542 research outputs found
Spectro-temporal analysis of a sample of bursts from FRB 121102
FRB~121102 was the first Fast Radio Burst (FRB) that was shown to repeat.
Since its discovery in 2012, more than two hundred bursts have been detected
from the source. These bursts exhibit a diverse range of spectral and temporal
characteristics and many questions about their origin and form remain
unanswered. Here, we present a sample of radio bursts from FRB 121102 detected
using the Lovell telescope at Jodrell Bank Observatory. We show four examples
of bursts that show peculiar spectro-temporal characteristics and compare them
with properties of bursts of FRB~121102 detected at other observatories. We
report on a precursor burst that is separated by just 17~ms from the main
burst, the shortest reported separation between two individual bursts to date.
We also provide access to data for all the detections of FRB~121102 in this
campaign.Comment: 3 pages, 1 Figure, to be published in RNAA
Limits on Absorption from a 332-MHz survey for Fast Radio Bursts
Fast Radio Bursts (FRBs) are bright, extragalactic radio pulses whose origins
are still unknown. Until recently, most FRBs have been detected at frequencies
greater than 1 GHz with a few exceptions at 800 MHz. The recent discoveries of
FRBs at 400 MHz from the Canadian Hydrogen Intensity Mapping Experiment (CHIME)
telescope has opened up possibilities for new insights about the progenitors
while many other low frequency surveys in the past have failed to find any
FRBs. Here, we present results from a FRB survey recently conducted at the
Jodrell Bank Observatory at 332 MHz with the 76-m Lovell telescope for a total
of 58 days. We did not detect any FRBs in the survey and report a 90 upper
limit of 5500 FRBs per day per sky for a Euclidean Universe above a fluence
threshold of 46 Jy ms. We discuss the possibility of absorption as the main
cause of non-detections in low frequency (< 800 MHz) searches and invoke
different absorption models to explain the same. We find that Induced Compton
Scattering alone cannot account for absorption of radio emission and that our
simulations favour a combination of Induced Compton Scattering and Free-Free
Absorption to explain the non-detections. For a free-free absorption scenario,
our constraints on the electron density are consistent with those expected in
the post-shock region of the ionized ejecta in Super-Luminous SuperNovae
(SLSNe).Comment: 12 pages, 9 Figures, 2 Tables, Second revision submitted to MNRA
Digital holographic microscopy: a quantitative label-free microscopy technique for phenotypic screening
Digital Holographic Microscopy (DHM) is a label-free imaging technique allowing visualization of transparent cells with classical imaging cell culture plates. The quantitative DHM phase contrast image provided is related both to the intracellular refractive index and to cell thickness. DHM is able to distinguish cellular morphological changes on two representative cell lines (HeLa and H9c2) when treated with doxorubicin and chloroquine, two cytotoxic compounds yielding distinct phenotypes. We analyzed parameters linked to cell morphology and to the intracellular content in endpoint measurements and further investigated them with timelapse recording. The results obtained by DHM were compared with other optical label-free microscopy techniques, namely Phase Contrast, Differential Interference Contrast and Transport of Intensity Equation (reconstructed from three bright-field images). For comparative purposes, images were acquired in a common 96-well plate format on the different motorized microscopes. In contrast to the other microscopies assayed, images generated with DHM can be easily quantified using a simple automatized on-the-fly analysis method for discriminating the different phenotypes generated in each cell line. The DHM technology is suitable for the development of robust and unbiased image-based assays
Constraints on Crustal Structure in the Vicinity of the Adriatic Indenter (European Alps) From Vp and Vp/Vs Local Earthquake Tomography
In this study, 3-D models of P-wave velocity (Vp) and P-wave and S-wave ratio (Vp/Vs) of the crust and upper mantle in the Eastern and eastern Southern Alps (northern Italy and southern Austria) were calculated using local earthquake tomography (LET). The data set includes high-quality arrival times from well-constrained hypocenters observed by the dense, temporary seismic networks of the AlpArray AASN and SWATH-D. The resolution of the LET was checked by synthetic tests and analysis of the model resolution matrix. The small inter-station spacing (average of âŒ15 km within the SWATH-D network) allowed us to image crustal structure at unprecedented resolution across a key part of the Alps. The derived P velocity model revealed a highly heterogeneous crustal structure in the target area. One of the main findings is that the lower crust is thickened, forming a bulge at 30â50 km depth just south of and beneath the Periadriatic Fault and the Tauern Window. This indicates that the lower crust decoupled both from its mantle substratum as well as from its upper crust. The Moho, taken to be the iso-velocity contour of Vp = 7.25 km/s, agrees with the Moho depth from previous studies in the European and Adriatic forelands. It is shallower on the Adriatic side than on the European side. This is interpreted to indicate that the European Plate is subducted beneath the Adriatic Plate in the Eastern and eastern Southern Alps
Illuminating Vestige: Amateur Archaeology and the Emergence of Historical Consciousness in Rural France
