Liquid mixture is everywhere in the chemical industry and widely studied by researchers. An accurate prediction of its physicochemical property is of vital importance in developing efficient process optimization. However, measurements from experiment are usually time consuming and inefficient. Furthermore, clear understanding of many of fundamental physicochemical phenomena hasn't been obtained, which restricts the development of novel products. Molecular simulation techniques have become an impressive tool to deal with these challenges during past decades. This thesis mainly applied molecular simulation to predict the physicochemical properties of industrially relevant mixtures and investigate the molecular mechanism behind observed phenomena. Among various properties, cohesive energy is the central focus, which reveals intermolecular interactions between molecules of different types. Mixture systems of two different areas of application were studied. The first is amorphous polymer-plasticizer mixtures, which, with varying composition, correspond to plastic products of different grades for application in different areas. The most important class of plasticizers are phthalate diesters, in which di (2-ethylhexyl) phthalate (DEHP) is the most frequently used compound. However, phthalates are prone to migration loss from the host poly(vinyl chloride) (PVC), which results in the contamination of surrounding environment, gradual deterioration of plastics performance, and potential harm to human health. It has thus prompted tightening governmental regulation on their usage. With this background, we aim to address three challenges: (I) model plasticized PVC to predict its physicochemical property, (II) obtain molecular insight into plasticization and plasticizer diffusion pattern inside PVC, (III) correlate plasticizer performance -- compatibility, efficacy, and mobility -- with its molecular structure. Cohesive energy plays a central role especially in understanding plasiticzer compatibility and migration tendency. Our modeling and simulation protocol is firstly tested on phthalates, where the simulated plasticization efficacy and thermodynamic compatibility with the host polymer agree well with all known experimental observations. Furthermore, through simulation of plasticizer diffusion pattern, we found relaxation of the alkyl side chains is a key factor in plasticizer migration. Next, we expand our simulation to a wider group of plasticizers including adipates, trimellitates, and citrates. The computed mixing enthalpy and Young's modulus again show an excellent agreement with available experimental data. Dependance of plasticizer performance on seven molecular design parameters are evaluated. The obtained relationship clearly tells us decreasing leg length or increasing branching on the leg will raise plasticizer compatibility with PVC, changing the torso group from benzene ring to alkane chain will highly improve plasticizer efficacy, and attaching three legs on the torso will decrease plasticizer mobility. As a side outcome, we also report a nontrivial chain-length dependence of the cohesive energy and solubility parameter of long-chain polymers, which is an important consideration in the calculation of these quantities using molecular simulation. The second area is azeotropes, the separation of which in chemical processes is usually very difficult due to the same composition in vapor and liquid phases at the azeotropic point. So far, a fundamental understanding of azeotrope formation is still missing. In this thesis, we aim to address two fundamental questions: (I) the mechanism for ethanol/benzene azeotrope formation, (II) classification of different polar-polar positive azeotropes. First, Gibbs ensemble Monte Carlo (GEMC) simulation is performed to predict the vapor-liquid equilibrium (VLE) phase diagram of ethanol/benzene, including an azeotrope point. The results match well with experiments. Free energy and cohesive energy profiles analyses are then performed. From a thorough liquid structure analysis, we conclude a three-stage mechanism for azeotrope formation: 1) formation of small ethanol clusters at low composition, 2) microscopic phase separation between ethanol and benzene, 3) isolation of benzene. This approach is then extended to four additional polar-polar mixtures (ethyl acetate/methanol, ethyl acetate/ethanol, ethanol/water, and 1-propanol/water) to obtain their VLE diagrams, which again match well with experiments. Free energy and cohesive energy analyses indicate that there are two types of mechanisms, a three-stage mechanism with weak cross-interactions (for the first two mixtures) and a three-stage mechanism with strong cross-interactions (for the last two mixtures). So far, our analyses on mixture liquid micro-structure can partially prove the existence and classification of those mechanisms. Overall, the successful prediction in physicochemical properties of two liquid mixtures with very different molecular scales proves the robustness of our study strategy, which could be used to study any liquid mixtures and understand their related physicochemical phenomena. / Thesis / Doctor of Philosophy (PhD)

Yes / This contribution discusses the national security objectives and the political parameters of the Obama administration’s decision to shift towards a counterinsurgency strategy and increase troop levels in Afghanistan. On the basis of the key strategic documents that formed the basis of the interagency process, as well as the political constraints under which the Obama administration was operating, it is possible to understand the key factors that defined the policy. The article also explain the various contradictions between the geopolitical context, the strategic objectives as defined by Obama and means to achieve them. On the basis of such analysis it is clear that the policy could at best achieve a partial success.

