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An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The resonant tunneling diode (RTD) with mesoscopic double barrier structure has recently been employed to implement compact and versatile cellular neural/nonlinear networks (CNN's) by exploiting its unique folded-back non-linear I-V and C-V characteristics. This paper describes the design of a 128/spl times/128 RTD-based CNN along with the design of feed-forward and feedback templates for executing several commonly used image processing functions. In order to verify the image processing functions of RTD-based CNN's, full-array circuit simulations have been performed by using the quantum spice simulator that was designed at the University of Michigan. Unlike some previous designs that employed imprecise PWL model of the RTD, the RTD is represented as an internal component in the quantum spice simulator by a rigorously derived and accurate physics-based model. Due to the nano-scale quantum well defined by the double barrier structure, RTD has quantized states within the quantum well while outside the well electron energy is given by the Fermi-Dirac distribution function. Hence, the I-V and C-V characteristics of the RTD have been derived from the self-consistent solution of the Schrodinger and the Poisson's equations. The stability and settling time of the RTD-based CNN arrays are also described in this paper.
We present a cosmological analysis of the Lick Observatory Supernova Search (LOSS) Type Ia supernova (SN Ia) photometry sample introduced by Ganeshalingam et al. (2010). These SNe provide an effective anchor point to estimate cosmological parameters when combined with datasets at higher redshift. The data presented by Ganeshalingam et al. (2010) have been rereduced in the natural system of the KAIT and Nickel telescopes to minimise systematic uncertainties. We have run the light-curve-fitting software SALT2 on our natural-system light curves to measure light-curve parameters for LOSS light curves and available SN Ia datasets in the literature. We present a Hubble diagram of 586 SNe in the redshift range z=0.01-1.4 with a residual scatter of 0.176 mag. Of the 226 low-z objects in our sample, 91 objects are from LOSS, including 45 SNe without previously published distances. Assuming a flat Universe, we find that the best fit for the dark energy equation-of-state parameter w = -0.86^+0.13_-0.16 (stat) +- 0.11 (sys) from SNe alone, consistent with a cosmological constant. Our data prefer a Universe with an accelerating rate of expansion with 99.999% confidence. When looking at Hubble residuals as a function of host-galaxy morphology, we do not see evidence for a significant trend, although we find a somewhat reduced scatter in Hubble residuals from SNe residing within a projected distance < 10 kpc of the host-galaxy nucleus (\sigma = 0.156 mag). We find that Hubble residuals do not correlate with the expansion velocity of Si II \lambda 6355 measured in optical spectra near maximum light. Our data are consistent with no presence of a local "Hubble bubble." Improvements in cosmological analyses within low-z samples can be achieved by better constraining calibration uncertainties in the zero points of photometric systems.
Conventional storage of large amounts of hydrogen in its molecular form is difficult and expensive because it requires employing either extremely high pressure gas or very low temperature liquid. Because of the importance of hydrogen as a fuel, the DOE has set system targets for hydrogen storage of gravimetric (5.5 wt%) and volumetric (40 g/L) densities to be achieved by 2015. From our continuous efforts on hydrogen storage, it is believed that metalation of highly porous solids with high-valence metals is promising and provides a rational direction to realize high volumetric hydrogen density near room temperature. This grant was focused on the study of high surface area covalent organic frameworks (COFs) with these specific objectives (1) to introduce potential metal binding sites through the COF synthesis and (2) to implement metalation experiments and evaluate their respective hydrogen adsorption properties. To maximize our efforts, simulation calculations were also performed (prior to experiments) for the prediction of binding enthalpy of hydrogen for molecular building units containing transition metals and promising COF structures to increase volumetric hydrogen uptake at room temperature. In this effort, first molecular building units with optimal binding energy for hydrogen storage (20 kJ/mol) were designed by quantum mechanical (QM) methods. Employing these results, it was revealed that one of metalated COFs takes up 60 g/L (total) of H2 at 100 bar and 298 K. To realize proposed COF structures, chemistry of COF synthesis has been developed; for instance, new air stable COFs were synthesized via hydrazone (COF-41 to 43) and imine condensation (COF-301, 320, 340, and 366) and some of them were tested the effect on metalation. Finally, a new triazine COF with high volumetric hydrogen uptake capacity was presented as a proposed future direction.
Metallic glasses are commonly found to favor denser packing structures and icosahedral order in experiments, simulations, and theoretical models. Here we present a molecular dynamics simulation study of Cu-Zr metallic glasses, prepared through a pressure-mediated pathway. The resulting glasses exhibit anomalous structure-property relationships; these glasses are less energetically stable, concomitant with a denser atomic packing and a significant increase in icosahedral short-range order. The enhanced icosahedral order is shown to be accompanied by a pressure-mediated change in chemical short-range order. The results demonstrate that in amorphous alloys (nonmonatomic), theoretical frameworks of the two-order-parameter model must be generalized to account for chemical degrees of freedom.
This report presents results of a two year research program to study damage mechanisms associated with high-temperature, high-pressure, hydrogen service (i.e., coal conversion applications) and affecting metallurgical stability and mechanical properties, in particular, fatigue crack propagation and creep rupture properties, of weld metal and heat affected zone (HAZ) regions in thick section weldments in two Cr-Mo steels, namely 3Cr-1-1/2Mo-1/2Ni steel, hereafter referred to as Berkeley steel, and 3Cr-1Mo-1/4V-Ti-B, referred to as JSW (Japan Steel Works) steel. In addition, suggestions on how microstructures might be modified to avoid such damage are discussed. As base metal tests on specimens from laboratory-sized heats had shown good resistance to environmentally-induced damage, the objective of the work was to discern whether such properties could be maintained in thick-section weldments in materials taken from relatively large (commercial size) heats. Both materials, in the PWHT/undamaged state, exhibited identical fatigue crack growth behavior above approx.10/sup -6/ mm/cycle. At near-threshold levels, the JSW steel displayed marginally lower growth rates and a higher threshold stress intensity, ..delta..K/sub TH/. When PWHT materials were exposed to environmentally-induced damage (i.e., high temperature/high pressure hydrogen), little effect was observed on fatigue propagation behavior at both near-threshold and higher growth rates. 72 refs., 41 figs.,more » 13 tabs.« less
