Elementary Proofs Of Two Theorems Involving Arguments Of Eigenvalues Of A Product Of Two Unitary Matrices

We give elementary proofs of two theorems concerning bounds on the maximum argument of the eigenvalues of a product of two unitary matrices --- one by Childs \emph{et al.} [J. Mod. Phys., \textbf{47}, 155 (2000)] and the other one by Chau [arXiv:1006.3614]. Our proofs have the advantages that the necessary and sufficient conditions for equalities are apparent and that they can be readily generalized to the case of infinite-dimensional unitary operators.Comment: 8 pages in Revtex 4.1 preprint format, to appear in Journal of Inequalities and Application

Phase II of the ASCE Benchmark Study on SHM

The task group on structural health monitoring of the Dynamic Committee of ASCE was formed in 1999 at the 12 th Engineering Mechanics Conference. The task group has designed a number of analytical studies on a benchmark structure and there are plans to follow these with an experimental program. The first phase of the analytical studies was completed in 2001. The second phase, initiated in the summer of 2001, was formulated in the light of the experience gained on phase I and focuses on increasing realism in the simulation of the discrepancies between the actual structure and the mathematical model used in the analysis. This paper describes the rational that lead the SHM task group to the definition of phase II and presents the details of the cases that are being considered

Poles of regular quaternionic functions

This paper studies the singularities of Cullen-regular functions of one quaternionic variable. The quaternionic Laurent series prove to be Cullen-regular. The singularities of Cullen-regular functions are thus classified as removable, essential or poles. The quaternionic analogues of meromorphic complex functions, called semiregular functions, turn out to be quotients of Cullen-regular functions with respect to an appropriate division operation. This allows a detailed study of the poles and their distribution.Comment: 14 page

Topology design and performance analysis of an integrated communication network

A research study on the topology design and performance analysis for the Space Station Information System (SSIS) network is conducted. It is begun with a survey of existing research efforts in network topology design. Then a new approach for topology design is presented. It uses an efficient algorithm to generate candidate network designs (consisting of subsets of the set of all network components) in increasing order of their total costs, and checks each design to see if it forms an acceptable network. This technique gives the true cost-optimal network, and is particularly useful when the network has many constraints and not too many components. The algorithm for generating subsets is described in detail, and various aspects of the overall design procedure are discussed. Two more efficient versions of this algorithm (applicable in specific situations) are also given. Next, two important aspects of network performance analysis: network reliability and message delays are discussed. A new model is introduced to study the reliability of a network with dependent failures. For message delays, a collection of formulas from existing research results is given to compute or estimate the delays of messages in a communication network without making the independence assumption. The design algorithm coded in PASCAL is included as an appendix

Experimental study of multiple cracks detection utilizing a probabilistic approach

This paper studies the possibility of using measured transient vibration data in the detection of multiple cracks on beams by following the Bayesian probabilistic framework. The proposed method adopts different classes of models in modelling a beam with different numbers of cracks. The number of cracks on the beam can then be identified by calculating the probability of a model class conditional on a given set of measured transient vibration data. By following the Bayesian probabilistic framework, the posterior probability density functions (PDFs) for a set of crack parameters, such as the crack locations and the corresponding extents, can be calculated. The PDFs allow engineers to quantify the uncertainties associated with the results of crack detection. The paper reports not only the theoretical developed but also the experimental verification of the proposed method

Gastrointestinal Stromal Tumor in Pregnancy: A Case Report

Background. Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the digestive tract and are diagnosed relatively seldom in pregnancy. Case. We describe a remarkable clinical course and long-term outcome, now nine years after first diagnosis, of a massive and metastatic, with a high malignancy grade GIST case, found in and treated from the first trimester of pregnancy onwards. Conclusion. GIST occurring during pregnancy is extremely rare. However, early diagnosis is important for optimal management. The recent better understanding of oncogenesis, the use of immunohistochemistry for differential diagnosis of GISTs, and the use of imatinib mesylate as the treatment of first choice are—as shown in this case—important for care of pregnant women with this type of malignancy

