Kitami Institute of Technology, Japan
Since Superconducting Magnetic Energy Storage (SMES) system has the ability to provide both active and reactive power simultaneously and quickly, increasing attention has been focused recently on smoothing of wind power fluctuations by SMES control. In this study, the SMES system with a voltage-source IGBT converter is modeled as a controllable energy storage device installed at a wind farm. The objective of the proposed SMES system is to provide both active and reactive powers, which can significantly decrease the voltage and power fluctuations of grid connected fixed speed wind generators. To smooth the output power, determination of the reference output power is an important problem, because in some cases more energy storage is needed when wind speed is very low. So, to generate the output power reference, Exponential Moving Average (EMA) of the wind generator output is used in this study. Real wind speed data is used in the simulation analyses, which validates the effectiveness of the proposed control strategy. Simulation results clearly show that the proposed SMES system can smooth well the wind generator output power and also maintain the terminal voltage at rated level.
American International University Bangladesh (AIUB)
Bangladesh University of Engineering and Technology (BUET)
In this paper, a method for designing a 980 nm In0.2Ga0.8As/GaAs quantum well (QW) VCSEL has been presented. Using this method the strain induced shift of In0.2Ga0.8As has been computed which has been used in the computation of energy gap for the above mentioned combination of materials in the active region. The material gain for this strained In0.2Ga0.8As/GaAs QW has been computed for analyzing the performance of the VCSEL. The material gain and transparency carrier density for GaAs and In0.2Ga0.8As materials are optimized with the aim of designing a 980 nm In0.2Ga0.8As/GaAs QW VCSEL. A higher material gain with lower transparency carrier density is chosen for designing a 980 nm VCSEL. For the designed VCSEL, appropriate threshold current and modal gain have been computed. Using theses values the plots of output power vs. time as well as modulation performance have been obtained. From the plots of bias voltage vs. injection current it is found that a small voltage of 1.8 volt is required to reach the threshold current of 1.5 mA at 250C. From the plot of output power vs. time at 300K a maximum optical output power of 5 mW is obtained at 7.4 mA (≈ 5Ith) injection current and the corresponding obtained modulation bandwidth is 16.5 GHz which indicates the superior performance of the designed VCSEL compared to the similar results of other research works.
Khulna University of Engineering and Technology (KUET), Bangladesh
Khulna University of Engineering and Technology (KUET), Bangladesh
American International University Bangladesh (AIUB)
A position sensorless Interior Permanent Magnet Synchronous Motor (IPMSM) drive system is proposed in this paper. The drive system is powered through a Space Vector Modulated (SVM) voltage source inverter. A Real Time Recurrent Neural Network (RTRNN) was applied to estimate the back emf components along stationary α- and β- axes from the input stationary two-axis phase voltages, corresponding phase currents, and motor speed error data. The RTRNN back emf model contains variables of the two- axis and was trained off-line. The RTRNN estimated the back emfs accurately. The rotor position information was used for vector control of the IPMSM drive through Park’s transformation. A Proportional plus Integral plus Derivative (PID) controller was used to control the motor variables in closed loop. The effectiveness of the drive system was tested for different operating conditions and perturbation of parameters. The proposed control system was found to work satisfactorily under these test conditions.
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
The performance of Erbium Doped Fiber Amplifier (EDFA), Single Mode Fiber (SMF) and Dispersion Compensating Fiber (DCF) in a dynamic and reconfigurable Wavelength Division Multiplexing (WDM) system has been demonstrated in this simulation study. Eight WDM channels, each channel running at 40 Gbps, are transmitted through SMF, DCF and EDFAs. The effect of long distance transmission of optical signals to the value of OSNR, Q factor and bit error rate (BER) performance in the WDM optical network, keeping the Bit Error Rate (BER) or eye pattern in acceptable range has been observed. The WDM system trial using EDFA’s, SMF and DCF shows acceptable but deteriorated eye patterns and bit error penalties upto 420 km of transmission distance. Output power of the system was kept almost constant (-12 dBm) for the whole simulation process. Our simulation model can inhibit dispersion to a minimum possible limit due to the application of DCF (dispersion value is -85 ps/nm/km) along with the single mode fiber (dispersion value is 17 ps/nm/km). Gain flatness is also maintained by keeping the value of input power and output power equal while performance of the network is analyzed.
