1,848 research outputs found
Estimating Parasitism of Colorado Potato Beetle Eggs, \u3ci\u3eLeptinotarsa Decemlineata\u3c/i\u3e (Coleoptera: Chrysomelidae), by \u3ci\u3eEdovum Puttleri\u3c/i\u3e (Hymenoptera: Eulophidae)
A computer simulation was used to evaluate methods for estimating parasitism of Colorado potato beetle egg mass populations by Edovum puttleri. The algorithm incorporated the specific attack behavior of E. puttleri, and a development time for parasitized egg masses of ca. 2.9 times that of healthy egg masses. Of the methods compared, a modification of Southwood\u27s graphical technique was found to be most accurate in relation to the true parasitism derived from the algorithm. A regression equation is presented to correct the error in this method at high levels of parasitism. A second simulation was used to test the accuracy of this correcter where in a jacknife procedure was used to generate a mean and variance for estimates of parasitism
Measuring the vertical age structure of the Galactic disc using asteroseismology and SAGA
The existence of a vertical age gradient in the Milky Way disc has been
indirectly known for long. Here, we measure it directly for the first time with
seismic ages, using red giants observed by Kepler. We use Stroemgren photometry
to gauge the selection function of asteroseismic targets, and derive colour and
magnitude limits where giants with measured oscillations are representative of
the underlying population in the field. Limits in the 2MASS system are also
derived. We lay out a method to assess and correct for target selection effects
independent of Galaxy models. We find that low mass, i.e. old red giants
dominate at increasing Galactic heights, whereas closer to the Galactic plane
they exhibit a wide range of ages and metallicities. Parametrizing this as a
vertical gradient returns approximately 4 Gyr/kpc for the disc we probe,
although with a large dispersion of ages at all heights. The ages of stars show
a smooth distribution over the last 10 Gyr, consistent with a mostly quiescent
evolution for the Milky Way disc since a redshift of about 2. We also find a
flat age-metallicity relation for disc stars. Finally, we show how to use
secondary clump stars to estimate the present-day intrinsic metallicity spread,
and suggest using their number count as a new proxy for tracing the ageing of
the disc. This work highlights the power of asteroseismology for Galactic
studies; however, we also emphasize the need for better constraints on stellar
mass-loss, which is a major source of systematic age uncertainties in red giant
stars.Comment: MNRAS, accepted. SAGA website and data at
http://www.mso.anu.edu.au/saga/data_access.htm
High entropy alloys obtained by field assisted powder metallurgy route: SPS and microwave heating
The aim of this work was to investigate the field assisted powder metallurgy route for producing HEAs at equimolar composition, i.e. FeCoNiCrAl, starting from metal powders. Both mixed, mechanically activated and mechanically alloyed powders have been used. The powders obtained by mechanical alloying were synthesized only by SPS, whereas the remaining ones were sintered by SPS or microwave heating. The investigated field assisted sintering techniques allowed an extremely short alloying time, high energy density on the load and negligible contamination by the surrounding environment. Both the conducted sintering-synthesis technology resulted not definitive to produce chemical homogeneity and to obtain a single stable structure. Thus a subsequently heat treatment was required. The post heat treatment, indeed, led to a single crystalline structure (FCC) and the material was fully recrystallized. After heat treatment samples are isomorphic: they exhibit two different phases with the same FCC cell, but different chemical composition, in detail Fe-Cr richer and Al-Ni richer. SPS-ed samples present a reduced porosity, while microwave processed ones are much more porous and this is reflected in the mechanical properties
Factors affecting pre-failure instability of sand under plane-strain conditions
Experimental data obtained from a plane-strain appara- tus are presented in this paper to show that a pre-failure instability in the form of a rapid and sustained increase in strain rate can occur for both contractive and dilative sand under fully drained conditions. However, this type of instability is different from the runaway type of instability observed under undrained conditions, and has therefore been called conditional instability. Despite the differences, the conditions for both types of instability are the same for contractive sand. There are also other factors that affect the pre-failure instability of sand ob- served in the laboratory. These include the stress ratio, void ratio, sand state, load control mode and reduction rate of the effective confining stress. In this paper, these factors are discussed and analysed using experimental data obtained from undrained instability (or creep) tests and constant shear drained (CSD) tests carried out under plane-strain conditions
Partida e operação de um reator aeróbio de nitritação parcial para o tratamento de dejetos de suínos com remoção simultânea de COT.
Projeto: 02.07.06.007
Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for the interpretation of interferometric observations
Context. Theoretical predictions from models of red giant branch stars are a
valuable tool for various applications in astrophysics ranging from galactic
chemical evolution to studies of exoplanetary systems. Aims. We use the
radiative transfer code OPTIM3D and realistic 3D radiative-hydrodynamical (RHD)
surface convection simulations of red giants to explore the impact of
granulation on interferometric observables. Methods. We compute intensity maps
for the 3D simulation snapshots in two filters: in the optical at 5000 \pm 300
{\AA} and in the K band 2.14 0.26 {\mu}m FLUOR filter, corresponding to
the wavelength-range of instruments mounted on the CHARA interferometer. From
the intensity maps, we construct images of the stellar disks, accounting for
center-to-limb variations. We then derive interferometric visibility amplitudes
and phases. We study their behavior with position angle and wavelength.
