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Sökning: WFRF:(Angelopoulos E.)

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  • Föregående 1[2]3Nästa
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11.
  • Tao, J. B., et al. (författare)
  • Kinetic instabilities in the lunar wake : ARTEMIS observations
  • 2012
  • Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. A03106
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission is a new two-probe lunar mission derived from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. On 13 February 2010, one of the two probes, ARTEMIS P1 (formerly THEMIS-B), made the first lunar wake flyby of the mission. We present detailed analysis of the electrostatic waves observed on the outbound side of the flyby that were associated with electron beams. Halekas et al. (2011) derived a net potential across the lunar wake from observations and suggested that the net potential generated the observed electron beams and the electron beams in turn excited the observed electrostatic waves due to kinetic instabilities. The wavelengths and velocities of the electrostatic waves are estimated, using high-resolution electric field instrument data with cross-spectrum analysis and cross-correlation analysis. In general, the estimated wavelengths vary from a few hundred meters to a couple of thousand meters. The estimated phase velocities are on the order of 1000 km s(-1). In addition, we perform 1-D Vlasov simulations to help identify the mode of the observed electrostatic waves. We conclude that the observed electrostatic waves are likely on the electron beam mode branch.</p>
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12.
  • Öieroset, M., et al. (författare)
  • Reconnection With Magnetic Flux Pileup at the Interface of Converging Jets at the Magnetopause
  • 2019
  • Ingår i: Geophysical Research Letters. - AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 46:4, s. 1937-1946
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We report Magnetospheric Multiscale observations of reconnection in a thin current sheet at the interface of interlinked flux tubes carried by converging reconnection jets at Earth's magnetopause. The ion skin depth-scale width of the interface current sheet and the non-frozen-in ions indicate that Magnetospheric Multiscale crossed the reconnection layer near the X-line, through the ion diffusion region. Significant pileup of the reconnecting component of the magnetic field in this and three other events on approach to the interface current sheet was accompanied by an increase in magnetic shear and decrease in , leading to conditions favorable for reconnection at the interface current sheet. The pileup also led to enhanced available magnetic energy per particle and strong electron heating. The observations shed light on the evolution and energy release in 3-D systems with multiple reconnection sites. Plain Language Summary The Earth and the solar wind magnetic fields interconnect through a process called magnetic reconnection. The newly reconnected magnetic field lines are strongly bent and accelerate particles, similar to a rubber band in a slingshot. In this paper we have used observations from NASA's Magnetospheric MultiScale spacecraft to investigate what happens when two of these slingshot-like magnetic field lines move toward each other and get tangled up. We found that the two bent magnetic field lines tend to orient themselves perpendicular to each other as they become interlinked and stretched, similar to what rubber bands would do. This reorientation allows the interlinked magnetic fields to reconnect again, releasing part of the built-up magnetic energy as strong electron heating. The results are important because they show how interlinked magnetic fields, which occur in many solar and astrophysics contexts, reconnect and produce enhanced electron heating, something that was not understood before.</p>
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13.
  • Angelopoulos, Angelos, et al. (författare)
  • Dispersion relation analysis of the neutral kaon regeneration amplitude in carbon
  • 1999
  • Ingår i: European Physical Journal C. - Springer Berlin/Heidelberg. - 1434-6044 .- 1434-6052. ; 10:1, s. 19-25
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We apply a forward dispersion relation to the regeneration amplitude for kaon scattering on 12" style="position: relative;" tabindex="0" id="MathJax-Element-1-Frame" class="MathJax"&gt;12C using all available data. The CPLEAR data at low energies allow the determination of the net contribution from the subthreshold region which turns out to be much smaller than earlier evaluations, solving a long standing puzzle.</p>
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14.
