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排序方式: 共有248条查询结果,搜索用时 15 毫秒
41.
Geert Silversmit Hilde Poelman Philippe M. Heynderickx Sergey Nikitenko Philippe F. Smet Roger De Gryse Guy B. Marin 《Journal of Physics and Chemistry of Solids》2009,70(9):1274-88
The redox behaviour of a CuO-CeO2/Al2O3 catalyst is studied under propane reduction and re-oxidation. The evolution of the local Cu and Ce structure is studied with in-situ transmission X-ray absorption spectroscopy (XAS) at the Cu K and Ce L3 absorption edges.CuO and CeO2 structures are present in the catalyst as such. No structural effect on the local Cu structure is observed upon heating in He up to 873 K or after pre-oxidation at 423 K.Exposure to propane at reaction temperature (600-763 K) fully reduces the Cu2+ cations towards metallic Cu0. Quick EXAFS spectra taken during reduction show a small amount of intermediate Cu1+ species. Parallel to the CuO reduction, CeO2 is also reduced in the same temperature range. About 25% of the Ce4+ reduces rapidly to Ce3+ in the 610-640 K temperature interval, while beyond 640 K a further slower reduction of Ce4+ to Ce3+ occurs. At 763 K, Ce reduction is still incomplete with 32% of Ce3+.Re-oxidation of Cu and Ce is fast and brings back the original oxides.The propane reduction of the CuO-CeO2/Al2O3 catalyst involves both CuO and CeO2 reduction at similar temperatures, which is ascribed to an interaction between the two compounds. 相似文献
42.
Robert S. Jansen Hilde Rosing Jan H.M. Schellens Jos H. Beijnen 《Journal of chromatography. A》2009,1216(15):3168-3174
The development of a method for the separation of 2′-2′-difluorodeoxycytidine (gemcitabine, dFdC), 2′-2′-difluorodeoxyuridine (dFdU) and their mono-, di- and triphosphates using a porous graphitic carbon column (Hypercarb), without ion-pairing agent, is described. The retention of dFdC and dFdU could be controlled with an organic modifier (acetonitrile, CH3CN) and the retention of the anionic nucleotides with an eluting ion (bicarbonate). Separation of all analytes was achieved using a 0–25 mM ammonium bicarbonate gradient in CH3CN–H2O (15:85, v/v). Under these conditions, however, very long re-equilibration times were required. Injection of an acidic solution (100 μL 10% formic acid in H2O, v/v; 2.65 M) after running a gradient directly restored the separation capabilities of the column. Still, separation between the analytes slowly deteriorated over a period of months. These problems were solved by preconditioning the column with a pH buffered hydrogen peroxide (H2O2) solution (0.05% H2O2 in CH3CN–H2O (15:85, v/v), pH 4) before starting an analytical run. The oxidation of the stationary phase with H2O2 prevented its slow reduction, which most likely caused the decreasing retention times. The analytes were detected using tandem mass spectrometry. 相似文献
43.
We consider two player electromagnetic evasion-pursuit games where each player must incorporate
significant uncertainty into their design strategies to disguise
their intension and confuse their opponent. In this paper, the
evader is allowed to make dynamic changes to his strategies in
response to the dynamic input with uncertainty from the
interrogator. The problem is formulated in two different ways. One
is based on the evolution of the probability density function of
the intensity of reflected signal and leads to a controlled forward Kolmogorov or Fokker-Planck equation. The other formulation is based on the
evolution of expected value of the intensity of reflected signal and leads to controlled backward Kolmogorov equations.
In addition, a number of numerical results are presented to
illustrate the usefulness of the proposed approach in exploring
problems of control in a general dynamic game setting. 相似文献
44.
Qayyum AA Vejlstrup NG Ahtarovski KA Kofoed KF Kastrup J 《Magnetic resonance imaging》2012,30(6):889-892
Since the introduction of percutaneous coronary intervention for coronary artery disease, thousands of patients have been treated with the implantation of coronary stents. Moreover, several of the patients with coronary stent undergo cardiac magnetic resonance (CMR) imaging every year. This case report is of a 77-year-old man who was previously treated with the implantation of a coronary stent in the left circumflex artery. He underwent CMR imaging, which revealed a process 14×21 mm in the left atrium. Cardiac contrast computed tomography did not demonstrate any cardiac pathology. While the signal loss on MRI associated with implanted metallic devices is known, we report a case where an implanted coronary stent in the left circumflex artery led to an intracardiac signal loss mimicking intracardiac thrombus/tumor. 相似文献
45.
A group action is called polar if there exists an immersed submanifold (a section) which intersects all orbits orthogonally. We show how to construct a manifold admitting a polar group action by prescribing its isotropy groups along a fundamental domain in the section. This generalizes a classical construction for cohomogeneity-one manifolds.We give many examples showing the richness of this class of group actions and relate the topology of the section to the topology of the manifold. 相似文献
46.
47.
Karsten Grove 《Geometriae Dedicata》1989,29(3):327-334
A notion of optimal pinching for positively curved manifolds in introduced, and a corresponding rigidity problem is discussed. For the lowest dimensional non-standard homogeneous manifold of positive curvature, SU(3)/T, an estimate is given. 相似文献
48.
Kinetics of Lifetime Changes in Bimetallic Nanocatalysts Revealed by Quick X‐ray Absorption Spectroscopy 下载免费PDF全文
Dr. Matthias Filez Dr. Hilde Poelman Dr. Evgeniy A. Redekop Dr. Vladimir V. Galvita Dr. Konstantinos Alexopoulos Dr. Maria Meledina Dr. Ranjith K. Ramachandran Dr. Jolien Dendooven Prof. Christophe Detavernier Prof. Gustaaf Van Tendeloo Dr. Olga V. Safonova Dr. Maarten Nachtegaal Prof. Bert M. Weckhuysen Prof. Guy B. Marin 《Angewandte Chemie (International ed. in English)》2018,57(38):12430-12434
49.
50.
Stokvis E Nan-Offeringa LG Ouwehand M Tibben MM Rosing H Schnaars Y Grigat M Romeis P Schellens JH Beijnen JH 《Rapid communications in mass spectrometry : RCM》2004,18(13):1465-1471
The development of a liquid chromatography/tandem mass spectrometric assay for the quantitative analysis of the novel tubulin inhibitor D-24851 in human plasma and urine is described. D-24851 and the deuterated internal standard were extracted from 250 microL of plasma or urine using hexane/ether (1:1, v/v). Subsequently, 10-microL aliquots of reconstituted extracts were injected onto an Inertsil ODS analytical column (50 x 2.0 mm i.d., 5 microm particle size). An eluent consisting of methanol/5 mM ammonium acetate, 0.004% formic acid in water (80:20, v/v) was pumped at a flow rate of 0.2 mL/min. An API 365 triple quadrupole mass spectrometer was used in the multiple reaction monitoring mode for sensitive detection. For human plasma a dynamic range of 1-1000 ng/mL was validated, and for human urine a range of 0.25-50 ng/mL. Validation was performed according to the most recent FDA guidelines and all results were within requirements. The assay has been successfully applied to support a phase I clinical trial with orally administered D-24851. 相似文献