25,166 research outputs found
Knowledge for Development
No full textMetadata only recordThis website, established by the Technical Centre for Agricultural and Rural Cooperation (CTA), serves as an open forum for professionals, stakeholders, policy makers, farmers, and researchers in the field of agriculture to share information about initiatives, studies, and results in order to facilitate collaboration concerning policy development with the greater goal of assisting the development, adaptation, and adoption of science and technology in agriculture in African, Caribbean, and Pacific nations
HAWC J2227+610: a potential PeVatron candidate for the CTA in the northern hemisphere [Elektronisk resurs]
No full textRecent observations of the gamma-ray source HAWC J2227+610 by Tibet AS+MD and LHAASO confirm the special interest of this source as a galactic PeVatron candidate in the northern hemisphere. HAWC J2227+610 emits Very High Energy (VHE) gamma-rays up to 500 TeV, from a region coincident with molecular clouds and significantly displaced from the nearby pulsar J2229+6114. Even if this morphology favours an hadronic origin, both leptonic or hadronic models can describe the current VHE gamma-ray emission. The morphology of the source is not well constrained by the present measurements and a better characterisation would greatly help the understanding of the underlying particle acceleration mechanisms. The Cherenkov Telescope Array (CTA) will be the future most sensitive Imaging Atmospheric Cherenkov Telescope and, thanks to its unprecedented angular resolution, could contribute to better constrain the nature of this source. The present work investigates the potentiality of CTA to study the morphology and the spectrum of HAWC J2227+610. For this aim, the source is simulated assuming the hadronic model proposed by the Tibet AS+MD collaboration, recently fitted on multi-wavelength data, and two spatial templates associated to the source nearby molecular clouds. Different CTA layouts and observation times are considered. A 3D map based analysis shows that CTA is able to significantly detect the extension of the source and to attribute higher detection significance to the simulated molecular cloud template compared to the alternative one. CTA data does not allow to disentangle the hadronic and the leptonic emission models. However, it permits to correctly reproduce the simulated parent proton spectrum characterized by a ∼ 500 TeV cutoff. © Copyright owned by the author(s) under the terms of the Creative Commons
The Structure of Scientific Collaboration Networks in Scientometrics
No full textThe structure of scientific collaboration networks in scientometrics was investigated at the level of individuals by using bibliographic data of all papers published in the international journal Scientometrics retrieved from the Science Citation Index (SCI) during 1978 to 2004. Combined analysis of social network analysis (SNA), co-occurrence analysis, cluster analysis and frequency analysis of words was explored to reveal: (1) The microstructure of the collaboration network on scientists’ aspects of scientometrics; (2) The major collaborative fields of the collaborative sub-networks; (3) The collaborative center of the collaboration network in scientometrics
HAWC J2227+610: a potential PeVatron candidate for the CTA in the northern hemisphere
No full textInternational audienceRecent observations of the gamma-ray source HAWC J2227+610 by Tibet AS+MD and LHAASOconfirm the special interest of this source as a galactic PeVatron candidate in the northern hemisphere. HAWC J2227+610 emits Very High Energy (VHE) gamma-rays up to 500 TeV, froma region coincident with molecular clouds and significantly displaced from the nearby pulsarJ2229+6114. Even if this morphology favours an hadronic origin, both leptonic or hadronicmodels can describe the current VHE gamma-ray emission. The morphology of the source is notwell constrained by the present measurements and a better characterisation would greatly helpthe understanding of the underlying particle acceleration mechanisms. The Cherenkov TelescopeArray (CTA) will be the future most sensitive Imaging Atmospheric Cherenkov Telescope and,thanks to its unprecedented angular resolution, could contribute to better constrain the nature ofthis source. The present work investigates the potentiality of CTA to study the morphology andthe spectrum of HAWC J2227+610. For this aim, the source is simulated assuming the hadronicmodel proposed by the Tibet AS+MD collaboration, recently fitted on multi-wavelength data, andtwo spatial templates associated to the source nearby molecular clouds. Different CTA layouts andobservation times are considered. A 3D map based analysis shows that CTA is able to significantlydetect the extension of the source and to attribute higher detection significance to the simulatedmolecular cloud template compared to the alternative one. CTA data does not allow to disentanglethe hadronic and the leptonic emission models. However, it permits to correctly reproduce thesimulated parent proton spectrum characterized by a ∼ 500 TeV cutoff
The Cherenkov Telescope Array: layout, design and performance
No full textThe Cherenkov Telescope Array (CTA) will be the next generation very-high-energy gamma-ray observatory. CTA is expected to provide substantial improvement in accuracy and sensitivity with respect to existing instruments thanks to a tenfold increase in the number of telescopes and their state-of-the-art design. Detailed Monte Carlo simulations are used to further optimise the number of telescopes and the array layout, and to estimate the observatory performance using updated models of the selected telescope designs. These studies are presented in this contribution for the two CTA stations located on the island of La Palma (Spain) and near Paranal (Chile) and for different operation and observation conditions
The ASTRI Project in the Framework of the Cherenkov Telescope Array
