共查询到20条相似文献，搜索用时 375 毫秒
1.
《New Astronomy》2015
The inertial and gravitational mass of electromagnetic radiation (i.e., a photon distribution) in a cavity with reflecting walls has been treated by many authors for over a century. After many contending discussions, a consensus has emerged that the mass of such a photon distribution is equal to its total energy divided by the square of the speed of light. Nevertheless, questions remain unsettled on the interaction of the photons with the walls of the box. In order to understand some of the details of this interaction, a simple case of a single photon with an energy bouncing up and down in a static cavity with perfectly reflecting walls in a constant gravitational field , constant in space and time, is studied and its contribution to the weight of the box is determined as a temporal average. 相似文献
2.
J. A. Vera 《Astrophysics and Space Science》2009,323(4):375-382
The non-canonical Hamiltonian dynamics of a triaxial gyrostat in Newtonian interaction with two punctual masses is considered.
This serves as a model for the study of the attitude dynamics of a spacecraft located at a Lagrangian equilibrium point of
the system formed by a binary asteroid and a spacecraft. Using geometric-mechanics methods, the approximated dynamics that
arises when developing the potential in series of Legendre functions and truncating the series to the second harmonics is
studied. Working in the reduced problem, the existence of equilibria in Lagrangian form are studied, in analogy with classic
results on the topic. In this way, the classical results on equilibria of the three-body problem, as well as other results
by different authors that use more conventional techniques for the case of rigid bodies, are generalized. The rotational Poisson
dynamics of a spacecraft located at a Lagrangian equilibrium and the study of the nonlinear stability of some important equilibria
are considered. The analysis is done in vectorial form avoiding the use of canonical variables and the tedious expressions
associated with them. 相似文献
3.
4.
《天文和天体物理学研究(英文版)》2021,(5)
In this paper, we present the analysis of the stellar system HIP 101227 to determine the actual number of components in the system, and their properties. We use dynamical modeling and complex spectrophotometric(involving atmospheric modeling) techniques with recent data, to determine the physical properties and orbital solution for the system, respectively, with better accuracy than past studies. Based on our analysis, we found that the system is more consistent with being a quadruple rather than a binary or a triple system as suggested by previous studies. The total mass of the system determined from our SED analysis is 3.42 ± 0.20 M, which is distributed almost equally between the four stars. The stars are found to be zero-age main sequence stars; i.e., at the last stage of pre-main sequence, with age less than 200 Myr and spectral types K0. All four stars have very similar physical characteristics, suggesting that the fragmentation process is the most likely theory for the formation and evolution of the system. 相似文献
5.
This paper reports on the discovery that an eclipsing binary system, EPIC 202843107, has aδ Scuti variable component. The phased light curve from the Kepler space telescope presents a detached configuration. The binary modeling indicates that the two component stars have almost the same radius and may have experienced orbital circularization. Frequency analyses are performed for the residual light curve after subtracting the binary variations. The frequency spectrum reveals that one component star is a δ Scuti variable. A large frequency separation is cross-identified with the corresponding histogram, the Fourier transform and the echelle diagram method. The mean density of the δ Scuti component is estimated to be 0.09 g cm~(-3) based on the large separation and density relation. Systems like EPIC 202843107 are helpful to study the stellar evolution and physical state of binary stars. 相似文献
6.
C. Johan Masreliez 《Astrophysics and Space Science》2010,326(2):281-291
The phenomenon of inertia is modeled by a new process, which semi-discretely changes the metrical scale of spacetime. This
process explains inertia as a curved spacetime phenomenon, since all accelerating trajectories take place on geodesics of
general relativity. By this approach inertial reference frames are Minkowskian manifolds imbedded in a five-dimensional space.
It would imply a revised interpretation of special relativity, which preserves a universal temporal reference. If acceleration
curves spacetime, it would also imply the existence of an energy-momentum tensor with net energy, which under certain conditions
could become negative. 相似文献
7.
The proposed model explains the Moon formation as a result of a thermo-nuclear explosion due to which a big land mass was torn off from the Earth. Within the model framework, on the one hand, the data on the Moon’s physical and chemical parameters are in good agreement. On the other hand, this model corresponds to modern ideas about the dynamism of the Earth’s geological structure which presupposes the presence of a powerful energy source in the Earth’s core, which might have thermonuclear origin. 相似文献
8.
E. Unda-Sanzana T. R. Marsh B. T. Gänsicke P. F. L. Maxted L. Morales-Rueda V. S. Dhillon T. D. Thoroughgood E. Tremou C. A. Watson R. Hinojosa-Goñi 《Monthly notices of the Royal Astronomical Society》2008,388(2):889-897
GD 552 is a high proper motion star with the strong, double-peaked emission lines characteristic of the dwarf nova class of cataclysmic variable (CV) star, and yet no outburst has been detected during the past 12 yr of monitoring. We present spectroscopy taken with the aim of detecting emission from the mass donor in this system. We fail to do so at a level which allows us to rule out the presence of a near-main-sequence star donor. Given GD 552's orbital period of 103 min, this suggests that it is either a system that has evolved through the ∼80-minute orbital period minimum of CV stars and now has a brown dwarf mass donor, or that has formed with a brown dwarf donor in the first place. This model explains the low observed orbital velocity of the white dwarf and GD 552's low luminosity. It is also consistent with the absence of outbursts from the system. 相似文献
9.
