Determination of Dipyrone in pharmaceutical preparations based on the chemiluminescent reaction of the quinolinic hydrazide-H2O2-vanadium (IV) system and flow injection analysis

A rapid, economic and sensitive chemiluminescent method involving flow-injection analysis was developed for the determination of dipyrone in pharmaceutical preparations. The method is based on the chemiluminescent reaction between quinolinic hydrazide and hydrogen peroxide in a strongly alkaline medium, in which vanadium(IV) acts as a catalyst. Principal chemical and physical variables involved in the flow-injection system were optimized using a modified simplex method. The variations in the quantum yield observed when dipyrone was present in the reaction medium were used to determine the concentration of this compound. The proposed method requires no preconcentration steps and reliably quantifies dipyrone over the linear range 1–50 µg/mL. In addition, a sample throughput of 85 samples/h is possible. Copyright © 2011 John Wiley & Sons, Ltd.

Evolución del conocimiento del hormigón estructural hasta 1973

Esta tesis analiza los criterios con que fueron proyectadas y construidas las estructuras de hormigón hasta 1973, fecha coincidente con la Instrucción EH-73, que en contenido, formato y planteamiento, consagró la utilización de los criterios modernamente utilizados hasta ahora. Es heredera, además, de las CEB 1970. Esos años marcan el cambio de planteamiento desde la Teoría Clásica hacia los Estados Límite. Los objetivos perseguidos son, sintéticamente: 1) Cubrir un vacío patente en el estudio de la evolución del conocimiento. Hay tratados sobre la historia del hormigón que cubren de manera muy completa el relato de personajes y realizaciones, pero no, al menos de manera suficiente, la evolución del conocimiento. 2) Servir de ayuda a los técnicos de hoy para entender configuraciones estructurales, geometrías, disposiciones de armado, formatos de seguridad, etc, utilizados en el pasado, lo que servirá para la redacción más fundada de dictámenes preliminares sobre estructuras existentes. 3) Ser referencia para la realización de estudios de valoración de la capacidad resistente de construcciones existentes, constituyendo la base de un documento pre-normativo orientado en esa dirección. En efecto, esta tesis pretende ser una ayuda para los ingenieros de hoy que se enfrentan a la necesidad de conservar y reparar estructuras de hormigón armado que forman parte del patrimonio heredado. La gran mayoría de las estructuras, fueron construidas hace más de 40 años, por lo que es preciso conocer los criterios que marcaron su diseño, su cálculo y su construcción. Pretende determinar cuáles eran los límites de agotamiento y por tanto de seguridad, de estructuras dimensionadas con criterios de antaño, analizadas por la metodología de cálculo actual. De este modo, se podrá determinar el resguardo existente “real” de las estructuras dimensionadas y calculadas con criterios “distintos” a los actuales. Conocer el comportamiento de las estructuras construidas con criterios de la Teoría Clásica, según los criterios actuales, permitirá al ingeniero de hoy tratar de la forma más adecuada el abanico de necesidades que se puedan presentar en una estructura existente. Este trabajo se centra en la evolución del conocimiento por lo que no se encuentran incluidos los procesos constructivos. En lo relativo a los criterios de proyecto, hasta mediados del siglo XX, éstos se veían muy influidos por los ensayos y trabajos de autor consiguientes, en los que se basaban los reglamentos de algunos países. Era el caso del reglamento prusiano de 1904, de la Orden Circular francesa de 1906, del Congreso de Lieja de 1930. A partir de la segunda mitad del siglo XX, destacan las aportaciones de ingenieros españoles como es el caso de Alfredo Páez Balaca, Eduardo Torroja y Pedro Jiménez Montoya, entre otros, que permitieron el avance de los criterios de cálculo y de seguridad de las estructuras de hormigón, hasta los que se conocen hoy. El criterio rector del proyecto de las estructuras de hormigón se fundó, como es sabido, en los postulados de la Teoría Clásica, en particular en el “momento crítico”, aquel para el que hormigón y acero alcanzan sus tensiones admisibles y, por tanto, asegura el máximo aprovechamiento de los materiales y sin pretenderlo conscientemente, la máxima ductilidad. Si el momento solicitante es mayor que el crítico, se dispone de armadura en compresión. Tras el estudio de muchas de las estructuras existentes de la época por el autor de esta tesis, incluyendo entre ellas las Colecciones Oficiales de Puentes de Juan Manuel de Zafra, Eugenio Ribera y Carlos Fernández Casado, se concluye que la definición geométrica de las mismas no se corresponde exactamente con la resultante del momento crítico, dado que como ahora resultaba necesario armonizar los criterios de armado a nivel sección con la organización de la ferralla a lo largo de los diferentes elementos estructurales. Los parámetros de cálculo, resistencias de los materiales y formatos de seguridad, fueron evolucionando con los años. Se fueron conociendo mejor las prestaciones de los materiales, se fue enriqueciendo la experiencia de los propios procesos constructivos y, en menor medida, de las acciones solicitantes y, consiguientemente, acotándose las incertidumbres asociadas lo cual permitió ir ajustando los coeficientes de seguridad a emplear en el cálculo. Por ejemplo, para el hormigón se empleaba un coeficiente de seguridad igual a 4 a finales del siglo XIX, que evolucionó a 3,57 tras la publicación de la Orden Circular francesa de 1906, y a 3, tras la Instrucción española de 1939. En el caso del acero, al ser un material bastante más conocido por cuanto se había utilizado muchísimo previamente, el coeficiente de seguridad permaneció casi constante a lo largo de los años, con