共查询到20条相似文献，搜索用时 781 毫秒
1.
Martin A. Pomerantz 《Journal of The Franklin Institute》1974,298(4):363-383
Solar and galactic cosmic rays are of profound astrophysical interest. One facet of contemporary cosmic ray research utilizes these energetic particles as space probes for studying the characteristics of the solar-controlled interplanetary medium, the heliosphere, which is essentially the extension of the solar corona to a considerable distance beyond the orbit of earth. Solar cosmic ray observations in particular contribute to our understanding of the earth's environs, the interplanetary medium, and the sun itself. Appropriately deployed ground-based cosmic ray detectors utilize the earth as a spacedraft for carrying out experiments that are far beyond the capacity of artificial satellites. In interpreting the observations, however, the effects of the geomagnetic field and of the atmosphere must be taken into account by appropriate analytical procedures. Theoretical models account for many of the characteristics of the observed modulations and anisotropies, which manifest themselves as temporal or spatial intensity variations. Analysis of the measurements in terms of various models provides an understanding of the physical mechanisms, as well as the determination of the relevant parameters. Properties of solar cosmic rays that have been investigated include spectra, angular distributions, transport mechanisms and the acceleration to relativistic energies. 相似文献
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地球空间包括地球中高层大气、电离层和磁层,其环境变化深刻影响着人类生活,如空间灾害性事件的发生,可能危害地面电网安全,造成星地无线电通讯中断。在科技部、国家自然科学基金委和中国科学院等部门支持下,北京空间环境国家野外科学观测研究站通过研制和发展一批具有国际先进水平的观测仪器,建立了电离层、中高层大气和地磁等多学科综合观测台链,并开发成功新的探测模式和诊断技术,实现对我国上空多种空间环境参量的科学观测,揭示其区域特征和空间精细结构与变化,推动数据服务于原创科学研究和空间天气预报保障任务。基于观测数据,通过发展理论模式,采用数据分析与数值模拟相结合等研究方法,系统研究了大气层-电离层耦合、磁层-电离层耦合和太阳辐射的光电离光化学3类最为重要的驱动过程对电离层变化性的影响和控制作用。 相似文献
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S.A. Korff 《Journal of The Franklin Institute》1940,229(1):21-27
Instrument carrying balloon flights using the radio-cosmic-ray technique have been made during the day and the night, to investigate the amount of the diurnal variation at high altitudes. It was found that the effect, if any, is smaller than the experimental error of two per cent., and is estimated to be about 1.5 per cent. of the radiation at these levels. This permits a definite upper limit to be set to any contribution of solar origin to the ionization at levels up to 0.3 meters of water equivalent below the top of the atmosphere, which could be produced by photons in that spectral region to which mass-absorption laws apply, namely X-radiation. The magnitude of the effect is in agreement with the view advanced by Vallarta, that a magnetic field on the sun would produce a small diurnal change in the intensity of the softer portion of the cosmic ray intensity. 相似文献
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This paper discusses the INAA results of REE in clays atand near some Permian/Triassic boundaries of South China.It showsthat the REE patterns of boundary clays differ from those of non-boundary clays.One difference is that the boundary clays are moreenriched in LREE,with steeper slope of REE and a smaller Eu nega-tive anomaly than the non-boundary clays.Another difference is that theboundary clays show a small Ce negative anomaly,but no Ce anomalyoccurs in the non-boundary clays.From these REE patterns and some other experimental facts,it isproposed that the P/T boundary clay may be a mixed product consistingof the acidic-intermediate ash and the upper crust substance representingsputtering component,and the calculated fraction of the former andlatter is 7/3. 相似文献
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Wei Lin Joseph L Kirschvink Greig A Paterson Dennis A Bazylinski Yongxin Pan 《国家科学评论(英文版)》2020,7(2):472
A broad range of organisms, from prokaryotes to higher animals, have the ability to sense and utilize Earth''s geomagnetic field—a behavior known as magnetoreception. Although our knowledge of the physiological mechanisms of magnetoreception has increased substantially over recent decades, the origin of this behavior remains a fundamental question in evolutionary biology. Despite this, there is growing evidence that magnetic iron mineral biosynthesis by prokaryotes may represent the earliest form of biogenic magnetic sensors on Earth. Here, we integrate new data from microbiology, geology and nanotechnology, and propose that initial biomineralization of intracellular iron nanoparticles in early life evolved as a mechanism for mitigating the toxicity of reactive oxygen species (ROS), as ultraviolet radiation and free-iron-generated ROS would have been a major environmental challenge for life on early Earth. This iron-based system could have later been co-opted as a magnetic sensor for magnetoreception in microorganisms, suggesting an origin of microbial magnetoreception as the result of the evolutionary process of exaptation. 相似文献
