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排序方式: 共有59条查询结果,搜索用时 432 毫秒
31.
32.
K H?kansson RA Zubarev RV Coorey VL Talrose P H?kansson 《Rapid communications in mass spectrometry : RCM》1999,13(12):1169-1174
An HMX/insulin two-layer system was chosen as a model for further investigation of the matrix properties of explosive materials for protein analytes in plasma desorption mass spectrometry. The dependencies of the molecular ion yield and average charge state as a function of the analyte thickness were studied. An increase in the charge state of multiply protonated molecular species was confirmed as the major matrix effect, with the average charge state z at the smallest thickness studied being higher than in matrix-assisted laser desorption/ionization and closer to the value obtained in electrospray ionization under standard acidic conditions. Observed charge state distributions are significantly narrower than the corresponding Poisson distributions, which suggests that the protonation of insulin is limited in plasma desorption by the number of basic sites in the molecule, similar to electrospray ionization. Both the curve displaying total molecular ion yield and the one showing the total charge (proton) yield as a function of the insulin thickness have maxima at a thickness different from an insulin monolayer. These observations diminish the significance of a matrix/analyte interface mechanism for the explosive matrix assistance. Instead, a mechanism related to the chemical energy release during conversion of the explosive after the ion impact is proposed. As additional mechanisms, enhanced protonation of the analyte through collisions with products of the explosive decay is considered, as well as electron scavenging by other products, which leads to a higher survival probability of positively charged protein molecular ions. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
33.
The study of the propagation of waves in randomly diluted models is presented. Porosity (crack-like) models are simulated by constructing typical elastic percolation networks with random microscopic heterogeneities in order to resemble rock media. Central and bond-bending forces (Born Hamiltonian) models are considered. For each experimental case, the elastic energy of the system is relaxed in equilibrium and then the model is excited by a pulse source in order to produce wave propagation. First, a review is presented of the well established velocity-porosity relationship from rock physics, which shows a linear trend from small porosities up to the critical porosity (percolation threshold) where the rocks fall apart. From the wave propagation analysis a general trend is observed for the attenuation of waves, from the small to the large porosity models, suggesting multiple scattering effects similar to those reported from effective-medium approximations of wave scattering due to random heterogeneities. Finally, the results are compared with those obtained from laboratory experiments on dry rocks with different porosities and different applied stress regimes. 相似文献
34.
J Gaudin C Ozkan J Chalupský S Bajt T Burian L Vyšín N Coppola SD Farahani HN Chapman G Galasso V Hájková M Harmand L Juha M Jurek RA Loch S Möller M Nagasono M Störmer H Sinn K Saksl R Sobierajski J Schulz P Sovak S Toleikis K Tiedtke T Tschentscher J Krzywinski 《Optics letters》2012,37(15):3033-3035
The interaction of free electron laser pulses with grating structure is investigated using 4.6±0.1 nm radiation at the FLASH facility in Hamburg. For fluences above 63.7±8.7 mJ/cm2, the interaction triggers a damage process starting at the edge of the grating structure as evidenced by optical and atomic force microscopy. Simulations based on solution of the Helmholtz equation demonstrate an enhancement of the electric field intensity distribution at the edge of the grating structure. A procedure is finally deduced to evaluate damage threshold. 相似文献
35.
36.
Béla Kovács Jozsef Prokisch Jaka Loch Zoltá Gyori 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Parameters of HNO3-H2O2 wet digestion sample preparation method and inductively coupled plasma atomic emission spectrometer 相似文献
37.
H. İBRAHİM UĞRAŞ ÜMİT ÇAKIR AKIN AZİZOĞLU TURGUT KILIÇ ÇAKIL ERK 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(1-2):159-165
Hexadecanoyl, dihexadecanoyl, dioctadecaneoyl, di-10-undecenoyl, and dicis-9-octadecenoyl derivatives of benzo[18]crown-6, dibenzo[18]crown-6 and dibenzo[24]-8 were synthesized by the condensation of carboxylic acids (palmitic, stearic, oleic and undecenoic acid) with benzo and dibenzo crown ethers in the presence of zinc chloride. The extraction equilibrium constants of such macrocyclic ethers with long side chains were estimated using chloroform/water and dichloromethane/water membranes transfer of Na-PAR (4-(2-pyridylazo)-resorcinol mono sodium monohydrate) with UV–Vis spectroscopy. It was found that they were in the range of 10.88–11.71 in dichloromethane and 8.04–11.77 in chloroform. These results actually show that the Na+ binding effect of macrocyclic ethers depends on the type and the length of side chains. The geometrical properties of the molecules were studied employing semi-empirical calculations by simulated annealing technique. The frontier molecular orbital energies and dipole moments were also examined. The biological activity results showed that the synthesized crown ethers have no activity against the studied microorganisms. 相似文献
38.
S.D. Ellis J. Huston K. Hatakeyama P. Loch M. Tnnesmann 《Progress in Particle and Nuclear Physics》2008,60(2):484-551
In this article, we review some of the complexities of jet algorithms and of the resultant comparisons of data to theory. We review the extensive experience with jet measurements at the Tevatron, the extrapolation of this acquired wisdom to the LHC and the differences between the Tevatron and LHC environments. We also describe a framework (SpartyJet) for the convenient comparison of results using different jet algorithms. 相似文献
39.
Jennifer A. Loch Cornelia Borgmann Robert H. Crabtree 《Journal of molecular catalysis. A, Chemical》2001,170(1-2):75-80
New syntheses of PEG-(OCH2C5H4N)2 and PEG-(OC6H4PPh2)2 (PEG: poly(ethylene glycol)) conjugates are reported. An iridium hydrogenation catalyst 1, is shown to catalyze hydrogenation in a water/substrate two-phase system. Attachment of 1 to PEG to make 2 and 3 succeeds in making the complex water-soluble and allows it to retain some of its catalytic ability, but leads to micelle formation that inhibits the separation of organic and aqueous phases. 相似文献
40.
N. RAÏSSI 《Natural Resource Modeling》2001,14(2):287-310
ABSTRACT. After the extension of the Exclusive Economic Zone, in 1977, to 200 miles, most fish stocks came under jurisdiction of the adjacent coastal states. This development opened prospects of effective management of the open sea fisheries. Coastal states have the right to plan out the operation of so-called by Clarke and Munro “distant water fishing nations” from their Exclusive Economic Zone. Under some arrangements, a foreign fleet is allowed to harvest the resource in the Exclusive Economic Zone area. Clarke and Munro, in [1987] and [1991], focus on the issue of optimum terms and conditions of access and, in doing so, built a multiobjective model. The main goal of the present work is the development of a more general model including more variables and parameters related to the presence of a domestic fleet as well as a distant water fishing nation. The main difficulty resides in sharing the harvesting between the two fleets. The study responds to the realistic problemof coastal states who own enough resource stocks to allow harvesting by several kinds of fleets. Two optimal scenarios are developed, in each of them a solution is given. 相似文献