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191.
An estuarine two‐dimensional vertical finite‐element model of tidal flow has been established by laterally integrating Navier–Stokes equation. To this end, a moving grid finite‐element method has been used. An arbitrarily shaped quadrilateral element has been selected. This model has been validated by using field data from two monitoring stations at the North Passage of the Changjiang Estuary. Using this numerical model, two types of modelled results were obtained: (1) vertical distributions of tidal current velocities at the North Passage of the Changjiang Estuary; (2) longitudinal distributions of tidal current velocities at maximum flood tide, at high slack water, at maximum ebb tide and at low slack water tide at the North Passage of the Changjiang Estuary. The conclusion is that the model provides a reasonable agreement with observed data. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
192.
Many applications aim to learn a high dimensional parameter of a data generating distribution based on a sample of independent and identically distributed observations. For example, the goal might be to estimate the conditional mean of an outcome given a list of input variables. In this prediction context, bootstrap aggregating (bagging) has been introduced as a method to reduce the variance of a given estimator at little cost to bias. Bagging involves applying an estimator to multiple bootstrap samples and averaging the result across bootstrap samples. In order to address the curse of dimensionality, a common practice has been to apply bagging to estimators which themselves use cross-validation, thereby using cross-validation within a bootstrap sample to select fine-tuning parameters trading off bias and variance of the bootstrap sample-specific candidate estimators. In this article we point out that in order to achieve the correct bias variance trade-off for the parameter of interest, one should apply the cross-validation selector externally to candidate bagged estimators indexed by these fine-tuning parameters. We use three simulations to compare the new cross-validated bagging method with bagging of cross-validated estimators and bagging of non-cross-validated estimators. 相似文献
193.
Noise and flow field measurements are reported for an inverted profile coannular jet (where the annular jet speed exceeds the center jet speed) under simulated flight conditions. The annular and center jets were cold and both were operated subsonically. Forward flight was simulated by placing the coannular jet inside a larger open jet. Acoustic measurements show the effects of inverted profile shape and simulated flight on far field directivity, total radiated power, and spectral content. Measurements of total acoustic power demonstrate that the acoustic efficiency of inverted profile jets is about 3 dB less than the efficiency of “top hat” profile jets, and that the noise decreases as the seventh power of the relative jet velocity in the limit of small flight velocity, Uf. Flow measurements demonstrate that the jet spreading parameter λ = (Uj ? Uf)/(Uj + Uf) scales the thickness of the outer shear layer and the passage frequencies of the large turbulence scales. Comparisons between the turbulence time scales and the noise spectra suggest that coherent noise sources may become more important in forward flight. 相似文献
194.
V. A. Ditlov A. U. Gatchegov W. Enge F. Petersen M. Danziger A. Schulz V. Trofimov 《Radiation measurements》1997,28(1-6):137-144
Here we have made an attempt to describe etching along and perpendicular to the ion track axis with the many-hit response model. From experiments where sheets of Makrofol KG film were exposed to Au and Xe ions it was found that Vt/Vb depends on restricted energy loss (REL). Then, for the many-hit model the registration parameters of the detectors were found and were used for the calculation of the radial distributions of the transversal etching rate and were compared with experimental data. 相似文献
195.
R.B. Beeken J.J. Garbe N.R. Petersen M.R. Stoneman 《Journal of Physics and Chemistry of Solids》2004,65(5):1011-1014
The total electrical conductivities at room temperature of Ag6PSe5Cl, Ag6PSe5Br, and Ag6PSe5I were found to be 2.0×10−4, 5.6×10−4, and 6.8×10−4 S/cm, respectively. In the chloride and iodide compounds, the electronic contribution comprises approximately 1% of the total conductivity, although it exceeds 10% of the total conductivity in the bromide compound. Ag6PSe5Cl and Ag6PSe5Br exhibit purely Arrhenius behavior throughout the temperature range 150-300 K. Ag6PSe5I exhibits a second-order anomaly in electrical conductivity at 324 K. 相似文献
196.
The features of the latent track in polycarbonate can be analysed by measuring the diffusion constant under ultra high vacuum conditions. Stacks of 30 μm Makrofol KG foils were irradiated with uranium ions of 11.4 MeV/u at the GSI Darmstadt, Germany. We used different fluences from 3·1010 to 5·1011 ions/cm2. The diffusion constant was determined by the time-lag-method [1]. A quadrupole mass filter was used to observe the diffusion of the gas. We measured the diffusion of argon through different foils of each stack at room temperature. In all cases also unirradiated foils were measured. The dependence of the permeability and the diffusion constant on the ion fluence and the energy loss of the ions will be given and indications on the size of latent ion tracks concerning gas diffusion will be discussed. 相似文献
197.
The permeability of oxygen in water through polycarbonate is observed for thin Makrofol KG and Polyethylenterephthalat (PETP) foils of different thicknesses.
For each thickness the oxygen permeability through the polymer foils has been measured for unirradiated and with a high fluence irradiated foils. It was found that the permeability of oxygen through irradiated Makrofol KG foils is up to a factor of two higher than unirradiated foils.
The foils were irradiated with 79Au ions at the energy of 11.65 MeV/u at GSI Darmstadt, Germany. 相似文献
198.
Free chromate in lignosulfonates is determined by ion chromatography with a suppressor column. An interfering peak appears when the standard conductivity detector is used. With an on-line atomic absorption spectrometric detector, the chromatograms show two chromium-containing peaks, the second of which can be linearly related to chromate. The first peak is probably related to an unidentified anionic complex of Cr(III) with lignosulfonate. 相似文献
199.
J. C. Petersen 《Journal of Molecular Spectroscopy》1985,110(2):277-300
The cw dye laser excitation spectrum of the (110)-(000) and (021)-(000) vibronic bands of the
system of DNO was observed between 16530 and 16860 cm−1 with Doppler-limited resolution. A rotational analysis of the two bands gave values for the rotational constants and centrifugal distortion constants. DNO was produced by the pyrolysis method and more than 1200 lines were observed in the two bands. A total of 1112 of these lines could be assigned to 9 and 11 subbands of the (110)-(000) and (021)-(000) bands, respectively. The molecular constants determined reproduce the observed transition frequencies with an average deviation of 0.011 and 0.008 cm−1, respectively. Extensive perturbations in the excited state were found in most of the subbands. “Extra” lines were observed in connection with several of these perturbations. Accurate determination of the dissociation energy has been obtained; D0 = 17010 ± 10 cm−1. 相似文献
200.
C.R. Pollock F.R. Petersen D.A. Jennings J.S. Wells A.G. Maki 《Journal of Molecular Spectroscopy》1984,107(1):62-71
The absolute frequencies of 39 lines in the 0002-0000, 2001-0000, and 1201-0000 bands of N2O in the range 4300–4800 cm?1 have been measured by heterodyne frequency techniques. The lines were each measured in Doppler-limited absorption, with a color-center laser as a tunable probe of the N2O and two stabilized CO2 lasers as reference frequencies. New rovibrational constants have been fitted to these measurements. Tables of calculated transition frequencies are given, with estimated absolute uncertainties as small as 10?4 cm?1. The pressure shifts of four lines have been measured, and the values fall within the range of 0 to ?2 MHz/kPa (0 to ?0.2 MHz/Torr). 相似文献