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  • 851.
    Xu, F.
    et al.
    Universit ̈at Konstanz, Germany.
    Holmqvist, Cecilia
    Norwegian University of Science and Technology, Norway.
    Belzig, W.
    Universit ̈at Konstanz, Germany.
    Over-bias light emission due to higher order quantum noise of a tunnel junction2015In: 2015 International Conference on Noise and Fluctuations (ICNF), IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    Understanding tunneling from an atomically sharp tip to a metallic surface requires to account for interactions on a nanoscopic scale. Inelastic tunneling of electrons generates emission of photons, whose energies intuitively should be limited by the applied bias voltage. However, experiments [Phys. Rev. Lett. 102, 057401 (2009)] indicate that more complex processes involving the interaction of electrons with plasmon polaritons lead to photon emission characterized by over-bias energies. We propose a model of this observation in analogy to the dynamical Coulomb blockade, originally developed for treating the electronic environment in mesoscopic circuits. We explain the experimental finding quantitatively by the correlated tunneling of two electrons interacting with an LRC circuit modeling the local plasmon-polariton mode. To explain the over-bias emission, the non-Gaussian statistics of the tunneling dynamics of the electrons is essential.

  • 852.
    Xu, F.
    et al.
    Universität Konstanz, Germany.
    Holmqvist, Cecilia
    Universität Konstanz, Germany.
    Belzig, W.
    Universität Konstanz, Germany.
    Overbias Light Emission due to Higher-Order Quantum Noise in a Tunnel Junction2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 113, article id 066801Article in journal (Refereed)
    Abstract [en]

    Understanding tunneling from an atomically sharp tip to a metallic surface requires us to account for interactions on a nanoscopic scale. Inelastic tunneling of electrons generates emission of photons, whose energies intuitively should be limited by the applied bias voltage. However, experiments [G. Schull et al., Phys. Rev. Lett. 102, 057401 (2009)] indicate that more complex processes involving the interaction of electrons with plasmon polaritons lead to photon emission characterized by overbias energies. We propose a model of this observation in analogy to the dynamical Coulomb blockade, originally developed for treating the electronic environment in mesoscopic circuits. We explain the experimental finding quantitatively by the correlated tunneling of two electrons interacting with a LRC circuit modeling the local plasmon-polariton mode. To explain the overbias emission, the non-Gaussian statistics of the tunneling dynamics of the electrons is essential.

  • 853.
    Xu, F.
    et al.
    Univ Konstanz, Germany.
    Holmqvist, Cecilia
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Rastelli, G.
    Univ Konstanz, Germany.
    Belzig, W.
    Univ Konstanz, Germany.
    Dynamical Coulomb blockade theory of plasmon-mediated light emission from a tunnel junction2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 24, article id 245111Article in journal (Refereed)
    Abstract [en]

    Inelastic tunneling of electrons can generate the emission of photons with energies intuitively limited by the applied bias voltage. However, experiments indicate that more complex processes involving the interaction of electrons with plasmon polaritons lead to photon emission with overbias energies. We recently proposed a model of this observation in Phys. Rev. Lett. 113, 066801 (2014), in analogy to the dynamical Coulomb blockade, originally developed for treating the electromagnetic environment in mesoscopic circuits. This model describes the correlated tunneling of two electrons interacting with a local plasmon-polariton mode, represented by a resonant circuit, and shows that the overbias emission is due to the non-Gaussian fluctuations. Here we extend our model to study the overbias emission at finite temperature. We find that the thermal smearing strongly masks the overbias emission. Hence, the detection of the correlated tunneling processes requires temperatures k(B)T much lower than the bias energy eV and the plasmon energy h omega(0), a condition which is fortunately realized experimentally.

