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Liquefaction Characteristics of Sand Reinforced with Small Percentages of Polypropylene FIberTripathi, Sudhir Kumar 01 May 2018 (has links)
Liquefaction of soil is one of the major contributing factors for damages of infrastructures and utility services during earthquake. Liquefaction occurs when short strong shaking creates undrained loading condition in saturated soil deposit thereby increases pore water pressure, which eventually equals the effective confining pressure resulting in significant reduction in shear strength and bearing capacity of soil deposit. Several studies have been conducted to investigate the effect of polypropylene fiber on sand deposit as a measure to prevent liquefaction but most of them are based on static tests. Therefore, the present study, tries to understand liquefaction characteristics of sand reinforced with polypropylene fiber based on cyclic triaxial test. The main objectives of this study are (i) to explore the effect of polypropylene fiber on pore pressure generation and deformation characteristics of sand, and (ii) to observe the effect of confining pressure on liquefaction characteristics of sand-fiber mixture. A series of stress controlled cyclic triaxial tests were performed at 5 and 10 psi effective confining pressures. At 5 psi effective confining pressure, specimens of clean sand, and sand containing 0.05, 0.075, 0.1, and 0.3% polypropylene fiber by dry weight were tested at 0.2, 0.25, 0.3, and 0.4 Cyclic Stress Ratio (CSR). However, at 10 psi effective confining pressure, specimens were also tested for 0.5%, and 0.75% fiber in addition to those at 5 psi confining pressure at 0.2, 0.3, and 0.4 CSR. Based on the test results, it was observed that, cyclic shear stress increases with the increase in initial effective confining pressure. Also, for a given CSR, liquefaction resistance decreased with the increase in effective confining pressure. Furthermore, significant improvement in liquefaction resistance was observed when the fiber content exceeded beyond 0.075% at 5 psi confining stress. However, at 10 psi confining pressure, addition of fiber did not help in improvement of liquefaction resistance of sand except when cyclic shear stress was applied at 0.2 CSR. At 0.2 CSR, although the specimens did liquefy based on pore pressure generation criteria at all fiber contents, specimens containing 0.5% and 0.75% fiber did not ever reach 2.5% and 5% DA (Double Amplitude) deformation throughout 1000 loading cycles.
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Electrochemical and spectroelectrochemical studies of dyes used in dye-sensitized solar cellsFattori, Alberto January 2010 (has links)
Electrochemical and spectroelectrochemical techniques were employed to investigate the redox characteristics of dyes for dye sensitized solar cells (DSCs) adsorbed at the surface of fluorine-doped tin oxide (FTO) and FTO TiO2 electrodes. In this work are studied Ru-based dyes such as cis-bis(isothiocyanato)-bis(2,2’-bipyridyl- 4,4’dicarboxylato)-ruthenium(II) (N719) and (cis-RuLL'(SCN)2 with L=4,4'- dicarboxylic acid-2,2'-bipyridine and L'=4,4'-dinonyl-2,2'-bipyridine) known as Z907, and indoline organic dyes coded as D102, D131, D149, and D205. The adsorption, diffusion and stability of adsorbed dyes were studied using cyclic voltammetry in acetonitrile and 0.1 M NBu4PF6. The adsorption technique at FTO electrodes was optimized in order to be reproducible so that electrochemical studies as a function of dye coverage were carried out. Langmuirian binding constants were approximately estimated for all dyes adsorbed at FTO electrodes. Rate constants for the chemical degradation of the oxidized dye were also obtained. Is shown that degradation of the dyes mainly occurs at the surface of FTO and only insignificant degradation is evident once the dyes are adsorbed on TiO2. The degradation of dye adsorbed on FTO is shown to affect charge transport from the nonporous TiO2 via electron hopping. Spectroelectrochemical studies of indoline dyes adsorbed on FTO/TiO2 electrodes revealed a red shift of absorption peaks after oxidation and the presence of a strong charge transfer band in the near IR that suggest delocalization of holes in the dye layer. This is consistent with observation that the diffusion coefficient for hole conduction in the adsorbed dye layer is several orders of magnitude higher for the organic dyes compared to the Ru-based dyes. DSCs fabricated using indoline dyes showed good performance. Incident photon-tocurrent conversion efficiency (IPCE) spectra and I-V characteristics are presented.
