Grandes partes dos estudos disponíveis na literatura sobre o comportamento dos materiais com microestruturas martensítica e bainítica relatam que a microestrutura bainítica, comparativamente à martensita revenida, promove melhores propriedades de impacto. No presente trabalho foi proposto o estudo de comportamento ao impacto de aços SAE 4140 e SAE 01 (VND) sob diferentes condições de tratamento térmico. Ao todo foram feitos 57 corpos de prova CHARPY para cada tipo de aço divididos em 3 lotes que foram então: temperados e revenidos, com e sem banho criogênico e austemperados. A dureza final após tratamento térmico foi similar nos diferentes tratamentos térmicos. Os resultados obtidos para os dois tipos de aço mostram que os corpos de provas que passaram pelo tratamento térmico de têmpera, revenido e banho criogênico apresentaram melhor tenacidade ao impacto. / Studies available in the literature about bainitic and martensitic microstructure report that bainitic microstructure compared to tempered martensite has better impact properties. In present work has proposed the study of the impact performance of steel SAE 4140 and SAE 01 (VND) under different conditions of heat treatment. A total 57 CHARPY specimens were divided in 3 sets, which were quenched and tempered, with and without cryogenic bath and austempered. The final hardness after heat treatment was similar in the different heat treatments. The results obtained for the two tipes of steel showed better impact performance for samples submitted to quenching tempering and cryogenie bath.

There are numerous numerical and experimental studies to find correlations of octane rating with fuel properties. This thesis was based on the hypothesis that quenching characteristics at ignition locations impact the flame development. Conversely, determination of quenching characteristics might serve as an effective measure to determine the fuel mixture octane number. This hypothesis was tested with premixed flame experiments using primary reference fuels (iso-octane and n-heptane) and commercial grade gasoline. Premixed flame experiments were conducted on a flat flame burner. Primary reference fuels of different ratios were taken and correlated to their respective thermal quenching condition by introducing co-flowing inert gasses at room temperature with fuel-air mixture. The inert gasses that were used in the experiment are nitrogen and helium and the results are analyzed using a camera and an imaging spectrometer. The experimental results support the hypothesis that flame quenching can be correlated to fuel mixture octane number, and holds potential as an alternative method to determine the octane number.

Les matrices d'excitation et d'émission de fluorescence (MEEF) sont utilisées pour caractériser la matière organique naturelle (MON). Afin de mieux exploiter ces informations, un algorithme trilinéaire, PARAFAC, est employé. Après l'élimination des diffusions Rayleigh et Raman et la correction de l'effet d'écran, cette méthode permet de séparer les composants spectraux présents dans les MEEF.Ce travail présente deux études : la qualification et la quantification de la MON selon son origine environnementale et le calcul des constantes de complexation de la MON et du cuivre sous forme ionique.Les composants spectraux et leurs intensités relatives sont calculés par PARAFAC à partir 1146 échantillons regroupés suivant les missions, leur type de milieu, ou le niveau de salinité. Pour étudier ces composants, une nouvelle représentation spectrale est proposée afin de mettre en évidence leur variabilité spectrale. Les résultats montrent que le regroupement d'échantillons d'origine diverse conserve le recouvrement spectral global et les intensités relatives. Sur l'ensemble du domaine spectral, les zones correspondant aux substances humiques sont peu variables, comparées à la zone protéinique.La complexation des métaux par la MON est analysée par une technique combinant quatre outils : l'ajout logarithmique d'ions métalliques, la mesure de MEEF, la méthode PARAFAC et l'algorithme PROSECE. La mesure du quenching de fluorescence ne se limite pas seulement à la modélisation d'une intensité de fluorescence mais à celle de l'intensité relative de chaque composant PARAFAC surpassant ainsi les méthodes utilisées jusqu'à présent. Finalement, l'application de cette technique originale permet de quantifier les propriétés de complexation de la MON à l'aide d'un modèle de complexation utilisant 2 sites de complexation par composant en utilisant la totalité du signal de fluorescence.

