A DISCRETIZATION SCHEME FOR AN ONE-DIMENSIONAL REACTION-DIFFUSION EQUATION WITH DELAY AND ITS DYNAMICS

The goal of this paper is to present an approximation scheme for a reaction-diffusion equation with finite delay, which has been used as a model to study the evolution of a population with density distribution u, in such a way that the resulting finite dimensional ordinary differential system contains the same asymptotic dynamics as the reaction-diffusion equation.

Self-assembling of phenothiazine compounds investigated by small-angle X-ray scattering and electron paramagnetic resonance spectroscopy

Small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) have been carried out to investigate the structure of the self-aggregates of two phenothiazine drugs, chlorpromazine (CPZ) and trifluoperazine (TFP), in aqueous solution. In the SAXS studies, drug solutions of 20 and 60 mM, at pH 4.0 and 7.0, were investigated and the best data fittings were achieved assuming several different particle form factors with a homogeneous electron density distribution in respect to the water environment. Because of the limitation of scattering intensity in the q range above 0.15 angstrom(-1), precise determination of the aggregate shape was not possible and all of the tested models for ellipsoids, cylinders, or parallelepipeds fitted the experimental data equally well. The SAXS data allows inferring, however, that CPZ molecules might self-assemble in a basis set of an orthorhombic cell, remaining as nanocrystallites in solution. Such nanocrystals are composed of a small number of unit cells (up to 10, in c-direction), with CPZ aggregation numbers of 60-80. EPR spectra of 5- and 16-doxyl stearic acids bound to the aggregates were analyzed through simulation, and the dynamic and magnetic parameters were obtained. The phenothiazine concentration in EPR experiments was in the range of 5-60 mM. Critical aggregation concentration of TFP is lower than that for CPZ, consistent with a higher hydrophobicity of TFP. At acidic pH 4.0 a significant residual motion of the nitroxide relative to the aggregate is observed, and the EPR spectra and corresponding parameters are similar to those reported for aqueous surfactant micelles. However, at pH 6.5 a significant motional restriction is observed, and the nitroxide rotational correlation times correlate very well with those estimated for the whole aggregated particle from SAXS data. This implies that the aggregate is densely packed at this pH and that the nitroxide is tightly bound to it producing a strongly immobilized EPR spectrum. Besides that, at pH 6.5 the differences in motional restriction observed between 5- and 16-DSA are small, which is different from that observed for aqueous surfactant micelles.

Formation of soliton trains in Bose-Einstein condensates as a nonlinear Fresnel diffraction of matter waves

The problem of generation of atomic soliton trains in elongated Bose-Einstein condensates is considered in framework of Whitham theory of modulations of nonlinear waves. Complete analytical solution is presented for the case when the initial density distribution has sharp enough boundaries. In this case the process of soliton train formation can be viewed as a nonlinear Fresnel diffraction of matter waves. Theoretical predictions are compared with results of numerical simulations of one- and three-dimensional Gross-Pitaevskii equation and with experimental data on formation of Bose-Einstein bright solitons in cigar-shaped traps. (C) 2003 Elsevier B.V. All rights reserved.

Dipolar Bose-Einstein condensate in a ring or in a shell

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Competition between local potentials and attractive particle-particle interactions in superlattices

Naturally occuring or man-made systems displaying periodic spatial modulations of their properties on a nanoscale constitute superlattices. Such modulated structures are important both as prototypes of simple nanotechnological devices and as particular examples of emerging spatial inhomogeneity in interacting many-electron systems. Here we investigate the effect different types of modulation of the system parameters have on the ground-state energy and the charge-density distribution of the system. The superlattices are described by the inhomogeneous attractive Hubbard model, and the calculations are performed by density-functional and density-matrix renormalization group techniques. We find that modulations in local electric potentials are much more effective in shaping the system's properties than modulations in the attractive on-site interaction. This is the same conclusion we previously [M.F. Silva, N.A. Lima, A.L. Malvezzi, K. Capelle, Phys. Rev. B 71 (2005) 125130.] obtained for repulsive interactions, suggesting that it is not an artifact of a specific state, but a general property of modulated structures. (c) 2007 Elsevier Ltd. All rights reserved.