  • 854.
    Yadav, K. K.
    et al.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Godambe, S.
    Bhabha Atomic Research Centre, India.
    Koul, M. K.
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Bhatt, N.
    Bhabha Atomic Research Centre, India.
    Bhattacharyya, S.
    Bhabha Atomic Research Centre, India.
    Chanchalani, K.
    Bhabha Atomic Research Centre, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Sahayanathan, S.
    Bhabha Atomic Research Centre, India.
    Sharma, M.
    Bhabha Atomic Research Centre, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Observations of TeV γ-rays from Mrk 421 during December 2005 to April 2006 with the TACTIC telescope2007In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 27, no 5, p. 447-454Article in journal (Refereed)
    Abstract [en]

    The TACTIC γ-ray telescope has observed Mrk 421 on 66 clear nights from December 07, 2005 to April 30, 2006, totalling ∼202 h of on-source observations. Here, we report the detection of flaring activity from the source at ⩾1 TeV energy and the time-averaged differential γ-ray spectrum in the energy range 1–11 TeV for the data taken between December 27, 2005 and February 07, 2006 when the source was in a relatively higher state as compared to the rest of the observation period. Analysis of this data spell, comprising ∼97 h reveals the presence of a ∼12.0σ γ-ray signal with daily flux of >1 Crab unit on several days. A pure power law spectrum with exponent −3.11 ± 0.11 as well as a power law spectrum with an exponential cutoff (Γ = −2.51 ± 0.26 and E0 = (4.7 ± 2.1) TeV) are found to provide reasonable fits to the inferred differential spectrum within statistical uncertainties. We believe that the TeV light curve presented here, for nearly 5 months of extensive coverage, as well as the spectral information at γ-ray energies of >5 TeV provide a useful input for other groups working in the field of γ-ray astronomy.

  • 855. Yadav, K. K.
    et al.
    Rannot, R. C.
    Chandra, P.
    Tickoo, A. K.
    Thoudam, Satyendra
    Venugopal, K.
    Bhatt, N.
    Bhattacharyya, S.
    Chanchalani, K.
    Dhar, V. K.
    Godambe, S. V.
    Goyal, H. C.
    Kothari, M.
    Kotwal, S.
    Koul, M. K.
    Koul, R.
    Sahaynathan, S.
    Sharma, M.
    Search for TeV γ-rays from H1426+428 during 2004-2007 with the TACTIC telescope2009In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 36, no 8Article in journal (Refereed)
    Abstract [en]

    The BL Lac object H1426+428 (z ≡ 0.129) is an established source of TeV γ-rays and detections of these photons from this object also have important implications for estimating the extragalactic background light in addition to the understanding of the particle acceleration and γ-ray production mechanisms in the AGN jets. We have observed this source for about 244 h in 2004, 2006 and 2007 with the TACTIC γ-ray telescope located at Mt Abu, India. Detailed analysis of these data do not indicate the presence of any statistically significant TeV γ-ray signal from the source direction. Accordingly, we have placed an upper limit of ≤1.18 × 10−12 photons cm−2 s−1 on the integrated γ-ray flux at 3σ significance level.

  • 856.
    Zacharias, M.
    et al.
    Heidelberg Univ, Germany ; North West Univ, South Africa.
    Bottcher, M.
    North West Univ, South Africa.
    Chakraborty, N.
    Max Planck Inst Kernphys, Germany.
    Cologna, G.
    Heidelberg Univ, Germany.
    Jankowsky, F.
    Heidelberg Univ, Germany.
    Lenain, J. -P
    Mohamed, M.
    Heidelberg Univ, Germany.
    Prokoph, Heike
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Wagner, S.
    Heidelberg Univ, Germany.
    Wierzcholska, A.
    Inst Fizyki Jadrowej PAN, Poland.
    Zaborov, D.
    Ecole Polytech, CNRS, France.
    The Complex VHE And Multiwavelength Flaring Activity Of The FSRQ PKS 1510-089 In May 20152017In: HIGH ENERGY GAMMA-RAY ASTRONOMY / [ed] Aharonian, FA Hofmann, W Rieger, FM, American Institute of Physics (AIP), 2017, article id UNSP 050023Conference paper (Refereed)
    Abstract [en]

