1,733 research outputs found

    Sensitivity analysis of statistical measures for the reconstruction of microstructures based on the minimization of generalized least-square functionals

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    For the simulation of micro-heterogeneous materials the FE2-method provides incorporation of the mechanical behavior at the microscale in a direct manner by taking into account a microscopic boundary value problem based on a representative volume element (RVE). A main problem of this approach is the high computational cost, when we have to deal with RVEs that are characterized by a complex geometry of the individual constituents. This leads to a large number of degrees of freedom and history variables at the microscale which needs a large amount of memory, not to mention the high computation time. Therefore, methods that reduce the complexity of such RVEs play an important role for efficient direct micro-macro transition procedures. In this contribution we focus on random matrix-inclusion microstructures and analyze several statistical measures with respect to their influence on the characterization of the inclusion phase morphology. For this purpose we apply the method proposed in Balzani and Schr¨oder (2008); Balzani et al. (2009a), where an objective function is minimized which takes into account differences between statistical measures computed for the original binary image of a given real microstructure and a simplified statistically similar representative volume element (SSRVE). The analysis with respect to the capability of the resulting SSRVEs to reflect the mechanical response in some simple independent virtual experiments allows for an estimation of the importance of the investigated statistical measures

    Convergence of simple adaptive Galerkin schemes based on h − h/2 error estimators

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    We discuss several adaptive mesh-refinement strategies based on (h − h/2)-error estimation. This class of adaptivemethods is particularly popular in practise since it is problem independent and requires virtually no implementational overhead. We prove that, under the saturation assumption, these adaptive algorithms are convergent. Our framework applies not only to finite element methods, but also yields a first convergence proof for adaptive boundary element schemes. For a finite element model problem, we extend the proposed adaptive scheme and prove convergence even if the saturation assumption fails to hold in general

    Nanosecond laser texturing for high friction applications

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    AbstractA nanosecond pulsed Nd:YAG fibre laser with wavelength of 1064nm was used to texture several different steels, including grade 304 stainless steel, grade 316 stainless steel, Cr–Mo–Al ‘nitriding’ steel and low alloy carbon steel, in order to generate surfaces with a high static friction coefficient. Such surfaces have applications, for example, in large engines to reduce the tightening forces required for a joint or to secure precision fittings easily. For the generation of high friction textures, a hexagonal arrangement of laser pulses was used with various pulse overlaps and pulse energies. Friction testing of the samples suggests that the pulse energy should be high (around 0.8mJ) and the laser pulse overlap should be higher than 50% in order to achieve a static friction coefficient of more than 0.5. It was also noted that laser processing increases the surface hardness of samples which appears to correlate with the increase in friction. Energy-Dispersive X-ray spectroscopy (EDX) measurements indicate that this hardness is caused by the formation of hard metal-oxides at the material surface

    An elementary method of calculating an explicit form of Young measures in some special cases

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    We present an elementary method of explicit calculation of Young measures for certain class of functions. This class contains in particular functions of a highly oscillatory nature which appear in optimization problems and homogenization theory. In engineering such situation occurs for instance in nonlinear elasticity (solid-solid phase transition in certain elastic crystals). Young measures associated with oscillating minimizing sequences gather information about their oscillatory nature and therefore about underlying microstructure. The method presented in the paper makes no use of functional analytic tools. There is no need to use generalized version of the Riemann {Lebesgue lemma and to calculate weak* limits of functions. The main tool is the change of variable theorem. The method applies both to sequences of periodic and nonperiodic functions.Comment: 11 pages, no figures An article in its new version due to the reviewers' remarks. All the results stated and proved in multidimensional version; corrected innacuracie

    Magnetizing a complex plasma without a magnetic field

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    We propose and demonstrate a concept that mimics the magnetization of the heavy dust particles in a complex plasma while leaving the properties of the light species practically unaffected. It makes use of the frictional coupling between a complex plasma and the neutral gas, which allows to transfer angular momentum from a rotating gas column to a well-controlled rotation of the dust cloud. This induces a Coriolis force that acts exactly as the Lorentz force in a magnetic field. Experimental normal mode measurements for a small dust cluster with four particles show excellent agreement with theoretical predictions for a magnetized plasma

