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Recent Experimental Results (recent + experimental_result)
Selected AbstractsDynamics of Dislocations in a 2D Plasma CrystalCONTRIBUTIONS TO PLASMA PHYSICS, Issue 4-5 2009V. Nosenko Abstract Recent experimental results on the dislocation dynamics in a two-dimensional plasma crystal are reviewed. A single layer of micron-size microspheres was suspended in the sheath of a capacitively coupled rf discharge. The particles self-organized in a triangular lattice. Edge dislocations were created in pairs in this plasma crystal when the internal shear stress built up above a threshold, due to the crystal's slow differential rotation. Basic stages of dislocation nucleation were identified and studied, from gradual pile-up of shear strain in the crystal to eventual escape of free dislocations. After nucleation, dislocations moved supersonically with respect to the shear waves and generated shear-wave Mach cones (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanotribology , Fundamental Studies of Friction and Plasticity,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Roland Bennewitz Nanotribology explores the mechanical properties of materials at small length scales, where deviations from the scaling laws of macroscopic descriptions are observed. Atomic force microscopy is introduced as an important instrument in nanotribology for imaging friction contrasts on heterogeneous surfaces, for quantitative friction studies, and for the observation of single dislocation processes in plastic deformation. Recent experimental results for the frictional properties of carbon-based materials are discussed. Friction studies using microstructured surfaces are presented as an attempt to bridge the gap between nanotribological and macroscopic friction studies. [source] A predictor,corrector scheme for the optimization of 3D crack front shapesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1-2 2005K. KOLK ABSTRACT A predictor,corrector scheme is presented to improve the shape of 3D crack fronts within the 3D simulation of fatigue crack growth. This concept is fully functional for mode-I, and an extension for mixed-mode problems is presented. The whole procedure is embedded in an automatic incremental crack growth algorithm for arbitrary 3D problems with linear elastic material behaviour. The numerical simulation is based on the 3D dual boundary element method (Dual BEM) and on an optimized evaluation of very accurate stress intensity factors (SIFs) and T-stresses. As part of the proposed predictor,corrector scheme, 3D singularities along the crack front especially in the vicinity of the intersection of the crack front and the boundary are considered. The knowledge of these singularities allows the specification of crack front shapes with bounded energy release rate. Numerical examples with complex cross-sections are presented to show the efficiency of the proposed crack growth algorithm. The obtained results are in good agreement with recent experimental results. [source] Free energy and structure of polyproline peptides: An ab initio and classical molecular dynamics investigationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2010Mahmoud Moradi Abstract Depending on their environment, polyproline peptides form chiral helices that may be either left- (PPII) or right-handed (PPI). Here, we have characterized both the structure and free energy landscapes of Ace-(Pro)n -Nme (n an integer less than 13) peptides, in vacuo and in implicit water environments. Both ab initio and classical molecular dynamics methods were used. In terms of the latter, we used a recently developed Adaptively Biased Molecular Dynamics (ABMD) method in conjunction with three different force fields (ff99, ff99SB, ff03) and two different Generalized Born models for the implicit solvent environment. Specifically, the ABMD method provides for an accurate description of the free energy landscapes in terms of a set of collective variables, which were carefully chosen as to reflect the "slow modes" of the polyproline peptides. These are primarily based on the cis - trans isomerization associated with the prolyl bonds. In agreement with recent experimental results, the peptides form not only the pure PPII or PPI structures but also a large number of stable conformers having more or less similar free energies, whose distributions we have characterized. