Etude de l’effet de la couche limite sur les profils de vitesse du béton pompé

The rheological properties of concrete are significantly influencing the relation between pumping pressure and discharge rate. The concrete rheology is often characterized by a rheological law in stationary conditions (time independent), giving the evolution of shear stresses as a function of shear rate. In case of traditional concrete, this evolution is typically described by a Bingham model, while for a self-compacting concrete with low water/powder ratio, the evolution often becomes non-linear and can be described by a modified Bingham or Herschel-Bulkley model, considering shear-thickening. In these models, a critical shear stress is typically considered above which the concrete starts to flow. Furthermore, a consistency parameter is considered (and in case of non-linear behavior also an index) to describe the intensity of the evolution. As a consequence, the relation between pressure and discharge rate can be linear or non-linear, depending on the concrete pumped. As the rheological parameters of the concrete are directly relevant for the prediction of the pumping pressure, the accurate measurement of these parameters is a challenging task. As the rheological properties of concrete cannot be directly measured as a physical quantity, concrete rheometers can only be used to determine the rheological parameters in an indirect way, by measuring other physical values like speed, couple or pressure. Different methods can be applied in order to convert the measured physical values to obtain the rheological properties. The most direct method consist of calibrating the rheometers by testing materials with known rheological parameters. A higher precision in this approach can be obtained by testing a higher number of known materials. However, in order to cover the whole range of rheological properties of concrete, a very high number of known materials would have to be tested, which would thus become very cumbersome. Instead of performing this calibration in an experimental way, it can be done in a numerical way. This kind of numerical calibration is the topic of chapter 2 of the doctoral thesis. Besides the rheology of the concrete, tribology is also an important factor determining the pumping characteristics. Tribology enables to characterize the behavior of concrete in the interface with the surface of the pumping pipe. For traditional concrete with high yield stress, the flow of concrete in the pumping pipe is dominated by the slip layer or lubrication layer near the surface, while the bulk of the concrete is flowing as a plug. This slip layer can only be formed due to shear stresses in this area, and is considered to be the consequence of three phenomenons: geometrical wall effect, structural breakdown, and dynamic segregation. These phenomenons induce a reduction of the viscosity of the concrete within a layer of a few millimeter near the surface of the pumping pipe. As a result, a non-homogeneous flow is induced. Due to the occurrence of the slip layer, an additional speed component is added to the speed profile already induced by shear of the concrete. In order to characterize the concrete behavior near the surface, tribometers are being used, simulating the relative movement between concrete and the surface. In case of traditional concrete, with high yield stress, due to the relative movement only the slip layer is sheared, while the bulk concrete is not sheared. In this case, the use of tribometers results in a yield stress and a viscous constant of the slip layer. These two parameters enable to define a linear relation between shear stress and shear rate in the interface. Meanwhile, in case of self-compacting concrete, the concrete is also sheared, leading to very complicated tribology measurements. For this reason, it is very difficult to characterize the behavior of self-compacting concrete near the interface by means of a tribometer. This situations complicates the prediction of the relation between pumping pressure and discharge rate. In order to characterize and quantify the effect of the slip layer, an experimental method enabling the measurement of the velocity profile in the flowing concrete in an open pipe has been developed. By measuring the velocity profile, it is possible to determine the thickness of the slip layer and the velocities in the slip layer. An experimental research program studying the effect of the mix design on the slip layer thickness has been carried out. An experimental method to sample the material of the slip layer has been developed in order to determine its rheological properties. This study, performed on self-compacting concrete, enables to relate the rheology of the slip layer to the rheology of the bulk concrete. Finally, the experimental results are implemented in a numerical simulation method. The results of the numerical simulation enable to validate the experimental methods and the obtained experimental results. Based on the available rheological models like the Bingham model, modified Bingham model or Herschel-Bulkley model, it is possible to predict the relation between the pressure gradients and the discharge rate, considering the Poiseuille formula for a laminar flow in a circular pipe. Knowing the thickness of the slip layer and the relation between rheological properties of slip layer and bulk concrete, it is possible to predict the relation between pumping pressures and discharge rates. A numerical application has been performed in order to compare the numerical results with the experimental results obtained within a series of previously performed pumping tests available in literature

