Study of magnetic and magnetocaloric properties of La0.6Pr0.1Ba0.3MnO3 and La0.6Pr0.1Ba0.3Mn0.9Fe0.1O3 perovskite-type manganese oxides

The compositional dependence of the magnetic and magnetocaloric properties of La_0.6Pr_0.1Ba_0.3MnO₃ (LPBMO) and La_0.6Pr_0.1Ba_0.3Mn_0.9Fe_0.1O₃ (LPBMFO) were investigated. Polycrystalline samples were prepared by the standard solid-state reaction method. Temperature-dependent magnetization measurements and Arrott analysis reveal second-order ferromagnetic transitions in both samples with Curie temperature increasing with doping iron from 94 K for LPBMO to 277 K for LPBMFO. Magnetic entropy change \( | {\Delta S_{\text{M}} } | \) was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field-dependent magnetization curves. However, the analysis of the magnetocaloric effect (MCE) using Landau theory of phase transition shows that the contributions to the free energy from the presence of ferromagnetic clusters are strongly influencing the MCE by coupling with the order parameter around the Curie temperature.     

Morphology, Structural, Magnetic, and Magnetocaloric Properties of Pr0.7Ca0.3MnO3 Nanopowder Prepared by Mechanical Ball Milling Method

A sample of Pr_0.7Ca_0.3MnO₃ nanopowder was prepared by the ball milling method. The crystal structure examined by X-ray powder diffraction indicates that the sample is single phase and crystallizes in the orthorhombic perovskite system with Pnma space group at room temperature. The average crystallite size of 29 nm was obtained by X-ray diffraction. Magnetic measurements showed that the sample exhibits a ferromagnetic-to-paramagnetic transition at a Curie temperature close to 120 K. The magnetic entropy change |ΔS _M | has been deduced by the Maxwell relation method. The maximum value of the magnetic entropy change $\vert \Delta {S}_{M}^{\max} \vert$ obtained from the M(H) plot data is found to be 0.86 J/kg?K for an applied magnetic field of 2 T. At this value of magnetic field the relative cooling power (RCP) is 44.05 J/kg. At low temperature, large change in magnetic entropy has been observed in the sample. Our result on magnetocaloric properties suggests that Pr_0.7Ca_0.3MnO₃ nanopowder is attractive as a possible refrigerant for low-temperature magnetic refrigeration.     

Integration of magneto-optical garnet films by metal-organicchemical vapor deposition

This paper presents a novel technique for integrating yttrium iron garnets, namely Ce:YIG, onto semiconductor platforms using metal-organic chemical vapor deposition (MOCVD). Large amounts of cerium (Ce) could be incorporated into the garnet structure because of the nonequilibrium nature of the technique. The method can alloy up to 54% Ce, thereby increasing the refractive index and enhancing the Faraday rotation of the YIG films. Faraday rotations as high as 0.4°/μm at 1.3 μm were achieved in MOCVD-grown garnets, exceeding the rotations of bismuth-doped YIG films (0.15°/μm at 1.3 μm) grown by liquid-phase epitaxy. The easy axis of magnetization is within the plane of the films. When the garnet films were sputtered onto (100) magnesia (MgO) buffer layers, their hysteresis loops indicated that they were isotropic     

Inorganic/organic (SiO₂)/PEO hybrid electrospun nanofibers produced from a modified sol and their surface modification possibilities

Ceramic silica (SiO(2)) hybrid nanofibers were prepared by electrospinning of solutions containing biocompatible polymer and modified silica precursors. The new hybrid nanofibers are based on polyethylene oxide (PEO) and a new solution of modified sol-gel particles of mixture containing tetraethoxysilane (TEOS) and 3-glycidyloxypropyltriethoxysilane (GPTEOS) in a weight ratio of 3:1. Adding high-molecular-weight PEO into the silica sol is found to enhance the formation of the silica nanofibers and leads to reduce the water-soluble carrying polymer down to 1.2%wt. Transmission electron microscopy (TEM) and attenuated total reflection fourier transformation infrared ATR-FTIR measurements are suggested that PEO is encapsulated by the silica component. This excellent formulation renders electrospinning of SiO(2) a robust process for an easy production of controllable silicate nanofibrous matrices. For instance, nanofibers with average diameter down to 400 nm are accessible by varying the weight ratio between the polymer and the inorganic precursor. These are reduced to 120 nm after the pyrolysis process. Moreover, the surface of the nanofibers could be easily modified, either by Al(3+) leading to aluminium silicate coatings, or by incorporation of Ca(2+) ions and subsequent bioactive hydroxyl carbonate apatite (HAP) formation. These hybrid silica nanofibers are possess a unique collective properties can have a great impact either in high-temperature reinforced materials and filtration or in biomedical applications such as in dentistry and bone tissue engineering.     

Low cost and high efficiency of single phase photovoltaic system based on microcontroller

This paper presents a theoretical and practical study of a single phase photovoltaic conversion system. It consists of a step down converter to charge a battery with the maximum power available from photovoltaic generator (PVG) and a single phase voltage source inverter (VSI) to produce a stable AC voltage (220 V/50 Hz) with lower total harmonic distortion (THD). A new perturb and observe algorithm is designed and implemented in a cheaper microcontroller PIC 16F876 where the duty cycle perturbation and the sampling period are selected to insure the stability of the PV system around the maximum power. The control strategy adopted for the inverter is the Selective Harmonic Eliminated Pulse Width Modulation (SHE PWM). The pulses are calculated and transferred on the PIC 16F876 memory. With this technique, inverter losses are decreased and the output voltage is easily filtered with a simple low pass filter producing a perfectly sine wave form voltage. The battery is sized to supply loads in non-sunny times.With optimization of its various components, the conventional single phase PV system has a low cost, high efficiency but also good power quality which represents a good opportunity to use it in many stand alone photovoltaic applications such as houses lighting. An experimental system has been made to demonstrate the efficiency of the photovoltaic system and to validate simulations done by Matlab–Simulink environment.     

