Driven by economic, technical, and environmental reasons, the energy sector is moving into an era where large portions of increases in electrical energy demand will be met through widespread installation of distributed resources or what's known as distributed generation (DG). DG units can operate in parallel to the main grid or in a micro-grid mode. The later is formed by a cluster of DG units connected to a distribution network to maintain the reliability of critical loads, mainly when the grid supply is not available. Distributed resources include variable frequency sources, high frequency sources, and direct energy conversion sources producing dc voltages or currents. The majority of distributed resources are interfaced to the utility grid or to the customer load via dc-ac pulse-width-modulated (PWM) voltage source inverter (VSI) systems. However, these interfaces introduce new issues, such as the absence of the physical inertia, wide-band of dynamics, limited overload capability, susceptibility to parameters variation, and switching harmonics generation. In addition, the uncertain and dynamic nature of the distribution network challenges the stability and control effectiveness of a grid-connected inverter-based DG interface. Generally, difficulties appear in the form of grid impedance and interfacing parameter variations, fast and slow grid-voltage disturbances, grid distortion and unbalance, and interactions between the inverter ac-side filter and the grid. On the other hand, a micro-grid system will be dominated by inverter-based DG units. Unlike conventional power system generators, inverter-based DG units have no physical inertia. This fact makes the micro-grid system potentially susceptible to oscillations resulting from system disturbances. Severe and random disturbances might be initiated in a micro-grid system, due to load changes, the power sharing mechanism of the inverters and other generators, and interactions between the DG interface and the network. Motivated by the aforementioned difficulties, this thesis presents new control algorithms for the DG interface that guarantee stable and high power quality injection under the occurrence of network disturbances and uncertainties, in both the grid-connected and micro-grid systems. The control architecture of the proposed DG interface relies on the following subsystems. First, a newly designed deadbeat current regulation scheme is proposed. The proposed design guarantees high power quality current injection under the presence of different disturbing parameters such as grid voltage distortion, interfacing parameter variation, and inverter system delays. Further, it utilizes the maximum dynamic performance of the inverter in a way that provides a high bandwidth and decoupled control performance for the outer control loops. Different topologies of the ac-side filter are considered for the current control design. Second, a novel adaptive discrete-time grid-voltage sensorless interfacing scheme for DG inverters is proposed. The adaptive interface relies on a new interface-monitoring unit that is developed to facilitate accurate and fast estimation of the interfacing impedance parameters and the grid voltage vector (magnitude and position) at the point of common coupling. The estimated grid voltage is utilized to realize a grid-voltage sensorless interfacing scheme, whereas the interfacing parameters are utilized for the self-tuning control and interface-parameter monitoring. Further, a simple and robust synchronization algorithm and a voltage-sensorless average power control loop are proposed to realize an adaptive voltage-sensorless DG interface. The voltage-sensorless interface positively contributes to the elimination of the residual negative sequence and voltage feed-forward compensation errors, and to the robustness of the power sharing mechanism in paralleled inverter systems, where the power-sharing mechanism is generally based on open-loop controllers. Third, a new voltage control scheme for the DG interface featuring fast load voltage regulation and effective mitigation of fast voltage disturbances is proposed. The proposed voltage control scheme targets the problem of fast and large-signal-based voltage disturbances, which is common in typical distribution feeders. A hybrid voltage controller combining a linear with a variable-structure-control element is proposed for the DG interface. Positive and dual-sequence versions of the proposed voltage controller are developed to address the issue of unbalanced voltage disturbances. The proposed voltage controller successfully embeds a wide band of frequency modes through an equivalent internal model. Subsequently, wide range of balanced and unbalanced voltage perturbations, including capacitor-switching disturbances, can be effectively mitigated. Fourth, to constrain the drift of the low frequency modes in a conventional droop-controlled micro-grid, a new transient-based droop controller with adaptive transient-gains is proposed. The proposed power-sharing controller offers an active damping feature that is designed to preserve the dynamic performance and stability of each inverter unit at different loading conditions. Unlike conventional droop controllers, the proposed droop controller yields two-degree of freedom tunable controller. Subsequently, the dynamic performance of the power-sharing mechanism can be adjusted, without affecting the static droop gain, to damp the oscillatory modes of the power-sharing controller. The overall robust DG interface facilitates a robust micro-grid operation and safe plug-and-play integration of DG units on existing distribution systems; hence increasing the system penetration of DG. The direct result of this development is huge financial saving for utilities by capturing the salient features of deploying DG into existing utility networks. Further, these developments are significant to the industry as they provide the blue print for reliable control algorithms in future DG units, which are expected to operate under challenging system conditions.