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A circumferential stretch bioreactor for mechanical conditioning of smooth muscle ringsCooper, Jennifer Lee 30 April 2014 (has links)
Vascular grafts are used to repair, replace, or bypass diseased arteries, and there is a growing need for tissue-engineered blood vessels (TEBVs) as replacement grafts. Three-dimensional, self-assembled smooth muscle cell (SMC) rings can be fabricated and fused to create SMC tissue tubes with a structure similar to native vessels; however, this approach is limited by the underdeveloped mechanical integrity of the tissue. Thus, the goal of this research is to design, manufacture, and validate a cyclic circumferential stretch bioreactor to mechanically stimulate SMC tissue rings, with the goal of developing rings that can withstand the physiological forces of the in vivo environment. The bioreactor consists of a closed cam-syringe-tubing system that forces fluid into the tubing with each rotation of the cam, thereby distending and relaxing the tubing. Various sized cams were implemented to modify the distension of the tubing (5%, 7.5%, 10%, and 15% stretch magnitudes). Tissue rings are placed on the tubing, which is housed in a custom culture chamber. The tubing was validated using DVT® imaging technology to distend approximately 5, 7.5, 10, and 15% under static conditions. High density mapping was used to analyze the dynamic distension of the tubing and tissue rings. During bioreactor operation, the tubing distends 1-2% less than expected for the fabricated cams (5, 7.5, 10, 15%), and the tissue ring distends 31-56% less than the tubing on which it is located. To assess the effects of cyclic distension, 7-day-old SMC rings were cultured dynamically for 7 days and exposed to 0%, 5%, 7.5%, 10%, or 15% cyclic stretch (1 Hz, 100% duty cycle). Histology and immunohistochemistry indicate that both stretched and non-stretched rings synthesized collagen and glycosaminoglycans, but the contractile proteins á-smooth muscle actin and calponin were not synthesized. A decrease in cell density was observed as the magnitude of stretch increased, and the 5-15% stretched samples demonstrated more cellular alignment than the 0% stretch control samples. Mechanical testing analysis concluded that the stretched rings exhibited a reduction in ultimate tensile strength, maximum tangent modulus, maximum strain, and maximum load compared to unstretched control samples. It is anticipated that future work, including modifications of the culture medium and mechanical stimulation parameters (eg. reduced duty cycle, reduced frequency), has the potential to achieve the expected outcome of this research - a strong, aligned, contractile vascular smooth muscle cell tissue ring through dynamic culture using a cyclic circumferential stretch bioreactor.
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The synthesis of a water-soluble molecule containing a hydrophobic cavity.Mandeville, W. Harry January 1975 (has links)
Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Chemistry. / Vita. / Includes bibliographical references. / Ph.D.
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Iron macrocycle complexesKoch, Stephen Andrew January 1975 (has links)
Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Chemistry. / Vita. / Bibliography: leaves [95]-99. / by Stephen Koch. / Ph.D.
