624 research outputs found
Gamma-Ray Bursts: Temporal Scales and the Bulk Lorentz Factor
For a sample of Swift and Fermi GRBs, we show that the minimum variability
timescale and the spectral lag of the prompt emission is related to the bulk
Lorentz factor in a complex manner: For small 's, the variability
timescale exhibits a shallow (plateau) region. For large 's, the
variability timescale declines steeply as a function of (). Evidence is also presented for an intriguing
correlation between the peak times, t, of the afterglow emission and the
prompt emission variability timescale.Comment: Accepted for publication in Ap
An Integrated Circuit for Signal Processing of the AMS RICH Photmultipliers Tubes
An analog integrated circuit has been designed, in a BiCMOS 0.8 micron
technology, for the feasability study of the signal processing of the AMS RICH
photomultiplier tubes. This low power, three channel gated integrator includes
its own gate and no external analog delay is requiered. It processes PMT pulses
over a dynamic range of more than 100. A logic output that indicates whether
the analog charge has to be considered is provided. This gated integrator is
used with a compact DSP based acquisition system in a 132 channels RICH
prototype. The charge calibration of each channel is carried out using a LED.
The pedestal measurement is performed on activation of a dedicated input. The
noise contribution study of the input RC network and amplifiers is presented.Comment: IEEE symp. on Nucl. Sci. and Med. Imaging, Toront
On multiplicities in length spectra of arithmetic hyperbolic three-orbifolds
Asymptotic laws for mean multiplicities of lengths of closed geodesics in
arithmetic hyperbolic three-orbifolds are derived. The sharpest results are
obtained for non-compact orbifolds associated with the Bianchi groups SL(2,o)
and some congruence subgroups. Similar results hold for cocompact arithmetic
quaternion groups, if a conjecture on the number of gaps in their length
spectra is true. The results related to the groups above give asymptotic lower
bounds for the mean multiplicities in length spectra of arbitrary arithmetic
hyperbolic three-orbifolds. The investigation of these multiplicities is
motivated by their sensitive effect on the eigenvalue spectrum of the
Laplace-Beltrami operator on a hyperbolic orbifold, which may be interpreted as
the Hamiltonian of a three-dimensional quantum system being strongly chaotic in
the classical limit.Comment: 29 pages, uuencoded ps. Revised version, to appear in NONLINEARIT
A New Frequency-Luminosity Relation for Long GRBs?
We have studied power density spectra (PDS) of 206 long Gamma-Ray Bursts
(GRBs). We fitted the PDS with a simple power-law and extracted the exponent of
the power-law (alpha) and the noise-crossing threshold frequency (f_th). We
find that the distribution of the extracted alpha peaks around -1.4 and that of
f_th around 1 Hz. In addition, based on a sub-set of 58 bursts with known
redshifts, we show that the redshift-corrected threshold frequency is
positively correlated with the isotropic peak luminosity. The correlation
coefficient is 0.57 +/- 0.03.Comment: 9 pages, 17 figures, 1 table; Accepted for publication in MNRA
A haplotype map of allohexaploid wheat reveals distinct patterns of selection on homoeologous genomes
Citation: Jordan, K. W., Wang, S., Lun, Y., Gardiner, L. J., MacLachlan, R., Hucl, P., . . . Akhunov, E. (2015). A haplotype map of allohexaploid wheat reveals distinct patterns of selection on homoeologous genomes. Genome Biology, 16(1).
