In this study, theoretical and computational approaches have been utilized to investigate the mechanisms of natural and artificial metalloproteases. The active sites of most natural metalloproteases contain a tetrahedral zinc center, coordinated by three amino acid residues combinated from His(N), Cys(S), Glu(O), and Asp(O) with a water molecule as the fourth ligand. However, the roles played by the ligands environment in the catalytic functions of enzyme are not clear. In this study, the effects of different ligand combinations (NS2, N2S, N2O, N3, S3, NO2 and NSO) in the mechanism were investigated energy barriers were compared. The machanism and energetics of the substrate bound artificial metalloproteases Ni(II)cyclen (cyclen: 1,4,7,10-tetraazacyclododecane) and Cd(II)cyclen have been investigated. In addition, the mechanism of hydrolysis of Phe-Phe peptide bond catalyzed by another artificial metalloprotease [Pd(H2O)4]2+ has also been studied.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

In this thesis, quantum chemistry, in particular the B3LYP density functional method, is used to investigate a number of methyl transfer enzymes. Quantum chemical methodology is today a very important tool in the elucidation of properties and reaction mechanisms of enzyme active sites. The enzymes considered in this thesis are the S-adenosyl L-methionine-dependent enzymes - glycine N-methyltransferase, guanidinoacetate methyltransferase, phenylethanolamine N-methyltransferase, and histone lysine methyltransferase. In addition, the reaction mechanism of the DNA repairing enzyme O6-methylguanine methyltransferase is studied. Active site models of varying sizes were designed and stationary points along the reaction paths were optimized and characterized. Potential energy surfaces for the reactions were calculated and the feasibility of the suggested reaction mechanisms was able to be judged. By systematically increasing the size of the models, deeper insight into the details of the reactions was obtained, the roles of the various active site residues could be analyzed, and, very importantly, the adopted modeling strategy was evaluated. / QC 20100927

An improved robot manipulator decentralized non-linear adaptive controller that performs well in the presence of disturbances with unknown parameters and non-linearities is presented in this work. The proposed decentralized adaptive structure is a modification of the controller developed by Seraji [13-17] and is characterized by an auxiliary signal that compensates for the unmodeled dynamics and improves the tracking performance, by a feedforward component based on the inverse system to ensure high performance over a wide range and by a PD feedback component of constant gain to improve the speed of response of the system. As a result, a very accurate and fast path tracking is achieved despite the non-linearities. The scheme requires only the measurement of angular speed and displacement of each joint, and it does not require any knowledge about the mathematical model of the manipulator. Due to its decentralized structure, it can be implemented on parallel processors to speed up the operation. The main advantages of the proposed control scheme over similar controllers are that the control activity is smoother, it is less sensitive to sampling size and to the time period elapsed when the whole trajectory is traversed, as verified by simulations of several test conditions of-two of the joints of the PUMA 560 robot arm. / Graduation date: 1991

The development of modern industries calls for the robotic manipulators with high speed and accurate tracking performance. Many authors have paid attention to robust control of robotic manipulators; however, only few authors have also considered the control problem of manipulators with power limitation. In this dissertation, the robotic manipulator is modeled as an uncertain system, with such uncertainties as varying moments of inertia, damping and payloads during tracking. The resulting uncertain part of the system is norm-bounded by a known constant. The total control consists of a linear part with gain matrix K, and a nonlinear part Δv, typically used for control of uncertain dynamical systems. Saturation of the resulting controller is assumed, with bounds imposed by the power limitation of actuators. It is proved at the dissertation that such a system is globally uniformly practically stable. The distribution of the control power between two controllers is discussed. It is found that when small gain matrix K is used and Δv dominates the controller, the solution to the system can approach a smaller region with faster response; that is, higher tracking accuracy is obtained. Theoretical analysis is provided to support the proposed control scheme. A two-link robotic manipulator is simulated with the results confirming the prediction. / Graduation date: 1992

