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Advanced spectroscopic investigation of colour centres in LiF crystals irradiated with monochromatic hard x-rays
Get PDFNominally-pure lithium fluoride (LiF) crystals were irradiated with monochromatic hard x-rays of energy 5, 7, 9 and 12 keV at the METROLOGIE beamline of the SOLEIL synchrotron facility, in order to understand the role of the selected x-ray energy on their visible photoluminescence (PL) response, which is used for high spatial resolution 2D x-ray imaging detectors characterized by a wide dynamic range. At the energies of 7 and 12 keV the irradiations were performed at five different doses corresponding to five uniformly irradiated areas, while at 5 and 9 keV only two irradiations at two different doses were carried out. The doses were planned in a range between 4 and 1.4 × 103 Gy (10.5 mJ cm−3 to 3.7 J cm−3), depending on the x-ray energy. After irradiation at the energies of 7 and 12 keV, the spectrally-integrated visible PL intensity of the F2 and F3+ colour centres (CCs) generated in the LiF crystals, carefully measured by fluorescence microscopy under blue excitation, exhibits a linear dependence on the irradiation dose in the investigated dose range. This linear behaviour was confirmed by the optical absorption spectra of the irradiated spots, which shows a similar linear behaviour for both the F2 and F3+ CCs, as derived from their overlapping absorption band at around 450 nm. At the highest x-ray energy, the average concentrations of the radiation-induced F, F2 and F3+ CCs were also estimated. The volume distributions of F2 defects in the crystals irradiated with 5 and 9 keV x-rays were reconstructed in 3D by measuring their PL signal using a confocal laser scanning microscope operating in fluorescence mode. On-going investigations are focusing on the results obtained through this z-scanning technique to explore the potential impact of absorption effects at the excitation laser wavelength
Challenging the status quo in invasive species assessment using mechanistic physiologically based demographic modeling
Get PDFThe increased incidence of invasive species introductions is a hallmark of global change, but their associated environmental and economic impacts are vastly underestimated. Assessing and managing the impact of invasive species requires understanding their weather driven dynamics as a basis for predicting their potential geographic distribution and relative abundance. Current de-facto standards for invasive species assessment are correlative approaches lacking mechanistic underpinnings, and hence fail to capture the weather driven biology limiting their explanatory and predictive capacity to forewarn policy makers of species invasiveness (i.e., its potential geographic distribution and relative abundance under extant and/or climate change weather). The idiosyncratic time-place nature of biological invasions and the inability of correlative approaches to incorporate biological information call for development of a unifying prospective approach across species. Physiologically based demographic models (PBDMs) provide a holistic basis for assessment of invasive species addressing many limitations of correlative approaches while accommodating higher level of biological complexity using a similar number of parameters. We use the South American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) as a case study in the Palearctic and compare the predictions of our PBDM model to those of three analyses based on the correlative CLIMEX model. The PBDM outperformed CLIMEX with comparable CLIMEX predictions only after the pest had reached its potential geographic distribution (i.e., post hoc), using 6–10 vs. 13 parameters, respectively. We suggest creating dedicated laboratories to gather appropriate biological data and developing generalized software to build mechanistic models for assessing invasive species of any taxa
Computational Thermal-Fluid Dynamics analyses of borated water distribution in the Vacuum Vessel of the Divertor Tokamak Test facility
Get PDFThis work presents the full set of 3D Computational Thermal-Fluid Dynamics (CFD) analyses of the Divertor Tokamak Test (DTT) Vacuum Vessel (VV). The VV D-shaped double shell structure, divided into 18 Regular and Special sectors, is actively maintained at the operating temperature of 60 °C by borated water in forced flow to counteract the thermal loads and the heat transfer with the surroundings. Due to manufacturing and integration constraints, the different sectors cannot share the same design: the water will flow in the free space between the two shells composing the VV but, given the complexity of the geometry, a careful hydraulic design is mandatory, to avoid local stagnation points which may cause either overheating or freezing. The different hydraulic paths are separately analysed with the Star-CCM+ software, with a SST k−ω turbulence closure, proving the effectiveness of their design (pressure drop, temperature constraints and stagnation/backflow). In addition, the borated water mass flow rate distribution among the different paths is assessed. To conclude, results from CFD analyses are exploited to approximate the hydraulic characteristic of each sector and to develop a system-level model of the full VV with the Modelica language. The overall VV pressure drop of Δp=2810 Pa, the outlet mixing temperature of Tout,mix=333.06 K and a mass flow rate distribution close to the homogeneous condition (≈2.22 kg s−1 in each sector) confirm that no relevant issues are found in the current VV design from the thermal-hydraulic point of view
