SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The formate dehydrogenase from Candida boidinii was combined with NH 2 -TEMPO to form a novel hybrid anode to oxidize glycerol to carbon dioxide at near-neutral pH.
The role of solvent in molecular recognition systems is under-researched and often ignored, especially when the solvent is considered “non-interacting”. This study concerns the role of toluene solvent in cesium(I) recognition by calix[4]pyrrole. We show that π-donor interactions bind toluene molecules onto the open face of the cation-receptor complex, thus “capping the calix.” As a result, by characterizing this unusual aromatically-saturated complex, we show how “non-interacting” aromatic solvents can directly coordinate receptor-bound cations and thus influence recognition.
A wearable sweat biosensing device is demonstrated that stimulates sweat and continuously measures sweat ethanol concentrations at 25 s intervals, which is then correlated with blood ethanol during a >3 hour testing phase.
The catalytic mechanism and reaction network of oxidative coupling of methane over La 2 O 3 are thoroughly investigated by density functional theory calculations.
We report Hydrogen (H 2 ) is a prospective zero-carbon and high-energy-density fuel alternative to fossil fuels for generating power and clean energy. Ammonia (NH 3 ) is a promising H 2 (17.7%) carrier, which can easily overcome the challenges associated with H 2 storage and transportation. Thermocatalytic ammonia decomposition reaction (ADR) is an effective way to produce clean H 2 but it relies on the use of expensive and rare ruthenium (Ru)-based catalysts at elevated temperatures (>500 °C), hence is not sustainable and economically feasible. Herein, we report a synergistic strategy to design a heterostructured Ru-free catalyst, consisting of CoNi alloy nanoparticles well-dispersed on a MgO–CeO 2 –SrO mixed oxide support with potassium promotion. The resulting K–CoNi alloy –MgO–CeO 2 –SrO catalyst presents 97.7% and 87.5% NH 3 conversion efficiency at 450 °C at gas hourly space velocities (GHSVs) of 6000- and 12 000-mL h -1 g cat -1 , respectively. At 500 °C, the H 2 production rate (57.75 mmol g cat -1 min -1 ) becomes comparable to that of most of the reported Ru-based catalysts. The catalyst stability has been successfully demonstrated in both a fixed-bed reactor under high pressure (120 h at 5.0 bar) and a membrane reactor prototype (600 h at 1.5 bar) at 500 °C. High-temperature in situ XPS analysis, temperature-programmed desorption/reduction, and density functional theory calculations have been carried out to elucidate the possible active sites and performance enhancement mechanisms. This work highlights the importance of constructing optimal interfaces between active metal nanoparticles and oxide support for boosting the NH 3 to H 2 conversion efficiency and long-term stability.
Explore the source record for details and available documents.
The ordinary mode instability can be driven by drifting bi-Maxwellian plasma particle distributions with and without temperature anisotropy. Here, the linear instability analysis is generalized for realistic settings, when the plasma streams are magnetized and hot enough. The new parametrization proposed in this study enables a better understanding of the interplay of counterstreaming and temperature anisotropy, providing the derivation of new regimes of the ordinary mode instability. Accurate analytical forms are derived for the instability conditions for general values of the temperature anisotropy, the streaming velocity, and the parallel plasma beta. To keep the analysis straightforward, the role of ions is minimized.
The linear marginal instability analysis of the ordinary perpendicular mode instability of drifting bi-Maxwellian plasma particle distributions with and without temperature anisotropy is extended by including the modifications of heavier ion species. For general values of the temperature anisotropy, the streaming velocity, and the parallel plasma beta, accurate marginal stability conditions are derived, which enable a better understanding of the interplay of counterstreaming and temperature anisotropy.
We have explored Pauli paramagnetism, Landau diamagnetism, and de Haas-van Alphen effect in a single framework, and unified these three effects for all temperatures as well as for all strengths of magnetic field. Our result goes beyond Pauli-Landau result on the magnetism of the 3-D ideal gas of electrons, and is able to describe crossover of the de Haas-van Alphen oscillation to the saturation of magnetization. We also have obtained a novel asymptotic series expansion for the low temperature properties of the system.
A combined electron-ion spectrometer has been built to study dissociation kinematics of molecular ions upon various electronic decay processes ensuing from ionization of neutral molecules. The apparatus can be used with various ionization agents. Ion time-of-flight (ToF) spectra arising from various electronic decay processes are acquired by triggering the ToF measurement in coincidence with energy analyzed electrons. The design and the performance of the spectrometer in a photoionization experiment is presented in detail. Electron spectra and ion time of flight spectra resulting from valence and 2p{sub 1/2} ionization of Argon and those from valence ionization of CO are presented to demonstrate the capability of the instrument. The fragment ion spectra show remarkable differences (both kinematic and cross sectional) dependent on the energy of the ejected electron, corresponding to various electron loss and decay mechanisms in dissociative photoionization of molecules.
Polarization-dependent differential cross section (PDDCS) is one of the three-vector correlations (k, k{sup ′}, j) in molecular collisions, which provides the most detailed insights into the steric requirements of chemical reactions, i.e., how the reactivity depends on the polarization of reagents. Only quite recently has such quantity been fully realized experimentally in the study of the reaction of the aligned CHD{sub 3}(v{sub 1} = 1, |jK〉 = |10〉) molecules with Cl({sup 2}P{sub 3/2}) atoms. Theoretically, PDDCS is a relatively new concept; experimental realization of the theoretical construct requires some careful considerations that are not readily available in the literature. Here, we present the “know-how” behind the full PDDCS measurements to fill the gaps and to provide a clear roadmap for future applications. To make the connection apparent between the methodology presented here and the stereodynamics revealed in previous reports, the same Cl + aligned CHD{sub 3} reaction is used for illustration.
