MOHAMED BELHAJ - Academia.edu (original) (raw)

Papers by MOHAMED BELHAJ

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Archives des maladies du coeur et des vaisseaux, 1983

A second case of double coarctation of the thoracic aorta is reported, the first having been obse... more A second case of double coarctation of the thoracic aorta is reported, the first having been observed at the Marie-Lannelongue Surgical Center in an older child. This case was a 3 months infant in which the missed pre- and postoperative diagnosis led to reoperation after control catheter and angiographic studies. These investigations were carried out one month after the first operation because of persistent severe cardiac failure. Surgical cure in two stages consisted in a Waldhausen plastic enlargement procedure and a Crafoord-type resection anastomosis, ensuring the best chances for a good result.

Cornell University - arXiv, Oct 10, 2017

How to Achieve Inclusive Growth

The past two decades have seen a rapid increase in interest in financial inclusion, both from pol... more The past two decades have seen a rapid increase in interest in financial inclusion, both from policymakers and researchers. This chapter surveys the main findings from the literature, documenting the trends over time and gaps that have arisen across regions, income levels, and gender, among others. It points out that structural, as well as policy-related, factors, such as encouraging banking competition or channelling government payments through bank accounts, play an important role, and describes the potential macro and microeconomic benefits that can be derived from greater financial inclusion. It argues that policy should aim to identify and reduce frictions holding back financial inclusion, rather than targeting specific levels of inclusion. Finally, it suggests areas for future research.

2022 IEEE Global Engineering Education Conference (EDUCON)

This document shows three TEEY measurements made in the spatial environment department (DESP) of ... more This document shows three TEEY measurements made in the spatial environment department (DESP) of ONERA Toulouse. It has been measure by Mohamed Belhaj and Thomas Gineste on both clean and technical silver samples in 2014.

This study presents a round robin comparison of absolute electron yields of conducting and insula... more This study presents a round robin comparison of absolute electron yields of conducting and insulating materials performed in four international laboratories. Measurements are reported for two standard elemental conducting samples with reproducible sample preparation for Au and highly oriented pyrolytic graphite (HOPG). The primary objectives of the study were to determine the consistency and uncertainties of these absolute yields measurements, and to investigate the effects of the similarities and differences of the diverse facilities. In this initial round robin study, HOPG total electron yield results were found to be more reproducible than those for Au. Surface contamination significantly affected the total electron yield, even for relatively inert conductive samples like Au and HOPG.

Ce projet de coopération internationale, développé par l’Université de Cadix (Espagne) et l’U... more Ce projet de coopération internationale, développé par l’Université de Cadix (Espagne) et l’Université de Sfax (Tunisie) a cherché à atteindre le renforcement des capacités des femmes tunisiennes à l’utilisation des technologies et des pratiques communicatives, à travers l’apprentissage transformateur et collaboratif, afin de promouvoir l’égalité de la femme en matière d’accès au savoir, à l’emploi et à l’indépendance économique. Grâce au financement de l’Agence Andalouse de Coopération Internationale pour le Développement (AACID) de la Junta de Andalucía, pendant l’année scolaire 2017-2018 les deux universités ont réussi l’objectif de développer un programme de formation conjointe, en collaboration avec d’autres agents sociaux, à propos des connaissances et aptitudes reliées à l’utilisation de la technologie et le changement social, dès une stratégie de développement endogène et innovateur et dès une pratique solidaire et autonomisé qui contribuent au fait que les femmes tunisiennes deviennent des agents de transformation sociale.Este proyecto de cooperación internacional desarrollado por la Universidad de Cádiz (España) y la Universidad de Sfax (Túnez) ha buscado el logro de contribuir al fortalecimiento de las capacidades de las mujeres tunecinas en el uso de las tecnologías y las prácticas comunicativas a través del aprendizaje transformativo y colaborativo a fin de promover la igualdad de la mujer en el acceso al conocimiento, al empleo y a la independencia económica. Gracias a la financiación otorgada por la Agencia Andaluza de Cooperación Internacional para el Desarrollo (AACID) de la Junta de Andalucía, durante el curso académico 2017-2018 ambas universidades cumplieron el objetivo de desarrollar un programa de capacitación conjunto, en colaboración con otros agentes sociales, sobre conocimientos y habilidades relacionados con el uso de la tecnología y el cambio social, desde una estrategia de desarrollo endógeno e innovador y desde una práctica solidaria y empoderada que contribuyan a que las mujeres tunecinas se conviertan en agentes de transformación social.1-23