A. Granik 《Astrophysics and Space Science》1981,74(2):491-495
Nonlinear Alfvén waves, which in the infinitely conducting plasma are noncompressive and have a constant magnetic field strength (B
2=const), propagate in a turbulent plasma. The latter is characterized by a big (but finite) electrical conductivity eff due to micro-instabilities. The Alfvén wave in such a medium is governed by the diffusion equation. It is shown that an initial periodic perturbation (withB
2=const) while still being incompressive, decays due to dissipation. 相似文献
10.
11.
12.
Energy accumulation in a current sheet (CS) can occur during the injection of a fast plasma jet in a perpendicular magnetic field. A similar situation can occur in the solar corona when a flux of plasma appears under a magnetic arch. The flare can be produced at the CS disruption. The CS creation during plasma jet interaction with the magnetic field is demonstrated by numerical MHD simulation. The choice of dimensionless parameters Re, Rem,, II, which are suitable for simulation of coronal phenomena, is discussed. When jet injection ceases, the CS evolution produces an unstable state and fast magnetic energy dissipation is observed. 相似文献
13.
T. Granzer 《Astronomische Nachrichten》2006,327(8):792-795
Robotic telescopes are more and more commonly used in today's astronomical research. In fact, several facilities are spread around the globe, already forming a loose net. A big leap forward would lie in the capabilities to share observations between different telescopes. One gains immediately weather independence and the possibility of continuous observations from a working network. In this paper, the three robotic telescope operated under the hood of the Astrophysical Institute Potsdam are introduced, the potential of a robotic telescope network are sketched out and principle hints on accomplishing such a network are outlined. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
14.
15.
Maxwell’s ring-type configuration (i.e. an N-body model where the ν = Ν − 1 bodies have equal masses and are located at the vertices of a regular ν-gon while the N-th body with a different mass is located at the center of mass of the system) has attracted special attention during the
last 15 years and many aspects of it have been studied by considering Newtonian and post-Newtonian potentials (Mioc and Stavinschi
1998, 1999), homographic solutions (Arribas et al.
2007) and relative equilibrium solutions (Elmabsout 1996), etc. An equally interesting problem, known as the ring problem of (N + 1) bodies, deals with the dynamics of a small body in the combined force field produced by such a configuration. This is
the problem we are dealing with in the present paper and our aim is to investigate the variations in the dynamics of the small
body in the case that the central primary is also a radiating source and therefore acts on the particle with both gravitation
and radiation. Based on the general outlines of Radzievskii’s model, we study the permitted and the existing trapping regions
of the particle, its equilibrium locations and their parametric variations as well as the existence of focal points in the
zero-velocity diagrams. The distribution of the characteristic curves of families of planar symmetric periodic orbits and
their stability for various values of the radiation coefficient of the central body is additionally investigated. 相似文献
16.
Dagoberto Escobar Carlos R. Fadragas Genly Leon Yoelsy Leyva 《Astrophysics and Space Science》2014,349(1):575-602
In this work we present a phase space analysis of a quintessence field and a perfect fluid trapped in a Randall-Sundrum’s Braneworld of type 2. We consider a homogeneous but anisotropic Bianchi I brane geometry. Moreover, we consider the effect of the projection of the five-dimensional Weyl tensor onto the three-brane in the form of a negative Dark Radiation term. For the treatment of the potential we use the “Method of f-devisers” that allows investigating arbitrary potentials in a phase space. We present general conditions on the potential in order to obtain the stability of standard 4D and non-standard 5D de Sitter solutions, and we provide the stability conditions for both scalar field-matter scaling solutions, scalar field-dark radiation solutions and scalar field-dominated solutions. We find that the shear-dominated solutions are unstable (particularly, contracting shear-dominated solutions are of saddle type). As a main difference with our previous work, the traditionally ever-expanding models could potentially re-collapse due to the negativity of the dark radiation. Additionally, our system admits a large class of static solutions that are of saddle type. These kinds of solutions are important at intermediate stages in the evolution of the universe, since they allow the transition from contracting to expanding models and viceversa. New features of our scenario are the existence of a bounce and a turnaround, which lead to cyclic behavior, that are not allowed in Bianchi I branes with positive dark radiation term. Finally, as specific examples we consider the potentials V∝sinh?α (β?) and V∝[cosh(ξ?)?1] which have simple f-devisers. 相似文献
17.
