A new structural motif for photoinitiated electron collection: Ru,Rh bimetallics providing insight into H2 production via photocatalysis of water reduction by Ru,Rh,Ru supramolecules

Ru,Rh,Ru complexes are photocatalysts for the reduction of H(2)O to H(2)via a Rh(I) intermediate. The herein reported Ru,Rh bimetallics undergo PEC but do not catalyze the reduction of H(2)O, establishing intact supramolecules are photoactive in the Ru,Rh,Ru systems. The Ru,Rh(I) photoproduct dimerizes via Rh-Rh bond formation, deactivating the Rh(I) center sterically prohibited in the Ru,Rh,Ru trimetallic systems.     

2-microm Doppler lidar transmitter with high frequency stability and low chirp

A coherent Doppler lidar system was frequency stabilized in a master-slave configuration by a phase-modulation technique. The short-term frequency stability, ~0.2 MHz rms, was maintained in a vibrational environment on a ship during a field campaign in the tropical Pacific Ocean. The long-term frequency stability was <2.6 kHz/h. Thus, in many applications, shot-to-shot frequency correction can be disregarded, which will result in increased speed and simplicity of the data-acquisition system. A frequency chirp could not be detected. These properties permit Doppler wind measurements with high efficiency and duty cycles to be made, even on airborne and spaceborne platforms.     

Bipyrimidine-Bridged Mixed-Metal Trimetallic Complexes of Ruthenium(II) with Rhodium(III) or Iridium(III), {[(bpy)(2)Ru(bpm)](2)MCl(2)}(5+)

Bipyrimidine-bridged trimetallic complexes of the form {[(bpy)(2)Ru(bpm)](2)MCl(2)}(5+), where M = Rh(III) or Ir(III), bpy = 2,2'-bipyridine, and bpm = 2,2'-bipyrimidine, have been synthesized and characterized. These complexes are of interest in that they couple catalytically active rhodium(III) and iridium(III) metals with light-absorbing ruthenium(II) metals within a polymetallic framework. Their molecular composition is a light absorber-electron collector-light absorber core of a photochemical molecular device (PMD) for photoinitiated electron collection. The variation of the central metal has some profound effects on the observed properties of these complexes. The electrochemical data for the title trimetallics consist of a Ru(II/III) oxidation and sequential reductions assigned to the bipyrimidine ligands, Ir or Rh metal centers, and bipyridines. In both trimetallic complexes, the first oxidation is Ru based and the bridging ligand reductions occur prior to the central metal reduction. This illustrates that the highest occupied molecular orbital (HOMO) is localized on the ruthenium metal center and the lowest unoccupied molecular orbital resides on the bpm ligand. This bpm-based LUMO in {[(bpy)(2)Ru(bpm)](2)RhCl(2)}(5+) is in contrast with that observed for the monometallic [Rh(bpm)(2)Cl(2)](+) where the Rh(III)/Rh(I) reduction occurs prior to the bpm reduction. This orbital inversion is a result of bridge formation upon construction of the trimetallic complex. Both the Ir- and Rh-based trimetallic complexes exhibit a room temperature emission centered at 800 nm with tau = 10 ns. A detailed comparison of the spectroscopic, electrochemical, and spectroelectrochemical properties of these polymetallic complexes is described herein.     

Positive muon spin depolarization in quenched aluminium dilute alloys

Aluminum dilute alloys (Al-0.047 at% Mg, Al-0.052 at% Cu and Al-0.051 at% Si) were quenched from 600 and 450C. The positive muon behavior in the quenched alloys has been studied. Three peaks (Peak I, II and III) are found. Peak I is due to the trapping and detrapping of positive muons at single impurity atoms. The muon spin depolarization rate at the trap in Peak I was found to be 0.36sec^–1. Peak II is connected to impurity clusters. Peak III is the trapping of muons at quenched-in vacancies. The depolarization rate at the trapping site was found to be 0.2sec^–1. The activation energy of the trapping rate was found to be 25 meV. As the quenched-in vacancies annealed out, the trapping rates decreased to near zero.     

A note on the titration of lead chlorofluoride precipitates using the volhard method

Since it has been reported that a fading end-point is obtained when the Volhard method is used for the titration of lead chlorofluoride precipitates, a wide range of fluoride concentrations has been examined using this method. The effect of adding various reagents to bind the fluoride ion has been examined. Aluminium ions and boric acid have some effect, but that of ferric ions is the most pronounced.     

The effect of microstructural representation on simulations of microplastic ratcheting

This paper assesses the sensitivity of cyclic plasticity to microstructure morphology by examining and comparing the microplastic ratcheting behavior of different idealized microstructures (square, hexagonal, tessellated, and digitized from experimental data). This analysis demonstrates the sensitivity of computational accuracy to the various approximations in microstructural representation. The methodology used to perform this study relies on a coupling between microstructural characterization, mechanical testing and numerical simulations to investigate the influence of the microstructure on the purely tensile uniaxial microplastic ratcheting behavior of pure nickel polycrystals. The morphology and deformation behavior of polycrystals were characterized using electron back-scatter diffraction (EBSD), while a finite element model (FEM) of crystal plasticity was used in a computational framework. The predicted cyclic behavior is compared to experimental results both at the macroscopic and microstructural scales. The stress–strain response is less sensitive to the details of the microstructural representation than might be expected with all representations displaying similar macroscopic constitutive response. However, the details of the plastic strain distribution at the microstructural scale and the related estimations of damage mechanics vary substantially from one microstructural representation to another.     

Raman microscopy of a small uniaxial crystal: Tetragonal aspartame

A general method is presented for determining the shape and orientation of the Raman tensor of a molecule in a uniaxial crystal using a Raman microscope. First, equations are derived to connect the Raman tensor components (α_xx, α_yy, etc.) of a molecule to the Raman tensor components (α_aa, α_cc, etc.) of a crystal that is composed of molecules in a uniaxial arrangement, with an orientation specified by the two angles χ and θ. Next, a method is presented to obtain a correct set of values of the intensity ratios I_ac/I_aa and I_cc/I_aa from observed values of the intensity ratios measured with a Raman microscope. To augment the experimental data, the depolarization ratio ρ (for a completely random molecular orientation) is plotted as a function of r₁ = α_xx/α_zz and r₂ = α_yy/α_zz, so that a possible set of r₁ and r₂ values can be found from an observed value of ρ. The method has been applied to an aspartame IIA crystal (P4₁). A set of values of r₁, r₂, χ and θ has been determined for each of the following Raman fundamentals: 1741 cm⁻¹ (ester CO stretch), 1667 cm⁻¹ (amide I), 1275 cm⁻¹ (amide III) and 1204 cm⁻¹ (C C_phenyl stretch), excited at 488.0 nm.