Entropy Generation and Optimization of Laminar Forced Convection Air Cooling in a Horizontal Channel Containing Heated Sources

A forced convection air-cooling of two identical heat sources mounted in a horizontal channel is numerically studied. Four effects of Reynolds number, separation distance, height and width of the components on the flow structure and heat transfer inside the channel have been examined. The entropy generation minimization method (EGM) is employed to optimize the heat transfer and fluid flow in the channel. The flow field is governed by the Navier–Stokes equation and the thermal field by the energy equation. The finite volume method and the SIMPLER algorithm are used to solve the continuity, momentum, energy and entropy generation equations. Results show that the mean Nusselt number increases with increase of the following parameters: Reynolds number, separation distance, height and width of the components. However, these parameters increase the total entropy generation, and thus provokes the degradation of the fan energy. The optimal values of separation distance, height and width heat source are: [(Sopt= 1 with W=0.25, C=0.25, Re=50, η=1.134), (Copt=0.3 with W=0.25, S=0.25, Re=100, η=0.895) and (Wopt= 0.1 S=0.25, C=0.25, Re=200, η=1.004)], respectively, where η is the optimization factor (=Num/S_T^*) and is defined as the ratio of Nusselt number to the total entropy generation. Finally, the optimal and the best configuration for maximum heat transfer and minimum entropy generation is observed at Re=50, S=1, C=0.25 and W=0.25

Linear and nonlinear optical properties of the CdSe nanocrystals embedded in PMMA matrix

CdSe nanocrystals (NCs) were prepared using a colloidal solution and dispersed in polymethylmethacrylate (PMMA) matrix. Using spin coating technique, thin films deposited on glass substrates were prepared. Their structural and optical properties were investigated by X-ray diffraction, atomic force microscopy (AFM) and UV-visible absorption, respectively. The absorption spectra of these dispersed NCs exhibit excitonic peaks resulting from the electron-hole coupling transitions. Due to a quantum confinement effect, a blue shift is deduced by comparison of such transition with respect to reported bulk band gap. Assuming a spherical like shape for these NCs, the crystallites radius (R) was estimated by applying the effective mass approximation model and was about 2.92 nm. Such a weak radius value compared to Bohr radius (RB = 5.5 nm) leads to a strong quantum confinement regime. Moreover, the influence of this confinement effect on nonlinear optical (NLO) properties was also studied. Quadratic and cubic NLO properties were investigated by second and third harmonic generation techniques (SHG and THG) with a Q-switched Nd:YAG laser working at 1064 nm fundamental wavelength. The NLO susceptibilities Χ<2>eff, Χ<3>eff were measured to be equal to 2.27.10-10(m/V) and 2.28.10-20(m2/V2), respectively

Optical properties of the ZnSe nanocrystals embedded in PMMA matrix

In this paper we report linear and nonlinear optical properties of the thin films based on nanocrystals ZnSe embedded in centrosymmetric matrix PMMA, deposited by spin coating technique. Absorption and emission spectroscopy are shown respectively a blue shift and a strong band emission near the band gap of bulk material ZnSe, which is tunable with particles size. Blue shift of the absorption edge used to evaluate the average size of nanoparticles by using the E.M.A model. The size of NCs of ZnSe was estimated to 1.98 nm, compared to the exciton Bohr radius of bulk material. We established a strong quantum confinement state for the NCS ZnSe. Using Nd:YAG laser at 1064 nm in picoseconds regime, Second order susceptibilities were measured by SHG technique. The obtained value was four order of magnitude larger compared with the bulk (ZnSe) value

Design, structural and theoretical characterizations of novel Schiff base compounds: Enzymes inhibitory potential using in vitro and in silico methods

The aim of this paper is to further explore the enzymatic properties of two synthetic Schiff base compounds. The corresponding copper complex (Cu(L)), with its Schiff base ligand (HL) have been synthesized and their spectroscopic (IR, UV-visible., NMR (H,C, Dept-135) and MS), thermogravimetric (TG/DTG), electrochemical (CV) and theoretical (Density Functional Theory) using the hybrid B3LYP/6–31 G(d,p) method) properties have been studied and well discussed. The electrochemical behaviour of Cu(L) displays the Cu(III)/Cu(II) and Cu(lI)/Cu(I) redox processes. The molecular structure of HL is confirmed by X-ray diffraction analysis. HL crystalized in the triclinic system with the space group of P-1. The morphological structures are also analyzed by X-ray powder diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy. To improve their biological activities, inhibition of the target proteins, acetylcholinesterase (AChE), butyrylcholinesterase (BChE), Tyrosinase (TYR), and Urease enzymes are tested in vitro and in silico using molecular docking. Furthermore, their ADMET parameters are analyzed. The drug-likeness results indicate that HL followed to Lipinski’s, Ghose’s, Veber’s, Egan’s and Muegge’s rules contrary to its copper complex which followed only to Veber’s rule. Due to the importance of cytochrome P450s proteins for detoxification, five major CYP isoforms (CYP1A2, CYP2C19, CYP2C9, CYP2D6, and CYP3A4) are also considered during in silico prediction.The authors thank the Algerian Ministry of Higher Education and Scientific Research (MESRS) and the Director General for Scientific Research and Technological Development (DGRSDT) for the financial support