Hypothetical porous medium concept as a virtual swirl tape: A novel modelling technique towards efficient CFD simulation of swirl tape cooling pipe
No full textThe EU-DEMO divertor target cooling circuit is equipped with Swirl Tape (ST) inserts to improve its thermo-hydraulic performance in terms of heat transfer coefficient and critical heat flux. Due to the presence of the STs, accurate 3D CFD-based thermofluid-dynamic assessments of the divertor targets cooling circuit require a high computational cost and a laborious pre-processing modelling effort. To this end, a cost-efficient CFD simulation technique based on an equivalent porous medium concept, namely the Virtual Swirl Tape (VST) approach, has been developed. In this work, the mathematical formulation of different VSTs models is presented, and the porous media calibration procedure and validation are shown. This technique enables the reduction of computational costs by decreasing the number of volumes required for a single Plasma-Facing Unit (PFU) assembly cooling channel by a factor of 10, while lowering the calculation time by ≈86%. The results obtained show that it is possible to correctly reproduce the friction factor profile and pressure drop of a PFU assembly cooling channel, this latter with errors within 10% considering a wide range of coolant inlet velocities. Some limitations have been observed concerning the VST thermal performance, which is still unsatisfactory and requires further development. The VST approach has been studied using the commercial CFD code ANSYS CFX, coupled with a multi-objective optimization algorithm available in the ANSYS Direct Optimization tool
Verification of parameterizations for clear sky downwelling longwave irradiance in the Arctic
No full textGround-based high resolution observations of downward longwave irradiance (DLI), surface air temperature, water vapor surface partial pressure and column amount, zenith sky infrared (IR) radiance in the atmospheric window, and all-sky camera images are regularly obtained at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W), northwestern Greenland. The datasets for the years 2017 and 2018 have been used to assess the performance of different empirical formulas used to infer clear sky DLI. An algorithm to identify clear sky observations has been developed, based on value, variability, and persistence of zenith sky IR radiance. Seventeen different formulas to estimate DLI have been tested against the THAAO dataset, using the originally determined coefficients. The formulas that combine information on total column water vapor and surface air temperature appear to perform better than others, with a mean bias with respect to the measured DLI smaller than 1 W m-2 and a root mean squared error (RMSE) around 6 W m-2. Unexpectedly, some formulas specifically developed for the Arctic are found to produce poor statistical results. This is attributed partly to limitations in the originally used dataset, which does not cover a whole year or is relative to very specific condition (i.e., the presence of an ice sheet). As expected, the bias displays a significant improvement when the coefficients of the different formulas are calculated using the THAAO dataset. The presence of 2 full years of data allows the determination and the applicability of the coefficients for singular years and the evaluation of results. The smallest values of the bias and RMSE reach 0.1 and 5 W m-2, respectively. Overall, the best results are found for formulas that use both surface parameters and total water vapor column content, and have been developed from global datasets. Conversely, formulas that express the atmospheric emissivity as a linear function of the logarithm of the column integrated water vapor appear to reproduce poorly the observations at THAAO
A GIS-Based Approach for Shallow Landslides Risk Assessment in the Giampilieri and Briga Catchments Areas (Sicily, Italy)
No full textShallow landslides pose a widely growing hazard and risk, globally and particularly in Mediterranean areas. The implementation of adequate adaptation and mitigation measures necessarily requires the development of practical and affordable methodologies and technologies for assessing the shallow landslides hazard and its territorial impact. The assessment of shallow landslide hazard maps involves two different and sequential steps: the susceptibility and the runout analysis, respectively, aimed at the identification of the initiation and the propagation areas. This paper describes the application in the Giampilieri and Briga Villages area (Sicily, Italy) of a shallow landslide risk process at a basin scale with an innovative approach in the runout assessment segment. The runout analysis was conducted using specific GIS tools employing an empirical–geometric approach at a basin scale. The exposure and vulnerability values of the elements at risk were assigned using a qualitative and semi-quantitative approach, respectively. The results highlight the effectiveness of the procedure in producing consistent runout hazard and risk assessments in the valley areas where the more important and vulnerable exposed elements are located. This study contributes to addressing the public administration demand for valuable and user-friendly tools to manage and drive regional planning
Multi-Sensor Quench Detection System for an HTS Slotted Superconducting Cable
