共查询到20条相似文献，搜索用时 484 毫秒
1.
Jeffrey M. Aristoff Joshua T. Horwood Aubrey B. Poore 《Celestial Mechanics and Dynamical Astronomy》2014,118(1):13-28
We present a new variable-step Gauss–Legendre implicit-Runge–Kutta-based approach for orbit and uncertainty propagation, VGL-IRK, which includes adaptive step-size error control and which collectively, rather than individually, propagates nearby sigma points or states. The performance of VGL-IRK is compared to a professional (variable-step) implementation of Dormand–Prince 8(7) (DP8) and to a fixed-step, optimally-tuned, implementation of modified Chebyshev–Picard iteration (MCPI). Both nearly-circular and highly-elliptic orbits are considered using high-fidelity gravity models and realistic integration tolerances. VGL-IRK is shown to be up to eleven times faster than DP8 and up to 45 times faster than MCPI (for the same accuracy), in a serial computing environment. Parallelization of VGL-IRK and MCPI is also discussed. 相似文献
2.
Emmanuel E. Etim Prasanta Gorai Ankan Das Elangannan Arunan 《Astrophysics and Space Science》2018,363(1):6
There are numerous complex organic molecules containing carbon and oxygen atoms which show either C–C–O or C–O–C bonding backbone. This paper examines altogether 51 C–C–O and C–O–C bonding backbone molecules from ten different isomeric groups (C2H2O, C3H2O, C2H4O, C2H4O2, C3H4O, C2H6O, C2H6O2, C3H6O, C3H6O2, C3H8O) to summarize the present astronomical status of these molecules. Accurate calculations of enthalpy of formation of these molecules show that the isomers with C–C–O backbone are more stable than the C–O–C backbone. Interestingly, a detailed analysis of relevant astromolecules indicates that most of the observed astromolecules have the C–C–O backbone. As a matter of fact, of all the molecules examined in this study, 80% of the astronomically observed species have the C–C–O backbone while only 20% have the C–O–C backbone. In general, interstellar abundance of a molecule is controlled by some factors such as kinetics, formation and destruction pathways,thermodynamics etc. A proper consideration of these factors could explain the observed abundances of these molecules. All these possible key factors are discussed in this paper. 相似文献
3.
Lorenzo Iorio 《Celestial Mechanics and Dynamical Astronomy》2001,79(3):201-230
The general relativistic Lense—Thirring effect can be measured by inspecting a suitable combination of the orbital residuals of the nodes of LAGEOS and LAGEOS II and the perigee of LAGEOS II. The solid and ocean Earth tides affect the recovery of the parameter by means of which the gravitomagnetic signal is accounted for in the combined residuals. Thus an extensive analysis of the perturbations induced on these orbital elements by the solid and ocean Earth tides is carried out. It involves the l=2 terms for the solid tides and the l=2,3,4 terms for the ocean tides. The perigee of LAGEOS II turns out to be very sensitive to the l=3 part of the ocean tidal spectrum, contrary to the nodes of LAGEOS and LAGEOS II. The uncertainty in the solid tidal perturbations, mainly due to the Love number k
2, ranges from 0.4% to 1.5%, while the ocean tides are uncertain at 5–15% level. The obtained results are used in order to check in a preliminary way which tidal constituents the Lense-Thirring shift is sensitive to. In particular it is tested if the semisecular 18.6-year zonal tide really does not affect the combined residuals. It turns out that, if modeled at the level of accuracy worked out in the paper, the l=2,4 m=0 and also, to a lesser extent, the l=3, m=0 tidal perturbations cancel out.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
4.
The solar cycle appears to be remarkably synchronized with the gravitational torques exerted by the tidally dominant planets Venus, Earth and Jupiter. Recently, a possible synchronization mechanism was proposed that relies on the intrinsic helicity oscillation of the current-driven Tayler instability which can be stoked by tidal-like perturbations with a period of 11.07 years. Inserted into a simple \(\alpha \)–\(\Omega \) dynamo model these resonantly excited helicity oscillations led to a 22.14 years dynamo cycle. Here, we assess various alternative mechanisms of synchronization. Specifically we study a simple time-delay model of Babcock–Leighton type dynamos and ask whether periodic changes of either the minimal amplitude for rising toroidal flux tubes or the \(\Omega \) effect could eventually lead to synchronization. In contrast to the easy and robust synchronizability of Tayler–Spruit dynamo models, our answer for those Babcock–Leighton type models is less propitious. 相似文献
5.
