Wilson renormalization of a reaction-diffusion process

Healthy and sick individuals (A and B particles) diffuse independently with diffusion constants D_A and D_B. Sick individuals upon encounter infect healthy ones (at rate k), but may also spontaneously recover (at rate 1/\tau). The propagation of the epidemic therefore couples to the fluctuations in the total population density. Global extinction occurs below a critical value \rho_{c} of the spatially averaged total density. The epidemic evolves as the diffusion--reaction--decay process A + B --> 2B, B --> A , for which we write down the field theory. The stationary state properties of this theory when D_A=D_B were obtained by Kree et al. The critical behavior for D_A<D_B is governed by a new fixed point. We calculate the critical exponents of the stationary state in an \eps expansion, carried out by Wilson renormalization, below the critical dimension d_{c}=4. We then go on to to obtain the critical initial time behavior at the extinction threshold, both for D_A=D_B and D_A<D_B. There is nonuniversal dependence on the initial particle distribution. The case D_A>D_B remains unsolved.Comment: 26 pages, LaTeX, 6 .eps figures include

Monitoring nanoparticle dissolution via fluorescence-colour shift

[La(OH)]2+[ICG]−2 and [La(OH)]2+2[PTC]4− inorganic–organic hybrid nanoparticles (IOH-NPs) with indocyanine green (ICG) and perylene-3,4,9,10-tetracarboxylate (PTC) as fluorescent dye anions are used for emission-based monitoring of the dissolution of nanoparticles. Whereas ICG shows a deep red emission in the solid [La(OH)]2+[ICG]−2 IOH-NPs, the emission of PTC in the solid [La(OH)]2+2[PTC]4− IOH-NPs is completely quenched due to π-stacking. After nanoparticle dissolution, the emission of freely dissolved ICG is weak, whereas freely dissolved PTC shows intense green emission. We report on the synthesis of IOH-NPs and nanoparticle characterization as well as on the fluorescence properties and how to avoid undesirable energy transfer between different fluorescent dyes. The emission shift from red (intact solid nanoparticles) to green (freely dissolved dye anions), indicating nanoparticle dissolution, is shown for aqueous systems and verified in vitro. Based on this first proof-of-the-concept, the IOH-NP marker system can be interesting to monitor nanoparticle dissolution in cells and tissues of small animals and to evaluate cell processes and/or drug-delivery strategies

X-Ray Scattering at FeCo(001) Surfaces and the Crossover between Ordinary and Normal Transitions

In a recent experiment by Krimmel et al. [PRL 78, 3880 (1997)], the critical behavior of FeCo near a (001) surface was studied by x-ray scattering. Here the experimental data are reanalyzed, taking into account recent theoretical results on order-parameter profiles in the crossover regime between ordinary and normal transitions. Excellent agreement between theoretical expectations and the experimental results is found.Comment: 9 pages, Latex, 1 PostScript figure, to be published in Phys.Rev.

Determinação de polifenóis como subsídio para seleção de variedades do Banco Ativo de Germoplasma de Uva.

A proposta do presente trabalho é analisar os teores de polifenóis bioativos em variedades do Banco Ativo de Germoplasma (acessos) e/ou novas variedades em fase de criação (seleções), através da técnica de Cromatografia Líquida de Alta Eficiência (HPLC)

Aging in ferromagnetic systems at criticality near four dimensions

We study the off-equilibrium response and correlation functions and the corresponding fluctuation-dissipation ratio for a purely dissipative relaxation of an O(N) symmetric vector model (Model A) below its upper critical dimension. The scaling behavior of these quantities is analyzed and the associated universal functions are determined at first order in epsilon expansion in the high-temperature phase and at criticality. A non trivial limit of the fluctuation-dissipation ratio is found in the aging regime.Comment: 11 pages, 1 figur

Zero mode in the time-dependent symmetry breaking of λϕ4\lambda\phi^4 theory

We apply the quartic exponential variational approximation to the symmetry breaking phenomena of scalar field in three and four dimensions. We calculate effective potential and effective action for the time-dependent system by separating the zero mode from other non-zero modes of the scalar field and treating the zero mode quantum mechanically. It is shown that the quantum mechanical properties of the zero mode play a non-trivial role in the symmetry breaking of the scalar $\lambda \phi^4$ theory.Comment: 10 pages, 3 figure

Caracterizacao de acessos de batata-doce atraves de danos causados nas raizes por crisomelideos e pela broca da raiz.

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