American International University-Bangladesh (AIUB)
Bangladesh University of Engineering and Technology (BUET)
In this paper, the effects of using GaAs and AlAs in alternate Distributed Bragg Reflector (DBR) layers for a VCSEL have been investigated using computer simulation. It has been shown that by using GaAs and AlAs in alternate DBR layers, high reflectivity of 99.9% can be achieved using 20 pairs of layers on a single side. Next, the effects of using Amorphous Silicon and SiO2 in alternate DBR layers for a VCSEL have been investigated. It has been shown that only 4 pairs are needed to achieve 99.9% reflectivity. This is a significant saving of layers (space) compared to using semiconductor DBR layers. However, the semiconductor DBR layers mentioned above are advantageous because absorption of light in each layer of the dielectric DBR layers is high. The result obtained from this comparative study is expected to be valuable in developing new types of structures of VCSEL.
American International University-Bangladesh (AIUB)
Asian Institute of Technology, AIT, Thailand
A typical wireless channel frequency response varies randomly both in frequency and in distance, causing intersymbol interference (ISI) and thus degrading the system BER. This problem becomes more severe when the signal bandwidth increases. In addition, when the system bandwidth is large, narrowband beamforming techniques that help overcome the problem in narrowband systems cannot be applied since gain and phase-shifting devices become inadequate when variation of modulation function within group delay profile is noticeable for spatially allocated antennas. We focus on broadband beamforming techniques for broadband systems using tapped delay line (TDL) filters. A minimum mean square error processor with TDL structure has been designed where we don’t consider presteering delay as a constraint to avoid computation complexities as antennas’ directivities gains can be controlled precisely by unequal taps distribution among the spatially separated antennas. This processor will be suitable to support higher data rate with better reliability for third generation mobile communication systems specially W-CDMA and low orbit satellite communications or high altitude stratospheric platform (HAPS) as third generation mobile systems (UMTS/IMT-2000/FPLMTS) is based on Wideband CDMA whose air interface was designed to enable smart antenna deployment for increased capacity and coverage. Performance improvement of antenna arrays with TDL filters compared to existing systems for such applications will be discussed.
Jadavpur University, Kolkata, India
Jadavpur University, Kolkata, India
Jadavpur University, Kolkata, India
College of Engineering, Bangalore, India
College of Engineering, Bangalore, India
Data security schemes in computer networks have achieved increasing importance in the present age of universal electronic connectivity, of viruses and hackers, of electronic eavesdropping and electronic deceit. Spin based devices have secured attractive features to embed them in VLSI/ULSI chips for higher density of integration, better computational speed and also less cost. Cellular Automata has several characteristics, which can be utilized to provide better data security in computer networks. Such security scheme can be achieved using software as well as hardware. The hardware implementation can assure speed improvement. Spin logic based circuits will further improve the speed and hence in the present work we have proposed single spin logic circuits for Cellular Automata based data security scheme in computer networks.
American International University-Bangladesh (AIUB)
Kitami Institute of Technology, Japan
Kitami Institute of Technology, Japan
In this paper, a discrete time optimal control system synthesis is proposed for speed control of an interior permanent magnet synchronous motor (IPMSM) taking core loss into account. The effects of core loss deteriorate the linearity of torque control. Therefore, we include a current ratio term to design the proposed optimal control. For the vector control system and the loss minimization control system, the ratio of magnetizing d-axis current to q-axis current is not same value. A state space having multi-input and multi-output (MIMO) is developed from which the proposed discrete time linear model is developed. The proposed controller acts like proportional and integral controller by incorporating an augmented system. The integral term eliminates the steady state error of speed. The performance of our proposed controller is demonstrated by simulation studies, which are performed by Matlab. The simulation results show that the accurate speed control is achieved.
American International University - Bangladesh (AIUB)
University of Engineering and Technology (BUET)
In this paper, a new analytical model has been presented to calculate the internal electric field distribution of a vertical cavity surface emitting laser (VSCEL). Using Sampled Transfer Matrix Method (STMM), the field equations have been deduced for this model. Using this model one can determine the amount of optical feedback inside a VCSEL from the external reflector. The variations of threshold current, differential quantum efficiency and output power due to external reflector positions obtained by this model have been computed. The obtained results were compared with the theoretical and experimental results obtained by other researchers and good agreement has been observed.
