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Search Results: 1 - 10 of 512290 matches for " I. A. Ryabchikova "
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The biological potency of benzapyrene in the humates composition  [PDF]
L. I. Belykh, I. A. Ryabchikova, S. S. Timofeyeva
Agricultural Sciences (AS) , 2013, DOI: 10.4236/as.2013.412085
Abstract:

The aim of the paper was to determine benz(a)-pyrene in the preparations containing humates and study the benz(a)pyrene biological potency for the agricultural plants. The research methodology included the determination of the dependencies in the system “substance concentration (dose)effect on the plant”. Concentrations of benz(a)pyrene in 12 samples of the humates preparations and fertilizers based on their trademarks “Irkutsk humates”, obtained from brown coal, varied in the range from 0.3 to 50 mcg/kg, which creates no soil contamination in conditions of the use of preparations. Between contents of benz(a)pyrene and humates there is a correlation (rxy = 0.95; α = 0.05). It is ascertained that the effects of stimulation and/or inhibition of the growth and yield of agricultural plants depend on the concentration of benz(a)pyrene and the method of plant processing. Optimal concentrations of benz(a)pyrene were 150-200 ng/dm3 for preplant way of processing of potato tubers, 3-10 ng/dm3for top dressing (spraying) and 0.1-0.3 ng/dm3for dressing under the roots (hydroponic). The obtained results allowed us to offer one of the possible mechanisms of biological potency of humates as the plant growth stimulants, and also a way testing of the preparations by screening of their benz(a)pyrene content.

Influence of Departures from LTE on Oxygen Abundance Determination
T. M. Sitnova,L. I. Mashonkina,T. A. Ryabchikova
Physics , 2013,
Abstract: We performed non-LTE calculations for O I with the plane-parallel model atmospheres for a set of stellar parameters corresponding to A-K type stars. The model atom of Przybilla et al. (2000) was updated using the best theoretical and experimental atomic data available so far. Non-LTE leads to strengthening the O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The departures from LTE grow toward higher effective temperature and lower surface gravity. In the entire temperature range and log g = 4, the non-LTE correction does not exceed 0.05 dex in absolute value for O I lines in the visible spectral range. The non-LTE corrections are significantly larger for the infrared O I 7771-5 A lines and reach -1.9 dex in the model atmosphere with Teff = 10000 K and log g = 2. To differentiate the effects of inelastic collisions with electrons and neutral hydrogen atoms on the statistical equilibrium (SE) of O I, we derived the oxygen abundance for the three well studied A-type stars Vega, Sirius, and HD 32115. For each star, non-LTE leads to smaller difference between the infrared and visible lines. For example, for Vega, this difference reduces from 1.17 dex in LTE down to 0.14 dex when ignoring LTE. To remove the difference between the infrared and visible lines in A-type stars completely, one needs to reduce the used electron-impact excitation rates by Barklem (2007) by a factor of 4. In the case of Procyon and the Sun, inelastic collisions with H I affect the SE of O I, and agreement between the abundances from different lines is achieved when using the Drawin's formalism to compute collisional rates. The solar mean oxygen abundance from the O I 6300, 6158, 7771-5, and 8446 A lines is log epsilon = 8.74+-0.05, when using the MAFAGS-OS solar model atmosphere and log epsilon = 8.78+-0.03, when applying the 3D corrections from the literature.
Multi-element Doppler imaging of kappa Psc
N. Piskunov,H. C. Stempels,T. A. Ryabchikova,V. Malanushenko,I. Savanov
Physics , 1998,
Abstract: kappa Psc (HD 220825) is a typical Chromium Ap star that happens to have optimal parameters for Doppler imaging (DI). Its short rotational period of less then 2 days, rotational velocity of ~40 km/s, and a moderate inclination of the rotational axis put modest requirements on spectroscopic observations. Anomalies of iron peak elements are clearly present, but small enough to cause significant deviations from model atmospheres with scaled solar abundances. We applied DI to kappa Psc once before, determining the distribution of Cr (Ryabchikova et al. 1996, hereafter Paper I). However, due to strong blending of Fe, the image was based on two short (~2 Angstroems) spectral intervals, dominated by Cr lines. Since the first paper we obtained additional spectra and developed a new code that allows to perform multi-element DI and thus to use larger spectral interval(s). We demonstrate the abilities of the new code and present new maps of Cr and Fe. A much larger time base allowed us to improve the rotational period of kappa Psc as well.
