5,599 research outputs found
Magnetar-like activity from the central compact object in the SNR RCW103
The 6.67 hr periodicity and the variable X-ray flux of the central compact
object (CCO) at the center of the SNR RCW 103, named 1E 161348-5055, have been
always difficult to interpret within the standard scenarios of an isolated
neutron star or a binary system. On 2016 June 22, the Burst Alert Telescope
(BAT) onboard Swift detected a magnetar-like short X-ray burst from the
direction of 1E 161348-5055, also coincident with a large long-term X-ray
outburst. Here we report on Chandra, NuSTAR, and Swift (BAT and XRT)
observations of this peculiar source during its 2016 outburst peak. In
particular, we study the properties of this magnetar-like burst, we discover a
hard X-ray tail in the CCO spectrum during outburst, and we study its long-term
outburst history (from 1999 to July 2016). We find the emission properties of
1E 161348-5055 consistent with it being a magnetar. However in this scenario,
the 6.67 hr periodicity can only be interpreted as the rotation period of this
strongly magnetized neutron star, which therefore represents the slowest pulsar
ever detected, by orders of magnitude. We briefly discuss the viable slow-down
scenarios, favoring a picture involving a period of fall-back accretion after
the supernova explosion, similarly to what is invoked (although in a different
regime) to explain the "anti-magnetar" scenario for other CCOs.Comment: 6 pages, 3 figures. To be published in the Astrophysical Journal
Letters; replaced to match the version accepted for publication on 2016
August 1
CMB Polarization Systematics, Cosmological Birefringence and the Gravitational Waves Background
Cosmic Microwave Background experiments must achieve very accurate
calibration of their polarization reference frame to avoid biasing the
cosmological parameters. In particular, a wrong or inaccurate calibration might
mimic the presence of a gravitational wave background, or a signal from
cosmological birefringence, a phenomenon characteristic of several
non-standard, symmetry breaking theories of electrodynamics that allow for
\textit{in vacuo} rotation if the polarization direction of the photon.
Noteworthly, several authors have claimed that the BOOMERanG 2003 (B2K)
published polarized power spectra of the CMB may hint at cosmological
birefringence. Such analyses, however, do not take into account the reported
calibration uncertainties of the BOOMERanG focal plane. We develop a formalism
to include this effect and apply it to the BOOMERanG dataset, finding a
cosmological rotation angle . We also
investigate the expected performances of future space borne experiment, finding
that an overall miscalibration larger then for Planck and
for EPIC, if not properly taken into account, will produce a bias on the
constraints on the cosmological parameters and could misleadingly suggest the
presence of a GW background.Comment: 10 pages, 3 figure
Numerical investigation on the residual stresses in welded T-joints made of dissimilar materials
Abstract This study used the Finite Element (FE) method to numerically analyze the thermo-mechanical behavior and residual stresses in dissimilar welded T-joints. Residual stresses induced by the fusion arc-welding of steel joints in power generation plants are a concern to the industry. The structural integrity assessment of welded structures requires the consideration of weld-induced residual stresses for the safe operations in power plants, which may be compromised by their presence. Details on the used thermo-mechanical FE model and the results analysis are herein presented
Improving relevance feedback-based query expansion by the use of a weighted word pairs approach
In this article, the use of a new term extraction method for query expansion (QE) in text retrieval is investigated. The new method expands the initial query with a structured representation made of weighted word pairs (WWP) extracted from a set of training documents (relevance feedback). Standard text retrieval systems can handle a WWP structure through custom Boolean weighted models. We experimented with both the explicit and pseudorelevance feedback schemas and compared the proposed term extraction method with others in the literature, such as KLD and RM3. Evaluations have been conducted on a number of test collections (Text REtrivel Conference [TREC]-6, -7, -8, -9, and -10). Results demonstrated that the QE method based on this new structure outperforms the baseline
Learning to Classify Text Using a Few Labeled Examples
It is well known that supervised text classification methods need to learn from many labeled examples to achieve a high accuracy. However, in a real context, sufficient labeled examples are not always available. In this paper we demonstrate that a way to obtain a high accuracy, when the number of labeled examples is low, is to consider structured features instead of list of weighted words as observed features. The proposed vector of features considers a hierarchical structure, named a mixed Graph of Terms, composed of a directed and an undirected sub-graph of words, that can be automatically constructed from a set of documents through the probabilistic Topic Model
