期刊文献+
共找到36,879篇文章
< 1 2 250 >
每页显示 20 50 100
Effect of Doppler Shifts on Photon and Particle Flux of Beams 预览
1
作者 Samuel Lewis Reich 《高能物理(英文)》 2019年第4期995-998,共4页
Reasons are given for a Doppler shift on the number of observed (sensed) photons in a light beam not just a shift in frequency, also a similar (non-relativistic) effect on the number of observed (sensed) particles (wi... Reasons are given for a Doppler shift on the number of observed (sensed) photons in a light beam not just a shift in frequency, also a similar (non-relativistic) effect on the number of observed (sensed) particles (with non-zero rest mass) in a particle beam. Optics texts have neither effect. 展开更多
关键词 PHOTON FLUX BEAMS INTENSITY IRRADIANCE PARTICLE FLUX
在线阅读 免费下载
Tuning the intensity statistics of random speckle patterns
2
作者 孟凡 赵乐 +1 位作者 张云佐 霍磊 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第5期327-331,共5页
Speckle patterns are a fundamental tool in a variety of physical and optical applications.Here,we investigate a method of precisely tuning the intensity statistics of random speckle patterns into a desirable pattern t... Speckle patterns are a fundamental tool in a variety of physical and optical applications.Here,we investigate a method of precisely tuning the intensity statistics of random speckle patterns into a desirable pattern that possesses the same spatial correlation length and similar statistics distribution.This tuning mechanism relies on the derivation of the transform function and transmission matrix,which achieves different contrasts while maintaining the same average value or energy level.The statistics properties of the generated speckle patterns are further investigated by analyzing the standard deviation under different fitting parameters.Precisely tuning the intensity statistics of random speckle patterns could be useful for both fundamental research and practical applications,such as microscopy,imaging,and optical manipulation. 展开更多
关键词 RANDOM SPECKLE pattern INTENSITY STATISTICS local INTENSITY TRANSFORMATION optical MANIPULATION
Two Important Features of the 156 Deadliest Tropical Cyclones (1851-1996) in the North Atlantic 预览
3
作者 Bomin Chen Jiqing Tan Huiyi Fan 《大气和气候科学(英文)》 2019年第1期75-83,共9页
Damages and deaths due to a tropical cyclone (TC) can easily occur at three places belong to a TC: the small ring area (SRA) of maximum sustaining wind around TC eye, the large ring area (LRA) of the rotating wind fie... Damages and deaths due to a tropical cyclone (TC) can easily occur at three places belong to a TC: the small ring area (SRA) of maximum sustaining wind around TC eye, the large ring area (LRA) of the rotating wind