Palladium-catalyzed alkoxycarbonylation of (Z)-2-en-4-yn carbonates leading to 2,3,5-trienoates

Pd(0)-catalyzed carbonylation of (Z)-2-en-4-yn carbonates in the presence of a balloon pressure of CO in an alcohol donates vinylallenyl esters with an exclusively E-configuration and in high yields. The fact that no such reactivity could be observed with E-configured enyne carbonates may indicate that the reaction is promoted via the cooperative coordination of palladium with both alkynyl and carbonate moieties.     

Evaluating Mohr–Coulomb yield criterion for plastic flow in model metallic glasses

The yielding of metallic glasses (MGs) is generally considered to be dependent on pressure or normal stress, which is usually described by the Mohr–Coulomb yield criterion. Experimentally, the orientation of the shear band angle or fracture angles in MG is roughly 40° to 42° in uniaxial compression and 50° to 59° in uniaxial tension, both with respect to the loading direction. However, the amounts of deviation from the maximum shear stress direction (45°) under uniaxial tension and compression are quite different, which seems to be inconsistent with the Mohr–Coulomb yield criterion. Here we carried out molecular dynamics simulations to study the incipient plasticity of model Dzugutov glasses subjected to various uniaxial and biaxial stress states. The yield points are defined as the sharp rise of the population of atoms participating in non-affine deformations, in addition to the traditional offset method. The yield surfaces thus created agree well with the Mohr–Coulomb yield criterion. Furthermore, the orientations of the embryonic shear bands (instead of the fully-grown shear bands, or fracture planes) are measured, which also follow predictions based on the Mohr–Coulomb criterion. Our simulation results call for orientational measurement of incipient shear bands in experiments to critically examine the Mohr–Coulomb yield criterion in MG systems.     

Fabrication and Characterization of Monolithically Fused Wavelength-Independent 1 × 4 Couplers

A new method for the fabrication of a monolithic 1 × 4 single-mode fused coupler is described together with details of its performance in terms of coupling ratio, spectral response and polarization sensitivity. The fabricated device exhibits ultra-broadband performance with low polarization dependent loss. The coupling pattern exhibits identical coupling to all interacting fibers, enabling an easy control on fabrication parameters of the device.     

Analytical sequences of upper and lower solutions for a class of elliptic equations

Comparison arguments are applied to derive decreasing sequences of upper solutions and increasing sequences of lower solutions for a class of nonlinear elliptic equations. The monotonicity of the two sequences is proven. These polynomial sequences are obtained by applying new algorithms and solving linear differential equations. The obtained upper and lower solutions are analytic and have closed forms. Different examples are presented to explore the effectiveness of the new algorithms. The presented ideas and algorithms can be extended to deal with different classes of equations.     

Selective reagents for solvent extraction of metals—II. Bis-quinaldic acids

Bis-quinoline-2-carboxylic acids in which the quinoline rings were joined via ether linkages to the 8-position have been synthesized and tested for metal extraction. The reagents extracted Cu²⁺ and Zn²⁺ selectively in the presence of Fe²⁺ and Fe³⁺ from aqueous sulphate solution.     

Blue and near-UV phosphorescence from iridium complexes with cyclometalated pyrazolyl or N-heterocyclic carbene ligands

