Imaging Gaseous Detector based on Micro Processing Technology

The development of gaseous detectors has been exciting again since the appearance of a MicroStrip Gas Chamber(MSGC) in 1988, which is made using a micro-electronics technology. These days lots of variations of the advanced gaseous detectors are being intensively studied in the world. We have developed the two-dimensional MSGC having a 10 cm square detection area and the ultra fast readout system for a real time X-ray imaging. The MSGC was made using Multi-Chip Module (MCM) technology, and has a very thin substrate of 17 $\mu$m, lots of thin anodes and back strips both with 200 $\mu$m pitches. This enables us to get fast digital X-ray images with recording both the timing and an energy of each X-ray photon. In addition, an intermediate gas multiplier has been realized using a capillary plate having a conductive surface of a capillary. The MSGC combined with the conductive capillary plate can be steadily operated with a high gain under intense irradiation. Here we also report new approaches of X-ray crystal structure analyses using timing information obtained by the MSGC.Comment: 14 papges, 10 figures, to appear in the proceedings of Solid State Detectors for 21st Century (Nucl. Instru. and Meth. A

Local enrichment of NURBS patches using a non-intrusive coupling strategy: Geometric details, local refinement, inclusion, fracture

International audienceIn this work, we apply a non-intrusive global/local coupling strategy for the modelling of local phenomena in a NURBS patch. The idea is to consider the NURBS patch to be enriched as the global model. This results in a simple, flexible strategy: first, the global NURBS patch remains unchanged, which completely eliminates the need for costly re-parametrization procedures (even if the local domain is expected to evolve); then, easy merging of a linear NURBS code with any other existing robust codes suitable for the modelling of complex local behaviour is possible. The price to pay is the number of iterations of the non-intrusive solver but we show that this can be strongly reduced by means of acceleration techniques. The main development for NURBS is to be able to handle non-conforming geometries. Only slight changes in the implementation process, including the setting up of suitable quadrature rules for the evaluation of the interface reaction forces, are made in response to this issue. A range of numerical examples in two-dimensional linear elasticity are given to demonstrate the performance of the proposed methodology and its significant potential to treat any case of local enrichment in a NURBS patch simply

Éléments finis isogéométriques massifs coque sans verrouillage pour des simulations en mécanique non linéaire des solides

