排序方式： 共有43条查询结果，搜索用时 15 毫秒
21.
A. E. Vol’vach L. N. Vol’vach A. M. Kut’kin M. G. Larionov M. Villata K. M. Panteri A. Lahteenmaki M. Tornikoski P. Savolainen G. Tammi A. F. Aller H. D. Aller S. G. Sergeev V. T. Doroshenko Yu. S. Efimov S. A. Klimanov S. V. Nazarov G. V. Borman A. B. Pushkarev V. I. Zhdanov E. V. Fedorova I. B. Vavilova N. G. Chesnok 《Astronomy Reports》2011,55(7):608-615
Long-term monitoring data at five radio frequencies from 4.8 to 37 GHz obtained at the Crimean Astrophysical Observatory, Metsahovi Radio Observatory of Aalto University, and the University of Michigan Radio Astronomy Observatory are used to analyze variations of the flux of the Active Galactic Nucleus (AGN) 3C 454.3. The dynamical characteristics of the three latest powerful flares from 2004 to 2010 are analyzed in detail. Observations in the gamma-ray (0.1–300 GeV), X-ray (2–10 kev, 15–50 keV), and optical are also used. Delays in the development of flares at different frequencies are derived. An empirical frequency dependence for the delays of flares from the gamma-ray to the radio is determined, which can be fit using a logarithmic low and remains the same from flare to flare. The physical characteristics of the central region of the AGN 3C 454.3 are used to estimate the size of its Strömgren sphere, taking into account the relevant mechanisms for heating and cooling the medium, as well as the adopted laws for the variation of the density and temperature with distance from the source of ionization. A model for the location of the radiation regions in the jet at various frequency ranges during the development of flares is proposed. 相似文献
22.
Observations of Koronis asteroid family members (158) Koronis, (277) Elvira, (311) Claudia, (321) Florentina, and (720) Bohlinia made during the period 1998-2001 yielded 61 new individual rotation lightcurves to augment previous surveys (R.P. Binzel, 1987, Icarus 72, 135-208; S.M. Slivan, R.P. Binzel, 1996, Icarus 124, 452-470) and allow determination of the senses of rotation and spin vector orientations for these objects. Spin vector reductions were performed on these five objects and also on family members (167) Urda, (208) Lacrimosa, (534) Nassovia, and (1223) Neckar using both a combination of amplitude-magnitude and epoch methods and a convex inversion method. A total of 213 individual lightcurves were analyzed to determine sidereal rotation periods, pole solutions and obliquities, associated photometric parameters, and model shapes for each object. We checked our methods and results using the (243) Ida Master Dataset of lightcurves (R. P. Binzel et al., 1993, Icarus 105, 310-325) and found that the true pole determined from the Galileo fly by of this irregularly shaped member of the Koronis family falls just at the edge of the estimated uncertainty of our own solution. Our findings for the spin vector distribution of 10 members within the Koronis family represent the first systematic study of spin states within a well-established Hirayama family, and provide observational constraints for models of the physics of family formation and spin vector evolution in the main belt. 相似文献
23.
Mikko Kaasalainen Petr Pravec Lenka Šarounová Jenni Virtanen Anders Erikson Josef ?urech Johan S.V. Lagerros Claes-Ingvar Lagerkvist John Davies Peter Kušnirák Vasilij G. Shevchenko Irina N. Belskaya 《Icarus》2004,167(1):178-196
We present new observations and models of the shapes and rotational states of the eight near-Earth Asteroids (1580) Betulia, (1627) Ivar, (1980) Tezcatlipoca, (2100) Ra-Shalom, (3199) Nefertiti, (3908) Nyx, (4957) Brucemurray, and (5587) 1990 SB. We also outline some of their solar phase curves, corrected to common reference geometry with the models. Some of the targets may feature sizable global nonconvexities, but the observable solar phase angles were not sufficiently high for confirming these. None is likely to have a very densely cratered surface. We discuss the role of the intermediate topographic scale range in photometry, and surmise that this scale range is less important than large or small scale lengths. 相似文献
24.
A number of X-ray instruments have been active in observing the solar coronal X-ray radiation this decade. We have compared
XSM observations with simultaneous GOES and RHESSI observations. We present flux calibrations for all instruments and compare
XSM and GOES total emission measures (TEM) and temperatures (T). 相似文献
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26.
