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排序方式: 共有264条查询结果,搜索用时 250 毫秒
81.
James P. Johansen Alejandro M. CastroPablo M. Carrica 《International Journal of Multiphase Flow》2010
Measurements of gas volume fraction, bubble velocity, chord length and bubble size distributions were performed on the research vessel Athena II operating in Saint Andrew Bay in the gulf coast near Panama City, FL. Double tipped sapphire optical local phase-detection probes were used to acquire indicator functions downstream of the breaking bow wave, behind the masker and at the stern. These indicator functions were also taken at different depths, operating speeds and headings respect to the waves. The data processing includes the computation of velocity of individual bubbles and chord lengths, resulting in chord length distributions. These chord length distributions are used to obtain bubble size distributions using a novel procedure described in detail herein. Uncertainty analysis is performed for gas volume fraction, average bubble velocity and chord length. The results indicate that air entrainment increases with ship speed and sailing against the waves at all positions. The bow wave exhibits unsteady breaking that creates bubble clouds, which were characterized and identified by signal processing. At the stern a very strong dependence of bubble size with depth was found, with evidence that small bubbles (smaller than 500 μm) are transported through the bottom of the hull and reach the transom. The roller present at the transom, the associated strong unsteadiness and bubble entrainment are well captured, as indicated by the stern results, showing the frothy nature of the upper layer. 相似文献
82.
Thermal fixing in a La(3)Ga (5)SiO (14):Pr (3+) photorefractive crystal is demonstrated all the way down to room temperature. This, to our knowledge, is the first report of such an effect in any photorefractive material. From the temperature dependence of the process the activation energy of the carriers involved in the fixing process is measured to be E(A)=0.89 eV . Further, an effective photorefractive charge density of (1.4+/-0.2)x10(16) cm (-3) and Debye screening length of (6.8+/-0.7)x10(-6) cm is measured. 相似文献
83.
Single-mode operation of a laser-diode array with frequency-selective phase-conjugate feedback 总被引:2,自引:0,他引:2
A new technique for single-mode operation of laser-diode arrays is presented. A gain-guided GaAlAs laser diode array is coupled to an external frequency-selective phase-conjugate feedback system that contains a photorefractive barium titanate crystal, a Fabry-Perot etalon, and a spatial filter. The etalon is the key component, and it forces the array, which has low spatial and spectral coherence when it runs freely, to oscillate in a single spatial and a single longitudinal mode. At a drive current of two times the threshold current, the far-field pattern is reduced to only 1.4 times the diffraction limit, the spectral bandwidth is less than 0.02 nm, and the coherence length is increased by a factor of 70. The technique has general validity and can be applied to various other multimode laser systems. 相似文献
84.
Ab initio calculations have been carried out for the hydrogen peroxide molecule with different size Gaussian basis sets in an attempt to determine the relative importance of carefully refined geometry and improvement of the wave function for calculation of the trans rotational barrier,d-type polarization functions on the oxygen atoms are found to be essential for calculation of a trans rotational barrier. Using the (O/7,3,1)(H/4,1) basis set, a trans rotational barrier of 0.63 kcal/mole is calculated (exp. value, 1.1 kcal/mole). Except for refined calculations approaching the Hartree-Fock limit, careful geometry optimization is found to be of secondary importance to the inclusion ofd-type functions on the oxygen atoms and may be carried out satisfactorily using a smaller basis set than is used for the energy calculations. The (O/7,3) (H/4,1) basis set which includesp-type polarization functions on the hydrogen atoms yields geometrical parameters in good agreement with experiment as well as good charge distribution between the hydrogen and oxygen atoms.
Zusammenfassung Ab-initio Rechnungen für das Wasserstoffperoxidmolekül wurden mit Basissätzen verschiedener Größe durchgeführt um den Einfluß einer genauen Geometrie und einer Verbesserung der Wellen-funktion auf die Berechnung dertrans-Rotationsbarriere zu untersuchen. Es zeigte sich, daßd-Polarisationsfunktionen für solche Rechnungen äußerst wichtig sind. Mit dem Basissatz (O/7,3,1) (H/4,1) wurde die Rotationsbarriere mit 0,63 kcal/Mol berechnet (exp.: 1.1 kcal/Mol). Außer bei Rechnungen nahe am Hartree-Fock-Limit zeigte sich, daß die Geometrieoptimisierung gegenüber der Mitnahme vond-Funktionen von sekundärer Bedeutung ist und daher mit einem kleineren Basissatz durchgeführt werden kann, als die Energieberechnung. Der (O/7,3) (H/4,1) Basissatz, derp-Funktionen am Wasserstoffatom einschließt gibt die Geometrie und die Ladungsverteilung zwischen Wasserstoff- und Sauerstoffatom in guter Übereinstimmung mit dem Experiment.相似文献
85.
