准晶体的构筑原理及微粒分数维结构模型   总被引：7，自引：1，他引：7  

彭志忠 《地球科学》1985,(4)

准晶体的原子构造中两个原理在起作用,即二十面体原理和黄金中值原理。二十面体原理是指大小相近的原子形成孤立的十二次配位体时,二十面体配位形式在能量上最有利。黄金中值原理是指在准晶体中原子的排列符合黄金中值律。这两个原理适用于由少量原子构成的体系,也适用于某些生物的结构。运用这两个原理于准晶体微粒,我们获得了最简单的准晶体结构模型。此模型可以解释Al-Mn准晶体的高分辨图的所有细节。此模型与Hiraga模型以及Bursill和彭菊琳模型都不相同。在此模型中Al_(12)Mn二十面体不是共棱的。这一模型具有分数维结构的待征,因此称之为准晶体的微粒分数维结构模型。  相似文献   

Research Status and Progress of Balloon-borne Cloud and Precipitation Particles Probe     

Peng Wang  Lei Liu  Xichuan Liu  Shuai Hu  Shijun Zhao  Wenming Ji  Taichang Gao 《地球科学进展》1986,35(7):704-714

The accurate observation of the microphysical structure of cloud and precipitation plays an important role in understanding the formation of clouds and precipitation. In-situ measurement using measuring instruments carried by meteorological balloons is an effective way to obtain the microphysical properties of cloud and precipitation particles, which is a supplementary means for aircraft to observe cloud and precipitation particles. This observation method plays a more and more important role in in-situ measurement. According to the difference of the working principle of the existing balloon-borne cloud and precipitation particles probes, the detectors can be divided into particle impact-sampling sensors, particle imaging sensors, light-scattering sensors, light intensity attenuation sensors and charge measurement sensors. The working principles, key technologies and main advantages and disadvantages of typical instruments were summarized, and their applications to detailed cloud structure acquisition, cloud remote sensing method establishment, cloud and precipitation physical process research and parameterization, and scientific observation of thunderstorm clouds were briefly introduced. Finally, the development trend of balloon-borne cloud precipitation particle detectors was prospected, which will provide reference for related technical research and equipment development.  相似文献   

Cloud tracking using satellite data for predicting the probability of heavy rainfall events in the Mediterranean area     

L. Lanza  M. Conti 《Surveys in Geophysics》1995,16(2):163-181

The use of cloud tracking techniques and storm identification procedures is proposed in this paper with the aim of predicting the evolution of cloud entities associated with the highest rainfall probability within a given meteorological scenario. Suitable algorithms for this kind of analysis are based on the processing of digital images in the thermal infrared (IR) band from geostationary satellites: a selection of such algorithms is described in some detail together with a few real case applications. Three heavy rainfall events have been selected for this purpose with reference to the extreme meteorological situation observed during Fall 1992 and 1993 over the Mediterranean area. A window from 30 to 60 °N and from 20 °W to 30 °E has been identified for the analysis of data from the radiometer on board the ESA Meteosat platform. In conclusion, the suitability of cloud tracking techniques for predicting the probability of heavy rainfall events is discussed provided that the former are associated with proper modeling of small scale rainfall distribution.  相似文献   

IAP AGCM中短波辐射方案的改进研究II·短波辐射方案的改进     

张凤  曾庆存 《气候与环境研究》2005,(3)

在Version 2的基础上,对短波辐射方案进行进一步的改进:引入了新增非灰体气体吸收效应、冰晶粒子形状效应和尺度效应以及云的不均匀性效应(称为Version 3)。数值模拟试验结果表明:Version 3能更好地模拟出全球冬、夏季的降水场、海平面气压场及地表气温场的主要分布特征,并且能相当准确地反映出这几个场的季节性变化特征。Version 3对这3个场的模拟能力明显优于原版本(Version 1)。此外,它对东亚地区的季风降雨具有很好的模拟能力,能较好地反映东亚区域降水的季节性变化。可见,Version 3为进一步研究云-辐射相互作用提供了很好的模式基础。本工作还清楚地表明,模式的进一步发展必须进行对相关物理过程中各个因子的更精确刻画,只有这样,模式才能得到更好的模拟能力。  相似文献   

NUMERICAL STUDY ON THE MIXING OF UNSORTED SEDIMENT PARTICLES DISCHARGED INTO A CROSS-FLOW BY MULTIPHASE PARTICLE-IN-CELL （MP-PIC） METHOD     

Jie GU Chiwai LI Hong YANG Yong ZHAN 《国际泥沙研究》2007,22(2):150-159

The mixing characteristics of dredged sediments of variable size discharged into cross-flow are studied by an Eulerian-Lagrangian method. A three-dimensional (3D) numerical model has been developed by using the modified k-ε parameterization for the turbulence in fluid phase/water and a Lagrangian method for the solid phase/sediments. In the model the wake turbulence induced by sediments has been included as additional source and sink terms in the k-ε model; and the trajectories of the sediments are tracked by the Lagrangian method in which the sediment drift velocities in cross-flow are computed by a multiphase particle-in-cell (MP-PIC) method and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumped sediment cloud is governed by the total buoyancy on the cloud, the drag force on each particle and velocity of cross-flow. The cross-flow destroys more or less the double vortices occurred in stagnant ambience and dominates the longitudinal movement of sediment cloud. The computed results suggest satisfactory agreement by comparison with the experimental results of laboratory.  相似文献   

The fate of inorganic colloidal particles in Lake Brienz     

Vincent Chanudet  Montserrat Filella 《Aquatic Sciences - Research Across Boundaries》2007,69(2):199-211

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Integral inversion of SST data of type GRACE     

