Root phosphatase activity is a competitive trait affiliated with the conservation gradient in root economic space

Background:The diversity of resource acquisition strategies of plant roots determines the species coexistence patterns to a certain extent.However,few root physiological traits have been investigated,such as root phosphatase activity(PA)that affects plant phosphorus(P)uptake.Methods:Root PA and classical root functional traits were investigated for 21 coexisting species in a deciduous broad-leaved forest in warm temperate-subtropical transition zone,China.We analyzed the root order variation of absorptive fine root PA,clarified the attribution of root PA in root economic space(RES)and the different P acquisition strategies of co-occurring species based on the multidimensional RES theory,and determined the dominant factors affecting interspecific variation in root PA.Results:There was no distinct pattern of PA variation with root order in the first three root orders of absorptive fine roots,and root PA was constrained by phylogeny.Root PA is a competitive trait affiliated with the conservation gradient in RES.The tight linkages among root PA,mycorrhizal colonization,diameter,specific root length,and nitrogen concentration suggested trade-offs among P acquisition strategies of co-occurring species,i.e.species with long and fine roots acquire inorganic P by actively exploring the soil and secreting phosphatase to mineralize and hydrolyze organic P,while species with short and thick roots obtain P mainly by investing C in mycorrhizal partners.Conclusions:Collectively,our study provides an insight into the forest species coexistence in climatic transition zones,i.e.species coexistence mechanisms based on diverse phosphorus acquisition strategies.

Relationship Between Individuals’Epidemic Risk Perception Within Living Space and Subjective Well-Being:Empirical Evidence from China after the First Wave of COVID-19

It is common to observe the epidemic risk perception(ERP)and a decline in subjective well-being(SWB)in the context of public health events,such as Corona Virus Disease 2019(COVID-19).However,there have been few studies exploring the impact of individuals’ERP within living space on their SWB,especially from a geographical and daily activity perspective after the resumption of work and other activities following a wave of the pandemic.In this paper,we conducted a study with 789 participants in urban China,measuring their ERP within living space and examining its influence on their SWB using path analysis.The results indicated that individuals’ERP within their living space had a significant negative effect on their SWB.The density of certain types of facilities within their living space,such as bus stops,subway stations,restaurants,fast food shops,convenience shops,hospitals,and public toilets,had a significantly negative impact on their SWB,mediated by their ERP within living space.Additionally,participation in out-of-home work and other activities not only increased individuals’ERP within living space,but also strengthened its negative effect on their SWB.

基于CiteSpace的国内城市住区儿童户外活动空间研究进展

在各大城市积极响应“儿童友好城市”建设及国内生育政策开放的双重背景下,儿童活动愈发受到重视,针对作为儿童成长环境与生活空间的住区户外活动区域进行深入研究的需求也愈发迫切。文章采用文献计量法,利用CiteSpace的可视化功能,以中国知网中有关住区儿童户外活动空间的期刊文献为对象,分别从文献数量、文献来源、研究热点、演进规律进行综合分析,进而对研究现状进行系统梳理及提炼,以期为未来儿童活动的住区空间研究提供必要依据与启发。

COVID-19 lockdown has indirect,non-equivalent effects on activity patterns of Reeves's Pheasant(Syrmaticus reevesii)and sympatric species

