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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
161

Sistema de análises em fluxo empregando multicomutação para avaliação de toxicidade aguda com Vibrio fischeri / A multicommuted flow-based system for acute toxicity evaluation with Vibrio fischeri

Andressa Adame 25 April 2014 (has links)
Um sistema de análises em fluxo com multicomutação foi desenvolvido para a mecanização do bioensaio de toxicidade aguda com a bactéria Vibrio fischeri, o qual é baseado na diminuição da luminescência bacteriana causada por espécies tóxicas.Microbombas solenoide foram utilizadas para melhorar as condições de mistura, permitindo também que diluições fossem realizadas em linha com a alteração do volume de amostra e a sobreposição parcial entre a zona da amostra e a suspensão bacteriana. Uma cela de fluxo em espiral, posicionada na janela de emissão de um espectrofluorímetro, foi empregada para as medidas de luminescência e um banho de água construído em laboratório, baseado no efeito Peltier, foi utilizado para manter a temperatura do bioensaio em (13,0±0,1) °C. Um pequeno volume da suspensão bacteriana (120 ?L) foi selecionado visando minimizar o consumo e, consequentemente, os custos do ensaio. O tempo de contato entre a suspensão bacteriana e a amostra foi reduzido para 5 min para aumentar a frequência de amostragem e evitar a atenuação da luminescência devido ao tempo de vida curto das bactérias. Os valores de CE50 para os controles positivos foram estimados em 2,5 ± 0,7, 2,0 ± 0,5 e 10 ± 4 mg L-1 para o Zn(II), Cu(II), e Cr(VI), respectivamente, sendo concordantes com os valores da literatura. Os valores de CE50 para alguns poluentes emergentes (parabenos, cafeína, acetaminofeno, diclofenaco e ácido salicílico) concordaram com os obtidos utilizando o kit comercial BioTox(TM), realizado em micro placa, a nível de confiança de 95 %. Os coeficientes de variação foram estimados em 2,4 e 2 % (n = 10), na ausência e na presença de 0,6 mg L-1 de Zn(II), respectivamente. O sistema de análises em fluxo proposto é, então, uma alternativa simples, rápida, robusta e precisa para a determinação da toxicidade aguda utilizando pequenos volumes de amostra e suspensão bacteriana. Além disso, o sistema apresenta vantagens em comparação com os bioensaios em batelada e em fluxo, tais como ajuste de salinidade e diluições das amostras em linha e a determinação da cinética de toxicidade das espécies químicas / A multicommuted flow system was developed for automation of the acute toxicity bioassay using Vibrio fischeri bacteria, which exploits the decrease of the bacterial luminescence caused by toxic species. Solenoid micro-pumps were employed to improve mixing conditions and to perform on-line dilutions of the tested compounds by changing the sample volume and exploiting the partial overlap between sample zone and the bacterial suspension. A spiral flow cell, placed at the emission window of a spectrofluorimeter, was employed for signal measurement and a lab-made water bath based on the Peltier effect was used for maintain the temperature of the bioassay at (13.0±0.1) oC. A low volume of the bacterial suspension (120 ?L) was selected in order to minimize its consumption and, consequently, the costs of the assay. The contact time between bacterial suspension and sample was reduced to 5 min to increase the sampling rate and to avoid luminescence fading due to the bacteria short lifetime. EC50 values for positive controls were estimated as 2.5 ± 0.7, 2.0 ± 0.5 and 10 ± 4 for Zn(II), Cu(II), and Cr(VI), respectively, being in agreement with literature values. The EC50 values for some emerging pollutants (parabens, caffeine, acetaminophen, diclofenac and salicylic acid) agreed with those obtained from commercial BioTox(TM) kit performed in micro plate at the 95% confidence level. The coefficients of variation were estimated as 2.4 and 2 % (n=10), in the absence and presence of 0.6 mg L-1 Zn(II), respectively. The proposed flow system is then a simple, fast, robust and accurate alternative for acute toxicity determination, using low sample and bacterial suspension volumes. Furthermore, the system presents advantages in comparison to batch and previous flow-based bioassays, such as the achievement of in-line salinity adjustment and sample dilutions, and the determination of toxicity kinetic for every assayed chemical species
162

Sistemas de análises químicas em fluxo explorando multi-impulsão, interface única ou quimiometria / Flow systems exploiting multi-pumping, single interface or chemometry