Wideband phased arrays require very tight element spacing to permit wide angle scanning of the main beam over the wide bandwidth. The consequence of tight spacing is very high mutual coupling among the elements in the array. Previous efforts by Virginia Tech Antenna Group has shown that the strong coupling can be utilized in arrays to obtain broadband frequency response while maintaining a small element spacing. However, mutual coupling between elements in a tightly coupled array can sometimes dramatically change the operating frequency, bandwidth, and radiation pattern from that of the single isolated element. Thus, there are some fundamental questions that remain regarding the effective operation of highly coupled arrays for beam forming, beam scanning, and aperture reconfiguration. Existing antenna pattern analysis techniques including the active element pattern method are inadequate for the application in highly coupled arrays. This dissertation focuses on the development of a new antenna array analysis technique. The presented method is based on the scattering parameter network descriptions of the array elements, associated feed network and the active element patterns. The developed model is general. It can be applied to an array of any size and configuration. The model can be utilized to determine directivity, gain and realized gain of arrays as well as their radiation efficiency and impedance mismatch. Using the network model, the relationship between radiation pattern characteristics and the input impedance characteristics of the array antennas becomes clear. Three types of source impedance matching conditions for array antennas are investigated using the model. A numerically simulated array of strip dipole array is used to investigate the effects of various impedance matching methods on the radiation pattern and impedance bandwidth. An application of network analysis is presented on an experimental investigation of $3\times 3$ Foursquare array test bed to further verify the concepts. / Ph. D.

yes / The envelope correlation for a two-element antenna array may be calculated using the antenna radiation fields, or more simply from the scattering parameters of the system. The use of scattering parameters provides a major simplification over the direct use of field data. In this paper we propose a modification of the scattering parameter method which also includes the antenna losses. This approach has the advantage of simplifying the antenna design process, especially when low envelope correlations are needed. It also offers a better prediction of the spatial envelope correlation, and a good framework for understanding the effects of the mutual coupling. The accuracy of this proposed method is illustrated by two examples.

Although many efforts and strategies have been implemented to reduce over-pumping of aquifer-systems, land subsidence is still a serious issue worldwide. Accurate aquifer characterization is critical to understand the response of an aquifer-system to prolonged pumping but is often difficult and expensive to conduct. The purpose of this thesis is to determine the validity of estimating aquifer-system parameters from a single cumulative compaction record and corresponding nested water-level data deconvolved into temporal components. Over a decade of compaction and water-level data were collected from an extensometer and multi-level piezometer at the Lorenzi site in Las Vegas Valley and when graphed yearly, seasonal, and daily signals are observed. Each temporal signal reflects different characteristics of the aquifer-system, including the distinction between aquifer and aquitard parameters, as the three temporal stresses influence the compaction record uniquely. Maximum cross-correlation was used to determine the hydrodynamic lag between changing water-levels and subsidence within the seasonal signal while principal components analysis was used to statistically verify the presence of the three temporal signals. Assumptions had to be made but nearly all estimated Lorenzi site aquifer-system parameters fell either within the reasonable range or were similar in magnitude to parameter values estimated in previous studies. Unfortunately, principal components analysis was unable to detect the three temporal signals. A cumulative compaction record may be difficult to obtain but analyzing the precision measurements of an extensometer results in precise aquifer-system parameters and as the precision of aquifer-system parameters increase so does the ability to sustainably manage groundwater. / Master of Science

Transmission line parameters play a significant role in a variety of power system applications. The accuracy of these parameters is of paramount importance. Traditional methods of determining transmission line parameters must take a large number of factors into consideration. It is difficult and in most cases impractical to include every possible factor when calculating parameter values. A modern approach to the parameter identification problem is an online method by which the parameter values are calculated using synchronized voltage and current measurements from both ends of a transmission line. One of the biggest problems facing the synchronized measurement method is line transposition. Several methods have been proposed that demonstrate how the line parameters of a transposed line may be estimated. However, the present case of today's power systems is such that a majority of transmission lines are untransposed. While transposed line methods have value, they cannot be applied in real-world scenarios. Future efforts of using synchronized measurements to estimate transmission line parameters must focus on the development and refining of untransposed line methods. This thesis reviews the existing methods of estimation transmission line parameters using synchrophasor measurements and proposes a new method of estimating the parameters of an untransposed line. After the proposal of this new method, a sensitivity analysis is conducted to determine its performance when noise is present in the measurements. / Master of Science

