TY - GEN A1 - Fraschetti, Federico A1 - Pohl, Martin T1 - Two-zone model for the broadband crab nebula spectrum BT - microscopic interpretation T2 - The European physical journal : Web of Conferences : proceedings N2 - We develop a simple two-zone interpretation of the broadband baseline Crab nebula spectrum between 10(-5) eV and similar to 100 TeV by using two distinct log-parabola energetic electrons distributions. We determine analytically the very-high energy photon spectrum as originated by inverse-Compton scattering of the far-infrared soft ambient photons within the nebula off a first population of electrons energized at the nebula termination shock. The broad and flat 200 GeV peak jointly observed by Fermi/LAT and MAGIC is naturally reproduced. The synchrotron radiation from a second energetic electron population explains the spectrum from the radio range up to similar to 10 keV. We infer from observations the energy dependence of the microscopic probability of remaining in proximity of the shock of the accelerating electrons. Y1 - 2017 U6 - https://doi.org/10.1051/epjconf/201713602009 SN - 2100-014X VL - 136 PB - EDP Sciences CY - Les Ulis ER - TY - GEN A1 - Maier, Philipp A1 - Wolf, Jürgen A1 - Keilig, Thomas A1 - Krabbe, Alfred A1 - Duffard, Rene A1 - Ortiz, Jose-Luis A1 - Klinkner, Sabine A1 - Lengowski, Michael A1 - Müller, Thomas A1 - Lockowandt, Christian A1 - Krockstedt, Christian A1 - Kappelmann, Norbert A1 - Stelzer, Beate A1 - Werner, Klaus A1 - Geier, Stephan A1 - Kalkuhl, Christoph A1 - Rauch, Thomas A1 - Schanz, Thomas A1 - Barnstedt, Jürgen A1 - Conti, Lauro A1 - Hanke, Lars T1 - Towards a European Stratospheric Balloon Observatory BT - the ESBO design study T2 - Ground-based and Airborne Telescopes VII N2 - This paper presents the concept of a community-accessible stratospheric balloon-based observatory that is currently under preparation by a consortium of European research institutes and industry. We present the technical motivation, science case, instrumentation, and a two-stage image stabilization approach of the 0.5-m UV/visible platform. In addition, we briefly describe the novel mid-sized stabilized balloon gondola under design to carry telescopes in the 0.5 to 0.6 m range as well as the currently considered flight option for this platform. Secondly, we outline the scientific and technical motivation for a large balloon-based FIR telescope and the ESBO DS approach towards such an infrastructure. KW - astronomy KW - balloon telescopes KW - UV KW - far infrared KW - detectors KW - observatory Y1 - 2018 SN - 978-1-5106-1954-8 U6 - https://doi.org/10.1117/12.2319248 SN - 0277-786X SN - 1996-756X VL - 10700 PB - SPIE-INT Soc Optical Engineering CY - Bellingham ER - TY - GEN A1 - Stich, Michael A1 - Beta, Carsten T1 - Time-Delay Feedback Control of an Oscillatory Medium T2 - Biological Systems: Nonlinear Dynamics Approach N2 - The supercritical Hopf bifurcation is one of the simplest ways in which a stationary state of a nonlinear system can undergo a transition to stable self-sustained oscillations. At the bifurcation point, a small-amplitude limit cycle is born, which already at onset displays a finite frequency. If we consider a reaction-diffusion system that undergoes a supercritical Hopf bifurcation, its dynamics is described by the complex Ginzburg-Landau equation (CGLE). Here, we study such a system in the parameter regime where the CGLE shows spatio-temporal chaos. We review a type of time-delay feedback methods which is suitable to suppress chaos and replace it by other spatio-temporal solutions such as uniform oscillations, plane waves, standing waves, and the stationary state. Y1 - 2019 SN - 978-3-030-16585-7 SN - 978-3-030-16584-0 U6 - https://doi.org/10.1007/978-3-030-16585-7_1 SN - 2199-3041 SN - 2199-305X VL - 20 SP - 1 EP - 17 PB - Springer CY - Cham ER - TY - GEN A1 - Rastogi, Abhishake T1 - Tikhonov regularization with oversmoothing penalty for linear statistical inverse learning problems T2 - AIP Conference Proceedings : third international Conference of mathematical sciences (ICMS 2019) N2 - In this paper, we consider the linear ill-posed inverse problem with noisy data in the statistical learning setting. The Tikhonov regularization scheme in Hilbert scales is considered in the reproducing kernel Hilbert space framework to reconstruct the estimator from the random noisy data. We discuss the rates of convergence for the regularized solution under the prior assumptions and link condition. For regression functions with smoothness given in terms of source conditions the error bound can explicitly be established. KW - Statistical inverse problem KW - Tikhonov