scholarly journals The impact of Jean-Paul Zahn discoveries on rotation and evolution

2019 ◽  
Vol 82 ◽  
pp. 137-151
Author(s):  
A. Maeder ◽  
G. Meynet
Keyword(s):  
Binary Stars ◽  
Dominant Role ◽  
Close Binaries ◽  
Stellar Rotation ◽  
Jean Paul ◽  
Low Metallicity ◽  
Main Effects ◽  
The Impact ◽  
Rotational Coupling ◽  
Internal Coupling

We first review the main effects of stellar rotation on evolution along the fundamental discoveries by Jean-Paul. Then, we examine some of the consequences of rotation in the evolution of single and binary stars. The proper account of meridional circulation in close binaries tends to increase the synchronization time because meridional currents always counteract the tidal interaction. We consider the case of the very low metallicity Z stars, in particular the CEMP-no stars, where rotational mixing may have played a dominant role in their strange chemical composition. Then, turning to “What are the mysteries?”, we emphasize that all over the evolution and for various masses the present models seem to still have a lack of rotational coupling between cores and envelopes. We suggest that magnetic fields may produce this missing internal coupling.

scholarly journals Inverse tides in pulsating binary stars

2020 ◽  
Vol 501 (1) ◽  
pp. 483-490
Author(s):  
Jim Fuller
Keyword(s):  
Binary Stars ◽  
Close Binary ◽  
Close Binaries ◽  
Spin Orbit ◽  
Misalignment Angle ◽  
Stellar Rotation ◽  
Transfer Energy ◽  
Pulsating Stars ◽  
Mode Amplitude ◽  
Rotation Periods

ABSTRACT In close binary stars, the tidal excitation of pulsations typically dissipates energy, causing the system to evolve towards a circular orbit with aligned and synchronized stellar spins. However, for stars with self-excited pulsations, we demonstrate that tidal interaction with unstable pulsation modes can transfer energy in the opposite direction, forcing the spins of the stars away from synchronicity, and potentially pumping the eccentricity and spin–orbit misalignment angle. This ‘inverse’ tidal process only occurs when the tidally forced mode amplitude is comparable to the mode’s saturation amplitude, and it is thus most likely to occur in main-sequence gravity mode pulsators with orbital periods of a few days. We examine the long-term evolution of inverse tidal action, finding the stellar rotation rate can potentially be driven to a very large or very small value, while maintaining a large spin–orbit misalignment angle. Several recent asteroseismic analyses of pulsating stars in close binaries have revealed extremely slow core rotation periods, which we attribute to the action of inverse tides.

Migration and transformation characteristics of DOM in fine sand and marl rock

2016 ◽  
Vol 74 (1) ◽  
pp. 157-164 ◽  
Author(s):  
Xinyi Wang ◽  
Xiaoge Zhen ◽  
Renzheng Li ◽  
Xiaoman Liu ◽  
Tiantian Wang ◽  
...  
Keyword(s):  
Biological Effects ◽  
Dominant Role ◽  
Fine Sand ◽  
Early Experiment ◽  
Medium Term ◽  
Seepage Velocity ◽  
Adsorption Effect ◽  
Main Effect ◽  
Main Effects ◽  
The Impact

This paper mainly studied migration and transformation characteristics of dissolved organic matter (DOM) in underground aquifers. To achieve the research purpose, we carried out the dynamic column experiments of the DOM at different conditions indoors. In the experiment, the water of Wujiang River from Pingdingshan Coal-field is used as water sample, meanwhile, fine sand and marl rock are used as testing rock sample. A comparative study on migration and transformation characteristics of the DOM in different rock samples is done. The results show that, in the fine sand, the main effects are convection and dispersion, while the adsorption and biological effects are very weak. However, in the marl rock, besides existing convection and dispersion, the adsorption and biological effect are quite significant. And in the marl rock, convection and dispersion plays a major role in the early experiment, while adsorption is the main effect in the medium term, then the biodegradation dominates the final stage. With the increasing of temperature and seepage velocity in the fine sand, the impact of the convection effect becomes gradually weak, the dispersion effect gradually enhances, and, however, convection effect is still playing a dominant role. With the temperature rising in the marl rock, the adsorption effect becomes weak, but biodegradation is enhanced. As the seepage velocity increases in the marl rock, the adsorption and biodegradation both decrease.