The Sustainable Water Interactive for Tomorrow (SWIFT) project in eastern Virginia is a Managed Aquifer Recharge project designed to alleviate the depletion of the Potomac Aquifer System due to unsustainable groundwater withdrawals. At the SWIFT Research Center (SWIFTRC) in Nansemond, VA, a pilot testing well (TW-1) has been implemented to help determine the feasibility of full-scale implementation. The pumping data from TW-1 and observation head data from surrounding monitoring wells (MW) at the SWIFTRC were used to calculate hydrogeological parameters (transmissivity, hydraulic conductivity, specific storage, and storage coefficient). Two sets of data were analyzed from before and after TW-1 was rehabilitated to account for the change in the flow distribution to each screen in TW-1. Comparing the results to past literature, the calculated (Theis and Cooper-Jacob methods) hydraulic conductivity/transmissivity values are within the same order of magnitude. Using borehole logs as well as apparent conductance and resistivity logs, multiple single and multi-layered models for both the upper and middle Potomac aquifers were produced with MODFLOW. Parameter estimation using MODFLOW and PEST and the two sets of observation data resulted in hydrogeological parameters similar to those calculated using Theis and Cooper-Jacob methods. The change in the hydraulic conductivity and specific storage between the pre and post rehabilitation flow distributions is proportional to that change in the flow distribution. For future modeling of the aquifer system, the hydrogeological parameters from the model using the 4/26/19 data set with the post rehabilitation flow distribution is recommended. Drawdown results from a multi-layered MODFLOW model were compared to results using the Theis method using both the Theis-calculated and MODFLOW-PEST modeled hydrogeological parameters. The results were nearly identical except for the Upper Potomac Aquifer (UPA) layer 1, as the model has a large change in aquifer thickness with distance from TW-1 that the Theis-based calculations do not consider. Travel times from the monitoring wells to TW-1 were calculated with the single and multi-layered models pumping 700 GPM from TW-1. Travel times from the SWIFT MW within the UPA sublayers ranged from 204 to 597 days depending on the sublayer, while travel times from the USGS MW within the UPA sublayers ranged from 2,395 to 7,859 days. For the single layer model of the UPA, the travel time from the SWIFT MW to TW-1 was 372 days while the travel time from the USGS MW was 4,839 days. Travel times from the SWIFT MW within the MPA sublayers were 416 and 1,195 days, while travel times from the USGS MW within the MPA sublayers were 4,339 and 11,245 days. For the single layer model of the MPA, the travel time from the SWIFT MW to TW-1 was 743 days while the travel time from the USGS MW was 7,545 days. / Master of Science / The Sustainable Water Interactive for Tomorrow (SWIFT) project in eastern Virginia is a project designed to help slow the depletion of the Potomac Aquifer System due to unsustainable groundwater withdrawals. At the SWIFT Research Center (SWIFTRC) in Nansemond, VA, a testing well (TW-1) has been implemented to help determine if the full-scale implementation of the SWIFT project is feasible. The pumping data from TW-1 and observation head data from surrounding monitoring wells (MW) at the SWIFTRC were used to calculate hydrogeological parameters (transmissivity, hydraulic conductivity, specific storage, and storage coefficients). These parameters help describe the behavior of the aquifer system. Two sets of data were analyzed from before and after TW-1 was rehabilitated to account for the change in the flow distribution within TW-1. Comparing the results to past literature, the calculated (using analytical methods, Theis and Cooper-Jacob methods) hydraulic conductivity/transmissivity values are within the same order of magnitude. Using data from the boreholes, multiple single and multi-layered models for both the upper and middle Potomac aquifers were produced with MODFLOW, a groundwater modeling software. Estimating parameters using observation data within MODFLOW resulted in hydrogeological parameters similar to those calculated using the Theis and Cooper-Jacob methods. The change in the hydraulic conductivity and specific storage between the pre and post rehabilitation flow distributions within TW-1 is proportional to that change in the flow distribution. For future modeling of the aquifer system, the hydrogeological parameters from the model using the 4/26/19 (most recent) data set with the post rehabilitation (more current) flow distribution is recommended. Drawdown (decrease in the water table) results from a multi-layered MODFLOW model were compared to results using the Theis method using both the Theis-calculated and MODFLOW modeled hydrogeological parameters. The results were nearly identical except for the Upper Potomac Aquifer (UPA) layer 1, as the model has a large change in aquifer thickness with distance from TW-1 that the Theis-based calculations do not consider. The time it took for a particle of water to travel from the monitoring wells to TW-1 were calculated with the single and multi-layered models pumping 700 GPM from TW-1. Travel times from the SWIFT MW within the UPA sublayers ranged from 204 to 597 days depending on the sublayer, while travel times from the USGS MW within the UPA sublayers ranged from 2,395 to 7,859 days. For the single layer model of the UPA, the travel time from the SWIFT MW to TW-1 was 372 days while the travel time from the USGS MW was 4,839 days. Travel times from the SWIFT MW within the MPA sublayers were 416 and 1,195 days, while travel times from the USGS MW within the MPA sublayers were 4,339 and 11,245 days. For the single layer model of the MPA, the travel time from the SWIFT MW to TW-1 was 743 days while the travel time from the USGS MW was 7,545 days.

