Hops are one of the four main ingredients used to produce beer. Many studies have been done to analyze the science behind growing and harvesting hops, creating hop hybrids, and how to brew beer with hops. However, there has been little research done revolving around the economic demand and supply model of the hop market. The objectives of this study are to create an econometric model of supply and demand of hops in the United States from 1981 to 2012, and to identify important exogenous variables that explain the supply and demand of hops using the two-stage least squares (2SLS) method of analysis. Using the 2SLS method, the demand model yielded that the US beer production variable is significant at the 10 percent level. For every 1 percent change in US beer production, there will be a 6.25 percent change in quantity of hops demanded in the same direction. The supply model showed that US acreage is significant at the 1 percent level. For every 1 percent change in US acreage, there will be a 0.889 percent change in quantity of hops supplied in the same direction. The implications of this study are viewed in relation to both producers and consumers.

The trade-off between linearity and efficiency is the key limiting factor to wideband power amplifier design. Current wireless research focuses much of its effort on building power amplifiers with the two aforementioned criteria going hand in hand to build an optimal design. This thesis investigates the sources of nonlinearity associated with GaN high electron mobility transistors (HEMT), and their subsequent effects on the linearity metrics of the power amplifier. The investigation began with an analysis of the sources of nonlinearity, and then a design-based approach to mitigate those sources of nonlinearity was developed. This design approach was compared with existing trends in power amplifier design. The device technology used in the design was CREE GaN HEMT (45W and 6W). In this report, a systematic approach to designing a two stage power amplifier is discussed, and analyzed for design of linear and highly efficient power amplifiers for base stations. The designed power amplifier consists of two stages: a driver stage and a power stage. The driver stage aimed to linearize the power stage by using circuit analysis and transistor properties along with providing the necessary gain. The power stage was built to complement the driver stage and to achieve high efficiency for the power amplifier. An inter-stage matching network placed between the two stages allowed for the required matching of impedances; transmission lines in the bias feed controlled the harmonic impedances for optimal performance without disrupting performance at fundamental frequencies. This approach effectively improved, and maintained, high efficiency over 200MHz of bandwidth. The design approach was simulated and fabricated in order to test the feasibility of linear power amplifier operation with the use of digital pre-distortion (DPD). The fabricated prototype achieved about 70% peak efficiency over the bandwidth and maintained linearity above 40dBc adjacent channel leakage ratio (ACLR) and below 3% error vector magnitude (EVM). The measurement results indicated that the need for DPD was eliminated when the power amplifier was operating in back-off at the center frequency (800MHz). This thesis compares the prototyped design with existing multistage designs which use linear drivers. The report provides conclusions derive from measurement results and bandwidth limitations faced throughout the course of the design. Lastly, potential research directions, which may allow researchers to overcome the limitations of this design, are discussed.

The trade-off between linearity and efficiency is the key limiting factor to wideband power amplifier design. Current wireless research focuses much of its effort on building power amplifiers with the two aforementioned criteria going hand in hand to build an optimal design. This thesis investigates the sources of nonlinearity associated with GaN high electron mobility transistors (HEMT), and their subsequent effects on the linearity metrics of the power amplifier. The investigation began with an analysis of the sources of nonlinearity, and then a design-based approach to mitigate those sources of nonlinearity was developed. This design approach was compared with existing trends in power amplifier design. The device technology used in the design was CREE GaN HEMT (45W and 6W). In this report, a systematic approach to designing a two stage power amplifier is discussed, and analyzed for design of linear and highly efficient power amplifiers for base stations. The designed power amplifier consists of two stages: a driver stage and a power stage. The driver stage aimed to linearize the power stage by using circuit analysis and transistor properties along with providing the necessary gain. The power stage was built to complement the driver stage and to achieve high efficiency for the power amplifier. An inter-stage matching network placed between the two stages allowed for the required matching of impedances; transmission lines in the bias feed controlled the harmonic impedances for optimal performance without disrupting performance at fundamental frequencies. This approach effectively improved, and maintained, high efficiency over 200MHz of bandwidth. The design approach was simulated and fabricated in order to test the feasibility of linear power amplifier operation with the use of digital pre-distortion (DPD). The fabricated prototype achieved about 70% peak efficiency over the bandwidth and maintained linearity above 40dBc adjacent channel leakage ratio (ACLR) and below 3% error vector magnitude (EVM). The measurement results indicated that the need for DPD was eliminated when the power amplifier was operating in back-off at the center frequency (800MHz). This thesis compares the prototyped design with existing multistage designs which use linear drivers. The report provides conclusions derive from measurement results and bandwidth limitations faced throughout the course of the design. Lastly, potential research directions, which may allow researchers to overcome the limitations of this design, are discussed.

