7,832 research outputs found
Phase transition in hierarchy model of Bonabeau et al
The model of Bonabeau explains the emergence of social hierarchies from the
memory of fights in an initially egalitarian society. Introducing a feedback
from the social inequality into the probability to win a fight, we find a sharp
transition between egalitarian society at low population density and
hierarchical society at high population density.Comment: 3 pages including two figs.; for Int. J. Mod. Phys.
Critical Casimir Forces for Films with Bulk Ordering Fields
The confinement of long-ranged critical fluctuations in the vicinity of
second-order phase transitions in fluids generates critical Casimir forces
acting on confining surfaces or among particles immersed in a critical solvent.
This is realized in binary liquid mixtures close to their consolute point
which belong to the universality class of the Ising model. The
deviation of the difference of the chemical potentials of the two species of
the mixture from its value at criticality corresponds to the bulk magnetic
filed of the Ising model. By using Monte Carlo simulations for this latter
representative of the corresponding universality class we compute the critical
Casimir force as a function of the bulk ordering field at the critical
temperature . We use a coupling parameter scheme for the computation
of the underlying free energy differences and an energy-magnetization
integration method for computing the bulk free energy density which is a
necessary ingredient. By taking into account finite-size corrections, for
various types of boundary conditions we determine the universal Casimir force
scaling function as a function of the scaling variable associated with the bulk
field. Our numerical data are compared with analytic results obtained from
mean-field theory.Comment: 12 pages, 4 figure
Performance of a model cascade thrust reverser for short-haul applications
Aerodynamic and acoustic characteristics are presented for a cowlmounted, model cascade thrust reverser suitable for short-haul aircraft. Thrust reverser efficiency and the influence on fan performance were determined from isolated fan-driven models under static and forward velocity conditions. Cascade reverser noise characteristics were determined statically in an isolated pipe-flow test, while aerodynamic installation effects were determined with a wind-tunnel, fan-powered airplane model. Application of test results to short-haul aircraft calculations demonstrated that such a cascade thrust reverser may be able to meet both the performance and noise requirements for short-haul aircraft operation. However, aircraft installation effects can be quite significant
Fluid adsorption near an apex: Covariance between complete and critical wetting
Critical wetting is an elusive phenomenon for solid-fluid interfaces. Using
interfacial models we show that the diverging length scales, which characterize
complete wetting at an apex, precisely mimic critical wetting with the apex
angle behaving as the contact angle. Transfer matrix, renormalization group
(RG) and mean field analysis (MF) shows this covariance is obeyed in 2D, 3D and
for long and short ranged forces. This connection should be experimentally
accesible and provides a means of checking theoretical predictions for critical
wetting.Comment: 4 pages, 1 figure, submitted to Physical Review Letter
Two Parameters for Three Dimensional Wetting Transitions
Critical effects at complete and critical wetting in three dimensions are
studied using a coupled effective Hamiltonian H[s(y),\ell]. The model is
constructed via a novel variational principle which ensures that the choice of
collective coordinate s(y) near the wall is optimal. We highlight the
importance of a new wetting parameter \Omega(T) which has a strong influence on
critical properties and allows the status of long-standing Monte-Carlo
simulation controversies to be re-examined.Comment: 4 pages RevTex, 2 encapsulated postscript figures, to appear in
Europhys. Let
Current-mediated synchronization of a pair of beating non-identical flagella
The basic phenomenology of experimentally observed synchronization (i.e., a
stochastic phase locking) of identical, beating flagella of a biflagellate alga
is known to be captured well by a minimal model describing the dynamics of
coupled, limit-cycle, noisy oscillators (known as the noisy Kuramoto model). As
demonstrated experimentally, the amplitudes of the noise terms therein, which
stem from fluctuations of the rotary motors, depend on the flagella length.
Here we address the conceptually important question which kind of synchrony
occurs if the two flagella have different lengths such that the noises acting
on each of them have different amplitudes. On the basis of a minimal model,
too, we show that a different kind of synchrony emerges, and here it is
mediated by a current carrying, steady-state; it manifests itself via
correlated "drifts" of phases. We quantify such a synchronization mechanism in
terms of appropriate order parameters and - for an ensemble of
trajectories and for a single realization of noises of duration ,
respectively. Via numerical simulations we show that both approaches become
identical for long observation times . This reveals an ergodic
behavior and implies that a single-realization order parameter is
suitable for experimental analysis for which ensemble averaging is not always
possible.Comment: 10 pages, 2 figure
Interfacial Structural Changes and Singularities in Non-Planar Geometries
We consider phase coexistence and criticality in a thin-film Ising magnet
with opposing surface fields and non-planar (corrugated) walls. We show that
the loss of translational invariance has a strong and unexpected non-linear
influence on the interface structure and phase diagram. We identify 4
non-thermodynamic singularities where there is a qualitative change in the
interface shape. In addition, we establish that at the finite-size critical
point, the singularity in the interface shape is characterized by two distint
critical exponents in contrast to the planar case (which is characterised by
one). Similar effects should be observed for prewetting at a corrugated
substrate. Analogy is made with the behaviour of a non-linear forced oscillator
showing chaotic dynamics.Comment: 13 pages, 3 figure
INDUCTION OF TOLERANCE TO HETEROLOGOUS PROTEINS AND THEIR CATABOLISM IN C57BL/6 MICE
C57BL/6 mice were rendered tolerant to one or another of 13 soluble protein antigens. Tolerance was induced by a single injection of 20 mg protein within 24 hours after birth. The duration of the unresponsive state was measured and compared with the rates of catabolism of the antigens as determined in adult and new born mice. The data presented fail to show a correlation between the persistence of labeled protein antigen and the duration of tolerance. In several occasions, even an inverse relationship between duration of the unresponsive state and persistence was demonstrated. The results, therefore, strongly indicate that the duration of tolerance is not dependent on the rates of catabolism of the antigens. Several of the commercial protein preparations used in this study contained minor impurities to which the animals were generally not rendered tolerant. By means of diffusion in agar techniques, it was demonstrated that mice injected at birth with a tolerance-inducing dose of antigen would generally not reveal precipitating antibodies to this antigen after the tolerant state had been abolished. A speculative explanation was given in terms of quantitative or qualitative differences of antibodies found in such animals as compared to the immunized control mice. After the 3rd or 4th day of life, newborn mice catabolized I131-labeled heterologous proteins at the same rates as adult mice. The apparent slow elimination during the first days of life was, at least in part, the result of retention of nonprotein-bound I131
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