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311.
Alexander F. Zakharov Gabriele Ingrosso Francesco De Paolis Achille A. Nucita Francesco Strafella Sebastiano Calchi Novati Philippe Jetzer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
There are different methods for finding exoplanets such as radial spectral shifts, astrometrical measurements, transits, timing etc. Gravitational microlensing (including pixel-lensing) is among the most promising techniques with the potentiality of detecting Earth-like planets at distances about a few astronomical units from their host star or near the so-called snow line with a temperature in the range 0–100 °C on a solid surface of an exoplanet. We emphasize the importance of polarization measurements which can help to resolve degeneracies in theoretical models. In particular, the polarization angle could give additional information about the relative position of the lens with respect to the source. 相似文献
312.
Raggio J Pintado A Ascaso C De La Torre R De Los Ríos A Wierzchos J Horneck G Sancho LG 《Astrobiology》2011,11(4):281-292
The Lithopanspermia space experiment was launched in 2007 with the European Biopan facility for a 10-day spaceflight on board a Russian Foton retrievable satellite. Lithopanspermia included for the first time the vagrant lichen species Aspicilia fruticulosa from Guadalajara steppic highlands (Central Spain), as well as other lichen species. During spaceflight, the samples were exposed to selected space conditions, that is, the space vacuum, cosmic radiation, and different spectral ranges of solar radiation (λ?≥?110, ≥200, ≥290, or ≥400?nm, respectively). After retrieval, the algal and fungal metabolic integrity of the samples were evaluated in terms of chlorophyll a fluorescence, ultrastructure, and CO(2) exchange rates. Whereas the space vacuum and cosmic radiation did not impair the metabolic activity of the lichens, solar electromagnetic radiation, especially in the wavelength range between 100 and 200?nm, caused reduced chlorophyll a yield fluorescence; however, there was a complete recovery after 72?h of reactivation. All samples showed positive rates of net photosynthesis and dark respiration in the gas exchange experiment. Although the ultrastructure of all flight samples showed some probable stress-induced changes (such as the presence of electron-dense bodies in cytoplasmic vacuoles and between the chloroplast thylakoids in photobiont cells as well as in cytoplasmic vacuoles of the mycobiont cells), we concluded that A. fruticulosa was capable of repairing all space-induced damage. Due to size limitations within the Lithopanspermia hardware, the possibility for replication on the sun-exposed samples was limited, and these first results on the resistance of the lichen symbiosis A. fruticulosa to space conditions and, in particular, on the spectral effectiveness of solar extraterrestrial radiation must be considered preliminary. Further testing in space and under space-simulated conditions will be required. Results of this study indicate that the quest to discern the limits of lichen symbiosis resistance to extreme environmental conditions remains open. 相似文献
313.
M. C. De Sanctis A. Coradini E. Ammannito G. Filacchione M. T. Capria S. Fonte G. Magni A. Barbis A. Bini M. Dami I. Ficai-Veltroni G. Preti VIR Team 《Space Science Reviews》2011,163(1-4):329-369
The Dawn spectrometer (VIR) is a hyperspectral spectrometer with imaging capability. The design fully accomplishes Dawn’s scientific and measurement objectives. Determination of the mineral composition of surface materials in their geologic context is a primary Dawn objective. The nature of the solid compounds of the asteroid (silicates, oxides, salts, organics and ices) can be identified by visual and infrared spectroscopy using high spatial resolution imaging to map the heterogeneity of asteroid surfaces and high spectral resolution spectroscopy to determine the composition unambiguously. The VIR Spectrometer—covering the range from the near UV (0.25 μm) to the near IR (5.0 μm) and having moderate to high spectral resolution and imaging capabilities—is the appropriate instrument for the determination of the asteroid global and local properties. VIR combines two data channels in one compact instrument. The visible channel covers 0.25–1.05 μm and the infrared channel covers 1–5.0 μm. VIR is inherited from the VIRTIS mapping spectrometer (Coradini et al. in Planet. Space Sci. 46:1291–1304, 1998; Reininger et al. in Proc. SPIE 2819:66–77, 1996) on board the ESA Rosetta mission. It will be operated for more than 2 years and spend more than 10 years in space. 相似文献
314.
