7,946 research outputs found
Photometric and spectroscopic variations of the Be star HD 112999
Be objects are stars of B spectral type showing lines of the Balmer series in
emission. The presence of these lines is attributed to the existence of an
extended envelope, disk type, around them. Some stars are observed in both the
Be and normal B-type spectroscopic states and they are known as transient Be
stars. In this paper we show the analysis carried out on a new possible
transient Be star, labelled HD 112999, using spectroscopic optical observations
and photometric data.Comment: 10 pages, 5 figures, accepted for publication in IBV
Supercritical biharmonic equations with power-type nonlinearity
The biharmonic supercritical equation , where and
, is studied in the whole space as well as in a
modified form with as right-hand-side with an additional
eigenvalue parameter in the unit ball, in the latter case together
with Dirichlet boundary conditions. As for entire regular radial solutions we
prove oscillatory behaviour around the explicitly known radial {\it singular}
solution, provided , where
is a further critical exponent, which was introduced in a recent work by
Gazzola and the second author. The third author proved already that these
oscillations do not occur in the complementing case, where .
Concerning the Dirichlet problem we prove existence of at least one singular
solution with corresponding eigenvalue parameter. Moreover, for the extremal
solution in the bifurcation diagram for this nonlinear biharmonic eigenvalue
problem, we prove smoothness as long as
A spectroscopic survey of the youngest field stars in the solar neighbourhood. I. The optically bright sample
We present the first results of a ground-based programme conducted on 1-4m
class telescopes. Our sample consists of 1097 active and presumably young
stars, all of them being optical counterparts of RASS X-ray sources in the
northern hemisphere. We concentrate on the 704 optically brightest
(V_Ticho<=9.5 mag) candidates. We acquired high-res spectroscopy in the
Halpha/Li spectral regions for 426 of such stars without relevant literature
data. We describe the sample and the observations and we start to discuss its
physical properties. We used a cross-correlation technique and other tools to
derive accurate radial/rotational velocities and to perform a spectral
classification for both single and SB2 stars. The spectral subtraction
technique was used to derive chromospheric activity levels and Li abundances.
We estimated the fraction of young single stars and multiple systems in stellar
soft X-ray surveys and the contamination by more evolved systems, like RS
CVn's. We classified stars on the basis of Li abundance and give a glimpse of
their sky distribution. The sample appears to be a mixture of young
Pleiades-/Hyades- like stars plus an older Li-poor population (~1-2 Gyr). 7
stars with Li abundance compatible with the age of IC 2602 (~30 Myr) or younger
were detected as well, although 2 appear to be Li-rich giants. The discovery of
a large number of Li-rich giants is another outcome of this survey. The
contamination of soft X-ray surveys by old systems in which the activity level
is enhanced by tidal synchronisation is not negligible, especially for K-type
stars. 5 stars with Li content close to the primordial abundance are probably
associated with known moving groups in the solar neighbourhood. Some of them
are PTTS candidates according to their positions in the HR diagram.Comment: 16 pages, 12 figures, 6 tables; 2 figures and 2 tables in electronic
form only. Paper accepted by Astronomy and Astrophysic
High-performance analog front-end (AFE) for EOG systems
Electrooculography is a technique for measuring the corneo-retinal standing potential of the human eye. The resulting signal is called the electrooculogram (EOG). The primary applications are in ophthalmological diagnosis and in recording eye movements to develop simple human–machine interfaces (HCI). The electronic circuits for EOG signal conditioning are well known in the field of electronic instrumentation; however, the specific characteristics of the EOG signal make a careful electronic design necessary. This work is devoted to presenting the most important issues related to the design of an EOG analog front-end (AFE). In this respect, it is essential to analyze the possible sources of noise, interference, and motion artifacts and how to minimize their effects. Considering these issues, the complete design of an AFE for EOG systems is reported in this work.info:eu-repo/semantics/publishedVersio
The spatially-resolved star formation histories of CALIFA galaxies: Implications for galaxy formation
This paper presents the spatially resolved star formation history (SFH) of
nearby galaxies with the aim of furthering our understanding of the different
processes involved in the formation and evolution of galaxies. To this end, we
apply the fossil record method of stellar population synthesis to a rich and
