Probing Yukawian gravitational potential by numerical simulations. I. Changing N-body codes

In the weak field limit general relativity reduces, as is well known, to the Newtonian gravitation. Alternative theories of gravity, however, do not necessarily reduce to Newtonian gravitation; some of them, for example, reduce to Yukawa-like potentials instead of the Newtonian potential. Since the Newtonian gravitation is largely used to model with success the structures of the universe, such as for example galaxies and clusters of galaxies, a way to probe and constrain alternative theories, in the weak field limit, is to apply them to model the structures of the universe. In the present study, we consider how to probe Yukawa-like potentials using N-body numerical simulations.     

An analytic approach to the measurement of nestedness in bipartite networks

We present an index that measures the nestedness pattern of bipartite networks, a problem that arises in theoretical ecology. Our measure is derived using the sum of distances of the occupied elements in the incidence matrix of the network. This index quantifies directly the deviation of a given matrix from the nested pattern. In the simplest case the distance of the matrix element a_i,j is d_i,j=i+j, the Manhattan distance. A generic distance is obtained as d_i,j=(i^χ+j^χ)^1/χ. The nestedness index is defined by ν=1−τ, where τ is the “temperature” of the matrix. We construct the temperature index using two benchmarks: the distance of the complete nested matrix that corresponds to zero temperature and the distance of the average random matrix where the temperature is defined as one. We discuss an important feature of the problem: matrix occupancy ρ. We address this question using a metric index χ that adjusts for matrix occupancy.     

Thermoluminescence response of the larimar rocks

The aim of this paper is to evaluate the thermoluminescent (TL) response of a larimar, a variety of pectolite (NaCa₂Si₃O₈[OH]). It is a blue pectolite only found on the terrestrial crust of the province of Barahona, in the south-western region of the Dominican Republic. The larimar rock used in this study, presented a light-blue color with brown areas. X-ray powder diffractometry (XRD), showed that the light-blue portion of the rock is composed essentially by pectolite and the brown portion is composed by a mixture of minerals. Aliquots of 5 mg of light-blue portions were irradiated with gamma rays with doses from 10 to 10⁴ Gy and the TL glow curves were obtained from 50 to 400 °C. The glow curve showed a broad peak around 150 °C and a peak near 280 °C. Different pre-heat condition were used to remove the broad peak. The TL emission of the main peak appeared in the region of 580 nm. The TL response of the main peak showed a linear behavior up to 2500 Gy and a sub-linear behavior above this dose value. Studies of the 30 day fading effects in TL signal using a pre-heating temperature around 180 °C during 15 min were carried out and fading near 25% was observed.     

A generalization of Lee codes

Motivated by a problem in computer architecture we introduce a notion of the perfect distance-dominating set (PDDS) in a graph. PDDSs constitute a generalization of perfect Lee codes, diameter perfect codes, as well as other codes and dominating sets. In this paper we initiate a systematic study of PDDSs. PDDSs related to the application will be constructed and the non-existence of some PDDSs will be shown. In addition, an extension of the long-standing Golomb–Welch conjecture, in terms of PDDS, will be stated. We note that all constructed PDDSs are lattice-like which is a very important feature from the practical point of view as in this case decoding algorithms tend to be much simpler.     

Pyrolysis of atmospheric residue of petroleum (ATR) using AlSBA-15 mesoporous material by TG and Py-GC/MS

The mesoporous material AlSBA-15 with Si/Al molar ratio of 25 was synthesized by the hydrothermal method and characterized by X-ray diffraction and nitrogen adsorption. This is a promising material in the field of catalysis, particularly for petroleum refining, since their mesopores facilitate the accessibility of large hydrocarbon molecules to the active sites of AlSBA-15, producing light hydrocarbons. In order to evaluating the catalytic activity of AlSBA-15, a sample of ca. 10 % in mass of this solid was physically mixed with atmospheric residue of petroleum (ATR) and heated in a thermobalance from room temperature up to 900 °C, under nitrogen atmosphere. From TG curves, it was observed a reduction in the onset temperature, when AlSBA-15 was used as catalyst for the degradation process of ATR. The kinetic model proposed by Ozawa–Flynn–Wall yielded some kinetic parameters to determine the apparent activation energy of the degradation, evidencing the efficiency of the mesoporous material, since there was a decrease in the activation energy for the catalytic degradation. The ATR alone and mixed with AlSBA-15 was also heated in a pyrolysis reactor coupled to a gas chromatograph and mass spectrometer (Py-GC/MS). From the chromatograms, it was observed an increase in the yield of hydrocarbons in the range of gasoline and diesel derived from the catalytic process. These results are due to the combination of the mesoporosity and acidity of the AlSBA-15 for application in the process of pyrolysis of hydrocarbons molecules constituents of the ATR.     

Existence of solutions and optimal control for a model of tissue invasion by solid tumours

In this paper we study the distributed optimal control problem for the two-dimensional mathematical model of cancer invasion. Existence of optimal state-control and stability is proved and an optimality system is derived.     

Marine sponge melanin: a new source of an old biopolymer

Various types of melanin have already been found in the majority of organisms, being this biopolymer considered as one of the major pigments present in nature. The presence of this pigment in marine sponges (Phylum Porifera, one of the simplest multicellular organisms) was postulated, but never characterized. In this context this work aims the extraction and characterization of a dark pigment observed in four different marine sponges species (Erylus mamillaris, Erylus discophorus var. deficiens, Pachymatisma johnstonia, Dercitus bucklandi). Characterization of the extracted biopolymer was performed using solid state analytical techniques, due to the characteristic non-solubility of melanin. Therefore, characterization techniques like SEM–EDS, IR, UV–vis, MALDI-MS, elemental analysis and X-ray powder diffraction (XRD) were used to identify the biopolymer. The results showed that the extracted material was obtained with high purity, being identified as melanin. The results also emphasize a large structure variability present in this pigment, showing different structure arrangements and composition depending on its source, which influences the UV behaviour. The structural characterization of this class of pigments is fundamental, allowing a better understanding of melanin properties.