3,891 research outputs found
Acerca de los Problemas de Acceso al Campo y las Relaciones con Informantes Clave en Instituciones Universitarias
En esta comunicación presentamos algunas notas metodológicas sobre las particularidades que asume el trabajo de investigación social acerca de las instituciones universitarias. Elaboramos estas reflexiones a partir de un estudio comparado sobre las polÃticas de vinculación con el sector productivo desarrolladas en los años noventa por cuatro universidades argentinas de perfiles organizacionales diferentes seleccionadasad hoc, estudio llevado a cabo en el Centro de Estudios Avanzados de la Universidad de Buenos Aire
Introgression Among Cultivated and Wild Grapevine in Tuscany
Wild grapevine, Vitis vinifera L. subsp. sylvestris (Gmelin, Hegi) is spontaneous to Europe
and common in Tuscany. In this study, wild grapevines were identified in 22 populations
from eight locations in Tuscan Maremma (Grosseto and Siena province). The plants
were propagated by cuttings, collected in a vineyard, genotyped by nuclear simple
sequence repeats (SSRs), chloroplast SSRs and single nucleotide polymorphisms
(SNPs), and compared to locally cultivated varieties (Vitis vinifera L. subsp. sativa)
and to non-vinifera and non-vitis genotypes. The identity analysis revealed that some
individuals were redundant genotypes, suggesting natural vegetative propagation. In
addition, four of the supposed V.v. sylvestris were in fact naturalized V.v. sativa. The
majority of putative sylvestris genotypes had chlorotype A, while the remainder had
chlorotype D, as the majority of Vitis vinifera subsp. sativa cultivated in Italy. Some of the
recovered sylvestris genotypes appeared to be natural crosses with cultivated grapevine
varieties in Tuscany, and their chlorotype suggests a higher pollen flow from sativa to
the sylvestris genotypes than in the opposite direction. In addition, other genotypes
appeared to be crosses within sylvestris, sylvestris-sativa or sylvestris-sylvestris siblings,
or equivalent relationships. These relationships suggest a noticeably level of sexual
reproductive activities among sylvestris and sylvestris-sativa genotypes. A cluster and
structure analysis clearly differentiated the true sylvestris from the sativa, and the nonvinifera
or non-vitis genotypes, and also highlighted a possible introgression of sylvestris
into some Italian and French cultivated varieties. The results therefore suggest that,
in addition to the primary ancient center of domestication from the Near East to
Central Asia, the introgression among cultivated and wild grapevine occurred in other
centers of diversification along the migration routes, contributing to the domestication
processes, and suggesting that these processes are still ongoing despite the reduction
in populations of sylvestris. The results also highlight that the GrapeReSeq 18K Vitis
genotyping chip are suitable for non-vitis genotyping and that the range of SNPs
heterozygosity in sylvestris appears to be up to 6% less and does not overlap the
heterozygosity range of sativa genotypes
The effect of the environment on the Faber Jackson relation
We investigate the effect of the environment on the Faber Jackson (FJ)
relation, using a sample of 384 nearby elliptical galaxies and estimating
objectively their environment on the typical scale of galaxy clusters. We show
that the intrinsic scatter of the FJ is significantly reduced when ellipticals
in high density environments are compared to ellipticals in low density ones.
This result, which holds on a limited range of overdensities, is likely to
provide an important observational link between scaling relations and formation
mechanisms in galaxies.Comment: accepted by Ap
The interplay between voluntary vaccination and reduction of risky behavior: a general behavior-implicit SIR model for vaccine preventable infections
The onset in the last 15 years of behavioral epidemiology has opened many new avenues for epidemiological modelers. In this manuscript we first review two classes of behavioral epidemiology models for vaccine preventable diseases, namely behaviour-implicit SIR models with prevalence-dependent vaccination (at birth and among older individuals), and prevalence-dependent contact rate.
Subsequently, we briefly propose a general framework of behavior–dependent nonlinear and linear Forces of Infection (FoI) valid for a vast family of infectious diseases, and including delays and ‘epidemic memory’ effects.
