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Prospecção e identificação de compostos bioativos de subprodutos agroindustriais / Prospecting and identifying bioactive compounds in agroindustrial byproductsTatiane Luiza Cadorin Oldoni 25 January 2011 (has links)
Atualmente, milhões de toneladas de subprodutos são produzidas durante o processamento de alimentos pelas agroindústrias. A maioria deles é rica em compostos bioativos, principalmente os fenólicos, os quais são responsáveis por várias atividades biológicas. Assim, este trabalho teve como objetivos avaliar o conteúdo de compostos fenólicos totais e a atividade antioxidante de três subprodutos agroindustriais engaço e bagaço de uva (Vitis vinifera) da variedade Cabernet Sauvignon e película de amendoim (Arachis hypogaea) , otimizar o processo de extração de compostos bioativos e selecionar o subproduto de maior potencial para a realização do fracionamento e isolamento bioguiado dos compostos responsáveis pela atividade antioxidante. Os subprodutos foram coletados no primeiro semestre de 2010, congelados e liofilizados. O conteúdo de compostos fenólicos totais dos extratos foi determinado pelo método de Folin-Ciocalteu e o potencial antioxidante durante a otimização do processo de extração foi avaliado pelo método de sequestro do radical DPPH. O processo de otimização da extração de compostos antioxidantes foi realizado primeiramente usando modelos univariáveis e, em seguida, foi desenvolvido planejamento fatorial 22 utilizando como variáveis a concentração de solvente e a temperatura de extração. Na última etapa do processo de otimização da extração, foi feito experimento utilizando ultrassom. Para os três subprodutos, observou-se maior sequestro do radical DPPH com o aumento da temperatura de extração e concentração de acetona. As melhores condições para a extração de compostos com atividade antioxidante foram concentração de acetona de 60% e temperatura de extração de 70oC em banho termostatizado. A partir dos resultados obtidos neste estudo, foi feito o isolamento bioguiado dos compostos bioativos da película de amendoim, pois foi o subproduto que apresentou o maior teor de compostos fenólicos e a maior atividade antioxidante. O extrato bruto da película de amendoim foi primeiramente purificado utilizando a resina Amberlite XAD2 para gerar duas frações, as quais foram denominadas frações metanólica (Fr-Met) e aquosa (Fr-aquosa). Após a avaliação da atividade antioxidante dessas frações pelas técnicas de sequestro dos radicais DPPH e ABTS, além da determinação do perfil químico por cromatografia líquida de alta eficência (CLAE), a Fr-Met, a mais bioativa, foi recromatografada em coluna gel Sephadex LH-20. Nesse processo, foram obtidas 123 subfrações, as quais foram reagrupadas, após análise de cromatografia em camada delgada (CCD), em 18 subfrações. Essas subfrações foram avaliadas quanto à atividade antioxidante e a subfração 10, que apresentou elevada atividade antioxidante, foi submetida ao isolamento dos compostos pela técnica de CLAE semipreparativa. Dois compostos foram isolados e denominados composto 1 e composto 2. O composto 1 foi o mais potente, apresentando capacidade de sequestro do radical DPPH, em termos de IC50, de 18,25 \'mü\'g.mL-1, e redução do Fe3+ de 7,59 mmol Fe2+.g-1, valores maiores do que os do antioxidante sintético BHT. Os resultados de atividade antioxidante avaliada pelo método ABTS mostraram que o composto 1 (6,54 mmol TEAC.g-1) possui atividade próxima a padrões naturais com reconhecida atividade, como quercetina e catequina. Por meio da técnica de ressonância magnética nuclear (RMN), foi possível identificar o composto 1 como epicatequina- (2\'beta\'\'SETA\'O\'SETA\'7,4\'beta\'\'SETA\'6)-[epicatequina-(4\'beta\'\'SETA\'8)]-catequina e o composto 2 como epicatequina- (2\'beta\'\'SETA\'O\'SETA\'7,4\'beta\'\'SETA\'8)-[epicatequina-(4\'beta\'\'SETA\'8)]-catequina-(4\'alfa\'\'SETA\'8)-epicatequina, ambos pertencentes à classe das proantocianidinas. Os resultados obtidos neste estudo mostraram que os subprodutos agroindustriais analisados são ricos em compostos fenólicos de alta atividade antioxidante e, portanto, devem