Rhodium-benzimidazolidin-2-ylidene catalyzed addition of arylboronic acids to aldehydes

Six rhodium–carbene complexes (2a–f) have been prepared and the new compounds characterized by C, H, N analyses, ¹H-n.m.r. and ¹³C-n.m.r. Phenylboronic acid reacts with aldehydes in the presence of a catalytic amount of rhodium(I)–carbene complex, RhCl(COD)(1,3-dialkylbenzimidazolidin-2-ylidene), (2a–f), to give the corresponding aryl secondary alcohols in good yields.     

Development and validation of a viscoelastic finite element model of an L2/L3 motion segment

The prediction of the time dependent response of the spine to dynamic loading conditions is essential in understanding the injury mechanisms leading to occupationally related low back disorders (OLBD). Many previous finite element (FE) models of the lumbar spine have over-simplified the geometry and the material properties of their elements, yielding results limited generalizability. This study reports on the development and validation of a nonlinear viscoelastic FE model that can quantify the mechanical responses of the L2/L3 motion segment to time varying external loads. This model was developed by consideration of the intrinsic material properties of its individual constituents. A piecewise parameter identification method was adopted due to the inherent complexity in determining the role and contribution of each element to the overall behavior of the motion segment. The results of simulation of four loading conditions (quasistatic, constant loading rate, creep and cyclic relaxation) showed a satisfactory agreement with experimental observations in the literature. The detailed estimates of the state of stress/strain of this validated FE model can be used to test the role of epidemiological risk factors such as prolonged awkward posture, speed of lift (strain rate effect) and complex repetitive loading in OLBD.     

Tunable Two-Frequency Lasers for Lifetime Measurements

We built a compact two-tunable-frequency longitudinally pumped solid-state laser specially designed to measure atomic lifetimes. Weak coupling between the laser eigenstates permits the obtaining of a continuously tunable frequency difference between 0 and 10 GHz. Such a source provides either a linear polarization rotating at such frequencies, or a sinusoidally modulated intensity with a 100% modulation amplitude. As an example, the fluorescence lifetime of the first excited state of Cr⁴⁺ in YAG is measured in the zero-fluence limit using a two-frequency Nd:YAG laser at 1064 nm.     

Near‐IR‐Triggered,Remote‐Controlled Release of Metal Ions: A Novel Strategy for Caged Ions

A ligand incorporating a dithioethenyl moiety is cleaved into fragments which have a lower metal‐ion affinity upon irradiation with low‐energy red/near‐IR light. The cleavage is a result of singlet oxygen generation which occurs on excitation of the photosensitizer modules. The method has many tunable factors that could make it a satisfactory caging strategy for metal ions.     

ESR and TL studies of irradiated Anatolian laurel leaf (Laurus nobilis L.)

Laurel leaf (Laurus nobilis L.) samples that originated from Turkey were analyzed by electron spin resonance (ESR) and thermoluminescence (TL) techniques before and after γ-irradiation. Unirradiated (control) laurel leaf samples exhibit a weak ESR singlet centered at g=2.0020. Besides this central signal were two weak satellite signals situated about 3 mT left and right to it in radiation-induced spectra. The dose–response curve of the radiation-induced ESR signal at g=2.0187 (the left satellite signal) was found to be described well by a power function. Variation of the left satellite ESR signal intensity of irradiated samples at room temperature with time in a long term showed that cellulosic free radicals responsible for the ESR spectrum of laurel leaves were not stable but detectable even after 100 days. Annealing studies at four different temperatures were used to determine the kinetic behavior and activation energy of the radiation-induced cellulosic free radicals responsible from the left satellite signal (g=2.0187) in laurel leaves. TL measurements of the polymineral dust isolated from the laurel leaf samples allowed distinguishing between irradiated and unirradiated samples.     

