Dynamics and Thermodynamics of a Novel Phase of NaAlH4

We characterize a novel orthorhombic phase (gamma) of NaAlH4, discovered using first-principles molecular dynamics, and discuss its relevance to the dehydrogenation mechanism. This phase is close in energy to the known low-temperature structure and becomes the stabler phase above 320 K, thanks to a larger vibrational entropy associated with AlH4 rotational modes. The structural similarity of gamma-NaAlH4 to alpha-Na3AlH6 suggests it acts as a key intermediate during hydrogen release. Findings are consistent with recent experiments recording an unknown phase during dehydrogenation.Comment: 10 pages, 4 figures, 1 table + supplementary info; In press (Physical Review Letters

RECREATIONAL MUSIC-MAKING IN MUSIC PEDAGOGY: A MANIFESTO FOR CHANGE

The arts are an essential part of any student’s well rounded education. The future of music in education will depend on its ability to deliver relevant, effective, and measurable outcomes. However, the expectations and performance nature of traditional curricula often foster a sense of musical elitism and ostracizes students that are solely interested in music as a recreational outlet. Incorporating recreational music-making into education can provide opportunities for students to experience self-expression, creativity, social connection, and enjoyment. These values will not only enhance their education, but also lead to acquired skills for use in all areas of their lives. Activities such as drum circles, for example, break down the musical elitism that has been reenforced through barriers of economy (purchasing instruments), technique (learning a required skill set), and language (learning to read music). This document will establish a case for recreational music-making in education through examination of the role of music education, the concept of recreational musicmaking, and the numerous health and wellness benefits associated with recreational music-making. Included will be a discussion of elementary, secondary, and higher education music curricula. Additionally, the importance of using percussion instruments will be established along with explanations of basic techniques. Finally, a discourse about the language barrier in music is included. The intended results of this document include creating an educated audience for music professionals, a larger presence of music-making in society, music advocacy and support, improved creativity and self-expression for professional and amateur musicians, strengthened community connections, and an overall improvement in health and well-being for music participants

Assessing carbon-based anodes for lithium-ion batteries: A universal description of charge-transfer binding

Many key performance characteristics of carbon-based lithium-ion battery anodes are largely determined by the strength of binding between lithium (Li) and sp2 carbon (C), which can vary significantly with subtle changes in substrate structure, chemistry, and morphology. Here, we use density functional theory calculations to investigate the interactions of Li with a wide variety of sp2 C substrates, including pristine, defective, and strained graphene; planar C clusters; nanotubes; C edges; and multilayer stacks. In almost all cases, we find a universal linear relation between the Li-C binding energy and the work required to fill previously unoccupied electronic states within the substrate. This suggests that Li capacity is predominantly determined by two key factors -- namely, intrinsic quantum capacitance limitations and the absolute placement of the Fermi level. This simple descriptor allows for straightforward prediction of the Li-C binding energy and related battery characteristics in candidate C materials based solely on the substrate electronic structure. It further suggests specific guidelines for designing more effective C-based anodes. The method should be broadly applicable to charge-transfer adsorption on planar substrates, and provides a phenomenological connection to established principles in supercapacitor and catalyst design.Comment: accepted by Physical Review Letter

Assessment of CFD Hypersonic Turbulent Heating Rates for Space Shuttle Orbiter

Turbulent CFD codes are assessed for the prediction of convective heat transfer rates at turbulent, hypersonic conditions. Algebraic turbulence models are used within the DPLR and LAURA CFD codes. The benchmark heat transfer rates are derived from thermocouple measurements of the Space Shuttle orbiter Discovery windward tiles during the STS-119 and STS-128 entries. The thermocouples were located underneath the reaction-cured glass coating on the thermal protection tiles. Boundary layer transition flight experiments conducted during both of those entries promoted turbulent flow at unusually high Mach numbers, with the present analysis considering Mach 10{15. Similar prior comparisons of CFD predictions directly to the flight temperature measurements were unsatisfactory, showing diverging trends between prediction and measurement for Mach numbers greater than 11. In the prior work, surface temperatures and convective heat transfer rates had been assumed to be in radiative equilibrium. The present work employs a one-dimensional time-accurate conduction analysis to relate measured temperatures to surface heat transfer rates, removing heat soak lag from the flight data, in order to better assess the predictive accuracy of the numerical models. The turbulent CFD shows good agreement for turbulent fuselage flow up to Mach 13. But on the wing in the wake of the boundary layer trip, the inclusion of tile conduction effects does not explain the prior observed discrepancy in trends between simulation and experiment; the flight heat transfer measurements are roughly constant over Mach 11-15, versus an increasing trend with Mach number from the CFD

