4,997 research outputs found
Preasymptotic multiscaling in the phase-ordering dynamics of the kinetic Ising model
The evolution of the structure factor is studied during the phase-ordering
dynamics of the kinetic Ising model with conserved order parameter. A
preasymptotic multiscaling regime is found as in the solution of the
Cahn-Hilliard-Cook equation, revealing that the late stage of phase-ordering is
always approached through a crossover from multiscaling to standard scaling,
independently from the nature of the microscopic dynamics.Comment: 11 pages, 3 figures, to be published in Europhys. Let
Heterogeneous pair approximation for voter models on networks
For models whose evolution takes place on a network it is often necessary to
augment the mean-field approach by considering explicitly the degree dependence
of average quantities (heterogeneous mean-field). Here we introduce the degree
dependence in the pair approximation (heterogeneous pair approximation) for
analyzing voter models on uncorrelated networks. This approach gives an
essentially exact description of the dynamics, correcting some inaccurate
results of previous approaches. The heterogeneous pair approximation introduced
here can be applied in full generality to many other processes on complex
networks.Comment: 6 pages, 6 figures, published versio
The non-linear q-voter model
We introduce a non-linear variant of the voter model, the q-voter model, in
which q neighbors (with possible repetition) are consulted for a voter to
change opinion. If the q neighbors agree, the voter takes their opinion; if
they do not have an unanimous opinion, still a voter can flip its state with
probability . We solve the model on a fully connected network (i.e.
in mean-field) and compute the exit probability as well as the average time to
reach consensus. We analyze the results in the perspective of a recently
proposed Langevin equation aimed at describing generic phase transitions in
systems with two ( symmetric) absorbing states. We find that in mean-field
the q-voter model exhibits a disordered phase for high and an
ordered one for low with three possible ways to go from one to the
other: (i) a unique (generalized voter-like) transition, (ii) a series of two
consecutive Ising-like and directed percolation transition, and (iii) a series
of two transitions, including an intermediate regime in which the final state
depends on initial conditions. This third (so far unexplored) scenario, in
which a new type of ordering dynamics emerges, is rationalized and found to be
specific of mean-field, i.e. fluctuations are explicitly shown to wash it out
in spatially extended systems.Comment: 9 pages, 7 figure
Terahertz detection schemes based on sequential multi-photon absorption
We present modeling and simulation of prototypical multi bound state quantum
well infrared photodetectors and show that such a detection design may overcome
the problems arising when the operation frequency is pushed down into the far
infrared spectral region. In particular, after a simplified analysis on a
parabolic-potential design, we propose a fully three-dimensional model based on
a finite difference solution of the Boltzmann transport equation for realistic
potential profiles. The performances of the proposed simulated devices are
encouraging and support the idea that such design strategy may face the
well-known dark-current problem.Comment: 3 pages, 2 figures; submitted to Applied Physics Letter
Voter models on weighted networks
We study the dynamics of the voter and Moran processes running on top of
complex network substrates where each edge has a weight depending on the degree
of the nodes it connects. For each elementary dynamical step the first node is
chosen at random and the second is selected with probability proportional to
the weight of the connecting edge. We present a heterogeneous mean-field
approach allowing to identify conservation laws and to calculate exit
probabilities along with consensus times. In the specific case when the weight
is given by the product of nodes' degree raised to a power theta, we derive a
rich phase-diagram, with the consensus time exhibiting various scaling laws
depending on theta and on the exponent of the degree distribution gamma.
Numerical simulations give very good agreement for small values of |theta|. An
additional analytical treatment (heterogeneous pair approximation) improves the
agreement with numerics, but the theoretical understanding of the behavior in
the limit of large |theta| remains an open challenge.Comment: 21 double-spaced pages, 6 figure
High performance dash on warning air mobile, missile system
An aircraft-missile system which performs a high acceleration takeoff followed by a supersonic dash to a 'safe' distance from the launch site is presented. Topics considered are: (1) technological feasibility to the dash on warning concept; (2) aircraft and boost trajectory requirements; and (3) partial cost estimates for a fleet of aircraft which provide 200 missiles on airborne alert. Various aircraft boost propulsion systems were studied such as an unstaged cryogenic rocket, an unstaged storable liquid, and a solid rocket staged system. Various wing planforms were also studied. Vehicle gross weights are given. The results indicate that the dash on warning concept will meet expected performance criteria, and can be implemented using existing technology, such as all-aluminum aircraft and existing high-bypass-ratio turbofan engines
Phase-ordering of conserved vectorial systems with field-dependent mobility
The dynamics of phase-separation in conserved systems with an O(N) continuous
symmetry is investigated in the presence of an order parameter dependent
mobility M(\phi)=1-a \phi^2. The model is studied analytically in the framework
of the large-N approximation and by numerical simulations of the N=2, N=3 and
N=4 cases in d=2, for both critical and off-critical quenches. We show the
existence of a new universality class for a=1 characterized by a growth law of
the typical length L(t) ~ t^{1/z} with dynamical exponent z=6 as opposed to the
usual value z=4 which is recovered for a<1.Comment: RevTeX, 8 pages, 13 figures, to be published in Phys. Rev.
Marine 5-thiohistidines as protective molecules from skin damage
Introduction Marine environment is a great source of bioactive molecules, whose biological properties and applications are often used especially to prevent skin diseases
and aging caused by UVAÂexposure. Ovothiols are methylÂ5Âthiohistidines from marine invertebrates, bacteria, and microalgae, which protect cells from environmental
stressors. Recently, we have shown that, ovothiol, isolated from sea urchin eggs, exerts antiÂinflammatory and antioxidant activities on human endothelial cells, and
exhibits antifibrotic effect in an in vivo model of liver fibrosis.info:eu-repo/semantics/publishedVersio
Non perturbative renormalization group approach to surface growth
We present a recently introduced real space renormalization group (RG)
approach to the study of surface growth.
The method permits us to obtain the properties of the KPZ strong coupling
fixed point, which is not accessible to standard perturbative field theory
approaches. Using this method, and with the aid of small Monte Carlo
calculations for systems of linear size 2 and 4, we calculate the roughness
exponent in dimensions up to d=8. The results agree with the known numerical
values with good accuracy. Furthermore, the method permits us to predict the
absence of an upper critical dimension for KPZ contrarily to recent claims. The
RG scheme is applied to other growth models in different universality classes
and reproduces very well all the observed phenomenology and numerical results.
Intended as a sort of finite size scaling method, the new scheme may simplify
in some cases from a computational point of view the calculation of scaling
exponents of growth processes.Comment: Invited talk presented at the CCP1998 (Granada
- …