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

Computer Aided Diagnosis System for Wireless Capsule Endoscopy Video

Along with the advancing of technology in wireless and miniature camera, Wireless Capsule Endoscopy (WCE), the combination of both, enables a physician to diagnose patient's digestive system without actually perform a surgical procedure. Although WCE is a technical breakthrough that allows physicians to visualize the entire small bowel noninvasively, the video viewing time takes 1 - 2 hours. Not only it sets a limit on the wide application of this technology but also it incurs considerable amount of cost. Therefore, it is important to automate such process so that the medical clinicians only focus on interested events. As an extension from our previous work that characterizes the motility of digestive tract in WCE videos, we propose a new assessment system for energy based events detection (EG-EBD) to classify the events in WCE videos. For the system, we first extract general features of a WCE video that can characterize the intestinal contractions in digestive organs. Then, the event boundaries are identified by using High Frequency Content (HFC) function. The segments are classified into WCE event by special features. In this system, we focus on entering duodenum, entering cecum, and active bleeding. This assessment system can be easily extended to discover more WCE events, such as detailed organ segmentation and more diseases, by using new special features. In addition, the system provides a score for every WCE image for each event. Using the event scores, the system helps a specialist to speedup the diagnosis process

rac-4-[4-Cyano-2-(hy­droxy­meth­yl)phen­yl]-4-(4-fluoro­phen­yl)-4-hy­droxy-N,N-dimethyl­butanaminium hemifumarate

In the title salt, C20H24FN2O2 +·0.5C4H2O4 2−, the fumarate anion is located on an inversion centre. In the cation, the two benzene rings are nearly perpendicular to each other, making a dihedral angle of 87.41 (10)°. The cation is linked to the anion by a bifurcated N—H⋯O hydrogen bond. Classical O—H⋯O and weak C—H⋯F hydrogen bonding is also present in the crystal structure. Three C atoms of the N,N-dimethyl­butanaminium moiety are disordered over two sites with refined site occupancies of 0.466 (14) and 0.534 (14)

Electrodeposition of conducting polymer fibers

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (leaf 35).Conducting polymers are materials that possess the electrical conductivity of metals while still retaining the mechanical properties such as flexibility of traditional polymers. Polypyrrole (PPy) is one of the more commonly studied electrically conducting polymers due to its high conductivity and stability in ambient conditions. A one step electrochemical process for growing macroscopic conducting polymer fibers previously described in Li et al's article (Science, 1993) was used to grow PPy fibers. Based on a schematic of the electrochemical flow cell used in the electrodeposition process, a physical electrochemical flow cell was constructed. Several trials were carried out in an attempt to repeatedly grow polymer fibers. The fibers grown from successful trials were analyzed and characterized by qualities such as length, diameter, surface texture, conductivity, and elasticity. There is room for further study involving optimization of parameters such as temperature, monomer concentration, and flow velocity of the monomer solution.by Angela Y. Chen.S.B

Controlled Morphological Structure of Ceria Nanoparticles Prepared by Spray Pyrolysis

AbstractCeria based materials have been widely used as catalyst supporters and electrolytes. Different applications require different morphologies, and the microstructural control during the synthesis is crucial. In the study, ceria particles were prepared from various precursors using a spray pyrolysis (SP). Comparing to the hollow and porous particles, the formation mechanism with solid spherical structure is not clarified readily. The ceria particles were characterized by transmission electron microscopy, thermogravimetry analysis and X-ray photoelectron spectroscopy. This experimental result suggests that the morphology is controlled by the precursors and could be related to their decomposed behavior during the heating process in SP

Fisher information analysis on quantum-enhanced parameter estimation in electromagnetically-induced-transparency spectrum with single photons

Electromagnetically-induced-transparency (EIT) spectroscopy has been used as a sensitive sensor in quantum metrology applications. The sensitivity of a sensor strongly depends on the measurement precision of EIT spectrum. In this work, we present a theoretical study of the spectral lineshape measurement on a three-level $\Lambda$-type EIT media based on Fisher information (FI) analysis. Using two kinds of probing source: the single-photon Fock state and the coherent state, we calculate the FI in an EIT medium and quantify the quantum advantage and limitations of the single-photon probe. The analysis of FI structure also provides a clear picture to classify the spectral lineshape into two different regimes, the EIT and Aulter-Townes splitting (ATS). This work provides a systematic analysis of the single-photon EIT spectrum, which provides essential knowledge of quantum sensing based on EIT and deepens our understanding of spectral characteristics of $\Lambda$-type media.Comment: 15 pages, 15 figure