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排序方式: 共有298条查询结果,搜索用时 31 毫秒
31.
Gunaratne T Rodgers MA Felder D Nierengarten JF Accorsi G Armaroli N 《Chemical communications (Cambridge, England)》2003,(24):3010-3011
Transient absorption spectrometry of Cu(I)-phenanthrolines in CH2Cl2 reveals ligand-independent dynamic processes lasting 15 ps, which are associated with the peculiar structural rearrangements occurring for this class of compounds upon photoexcitation. 相似文献
32.
Ideas and tools from statistical physics have recently been applied to the investigation of human dynamics. The timing of human activities, in particular, has been studied both experimentally and analytically. Empirical data show that, in many different situations, the time interval separating two consecutive tasks executed by an individual follows a heavy-tailed probability distribution rather than Poisson statistics. To account for this data, human behaviour has been viewed as a decision-based queuing system where individuals select and execute tasks belonging to a finite list of items as an increasing function of a task priority parameter. It is then possible to obtain analytically the empirical result P(τ)∼1/τ, where P(τ) is the waiting time probability distribution.Here a continuous model of human dynamics is introduced using instead an infinite queuing list. In contrast with the results obtained by other models in the finite case we find a waiting time distribution explicitly depending on the priority distribution density function ρ. The power-law scaling P(τ)∼1/τ is then recovered when ρ is exponentially distributed. 相似文献
33.
We introduce and analyze a model of a multi-directed Eulerian network, that is a directed and weighted network where a path exists that passes through all the edges of the network once and only once. Networks of this type can be used to describe information networks such as human language or DNA chains. We are able to calculate the strength and degree distribution in this network and find that they both exhibit a power law with an exponent between 2 and 3. We then analyze the behavior of the accelerated version of the model and find that the strength distribution has a double slope power-law behavior. Finally we introduce a non-Eulerian version of the model and find that the statistical topological properties remain unchanged. Our analytical results are compared with numerical simulations. 相似文献
34.
Tarun Gheyi Logan Rodgers Richard Romero J. Michael Sauder Stephen K. Burley 《Journal of the American Society for Mass Spectrometry》2010,21(10):1795-1801
A strategy for increasing the efficiency of protein crystallization/structure determination with mass spectrometry has been
developed. This approach combines insights from limited proteolysis/mass spectrometry and crystallization via in situ proteolysis.
The procedure seeks to identify protease-resistant polypeptide chain segments from purified proteins on the time-scale of
crystal formation, and subsequently crystallizing the target protein in the presence of the optimal protease at the right
relative concentration. We report our experience with 10 proteins of unknown structure, two of which yielded high-resolution
X-ray structures. The advantage of this approach comes from its ability to select only those structure determination candidates
that are likely to benefit from application of in situ proteolysis, using conditions most likely to result in formation of
a stable proteolytic digestion product suitable for crystallization. 相似文献
35.
Gary R. Rodgers William J. P. Neish 《Monatshefte für Chemie / Chemical Monthly》1986,117(6-7):879-882
Expansion of the xanthine ring system has been accomplished by linear formation of a benzo, pyrido or pyrazino ring between the pyrimidine and imidazole portions.
Linear expandierte Xanthine (Kurze Mitteilung)
Zusammenfassung Durch Einbau eines Benzo-, Pyrido- oder Pyrazino-Ringes zwischen den Pyrimidin- und Imidazoleinheiten wurde die lineare Expansion des Xanthin-Ringsystems erreicht.相似文献
36.
This study examined the behaviour of two completion aggregates that were placed on a silty sandy formation material and subjected to repeated loading in a large-scale testing rig. The completion aggregates were (i) a good quality limestone, and (ii) a poor quality schist, and are used in the construction of unbound forest roads in Ireland. The schist was tested on its own and in combination with the completion limestone aggregate for up to 150,000 load applications with a maximum loading pressure of 1000 kPa. Measurements of surface deflections and formation pressures were made during each test. A combination of a 200 mm layer of the limestone aggregate placed on top of a 250 mm layer of the schist aggregate produced the lowest permanent deformations, resilient deflections, and resilient pressures under dry and wet undrained conditions. 相似文献
37.
