A Crame/spl acute/r-Rao-type estimation lower bound for systems with measurement faults

A Crame/spl acute/r-Rao-type lower bound is presented for systems with measurements prone to discretely-distributed faults, which are a class of hybrid systems. Lower bounds for both the state and the Markovian interruption variables (fault indicators) of the system are derived, using the recently presented sequential version of the Crame/spl acute/r-Rao lower bound (CRLB) for general nonlinear systems. Because of the hybrid nature of the systems addressed, the CRLB cannot be directly applied due to violation of its associated regularity conditions. To facilitate the calculation of the lower bound, the hybrid system is first approximated by a system in which the discrete distribution of the fault indicators is replaced by an approximating continuous one. The lower bound is then obtained via a limiting process applied to the approximating system. The results presented herein facilitate a relatively simple calculation of a nontrivial lower bound for the state vector of systems with fault-prone measurements. The CRLB-type lower bound for the interruption process variables turns out to be trivially zero, however, a nontrivial, non-CRLB-type bound for these variables has been recently presented elsewhere by the authors. The utility and applicability of the proposed lower bound are demonstrated via a numerical example involving a simple global positioning system (GPS)-aided navigation system, where the GPS measurements are fault-prone due to their sensitivity to multipath errors.     

Father absence: Effects of stepfathers upon psychosocial development in males.

Administered the Ego Identity Scale to 39 male university students with stepfathers; 47 with no stepfather, who had remained fatherless from the time of father absence to the time of the study; and 39 with fathers, who had never experienced father absence. It was hypothesized that males with stepfathers would attain levels of psychosocial functioning equivalent to that of father-present males and that the functioning of Ss without stepfathers would be at levels significantly below that evidenced by Ss in the other 2 groups. Both hypotheses were partially supported, and results indicate that stepfathering is an important factor in mitigating the typically deleterious effects of father absence. Results also show that the effects of early father absence persisted into late adolescence. Three factors which may account for the positive effects of gaining a stepfather for the male child are postulated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Detailed experiments on helium-neon FM lasers

Results are reported on the detailed measurements of the operating characteristics of an He-Ne FM laser oscillating at 6328Å. Experiments were performed in both the "phase-locked" and the "FM" regions of operation, with particular emphasis on the FM region. In the phase-locked region, the pulsed output of the FM laser was observed and studied. In the FM region, measurements were made to study the laser power output, modulation index, and distortion (deviation from an ideal FM signal) as functions of the amplitude and frequency of the applied phase perturbation. Most of these experiments were performed under conditions of low laser excess gain (relatively few modes above threshold for the free-running laser); however, the results are useful for predicting the behavior of FM laser operation with larger excess gain. In addition to describing the practical operation of an FM laser, these experiments provide a check on the applicability of the FM laser theory of Harris and McDuff. An exact quantitative comparison between theory and experiment was not attempted, but the qualitative agreement is very good.     

Theory of optical parametric oscillation internal to the laser cavity

Since the fields inside a laser cavity are much higher than the external fields, an analysis of a parametric oscillator with the nonlinear crystal internal to the laser is performed. Using self-consistency equations as the starting point, the equations of motion of such an oscillator are derived. Depending on various cavity, pumping, and nonlinearity parameters, these lead to several types of oscillation with distinctly different operating characteristics: (1) efficient parametric oscillation similar to that of previous analyses; (2) inefficient parametric oscillation resulting from the fact that the nonlinear interaction drives the phases rather than the amplitudes of the signal, idler, and pump; and (3) a pulsing output from the oscillator with repetitive pulses of the signal and idler. A stability analysis of these various regions shows that they are mutually exclusive and can be experimentally chosen by changing the laser gain, the oscillator output coupling, or the strength of the nonlinear interaction. It is shown that the internal oscillator efficiency rapidly approaches the Manley-Rowe limit, as the available pump power becomes several times greater than that required for threshold. The efficiency of an external oscillator having a triply resonant optical cavity is found to be generally less than that of the corresponding internal oscillator.     

Gradient Clock Synchronization in Dynamic Networks

Over the last years, large-scale decentralized computer networks such as peer-to-peer and mobile ad hoc networks have become increasingly prevalent. The topologies of many of these networks are often highly dynamic. This is especially true for ad hoc networks formed by mobile wireless devices.     

Eigenfactor solution of the matrix Riccati equation--A continuous square root algorithm

This paper introduces a new algorithm for solving the matrix Riccati equation. Differential equations for the eigenvalues and eigenvectors of the solution matrix are developed in which their derivatives are expressed in terms of the eigenvalues and eigenvectors themselves and not as functions of the solution matrix. The solution of these equations yields, then, the time behavior of the eigenvalues and eigenvectors of the solution matrix. A reconstruction of the matrix itself at any desired time is immediately obtained through a trivial similarity transformation. This algorithm serves two purposes. First, being a square root solution, it entails all the advantages of square root algorithms such as nonnegative definiteness and accuracy. Secondly, it furnishes the eigenvalues and eigenvectors of the solution matrix continuously without resorting to the complicated route of solving the equation directly and then decomposing the solution matrix into its eigenvalues and eigenvectors. The algorithm which handles cases of distinct as well as multiple eigenvalues is tested on several examples. Through these examples it is seen that the algorithm is indeed more accurate than the ordinary one. Moreover, it is seen that the algorithm works in cases where the ordinary algorithm fails and even in cases where the closed-form solution cannot be computed as a result of numerical difficulties.