An Exact Anisotropic Quark Star Model

We present an exact analytical solution of the gravitational field equations describing a static spherically symmetric anisotropic quark matter distribution. The radial pressure inside the star is assumed to obey a linear equation of state, while the tangential pressure is a complicated function of the radial coordinate. In order to obtain the general solution of the field equations a particular density profile inside the star is also assumed. The anisotropic pressure distribution leads to an increase in the maximum radius and mass of the quark star, which in the present model is around three solar masses.     

A Model for Contact Binary Systems

A model for contact binary systems is presented, which incorporates the following special features: a) The energy exchange between the components is based on the understand-ing that the energy exchange is due to the release of potential, kinetic and thermal energies of the exchanged mass. b) A special form of mass and angular momentum loss occurring in contact binaries is losses via the outer Lagrangian point. c) The effects of spin, orbital rota-tion and tidal action on the stellar structure as well as the effect of meridian circulation on the mixing of the chemical elements are considered. d) The model is valid not only for low-mass contact binaries but also for high-mass contact binaries. For illustration, we used the model to trace the evolution of a massive binary system consisting of one 12M and one 5M star. The result shows that the start and end of the contact stage fall within the semi-detached phase during which the primary continually transfers mass to the secondary. The time span of the contact stage is short and the mass transfer rate is very large. Therefore, the contact stage can be regarded as a special part of the semi-detached phase with a large mass transfer rate. Both mass loss through the outer Lagrangian point and oscillation between contact and semi-contact states can occur during the contact phase, and the effective temperatures of the primary and the secondary are almost equal.     

Model Estimates of Non-Hydrostatic Stresses in the Martian Crust and Mantle: 2−Three-Level Model

Regions of maximum shear and tension-compression stresses in the Martian interior have been revealed using the three-level compensation model. Nonequilibrium relief, density anomalies at the crust?mantle boundary, and density anomalies at the base of the lithosphere are the sources of the anomalous gravitational field. The thickness of elastic lithosphere positioned on a weak layer that has partially lost its elastic properties varies from 150 to 500 km. The weakening of the layer under the lithosphere is simulated by a tenfold lower value of the shear modulus down to the core boundary. In general, the stresses for the threelevel compensation model differ from the values obtained for the two-level model (nonequilibrium relief and density anomalies at the crust?mantle boundary are the sources of the anomalous gravitational field) by 5?10%. Considerable differences between the models of two-level and three-level compensation are revealed beneath Hellas and Argyre regions.     

Comet Splitting – Observations and Model Scenarios

Splitting events affect cometary nuclei to a different level of severity ranging from complete disruption of the nucleus (e.g., C/1999 S4 LINEAR) to separation of major fragments (e.g., 73P/Schwassmann-Wachmann 3) and spill-offs of smaller boulders (e.g., C/2001 A2 LINEAR).Fragmentation of comets produces secondary products over a wide range of sizes (from cometesimals to sub-micron dust). It is detectable through the presence of fragments (with own comae and tails) in the coma of the parent nucleus, through outbursts in its activity and through arc-lets (“coma wings”)associated with fragments. The secondaries have different life times and show different non-gravitational forces. Nucleus splitting is also considered to generate whole families of comets (Kreutz group) or — if gravitational bound — multiple nuclei (e.g., C/1995 O1 Hale-Bopp). It may explain the striae phenomena seen in dust tails of bright comets (C/1995 O1 Hale-Bopp) and the detection of chains of impact craters onother bodies in the solar system. As process of significant mass loss it is relevant for the scenario of nucleus extinction, at the same time it also plays a role for the number statistics of existing (observable) comets and for the size distribution of comet nuclei. Various model scenarios for nucleus splitting are proposed: tidal disruption, rotational splitting, break-up due to internal gas pressure, fragmentation due to collision with other bodies. Only in one case, Comet D/1993 F1Shoemaker-Levy 9, the physical process of fragmentation could be undoubtedly identified. In any case, comet splitting provides important insights inthe internal structure, surface layering and chemistry of comet nuclei.     

Electrophysical Model of the Moon’s Soil

Solar System Research - Based on the analysis of the data available in the literature on laboratory measurements of the dielectric characteristics of the lunar soil samples delivered to the Earth...     