Columns subjected to time varying axial load may exhibit dynamic instability due to parametric resonance. This type of instability is inherent in structures; it is not due to material or geometrical imperfections, and can occur even in perfectly constructed structures. This characteristic makes parametric resonance a very difficult to predict and therefore dangerous phenomenon. In this thesis the stability of a structural column under bounded noise axial load is studied by use of Lyapunov exponents. Bounded noise is especially useful as a loading because it may be used to represent both wide and narrow band processes, making the stability equations developed general enough to handle a wide variety of real world probabilistic loadings. The equation of motion of the first mode of vibration for this system is a second-order nonlinear stochastic ordinary differential equation. The nonlinearity makes the system exhibit bifurcating behaviour where stability shifts from the trivial solution to a non-zero mean stationary solution. The stability of the trivial and non-trivial solutions is important in obtaining a complete picture of the dynamical behaviour of the system. The effect that damping, the amplitude of noise, and the level of nonlinearity have on the stability of a structural column is studied using both analytical and numerical approaches. The largest Lyapunov exponent of the trivial solution is determined analytically by using time averaged versions of the original equation of motion. The validity of the analytical time averaged equation of motion is also verified with Monte Carlo simulations. Due to the mathematical complexity the largest Lyapunov exponent of the non-trivial stationary solutions is obtained using Monte Carlo simulation only.

Drug stability is one of the vital subjects in the pharmaceutical industry. All drug products should be kept stable and protected against any chemical, physical, and microbiological degradation to ensure their efficacy and safety until released for public use. Hence, stability is very important to be estimated or predicted. This work involved studying the stability of three different drug agents using three different mathematical models. These models included both empirical models (linear regression and artificial neural network), and mechanistic (kinetic) models. The stability of each drug in the three cases studied was expressed in terms of concentration, hardness, temperature and humidity. The predicted values obtained from the models were compared to the observed values of drug concentrations obtained experimentally and then evaluated by calculating the mean of squared. Among the models used in this work, the mechanistic model was found to be the most accurate and reliable method of stability testing given the fact that it had the smallest calculated errors. Overall, the accuracy of these mathematical models as indicated by the proximity of their stability measurements to the observed values, led to the assumption that such models can be reliable and time-saving alternatives to the analytical techniques used in practice.

Bargaining theory seeks to answer the question of how to divide a jointly generated surplus between multiple agents. John Nash proposed the Nash Bargaining Solution to answer this question for the special case of two agents. Kleinberg and Tardos extended this idea to network games, and introduced a model they call the Bargaining Game. They search for surplus divisions with a notion of fairness, defined as balanced solutions, that follow the Nash Bargaining Solution for all contracting agents. Unfortunately, many networks exist where no balanced solution can be found, which we call unstable. In this thesis, we explore methods of changing unstable network structures to find fair bargaining solutions. We define the concept of Blocking Sets, introduced by Biro, Kern and Paulusma, and use them to create stability. We show that by removing a blocking set from an unstable network, we can find a balanced bargaining division in polynomial time. This motivates the search for minimal blocking sets. Unfortunately this problem is NP-hard, and hence no known efficient algorithm exists for solving it. To overcome this hardness, we consider the problem when restricted to special graph classes. We introduce a O(1)-factor approximation algorithm for the problem on planar graphs with unit edge weights. We then provide an algorithm to solve the problem optimally in graphs of bounded treewidth, which generalize trees.