Length–weight relationships for some plecoptera and ephemeroptera from a carbonate stream in central Apennine (Italy)
The relationship between dry weight and body length for larvae of Plecoptera (Leuctra spp., Isoperla grammatica, Nemoura cinerea) and Ephemeroptera (Baetis spp., Habrophlebia fusca, Paraleptophlebia submarginata, Ecdyonurus helveticus, Rhithrogena semicolorata), collected from a carbonate stream in the Apennine (central Italy), is reported. The power equation f(x) = Ax B has been applied to fit the curves of dry weight vs. body size (length) in the ranges 0.03–13.00 mg and 2–14 mm, respectively; a total of 674 larvae were examined. The power model was in very good agreement with experimental data. Moreover, the error between measured and estimated weight was in the 4–20% range. The data on Isoperla grammatica, Leuctra spp., Rhithrogena semicolorata and Baetis spp. were compared to those in a previous study in a different geographical setting (south-western Germany's Black Forest) obtaining similar results but with lower errors. We used and compared two methods: the weighted least-square method (WLS) and an analysis of covariance (ANCOVA). The values of the A and B coefficients obtained with the two methods were very similar (<6% discrepancy for either A or B). We found the best fits for all the examined Plecoptera (species, genus, and order level), while the results for Ephemeroptera were varied, with loose fits at the order level and also for Leptophlebiidae collectively considered
Platinum-Nucleos(t)ide Compounds as Possible Antimetabolites for Antitumor/Antiviral Therapy: Properties and Perspectives
Nucleoside analogues (NAs) are a family of compounds which include a variety of purine and pyrimidine derivatives, widely used as anticancer and antiviral agents. For their ability to compete with physiological nucleosides, NAs act as antimetabolites exerting their activity by interfering with the synthesis of nucleic acids. Much progress in the comprehension of their molecular mechanisms has been made, including providing new strategies for potentiating anticancer/antiviral activity. Among these strategies, new platinum-NAs showing a good potential to improve the therapeutic indices of NAs have been synthesized and studied. This short review aims to describe the properties and future perspectives of platinum-NAs, proposing these complexes as a new class of antimetabolites
Data-driven appraisal of renewable energy potentials for sustainable freshwater production in Africa
Clean water scarcity plagues several hundred million people worldwide, representing a major global problem. Nearly half of the total population lacking access to safe and drinkable water lives in Africa. Nonetheless, the African continent has a remarkable yet untapped potential in terms of renewable energy production, which may serve to produce clean water from contaminated or salty resources and for water extraction and distribution. In this view, the analysis of possible scenarios relies on data-driven approaches due to the scale of the problem and the general lack of comprehensive, direct on-site experience. In this work, we aim to systematically review and map the renewable potentials against the freshwater shortage in Africa to gain insight on perspective possible policies and provide a readily usable and well-structured framework and database for further analyses. All reported datasets are critically discussed, organized in tables, and classified by a few metadata to facilitate their usability in further analyses. The accompanying discussion focuses on regions that, in the near future, are expected to significantly exploit their renewable energy potentials, and on the reasons at the basis of the local water shortage, including technological and distribution problems
Amplitudes of thermal and kinetic Sunyaev-Zel'dovich signals from small-scale CMB anisotropies
While the arcminute-scale Cosmic Microwave Background (CMB) anisotropies are
due to secondary effects, point sources dominate the total anisotropy power
spectrum. At high frequencies the point sources are primarily in the form of
dusty, star-forming galaxies. Both Herschel and Planck have recently measured
the anisotropy power spectrum of cosmic infrared background (CIB) generated by
dusty, star-forming galaxies from degree to sub-arcminute angular scales,
including the non-linear clustering of these galaxies at multipoles of 3000 to
6000 relevant to CMB secondary anisotropy studies. We scale the CIB angular
power spectra to CMB frequencies and interpret the combined WMAP-7 year and
arcminute-scale Atacama Cosmology Telescope (ACT) and South Pole Telescope
(SPT) CMB power spectra measurements to constrain the Sunyaev-Zel'dovich (SZ)
effects. Allowing the CIB clustering amplitude to vary, we constrain the
amplitudes of thermal and kinetic SZ power spectra at 150 GHz.Comment: 8 pages, 3 figures, 2 table
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