Research on the Stability of the Circular Restricted Three-body Problem with Radiation and Oblateness

The velocity scaling factor method based on the least squares principle is regarded as the most efficient, stable, and widely-used method among all the manifold correction methods. The stability of the restricted three-body problem where the primary body is a source of radiation and the secondary body is an oblate spheroid is discussed by using the velocity scaling factor method. The numerical simulations suggest that (1) the number of the chaotic orbits will increase if only the oblate spheroid perturbation is considered; (2) the number of the regular orbits will increase if only considering the radiation pressure; (3) when both the radiation and oblateness perturbation exist, the radiation plays a dominant role, and the probability of regular motion of the system will increase.     

A Visual Method of Time Scale Determination using a PC for Radio Sources

Variability is one of the extremely observational properties. In the radio bands, variability is caused by the shock in the jet. In this case, emissions increase rapidly following an exponential curve, and then decrease rapidly also in an exponential curve. The variability time scale is important with regard to the physics carrying on in the jet. However, it is not easy to fit the light curve. In this paper, we proposed a method of light curve fitting on a PC machine, in which the theoretical exponential light curve is adopted to the observations using the least regression method. Using this method, anybody can fit the light curve and get the time scale by moving and clicking the mouse. We also used this method to some light curves obtained from the archive and compared our results with those in the literature.     

Hydromagnetic flow past a continuously moving semi-infinite plate for large suction

The similarity solution for hydromagnetic flow of an incompressible viscous electrically conducting fluid past a continuously moving semi-infinite porous plate in the presence of a magnetic field has been obtained for the case of small magnetic Reynolds number. The perturbation method has been used to solve the similarity equations at large suction. The resulting equations have been solved by analytical method. The effect of the magnetic parameter is to increase the skin-friction coefficient while it has no significant effect on the Nusselt number.     

On the possibility of investigation of the magnetic field structure in subphotospheric layers of the Sun according to observations of sunspot torsional oscillations

A method of investigation of the magnetic field structure in subphotospheric layers of the Sun has been developed. The method is based on observations of the torisonal oscillations of single sunspots. Characteristics of the torsional oscillations have been obtained from observations of the longitudinal magnetic field and radial velocities of seven single sunspots in the photospheric line Fe I λ5253 Å. The parameters of the torsional oscillations and magnetic tubes in the deep layers have been determined. The radius of the cross section of a magnetic flux tube forming a sunspot is greatest near the Sun’s surface and is approximately equal to the radius of a sunspot umbra. Down to the deeper layers, it decreases quite quickly. The longitudinal electric current appearing in the magnetic tube changes direction. The typical time of the current changes is determined by the period of the torsional oscillations. The intensity of the longitudinal magnetic field in the tube increases with depth. The Alfven wave velocity averaged over the length of a magnetic tube is tens or hundreds of times less than this velocity in a sunspot umbra. It decreases with an increase in the period of oscillations. A decrease in the Alfven wave velocity leads to an increase in the twisting angle of magnetic field lines.     

Equilibrium structure of stars with radiation pressure in the presence of a magnetic field

Equilibrium configuration of the upper Main-Sequence stars, with significant radiation pressure and having an interior magnetic field (matching with an external dipole field) has been cosidered. The structural parameters have been calculated for low and high magnetic fields by using a first-order perturbation method and a modified perturbation technique respectively. With the increase of radiation pressure, the star is seen to become more centrally condensed.     

A Kalman Filter Technique for Improving Medium-Term Predictions of the Sunspot Number

In this work we describe a technique developed to improve medium-term prediction methods of monthly smoothed sunspot numbers. Each month, the predictions are updated using the last available observations (see the monthly output in real time at ). The improvement of the predictions is provided by applying an adaptive Kalman filter to the medium-term predictions obtained by any other method, using the six-monthly mean values of sunspot numbers covering the six months between the last available value of the 13-month running mean (the starting point for the predictions) and the “current time” (i.e. now). Our technique provides an effective estimate of the sunspot index at the current time. This estimate becomes the new starting point for the updated prediction that is shifted six months ahead in comparison with the last available 13-month running mean, and it provides an increase of prediction accuracy. Our technique has been tested on three medium-term prediction methods that are currently in real-time operation: The McNish–Lincoln method (NGDC), the standard method (SIDC), and the combined method (SIDC). With our technique, the prediction accuracy for the McNish–Lincoln method is increased by 17 – 30%, for the standard method by 5 – 21% and for the combined method by 6 – 57%.     

