Envelope tomography of long-period variable stars: I. The Schwarzschild mechanism and the Balmer emission lines

This paper is the first one in a series devoted to the study of the dynamics of the atmospheres of long-period variable stars. Results from a two-month-long monitoring of the Mira variables RT Cyg and X Oph around maximum light with the ELODIE spectrograph at the Haute-Provence Observatory are presented. The monitoring covers phases 0.80 to 1.16 for RT Cyg and phases 0.83 to 1.04 for X Oph. The cross-correlation profile of the spectrum of RT Cyg with a K0 III mask confirms that the absorption lines of RT Cyg in the optical domain appear double around maximum light. No line doubling was found in the optical spectrum of X Oph around maximum light, indicating that this feature is not common to all long-period variables. This paper also presents the application to RT Cyg of a new tomographic technique deriving the velocity field across the atmosphere by cross-correlating the optical spectrum with numerical masks constructed from synthetic spectra and probing layers of increasing depths. This technique reveals that both the temporal evolution of the line doubling, and its variation with depth in the atmosphere of RT Cyg, are consistent with the ``Schwarzschild scenario''. This scenario relates the temporal evolution of the red and blue peaks of the double absorption lines to the progression of a shock wave in the atmosphere. The temporal evolution of the Balmer Halpha, H beta, Hgamma and Hdelta emission lines around maximum light is also presented for RT Cyg and X Oph. The velocity variations of Halpha and of the absorption lines are discussed in the framework of two competing models for the formation of Balmer emission lines in long-period variable stars.Comment: 11 pages, 8 figures, Latex, accepted for publication in Astronomy and Astrophysics main journal. Also available at http://www-astro.ulb.ac.be/Html/ps.htm

ПИТАННЯ ВИЗНАЧЕННЯ ХАРАКТЕРИСТИК КОЛІСНИХ ТРАНСПОРТНИХ ЗАСОБІВ З ГІБРИДНИМИ ДВИГУНАМИ У ВІДПОВІДНОСТІ З УКРАЇНСЬКИМ КЛАСИФІКАТОРОМ ТОВАРІВ ЗОВНІШНЬОЕКОНОМІЧНОЇ ДІЯЛЬНОСТІ

This article discusses the problematic issues of the study of the characteristics of wheeled plug-in hybrid electric vehicles (PHEVs) in accordance with the requirements of the Ukrainian classification of goods of foreign economic activity. Existing types of hybrid power plants are considered. We consider the problems that are solved by experts in automotive industry in the study of wheeled vehicles with hybrid power plants. Problems of determining the type of hybrid power plant of a wheeled vehicle, the principle of its operation, and, consequently, the influence of this on the determination of the code according to the UKT ZED (Ukrainian Classification of Goods for Foreign Economic Activity) are considered. Currently, in expert practice, there is no single approach in carrying out research to determine which characteristics the wheeled vehicle meets according to the Ukrainian Classifier of Goods of Foreign Economic Activity. In this article the main types and types of hybrid power units, the principles of their operation and the effect on the definition of the code under the UKT ZED are given. In relation to wheeled vehicles to one or another code under the UKT ZED it is necessary to determine the scheme of the operation of the hybrid power plant. In this case, hybrid power units operating on a parallel and serially parallel circuit should be classified in the code of code 8703 2 "Other vehicles with spark ignition internal combustion engine and crankshaft coupling" or 8703 3 "Other vehicles from an internal combustion engine with compression ignition (diesel or semi-diesel), and hybrid power plants that operate in a sequential scheme to the code number 8703 90 90 00 "other" as not falling under the requirements of the other the position of the booty on the principle of its work.Рассмотрены проблемные вопросы исследования характеристик колесных транспортных средств с гибридными силовыми установками в соответствии с требованиями Украинского классификатора товаров внешнеэкономической деятельности. Названы существующие типы гибридных силовых установок. Очерчены задачи, которые решаются экспертами- автотовароведами при исследовании колесных транспортных средств с гибридными силовыми установками. Рассмотрены проблемы определения типа гибридной силовой установки колесного транспортного средства, принципа его работы и, как следствие, влияния этого на определение кода по УКТВЭД. В настоящее время в экспертной практике нет единого подхода к проведению исследований, позволяющих определить, каким характеристикам колесное транспортное средство соответствует украинскому классификатору товаров внешнеэкономической деятельности. Приведены основные типы и виды гибридных силовых агрегатов, принципы их работы и влияние на определение кода по УКТВЭД. При отнесении КТС к тому или иному коду по УКТВЭД необходимо определиться со схемой работы гибридной силовой установки. При этом гибридные силовые установки, работающие по параллельной и последовательно — параллельной схеме, должны быть отнесены к товарной позиции кода 8703 2 — «другие транспортные средства с двигателем внутреннего сгорания с искровым зажиганием и с кривошипно-шатунным механизмом» или 8703 3 — «другие транспортные средства с двигателем внутреннего сгорания с воспламенением от сжатия (дизелем или полудизелем)», а гибридные силовые установки, работающие по последовательной схеме, к товарной позиции кода 8703 90 90 00 — «другие», как такие, что не попадают под требования других товарных позиций по принципу своей работы.Розглянуто проблемні питання щодо дослідження характеристик колісних транспортних засобів з гібридними двигунами відповідно до вимог Українського класифікатора товарів зовнішньоекономічної діяльності. Розглянуто існуючі типи гібридних силових установок. Вивчено завдання, що вирішуються експертами автотоварознавцями при дослідженні колісних транспортних засобів з гібридними двигунами

