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تسجيل مستخدم جديدPublication statistics on Sun and heliosphere
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C.J. Schrijver
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The professional literature provides one means to review the evolution and geographic distribution of the scientific communities engaged in solar and heliospheric physics. With help of the Astrophysics Data System (NASA/ADS), I trace the growth of the research community over the past century from a few dozen researchers early in the 20-th Century to over 4,000 names with over refereed 2,000 publications in recent years, with 90% originating from 20 countries, being published in 90 distinct journals. Overall, the lead authors of these publications have their affiliations for 45% in Europe, 29% in the Americas, 24% in Australasia, and 2% in Africa and Arab countries. Publications most frequently appear (in decreasing order) in the Astrophysical Journal, the Journal of Geophysical Research (Space Physics), Solar Physics, Astronomy and Astrophysics, and Advances in Space Research (adding up to 59% of all publications in 2015).
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Swift is a satellite equipped with gamma-ray, X-ray, and optical-UV instruments aimed at discovering, localizing and collecting data from gamma-ray bursts (GRBs). Launched at the end of 2004, this small-size mission finds about a hundred GRBs per yea
r, totaling more than 700 events as of 2012. In addition to GRBs, Swift observes other energetic events, such as AGNs, novae, and supernovae. Here we look at its success using bibliometric tools; that is the number of papers using Swift data and their impact (i.e., number of citations to those papers). We derived these for the publication years 2005 to 2011, and compared them with the same numbers for other major observatories. Swift provided data for 1101 papers in the interval 2005-2011, with 24 in the first year, to 287 in the last year. In 2011, Swift had more than double the number of publications as Subaru, it overcame Gemini by a large fraction, and reached Keck. It is getting closer to the ~400 publications of the successful high-energy missions XMM-Newton and Chandra, but is still far from the most productive telescopes VLT (over 500) and HST (almost 800). The overall average number of citations per paper, as of November 2012, is 28.3, which is comparable to the others, but lower than Keck (41.8). The science topics covered by Swift publications have changed from the first year, when over 80% of the papers were about GRBs, while in 2011 it was less than 30%.
Mutual quasi-periodicities near the solar-rotation period appear in time series based on the Earths magnetic field, the interplanetary magnetic field, and signed solar-magnetic fields. Dominant among these is one at 27.03 +/- 0.02 days that has been
highlighted by Neugebauer, et al. 2000, J. Geophys. Res., 105, 2315. Extension of their study in time and to different data reveals decadal epochs during which the ~ 27.0 day, a ~ 28.3 day, or other quasi-periods dominate the signal. Space-time eigenvalue analyses of time series in 30 solar latitude bands, based on synoptic maps of unsigned photospheric fields, lead to two maximally independent modes that account for almost 30% of the data variance. One mode spans 45 degrees of latitude in the northern hemisphere and the other one in the southern. The modes rotate around the Sun rigidly, not differentially, suggesting connection with the subsurface dynamo. Spectral analyses yield familiar dominant quasi periods 27.04 +/- 0.03 days in the North and at 28.24 +/- 0.03 days in the South. These are replaced during cycle 23 by one at 26.45 +/- 0.03 days in the North. The modes show no tendency for preferred longitudes separated by ~ 180 degrees.
The Sun has remained a difficult source to image for radio telescopes, especially at the low radio frequencies. Its morphologically complex emission features span a large range of angular scales, emission mechanisms involved and brightness temperatur
es. In addition, time and frequency synthesis, the key tool used by most radio interferometers to build up information about the source being imaged is not effective for solar imaging, because many of the features of interest are short lived and change dramatically over small fractional bandwidths. Building on the advances in radio frequency technology, digital signal processing and computing, the kind of instruments needed to simultaneously capture the evolution of solar emission in time, frequency, morphology and polarization over a large spectral span with the requisite imaging fidelity, and time and frequency resolution have only recently begun to appear. Of this class of instruments, the Murchison Widefield Array (MWA) is best suited for solar observations. The MWA has now entered a routine observing phase and here we present some early examples from MWA observations.
We obtain analytical approximations for the expectation and variance of the Spectral Kurtosis estimator in the case of Gaussian and coherent transient time domain signals mixed with a quasi-stationary Gaussian background, which are suitable for pract
ical estimations of their signal-to-noise ratio and duty-cycle relative to the instrumental integration time. We validate these analytical approximations by means of numerical simulations and demonstrate that such estimates are affected by statistical uncertainties that, for a suitable choice of the integration time, may not exceed a few percent. Based on these analytical results, we suggest a multiscale Spectral Kurtosis spectrometer design optimized for real-time detection of transient signals, automatic discrimination based on their statistical signature, and measurement of their properties.
We implemented a website to deal with main effects on Cosmic Ray access to the Earth, i.e. the Solar Modulation and the Geomagnetic Field effect. In helmod.org the end user can easily access a web interface to results catalog of the HelMod Monte Carl
o Code. This Model uses a Monte Carlo Approach to solves the Parker Transport Equation, obtaining a modulated proton flux for a period (monthly average) between January 1990 and december 2007. geomagsphere.org is instead based on GeoMag Backtracing Code, that solves the Lorentz equation with a Runge-Kutta method of 6th order, and, reversing charge sign and velocity, reconstruct particle trajectories in the Earth Magnetosphere back in time. We use last models of internal (IGRF-11) and external (Tsyganenko 1996 -T96- and 2005 -T05-) field components valid up to 2015. Particles are backtraced to the outer (magnetopause) or inner boundary to separate Primary (allowed trajectory) from Secondary (forbidden) Cosmic Rays. This code has been used both for reproducing known effects as East-West effect and rigidity cutoff calculations. In geomagsphere.org the user can choose the external field model from Tsyganenko (T96 or T05) and obtain for a fixed position and date from 1st Jan. 1968 (T96) and 1st Jan. 1995 (T05) respectively till 31$^{st}$ Dec 2012, the vertical rigidity cutoff estimation obtained with the backtracing technique with a rigidity step of 0.1 GV. For a more precise calculation (0.01 GV), requiring more CPU time, results are sent to the user by email (mail model)
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