309 research outputs found
Dynamo-generated magnetic fields in fast rotating single giants
Red giants offer a good opportunity to study the interplay of magnetic fields
and stellar evolution. Using the spectro-polarimeter NARVAL of the Telescope
Bernard Lyot (TBL), Pic du Midi, France and the LSD technique, we began a
survey of magnetic fields in single G-K-M giants. Early results include 6
MF-detections with fast rotating giants, and for the first time a magnetic
field was detected directly in an evolved M-giant: EK Boo. Our results could be
explained in the terms of -- dynamo operating in these giants.Comment: 2 pages, 1 figure, proceedings of IAUS259: Cosmic Magnetic Field
Studies on the Composition of Organic and Conventional Milk Products
The changes in the basic physicochemical characteristics and the lipid composition of Bulgarian organic and conventional dairy products (cow's yoghurt and cow's cheese) during the winter and summer period have been investigated. There were no significant changes in the basic physicochemical characteristics for organic and conventional milk products (fat content in dry matter, content of milk protein, dry matter, acidity, salt content) in the studied periods. Organic yoghurt has lower acidity in comparison with conventional yoghurt. Organic cheese is the only one with a degree of maturity (21.7% and 20.5%), corresponding to the regulated value in the Bulgarian state standards for cheese (not less than 14%). The lipids have identical fatty acid composition, dominated by saturated fatty acids (68.7% -74.5%) and that their content is higher in winter. During the summer period quantities of trans fatty acids in mono- (C18:1) and polyunsaturated fatty acids (C18: 2 and C18: 3) was higher than in winter. The content of tocopherols in the yoghurt fats is minimal, as their values in summer period is higher, such in the various trademarks cheese tocopherols not detected
Fast and Simple Relational Processing of Uncertain Data
This paper introduces U-relations, a succinct and purely relational
representation system for uncertain databases. U-relations support
attribute-level uncertainty using vertical partitioning. If we consider
positive relational algebra extended by an operation for computing possible
answers, a query on the logical level can be translated into, and evaluated as,
a single relational algebra query on the U-relation representation. The
translation scheme essentially preserves the size of the query in terms of
number of operations and, in particular, number of joins. Standard techniques
employed in off-the-shelf relational database management systems are effective
for optimizing and processing queries on U-relations. In our experiments we
show that query evaluation on U-relations scales to large amounts of data with
high degrees of uncertainty.Comment: 12 pages, 14 figure
The influence of Sofia's destination image on satisfaction, intention to recommend, and post-visit intentions towards Bulgarian products: Does unique image matter?
This thesis is studying the destination image of an emerging tourist destination – Sofia, Bulgaria. The city’s number of foreign tourists has increased with 18 per cent in 2017. As destination image has been proven to be an important factor influencing significantly both pre-visit and post-visit intentions, the city is in pressing need to create a strong image in tourists’ minds.
Based on previous literature, a conceptual model investigating the relationships between the different components of destination image, tourism satisfaction, intention to recommend, and post-visit intentions towards Bulgarian products was proposed and tested. Destination image was studied with three components – cognitive, affective, and unique. The latter has been often overlooked in previous studies and there is not much clarity about its conceptualization and measurement. This study provides more information about the concept but it also proposes a new method of measuring it through text-mining of user-generated blog posts.
