分类： 机械工程 >> 机械制造自动化 提交时间： 2022-05-31
摘要： With growing interest in Laser Additive Manufacturing (LAM) of High-entropy alloys (HEAs) during most recent years, the design of compositional elements and process strategies are primary methods to overcome undesirable microstructures and defects. Here we propose a new approach, a novel real-time Laser Shocking of Melt Pool (LSMP), to obtain melt pool modifications for yielding HEAs with desired characteristics. LSMP utilizes a pulsed laser shocking a liquid melt pool caused by a continuous wave laser, enabling non-destructive and real-time modulations for high-performance HEAs. The numerical simulation reveals the convection mechanism of the melt pool in the LSMP process, and the intervention of the pulsed laser promotes melt pool flow type to convert the Marangoni effect into a multi-convective ring, which accelerates melt pool flow and inhibits columnar crystal growth. Experimental results show the evolution law of the microstructure in the LSMP process. The microstructure of CrFeCoNi HEAs undergoes a Columnar-Equiaxed Transition (CET), and higher hardness is obtained. Laser shock is demonstrated to be an effective in-situ modulative tool for controlled additive manufacturing.
分类： 地球科学 >> 地理学 提交时间： 2022-05-30 合作期刊: 《干旱区科学》
摘要： Abstract: Hydrothermal condition is mismatched in arid and semi-arid regions, particularly in Central Asia (including Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan, and Turkmenistan), resulting many environmental limitations. In this study, we projected hydrothermal condition in Central Asia based on bias-corrected multi-model ensembles (MMEs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) under four Shared Socioeconomic Pathway and Representative Concentration Pathway (SSP-RCP) scenarios (SSP126 (SSP1-RCP2.6), SSP245 (SSP2-RCP4.5), SSP460 (SSP4-RCP6.0), and SSP585 (SSP5-RCP8.5)) during 20152100. The bias correction and spatial disaggregation, water-thermal product index, and sensitivity analysis were used in this study. The results showed that the hydrothermal condition is mismatched in the central and southern deserts, whereas the region of Pamir Mountains and Tianshan Mountains as well as the northern plains of Kazakhstan showed a matched hydrothermal condition. Compared with the historical period, the matched degree of hydrothermal condition improves during 20462075, but degenerates during 20152044 and 20762100. The change of hydrothermal condition is sensitive to precipitation in the northern regions and the maximum temperatures in the southern regions. The result suggests that the optimal scenario in Central Asia is SSP126 scenario, while SSP585 scenario brings further hydrothermal contradictions. This study provides scientific information for the development and sustainable utilization of hydrothermal resources in arid and semi-arid regions under climate change.
分类： 地球科学 >> 地理学 提交时间： 2022-05-30 合作期刊: 《干旱区科学》
HUANG Xiaoran
BAO Anming
GUO Hao
MENG Fanhao
ZHANG Pengfei
ZHENG Guoxiong
YU Tao
QI Peng
Vincent NZABARINDA
