基于分形曲面尺度斜率特征的弱小目标检测

鉴于弱小目标检测所固有的难点及常用的检测方法不能准确、稳定地检测出目标,提出了运用分形曲面尺度斜率特征检测弱小目标的方法。通过实际数据分析可以得出:相比常用的分形维数和分形拟合误差等检测特征,分形曲面尺度斜率特征在表征人造目标与自然背景的差异上更加明显,在抗图像噪声干扰上也更为优异,有着更强的鲁棒性。该方法普遍适用于检测自然环境中的弱小目标,尤其在对空弱小目标方面,检测概率更高。无论背景、飞行姿态、目标类型发生怎样的变化,经本文算法运算后只需一步简易的分割就可以检测出微弱暗小目标。     

空间相关的二维海杂波仿真与混沌评估

在舰载雷达设计和性能评估的过程中,海杂波的仿真模拟是必需的。根据实际雷达回波的信号形式,使用ZMNL法产生距离和方位均统计相关的二维海杂波数据。混沌特性可以用来描述实测海杂波数据,因此使用分形维数和最大Lyapunov指数来评估仿真数据与实测数据的相似程度,从非线性角度描述了二维仿真海杂波的实用性。     

复杂电磁环境信号分形特性验证

为了证明复杂电磁环境信号是否具有分形特征,根据分形的基本性质,采用基于数学形态学的分形维数估计方法,验证了电磁环境信号的标度不变性;通过分析长程相关性与自相似性的关系,推导Hurst指数验证分形自相似性的方法,验证电磁环境信号的自相似性;通过分析电磁环境信号局部分形特征,验证了其多重分形特性。理论分析和仿真计算结果表明,复杂电磁环境信号具有分形特征,为利用分形理论研究复杂电磁环境奠定了基础。     

细节中的风景：景观风貌图像的高频细节和幂律特征

结合大数据的街景,风景园林师能够快速、有效地对建成环境的感受进行评价。但是目前街景分析主要依靠图像内容语义分割等高级认知,较少考虑人视知觉初级加工特征。研究证据表明在视知觉初级加工中,丰富的高频细节信息可以提升人们对环境的喜好并强化环境恢复效果。为了探索不同景观风貌的细节差异,筛选了150张自然景观、69张城市景观、60张不同林冠覆盖率的树林景观以及31张中国古典园林典型景观图像,并对代表它们的高频细节信息进行了傅里叶斜率分析。结果表明,看似简单的自然要素,如岩体和砂石、水面、修剪草坪等,比城市人工景观的细节要丰富多变,其傅里叶斜率仍然更接近自然。特别指出的是,中国古典园林的傅里叶斜率更加接近典型自然,呈现出更加丰富、更加类似于自然的复杂细节。本研究拓展了提升街道环境感受的可能的途径,即除了利用植物等自然要素之外,还有可能通过模拟自然丰富多变的细节和形态来实现。     

粗集料形态特征的定量评价指标研究

为了提出能够合理评价粗集料形态特征(形状、棱角)的定量指标,采用洛杉矶磨耗仪对4.75~9.5mm,9.5~13.2mm,13.2~16mm,16~19mm共4档粗集料分别磨耗0,600,1 200次,以改变粗集料的形态特征,然后通过自主研制的粗集料形态特征研究系统(MASCA)测得粗集料轴向系数、凸度、粗糙度、棱角参数、圆度、分形维数共6个定量评价指标值,并运用二元方差法比较它们对颗粒形态变化的敏感性,发现分形维数是能够合理评价粗集料形态特征的最优定量指标.为验证这一结论,利用磨耗得到的不同形态特征的粗集料分别成型AC-16,SAC-16,SMA-16级配类型混合料试件进行车辙试验和贯入剪切试验,验证结果表明分形维数与沥青混合料高温性能之间具有很好的相关性.     