This article provides a historical ethnography of an abrupt and transient awakening of interest in Roman vestige during the 1970s in rural France, and explores its implications for comparative understanding of historical consciousness in Western Europe. Drawing on ethnographic fieldwork in Languedoc, and particularly the commune of MonadiĂšres, it details a vogue for collecting pottery shards scattered in a nearby lagoon that developed among local inhabitants. The article frames this as a ritualized âexpressive historicityâ emergent from political economic restructuring, cultural transformation, and time-space compression. It analyses the catalyzing role of a historian who introduced discursive forms into the commune for symbolizing the shards, drawn from regionalist and socialist historiography, which local people adapted to rearticulate the historicity of lived experience as a novel, hybrid genre of âhistorical consciousness.â These activities are conceptualized as a âreverse historiography.â Elements of historiographical and archaeological discoursesâfor example, chronological depth, collation and evaluation of material relicsâare reinvented to alternate ends, partly as a subversive âresponseâ to contact with such discourses. The practice emerges as a mediation of distinct ways of apprehending the world at a significant historical juncture. Analysis explores the utility of new anthropological theories of âhistoricityââan alternative to the established âhistorical idiomâ for analyzing our relations with the pastâwhich place historiography within the analytical frame, and enable consideration of the temporality of historical experience. Findings suggest that the alterity of popular Western cultural practices for invoking the past would reward further study
Some recent advances for limit theorems
We present some recent developments for limit theorems in probability theory, illustrating the variety of this field of activity. The recent results we discuss range from Steinâs method, as well as for infinitely divisible distributions as applications of this method in stochastic geometry, to asymptotics for some discrete models. They deal with rates of convergence, functional convergences for correlated random walks and shape theorems for growth models
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Dedifferentiation of committed epithelial cells into stem cells in vivo
Summary Cellular plasticity contributes to the regenerative capacity of plants, invertebrates, teleost fishes, and amphibians. In vertebrates, differentiated cells are known to revert into replicating progenitors, but these cells do not persist as stable stem cells. We now present evidence that differentiated airway epithelial cells can revert into stable and functional stem cells in vivo. Following the ablation of airway stem cells, we observed a surprising increase in the proliferation of committed secretory cells. Subsequent lineage tracing demonstrated that the luminal secretory cells had dedifferentiated into basal stem cells. Dedifferentiated cells were morphologically indistinguishable from stem cells and they functioned as well as their endogenous counterparts to repair epithelial injury. Indeed, single secretory cells clonally dedifferentiated into multipotent stem cells when they were cultured ex vivo without basal stem cells. In contrast, direct contact with a single basal stem cell was sufficient to prevent secretory cell dedifferentiation. In analogy to classical descriptions of amphibian nuclear reprogramming, the propensity of committed cells to dedifferentiate was inversely correlated to their state of maturity. This capacity of committed cells to dedifferentiate into stem cells may play a more general role in the regeneration of many tissues and in multiple disease states, notably cancer
The LOFAR Transients Pipeline
Current and future astronomical survey facilities provide a remarkably rich
opportunity for transient astronomy, combining unprecedented fields of view
with high sensitivity and the ability to access previously unexplored
wavelength regimes. This is particularly true of LOFAR, a
recently-commissioned, low-frequency radio interferometer, based in the
Netherlands and with stations across Europe. The identification of and response
to transients is one of LOFAR's key science goals. However, the large data
volumes which LOFAR produces, combined with the scientific requirement for
rapid response, make automation essential. To support this, we have developed
the LOFAR Transients Pipeline, or TraP. The TraP ingests multi-frequency image
data from LOFAR or other instruments and searches it for transients and
variables, providing automatic alerts of significant detections and populating
a lightcurve database for further analysis by astronomers. Here, we discuss the
scientific goals of the TraP and how it has been designed to meet them. We
describe its implementation, including both the algorithms adopted to maximize
performance as well as the development methodology used to ensure it is robust
and reliable, particularly in the presence of artefacts typical of radio
astronomy imaging. Finally, we report on a series of tests of the pipeline
carried out using simulated LOFAR observations with a known population of
transients.Comment: 30 pages, 11 figures; Accepted for publication in Astronomy &
Computing; Code at https://github.com/transientskp/tk
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Next-generation carrier screening
Purpose: Carrier screening for recessive Mendelian disorders traditionally employs focused genotyping to interrogate limited sets of mutations most prevalent in specific ethnic groups. We sought to develop a next-generation DNA sequencingâbased workflow to enable analysis of a more comprehensive set of disease-causing mutations. Methods: We utilized molecular inversion probes to capture the protein-coding regions of 15 genes from genomic DNA isolated from whole blood and sequenced those regions using the Illumina HiSeq 2000 (Illumina, San Diego, CA). To assess the quality of the resulting data, we measured both the fraction of the targeted region yielding high-quality genotype calls, and the sensitivity and specificity of those calls by comparison with conventional Sanger sequencing across hundreds of samples. Finally, to improve the overall accuracy for detecting insertions and deletions, we introduce a novel assembly-based approach that substantially increases sensitivity without reducing specificity. Results: We generated high-quality sequence for at least 99.8% of targeted base pairs in samples derived from blood and achieved high concordance with Sanger sequencing (sensitivity >99.9%, specificity >99.999%). Our novel algorithm is capable of detecting insertions and deletions inaccessible by current methods. Conclusion: Our next-generation DNA sequencingâbased approach yields the accuracy and completeness necessary for a carrier screening test
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