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271.
The solar EUV irradiance is of key importance for space weather. Most of the time, however, surrogate quantities such as EUV indices have to be used by lack of continuous and spectrally resolved measurements of the irradiance. The ability of such proxies to reproduce the irradiance from different solar atmospheric layers is usually investigated by comparing patterns of temporal correlations. We consider instead a statistical approach. The TIMED/SEE experiment, which has been continuously operating since February 2002, allows for the first time to compare in a statistical manner the EUV spectral irradiance to five EUV proxies: the sunspot number, the f10.7, Ca K, and Mg II indices, and the He I equivalent width.  相似文献   
272.
In this paper we present a new mechanism of the main energy conversion of the solar flare. Since a flare inducing prominence (flux tube) rises Vz ? 300 km s−1, the plasmas below it cannot continuously eject with Alfvén speeds of VA = 3000 km s−1 but probably with Vz ≈ ±100 km s−1. Plasma up and downflows with VA will within a short duration be blocked between the chromosphere where reconnected flux tubes are piling up, and the slowly rising flux rope. Hence the Petschek slow shock mechanism is difficult to be realized as a major energy converting mechanism.  相似文献   
273.
Substorm evolution of the near-Earth (|X|<15 RE) plasma sheet has been emphasized recently because the inner tail is thought to link closely to the substorm auroral activity in the ionosphere during the early stage of substorms. In this paper, we discuss how the inner tail substorm phenomena during the late substorm growth phase and early expansion phase are accounted for by the two prevailing substorm models, namely, the near-Earth neutral line model and the current disruption model. We find that the late growth phase features are more satisfactorily accounted for by the current disruption model than by the near-Earth neutral line model. In addition, detailed observations on current disruption show evidence inconsistent with the proposed idea of dipolarization being due to plasma flow braking from reconnection in the mid-tail region, which poses a difficulty to the near-Earth neutral line model as well.  相似文献   
274.
The Juno Waves Investigation   总被引:1,自引:0,他引:1  
Jupiter is the source of the strongest planetary radio emissions in the solar system. Variations in these emissions are symptomatic of the dynamics of Jupiter’s magnetosphere and some have been directly associated with Jupiter’s auroras. The strongest radio emissions are associated with Io’s interaction with Jupiter’s magnetic field. In addition, plasma waves are thought to play important roles in the acceleration of energetic particles in the magnetosphere, some of which impact Jupiter’s upper atmosphere generating the auroras. Since the exploration of Jupiter’s polar magnetosphere is a major objective of the Juno mission, it is appropriate that a radio and plasma wave investigation is included in Juno’s payload. This paper describes the Waves instrument and the science it is to pursue as part of the Juno mission.  相似文献   
275.
    
We have studied the induction of morphological transformation of Syrian hamster embryo cells by low doses of heavy ions with different linear energy transfer (LET), ranging from 13 to 400 keV/μm. Exponentially growing cells were irradiated with 12C or 28Si ion beams generated by the Heavy Ion Medical Accelerator in Chiba (HIMAC), inoculated to culture dishes, and transformed colonies were identified when the cells were densely stacked and showed a crisscross pattern. Over the LET range examined, the frequency of transformation induced by the heavy ions increased sharply at very low doses no greater than 5 cGy. The relative biological effectiveness (RBE) of the heavy ions relative to 250 kVp X-rays showed an initial increase with LET, reaching a maximum value of about 7 at 100 keV/μm, and then decreased with the further increase in LET. Thus, we confirmed that high LET heavy ions are significantly more effective than X-rays for the induction of in vitro cell transformation.  相似文献   
276.
Activity of auxin polar transport in inflorescence axes of Arabidopsis thaliana grown under simulated microgravity conditions was studied in relation to the growth and development. Seeds were germinated and allowed to grow on an agar medium in test tubes on a horizontal clinostat. Horizontal clinostat rotation substantially reduced the growth of inflorescence axes and the productivity of seeds of Arabidopsis thaliana (ecotypes Landsberg erecta and Columbia), although it little affected seed germination, development of rosette leaves and flowering. The activity of auxin polar transport in inflorescence axes decreased when Arabidopsis plants were grown on a horizontal clinostat from germination stage, being ca. 60% of 1 g control. On the other hand, the auxin polar transport in inflorescence axes of Arabidopsis grown in 1 g conditions was not affected when the segments were exposed to various gravistimuli, including 3-dimensional clinorotation, during transport experiments. Pin-formed mutant of Arabidopsis, having a unique structure of the inflorescence axis with no flower and extremely low levels of the activity of auxin polar transport in inflorescence axes and endogenous auxin, did not continue its vegetative growth under clinostat rotation. These facts suggest that the development of the system of auxin polar transport in Arabidopsis is affected by microgravity, resulting in the inhibition of growth and development, especially during reproductive growth.  相似文献   
277.
