544 research outputs found
Effects of increasing the farm produced content in organic feeds on pig performances
In three experimental facilities (Exp.1, 2 and 3), two organic diets, one complex including processed feedstuffs as wheat bran and heat-treated soya beans (control), the other simplified and containing over 80 % of cereal and pulses (CP), were compared for growing-finishing pigs. The base components of the CP diets were moist maize grain, wheat and faba beans in Exp.1, triticale plus coloured-flowered peas in Exp.2, and triticale, oats, white-flowered peas and faba beans in Exp.3. The diets were formulated with similar energetic values and a lysine content (0.70 g ileal digestible lysine /MJ NE) 20 % lower than the conventional mean requirement for growing pigs. However, the CP diet had a lysine proportion 30% lower than requirement in Exp.1 and did not achieve the ideal protein pattern in Exp. 2 and 3. Diets were given in all experiments from 35 to 115 kg according to a feeding plan. Respectively 96, 100 and 80 pigs were used in Exp.1, 2 and 3 and were blocked in straw bedded pens of 4, 25 and 40.
In Exp.1, pigs receiving the control diet had a lower average feed intake than those offered the CP diet (p0.05), 760 and 719 in Exp.2 (p=0.04) and 684 and 677 in Exp.3 (p>0.05). The feed conversion rate (g/g) was high and reached respectively 3.28 and 3.41 in Exp.1 (p=0.01), 3.2 and 3.,4 in Exp.2, 3.3 and 3.4 in Exp.3. The lean meat rate did not differ significantly in Exp.1, 2 and 3, for pigs given control and CP diets. The study underlines that with a moderate growth objective, an organic feed with a low energetic and protein concentration can yield a satisfying lean meat rate. In spite of a tendency for lower performances, especially concerning the feed conversion rate, a simplified diet based on cereal and pulses can be used, taking into account its economical interest for organic pig production
Pore evolution in interstellar ice analogues: simulating the effects of temperature increase
Context. The level of porosity of interstellar ices - largely comprised of
amorphous solid water (ASW) - contains clues on the trapping capacity of other
volatile species and determines the surface accessibility that is needed for
solid state reactions to take place. Aims. Our goal is to simulate the growth
of amorphous water ice at low temperature (10 K) and to characterize the
evolution of the porosity (and the specific surface area) as a function of
temperature (from 10 to 120 K). Methods. Kinetic Monte Carlo simulations are
used to mimic the formation and the thermal evolution of pores in amorphous
water ice. We follow the accretion of gas-phase water molecules as well as
their migration on surfaces with different grid sizes, both at the top growing
layer and within the bulk. Results. We show that the porosity characteristics
change substantially in water ice as the temperature increases. The total
surface of the pores decreases strongly while the total volume decreases only
slightly for higher temperatures. This will decrease the overall reaction
efficiency, but in parallel, small pores connect and merge, allowing trapped
molecules to meet and react within the pores network, providing a pathway to
increase the reaction efficiency. We introduce pore coalescence as a new solid
state process that may boost the solid state formation of new molecules in
space and has not been considered so far.Comment: 9 pages, 8 figures Accepted for publication in A&
Space-time evolution of electron cascades in diamond
Here we describe model calculations to follow the spatio-temporal evolution
of secondary electron cascades in diamond. The band structure of the insulator
has been explicitly incorporated into the calculations as it affects
ionizations from the valence band. A Monte-Carlo model was constructed to
describe the path of electrons following the impact of a single electron of
energy E 250 eV. The results show the evolution of the secondary electron
cascades in terms of the number of electrons liberated, the spatial
distribution of these electrons, and the energy distribution among the
electrons as a function of time. The predicted ionization rates (5-13 electrons
in 100 fs) lie within the limits given by experiments and phenomenological
models. Calculation of the local electron density and the corresponding Debye
length shows that the latter is systematically larger than the radius of the
electron cloud. This means that the electron gas generated does not represent a
plasma in a single impact cascade triggered by an electron of E 250 eV energy.
