Thermal expansion in the Burns-phase of barium titanate stannate

The thermal expansion S_T has been measured in the system BaTi_1−xSn_xO₃, both for the pure compositions x=0 (BT) and x=1 (BS), and for solid solutions 0.025≤x≤0.2 (BTS). For all ceramics examined, a non-linear temperature dependence S_T(T) has been observed at elevated temperatures This is related to thermally generated impurities and, below the Burns-temperature T_d of BT and BTS, to the non-linear strain contribution of polar nanoregions. With increasing Sn-content x, a steep increase of the Burns-temperature is found in BTS for compositions x≥0.025.     

The influence of the ideal mixing entropy on concentration profiles and diffusion paths in ternary systems

The diffusion profiles and the reaction paths in ternary solid solutions are determined by both thermodynamics and kinetics. The matrix of the diffusion coefficient can be described as the product of the Hessian matrix for the thermodynamic influences and the Onsager matrix for kinetic influences.In this paper the interest is focused on the influence of the ideal part of the Hessian matrix, i.e. the ideal mixing entropy on interdiffusion. The ideal diffusion profiles are calculated by a computer simulation and they are compared with experimental results from the literature. These comparisons reveal that in most cases the qualitative shape of the diffusion profiles and of the reaction paths can be considered as caused by the ideal mixing entropy. Surprisingly, the shape of the diffusion profiles turns out to depend on the component that was chosen as the so-called solvent of the ternary mixture. This means that the ideal reaction paths do not show the triangular symmetry expected for an ideal ternary system. Especially, reaction paths between starting positions showing the same concentration of one of the three components do not run along straight lines.     

A predictor-corrector technique for constrained least-squares regularization

Summary The paper describes a numerical strategy for the approximate solution of nonlinear, discretized, inverse problems by regularization. It is assumed that the solution of the associated direct problems and the computation of Fréchet derivatives are expensive. In order to minimize the amount of work, a predictor-corrector type algorithm is proposed. From a series of solutions to problems with a coarse discretization one obtains a starting approximation for a problem with a fine discretization.     

Buchsbaum* complexes

A class of finite simplicial complexes, which we call Buchsbaum* over a field, is introduced. Buchsbaum* complexes generalize triangulations of orientable homology manifolds as well as doubly Cohen-Macaulay complexes. By definition, the Buchsbaum* property depends only on the geometric realization and the field. Characterizations in terms of simplicial homology are given. It is proved that Buchsbaum* complexes are doubly Buchsbaum. Various constructions, among them one which generalizes convex ear decompositions, are shown to yield Buchsbaum* simplicial complexes. Graph theoretic and enumerative properties of Buchsbaum* complexes are investigated.     

On the solid state phases of poly(trans-1,4-butadiene)

Summary The method of semiempiric-atomistic calculations is applied to a polydiene. For this purpose a Coulomb term has to be added to a potential set used successfully for polyolefines. All stable 4 *p/q helices of poly(trans-1,4-butadiene) are calculated. This yields a conformation for the low temperature phase which is in agreement with X-ray data in the literature. Chain conformations are proposed for the high temperature phase carefully considering the energies (determined in the single chain approximation) and the packing properties.Experimentelly, the enthalpy and entropy differences between the phases, calculated only intramolecularly, are determined by high pressure dilatometry and calorimetry. A commercial material is investigated in the full pressure range up to 3 kbar; for low pressure dilatometry and calormetry a purely trans polymer, initially in extended chain conformation, is used. Experimental data are compared with calculated values and discrepancies are discussed.

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Zusammenfassung Die Methode der semiempirisch-atomistischen Rechnung wird auf ein Polydien angewendet. Dazu wird ein bei Polyolefinen bewährter Potentialsatz um einen Coulombterm erweitert. Berechnet werden alle stabilen 4 *p/q Helices des Poly-trans-1,4-butadiens, und es ergibt sich eine Konformation für die Tieftemperaturphase, die mit Röntgendaten in der Literatur übereinstimmt. Für die Hochtemperaturphase werden Kettenkonformationen vorgeschlagen, bei denen die in der Einzelkettennäherung bestimmte Energie und die Packung berücksichtigt wird.Die Enthalpie- und Entropieunterschiede zwischen beiden Phasen, die bisher nur intramolekular berechnet sind, werden experimentell mit den Methoden der Hochdruckdilatometrie und der Kalorimetrie bestimmt. Dabei wird im Hochdruckbereich bis 3 kbar ein handelsübliches Material gemessen, im Niederdruckbereich und kalorimetrisch aber ein reines trans-Polymeres, das anfangs gestrecktkettig vorliegt. Die experimentellen Werte werden mit den berechneten verglichen, und ihre Unterschiede werden diskutiert.

     

UHV Studies of Methanol Decomposition on Mono‐ and Bimetallic CoPd Nanoparticles Supported on Thin Alumina Films

Bimetallic nanoparticles often turn out to be superior to the corresponding monometallic systems with respect to their catalytic properties. To study such effects for the methanol decomposition reaction, model catalysts were prepared by physical vapor deposition of Pd and Co under ultrahigh‐vacuum (UHV) conditions. Monometallic Pd and Co particles as well as CoPd core–shell particles were generated on an epitaxial alumina film grown on NiAl(110). The interaction with methanol is examined by temperature‐programmed desorption of methanol and carbon monoxide and by X‐ray photoelectron spectroscopy. The decomposition of methanol proceeds in two reaction pathways independent of the particle composition: complete dehydrogenation towards carbon monoxide and hydrogen, and C? O bond scission yielding carbon deposits. Pd is the most active material studied here. The relative importance of the two channels varies for the different particle systems: on Pd dehydrogenation is preferred, whereas the C? O bond cleavage is more pronounced on Co. The bimetallic clusters show a moderate performance for both pathways. Carbon deposition poisons the model catalysts by blocking the adsorption sites for methoxide, which is the first intermediate product during methanol decomposition. In particular on Co, large amounts of carbon deposits can also be caused by dissociation of the final product of the dehydrogenation pathway, carbon monoxide. A comparison with the results of methanol decomposition on Co, Pd, and CoPd catalysts in continuous‐flow reactors demonstrates that the findings of the present UHV study are relevant for catalytic performance under high‐pressure conditions.     

Automated, high-resolution micropipet aspiration reveals new insight into the physical properties of fluid membranes

We describe recent advances in our experimental approach to examine the physical properties of biological and artificial membranes by automated micropipet aspiration. New instrumentation allows us to apply fast yet precise tension protocols to membranes while continuously recording the membrane deformation with high-speed videomicroscopy. Robust algorithms for subpixel geometric measurements track the displacements of membrane edges with resolution of a few nanometers and enable us to determine changes of the membrane area and enclosed volume of pipet-aspirated cells or vesicles with exceptional accuracy. Experimentation and data analysis are greatly facilitated by custom-written software whose basic design is described here as well. Example measurements demonstrate how this technique has significantly improved the amount and reliability of data obtained by various types of micropipet-aspiration experiments, allowing us to study interesting aspects of membrane behavior that have eluded earlier techniques.     

Patenting and licensing of university-based genetic inventions--a view from experience at Stanford University's Office of Technology Licensing

University technology transfer offices license inventions created at universities to companies looking for tools, additions to their product pipelines, improvements or start-up opportunities. This paper will cover the motivations for conducting university technology transfer, an overview of Stanford's Office of Technology Licensing and its patenting and licensing practices, models of royalty sharing at university technology transfer offices, and patenting and licensing genetic information inventions at Stanford University. The terms 'invention' and 'technology' are used interchangeably throughout the paper.