A high-performance size-exclusion chromatography procedure using Nucleosil Diol has been developed which provides the simultaneous determination of macromolecular dextran metronidazole monosuccinate ester prodrugs and the hydrolysis products metronidazole and metronidazole monosuccinate. Various factors influencing the chromatographic behaviour of the compounds are discussed. Baseline separation of the three substances was achieved within 8 min by using a 0.05 M phosphate buffer pH 7.5 eluent at a flow-rate of 2 ml min-1. The detection limit at 320 nm for a conjugate with a degree of substitution of 4.61 was found to be 3.5 micrograms ml-1. 相似文献
86.
A sensitive and selective method for the determination of pholcodine and its metabolites in urine using capillary gas chromatography with nitrogen detection is described. The procedure includes enzymatic hydrolysis of urine by beta-glucuronidase and sample pretreatment on C2 solid-phase extraction columns. Validation of the method showed good sensitivity, precision and reproducibility. The method was useful for the study of pholcodine metabolism in man. Pholcodine was found to conjugate with glucuronic acid. Morphine was identified as a metabolite and another unidentified metabolite was also detected. 相似文献
87.
Tom H. Johansen 《Journal of Crystal Growth》1987,80(2):343-350
We derive the exact analytical expression for the meniscus volume in terms of the crystal radius R, the melt contact angle θL, and the meniscus height h for the axisymmetric planar growth interface Czochralski configuration. This relation is applied together with motion and mass balance considerations to find the general rate of change in the force experience by the weighing cell in a standard diameter control arrangement. In contrast to the classical work of Bardsley et al. (1977), which is limited to the close viscinity of stationary right cylinder growth, our results are valid for growth developing any crystal profile. In addition, they also account for the fall of melt level due to finite crucible size. The magnitudes of the capillary contributions to the force, and their implications for diameter servo control, are discussed over a wide range of profile parameters using the Tsivinskii formula for h = h (R, θL). 相似文献
88.
89.
M. S. Johansen P. Alstrom J. Borg M. T. Levinsen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):665-676
Significant statistical bias in LDA measurements and how to adequately deal with it is a subtle problem when dealing with
turbulent flows. In order to attempt a clarification we have performed measurements on a non-standard “grid experiment” where
a clear bias effect is found. We have investigated the effect of several corrective measures and find that best results, in
the sense of having the first moment converge to zero, are obtained when using the time between events as statistical weights.
The corrected time series have been used to check for extended self-similarity (ESS). Even though no scaling regime is seen
for the third moment and the flow certainly is neither isotropic nor homogeneous, perfect ESS scaling based on the absolute
third moment is observed up to the twelfth moment, extending into a time domain regime where the Taylor hypothesis of frozen
turbulence is obviously violated. Reversing the argument this indicates that the correction scheme needed can be experimentally
decided on using the criterion stated above and especially so if ESS is to be expected. Finally we have used the corrected
data to quantify the deviations from Gaussian behavior of the velocity difference probability density function for a weakly
turbulent flow. Through comparison with results on the Gaussian-Lorentzian distribution we find that the even part of the
experimental distribution can be reproduced quite well by a single-parameter family of distributions with second moment equal
unity.
Received 5 August 1998 and Received in final form 21 December 1998 相似文献
90.
Eriksson J Malmsten M Tiberg F Callisen TH Damhus T Johansen KS 《Journal of colloid and interface science》2005,285(1):94-99
The effects of enzyme structure and activity on the degradation of model cellulose substrates were investigated by ellipsometry for the cellulase Humicola insolens GH45. The inactive variant D10N was found to adsorb at the cellulose surface but also to be incorporated into the cellulose films to an extent that depended on pH. For the native protein, the initial adsorption monitored for the inactive variant D10N was followed by enzyme-mediated degradation of the cellulose films. Again, a dependence on pH was found, such that higher pH resulted in slower enzymatic degradation. Removing the carbohydrate-binding module eliminated this pH dependence but also resulted in a decreased adsorption to the cellulose surface, and in a decreased net catalytic effect. 相似文献