Bangladesh University of Engineering and Technology (BUET)
Bangladesh University of Engineering and Technology (BUET)
Bangladesh University of Engineering and Technology (BUET)
Bangladesh University of Engineering and Technology (BUET)
A self-consistent quantitative analytical model of temperature dependence of THz QCL structure for high temperature operation is presented in this work. This analysis uses standard wave function approximation and effective mass approximation for solving the quantum mechanical transport equations in the gain medium of QCL. Relevant scattering mechanisms are modeled using Fermi’s golden rule for obtaining the parameters related to electronic transport in QCL. These parameters are then utilized for investigating the temperature dependence of existing terahertz quantum cascade lasers. Temperature versus lifetime plot and temperature versus threshold current density plot were obtained after simulation. These plots were compared with the similar plots, experimentally obtained by other research groups. The results obtained from this model have the ability to provide a quantitative treatment of THz QCL structure at temperatures greater than 120K.
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
The channel transition near video-on-demand system should be seamless so that the users currently watching the video do not experience any disruption due to this transition. Existing seamless channel transition scheme pads a dummy video stream at the end of the original video stream to produce exact correspondence between segments, but this approach causes some wastage of bandwidth and increase in average user waiting time. A Fast Broadcasting scheme with preloading a postfix of the original video stream in the client buffer reduces the average user waiting time but the bandwidth wastage problem cannot be solved. In this scheme, some segments are broadcasted though it was in the clients’ buffer. This paper proposes a tailored fast broadcasted scheme that the bandwidth requirement by not transmitting the segments those results in wastage of bandwidth keeping the buffer requirement same.
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
Grid services are heavily used for handling large distributed computations. They are also very useful to handle heavy data intensive applications where data are distributed in different sites. Most of the data grid services used in such situations are meant for homogeneous data source. In case of Heterogeneous data sources, most of the grid services that are available are designed such a way that they must be identical in schema definition for their smooth operation. But there can be situations where the grid site databases are heterogeneous and their schema definition is different from the central schema definition. In this paper we propose a light weight coherent grid service for heterogeneous data sources that is very easily install. It can map and convert the central SQL schema into that of the grid members and send queries to get according results from heterogeneous data sources.
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
Market is an essential urban service which provides the daily needs: food, vegetable, grocery etc. to the urban habitants. Street markets of various kinds like fresh food, clothing, flower, and even furniture, electronics, are inseparable part of everyday living of Asian street culture. In developing countries like Bangladesh, street market is such an informal urban service which plays the role of Super markets, Departmental Store or Marts in developed countries. These markets also play key role in creation of employment and thus minimizing unemployment and underemployment. Dhaka being the densely populated capital city of Bangladesh with scarce resources and infrastructural support, very often fails to address the essential urban services for citizens properly. High paced urbanization, rural to urban movement, high population growth has led to an increased demand for urban services. However, the number of authorized markets, their area-wise distribution is imbalanced with sporadic growth in urban Dhaka. To bridge the gaps and to meet this growing demand, some spontaneously grown street markets are being observed at different locations of metropolitan Dhaka ignoring planning principles and government policies. This study unveils that the users are satisfied with the service they are receiving at the vicinity of their neighborhood. Its uniqueness lies in periodicity, temporariness, short duration on daily basis, location and range of people served. The study explores impact on the urban system of this mega city by identifying the factors influencing growth of these localized periodic street markets.
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
The feasibility of existing light water reactor (LWR) is studied to transmute long-lived minor actinides (MAs) in order to ease the burden of high-level radioactive waste disposal problem. For these studies, conventional LWR is considered with two types of U-free fuels, one with uranium-free inert matrix fuel PuO2+ZrO2 (ROX) and the other one with thorium based U-free fuel PuO2+ThO2 (TOX). The transmutation capability of MAs by the U-free fueled LWR is compared with that by the conventional PuO2+UO2 (MOX) fueled LWR. By loading 200-1000 kg/GWe of MAs, (which is equivalent to 0.2-1.0 a/o in ROX fuel) in ROX, TOX and MOX fuels, some parametric studies have been performed to find out an adequate amount of initial loaded MA in LWR. From these studies it is found that the effective amount of initial loaded MAs is 0.5 a/o. By loading 0.5 a/o of MAs in ROX+MA fueled LWR, it is possible to transmute 76% of the initial loaded MAs. Where as it is possible to transmute only 58% of the initial loaded MAs by the TOX+MA and MOX+MA fueled LWR. Moreover, ROX+MA fueled LWR has higher (82%) Pu transmutation capability compared to the TOX+MA and MOX+MA fueled LWR.