Mutual quasi-periodicities near the solar-rotation period appear in time series based on the Earth’s magnetic field, the interplanetary
magnetic field, and signed solar-magnetic fields. Dominant among these is one at 27.03±0.02 days that has been highlighted
by Neugebauer et al. (J. Geophys. Res.
105, 2315, 2000). Extension of their study in time and to different data reveals decadal epochs during which the ≈ 27.0 days, or a ≈ 28.3 days,
or other quasi-periods dominate the signal. Space-time eigenvalue analyses of time series in 30 solar latitude bands, based
on synoptic maps of unsigned photospheric fields, lead to two maximally independent modes that account for almost 30% of the
data variance. One mode spans 45° of latitude in the northern hemisphere and the other one in the southern. The modes rotate
around the Sun rigidly, not differentially, suggesting connection with the subsurface dynamo. Spectral analyses yield familiar
dominant quasi-periods 27.04±0.03 days in the North and at 28.24±0.03 days in the South. These are replaced during cycle 23
by one at 26.45±0.03 days in the North. The modes show no tendency for preferred longitudes separated by ≈ 180°. 相似文献
6.
In this paper we consider Chameleonic Generalized Brans–Dicke Cosmology in the framework of FRW universes. The bouncing solution
and phantom crossing is investigated for the model. Two independent cosmological tests: Cosmological Redshift Drift (CRD)
and distance modulus are applied to test the model with the observation. 相似文献
7.
We present the main results of the Ph.D. thesis carried out by López-Sánchez (Ph.D. thesis, 2006), in which a detailed morphological, photometric and spectroscopic analysis of a sample of 20 Wolf–Rayet (WR) galaxies was performed. The main aims are the study of the star formation and O and WR stellar populations in these galaxies, and the role that interactions between low surface brightness companion objects have in the triggering of the bursts. We analyze the morphology, stellar populations, physical conditions, chemical abundances and kinematics of the ionized gas, as well as the star-formation activity of each system. 相似文献
8.
The Tully–Fisher relationship (TFR) has been shown to have a relatively small observed scatter of ∼±0.35 mag implying an intrinsic
scatter < ±0.30 mag. However, when the TFR is calibrated from distances derived from the Hubble relation for field galaxies
scatter is consistently found to be ±0.64 to ±0.84 mag. This significantly larger scatter requires that intrinsic TFR scatter
is actually much larger than ±0.30 mag, that field galaxies have an intrinsic TFR scatter much larger than cluster spirals,
or that field galaxies have a velocity dispersion relative to the Hubble flow in excess of 1000 km s−1. Each of these potential explanations faces difficulties and contradicted by available data and the results of previous studies.
An alternative explanation is that the measured redshifts of galaxies are composed of a cosmological redshift component predicted
from the value of the Hubble constant and a superimposed intrinsic redshift component previously identified in other studies.
This intrinsic redshift component may exceed 5000 km s−1 in individual galaxies. In this alternative scenario a possible value for the Hubble constant is 55–60 km s−1 Mpc−1. 相似文献
9.
10.
Eismont N. A. Kovalenko I. D. Nazarov V. N. Nazirov R. R. Korotkov F. V. Pogodin A. V. Mzhelskii P. V. Mikhailov E. A. Ditrikh A. V. Tregubov A. I. 《Astronomy Letters》2020,46(4):263-274
Astronomy Letters - The Spectrum–Röntgen–Gamma (SRG) space observatory was launched from Baikonur on July 13, 2019, and is currently on a flight trajectory in the vicinity of the... 相似文献
11.
Snapshot spectroscopic imagers/instruments (SSI) are a class of spectroscopic instruments that are capable of acquiring spectral information of a given field of view in a single frame. Standard spectroscopic instruments like a grating-based spectrograph or a Fabry–Pérot-based spectrograph obtain two dimensional data of 2D space or 1D space and 1D wavelength. But SSIs have three dimensional data of 2D space and wavelength embedded in two dimensional detector/image plane. So standard data reduction techniques are not applicable. Lenslet array spectroscope is a novel SSI which images the object on to a hybrid spatio-spectral image plane. A procedure to extract the spatial and spectral information of the field of view from this hyperplane is presented. We demonstrate the snapshot capabilities of this instrument to study dynamic activities of the Sun as inferred from two measurements: (i) Evershed flow in a sunspot in NOAA 12526 at Fe?i 6301.5 Å and (ii) oscillations in a quiescent prominence at H\(\upalpha \) 6562.8 Å. This instrument can be used for large or small scale structures, making it efficient for studying a wide range of dynamic activities like helioseismology, Moreton waves, prominence oscillation etc. 相似文献
12.