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《Information processing & management》2023,60(3):103289
Anomalous event recognition requires an instant response to reduce the loss of human life and property; however, existing automated systems show limited performance due to considerations related to the temporal domain of the videos and ignore the significant role of spatial information. Furthermore, although current surveillance systems can detect anomalous events, they require human intervention to recognise their nature and to select appropriate countermeasures, as there are no fully automatic surveillance techniques that can simultaneously detect and interpret anomalous events. Therefore, we present a framework called Vision Transformer Anomaly Recognition (ViT-ARN) that can detect and interpret anomalies in smart city surveillance videos. The framework consists of two stages: the first involves online anomaly detection, for which a customised, lightweight, one-class deep neural network is developed to detect anomalies in a surveillance environment, while in the second stage, the detected anomaly is further classified into the corresponding class. The size of our anomaly detection model is compressed using a filter pruning strategy based on a geometric median, with the aim of easy adaptability for resource-constrained devices. Anomaly classification is based on vision transformer features and is followed by a bottleneck attention mechanism to enhance the representation. The refined features are passed to a multi-reservoir echo state network for a detailed analysis of real-world anomalies such as vandalism and road accidents. A total of 858 and 1600 videos from two datasets are used to train the proposed model, and extensive experiments on the LAD-2000 and UCF-Crime datasets comprising 290 and 400 testing videos reveal that our framework can recognise anomalies more effectively, outperforming other state-of-the-art approaches with increases in accuracy of 10.14% and 3% on the LAD-2000 and UCF-Crime datasets, respectively. 相似文献
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It has been known that there are different kinds of small-scale active phenomena on the Sun. They are classified into spicules, macrospicules, and H-alpha jets, X-ray jets, etc., according to their sizes, velocities, lifetimes, and so on. All these phenomena are related to small-scale magnetic fields. The problems of solar upper atmospheric heating and solar wind acceleration have never been solved. Small-scale magnetic fields and activities are considered to play key roles in heating upper atmosphere and in accelerating solar wind. 相似文献
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The South China Sea, as ‘a non-volcanic passive margin basin’ in the Pacific, has often been considered as a small-scale analogue of the Atlantic. The recent ocean drilling in the northern South China Sea margin found, however, that the Iberian model of non-volcanic rifted margin from the Atlantic does not apply to the South China Sea. In this paper, we review a variety of rifted basins and propose to discriminate two types of rifting basins: plate-edge type such as the South China Sea and intra-plate type like the Atlantic. They not only differ from each other in structure, formation process, lifespan and geographic size, but also occur at different stages of the Wilson cycle. The intra-plate rifting occurred in the Mesozoic and gave rise to large oceans, whereas the plate-edge rifting took place mainly in the mid-Cenozoic, with three-quarters of the basins concentrated in the Western Pacific. As a member of the Western Pacific system of marginal seas, the South China Sea should be studied not in isolation on its origin and evolution, but in a systematic context to include also its neighboring counterparts. 相似文献
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经过50年的发展,中国科学院大气物理研究所华北香河气候与环境综合野外科学观测研究站（以下简称“香河站”）已具备从边界层到中高层气候环境的综合探测能力,加入了多个国内外大气探测网,是国际上少有的大气综合野外科学试验站。21世纪以来,香河站开展多次国际大型综合观测试验,在长期连续观测数据基础上,开展了中高层大气能量传播和物质交换、边界层大气物理化学和空气质量、太阳能监测预报等基础和应用研究,取得了一批有显示度的研究成果。继往开来,香河站将深耕先进探测仪器设备研制和更新改造,提升中高层大气热动力探测和边界层物理化学过程探测能力,建成集观测、试验和研究于一体的野外大气综合探测基地,提升对中层大气基本过程、上下大气层交换过程和机理、污染减排天气气候和环境效应等问题的科学认识,为我国在全球气候与环境议题上取得话语权和国家安全提供科技支撑。 相似文献
