Triple encounters in the linear three-body problem with equal masses     

V. V. Orlov  A. V. Petrova  A. I. Martynova 《Astronomy Reports》2002,46(11):932-941

The paper considers triple encounters in the linear three-body problem for the case of equal masses. Triple encounters are described using two parameters: the virial coefficient k and the angle ? such that tan $\varphi = \dot r/\dot \rho$ , where $\dot r$ and $\dot \rho$ are the velocities of the “central” body relative to each of the “outer” bodies. The equations of motion are integrated numerically up to one of the following times: the time for a receding body to turn, the time for this body to reach some critical distance, the time for some escape criterion to be fulfilled, or to some critical time. Evolutionary scenarios for the triple system are determined as a function of the initial conditions. The dependences of the ejection length on k and $\dot \varphi$ are derived. The initial conditions corresponding to escape form a continuous region with k>0.5. The regions into which the right and left bodies depart alternate and are symmetrical about the lines of triple close encounters (?=45°,225°). Regions of stable motions in the vicinity of the central periodic orbit of Schubart (k?0.206; ?=135°,315°) are identified. Linear structures emanate from the peak of the region of stability, which divide the region for the initial conditions into alternating zones with identical evolutionary scenarios.  相似文献   

Dynamical stability of triple stars     

V. V. Orlov  A. V. Petrova 《Astronomy Letters》2000,26(4):250-260

The dynamical stability of 38 observed hierarchical triple stars with known orbital elements of the internal and external binary subsystems and component masses is considered. Four different criteria of dynamical stability are used. The observed stability parameters and their critical values are calculated by taking into account errors in the orbital elements and component masses. Most triple systems are stable. According to some criteria, several triple stars (ADS 440, ξ Tau, λ Tau, ADS 3358, VV Ori, ADS 10157, HZ Her, Gliese 795, ADS 15971, and ADS 16138) may be dynamically unstable. This result is probably associated with unreliability of the empirical stability criteria and/or with errors in the observed quantities.  相似文献   

Mental preparation for climate adaptation: The role of cognition and culture in enhancing adaptive capacity of water management in Kiribati   总被引：3，自引：0，他引：3  

Natasha Kuruppu^{Author Vitae}  Diana LivermanAuthor Vitae 《Global Environmental Change》2011,21(2):657-669

In many Least Developed Countries (LDCs) and Small Island Developing States (SIDS), such as in Kiribati, formal national adaptation programmes are currently being operationalised or are in the pipeline. A key focus is on motivating householders to adapt in anticipation of climate change through pilot community projects. In this paper, we argue that the water sector must pay equal attention to how communities cognitively perceive the process of adaptation if interventions are to be effective. Adopting a cognitive model to gain such insights we conclude that individual's belief in their own abilities to manage water stress play a crucial role in driving intentions to adapt and therefore greater attention needs to be placed on understanding the underling drivers shaping such beliefs.  相似文献   

The effect of synchrotron absorption on the observed radio luminosities of pulsars     

S. A. Petrova 《Monthly notices of the Royal Astronomical Society》2002,336(3):774-784

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Polarimetry of Mars in High-Transparency Periods: How Reliable Are the Estimates of Aerosol Optical Properties?     

Dlugach  Zh. M.  Petrova  E. V. 《Solar System Research》2003,37(2):87-100

The influence of various factors on the interpretation of polarimetric observations of Mars performed under high-transparency atmospheric conditions was investigated. It was demonstrated that the technique proposed by Morozhenko (1974) for the data interpretation does not allow the optical characteristics of cloud particles to be estimated unambiguously. In particular, it turns out that both the model of a thin layer composed of very small silicate particles and the model of very small ice particles in a thin layer fit the data of measurements at a phase angle of 25°. Numerical simulations showed that reliable information on the reflectance characteristics of the Martian surface in a wide spectral range, including blue and ultraviolet wavelengths, is necessary to obtain reliable estimates of aerosol optical properties. Our calculations confirmed that the scattering on ice-cloud particles could introduce a significant ambiguity in the interpretation of the available polarimetric data. Besides, small particles, both ice and silicate, existing in the upper atmospheric layer can substantially mask the layer of larger particles below, which becomes invisible for remote sensing.  相似文献   

Comparison of stellar orbits in various models of the galaxy     

S. Ninković  V. V. Orlov  A. V. Petrova 《Astronomy Letters》2002,28(3):163-168

We compare the properties of orbits in five different rotationally symmetric models of the regular Galactic force field. Our goal is to estimate the possible range of the discrepancies in stellar orbital elements attributable to the choice of the model for the Galactic potential. For disk objects, the discrepancies in eccentricities e attributable to the choice of the model do not exceed 0.05. The relative distances h from the symmetry plane can differ by more than a factor of 2. Since there are resonance regions, the types of orbits (box-shaped or tube-shaped) cannot be reliably identified. The situation is even worse for halo objects: the discrepancies in h can exceed 100%, and identifying the type of orbits is also highly problematic.  相似文献   

