21,261 research outputs found
Locating the Source of Diffusion in Large-Scale Networks
How can we localize the source of diffusion in a complex network? Due to the
tremendous size of many real networks--such as the Internet or the human social
graph--it is usually infeasible to observe the state of all nodes in a network.
We show that it is fundamentally possible to estimate the location of the
source from measurements collected by sparsely-placed observers. We present a
strategy that is optimal for arbitrary trees, achieving maximum probability of
correct localization. We describe efficient implementations with complexity
O(N^{\alpha}), where \alpha=1 for arbitrary trees, and \alpha=3 for arbitrary
graphs. In the context of several case studies, we determine how localization
accuracy is affected by various system parameters, including the structure of
the network, the density of observers, and the number of observed cascades.Comment: To appear in Physical Review Letters. Includes pre-print of main
paper, and supplementary materia
Detection of a variable ultra-fast outflow in the Narrow Line Seyfert 1 galaxy PG 1448+273
Relativistically blueshifted absorption features of highly ionised ions, the
so-called ultra-fast outflows (UFOs), have been detected in the X-ray spectra
of a number of accreting supermassive black holes. If these features truly
originate from accretion disc winds accelerated to more than 10 per cent of the
speed of light, their energy budget is very significant and they can contribute
to or even drive galaxy-scale feedback from active galactic nuclei (AGN).
However, the UFO spectral features are often weak due to high ionisation of the
outflowing material, and the inference of the wind physical properties can be
complicated by other spectral features in AGN such as relativistic reflection.
Here we study a highly accreting Narrow Line Seyfert 1 galaxy PG 1448+273. We
apply an automated, systematic routine for detecting outflows in accreting
systems and achieve an unambiguous detection of a UFO in this AGN. The UFO
absorption is observed in both soft and hard X-ray bands with the XMM-Newton
observatory. The velocity of the outflow is (26900 +- 600) km/s (~0.09c), with
an ionisation parameter of log ({\xi} / erg cm s^-1)=4.03_{-0.08}^{+0.10} and a
column density above 10^23 cm^-2. At the same time, we detect weak warm
absorption features in the spectrum of the object. Our systematic outflow
search suggests the presence of further multi-phase wind structure, but we
cannot claim a significant detection considering the present data quality. The
UFO is not detected in a second, shorter observation with XMM-Newton,
indicating variability in time, observed also in other similar AGN.Comment: Accepted for publication in MNRAS. 14 pages, 11 figures, 1 tabl
The Friedreich ataxia GAA repeat expansion mutation induces comparable epigenetic changes in human and transgenic mouse brain and heart tissues
Friedreich ataxia (FRDA) is caused by a homozygous GAA repeat expansion mutation
within intron 1 of the FXN gene, leading to reduced expression of frataxin protein.
Evidence suggests that the mutation may induce epigenetic changes and heterochromatin
formation, thereby impeding gene transcription. In particular, studies using FRDA patient
blood and lymphoblastoid cell lines have detected increased DNA methylation of specific
CpG sites upstream of the GAA repeat and histone modifications in regions flanking the
GAA repeat. In this report we show that such epigenetic changes are also present in
FRDA patient brain, cerebellum and heart tissues, the primary affected systems of the
disorder. Bisulfite sequence analysis of the FXN flanking GAA regions reveals a shift in
the FRDA DNA methylation profile, with upstream CpG sites becoming consistently
hypermethylated and downstream CpG sites becoming consistently hypomethylated. We
also identify differential DNA methylation at three specific CpG sites within the FXN
promoter and one CpG site within exon 1. Furthermore, we show by chromatin
immunoprecipitation (ChIP) analysis that there is overall decreased histone H3K9
acetylation together with increased H3K9 methylation of FRDA brain tissue. Further
studies of brain, cerebellum and heart tissues from our GAA repeat expansion-containing
FRDA YAC transgenic mice reveal comparable epigenetic changes to those detected in
FRDA patient tissue. We have thus developed a mouse model that will be a valuable
resource for future therapeutic studies targeting epigenetic modifications of the FXN gene
to increase frataxin expression
Evidence for a Variable Ultrafast Outflow in the Newly Discovered Ultraluminous Pulsar NGC 300 ULX-1
Ultraluminous pulsars are a definite proof that persistent super-Eddington