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In this paper, we propose a continuous flow droplet-based microfluidic platform for magnetic particle-based assays by employing in-droplet washing. The droplet-based washing was implemented by traversing functionalized magnetic particles across a laterally merged droplet from one side (containing sample and reagent) to the other (containing buffer) by an external magnetic field. Consequently, the magnetic particles were extracted to a parallel-synchronized train of washing buffer droplets, and unbound reagents were left in an original train of sample droplets. To realize the droplet-based washing function, the following four procedures were sequentially carried in a droplet-based microfluidic device: parallel synchronization of two trains of droplets by using a ladder-like channel network; lateral electrocoalescence by an electric field; magnetic particle manipulation by a magnetic field; and asymmetrical splitting of merged droplets. For the stable droplet synchronization and electrocoalescence, we optimized droplet generation conditions by varying the flow rate ratio (or droplet size). Image analysis was carried out to determine the fluorescent intensity of reagents before and after the washing step. As a result, the unbound reagents in sample droplets were significantly removed by more than a factor of 25 in the single washing step, while the magnetic particles were successfully extracted into washing buffer droplets. As a proof-of-principle, we demonstrate a magnetic particle-based immunoassay with streptavidin-coated magnetic particles and fluorescently labelled biotin in the proposed continuous flow droplet-based microfluidic platform. 相似文献
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An optical transparent 3-D Integrated Microchannel-Electrode System (3-DIMES) has been developed to understand the particles'' movement with electrokinetics in the microchannel. In this system, 40 multilayered electrodes are embedded at the 2 opposite sides along the 5 square cross-sections of the microchannel by using Micro Electro-Mechanical Systems technology in order to achieve the optical transparency at the other 2 opposite sides. The concept of the 3-DIMES is that the particles are driven by electrokinetic forces which are dielectrophoretic force, thermal buoyancy, electrothermal force, and electroosmotic force in a three-dimensional scope by selecting the excitation multilayered electrodes. As a first step to understand the particles'' movement driven by electrokinetic forces in high conductive fluid (phosphate buffer saline (PBS)) with the 3-DIMES, the velocities of particles'' movement with one pair of the electrodes are measured three dimensionally by Particle Image Velocimetry technique in PBS; meanwhile, low conductive fluid (deionized water) is used as a reference. Then, the particles'' movement driven by the electrokinetic forces is discussed theoretically to estimate dominant forces exerting on the particles. Finally, from the theoretical estimation, the particles'' movement mainly results from the dominant forces which are thermal buoyancy and electrothermal force, while the velocity vortex formed at the 2 edges of the electrodes is because of the electroosmotic force. The conclusions suggest that the 3-DIMES with PBS as high conductive fluid helps to understand the three-dimensional advantageous flow structures for cell manipulation in biomedical applications. 相似文献
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Tunable pores (TPs) have been used for resistive pulse sensing of 1 μm superparamagnetic beads, both dispersed and within a magnetic field. Upon application of this field, magnetic supraparticle structures (SPSs) were observed. Onset of aggregation was most effectively indicated by an increase in the mean event magnitude, with data collected using an automated thresholding method. Simulations enabled discrimination between resistive pulses caused by dimers and individual particles. Distinct but time-correlated peaks were often observed, suggesting that SPSs became separated in pressure-driven flow focused at the pore constriction. The distinct properties of magnetophoretic and pressure-driven transport mechanisms can explain variations in the event rate when particles move through an asymmetric pore in either direction, with or without a magnetic field applied. Use of TPs for resistive pulse sensing holds potential for efficient, versatile analysis and measurement of nano- and microparticles, while magnetic beads and particle aggregation play important roles in many prospective biosensing applications. 相似文献
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源地冷空气强度变异与冷涌活动特征的数值试验 总被引：2，自引：0，他引：2
