On coherent scattering in stellar atmospheres

An exact solution of the transfer equation for coherent scattering in stellar atmospheres with Planck's function as a sum of elementary functions, is obtained in a simple form with the help of the author's new representation of H-functions of Radiative Transfer.     

On the effect of anisotropy on stellar models

The relevance of anisotropy in compact models is shown by the construction of a stellar model, this can influence the behavior of density, pressure and speed of sound in such grade that if the anisotropy disappear it could produce a regular model of perfect fluid which is not physically acceptable. The present anisotropic model has dependence in two parameters n associated with the anisotropy and w related with the rate of compactness \(u=GM/c^2R\), this is regular and physically acceptable. That is the speed of sound is positive and lower than the light speed, the density as well as radial and tangential pressure are monotonic decrescent functions. The compactness values for which the radial and tangential speed of sound are monotonic decrescent functions and the solution is potentially stable occurs for \(u\le 0.2073450586\), and in particular for the maximum value of u \(n\in [-0.771108398\), \(-0.231572621]\). While if \(n=1\) we get a model of perfect regular fluid but the density and speed of sound can not be both positive at the origin, so the solution is not physically acceptable in the absence of anisotropic pressures.     

Simulations of stellar convection with CO5BOLD

High-resolution images of the solar surface show a granulation pattern of hot rising and cooler downward-sinking material – the top of the deep-reaching solar convection zone. Convection plays a role for the thermal structure of the solar interior and the dynamo acting there, for the stratification of the photosphere, where most of the visible light is emitted, as well as for the energy budget of the spectacular processes in the chromosphere and corona. Convective stellar atmospheres can be modeled by numerically solving the coupled equations of (magneto)hydrodynamics and non-local radiation transport in the presence of a gravity field. The CO5BOLD code described in this article is designed for so-called “realistic” simulations that take into account the detailed microphysics under the conditions in solar or stellar surface layers (equation-of-state and optical properties of the matter). These simulations indeed deserve the label “realistic” because they reproduce the various observables very well – with only minor differences between different implementations. The agreement with observations has improved over time and the simulations are now well-established and have been performed for a number of stars. Still, severe challenges are encountered when it comes to extending these simulations to include ideally the entire star or substellar object: the strong stratification leads to completely different conditions in the interior, the photosphere, and the corona. Simulations have to cover spatial scales from the sub-granular level to the stellar diameter and time scales from photospheric wave travel times to stellar rotation or dynamo cycle periods. Various non-equilibrium processes have to be taken into account. Last but not least, realistic simulations are based on detailed microphysics and depend on the quality of the input data, which can be the actual accuracy limiter. This article provides an overview of the physical problem and the numerical solution and the capabilities of CO5BOLD, illustrated with a number of applications.     

Effects of electric fields on thermal convection in gases

Summary Extensive measurements of the coefficient of electroconvective heat transfer have been carried out in gases: air, Ar, N₂, O₂, freon-12 and freon-22, using a single platinum wire mounted along the axis of a copper cylinder. The diameter of the cylinder was 53 mm, while that of the wire was 0.025 mm. Electroconvective heat transfer coefficients have been measured as a function of electric field, pressure, orientation and frequency of the applied electric field in the earth's gravitational field. The results reveal a complicated interaction between the electric-field gradient and thermal convection. The present work indicates that the Senftleben mechanism alone cannot account for the observed phenomena.     

On the energy in relativistic stellar dynamics

Using the results of the preceding paper we evaluate in the post-Newtonian approximation the energy integral for a system of extended bodies with arbitrary internal structure and internal motions.On leave of absence from the Astronomy Department, University of Thessaloniki, Thessaloniki, Greece.     

The role of gravitational fields in stellar physics and the evolution of the universe

The assertion that the gravitational field is a material matter with all the attributes of any other matter (energy density, pressure, four-velocity of the elements, and interaction of the elements with one another and with other material objects) is shown to modify the physical notions of the dynamics of bodies, Riemannian space, the internal structure of a star, the evolution of the universe, etc. Instead of the black holes of the geometrized approach to the theory of gravitation, we have objects with a researchable internal structure, which explains, e.g., the observed attenuation of the boundaries of the emission spectra of matter that falls into supermassive objects. The problem of dark matter is explained. The generally accepted understanding of matter (without adding any free parameters to the theory) is shown to allow a scenario of the universe that is permanently pulsating between the states of the maximum and minimum density of matter. The scenario is shown to be in good agreement with the recent observational data.     