Two approaches are reported to achieve efficient blue to near-UV emission from triscyclometalated iridium(III) materials related to the previously reported complex, fac-Ir(ppz)(3) (ppz = 1-phenylpyrazolyl-N,C(2)'). The first involves replacement of the phenyl group of the ppz ligand with a 9,9-dimethyl-2-fluorenyl group, i.e., fac-tris(1-[(9,9-dimethyl-2-fluorenyl)]pyrazolyl-N,C(2)')iridium(III), abbreviated as fac-Ir(flz)(3). Crystallographic analysis reveals that both fac-Ir(flz)(3) and fac-Ir(ppz)(3) have a similar coordination environment around the Ir center. The absorption and emission spectra of fac-Ir(flz)(3) are red shifted from those of fac-Ir(ppz)(3). The fac-Ir(flz)(3) complex gives blue photoluminescence (PL) with a high efficiency (lambda(max) = 480 nm, phi(PL) = 0.38) at room temperature. The lifetime and quantum efficiency were used to determine the radiative and nonradiative rates (1.0 x 10(4) and 2.0 x 10(4) s(-1), respectively). The second approach utilizes N-heterocyclic carbene (NHC) ligands to form triscyclometalated Ir complexes. Complexes with two different NHC ligands, i.e., iridium tris(1-phenyl-3-methylimidazolin-2-ylidene-C,C(2)'), abbreviated as Ir(pmi)(3), and iridium tris(1-phenyl-3-methylbenzimidazolin-2-ylidene-C,C(2)'), abbreviated as Ir(pmb)(3), were both isolated as facial and meridianal isomers. Comparison of the crystallographic structures of the fac- and mer-isomers of Ir(pmb)(3) with the corresponding Ir(ppz)(3) isomers indicates that the imidazolyl-carbene ligand has a stronger trans influence than pyrazolyl and, thus, imparts a greater ligand field strength. Both fac-Ir(pmi)(3) and fac-Ir(pmb)(3) complexes display strong metal-to-ligand-charge-transfer absorption transitions in the UV (lambda = 270-350 nm) and phosphoresce in the near-UV region (E(0)(-)(0) = 380 nm) at room temperature with phi(PL) values of 0.02 and 0.04, respectively. The radiative decay rates for fac-Ir(pmi)(3) and fac-Ir(pmb)(3) (5 x 10(4) s(-1) and 18 x 10(4) s(-1), respectively) are somewhat higher than that of fac-Ir(flz)(3), but the nonradiative rates are two orders of magnitude faster (i.e., (2-4) x 10(6) s(-1)).     

On the protonation equilibria of sephadex C-25 and C-50

The system H(+)Na(+) has been studied on Sephadex C-25 and C-50 at two ionic strengths by potentiometry. The data have been fitted by the H?gfeldt three-parameter model. For ionic strength 0.100 M (Na)ClO(4) an excellent fit is obtained with a standard deviation of +/-0.013 for both gels. For ionic strength 0.010 M (Na)ClO(4) a satisfactory fit could only be obtained by excluding the lowest and highest pH-value for each gel.     

Total synthesis and selective activity of a new class of conformationally restrained epothilones

Stereoselective total syntheses of two novel conformationally restrained epothilone analogues are described. Evans asymmetric alkylation, Brown allylation, and a diastereoselective aldol reaction served as the key steps in the stereoselective synthesis of one of the two key fragments of the convergent synthetic approach. Enzyme resolution was employed to obtain the second fragment as a single enantiomer. The molecules were assembled by esterification, followed by ring-closing metathesis. In preliminary cytotoxicity studies, one of the analogues showed strong and selective growth inhibitory activity against two leukemia cell lines over solid human tumor cell lines. The precise biological mechanism of action and high degree of selectivity of this analogue remain to be examined.     

Evolutionary algorithm-based PID controller tuning for nonlinear quarter-car electrohydraulic vehicle suspensions

The basic challenge associated with the design of vehicle suspension system is the attainment of an optimal trade-off between the various design objectives. This study presents the design of proportional-integral-derivative (PID) controller for a quarter-car active vehicle suspension system (AVSS) using evolutionary algorithms (EA) such as the particle swarm optimization (PSO), genetic algorithm (GA) and differential evolution (DE). Each of the EA-based PID controllers showed overall improvement in suspension travel, ride comfort, settling time and road holding from the manually tuned controller and the passive vehicle suspension system. These improvements were, however, achieved at the cost of increased actuator force, power consumption and spool-valve displacement. DE-optimized PID control resulted in the best minimized suspension performance, followed by the GA and PSO, respectively. Frequency-domain analysis showed that all the signals were attenuated within the whole body vibration frequency range and the EA-optimized controllers had RMS frequency weighted body acceleration of the vehicle within allowable limits for vibration exposure. Robustness analysis of the DE-optimized PID-controlled AVSS to model uncertainties is carried out in the form of variation in vehicle sprung mass loading, tyre stiffness and speed.