IDENTIFICATION DES PARAMETRES VISCOELASTIQUE ET VISCOPLASTIQUE D’UN MODELE RHEOLOGIQUE PAR LA TECHNIQUE DES ALGORITHMES GENETIQUES

Le présent travail s’intéresse principalement à l’identification rhéologique des paramètres viscoélastiques et viscoplastiques d’un polymère semi-cristallin, un polyamide 6 en l’occurrence. Le modèle de comportement proposé est un mécanisme analogique composé d’une partie viscoélastique représentée par le modèle de Kelvin-Voigt à élasticité instantanée et une partie viscoplastique décrite par le modèle généralisé de Bingham. Deux variantes du modèle sont étudiées dont la première représente un modèle bilinéaire alors que la seconde est un modèle non linéaire. Le fonctionnement du modèle rhéologique est traduit en équations mathématiques. Un essai de traction à vitesse de déformation constante est mené en vue d’en exploiter les résultats pour l’identification des paramètres du modèle. A cet effet, une fonction objectif permettant de minimiser l’écart entre ces résultats expérimentaux et ceux de la simulation est mise en place. Le modèle de comportement non linéaire étant très compliqué et possédant un grand nombre de paramètres, il est privilégié une identification par analyse inverse basée sur la technique des algorithmes génétiques. Les paramètres viscoélastiques et viscoélastiques, y compris le seuil de plasticité, étant identifiés, les résultats expérimentaux et simulés sont comparés et discutés. Le modèle bilinéaire décrit le comportement de façon peu précise mais avec un cout de calcul réduit. Par ailleurs, une bonne concordance a été constatée entre la simulation et l’expérimentation dans la variante non linéaire à l’issue d’une étape de réidentification fondée sur une identification préalable

Self-Stabilizing Byzantine Resilient Topology Discovery and Message Delivery

Traditional Byzantine resilient algorithms use $2f + 1$ vertex disjoint paths to ensure message delivery in the presence of up to f Byzantine nodes. The question of how these paths are identified is related to the fundamental problem of topology discovery. Distributed algorithms for topology discovery cope with a never ending task, dealing with frequent changes in the network topology and unpredictable transient faults. Therefore, algorithms for topology discovery should be self-stabilizing to ensure convergence of the topology information following any such unpredictable sequence of events. We present the first such algorithm that can cope with Byzantine nodes. Starting in an arbitrary global state, and in the presence of f Byzantine nodes, each node is eventually aware of all the other non-Byzantine nodes and their connecting communication links. Using the topology information, nodes can, for example, route messages across the network and deliver messages from one end user to another. We present the first deterministic, cryptographic-assumptions-free, self-stabilizing, Byzantine-resilient algorithms for network topology discovery and end-to-end message delivery. We also consider the task of r-neighborhood discovery for the case in which $r$ and the degree of nodes are bounded by constants. The use of r-neighborhood discovery facilitates polynomial time, communication and space solutions for the above tasks. The obtained algorithms can be used to authenticate parties, in particular during the establishment of private secrets, thus forming public key schemes that are resistant to man-in-the-middle attacks of the compromised Byzantine nodes. A polynomial and efficient end-to-end algorithm that is based on the established private secrets can be employed in between periodical re-establishments of the secrets

To Reach the Light: The Monumental Byzantine Stairs of Caesarea, a Conservation and Restoration Project

Ancient Caesarea has founded in the years 25-10 BC and named after Emperor Augustus. Throughout history, from the early Roman until the Byzantine period, Caesarea was a major city and one of the largest and most important port cities in the Mediterranean. During the Byzantine period, the city encompassed an area three times larger than that delimited by the Herodian wall and became an important center of Christianity. The monumental stairs led to the Byzantine Octagonal Church built upon giant arch above the remains of the enormous Roman stairs of Augustus temple. Stairs led a large number of people from the vast harbor, to the Temple platform. The Byzantine arch located 17 meters from the ancient quay, is 8 meters width and 4-meter long, built with specific technology from local sandstone named Kurkar. The arch fall after the Byzantine period and the staircases severely damaged due to the long exposure of almost 1500 years and environmental conditions such as capillary rise, daily winds carrying sand, high temperature, moisture, salts, and deliberate destruction, for instance, stones robber and collapse parts from the wall. The characteristics of the Kurkar with sustained deterioration and this environmental condition have led to different conservation problems, at various levels of severity erosion, the disintegration in both bonding materials and stones. The conservation measures' purpose is to stop the ongoing weathering process and prevent a deterioration state of the staircases, to restore the arch and stabilize the structure of the stairs to carry 48 tons of the restore arch. The findings of the project show that a suitable solution to ensure effective and sustainable protection of complicated staircases structure from destruction and various weathering condition to carry new massive arch depends on understanding the ancient application of building technologies and techniques, the use of original bonding material, integrated monitoring, and ongoing maintenance

First observations and performance of the RPW instrument onboard the Solar Orbiter mission