With the introduction of IsoGeometric Analysis (IGA), the calculation of shell has become possible using the exact geometry for coarse meshes. In order to that, Lagrange polynomials are replaced by NURBS functions, the most commonly used technology in Computer-Aided Design, to perform the analysis. In addition, NURBS functions have a higher order of continuity, which leads to higher per-degree-of-freedom accuracy of the shell solution than with classical Finite Elements Analysis (FEA). IGA has now been widely applied in shell formulations. Nevertheless, it has still rarely been studied in the context of solid-shell models. This second shell approach is, however, very useful for engineers, since it enables to calculate thin structures using 3D solid elements, i.e. involving only displacements as degrees of freedom. The difficulty in shell analysis is to deal with locking which highly deteriorates the convergence of the solution. The NURBS framework does not enable to solve the problem directly. Then, to really benefit from NURBS in shells, specific strategies need to be implemented to answer the locking issue. This is the goal of the thesis in the context of solid-shell elements. The first work has consisted, on a curved beam problem, in extending the locking-free methods usually encountered in FEA to the NURBS context. The study resulted in the development of two new strategies for NURBS: the first one is based on a selective reduced integration technique and the second one makes use of a B-bar projection. The global formalism offered by the B-bar method appearing more suitable for NURBS, it has then been investigated for solid-shell elements. More precisely, a mixed formulation has first been elaborated from which, it has been possible to derive the equivalent B-bar projection. From a theoretical point of view, this strategy constitutes the most important result of this work: a systematic method to construct a consistent B-bar projection is to write a mixed formulation. With regards to the implementation, the main idea to treat locking of the solid-shell elements has been to modify the average of the strain and stress components across the thickness of the shell. Hourglass control has also been added to stabilize the element in particular situations. The resulting element is of good quality for low order approximations and coarse meshes: the quadratic version seems to be more accurate than basic NURBS elements of order 4. The proposed method leads to a global stiffness matrix of small size but full. This problem is inherent to NURBS functions. It has been limited here by using a local least squares procedure to approach the B-bar projection. Finally, the mixed element has been successfully extended to geometric non-linearity which reflects the ability of the methodology to be used in complex simulations.Avec l’arrivée de l’Analyse IsoGéométrique (IGA), le calcul de coque est devenu possible en utilisant la géométrie exacte pour des maillages grossiers. Pour cela, les polynômes de Lagrange sont remplacés pour l’interpolation par des fonctions NURBS (technologie la plus courante en conception assistée par ordinateur). De plus, ces fonctions possèdent une continuité supérieure ce qui offre une meilleure précision qu’un calcul éléments finis à nombre de degrés de liberté égal. L’IGA a déjà été développée pour les formulations coques. Elle n’a été cependant que très peu étudiée pour les modèles massifs coque. Pourtant, cette deuxième approche est très utilisée par l’ingénieur car elle permet de calculer des structures minces à l’aide d’éléments continus 3D, c’est-à-dire en faisant intervenir uniquement des inconnues en déplacements. La difficulté en calcul de coque est de faire face au verrouillage qui conduit à une forte dégradation de la convergence de la solution. Le cadre NURBS ne permet pas lui-même de résoudre ce problème. La meilleure efficacité de l’approximation NURBS ne peut donc être atteinte sans le développement de techniques particulières pour supprimer le verrouillage. C’est le but de cette thèse dans le cadre des éléments massifs coque. Le premier travail a consisté, sur un problème de poutre courbe, à étendre les méthodes sans verrouillage habituelles au contexte NURBS. Deux nouvelles stratégies ont alors été développées pour les NURBS : la première est basée sur une technique d’intégration réduite tandis que la seconde fait appel à une projection B-bar. Le formalisme général des méthodes B-bar semblant plus adapté, c’est celui-ci que nous avons développé ensuite pour les éléments massifs coque. Plus précisément, nous avons mis en place une formulation mixte de laquelle nous avons pu dériver la projection B-bar équivalente. Cette démarche constitue d’un point de vue théorique le résultat principal du travail : une méthode systématique pour construire une projection B-bar consistante est de passer par une formulation mixte. D’un point de vue mise en œuvre, l’idée principale pour traiter le verrouillage des éléments massifs coque a été de modifier l’interpolation de la moyenne dans l’épaisseur de la coque des composantes du tenseur des contraintes. Un contrôle de hourglass a aussi été ajouté pour stabiliser l’élément dans certaines situations. L’élément obtenu est de bonne qualité pour une interpolation de bas degrés et des maillages grossiers : la version quadratique semble plus précise que des éléments standards NURBS de degré 4. La méthode proposée conduit à une matrice de rigidité globale de petite taille mais pleine. Ce problème est inhérent aux NURBS. Il a pu être limité ici en utilisant une procédure de type moindres carrés locaux pour approcher la projection B-bar. Finalement, l’élément mixte a été étendu avec succès en non linéaire géométrique ce qui témoigne du potentiel de la méthode pour mener des simulations complexes

Reduced Order Modeling based Inexact FETI-DP solver for lattice structures

This paper addresses the overwhelming computational resources needed with standard numerical approaches to simulate architected materials. Those multiscale heterogeneous lattice structures gain intensive interest in conjunction with the improvement of additive manufacturing as they offer, among many others, excellent stiffness-to-weight ratios. We develop here a dedicated HPC solver that benefits from the specific nature of the underlying problem in order to drastically reduce the computational costs (memory and time) for the full fine-scale analysis of lattice structures. Our purpose is to take advantage of the natural domain decomposition into cells and, even more importantly, of the geometrical and mechanical similarities among cells. Our solver consists in a so-called inexact FETI-DP method where the local, cell-wise operators and solutions are approximated with reduced order modeling techniques. Instead of considering independently every cell, we end up with only few principal local problems to solve and make use of the corresponding principal cell-wise operators to approximate all the others. It results in a scalable algorithm that saves numerous local factorizations. Our solver is applied for the isogeometric analysis of lattices built by spline composition, which offers the opportunity to compute the reduced basis with macro-scale data, thereby making our method also multiscale and matrix-free. The solver is tested against various 2D and 3D analyses. It shows major gains with respect to black-box solvers; in particular, problems of several millions of degrees of freedom can be solved with a simple computer within few minutes.Comment: 30 pages, 12 figures, 2 table