DU Weibing
摘要： Abstract: Glaciers are highly sensitive to climate change and are undergoing significant changes in mid-latitudes. In this study, we analyzed the spatiotemporal changes of typical glaciers and their responses to climate change in the period of 19902015 in 4 different mountainous sub-regions in Xinjiang Uygur Autonomous Region of Northwest China: the Bogda Peak and Karlik Mountain sub-regions in the Tianshan Mountains; the Yinsugaiti Glacier sub-region in the Karakorum Mountains; and the Youyi Peak sub-region in the Altay Mountains. The standardized snow cover index (NDSI) and correlation analysis were used to reveal the glacier area changes in the 4 sub-regions from 1990 to 2015. Glacial areas in the Bogda Peak, Karlik Mountain, Yinsugaiti Glacier, and Youyi Peak sub-regions in the period of 19902015 decreased by 57.7, 369.1, 369.1, and 170.4 km², respectively. Analysis of glacier area center of gravity showed that quadrant changes of glacier areas in the 4 sub-regions moved towards the origin. Glacier area on the south aspect of the Karlik Mountain sub-region was larger than that on the north aspect, while glacier areas on the north aspect of the other 3 sub-regions were larger than those on the south aspect. Increased precipitation in the Karlik Mountain sub-region inhibited the retreat of glaciers to a certain extent. However, glacier area changes in the Bogda Peak and Youyi Peak sub-regions were not sensitive to the increased precipitation. On a seasonal time scale, glacier area changes in the Bogda Peak, Karlik Mountain, Yinsugaiti Glacier, and Youyi Peak sub-regions were mainly caused by accumulated temperature in the wet season; on an annual time scale, the correlation coefficient between glacier area and annual average temperature was 0.72 and passed the significance test at P
分类： 能源科学 >> 能源（综合） 提交时间： 2022-05-30
摘要： Solar stills are considered an effective method to solve the scarcity of drinkable water. However, it is still missing a way to forecast its production. Herein, it is proposed that a convenient forecasting model which just needs to input the conventional weather forecasting data. The model is established by using machine learning methods of random forest and optimized by Bayesian algorithm. The required data to train the model is obtained from daily measurements lasting 9 months. To validate the accuracy model, the determination coefficients of two types of solar stills are calculated as 0.935 and 0.929, respectively, which are much higher than the value of both multiple linear regression (0.767) and the traditional models (0.829 and 0.847). Moreover, by appling the model, it is predicted that the freshwater production of four cities in China. The predicted production is approved to be reliable by a high value of correlation (0.868) between the predicted production and the solar insolation. With the help of the forecasting model, it would greatly promote the global application of solar stills.
分类： 天文学 >> 天文学 提交时间： 2022-05-30 合作期刊: 《天文研究与技术》