The greenhouse effect of planetary atmospheres

Summary The greenhouse effect of the atmosphere is the main factor of possible climate changes of anthropogenic origin. The growing pollution of the atmosphere leads to an increase of the concentration of such gaseous components as sulphur and carbon dioxides, carbon oxide, halocarbons, nitrous oxides, etc. Of great importance is also the consideration of the aerosols, both injected directly into the atmosphere and formed as a result of the conversion of chemical gas into particles (first of all, it concerns the sulphate aerosol). All the above gaseous components, as well as aerosols, have the absorption bands in the IR spectral range, which determines their contribution to the greenhouse effect of the atmosphere, mainly governed by water vapour and carbon dioxide. The traditional attention to the problem of the CO₂ contribution to the greenhouse effect has somewhat overshadowed the significance of the different components. The data characterizing the significance of the different components of the greenhouse effect are considered. The results of studying the absorption spectra of methane, nitrous oxides, sulphuric gas, ammonia, nitric-acid vapours and other components are discussed. The assessments of their contribution to the greenhouse effect are given. The important role of the small-size fraction of the atmospheric aerosols as a factor of the greenhouse effect is discussed. Both the analysis of the causes of the Earth's climate variability and the relevant investigation of the atmospheric greenhouse effect determine the expediency of analysing the conditions of the greenhouse effect formation on other planets, that is the consideration of different planetary atmospheres as the specific models of the greenhouse effect formation. To solve such a problem, data are needed on the composition and structural parameters of the atmospheres and the quantitative characteristics of the absorption spectra associated with the specific conditions of various atmospheres. In connection with this, laboratory studies of the IR absorption spectra of the synthetical CO₂ atmospheres were carried out. Some results from these studies are discussed. Calculations of the thermal-emission fluxes' spectral distribution in the atmospheres of Mars, Venus and Jupiter were performed to analyse the conditions of the greenhouse effect formation in the atmospheres of these planets. Calculations were made which concern the optical properties of Venus clouds and dust aerosols of Mars,i.e. the contribution of clouds and aerosols into the greenhouse effect was analysed. The conditions favourable to the antigreenhouse effect formation are specified.

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Riassunto L'effetto serra dell'atmosfera è il fattore principale di possibili cambiamenti climatici di origine antropogenica. Il crescente inquinamento dell'atmosfera porta all'aumento della concentrazione di componenti gassosi come anidride carbonica e anidride solforosa, ossido di carbonio, alocarboni, protossido d'azoto, ecc. Di grande importanza è anche la considerazione dell'aerosol sia introdotto direttamente nell'atmosfera che formato come risultato della conversione di gas chimico in particelle (prima di tutto, riguardo l'aerosol di zolfo). Tutti i suddetti componenti gassosi, come pure l'aerosol, hanno bande di assorbimento nell'infrarosso, e ciò determina il loro contributo all'effetto serra dell'atmosfera, regolato principalmente dal vapore acqueo e dall'anidride carbonica. L'attenzione tradizionalmente rivolta al problema del contributo della CO₂ all'effetto serra ha qualche volta lasciato in ombra il significato di componenti diversi. Si considerano i dati che caratterizzano il significato di componenti diversi all'effetto serra. Si discutono i risultati dello studio degli spettri di assorbimento del metano, del protossido d'azoto, del gas solforico, dell'ammoniaca, dei vapori di acido nitrico e di altri componenti. Si danno valutazioni dei loro contributi all'effetto serra. Si discute l'importante ruolo della frazione di piccole dimensioni dell'aerosol atmosferico come fattore dell'effetto serra. Sia l'analisi delle cause della variabilità del clima terrestre che l'importante studio dell'effetto serra dell'atmosfera determinano l'utilità di analizzare le condizioni di formazione dell'effetto serra in altri pianeti, cioè le diverse atmosfere planetarie come modelli specifici per la formazione dell'effetto serra. Per risolvere tale problema, sono necessari dati sulla composizione e sui parametri strutturali delle atmosfere e le caratteristiche quantitative degli spettri di assorbimento associati con le condizioni specifiche delle varie atmosfere. In relazione a ciò, sono stati compiuti studi in laboratorio degli spettri di assorbimento IR di atmosfere artificiali con CO₂. Si discutono alcuni risultati di questi studi. Si sono eseguiti calcoli della distribuzione spettrale di flussi ad emissione termica nelle atmosfere di Marte, Venere e Giove, per analizzare le condizioni di formazione dell'effetto serra nell'atmosfera di questi pianeti. Si sono eseguiti calcoli che riguardano le proprietà ottiche delle nubi di Venere e dell'aerosol della polvere di Marte, cioè si è analizzato il contributo di aerosol e nubi alla formazione dell'effetto serra. Si specificano le condizioni favorevoli alla formazione dell'effetto anti-serra.

