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- Lu, W, et al.
(författare)
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Reliability assessment and degradation analysis of 1.3 µm GaInNAs lasers
- 2009
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 106:9, s. 093110-
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Tidskriftsartikel (refereegranskat)abstract
- The degradation of 1.3 mu m GaInNAs lasers was investigated using accelerated aging tests. This was followed by comprehensive characterization, including standard light-current-voltage (L-I-V) characterization, capacitance measurements, photoluminescence microscopy (PLM), on-axis amplified spontaneous emission (ASE) spectra measurements, and photocurrent (PC) and electroluminescence (EL) spectroscopies. The slope efficiency of the device dropped by 50% with a 300% increase in the threshold current after the accelerated aging test. The ideality factors of the aged devices are higher than those of the unaged devices. PLM images showed no evidence of catastrophic optical mirror damage. The measured capacitances of the aged devices are all similar to those of the unaged devices, indicating that there was no significant dopant diffusion in the junction region. Fourier transforms of the ASE spectra showed that no intracavity defects were present in the aged lasers, suggesting that intracavity defects are not responsible for the rapid degradation of the aged devices. Although the PC measurements showed defects at 0.88-0.95 eV and at similar to 0.76 eV, these defect signatures did not increase with aging. On the other hand, EL measurements revealed that radiative deep level defects were generated during the aging tests. which may be related to the degradation of the devices. Based on the above measurement results, we identify, the generation Of radiative deep level defects as the main causes of degradation of these devices.
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- Mikkola, T. M., et al.
(författare)
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Influence of long-term postmenopausal hormone-replacement therapy on estimated structural bone strength: A study in discordant monozygotic twins
- 2011
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Ingår i: Journal of Bone and Mineral Research. - : Wiley. - 0884-0431. ; 26:3, s. 546-52
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Tidskriftsartikel (refereegranskat)abstract
- Although postmenopausal hormone-replacement therapy (HRT) is known to prevent fractures, knowledge on the influence of long-term HRT on bone strength and its determinants other than areal bone mineral density is scarce. This study used a genetically controlled design with 24 monozygotic female twin pairs aged 54 to 72 years in which one cotwin was using HRT (mean duration 8 years) and the other had never used HRT. Estimated bone strength, cross-sectional area, volumetric bone mineral density, bone mineral mass, and cross-sectional density and mass distributions were assessed in the tibial shaft, distal tibia, and distal radius with peripheral computed tomography (pQCT). In the tibial shaft, HRT users had 9% [95% confidence interval (CI) 3%-15%] higher estimated bending strength than their nonusing cotwins. Larger cortical area and higher cortical bone mineral density accounted for this difference. The cortex was larger in the HRT users in the endocortical region. In the distal tibia, estimated compressive strength was 24% (95% CI 9%-40%) higher and in the distal radius 26% (95% CI 11%-41%) higher in the HRT users than in their nonusing cotwins owing to higher volumetric bone mineral density. No difference between users and nonusers was observed in total bone cross-sectional area in any measured bone site. The added mineral mass in the HRT users was distributed evenly within and between bone sites. In postmenopausal women, long-term HRT preserves estimated bone strength systemically by preventing bone mineral loss similarly in body weight-loaded and non-weight-loaded bone. (c) 2011 American Society for Bone and Mineral Research.
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- Tröstl, Jasmin, et al.