摘要： 为提高地平式太阳望远镜库德焦面的指向跟踪精度，文章首先仿真了库德光路中主光轴、方位轴、高度轴、消旋轴不同心时在库德焦面上引入的跟踪误差，分析了库德焦面指向跟踪误差的复杂性，这一问题无法用夜天文望远镜卡焦指向模型解决。然后文章提出了一种基于机器学习的支持向量回归方法来构建太阳望远镜库德焦面的指向跟踪模型，并在NVST望远镜进行了实测建模和实验论证。实验结果表明：在模型改正之前，NVST在库德焦面的指向误差最大值是650.55角秒、RMS是115.88角秒，30分钟跟踪误差是6.46角秒；模型改正之后，指向误差最大值是25.02角秒、RMS值是3.98角秒，30分钟跟踪误差是1.10角秒。由此可见，基于机器学习的支持向量回归建模方法能有效提高地平式太阳望远镜库德焦面的指向跟踪精度。
分类： 天文学 >> 天文学 提交时间： 2022-05-30 合作期刊: 《天文研究与技术》
摘要： 耀斑和日冕物质抛射（Coronal Mass Ejection，CME）期间产生的非热高能粒子流和激波是产生灾害性空间天气事件的两种主要因素，它们主要观测特征分别是具有快速频率漂移特征的射电Ⅲ型暴和具有较为缓慢频率漂移的射电Ⅱ型暴。本文主要介绍了使用概率霍夫变换(Probabilistic Hough Transform)的方法，在观测数据中自动识别出太阳射电Ⅲ型暴和Ⅱ型射电暴，并提取射电Ⅲ和Ⅱ型暴的特征参数，最后利用识别出的射电Ⅱ型暴的物理参数估计了CME激波的速度。
分类： 天文学 >> 天文学 提交时间： 2022-05-30 合作期刊: 《天文研究与技术》
摘要： 相控阵馈源是将阵列天线放置于射电望远镜焦面场处，用以实现更高增益及更灵活波束调控的接收机技术。鉴于其与阵列天线一样，是由多个天线单元以一定方式组合排列而成，工作时阵元之间产生电磁耦合在所难免。本文选用螺旋天线作为阵列天线单元，工作频率为1.25GHz，对独立天线进行仿真优化后，该天线-10dB阻抗带宽仅为70MHz。依托该天线单元建立55矩形排布螺旋天线阵列模型，分别选取阵元间距为1、0.5、0.25、0.125倍波长（1.25GHz@0.24m），以此验证不同阵元间距下的互耦效应对整个阵列带宽的影响。最终通过对各阵元输入阻抗进行匹配，仿真得到在0.25倍波长间距下，阵列中心阵子的-10dB阻抗带宽可扩展至550MHz，而阵列天线的带宽也基本表征了将其用作相控阵馈源的工作带宽。上述工作加深了对阵列天线带宽特性的理解，也为实际应用于射电望远镜系统的相控阵馈源实现更宽的工作带宽提供了可能。
分类： 动力与电气工程 >> 电气工程 提交时间： 2022-05-29
摘要： 新能源电力系统的动态特性复杂，存在众多稳定分析方法及稳定判据。不同稳定方法/判据对应的物理解释和适用范围不同，目前难以从理论上回答各类判据适合解决的问题，以及它们所对应的物理解释是否合理。该文分为两部分，第一部分提出稳定判据的适用性评估方法，并尝试回答与稳定判据对应的物理解释是否合理；第二部分应用该方法分析部分典型判据的适用场合，并尝试给出其物理解释。第一部分首先回顾归纳现有稳定判据的推演机理，以及各判据背后对应的物理意义。其次，从稳定性等价、标称性和鲁棒性3个角度，提出稳定判据的适用性3个定性原则，并提出基于环路增益灵敏度的定量化指标。最后，以并网变流器为例，说明频域分析中若干基于阻抗的分析方法的性质，并探讨了其适用范围。电力系统中其它典型判据的适用性及其物理解释等工作将在第二部分展开探讨。
分类： 动力与电气工程 >> 电气工程 提交时间： 2022-05-29
摘要： 该文第一部分从稳定性等价、标称性和鲁棒性3个角度，提出稳定分析方法/判据适应性的定性原则和量化评估指标。第二部分将进一步针对同步机、变流器和双馈机组等典型设备，分析现有稳定判据的适用性及判据对应的失稳物理解释是否合理，并从主导输出变量角度探讨稳定问题的分类方法。首先，利用所提评估指标，验证现有同步机低频振荡和次同步振荡/谐振的稳定分析方法和物理解释的合理性；其次，利用所提评估指标分析变流器和双馈机组振荡问题，探讨其适用的稳定判据、导出机理及主导输出变量；最后，提出基于物理机理及主导输出变量的设备稳定分类新思路，从矢量角度将设备稳定性分为相角主导的同步稳定、幅值主导的电压稳定和它们特殊组合而成的电气谐振3类。同时还探讨宽频带振荡概念、设备稳定和系统稳定间的联系及稳定分类的可拓展性等问题。
分类： 核科学技术 >> 乏燃料后处理技术 提交时间： 2022-05-28
摘要： Nuclearmateriallicenseholdershoulddevelopanuclear materialaccountingmanagementsystemandachievethe closedbalance. Accordingtoregulationsrequirements, nuclear materialaccountancyimplementationisbasedonphysical inventoryandmaterialmeasurement. Generally, thespentfuel reprocessingplantoperatesuninterrupted, annualthroughput ofnuclearmaterialsishuge, differentmeasurementand analysistechniquesareconfiguredcombingthereprocessing process. Sotheclosedbalanceapproachofnuclearmaterials accountingisagreatchallenge. Inordertoimprovethe accuracyandreliabilityofnuclearmaterial, enhancethe timelinessofabnormaldetection, near-realtimeaccounting prospectofspentfuelreprocessingplantwasresearched. Inthis paper, thecrucialaspectaffectingtheclosedbalanceofnuclear materialswasdiscussed, thefactorssuchasthehead-end receiver-shipperdifference, theon-lineprocessmonitoring accuracy,theapplicabilityoftheinternationaltargetvalueof nuclearmaterialmeasurementuncertainty, andalsothe nuclearmaterialbalancemodelofreprocessingplants. As summarized,proposedsuggestionsandsolutionsfornuclear materialbalanceinspentfuelreprocessingplantwasput forwardontheendofthepaper.
