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Alternating Layers (alternating + layer)
Selected AbstractsA new Cosserat-like constitutive model for bedded salt rocksINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2009Yin-Ping Li Abstract Salt rocks are commonly used as geologic host rocks for storage of gas and crude oil, and are being considered for the disposal of radioactive waste. Different from the salt rock domes in many countries, the salt rock formations in China are usually laminar with many alternating layers, i.e. rock salt, anhydrite, and/or mudstone. Considering the unique stratigraphic characteristics of these salt rocks, a new Cosserat-like medium constitutive model is proposed in order to facilitate efficient modeling of the mechanical behavior of these formations. In this model, a new representative volume element, containing two different layers, is employed to simulate the compatibility of the meso-displacement between two different layers and also the bending effect. A new method for the deformation and failure analysis of bedded salt rocks is derived therefrom. Having the macro-average stresses, the conventional stresses in the different layers can be obtained in sequence. The conventional stresses can then be utilized in a routine way for the strength and failure analysis. For the initial numerical modeling, the new Cosserat-like medium is reduced to a transversely isotropic one. The simplified constitutive model for layered media is then implemented into FLAC3D codes. A test sample validates that the results by using the numerical model are in good agreement with that by using the built-in model, and the mesh size for the new model is reduced greatly. Finally, an application for the stability of oil storage caverns in deep thinly bedded salt rocks is carried out. The effects on convergence of storage caverns and on the failure of surrounding rock due to the presence of the mudstone interlayers (hard phase) are discussed in detail. Copyright © 2009 John Wiley & Sons, Ltd. [source] Influence of wurtzite,zinc-blende interfacial energy on growth and crystal phase of the III-V nanowiresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Maxim Lubov Abstract Influence of wurtzite,zinc-blende energy on nucleation rate and growth kinetics is studied. The physical model of III-V nanowires growth is proposed. We show that wurtzite,zinc-blende interfacial energy caused formation of the zinc-blende structure on the initial stage of nanowires growth. Role of the fluctuations in quasi-periodic crystal structure formation representing alternating layers of wurtzite and zinc-blende phase is revealed. Calculations of the growth of the nanowire growth accounting fluctuations in the droplet alloy are carried out. The results of the calculations are in a good agreement with available experimental data. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structures of relevant ammonium salts in fertilizersACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010J. M. Montejo-Bernardo The crystal structures of two double salts of ammonium nitrate (AN) and ammonium sulfate (AS) are reported. The double salts 2NH4NO3·(NH4)2SO4 (2AN·AS) and 3NH4NO3·(NH4)2SO4 (3AN·AS) show a very similar crystal structure packing with alternating layers of anions and cations. The solid-state ionic distribution is controlled by an extensive hydrogen-bonding network with ammonium groups as the donors and O atoms acting as the acceptors. Crystallographic studies were conducted at both room temperature (293,K) and 100,K. Increasing the temperature involves shortening the b axis in the case of the 3AN·AS salt. Quantification of fertilizer mixtures using the Rietveld method was also carried out by means of the structural models reported in this paper for both salts. [source] Hexane-1,6-diaminium chloride [hydrogen bis(chloroacetate)]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009Agnieszka Paul In the structure of the title compound, C6H18N22+·H(C2H2ClO2)2,·Cl,, the hexane-1,6-diaminium dication is disordered over two sets of positions, with almost equal occupancies. Both alternative positions of the dication are in the fully extended conformation, situated on an inversion centre at (, , ). Two chloroacetic acid moieties, related by another centre of symmetry at (, , ), are connected by a very short symmetrical O...H...O hydrogen bond [O...O = 2.452,(2),Å], with the H atom at the centre of inversion. These two fragments thus effectively form the hydrogen bis(chloroacetate) monoanion, and the overall charge is balanced by an additional chloride anion which resides on a twofold axis. The ions form a layer structure, with alternating layers of dications and anions running along the [101] direction, linked via hydrogen bonds. There are two N,H...O interactions and two N,H...Cl, interactions. [source] Bis(1,3,4-trimethylpyridinium) tetrachloridocuprate(II) and bis(1,3,4-trimethylpyridinium) tetrabromidocuprate(II): an examination of the A2CuX4Fdd2 structure typeACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Marcus R. Bond The title bis(1,3,4-trimethylpyridinium) tetrahalidocuprate(II) structures, (C8H12N)2[CuCl4], (I), and (C8H12N)2[CuBr4], (II), respectively, consist of flattened [CuX4]2, tetrahedral complex anions and planar 1,3,4-trimethylpyridinium cations. Chloride compound (I) is a rare example of an A2CuCl4 structure with an elongated unit cell in the polar space group Fdd2. The [CuCl4]2, anions have twofold rotational symmetry and are arranged in distorted hexagonal close-packed (hcp) layers, which are interleaved with layers of cations, each in a four-layer repeat sequence, to generate the elongated axis. The organic cations stack along [101] or [10] in alternating layers. The methyl groups meta on the cation ring and the larger of the trans Cl,Cu,Cl angles both face the same direction along the polar axis and are the most prominent features determining the polarity of the structure. Bromide compound (II) crystallizes in a centrosymmetric structure with a similar layer structure but with only a two-layer repeat sequence. Here, symmetry-inequivalent cations are segregated into alternating layers with cations, forming hcp layers of inversion-related cation pairs in one layer and parallel stacks of cations in the other. The change in space group when the larger Br, ion is present suggests that the 1,3,4-trimethylpyridinium ion has a minimal size to allow the Fdd2 A2CuX4 structure type. [source] A pseudo-merohedrally twinned rare-earth sulfate: K6[Ce(HSO4)2(SO4)4]·H2O, a novel structure typeACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2007Vratislav Langer A novel structure type of an acidic rare-earth sulfate, hexapotassium cerium dihydrogensulfate tetrasulfate monohydrate, is reported. The crystal is twinned, mimicking tetragonal symmetry. The CeIV atom is nine-coordinate, connecting to one corner-sharing and four edge-sharing sulfate groups. One of the potassium ions is disordered over two general positions. The compound is unique as it contains rare-earth monomers, [Ce(HSO4)(SO4)4]5,. The structure is composed of these monomers, water molecules, discrete hydrogensulfate ions and potassium ions held together by ionic interactions. There are two types of alternating layers in the structure, with compositions [K4Ce(HSO4)(SO4)4], and [K2(HSO4)(H2O)]+. [source] | ||||||||||