un valor igual a 2. Otra de las causas de la evolución de los parámetros de cálculo fue el mejor conocimiento del comportamiento de las estructuras merced a la vasta tarea de planificación y ejecución de ensayos, con los estudios teóricos consiguientes, realizados por numerosos autores, principalmente austríacos y alemanes, pero también norteamericanos y franceses. En cuanto a los criterios de cálculo, puede sorprender al técnico de hoy el conocimiento que tenían del comportamiento del hormigón desde los primeros años del empleo del mismo. Sabían del comportamiento no lineal del hormigón, pero limitaban su trabajo a un rango de tensióndeformación lineal porque eso aseguraba una previsión del comportamiento estructural conforme a las hipótesis de la Elasticidad Lineal y de la Resistencia de Materiales, muy bien conocidas a principios del s. XX (no así sucedía con la teoría de la Plasticidad, aún sin formular, aunque estaba implícita en los planteamientos algunos ingenieros especializados en estructuras de fábrica (piedra o ladrillo) y metálicas. Además, eso permitía independizar un tanto el proyecto de los valores de las resistencias reales de los materiales, lo que liberaba de la necesidad de llevar a cabo ensayos que, en la práctica, apenas se podían hacer debido a la escasez de los laboratorios. Tampoco disponían de programas informáticos ni de ninguna de las facilidades de las que hoy se tienen, que les permitiera hacer trabajar al hormigón en un rango no lineal. Así, sabia y prudentemente, limitaban las tensiones y deformaciones del material a un rango conocido. El modus operandi seguido para la elaboración de esta tesis, ha sido el siguiente: -Estudio documental: se han estudiado documentos de autor, recomendaciones y normativa generada en este ámbito, tanto en España como con carácter internacional, de manera sistemática con arreglo al índice del documento. En este proceso, se han detectado lagunas del conocimiento (y su afección a la seguridad estructural, en su caso) y se han identificado las diferencias con los procedimientos de hoy. También ha sido necesario adaptar la notación y terminología de la época a los criterios actuales, lo que ha supuesto una dificultad añadida. -Desarrollo del documento: A partir del estudio previo se han ido desarrollando los siguientes documentos, que conforman el contenido de la tesis: o Personajes e instituciones relevantes por sus aportaciones al conocimiento de las estructuras de hormigón (investigación, normativa, docencia). o Caracterización de las propiedades mecánicas de los materiales (hormigón y armaduras), en relación a sus resistencias, diagramas tensión-deformación, módulos de deformación, diagramas momento-curvatura, etc. Se incluye aquí la caracterización clásica de los hormigones, la geometría y naturaleza de las armaduras, etc. o Formatos de seguridad: Se trata de un complejo capítulo del que se pretende extraer la información suficiente que permita a los técnicos de hoy entender los criterios utilizados entonces y compararlos con los actuales. o Estudio de secciones y piezas sometidas a tensiones normales y tangenciales: Se trata de presentar la evolución en el tratamiento de la flexión simple y compuesta, del cortante, del rasante, torsión, etc. Se tratan también en esta parte del estudio aspectos que, no siendo de preocupación directa de los técnicos de antaño (fisuración y deformaciones), tienen hoy mayor importancia frente a cambios de usos y condiciones de durabilidad. o Detalles de armado: Incluye el tratamiento de la adherencia, el anclaje, el solapo de barras, el corte de barras, las disposiciones de armado en función de la geometría de las piezas y sus solicitaciones, etc. Es un capítulo de importancia obvia para los técnicos de hoy. Se incluye un anejo con las referencias más significativas a los estudios experimentales en que se basaron las propuestas que han marcado hito en la evolución del conocimiento. Finalmente, junto a las conclusiones más importantes, se enuncian las propuestas de estudios futuros. This thesis analyzes the criteria with which structures of reinforced concrete have been designed and constructed prior to 1973. Initially, the year 1970 was chosen as starting point, coinciding with the CEB recommendations, but with the development of the thesis it was decided that 1973 was the better option, coinciding with the Spanish regulations of 1973, whose content, format and description introduced the current criteria. The studied period includes the Classic Theory. The intended goals of this thesis are: 1) To cover a clear gap in the study of evolution of knowledge about reinforced concrete. The concept and accomplishments achieved by reinforced concrete itself has been treated in a very complete way by the main researchers in this area, but not the evolution of knowledge in this subject area. 2) To help the engineers understand structural configurations, geometries, dispositions of steel, safety formats etc, that will serve as preliminary judgments by experts on existing structures. To be a reference to the existing studies about the valuation of resistant capacity of existing constructions, constituting a basic study of a pre-regulation document. This thesis intends to be a help for the current generation of engineers who need to preserve and repair reinforced concrete structures that have existed for a significant number of years. Most of these structures in question were constructed more than 40 years ago, and it is necessary to know the criteria that influenced their design, the calculation and the construction. This thesis intends to determine the safety limits of the old structures and analyze them in the context of the current regulations and their methodology. Thus, it will then be possible to determine the safety of these structures, after being measured and calculated with the current