Abundance analysis of two late A-type stars HD 32115 and HD 37594
I. F. Bikmaev,T. A. Ryabchikova,H. Bruntt,F. A. Musaev,L. I. Mashonkina,E. V. Belyakova,V. V. Shimansky,P. S. Barklem,G. Galazutdinov
Physics , 2002, DOI: 10.1051/0004-6361:20020593
Abstract: We have performed abundance analysis of two slowly rotating, late A-type stars, HD 32115 (HR 1613) and HD 37594 (HR 1940), based on obtained echelle spectra covering the spectral range 4000-9850 AAngstrom. These spectra allowed us to identify an extensive line list for 31 chemical elements, the most complete to date for A-type stars. Two approaches to abundance analysis were used, namely a ``manual'' (interactive) and a semi-automatic procedure for comparison of synthetic and observed spectra and equivalent widths. For some elements non-LTE (NLTE) calculations were carried out and the corresponding corrections have been applied. The abundance pattern of HD 32115 was found to be very close to the solar abundance pattern, and thus may be used as an abundance standard for chemical composition studies in middle and late A stars. Further, its H-alpha line profile shows no core-to-wing anomaly like that found for cool Ap stars and therefore also may be used as a standard in comparative studies of the atmospheric structures of cool, slowly rotating Ap stars. HD 37594 shows a metal deficiency at the level of -0.3 dex for most elements and triangle-like cores of spectral lines. This star most probably belongs to the Delta Scuti group.
Search for the 3He isotope in the atmospheres of HgMn stars
I. Stateva,T. Ryabchikova,I. Iliev
Physics , 1998,
Abstract: We carried out a detailed analysis of the helium lines at 4921, 5876 and 6678 A in the spectra of the HgMn stars HD 58661, HD 172044, HD 185330 and HD 186122. For the first of these lines, the isotopic shift reaches +0.33 A for pure 3He, while for the last one, the maximum shift is +0.50 A. The 5876 line does not show any significant isotopic shift and is chosen for comparison. No trace of 3He was found in the atmosphere of HD 172044, while its presence was confirmed in HD 185330. This isotope is clearly present in the atmosphere of HD 58661. The results obtained for HD 186122 were ambiguous, 3He being apparently present in the 4921 line but not in the 6678 line, possibly because the latter is very weak.
Eu III identification and Eu abundance in cool CP stars
T. Ryabchikova,N. Piskunov,I. Savanov,F. Kupka
Physics , 1998,
Abstract: We report the first identification of the Eu III lambda 6666.317 line in optical spectra of CP stars. This line is clearly present in the spectra of HR 4816, 73 Dra, HR 7575, and beta CrB, while it is marginally present or absent in spectra of the roAp stars alpha Cir, gamma Equ, BI Mic, 33 Lib, and HD 24712.
Abundance analysis of SB2 binary stars with HgMn primaries
T. Ryabchikova
Physics , 1998,
Abstract: We present a short review of the abundances in the atmospheres of SB2 systems with Mercury-Manganese (HgMn) primaries. Up to now a careful study has been made for both components of 8 out of 17 known SB2 binaries with orbital periods shorter than 100 days and mass ratio ranging from 1.08 to 2.2. For all eight systems we observe a lower Mn abundance in the secondary's atmospheres than in the primary's. Significant difference in the abundances is also found for some peculiar elements such as Ga, Xe, Pt. All secondary stars with effective temperatures less than 10000 K show abundance characteristics typical of the metallic-line stars.
