Dynamic Server Allocation over Time Varying Channels with Switchover Delay

We consider a dynamic server allocation problem over parallel queues with randomly varying connectivity and server switchover delay between the queues. At each time slot the server decides either to stay with the current queue or switch to another queue based on the current connectivity and the queue length information. Switchover delay occurs in many telecommunications applications and is a new modeling component of this problem that has not been previously addressed. We show that the simultaneous presence of randomly varying connectivity and switchover delay changes the system stability region and the structure of optimal policies. In the first part of the paper, we consider a system of two parallel queues, and develop a novel approach to explicitly characterize the stability region of the system using state-action frequencies which are stationary solutions to a Markov Decision Process (MDP) formulation. We then develop a frame-based dynamic control (FBDC) policy, based on the state-action frequencies, and show that it is throughput-optimal asymptotically in the frame length. The FBDC policy is applicable to a broad class of network control systems and provides a new framework for developing throughput-optimal network control policies using state-action frequencies. Furthermore, we develop simple Myopic policies that provably achieve more than 90% of the stability region. In the second part of the paper, we extend our results to systems with an arbitrary but finite number of queues.Comment: 38 Pages, 18 figures. arXiv admin note: substantial text overlap with arXiv:1008.234

Longest-queue-first scheduling under SINR interference model

We investigate the performance of longest-queue-first (LQF) scheduling (i.e., greedy maximal scheduling) for wireless networks under the SINR interference model. This interference model takes network geometry and the cumulative interference effect into account, which, therefore, capture the wireless interference more precisely than binary interference models. By employing the ρ-local pooling technique, we show that LQF scheduling achieves zero throughput in the worst case. We then propose a novel technique to localize interference which enables us to decentralize the LQF scheduling while preventing it from having vanishing throughput in all network topologies. We characterize the maximum throughput region under interference localization and present a distributed LQF scheduling algorithm. Finally, we present numerical results to illustrate the usefulness and to validate the theory developed in the paper.United States. Army Research Office. Multidisciplinary University Research Initiative (Grant W911NF-08-1-0238)National Science Foundation (U.S.) (Grant CNS-0915988)United States. Defense Threat Reduction Agency (Grant HDTRA1-07-1-0004

Last Round Convergence and No-Instant Regret in Repeated Games with Asymmetric Information

This paper considers repeated games in which one player has more information about the game than the other players. In particular, we investigate repeated two-player zero-sum games where only the column player knows the payoff matrix A of the game. Suppose that while repeatedly playing this game, the row player chooses her strategy at each round by using a no-regret algorithm to minimize her (pseudo) regret. We develop a no-instant-regret algorithm for the column player to exhibit last round convergence to a minimax equilibrium. We show that our algorithm is efficient against a large set of popular no-regret algorithms of the row player, including the multiplicative weight update algorithm, the online mirror descent method/follow-the-regularized-leader, the linear multiplicative weight update algorithm, and the optimistic multiplicative weight update

Enhancing Symbolic Execution of Heap-based Programs with Separation Logic for Test Input Generation

Symbolic execution is a well established method for test input generation. Despite of having achieved tremendous success over numerical domains, existing symbolic execution techniques for heap-based programs are limited due to the lack of a succinct and precise description for symbolic values over unbounded heaps. In this work, we present a new symbolic execution method for heap-based programs based on separation logic. The essence of our proposal is context-sensitive lazy initialization, a novel approach for efficient test input generation. Our approach differs from existing approaches in two ways. Firstly, our approach is based on separation logic, which allows us to precisely capture preconditions of heap-based programs so that we avoid generating invalid test inputs. Secondly, we generate only fully initialized test inputs, which are more useful in practice compared to those partially initialized test inputs generated by the state-of-the-art tools. We have implemented our approach as a tool, called Java StarFinder, and evaluated it on a set of programs with complex heap inputs. The results show that our approach significantly reduces the number of invalid test inputs and improves the test coverage

Spitzer observations of the N157B supernova remnant and its surroundings

(Aims): We study the LMC interstellar medium in the field of the nebula N157B, which contains a supernova remnant, an OB association, ionized gas, and high-density dusty filaments in close proximity. We investigate the relative importance of shock excitation by the SNR and photo-ionization by the OB stars, as well as possible interactions between the supernova remnant and its environment. (Methods): We apply multiwavelength mapping and photometry, along with spatially resolved infrared spectroscopy, to identifying the nature of the ISM using new infrared data from the Spitzer space observatory and X-ray, optical, and radio data from the literature. (Results): The N157B SNR has no infrared counterpart. Infrared emission from the region is dominated by the compact blister-type HII region associated with 2MASS J05375027-6911071 and excited by an O8-O9 star. This object is part of an extended infrared emission region that is associated with a molecular cloud. We find only weak emission from the shock-indicator [FeII], and both the excitation and the heating of the extended cloud are dominated by photo-ionization by the early O stars of LH99. (Conclusions): Any possible impact by the expanding SNR does not now affect the extended cloud of molecules and dust, despite the apparent overlap of SNR X-ray emission with infrared and Ha emission from the cloud. This implies that the supernova progenitor cannot have been more massive than about 25 solar masses.Comment: 10 pages, 8 figures, published in A&

Evolution of Linear Absorption and Nonlinear Optical Properties in V-Shaped Ruthenium(II)-Based Chromophores