Evandro Roberto Alves 09 October 2009 (has links)
Os sistemas de análises em fluxo com multi-impulsão (MPFS) têm como característica principal o emprego de bombas solenóide como unidade propulsora de fluidos, as quais proporcionam fluxo pulsado. Este regime de fluxo foi avaliado em função das condições de mistura entre as soluções envolvidas, transferência de calor e difusão gasosa. A associação dos métodos quimiométricos de análises e dos sistemas MPFS foi demonstrada em relação à determinação espectrofotométrica de glicose, frutose e glicerol em vinhos fermentiscíveis e caldos de cana-de-açúcar. O método se fundamentou na reação dos carboidratos com metaperiodato de sódio e posterior oxidação de iodeto pelo metaperiodato remanescente com monitoramento de [I3 -] produzido. O tratamento dos dados envolveu calibração multivariada, empregando o algoritmo PLS e os resultados são concordantes com aqueles obtidos por cromatografia líquida de troca aniônica com detecção por amperometria pulsada. O sistema proposto é simples e robusto, capaz de analisar 120 amostras por hora. O fluxo pulsado proporcionou melhoria no desenvolvimento reacional no que diz respeito à transferência de calor e difusão gasosa. Esse aspecto se deve principalmente ao aumento do transporte de massas no sentido radial. Estes fatos foram constatados na determinação espectrofotométrica de açúcares redutores totais (ART) e etanol. O sistema MPFS proposto para a determinação de ART envolveu hidrólise ácida da sacarose e degradação alcalina dos carboidratos. A natureza do fluxo pulsado possibilitou o uso de menores temperaturas de um banho termostatizado durante as etapas de hidrólise e degradação, bem como a diminuição da alcalinidade. Para a mecanização da determinação espectrofotométrica de etanol envolvendo a redução de Cr(VI) a Cr(III) sob condições ácidas, foi desenvolvido um sistema MPFS, o qual se demonstrou eficiente e adequado para procedimentos que envolvem difusão gasosa. Após otimização dos principais parâmetros envolvidos, os mesmos foram comparados empregando o sistema de multi-comutação, cujo fluxo é laminar. Melhores resultados analíticos foram obtidos no sistema proposto, que resultou em boa sensibilidade. Em relação aos sistemas de análises em fluxo que exploram interface reacional única (SIFA), foram demonstradas suas potencialidades através da implementação de procedimentos que envolvem determinações simultâneas, sem a necessidade de reconfigurações no módulo de análises. Ainda, a simplificação da etapa de otimização foi espectrofotometricamente avaliada através da determinação de alumínio, ferro total e P-PO4. O sistema proposto é de configuração simples e capaz de analisar 130, 140 e 90 amostras de alumínio, ferro total e fósforo por hora, respectivamente / Multi-pumping flow systems (MPFS) present as an unique feature the use of solenoid pumps as fluid propelling devices, which deliver pulsed flows. This flow regime was evaluated in order to improve mixing conditions between the involved solutions, heating transfer and gas diffusion.The association of the chemometric methods of analysis and MPFS systems was demonstrated in the spectrophotometric determination of glucose, fructose and glycerol in musts and sugar cane juices. The method involved metaperiodate oxidation of carbohydrates and further oxidation of remainder metaperiodate iodide yield in the [I3 -] complex that was spectrophotometrically monitored. Data treatment involved multivariate calibration relying on the PLS algorithm and results were in agreement with liquid anion chromatography with pulsed amperometric detection. The proposed system is simple and rugged, allowing 120 samples to be run per hour. The pulsed flow led to a enhanced in heating transfer and gas diffusion, in view of the enhanced radial mass transport. These aspects were verified in the spectrophotometric determination of total reducing sugars (TRS) and ethanol. The proposed MPFS system for TRS determination involved in-line hydrolysis of sucrose and alkaline degradation of the carbohydrates. The intrinsic characteristic of pulsed flow allowed the use of lower temperatures in bath thermostatization during hydrolysis and degradation steps, as well as a lower alkalinity. The MPFS for spectrophotometric determination of ethanol involving diffusion towards an acceptor stream, reduction of Cr(VI) to Cr(III) under acidic condition, and Cr*(III) monitoring proved to be eficient and amenale to analytical procedures involving gas diffusion. After optimization of the main parameters, the system was compared with a multicommuted flow system (MCFA) that exploits a laminar flow. Better analytical results were obtained with the proposed system which demonstrated fair sensitivity. Regarding flow systems exploiting a single reaction interface (SIFA), their potentialities were demonstrated by implementing analytical procedures for simultaneous determination without requiring reconfigurations in the flow manifold. In this proposed system the simplification of the optimization step was atained, and the approach was evaluated in relation to spectrophotometrically determination of aluminum, total iron and phosphate. The system exhibits simple configuration and allows 130, 140 and 90 samples of aluminum, total iron and phosphate to be run per hour, respectivelly
163

Sistemas de análises químicas em fluxo explorando multi-impulsão, interface única ou quimiometria / Flow systems exploiting multi-pumping, single interface or chemometry

