Relating turbulent pressure and macroturbulence across the HR diagram with a possible link toγDoradus stars

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

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Sakurai’s Object: Constraints from its Variability?

Highlights of Astronomy ◽

10.1017/s1539299600021110 ◽

1998 ◽

Vol 11 (1) ◽

pp. 360-360

Author(s):

T. Gautschy ◽

H.W. Duerbeck ◽

A.M. Van Genderen ◽

S. Benetti

Keyword(s):

Cooling Rate ◽

Nuclear Energy ◽

Stability Analyses ◽

The Past ◽

Stellar Pulsations ◽

First Results ◽

Effective Temperatures ◽

Stellar Envelopes ◽

Light Variability ◽

Hr Diagram

The peculiar outburst of the star baptized Sakurai’s Object (SO) is a conceivable example of a late He shell flash in a post-AGB object. The new source of nuclear energy forces such objects toward high luminosities and eventually low effective temperatures; they cross the HR diagram in a comparable fashion as FG Sge did in the past - i.e., they move noticeably on the HR diagram on human timescales. From monitoring campaigns of SO during the last year, first estimates of its cooling rate were derived and in particular cyclic light variability was established. We present first results from attempts to model stellar envelopes appropriate for SO. As we hypothesize the light variability to be attributable to stellar pulsations, we aim at constraining the basic stellar parameters based on stability analyses of our envelope models. Radial, nonadiabatic stability computations provided predictions of the modal content which should be observable as SO evolves. The particular components in such mode spectra of SO as they are to appear in the coming years should indeed help to constrain basic stellar parameters such as mass and luminosity.

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Study on flow field and aerodynamic noise of electric vehicle rearview mirror

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1177/09544070211022896 ◽

2021 ◽

pp. 095440702110228

Author(s):

Xiaowei Hao ◽

Zhigang Yang ◽

Qiliang Li

Keyword(s):

Flow Field ◽

Proper Orthogonal Decomposition ◽

Electric Vehicle ◽

Sound Pressure ◽

Pressure Level ◽

Orthogonal Decomposition ◽

Aerodynamic Noise ◽

Turbulent Pressure ◽

Rearview Mirror ◽

Proper Orthogonal

With the development of new energy and intelligent vehicles, aerodynamic noise problem of pure electric vehicles at high speed has become increasingly prominent. The characteristics of the flow field and aerodynamic noise of the rearview mirror region were investigated by large eddy simulation, acoustic perturbation equations and reduction order analysis. By comparing the pressure coefficients of the coarse, medium and dense grids with wind tunnel test results, the pressure distribution, and numerical accuracy of the medium grid on the body are clarified. It is shown from the flow field proper orthogonal decomposition of the mid-section that the sum of the energy of the first three modes accounts for more than 16%. Based on spectral proper orthogonal decomposition, the peak frequencies of the first-order mode are 19 and 97 Hz. As for the turbulent pressure of side window, the first mode accounts for approximately 11.3% of the total energy, and its peak appears at 39 and 117 Hz. While the first mode of sound pressure accounts for about 41.7%, and the energy peaks occur at 410 and 546 Hz. Compared with traditional vehicle, less total turbulent pressure level and total sound pressure level are found at current electric vehicle because of the limited interaction between the rearview mirror and A-pillar.

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The Metallicity Distribution of Late Type Dwarfs

Highlights of Astronomy ◽

10.1017/s1539299600022292 ◽

1998 ◽

Vol 11 (1) ◽

pp. 571-571

Author(s):

M. Haywood ◽

J. Palasi ◽

A. Gómez ◽

L. Meillon Dasgal

Keyword(s):

Star Formation Rate ◽

Formation Rate ◽

Angular Separation ◽

Stellar Populations ◽

Late Type ◽

Limited Sample ◽

Hipparcos Catalogue ◽

Galactic Stellar Populations ◽

Metallicity Distribution ◽

Hr Diagram

The Hipparcos catalogue provides an accurate and extensive sampling of the solar neighbourhood HR diagram. The morphology of this diagram depends on selection criteria of the catalogue such as the limiting magnitude, angular separation and on the characteristics of the stellar populations near the sun (space density, metallicity, star formation rate, etc). Since the Hipparcos data are so accurate, one needs to model precisely the different selection bias and, at the same time, parametrize models of the galactic stellar populations with sufficient flexibility that as much information as possible can be grasped from the catalogue. Comparisons between our model and the Hipparcos catalogue will be presented elsewhere. Since the quantity of information contained in the Hipparcoscatalogue is so important, models ought to be complex, and external contraints, obtained prior to any general comparison with the model, are welcome. A major factor that influences the distribution of the stars in the HR diagram is the metallicity. For the late type stars, the metallicity distribution can be best studied by re-analysing a volume-limited sample of stars from the catalogue.

