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41.
Bettina Albers 《PAMM》2014,14(1):697-698
The propagation of sound waves in Del Monte sand filled by an air-water mixture is studied by a linear model. Even if it does not include an operator to describe the hysteresis of the capillary pressure curve, hysteresis is accounted for: the wave analysis is performed for the two limit cases of main drying and main wetting. In the van Genuchten law both drying and wetting data are applied. Four waves appear: one transversal wave and three longitudinal waves. For the waves driven mainly by the skeleton it could be expected that the influence of consideration of the hysteresis in the capillary pressure curve is negligible. In contrast, the numerical results for the waves driven by the pore fluids exhibit a smaller influence than expected. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
42.
Peter Esser Bettina Pohlmann Hans-Dieter Scharf 《Angewandte Chemie (International ed. in English)》1994,33(20):2009-2023
The light of the sun can be used directly for changing chemical structures photochemically. Any industrial application must conform to the limitations imposed by the spectral distribution of the photons from the sun, the interruptions to the radiation due to the day/night rhythm, and the weather. In this review, we describe the photochemical potential of the sun, give a fundamental treatment of the concept of photoreactors driven by sunlight (abbreviated to solar photoreactors), and give an account of the realization of this concept in the first pilot plant on the “Plataforma Solar de Almeria” in southern Spain and in other activities in this field. Based on experimental data from photochemical investigations on the pilot plant scale, possibilities, limitations, and the potential growth of solar photochemistry are described. Solar photochemistry, in our opinion, is a technique which could make a contribution to the chemistry of the future because of its photochemical synthesis potential, the avoidance of waste products, and the direct utilization of the sun, not only as a primary energy source, but also as a reaction partner. 相似文献
43.
Solid solutions in the system zinc sulfide/zinc phosphide (Zn(2+)(x)S(2-2xP(2x)) were investigated using the cyclic cluster model within the semiempirical MSINDO method. Results of cyclic cluster calculations for binding energies of the perfect ZnS and Zn(3)P(2) are presented and compared with the experimental data. The miscibility of ZnS and Zn(3)P(2) over the whole composition range of 0 < x < 1 was investigated by calculating the Gibbs free energy of mixing Delta(M)G for different values of x. A miscibility gap was found at both ends of the composition range and compared with experimental data. 相似文献
44.
A rectangular cartogram is a type of map where every region is a rectangle. The size of the rectangles is chosen such that their areas represent a geographic variable (e.g., population). Good rectangular cartograms are hard to generate: The area specifications for each rectangle may make it impossible to realize correct adjacencies between the regions and so hamper the intuitive understanding of the map.
We present the first algorithms for rectangular cartogram construction. Our algorithms depend on a precise formalization of region adjacencies and build upon existing VLSI layout algorithms. Furthermore, we characterize a non-trivial class of rectangular subdivisions for which exact cartograms can be computed efficiently. An implementation of our algorithms and various tests show that in practice, visually pleasing rectangular cartograms with small cartographic error can be generated effectively. 相似文献
45.
Functionalized 2,3-benzoxepins were prepared by cyclopropanation of benzopyrylium triflates with diazoesters and subsequent TFA-mediated ring enlargement. 相似文献
46.
Christine Gally Dr. Bettina M. Nestl Prof. Dr. Bernhard Hauer 《Angewandte Chemie (International ed. in English)》2015,54(44):12952-12956
The asymmetric dihydroxylation of olefins is of special interest due to the facile transformation of the chiral diol products into valuable derivatives. Rieske non‐heme iron oxygenases (ROs) represent promising biocatalysts for this reaction as they can be engineered to efficiently catalyze the selective mono‐ and dihydroxylation of various olefins. The introduction of a single point mutation improved selectivities (≥95 %) and conversions (>99 %) towards selected alkenes. By modifying the size of one active site amino acid side chain, we were able to modulate the regio‐ and stereoselectivity of these enzymes. For distinct substrates, mutants displayed altered regioselectivities or even favored opposite enantiomers compared to the wild‐type ROs, offering a sustainable approach for the oxyfunctionalization of a wide variety of structurally different olefins. 相似文献
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48.
Gertraud Malsiner-Walli Sylvia Frühwirth-Schnatter Bettina Grün 《Journal of computational and graphical statistics》2017,26(2):285-295
The use of a finite mixture of normal distributions in model-based clustering allows us to capture non-Gaussian data clusters. However, identifying the clusters from the normal components is challenging and in general either achieved by imposing constraints on the model or by using post-processing procedures. Within the Bayesian framework, we propose a different approach based on sparse finite mixtures to achieve identifiability. We specify a hierarchical prior, where the hyperparameters are carefully selected such that they are reflective of the cluster structure aimed at. In addition, this prior allows us to estimate the model using standard MCMC sampling methods. In combination with a post-processing approach which resolves the label switching issue and results in an identified model, our approach allows us to simultaneously (1) determine the number of clusters, (2) flexibly approximate the cluster distributions in a semiparametric way using finite mixtures of normals and (3) identify cluster-specific parameters and classify observations. The proposed approach is illustrated in two simulation studies and on benchmark datasets. Supplementary materials for this article are available online. 相似文献
49.
50.
Beeskow-Strauch B Schicks JM Spangenberg E Erzinger J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(16):4376-4384
The sequestration of industrially emitted CO(2) in gas hydrate reservoirs has been recently discussed as an option to reduce atmospheric greenhouse gas. This CO(2) contains, despite much effort to clean it, traces of impurities such as SO(2) and NO(2) . Here, we present results of a pilot study on CO(2) hydrates contaminated with 1% SO(2) or 1% NO(2) and show the impact on hydrate formation and stability. Microscopic observations show similar hydrate formation rates, but an increase in hydrate stability in the presence of SO(2). Laser Raman spectroscopy indicates a strong enrichment of SO(2) in the liquid and hydrate phase and its incorporation in both large and small cages of the hydrate lattice. NO(2) is not verifiable by laser Raman spectroscopy, only the presence of nitrate ions could be confirmed. Differential scanning calorimetry analyses show that hydrate stability and dissociation enthalpy of mixed CO(2)-SO(2) hydrates increase, but that only negligible changes arise in the presence of NO(2) impurities. X-ray diffraction data reveal the formation of sI hydrate in all experiments. The conversion rates of ice+gas to hydrate increase in the presence of SO(2), but decrease in the presence of NO(2). After hydrate dissociation, SO(2) and NO(2) dissolved in water and form strong acids. 相似文献