Results. We provide average limb-darkening coefficients for different
metallicities and wavelength-ranges. We detail the prospects for the detection
and characterization of granulation and center-to-limb variations of red giant
stars with today's interferometers. We find that the effect of
convective-related surface structures depends on metallicity and surface
gravity. We provided theoretical closure phases that should be incorporated
into the analysis of red giant planet companion closure phase signals. We
estimate 3D-1D corrections to stellar radii determination: 3D models are ~ 3.5%
smaller to ~ 1% larger in the optical with respect to 1D, and roughly 0.5 to
1.5% smaller in the infrared. Even if these corrections are small, they are
important to properly set the zero point of effective temperature scale derived
by interferometry and to strengthen the confidence of existing red giant
catalogues of calibrating stars for interferometry.Comment: Accepted for publication on Astronomy & Astrophysics, 14 pages, 13
figure
SPS-assisted Synthesis of SICp reinforced high entropy alloys: reactivity of SIC and effects of pre-mechanical alloying and post-annealing treatment
In this work a traditional high entropy alloy (FeCoNiCrAl) was reinforced by uniformly distributed reactive silicon carbide (SiC) particles by a powder metallurgy synthetic route, using as precursors simply mixed powders or mechanically prealloyed ones. The reactive sintering produced a single isomorphic BCC structure. The sample microstructure resulted equiassic, more homogenous in samples based on prealloyed powders. The instability of SiC in the presence of metal precursors resulted in the formation of more stable carbides and silicides, as well as in carbon diffusion in the high entropy alloy matrix and partially unreacted SiC particles. The formation of these newly formed fine precipitates, as well as the presence of residual SiC were useful to increase the hardness of the alloy
Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites
We present a high resolution spectroscopic analysis of 62 red giants in the
Milky Way globular cluster NGC5286. We have determined abundances of
representative light proton-capture, alpha, Fe-peak and neutron-capture element
groups, and combined them with photometry of multiple sequences observed along
the colour-magnitude diagram. Our principal results are: (i) a broad, bimodal
distribution in s-process element abundance ratios, with two main groups, the
s-poor and s-rich groups; (ii) substantial star-to-star Fe variations, with the
s-rich stars having higher Fe, e.g. _s-rich - _s-poor ~
0.2~dex; and (iii) the presence of O-Na-Al (anti-)correlations in both stellar
groups. We have defined a new photometric index, c_{BVI}=(B-V)-(V-I), to
maximise the separation in the colour-magnitude diagram between the two stellar
groups with different Fe and s-element content, and this index is not
significantly affected by variations in light elements (such as the O-Na
anticorrelation). The variations in the overall metallicity present in NGC5286
add this object to the class of "anomalous" GCs. Furthermore, the chemical
abundance pattern of NGC5286 resembles that observed in some of the anomalous
GCs, e.g. M22, NGC1851, M2, and the more extreme Omega Centauri, that also show
internal variations in s-elements, and in light elements within stars with
different Fe and s-elements content. In view of the common variations in
s-elements, we propose the term s-Fe-anomalous GCs to describe this sub-class
of objects. The similarities in chemical abundance ratios between these objects
strongly suggest similar formation and evolution histories, possibly associated
with an origin in tidally disrupted dwarf satellites.Comment: 28 pages, 21 figures, accepted for publication in MNRA
Asteroseismic properties of solar-type stars observed with the NASA K2 mission: results from Campaigns 1-3 and prospects for future observations
We present an asteroseismic analysis of 33 solar-type stars observed in short
cadence during Campaigns (C) 1-3 of the NASA K2 mission. We were able to
extract both average seismic parameters and individual mode frequencies for
stars with dominant frequencies up to ~3300{\mu}Hz, and we find that data for
some targets are good enough to allow for a measurement of the rotational
splitting. Modelling of the extracted parameters is performed by using
grid-based methods using average parameters and individual frequencies together
with spectroscopic parameters. For the target selection in C3, stars were
chosen as in C1 and C2 to cover a wide range in parameter space to better
understand the performance and noise characteristics. For C3 we still detected
oscillations in 73% of the observed stars that we proposed. Future K2 campaigns
hold great promise for the study of nearby clusters and the chemical evolution
and age-metallicity relation of nearby field stars in the solar neighbourhood.
We expect oscillations to be detected in ~388 short-cadence targets if the K2
mission continues until C18, which will greatly complement the ~500 detections
of solar-like oscillations made for short-cadence targets during the nominal
Kepler mission. For ~30-40 of these, including several members of the Hyades
open cluster, we furthermore expect that inference from interferometry should
be possible.Comment: 17 pages, 15 figures, 4 tables; accepted for publication in PAS
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