共查询到20条相似文献,搜索用时 31 毫秒
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We have shown that a current-carrying plasma loop can be heated by magnetic pinch driven by the pressure imbalance between inside and outside the loop, using a 3-dimensional electromagnetic (EM) particle code. Both electrons and ions in the loop can be heated in the direction perpendicular to the ambient magnetic field, therefore the perpendicular temperature can be increased about 10 times compared with the parallel temperature. This temperature anisotropy produced by the magnetic pinch heating can induce a plasma instability, by which high-frequency electromagnetic waves can be excited. The plasma current which is enhanced by the magnetic pinch can also excite a kinetic kink instability, which can heat ions perpendicular to the magnetic field. The heating mechanism of ions as well as the electromagnetic emission could be important for an understanding of the coronal loop heating and the electromagnetic wave emissions from active coronal regions. 相似文献
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《天文和天体物理学研究(英文版)》2016,(3)
We apply a new statistical analysis technique, the Mean Field approach to Independent Component Analysis(MF-ICA) in a Bayseian framework, to galaxy spectral analysis. This algorithm can compress a stellar spectral library into a few Independent Components(ICs), and the galaxy spectrum can be reconstructed by these ICs. Compared to other algorithms which decompose a galaxy spectrum into a combination of several simple stellar populations, the MF-ICA approach offers a large improvement in efficiency. To check the reliability of this spectral analysis method, three different methods are used:(1) parameter recovery for simulated galaxies,(2) comparison with parameters estimated by other methods, and(3) consistency test of parameters derived with galaxies from the Sloan Digital Sky Survey. We find that our MF-ICA method can not only fit the observed galaxy spectra efficiently, but can also accurately recover the physical parameters of galaxies. We also apply our spectral analysis method to the DEEP2 spectroscopic data, and find it can provide excellent fitting results for low signal-to-noise spectra. 相似文献
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Florian Freistetter 《Celestial Mechanics and Dynamical Astronomy》2009,104(1-2):93-102
Due to close encounters with the inner planets, Near-Earth-Asteroids (NEAs) can have very chaotic orbits. Because of this chaoticity, a statistical treatment of the dynamical properties of NEAs becomes difficult or even impossible. We propose a new way to classify NEAs by using methods from Fuzzy Logic. We demonstrate how a fuzzy characterization of NEAs can be obtained and how a subsequent analysis can deliver valid and quantitative results concerning the long-term dynamics of NEAs. 相似文献
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The impact of a supernova explosion on the magnetosphere of a neutron star in a massive binary system is considered. The supernova shock impact on a plasma-filled neutron star magnetosphere can give rise to a long magnetospheric tail with a considerable store of magnetic energy. Magnetic reconnection in the formed current sheet can transform the magnetic energy stored in the tail into the kinetic energy of charged particles. The plasma instabilities excited by beams of accelerated relativistic particles can lead to the formation of a short pulse of coherent radio emission with parameters similar to those measured for the bright extragalactic millisecond radio burst detected in 2007. 相似文献
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C. de Vegt 《Astrophysics and Space Science》1991,177(1-2):3-15
The consequent application of present optical technology for the construction of substantially improved instrumentation in photographic astrometry and the application of rigorous reduction techniques provide all means for the construction of new, global position catalogs with a precision of a few 0.01 arcsec. At the same time the limiting magnitude of those catalogs can be extended to about 17 without decreasing positional accuracy. High speed measuring machines combined with real time reductions and storage on optical disks can handle the huge amount of information on a single plate. The throughout application of block adjustment reduction of global and hemisphere covering catalogs can provide a rigid stellar net which can be adjusted for the first time to a quasar based future reference frame directly. Instrumental requirements and optimal reduction techniques for achieving this goal are discussed. 相似文献
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By linear perturbation theory, a sensitivity study is presented to calculate the contribution of the Mars gravity field to the orbital perturbations in velocity for spacecrafts in both low eccentricity Mars orbits and high eccentricity orbits(HEOs). In order to improve the solution of some low degree/order gravity coefficients, a method of choosing an appropriate semimajor axis is often used to calculate an expected orbital resonance, which will significantly amplify the magnitude of the position and velocity perturbations produced by certain gravity coefficients. We can then assess to what degree/order gravity coefficients can be recovered from the tracking data of the spacecraft. However, this existing method can only be applied to a low eccentricity orbit, and is not valid for an HEO. A new approach to choosing an appropriate semimajor axis is proposed here to analyze an orbital resonance. This approach can be applied to both low eccentricity orbits and HEOs. This small adjustment in the semimajor axis can improve the precision of gravity field coefficients and does not affect other scientific objectives. 相似文献
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Previous statistical analyses of a large number of SOHO/MDI full disk longitu-dinal magnetograms provided a result that demonstrated how responses of solar flares to photospheric magnetic properties can be fitted with sigmoid functions. A logistic model reveals that these fitted sigmoid functions might be related to the free energy storage process in solar active regions. Although this suggested model is rather simple, the free energy level of active regions can be estimated and the probability of a solar flare with importance over a threshold can be forecast within a given time window. 相似文献
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Detection of a composite flux in photometry can serve as an indication of a photometrically unresolved binarity and can contribute
to the parameterization of the components of binary systems. A main goal of the present study is to develop a method of automatic
photometric detection of binaries, based on multi-color photometry, theoretical stellar spectral energy distributions and
general understanding of binary evolution. In particular, we consider an ultraviolet photometry where, in combination with
optical and infrared photometry, interstellar reddening can be easier distinguished from temperature reddening. 相似文献