ser mais bem explorados pelas indústrias de alimentos e farmacêutica / Nowadays, millions of tons of by-products are produced during food processing in agroindustrial plants. Most of them are rich in bioactive compounds, mainly phenolic substances, responsible for several biological activities. Therefore, this study aimed at assessing the total phenolic compound content and the antioxidant activity of three agroindustrial by-products Cabernet Sauvignon grape stalks and pomace (Vitis vinifera) and peanut skin (Arachis hypogaea) , optimizing the process to extract the bioactive compounds, and selecting the by-product with the highest potential for bioguided fractionation and isolation of the compounds responsible for antioxidant activity. All the by-products were collected in the first semester of 2010, frozen, and lyophilized. Total phenolic compound content was determined using the Folin-Ciocalteu method and antioxidant potential during optimization of the extraction process was assessed by the DPPH radical-scavenging method. The process used to optimize the extraction of antioxidant compounds was carried out initially using univariate models and, after that, a 22 factorial planning was developed using solvent concentration and extraction temperature as variables. In the last phase of the process used to optimize the extraction, we performed an experiment using ultrasound. For the three byproducts analyzed we observed higher DPPH radical-scavenging activity as the extraction temperature and acetone concentration increased. The best conditions for the extraction of antioxidant compounds were acetone at 60% and extraction temperature of 70oC in thermostatic bath. Based on the results of this study, we carried out the bioguided isolation of bioactive compounds from peanut skin, since this was the by-product that presented the highest phenolic compound content and antioxidant activity. Peanut skin crude extract was purified using Amberlite XAD2 resin to generate two fractions, named methanol (Met-Fr) and aqueous fractions (Aqu-Fr). After evaluating the antioxidant activity of these fractions using the DPPH and ABTS radical-scavenging methods, as well as determining their chemical profile by high performance liquid chromatography (HPLC), Met-Fr, the fraction presenting the highest bioactivity, was rechromatographed on a Sephadex LH-20 gel column. During this process, 123 subfractions were obtained and they were regrouped, after thin-layer chromatography (TLC), into 18 subfractions. These subfractions were evaluated as to their antioxidant activity and subfraction 10, which presented high antioxidant activity, underwent isolation of compounds using semipreparative HPLC. Two compounds were isolated and named compound 1 and compound 2. Compound 1 was the most potent, presenting DPPH radical-scavenging activity, in terms of IC50, of 18.25 \'mü\'g.mL-1, and Fe3+ reduction of 7.59 mmol Fe2+.g-1, values that are higher than the synthetic antioxidant BHT. The results of antioxidant activity evaluated by the ABTS radical-scavenging method showed that compound 1 (6.54 mmol TEAC.g-1) has activity similar to natural standards with known activity, such as quercetin and catechin. Using the nuclear magnetic resonance (NMR) technique we identified compound 1 as epicatechin-(2\'beta\'\'SETA\'O\'SETA\'7,4\'beta\'\'SETA\'6)-[epicatechin- (4\'beta\'\'SETA\'8)]-catechin and compound 2 as epicatechin-(2\'beta\'SETA\'O\'SETA7,4\'beta\'\'SETA\'8)-[epicatechin-(4\'beta\'\'SETA\'8)]- catechin-(4\'alfa\'\'SETA\'8)-epicatechin, both belonging to the proantocianidin class. The results obtained in the present study showed that the agroindustrial by-products analyzed are rich in phenolic compounds with high antioxidant activity and, therefore, should be more explored by food and pharmaceutical industries
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Tratamento em duas fases na purificação de efluentes de lixiviados pela integração dos processos de eletrocoagulação e oxidação biológica / Treatment in two phases for the purification of leachate effluents by the integration of electrocoagulation and biological oxidation processesPauli, Aline Roberta de 28 February 2018 (has links)
