Papers by Keyword: Stability

Abstract: The stability of rectangular thin plates of Shape Memory Alloys during the forward martensitic phase transition induced by uniform cooling under constant stresses was studied. A model of the constitutive equations of Shape Memory Alloys describing phase structural deformation and taking into account thermomechanical coupling and resistance asymmetry was used. It was shown within the limits of this model that the structural deformation during the loss of stability could not occur. Analytical solutions obtained for different statements of the stability problem were compared. For some statements the curves separating the areas of stability and instability in the plane of stresses had concave parts were obtained. It was shown that increase of the plate thickness brought about rising the influence of the phase deformation on the stability loss process.

Abstract: Stability of nanolubricants is a basic requirement for heat transfer application since it is directly related to the properties of nanolubricants. However, the particle suspension is the major issue of creating a new nanolubricant. The objective of the present study is to compare the effect of different dispersion methods on the stability of graphene in polyester oil-based lubricant. Nanolubricant are prepared by different two-step method, including magnetic stirrer, overhead stirrer, and sonication. The stability of nanolubricant was measured by sedimentation observation, metallographic microscopy, and zeta potential. The results show that the overhead stirrer method was the most effective at providing a more stable suspension.

Abstract: Recently, perovskite nanocomposites have attracted much ‎attention as active layers due to the relatively high stable efficiency of solar cells based on them. In this ‎paper, we study perovskite nanocomposite layers based on ‎semiconductive/nonconductive molecules or polymers, their deposition methods, properties, and ‎influence on the device performance. We have found that the quality of the ‎perovskite layer (morphology and crystallinity, cross-linked grains, trap states density, as well as ‎conductivity and charge carrier mobility) is strongly affected by various factors ‎related to the additive: such as type (i. e. semiconductive or nonconductive, ‎molecule or polymer), chemical structure (backbone length and ‎molecular weight, functional groups, π system, side chains, donating atoms and basicity), amount,‎ solubility, conductivity, photoactivity, polarity, hydrophobicity, and addition methods. Due to the small amounts added, these additives can lead to slight changes in energy levels, bandgap (E_g), and light absorption ‎properties. Ultimately, using the suitable deposition method and additive at an optimal amount can ‎greatly improve the stability and efficiency of the devices and reduce ‎hysteresis.

Abstract: The inorganic perovskite CsPbBr₃ is a promising candidate for photovoltaic and light-emitting devices, but stability concerns hinder its commercial application. The purpose of this study is to investigate the effect of annealing temperature on the morphology and luminescence stability of inorganic CsPbBr₃ perovskite at 90°C, 100°C, 110°C, and 120°C. The CsPbBr₃ was prepared by Ligand Assisted Reprecipitation (LARP). The TEM images revealed the formation of nanoplatelets of inorganic CsPbBr₃ perovskite with an average particle size of 35 nm. The morphological stability of as-synthesized CsPbBr₃ after annealing at a defined temperature was demonstrated using X-Ray Diffraction characterization and SEM imaging. The crystal structure remains stable with a cubic structure even when heated to 120°C. UV-Vis absorbance and photoluminescence intensity spectra confirmed the luminescence stability of the as-prepared CsPbBr₃ after annealing process.

Abstract: Within the framework of the Economic Community of West African States (ECOWAS) countries power networks interconnection project carried by the West African Power Pool (WAPP), operating guidelines have been defined by WAPP and ECOWAS Regional Electricity Regulatory Authority (ERERA) to ensure efficient operation of the interconnected network. Each operator is obliged to comply with these directives to guarantee the stability and reliability of energy supply to ECOWAS countries. The purpose of this paper is to carry out the study of the power flow on the existing Togo and Benin power transmission network and to propose solutions for compliance with the requirements relating to the voltage level required on the interconnection lines or at connection points with neighboring power network operators. The dynamic stability of generators will also be studied to assess the behavior of the network during major disturbances. CEB (Communauté Electrique du Bénin in french) is the power transmission network operator of the Republic of Togo and the Republic of Benin. After the inventory of CEB transmission and production infrastructure and the consumption report, the model of CEB power network is produced as well as the single-line diagram. The power flow calculation is performed with the Newton-Raphson algorithm and the node voltages were calculated using the Cyme software. From the voltage values obtained at the various nodes and depending on the behavior of each generator, solutions are proposed to improve the voltage plan of the power network in accordance with the recommendations of the Regulatory Authority.

