Comparison of convolutional neural networks for cloudy optical images reconstruction from single or multitemporal joint SAR and optical images

With the increasing availability of optical and synthetic aperture radar (SAR) images thanks to the Sentinel constellation, and the explosion of deep learning, new methods have emerged in recent years to tackle the reconstruction of optical images that are impacted by clouds. In this paper, we focus on the evaluation of convolutional neural networks that use jointly SAR and optical images to retrieve the missing contents in one single polluted optical image. We propose a simple framework that ease the creation of datasets for the training of deep nets targeting optical image reconstruction, and for the validation of machine learning based or deterministic approaches. These methods are quite different in terms of input images constraints, and comparing them is a problematic task not addressed in the literature. We show how space partitioning data structures help to query samples in terms of cloud coverage, relative acquisition date, pixel validity and relative proximity between SAR and optical images. We generate several datasets to compare the reconstructed images from networks that use a single pair of SAR and optical image, versus networks that use multiple pairs, and a traditional deterministic approach performing interpolation in temporal domain.Comment: 17 page

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Characterization of Structured Doping Areas Diffused from Doped CVD Layers on Crystalline Si Substrates

Due to the special cell design, BC-BJ solar cells require adapted characterization methods, in particular to investigate the junction of the highly doped regions on the cell's rear. The focus of this Master Thesis was the development and implementation of a method to characterize single pn-junctions, which are located on the back of a BC-BJ solar cell. To achieve this objective, an simple process flow was developed to produce suiting samples with a single illuminated pn-junction and two TLM fields. For this purpose, the development of a precise alignment method was essential, which allows alignment with an accuracy of ~20 micrometer. All local processing steps are aligned directly or indirectly with the initially produced pn-junction. This applies to the contact openings, the metallization, and even the illumination mask, which is positioned on the front of the sample during the illuminated J-V curve measurement.Simulations conducted with Sentaurus Synopsis show, that the characterization method can distinguish samples with and without intrinsic gap region between the highly doped regions on the back of the cell, if this region is not defect free. A difference in the fill factor of 1.9 % between samples with and without the intrinsic gap is expected for the 'zebra structure', without consideration of tunnel recombination, which would further increase this difference. Furthermore, a comparison was made between the simulations programs Sentaurus Synopsis and Quokka, and differences were presented. In the parameter range of a highly efficient IBC solar cells, there is only a small error for the J-V characteristic quantities. In a more detailed investigation with the FELA, differences in the resistance loss at the BSF contact were found, which indicate that this loss channel is differently implemented into the two simulation programs. Due to the general consistency of the simulation results, Quokka was used as a simulation program to illustrate the influence of certain experimental parameters in the analysis.The difficulties encountered in the preparation of samples with a single pn-junction and the results obtained, were presented in the context of the individual process steps. In particular, the local removal of dielectric layers was discussed. This layer removal is relevant for the creation of the pn-junction, which is formed in a single diffusion process from borosilicate glass and POCl3 gas, but also for the opening of the contact surfaces. The local removal of dielectric layers by means of photolithography and laser ablation (ns and ps pulsed lasers) was carried out, analyzed, and comparisons were drawn between the two methods. The focus was clearly on laser ablation due to the industrial relevance of this method. In addition, J-V measurements show that the applied photolithography process does not provide performance advantages over laser ablation. Consequences of effects such as laser doping (with the ns pulsed laser), surface roughening in overlap areas, and shading CVD material remains were observed, characterized and tested for relevance in the sample production process. As a result, a process could be presented for the production of pn-junctions with and without the intrinsic region.Furthermore, the contacts were characterized by TLM measurements. Specific contact resistances of 9-24 mOhmcm2 were measured for the deposited Ti/Pd/Ag and Al/Ag contacts. The contact formation takes place directly during the deposition or during a short thermal annealing process. The specific contact resistance values are independent of the selected method of contact opening and the deposited metal. Shunt problems were also analyzed and corrected.Further relevant findings were obtained with regard to surface passivation. With thermal anneal, a high passivation quality could be achieved with Al2O3 and a-Si passivation. For this purpose, the passivation layers were coated with SiNx and thermally annealed at a temperature between 300 and 420 °C. A recombination parameter J_0 below 30 fA/cm2 was obtained for a 140 Ohm/sq p-type emitter passivated with Al2O3 or a-Si. The J-V measurements also underline the importance of adequate surface passivation. The passivation quality was tested for the rear (BSF, laser treated surface and emitter) and the front surface (texture). The absorption of a-Si was also analyzed because of its relevance for the passivation of the front surface with a-Si.The processing difficulties seem to be overcome at this time, which is why further sample processing with the presented manufacturing process should lead to a result with high characteristic quantities. In particular the increased lifetime, due to the postponed texturing step, and the non-existent laser doping, due to the use of the ps laser on the entire area that has to be ablated, are an improvement to the last processed samples. With these processed samples, the comparison between samples with and without the intrinsic gap can then be drawn. A clear distinction between these samples would be a milestone for the characterization method and would provide the proof-of-concept. Further investigations, with applied reverse bias voltage or with varied rear surface passivation, could provide additional information on the properties of the pn-junction.In addition, the concept can be extended to more than one pn-junction per sample. Sufficient information on the contact formation on samples has already been collected in the course of this work, which is why the TLM structure is no longer required on all samples. Adding pn-junctions on a sample has the advantage that a considerably higher number of measurable pn-junctions can be produced. In addition, conclusions about possible processing problems can be classified more easily. Alternating p- and n-doped regions on the entire sample's rear side also represent an approximation to the structure of an IBC solar cell.Moreover, an examination of the pn-junction using KPFM would be useful. Following the proposal in this work, the pn-junction could be polished at a small angle to the surface so as to obtain a depth resolution of the pn-junction with KPFM measurement. Accordingly, one obtains insight into the doping profile as a resolution in depth.publishe