diverse data set of 436 galaxies observed with integral field spectroscopy in
the CALIFA survey. The sample covers a wide range of Hubble types, with stellar
masses ranging from to . Spectral
synthesis techniques are applied to the datacubes to retrieve the spatially
resolved time evolution of the star formation rate (SFR), its intensity
(), and other descriptors of the 2D-SFH in seven bins of
galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd), and five bins of stellar
mass. Our main results are: a) Galaxies form very fast independently of their
current stellar mass, with the peak of star formation at high redshift (). Subsequent star formation is driven by and morphology, with less
massive and later type spirals showing more prolonged periods of star
formation. b) At any epoch in the past the SFR is proportional to ,
with most massive galaxies having the highest absolute (but lowest specific)
SFRs. c) While nowadays is similar for all spirals, and
significantly lower in early type galaxies (ETG), in the past scales well with morphology. The central regions of today's ETGs are
where reached the highest values (Gyrpc), similar to those measured in high redshift
star forming galaxies. d) The evolution of in Sbc systems
matches that of models for Milky-Way-like galaxies, suggesting that the
formation of a thick disk may be a common phase in spirals at early epochs.Comment: 21 pages, 11 figures, 1 table, accepted for publication in Astronomy
& Astrophysics, abstract abridged for arXiv submissio
Representation theory of super Yang-Mills algebras
We study in this article the representation theory of a family of super
algebras, called the \emph{super Yang-Mills algebras}, by exploiting the
Kirillov orbit method \textit{\`a la Dixmier} for nilpotent super Lie algebras.
These super algebras are a generalization of the so-called \emph{Yang-Mills
algebras}, introduced by A. Connes and M. Dubois-Violette in \cite{CD02}, but
in fact they appear as a "background independent" formulation of supersymmetric
gauge theory considered in physics, in a similar way as Yang-Mills algebras do
the same for the usual gauge theory. Our main result states that, under certain
hypotheses, all Clifford-Weyl super algebras \Cliff_{q}(k) \otimes A_{p}(k),
for , or and , appear as a quotient of all super
Yang-Mills algebras, for and . This provides thus a family
of representations of the super Yang-Mills algebras
Comportamiento de cuatro especies en sistemas múltiples de producción
Con el objeto de analizar el comportamiento de los cultivos múltiples, tanto en lo referente al rendimiento cultural de las especies intervinientes, como en el uso más eficiente del suelo y la competencia entre ellas, se compararon cuatro consociaciones: Maíz-Poroto, Maíz- Mandioca, Maní-Mandioca y Poroto-Mandioca; con sus respectivos monocultivos. Se realizaron diseños de bloques al azar con cuatro repeticiones, exponiendo los resultados al análisis de la variancia y test de Tuckey (a= 0,05), determinando el Uso Eficiente de la Tierra (U.E.T.), y la tasa de competencia entre especies mediante las siguientes ecuaciones: U.E.T. = (C.A./M.A.) + (C.B./M.B.); y Tcx = {Ax/Mx) I (Ay/My) X (Ey/Ex). Las experiencias se realizaron en el Departamento Capital de la Provincia de Corrientes, con un clima subhúmedo, mesotermal, con poca o nula deficiencia de agua; y sobre un suelo Udipsamment álfico, mixto, hipertérmico, identificado como serie Ensenada Grande. Los resultados obtenidos se muestran favorables en todos los aspectos a las alternativas consociadas con valores de U.E.T (uso eficiente de tierra) que oscilan entre 1.38 y 1.51 mostrándose la mandioca como la de mejor comportamiento en las consociaciones. Los rendimientos de las especies en consociación, superaron a los monocultivos en iguales superficies en un 40 a 60 % en promedio
The economics of Theocracy
This paper models theocracy as a regime where the clergy in power retains knowledge of the cost of political production but which is potentially incompetent or corrupt. This is contrasted with a secular regime where government is contracted out to a secular ruler, and hence the church loses the possibility to observe costs and creates for itself a hidden-information agency problem. The church is free to choose between regimes – a make-or-buy choice – and we look for the range of environmental parameters that are most conducive to the superiority of theocracy and therefore to its occurrence and persistence, despite its disabilities. Numerical solution of the model indicates that the optimal environment for a theocracy is likely to be one in which the “bad” (high-cost) state is disastrously bad but the probability of its occurrence is not very high. A broad review of the historical evidence yields some suggestive support to the predictions of the model. Finally, the model is shown to be applicable to the make-or-buy-government choices of other groups, such as organized labor and the military
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