Alves, Evandro Roberto 09 October 2009 (has links)
Os sistemas de análises em fluxo com multi-impulsão (MPFS) têm como característica principal o emprego de bombas solenóide como unidade propulsora de fluidos, as quais proporcionam fluxo pulsado. Este regime de fluxo foi avaliado em função das condições de mistura entre as soluções envolvidas, transferência de calor e difusão gasosa. A associação dos métodos quimiométricos de análises e dos sistemas MPFS foi demonstrada em relação à determinação espectrofotométrica de glicose, frutose e glicerol em vinhos fermentiscíveis e caldos de cana-de-açúcar. O método se fundamentou na reação dos carboidratos com metaperiodato de sódio e posterior oxidação de iodeto pelo metaperiodato remanescente com monitoramento de [I3 -] produzido. O tratamento dos dados envolveu calibração multivariada, empregando o algoritmo PLS e os resultados são concordantes com aqueles obtidos por cromatografia líquida de troca aniônica com detecção por amperometria pulsada. O sistema proposto é simples e robusto, capaz de analisar 120 amostras por hora. O fluxo pulsado proporcionou melhoria no desenvolvimento reacional no que diz respeito à transferência de calor e difusão gasosa. Esse aspecto se deve principalmente ao aumento do transporte de massas no sentido radial. Estes fatos foram constatados na determinação espectrofotométrica de açúcares redutores totais (ART) e etanol. O sistema MPFS proposto para a determinação de ART envolveu hidrólise ácida da sacarose e degradação alcalina dos carboidratos. A natureza do fluxo pulsado possibilitou o uso de menores temperaturas de um banho termostatizado durante as etapas de hidrólise e degradação, bem como a diminuição da alcalinidade. Para a mecanização da determinação espectrofotométrica de etanol envolvendo a redução de Cr(VI) a Cr(III) sob condições ácidas, foi desenvolvido um sistema MPFS, o qual se demonstrou eficiente e adequado para procedimentos que envolvem difusão gasosa. Após otimização dos principais parâmetros envolvidos, os mesmos foram comparados empregando o sistema de multi-comutação, cujo fluxo é laminar. Melhores resultados analíticos foram obtidos no sistema proposto, que resultou em boa sensibilidade. Em relação aos sistemas de análises em fluxo que exploram interface reacional única (SIFA), foram demonstradas suas potencialidades através da implementação de procedimentos que envolvem determinações simultâneas, sem a necessidade de reconfigurações no módulo de análises. Ainda, a simplificação da etapa de otimização foi espectrofotometricamente avaliada através da determinação de alumínio, ferro total e P-PO4. O sistema proposto é de configuração simples e capaz de analisar 130, 140 e 90 amostras de alumínio, ferro total e fósforo por hora, respectivamente / Multi-pumping flow systems (MPFS) present as an unique feature the use of solenoid pumps as fluid propelling devices, which deliver pulsed flows. This flow regime was evaluated in order to improve mixing conditions between the involved solutions, heating transfer and gas diffusion.The association of the chemometric methods of analysis and MPFS systems was demonstrated in the spectrophotometric determination of glucose, fructose and glycerol in musts and sugar cane juices. The method involved metaperiodate oxidation of carbohydrates and further oxidation of remainder metaperiodate iodide yield in the [I3 -] complex that was spectrophotometrically monitored. Data treatment involved multivariate calibration relying on the PLS algorithm and results were in agreement with liquid anion chromatography with pulsed amperometric detection. The proposed system is simple and rugged, allowing 120 samples to be run per hour. The pulsed flow led to a enhanced in heating transfer and gas diffusion, in view of the enhanced radial mass transport. These aspects were verified in the spectrophotometric determination of total reducing sugars (TRS) and ethanol. The proposed MPFS system for TRS determination involved in-line hydrolysis of sucrose and alkaline degradation of the carbohydrates. The intrinsic characteristic of pulsed flow allowed the use of lower temperatures in bath thermostatization during hydrolysis and degradation steps, as well as a lower alkalinity. The MPFS for spectrophotometric determination of ethanol involving diffusion towards an acceptor stream, reduction of Cr(VI) to Cr(III) under acidic condition, and Cr*(III) monitoring proved to be eficient and amenale to analytical procedures involving gas diffusion. After optimization of the main parameters, the system was compared with a multicommuted flow system (MCFA) that exploits a laminar flow. Better analytical results were obtained with the proposed system which demonstrated fair sensitivity. Regarding flow systems exploiting a single reaction interface (SIFA), their potentialities were demonstrated by implementing analytical procedures for simultaneous determination without requiring reconfigurations in the flow manifold. In this proposed system the simplification of the optimization step was atained, and the approach was evaluated in relation to spectrophotometrically determination of aluminum, total iron and phosphate. The system exhibits simple configuration and allows 130, 140 and 90 samples of aluminum, total iron and phosphate to be run per hour, respectivelly
164

Desenvolvimento de procedimentos analíticos explorando microextração líquido-líquido em fluxo para a determinação de espécies de interesse em águas e leite / Development of analytical procedures exploiting flow-based liquid-liquid microextraction for the determination of species of interest in waters and milk

Nascimento, Carina de Fátima 26 February 2018 (has links)
Três procedimentos analíticos envolvendo microextração líquido-líquido (MELL) em fluxo foram desenvolvidos para as determinações de formaldeído em leite, detergentes aniônicos em águas de rios e bisfenol A (BPA) em águas de torneira. Microextração líquido-líquido dispersiva (MELLD) foi empregada no primeiro e no segundo procedimentos. O primeiro procedimento foi conduzido em um sistema fluxo-batelada no qual a quantificação espectrofotométrica era realizada diretamente na câmara de mistura/reação, através do acoplamento de fibras ópticas. No segundo, foi explorada a estratégia lab-in-syringe, em que a formação do par iônico entre os detergentes aniônicos e corante catiônico azul de metileno, bem como MELLD ocorriam no interior da seringa, sendo os analitos quantificados na fase orgânica por espectrofotometria. O terceiro procedimento envolveu MELL em sistema de análises por injeção sequencial (SIA), baseada na formação de um filme de 1-octanol na parede da bobina de extração. O extrato foi eluído com etanol e a quantificação de BPA foi realizada por espectrofluorimetria. As linearidades das curvas analíticas, os limites de detecção e os limites de quantificação ao nível de 95% de confiança foram: 0,5-5,0 mg L-1, 100 e 300 ?g L-1 para formaldeído, 0,03-0,5 mg L-1, 9,0 e 29,0 ?g L-1 para detergentes, e 5,0 - 100 ?g L-1, 1,8 ?g L-1 e 5,4 ?g L-1 para BPA. Os procedimentos desenvolvidos não apresentaram efeitos de matriz, e as recuperações se situaram entre 91 e 112%. A precisão e exatidão do procedimento foram concordantes com os procedimentos de referência, ao nível de 95% de confiança. Todos os procedimentos apresentaram coeficientes de variação menores do que 3,5% (n=10), frequência de amostragem de 10-17 h-1, consumiram apenas 30-40 µL de solventes orgânicos e geraram 2,7-6,7 mL de resíduos por determinação / Three analytical procedures involving flow-based liquid-liquid microextraction (LLME) were developed for the determinations of formaldehyde in milk, anionic detergents in river waters, and bisphenol A (BPA) in tap waters. The first and second procedures involved dispersive liquid-liquid microextraction (DLLME) and spectrophotometric detection. The first one was carried out in a flow-batch system, in which the spectrophotometric quantification was performed directly in the mixing/reaction chamber by coupling optical fibers. The second one exploited the lab-in-syringe strategy, in which the ion-pair formation between the anionic detergents and the methylene blue cationic dye, as well as DLLME, were carried out inside the syringe. The third procedure involved LLME in a sequential injection system based on the formation of a 1-octanol film on the inner wall of the extraction coil. The extract was eluted with ethanol and BPA was quantified by spectrofluorimetry. Linear response ranges, detection and quantification limits estimated at the 95% confidence level were: 0.5-5.0 mg L-1, 100 and 300 ?g L-1 for formaldehyde; 0.03-0.5 mg L-1, 9.0 and 29.0 ?g L-1 for detergents, and 5.0-100 ?g L-1, 1.8 and 5.4 ?g L-1 for BPA. Matrix effects were not observed for the assayed samples and recoveries ranged from 91 to 112%. Accuracy and precision of the results agreed with those attained by reference procedures at the 95% confidence level. All procedures yielded coefficients of variation lower than 3.5% (n = 10), sampling rates within 10 and 17 h-1, consumed only 30-40 ?L of organic solvents, and generated 2.7-6.7 mL of waste by determination
165

