Magnetic nanoparticles were synthesized and coated by the situ-coprecipitation method with FeCl3.6H2O and FeCl2.4H2O precursors in the presence of NH4OH (or NaOH) reduction and PEG coated agent. Preparation of modified magnetic nanoparticles were performed at two different temperatures under the influence of different alkaline media. The effect of strength of alkaline media and reaction temperature of the magnetic properties (Magnetic saturation, Magnetic remanent, coercive force (of modified MNPs were investigated. To study structure, morphology, optic and magnetic properties MNPs were characterized by XRD, FTIR, TEM and VSM analyzes.The results showed that modified magnetic nanoparticles have superparamagnetic properties and have high magnetic saturation and small coercive force, so the magnetic properties of the modified MNPs are depended to the strength of the alkaline remanent directly. The saturation magnetization of the synthesized sample in NH4OH and NaOH at 80° C was determined as 60.94 and 49.39 emu/g, respectively. Also increasing temperature, improves magnetic properties coated MNPs) at temperatures below the blocking temperature. (The results of the XRD analysis showed that the structure of the modified magnetic nanoparticles is inverted spinel and the size of the nanoparticles synthesized in the ammonia media is smaller than the other media. The results of FTIR optical analysis revealed that the peaks at ~570 and ~440 cm^(-1) indicates the bond Fe-O. TEM analysis indicated that the shape of the MNPs is pseudo-spherical. VSM analysis indicated that the magnetic nanoparticles synthesized in stronger alkaline media (ammonia) and high temperature showed better magnetic behavior by higher magnetic properties. تفاصيل المقالة

We have calculated the branching ratio of the non-resonant B→D^- π^+ π^+ π^- four body decay using a simple model based on the framework of the naïve factorization approach where one can ommit the nonfactorization effects. In naive factorization approach, according to the Feynman diagram, there are only two tree diagrams for this decay mode. In the first diagram, the matrix element of decay mode is factorized into a B→D form factor multiplied by a 3π decay constant and in the second diagram, the matrix element is factorized into a B→Dπ form factor multiplied by a 2π decay constant, According to the rest mass of the particles, we assume that in the rest frame of B meson, the D meson remains stationary, so we obtain the value (3.47±0.14)×10^(-3) for the branching ratio of the B→D^- π^+ π^+ π^- decay mode in naive factorization approach, while the experimental results is (3.9±1.9)×10^(-3). تفاصيل المقالة

This paper presents the small-signal modeling of a synchronous Cuk converter using state-space averaging method. In the proposed isolated converter, the conduction and switching losses reduced by replacing the traditional diode with transistor and employing an auxiliary circuit. It causes the conversion efficiency of the photovoltaic system to be increased and better matching of the supplied load. Also this circuit has significant advantage over other topologies since it enables low voltage ripple on both input/output sides of the converter and better dynamic response. The low frequency small-signal model is done using state space averaging technique and two main power-stage transfer functions are derived, which are control-to-output voltage transfer function and input-to-output voltage transfer function. Using the proposed model of the converter we can analyze and simulate the time domain transient behavior of the system accurately and intuitively. Finally, the accuracy and validity of the proposed system model is verified by simulation results. تفاصيل المقالة

In this paper, a novel technique to improve the input dynamic range and bandwidth of the microwave power detectors (PDs) simultaneously is presented, which utilizes the piecewise linear approximation in conjunction with the distributed structure to achieve the goals. RF to DC conversion is proved for the proposed PD core, including only a MOS transistor that is capable to convert a part of its RF input signal to a DC value, proportional to the RF input power. This is an efficient method that requires less number of active devices and therefore saves more power consumption and active chip area, rather than the previous conventional methods. The analysis of circuit based on the transmission line theory is discussed and the transfer function is extracted mathematically for the proposed model. Moreover, a transistor level design is performed using a 0.15um pHEMT GaAs technology for 24GHz applications. The post layout simulation results are presented. تفاصيل المقالة