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Towards an Improved Model of the Galaxy

Highlights of Astronomy ◽

10.1017/s1539299600022280 ◽

1998 ◽

Vol 11 (1) ◽

pp. 570-570

Author(s):

Johan Holmberg ◽

Lennart Lindegren ◽

Chris Flynn

Keyword(s):

Three Dimensional ◽

Direct Determination ◽

Galactic Structure ◽

Open Clusters ◽

Selection Effects ◽

Observational Errors ◽

Red Giant ◽

Improved Model ◽

First Time ◽

Hr Diagram

We use the Hipparcos survey to derive an improved model of the local galactic structure. The availability of parallaxes for all the stars permits direct determination of stellar distributions, eliminating the basic indeterminacy of classical methods based on star counts. Hipparcos gives for the first time a truly three-dimensional view of the solar vicinity, and a complete, homogeneous and highly accurate set of magnitudes and colours. This means that new techniques can be applied in the treatment of the data which place strong constraints on a model that tries to describe the local Galactic structure. Here we investigate how well a static model of low complexitycan describe the Hipparcos observations. The interpretation of the Hipparcos data is complicated by various observational errors and selection effects that are hard to treat correctly. We do not try to correct the data, but instead use a model and subject this model to the same observational errors and selection effects. A model catalogue is created that can be compared with the observed catalogue directly in the observational domain, thereby eliminating the effects from various biases. Many features in the HR diagram are for the first time seen in field stars thanks to Hipparcos, such as the slanted red giant clump, previously seen in rich old open clusters such as Berkeley 18. This and other features ofthe observed HR diagram are well reproduced by the model thanks to the rather detailed modelling of the joint Mv/B — V distribution. Actually, separate distributions were derived for the three different components, disk, thick disk and halo, using the kinematic characteristics of the components to discriminate between them.

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Processes controlling the initial mass function: interstellar turbulence and magnetic fields

Symposium - International Astronomical Union ◽

10.1017/s0074180900239806 ◽

1991 ◽

Vol 147 ◽

pp. 407-408

Author(s):

R. C. Fleck

Keyword(s):

Magnetic Fields ◽

Mass Function ◽

Diffusion Time ◽

Interstellar Cloud ◽

Initial Mass Function ◽

Mass Scaling ◽

Interstellar Turbulence ◽

Time Scaling ◽

Turbulent Pressure ◽

Low Mass

The observed flattening of the initial stellar mass function at low mass can be accounted for in terms of the different interstellar cloud size-mass scaling and different ambipolar diffusion time scaling for small, thermally-supported clouds and larger clouds supported primarily by turbulent pressure.

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Luminosity Calibration of Giants and Supergiants, G0–M5

Symposium - International Astronomical Union ◽

10.1017/s0074180900055108 ◽

1973 ◽

Vol 54 ◽

pp. 68-77

Author(s):

Ph. C. Keenan

Keyword(s):

Calibration Curves ◽

Hr Diagram

Calibration curves giving Mv for stars of luminosity classes III, II, Ib, Iab and 0 are derived and shown graphically in the HR diagram. There are serious gaps in which the calibration needs to be improved.

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A new noise detected in the ocean

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315407058225 ◽

2007 ◽

Vol 87 (5) ◽

pp. 1255-1256 ◽

Cited By ~ 3

Author(s):

Angel Guerra ◽

Xavier Martinell ◽

Angel F. González ◽

Michael Vecchione ◽

Joaquin Gracia ◽

...

Keyword(s):

Ambient Noise ◽

Sound Production ◽

Biological Activities ◽

Physical Processes ◽

Defensive Strategy ◽

Reflection And Refraction ◽

Turbulent Pressure ◽

In The Wild ◽

The Many ◽

Many Sources

Many observers have noted that the sea is full of loud sounds, both ongoing and episodic. Among the many sources of natural ambient noise are wave action, physical processes such as undersea earthquakes, and biological activities of shrimps, fish, dolphins and whales. Despite interest by acoustics experts, sound production by cephalopods has been reported only twice, both involving squid. The ‘faint poppings’ produced were thought to result from fluttering of the thin external lips of the squid's funnel while water is being expelled through it. Otherwise, no information is available on cephalopod sounds. Here we present a noise produced by a stressed common octopus. The event was filmed and recorded in the wild. The hypothesis we offer to explain how this sound was produced is cavitation, which has been documented in several biological systems. In our case, the water expelled through the funnel may have created a jet with a velocity so high that the turbulent pressure dropped locally below the vapour pressure of the water. Seawater contains gas microbubbles, which will grow in size when they are entrained in the region of low pressure. Subsequently, the bubbles collapse violently when pressure rises again. The sound produced by the octopus is like a gunshot, and distinct lights observed at the same time contradict the existence of a simple pressure wave and point to the possible presence of gas-bubbles, which would change the light intensity by reflection and refraction of the sunlight. This behaviour seems to be a defensive strategy to escape from vibration-sensitive predators.

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