On the duality of finite element discretization error control in computational Newtonian and Eshelbian mechanics

In this paper, goal-oriented a posteriori error estimators of the averaging type are presented for the error obtained while approximately evaluating theJ-integral in nonlinear elastic fracture mechanics. Since the value of the J-integral is one component of the material force acting on the crack tip of a pre-cracked elastic body, the appropriate mechanical framework to be chosen is the one named after Eshelby rather than classical Newtonian mechanics. However, in a finite element setting, the discretized Eshelby problem is generally not solved explicitly. Rather, its solution is approximated by the finite element solution of the corresponding discretized dual Newton problem. As a consequence, discrete material forces arise not only at the crack tip but also at other nodes of the current finite element mesh. It is the objective of this paper to establish goal-oriented a posteriori error estimators in both the framework of Eshelbian and Newtonian mechanics and to elaborate their dual relations. This allows to control the error of the J-integral while, at the same time, no further discrete material forces arise during the adaptive mesh refinement process which could lead to misleading mechanical interpretations of the results obtained by the finite element method. The paper is concluded by numerical examples that illustrate our theoretical results. Dedicated to the memory of the esteemed colleague Professor Karl Popp, University of Hannover, who unexpectedly passed away on April 24, 2005.     

Depression ratings, reported sexual risk behaviors, and methamphetamine use: Latent growth curve models of positive change among gay and bisexual men in an outpatient treatment program.

Although the cessation of substance use is the principal concern of drug treatment programs, many individuals in treatment experience co-occurring problems such as mood disruptions and sexual risk behaviors that may complicate their recovery process. This study assessed relationships among dynamic changes tracked over time in methamphetamine use, depression symptoms, and sexual risk behaviors (unprotected anal intercourse) in a sample of 145 methamphetamine-dependent gay and bisexual males enrolled in a 16-week outpatient drug treatment research program. Participants were randomly assigned into 1 of 4 conditions: contingency management (CM), cognitive behavioral therapy (CBT; the control condition), combined CM and CBT, and a tailored gay-specific version of the CBT condition. Using latent growth curve models, the authors assessed the relationship of means (intercepts) and the slopes of the 3 measures of interest over time to test whether changes in methamphetamine use predicted declining rates of depression and risky sexual behavior in tandem. Participants with the greatest downward trajectory in methamphetamine use (urine verified) reported the greatest and quickest decreases in reported depressive symptoms and sexual risk behaviors. The control group reported the most methamphetamine use over the 16 weeks; the tailored gay-specific group reported a more rapidly decreasing slope in methamphetamine use than the other participants. Findings indicate that lowering methamphetamine use itself has a concurrent and synergistic effect on depressive symptoms and risky sexual behavior patterns. This suggests that some users who respond well to treatment may show improvement in these co-occurring problems without a need for more intensive targeted interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alternatives to Lead as a Machinability Enhancer in Free Cutting Steels

Low levels of lead are added to free cutting steels to improve machinability. For environmental reasons, there is interest in alternatives to lead that are technically and commercially viable. The machining performance of eight low carbon free cutting steels with alternative machinability enhancers, including additions of bismuth, increased sulphur (with and without tellurium), tin and phosphorus, has been investigated. In tests with high speed steel tools and lubricant, the leaded steel showed the best performance in terms of production rate, surface finish and chip form. In tests with coated carbide tools at a range of cutting speeds the standard non‐leaded 11 SMn30 steel performed well in terms of tool wear, but showed poorer chip form than the leaded steel. The steels with increased sulphur showed improved performance compared with the 11SMn30 steel in tests using high speed steel tools and lubricant, but did not approach the leaded steel in terms of production rate. The steels containing tin did not generally perform better than the 11 SMn30 steel. The 11 SMn30Bi steel gave performance approaching that of the leaded steel in tests with high speed steel tools and lubricant. However, the cost of this addition may make it uneconomic for large scale use.     

Latent variable assessment of outcomes in a nurse-managed intervention to increase latent tuberculosis treatment completion in homeless adults.