regularization KW - Hilbert Scales KW - Reproducing kernel Hilbert space KW - Minimax convergence rates Y1 - 2019 SN - 978-0-7354-1930-8 U6 - https://doi.org/10.1063/1.5136221 SN - 0094-243X VL - 2183 PB - American Institute of Physics CY - Melville ER - TY - GEN A1 - Dolezalova, Barbora A1 - Kubatova, Brankica A1 - Kubat, Jiri A1 - Hamann, Wolf-Rainer T1 - The Quasi-WR Star HD 45166 Revisited T2 - Radiative signatures from the cosmos N2 - We studied the wind of the quasi Wolf-Rayet (qWR) star HD 45166. As a first step we modeled the observed UV spectra of this star by means of the state-of-the-art Potsdam Wolf-Rayet (PoWR) atmosphere code. We inferred the wind parameters and compared them with previous findings. Y1 - 2019 SN - 978-1-58381-925-8 SN - 1050-3390 VL - 519 SP - 197 EP - 200 PB - Astronomical soc pacific CY - San Fransisco ER - TY - GEN A1 - Rychkov, Andrey A1 - Stojharov, Valery A1 - Kuznetsov, Alexey A1 - Rychkov, Dmitry T1 - The influence of recrystallization regimes on electret charge stability in low-density polyethylene films T2 - 2018 IEEE 2nd International Conference on Dielectrics (ICD) N2 - The electret state stability in nonpolar semicrystalline polymers is largely determined by the traps located at crystalline/ amorphous phase interfaces. Thus, the thermal history of such polymers should considerably influence their electret properties. In the present work, we investigate how recrystallization influences charge stability in low-density polyethylene corona electrets. It has been found that electret charge stability in quenched samples is higher than in slowly-crystallized ones. Phenomenologicaly, this can be explained by the increased number of deeper traps in samples with smaller crystallite size. KW - electrets KW - low-density polyethylene KW - crystallinity KW - quenching KW - recrystallization Y1 - 2018 SN - 978-1-5386-6389-9 SN - 978-1-5386-6388-2 SN - 978-1-5386-6390-5 U6 - https://doi.org/10.1109/ICD.2018.8514638 PB - IEEE CY - New York ER - TY - GEN A1 - Parsons, R. D. A1 - Schüssler, F. A1 - Garrigoux, T. A1 - Balzer, A. A1 - Füssling, Matthias A1 - Hoischen, Clemens A1 - Holler, M. A1 - Mitchell, A. A1 - Pühlhofer, G. A1 - Rowell, G. A1 - Wagner, S. A1 - Bissaldi, E. A1 - Tam, P. H. T. T1 - The HESS II GRB Observation Scheme T2 - AIP conference proceedings / American Institute of Physics N2 - Gamma-ray bursts (GRBs) are some of the Universe’s most enigmatic and exotic events. However, at energies above 10 GeV their behaviour remains largely unknown. Although space based telescopes such as the Fermi-LAT have been able to detect GRBs in this energy range, their photon statistics are limited by the small detector size. Such limitations are not present in ground based gamma-ray telescopes such as the H.E.S.S. experiment, which has now entered its second phase with the addition of a large 600 m2 telescope to the centre of the array. Such a large telescope allows H.E.S.S. to access the sub 100-GeV energy range while still maintaining a large effective collection area, helping to potentially probe the short timescale emission of these events. We present a description of the H.E.S.S. GRB observation programme, summarising the performance of the rapid GRB repointing system and the conditions under which GRB observations are initiated. Additionally we will report on the GRB follow-ups made during the 2014-15 observation campaigns. Y1 - 2017 SN - 978-0-7354-1456-3 U6 - https://doi.org/10.1063/1.4968980 SN - 0094-243X SN - 1551-7616 VL - 1792 IS - 1 PB - American Institute of Physics CY - Melville ER - TY - GEN A1 - Shprits, Yuri Y. A1 - Horne, Richard B. A1 - Kellerman, Adam C. A1 - Drozdov, Alexander T1 - The dynamics of Van Allen belts revisited T2 - Nature physics N2 - In an effort to explain the formation of a narrow third radiation belt at ultra-relativistic energies detected during a solar storm in September 20121, Mann et al.2 present simulations from which they conclude it arises from a process of outward radial diffusion alone, without the need for additional loss processes from higher frequency waves. The comparison of observations with the model in Figs 2 and 3 of their Article clearly shows that even with strong radial diffusion rates, the model predicts a third belt near L* = 3 that is twice as wide as observed and approximately an order of magnitude more intense. We therefore disagree with their interpretation that “the agreement between the absolute fluxes from the model and those observed by REPT [the Relativistic Electron Proton Telescope] shown on Figs 2 and 3 is excellent.” Previous studies3 have shown that outward radial diffusion plays a very important role in the dynamics