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281.
282.
异常事件检测技术是当前智能监控技术研究领域关注的一个热点,作为计算机视觉的重要研究内容,其主要目标是利用计算机自动检测出可被视为异常的事件。传统方法存在低层视频特征描述能力弱,异常检测方法计算代价大,对复杂场景建模时鲁棒性差等方面的限制。本文结合国内外的研究现状和目前的主流方法,介绍了监控视频中异常事件检测涉及的基本技术,分析了各类监控视频特征提取方法、特征学习模型和异常检测方法的优缺点,整理归纳了可用于监控视频中异常事件检测的常用实验数据集,最后讨论了监控视频中异常事件检测技术的难点、挑战及未来发展趋势。 相似文献
283.
284.
J. Büchner 《Space Science Reviews》2006,124(1-4):345-360
Reconnection is a major commonality of solar and magnetospheric physics. It was conjectured by Giovanelli in 1946 to explain
particle acceleration in solar flares near magnetic neutral points. Since than it has been broadly applied in space physics
including magnetospheric physics. In a special way this is due to Harry Petschek, who in 1994 published his ground breaking
solution for a 2D magnetized plasma flow in regions containing singularities of vanishing magnetic field. Petschek’s reconnection
theory was questioned in endless disputes and arguments, but his work stimulated the further investigation of this phenomenon
like no other. However, there are questions left open. We consider two of them – “anomalous” resistivity in collisionless
space plasma and the nature of reconnection in three dimensions. The CLUSTER and SOHO missions address these two aspects of
reconnection in a complementary way -- the resistivity problem in situ in the magnetosphere and the 3D aspect by remote sensing of the Sun. We demonstrate that the search for answers to both questions
leads beyond the applicability of analytical theories and that appropriate numerical approaches are necessary to investigate
the essentially nonlinear and nonlocal processes involved. Necessary are both micro-physical, kinetic Vlasov-equation based
methods of investigation as well as large scale (MHD) simulations to obtain the geometry and topology of the acting fields
and flows. 相似文献
285.
M. Fujimoto W. Baumjohann K. Kabin R. Nakamura J. A. Slavin N. Terada L. Zelenyi 《Space Science Reviews》2007,132(2-4):529-550
The small intrinsic magnetic field of Mercury together with its proximity to the Sun makes the Hermean magnetosphere unique in the context of comparative magnetosphere study. The basic framework of the Hermean magnetosphere is believed to be the same as that of Earth. However, there exist various differences which cause new and exciting effects not present at Earth to appear. These new effects may force a substantial correction of our naïve predictions concerning the magnetosphere of Mercury. Here, we outline the predictions based on our experience at Earth and what effects can drastically change this picture. The basic structure of the magnetosphere is likely to be understood by scaling the Earth’s case but its dynamic aspect is likely modified significantly by the smallness of the Hermean magnetosphere and the substantial presence of heavy ions coming from the planet’s surface. 相似文献
286.
G. Murtaza S. IqbalM.A. Ameen A. Iqbal 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We have used the technique of expansion in Empirical Orthogonal Functions (EOFs) to develop regional models of the critical frequencies of E and F2 layers (foE, foF2), peak height (hmF2), and semi-thickness of F2 layer (YmF2) over Pakistan. In the present study levels of solar activity specified by Smoothed Sunspot Number (R) from 10 to 200 are taken into account. The magnetic dip angle for the model ranges from 30° to 60°. We have compared the regional model and the International Reference Ionosphere (IRI) with measurements of three ionosondes in Pakistan. The model parameters foE and foF2 are found overall comparable to the observed hourly median values during daytime at Karachi (geographic latitude = 24.95°N, longitude = 67.13°E, magnetic inclination = 37°), Multan (30.18°N, 71.48°E, 45°) and Islamabad (33.75°N, 73.13°E, 51.5°) during the years 1988, 1996 and 2000. For hmF2 the computed values by regional and IRI model for the year 1995 are found close to each other. However, for YmF2the results are better during daytime as compared to nighttime. 相似文献
287.