Investigation of photoprotective, anti-inflammatory, antioxidant capacities and lc–esi–ms phenolic profile of astragalus gombiformis pomel

Plant-derived compounds have recently been gaining popularity as skincare factors due to their ability to absorb ultraviolet radiations and their anti-inflammatory, and antioxidant properties. In this light, this work aimed to evaluate in vitro the pharmacological activities of the butanolic extract prepared from the aerial parts of Astragalus gombiformis Pomel, an endemic species to southern Algeria. The sun protection factor was used to assess the photoprotective effect (SPF), the protein denaturation method to determine the anti-inflammatory activity, and brine shrimp nauplii and OxHLIA assay, respectively, to assess the cytotoxicity and antioxidant capacity of A. gombiformis. In addition, LC–ESI–MS analysis was employed for the characterization of the phenolic constituents of A. gombiformis. The results showed that A. gombiformis had high capacity for absorbing UV radiations with an SPF of 37.78 ± 0.85 and significant anti-inflammatory activity with a percentage inhibition of 75.38% which is close to that of diclofenac and ketoprofen. In addition, A. gombiformis was found to have effective cytotoxicity against Artemia nauplii with a DC50 value of about 44.7 µg/mL, but a weak hemolytic effect against human erythrocytes. LC–ESI–MS results detected the presence of 17 phenolic compounds with a predominance of cirsiliol, silymarin, quercitrin (quercetin-3-O-rhamnoside), and kaempferol. Taken together, these results suggest that A. gombiformis extract could be used as a skincare agent in cosmetic formulations, providing excellent antioxidant and anti-inflammatory protection, allowing the treatment of skin conditions, as well as a pharmaceutical agent with multidimensional applications.The authors are grateful to the Algerian Ministry of Higher Education and Scientific Research and the National Centre for Biotechnology Research (C.R.B.T) for their respective financial and material supports

Correlation between mechanical and microstructural properties of molybdenum nitride thin films deposited on silicon by reactive RF magnetron discharge

Molybdenum nitride thin films were deposited on (100) silicon substrates by R.F. magnetron sputtering of a Mo target in a (Ar-N2) gas mixtures. The films were studied by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction. The nanomechanical properties have been determined by nanoindentation and Peak-Force Quantitative Nanomechanical Mapping (PF-QNM). The total internal stresses were determined by curvature measurements and the Stoney formula. As thin film composition influences the morphology, the stress state and the mechanical properties, modifications are expected in this study where the nitrogen content is tuned. The film exhibits a polycrystalline structure with preferred orientation along (111) plane. The increase of the nitrogen content in the coating (N/Mo =1.1) induces a broadening of the full width at half maximum (FWHM) of the (111) diffraction peak, which is attributed to the presence of smaller crystallites. The residual stress and mechanical properties variation were correlated to the structural transition from γ-Mo2N to hexagonal and cubic MoN. The results show a good agreement between the nanomechanical properties obtained by nanoindentation and PF-QNM

LC-MS Analysis and Antioxidant Activity of the Hydro-alcoholic Extract of Melissa Officinalis L. from Algeria

The present work focuses on evaluation of the chemical composition and antioxidant activity of the hydro-methanolic extract of Melissa officinalis from Algeria. The liquid chromatography-mass spectrometry analysis allowed the identification of six compounds: caffeic acid, caftaric acid, hydroxyjasmonic acid glucoside, caftaric acid glucoside, rosmarinic acid and sagerinic acid. The in-vitro antioxidant activity of the hydro-methanolic extract was evaluated by using four different methods including: radical scavenging assay (DPPH), scavenging activity (ABTS), cupric reducing antioxidant capacity, and ferric reducing power assay. The extract exhibited a relatively strong antioxidant activity compared to the synthetic antioxidants. The highest radical scavenging activity was registered using DPPH and ABTS methods, IC50= 20.53±2.64 μg/mL and 22.50±0.67 μg/mL, respectively. These results suggest that Melissa officinalis L. could be considered a potential source of natural antioxidants with potential interest in the agrochemical and pharmaceutical industries