Thierry Combot 《Celestial Mechanics and Dynamical Astronomy》2013,115(4):397-404
We present various properties of algebraic potentials, and then prove that some Morales–Ramis theorems readily apply for such potentials even if they are not in general meromorphic potentials. This allows in particular to precise some non-integrability proofs in Celestial Mechanics, where the mutual distances between the bodies appear in the potential, and thus making this analysis unavoidable. 相似文献
13.
《New Astronomy Reviews》2002,46(2-7):357-360
We highlight a group of peculiar double radio sources we christen HYMORS: HYbrid MOrphology Radio Sources. These HYMORS appear to have an FR I type radio lobe on one side of the active nucleus but an FR II type lobe on the opposite side. Such objects range in size from ∼0.01 Mpc to ∼1 Mpc. The mere existence of these hybrid sources causes severe difficulties for models which attribute the differences between FR I and FR II radio sources to some intrinsic property of the compact central engine, or the composition of the jet plasma. HYMORS support models for the FR dichotomy based upon the interaction of the jet plasma with the ambient medium, in that asymmetries in the external environment could more naturally produce the observed hybrid morphologies. 相似文献
14.
H. Alinejad 《Astrophysics and Space Science》2010,325(2):209-215
For an unmagnetized collisionless electron–positron–ion plasma, the effects of trapped and non-thermal electron distributions
are incorporated in the study of arbitrary amplitude ion-acoustic solitary structures. Both highly and weakly analyses are
examined by deriving an energy integral equation involving the Sagdeev potential for the large amplitude limit, and obtaining
the non-linear partial-differential equations for the small but finite amplitude limit. It is shown that there exist ion-acoustic
solitary waves with qualitatively different structures in a way that depend on the population of trapped and non-thermal electrons.
In the presence of trapped electrons, fully non-linear analyses show that plasma can support only arbitrary amplitude compressive
solitary waves. On the other hand, a consideration of the fast or non-thermal electron distribution provides the possibility
of the coexistence of large amplitude compressive and rarefactive solitary waves, whereas both of them are decoupled in the
small amplitude limit. It is found that the effects of such electron distributions and positron concentration change the maximum
values of the Mach number and the amplitude for which solitary waves can exist. Furthermore, the non-thermally distributed
electrons provide a KdV equation in the small amplitude limit, whereas the trapped electrons give rise to a modified KdV equation
which exhibits a stronger non-linearity. 相似文献
15.
Propagation of small but finite amplitude ion acoustic solitons and double layers are investigated in electron–positron–ion
plasmas in presence of highly negatively charged impurities or dust. The presence of negatively charged dust particulates
can result in existence of two critical concentrations of ion–electron density ratio α. One of them α
D
decides the existence of double layers, whereas the other one α
R
decides the nature of the solitons and double layers. The system supports both compressive and rarefactive solitons as well
as double layers. The parameter regimes of transitions from compressive to rarefactive solitons and double layers are also
specified. 相似文献
16.
We have investigated the role of the 200yr period discovered by Vienne and Duriez (1992) on the tidal evolution of the Mimas–Tethys system through the 2:4 ii present resonance. Three terms are found to generate this period. We present a perturbedpendulum model in which these terms bring about a perturbation to the ideal ii resonance pendulum, which is in a direct ratio to the eccentricity e of Tethys. Although e is now very small, it is shown that this quantity could have been much greater in the past. We also show, thanks to this model, that these terms may have brought about a stochastic layer of noticeable width at the time of capture in the ii resonance, with the consequence that the possible values of the inclination i of Mimas before capture range from 0.4° to 0.6° (these uncertainties arise from the present uncertainties on e). The role of each one of the three terms is examined in the appearance of chaos. A capture into the 1/1 secondary resonance (between the libration period of the primary ii resonance and the period of about 200yr) is found possible. It means that the system could have experienced several captures in the primary resonance, instead of a single one, and that i could have been, with this assumption, much lower than 0.4°. A probability of capture into this secondary resonance as a function of the eccentricity of Tethys on encounter is derived, using Malhotra's method (Malhotra, 1990). Allan's values of i = 0.42° and e 0 (Allan, 1969) are therefore called into question, and taking e 0 is shown to be absolutely necessary if we want to understand the phenomena at work in the Mimas–Tethys system. 相似文献
17.
