4,425 research outputs found
Comparative Fatigue Tests of Riveted Joints of Alclad 24S-T, Alclad 24S-T81, Alclad 24S-RT, Alclad 24S-T86 and Alclad 75S-T Sheet
Different roles of similarity and predictability in auditory stream segregation
Sound sources often emit trains of discrete sounds, such as a series of footsteps. Previously, two dif¬ferent principles have been suggested for how the human auditory system binds discrete sounds to¬gether into perceptual units. The feature similarity principle is based on linking sounds with similar characteristics over time. The predictability principle is based on linking sounds that follow each other in a predictable manner. The present study compared the effects of these two principles. Participants were presented with tone sequences and instructed to continuously indicate whether they perceived a single coherent sequence or two concurrent streams of sound. We investigated the influence of separate manipulations of similarity and predictability on these perceptual reports. Both grouping principles affected perception of the tone sequences, albeit with different characteristics. In particular, results suggest that whereas predictability is only analyzed for the currently perceived sound organization, feature similarity is also analyzed for alternative groupings of sound. Moreover, changing similarity or predictability within an ongoing sound sequence led to markedly different dynamic effects. Taken together, these results provide evidence for different roles of similarity and predictability in auditory scene analysis, suggesting that forming auditory stream representations and competition between alter¬natives rely on partly different processes
The bulge luminosity functions in the MSX infrared bands
We use an inversion technique to derive the luminosity functions of the
Galactic bulge from point source counts extracted from the Midcourse Space
Experiment's Point Source Catalog (version 1.2).Comment: 5 pages, 2 figures, to be published in A&
The Two Phases of Galaxy Formation
Cosmological simulations of galaxy formation appear to show a two-phase
character with a rapid early phase at z>2 during which in-situ stars are formed
within the galaxy from infalling cold gas followed by an extended phase since
z<3 during which ex-situ stars are primarily accreted. In the latter phase
massive systems grow considerably in mass and radius by accretion of smaller
satellite stellar systems formed at quite early times (z>3) outside of the
virial radius of the forming central galaxy. These tentative conclusions are
obtained from high resolution re-simulations of 39 individual galaxies in a
full cosmological context with present-day virial halo masses ranging from 7e11
M_sun h^-1 < M_vir < 2.7e13 M_sun h^-1 and central galaxy masses between 4.5e10
M_sun h^-1 < M_* < 3.6e11 M_sun h^-1. The simulations include the effects of a
uniform UV background, radiative cooling, star formation and energetic feedback
from SNII. The importance of stellar accretion increases with galaxy mass and
towards lower redshift. In our simulations lower mass galaxies (M_* > 1.7e11 M_sun h^-1) assembly is dominated by accretion and
merging with about 80 per cent of the stars added by the present-day. In
general the simulated galaxies approximately double their mass since z=1. For
massive systems this mass growth is not accompanied by significant star
formation. The majority of the in-situ created stars is formed at z>2,
primarily out of cold gas flows. We recover the observational result of
archaeological downsizing, where the most massive galaxies harbor the oldest
stars. We find that this is not in contradiction with hierarchical structure
formation. Most stars in the massive galaxies are formed early on in smaller
structures, the galaxies themselves are assembled late.Comment: 13 pages, 13 figures, accepted for publication in Ap
A decomposition theorem for compact groups with application to supercompactness
We show that every compact connected group is the limit of a continuous
inverse sequence, in the category of compact groups, where each successor
bonding map is either an epimorphism with finite kernel or the projection from
a product by a simple compact Lie group. As an application, we present a proof
of an unpublished result of Charles Mills from 1978: every compact group is
supercompact.Comment: 12 page
A yellowwood by any other name: molecular systematics and the taxonomy of Podocarpus and the Podocarpaceae in southern Africa
We briefly review the taxonomic history of the Podocarpaceae, with an emphasis on the recognition of numerous segregate genera out of Podocarpus sensu lato. Despite some controversy over the recognition of these genera, molecular data (DNA sequences) provide evidence that supports this taxonomy. The implications for African Podocarpaceae are discussed. In particular, molecular data support the recognition of Afrocarpus as distinct from Podocarpus. Additional taxonomic problems concerning the possible segregation of Podocarpus milanjianus from P. latifolius are addressed using DNA sequence data from the nuclear internal transcribed spacer 2 (ITS2) region. Results of this are inconclusive, and suggest that alternative DNA-based evidence, such as from AFLPs or microsatellites, may be more informative in resolving such species complexes in African Podocarpus
Polarity- and valence-dependent effects of prefrontal transcranial direct current stimulation on heart rate variability and salivary cortisol
Transient expression analysis of allelic variants of a VNTR in the dopamine transporter gene (DAT1)
BACKGROUND: The 10-repeat allele of a variable number tandem repeat (VNTR) polymorphism in the 3'-untranslated region of the dopamine transporter gene (DAT1) has been associated with a range of psychiatric phenotypes, most notably attention-deficit hyperactivity disorder. The mechanism for this association is not yet understood, although several lines of evidence implicate variation in gene expression. In this study we have characterised the genomic structure of the 9- and 10-repeat VNTR alleles, and directly examined the role of the polymorphism in mediating gene expression by measuring comparative in vitro cellular expression using a reporter-gene assay system. RESULTS: Differences in the sequence of the 9- and 10- repeat alleles were confirmed but no polymorphic differences were observed between individuals. There was no difference in expression of reporter gene constructs containing the two alleles. CONCLUSIONS: Our data suggests that this VNTR polymorphism may not have a direct effect on DAT1 expression and that the associations observed with psychiatric phenotypes may be mediated via linkage disequilibrium with other functional polymorphisms
Transcriptomic analysis of autistic brain reveals convergent molecular pathology.