field around SRA and the skin air belt (SKAB) around LRA. However, weather forecasters only use the intensity of the SRA of a TC as the proxy to gauge the whole TC intensity, which led to many “non-major” TCs proved to be “deadly” TCs. This is called as “over-generalization problem” (OGP). Here we introduce a new way to measure the intensity of a TC. After investigating 156 deadly TCs in North Atlantic, we found an important feature: 83.3% of the top 156 deadliest TCs usually made landfalls along “five major tracks”. Furthermore, we found that the new intensity of those “deadliest” TCs kept almost unchanged with the increasing of time intervals at earlier stage from the genesis points, whereas the new intensity of those “safe” TCs increased in a line with much steeper slope. Using these two features, weather forecasters can have two more options to identify those “non-major” and “deadly” TCs by SSHS in future. 展开更多
关键词 Over-Generalization Problem TROPICAL CYCLONE INTENSITY
在线阅读 免费下载
Weakly-coupled mode division multiplexing over conventional multi-mode fiber with intensity modulation and direct detection
4
作者 Juhao LI Zhongying WU +7 位作者 Dawei GE Jinglong ZHU Yu TIAN Yichi ZHANG Jinyi YU Zhengbin LI Zhangyuan CHEN Yongqi HE 《中国光电子学前沿:英文版》 EI CSCD 2019年第1期31-40,共10页
Multi-mode fiber(MMF)links are expected to greatly enhance capacity to cope with rapidly increasing data traffic in optical short-reach systems and networks.Recently,mode division multiplexing(MDM)over MMF has been pr... Multi-mode fiber(MMF)links are expected to greatly enhance capacity to cope with rapidly increasing data traffic in optical short-reach systems and networks.Recently,mode division multiplexing(MDM)over MMF has been proposed,in which different modes in MMF are utilized as spatial channels for data transmission.Stronglycoupled MDM techniques utilizing coherent detection and multiplex-input-multiplex-output(MIMO)digital signal processing(DSP)are complex and expensive for shortreach transmission.So the weakly-coupled approach by significantly suppressing mode coupling in the fiber and optical components has been proposed.In this way,the signals in each mode can be independently transmitted and received using conventional intensity modulation and direct detection(IM-DD).In this paper,we elaborate the key technologies to realize weakly-coupled MDM transmission over conventional MMF,including mode characteristic in MMF and weakly-coupled mode multiplexer/ demultiplexer(MUX/DEMUX).We also present the upto-date experimental results for weakly-coupled MDM transmission over conventional OM3 MMF.We show that weakly-coupled MDM scheme is promising for high-speed optical interconnections and bandwidth upgrade of already-deployed MMF links. 展开更多
