• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 32
  • 20
  • 19
  • 14
  • 8
  • 6
  • 4
  • 4
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 126
  • 24
  • 24
  • 23
  • 22
  • 22
  • 21
  • 17
  • 15
  • 14
  • 13
  • 10
  • 10
  • 9
  • 8
  • 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.
41

Mise en place d'une mesure rapide de la composition chimique de l'aérosol en zone urbaine : étude en mégapoles

D'Argouges, Odile 06 November 2009 (has links) (PDF)
L'augmentation continue de la population urbaine s'accompagne d'une augmentation de la taille des villes et de l'apparition de mégapoles, particulièrement en Asie du sud-est. Ces agglomérations sont des sources intenses de pollution et en particulier de particules atmosphériques. Pour en étudier les différents impacts (sur le climat, l'environnement ou la santé) il est important de documenter les sources et les transformations rapides des polluants, ce que permettent les mesures en temps quasi-réel de leur composition chimique. C'est dans ce cadre que ce travail de thèse se propose de développer et qualifier un parc instrumental de terrain capable de documenter la chimie de l'aérosol sur des pas de temps court (au moins horaires). Cet ensemble permet la mesure des ions majeurs par technique PILS (Particle-Into-Liquid-Sampler), de la fraction carbonée (EC-OC) par technique thermo-optique (EC-OC Sunset Field Analyzer) et celle de la fraction organique hydrosoluble également par technique PILS. La masse totale de l'aérosol est obtenue sans artefact avec un TEOM-FDMS. L'optimisation et la qualification des instruments sont abordées, et le potentiel du parc (à différents stades de son développement) est évalué à partir de résultats obtenus pour les mégapoles contrastées Paris (Mai-Juin 2007) et Pékin (Août 2007). Cet ensemble instrumental permet de reconstruire la masse (PM2.5) et les propriétés optiques des aérosols sur des pas de temps horaires, d'aider à l'identification et à la déconvolution des sources d'aérosols (sources locales/régionales ou primaires/secondaires) ainsi que d'affiner la connaissance de l'aérosol organique à travers sa fraction insoluble/soluble.
42

Dynamics of the Toc GTPases: Modulation by Nucleotides and Transit Peptides Reveal a Mechanism for Chloroplast Protein Import

Reddick, Lovett Evan 01 May 2010 (has links)
The chloroplast is the green organelle in the plant cell responsible for harvesting energy from sunlight and converting it into sugars and ATP. Origins of this organelle can be traced back to an endosymbiotic event in which a primitive eukaryotic cell capable of oxidative phosphorylation engulfed a free-living cyanobacterium capable of photosynthetic respiration (1). Immediately following this event the details are not clear, however what is known is that over the course of evolution, the engulfed cyanobacteria relinquished approximately 97% of its protein coding sequences to the host cell nucleus, thus making the newly formed chloroplast reliant on its host cell (2). This resulted in the requirement of a post-translational import mechanism (3,4). Accomplishing posttranslational import are Translocons of the Outer and Inner Chloroplast membranes, or TOC and TIC complexes (5). These complexes are comprised of multiple proteins whose function is the efficient and robust recognition of chloroplast-destined preproteins and their subsequent import. Preproteins are synthesized in the cytosol with a cleavable Nterminal extension of approximately 50-150 amino acids known as a transit peptide (6-8). It is the transit peptide that is recognized by the Toc complex which facilitates the import of the preprotein (9). It is this transit peptide mediated chloroplast protein import mechanism that will be the subject of this dissertation. Presented in Chapter II is an analysis of the basal enzymology of the isolated, soluble forms of the Toc GTPases. Chapter III analyzes the homo- and heterodimeric interaction between Toc proteins and how this oligomerization can be modulated. Chapter IV presents evidence that the transit 2 peptide interacts with the Toc proteins in such a way as to increase enzymatic activity as well as bias the dimeric equilibria. Analysis of the data presented in Chapters II, III and IV allow the creation of a chloroplast protein import model, Chapter V, to potentially explain the observed phenomenon. Finally, Chapter VI presents potential future directions for this research.
43