Yes / The purpose of granulation is to improve the flowability of powders, whilst reducing the dustiness and potential of segregation. The focus of this project is to understand the effects of the process parameters of fluidized bed granulation on the granule size distribution of the final product using gFP simulation software (Siemens PSE, UK). The wet granulation process has become predominant and important in the pharmaceutical industry, due to its cost-effectiveness and its robustness in product formulation. The process parameters that were subject of this study include the air flow rate of 20, 40 and 60 m3/hr., the binder concentration of 6, 9 and 12 wt.%, and the binder spray rate of 7.14, 14.28 and 21.42 ml/min. The results show that binder spray rate has the most impact on the granule size distribution, where an increase in binder spray rate is associated with a higher incidence of larger granules in the product. The air flow rate and the binder concentration have a negligible impact on the granule size distribution when agglomeration and consolidation models are not implemented in the simulation. / My sincere gratitude goes to Ghana Scholarship Secretariat for sponsoring this research and Siemens PSE UK for providing the software resource force this research.

No / Achieving an environmentally friendly fuel with respect to minimum sulfur compounds has recently became a significant issue for petroleum refining industries. This paper focuses on investigating oxidative desulfurization (ODS) process for removal of sulfur compounds found in light gas oil (LGO) in a batch reactor (at different reaction temperatures and batch time) using a novel nano-catalyst based on 4% iron oxide (Fe2O3) as an active component. Precipitation and Impregnation methods are used to prepare the nano-gamma alumina (γ-alumina) and to generate the new synthetic homemade nanocatalyst. A mathematical model is formulated for the ODS process to estimate the optimal kinetic parameters within gPROMS package. An excellent consistency with the experimental data of all runs with error less than 5% have obtained. The optimization results display that the new nanocatalyst prepared here is effective in removing more than 97% of the sulfur compounds from LGO resulting in a cleaner fuel. / The authors thank Petroleum Research and Development Center, The Iraqi Ministry of Oil /Baghdad, IRAQ for its financial support.

Yes / Due to the environmental legislations related to sulfur content and proceeding with the challenges to find an appropriate catalyst of such contamination producing clean fuel, a main thrust for improving of more efficient technologies on new oxidative catalyst is viewed a vital issue in fuel quality development. So, in this study, the sulfur compound (ethyl mercaptan) presents in light naphtha feedstock is removed by oxidative desulfurization (ODS) in a batch reactor using a new homemade nano-catalyst and air as oxidant under different reaction conditions (reaction temperatures, reaction time and the initial sulfur concentrations) that has not been studied in such field. The catalyst is zinc oxide supported on zeolite nanoparticles which is locally prepared by Incipient Wetness Impregnation (IWI) method. Mathematical model of the relevant reactions is also developed in this study to match the experimental results via obtaining the optimal kinetic parameters utilizing optimization techniques within gPROMS program. Such optimization is conducted using two approaches (linear and nonlinear regression) and the results showed that the nonlinear approach is more accurate than linear approach. The optimal kinetic parameters are then used to achieve a clean fuel via getting the optimal operation conditions based on the maximum conversion. Where, higher than 99% of the process conversion has obtained at temperature of 327.4 K, reaction time at163.6 min and initial concentration of 335.3 ppm.