Rate and Gain Limitations of MSGC's and MGC's Combined with GEM and other Preamplification Structures

We have studied the rate and gain limits of diamond-coated Microstrip Gas Counters (MSGC's) and Micro-Gap Counters (MGC's) when combined with various preamplification structures: Gas Electron Multiplier (GEM), Parallel-Plate Avalanche Chamber (PPAC) or a MICROMEGAS-type structure. Measurements were done both with X rays and alpha particles with various detector geometries and in different gas mixtures at pressures from 0.05 to 10 atm. The results obtained varied significantly with detector design, gas mixture and pressure, but some general features can be identified. We found that in all cases, bare MSGC'S, MGC'S, PPAC's and MICROMEGAS, the maximum achievable gain drops with rate. The addition of preamplification structures significantly increases the gain of MSGC's and MGC'S, but this gain is still rate dependent. There would seem to be a general rate-dependent effect governing the usable gain of all these detectors. We speculate on possible mechanisms for this effect, and identify a safe, spark-free, operation zone for each system (detector + preamplification structure) in the rate-gain coordinate plane

Lanthanide-based peptide biosensor to monitor CDK4/cyclin D kinase activity

We describe a lanthanide biosensor that responds to CDK4 kinase activity in melanoma cell extracts through a significant and dose dependent increase in luminescence, thanks to sensitization of a DOTA[Tb3+] complex incorporated into a CDK4 substrate peptide by a unique tryptophan residue in an adjacent phosphoaminoacid binding moietyThis work was funded by the CNRS (Centre National de la Recherche Scientifique) and a Marie-Curie fellowship EC-FP7 Framework (PIEF-GA-2013-623151) supporting JAGV. CB was funded by the INCA (PRTK-2014). Financial support from the Spanish MINECO (CTQ2015-70698-R), the Xunta de Galicia (Centro singular de investigacio´n de Galicia accreditation 2016–2019), and the European Union (European Regional Development Fund – ERDF), are gratefully acknowledgedS

Operation of microstrip gas chambers manufactured on glass coated with high resistivity diamond-like layers

We describe recent observations and measurements realized with micro-strip gas chambers (MSGCs) manufactured on boro-silicate glass coated with a thin layer of diamond-like carbon (DLC) having a surface resistivity around 4.10$^{16}\Omega/\Box$. The role of the back-pla electrode configuration and potential in the detector performance has been studied. Even for this very high resistivity of the coatings, MSGCs operate differently from those manufactured on bare boro-silicate glass; the charge gain increases with the radiation flux for counting rates above 103 Hz/mm2, reaching a value 60% higher for 105 Hz/mm2. This behavior does not depend on the presence and potential of the back plane electrode; however, both maximum gain and rate capability are influenced by the drift field. From this study, compared with measurements realized previously with other detectors, we deduce that for stable high rate operation of MSGCs the resistivity of the coating should not exceed ~10$^{15}\Omega/\Box$

New observations with the gas electron multiplier (GEM)

We describe recent measurements realized with the Gas Electron Multiplier (GEM) mesh added as pre-amplification element to a multiwire and a micro-strip chamber. Large, stable combined gains are obtained, with good uniformity and energy resolution, in a wide range of filling gases including non-flammable mixtures; coupled to a micro-strip plate, the pre-amplification element allows to maintain the high rate capability and resolution at considerably lower operating voltages, completely eliminating discharge problems. Charge gains are large enough to allow detection of signals in the ionization mode on the last element, permitting the use of a simple printed circuit as read-out electrode; two-dimensional read-out can then be easily implemented. The absence of charge multiplication in the last stage avoids charge build-up on the substrate and prevents ageing phenomena. A new generation of simple, reliable and cheap fast position sensitive detectors seems at hand