Phase Transitions in Vycor Studied by Optical Techniques

Wetting fluids condense in porous media for pressures smaller than their saturated vapor pressure. Unlike in bulk conditions, the transition from gas to liquid is strongly hysteretic. Drying the material requires to reduce the pressure well below the condensation pressure. Understanding the origin of this hysteresis, and the underlying evaporation mechanisms, is an active field of research.In my Bachelor Thesis I examine this hysteretic cycle for n-hexane in the porous environment of Vycor. For that purpose, I built a new experimental set-up which allows simultaneously to obtain precise isotherms and to optically probe the sample. Specific attention was brought on the kink of the evaporation branch and small-angle light scattering was used to measure the fluid correlations at this point. The results show a recurring heterogeneity in the sample upon evaporation.publishe

Comparison of convolutional neural networks for cloudy optical images reconstruction from single or multitemporal joint SAR and optical images

International audienceWith the increasing availability of optical and synthetic aperture radar (SAR) images thanks to the Sentinel constellation, and the explosion of deep learning, new methods have emerged in recent years to tackle the reconstruction of optical images that are impacted by clouds. In this paper, we focus on the evaluation of convolutional neural networks that use jointly SAR and optical images to retrieve the missing contents in one single polluted optical image. We propose a simple framework that ease the creation of datasets for the training of deep nets targeting optical image reconstruction, and for the validation of machine learning based or deterministic approaches. These methods are quite different in terms of input images constraints, and comparing them is a problematic task not addressed in the literature. We show how space partitioning data structures help to query samples in terms of cloud coverage, relative acquisition date, pixel validity and relative proximity between SAR and optical images. We generate several datasets to compare the reconstructed images from networks that use a single pair of SAR and optical image, versus networks that use multiple pairs, and a traditional deterministic approach performing interpolation in temporal domain

Process Development for Additive Manufacturing of Alumina Toughened Zirconia for 3D Structures by Means of Two-Photon Absorption Technique

Additive manufacturing is well established for plastics and metals, and it gets more and more implemented in a variety of industrial processes. Beside these well-established material platforms, additive manufacturing processes are highly interesting for ceramics, especially regarding resource conservation and for the production of complex three-dimensional shapes and structures with specific feature sizes in the µm and mm range with high accuracy. The usage of ceramics in 3D printing is, however, just at the beginning of a technical implementation in a continuously and fast rising field of research and development. The flexible fabrication of highly complex and precise 3D structures by means of light-induced photopolymerization that are difficult to realize using traditional ceramic fabrication methods such as casting and machining is of high importance. Generally, slurry-based ceramic 3D printing technologies involve liquid or semi-liquid polymeric systems dispersed with ceramic particles as feedstock (inks or pastes), depending on the solid loading and viscosity of the system. This paper includes all types of photo-curable polymer-ceramic-mixtures (feedstock), while demonstrating our own work on 3D printed alumina toughened zirconia based ceramic slurries with light induced polymerization on the basis of two-photon absorption (TPA) for the first time. As a proven exemplary on cuboids with varying edge length and double pyramids in the µm-range we state that real 3D micro-stereolithographic fabrication of ceramic products will be generally possible in the near future by means of TPA. This technology enables the fabrication of 3D structures with high accuracy in comparison to ceramic technologies that apply single-photon excitation. In sum, our work is intended to contribute to the fundamental development of this technology for the representation of oxide-ceramic components (proof-of-principle) and helps to exploit the high potential of additive processes in the field of bio-ceramics in the medium to long-term future