2,731 research outputs found
The Applegate mechanism in Post-Common-Envelope Binaries: Investigating the role of rotation
Eclipsing time variations (ETVs) are observed in many close binary systems.
In particular, for several post-common-envelope binaries (PCEBs) that consist
of a white dwarf and a main sequence star, the O-C diagram suggests that real
or apparent orbital period variations are driven by Jupiter-mass planets or as
a result of magnetic activity, the so-called Applegate mechanism. The latter
explains orbital period variations as a result of changes in the stellar
quadrupole moment due to magnetic activity. We explore the feasibility of
driving ETVs via the Applegate mechanism for a sample of PCEB systems,
including a range of different rotations. Using the MESA code we evolve 12
stars with different masses and rotation rates. We apply a simple dynamo model
to their radial profiles to investigate on which scale the predicted activity
cycle matches the observed modulation period, and quantify the uncertainty, and
further calculate the required energies to drive que Applegate mechanism. We
show that the Applegate mechanism is energetically feasible in 5 PCEB systems,
and note that these are the systems with the highest rotation rate compared to
the critical rotation rate of the main-sequence star. The results suggest that
the ratio of physical to critical rotation in the main sequence star is an
important indicator for the feasibility of Applegate's mechanism, but exploring
larger samples will be necessary to probe this hypothesis.Comment: 9 pages, 5 figures. Accepted for publication in A&
Effect of energy density and virginiamycin supplementation in diets on growth performance and digestive function of finishing steers.
ObjectiveThis study was determined the influence of virginiamycin supplementation on growth-performance and characteristics of digestion of cattle with decreasing dietary net energy value of the diet for maintenance (NEm) from 2.22 to 2.10 Mcal/kg.MethodsEighty crossbred beef steers (298.2±6.3 kg) were used in a 152-d performance evaluation consisting of a 28-d adaptation period followed by a 124-d growing-finishing period. During the 124-d period steers were fed either a lesser energy dense (LED, 2.10 Mcal/kg NEm) or higher energy dense (HED, 2.22 Mcal/kg NEm) diet. Diets were fed with or without 28 mg/kg (dry matter [DM] basis) virginiamycin in a 2×2 factorial arrangement. Four Holstein steers (170.4±5.6 kg) with cannulas in the rumen (3.8 cm internal diameter) and proximal duodenum were used in 4×4 Latin square experiment to study treatment effects on characteristics of digestion.ResultsNeither diet energy density nor virginiamycin affected average daily gain (p>0.10). As expected, dry matter intake and gain efficiency were greater (p<0.01) for LED- than for HED-fed steers. Virginiamycin did not affect estimated net energy value of the LED diet. Virginiamycin increased estimated NE of the HED diet. During daylight hours when the temperature humidity index averaged 81.3±2.7, virginiamycin decreased (p<0.05) ruminal temperature. Virginiamycin did not influence (p>0.10) ruminal or total tract digestion. Ruminal (p = 0.02) and total tract digestion (p<0.01) of organic matter, and digestible energy (p<0.01) were greater for HED vs LED. Ruminal microbial efficiency was lower (p<0.01) for HED vs LED diets.ConclusionThe positive effect of virginiamycin on growth performance of cattle is due to increased efficiency of energy utilization, as effects of virginiamycin on characteristics of digestion were not appreciable. Under conditions of high ambient temperature virginiamycin may reduce body temperature
Non-critically squeezed light via spontaneous rotational symmetry breaking
We theoretically address squeezed light generation through the spontaneous
breaking of the rotational invariance occuring in a type I degenerate optical
parametric oscillator (DOPO) pumped above threshold. We show that a DOPO with
spherical mirrors, in which the signal and idler fields correspond to first
order Laguerre-Gauss modes, produces a perfectly squeezed vacuum with the shape
of a Hermite-Gauss mode, within the linearized theory. This occurs at any
pumping level above threshold, hence the phenomenon is non-critical.
