平流扩散差分方程的新正定性重整化方案设计和试验

质量守恒是平流扩散差分方程所必须满足的基本性质,但是由于差分格式不具有正定性(positive-definite),因此在积分过程中负质量的产生会导致总质量不守恒.针对这一问题,本文从负质量产生的物理意义出发,提出了一个简单有效的新正定性重整化方案,通过点源平流扩散试验表明,该方案不但解决了平流扩散差分方程的正定性问题,同时保证了总质量守恒性.与WRF模式中采用的"重整化方案"相比,具有物理含义清楚、并且简单易行的优点.     

宽温域蓝相液晶材料

蓝相常在高手性液晶体系的清亮点附近温度区间出现,由于具有优异的光学特性如无双折射现象和选择性反射可见光等,近年来蓝相在光电和光子领域越来越受到人们的关注。本文综述了蓝相的发现、分子排列和光学特性等,详细介绍了宽温域蓝相液晶材料在国内外的研究进展和应用现状。最后分析了蓝相液晶用于平板显示领域在技术方面存在的主要问题和未来发展方向。     

CORRECTIONS TO THE COLLISION TERM IN THE BGK BOLTZMANN EQUATION

With the discrete method of the hexagonal cell and three different velocities of particle population in each cell, a two-dimensional lattice Boltzmann model is developed in this paper.^[1,2] The collision operator in the Boltzmann equation is expanded to fourth order using the Taylor expansion.^[3,4] With this model, good results have been obtained from the numerical simulation of the reflection phenomenon of the shock wave on the surface of an obstacle, and the numerical stability is also good. Thus the applicability of the D2Q 19 model is verified.     

Physical Mechanism of Formation of the Bimodal Structure in the Meiyu Front System

The bimodal structure of the Meiyu front system is readdressed after Zhou et al.（2005）. The physical mechanism of the formation of the bimodal distribution is discussed. The bimodal structure of the Melyu front system considerably results from atmospheric moisture gradients, though atmospheric temperature gradients are also not negligible. According to the definition of equivalent potential temperature, and by scale analysis, we find that atmospheric equivalent potential temperature gradients, which could be regarded as an indicator of the Meiyu front system, could be mainly attributed to the variations of atmospheric potential temperature gradients with a scaling factor of 1 and moisture gradients multiplied by a scaling factor of an order of about 2.5 × 10^3, which means that small variations of atmospheric moisture gradients could lead to large variations of equivalent potential temperature gradients, and thus large variations of the Meiyu front system. Quantitative diagnostics with a mesoscale simulation data in the vicinity of the Meiyu front system show that moisture gradients contribute to equivalent potential temperature gradients more than potential temperature gradients.     

Moist Potential Vorticity and Up—Sliding Slantwise Vorticity Development

By using the moist potential vorticity equation derived from complete atmospheric equations including the effect of mass forcing,the theory of up-sliding slantwise voriticity development (USVD) is proposed based on the theory of slantwise vorticity development.When an air parcel slides up along a slantwise isentropic surface,its vertical component of relative vorticity is developed.Based on the theory of USVD,a complete vertical vorticity equation is expected with mass forcing ,which explicitly includes the effect of both internal forcings and external forcings.     

超声法制备PbS纳米晶

超声波辐射下,以硝酸铅、硫代乙酰胺为原料制备了PbS纳米晶,用TEM和XRD研究了聚乙二醇用量和反应时间对PbS纳米晶的影响。结果表明,超声波能抑制颗粒团聚;聚乙二醇具有良好的分散性和一维导向性。PbS纳米晶粒径较细、纳米棒长度为2μm。     

Comparison of Two Kinds of Atmospheric Vorticity Equations

Comparison of two kinds of atmospheric vorticity equations, i.e. the traditional vorticity equation and the complete-form vorticity equation, is performed. The result shows that the two kinds of the vorticity equations can transform from each other and they are consistent in physical essence, while the complete vorticity equation has more advantages in diagnosis. Finally, the application of the complete form vorticity equation is analysed briefly with real data.     

Thermal aspect of the diurnal variation of tropical convective and stratiform rainfall

The diurnal variation of radiation plays a key role in determining the diurnal variations of tropical oceanic convective and stratiform rainfall, and the examination of such a relationship requires a direct link between the radiation term in a heat budget and the surface rain rate in a cloud budget. Thus, the thermally related surface rainfall budgets derived from the combination of cloud and heat budgets are analysed with two-dimensional equilibrium cloud-resolving model simulation data to study the effects of sea surface temperature (SST) and cloud radiative, and microphysical processes on the diurnal variations of convective and stratiform rainfall. The results show that the increase in SST, the inclusion of diurnal variation of SST and the exclusion of cloud radiative processes increase negative diurnal anomalies of heat divergence over rainfall-free regions during the nighttime through changing the vertical structures of diurnal anomaly of radiation in the troposphere. The strengthened negative diurnal anomalies of heat divergence over rainfall-free regions enhance positive diurnal anomalies of heat divergence over convective regions, which intensifies the positive diurnal anomaly of convective rainfall. The exclusion of microphysical effects of ice clouds increases the negative diurnal anomaly of heat divergence over rainfall-free regions during the nighttime through reducing latent heat; this appears to enhance the positive diurnal anomaly of heat divergence over raining stratiform regions, and thus stratiform rainfall.     

A phase analysis of vorticity vectors associated with tropical convection

Three new vorticity vectors have been proposed by Gao et al to study the two-dimensional tropical convection. In the present paper, phase relations between surface rain rate and the vorticity vectors are analysed with the calculations of lag correlation coefficients based on hourly zonally-averaged mass-integrated cloud-resolving simulation data. The cloud-resolving model is integrated with the vertical velocity, zonal wind, horizontal thermal and moisture advections, and sea surface temperature observed and derived from tropical ocean global atmosphere - coupled ocean atmosphere response experiment （TOGA-COARE） for 10 days. Maximum local increase of the vertical component of the convective vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interaction between vorticity and zonal gradient of ice heating. While maximum local increase of the vertical component of the moist vorticity vector leads maxfinum surface rain rate by 2 hours mainly because of the interaction between zonal specific humidity gradient and zonal buoyancy gradient. And the maximum local decrease of the zonal component of the dynamic vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interactions between vorticity and vertical pressure gradient as well as vorticity and buoyancy.