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Abstract: The positive effect of intermetallic ordering of platinum alloy nanoparticles on oxygen reduction reaction (ORR) activity has been well established. What is still missing is an understanding of selective leaching of the less noble metal from the ordered structure and its correlation to longterm ORR performance. Using a combination of kinetic Monte Carlo simulations and advanced characterization techniques, we provide unprecedented insight into dealloying of intermetallic PtCu3 nanoparticles a well-known binary alloy. Comparison of ordered and disordered samples with identical initial compositions and particle size distributions reveals an unexpected correlation: whereas the copper dealloying rates in the ordered and disordered counterparts are almost the same, in the ordered structure Pt atoms are surrounded by 15−30% more Cu atoms throughout all the stages of acid leaching. This more convenient Pt−Cu coordination explains the statistically significant increase of 23−37% in ORR activity of the ordered structure at all stages of alloy degradation.
Keywords: ORR activity, fuel cells, platinum alloy, nanoparticle stability, intermetallic ordering, kinetic Monte Carlo, dealloying, in situ ICP-MS
Published in RUNG: 27.09.2016; Views: 5668; Downloads: 0
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Keywords: microscopy, imaging systems, thermal lensing, medical imaging, biological imaging, cell analysis
Published in RUNG: 17.05.2016; Views: 4481; Downloads: 143
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Abstract: The aim of this thesis is to investigate the effects that a lightlike singular hypersurface can have on a congruence of timelike (spacelike) geodesics and to extend the existing theory to the case of null geodesics. The introduction discusses the applications of singular hypersurfaces for the description of physical phenomena, their major classfications and includes a short discussion of the two theoretical approaches that exist to study singular hypersurfaces. The second chapter contains detailed description of these approaches. The theoretical frameworks for both cases of lightlike and timelike (spacelike) hypersurfaces are developed. This chapter also discusses the application of these theories to the case when the hypersurface contains a plane fronted lightlike signal. The final chapter starts with a discussion of the effects that a lightlike singular hypersurface can have on a congruence of timelike (spacelike) geodesics. A new approach to these calculations is presented together with an extension of the theory to the case of a congruence of null geodesics. At the end of the chapter a concrete example and its similarities with the case of timelike geodesics is discussed. In conclusion, the thesis suggests a new mathematical framework for describing a congruence of null geodesics crossing a singular null hypersurface. The results may be applied in experimental physics to detect impulsive signals which are located in singular null hypersurfaces and to this end there is a discussion of the properties and possibilities for a detector of impulsive lightlike signals, which include gravitational waves.
Keywords: singular hypersurface, impulsive signal, gravitational wave, null geodesic, timelike (spacelike) geodesic
Published in RUNG: 16.05.2016; Views: 7564; Downloads: 261
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Abstract: We revisit the theory of null shells in general relativity, with a particular emphasis on null shells placed at horizons of black holes. We study in detail the considerable freedom that is available in the case that one solders two metrics together across null hypersurfaces (such as Killing horizons) for which the induced metric is invariant under translations along the null generators. In this case the group of soldering transformations turns out to be infinite dimensional, and these solderings create non-trivial horizon shells containing both massless matter and impulsive gravitational wave components. We also rephrase this result in the language of Carrollian symmetry groups. To illustrate this phenomenon we discuss in detail the example of shells on the horizon of the Schwarzschild black hole (with equal interior and exterior mass), uncovering a rich classical structure at the horizon and deriving an explicit expression for the general horizon shell energy- momentum tensor. In the special case of BMS-like soldering supertranslations we find a conserved shell-energy that is strikingly similar to the standard expression for asymptotic BMS supertranslation charges, suggesting a direct relation between the physical properties of these horizon shells and the recently proposed BMS supertranslation hair of a black hole.
Keywords: Black Holes, Classical Theories of Gravity, Space-Time Symmetries
Published in RUNG: 10.03.2016; Views: 4738; Downloads: 0
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Abstract: V magistrskem delu obravnavamo problematiko strateškega managementa v izbrani turistični destinaciji, ker smo na področju raziskovanja in predhodnega preučevanja omenjene problematike identificirali raziskovalno vrzel. Namen magistrskega dela je, na podlagi sistematičnega pregleda domače in tuje strokovne literature ter zasnovi konceptualnega modela strategije razvoja turizma, empirično preveriti stopnjo razvitosti strateškega načrtovanja turistične in gostinske dejavnosti v izbrani turistični destinaciji ter podati morebitne predloge za izboljšanje stanja. Za empirični del raziskave smo uporabili kvalitativno metodo raziskovanja in oblikovali raziskovalna vprašanja ter nato opravili intervju s štirimi predstavniki turističnih ponudnikov in tremi predstavniki organizacij, ki so vpete v lokalni turizem. Ugotovili smo, da tako konkurenčne prednosti kot družbena odgovornost in vrednote statistično značilno vplivajo na uspešnost turističnega podjetja. Izidi iz raziskave predstavljajo prispevek k širšemu vpogledu na strateški management v turizmu ter bodo uporabni za vse tiste, ki se teoretično, raziskovalno ali strokovno ukvarjajo s to dejavnostjo.
Keywords: Management, organizacija, raziskava, strateški management, turistična destinacija
Published in RUNG: 29.09.2015; Views: 6652; Downloads: 461
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