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Excitation dynamics in a three-quantum dot system driven by optical near-field interaction: towards a nanometric photonic deviceJOURNAL OF MICROSCOPY, Issue 3 2003K. Kobayashi Summary Using density operator formalism, we discuss interdot excitation energy transfer dynamics driven by the optical near-field and phonon bath reservoir, as well as coherent excitation dynamics of a quantum dot system. As an effective interaction between quantum dots induced by the optical near-field, the projection operator method gives a renormalized dipole interaction, which is expressed as a sum of the Yukawa functions and is used as the optical near-field coupling of quantum dots. We examine one- and two-exciton dynamics of a three-quantum dot system suggesting a nanometric photonic switch, and numerically obtain a transfer time comparable with the recent experimental results for CuCl quantum dots. [source] Compensation: an alternative method for analyzing diversity-productivity experimentsOIKOS, Issue 3 2002Peter B. Adler Although recent experimental results demonstrate a positive effect of diversity on primary productivity, the interpretation of these experiments has been controversial, creating a need for new methods of analysis. The methods developed in response to this need all use the production of individual species grown in monocultures to calculate the expected production of each species mixture, then analyze departures from these expectations as a function of species richness. We propose an alternative method that treats the same assembly experiments as species removals, and calculates the expected production of each mixture based on the production of individual species when grown together in the full community (the experimental mixture containing all species in the pool). Using the observed production of the full community, and the observed and expected productions of less diverse mixtures, we calculate an index of compensation that measures the degree of functional recovery following species loss. To explore whether losses of dominant versus subordinate species have different ecosystem effects, we suggest a multiple regression approach that tests the influence of both species richness and expected production on compensation. If compensation varies with species richness or expected production consistently in many experimental systems, then we may be able to predict the ecosystem effect of different types of extinctions. While existing monoculture approaches more directly test hypotheses about complementary resource use, the compensation approach offers two advantages: 1) it is more appropriate for testing how extinctions will affect ecosystem function, and 2) it may provide an important link between assembly experiments in artificial communities and removal experiments in natural systems. [source] Novel effects in finite-length silicon nanowiresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008A. D. Zdetsis Abstract By considering silicon nanowires in real space, we have shown by ab initio theoretical calculations that unstable nanowires bend under relaxation. These nanowires usually incorporate in their surface silicon dihydrides parallel to the nanowires axis. On the other hand, nanowires without such parallel dihydrides remain straight and are characterized by increased stability or "magicity". Reconstructed nanowires have analogous properties but they are characterized by much higher stability. This bending of the nanowires cannot be accounted for by the usual k-space models which use a one-dimensional periodic arrangement of the simulation cell. Our theoretical models are based on STM images and schematic views from recent experimental results [Science 229, 1874, (2003)]. Our results are in full accord with these experimental data and interpretations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multipolar Ordering in Electro- and Magnetostatic Coupled NanosystemsCHEMPHYSCHEM, Issue 9 2008Elena Y. Vedmedenko Dr. habil. Abstract Electric and magnetic multipole moments and polarizabilities are important quantities in studies of intermolecular forces, non-linear optical phenomena, electrostatic, magnetostatic or gravitational potentials and electron scattering. The experimental determination of multipole moments is difficult and therefore the theoretical prediction of these quantities is important. Depending on purposes of the investigation several different definitions of multipole moments and multipole,multipole interactions are used in the literature. Because of this variety of methods it is often difficult to use published results and, therefore, even more new definitions appear. The first goal of this review is to give an overview of mathematical definitions of multipole expansion and relations between different formulations. The second aim is to present a general theoretical description of multipolar ordering on periodic two-dimensional lattices. After a historical introduction in the first part of this manuscript the static multipole expansion in cartesian and spherical coordinates as well as existing coordinate transformations are reviewed. On the basis of the presented mathematical description multipole moments of several symmetric charge distributions are summarized. Next, the established numerical approach for the calculation of multipolar ground states, namely Monte Carlo simulations, are reviewed. Special emphasis is put on the review of ground states in multipolar systems consisting of moments of odd or even order. The last section is devoted to the magnetization reversal in dense packed nanomagnetic arrays, where the magnetic multipole,multipole interactions play an important role. Comparison between the theory and recent experimental results is given. [source] | ||||||||||||||||