389 research outputs found
Galaxy pairs in the Sloan Digital Sky Survey - IX: Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer
Interactions between galaxies are predicted to cause gas inflows that can
potentially trigger nuclear activity. Since the inflowing material can obscure
the central regions of interacting galaxies, a potential limitation of previous
optical studies is that obscured Active Galactic Nuclei (AGNs) can be missed at
various stages along the merger sequence. We present the first large
mid-infrared study of AGNs in mergers and galaxy pairs, in order to quantify
the incidence of obscured AGNs triggered by interactions. The sample consists
of galaxy pairs and post-mergers drawn from the Sloan Digital Sky Survey that
are matched to detections by the Wide Field Infrared Sky Explorer (WISE). We
find that the fraction of AGN in the pairs, relative to a mass-, redshift- and
environment-matched control sample, increases as a function of decreasing
projected separation. This enhancement is most dramatic in the post-merger
sample, where we find a factor of 10-20 excess in the AGN fraction compared
with the control. Although this trend is in qualitative agreement with results
based on optical AGN selection, the mid-infrared selected AGN excess increases
much more dramatically in the post-mergers than is seen for optical AGN. Our
results suggest that energetically dominant optically obscured AGNs become more
prevalent in the most advanced mergers, consistent with theoretical
predictions.Comment: 8 pages, 7 figures accepted to MNRAS (with minor revisions
Lunar hand tools
Tools useful for operations and maintenance tasks on the lunar surface were determined and designed. Primary constraints are the lunar environment, the astronaut's space suit and the strength limits of the astronaut on the moon. A multipurpose rotary motion tool and a collapsible tool carrier were designed. For the rotary tool, a brushless motor and controls were specified, a material for the housing was chosen, bearings and lubrication were recommended and a planetary reduction gear attachment was designed. The tool carrier was designed primarily for ease of access to the tools and fasteners. A material was selected and structural analysis was performed on the carrier. Recommendations were made about the limitations of human performance and about possible attachments to the torque driver
Temporal pattern of africanization in a feral honeybee population from Texas inferred from mitochondrial DNA
The invasion of Africanized honeybees (Apis mellifera L.) in the Americas provides a window of opportunity
to study the dynamics of secondary contact of subspecies of bees that evolved in allopatry in ecologically distinctive
habitats of the Old World. We report here the results of an 11-year mitochondrial DNA survey of a feral honeybee
population from southern United States (Texas). The mitochondrial haplotype (mitotype) frequencies changed radically
during the 11-year study period. Prior to immigration of Africanized honeybees, the resident population was essentially
of eastern and western European maternal ancestry. Three years after detection of the first Africanized swarm there
was a mitotype turnover in the population from predominantly eastern European to predominantly A. m. scutellata
(ancestor of Africanized honeybees). This remarkable change in the mitotype composition coincided with arrival of
the parasitic mite Varroa destructor, which was likely responsible for severe losses experienced by colonies of European
ancestry. From 1997 onward the population stabilized with most colonies of A. m. scutellata maternal origin.PRODEP II - Medida 5/Acção 5.
Identification of africanized honey bee (Hymenoptera: apidae) mitochondrial DNA: validation of a rapid polymerase chain reaction-based assay
Polymerase chain reaction (PCR)-ampliÞed mitochondrialDNA(mtDNA)assays have
been used in studies of the Africanization process in neotropical feral and managed honey bee
populations. The approach has been adopted, in conjunction with morphometric analysis, to identify
Africanized bees for regulatory purposes in the United States such as in California. In this study, 211
Old World colonies, representing all known introduced subspecies in the United States, and 451
colonies from non-Africanized areas of the southern United States were screened to validate a rapid
PCR-based assay for identiÞcation of Africanized honey bee mtDNA. This PCR-based assay requires
a single enzyme digestion (BglII) of a single PCR-ampliÞed segment of the cytochrome b gene. The
BglII polymorphism discriminates the mitochondrial haplotype (mitotype) of Apis mellifera scutellata