The outbreak of the COVID-19 pandemic has brought massive shifts in human activities through a global blockade,directly affecting wildlife survival.However,the indirect impacts of changes in human activities are often easily overlooked.We conducted surveys of Reeves's Pheasant(Syrmaticus reevesii)and its sympatric species by camera traps in forest-type nature reserves in three different scenarios:pre-lockdown,lockdown and postlockdown.An increase in livestock activities observed during the lockdown and post-lockdown period in our study area provided us an opportunity to investigate the indirect impact of the lockdown on wildlife.The prelockdown period was used as a baseline to compare any changes in trends of relative abundance index,activity patterns and temporal spacing of targeted species and livestock.During the lockdown period,the relative abundance index of livestock increased by 50%and there was an increase in daytime activity.Reeves's Pheasant showed avoidance responses to almost all sympatric species and livestock in three different periods,and the livestock avoidance level of Reeves's Pheasant during the lockdown period was significantly and positively correlated with the relative abundance index of livestock.Species-specific changes in activity patterns of study species were observed,with reduced daytime activities of Hog Badger and Raccoon Dog during and after the confinement periods.This study highlights the effect of the COVID-19 lockdown on the responses of wildlife by considering the changes in their temporal and spatial use before,during and after lockdown.The knowledge gained on wildlife during reduced human mobility because of the pandemic aids in understanding the effect of human disturbances and developing future conservation strategies in the shared space,to manage both wildlife and livestock.

Environmental Design of Urban Outdoor Public Spaces Based on Children's Activities

This paper analyzed current situation of domestic and foreign children's outdoor spaces, and the relationship between urban public spaces and children's behaviors, summarized design principles and techniques to improve use efficiency of urban outdoor public spaces and facilities, create public spaces capable of meeting psychological behavior needs of children.

Suitability Evaluation of Physical Activity Places in Urban Parks for Children's Play Activities:A Case Study of Four Urban Parks in Handan

Taking 4 urban parks in Handan City as the research objects, 41 suitability evaluation indicators are selected according to the relevant literature reading. The common factors are extracted through factor analysis and the importance questionnaire and summarized into 6 dimensions, namely children's play facilities and auxiliary facility quality factor, natural environment participation factor, children's play space convenience factor, artificial environment participation factor, space environment quality and safety factor, children's game activity facility perfection factor, and the weights of public factors and indicators are calculated. Then the index score is calculated through field measurement and satisfaction survey, and the IPA analysis method is used to draw the coordinate map of key optimization indicators for 4 parks. Finally, corresponding optimization suggestions are put forward for Handan urban parks according to the analysis and evaluation results.

Effectiveness of Activity Expression in VR System to Build Consensus for Public Space Planning

The objective of this study was to clarify the effectiveness of expressing activities in a virtual reality(VR)system for public space planning to support consensus building with citizens,based on the idea that it is important to consider people’s activities when creating attractive public spaces.We constructed a VR system comprising a background expressed in 3D computer graphics(3DCG)and activities expressed in real video image.As a result of the evaluation experiment,it became easier to visualize the utilization of space by expressing an activity.Although its effectiveness was clarified,some problems regarding the functioning of the system were highlighted.

月球样品的中子活化分析技术研究

月球的起源是月球研究的核心问题。月球探测任务返回的数据和样品极大地提高了人类对地月系统的认知,同时也发现了更多未解之谜,亟待未来的探测任务和科学研究来解答。嫦娥五号月壤是我国首次地外天体采集返回的样品,也是继美国和苏联探月采样任务45年后人类再次获得的月球样品。鉴于月球样品的珍贵性和特殊性,利用先进技术开展其全元素含量的非破坏精准分析对于认识月球演化和月球资源就地开发利用具有重要的意义。依托大型核反应研究堆和加速器中子注量率优势,利用中子活化分析技术可实现月球样品中的全元素非破坏分析:1)仪器中子活化分析技术(INAA)可测量Na—U元素之间的60余种元素;2)瞬发γ中子活化分析技术(PGNAA)可补充测量INAA不适合测量的元素如H、B、C、N等;3)中子深度剖面分析技术(NDP)可测量样品近表面(微米级)聚变能源3He的浓度深度分布;4)缓发中子测量技术(DNC)可定量样品中痕量裂变核素如^(235)U和^(239)Pu,并结合INAA可测量238U/235U同位素比值;5)14 MeV快中子活化分析技术(FNAA)可测量INAA和PGNAA不灵敏或不适合测量的元素如O、Si、P等。因此,中子活化分析技术(NAA)可有效解决月球样品中全元素、非破坏和精准测量问题,为我国深空探测珍贵样品研究提供核分析技术支撑。