    The blazar PKS 1510-089 was the first of the flat spectrum radio quasar type, which had been detected simultaneously by a ground based Cherenkov telescope (H.E.S.S.) and the LAT instrument on board the Fermi satellite. Given the strong broad line region emission defining this blazar class, and the resulting high optical depth for VHE (E > 100 GeV) gamma-rays, it was surprising to detect VHE emission from such an object. In May 2015, PKS 1510-089 exhibited high states throughout the electromagnetic spectrum. Target of Opportunity observations with the H.E.S.S. experiment revealed strong and unprecedented variability of this source. Comparison with the lightcurves obtained with the Fermi-LAT in HE gamma-rays (100 MeV < E < 100 GeV) and ATOM in the optical band shows a complex relationship between these energy bands. This points to a complex structure of the emission region, since the one-zone model has difficulties to reproduce the source behavior even when taking into account absorption by ambient soft photon fields. It will be shown that the presented results have important consequences for the explanation of FSRQ spectra and lightcurves, since the emission region cannot be located deep inside the broad line region as is typically assumed. Additionally, acceleration and cooling processes must be strongly time-dependent in order to account for the observed variability patterns.

  • 857. Zahid, Ferdows
    et al.
    Ghosh, Avik
    Paulsson, Magnus
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Polizzi, Eric
    Datta, Supriyo
    Charging-induced asymmetry in molecular conductors2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 24, article id 245317Article in journal (Refereed)
  • 858. Zahid, Ferdows
    et al.
    Paulsson, Magnus
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Datta, Supriyo
    Electrical Conduction through Molecules2003In: Advanced Semiconductors and Organic Nano-Techniques / [ed] H. Morkoc, Academic Press , 2003Chapter in book (Other academic)
  • 859. Zioutas, K.
    et al.
    Adiels, L.
    Backenstoss, G.
    Bergstrom, I.
    Carius, Staffan
    Charalambous, S.
    Findeisen, C.
    Fransson, K.
    Kerek, A.
    Pavlopoulos, P.
    Repond, J.
    Tauscher, L.
    Troster, D.
    Papadopoulou, Th.
    Tracas, N. D.
    Baryonium physics1983In: Proceedings of the 1st Hellenic School on Elementary Particle Physics / [ed] Papadopoulou, Th., Tracas, N.D., Institution of Electrical Engineers (IEE), 1983, p. 437-466Conference paper (Refereed)
    Abstract [en]

    Various theoretical ideas on nuclear physics, quark models, and the dual topological unitarization lead to the expectation of massive mesons, called baryonium, coupled strongly to the ppmacr channel but weakly to mesons, thus resulting in a virtually high stability, particularly below the ppmacr threshold. Such states are relevant to nuclear physics owing to the fact that the badly explored short-range forces in the NN interactions are just the most relevant ones in the NNmacr systems. From the known NN potential, one is led to expect short-range attraction in NNmacr systems, and this should result in quasinuclear bound states in the vicinity of threshold.

