Thermal diffusion and bending kinetics in nematic elastomer cantilever

Vertically aligned monodomain nematic liquid-crystal elastomers contract when heated. If a temperature gradient is applied across the width of such a cantilever, inhomogeneous strain distribution leads to bending motion. We modelled the kinetics of thermally induced bending in the limit of a long thin strip and the predicted time variation of curvature agreed quantitatively with experimental data from samples with a range of critical indices and nematic-isotropic transition temperatures. We also deduced a value for the thermal diffusion coefficient of the elastomer.     

Synthesis, structure, and bonding of Sc4MgxCu15-xGa approximately 7.5 (x=0, 0.5). Two incommensurately modulated scandium substitution derivatives of cubic Mg2Cu6Ga5

The substitution of scandium for magnesium in Mg2Cu6Ga5 (Mg2Zn11-type) yields an irrational superstructure phase that includes the refined compositions, Sc4Mg0.50(2)Cu14.50(2)Ga7.61(2) and Sc4Cu14.76(2)Ga7.51(2). These crystallize in Cmmm, a=approximately 8.31 A, b=approximately 21.72 A, c=approximately 8.30 A. The structures feature Sc2 dimers, Cu6 octahedra, a 3D CuGa (Cu12Ga2) framework, and arachno gallium-centered Cu4Ga6 icosahedra that are condensed into zigzag chains. The arrangement of these building blocks exhibits a topologic relationship to Mg2Cu6Ga5. Further studies reveal that the quaternary compound exhibits incommensurate modulations along a, with q=(0.694, 0, 0). Structure refinements with superspace group Xmmm(a00)000 led to saw-tooth modulations for two fractional or mixed sites that avoid short Cu-Ga distances. Band structure analyses reveal that the Fermi surface and bonding are sensitive to the incommensurately modulated atoms.     

Continuous‐scan capability at SSRL and applications to X‐ray diffraction

Typical X‐ray diffraction measurements are made by moving a detector to discrete positions in space and then measuring the signal at each stationary position. This step‐scanning method can be time‐consuming, and may induce vibrations in the measurement system when the motors are accelerated and decelerated at each position. Furthermore, diffraction information between the data points may be missed unless a fine step‐scanning is used, which further increases the total measurement time. To utilize beam time efficiently, the motor acceleration and deceleration time should be minimized, and the signal‐to‐noise ratio should be maximized. To accomplish this, an integrated continuous‐scan system was developed at the Stanford Synchrotron Radiation Lightsource (SSRL). The continuous‐scan system uses an in‐house integrated motor controller system and counter/timer electronics. SPEC software is used to control both the hardware and data acquisition systems. The time efficiency and repeatability of the continuous‐scan system were tested using X‐ray diffraction from a ZnO powder and compared with the step‐scan technique. Advantages and limitations of the continuous‐scan system and a demonstration of variable‐velocity continuous scan are discussed.     

M2Ba2Sn6 (m =yb, ca): metallic zintl phases with a novel tin chain substructure

The compounds M2Ba2Sn6 (M = Yb, Ca) have been synthesized by solid-state reactions in welded Ta tubes at high temperature. Their structures were determined by single-crystal X-ray diffraction studies to be orthorhombic; space group Cmca (No. 64); Z = 8; a = 15.871(3), 15.912 (3) A; b = 9.387(2), 9.497(2) A; c = 17.212(3), 17.184(3) A; and V = 2564.3(9), 2597.0(9) A3, respectively. These contain infinite tin chains along constructed from butterflylike 3-bonded Sn tetramers interconnected by pairs of 2-bonded Sn. The chains are further interconnected into corrugated layers by somewhat longer Sn-Sn bonds along c. The compounds with the chains alone would be Zintl phases, but the interchain bonding makes them formally one-electron rich per formula unit. The electronic structures calculated by extended Hückel and TB-LMTO-ASA methods indicate that these compounds are metallic but with a deep pseudogap at the Fermi level. States that bind the extra electrons lie just below EF and involve important Yb(Ca)-Sn contributions. The origin of metallic Zintl phases is briefly discussed.     

Ca4Au10In3: synthesis, structure, and bonding analysis. The chemical and electronic transformations from the isotypic Zr7Ni10 intermetallic

The title compound, Ca(4)Au(10)In(3) (e/a = 1.59), was synthesized by conventional high-temperature solid-state reactions and structurally analyzed by single-crystal X-ray diffraction: space group Cmca, a = 13.729(4) A, b = 10.050(3) A, c = 10.160(3) A, Z = 4. The structure, isotypic with that of Zr(7)Ni(10), features a novel three-dimensional [Au(10)In(3)] polyanionic framework built from sinusoidal Au layers that are interconnected by significant Au-Au and Au-In interactions. A prominent electronic feature is the presence of a pseudogap and empty bonding states above the Fermi level according to LMTO calculations, reminiscent of the tunable electronic properties discovered for Mg(2)Zn(11)-type phases. The natures of the chemical and electronic redistributions from Zr(7)Ni(10) to Ca(4)Au(10)In(3) are considered. The Au backbone appears to be particularly important.     

Different cation arrangements in Au-In networks. Syntheses and structures of six intermetallic compounds in alkali-metal-Au-In systems

Six robust intermetallic compounds with cations in three different tunnel-like structures have been synthesized in alkali-metal-Au-In systems via high-temperature solid-state methods and characterized by X-ray diffraction: AAu(4)In(6) [A = K (I), Rb (II), P6m(2), Z = 1], K(1.76(6))Au(6)In(4) (III, I4/mcm, Z = 4), and A(x)Au(2)In(2) [x approximately 0.7, A = K (IV), Rb (V), Cs (VI), P4(2)/nmc, Z = 8]. The first type is constructed from a single cage unit: an alkali-metal-centered 21-vertex polyhedron A@Au(9)In(12) with 6-9-6 arrangement of planar rings. The others contain uniaxial arrays of tunnels built of differently puckered eight- and four-member Au/In rings. The largely different cation distributions depend on the tunnel constitutions and cation sizes. Tight-binding electronic structure calculations by linear muffin-tin-orbital (LMTO) methods were performed for I and idealized III in order to help understand their chemical bonding. These also reveal large differences in relativistic effects for Au d orbitals, as well as for different Au sites in each structure.     

使用色散可调啁啾光纤光栅在常规单模光纤中实现超过100km,10Gb/s的转输 *

报道了用简单的应力方法使均匀光栅成为线性啁啾光纤光栅的技术 ,并推导出了相应理论 ,发现最大色散补偿带宽与色散的乘积近似为常数 .在常规单模光纤G652,10Gb/s系统中实现超过100km的色散补偿 .     

The Antimony‐Based Type I Clathrate Compounds Cs8Cd18Sb28 and Cs8Zn18Sb28

In phase : The title compounds lie in a new region of phase space for such a structure, and have stoichiometries in accord with a classical Zintl phase formulation. The small semiconductor gaps indicated by DFT calculations are also supported by their diamagnetic susceptibilities.