Structural and functional analysis of Toc75

Dave, Ashita Mukul 01 December 2010 (has links)
The majority of chloroplast proteins are nuclear-encoded and post-translationally imported into the chloroplast. These newly imported proteins are translocated from the cytosolic compartment to the stroma by the Translocons of the Outer/Inner membranes of Chloroplast (TOC/TIC). In order to understand protein transport across the chloroplast outer membrane, it is crucial to investigate the structure and function of these complexes. The TOC complex is composed of the beta-barrel channel protein Toc75 and the GTPase receptors Toc34 and Toc159. Toc75 is a member of the OMP85 (Outer Member Protein, 85 kDa) superfamily. Other proteins of the OMP85 superfamily also exist in Gram-negative bacteria and mitochondria. The members of this family contain a C-terminal transmembrane beta-barrel and a soluble N-terminus with a varying numbers of POTRA (POlypeptide TRansport Associated) domains. The recent crystal structures of the POTRA domains of Gram-negative bacteria reveal that these domains are localized in the periplasmic side. This thesis identifies the orientation of the POTRA domains as being localized in the cytosol and provides initial evidence for their involvement in the protein import. Three POTRA domains of psToc75 were identified, purified in E. coli and characterized by MALDI-TOF mass spectrometry and circular dichroism. Using variety of immunofluorescence methods, such as flow cytometry and LSCM, the topology of the POTRA domains was investigated. Chloroplast agglutination assays were used to assess the location of immuno-reactive fragments of the POTRA domains, which supported the results from the flow cytometry and LSCM. Finally, thermolysin was used to probe the surface of the isolated intact chloroplasts. Proteolytic digestion along with the data obtained from flow cytometry, LSCM and agglutination assays suggested the orientation of the N-terminal POTRA domains facing the cytosol, followed by a C-terminal beta-barrel domain. The import competence of individual POTRA domains was determined by in vitro chloroplast import and binding competition assays. POTRA1 inhibited the binding of the precursor of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase to intact chloroplasts, while POTRA3 inhibited the import of radiolabeled precursors into isolated chloroplasts; however, in both assays, the inhibition of precursor binding and import was to a lesser extent than non-labeled prSSU.
44

Modellering av organiskt material i avloppsvatten vid mekanisk tillverkning av pappersmassa : Regressionsanalys baserad på COD- och TOC-analyser vid olika grader av blekning och raffinering

Carlström, Johan January 2012 (has links)
I avloppsreningen på Hallsta pappersbruk i Hallstavik reduceras dagligen tonvis med organiskt material innan avloppsvattnet släpps ut i den intilliggande Edeboviken. Bruket är ett så kallat integrerat pappersbruk vilket innebär att man tillverkar både pappersmassan och pappret på plats. Det är främst vid framställningen av massa som det organiska materialet löses ut ur veden och hamnar i processvattnet som så småningom når brukets avloppsreningsverk. På bruket tillverkas papper i olika ljusheter, vilket kräver olika stora insatser i form av blekkemikalier så som väteperoxid och hydrosulfit (även känt som ditionit). Blekningen varierar över tid i produktionscykler och det är sedan tidigare känt att en ökad blekning av massan löser ut mer organiska föreningar. I framtiden förväntas andelen högblekta produkter öka, vilket sannolikt leder till ökad belastning på reningsverket. Det finns även planer på att öka andelen papper av sådan kvalitet som kräver att massan raffineras hårdare (så att den blir finare mald) och frågan har lyfts huruvida denna behandling leder till mer organiskt material till avloppet. Ökad kunskap om hur flödet av organiskt material till avloppet varierar är då detta skrivs (2012) värdefull i minst två tillämpningar på Hallsta pappersbruk. Den ena tillämpningen är vid utredningen av potentialen för en biogasanläggning på bruket, där det organiska materialet utgör en begränsande resurs vid framställningen av biogas, varför det vore värdefullt att veta hur stora mängder organiskt material som kan förväntas vid olika produktionsfall. Den andra tillämpningen är vid doseringen av kväve och fosfor i reningsanläggningen som görs för att mikroorganismerna som används för att rena vattnet ska kunna arbeta optimalt. Huvudsyftet med detta arbete var att skapa en modell för hur mängden organiskt material i olika avloppsströmmar beror på graden av blekning, samt i viss mån raffineringen. Det organiska materialet analyserades som TOC (Total Organic Carbon) och COD (Chemical Oxygen Demand). Ett tydligt samband mellan blekning med väteperoxid och mängden organiskt material i avloppet observerades i en av delströmmarna. Hydrosulfitblekning sågs inte öka mängden organiskt material i avloppsvattnet. En modell för den totala belastningen på avloppsreningsanläggning sattes också ihop, som utifrån planerad dosering av väteperoxid ger en uppskattning av halten TOC i inflödet till anläggningen. Modellen fångar upp den cykliska variation i TOC som observerades över tid, men lämnar lite att önska i fråga om absoluta nivåer.
45

