CAD系统中产品设计三维实体建模方法的研究

三维建模是应用CAD系统进行产品设计的重要步骤。现在市场上已有不少的CAD系统，但是不同系统中的三维建模方法却是基本相同的。在这些三维建模的方法中，往往对用户施加了许多的限制，使得用户无法建立复杂的三维实体。笔者提出了一种新的三维建模方法－折叠法，应用这种方法的概念和原理，可以开发出先进的三维建模CAD系统。折叠二维平面图形构成三维实体是作者提出的一种新概念。     

Properties of paper coated with kaolin: The influence of the rheological modifier

The first part of this paper analyses the influence of the molecular weight and concentration of carboxymethyl cellulose (CMC) and of kaolin concentration on rheology of the coating colours and on paper properties coated with ultra lightweight coatings (ULWC). In the second part, relationships between the rheological characteristics of the coating colour formulations and coated paper surface quality was also studied.New indexes on paper roughness at micro-scale are presented (RZI and SRI). In general, they show good correlation with sheet gloss. A new gloss index (SGI) is presented, accounting for the contribution of gloss from machine direction (MD) and cross direction (CD). Porosimetry was used to access microstructural characteristics in order to correlate them with light scattering and gloss properties. The former property is closely related to Hg intrusion volume of the coated layer while gloss is related to surface porosity with pore diameters in the range of 7–15 μm as measured by Hg intrusion volume.     

Viscosities of nonelectrolyte liquid mixtures. III. Selected binary and quaternary mixtures

This paper is the final in a series of three viscosity and density studies of pure n-alkanes and selected binary and quaternary mixtures. A standard U-tube viscometer was used for viscosity measurements, and a Pyrex flask-type pycnometer was used for density determinations. Results are given here for pure alkane and selected binary mixtures of n-tetradecane + n-octane, for selected quaternary mixtures of n-hexadecane + n-dodecane + n-decane + n-hexane, and for pure and selected quaternary mixtures of n-hexadecane + n-dodecane + n-nonane + n-heptane at 303.16 and 308.16 K. The principle of congruence was tested, as was the Grunberg and Nissan equation, as they have been shown to be useful as prediction techniques for other n-alkane binary mixtures. Comparisons were made between the two groups of quaternary alkane mixtures and the binary n-tetradecane + n-octane mixtures of the same pseudo composition to understand better the dependence of mixture viscosities on the composition parameter.     

Group contributions to activity coefficients from the hard sphere expansion corresponding states theory

A new method has been developed for predicting liquid activity coefficients in ternary mixtures from group contributions. In this method, activity coefficients are obtained from the excess Gibbs free energy of mixing at constant temperature and pressure. In calculating this excess function, the constituent and mixture Gibbs free energies are each represented by an expansion about a pure reference fluid in powers of ratios of hard-sphere diameters and molecular attraction parameters. When the pure component differs from the reference by a single structural group, these ratios represent, respectively, the size contribution and the attraction contribution of this group to the thermodynamic property of the pure fluid. Contributions of intermolecular repulsion to the excess Gibbs free energy are calculated directly from hard-sphere equations of state for the mixture and pure components. The effect of polar contributions calculated by a Padé approximant is also examined. Results indicate that the method developed from the hard-sphere expansion corresponding-states theory is useful for predicting activity coefficients in ternary mixtures when unlike-pair interaction parameters are fitted to binary activity coefficient data. Furthermore, the method shows promise in providing a theoretical basis for applying group contributions to activity coefficients.Nomenclature A Residual Helmholtz free energy - C _p Constant-pressure heat capacity - H _vap Heat of vaporization - P ^s Saturated vapor pressure - R Gas constant - T Temperature - U ^HS Hard-sphere internal energy - V _c Critical volume - V ^L Liquid volume - x Dimensionless residual thermodynamic property - Z Compressibility factor - d Center-to-center distance between two touching molecules - k Boltzmann constant - n Moles - x Liquid mole fraction - y Vapor mole fraction - Volume expansivity - Liquid activity coefficient - Minimum molecular attraction potential - Isothermal compressibility - Permanent dipole moment - 3.14159... - Density - Fugacity coefficient Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

New shape factor for corresponding states principle

1 INTRODUCTIONThe CSP(Corresponding States Principle)has been considered to be a useful methodfor the prediction of fluid properties from a minimum amount of information.One ofits form,the shape factor methods is developed through relating the pVT of any interestedpure fluid"a"to that of another"0"by writing     

心理学视域下幽闭恐惧症的防御策略和治疗方法

幽闭恐惧症属于恐惧症的一种表现形式,如果不及时进行心理疏导或矫正,病症会进一步加重,将严重影响其正常的生活和工作。面对幽闭恐惧症患者承受的痛苦,除了从病理性角度进行治疗外,还需要从心理角度和人文关怀等各方面给予更多的关注,研究其患病的原因和机制,并提出防御和治疗幽闭恐惧症的策略和方法,尽早让幽闭恐惧症患者远离痛苦。     

相应流量自动化实时报汛技术研究与应用

为了研制相应流量计算模型,对常用的相应流量计算模型的适用范围、精度进行了分析,包括单一线模型、单值化模型、动态差分模型、经验绳套模型。针对不同流量的计算方法,结合人机交互技术,建立了相应流量计算模型。通过选择具有不同水位流量关系的典型水文测站,对模型的预报精度进行了验证。验证结果表明：一次洪水过程的大部分时段预报结果与实测结果吻合较好,预报精度提高;测站水位流量关系的静态单值化精度对相应流量自动化实时报汛精度影响很大,是今后继续深入研究的一个方向。     

椭圆管外流动熵产及放热系数的数值分析

以椭圆管加热水流动为研究对象,对椭圆管加热水流动系统进行了二维数值模拟。通过联立求解流体力学基本方程和熵产方程,获得了熵产、放热系数与雷诺数和纵、横向间距的变化关系。数值分析结果表明:熵产主要发生在管壁表面附近,而在系统内部区域熵产较小,可以忽略;熵产随雷诺数的增大而增大,随纵、横向间距增加而减小,熵产与雷诺数、纵、横向间距存在对应关系,纵、横向间距宜在1.75～2.0间;在相同的雷诺数值时,熵产、放热系数沿流动方向呈现单调减小的趋势;不同的雷诺数值,熵产、放热系数不同,单调减小的趋势相同。放热系数随Re的增大而增大,且与雷诺数存在对应关系。纵向总放热系数随纵、横向间距增大而减小,且存在对应关系。     

基于倒排索引的密文数据库检索方法研究

针对实际密文数据库的应用,在全文检索倒排索引技术的基础上,设计了一种通过密文倒排索引文件对其进行快速检索的方法。密文索引文件中主要包含有索引项、相对应的记录主键等信息。检索时,通过用检索词匹配索引文件中的索引项,找到对应的记录主键集合,再根据记录主键集合查询密文数据库,获取相应的密文数据,进行解密即可获取明文数据信息。整个检索过程中不对数据库进行解密,从而实现了在不解密的情况下对密文数据库的快速检索。