Crystal nucleation and cluster-growth kinetics in a model glass under shear

Crystal nucleation and growth processes induced by an externally applied shear strain in a model metallic glass are studied by means of nonequilibrium molecular dynamics simulations, in a range of temperatures. We observe that the nucleation-growth process takes place after a transient, induction regime. The critical cluster size and the lag-time associated with this induction period are determined from a mean first-passage time analysis. The laws that describe the cluster growth process are studied as a function of temperature and strain rate. A theoretical model for crystallization kinetics that includes the time dependence for nucleation and cluster growth is developed within the framework of the Kolmogorov-Johnson-Mehl-Avrami scenario and is compared with the molecular dynamics data. Scalings for the cluster growth laws and for the crystallization kinetics are also proposed and tested. The observed nucleation rates are found to display a nonmonotonic strain rate dependency

Understanding the dynamical structure of pulsating stars: The Baade-Wesselink projection factor of the delta Scuti stars AI Vel and beta Cas

Aims. The Baade-Wesselink method of distance determination is based on the oscillations of pulsating stars. The key parameter of this method is the projection factor used to convert the radial velocity into the pulsation velocity. Our analysis was aimed at deriving for the first time the projection factor of delta Scuti stars, using high-resolution spectra of the high-amplitude pulsator AI Vel and of the fast rotator beta Cas. Methods. The geometric component of the projection factor (i.e. p0) was calculated using a limb-darkening model of the intensity distribution for AI Vel, and a fast-rotator model for beta Cas. Then, using SOPHIE/OHP data for beta Cas and HARPS/ESO data for AI Vel, we compared the radial velocity curves of several spectral lines forming at different levels in the atmosphere and derived the velocity gradient associated to the spectral-line-forming regions in the atmosphere of the star. This velocity gradient was used to derive a dynamical projection factor p. Results. We find a flat velocity gradient for both stars and finally p = p0 = 1.44 for AI Vel and p = p0 = 1.41 for beta Cas. By comparing Cepheids and delta Scuti stars, these results bring valuable insights into the dynamical structure of pulsating star atmospheres. They suggest that the period-projection factor relation derived for Cepheids is also applicable to delta Scuti stars pulsating in a dominant radial mode

А FIELD-PANEL METHOD FOR TRANSONIC LIFTING WING CALCULATION

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Self consistent modelling of the projection factor for interferometric distance determination

Astronomy and Astrophysics, v. 428, p. 131-137, 2004. http://dx.doi.org/10.1051/0004-6361:20041419International audienc

The Baade-Wesselink p-factor applicable to LMC Cepheids

Context. Recent observations of LMC Cepheids bring new constraints on the slope of the period-projection factor relation (hereafter Pp relation) that is currently used in the Baade-Wesselink (hereafter BW) method of distance determination. The discrepancy between observations and theoretical analysis is particularly significant for short period Cepheids Aims. We investigate three physical effects that might possibly explain this discrepancy: (1) the spectroscopic S/N that is systematically lower for LMC Cepheids (around 10) compared to Galactic ones (up to 300), (2) the impact of the metallicity on the dynamical structure of LMC Cepheids, and (3) the combination of infrared photometry/interferometry with optical spectroscopy. Methods. To study the S/N we use a very simple toy model of Cepheids. The impact of metallicity on the projection factor is based on the hydrodynamical model of delta Cep already described in previous studies. This model is also used to derive the position of the optical versus infrared photospheric layers. Results. We find no significant effect of S/N, metallicity, and optical-versus-infrared observations on the Pp relation. Conclusions. The Pp relation of Cepheids in the LMC does not differ from the Galactic relation. This allows its universal application to determine distances to extragalactic Cepheids via BW analysis.Comment: accepted in A&A LETTER

Exact solutions of basic variational inverse boundary value problem of aerohydrodynamics

The problems of determining the maximum lift attainable on wing profile and the corresponding profile form are considered, in particular, for the ideal incompressible fluid model the construction of exact solutions different from a circle (with non-circle extremal) is reported

STUDY OF TURBULENT FLOW OVER А РС-9 TRAINER WING SECТION WIТH ТНЕ USE OF CFD FLOTRAN

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