  • 860.
    Zucca, P.
    et al.
    ASTRON, Netherlands.
    Morosan, D. E.
    Trinity Coll Dublin, Ireland.
    Rouillard, A. P.
    Inst Rech Astrophys & Planetol, France.
    Fallows, R.
    ASTRON, Netherlands.
    Gallagher, P. T.
    Trinity Coll Dublin, Ireland.
    Magdalenic, J.
    Royal Observ Belgium, Belgium.
    Klein, K-L
    Observ Paris, France.
    Mann, G.
    Leibniz Inst Astrophys Potsdam AIP, Germany.
    Vocks, C.
    Leibniz Inst Astrophys Potsdam AIP, Germany.
    Carley, E. P.
    Trinity Coll Dublin, Ireland.
    Bisi, M. M.
    RAL Space, UK.
    Kontar, E. P.
    Univ Glasgow, UK.
    Rothkaehl, H.
    Polish Acad Sci, Poland.
    Dabrowski, B.
    Univ Warmia & Mazury, Poland.
    Krankowski, A.
    Univ Warmia & Mazury, Poland.
    Anderson, J.
    Helmholtz Zentrum Potsdam, Germany.
    Asgekar, A.
    ASTRON, Netherlands;Shell Technol Ctr, India.
    Bell, M. E.
    Univ Technol Sydney, Australia.
    Bentum, M. J.
    ASTRON, Netherlands;Eindhoven Univ Technol, Netherlands.
    Best, P.
    Univ Edinburgh, UK.
    Blaauw, R.
    ASTRON, Netherlands.
    Breitling, F.
    Leibniz Inst Astrophys Potsdam AIP, Germany.
    Broderick, J. W.
    ASTRON, Netherlands.
    Brouw, W. N.
    ASTRON, Netherlands;Kapteyn Astron Inst, Netherlands.
    Brueggen, M.
    Univ Hamburg, Germany.
    Butcher, H. R.
    Australian Natl Univ, Australia.
    Ciardi, B.
    Max Planck Inst Astrophys, Germany.
    de Geus, E.
    ASTRON, Netherlands;SmarterVision BV, Netherlands.
    Deller, A.
    ASTRON, Netherlands;Swinburne Univ Technol, Australia.
    Duscha, S.
    ASTRON, Netherlands.
    Eisloeffel, J.
    Thuringer Landessternwarte,Germany.
    Garrett, M. A.
    Univ Manchester, UK;Leiden Univ, Netherlands.
    Griessmeier, J. M.
    Univ Orleans, France;CNRS, France.
    Gunst, A. W.
    ASTRON, Netherlands.
    Heald, G.
    ASTRON, Netherlands;CSIRO Astron & Space Sci, Australia.
    Hoeft, M.
    Eindhoven Univ Technol, Netherlands.
    Horandel, J.
    Radboud Univ Nijmegen, Netherlands.
    Iacobelli, M.
    ASTRON, Netherlands.
    Juette, E.
    Ruhr Univ Bochum, Germany.
    Karastergiou, A.
    Univ Oxford, UK.
    van Leeuwen, J.
    Trinity Coll Dublin, Ireland;Univ Amsterdam, Netherlands.
    McKay-Bukowski, D.
    Univ Tromso, Norway;STFC Rutherford Appleton Lab, UK.
    Mulder, H.
    ASTRON, Netherlands.
    Munk, H.
    ASTRON, Netherlands;Radboud Univ Nijmegen, Netherlands.
    Nelles, A.
    Univ Calif Irvine, USA.
    Orru, E.
    ASTRON, Netherlands.
    Paas, H.
    Univ Groningen, Netherlands.
    Pandey, V. N.
    ASTRON, Netherlands;Observ Paris, France.
    Pekal, R.
    Poznan Supercomp & Networking Ctr PCSS, Poland.
    Pizzo, R.
    ASTRON, Netherlands.
    Polatidis, A. G.
    ASTRON, Netherlands.
    Reich, W.
    Max Planck Inst Radioastron, Germany.
    Rowlinson, A.
    ASTRON, Netherlands.
    Schwarz, D. J.
    Univ Bielefeld, Germany.
    Shulevski, A.
    Kapteyn Astron Inst, Netherlands.
    Sluman, J.
    ASTRON, Netherlands.
    Smirnov, O.
    Rhodes Univ, South Africa;SKA South Africa, South Africa.
    Sobey, C.
    Curtin Univ, Australia.
    Soida, M.
    Jagiellonian Univ, Poland.
    Thoudam, Satyendra
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Toribio, M. C.
    ASTRON, Netherlands;Kapteyn Astron Inst, Netherlands.
    Vermeulen, R.
    ASTRON, Netherlands.
    van Weeren, R. J.
    Kapteyn Astron Inst, Netherlands.
    Wucknitz, O.
    Max Planck Inst Radioastron, Germany.
    Zarka, P.
    Observ Paris, France.
    Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 615, article id A89Article in journal (Refereed)
    Abstract [en]

    Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20-90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon. Methods. The type II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory (STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary. Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with theta(Bn)similar to 70 degrees. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3-1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4-1.6.

15161718 851 - 860 of 860
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