结合主动光源和改进YOLOv5s模型的夜间柑橘检测方法

【目的】解决夜间环境下遮挡和较小柑橘难以准确识别的问题,实现采摘机器人全天候智能化作业。【方法】提出一种结合主动光源的夜间柑橘识别方法。首先,通过分析主动光源下颜色特征不同的夜间柑橘图像,选择最佳的光源色并进行图像采集。然后,提出一种夜间柑橘检测模型BI-YOLOv5s,该模型采用双向特征金字塔网络(Bi-FPN)进行多尺度交叉连接和加权特征融合,提高对遮挡和较小果实的识别能力;引入Coordinate attention(CA)注意力机制模块,进一步加强对目标位置信息的提取;采用融入Transformer结构的C3TR模块,在减少计算量的同时更好地提取全局信息。【结果】本文提出的BI-YOLOv5s模型在测试集上的精准率、召回率、平均准确率分别为93.4%、92.2%和97.1%,相比YOLOv5s模型分别提升了3.2、1.5和2.3个百分点。在所采用的光源色环境下,模型对夜间柑橘识别的正确率为95.3%,相比白光环境下提高了10.4个百分点。【结论】本文提出的方法对夜间环境下遮挡和小目标柑橘的识别具有较高的准确性,可为夜间果蔬智能化采摘的视觉精准识别提供技术支持。

模型信息联合校正型自抗扰控制策略

为解决微电网受到不确定扰动时,会对直-直变换器输出的电能质量产生严重影响的问题,该文提出一种模型信息联合校正型自抗扰控制技术(ADRC-MIR)。在该控制策略中,首先借助串联超前校正的思想,以比例微分校正环节对线性扩张状态观测器的扰动观测传递函数进行修正,使其可实现对总和扰动更精确的跟踪;然后,根据状态空间平均法从被控系统中提取部分模型信息,将其写入修正后的线性扩张状态观测器的系数矩阵并最终构建出ADRC-MIR;随后基于理论推导,给出改进控制器的参数整定公式及其物理意义,并从噪声抑制、扰动抑制及其频域特性等方面指出改进后的控制器可提升控制品质的原因。最后通过对比不同工况下的数值仿真验证所提控制策略的可行性与正确性。

基于混合强化学习的主动配电网故障恢复方法

针对高比例新能源接入的配电网故障恢复问题,提出一种基于混合强化学习的主动配电网故障恢复方法。首先,以故障损失最小为恢复目标、配电网安全运行要求为约束条件,构造主动配电网的故障恢复模型;其次,建立用于故障恢复的强化学习环境,根据状态空间和动作空间特点,提出一种混合强化学习方法,该方法使用竞争架构双深度Q网络算法处理离散动作空间,进行开关动作;然后,使用深度确定性策略梯度算法处理连续动作空间,调节电源出力;最后,通过IEEE33节点系统仿真实验验证所提方法的可行性和优越性。

文化记忆理论视角下三线工业遗产的活化设计策略研究

三线工业遗产是我国社会主义工业化独立自主探索的典型代表,亟需厘清从记忆传承到文化认同的逻辑理路和实践进路。本文以文化记忆理论视角明确了三线工业遗产具备时间、空间、功能三个维度且存在互济、内嵌的逻辑关系,通过建构的方式形成凝聚性结构空间;分析了文化记忆空间营造的过程中的文化记忆要素特性,从文本、意象、仪式三系统进行文化表征、符号象征化的实践路径探讨;总结出参与—唤醒—认同的递进式活化路径,最后提出记忆重现、场景营造、记忆共创的可行性设计策略,为提升三线精神在中华民族红色精神传承中的结构性力量提供有益参考。

