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31.
The aim of this paper is to evaluate the influence of the surface free energy upon the propagation of the eigenmodes of structures, by studying successively (a) the Rayleigh wave for an elastic half-space, (b) the Lamb waves for an elastic layer, and (c) the guided modes for a tri-layer structure (e.g., metal/adhesive/metal). The surface free energy is a parameter which appears in the jump conditions of stresses and displacements at each interface, and which consequently modifies the eigenmodes, solutions of the boundary conditions system. As expected, the Rayleigh wave is dispersive and its velocity increases when the surface free energy increases. In the same way, the velocity of Lamb waves also increases except at normal angle of propagation where the surface free energy does not arise. Moreover, near the Rayleigh angle, the behaviour of the A0 and S0 Lamb modes varies strongly according to the surface free energy. Similar results are observed for the tri-layer structure. 相似文献
32.
33.
Horst W. Hamacher Martine Labbé Stefan Nickel Anders J.V. Skriver 《Annals of Operations Research》2002,110(1-4):33-53
Locating a facility is often modeled as either the maxisum or the minisum problem, reflecting whether the facility is undesirable (obnoxious) or desirable. But many facilities are both desirable and undesirable at the same time, e.g., an airport. This can be modeled as a multicriteria network location problem, where some of the sum-objectives are maximized (push effect) and some of the sum-objectives are minimized (pull effect).We present a polynomial time algorithm for this model along with some basic theoretical results, and generalize the results also to incorporate maximin and minimax objectives. In fact, the method works for any piecewise linear objective functions. Finally, we present some computational results. 相似文献
34.
Moroni L Gellini C Salvi PR Marcelli A Foggi P 《The journal of physical chemistry. A》2008,112(44):11044-11051
S1 --> S(n) spectra of porphyrin, diprotonated porphyrin, and tetraoxaporphyrin dication have been measured in the energy range 2-3 eV above S1 at room temperature in solution by means of transient absorption spectroscopy exciting with femtosecond pulses. Highly excited pi pi* states not active in the conventional S0 --> S(n) spectrum have been observed. The experimental data are discussed on the basis of the time dependent density functional theory taking advantage of large scale calculations of configuration interaction between singly excited configurations (DF/SCI). The DF/SCI calculation on porphyrin has allowed to assign g states active in the S1 --> S(n) spectrum. Applying the same calculation method to tetraoxaporphyrin dication the S0 --> S(n) spectrum is reproduced relatively to the Q and B (Soret) bands as well as to the weaker E(u) bands at higher energy. According to our calculation the S1 --> S(n) transient spectrum is related to states of g symmetry mainly arising from excitations between doubly degenerate pi and pi* orbitals such as 2e(g) --> 4e(g). In the case of diprotonated porphyrin it is shown that the complex of the macrocycle with two trifluoroacetate anions plays a significant role for absorption. Charge transfer excitations from the anions to the macrocycle contribute to absorption above the Soret band, justifying the intensity enhancement of the S0 --> S(n) spectrum with respect to the other two macrocyclic systems. 相似文献
35.
The use of quasi-isoelectric buffers consisting of narrow pH cuts of carrier ampholytes (NC) has been investigated to limit protein adsorption on capillary walls during capillary zone electrophoresis experiments. To quantify protein adsorption on the silica surface, a method derived from that of Towns and Regnier has been developed. alpha-Lactalbumin (14 kDa, pI 4.8) and alpha-chymotrypsinogen A (25 kDa, pI 9.2) have been used as model proteins. Acidic narrow pH cuts of carrier ampholytes (NC, pH 3.0) obtained from fractionation of Serva 4-9 carrier ampholytes were used as BGE in bare-silica capillaries, and allowed to decrease significantly protein adsorption, as compared to experiments performed with classical formate buffer. The use of NC as BGE appeared to be as efficient as the use of polydimethylacrylamide coating to prevent protein adsorption. This increase of protein recovery when using NC was attributed to the interaction of carrier ampholytes with the silica surface, leading to a shielding of the capillary wall. 相似文献
36.
Martin C Pignon F Magnin A Meireles M Lelièvre V Lindner P Cabane B 《Langmuir : the ACS journal of surfaces and colloids》2006,22(9):4065-4075
Aqueous dispersions of nanometric clay platelets (Laponite) have been dewatered through different techniques: centrifugation, mechanical compression, and osmotic stress (dialysis against a polymer solution). The positional and orientational correlations of the particles have been determined through small-angle neutron scattering. Uniaxial compression experiments produce concentrated dispersions (volume fraction > 0.03) in which the platelets have strong orientational and positional correlations. The orientational correlations cause the platelets to align with their normal along a common axis, which is the axis of compression. The positional correlations cause the platelets to be regularly spaced along this direction, with a spacing that matches the average volume per particle in the dispersion. The swelling law (volume fraction versus separation distance) is one-dimensional, as in a layered system. Changes in the applied osmotic pressure cause the water content of the dispersion to either rise or decrease, with time scales that are controlled by interparticle friction forces and by hydrodynamic drag. At long times, the dispersions approach osmotic equilibrium, which can be defined as the common limit of swelling and deswelling processes. The variation of the equilibrium water content with the applied osmotic pressure has been determined over 1 decade in volume fractions (0.03 < phi < 0.3) and 3 decades in pressures. This equation of state matches the predictions made from the knowledge of the forces and thermal agitation for all components in the dispersion (particles, ions, and water). 相似文献
37.