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Redução eletroquímicas dos complexos diimínicos de ferro (II) em acetonitrila / Electrochemical reduction of iron complexes diimínios (II) acetonitrileIha, Neyde Yukie Murakami 26 August 1977 (has links)
As reduções eletroquímicas dos complexos de ferro(II) FeL32+, com ligantes diimínicos alifáticos, L=CH3-N=C(R)-C-(R\')=N-CH3, onde R,R\' = H,H; H,CH3; CH3,CH3; e ligantes diimínicos mistos, L = C5H4N-C(R\')=N-(R\"), onde R\',R\"= H,CH3; CH3,CH3 foram estudadas através de polarografia e voltametria cíclica em acetonitrila em perclorato de tetraetilamônio 0,2M a 25,0ºC. Utilizam-se eletrodo plano de platina.ou eletrodo gotejante de mercúrio como eletrodos de trabalho para a voltametria cíclica e polarografia, respectivamente. Os eletrodos auxiliar e de referência são fio de platina e Ag/AgCl , respectivamente. Os polarogramas obtidos para esses complexos no intervalo de potenciais de 0,0 a -2,4 V vs Ag/AgCl mostram duas a quatro ondas de redução. As duas primeiras etapas são controladas por difusão e os processos de eletrodo podem ser descritos como monoeletrônicos e reversíveis, com a estabilização dos baixos estados de oxidação Fe(I) e F:(0) em acetonitrila. Para o derivado R,R\' = H,CH3, observam-se três ondas reversíveis e monoeletrônicas indicando a estabilização do complexo com ferro no estado de oxidação formal (-I).Comportamento semelhante foi encontrado para complexos de ferro(II) com 2,2\'-dipiridina e 1,10 fenantrolina (. Electrochim. Acta. 13. 335 (1968) ). A estabilização dos baixos estados de oxidação deve-se ao caráter aceptor de elétrons dosoligantes diimínicos, como indicado pelo espectro de transferência de carga e,depende da presença do grupo cromofórico. Verifica-se ainda que quanto maior o valor de 10 Dq, maior a retrodoação e, maior a estabilização dos baixos estados de oxidação. Os voltamogramas cíclicos apresentam dois a três picos de redução no intervalo de potenciais de 0,0 a - 2,2V vs Ag/AgCl. A primeira etapa de redução é bem caracterizada como processo monoe1etrônico e reversível Na redução dos derivados alifáticos R,R\' = H,H; CH3.CH3; há um grande aumento da corrente de pico e os potenciais são deslocados cerca de 0,18V para regiões mais negativas. Isso é interpretado em termos de adsorção do reagente na superfície do eletrodo de platina. É interessante notar que apenas os complexos. que apresentam substituintes simétricos adsorvem na superfície do eletrodo. / The electrochemical reduction of the iron(II) complexes, FeL32+ with aliphatic diimine ligands, CH3-N=C(R)-C(R\')=N-CH3, where R,R\'= H,H; H,CH3; CH3,CH3, and mixed diimine ligands. L = C5H4N-C(R\')=N(R\"), where R\',R\" = H, CH3; CH3,CH3, was studied by means of polarography, and cyclic voltammetry in acetonitrile containing 0,2M tetraethylammonium perchlorate at 25,0ºC. A platinum disk or a dropping mercury electrode were used as working e1ectrodes for the cyclic voltammetric and polarographic experiments, respectively. A platinum wire and Ag/AgCl were employed as auxiliar and reference electrodes, respectively. The polarograms obtained for these complexes in the 0.0 to -2,4 V vs Ag/AgCl potential range exhibit two to four reduction waves. The first two reduction waves were shown to correspond to reversible one electron reductions yielding stable complexes of iron in the formal oxidation states (I) and (O). For the derivative R\',R\" = H,CH3, three reversible one electron waves were found, indicating the stability of the complex with iron in the formal oxidation state (-I). A similar be havior has been found for the 2,2\'-dipyridine and 1,10-phenan -throline complexes of iron(II) (Electrochim. Acta,.13, 335(1968)). The stabilization of the low valence states is due to the strong acceptor properties of the diimine ligands. This acceptor character is reflected in the appearence of a characteristic intense inverse charge transfer band in the visible region. in the presence of the diimine chromophore. Increased stabilization of the low oxidation states is correlated with an increase in the magnitude of the ligand-field strength (10 Dq), i.e., increased back-donation. Two or three reduction peaks were observed in the cyclic voltammograms in the region of 0.0 to -2.2 V vs Ag/AgCl. The first reduction of the aliphatic derivatives R,R =\' H,H ; CH3, CH3, there is a large increase in peak currents and a shift of 0.18 V to more negative potentials. This is interpretable in terms of the platinum electrode, It is interesting to note that only the complexes which have symmetrical ligands exhibit adsorption at the electrode surface.