K. Issautier C. Perche S. Hoang C. Lacombe M. Maksimovic J.-L. Bougeret C. Salem 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,35(12):2141-2146
We present the solar wind plasma parameters obtained from the Wind spacecraft during more than nine years, encompassing almost the whole solar cycle 23. Since its launch in November 1994 Wind has frequently observed the in-ecliptic solar wind upstream of the Earth’s bow shock. The WIND/WAVES thermal noise receiver was specially designed to measure the in situ plasma thermal noise spectra, from which the electron density and temperature can be accurately determined. We present and discuss histograms of such measurements performed from 1994 to 2003. Using these large data sets, we study the density and core temperature variations with solar activity cycle and with different regimes of the solar wind. We confirm the anticorrelation of the electron density with the sunspot number, and obtain a positive correlation of the core temperature, with the sunspot number. 相似文献
288.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(1):1137-1145
The relationship of auroral activity indices (AE, Kp, SME) with interplanetary medium parameters during the main phase of magnetic storms is studied. For the period 1990–2020, 142 magnetic storms driven by (41) Sheath, (61) CIR, and (40) ICME events are selected. It is found that the correlation coefficient between average values of the SME index and the SW electric field for Sheath (r = 0.75) is close to correlation coefficients for CIR and ICME events. The correlation coefficient between Kpaver&Eswaver (r = 0.72) is higher than the correlation coefficient between AEaver&Eswaver (r = 0.63) at the main phase of magnetic storms induced by the Sheath events. It is shown that average values of SW dynamic pressure and IMF σB fluctuations correlate each other for all types of SW. 相似文献
289.
Minchul Yoon Jong-il Choi Masamichi Yamashita 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The composting system is the most efficient method for processing organic waste in space; however, the composting activity of microorganisms can be altered by cosmic rays. In this study, the effect of ionizing irradiation on composting bacteria was investigated. Sequence analyses of amplified 16S rRNA, 18S rRNA, and amoA genes were used to identify hyperthermal composting microorganisms. The viability of microorganisms in compost soil after gamma irradiation was directly determined using LIVE/DEAD BacLight viability kit. The dominant bacterial genera were Weissella cibaria and Leuconostoc sp., and the fungal genera were Metschnikowia bicuspidata and Pichia guilliermondii. Gamma irradiation up to a dose of 10 kGy did not significantly alter the microbial population. Furthermore, amylase and cellulase activities were maintained after high-dose gamma irradiation. Our results show that hyperthermal microorganisms can be used to recycle agricultural and fermented material in space stations and other human-inhabiting facilities on the Moon, Mars, and other planets. 相似文献
290.
O.S. Oyekola 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Measurements of the critical frequency, foF2 recorded over Ibadan: 7.4°N, 3.9°E (geographic), 6°S (dip angle) have been compared with the International Reference Ionosphere (IRI-2007) model for solar maximum geomagnetically quiet conditions, with a view to determining what modifications might bring about better predictions for the model. Our results reveal that the present version of IRI essentially reproduces diurnal trends and the general features of the experimental observations for all seasons, except for nighttime June solstice periods, which the model seriously overestimated. The model errors ranging from 50% to 125% over the four seasons considered in this study. It is also indicated that the percentage relative deviations between the observed and the modeled values vary approximately from −11% to 12% (March), −34% to 11% (June), −16% to 12% (September), and −10% to 13% (December). An unexpected feature of foF2 is obvious and remarkable reduction in values during nighttime June solstice periods compared to that in other seasons. Relationship between equatorial vertical drift and foF2 is also investigated. However, cross correlation analysis reveals strong anti-correlation between vertical drift and critical frequency during the daytime hours, but exceptionally opposite is the case for the nighttime sector. The discrepancies which are noted, particularly during June solstice season are attributed to processes most likely within the thermosphere and from meteorological influences during quiet magnetic conditions. 相似文献