AN INVESTIGATION OF THE ELECTRONIC-STRUCTURE OF THE ANTITUMOR DRUG ELLIPTICINE AND ITS DERIVATIVES .1. GEOMETRICAL AM1 STUDY

Ellipticine and its derivatives are a class of molecules that show antitumor and cytotoxic activity with a multimodal mechanism of action. In this paper we report a preliminary Austin Method One (AM1) study of ellipticine and some molecules derived from it. We have observed a relationship between charge density distribution and biological selectivity. A mechanism that could improve cytotoxic activity is proposed.

Changes in coral reef communities and an associated reef fish species, Cephalopholis cruentata (Lacepede), after 30 years on Curacao (Netherlands Antilles)

Using the same methodology and identical sites, we repeat a study dating from 1973 and quantify cover of hard coral species, soft corals, sponges, hard substratum and soft substratum, and density of a commercially important reef fish species, the graysby Cephalopholis cruentata, along a depth-gradient of 3-36 m oil the coral reefs of Curacao. The objective was to determine the multi-decade change in benthic coral reef cover and structural complexity, and their effect oil densities of an associated reef fish species. Total hard coral cover decreased on average from 52% in 1973 to 22% in 2003, representing a relative decline of 58%. During this time span, the cover of hard substratum increased considerably (from 11 to 58%), as did that of soft corals (from 0.1 to 2.2%), whereas the cover of sponges showed no significant change. Relative decline of hard coral cover and of reef complexity was greatest in shallow waters (near the coast), which is indicative of a combination of anthropogenic influences from shore and recent storm damage. Cover of main reef builder coral species (Agaricia spp., Siderastrea siderea, Montastrea annularis) decreased more than that of other species, and resulted in a significant decrease in reef complexity. Although density of C. cruentata was highly correlated to cover of Montastrea and Agaricia in 1973, the loss of coral cover did not show any effect on the total density of C. cruentata in 2003. However, C. cruentata showed a clear shift in density distribution from shallow water in 1973 to deep water in 2003. It call be concluded that the reefs of Curacao have degraded considerably in the last three decades, but that this has had no major effect on the population size of one commercially important coral-associated fish species.

Two dimensional computer simulation of plasma immersion ion implantation

The biggest advantage of plasma immersion ion implantation (PIII) is the capability of treating objects with irregular geometry without complex manipulation of the target holder. The effectiveness of this approach relies on the uniformity of the incident ion dose. Unfortunately, perfect dose uniformity is usually difficult to achieve when treating samples of complex shape. The problems arise from the non-uniform plasma density and expansion of plasma sheath. A particle-in-cell computer simulation is used to study the time-dependent evolution of the plasma sheath surrounding two-dimensional objects during process of plasma immersion ion implantation. Before starting the implantation phase, steady-state nitrogen plasma is established inside the simulation volume by using ionization of gas precursor with primary electrons. The plasma self-consistently evolves to a non-uniform density distribution, which is used as initial density distribution for the implantation phase. As a result, we can obtain a more realistic description of the plasma sheath expansion and dynamics. Ion current density on the target, average impact energy, and trajectories of the implanted ions were calculated for three geometrical shapes. Large deviations from the uniform dose distribution have been observed for targets with irregular shapes. In addition, effect of secondary electron emission has been included in our simulation and no qualitative modifications to the sheath dynamics have been noticed. However, the energetic secondary electrons change drastically the plasma net balance and also pose significant X-ray hazard. Finally, an axial magnetic field has been added to the calculations and the possibility for magnetic insulation of secondary electrons has been proven.