Spillover Effects of Emotional Labor in Customer Service Encounters toward Coworker Harming: A Resource Depletion Perspective

This research examines how the implications of emotional labor can transfer from customer encounters to coworker interactions using temporally lagged data from a sample of frontline service employees. The results show that surface acting in customer service encounters is positively, and deep acting is negatively, related to ego depletion. Employees’ ego depletion, in turn, is positively associated with their interpersonally harmful behavior toward coworkers. Hence, ego depletion appears as a mediating variable that translates the implications of distinct emotional labor strategies into coworker harming. Moreover, emotion regulation self-efficacy moderates the role of surface acting. The positive indirect relationship between surface acting and coworker harming, via ego depletion, is buffered among employees with higher emotion regulation self-efficacy. These findings shed new light on the complex and far-reaching consequences of emotional labor. We demonstrate the relevance of emotional labor to third parties not directly involved in customer service encounters and highlight important mediators and boundary conditions of these indirect relations

Unification of bulk and interface electroresistive switching in oxide systems

We demonstrate that the physical mechanism behind electroresistive switching in oxide Schottky systems is electroformation, as in insulating oxides. Negative resistance shown by the hysteretic current-voltage curves proves that impact ionization is at the origin of the switching. Analyses of the capacitance-voltage and conductance-voltage curves through a simple model show that an atomic rearrangement is involved in the process. Switching in these systems is a bulk effect, not strictly confined at the interface but at the charge space region.Comment: 4 pages, 3 figures, accepted in PR

Stability of Filters for the Navier-Stokes Equation

Data assimilation methodologies are designed to incorporate noisy observations of a physical system into an underlying model in order to infer the properties of the state of the system. Filters refer to a class of data assimilation algorithms designed to update the estimation of the state in a on-line fashion, as data is acquired sequentially. For linear problems subject to Gaussian noise filtering can be performed exactly using the Kalman filter. For nonlinear systems it can be approximated in a systematic way by particle filters. However in high dimensions these particle filtering methods can break down. Hence, for the large nonlinear systems arising in applications such as weather forecasting, various ad hoc filters are used, mostly based on making Gaussian approximations. The purpose of this work is to study the properties of these ad hoc filters, working in the context of the 2D incompressible Navier-Stokes equation. By working in this infinite dimensional setting we provide an analysis which is useful for understanding high dimensional filtering, and is robust to mesh-refinement. We describe theoretical results showing that, in the small observational noise limit, the filters can be tuned to accurately track the signal itself (filter stability), provided the system is observed in a sufficiently large low dimensional space; roughly speaking this space should be large enough to contain the unstable modes of the linearized dynamics. Numerical results are given which illustrate the theory. In a simplified scenario we also derive, and study numerically, a stochastic PDE which determines filter stability in the limit of frequent observations, subject to large observational noise. The positive results herein concerning filter stability complement recent numerical studies which demonstrate that the ad hoc filters perform poorly in reproducing statistical variation about the true signal

Implementing Unitarity in Perturbation Theory

Unitarity cannot be perserved order by order in ordinary perturbation theory because the constraint UU^\dagger=\1 is nonlinear. However, the corresponding constraint for $K=\ln U$, being $K=-K^\dagger$, is linear so it can be maintained in every order in a perturbative expansion of $K$. The perturbative expansion of $K$ may be considered as a non-abelian generalization of the linked-cluster expansion in probability theory and in statistical mechanics, and possesses similar advantages resulting from separating the short-range correlations from long-range effects. This point is illustrated in two QCD examples, in which delicate cancellations encountered in summing Feynman diagrams of are avoided when they are calculated via the perturbative expansion of $K$. Applications to other problems are briefly discussed.Comment: to appear in Phys. Rev.