<p>In this thesis we try to construct a stability condition on the quintic threefold. We have not succeeded in proving the existence of such a stability condition. However we have constructed a stability condition on a quotient category of projective space that approximates the quintic. We conjecture the existence of a stability condition on the quintic threefold generated by spherical objects and explore some consequences.</p> / Dissertation

The growth of the heterotrophic plate count in distribution system, causing deterioration of drinking water quality, is called biological re-growth or after-growth. There are many methods to solve above problems such as disinfecting and washing in pipeline. Among them, to lower the concentration of assimilable organic carbon(AOC) in drinking water under a certain level is showed the best control method for inhibiting the growth of microorganisms. AOC is showed as an item of the organic amounts by using microorganisms. The samples of water after disinfecting is took into bacterial of P17 and NOX. Then we measure the growth number counts of two kind of bacterial in their plate to transfer and obtain the concentration of AOC. In this study we investigate the variation of AOC in a tradition water treatment plant and its distribution system by using the results of sampling and analysis of the related items of water quality. Results showed the proportional of AOC-P17 was highest in contains of AOC. The removal of AOC during processes of water treatment was effectively found. But the pre-chlorination caused the increase of AOC level in water let the concentration of AOC be detected over 50£gg acetate-C/L in treated water and the distribution system. AOC level decreased with the increasing distance of distribution system. For the well relation with drinking water quality and treatment units, we should control the biological stability to obtain a good water quality of treated water. Finally we analysis 13 items of water quality by using AutoNet(6.03) with AOC to do the prediction model work. After data simulation and training analysis, three models of AOC prediction (denoted as WTP, Distribution system and WTP& Distribution system) were obtained. The comparisons of three models in inner and outer verification showed good correlation results as well.

The improvement of performance and the maintenance of stability of a portable air-breathing PEMFC are studied in this thesis. The water content within proton exchange membrane affects strongly on the performance and stability of a PEMFC stack, in which water within membrane can form a conduction channel to provide hydrogen ion transferring from anode to cathode. The over-dried condition caused by a long time operation can also be avoided to prevent the membrane from damaging. Thus the proper humidification of a stack is important for a portable air-breathing PEMFC system. The traditional humidifier is too bulky to be suitable for portable fuel cells. A simple humidification system developed in this research is making use of the water stored in the stack bottom and the self-generating heat by chemical reaction to drive the passive humidification system of this stack. The water at the bottom of the tank can be sucked with cotton threads in cathode and a piece of cotton cloth by capillary phenomenon and transfer to the membrane of MEA. The cotton threads humidification in cathode is enough in low and middle current density in this study. It is not enough in high current density due to the large water vapor dissipation in the cathode surface, so a cotton cloth in anode is added to increase the evaporating surface to supply water to membrane. This passive humidification system does not need extra energy, and it only employs the heat generated by the cells. The system follows the simple principle, which is always obeyed in a portable fuel cell system. A 16-cell HFC stack developed in this research adopts carbon fibers as current collectors. Two pieces of 8-cell anodes is placed in the inner sides of the stack, and the 8-cell cathode is located on external sides, which is exposed directly to the ambient air. The 16-cell can connect in series or parallel. The experimental results show that it is helpful to add cotton threads in cathode and cotton cloth in anode to improve the stability of the 16-cell stack during a the long period operation. The 16-cell HFC stack has succeeded in the operation and charging for an IPhone, digital photo frame, and LED light. The experiments have proved that this type of the lightweight humidification system is helpful in the future portable hydrogen fuel cell applications.

In the past decade, aggressive scaling of transistor feature size has been a primary force driving higher Static Random Access Memory (SRAM) integration density. Due to the scaling, nanometer SRAM designs are getting more and more stability issues. The traditional way of analyzing stability is the Static Noise Margins (SNM). However, SNM has limited capability to capture critical nonlinearity, so it becomes incapable of characterizing the key dynamics of SRAM operations with induced soft-error. This thesis defines new stability margin metrics using a system-theoretic approach. Nonlinear system theories will be applied rigorously in this work to construct new stability concepts. Based on the phase portrait analysis, soft-error can be explained using bifurcation theory. The state flipping requires a minimum noise current (Icritical) and time (Tcritical). This work derives Icritical analytically for simple L1 model and provides design insight using a level one circuit model, and also provides numerical algorithms on both Icritical and Tcritial for higher a level device model. This stability analysis provides more physical characterization of SRAM noise tolerance property; thus has potential to provide needed yield estimation.