Use of an Analytical Theory for the Physical Libration of the Moon to Detect Free Nutation of the Lunar Core     

Petrova  N. K.  Nefedyev  Yu. A.  Zagidullin  A. A.  Andreev  A. O. 《Astronomy Reports》2018,62(12):1021-1025

A brief review of modern observational achievements and the theoretical basis of physical libration of the Moon is presented. Special attention is given to the inferred existence of a lunar core and determination of its parameters. The creation of a theory of physical libration of the Moon, which requires analyses of semi-empirical series of long-term laser observations and the use of the highly accurate DE421 dynamical ephemeris, is related to this. A large role in this area has been played by the analytical theory of physical libration of the Moon constructed by Yu.V. Barkin, which made it possible for the first time to derive parameters of the free nutation of the lunar core from observations. This paper is based on a talk given at the conference “Modern Astrometry 2017,” dedicated to the memory of K.V. Kuimov (Sternberg Astronomical Institute, Moscow State University, October 23–25, 2017).

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Biomass allometric equation and expansion factor for a mountain moist evergreen forest in Mozambique     

Sá Nogueira Lisboa  Benard Soares Guedes  Natasha Ribeiro  Almeida Sitoe 《Carbon balance and management》2018,13(1):23

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Computer simulation of observations of stars from the moon using the polar zenith telescope of the Japanese project ILOM     

N. K. Petrova  H. Hanada 《Solar System Research》2013,47(6):463-476

The paper briefly describes the purpose and features of the Japanese project ILOM (In-situ Lunar Orientation Measurement) in which it is planned to install the zenith telescope with a CCD lens on one of the poles of the Moon for the observation of stars in order to determine the physical libration of the Moon (PhLM). The studies presented in this paper are the result of the first stage of the theoretical support of the project:

1. The compilation of the list of stars within the field of view of the telescope during the precessional motion of the lunar pole.
2. Modeling and analysis of the behavior of stellar tracks during the observation period.
3. Simulation and testing of the sensitivity of the measured selenographic star coordinates to changes in the parameters of the dynamic model of the Moon and the elastic parameters of the lunar body.

Direct and inverse PhLM problems are discussed. Within the scope of the direct problem visible “daily parallels” and one-year star tracks are calculated. Their behavioral features when observed from the lunar surface are shown. At this stage of the simulation selenographic star coordinates for the four models of the gravitational field of the Moon have been compared, i.e., the model constructed on the basis of the lunar laser ranging (LLR), GLGM-2, LP150Q, and SGM100h. It is shown that even when comparing modern models LP150Q and SGM100h stellar tracks differ from the arc by more than 10 ms of arc. At the stage of the inverse problem, the manifestation of viscoelastic properties of the Moon in selenographic coordinates has been studied. In the spectrum of the simulated residual differences harmonics have been identified which can serve as indicators to refine parameters, Love number k ₂ and the delay time characterizing the viscous properties of the lunar body.  相似文献   

Light scattering by morphologically complex objects and opposition effects (a review)     

E. V. Petrova  V. P. Tishkovets 《Solar System Research》2011,45(4):304-322

Over the last decade, considerable progress has been achieved in the theory of light scattering by morphologically complex objects, which extends the potential of correct interpretation of photometric and polarimetric observations. This especially concerns the backscattering domain, where the opposition effects in brightness and polarization are observed. Although the equations of radiative transfer and weak localization (coherent backscattering) are rigorously valid only for sparse media, the results of exact computer solutions of the Maxwell equations for a macroscopic volume filled with randomly positioned particles show that their application area can be wider. In particular, the observations can be correctly interpreted if the packing density of particles in the medium reaches 20–30%. The recently suggested approximate solution of the coherent backscattering problem allowed interesting effects in the spectra of Saturn’s satellites to be explained. In the densely packed media, the effects that are impossible in the sparse media and caused by the near-field contribution can be observed. To calculate the characteristics of radiation reflected by such a medium, it is not sufficient to solve the radiative transfer and weak localization equations, even if they are written in a form without the far-zone limitations. Nowadays, the influence of the interaction of particles in the near field can be analyzed only for the restricted ensembles of particles. It shows that the substantial increase of the packing density essentially changes the phase functions of intensity and polarization in the backscattering domain. This allows the packing density of particles in the medium and their absorbing properties to be estimated from the shape of the phase curves measured. However, the task of quantitative interpretation of the measurements of radiation reflected by a densely packed medium, in terms of sizes of particles, their refractive index, and packing density, still remains unsolved.  相似文献