Investigation of shrinkage behaviour of polyester reinforced by woven glass fabrics

Le moulage de composites a renforts tisses sur des formes complexes ayant une double courbure conduit a un réarrangement complexe des différentes couches du stratifie. Ces changements qui se produisent durant la mise en forme modifient les propriétés mécaniques et thermiques du matériau et créent des niveaux de contraintes et déformations résiduelles difficilement prévisibles. Cette étude vise à prédir les facteurs suivant: les coefficients de retrait des composites tisses, Ie réarrangement des fibres qui s'effectue durant Ie moulage de formes complexes en composite a fibres tissées, ansi que les contraintes et déformations résiduelles qui en découlent. Le coefficient de retrait est estime a partir de la théorie classique des stratifiés et de l'extension non linéaire. La réorientation des fibres et la variation de l'épaisseur des couches constituantes sont prédites en utilisant la méthode du filet à rotules. La variation de l'épaisseur des plis est calculée pour Ie cas d'un moulage avec matrice simple. Les distorsions de la pièce moulée sont calculées avec un modèle par éléments finis qui tient compte du réarrangement complexe des couches. Un modèle pour la caractérisation du comportement mécanique des composites a renfort tisse, base sur Ie modèle mosaïque, est présenté et utilise pour la modélisation de la structure. En étudiant Ie coefficient de retrait, on en déduit que la résine tend a se contracter dans la direction perpendiculaire a la direction des fibres tandis qu'il y a expansion dans la direction des fibres. Pour des lamines fabriques à partir de tissus non-symétriques tels que Ie «satin8» et de la résine polyester ayant durci à la température ambiante, il y a une grande déformation hors du plan du tissu après durcissement. Conséquemment, Ie coefficient de retrait a été déterminé de deux façons : par la théorie classique des stratifiés et aussi par l'extension non linéaire. Les résultats montrent que la prédiction basée sur la solution non-linéaire est conforme au résultat expérimental.Abstract: Forming of fabric composites into complex parts such as double curvature shells leads to complex redistribution and reorientation of fibres in the composite. This study deals with the prediction of the shrinkage coefficient of fabric composite, the fibre reorientation and layer thickness variation during forming of fabric composites as well as the resulting residual stress and deformation after moulding. The shrinkage coefficient is evaluated using the classical laminate theory and the non-linear extension. The fibre reorientation is predicted using the pin-jointed net theory. The layer thickness variation is calculated according to single die moulding. A finite element model using calculated rearrangement of the laminate is generated for the residual distortion prediction of the complex part. A model for the analysis of the mechanical behaviour of fabric composite, based on the mosaic model, is presented and used in the finite element model. The prediction of the rearrangement of the laminate and the distortion were compared to experiments on rounded top cone parts. To study the influence of behaviour of the fabric structures, two different glass polyester fabric composites were used: plain weave composite and 8 harness satin."--Résumé abrégé par UM

Performance Investigation of High-Speed Train OFDM Systems under the Geometry-Based Channel Model

The high-speed of train (HST) in combination with the high carrier frequency of HST systems leads to the severe inter carrier interference (ICI) in the HST orthogonal frequency division multiplexing (HST-OFDM) systems. To avoid the complexity in OFDM receiver design for ICI eliminations, the OFDM system parameters such as symbol duration, signal bandwidth, and the number of subcarriers should be chosen appropriately. This paper aims to propose a process of HST-OFDM system performance investigation to determine these parameters in order to enhance spectral efficiency and meet a given quality-of-service (QoS) level. The signal-to-­interference-­plus-­noise ratio (SINR) has been used as a figure of merit to analyze the system performance instead of signal-to-noise ratio (SNR) as most of recent research studies. Firstly, using the non-stationary geometry-based stochastic HST channel model, the SINR of each subcarrier has been derived for different speeds of the train, signal bandwidths, and number of subcarriers. Consequently, the system capacity has been formulated as the sum of all the single channel capacity from each sub-carrier. The constraints on designing HST-OFDM system parameters have been thoughtfully analyzed using the obtained expressions of SINR and capacity. Finally, by analyzing the numerical results, the system parameters can be found for the design of HST-OFDM systems under different speeds of train. The proposed process can be used to provide hints to predict performance of HST communication systems before doing further high cost implementations as hardware designs

Performance Investigation of High-Speed Train OFDM Systems under the Geometry-Based Channel Model