criteria. This will allow the engineers to optimize the treatment of such a structure. This work considers the evolution of the knowledge, so constructive methods are not included. Related to the design criteria, there existed until middle of the 20th century a large number of diverse European tests and regulations, such as the Prussian norm of 1904, the Circular French Order of 1906, the Congress of Liège of 1930, as well as individual engineers’ own notes and criteria which incorporated the results of their own tests. From the second half of the 20th century, the contributions of Spanish engineers as Alfredo Páez Balaca, Eduardo Torroja and Pedro Jiménez Montoya, among others, were significant and this allowed the advancement of the criteria of the calculation of safety standards of concrete structures, many of which still exist to the present day. The design and calculation of reinforced concrete structures by the Classic Theory, was based on the ‘Critical Bending Moment’, when concrete and steel achieve their admissible tensions, that allows the best employment of materials and the best ductility. If the bending moment is major than the critical bending moment, will be necessary to introduce compression steel. After the study of the designs of many existing structures of that time by the author of this thesis, including the Historical Collections of Juan Manuel de Zafra, Eugenio Ribera and Carlos Fernandez Casado, the conclusion is that the geometric definition of the structures does not correspond exactly with the critical bending moment inherent in the structures. The parameters of these calculations changed throughout the years. The principal reason that can be outlined is that the materials were improving gradually and the number of calculated uncertainties were decreasing, thus allowing the reduction of the safety coefficients to use in the calculation. For example, concrete used a coefficient of 4 towards the end of the 19th century, which evolved to 3,57 after the publication of the Circular French Order of 1906, and then to 3 after the Spanish Instruction of 1939. In the case of the steel, a much more consistent material, the safety coefficient remained almost constant throughout the years, with a value of 2. Other reasons related to the evolution of the calculation parameters were that the tests and research undertaken by an ever-increasing number of engineers then allowed a more complete knowledge of the behavior of reinforced concrete. What is surprising is the extent of knowledge that existed about the behavior of the concrete from the outset. Engineers from the early years knew that the behavior of the concrete was non-linear, but they limited the work to a linear tension-deformation range. This was due to the difficulties of work in a non-linear range, because they did not have laboratories to test concrete, or facilities such as computers with appropriate software, something unthinkable today. These were the main reasons engineers of previous generations limited the tensions and deformations of a particular material to a known range. The modus operandi followed for the development of this thesis is the following one: -Document study: engineers’ documents, recommendations and regulations generated in this area, both from Spain or overseas, have been studied in a systematic way in accordance with the index of the document. In this process, a lack of knowledge has been detected concerning structural safety, and differences to current procedures have been identified and noted. Also, it has been necessary to adapt the notation and terminology of the Classic Theory to the current criteria, which has imposed an additional difficulty. -Development of the thesis: starting from the basic study, the next chapters of this thesis have been developed and expounded upon: o People and relevant institutions for their contribution to the knowledge about reinforced concrete structures (investigation, regulation, teaching). Determination of the mechanical properties of the materials (concrete and steel), in relation to their resistances, tension-deformation diagrams, modules of deformation, moment-curvature diagrams, etc. Included are the classic characterizations of concrete, the geometry and nature of the steel, etc. Safety formats: this is a very difficult chapter from which it is intended to provide enough information that will then allow the present day engineer to understand the criteria used in the Classic Theory and then to compare them with the current theories. Study of sections and pieces subjected to normal and tangential tensions: it intends to demonstrate the evolution in the treatment of the simple and complex flexion, shear, etc. Other aspects examined include aspects that were not very important in the Classic Theory but currently are, such as deformation and fissures. o Details of reinforcement: it includes the treatment of the adherence, the anchorage, the lapel of bars, the cut of bars, the dispositions of reinforcement depending on the geometry of the pieces and the solicitations, etc. It is a chapter of obvious importance for current engineers. The document will include an annex with the most references to the most significant experimental studies on which were based the proposals that have become a milestone in the evolution of knowledge in this area. Finally, there will be included conclusions and suggestions of future studies. A deep study of the documentation and researchers of that time has been done, juxtaposing their criteria and results with those considered relevant today, and giving a comparison between the resultant safety standards according to the Classic Theory criteria and currently used criteria. This thesis fundamentally intends to be a guide for engineers who have to treat or repair a structure constructed according to the Classic Theory criteria.

