Plant diversity, population structure, and regeneration status in disturbed tropical forests in Assam, northeast India

We investigated the plant population structure and the phy- tosociological and regeneration status in two disturbed tropical forests in Assam Province, the Hojai Reserve Forest and Kumorakata Reserve Forest. A total of 166 species （80 trees, 20 shrubs and 66 herbs） of 136 genera and 63 families were recorded in both study sites. The disturbance index at the two sites, Kumorakata Reserve Forest and Hojai Reserve Forest, were recorded at 11.4% and 3.70% respectively. Reverse J-shaped population curve and exploitation of tree species in higher girth classes were recorded at both study sites. In the girth classes （10-30 cm, 30-60 cm, 60-90 cm and 90-120 cm in size） the percentage of cut stump density was higher than the percentage of individual living trees. The 18% （Kumorakata Reserve Forest） and 7% （Hojai Reserve Forest） spe- cies were recorded as not regenerating. Illegal felling and over-exploitation of forest resources may lead to species-specific changes in the population structure and can alter the future structure and composi- tion of the forests.

A new generalized fractional Dirac soliton hierarchy and its fractional Hamiltonian structure

Based on the differential forms and exterior derivatives of fractional orders, Wu first presented the generalized Tu formula to construct the generalized Hamiltonian structure of the fractional soliton equation. We apply the generalized Tu formula to calculate the fractional Dirac soliton equation hierarchy and its Hamiltonian structure. The method can be generalized to the other fractional soliton hierarchy.

Analysing the structure of the optical path length of a supersonic mixing layer by using wavelet methods

The nano-particle-based planar laser scattering （NPLS） technique is used to measure the density distribution in the supersonic mixing layer of the convective Mach number 0.12, and the optical path difference （OPL）, which is quite crucial for the study of aero-optics, is obtained by post processing. Based on the high spatiotemporal resolutions of the NPLS, the structure of the OPL is ana]ysed using wavelet methods. The coherent structures of the OPL are extracted using three methods, including the methods of thresholding the coefficients of the orthogonal wavelet transform and the wavelet packet transform, and preserving a number of wavelet packet coefficients with the largest amplitudes determined by the entropy dimension. Their performances are compared, and the method using the wavelet packet is the best. Based on the viewpoint of multifractals, we study the OPL by the wavelet transform maxima method （WTMM）, and the result indicates that its scaling behaviour is evident.

Influence of Hydrogen on Dislocation Structure in a Duplex Stainless Steel

The dislocation structure of specimens of a duplex stainless steel with precharged hydrogen has been investigated by transmission electron microscopy.The result showed the hydrogen acti- vated dislocation source on phase boundaries of ferrite/austenite and makes certain dislocations in austenite grains move.The dislocation appearances in each phase in specimens uncharged with hydrogen have been given for comparison.

Design, Synthesis, Crystal Structure and Photophysical Properties of New Oxadiazole Extended Viologen Fluorophore

Viologens (N,N'-dimethyl-4,4-bipyridinium) are advanced functional materials, found important applications in electrochromic devices, molecular machines, organic batteries, and carbohydrate oxidation catalysts in alkaline fuel. In this article, we investigated the design, synthesis and photophysical properties of N,N'-dimethyl-2,5-Bis(pyridinium)oxadiazole 4 and its precursor 2,5- Bis(pyridine)oxadiazole 2. The crystal structure and photophysical properties of viologen 4 and precursor 2 have been determined. The viologen molecule 4 crystallized in monoclinic form, space group P21/n with four molecules in unit cell. Precursor molecule 2 also crystalized in monoclinic form, space group C2/c with four molecules in unit cell. From X-rd data, we found three cations in the molecular structure of viologen molecule 4, which is unusual in viologens. In the three-dimensional molecular packing diagram of molecule 4, the three cations and iodate anions are stabilized by C···C, C···I, N···I, N···H, H···I, N—H···I and C—H···I. The dihedral angle between planes having oxadiazole and two benzene rings are 5°and 8°, suggesting the molecule 4 is a slightly strained one. The molecular structure of precursor molecule 2 stabilized by C···C and N···H short contacts between the molecules. The molecule 4 displayed strong absorbance at 315 nm and emissions between 390 - 410 nm.

The MuItilayer Fabric Structures for Conveyer Belts

The fabric structures for both the base structures and thecover of multilayer conveyer belts are introduced in thispaper.It is also of general significances to use these fab-rics in composite materials.

