Electrochemical Study of the Corrosion Inhibitory Capacity of Calcined Attapulgite in Reinforced Concrete Medium

The durability of reinforced concrete structures is greatly influenced by the corrosion of the reinforcement. In addition to air pollution related to the repair of corroded structures, chloride ions are the main factors of corrosion of reinforced concrete structures. This study aims to valorize a clay inhibitor against reinforcement corrosion in reinforced concrete. This clay (Attapulgite) was incorporated into reinforced concretes at different percentages of substitution of calcined attapulgite (0%, 5% and 10%) to cement in the formulation. The corrosion inhibitory power of attapulgite is evaluated in reinforced concretes subjected to the action of chloride ions at different intervals in the NaCl solution (1 day, 21 days and 45 days) by electrochemical methods (zero current chronopotentiometry, polarization curves and electrochemical impedance spectroscopy). This study showed that in the presence of chloride ions, the composition based on 10% attapulgite has an appreciable inhibitory effect with an average inhibitory efficiency of 82%.

Evaluation of the Inhibitory Gel Aloe vera against Corrosion of Reinforcement Concrete in NaCl Medium

Most reinforced concrete structures in seaside locations suffer from corrosion damage to the reinforcement, limiting their durability and necessitating costly repairs. To improve their performance and durability, we have investigated in this paper Aloe vera extracts as a green corrosion inhibitor for reinforcing steel in NaCl environments. Using electrochemical methods (zero-intensity chronopotentiometry, Tafel lines and electrochemical impedance spectroscopy), this experimental work investigated the effect of these Aloe vera (AV) extracts on corrosion inhibition of concrete reinforcing bar (HA, diameter 12mm) immersed in a 0.5M NaCl solution. The results show that Aloe vera extracts have an average corrosion-inhibiting efficacy of around 86% at an optimum concentration of 20%.

Image quality assessment based on perceptual grouping

To further explore the human visual system（ HVS）,the perceptual grouping（ PG）, which has been proven to play an important role in the HVS, is adopted to design an effective image quality assessment（ IQA） model. Compared with the existing fixed-window-based models, the proposed one is an adaptive window-like model that introduces the perceptual grouping strategy into the IQA model. It works as follows： first,it preprocesses the images by clustering similar pixels into a group to the greatest extent; then the structural similarity is used to compute the similarity of the superpixels between reference and distorted images; finally, it integrates all the similarity of superpixels of an image to yield a quality score. Experimental results on three databases（ LIVE, IVC and MICT） showthat the proposed method yields good performance in terms of correlation with human judgments of visual quality.

Electrochemical characterization of Ti12Mo5Ta alloys in contact with saline medium

The electrochemical behaviours of unrecrystallized and recrystallized Ti12Mo5Ta alloys were compared with those of the unrecrystallized Ti12 Mo alloy and commercial pure titanium（cp-Ti）. Experiments were carried out using physiological 0.9% NaCl solution（pH 2.3） at 37 °C. Very low passive current densities（in order of 10-6 A/cm2） were obtained from the anodic polarization curves, indicating high resistances of all samples in acidified 0.9% Na Cl solution. Scanning electron microscopy（SEM） was employed to observe the surface morphology and all sample surfaces were identically corroded, no pitting, cracks, or other defects appeared on the sample surfaces after anodic potentiodynamic polarization tests. Equivalent circuit was used for modeling the electrochemical impedance spectroscopy（EIS） data, in order to characterize the sample surface and better understand the effect of Mo and Ta addition on the cp-Ti and the effect of recrystallization. The EIS results confirm that all titanium samples exhibit passivity in physiological 0.9% NaCl solution（pH 2.3） at open circuit potential（polarization resistance is around 105 Ω·cm2）. The corrosion resistance of these samples in physiological 0.9% NaCl solution（pH 2.3） at 37 °C is in the following order of recrystallized Ti12Mo5Ta〉 unrecrystallized Ti12Mo5Ta 〉 unrecrystallized Ti12Mo 〉 cp-Ti.

