Elastic properties of GaxIn1−xP semiconductor

A theoretical procedure is presented for the study of elastic properties of the ternary alloy Ga_xIn_1−xP. The calculations are based on the pseudopotential formalism in which local potential coupled with the virtual crystal approximation (VCA) is applied to evaluate elastic constants c₁₁, c₁₂ and c₄₄, bulk modulus, shear modulus, Young's modulus and Poisson's ratio for the entire range of the alloy composition x of the ternary alloy Ga_xIn_1−xP. The effect of compositional disorder is included. Our results for parent compounds are compared to experimental and other theoretical calculations and showed generally good agreement. The inclusion of compositional disorder increases values of all elastic constants. During the present study it is found that elastic constant c₁₁ is largely influenced by compositional disorder.     

Application of Volterra and Wiener Theories for Nonlinear Parameter Estimation in a Rotor-Bearing System

Volterra and Wiener theories provide the concepts of linear,bilinear, tri-linear, etc., kernels, which upon convolution with theexcitation force, can be employed to represent the response of anonlinear system. Based on these theories, higher-order frequencyresponse functions (FRFs) are employed to estimate the nonlinearstiffness of rolling element bearings, supporting a rigid rotor. Therotor-bearing assembly is idealized as a single-degree-freedom system,with cubic nonlinearity. The analysis involves a third-order kernelrepresentation of the system response. The first and third-order kerneltransforms are extracted from the measurements of the appliedwhite-noise excitation and the resultant response. A third-order kernelfactor is synthesized from this first-order kernel and is processedalong with the third-order kernel for estimation of the nonlinearparameter. Damping is assumed to be linear in the analysis. Theprocedure is demonstrated through measurements on a laboratory test rig.     

Enantioselective formal hydration of α,β-unsaturated acceptors: asymmetric conjugate addition of silicon and boron nucleophiles

The direct enantioselective 1,4-addition of water to α,β-unsaturated acceptors is an open challenge in asymmetric catalysis. Enantioselective conjugate addition of either silicon or boron nucleophiles and subsequent enantiospecific oxidative degradation of the carbon-element bond represents, however, an attractive detour. A single extra step thereby enables an indirect enantiocontrolled construction of (in a broader sense) aldols from α,β-unsaturated carbonyl and carboxyl compounds. While that strategy had been obvious for a long time, it was recent stunning progress in transition metal-catalysed activation of interelement linkages that brought about the solution to that long-standing problem. A concise introduction of existing protocols for stereoselective 1,4-addition of oxygen nucleophiles is followed by a comprehensive summary of the recent rapid advances in transition metal-catalysed (and metal-free) asymmetric conjugate transfer of nucleophilic silicon and boron onto α,β-unsaturated acceptors.     

Measurement of transverse vibrations/visualization of mode shapes in square plate by using digital speckle pattern interferometry and wavelet transform

New filtering scheme is investigated and implemented on digital speckle pattern interferometric fringes to enhance the signal-to-noise ratio (SNR) in the speckle interferograms. To establish the potential of new filtering scheme the experiment was conducted on the vibrating cantilever beam. Experimental results revealed that the new filtering scheme is more powerful than other known filtering schemes (Kumar et al. Opt Laser Eng 2004;41:81–93. Kumar et al. Opt Laser Technol 2001;33:567–571. Shakher et al. Opt Eng 2002;41:176–180. Shakher et al. Proceedings ICICS, Singapore, 9–12 September 1997, p. 953–956. Bowler et al. Proceedings of IEE second international conference on image processing, London, 1986, p. 24–26. Lim. Opt Eng 1981;20:670–678. Devila et al. J Mod Opt 1995;42:1795–1804; Kaufmann et al. Opt Eng 1996;35:9–14). The new scheme reduced the speckle noise and improved SNR in speckle interferograms. Further, the new investigated filtering scheme is implemented to study the mode shapes of square plates under two different boundary conditions. In the first condition all the edges of the square plate were fixed while in the second condition two adjacent edges were fixed and the remaining two edges were free. From the experimental results it is clear that the mode shapes are more distinctly visible with the implementation of the new filtering scheme as compared to other known schemes. Under both the boundary conditions the recorded resonance frequencies were compared with the calculated values of resonance frequencies based on classical theory. The results obtained form DSPI show good agreement with classical theory.     

Electron spin resonance and kinetic study of the photolysis of p-Flouranil (tetrafluoro-p-benzoquinone) in dioxane

The photochemistry of p-fluoranil in dioxane was studied by electron spin resonance (ESR) and the ESR-rotating sector technique. The transient photoradical is identified as the p-tetrafluorobenzosemiquinone neutral radical with a hyperfine splitting of 1.1 gauss for the hydroxy proton and the fluorine hyperfine splittings of 3.8 and 14.1 gauss for the meta and ortho fluorines, respectively. The radicals decayed by self-disproportionation with a second-order rate constant at room temperature of approximately 3.2 × 10⁹M^?1s^?1. The activation energy of the decay process is found to be about 2.4 ± 0.4 kcal/mole.     

Ab initio quantum chemical investigation of intramolecular magnetic interaction in some diradical derivatives of imino nitroxide and nitronyl nitroxide

The magnetic properties of the monoradicals 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl (1) and 2-(4-phenyl acetylene)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide (2) and the diradicals 2,2'-(1,2-ethynediyldi-4,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl] (3), 2,2'-(1,2-ethynediyldi-4,1 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidozolyl-oxyl] (4), and 2,2'-(1,2-ethynediyldi-4,1 3,1-phenylene)bis[4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide] (5) are investigated by ab initio quantum chemical methods. The rule of spin alternation in the unrestricted Hartree-Fock (UHF) method clearly shows that the radical sites are antiferromagnetically coupled in 3 and ferromagnetically coupled in 4 and 5, which is consistent with a previous experiment. The molecular geometries are optimized at Hartree-Fock levels. This is followed by single-point calculations using the density functional (UB3LYP) treatment and the multiconfigurational complete active space self-consistent field (CASSCF) methodology. Magnetic exchange coupling constants are determined from the broken-symmetry approach. The calculated J values, -3.60 cm(-1) for 3, 0.16 cm(-1) for 4, and 0.67 cm(-1) for 5, are in excellent agreement with the observed values. Because of the very large size of the diradicals 3-5, the CASSCF (10,10) calculations cannot yield realistic J values. Nevertheless, the CASSCF calculations support the antiferromagnetic nature of the magnetic coupling in 3 and the ferromagnetic nature of the coupling in 4 and 5. The existence of an intramolecular magnetic coupling in 3-5 is also confirmed through computations of the isotropic hyperfine coupling constants for monoradicals 1 and 2 as well as diradicals 3-5.     

On weighted absolute convergence of multiple Fourier series of a function of $${(p_{1} ,\ldots,p_{N})}$$–$${(\Lambda^1 ,\ldots ,\Lambda^N)}$$(Λ1,…,ΛN)– BV

We obtain a sufficient condition for the weighted β-absolute convergence of the multiple Fourier series

$$\sum_{k_{1} \in\mathbb{Z}} \cdots \sum_{k_{N} \in\mathbb{Z}} \gamma_{k_{1} ,\ldots ,k_{N}} |\hat{f}(k_1 ,\ldots ,k_N)|^\beta,$$

where \({0 < \beta < 2}\) and \({\gamma_{k_{1} ,\ldots ,k_{N}}}\) is a weight sequence, of a function f of the class \({(\Lambda^1 ,\ldots ,\Lambda^N)BV^{(p_{1} ,\ldots ,p_{N})}([0, 2\pi]^N)}\).