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
Pusan National University, Pusan, South Korea
Sphelarite ZnS nanoparticls were synthesized from aqueous medium with three different ZnCl2 concentrations. The particle sizes in solid form were found as 2- and 7-nm, that were determined by the X-ray diffraction and transmission electron microscopy analysis. We investigated the ultraviolet–visible absorption behavior of these nanoparticls with respect to the amounts of excess S or Zn at the surfaces in a particular dispersing agent, either ethanol or water. The surface analysis was carried out by the X-ray photoelectron spectroscopy. We observed tremendous variation of UV absorption only due to the variation of surface atoms, while particles in solid state were of same sizes and identical crystallinity. Moreover, we observed abrupt change of UV absorption of the nanoparticle systems when the dispersing agent is changed from ethanol to water, and vice versa.
Fraunhofer Institute for Solar Energy Systems, Germany
In this work we investigated the effects of a wet thermal oxidation step at 800°C for four hours on standard multicrystalline silicon block material. The effective lifetimes were measured by the Carrier Density Imaging (CDI) and Quasi Steady State Photoconductance (QSSPC) methods after SiNx surface passivation. The averaged lifetime was significantly decreased by the oxidation step. An increase in the concentration of interstitial iron as well as an increase in the concentration of trapping centers after the oxidation step was observed. A detailed investigation of regions of interest typical for that material revealed an increase in recombination active defect concentration in areas with a high density of grain boundaries and dislocations. The resulting higher recombination activity in these areas may be due to a change in density or recombination activity of precipitates along grain boundaries and dislocations or increased recombination strength.
Islamic University of Gaza, Palestine
Mathematics at the Ministry of education in Gaza, Palestine
In this paper, we construct idempotent generators of cyclic codes over the rings F2 +uF2 , F2 + uF2 + u2F2 and F3 + uF3 and study their properties. Finally we will generalize the results to linear cyclic codes over the commutative chain rings Fp + uFp + …+ uk 1Fp where p is prime number.
Benha University, Benha 13518, Egypt
Benha University, Benha 13518, Egypt
In the present paper we discuss the approximate evaluation of the resolvent R(x,y) for Fredholm kernel k (x,y) in the space with weight function and bounded almost everywhere on , we also discuss the error bounds for the approximate resolvent using the linear polynomial operators. This approximation is discussed for Dirichlet, Vallee – Poussin, Fejer, Rogozinski and Jackson operators.
American International University Bangladesh (AIUB)
Similarity solution of an unsteady magneto-hydrodynamic flow past a uniform moving horizontal plate with Hall effect in a rotating system has been studied. The governing partial differential equations of the MHD boundary layer flow are reduced to ordinary differential equations by introducing suitable similarity transformations. The similarity equations are then solved numerically by using Range-Kutta six order integration scheme and Nachtshiem-Swigert iteration technique. The obtained results of the numerical solution are then presented graphically in the form of axial and transverse velocity profiles. Finally the corresponding skin friction components are also calculated and displayed in a table showing the effects of various parameters on them.
Islamic University of Gaza, Palestinian Authority
The concept of weak isomorphism was introduced by A. Goetz [2] Weak isomorphisms of Boolean and Post algebras were examined by T. Traczyk [5]. Automorphisms groups of P¬2-lattices were examined by K. Tabash [4].
Victoria University of Bangladesh
American International University Bangladesh (AIUB)
The present study is based on data collected randomly for 1052 respondents of Tongi Pourshova under Gazipur district. The respondents are females of couples.Fifty one percent mothers prefer further at least one child. Those who do not want further child they have around 3 ever born children. This study indicates that high parity level discourage the mothers to have further children.Those who have preferred further children, either they have low fertility level or they wanted more children the assistance in family activities. For the assistance in agriculture work some mothers desire only son irrespective of their parity level. However, negative association is observed between preference of further children and level of parity.
