Comparative evaluation of the antioxidant potential of some Iranian medicinal plants

Medicinal plants are a source for a wide variety of natural antioxidants. In the study reported here, we have conducted a comparative study between five medicinal plants having the same geographic origin: the Hamadan region in the west of Iran and growing in the same natural conditions. The amount of total phenolics and total flavonoids for parts of these plants used in Iranian popular medicine were evaluated. Furthermore, antioxidant activities for these parts using vitamin C equivalent antioxidant capacity (VCEAC) test were also evaluated. The results show that the antioxidant activities varied greatly among the different plant parts used in this study and some plants are rich in natural antioxidants especially leaves of Lavandula officinalis and of Melissa officinalis. A positive correlation between total phenolic or flavonoid contents and VCEAC was found with a correlation coefficient of R² = 0.961 and R² = 0.817, respectively. These findings show that phenolics in these plants provide substantial antioxidant activity.     

Performance comparison of AlGaAs,GaAs and InGaP tunnel junctions for concentrated multijunction solar cells

Four tunnel junction (TJ) designs for multijunction (MJ) solar cells under high concentration are studied to determine the peak tunnelling current and resistance change as a function of the doping concentration. These four TJ designs are: AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs. Time‐dependent and time‐average methods are used to experimentally characterize the entire current–voltage profile of TJ mesa structures. Experimentally calibrated numerical models are used to determine the minimum doping concentration required for each TJ design to operate within a MJ solar cell up to 2000‐suns concentration. The AlGaAs/GaAs TJ design is found to require the least doping concentration to reach a resistance of <10⁻⁴ Ω cm² followed by the GaAs/GaAs TJ and finally the AlGaAs/AlGaAs TJ. The AlGaAs/InGaP TJ is only able to obtain resistances of ≥5 × 10⁻⁴ Ω cm² within the range of doping concentrations studied. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel miniaturized multiband antenna and applications for smart navigation media

This article presents a novel low‐cost integrated multiband antenna design customized for navigation media applications. The distinctive feature of the design consists in using a broadband planar dipole with four arms and a miniaturized feeding‐point, easy to deploy inside the tracking devices, and cost‐effective for supply chain industry. The article first introduces the main challenges and the benefits of miniaturizing antennas for supply‐chain and particularly for navigation media system which is the case‐study. Further the parametric study and final dimensions of the design and the simulation results are discussed. The proposed design is fabricated and the measurements of the radiation pattern and the return loss are performed proving that the antenna with maximum gain up to 10 dBi and S₁₁ up to ?30 dB, exhibits excellent performance for all the frequencies required in the navigation media systems such as 1.6, 1.8, 2.3, 2.4, 2.6, 3.6, and 5.8 GHz. The proposed design was implemented and tested inside a tracking device mounted on a vehicle and compared with existing commercial antennas. This study showed that the proposed antenna is suitable for tracking devices as it is miniaturized for internal integration and it has better 4G and GPS signal detection and low power consumption comparatively with existing commercial antennas.     

Copper Extraction Kinetics by Beta-Diketone Derivatives (Acylpyrazolones and Acylisoxazolones) in Water/Chloroform Biphasic System

Abstract

Copper(II) extraction and back-extraction rates were determined in a water/chloroform system using a bell-shaped transport cell. Various 1-phenyl-3-methyl-4-acyl-pyrazol-5-ones (with acyl = benzoyl, 2-thenoyl, octadecanoyl, p-tert-butylbenzoyl, 3-phenyl-propanoyl, and iso-nonanoyl) and 3-phenyl-4-acylisoxazol-5-ones (with acyl = benzoyl and p-tert-butylbenzoyl) were considered. The back-extraction rate is shown to be limited by the diffusion of the complex in the organic unstirred layer, whatever the stirring speed and whatever the ligand considered. At low stirring speed, the extraction rate appears to be limited by the diffusion of either a complex or a ligand species in the unstirred layers, depending on the pH. At high stirring speed, the extraction rate is limited by the interfacial complexation. The extraction rate dependence on side-group variation cannot be correlated with hydrophobicity or acidity of the extractants and may be explained by structural differences of the CO vicinal group of the acyl.     

Mechanical properties of nickel manganites-based ceramics used as negative temperature coefficient thermistors (NTC)

A series of nickel manganite ceramics of composition Ni_xMn_3−xO₄ (0.28 ≤ x ≤ 1) has been prepared by sintering powders obtained using two different ways: the classic solid/solid reaction and the co-precipitation method (soft chemistry). The evolution of the three-point bend strength has been correlated to the density and the structure of the ceramics. As expected, the strength decreases with increasing porosity. A correlation has been observed between the flexure strength and the structure of the spinel phase. The bend strength increases as the structural distortion (c/a ratio) increases, probably due to a lowering of symmetry rather then a modification of the bond strength. Moreover, we show that a modification of the oxidation state does not affect the value of the flexure strength.     

