Combining Spot and Futures Markets: A Hybrid Market Approach to Dynamic Spectrum Access

Dynamic spectrum access is a new paradigm of secondary spectrum utilization and sharing. It allows unlicensed secondary users (SUs) to exploit opportunistically the under-utilized licensed spectrum. Market mechanism is a widely-used promising means to regulate the consuming behaviours of users and, hence, achieves the efficient allocation and consumption of limited resources. In this paper, we propose and study a hybrid secondary spectrum market consisting of both the futures market and the spot market, in which SUs (buyers) purchase under-utilized licensed spectrum from a spectrum regulator, either through predefined contracts via the futures market, or through spot transactions via the spot market. We focus on the optimal spectrum allocation among SUs in an exogenous hybrid market that maximizes the secondary spectrum utilization efficiency. The problem is challenging due to the stochasticity and asymmetry of network information. To solve this problem, we first derive an off-line optimal allocation policy that maximizes the ex-ante expected spectrum utilization efficiency based on the stochastic distribution of network information. We then propose an on-line VickreyCClarkeCGroves (VCG) auction that determines the real-time allocation and pricing of every spectrum based on the realized network information and the pre-derived off-line policy. We further show that with the spatial frequency reuse, the proposed VCG auction is NP-hard; hence, it is not suitable for on-line implementation, especially in a large-scale market. To this end, we propose a heuristics approach based on an on-line VCG-like mechanism with polynomial-time complexity, and further characterize the corresponding performance loss bound analytically. We finally provide extensive numerical results to evaluate the performance of the proposed solutions.Comment: This manuscript is the complete technical report for the journal version published in INFORMS Operations Researc

Characterization of Structure and Function of SECA Domains

SecA is a central component of the general secretion system that is essential for growth and virulence of bacteria. A series of fluorescein analogs were tested against ATPase activities of Escherichia coli SecA. Rose Bengal (RB) and Erythrosin B are potent inhibitors abolishing the activities of three forms of SecA ATPase with IC50 in µM range. Both inhibit SecA intrinsic ATPase with two mechanisms depending on ATP concentrations, indicating they influence the two non-identical nucleotide binding sites differently. RB shows different inhibitory effects against three forms of SecA ATPase activities, suggesting that the inhibition is related to the conformation of SecA. RB with IC50 at sub-µM level is the most potent inhibitor of SecA ATPases and SecA-dependent protein translocation to date. The fluorescein analogs inhibit intrinsic ATPase of Bacillus subtilis SecA similarly, and also exhibit antibacterial effects in E. coli and B. subtilis. Our findings indicate the value of fluorescein analogs as probes for mechanistic studies of SecA and the potential development of new SecA-targeted antimicrobial agents. A series of SecA derivatives with truncated C-terminus within the first long α-helix of the helix-bundle extending the ATPase catalytic domain of N68 was analyzed. These SecA variants interact with lipids, and those containing the C-terminal portion of the long α-helix starting at residues #639 form the ring-like structure in liposomes, indicating the critical domains for forming the protein-conducting channel. The presence and length of the C-domain influence the response to RB of NBDII mutants and C-terminal truncates of SecA. Thus this region may interact with the inhibitors and is involved in the structure and regulation of SecA ATPase activity. B. subtilis SecA was analyzed for interspecies comparison. Despite sharing high homology, this SecA homolog cannot complement E. coli mutants with SecA defect. Phospholipids do not stimulate ATPase activities of B. subtilis SecA, but induce its conformational changes, leading to the lipid-specific domains and ring-like structures similar to E. coli SecA. These pore-ring structures may represent part of the protein-conducting channels. Therefore, the potential structural roles of SecA in the protein translocation machinery may be universal in both Gram-negative and Gram-positive bacteria

Angles of vision: four stories

A collection of short storiesN/

The Investigation of Mandarin Aspect: With Special Reference to the Ba-Construction

This thesis is an investigation of the aspect system in Taiwanese Mandarin (TM). It examines the four aspect particles le, guo, zai, zhe and two constructions, the reduplicative verb construction and the resultative verb construction. It also explores the aspect of the ba-construction used in TM. Different from previous research, this study adopts the three-dimension model of aspect established by Declerck, Reed, & Cappelle (2006) as the basic framework. To better apply the model to analysing the aspect in TM, I draw from Depraetere's (1995) conceptual definition of (non)boundedness, the semantic feature that the actualisation aspect pivots on, to conduct the analysis at the actualisational level. I also use Klein's (1994) framework, treating the perfect as a category of aspect, rather than of tense. Additionally, Smith's (1997) approach of temporal boundary to define the viewpoint aspect is also used in this study. Chapter 1 lays the conceptual foundation of the thesis, introducing the general background, the sociolinguistic background of Taiwan, the aims and approach of this research and key terminologies. Chapter 2 reviews Smith’s and Klein’s frameworks of aspect as well as the syntactic account of the ba-construction proposed by Sybesma (1999) and C.-T. J. Huang, Li, & Li (2009). In the end, I propose a syntactic structure for the ba-construction. Chapter 3 is the full analysis of the aspect in TM on the basis of the three-dimension model. In this approach, TM is analysed as a language having the dichotomous perfective/imperfective opposition. It also distinguishes between the continuous and the progressive aspects. Chapter 4 then analyses the aspect of the ba-construction according to the aspect system developed in Chapter 3