关键词 MULTI-MODE FIBER (MMF) MODE DIVISION MULTIPLEXING (MDM) weak MODE coupling intensity modulation and direct detection (IM-DD)
高水平青年男子足球运动员赛前热身活动的负荷量化研究 预览
5
作者 徐丕同 Paulo Henriques +1 位作者 赵硕 刘鸿优 《体育科研》 2019年第4期17-21,共5页
采用可穿戴电子设备,对2019赛季“全国青少年男子足球超级联赛”19岁以下年龄组的一支参赛球队的24名青年运动员参加的8场正式比赛的赛前热身活动和比赛负荷进行量化分析。结果显示:(1)该运动队的赛前热身时间平均为(27.8±4.6)min... 采用可穿戴电子设备,对2019赛季“全国青少年男子足球超级联赛”19岁以下年龄组的一支参赛球队的24名青年运动员参加的8场正式比赛的赛前热身活动和比赛负荷进行量化分析。结果显示:(1)该运动队的赛前热身时间平均为(27.8±4.6)min,首发球员和替补球员在赛前热身活动中的各项负荷量化指标皆体现出极其显著的中等至非常大程度差异(P<0.001,ES值介于0.72和3.17);(2)首发且打满全场的运动员赛前热身活动的跑动总距离占比赛跑动总距离的18.6%±3.2%,加速度负荷总量占24.5%±4.1%,首发打满全场、首发被换下、替补45min以上和替补未满45min四组不同出场时间的运动员的赛前热身活动的各项负荷指标占比赛负荷指标的比重皆体现出显著性差异(P<0.013,ηp2介于0.10和0.44)。研究认为,赛前热身活动的负荷量应该被计入比赛日的负荷总量,用于足球运动员的训练负荷管理与训练任务设计参照,且不同出场时间带来的负荷差异应该被纳入考量范围。 展开更多
关键词 足球 热身 负荷量 负荷强度 跑动距离
在线阅读 下载PDF
CO2高温光谱参数测量系统设计与实验 预览
6
作者 陈玖英 周梅 +2 位作者 刘建国 阚瑞峰 李传荣 《红外与毫米波学报》 SCIE EI CAS CSCD 北大核心 2019年第3期358-364,共7页
CO2 和 CO 被称为燃烧效率指示性气体燃烧流场中 CO2 的精确测量对工业燃烧过程的节能减排和发动机燃烧状态诊断等都具有重要意义.研究 CO2 气体的高温光谱参数包括:线强、自加宽系数、温度系数可提高燃烧过程中 CO2 浓度的测量精度和... CO2 和 CO 被称为燃烧效率指示性气体燃烧流场中 CO2 的精确测量对工业燃烧过程的节能减排和发动机燃烧状态诊断等都具有重要意义.研究 CO2 气体的高温光谱参数包括:线强、自加宽系数、温度系数可提高燃烧过程中 CO2 浓度的测量精度和可靠性.为了获得可用于燃烧诊断的 CO2 吸收线的高温光谱参数基于可调谐半导体激光吸收光谱技术设计了一套最高温度可达2-0173 K 的精确控温控压气体光谱参数测量系统.采用该系统开展了CO2R(50e)吸收线(中心频率为5007.787cm )的高温光谱测量实验获得了温度范围1212~1873K内多个压强下的纯 CO2 气体的大量高温吸收光谱经热辐射背景扣除、基线拟合、时频转换、多线组合非线性最小二乘法拟合等数据处理过程得到温度范围1212~1873K内CO2R(50e)吸收线的线强、自加宽系数及温度系数其中线强不确定度<1.5%自加宽系数不确定度小于4.5%.这些参数是对现有数据库的补充和完善对燃烧诊断中的CO2浓度检测有很大帮助能够满足燃烧过程中 CO2 浓度精确反演的需求. 展开更多
关键词 可调谐半导体激光吸收光谱 高温光谱 线强 自加宽系数 温度系数
在线阅读 下载PDF
Low-intensity microcurrent therapy promotes regeneration of atrophied calf muscles in immobilized rabbits 预览
7
作者 Gi Young Park Dong Rak Kwon Yong Suk Moon 《生物医学研究杂志:英文版》 CAS CSCD 2019年第1期30-37,共8页
The purpose of this study was to investigate the intensity-specific regenerative effects of microcurrent therapy on gastrocnemius muscle atrophy induced by cast-immobilization in rabbits. Fifteen rabbits were randomly... The purpose of this study was to investigate the intensity-specific regenerative effects of microcurrent therapy on gastrocnemius muscle atrophy induced by cast-immobilization in rabbits. Fifteen rabbits were randomly allocated to 3 groups after cast removal: cast-immobilization and sham microcurrent therapy for 2 weeks(group 1);castimmobilization and microcurrent therapy(25 μA) for 2 weeks(group 2);cast-immobilization and microcurrent therapy(5,000 μA) for 2 weeks(group 3). Clinical parameters [calf circumference, compound muscle action potential(CMAP) of the tibial nerve, thickness of gastrocnemius muscle], cross