Propriedades físicas e indicador de qualidade de um latossolo vermelho submetido a diferentes sistemas de uso e manejo

The conventional system for soil management and preparation has the intensive mechanization as its basic principle and that changes soil properties, especially physical ones, faster and significantly. This study aimed to obtain and compare physical properties such as distribution of particle sizes, density, distribution of pore sizes, curves of water retention and degradation index of a Red Latosol, under intensive cultivation and no-cultivation for six years. Soil samples were collected at depths of 0.1, 0.2, 0.3, 0.4, 0.6, 0.8 and 1.0 m. There was a clay increment as a result of cultivated soil increase. The no-till soil density decreased as depth increased; however, in the arable layer (0.3 m) of the cultivated soil, the opposite was verified. The largest volume of pores was verified in the cultivated soil, especially in the superficial layers. In the smallest applied tension (0.001 MPa), the cultivated soil retained more water; however, starting from 0.033 MPa, the highest humidity values occurred in the no-till soil. The highest degradation index was observed at a depth of 0.1 m in no-till soil. However, that value was superior (0.020) to what is physically considered very poor soil.

Avaliação da distribuição da densidade em MDF a partir da técnica da onda de ultra-som

The goal of this research was to determine the density distribution in medium density fiberboard (MDF), manufactured with polyurethane derived from castor oil using, ultrasonic wave technique. The equipment used in this test is Steinkamp BP7 with plan and exponential transducers, both with 45 kHz frequencies, located in several zones on the plate in order to determine wave ultrasonic velocity. The Pinus caribaea and Eucalyptus grandis fiberboard were manufactured in the quality control and products development laboratory of Duratex with 500 mm long, 500 mm large, 8 and 15 mm of thickness. Three MDF for each fiber specimen and thickness were fabricated, totalizing twelve plates tested. The MDF were produced with 5% polyurethane addition, in temperature of 160°C, tension press of 53 bars and addition of moisture content of 12%. For determination of fiberboard density, samples were extracted from the same zones where the wave ultrasonic velocity was determined. In this case, DAX-Ray equipment was used. Statistical analysis shows good agreement with wave ultrasonic velocity and the density profile, validating the application of non-destructive technique in order to determine the density profile of MDF's.

Non-conventional applications of computerized tomography: Analysis of solid dosage forms produced by pharmaceutical industry

X-ray computed tomography (CT) refers to the cross-sectional imaging of an object measuring the transmitted radiation at different directions. In this work, we describe a non-conventional application of computerized tomography: visualization and improvements in the understanding of some internal structural features of solid dosage forms. A micro-CT X-ray scanner, with a minimum resolution of 30 μm was used to characterize some pharmaceutical tablets, granules, controlled-release osmotic tablet and liquid-filled soft-gelatin capsules. The analysis presented in this work are essentially qualitative, but quantitative parameters, such as porosity, density distribution, tablets dimensions, etc. could also be obtained using the related CT techniques. © 2010 American Institute of Physics.

Stability and collapse of fermions in a binary dipolar boson-fermion 164Dy-161Dy mixture

We suggest a time-dependent mean-field hydrodynamic model for a binary dipolar boson-fermion mixture to study the stability and collapse of fermions in the 164Dy-161Dy mixture. The condition of stability of the dipolar mixture is illustrated in terms of phase diagrams. A collapse is induced in a disk-shaped stable binary mixture by jumping the interspecies contact interaction from repulsive to attractive by the Feshbach resonance technique. The subsequent dynamics is studied by solving the time-dependent mean-field model including three-body loss due to molecule formation in boson-fermion and boson-boson channels. Collapse and fragmentation in the fermions after subsequent explosions are illustrated. The anisotropic dipolar interaction leads to anisotropic fermionic density distribution during collapse. This study is carried out in three-dimensional space using realistic values of dipolar and contact interactions. © 2013 American Physical Society.

Recuperação de perfis atmosféricos a partir de ocultação GPS: fundamentos, implementação e análise de resultados

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Inomogeneidades estruturais em amostras nanoscópicas de supercondutores de alta temperatura crítica

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Atributos físicos e químicos de um latossolo vermelho cultivado com cana-de-açúcar, com a conservação do palhiço e aplicações de torta de filtro e vinhaça

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)