Dynamic behavior of the voter model on fractals: logarithmic-periodic oscillations as a signature of time discrete scale invariance

The understanding of the dynamic behavior of the voter model, in low-dimensional media, is a very interesting open topic. In fact, due to the absence of the interfacial tension, only the interfacial noise becomes relevant during the coarsening processes, bringing the possibility of studing a new physical process. In this way, it is known that below the upper critical dimension (d < 2) and starting from a disordered configuration, a critical coarsening process takes place, and the density of interfaces, ρ(t), decays as a power-law function of time. Recently published numerical studies performed on low-dimensional fractal substrates (d _F < 2) [Physica A 362, 338 (2006)] show the existence of logarithmic-periodic oscillations superimposed on the standard ρ(t) power-law behavior, but the origin of those oscillations remains unclear. In this work, we provide an explanation of these oscillations in terms of the interplay between the dynamics of the voter model and the discrete scale invariance of the underlying fractal substrate. Our arguments are verified by means of extensive numerical simulations carried out on different fractal substrates.     

Settling the question of optimum concentration and methodology used for adding an antioxidant to PS/PP polyblend

The method of addition of antioxidants to immiscible polymer blends can influence the end use performance of a polyblend artifact. This work is aimed at determining the most suitable procedure for adding antioxidants to a polystyrene (PS)‐polypropylene (PP) blend (80/20), and its optimum concentration using three different methodologies. The effects of UV exposure on mechanical properties of the polyblends were examined. Results show that both the method of addition and concentration of the antioxidant do not alter mechanical properties, nevertheless, a concentration of 0.1% w/w is recommended.     

Diffusion on two-dimensional percolation clusters with multifractal jump probabilities

By means of Monte Carlo simulations we studied the properties of diffusion limited recombination reactions (DLRR's) and random walks on two dimensional incipient percolation clusters with multifractal jump probabilities. We claim that, for these kind of geometric and energetic heterogeneous substrata, the long time behavior of the particle density in a DLRR is determined by a random walk exponent. It is also suggested that the exploration of a random walk is compact. It is considered a general case of intersection ind euclidean dimension of a random fractal of dimension D_F and a multifractal distribution of probabilities of dimensionsD _q (q real), where the two dimensional incipient percolation clusters with multifractal jump probabilities are particular examples. We argue that the object formed by this intersection is a multifractal of dimensionsD' _q =D _q +D _F -d, for a finite interval ofq.     

Correlation between roughness and porosity in rocks

The porosity of rocks is a very important parameter in the determination of the performance of oil wells. Optical methods allow us to study surface roughness and different materials that have surface properties with random characteristics.Therefore, we have extended these applications to porosity analysis. In our method, we have used the speckle produced by the scattered light from a porous rock, illuminated by a laser beam, and found a linear relationship between the decorrelation of the speckle intensity distribution and the porosity magnitude. In this paper we present the results for samples extracted from oil wells in Argentina.     

Determination of drug-macromolecule binding parameters by numerical analysis

A method is described for calculating the binding parameters of a drug to a macromolecule from data obtained by indirect techniques, such as spectroscopy, assuming the existence of only one class of binding sites. A critical evaluation of the performance of the method is presented, showing that the errors which previously reported methods may produce are avoided. Some examples that make use of experimental data determined for phenylbutazone and oxyphenbutazone by means of UV difference spectroscopy are given.     

On the Griffiths group of the cubic sevenfold

Partially supported by Science Project Geometry of Algebraic Varieties, n. 0-198-SC1, and by fundings from M.U.R.S.T. and G.N.S.A.G.A. (C.N.R.), Italy     

Intermittent compression of N-alkyl-N,N-dimethylamine N-oxides encapsulated in a container with bis[2]catenane topology

Abstract

We report the encapsulation of a homologous series of N-alkyl-N,N-dimethylamine N-oxides in a molecular container with bis[2]catenane topology. N-oxides with short alkyl chains are co-encapsulated with one solvent molecule. Elongation of the alkyl chain from R = methyl to pentyl produced the progressive compression of the guest. The hexyl N-oxide reduces its compression by being singly encapsulated. Longer N-oxides (R = octyl to decyl) had to fold to adapt to the capsule’s dimensions and also experience a progressive compression. The mechanically interlocked nature of the container and the polar functionalisation of its cavity are responsible for the assembly of encapsulation complexes in solution displaying high packing coefficients (0.65–0.70). The high energy conformations adopted by the alkyl chains of the bound N-oxides are deduced from NMR experiments and molecular modelling studies.     

The influence of a quality system according to ISO/IEC 17025 on the performance of Brazilian laboratories in proficiency testing in the environmental area

This paper presents a performance analysis of laboratories in proficiency testing (PT) with the main objective of evaluating whether having accreditation to ISO/IEC 17025 or not having an implemented quality system has an influence on the performance of these laboratories. This research was conducted with data from an accredited PT scheme of physical–chemical water analyses. Nine metals were considered in the analysis, with a total of 896 results. The performance indicator was z-score. The proposed analysis was conducted through statistical methods of analysis of variance, Dunnett’s test, Chi-square and cross-tabulation. It was verified that there is a significant difference between the performance of accredited laboratories, recognised laboratories, and laboratories that do not have an implemented quality system. It was established that an accredited or recognised quality system has a positive influence on the laboratory performance, resulting in a lower z-score (in module) and in a larger percentage of satisfactory results.