排序方式： 共有31条查询结果，搜索用时 31 毫秒
1.
A. Mura S. Orsini E. Kallio S. Barabash A. Grigoriev H. Andersson M. Yamauchi N. Krupp K. Asamura C.C. Curtis B.R. Sandel M. Grande J.U. Kozyra S. McKenna-Lawlor R. D’Amicis S. Massetti P.C. Brandt R.A. Frahm 《Planetary and Space Science》2008,56(6):840-845
The Analyzer of Space Plasma and EneRgetic Atoms (ASPERA-3) on board Mars Express is designed to study the interaction between the solar wind and the atmosphere of Mars and to characterize the plasma and neutral gas environment in near-Mars space. Neutral Particle Detectors (NPD-1 and 2), which form part of the ASPERA-3 instrument suite, are Energetic Neutral Atom (ENA) detectors which use the time-of-flight (ToF) technique to resolve the energy of detected particles. In the present study, we perform a statistical analysis of NPD ToF data collected between 14 March 2004 and 17 June 2004 when Mars Express was located at the dayside of Mars looking toward the planet. After pre-processing and removal of UV contamination, the ToF spectra were fitted with simple analytical functions so as to derive a set of parameters. The behavior of these parameters, as a function of spacecraft position and attitude, is compared with a model, which describes ENA generation by charge exchange between shocked solar wind protons and extended Martian exosphere. The observations and the model agree well, indicating that the recorded signals are charge-exchanged shocked solar wind. 相似文献
2.
E. Kallio T.L. Zhang R. Jarvinen P. Janhunen J.-A. Sauvaud J.-J. Thocaven H. Andersson K. Brinkfeldt M. Holmström M. Yamauchi W. Baumjohann A.J. Coates D.O. Kataria K.C. Hsieh M. Grande T. Säles P. Riihelä N. Krupp J.G. Luhmann S. Orsini A. Mura M. Maggi P. Brandt K. Szego R.A. Frahm J.R. Sharber P. Bochsler 《Planetary and Space Science》2008,56(6):796-801
Plasma and magnetic field measurements made onboard the Venus Express on June 1, 2006, are analyzed and compared with predictions of a global model. It is shown that in the orbit studied, the plasma and magnetic field observations obtained near the North Pole under solar minimum conditions were qualitatively and, in many cases also, quantitatively in agreement with the general picture obtained using a global numerical quasi-neutral hybrid model of the solar wind interaction (HYB-Venus). In instances where the orbit of Venus Express crossed a boundary referred to as the magnetic pileup boundary (MPB), field line tracing supports the suggestion that the MPB separates the region that is magnetically connected to the fluctuating magnetosheath field from a region that is magnetically connected to the induced magnetotail lobes. 相似文献
3.
The possible avenues for photoelectron transport were determined during southern hemisphere winter at Mars by using a mapping analysis of the theoretical magnetic field. Magnetic field line tracing was performed by superposing two magnetic field models: (1) magnetic field derived from a three-dimensional (3D) self-consistent quasi-neutral hybrid model which does not contain the Martian crustal magnetic anomalies and (2) a 3D map of the magnetic field associated with the magnetic anomalies based on Mars Global Surveyor magnetic field measurements. It was found that magnetic field lines connected to the nightside of the planet are mainly channeled within the optical shadow of the magnetotail whereas magnetic field lines connected to the dayside of the planet are observed to form the remainder of the magnetosphere. The simulation suggests that the crustal anomalies create “a magnetic shield” by decreasing the region near Mars which is magnetically connected to the Martian magnetosphere. The rotation of Mars causes periodic changes in magnetic connectivity, but not to qualitative changes in the overall magnetic field draping around Mars. 相似文献
4.
