372 research outputs found
Unconventional rf photoresponse from a superconducting spiral resonator
Superconducting thin film resonators employing strip geometries show great
promise in rf/microwave applications due to their low loss and compact nature.
However, their functionality is limited by nonlinear effects at elevated
rf/microwave powers. Here, we show that by using a planar spiral geometry
carrying parallel currents in adjacent turns, this limitation can be minimized.
We investigate the rf current distributions in spiral resonators implemented
with Nb thin films via laser scanning microscopy. The rf current density
profile along the width of the individual turns of the resonators reveals an
unconventional trend: maximum current in the middle of the structure and
decaying toward its edges. This unusual behavior is associated with the
circular nature of the geometry and the cancellation of magnetic field between
the turns, which is favorable for handling high powers since it allows the
linear characteristics to persist at high rf current densities.Comment: 8 pages, 7 figure
Microscopic examination of hot spots giving rise to nonlinearity in superconducting resonators
We investigate the microscopic origins of nonlinear rf response in
superconducting electromagnetic resonators. Strong nonlinearity appearing in
the transmission spectra at high input powers manifests itself through the
emergence of jumplike features near the resonant frequency that evolve toward
lower quality factor with higher insertion loss as the rf input power is
increased. We directly relate these characteristics to the dynamics of
localized normal regions (hot spots) caused by microscopic features in the
superconducting material making up the resonator. A clear observation of
hot-spot formation inside a Nb thin film self-resonant structure is presented
by employing the microwave laser scanning microscope, and a direct link between
microscopic and macroscopic manifestations of nonlinearity is established.Comment: 5 pages, 4 figure
Experimental and computational study on dynamic analysis of cracked simply supported structures under moving mass
In this study, the influences of crack parameters like crack location from the left end, crack height, number of cracks and the magnitude of mass and the velocity of the transit load on the vertical displacements of the cracked simply supported beams subjected to transit mass are investigated. The transverse open cracks with numerous damage scenerios are considered for the mathematical modelling of the system. The governing equations of motion for the system have been obtained and the equations have been solved by the help of Duhamel integral technique. The theoretical formulation has been exemplified with numerical studies. By utilizing ANSYS Workbench 2020, transient structural analysis has been carried out. The mode shapes and the frequency ratios of damaged simply supported beam have also been determined. To validate the numerical and FEM models, the experiments with damaged beams have been carried out in the laboratory. It has been proven that the results of the theoretical and FEM models are well convergent with the experimental data. The results gathered from the numerical analysis, FEA as well as experimental study have been presented with comparative graphs and tables. The outcomes of the examinations have been interpreted in the conclusions part. It has been observed that subject parameters are of considerable significance on the time dependent response of the cracked beams
Classical Analogue of Electromagnetically Induced Transparency with a Metal-Superconductor Hybrid Metamaterial
Metamaterials are engineered materials composed of small electrical circuits
producing novel interactions with electromagnetic waves. Recently, a new class
of metamaterials has been created to mimic the behavior of media displaying
electromagnetically induced transparency (EIT). Here we introduce a planar EIT
metamaterial that creates a very large loss contrast between the dark and
radiative resonators by employing a superconducting Nb film in the dark element
and a normal-metal Au film in the radiative element. Below the critical
temperature of Nb, the resistance contrast opens up a transparency window along
with a large enhancement in group delay, enabling a significant slowdown of
waves. We further demonstrate precise control of the EIT response through
changes in the superfluid density. Such tunable metamaterials may be useful for
telecommunication because of their large delay-bandwidth products.Comment: 4 pages, 4 figure
Observation of Biexcitons in Nanocrystal Solids in the Presence of Photocharging
Cataloged from PDF version of article.T In nanocrystal quantum dots (NQDs), generating multiexcitons