分类： 心理学 >> 认知心理学 提交时间： 2022-05-28
摘要： 元认知是对认知的认知，包含认知的各个方面，近年来元认知与面部认知的结合开始得到关注。两者结合切入点包括元认知错觉（达克效应和自我中心偏见）在面部认知中的适用性，以及面部认知现象（异族效应和熟悉度优势）在元认知中的适用性。研究方法根据测量时间点和评估对象的选取而各有侧重。当前研究尚停留在元认知监测层面，未来可扩展至面部认知的元认知控制、与机器学习结合等方向，为理解面部认知提供新角度，扩展其应用价值。
分类： 生物学 >> 生物医药 分类： 计算机科学 >> 计算机应用技术 提交时间： 2022-05-26
摘要： 直至现在，图像质量评价都没有涉及色彩问题。图像质量评价的文献多是评价图像质量（在压缩、传输等图像处理过程中）的变差（降质）程度。平面图像是一种二维的亮度分布。亮度是图像视觉质量的核心参量，没有亮度就没有图像，也就没有论及图像质量的可能。本文提出了三个层次的图像视觉感知质量评价(VPQA)指标：单幅单参数图像质量评价(SS_IQA)，单幅五参数精细图像质量评价(SF_IQA)，考虑彩色保真性的增强图像质量评价(CF_IQA)。横向论，可分为单幅的图像质量评价（SIQA），多幅图像质量比较，图像增强中的质量评价等三个方面。图像视觉质量评价是智能最佳化图像增强的不可或缺的工具。
分类： 心理学 >> 心理测量 提交时间： 2022-05-26
摘要： 多级属性是将诊断测验中传统的二值(即两种水平，通常定义为0和1)属性定义为多值 (多个水平可以为0，1，)，它不但可以描述学生对于知识属性是否掌握，而且可以描述学生在属性上的掌握程度，这样使得诊断测验能提供给被试更丰富的知识掌握详情。本文将适用于二级属性Q矩阵的统计量 (S 统计量)拓展到多级属性下的Q矩阵验证和估计，在两种常见的条件下，设计了两种估计算法：联合估计算法和在线估计算法。模拟实验结果表明：联合估计算法适用于对专家界定的初始Q矩阵进行验证，当初始Q矩阵中包含较少的错误时，通过联合估计算法有很大可能恢复正确的Q矩阵；在线估计算法适用于对新项目进行属性向量和项目参数的在线标定，基于一定数量的基础项目，在线估计算法对于新项目的估计也能达到较满意的成功率。实证数据分析则进一步展示了该方法的使用。
分类： 心理学 >> 认知心理学 提交时间： 2022-05-26
摘要： 当两个或两个以上项目进行一体化编码时，熟悉性也能够支持联结再认，这一观点已经得到大量研究证据的支持。然而，关于一体化如何影响联结再认和构成联结的单个项目再认仍存在分歧。通过回顾现有研究发现：（1）一体化一致性是调节一体化与联结再认关系的重要因素；（2）认知资源有限和新/旧词语义相关性是影响一体化对项目再认作用的重要因素；（3）一体化的发生机制存在 项目假说、图式假说以及精细加工假说三种可能的理论解释。未来研究不仅需要控制一体化一致性，还可以比较不同一体化方式的作用大小以及探索一体化效应的毕生发展规律。
分类： 地球科学 >> 地理学 提交时间： 2022-05-25 合作期刊: 《干旱区科学》
摘要： Abstract: Hydraulic erosion associated with seasonal freeze-thaw cycles is one of the most predominant factors, which drives soil stripping and transportation. In this study, indoor simulated meltwater erosion experiments were used to investigate the sorting characteristics and transport mechanism of sediment particles under different freeze-thaw conditions (unfrozen, shallow-thawed, and frozen slopes) and runoff rates (1, 2, and 4 L/min). Results showed that the order of sediment particle contents was silt>sand>clay during erosion process on unfrozen, shallow-thawed, and frozen slopes. Compared with original soils, clay and silt were lost, and sand was deposited. On unfrozen and shallow-thawed slopes, the change of runoff rate had a significant impact on the enrichment of clay, silt, and sand particles. In this study, the sediment particles transported in the form of suspension/saltation were 83.58%86.54% on unfrozen slopes, 69.24%84.89% on shallow-thawed slopes, and 83.75%87.44% on frozen slopes. Moreover, sediment particles smaller than 0.027 mm were preferentially transported. On shallow-thawed slope, relative contribution percentage of suspension/saltation sediment particles