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Desenvolvimento de modelo hipoplástico aplicável a carregamentos cíclicos. / Development of a hypoplastic model applicable to cyclic loading.Costa, Marcelo Saad Taulois da 27 June 2017 (has links)
Modelos constitutivos são relações matemáticas entre grandezas físicas que buscam descrever o comportamento dos materiais quando submetidos a ações externas. A hipoplasticidade é um modelo constitutivo desenvolvido para solos a partir de uma modificação da equação hipoelástica. Este modelo tem como principais características a existência de uma única equação constitutiva e o seu caráter não linear, o que lhe confere a propriedade de introduzir deformações irreversíveis desde o início das ações externas. Neste trabalho são estudados dois novos modelos desenvolvidos com o objetivo de melhorar as previsões para carregamentos cíclicos. O primeiro, denominado hipoplasticidade estendida, é caracterizado pela introdução de superfícies de memória e uma nova equação constitutiva específica para o recarregamento. O segundo modelo, a hipoplasticidade cíclica, é uma modificação deste último onde são introduzidos fatores capazes de modificar as superfícies de memória. Os novos modelos são primeiramente aplicados em situações teóricas para verificar sua aplicabilidade. Posteriormente, utilizando dados experimentais, é feita sua calibração e aplicação para então compararem-se as previsões teóricas com os resultados experimentais. Verifica-se que os novos modelos contemplam avanços significativos na previsão do comportamento dos solos sob carregamentos cíclicos. Para permitir um número maior de simulações foi desenvolvida uma planilha eletrônica com a capacidade de representar quantos ciclos sejam desejados, efetuar a alteração dos parâmetros do solo durante a calibração do modelo de maneira fácil e rápida, assim como visualizar para cada um dos intervalos se foi utilizada a equação geral ou a específica do recarregamento. / Constitutive models are mathematical relationships between physical quantities that approximate the behavior of materials when subjected to external actions. Hypoplasticity is a constitutive model developed for soils from a modification of the hypoelastic equation. The main features of this model are the existence of a unique constitutive equation and its nonlinear character, which gives it the property of introducing irreversible deformation from the beginning of external actions. In this work two new models developed in order to improve the predictions of cyclic loading are studied. The first one, which is called extended hypoplacity, has as its main feature the addition of a memory surface and the introduction of a new equation specific for reloading. The second model, cyclic hypoplasticity, which is a modification of this last one, is characterized by the introduction of factors that are capable of modifing the memory surfaces. The new models are first checked in theoretical situations to verify their applicability. Subsequently, using experimental data, the models are calibrated, applied, and then compared to experimental results. The new models include significant advances in predicting soil behavior under cyclic loading. To allow a larger number of simulations, a spreadsheet was developed with the following abilities: simulate as many cycles as are desired; easy to change soil\'s parameters during the calibration phase; and display for each of the intervals which of the equations was used.
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Control of intracellular calcium level in vascular endothelial cells: role of cGMP and TRP channel.January 2001 (has links)