The financial condition of US Gulf of Mexico recreational-for-hire (RFH) fishing firms post-hurricane damage was examined within the context of the industry’s contribution to the resiliency of coastal socio-ecological systems (SES). Three key financial ratios—return-on-assets, assets turnover ratio, and debt-to-assets ratio—were calculated for 2009 from balance sheets and cash flow statements constructed from surveys of 247 RFH firms operating in the five Gulf states. The ratios were then recalculated using reported damage and operational losses from at least one named storm in the 2004–2008 period and combined with the results of a logistic regression model of profitability loss to assess the resiliency of the RFH industry. Results suggest that RFH firm resiliency was a function of operating class (head, charter, and guide boats), homeport, and the way in which the business was structured. Firms appeared to be the most resilient when they employed smaller vessels in intensively managed operations, perhaps due to their ability to move a vessel out of the path of storms and because their profitability and efficiency advantages allowed for self-insurance against losses. As a result, community contributions to, and benefits from, resiliency in the RFH industry may hinge on the development of more modern port facilities and well-functioning insurance markets. 相似文献
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Patrik Kraufvelin Ari T. Ruuskanen Niko Nappu Mikko Kiirikki 《Estuarine, Coastal and Shelf Science》2007,72(4):665-674
During the reproduction period of Fucus vesiculosus, which occurs only once a year (in May–June) along the Finnish coast of the northern Baltic Sea, a thick carpet of filamentous algae often covers hard substrates suitable for zygote settlement. By placing out artificial substrates into the field, monthly over a period of eight months prior to F. vesiculosus settlement (October 2001–June 2002), we investigated the autumn/winter/spring colonisation and succession of filamentous algae and their possible relationships with the settlement success of F. vesiculosus under naturally variable field conditions. The substrates exposed in October 2001 became covered by filamentous brown algal Pilayella littoralis mats, which persisted over the settlement period of F. vesiculosus, but now also were accompanied by large amounts of the filamentous green alga Cladophora glomerata. The substrates exposed from November 2001 onwards hosted smaller amounts of P. littoralis during the winter and different filamentous algal communities at the time of F. vesiculosus settlement, i.e. less P. littoralis and C. glomerata, but Dictyosiphon foeniculaceus, Ceramium tenuicorne and Ulva intestinalis instead. We observed recruits of F. vesiculosus on all substrates, except on the ones placed out in October 2001. Significantly more P. littoralis and C. glomerata on the October substrates may explain the failed F. vesiculosus recruitment, although we could not establish direct causal or correlational relationships between filamentous algae and F. vesiculosus settlement. We compared the results with a previous un-replicated pilot study in the same area demonstrating similar response patterns. 相似文献
28.
Insilico evaluation of plant genetic resources to search for traits for adaptation to climate change
29.
River ice cover influence on sediment transportation at present and under projected hydroclimatic conditions 
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下载免费PDF全文 Maria Kämäri Petteri Alho Noora Veijalainen Juha Aaltonen Mikko Huokuna Eliisa Lotsari 《水文研究》2015,29(22):4738-4755
A large number of rivers are frozen annually, and the river ice cover has an influence on the geomorphological processes. These processes in cohesive sediment rivers are not fully understood. Therefore, this paper demonstrates the impact of river ice cover on sediment transport, i.e. turbidity, suspended sediment loads and erosion potential, compared with a river with ice‐free flow conditions. The present sediment transportation conditions during the annual cycle are analysed, and the implications of climate change on wintertime geomorphological processes are estimated. A one‐dimensional hydrodynamic model has been applied to the Kokemäenjoki River in Southwest Finland. The shear stress forces directed to the river bed are simulated with present and projected hydroclimatic conditions. The results of shear stress simulations indicate that a thermally formed smooth ice cover diminishes river bed erosion, compared with an ice‐free river with similar discharges. Based on long‐term field data, the river ice cover reduces turbidity statistically significantly. Furthermore, suspended sediment concentrations measured in ice‐free and ice‐covered river water reveal a diminishing effect of ice cover on riverine sediment load. The hydrodynamic simulations suggest that the influence of rippled ice cover on shear stress is varying. Climate change is projected to increase the winter discharges by 27–77% on average by 2070–2099. Thus, the increasing winter discharges and possible diminishing ice cover periods both increase the erosion potential of the river bed. Hence, the wintertime sediment load of the river is expected to become larger in the future. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
30.
N. S. Kardashev A. V. Alakoz A. S. Andrianov M. I. Artyukhov W. Baan V. E. Babyshkin N. Bartel O. S. Bayandina I. E. Val’tts P. A. Voitsik A. Z. Vorobyov C. Gwinn J. L. Gomez G. Giovannini D. Jauncey M. Johnson H. Imai Y. Y. Kovalev S. E. Kurtz M. M. Lisakov A. P. Lobanov V. A. Molodtsov B. S. Novikov A. V. Pogodin M. V. Popov A. S. Privesenzev A. G. Rudnitski G. M. Rudnitski T. Savolainen T. V. Smirnova A. M. Sobolev V. A. Soglasnov K. V. Sokolovsky E. N. Filippova V. V. Khartov M. E. Churikova A. E. Shirshakov V. I. Shishov P. Edwards 《Solar System Research》2017,51(7):535-554
The RadioAstron ground-space interferometer provides the highest angular resolution achieved now in astronomy. The detection of interferometric fringes from quasars with this angular resolution on baselines of 100–200 thousand km suggests the brightness temperatures which exceed the Compton limit by two orders of magnitude. Polarimetric measurements on ground-space baselines have revealed fine structure testifying to recollimation shocks on scales of 100–250 μas and a helical magnetic field near the base of radio emission in BL Lacertae. Substructure within a the scattering disk of pulsar emission on interferometer baselines (from 60000 to 250000 km) was discovered. This substructure is produced by action of the interstellar interferometer with an effective baseline of about 1 AU and the effective angular resolution of better than 1 μas. Diameters of scattering disks were measured for several pulsars, and distances to diffusing screens were evaluated. The ground-space observations of sources of the maser radiation in lines of water and hydroxyl have shown that the maser sources in star-forming regions remain unresolved on baselines, which considerably exceed the Earth diameter. These very compact and bright features with angular sizes of about 20–60 μas correspond to linear sizes of about 5–10 million km (several solar diameters). 相似文献