Variance and Convergence Analysis of Monte Carlo Line and Segment Sampling

Recently researchers have started employing Monte Carlo‐like line sample estimators in rendering, demonstrating dramatic reductions in variance (visible noise) for effects such as soft shadows, defocus blur, and participating media. Unfortunately, there is currently no formal theoretical framework to predict and analyze Monte Carlo variance using line and segment samples which have inherently anisotropic Fourier power spectra. In this work, we propose a theoretical formulation for lines and finite‐length segment samples in the frequency domain that allows analyzing their anisotropic power spectra using previous isotropic variance and convergence tools. Our analysis shows that judiciously oriented line samples not only reduce the dimensionality but also pre‐filter C⁰ discontinuities, resulting in further improvement in variance and convergence rates. Our theoretical insights also explain how finite‐length segment samples impact variance and convergence rates only by pre‐filtering discontinuities. We further extend our analysis to consider (uncorrelated) multi‐directional line (segment) sampling, showing that such schemes can increase variance compared to unidirectional sampling. We validate our theoretical results with a set of experiments including direct lighting, ambient occlusion, and volumetric caustics using points, lines, and segment samples.     

辽宁省鸡源空肠弯曲菌耐药性监测与分析

目的了解辽宁省内鸡源空肠弯曲杆菌耐药性情况。方法采用特异性选择培养基分离出空肠弯曲菌,并使用生化反应和分子生物学方法双重方法进行鉴定,并进行耐药性分析。结果采集的辽宁省某屠宰场的鸡盲肠共198份样品,分离鉴定得到60株空肠弯曲菌,分离率为30.3%。同时对60株空肠弯曲菌进行了药物敏感性检测。结论 60株空肠弯曲菌几乎均对红霉素、庆大霉素、克林霉素和萘啶酸耐药,其MIC90值均高于所测试的最高药物浓度。空肠弯曲杆菌氟苯尼考和泰利霉素的敏感性最强。     

Chewing,rumen pool characteristics,and lactation performance of dairy cows fed 2 concentrations of a corn wet-milling coproduct with different forage sources

We used a novel corn wet-milling coproduct [CMP; approximately 70% dry matter, 28% crude protein, 36% neutral detergent fiber (NDF), and 18% nonstructural carbohydrates] in diets formulated to contain 18.4% forage NDF, 17.4% crude protein, 20.2% starch, and 3.7% sugar. Six primiparous, rumen-cannulated Jersey cows were assigned to a 6 × 6 Latin square design with a 2 × 3 factorial arrangement of treatments. Diets were formulated to contain 20 and 30% CMP with 3 forage sources [corn silage (CS) and 40.5% NDF, CS replaced with 10% alfalfa hay (AH) and 45.0% NDF, or CS replaced with 7% grass hay (GH) and 67.4% NDF], with each providing 18.4% forage NDF in the diet. Total-tract digestibilities of NDF, N, and organic matter were not affected by treatment. Similarly, no treatment effects were detected for kinetics of NDF disappearance in situ from CMP or respective forage source or for N disappearance in situ from CMP. Grass hay increased total and liquid pool size of rumen contents compared with AH (by 3.2 and 3.0 kg, respectively). Total time spent chewing increased in cows fed GH by over 35 min compared with those fed AH, partially due to a trend for increased minutes spent ruminating. Mean particle size of rumen contents also tended to be higher in the GH (0.55 mm) than AH (0.69 mm) diets. No effects on production of milk or milk components were detected, but dry matter intake (DMI) tended to decrease when CMP increased from 20 to 30%. Gross feed efficiency (fat-corrected milk/DMI) tended to be greater when cows were fed AH and GH compared with CS and was greater for AH than GH diets. In diets containing low starch, increasing CMP from 20 to 30% potentially maintained similar fat-corrected milk production with lower DMI. However, more consideration also should be given to interactions among forages with respect to fill, digestion, and passage of fiber with increased inclusion rates of CMP.     

激光热源偏移对6mm A7N01铝合金激光-MIG复合焊焊接头的质量影响

针对铝合金激光-MIG复合焊接过程中的热源偏移问题,采用激光-MIG复合焊对6 mm厚A7N01P-T4铝合金进行焊接,给定热源对中偏移,并分析无对中偏移及有对中量偏移的焊接接头宏观成形、微观组织、力学性能,以此研究热源对中偏移对6 mm厚A7N01铝合金激光-MIG复合焊接接头的影响。研究结果表明,有热源对中偏移的试板接头内部存在少量的气孔缺陷,与无对中偏移试板相比,拉伸性能下降21 MPa。     