Análise de acetona em ar exalado: desenvolvimento de método eletroanalítico e algoritmo para processamento de sinais

Propõe-se método novo e completo para análise de acetona em ar exalado envolvendo coleta com pré-concentração em água, derivatização química e determinação eletroquímica assistida por novo algoritmo de processamento de sinais. Na literatura recente a acetona expirada vem sendo avaliada como biomarcador para monitoramento não invasivo de quadros clínicos como diabetes e insuficiência cardíaca, daí a importância da proposta. Entre as aminas que reagem com acetona para formar iminas eletroativas, estudadas por polarografia em meados do século passado, a glicina apresentou melhor conjunto de características para a definição do método de determinação por voltametria de onda quadrada sem a necessidade de remoção de oxigênio (25 Hz, amplitude de 20 mV, incremento de 5 mV, eletrodo de gota de mercúrio). O meio reacional, composto de glicina (2 mol·L-1) em meio NaOH (1 mol·L-1), serviu também de eletrólito e o pico de redução da imina em -1,57 V vs. Ag|AgCl constituiu o sinal analítico. Para tratamento dos sinais, foi desenvolvido e avaliado um algoritmo inovador baseado em interpolação de linha base por ajuste de curvas de Bézier e ajuste de gaussiana ao pico. Essa combinação permitiu reconhecimento e quantificação de picos relativamente baixos e largos sobre linha com curvatura acentuada e ruído, situação em que métodos convencionais falham e curvas do tipo spline se mostraram menos apropriadas. A implementação do algoritmo (disponível em http://github.com/batistagl/chemapps) foi realizada utilizando programa open source de álgebra matricial integrado diretamente com software de controle do potenciostato. Para demonstrar a generalidade da extensão dos recursos nativos do equipamento mediante integração com programação externa em linguagem Octave (open source), implementou-se a técnica da cronocoulometria tridimensional, com visualização de resultados já tratados em projeções de malha de perspectiva 3D sob qualquer ângulo. A determinação eletroquímica de acetona em fase aquosa, assistida pelo algoritmo baseado em curvas de Bézier, é rápida e automática, tem limite de detecção de 3,5·10-6 mol·L-1 (0,2 mg·L-1) e faixa linear que atende aos requisitos da análise em ar exalado. O acetaldeído, comumente presente em ar exalado, em especial, após consumo de bebidas alcoólicas, dá origem a pico voltamétrico em -1,40 V, contornando interferência que prejudica vários outros métodos publicados na literatura e abrindo possibilidade de determinação simultânea. Resultados obtidos com amostras reais são concordantes com os obtidos por método espectrofotométrico, em uso rotineiro desde o seu aperfeiçoamento na dissertação de mestrado do autor desta tese. Em relação à dissertação, também se otimizou a geometria do dispositivo de coleta, de modo a concentrar a acetona num volume menor de água gelada e prover maior conforto ao paciente. O método completo apresentado, englobando o dispositivo de amostragem aperfeiçoado e o novo e efetivo algoritmo para tratamento automático de sinais voltamétricos, está pronto para ser aplicado. Evolução para um analisador portátil depende de melhorias no limite de detecção e facilidade de obtenção eletrodos sólidos (impressos) com filme de mercúrio, vez que eletrodos de bismuto ou diamante dopado com boro, entre outros, não apresentaram resposta.