gradually increased with the increase in runoff rate, and an opposite trend occurred on unfrozen and frozen slopes. At the same runoff rate, freeze-thaw process had a significant impact on the relative contribution percentage of sediment particle transport via suspension/saltation and rolling during erosion process. The research results provide an improved transport mechanism under freeze-thaw condition for steep loessal slopes.
分类： 地球科学 >> 地理学 提交时间： 2022-05-25 合作期刊: 《干旱区科学》
摘要： Abstract: Wind controls the formation and development of sand dunes. Therefore, understanding the wind regimes is necessary in sand dune research. In this study, we combined the wind data from 2017 to 2019 at four meteorological stations (Cherigele and Wuertabulage stations in the lake basins, and Yikeri and Sumujilin stations on the top of sand dunes) in the hinterland of the Badain Jaran Desert in China, with high resolution Google Earth images to analyze the correlation between the wind energy environments and dune morphology. The results of data analysis indicated that both the wind direction and sand drift intensity exhibited notable spatial and temporal variations. The highest level of wind activity was observed in spring. Northwesterly and northeasterly winds were the dominant in the Badain Jaran Desert. At the Cherigele, Wuertabulage, and Yikeri stations, the drift potential (DP) was below 200.00 vector units (VU). The wind energy environments in most areas could be classified as low-energy environments. The resultant drift direction differed at different stations and in different seasons, but the overall direction was mainly the southeast. The resultant drift potential (RDP)/DP ratio was greater than 0.30 in most parts of the study area, suggesting that the wind regimes mainly exhibited unimodal or bimodal characteristics. Differences between the thermodynamic properties and the unique landscape settings of lakes and sand dunes could alter the local circulation and intensify the complexity of the wind regimes. The wind regimes were weaker in the lake basins than on the top of sand dunes. Transverse dunes were the most dominant types of sand dunes in the study area, and the wind regimes at most stations were consistent with sand dune types. Wind was thus the main dynamic factor affecting the formation of sand dunes in the Badain Jaran Desert BJD. The results of this study are important for understanding the relationship between the wind regimes and aeolian landforms of the dune field in the deserts.