Tokyo University of Agriculture and Technology, Japan
Tokyo University of Agriculture and Technology, Japan
Tokyo University of Agriculture and Technology, Japan
Tokyo University of Agriculture and Technology, Japan
Small Hydro-power installation in a rural community paves the way to economic development and positive environmental impact of the area. Kuromori Pico Hydro Power Plant (PHPP), a demo-project of 21st Center of Excellence (COE) program of Tokyo University of Agriculture and Technology (TUAT), is capable of generating continuous power of about 515W. Here, installation of a PHPP in a rural area and its output evaluation is discussed in this study. Different methods are applied to investigate the proper site of installation by field survey. In the future, this type of small source can be increased to some numbers which is possible to be connected with one another working as a micro gird system to supply electricity independently according to the necessary demand. To optimize the plant generation, a proper load management is necessary. It is the aim of this paper to allocate and schedule properly the load or demand using the concept of Demand Side management (DSM). With the advent of electronic load controller, output of generator is regulated through a dummy load. Ways and means of utilizing energy from this load will also be dealt in this study to maximize the usefulness of the generated power from the plant.
American International University Bangladesh (AIUB)
This paper presents a novel approach for designing low cost, high performance PC-based computerized numerical controlled automation systems. The paper illustrates the presented approach through the implementation of a PC-based CNC automated PCB drilling machine. The design employs a PC as the main driving force thus allowing it to make the system far more economical to implement than the stand-alone CNC systems. The implemented system also solves several precision related issues of PC-based CNC systems through the use of software-generated signals rather than the usual circuit level signal generators. This allows the presented system to function under non real-time kernel operating systems with high-level of precision. It offers considerable economical benefits. The performance of the proposed design is assessed through several trial runs of the implemented machine. Test results of the trial runs have shown the expected precision level with no visible disagreements.
American International University Bangladesh (AIUB)
Bangladesh University of Engineering & Technology
Anna University, Chennai, India
Anna University, Chennai, India
Single crystals of Ammonium Oxalate monohydrate (AO) were grown from aqueous solution in pure form and in presence of Ethylenedinitrilotetraacetic acid (EDTA) and some rare earth impurities like Sm+3, La+3, Gd+3 by the slow cooling method. Well faceted AO crystals with the dimensions of 1.0 x 1.0 x 2.0 cm3 were obtained. X-ray diffractometry, Fourier transform infrared (FT-IR) spectroscopy and Vicker’s microhardness measurements were carried out to study the structural and mechanical properties of the grown crystals. FT-IR spectra confirmed the presence of different vibrational modes of oxalate group in the grown samples. X-ray diffraction analysis confirmed the crystalline structure of the grown samples of which the pure specimen showed good agreement with the standard data. The microhardness study showed a significant increase in hardness values of AO crystals grown in presence of impurities.
American International University Bangladesh (AIUB)
The present paper investigates the effects of mixed temperature- and depth-dependent viscosity on an unsteady flow of an incompressible fluid on a rotating disk. We assume that the fluid viscosity strongly depends on temperature and depth which may be directly applicable to the earth’s mantle and a uniform mid-ocean ridge basalt reservoir in whole mantle flow. The system of axial symmetric non-linear partial differential equations governing the unsteady flow and heat transfer is written in cylindrical polar coordinates, and reduced to non linear ordinary differential equations by introducing suitable similarity parameters. Solutions for the flow and temperature fields are obtained numerically assuming large Prandtl number by using Runge-Kutta and Shooting methods. The nature of radial, tangential and axial velocities and temperature are presented for changing various non-dimensional parameters at different layers of the medium. The coefficients of skin frictions and the rate of heat transfer are calculated at different parameters.
