Etude numérique statistique des champs locaux de contraintes en surface de polycristaux cubiques et hexagonaux en élasticité

The first stages of fatigue damage in metallic polycrystalline materials are governed by local mechanical field at the grain scale. Fatigue crack initiation is often related to the emergence of persistent slip band at surface.Localization of cyclic plasticity occurs within grains of polycristals in which elastic stress field can be highly heterogeneous due to the granular microstructure and crystalline anisotropic elasticity. The main goal of this study is to evaluate and analyse statistically the stress fields in surface grains of polycristals. In this work, the elasticregime only is considered in order to study the subsequent activation of plastic slip and its variability. The possibleconsequences regarding crack formation are also addressed but in a lesser extent. The methodology is based on fullfield finite element numerical simulation of the elastic response of a set of polycrystalline aggregates in which grains orientation is chosen randomly.The two materials chosen for this study exhibit different characteristics regarding crystal elasticity and slip systems.The first one is an austenitic stainless steels 316L (face centered cubic) and the second one a titanium alloy TA6V(hexagonal close packed). The distribution of resolved shear stress within several sets of surface grains, for different classes of crystal orientation, are analysed in relation to local crystallographic configurations in order to identify those which promote - or prevent from - plastic slip activation. For TA6V, the results suggest in particular that basal slip is activated earlier than prismatic slip. In addition, the simulation strategy has been modified tomodel the presence of some sharp band-like crystallographic textures named “macrozones” whose influence has been qualitatively predicted. Plastic slip activation in TA6V is also studied experimentally. In situ tensile test using SEM has shown the earlier activation of basal slip. Experimental data has been combined with simulated distribution of resolved shear stress in order to estimate the critical resolved shear stress of basal and prismatic slip systems.Les premiers stades d'endommagement par fatigue au sein des matériaux métalliques polycristallins sont pilotés par les champs mécaniques locaux se développant à l'échelle des grains en surface. La formation de bandes de glissement persistantes est souvent à l'origine des fissures de fatigue. Cette localisation de la plasticité cyclique apparaît au sein de grains d'un polycristal dans lequel les champs de contraintes élastiques peuvent être fortement hétérogènes en fonction de la microstructure granulaire et de l'anisotropie élastique cristalline. La majeure partie de ce travail est consacrée à évaluer puis à analyser statistiquement les champs de contraintes au sein des grains de surface de polycristaux. Ce travail s'est concentré sur la réponse élastique des matériaux considérés afin d'étudier l'activation du glissement plastique et sa variabilité, puis, de façon un peu moins directe, ses conséquences vis-à-vis de la formation des fissures de fatigue. La méthodologie retenue est basée sur la simulation numérique en champs complets par éléments-finis de la réponse élastique d'un ensemble d'agrégats polycristallins dont les orientations cristallographiques sont tirées aléatoirement.Deux matériaux très différents du point de vue de l'élasticité cristalline et des systèmes de glissement ont été choisis comme support de l'étude. Le premier est l'acier inoxydable austénitique 316L à structure cubique à faces centrées et le second l'alliage de titane TA6V à structure hexagonale compacte. Les distributions de la cission résolue au sein d'ensembles de grains de surface, par classe d'orientation, sont analysées en relation avec les configurations cristallographiques locales afin d'identifier celles qui favorisent - ou au contraire inhibent - l'activation du glissement plastique. Les résultats obtenus, dans le cas du TA6V, suggèrent notamment une activation plus précoce et importante du glissement basal devant le glissement prismatique. De plus, la stratégie de simulation a été adaptée pour rendre compte de la présence de zones texturées appelées « macrozones » dont l'influence sur l'activation de plasticité peut être qualitativement prédite. L'activation du glissement dans le TA6V est également étudiée expérimentalement par la réalisation d'un essai in situ sous MEB où la précocité du glissement basal est constatée.Cet essai a également permis de caractériser la cinétique d'activation des différents types de glissements. Ces données, couplées aux statistiques des cissions simulées, permettent une estimation de la cission résolue critique sur les 2 types de glissement

Higuchi Fractal Properties of Onset Epilepsy Electroencephalogram

Epilepsy is a medical term which indicates a common neurological disorder characterized by seizures, because of abnormal neuronal activity. This leads to unconsciousness or even a convulsion. The possible etiologies should be evaluated and treated. Therefore, it is necessary to concentrate not only on finding out efficient treatment methods, but also on developing algorithm to support diagnosis. Currently, there are a number of algorithms, especially nonlinear algorithms. However, those algorithms have some difficulties one of which is the impact of noise on the results. In this paper, in addition to the use of fractal dimension as a principal tool to diagnose epilepsy, the combination between ICA algorithm and averaging filter at the preprocessing step leads to some positive results. The combination which improved the fractal algorithm become robust with noise on EEG signals. As a result, we can see clearly fractal properties in preictal and ictal period so as to epileptic diagnosis

