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排序方式: 共有382条查询结果,搜索用时 15 毫秒
91.
We prove convergence to equilibrium with explicit rates for various kinetic equations with relatively bad control of the distribution tails: in particular, Boltzmann-type equations with (smoothed) soft potentials. We compensate the lack of uniform-in-time estimates by the use of precise logarithmic Sobolev-type inequalities, and the assumption that the initial datum decays rapidly at large velocities. Our method not only gives explicit results on the times of convergence, but is also able to cover situations in which compactness arguments apparently do not apply (even mere convergence to equilibrium was an open problem for soft potentials). 相似文献
92.
A. Filisetti R. Serra T. Carletti M. Villani I. Poli 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(2):249-256
We consider generic protocells models allowing linear and non-linear
kinetics for the main involved chemical reactions. We are interested
in understanding if and how the protocell division and the metabolism
do synchronise to give rise to sustainable evolution of the protocell. 相似文献
93.
Nonlinear Isolator Dynamics at Finite Deformations: An Effective Hyperelastic,Fractional Derivative,Generalized Friction Model 总被引:3,自引:0,他引:3
In presenting a nonlinear dynamic model of a rubber vibrationisolator, the quasistatic and dynamic motion influences on theforce response are investigated within the time and frequencydomain. It is found that the dynamic stiffness at the frequency ofa harmonic displacement excitation, superimposed upon the longterm isolator response, is strongly dependent on staticprecompression, dynamic amplitude and frequency. The problems ofsimultaneously modelling the elastic, viscoelastic and frictionforces are removed by additively splitting them, modelling theelastic force response by a nonlinear, shape factor basedapproach, displaying results that agree with those of aneo-Hookean hyperelastic isolator at a long term precompression.The viscoelastic force is modeled by a fractional derivativeelement, while the friction force governs from a generalizedfriction element displaying a smoothed Coulomb force. A harmonicdisplacement excitation is shown to result in a force responsecontaining the excitation frequency and its every otherhigher-order harmonic, while using a linearized elastic forceresponse model, whereas all higher-order harmonics are present forthe fully nonlinear case. It is furthermore found that the dynamicstiffness magnitude increases with static precompression andfrequency, while decreasing with dynamic excitationamplitude – eventually increasing at the highest amplitudes due tononlinear elastic effects – with its loss angle displaying amaximum at an intermediate amplitude. Finally, the dynamicstiffness at a static precompression, using a linearized elasticforce response model, is shown to agree with the fully nonlinearmodel except at the highest dynamic amplitudes. 相似文献
94.
Fredriksson MJ Petersson P Axelsson BO Bylund D 《Journal of chromatography. A》2010,1217(52):8195-8204
A method for tracking of sample components during liquid chromatography-mass spectrometry (LC-MS) method development has been proposed. The method manages to, fully automatically and without user intervention, find the chromatographic peaks in the data sets, discriminate them to sample components and track them when the separation conditions have been changed. The algorithm utilises the resolution obtained from all considered data sets and has the ability to discriminate the non informative parts. The technique has a great sensitivity even in cases where a majority of the tracked components cannot easily be spotted by means of traditional total ion chromatogram (TIC) or base peak chromatogram (BPC) representations. The method was tested on an experimental sample using six different columns and an average of 79% of the suggested sample components could be successfully tracked at a minimum area of 0.05% of the main component in the sample. 66 components with 79-92% of the total suggested component area were able to be tracked between all data sets. The method could be used to rapidly investigate selectivity during different types of separation conditions. 相似文献
95.