No full textThe Cherenkov Telescope Array (CTA) will be the next generation facility to investigate the very high-energy gamma-ray emission from a large variety of celestial sources. The full array, installed at two sites, one in the northern and one in the southern hemisphere, will start to operate at the beginning of the next decade. In the meantime, a few telescope prototypes have been developed and some pre-production CTA telescopes have been planned. Within this framework, the Italian National Institute for Astrophysics (INAF) is leading the ASTRI project, whose aim is two-fold. The ASTRI Collaboration has successfully developed and installed in Sicily a prototype of the CTA small-sized telescopes (SST), according to an innovative dual-mirror (2M) optical solution and equipped with a silicon-based photo-detector Cherenkov camera. Moreover, INAF is leading the development of one of the mini-arrays of pre-production CTA telescopes composed of at least nine dual-mirror telescopes and proposed to be installed at the CTA southern site in 2018. The ASTRI mini-array of SST pre-production CTA telescopes will be able to both verify some of the adopted innovative solutions, such as the wide field of view, and to investigate sources emitting at energies from a few TeV up to hundreds of TeV. We discuss the preliminary results obtained by the ASTRI SST-2M prototype during its ongoing commissioning phase, the expected Monte Carlo performance of the ASTRI mini-array of SST pre-production CTA telescopes, and provide an overview of the scientific topics that can be addressed both, as a stand-alone mini-array and in synergy with other pre-production CTA telescopes
Collaboration in Iranian Scientific Publications
No full textThis study looks at international collaboration in Iranian scientific publications through the ISI Science Citation Index® (SCI) for the years 1995-1999, inclusive. These results are compared to and contrasted with the earlier findings for the periods covering 1985-1994 (Osareh & Wilson 2000). The results of Iran's increasing productivity over a 15-year period are presented. Iran doubled its output in the first two five-year periods and increased 2.8-fold from the second to the third five-year period. The rise in Iran's scientific publication output is due mainly to factors such as the ending of the war, better economic conditions, recent changes in the Iranian government's policy, basic changes in the political environment brought about by the Reformers, expansion of the Iranian presses for national publications, and the recent return of a large number of students trained overseas through government scholarships. External changes also account for the increased productivity, e.g., the acceptance of three Iranian source journals by the SCI, increased access to international databases through the Internet and better electronic communication facilities for international collaboration. One of the most important and significant factors that caused this dramatic rise seems to be the government's research policies in the last few years. Since 1999, the Iran Science, Research and Technology Ministry, has encouraged researchers to publish their non-Farsi language articles in highly ranked international scientific journals, for example, by giving prizes to researchers who publish their articles in ISI-ranked journals
The Small-Sized Telescopes for the Southern Site of the Cherenkov Telescope Array
No full textThe Cherenkov Telescope Array (CTA) will use three telescope sizes to efficiently detect cosmic gamma rays in the energy range from several tens of GeV to hundreds of TeV. The Small-Sized Telescopes (SSTs) will form the largest section of the array, covering an area of many square kilometres on the CTA southern site in Paranal, Chile. Up to 70 SSTs will be implemented by an international consortium of institutes and teams as an in-kind contribution to the CTA Observatory. The SSTs will provide unprecedented sensitivity to gamma rays above 1 TeV and the highest angular resolution of any instrument above the hard X-ray band. CTA has recently finalised the technology that will be used for the SSTs: the telescopes will be a dual-reflector design with a primary reflector of ~4 m diameter, equipped with an SiPM-based camera with full waveform readout from 2000 channels covering a 9 field of view. The Schwarzschild-Couder optical configuration leads to a small plate-scale, and consequently a compact, cost-efficient camera. In this contribution, we describe the experience gained operating telescope and camera prototypes during the CTA preparatory phase, and the development of the final SST design
A fast muon tagger method for Imaging Atmospheric Cherenkov Telescopes
No full textThe Cherenkov Telescope Array (CTA) will be the next major observatory for Very High Energy (VHE) γ-ray astronomy. Its optical throughput calibration relies on muon Cherenkov rings. This work is aimed at developing a fast and efficient muon tagger at the camera level for the CTA telescopes. A novel technique to tag muons using the capabilities of silicon photomultiplier Compact High-Energy Camera CHEC-S, one of the design options for the camera of the Small Size Telescopes (SSTs), has been developed, studying and comparing different algorithms such as circle fitting, machine learning and simple pixel counting. Their performance in terms of efficiency and computation speed was investigated using simulations with varying levels of night sky background light. The application of the best performing method to the Large Size Telescope (LST) camera has been also studied, with the goal of improving the speed of the muon preselection
Science with the Cherenkov Telescope Array
No full textThis book summarizes the science to be carried out by the upcoming Cherenkov Telescope Array, a major ground-based gamma-ray observatory that will be constructed over the next six to eight years. The major scientific themes, as well as core program of key science projects, have been developed by the CTA Consortium, a collaboration of scientists from many institutions worldwide. CTA will be the major facility in high-energy and very high-energy photon astronomy over the next decade and beyond. CTA will have capabilities well beyond past and present observatories. Thus, CTA's science program is expected to be rich and broad and will complement other major multiwavelength and multimessenger facilities. This book is intended to be the primary resource for the science case for CTA and it thus will be of great interest to the broader physics and astronomy communities. The electronic version (e-book) is available in open access
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