Characterization of the Omni-Processor Sewage Sludge Ash for Reuse as Construction Material

Omni Processors(OP)are machines which use sludge as a fuel to generate electricity and clean water,but create ash at the same time.In the present study,fly ash and bottom ash are investigated as materials for potential reuse in the construction field.First,the granular size,density and Blaine finesse are determined.Then,the chemical composition and microstructure are obtained by means of X-ray fluorescence and Scanning Electron Microscopy-Energy Dispersive Spectroscopy(SEM-EDS),respectively.Finally,ashes reactivity is determined by two chemical methods(modified Chapelle test,bound water content R3)and a mechanical method(pozzolanic activity index).The characterization results indicate two material types:fly ash similar to cement and bottom ash similar to fine sand.That’s why the mortars mechanical strength with fly ash 0%-30%is better than that with bottom ash at the same rate.Fly ash slightly decreases the mechanical strength of mortars while bottom ash induces a much more significant decrease.

Bending and Free Vibration Analysis of Porous-Functionally-Graded(PFG)Beams Resting on Elastic Foundations

The bending and free vibration of porous functionally graded(PFG)beams resting on elastic foundations are analyzed.The material features of the PFG beam are assumed to vary continuously through the thickness according to the volume fraction of components.The foundation medium is also considered to be linear,homogeneous,and isotropic,and modeled using the Winkler-Pasternak law.The hyperbolic shear deformation theory is applied for the kinematic relations,and the equations of motion are obtained using the Hamilton’s principle.An analytical solution is presented accordingly,assuming that the PFG beam is simply supported.Comparisons with the open literature are implemented to verify the validity of such a formulation.The effects of the elastic foundations,porosity volume percentage and span-to-depth ratio are finally discussed in detail.

Design of Printed Dipole Array for Omnidirectional Radiation Pattern

In this paper, we describe 2 kinds of printed dipole arrays and compare the performances of these arrays in term of reflexion coefficient, radiation pattern and dimensions. It is interesting to design array in order to obtain better performances in term of omnidirectional radiation pattern in comparison with single element. We choose this elementary source in order to obtain compact array with good performances. These antenna arrays are designed to have omnidirectional radiation pattern with horizontal polarization. We present an application dedicated to compact base station in the last section.

Design of Reconfigurable Band Notches Antenna for Cognitive Radio Applications

In this paper, an antenna with reconfigurable band notches, for cognitive radio applications, is proposed. The antenna can be operated as ultra wideband, and is reconfigurable in terms of the ability to select a notched band in the SRR resonant frequency. The reconfigurable band notches are induced using a band-stop filter based on split-ring resonators (SRRs), and are controlled using electronic switches mounted over the SRRs. For this sake, the design of the band-stop filter is proposed. A prototype of filter is fabricated and measured. The incorporation of a band-stop filter, into a wideband antenna, is then looked into. The proposed antenna is designed and simulated using Ansoft HFSS. A prototype of the antenna is fabricated and measured. A good analogy between simulated and measured results is obtained.

Design of Ellipse Antenna Array for Cellular Phone Localization Systems

This paper describes our contribution in the ANR (Agence Nationale de la Recherche) project called GELOCOM (GEo-LOCalisation de telephOnes Mobiles) managed by the THALES Communications company, dedicated to the emergency localization of cellular phones. This contribution takes place in the field of antennas, with the development of broad-band systems: a circular array of six elements with separated outputs for the receiving part. In this paper, we present the design and the characterization of broad-band double ellipse array antenna. This special structure is chosen in order to obtain a good omnidirectional radiation pattern, enhance the gain and maximize the V/H polarization ratio. In comparison with the already existing antenna systems in the wireless market for similar purposes, the proposed antenna has considerably shown better performance which makes it competitive among other antenna models. For the design and optimization of antennas, we use CST MWS software. The antennas have been designed and successfully measured.