线性自抗扰控制系统的稳定性分析方法

针对二阶线性系统和二阶线性自抗扰控制,提出了基于误差的稳定性分析方法。该方法通过观测误差、跟踪误差状态量建立闭环系统状态空间模型,借助状态空间模型的特征值分析闭环系统的收敛性,并运用李雅普诺夫法判断系统的稳定性。与基于劳斯判据的稳定性分析方法相比较,二者的分析结论一致,算例和仿真结果验证了所提方法的简单性和有效性。此外,通过仿真和蒙特卡洛实验验证了自抗扰控制相比于PID控制在跟踪性能、抗扰能力和鲁棒性等方面的优势。

外空安全与环境治理:进展、挑战与机遇

随着人类航天活动的迅猛发展,外空环境日益复杂无序,外空安全的威胁显著上升,外层空间长期可持续性面临严重挑战。本文全面介绍了外空安全面临的最新态势,系统分析了空间碎片数量逐年增多、低轨大规模星座迅猛部署、新型航天活动快速喷发、外空资源争夺日趋激烈、外空军事化愈演愈烈等对外空安全和外空长期可持续的冲击。本文指出,从外空命运共同体、国家空间资产安全、航天强国建设出发,外空环境治理是大势所趋和唯一出路,孕育着航天技术创新、产业革命、法规建制等重大机遇。基于国情提出了我国对策和发展建议。

星载激光雷达视轴监测系统设计

提出了一种针对星载激光雷达在轨高精度光轴监测与标定需求的多光轴监测方法,该方法基于主动激光光源。通过使用785 nm的激光,分束后分别照射到星敏感器的基准棱镜和接收望远镜的取光棱镜,反射信号被聚焦至监视相机的焦平面,实现了对接收光轴及星敏光轴的精确监测。此外,监视相机还同步采集发射激光的部分能量,用于测量监测发射光轴。文中详细描述了光学系统的设计流程及关键组件的优化方案,并通过地面真空环境试验及在轨监测数据进行了验证。设计结果表明,各监视通道的成像质量达到了衍射极限,收发光轴的设计精度分别为0.09μrad和2.28μrad,关键组件取光棱镜的温控精度达到了±0.2℃。地面的真空热光试验结果进一步验证了该方案的高精度光轴监视能力,收发光轴的监测精度均优于3μrad。最后通过分析激光雷达入轨后的测量数据,确认了视轴监测系统的工作稳定性,成功实现了在轨的高精度光轴监视。该研究成果为星载激光雷达提供了一种有效的在轨高精度光轴监测与标定解决方案。

结合聚类边界采样的主动学习

主动学习是一种机器学习方法,需要选择最有价值的样本进行标注。目前,主动学习在应用时面临着一些挑战,其依赖分类器的先验假设,这容易导致分类器性能意外下降,同时需要一定规模的样本作为启动条件。聚类可以降低问题规模,是主动学习的一种有效手段。为此,结合密度聚类边界采样,开展主动学习方法的研究。针对容易产生分类错误的聚类边界区域,通过计算样本密度,提出一种密度峰值聚类边界点采样方法;在此基础上,给出密度熵的定义,并利用密度熵对聚类边界区域进行启发式搜索,提出一种基于聚类边界采样的主动学习方法。试验结果表明,与文献中的5种主动学习算法相比,该算法能够以更少标记量获得同等甚至更高的分类性能,是一种有效的主动学习算法;在标记不足,无标签样本总量20%的情况下,算法在Accuracy、F-score等指标上取得较好的结果。

迈向白色景观:寒地城市中小河流滨水空间居民冬季户外活动的环境特征偏好研究

城市中小河流滨水空间是承载居民户外活动的重要载体,寒地冬季严酷的气候条件使河流由蓝色水域空间转变成白色冰雪空间,特殊的水体形态使居民的活动水平产生较大变化。聚焦寒地城市中小河流滨水空间的居民冬季户外活动,构建可达性、场所特征、服务设施和维护管理4类维度下的17项环境特征要素指标,通过问卷调查与Kano模型得出户外活动的环境特征偏好要素序列,基于行为类型讨论要素指标对冬季户外活动的影响。结果显示,河流白色景观对提升冬季健康福祉具有重要意义,对维护管理提出了更高的要求。寒地滨水空间的流动行为更关注步行体验,强调线性路径的空间畅通和微气候舒适,驻留行为更关注冬季运动和防风防寒设施的配给。研究成果可为寒地城市居民健康福祉的规划建设提供决策支持。