Flow behind an attached shock wave in a radiating gas

A simple method is used to determine the curvature of an attached shock wave and the flow variable gradients behind the shock curve at the tip of a straight-edged wedge placed symmetrically in a supersonic flow of a radiating gas near the optically thin limit. The shock curvature and the flow variable gradients along the wedge at the tip are computed for a wide range of upstream flow Mach numbers and wedge angles. Several interesting results are noted; in particular, it is found that the effect of an increase in the upstream flow Mach number or the radiative flux is to enhance the shock wave curvature which, however, decreases with an increase in the specific heat ratio or the wedge angle.     

Mass model of spiral galaxies disk

The study of rotation curves is the most powerful tool for determining mass distributions inside spiral galaxies. Since the first trial by Burbidgeet al. (1959), followed by Brandt (1960), few methods have been proposed for the determination of the masses of galaxies (Faber and Gallagher, 1979). Monnet and Simien (1977) recently proposed a method based on a two component model (bulge and disk) which permits to compute the total mass providing that the photometry is well-known. We suggest here a method based on a new simple parametrization of the optical rotation curve. This method indicates disk masses substantially higher than the provious estimates and suggests an exponential increase of theM/L ratio in the disk toward the outer parts of the Galaxies.     

Acceleration feedback control(AFC) enhanced by disturbance observation and compensation(DOC) for high precision tracking in telescope systems

In this paper, a cascade acceleration feedback control(AFC) enhanced by a disturbance observation and compensation(DOC) method is proposed to improve the tracking precision of telescope systems.Telescope systems usually suffer some uncertain disturbances, such as wind load, nonlinear friction and other unknown disturbances. To ensure tracking precision, an acceleration feedback loop which can increase the stiffness of such a system is introduced. Moreover, to further improve the tracking precision, we introduce the DOC method which can accurately estimate the disturbance and compensate it. Furthermore,the analysis of tracking accuracy used by this method is proposed. Finally, a few comparative experimental results show that the proposed control method has excellent performance for reducing the tracking error of a telescope system.     

On the applicability of Goldberg and Unno's method to the determination of microturbulent velocities in an atmosphere with convection

The method of Goldberg and Unno for the determination of microturbulent velocities in a stellar atmosphere is only applicable if there are no macroturbulent or convective motions.If such motions occur, as in the solar photosphere, the derived results are false and may lead to misinterpretations such as an increase of the microturbulent velocity with depth or anisotropic microturbulence.     

A Research on the Pulsar Timing Based on Kalman Filtering

The pulsar is a high-speed rotationing neutron star with a stable rotational period, being not disturbed and destroyed artificially, and can be taken as the reference quantity of the absolute time. In this article a kind of pulsar time service method based on the Kalman filtering algorithm is proposed, and the simulation analysis of the clock error control based on the Kalman filtering and of the effect of the pulsar catalogue error and the measuring accuracy of the pulsar time of arrival (TOA) on the accuracy of time service is made by taking a certain solar synchronous orbit as an example. The result shows that by utilizing this method the clock error of the satellite-borne clock can be effectively eliminated and its time-dependent increase is restrained, thereby solving the problem that the accuracy of the spacecraft-borne low cost clock can not meet the needs.     

Fast magnetoacoustic solitary waves in dense magnetoplasmas in a cylindrical geometry

Nonlinear properties of the quantum magnetoacoustic wave are studied in electron-ion magnetoplasmas. In this regard, cylindrical Korteweg deVries (CKdV) equation is derived for small amplitude perturbations. The solution of the planar KdV equation is obtained using the tanh method and is subsequently used as an initial profile to solve the CKdV equation. It is found that the system under consideration admits compressive solitary structures. Finally, it is found that the amplitude as well as the width of the nonplanar magnetosonic solitary structure increases with the increase in the magnetic field whereas a decrease is observed with the increase in number density of the system. The present study may be beneficial to understand the nonlinear wave propagation in nonplanar geometries in dense plasmas.     

