Characteristics of turbulence transport for momentum and heat in particle-laden turbulent vertical channel flows

The dynamic and thermal performance of particle-laden turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with a focus on the contributions of particle feedback effect to momentum and heat transfer of turbulence. We take into account the effects of particles on flow drag and Nusselt number and explore the possibility of drag reduction in con-junction with heat transfer enhancement in particle-laden turbulent flows.The effects of particles on momentum and heat transfer are analyzed,and the possibility of drag reduc-tion in conjunction with heat transfer enhancement for the prototypical case of particle-laden turbulent channel flows is addressed.We present results of turbulence modification and heat transfer in turbulent particle-laden channel flow,which shows the heat transfer reduction when large inertial parti-cles with low specific heat capacity are added to the flow. However,we also found an enhancement of the heat transfer and a small reduction of the flow drag when particles with high specific heat capacity are involved.The present results show that particles,which are active agents,interact not only with the velocity field,but also the temperature field and can cause a dissimilarity in momentum and heat transport.This demonstrates that the possibility to increase heat transfer and suppress friction drag can be achieved with addition of par-ticles with different thermal properties.     

基于向前和向后间隔偏最小二乘的特征光谱选择方法

在近红外光谱分析中,向前间隔偏最小二乘法（FiPLS）和向后间隔偏最小二乘法（BiPLS）是常用的基于波长变量选择的建模方法,其模型精度较高,但贪婪搜索特性较强,导致选出的波段并不能较好地反映待测成分的信息。针对该问题,提出一种基于两者组合策略的光谱特征波段选择方法（FB-iPLS）。在光谱分段的基础上,既利用FiPLS选取有用波段,同时利用BiPLS删除无用波段,来交互执行特征变量的选择与删除,对目标特征波段进行双向选择,用于提高模型的稳健性。用该方法建立水中乙醇含量的定量预测模型,并与FiPLS和BiPLS算法对比。由于光谱分段大小会对模型的结果有影响,该实验还考查这三种方法在不同光谱分段处的结果。在光谱划分60段时,提出的FB-iPLS方法取得最佳预测性能,其校正集与验证集相关系数r分别为0.967 7,0.967 0,交互验证均方根误差RMSECV分别为0.088 8,0.057 1。与FiPLS和BiPLS相比,该方法无论在不同光谱分段区间还是在各自最优与最差分段处,模型的整体预测性能都有所提高。实验结果表明,提出的方法能改善BiPLS与FiPLS贪婪搜索的特性,对特征波段的选取更高效、更具代表性,能进一步提高模型的预测性能。     

Comparison of models and visualization of total volatile basic nitrogen content in mutton using hyperspectral imaging and variable selection methods

Hyperspectral imaging combined with variable selection methods was used to perform the rapid and accurate detection and visualization of total volatile basic nitrogen content in mutton. For each sample, several spectra were extracted from the region of muscle pixels for modeling, and the model performance was improved and better than the model established with average spectrum extracting from each sample. By two steps of variable screening with competitive adaptive reweighted sampling and stepwise regression methods, the efficient dimensionality reduction of spectral data was achieved, and the important characteristic variables were selected. The nonlinear model significantly improved the model predictive capability, and the visualization distribution map based on the model was consistent with the actual change of meat spoilage.     

刚竹毒蛾危害下的毛竹叶片光谱特征波长研究

旨在获取刚竹毒蛾危害下的毛竹叶片光谱特征波长,以助于该虫害的有效、准确识别。将于福建省顺昌县实测的105条高光谱数据随机划分为实验组(71条)和验证组(34条)。基于实验组数据,利用单因素方差分析获取健康、轻度危害、中度危害、重度危害等虫害等级间具有极显著差异的波长;结合常用遥感卫星的波段设置对上述波长进行筛选,采用欧式距离、相关系数及光谱角匹配等3种方法判定其虫害判别能力,获取特征波长,并引入验证组样本对其予以验证。结果表明：(1)受害叶片的光谱反射率明显低于健康叶片,虫害等级越高,其反射率越低;(2)受害叶片的光谱特征变化较大,随着虫害等级的上升,其光谱曲线中的“绿峰”及“红谷”趋于消失,“红边”斜率逐渐减小;(3)确定原始光谱703.43~898.56 nm及一阶微分光谱497.68~540.72,554.53~585.25和596.24~618.23 nm为刚竹毒蛾危害下的毛竹叶片光谱特征波长,其对该虫害具有较强的判别能力。该研究从叶片尺度剖析了寄主对刚竹毒蛾的响应机理,是“地-天”耦合的理论基础,可为虫害遥感监测技术体系的建立提供重要依据。     

Asymptotic energy of lattices

The energy of a simple graph G arising in chemical physics, denoted by E(G), is defined as the sum of the absolute values of eigenvalues of G. As the dimer problem and spanning trees problem in statistical physics, in this paper we propose the energy per vertex problem for lattice systems. In general for a type of lattice in statistical physics, to compute the entropy constant with toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions are different tasks with different hardness and may have different solutions. We show that the energy per vertex of plane lattices is independent of the toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions. In particular, the asymptotic formulae of energies of the triangular, 3³.4², and hexagonal lattices with toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions are obtained explicitly.     

