5,383 research outputs found
Correlation of Low z Lyman-alpha Absorbers with HI-selected Galaxies
In this work, observational evidence for the connection between low column
density Lyman-alpha absorbers and large-scale structure traced by gas-rich
galaxies is investigated. The HI Parkes All Sky Survey (HIPASS) galaxy
catalogue is cross-correlated with known low redshift, low column density
Lyman-alpha absorbers from the literature. The absorber-galaxy
cross-correlation function shows that on scales from 1 to 10 h^-1 Mpc,
absorbers are imbedded in halos with masses similar to that of galaxy groups.
This statistical evidence suggests that galaxy groups could be the dominant
environment of low column density Lyman-alpha absorbers at z=0.Comment: 3 pages, 1 figure, to appear in IAU 199 conf. proc.: "Probing
Galaxies through Quasar Absorption Lines," eds. Williams, Shu, Menar
Cross correlation of Lyman-alpha absorbers with gas-rich galaxies
The HI Parkes All Sky Survey (HIPASS) galaxy catalogue is cross-correlated
with known low redshift, low column density (N_HI <10^15 cm^-2) Lyman-alpha
absorbers from the literature. The redshift-space correlation is found to be
similar in strength to HIPASS galaxy self-clustering (correlation length
s_0,ag=6+/-4 and s_0,gg=3.1+/-0.5 h^-1 Mpc respectively). In real-space the
cross-correlation is stronger than the galaxy auto-correlation (correlation
length r_0,ag=7.2+/-1.4 and r_0,gg=3.5+/-0.7 h^-1 Mpc respectively) on scales
from 1-10 h^-1 Mpc, ruling out the mini-halo model for the confinement
Lyman-alpha absorbers at the 99 percent confidence level. Provided that the
cause of the strong cross-correlation is purely gravitational, the ratio of
correlation lengths suggest that absorbers are embedded in dark matter haloes
with masses log(M/Msun)=14.2 h^-1, similar to those of galaxy groups. The
flattening of the cross-correlation at separations less than ~600 h^-1 kpc
could correspond to the thickness of filaments in which absorbers are embedded.
This work provides indirect statistical evidence for the notion that galaxy
groups and large-scale filaments, particularly those that comprise gas-rich
galaxies, are the dominant environments of low column density Lyman-alpha
absorbers at z=0.Comment: 10 pages, 10 figures, accepted for publication in MNRAS, minor typos
fixed and references update
Evolution of damped Lyman alpha kinematics and the effect of spatial resolution on 21-cm measurements
We have investigated the effect of spatial resolution on determining
pencil-beam like velocity widths and column densities in galaxies. Three 21-cm
datasets are used, the HIPASS galaxy catalogue, a subset of HIPASS galaxies
with ATCA maps and a high-resolution image of the LMC. Velocity widths measured
from 21-cm emission in local galaxies are compared with those measured in
intermediate redshift Damped Lyman alpha (DLA) absorbers. We conclude that
spatial resolution has a severe effect on measuring pencil-beam like velocity
widths in galaxies. Spatial smoothing by a factor of 240 is shown to increase
the median velocity width by a factor of two. Thus any difference between
velocity widths measured from global profiles or low spatial resolution 21-cm
maps at z=0 and DLAs at z>1 cannot unambiguously be attributed to galaxy
evolution. The effect on column density measurements is less severe and the
values of dN/dz from local low-resolution 21-cm measurements are expected to be
overestimated by only ~10 per cent.Comment: 5 pages, 6 figures, accepted for publication in MNRAS letter
Migration To Rural Communities In The Midwest: Economic Wellbeing And Women At The Household Level
Migration patterns are changing from large metropolis to rural towns. Rather than temporary migration of male heads of households the patterns are now for families to migrate in various stages. Rural Missouri towns have attracted newcomers. Foreign born Hispanics in non metro Missouri have low income earnings, and education, mobility and being woman have a negative effect on income earnings, as regression results show. The livelihoods of rural newcomers are vulnerable, with low income, multiple adults working in the households and with limited English proficiency. This is consistent with the life stories of women in a small town near a meat processing plant in Missouri.Community/Rural/Urban Development, Consumer/Household Economics,
Pathogen avoidance by insect predators
Insects can detect cues related to the risk of attack by their natural enemies. Pathogens are among the natural enemies of insects and entomopathogenic fungi attack a wide array of host species. Evidence documents that social insects in particular have adapted behavioural mechanisms to avoid infection by fungal pathogens. These mechanisms are referred to as 'behavioural resistance'. However, there is little evidence for similar adaptations in non-social insects.
We have conducted experiments to assess the potential of common insect predators to detect and avoid their entomopathogenic fungal natural enemy Beauveria bassiana. The predatory bug Anthocoris nemorum was able to detect and avoid nettle leaves that were treated with B. bassiana. Females laid fewer eggs on leaf halves contaminated with the pathogen. Similarly, females were very reluctant to contact nettle leaves contaminated with the fungus compared to uncontaminated control leaves in âno-choiceâ experiments.
Adult seven spot ladybirds, Coccinella septempunctata, overwinter in the litter layer often in groups. Adult C. septempunctata modified their overwintering behaviour in relation to the presence of B. bassiana conidia in soil and sporulating conspecifics by moving away from sources of infection. Furthermore active (non-overwintering) adult C. septempunctata were also able to detect and avoid B. bassiana conidia on different substrates; bean leaves, soil and sporulating on dead conspecifics.
Our studies show that insect predators have evolved mechanisms to detect and avoid pathogens that they are susceptible to. Fungal pathogens may be significant mortality factors among populations of insect predators, especially long-lived species that must diapause before reproduction. Likewise, actively foraging species are more likely to come in contact with pathogens than predators that sit and wait for prey. These particular groups of insects will benefit from adaptations to avoid pathogens
Maize in the Philippines: Production Systems, Constraints, and Research Priorities
Crop Production/Industries,
Alien Registration- Gray, Emma V. (Easton, Aroostook County)
https://digitalmaine.com/alien_docs/26315/thumbnail.jp
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