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In the automated(computerized) meridian circle, the graduation error can be calibrated in a short time: a complete determination of the graduation error takes a few days, while a coarse measurement of the first ten dominant Fourier components of the graduation error takes only 15 min. Thus, we can monitor the annual and diurnal variations of the graduation. In our regular observations, the annual variation can be thus corrected for. This kind of correction seems to be necessary, judging from the observing accuracy of modern meridian observations. On the other hand, we could not detect a change of the graduation within one clear day as far as the dominant components of the diameter error are concerned. In our case we can therefore assume the graduation error to be constant within one day. 相似文献
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When three point masses form a hierarchical triple system, the short-period orbit can be severely modified by the long-period orbit if the two orbits are inclined to each other by more than about 39^deg (). Such an inclination can induce ‘Kozai cycles’ (Kozai, 1962), in which the eccentricity of the inner orbit cycles by a large amount while its period and therefore semimajor axis remains roughly constant. During those periastra when the eccentricity is largest, tidal friction may become important, and this can result in a secular shrinkage of the orbit, until it becomes circularised at a period of a few days.However, apsidal motion due to either GR or to the quadrupolar distortion of the components (if they are no longer treated as point masses) can reduce the range of eccentricity. We explore the limits on outer and inner orbital period that these perturbations imply.If the components are F/G/K/M dwarfs, then rotationally-driven dynamo activity can become important at the short periods that can occur in the right circumstances. It can cause the period to shorten further. The result may be a contact binary, and/or a merger in which the two stars of the inner pair coalesce to form a single rapidly rotating star. We suggest that this may be the origin of AB Dor, a very rapidly rotating K dwarf that is probably about 50 Myr old. 相似文献
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B. Kmpfer 《Astronomische Nachrichten》1982,303(4):231-236
Cold stars can become unstable due to a phase transition in the centre. By small perturbations the collapse is triggered toward a new stable configuration. The features of the collapse are studied by means of a parameter-independent model with piece by piece uniform density. Possible consequences of such a collapse for neutron stars are: extreme speed-up, heating and a supernova-like release of binding energy. The dynamical stability properties of the model are considered in the framework of General Relativity. In particular the very beginning of the collapse can be treated by analytical means. In a certain range relativistic effects can prevent a configuration to collapse. 相似文献
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State transitions triggered by inverse magnetic field: probably applied in high-mass X-ray binaries?
《天文和天体物理学研究(英文版)》2016,(3)
Previous works suggested that the state transitions in an X-ray binary can be triggered by accreting an inverse magnetic field from its companion star. A key point of this mechanism is the accretion and magnification of large-scale magnetic fields from the outer boundary of a thin disk. However, how such a process can be realized is still an open question. In this work, we check this issue in a realistic X-ray binary system. According to our calculations, a quite strong initial magnetic field, B~10~2- 10~3 G, is required in order to assure that the large-scale magnetic field can be effectively dragged inward and magnified with the accretion of gas. Thus, such a picture probably can be present in high-mass X-ray binaries possessing a strong stellar magnetic field, e.g., Cyg X-1. 相似文献
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Tommaso Giannantonio Robert Crittenden 《Monthly notices of the Royal Astronomical Society》2007,381(2):819-826
In this paper, we show how the rescattering of cosmic microwave background photons after cosmic reionization can give a significant linear contribution to the temperature–matter cross-correlation measurements. These anisotropies, which arise via a late-time Doppler effect, are on scales much larger than the typical scale of non-linear effects at reionization; they can contribute to degree scale cross-correlations and could affect the interpretation of similar correlations resulting from the integrated Sachs–Wolfe effect. While expected to be small at low redshifts, these correlations can be large given a probe of the density at high redshift, and so could be a useful probe of the cosmic reionization history. 相似文献
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D. J. Scheeres 《Celestial Mechanics and Dynamical Astronomy》2017,128(2-3):131-148
When gravitational aggregates are spun to fission they can undergo complex dynamical evolution, including escape and reconfiguration. Previous work has shown that a simple analysis of the full 2-body problem provides physically relevant insights for whether a fissioned system can lead to escape of the components and the creation of asteroid pairs. In this paper we extend the analysis to the full 3-body problem, utilizing recent advances in the understanding of fission mechanics of these systems. Specifically, we find that the full 3-body problem can eject a body with as much as 0.31 of the total system mass, significantly larger than the 0.17 mass limit previously calculated for the full 2-body problem. This paper derives rigorous limits on a fissioned 3-body system with regards to whether fissioned system components can physically escape from each other and what other stable relative equilibria they could settle in. We explore this question with a narrow focus on the Spherical Full Three Body Problem studied in detail earlier. 相似文献
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《New Astronomy》2022
Radio frequency interference (RFI) identification is a key step in radio data processing. In order to efficiently process huge volumes of data produced by modern large radio telescopes, such as the Five-hundred-meter Aperture Spherical radio Telescope (FAST), exceptional balance between accuracy and performance (throughput) is required for RFI flagging algorithms. RFI-Net is a single-process RFI identification package based on deep learning technique, and has achieved a higher flagging accuracy than the classical SumThreshold method. In this paper, we present a scalable RFI flagging toolkit, which can drive parallel workflows on multi-CPU and multi-GPU clusters, with RFI-Net as its core detector. It can automatically schedule the workload and aggregate itself after errors according to the running environment. Moreover, its main components are all pluggable, and can be easily customized according to requirements. The experiments with real data of FAST showed that using eight parallel workflows, the toolkit can process sky survey data at a speed of 66.79 GB/h, which means quasi-real-time RFI flagging can be achieved considering the data rate of FAST extragalactic spectral line observations. 相似文献