Formation of Hybrid Ring Structure of Cyanurate/Isocyanurate in the Reaction be-tween 2,4,6-Tris(4-Phenyl-Phenoxy)-1, 3,5-Triazine and Phenyl Glycidyl Ether

Reaction products of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine derived from 4-phenylphenol cyanate ester and phenyl glycidyl ether were analyzed. In addition to an isocyanurate compound and an oxazolidone compound which were well known as reaction products of cyanate esters and epoxy resins, compounds with hybrid ring structure of cyanurate/isocyanurate were determined. Gibbs free energies of the compound having hybrid ring structure of cyanurate/isocyanurate with two isocyanurate moiety were found to be lower than that of the compound with cyanurate ring structure through calculations. Calculation data supported the existence of hybrid ring structure of cy-anurate/isocyanurate. It was revealed that isomerization from cyanurate to isocyanurate occurs via hybrid ring structure of cyanurate/isocyanurate in the reaction of aryl cyanurate and epoxy.

多脉冲固体火箭发动机长尾喷管多层热防护结构传热烧蚀特性

针对多脉冲固体火箭发动机长尾喷管热防护结构的传热烧蚀问题,提出了由C/C抗烧蚀层、碳/酚醛相变吸热层和钢壳体结构组成的多层热防护结构,建立了基于热物性参数随时间和温度变化的传热烧蚀数学模型,采用有限差分隐式格式进行求解。在验证了多层防热结构传热烧蚀计算框架准确性的基础上,开展了长尾喷管多层热防护结构传热烧蚀响应过程仿真研究,分析了脉冲间隔时间对多层热防护结构传热烧蚀响应的影响规律。研究结果表明:与传统固体火箭发动机相比,多脉冲发动机工作时碳/酚醛层内热物性参数与热解反应变化较大,导致多层结构内能量分布更加均匀,使得钢壳体外表面温度显著升高,同时C/C抗烧蚀层表面烧蚀量显著下降;随着脉冲间隔时长的增加,C/C抗烧蚀层烧蚀量逐渐下降,碳/酚醛层内热解程度逐渐降低,钢壳体外表面温度先升高后下降,脉冲间隔时长60 s时钢外壳表面温度达到最大值。

微小多孔介质燃烧器内富氢甲烷全预混燃烧与热性能特性

提出一种可作为微小热源的填充多孔介质的带有瑞士卷预热通道的微小燃烧器,探究了不同燃烧室高度下燃烧器内60%氢气-40%甲烷-空气全预混火焰吹熄极限等燃烧特性.结果表明不同燃烧室高度下的火焰吹熄极限差别不大.同一燃烧室高度下,吹熄极限随雷诺数的减小而变宽,这主要是因为雷诺数较小时的火焰拉伸作用较小.大部分工况下火焰呈现规则的圆形.当雷诺数较大时,燃烧器上壁面外表面温度的最大值和平均值随当量比的增大均增大,同一当量比下增大雷诺数也是类似的结果.当雷诺数较小时,当量比对上述外壁面温度分布特性影响较小.可为实现清洁高效燃烧的全预混燃烧技术的工程应用提供理论基础.

Local Geometric Proof of Riemann Conjecture

Riemann hypothesis (RH) is a difficult problem. So far one doesn’t know how to go about it. Studying ζ and using analysis method likely are two incor-rect guides. Actually, a unique hope may study Riemann function , , by geometric analysis, which has the symmetry: v=0 if β=0, and basic expression . We show that |u| is single peak in each root-interval of u for fixed β ∈(0,1/2]. Using the slope ut, we prove that v has opposite signs at two end-points of Ij. There surely exists an inner point such that , so {|u|,|v|/β} form a local peak-valley structure, and have positive lower bound in Ij. Because each t must lie in some Ij, then ||ξ|| > 0 is valid for any t (i.e. RH is true). Using the positivity of Lagarias (1999), we show the strict monotone for β > β0 ≥ 0 , and the peak-valley structure is equiva-lent to RH, which may be the geometric model expected by Bombieri (2000). This research follows Liuhui’s methodology: “Computing can detect the un-known and method”.

基于相对联系数的区域水利高质量发展评价指标体系筛选方法

为综合判断在区域水利高质量发展目标、发展途径、发展条件相互作用下区域水资源-经济社会-生态环境复合系统不断协同优化的系统高质量发展水平状态,构建了由发展目标、发展途径和发展条件3个子系统组成的区域水利高质量发展初步评价指标体系。为定量分析初步评价指标体系的专家咨询信息,根据专家指标排序合理性模糊关系的取值区间特点提出了相对联系数,用相对联系数的平均集对势估计各专家指标排序合理性的权重,进而可得各指标重要性的专家综合排序值,据此筛选初步评价指标体系,构建了基于相对联系数的区域水利高质量发展评价指标体系筛选方法(SM-RCN)。SM-RCN在陕西省的应用结果表明:筛选后的指标体系汇聚了各专家对区域水利高质量发展主要影响指标的综合评判;SM-RCN可克服评价指标体系构建过程缺乏定量分析依据的不足,可识别不同专家、同一专家对不同评价方面的指标排序合理性的程度。该筛选方法在区域水利现代化、水资源空间均衡、水资源承载力等评价指标体系构建过程中具有应用前景。

