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排序方式: 共有257条查询结果,搜索用时 15 毫秒
1.
A parallel method for time discretization of parabolic equations based on Laplace transformation and quadrature 总被引:5,自引:0,他引:5
We consider the discretization in time of an inhomogeneous parabolicequation in a Banach space setting, using a representation ofthe solution as an integral along a smooth curve in the complexleft half-plane which, after transformation to a finite interval,is then evaluated to high accuracy by a quadrature rule. Thisreduces the problem to a finite set of elliptic equations withcomplex coefficients, which may be solved in parallel. The paperis a further development of earlier work by the authors, wherewe treated the homogeneous equation in a Hilbert space framework.Special attention is given here to the treatment of the forcingterm. The method is combined with finite-element discretizationin spatial variables. 相似文献
2.
Antibacterial activity of methylated chitosan and chitooligomer derivatives: Synthesis and structure activity relationships 总被引:1,自引:0,他引:1
Ögmundur Vidar Rúnarsson Tapio Nevalainen Tomi Järvinen Jón M. Einarsson Margrét Valdimarsdóttir 《European Polymer Journal》2007,43(6):2660-2671
The purpose of this study was to synthesize series of methylated chitosaccharide derivatives, possessing various degree of methylation, and to determine their structure activity relationship (SAR) with regard to their antibacterial effect against Staphylococcus aureus. Chitosan polymer and chitooligomers were used as starting materials and were methylated by reaction with methyl iodide. Depending on the reaction conditions the degree of N-quaternization ranged from 0% to 74%, with varying degree of N,N-dimethylation, N-monomethylation and O-methylation. More selective N-quaternization could be obtained with protection group strategy. At pH 5.5 the chitosaccharide polymers and their methylated derivatives were active against S. aureus with minimal inhibitory concentration (MIC) ranging from 16 to 512 μg/mL. At pH 7.2 the non-quaternized derivatives were inactive but their highly N-quaternized derivatives showed MIC as low as 8 μg/mL. The chitooligomers, as well as their derivatives, were inactive at both pH’s. The SAR studies revealed that N-quaternization was mainly responsible for the antibacterial effects at pH 7.2, whereas it did not contribute to the antibacterial activity under acidic conditions. 相似文献
3.
Hybrid density functional calculations on [Cr(NR)2C3H7(C2H4)]+ (R = H, tBu) have revealed a facile reductive elimination reaction involving beta-hydrogen transfer from the alkyl chain, suggesting that the active species in ethylene polymerisation with bis(imido)chromium(VI) precursors contains a reduced chromium atom. 相似文献
4.
Within an energy range of 2.4 eV, we have explored 29 of the 36 states of the diatomic molecule VC that arise from the atoms in their ground state, V(4s23d3;4F)+C(2s2 2p2;3P). We use multireference methods with large atomic natural orbital basis sets. The ground state is of 2Delta symmetry with the first two excited states, 4Delta and 2Sigma+, located 4.2 and 7.0 kcal/mol above the X state. All the states examined in this work are relatively strongly bound and show significant charge transfer from V to C. The binding energy of the X 2Delta state is estimated to be 95.3 kcal/mol in good agreement with the experimental value. 相似文献
5.
Li Caldeira Balkeståhl Erik Thomé on behalf of the PANDA Collaboration 《Hyperfine Interactions》2014,229(1-3):79-83
Strangeness and charm production provide an excellent probe of QCD in the confinement domain. With the PANDA detector at FAIR, this can be studied in e.g., hyperon production in the p?p → ?Y reactions. In PANDA, all ground state strange hyperons and single charmed Λ’s will be accessible. Simulations show that the differential cross sections and spin observables can be well reconstructed for these reaction channels. 相似文献
6.
Vidar Bj⊘rnstad 《合成通讯》2013,43(10):1793-1800
Conversion of a cyclic carbonyl carbon into a quaternary carbon has been effected by a Wittig–Horner reaction with diethyl (N-benzyliden)aminomethylphosphonate and a subsequent alkylation with a protected vinyl ketone. The product was a substrate for spiroannulation after initial hydrolysis. The reaction sequence was carried out as a one-pot reaction. 相似文献
7.