Analyzing Effects of Institutional Quality on Banking Stability: Evidence from Asean Countries

Purpose: The aim of this study is to examine the effect of institutional quality on bank stability using bank-level data from 2010 to 2020.   Theoretical framework: The study considers institutions from the perspective of governance institutions. Accordingly, the concept of government institutions is related to the country's organizational foundation in terms of governance, implying institutional quality.   Design/methodology/approach: The study uses GMM method and also choose the Zscore as the primary variable for bank stability.   Findings: The results show that institutional quality increases the stability of banks. Moreover, with the threshold model, the results show that countries with institutional quality above the threshold will increase the stability of banks. In addition, macroeconomic and banking characteristics variables such as total assets, income diversification, quality of control, inflation, and GDP growth rate have a high significance in the model.   Research, Practical & Social implications: The study shows The study's empirical results have specific policy implications for the Government in implementing policies related to institutional quality to improve bank stability.   Originality/value:   there are not many researches done to investigate institutional quality to improve bank stability. Moreover, from economic crisis, the matter of banking stability is among main concerns of many researches. Second, previous researches just focus on the aspect of corruption and ignore other aspects or other factors. That’s why authors conduct this research

Jamming Signal Cancellation by Channel Inversion Power Control for Preserving Covert Communications, Journal of Telecommunications and Information Technology, 2023, nr 2

Uninformed jammers are used to facilitate covert communications between a transmitter and an intended receiver under the surveillance of a warden. In reality, the signals the uniformed jammer emits to make the warden’s decision uncertain have inadvertently interfered with the detection of the intended receiver. In this paper, we apply truncated channel inversion power control (TCIPC) to both the transmitter and the uninformed jammer. The TCIPC scheme used on the uninformed jammer may help the intended receiver remove jamming signals using the successive interference cancellation (SIC) technique. Under the assumption that the warden knows the channel coefficient between two intended transceivers and achieves the optimal detection power threshold, we form the optimization problem to maximize the effective transmission rate (ETR) under covertness and decoding constraints. With the aim of enhancing covertness-related performance, we achieve the optimal power control parameters and determine system parameter-related constraints required for the existence of these solutions. According to the simulations, the use of the TCIPC scheme on the uninformed jammer significantly improves covertness-related performance in comparison to that of random power control (RPC) and constant power control (CPC) schemes. In addition, simulation results show that, for the TCIPC scheme: 1) the maximum ETR tends to converge as the transmitter’s or the uninformed jammer’s maximum transmit power increases, and 2) there exists an optimal value of the transmitter’s predetermined transmission rate to achieve the optimal performance

An Approximate Evaluation of BER Performance for Downlink GSVD-NOMA with Joint Maximum-likelihood Detector, Journal of Telecommunications and Information Technology, 2022, nr 3

Generalized Singular Value Decomposition (GSVD) is the enabling linear precoding scheme for multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) systems. In this paper, we extend research concerning downlink MIMO-NOMA systems with GSVD to cover bit terror rate (BER) performance and to derive an approximate evaluation of the average BER performance. Specifically, we deploy, AT the base station, the well-known technique of joint-modulation to generate NOMAsymbols and joint maximum-likelihood (ML) to recover the transmitted data at end user locations. Consequently, the joint ML detector offers almost the same performance, In terms of average BER as ideal successive interference cancellation. Next, we also investigate BER performance of other precoding schemes, such as zero-forcing, block diagonalization, and simultaneous triangularization, comparing them with GSVD. Furthermore, BER performance is verified in different configurations in relation to the number of antennas. In cases where the number of transmit antennas is greater than twice the number of receive antennas, average BER performance is superior

A Murnaghan-Nakayama rule for Grothendieck polynomials of Grassmannian type

We consider the Grothendieck polynomials appearing in the K-theory of Grassmannians, which are analogs of Schur polynomials. This paper aims to establish a version of the Murnaghan-Nakayama rule for Grothendieck polynomials of the Grassmannian type. This rule allows us to express the product of a Grothendieck polynomial with a power sum symmetric polynomial into a linear combination of other Grothendieck polynomials.Comment: 10 pages, 7 figure

Analyzing surface EMG signals to determine relationship between jaw imbalance and arm strength loss