Desenvolvimento de procedimentos analíticos limpos e com alta sensibilidade para a determinação de espécies de interesse ambiental / Development of clean analytical procedures with high sensitivity for determination of species of environmental interest

Melchert, Wanessa Roberto 28 May 2009 (has links)
Procedimentos analíticos limpos e com alta sensibilidade foram desenvolvidos para a determinação de espécies de interesse ambiental (carbaril, sulfato e cloro livre). Os procedimentos foram baseados no acoplamento de sistemas de análises em fluxo com microbombas solenoides à espectrofotometria com longo caminho óptico ou em procedimentos de extração em ponto nuvem, visando a concentração das espécies de interesse sem o emprego de solventes tóxicos. A determinação de carbaril em águas naturais foi baseada em uma dupla extração em ponto nuvem: uma etapa de clean-up para a remoção de substâncias orgânicas interferentes e outra de pré-concentração do indofenol formado na reação com a forma oxidada do p-aminofenol. Resposta linear foi observada entre 10 e 500 µg L-1, com absortividade molar aparente estimada em 4,6x105 L mol-1 cm-1. O limite de detecção foi estimado em 7 µg L-1 e coeficiente de variação em 3,4% (n = 8). Recuperações entre 91 e 99% foram estimadas para adições de carbaril em amostras de águas naturais. Uma cela simples e de baixo custo com 30 cm de caminho óptico foi construída para medidas espectrofotométricas. A cela apresenta características desejáveis como baixa atenuação do feixe de radiação e volume interno (75 µL) comparável a de uma cela convencional. O desempenho da cela foi avaliado na determinação de fosfato utilizando o método azul de molibdênio com resposta linear obtida entre 0,05 e 0,8 mg L-1 de fosfato (r = 0,999). O aumento na sensibilidade (30,4 vezes) em comparação com o obtido com uma cela de fluxo convencional de 1 cm está de acordo com o estimado pela lei de Lambert-Beer. A formação do indofenol foi também explorada para a determinação de carbaril no procedimento em fluxo com celas de 30 e 100 cm. Respostas lineares; limite de detecção e coeficiente de variação foram estimados entre 50 - 750 e 5 - 200 µg L-1; 4,0 e 1,7 µg L-1 e 2,3 e 0,7%, respectivamente, para as celas de 30 e 100 cm. O procedimento proposto foi seletivo para a determinação de carbaril, sem interferências de outros pesticidas carbamatos. O resíduo gerado foi tratado com persulfato de potássio e irradiação ultravioleta, com redução de 94% do carbono orgânico total, não sendo o resíduo degradado considerado tóxico, frente às bactérias Vibrio-fischeri. A determinação de sulfato foi baseada em medidas turbidimétricas com cela de fluxo de 1 cm, com resposta linear observada entre 20 - 200 mg L-1. Deriva de linha base não foi observada em função do fluxo pulsado gerado pelas microbombas solenoides. O limite de detecção e o coeficiente de variação (n = 20) foram estimados em 3 mg L-1 e 2,4%, respectivamente, com frequência de amostragem de 33 determinações por hora. Para aumentar a sensibilidade, uma cela de fluxo de 100 cm foi empregada e deriva de linha base foi evitada utilizando uma etapa de limpeza periódica com EDTA em meio alcalino. Resposta linear foi observada entre 7 - 16 mg L-1 com limite de detecção de 150 µg L-1 e coeficiente de variação de 3,0% (n = 20). A frequência de amostragem foi estimada em 25 determinações por hora. Resultados obtidos para amostras de águas naturais e de chuva foram concordantes a nível de confiança de 95% com o procedimento turbidimétrico em batelada. A determinação de cloro livre em águas naturais e de torneira foi baseada na reação com N,N-dietil-p-fenilenodiamina, com resposta linear entre 5 e 100 µg L-1 de hipoclorito e limite de detecção e coeficiente de variação estimados em 0,23 µg L-1 e 3,4%, respectivamente. A frequência de amostragem foi estimada em 58 determinações por hora. / Clean analytical procedures with high sensitivity for the determination of species of environmental interest (carbaryl, sulphate and chlorine) were developed. Flow systems with solenoid micropumps were coupled to long optical pathlength spectrophotometry or cloud point extraction procedures, aiming the concentration of species for determination without employing toxic solvents. Carbaryl determination in natural waters was based on a double cloud point extraction: a clean-up step for removal of interfering organic species and pre-concentration of the indophenol blue, formed in the reaction with the oxidized of p-aminophenol. Linear response was observed between 10 and 50 µg L-1, with apparent molar absortivity estimated as 4.6x105 L mol-1 cm-1. Detection limit was estimated as 7 mg L-1 and the coefficient of variation as 3.4% (n = 8). Recoveries between 91 and 99% were obtained for carbaryl spiked to natural waters. A simple and low cost flow cell with 30 cm optical path was constructed for spectrophotometric measurements. The cell shows desirable characteristics such as reduced attenuation of the radiation beam and internal volume (75 µL) comparable to conventional flow cells. The performance was evaluated by phosphate determination by the molibdenium blue method, with linear response between 0.05 and 0.8 mg L-1 of phosphate (r = 0.999). The increase in sensitivity (30.4 fold) in comparison to the obtained with a conventional 1 cm optical path flow cell agreed to theoretical value estimated by the Lambert-Beer law. The determination of carbaryl was also carried out in a flow system coupled to 30 and 100 cm optical path flow cells, also exploiting the formation of indophenol compound. Linear responses, detection limits and coefficients of variation were 50 - 750 and 5 - 200 µg L-1;4.0 and 1.7 µg L-1 and 2.3 and 0.7%, respectively, for 30 and 100 cm cells. The proposed procedure was selective for the determination of carbaryl, without interferences of other carbamate pesticides. The waste of the analytical procedure was treated with potassium persulphate and ultraviolet irradiation, with decrease of 94% of total organic carbon. The residue after treatment was not toxic for Vibrio-fischeri bacteria. Sulphate determination was based on turbidimetric measurements with 1-cm flow cell, with linear response between 20 and 200 mg L-1. Baseline drift was avoided in view of the pulsed flow related to the solenoid micropumps. The detection limit and the coefficient of variation were estimated as 3 mg L-11 and 2.4%, respectively, for a sampling rate of 33 determinations per hour. Aiming the increase in sensitivity, a 100 cm optical path flow cell was employed and baseline drift was avoided with a washing, step employing EDTA in alkaline medium. Linear response was observed between 7 - 16 mg L-1, with a detection limit of 150 µg L-1, coefficient of variation of 3.0% (n = 20) and sampling rate of 25 determinations per hour. Results obtained natural and rain for water samples agreed at 95% confidence level with the batch turbidimetric procedure. The determination of free chlorine in natural and tap waters was based on the reaction with N,N-diethyl-p-phenylenediamine, with linear response between 5 and 100 µg L-1, and detection limit and coefficient of variation estimated as 0.23 µg L-1 and 3.4%, respectively. Sampling rate was estimated as 58 determinations per hour.
166

