452 research outputs found
On the interaction between tides and convection
We study the interaction between tides and convection in astrophysical bodies
by analysing the effect of a homogeneous oscillatory shear on a fluid flow.
This model can be taken to represent the interaction between a large-scale
periodic tidal deformation and a smaller-scale convective motion. We first
consider analytically the limit in which the shear is of low amplitude and the
oscillation period is short compared to the timescales of the unperturbed flow.
In this limit there is a viscoelastic response and we obtain expressions for
the effective elastic modulus and viscosity coefficient. The effective
viscosity is inversely proportional to the square of the oscillation frequency,
with a coefficient that can be positive, negative or zero depending on the
properties of the unperturbed flow. We also carry out direct numerical
simulations of Boussinesq convection in an oscillatory shearing box and measure
the time-dependent Reynolds stress. The results indicate that the effective
viscosity of turbulent convection falls rapidly as the oscillation frequency is
increased, attaining small negative values in the cases we have examined,
although significant uncertainties remain because of the turbulent noise. We
discuss the implications of this analysis for astrophysical tides.Comment: 14 pages, 5 figures, to be published in MNRA
Study of influence of heat stress on some physiological and productive traits in Holstein-Friesian dairy cows
Received: October 6th, 2020 ; Accepted: February 1st, 2021 ; Published: March 18th, 2021 ; Correspondence: [email protected] aim of the research was to study the effect of heat stress (HS) on some physiological
and productive traits in Holstein-Friesian dairy cows. The study included 22 cows on different
parities. In the building where the cows were housed, the temperature-humidity index (THI) was
reported at 10:00 and 15:00 h, at the same time the rectal temperature (RT) and respiratory rate
(RR) were reported for each of the examined cows. The daily rumen activity was taken from the
SCR system by Allflex. The average THI values in May were 71, in June - 75, in July - 74, and
in August - 77, from which it follows that in the summer months the cows were in conditions of
mild to moderate heat stress throughout the day. The average daily milk yield of the cows increased
from May to June and reached 41.44 kg day-1
, then decreased in July and August to 37.2 and
32.48 kg day-1
, respectively. With an increase in the THI values, an increase in the RR and RT
was registered, as in THI above 79 the RR was 56.54 per min, and the RT was 39.33 °C. With
increasing the THI values, the rumination of the cows decreased from 563 per day at THI < 72 to
542.5 at THI > 79. In cows with high daily milk yield, a higher RT was registered, and in cows with
more than 50 kg per day, the RT was 39.09 °С. A more intense rumination was found in cows
with higher daily milk yield. In cows with an average daily milk yield of 33.26 kg, an average of
450 ruminations per day were reported, and in those with an average milk yield of up to 42.89 kg
- 650 ruminations per day. From the research conducted it was found that the studied
physiological traits - rectal temperature, respiration rate and rumination are influenced by HS and
the intensity of this effect depend on the daily milk yield of cows and THI levels
High Precision Photometry for K2 Campaign 1
The two reaction wheel K2 mission promises and has delivered new discoveries
in the stellar and exoplanet fields. However, due to the loss of accurate
pointing, it also brings new challenges for the data reduction processes. In
this paper, we describe a new reduction pipeline for extracting high precision
photometry from the K2 dataset, and present public light curves for the K2
Campaign 1 target pixel dataset. Key to our reduction is the derivation of
global astrometric solutions from the target stamps, from which accurate
centroids are passed on for high precision photometry extraction. We extract
target light curves for sources from a combined UCAC4 and EPIC catalogue --
this includes not only primary targets of the K2 campaign 1, but also any other
stars that happen to fall on the pixel stamps. We provide the raw light curves,
and the products of various detrending processes aimed at removing different
types of systematics. Our astrometric solutions achieve a median residual of ~
0.13". For bright stars, our best 6.5 hour precision for raw light curves is
~20 parts per million (ppm). For our detrended light curves, the best 6.5 hour
precisions achieved is ~15 ppm. We show that our detrended light curves have
fewer systematic effects (or trends, or red-noise) than light curves produced
by other groups from the same observations. Example light curves of transiting
planets and a Cepheid variable candidate, are also presented. We make all light
curves public, including the raw and de-trended photometry, at
http://k2.hatsurveys.org.Comment: submitted to MNRA
HAT-P-55b: A Hot Jupiter Transiting a Sun-like Star
We report the discovery of a new transiting extrasolar planet, HAT-P-55b. The
planet orbits a V = 13.207 +/- 0.039 sun-like star with a mass of 1.013 +/-
0.037 solar masses, a radius of 1.011 +/- 0.036 solar radii and a metallicity
of -0.03 +/- 0.08. The planet itself is a typical hot Jupiter with a period of
3.5852467 +/- 0.0000064 days, a mass of 0.582 +/- 0.056 Jupiter masses and a
radius of 1.182 +/- 0.055 Jupiter radii. This discovery adds to the increasing
sample of transiting planets with measured bulk densities, which is needed to
put constraints on models of planetary structure and formation theories.Comment: 7 pages, 4 figures, accepted for publication in PAS
Adsorption of Indium on a InAs wetting layer deposited on the GaAs(001) surface
In this work we perform a first-principles study of the adsorption properties
of an In adatom deposited on 1.75 monolayers (ML) InAs, forming a wetting layer
on GaAs with the or
reconstruction. The structural properties of these reconstructions have been
studied: we determine the equilibrium geometry of the surfaces and their
stability for various growth conditions. We have then carried out a detailed
study of the potential energy surface (PES) for an In adsorbate, finding the
minima and the saddle points. The main characteristics of the PES and the
bonding configurations of the In adatom on the surface are analyzed by
comparing with analogous studies reported in the literature, trying to extract
the effects due to: (i) the compressive strain to which the InAs adlayer is
subjected, (ii) the particular surface reconstruction, and (iii) the wetting
layer composition. We found that, in general, stable adsorption sites are
located at: (i) locations besides the As in-dimers, (ii) positions bridging two
As in-dimers, (iii) between two adjacent ad-dimers (only in ), and
(iv) locations bridging two As ad-dimers. We find also other shallower
adsorption sites which are more reconstruction specific due to the lower
symmetry of the reconstruction compared to the
reconstruction
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