Minia University, 61519 El-Minia, Egypt
Assiut University, 71516 Assiut, Egypt
Kanazawa University
This paper investigates dynamics of semiconductor lasers under optical feedback during transitions to chaos. Influence of the external-cavity length on the route-to-chaos is elucidated. The study is based on numerical solution of a time-delay model of rate equations. The route to chaos is period doubling when the ratio of the relaxation frequency to the external-cavity resonance frequency is less than unity. The route is sub-harmonic when the frequency ratio is slightly higher than unity, and is quasi-periodic characterized by the compound-cavity frequency and the relaxation frequency as well as their difference when the ratio is far above unity.
American International University Bangladesh (AIUB)
Bangladesh University of Engineering and Technology (BUET)
In this paper, the reflectivity of a VCSEL has been calculated by choosing the refractive indices of the two layers in a period of a DBR stack alternately as high and low at first, and next, by choosing a period of low and high. Computation has been done by considering an even number of layers in the stack (i.e., N = 40) at first, and next, computation has been done by considering an odd number of layers in the stack (i.e., N = 39). Higher reflectivity has been achieved for a high value of refractive index in the first layer compared to second one by considering both even and odd number of layers in the DBR stack. A reflectivity of 99.9% has been achieved for 40 layers in the stack using GaAs (n = 3.52) as the first layer and AlAs (n = 2.95) as the second layer in a period of the stack. For the same number of layers 98% reflectivity has been achieved using AlAs (n = 2.95) as the first layer and GaAs (n = 3.52) as the second layer in a period of the stack. Nearly same results have been observed for an odd number of layers in the stack. It has been observed that the order of the refractive indices of DBR layers in a period of the stack effects the overall mirror reflectivity. The reflectivity has also been calculated by increasing the refractive index of the substrate. The reflectivity is increased by increasing the refractive index of the substrate for a high value of refractive index in the first layer compared to second one.
Assiut University, 71516 Assiut, Egypt
Minia University, 61519 El-Minia, Egypt
Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
This paper investigates influence of the linewidth enhancement factor on the output of 980-InGaAs/InP fiber grating lasers operating under strong optical feedback. The study is based on intensive numerical integration of an improved time-delay rate equations of semiconductor lasers over wide ranges of the linewidth enhancement factor and ratio of the grating reflectivity to that of the anti-reflecting front facet. The results show that the laser operates in continuous wave and pulsation at small values of the linewidth enhancement factor. Under large values of the factor, the laser happens to exhibit chaos and pulsation. However, such pulsation is predicted to be more stable due to locking of the laser oscillation at the external cavity resonance frequency.
Multimedia University, Jalan Multimedia, 63100 Cyberjaya
University of Malaya
University of Malaya
Multimedia University, Jalan Multimedia, 63100 Cyberjaya
This paper presents the design and implementation of a Field-Oriented Control (FOC) IC for 3 phase induction motors using the Complex Programmable Logic Design (CPLD). This paper develops a hardware prototype for controlling a 3-phase induction motor. The control structures are realized using CPLDs from Altera Inc. All control functions including the space vector modulation based PWM waveform generation, field oriented control algorithm and rotor flux position estimation have been realized using CPLD based programmable logic gates. The constructed FOC IC consists of 6844 logic elements and is realized using Cyclone, EPIC12q240C8 from Altera Inc. The fixed point format and 16 bit integer arithmetic have been employed in the numbering system employed in this design. The sampling rate can be programmed up to 1 MHz. Experimental results are included in this paper to illustrate the performance of the designed FOCIC.
Tokyo Metropolitan University, Japan
Tokyo Metropolitan University, Japan
Tokyo Metropolitan University, Japan
Ultra-wideband characteristics of finite-sized self-complementary planar on-chip antennas integrated with semiconductor mesa structure are studied with the target of realizing a monolithic integrated antenna for terahertz applications. Effects of geometrical structure on antenna characteristics are numerically studied taking differences of mesa structures and antenna shapes at the outer edge into account. It is found that, as long as the semiconductor mesa size is smaller than 1/30 of the on-chip antenna, the mesa size is relatively enough small to obtain sufficiently broadband input impedance and radiation efficiency in THz range. The magnitude of the broadband input impedance dominantly depends on the volume and the structural design of the semiconductor mesa structure. The radiation pattern and efficiency are influenced by asymmetric structure of the several-m-sized mesa, which becomes clear if the frequency is above 2 THz.
American International University Bangladesh (AIUB)
Kitami Institute of Technology, Japan
Kitami Institute of Technology, Japan
PI controller is still the most commonly used controller in the industrial applications despite the development of advanced control techniques due to their simplicity. Usually, the conventional PI controller constants are determined by trial and error, which suffer from the instability for the variation of disturbance and system parameters. Also, always steady state error is occurred where PI controller constants are chosen by trial and error. Therefore, to overcome such a drawback, in this paper an improved PI speed control of SVM technique of PWM inverter fed indirect field-oriented induction motor is designed. To improve the steady state error and the stability of the proposed PI controller, the gain of PI controller is selected using the pole-placement technique. The poles of closed loop controller are chosen as negative real from the dynamic motion of induction motor. The effectiveness of the proposed method has been demonstrated by simulation study. The simulation results show good performance using the improved PI controller.