An Analytic Model of Galactic Winds and Mass Outflows

Galactic winds and mass outflows are observed both in nearby starburst galaxies and in high-redshift star-forming galaxies. We develop a simple analytic model to understand the observed superwind phenomenon with a discussion of the model uncertainties. Our model is built upon the model of McKee & Ostriker for the interstellar medium. It allows one to predict how properties of a superwind, such as wind velocity and mass outflow rate, are related to properties of its starforming host galaxy, such as size, gas density and star formation rate. The model predicts a threshold of star formation rate density for the generation of observable galactic winds. Galaxies with more concentrated star formation activities produce superwinds with higher velocities. The predicted mass outflow rates are comparable to (or slightly larger than) the corresponding star formation rates. We apply our model to both local starburst galaxies and high-redshift Lyman break galaxies, and find its predictions to be in good agreement with current observations. Our model is simple and so can be easily incorporated into numerical simulations and semi-analytical models of galaxy formation.     

An Analytical Model of the Comet's Collision with Jupiter

We employ an simplified analytical model to investigate the wave motion produced by the impact of Comt SL9 on the Jovian atmosphere and,under the assumption that all the kinetic energy of a comet fragment is completely converted in-to the energy of wave motions in the Jovian atmosphere,derive an analytical fromula describing the relation between the resulting wave motion in the atmosphere and the parameters of a comet fragment (the radius,density and speed).     

Solar Dynamo Model with Diamagnetic Pumping and Nonlocal α-Effect

A combination of diamagnetic pumping and a nonlocal α-effect of the Babcock–Leighton type in a solar dynamo model is shown to reproduce observations of solar magnetic activity. The period of the solar cycle can be reproduced without reducing magnetic diffusivity in the bulk of the convection zone below the standard mixing-length value of 10¹³?cm²?s^?1. The simulated global fields are antisymmetric about the equator, and the toroidal-to-poloidal field ratio is about one thousand. However, the time–latitude diagrams of magnetic fields in the model without meridional flow differ from observations. Only when the meridional flow is included and the α-effect profile peaking at mid-latitudes is applied, can the observed butterfly diagrams be reproduced.     

An Impulsive Heating Model for the Evolution of Coronal Loops

It was suggested by Parker that the solar corona is heated by many small energy release events generally called microflares or nanoflares. More and more observations showed flows and intensity variations in nonflaring loops. Both theories and observations have indicated that the heating of coronal loops should actually be unsteady. Using SOLFTM (Solar Flux Tube Model), we investigate the hydrodynamics of coronal loops undergoing different manners of impulsive heating with the same total energy deposition. The half length of the loops is 110 Mm, a typical length of active region loops. We divide the loops into two categories: loops that experience catastrophic cooling and loops that do not. It is found that when the nanoflare heating sources are in the coronal part, the loops are in non-catastrophic-cooling state and their evolutions are similar. When the heating is localized below the transition region, the loops evolve in quite different ways. It is shown that with increasing number of heating pulses and inter-pulse time, the catastrophic cooling is weakened, delayed, or even disappears altogether.     

A Composite Model for GHz Peaked Spectra of Radio Sources

GHz-Peaked Spectrum (GPS) radio sources are powerful and compact sources with convex spectra. With increasing observational findings, it has been realized that either Synchrotron Self-Absorption (SSA) alone or Free-Free Absorption (FFA) alone is not enough to account for all the spectral features. We present a model consisting of an SSA region partially covered by FFA plasma, and derive a composite spectral formula. By applying the model to a sample of 19 GPS sources having strong absorption, it is found that the external FFA process makes the SSA peak frequency linearly shift to a higher (observed) peak frequency. The shift indicates that the FFA does play a role at the frequency close to the observed peak frequency.     

Disk-Corona Model in Active Galactic Nuclei： an Observational Test

We compiled a sample of 98 radio-quiet active galactic nuclei observed by ASCA, Chandra, XMM-Newton, INTEGRAL and Swift with the aim of testing the formation of hot corona and the magnetic shear stress operating in a disk-corona system. We found a strong correlation between the hard X-ray luminosity, bolometric luminosity L Bol and Eddington luminosity LEdd, in the sense that the fraction f of hard X-ray to the bolometric luminosity is inversely proportional to the Eddington ratio. This correlation favors the shear stress tensor being of the form of trφ∝ Pgas, with which the disk-corona structure is stable.     