L. (ancestor of Africanized bees) from that of A. m. mellifera, A. m. caucasia, A. m. ligustica, A. m.
carnica, A. m. lamarcki, A. m. cypria, A. m. syriaca, and some A. m. iberiensis, but not from that of
A. m. intermissa and some A. m. iberiensis. Nonetheless, given the very low frequency ( 1%) of African
non-A. m. scutellata mitotype present before arrival of Africanized bees in the United States, cytochrome
b/BglII assay can be used to identify maternally Africanized bees with a high degree of
reliability
Changes in extreme, cold-season synoptic precipitation events under global warming
We analyze regional climate model (RCM) simulations of daily, spatially distributed extreme precipitation events, using co-operative network observations and output from 10-year RCM simulations of present and future-scenario climates. We examine an Upper Mississippi River Basin region during October–March for daily amounts that exceed the 99.95th percentile and that occur simultaneously at several observation sites or model grid points. For the observations and each simulation, nearly all such extreme regional events occur when a slow moving, cut-off-low system develops over the Rockies and Great Plains and steadily pumps moisture into the Upper Mississippi region from the Gulf of Mexico. The threshold for the extreme events increases in the future scenario by an amount similar to the increase in saturation specific humidity. The results suggest robust circulation behavior for such extremes in the face of climate change
Children\u27s Judgments of Age
Age judgments of human figures by children, ranging in age from 3 through 9 years, were investigated. The stimuli consisted of 4 different male figures drawn according to typical physical characteristics of the middle-aged adult, adolescent child, and infant. The figures were reproduced in 2 sizes and were matched in all possible pairings. Ss\u27 accuracy in age judgments increased steadily over the 7 age levels. The errors of young Ss were primarily due to a figural-size response set. Older Ss made increasing use of other physical features in making their judgments. Implications of these findings were discussed with references to the theoretical framework of Piaget
Effects of Concurrent Resistance and Aerobic Training on Load-Bearing Performance and the Army Physical Fitness Test
The purpose of this research was to determine the effects of high intensity endurance training (ET) and resistance training (RT) alone and in combination on various military tasks. Thirty-five male soldiers were randomly assigned to one of four training groups: total body resistance training plus endurance training (RT + ET), upper body resistance training plus endurance training [UB + ET), RT only, and ET only. Training was performed 4 days per week for 12 weeks. Testing occurred before and after the 12-week training regimen. All groups significantly improved push-up performance, whereas only the RT + ET group did not improve sit-up performance. The groups that included ET significantly decreased 2-mile run time, however, only RT + ET and UB + ET showed improved loaded 2-mile run time. Leg power increased for groups that included lower body strengthening exercises (RT and RT + ET). Army Physical Fitness Test performance, loaded running, and leg power responded positively to training, however, it appears there is a high degree of specificity when concurrent training regimens are implemented
Young mixed planted forests store more carbon than monocultures—a meta-analysis
Although decades of research suggest that higher species richness improves ecosystem functioning and stability, planted forests are predominantly monocultures. To determine whether diversification of plantations would enhance aboveground carbon storage, we systematically reviewed over 11,360 publications, and acquired data from a global network of tree diversity experiments. We compiled a maximum dataset of 79 monoculture to mixed comparisons from 21 sites with all variables needed for a meta-analysis. We assessed aboveground carbon stocks in mixed-species planted forests vs. (a) the average of monocultures, (b) the best monoculture, and (c) commercial species monocultures, and examined potential mechanisms driving differences in carbon stocks between mixtures and monocultures. On average, we found that aboveground carbon stocks in mixed planted forests were 70% higher than the average monoculture, 77% higher than commercial monocultures, and 25% higher than the best performing monocultures, although the latter was not statistically significant. Overyielding was highest in four-species mixtures (richness range 2–6 species), but otherwise none of the potential mechanisms we examined (nitrogen-fixer present vs. absent; native vs. non-native/mixed origin; tree diversity experiment vs. forestry plantation) consistently explained variation in the diversity effects. Our results, predominantly from young stands, thus suggest that diversification could be a very promising solution for increasing the carbon sequestration of planted forests and represent a call to action for more data to increase confidence in these results and elucidate methods to overcome any operational challenges and costs associated with diversification
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