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Previous issue date: 2018-02-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work aims to remove efficiently organic and inorganic pollutants from a municipal sanitary landfill leachate effluent (SLLE) through of the integrated purification treatment application, composed by the electrocoagulation (ECP) and biological oxidation processes (BOP), looking for the drastic drop on the toxicity. In the first treatment phase, an ECP-based reactor was constructed consisting in a series of 6 aluminum electrode, providing an effective area of 350 cm2 and a useful volume of 1,0 L. In the framework of the response surface methodology (RSM), a 3³ complete factorial experimental design (CFED) at three levels of the three ECP important parameters: initial pH, electric current density (ECD) and electrolysis time (ET) was regarded. A set of responses related to the ECP treatment, such as, the reduction of color, turbidity, COD and iron concentration, was interpreted within the RSM. Additionally, the Analysis of Variance (ANOVA was applied to assess the quality of the second-order polynomial mathematical models that were adjusted to the CFED data. Keeping fixed the best ECP condition (pH and ECD) for the pollutant removals, a set of kinetic tests was carried out regarding a wide range of ET values. The toxicity of ECP treated samples was assessed by the application of bioassays based on the mortality level of the brine shrimp (Artemia salina) and the germination of Lactuca sativa seeds. The toxicity level was assessed by a statistical estimation of the median lethal concentration (LC50) through the application of bioassays with Artemia salina and Lactuca sativa. The biodegradability index by applying the Zahn Wellens test was also assessed. Keeping fixed the ECP condition for which was obtained the lowest toxicity and the highest biodegradability index, the second phase of treatment by BOP was performed. In this regard, a biological reactor with a useful volume of 3.5 L was adjusted to operate keeping fixed the condition of pH 7, temperature of 33 oC and dissolved oxygen of 50%. A relation food/microorganism of one was considered. After that, the residual ammonia in samples was completely removed applying the stripping method (air injection of 50 Lh-1). From the CFED data related to the first treatment phase, the best ECP condition was found by setting the pH at 5, ET at 120 min and ECD at 128.57 Am-2 for which was obtained the maximum removal of 99, 98, 68 e 99% for color, turbidity, COD and iron concentration, respectively. From the kinetic tests, it was possible to verify that the application of the ECP has actually reduced the SLLE toxicity being an ET of 5 min enough to achieve the minimum time required to obtain the lowest toxicity index (LC50 of 43%) that was found in both biotests. The highest biodegradability index was found when an ET value of 45 min. was regarded. The second POB treatment has showed a significant performance on removals of the organic parameters, with values of 95% and 89% for COD and DOC, respectively. Because of achieving an almost 100% removal of the ammoniacal nitrogen, the main result was the substantial improvement on the LC50 value about of 95%, as suggested by the A. salina biotest. Thus, although there were small amounts of pollutants after both treatments (PEC and POB), an almost total toxicity depletion. / Este trabalho, tem como objetivo remover eficientemente os poluentes orgânicos e inorgânicos de efluente de lixiviado proveniente de aterro sanitário municipal mediante a aplicação do tratamento de purificação integrado composto pelos Processos de Eletrocoagulação (PEC) e Oxidação Biológica (POB), visando especificamente a queda da toxicidade e o cumprimento da condição ambientalmente segura para o descarte final em corpos hídricos. Para o PEC, construiu-se um reator com 6 eletrodos de alumínio, tendo uma área efetiva de 350 cm2 e um volume efetivo de efluente de 1,0 L. No contexto da Metodologia de Superfícies de Resposta (MSR), foi proposto um planejamento experimental 3³, variando-se