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891.
本文在u=u(z),k_y=k_y(x,z),k_z=k_z(x,z)及考虑下垫面对浓度场有清除作用的前提下,求解了定常连续点源三维湍流扩散方程,得到浓度场的分析解。解中含有随稳定度而变的参数。应用Project Prairie Grass的地面源试验资料,经验地定出了从中等不稳定到中等稳定时适用于小尺度扩散的有关参数。将本模式用来计算上述试验中的浓度,除较少的例外情况外,个例的计算浓度与实验浓度的相对误差平均在200%以内,并对误差原因进行了讨论。最后对下垫面影响的不同大小计算了清除作用对地面源浓度场的影响。 相似文献
892.
893.
894.
An Arctic Ocean eddy in sub-surface layer is analyzed in this paper by use of temperature,salinity and current profiles data obtained at an ice camp in the Canada Basin during the second Chinese Arctic Expedition in summer of 2003.In the vertical temperature section,the eddy shows itself as an isolated cold water block at depth of 60 m with a minimum temperature of-1.5℃,about 0.5℃ colder than the ambient water.Isopycnals in the eddy form a pattern of convex,which indicates the eddy is anticyclonic.Although maximum velocity near 0.4 m s-1 occurs in the current records observed synchronously,the current pattern is far away from a typical eddy.By further analysis,inertial frequency oscillations with amplitudes comparable with the eddy velocity are found in the sub-surface layer currents.After filter the inertial current and mean current,an axisymmetric current pattern of an eddy with maximum velocity radius of 5 km is obtained.The analysis of the T-S characteristics of the eddy core water and its ambient waters supports the conclusion that the eddy was formed on the Chukchi Shelf and migrated northeastward into the northern Canada Basin. 相似文献
895.
Fully coupled, porous solid–fluid formulation, implementation and related modeling and simulation issues are presented in this work. To this end, coupled dynamic field equations with u?p?U formulation are used to simulate pore fluid and soil skeleton (elastic–plastic porous solid) responses. Present formulation allows, among other features, for water accelerations to be taken into account. This proves to be useful in modeling dynamic interaction of media of different stiffnesses (as in soil–foundation–structure interaction). Fluid compressibility is also explicitly taken into account, thus allowing excursions into modeling of limited cases of non‐saturated porous media. In addition to these features, present formulation and implementation models in a realistic way the physical damping, which dissipates energy. In particular, the velocity proportional damping is appropriately modeled and simulated by taking into account the interaction of pore fluid and solid skeleton. Similarly, the displacement proportional damping is physically modeled through elastic–plastic processes in soil skeleton. An advanced material model for sand is used in present work and is discussed at some length. Also explored in this paper are the verification and validation issues related to fully coupled modeling and simulations of porous media. Illustrative examples describing the dynamical behavior of porous media (saturated soils) are presented. The verified and validated methods and material models are used to predict the behavior of level and sloping grounds subjected to seismic shaking. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
896.
The soil freeze–thaw controls the hydrological and carbon cycling and thus affects water and energy exchanges at land surface. This article reported a newly developed algorithm for distinguishing the freeze/thaw status of surface soil. The algorithm was based on information from Advanced Microwave Scanning Radiometer Enhanced (AMSR‐E) which records brightness temperature (Tb) in the afternoon and after midnight. The criteria and discriminant functions were obtained from both radiometer observations and model simulations. First of all, the microwave radiation from freeze–thaw soil was examined by carrying out experimental measurements at 18·7 and 36·5 GHz using a Truck‐mounted Multi‐frequency Microwave Radiometer (TMMR) in the Heihe River of China. The experimental results showed that the soil moisture is a key component that differentiates the microwave radiation behaviours during the freeze–thaw process, and the differences in soil temperature and emissivity between frozen and thawed soils were found to be the most important criteria. Secondly, a combined model was developed to consider the impacts of complex ground surface conditions on the discrimination. The model simulations quite followed the trend of in situ observations with an overall relation coefficient (R) of approximately 0·88. Finally, the ratio of Tb18·7H (horizontally polarized Tb at 18·7 GHz) to Tb36·5V was considered primarily as the quasi‐emissivity, which is more reasonable and explicit in measuring the microwave radiation changes in soil freezing and thawing than the spectral gradient. By combining Tb36·5V to indicate the soil temperature variety, a Fisher linear discrimination analysis was used to establish the discriminant functions. After being corrected by TMMR measurements, the new discriminant algorithm had an overall accuracy of 86% when validated by 4‐cm soil temperature. The multi‐year discriminant results also provided a good agreement with the classification map of frozen ground in China. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
897.
The effects of degraded porphyran (P1) and natural porphyran (P) on the lifespan and vitality of Drosophila melanogaster are studied. The porphyrans, added daily to the food medium at 0.2% and 1% concentrations, can significantly increase the lifespan in average of 55.79 and 58.23 d in 0.2% P1 diet females and 1% P1 diet males, extending by 12.29% and 8.60% over the corresponding controls, respectively. The effects of porphyrans on D. melanogaster in heat-stress condition were also examined, and found a remarkable increase in survival time. The results which are consistently associated with the use of porphyrans are related to their free radical scavenger action. Considerable increase in vitality demonstrated that vitalities of middle-aged fly (assessed by measuring their mating capacity) was observed after porphyrans addition. Therefore, porphyrans are effective in reducing the rate of aging, and P1 in low molecular weight is better than natural P. 相似文献
898.
Jun-Liang Zhao Li Chen 《中国天文和天体物理学报》2007,7(4):572-578
On the reasonable hypothesis that the internal motions of member stars of a cluster are random and isotropic, a method which can be used to estimate the velocity distance of the cluster and its uncertainty is developed. The velocity distance so determined is an absolute distance estimate, and is completely independent of the (widely used) luminosity distance, which is a relative distance estimate. Using the published high-accuracy observational data of radial velocities and proper motions of the stars in the open cluster M11 region, we have determined the distance of M11 to be 1.89 ± 0.52kpc. This is in quite good agreement with the published luminosity distances of the cluster. We briefly discuss the problems concerned, including the sources of errors in the method and its applicable range. 相似文献
899.
A model is presented using the electron cyclotron maser instability driven by a loss-cone distribution (taking account of the relativistic effects for electron cyclotron frequency and electron velocity as well as Landau damping and cyclotron damping) to excite the UFFS (Ultra-Fast Fine Structures) of microwave bursts and adopting a nonlinear density wave as a trigger mechanism to explain the millisecond time structure of the UFFS.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
900.
We present a direct comparison between two different techniques: time-distance helioseismology and a local correlation tracking
method for measuring mass flows in the solar photosphere and in a near-surface layer. We applied both methods to the same
dataset (MDI high-cadence Dopplergrams covering almost the entire Carrington rotation 1974) and compared the results. We found
that, after necessary corrections, the vector flow fields obtained by these techniques are very similar. The median difference
between directions of corresponding vectors is 24°, and the correlation coefficients of the results for mean zonal and meridional
flows are 0.98 and 0.88, respectively. The largest discrepancies are found in areas of small velocities where the inaccuracies
of the computed vectors play a significant role. The good agreement of these two methods increases confidence in the reliability
of large-scale synoptic maps obtained by them. 相似文献