Psychomotor performance during a 28 day head-down tilt with and without lower body negative pressure 总被引:4,自引:0,他引:4
Pavy Le-Traon A Rous De Feneyrols A Cornac A Abdeseelam R N'uygen D Lazerges M Guell A Bes A 《Acta Astronautica》1994,32(4):319-330
Several factors may affect psychomotor performance in space: sensory-motor changes, sleep disturbances, psychological modifications induced by the social isolation and confinement. However, psychomotor performance is difficult to assess. A battery of standardized and computerized tests, so-called "Automated Portable Test System" (APTS) was devised to ascertain the cognitive, perceptive and motor abilities and their possible fluctuations according to environmental effects. Antiorthostatic bedrest, often used to simulate weightlessness, (particularly cardiovascular modifications) also constitutes a situation of social confinement and isolation. During two bedrest experiments (with head-down tilt of -6 degrees) of 28 days each, we intended to assess psychomotor performance of 6 males so as to determine whether: on the one hand, it could be altered by remaining in decubitus; on the other, the Lower Body Negative Pressure sessions, designed to prevent orthostatic intolerance back on Earth, could improve the performance. To accomplish this, part of the APTS tests as well as an automated perceptive attention test were performed. No downgrading of psychomotor performance was observed. On the contrary, the tasks were more accurately performed over time. In order to assess the experimental conditions on the acquisition phase, the learning curves were modelled. A beneficial effect of the LBNP sessions on simple tests involving the visual-motor coordination and attention faculties can only be regarded as a mere trend. Methods used in this experiment are also discussed. 相似文献
315.
To resolve problems of complicated clutter, fast-varying scenes, and low signal-clutterratio (SCR) in application of target detection on sea for space-based radar (SBR), a target detection approach based on adaptive waveform design is proposed in this paper. Firstly, complicated sea clutter is modeled as compound Gaussian process, and a target is modeled as some scatterers with Gaussian reflectivity. Secondly, every dwell duration of radar is divided into several sub-dwells. Regular linear frequency modulated pulses are transmitted at Sub-dwell 1, and the received signal at this sub-dwell is used to estimate clutter covariance matrices and pre-detection. Estimated matrices are updated at every following sub-dwell by multiple particle filtering to cope with fast-varying clutter scenes of SBR. Furthermore, waveform of every following sub-dwell is designed adaptively according to mean square optimization technique. Finally, principal component analysis and generalized likelihood ratio test is used for mitigation of colored interference and property of constant false alarm rate, respectively. Simulation results show that, considering configuration of SBR and condition of complicated clutter, 9 dB is reduced for SCR which reliable detection requires by this target detection approach. Therefore, the work in this paper can markedly improve radar detection performance for weak targets. 相似文献
316.
叙述了量具研磨机的结构工作原理(不含千分尺部分)以及各种参数变化对研磨的影响。对存在的问题进行了系统归类和对比分析,提出了改进方法,如单独配研磨器减少研磨行程,利用钳口铜块画刻线确定卡尺位置,找正主尺与直角尺两侧面重合而确保外量爪与滑块平行。 相似文献
317.
De Fina S. Ruggieri M. Bosisio A.V. 《IEEE transactions on aerospace and electronic systems》2003,39(1):82-93
The scientific mission DAVID (Data and Video Interactive Distribution) of the Italian Space Agency (ASI) will pioneer the use of the W-band for a challenging telecommunications experiment. The unavailability of channel measurements and the technological limitations in that frequency range imply a system assessment based on channel extrapolation and a wise error control strategy. In that frame, a system approach is proposed that will allow the exploitation of the W-band for high capacity satellite communications. The results obtained through that approach in the assessment of the DAVID W-band experiment are provided and their perspectives identified and discussed. 相似文献
318.
卫星用累积检漏技术是目前世界各国宇航工程检漏工作者较多采用的一种检漏方法,但在使用该方法时必须配备定量比对校验方法。介绍了各国常用的三种定量比对校验方法:标准漏孔比对法、定量气体浓度比对法和定量气体量比对法。对这三种校验方法进行了比较和分析,并从优点、缺点和技术含量三个方面进行了综合评估,认为累积检漏法中的氦质谱检漏仪选用定量气体浓度比对法较合理些。这种方法具有检漏时间短、检测误差小等特点。 相似文献
319.
Ruggieri M. De Fina S. Pratesi M. Saggese E. Bonifazi C. 《IEEE transactions on aerospace and electronic systems》2002,38(4):1377-1387
The data collection experiment (DCE) of the scientific mission DAVID (DAta and Video Interactive Distribution) of the Italian Space Agency (ASI) will pioneer the use of the W-band for telecommunications experiments. In particular the collection of high volumes of data from remote or virtually remote sites will be achieved through the exploitation of a W-band link in a time window of a few minutes per satellite pass. The experiment will hence demonstrate the capability of the W-band channel to be used reliably for a telecommunication link. At the same time, the experiment will provide useful elements for the characterisation of the W-band channel, in order to be able to design properly future operational systems working at W-band. 相似文献
320.