SOSNet:一种非对称编码器-解码器结构的非小细胞肺癌CT图像分割模型

非小细胞肺癌严重损害人类健康,早期非小细胞肺癌CT(Computed Tomography)图像中的肿瘤结节体积小,不易发现,极易造成漏诊和误诊.为了精确分割非小细胞肺癌CT图像中的小体积肿瘤结节,本文提出SOSNet(Small Object Segmentation Networks)自动分割模型,利用ResNet(Residual Network)基础层和空洞卷积构造非对称编码器-解码器结构作为分割主网络,利用轴向取反注意力模块ARA(Axial Reverse Attention)逐步擦除背景中对分割有影响的结构,再使用结构细化模块SR(Structure Refinement)对主网络输出的粗略特征图进行结构细化,从而实现非小细胞肺癌肿瘤结节分割.在非小细胞肺癌公开数据集的实验测试表明,本文提出的小目标自动分割模型SOSNet可以有效分割出非小细胞肺癌CT图像中的小体积肿瘤结节,其mDice(mean-Dice)、mIoU(mean Intersection over Union)、Sensitivity、F1、Specificity、平均绝对误差MAE(Mean Absolute Error)均优于当前最先进的小目标分割模型CaraNet(Context Axial Reverse Attention Network).

西北江下游河流底栖动物群落健康评价

2020年12月在西北江下游河流设置11个采样点,调查底栖动物群落结构,应用底栖动物完整性指数(B-IBI)评价河流健康状况,并分析B-IBI值与环境因子的关系。结果表明,参照点位的B-IBI值在0.59~4.00之间,处于中等—优状态;受损点位的B-IBI值在0~0.82之间,处于很差—良好状态,其中较差和很差状态占比为87.5%。氨氮浓度与B-IBI值呈现极显著的负相关性,降低水污染负荷是促进底栖动物群落恢复健康的有效途径。在水质已经实现好转的基础上,可通过营造河底卵石生境来促进底栖动物群落恢复,同时也应加强河岸带的修复。

数字普惠金融赋能河北省民族地区特色产业结构升级的影响研究

随着我国经济进入高质量发展阶段,产业结构的优化升级成为推动经济发展的关键因素。本文选取河北省民族地区作为研究对象,构建特色产业结构升级指数,运用固定效应模型,实证分析了数字普惠金融对河北省民族地区特色产业结构升级的影响效应,数字普惠金融覆盖广度层面、使用深度层面和使用程度层面分别提出了数字普惠金融助力河北省民族地区特色产业结构升级的相应政策建议。

玻璃纤维增强柔性冷水管截面设计及强度分析

海洋温差能因具有能源稳定、环保可持续等特点,而具有较高的开发利用价值.冷海水管设计是温差能电站建造的重要环节,为降低成本,提出一种分段设计方法.首先,利用ABAQUS软件对直径为1 m的大口径玻璃纤维增强柔性冷水管进行截面设计,并运用ORCAFLEX软件分析缓波形布置冷水管的整体受力情况;其次,根据整体受力分析结果将冷水管按深度分段,再通过ABAQUS软件建立局部分析模型,计算得到不同分段冷水管满足内压、外压、拉伸载荷及弯矩组合载荷强度要求的增强层最少纤维缠绕层数;最后,提出分段设计截面的方法.研究结果表明,采用分段设计截面的方法,可大幅减少冷水管纤维增强层材料的用量,降低冷水管的制作成本,为大口径玻璃纤维增强冷水管的设计提供参考.

基于神经网络的拓扑与打印方向同步优化

三维打印能够制造复杂的结构,并广泛应用于航空,工业,医学等诸多行业,但它也存在着一些局限性.而拓扑优化方法是在空间内寻求最佳的材料分布,从而使用更少的材料实现更轻的部件与同样的性能.近年来,三维打印结合拓扑优化的方法受到了广泛关注.众所周知,零件的打印方向会影响打印效果,并与拓扑结构,支撑体积等方面具有密切关系.鉴于此,文中提出了一种基于神经网络的打印方向优化框架.为了验证算法的可行性,根据结构柔度与所需支撑体积构造可微的损失函数,并使用人工神经网络同时对结构拓扑与打印方向进行优化.通过在二维和三维上的大量实验证明,方向优化可以在保证柔度变化不大的情况下显著减少支撑体积数量,降低打印成本.

