Nanocrystalline MgO samples (11.5 and 12.6 nm) derived from two different precursors: characterization and catalytic activity

Decanoic acid/expanded graphite composite phase change materials (DA/EG-PCMs) with high stability and excellent thermal conductivity were fabricated by blending expanded graphite (EG) and decanoic acid (DA). The structure, thermo-physical properties, and the formation mechanism of DA/EG-PCMs were investigated. The obtained results demonstrate that EG exhibits a network-like porous structure, which is superimposed of 10–50 μm thick graphite sheet. Therefore, DA can be effectively encapsulated through the binding between micropores and the surface adsorption of EG resulting in a relatively smaller DA/EG-PCMs particle with better dispersibility. In addition, adding EG into DA also increased both the thermal stability and the thermal conductivity while decreasing the charging and discharging time, which resulted in improved thermal efficiencies. Although adding EG can negatively influence the phase change behavior of DA, the temperature and enthalpy of phase change were still as high as 34.9 °C and 153.1 J g^?1, respectively. Based on a combination of experimental results and a comprehensive analysis of the phase transformation kinetics, it is concluded that DA/EG-PCMs with 10 mass% EG with improved thermal properties can meet the requirements for efficient temperature control in low-to-medium environments.     

Étude de la thermogravitation dans une couche fluide horizontaleStudy of thermogravitation in a horizontal fluid layer

We propose an analytical and numerical study of the combined action of the thermodiffusion and the convection in a binary mixture. The combination of these two phenomena is called thermogravitational diffusion. We are interested in quantifying the separation in a horizontal parallelepipedic cavity filled with a binary mixture and subjected to a constant horizontal temperature gradient on the two horizontal walls, the other walls being thermally insulated and impermeable. This new procedure is different from the classical one where the cavity is vertical and differentially heated on the two vertical walls. To cite this article: B. Elhajjar et al., C. R. Mecanique 334 (2006).     

On a Free Boundary Problem

This paper considers a discontinuous semilinear elliptic problem: \[ -\Delta u=g(u)H(u-\mu )\quad \text{in }\Omega,\qquad u=h\quad \text{on }% \partial \Omega, \] −Δu=g(u)H(u−μ) in Ω, u=h on ∂Ω, where H is the Heaviside function, μ a real parameter and Ω the unit ball in ℝ². We deal with the existence of solutions under suitable conditions on g, h, and μ. It is shown that the free boundary, i.e. the set where u=μ, is sufficiently smooth.     

Impacts of Gum Arabic and Polyvinylpyrrolidone (PVP) with Salicylic Acid on Peach Fruit (Prunus persica) Shelf Life

Peaches are grown in many Egyptian orchards for local and global fresh market sales. The interior fruit tissue breakdown (IFTB), often resulting in decayed peaches, is a severe problem during marketing. Therefore, to minimize FTB of peaches, in this study, gum arabic (GA) and polyvinylpyrrolidone (PVP) were mixed with different concentrations of salicylic acid (SA) (0, 1, and 2 mM) and were applied as edible coating to extend the shelf life of peach fruits. Mature peaches were selected and harvested when peaches reached total soluble solid content (SSC: 8.5%) and fruit firmness of about 47 N. Fruits were coated and stored at room temperature (26 ± 1 °C and air humidity 51 ± 1%) for 10 days during two seasons: 2020 and 2021. Fruit coated with GA/PVP-SA 2 mM showed a significant (p < 0.05) inhibition in degrading enzyme activities (CWDEs), such as lipoxygenase (LOX), cellulase (CEL), and pectinase (PT), compared to uncoated and coated fruits during the shelf-life period. Hence, cell wall compartments were maintained. Consequently, there was a reduction in browning symptoms in fruits by inhibiting polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities. Thus, the fruit skin browning index showed almost no symptoms. The lipid peroxidation process and ionic permeability declined as well. The result suggests that, by applying GA/PVP-SA 2 mM as an edible coating, fruit tissue breakdown can be minimized, and the shelf life of peach can be extended up to 10 days without symptoms of tissue breakdown.     