We construct the equation of state in a wide-density range for neutron stars within relativistic Hartree-Fock approximation. The properties of uniform and nonuniform nuclear matter are studied consistently. The tensor couplings of vector mesons to baryons due to exchange contributions (Fock terms) are included, and the change of baryon internal structure in matter is also taken into account using the quark-meson coupling model. The Thomas-Fermi calculation is adopted to describe nonuniform matter, where the lattice of nuclei and the neutron drip out of nuclei are considered. Even if hyperons exist in the core of a neutron star, we obtain the maximum neutron-star mass of 1.95M{sub ⊙}, which is consistent with the recently observed massive pulsar, PSR J1614-2230. In addition, the strange vector (φ) meson also plays a important role in supporting a massive neutron star.
We present a full analytical solution of the multiconfigurational strongly correlated mixed-valence problem corresponding to the N-Hubbard ring filled with N−1 electrons, and infinite on-site repulsion. While the eigenvalues and the eigenstates of the model are known already, analytical determination of their degeneracy is presented here for the first time. The full solution, including degeneracy count, is achieved for each spin configuration by mapping the Hubbard model into a set of Hückel-annulene problems for rings of variable size. The number and size of these effective Hückel annulenes, both crucial to obtain Hubbard states and their degeneracy, are determined by solving a well-known combinatorial enumeration problem, the necklace problem for N−1 beads and two colors, within each subgroup of the C{sub N−1} permutation group. Symmetry-adapted solution of the necklace enumeration problem is finally achieved by means of the subduction of coset representation technique [S. Fujita, Theor. Chim. Acta 76, 247 (1989)], which provides a general and elegant strategy to solve the one-hole infinite-U Hubbard problem, including degeneracy count, for any ring size. The proposed group theoretical strategy to solve the infinite-U Hubbard problem for N−1 electrons is easily generalized to the case of arbitrary electron count L, by analyzing the permutation group C{sub L} and all its subgroups.
We utilized both resonant ultrasound spectroscopy (RUS) and Schaefer-Bergmann diffraction patterns (SBDP) to measure the elastic stiffness coefficients of the trigonal, non-piezo-electric crystal α−BaB{sub 2}O{sub 4}. RUS determines the elastic coefficients of a sample by matching measured resonant frequencies to a model of resonances. SBDP deduces the elastic coefficients by fitting the measured shape of the acousto-optic diffraction pattern to an acoustic slowness surface cross-section. We present our measured elastic coefficients of α−BaB{sub 2}O{sub 4} from both RUS and SBDP experiments.
The metal-oxide-graphene heterostructures have abundant physical connotations. As one of the most important physical properties, the electric transport property of the gold-chromium oxide-graphene heterostructure has been studied. The experimental measurement shows that the conductive mechanism is dominated by the space-charge-limited transport, a kind of bulk transport of an insulator with charge traps. Combining the theoretical analysis, some key parameters such as the carrier mobility and trap energy also are obtained. The study of the characteristics of the metal-oxide-graphene heterostructures is helpful to investigate the graphene-based electronic and photoelectric devices.
Nuclear magnetic resonance (NMR) assignment of small molecules is presented as a typical example of a combinatorial optimization problem in chemical physics. Three strategies that help improve the efficiency of solution search by the branch and bound method are presented: 1. reduction of the size of the solution space by resort to a condensed structure formula, wherein symmetric nuclei are grouped together; 2. partitioning of the solution space based on symmetry, that becomes the basis for an efficient branching procedure; and 3. a criterion of selection of input restrictions that leads to increased gaps between branches and thus faster pruning of non-viable solutions. Although the examples chosen to illustrate this work focus on small-molecule NMR assignment, the results are generic and might help solving other combinatorial optimization problems.
We report MP2 and CCSD(T) binding energies with basis sets up to pentuple zeta quality for the m = 2-6, 8 clusters. Or best CCSD(T)/CBS estimates are -4.99 kcal/mol (dimer), -15.77 kcal/mol (trimer), -27.39 kcal/mol (tetramer), -35.9 ± 0.3 kcal/mol (pentamer), -46.2 ± 0.3 kcal/mol (prism hexamer), -45.9 ± 0.3 kcal/mol (cage hexamer), -45.4 ± 0.3 kcal/mol (book hexamer), -44.3 ± 0.3 kcal/mol (ring hexamer), -73.0 ± 0.5 kcal/mol (D 2d octamer) and -72.9 ± 0.5 kcal/mol (S4 octamer). We have found that the percentage of both the uncorrected (dimer) and BSSE-corrected (dimer CP e ) binding energies recovered with respect to the CBS limit falls into a narrow range for each basis set for all clusters and in addition this range was found to decrease upon increasing the basis set. Relatively accurate estimates (within < 0.5%) of the CBS limits can be obtained when using the “ 2/3, 1/3” (for the AVDZ set) or the “½ , ½” (for the AVTZ, AVQZ and AV5Z sets) mixing ratio between dimer e and dimer CP e . Based on those findings we propose an accurate and efficient computational protocol that can be used to estimate accurate binding energies of clusters at the MP2 (for up to 100 molecules) and CCSD(T) (for up to 30 molecules) levels of theory. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is a multi program national laboratory operated for DOE by Battelle. This research also used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. AC02-05CH11231.
Explore the source record for details and available documents.