2,685 research outputs found
Monitoring of the radio galaxy M 87 at Very High Energy with MAGIC during a low emission state between 2012 and 2015
No full textWe present the preliminary results from observing the nearby radio galaxy M 87 for 156 hours (between the years 2012 and 2015) with the MAGIC telescopes, which lead to a significant very high energy (VHE, E > 100 GeV) detection of the source in quiescent states each year. Our VHE analysis combined with quasi-simultaneous data at other energies (from gamma-rays, X-rays, optical and radio) provides a unique opportunity to study the source variability and its broadband spectral energy distribution, which is found to disfavour a one-zone synchrotron/synchrotron self-Compton model. Therefore, other alternative scenarios for the photon emission are explored. We also find that the VHE emission is compatible with being produced close to the source radio core as previous data already indicated. A detailed paper presenting full results of the observing campaign is in preparatio
P- versus S-wave
No full text.02> m , U. Meyer-Berkhout h , L. Montanet c , A. Noble m , K. Peters a , G. Pinter b , S. Ravndal a , A.H. Sanjari i , E. Schafer g , B. Schmid m , P. Schmidt d , S. Spanier g , C. Straßburger g , U. Strohbusch d , M. Suffert k , D. Urner m , C. Volcker h , D. Walther a , U. Wiedner d , N. Winter e , J. Zoll c , C. Zupancic h a Universitat Bochum, D-4630 Bochum, FRG b Academy of Science, H-1525 Budapest, Hungary c CERN, CH-1211 Gen`eve, Switzerland d Universitat Hamburg, D-2000 Hamburg, FRG e Universitat Karlsruhe, W-7500 K
Hypericin and hypericin-like substances: analytical problems
No full textHypericin is a substance derived from Hypericum perforatum L., a plant utilized in the production of extracts used to aromatize alcoholic beverages and soft drinks and limited in food and beverages by the E.E.C. Directives on Flavouring. This paper deals with the H.P.L.C. method developed to cover the lack of official and recommended methods concerning hypericin. It also considers the effect of alcoholic content on extraction by infusion of hypericin and testifies to the presence of hypericin-like substances in Hypericum perforatum L. extracts, inexplicably not limited by law
Decomposing blazar spectra into lepto‐hadronic emission components
No full textThe recently reported coincidences between high‐energy neutrino events and major blazar outbursts reinforce the relevance of lepto‐hadronic emission models for blazars. We study the influence of physical parameters on the neutrino output by modeling blazar spectral energy distributions self‐consistently assuming a relativistically propagating acceleration zone surrounded by a larger cooling zone. We find that the gross features of the spectral energy distribution can readily be explained with the model. A rigorous test requires time‐resolved measurements of blazar spectral energy distributions during an outburst and high‐statistics neutrino measurements to discriminate the leptonic and hadronic emission component
Simulation study of overtaking of ion-acoustic solitons in the fully kinetic regime
No full textThe overtaking collisions of ion-acoustic solitons in the presence of trapping effects of electrons are studied based on a fully kinetic simulation approach. The method is able to provide all the kinetic details of the process alongside the fluid-level quantities self consistently. Solitons are produced naturally by utilizing the chain formation phenomenon, and then are arranged in a new simulation box to test the different scenarios of overtaking collisions. Three achievements are reported here. First, simulations prove the long-time life span of the ion-acoustic solitons in the presence of trapping effect of electrons (kinetic effects), which serves as the benchmark of the simulation code. Second, their stability against overtaking mutual collisions is established by creating collisions between solitons with different number and shapes of trapped electrons, i.e., different trapping parameter. Finally, details of solitons during collisions for both ions and electrons are provided on both fluid and kinetic levels. These results show that on the kinetic level, trapped electron population accompanying each of the solitons are exchanged between the solitons during the collision. Furthermore, the behavior of electron holes accompanying solitons contradicts the theory about the electron holes interaction developed based on kinetic theory. They also show behaviors much different from other electron holes witnessed in processes such as nonlinear Landau damping (Bernstein-Greene-Kruskal -BGK- modes) or beam-plasma interaction (like two-beam instability
Fully kinetic simulation study of ion-acoustic solitons in the presence of trapped electrons
No full textThe nonlinear fluid theory developed by Schamel suggests a modified KdV equation to describe the temporal evolution of ion acoustic (IA) solitons in the presence of trapped electrons. The validity of this theory is studied here by verifying solitons' main characteristic, i.e., stability against successive mutual collisions. We have employed a kinetic model as a more comprehensive theory than the fluid one, and utilized a fully kinetic simulation approach (both ions and electrons are treated based on the Vlasov equation). In the simulation approach, these solitons are excited self-consistently by employing the nonlinear process of IA solitons formation from an initial density perturbation (IDP). The effect of the size of IDPs on the chain formation is proved by the simulation code as a benchmark test. It is shown that the IA solitons, in the presence of trapped electrons, can retain their features (both in spatial and velocity direction) after successive mutual collisions. The collisions here include encounters of IA solitons with the same trapping parameter, while differing in size. Kinetic simulation results reveal a complicated behavior during a collision between IA solitons in contrast to the fluid theory predictions and simulations. In the range of parameters considered here, two oppositely propagating solitons rotate around their collective center in the phase space during a collision, independent of their trapping parameters. Furthermore, they exchange some portions of their trapped population
Scattering of electron holes in the context of ion-acoustic regime
No full textMutual collisions between ion-acoustic solitary waves are studied based on a fully kinetic simulation approach. Two cases, small and large relative
velocities, are studied, and the effect of trapped electron population on the collision process is focused upon. It is shown that, for the case of small
relative velocity, the repelling force between the trapped populations of electrons results in scattering of electron holes. However, this phenomenon
cannot be witnessed if the relative velocity is considerably high since the impact of trapped population remains very wea
Study of trapping effect on ion-acoustic solitary waves based on a fully kinetic simulation approach
No full textA fully kinetic simulation approach, treating each plasma component based on the Vlasov equation, is adopted to study the disintegration of an initial density perturbation into a number of ion-acoustic solitary waves (IASWs) in the presence of the trapping effect of electrons. The nonlinear fluid theory developed by Schamel [Plasma Phys. 13, 491 (1971); J. Plasma Phys. 7, 1 (1972); Plasma Phys. 14, 905 (1972); J. Plasma Phys. 9, 377 (1973); Phys. Scr. 20, 306 (1979)] has identified three separate regimes of ion-acoustic solitary waves based on the trapping parameter. Here, the disintegration process and the resulting self-consistent IASWs are studied in a wide range of trapping parameters covering all the three regimes continuously. The dependency of features such as the time of disintegration, the number, speed, and size of IASWs on the trapping parameter are focused upon. It is shown that an increase in this parameter slows down the propagation of IASWs while decreases their sizes in the phase space. These features of IASWs tend to saturate for large values of trapping parameters. The disintegration time shows a more complicated behavior than what was predicted by the theoretical approach. Also for the case of trapping parameters bigger than one, propagation of IASWs is observed in contrast with the theoretical predictions. The kinetic simulation results unveil a smooth and well-defined dependency of solitary waves' features on the trapping parameter, showing the possibility of bridging all the three regimes. Finally, it is shown that for β around zero, the electron phase space structure of the accompanying vortex stays symmetric. The effect of the electron-to-ion temperature ratio on the disintegration and the propagation of IASWs are considered as a benchmarking test of the simulation code (in the nonlinear regime
Staging of intraosseous extent of osteosarcoma: correlation of preoperative CT and MR imaging with pathologic macroslides
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