Crystal Structure and Magnetic Properties in B-Site-Disordered La1.75Ca0.25MnMO6 (with M = Ti and Fe) Double Perovskites

Journal of Superconductivity and Novel Magnetism - Double perovskite La1.75Ca0.25MnMO6 (with M?=?Ti and Fe) systems were elaborated employing a solid-state reaction method. The...     

High temperature resistant insulated hybrid yarns for carbon fiber reinforced thermoplastic composites

With the increased use of carbon fiber reinforced composites (CFRC), the demand for the integration of insulated conductive wire/yarns in CFRC is increasing for additional function integrations such as sensoric, actoric, signal transfer, heating, etc. Between thermoset and thermoplastic matrix composites, the integration of insulated conductive materials is comparatively difficult due to the requirements of higher temperature and pressure during the consolidation of thermoplastic composites. Therefore, the need for insulating material able to withstand higher temperature for the use in thermoplastic CFRC is also high. Using DREF friction spinning technique, it is possible to manufacture yarns with a core‐sheath structure in which, as the core conductive wire/yarns and as the sheath different fiber formed materials can be used for the insulation of the core. In this study, the aspects of using different short/staple fibers such as polyester, Glass and Kynol as the sheath and the usable temperature range are revealed. Furthermore, the insulation property of such fibers after the application of different temperatures has been reported. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1179‐1184, 2013     

Epidemiology and antibiotic resistance of Salmonella enterica Serovar Kentucky isolates from Tunisia: The new emergent multi-drug resistant serotype

Since 2002, the emergence of multidrug resistant Salmonella enterica serovar Kentucky (S. Kentucky) and the associated salmonellosis with treatment failure were declared in different parts of the world and were in most of the case contracted during travels to Northeast and Eastern Africa. In the present work, we reported an epidemiological study of S. Kentucky isolated from different environmental and clinical origins in Tunisia, using Pulsed-field gel electrophoresis (PFGE); Enterobacterial Repetitive Intergenic Consensus (ERIC-2) fingerprinting; Plasmid profiling; and antibiotic resistance profiles. ERIC-2 fingerprinting allowed the differentiation of 14 different patterns versus only 4 pulsotypes. Besides, a high proportion of strains were found to be nontypeable by XbaI-PFGE and/or by plasmid profiling (plasmid-free strains). The antibiotic resistance was mainly detected against streptomycin (80.7%), sulfonamides (42.1%) and tetracycline (15.7%). Furthermore, two avian strains were shown to be resistant to trimethoprim–sulfamethoxazole and three clinical strains have demonstrated multidrug-resistant phenotypes (against 5 to 10 antibiotics) and all of them exhibited resistance against nalidixic acid, ciprofloxacin, ofloxacin and tetracycline.ERIC-2 PCR was found to be the most discriminative. However, combination of the three typing methods offer a better mean for differentiating S. Kentucky isolates, monitoring the multiresistant types and determination of their origin.     

高取代度淀粉醋酸酯合成工艺优化及结构表征

以玉米淀粉为实验材料,在催化剂用量、醋酸与醋酸酐体积比、反应时间、反应温度4个单因素试验基础上,利用响应面试验设计法进行试验设计,获得取代度与各单因素的函数关系,并建立高取代度淀粉醋酸酯合成工艺模型。通过回归方程和响应曲面,得到淀粉醋酸酯最佳合成工艺为催化剂用量0.11mL、醋酸与醋酸酐体积比1:1.39、反应时间1.59h、反应温度87.61℃。验证实验结果显示,在此条件下淀粉醋酸酯取代度为2.95。傅里叶红外光谱分析表明,淀粉醋酸酯葡萄糖单元上的羟基逐渐发生酯化,而且随着取代度测定值升高,乙酰基含量增大。扫描电镜照片显示,淀粉醋酸酯表面变得更为粗糙,孔隙增多且呈蜂窝状,说明酯化反应不仅发生在淀粉颗粒表面,同时也发生在淀粉颗粒内部。     

Combinatorial effects of mechanical activation and chemical stimulation on the microwave assisted acetylation of corn (Zea mays) starch

The changes in the physical characteristics of ball milled corn starch (BMS) after chemical modification were investigated. The SEM and XRD analysis of BMS granules showed a fragmented aspect with a total loss of their initial crystallinity and an increase of their potential hydroxyl substitution sites. This morphology facilitated the access of the esterifying solvents into the starch molecule as corroborated by the spectacular increase of the water solubility index (WSI) and water absorption index (WAI). Following the acetylation, the degree of substitution (DS) increased up to 2.83 with the augmentation of the iodine catalyst content (p = 0.011). However, under the same condition of esterification, the DS of the BMS was slightly lower in comparison to the control, due to an increase in the number of free hydroxyl groups. Consequently to the modification, a reduction in the T_g, strong hydrophobicity and important exo‐corrosion affecting the granules were noticed.