Acquisition of stability data for pesticides in water sample through proficiency tests

Accreditation and Quality Assurance - In the framework of a proficiency test for multiresidue determination, three water samples, coming from the same batch, were sent to each of the 25...     

Multifunctional Electrocatalytic Cathodes Derived from Metal–Organic Frameworks for Advanced Lithium-Sulfur Batteries

The rechargeable lithium-sulfur (Li-S) battery is a promising candidate for the next generation of energy storage technology, owing to the high theoretical capacity, high specific energy density, and low cost of electrode materials. The main drawbacks in the development of long-life Li-S batteries are capacity fading and the sluggish kinetics at the cathode caused by the polysulfides shuttle. These limitations are addressed through the design of novel nanocages containing cobalt phosphide (CoP) nanoparticles embedded in highly porous nitrogen-doped carbon (CoP-N-GC) by thermal annealing of ZIF-67 in a reductive atmosphere followed by a phosphidation step using sodium hypophosphite. The CoP nanoparticles, with large surface area and uniform homogeneous distribution within the N-doped nanocage graphitic carbon, act as electrocatalysts to suppress the shuttle of soluble polysulfides through strong chemical interactions and catalyze the sulfur redox. As a result, the S@CoP-N-GC electrode delivers an extremely high specific capacity of 1410 mA h g⁻¹ at 0.1 C (1 C=1675 mA g⁻¹) with an excellent coulombic efficiency of 99.7 %. Moreover, capacity retention from 864 to 678 mA h g⁻¹ is obtained after 460 cycles with a very low decay rate of 0.046 % per cycle at 0.5 C. Therefore, the combination of the CoP catalyst and polar conductive porous carbon effectively stabilizes the sulfur cathode, enhancing the electrochemical performance and stability of the battery.     

Ferromagnetism,half-metallicity and spin-polarised electronic structures characterisation insights in Ca1−xTixO

ABSTRACT

In this study, we have computed the structural, electronic and half-metallic ferromagnetic properties of Ca_1?xTi_xO compounds at concentrations x?=?0.125, 0.25, 0.5 and 0.75 by employing the first-principle approaches of density functional theory. The generalised gradient approximation of Wu and Cohen (GGA-WC) is used to calculate the structural parameters, whereas the electronic structures and magnetic properties are characterised by the accurate Tran–Blaha-modi?ed Becke–Johnson potential (TB-mBJ). The lattice constant, bulk modulus and indirect gap of CaO are in good agreement with other theoretical and experimental results. The Ca_0.25Ti_0.75O at x?=?0.75 has metallic ferromagnetic nature. The Ca_0.875Ti_0.125O, Ca_0.75Ti_0.25O and Ca_0.50Ti_0.50O compounds have total magnetic moments of 2?μ_B per Ti atom with a half-metallic character, a spin polarisation of 100% and a large half-metallic gap of 1.345?eV for x?=?0.125. Therefore, the Ca_1?xTi_xO material with a low concentration of Ti is a true half-metallic ferromagnet and seems to be a promising candidate for semiconductor spintronics.     

Silicene structures on silver surfaces

In this paper we report on several structures of silicene, the analog of graphene for silicon, on the silver surfaces Ag(100), Ag(110) and Ag(111). Deposition of Si produces honeycomb structures on these surfaces. In particular, we present an extensive theoretical study of silicene on Ag(111) for which several recent experimental studies have been published. Different silicene structures were obtained only by varying the silicon coverage and/or its atomic arrangement. All the structures studied show that silicene is buckled, with a Si-Si nearest neighbor distance varying between 2.28 and 2.5 ?. Due to the buckling in the silicene sheet, the apparent (lateral) Si-Si distance can be as low as 1.89 ?. We also found that for a given coverage and symmetry, one may observe different scanning tunneling microscopy images corresponding to structures that differ by only a translation.