Ove Alexander Høgmoen Åstrand Lars Peter Engeset Austdal Ragnhild E. Paulsen Trond Vidar Hansen Pål Rongved 《Tetrahedron》2013
Herein the synthesis and characterization of new, lipophilic highly Zn2+-selective fluorescent probes are reported. High affinity for zinc (Kd 1.1–8.0 nM) over other biologically relevant metals and mixtures of metals was observed. Excitation at 360 nm afforded an emission spectrum with maximum at 530 nm for the zinc bound complex. The linear relationship between fluorescence intensity and zinc concentration indicates that FZnA-probes can be used for quantification. The probes have been synthesized in 28–45% overall yield and the feasibility for further functionalization with biologically relevant side chains has been demonstrated. In vitro studies using PC12 cells and 10 μM of one of the novel probes (FZnA-Ada) visualized endogenous labile Zn2+ after 45 min incubation time. 相似文献
8.
Andrea Thom Tim Ricken Joachim Bluhm Renatus Widmann Martin Denecke Tobias Gehrke 《PAMM》2015,15(1):433-434
To simulate the processes of methane oxidation in landfill cover layers, a new computational model was created. The purpose of the model is to allow a forecast on the performance of methanotrophic activity in landfill cover layers under changing environmental conditions. Therefore, a thermodynamic consistent model based on the well-known Theory of Porous Media (TPM) combined with the mixture theory was developed, which analyzes the relevant gas productions of methane, oxygen and carbon dioxide. Diffusion, advection and conversion processes are considered as well as the energy production during methane oxidation. With the help of the thermal imaging technique a new experimental setup was developed in order to validate the coupled model in terms of the heat generation. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
Catalytic,Asymmetric Synthesis of Phosphonic γ‐(Hydroxyalkyl)butenolides with Contiguous Quaternary and Tertiary Stereogenic Centers
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Marcus Frings Dr. Isabelle Thomé Dr. Ingo Schiffers Dr. Fangfang Pan Prof. Dr. Carsten Bolm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1691-1700
A procedure that enables high yielding access to phosphonic γ‐(hydroxyalkyl)butenolides with excellent regio‐, diastereo‐ and enantiocontrol is reported. The simultaneous construction of up to two adjacent quaternary stereogenic centers by a catalytic asymmetric vinylogous Mukaiyama aldol reaction unites biologically and medicinally relevant entities, namely α‐hydroxy phosphonates and γ‐(hydroxyalkyl)butenolides. This is achieved by utilizing a readily available chiral copper‐sulfoximine catalyst showing a broad functional group tolerance for both the electrophilic and nucleophilic reactants. A discussion about potential factors affecting the observed level of enantioselectivity, which stems from the enantiopure sulfoximine ligand, is also included. 相似文献
10.
Total Synthesis of the Anti‐inflammatory and Pro‐resolving Lipid Mediator MaR1n−3 DPA Utilizing an sp3–sp3 Negishi Cross‐Coupling Reaction
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Jørn Eivind Tungen Dr. Marius Aursnes Dr. Jesmond Dalli Dr. Hildur Arnardottir Prof. Dr. Charles Nicholas Serhan Prof. Dr. Trond Vidar Hansen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14575-14578
The first total synthesis of the lipid mediator MaR1n?3 DPA ( 5 ) has been achieved in 12 % overall yield over 11 steps. The stereoselective preparation of 5 was based on a Pd‐catalyzed sp3–sp3 Negishi cross‐coupling reaction and a stereocontrolled Evans–Nagao acetate aldol reaction. LC‐MS/MS results with synthetic material matched the biologically produced 5 . This novel lipid mediator displayed potent pro‐resolving properties stimulating macrophage efferocytosis of apoptotic neutrophils. 相似文献