4,179 research outputs found
A Comment on "Brans-Dicke Cosmology with a scalar field potential"
We show that a recent letter claiming to present exact cosmological solutions
in Brans-Dicke theory actually uses a flawed set of equations as the starting
point for their analysis. The results presented in the letter are therefore not
valid.Comment: 2 pages, no figures. To appear in Europhysics Letter
Effect of the number of vortices on the torque scaling in Taylor-Couette flow
Torque measurements in Taylor-Couette flow, with large radius ratio and large
aspect ratio, over a range of velocities up to a Reynolds number of 24 000 are
presented. Following a specific procedure, nine states with distinct number of
vortices along the axis were found and the aspect ratio of the vortices were
measured. The relationship between the speed and the torque for a given number
of vortices is reported. In the turbulent Taylor vortex flow regime, at
relatively high Reynolds number, a change in behaviour is observed
corresponding to intersections of the torque-speed curves for different states.
Before each intersection, the torque for a state with larger number of vortices
is higher. After each intersection, the torque for a state with larger number
of vortices is lower. The exponent, from the scaling laws of the torque, always
depends on the aspect ratio of the vortices. When the Reynolds number is
rescaled using the mean aspect ratio of the vortices, only a partial collapse
of the exponent data is found.Comment: 11 pages, 6 figure
Robust ab initio calculation of condensed matter: transparent convergence through semicardinal multiresolution analysis
We present the first wavelet-based all-electron density-functional
calculations to include gradient corrections and the first in a solid. Direct
comparison shows this approach to be unique in providing systematic
``transparent'' convergence, convergence with a priori prediction of errors, to
beyond chemical (millihartree) accuracy. The method is ideal for exploration of
materials under novel conditions where there is little experience with how
traditional methods perform and for the development and use of chemically
accurate density functionals, which demand reliable access to such precision.Comment: 4 pages, 3 figures, 4 tables. Submitted to Phys. Rev. Lett. (updated
to include GGA
Principales sucesos nacionales del primer semestre de 2009
Síntesis cronológica sobre los principales sucesos en México durante del primer semestre de 2009.ITESO, A.C
Notas en torno a las autodefensas michoacanas
En torno al movimiento de las autodefensas michoacanas, que a decir de uno de sus líderes se armaron contra el "gobierno alterno del crimen organizado”, se presentan algunas notas que buscan definir lo que son y cómo están organizadas, se analiza el caso desde las dimensiones económica, política y cultural; se presenta el papel que desempeñan algunos actores involucrados, y se sugieren algunas hipótesis sobre el fenómeno.ITESO, A.C
Locally induced neural stem cells/pluripotent stem cells for in vivo cell replacement therapy
ABSTRACT: Neural stem cells hold the key to innovative new treatments for age-associated degeneration and traumatic injury to the brain and spinal cord. We hypothesized that the in vivo induced pluripotent stem cells or neural stem cells through 'forced gene expression' can be used to repair damaged brain areas or treat degenerative diseases. Hopefully, these in vivo patient-specific stem cells can bring a new avenue for cell replacement therapies.published_or_final_versio
A K-band spectral mini-survey of Galactic B[e] stars
We present a mini-survey of Galactic B[e] stars mainly undertaken with the
Large Binocular Telescope (LBT). B[e] stars show morphological features with
hydrogen emission lines and an infrared excess, attributed to warm
circumstellar dust. In general, these features are assumed to arise from dense,
non-spherical, disk-forming circumstellar material in which molecules and dust
can condensate. Due to the lack of reliable luminosities, the class of Galactic
B[e] stars contains stars at very different stellar evolutionary phases like
Herbig AeBe, supergiants or planetary nebulae. We took near-infrared long-slit
K-band spectra for a sample of Galactic B[e] stars with the LBT-Luci I.
Prominent spectral features, such as the Brackett gamma line and CO band heads
are identified in the spectra. The analysis shows that the stars can be
characterized as evolved objects. Among others we find one LBV candidate
(MWC314), one supergiant B[e] candidate with 13CO (MWC137) and in two cases
(MWC623 and AS 381) indications for the existence of a late-type binary
companion, complementary to previous studies. For MWC84, IR spectra were taken
at different epochs with LBT-Luci I and the GNIRS spectrograph at the Gemini
North telescope. The new data show the disappearance of the circumstellar CO
emission around this star, previously detectable over decades. Also no signs of
a recent prominent eruption leading to the formation of new CO disk emission
are found during 2010 and 2013.Comment: 10 pages, 7 figures, 4 tables, accepted for publication in MNRAS (in
press
D'atri spaces of type k and related classes of geometries concerning jacobi operators
In this article we continue the study of the geometry of -D'Atri spaces,
( denotes the dimension of the manifold) began by
the second author. It is known that -D'Atri spaces, are related
to properties of Jacobi operators along geodesics, since she has shown
that , are invariant
under the geodesic flow for any unit tangent vector . Here, assuming that
the Riemannian manifold is a D'Atri space, we prove in our main result that
is also invariant under the geodesic flow if . In addition, other properties of Jacobi operators related to the
Ledger conditions are obtained and they are used to give applications to
Iwasawa type spaces. In the class of D'Atri spaces of Iwasawa type, we show two
different characterizations of the symmetric spaces of noncompact type: they
are exactly the -spaces and on the other hand they are -D'Atri
spaces for some In the last case, they are -D'Atri for all
as well. In particular, Damek-Ricci spaces that are -D'Atri
for some are symmetric.
Finally, we characterize -D'Atri spaces for all as the -spaces (geodesic symmetries preserve the principal curvatures of
small geodesic spheres). Moreover, applying this result in the case of 4%
-dimensional homogeneous spaces we prove that the properties of being a D'Atri
(1-D'Atri) space, or a 3-D'Atri space, are equivalent to the property of being
a -D'Atri space for all .Comment: 19 pages. This paper substitute the previous one where one Theorem
has been deleted and one section has been adde
Universe acceleration and fine structure constant variation in BSBM theory
In this work we investigate the utility of using SNe Ia observations in
constraining the cosmological parameters in BSBM theory where a scalar field is
responsible for both fine structure constant variation and late time universe
acceleration. The model is discussed in the presence of an exponential self
potential for the scalar field. Stability and phase space analysis of the
solutions are studied. The model is tested against observational data for
Hubble parameter and quasar absorption spectra. With the best fitted model
parameters, the theory predicts a good match with the experimental results and
exhibits fine structure constant variation. The analysis also shows that for
the equation of state parameter, recent universe acceleration and possible
phantom crossing in future is forecasted.Comment: 14 pages, 10 figures, final version with minor modification accepted
to be published in JCA
Desplazamiento cotidiano de estudiantes entre comunas de Chile: evidencia y recomendaciones de política para la nueva institucionalidad de la Educación Pública
Donoso-Diaz, S (Donoso-Diaz, Sebastian) ; Arias-Rojas, O (Arias-Rojas, Oscar). Univ Talca, Talca, Chile.A key feature of the Chilean school system is the discrimination in educational provision, showing a strong association between learning outcomes, on the one hand, and cultural capital and income of households, on the other. This discrimination forces families to seek educational institutions according to their expectations, generating mobility of students from their communities of origin to other communities. The analysis of the Chilean survey of households in 2006 allowed to quantify this phenomenon (student commuting), and demonstrated the existence of patterns associated with the dynamics of settlement of the population along the country: low mobility in the end regions, intermediate in the central regions of the country, and high in the Metropolitan Region of Santiago. According to these results, we discuss policy recommendations essential to incorporate the territorial dimension in the design of the new institutions of public education in Chile
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