不同产地白兰地酒中金属元素含量的测定及特征分析

微波消解样品,FAAS,GFAAS和AFS对法国产及某国产白兰地酒中微量金属元素含量进行测定,对所测20种金属元素相关性进行了分析,给出了法国产及某国产白兰地酒在金属元素含量间存在的相关性、相关性特征及影响因素。     

基于特征波段的黄酒近红外光谱检测模型递归更新方法

近红外光谱是一种快速、无损的定量分析工具。为了提高黄酒关键参数的检测水平,采用近红外光谱法进行定量分析。检测过程中,由于受环境波动、仪器老化、原料变化等因素的影响,基于旧样品所建的模型的精确度逐渐下降。为保持模型的预测精度,引入递归偏最小二乘(recursive partial least square, RPLS)对模型进行更新。以往此方法多使用全谱信息扩充建模集并进行递归计算,光谱的变量多,且包含环境影响等干扰信息,更新计算量大,且精度的提升效果不明显。考虑到黄酒生产过程中特征波段变化小的特性,提出了一种基于特征波段的黄酒近红外光谱检测模型递归更新方法。先采用相关系数法提取特征波段建立低维模型,在采集到新样品理化值后,再利用其特征波段光谱信息,使用递归偏最小二乘对低维模型进行更新。此方法被应用于黄酒总酸的近红外检测模型更新。模型评价使用相关系数r,预测标准偏差RMSEP和预测相对分析误差RPD三个指标。结果表明：采用本方法后,模型稳定性显著优化,计算效率有所提升,模型预测效果良好,三个评价指标分别达到0.965 7,0.184 3和3.736 2,较全谱PRLS时分别提高3%,24%和31%,在实际应用中有一定的参考价值。     

近红外光谱和特征光谱的山茶油掺假鉴别方法研究

山茶油素有"东方橄榄油"美誉,实现掺假山茶油的鉴别具有重要实用价值,采用近红外光谱技术对掺有葵花油的山茶油进行检测。分别以1%,5%,10%为梯度制备掺假比例不同的山茶油样品,并根据掺假比例将其分为A组(0%~5%)和B组(6%~10%)共11个样品,C组(15%~40%)6个和D组(50%~100%)6个样品。将每个掺假样品充分混匀后再分为9份,依次采集其1 000~2 500nm范围的吸收光谱,共获得207条光谱曲线。每组样品的光谱数据按2∶1随机分为训练集与验证集。经去除首尾噪声后,通过主成分分析法(principal component analysis,PCA)降维,并利用前四个主成分建立了鉴别山茶油不同掺假等级的主成分-支持向量机判别模型,训练集与验证集的总体判别准确率分别达96.38%和94.20%;进一步,通过对前四个主成分的载荷系数的分析,并结合原始光谱,提取建模过程中权重较大的波长并解析其化学含义,最终确定出五个特征波长:1 212,1 705,1 826,1 905及2 148nm,以此波长重新建立近红外特征光谱山茶油掺假等级判别模型,对训练集与验证集的总体判别准确率也达到了94.20%和92.75%。研究结果表明,利用近红外光谱和特征光谱均能够较好实现山茶油掺假等级的鉴别,同时所建立的近红外特征光谱模型也为设计相应的掺假山茶油实用便携式检测仪器提供了理论基础。     

0~#柴油燃烧初期火焰光谱分析

为推进柴油燃烧初期智能识别与抑制灭火技术的发展,通过小尺度油池实验和光谱分析的方法,首次对0~#柴油燃烧初期火焰光谱进行了初步研究,得到0~#柴油燃烧初期火焰光谱的整体特性:在200~380nm的近紫外波段,光谱强度最弱,强度与波长关系不大,特征谱带数量最少,基本没有明显的谱峰;在380~780nm的可见光波段,光谱强度最强,强度随波长的增大而增大,特征谱带最多,存在较多明显的谱峰;在780~1 100nm的近红外波段,光谱强度相对较大,在780nm处出现强度的拐点,强度随波长的增大而减小,特征谱带较多,存在一定数量较为明显的谱峰。进一步对其火焰光谱进行分析得到:燃烧过程中主要的中间产物自由基包括OH,CN,CH,C_2,H2O等;火焰光谱中主要的特征谱带包括OH自由基306.4nm系统谱带和振动转动谱带、CN自由基紫色光区和红色光区谱带、CH自由基431.5nm谱带、C_2自由基Swan和Phillips近红外谱带、H2O分子振动转动谱带等;特征谱带特征波长及时间的分布情况和主要生成机制;在本实验批次0~#柴油中存在金属K元素,其特征谱线在761和769nm处出现明显的谱峰;在431,512,516,547,589,766,769,891和927nm出现较为明显的特征谱峰,适合作为0~#柴油燃烧初期火焰识别的标志。     

塑料激光诱导击穿光谱技术快速分类应用研究

在大气环境中,采用激光诱导击穿光谱技术与支持向量机算法相结合,对来自不同厂家不同颜色的20种工业塑料进行分类研究。首先对分类结果有影响的实验参数进行优化,在最佳的实验参数条件下进行光谱采集,采用6条非金属元素特征谱线,有效缩短了训练支持向量机分类模型所需时间,从而提高了塑料的分类效率。实验结果表明,利用碳、氢、氧、氮等主量非金属元素对这些工业塑料样品进行分类,测试集1 000个光谱数据中有996个识别正确,算术平均识别精度达到99.6%。在选取较少的主量非金属特征谱线的情况下,结合采用支持向量机算法,可以实现激光诱导击穿光谱技术对更多类型的塑料制品快速、高精度分类,为激光诱导击穿光谱技术在实现塑料分类方面提供了数据参考。