On-line microwave-based preconcentration device for inductively coupled plasma atomic emission spectrometry: Application to the elemental analysis of spirit samples

A microwave-based thermal nebulizer (MWTN) has been employed for the first time as on-line preconcentration device in inductively coupled plasma atomic emission spectrometry (ICP-AES). By the appropriate selection of the experimental conditions, the MWTN could be either operated as a conventional thermal nebulizer or as on-line analyte preconcentration and nebulization device. Thus, when operating at microwave power values above 100 W and highly concentrated alcohol solutions, the amount of energy per solvent mass liquid unit (EMR) is high enough to completely evaporate the solvent inside the system and, as a consequence, the analyte is deposited (and then preconcentrated) on the inner walls of the MWTN capillary. When reducing the EMR to the appropriate value (e.g., by reducing the microwave power at a constant sample uptake rate) the retained analyte is swept along by the liquid-gas stream and an analyte-enriched aerosol is generated and next introduced into the plasma cell. Emission signals obtained with the MWTN operating in preconcentration-nebulization mode improved when increasing preconcentration time and sample uptake rate as well as when decreasing the nozzle inner diameter. When running with pure ethanol solution at its optimum experimental conditions, the MWTN in preconcentration-nebulization mode afforded limits of detection up to one order of magnitude lowers than those obtained operating the MWTN exclusively as a nebulizer. To validate the method, the multi-element analysis (i.e. Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Pb and Zn) of different commercial spirit samples in ICP-AES has been performed. Analyte recoveries for all the elements studied ranged between 93% and 107% and the dynamic linear range covered up to 4 orders of magnitude (i.e. from 0.1 to 1000 μg L−1). In these analysis, both MWTN operating modes afforded similar results. Nevertheless, the preconcentration-nebulization mode permits to determine a higher number of analytes due to its higher detection capabilities.

Screen-printed electrode based electrochemical detector coupled with ionic liquid dispersive liquid–liquid microextraction and microvolume back-extraction for determination of mercury in water samples

A novel approach is presented, whereby gold nanostructured screen-printed carbon electrodes (SPCnAuEs) are combined with in-situ ionic liquid formation dispersive liquid–liquid microextraction (in-situ IL-DLLME) and microvolume back-extraction for the determination of mercury in water samples. In-situ IL-DLLME is based on a simple metathesis reaction between a water-miscible IL and a salt to form a water-immiscible IL into sample solution. Mercury complex with ammonium pyrrolidinedithiocarbamate is extracted from sample solution into the water-immiscible IL formed in-situ. Then, an ultrasound-assisted procedure is employed to back-extract the mercury into 10 µL of a 4 M HCl aqueous solution, which is finally analyzed using SPCnAuEs. Sample preparation methodology was optimized using a multivariate optimization strategy. Under optimized conditions, a linear range between 0.5 and 10 µg L−1 was obtained with a correlation coefficient of 0.997 for six calibration points. The limit of detection obtained was 0.2 µg L−1, which is lower than the threshold value established by the Environmental Protection Agency and European Union (i.e., 2 µg L−1 and 1 µg L−1, respectively). The repeatability of the proposed method was evaluated at two different spiking levels (3 and 10 µg L−1) and a coefficient of variation of 13% was obtained in both cases. The performance of the proposed methodology was evaluated in real-world water samples including tap water, bottled water, river water and industrial wastewater. Relative recoveries between 95% and 108% were obtained.

