Exploiting Full-duplex Receivers for Achieving Secret Communications in Multiuser MISO Networks

We consider a broadcast channel, in which a multi-antenna transmitter (Alice) sends $K$ confidential information signals to $K$ legitimate users (Bobs) in the presence of $L$ eavesdroppers (Eves). Alice uses MIMO precoding to generate the information signals along with her own (Tx-based) friendly jamming. Interference at each Bob is removed by MIMO zero-forcing. This, however, leaves a "vulnerability region" around each Bob, which can be exploited by a nearby Eve. We address this problem by augmenting Tx-based friendly jamming (TxFJ) with Rx-based friendly jamming (RxFJ), generated by each Bob. Specifically, each Bob uses self-interference suppression (SIS) to transmit a friendly jamming signal while simultaneously receiving an information signal over the same channel. We minimize the powers allocated to the information, TxFJ, and RxFJ signals under given guarantees on the individual secrecy rate for each Bob. The problem is solved for the cases when the eavesdropper's channel state information is known/unknown. Simulations show the effectiveness of the proposed solution. Furthermore, we discuss how to schedule transmissions when the rate requirements need to be satisfied on average rather than instantaneously. Under special cases, a scheduling algorithm that serves only the strongest receivers is shown to outperform the one that schedules all receivers.Comment: IEEE Transactions on Communication

Loyalty discounts

This paper considers the use of loyalty inducing discounts in vertical supply chains. An upstream manufacturer and a competitive fringe sell differentiated products to a retailer who has private information about the level of stochastic demand. We provide a comparison of market outcomes when the manufacturer uses two-part tariffs (2PT), all-unit quantity discounts (AU), and market share discounts (MS). We show that retailer's risk attitude affects manufacturer's preferences over these three pricing schemes. When the retailer is risk-neutral, it bears all the risk and all three schemes lead to the same outcome. When the retailer is risk-averse, 2PT performs the worst from manufacturer s perspective but it leads to the highest total surplus. For a wide range of parameter values (but not for all) the manufacturer prefers MS to AU. By limiting the retailer's product substitution possibilities MS makes the demand for manufacturer s product more inelastic. This reduces the amount (share of total profits) the manufacturer needs to leave to the retailer for the latter to participate in the scheme.This study is funded from the Valencian Economic Research Institute (IVIE) and the European Commission

Extensible Automated Constraint Modelling

In constraint solving, a critical bottleneck is the formulationof an effective constraint model of a given problem. The CONJURE system described in this paper, a substantial step forward over prototype versions of CONJURE previously reported, makes a valuable contribution to the automation of constraint modelling by automatically producing constraint models from their specifications in the abstract constraint specification language ESSENCE. A set of rules is used to refine an abstract specification into a concrete constraint model. We demonstrate that this set of rules is readily extensible to increase the space of possible constraint models CONJURE can produce. Our empirical results confirm that CONJURE can reproduce successfully the kernels of the constraint models of 32 benchmark problems found in the literature

Precession of the Isolated Neutron Star PSR B1828-11

Stairs, Lyne & Shemar have found that arrival time residuals from PSR B1828-11 vary periodically with a period of 500 days. This behavior can be accounted for by precession of the radiopulsar, an interpretation that is reinforced by the detection of variations in its pulse profile on the same timescale. Here, we model the period residuals from PSR B1828-11 in terms of precession of a triaxial rigid body. We include two contributions to the residuals: (i) the geometric effect, which arises because the times at which the pulsar emission beam points toward the observer varies with precession phase; (ii) the spindown contribution, which arises from any dependence of the spindown torque acting on the pulsar on the angle between its spin and magnetic axes. We use the data to probe numerous properties of the pulsar, most notably its shape, and the dependence of its spindown torque on the angle between its spin and magnetic axes, for which we assume a sum of a spin-aligned component (with a weight 1-a) and a dipolar component perpendicular to the magnetic beam axis (weight a), rather than the vacuum dipole torque (a=1). We find that a variety of shapes are consistent with the residuals, with a slight statistical preference for a prolate star. Moreover, a range of torque possibilities fit the data equally well, with no strong preference for the vacuum model. In the case of a prolate star we find evidence for an angle-dependent spindown torque. Our results show that the combination of geometrical and spin-down effects associated with precession can account for the principal features of PSR B1828-11's timing behavior, without fine tuning of the parameters.Comment: 22 pages, 14 figures, submitted to MNRAS; added references, corrected typo