https://doi.org/10.1186/s13059-015-0606-4Background: Bread wheat is an allopolyploid species with a large, highly repetitive genome. To investigate the impact of selection on variants distributed among homoeologous wheat genomes and to build a foundation for understanding genotype-phenotype relationships, we performed population-scale re-sequencing of a diverse panel of wheat lines. Results: A sample of 62 diverse lines was re-sequenced using the whole exome capture and genotyping-by-sequencing approaches. We describe the allele frequency, functional significance, and chromosomal distribution of 1.57 million single nucleotide polymorphisms and 161,719 small indels. Our results suggest that duplicated homoeologous genes are under purifying selection. We find contrasting patterns of variation and inter-variant associations among wheat genomes; this, in addition to demographic factors, could be explained by differences in the effect of directional selection on duplicated homoeologs. Only a small fraction of the homoeologous regions harboring selected variants overlapped among the wheat genomes in any given wheat line. These selected regions are enriched for loci associated with agronomic traits detected in genome-wide association studies. Conclusions: Evidence suggests that directional selection in allopolyploids rarely acted on multiple parallel advantageous mutations across homoeologous regions, likely indicating that a fitness benefit could be obtained by a mutation at any one of the homoeologs. Additional advantageous variants in other homoelogs probably either contributed little benefit, or were unavailable in populations subjected to directional selection. We hypothesize that allopolyploidy may have increased the likelihood of beneficial allele recovery by broadening the set of possible selection targets. © 2015 Jordan et al.; licensee BioMed Central.Additional Authors: Talbert, L.;Bansal, U. K.;Bariana, H. S.;Hayden, M. J.;Pozniak, C.;Jeddeloh, J. A.;Hall, A
Counting and effective rigidity in algebra and geometry
The purpose of this article is to produce effective versions of some rigidity
results in algebra and geometry. On the geometric side, we focus on the
spectrum of primitive geodesic lengths (resp., complex lengths) for arithmetic
hyperbolic 2-manifolds (resp., 3-manifolds). By work of Reid, this spectrum
determines the commensurability class of the 2-manifold (resp., 3-manifold). We
establish effective versions of these rigidity results by ensuring that, for
two incommensurable arithmetic manifolds of bounded volume, the length sets
(resp., the complex length sets) must disagree for a length that can be
explicitly bounded as a function of volume. We also prove an effective version
of a similar rigidity result established by the second author with Reid on a
surface analog of the length spectrum for hyperbolic 3-manifolds. These
effective results have corresponding algebraic analogs involving maximal
subfields and quaternion subalgebras of quaternion algebras. To prove these
effective rigidity results, we establish results on the asymptotic behavior of
certain algebraic and geometric counting functions which are of independent
interest.Comment: v.2, 39 pages. To appear in Invent. Mat
A European lens upon adult and lifelong learning in Asia
In this article, we seek to assess the extent to which adult and lifelong learning policies and practices in Asia have distinctiveness by comparison to those found in western societies, through an analysis of inter-governmental, national and regional policies in the field. We also inform our study through the analysis of the work of organisations with an international remit with a specific focus on Asia and Europe. In one case, the Asia–Europe Meeting Lifelong Learning (ASEM LLL) Hub has a specific function of bringing together researchers in Asia and Europe. In another, the PASCAL Observatory has had a particular focus on one aspect of lifelong learning, that of learning cities, with a concentration in its work on Asia and Europe. We focus on learning city development as a particular case of distinction in the field. We seek to identify the extent to which developments in the field in Asia have influenced and have been influenced by practices elsewhere in world, especially in Europe, and undertake our analysis using theories of societal learning/the learning society, learning communities and life-deep learning. We complement our analysis through assessment of material contained in three dominant journals in the field, the International Journal of Lifelong Education, the International Review of Education and Adult Education Quarterly, each edited in the west
Are Trp53 rescue of Brca1 embryonic lethality and Trp53/Brca1 breast cancer association related?
Brca1 is involved in multiple biological pathways including DNA damage repair, transcriptional regulation, and cell-cycle progression. A complex pattern of interactions of Brca1 with Trp53 has also emerged. Xu and coworkers found that haploid loss of Trp53 significantly reduces the embryonic lethality observed in mice with a homozygous in-frame deletion of Brca1 exon 11. They report that widespread apoptosis correlates with the embryonic lethality resulting from this homozygous Δ11 Brca1 mutation. A mechanism responsible for Brca1-associated carcinogenesis is proposed. These experiments extend our knowledge of a complex Brca1/Trp53 relationship. However, the precise mechanisms through which Brca1 interacts with Trp53 to suppress mammary tumor formation have yet to be elucidated
Using resource graphs to represent conceptual change
We introduce resource graphs, a representation of linked ideas used when
reasoning about specific contexts in physics. Our model is consistent with
previous descriptions of resources and coordination classes. It can represent
mesoscopic scales that are neither knowledge-in-pieces or large-scale concepts.
We use resource graphs to describe several forms of conceptual change:
incremental, cascade, wholesale, and dual construction. For each, we give
evidence from the physics education research literature to show examples of
each form of conceptual change. Where possible, we compare our representation
to models used by other researchers. Building on our representation, we
introduce a new form of conceptual change, differentiation, and suggest several
experimental studies that would help understand the differences between
reform-based curricula.Comment: 27 pages, 14 figures, no tables. Submitted for publication to the
Physical Review Special Topics Physics Education Research on March 8, 200
Pharmaceuticals in sewage systems and surface waters – status quo
Item does not contain fulltex
- …