Determinação voltamétrica de zinco empregando eletrodos quimicamente modificados com bismuto

This dissertation presents the development of voltammetric methods to zinc determination in multivitamin commercial samples, talc, and art materials for painting (soft pastel) combining an alkaline extraction with 1.0 mol L-1 NaOH aqueous solution and bismuth modified electrodes. Two electrodes were used to zinc quantification in the samples, bismuth film electrode (BiFE) plated in situ onto glassy carbon and carbon paste electrode chemically modified with strongly acidic ion exchange resin Amberlite® IR 120 and bismuth nanostructures (EPCAmbBi). It was verified that the best concentration of Bi3+ for Bi film deposition onto glassy carbon was 4.0 μmol L-1 using an 0.1 mol L-1 acetate buffer aqueous solution (pH = 4.5) as supporting electrolyte. The best condition to formation of Bi nanostructures in the EPC modified with 10 % Amberlite® IR 120 was the use of 30 s to pre-concentration (open circuit) in 0.5 mmol L-1 Bi3+ aqueous solution (pH 5.5) prepared with supporting electrolyte solution. The obtained analytical curve for Zn2+ using BiFE presented linear range from 0.5 to 5.0 μmol L-1, the limit of detection (LD) was 41 nmol L-1. For EPCAmbBi only one linear range was observed for the analytical curve varying the Zn2+ concentration from 0.05 to 8.2 μmol L-1, LD obtained in this curve it was equal to 10 nmol L-1. The EPCAmbBi presented the most intense and sharp anodic stripping peaks for Zn2+ presenting, therefore, a better voltammetric profile, with sensitivity higher than obtained with the BiFE. Moreover, the EPCAmbBi presented a LD lower than that obtained with the BiFE. Alkaline extraction was an efficient sample pretreatment to extract Zn2+ from solid samples, besides that, this procedure was less susceptible to interferences from Cu2+, since it remains at extracting vessel as insoluble Cu(OH)2. The combination of alkaline extraction with the EPCAmbBi is a simple, fast, efficient and low cost for the zinc determination in pharmaceutical formulations and art materials for painting (soft pastel) samples, which can be employed as a low-cost alternative method to the atomic absorption spectroscopy.

Desenvolvimento e validação de método voltamétrico para determinação de ferro e sua especiação química em água intersticial no sedimento da Lagoa dos Patos-RS

Os sedimentos podem atuar tanto como acumuladores quanto como fontes de poluentes. Em função das atividades portuárias locais estarem em ritmo de crescimento pela ampliação do porto de Rio Grande (RS), estudos que mostrem a situação do local investigado são importantes a fim de prever o aporte do ferro nesse ambiente. Neste trabalho, a especiação química do ferro e a determinação da concentração do metal total e dissolvido em amostras de águas intersticiais no sedimento do Saco do Mendanha (RS) foram avaliadas, utilizando a Voltametria Adsortiva de Redissolução Catódica com o ligante 2,3-Dihidroxinaftaleno. O objetivo principal desse trabalho foi validar a metodologia analítica para realizar a especiação química do ferro em águas intersticiais, o que englobou a faixa linear de trabalho, limites de detecção e de quantificação, a exatidão e precisão. O Limite de Detecção encontrado foi de 0,11 nmol L-1 . Foram determinadas as concentrações de ferro total, dissolvido e lábil em três frações distintas: na interface água/sedimento, entre 0 e -5 cm; e entre -15 e -20 cm de profundidade na coluna sedimentar. Nas amostras analisadas, a concentração de ferro lábil encontrada foi entre 4,64 – 135,37 µmol L-1 ; a concentração do metal dissolvido foi de 6,25 – 322,70 µmol L-1 e de ferro total entre 83,36 – 390,30 µmol L-1 . A concentração do metal lábil em comparação com a fração dissolvida e total indica a presença de complexos estáveis entre o metal e a matéria orgânica natural presente na água intersticial, tornando dessa forma, o metal menos biodisponível para a biota local. Durante os meses de amostragem do sedimento, foi observada variação da concentração do metal, onde no mês de abril ocorreu o maior aporte do metal da coluna d’água para o sedimento. Essa transferência do metal para o sedimento pode estar relacionada pela forte mudança na salinidade no local de amostragem, passando de 16 no mês de fevereiro para 33 no mês de abril e para próximo de zero nos meses de agosto e novembro de 2009.

