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1.
Th. Pretorius G. Habedank J. Woitschig F. Vollertsen 《Materialwissenschaft und Werkstofftechnik》2006,37(1):85-91
Thermal treatments of steel components with the goal of hardening often result in distortion by releasing the residual stresses which were brought into the specimen during the preceding processing steps. The goal of the presented work is the minimization of this distortion. By generating definite residual stress fields and investigating the resulting distortion, the distortion mechanism can be observed in detail. A flexible and reproducible way to generate such residual stress fields inside a specimen is by means of local thermal treatment with a laser beam. Computer simulations as well as experiments were carried out using an idealized tooth of a gearwheel (finger sample) as a model system. The deformation of the samples due to the laser heat treatment and the stress fields generated inside the samples were determined with respect to different process parameters. 相似文献
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GW Mathern JK Pretorius HI Kornblum D Mendoza A Lozada JP Leite L Chimelli DE Born I Fried AC Sakamoto JA Assirati WJ Peacock GA Ojemann PD Adelson 《Canadian Metallurgical Quarterly》1998,5(3):151-176
This study determined whether hippocampal kainate (KA) receptor mRNA levels were increased or decreased in temporal lobe epilepsy patients compared with nonseizure autopsies. Hippocampal sclerosis (HS; n = 17), nonsclerosis (non-HS; n = 11), and autopsy hippocampi (n = 9) were studied for KA1-2 and GluR5-7 mRNA levels using semiquantitative in situ hybridization techniques, along with neuron densities. Compared with autopsy hippocampi, HS and non-HS cases showed decreased GluR5 and GluR6 hybridization densities per CA2 and/or CA3 pyramid. Furthermore, HS patients demonstrated increased KA2 and GluR5 hybridization densities per granule cell compared with autopsy hippocampi. These findings indicate that chronic temporal lobe seizures were associated with differential changes in hippocampal KA1-2 and GluR5-7 hybridization densities that vary by subfield and pathology group. In temporal lobe epilepsy patients, these results support the hypothesis that pyramidal cell GluR5 and GluR6 mRNA levels are decreased as a consequence of seizures, and in HS patients granule cell KA2 and GluR5 mRNA levels are increased in association with aberrant fascia dentata mossy fiber sprouting and/or hippocampal neuronal loss. 相似文献
5.
The solubility and activity–composition relations of chromium oxide in melts of the systems CaO–CrO x –SiO2 and CaO–Al2 O3 –CrO x –SiO2 have been determined at 1500°C by equilibrating melts with Pt–Cr alloys at known oxygen pressures. It is shown that the increase in the concentration of divalent chromium ions, as the oxygen pressure and the basicity of melt decrease, results in a dramatic increase in the solubility of chromium oxide in the liquid phase. An increase in the Al2 O3 content of the melt leads to a decrease in the solubility of chromium oxide over the whole composition range studied. The activity coefficient of CrO has been found to increase with increasing melt basicity and decreasing oxygen pressure whereas the activity coefficient of CrO1.5 decreases sharply with increasing melt basicity for siliceous melts but levels off at a basicity ratio (wt% CaO/wt% SiO2 ) of about 0.7. An increase in the Al2 O3 content of the melts results in an increase in the activity coefficient of CrO. 相似文献
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Most graph visualization techniques focus on the structure of graphs and do not offer support for dealing with node attributes and edge labels. To enable users to detect relations and patterns in terms of data associated with nodes and edges, we present a technique where this data plays a more central role. Nodes and edges are clustered based on associated data. Via direct manipulation users can interactively inspect and query the graph. Questions that can be answered include, “which edge types are activated by specific node attributes?” and, “how and from where can I reach specific types of nodes?” To validate our approach we contrast it with current practice. We also provide several examples where our method was used to study transition graphs that model real‐world systems. 相似文献
7.