três parâmetros importante do PEC: pH inicial, Densidade de Corrente Elétrica (DCE) e Tempo de Eletrólise (TE). As respostas ao tratamento por PEC (cor, turbidez, DQO e concentração de ferro) foram interpretadas dentro da MSR, verificando pela Análise de variância (ANOVA) a qualidade da representatividade dos modelos matemáticos, polinomiais de segunda ordem, ajustados aos dados. Mantendo fixa a melhor condição de remoção de poluentes pelo PEC quanto ao pH e DCE, experimentos cinéticos foram realizados considerando um amplo intervalo de TE. O nível de toxicidade foi inferido a partir da estimativa estatística da concentração letal mediana (CL50) mediante a aplicação de biotestes utilizando o microcrustáceo Artemia salina e sementes de Lactuca sativa. Avaliou-se o índice de biodegradabilidade, segundo o teste de Zahn Wellens. Na menor toxicidade e o maior índice de biodegradabilidade do lixiviado tratado pelo PEC foi realizada a aplicação da segunda fase de tratamento por POB. Para tanto, foi ajustado o reator biológico, com volume útil de 3,5 L a operar, de forma controlada, na condição de pH 7, temperatura de 33 oC e oxigênio dissolvido de 50%. Utilizou-se uma relação alimento/microrganismo igual a um. Após a realização da integração dos processos, foi feita a remoção de amônia residual do efluente pelo método de arraste (injeção de ar a 50 Lh-1). Da análise do planejamento da primeira fase de tratamento, encontrou-se a melhor condição do PEC no valor de pH igual a 5; TE em 120 min e DCE em 128,57 Am-2 cujo efeito foi a obtenção da máxima remoção de 99, 98, 68 e 99% na cor, turbidez, DQO e concentração de ferro, respectivamente. A partir dos testes cinéticos, foi possível verificar que o PEC reduziu consideravelmente a toxicidade, sendo o TE de 5 minutos a condição de menor toxicidade (CL50 de 43%) que foi encontrada por ambos os biotestes. O índice de biodegradabilidade do efluente de lixiviado tratado teve um aumento de aproximadamente 20% em relação ao efluente bruto para todos os tempos de tratamento por PEC; porém, o maior índice de biodegradabilidade foi encontrado quando houve um TE de 45 minutos. O segundo tratamento por POB apresentou expressiva remoção dos parâmetros orgânicos, sendo obtidas remoções de 95% e 89% para a DQO e o COD, respectivamente. Após a aplicação do processo de arraste de amônia, uma remoção de quase 100% do nitrogênio amoniacal foi alcançada, obtendo uma a CL50 da ordem de 95%, como revelada pelo bioteste com A. salina. Portanto, embora houvesse quantidades pequenas de poluentes após ambos os tratamentos (PEC e POB), atingiu-se a quase total depleção da toxicidade.
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Development of New Structural Health Monitoring TechniquesFekrmandi, Hadi 16 March 2015 (has links)
During the past two decades, many researchers have developed methods for the detection of structural defects at the early stages to operate the aerospace vehicles safely and to reduce the operating costs. The Surface Response to Excitation (SuRE) method is one of these approaches developed at FIU to reduce the cost and size of the equipment. The SuRE method excites the surface at a series of frequencies and monitors the propagation characteristics of the generated waves. The amplitude of the waves reaching to any point on the surface varies with frequency; however, it remains consistent as long as the integrity and strain distribution on the part is consistent. These spectral characteristics change when cracks develop or the strain distribution changes. The SHM methods may be used for many applications, from the detection of loose screws to the monitoring of manufacturing operations.
A scanning laser vibrometer was used in this study to investigate the characteristics of the spectral changes at different points on the parts. The study started with detecting a load on a plate and estimating its location. The modifications on the part with manufacturing operations were detected and the Part-Based Manufacturing Process Performance Monitoring (PbPPM) method was developed. Hardware was prepared to demonstrate the feasibility of the proposed methods in real time.