A Model of the Circumstellar Envelope of Luminous Blue Variables

The continuum energy distributions of the luminous blue variables R127 and R110 in the outburst phase are fitted with a circumstellar envelope model.Both stars show two peaks in their continuum, one near 1250A and the other in the optical band. We suggest that their UV and optical fluxes may have different origins: the UV flux comes from the central star while the optical flux comes from an expanding circumstellar envelope. We construct a model for LBVs consisting of two LTE atmosphere models with different temperatures, and find it to be in agreement with the observed spectral energy distributions of R127 and R110.According to our numerical experiments, R127‘s continuum is composed of fluxes from a circumstellar envelope of Teff = 8000K, R = 485R⊙, and log g = 1,and from a central star of Tef = 17000K, R = 135R⊙, and log g = 2.5 with a permeating factor f = 0.5; while R110‘s continuum can be fitted by a circumstellar envelope of Teff =7000K, R = 350R⊙, and logg = 0.5, and a central star of Teff =25 000 K, R = 27R⊙, and log g 3.0 with a permeating factor f = 0.65.Both models show that the non-spherically symmetric, optically thick regions are formed surrounding the central star in the outburst phase. The light of the central star is shielded by the circumstellar envelope so that the visual brightness increases with the decrease/increase of the temperature/radius of the optically thick regions.     

A Model of the Mira–Type Star T UMi

Stellar evolution calculations were carried out from the main sequence to the final stage of the asymptotic giant branch for stars with initial masses 1 M_⊙ ≤ M_ZAMS ≤ 2 M_⊙ and metallicity Z = 0.01. Selected models of evolutionary sequences were used as initial conditions for solution of the equations of radiation hydrodynamics and time–dependent convection describing radial stellar pulsations. The study was aimed to construct the hydrodynamic models of Mira–type stars that show the secular decrease in the pulsation period Π commenced in 1970th at Π = 315 day. We show that such a condition for the period change is satisfied with evolutionary sequences 1 M_⊙ ≤ M_ZAMS ≤ 1.2 M_⊙ and the best agreement with observations is obtained for M_ZAMS = 1.2 M_⊙. The pulsation period reduction is due to both the stellar radius decrease during the thermal pulse of the helium burning shell and mode switch from the fundamental mode to the first overtone. Theoretical estimates of the fundament parameters of the star at the onset of pulsation period reduction are as follows: the mass is M = 0.93 M_⊙, the luminosity is L = 4080 L_⊙, and the radius is R = 220 R_⊙. The mode switch occurs 35 years after the onset of period reduction.     

An Annular Gap Acceleration Model for γ-ray Emission of Pulsars

If the binding energy of the pulsar's surface is not so high (the case of a neutron star), both negative and positive charges will flow out freely from the surface of the star. An annular free flow model for γ-ray emission of pulsars is suggested. It is emphasized that: (1) Two kinds of acceleration regions (annular and core) need to be taken into account. The annular acceleration region is defined by the magnetic field lines that cross the null charge surface within the light cylinder. (2) If the potential drop in the annular region of a pulsar is high enough (normally the case for young pulsars), charges in both the annular and the core regions could be accelerated and produce primary gamma-rays. Secondary pairs are generated in both regions and stream outwards to power the broadband radiations. (3) The potential drop grows more rapidly in the annular region than in the core region. The annular acceleration process is a key process for producing the observed wide emission beams. (4) The advantages of both the polar cap and outer gap models are retained in this model. The geometric properties of the γ-ray emission from the annular flow are analogous to that pre-sented in a previous work by Qiao et al., which match the observations well. (5) Since charges with different signs leave the pulsar through the annular and the core regions respectively, the current closure problem can be partially solved.     

A Friedmann-Lemaître Universe Model with a Positive Cosmological Constant

The possibility of using a Friedmann-Lemaître model with a non-zero cosmological constant is investigated on the basis of analyses of the RATAN-600 and 87GB radio surveys and optical constraints. A zero deceleration parameter and critical matter density are features of the model. The model is in agreement with current observational data, including estimates of the age of the Universe, Hubble constant measurements, and the - z relation. A value for the cosmological constant is determined and its physical nature discussed.     

