Hrachya Kyureghian’s research while affiliated with University of Nebraska–Lincoln and other places

An excellent candidate for an earth abundant absorber material is WSe2 which can be directly grown as a p-type semiconductor with a band gap near 1.4 eV. In this work we present the structural, optical, and electrical properties of thin film WSe2 grown via the selenization of sputter deposited tungsten films. We will show that highly textured films with an optical band gap in range of 1.4 eV, and absorption coefficients greater than 105/cm across the visible spectrum can be easily achieved. In addition we will present Hall Effect and carrier density measurements as well, where will show densities in the 1017cm-3 range and p-type Hall mobilities greater than 10 cm2/V-s range can be obtained. We employ these results to numerically simulate solar cells based on this material, where we will show efficiencies greater than 20% are possible.

We consider a standard linear city model with two firms, where firms and consumers both incur transport costs. This is done by assuming that the total transport cost is shared by the buyers and sellers according to an exogenously given rule. In the model, firms choose locations and prices, with the transportation cost being linear in distance. We first derive the profit function for the two-stage transport cost sharing game and find that it has a complex form. We then invoke simplifying assumptions and solve for two different games. We provide a complete characterization for the equilibrium of the location game between the two firms by assuming fixed prices. We then examine the price game when the two firms are constrained to locate at the same spot. The equilibria of these two games provide insights about the complex two-stage game.

We consider a linear city model where both firms and consumers have to incur transport costs. Following a standard Hotelling (1929) type framework we analyze a duopoly where firms facing a continuum of consumers choose locations and prices, with the transportation rate being linear in distance. From a theoretical point of view such a model is interesting since mill pricing and uniform delivery pricing arise as special cases. Given the complex nature of the profit function for the two-stage transport cost sharing game, we invoke simplifying assumptions and solve for two different games. We provide a complete characterization for the equilibrium of the location game between the duopolists by removing the price choice from the strategy space. We then find that if the two firms are constrained to locate at the same spot, the resulting price competition leads to a mixed strategy equilibrium with discriminatory rationing. In equilibrium both firms always have positive expected profits. Finally, we derive a pure strategy equilibrium for the two-stage game. Results are then compared with the mill pricing and uniform delivery pricing models.

Chapter 2 deals with a linear city model la Hotelling where the two firms share linear transport costs with their customers. Mill pricing and uniform delivery pricing are special limiting cases. We characterize the conditions for the existence of a pure strategy equilibrium in the two-stage location-price game. These enable us to identify the causes for non-existence in the two limiting cases. We solve for the equilibrium of a location game between the duopolists with an exogenously given price. When the two firms are constrained to locate at the same central spot, we show the nonexistence of pure strategy equilibria, conjecture the existence of mixed strategy equilibria, and show that any such possible equilibria will always yield positive expected profits.

Chapter 2 deals with a linear city model ̉la Hotelling where the two firms share linear transport costs with their customers. Mill pricing and uniform delivery pricing are special limiting cases. We characterize the conditions for the existence of a pure strategy equilibrium in the two-stage location-price game. These enable us to identify the causes for non-existence in the two limiting cases. Chapter 3 provides simulations as well as theoretical analysis of potential spatial separation of heterogeneous agents operating on a two-dimensional grid space that represents a city. Heterogeneity refers to a characteristic which is also a determinant of individual valuation of land. We study spatial separation with respect to the distinguishing characteristic and investigate the details of emerging spatial patterns. Simulations suggest that the process of interaction with little trade friction goes through stages which resemble its end-state with high trade friction. Chapter 4 simulations, in addition to some theory, are used to investigate certain aspects of a city formation process. The model assumes two types of economic agents, workers and employers, operating on a two-dimensional grid. The agents have simple preferences, positive for the opposite type and negative for the own type in the own location. In addition, they have positive or negative preference for agglomeration in the own location. The model helps build intuition about a potentially important factor for agglomeration formation, namely, the disparity between entrepreneurial and technical skills in localities. We also determine the minimum level of positive preference for agglomeration that leads to agglomeration formation. System requirements: PC, World Wide Web browser and PDF reader. Available electronically via Internet. Title from electronic submission form. Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 2000. Vita. Abstract. Includes bibliographical references.