Using low-cost piezoelectric elements and the non-contact scanning laser vibrometer successfully, the data was collected for the SuRE and PbPPM methods. Locational force, loose bolts and material loss could be easily detected by comparing the spectral characteristics of the arriving waves. On-line methods used fast computational methods for estimating the spectrum and detecting the changing operational conditions from sum of the squares of the variations. Neural networks classified the spectrums when the desktop – DSP combination was used. The results demonstrated the feasibility of the SuRE and PbPPM methods.
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Development of New Structural Health Monitoring TechniquesFekrmandi, Hadi 16 March 2015 (has links)
During the past two decades, many researchers have developed methods for the detection of structural defects at the early stages to operate the aerospace vehicles safely and to reduce the operating costs. The Surface Response to Excitation (SuRE) method is one of these approaches developed at FIU to reduce the cost and size of the equipment. The SuRE method excites the surface at a series of frequencies and monitors the propagation characteristics of the generated waves. The amplitude of the waves reaching to any point on the surface varies with frequency; however, it remains consistent as long as the integrity and strain distribution on the part is consistent. These spectral characteristics change when cracks develop or the strain distribution changes. The SHM methods may be used for many applications, from the detection of loose screws to the monitoring of manufacturing operations.
A scanning laser vibrometer was used in this study to investigate the characteristics of the spectral changes at different points on the parts. The study started with detecting a load on a plate and estimating its location. The modifications on the part with manufacturing operations were detected and the Part-Based Manufacturing Process Performance Monitoring (PbPPM) method was developed. Hardware was prepared to demonstrate the feasibility of the proposed methods in real time.
Using low-cost piezoelectric elements and the non-contact scanning laser vibrometer successfully, the data was collected for the SuRE and PbPPM methods. Locational force, loose bolts and material loss could be easily detected by comparing the spectral characteristics of the arriving waves. On-line methods used fast computational methods for estimating the spectrum and detecting the changing operational conditions from sum of the squares of the variations. Neural networks classified the spectrums when the desktop – DSP combination was used. The results demonstrated the feasibility of the SuRE and PbPPM methods.
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Study Of Multiple Asperity Sliding ContactsMuthu Krishnan, M 07 1900 (has links) (PDF)
Surfaces are rough, unless special care is taken to make them atomically smooth. Roughness exists at all scales, and any surface-producing operation affects the roughness in certain degrees, specific to the production process. When two surfaces are brought close to each other, contact is established at many isolated locations. The number and size of these contact islands depend on the applied load, material properties of the surfaces and the nature of roughness. These contact islands affect the tribological properties of the contacting surfaces. The real contact area, which is the sum total of the area of contacting islands, is much smaller than the apparent contact area dictated by the macroscopic geometry of the contacting surfaces. Since the total load is supported by these contact islands, the local contact pressure will be very high, and dependent on the local microscopic geometry of the roughness. Thus understanding the deformation behaviour of the rough surfaces will lead to better understanding of friction and wear properties of the surfaces. In this work, the interaction of these contact islands with each other is studied when two surfaces are in contact and sliding past each other.
Asperities can be thought of as basic units of roughness. The geometry and the distribution of heights of asperities can be used to define the roughness. For example, one of the earliest models of roughness is that of hemispherical asperities carrying smaller hemispherical asperities on their back, which in turn carry smaller asperities, and soon. In the present study the asperities are assumed to be of uniform size, shape and distribution. Normal and tangential loading response of these asperities with a rigid indenter is studied through elastic-plastic plane strain finite element studies.
As a rigid indenter is loaded onto a surface with a regular array of identical asperities, initial contact is established at a single asperity. The plastic zone is initially confined within the asperity. When the load is increased ,the elastic-plastic boundary moves towards the free surface of the asperity, and the contact pressure decreases. The geometry and spacing are determined when the neighbouring asperities come into contact. The plastic zone in these asperities is constrained, and hence contact pressure sustained by these asperities is larger. As the indentation progresses, more asperities come into contact in a similar way. If a tangential displacement is now applied to the indenter, the von Mises stress contours shift in the direction of indenter displacement. As the tangential displacement increases, the number of asperities in contact with the indenter decreases gradually before reaching a steady sliding state.
