Weber A.Z.,Lawrence Berkeley National Laboratory |
Borup R.L.,Los Alamos National Laboratory |
Darling R.M.,UTRC - United Technologies Research Center |
Das P.K.,Northumbria University |
And 13 more authors.
Journal of the Electrochemical Society | Year: 2014
Polymer-electrolyte fuel cells are a promising energy-conversion technology. Over the last several decades significant progress has been made in increasing their performance and durability, of which continuum-level modeling of the transport processes has played an integral part. In this review, we examine the state-of-the-art modeling approaches, with a goal of elucidating the knowledge gaps and needs going forward in the field. In particular, the focus is on multiphase flow, especially in terms of understanding interactions at interfaces, and catalyst layers with a focus on the impacts of ionomer thin-films and multiscale phenomena. Overall, we highlight where there is consensus in terms of modeling approaches as well as opportunities for further improvement and clarification, including identification of several critical areas for future research. © The Author(s) 2014. Published by ECS. All rights reserved. Source
Simpson S.,SUNY College of Technology at Alfred |
Hooper J.,Jagiellonian University |
Miller D.P.,State University of New York at Buffalo |
Kunkel D.A.,University of Nebraska - Lincoln |
And 2 more authors.
Journal of Physical Chemistry C | Year: 2016
First-principles calculations reveal that upon adsorption to the Cu(111) surface, the C-C single bonds within the p-benzoquinonemonoimine zwitterion (ZI) contract by about 6%. A detailed analysis reveals that the bond shortening is primarily a result of backdonation from Cu orbitals of s and d symmetry to the lowest unoccupied orbital (LUMO) of the ZI. This LUMO is π∗-antibonding across the molecule and π-bonding across the C-C bond that shortens. We illustrate that the level alignment between the Fermi level of the surface and the frontier molecular orbitals of the ZI, the topology of the LUMO, and the distance between the substrate and the adsorbate are important factors enabling bond strengthening via backdonation. An extended transition state-natural orbitals for chemical valence (ETS-NOCV) analysis is applied to molecular models for this system, and it confirms that the surface → LUMO backdonation on Cu(111) is larger than on Ag(111) and Au(111). (Chemical Equation Presented). © 2016 American Chemical Society. Source
Henry R.B.C.,University of Oklahoma |
Balick B.,University of Washington |
Dufour R.J.,Rice University |
Kwitter K.B.,Williams College |
And 5 more authors.
Astrophysical Journal | Year: 2015
The goal of the present study is twofold. First, we employ new HST/STIS spectra and photoionization modeling techniques to determine the progenitor masses of eight planetary nebulae (IC 2165, IC 3568, NGC 2440, NGC 3242, NGC 5315, NGC 5882, NGC 7662, and PB 6). Second, for the first time we are able to compare each object's observed nebular abundances of helium, carbon, and nitrogen with abundance predictions of these same elements by a stellar model that is consistent with each object's progenitor mass. Important results include the following: (1) the mass range of our objects' central stars matches well with the mass distribution of other central stars of planetary nebulae and white dwarfs; (2) He/H is above solar in all of our objects, in most cases likely due to the predicted effects of first dredge-up; (3) most of our objects show negligible C enrichment, probably because their low masses preclude third dredge-up; (4) C/O versus O/H for our objects appears to be inversely correlated, which is perhaps consistent with the conclusion of theorists that the extent of atmospheric carbon enrichment from first dredge-up is sensitive to a parameter whose value increases as metallicity declines; (5) stellar model predictions of nebular C and N enrichment are consistent with observed abundances for progenitor star masses ≤1.5 Mo. Finally, we present the first published photoionization models of NGC 5315 and NGC 5882. © 2015. The American Astronomical Society. All rights reserved.. Source
Buell J.F.,SUNY College of Technology at Alfred
Monthly Notices of the Royal Astronomical Society | Year: 2012
Thermally pulsing asymptotic giant branch models of globular cluster stars are calculated using a synthetic model with the goal of reproducing the chemical composition, core masses and other observational parameters of the four known globular cluster planetary nebulae as well as roughly matching the overall cluster properties. The evolution of stars with an enhanced helium abundance (Y) and blue stragglers are modelled. New pre-thermally pulsing asymptotic giant branch mass losses for red giant branch and early asymptotic giant branch stars are calculated from the Padova stellar evolution models. The new mass losses are calculated to get the relative differences in mass losses due to enhanced helium abundances. The global properties of the globular cluster planetary nebula are reproduced with these models. The metallicity, mass of the central star, overall metallicities, helium abundance and the nebular mass are matched to the observational values. Globular cluster planetary nebulae JaFu 1 and JaFu 2 are reproduced by assuming progenitor stars with masses near the typical main-sequence turn-offs of globular clusters and with enhanced helium abundances very similar to the enhancements inferred from fitting isochrones to globular cluster colour-magnitude diagrams. The globular cluster PN GJJC-1 can be roughly fitted by a progenitor star with very extreme helium enhancement (Y≈ 0.40) near the turn-off producing a central star with the same mass as inferred by observations and a very low nebular mass. The abundances and core mass of planetary nebula Ps 1 and its central star (K648) are reproduced by a blue straggler model. However, it turned out to be impossible to reproduce its nebular mass, and it is concluded some kind of binary scenario may be needed to explain K648. © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source
Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 30.00K | Year: 2013
The project is developing a multidisciplinary, multi-campus program minor in energy science, technology, and policy, through a unique regional partnership consisting of public and private four-year and two-year colleges. Project objectives include: 1) successful design and implementation of a multi-institution energy education program that is leveraging institutional academic strengths and access to student populations at the different campuses; 2) design of a program valuable for students in both technical (i.e. architecture, engineering, and science) and non-technical (i.e. business, accounting, and general studies) majors, at both two-year and four-year colleges; 3) enhancement of STEM learning through multidisciplinary curricula, experiential learning through
internships and research, and incorporation of stakeholder input in course and program development; and 4) recruitment and retention of students from underrepresented and underserved populations.
The project is enhancing collaboration with STEM education community and is helping to promote the two- to four-year college transition and beyond. By coordinating the program across multiple campuses, the project is facilitating articulation among institutions. Several of the schools involved have large populations of students traditionally underrepresented in STEM fields, and all have significant programs aimed at recruitment and retention. The project is working to increase participation from those groups significantly.