Finally and mainly, we develop a new general behavioral SIR model. This model combines the two aforementioned types of behavioral phenomena, previously considered only separately, into a single unified model for behavioral responses. The resulting model allows to develop a general phenomenological theory of the effects of behavioral responses within SIR models for endemic infections. In particular, the model allows to complete the picture about the complicate interplay between different behavioral responses acting on different epidemiological parameters in triggering sustained oscillations of vaccine coverage, risky behavior, and infection prevalence
Existence and uniqueness of limit cycles in a class of second order ODE's with inseparable mixed terms
We prove a uniqueness result for limit cycles of the second order ODE . Under mild additional conditions, we
show that such a limit cycle attracts every non-constant solution. As a special
case, we prove limit cycle's uniqueness for an ODE studied in \cite{ETA} as a
model of pedestrians' walk. This paper is an extension to equations with a
non-linear of the results presented in \cite{S}
Infrared Surface Brightness Fluctuations of the Coma Elliptical NGC 4874 and the Value of the Hubble Constant
We have used the Keck I Telescope to measure K-band surface brightness
fluctuations (SBFs) of NGC 4874, the dominant elliptical galaxy in the Coma
cluster. We use deep HST WFPC2 optical imaging to account for the contamination
due to faint globular clusters and improved analysis techniques to derive
measurements of the SBF apparent magnitude. Using a new SBF calibration which
accounts for the dependence of K-band SBFs on the integrated color of the
stellar population, we measure a distance modulus of 34.99+/-0.21 mag (100+/-10
Mpc) for the Coma cluster. The resulting value of the Hubble constant is 71+/-8
km/s/Mpc, not including any systematic error in the HST Cepheid distance scale.Comment: ApJ Letters, in press. Uses emulateapj5.st
Bearings-Only Guidance in Cis-Lunar Rendezvous
The current plans of returning to the Moon involve rendezvous and docking/berthing operations
with a passive permanent station, whose targeted orbit is a Near Rectilinear Halo
Orbit. In this work a preliminary guidance algorithm for the close-range rendezvous phase
is proposed, based on a sample mission application, assuming the active chaser can measure
relative angles only to the target. The navigation performance is affected by the maneuvers
performed because their execution is necessary to make the problem observable. The relative
motion equations with third body perturbation are considered directly in the guidance
algorithm, with the additional aim of improving observability during the approach trajectory.
Numerical simulations are presented to validate the proposed methodology
Searching for dark photons at the LHeC and FCC-he
Extensions of the Standard Model (SM) gauge group with a new U(1)X predict an additional gauge boson. Through kinetic mixing with the SM photons featured by a coupling ε, the ensuing so-called dark photons γ′, which acquire mass as a result of the breaking of the gauge group U(1)X, can interact with the SM field content. These massive dark photons can therefore decay to pairs of leptons, hadrons, or quarks, depending on their mass mγ′. In this work, we discuss searches for dark photons in the mass range around and below 1 GeV at the LHeC and FCC-he colliders. The signal is given by the displaced decays of the long-lived dark photon into two charged particles. We discuss the impact of conceivable irreducible (SM and machine-related) backgrounds and different signal efficiencies. Our estimates show that the LHeC and FCC-he can test a domain that is complementary to other present and planned experiments
The Fundamental Plane of Early-Type Galaxies as a Confounding Correlation
Early-type galaxies are characterized by many scaling relations. One of them,
the so-called fundamental plane is a relatively tight correlation between three
variables, and has resisted a clear physical understanding despite many years
of intensive research. Here, we show that the correlation between the three
variables of the fundamental plane can be the artifact of the effect of another
parameter influencing all, so that the fundamental plane may be understood as a
confounding correlation. Indeed, the complexity of the physics of galaxies and
of their evolution suggests that the main confounding parameter must be related
to the level of diversification reached by the galaxies. Consequently, many
scaling relations for galaxies are probably evolutionary correlations
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