The tangential sliding force experienced by the indenter arises from two components. One is the frictional resistance between the contacting surfaces and the other is due to the plastic deformation of the substrate. If the surface is completely elastic, it has been seen that the sliding force is purely due to the specified friction coefficient. For the smooth surface, as the subsurface makes the transition from purely elastic to confined plastic zone, plasticity breaks out on the free surface, hence the sliding force increases. For surfaces with asperities, even at very small load, the asperities deform plastically and hence the sliding force is considerably higher.
The frictional force is experimentally measured by sliding a spherical indenter on smooth and rough surfaces. These experimental results are qualitatively compared with two dimensional finite element results. It has been observed that for rough surface, sliding force is considerablyhigherthanthesmoothsurface,asisobservedinsimu-lations at lower loads. In contrast to the simulations, the sliding force decreases at higher loads for both the smooth and rough surfaces.
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Ação antioxidante de extratos de especiarias e suas misturas binárias e ternárias sobre a estabilidade oxidativa de óleo de soja / Antioxidant activity of spices extracts and their binary and ternary mixtures on soybean oil oxidative stabilityMarilis Yoshie Hayashi Shimano 01 October 2012 (has links)
A oxidação de lipídeos produz compostos indesejáveis que alteram as características organolépticas de alimentos lipídicos e reduzem a qualidade nutricional. Nas indústrias alimentícia, cosmética e farmacêutica são adicionados antioxidantes sintéticos para retardar ou prevenir a deterioração lipídica. Devido aos estudos sobre a possível toxicidade dos antioxidantes sintéticos e ao apelo por compostos ativos naturais, o uso de antioxidantes naturais presentes em ervas e especiarias representa uma alternativa promissora. No presente trabalho foram estudadas as condições de obtenção de extratos hidroalcoólicos de especiarias e sua aplicação em óleo de soja refinado em teste acelerado. O estudo do efeito da temperatura e do grau de hidratação do etanol sobre o teor de compostos fenólicos totais dos extratos de alecrim, orégano, sálvia e tomilho foi realizado com aplicação de planejamento experimental e metodologia de superfícies de resposta. As condições para uma extração eficiente dos compostos fenólicos de alecrim e tomilho desidratados foram o uso de etanol 50% (v/v) e temperatura entre 45 a 50°C. Extrato de sálvia com maiores concentrações em fenólicos totais foram obtidos com etanol 50% (v/v) em uma faixa de temperatura de 57,5 a 60°C. O extrato de orégano requer uso de etanol 40-50% (v/v), em qualquer temperatura na faixa estudada (30 a 60°C). Os compostos identificados por cromatografia gasosa acoplada à espectrometria de massas foram os ácidos cafeico e dihidrocafeico, timol e arbutina. Os extratos de alecrim, orégano e tomilho preparados nas condições otimizadas, bem como suas misturas binárias e ternárias, foram adicionados ao óleo de soja refinado e submetidos a teste acelerado em estufa a 60°C. Os resultados de Índice de Peróxido e Absortividade na faixa do ultravioleta evidenciaram que as misturas de extratos foram capazes de oferecer proteção antioxidante ao óleo de soja refinado. Combinações com alecrim apresentaram os melhores efeitos protetores, sendo a melhor combinação das proporções 15% de tomilho, 65% de alecrim e 20% de orégano, totalizando 100 mg de compostos fenólicos totais/g de óleo. / The lipid oxidation produces undesirable compounds that alter the organoleptic characteristics of food lipids and reduce the nutritional quality. In the food, cosmetics and pharmaceutical industries, synthetic antioxidants are added to retard or prevent the lipid deterioration. Due to the possible toxicity of synthetic antioxidants and the call for active natural compounds, the use of natural antioxidants present in herbs and spices is a promising alternative. Thus, this study evaluated the antioxidant activity of extracts of spices and their mixtures on refined soybean oil. The study of temperature and solvent mixture