Jan-Michael Frahm Marc Pollefeys Svetlana Lazebnik David Gallup Brian Clipp Rahul Raguram Changchang Wu Christopher Zach Tim Johnson 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(6):538-549
This paper presents a system approaching fully automatic 3D modeling of large-scale environments. Our system takes as input either a video stream or collection of photographs obtained from Internet photo sharing web-sites such as Flickr. The system achieves high computational performance through algorithmic optimizations for efficient robust estimation, the use of image-based recognition for efficient grouping of similar images, and two-stage stereo estimation for video streams that reduces the computational cost while maintaining competitive modeling results. In addition to algorithmic advances, we achieve a major improvement in computational speed through parallelization and execution on commodity graphics hardware. These improvements lead to real-time video processing and to reconstruction from tens of thousands of images within the span of a day on a single commodity computer. We demonstrate modeling results on a variety of real-world video sequences and photo collections. 相似文献
5.
Ellery Frahm 《Geoarchaeology》2012,27(2):166-174
As new analytical techniques are brought to sourcing studies and researchers compile data into multi‐laboratory databases, systematic evaluation is essential. The importance of precision and accuracy is clear, but Shackley (2005) also calls for “archaeological accuracy.” Hughes (1998) offered a framework to consider precision and accuracy alongside the concepts of reliability and validity. These four concepts can serve as a foundation to evaluate archaeological sourcing data and procedures, but adoption of Hughes’ framework has been nearly nonexistent. Unfortunately, Hughes’ formulations of reliability and validity are somewhat at odds with their conventional definitions, hindering his framework. Furthermore, the concept of precision has become outdated in analytical circles, and superfluous terms (e.g., replicability) have emerged in the archaeological literature. Here I consider the basis of Hughes’ framework and how its four components, when applied consistently by the sourcing community, are best applied to evaluate analytical data and techniques for sourcing. 相似文献
6.
Y. Soobiah A.J. Coates D.O. Kataria R.A. Frahm J.R. Scherrer R. Lundin H. Andersson A. Grigoriev H. Koskinen T. Säles W. Schmidt J. Luhmann D. Williams C.C. Curtis B.R. Sandel M. Carter A. Fedorov S. McKenna-Lawler R. Cerulli-Irelli P. Wurz N. Krupp M. Fränz C. Dierker 《Icarus》2006,182(2):396-405
Mars Express (MEX) Analyser of Space Plasmas and Energetic Atoms (ASPERA-3) data is providing insights into atmospheric loss on Mars via the solar wind interaction. This process is influenced by both the interplanetary magnetic field (IMF) in the solar wind and by the magnetic ‘anomaly’ regions of the martian crust. We analyse observations from the ASPERA-3 Electron Spectrometer near to such crustal anomalies. We find that the electrons near remanent magnetic fields either increase in flux to form intensified signatures or significantly reduce in flux to form plasma voids. We suggest that cusps intervening neighbouring magnetic anomalies may provide a location for enhanced escape of planetary plasma. Initial statistical analysis shows that intensified signatures are mainly a dayside phenomenon whereas voids are a feature of the night hemisphere. 相似文献
7.
A. Fedorov E. Budnik C. Mazelle R. Lundin M. Holmström M. Yamauchi J.-J. Thocaven R. Frahm J. Scherrer D.R. Linder E. Kallio T. Säles W. Schmidt J. Luhmann D. Williams C.C. Curtis B.R. Sandel M. Carter S. Orsini M. Maggi P. Bochsler J. Woch K. Asamura 《Icarus》2006,182(2):329-336
We present the first results from the ion mass analyzer IMA of the ASPERA-3 instrument on-board of Mars Express. More than 200 orbits for May 2004-September 2004 time interval have been selected for the statistical study of the distribution of the atmospheric origin ions in the planetary wake. This study shows that the martian magnetotail consists of two different ion regimes. Planetary origin ions of the first regime form the layer adjacent to the magnetic pile-up boundary. These ions are accelerated to energy greater than 2000 eV and exhibit a gradual decreasing of energy down to the planetary tail. The second plasma regime is observed in the planetary shadow. The heavy ions (considered as planetary ones) are accelerated to the energy of the solar wind protons. Obviously the acceleration mechanism is different for the different plasma regimes. Study of two plasma regimes in the frame referred to the interplanetary magnetic field (IMF) direction (we used MGS magnetometer data to obtain the IMF clock angle) clearly shows their spatial anisotropy. The monoenergetic plasma in the planetary shadow is observed only in the narrow angular sector around the positive direction of the interplanetary electric field. 相似文献
8.