sectional area of gastrocnemius muscle fibres,and immunohistochemistry was evaluated. The clinical parameters representing mean atrophic changes in group 2 were significantly lower than those in group 3. The cross sectional area of the gastrocnemius muscle fibres and immunohistochemical parameters in group 2 were significantly greater than those in group 3. The results showed that low-intensity microcurrent therapy can more effectively promote regeneration in atrophied gastrocnemius muscle than high-intensity microcurrent therapy. 展开更多
关键词 microcurrent INTENSITY ATROPHY MUSCLE cast
在线阅读 免费下载
Fire monitoring in coal mines using wireless underground sensor network and interval type-2 fuzzy logic controller 预览
8
作者 Sweta Basu Sutapa Pramanik +2 位作者 Sanghamitra Dey Gautam Panigrahi Dipak Kumar Jana 《国际煤炭科学技术学报:英文版》 2019年第2期274-285,共12页
From the view of underground coal mining safety system, it is extremely important to continuous monitoring of coal mines for the prompt detection of fires or related problems inspite of its uncertainty and imprecise c... From the view of underground coal mining safety system, it is extremely important to continuous monitoring of coal mines for the prompt detection of fires or related problems inspite of its uncertainty and imprecise characteristics. Therefore, evaluation and inferring the data perfectly to prevent fire related accidental risk in underground coal mining (UMC) system are very necessary. In the present article, we have proposed a novel type-2 fuzzy logic system (T2FLS) for the prediction of fire intensity and its risk assessment for risk reduction in an underground coal mine. Recently, for the observation of underground coal mines, wireless underground sensor network (WUSN) are being concerned frequently. To implement this technique IT2FLS, main functional components are sensor nodes which are installed in coal mines to accumulate different imprecise environmental data like, temperature, relative humidity, different gas concentrations etc. and these are sent to a base station which is connected to the ground observation system through network. In the present context, a WUSN based fire monitoring system is developed using fuzzy logic approach to enhance the consistency in decision making system to improve the risk chances of fire during coal mining. We have taken Mamdani IT2FLS as fuzzy model on coal mine monitoring data to consider real-time decision making (DM). It is predicted from the simulated results that the recommended system is highly acceptable and amenable in the case of fire hazard safety with compared to the wired and off-line monitoring system for UMC. Legitimacy of the suggested model is prepared using statistical analysis and multiple linear regression analysis. 展开更多