基于频率超前校正的VSG并联系统有功振荡抑制策略

针对虚拟同步发电机(virtual synchronous generator,VSG)在外界扰动时存在的有功暂态振荡问题,提出一种基于频率超前校正的VSG并联系统有功振荡抑制策略。首先,建立VSG并联系统有功环小信号模型,分析负载功率突变时的VSG有功振荡机理。然后,基于微分超前校正思想并结合VSG有功环控制结构,将有功功率反馈至频率偏差之上,从而增大系统阻尼程度并抑制VSG并联系统有功暂态振荡。接下来,建立改进型VSG并联系统状态空间模型,通过根轨迹分析系统动态响应性能。最后,通过Matlab/Simulink仿真和实验验证了该方案能够有效抑制VSG并联系统有功暂态振荡,并且不影响其稳态有功特性。

职住学空间测度及儿童通学决策的影响机理——以昆明市双职工家庭为例

当代城市家庭选择居住地时往往将临近学校作为重要参考,在缩小学住距离的同时加剧了职住分离。选取昆明市561个有学龄儿童的双职工家庭为研究对象,分析家庭空间分异对儿童通学决策的影响。首先,基于时间地理学理论构建考虑职住学三个锚点的家庭活动空间及测度理论模型。其次,根据测度结果将家庭活动空间划分为职住学就近型和职住学分离型两类。最后,建立结构方程模型分别探究两种模式下父母工作时长以及父母儿童组合时间窗对儿童通学时空行为的影响。研究结果表明:相对于学住距离,父母的职住距离和工作时长对通学行为的影响更为显著,因此就近入学政策对于促进儿童步行上学的作用有限;对于职住学分离型家庭,父母下班与儿童放学组合时间窗的宽裕程度对儿童出行影响显著,组合时间窗越宽裕,儿童小汽车出行的可能越大,因此弹性放学时间的效果也有待商榷;儿童在通学行为中的性别差异主要在职住学分离型家庭中体现。

基于主动激励的掘进机回转台振动抑制研究

悬臂式掘进机截割过程由于煤岩形状、硬度分布的随机性,当截割到硬岩时截割头会产生无规则的剧烈振动,瞬时高强度的冲击对掘进机关键受力部件回转台影响最大,其动态可靠性和寿命影响着截割效率和截割稳定性,为减弱截割过程回转台的振动,首先,基于截割现场回转台易失效损坏现象,建立截割过程回转台力学模型,推导回转台力学方程,研究回转台受力随截割参数变化规律;通过搭建截割试验台,测试截割过程回转台振动响应,结合有限元进行回转台振动模态分析,求解回转台前6阶固有频率及振型,分析回转台剧烈振动的原因。其次,基于工况路径分析理论,建立截割过程回转台工况传递路径分析模型,模拟回转台合成振动,分析各激励点对回转台振动贡献量及贡献程度,准确找到回转台主要激振源。最后,通过施加外部主动激励的方式,分析不同激励频率加载下回转台振动情况,探寻能够降低截割过程回转台振动的激励频段。试验结果表明:外部激振频率处于20~60 Hz,回转台振动幅值降低明显,此频段激励频率对回转台振动控制效果良好,有益于提高回转台寿命,且激振频率为40 Hz时回转台振动最小,回转台振动抑制效果最佳。研究结果有益于丰富回转台振动相关研究理论,实现在不改变机械结构基础上,降低回转台受力与结构变形,可为掘进机回转台的振动问题提供理论参考。