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Summary The influence of column temperature (0–28 °C) and solute molecular size on the retention and enantioselectivity of a series of D, L dansyl amino acids with a non-polar side chain (valine, leucine, phenylalanine and tryptophan) were investigated using a vancomycin-based chiral stationary phase (CSP). The enthalpic and entropic terms for the solute-CSP association were determined from the linear vant Hoff plots. Two solute groups were distinguished in relation to these thermodynamic quantities: the solute group I (dansyl valine, dansyl leucine, dansyl phenylalanine) for which large negative values of enthalpic terms were obtained and the solute group II (dansyl tryptophan) for which H value was much less negative. The enthalpy-entropy compensation study revealed that the interaction mechanism was identical for the group I solute enantiomers but changed for D, L dansyl tryptophan. This was further exemplified as the group I compound enantiomers were resolved over the temperature range while the enantiomers of dansyl tryptophan were not separated in the operating conditions. Relationships between both the solute retention factors and apparent enantioselectivity, and the accessible surface area of the amino acid side chain indicated that when the solute molecular size increased (i) the retention was enhanced by the hydrophobic effect and (ii) the chiral discrimination decreased dependent, at least in part, on a steric hindrance phenomenon at the vancomycin aglycone pocket. 相似文献
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M. Huth M. Jourdan H. Adrian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):695-699
The node structure of the superconducting order parameter of the heavy-fermion system is analyzed within the weak-coupling theory. A pairing interaction induced by the exchange of antiferromagnetic spin excitations
is assumed as suggested by recent inelastic neutron scattering experiments and tunneling spectroscopy. The multi-sheeted Fermi
surface is taken into account. Based on a model susceptibility for the simple antiferromagnetic structure of , line nodes result at the rim of the magnetic Brillouin zone.
Received 29 July 1999 相似文献
25.
An experimental investigation on gaseous mixing zones originated from the Richtmyer-Meshkov instability has been undertaken
in a square cross section shock tube. Mass concentration fields, of one of the two mixing constituents, have been determined
within the mixing zone when the shock wave passes from the heavy gas to the light one, from one gas to an other of close density,
and from the light gas to the heavy one. Results have been obtained before and after the coming back of the reflected shock
wave. The diagnostic method is based on the infrared absorption of one of the two constituents of the mixing zone. It is shown
that the mixing zone is strongly deformed by the wall boundary layer. The consequence is the presence of strong gradients
of concentration in the direction perpendicular to the shock wave propagation. Finally, it is pointed out that the mixing
goes more homogeneous when the Atwood number tends to zero. 相似文献
26.
G. Jourdan L. Biamino C. Mariani C. Blanchot E. Daniel J. Massoni L. Houas R. Tosello D. Praguine 《Shock Waves》2010,20(4):285-296
The mitigation of a planar shock wave caused by a cloud of calibrated water droplets was studied both experimentally and numerically.
Experiments were carried out, with different shock wave Mach numbers ranging from 1.1 to 1.8, in a vertical shock tube coupled
with a droplet generator which produced a well-characterized cloud of droplets of 120, 250 and 500 μm in diameter. By exploiting
such an experimental set-up, we successfully measured the attenuation of a normal shock wave when passing through the water
droplet cloud. This series of experiments allowed to identify the main parameters of this investigation and a clear dependence
between the attenuation of the shock wave and terms governing the regimes of droplet breakup has been found. On the other
hand, to support this experimental approach, 1D unsteady calculations were performed in similar configurations. Although the
mathematical model based on an Eulerian/Eulerian approach was actually incomplete, the first comparisons between the experiments
and the simulations were rather interesting and pointed out the need to improve the physical model, by taking into account
the fragmentation and the vaporization of the droplets submitted to the shock wave as well as the size distribution of the
water spray. 相似文献
27.
We consider the on-line computation of the lattice of maximal antichains of a finite poset
. This on-line computation satisfies what we call the linear extension hypothesis: the new incoming vertex is always maximal in the current subposet of
. In addition to its theoretical interest, this abstraction of the lattice of antichains of a poset has structural properties which give it interesting practical behavior. In particular, the lattice of maximal antichains may be useful for testing distributed computations, for which purpose the lattice of antichains is already widely used. Our on-line algorithm has a run time complexity of
, where |P| is the number of elements of the poset,
, |MA(P)| is the number of maximal antichains of
and (P) is the width of
. This is more efficient than the best off-line algorithms known so far. 相似文献
28.
A. Jourdan P. Doussi re D. Leclerc S. Gurib F. Masetti N. Vodjdani F. Ratovelomanana A. Enard G. Morthier R. Baets C. J rgensen T. Durhuus B. Mikkelsen S. L. Danielsen K. Stubjkaer M. Schilling K. Wü nstel W. Idler D. Chiaroni 《Fiber and Integrated Optics》1996,15(3):193-210
We present the latest results about all-optical wavelength conversion obtained within the European Union—funded RACE ATMOS project. In particular, solutions based on carrier depletion in Distributed Brag Reflector lasers have reached penalty-free polarization-insensitive operation at up to 2.5 Gbit/s, while solutions based on Semiconductor Optical Amplifiers (SOAS) under cross-gain modulation have been demonstrated at more than 20 Gbit/s. The study of cross-phase modulation in SOAs has also been performed, leading to the monolithic integration of SOAs within an interferometer, according to structures proposed by the project. Penalty-free operation at up to 10 Gbit/s as well as signal reshaping have been obtained with such devices. Besides the study of components, wavelength converters have been used in several demonstrators assessing their maturity and compatibility with photonic-switching applications. 相似文献
29.
Epitaxial thin films of the heavy fermion superconductor UNi2Al3 with Tc(max)=0.98 K were investigated. The transition temperature Tc depends on the current direction which can be related to superconducting gaps opening at different temperatures. Also the influence of the magnetic ordering at TN approximately 5 K on R(T) is strongly anisotropic, indicating different coupling between the magnetic moments and itinerant charge carriers on the multisheeted Fermi surface. The upper critical field Hc2(T) suggests an unconventional spin-singlet superconducting state. 相似文献
30.