Structure-function analysis of the acidic domain of the Arabidopsis Toc159 receptors

Richardson, Lynn January 2008 (has links)
Most chloroplast proteins are encoded in the nucleus and translated in the cytosol with an N-terminal transit peptide, which facilitates recognition by the receptors of the translocon at the outer membrane of chloroplasts (Toc). The Toc159 family of receptors in Arabidopsis thaliana are the primary chloroplast preprotein receptors. Members of this family differentially associate with either atToc33 or atToc34 (“at” designates the species of origin, Arabidopsis thaliana) to form structurally and functionally distinct Toc complexes; atToc159/33-containing complexes import photosynthetic preproteins, and atToc132(120)/34-containing complexes import non-photosynthetic, plastid house-keeping proteins. The Toc159 receptors are most variable in their N-terminal A-domain, suggesting that this domain may contribute to their functional specificity. The A-domain has structural properties characteristic of intrinsically unstructured protein (IUP) domains, including an abundance of acidic amino acid residues, aberrant mobility during SDS-PAGE and sensitivity to proteolysis. The overall objective of this study was to gain insight into the function of the A-domain. First, to investigate the role of the A-domain in the assembly of structurally distinct Toc complexes, full-length, truncated and domain-swapped variants of atToc159 and atToc132 were targeted in vitro to chloroplasts isolated from wild type (WT) Arabidopsis, and atToc33 and atToc34 null mutants (ppi1 and ppi3, respectively). Insertion of atToc132 was less efficient than atToc159, and was not affected by the removal or swapping of the A-domain. In contrast, removal of the A-domain of atToc159 resulted in decreased insertion, most notably into ppi1 chloroplasts, suggesting that the A-domain is important for insertion, especially into atToc34-containing complexes. These results indicate that the A-domain does play a role in targeting, and may also suggest different roles for the A-domain in targeting of atToc159 and atToc132. Second, a structural analysis of the A-domain of atToc132 and atToc159 was performed using CD and fluorescence spectroscopy to gain insight into their potential function(s). The A-domains were found to be unstructured at physiological pH, and their secondary structure increased with increasing temperature and decreasing pH, which are characteristics of IUPs. IUPs are commonly involved in protein-protein interactions, and their unstructured nature may suggest a role for the A-domains in binding transit peptides, accounting for the ability of the Toc159 receptors to differentially distinguish between a large number of diverse transit peptides that possess low sequence conservation.
46

Flygplansavisningens miljöpåverkan vid svenska flygplatser / The environmental Impact of Aircraft De-icing at Swedish Airports