The high-speed of train (HST) in combination with the high carrier frequency of HST systems leads to the severe inter carrier interference (ICI) in the HST orthogonal frequency division multiplexing (HST-OFDM) systems. To avoid the complexity in OFDM receiver design for ICI eliminations, the OFDM system parameters such as symbol duration, signal bandwidth, and the number of subcarriers should be chosen appropriately. This paper aims to propose a process of HST-OFDM system performance investigation to determine these parameters in order to enhance spectral efficiency and meet a given quality-of-service (QoS) level. The signal-to-­interference-­plus-­noise ratio (SINR) has been used as a figure of merit to analyze the system performance instead of signal-to-noise ratio (SNR) as most of recent research studies. Firstly, using the non-stationary geometry-based stochastic HST channel model, the SINR of each subcarrier has been derived for different speeds of the train, signal bandwidths, and number of subcarriers. Consequently, the system capacity has been formulated as the sum of all the single channel capacity from each sub-carrier. The constraints on designing HST-OFDM system parameters have been thoughtfully analyzed using the obtained expressions of SINR and capacity. Finally, by analyzing the numerical results, the system parameters can be found for the design of HST-OFDM systems under different speeds of train. The proposed process can be used to provide hints to predict performance of HST communication systems before doing further high cost implementations as hardware designs

Combined Therapeutic Plasma Exchange and Continuous Renal Replacement Therapy in Children With Dengue-Associated Acute Liver Failure and Shock Syndrome: Single-Center Cohort From Vietnam

Objectives: Pediatric acute liver failure (PALF) is a fatal complication in patients with severe dengue. To date, clinical data on the combination of therapeutic plasma exchange (TPE) and continuous renal replacement therapy (CRRT) for managing dengue-associated PALF concomitant with shock syndrome are limited. Design: Retrospective cohort study (January 2013 to June 2022). Patients: Thirty-four children. Setting: PICU of tertiary Children's Hospital No. 2 in Vietnam. Interventions: We assessed a before-versus-after practice change at our center of using combined TPE and CRRT (2018 to 2022) versus CRRT alone (2013 to 2017) in managing children with dengue-associated acute liver failure and shock syndrome. Clinical and laboratory data were reviewed from PICU admission, before and 24 h after CRRT and TPE treatments. The main study outcomes were 28-day in-hospital mortality, hemodynamics, clinical hepatoencephalopathy, and liver function normalization. Measurements and main results: A total of 34 children with a median age of 10 years (interquartile range: 7-11 yr) underwent standard-volume TPE and/or CRRT treatments. Combined TPE and CRRT ( n = 19), versus CRRT alone ( n = 15), was associated with lower proportion of mortality 7 of 19 (37%) versus 13 of 15 (87%), difference 50% (95% CI, 22-78; p < 0.01). Use of combined TPE and CRRT was associated with substantial advancements in clinical hepatoencephalopathy, liver transaminases, coagulation profiles, and blood lactate and ammonia levels (all p values < 0.001). Conclusions: In our experience of children with dengue-associated PALF and shock syndrome, combined use of TPE and CRRT, versus CRRT alone, is associated with better outcomes. Such combination intervention was associated with normalization of liver function, neurological status, and biochemistry. In our center we continue to use combined TPE and CRRT rather than CRRT alone.journal articl

Revisiting LARS for Large Batch Training Generalization of Neural Networks

LARS and LAMB have emerged as prominent techniques in Large Batch Learning (LBL), ensuring the stability of AI training. One of the primary challenges in LBL is convergence stability, where the AI agent usually gets trapped into the sharp minimizer. Addressing this challenge, a relatively recent technique, known as warm-up, has been employed. However, warm-up lacks a strong theoretical foundation, leaving the door open for further exploration of more efficacious algorithms. In light of this situation, we conduct empirical experiments to analyze the behaviors of the two most popular optimizers in the LARS family: LARS and LAMB, with and without a warm-up strategy. Our analyses give us a comprehension of the novel LARS, LAMB, and the necessity of a warm-up technique in LBL. Building upon these insights, we propose a novel algorithm called Time Varying LARS (TVLARS), which facilitates robust training in the initial phase without the need for warm-up. Experimental evaluation demonstrates that TVLARS achieves competitive results with LARS and LAMB when warm-up is utilized while surpassing their performance without the warm-up technique

