Porous Si/Cu6Sn5/C composite containing native oxides as anode material for lithium-ion batteries

Journal of Materials Science: Materials in Electronics - Porous Si/Cu6Sn5/C composite containing native oxides was prepared via solid-state mechanical milling and wet chemical etching. This...     

Preparation and luminescence properties of novel K2ZnP2O7: Mn2+ green phosphor

Novel green-emitting phosphors K₂Zn_1???xP₂O₇: x mol% Mn²⁺ have been successfully prepared using classical solid-state reaction method in air atmosphere, doped by different Mn²⁺ ion contents, namely x?=?0.5, 1, 1.25 and 1.5 mol%. The samples were characterized by the thermogravimetric (ATD/ATG/DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), steady and time-resolved photoluminescence techniques. It was found that all K₂Zn_1???xP₂O₇: x mol% Mn²⁺ samples crystallize in the tetragonal phase with P4₂/mnm space group. Upon 425 nm excitation, K₂ZnP₂O₇: Mn²⁺ exhibits an intense broad green asymmetric emission band peaking at 520 nm, owing to the ⁴T₁→⁶A₁(⁶ S) transition of Mn²⁺ ion in K₂ZnP₂O₇. In addition, it is suggested that Mn²⁺ ions occupy more than one symmetry site in the host K₂ZnP₂O₇. The optimal Mn²⁺ ion concentration in K₂ZnP₂O₇:Mn²⁺ phosphor is 1 mol % and with the lifetime 9.81 ms.

     

Understanding Fundamentals and Reaction Mechanisms of Electrode Materials for Na‐Ion Batteries

Development of efficient, affordable, and sustainable energy storage technologies has become an area of interest due to the worsening environmental issues and rising technological dependence on Li‐ion batteries. Na‐ion batteries (NIBs) have been receiving intensive research efforts during the last few years. Owing to their potentially low cost and relatively high energy density, NIBs are promising energy storage devices, especially for stationary applications. A fundamental understanding of electrode properties during electrochemical reactions is important for the development of low cost, high‐energy density, and long shelf life NIBs. This Review aims to summarize and discuss reaction mechanisms of the major types of NIB electrode materials reported. By appreciating how the material works and the fundamental flaws it possesses, it is hoped that this Review will assist readers in coming up with innovative solutions for designing better materials for NIBs.     

Fuzzy generalized fast marching method for 3D segmentation of brain structures

The aim of this work is to develop a new model for segmentation of brain structures in medical brain MR images. Brain segmentation is a challenging task due to the complex anatomical structure of brain structures as well as intensity nonuniformity, partial volume effects and noise. Generally the structures of interest are of relatively complicated size and have significant shape variations, the structures boundaries may be blurry or even missing, and the surrounding background is full of irrelevant edges. Segmentation methods based on fuzzy models have been developed to overcome the uncertainty caused by these effects. In this study, we propose a robust and accurate brain structures segmentation method based on a combination of fuzzy model and deformable model. Our method breaks up into two great parts. Initially, a preliminary stage allows to construct the various information maps, in particular a fuzzy map, used as a principal information source, constructed using the Fuzzy C‐means method (FCM). Then, a deformable model implemented with the generalized fast marching method (GFMM), evolves toward the structure to be segmented, under the action of a normal force defined from these information maps. In this sense, we used a powerful evolution function based on a fuzzy model, adapted for brain structures. Two extensions of our general method are presented in this work. The first extension concerns the addition of an edge map to the fuzzy model and the use of some rules adapted to the segmentation process. The second extension consists of the use of several models evolving simultaneously to segment several structures. Extensive experiments are conducted on both simulated and real brain MRI datasets. Our proposed approach shows promising and achieves significant improvements with respect to several state‐of‐the‐art methods and with the three practical segmentation techniques widely used in neuroimaging studies, namely SPM, FSL, and Freesurfer.     

On the Moser- and super-reduction algorithms of systems of linear differential equations and their complexity