关键词 Type-2 fuzzy logic UNDERGROUND coal mining system MINE environment FIRE and risk monitoring of MINE WIRELESS sensor networks FIRE Intensity
在线阅读 下载PDF
A family of non-conforming crack front elements of quadrilateral and triangular types for 3D crack problems using the boundary element method
9
作者 Guizhong XIE Fenglin ZHOU +2 位作者 Hao LI Xiaoyu WEN Fannian MENG 《机械工程前沿:英文版》 CSCD 2019年第3期332-341,共10页
This study focuses on establishing nonconforming crack front elements of quadrilateral and triangular types for 3D crack problems when the dual boundary element method is applied. The asymptotic behavior of the physic... This study focuses on establishing nonconforming crack front elements of quadrilateral and triangular types for 3D crack problems when the dual boundary element method is applied. The asymptotic behavior of the physical variables in the area near the crack front is fully considered in the construction of the shape function. In the developed quadrilateral and triangular crack front elements, the asymptotic term, which captures the asymptotic behavior of the physical variable, is multiplied directly by the conventional Lagrange shape function to form a new crack front shape function. Several benchmark numerical examples that consider pennyshaped cracks and straight-edge crack problems are presented to illustrate the validity and efficiency of the developed crack front elements. 展开更多
关键词 TAYLOR expansion CRACK FRONT ELEMENTS stress intensity factors dual boundary element method
Intensity detecting refractive index sensors with long-period fiber gratings written in STS structure
10
作者 阮祖亮 裴丽 +4 位作者 郑晶晶 王建帅 吴良英 宁提纲 王吉 《中国光学快报:英文版》 SCIE EI CAS CSCD 2019年第7期12-16,共5页
A refractive index intensity detecting sensor with long-period grating written in the single-mode–thin-core–single-mode fiber(STS) structure is proposed and optimized theoretically.The sensor is composed of two sing... A refractive index intensity detecting sensor with long-period grating written in the single-mode–thin-core–single-mode fiber(STS) structure is proposed and optimized theoretically.The sensor is composed of two single-mode fibers connected by a section of long-period fiber grating fabricated on thin-core fiber.After optimization and benefitting from the phase matching point, the loss peak of the structure can reach 62.8dB theoretically.The wavelength of the characteristic peak is fixed at the phase matching point, so intensity detection can be achieved.The sensitivity can reach 272.5dB/RIU.The structural optimization in this Letter provides a reference for the fabrication of an easy-made all-fiber sensor without extra cladding. 展开更多
