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When some magnetic field lines connect a Kerr black hole with a disk rotating around it, energy and angular momentum are transferred between them. If the black hole rotates faster than the disk, ca&solm0;GMH>0.36 for a thin Keplerian disk, then energy and angular momentum are extracted from the black hole and transferred to the disk (MH is the mass and aMH is the angular momentum of the black hole). This way, the energy originating in the black hole may be radiated away by the disk. The total amount of energy that can be extracted from the black hole spun down from ca&solm0;GMH=0.998 to ca&solm0;GMH=0.36 by a thin Keplerian disk is approximately 0.15MHc2. This is larger than approximately 0.09MHc2, which can be extracted by the Blandford-Znajek mechanism.  相似文献   
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A multidisciplinary approach involving various remote sensing instruments is used to investigate Apollinaris Mons, a prominent volcano on Mars, as well as the surrounding plains for signs of prolonged hydrologic and volcanic, and possibly hydrothermal activity. The main findings include (1) evidence from laser altimetry indicating the large thickness (1.5–2 km at some locations) of the fan deposits draping the southern flank contrary to previous estimates, coupled with possible layering which point to a significant emplacement phase at Apollinaris Mons, (2) corroboration of Robinson et al. (Robinson, M.S., Mouginis-Mark, P.J., Zimbelman, J.R., Wu, S.S.C., Ablin, K.K., Howington-Kraus, A.E. [1993]. Icarus 104, 301–323) hypothesis regarding the formation of incised valleys on the western flanks by density current erosion which would indicate magma–water interaction or, alternatively, volatile-rich magmas early in the volcano’s history, (3) mounds of diverse geometric shapes, many of which display summit depressions and occur among faults and fractures, possibly marking venting, (4) strong indicators on the flanks of the volcano for lahar events, and possibly, a caldera lake, (5) ubiquitous presence of impact craters displaying fluidized ejecta in both shield-forming (flank and caldera) materials and materials that surround the volcano that are indicative of water-rich target materials at the time of impact, (6) long-term complex association in time among shield-forming materials and Medusae Fossae Formation.The findings point to a site of extensive volcanic and hydrologic activity with possibly a period of magma–water interaction and hydrothermal activity. Finally, we propose that the mound structures around Apollinaris should be prime targets for further in situ exploration and search for possible exobiological signatures.  相似文献   
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We present preliminary results of the EXOSAT X-ray observations and quasisimultaneous and simultaneous optical photometry of the X-ray source EX0020528+1454.8=1E0205+149 found independently as an serendipitous source both with Einstein and EXOSAT satellites. The optical counterpart is a pair of dMe stars. Our results indicate that the object is variable both in X-rays and optical wavelenghts, and probably belongs to dMe flare stars.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.  相似文献   
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Solar prominences have been simultaneously observed in the integrated light of the He D3 and the Hβ emissions on two successive days, using the SST on La Palma with its tip-tilt mirror locked on a nearby white-light limb facular grain. The spatial and the temporal variation of the integrated line intensities and their ratio shows mainly two characteristics: (A) Constant emission ratio (even) in regions with substantial intensity variations and (B) varying emission ratio (often) tightly related to intensity structures of the prominence. (A) May be explained by a different number of superposing threads along the line of sight having very similar physical state. (B) Indicates threads with different intrinsic physical states; these may depend on the gas pressure or the inner structure of each thread, i.e., the “packing density,” affecting the penetration of ionizing EUV radiation, which affects the He i level populations and thus the rate of the triplet excitation.  相似文献   
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Car routing solutions are omnipresent and solutions for pedestrians also exist. Furthermore, public or commercial buildings are getting bigger and the complexity of their internal structure has increased. Consequently, the need for indoor routing solutions has emerged. Some prototypes are available, but they still lack semantically-enriched modelling (e.g., access constraints, labels, etc.) and are not suitable for providing user-adaptive length-optimal routing in complex buildings. Previous approaches consider simple rooms, concave rooms, and corridors, but important characteristics such as distinct areas in huge rooms and solid obstacles inside rooms are not considered at all, although such details can increase navigation accuracy. By formally defining a weighted indoor routing graph, it is possible to create a detailed and user-adaptive model for route computation. The defined graph also contains semantic information such as room labels, door accessibility constraints, etc. Furthermore, one-way paths inside buildings are considered, as well as three-dimensional building parts, e.g., elevators or stairways. A hierarchical structure is also possible with the presented graph model.  相似文献   
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Recent viewpoints concerning the state of research in transport geography have touched on the issue of insularity and the need to bridge the divide between the largely spatial–analytical or quantitative research in transport geography and the critical or qualitative research prevalent in urban, economic, and most other subfields of human geography. Transport geography has been criticized by some for being a quiet corner of our discipline that has lost its centrality largely because it remains within the analytical framework of the 1960s. This article explores these sentiments by reexamining recent transport-oriented research in highly cited geography journals to assess the degree to which the qualitative–quantitative divide exists within transport geography and between transport and other subfield in human geography, as well as to explore issues of productivity and centrality of transport-oriented research in geography. Results indicate that geographical research involving transport topics is much more prevalent and reflects a wider range of epistemological and methodological approaches than is frequently assumed. Nevertheless, there is still a considerable divide between “mainstream” transport geography and other human geographical research that necessitates much more interaction between transport and other subfields and greater incorporation of alternative research approaches within the mainstream of transport geography. To that end, we propose a preliminary critical transport geography research agenda that is open to a variety of methodological approaches, including quantitative analysis.  相似文献   
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This article analyzes the interrelationship among resource consumption, sociospatial justice, and what is popularly known as global warming by interrogating the ecological footprint of professional geographers, especially in terms of their conference-going involving air travel. In this spirit, the article introduces and employs the concepts of ecological privilege (as well as its inextricably related antithesis, ecological disadvantage) and dys-ecologism as a way to understand the roots and implications of professional geographers’ fossil fuel use and those of globally advantaged classes more broadly. To illustrate this, the article measures the flight-related ecological footprint of the 2011 annual meeting of the Association of American Geographers (AAG) in Seattle, Washington. In doing so, the article examines how professional geographers, in the form of the AAG, have responded to their travel-related ecological footprint. It thus highlights the importance of scrutinizing the complex and dynamic interrelationships among consumption; associated socioecological benefits and detriments and their systemic manifestations; and hierarchy-related and power-infused categories of race, class, and nation—and their spatialities.  相似文献   
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