E. Dubinin D. Winningham J. Woch S. Barabash R. Frahm A.J. Coates J.-A. Sauvaud H. Andersson A. Grigoriev K. Asamura K.S. Hsieh H. Koskinen P. Riihelä T. Säles J. Luhmann R. Cerulli-Irelli M. Maggi D. Williams P. Wurz C. Dierker M. Carter 《Icarus》2006,182(2):343-349
The ASPERA-3 experiment onboard the Mars Express spacecraft revealed, near the wake boundary of Mars, a spatially narrow, strip-like plasma structure composed of magnetosheath-like electrons and planetary ions. The peak electron energy often exceeds the peak energy at the bow shock that indicates a significant heating (acceleration) during the structure formation. It is shown that this structure is formed during efficient plasma penetration into the martian magnetosphere in the region near the terminator. The penetration of sheath electrons and their gradual heating (acceleration) is accompanied by a change of the ion composition from a solar wind plasma to a planetary plasma dominated by oxygen ions. A possible mechanism of plasma inflow to the magnetosphere is discussed. 相似文献
9.
K. Brinkfeldt H. Gunell P. C:son Brandt R.A. Frahm E. Kallio Y. Futaana R. Lundin M. Yamauchi J.R. Sharber A.J. Coates D.O. Kataria T. Säles W. Schmidt J. Luhmann D. Williams C.C. Curtis B.R. Sandel M. Carter A. Fedorov S. McKenna-Lawler R. Cerulli-Irelli P. Wurz N. Krupp M. Fränz C. Dierker 《Icarus》2006,182(2):439-447
We present measurements with an Energetic Neutral Atom (ENA) imager on board Mars Express when the spacecraft moves into Mars eclipse. Solar wind ions charge exchange with the extended Mars exosphere to produce ENAs that can spread into the eclipse of Mars due to the ions' thermal spread. Our measurements show a lingering signal from the Sun direction for several minutes as the spacecraft moves into the eclipse. However, our ENA imager is also sensitive to UV photons and we compare the measurements to ENA simulations and a simplified model of UV scattering in the exosphere. Simulations and further comparisons with an electron spectrometer sensitive to photoelectrons generated when UV photons interact with the spacecraft suggest that what we are seeing in Mars' eclipse are ENAs from upstream of the bow shock produced in charge exchange with solar wind ions with a non-zero temperature. The measurements are a precursor to a new technique called ENA sounding to measure solar wind and planetary exosphere properties in the future. 相似文献
10.
H. Gunell K. Brinkfeldt P. C:son Brandt E. Kallio Y. Futaana H. Andersson A. Grigoriev R.A. Frahm J.R. Scherrer D.R. Linder T. Säles W. Schmidt J. Kozyra E. Roelof S. Livi K.C. Hsieh M. Grande J.-A. Sauvaud J.-J. Thocaven S. Orsini M. Maggi P. Bochsler J. Woch K. Asamura 《Icarus》2006,182(2):431-438
Measurements of energetic neutral atoms (ENA) generated in the magnetosheath at Mars are reported. These ENAs are the result of charge exchange collisions between solar wind protons and neutral oxygen and hydrogen in the exosphere of Mars. The peak of the observed ENA flux is . For the case studied here, i.e., the passage of Mars Express through the martian magnetosheath around 20:15 UT on 3 May 2004, the measurements agree with an analytical model of the ENA production at the planet. It is possible to find parameter values in the model such that the observed peak in the ENA count rate during the spacecraft passage through the magnetosheath is reproduced. 相似文献