Rapid Water Reduction to H_2 Catalyzed by a Cobalt Bis(iminopyridine) Complex

A cobalt bis(iminopyridine) complex is a highly active electrocatalyst for water reduction, with an estimated apparent second order rate constant k_(app) ≤ 10^7 M^(–1)s^(–1) over a range of buffer/salt concentrations. Scan rate dependence data are consistent with freely diffusing electroactive species over pH 4–9 at room temperature for each of two catalytic reduction events, one of which is believed to be ligand based. Faradaic H_2 yields up to 87 ± 10% measured in constant potential electrolyses (−1.4 V vs SCE) confirm high reactivity and high fidelity in a catalyst supported by the noninnocent bis(iminopyridine) ligand. A mechanism involving initial reduction of Co^(2+) and subsequent protonation is proposed

Growth of Intermediate-Mass Black Holes in Globular Clusters

We present results of numerical simulations of sequences of binary-single scattering events of black holes in dense stellar environments. The simulations cover a wide range of mass ratios from equal mass objects to 1000:10:10 solar masses and compare purely Newtonian simulations to simulations in which Newtonian encounters are interspersed with gravitational wave emission from the binary. In both cases, the sequence is terminated when the binary's merger time due to gravitational radiation is less than the arrival time of the next interloper. We find that black hole binaries typically merge with a very high eccentricity (0.93 < e < 0.95 pure Newtonian; 0.85 < e < 0.90 with gravitational wave emission) and that adding gravitational wave emission decreases the time to harden a binary until merger by ~ 30% to 40%. We discuss the implications of this work for the formation of intermediate-mass black holes and gravitational wave detection.Comment: 28 pages including 9 figures, submitted to Ap

Network ST radar and related measurements at Pennsylvania State University

Mesoscale meteorological measurements, analysis and prediction are some of the principal areas of research in the Department of Meteorology at Penn State. In anticipation of a staged turn-on of the three systems during the Summer and Fall of 1984, the nonconstruction-related efforts have focused on the software development necessary to allow essentially immediate use of network data. A 16-bit microcomputer has been programmed to serve as the network controller, communications interface and, at least for real-time purposes, the operational display system. Insofar as possible we have in this task built upon our substantial accumulated experience in working with the processing and display of Doppler sodar system signals. Once the radar-derived wind and turbulence profiles are communicated to the various interconnected Departmental computers they become just one component of a comprehensive data base which can be applied to a diverse set of ongoing basic and operational research programs

The Day After Tomorrows Doctors: UK Undergraduate Medical Student Resilience, Reports on the Symposium 2016

There is growing evidence that students and qualified doctors’ are experiencing high levels of workplace stress and burnout. Many medical students find student training and subsequently the transition to foundation year difficult. Medical schools have been tasked by the GMC to teach personal resilience as part of professional development. Despite this responsibility, it is far from clear whether medical schools have in fact integrated topics such as stress management, resilience training and self-care into their professional development curriculum. As far as we can establish this is the first meeting of UK medical educators to specifically address this topic

Impact of upper-level jet-generated inertia-gravity waves on surface wind and precipitation

International audienceA meteorological case study for the impact of inertia-gravity waves on surface meteorology is presented. The large-scale environment from 17 to 19 December 1999 was dominated by a poleward breaking Rossby wave transporting subtropical air over the North Atlantic Ocean upward and north-eastward. The synoptic situation was characterized with an upper tropospheric jet streak passing Northern Europe. The unbalanced jet spontaneously radiated inertia-gravity waves from its exit region. Near-inertial waves appeared with a horizontal wavelength of about 200 km and an apparent period of about 12 h. These waves transported energy downwards and interacted with large-scale convection. This configuration is simulated with the nonhydrostatic Fifth-Generation Mesoscale Model. Together with simplified runs without orography and moisture it is demonstrated that the imbalance of the jet (detected with the cross-stream ageostrophic wind) and the deep convection (quantified with the latent heat release) are forcing inertia-gravity waves. This interaction is especially pronounced when the upper tropospheric jet is located above a cold front at the surface and supports deep frontal convection. Weak indication was found for triggering post-frontal convection by inertia-gravity waves. The realism of model simulations was studied in an extended validation study for the Baltic Sea region. It included observations from radar (DWDPI, BALTRAD), satellite (GFZGPS), weather stations (DWDMI) and assimilated products (ELDAS, MESAN). The detected spatio-temporal patterns show wind pulsations and precipitation events at scales corresponding to those of inertia-gravity waves. In particular, the robust features of strong wind and enhanced precipitation near the front appeared with nearly the same amplitudes as in the model. In some datasets we found indication for periodic variations in the post-frontal region. These findings demonstrate the impact of upper tropospheric jet-generated inertia-gravity waves on the dynamics of the boundary layer. It also gives confidence to models, observations and assimilation products for covering such processes. In an application for the Gotland Basin in the Baltic Sea, the implications of such mesoscale events on air-sea interaction and energy and water budgets are discussed