This is important as it justifies the independent-electron approximation used
in the model. At 1 fs, the (average) spatial distribution of secondary
electrons is anisotropic with the electron cloud elongated in the direction of
the primary impact. The maximal radius of the cascade is about 50 A at this
time. As the system cools, energy is distributed more equally, and the spatial
distribution of the electron cloud becomes isotropic. At 90 fs maximal radius
is about 150 A. The Monte-Carlo model described here could be adopted for the
investigation of radiation damage in other insulators and has implications for
planned experiments with intense femtosecond X-ray sources.Comment: 26 pages, latex, 13 figure
The first frost in the Pipe Nebula
Spectroscopic studies of ices in nearby star-forming regions indicate that
ice mantles form on dust grains in two distinct steps, starting with polar ice
formation (H2O rich) and switching to apolar ice (CO rich). We test how well
the picture applies to more diffuse and quiescent clouds where the formation of
the first layers of ice mantles can be witnessed. Medium-resolution
near-infrared spectra are obtained toward background field stars behind the
Pipe Nebula. The water ice absorption is positively detected at 3.0 micron in
seven lines of sight out of 21 sources for which observed spectra are
successfully reduced. The peak optical depth of the water ice is significantly
lower than those in Taurus with the same visual extinction. The source with the
highest water-ice optical depth shows CO ice absorption at 4.7 micron as well.
The fractional abundance of CO ice with respect to water ice is 16+7-6 %, and
about half as much as the values typically seen in low-mass star-forming
regions. A small fractional abundance of CO ice is consistent with some of the
existing simulations. Observations of CO2 ice in the early diffuse phase of a
cloud play a decisive role in understanding the switching mechanism between
polar and apolar ice formation.Comment: 17 pages, 8 figures, accepted by A&
Finding all maximal perfect haplotype blocks in linear time
Recent large-scale community sequencing efforts allow at an unprecedented level of detail the identification of genomic regions that show signatures of natural selection. Traditional methods for identifying such regions from individuals' haplotype data, however, require excessive computing times and therefore are not applicable to current datasets. In 2019, Cunha et al. (Advances in bioinformatics and computational biology: 11th Brazilian symposium on bioinformatics, BSB 2018, Niteroi, Brazil, October 30 - November 1, 2018, Proceedings, 2018. 10.1007/978-3-030-01722-4_3) suggested the maximal perfect haplotype block as a very simple combinatorial pattern, forming the basis of a new method to perform rapid genome-wide selection scans. The algorithm they presented for identifying these blocks, however, had a worst-case running time quadratic in the genome length. It was posed as an open problem whether an optimal, linear-time algorithm exists. In this paper we give two algorithms that achieve this time bound, one conceptually very simple one using suffix trees and a second one using the positional Burrows-Wheeler Transform, that is very efficient also in practice.Peer reviewe
The role of carbon grains in the deuteration of H2
Aims: The production of molecular hydrogen and its deuterated forms onto
carbonaceous dust grains is investigated in detail. The goal of this study is
to estimate the importance of the chemistry occuring on grain surfaces for the
deuteration of H2. Furthermore, we aim to find a robust and general surface
chemical model which can be used in different astrophysical environments.
Methods: Surface processes are described for the cases of graphitic and
amorphous--carbon grains, where laboratory work is available.
Langmuir--Hinshelwood as well as Eley--Rideal surface chemistries are included
in the model and their relative contributions are highlighted. Analytic
expressions are derived for H2, HD, and D2 formation efficiencies for both type
of grains. Rate equations are tested against stochastic methods. Results: As
expected, rate equations and stochastic methods diverge for grain sizes lower
than a critical value acrit. For grain sizes below this critical value, D2
formation decreases to favour HD formation. The formation efficiencies of H2
and D2 can be calculated by adding a correction factor to the rate equations
methods. We found that because of the presence of chemisorbed sites, which can
store atoms to form molecules up to high grain temperatures, the formation
efficiency of HD and D2 is very high compared to models where only
physisorption sites are taken into account. When considering a realistic
distribution of dust grains, we found that the formation rate of H2 and HD is
enhanced by an order of magnitude if small grains are taken into account. The
processes described in this paper, that allow a strong enhancement of the
deuterated forms of molecular hydrogen, could explain the high degree of
deuterium fractionation observed in protostellar environments.Comment: 17 pages 25 figure
Accretion and photodesorption of CO ice as a function of the incident angle of deposition
Non-thermal desorption of inter- and circum-stellar ice mantles on dust
grains, in particular ultraviolet photon-induced desorption, has gained
importance in recent years. These processes may account for the observed gas
phase abundances of molecules like CO toward cold interstellar clouds. Ice
mantle growth results from gas molecules impinging on the dust from all
directions and incidence angles. Nevertheless, the effect of the incident angle
for deposition on ice photo-desorption rate has not been studied. This work
explores the impact on the accretion and photodesorption rates of the incidence
angle of CO gas molecules with the cold surface during deposition of a CO ice
layer. Infrared spectroscopy monitored CO ice upon deposition at different
angles, ultraviolet-irradiation, and subsequent warm-up. Vacuum-ultraviolet
spectroscopy and a Ni-mesh measured the emission of the ultraviolet lamp.