The role of nearby galactic sources, the supernova remnants, in formation of observed energy spectrum and large-scale anisotropy of high-energy cosmic rays is studied. The list of these sources is made up based on radio, X-ray and gamma-ray catalogues. The distant sources are treated statistically as ensemble of sources with random positions and ages. The source spectra are defined based on the modern theory of cosmic ray acceleration in supernova remnants while the propagation of cosmic rays in the interstellar medium is described in the frameworks of galactic diffusion model. Calculations of dipole component of anisotropy are made to reproduce the experimental procedure of “two-dimensional” anisotropy measurements. The energy dependence of particle escape time in the process of acceleration in supernova remnants and the arm structure of sources defining the significant features of anisotropy are also taken into account. The essential new trait of the model is a decreasing number of core collapse SNRs being able to accelerate cosmic rays up to the given energy, that leads to steeper total cosmic ray source spectrum in comparison with the individual source spectrum. We explained simultaneously the new cosmic ray data on the fine structure of all particle spectrum around the knee and the amplitude and direction of the dipole component of anisotropy in the wide energy range 1 TeV–1 EeV. Suggested assumptions do not look exotic, and they confirm the modern understanding of cosmic ray origin. 相似文献
18.
We address the physical and kinematical properties of Wolf–Rayet [WR] central stars(CSs) and their host planetary nebulae(PNe). The studied sample comprises all [WR] CSs that are currently known. The analysis is based on recent observations of the parallax, proper motion, and color index of [WR] CSs from the Gaia space mission’s early third release(eDR3) catalog, as well as common nebular characteristics. The results revealed an evolutionary sequence, in terms of decreasing Teff, from... 相似文献
19.
Statistical analysis of the relationship between type II radio bursts appearing in the metric (m) and decameter-to-hectometer
(DH) wavelength ranges is presented. The associated X-ray flares and coronal mass ejections (CMEs) are also reported. The
sample is divided into two classes using the frequency-drift plots: Class I, representing those events where DH-type-II bursts
are not continuation of m-type-II bursts and Class II, where the DH-type-II bursts are extensions of m-type-II bursts. Our
study consists of three steps: i) comparison of characteristics of the Class I and II events; ii) correlation of m-type-II and DH-type-II burst characteristics with X-ray flare properties and iii) correlation of m-type-II and DH-type-II burst characteristics with CME properties. We have found no clear correlation between
properties of m-type-II bursts and DH-type-II bursts. For example, there is no correlation between drift rates of m-type-II
bursts and DH-type-II bursts. Similarly there is no correlation between their starting frequencies. In Class I events we found
correlations between X-ray flare characteristics and properties of m-type-II bursts and there is no correlation between flare
parameters and DH-type-II bursts. On the other hand, the correlation between CME parameters and m-type-II bursts is very weak,
but it is good for CME parameters and DH-type-II bursts. These results indicate that Class I m-type-II bursts are related
to the energy releases in flares, whereas DH-type-II bursts tend to be related to CMEs. On the contrary, for Class II events
in the case of m-type-II and DH-type-II bursts we have found no clear correlation between both flare and CMEs. 相似文献
20.
Interaction of the 30–300 keV electrons with whistlers in solar coronal loops is studied using a quasi-linear approach. We show that the electron–whistler interaction may play a dominant role in the formation of fast electron spectra within the solar flare loops with the plasma temperature 107 K and plasma density 1011 cm–3. It is found that Landau damping of whistlers provides weak and intermediate pitch-angle diffusion regimes of fast electrons in coronal loops. The level of whistler turbulence in the weak diffusion regime under flare conditions is estimated as 10–7 of the energy density in the thermal particles. The `top – footpoint' relations between the hard X-ray flux densities and spectra are derived. The reason for a `broken' spectrum of the flare microwave emission is discussed. 相似文献