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31.
Feifel R Burmeister F Sałek P Piancastelli MN Bässler M Sorensen SL Miron C Wang H Hjelte I Björneholm O Naves de Brito A Gel'mukhanov FK Agren H Svensson S 《Physical review letters》2000,85(15):3133-3136
The femtosecond dissociation of HCl after core excitation has been studied through the resonant Auger decay. The spectra contain contributions from decay occurring at both "molecular" and "atomic" internuclear distances. We have observed a new interference mechanism in these spectra: An atomic spectral line develops into a negative spectral contribution, a "hole," when detuning the excitation energy from the maximum of the Cl2p(-1)sigma(*) resonance. Resonant x-ray scattering theory quantitatively explains this behavior as due to a novel destructive continuum-continuum interference between molecular and atomic contributions to the Auger decay. 相似文献
32.
Bjorneholm O Bassler M Ausmees A Hjelte I Feifel R Wang H Miron C Piancastelli MN Svensson S Sorensen SL Gel'mukhanov F Agren H 《Physical review letters》2000,84(13):2826-2829
By exploiting the core-excitation-induced dissociation of O2, we find that the Auger emission exhibits a Doppler-like energy shift. We show this to be a manifestation of localization of the core hole and propose that the problem of core-hole localization versus delocalization in core-hole spectroscopies may be resolved by considering the nature of the measurement. 相似文献
33.
Clean TROSY: compensation for relaxation-induced artifacts 总被引:1,自引:0,他引:1
Schulte-Herbrüggen T Sorensen OW 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,144(1):123-128
TROSY pulse sequences for recording, e.g., (1)H-(15)N chemical shift correlation spectra of proteins are designed to select only one of four two-dimensional multiplet components. However, all of the variants published so far are prone to relaxation-induced artifacts at the positions of two of the other multiplet components. This article introduces modifications to the two spin-state-selective coherence transfer building blocks of the TROSY mixing sequence resulting in a clean TROSY spectrum with the artifacts largely suppressed. It works by having the new mixing sequence generate peaks of opposite phase at the positions of the relaxation artifacts. The clean TROSY pulse sequence is marginally shorter than the original one and contains the same pulses. Experimental demonstration is presented for the (15)N-labeled proteins RAP 17-97 (N-terminal domain of alpha(2)-macroglobulin receptor associated protein) and EQT, equinatoxin II, from the Mediterranean anemone Actinia equina. 相似文献
34.
The propagation of ultrasound through an austenitic weld is investigated experimentally as well as in a numerical simulation. The weld is insonified at normal incidence to the fusion line with a longitudinal contact transducer. In order to experimentally trace the ultrasound through the weld, slices of different thicknesses from the original weld have been fabricated. Through-transmission A-scans have then been produced for each weld slice and compared with the corresponding numerical simulation. A comparison of the direction of ultrasound propagation through the weld for the two approaches shows quite good agreement. However, attenuation due to scattering at grain boundaries in the weld is poorly modelled in the simulation. In order to improve this, a better model of the weld is needed. 相似文献
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37.
Seike H Sorensen EJ 《Synlett : accounts and rapid communications in synthetic organic chemistry》2008,2008(5):695-701
Three key reactions, an efficient Ugi four-component coupling, a regiospecific, base-mediated elimination reaction, and an intramolecular nitrone/alkene [3+2] cycloaddition, were used to achieve an effective synthesis of the tricyclic molecular framework of the immunosuppressant FR901483. The outcome of a control experiment supports the idea that an internal deprotonation by an alkoxide ion is the origin of the site selectivity observed in the base-induced elimination of hydroxy mesylate 17. 相似文献
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39.
Victor J. Bellitto Mikhail I. Melnik Daniel N. Sorensen Joseph C. Chang 《Journal of Thermal Analysis and Calorimetry》2010,102(2):557-562
We studied the surface and thermal properties of seven different varieties of cyclotrimethylene-trinitramine (RDX) crystalline
explosives from five manufacturers using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The specific
varieties of the RDX studied were acquired from the previous Reduced Sensitivity RDX Round Robin program. They were chosen
because intensive characterization of the materials already existed including shock sensitivity and cyclotetramethylene-tetranitramine
(HMX) impurity levels. AFM scans revealed a diversity of surface defects. To quantify the surface defects on the crystalline
surface of the RDX particles, surface roughness measurements were acquired. Statistical analysis was undertaken to correlate
the observed surface, HMX impurity levels, and DSC thermal curve properties with the known shock sensitivities of the material.
It was determined that a statistically significant relationship exists between surface roughness and the shock sensitivity
of the material while no relationship was observed between the DSC thermal properties and either surface roughness or shock
sensitivity. The HMX content greatly affected the thermal properties of RDX but was uncorrelated with the shock sensitivity. 相似文献
40.
An efficient four-step synthesis of PA-824, a promising antituberculosis drug candidate, has been developed. This concise approach offers significant improvements over the synthetic route currently used for large-scale production. 相似文献