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Number of results: 9
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Abstract

Philip Sabin points out that modern wargames not only contain substantial amounts of historical information but also arrange it into interactive models which depict historical processes in a simplified manner. Such models can be used in historical research as well, complementing the discourse through more holistic and mathematically strict accounts, and providing tools that impose some discipline on counter- factual speculation.
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Abstract

Assessment of the flexural buckling resistance of bisymmetrical I-section beam-columns using FEM is widely discussed in the paper with regard to their imperfect model. The concept of equivalent geometric imperfections is applied in compliance with the so-called Eurocode’s general method. Various imperfection profiles are considered. The global effect of imperfections on the real compression members behaviour is illustrated by the comparison of imperfect beam-columns resistance and the resistance of their perfect counterparts. Numerous FEM simulations with regard to the stability behaviour of laterally and torsionally restrained steel structural elements of hot-rolled wide flange HEB section subjected to both compression and bending about the major or minor principal axes were performed. Geometrically and materially nonlinear analyses, GMNA for perfect structural elements and GMNIA for imperfect ones, preceded by LBA for the initial curvature evaluation of imperfect member configuration prior to loading were carried out. Numerical modelling and simulations were conducted with use of ABAQUS/Standard program. FEM results are compared with those obtained using the Eurocode’s interaction criteria of Method 1 and 2. Concluding remarks with regard to a necessity of equivalent imperfection profiles inclusion in modelling of the in-plane resistance of compression members are presented.
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Abstract

I n t r o d u c t i o n: Complications occurring aft er neurosurgical procedures which lead to reoperations are associated with poor treatment outcomes. Th e aim of our study was to establish predictive factors of unplanned early reoperations aft er intracranial meningioma removal. Ma t e r i a l s a n d M e t h o d s: We retrospectively analyzed 177 patients who underwent craniotomy due to an intracranial meningioma. Early reoperation was defi ned as reoperation during the same hospital stay. We used a χ2 test for proportional values and t-test and Mann-Whitney U tests as appropriate for continuous variables. To determine the potential predictors of early reoperation we used univariate and multivariate logistic regression analyses. R e s u l t s: A total of 13 (7.34%) patients underwent unplanned early reoperation. Th ese patients underwent retrosigmoid craniotomies (25.00% vs. 6.40%; p = 0.047), suff ered from ischemic heart disease (66.67% vs. 6.64%; p <0.01) and atrial fi brillation (60.00% vs. 6.25%; p <0.01), were receiving heparin (50.00% vs. 6.74%; p <0.01) and anticoagulants (66.67% vs. 6.21%; p <0.01) signifi cantly more oft en than the general study population. In multivariate logistic regression analysis anticoagulant use (OR: 31.463; 95% CI: 1.139–868.604; p = 0.04) and retrosigmoid craniotomy (OR: 6.642; 95% CI: 1.139–38.73; p = 0.034) remained independently associated with a higher risk of early reoperation. C o n c l u s i o n s: Patients who underwent retrosigmoid craniotomy, those with a history of ischemic heart disease or atrial fi brillation and those who take heparin or anticoagulants are more likely to require early reoperation. Retrosigmoid craniotomy and anticoagulant use are independent risk factors for early reoperation.
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Abstract

The investigations were inspired with the problem of cracking of steel castings during the production process. A single mechanism of decohesion – the intergranular one – occurs in the case of hot cracking, while a variety of structural factors is decisive for hot cracking initiation, depending on chemical composition of the cast steel. The low-carbon and low-alloyed steel castings crack due to the presence of the type II sulphides, the cause of cracking of the high-carbon tool cast steels is the net of secondary cementite and/or ledeburite precipitated along the boundaries of solidified grains. Also the brittle phosphor and carbide eutectics precipitated in the final stage solidification are responsible for cracking of castings made of Hadfield steel. The examination of mechanical properties at 1050°C revealed low or very low strength of high-carbon cast steels.
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