Magnetic Doppler imaging of the roAp star HD 24712
T. Lüftinger,O. Kochukhov,T. Ryabchikova,N. Piskunov,W. W. Weiss,I. Ilyin
Physics , 2009, DOI: 10.1051/0004-6361/200811545
Abstract: We present the first magnetic Doppler images of a rapidly oscillating Ap (roAp) star. We deduce information about magnetic field geometry and abundance distributions of a number of chemical elements on the surface of the hitherto best studied roAp star, HD 24712, using the magnetic Doppler imaging (MDI) code, INVERS10, which allows us to reconstruct simultaneously and consistently the magnetic field geometry and elemental abundance distributions on a stellar surface. For this purpose we analyse time series spectra obtained in Stokes I and V parameters with the SOFIN polarimeter at the Nordic Optical Telescope and recover surface abundance structures of sixteen different chemical elements, respectively ions, including Mg, Ca, Sc, Ti, Cr, Fe, Co, Ni, Y, La, Ce, Pr, Nd, Gd, Tb, and Dy. For the rare earth elements (REE) Pr and Nd separate maps were obtained using lines of the first and the second ionization stage. We find and confirm a clear dipolar structure of the surface magnetic field and an unexpected correlation of elemental abundances with respect to this field: one group of elements accumulates solely where the positive magnetic pole is visible, whereas the other group avoids this region and is enhanced where the magnetic equatorial region dominates the visible stellar surface. We also observe relative shifts of abundance enhancement- or depletion regions between the various elements exhibiting otherwise similar behaviour.
A self consistent chemically stratified atmosphere model for the roAp star 10 Aquilae
Nicole Nesvacil,Denis Shulyak,Tanya A. Ryabchikova,Oleg Kochukhov,Artur Akberov,Werner W. Weiss
Physics , 2012, DOI: 10.1051/0004-6361/201220320
Abstract: Context: Chemically peculiar A type (Ap) stars are a subgroup of the CP2 stars which exhibit anomalous overabundances of numerous elements, e.g. Fe, Cr, Sr and rare earth elements. The pulsating subgroup of the Ap stars, the roAp stars, present ideal laboratories to observe and model pulsational signatures as well as the interplay of the pulsations with strong magnetic fields and vertical abundance gradients. Aims: Based on high resolution spectroscopic observations and observed stellar energy distributions we construct a self consistent model atmosphere, that accounts for modulations of the temperature-pressure structure caused by vertical abundance gradients, for the roAp star 10 Aquilae (HD 176232). We demonstrate that such an analysis can be used to determine precisely the fundamental atmospheric parameters required for pulsation modelling. Methods: Average abundances were derived for 56 species. For Mg, Si, Ca, Cr, Fe, Co, Sr, Pr, and Nd vertical stratification profiles were empirically derived using the ddafit minimization routine together with the magnetic spectrum synthesis code synthmag. Model atmospheres were computed with the LLModels code which accounts for the individual abundances and stratification of chemical elements. Results: For the final model atmosphere Teff=7550 K and log g=3.8 were adopted. While Mg, Si, Co and Cr exhibit steep abundance gradients Ca, Fe and Sr showed much wider abundance gradients between log tau_5000=-1.5 and 0.5. Elements Mg and Co were found to be the least stratified, while Ca and Sr showed strong depth variations in abundance of up to ~ 6 dex.
The Core-Wing Anomaly of Cool Ap Stars: Abnormal Balmer Profiles
Charles R. Cowley,S. Hubrig,T. A. Ryabchikova,G. Mathys,N. Piskinov,P. Mittermayer
Physics , 2000, DOI: 10.1051/0004-6361:20000539
Abstract: Paper by Cowley et al. The Core-Wing Anomaly Etc. The profiles of H$\alpha$ in a number of cool Ap stars are anomalous. Broad wings, indicative of temperatures in the range 7000-8000K end abruptly in narrow cores. The widths of these cores are compatible with those of dwarfs with temperatures of 6000K or lower. This profile has been known for Przybylski's star, but it is seen in other cool Ap's. The H$\beta$ profile in several of these stars shows a similar core-wing anomaly (CWA). In Przybylski's star, the CWA is probably present at higher Balmer members. We are unable to account for these profiles within the context of LTE and normal dwarf atmospheres. We conclude that the atmospheres of these stars are not ``normal.'' This is contrary to a notion that has long been held.
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