No full textQuench caused by electromechanical instabilities is a major concern in high-temperature superconducting (HTS) magnets, and quench detection methods, alternative to common voltage-based systems, are currently under study. In this work, we describe the experimental design and set-up, and we report the results of studies carried out on a cable equipped with bismuth strontium calcium copper oxide (BSCCO) tapes. The sample layout comprises an aluminum slotted core, cooled via a forced flow of liquid nitrogen in the central channel, and liquid nitrogen cooled termination. To trigger a quench in a well-defined position within the stack, a localized small magnetic field is employed to reduce the critical current density in the central zone of the cable. Various configuration of sensors including temperature sensors, voltage taps, and fiber Bragg grating (FBG) are installed, with the final aim of developing a fast and reliable quench detection set-up for the stacked-tapes HTS cable. It is shown that the response for both temperature and FBG signals are comparable for what concerns sensitivity and velocity, and both follow the voltage evolution in time. All in all, the developed setup with the multi-sensor allowed characterizing the electrical and thermal aspects of an HTS slotted-core superconducting cable during a localized magneto-thermal quench
Supercooled liquid water clouds observed over Dome C, Antarctica: temperature sensitivity and cloud radiative forcing
No full textClouds affect the Earth climate with an impact that depends on the cloud nature (solid and/or liquid water). Although the Antarctic climate is changing rapidly, cloud observations are sparse over Antarctica due to few ground stations and satellite observations. The Concordia station is located on the eastern Antarctic Plateau (75° S, 123° E; 3233m above mean sea level), one of the driest and coldest places on Earth. We used observations of clouds, temperature, liquid water, and surface irradiance performed at Concordia during four austral summers (December 2018-2021) to analyse the link between liquid water and temperature and its impact on surface irradiance in the presence of supercooled liquid water (liquid water for temperature less than 0 °C) clouds (SLWCs). Our analysis shows that, within SLWCs, temperature logarithmically increases from -36:0 to -16:0 °C when liquid water path increases from 1.0 to 14.0 gm-2. The SLWC radiative forcing is positive and logarithmically increases from 0.0 to 70.0Wm-2 when liquid water path increases from 1.2 to 3.5 gm-2. This is mainly due to the downward longwave component that logarithmically increases from 0 to 90Wm-2 when liquid water path increases from 1.0 to 3.5 gm-2. The attenuation of shortwave incoming irradiance (that can reach more than 100Wm-2) is almost compensated for by the upward shortwave irradiance because of high values of surface albedo. Based on our study, we can extrapolate that, over the Antarctic continent, SLWCs have a maximum radiative forcing that is rather weak over the eastern Antarctic Plateau (0 to 7Wm-2) but 3 to 5 times larger over West Antarctica (0 to 40Wm-2), maximizing in summer and over the Antarctic Peninsula
THz Data Analysis and Self-Organizing Map (SOM) for the Quality Assessment of Hazelnuts
Get PDFIn recent years, the use of techniques based on electromagnetic radiation as an investigative tool in the agri-food industry has grown considerably, and between them, the application of imaging and THz spectroscopy has gained significance in the field of food quality control. This study presents the development of an experimental setup operating in transmission mode within the frequency range of 18 to 40 GHz, which was specifically designed for assessing various quality parameters of hazelnuts. The THz measurements were conducted to distinguish between healthy and rotten hazelnut samples. Two different data analysis techniques were employed and compared: a traditional approach based on data matrix manipulation and curve fitting for parameter extrapolation, and the utilization of a Self-Organizing Map (SOM), for which we use a neural network commonly known as the Kohonen neural network, which is recognized for its efficacy in analyzing THz measurement data. The classification of hazelnuts based on their quality was performed using these techniques. The results obtained from the comparative analysis of coding efforts, analysis times, and outcomes shed light on the potential applications of each method. The findings demonstrate that THz spectroscopy is an effective technique for quality assessment in hazelnuts, and this research serves to clarify the suitability of each analysis technique
Measurement of the fraction of jet longitudinal momentum carried by Λc+ baryons in pp collisions
No full textRecent measurements of charm-baryon production in hadronic collisions have questioned the universality of charm-quark fragmentation across different collision systems. In this work the fragmentation of charm quarks into charm baryons is probed, by presenting the first measurement of the longitudinal jet momentum fraction carried by Λc+ baryons, z∥ch, in hadronic collisions. The results are obtained in proton-proton (pp) collisions at s=13 TeV at the LHC, with Λc+ baryons and charged (track-based) jets reconstructed in the transverse momentum intervals of 3≤pTΛc+<15 GeV/c and 7≤pTjet ch<15 GeV/c, respectively. The z∥ch distribution is compared to a measurement of D0-tagged charged jets in pp collisions as well as to pythia 8 simulations. The data hints that the fragmentation of charm quarks into charm baryons is softer with respect to charm mesons, in the measured kinematic interval, as predicted by hadronization models which include color correlations beyond leading-color in the string formation