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Резюме Оранжерейный эффект атмосферы представляет основной фактор возможных климатических изменений антропогенного происхождения. Растущее загрязнение атмосферы приводит к увеличению концентрации таких газообразных компонент, как двуокиси серы и углерода, окись углерода, голоуглероды, окислы азота и др. Важное внимание уделяется также аэрозолям, которые инжектируются непосредственно в атмосферу и образуются в результате превращения химических газов в частицы (прежде всего, сульфатный аэрозоль). Все вышеуказанные газообразные компоненты, а также аэрозоли имеют зоны поглощения в инфракрасной спектральной области, которая определяет их вклад в оранжерейный эффект атмосферы, определяемый, в основном, парами воды и двуокисью углерода. Традиционное внимание к проблеме концентрации CO₂ при анализе оранжерейного эффекта отчасти уменьшает значимость других компонент. Рассматриваются данные, характеризующие значимость различных компонент для оранжерейного эффекта. Обсуждаются результаты исследования спектров поглощения метана, окислов азота, серного газа, аммиака, паров азотной кислоты и других компонент. Приводятся оценки их вклада в оранжерейный эффект. Обсуждается важная роль атмосферного аэрозоля в оранжерейном эффекте. Анализ причин непостоянства климата на Земле и исследование атмосферного оранжерейного эффекта позволяют определить целесообразность анализа условий образования оранжерейного эффекта на других планетах, посредством рассмотрения различных планетарных атмосфер, как специальных моделей образования оранжерейного эффекта. Для решения такой проблемы необходимы данные по составу и спектраляным параметрам атмосфер и количественные характеристики спектров поглощения, связанные с условиями различных атмосфер. В связи с этим были проведены лабораторные исследования спектров инфракрасного поглощения искусственных CO₂ атмосфер. Обсуждаются некоторые результаты этих исследований. С целью анализа условий образования оранжерейного эффекта в атмосферах Марса, Венеры и Юпитера проведены вычисления спектрального распределения потоков теплового излучения в атмосферах этих планет. Анализируется вклад облаков на Венере и пылевых аэрозолей на Марсе в оранжерейный эффект. Определяются условия, благоприятные для образования антиоранжерейного эффекта.

     

On the spherical symmetry of static stellar models

This paper completes the proof of the necessity of spherical symmetry in the static general-relativistic stellar models that have equations of state satisfying certain inequalities. The technical assumption — that there exists a reference spherical stellar model — that was essential in the previous discussions of this problem is removed. This paper also extends beyond previous discussions the class of equations of state included in the proof. The analysis of the equations for spherical stellar models, used here to demonstrate the existence of a reference spherical model, may also be of independent interest.     

转动效应对恒星热力学结构与演化的影响研究

转动效应对恒星结构与演化的两大方面的影响体现在动力学效应和元素混合上.本文利用国际MESA程序,研究了转动效应对20 M_⊙恒星在主序阶段热力学结构的影响.发现转动的动力学效应能使恒星中心温度变低,减少了恒星表面的不透明度,中心平均分子量和表面熵.由于动力学效应对恒星热结构的调整,降低了恒星的氢燃烧率,恒星向低温和低光度端演化.转动的元素混合效应减小了恒星的中心温度、密度、压强、紧密度、表面不透明度和平均分子量,使恒星表面氦元素、氮元素明显超丰,中心燃烧核区域变大,延长恒星在主序阶段的寿命.     

The effect of a gravitational induction force on the stellar orbits in galaxies

This paper explores the effect of a gravitational induction force, similar to gravito-electromagnetism but of several orders of magnitude larger, on a spiral galaxy. This would provide, because of the huge amount of mass currents associated with spirals, a rather large gravitational induction force. Standard gravitational dynamics is modified by adding an anti-symmetric force tensor analogous to electromagnetism. By choosing a special free space solution to the Einstein field equations, it was found that the resulting force field would drop off by an r ⁻¹ rather than an r ⁻² rule. Thus this new induction force would grow to dominance over the large distances associated with galaxies. Any r ⁻¹ force will produce the flat rotation curves that are observed in disk galaxies as well as explain the Tully-Fisher relationship. It would also explain why the inner core of the spirals remain Newtonian. Quite surprisingly, this simple hypothesis also seems to offer explanations for many other observed phenomena as well.     

On the effect of magnetic fields on alloys with isothermal kinetics of martensitic transformation

The effect of magnetic treatment on the isothermal martensitic transformation in the Fe-24% Ni-4% Mn alloy has been investigated. The martensitic transformation in a dc magnetic field at liquid-helium temperature has been analyzed.     