Transport Properties of a GaAs/InGaAs/GaAs Quantum Well: Temperature, Magnetic Field and Many-body Effects

We investigate the zero and finite temperature transport properties of a quasi-two-dimensional electron gas in a GaAs/InGaAs/GaAs quantum well under a magnetic field, taking into account many-body effects via a local-field correction. We consider the surface roughness, roughness-induced piezoelectric, remote charged impurity and homogenous background charged impurity scattering. The effects of the quantum well width, carrier density, temperature and local-field correction on resistance ratio are investigated. We also consider the dependence of the total mobility on the multiple scattering effect

Entrepreneurship and Factors Affecting Entrepreneurial Decisions

In recent years, entrepreneurship has become an important topic in both academic and practice to find policies to promote entrepreneurship and contribute to economic development. This chapter first presents some arguments about entrepreneurship based on theoretical and practical approaches to entrepreneurship, digital entrepreneurship, and sustainable entrepreneurship. Second, the presentation of the survey results on factors affecting the business decisions of young entrepreneurs of Vietnam’s generation Y. The results show that nine factors influence the business decisions of young entrepreneurs of the Y generation in Vietnam, such as entrepreneurial education, the background of the family, entrepreneurial ecosystem, knowledge, social valuation, opportunity perception, attitude, business performance, and purposeful entrepreneurial competence. The results highlight the role of entrepreneurship educated, social valuation, perceived opportunity, etc. Hence, to promote success in entrepreneurial entrepreneurship, strengthen entrepreneurial education, and proposed a strategy to complete the entrepreneurial ecosystem

Extracting Fetal Electrocardiogram from Being Pregnancy Based on Nonlinear Projection

Fetal heart rate extraction from the abdominal ECG is of great importance due to the information that carries in assessing appropriately the fetus well-being during pregnancy. In this paper, we describe a method to suppress the maternal signal and noise contamination to discover the fetal signal in a single-lead fetal ECG recordings. We use a locally linear phase space projection technique which has been used for noise reduction in deterministically chaotic signals. Henceforth, this method is capable of extracting fetal signal even when noise and fetal component are of comparable amplitude. The result is much better if the noise is much smaller (P wave and T wave can be discovered)

A Multi-Criteria based Software Defined Networking System Architecture for DDoS-Attack Mitigation

Nowadays, Software-Defined Networking (SDN) has become a promising network architecture in which network devices are controlled in a separate Control Plane (i.e., SDN controller). In a specific aspect, employing SDN in a network offers an attractive network security solution due to its flexibility in building and adding more new software security rules. From another perspective, attack prediction and mitigation, especially for Distributed Denial of Service (DDoS) attacks, are still challenges in SDN environments since a SDN control system works probably slower than a non-SDN one and theSDN controller can become a target of attacks. In this article, at first, we analyze a real traffic use case in order to derive DDoS indicators and thresholds. Secondly, we design an Openflow/SDN-based Attack Mitigation Architecture that is able to quickly mitigate DDoS attacks on the fly. The design solves the existing problems of the Openflow protocol, reducing the traffic volume traversing over the interface between the data plane (switch) and the control plane (SDN controller) and decreasing the buffer size at the Openflow switch. Applying our proposed Fuzzy Logic-based DDoS Mitigation algorithm that deploys multiple criteria for DDoS detection - FDDoM, the system demonstrates the ability to detect and filter 97% of attack flows and reach a False Positive Rate of 5% that are acceptable figures in real system management. The results also show that the network resource which is required to cope and maintain flow entries is 50% reduced during attack time

Ultrasonic-Assisted Cathodic Plasma Electrolysis Approach for Producing of Graphene Nanosheets

In this chapter, we review on the production of graphene by ultrasonic-assisted cathodic plasma electrolysis approach which involves a combination process of conventional electrolysis and plasma at ambient pressure and moderate temperature. Firstly, we review on the techniques for electrochemical preparation of graphene. Then, we briefly describe plasma electrolysis approach for producing of graphene. The mechanism, advantages, and disadvantages of this technique are discussed in detail

Design and Analysis of Ternary m-sequences with Interleaved Structure by d-Transform

Multilevel sequences find more and more applications in modern modulation schemes [4QPSK, 8QPSK,16QAM..]  for the 3G ,4G system air interface [1,2].Furthermore, in modern cryptography they are also widerly used. It is also interesting to point out that the length L of these sequences are composite numbers( L=NS),that means the sequence can be easily implemented by interleaving S subsequences, each of length S.Therefore, the methods to develop multilevel sequence with interleaved structure draw a lot of attentions [3, 4]. In this contribution, a method for design and analysis of ternary m-sequences with interleaved structure is presented, based on the d-transform, Which turns out to be a very effective and versal tool for this purpose. Simulations have been made to verify the theory. We first introduce d-transform and its properties and then work out the procedure to design an interleaving sequence in d-transform. Keywords: d-transform,q-ary sequences, interleaved sequence