Värderarens val av metod : Påverkansfaktorer vid företagsvärdering

Benedicks, Anne, Öberg, Veronica January 2007 (has links)
<p>Title: The appraiser’s choice of valuation method – factors that influences the choice of company valuation methods</p><p>Seminar date: 04/06/07</p><p>Course: Master thesis in Business Administration, 10 Swedish credits.</p><p>Authors: Anne Benedicks and Veronica Öberg</p><p>Advisor: Eron Oxing</p><p>Profession of category: Financial analysts, auditors and company lawyers.</p><p>Key words: Company valuation, valuation methods, cash flow analysis, comparative valuation, the net asset value method.</p><p>The Main Issue: What is of decisive importance when choosing a special company valuation method?</p><p>Purpose: The purpose of this paper is to identify, analyse and evaluate the most common methods of valuation for financial analysts, auditors and company lawyers and those factors that influences the choice of method.</p><p>Method: A multiple survey has been implemented for the actual profession categories. Primary data was collected through semi-structured interviews and a questionnaire survey.</p><p>Theoretical: The theoretical frame of reference is based upon the paper’s dependent variable, i.e. the role of the appraiser. The appraiser is dependent of following undependent variables: comparative valuation of company, situations of valuation, relevant information, the processes of valuation, the methods of valuation and common custom valuation.</p><p>Empiricism: Material from the interviews and the questionnaire survey shows how the professional category respectively acts when they valuate a company and why and which valuation method is used. According to the interviews the financial analysts often uses comparative evaluation, the auditor uses the cash flow analysis while the lawyer chooses the net asset value method.</p><p>Conclusion: The result of this paper considerable agrees to earlier research within the field. The main underlying factor for the appraiser to choose a certain evaluation method is simply depending on the actual situation. Example of other determining factors is customer relations, access to relevant information and which type of business under evaluation.</p> / <p>Yrkesgrupper: Finansanalytiker, revisorer och jurister.</p><p>Problemformulering: Vad är avgörande för att en specifik företagsvärderingsmetod väljs?</p><p>Syfte: Syftet med uppsatsen är att identifiera, analysera och utvärdera vilka de vanligast förekommande värderingsmetoderna är för finansanalytiker, revisorer och jurister samt vilka faktorer som påverkar valet av metod.</p><p>Metod: En flerfallstudie har gjorts hos de berörda yrkeskategorierna. Primärdata samlades in genom semistrukturerade intervjuer samt enkätundersökning.</p><p>Teoretisk referensram: Den teoretiska referensramen utgår från uppsatsens beroende variabel, värderarens roll. De oberoende variabler som värderaren är beroende av är: relativ företagsvärdering, värderingssituationer, informationskällor, värderingsprocessen, värderingsmetoder och god värderingssed.</p><p>Empiri: Material från intervjuer och enkätundersökning visar på hur respektive yrkeskategori handlar i en företagsvärderingssituation samt varför och med vilken värderingsmetod. Enligt intervjuerna använder finansanalytikern oftast jämförande värdering, revisorn väljer kassaflödesanalys medan juristen väljer substansvärdemetoden.</p><p>Slutsats: Uppsatsens resultat överensstämmer på ett bra sätt med tidigare forskning inom området. Den största bakomliggande faktorn till att värderaren väljer en viss värderingsmetod beror oftast på situationen. Exempel på andra avgörande element är relationen till kunden, tillgång till information samt vilken typ av företag som ska värderas.</p>
167