scholarly journals Mass Transfer between Binary Stars

1980 ◽  
Vol 88 ◽  
pp. 123-126 ◽  
Author(s):  
Jerry L. Modisette ◽  
Youi Kondo
Keyword(s):  
Energy Source ◽  
Binary System ◽  
Binary Stars ◽  
Roche Lobe ◽  
Major Determinant ◽  
Close Binaries ◽  
Stellar Winds ◽  
Stellar Rotation ◽  
Limiting Case ◽  
Centrifugal Action

The transfer of mass from one component of a binary system to its companion can involve ejection of the mass by radiation pressure, by Roche lobe overflow, by centrifugal action through the coupling of the upper atmosphere to the stellar rotation through magnetic fields, and by the dynamics of the atmospheric fluid under the action of an energy source at the photosphere or lower chromosphere. We will primarily address the latter mechanism, which commonly goes under the title of stellar winds. The major determinant of a stellar wind is the energy source. In the case of a binary system, the dynamic effects of the system on the flow pattern, particularly for close binaries, is a second major determinant, once an energy source is available to drive the wind. Roche lobe overflow might be thought of as a limiting case in which the system dynamics predominate.

scholarly journals The implications of close binary stars for star-disk interactions

2007 ◽  
Vol 3 (S243) ◽  
pp. 315-324 ◽  
Author(s):  
Robert D. Mathieu
Keyword(s):  
Binary Stars ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Close Binary ◽  
Close Binaries ◽  
Spectral Energy ◽  
Stellar Rotation ◽  
Single Star ◽  
Accretion Flows ◽  
T Tauri

AbstractThe presence of close (≲ 0.1 AU) stellar companions must greatly alter the circumstellar environment of classical T Tauri stars, including severe truncation if not elimination of circumstellar disks. It is thus remarkable how little impact the presence of a close companion has on our observable diagnostics for accretion and outflow. Emission line shapes, degrees of continuum veiling, and spectral energy distributions are all indistinguishable between single classical T Tauri stars and classical T Tauri close binaries. Some of the most classical T Tauri stars that laid the foundation for our single-star accretion-disk paradigm have turned out to have close companions. Periodicities in spectral signatures are suggestive of the presence of accretion flows from circumbinary disks to the circumstellar regions; the subsequent flow of material through the circumstellar region to the stellar surface in the presence of a stellar magnetosphere is unstudied. Observations of stellar rotation distributions in close binaries suggest that inner disk regions may act to regulate stellar angular momentum.

scholarly journals Mass Transfer between Binary Stars

1980 ◽  
Vol 5 ◽  
pp. 863-865
Author(s):  
Jerry L. Modisette
Keyword(s):  
Energy Source ◽  
Mass Transfer ◽  
Binary System ◽  
Magnetic Fields ◽  
Binary Stars ◽  
Free Particle ◽  
Major Determinant ◽  
Close Binaries ◽  
Stellar Rotation ◽  
Continuum Flow

The transfer of mass from one component of a binary system to its companion can involve ejection of the mass by radiation pressure, by Roche lobe overflow, by centrifugal action through the coupling of the upper atmosphere to the stellar rotation through magnetic fields, and by the dynamics of the atmospheric fluid under the action of an energy source at the photosphere or lower chromosphere. I will primarily address the latter mechanism, which commonly goes under the title of stellar winds. The major determinant of a stellar wind is the energy source. In the case of a binary system, the dynamic effects of the system on the flow pattern, particularly for close binaries, is a second major determinant, once an energy source is available to drive the wind.In addition to ejection, the transfer of mass requires capture of the ejected matter by the companion. The first issue is free particle vs. continuum flow. I will only consider continuum flow, as I doubt the applicability of the free particle concept to any binary system with significant mass transfer, because of the scale height and because of the likely presence of magnetic fields in the interstellar plasma. For more distant binaries, rather simple considerations show that the capture of matter for continuum flow can be enhanced over that for free particle flow.