Molecules ejected from the ice to the gas during irradiation or warm-up were
characterized by a quadrupole mass spectrometer. The photodesorption rate of CO
ice deposited at 11 K and different incident angles was rather stable between 0
and 45. A maximum in the CO photodesorption rate appeared around
70-incidence deposition angle. The same deposition angle leads to the
maximum surface area of water ice. Although this study of the surface area
could not be performed for CO ice, the similar angle dependence in the
photodesorption and the ice surface area suggests that they are closely
related. Further evidence for a dependence of CO ice morphology on deposition
angle is provided by thermal desorption of CO ice experiments
Porosity measurements of interstellar ice mixtures using optical laser interference and extended effective medium approximations
Aims. This article aims to provide an alternative method of measuring the
porosity of multi-phase composite ices from their refractive indices and of
characterising how the abundance of a premixed contaminant (e.g., CO2) affects
the porosity of water-rich ice mixtures during omni-directional deposition.
Methods. We combine optical laser interference and extended effective medium
approximations (EMAs) to measure the porosity of three astrophysically relevant
ice mixtures: H2O:CO2=10:1, 4:1, and 2:1. Infrared spectroscopy is used as a
benchmarking test of this new laboratory-based method. Results. By
independently monitoring the O-H dangling modes of the different water-rich ice
mixtures, we confirm the porosities predicted by the extended EMAs. We also
demonstrate that CO2 premixed with water in the gas phase does not
significantly affect the ice morphology during omni-directional deposition, as
long as the physical conditions favourable to segregation are not reached. We
propose a mechanism in which CO2 molecules diffuse on the surface of the
growing ice sample prior to being incorporated into the bulk and then fill the
pores partly or completely, depending on the relative abundance and the growth
temperature.Comment: 9 pages, 6 figures, 1 table. Accepted for publication in A&
Near-arcsecond resolution observations of the hot corino of the solar type protostar IRAS 16293-2422
Complex organic molecules have previously been discovered in solar type
protostars, raising the questions of where and how they form in the envelope.
Possible formation mechanisms include grain mantle evaporation, interaction of
the outflow with its surroundings or the impact of UV/X-rays inside the
cavities. In this Letter we present the first interferometric observations of
two complex molecules, CH3CN and HCOOCH3, towards the solar type protostar
IRAS16293-2422. The images show that the emission originates from two compact
regions centered on the two components of the binary system. We discuss how
these results favor the grain mantle evaporation scenario and we investigate
the implications of these observations for the chemical composition and
physical and dynamical state of the two components.Comment: 5 pages (apjemulate), 2 figures; accepted by ApJ
Formation of Water in the Warm Atmospheres of Protoplanetary Disks
The gas-phase chemistry of water in protoplanetary disks is analyzed with a
model based on X-ray heating and ionization of the disk atmosphere. Several
uncertain processes appear to play critical roles in generating the column
densities of warm water that are detected from disks at infrared wavelengths.
The dominant factors are the reactions that form molecular hydrogen, including
formation on warm grains, and the ionization and heating of the atmosphere. All
of these can work together to produce a region of high water abundances in the
molecular transition layer of the inner disk atmosphere, where atoms are
transformed into molecules, the temperature drops from thousands to hundreds of
Kelvins, and the ionization begins to be dominated by the heavy elements. Grain
formation of molecular hydrogen and mechanical heating of the atmosphere can
play important roles in this region and directly affect the amount of warm
water in protoplanetary disk atmospheres. Thus it may be possible to account
for the existing measurements of water emission from Tauri disks without
invoking transport of water from cooler to warmer regions. The hydroxyl radical
OH is under-abundant in this model of disk atmospheres and requires
consideration of additional production and excitation processes
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