An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations. 相似文献
38.
Grant J Rodgers CA Chickering CD Hill SJ Stry JJ 《Journal of AOAC International》2010,93(4):1293-1301
An analytical method is presented for the determination of chlorantraniliprole residues in crops. Chlorantraniliprole residues were extracted from crop matrixes with acetonitrile after a water soak. The extracts were passed through a strong anion-exchange (SAX) SPE cartridge stacked on top of a reversed-phase (RP) polymer cartridge. After both cartridges were rinsed and vacuum-dried, the SAX cartridge was removed, and chlorantraniliprole was eluted from the RP polymer cartridge with acetonitrile. The acetonitrile eluate was evaporated to dryness, reconstituted, and analyzed using an LC/MS/MS instrument equipped with an atmospheric pressure chemical ionization source. The method was successfully validated at 0.010, 0.10, and 10 mg/kg for the following crop matrixes: potatoes, sugar beets (tops), lettuce, broccoli, soybeans, soybean forage, tomatoes, cucumbers, oranges, apples, pears, peaches, almonds (nutmeat), rice grain, wheat grain, wheat hay, corn stover, alfalfa forage, cottonseed, grapes, and corn grain. The average recoveries from all crop samples fortified at the method LOQ ranged from 91 to 108%, with an overall average recovery of 97%. The average recoveries from all crop samples fortified at 10 times the method LOQ ranged from 89 to 115%, with an overall average recovery of 101%. For all of the fortified control samples analyzed in this study, the overall average recovery was 99%. 相似文献
39.
In classical projective geometry, a double six of lines consists of 12 lines ? 1, ? 2, . . . , ? 6, m 1, m 2, . . . , m 6 such that the ? i are pairwise skew, the m i are pairwise skew, and ? i meets m j if and only if i ≠ j. In the 1960s Hirschfeld studied this configuration in finite projective spaces PG(3, q) showing they exist for almost all values of q, with a couple of exceptions when q is too small. We will be considering double-k sets in the symplectic geometry W(q), which is constructed from PG(3, q) using an alternating bilinear form. This geometry is an example of a generalized quadrangle, which means it has the nice property that if we take any line ? and any point P not on ?, then there is exactly one line through P meeting ?. We will discuss all of this in detail, including all of the basic definitions needed to understand the problem, and give a result classifying which values of k and q allow us to construct a double k-set of lines in W(q). 相似文献
40.
Marina Soncin Alessandra Busetti Franco Fusi Giulio Jori Michael A. J. Rodgers 《Photochemistry and photobiology》1999,69(6):708-712
Cu(II)-hematoporphyrin (CuHp) was efficiently accumulated by B78H1 amelanotic melanoma cells upon incubation with porphyrin concentrations up to 52 microM. When the cells incubated for 18 h with 13 microM CuHp were irradiated with 532 nm light from a Q-switched Nd: YAG laser operated in a pulsed mode (10 ns pulses, 10 Hz) a significant decrease in cell survival was observed. The cell photoinactivation was not the consequence of a photodynamic process, as CuHp gave no detectable triplet signal upon laser flash photolysis excitation and no decrease in cell survival was observed upon continuous wave irradiation. Thus, it is likely that CuHp sensitization takes place by photothermal pathways. The efficiency of the photoprocess was modulated by different parameters; thus, while varying the amount of added CuHp in the 3.25-26 microM range had little effect, pulse energies larger than 50 mJ and irradiation times of at least 120 s were necessary to induce a cell inactivation of about 50%. The porphyrin-cell incubation time prior to irradiation had a major influence on cell survival, suggesting that the nature of the CuHp microenvironment can control the efficiency of photothermal sensitization. 相似文献