Marklund, Lars January 2004 (has links)
The aim of this thesis was to answer a number of questions about the environmental consequences of aircraft de-icing. A further aim was to suggest how the environmental consequences due to the release of de-icing fluids can be measured and reduced. The main impact of the aircraft de-icing on the environment is due to the large oxygen demand for the degradation of glycol based de-icing fluids which are released in the environment. The effect of the increase in oxygen demand depends on where the degradation occurs in the ecosystem. In a sensitive ecosystem, the large demand of oxygen could provide an anaerobic environment which would be harmful for many types of organisms. In order to reduce the negative effects of the applied de-icing fluid, there is some type of collection system at every regular airport in Sweden. The methods of collection can be divided into two general groups, hydrological isolation or vacuum sweeper trucks. When the area used for hydrological isolation is relatively small it is called a central de-icing pad. This thesis investigates which methods are being used at 16 of the Swedish airports with the most intense de-icing activity. Of all of these airports, only one does not use vacuum sweeper trucks. Six of the airports use central de-icing pads and five use hydrological isolation of a larger area. The investigation of the efficiency of each method showed no significant differences. This is due to the lack of accurate measurements and that different measurement methods are employed at different airports. This thesis also examines which methods for measuring the efficiency are being used, their weaknesses and what alternatives methods are available. Suggestions are also given to minimize the environmental consequences of aircraft de-icing, taken into account both leakage of the de-icing fluid and its judicious use. The case study of Stockholm-Bromma Airport includes a more detailed investigation of the de-icing activities and a rough mass balance is established. The aim of establisheing the mass balance is to determine the extent of collection of the de-icing fluids, their runoff to the storm water system or arrival at a diffuse sink. The results show that even if the collection is low, only a small part of the de-icing fluids reaches the storm water system. A relatively large part goes to the diffuse sinks where the de-icing fluids degrade on the soil surface or percolate into the soil. In the case study there is also an investigation of the probable impacts on the surrounding environment due to aircraft de-icing at Stockholm-Bromma Airport and suggestions are made how to reduce the impact. / Det primära syftet med examensarbetet har varit att besvara ett antal frågeställningar om flygplansavisningens miljöpåverkan. Frågeställningar som behandlar hur flygplansavisningens miljöpåverkan kan uppskattas/mätas samt reduceras. Den miljöpåverkan flygplansavisningen ger upphov till består främst av den syreförbrukning som orsakas vid nedbrytningen av den använda, glykolbaserade avisningsvätskan. Hur stor denna miljöbelastning blir beror till stor del av var nedbrytningen äger rum. I känsliga ekosystem ger syreförbrukningen upphov till syrefattiga miljöer vilket många organismer missgynnas av. För att reducera de negativa effekter som använd avisningsvätska kan ge upphov till sker på alla svenska reguljära flygplatser ett tillvaratagande av den använda avisningsvätskan. Uppsamlingsmetoderna som används kan uppdelas i två huvudprinciper. Den ena är att området där avisning sker begränsas hydrologiskt och den andra metoden är uppsamling med ”vakuum-sugbil”. Den hydrologiska avgränsningen kan göras för ett mindre område och benämns då som en stationär avisningsyta. Examensarbetet utreder vilka uppsamlingsmetoder för avisningsvätska som används på 16 av de svenska flygplatserna med mest avisningsaktivitet. Vid de undersökta flygplatserna används ”vakuum-sugbil” på alla utom en. På sex av flygplatserna används stationära avisningsplatser och större avgränsade områden för uppsamling finns vid fem flygplatser. Ingen signifikant skillnad i effektivitet (uppsamlingsgrad) kunde påvisas mellan de olika uppsamlingsmetoderna. Anledningen till detta kan ligga i att mätmetoderna skiljer sig mellan de olika flygplatserna och att det är mycket svårt att mäta eller uppskatta effektiviteten. Examensarbetet utreder även vilka mätmetoder som används, deras svagheter samt alternativ till dessa. Förslag ges även till allmänna åtgärder för att minimera flygplansavisningens miljöpåverkan ur såväl utsläppssynpunkt som för resursåtgång. En fallstudie av Stockholm-Bromma flygplats ger en betydligt djupare utredning än för övriga flygplatser och en grov massbalans upprättas för den använda glykolen. Massbalansen upprättas för man ska kunna avgöra hur stora mängder av den använda avisningsvätskan som samlas upp, lämnar flygplatsen via dagvattennätet eller når diffusa sänkor. Resultaten visar att även om uppsamlingsgraden är liten är belastningen på dagvattennätet ringa. En stor andel når de s.k. diffusa sänkorna och bryts ner på markytan eller perkolerar ner genom marken. I fallstudien utreds även den troliga påverkan på vattenrecipienter och omkringliggande närmiljö. Förslag ges även på hur man på bästa sätt skall reducera den miljöpåverkan som den använda avisningsvätskan ger upphov till.
47

Structure-function analysis of the acidic domain of the Arabidopsis Toc159 receptors

Richardson, Lynn January 2008 (has links)
Most chloroplast proteins are encoded in the nucleus and translated in the cytosol with an N-terminal transit peptide, which facilitates recognition by the receptors of the translocon at the outer membrane of chloroplasts (Toc). The Toc159 family of receptors in Arabidopsis thaliana are the primary chloroplast preprotein receptors. Members of this family differentially associate with either atToc33 or atToc34 (“at” designates the species of origin, Arabidopsis thaliana) to form structurally and functionally distinct Toc complexes; atToc159/33-containing complexes import photosynthetic preproteins, and atToc132(120)/34-containing complexes import non-photosynthetic, plastid house-keeping proteins. The Toc159 receptors are most variable in their N-terminal A-domain, suggesting that this domain may contribute to their functional specificity. The A-domain has structural properties characteristic of intrinsically unstructured protein (IUP) domains, including an abundance of acidic amino acid residues, aberrant mobility during SDS-PAGE and sensitivity to proteolysis. The overall objective of this study was to gain insight into the function of the A-domain. First, to investigate the role of the A-domain in the assembly of structurally distinct Toc complexes, full-length, truncated and domain-swapped variants of atToc159 and atToc132 were targeted in vitro to chloroplasts isolated from wild type (WT) Arabidopsis, and atToc33 and atToc34 null mutants (ppi1 and ppi3, respectively). Insertion of atToc132 was less efficient than atToc159, and was not affected by the removal or swapping of the A-domain. In contrast, removal of the A-domain of atToc159 resulted in decreased insertion, most notably into ppi1 chloroplasts, suggesting that the A-domain is important for insertion, especially into atToc34-containing complexes. These results indicate that the A-domain does play a role in targeting, and may also suggest different roles for the A-domain in targeting of atToc159 and atToc132. Second, a structural analysis of the A-domain of atToc132 and atToc159 was performed using CD and fluorescence spectroscopy to gain insight into their potential function(s). The A-domains were found to be unstructured at physiological pH, and their secondary structure increased with increasing temperature and decreasing pH, which are characteristics of IUPs. IUPs are commonly involved in protein-protein interactions, and their unstructured nature may suggest a role for the A-domains in binding transit peptides, accounting for the ability of the Toc159 receptors to differentially distinguish between a large number of diverse transit peptides that possess low sequence conservation.
48