Radiation-Hard Quartz Cerenkov Calorimeters

New generation hadron colliders are going to reach unprecedented energies and radiation levels. Quartz has been identified as a radiation-hard material that can be used for Cerenkov calorimeters of the future experiments. We report from the radiation hardness tests performed on quartz fibers, as well as the characteristics of the quartz fiber and plate Cerenkov calorimeters that have been built, designed, and proposed for the CMS experiment

Recovery Risk in Stock Returns

In this paper we argue that book-to-market and size attributes represent sensitivities of firm returns to several risk factors, and in so doing they subsume the information in other attributes. Although this gives them high cross-sectional explanatory power, they are not very indicative if we are concerned with testing whether an individual risk factor is priced. In that regard, claiming that financial distress is not priced, by only considering probability of bankruptcy, seems premature. Rational investors may also care about recovery rates and the relatively higher mean returns observed for small firms with very low book-to-market ratios is consistent with this view. To analyse recovery risk, we construct mimicking portfolios by sorting stocks on less noisy attributes such as fixed-assets and intangible-assets ratios. We find that recovery risk mimicking portfolios exhibit typical risk factor characteristics, and perform well in explaining the cross-section of returns. The results suggest that recovery risk factor is a good candidate to be priced, and much of the explanatory power of the size attribute comes from the fact that it embodies useful information regarding recovery risk. Overall, our findings have important portfolio management implications.

New formulations of the Hop-Constrained Minimum Spanning Tree problem via Miller–Tucker–Zemlin constraints

Cataloged from PDF version of article.Given an undirected network with positive edge costs and a natural number p, the Hop-Constrained Minimum Spanning Tree problem (HMST) is the problem of finding a spanning tree with minimum total cost such that each path starting from a specified root node has no more than p hops (edges). In this paper, we develop new formulations for HMST. The formulations are based on Miller–Tucker–Zemlin (MTZ) subtour elimination constraints, MTZ-based liftings in the literature offered for HMST, and a new set of topologyenforcing constraints. We also compare the proposed models with the MTZ-based models in the literature with respect to linear programming relaxation bounds and solution times. The results indicate that the new models give considerably better bounds and solution times than their counterparts in the literature and that the new set of constraints is competitive with liftings to MTZ constraints, some of which are based on well-known, strong liftings of Desrochers and Laporte (1991). 2011 Elsevier B.V. All rights reserved

Melting of PCM in a thermal energy storage unit: Numerical investigation and effect of nanoparticle enhancement

The present paper describes the analysis of the melting process in a single vertical shell-and-tube latent heat thermal energy storage (LHTES), unit and it is directed at understanding the thermal performance of the system. The study is realized using a computational fluid-dynamic (CFD) model that takes into account of the phase-change phenomenon by means of the enthalpy method. Fluid flow is fully resolved in the liquid phase-change material (PCM) in order to elucidate the role of natural convection. The unsteady evolution of the melting front and the velocity and temperature fields is detailed. Temperature profiles are analyzed and compared with experimental data available in the literature. Other relevant quantities are also monitored, including energy stored and heat flux exchanged between PCM and HTF. The results demonstrate that natural convection within PCM and inlet HTF temperature significantly affects the phase-change process. Thermal enhancement through the dispersion of highly conductive nanoparticles in the base PCM is considered in the second part of the paper. Thermal behavior of the LHTES unit charged with nano-enhanced PCM is numerically analyzed and compared with the original system configuration. Due to increase of thermal conductivity, augmented thermal performance is observed: melting time is reduced of 15% when nano-enhanced PCM with particle volume fraction of 4% is adopted. Similar improvements of the heat transfer rate are also detecte

Optimization of transportation requirements in the deployment of military units

Cataloged from PDF version of article.We study the deployment planning problem (DPP) that may roughly be defined as the problem of the planning of the physical movement of military units, stationed at geographically dispersed locations, from their home bases to their designated destinations while obeying constraints on scheduling and routing issues as well as on the availability and use of various types of transportation assets that operate on a multimodal transportation network. The DPP is a large-scale real-world problem for which analytical models do not exist.We propose a model for solving the problem and develop a solution methodology which involves an effective use of relaxation and restriction that significantly speeds up a CPLEX-based branch-and-bound. The solution times for intermediate-sized problems are around 1 h at maximum, whereas it takes about a week in the Turkish Armed Forces to produce a suboptimal feasible solution based on trial-and-error methods. The proposed model can be used to evaluate and assess investment decisions in transportation infrastructure and transportation assets as well as to plan and execute cost-effective deployment operations at different levels of planning. 2005 Elsevier Ltd. All rights reserved