To understand protein stability and the mechanism of protein folding, it is essential that we gain a better understanding of the ensemble of conformations that make up the denatured state of a protein. The primary goal of the research described here was to see what we might learn about the denatured state using fluorescence. To this end, tryptophan was introduced at five sites in Ribonuclease Sa (RNase Sa): D1W, Y52W, Y55W, T76W, and Y81W. The fluorescent properties of the denatured states of these five proteins were studied and compared to the fluorescent properties of eight model compounds: N-acetyl-tryptophan-amide (NATA), N-acetyl-Ala-Trp-Ala-amide (AWA), N-acetyl-Ala-Ala-Trp-Ala-Ala-amide (AAWAA), and five pentapeptides based on the sequence around the original tryptophan substitutions in RNase Sa. Regardless of the denaturant, λmax for the proteins and model compounds differed very little, 349.3 ± 1.2 nm. However, significant differences were observed in the fluorescence intensity at λmax (IF), suggesting that IF is more sensitive to the immediate environment than λmax. The differences in IF are due in part to quenching by neighboring side chains. More importantly, IF was always significantly greater in the protein than in its corresponding pentapeptide, indicating that the protein exerts an effect on the tryptophan, which cannot be mimicked by the pentapeptide models. Acrylamide and iodide quenching experiments were also performed on the model compounds and proteins. Significant differences in the Stern-Volmer quenching constant (KSV) were also observed between the proteins and between the proteins and their corresponding pentapeptides. Importantly, the KSV for the protein was always less than in its corresponding pentapeptide. These data along with the IF data show that non-local structure in the unfolded state influences tryptophan fluorescence and accessibility. In summary, these and our other studies show that fluorescence can be used to gain a better understanding of the denatured states of proteins.

No description available.

Estuary is a complex region due to the mixing of fresh and sea water as well as the mixing of terrestrial and marine dissolved organic matters (DOM), so that the sorption behavior between hydrophobic organic compounds and dissolved organic matters is very complicated to estimate. By applying fluorescence quenching method, we investigated the influence of the mixing of binary dissolved organic matters from different sources on the binding constant (Kdoc) of pyrene and DOM. Results show that the kinetic of mixing of binary DOMs influences the binding constant, that means if there weren¡¦t enough standing time for mixing of binary DOMs, it would cause some bias in estimating the binding constants of pyrene and DOMs mixture. In this study, we also found that there exists a linear relationship on the binding constants between pyrene and DOMs mixture against mixing ratios. In addition, the mixing mechanism of SRNOM and LHA was dominated by diffusion process from the results of initial mixing efficiency. However, the diffusion process might not be the only mechanism of the mixing reaction of SHHA and LHA, other factors should be considered. Further investigations should be done to find out the dominating factors on the mixing of SHHA and LHA system in the future.

In this study, we measured the binding constant, KCOC, between several humic acids and benzo(h)quinoline, a nitrogen contained PAHs via using fluorescence quenching method. KCOC of humic acids and phenanthrene, a parent PAHs, is also studied in comparison. Moreover, pH and ionic strength effect on the KCOC were investigated. According to our results, the phenanthrene¡¦s KCOC decreases as the pH increases due to the lower hydrophobicity of humic acid in higher pH values. The variation of benzo(h)quinoline¡¦s KCOC with pH exhibits a more complicated trend, with a maximum value at pH close to the pKb of benzo(h)quinoline. For pH lower than pKb, benzo(h)quinoline is protonated to be benzo(h)quinolinium, a cation, so that the ionic exchange is the dominant prosess in sorption mechanism. Therefore, the binding sites of humic acid increase with pH such that the KCOC increases with pH. In contrast, different mechanism involved in the binding for pH higher than pKb, neutral benzo(h)qunoline becomes dominant and hydrophobic interaction controls the binding prosess in sorption mechanism. At last, the composition of different functional groups of humic acid is also found significant in the binding affinity of benzo(h)qunoline or phenanthrene. Moreover, the benzo(h)qunoline¡¦s KCOC exhibits decreasing trend with increasing magnesium ionic strength because of the reduction of molecular size as well as the benzo(h)qunoline binding sites of humic acid. Findings from this study could provide valuable information for numerical simulation of transport and fates of HOPs in aquatic environment.