关键词 long-period FIBER GRATINGS WRITTEN index INTENSITY detecting SENSOR
上海市建筑物震害损失快速评估系统 预览
11
作者 胡峻 赵鹏 《智能城市》 2019年第18期3-5,共3页
根据震害机理分析,承灾体震害程度由地震作用、承灾体易损性、承灾体属性三要素决定。结合上海特大城市特点,基于现有强震动观测台网,结合建筑物震害易损性矩阵和建筑物GIS信息数据库,构建了一套针对建筑物进行震害损失评估的系统。借... 根据震害机理分析,承灾体震害程度由地震作用、承灾体易损性、承灾体属性三要素决定。结合上海特大城市特点,基于现有强震动观测台网,结合建筑物震害易损性矩阵和建筑物GIS信息数据库,构建了一套针对建筑物进行震害损失评估的系统。借助该系统,能够快速获取建筑物的震害损失分布情况,并直观的在GIS底图进行展现。 展开更多
关键词 震害损失 快速评估 烈度 易损性
在线阅读 下载PDF
合肥市城市用地变化分析 预览
12
作者 董兆丰 陈莉 《洛阳理工学院学报:自然科学版》 2019年第3期35-39,共5页
利用合肥市2011年~2017年的城市土地利用数据,分析合肥市2011年~2017年土地利用结构变化情况和城市土地利用集约化程度。结果表明:合肥市城市土地利用结构发生变化,其中未利用地变化最为明显,建设用地规模逐年增大,耕地变化不显著却呈... 利用合肥市2011年~2017年的城市土地利用数据,分析合肥市2011年~2017年土地利用结构变化情况和城市土地利用集约化程度。结果表明:合肥市城市土地利用结构发生变化,其中未利用地变化最为明显,建设用地规模逐年增大,耕地变化不显著却呈现出了逐年下降的趋势,同时城市土地利用集约化程度不断提升,利用更加科学有效的手段、合理利用城市土地资源,实现城市土地资源可持续利用显得日益重要。 展开更多
关键词 合肥市 城市土地 利用化 土地利用 集约化程度
在线阅读 下载PDF
幼儿体育活动强度自评量表的研制与应用
13
作者 罗冬梅 姚天聪 +2 位作者 屈莎 赵星 周嘉琳 《北京体育大学学报》 CSSCI 北大核心 2019年第4期139-149,共11页
目的:在前期研究成果的基础上,参考借鉴国内外现有体育活动强度评价量表,充分考虑幼儿的认知水平,通过实验研制一套科学合理具有普适性的幼儿体育活动强度自评量表。方法:选取2所幼儿园大班幼儿116人进行量表研制。通过台阶高度和踏步... 目的:在前期研究成果的基础上,参考借鉴国内外现有体育活动强度评价量表,充分考虑幼儿的认知水平,通过实验研制一套科学合理具有普适性的幼儿体育活动强度自评量表。方法:选取2所幼儿园大班幼儿116人进行量表研制。通过台阶高度和踏步频率负荷递增的方式分析量表的合理性,测试过程中让幼儿利用量表进行自评,同时全程记录心率和加速度计数据。使用单因素重复测量方差分析检验各自评等级的平均心率差异,用Spearman等级相关和配对样本T检验分析量表的重测信度,另用Spearman等级相关分析量表的效标效度。结果:幼儿自评等级与加速度计Count值和心率的相关系数均较高(P<0. 001),说明量表能够较好反映幼儿运动中的物理强度和生理变化。心率在各等级间均有显著性差异(P<0. 001),说明量表对不同强度活动的区分度较好。2次测试的自评等级高度相关(P<0. 05)且无显著性差异(P>0. 05),即量表的重测信度较好。幼儿在园内日常活动的量表自评等级与心率的相关系数较高(R=0. 604,P<0. 001),说明量表具有较好的校标效度。结论:研制获得了《幼儿体育活动强度自评量表》。该量表是一个包含6个选项的以卡通图画为主要表现形式的幼儿自评量表。该量表各等级与客观指标的相关性较好,具有良好的信度和效度,且具有较好的普适性,可用于幼儿日常体育活动强度的评价,以帮助教师更合理地为幼儿安排各类体育活动课程。 展开更多
关键词 幼儿 体育活动 强度 量表 自评
GC-O吸闻技术应用于饮品异常风味筛查的研究 预览
14
作者 王丽华 孙志伟 王晓宁 《饮料工业》 2019年第4期6-12,共7页
GC-O吸闻技术是将气相色谱(GC)与嗅闻仪相结合对样品中挥发性组分进行分析的一项技术,能从复杂混合物中筛选出具有活性气味组分的有效方法,该技术是将仪器和人的感官分析相结合来研究样品特征气味组分的强度贡献值。本研究利用GC-O吸闻... GC-O吸闻技术是将气相色谱(GC)与嗅闻仪相结合对样品中挥发性组分进行分析的一项技术,能从复杂混合物中筛选出具有活性气味组分的有效方法,该技术是将仪器和人的感官分析相结合来研究样品特征气味组分的强度贡献值。本研究利用GC-O吸闻技术,对比分析植物蛋白饮品的包装材质含有的15种添加剂对饮品风味的异常干扰,并筛查定性出饮品中受材质影响的异常气味组分。结果表明:乙酸丙酯、乙酸丁酯等四种强气味组分对饮品的风味干扰有显著相关性。 展开更多
关键词 GC-O吸闻技术 气味活性组分 包装材质 异常风味 强度 筛查
在线阅读 免费下载
Impacts of vegetation over bedforms on flow characteristics in gravel-bed rivers 预览
15
作者 Hossein Afzalimehr Mohammad Reza Maddahi +1 位作者 Jueyi Sui Majid Rahimpour 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第5期986-998,共13页