accretion occurs in nature. They support the scenario according to which most
Ultraluminous X-ray Sources (ULXs) are super-Eddington accretors of stellar
mass rather than sub-Eddington intermediate mass black holes. An important
prediction of theories of supercritical accretion is the existence of powerful
outflows of moderately ionized gas at mildly relativistic speeds. In practice,
the spectral resolution of X-ray gratings such as RGS onboard XMM-Newton is
required to resolve their observational signatures in ULXs. Using RGS, outflows
have been discovered in the spectra of 3 ULXs (none of which are currently
known to be pulsars). Most recently, the fourth ultraluminous pulsar was
discovered in NGC 300. Here we report detection of an ultrafast outflow (UFO)
in the X-ray spectrum of the object, with a significance of more than
3{\sigma}, during one of the two simultaneous observations of the source by
XMM-Newton and NuSTAR in December 2016. The outflow has a projected velocity of
65000 km/s (0.22c) and a high ionisation factor with a log value of 3.9. This
is the first direct evidence for a UFO in a neutron star ULX and also the first
time that this its evidence in a ULX spectrum is seen in both soft and hard
X-ray data simultaneously. We find no evidence of the UFO during the other
observation of the object, which could be explained by either clumpy nature of
the absorber or a slight change in our viewing angle of the accretion flow.Comment: 10 pages, 4 figures. Accepted to MNRA
Importance of a National arthroplasty register for Identification by medical examiner
ABSTRACTMass catastrophes are realities that come to pass with lamentable frequency. In such situations, one of the fundamental forensic problems is in relation to identifying the victims. All the elements that might be capable of contributing towards this identification process are essential, and among these are orthopedic prostheses, which frequently remain intact. These prostheses consist basically of polymers, ceramics or metals. Metal components, which are usually composed of titanium, chromium, cobalt or steel alloys, are resistant to violent trauma or high temperatures. Human identification is possible if the identity of the implant is established and if this can be correlated with the individual in whom it was implanted. The logo on the prosthesis establishes who the manufacturer was and the serial number can be compared with the clinical process or with a prosthesis register, as has been implemented in several countries. The information in the database should include the patient's name, the implant model and its serial number, for consultation only in cases of forensic identification, while obviously respecting ethical issues of privacy. This article highlights the importance of creating a national prosthesis register
Mapeamento da expansão agrícola no estado do Mato Grosso em 11 anos a partir de técnica baseada em séries temporais de imagens de NDVI.
O objetivo deste estudo foi aplicar uma metodologia baseada na análise espectro-temporal de imagens do índice de vegetação NDVI (Normalized Difference Vegetation Index), adquiridas do sensor MODIS (Moderate Resolution Imaging Spectroradiometer), com resolução espacial de 250 metros, para a geração de mapas da agricultura anual no estado do Mato Grosso nas safras 2000/2001 e 2011/2012, de modo a especializar o processo de expansão da agricultura neste período.SBSR 2013
On the quantumness of correlations in nuclear magnetic resonance
Nuclear Magnetic Resonance (NMR) was successfully employed to test several
protocols and ideas in Quantum Information Science. In most of these
implementations the existence of entanglement was ruled out. This fact
introduced concerns and questions about the quantum nature of such bench tests.
In this article we address some issues related to the non-classical aspects of
NMR systems. We discuss some experiments where the quantum aspects of this
system are supported by quantum correlations of separable states. Such
quantumness, beyond the entanglement-separability paradigm, is revealed via a
departure between the quantum and the classical versions of information theory.
In this scenario, the concept of quantum discord seems to play an important
role. We also present an experimental implementation of an analogous of the
single-photon Mach-Zehnder interferometer employing two nuclear spins to encode
the interferometric paths. This experiment illustrate how non-classical
correlations of separable states may be used to simulate quantum dynamics. The
results obtained are completely equivalent to the optical scenario, where
entanglement (between two field modes) may be present
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