本文用数值试验的方法讨论了冬季风冷涌期冷源与中低纬间的相互作用。结果表明,冷源较强时,冷空气较为平直地南传;冷源减弱时,南传路径较大地绕青藏高原呈弧形弯曲。同时,冷涌对低纬地区的作用强度与中纬冷源强度间并不存在简单的线性对应关系。对低纬地区强东北风形成,非地转和非地转平流作用可以同等重要。试验结果还指出,在一般强度的冷涌过程中,东亚低纬对中高纬的反馈作用是不明显的。但对中高纬源相当强的冷涌过程,低纬的反馈作用却很清楚。这种作用的形成与东亚局地Hadley环流上层支的加强有关。 相似文献
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根据SOHO飞船上的LASCO和EIT探测器和GOES卫星的关于太阳活动的观测资料以及ACE和Wind飞船在地球轨道附近关于太阳风等离子体和行星际磁场的观测数据,分析了日冕物质抛射(CME)、行星际磁云和地磁暴的相关性.包括具有地磁效应的晕状CME的日面源区位置分布,日冕物质抛射的中等周期分析,产生地磁暴的行星际参数的阈值等等.作为行星际复杂抛射的一种,首次提出了多重磁云的概念.通过分析观测事例,总结出了多重磁云的一些观测特征,并认为其具有潜在的强大的地磁效应.此外,利用观测资料,研究了激波进入磁云并引起地磁暴的现象.通过建立简单的理论模型,初步分析了激波在穿越磁云的过程中,所能引起的地磁暴的强度的变化. 相似文献
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Yimin Liu Mengmeng Lu Haijun Yang Anmin Duan Bian He Song Yang Guoxiong Wu 《国家科学评论(英文版)》2020,7(3):534
This paper reviews recent advances regarding land–atmosphere–ocean coupling associated with the Tibetan Plateau (TP) and its climatic impacts. Thermal forcing over the TP interacts strongly with that over the Iranian Plateau, forming a coupled heating system that elevates the tropopause, generates a monsoonal meridional circulation over South Asia and creates conditions of large-scale ascent favorable for Asian summer monsoon development. TP heating leads to intensification and westward extension (northward movement) of the South Asian High (Atlantic Intertropical Convergence Zone), and exerts strong impacts on upstream climate variations from North Atlantic to West Asia. It also affects oceanic circulation and buoyancy fields via atmospheric stationary wave trains and air–sea interaction processes, contributing to formation of the Atlantic Meridional Overturning Circulation. The TP thermal state and atmospheric–oceanic conditions are highly interactive and Asian summer monsoon variability is controlled synergistically by internal TP variability and external forcing factors. 相似文献
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青藏高原是世界上总辐射量最高的地区,也是全球超太阳常数的极值区域之一。此处形成了一个"嵌入"对流层中部大气的巨大的热源,可以伸展到自由大气,其超越了世界上任何超级城市群落所产生的中空热岛效应,对全球与区域大气环流系统变化的动力"驱动"产生了难以估计的效应。与地形热力过程季节变化密切相关的亚洲夏季风是世界上范围最广和强度最强的季风;从冬季到早春季节转换过程中,由于太阳辐射的影响造成青藏高原大地形感热的"快速响应"及其相对高值动态移动,在盛夏梅雨及其云降水带前沿线恰好停滞于中国"三阶梯"地形分布山地—平原过渡区。此现象表明,青藏高原可能扮演着夏季风过程陆地—海洋—大气相互作用的关键角色。中国区域低云量与总云量极值区均与青藏高原大江大河的源头(长江、澜沧江、雅鲁藏布江等)、中东部湖泊群与冰川集中区空间分布几乎吻合,这表明"亚洲水塔"形成的关键因素与"世界屋脊"特有的云降水结构不可分割。研究表明,青藏高原大气热源对局地与下游区域云降水过程水汽输送流型等均有显著影响。长江流域降水与全国低云量存在一个明显沿长江流域的带状高相关结构,充分表明长江流域降水与上游"亚洲水塔""热驱动"以及对流系统具有重要相关关系。从跨赤道经向环流的视角可发现,夏季南、北半球跨赤道气流低层强偏南、高层强偏北气流出现在东亚地区和北美区域两大地形对应的赤道区,这2个跨赤道极值区恰与青藏高原、落基山高原位置相对应。青藏高原纬向与经向环流圈结构与区域-全球大气环流相关机制,印证了"世界屋脊"隆起大地形的"热驱动"及其对流活动在全球能量、水分循环的作用。青藏高原特殊水汽三维结构分布和跨半球的纬向和经向大气垂直环流图表明青藏高原对全球尺度大气环流变化的贡献显著。文章进一步以东亚、全球水循环的视角,提出了青藏高原作为全球性大气"水塔"的观念,认为在高原地区一个水塔的"供水"和"蓄水"循环体系,特别是高原地表冰川、积雪和湖泊作为"蓄水池"系统,使得所有的河流可作为"输水管道",将"水塔"的水向周边区域输送出去,高层大气也提供向外输送的渠道。青藏高原特殊的跨半球大气水分循环可构建"世界水塔"与其周边地区独特的水文功能概念,综合描绘了青藏高原"世界水塔"及其地球上一个完整的行星尺度陆地—海洋—大气水分循环物理图像。 相似文献
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We present the conformal coating of non-spherical magnetic particles in a co-laminar flow
microfluidic system. Whereas in the previous reports spherical particles had been coated with thin
films that formed spheres around the particles; in this article, we show the coating of
non-spherical particles with coating layers that are approximately uniform in thickness. The novelty
of our work is that while liquid-liquid interfacial tension tends to minimize the surface area of
interfaces—for example, to form spherical droplets that encapsulate spherical particles—in our
experiments, the thin film that coats non-spherical particles has a non-minimal interfacial area. We
first make bullet-shaped magnetic microparticles using a stop-flow lithography method that was
previously demonstrated. We then suspend the bullet-shaped microparticles in an aqueous solution and
flow the particle suspension with a co-flow of a non-aqueous mixture. A magnetic field gradient from
a permanent magnet pulls the microparticles in the transverse direction to the fluid flow, until the
particles reach the interface between the immiscible fluids. We observe that upon crossing the
oil-water interface, the microparticles become coated by a thin film of the aqueous fluid. When we
increase the two-fluid interfacial tension by reducing surfactant concentration, we observe that the
particles become trapped at the interface, and we use this observation to extract an approximate
magnetic susceptibility of the manufactured non-spherical microparticles. Finally, using
fluorescence imaging, we confirm the uniformity of the thin film coating along the entire curved
surface of the bullet-shaped particles. To the best of our knowledge, this is the first
demonstration of conformal coating of non-spherical particles using microfluidics. 相似文献