characterize these
power-law divergences by using a finite-size scaling method.Comment: 5 pages, 7 figure
Event-Driven Simulation of the Dynamics of Hard Ellipsoids
We introduce a novel algorithm to perform event-driven simulations of hard
rigid bodies of arbitrary shape, that relies on the evaluation of the geometric
distance. In the case of a monodisperse system of uniaxial hard ellipsoids,we
perform molecular dynamics simulations varying the aspect-ratio X0 and the
packing fraction phi. We evaluate the translational Dtrans and the rotational
Drot diffusion coefficient and the associated isodiffusivity lines in the
phi-X0 plane. We observe a decoupling of the translational and rotational
dynamics which generates an almost perpendicular crossing of the Dtrans and
Drot isodiffusivity lines. While the self intermediate scattering function
exhibits stretched relaxation, i.e. glassy dynamics, only for large phi and X0
about equals to 1, the second order orientational correlator C2(t) shows
stretching only for large and small X0 values. We discuss these findings in the
context of a possible pre-nematic order driven glass transition.Comment: Proceedings of IWCS2007 Sendai (Japan
Can the frequency-dependent specific heat be measured by thermal effusion methods?
It has recently been shown that plane-plate heat effusion methods devised for
wide-frequency specific-heat spectroscopy do not give the isobaric specific
heat, but rather the so-called longitudinal specific heat. Here it is shown
that heat effusion in a spherical symmetric geometry also involves the
longitudinal specific heat.Comment: Paper presented at the Fifth International Workshop on Complex
Systems (Sendai, September, 2007), to appear in AIP Conference Proceeding
Fluctuation effects in the theory of microphase separation of diblock copolymers in the presence of an electric field
We generalize the Fredrickson-Helfand theory of the microphase separation in
symmetric diblock copolymer melts by taking into account the influence of a
time-independent homogeneous electric field on the composition fluctuations
within the self-consistent Hartree approximation. We predict that electric
fields suppress composition fluctuations, and consequently weaken the
first-order transition. In the presence of an electric field the critical
temperature of the order-disorder transition is shifted towards its mean-field
value. The collective structure factor in the disordered phase becomes
anisotropic in the presence of the electric field. Fluctuational modulations of
the order parameter along the field direction are strongest suppressed. The
latter is in accordance with the parallel orientation of the lamellae in the
ordered state.Comment: 16 page
Phase transition in the Jarzynski estimator of free energy differences
The transition between a regime in which thermodynamic relations apply only
to ensembles of small systems coupled to a large environment and a regime in
which they can be used to characterize individual macroscopic systems is
analyzed in terms of the change in behavior of the Jarzynski estimator of
equilibrium free energy differences from nonequilibrium work measurements.
Given a fixed number of measurements, the Jarzynski estimator is unbiased for
sufficiently small systems. In these systems, the directionality of time is
poorly defined and configurations that dominate the empirical average, but
which are in fact typical of the reverse process, are sufficiently well
sampled. As the system size increases the arrow of time becomes better defined.
The dominant atypical fluctuations become rare and eventually cannot be sampled
with the limited resources that are available. Asymptotically, only typical
work values are measured. The Jarzynski estimator becomes maximally biased and
approaches the exponential of minus the average work, which is the result that
is expected from standard macroscopic thermodynamics. In the proper scaling
limit, this regime change can be described in terms of a phase transition in
variants of the random energy model (REM). This correspondence is explicitly
demonstrated in several examples of physical interest: near-equilibrium
processes in which the work distribution is Gaussian, the sudden compression of
an ideal gas and adiabatic quasi-static volume changes in a dilute real gas.Comment: 29 pages, 5 figures, accepted for publication in Physical Review E
(2012
Nights at the museum: integrated arts and microbiology public engagement events enhance understanding of science whilst increasing community diversity and inclusion
This study uses integrated art and science events to explore a blended approach in improving public understanding of current scientific topics and widening participation within the local community. The events were a Halloween-inspired microbiology-themed series of interactive exhibitions hosted within a national museum as part of an existing series of adult education evenings. A representative sample of 102 mixed methods exit questionnaires, based on determining (i) audience diversity and (ii) understanding of scientific topics, were analysed by qualitative and quantitative approaches, and a post-attendance focus group was carried out to determine longer term impact of the event. Participants were grouped as 'Science', 'Arts', 'Both' or 'Neither', according to their past experience and engagement. These events welcomed more participants from the Arts and Neither subsections hence engaging a group of people who would not usually visit science public engagement events or comparative events hosted in traditional academic settings, highlighting the importance of venue choice in reaching new audiences and widening participation. An increase in perceived understanding of science was observed by all groups of participants with reported enjoyment focused around the science talks, presentations and blended art-science activities. A putative impact in science capital is observed with participants reporting an increased likelihood of attending science events in the future. Furthermore, increased discussion and awareness of science in society is evidenced by participants. Blended art and microbiology exhibitions enhance the accessibly of science public engagement events and is likely to increase science capital; the impact of this on cognitive polyphasia is also discussed
- …