Prowess – A Software Model for the Ooty Wide Field Array

One of the scientific objectives of the Ooty Wide Field Array (OWFA) is to observe the redshifted Hi emission from z ～ 3.35. Although predictions spell out optimistic outcomes in reasonable integration times, these studies were based purely on analytical assumptions, without accounting for limiting systematics. A software model for OWFA has been developed with a view to understanding the instrument-induced systematics, by describing a complete software model for the instrument. This model has been implemented through a suite of programs, together called Prowess, which has been conceived with the dual role of an emulator as well as observatory data analysis software. The programming philosophy followed in building Prowess enables a general user to define an own set of functions and add new functionality. This paper describes a co-ordinate system suitable for OWFA in which the baselines are defined. The foregrounds are simulated from their angular power spectra. The visibilities are then computed from the foregrounds. These visibilities are then used for further processing, such as calibration and power spectrum estimation. The package allows for rich visualization features in multiple output formats in an interactive fashion, giving the user an intuitive feel for the data. Prowess has been extensively used for numerical predictions of the foregrounds for the OWFA Hi experiment.     

Effects of Magnetic Fields on Neutrino-dominated Accretion Model for Gamma-ray Bursts

Many models of gamma-ray bursts suggest a common central engine:a black hole of several solar masses accreting matter from a disk at an accretion rate from 0.01 to 10 M_⊙s~(-1),the inner region of the disk is cooled by neutrino emission and large amounts of its binding energy are liberated,which could trigger the fireball.We improve the neutrino- dominated accreting flows by including the effects of magnetic fields.We find that more than half of the liberated energy can be extracted directly by the large-scale magnetic fields in the disk,and it turns out that the temperature of the disk is a bit lower than the neutrino-dominated accreting flows without magnetic field.Therefore,the outflows are magnetically-dominated rather than neutrino dominated.In our model,the neutrino mechanism can fuel some GRBs (not the brightest ones),but cannot fuel X-ray flares.The magnetic processes(both BZ and electromagnetic luminosity from a disk)are viable mechanisms for most of GRBs and their following X-ray flares.     

A Check on the Cardassian Expansion Model with Type-la Supernovae Data

We use the magnitude-redshift relation for the type la supernova data compiled by Riess et al. to analyze the Cardassian expansion scenario. This scenario assumes the universe to be flat, matter dominated, and accelerating, but contains no vacuum contribution. The best fitting model parameters are H0 = 65.3kms-1 Mpc-1, n=0.35 and (?)m = 0.05. When the highest redshift supernova, SN 1997ck, is excluded, H0 remains the same, but n becomes 0.20 and (?)m, 0.15, and the matter density remains unreasonably low. Our result shows that this particular scenario is strongly disfavoured by the SNela data.     

Cylindrical Jet—Wind interaction Model of Gamma—Ray Burst Afterglows

Observations on relativistic jets in radio galaxies, active galactic nuclei, and "microquasars" revealed that many of these outflows are cylindrical, not conical. So it is worthwhile to investigate the evolution of cylindrical jets in gamma-ray bursts. We discuss afterglows from cylindrical jets in a wind environment. Numerical results as well as analytic solutions in some special cases are presented. Our light curves are steeper compared to those in the homogeneous interstellar medium case, carefully considered by Cheng, Huang & Lu. We conclude that some afterglows, used to be interpreted as isotropic fireballs in a wind environment, can be fitted as well by cylindrical jets interacting with a wind.     

Properties of Optical and X-ray Selected AGN-Probing the Unified Model of AGN

1 .Introduction1 .1　TheUnifiedModelofAGNThereisawidearrayofapparentlydiversetypesofActiveGalacticNuclei(AGN) .InarecentapproachthesedifferenttypesareexplainedwithinoneUnifiedModel(seereviewse .g .byUrry&Padovani 1 995,Wills 1 999) .Amajorideaofthismodelisthatthecentralengineandthebroadlineregionarepartiallyobscured ;differentappearancesoftheAGNmaybetheresultofviewingsimilarcentralenginesatdifferentorientations theviewingangleisaprimaryparameter.1 .2　TheSampleInordertostudytheAGNphe…