effects on the phenolic extraction from dried rosemary, oregano, sage and thyme was performed according to response surface methodology and mathematical models. The conditions for an efficient extraction of the phenolic compounds from rosemary and thyme were ethanol 50% at 45-50°C; from sage was ethanol 50% at a temperature range from 57.5 to 60°C, and from oregano was ethanol 40-50% at any temperature in the studied range (30- 60°C). The compounds identified by gas chromatography-mass spectrometry were dihydrocaffeic and caffeic acids, thymol and arbutin. Selected hydroalcoholic extracts of rosemary, oregano and thyme were added to soybean oil subjected to accelerated storage tests. Peroxide values and absorptivity at UV showed that mixtures of extracts were able to provide antioxidant protection to soybean oil. Mixtures with rosemary showed better protective effects than the others. The region of the surface response of the mixtures in which the best protection is offered lies in the proportions of rosemary from 0.50 to 0.80, 0.10 to 0.30 of oregano and thyme from 0.05 to 0.30, in a total of 100 mf GAE/g oil.
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Characterizing Liquid-Fluid Interfaces Using Surface Light Scattering SpectroscopyThapa, Nabin K. 26 July 2019 (has links)
No description available.
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Development of a Functional Shelf Stable High Protein Dairy Beverage with Oat-beta-glucanVasquez Orejarena, Eva G. 21 November 2016 (has links)
No description available.
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Aligned and oriented polyaniline nanofibers: frabrication and applicationsChiou, Nan-Rong 21 September 2006 (has links)
No description available.
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Effects of acid hydrolysis conditions on cellulose nanocrystal yield and properties: A response surface methodology studyDong, Shuping 04 June 2014 (has links)
Cellulose nanocrystals (CNCs) are frequently prepared by sulfuric acid hydrolysis of a purified cellulose starting material. CNC yields, however, are generally low, often below 20%. This study employs response surface methodology to optimize the hydrolysis conditions for maximum CNC yield. Two experimental designs were tested and compared: the central composite design (CCD) and the Box–Behnken design (BBD).
The three factors for the experimental design were acid concentration, hydrolysis temperature, and hydrolysis time. The responses quantified were CNC yield, sulfate group density, ζ-potential, z-average diameter, and Peak 1 value. The CCD proved suboptimal for this purpose because of the extreme reaction conditions at some of its corners, specifically (1,1,1) and (–1,–1, –1). Both models predicted maximum CNC yields in excess of 65% at similar sulfuric acid concentrations (~59 wt %) and hydrolysis temperatures (~65 °C).
With the BBD, the hydrolysis temperature for maximum yield lay slightly outside the design space. All three factors were statistically significant for CNC yield with the CCD, whereas with the BBD, the hydrolysis time in the range 60–150 min was statistically insignificant. With both designs, the sulfate group density was a linear function of the acid concentration and hydrolysis temperature and maximal at the highest acid concentration and hydrolysis temperature of the design space. Both designs showed the hydrolysis time to be statistically insignificant for the ζ-potential of CNCs and yielded potentially data-overfitting regression models. With the BBD, the acid concentration significantly affected both the z-average diameter and Peak 1 value of CNCs.
However, whereas the z-average diameter was more strongly affected by the hydrolysis temperature than the hydrolysis time, the Peak 1 value was more strongly affected by the hydrolysis time. The CCD did not yield a valid regression model for the Peak 1 data and a potentially data-overfitting model for the z-average diameter data. A future optimization study should use the BBD but slightly higher hydrolysis temperatures and shorter hydrolysis times than used with the BBD in this study (45–65 °C and 60–150 min, respectively). / Master of Science
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