Numerical simulation of ratcheting and fatigue behaviour of mitred pipe bends under in-plane bending and internal pressure

This paper investigates the ratcheting and fatigue behaviour of 90 degree single unreinforced mitred pipe bends subjected to a cyclic in-plane closing moment with a non-zero mean value and constant internal pressure. An experiment was conducted to induce ratcheting and low cycle failure of the mitred pipe bend. Material and structural response is considered both locally and globally using strain gauges at the locations of highest strain and also by measuring the displacement of the mitre end. These results along with the number of cycles to failure are compared with those produced from nonlinear finite element analysis. The predicted crosshead displacement from the multi linear model showed a good agreement with the test results. However, the finite element model failed to accurately replicate the strain level or trend from the tests, indicating the weakness of the material model used in simulating the cyclic hardening effect. It was also found that the FE models proposed were not able to model the final failure mode of the mitre due to the exclusion of crack simulation in the analysis, i.e. interaction between ratcheting and low cycle fatigue cracking was not considered in the idealised numerical model

The Stink Bugs (Hemiptera: Heteroptera: Pentatomidae) of Missouri

The stink bug (Hemiptera: Pentatomidae) fauna of Missouri was last treated more than 70 years ago. Since then, many more specimens have become available for study, substantial papers on regional faunas have been published, and many revisions and other taxonomic changes have taken place. As a consequence, 40% of the names from the previous Missouri state list have changed or the taxa have been removed. The fauna of stink bugs known from Missouri based on specimens from museums, other collections, and the literature is presented. Included for each species is a general overview of biological and ecological information, overall distribution, and local distribution among Missouri Natural Divisions. Also presented for Missouri specimens are biological label data and extreme dates of adult collection. All totaled, 57 species are now known from the state, eight of which represent new state records: Asopinae: Alcaeorrhynchus grandis (Dallas), Tylospilus acutissimus (Stål); Pentatominae: Banasa calva (Say), Banasa euchlora Stål, Cosmopepla intergressa (Uhler), Halyomorpha halys (Stål), Neottiglossa undata (Say); Podopinae: Amaurochrous brevitylus Barber and Sailer

Tools for distributed application management

Distributed application management consists of monitoring and controlling an application as it executes in a distributed environment. It encompasses such activities as configuration, initialization, performance monitoring, resource scheduling, and failure response. The Meta system (a collection of tools for constructing distributed application management software) is described. Meta provides the mechanism, while the programmer specifies the policy for application management. The policy is manifested as a control program which is a soft real-time reactive program. The underlying application is instrumented with a variety of built-in and user-defined sensors and actuators. These define the interface between the control program and the application. The control program also has access to a database describing the structure of the application and the characteristics of its environment. Some of the more difficult problems for application management occur when preexisting, nondistributed programs are integrated into a distributed application for which they may not have been intended. Meta allows management functions to be retrofitted to such programs with a minimum of effort

The UN-Intended Effects of Risky Mandates

In May 1948, the United Nations launched its first peacekeeping mission named the United Nations Truce Supervision Organization (UNTSO). Since this first mission, the United Nations has launched over 70 peacekeeping missions in regions such as Europe, Latin America, Asia, and Africa (Bellamy and Williams, 2015). The overarching goal of the United Nations, and the Security Council as the organ responsible for authorizing peacekeeping missions, is to protect international peace (United Nations, 1945a). However, the means of achieving international peace differs across missions. One source of variation concerning the means of achieving peace is found in peacekeeping mission mandates. While these mandates are determined on a case-by-case basis (United Nations Secretariat, 2008), scholars and policymakers find that mandates are becoming increasingly risky regarding peacekeeper physical security due to the surge in mandates that authorize the use of force (Howard and Dayal, 2018). Furthermore, the conflict environment has made mandate implementation increasingly dangerous, as seen by the overall increase in peacekeeper fatalities (Henke, 2019). The rise in the number of peacekeeping missions, increased peacekeeper fatalities, and the frequent authorization of risky mandates risk leads to the question, how does mandate risk affect peacekeeping mission outcomes? I argue that missions with high-risk mandates and dangerous conflict environments generate sub-optimal mission outcomes, specifically, fewer troop contributions from troop-contributing states, smaller troop deployments in the host state, and shorter force commander tenures. The dissertation is organized in the following way. In Chapter 1, I motivate the dissertation using qualitative and quantitative evidence to create the empirical puzzle. In Chapter 2, I explain the literature on the foundational and modern questions of peacekeeping research. With this information, I then introduce the three literatures I intend to address in the dissertation, which are troop contributions, local troop deployments, and force commander tenure, that concludes with the gaps my work fills. Chapter 3 contains a brief discussion on the mission creation process that ranges from initial authorization to putting “boots on the ground” in the mission host state. Following the background knowledge, I develop three chapters with unique theoretical arguments and empirical models to determine the effect of mission mandates on various outcomes. Chapter 4 introduces the concept and measure of mandate risk employed through the remainder of the dissertation. From this explanation, I argue that higher levels of mandate risk and conflict environment danger increase the perceived costs of troop contributions, leading to reduced troop contribution levels. In Chapter 5, I generate the force commander’s dilemma to demonstrate that mandate risk and conflict danger are associated with small troop deployments in the host state and the conclusion that the reducing effect of mandates deteriorates after a significant amount of time. I argue in Chapter 6 that risky mandates and dangerous conflict conditions should reduce force commander tenures, but empirical models do not provide evidence in support of the argument. Last, I summarize each chapter’s conclusions, ramifications for the peacekeeping literature, policy implications, and directions for future work in Chapter 7

On Nesting Monte Carlo Estimators

Many problems in machine learning and statistics involve nested expectations and thus do not permit conventional Monte Carlo (MC) estimation. For such problems, one must nest estimators, such that terms in an outer estimator themselves involve calculation of a separate, nested, estimation. We investigate the statistical implications of nesting MC estimators, including cases of multiple levels of nesting, and establish the conditions under which they converge. We derive corresponding rates of convergence and provide empirical evidence that these rates are observed in practice. We further establish a number of pitfalls that can arise from naive nesting of MC estimators, provide guidelines about how these can be avoided, and lay out novel methods for reformulating certain classes of nested expectation problems into single expectations, leading to improved convergence rates. We demonstrate the applicability of our work by using our results to develop a new estimator for discrete Bayesian experimental design problems and derive error bounds for a class of variational objectives.Comment: To appear at International Conference on Machine Learning 201

Looking for Help Long Overdue: Where Has Higher Education Been?

For more than a decade, the American public has carped and complained about the condition of American education. Some have gone so far as to wring their hands over the apparent futility of reform efforts. Overall, the nation has found the state of its public elementary and secondary education unacceptable. It has especially lamented the tragic condition of urban public schools, yet it docs not seem to know what to do about it