Synthesis of V-containing Keggin polyoxometalates: Versatile catalysts for the synthesis of fine chemicals?

Vanadium-containing polyoxometalates (POM): H₄PVMo₁₁O₄₀, H₅PV₂Mo₁₀O₄₀ and H₆PV₃Mo₉O₄₀ were synthesized by two distinct procedures and characterised by XRD, ³¹P MAS-NMR, FT-IR, BET, UV–vis and SEM. These vanadium-substituted POM were shown to be able to oxidize benzene into phenol with nearly 100% selectivity in the presence of H₂O₂. Furthermore, other aromatics were also oxidised to the corresponding phenols or ketones at appreciable degrees of conversion. However, the question of their stability toward leaching arises and has been investigated. While, there appears to be a correlation for liquid-phase reactions between the yields toward oxygenates and the vanadium content in the Keggin structure, we were also able to observe a decrease in the stability of these POM after successive catalytic runs. Furthermore, POM crystals having a regular size and shape, with peculiar orientation have been prepared and hence exhibited the highest catalytic activity.     

Numerical study of natural convection and acoustic waves using the lattice Boltzmann method

In this paper, the lattice Boltzmann method is used to study the acoustic waves propagation inside a differentially heated square enclosure filled with air. The waves are generated by a point sound source located at the center of this cavity. The main aim of this simulation is to simulate the interaction between the thermal convection and the propagation of these acoustic waves. The results have been validated with those obtained in the literature and show that the effect of natural convection on the acoustic waves propagation is almost negligible for low Rayleigh numbers (Ra ≤ 10⁴), which begins to appear when the Rayleigh number begins to become important (Ra ≥ 10⁵) and it becomes considerable for large Rayleigh numbers (Ra ≥ 10⁶) where the thermal convection is important.     

Total phenolics,flavonoids, anthocyanins and antioxidant activity following simulated gastro-intestinal digestion and dialysis of apple varieties: Bioaccessibility and potential uptake

In the present study, an in vitro model simulating gastrointestinal (GI) digestion, including dialysability, was adapted to assess free soluble polyphenols from apples (four varieties). Results indicated that polyphenol release was mainly achieved during the gastric phase (ca. 65% of phenolics and flavonoids), with a slight further release (<10%) during intestinal digestion. Anthocyanins present after the gastric phase (1.04–1.14 mg/100 g) were not detectable following intestinal digestion. Dialysis experiments employing a semipermeable cellulose membrane, presenting a simplified model of the epithelial barrier, showed that free soluble dialysable polyphenols and flavonoids were 55% and 44% of native concentrations, respectively, being approximately 20% and 30% lower than that of the GI digesta. Similar results were found for the antioxidant capacity of dialysable antioxidants, being 57% and 46% lower compared to total antioxidants in fresh apples (FRAP and ABTS test, respectively). It is suggested that some polyphenols are bound to macromolecular compounds that are non-dialysable, that the presented method allowed the study of free soluble polyphenols available for further uptake, and that both chemical extraction and concentrations in final digesta would overestimate polyphenol availability.     

Production threshold impact on a GEANT4 calculation of the power deposition in a fast domain: MEGAPIE spallation target

The calculation time in the Monte Carlo simulations consistently represents an essential issue. It is often very long, and its decrease constitutes a challenge for the simulator. Generally, an MC simulation is qualified as quality or not according to two main criteria: the calculation time and the accuracy of the results. However, in most cases, the optimization of one criterion affects negatively the other. Therefore, a compromise between both of them is always required in this kind of simulation. The present work aims at studying the impact of the production threshold(or cut) of the GEANT4 toolkit on the calculation of the power deposition in the MEGAPIE spallation target.The production threshold of secondaries is a GEANT4 intrinsic parameter. It indicates the limit of energy we can reach in the production of secondary particles. This study has allowed us to make the following conclusions. First,the influence of the cut on the calculation of the deposited power depends on the volume size, its arrangement and the importance of the electromagnetic processes occurring within. Second, the accuracy of the calculations can be acceptable only below a given value of the cut energy.Third, this accuracy remains almost unchangeable from a certain value of the cut. The study has also made it possible to explore the prevalence of certain interactions in the zone of spallation in the MEGAPIE target.