Heterogeneous shear in hard sphere glasses

There is growing evidence that the flow of driven amorphous solids is not homogeneous, even if the macroscopic stress is constant across the system. Via event-driven molecular dynamics simulations of a hard sphere glass, we provide the first direct evidence for a correlation between the fluctuations of the local volume fraction and the fluctuations of the local shear rate. Higher shear rates do preferentially occur at regions of lower density and vice versa. The temporal behavior of fluctuations is governed by a characteristic time scale, which, when measured in units of strain, is independent of shear rate in the investigated range. Interestingly, the correlation volume is also roughly constant for the same range of shear rates. A possible connection between these two observations is discussed.     

Structure, hydrophobicity, and hydrothermostability of MCM-41 organo-inorganic mesoporous silicates silylated with dimethoxydimethylsilane and dichloromethylphenylsilane

Changes in the structure, hydrophobicity, and hydrothermal stability of organo-inorganic composite materials based on MCM-41 as a result of silylation with dimethoxydimethylsilane (DMODMS) and dichloromethylphenylsilane (DCMPS) were considered. Based on the data on the competitive adsorption of water and toluene it was shown, using the Weitkamp procedure, that the grafting of organosilyl groups affects the sorption properties of mesoporous materials. Hydrothermal treatment led to considerable changes in the structure and properties of the materials. The thermal stability of MCM-41 composites and changes in their hydrophilicity due to the grafting of DMODMS and DCMPS and hydrothermal treatment were studied by thermogravimetry.     

Confined‐Space Alloying of Nanoparticles for the Synthesis of Efficient PtNi Fuel‐Cell Catalysts

The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, that is, its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen reduction reaction associated with nanoscale Pt alloys, and the excellent durability of an advanced nanostructured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0 A mg_Pt^?1. Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined‐space alloying of the nanoparticles in a controlled manner in the pores of the support.     

Admissibility of kneading sequences and structure of Hubbard trees for quadratic polynomials

Hubbard trees are invariant trees connecting the points of thecritical orbits of post-critically finite polynomials. Douadyand Hubbard showed in the Orsay Notes that they encode all combinatorialproperties of the Julia sets. For quadratic polynomials, onecan describe the dynamics as a subshift on two symbols, anditinerary of the critical value is called the kneading sequence.Whereas every (pre)periodic sequence is realized by an abstractHubbard tree (see the authors’ preprint from 2007), notevery such tree is realized by a quadratic polynomial. In thispaper, we give an Admissibility Condition that describes preciselywhich sequences correspond to quadratic polynomials. We identifythe occurrence of the so-called ‘evil branch points’as the sole obstruction to being realizable. We also show howto derive the properties of periodic (branch) points in thetree (their periods, relative positions, number of arms andwhether they are evil or not) from the kneading sequence.     

In situ muSR and NMR investigation of methanol dissociation on carbon-supported nanoscaled Pt-Ru catalyst

In situ muSR and nuclear magnetic resonance (NMR) experiments on the investigation of methanol decomposition on Pt-Ru nanoscaled catalyst supported on Vulcan XC-72 carbon black (Pt-Ru/Vulcan XC-72) are presented. Avoided-level-crossing muon spin resonance measurements reveal the resonance line at magnetic field 2.018 T, we assign to transient CH₂?OMu? formaldehyde muonated radical. Results obtained allow us to estimate the contribution of chemical decomposition reaction process for the formaldehyde—carbon oxide—hydrogen conversion on Pt-Ru/Vulcan XC-72 catalytic material. NMR spectrum of the methanol covered Pt-Ru/Vulcan XC-72 consists of three broad resonance lines. Two of them are assigned to OH and CH₃ groups of methanol bound to the carbon black surface. Following the existing literature, which indicates that polymerization of formaldehyde readily takes place when the monomer is adsorbed on some active surface, the third one is assigned to the resonance signal of oligomeric species of formaldehyde. Taking into account the results of our experiments on electrochemical hydrogenation of carbon nanotubes, we do not exclude that the hydrogen arising as a result of methanol decomposition would also contribute to this signal. The high surface area of amorphous carbon nanoparticles of Vulcan XC-72 is favourable to adsorb the hydrogen on their surface.     

On the Reconstruction and Computation of Dual-Phase Steel Microstructures Based on 3D EBSD Data

In this contribution we reconstruct the three dimensional microstructure of a dual-phase steel based on the tomographic experimental data provided by the 3D electron backscatter diffraction (3D EBSD) method. The cross sections of the resulting microstructure are compared to the 2D reconstruction, which are obtained directly from the 3D EBSD data. We also perform FE-simulations based on these geometries and observe comparable results in 2D and 3D. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Über die Reaktivität des Schwefeldioxid-Radikalanions gegenüber reduzierbaren Substraten

A survey of reactions of the electrolytically prepared sulfurdioxide anion radical with various substrates containing reducible groups under aprotic and slightly protic conditions is presented. Beyond known reactions with mono-, vicinal and 1,-dihalides only -halogencarbonyl-, polyhalide-, nitro- and nitrosocompounds are reducible by this reagent. Aldehydes and carboxylic acid halides react but retain their state of oxidation. Anhydrides, esters and ketones are almost inert. Mechanisms are discussed and the scope for the use of S₂O ₄ ^– as a nucleophile for the synthesis of sulfones and as a reducing agent is defined.