The effect of scale on the morphology, mechanics and transmissivity of single rock fractures

Fardin, Nader January 2003 (has links)
This thesis investigates the effect of scale on themorphology, mechanics and transmissivity of single rockfractures using both laboratory and in-situ experiments, aswell as numerical simulations. Using a laboratory 3D laserscanner, the surface topography of a large silicon-rubberfracture replica of size 1m x 1m, as well as the topography ofboth surfaces of several high-strength concrete fracturereplicas varying in size from 50mmx50mm to 200mm x 200mm, werescanned. A geodetic Total Station and an in-situ 3D laser radarwere also utilized to scan the surface topography of a largenatural road-cut rock face of size 20m x 15m in the field. Thisdigital characterization of the fracture samples was then usedto investigate the scale dependency of the three dimensionalmorphology of the fractures using a fractal approach. Thefractal parameters of the surface roughness of all fracturesamples, including the geometrical aperture of the concretefracture samples, were obtained using the Roughness-Lengthmethod. The results obtained from the fractal characterization ofthe surface roughness of the fracture samples show that bothfractal dimension, D, and amplitude parameter, A, for aself-affine surface are scale-dependent, heterogeneous andanisotropic, and their values generally decrease withincreasing size of the sample. However, this scale-dependencyis limited to a certain size—defined as the stationaritythreshold, where the surface roughness parameters of thefracture samples remain essentially constant beyond thisstationarity threshold. The surface roughness and thegeometrical aperture of the tested concrete fracture replicasin this study did not reach stationarity due to the structuralnon-stationarity of their surface at small scales. Although theaperture histogram of the fractures was almost independent ofthe sample size, below their stationarity threshold both theHurst exponent, Hb, and aperture proportionality constant, Gb,decrease on increasing the sample sizes. To investigate the scale effect on the mechanical propertiesof single rock fractures, several normal loading and directshear tests were performed on the concrete fracture replicassubjected to different normal stresses under Constant NormalLoad (CNL) conditions. The results showed that both normal andshear stiffnesses, as well as the shear strength parameters ofthe fracture samples, decrease on increasing the sample size.It was observed that the structural non-stationarity of surfaceroughness largely controls the contact areas and damage zoneson the fracture surfaces as related to the direction of theshearing. The aperture maps of the concrete fracture replicas ofvarying size and at different shear displacements, obtainedfrom numerical simulation of the aperture evolution duringshearing using their digitized surfaces, were used toinvestigate the effect of scale on the transmissivity of thesingle rock fractures. A FEM code was utilized to numericallysimulate the fluid flow though the single rock fractures ofvarying size. The results showed that flow rate not onlyincreases on increasing the sample size, but also significantlyincreases in the direction perpendicular to the shearing, dueto the anisotropic roughness of the fractures. <b>Key words:</b>Anisotropy, Aperture, Asperity degradation,Contact area, Finite Element Method (FEM), Flow analysis,Fractals, Fracture morphology, Heterogeneity,Stress-deformation, Surface roughness, Roughness-Length method,Scale dependency, Stationarity, Transmissivity, 3D laserscanner.
168

Värderarens val av metod : Påverkansfaktorer vid företagsvärdering

Benedicks, Anne, Öberg, Veronica January 2007 (has links)
Title: The appraiser’s choice of valuation method – factors that influences the choice of company valuation methods Seminar date: 04/06/07 Course: Master thesis in Business Administration, 10 Swedish credits. Authors: Anne Benedicks and Veronica Öberg Advisor: Eron Oxing Profession of category: Financial analysts, auditors and company lawyers. Key words: Company valuation, valuation methods, cash flow analysis, comparative valuation, the net asset value method. The Main Issue: What is of decisive importance when choosing a special company valuation method? Purpose: The purpose of this paper is to identify, analyse and evaluate the most common methods of valuation for financial analysts, auditors and company lawyers and those factors that influences the choice of method. Method: A multiple survey has been implemented for the actual profession categories. Primary data was collected through semi-structured interviews and a questionnaire survey. Theoretical: The theoretical frame of reference is based upon the paper’s dependent variable, i.e. the role of the appraiser. The appraiser is dependent of following undependent variables: comparative valuation of company, situations of valuation, relevant information, the processes of valuation, the methods of valuation and common custom valuation. Empiricism: Material from the interviews and the questionnaire survey shows how the professional category respectively acts when they valuate a company and why and which valuation method is used. According to the interviews the financial analysts often uses comparative evaluation, the auditor uses the cash flow analysis while the lawyer chooses the net asset value method. Conclusion: The result of this paper considerable agrees to earlier research within the field. The main underlying factor for the appraiser to choose a certain evaluation method is simply depending on the actual situation. Example of other determining factors is customer relations, access to relevant information and which type of business under evaluation. / Yrkesgrupper: Finansanalytiker, revisorer och jurister. Problemformulering: Vad är avgörande för att en specifik företagsvärderingsmetod väljs? Syfte: Syftet med uppsatsen är att identifiera, analysera och utvärdera vilka de vanligast förekommande värderingsmetoderna är för finansanalytiker, revisorer och jurister samt vilka faktorer som påverkar valet av metod. Metod: En flerfallstudie har gjorts hos de berörda yrkeskategorierna. Primärdata samlades in genom semistrukturerade intervjuer samt enkätundersökning. Teoretisk referensram: Den teoretiska referensramen utgår från uppsatsens beroende variabel, värderarens roll. De oberoende variabler som värderaren är beroende av är: relativ företagsvärdering, värderingssituationer, informationskällor, värderingsprocessen, värderingsmetoder och god värderingssed. Empiri: Material från intervjuer och enkätundersökning visar på hur respektive yrkeskategori handlar i en företagsvärderingssituation samt varför och med vilken värderingsmetod. Enligt intervjuerna använder finansanalytikern oftast jämförande värdering, revisorn väljer kassaflödesanalys medan juristen väljer substansvärdemetoden. Slutsats: Uppsatsens resultat överensstämmer på ett bra sätt med tidigare forskning inom området. Den största bakomliggande faktorn till att värderaren väljer en viss värderingsmetod beror oftast på situationen. Exempel på andra avgörande element är relationen till kunden, tillgång till information samt vilken typ av företag som ska värderas.
169