Lau Kin Ling. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 97-103). / Abstracts in English and Chinese. / Contents --- p.1 / Chapter Chapter 1 --- Introduction --- p.5 / Chapter 1.1 --- Calcium Signaling in Endothelial Cells --- p.5 / Chapter 1.1.1 --- Calcium and its functions --- p.5 / Chapter 1.1.2 --- "Second Messengers: Inositol-1,4,5-Triphosphate and Diacylglycerol" --- p.6 / Chapter 1.1.3 --- Propagation of Ca2+ Signals --- p.8 / Chapter 1.1.4 --- Ca2+-ATPases --- p.9 / Chapter 1.1.5 --- Regulation of Sarcoplasmic Reticulum --- p.10 / Chapter 1.1.6 --- Agonist-induced Ca2+ Entry --- p.11 / Chapter 1.2 --- Mechanism of Store-Operated Ca2+ Entry --- p.14 / Chapter 1.2.1 --- Signaling Mechanisms of SOC --- p.14 / Chapter 1.2.1.1 --- A Diffusible Messenger --- p.14 / Chapter 1.2.1.2 --- Conformational Coupling --- p.15 / Chapter 1.2.1.3 --- Vesicle Secretion --- p.16 / Chapter 1.3 --- Regulation of Ca2+ Entry by cGMP --- p.20 / Chapter 1.4 --- Molecular Structres of Store-operated Channels --- p.22 / Chapter 1.4.1 --- Drosophila Transient Receptor Potential (trp) Gene --- p.22 / Chapter 1.4.2 --- Trpl Gene --- p.23 / Chapter Chapter 2 --- Methods and Materials --- p.27 / Chapter 2.1 --- Materials --- p.27 / Chapter 2.1.1 --- Phosphate-buffered saline --- p.27 / Chapter 2.1.2 --- Culture Media and Materials --- p.27 / Chapter 2.2 --- Preparations and Culture of Cells --- p.28 / Chapter 2.2.1 --- Culture of Rat Aortic Endothelial Cells --- p.28 / Chapter 2.2.2 --- Culture of Human Bladder Epithelial Cell Line --- p.29 / Chapter 2.2.3 --- Culture of Human Embryonic Kidney Epithelial Cell Line --- p.29 / Chapter 2.3 --- Cell. Subculture and Marvest --- p.29 / Chapter 2.4 --- Intracellular Free Calcium Ions ([Ca2+]i) measurment --- p.30 / Chapter 2.4.1 --- Chemicals --- p.30 / Chapter 2.4.2 --- Bathing solutions --- p.31 / Chapter 2.4.3 --- Preparations of Cells for [Ca2+]i Measurement --- p.31 / Chapter 2.4.3.1 --- Plating cells on Glass Cover Slips for [Ca2+]i Measurement with PTI RatioMaster Fluorescence System --- p.31 / Chapter 2.4.3.2 --- Plating cells on Glass Cover Slips for [Ca2+]i Measurement with Confocal Imaging System and Confocal Laser Scanning Microscopy --- p.32 / Chapter 2.4.4 --- PTI RatioMaster Fluorescence System --- p.35 / Chapter 2.4.4.1 --- Experimental Setup --- p.35 / Chapter 2.4.4.2 --- Fura-2/AM Dye loading --- p.35 / Chapter 2.4.4.3 --- Background Fluorescence and [Ca ]i Measurement --- p.37 / Chapter 2.4.5 --- Confocal Imaging System --- p.37 / Chapter 2.4.5.1 --- Experimental Setup --- p.37 / Chapter 2.4.5.2 --- Fluo-3/AM Dye Loading --- p.39 / Chapter 2.4.5.3 --- [Ca2+]i Measurement --- p.39 / Chapter 2.4.6 --- Confocal Laser Scanning Microscopy --- p.40 / Chapter 2.4.6.1 --- Principles --- p.40 / Chapter 2.5 --- Cloning and expression of Trpl in HEK293 cell line --- p.43 / Chapter 2.5.1 --- Cloning of Htrpl Gene into pcDNA3 Vector --- p.43 / Chapter 2.5.1.1 --- Enzyme Digestion --- p.43 / Chapter 2.5.1.2 --- Gel electrophoresis and Isolation of Htrpl by GeneCIean II Kit --- p.44 / Chapter 2.5.1.3 --- Ligation of Trpl and pcDNA3 Vector --- p.44 / Chapter 2.5.1.4 --- Transformation --- p.47 / Chapter 2.5.1.5 --- Purification of cloned Trpl-pcDNA3 by QIAprep Spin Miniprep Kit --- p.47 / Chapter 2.5.2 --- Transfection of HEK293 Cells with Htrpl and pEGFP-Nl Vector --- p.48 / Chapter 2.5.2.1 --- Cell Preparation for Transfection --- p.48 / Chapter 2.5.2.2 --- Transfection --- p.48 / Chapter 2.5.3 --- Fluorescence Labeling of Expressed Htrpl Channel in HEK293 Cells --- p.49 / Chapter 2.5.3.1 --- Immunostaining with Anti-TRPCl Antibody --- p.49 / Chapter 2.5.3.2 --- Labeling with FITC2° Antibody --- p.50 / Chapter Chapter 3 --- Results --- p.51 / Chapter 3.1 --- Propagation of Ca2+ Signaling --- p.51 / Chapter 3.2. --- Effect of cGMP on SERCA --- p.55 / Chapter 3.2.1 --- ATP stimulated Ca2+ release from internal stores --- p.55 / Chapter 3.2.2 --- Effect of cGMP on the falling phase of [Ca2+]i --- p.55 / Chapter 3.2.3 --- Effect of CPA on the falling phase of [Ca2+]i --- p.58 / Chapter 3.2.4 --- Effect of KT5823 on cGMP --- p.63 / Chapter 3.3. --- Effect of cGMP on bradykinin-activated capacitative Ca2+ entry --- p.65 / Chapter 3.3.1 --- Bradykinin induced capacitative Ca2+ entry --- p.65 / Chapter 3.3.2 --- Effect of cGMP on Ca2+ entry activated by bradykinin --- p.67 / Chapter 3.3.3 --- Effect of KT5823 on the inhibitory effect of cGMP on Ca2+ entry activated by bradykinin --- p.67 / Chapter 3.3.4. --- Effect of cGMP and KT5823 on capacitative Ca2+ entry activated by a combination of different agonists. --- p.71 / Chapter 3.4 --- Cloning and expression of htrpl in HEK 293 cell line --- p.75 / Chapter 3.4.1 --- Optimizing transfection conditions using pEGFP-Nl --- p.78 / Chapter 3.4.2 --- Transient transfection of htrpl channel in HEK293 cells --- p.81 / Chapter 3.4.3 --- Channel properties of expressed htrpl channel --- p.84 / Chapter Chapter 4 --- Discussion --- p.88 / Chapter 4.1 --- Ptopagation of Ca2+ Signaling --- p.88 / Chapter 4.2 --- Effect of cGMP on[Ca2+]i of Vascular Endothelial Cells --- p.89 / Chapter 4.2.1 --- Effect of cGMP on SERCA --- p.89 / Chapter 4.2.2 --- Effect of cGMP on Regulation of Agonist-Activated Capacitative Ca2+ Entry --- p.92 / Chapter 4.2.3 --- Physiological Property of Expressed Htrpl in HEK293 cells --- p.95 / References --- p.97
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Ammonia Production at Ambient Temperature and Pressure: An Electrochemical and Biological ApproachPaschkewitz, Timothy Michael 01 July 2012 (has links)
The majority of power generated worldwide is from combustion of fossil fuels. The sustainability and environmental impacts of this non renewable process are severe. Alternative fuels and power generation systems are needed, however, to cope with increasing energy demands. Ammonia shows promise for use in power generation, however it is costly to produce and very few methods of using it as a fuel are developed. To address the need for alternative methods of ammonia synthesis, this research designed and tested a bioelectrochemical device that generates NH3 through electrode induced enzyme catalysis. The ammonia generating device consists of an electrode modified with a polymer that contains whole cell Anabaena variabilis, a photosynthetic cyanobacterium. A. variabilis contains nitrogenase and nitrate/nitrite reductase, catalysts for the production of ammonia. In this system, the electrode supplies driving force and generates a reductive microenvironment near cells to facilitate enzymatic production of NH3 at ambient temperatures and pressures.
Farm animal wastes contain significant amounts of NO2- and NO3-, which can leech into groundwater sources and contaminate them. The system described here recycles NO2- and NO3- to NH4sup+ by the nitrate/nitrite reductase enzyme. Unlike nitrogen fixation by the nitrogenase enzyme whose substrate is atmospheric N2, the substrates for nitrate/nitrite reductase are NO2- and NO3-. The ammonia produced by this system shows great potential as a crop fertilizer.
While the substrates and enzymatic basis for ammonia production by nitrogenase and nitrate/nitrite reductase are very different, there is utility in the comparison of commercially produced ammonia by the Haber Bosch synthesis and by the bioelectrocatalytic device described here. In one day, the Haber Bosch process produces 1800 tons of NH3 at an energetic cost of $500/ton. Per ton of ammonia, the Haber Bosch process consumes 28 GJ of energy. The bioelectrocatalytic device produces 1 ton of NH3 for $10/ton, consuming only 0.04 GJ energy, which can be obtained by sunlight via installation of a photovoltaic device. Thus, the system presented here demonstrates ammonia production with significant impact to the economy.