The influence of the growth rate on the eutectic spacings,undercoolings and microhardness of directional solidified bismuth–lead eutectic alloy

Bi–Pb alloy at the eutectic composition was unidirectionally solidified upwards with five different growth rates (V = 7.05–113.09 μm/s) at constant temperature gradient (G = 2.18 K/mm) in a Bridgman type directional growth furnace in order to investigate dependency of eutectic spacing (λ), minimum undercooling (ΔT) and microhardness (HV) on the growth rates (V). The values of λ and HV were measured from the quenched samples and the minimum undercooling (ΔT) were determined from the Jackson–Hunt eutectic theory. The dependency of eutectic spacings, microhardness and undercooling on growth rate was investigated. According to these results it has been found that the value of λ decreases with increasing the value of V and that the values of HV and ΔT increase for a constant G. The values of λ²V, λΔT and ΔTV^?0.5 were determined by using the values of λ, ΔT and V. The results obtained in the present work have been compared with those predicted by the Jackson–Hunt eutectic theory and with similar experimental results.     

Effects of the AlN nucleation layer thickness on the crystal structures of an AlN epilayer grown on the 6H-SiC substrate

The influence of the LT-AlN(NL) growth times on the mosaic structure parameters of the AlN layer grown on the LT-AlN(NL)/6H-SiC structures as well as the dislocation densities and the strain behaviours in the AlN epilayers has been investigated using XRD measurements. The growth times of the LT-AlN(NL) were changed to 0, 60, 120, 180, and 240?s. We observed that the mosaic structure parameters of the AlN epilayers were slightly affected by the LT-AlN(NL) growth times. However, the dislocation densities in the AlN layer are affected by the growth times of the LT-AlN(NL) layer. The highest edge dislocation density (5.48?×?10¹⁰?±?2.3?×?10⁹?cm^?2) was measured for the sample in which 120?s grown LT-AlN(NL) was used. On the other hand, highest screw type dislocation density (1.21?×?10¹⁰?±?1.7?×?10⁹?cm^?2) measured in the sample E that contains 240?s growth LT-AlN(NL). The strain calculation results show that the samples without LT-AlN(NL) suffered maximum compressive in-plane strain (?10.9?×?10^?3?±?1.8?×?10^?4), which can be suppressed by increasing the LT-AlN(NL) growth times. The out-of-plane strain also has a compressive character and its values increase with LT-AlN(NL) growth times between 60 and 180?s. Same out-of-plane strain values were measured for the LT-AlN(NL) growth times of 180 and 240?s. Furthermore, the form of the biaxial stress in the AlN epilayer changed from compressive to tensile when the LT-AlN(NL) growth times were greater than 120?s.     

Ab Initio Study on Hypothetical Silver Nitride

We perform the ab initio calculations based on norm-conserving pseudopotentials and density functional theory to investigate the structural, elastic, and thermodynamical properties for silver nitride （AgN） compound that is a member of the 4d transition metal group and has not been synthesized yet. The obtained results are compared with the other available theoretical data, and the agreement is, generally, quite good. We also present the pressure-dependent behaviour of some mechanical and thermodynamical properties for the same compounds.     

First-principles investigation of the structural,dynamical, electronic,and elastic properties of WGe2 and W5Ge3

ABSTRACT

We have investigated the structural, dynamical, elastic, and electronic properties of WGe₂ and W₅Ge₃ compounds in different phases. We have considered the C11_b (tetragonal, space group I4/mmm) and C23 (orthorhombic, space group Pnma) strukturbericht phases for WGe₂ compound and D8₁ (tetragonal, space group I4/mcm), D8_m (tetragonal space group I4/mcm) strukturbericht phases for W₅Ge₃ compound. The structural parameters, formation enthalpies, phonon dispersion curves, elastic constants, mechanical modulus, anisotropic factors, thermal conductivities, and electronic structures have been investigated using generalised gradient approximation within in the plane wave pseudopotential density functional theory. The calculated lattice constants are in a good agreement with the experimental data. The considered phases for WGe₂ and W₅Ge₃ compounds have a metallic character. The results indicated that all phases for compounds are both mechanically stable and dynamically stable except for W₅Ge₃-D8₁. The anisotropy in some mechanical modulus has been investigated using several elastic anisotropy indexes and directional dependence of compressibility, Young’s moduli, shear moduli, and Poisson’s ratio.