Yield and cyclic behaviour of a strain space multiple mechanism model for granular materials     

Susumu Iai  Osamu Ozutsumi 《国际地质力学数值与分析法杂志》2005,29(4):417-442

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In situ imaging of μm and sub-μm-sized grains in a cometary environment by atomic force microscopy     

J. Romstedt  A. Jäckel  W. KlöckK. Nakamura  H. ArendsK. Torkar  W. Riedler 《Planetary and Space Science》2002,50(3):347-352

The micro-imaging dust analysis system (MIDAS) is an essential element among the scientific payload on the international Rosetta mission to comet 46P/Wirtanen. The MIDAS instrument based on an atomic force microscope (AFM) collects small particles drifting outwards from the nucleus surface. AFM is able to image small structures in 3D at nanometer-scale resolution. These images provide morphological and statistical information like grain size distribution on the dust population. In order to support the development of the flight hardware, optimisation of the control functions and consolidation of a proper scheme of data interpretation, laboratory studies with similar instruments were carried out. The obtained data demonstrate the capabilities of this technique. For the first time an instrument is able to observe the smallest (nm-sized) grains which are predicted by models and were to a certain extent deduced from previous measurements on the Giotto and Vega missions to comet 1P/Halley. On larger (μm-sized) particles the complex morphology will be visualised with high precision in 3D, and if present, within these aggregates crystalline materials with defined crystal faces can be identified.  相似文献   

Comparative Study of LiNbO3 and Servo Controlled Air Gap Fabry-Perot Etalons for Solar Application     

Choudhary Debi Prasad  Sanjay Gosain 《Experimental Astronomy》2002,13(3):153-158

In this note, we compare the LiNbO₃ and Piezo-Electrically(PE) servo controlled air gap Fabry-Perot etalons for observing the Sun. An identical test setup was used to evaluate the instrumental parameters of the two etalons. It is found that for the etalons with similar finesse the advantage of using PE Etalons is tunability over entire Free Spectral Range. On the other hand, the LiNbO₃ etalons have advantage of wider acceptance angle. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Quick triggering of magnetic reconnection in magnetotail     

Iku Shinohara  Kenny G. Tanaka  Masaki Fujimoto 《Earth, Moon, and Planets》2007,100(3-4):225-232

Recently, quick triggering of magnetic reconnection (QMRT) even in an ion-scale current sheet is found to be possible with the help of the nonlinear evolution of the lower hybrid drift instability (LHDI). The details of the QMRT mechanism are reviewed mostly based on three-dimensional full-particle simulation results of our group. QMRT is mediated by LHDI and its time scale is comparable to the saturation time scale of LHDI. Depending on the initial current sheet thickness, two types of QMRT, so-called Type-I and Type-II QMRT, are demonstrated.  相似文献   

Predictions on the application of the Hanle effect to map the surface magnetic field of Jupiter     

L. Ben-Jaffel  W. Harris  F. Roesler  J. Jossang 《Icarus》2005,178(2):297-311

In this paper we evaluate the possibility of detecting, for the first time, the surface magnetic field of Jupiter (∼1 bar level) by observing the change of linear polarization induced by the Hanle effect on the H Lyman-alpha (Lyα) emission line of the planet. We find that, indeed, the Hanle effect, which results from the interaction between a local magnetic field and the atomic polarization induced by absorption of anisotropic radiation, is sensitive to relatively weak values of the strength of the magnetic fields expected on planets. First, we show that for the Lyα emission backscattered by atomic H in the presence of a magnetic field, the Hanle effect is polarizing. This new result is in total contrast to the depolarizing effect predicted and observed for emission lines scattered at right angles in solar prominences. Additionally, to estimate the polarization rate for the case of Jupiter, we have considered three magnetic field models: a dipole field for reference, an O₄ based model [Connerney, J.E.P., 1981. The magnetic field of Jupiter—A generalized inverse approach. J. Geophys. Res. 86, 7679-7693], and finally, an O₆ based model [Khurana, K.K., 1997. Euler potential models of Jupiter's magnetospheric field. J. Geophys. Res. 102, 11295-11306]. In all models, we show that for the jovian backscattered Lyα line, the Hanle effect does enhance the Lyα linear polarization; the polarization rate may exceed 2% at specific regions of the jovian disc, making detection possible either remotely or from an orbiter around Jupiter. In general, depending on the instrumental sensitivity and the observing strategy used, we show that accurate mapping of the linear polarization rate at the planetary surface (thermosphere) or off-disc (corona) may provide a rather accurate estimate of the jovian total magnetic field strength on large area scales.  相似文献   