基于孔结构参数的混凝土气体扩散模型

提出了一种反映混凝土孔结构特征的毛细管束几何模型,并运用分形维数表征了孔数目、孔隙率和曲折度等参数.通过水饱和度与气体有效扩散空间的关系,建立了考虑水饱和度影响的混凝土气体扩散模型,并运用该模型分析了水饱和度、水灰比和环境温度等对气体扩散系数的影响.结果表明:水饱和度是影响混凝土中气体扩散性能的一个主要参数,当水饱和度达到85%(质量分数)时,对气体扩散系数的影响最为显著.     

切缝药包不耦合装药爆破损伤破坏的分形研究

为研究不同不耦合系数下切缝药包的爆后损伤破坏特征,以有机玻璃为试验材料,对不耦合系数1.33、1.67、2.00、2.33、2.67的切缝药包爆破损伤破坏进行分析。基于分形理论中计盒维数的原理,编写MATLAB程序分别计算5种不耦合系数下切缝药包在切缝方向以及垂直切缝方向爆生裂纹的分形维数。对爆后裂纹长度以及数量进行统计分析,结果表明:①在试验选取的不耦合系数范围内,切缝方向裂纹的分形维数显著大于垂直切缝方向的分形维数,切缝药包对于爆生裂纹扩展方向的控制具有明显效果;②在试验选取的不耦合系数中存在最佳不耦合系数1.67,在该不耦合系数下切缝方向爆生裂纹分形维数达到最大值,裂纹长度最大,爆破损伤破坏的定向控制效果最佳;③在不耦合系数大于1.67后,随着切缝药包不耦合系数的逐渐增大,切缝方向的裂纹扩展长度逐渐变短。     

Comparative evaluation of microwave‐assisted extraction and preheated solvent extraction of bioactive compounds from a plant material: a case study with cabbages

Preheated solvent extraction (PSE) was evaluated via the analysis of the extraction kinetics, microstructure of extracted samples and energy consumption as alternative to microwave‐assisted extraction (MAE). Cabbage outer leaves and ethanol were used as test material and extraction solvent, respectively. MAE was first optimised in terms of glucosinolates and phenolics yields; total antioxidant activity of the extracts was also assessed. MAE at a specific absorbed power of 0.37 W g^?1 for 9 min was selected as optimum condition to extract glucosinolates and phenolics, while PSE was optimised at 6 min of the extraction. The highest normalised total glucosinolates and phenolic contents as well as antioxidant activities of the extracts obtained via MAE were not significantly different from those obtained via PSE. Confocal laser scanning microscopy revealed no significant differences in cabbage cell damages rendered by MAE and PSE. PSE nevertheless exhibited slightly higher specific energy consumption than MAE.     

Fractal characterization of ceramic crack patterns after thermal shocks

This work utilized a combination of experimental evidence and fractal geometric method to assess the effect of crack extension concerning the thermal shock on residual strength of ceramics. Sintered alumina (Al₂O₃) ceramic slabs were bundled and quenched in water under different thermal shock temperatures. The fractal dimension of thermal shock crack patterns on the interior surface and the cooled surface was calculated by the Box-counting method. Fracture energy of a fractal pattern of microcracks in quasi-brittle solids was employed to explain the relationship between crack length and fractal dimensions. The results show that if the crack propagation has the same crack length but a larger fractal dimension, it will absorb more fracture energy. The thermal shock crack patterns of Al₂O₃ ceramics with different grain sizes were analyzed, and the smaller grain size ceramic had a higher fractal dimension of crack patterns than the larger one.     

Dried jujube classification using support vector machine based on fractal parameters and red,green and blue intensity

A new method that combines fractal theory and red, green and blue (RGB) colour intensity was developed to sort dried jujube fruits by using support vector machine (SVM). Our result shows that the new method is fast and accurate in dried jujube fruits classification. The SVM models based on fractal parameters only achieved 85.18–92.73% total accuracy rate. The total classification accuracy of SVM based on RGB intensity values was 94.44%. However, the SVM models based on combining fractal parameters with RGB intensity values achieved 94.44–98.15% total accuracy rate. The best classification accuracy (98.15%) was found when using SVM model based on combining fractal measures (FM) with RGB intensity values (C = 512, γ = 0.0078125). Therefore, the SVM model based on combining FMs with RGB intensity is recommended in dried jujube fruits classification.