Uniformly Area Expanding Flows in Spacetimes

The central object of study of this thesis is inverse mean curvature vector flow of two-dimensional surfaces in four-dimensional spacetimes. Being a system of forward-backward parabolic PDEs, inverse mean curvature vector flow equation lacks a general existence theory. Our main contribution is proving that there exist infinitely many spacetimes, not necessarily spherically symmetric or static, that admit smooth global solutions to inverse mean curvature vector flow. Prior to our work, such solutions were only known in spherically symmetric and static spacetimes. The technique used in this thesis might be important to prove the Spacetime Penrose Conjecture, which remains open today. Given a spacetime $(N^{4}, \overline{g})$ and a spacelike hypersurface $M$. For any closed surface $\Sigma$ embedded in $M$ satisfying some natural conditions, one can "steer" the spacetime metric $\overline{g}$ such that the mean curvature vector field of $\Sigma$ becomes tangential to $M$ while keeping the induced metric on $M$. This can be used to construct more examples of smooth solutions to inverse mean curvature vector flow from smooth solutions to inverse mean curvature flow in a spacelike hypersurface.Comment: 134 pages, 12 figures. This is my Ph.D. thesis, department of mathematics, Duke University, April 201

Two Essays on Value Co-Creation

In the past few decades, customer co-creation has received a significant amount of attention in both practice and academics. Prahalad and Ramaswamy (2000) advocated co-opting customer competence as a competitive strategy. The purpose of this dissertation is to investigate how to engage customers and employees into the value co-creation process. This dissertation is composed of two essays. Essay 1 focuses on customer co-creation behaviors and Essay 2 examines employee co-creation behaviors. Motivating customers to participate in the value co-creation process can help the firm achieve their long-term financial successes. However, the psychological mechanism underlying customer co-creation behavior is still not fully understood. Particularly, the goal-driven nature of customer co-creation is largely ignored in the literature. The objective of the first essay is to examine the dual role of goal self-concordance in customer co-creation behavior. Two studies will be conducted to examine each role respectively. Using four experiments, Study 1 examines the motivational power of goal self-concordance on customer co-creation behavior. Specifically, goal self-concordance is positively related to customers’ trying to participate in the co-creation process and anticipatory self-enhancement fully mediates the above relationship. Moreover, the results find that goal specificity weakens the relationship between goal self-concordance and anticipatory self-enhancement. In Study 2, three experiments are conducted to test the moderating effect of goal self-concordance on the relationship between co-creation goal achievement and customers’ perceived self-enhancement. The results find that customers’ perceived self-enhancement after co-creation goal achievement is positively related to customer satisfaction and their future co-creation behaviors and goal self-concordance mainly focuses on the direct effect to self-enhancement. Therefore, the moderating effect of goal self-concordance is not supported in this study. Theoretical and practical implications are also discussed. Essay 2 focuses on employee co-creation behaviors. Although customer co-creation has received a significant amount of attention in both practice and academics, most of the previous studies were conducted from the customer perspective while little is known about how employees are involved in the value co-creation process. To shed new light on employee co-creation behavior, a scale of employee co-creation behavior is developed first, and then a theoretical model that investigates the antecedents and consequences of employee co-creation behavior is tested. To test the hypothesized model, a self-administered survey of 225 employees from a major Auto 4S store chain in China was conducted. The results find that both customer orientation and perceived organizational support are positively associated with employee co-creation behavior, which in turn influences employees’ job satisfaction and job stress. Moreover, firm cross-functional cooperation strengthens the relationships between perceived organizational support and employee co-creation behavior. The findings of the study will provide implications to managers regarding how to measure employee co-creation behavior and how to engage employees into the value co-creation process

Turbo space-time coding for mimo systems : designs and analyses

Multiple input multiple output (MIMO) systems can provide high diversity, high data rate or a mix of both, for wireless communications. This dissertation combines both modes and suggests analyses and techniques that advance the state of the art of MIMO systems. Specifically, this dissertation studies turbo space-time coding schemes for MIMO systems. Before the designs of turbo space-time codes are presented, a fundamental tool to analyze and design turbo coding schemes, the extrinsic information transfer (EXIT) chart method, is extended from the binary/nonbinary code case to coded modulation case. This extension prepares the convergence analysis for turbo space-time code. Turbo space-time codes with symbols precoded by randomly chosen unitary time variant linear transformations (TVLT) are investigated in this dissertation. It is shown that turbo codes with TVLT achieve full diversity gain and good coding gain with high probability. The probability that these design goals are not met is shown to vanish exponentially with the Hamming distance between codewords (number of different columns). Hence, exhaustive tests of the rank and the determinant criterion are not required. As an additional benefit of the application of TVLT, with the removal of the constant modulation condition, it is proved that throughput rates achieved by these codes are significantly higher than the rates achievable by conventional space-time codes. Finally, an EXIT chart analysis for turbo space-time codes with TVLT is developed, with application to predicting frame error rate (FER) performance without running full simulation. To increase the data rate of turbo-STC without exponentially increasing the decoding complexity, a multilevel turbo space-time coding scheme with TVLT is proposed. An iterative joint demapping and decoding receiver algorithm is also proposed. For MIMO systems with a large number of transmit antennas, two types of layered turbo space-time (LTST) coding schemes are studied. For systems with low order modulation, a type of LTST with a vertical encoding structure and a low complexity parallel interference cancellation (PlC) receiver is shown to achieve close to capacity performance. For high order modulation, another type of LTST with a horizontal encoding structure, TVLT, and an ordered successive interference cancellation (OSIC) receiver is shown to achieve better performance than conventional layered space-time coding schemes, where ordering is not available in the SIC detection

Revenue Sharing with Multiple Airlines and Airports

This paper investigates the effects of concession revenue sharing between an airport and its airlines. It is found that the degree of revenue sharing will be affected by how carriers’ services are related (complements, independent, or substitutes). In particular, when carriers provide substitutable services, the sharing proportions might become negative if horizontal substitutability is sufficiently strong. In these situations, while revenue sharing improves profit, it reduces social welfare. It is further found that airport competition results in a higher degree of revenue sharing than would be had in the case of single airports. Nevertheless, the airport-airline chains may derive lower profits through this revenue-sharing rivalry, and the situation is similar to a classic Prisoners’ Dilemma. As the airport-airline chains move further away from their joint profit maximum, social welfare rises beyond the level achievable by single airports. Our analysis also shows that the (equilibrium) revenue-sharing proportion at an airport decreases in the number of its carriers, and increases in the number of carriers at the competing airports. Finally, the effects of the pure sharing contract are compared with those of the two-part sharing contract

A bibliometric analysis of Technology Acceptance Models in Tourism-Culture-Museum and Mainstream Service Contexts

Technology Acceptance Model (TAM) is the most commonly used theoretical understanding of technology adoption research and also the most powerful model applied to describe personal acceptance decisions. Prior studies fail to become comprehensive due to confining in one industry, so authors review top journal articles in mainstream service and tourism-related industries as well as identify the diverse trendy and similar grounds through a bibliometric analysis. Totally 16 top SSCI journals selected for this research and find all the articles mention TAM. After excluding 79 papers not based on the theory of TAM, 100 papers remain. The analysis focused on descriptive statistical analysis through CiteSpace and content analysis to distinguish similarities and differences between two diverse industries. This study contributes to visualizing the progress of TAM in two industries from a comprehensive perspective and provides clues for a future investigation related to TAM. This is the pioneer study to investigate TAM in two fields using qualitative and visualized bibliometric analysis