To assess predictors of latent tuberculosis infection (LTBI) completion by using structural equation modeling (SEM) among homeless adults, a group at great risk for LTBI and active tuberculosis (TB). LTBI therapy is effective in stemming the progression to active TB, yet treatment adherence among homeless persons is difficult to attain. Design: By using SEM, the authors assessed predictors of LTBI completion among a sample of 494 homeless adults in Los Angeles, CA, who received either a nurse case-managed program (NCM) or a usual care program. Main Outcome Measures: Latent variables were created with the baseline variables of site type, age, intervention status, dissatisfaction with health care, depression, TB risk assessment, alcohol use, heroin or cocaine use, and TB knowledge. Outcome variables included many of the same baseline variables as well as treatment completion. Results: LTBI treatment completion (100% adherence) was significantly and positively associated with participation in NCM, older age, and less heroin or cocaine use. NCM also predicted greater TB knowledge, greater ease of treatment, and more satisfaction with treatment (NCM completion rate = 64%, control rate = 42%). Conclusion: The culturally competent NCM program, combined with active tracking and incentives, was successful in a difficult-to-treat and highly transient population. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiwalled Carbon Nanotubes Catalytically Grown from Amorphous Silica Films Deposited by Combustion CVD

Homogeneous mixtures containing iron oxide and amorphous SiO₂ were obtained through the co-deposition of these oxides via combustion chemical vapor deposition technique (CCVD). This technique allows the deposition of thin films with low-cost precursors and equipments. After deposition, the deposited samples were submitted to a heat treatment in an atmosphere composed of natural gas and H₂ at 1000°C, in order to promote the growth of carbon nanotubes. Multiwalled carbon nanotubes, with diameters smaller than 15 nm, were obtained.     

Variational Multiscale Large Eddy Simulation of Turbulent Flow in a Diffuser

In the present study, variational multiscale large eddy simulation (LES) is applied to turbulent flow in a diffuser, which represents a challenging test case due to the appearance of flow separation and subsequent reattachment. Two different scale-separating operators based on multigrid operators are used for separating large and small resolved scales. Dynamic as well as constant-coefficient-based subgrid-scale modeling are employed in the variational multiscale LES. The results show that the variational multiscale LES with a simple constant-coefficient Smagorinsky model using a projective scale-separating operator yields a very good prediction of most of the crucial flow features. Furthermore, it turns out to be by far the most computationally efficient approach, resulting in a computing time reduction of about 18% compared to the traditional LES with a dynamic Smagorinsky model. The variational multiscale LES with a dynamic Smagorinsky model does not prove to be a superior approach.     

Frequency estimation from proper sets of correlations

As a complement to the periodogram, low-complexity frequency estimators are of interest. One such estimator is based on Prony's method and rely on phase information of the auto correlations. Without prior knowledge of the frequency (e.g., a given frequency interval), the frequency cannot be unambiguously estimated from a single correlation only. We introduce a new method of phase unwrapping using an arbitrary number (more than one) of correlations. From this arbitrary set of correlations, we propose a weighted average estimator. We derive the asymptotic performance and show how the correlation lags should be properly chosen. From a design aspect, there is often a restriction of using a fixed number of computations. In addition, we therefore propose a strategy to find a proper set of correlation lags subject to a given computational complexity. Finally, simulation results that lend support to the theoretical findings are included     

Toward behavioral intelligence in the Semantic Web

Realizing the Web's full potential will require the development and support of agents that function as schedulers, planners, and searchers who, with minimal direction, can serve as an omnipresent staff of advisers, secretaries, brokers, and research assistants. Electronic commerce has brought this capability tantalizingly near. Organizations and individuals have connected an enormous variety of products and services to the Internet, making them accessible to other programs through simple communication protocols. Now the AI community must determine how it can build intelligent agents to exploit these services. One strategy would change the Web itself, making it accessible to existing AI modeling, and reasoning techniques. In this semantic Web, service and content providers would mark pages in accordance with standardized conventions designed to reduce ambiguity and make automated reasoning easier. The paper considers the development of a distributed intelligence and bringing agents to the Web. It discusses DAML-S which provides support for composite services, combinations of simpler services, or behaviors, and the coordination mechanisms, or reactive plans, used to combine those behaviors.     

Late join algorithms for distributed interactive applications

Distributed interactive applications such as shared whiteboards and multiplayer games often support dynamic groups where users may join and leave at any time. A participant joining an ongoing session has missed the data that have previously been exchanged by the other session members. It is therefore necessary to initialize the application instance of the latecomer with the current state. In this paper, we propose a late join algorithm for distributed interactive applications that provides such an initialization of applications. The algorithm is scalable and robust and can be easily adapted to the needs of different applications by means of late join policies. The behavior of the late join algorithm and the impact of design alternatives are investigated in detail by means of an extensive simulation study. This study also shows that an improper handling of the late join problem can cause very high application and network load.