offers an enabling tool for enhancing NQD-based devices. However, the photocharging
effect makes understanding multiexciton kinetics in NQD solids fundamentally
challenging, which is critically important for solid-state devices. To date,
this lack of understanding and the spectral temporal aspects of the multiexciton
recombination still remain unresolved in solid NQD ensembles, which is mainly due
to the confusion with recombination of carriers in charged NQDs. In this work, we
reveal the spectral temporal behavior of biexcitons (BXs) in the presence of
photocharging using near-unity quantum yield CdSe/CdS NQDs exhibiting substantial suppression of Auger recombination. Here, recombinations of
biexcitons and single excitons (Xs) are successfully resolved in the presence of trions in the ensemble measurements of time-correlated single-photon
counting at variable excitation intensities and varying emission wavelengths. The spectral behaviors of BXs and Xs are obtained for three NQD samples with
different core sizes, revealing the strength tunability of the X X interaction energy in these NQDs. The extraction of spectrally resolved X, BX, and trion
kinetics, which are otherwise spectrally unresolved, is enabled by our approach introducing integrated time-resolved fluorescence. The results are further
experimentally verified by cross-checking excitation intensity and exposure time dependencies as well as the temporal evolutions of the
photoluminescence spectra, all of which prove to be consistent. The BX and X energies are also confirmed by theoretical calculations. These findings
fill an important gap in understanding the spectral dynamics of multiexcitons in such NQD solids under the influence of photocharging effects, paving the
way to engineering of multiexciton kinetics in nanocrystal optoelectronics, including NQD-based lasing, photovoltaics, and photodetection
Comparison between the STENTYS self-apposing bare metal and paclitaxel-eluting coronary stents for the treatment of saphenous vein grafts (ADEPT trial)
Comparison between the STENTYS self-apposing bare metal and paclitaxel-eluting coronary stents for the treatment of saphenous vein grafts (ADEPT trial)
Aims To describe the safety and performance of STENTYS self-expandable bare metal stents (BMS) versus paclitaxel-eluting stents (PES) in saphenous vein grafts (SVGs). Methods and Results A randomised controlled trial was performed in four hospitals in three European countries between December 2011 and December 2013. Patients with de novo lesions (>50% stenosis) in an SVG with a diameter between 2.5–6 mm were included. Primary endpoint was late lumen loss at 6 months. Secondary endpoints included procedural success and the occurrence of major adverse cardiac events (MACE) at 12 months. A total of 57 patients were randomised to STENTYS self-apposing BMS (n = 27) or PES (n = 30). Procedural success was obtained in 89.5%. No significant differences in late lumen loss were found between BMS and PES at 6 months (0.53 mm vs 0.47; p = 0.86). MACE rates at 12 months were comparable in both groups (BMS 22.2% vs. PES 26.7%; p = 0.70). Conclusions Treatment of SVGs with STENTYS self-expandable stents is safe and effective. No significant differences were found in late lumen loss and MACE between BMS and PES
Crystal Reorientation and Amorphization Induced by Stressing Efficient and Stable P-I-N Vacuum-Processed MAPbI3 Perovskite Solar Cells
Herein, the long‐term stability of vacuum‐deposited methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs) with power conversion efficiencies (PCEs) of around 19% is evaluated. A low‐temperature atomic layer deposition (ALD) Al2O3 coating is developed and used to protect the MAPbI3 layers and the solar cells from environmental agents. The ALD encapsulation enables the MAPbI3 to be exposed to temperatures as high as 150 °C for several hours without change in color. It also improves the thermal stability of the solar cells, which maintain 80% of the initial PCEs after aging for ≈40 and 37 days at 65 and 85 °C, respectively. However, room‐temperature operation of the solar cells under 1 sun illumination leads to a loss of 20% of their initial PCE in 230 h. Due to the very thin ALD Al2O3 encapsulation, X‐ray diffraction can be performed on the MAPbI3 films and completed solar cells before and after the different stress conditions. Surprisingly, it is found that the main effect of light soaking and thermal stress is a crystal reorientation with respect to the substrate from (002) to (202) of the perovskite layer, and that this reorientation is accelerated under illumination
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