Substitutional Atom Influence on the Electronic and Transport Properties of Mn4Si7

Mn₄Si₇ has been substituted with the following elements: Cu, Fe, Re and Cr on the Mn site, and Al, B, Ge, Sn, Ga, In, Na and Tl on the Si site. The Seebeck coefficient, electrical conductivity and power factor of the substitutional alloys have been evaluated by using density functional theory calculations, and the temperature dependence of the electronic transport properties has been investigated at different charge carrier concentrations by solving the semi-classical Boltzmann transport equation. We show that the substitution of Cu for Mn worsens the thermoelectric properties, while that with Fe appears the?most efficient for increasing the power factor. For In and Tl substitutions, the Seebeck coefficient is increased due to the high d-states contribution in the density of states at the Fermi level. Although the power factor is limited by a poor electrical conductivity, Mn₃₂Si₅₅Tl could exhibit a good figure of merit provided that the amount of Tl atoms is low (at most 1 at.%) and the charge carrier concentration is not too high (around 10²⁰ cm^?3).     

Some physicochemical properties of methyl methacrylate-grafted nylon 6. II.

Graft copolymerization of methyl methacrylate on nylon 6 was investigated using KMnO₄ as initiator at 60°C. The optimum conditions of the grafting process using various amounts of methyl methacrylate have been utilized. Physical and chemical properties of the grafted nylon such as moisture regain, density, and infrared spectra are studied. Furthermore, the dyeing behavior of the grafted nylon toward acid and direct dyes is also investigated. The rate of graft copolymerization (R_p) of methyl methacrylate with this system was evaluated and expressed by the following equation depending upon the potassium permanganate concentration used: The degree of polymerization of isolated poly(methyl methacrylate) from the grafted nylon was found to be a first-order dependence.     

CMOS RF switched capacitor bandpass filter tuned by ring VCO

A new RF switched capacitor bandpass filter and its command circuit made up of a ring voltage controlled oscillator with ‘XOR’ gates are proposed. Implemented in a standard CMOS technology, this circuit is intended to be used in a subset of professional mobile phone applications [380–520 MHz]. Experiments carried out on a prototype show a tunable center frequency range of 260 MHz [240–500 MHz], with a quality factor that can be as high as 300.     

CARBON DIOXIDE STANDARD EMISSIVITY BY MIXED GRAY-GASES MODEL

Conventional fossil fuels are of carbon-hydrogen composition. A number of alternative fuels, e.g., coal, lignite, are carbon-based fuels. The high temperature combustion of such fuels would generate carbon dioxide, and if hydrogen is present, water vapor. The knowledge of the emissivities of carbon dioxide and water vapor is very important in burner design and thermal efficiency calculations. The present work utilizes a gray-plus-clear gas model to approximate standard carbon dioxide emissivities. The model developed covers a temperature range of 300-1800 K and a pL range of 0.05 to 1000 cm atm. The results indicated that a mixture of six gray gases was adequate to cover the whole range. Comparison of calculated and tabulated results showed that in the range of industrial application, the present model has an error range of —4.2 to 5.9 percent. Comparison with Leckner's model shows the superiority of the present work.     

An optimal design of single tuned filter in distribution systems

This paper proposes an optimal design of single tuned shunt passive filter for the Underground Ramsis Metro Substation (URMS) using linear programming technique as a conventional technique and fuzzy linear programming (FLP) technique as a modern technique. The optimal filter parameters are obtained to overcome the harmonics generated in the voltage and current waveforms, due to the non-linear characteristics of the rectifiers, which distort the voltage and current waveforms at the point of common coupling (PCC). The harmonic levels are analyzed at different loading conditions using the fast Fourier transform (FFT) on MATLAB optimization program. The proposed optimal design of harmonic filter is based on minimizing the cost of the filter parameters and its losses. Both techniques are applied on the system under study. From the results, the THD levels of the line current and the bus voltage are reduced to be within the standard limits. A comparison between the optimal design filters is carried out using the LP and FLP techniques. However, the lowest cost of filter is obtained using the FLP technique.     

Reflection and refraction of incident p-, T-, and SV-waves at interface between magnetized two solid-liquid media with heat sources and initial stress with and without thermal relaxation times

We investigate the problem of reflection and refraction of thermoelastic waves at a magnetized solid-liquid interface in presence of initial stress. In the context of Green-Lindsay and coupled thermoelastic theories of thermoelasticity, the problem has been solved and the effect of magnetic field, external heat sources, and initial stress on p-, T-, and SV-waves propagation have been discussed. The boundary conditions at the interface for displacement continuity, vanishing the tangential displacement, continuity of normal force, tangential force, and continuity of temperature are applied. The amplitudes ratios for the incident p-, T-, and SV-waves have been obtained. The effect of the initial stress, heat sources, and magnetic field on the reflection and transmitted coefficients for the incident waves have been discussed.     

Dyeing of nylon 6 fabric with a bifunctional sulphatoethylsulphone reactive disperse dye

A bifunctional reactive disperse dye containing two temporarily anionic sulphatoethylsulphone groups was synthesised and applied to nylon 6 fabric by exhaust dyeing at a variety of pH levels and temperatures. A monofunctional reactive disperse dye containing one temporarily anionic sulphatoethylsulphone group was also synthesised, and its dyeing behaviour was compared with the bifunctional dye. The bifunctional reactive disperse dye exhibited high exhaustion and total fixation yield under alkaline conditions. The results also indicate that the introduction of two temporarily anionic sulphatoethylsulphone groups of the bifunctional dye gave an enhancement in dyeing performance compared with that of the monofunctional dye. The dyes also showed very good levelling and fastness properties on nylon 6 fabric.     

Improving secret key generation for wireless communications in FDD mode

Most recent research on channel‐based key generation oriented to time division duplex system because the channel reciprocity feature is applied directly for secret key generation. Most of commercial cellular systems depend on frequency division duplex (FDD) systems. In this paper, we investigate the impact of uplink and downlink of FDD systems for the generation of shared secret keys between two parties in the presents of passive eavesdropper. In addition, we are considering improving the rate of the secret key for wireless communication in FDD mode. The main idea is to use the fading coefficient of the channels between the relay and other parties as an additional random common source for the secret key generation. Also, explore the using of channel estimation techniques to reduce the channel training sequence and study its effect on the generation of shared key for wireless communications in FDD mode. We derive the upper bound of the generated shared key rate for four scenarios and give numerical examples to reveal the performance of our suggested improvement approaches.     

Long-term load forecasting and economical operation of wind farms for Egyptian electrical network

Several traditional methods have been presented for long-term load forecasting of electrical power systems without sufficient accuracy of the relevant results. In this paper, in order to improve the results accuracy, the artificial neural network (ANN) technique for long-term peak load forecasting is modified and proposed as an alternative technique in long-term load forecasting. The modified technique is applied on the Egyptian electrical network dependent on its historical data to predict the electrical peak load demand forecasting up to year 2017. This technique is compared with extrapolation of trend curves as a traditional method. Installed power generation capacities of Egyptian electrical network up to year 2017 are estimated dependent on the peak load forecasting of this network. Also, a proposed methodology to assess the economical operation of the wind farms (WFs) beside the conventional power system (CPS) is introduced. This methodology includes a mathematical model to develop the economical operation of wind farms on the whole power generation capacity through a considered period.