Privacy-Preserving Schema Reuse

As the number of schema repositories grows rapidly and several web-based platforms exist to support publishing schemas, \emph{schema reuse} becomes a new trend. Schema reuse is a methodology that allows users to create new schemas by copying and adapting existing ones. This methodology supports to reduce not only the effort of designing new schemas but also the heterogeneity between them. One of the biggest barriers of schema reuse is about privacy concerns that discourage schema owners from contributing their schemas. Addressing this problem, we develop a framework that enables privacy-preserving schema reuse. Our framework supports the contributors to define their own protection policies in the form of \emph{privacy constraints}. Instead of showing original schemas, the framework returns an \emph{anonymized schema} with maximal \emph{utility} while satisfying these privacy constraints. To validate our approach, we empirically show the efficiency of different heuristics, the correctness of the proposed utility function, the computation time, as well as the trade-off between utility and privacy

Tag-based Paper Retrieval: Minimizing User Effort with Diversity Awareness

As the number of scientific papers getting published is likely to soar, most of modern paper management systems (e.g. ScienceWise, Mendeley, CiteULike) support tag-based retrieval. In that, each paper is associated with a set of \emph{tags}, allowing user to search for relevant papers by formulating tag-based queries against the system. One of the most critical issues in tag-based retrieval is that user often has difficulties in precisely formulating his information need. Addressing this issue, our paper tackles the problem of automatically suggesting new tags for user when he formulates a query. The set of tags are selected in such a way that resolves query ambiguity in two aspects: \emph{informativeness} and \emph{diversity}. While the former reduces user effort in finding the desired papers, the latter enhances the variety of information shown to user. Through studying theoretical properties of this problem, we propose a heuristic-based algorithm with several salient performance guarantees. We also demonstrate the efficiency of our approach through extensive experimentation using real-world datasets

Towards Enabling Schema Reuse with Privacy Constraints

As the number of schema repositories grows rapidly and several web-based platforms exist to support publishing schemas, \emph{schema reuse} becomes a new trend. Schema reuse is a methodology that allows users to create new schemas by copying and adapting existing ones. This methodology supports to reduce not only the effort of designing new schemas but also the heterogeneity between them. One of the biggest barriers of schema reuse is privacy concerns that discourage the participants from contributing their schemas. Addressing this problem, we develop a framework that enables privacy-preserving schema reuse. To this end, our framework supports users to define their own protection policies in the form of \emph{privacy constraints}. Instead of showing original schemas, the framework returns an \emph{anonymized schema} with maximal \emph{utility} while satisfying these privacy constraints. To validate our approach, we empirically show the efficiency of different heuristics, the correctness of the proposed utility function, the computation time, as well as the trade-off between utility and privacy

Female leadership, internet use, and performance of agricultural cooperatives in Vietnam

Supporting agricultural cooperatives might contribute to the livelihood improvement of many small-scale farmers in developing countries. This research examines the factors affecting the internet use of agricultural cooperatives with a focus on female leadership, its effects on cooperatives’ economic, social, and innovative performance, and the distributional effects of internet use on economic performance. Our analysis relied on the data of 3,512 agricultural cooperatives collected in 2021 from Vietnam. We addressed the endogeneity issue of internet use in impact assessment by employing an instrumental variable approach. Our results show that female leadership was positively and significantly associated with internet use and that internet use had a positive and significant effect on returns on assets, returns on equity, labor productivity, payment per laborer, contribution to labor union and insurance per laborer, and innovation in products of agricultural cooperatives. In addition, unconditional quantile regressions show that internet use in agricultural cooperatives exacerbated income inequality. Enhancing female leadership and promoting rural education were recommended to improve agricultural cooperatives’ performance

BATC - A Benchmark for Aggregation Techniques in Crowdsourcing

As the volumes of AI problems involving human knowledge are likely to soar, crowdsourcing has become essential in a wide range of world-wide-web applications. One of the biggest challenges of crowdsourcing is aggregating the answers collected from crowd workers; and thus, many aggregate techniques have been proposed. However, given a new application, it is difficult for users to choose the best-suited technique as well as appropriate parameter values since each of these techniques has distinct performance characteristics depending on various factors (e.g. worker expertise, question difficulty). In this paper, we develop a benchmarking tool that allows to (i) simulate the crowd and (ii) evaluate aggregate techniques in different aspects (accuracy, sensitivity to spammers, etc.). We believe that this tool will be able to serve as a practical guideline for both researchers and software developers. While researchers can use our tool to assess existing or new techniques, developers can reuse its components to reduce the development complexity