Vacuum components of a dipole magnet exposed to the proton beam in the LHC at CERN were extracted... more Vacuum components of a dipole magnet exposed to the proton beam in the LHC at CERN were extracted from the LHC ring during the technical stop 2016 – 2017. Chemical analysis as well as Secondary Electron Yield (SEY) meas- urements were performed on their surface after a month of air exposure, to study possible surface modifications induced by the electron cloud bombardment during operation. The study shows that surfaces exposed to the cloud exhibit a lower maximum SEY and a lower copper hydroxide contribution than the same surface, never exposed to the beam. In addition, carbon graphitization could be detected on one of the LHC extracted components. These three features were previously identified as main characteristics of a copper surface conditioned by electron irradiation. This demonstrates that the LHC extracted components were at least partially conditioned in the accelerator under the effect of electron cloud.

Low energy electrons of few tens of eV may cause Multipactor breakdowns in waveguides driven by t... more Low energy electrons of few tens of eV may cause Multipactor breakdowns in waveguides driven by the Secondary Electron Emission Yield (SEY) of the walls. This risk is lowered by using low emissive surfaces and this topic has been studied experimentally and with numerical simulations. The dependence of the SEY on surface properties is well known. Surface morphology has been widely used to reduce the SEY by forming roughness patterns on the surface. All patterns do not have the same efficiency so their analysis in term of SEY is relevant. Monte-Carlo simulation codes can be used to study the processes behind the SEY. The MicroElec module of GEANT4 has recently been extended with more materials and processes, and validated with experimental data for SEY calculations. In this work, simulation results are shown for a bulk sample capped with different roughness patterns. The effects of the shape parameters on the SEY are studied for typical dimensions between 20 μm and 100 μm. The results...

IEEE Transactions on Microwave Theory and Techniques, 2021

Multipactor prediction methods are of high relevance for the space industry in order to prevent i... more Multipactor prediction methods are of high relevance for the space industry in order to prevent its appearance during the design phase of RF high-power components. Up to the present time, prediction for multicarrier signals has been covered by an empirical rule, the 20-gap-crossing rule (20GCR), proposed in the 2003 version of the multipactor standard published by the European Cooperation for Space Standardization (ECSS). The 20GCR has been widely used by the space industry, although some studies have demonstrated that it might be inaccurate in some situations. The latest version of the ECSS multipactor standard, published in 2020, presents two novel methods for multipactor prediction with multicarrier signals: the pulsed method and the envelope sweep (ES) method, both simple, accurate enough, and suitable for industry standards. While the pulsed model is a simple and fast method based on a 1-D analytical theory, the ES method is more accurate and able to deal with real 3-D microwave structures. This article details both multipactor prediction methods, as well as their practical validation with a large dataset from previous analytical studies and experimental activities.

