| 1. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 2. |
- Bonfanti, A., et al.
(författare)
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TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 671
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Tidskriftsartikel (refereegranskat)abstract
- Context. TOI-1055 is a Sun-like star known to host a transiting Neptune-sized planet on a 17.5-day orbit (TOI-1055 b). Radial velocity (RV) analyses carried out by two independent groups using nearly the same set of HARPS spectra have provided measurements of planetary masses that differ by ∼2σ. Aims. Our aim in this work is to solve the inconsistency in the published planetary masses by significantly extending the set of HARPS RV measurements and employing a new analysis tool that is able to account and correct for stellar activity. Our further aim was to improve the precision on measurements of the planetary radius by observing two transits of the planet with the CHEOPS space telescope. Methods. We fit a skew normal function to each cross correlation function extracted from the HARPS spectra to obtain RV measurements and hyperparameters to be used for the detrending. We evaluated the correlation changes of the hyperparameters along the RV time series using the breakpoint technique. We performed a joint photometric and RV analysis using a Markov chain Monte Carlo scheme to simultaneously detrend the light curves and the RV time series. Results. We firmly detected the Keplerian signal of TOI-1055 b, deriving a planetary mass of Mb = 20.4-2.5+2.6 MO (∼12%). This value is in agreement with one of the two estimates in the literature, but it is significantly more precise. Thanks to the TESS transit light curves combined with exquisite CHEOPS photometry, we also derived a planetary radius of Rb = 3.490-0.064+0.070 RO (∼1.9%). Our mass and radius measurements imply a mean density of ρb = 2.65-0.35+0.37 g cm-3 (∼14%). We further inferred the planetary structure and found that TOI-1055 b is very likely to host a substantial gas envelope with a mass of 0.41-0.20+0.34 MO and a thickness of 1.05-0.29+0.30 RO. Conclusions. Our RV extraction combined with the breakpoint technique has played a key role in the optimal removal of stellar activity from the HARPS time series, enabling us to solve the tension in the planetary mass values published so far for TOI-1055 b.
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| 3. |
- Serrano, L. M., et al.
(författare)
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A low-eccentricity migration pathway for a 13-h-period Earth analogue in a four-planet system
- 2022
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 6:6, s. 736-750
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Tidskriftsartikel (refereegranskat)abstract
- It is commonly accepted that exoplanets with orbital periods shorter than one day, also known as ultra-short-period (USP) planets, formed further out within their natal protoplanetary disks before migrating to their current-day orbits via dynamical interactions. One of the most accepted theories suggests a violent scenario involving high-eccentricity migration followed by tidal circularization. Here we present the discovery of a four-planet system orbiting the bright (V = 10.5) K6 dwarf star TOI-500. The innermost planet is a transiting, Earth-sized USP planet with an orbital period of ~13 hours, a mass of 1.42 ± 0.18 M⊕, a radius of 1.166−0.058+0.061R⊕ and a mean density of 4.89−0.88+1.03gcm−3. Via Doppler spectroscopy, we discovered that the system hosts 3 outer planets on nearly circular orbits with periods of 6.6, 26.2 and 61.3 days and minimum masses of 5.03 ± 0.41 M⊕, 33.12 ± 0.88 M⊕ and 15.05−1.11+1.12M⊕, respectively. The presence of both a USP planet and a low-mass object on a 6.6-day orbit indicates that the architecture of this system can be explained via a scenario in which the planets started on low-eccentricity orbits then moved inwards through a quasi-static secular migration. Our numerical simulations show that this migration channel can bring TOI-500 b to its current location in 2 Gyr, starting from an initial orbit of 0.02 au. TOI-500 is the first four-planet system known to host a USP Earth analogue whose current architecture can be explained via a non-violent migration scenario.
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| 4. |
- Georgoulas, George, et al.
