基于PDF项目文档管理系统的设计与实现

目的设计一种基于.NET平台和PDF智能文档的开放式项目文档管理系统。方法通过分析基于PDF的项目文档管理系统的结构,在.NET平台下使用组件技术和PDF表单技术实现了基于PDF的项目文档管理系统。结果重点论述了PDF表单图形图像控件的实现、PDF文档内容的搜集、非PDF格式文档的转换等关键技术。通过在某企业的实际应用,验证了系统的功能。结论对提高项目管理水平和企业信息化发展具有较大的价值。     

用PDF方程法分析悬沙垂线浓度分布

从颗粒运动的PDF(概率密度分布函数)输运方程出发。建立颗粒相的质量、动量和脉动速度二阶矩方程．对于明渠二维恒定均匀流。利用垂向动量方程导出了新的泥沙扩散方程。表明颗粒脉动强度梯度、升力、重力沉降和紊动扩散都影响悬沙运动。说明了传统扩散方程的不足．理论分析了水沙两相物理属性和水流条件对泥沙扩散系数和浓度分布特征的影响。并通过细颗粒试验资料的分析进行了定量研究．     

Deterministic and stochastic analyses of chaotic and overturning responses of a slender rocking object

The relationship between chaos and overturning in the rocking response of a rigid object under periodic excitation is examined from both deterministic and stochastic points of view. A stochastie extension of the deterministic Melnikov function (employed to provide a lower bound for the possible chaotic domain in parameter space) is derived by taking into account the presence of random noise. The associated Fokker-Planck equation is derived to obtain the joint probability density functions in state space. It is shown that global behavior of the rocking motion can be effectively studied via the evolution of the joint probability density function. A mean Poincaré mapping technique is developed to average out noise effects on the chaotic response to reconstruct the embedded strange attractor on the Poincaré section. The close relationship between chaos and overturning is demonstrated by examining the structure of the invariant manifolds. It is found that the presence of noise enlarges the boundary of possible chaotic domains in parameter space and bridges the domains of attraction of coexisting responses. Numerical results consistent with the Foguel alternative theorem, which discerns asymptotic stabilities of responses, indicate that the overturning attracting domain is of the greatest strength. The presence of an embedded strange attractor (reconstructed using the mean Poincaré mapping technique) indicates the existence of transient chaotic rocking response.     

EBU和PDF模型在燃烧室上的应用

使用FLUENT软件中两种常用燃烧模型———有限速率涡耗散(EBU)模型和PDF模型对高温升燃烧室进行了计算,得到了两种模型下的速度场,温度场等特性,并对结果进行了分析。获得了适合高温升燃烧室计算的模型。     

IMS中端到端QoS架构分析

要实现端到端的QoS既需要接入网、核心网和外部网络的不同域间的共同保证,还需要承载层和业务应用层的相互配合。IMS是建立在承载网络基础上的控制层网络,采用基于策略的机制提供QoS控制。IMS基于策略的架构就是为了要提供不同域间、上下层间的相互协同。介绍了IMS QoS支持机制,描述了IMS QoS的体系结构及信令控制流程,分析了该架构的不足之处,并提出了相关的改进方案。     

抬举湍流H2/N2射流火焰的PDF模拟

采用数值目的研究了一个高温燃烧产物环境中的抬举湍流H₂/N₂射流火焰,对火焰的自然和抬举特性进行了研究.采用标量联合概率密度函数(PDF)目的处理详细的化学动力学过程,而湍流流场采用一个多时间尺度(MTS)k-ε湍流模型计算.计算中结合了一套描述氢气氧化的详细化学反应动力学机理.计算结果和实验数据进行了对比,表明所采用的模型可以精确的模拟火焰抬举高度和自然的过程.     

SPIHT算法及其在基于二维条码的防伪证件中的应用

针对基于PDF417二维条码的防伪证件中的照片压缩问题,将小波变换和SPIHT算法相结合,实现了一种图像压缩方法。该算法首先将证件照片进行小波分解,然后根据人眼视觉特性,把小波分解系数进行SPIHT量化编码,可将证件照片压缩到PDF417条码存储空间限制的1108个字节以内。实验表明本算法具有较好的图像压缩效果和图像重建质量。     

Monitoring the Structure Evolution of Titanium Oxide Photocatalysts: From the Molecular Form via the Amorphous State to the Crystalline Phase

Amorphous Ti_xO_y with high surface area has attracted significant interest as photocatalyst with higher activity in ultraviolet (UV) light-induced water splitting applications compared to commercial nanocrystalline TiO₂. Under photocatalytic operation conditions, the structure of the molecular titanium alkoxide precursor rearranges upon hydrolysis and leads to higher connectivity of the structure-building units. Structurally ordered domains with sizes smaller than 7 Å form larger aggregates. The experimental scattering data can be explained best with a structure model consisting of an anatase-like core and a distorted shell. Upon exposure to UV light, the white Ti_xO_y suspension turns dark corresponding to the reduction of Ti⁴⁺ to Ti³⁺ as confirmed by electron energy loss spectroscopy (EELS). Heat-induced crystallisation was followed by in situ temperature-dependent total scattering experiments. First, ordering in the Ti−O environment takes place upon to 350 °C. Above this temperature, the distorted anatase core starts to grow but the structure obtained at 400 °C is still not fully ordered.     

PDFCreator在图书馆文档数字化中的应用实践——以西南林业大学图书馆为例

介绍了西南林业大学图书馆利用PDFCreator开源软件开发文档数字化模块的过程,阐述了将其应用到论文提交系统中,实现了将任意可打印文档转换为PDF文档的成功经验。     

Reliability sensitivity by method of moments

Based on the available methods of moments for structural system reliability assessment and point estimate methods for the first few moments of performance functions, an effective method is proposed to analyze reliability sensitivity of a structural system. The proposed method for analyzing reliability sensitivity includes two steps. Firstly, the reliability sensitivity, usually measured by partial differential of the failure probability _Pf$P_f$ with respect to distribution parameter θ$\theta$ of the basic random variable is derived according to the moment based reliability assessment. The derived expression of ∂_Pf/∂θ$\partial P_f/\partial \theta$ is related to the derivative of the performance function moment α$\alpha$ with respect to θ$\theta$. Secondly, by using the integral formulation between α$\alpha$ and the probability density function (PDF) of the basic random variable, ∂α/∂θ$\partial \alpha /\partial \theta$ could be derived as an expectation of a transformed performance function, and the expectation could be approximated by the point estimate methods. Through the two steps above, the reliability sensitivity can be obtained easily. The obvious advantages of the proposed method include independence of the explicit expression of the performance function, no limitations on the types of PDF of the basic random variables, wide applicability for multiple failure modes and high efficiency for low and medium dimensional problem, which are illustrated by the given examples. However, the efficiency of this method decreases as the dimension of the basic random variables increase, therefore, it is not suitable for the high dimensional problems.