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91.
Jean-Franç ois Coulombel Thierry Goudon 《Transactions of the American Mathematical Society》2007,359(2):637-648
We construct global smooth solutions to the multidimensional isothermal Euler equations with a strong relaxation. When the relaxation time tends to zero, we show that the density converges towards the solution to the heat equation.
92.
K. Rßner M. Hümmer A. Benkert A. Forchel 《Physica E: Low-dimensional Systems and Nanostructures》2005,30(1-2):159-163
We have successfully fabricated and characterized room temperature continuous wave (cw) GaInAsSb/AlGaAsSb distributed feedback lasers emitting in the wavelength region between 2.499 and 2.573 μm. To the best of our knowledge, this is the longest emission wavelength realized with a GaSb-based DFB laser diode. The laser structure used for DFB processing was grown by solid source molecular beam epitaxy. A DFB concept requiring no subsequent overgrowth step was used by defining first-order Cr-Bragg gratings laterally patterned to a ridge waveguide. Threshold currents smaller than 60 mA and room temperature cw output powers up to 6.5 mW were obtained. The laser diodes show single mode emission with side mode suppression ratios (SMSR) of up to 32 dB. 相似文献
93.
Rodrigo París José Luis de la Fuente 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3538-3549
Different diblock copolymers constituted by one segment of a monomer supporting a reactive functional group, like allyl methacrylate (AMA), were synthesized by atom transfer radical polymerization (ATRP). Bromo‐terminated polymers, like polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(butyl acrylate) (PBA) were employed as macroinitiators to form the other blocks. Copolymerizations were carried out using copper chloride with N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as the catalyst system in benzonitrile solution at 70 °C. At the early stage, the ATRP copolymerizations yielded well‐defined linear block copolymers. However, with the polymerization progress a change in the macromolecular architecture takes place due to the secondary reactions caused by the allylic groups, passing to a branched and/or star‐shaped structure until finally yielding gel at monomer conversion around 40% or higher. The block copolymers were characterized by means of size exclusion chromatography (SEC), 1H NMR spectroscopy, and differential scanning calorimetry (DSC). In addition, one of these copolymers, specifically P(BA‐b‐AMA), was satisfactorily modified through osmylation reaction to obtain the subsequent amphiphilic diblock copolymer of P(BA‐b‐DHPMA), where DHPMA is 2,3‐dihydroxypropyl methacrylate; demonstrating the feasibility of side‐chain modification of the functional obtained copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3538–3549, 2007 相似文献
94.
On‐line coupling of LC and ICP‐MS has been used for fractionation and detection of species of Cu, Fe, I, Se and Zn in human serum. It has been shown that anion exchange chromatography provided better separation capability (both intra‐ and inter‐element) than size‐exclusion chromatography. The mobile phases for ion exchange chromatography consisted of Tris–HNO3 buffer and ammonium salt (nitrate, acetate or formate). Formate was found to be the best mobile phase counter ion, enabling good chromatographic separation, and is acceptable for mass spectrometry too. The quantitative evaluation of element concentrations adhering to individual fractions was performed by the peak area normalization method. The repeatability of results ranged from 3 to 15% (depending on the element concentration level) and represented the main part of the result uncertainty. The accuracy of Cu and Zn fraction determinations was confirmed by comparison with the isotope dilution technique. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
95.
E. V. Ermanyuk 《Experiments in fluids》2002,32(2):242-251
This paper presents a study on affine similitude for the force coefficients of an arbitrary body oscillating in a uniformly
stratified fluid. A simple formula is derived that gives a relation between the force coefficients for a body oscillating
in homogeneous and uniformly stratified ideal fluids. In particular, it implies the existence of a universal nondimensional
similitude criterion for a family of affinely similar bodies, namely, the bodies that can be transformed into each other by
vertical dilation of the initial coordinate system. Theoretical results are verified by experiments with a set of spheroids
having different length-to-diameter ratios. The experimental technique for evaluation of the frequency-dependent force coefficients
is based on Fourier analysis of the time-history of damped oscillation tests.
Received: 25 September 2000 / Accepted: 6 July 2001 Published online: 29 November 2001 相似文献
96.
97.
Buffer gas beam coolers may become excellent beam preparation devices for high-resolution mass separation. The small beam
emittance provided makes efficient isobar resolution a realistic goal. In order to fulfill the needs of future facilities
providing high-intensity beams of rare isotopes, it is desirable to increase the beam intensity limit of such devices from
typically several tens of nanoamperes to microamperes. This requires the usage of high-voltage radiofrequencies in a low-pressure
gas environment. A buffer gas beam cooler, dedicated to this purpose, is under development at the NSCL. The study of voltage
breakdowns under such conditions and the design of an electrode system minimizing them is mandatory.
相似文献
98.
P. Paasche T. Valenzuela D. Biswas C. Angelescu G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):295-300
We have examined experimentally the motional spectrum of an electron cloud confined in a Penning trap. When the axial oscillation
is excited by a radio frequency field the resonance exhibits a double structure. Both components depend differently on the
number of trapped electrons and have different shape and width. We conclude that one of them corresponds to the excitation
of the individual electrons while the other is the center-of-mass mode of the cloud. The threshold behaviour of the center-of-mass
resonance suggests that it is a parametric instability of a Mathieu type equation of motion.
Received 11 July 2001 and Received in final form 12 November 2001 相似文献
99.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
100.
We study the propagation of the light mesons σ,ω,ρ, and a0(980) in dense hadronic matter in an extended derivative scalar coupling model. Within the scheme proposed it is possible
to unambiguously define effective density-dependent couplings at the Lagrangian level. We first apply the model to study asymmetric
nuclear matter with fixed isospin asymmetry, and then we pay particular attention to hypermatter in β-equilibrium. The equation
of state and the potential contribution to the symmetry coefficient arising from the mean-field approximation are investigated.
Received: 16 October 2001 / Accepted: 10 January 2002 相似文献