Multi-bit sigma-delta modulators with enhanced dynamic-range using non-linear DAC for hearing aids

15th IEEE International Conference on Electronics, Circuits and Systems, Malta

A New Method of Current Switching for Linear Wide-Range Measurement Systems

This new and general method here called overflow current switching allows a fast, continuous, and smooth transition between scales in wide-range current measurement systems, like electrometers. This is achieved, using a hydraulic analogy, by diverting only the overflow current, such that no slow element is forced to change its state during the switching. As a result, this approach practically eliminates the long dead time in low-current (picoamperes) switching. Similar to a logarithmic scale, a composition of n adjacent linear scales, like a segmented ruler, measures the current. The use of a linear wide-range system based on this technique assures fast and continuous measurement in the entire range, without blind regions during transitions and still holding suitable accuracy for many applications. A full mathematical development of the method is given. Several computer realistic simulations demonstrated the viability of the technique.

Range of validity of weakly non-linear theory in Rayleigh-Bénard problem

In this paper we examine the equilibrium states of finite amplitude flow in a horizontal fluid layer with differential heating between the two rigid boundaries. The solutions to the Navier-Stokes equations are obtained by means of a perturbation method for evaluating the Landau constants and through a Newton-Raphson iterative method that results from the Fourier expansion of the solutions that bifurcate above the linear stability threshold of infinitesimal disturbances. The results obtained from these two different methods of evaluating the convective flow are compared in the neighborhood of the critical Rayleigh number. We find that for small Prandtl numbers the discrepancy of the two methods is noticeable. © 2009 The Physical Society of Japan.

Range of validity of weakly non-linear theory in Rayleigh-Bénard convection

In this paper we examine the equilibrium states of periodic finite amplitude flow in a horizontal channel with differential heating between the two rigid boundaries. The solutions to the Navier-Stokes equations are obtained by means of a perturbation method for evaluating the Landau coefficients and through a Newton-Raphson iterative method that results from the Fourier expansion of the solutions that bifurcate above the linear stability threshold of infini- tesimal disturbances. The results obtained from these two different methods of evaluating the convective flow are compared in the neighbourhood of the critical Rayleigh number. We find that for small Prandtl numbers the discrepancy of the two methods is noticeable.

A new method of current switching for linear wide-range measurement systems

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

Influência da idade no comportamento da frequência cardíaca na transição repouso-exercício: uma análise por deltas e regressão linear

BACKGROUND: Changes in heart rate during rest-exercise transition can be characterized by the application of mathematical calculations, such as deltas 0-10 and 0-30 seconds to infer on the parasympathetic nervous system and linear regression and delta applied to data range from 60 to 240 seconds to infer on the sympathetic nervous system. The objective of this study was to test the hypothesis that young and middle-aged subjects have different heart rate responses in exercise of moderate and intense intensity, with different mathematical calculations. METHODS: Seven middle-aged men and ten young men apparently healthy were subject to constant load tests (intense and moderate) in cycle ergometer. The heart rate data were submitted to analysis of deltas (0-10, 0-30 and 60-240 seconds) and simple linear regression (60-240 seconds). The parameters obtained from simple linear regression analysis were: intercept and slope angle. We used the Shapiro-Wilk test to check the distribution of data and the t test for unpaired comparisons between groups. The level of statistical significance was 5%. RESULTS: The value of the intercept and delta 0-10 seconds was lower in middle age in two loads tested and the inclination angle was lower in moderate exercise in middle age. CONCLUSION: The young subjects present greater magnitude of vagal withdrawal in the initial stage of the HR response during constant load exercise and higher speed of adjustment of sympathetic response in moderate exercise.

Active Dendrites Enhance Neuronal Dynamic Range

Since the first experimental evidences of active conductances in dendrites, most neurons have been shown to exhibit dendritic excitability through the expression of a variety of voltage-gated ion channels. However, despite experimental and theoretical efforts undertaken in the past decades, the role of this excitability for some kind of dendritic computation has remained elusive. Here we show that, owing to very general properties of excitable media, the average output of a model of an active dendritic tree is a highly non-linear function of its afferent rate, attaining extremely large dynamic ranges (above 50 dB). Moreover, the model yields double-sigmoid response functions as experimentally observed in retinal ganglion cells. We claim that enhancement of dynamic range is the primary functional role of active dendritic conductances. We predict that neurons with larger dendritic trees should have larger dynamic range and that blocking of active conductances should lead to a decrease in dynamic range.