scholarly journals Mathematical Status of the Fission Theory

1989 ◽  
Vol 8 ◽  
pp. 129-131 ◽  
Author(s):  
N. R. Lebovitz
Keyword(s):  
Internal Consistency ◽  
Classical Theory ◽  
Binary Stars ◽  
Dominant Role ◽  
Close Binaries ◽  
Theoretical Status ◽  
Mass Ratios ◽  
Mathematical Problems

AbstractA review is given of the current mathematical and theoretical status of the possibility of the formation of binary stars by fission. It is emphasized that none of the competing theories is completely deductive: each begins with a preconception of how fission might occur, and considers mathematical problems that bear on the viability of that preconception. The classical fission theory turned out to lack internal consistency. The present author’s version of the theory, revised from the classical theory in that viscosity plays a negligible rather than a dominant role, appears to be internally consistent and compatible with the idea that close binaries with mass ratios near one may form in this way. The version of the theory described elsewhere in this volume by Durisen, which fails to produce binaries, is based on a preconception of the route to fission different from the classical one. Its failure to produce binaries therefore reflects only on that route, and not on other possible routes to fission.

scholarly journals Evaluating the impact of binary parameter uncertainty on stellar population properties

2020 ◽  
Vol 495 (4) ◽  
pp. 4605-4621 ◽  
Author(s):  
E R Stanway ◽  
A A Chrimes ◽  
J J Eldridge ◽  
H F Stevance
Keyword(s):  
Binary Stars ◽  
Stellar Population ◽  
Stellar Populations ◽  
Star Formation History ◽  
High Mass ◽  
Substantial Impact ◽  
Binary Parameter ◽  
Formation History ◽  
Low Metallicity ◽  
The Impact

ABSTRACT Binary stars have been shown to have a substantial impact on the integrated light of stellar populations, particularly at low metallicity and early ages – conditions prevalent in the distant Universe. But the fraction of stars in stellar multiples as a function of mass, their likely initial periods and distribution of mass ratios are all known empirically from observations only in the local Universe. Each has associated uncertainties. We explore the impact of these uncertainties in binary parameters on the properties of integrated stellar populations, considering which properties and time-scales are most susceptible to uncertainty introduced by binary fractions and whether observations of the integrated light might be sufficient to determine binary parameters. We conclude that the effects of uncertainty in the empirical binary parameter distributions are likely smaller than those introduced by metallicity and stellar population age uncertainties for observational data. We identify emission in the He ii 1640 Å emission line and continuum colour in the ultraviolet–optical as potential indicators of a high-mass binary presence, although poorly constrained metallicity, dust extinction, and degeneracies in plausible star formation history are likely to swamp any measurable signal.

The impact of applying the Common Customs Tariff on the armenian export of Cut and Polished Gems to Russia

2019 ◽  
pp. 33-41
Author(s):  
V. L. Harutyunyan ◽  
S. V. Dokholyan ◽  
A. R. Makaryan
Keyword(s):  
Manufacturing Sector ◽  
Practical Implication ◽  
Dominant Role ◽  
New Technology ◽  
Manufacturing Companies ◽  
Medium Term ◽  
Diamond Cutting ◽  
Global Trends ◽  
The Common ◽  
The Impact