American International University-Bangladesh (AIUB)
American International University-Bangladesh (AIUB)
In recent years much avant-garde architectural work has been dominated by a process based theoretical paradigm, inspired largely by various thinkers, critics, and philosophers. This particular ‘process practice’ attempts to address the paradox at the heart of contemporary production, by looking dialectically at the relationship between structure, pattern and ornament in nature with brainstorming and use of computer simulation. The goal of this paper is to expose the development of a computer optimized system that can generate solutions for defining spaces involving a number of contextual relationships of activities. This can be termed as natural behavior and cultural concern in computational architecture. In particular, this research undertakes a pilot study on pattern and behavior in nature and implements the findings in to an architectural problem. The Initial Research focuses on Theory of emergence, Analysis of swarm behavior, and Analysis of ant system. Specific urban sites with different behavior patterns are chosen in Barcelona where this process is implemented to examine how they respond to this course of action. This method provides an optimized solution which can be called ‘bottom up’ solution instead of a ‘top down’ solution (where architects play the role as they are the decisive decision makers) for an architectural problem. Briefly put, it is the use of computers to model nature- architecture, and simultaneously the study of nature to improve the usage or computer where architecture is the platform for the research. This essay illustrates how new digital tools are being used to understand and design cities.
American International University Bangladesh (AIUB)
Shahjalal University of Science & Technology., Sylhet, Bangladesh
This study has focused on the quaternary water/reactant/oil/surfactant system. The goal of this work is to investigate the influence of reactant on the phase behavior of the micro emulsion. In addition to that the reactant-surfactant interaction can lead to significant changes in the phase behavior and particle size. Monte Carlo computer simulation and laboratory test results is used to verify this behavior. The comparison reveals that computer simulation can be helpful for investigating micro emulsion region of quaternary system. It is evident from the results that two dimensional Monte Carlo simulation program is capable of providing reasonable results. The paper is ended with a recommendation for future research with three dimensional Monte Carlo model in order to get better result though it takes reasonable higher time.
American International University Bangladesh (AIUB)
American International University Bangladesh (AIUB)
This study focused on capital machinery manufacturing enterprises of Bangladesh relating to density of indigenous technology. To determine the impact of indigenous technology on the on the growth of capital machinery manufacturing Small and medium sized enterprises, 150 enterprises were surveyed. Result of the demonstrated that with the supply of advanced manufacturing technology and indigenous industrial technology from local sources, the growth of industrial machineries enterprises could be enhanced. This study proposed an empirical formula in order to use in making assessment of requirements of indigenous advanced manufacturing technology and industrial technology for the sustainable growth of capital manufacturing enterprises. This study ended with recommendations for the growth of these enterprises with an aim to supply higher percentage capital machineries from local sources to manufacturing industries.
Ahsanullah University of Science and Technology (AUST),
Bangladesh University of Engineering and Technology (BUET)
Bangladesh University of Engineering and Technology (BUET)
A parametric study of two-dimensional steady-state natural convection in a modified square enclosure has been numerically studied. An isoflux heat source is placed at the left vertical wall, while the right vertical wall is kept at constant cold temperature, and two remaining walls which are elliptic, are assumed to be adiabatic. The fluid concerned is air with Prandtl number fixed at 0.71. The dimensionless mass, momentum and energy equations are solved by Galerkin finite element method. The streamlines and isotherms are produced; heat transfer characteristics are obtained for Rayleigh numbers from 103 to 106. The numerical results indicate that the replacement of straight horizontal walls with the elliptic arcs significantly affects the flow and temperature fields, thus yielding an increase of the heat transfer rate. A good comparison between the present numerical predictions and the previously published data has been achieved.
University of Waterloo, Canada
Metals and alloys are susceptible to different types of environmentally induced cracking such as stress corrosion cracking, hydrogen induced cracking or hydrogen embrittlement, corrosion fatigue cracking, and liquid metal cracking. This paper presents a review of stress corrosion cracking, which mainly occurs in susceptible alloys due to synergism between tensile stress and corrosive environment. It highlights the conditions for the occurrence of stress corrosion cracking, and discusses the principal factors such as geometry of alloy component, metallurgical characteristics, surrounding environment, acting tensile stress, interaction or exposure time and temperature, which affect stress corrosion cracking. In addition, different stages and mechanisms of stress corrosion cracking have been discussed briefly. This paper also illuminates the major preventive measures for stress corrosion cracking.