(författare)
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Principal component analysis of the start-up transient and hidden Markov modeling for broken rotor bar fault diagnosis in asynchronous machines
- 2013
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Ingår i: Expert systems with applications. - : Elsevier BV. - 0957-4174 .- 1873-6793. ; 40:17, s. 7024-7033
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a novel computational method for the diagnosis of broken rotor bars in three phase asynchronous machines. The proposed method is based on Principal Component Analysis (PCA) and is applied to the stator’s three phase start-up current. The fault detection is easier in the start-up transient because of the increased current in the rotor circuit, which amplifies the effects of the fault in the stator’s current independently of the motor’s load. In the proposed fault detection methodology, PCA is initially utilized to extract a characteristic component, which reflects the rotor asymmetry caused by the broken bars. This component can be subsequently processed using Hidden Markov Models (HMMs). Two schemes, a multiclass and a one-class approach are proposed. The efficiency of the novel proposed schemes is evaluated by multiple experimental test cases. The results obtained indicate that the suggested approaches based on the combination of PCA and HMM, can be successfully utilized not only for identifying the presence of a broken bar but also for estimating the severity (number of broken bars) of the fault.
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| 5. |
- Llatser, I., et al.
(författare)
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Characterization of graphene-based nano-antennas in the terahertz band
- 2012
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Ingår i: Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012. - : IEEE. - 9781457709180 ; , s. 194-198
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Konferensbidrag (refereegranskat)abstract
- Graphene-enabled wireless communications constitute a novel paradigm which has been proposed to implement wireless communications at the nanoscale. Indeed, graphene-based nano-antennas just a few micrometers in size have been predicted to radiate electromagnetic waves at the terahertz band. In this work, the performance of a graphene-based nano-patch antenna in transmission and reception is numerically analyzed. The resonance frequency of the nano-antenna is calculated as a function of its length and width, both analytically and by simulation. The influence of a dielectric substrate with a variable size, and the position of the patch with respect to the substrate is also evaluated. Finally, the radiation pattern of a graphene-based nano-patch antenna is compared to that of an equivalent metallic antenna. These results will prove useful for designers of future graphene-based nano-antennas, which will enable wireless communications at the nanoscale.
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| 6. |
- Pupkaite, Justina, et al.
(författare)
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Delivering More of an Injectable Human Recombinant Collagen III Hydrogel Does Not Improve Its Therapeutic Efficacy for Treating Myocardial Infarction
- 2020
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Ingår i: ACS Biomaterials Science & Engineering. - : AMER CHEMICAL SOC. - 2373-9878. ; 6:7, s. 4256-4265
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Tidskriftsartikel (refereegranskat)abstract
- Injectable hydrogels are a promising method to enhance repair in the heart after myocardial infarction (MI). However, few studies have compared different strategies for the application of biomaterial treatments. In this study, we use a clinically relevant mouse MI model to assess the therapeutic efficacy of different treatment protocols for intramyocardial injection of a recombinant human collagen III (rHCIII) thermoresponsive hydrogel. Comparing a single hydrogel injection at an early time point (3 h) versus injections at multiple time points (3 h, 1 week, and 2 weeks) post-MI revealed that the single injection group led to superior cardiac function, reduced scar size and inflammation, and increased vascularization. Omitting the 3 h time point and delivering the hydrogel at 1 and 2 weeks post-MI led to poorer cardiac function. The positive effects of the single time point injection (3 h) on scar size and vascular density were lost when the hydrogels collagen concentration was increased from 1% to 2%, and it did not confer any additional functional improvement. This study shows that early treatment with a rHCIII hydrogel can improve cardiac function post-MI but that injecting more rHCIII (by increased concentration or more over time) can reduce its efficacy, thus highlighting the importance of investigating optimal treatment strategies of biomaterial therapy for MI.
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| 7. |
- van Doremalen, Ric, et al.
(författare)
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Wireless activity monitor using 3D integration
- 2009
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Ingår i: Proceedings of Symposium on Design, Test, Integration and Package of MEMS/MOEMS (DTIP 2009), Rome, Italy.
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Konferensbidrag (refereegranskat)
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