BACKGROUND: This study investigated the relationship between dental occlusion and arm strength; in particular, the imbalance in the jaw can cause loss in arm strength phenomenon. One of the goals of this study was to record the maximum forces that the subjects can resist against the pull-down force on their hands while biting a spacer of adjustable height on the right or left side of the jaw. Then EMG measurement was used to determine the EMG-Force relationship of the jaw, neck and arms muscles. This gave us useful insights on the arms strength loss due to the biomechanical effects of the imbalance in the jaw mechanism. METHODS: In this study to determine the effects of the imbalance in the jaw to the strength of the arms, we conducted experiments with a pool of 20 healthy subjects of both genders. The subjects were asked to resist a pull down force applied on the contralateral arm while biting on a firm spacer using one side of the jaw. Four different muscles – masseter muscles, deltoid muscles, bicep muscles and trapezoid muscles – were involved. Integrated EMG (iEMG) and Higuchi fractal dimension (HFD) were used to analyze the EMG signals. RESULTS: The results showed that (1) Imbalance in the jaw causes loss of arm strength contra-laterally; (2) The loss is approximately a linear function of the height of the spacers. Moreover, the iEMG showed the intensity of muscle activities decreased when the degrees of jaw imbalance increased (spacer thickness increased). In addition, the tendency of Higuchi fractal dimension decreased for all muscles. CONCLUSIONS: This finding indicates that muscle fatigue and the decrease in muscle contraction level leads to the loss of arm strength

Newton polytope of good symmetric polynomials

We introduce a general class of symmetric polynomials that have saturated Newton polytope and their Newton polytope has integer decomposition property. The class covers numerous previously studied symmetric polynomials.Comment: 10 pages, 3 figure

Influence Of Fabrication Condition on the Microstructural and Optical Properties of Lead-Free Ferroelectric Bi0.5_{0.5}Na0.5_{0.5}TiO3_{3} Materials

Lead-free ferroelectric materials have attracted considerable attention due to the increasing potential application in environmental benign materials. Among lead-free ferroelectric materials, the Bi0.5Na0.5TiO3 (BNT) materials were more studied because it exhibited the good ferroelectric and piezoelectric properties which could be promising candidate materials replacing Pb(Zr,Ti)O3. In this work, the lead-free ferroelectric BNT materials were synthesized by sol-gel method. The effects of fabrication process to microstructural and optical properties were studied which includes Na precursor concentration and calcining temperature. The result indicated that the Na precursor concentration were higher 40 mol.% and the calcining temperature

Impact of Vocational Education and Training On Decent Job Opportunities Regarding Information and Communication Technology

Vocational education and training plays a crucial part in the creation of decent job. The fast growth of information and communication technology (ICT) during the past ten years has increased work opportunities for laborers. This research uses the yearly labor force survey data to study the impact of vocational education and training on decent job opportunities for employees in the context of Vietnam's information and communication technology development. The logit model results indicate that the 2020 rate of decent jobs is still low, at approximately 25.6 percent. However, vocational education and training and the advancement of ICT positively affect decent job opportunities. This long-lasting impact affects laborers in various areas, regions, and industries. These findings suggest that vocational education and training and ICT must play a significant role in transitioning from precarious to more secure employment, so laborers must acquire professional knowledge and information technology skills

Genetic diversity analysis of black pepper (Piper spp.) with RAPD markers

Black pepper is a well-known export commodity in Vietnam, but pepper production has been decreasing in recent years. The lack of knowledge about the origin and genetic characteristics of pepper varieties may create variety degradation and loss of product quality. Therefore, it is necessary to study the genetic diversity of existing local and imported pepper varieties and effectively propagate and create new varieties with high yields and quality. In this study, RAPD markers were used with 100 RAPD UBC primers to study genetic diversity. Twelve RAPD primers were selected to amplify 39 pepper cultivars, and 40 polymorphic DNA bands were created with sizes ranging from 200 to 1400 bp. Five of the 12 primers amplified all 39 cultivars. The genetic diversity of lines/cultivars in the pepper population is relatively high. The phylogenetic tree of the 39 cultivars has two branches showing similarity ranging from 41.8 to 51%. The first branch includes five pepper individuals, and the second consists of 34 individuals. There is a high diversity among the pepper cultivars in the same population