Grundlegende Untersuchung über ein neues Schweißverfahren namens HFDB (Hybrid Friction Diffusion Bonding)

Wissenschaftliche und technologische Fragestellungen im Bereich des Fügens von Werkstoffen in Transport- und Energieindustrie waren der Ausgangspunkt für die Entwicklung eines neuen Fügeverfahrens.Das Fügen von ungleichartigen Werkstoffen ist mit Herausforderungen behaftet.Integrale Strukturen in Flugzeugen benötigen Fügeverfahren, die in Festigkeit und Schmelzpunkt unterschiedliche Metalle wie Titan als Rissstopper sowie Aluminium als Rumpfschale verbinden können. Intermetallische Phasen der im Schmelzpunkt sowie Wärmeausdehungskoeffizienten differierenden Metalle erschweren dies.In Verbundstrukturen aus Aluminium und Kunststoffen mit Schichtdicken von wenigen zehntel Millimetern sollen die Aluminium-Schichten miteinander verbunden werden ohne den dazwischen liegenden Kunststoff zu zerstören.Das Verbinden ungleichartiger Werkstoffe stößt bei herkömmlichen Fügeverfahren dann an seine Grenzen, wenn keine Adhäsion wie bei Klebungen, sondern eine Verbindung auf atomarer Ebene verlangt wird. Soll dazu noch makroskopisches Durchmischen der Fügepartner, sowie eine zu starke Wärmeenergieeinbringung unterbleiben, scheiden die meisten heutigen Fügeverfahren aus.Die Fragestellung des Verbindens ungleichartiger Metalle führte im Rahmen der vorlieg¬enden Arbeit zur Entwicklung eines neuen reib-/diffusionsbasierten Fügeverfahren.Basierend auf vorliegenden Erfahrungswerten des Rührreibschweißverfahrens (Friction Stir Welding, FSW) wurden Reibwerkzeuge hergestellt und an dünnen Aluminium / Aluminium Überlappverbindungen untersucht. Die ersten Vorversuche waren viel versprechend, eine Verbindung wurde erzielt. Da das Ziel für dieses neue Fügeverfahren ungleichartige Werkstoffe sowie Folienstärken einschloss, wurden weitere Werkstoffkombinationen untersucht. Im Zuge der Grund¬lagenuntersuchung wurden mit dem neuen Verfahren Fügeversuche mit gleichartigen und ungleichartigen Metallen (EN AW-Al Cu4Mg1; EN AW-Al Zn5,5MgCu; EN AW-1050A; X5 CrNi 18 10; Ti6Al4V; Magnesiumknetlegierung AZ31) in Dicken von 0,1 mm bis 0,7 mm durchgeführt, sowie die Anwendung des neuen Verfahrens am Mock-Up eines Rohrbündelwärmeübertragers erprobt.Weiterhin wurde für die anvisierte Probenlänge eine Klammerung entworfen, die ein Beulen der dünnen Bleche während des Fügens verhindern sollte.Die Charakterisierung des neuen Fügeverfahren wurde mit metallographischen sowie mechanischen Charakterisierungsverfahren (REM, µCT, Nanoindenter, EDX, Schäl-/Scherzugversuche, optische Mikroskopie) durchgeführt.Die Ergebnisse der EDX Untersuchungen zeigen, dass metallische Verbindungen sowohl bei den Al / Al als auch den Al / Ti Proben vorliegen. Die vergleichenden Ergebnisse der mechanischen Charakterisierung mit dem Diffusionsschweißverfahren (Diffusion Bonding, DB) zeigen ähnliche Schälzugkräfte bei deutlich reduzierten Prozesstemperaturen und –zeiten für das neue Verfahren. Die µCT Untersuchungen weisen darauf hin, dass keine vertikale Durchmischung wie beim FSW vorliegt. Eine Gefügeuntersuchung in Verbindung mit einem analytischen Vergleich zum DB Verfahren zeigt, dass das neue Verfahren diffusionsbasiert arbeitet

Transit in Regional Economic Development: The Case of the Kaliningrad Exclave

The study analyses the role of the transit function in the development of a regional transport system drawing on the example of the Kaliningrad exclave region (Russia). The article studies the role and extent of the impact of changes in the volume and structure of transit operations on the value-added creation in the regional economy. The assessment of the transit function was conducted using analytical software for strategizing and situational forecasting of the socio-economic development of the Kaliningrad region, the analogue of which is the CGE-model. The article describes the results of the regional value-added modelling based on the integrated index of gross regional product (GRP) and the changing volume and structure of transit cargo. The article explores the transit specialisation options for the Kaliningrad region based on different scenarios of its social and economic development and the changes in external factors. The results can be applied to similar studies on assessing the transit potential of a particular territory and developing measures to support the transportation system development in other regions

Mejora del proceso de compras y recepción de materiales y servicios en el área administrativa de AMBEV Centroamérica

Propone la mejora del proceso de compras y recepción de materiales y servicios en el área administrativa de AMBEV Centroaméric