Leonard Staphorst Mike Holland Leon Pretorius Marthinus Willem Pretorius 《Engineering Management Journal; EMJ》2017,29(1):26-44
Strengthening intellectual property rights for publicly financed research and development (R&D) ensures that research organizations maximize the full national value of the intellectual property that they generate, but potential negative spillover effects on the perceived value of a research alliance might deter an existing alliance partner from continued collaboration or a potential alliance partner from future collaboration. This study, performed in 2010 within the context of the Council for Scientific and Industrial Research in South Africa, aimed to develop a structural equation modeling-based value-mediation governance decision-making model that will enable engineering managers at publicly financed R&D organizations to select optimal governance modes for the research alliances they are establishing to grow their organizations’ R&D capabilities. 相似文献
8.
Barbara A. Kitchenham Pearl Brereton Mark Turner Mahmood K. Niazi Stephen Linkman Rialette Pretorius David Budgen 《Empirical Software Engineering》2010,15(6):618-653
Systematic literature reviews (SLRs) are a major tool for supporting evidence-based software engineering. Adapting the procedures
involved in such a review to meet the needs of software engineering and its literature remains an ongoing process. As part
of this process of refinement, we undertook two case studies which aimed 1) to compare the use of targeted manual searches
with broad automated searches and 2) to compare different methods of reaching a consensus on quality. For Case 1, we compared
a tertiary study of systematic literature reviews published between January 1, 2004 and June 30, 2007 which used a manual
search of selected journals and conferences and a replication of that study based on a broad automated search. We found that
broad automated searches find more studies than manual restricted searches, but they may be of poor quality. Researchers undertaking
SLRs may be justified in using targeted manual searches if they intend to omit low quality papers, or they are assessing research
trends in research methodologies. For Case 2, we analyzed the process used to evaluate the quality of SLRs. We conclude that
if quality evaluation of primary studies is a critical component of a specific SLR, assessments should be based on three independent
evaluators incorporating at least two rounds of discussion. 相似文献
9.
The objective of this study is to develop a method for determining the mental workload imposed on train control officers that is objective and quantifiable and can stand up to the tests of validity and reliability. This technical note reports on the methodology used in the development process, as well as the assessment of the criteria considered for the mental workload index (MWLI). The MWLI aims at solving an existing operational shortcoming and could be used as a tool for predicting the mental workload imposed on an operator at a particular train control centre. The method could be applied to manage and improve operational safety in the rail transport environment. A participative approach was followed in the development process. A work group comprising expert users of the system was involved in identifying task factors and assigning weights for task and moderating factors. The newly developed MWLI consists of three task factors and 11 moderating factors, each with a different weight in terms of its contribution to overall mental workload. The work group performed several iterations to reach final consensus and acceptance of the factors and their respective contributions to the MWLI. The criteria and development processes are discussed and the final index with the task and moderating factors is presented. 相似文献
10.
Lipinski B Pretorius E Oberholzer HM Van Der Spuy WJ 《Microscopy research and technique》2012,75(9):1185-1190
Stroke is associated with the intracerebral formation of fibrin clots which may lead to irreversible brain damage. Thrombolytic therapies employ a variety of natural and/or recombinant plasminogen activators to initiate fibrinolytic degradation of cerebral thrombi. However, such therapies when installed beyond 4‐ to 6‐h window, may fail to achieve the expected outcome. This is due to the hydroxyl radical‐induced modification of fibrin(ogen) molecules rendering them refractory to fibrinolytic degradation, but no cause of the increased free radical generation in stroke was offered. Here, we show by means of electron microscopy that iron ions added to human blood dramatically enhances fibrin fibers formation with thrombin, and significantly delays fibrinolysis during spontaneous clotting of native blood. Iron ions caused the appearance dense matted fibrin deposits, similar, if not identical, to those observed in plasma of patients with stroke. These results may explain a known relationship between thrombotic diseases and the increased body concentrations of free iron and/or hemoglobin derivatives. We conclude that any action resulting in the inhibition of hemostatic abnormalities, as well as in the reduction of body free iron and scavenging of hydroxyl radicals (e.g., by polyphenols) can potentially prevent pathological reactions associated with consequences of stroke. Microsc. Res. Tech. 75:1185–1190, 2012. © 2012 Wiley Periodicals, Inc. 相似文献