[pt] Este trabalho apresenta um método numérico para solução de escoamentos bidimensionais de fluidos incompressíveis e imiscíveis com presença de interfaces. As equações de conservação são discretizadas através do método de volumes finitos. A modelagem de interface se baseia no método VOF, em que a quantidade relativa de um dos fluidos em cada volume de volume de controle é descrita por uma variável, aqui denominada saturação. Conhecida a distribuição desta variável, é possível a reconstrução da interface quando necessário. A principal particularidade do presente trabalho é que a reconstrução da interface leva em conta seu ângulo de inclinação dentro de cada volume de controle. Isto permite que a advecção da interface se realize com maior precisão do que normalmente se encontra nos trabalhos desenvolvidos a partir do método VOF. Este ângulo de inclinação é obtido partir das saturações da célula analisada e das duas células vizinhas também cortadas pela interface. A determinação da curvatura da interface, importante para o cálculo da pressão capilar, também é facilitada a partir do presente esquema. Domínios axisimétricos, onde os volumes de controle apresentam geometrias mais complexas, também são bem resolvidos, utilizando-se um tratamento especial para os volumes de controle junto ao eixo. Prevê-se ainda a especificação do ângulo de contato da interface com uma parede sólida. Foram testados com sucesso vários problemas, apresentando bons resultados e garantindo a validação do método. / [en] The present work presents a numerical method for the solution of two-dimensional flows of incompressible and immicible fluids in the presence of na interface. The conservation equations are discretized by the finite volume method. The interface modeling is based on the VOF method, in which the relative amount of the fluids in each control volume is described by a variable, denominated here as saturation. Once the distribution of this quantity is known, it is possible to construct the interface, when needed. The main contribution of this work is related to the reconstruction of the interface. For that purpose, it is taken into account the interface angle of inclination inside the control volume. This allows a more precise interface advection that it is usually found with the algorithms based on the VOF method. The interface angle inside a cell is obtained based on its saturation ando n the saturationof two adjacentcells crossed by the interface. By the presents scheme, the interface curvature needed to calculate the capillary pressure can then be easily obtained. Axi-symmetric domains were also considered. For these cases, an special treatment near the axis was necessary. Finally, the algorithm allows the specification of the interface contact angle with a solid surface. Several test problems were examined, presenting good results, validating the method.

Joint models for longitudinal and survival data are a class of models that jointly analyse an outcome repeatedly observed over time such as a bio-marker and associated event times. These models are useful in two practical applications; firstly focusing on survival outcome whilst accounting for time varying covariates measured with error and secondly focusing on the longitudinal outcome while controlling for informative censoring. Interest on the estimation of these joint models has grown in the past two and half decades. However, minimal effort has been directed towards developing diagnostic assessment tools for these models. The available diagnostic tools have mainly been based on separate analysis of residuals for the longitudinal and survival sub-models which could be sub-optimal. In this thesis we make four contributions towards the body of knowledge. We first developed influence diagnostics for the shared parameter joint model for longitudinal and survival data based on Cook's statistics. We evaluated the performance of the diagnostics using simulation studies under different scenarios. We then illustrated these diagnostics using real data set from a multi-center clinical trial on TB pericarditis (IMPI). The second contribution was to implement a variance shift outlier model (VSOM) in the two-stage joint survival model. This was achieved by identifying outlying subjects in the longitudinal sub-model and down-weighting before the second stage of the joint model. The third contribution was to develop influence diagnostics for the multivariate joint model for longitudinal and survival data. In this setting we considered two longitudinal outcomes, square root CD4 cell count which was Gaussian in nature and antiretroviral therapy (ART) uptake which was binary. We achieved this by extending the univariate case i based on Cook's statistics for all parameters. The fourth contribution was to implement influence diagnostics in joint models for longitudinal and survival data with multiple failure types (competing risk). Using IMPI data set we considered two competing events in the joint model; death and constrictive pericarditis. Using simulation studies and IMPI dataset the developed diagnostics identified influential subjects as well as observations. The performance of the diagnostics was over 98% in simulation studies. We further conducted sensitivity analyses to check the impact of influential subjects and/or observations on parameter estimates by excluding them and re-fitting the joint model. We observed subtle differences, overall in the parameter estimates, which gives confidence that the initial inferences are credible and can be relied on. We illustrated case deletion diagnostics using the IMPI trial setting, these diagnostics can also be applied to clinical trials with similar settings. We therefore make a strong recommendation to analysts to conduct influence diagnostics in the joint model for longitudinal and survival data to ascertain the reliability of parameter estimates. We also recommend the implementation of VSOM in the longitudinal part of the two-stage joint model before the second stage.

