Discovery of the Ternary Nanolaminated Compound Nb_{2}GeC by a Systematic Theoretical-Experimental Approach

Since the advent of theoretical materials science some 60?years ago, there has been a drive to predict and design new materials in?silicio. Mathematical optimization procedures to determine phase stability can be generally applicable to complex ternary or higher-order materials systems where the phase diagrams of the binary constituents are sufficiently known. Here, we employ a simplex-optimization procedure to predict new compounds in the ternary Nb-Ge-C system. Our theoretical results show that the hypothetical Nb_{2}GeC is stable, and excludes all reasonably conceivable competing hypothetical phases. We verify the existence of the Nb_{2}GeC phase by thin film synthesis using magnetron sputtering. This hexagonal nanolaminated phase has a and c lattice parameters of ～3.24 ? and 12.82??.     

Network formation by epoxidised soybean oil in plastisol poly(vinyl chloride)

Epoxidised soybean oil, ESBO, is a well known additive used in plasticized poly(vinyl chloride) (PVC) since it functions both as plasticizer and as stabilizer. This paper describes what happens to the material when ESBO is used as primary plasticizer in plastisol- and in suspension PVC without any additional stabilizer. When 50 ph ESBO was added to 100 ph plastisol PVC and then aged in a Werner Mathis oven at 180 °C for various lengths of time, the E-modulus increased with ageing time due the formation of a crosslinked network induced by a polymerization reaction of the epoxy groups in the ESBO. The network and the PVC were analyzed by NMR which showed that reaction between PVC and ESBO had occurred, and that the network consisted primarily of ESBO. The same experiment performed with suspension PVC instead of plastisol PVC did not result in any crosslinking of the ESBO. The ring opening of the epoxy which starts the polymerization of ESBO is most likely catalyzed by an additive used in the polymerization of plastisol PVC.     

泥沙输运模拟综述——现状及其发展趋势

随着流体力学中数值方法的飞速发展,计算模型已经成为研究流体运动,泥沙输运和不同环境(诸如河流,湖泊及沿海地区)中相应污染物归趋过程等方面非常有吸引力的工具,在过去的30多年里,发展了许多计算水动力学/泥沙输运模型.文章追溯当前具有代表性的(一维、二维、三维)模型的发展历程,描述他们各自的特点,优势及局限,力图作为对模型方面感兴趣读者的第一指南,同时也为大家讨论模型的局限性,未来的发展趋势和研究需求方面搭建一个平台.给出了模型的表达,时空特性,水动力学和沉积物的耦合方式,处理非恒定流,推移质和悬移质,泥沙交换过程,泥沙类型(粘性或非粘性)及非均匀泥沙输运的能力.总结了不同模型的应用实例,读者可以运用这些例子作为研究模型设置,模型率定及模型验证的参考.给出了选择泥沙输运模型应遵循的原则,模型输入及率定方面存在的问题及改进的途径.探讨了现有水动力学/泥沙输运模型在处理复杂湍流,泥沙携带,流动与输沙耦合,非均匀泥沙,离散和扩散系数,河岸来沙处理等方面的局限性及改进的方向.最后,对基于多相流思想的泥沙输运模型及其它一些交叉性问题作了评述与展望.     

The rheological properties of AgI and Li2SO4 solid electrolytes,I.

Summary The plastic deformations of the high-temperature modifications of AgI and Li₂SO₄ have been studied with a rotational viscometer between 640 and 829 K and between 1054 and 1133 K, respectively. Thixotropic behaviour was observed and the regeneration times were 24 h for AgI at 809 K and 8.4 h for Li₂SO₄ at 1054 K. A change in the yield mechanism in AgI is indicated at the cation order-disorder transition point 705 K. The activation parameters will be discussed in a following paper.

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Zusammenfassung Die plastische Deformierbarkeit der Hochtemperatur-Modifikationen von AgJ und Li₂SO₄ wurde mit einem Rotations-Viskosimeter zwischen jeweils 640 und 829 K bzw. 1054 und 1133 K bestimmt. Es wurde thioxotropes Verhalten gefunden. Die Regenerationszeiten waren für AgJ bei 809 K 24 h und für Li₂SO₄ bei 1054 K 8.4 h. Eine Veränderung des Fließmechanismus wird am Kationen-Ordnungs-Unordnungs-(order-disorder)Umwandlungspunkt bei 705 K gefunden. Die Aktivierungs-Parameter sollen in einer folgenden Publikation diskutiert werden.