In the present study,among six gravel-bed river reaches,two natural gravel-bed river reaches with approximately similar bedforms and flow conditions have been found,one river reach with vegetation on bedforms and the ... In the present study,among six gravel-bed river reaches,two natural gravel-bed river reaches with approximately similar bedforms and flow conditions have been found,one river reach with vegetation on bedforms and the other without vegetation on bedforms.Based on field measurements,the impacts of vegetation over bedforms on flow characteristics have been investigated.Flow velocity,Reynolds stress and turbulence intensity distributions over bedforms with vegetation have been compared with those over gravel bedforms without vegetation.By using the quadrant analysis,the dominant events of turbulent flow structures have been assessed for flows over gravel bedforms with vegetation and without vegetation.Results show that the effect of vegetation enhances the anisotropy in turbulence and generates strong secondary currents,which lead to the occurrence of dip phenomenon at the stoss section and the crest of vegetated bedforms.The change of bed roughness from gravel bed to vegetated bed causes a development of a new boundary layer.This resulted in the different shape of velocity distributions over bedforms with vegetation from those over bedforms without vegetation,which can affect the lives of aquatic animals.Reynolds shear stress at downstream section of gravel bedform without vegetation is much higher than that of vegetated bedform,which shows that the erosion takes place from downstream of vegetated bedforms,while in the bare beds;the deposition is at downstream of bedforms.It is found that the presence of vegetation causes a chaotic distribution pattern of Reynolds shear stress,while it has more orderly pattern at the downstream section of gravel bedform without vegetation.Besides,the distribution of turbulence intensity in the lee side of vegetated bedform has a concave shape and in the stoss section,turbulence is generated in ejections and sweeps near the vegetation cover.These findings are significant to the practice of river ecological restoration. 展开更多
关键词 BEDFORM Reynolds shear stress distribution turbulence intensity VEGETATION velocity profiles
在线阅读 下载PDF
刮痧力度及时间间隔对刮痧效果的影响 预览
16
作者 邱灵慧 王铁山 +6 位作者 刘碧原 臧颖颖 陈昕力 刘玥婷 陈慧昀 王朝阳 卢涛 《世界中医药》 CAS 2019年第5期1139-1143,共5页
目的:观察不同力度对刮痧效果的影响,初步探讨刮痧的作用机制以及效应周期,进一步探究刮痧治疗的最佳间隔时间。方法:用自制的特殊刮痧板控制使刮痧频次等参数保持一致,分别以1N、3N和9N的力进行刮痧,通过ELISA方法检测刮痧后IL-1α、I... 目的:观察不同力度对刮痧效果的影响,初步探讨刮痧的作用机制以及效应周期,进一步探究刮痧治疗的最佳间隔时间。方法:用自制的特殊刮痧板控制使刮痧频次等参数保持一致,分别以1N、3N和9N的力进行刮痧,通过ELISA方法检测刮痧后IL-1α、IL-6的变化,结合皮肤HE染色法探究不同力度刮痧对机体的影响,选择适合的刮痧力度,通过血常规和流式细胞术检测刮痧后不同时间点的白细胞总数、淋巴细胞总数及T细胞亚群等的变化,初步探讨刮痧的作用机制和效应周期。结果:1N的力度刮痧未引起明显的变化,9N的力度刮痧造成了较严重的皮肤损伤和大量炎性反应因子释放,3N的力度刮痧较为适中,引起了机体适度的应激反应。以3N的力度刮痧后,血液中白细胞总数和淋巴细胞总数及IL-1α、IL-6缓慢升高,在1h到24h之间达到峰值,之后缓慢下降,在72h左右恢复正常水平。结论:3N的力比较适合于刮痧实验,在刮痧之后1h到24h,刮痧对免疫系统的增强作用达到峰值,在72h左右回归正常值,初步提示可以开始下一次刮痧治疗。 展开更多