Imperfections of the rotational symmetry, due e.g. to cavity anisotropy, are
shown to have a small impact, hence the result is not singular.Comment: 4 pages, 1 figure, replaced with resubmitted versio
Quantum coherence enfeebled by classical uncertainties
The fundamental indication of the departure of quantum mechanics from the classical world is the so-called quantum coherence. Typically, we define it as the characteristic of systems which are in a superposition of states yielding interference patterns in certain kinds of experiments. In addition to its captivating philosophical implications, quantum coherence turned out to be a valuable tool in different areas, ranging from quantum information to biology, where it was used to describe several fundamental processes. Here, we go one step further to study how classical uncertainties in a mixture of similar states reduce quantum coherence in quantum scattering theory. To this end, we deal with different examples, all of them with roots in the widely studied Feynman's two-slit thought experiment. We finally propose an operational and intuitive definition of the concept of coherence length whose implications largely transcend the simplicity of the corresponding mathematical development, as it is demonstrated when applied to the analysis of some recent atomic and molecular processes.Fil: Barrachina Tejada, Raul Oscar. Comisión Nacional de EnergÃa Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Navarrete, F.. Universität Rostock; AlemaniaFil: Ciappina, M. F.. Technion - Israel Institute of Technology; Israe
Bulge RR Lyrae stars in the VVV tile
The VISTA Variables in the V\'ia L\'actea (VVV) Survey is one of the six ESO
public surveys currently ongoing at the VISTA telescope on Cerro Paranal,
Chile. VVV uses near-IR () filters that at present provide
photometry to a depth of mag in up to 36 epochs spanning
over four years, and aim at discovering more than 10 variable sources as
well as trace the structure of the Galactic bulge and part of the southern
disk. A variability search was performed to find RR Lyrae variable stars. The
low stellar density of the VVV tile , which is centered at
() (), makes it suitable to search for
variable stars. Previous studies have identified some RR Lyrae stars using
optical bands that served to test our search procedure. The main goal is to
measure the reddening, interstellar extinction, and distances of the RR Lyrae
stars and to study their distribution on the Milky Way bulge. A total of 1.5 sq
deg were analyzed, and we found 39 RR Lyrae stars, 27 of which belong to the
ab-type and 12 to the c-type. Our analysis recovers all the previously
identified RR Lyrae variables in the field and discovers 29 new RR Lyrae stars.
The reddening and extinction toward all the RRab stars in this tile were
derived, and distance estimations were obtained through the period--luminosity
relation. Despite the limited amount of RR Lyrae stars studied, our results are
consistent with a spheroidal or central distribution around and
kpc. for either the Cardelli or Nishiyama extinction law.Comment: 10 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Sedimentary heterogeneity and petrophysical characterization of Barremian tsunami and barrier island/inlet deposits: The Aliaga outcrop as a reservoir analogue (Galve sub-basin, eastern Spain)
The present study examined two sandstone deposits in the Aliaga outcrop as a reservoir analogue over a distance of 200-m-long and attempted to establish a correlation between sand facies and the petrophysical properties of the sandstones in order to investigate the reservoir heterogeneity. The Aliaga reservoir analogue represents the upper part of Camarillas Fm., deposited during the Barremian synrift phase of the Galve sub-basin (Iberian Basin, Spain). It is characterized by a transitional sedimentary interval from sandy-dominant deposits to carbonate-dominant deposits, which were deposited under the same palaeoenvironmental conditions (in relation to systems of back-barrier sedimentation).
The description of the Aliaga outcrop provided here consists of lithological descriptions of two sandstone deposits: a tsunami and a barrier island/inlet, at both mesoscopic (decimetres to tens of metres) and microscopic scales (millimetres to centimetres). Both deposits recognized at the basin scale were described in terms of sand grain size, sand sorting and cementation; further cores were drilled along outcrop to collect samples for porosity and permeability measurements.
Both sandstone reservoirs are the result of different sedimentary processes that determined facies characteristics, as the different petrophysical properties observed in these deposits. Consequently, the sedimentary process controls the heterogeneity of the sandstones facies and thus, the sand heterogeneity controls the distribution of the petrophysical properties. The classification of sand facies in terms of sand sorting seems to be more appropriate for describing sand heterogeneity; accordingly, petrophysical parameters in both deposits were also influenced by sand sorting.
The sand facies and petrophysics heterogeneity of the described deposits can be hierarchically ordered. First-order heterogeneity is related to the basin scale, second-order heterogeneity is related to genesis and the conditions of sediment deposition, and third-order heterogeneity is related to synsedimentary faults and/or post-sedimentation events.This research is a contribution to the project: Análisis de Cuencas Sedimentarias Continentales, of the Gobierno de Aragón, the Análisis de Cuencas Sedimentarias Group of the UCM-CAM, and the projects CGL2011-23717 (Ministerio de Ciencia e Innovación of the Spanish Government and FEDER) and UZ2015-CIE-10 (University of Zaragoza). Additional financial support was provided by a Cnpq (Conselho Nacional de Pesquisa e Desenvolvimento Tecnologico, Brasil) Research Grant (200147/2011-0) and an IAS Schema 1st session 2014 Postgraduate Grant to F. Veloso.Peer reviewe
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