Study of Attapulgite as an Additive in Reinforced Concrete by Substitution of Cement and Its Effects on the Durability Properties of Hardened Concrete

The valorization of Senegalese attapulgite clay in concrete, as a solution against the exhaustion of the cement deposits was studied. In that purpose, attapulgite was first calcined at 800°C to make it reactive and added in concrete by substitution of Portland cement (CEM I 52.5N) at contents of 0, 5 and 10% by conserving a constant water/cement ratio value of 0.65. The effects of the partial replacement of cement by attapulgite on the physicochemical and mechanical properties of the concrete as well as on the steel-concrete bond were examined. For this purpose, the water porosity, the intrinsic permeability and the density of the clay-based concrete were evaluated. Compression, tensile and pull-out tests were carried out to determine the impact of clay on the Young modulus, the compressive and tensile strengths and the steel-concrete bond. This study was completed by a characterization of the pozzolanic reactivity of calcined attapulgite. All the results of these studies were compared with those of Portland cement as a reference. The substitution of cement by attapulgite up to 10% in concrete has only a small influence on its porosity and permeability and confers to the concrete gain in compressive strength of 11%. However, it caused a loss of steel-concrete bond of 10%.

Multi-Band Antenna with Three Folded Monopoles for Mobile Communication Systems

This paper presents the design and the experimental characterization of a new multi-band antenna consisting of three folded monopoles dedicated to mobile communication systems. The originality of this paper is to get the PMR (Professional or Private Mobile Radio) band with the GSM (Global System for Mobile Communications), DCS (Digital Cellular System) and UMTS (Universal Mobile Telecommunications System) bands. The main lobe of the antenna radiates in the zenith direction with a linear polarization over all bands. It is interesting to design the proposed antenna in order to obtain better performances in terms of directive radiation pattern (especially in the PMR band) in comparison with the already existing antenna systems in the wireless market for similar purposes. The prototype was studied with the software CST-MWS (Micro wave studio 2012). The antenna has been designed and successfully measured.

并行嵌入式系统中具有通信竞争任务调度问题的高级列表调度方法

现代嵌入式系统正在向使用多核或多处理器进行并行处理的方向发展.针对并行嵌入式系统中具有通信竞争情况下的任务调度问题,文中提出3项高级技术以提高列表调度方法的性能.首先使用5组(已存在的两组和新提出的3组)节点等级作为节点优先权来生成节点列表;然后使用关键子节点技术来改善调度过程中处理器的选择;最后使用通信延迟技术扩大通信连接线上的空闲时间区间.文中还给出了组合使用这3项技术的高级动态列表调度方法.实验结果表明,在中等通信代价和高通信代价的情况下,组合高级动态方法能够有效地缩短调度长度,可以在通信代价很高时通过优化使用硬件资源使调度结果加速高达80%.

From individual elements to macroscopic materials: in search of new superconductors via machine learning

An approach to supervised classification and regression of superconductive materials is proposed which builds on the DeepSet technology.This enables us to provide the chemical constituents of the examined compounds as an input to the algorithm,while avoiding artefacts that could originate from the chosen ordering in the list.The performance of the method are successfully challenged for both classification(tag a given material as superconducting)and regression(quantifying the associated critical temperature).We then searched through the International Mineralogical Association list with the trained neural network.Among the obtained superconducting candidates,three materials were selected to undergo a thorough experimental characterization.Superconductivity has been indeed confirmed for the synthetic analogue of michenerite,PdBiTe,and observed for the first time in monchetundraite,Pd2NiTe2,at critical temperatures in good agreement with the theory predictions.This latter is the first certified superconducting material to be identified by artificial intelligence methodologies.

