Long-range electron transfer in structurally engineered pentaammineruthenium (histidine-62) cytochrome c

In many biological processes, long-range electron transfer (ET) plays a key role. When the three-dimensional structures of proteins are accurately known, use of modified proteins and protein-protein complexes provides an experimental approach to study ET rates between two metal centers. For Ru(His)- modified proteins, the introduction of histidine residues at any desired surface location by site-directed mutagenesis opens the way for systematic investigations of ET pathways

Model-Based Ultrasonic NDE System Qualification Methodology

The use of computer models of ultrasonic NDE inspections is a convenient and cost-effective alternative and/or companion to experimental reliability trials used for qualifying the detection reliability of a given inspection system applied to a given inspection task. In addition, the use of such models permits qualification of ultrasonic inspection of new component designs even before such components exist. This paper presents the current status of the implementation of a model-based software package for these system qualification applications. A brief overview of the model elements and assumptions will be followed by a discussion of the detection system qualification methodology and, finally, by model-predicted qualification results with associated experimental data

Rotation and Macroturbulence in Metal-poor Field Red Giant and Red Horizontal Branch Stars

We report the results for rotational velocities, Vrot sin i, and macroturbulence dispersion, zeta(RT), for 12 metal-poor field red giant branch stars and 7 metal-poor field red horizontal branch stars. The results are based on Fourier transform analyses of absorption line profiles from high-resolution (R ~ 120,000), high-S/N (~ 215 per pixel) spectra obtained with the Gecko spectrograph at CFHT. We find that the zeta(RT) values for the metal-poor RGB stars are very similar to those for metal-rich disk giants studied earlier by Gray and his collaborators. Six of the RGB stars have small rotational values, less than 2.0 km/sec, while five show significant rotation, over 3 km/sec. The fraction of rapidly rotating RHB stars is somewhat lower than found among BHB stars. We devise two empirical methods to translate the line-broadening results obtained by Carney et al. (2003, 2008) into Vrot sin i for all the RGB and RHB stars they studied. Binning the RGB stars by luminosity, we find that most metal-poor field RGB stars show no detectable sign, on average, of rotation. However, the most luminous stars, with M(V) <= -1.5, do show net rotation, with mean values of 2 to 4 km/sec, depending on the algorithm employed, and these stars also show signs of radial velocity jitter and mass loss.Comment: accepted for publication in the Astronomical Journa

Solar fuels editorial

Every major change in the living standards for humans on our planet has had an energy revolution at its heart – the advent of the industrial age with the steam engine and use of coal, the internal combustion engine and large-scale electricity generation. The energy demand, primarily from emerging economies, will double by 2050. The countervailing urgency of the threat of climate change requires a major shift in our energy sourcing, creating four new trends that will shape the current century: electrification, decarbonization, localization, and optimization

Evaluation of Pt, Ni, and Ni–Mo electrocatalysts for hydrogen evolution on crystalline Si electrodes

The dark electrocatalytic and light photocathodic hydrogen evolution properties of Ni, Ni–Mo alloys, and Pt on Si electrodes have been measured, to assess the viability of earth-abundant electrocatalysts for integrated, semiconductor coupled fuel formation. In the dark, the activities of these catalysts deposited on degenerately doped p^+-Si electrodes increased in the order Ni < Ni–Mo ≤ Pt. Ni–Mo deposited on degenerately doped Si microwires exhibited activity that was very similar to that of Pt deposited by metal evaporation on planar Si electrodes. Under 100 mW cm^(−2) of Air Mass 1.5 solar simulation, the energy conversion efficiencies of p-type Si/catalyst photoelectrodes ranged from 0.2–1%, and increased in the order Ni ≈ Ni–Mo < Pt, due to somewhat lower photovoltages and photocurrents for p-Si/Ni–Mo relative to p-Si/Ni and p-Si/Pt photoelectrodes. Deposition of the catalysts onto microwire arrays resulted in higher apparent catalytic activities and similar photoelectrode efficiencies than were observed on planar p-Si photocathodes, despite lower light absorption by p-Si in the microwire structures

Modeling Ultrasonic Beam Propagation in Graphite Composites

A continuing project at the Center for NDE in Ames involves the development of models which predict the probability of detecting flaws using a given inspection system.[1] Our general approach as it applies to through-transmission immersion inspections is as follows. With the two transducers to be used in the inspection, a reference experiment is performed to determine relevant information concerning equipment characteristics and transducer efficiencies. This may be done by placing a calibration specimen into the ultrasonic beam and measuring the time-domain electrical signal in the output cable of the receiver. Using models, we then predict how this received electrical signal would be changed if the calibration specimen were removed and unflawed and flawed components were placed into the beam in turn. The two components are assumed to have identical geometries except for a hypothetical flaw of given type, size, and orientation. If the difference between the predicted output signals for the two components is sufficiently large, compared to system noise, then the hypothetical flaw is said to be detectable

Evaluation of Ultrasonic Beam Models for the Case fo a Piston Transducer Radiating Through A Liquid-Solid Interface

In order to accurately predict the performance of immersion ultrasonic inspection techniques, it is necessary to have a model for the transducer radiation process. This model should include the case of propagation of the ultrasonic beam at oblique incidence through liquid-solid interfaces of complex geometries. Included should be the effects of diffraction, refraction, focussing and aberrations upon the beam shape

Catalysis of Proton Reduction by a [BO_4]-Bridged Dicobalt Glyoxime

We report the preparation of a dicobalt compound with two singly proton-bridged cobaloxime units linked by a central [BO_4] bridge. Reaction of a doubly proton-bridged cobaloxime complex with trimethyl borate afforded the compound in good yield. Single-crystal X-ray diffraction studies confirmed the bridging nature of the [BO_4] moiety. Using electrochemical methods, the dicobalt complex was found to be an electrocatalyst for proton reduction in acetonitrile solution. Notably, the overpotential for proton reduction (954 mV) was found to be higher than in the cases of two analogous single-site cobalt glyoximes under virtually identical conditions

Catalytic hydrogen evolution from a covalently linked dicobaloxime

A dicobaloxime in which monomeric Co(III) units are linked by an octamethylene bis(glyoxime) catalyzes the reduction of protons from p-toluenesulfonic acid as evidenced by electrocatalytic waves at -0.4 V vs. the saturated calomel electrode (SCE) in acetonitrile solutions. Rates of hydrogen evolution were determined from catalytic current peak heights (k_(app) = 1100 ± 70 M^(-1) s^(-1)). Electrochemical experiments reveal no significant enhancement in the rate of H2 evolution from that of a monomeric analogue: The experimental rate law is first order in catalyst and acid consistent with previous findings for similar mononuclear cobaloximes. Our work suggests that H_2 evolution likely occurs by protonation of reductively generated Co^(II)H rather than homolysis of two Co^(III)H units