对参差脉冲重复间隔脉冲列的重频分选

分析了一种常见的参差脉冲重复间隔脉冲列的固有性质,其子周期在某范围内可以构成一等差数列,并在此基础上提出了一种新的基于直方图统计的重频分选算法．并对脉冲列的抽取算法做了改进,通过使用变步长的方法来确定起始脉冲．该算法提高了确定起始脉冲的正确率和脉冲抽取的效率．仿真结果表明该算法非常适合于参差脉冲重复间隔脉冲列的分选．     

PECVD制备Al-Al2O3复合阻氢涂层的研究

为了提高不锈钢的阻氢性能,利用PECVD(等离子体增强化学气相沉积)技术在不锈钢表面上制备了Al薄膜,经真空热氧化处理(480℃)获得了Al-Al2O3复合薄膜.用表面分析手段SEM、 XRD、 EDS和XPS对所制备涂层的表面形貌、相结构、表面成分、表面元素的化学态进行了分析,并对其进行了阻氘性能研究.结果表明:该技术能够获得均匀、致密复合薄膜;在低于350℃时,阻氘效果非常好,几乎没有渗透,在350℃到450℃之间,阻氘因子能够达到250左右,但在高于450℃后,渗透非常明显.     

Optimization of a heavy-duty compression-ignition engine fueled with diesel and gasoline-like fuels

Optimal injection strategies for a heavy-duty compression-ignition engine fueled with diesel and gasoline-like fuels (#91 gasoline and E10) and operated under mid- and high-load conditions are investigated. A state-of-the-art engine CFD tool with detailed fuel chemistry was used to evaluate the engine performance and pollutant emissions. The CFD tools feature a recently developed efficient chemistry solver that allowed the optimization tasks to be completed in practical computer times. A Non-dominated Sorting Genetic Algorithm II (NSGA II) was coupled with the CFD tool to seek optimal combinations of injection system variables to achieve clean and efficient combustion. The optimization study identified several key parameters that influence engine performance. It was found that the fuel volatility and reactivity both play important roles at the mid-load condition, while the high-load condition is less sensitive to the fuel reactivity. However, high volatility fuels, such as gasoline and E10, were found to be beneficial to fuel economy at high-load. The study indicates that with an optimized injection system gasoline-like fuels are promising for heavy-duty CI engines due to their lower NOx and soot emissions and higher fuel economy compared to conventional diesel fuels. However, the high in-cylinder gas pressure rise rate associated with Partially Premixed Combustion of gasoline-like fuels can become problematic at high-load and the low-load operating limit is also a challenge. Potential solutions are discussed based on the present optimization results.     

Simulation and verification of ohmic heating in static heater using MRI temperature mapping

Mathematical modeling of ohmic heating of liquid-particulate mixtures allows insight into the heating behavior, but model verification that uses only a selected number of points in an ohmic heating system is inadequate because of the unknown temperature distribution within the heated food materials, including the locations of hot and cold spots. In this study, ohmic heating of liquid-particulate mixtures was simulated using the finite-element analysis with the commercial software FEMLAB, and the model predictions were verified against temperature maps obtained using magnetic resonance imaging (MRI). A factor ignored by the previous modeling works, the electricity-to-heat conversion efficiency, was considered in the model, resulting in an improved model performance. The electrical conductivity and its temperature dependence for all the materials used in the simulation were determined under consistent electric field strength as the simulated ohmic heating processes. Other factors/parameters affecting model prediction, such as the boundary conditions and heat transfer coefficients, were also determined in situ for an accurate parametric input. The model predictions yielded good agreement with the MRI temperature maps. Results showed that the electrical conductivity of the materials is the most critical factor causing heating rate variations between the particulate phase and the liquid phase. The heating rate variations could be overcome by adjusting the electrical conductivity of the food materials before ohmic heating. This modeling procedure can be used for designing and controlling ohmic heating processes to ensure thermal sterilization and safety of ohmically heated food products.     

SAR方位模糊分析与抑制

方位模糊是合成孔径雷达特别是星载合成孔径雷达应用中所要解决的一个重要问题.本文给出了合成孔径雷达回波模型,分析了回波信号的特点,以及方位模糊产生的原因.从图像处理的角度出发提出了一种抑制方位模糊的方法,该方法主要思路是根据成像原理和成像参数,以及带有方位模糊的回波信号的特点,构建一个滤波器,用这个滤波器对压缩后的信号进行反卷积运算,从而达到抑制方位模糊的效果.通过点目标的仿真,验证了该方法的可行性.     

影响胶态分散凝胶成胶性能因素研究

研究了各种因素对聚合物（ＨＰＡＭ）／柠檬酸铝／盐体系胶态分散弟胶（ＣＤＧ）的形成（通过成胶时间测定）和性能（通过孔隙阻力因子的测定）。孔隙阻力因子ＦＰＲ为相同聚合物浓度的ＣＤＧ和ＨＰＡＭ溶液分别流过填砂滤层所需的时间之比,可代表ＣＤＧ在多孔介质中的相对强度。研究结果表明：ＣＤＧ的性能随所用ＨＰＡＭ分子相对质量提高而;ＮａＣｌ的存在（≤７０００ｍｇ／Ｌ）可促进ＣＤＧ的形成;在下列条件下可形成稳定的Ｃ     

低脉冲重复频率合成孔径激光雷达成像

为提高合成孔径激光雷达(SAL)的分辨率,从激光脉冲调制与脉冲重复频率(PRF)的矛盾入手,提出了一种沿方位向放置多个望远镜接收的系统设计方法,利用空间自南度解决由于较低PRF带来的方位模糊问题.分析了SAL系统由于平台连续运动的影响(表现为多普勒频移项),提出了多普勒平移补偿方法.通过仿真实验验证了本文所提系统设计的...     

一种新的重频分选检测门限选择算法

在小波理论的基础上提出了一种新的重频分选检测门限选择算法，并在此基础上对原有的重频分选算法给予改进。原有的重频分选算法检测门限选择单一，不适用于脉冲列分布不均匀的信号环境，该算法克服了这些缺点，不仅适用于脉冲列分布均匀的情况，而且适用于脉冲列分布不均匀的情况。仿真结果表明该算法较传统的CDIF算法对固定PRI形式的雷达脉冲列的分选有较好的效果。     

SAR成像系统重频抖动的影响及补偿

合成孔径雷达(SAR)系统要求时间严格同步,从而可利用脉冲间的相干性进行方位处理。推导了重频抖动造成的时间同步误差对SAR成像方位聚焦的影响以及其极限值,并给出了补偿方法。采用实际系统参数进行了仿真验证,并分析了存在重频抖动误差的实际SAR成像雷达系统,实测数据处理和补偿结果验证了理论的有效性。所提方法对实际雷达系统的设计、问题分析和SAR成像处理误差补偿有指导意义,具有较高的实用价值。     

变线性调频斜率符号在合成孔径雷达中的应用

针对合成孔径雷达（SAR）距离模糊的特点，探讨TPRF间变发射波形调频斜率符号法及其工程应用，并将变符号法和常规方法进行了仿真对比。