Värdeflödesanalys på DIAB AB Laholm

Mehmedovic, Edin January 2006 (has links)
This report is the result of a 20-points project at the University of Jönköping. The project was carried out in form of a case study with the object of analysing the value flow at DIAB AB’s confection department in Laholm. The aim of this project is to submit proposals to the production management on how to increase the efficiency of the production flow at the confection department and reduce the capital accumulation in form of products in work. The information in this report is gathered from interviews, observations and measurements. Furthermore, a literature study was carried out in view to find suitable theories when analysing present as well as future suggested production conditions. This report is based on four main questions: • What does the existing process of the value flow for the most produced product family look like? • How does the process of the value flow for GS perform considering the through-put-time? o How long through-put-time does a representative product of the GS-family have? o How long is the value- and no value adding time for that product along its production flow? • Which production related disturbances and cost prompters exist in the present value flow process? • How could the process of the value flow for GS be made more efficient, less persistent to disturbances and more competitive? The existing process of the value flow for the most producing product family has been mapped and is illustrated in appendix 3. For now, the process includes nine working stations along the production chain. The through-put-time of a representative GS-product is according to my survey 18,5 days. The value adding time is only 16,1 minutes, that is 0,061 % of the entire through-put-time. The remaining time, in other words the no value adding time, is 440 hours and it represents mainly storage and transport of products. The representative production disturbances and cost prompters that characterise the process of the value flow contain material related disturbances, a high number of long shifts, long storage time prior to the customer order point and with that, high capital accumulation and finally unnecessary transports. Improvement proposals aim to increase the efficacy of the process of the value flow and reduce the capital amounts by shifting from the present production strategy involving manufacturing towards order (TMO) to assembling towards order (MMO). In order to make this possible a semi-manufactured storage will be introduced after the standard confection which will represent the new decoupling point. The production at the standard confection will then occur according to the semi-manufactured storage. The standard confection should produce in larger aggregated order quantities based on prognosis in order to benefit from the advantages of economy of scale and the production must proceed in a continuous flow according to the FIFU-system (First In First Out). In addition to that, the special confection must produce according to a pull-system and only when the customer makes a request. The tact-time of the GS products should constitute a limit for all the cycle times along the production chain, both on the standard- and special confection. This is partly due to creating a constant and balanced production flow which enables short through-put-time and partly due to avoiding in-between-storage as a result of various bottlenecks.
170