全数字智能脉冲弧焊电源系统设计与实现

高性能的焊接电源系统是满足脉冲焊接工艺、实现电弧精细控制、保证高质量焊接效果的关键．提出了全数字脉冲逆变弧焊电源的系统方案,阐述了电源主回路结构,详细描述了控制系统硬件电路设计,提出了基于VHDL的焊接工艺时序和焊接电弧稳定控制的主控系统软件设计方法和基于32位单片机的上位机功能定位,深入研究了可实现的抗干扰措施和提高系统实时性的方法．最后介绍了系统设计过程中所需的测试试验．结果表明,所设计的全数字智能脉冲弧焊电源具有较高的灵活性、抗干扰性和可靠性,能够满足苛刻的电弧特性要求,获得满意的焊接质量．     

镁合金真空电子束焊接匙孔热效应数值模拟

分析了镁合金真空电子束焊接过程中的匙孔热效应特征,针对真空电子束焊接工艺建立了适用于镁合金焊接的复合热源模型.考虑到焊接过程中存在的高温金属蒸气等离子体及真空电子束焊接"匙孔"深熔效应特征,模型由高斯面热源和圆锥体热源复合而成,利用高斯面热源功率分配系数和圆锥体热源功率分配系数的不同取值,模拟电子束焊接的不同聚焦状态,并得到电子束聚焦状态与散焦状态下的焊接温度场变化,进而通过计算得到聚焦状态变化下的匙孔形状和焊缝成形.结果表明,模拟结果与其具有较好的一致性.     

多束流电子束薄板焊接应力变形数值模拟

为了减小薄板结构的焊接变形,基于电子束高频偏转扫描技术在焊缝两侧添加辅助扫描热源实现了多束流电子束焊接及焊前预热. 建立了矩形均匀加热辅助热源模型,采用热弹塑性有限元分析方法对1.5 mm厚304不锈钢薄板进行多束流电子束焊接数值模拟,并进行了试验验证. 结果表明,焊后残余应力和变形的实测结果与模拟结果吻合良好,多束流电子束焊接方法不仅可以改变熔池前方材料的受力状态,而且可以减小熔池形成瞬间熔池前方材料的压应力峰值,有利于减小熔池的前方压缩塑性应变,进而减小薄板结构的焊接变形.     

The effect of optimized carbon source on the synthesis and composition of exopolysaccharides produced by Lactobacillus paracasei

This study aimed to predict the optimal carbon source for higher production of exopolysaccharides (EPS) by Lactobacillus paracasei TD 062, and to evaluate the effect of this carbon source on the production and monosaccharide composition of EPS. We evaluated the EPS production capacity of 20 strains of L. paracasei under the same conditions. We further investigated L. paracasei TD 062, which showed the highest EPS-producing activity (0.609 g/L), by examining the associated biosynthesis pathways for EPS. Genomics revealed that fructose, mannose, trehalose, glucose, galactose, and lactose were carbon sources that L. paracasei TD 062 could use to produce EPS. We identified an EPS synthesis gene cluster that could participate in transport, export, and sugar chain synthesis, and generate 6 sugar nucleotides. Experimental results showed that the sugar content of the EPS produced using fermentation with the optimized carbon source (fructose, mannose, trehalose, glucose, galactose, and lactose) increased by 115%. Furthermore, use of the optimized carbon source changed the monosaccharide content of the associated EPS. The results of enzyme activity measurements showed significant increases in the activity of 2 key enzymes involved in the glycoside synthesis pathway. Our study revealed that optimizing the carbon source provided for fermentation not only increased the production of EPS, but also affected the composition of the monosaccharides by increasing enzyme activity in the underlying synthesis pathways, suggesting an important role for carbon source in the production of EPS by L. paracasei TD 062.     

甜菜叶片表型与其产质量的关系

甜菜生产用种主要依靠进口,来源不同的品种表型各异,甜菜高产高糖的表型特征,是育种和栽培管理最直观和简捷的指标.本研究利用丰产和高糖两种类型的2对甜菜品种为材料,通过连续两年对不同类型甜菜营养生长期叶片的形态指标进行比较,分析各指标与甜菜产量和含糖的关系.研究结果表明,丰产型甜菜品种在整个生育期的叶片长度和生育前期叶面积...     

基于包络理论的谐波传动共轭齿廓求解和啮合分析

针对数值求解谐波传动共轭齿廓推导复杂,不易求解等问题,运用一种根据柔轮运动轨迹包络的方法求解共轭齿廓,同时调整柔轮齿廓的沿轴向的不同齿高,使柔轮齿与共轭钢轮齿啮合时不发生干涉。为分析柔轮的齿根圆半径和转矩对柔轮应力的影响,通过Ansys Workbench建立了多体接触模型,探究了齿根圆半径和加载不同转矩对柔轮应力的影响规律。结果表明:柔轮应力对齿廓参数变化的敏感度高于所加载的转矩,因为谐波传动为多齿啮合传动,单个齿所受的应力较小,载荷对柔轮应力的影响相对小于齿廓参数的影响。