(författare)
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The role of low-volatility organic compounds in initial particle growth in the atmosphere
- 2016
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 533:7604, s. 527-531
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Tidskriftsartikel (refereegranskat)abstract
- About half of present-day cloud condensation nuclei originate from atmospheric nucleation, frequently appearing as a burst of new particles near midday(1). Atmospheric observations show that the growth rate of new particles often accelerates when the diameter of the particles is between one and ten nanometres(2,3). In this critical size range, new particles are most likely to be lost by coagulation with pre-existing particles(4), thereby failing to form new cloud condensation nuclei that are typically 50 to 100 nanometres across. Sulfuric acid vapour is often involved in nucleation but is too scarce to explain most subsequent growth(5,6), leaving organic vapours as the most plausible alternative, at least in the planetary boundary layer(7-10). Although recent studies(11-13) predict that low-volatility organic vapours contribute during initial growth, direct evidence has been lacking. The accelerating growth may result from increased photolytic production of condensable organic species in the afternoon(2), and the presence of a possible Kelvin (curvature) effect, which inhibits organic vapour condensation on the smallest particles (the nano-Kohler theory)(2,14), has so far remained ambiguous. Here we present experiments performed in a large chamber under atmospheric conditions that investigate the role of organic vapours in the initial growth of nucleated organic particles in the absence of inorganic acids and bases such as sulfuric acid or ammonia and amines, respectively. Using data from the same set of experiments, it has been shown(15) that organic vapours alone can drive nucleation. We focus on the growth of nucleated particles and find that the organic vapours that drive initial growth have extremely low volatilities (saturation concentration less than 10(-4.5) micrograms per cubic metre). As the particles increase in size and the Kelvin barrier falls, subsequent growth is primarily due to more abundant organic vapours of slightly higher volatility (saturation concentrations of 10(-4.5) to 10(-0.5) micrograms per cubic metre). We present a particle growth model that quantitatively reproduces our measurements. Furthermore, we implement a parameterization of the first steps of growth in a global aerosol model and find that concentrations of atmospheric cloud concentration nuclei can change substantially in response, that is, by up to 50 per cent in comparison with previously assumed growth rate parameterizations.
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- Äkäslompolo, S, et al.
(författare)
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Calculating the 3D magnetic field of ITER for European TBM studies
- 2015
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Ingår i: Fusion Engineering and Design. - 0920-3796.
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic perturbation due to the ferromagnetic test blanket modules (TBMs) may deteriorate fast ion confinement in ITER. This effect must be quantified by numerical studies in 3D. We have implemented a combined finite element method (FEM) – Biot-Savart law integrator method (BSLIM) to calculate the ITER 3D magnetic field and vector potential in detail. Unavoidable geometry simplifications changed the mass of the TBMs and ferritic inserts (FIs) up to 26%. This has been compensated for by modifying the nonlinear ferromagnetic material properties accordingly. Despite the simplifications, the computation geometry and the calculated fields are highly detailed. The combination of careful FEM mesh design and using BSLIM enables the use of the fields unsmoothed for particle orbit-following simulations. The magnetic field was found to agree with earlier calculations and revealed finer details. The vector potential is intended to serve as input for plasma shielding calculations.
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- Äkäslompolo, S, et al.
(författare)
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ITER fast ion confinement in the presence of the European test blanket module
- 2015
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Ingår i: Nuclear Fusion. - 1741-4326 .- 0029-5515. ; 55:9, s. 093010-
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the confinement of thermonuclear alpha particles and neutral beam injected deuterons in the 15 MA Q = 10 inductive scenario in the presence of the magnetic perturbation caused by the helium cooled pebble bed test blanket module using the vacuum approximation. Both the flat top phase and plasma ramp-up are studied. The transport of fast ions is calculated using the Monte Carlo guiding center orbit-following code ASCOT. A detailed three-dimensional wall, derived from the ITER blanket module CAD data, is used for evaluating the fast ion wall loads. The effect of the test blanket module is studied for both overall confinement and possible hot spots. The study indicates that the test blanket modules do not significantly deteriorate the fast ion confinement.
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- Bilato, A., et al.
(författare)
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Impact of ICRF fast-ions on core turbulence and MHD activity in ASDEX upgrade
- 2023
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Ingår i: 24th Topical Conference On Radio-Frequency Power In Plasmas. - : AIP Publishing.
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Konferensbidrag (refereegranskat)abstract
- Experiments in various tokamaks and their analysis identify the fast ions (FI) generated by NBI and/or ICRF heating as one of the main causes of the observed improvement in core confinement: fast ions can reduce core microturbulence (mainly Ion-Temperature-Gradient (ITG) driven modes) either electrostatically or electromagnetically, or they can resonate with fishbones and high-frequency Alfvén modes, which in turn contribute in stabilizing ITG. In this perspective, we discuss recent experiments done on ASDEX Upgrade (AUG) where ICRF is the main actuator for FI generation for energies above 100 keV. Additionally, ICRF-FIs can substantially impact the MHD activity and its consequent effects on fast ion losses (FILs) and ion-cyclotron emission (ICE). We present dedicated AUG experiments with NBI-D further accelerated by ICRF.
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