The characterisation of hydrogen on nickel and cobalt catalysts

We have investigated a series of supported and unsupported nickel and cobalt catalysts, principally using neutron vibrational spectroscopy (inelastic neutron scattering, INS). For an alumina supported Ni catalyst we are able to detect hydrogen on the metal for the first time, all previous work has used Raney Ni. For an unsupported Ni foam catalyst, which has similar behaviour to Raney Ni but with a much lower density, the spectra show that there are approximately equal numbers of (100) and (111) sites, in contrast to Raney Ni that shows largely (111) sites. The observation of hydrogen on cobalt catalysts proved to be extremely challenging. In order to generate a cobalt metal surface, reduction in hydrogen at 250–300 °C is required. Lower temperatures result in a largely hydroxylated surface. The spectra show that on Raney Co (and probably also on a Co foam catalyst), hydrogen occupies a threefold hollow site, similar to that found on Co(101¯0). The reduced surface is highly reactive: transfers between cells in a high quality glovebox were sufficient to re-hydroxylate the surface.Publisher PDFPeer reviewe

When less is more: positive population-level effects of mortality

Experimental and theoretical studies show that mortality imposed on a population can counter-intuitively increase the density of a specific life-history stage or total population density. Understanding positive population-level effects of mortality is advancing, illuminating implications for population, community, and applied ecology. Reconciling theory and data, we found that the mathematical models used to study mortality effects vary in the effects predicted and mechanisms proposed. Experiments predominantly demonstrate stage-specific density increases in response to mortality. We argue that the empirical evidence supports theory based on stage-structured population models but not on unstructured models. We conclude that stage-specific positive mortality effects are likely to be common in nature and that accounting for within-population individual variation is essential for developing ecological theory

Biological control of broad mites (Polyphagotarsonemus latus) with the generalist predator Amblyseius swirskii

The broad mite is a serious pest of a variety of crops worldwide. Several phytoseiid mites have been described to control these mites. However, broad mites are still one of the major pest problems on greenhouse pepper in South-eastern Spain. The generalist predatory mite A. swirskii is widely used against other pests of pepper plants such as thrips and whiteflies, the latter being a vector of broad mites. We assessed the potential of A. swirskii to control broad mites. The oviposition rate of A. swirskii on a diet of broad mites was lower than on a diet of pollen, but higher than oviposition in the absence of food. Population-dynamical experiments with A. swirskii on single sweet pepper plants in a greenhouse compartment showed successful control of broad mites

Whether ideal free or not, predatory mites distribute so as to maximize reproduction

Ideal free distribution (IFD) models predict that animals distribute themselves such that no individual can increase its fitness by moving to another patch. Many empirical tests assume that the interference among animals is independent of density and do not quantify the effects of density on fitness traits. Using two species of predatory mites, we measured oviposition as a function of conspecific density. Subsequently, we used these functions to calculate expected distributions on two connected patches. We performed an experimental test of the distributions of mites on two such connected patches, among which one had a food accessibility rate that was twice as high as on the other. For one of the two species, Iphiseius degenerans, the distribution matched the expected distribution. The distribution also coincided with the ratio of food accessibility. The other species, Neoseiulus cucumeris, distributed itself differently than expected. However, the oviposition rates of both species did not differ significantly from the expected oviposition rates based on experiments on single patches. This suggests that the oviposition rate of N. cucumeris was not negatively affected by the observed distribution, despite the fact that N. cucumeris did not match the predicted distributions. Thus, the distribution of one mite species, I. degenerans, was in agreement with IFD theory, whereas for the other mite species, N. cucumeris, unknown factors may have influenced the distribution of the mites. We conclude that density-dependent fitness traits provide essential information for explaining animal distributions

Order of invasion affects the spatial distribution of a reciprocal intraguild predator

When intraguild predation is reciprocal, i.e. two predator species kill and feed on each other, theory predicts that well-mixed populations of the two species cannot coexist. At low levels of the shared resource, only the best competitor exists, whereas if the level of the common resource is high, the first species to arrive on a patch can reach high numbers, which prevents the invasion of the second species through intraguild predation. The order of invasion may therefore be of high importance in systems with reciprocal intraguild predation with high levels of productivity, with the species arriving first excluding the other species. However, natural systems are not well mixed and usually have a patchy structure, which gives individuals the possibility to choose patches without the other predator, thus reducing opportunities for intraguild predation. Such avoidance behaviour can cause spatial segregation between predator species, which, in turn, may weaken the intraguild interaction strength and facilitate their co-occurrence in patchy systems. Using a simple set-up, we studied the spatial distribution of two reciprocal intraguild predators when either of them was given priority on a patch with food. We released females of two predatory mite species sequentially and found that both species avoided patches on which the other species was resident. This resulted in partial spatial segregation of the species and thus a lower chance for the two species to encounter each other. Such behaviour reinforces segregation, because heterospecifics avoid patches with established populations of the other species. This may facilitate coexistence of two intraguild predators that would exclude each other in well-mixed populations