NH3 production by the bioelectrocatalytic is dependent upon A. var. cell density and electrode polarization. The faradaic current response from cyclic voltammetry is linearly related to cell density and ammonia production. Without electrode polarization, immobilized A. var. do not produce ammonia above the basal level of 2.8 ± 0.4 ΜM. Ten minutes after cycled potential is applied across the electrode, average ammonia output increases to 22 ± 8 ΜM depending on the mediator and substrate chemicals present. Ammonia is produced by this system at 25 °℃ and 1 atm. The electrochemical basis for enhanced NH3 by immobilized cyanobacteria is complex with multiple levels of feedback.
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EFFECTS OF HIGH FAT EXPOSURE ON SKELETAL MUSCLE AUTOPHAGY AND ENDOPLASMIC RETICULUM STRESSHerrenbruck, Adrienne Rose 01 January 2018 (has links)
Autophagy is a major degradation mechanism, responsible for clearing damaged and dysfunctional organelles, including the endoplasmic reticulum, a structure essential for protein synthesis and myocellular hypertrophy. Alterations in autophagy throughout various tissues of the body have been linked to various negative side effects such as decreased myocellular hypertrophy and insulin resistance. High fat diets lead to changes (both increases and decreases) in autophagy in various tissues throughout the body in a tissue-specific manner.
Skeletal muscle autophagy is decreased in myotubes cultured from obese women, however the mechanism by which this occurs is unknown. As the largest organ system in the human body, skeletal muscle serves an important role in overall metabolic health. Therefore, sufficient skeletal muscle autophagy is important for proper metabolic function. Moreover, a decrease in liver and pancreas autophagy has been found to lead to endoplasmic reticulum (ER) stress and the development of insulin resistance. Understanding the relationship between autophagy and ER stress in the skeletal muscle following a high fat diet may help elucidate a novel target for decreasing negative side effects.
Interestingly, both acute and chronic exercise have been shown to increase skeletal muscle autophagy. This points to a potential therapeutic treatment for those suffering with decreased skeletal muscle autophagy and may help improve ER stress.
The purpose of this study was to compare the in vivo and in vitro effects of high fat exposure on skeletal muscle autophagy. Additionally, the relationship of autophagy and ER stress in skeletal muscle was explored. Lastly, this project identified changes in skeletal muscle autophagy and ER stress following cyclic stretch, an in vitro model of exercise in C2C12 myotubes.
Eight-week-old C57BL/6J were fed a high fat diet for 16 weeks and tibialis anterior muscle examined for changes in autophagy markers. Gene expression (mRNA content) of autophagy markers Atg3 (p=0.011, fold change 1.37), Atg12 (p=0.026, 1.38), and Atg16L (p=0.004, 1.49) were increased in skeletal muscle of obese mice. Protein content was also measured, where increases in Atg3 (p = 0.04, 1.22), Atg12 (p = 0.027, 1.21), and Atg16L1(p = 0.021, 1.59) were found. However, there was no difference in LC3 II:I ration. No changes were seen in Atg5 or LC3.
Additionally, C2C12 myotubes were treated with equimolar palmitate and oleate for 24h then assessed for mRNA content of genes involved in autophagy and ER stress. Autophagy genes Atg5 (p = 0.007, fold change 1.78), Atg12 (p = 0.001, fold change 1.99), and LC3 (p = 0.01, fold change 2.02) were decreased with high fat treatment. Paradoxically, there was an increase in Atg16L (p = 0.005, fold change 1.90). There were no changes in protein content. ER stress was increased indicated by an increase of sXBP1 (p = 0.005, fold change 1.33). Furthermore, inhibition of autophagy lead to changes in ER morphology and ER stress.
To identify the impact of cyclic stretch on skeletal muscle autophagy and ER stress, C2C12 myotubes were subjected to 30 minutes of equibaxial stretch and examined for changes in autophagy and ER stress. Autophagy flux, measured by tyrosine release, increased by 34% (p = 0.04) following exercise and ER stress was decreased.
In conclusion, this study provides the novel finding that decreased skeletal muscle autophagy is sufficient for inducing ER stress. Additionally, cyclic stretch increases autophagy and improves ER homeostasis.
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