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Difference images quantify changes in the object scene over time. In this paper, we use the feature-specific imaging paradigm to present methods for estimating a sequence of difference images from a sequence of compressive measurements of the object scene. Our goal is twofold. First is to design, where possible, the optimal sensing matrix for taking compressive measurements. In scenarios where such sensing matrices are not tractable, we consider plausible candidate sensing matrices that either use the available a priori information or are nonadaptive. Second, we develop closed-form and iterative techniques for estimating the difference images. We specifically look at \ell2- and \ell1-based methods. We show that \ell2-based techniques can directly estimate the difference image from the measurements without first reconstructing the object scene. This direct estimation exploits the spatial and temporal correlations between the object scene at two consecutive time instants. We further develop a method to estimate a generalized difference image from multiple measurements and use it to estimate the sequence of difference images. For \ell1-based estimation, we consider modified forms of the total-variation method and basis pursuit denoising. We also look at a third method that directly exploits the sparsity of the difference image. We present results to show the efficacy of these techniques and discuss the advantages of each. [ABSTRACT FROM PUBLISHER]

We introduce a local-channel power control strategy applicable to multiple-hypothesis distributed detection systems communicating over slow-fading orthogonal multiple-access channels. In earlier work, it was demonstrated that performance could be improved by adjusting transmit power to maximize the J-divergence measure of a binary detection system. The local power control strategy introduced here further improves performance by exploiting a priori probabilities and local sensor statistics. Moreover, the local power optimization can be combined with additional power control based on the state of the propagation channel. We extend the optimization to systems performing multiple-hypothesis detection, and evaluate outage probability for these systems. Various numerical results are shown. [ABSTRACT FROM AUTHOR]

We introduce and evaluate the concept of switched-element direction finding. In a switched-element system, simultaneous data collection occurs on only a subset of the array's N elements at any given time. The data collection interval is divided into subintervals, and at each subinterval a multiplexer selects a different subset of M

We propose to combine directional antennas in a conformal array configuration with a matching two-stage receiver architecture to improve performance of code-division multiple-access (CDMA) communication systems in time-varying channels. We propose a reduced-dimension space-time (ST) RAKE architecture that matches the ST correlation structure of the data received by a circular array. In time-varying channels, this reduced-dimension architecture outperforms the full-dimension architecture due to improved convergence of its adaptive processor. [ABSTRACT FROM AUTHOR]

Concurrency control algorithms for database systems are usually regarded as methods for synchronizing Read and Write operations. Such methods are judged to be correct if they only produce serializable executions. However, Reads and Writes are sometimes inaccurate models of the operations executed by a database system. In such cases, serializability does not capture all aspects of concurrency control executions. To capture these aspects, we describe a proof schema for analyzing concurrency control correctness. We illustrate the proof schema by presenting two new concurrency algorithms for distributed database systems. [ABSTRACT FROM AUTHOR]

A replicated database is a distributed database in which copies of some data items are stored redundantly at multiple sites. In such a system, an execution of transactions is correct if it is equivalent to a serial execution of those transactions on a one copy database. We show that in any serializable execution, if all transactions see the failures and recoveries of data item copies in a consistent order, then the execution is correct. We model this condition using a modified type of serialization graph, and show that if this graph is acyclic then the corresponding execution is correct. We demonstrate the value of this model by using it to prove the correctness of an algorithm for synchronizing access to a replicated database. [ABSTRACT FROM AUTHOR]

Site initialization is the problem of integrating a new site into a running distributed database system (DDBS). Site recovery is the problem of integrating an old site into a DDBS when the site recovers from failure. Site backup is the problem of creating a static backup copy of a database for archival or query purposes. We present an algorithm that solves the site initialization problem. By modifying the algorithm slightly, we get solutions to the other two problems as well. Our algorithm exploits the fact that a correct DDBS must run a serializable concurrency control algorithm. Our algorithm relies on the concurrency control algorithm to handle all intersite synchronization. [ABSTRACT FROM AUTHOR]

SDD-1, A System for Distributed Databases, is a distributed database system being developed by Computer Corporation of America (CCA), Cambridge, MA. SDD-1 permits data to be stored redundantly at several database sites in order to enhance the reliability and responsiveness of the system and to facilitate upward scaling of system capacity. This paper describes the method used by SDD-1 for updating data that are stored redundantly. Redundant updating can be costly because it may potentially involve extensive intercomputer communication overhead in order to lock all copies of data being updated. The method described here avoids this overhead by identifying cases in which it is not necessary to perform this global database locking. The identification of transactions that do not require global locking is based on a predefinition of transaction classes performed by the database administrator using an analysis technique described herein. The classes defined are used at run time to decide what level of synchronization is needed for a given transaction. It is important to note that this predefinition activity in no way limits the transactions that the system can accept; it merely permits more efficient execution of those types of transactions that were anticipated. [ABSTRACT FROM AUTHOR]

Existing scholarship examines the moral status of markets, identifying some markets as "noxious"—markets deemed morally objectionable due to the background conditions preceding exchange or the resulting consequences. This literature primarily focuses on market exchanges between private parties. We broaden the analysis to include government markets—markets involving exchanges where either the buyer or seller, or both, are government officials. We develop a general theoretical framework to understand the conditions under which government markets are likely to be more or less noxious. We then apply the framework to the international arms trade to demonstrate its usefulness for understanding noxious government markets. [ABSTRACT FROM AUTHOR]

In spread spectrum (SS) communications, the input signal is spread over a wider bandwidth to avoid interference or interception. One of the most common SS techniques is direct sequence SS (DSSS). In this Letter, the authors propose non-cooperative compressive detection techniques for DSSS signals. The proposed compressive detection framework allows the use of random as well as designed measurement kernels. A technique for designing compressive measurement kernels which exploit DSSS signal structure and non-uniform usage of spreading codes is proposed. Theoretical and simulation results are provided to compare the performance of the proposed methods with their conventional counterparts. [ABSTRACT FROM AUTHOR]