Physical Review Accelerators and Beams, 2019

2016 IEEE MTT-S International Microwave Symposium (IMS), 2016

Radio-frequency (RF) systems used in vacuum can be damaged by electronic avalanches triggered by ... more Radio-frequency (RF) systems used in vacuum can be damaged by electronic avalanches triggered by the multipactor effect. This undesirable phenomenon can appear for RF components used in space communication payloads as well as in experimental fusion devices, among others. To determine the multipactor breakdown threshold, expensive multipactor experimental tests can be made or multipactor simulations can be performed. This second method uses the Total Electron Emission Yield (TEEY) curve as input and the breakdown threshold predicted by simulation highly depends on this curve. Consequently we decided to make a sensitivity study of multipactor breakdown threshold in relation to the TEEY curve variations. We study the silver conductor material with a RF waveguide transformer. Two critical energy regions are found for a small gap waveguide structure: energies around first cross-over energy and energies between the first crossover and the yield maximum. Electron emission data have to be accurate on these regions to get a coherent multipactor threshold. Six TEEY models are benchmarked with respect to their capability to accurately model these regions. Published by AIP Publishing.

IEEE Transactions on Electron Devices, 2015

In this paper, we present a fabrication process of graphene field effect transistors (GFETs) usin... more In this paper, we present a fabrication process of graphene field effect transistors (GFETs) using natural oxidation of aluminum as dielectrics, which provide an alternative fabrication choice for future flexible electronics with the large scale and arbitrary substrates. The high-quality monolayer graphene is preserved by our process, and the mobility up to 3250 cm 2 /Vs is measured after whole device fabrication. GFETs with double bottom-gate structure varying from 300 to 100 nm in gate length have been characterized by both static and dynamic measurements. The total gate capacitances of our device structure are evaluated based on the measurement results of scattering parameters. We report an intrinsic current gain cutoff frequency (f tint of 11 GHz and a maximum oscillation frequency (fmax of 8 GHz in devices with 100 nm gate length. Moreover, both the values of f tint and fmax for different gate lengths are also discussed. Our results indicate that the full process exhibits great potential, especially for graphene-based flexible electronics.

Annales de l’Institut Henri Poincaré D, 2014

We construct a Hopf algebra structure on the space of specified Feynman graphs of a quantum field... more We construct a Hopf algebra structure on the space of specified Feynman graphs of a quantum field theory. We introduce a convolution product and a semigroup of characters of this Hopf algebra with values in some suitable commutative algebra taking momenta into account. We then implement the renormalization described by A. Connes and D. Kreimer in [2] and the Birkhoff decomposition for two renormalization schemes: the minimal subtraction scheme and the Taylor expansion scheme.

SSRN Electronic Journal, 2011

Journal of Physics D: Applied Physics, 2009

A technique for the determination of the total electron emission yield (TEEY) of insulators or in... more A technique for the determination of the total electron emission yield (TEEY) of insulators or insulated conductors, due to low energy electron irradiation is described. It is based on the measurement of the surface potential variation induced by a pulsed electron beam with the help of a high-sensitivity Kelvin probe. The results obtained on a floating copper sample are in

IEEE Transactions on Plasma Science, 2012

ABSTRACT Secondary electron emission is one of the most fundamental problems in spacecraft chargi... more ABSTRACT Secondary electron emission is one of the most fundamental problems in spacecraft charging. An accurate prediction of secondary electron yield at low-energy electron impingement has long been a challenging problem due to both the complexity of the process and the difficulty in carrying out accurate measurements in a vacuum chamber. This paper discusses a correlated modeling and experimental study to investigate the facility effects on secondary electron emission yield measurement in a vacuum chamber.

IEEE Transactions on Plasma Science, 2013

ABSTRACT

The European Physical Journal Applied Physics, 2003

A method is described that allows the trapping charge kinetics in insulating materials during the... more A method is described that allows the trapping charge kinetics in insulating materials during their electron irradiation in a scanning electron microscope (SEM) to be studied and the total trapped charge to be evaluated. The method consists in analyzing the leakage and the displacement currents measured simultaneously, during and after irradiation, using an arrangement adapted to the SEM. The dynamic trapping properties of glass-ceramic are investigated and the time constants for charging and discharging processes are evaluated. By correlating the leakage and displacement currents, the total electron yield σ during irradiation is also determined.