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101.
Olaf Beyersdorff Arne Meier Sebastian M��ller Michael Thomas Heribert Vollmer 《Archive for Mathematical Logic》2011,50(7-8):727-742
Default logic is one of the most popular and successful formalisms for non-monotonic reasoning. In 2002, Bonatti and Olivetti introduced several sequent calculi for credulous and skeptical reasoning in propositional default logic. In this paper we examine these calculi from a proof-complexity perspective. In particular, we show that the calculus for credulous reasoning obeys almost the same bounds on the proof size as Gentzen??s system LK. Hence proving lower bounds for credulous reasoning will be as hard as proving lower bounds for LK. On the other hand, we show an exponential lower bound to the proof size in Bonatti and Olivetti??s enhanced calculus for skeptical default reasoning. 相似文献
102.
Linden AH Lange S Franks WT Akbey U Specker E van Rossum BJ Oschkinat H 《Journal of the American Chemical Society》2011,133(48):19266-19269
Methods enabling structural studies of membrane-integrated receptor systems without the necessity of purification provide an attractive perspective in membrane protein structural and molecular biology. This has become feasible in principle since the advent of dynamic nuclear polarization (DNP) magic-angle-spinning NMR spectroscopy, which delivers the required sensitivity. In this pilot study, we observed well-resolved solid-state NMR spectra of extensively (13)C-labeled neurotoxin II bound to the nicotinic acetylcholine receptor (nAChR) in native membranes. We show that TOTAPOL, a biradical required for DNP, is localized at membrane and protein surfaces. The concentration of active, membrane-attached biradical decreases with time, probably because of reactive components of the membrane preparation. An optimal distribution of active biradical has strong effects on the NMR data. The presence of inactive TOTAPOL in membrane-proximal situations but active biradical in the surrounding water/glycerol "glass" leads to well-resolved spectra, yet a considerable enhancement (ε = 12) is observed. The resulting spectra of a protein ligand bound to its receptor are paving the way for further DNP investigations of proteins embedded in native membrane patches. 相似文献
103.
Alexey P. Kostikov Joshua Chin Björn Wängler Klaus Jurkschat Ralf Schirrmacher 《Journal of fluorine chemistry》2011,132(1):27-6205
18F-labeled compounds play a major role in the development of new in vivo imaging agents for Positron Emission Tomography (PET), a non invasive imaging modality depicting the biodistribution of radioactive compounds in humans. Recently we reported a new method for the introduction of fluorine-18 into a range of organic molecules exploiting the very fast 18F-19F isotope exchange of fluorosilanes (termed SiFA compounds). Here, we wish to report the labeling of the first charged SiFA molecule N-(4-(di-tert-butylfluorosilyl)benzyl)-2-hydroxy-N,N-dimethylethylammonium bromide (SiFAN+Br−) serving as a lead compound in the development of SiFA-based prosthetic groups of reduced lipophilicity for biomolecule labeling. Mild conditions for synthesis of [18F]SiFAN+Br− and an easy purification procedure using simple C-18 solid phase cartridge have been developed yielding the [18F]SiFAN+Br− in radiochemical yields of 34% (non-decay corrected) within 40 min. A series of kinetic experiments were performed that show high isotopic exchange rate constants. Low activation energy (15.7 kcal/mol) and a large preexponential factor (7.9 × 1013 M−1 s−1) were calculated for the isotopic exchange reaction from a corresponding Arrhenius plot. For comparison, the 18F-fluorination of ethyleneglycol-di-p-tosylate via the formation of a carbon-18F bond showed a 1.3 kcal/mol higher activation energy and a much lower preexponential factor of 2.9 × 109 M−1 s−1. Moderate hydrophilicity (log D = 0.44), stability in aqueous media at pH up to 7.4 and a high specific activity of [18F]SiFAN+Br− (SA = 20.4 GBq/μmol, 0.55 Ci/μmol) make this charged SiFA compound useful for the development of novel SiFA-based 18F-labeling synthons. 相似文献
104.
A stress function method is presented in order to give a general solution of the incompatibility problem of three-dimensional linear anisotropic elasticity theory. A relation between the internal stress tensor in terms of derivatives of a sixth-order stress function tensor will be derived. Using this formulation the so far open problem of the representation of the second-order stress function tensor by the fourth-order stress function tensor in anisotropic elasticity theory is solved in general. 相似文献
105.
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107.
Arne Jensen 《Journal of Chemical Sciences》1994,104(4):599-651
We give an introduction to the spectral and scattering theory for Schr?dinger operators. An abstract short range scattering
theory is developed. It is applied to perturbations of the Laplacian. Particular attention is paid to the study of Stark Hamiltonians.
The main result is an explanation of the discrepancy between the classical and the quantum scattering theory for one-dimensional
Stark Hamiltonians. 相似文献
108.
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110.
The Mie Scattering Imaging method (MSI) gathers out‐of‐focus images of dispersed spherical particles present in a laser light sheet and extracts the individual particle diameter from these images. The general idea of the method has been around for more than a decade and a number of papers has dealt with it over recent years. Our work focuses on small particle sizes from 20 μm down to 2 μm, a range which has not been tackled so far although it is of great importance in particle systems. We present an optical set‐up with a special arrangement of camera lenses that allows to work in this range. An evaluation algorithm based on correlation of the experimental optical information with theoretical Mie scattering was found to give the most accurate results for particle sizing. Besides accuracy measurements on solid spheres the versatility of the method is demonstrated by an example of transient droplet growth between 2–7 μm. 相似文献