P. Novák 《Studia Geophysica et Geodaetica》2007,51(3):351-367

Satellite missions CHAMP and GRACE dedicated to global mapping of the Earth’s gravity field yield accurate satellite-to-satellite tracking (SST) data used for recovery of global geopotential models usually in a form of a finite set of Stokes’s coefficients. The US-German Gravity Recovery And Climate Experiment (GRACE) yields SST data in both the high-low and low-low mode. Observed satellite positions and changes in the intersatellite range can be inverted through the Newtonian equation of motion into values of the unknown geopotential. The geopotential is usually approximated in observation equations by a truncated harmonic series with unknown coefficients. An alternative approach based on integral inversion of the SST data of type GRACE into discrete values of the geopotential at a geocentric sphere is discussed in this article. In this approach, observation equations have a form of Green’s surface integrals with scalar-valued integral kernels. Despite their higher complexity, the kernel functions exhibit features typical for other integral kernels used in geodesy for inversion of gravity field data. The two approaches are discussed and compared based on their relative advantages and intended applications. The combination of heterogeneous gravity data through integral equations is also outlined in the article. panovak@kma.zcu.cz  相似文献   

Approaches for modeling longitudinal dispersion in pore-networks     

R.C. Acharya  S.E.A.T.M. Van der Zee  A. Leijnse 《Advances in water resources》2007

The purpose of this study is to quantify the dispersivity in the longitudinal direction by upscaling pore scale mixing over a network domain and to verify the dispersivity with that obtained through the more rigorous upscaling technique, the Brownian particle tracking model (BPTM). We model a porous medium with a network of pore-units that are comprised of pore bodies and bonds of finite volume. Such a pore-unit is assumed to be a mixing cell with the steady state flow condition for a single fluid. Dispersivity can be obtained by solving the mixing cell model (MCM) for the concentration in each pore-unit and by averaging the concentrations for a large number of pore units (as a function of time and space). A minimal size of network that ascertains an asymptotic value of dispersivity was determined and verified with large size pore networks. This numerically computed dispersivity is compared with the results from the BPTM for the same porous medium and flow conditions. We show that the dispersivity obtained from the MCM is equally reliable for the heterogeneous pore-networks and can be estimated as a function of pore size heterogeneity. For homogeneous networks with the MCM, the iteration time step plays an important role. On the other hand, for networks with the BPTM, the assumption of intra-bond velocity profile affects the results.  相似文献   

Laboratory simulation of the salt weathering of schist: II. Fragmentation of fine schist particles     

Tony Wells  Garry Willgoose  Philip Binning 《地球表面变化过程与地形》2007,32(5):687-697

Recent developments in long term landform evolution modelling have created a new demand for quantitative salt weathering data, and in particular data describing the size distribution of the weathered rock fragments. To enable future development of rock breakdown models for use in landscape evolution and soil production models, laboratory work was undertaken to extend existing schist/salt weathering fragmentation studies to include an examination of the breakdown of sub‐millimetre quartz chlorite schist particles in a seasonally wet tropical climate. Laser particle sizing was used to assess the impact of different experimental procedures on the resulting particle size distribution. The results reveal that salt weathering under a range of realistic simulated tropical wet season conditions produces a significant degree of schist particle breakdown. The fragmentation of the schist is characterized by splitting of the larger fragments into mid‐sized product with finer material produced, possibly from the breakdown of mid‐sized fragments when weathering is more advanced. Salinity, the salt addition method and temperature were all found to affect weathering rates. Subtle differences in mineralogy also produce variations in weathering patterns and rates. It is also shown that an increase in drying temperature leads to accelerated weathering rates, however, the geometry of the fracture process is not significantly affected. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Pb and Th in settling particles in the western Northwest Pacific Ocean: Particle flux and scavenging     

Masatoshi Yamada  Jian Zheng 《Continental Shelf Research》2007

A mooring of three conical time-series sediment traps was deployed at two sites in the western Northwest Pacific Ocean for 9 months. Total mass fluxes and activities of ²¹⁰Pb and ²³⁰Th were determined for the settling particles to elucidate their scavenging and transport processes. Sediment samples also were analyzed for ²¹⁰Pb activities. Total mass fluxes, ²¹⁰Pb fluxes and ²³⁰Th fluxes showed large seasonal variations and their weighted mean fluxes tended to increase with depth, with an especially large increase near-bottom. The ratios of the observed ²¹⁰Pb fluxes to the ²¹⁰Pb deficiency fluxes in the upper traps at the two sites were only 0.02 and 0.12, and were attributable to advective export of ²¹⁰Pb from the surface waters. Those ratios in the near-bottom traps ranged between 1.22 and 2.63. This suggests that these high ratios are due to effective particle scavenging, large lateral ²¹⁰Pb import and input of resuspended particles that have not become incorporated into the sediments. The mean total ²³⁰Th fluxes at the near-bottom traps were 4.2–6.7 times higher than that expected from production in the overlying water column. The ²¹⁰Pb activities in the surficial sediments were much lower than those in the near-bottom traps. The ²¹⁰Pb accumulation rates estimated from the excess ²¹⁰Pb inventory in the sediment column were 40–70% higher than the mean ²¹⁰Pb fluxes at the near-bottom traps. The ratios of the ²¹⁰Pb accumulation rates to the ²¹⁰Pb deficiency fluxes at the near-bottom traps ranged between 2.0 and 3.7. The high fluxes of particulate ²¹⁰Pb and ²³⁰Th at the near-bottom traps reflected a combination of enhanced scavenging of dissolved nuclides and the lateral redistribution of particulate matter by downslope and alongshore transports. However, it was not possible to discriminate among the various processes contributing to high nuclide fluxes.  相似文献