of the outer belt and is capable of explaining rapid reductions in the electron flux. It has also been shown that it can produce remnant belts (Fig. 2 of a long-term simulation study4). However, radial diffusion alone cannot explain the formation of the narrow third belt at multi-MeV during September 2012. An additional loss mechanism is required. Higher radial diffusion rates cannot improve the comparison of model presented by Mann et al. with observations. A further increase in the radial diffusion rates (reported in Fig. 4 of the Supplementary Information of ref. 2) results in the overestimation of the outer belt fluxes by up to three orders of magnitude at energy of 3.4 MeV. Observations at 2 MeV, where belts show only a two-zone structure, were not presented by Mann et al. Moreover, simulations of electrons with energies below 2 MeV with the same diffusion rates and boundary conditions used by the authors would probably produce very strong depletions down to L = 3–3.5, where L is radial distance from the centre of the Earth to the given field line in the equatorial plane. Observations do not show a non-adiabatic loss below L ∼ 4.5 for 2 MeV. Such different dynamics between 2 MeV and above 4 MeV at around L = 3.5 are another indication that particles are scattered by electromagnetic ion cyclotron (EMIC) waves that affect only energies above a certain threshold. Observations of the phase space density (PSD) provide additional evidence for the local loss of electrons. Around L* = 3.5–4 PSD shows significant decrease by an order of magnitude starting in the afternoon of 3 September (Fig. 1a), while PSD above L* = 4 is increasing. The minimum in PSD between L* = 3.5–4 continues to decrease until 4 September. This evolution demonstrates that the loss is not produced by outward diffusion. Radial diffusion cannot produce deepening minima, as it works to smooth gradients. Just as growing peaks in PSD show the presence of localized acceleration5, deepening minima show the presence of localized loss. Figure 1: Time evolution of radiation profiles in electron PSD at relativistic and ultra-relativistic energies. figure 1 a, Similar to Supplementary Fig. 3 of ref. 2, but using TS07D model10 and for μ = 2,500 MeV G−1, K = 0.05 RE G0.5 (where RE is the radius of the Earth). b, Similar to Supplementary Fig. 3 of ref. 2, but using TS07D model and for μ = 700 MeV G−1, corresponding to MeV energies in the heart of the belt. Minimum in PSD in the heart of the multi-MeV electron radiation belt between 3.5 and 4 RE deepening between the afternoon of 3 September and 5 September clearly show that the narrow remnant belt at multi-MeV below 3.5 RE is produced by the local loss. Full size image The minimum in the outer boundary is reached on the evening of 2 September. After that, the outer boundary moves up, while the minimum decreases by approximately an order of magnitude, clearly showing that this main decrease cannot be explained by outward diffusion, and requires additional loss processes. The analysis of profiles of PSD is a standard tool used, for example, in the study about electron acceleration5 and routinely used by the entire Van Allen Probes team. In the Supplementary Information, we show that this analysis is validated by using different magnetic field models. The Supplementary Information also shows that measurements are above background noise. Deepening minima at multi-MeV during the times when the boundary flux increases are clearly seen in Fig. 1a. They show that there must be localized loss, as radial diffusion cannot produce a minimum that becomes lower with time. At lower energies of 1–2 MeV, which corresponds to lower values of the first adiabatic invariant μ (Fig. 1b), the profiles are monotonic between L* = 3–3.5, consistent with the absence of scattering by EMIC waves that affect only electrons above a certain energy threshold6,7,8,9. In summary, the results of the modelling and observations presented by Mann et al. do not lend support to the claim of explaining the dynamics of the ultra-relativistic third Van Allen radiation belt in terms of an outward radial diffusion process alone. While the outward radial diffusion driven by the loss to the magnetopause2 is certainly operating during this storm, there is compelling observational and modelling2,6 evidence that shows that very efficient localized electron loss operates during this storm at multi-MeV energies, consistent with localized loss produced by EMIC waves. Y1 - 2018 U6 - https://doi.org/10.1038/nphys4350 SN - 1745-2473 SN - 1745-2481 VL - 14 IS - 2 SP - 102 EP - 103 PB - Nature Publ. Group CY - London ER - TY - GEN A1 - Loupos, Konstantinos A1 - Damigos, Yannis A1 - Amditis, Angelos A1 - Gerhard, Reimund A1 - Rychkov, Dmitry A1 - Wirges, Werner A1 - Schulze, Manuel A1 - Lenas, Sotiris-Angelos A1 - Chatziandreoglou, Christos A1 - Malliou, Christina A1 - Tsaoussidis, Vassilis A1 - Brady, Ken A1 - Frankenstein, Bernd T1 - Structural health monitoring system for bridges based on skin-like sensor T2 - IOP conference series : Materials science and engineering N2 - Structural health monitoring activities are of primal importance for managing transport infrastructure, however most SHM methodologies are based on point-based sensors that have limitations in terms of their spatial positioning requirements, cost of development and measurement range. This paper describes the progress on the SENSKIN EC project whose objective is to develop a dielectric-elastomer and micro-electronics-based sensor, formed from a large highly extensible capacitance sensing membrane supported by advanced microelectronic circuitry, for monitoring transport infrastructure bridges. Such a sensor could provide spatial measurements of strain in excess of 10%. The actual sensor along with the data acquisition module, the communication module and power electronics are all integrated into a compact unit, the SENSKIN device, which is energy-efficient, requires simple signal processing and it is easy to install over various surface types. In terms of communication, SENSKIN devices interact with each other to form the SENSKIN system; a fully distributed and autonomous wireless sensor network that is able to self-monitor. SENSKIN system utilizes Delay-/Disruption-Tolerant Networking technologies to ensure that the strain measurements will be received by the base station even under extreme conditions where normal communications are disrupted. This paper describes the architecture of the SENSKIN system and the development and testing of the first SENSKIN prototype sensor, the data acquisition system, and the communication system. Y1 - 2017 U6 - https://doi.org/10.1088/1757-899X/236/1/012100 SN - 1757-8981 VL - 236 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Cheilakou, E. A1 - Tsopelas, N. A1 - Anastasopoulos, A. A1 - Kourousis, D. A1 - Rychkov, Dmitry A1 - Gerhard, Reimund A1 - Frankenstein, B. A1 - Amditis, A. A1 - Damigos, Y. A1 - Bouklas, C. T1 - Strain monitoring system for steel and concrete structures T2 - Procedia Structural Integrity N2 - The present work is part of a collaborative H2020 European funded research project called SENSKIN, that aims to improve Structural Health Monitoring (SHM) for transport infrastructure through the development of an innovative monitoring and management system for bridges based on a novel, inexpensive, skin-like sensor. The integrated SENSKIN technology will be implemented in the case of steel and concrete bridges, and tested, field-evaluated and benchmarked on actual bridge environment against a conventional health monitoring solution developed by Mistras Group Hellas. The main objective of the present work is to implement the autonomous, fully functional strain monitoring system based on commercially available off-the-shelf components, that will be used to accomplish direct comparison between the performance of the innovative SENSKIN sensors and the conventional strain sensors commonly used for structural monitoring of bridges. For this purpose, the mini Structural Monitoring System (mini SMS) of Physical Acoustics Corporation, a comprehensive data acquisition unit designed specifically for long-term unattended operation in outdoor environments, was selected. For the completion of the conventional system, appropriate foil-type strain sensors were selected, driven by special conditioners manufactured by Mistras Group. A comprehensive description of the strain monitoring system and its peripheral components is provided in this paper. For the evaluation of the integrated system’s performance and the effect of various parameters on the long-term behavior of sensors, several test steel pieces instrumented with different strain sensors configurations were prepared and tested in both laboratory and field ambient conditions. Furthermore, loading tests were performed aiming to validate the response of the system in monitoring the strains developed in steel beam elements subject to bending regimes. Representative results obtained from the above experimental tests have been included in this paper as well. KW - Structural health monitoring KW - strain sensors KW - strain gauges KW - bridges KW - steel and concrete structures Y1 - 2018 U6 - https://doi.org/10.1016/j.prostr.2018.09.005 SN - 2452-3216 VL - 10 SP - 25 EP - 32 PB - Elsevier CY - Amsterdam ER -