On the thermodynamics of turbulent convection

The thermodynamic properties of a steady-state flow in the gravitational field have been determined by applying the entropy production equation and the Prigogine theorem to an ideal one-component turbulent gas under the assumption that fluctuations are polytropic. Applications to the problems of the surface layer dynamics and free convection are also considered.     

On the computation of angular distributions of radiation in planetary atmospheres

The discrete ordinate approximation to the radiative transfer equation is used to derive simple analytic expressions for the intensity in a vertically inhomogeneous plane parallel atmosphere. This approach allows one to compute the intensity at arbitrary depths and angles. The merit and soundness of these expressions, which are interpolatory in nature, are discussed and it is conjectured that they are superior to any other standard interpolation scheme as far as accuracy is concerned. The computational time also compares favorably with that of standard interpolation schemes such as cubic splines.     

On chaotic behavior of gravitating stellar shells

Motion of two gravitating spherical stellar shells around a massive central body is considered. Each shell consists of point particles with the same specific angular momenta and energies. In the case when one can neglect the influence of gravitation of one ("light") shell onto another ("heavy") shell ("restricted problem") the structure of the phase space is described. The scaling laws for the measure of the domain of chaotic motion and for the minimal energy of the light shell sufficient for its escape to infinity are obtained.     

On the threshold anisotropy for unstable spherical stellar systems

The radial orbit instability generally arises in anisotropic collisionless stellar systems with the dominance of radial motions over transverse ones. Using the simplest anisotropic generalization of polytrope models for spherical clusters as an example, we show that the instability growth rates become exponentially small as the isotropic limit is approached. Given the finite lifetime of real astronomical objects, these systems should be assumed to become stable at some finite radial anisotropy.     

A simple computational method for internal polarized radiation fields of finite slab atmospheres

An extended doubling method is formulated, which provides together with the emergent radiation also the internal polarized radiation field without additional iterations. Two sets of linear regular integral relations are derived, which have to be fulfilled by the surface Green's function matrix or, equivalently, by the Stokes vector of the slab albedo problem radiation field. The integral relations refer to the half range angular variable of the direction of incidence and to the full range angular variable of the direction of light propagation, respectively.     

On truncated-series approximations in the theory of Rayleigh-Benard convection

Two-dimensional convection is studied using truncated Fourier series. We discuss recently established mathematical criteria for the number of modes needed for representing the asymptotic behaviour of the solution. We then show that the numerical determination of the transition from steady to oscillating rolls requires at least 78 Fourier amplitudes.     

恒星能量下核子俘获反应率的晕核效应

恒星能量下俘获截面很难直接测量。¹⁰Be（n，γ）¹¹Be俘获反应涉及到非均匀宇宙大爆炸核合成，无直接测量实验截面数据。利用转移反应¹⁰Be（d，p）¹¹Be的渐近归一化系数（ANC）方法，计算了¹⁰Be（n，γ）¹¹Be俘获反应截面和反应率。¹¹Be是中子晕核。研究表明，在恒星能量下俘获到晕态的截面和反应率显著增大。     

Interaction of physical fields in the acoustomagnetic effect

Experimental studies of the acoustomagnetic effect in a magnetic fluid are performed. The linear sizes of magnetic nanoparticles of the dispersed phase are determined by the acoustogranulometric method. The mean deviation of the diameters of magnetic nanoparticles obtained at eight fixed frequencies in the range of 18?C65 kHz from their average values ??d _max?? = 16 nm and ??d _max?? = 9 nm is 4.4%. These results are in satisfactory agreement with the results obtained by the magnetorelaxometry method for magnetite nanoparticles. On the basis of experimental data, in the framework of the concentrational model, interaction between the elastic and thermal fields and between the magnetic and dynamic demagnetizing fields in the acoustomagnetic effect is studied. The conclusions of the model theory are confirmed by the experimental results.     

On stationary convection and oscillatory motions in ferromagnetic convection in a ferrofluid layer

It is shown analytically that the ‘principle of the exchange of stabilities’ (PES), in general, is not valid in ferromagnetic convection in a ferrofluid layer, for the case of free boundaries and hence a sufficient condition is derived for the validity of the PES. Upper bounds for the complex growth rate are then obtained. It is proved that the complex growth rate σ=σ_r+iσ_i (where σ_r and σ_i are, respectively, the real and imaginary parts of σ) of an arbitrary oscillatory motion of growing amplitude, in ferromagnetic convection in a ferrofluid layer, for the case of free boundaries lies inside a semicircle in the right half of the σ_rσ_i-plane whose center is at the origin and ²(radius)=RM₁/P_r, where R is the Rayleigh number,M₁ is the magnetic number and P_r is the Prandtl number. Further, bounds for the case of rigid ferromagnetic boundaries are also derived separately.