101,992 research outputs found
Asymmetric frictional sliding between incommensurate surfaces
No full textWe study the frictional sliding of two ideally incommensurate surfaces
with a third incommensurate sheet - a sort of extended lubricant - in
between. When the mutual ratios of the three periodicities in this
sandwich geometry are chosen to be the golden mean phi = (1 + root 5)/2,
this system is believed to be statically pinned for any choice of system parameters. In the present study we overcome this pinning and force the two "substrates" to slide with a mutual velocity V-ext, analyzing the resulting frictional dynamics. An unexpected feature is an asymmetry of the relative sliding velocity of the intermediate lubricating sheet relative to the two substrates. Strikingly, the velocity asymmetry takes an exactly quantized value which is uniquely determined by the
incommensurability ratio, and absolutely insensitive to all other
parameters. The reason for quantization of the velocity asymmetry will be addressed. This behavior is compared and contrasted to the
corresponding one obtained for a representative cubic irrational, the
spiral mean omega
Exactly quantized dynamics of classical incommensurate sliders
No full textWe report peculiar velocity quantization phenomena in the classical motion of an idealized 1D solid lubricant, consisting of a harmonic chain interposed between two periodic sliders. The ratio v(c.m.)/v(ext) of the chain center-of-mass velocity to the externally imposed relative velocity of the sliders stays pinned to exact "plateau" values for wide ranges of parameters, such as slider corrugation amplitudes, external
velocity, chain stiffness, and dissipation, and is strictly determined
by the commensurability ratios alone. The phenomenon is explained by one slider rigidly dragging the kinks that the chain forms with the other slider. Possible consequences of these results for some real systems are
discussed
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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3346: Samuel G. Freedman, author, 2013
No full textPhotograph of author Samuel G. Freedman, at NT Daily Slash meeting in the Mayborn School of Journalism at UNT
Increased affinity of small gold particles for glycerol oxidation over Au/TiO2 probed by NMR relaxation methods
No full textThe aerobic oxidation of glycerol in aqueous solution over Au/TiO2 catalysts has been studied, and the effect of Au loading by wet impregnation, in the range 0.5–5% Au, has been assessed. Low metal loading favors the deposition of smaller particles, whereas higher loadings lead to the formation of much larger gold particles, as revealed by scanning transmission electron microscopy (STEM) analysis. Reaction studies show that a higher metal loading has a detrimental effect on the catalyst activity, which decreases significantly as the Au load increases. In addition to reaction studies, 1H NMR T1/T2 relaxation time measurements have been used to assess the effect of metal loading and particle size on the adsorption properties of glycerol (reactant) and water (solvent) within the catalyst. The NMR results show that the adsorption properties of glycerol relative to water as a function of the Au loading have a similar trend to that observed for the reactivity, with glycerol exhibiting a higher surface affinity relative to water for the catalyst with low Au loading. The overall results indicate that metal loading significantly affects the typical Au particle size, which, in turn, affects both the reaction and adsorption properties of glycerol over the catalyst surface. In particular, the trend in T1/T2 ratio clearly indicates that glycerol has a much stronger affinity with smaller gold particles, which is an important factor in promoting glycerol oxidation. This result is of great significance in understanding the reactivity of polyols over supported gold catalysts and gives the first experimental evidence that smaller gold particles tend to be stronger adsorption sites for glycerol, in agreement with computational and theoretical studies
Elemental Mapping of Perovskite Solar Cells by Using Multivariate Analysis: An Insight into Degradation Processes.
No full textThe technology of perovskite-based solar cells is evolving rapidly, reaching certified power conversion efficiency values now exceeding 20 %. One of the main drawbacks hindering progress in the field is the long-term stability of the cells: the mixed halide perovskites used in most devices are sensitive to humidity and degrade on a timescale varying from hours to weeks. The degradation mechanisms are poorly understood, but likely arise from combined physical and chemical modifications at the nanometer scale. The characterization of pristine and degraded materials is difficult owing to their complex chemical and physical structure and their relatively poor stability. In this work, we investigated the changes in local composition and morphology of a standard device after 2 months of air exposure in the dark, using scanning transmission electron microscopy (STEM) with nanometer resolution for imaging and analysis. Because of a state-of-the-art technique that combines STEM and energy dispersive X-ray spectroscopy (EDX), and the use of different decomposition algorithms for multivariate analysis, we highlighted the migration of elements across the interfaces between the layers comprising the device. We also noticed a morphological degradation of the hole-transporting layer (HTL), representing one of the main factors enabling the infiltration of moisture in the device, which results in reduced performance
Poly(methyl methacrylate)-palladium clusters nanocomposite formation by supersonic cluster beam deposition : a method for microstructured metallization of polymer surfaces
No full textNanocomposite films were fabricated by supersonic cluster beam deposition (SCBD) of
palladium clusters on poly(methyl methacrylate) (PMMA) surfaces. The evolution of the electrical conductance with cluster coverage and microscopy analysis show that Pd clusters are implanted in the polymer and form a continuous layer extending for several tens of nanometres beneath the polymer surface. This allows the deposition, using stencil masks, of cluster-assembled Pd microstructures on PMMA showing a remarkably high adhesion compared with metallic films obtained by thermal evaporation. These results suggest that SCBD is a promising tool for the fabrication of metallic microstructures on flexible polymeric
substrates
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