The presented study discusses the issues of applying the Common Customs Tariff (CCT) rates of the Eurasian Economic Union (EAEU) on rough diamonds and the impact thereof on the exports of stones cut and polished inArmeniaand then exported toRussia.Aim. The study aims to identify the possible strategies Armenian diamond cutting and polishing companies could adopt as a response to the application of the CCT rates on rough diamonds and how it would affect exports to various destinations, namely to Russia.Tasks. The authors analyze the current state of the gems and jewelry sector and substantiate the need to either integrate it into the jewelry manufacturing sector or to apply various strategies to facilitate exports to either Russia or other destinations in the medium term in response to the application of the CCT rates.Methods. This study uses general scientific methods of cognition, including analytical and methodological approaches and elements of forecasting. Possible strategies the Armenian diamond cutting and polishing companies could adopt in the medium term in response to the application of the EAEU CCT rates are determined using the analytical research method, forecasts in the context of the developments in the Armenian gem processing and jewelry market and global trends, statistical data on the imports and exports of cut and polished gems and jewelry for 2014–2018 published by the UN Comtrade Statistics.Results. Statistics on the exports of processed diamonds from 2014 to 2018 highlights the issue associated with the loss of competitiveness suffered by Armenian companies (mainly in comparison with Indian diamond cutters). The major global trends in the diamond cutting and polishing business indicate that it could be virtually impossible for Armenian cutters and polishers to compete with Indian companies in the medium term if they do not comes to investing in new technology to achieve operational efficiency. For these companies, it is important not to lose the Russian market due to an increase in the tariff rate and concentrate on the processing of gems that are larger than 1 carat. Another strategy to avoid an increase in the customs tariff rates would depend on the Armenian government’s ability to negotiate with Russia in respect of direct imports of diamond stones from Russian manufactures. Two other options for Armenian cutters involve focusing on cutting and polishing of rubies, sapphires, emeralds, etc. or integrating into the jewelry sector either by being the primary supplier or by considering this business as a channel to sell processed diamond stones by setting up their own jewelry manufacturing companies.Conclusions. With CCT going into effect in January 2021 and India’s dominant role in the diamond cutting and polishing business, Armenia needs to carefully consider all of the strategies the Armenian companies could adopt, as discussed above. As a member state of the EAEU, Armenia freely exports to Russia, however, further exports to Russia would depend on Armenia’s ability to ensure that cost-effective operations are in place, or to concentrate on the processing of precious gems rather than diamonds, or to switch to the manufacturing of jewelry items as a major export item.Practical Implication. The findings of this study could be of interest to the Ministry of Economy of the Republic of Armenia and Business Armenia that could be used in elaborating the strategy for the development of Armenian gems and jewelry sector of the economy.

scholarly journals Impact of the COVID-19 Pandemic on the Romanian Labor Market

2020 ◽  
Vol 13 (1) ◽  
pp. 271
Author(s):  
Carmen Valentina Radulescu ◽  
Georgiana-Raluca Ladaru ◽  
Sorin Burlacu ◽  
Florentina Constantin ◽  
Corina Ioanăș ◽  
...  
Keyword(s):  
Labor Market ◽  
Health Insurance ◽  
Labor Force ◽  
Semantic Differential ◽  
Current Crisis ◽  
Health Crisis ◽  
Unemployed People ◽  
Lack Of Information ◽  
Main Effects ◽  
The Impact

The present research aims to establish the impact that the current crisis situation the planet is facing, namely the COVID-19 pandemic, has had so far on the Romanian labor force market. In this context, given the lack of information and information regarding this pandemic and its effects, the administration of a questionnaire among the population was considered to identify the research results. The method of semantic differential and the method of ordering the ranks were used for the interpretation of the results. With the help of this questionnaire, it will be possible to answer the question of the research in this study: What are the main effects of the COVID-19 pandemic on the Romanian labor market? The main results showed that the COVID-19 pandemic affected the Romanian workforce; the respondents of the applied questionnaire claimed that they obtained better results and maintained a similar income, but the health crisis also influenced the mentality of employees, with respondents stating that in the event of changing jobs, they would consider it very important for the new employer to ensure the conditions for preventing and combating COVID-19, as well as complex health insurance. However, analyzing at the macroeconomic level, it was found that the COVID-19 pandemic induced an increase in the number of unemployed people in the Romanian labor market.

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