4,957 research outputs found
The influence of chitin-urea amendments applied to an organic soil on a Meloidogyne hapla population and on the growth of greenhouse tomato
Cette expĂ©rience a Ă©tĂ© rĂ©alisĂ©e en serre dans le but d'Ă©valuer l'efficacitĂ© d'un amendement Ă base de chitine-urĂ©e appliquĂ© Ă un sol organique dans le but de rĂ©primer une population du nĂ©matode des nodositĂ©s (Meloidogyne hapla) provenant du QuĂ©bec et de dĂ©terminer le pouvoir pathogĂšne de ce nĂ©matode sur une culture de tomate (Lycopersicon esculentum). Les amendements de chitine-urĂ©e, aux doses de 0,2 et 0,4 % (vol:vol), n'ont pas rĂ©duit les populations du nĂ©matode prĂ©sentes avant la plantation. Les populations finales d'Ćufs de M. hapla ont Ă©tĂ© significativement augmentĂ©es dans les sols amendĂ©s avec la chitine-urĂ©e et un effet significatif positif de la dose a Ă©tĂ© enregistrĂ©. Le feuillage de tomate a Ă©tĂ© significativement rĂ©duit en prĂ©sence de M. hapla, et accru par l'amendement de chitine-urĂ©e. Ă la rĂ©colte, le poids des fruits n'a pas Ă©tĂ© affectĂ© par la prĂ©sence du M. hapla ni par la chitine-urĂ©e. Les populations finales d'oeufs de M. hapla Ă©taient associĂ©es avec des teneurs rĂ©duites en N et P, mais accrues en Ca dans les tissus foliaires.This experiment was conducted under greenhouse conditions to evaluate the efficiency of chitin-urea amendments to an organic soil against a Quebec population of the northern root-knot nematode (Meloidogyne hapla) and to assess the pathogenicity of this population on tomato (Lycopersicon esculentum). Chitin-urea amendments at 0.2 and 0.4% (vol:vol) were ineffective in reducing the preplant nematode populations. The final M. hapla egg populations were significantly increased in chitin-urea amended soils, and a signifiant positive dosage effect was recorded. Shoot growth of tomato plants was significantly reduced by M. hapla but was increased by chitin-urea. At harvest, fruit weights were neither affected by M. hapla nor by chitin-urea amendments. The final M. hapla egg population was linked to lower N and P levels, and to higher Ca levels in leaf tissues
Cool White Dwarfs Found in the UKIRT Infrared Deep Sky Survey
We present the results of a search for cool white dwarfs in the United
Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area
Survey (LAS). The UKIDSS LAS photometry was paired with the Sloan Digital Sky
Survey (SDSS) to identify cool hydrogen-rich white dwarf candidates by their
neutral optical colors and blue near-infrared colors, as well as faint Reduced
Proper Motion magnitudes. Optical spectroscopy was obtained at Gemini
Observatory, and showed the majority of the candidates to be newly identified
cool degenerates, with a small number of G- to K-type (sub)dwarf contaminants.
Our initial search of 280 deg2 of sky resulted in seven new white dwarfs with
effective temperature T_eff ~ 6000 K. The current followup of 1400 deg2 of sky
has produced thirteen new white dwarfs. Model fits to the photometry show that
seven of the newly identified white dwarfs have 4120 K <= T_eff <= 4480 K, and
cooling ages between 7.3 Gyr and 8.7 Gyr; they have 40 km/s <= v_tan <= 85 km/s
and are likely to be thick disk 10-11 Gyr-old objects. The other half of the
sample has 4610 K <= T_eff <= 5260 K, cooling ages between 4.3 Gyr and 6.9 Gyr,
and 60 km/s <= v_tan <= 100 km/s. These are either thin disk remnants with
unusually high velocities, or lower-mass remnants of thick disk or halo late-F
or G stars.Comment: To appear in ApJ, accepted April 18 2011. 34 pages include 11 Figures
and 5 Table
Eye movements may cause motor contagion effects
When a person executes a movement, the movement is more errorful while observing another personâs actions that are incongruent rather than congruent with the executed action. This effect is known as âmotor contagionâ. Accounts of this effect are often grounded in simulation mechanisms: increased movement error emerges because the motor codes associated with observed actions compete with motor codes of the goal action. It is also possible, however, that the increased movement error is linked to eye movements that are executed simultaneously with the hand movement because oculomotor and manual-motor systems are highly interconnected. In the present study, participants performed a motor contagion task in which they executed horizontal arm movements while observing a model making either vertical (incongruent) or horizontal (congruent) movements under three conditions: no instruction, maintain central fixation, or track the modelâs hand with the eyes. A significant motor contagion-like effect was only found in the âtrackâ condition. Thus, âmotor contagionâ in the present task may be an artifact of simultaneously executed incongruent eye movements. These data are discussed in the context of stimulation and associative learning theories, and raise eye movements as a critical methodological consideration for future work on motor contagion
The Field White Dwarf Mass Distribution
We revisit the properties and astrophysical implications of the field white
dwarf mass distribution in preparation of Gaia applications. Our study is based
on the two samples with the best established completeness and most precise
atmospheric parameters, the volume-complete survey within 20 pc and the Sloan
Digital Sky Survey (SDSS) magnitude-limited sample. We explore the modelling of
the observed mass distributions with Monte Carlo simulations, but find that it
is difficult to constrain independently the initial mass function (IMF), the
initial-to-final-mass relation (IFMR), the stellar formation history (SFH), the
variation of the Galactic disk vertical scale height as a function of stellar
age, and binary evolution. Each of these input ingredients has a moderate
effect on the predicted mass distributions, and we must also take into account
biases owing to unidentified faint objects (20 pc sample), as well as unknown
masses for magnetic white dwarfs and spectroscopic calibration issues (SDSS
sample). Nevertheless, we find that fixed standard assumptions for the above
parameters result in predicted mean masses that are in good qualitative
agreement with the observed values. It suggests that derived masses for both
studied samples are consistent with our current knowledge of stellar and
Galactic evolution. Our simulations overpredict by 40-50% the number of massive
white dwarfs (M > 0.75 Msun) for both surveys, although we can not exclude a
Salpeter IMF when we account for all biases. Furthermore, we find no evidence
of a population of double white dwarf mergers in the observed mass
distributions.Comment: 15 pages, 16 figures, accepted for publication in MNRA
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