Fe-mediated HER vs N_2RR: Exploring Factors that Contribute to Selectivity in P_3^EFe(N_2) (E = B, Si, C) Catalyst Model Systems

Mitigation of the hydrogen evolution reaction (HER) is a key challenge in selective small molecule reduction catalysis. This is especially true of catalytic nitrogen (N_2) and carbon dioxide (CO_2) reduction reactions (N_2RR and CO_2RR, respectively) using H^+/e• currency. Here we explore, via DFT calculations, three iron model systems, P_3^EFe (E = B, Si, C), known to mediate both N_2RR and HER, but with different selectivity depending on the identity of the auxiliary ligand. It is suggested that the respective efficiencies of these systems for N_2RR trend with the predicted N–H bonds strengths of two putative hydrazido intermediates of the proposed catalytic cycle, P_3^EFe(NNH_2)^+ and P_3^EFe(NNH_2). Further, a mechanism is presented for undesired HER consistent with DFT studies, and previously reported experimental data, for these systems; bimolecular proton-coupled-electron-transfer (PCET) from intermediates with weak N–H bonds is posited as an important source of H_2, instead of more traditional scenarios that proceed via metal hydride intermediates and proton transfer/electron transfer (PT/ET) pathways. Wiberg bond indices provide additional insight into key factors related to the degree of stabilization of P_3^EFe(NNH_2) species, factors that trend with overall product selectivity

The calibration of photographic and spectroscopic films: Reciprocity failure and thermal responses of IIaO film at liquid nitrogen temperatures

Reciprocity failure was examined for IIaO spectroscopic film. The results indicate reciprocity failure occurs at three distinct minimum points in time; 15 min, 30 min and 90 min. The results are unique because theory suggests only one minimum reciprocity failure point should occur. When incubating 70mm IIaO film for 15 and 30 min at temperatures of 30, 40, 50, and 60 C and then placing in a liquid nitrogen bath at a temperature of -190 C the film demonstrated an increase of the optical density when developed at a warm-up time of 30 min. Longer warm-up periods of 1, 2 and 3 hrs yield a decrease in optical density of the darker wedge patterns; whereas, shorter warm-up times yield an overall increase in the optical densities

Hydrogenolysis of [PhBP_3]Fe≡N-p-tolyl: Probing the Reactivity of an Iron Imide with H_2

This paper describes the reductive hydrogenolysis of a low-spin (S = 1/2) iron(III) imide. Pseudotetrahedral [PhBP_3]Fe^(III)≡N-p-tolyl is reduced by hydrogen at ambient temperature and pressure in benzene solution. The reduction appears to proceed in a stepwise fashion. An intermediate S = 2 iron(II) anilide, [PhBP_3]Fe(N(H)-p-tolyl), is observed and has been independently generated and structurally characterized. Prolonged hydrogenolysis in benzene results in the complete hydrogenolysis of the Fe−N linkage to release H2N-p-tolyl. The major iron-containing product formed from this step is the diamagnetic cyclohexadienyl complex, [PhBP_3]Fe(η^5-cyclohexadienyl), which has also been independently prepared and structurally characterized. Evidence is presented to suggest that the final [PhBP_3]Fe(η^5-cyclohexadienyl) product is formed via benzene insertion into a reactive [PhBP_3]Fe^(II)-H intermediate

Enhanced Ammonia Oxidation Catalysis by a Low-Spin Iron Complex Featuring Cis Coordination Sites

The goal of using ammonia as a solar fuel motivates the development of selective ammonia oxidation (AO) catalysts for fuel cell applications. Herein, we describe Fe-mediated AO electrocatalysis with [(bpyPy₂Me)Fe(MeCN)₂]²⁺, exhibiting the highest turnover number (TON) reported to date for a molecular system. To improve on our recent report of a related iron AO electrocatalyst, [(TPA)Fe(MeCN)₂]²⁺ (TON of 16), the present [(bpyPy₂Me)Fe(MeCN)₂]²⁺ system (TON of 149) features a stronger-field, more rigid auxiliary ligand that maintains cis-labile sites and a dominant low-spin population at the Fe(II) state. The latter is posited to mitigate demetalation and hence catalyst degradation by the presence of a large excess of ammonia under the catalytic conditions. Additionally, the [(bpyPy₂Me)Fe(MeCN)₂]²⁺ system exhibits a substantially faster AO rate (ca. 50×) at significantly lower (∼250 mV) applied bias compared to [(TPA)Fe(MeCN)₂]²⁺. Electrochemical data are consistent with an initial E₁ net H-atom abstraction step that furnishes the cis amide/ammine complex [(bpyPy₂Me)Fe(NH₂)(NH₃)]²⁺, followed by the onset of catalysis at E₂. Theoretical calculations suggest the possibility of N–N bond formation via multiple thermodynamically plausible pathways, including both reductive elimination and ammonia nucleophilic attack. In sum, this study underscores that Fe, an earth-abundant metal, is a promising metal for further development in metal-mediated AO catalysis by molecular systems