  • Angelopoulos, A., et al. (författare)
  • K 0–KÌ„0 mass and decay-width differences : CPLEAR evaluation
  • 1999
  • Ingår i: Physics Letters B. - Elsevier. - 0370-2693 .- 1873-2445. ; 471:2, s. 332-338
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The CPT-violation parameters Re(<em>δ</em>) and Im(<em>δ</em>) determined recently by CPLEAR are used to evaluate the K<sup>0</sup>–<img src="http://ars.els-cdn.com/content/image/1-s2.0-S0370269399013337-si10.gif" data-loaded="true" data-inlimgeid="1-s2.0-S0370269399013337-si10.gif" /> mass and decay-width differences, as given by the difference between the diagonal elements of the neutral-kaon mixing matrix (M−i<em>Γ</em>/2). The results – <img src="http://ars.els-cdn.com/content/image/1-s2.0-S0370269399013337-si11.gif" data-loaded="true" data-inlimgeid="1-s2.0-S0370269399013337-si11.gif" /> GeV and <img src="http://ars.els-cdn.com/content/image/1-s2.0-S0370269399013337-si12.gif" data-loaded="true" data-inlimgeid="1-s2.0-S0370269399013337-si12.gif" /> GeV – are consistent with CPT invariance. The CPT invariance is also shown to hold within a few times 10<sup>−3</sup>–10<sup>−4</sup> for many of the amplitudes describing neutral-kaon decays to different final states.</p>
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15.
  • Angelopoulos, Angelos, et al. (författare)
  • K0⇋ KÌ„0 transitions monitored by strong interactions : a new determination of the K L–K S mass difference
  • 2001
  • Ingår i: Physics Letters B. - Elsevier. - 0370-2693 .- 1873-2445. ; 503:1, s. 49-57
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The CPLEAR set-up (modified) has been used to determine the K<sub>L</sub>–K<sub>S</sub> mass difference by a method where neutral-kaon strangeness oscillations are monitored through kaon strong interactions, rather than semileptonic decays, thus requiring no assumptions on CPT invariance for the decay amplitudes. The result, <em>Δm</em>=(0.5343±0.0063<sub>stat</sub>±0.0025<sub>syst</sub>)×10<sup>10</sup>ℏ/s, provides a valuable input for CPT tests.</p>
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16.
  • Angelopoulos, Angelos, et al. (författare)
  • Physics at CPLEAR
  • 2003
  • Ingår i: Physics Reports. - Elsevier. ; 374:3, s. 165-270
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study of CP, T and CPT symmetries in the neutral-kaon system. A variety of measurements allowed us to determine with high precision the parameters which describe the time evolution of the neutral kaons and their antiparticles, including decay amplitudes, and the related symmetry properties. Limits concerning quantum-mechanical predictions (EPR, coherence of the wave function) or the equivalence principle of general relativity have been obtained. An account of the main features of the experiment and its performances is given here, together with the results achieved.</p>
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17.
  • Angelopoulos, Konstantinos, et al. (författare)
  • Model predictive control for software systems with CobRA
  • 2016
  • Ingår i: 11th International Symposium on Software Engineering for Adaptive and Self-Managing Systems, SEAMS 2016,Austin, United States,2016-05-16 - 2016-05-17. - Association for Computing Machinery (ACM).
  • Konferensbidrag (refereegranskat)abstract
    • Self-adaptive software systems monitor their operation and adapt when their requirements fail due to unexpected phenomena in their environment. This paper examines the case where the environment changes dynamically over time and the chosen adaptation has to take into account such changes. In control theory, this type of adaptation is known as Model Predictive Control and comes with a well-developed theory and myriads of successful applications. The paper focuses on modelling the dynamic relationship between requirements and possible adaptations. It then proposes a controller that exploits this relationship to optimize the satisfaction of requirements relative to a cost-function. This is accomplished through a model-based framework for designing self-adaptive software systems that can guarantee a certain level of requirements satisfaction over time, by dynamically composing adaptation strategies when necessary. The proposed framework is illustrated and evaluated through a simulation of the Meeting-Scheduling System exemplar.
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18.
  • Angelopoulos, Konstantinos, et al. (författare)
  • Model Predictive Control for Software Systems with CobRA
  • 2016
  • Ingår i: SEAMS '16 Proceedings of the 11th International Symposium on Software Engineering for Adaptive and Self-Managing Systems. - Austin, Texas, United States : ACM. - 978-1-4503-4187-5 ; s. 35-46
  • Konferensbidrag (refereegranskat)abstract
    • <p>Self-adaptive software systems monitor their operation and adapt when their requirements fail due to unexpected phenomena in their environment. This paper examines the case where the environment changes dynamically over time and the chosen adaptation has to take into account such changes. In control theory, this type of adaptation is known as Model Predictive Control and comes with a well-developed theory and myriads of successful applications. The paper focuses on modelling the dynamic relationship between requirements and possible adaptations. It then proposes a controller that exploits this relationship to optimize the satisfaction of requirements relative to a cost-function. This is accomplished through a model-based framework for designing self-adaptive software systems that can guarantee a certain level of requirements satisfaction over time, by dynamically composing adaptation strategies when necessary. The proposed framework is illustrated and evaluated through a simulation of the Meeting-Scheduling System exemplar.</p>
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19.