    The heart of a convex body

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    We investigate some basic properties of the {\it heart} (K)\heartsuit(\mathcal{K}) of a convex set K.\mathcal{K}. It is a subset of K,\mathcal{K}, whose definition is based on mirror reflections of euclidean space, and is a non-local object. The main motivation of our interest for (K)\heartsuit(\mathcal{K}) is that this gives an estimate of the location of the hot spot in a convex heat conductor with boundary temperature grounded at zero. Here, we investigate on the relation between (K)\heartsuit(\mathcal{K}) and the mirror symmetries of K;\mathcal{K}; we show that (K)\heartsuit(\mathcal{K}) contains many (geometrically and phisically) relevant points of K;\mathcal{K}; we prove a simple geometrical lower estimate for the diameter of (K);\heartsuit(\mathcal{K}); we also prove an upper estimate for the area of (K),\heartsuit(\mathcal{K}), when K\mathcal{K} is a triangle.Comment: 15 pages, 3 figures. appears as "Geometric Properties for Parabolic and Elliptic PDE's", Springer INdAM Series Volume 2, 2013, pp 49-6

    Amygdala responses to emotionally valenced stimuli in older and younger adults

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    ABSTRACT—As they age, adults experience less negative emotion, come to pay less attention to negative than to positive emotional stimuli, and become less likely to remember negative than positive emotional materials. This profile of findings suggests that, with age, the amygdala may show decreased reactivity to negative information while maintaining or increasing its reactivity to positive information. We used event-related functional magnetic resonance imaging to assess whether amygdala activation in response to positive and negative emotional pictures changes with age. Both older and younger adults showed greater activation in the amygdala for emotional than for neutral pictures; however, for older adults, seeing positive pictures led to greater amygdala activation than seeing negative pictures, whereas this was not the case for younger adults. Older adults experience less negative affect than younger adults in both cross-sectional and longitudinal studies (Carstensen, Pasupathi

    ifo Konjunkturprognose 2008/2009: Aufschwung geht zu Ende

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    Die Weltkonjunktur hat im Gefolge der US-Immobilienkrise und der Turbulenzen an den internationalen Finanzmärkten an Dynamik eingebüßt. Das vom ifo Institut erhobene Weltwirtschaftsklima hat sich im zweiten Quartal 2008 massiv verschlechtert; der Indikator fiel auf den niedrigsten Stand seit über sechs Jahren. Der Rückgang resultiert vor allem aus der ungünstigeren Einschätzung der derzeitigen wirtschaftlichen Lage, aber auch die Erwartungen für die nächsten sechs Monate wurden weiter nach unten revidiert. Die Verschlechterung des ifo Weltwirtschaftsklimas betrifft wiederum vor allem Nordamerika und Westeuropa. Der stärkste Rückgang des Klimaindikators ist wie schon in der vorangegangenen Umfrage in den USA zu verzeichnen. Die Expansion der Weltwirtschaft wird sich im Prognosezeitraum spürbar abkühlen. Der Anstieg des Bruttoinlandsprodukts wird sich verlangsamen, da der Höhepunkt des konjunkturellen Zyklus überschritten zu sein scheint. Zudem werden die anhaltende Unsicherheit auf den Finanzmärkten, die negativen Vermögenseffekte sinkender Hauspreise und Aktienkurse, die hohe Inflation sowie die zuletzt stark gestiegenen Ölpreise zunehmend bremsend wirken. Die deutsche Wirtschaft ist überaus schwungvoll in das neue Jahr gestartet. Nach den bisher vorliegenden amtlichen Ergebnissen stieg die gesamtwirtschaftliche Produktion im ersten Quartal 2008 saison- und kalenderbereinigt gegenüber dem Vorquartal um 1,5%. Nach der auch von Sondereffekten begünstigten kräftigen Ausweitung der gesamtwirtschaftlichen Produktion im ersten Quartal 2008 ist für das zweite Quartal mit einem leichten Rückgang des realen Bruttoinlandsprodukts zu rechnen. Im Durchschnitt des ersten Halbjahres 2008 ergibt sich im Vergleich zum zweiten Halbjahr 2007 saison- und kalenderbereinigt ein BIP-Zuwachs von 1,5%; im Vorjahresvergleich beläuft sich die Zunahme auf 2,7%
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