厚硬岩层结构调控低损开采方法及机理研究

为探究厚硬岩层采动结构对上覆岩层下沉破坏影响及新的低损开采方法,采用相似模拟、离散元数值模拟方法分析了厚硬基本顶采动破坏结构演化和堆积特征对覆岩下沉破坏的影响。相似模拟及数值模拟结果均表明,随采随垮的直接顶岩层和周期性破断的厚硬基本顶分别呈现小块度破坏杂乱堆积和大块度破断整齐堆积;受采动结构特征影响,直接顶岩层采动破坏产生的体积膨胀显著大于厚硬基本顶。根据模拟得到的采动岩层破坏堆积特征构建了厚硬基本顶条件下采动覆岩下沉计算模型。根据采动作用下随采随垮直接顶岩层采动破坏膨胀量显著大于周期性破断厚硬基本顶的规律,提出对厚硬基本顶进行采前大规模水力压裂并借助采动超前支承压力进一步破坏厚硬基本顶,降低厚硬基本顶采动破坏块度,使其随采随垮、杂乱堆积并充分充填采空区以控制上覆岩层下沉破坏,实现低损开采。采用数值模拟验证了压裂弱化厚硬岩层调控其采动结构,增大采动破坏岩层体积膨胀量,降低上覆岩层下沉的有效性。提出的厚硬岩层结构调控低损开采方法可为煤矿绿色高效开采提供一定的参考。

基于被动视觉的三维重建技术研究进展

基于被动视觉的三维重建技术方法多样、应用广泛。按照不同的分类方法,对基于被动视觉的三维重建技术研究进展进行了分析总结。首先,根据采集装置的数量进行分类,介绍了基于单目视觉、双目视觉和多目视觉的三维重建技术,并对各种方法的优缺点进行比较。其次,根据不同应用方法进行分类,对运动恢复结构法和深度学习法的研究进展进行了阐述。最后,对基于被动视觉的三维重建方法进行了综合对比分析,并对三维重建的应用和发展进行了展望。

矿震诱发高应力巷道厚顶煤动力失稳机制

【目的】厚煤层沿底掘进煤巷普遍存在厚顶煤,工作面矿震对巷道厚顶煤产生动载作用,易诱发厚顶煤动力失稳和冒顶-冲击复合灾害,亟需探究矿震动载作用下巷道厚顶煤动力失稳机制。【方法】以陕西彬长矿区深部厚顶煤巷道为工程背景,调研分析深部高应力巷道厚顶煤动力失稳特征,数值模拟研究不同静动载作用下巷道厚顶煤多场演化规律,提出矿震诱发高应力巷道厚顶煤动力失稳机制。【结果和结论】结果表明,巷道厚顶煤冒顶区域距回采工作面较远,冒顶后裸露平整顶板,顶板锚索拉断,冒顶区域附近均发生大能量矿震,呈现冒顶-冲击复合灾害现象。随静载增加,巷道围岩裂隙发育深度及变形不断增加;随动载作用时间和动载强度增大,顶煤震动速度、加速度及裂隙发育程度不断增大,顶煤离层量显著增加;顶板锚杆索均位于顶煤裂隙发育区,支护性能大幅降低。静动载作用下巷道厚顶煤累积损伤及离层量不断增大,大能量矿震动载使浅部破碎顶煤震动速度及加速度显著增大,作用在锚索上载荷超过其承载能力,锚索被拉断,浅部破碎煤体以较高速度冒落,诱发厚顶煤动力失稳和冒顶-冲击复合灾害。在此基础上,提出了采用重建厚顶煤主被动支护和加强卸压的深部巷道厚顶煤动力失稳灾害的防治方法。

传统村落景观基因的识别与关系序列结构研究

传统村落景观基因对于我国传统文化的保护以及血脉与乡愁的延续具有重要意义。该文以北方传统村落皇城村为例,采用N级编码与分类原理,在创新性识别传统村落景观基因基础上立体化呈现出不同景观基因间的关系序列结构,并明晰传统村落景观基因从外在物质载体到内在文化意涵的逻辑表达机制。研究表明:回归文化视角的传统村落景观基因包括物质景观基因、社会景观基因和精神景观基因三大类以及整体布局、土地利用、宗法礼制、社会关系和地方认同等10小类;传统村落景观基因的关系序列结构借由“精神-社会-物质”由内而外、从无形意涵到可视化载体的6条具象路径(“整体布局-宗法礼制-地方认同”“公共空间-宗法礼制-地方认同”“公共空间-民俗文化-地方认同”“土地利用-生计方式-地方认同”“土地利用-社会关系-地方认同”和“民居建筑-社会关系-地方认同”)进行表达。研究结论完善了传统村落景观基因理论,对实践中传统村落文脉的延续和传承具有指导意义。