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With 10 figures and 3 tables     

Influence of microtomy on measurements of orientation

The correct measurement of orientation and crystallinity on thin sections microtomed from larger specimens requires a knowledge of the influence of sectioning on these properties. In this work, the measuring technique used is FTIR, using dichroism to determine the orientation and regular FTIR to determine the degree of crystallinity. This paper shows that the sectioning influences the measured orientation of the sections in the case of both amorphous polycarbonate and crystalline polypropylene, while the crystallinity seems to be unaffected in the case of the unoriented samples.     

Infrared dichroism of glassy polycarbonate at small strains

The dichroism of the 889, 1364, and 3063 cm^?1 infrared absorption bands of glassy, amorphous polycarbonate has been measured as a function of the strain in the range 0 to 2% at 23°C. The data obtained for these three bands superpose rather well over this strain range. Negligible dichroism is observed up to about 0.6% strain; above this level, the dichroic ratio increases in an approximately linear manner. Independent mechanical data, obtained under comparable conditions of time-scale and temperature, are cited which show that a transition from approximately linear to marked non-linear viscoelastic behavior occurs with glassy polycarbonate in the range 0.7 to 1.0% strain. The coincidence on the strain axis of a relatively abrupt increase in optical absorption anisotropy with a distinct change in Young's modulus is discussed in terms of a recent molecular theory of deformation of glassy polymers. It is suggested that the data are consistent with the view that the transition from linear to nonlinear viscoelastic behavior in glassy polycarbonate is marked by the onset of significant rotation around backbone bonds.     

A new method for the detection of thermal oxidation in polyethylene pipes

Dumb-bell shaped specimens containing the inner wall surface of the pipe cut from 12 polyethylene pipes of different origin were subjected to constant uniaxial tensile loads at 313 K in air. The brittleness of the inner wall surface layer of the thermally oxidized pipes manifested itself in a shift of the unstable/stable necking transition to lower stresses and longer times. With the aid of optical and scanning electron microscopy, the brittleness of the inner wall surface layer of the oxidized pipes was demonstrated in distinctive surface cracks, which were the dominant feature of the drawn samples of the oxidized pipes. No such surface cracks were observed in the non-oxidized samples. The surface crack patterns were characterized in terms of crack frequency (longitudinal and transverse), width of fragments of cracked top layer (l_B), plastic strain of the fragments of the cracked top layer (ε_pl) and thickness of the cracked top layer (H). Correlations were found that can be interpreted according to basic principles of fracture mechanics. Through knowledge of, for example, ε_pl and l_B the values of the other variables can be predicted. The thickness of the cracked top layer corrected for the reduction in thickness due to plastic deformation is approximately equal to the thickness of the oxidized layer as determined by polarized microscopy. Drawing in an Instron Tensile Testing Machine at an elongation rate of 10 mm/min at 298 K also revealed the distinctive surface cracks in the oxidized samples. On the basis of these results, a new method for the detection of thermal oxidation in polyethylene pipes is proposed.     

Conformational analysis of a tetrasaccharide based on NMR spectroscopy and molecular dynamics simulations

The conformational preference of the human milk oligosaccharide lacto-N-neotetraose, beta-d-Galp-(1 --> 4)-beta-d-GlcpNAc-(1 --> 3)-beta-d-Galp-(1 --> 4)-d-Glcp, has been analyzed using (1)H,(1)H T-ROESY and (1)H,(13)C trans-glycosidic J coupling experiments in isotropic solution and (1)H,(13)C residual dipolar couplings (RDCs) obtained in lyotropic liquid crystalline media. Molecular dynamics simulations of the tetrasaccharide with explicit water as the solvent revealed that two conformational states are significantly populated at the psi glycosidic torsion angle, defined by C(anomeric)-O-C-H, of the (1 --> 3)-linkage. Calculation of order parameters, related to the molecular shape, were based on the inertia tensor and fitting of experimental RDCs to different conformational states showed that psi(+) > 0 degrees is the major and psi(-) < 0 degrees is the minor conformation in solution, in complete agreement with a two-state analysis based on the T-ROESY data. Attention was also given to the effect of salt (200 mM NaCl) in the anisotropic medium, which was a ternary mixture of n-octyl-penta(ethylene glycol), n-octanol, and D(2)O.     

CASPER: a computer program used for structural analysis of carbohydrates.

The computer program CASPER and its algorithms are described. The program is aimed at facilitating the determination of structures of oligosaccharides and regular polysaccharides, requiring as input either the one-dimensional 1H or 13C NMR spectrum or the 2D C,H-correlation NMR spectrum together with information on components and linkages. The databases, the method of simulating spectra, options of the program, and techniques for faster calculations are described as well as an example of a structural determination.