Inositol dehydrogenase (IDH, EC 1.1.1.18) from <i>Bacillus subtilis</i> catalyzes the reversible NAD⁺-dependent oxidation of the axial hydroxyl group of <i>myo</i>-inositol to form 2-keto-<i>myo</i>-inositol, NADH and H⁺. IDH is the first enzyme in catabolism of myo-inositol, and <i>Bacillus subtilis</i> is able to grow on <i>myo</i>-inositol as the sole carbon source. Our laboratory has previously shown that this enzyme has an unusual active site that can accommodate large hydrophobic substituents at 1L-4-position of <i>myo</i>-inositol.<p> In this dissertation, the further characterization of this IDH is described, with focus on the mechanism, inhibition, kinetics, substrate binding, and alteration of substrate specificity. A kinetic isotope effect study revealed that the chemical step of the reaction was not rate-limiting. In order to probe the inositol-binding site, five inositol analogues were synthesized and evaluated as competitive inhibitors. Recently the crystal structures of the <i>apo</i>-IDH, <i>holo</i>-IDH and ternary complex have been solved. Using structural information, as well as modeling and sequence alignment approaches, we predicted the active site structure of the enzyme. On the basis of these predictions, coenzyme specificity was converted from entirely NAD⁺-dependent to 6-fold preference for NADP⁺ over NAD⁺ by site-directed mutagenesis. The critical residues for coenzyme recognition were therefore identified. Besides coenzyme specificity alteration, eleven amino acid residues in and around the proposed <i>myo</i>-inositol active site were also modified to test their roles in order to improve our understanding of substrate binding and activation.