Giovanna Cancelliere Alessia Ciogli Ilaria D’Acquarica Francesco Gasparrini Jelena Kocergin Domenico Misiti Marco Pierini Harald Ritchie Patrizia Simone Claudio Villani 《Journal of chromatography. A》2010,1217(7):990-999
Three brush-type chiral stationary phases (CSPs) differing in the particle size of the starting silica particles have been prepared by covalent grafting of the π-acidic bis-(3,5-dinitrobenzoyl)-derivative of trans-1,2-diaminocyclohexane (DACH-DNB). Starting silica particles of 4.3, 2.6 and 1.9 micron were used to generate the final CSPs using an improved, highly reproducible synthetic methodology, that allowed to assemble and surface-graft the whole chiral selector in only two steps. The different CSPs have been packed in columns of various length and diameters, and fully characterized in terms of flow permeability, kinetic performances and enantioselectivity using a set of test solutes. Very high speed and high resolution applications together with stereodynamic HPLC examples are demonstrated on the columns with reduced particle diameters, on which separations of several enantiomeric pairs are routinely obtained with analysis times in the 15–40 s range. 相似文献
96.
Elena Badaloni Walter Cabri Alessia Ciogli Ilaria D’Acquarica Roberto Deias Francesco Gasparrini Fabrizio Giorgi Dorina Kotoni Claudio Villani 《Journal of chromatography. A》2010,1217(7):1024-1032
The aim of the present study was to extend the use of the “Inverted Chirality Columns Approach (ICCA)” previously developed for the identification and quantitation of the trace enantiomer in highly enriched samples of the camptothecin (CPT) family of drugs to a novel water-soluble CPT derivative, namely namitecan (ST1968), currently undergoing phase I clinical trials as anticancer agent. Namitecan, identified from a series of hydrophilic 7-oxyiminomethyl derivatives, contains a free terminal amino group, which traditionally hampers the analysis under normal-phase HPLC conditions. Nevertheless, commercially available Pirkle-type chiral stationary phases (CSPs) available in both the enantiomeric forms (i.e., having the same bound selector with opposite configuration) mainly operate under normal-phase HPLC conditions. For this reason, namitecan was pre-column N-protected with isocyanates A–D and their sulfur analogues E–H to reduce its polarity by converting the amino group into a fragment compatible with the chiral recognition mechanism (i.e., ureido and thioureido groups). Once the optimal columns system and derivatizing agents were selected, an original enantioselective HPLC–MS/MS technique was developed on the Whelk-O1 CSPs. 相似文献
97.
Within the area of short term airline operational planning, Tail Assignment is the problem of assigning flight legs to individual
identified aircraft while satisfying all operational constraints, and optimizing some objective function. In this article,
we propose that Tail Assignment should be solved as part of both the short and the long term airline planning. We further
present a hybrid column generation and constraint programming solution approach. This approach can be used to quickly produce
solutions for operations management, and also to produce close-to-optimal solutions for long and mid term planning scenarios.
We present computational results which illustrate the practical usefulness of the approach. 相似文献
98.
D'Acquarica I Gasparrini F Pierini M Villani C Zappia G 《Journal of separation science》2006,29(10):1508-1516
Dynamic HPLC on enantioselective stationary phases has become a well-established technique to investigate chiral molecules with internal motions that result in stereoinversion and occur on the time scale of the separation process. Kinetic parameters for the on-column interconversion phenomena can be extracted from experimental peak profiles by computer simulation or by direct calculation methods. The technique has been used in a wide range of temperatures and is complementary in scope to dynamic NMR spectroscopy. 相似文献
99.
100.
Kee JM Villani B Carpenter LR Muir TW 《Journal of the American Chemical Society》2010,132(41):14327-14329
Protein phosphorylation is one of the most common and extensively studied posttranslational modifications (PTMs). Compared to the O-phosphorylation of Ser, Thr, and Tyr residues, our understanding of histidine phosphorylation is relatively limited, particularly in higher eukaryotes, due to technical difficulties stemming from the intrinsic instability and isomerism of phosphohistidine (pHis). We report the design and synthesis of stable and nonisomerizable pHis analogues. These pHis analogues were successfully utilized in solid-phase peptide synthesis and semi-synthesis of histone H4. Significantly, the first antibody that specifically recognizes pHis was obtained using the synthetic peptide as the immunogen. 相似文献