A Study Focused on Rearranging the Dispatching Rules by Simulation Analysis to Improve the Performance of Batch-Typed Flowshop Manufacturing Systems

Pan, Yu-Sheng 10 August 2011 (has links)
In most of the manufacturing operations, production management staffs usually empirical rules or pilot run experiment results to decide production scheduling. However, the former methodology could go with high risk and uncertainty; the latter might partially verify some schedules and products due to the restricted manufacturing resources, and could easily cause delivery delay. This research performed a design of experimentation by computer simulation tool to develop a micro resistance manufacturing process model and compared the performance measurements among different dispatching rules so as to find the process bottleneck. Meanwhile, this research implemented the TOC (Theory of Constraints) theory to improve the manufacturing process and studied the efficiency of the improved process. This experiment took five performance measurements: product throughout, mean flowing time, mean tardiness time, mean queued job quantity and resources utilization in order to validate the results of the various dispatching rules and its performance simulating the real production process and further expects this model to become a reference scheduling model for batch-typed manufacturing processes. Additional production factors are also included into our experiments. For example, the proportion of product types produced, production timings of orders, manufacturing equipments operation time, numbers of manufacturing equipment and order delivery due date. The experiment results exhibit multi-type products of batch-typed flow shop manufacturing could use different dispatching rules based on product requirements to achieve production optimization and output maximization. TOC and adjustments of bottleneck machines can alleviate manufacturing equipment loading and reduce job queue quantity.
49

Prediction of THMs formation in water distribution system of Downtown Kaohsiung City

Shin, Jian-Ming 09 July 2012 (has links)
Chlorine is always used in disinfection process of water treatment plant (WTP) in Kaohsiung, and the major of disinfection by-products (DBPs) is THMs. Reaction of THMs producing were found in relation to lots of factors of water quality. Therefore we used SPSS to analysis the relation between water quality and THMs content for making prediction model of THMs formation in water distribution system in downtown Kaohsiung city. It is expected to estimate the concentration of THMs with a simple method, and to reduce THMs by controlling some items of water quality. While the variance of TOC value is low, we found that concentration of THMs is related to temperature, pH, and residual chlorine by regression method. In these items, residual chlorine had the highest correlation. While the variance of TOC value is high, the correlation between the three items and THMs is weaker than the front one. From this finding, TOC is best one fitting factor in prediction of THMs. In this study, we found that R-square value of Multivariate regression prediction is higher than the value of Univariate regression prediction probably for THMs producing is a complex reaction, so formation model was hard using only one item of water quality.
50

Etude géochimique des sédiments du lac de Cadagno et de la cinétique de déshydratation des stérols

Finck, Yvan 12 December 2003 (has links) (PDF)
Le but de ce travail consiste en l'étude géochimique des sédiments récents du lac alpin de Cadagno et de la cinétique de déshydratation des stérols dans ce milieu. L'examen en microscopie optique des tranches sédimentaires et l'analyse GC-MS des biomarqueurs de type n-alcanes, pristane, phytane, hopanoïdes et stéroïdes ont été utilisés pour préciser les conditions de déposition des sédiments. Des événements tels que des avalanches ainsi qu'une modification du taux de sédimentation ont notamment permis d'expliquer les fluctuations significatives du profil du TOC. L'étude cinétique a montré par ailleurs que le mécanisme de déshydratation des stérols dans ces sédiments est bactérien sélectif et non physico-chimique - ce qui a d'importantes conséquences pour l'étude géochimique de sédiments anciens. Dans le cadre de ce travail, une analyse de sédiments de Monterey (Californie, USA) datant du Miocène a également permis d'identifier une nouvelle classe de biomarqueurs potentiels, les 4,14-diméthylstéranes.

Page generated in 0.1495 seconds