A homogeneous cosmological model in Kaluza–Klein metric is obtained assuming a time-dependent equation of state. The solution is in fact generalization of an earlier work by Hajj and Boutros for a perfect fluid. It is also found that dimensional reduction of the extra space takes place such that the five-dimensional universe naturally evolves into an effective four-dimensional one. The dynamical behaviour of the model is examined and it is also found that with a decrease in extra space the observable three-dimensional space entropy increase thus accounting for the large value of entropy observable at present. 相似文献
18.
B. Guinot 《Celestial Mechanics and Dynamical Astronomy》1986,38(2):155-161
The International Atomic Time TAI is a physically realized time scale which is ultimately used for comparisons between observations and dynamical theories. Its definition should tell unambiguously what an ideal TAI should be. For terrestrial applications, TAI has been defined as a geocentric coordinate time. In Solar System Dynamics, a barycentric coordinate time is needed. In general, it is not possible to convert a coordinate time into another coordinate time. But a specific clock synchronized on TAI in the terrestrial system can be considered as reading a modified, proper time [TAI]i, which can be converted into a barycentric coordinate time. In this conversion appears a small location dependent term. By this process all the clocks of the TAI system give an unique barycentric time with the same metrological properties as TAI.
Résumé Le Temps Atomique International TAI est une échelle de temps physiquement réalisée qui est utilisée pour la comparaison entre les observations et les théories dynamiques. Sa définition doit exprimer sans ambiguïté ce que devrait être un TAI idéal. Pour les applications terrestres, TAI a été défini comme un temps-coordonnée géocentrique. Pour la dynamique du système solaire, on a besoin d'un tempscoordonnée barycentrique. En général, il n'est pas possible de convertir un temps-coordonnée en un autre temps-coordonnée. Mais une horloge particulière synchronisée sur le TAI dans le système terrestre peut être considérée comme marquant un temps-propre modifié [TAI]i: on peut alors convertir ce temps propre en un temps-coordonnée barycentrique. Dans cette conversion apparaît un terme petit dépendant de l'emplacement de l'horloge sur la Terre. Par ce procédé, toutes les horloges du système du TAI conduisent à un temps-coordonnée barycentrique unique qui bénéficie des mêmes propriété métrologiques que le TAI.相似文献
19.
We present the characteristics and demonstrate the performance of the Triple Etalon SOlar Spectrometer (TESOS) operated at the German Vacuum Tower Telescope (VTT) on Tenerife. The Fabry–Pérot interferometer TESOS is ideally suited for precise measurements of photospheric and chromospheric motion. Installed in 1997 and equipped with two etalons, TESOS has recently been completed with a third etalon and upgraded with two high-speed, backside-illuminated CCD cameras. The image scale of 0.089 arc sec pixel–1 is adapted to the resolution of the telescope. The improved system enables frame rates up to 5 frames per second. The spectral resolution of 300000 allows for spectral diagnostics of weak photospheric lines, including individual CH-lines within the G-band at 430.6 nm. 相似文献
20.
H. Lammer J. H. Bredehöft A. Coustenis M. L. Khodachenko L. Kaltenegger O. Grasset D. Prieur F. Raulin P. Ehrenfreund M. Yamauchi J.-E. Wahlund J.-M. Grießmeier G. Stangl C. S. Cockell Yu. N. Kulikov J. L. Grenfell H. Rauer 《Astronomy and Astrophysics Review》2009,17(2):181-249
This work reviews factors which are important for the evolution of habitable Earth-like planets such as the effects of the
host star dependent radiation and particle fluxes on the evolution of atmospheres and initial water inventories. We discuss
the geodynamical and geophysical environments which are necessary for planets where plate tectonics remain active over geological
time scales and for planets which evolve to one-plate planets. The discoveries of methane–ethane surface lakes on Saturn’s
large moon Titan, subsurface water oceans or reservoirs inside the moons of Solar System gas giants such as Europa, Ganymede,
Titan and Enceladus and more than 335 exoplanets, indicate that the classical definition of the habitable zone concept neglects
more exotic habitats and may fail to be adequate for stars which are different from our Sun. A classification of four habitat
types is proposed. Class I habitats represent bodies on which stellar and geophysical conditions allow Earth-analog planets
to evolve so that complex multi-cellular life forms may originate. Class II habitats includes bodies on which life may evolve
but due to stellar and geophysical conditions that are different from the class I habitats, the planets rather evolve toward
Venus- or Mars-type worlds where complex life-forms may not develop. Class III habitats are planetary bodies where subsurface
water oceans exist which interact directly with a silicate-rich core, while class IV habitats have liquid water layers between
two ice layers, or liquids above ice. Furthermore, we discuss from the present viewpoint how life may have originated on early
Earth, the possibilities that life may evolve on such Earth-like bodies and how future space missions may discover manifestations
of extraterrestrial life. 相似文献