The Radio and Plasma Waves (RPW) instrument on the ESA Solar Orbiter mission is designed to measure in situ magnetic and electric fields and waves from the continuum up to several hundred kHz. The RPW also observes solar and heliospheric radio emissions up to 16 MHz. It was switched on and its antennae were successfully deployed two days after the launch of Solar Orbiter on February 10, 2020. Since then, the instrument has acquired enough data to make it possible to assess its performance and the electromagnetic disturbances it experiences. In this article, we assess its scientific performance and present the first RPW observations. In particular, we focus on a statistical analysis of the first observations of interplanetary dust by the instrument’s Thermal Noise Receiver. We also review the electro-magnetic disturbances that RPW suffers, especially those which potential users of the instrument data should be aware of before starting their research work

Maternal mental health during COVID-19 pandemic outbreak: A cross-sectional comparative study

BackgroundAs COVID-19 spread in several countries, social distancing measures was implemented around the world, affecting the quality of lives for millions of people. The impact was more pronounced on vulnerable populations such as pregnant women, who are at even more risk due to their suppressed immune system. Moreover, mental health disorders are more common among pregnant women compared to non-pregnant. This study aims to assess the influence of social isolation measures due to the COVID-19 pandemic on the mental health of women in their third trimester and postpartum.Material and methodsThis is a cross-sectional survey-based study conducted in Khalid University Hospital, Riyadh, Saudi Arabia, between the months of April to May 2021, to explore depression and anxiety levels in females who gave birth during the COVID-19 pandemic. In addition to background demographic data, the survey included Patient Health Questionnaire-9 (PHQ-9) and Generalized Anxiety Disorder Scale-7 (GAD-7) were utilized to detect symptoms of depression and anxiety, respectively.ResultsA total of 283 women were included in this study, almost half of them were ante-natal (n-141) and the rest were post-natal (n = 124). 62.3% were in the age groups of 25–35 years. Based on the PHQ-9 scoring, 65% of the study sample had depression (ranging from mild to severe). Moreover, based on GAD-7 scoring, 49.1% had anxiety (ranging from mild to severe). No association was found between PHQ-9 and GAD-7 scores and different sociodemographic and obstetric factors. Additionally, the mean scores of women infected with COVID-19 vs. women who has never been diagnosed with COVID-19 were closely comparable.ConclusionsWe reported a high prevalence of depression and anxiety among pregnant women during COVID-19 pandemic. Policymakers and health care providers are advised to implement targeted preventive measures for pregnant women to improve mental health in times of epidemics

Fractional Derivative as Fractional Power of Derivative

Definitions of fractional derivatives as fractional powers of derivative operators are suggested. The Taylor series and Fourier series are used to define fractional power of self-adjoint derivative operator. The Fourier integrals and Weyl quantization procedure are applied to derive the definition of fractional derivative operator. Fractional generalization of concept of stability is considered.Comment: 20 pages, LaTe

Author Correction: The genetic legacy of continental scale admixture in Indian Austroasiatic speakers

This Article contains errors in the Methods section, under subsection ‘Samples collection and genotyping’

BepiColombo’s Cruise Phase: Unique Opportunity for Synergistic Observations

The investigation of multi-spacecraft coordinated observations during the cruise phase of BepiColombo (ESA/JAXA) are reported, with a particular emphasis on the recently launched missions, Solar Orbiter (ESA/NASA) and Parker Solar Probe (NASA). Despite some payload constraints, many instruments onboard BepiColombo are operating during its cruise phase simultaneously covering a wide range of heliocentric distances (0.28 AU–0.5 AU). Hence, the various spacecraft configurations and the combined in-situ and remote sensing measurements from the different spacecraft, offer unique opportunities for BepiColombo to be part of these unprecedented multipoint synergistic observations and for potential scientific studies in the inner heliosphere, even before its orbit insertion around Mercury in December 2025. The main goal of this report is to present the coordinated observation opportunities during the cruise phase of BepiColombo (excluding the planetary flybys). We summarize the identified science topics, the operational instruments, the method we have used to identify the windows of opportunity and discuss the planning of joint observations in the future

BepiColombo's Cruise Phase : Unique Opportunity for Synergistic Observations

The investigation of multi-spacecraft coordinated observations during the cruise phase of BepiColombo (ESA/JAXA) are reported, with a particular emphasis on the recently launched missions, Solar Orbiter (ESA/NASA) and Parker Solar Probe (NASA). Despite some payload constraints, many instruments onboard BepiColombo are operating during its cruise phase simultaneously covering a wide range of heliocentric distances (0.28 AU-0.5 AU). Hence, the various spacecraft configurations and the combined in-situ and remote sensing measurements from the different spacecraft, offer unique opportunities for BepiColombo to be part of these unprecedented multipoint synergistic observations and for potential scientific studies in the inner heliosphere, even before its orbit insertion around Mercury in December 2025. The main goal of this report is to present the coordinated observation opportunities during the cruise phase of BepiColombo (excluding the planetary flybys). We summarize the identified science topics, the operational instruments, the method we have used to identify the windows of opportunity and discuss the planning of joint observations in the future.Peer reviewe