306 research outputs found
Localization-delocalization transition of a reaction-diffusion front near a semipermeable wall
The A+B --> C reaction-diffusion process is studied in a system where the
reagents are separated by a semipermeable wall. We use reaction-diffusion
equations to describe the process and to derive a scaling description for the
long-time behavior of the reaction front. Furthermore, we show that a critical
localization-delocalization transition takes place as a control parameter which
depends on the initial densities and on the diffusion constants is varied. The
transition is between a reaction front of finite width that is localized at the
wall and a front which is detached and moves away from the wall. At the
critical point, the reaction front remains at the wall but its width diverges
with time [as t^(1/6) in mean-field approximation].Comment: 7 pages, PS fil
Reaction-diffusion wave fronts on comblike structures
From the Hamilton-Jacobi formalism, an explicit expression for the speed of wave front propagation along the backbone of comblike structures is obtained. This expression, through the waiting-time distribution function, takes into account the number of sites and their distribution in the secondary branches. Our theoretical results are supported by numerical simulations of the reaction random-walk process on the structure. Finally, a more complex situation such as the Peano basin structure is also considered, both theoretically and numerically, exhibiting a good agreement too
Local Unitary Quantum Cellular Automata
In this paper we present a quantization of Cellular Automata. Our formalism
is based on a lattice of qudits, and an update rule consisting of local unitary
operators that commute with their own lattice translations. One purpose of this
model is to act as a theoretical model of quantum computation, similar to the
quantum circuit model. It is also shown to be an appropriate abstraction for
space-homogeneous quantum phenomena, such as quantum lattice gases, spin chains
and others. Some results that show the benefits of basing the model on local
unitary operators are shown: universality, strong connections to the circuit
model, simple implementation on quantum hardware, and a wealth of applications.Comment: To appear in Physical Review
Anti-inflammatory and analgesic activities: Chemical constituents of essential oils of Ocimum gratissimum, Eucalyptus citriodora and Cymbopogon giganteus inhibited lipoxygenase L-1 and cyclooxygenase of PGHS
The following studies report the inhibitory effect produced by chemical constituents of essential oils of three plants used in traditional medicine as anti-inflammatory and analgesic drugs, in vitro, on soybean lipoxygenase L-1 and cyclooxygenase function of prostaglandin H synthase (PGHS), the two enzymes involved in the production of mediators of inflammation. The essential oils were extracted from plants of three families: O. gratissimum (Labiatae), C. giganteus (Poaceae), and E. citriodora (Myrtaceae). Their chemical composition was established by GC/MS analyses. Among the three essential oils, one showed evident inhibition of L-1 with IC50 value of 72 µg/mL for Eucalyptus citriodora. Only one essential oil that of O. gratissimum inhibited the two enzymes, cyclooxygenase function of PGHS and lipoxygenase L-1, with an IC50 values, respectively, of 125 µg/mL and 144 µg/mL, whereas that of C. giganteus and E. citriodora, two of them had no effect on cyclooxygenase. KEY WORDS: Essential oils, Soybean lipoxygenase (L-1), Cyclooxygenase function ofprostaglandine H synthase-1, PGHS, O. gratissimum (Labiatae), C. giganteus (Poaceae), E. citriodora (Myrtaceae), Enantia chlorantha, Inhibition Bull. Chem. Soc. Ethiop. 2003, 17(2), 191-197
К вопросу борьбы с обледенением стальных тросов
The understanding of biological processes, e.g. related to cardio-vascular disease and treatment, can significantly be improved by numerical simulation. In this paper, we present an approach for a multiscale simulation environment, applied for the prediction of in-stent re-stenos is. Our focus is on the coupling of distributed, heterogeneous hardware to take into account the different requirements of the coupled sub-systems concerning computing power. For such a concept, which is an extension of the standard multiscale computing approach, we want to apply the term Distributed Multiscale Computing
Multi-species pair annihilation reactions
We consider diffusion-limited reactions A_i + A_j -> 0 (1 <= i < j <= q) in d
space dimensions. For q > 2 and d >= 2 we argue that the asymptotic density
decay for such mutual annihilation processes with equal rates and initial
densities is the same as for single-species pair annihilation A + A -> 0. In d
= 1, however, particle segregation occurs for all q < oo. The total density
decays according to a dependent power law, rho(t) ~ t^{-\alpha(q)}. Within
a simplified version of the model \alpha(q) = (q-1) / 2q can be determined
exactly. Our findings are supported through Monte Carlo simulations.Comment: 4 pages, revtex; two figures include
Foundations of distributed multiscale computing: Formalization, specification, and analysis
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Formation of Liesegang patterns: A spinodal decomposition scenario
Spinodal decomposition in the presence of a moving particle source is
proposed as a mechanism for the formation of Liesegang bands. This mechanism
yields a sequence of band positions x_n that obeys the spacing law
x_n~Q(1+p)^n. The dependence of the parameters p and Q on the initial
concentration of the reagents is determined and we find that the functional
form of p is in agreement with the experimentally observed Matalon-Packter law.Comment: RevTex, 4 pages, 4 eps figure
General technique of calculating drift velocity and diffusion coefficient in arbitrary periodic systems
We develop a practical method of computing the stationary drift velocity V
and the diffusion coefficient D of a particle (or a few particles) in a
periodic system with arbitrary transition rates. We solve this problem both in
a physically relevant continuous-time approach as well as for models with
discrete-time kinetics, which are often used in computer simulations. We show
that both approaches yield the same value of the drift, but the difference
between the diffusion coefficients obtained in each of them equals V*V/2.
Generalization to spaces of arbitrary dimension and several applications of the
method are also presented.Comment: 12 pages + 2 figures, RevTeX. Submitted to J. Phys. A: Math. Ge
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