Two Dimensional Numerical Modelling Of Variably Saturated Flows

Muthineni, Srinivas 01 1900 (has links)
The prediction of moisture and contaminant transport through unsaturated soil to ground water is becoming increasingly important in the fields of hydrology, agriculture and environmental engineering. Computer aided simulation techniques enables one to conduct a series of systematic numerical experiments to analyze flow phenomenon in subsurface hydrology under various physical and chemical processes. The flow movement depends upon medium characteristics, initial and boundary conditions, which reflect, physical processes occurring below the ground. To understand the effects of physical process an efficient and accurate model is needed. Thus the model developed must be able to handle varied initial and boundary conditions. In this regard, infiltration into a very dry soil becomes a very important problem of study. Most of the earlier numerical models developed are concentrated on the development of an efficient algorithm or the modelling of a particular process which govern the flow in unsaturated or saturated-unsaturated homogeneous medium. Not much work has been done on the analysis of variably saturated flow in layered soil medium. Models to simulate unsaturated flow through dry soils, especially through layered soils with varied boundary conditions are very limited. Further, not much studies have been reported in the literature on the prediction of seepage face development and the phreatic surface movement in variably saturated media with layering. These aspects are very important in determining the flow field and the discharge from the domain. A detailed literature review covering above aspects has been made and is reported in this thesis. In the present work, two dimensional numerical models to predict the movement of wetting front in unsaturated domain and the movement of the phreatic surface in homogeneous and layered porous media under various initial and boundary conditions are developed based on finite difference and finite volume techniques. These models can handle flow in both rectangular flow domains and radial flow domains. The initial condition settings include the handling of very dry soil medium without any transformation of the governing equation, handling of infiltration and constant head conditions at the boundaries under steady state as well as transient scenarios. The models are also able to handle various soil moisture characteristics which depict the nonlinear behaviour between hydraulic conductivity, moisture content and pressure head in a soil media. A mixed form of the governing partial differential equation is used in the present study as it leads to better mass conservation. The finite difference model uses a central difference approximation for the space derivatives and an Eulerian backward difference approximation for the time derivative. The fully implicit formulation is solved iteratively using Strongly Implicit Procedure after making Picard approximation for the highly nonlinear coefficients. The process of infiltration into an initially dry soil leads to the development of a steep wetting front. As the finite volume technique is naturally an upwind method, it is expected to play a positive role in modelling such processes accurately. Hence, a finite volume model is also developed by approximating the convective part using a MUSCL approach and a fully implicit central difference method for the diffusive part of the governing equation. The models developed are validated using both experimental data and numerical solutions for problems reported in the literature. The validation problems cover a wide range of physical scenarios such as: infiltration into a very dry soil, infiltration into a dry soil column with gravity drainage, development of water table mound, steady state drainage in a sand filled wedge shaped tank with seepage face development and transient seepage face development in a rectangular domain. Five test problems are used for the validation of the models. The developed models perform very well for the test problems considered, indicating the models' capability in handling such situations. The results obtained by using the present models for simulating flow through highly unsaturated (very dry) soils show that the models perform very well when compared with models which use transformation techniques to handle such problems. The performance of the present models in comparison with the experimental data and numerical models available in the literature show the suitability of the present models in handling such situations. The present models are also used to analyse various types of unsaturated flow problems with varying initial and boundary conditions. The boundary conditions considered are no flow and /or free flow conditions along the left, right and bottom boundaries with infiltration condition along a part of the top boundary. For the various cases considered in the present study, infiltration rate varies from 5 cm/day to 50cm/day through an initially very dry soil of -15000 cm pressure head in homogeneous and layered soils. Different types of soil media considered vary from sandy loam, loam and clay with horizontal and vertical layering of these soils. A total number of 14 cases are analysed. The results are discussed in terms of pressure head variation in the flow domain along with moisture redistribution for all the cases under consideration. It is observed from these studies that the infiltration rate play an important role on the wetting front movement through layered soils depending on the type of layering and the boundary conditions considered. The soil properties of various layers affect the movement of wetting front by changing the direction of movement. Even though the wetting front movement is predominantly vertical, there is a tendency for the wetting front to move in the horizontal direction as it moves from a coarse soil to fine soil. It is also observed that the vertical layering of soils with different hydraulic conductivity helps in redirecting the flow towards the bottom boundary through the neighboring coarser layers. As finite volume method is more suitable for simulating sharp fronts, it is expected to perform better than finite difference method for simulating infiltration into very dry soils. So, a comparison is made between the performance of these two models by using the above test problems. It is observed from these studies that the performance of both the models are same except that the finite volume method takes much more CPU time than the finite difference model. Considering the type of problems tested, it is observed that for modelling unsaturated and saturated-unsaturated flows, finite difference method is better in comparison to finite volume method. It may be due to the predominant diffusive characteristics of the governing equation even while modelling flow through very dry soils. Proper estimation of the seepage height is an important aspect in finding the discharge through the porous medium. It is observed from the literature that the use of a saturated flow model in such situations can lead to an underestimation of the discharge through the porous medium. This effect is more important when dealing with small dimension problems. It is also observed that various parameters which govern the moisture movement through saturated-unsaturated regions affect proper estimation of the seepage face height and there by discharge. Various factors like effect of boundary conditions, type of soil layering, problem dimension and aspect ratio on seepage face development and the associated phreatic surface formation is studied in the present work. It is seen from the present study that the seepage face development is more in rectangular flow domain than in radial flow domain for both homogeneous and layered soils. It is also seen that the seepage face development in rectangular problems are more sensitive than radial flow problems for various factors considered. The seepage height is also influenced by the tail water level. It is seen from the present study that as the tail water level increases the seepage face reduces with no seepage face development for some of the cases studied. This influence is relatively less for radial flow problems. As the length of the domain increases the seepage height decreases. It is seen that for different cases with same horizontal dimension, as the height of the domain increases the seepage face height also increases. This phenomenon is observed for both homogeneous and layered soil medium. The influence of the aspect ratio, which is the ratio of the length to height of the domain indicate that as the aspect ratio increases the seepage height decreases. The type of the soil layering is observed to have a very strong influence on the seepage face development. The study for understanding the effect of soil layering on the development of seepage face and phreatic surface suggest that as the coarseness of the material increases, the phreatic surface become flatter and its steepness increases with the fineness of the soil. The present model is also used for studying the transient phreatic surface movement and the seepage face development. This is studied for homogeneous and layered rectangular soil medium. The present study is used to understand the effect of specific storage on the phreatic surface movement and the seepage face development. The studies indicate that the influence of specific storage on the seepage face development is insignificant in homogeneous soils with only very little effect in the early time for longer domains. It is also observed that the influence of the specific storage is significant in the case of layered soils. This effect depends on the type of layering and the problem dimension and is observed to have influence for relatively longer period. This observation suggests the importance of specific storage on transient seepage face development. When the specific storage effect is considered the drainage of the soil become faster resulting in a faster decline of the phreatic surface with time. The influence of specific storage is also studied considering the problem dimension effect. It is seen that as the aspect ratio increases, the effect of specific storage on the phreatic surface development decreases. The studies with change in the upstream boundary condition from a constant head to a no flow condition indicate that the effect of specific storage has no significant influence on the phreatic surface development for both homogeneous and layered soils.

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