A questionnaire was distributed to 314 foreign visitors of Sofia. The data analysis methods included descriptive statistics, principal component analysis, and multiple linear regressions. The results reveal that the unique image has a significant influence on all constructs, however, it is the affective which has the strongest impact. Moreover, the traditional affective image has the strongest influence on overall image and tourism satisfaction, which in turns has the strongest impact on traditional word-of-mouth. Cognitive image has influence on all constructs except on electronic word-of-mouth. Finally, post-visit intentions towards Bulgarian products are influenced by all variables, with the exception of tourism satisfaction.Esta tese tem como objetivo estudar a imagem de um destino turístico emergente - Sofia, Bulgária. Dado que o número de turistas estrangeiros na cidade aumentou 18% em 2017 e sendo a imagem de um destino considerada um fator importante na influência das intenções de pré-visita e pós-visita, Sofia necessita de criar uma imagem forte na mente dos turistas. Um modelo conceptual, que investiga as relações entre as diferentes componentes da imagem, a satisfação do turista, a intenção de recomendar e as intenções pós-visita face aos produtos búlgaros, foi proposto e testado. A imagem do destino foi estudada com três componentes - cognitiva, afetiva e única. Esta última tem sido muitas vezes ignorada na literatura e não há muita clareza sobre a sua conceptualização e medição. Este tese fornece mais informações sobre este construto, mas também propõe um método para a sua medição através da extração de textos de posts gerados por utilizadores de blogs. Aplicou-se um questionário a 314 turistas de Sofia. Os métodos de análise centraram-se em análises de componentes principais e regressões lineares múltiplas. Os resultados revelam que a imagem única influencia todos os construtos, no entanto, é a afetiva que tem o impacto mais forte. Além disso, a imagem afetiva tradicional tem a maior influência na imagem geral e na satisfação, o que, por sua vez, tem o impacto mais forte na WOM. A imagem cognitiva influencia todos os construtos, exceto eWOM. Finalmente, as intenções pós-visita aos produtos búlgaros são influenciadas por todas as variáveis, com exceção da satisfação
The different origins of magnetic fields and activity in the Hertzsprung gap stars, OU Andromedae and 31 Comae
Context: When crossing the Hertzsprung gap, intermediate-mass stars develop a
convective envelope. Fast rotators on the main sequence, or Ap star
descendants, are expected to become magnetic active subgiants during this
evolutionary phase. Aims: We compare the surface magnetic fields and activity
indicators of two active, fast rotating red giants with similar masses and
spectral class but diferent rotation rates - OU And (Prot=24.2 d) and 31 Com
(Prot=6.8 d) - to address the question of the origin of their magnetism and
high activity.
Methods: Observations were carried out with the Narval spectropolarimeter in
2008 and 2013.We used the least squares deconvolution technique to extract
Stokes V and I profiles to detect Zeeman signatures of the magnetic field of
the stars. We provide Zeeman-Doppler imaging, activity indicator monitoring,
and a precise estimation of stellar parameters. We use stellar evolutionary
models to infer the evolutionary status and the initial rotation velocity on
the main sequence.
Results: The detected magnetic field of OU And is a strong one. Its
longitudinal component Bl reaches 40 G and presents an about sinusoidal
variation with reversal of the polarity. The magnetic topology of OU And is
dominated by large scale elements and is mainly poloidal with an important
dipole component, and a significant toroidal component. The detected magnetic
field of 31 Com is weaker, with a magnetic map showing a more complex field
geometry, and poloidal and toroidal components of equal contributions. The
evolutionary models show that the progenitors of OU And and 31 Com must have
been rotat
Conclusions: OU And appears to be the probable descendant of a magnetic Ap
star, and 31 Com the descendant of a relatively fast rotator on the main
sequence.Comment: 16 pages, 12 figure
Search for surface magnetic fields in Mira stars. First detection in chi Cyg
In order to complete the knowledge of the magnetic field and of its influence
during the transition from Asymptotic Giant Branch to Planetary Nebulae stages,
we have undertaken a search for magnetic fields at the surface of Mira stars.
We used spectropolarimetric observations, collected with the Narval instrument
at TBL, in order to detect - with Least Squares Deconvolution method - a Zeeman
signature in the visible part of the spectrum. We present the first
spectropolarimetric observations of the S-type Mira star chi Cyg, performed
around its maximum light. We have detected a polarimetric signal in the Stokes
V spectra and we have established its Zeeman origin. We claim that it is likely
to be related to a weak magnetic field present at the photospheric level and in
the lower part of the stellar atmosphere. We have estimated the strength of its
longitudinal component to about 2-3 Gauss. This result favors a 1/r law for the
variation of the magnetic field strength across the circumstellar envelope of
chi Cyg. This is the first detection of a weak magnetic field at the stellar
surface of a Mira star and we discuss its origin in the framework of shock
waves periodically propagating throughout the atmosphere of these radially
pulsating stars. At the date of our observations of chi Cyg, the shock wave
reaches its maximum intensity, and it is likely that the shock amplifies a weak
stellar magnetic field during its passage through the atmosphere. Without such
an amplification by the shock, the magnetic field strength would have been too
low to be detected. For the first time, we also report strong Stokes Q and U
signatures (linear polarization) centered onto the zero velocity (i.e., at the
shock front position). They seem to indicate that the radial direction would be
favored by the shock during its propagation throughout the atmosphere.Comment: 9 pages, 4 figures accepted by Astronomy and Astrophysics (21
November 2013
A dominant magnetic dipole for the evolved Ap star candidate EK Eridani
EK Eri is one of the most slowly rotating active giants known, and has been
proposed to be the descendant of a strongly magnetic Ap star. We have performed
a spectropolarimetric study of EK Eri over 4 photometric periods with the aim
of inferring the topology of its magnetic field. We used the NARVAL
spectropolarimeter at the Bernard Lyot telescope at the Pic du Midi
Observatory, along with the least-squares deconvolution method, to extract high
signal-to-noise ratio Stokes V profiles from a timeseries of 28 polarisation
spectra. We have derived the surface-averaged longitudinal magnetic field Bl.
