Численное моделирование электронно-лучевого плавления и оценка КПД электронного луча

В работе предложена численная модель процесса плавления порошков титановых сплавов в условиях селективного электронно-лучевого сплавления. Приводится сравнение результатов моделирования с экспериментальными данными по сплавлению порошков сплава ВТ6 методом электронно-лучевого плавления при аддитивном производстве деталей. Установлено, что тепловой КПД электронного луча составляет порядка 25%, а 75% энергии пучка теряется.A numerical model of the process of the melting of powders of a titanium alloy VT6 during selective electron-beam melting is proposed. Comparison of numerical results with experimental data on selective electron-beam melting at additive manufacturing of parts is provided. It is established that the thermal efficiency of electron beam is about 25% and 75% of the beam energy is lost

Kommunikations- und Notationsverhalten von Erstsemesterstudierenden beim Lernen mit Videotutorials

Im BMBF-geförderten Projekt mamdim soll der Einfluss digitaler Medien auf das Lernen von beschreibender Statistik bei Studierenden unterschiedlicher Fachrichtungen in der Studieneingangsphase an verschiedenen Hochschulen untersucht werden. Mithilfe der Erfassung des Fachwissens, der Motivation und der Selbstwirksamkeitsüberzeugungen der Studierenden vor und nach einer videographierten Interventionsphase mit verschiedenen instruktionalen Formaten (z.B. Lernvideos, kommentierte Präsentationen) zur beschreibenden Statistik werden Gemeinsamkeiten und Unterschiede im Kommunikations- und Notationsverhaltens in den Blick genommen. In diesem Beitrag werden die Analysen der Videoaufnahmen eines Standortes (Lehramtsstudierende der Universität Bielefeld) beim Lernen mit Videotutorials mit beziehungsweise ohne inhaltsbezogene Fragen dargestellt

Structural, electronic and kinetic properties of the phase-change material Ge2Sb2Te5 in the liquid state

Phase-change materials exhibit fast and reversible transitions between an amorphous and a crystalline state at high temperature. The two states display resistivity contrast, which is exploited in phase-change memory devices. The technologically most important family of phase-change materials consists of Ge-Sb-Te alloys. In this work, we investigate the structural, electronic and kinetic properties of liquid Ge2Sb2Te5 as a function of temperature by a combined experimental and computational approach. Understanding the properties of this phase is important to clarify the amorphization and crystallization processes. We show that the structural properties of the models obtained from ab initio and reverse Monte Carlo simulations are in good agreement with neutron and X-ray diffraction experiments. We extract the kinetic coefficients from the molecular dynamics trajectories and determine the activation energy for viscosity. The obtained value is shown to be fully compatible with our viscosity measurements

It is not just a ‘trade‐off’: : indications for sink‐ and source‐limitation to vegetative and regenerative growth in an old‐growth beech forest

Summary Controls on tree growth are key issues in plant physiology. The hypothesis of our study was that the interannual variability of wood and fruit production are primarily controlled directly by weather conditions (sink limitation), while carbon assimilation (source limitation) plays a secondary role. We analyzed the interannual variability of weather conditions, gross primary productivity (GPP) and net primary productivity (NPP) of wood and fruits of an old‐growth, unmanaged Fagus sylvatica forest over 14 yr, including six mast years. In a multiple linear regression model, c . 71% of the annual variation in wood‐NPP could be explained by mean air temperature in May, precipitation from April to May (positive influence) and fruit‐NPP (negative influence). GPP of June to July solely explained c . 42% of the variation in wood‐NPP. Fruit‐NPP was positively related to summer precipitation 2 yr before ( R 2 = 0.85), and negatively to precipitation in May ( R 2 = 0.83) in the fruit years. GPP had no influence on fruit‐NPP. Our results suggest a complex system of sink and source limitations to tree growth driven by weather conditions and going beyond a simple carbon‐mediated ‘trade‐off’ between regenerative and vegetative growth

Fibronectin, Fibrinogen, and Laminin Act as Mediators of Adherence of Clinical Staphylococcal Isolates to Foreign Material

Bacterial adherence to polymer surfaces is a required early step in intravenous (iv) device infection. We collected eight strains of Staphylococcus aureus and 19 of coagulase-negative staphylococci from patients with proven iv device bacteremia and studied the role of plasma or connective-tissue proteins in promoting bacterial adherence to polymethylmethacrylate (PMMA) coverslips. Although only a negligible percentage of organisms adhered to albumin-coated PMMA, surface-bound fibronectin significantly promoted adherence of all isolates. Fibrinogen markedly promoted adherence of all S. aureus strains but of only four coagulase-negative strains. Thus, coagulase-negative staphylococci revealed a marked heterogeneity in adherence to fibrinogen-coated surfaces, a result suggesting the existence of heretofore unknown receptors for fibrinogen. Laminin promoted adherence of staphylococci to a much lower extent. Although strain specific, adherence of clinical staphylococcal isolates to foreign surfaces is significantly increased by fibronectin, fibrinogen, and laminin, an observation suggesting the possible contribution of these proteins to the pathogenesis of iv device infectio

Stoffwechselbelastungen zu Laktationsbeginn und ihr Einfluss auf die Eutergesundheit in ökologisch wirtschaftenden Milchviehbetrieben

As a part of the study „Health and performance of dairy cows in organic farming from an interdisciplinary point of view – an (intervention-) study on metabolic disorders and mastitis with regard to forage production, feeding management and husbandry practices” different udder health and metabolic parameters were determined in 106 dairy farms in Germany between January 2008 and April 2010. The objective of this study was to evaluate and compare udder health and metabolic data in dry period and early lactation within the scope of a preliminary analysis. The analysis shows that relations exist between disturbances of the metabolism health and the udder health. Significant correlations between ketosis and hypocalcämia and udder health make clear that their control is vital for animal health management in organic dairy farms