1,120 research outputs found

    Tuning a Resonance in the Fock Space: Optimization of Phonon Emission in a Resonant Tunneling Device

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    Phonon-assisted tunneling in a double barrier resonant tunneling device can be seen as a resonance in the electron-phonon Fock space which is tuned by the applied voltage. We show that the geometrical parameters can induce a symmetry condition in this space that can strongly enhance the emission of longitudinal optical phonons. For devices with thin emitter barriers this is achieved by a wider collector's barrier.Comment: 4 pages, 3 figures. Figure 1 changed, typos correcte

    Retrospective-Cost Adaptive Control of Uncertain Hammerstein-Wiener Systems with Memoryless and Hysteretic Nonlinearities

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97108/1/AIAA2012-4449.pd

    Comparison of mid-latitude single- And mixed-phase cloud optical depth from co-located infrared spectrometer and backscatter lidar measurements

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    The long-wave downwelling spectral radiance measurements performed by means of the Far-Infrared Radiation Mobile Observation System (FIRMOS) spectrometer at the summit of the Zugspitze (German Alps) in the winter 2018/19 allowed the retrieval of the optical and micro-physical properties of ice and mixed clouds, showing a good agreement of the statistical relationship between the ice water path and the ice optical depth with the ones from previous works. In this paper the optical depths retrieved from FIRMOS are initially compared with selected cases calculated from backscattering light detection and ranging (lidar) data by using a transmittance method. Then, in order to compare the whole FIRMOS dataset, the power-law relationship between backscattering and extinction is used to apply the Klett method and automatize the routine. Minimizing the root mean square differences, the exponent k of the power-law relationship is assessed to be 0.85 with a variability in the range of 0.60–1.10 for ice clouds and 0.50 with a variability within 0.30–0.70 for mixed clouds

    The far-infrared/radio correlation for a sample of strongly lensed dusty star-forming galaxies detected by Herschel

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    We investigate the radio/far-infrared (FIR) correlation for a sample of 28 bright high-redshift (1 z 4) star-forming galaxies selected in the FIR from the Herschel -ATLAS fields as candidates to be strongly gravitationally lensed. The radio information comes either from high sensitivity dedicated Australia Telescope Compact Array observations at 2.1 GHz or from cross-matches with the FIRST surv e y at 1.4 GHz. By taking advantage of source brightness possibly enhanced by lensing magnification, we identify a weak evolution with redshift out to z 4 of the FIR-to-radio luminosity ratio q FIR . We also find that the q FIR parameter as a function of the radio power L 1 . 4 GHz displays a clear decreasing trend, similarly to what is observed for optically/radio- selected lensed quasars found in literature, yet co v ering a complementary region in the q FIR –L 1 . 4 GHz diagram. We interpret such a behaviour in the framework of an in situ galaxy formation scenario, as a result of the transition from an early dust-obscured star-forming phase (mainly pinpointed by our FIR selection) to a late radio-loud quasar phase (preferentially sampled by the optical/radio selection)

    Time evolution of stimulated Raman scattering and two-plasmon decay at laser intensities relevant for shock ignition in a hot plasma

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    Laser–plasma interaction (LPI) at intensities 1015–1016 W cm2 is dominated by parametric instabilities which can be responsible for a significant amount of non-collisional absorption and generate large fluxes of high-energy nonthermal electrons. Such a regime is of paramount importance for inertial confinement fusion (ICF) and in particular for the shock ignition scheme. In this paper we report on an experiment carried out at the Prague Asterix Laser System (PALS) facility to investigate the extent and time history of stimulated Raman scattering (SRS) and two-plasmon decay (TPD) instabilities, driven by the interaction of an infrared laser pulse at an intensity 1:2 1016 W cm2 with a 100 mm scalelength plasma produced from irradiation of a flat plastic target. The laser pulse duration (300 ps) and the high value of plasma temperature (4 keV) expected from hydrodynamic simulations make these results interesting for a deeper understanding of LPI in shock ignition conditions. Experimental results show that absolute TPD/SRS, driven at a quarter of the critical density, and convective SRS, driven at lower plasma densities, are well separated in time, with absolute instabilities driven at early times of interaction and convective backward SRS emerging at the laser peak and persisting all over the tail of the pulse. Side-scattering SRS, driven at low plasma densities, is also clearly observed. Experimental results are compared to fully kinetic large-scale, two-dimensional simulations. Particle-in-cell results, beyond reproducing the framework delineated by the experimental measurements, reveal the importance of filamentation instability in ruling the onset of SRS and stimulated Brillouin scattering instabilities and confirm the crucial role of collisionless absorption in the LPI energy balance

    Quantum transport and momentum conserving dephasing

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    We study numerically the influence of momentum-conserving dephasing on the transport in a disordered chain of scatterers. Loss of phase memory is caused by coupling the transport channels to dephasing reservoirs. In contrast to previously used models, the dephasing reservoirs are linked to the transport channels between the scatterers, and momentum conserving dephasing can be investigated. Our setup provides a model for nanosystems exhibiting conductance quantization at higher temperatures in spite of the presence of phononic interaction. We are able to confirm numerically some theoretical predictions.Comment: 7 pages, 4 figure

    Which phase is measured in the mesoscopic Aharonov-Bohm interferometer?

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    Mesoscopic solid state Aharonov-Bohm interferometers have been used to measure the "intrinsic" phase, αQD\alpha_{QD}, of the resonant quantum transmission amplitude through a quantum dot (QD). For a two-terminal "closed" interferometer, which conserves the electron current, Onsager's relations require that the measured phase shift ÎČ\beta only "jumps" between 0 and π\pi. Additional terminals open the interferometer but then ÎČ\beta depends on the details of the opening. Using a theoretical model, we present quantitative criteria (which can be tested experimentally) for ÎČ\beta to be equal to the desired αQD\alpha_{QD}: the "lossy" channels near the QD should have both a small transmission and a small reflection
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