Pre-industrial-potential and Last Glacial Maximum global vegetation simulated with a coupled climate-biosphere model: diagnosis of bioclimatic relationships

The global climate–vegetation model HadSM3_TRIFFID has been used to estimate the equilibrium states of climate and vegetation with pre-industrial and last glacial boundary conditions. The present study focuses on the evaluation of the terrestrial biosphere component (TRIFFID) and its response to changes in climate and CO₂ concentration. We also show how, by means of a diagnosis of the distribution of plant functional types according to climate parameters (soil temperature, winter temperature, growing-degree days, precipitation), it is possible to get better insights into the strengths and weaknesses of the biosphere model by reference to field knowledge of ecosystems.The model exhibits profound changes between the vegetation distribution at the Last Glacial Maximum and today that are generally consistent with palaeoclimate data, such as the disappearance of the Siberian boreal forest (taiga), an increase in shrub cover in Europe and an increase of the subtropical desert area. The effective equatorial and sub-tropical tree area is reduced by 18%. There is also an increase in cover of wooded species in North-Western Africa and in Mexico. The analysis of bioclimatic relationships turns out to be an efficient method to infer the contributions of different climatic factors to vegetation changes, both at high latitudes, where the position of the boreal treeline appears in this model to be more directly constrained by the water stress than by summer temperature, and in semi-humid areas where the contributions of temperature and precipitation changes may partly compensate each other. Our study also confirms the major contribution of the decrease in CO₂ to environmental changes and carbon storage through its selective impact on gross primary productivity of C3 and C4 plants and a reduction by 25% of water-use efficiency. Specifically, the reduction in CO₂ concentration increases the amount of precipitation necessary to sustain at least 20% of grass fraction by 50 mm/year; the corresponding threshold for trees is increased by about 150 mm/year. As a consequence, a reduction in CO₂ concentration considerably widens the climatic range where grasses and shrubs dominate.     

Estimations of orbital parameters of exoplanets from transit photometry by using dynamical constraints

The probability of the detection of Earth-like exoplanets may increase in the near future after the launch of the space missions using the transit photometry as observation method. By using this technique only the semi-major axis of the detected planet can be determined, and there will be no information on the upper limit of its orbital eccentricity. However, the orbital eccentricity is a very important parameter, not only from a dynamical point of view, since it gives also information on the climate and the habitability of the Earth-like planets. In this paper a possible procedure is suggested for confining the eccentricity of an exoplanet discovered by transit photometry if an already known giant planet orbits also in the system.     

Coupling between the F-region and protonosphere: Numerical solution of the time-dependent equations

This paper describes a new method of solution of the time-dependent continuity and momentum equations for H⁺ and O⁺ in mid-latitude magnetic field tubes from the F-region to the equator. For each ion the equations are expressed as an integro-differential equation. This equation is treated as an ordinary differential equation and solved by a searching method. By means of this method, the distribution of H⁺ in the O⁺?H⁺ transition region and the protonosphere can be investigated and the influence of H⁺ fluxes on the F layer examined.As an example of application of the method a suggestion by Park (1971) about observed night-time enhancements of N_mF2 is examined. He suggested that lowering of the F layer some hours after a magnetic substorm may cause N_mF2 to increase because of increased ion influx from the protonosphere. In the present calculations the Flayer is maintained around a constant height for some time and then abruptly lowered. Under the conditions adopted the resulting increase in downward H⁺ flux is sufficient to maintain N_mF2 against the increased recombination but not to increase N_mF2 significantly. It is emphasised that these results are not conclusive.     

A Method for Determining the Coordinates of Meteor Shower Radiants from Meteor Radar Goniometric Data

We discuss a new method for measuring the coordinates of meteor shower radiants from meteor radar data. The method uses a high accuracy of radar goniometer measurements of one of the angular coordinates for meteor radiants and collective properties of incident meteor showers. It is based on a computer technology of searching for the coordinates of radiants using the intersections of meteor position lines on the celestial sphere and filtering nonrandom combinations of these intersections. The method allows the following: to detect meteor showers with a rate of more than 5 per day of observations and to separate meteor groups from different meteor showers with different radiants and velocities. The method makes it possible to increase the angular resolution from 10° × 10° achieved with a quasi-tomographic technique to 2° × 2°, with a prospect of a further increase in the accuracy through the individual reduction of separated meteor groups. We use the reduction of one-day-long observations during maximum activity of the Geminids meteor shower in 1993 to illustrate the potentialities of the method. We show an example of detecting a weak meteor shower that was active during December 1993.     