We fit the Stokes V profiles with a model of the large-scale magnetic field and
obtained Zeeman Doppler images of the surface magnetic strength and geometry.
Bl variations of up to about 80 G are observed without any reversal of its
sign, and which are in phase with photometric ephemeris. The activity
indicators are shown to vary smoothly on a timescale compatible with the
rotational period inferred from photometry (308.8 d.), however large deviations
can occur from one rotation to another. The surface magnetic field variations
of EK Eri appear to be dominated by a strong magnetic spot (of negative
polarity) which is phased with the dark (cool) photometric spot. Our modeling
shows that the large-scale magnetic field of EK Eri is strongly poloidal. For a
rotational axis inclination of i = 60{\deg}, we obtain a model that is almost
purely dipolar. In the dipolar model, the strong magnetic/photometric spot
corresponds to the negative pole of the dipole, which could be the remnant of
that of an Ap star progenitor of EK Eri. Our observations and modeling
conceptually support this hypothesis, suggesting an explanation of the
outstanding magnetic properties of EK Eri as the result of interaction between
deep convection and the remnant of an Ap star magnetic dipole.Comment: 8 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Detection of corn and sunflower oil adulterations of olive oils using fluorescence spectroscopy
A novel approach for the detection of admixtures of vegetable (corn and sunflower) oils in commercially available olive oils on a qualitative level is presented. Chemical analysis of the contents of fatty acids in each of the model systems under study is performed. The dependence of the ratio of the two main fluorescence intensity peaks 1 2 F / F and that of the linoleic to oleic acids C18:2 / C18:1 is studied. It is shown that an increase of the concentration of the adulterant the maximum of the first fluorescence peak exhibits a wavelength shift. Fluorescence analysis can be used for a qualitative real time determination of the presence of adulterants in olive oil by comparison of the observed particular fluorescence spectrum with those from a database of spectra of olive oils and adulterants from a particular region
Magnetic field structure in single late-type giants: Beta Ceti in 2010 - 2012
The data were obtained using two spectropolarimeters - Narval at the Bernard
Lyot Telescope, Pic du Midi, France, and ESPaDOnS at CFHT, Hawaii. Thirty-eight
circularly-polarized spectra have been collected in the period June 2010 -
January 2012. The Least Square Deconvolution method was applied for extracting
high signal-to-noise ratio line profiles, from which we measure the
surface-averaged longitudinal magnetic field Bl. Chromospheric activity
indicators CaII K, H_alpha, CaII IR (854.2 nm) and radial velocity were
simultaneously measured and their variability was analysed together with the
behavior of Bl. The Zeeman Doppler Imaging (ZDI) inversion technique was
employed for reconstruction of the large-scale magnetic field and two magnetic
maps of Beta Ceti are presented for two periods (June 2010 - December 2010 and
June 2011 - January 2012). Bl remains of positive polarity for the whole
observational period. The behavior of the line activity indicators is in good
agreement with the Bl variations. The two ZDI maps show a mainly axisymmetric
and poloidal magnetic topology and a simple surface magnetic field
configuration dominated by a dipole. Little evolution is observed between the
two maps, in spite of a 1 yr interval between both subsets. We also use
state-of-the-art stellar evolution models to constrain the evolutionary status
of Beta Ceti. We derive a mass of 3.5 M_sun and propose that this star is
already in the central-helium burning phase. Taking into account all our
results and the evolutionary status of the star, we suggest that dynamo action
alone may not be eficient enough to account for the high magnetic activity of
Beta Ceti. As an alternate option, we propose that it may be an Ap star
descendant presently undergoing central helium-burning and still exhibiting a
remnant of the Ap star magnetic field.Comment: 10 pages; 5 figures; 3 table
- …