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排序方式: 共有499条查询结果,搜索用时 15 毫秒
491.
Panayiotis Nikolaou Aaron M. Coffey Laura L. Walkup Brogan M. Gust Nicholas Whiting Hayley Newton Iga Muradyan Mikayel Dabaghyan Kaili Ranta Gregory D. Moroz Matthew S. Rosen Samuel Patz Michael J. Barlow Eduard Y. Chekmenev Boyd M. Goodson 《Magnetic resonance imaging》2014
Here we provide a full report on the construction, components, and capabilities of our consortium’s “open-source” large-scale (~ 1 L/h) 129Xe hyperpolarizer for clinical, pre-clinical, and materials NMR/MRI (Nikolaou et al., Proc. Natl. Acad. Sci. USA, 110, 14150 (2013)). The ‘hyperpolarizer’ is automated and built mostly of off-the-shelf components; moreover, it is designed to be cost-effective and installed in both research laboratories and clinical settings with materials costing less than $125,000. The device runs in the xenon-rich regime (up to 1800 Torr Xe in 0.5 L) in either stopped-flow or single-batch mode—making cryo-collection of the hyperpolarized gas unnecessary for many applications. In-cell 129Xe nuclear spin polarization values of ~ 30%–90% have been measured for Xe loadings of ~ 300–1600 Torr. Typical 129Xe polarization build-up and T1 relaxation time constants were ~ 8.5 min and ~ 1.9 h respectively under our spin-exchange optical pumping conditions; such ratios, combined with near-unity Rb electron spin polarizations enabled by the high resonant laser power (up to ~ 200 W), permit such high PXe values to be achieved despite the high in-cell Xe densities. Importantly, most of the polarization is maintained during efficient HP gas transfer to other containers, and ultra-long 129Xe relaxation times (up to nearly 6 h) were observed in Tedlar bags following transport to a clinical 3 T scanner for MR spectroscopy and imaging as a prelude to in vivo experiments. The device has received FDA IND approval for a clinical study of chronic obstructive pulmonary disease subjects. The primary focus of this paper is on the technical/engineering development of the polarizer, with the explicit goals of facilitating the adaptation of design features and operative modes into other laboratories, and of spurring the further advancement of HP-gas MR applications in biomedicine. 相似文献
492.
The purpose of this study was to investigate three elementary mathematics curricula to examine the accessibility for students with learning disabilities (LD) with regards to challenges associated with working memory. We chose to focus on students' experiences when finding the area of composite shapes due to the multiple steps involved for solving these problems and the potential for these problems to tax working memory. We conducted a qualitative analysis of how each curriculum provided opportunities for students with LD to engage with these problems. During our analysis, we focused on instruction that emphasized visual representations (e.g., manipulatives, drawings, and diagrams), facilitated mathematical conversations, and developed cognitive and metacognitive skills. Our findings indicated a need for practitioners to consider how each curriculum provides instruction for storage and organization of information as well as how each curriculum develops students' thinking processes and conceptual understanding of mathematics. We concluded that all three curricula provide potentially effective strategies for teaching students with LD to solve multi‐step problems, such as area of composite shapes problems, but teachers using any of these curricula will likely need to supplement the curriculum to meet the needs of students with LD. 相似文献
493.
C. P. Welsch A. I. Papash J. Harasimowicz O. Karamyshev G. A. Karamysheva D. Newton M. Panniello M. Putignano M. R. F. Siggel-King A. Smirnov 《Hyperfine Interactions》2014,229(1-3):139-146
The Ultra-low energy electrostatic Storage Ring (USR) at the future Facility for Low-energy Antiproton and Ion Research (FLAIR) will provide cooled beams of antiprotons in the energy range between 300 keV down to 20 keV. Based on the original design concept developed in 2005, the USR has been completely redesigned over the past few years by the QUASAR Group. The ring structure is now based on a ’split achromat’ lattice. This ensures compact ring dimensions of 10 m × 10 m, whilst allowing both, in-ring experiments with gas jet targets and studies with extracted beams. In the USR, a wide range of beam parameters shall be provided, ranging from very short pulses in the nanosecond regime to a coasting beam. In addition, a combined fast and slow extraction scheme will be featured that allows for providing external experiments with cooled beams of different time structure. Detailed investigations into the dynamics of low energy beams, including studies into the long term beam dynamics and ion kinetics, beam life time, equilibrium momentum spread and equilibrium lateral spread during collisions with an internal target were carried out. This required the development of new simulation tools to further the understanding of beam storage with electrostatic fields. In addition, studies into beam diagnostics methods for the monitoring of ultra-low energy ions at beam intensities less than 10 6 were carried out. This includes instrumentation for the early commissioning of the machine, as well as for later operation with antiprotons. In this paper, on overview of the technical design of the USR is given with emphasis on two of the most important operating modes, long term beam dynamics and the design of the beam diagnostics system. 相似文献
494.
We examine the vortical wake structure shed from a deformable Joukowski airfoil in an unbounded volume of inviscid and incompressible fluid. The deformable airfoil is considered to model a flapping fish. The vortex shedding is accounted for using an unsteady point vortex model commonly referred to as the Brown-Michael model. The airfoil’s deformations and rotations are prescribed in terms of a Jacobi elliptic function which exhibits, depending on a dimensionless parameter m, a range of periodic behaviors from sinusoidal to a more impulsive type flapping. Depending on the parameter m and the Strouhal number, one can identify five distinct wake structures, ranging from arrays of isolated point vortices to vortex dipoles and tripoles shed into the wake with every half-cycle of the airfoil flapping motion. We describe these regimes in the context of other published works which categorize wake topologies, and speculate on the importance of these wake structures in terms of periodic swimming and transient maneuvers of fish. 相似文献
495.