Anharmonic electron-phonon coupling in ultrasoft and locally disordered perovskites

Anharmonicity and local disorder(polymorphism)are ubiquitous in perovskite physics,inducing various phenomena observed in scattering and spectroscopy experiments.Several of these phenomena still lack interpretation from first principles since,hitherto,no approach is available to account for anharmonicity and disorder in electron–phonon couplings.Here,relying on the special displacement method,we develop a unified treatment of both and demonstrate that electron–phonon coupling is strongly influenced when we employ polymorphous perovskite networks.We uncover that polymorphism in halide perovskites leads to vibrational dynamics far from the ideal noninteracting phonon picture and drives the gradual change in their band gap around phase transition temperatures.We also clarify that combined band gap corrections arising from disorder,spin-orbit coupling,exchange–correlation functionals of high accuracy,and electron–phonon coupling are all essential.Our findings agree with experiments,suggesting that polymorphism is the key to address pending questions on perovskites’technological applications.

Primitive to conventional geometry projection for efficient phonon transport calculations

The primitive Wigner-Seitz cell and corresponding first Brillouin zone(FBZ)are typically used in calculations of lattice vibrational and transport properties as they contain the smallest number of degrees of freedom and thus have the cheapest computational cost.However,in complex materials,the FBZ can take on irregular shapes where lattice symmetries are not apparent.Thus,conventional cells(with more atoms and regular shapes)are often used to describe materials,though dynamical and transport calculations are more expensive.Here we discuss an efficient anharmonic lattice dynamic method that maps conventional cell dynamics to primitive cell dynamics based on translational symmetries.Such symmetries have not been utilized in typical lattice dynamical calculations.This leads to phase interference conditions that act like conserved quantum numbers and a conservation rule for phonon scattering that is hidden in conventional dynamics which significantly reduces the computational cost.We demonstrate this method for phonon transport in a variety of materials with inputs from first-principles calculations and attribute its efficiency to reduced scattering phase space and fewer summations in scattering matrix element calculations.

High-consistency proton exchange membrane fuel cells enabled by oxygen-electron mixed-pathway electrodes via digitalization design

Proton exchange membrane(PEM)fuel cell has been regarded as a promising approach to the decarbonization and diversification of energy sources.In recent years,durability and cost issues of PEM fuel cells are increasingly significant with the rapid increase of power density.However,the failure to maintain the cell consistency,as one major cause of the above issue,has attracted little attention.Therefore,this study intends to figure out the underlying cause of cell inconsistency and provide solutions to it from the perspective of multi-physics transport coupled with electrochemical reactions.The PEM fuel cells with electrodes under two compression modes are firstly discussed to fully explain the relationship of cell performance and consistency to electrode structure and multi-physics transport.The result indicates that one main cause of cell inconsistency is the intrinsic conflict between the separated transport and cooperated consumption of oxygen and electron throughout the active area.Then,a mixed-pathway electrode design is proposed to reduce the cell inconsistency by enhancing the mixed transport of oxygen and electron in the electrode.It is found that the mixing of pathways in electrodes at under-rib region is more effective than that at the under-channel region,and can achieve an up to 40%reduction of the cell inconsistency with little(3.3%)sacrificed performance.In addition,all the investigations are implemented based on a self-developed digitalization platform that reconstructs the complex physical–chemical system of PEM fuel cells.The fully observable physical information of the digitalized cells provides strong support to the related analysis.

Electron–phonon physics from first principles using the EPW code

EPW is an open-source software for ab initio calculations of electron–phonon interactions and related materials properties.The code combines density functional perturbation theory and maximally localized Wannier functions to efficiently compute electron–phonon coupling matrix elements,and to perform predictive calculations of temperature-dependent properties and phonon-assisted quantum processes in bulk solids and low-dimensional materials.Here,we report on significant developments in the code since 2016,namely:a transport module for the calculation of charge carrier mobility under electric and magnetic fields using the Boltzmann transport equation;a superconductivity module for calculations of phonon-mediated superconductors using the anisotropic multi-band Eliashberg theory;an optics module for calculations of phonon-assisted indirect transitions;a module for the calculation of small and large polarons without supercells;and a module for calculating band structure renormalization and temperature-dependent optical spectra using the special displacement method.For each capability,we outline the methodology and implementation and provide example calculations.