The notion of irreducible forms of systems of linear differential equations with formal power series coefficients as defined by Moser [Moser, J., 1960. The order of a singularity in Fuchs’ theory. Math. Z. 379–398] and its generalisation, the super-irreducible forms introduced in Hilali and Wazner [Hilali, A., Wazner, A., 1987. Formes super-irréductibles des systèmes différentiels linéaires. Numer. Math. 50, 429–449], are important concepts in the context of the symbolic resolution of systems of linear differential equations [Barkatou, M., 1997. An algorithm to compute the exponential part of a formal fundamental matrix solution of a linear differential system. Journal of App. Alg. in Eng. Comm. and Comp. 8 (1), 1–23; Pflügel, E., 1998. Résolution symbolique des systèmes différentiels linéaires. Ph.D. Thesis, LMC-IMAG; Pflügel, E., 2000. Effective formal reduction of linear differential systems. Appl. Alg. Eng. Comm. Comp., 10 (2) 153–187]. In this paper, we reduce the task of computing a super-irreducible form to that of computing one or several Moser-irreducible forms, using a block-reduction algorithm. This algorithm works on the system directly without converting it to more general types of systems as needed in our previous paper [Barkatou, M., Pflügel, E., 2007. Computing super-irreducible forms of systems of linear differential equations via Moser-reduction: A new approach. In: Proceedings of ISSAC’07. ACM Press, Waterloo, Canada, pp. 1–8]. We perform a cost analysis of our algorithm in order to give the complexity of the super-reduction in terms of the dimension and the Poincaré-rank of the input system. We compare our method with previous algorithms and show that, for systems of big size, the direct block-reduction method is more efficient.     

Stabilization via homogeneous feedback controls

In this paper, we provide an explicit homogeneous feedback control with the requirement that a control Lyapunov function exists for an affine control system and satisfies an homogeneous condition. We use a modified version of the Sontag formula to achieve our main goal. Moreover, we prove that the existence of an homogeneous control Lyapunov function for an homogeneous affine system leads to an homogeneous closed-loop system by using the previous feedback control.     

<Emphasis Type="SmallCaps">MiCa</Emphasis>: Lightweight and mobile collaboration across a collaborative editing service in the cloud

Nowadays, we assist to an explosion of mobile applications due to the rapid development of mobile devices, which are becoming the device of choice for people to collaborate with family members, friends and business colleagues and/or customers. Mobile devices (such as smartphones, tablets and laptops) are well-suited for information delivery than sophisticated desktop PCs in many professional areas (e.g. writing reports for disaster management). However, collaboratively editing a shared document in real-time through ad-hoc peer-to-peer mobile networks requires increasing amounts of computation, data storage and network communication. More particularly, preserving the consistency in a decentralized way of the manipulated shared document under constraints of the mobile applications, namely the freshness and the energy consumption, remains still problematic. In this paper, we propose a new cloud service-based approach, called MiCa (Mobile Collaboration in the Cloud), to achieve efficient and scalable real-time editing works by allowing mobile users an online access to abundant computing power and data storage. Our service is a two levels system. The first level provides self-protocol to create clones of mobiles, manage users’ groups and recover failed clones in the cloud. The second level supports safe mechanisms for synchronizing collaborative works in fully decentralized way. On the mobile side, the energy consumption is largely reduced since all procedures for maintaining consistency of shared documents are executed on the clone side. Based on three important criteria (energy consumption, network traffic and responsiveness time), an experimental evaluation demonstrates the efficiency and effectiveness of our service MiCa.     

Optimal control of nonlocal thermistor equations

We are concerned with the optimal control problem of the well known nonlocal thermistor problem, i.e. in studying the heat transfer in the resistor device whose electrical conductivity is strongly dependent on the temperature. Existence of an optimal control is proved. The optimality system consisting of the state system coupled with adjoint equations is derived, together with a characterisation of the optimal control. Uniqueness of solution to the optimality system, and therefore, the uniqueness of the optimal control, is established. The last part is devoted to numerical simulations.     

Toward the heat convection enhancement of nanofluids flowing in a 3D microchannel affected by a nonuniform magnetic field

In the present investigation, the behavior of laminar convective flow and heat transfer in a three-dimensional horizontal square duct using different water-based nanofluids (Fe₃O₄/water, and carbon nanotubes/water) is numerically investigated. The channel is subjected to a periodic partial or full magnetic field. The outer surface is subjected to a constant heat flux density. The problem is numerically solved via the finite volume method with a second-order precision. The numerical simulations covered a range of the Reynolds number 50 ≤ Re ≤ 400, Hartmann number 0 ≤ Ha ≤ 50, and concentration of nanoparticles 0 ≤ ϕ ≤ 0.02 for different modes of the magnetic field application and direction. Examination of the hydrodynamic and thermal behavior shows significant heat transfer performances obtained when applying transversal and partial periodic magnetic fields simultaneously. More precisely, it is found that the favorable protocol improved the heat transfer rate by 85% in the duct flowing by the Ferrofluid at Ha = 50. Furthermore, findings illustrate that the overall heat transfer rate presented in terms of the mean Nusselt number and the highest compromise (heat transfer augmentation-pressure losses diminution) are obtained in the case of Fe₃O₄ nanoparticles for all taken values of Reynolds and Hartmann numbers, whatever the manner and direction of the applied magnetic field.