Orientador: Jose Inacio Cotrim Vasconcellos / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-16T17:00:25Z (GMT). No. of bitstreams: 1 Silva_AntonioJoseRoqueda_M.pdf: 2799322 bytes, checksum: 205183224122a005e3f807b8c6ac1e56 (MD5) Previous issue date: 1989 / Resumo: Neste trabalho, estudamos o processo da formação de padrões espaciais como soluções de equação não-lineares, e, no caso, especificamente, as estruturas conhecidas como, Aneis de Liesegang. Em tal sistema os padrões são formados pela prescipitação descontinua do produto de uma reação química. Para sua descrição, utilizamos um conjunto de equações diferenciais do tipo reação-difusão, onde os termos não-lineares da reação química são substituidos por expressões que representem a precipitação. Para tanto, utilizamos equações fenomenologicas derivadas dos modelos clássicos para transições de primeira ordem. Após a escolha deste sistema, analisamos como suas soluções são afetadas pela variação das concentrações iniciais dos reagentes. O modelo foi aplicado para a prescipitação do iodeto de chumbo (PbI2), compreendendo três tipos de cálculos. No primeiro a concentração inicial do I- é fixada e variamos a do Pb2+ desde regiões onde não há formação de Aneis até aquela em que se forma um Anel, obtendo as concentrações [Pb2+]c onde as soluções mudam de comportamento. Repetindo o cálculo para valores distintos de [I-]. construimos uma. curva com os pontos ([I- ],[Pb2+]). Para os outros dois tipos de cálculos definimos a dif'erença D =[I-]/2-[Pb2+] e a razão S+1= [Pb2+][I-]2/Kpe, onde Kpe é o produto de solubilidade e as concentrações são as iniciais. Num dos cálculos, mantivemos D constante e variamos S+1, enquanto, no outro, o oposto é feito. Com este procedimento, mostramos, pela primeira vez. que um modelo como o descrito acima é capaz de reproduzir qualitativamente resultados experimentais / Abstract: We study in the present work the formation of spatial patterns as particular solutions of non-linear equations. We are interested in the specific process known as Liesegang Rings. In this system the patterns are formed by the discontinuos precipitation of a chemical reaction product. In order to model it, a system of reaction-diffusion differential equations is used, where terms describing the precipitation are used in place of the reactions terms. The precipitation is described via a first-order phase-transition classical theory equations. We are interested in the behavior of the solutions when we vary the initial concentrations of the reagents. Using the salt lead iodate (PbI2), we performed three types of calculations. In the first one, we fix the I - initial concentration and vary the Pb2+ one from regions where no rings are formed to regions where just one ring appears. We obtain in this way the concentration [Pb2+]c responsible for the change in the solution behavior. Repeating this procedure for different I - initial concentrations we build a curve for the points C[I-].[Pb2+]c). The difference D =[I-]/2-[Pb2+) and the quotient S+1=[Pb2+][I-]2/Kps, where Kps is the solubility product and all are initial, concentrations are defined for the last two numerical simulation. In the first one D is kept constant and S+1 is varied the opposit procedure being done in the other calculation. Therefore, we shown, for the first time, that a model like ours can provide results agreement at least qualitatively, with the experimental ones / Mestrado / Física / Mestre em Física

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My research has focused on the precipitation of iron minerals, mostly oxides and hydroxides, in aqueous systems across steep pH and Eh gradients. Unlike most work in this area, which involves loose precipitates filtered out of solutions, I have focused on precipitated aggregates and, more specifically, on those that are self-organized into dis-crete structures or patterns. This topic is actually quite narrow because such types of natu-ral material organization are rare within the geochemical realm compared with the mor-phological richness of crystals, not to mention the phantasmagoria of life.My investigation of iron-based examples has included three types of physical sys-tems: 1) growth of tubular structures around bubbles coming off a charged cathode in a free solution where convection dominates; 2) development of Liesegang patterns within gelled solutions due to reactions dominated by diffusion; and 3) formation of a cement-ing matrix within the aqueous interface between particles of silica. The third case in-volves physical characteristics of the first two in that it is primarily a tightly packed, dif-fusion-limited process, but at least initially the generation of gases can create mechani-cally driven flows through the interstitial spaces.All three systems and studies are inextricably related for both tubular ('vermi-form') structures and Liesegang patterns are commonly found in natural iron-cemented sediments such as massive laterite, ironstone deposits, and banded iron formations. They are also found on a much smaller scale within discrete 'concretions' and represent the two poles of the gradient between convection-based and diffusion-based systems. As Seilacher (2001) states concerning concretions, "the distribution and precipitation of dis-solved constituents, such iron and manganese, proceeds in two radically different mor-phospaces, which are typified by dendrites [and I would include tubes and other linear growth] on the one hand and Liesegang rings on the other." Both have been observed in my lab creations with surprising frequency and tenacity even in systems thought to be in-hibitory.

The aim of this study is to elucidate factors that effect growth of Sarcina lutea and Bacillus subtilis, exposed to the growth inhibitor SDS (Sodiumdodecylsulfat). Agar diffusion experiments revealed repeated, concentric zones of inhibition and stimulation upon exposure to Sodiumdodecylsulphate or to Amoxicillin. Temperature, nutrient concentration and inhibitor concentration were controlled. Formation of successively repeated zones of inhibition, stimulation, inhibition and stimulation is discussed: •The extension of the primary inhibition zone is due to the concentration of applied Sodium dodecyl sulphate.•Immediately outside the primary inhibition zone the bacteria have access to diffusing nutrients that have not been consumed in the primary inhabitation zone.•In zones of dense bacterial growth the bacteria may produce inhibiting substances, affecting growth of bacteria in adjacent zones.•In zones of dense bacterial growth the nutrients will soon become depleted, thus affecting bacteria in adjacent zones.