分类： 机械工程 >> 机械制造工艺与设备 提交时间： 2022-05-25 合作期刊: 《桂林电子科技大学学报》
摘要： 在电子封装领域中,所用的无铅钎料主要是二元或者三元Sn基共晶或近共晶合金,其基体相为富Sn相。为得到富Sn相的力学性能及应力-应变关系,由纳米压痕试验测试获得了富Sn相的弹性模量与硬度,并得到载荷-位移曲线。采用有限元反演分析的方法确定了富Sn相的特征应力和特征应变,并由量纲函数确定应变强化指数。将特征应力和特征应变强化指数等参数代入幂强化模型中,计算得到富Sn相的屈服强度为31.51 MPa,并最终确定富Sn相的应力-应变关系函数表达式。
分类： 农、林、牧、渔 >> 农业基础学科 提交时间： 2022-05-23 合作期刊: 《智慧农业（中英文）》
摘要： 本文首先阐述了科技革命的概念与满足条件，提出并分析了内生及外生农业颠覆性技术及其差异，特别是提出了跨界技术的概念并论证了其对农业科技进步的外生影响。然后分析了作为跨界技术的集大成者智慧农业技术的特点，智慧农业对传统农业生产技术与生产方式的替代以及智慧农业与农村经济转型的关系。在此基础上讨论了中国智慧农业发展所面临的问题。最后有针对性地提出了促进颠覆性技术创新和智慧农业发展的政策建议，包括加强关键颠覆性核心技术研发、改革现有的农业高等教育体系、推动跨界技术的农业产业化研发以及在高标准农田及规模化养殖场实施智慧农业生产等。
分类： 图书馆学、情报学 >> 情报学 提交时间： 2022-05-22
摘要： [目的] 大科学装置对促进重大科技成果产出具有重要作用，其集群化发展协同创新效应不 断引领区域产业创新发展。为了使大装置更好地发挥协同效应，需要更好地进行大装置规划布局。 [方法] 本研究从科研成果入手，提出一种通用的分析框架，可用于辅助分析大科学装置间学科层面的关联程度，作为以需求驱动规划的补充。以广东松山湖科学城为例，收集已有大装置（散裂中子源与同步辐射光源）与规划布局的大装置 Y 在国际上同类型装置的论文数据， 分析其学科层面的内在关联，用以辅助判断规划布局的装置与已有装置的匹配关联程度。 [结果] 已有装置（散裂中子源与同步辐射光源）关联度高，存在可能的互补关系，大装置 Y 与已有装置关联度则较低，如要布局建议还需要进一步专家论证。 [局限]本研究主要从装置产出成果来量化装置间联系，只可为决策者提供一种客观的数据视角和辅助参考，在大科学装置集群的规划方面，更重要的是国家整体的规划和区域对大科学装置的需求，本方法需要融合大科学装置的内在原理、运作流程以及专家知识，才可在规划布局中发挥真正的作用。 [结论] 该方法一定程度上能为大装置规划布局提供前瞻性的定量化参考，从而为大装置群的功能协调与未来发展提供预见性、全局性的优化方案。
分类： 生物学 >> 植物学 >> 应用植物学 提交时间： 2022-05-21 合作期刊: 《广西植物》
摘要： 气候变化是国际社会共同关注的环境问题，植物对气候变化的响应反映了植物应对气候变化的生长和生存策略。叶经济性状与植物对资源的获取、利用和储存直接相关，并且受到温度条件和CO2 浓度的显著影响。该文采用人工环境控制系统封顶式生长室研究广布湿地植物水葱（Scirpus validus）和香蒲（Typha orientalis）的叶经济性状对模拟增温（现行环境温度+2 ℃）和CO2 浓度倍增（增至850 μmol·mol-1）的响应。结果表明：（1）增温处理下，水葱净光合速率、氮含量和磷含量显著降低，但其胞间CO2 浓度和比叶重显著增加；CO2 浓度倍增处理下，水葱胞间CO2 浓度和净光合速率均显著降低，但比叶重显著增加。（2）增温处理下香蒲的比叶重也显著增加，而氮含量和磷含量显著降低；香蒲的光合参数、氮含量和磷含量在CO2 浓度倍增处理下均显著降低，而比叶重显著增加。（3）除碳含量外，水葱和香蒲的其他经济性状参数包括净光合速率、气孔导度、蒸腾速率、胞间CO2 浓度、氮含量、磷含量和比叶重均在响应增温和CO2 浓度升高过程中均发挥重要作用。总体而言，该研究结果反映了水葱和香蒲在功能性状上对增温和CO2 浓度升高的响应策略。两种植物的光合能力和养分含量在两种处理下均受到显著的抑制作用，而其抗逆能力升高，表明增温和CO2浓度升高不利于水葱和香蒲的生长。
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