The photoabsorption cross sections of NO have been measured in the wavelength range 150~200nm, and the cross sections deviation from Beer-Lambert law due to the insufficient resolution of light source is discussed qualitatively. From the steady state approximation of quenching reactions, the pressure dependence of foreign gas on the ratio of absorption intensity to the fluorescence intensity is derived. Furthermore, the non-Stern-Volmer behaviors of the C2£S(n=0) state of NO were discussed by assuming the non-predissociated (J<9/2) and the predissociated (J>9/2) rotational levels following different quenching mechanisms.

This thesis presents a modeling program to obtain equilibrium information for a fluorescent system. Determining accurate dissociation constants for equilibrium processes involving a fluorescent mechanism can prove to be quite challenging. Typically, titration curves and non-linear least squares fitting of the data using computer programs are employed to obtain such constants. However, these approaches only consider the total fluorescence signal and often ignore other energy transfer processes within the system. The current model considers the impact on fluorescence from equilibrium binding (viz., metal-ligand, ligand-substrate, etc.), quenching and resonance energy transfer. This model should provide more accurate binding constants as well as insights into other photonic processes. The equations developed for this model are discussed and are fit to experimental data from titrimetric experiments. Since the experimental data are generally in excess of the number of parameters that are needed to define the system, fitting is operated in an overdetermined mode and employs error minimization (either absolute or relative) to define goodness of fit. Examples of how changes in certain parameters affect the shape of the titrimetric curve are also presented. The detection of metal ions is very important, causing a need for the development of a metal ion sensor that provides selectivity, sensitivity, real-time in situ monitoring, and a flexible design. In order to be able to perform in situ monitoring of trace metal ions, FRET-pair labeled peptides were attached to a Tentagel[trademark] resin surface. After soaking in nonmetal and metal solutions (pH = 7.5), the resin beads gave an enhanced response in the presence of Hg²⁺ and Zn²⁺. Using a t-test, the signals of the beads that were soaked in a solution of each of these metal ions (and that of Cd²⁺) were determined to be significantly different from beads soaked in a solution without metal. However, the standard deviation between a set the beads was too large in order to differentiate a bead that was soaked in nonmetal solution versus one soaked in a metal containing solution. / text

Gram-negative bacteria use N-acyl homoserine lactones (AHLs) to sense population density and regulate gene expression, including virulent phenotypes. The quorum-quenching AHL lactonase from Bacillus thuringiensis cleaves the lactone ring of AHLs, disabling this mode of gene regulation. Despite the potential applications of this enzyme as an antibacterial weapon, little was known about it's lactone ring-opening mechanism. As a member of the metallo-beta-lactamase superfamily, AHL lactonase requires two divalent metal ions for catalysis. NMR experiments confirm that these metal ions are also involved in proper enzyme folding. The chemical mechanism of ring opening was explored using isotope incorporation studies, and hydrolysis was determined to proceed via a nucleophilic attack by a solvent-derived hydroxide at the carbonyl of the lactone ring. A transient, kinetically significant metal-leaving group interaction was detected in steady-state kinetic assays with AHL lactonase containing alternative divalent metal ions hydrolyzing a sulfur-containing substrate. High-resolution crystal structures implicated two residues in substrate binding and hydrolysis, Tyr194 and Asp108. Site-directed mutagenesis of these residues followed by steady-state kinetic studies with wild-type and mutant enzymes hydrolyzing a spectrum of AHL substrates revealed that mutations Y194F and D108N significantly affect catalysis. Combining these results allows the proposal of a detailed hydrolytic mechanism. The binding site for the N-acyl hydrophobic moiety was probed using steady-state kinetics with a variety of naturally occurring and non-natural AHL substrates, and these studies indicate that AHL lactonase will accept a broad range of homoserine lactone containing substrates. Crystal structures with AHL substrates and non-hydrolyzable analogs reveal two distinct binding sites for this N-acyl group. Based on the ability of this enzyme to accommodate a variety of substrates, AHL lactonase was shown to have the ability to quench quorum sensing regulated by a newly discovered class of homoserine lactone signal molecules possessing an N-aryl group using a bioassay. Steady-state kinetic studies confirm that this class of signal molecules are indeed substrates for AHL lactonase. / text