Device for measuring surface accumulation of dust: applications for future magnetic properties experiments on Mars     

H.P. Gunnlaugsson  K.M. Kinch  J.P. Merrison  H. Wahlgreen 《Planetary and Space Science》2004,52(8):693-698

A new optical instrument has been developed to precisely measure the local accumulation of dust particles on a surface. This device can be used in combination with applied magnetic or electric fields in order to investigate physical properties of the dust and its interactions with the surface. In this prototype instrument, permanent magnets were used to capture suspended magnetic dust in a Mars simulation wind tunnel. The scientific objectives that may be addressed with such a device are discussed.  相似文献   

Mapping of the cusp plasma precipitation on the surface of Mercury     

S Massetti  S Orsini  A Mura  H Lammer 《Icarus》2003,166(2):229-237

The presence of a magnetosphere around Mercury plays a fundamental role on the way the solar wind plasma interacts with the planet. Since the observations suggest that Mercury should occupy a large fraction of its magnetosphere and because of lack of an atmosphere, significant differences in solar wind-magnetosphere coupling are expected to exist with respect to the Earth case. On the basis of a modified Tsyganenko T96 model we describe the geometry of the magnetic field that could characterize Mercury, and its response to the variations of the impinging solar wind and of the interplanetary magnetic field. The investigation is focused on the shape and dimension of the open magnetic field regions (cusps) that allow the direct penetration of magnetosheath plasma through the exosphere of Mercury, down to its surface. The precipitating particle flux and energy are evaluated as a function of the open field line position, according to different solar wind conditions. A target of this study is the evaluation of the sputtered particles from the crust of the planet, and their contribution to the exospheric neutral particle populations. Such estimates are valuable in the frame of a neutral particle analyser to be proposed on board of the ESA/BepiColombo mission.  相似文献   

Net circular polarization in magnetic spectral lines produced by velocity gradients: Some analytical results     

M. Landolfi  E. Landi Degl'innocenti 《Solar physics》1996,164(1-2):191-202

The net circular polarization in a spectral line due to the combined effect of magnetic fields and velocity gradients is analyzed for a few schematic situations. In some particular cases, its dependence on the magnetic field, velocity field and line parameters can be expressed analytically.On leave from Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italia  相似文献   

Mechanisms of coronal heating     

S. R. Verma 《Journal of Astrophysics and Astronomy》2006,27(2-3):113-114

The Sun is a mysterious star. The high temperature of the chromosphere and corona present one of the most puzzling problems of solar physics. Observations show that the solar coronal heating problem is highly complex with many different facts. It is likely that different heating mechanisms are at work in solar corona. Recent observations show that Magnetic Carpet is a potential candidate for solar coronal heating.  相似文献   

基于STM32的地震观测台站通用智能电源控制器的研制     

李兴泉  邵玉平  刘江 《中国地震》2022,38(1):166-175

电源是一切电子设备的心脏,是保障电子设备正常运行的关键,但目前针对地震观测台站使用电源的相关研究较少,本文在分析目前台站电源存在问题的基础上,开发设计了适用于台站的通用智能电源控制器,该控制器以STM32F107微处理器为核心,设计了相应的信号采集、电压控制及驱动电路,整机功耗约0.6W、工作电压范围DC7～23V,其通过外接方式即可对台站原有供电系统进行功能扩展和优化,满足低功耗、易操作、高可靠等设计要求,具有较好的推广价值。  相似文献