In the poultry industry, further processed meat products have the highest share in the market, and because there is a growing demand of food products with enriched amounts of unsaturated fatty acids, the objectives of this research were to assess lipid oxidation development and quality characteristics of chicken meat as affected by dietary fat and vitamin E levels. Broilers were fed during six weeks with diets containing animal/vegetable, lard, palm kernel, soybean, conjugated linoleic acid, flaxseed, or menhaden oil. Each lipid diet was supplemented with either a control (33 or 42 mg/kg) or a supranutritional level (200-400 or 200 mg/kg) of vitamin E. Breast and thigh meat, or skin, were processed, packaged, and refrigerated as raw meat, cooked patties, or cooked sous vide meat. The results showed that the chicken meat fatty acid composition reflected those from the dietary fats. In the meat or skin there was a higher lipid oxidation susceptibility as the proportion of unsaturated fatty acids increased, shown as malonaldehyde values, particularly in the treatments with low supplemented level of vitamin E (P<0.05). The relative lipid oxidative stability of the meat decreased in consecutive order from raw, cooked sous vide, and cooked meat patties. Sous vide cooked meat developed lipid oxidation at a slow rate and showed not to be affected by nonheme iron values. Dietary fat and vitamin E level affected breast meat lightness (L* color space) values (P<0.05), but not muscle pH, Allo-Kramer shear force, or water holding capacity. In conclusion, the increment in the proportion of unsaturated fatty acids increases the susceptibility to lipid oxidation in the meat. Supranutritional supplementation levels of vitamin E are more effective at inhibiting the lipid oxidation development in chicken meat than some current levels used by the poultry industry. Neither dietary fat nor vitamin E level seems to affect the development of pale, soft, and exudative meat condition in chicken meat.

Tool chatter in longitudinal turning is addressed with a new perspective using a complex machining model describing the coupled tool-workpiece dynamics subject to nonlinear regenerative cutting forces, instantaneous depth-of-cut (DOC) and workpiece whirling due to material imbalance. The workpiece is modeled as a system of three rotors: unmachined, being machined and machined, connected by a flexible shaft. The model enables workpiece motions relative to the tool and tool motions relative to the machining surface to be three-dimensionally established as functions of spindle speed, instantaneous DOC, rate of material removal and whirling. Excluding workpiece vibrations from the cutting model is found improper. A rich set of nonlinear behaviors of both the tool and the workpiece including period-doubling bifurcation and chaos signifying the extent of machining instability at various DOCs is observed. Presented numerical results agree favorably with physical experiments reported in the literature. It is found that whirling is non-negligible if the fundamental characteristics of machining dynamics are to be fully understood. The 3D model is explored along with its 1D counterpart, which considers only tool motions and disregards workpiece vibrations. Numerical simulations reveal diverse behaviors for the 3D coupled and 1D uncoupled equations of motion for the tool. Most notably, observations made with regard to the inconsistency in describing stability limits raise the concern for using 1D models to obtain stability charts. The nonlinear 3D model is linearized to investigate the implications of applying linear models to the understanding of machining dynamics. Taylor series expansion about the operating point where optimal machining conditions are desired is applied to linearize the model equations of motion. Modifications are also made to the nonlinear tool stiffness term to minimize linearization errors. Numerical experiments demonstrate inadmissible results for the linear model and good agreement with available physical data in describing machining stability and chatter for the nonlinear model. Effects of tool geometry, feed rate, and spindle speed on cutting dynamics are also explored. It is observed that critical DOC increases with increasing spindle speed and small DOCs can induce cutting instability -- two of the results that agree qualitatively well with published experimental data.