26,445 research outputs found
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
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 methodological status of co-authorship networks
No full textA powerful strategy within the study of collaboration
in science is to posit that co-authorship patterns
represent social networks.
It is prerequisite to an application of Social
Network Analysis (SNA) to define the network
entities. A network analysis of the inter-institutional
collaboration in COLLNET on the basis
of co-authorships was conducted. The study reveals
that it is crucial whether the co-authorship
itself is seen as an author's relational property or
as a social event that brings the authors together.
The former possibility is represented by a onemode
network in which each author can be related
to each other author. Quite distinct from
that are two-mode networks, the latter approach.
They consist of two single data sets in which relations
are only possible between different sets.
Different modes of representations require
different network approaches. One is that co-authorship
networks are seen as one-mode networks,
which has the advantage of the application
of a variety of measures. In contrast, twomode
networks, the other option, cannot be analysed
by standard techniques but its distinctive
features demand a new conceptualisation of
measures. In conclusion, the two-mode perspective
is more promising because it allows a dual
perspective on collaboration in science which includes
researchers as well as their scientific output
Physics from Time Variability of the VHE Blazar PKS 2155-304
No full textBlazars are the principal extragalactic sources of very high energy gamma-ray emission in the Universe. These objects constitute a sub-class of Active Galactic Nuclei whose
emission is dominated by Doppler boosted non-thermal radiation from plasma outflowing at relativistic speeds from the central engine. This plasma outflow happens in the
form of large-scale collimated structures called jets, which can extend for Mpc in length and transport energy from the central engine of the galaxy to the larger scale intergalac-
tic medium. Over thirty such sources have been discovered to date by ground-based gamma-ray telescopes such as H.E.S.S., and PKS 2155-304 is the prototypical southern-hemisphere representative of this population of objects.
In this thesis I have studied in detail some aspects of the temporal variability of the jet emission from PKS 2155-304, combining coordinated observations across the electromagnetic spectrum, from optical polarimetric measurements to X-ray and ground-based gamma-ray data. The temporal properties of the dataset allowed us to derive important physical information about the structure and emission mechanisms of the source and put constraints to the location of the sites of VHE emission and particle acceleration within the jet. We have also derived a sensitive statistical measure, called Kolmogorov distance,
which we applied to the large outburst observed from PKS 2155-304 in July 2006, to derive the most stringent constraints to date on limits for the violation of Lorentz invariance induced by quantum-gravity effects from AGN measurements
Co-authorship Network of Scientometrics Research Collaboration
No full textThis paper examines the co-authorship network in the field of scientometrics using social network analysis techniques with the aim of developing an understanding of research collaboration in this scientific community. Using co-authorship data from 3125 articles published in the journal Scientometrics with a time span of more than three decades (1980-2012), we construct an evolving co-authorship network and calculate three centrality measures (closeness, betweenness, and degree) for 3024 authors, 1207 institutions, 68 countries and 22 academic fields in this network. This paper also discusses the usability of centrality measures in author ranking, and suggests that centrality measures can be useful indicators for impact analysis. Findings revealed that scientometrics was not dominated by a couple of key researchers as quite a significant number of popular researchers were identified. The United States occupies the topmost position in all measures except for degree centrality. The most active, central and collaborative academic discipline in scientometrics is Information & Library Science
The Search For Pulsar Wind Nebulae in the Very High Energy Gamma-ray Regime
No full textThe aim of this Thesis is to study the development of pulsar wind nebulae in the TeV regime and in doing so uncover more sources which have as yet not been observed at these wavelengths. It is found that the extent of pulsar wind nebula in the TeV gamma-ray increases with its age while no developmental relationship is seen concerning
the luminosity or spectral index of the nebulae when observed in the TeV gamma-ray regime due to uncertainties in the measurements available.
TeV gamma-ray upper limits are calculated for several nebulae observed in the X-ray regime allowing the strength of their magnetic fields to be constrained but only one new source, which was previously confused with its companion, was discovered, the Eel Nebula.
Predictions of the fluxes of many of the sources for which upper limits are derived in this work have been calculated from observations of their emission in X-rays and some of these sources should be uncovered with the next generation CTA instrument
HESS Prize
No full textThomas was awarded the H.E.S.S. prize for his numerous and highly valuable contributions to H.E.S.S. in the past few years. He played, in particular, a major role in the maintenance of the H.E.S.S. data acquisition system (DAQ), and contributed to the development and implementation of a mono classification scheme for the large telescope (CT5), which is the basis of the low-energy real-time analysis (RTA). This classification provides the fast and reliable backbone for the mono RTA, used to trigger follow-up observations of known variable sources like Active Galactic Nuclei (AGN) or the recently detected Gamma Ray Burst GRB 190829A, and to search for emission from new transients. In addition to his technical contributions to the H.E.S.S. collaboration, he participated in the data analysis and interpretation of several astrophysical sources, such as the binary system PSR B1259-63 with H.E.S.S.-I and H.E.S.S.-II data. His most significant achievement in the past months was his role in the successful implementation of the HESS DAQ cluster upgrade, which will ensure continued stable and reliable operation of H.E.S.S. in the coming years
The status of the HESS project
No full textThe High Energy Stereoscopic System (HESS) is a system of four, 107 m2 mirror area, imaging Cherenkov telescopes under construction in the Khomas Highland of Namibia (1800 m asl). The HESS system is characterised by a low threshold (~100 GeV) and a ~1% Crab flux sensitivity resulting from the good angular resolution and background rejection provided by the stereoscopic technique.
The first two telescopes are operational and first results are reported here. The remaining two telescopes (of HESS Phase-I) will be commissioned early in 2004
Working internationally: Crossing the boundaries of wound care
No full textWound care is an international area of nursing and medical expertise, and one where care intervention is truly inter-professional. Clinicians in all countries can collaborate with one another to improve patient care, ensuring that the patient’s journey is based on the best available evidence and research. With the growth of social media, video conferencing, Skype™, and other forms of virtual communication, it has never been easier for clinicians to communicate with one another, and become immersed in collaborative research and the sharing of best practice. Here, the authors present an insight into an effective collaboration between nurse academics based at universities in the UK and Australia
TeV Analysis of a Source-rich Region with the HAWC Observatory: Is HESS J1809-193 a Potential Hadronic PeVatron?
No full textHESS J1809-193 is an unidentified TeV source, first detected by the High Energy Stereoscopic System (H.E.S.S.) collaboration. The emission originates in a source-rich region that includes several supernova remnants (SNRs) and pulsars including SNR G11.1+0.1, SNR G11.0-0.0, and the young radio pulsar PSR J1809-1917. Originally classified as a pulsar wind nebula candidate, recent studies show the peak of the TeV region overlapping with a system of molecular clouds. This resulted in the revision of the original leptonic scenario to look for alternate hadronic scenarios. Marked as a potential PeVatron candidate, this region has been studied extensively by H.E.S.S. due to its emission extending up to several tens of TeV. In this work, we use 2398 days of data from the High Altitude Water Cherenkov (HAWC) observatory to carry out a systematic source search of the HESS J1809-193 region. We were able to resolve emission detected as an extended component (modelled as a symmetric Gaussian with a 1σ radius of 0;21) with no clear cutoff at high energies and emitting photons up to 210 TeV. We model the multiwavelength observations for the region around HESS J1809-193 using a time-dependent leptonic model and a lepto-hadronic model. Our model indicates that both scenarios could explain the observed data within the region of HESS J1809-193
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