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151.
152.
Newton MA Chapman KW Thompsett D Chupas PJ 《Journal of the American Chemical Society》2012,134(11):5036-5039
When materials are reduced to the nanoscale, their structure and reactivity can deviate greatly from the bulk or extended surface case. Using the archetypal example of supported Pt nanoparticles (ca. 2 nm diameter, 1 wt % Pt on Al(2)O(3)) catalyzing CO oxidation to CO(2) during cyclic redox operation, we show that high energy X-ray total scattering, used with subsecond time resolution, can yield detailed, valuable insights into the dynamic behavior of nanoscale systems. This approach reveals how these nanoparticles respond to their environment and the nature of active sites being formed and consumed within the catalytic process. Specific insight is gained into the structure of the highly active Pt surface oxide that formed on the nanoparticles during catalysis. 相似文献
153.
Németh K Chapman KW Balasubramanian M Shyam B Chupas PJ Heald SM Newville M Klingler RJ Winans RE Almer JD Sandi G Srajer G 《The Journal of chemical physics》2012,136(7):074105
An efficient implementation of simultaneous reverse Monte Carlo (RMC) modeling of pair distribution function (PDF) and EXAFS spectra is reported. This implementation is an extension of the technique established by Krayzman et al. [J. Appl. Cryst. 42, 867 (2009)] in the sense that it enables simultaneous real-space fitting of x-ray PDF with accurate treatment of Q-dependence of the scattering cross-sections and EXAFS with multiple photoelectron scattering included. The extension also allows for atom swaps during EXAFS fits thereby enabling modeling the effects of chemical disorder, such as migrating atoms and vacancies. Significant acceleration of EXAFS computation is achieved via discretization of effective path lengths and subsequent reduction of operation counts. The validity and accuracy of the approach is illustrated on small atomic clusters and on 5500-9000 atom models of bcc-Fe and α-Fe(2)O(3). The accuracy gains of combined simultaneous EXAFS and PDF fits are pointed out against PDF-only and EXAFS-only RMC fits. Our modeling approach may be widely used in PDF and EXAFS based investigations of disordered materials. 相似文献
154.
X. Liang R. Chapman K.-M. Spohr M.B. Smith P. Bednarczyk S. Naguleswaran F. Haas G. de Angelis S.M. Campbell P.J. Dagnall M. Davison G. Duchêne Th. Kröll S. Lunardi D.J. Middleton 《The European Physical Journal A - Hadrons and Nuclei》2001,10(1):41-47
High-spin states in neutron-rich Dy isotopes, populated in deep-inelastic processes produced by the interaction of 234 MeV
37Cl ions with a 160Gd target, have been studied using the highly sensitive EUROBALL IV gamma-ray detector array. The previously known level schemes
for 159,160,161,162Dy have been extended to significantly higher spin ( ? 30?) and the i
13/2 band crossing in 159Dy has been observed for the first time. The experimental results are discussed within the framework of cranked shell model
and projected shell model calculations with particular reference to the observed delayed band crossing in 162Dy.
Received: 20 October 2000 / Accepted: 16 January 2001 相似文献
155.
James Chapman Nigel L. Pickett Gabriel Kolawole Majid Motevalli Paul O'Brien 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):e501-e502
The title copper complex, [Cu(dl ‐DAP)2(H2O)2]·2H2O or [Cu(C3H7N2O2)2(H2O)2]·2H2O, prepared from the non‐protein amino acid dl ‐2,3‐diaminopropionic acid (dl ‐HDAP), has a center of symmetry and a distorted octahedral coordination, with four N atoms in equatorial positions and two water molecules in apical sites. The water molecule of crystallization is hydrogen bonded to the deprotonated carboxylate group of the ligand. 相似文献
156.
D. J. Rogers Y. Maeda K. Takei J. N. Chapman J. P. C. Bernards C. P. G. Schrauwen 《Journal of magnetism and magnetic materials》1994,130(1-3):433-441
We investigated the effect of a Ge underlayer and substrate temperature during film deposition (Ts) on the compositional distribution in Co79Cr21 films using spin echo nuclear magnetic resonance and preferential chemical etching. For films deposited at elevated Ts we observed drastic compositional separation (CS) leading to a Co enriched phase with approximately 5 at% Cr on both Ge and polyester. Chemical etching revealed chrysanthemum pattern (CP) type microstructures. For lower Ts films we observed less marked CS with a distinct etched microstructure in the film deposited on Ge and no clear etched microstructure in the film deposited on polyester. Results from NMR and chemical etching studies agreed very well with those from X-ray microanalysis. 相似文献
157.
158.
Techniques from complexity and criticality theory have fruitful applications to a wide range of natural and laboratory plasma systems. Here we review examples that have direct observational relevance, spanning fusion, the Earth's magnetosphere, the sun and astrophysical accretion disks. The complex systems techniques range from sandpiles to a novel loop-based dynamical model, together with modern approaches to model-independent data analysis. 相似文献
159.
S. T. Chapman P. A. García-Sánchez D. Llena V. Ponomarenko J. C. Rosales 《manuscripta mathematica》2006,120(3):253-264
Problems involving chains of irreducible factorizations in atomic integral domains and monoids have been the focus of much recent literature. If S is a commutative cancellative atomic monoid, then the catenary degree of S (denoted c(S)) and the tame degree of S (denoted t(S)) are combinatorial invariants of S which describe the behavior of chains of factorizations. In this note, we describe methods to compute both c(S) and t(S) when M is a finitely generated commutative cancellative monoid. 相似文献
160.
William R. Adams John A. Zollweg William B. Strett Walter G. Chapman Paulette Clancy 《Fluid Phase Equilibria》1988,40(3):247-257
Measurements of the excess enthalpy of krypton and xenon mixtures at 163 K are reported. These results are found to disagree with the only other published result. This discrepancy is discussed. Conformal solution theory is used to provide an unbiased prediction of the excess enthalpy. We review published experimental and calculated excess thermodynamic properties of the Kr/Xe system at zero pressure and 161.38 K and 165 K. 相似文献