谈长龙灌区渠道整治措施

本文根据江西省赣州市中型灌区节水配套改造项目原则和要求,针对兴国县长龙灌区渠系及其建筑物目前存在的问题,分别提出了相应的整治措施,为确保灌区渠道输水安全,进一步提高灌区水的利用率和灌溉保证率,从设计方法上提供有益的经验.     

Ignitable Liquid Classification and Identification Using the Summed-Ion Mass Spectrum

Abstract

The mass spectra calculated by summing the intensities of each nominal mass over all chromatographic times, the summed ion spectra, were calculated for a set of 440 commercially available ignitable liquids that had been analyzed by gas chromatography–mass spectrometry. Each ignitable liquid is generally comprised of a mixture of chemicals, and the mixtures may be very complex in some cases, e.g., petroleum distillates, gasoline, etc. The summed ion spectra were evaluated to determine if they contained sufficient information content to allow their use for rapid and accurate identification of the ignitable liquid in a database or library. The summed ion nominal mass spectra were encoded in one bit per channel at 1% transition intensity and a set of 96,580 unique pairwise comparisons were made between spectra, resulting in an average of approximately 50 differing channels per comparison. A subset of 62 summed ion spectra were further compared by a similarity metric and found by cluster analysis to group closely along the ASTM ignitable liquid classification scheme. Receiver operator characteristic analysis of the use of the similarity index in combination with the summed ion spectra was shown to provide 99% probability of correct liquid identification and 95% probability of correct ASTM classification by primary and sub-class. Interlaboratory tests found 95% probability of correct liquid identification and 85% probability of correct ASTM classification at the primary class level. These results demonstrate the use of the summed ion spectrum as a first step in the rapid identification of an ignitable liquid by database or library searching.     

基于网络编码的线性多跳网络最优功率分配

在瑞利衰落环境中,提出一种基于物理层网络编码的双向线性多跳网络最优功率分配方案。在系统中断概率一定的条件下,以最小化系统总功率为目标,利用凸优化理论获取各节点的分配功率。数值结果显示,该方案能得到各节点的最优发送功率,并且随着节点数目或者路径损失因子的增大,节省的系统总功率越多。     

瑞利信道下多门限频谱合作感知方法研究

随着通信方式由语音转向多媒体应用,人们对高速无线传送的需求与日俱增。然而由于有限的自然频谱,现行的静态频率分配机制不能满足快速激增的高速通信设备的要求。因此,需要能够提高频谱利用效率的创新技术,认知无线电的出现解决了这种频谱拥塞的问题,本文将研究在能量探测频谱感知过程中使用多门限判决方法,在认知无线电网络中,决策中心接收多个认知无线电的观测数值,做出决定判断是否存在主用户。研究表明在瑞利信道下进行能量探测的合作频谱感知,采用多门限的判决方法能使感知效果的到提升。     

一种基于DSP的电磁传感器信号频谱检测方法

电磁传感器输出信号易受到各种噪声的干扰,需要检测调理电路输出信号的信噪比,以达到衡量调理电路好坏的目的,针对这一问题,设计了一种基于D S P的简易式频谱分析仪。实验测试结果表明,该分析仪操作方便,精度较高,且相对于频谱仪成本更低,完全达到了预期目的。     

On the use of a spectrum-based model for linear viscoelastic materials

A new spectrum-based model for describing the behavior of time-dependent materials is presented. In this paper, unlike most prior modeling techniques, the time-dependent response of viscoelastic materials is not expressed through the use of series. Instead, certain criteria have been imposed to select a spectrum function that has the potential of describing a wide range of material behavior. Another consequence of choosing the spectrum function of the type used in this paper is to have a few closed form analytic solutions in the theory of linear viscoelasticity. The Laplace transform technique is used to obtain the necessary formulae for viscoelastic Lame' functions, relaxation and bulk moduli, creep bulk and shear compliance, as well as Poisson's ratio. By using the Elastic–Viscoelastic Correspondence Principle (EVCP), material constants appearing in the proposed model are obtained by comparing the experimental data with the solution of the integral equation for a simple tensile test. The resulting viscoelastic functions describe the material properties which can then be used to express the behavior of a material in other loading configurations. The model's potential is demonstrated and its limitations are discussed.     

M周期分数傅里叶变换的光栅信号去噪方法

用矩阵方法离散地实现了任意M周期的分数傅里叶变换(FRFT),它可实现变换级次及周期的自由选择。根据相应的噪声频谱,选取适当的级次及周期,可使FRFT构造一个极窄的带阻滤波器,将其中心频率对准相应噪声的窄谱,便可滤除与理想信号频谱重叠部分的噪声分量,同时保持信号分量。在实验中,用矩阵方法实现的FRFT对所测光栅信号进行了去噪处理,并与传统的傅里叶与小波分析去噪方法进行了对比,结果表明,只要选取适当的级次和周期(α=0.545,Μ=5)就可获得理想的去噪效果。     

CH4传感系统微弱光电信号处理电路的研究

为改善以CH4为目标气体的检测系统的信噪比,提高系统的检测灵敏度.基于微弱信号的锁定检测原理,以方波调制系统LED为光源,设计以锁相放大器为核心的微弱信号处理电路和计算机控制电路,将携带浓度信息的光强信号转换为直流电压输出.实验结果表明,电路输出电压与检测甲烷气体浓度呈线性关系.分析表明,理论上电路对甲烷浓度检测极限值为1.5×10-4.系统灵敏度可通过设计光源功率稳定电路和温度控制电路得到进一步提高.     

D100—32离心式煤气鼓风机的故障分析与改善

凌钢集团公司燃气厂的D100 -32离心式煤气鼓风机,轴承故障频繁,后通过振动和损坏模式分析,找出了故障原因,并对该故障的分析和解决过程进行阐述。     

Time derivative equations for mode I fatigue crack growth in metals

Predicting fatigue crack growth in metals remains a difficult task since the available models based on the Paris law are cycle-derivative equations (da/dN), while service loads are often far from being cyclic. This imposes a cycle-reconstruction of the load sequence, which significantly modifies the load history in the signal. The main objective of this paper is therefore to propose a set of time-derivative equations for fatigue crack growth in order to avoid any cycle reconstruction. The model is based on the thermodynamics of dissipative processes. Its main originality lies in the introduction of a supplementary state variable for the crack, which allows describing continuously the state of the crack throughout any complex load sequence. The state of the crack is considered to be fully characterized at the global scale by its length a, its plastic blunting ρ, and its elastic opening. In the equations, special attention is paid to the elastic energy stored inside the crack tip plastic zone, since, in practice, residual stresses at the crack tip are known to considerably influence fatigue crack growth. The model consists finally in two laws: a crack propagation law, which is a relationship between dρ/dt and da/dt and which observes the inequality stemming from the inequality of Clausius Duhem, and an elastic–plastic constitutive behaviour for the cracked structure, which provides dρ/dt versus load and which stems from the energy balance equation. The model was implemented and tested. It successfully reproduces the main features of fatigue crack growth as reported in the literature, such as the Paris law, the stress ratio effect, and the overload retardation effect.