In this research, Bayesian two-stage D-D optimal designs for mixture experiments with or without process variables under model uncertainty are developed. A Bayesian optimality criterion is used in the first stage to minimize the determinant of the posterior variances of the parameters. The second stage design is then generated according to an optimality procedure that collaborates with the improved model from first stage data. Our results show that the Bayesian two-stage D-D optimal design is more efficient than both the Bayesian one-stage D-optimal design and the non-Bayesian one-stage D-optimal design in most cases. We also use simulations to investigate the ratio between the sample sizes for two stages and to observe least sample size for the first stage. On the other hand, we discuss D-optimal second or higher order designs, and show that Ds-optimal designs are a reasonable alternative to D-optimal designs. / Ph. D.

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Since future microprocessors will have higher current in accordance with Moore's law, there are still challenges for voltage regulators (VRs). Firstly, high efficiency is required not only for easy thermal management, but also for saving on electricity costs for data centers, or battery life extension for laptop computers. At the same time, high power density is required due to the increased power of the microprocessors. This is especially true for data centers, since more microprocessors are required within a given space (per rack). High power density is also required for laptop computers to reduce the size and the weight. To improve power density, a high frequency is required to shrink the size of the output inductors and output capacitors of the multi-phase buck VR. It has been demonstrated that the output bulk capacitors can be eliminated by raising the VR control bandwidth to around 350kHz. Assuming the bandwidth is one-third of the switching frequency, a VR should run at 1MHz to ensure a small size. However, the efficiency of a 12V VR is very poor at 1MHz due to high switching losses. As a result, a 12V VR can only run at 300kHz to 600kHz, and the power density is very low. To attain high efficiency and high power density at the same time, two-stage power architecture was proposed. The concept is "Divide and Conquer". A single-stage VR is split into two stages to get better performance. The second stage has about 5V-6V input voltage; thus the duty cycle can be extended and the switching losses are greatly reduced compared with a single-stage VR. Moreover, a sub-20V MOSFET can be used to further improve the efficiency at high frequencies. The first stage of the proposed two-stage architecture is converting 12V to 5-6V. High efficiency is required for the first stage since it is in series with the second stage. Previous first stage which is a buck converter has good efficiency but bulky size due to low frequency operation. Another problem with using a buck converter is that light-load efficiency of the first stage is poor. To solve these problems, switched-capacitor voltage dividers are proposed. Since the first stage does not require voltage regulation, the sweet point for the voltage divider can be determined and high efficiency can be achieved. At the same time, since there are no magnetic components for the switched-capacitor voltage divider, high power density can be achieved. By very careful design, a power density of more than 2000W/in3 with more than 97% efficiency can be achieved for the proposed voltage divider. The light-load efficiency of the voltage divider can be as high as 99% by reducing the switching frequency at light load. As for the second stage, different low-voltage devices are evaluated, and the best device combinations are found for high-frequency operation. It has been demonstrated that 91% efficiency can be achieved with 600kHz frequency, and 89% efficiency can be achieved with a 1MHz frequency for the second stage. Moreover, adaptive on-time control method and a non-linear inductor structure are proposed to improve CCM and DCM efficiency for the second stage respectively. Previously the two-stage VR was only used as a CPU VR. The two-stage concept can also be applied to other systems. In this dissertation, the two-stage power architecture is applied to two different applications: laptop computers and high-end server microprocessors. The common characteristics of the two applications are their thermal design power (TDP) requirement. Thus the first stage can be designed with much lower power than the maximum system power. It has been demonstrated that the two-stage power architecture can achieve either higher efficiency or higher power density and a lower cost when compared with the single-stage VR. To get higher efficiency, a parallel two-stage power architecture, named sigma architecture, is proposed for VR applications. The proposed sigma VR takes advantage of the high-efficiency, fast-transient unregulated converter (DCX) and relies on this converter to deliver most of the output power, while using a low-power buck converter to achieve voltage regulation. Both the DCX converter and the buck converter can achieve around 90% efficiency when used in the sigma VR, which ensures 90% efficiency for the sigma VR. The small-signal model of the sigma VR is studied to achieve adaptive voltage positioning (AVP). The sigma power architecture can also be applied to low-power point of load (POL) applications to reduce the magnetic component size and improve the efficiency. Finally, the two-stage VR and the sigma VR are briefly compared. / Ph. D.