Experimental Characterization and Material Modelling of an AZ31 Magnesium Sheet Alloy at Elevated Temperatures under Consideration of the Tension-Compression Asymmetry

Magnesium sheet alloys have a great potential as a construction material in the aerospace and automotive industry. However, the current state of research regarding temperature dependent material parameters for the description of the plastic behaviour of magnesium sheet alloys is scarce in literature and accurate statements concerning yield criteria and appropriate characterization tests to describe the plastic behaviour of a magnesium sheet alloy at elevated temperatures in deep drawing processes are to define. Hence, in this paper the plastic behaviour of the well-established magnesium sheet alloy AZ31 has been characterized by means of convenient mechanical tests (e. g. tension, compression and biaxial tests) at temperatures between 180 and 230 °C. In this manner, anisotropic and hardening behaviour as well as differences between the tension-compression asymmetry of the yield locus have been estimated. Furthermore, using the evaluated data from the above mentioned tests, two different yield criteria have been parametrized; the commonly used Hill'48 and an orthotropic yield criterion, CPB2006, which was developed especially for materials with hexagonal close packed lattice structure and is able to describe an asymmetrical yielding behaviour regarding tensile and compressive stress states. Numerical simulations have been finally carried out with both yield functions in order to assess the accuracy of the material models

Denying the dangerous: preventing firearms from entering the hands of the dangerously mentally ill

Mass shootings in the United States tend to be succeeded by a period of great public attention to gun control laws. Often of particular concern is the National Instant Criminal Background Check System (NICS), which is promulgated by law to prevent statutorily defined individuals, including the dangerously mentally ill, from obtaining firearms. This thesis analyzed the NICS, particularly its ability or inability to prevent firearm access to the mentally ill. The examination looked at three criteria: (1) the weaknesses in the NICS that inhibit its ability in preventing the dangerously mentally ill from obtaining firearms, (2) how consistently applicable records are submitted to the NICS from the individual states, and (3) the proposed recommendations to change and create a more efficient NICS. Specific high-profile mass shootings in the United States were reviewed to illustrate legislative response to those shootings and the changes to the NICS, if any, that followed them. The goal was to identify any immediate deficiencies in the NICS and determine any corrective actions necessary to enhance it to produce a more reliable system. This research should serve as a roadmap for committees or individuals tasked with gun control legislation in the United States.http://archive.org/details/denyingdangerous1094544524Lieutenant, Philadelphia Police Department, Philadelphia PennsylvaniaApproved for public release; distribution is unlimited

Novel applications and methods for the computer-aided understanding and design of enzyme activity

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biological Engineering, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 140-160).Despite great progress over the past several decades in the development and application of computer-aided tools for engineering enzymes for a vast array of industrial applications. rational enzyme design remains an ongoing challenge in biotechnology. This thesis presents a set of novel applications and methods for the computer-aided understanding and design of enzyme activity. In the first part. we apply biophysical modeling approaches in order to design non-native substrate specificity in a key enzymatic step (the thiolase-catalyzed condensation of two acyl-CoA substrates) of an industrially useful de novo metabolic pathway. We present a model-guided. rational design study of ordered substrate binding applied to two biosynthetic thiolases. with the goal of increasing the ratio of C6/C4 products formed by the 31HIA pathway, 3-hydroxyhexanoic acid and 3-hydroxybutyric acid. We identify thiolase mutants that result in nearly ten-fold increases in C6/C4 selectivity. Our findings can extend to other pathways that employ the thiolase for chain elonglation, as well as expand our knowledge of sequence-structure-function relationship for this important class of enzymes. In the second part, we apply methods from machine learning to an ensemble of reactive and non-reactive, but "almost reactive" molecular dynamics trajectories in order to elucidate catalytic drivers in another industrially important model enzyme system, ketol-acid reductoisomerase. Using a small number of molecular features, we show that we can identify conformational states that are highly predictive of reactivity at specific time points relative to the progress of the prospective catalytic event and also that provide mechanistic insight into the reaction catalyzed by this enzyme. We then present a novel theoretical framework for evaluating the contribution to the overall catalytic rate of the conformational states found in the previous part to be predictive of reactivity. Leveraging a computational enhanced sampling technique called transition interface sampling, we show that trajectories sampled in such a manner as to selectively visit the conformations predicted to be characteristic of reactivity exhibit rate constants many orders of magnitude greater than trajectories not required to visit these reactive conformations. The results of this analysis illustrate the importance of incorporating dynamical information into existing frameworks for biocatalyst design.by Brian M. Bonk.Ph. D

Performance Assessment of ESL and EFL Students

Thirteen prototypical performance tasks were selected from over 100 based on their generic appropriateness for the target population and on posited difficulty levels (associated with plus or niinus values for linguistic code command, cognitive operations, and communicative adaptation, as discussed in Norris, Brown, Hudson, & Yoshioka, 1998, after Skehan, 1996, 1998). These l3 tasks were used to create three test forms (with one anchor task common to all forms), two for use in an ESL setting at the University of Hawai'i, and one for use in an EFL setting at Kanda University of International Studies in Japan. In addition, two sets ofrating scales were created based on task-dependent and task-independent categories. For each individual task, the criteria for the task-dependent categories were created in consultation with an advanced language learner, a language teacher, and a non-ESL teacher, all ofwhom were well-acquainted with the target population and the prototype tasks. These criteria for success were allowed to differ from task to task depending on the input ofour consultants. The task-independent categories were created for each of three theoretically motivated components of task difficulty in terms of the adequacy of: (linguistic) code command, cognitive operations, and communicative adaptation. A third rating scale was developed for examinees to rate their own performance in terms of their familiarity with the task, their performance on the task, and the difficulty of the task. Pilot data were gathered from ESL and EFL students at a wide range of proficiency levels. Their performances were scored by raters using the task dependent and task-independent criteria. Analyses included descriptive statistics, reliability estimates (interrater, Cronbach alpha, etc.), correlational analysis, and implicational scale analysis. The results are interpreted and discussed in terms of: (a) the distributions ofscores for the task-dependent and task-independent ratings, (b) test reliability and ways to improve the consistency of measurement, and (c) test validify and the relationship of our task-based test to theory

Numerical and experimental investigations on an extrusion process for a newly developed ultra-high-carbon lightweight steel for the automotive industry

In this study the material flow of a newly developed ultra-high-carbon lightweight steel (uhc-steel) with a high amount of aluminum was investigated in an extrusion process. Cylinder compression tests were performed for material characterization and frictional behaviour was determined by using ring compression tests. Numerical simulations were carried to determine the optimal die geometry as well as to calculate the process loads and dominated stresses in the die occurring during the process. Based on the numerical results, an extrusion process was designed and implemented. Experiments showed that the uhc-steel can be formed by extrusion however it is associated with a high wear rate.BMB

Introduction to the JOCN special issue on future PON architectures enabled by advanced technology

This JOCN Special Issue, which spans the September and October 2020 issues, investigates the future of passive optical networks (PONs) in light of new enabling technologies that are currently under consideration. The papers present a broad overview of topics of current interest, across both the physical and network layers. They investigate how new technologies (e.g., higher-speed direct detection transceivers, coherent systems, advanced digital signal processing, and new optoelectronic components) and new network-layer approaches may drive the medium- to long-term evolution of PONs

Quasiconformal and geodesic trees

A quasiconformal tree is a metric tree that is doubling and of bounded turning. We prove that every quasiconformal tree is quasisymmetrically equivalent to a geodesic tree with Hausdorff dimension arbitrarily close to 1