Regert M 《Journal of separation science》2004,27(3):244-254
Although organic materials are very sensitive to biochemical alteration processes, they may be preserved for millennia in various archaeological contexts. Remains of adhesives made during prehistory were discovered at different sites, in the form of residues adhering to flint tools and ceramic vessels or as free lumps in sediment. To characterise the natural substances exploited for adhesive production during late prehistory, we undertook GC and GC/MS analysis of 90 samples from 8 sites dating from the Neolithic to Iron Age periods. This paper discusses our approach to the study of organic adhesives preserved in archaeological contexts, with a particular focus on the presentation of the various categories of organic adhesives that we analysed and the choice of chromatographic conditions adapted to the specificity of such samples. The results obtained show that birch bark tar, a triterpenoid adhesive made by destructive distillation of white birch bark, was predominantly used during the neolithic period even though other materials such as various barks or organic fossil substance were also used. During the Bronze and Iron ages, which follow the Neolithic period, adhesive production is evolving through the expansion of the range of the natural substances used (identification of diterpenoid pine resin) and the addition of beeswax as a plasticiser to birch bark tar. By combining chromatographic analysis and archaeological data, it was thus possible to follow the evolution of adhesive making at the end of prehistory, testifying to the inventiveness of the craftsmen whatever the period considered. 相似文献
38.
Anton M. ter Laak Hendrik Timmerman Rob Leurs Paul H. J. Nederkoorn Martine J. Smit Gabriëlle M. Donné-Op den Kelder 《Journal of computer-aided molecular design》1995,9(4):319-330
Summary A modelling study has been carried out, investigating the binding of histamine (Hist), 2-methylhistamine (2-MeHist) and 2-phenylhistamine (2-PhHist) at two postulated agonistic binding sites on transmembrane domain 5 (TM5) of the histamine H1-receptor. For this purpose a conformational analysis study was performed on three particular residues of TM5, i.e., Lys200, Thr203 and Asn207, for which a functional role in binding has been proposed. The most favourable results were obtained for the interaction between Hist and the Lys200/Asn207 pair. Therefore, Lys200 was subsequently mutated and converted to an alanine, resulting in a 50-fold decrease of H1-receptor stimulation by histamine. Altogether, the data suggest that the Lys200/Asn207 pair is important for activation of the H1-receptor by histamine. In contrast, analogues of 2-PhHist seem to belong to a distinct subclass of histamine agonists and an alternative mode of binding is proposed in which the 2-phenyl ring binds to the same receptor location as one of the aromatic rings of classical histamine H1-antagonists. Subsequently, the binding modes of the agonists Hist, 2-MeHist and 2-PhHist and the H1-antagonist cyproheptadine were evaluated in three different seven--helical models of the H1-receptor built in homology with bacteriorhodopsin, but using three different alignments. Our findings suggest that the position of the carboxylate group of Asp116 (TM3) within the receptor pocket depends on whether an agonist or an antagonist binds to the protein; a conformational change of this aspartate residue upon agonist binding is expected to play an essential role in receptor stimulation.Abbreviations 2-MeHist
2-methylhistamine
- 2-PEA
2-pyridyl-ethylamine
- 2-PhHist
2-phenylhistamine
- CHO
Chinese hamster ovary
- Eint
interaction energy
- Estr
strain energy
- GES
global energy structure
- gpH1R
guinea pig H1-receptor
- GPCR
G-protein coupled receptor
- Hist
histamine
- N
proximal nitrogen
- N
tele nitrogen
- TM
transmembrane domain
- WT
wild type 相似文献
39.
Christelle de Bellefontaine Flore Josse Martine Domurado Dominique Domurado 《Applied biochemistry and biotechnology》1994,48(2):117-123
In order to detect low levels of enzyme activity, specifically glucose oxidase, in biological samples, an immunoenzymatic assay was developed since currently available methods could not be used because of either their lack of sensitivity or the conditions prevailing in our samples: turbidity of the medium, presence of redox systems other than glucose oxidase, and high concentration of proteins. The principle of the method is to coat a polystyrene surface with a fragment Fc-specific anti-IgG, then with an antibody directed against the looked-for enzyme, which is simultaneously the antigen and the enzyme activity required for immunoenzymatic detection. We applied this concept to biological samples after glucose oxidase administration to mice. This method achieves specificity and sensitivity (20 ng/mL or 1 ng) with samples of biological origin. No marker is needed since the antigen itself possesses an enzyme activity. This method, which requires a small sample volume (50 ΜL, 20 ΜL, if necessary), can be extended easily to the many enzymes currently used as markers. It could also be applied to the native enzymes of medical interest for which antibodies and a colorimetric reaction are available. 相似文献
40.
We describe an elementary argument from abstract ergodic theory that can be used to prove mixing of hyperbolic flows. We use
this argument to prove the mixing property of product measures for geodesic flows on (not necessarily compact) negatively
curved manifolds. We also show the mixing property for the measure of maximal entropy of a compact rank-one manifold. 相似文献