In this article, we describe a series of complexes with electron-rich cis-{Ru^(II)(NH_3)_4}^(2+) centers coordinated to two pyridyl ligands bearing N-methyl/arylpyridinium electron-acceptor groups. These V-shaped dipolar species are new, extended members of a class of chromophores first reported by us (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845−4859). They have been isolated as their PF_6− salts and characterized by using various techniques including ^1H NMR and electronic absorption spectroscopies and cyclic voltammetry. Reversible Ru^(III/II) waves show that the new complexes are potentially redox-switchable chromophores. Single crystal X-ray structures have been obtained for four complex salts; three of these crystallize noncentrosymmetrically, but with the individual molecular dipoles aligned largely antiparallel. Very large molecular first hyperpolarizabilities β have been determined by using hyper-Rayleigh scattering (HRS) with an 800 nm laser and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d → π^* metal-to-ligand charge-transfer (MLCT) and π → π^* intraligand charge-transfer (ILCT) bands. The latter measurements afford total nonresonant β_0 responses as high as ca. 600 × 10^(−30) esu. These pseudo-C_(2v) chromophores show two substantial components of the β tensor, β_(zzz) and β_(zyy), although the relative significance of these varies with the physical method applied. According to HRS, β_(zzz) dominates in all cases, whereas the Stark analyses indicate that β_(zyy) is dominant in the shorter chromophores, but β_(zzz) and β_(zyy) are similar for the extended species. In contrast, finite field calculations predict that β_(zyy) is always the major component. Time-dependent density functional theory calculations predict increasing ILCT character for the nominally MLCT transitions and accompanying blue-shifts of the visible absorptions, as the ligand π-systems are extended. Such unusual behavior has also been observed with related 1D complexes (Coe, B. J. et al. J. Am. Chem. Soc. 2004, 126, 3880−3891)

Destruction of density-wave states by a pseudo-gap in high magnetic fields: application to (TMTSF)2_2ClO4_4

A model is presented for the destruction of density-wave states in quasi-one-dimensional crystals by high magnetic fields. The model is consistent with previously unexplained properties of the organic conductors (TMTSF)$_2$ClO$_4$ and (BEDT-TTF)$_2$MHg(SCN)$_4$ (M=K,Rb,Tl). As the magnetic field increases quasi-one-dimensional density-wave fluctuations increase, producing a pseudo-gap in the electronic density of states near the transition temperature. When the pseudo-gap becomes larger than the mean-field transition temperature formation of a density-wave state is not possible.Comment: 4 pages, RevTeX, 2 figures in uuencoded compressed tar file. Small changes to text and Figure 1. Final version to appear in Physical Review Letter

Transplanckian axions !?

We discuss quantum gravitational effects in Einstein theory coupled to periodic axion scalars to analyze the viability of several proposals to achieve superplanckian axion periods (aka decay constants) and their possible application to large field inflation models. The effects we study correspond to the nucleation of euclidean gravitational instantons charged under the axion, and our results are essentially compatible with (but independent of) the Weak Gravity Conjecture, as follows: Single axion theories with superplanckian periods contain gravitational instantons inducing sizable higher harmonics in the axion potential, which spoil superplanckian inflaton field range. A similar result holds for multi-axion models with lattice alignment (like the Kim-Nilles-Peloso model). Finally, theories with $N$ axions can still achieve a moderately superplanckian periodicity (by a $\sqrt{N}$ factor) with no higher harmonics in the axion potential. The Weak Gravity Conjecture fails to hold in this case due to the absence of some instantons, which are forbidden by a discrete $\mathbf{Z}_N$ gauge symmetry. Finally we discuss the realization of these instantons as euclidean D-branes in string compactifications.Comment: 46 pages, 6 figures. Added references, clarifications, and missing factor of 1/2 to instanton action. Conclusions unchange

Clinicopathologic and Molecular Profiles of Microsatellite Unstable Barrett Esophagus-associated Adenocarcinoma

Microsatellite instability (MSI) has been reported in various tumors, with colon cancer as the prototype. However, little is known about MSI in Barrett esophagus (BE)-associated adenocarcinoma. Thus, the aim of this study was to compare the clinicopathologic and molecular features of BE-associated adenocarcinomas with and without MSI. The study cohort consisted of 76 patients with BE-associated adenocarcinomas (66 male, 10 female), with a mean age of 65.1 years. Immunohistochemistry (IHC) for MLH1, MSH2, MSH6, PMS2, and CD3 and in situ hybridization for Epstein-Barr virus-encoded RNA were performed. MLH1 and PMS2 expression was lost by IHC in 5 cases (6.6%); of these, 5 showed high-level MSI (MSI-H) by polymerase chain reaction assay, and 4 showed hMLH1 promoter methylation. Histologically, tumors with MSI-H were heterogenous and included conventional adenocarcinomas with tumor-infiltrating lymphocytes (n=1), medullary carcinoma (n=2), signet ring cells (n=1), and signet ring cell and mucinous components (n=1). Compared with tumors negative for MSI by IHC, BE-associated adenocarcinomas with MSI-H were associated with older patient age (P=0.0060), lymphovascular invasion (P=0.027), and significantly larger numbers of tumor-infiltrating lymphocytes (P<0.0001). However, there was no statistical difference in overall survival between the 2 groups (P=0.285). In conclusion, MSI-H is uncommon in BE-associated adenocarcinomas, but is associated with clinicopathologic features fairly similar to sporadic microsatellite unstable colorectal cancers. Given the growing evidence that indicates lack of benefits from adjuvant therapy with fluorouracil in the colonic counterpart, it may be important to identify MSI-H in BE-associated adenocarcinomas