Autism spectrum disorder (ASD) is a common, highly heritable neurodevelopmental condition characterized by marked genetic heterogeneity. Thus, a fundamental question is whether autism represents an aetiologically heterogeneous disorder in which the myriad genetic or environmental risk factors perturb common underlying molecular pathways in the brain. Here, we demonstrate consistent differences in transcriptome organization between autistic and normal brain by gene co-expression network analysis. Remarkably, regional patterns of gene expression that typically distinguish frontal and temporal cortex are significantly attenuated in the ASD brain, suggesting abnormalities in cortical patterning. We further identify discrete modules of co-expressed genes associated with autism: a neuronal module enriched for known autism susceptibility genes, including the neuronal specific splicing factor A2BP1 (also known as FOX1), and a module enriched for immune genes and glial markers. Using high-throughput RNA sequencing we demonstrate dysregulated splicing of A2BP1-dependent alternative exons in the ASD brain. Moreover, using a published autism genome-wide association study (GWAS) data set, we show that the neuronal module is enriched for genetically associated variants, providing independent support for the causal involvement of these genes in autism. In contrast, the immune-glial module showed no enrichment for autism GWAS signals, indicating a non-genetic aetiology for this process. Collectively, our results provide strong evidence for convergent molecular abnormalities in ASD, and implicate transcriptional and splicing dysregulation as underlying mechanisms of neuronal dysfunction in this disorder
Low X-Ray Luminosity Galaxy Clusters: Main goals, sample selection, photometric and spectroscopic observations
We present the study of nineteen low X-ray luminosity galaxy clusters (L 0.5--45 erg s), selected from the ROSAT
Position Sensitive Proportional Counters (PSPC) Pointed Observations (Vikhlinin
et al. 1998) and the revised version of Mullis et al. (2003) in the redshift
range of 0.16 to 0.7. This is the introductory paper of a series presenting the
sample selection, photometric and spectroscopic observations and data
reduction. Photometric data in different passbands were taken for eight galaxy
clusters at Las Campanas Observatory; three clusters at Cerro Tololo
Interamerican Observatory; and eight clusters at the Gemini Observatory.
Spectroscopic data were collected for only four galaxy clusters using Gemini
telescopes. With the photometry, the galaxies were defined based on the
star-galaxy separation taking into account photometric parameters. For each
galaxy cluster, the catalogues contain the PSF and aperture magnitudes of
galaxies within the 90\% completeness limit. They are used together with
structural parameters to study the galaxy morphology and to estimate
photometric redshifts. With the spectroscopy, the derived galaxy velocity
dispersion of our clusters ranged from 507 km~s for [VMF98]022 to 775
km~s for [VMF98]097 with signs of substructure. Cluster membership has
been extensively discussed taking into account spectroscopic and photometric
redshift estimates. In this sense, members are the galaxies within a projected
radius of 0.75 Mpc from the X-ray mission peak and with cluster centric
velocities smaller than the cluster velocity dispersion or 6000 km~s,
respectively. These results will be used in forthcoming papers to study, among
the main topics, the red cluster sequence, blue cloud and green populations;
the galaxy luminosity function and cluster dynamics.Comment: 13 pages, 6 tables, 9 figures. Uses emulateapj. Accepted for
publication in The Astronomical Journal. Some formatting errors fixe
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