El objetivo de esta tesis es estudiar el funcionamiento de los mercados de trabajo dónde los trabajadores son asignados a las empresas por procesos aleatorios usando modelos de asignación bilateral. En estos modelos, los agentes pertenecen a uno de dos conjuntos disjuntos -empresas y trabajadores- y cada agente tiene preferencias ordinales sobre el otro lado del mercado. El problema se reduce a una asignación de los miembros de estos dos conjuntos el uno al otro.En el segundo capítulo, titulado "On Random Matching Markets: Properties and Equilibria," se describe un algoritmo que empieza desde una asignación cualquiera y continua creando, a cada paso, una asignación provisional. En cada momento del tiempo, una empresa es elegida al azar y se considera el mejor trabajador en su lista de preferencias. Si este trabajador ya está asignado a una empresa mejor, la asignación no se altera. En caso contrario, el trabajador y la empresa quedan temporalmente juntos hasta que el trabajador reciba una propuesta de trabajo mejor. Seguidamente, se exploran algunas propiedades del algoritmo; por ejemplo, el algoritmo generaliza el famoso algoritmo de "deferred-acceptance" de Gale y Shapley. Luego se analizan los incentivos que los agentes enfrentan en el juego de revelación inducido por el algoritmo. El hecho de que las empresas son seleccionadas al azar introduce incertidumbre en el resultado final. Una vez que las preferencias de los agentes son ordinales, se utiliza un concepto de equilibrio ordinal, basado en la dominancia estocastica de primer orden.En el tercer capítulo, "Incentives in Decentralized Random Matching Markets," se considera un juego secuencial dónde los agentes actúan de acuerdo con las reglas generales del algoritmo. En este capítulo, las estrategias de los agentes pueden tomar una forma cualquiera y no tienen que coincidir con una lista de preferencias. El primer jugador es la Naturaleza, que elige una secuencia de empresas , que representa la incertidumbre existente en un mercado descentralizado. Luego, las empresas son elegidas de acuerdo con la sequencia y les es dada la oportunidad de hacer una propuesta. Ya que el juego es dinamico, se analizan los equilibrios de Nash ordinales perfectos en subjuegos.En "Random Stable Mechanisms in the College Admissions Problem," se considera el juego inducido por un mecanismo aleatorio estable. En este capítulo, se caracterizan los equilibrios de Nash ordinales. En particular, puede obtenerse una asignación en un equilibrio dónde las empresas revelan sus verdaderas preferencias si y sólo si la asignación es estable con respecto a las verdaderas preferencias.Por fin, en el último capítulo, se caracterizan los equilibrios perfectos ordinales en el juego inducido por un mecanismo aleatorio estable. / The purpose of this thesis is to explore the functioning of labor markets where workers are assigned to firms by means of random processes using two-sided matching models. In these models, agents belong to one of two disjoint sets -firms and workers- and each agent has ordinal preferences over the other side of the market. Matching reduces to assigning the members of these two sets to one another.In the second chapter, entitled "On Random Matching Markets: Properties and Equilibria," I describe an algorithm that starts with any matching situation and proceeds by creating, at each step, a provisional matching. At each moment in time, a firm is randomly chosen and the best worker on its list of preferences is considered. If this worker is already holding a firm he prefers, the matching goes unchanged. Otherwise, they are (temporarily) matched, pending the possible draw of even better firms willing to match this worker. Some features of this algorithm are explored; namely, it encompasses other algorithms in the literature, as Gale and Shapley's famous deferred-acceptance algorithm. I then analyze the incentives facing agents in the revelation game induced by the proposed algorithm. The random order in which firms are selected when the algorithm is run introduces some uncertainty in the output reached. Since agents' preferences are ordinal in nature, I use ordinal Nash equilibria, based on first-order stochastic dominance.In the third chapter, "Incentives in Decentralized Random Matching Markets," I take a step further by considering a sequential game where agents act according to the general rules of the algorithm. The original feature is that available strategies exhaust all possible forms of behavior: agents act in what they perceive to be their own best interest throughout the game, not necessarily according to a list of possible matches. The game starts with a move by Nature that determines the order of play, reflecting the inherently uncertain features of a decentralized market. Then, firms are selected according to the drawn order and given the opportunity to offer their positions. In order to account for the dynamic nature of the game, I characterize subgame perfect ordinal Nash equilibria.Following a different approach, in "Random Stable Mechanisms in the College Admissions Problem," I consider the game induced by a random stable matching mechanism. In this paper, I characterize ordinal Nash equilibria, providing simultaneously some results that extend to deterministic mechanisms. In particular, a matching can be obtained as the outcome of a play of the game where firms reveal their true preferences if and only if it is stable with respect to the true preferences.In closing, in the last chapter I characterize perfect equilibria in the game induced by a random stable mechanism.

No description available.

One of the main challenges that investors in the Clean Development Mechanism (CDM) project face is the management of the volatility of the price of Certified Emission Reduction (CERs). Large scale CDM projects require a long-term investment with significant amount of costs, and this type of investment is often irreversible. Project investors should quantitatively assess the CER trigger price that justifies the initiation of a CDM investment. The traditional discounted cash flow valuation is unable to capture the option value associated with uncertain investment, and thus it tends to underestimate the trigger price which initiates the investment. Real options theory explicitly considers the option value of delayed investment and can provide a better measurement of the trigger price. This paper presents a theoretical model of the CDM investment project and derives the CER trigger prices that guide investment decisions by using historical market data. It develops a stochastic dynamic programming model for both the geometric Brownian motion process and the mean-reverting process. An analytical solution for the trigger price is derived for the former process, and the trigger price is numerically estimated for the latter. By considering various parameter values, it analyzes the effects of different market environments on the trigger price.

Aim; The aim of this study is to increase our knowledge of stress resilience children coming from backgrounds of substance abuse and to look at what consequences they may encounter, for not being able to express their emotions and deal with happenings experienced in their upbringing. Method; A qualitative approach has been used with e-mail interviews to collect our material, with young adults whom see themselves as having a history of alcoholism in the nearest family when growing up and despite this managed well in life. Result: We have concluded that resiliency is a way of coping with stressful situations. It is a way of repressing emotions when the emotions become too unbearable. When repressing the emotions you are denying the self the right to development, the right to exist as a person. And this leads to co-dependency.