X‐ray spectroscopy for chemistry in the 2‐4 keV energy regime at the XMaS beamline: ionic liquids,Rh and Pd catalysts in gas and liquid environments,and Cl contamination in γ‐Al2O3 下载免费PDF全文
Paul B. J. Thompson Bao N. Nguyen Rachel Nicholls Richard A. Bourne John B. Brazier Kevin R. J. Lovelock Simon D. Brown Didier Wermeille Oier Bikondoa Christopher A. Lucas Thomas P. A. Hase Mark A. Newton 《Journal of synchrotron radiation》2015,22(6):1426-1439
The 2–4 keV energy range provides a rich window into many facets of materials science and chemistry. Within this window, P, S, Cl, K and Ca K‐edges may be found along with the L‐edges of industrially important elements from Y through to Sn. Yet, compared with those that cater for energies above ca. 4–5 keV, there are relatively few resources available for X‐ray spectroscopy below these energies. In addition, in situ or operando studies become to varying degrees more challenging than at higher X‐ray energies due to restrictions imposed by the lower energies of the X‐rays upon the design and construction of appropriate sample environments. The XMaS beamline at the ESRF has recently made efforts to extend its operational energy range to include this softer end of the X‐ray spectrum. In this report the resulting performance of this resource for X‐ray spectroscopy is detailed with specific attention drawn to: understanding electrostatic and charge transfer effects at the S K‐edge in ionic liquids; quantification of dilution limits at the Cl K‐ and Rh L3‐edges and structural equilibria in solution; in vacuum deposition and reduction of [RhI(CO)2Cl]2 to γ‐Al2O3; contamination of γ‐Al2O3 by Cl and its potential role in determining the chemical character of supported Rh catalysts; and the development of chlorinated Pd catalysts in `green' solvent systems. Sample environments thus far developed are also presented, characterized and their overall performance evaluated. 相似文献
496.
Kayla J. Pyper David K. Kempe Jade Y. Jung Li-Hsing J. Loh Nigel Gwini Benjamin D. Lang Brittney S. Newton Jonathan M. Sims Vladimir N. Nesterov Gregory L. Powell 《Journal of Cluster Science》2013,24(3):619-634
Microwave heating allows for the high-yield, one-step synthesis of the known triosmium complexes Os3(μ-Br)2(CO)10 (1), Os3(μ-I)2(CO)10 (2), and Os3(μ-H)(μ-OR)(CO)10 with R = methyl (3), ethyl (4), isopropyl (5), n-butyl (6), and phenyl (7). In addition, the new clusters Os3(μ-H)(μ-OR)(CO)10 with R = n-propyl (8), sec-butyl (9), isobutyl (10), and tert-butyl (11) are synthesized in a microwave reactor. The preparation of these complexes is easily accomplished without the need to first prepare an activated derivative of Os3(CO)12, and without the need to exclude air from the reaction vessel. The syntheses of complexes 1 and 2 are carried out in less than 15 min by heating stoichiometric mixtures of Os3(CO)12 and the appropriate halogen in cyclohexane. Clusters 3–6 and 8–10 are prepared by the microwave irradiation of Os3(CO)12 in neat alcohols, while clusters 7 and 11 are prepared from mixtures of Os3(CO)12, alcohol and 1,2-dichlorobenzene. Structural characterization of clusters 2, 4, and 5 was carried out by X-ray crystallographic analysis. High resolution X-ray crystal structures of two other oxidative addition products, Os3(CO)12I2 (12) and Os3(μ-H)(μ-O2CC6H5)(CO)10 (13), are also presented. 相似文献
497.
498.
Johannes Wieser Dr. Amy J. Knorpp Dr. Dragos C. Stoian Dr. Przemyslaw Rzepka Dr. Mark A. Newton Prof. Jeroen A. van Bokhoven 《Angewandte Chemie (International ed. in English)》2023,62(40):e202305140
The methane-to-methanol (MtM) conversion via the oxygen looping approach using copper-exchanged zeolites has been extensively studied over the last decade. While a lot of research has focussed on maximizing yield and selectivity, little has been directed toward productivity—a metric far more meaningful for evaluating industrial potential. Using copper-exchanged zeolite omega (Cu-omega), a material highly active and selective for the MtM conversion using the isothermal oxygen looping approach, we show that this material exhibits unprecedented potential for industrial valorization. In doing so, we also present a novel methodology combining operando XAS and mass spectrometry for the screening of materials for the MtM conversion in oxygen looping mode. 相似文献
499.
Rory C. McNulty Keir Penston Sharad S. Amin Sandro Stal Jie Yie Lee Mario Samperi Lluïsa Pérez-García Jamie M. Cameron Lee R. Johnson David B. Amabilino Graham N. Newton 《Angewandte Chemie (International ed. in English)》2023,62(12):e202216066
The mixing of [V10O28]6− decavanadate anions with a dicationic gemini surfactant ( gem ) leads to the spontaneous self-assembly of surfactant-templated nanostructured arrays of decavanadate clusters. Calcination of the material under air yields highly crystalline, sponge-like V2O5 ( gem -V2O5 ). In contrast, calcination of the amorphous tetrabutylammonium decavanadate allows isolation of a more agglomerated V2O5 consisting of very small crystallites ( TBA -V2O5 ). Electrochemical analysis of the materials’ performance as lithium-ion intercalation electrodes highlights the role of morphology in cathode performance. The large crystallites and long-range microstructure of the gem -V2O5 cathode deliver higher initial capacity and superior capacity retention than TBA -V2O5 . The smaller crystallite size and higher surface area of TBA -V2O5 allow faster lithium insertion and superior rate performance to gem -V2O5 . 相似文献