  • Angelopoulos, V., et al. (författare)
  • First Results from the THEMIS Mission
  • 2008
  • Ingår i: Space Science Reviews. - 0038-6308 .- 1572-9672. ; 141:1-4, s. 453-476
  • Forskningsöversikt (refereegranskat)abstract
    • <p>THEMIS was launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms. During the first seven months of the mission the five satellites coasted near their injection orbit to avoid differential precession in anticipation of orbit placement, which started in September 2007 and led to a commencement of the baseline mission in December 2007. During the coast phase the probes were put into a string-of-pearls configuration at 100 s of km to 2 R-E along-track separations, which provided a unique view of the magnetosphere and enabled an unprecedented dataset in anticipation of the first tail season. In this paper we describe the first THEMIS substorm observations, captured during instrument commissioning on March 23, 2007. THEMIS measured the rapid expansion of the plasma sheet at a speed that is commensurate with the simultaneous expansion of the auroras on the ground. These are the first unequivocal observations of the rapid westward expansion process in space and on the ground. Aided by the remote sensing technique at energetic particle boundaries and combined with ancillary measurements and MHD simulations, they allow determination and mapping of space currents. These measurements show the power of the THEMIS instrumentation in the tail and the radiation belts. We also present THEMIS Flux Transfer Events (FTE) observations at the magnetopause, which demonstrate the importance of multi-point observations there and the quality of the THEMIS instrumentation in that region of space.</p>
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20.
  • Artemyev, A. V., et al. (författare)
  • Field-Aligned Currents Originating From the Magnetic Reconnection Region : Conjugate MMS-ARTEMIS Observations
  • 2018
  • Ingår i: Geophysical Research Letters. - American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 45:12, s. 5836-5844
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Near-Earth magnetic reconnection reconfigures the magnetotail and produces strong plasma flows that transport plasma sheet particles and electromagnetic energy to the inner magnetosphere. An essential element of such a reconfiguration is strong, transient field-aligned currents. These currents, believed to be generated within the plasma sheet and closed at the ionosphere, are responsible for magnetosphere-ionosphere coupling during substorms. We use conjugate measurements from Magnetospheric Multiscale (MMS) at the plasma sheet boundary (around x approximate to- 10R(E)) and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) at the equator (around x approximate to- 60R(E)) to explore the potential generation region of these currents. We find a clear correlation between the field-aligned current intensity measured by MMS and the tailward plasma sheet flows measured by ARTEMIS. To better understand the origin of this correlation, we compare spacecraft observations with results from 3-D particle-in-cell simulations of magnetotail reconnection. The comparison reveals that field-aligned currents and plasma flows start, wax, and wane due to the development of a reconnection region between MMS (near-Earth) and ARTEMIS (at lunar distance). A weak correlation between the field-aligned current intensity at MMS and earthward flow magnitudes at ARTEMIS suggests that distant magnetotail reconnection does not significantly contribute to the generation of the observed near-Earth currents. Our findings support the idea that the dominant role of the near-Earth magnetotail reconnection in the field-aligned current generation is likely responsible for their transient nature, whereas more steady distant tail reconnection would support long-term field-aligned current system. Plain Language Summary Field-aligned currents connect the Earth magnetotail and ionosphere, proving energy and information transport from the region where main energy release process, magnetic reconnection, occurs to the region where the collisional energy dissipation takes place. Therefore, investigation and modeling of the field-aligned current generation is important problem of the magnetosphere plasma physics. However, field-aligned current investigation requires simultaneous observations of reconnection signatures in the magnetotail and at high latitudes. Simultaneous and conjugate operation of two multispacecraft missions, Magnetospheric Multiscale and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun, for the first time provide an opportunity for such investigation. Combining spacecraft observations with results from 3-D particle-in-cell simulations of magnetotail reconnection, we demonstrate that field-aligned currents and plasma flows start, wax, and wane due to the development of a reconnection region between near-Earth (Magnetospheric Multiscale location) and lunar distant tail (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun location). Our findings support the idea that the dominant role of the near-Earth magnetotail reconnection in the field-aligned current generation is likely responsible for their transient nature, whereas more steady distant tail reconnection would support long-term field-aligned current system.</p>
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