    
High energy, high-Z (HZE) particles are present in high-altitude and high-inclination satellite orbits. Most of the HZE dose above LET = 200 keV/micrometer is due to Fe nuclei. Individual HZE particles can damage several cells adjacent to one another along the particle track in tissue. The outcome has been described as a \"microlesion\" by D. Grahn. The present study attempts to define conditions for microlesions in specific tissues, to seek biological evidence that microlesions are produced, and to evaluate the microlesion as a potentially useful unit of dose in assessing hazards to spaceworkers. Microlesions in individuals cells and hair follicles have been described. Microbial studies have provided some evidence for independent secondary electron action. Whether or not a few hundred microlesions would be damaging to the whole organism depends upon the nature of damage to critical tissues. For example, cancer may occur if microlesions kill several cells in a straight line and mutate other cells alongside the particle track. Fe particle irradiation of the mouse Harderian gland (Fry et al., this issue) produces tumors efficiently. Microlesions in the lens, cornea, and retina need to be considered. Further dialogue is required before a final decision can be made concerning the most appropriate way to assess the HZE hazard.  相似文献   
278.
The lobes of the NASA ULDB pumpkin-shaped super-pressure balloons are made of a thin polymeric film that shows considerable time-dependent behaviour. A nonlinear viscoelastic model based on experimental measurements has been recently established for this film. This paper presents a simulation of the viscoelastic behaviour of ULDB balloons with the finite element software ABAQUS. First, the standard viscoelastic modelling capabilities available in ABAQUS are examined, but are found of limited accuracy even for the case of simple uniaxial creep tests on ULDB films. Then, a nonlinear viscoelastic constitutive model is implemented by means of a user-defined subroutine. This approach is verified by means of biaxial creep experiments on pressurized cylinders and is found to be accurate provided that the film anisotropy is also included in the model. A preliminary set of predictions for a single lobe of a ULDB is presented at the end of the paper. It indicates that time-dependent effects in a balloon structure can lead to significant stress redistribution and large increases in the transverse strains in the lobes.  相似文献   
279.
The X-ray spectrometer (XRS) on the SELENE (SELenological and ENgineering Explorer) spacecraft, XRS, will observe fluorescent X-rays from the lunar surface. The energy of the fluorescent X-ray depends on the elements of which the lunar soil consists, therefore we can determine elemental composition of the upper most lunar surface. The XRS consists of three components: XRF-A, SOL-B, and SOL-C. XRF-A is the main sensor to observe X-rays from the lunar surface. SOL-B is direct monitor of Solar X-ray using Si-PIN photodiode. SOL-C is another Solar X-ray monitor but observes the X-rays from the standard sample attached on the base plate. This enables us to analyze by a comparative method similar to typical laboratory XRF methods. XRF-A and SOL-C adopt charge coupled device as an X-ray detector which depletion layer is deep enough to detect X-rays. The X-ray spectra were obtained by the flight model of XRS components, and all components has been worked well to analyze fluorescent X-rays. Currently, development of the hardware and software of the XRS has been finished and we are preparing for system integration test for the launch.  相似文献   
280.
Cometary dust trails were first observed by IRAS; they are widely known to be the origins of meteoric showers. A new window has been opened for the study of dust trails, using ground-based observations. We succeeded in obtaining direct images of the 22P/Kopff dust trail with the Kiso 1.05-m Schmidt telescope. Following this initial success, we have continued to perform a dust trail survey at Kiso. As a result of this survey, we have detected dust trails along the orbit of six periodic comets, between February 2002 and March 2004. The optical depth of these dust trails are 10−9 to 10−8, which is consistent with IRAS measurements. In this paper, we describe the observations and data reduction procedures, and report the brief result obtained between February 2002 and March 2004.  相似文献   
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