Abstract: Gold nanoparticles (AuNPs) have received considerable attention recently because of their chemical properties and potential applications in the medical field.Monodispersed AuNPs in this paper are successfully synthesized by using some stabilized ligands including 3,5-dinitrobenzoic acid (DNBA) and sodium acetate (SA) dispersible in aqueous media, where NaBH₄ was used as a reducing agent to reduce KAuCl₄ from Au (III) to Au (0).The synthesized AuNPs are characterized by using UV–Vis spectroscopy to evaluate their surface plasmon resonance (SPR) absorption in a wavelength range of 500–650 nm. The size and morphology of AuNPs were determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS), where the results displayed that AuNPs with a strong SPR peak around 530 nm and 536 nm with an average size of 10 ± 1.2 nm and 14.0 ± 0.9 nm at the initial time for both DNBA-AuNP and SA-AuNP respectively. The synthesized AuNPs illustrate perfect chemical stability for more than 24 weeks in an aqueous solution. Therefore, the size of DNBA-AuNP was smaller and most stable than SA-AuNP, which may be due to 2 nitro groups that have resonance with the benzene ring leading to an increase in the stability of AuNPs.The stability of AuNPs in this work was monitored at a range of pH 2-12. Where high stability was showed at pH 6.6 ± 0.5, while the aggregation appears at more than pH 10 and less than pH.3.5.Herein, in this paper AuNPs have shown remarkable results against multi-drug resistance Pseudomonas aeruginosa. AuNP functionalized by SA ligand is shown to have a greater biological effect and be more effective than DNBA-AuNP. Due to the high stability of AuNP prepared in this work, it can be further tested to be an improved choice for more biomedical applications in the future.

Abstract: A novel electrocatalyst has been developed based on polypyrol-carbon nanofiber (PPy-CNF) support material to increase the stability of Pt/ PPy-CNF/GDL electrocatalyst in direct methanol fuel cell (DMFC). A novel conducting polymer (PPy)-CNF nanocomposites was prepared by a solution dispersion technique and used to support platinum nanoparticles. For preparation of catalyst ink, 20 wt.% Pt/PPy-CNF electrocatalyst with a platinum loading of 0.4 mg cm^-2 was prepared by ethylene glycol (EG) method. Physical and electrochemical properties were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) imaging and cyclic voltammetry (CV) experiments. FTIR results prove the existence of PPy in the support. SEM images showed that the one–dimensional CNFs were efficaciously covered by PPy. The TEM characterization revealed that the fine Pt nanoparticles prepared by polyol method were dispersed on the surface of the electrocatalyst successfully. XRD patterns also revealed that the mean size of Pt crystal nanoparticles was about 3.69, 6.51 and 2.91 nm for Pt/PPy-CNF, Pt/CNF and Pt/C electrocatalyst respectively. The size of the PPy on carbon paper has been measured in the range of 35-40nm by AFM. Based on the electrochemical properties and acceleration tests evaluated by cyclic voltammetry measurements and Chronoamperometric experiments it was found that the as prepared Pt/PPy-CNF/GDL electrode exhibited a comparable electrochemical surface are (ECSA), MOR activity and so stability (in the presence of methanol) with respect to the Pt/CNF /GDL and Pt/C/GDL commercial one. A rather significant reduction in the peak potential of methanol electro-oxidation from 0.69V for Pt/C/GDL to 0.76V for Pt/PPy-CNF/GDL electrode indicates that an increase in the activity for MOR is achieved by replacing the C by PPy-CNF. The corresponding ECSA values for the Pt/PPy-CNF/GDL, Pt/CNF/GDL and Pt/C/GDL electrodes were 108.69, 53.93 and 17.98 m²g^-1 respectively.

Abstract: In this paper, starting from recent data provided by the National Institute of Statistics, we analyze the tourism activity in Mehedinți County. We apply the regression method and analyze some models. We also compare the economic results with those of previous years. Also, in this paper we study the stability of dynamic systems with applications in economics. The stability study is done using the Leapunov function method. The originality of the paper consists in the way we choose the mathematical model in case of regression and in the way we choose the Leapunov function in case of dynamic systems in which we analyze stability.

Abstract: The paper deals with the analysis of performed repairs and the current state of drainage and ventilation system of the Plasy convent and their evaluation. The Plasy historic water system is described in detail based on the results of a long-term field and structural survey. At the same time, unsuitable interventions, particular the application of chemical barrier, were analysed. Recommendations for further measures in the framework of the rehabilitation of the whole convent are made.

Abstract: IIn this paper, two finite difference methods are used to solve the one-dimensional second order wave equation with constant coefficients subject to specified initial and boundary conditions. Two numerical experiments are considered. The two methods are Central in Time and Central in Space scheme with second order accuracy in both time and space, abbreviated as CTCS (2,2) and Central in Time and Central in Space scheme with second order accuracy in time and fourth order accuracy in space, abbreviated as CTCS (2,4). Properties such as consistency and stability are studied. We also perform spectral analysis of dispersive and dissipative properties of the two methods. Two numerical experiments are considered, and the numerical results are displayed.