Exploring kinetics and thermodynamics in fast-ion conductors and hydrogen-storage materials using ab-initio molecular dynamics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references (p. 173-190).We investigate the interplay between various kinetic processes and thermodynamic factors in three materials--silver iodide (AgI), cesium hydrogen sulfate (CsHSO4), and sodium alanate (NaAlH4)-using ab-initio molecular dynamics simulations. The time-averaged and instantaneous silver substructure in the fast-ion conductor AgI is analyzed, resulting in a set of ordering rules that govern the distribution of the mobile silvers in the first coordination shell surrounding an iodine. We find evidence of an independent phase transition of the silver ions which drives the structural transformation to the high-mobility phase. A thermodynamic motivation for the existence of fast-ion conduction is suggested in terms of an entropic stabilization associated with the decrease in silver mobility upon melting. We also find a unique chemical signature for the fourth nearest-neighbor silver to an iodine. This fourth silver is weakly bound and relatively unconstrained, and we isolate it as the predominant agent in the diffusion process. Next, a detailed statistical analysis is performed on simulations of the fuel-cell electrolyte CsHSO4 to isolate the interplay between the dynamics of the O-H chemical bonds, the ... H hydrogen bonds, and the SO4 tetrahedra in promoting proton conduction. A high reversal rate limits the apparent success rate of the otherwise rapid chemical-bond dynamics, which are dominated by the Grotthuss mechanism of proton transfer. Rapid angular hops in concert with small reorientations of the SO4 tetrahedra constitute a new dominant mechanism for hydrogen-bond network reorganization. The SO4 dynamics are found to control the attempt rate of chemical-bond dynamical events and the success rate of hydrogen-bond dynamical events; this enables a novel interpretation of the diminished CsHSO4/CsDSO4 isotope effect.(cont.) Two distinct timescales for SO4 reorientation events are linked to different diffusion mechanisms along different crystal directions. Finally, a graph-theoretic analysis of the hydrogen-bond network topology demonstrates an increased likelihood for diffusion in connectivity configurations favoring linear network chains over closed rings. We have discovered and characterized a new phase (-y) of the hydrogen-storage material NaAlH4 that is energetically close to the known ground state. The manifestation of this phase is kinetically inhibited in the bulk but is favored in a (001) surface slab above 225 K. The transition involves first activating the surface AlH4 rotational modes. This is followed by a lattice expansion perpendicular to the slab and a shear of successive lattice planes. A possible connection between 7-NaAlH4 and the dehydrogenation product Na3aAH6 is suggested. We also show that hydrogen transport in NaAlH4 can be treated independently from the observed phase transition, and that the presence of certain point defects can enable transport of hydrogen via a structural diffusion mechanism. A link between long-range hydrogen migration and the rotational mobility of A1Hz groups is demonstrated.by Brandon C. Wood.Ph.D

Environmental Stimulation Chamber for Nanosatellite Functional Testing

The goal of this project is to develop a nanosatellite thermal testing chamber for the Robotic Systems Laboratory at Santa Clara University. The nanosatellite industry has thrived in recent years and continues to grow at the level of universities and small businesses. To meet this demand, the team designed and built a testing bed capable of achieving environmental conditions adequate for testing nanosatellite hardware as a low-cost and low-maintenance alternative to more expensive and robust systems. Furthermore, the design can be fully manufactured and assembled at the university or small business level with inexpensive, sustainable, and commercially available components. The final product will save money and decrease energy consumption while fully realizing the thermal testing needs for nanosatellite communication hardware

An analysis method for conceptual design of complexity and autonomy in complex space system architectures

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics; and, (S.M.)--Massachusetts Institute of Technology, Technology and Policy Program, 2001.Includes bibliographical references (p. 97-99).by Brandon C. Wood.S.M

Industrial symbiosis: corn ethanol fermentation, hydrothermal carbonization, and anaerobic digestion

University of Minnesota M.S. thesis. December 2012. Major: Microbial Engineering. Advisor: Kenneth J. Valentas. 1 computer file (PDF); vii, 69 pages, appendices p. 50-69.The production of dry-grind corn ethanol results in the generation of intermediate products, thin and whole stillage, which require energy-intensive downstream processing for conversion into commercial co-products. Alternative treatment methods, specifically hydrothermal carbonization of thin and whole stillage coupled with anaerobic digestion were investigated to determine if they provide an opportunity to recover some of this value. By substantially eliminating evaporation of water, reductions in downstream energy consumption from 65-73% were achieved, while hydrochar, fatty acids, treated process water, and biogas co-products were generated, providing new opportunities for the industry. Processing whole stillage in this manner produced the four co-products, eliminated centrifugation and evaporation, and substantially reduced drying. With thin stillage, all co-products were again produced, as well as a high quality animal feed. Anaerobic digestion of the undiluted aqueous product stream from thin stillage hydrothermal carbonization reduced chemical oxygen demand (COD) in this product stream by more than 90% and converted 83% the initial COD to methane. Internal use of this biogas could entirely fuel the HTC process and reduce natural gas overall usage