The geology of the northeast quarter of the Powell, Ohio quadrangle

No embarg

Analysis of simulation methodology for calculation of the heat of transport for vacancy thermodiffusion

Computation of the heat of transport Q*(a) in monatomic crystalline solids is investigated using the methodology first developed by Gillan [J. Phys. C: Solid State Phys. 11, 4469 (1978)] and further developed by Grout and coworkers [Philos. Mag. Lett. 74, 217 (1996)], referred to as the Grout-Gillan method. In the case of pair potentials, the hopping of a vacancy results in a heat wave that persists for up to 10 ps, consistent with previous studies. This leads to generally positive values for Q*(a) which can be quite large and are strongly dependent on the specific details of the pair potential. By contrast, when the interactions are described using the embedded atom model, there is no evidence of a heat wave, and Q*(a) is found to be negative. This demonstrates that the dynamics of vacancy hopping depends strongly on the details of the empirical potential. However, the results obtained here are in strong disagreement with experiment. Arguments are presented which demonstrate that there is a fundamental error made in the Grout-Gillan method due to the fact that the ensemble of states only includes successful atom hops and hence does not represent an equilibrium ensemble. This places the interpretation of the quantity computed in the Grout-Gillan method as the heat of transport in doubt. It is demonstrated that trajectories which do not yield hopping events are nevertheless relevant to computation of the heat of transport Q*(a)

Atomic-scale simulation of the thermodiffusion of hydrogen in palladium

We report molecular-dynamics simulations of Pd:H to elucidate transport properties, with special focus placed on determining the temperature dependence of the heat of transport Q*. Simulation results are analyzed using the Green-Kubo approach. It is found that Q* describing the thermodiffusion of hydrogen increases linearly with temperature. By contrast, the reduced heat of transport Q*\u27 = Q* - h(2), with h(2) the partial enthalpy of hydrogen, is approximately temperature independent. By computing separately the potential, kinetic, and virial contributions to Q*, it is possible to understand key features of the thermodiffusion process. In particular, the sum of the kinetic and potential energy of hydrogen atoms is increased above that of an average hydrogen atom by an amount comparable to the migration energy during a successful hop. However, the virial term in the energy flux is less than what would be expected based on the average local stress contribution due to the hydrogen atoms. Detailed calculations show that the relevant component of the stress tensor due to a hopping hydrogen atom exhibits a minimum at the transition state. Hence, while Q* has significant positive contributions due to the excited nature of the hopping hydrogen atom, the reduced heat of transport Q*\u27 can still be negative. The results here present important insight into the failure of simple kinetic theories of thermodiffusion, and provide a new perspective that can be tested on other systems

Preserving Evolutionary History with Improved Confidence

We thank Faith (2019) and Mindell (2019) for their insightful perspectives on our study of the impact of phylogenetic imputation on the assessment of evolutionary distinctiveness (ED; Isaac et al., 2007). As Mindell highlights, the finding that ED scores for species on a phylogeny are remarkably robust despite having species missing from that phylogeny is encouraging; our results suggest that we can be confident in moving forward with prioritization of the species for which we have data. This is important because in some cases, for example, it may take considerable time to obtain samples from the missing species, resulting in further delay before the ED scores for those species already sampled can be used to inform management decisions. We cautioned, however, that the ED scores for those missing species may be imputed imprecisely, and so we gave guidelines for working with imputed species’ ED scores. With this in mind, we offer some additional thoughts resulting from the commentaries of Mindell and Faith

Primary Arthrodesis for Diabetic Ankle Fractures

A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author's publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.Background: Treatment of ankle fractures in patients with diabetes is associated with increased complication rates. Ankle arthrodesis is considered a salvage procedure after failed ankle fracture fixation, yet primary ankle arthrodesis has been proposed as a treatment option for patients with significant diabetes-related complications. To date, the characteristics of patients who undergo primary ankle arthrodesis and the associated outcomes have not been described. Methods: A retrospective review was performed of 13 patients with diabetes who underwent primary arthrodesis for traumatic ankle fracture. Patient demographics were characterized in addition to their diabetes complications, Adelaide Fracture in the Diabetic Ankle (AFDA) score, and fracture type. Outcomes assessed included reoperation rates, infection rates, wound complications, nonunion/malunion, amputation, and development of Charcot arthropathy postoperatively. Results: Patients who underwent primary arthrodesis had high rates of diabetes complications, average AFDA scores of 6.4, and high rates of severe injuries, including 38.5% open fractures and 69.2% fracture dislocations. The overall complication rate for primary arthrodesis of ankle fractures in diabetes patients was more than 75% in this cohort. Complications included a 38.5% reoperation rate, 38.5% infection rate, 53.8% wound complication rate, and 23.1% amputation rate. Despite a high nonunion rate at the attempted fusion sites, 89.9% of fractures healed and patients had a stable extremity. Conclusion: This review is the first to characterize the epidemiology and complications of diabetes patients undergoing primary ankle arthrodesis for ankle fractures. In this cohort, patients with multiple diabetic complications and severe injuries underwent primary arthrodesis, which led to an overall high complication rate. Further research is needed to determine the appropriate treatment option for these high-risk patients, and tibiotalocalcaneal stabilization without arthrodesis may be beneficial

Evaluation of two cockpit display concepts for civil tiltrotor instrument operations on steep approaches

A piloted simulation experiment was conducted using the NASA Ames Research Center Vertical Motion Simulator to evaluate two cockpit display formats designed for manual control on steep instrument approaches for a civil transport tiltrotor aircraft. The first display included a four-cue (pitch, roll, power lever position, and nacelle angle movement prompt) flight director. The second display format provided instantaneous flight path angle information together with other symbols for terminal area guidance. Pilots evaluated these display formats for an instrument approach task which required a level flight conversion from airplane-mode flight to helicopter-mode flight while decelerating to the nominal approach airspeed. Pilots tracked glide slopes of 6, 9, 15 and 25 degrees, terminating in a hover for a vertical landing on a 150 feet square vertipad. Approaches were conducted with low visibility and ceilings and with crosswinds and turbulence, with all aircraft systems functioning normally and were carried through to a landing. Desired approach and tracking performance was achieved with generally satisfactory handling qualities using either display format on glide slopes up through 15 degrees. Evaluations with both display formats for a 25 degree glide slope revealed serious problems with glide slope tracking at low airspeeds in crosswinds and the loss of the intended landing spot from the cockpit field of view