关键词 刮痧 力度 时间 免疫 组织切片 炎性反应因子 血常规 T淋巴细胞亚群
在线阅读 下载PDF
1954—2016年阿勒泰市春季寒潮过程频数及强度气候特征 预览
17
作者 博尔楠·哈不都拉 黄迆静 +2 位作者 江远安 赵江伟 哈那提·阿依提看 《沙漠与绿洲气象》 2019年第1期79-86,共8页
利用阿勒泰基准气候站日最低气温资料,资料长度为1954—2016年的春季(每年2月26日—5月31日),以日最低气温及其降温幅度为指标,整理出阿勒泰市63a寒潮过程数据库,分析阿勒泰市近63a来寒潮过程的频数以及强度相关6个指标的气候特征,结果... 利用阿勒泰基准气候站日最低气温资料,资料长度为1954—2016年的春季(每年2月26日—5月31日),以日最低气温及其降温幅度为指标,整理出阿勒泰市63a寒潮过程数据库,分析阿勒泰市近63a来寒潮过程的频数以及强度相关6个指标的气候特征,结果表明:(1)1954—2016年春季(3—5月)阿勒泰市共发生寒潮天气过程226次,平均每年发生3.6次;3月平均每年出现1.8次,4月1.1次,5月0.7次;共有17a为寒潮发生异常偏少年份,16a为异常偏多年份;3月上旬和3月中旬为春季寒潮过程发生最多的时段。(2)春季寒潮频数以每0.1次/10a的速率在递减;月际尺度上,3月和5月发生寒潮过程频数在递减,4月递增;年代际变化1950年代最多,2010—2016年最少。(3)春季寒潮过程持续日数在1耀7d,其中持续2d的寒潮过程最多,占春季寒潮过程的49%;持续时间在1耀3d的寒潮过程占92%。(4)春季寒潮降温过程平均降温幅度为-12.7℃,降温幅度平均值最大在3月;最大24、48h和72h降温幅度平均值分别为-8.9、-12.5益和-14.3℃。(5)春季寒潮降温过程最低气温平均值为-11.8℃;寒潮降温过程最低气温平均距平值为-7.6℃。 展开更多
关键词 寒潮过程 频数 强度 阿勒泰市
在线阅读 下载PDF
建筑管道抗震支吊架力学性能有限元分析 预览
18
作者 史旦达 谢文远 +2 位作者 孔戈 刘文白 别亦白 《计算机辅助工程》 2019年第2期56-62,73共8页
针对建筑管道抗震支吊架理论研究落后于工程应用实践的现状,以某抗震支吊架为研究对象,采用有限元法分析抗震支吊架的力学性能。对比数值计算结果与支吊架室内拉伸试验结果,验证有限元建模的可靠性。针对3种不同地震波,对支吊架结构的... 针对建筑管道抗震支吊架理论研究落后于工程应用实践的现状,以某抗震支吊架为研究对象,采用有限元法分析抗震支吊架的力学性能。对比数值计算结果与支吊架室内拉伸试验结果,验证有限元建模的可靠性。针对3种不同地震波,对支吊架结构的地震响应进行瞬态时程分析,并对连接螺栓的拉伸强度进行校核,探讨水平加速度方向、斜撑厚度和安装角度变化对支吊架结构抗震性能的影响。结果表明:在3种地震波作用下,支吊架结构均满足强度要求,且连接螺栓也未发生破坏;当水平加速度侧向输入时,支吊架结构的受力响应最大;随着斜撑厚度的增加和安装角度的减小,支吊架结构的抗震性能增强。 展开更多
关键词 抗震 支吊架 斜撑 地震响应 强度 有限元
在线阅读 下载PDF
基于非线性渐变式颜色映射的LIC改进算法 预览
19
作者 高茂庭 董红周 周凡 《计算机应用研究》 CSCD 北大核心 2019年第9期2834-2839,共6页
线积分卷积(LIC)算法展现的纹理反映了整个矢量场的方向结构,却不能展现矢量场的强度大小。针对此问题提出基于非线性渐变式颜色映射的LIC改进算法,将矢量场强度与白噪声结合作为LIC的输入纹理,运用Fast LIC思想并划分纹理区域同步执行... 线积分卷积(LIC)算法展现的纹理反映了整个矢量场的方向结构,却不能展现矢量场的强度大小。针对此问题提出基于非线性渐变式颜色映射的LIC改进算法,将矢量场强度与白噪声结合作为LIC的输入纹理,运用Fast LIC思想并划分纹理区域同步执行LIC运算来提高算法效率;再将矢量场强度作非线性变换,根据渐变式颜色映射方案使用Open CV处理引擎并行实现矢量场强度的颜色映射;最后由LIC得到的灰度纹理和颜色映射结果确定合成系数并构造累计函数增强两者结果,再进行线性合成运算得到最终可视化效果。在对全球海洋流场和风场两种典型的矢量场进行可视化以及与其他算法对比实验表明,改进算法得到的可视化效果纹理清晰,较好地展示出矢量场的方向和强度,能够更准确地反映矢量场的全方位信息和局部变化情况。 展开更多
关键词 线积分卷积 矢量场 场强 可视化 累计函数
在线阅读 下载PDF
1961~2016年四川盆地夏季高温热浪变化特征分析 预览
20
作者 黄小梅 赵旋 肖丁木 《高原山地气象研究》 2019年第2期14-22,共9页
利用27个测站逐日最高气温资料,对1961~2016年四川盆地夏季高温热浪的时空演变特征进行研究。结果表明:(1)四川盆地高温热浪频次、强度和持续时间均呈增加趋势,其中热浪强度的增加趋势最为显著。三者都经历了先较弱增加后明显减少再明... 利用27个测站逐日最高气温资料,对1961~2016年四川盆地夏季高温热浪的时空演变特征进行研究。结果表明:(1)四川盆地高温热浪频次、强度和持续时间均呈增加趋势,其中热浪强度的增加趋势最为显著。三者都经历了先较弱增加后明显减少再明显增加的年代际变化过程。20世纪80年代是热浪低发期,2010~2016年为明显高发期。(2)盆地高温热浪气候平均空间分布大致呈东南多(强)西北少(弱),空间差异显著,多发区主要集中在重庆西南部一带。三项指标除盆地东南边缘小部分为减少趋势外,基本呈增加趋势,增幅大值带均沿重庆北部至四川南部呈东北-西南走向。相比而言,盆地西部增加趋势比盆地东部更加显著。(3)盆地高温热浪频次、强度和持续时间均存在显著的年际变化周期,且具有较为一致的2年周期。相关分析表明,三者均与西太平洋副高脊线和北界位置存在显著的正相关。 展开更多
关键词 高温热浪 四川盆地 时空特征 频次 强度
在线阅读 免费下载
上一页 1 2 250 下一页 到第
使用帮助 返回顶部 意见反馈