Search

International audience; Weaning a patient from mechanical ventilation is a critical task in Intensive Care Units, but it can be made safer by using Lung Ultrasound scoring. This scoring is currently done visually by specialists based on Lung Ultrasound artifacts among which are A-lines. Automating this scoring may help standardizing results and saving time for clinicians. In this paper, we propose a method to automatically detect A-lines from a manual delineation of the pleural line, and by using both the intensity profile of the LUS image and morphological operations. A score is then assigned to significant lines and represents the possibility of them being A-lines. The proposed method shows promising results in differentiating A-lines from other elements with an Area Under the Curve of 0.95; furthermore, using a threshold at 0.5 to detect A-lines leads to very good performances with an accuracy of 95% and a F0.5-score of 0.84.

Discretization translates the continuous functions into discrete version making them more adaptable for numerical computation and application in applied mathematics and computer sciences. In this article, discrete analogues of a generalization method of generating a new family of distributions is provided. Several new discrete distributions are derived using the proposed methodology. A discrete Weibull-Geometric distribution is considered and various of its significant characteristics including moment, survival function, reliability function, quantile function, and order statistics are discussed. The method of maximum likelihood and the method of moments are used to estimate the model parameters. The performance of the proposed model is probed through a real data set. A comparison of our model with some existing models is also given to demonstrate its efficiency.

We present the synthesis and characterization of gallium nitride (GaN) pine tree-like nanostructures (PTLNs) grown by low-pressure chemical vapor deposition. A high yield of PTLNs is densely arranged with each PTLN having a typical length of 15.46 ± 3.38 μm. From Raman spectroscopy, we observe anE2Hpeak at 570 ± 6 cm-1which is the primary characteristic of wurtzite. X-ray and ultraviolet photoemission spectroscopy reveal that the electronic structures of GaN PTLNs indicate an n-type character, while the work function and valence band maximum are determined to be 3.30 ± 0.05 and 3.85 ± 0.08 eV, respectively. We confirm the electronic nature of our structure from the current-voltage characteristics exhibiting rectifying behavior. Density functional theory calculations of GaN PTLNs modeled by germanium-doped GaN nanowires are consistent with our experimental findings. To summarize, the energy-band diagram is presented for the future of GaN PTLNs in the optoelectronic and sensing applications. Ministry of Education (MOE) This research is supported by the Ministry of Education, Singapore, under its Academic Research Fund Tier 2, grant no. MOE2016-T2-1-052 and Tier 1, grant no. MOE2019-T1-002063. F.A. and H.H. would like to acknowledge Toray Science and Technology Research Grant 2021.

Three different configurations of GaN are analysed to show robust and tunable light emitters from localised point defects induced in GaN crystal by a femtosecond laser (fs-laser). Localised irradiations of GaN are achieved using a fs-laser. The laser-induced damage threshold is found at a fluence of 130 ± 10 mJ/cm2. Raman spectroscopy allows for the characterization of irradiated GaN crystal while quasi-resonant photoluminescence mapping reveals a defect-related visible emission corresponding to the fs-laser irradiated area. From three different configurations of GaN, emission peaks vary from 620 to 680 nm-wavelengths for thin film, MBE intrinsically doped and Mg-doped NWs of GaN, respectively. The red emission in GaN is localized thanks to the new laser-induced fabrication and the engineering of the defect emission paves the way to further lighting applications.

Semiconductor structures offer unique properties at the nanoscale. Mastering the growth of semiconductor crystals and fabrication processes is crucial towards developing better opto-electronic devices. Morphological variations at nanoscale have a direct effect on available electronics states, impacting fundamental electronic properties and photonics capabilities of the material. This thesis focuses on one-dimensional Gallium Nitride (GaN) nanowires, Graphene Quantum Dots (GQDs) and two-dimensional hexagonal-Boron Nitride (hBN). First, synthesis of semiconductor nanostructures with a focus on nanoparticle mediated growth of one-dimensional Gallium Nitride crystal is developed. Catalyst-assisted growth of GaN nanowires using a Low Pressure Chemical Vapour Deposition (LPCVD) system is shown. The choice of growth catalyst influences directly the GaN crystal and the morphology of nanowires along with growth parameters such as temperature, vacuum pressure, precursor gases or time. An uncommon nanostructure of GaN in the shape of pine trees is introduced. Next, promising emission from GaN nanowires and hBN monolayers in the visible range is reported. Defects in LPCVD-grown GaN nanowires show yellow and green luminescences. Besides, femto-second pulsed laser is used, on defect-free nanowires grown by molecular beam epitaxy, to intentionally induce optically-active defects. Above a laser threshold power the irradiated GaN nanowires melt, higher power sublimates the crystal. Irradiated GaN is characterised as Wurtzite crystal and show emission in the visible range, additionally to the band-to-band UV luminescence. Similar experiment on hBN monolayers show defect-related visible emission near the irradiated areas. Contrary to GaN nanowires, where a wide emission is observed, hBN defects show strong and sharp emission. Point defects created in hBN - monolayers and flakes - are shown to be single photons emitters. Finally, fabrication of efficient micro- and nano-scale emitters is of crucial importance for optical nano-devices. In conventional semiconductors, such as Si or GaAs, fabrication processes can involve expensive and time consuming electron beam lithography and etching. Using femto-second pulsed laser, efficient and cost-effective GaN and hBN-based localised micro and nanometer-size light emitters can be fabricated using optically active defect states. Coupling these nano-emitters with surface plasmons of another nanostructure can improve the emission rate as shown by coupling GQDs to single Bi2Te3 nanoplates. From synthesis by chemical vapour deposition methods to structural and optical characterisation, this thesis will show how emission wavelength can be modulated and localised micro-/nano-emitters be fabricated before coupling them with surface plasmons to improve the emission rate for more efficient and bright emitters. Doctor of Philosophy