Equilibrium Chemistry in a Brown Dwarf's Atmosphere: Cesium in Gliese 229B

We investigate the effect of hydrostatic scale heights lambda(T) in coronal loops on the determination of the vertical temperature structure T&parl0;h&parr0; of the solar corona. Every method that determines an average temperature at a particular line of sight from optically thin emission (e.g., in EUV or soft X-ray wavelengths) of a mutlitemperature plasma is subject to the emission measure-weighted contributions dEM&parl0;T&parr0;&solm0;dT from different temperatures. Because most of the coronal structures (along open or closed field lines) are close to hydrostatic equilibrium, the hydrostatic temperature scale height introduces a height-dependent weighting function that causes a systematic bias in the determination of the temperature structure T&parl0;h&parr0; as function of altitude h. The net effect is that the averaged temperature seems to increase with altitude, dT&parl0;h&parr0;&solm0;dh>0, even if every coronal loop (of a multitemperature ensemble) is isothermal in itself. We simulate this effect with differential emission measure distributions observed by SERTS for an instrument with a broadband temperature filter such as Yohkoh/Soft X-Ray Telescope and find that the apparent temperature increase due to hydrostatic weighting is of order DeltaT approximately T0h&solm0;r middle dot in circle. We suggest that this effect largely explains the systematic temperature increase in the upper corona reported in recent studies (e.g., by Sturrock et al., Wheatland et al., or Priest et al.), rather than being an intrinsic signature of a coronal heating mechanism.     

Determining chondrule size distributions from thin-section measurements

Abstract— A method is described for correcting thin-section-derived chondrule sizes for three common sources of bias: (1) the non-equatorial sectioning of chondrules, (2) the non-zero thickness of thin sections, and (3) the unequal probability of sectioning different size chondrules. Application of the correction procedure to chondrule data from CO chondrites results in a reduction of mean and median chondrule diameters, an increase in minimum diameters, and transforms nearly log-normal distributions to distributions that conform to a Weibull probability function. The Weibull-function form of CO chondrule size distributions is similar to the form of chondrule distributions in ordinary chondrites obtained by disaggregation analyses.     

Photographic photometry of the eclipsing binary ad bootes

A detailed two colour (BV) photoelectric photometry of the late-type eclipsing binary AD BOO was carried out in 1981 April–May. We found its period to be 2.0688112 d, double what was thought previously. The light curve outside the eclipses is basically flat with Irregular fluctuations of ˜0.075 mag. It is basically an Algol-type curve, with a principal minimum of 0.65 mag and a secondary minimum of 0.40 mag. The O-C diagram of the minimum epoch shows that the period has tended to increase. The photometric solution by the classical Russel-Merrill method gives k = 0.786. The principal minimum corresponds to a partial eclipse of the transit type.     

Variable inertia method: A novel numerical method for mantle convection simulation

3D numerical simulations have been very useful for the understanding of mantle convection of the earth. In almost all previous simulations of mantle convection, the (extended) Boussinesq approximation has been used. This method is implicit in the sense that buoyancy force and viscosity are balanced, and allows the use of long timesteps that are not limited by the CFL condition. However, the resulting matrix is ill-conditioned, in particular since the viscosity strongly depends on the temperature. It is not well-suited to modern large-scale parallel machines.In this paper, we propose an explicit method which can be used to solve the mantle convection problem. If we can reduce the sound speed without changing the characteristics of the flow, we can increase the timestep and thus can use the explicit method. In order to reduce the sound speed, we multiplied the inertia term of the equation of motion by a large and viscosity-dependent coefficient. Theoretically, we can expect that this modification would not change the flow as long as the Reynolds number and the Mach number are sufficiently smaller than unity. We call this method the variable inertia method (VIM).We have performed an extensive set of numerical tests of the proposed method for thermal convection, and concluded that it works well. In particular, it can handle differences in viscosity of more than five orders of magnitude.