American International University - Bangladesh (AIUB)
Asian Institute of Technology (AIT), Thailand
American International University – Bangladesh
In this paper, the effect of processing gain on broadband CDMA system has been investigated. Better performance of PN codes having higher code-lengths with higher cross-correlation is shown using the two-ray channel model, and Kasami spreading codes. For such chip sequence having higher code-lengths, higher signal bandwidth is needed. As broadband signal has both time and space dependency, better performance of broadband expression is verified in [13] with respect to narrowband expression. With such broadband expression, effect of processing gain with same bit rate is demonstrated through simulation.
American International University - Bangladesh (AIUB)
Bangladesh University of Engineering and Technology (BUET)
In this work, novel ideas of computing the threshold current and turn on delay of a Vertical Cavity Surface Emitting Laser (VCSEL) using a different set of equations have been presented. Threshold current of a VCSEL has been computed by solving the rate equations for different values of the injection current. In this work, threshold current of a VCSEL has been found to be 0.18 mA which is very much close to the value of 0.179 mA obtained after computing by using the formula of other researchers. Turn on delay of a VCSEL has also been computed by solving the rate equations. Results obtained by using the proposed method have been found to be in close agreement with those of the other researchers.
American International University - Bangladesh (AIUB)
A novel inverter switched single phase AC voltage rectifier is proposed in this paper. This AC to DC converter has advantages such as minimal or no filtering requirement, low operating frequency (50/60 Hz.) switching, simple structure and almost ripple free output dc voltage. This converter can be modified by changing the transformation ratio of the transformer for obtaining different output dc voltages. The switching timings (phase) of the control is determined by the phase of the current zero crossing to obtain the maximum efficiency.
American International University - Bangladesh (AIUB)
American International University - Bangladesh (AIUB)
Architecture in reality is perceived mainly through the display of space enclosures of different degrees, ranging from complete enclosure to openness. These degrees of enclosure are characterized either by subtle or often exuberant display of interplay between solids and voids. Mass and wall are the key features that play an important role in the formation of any specific relationship that develops between solids and voids.
The level of relationship between wall and mass therefore is critical in shaping the overall appearance of the work. As we look back in time, walls were simply used as means of enclosing the space that was to hold specific functions. Here the obvious priority was assigned to the space and the walls were simply enslaved in order of hierarchy. But, as the history of the built environment progressed with time, this pattern of relationship was challenged and being experimented by various architects. The experiments ranged from subtle variations in the thickness of wall with regard to the associated mass, or by emphasizing its existence by the use of varying height, color, texture, etc., or even by separating it from the mass that was believed to be the mother form in earlier days. Instead of being secondary to the space it enclosed, walls started taking the primary role in terms of announcing its existence.
This change in the pattern of relationship plays a major role in developing the formal language of modern architecture which needs to be acknowledged. The aim of this paper is to address this reinvention of the wall in terms of certain deviations in the pattern of relationship with mass referring to some of the significant works of the 20th century.
CUET
American International University - Bangladesh (AIUB)
Ghana University
Infra-red study of partially carbonized samples obtained from Anthracene and Phenanthrene in presence of AlCl3 in different mole ratios as a catalyst have been undertaken. This method has been found to be a potential tool for investigating the structures of the carbonized samples and also in locating some important properties like stretching and bending of bonds which have wide application in the manufacture of graphite.
Bangladesh University of Engineering & Technology
BCSIR
American International University - Bangladesh (AIUB)
Graphitizable organic materials such as polynuclear aromatic organic compounds and Bangladesh bituminous coals are characterized by their transition through a liquid or plastic state of optical anisotropy called carbonaceous mesophase as a prerequisite to graphitization. Sensitive-tint method of the reflected polarized light technique has been found suitable to study the initial formation of spherules, their coalescences and mosaic formation during mesophase period. The nucleation, growth and coalescence processes of the mesophase spherules establish the basis elements of the graphite microstructure.
Benha University, Benha 13518, Egypt
Benha University, Benha 13518, Egypt.
In the present paper we study the approximate solution for Fredholm integral equation of the second kind in the space L2p(x)[0,2π] with weight function p (x) ≥ 1 and bounded almost every where on [0,2π]. The technique of this study is based on linear polynomial operators Un (φ; x) which generate good approximation to the function φ (x) in the space L2p(x)[0,2π], where the given equation is replaced by Fredholm integral equation with degenerate kernel. The solution of the new equation is taken as an approximate solution to the original equation, and also we give estimates of the errors which arise in this connection. This approximation is discussed in details for Dirichlet, Vallee-Poussin, Féjer, Rogozinski and Jackson operators.
American International University - Bangladesh (AIUB)
The locally similar solution of an unsteady laminar forced convective boundary layer flow for a vertical porous plate in presence of viscous dissipation with the effects of variable viscosity ( ) and thermal conductivity ( ) has been studied under the action of transverse applied magnetic field. The boundary layer equations have been transformed into dimensionless nonlinear ordinary differential equations by similarity transformations. The nonlinear ordinary differential equations are then solved numerically by using Range-Kutta six order integration scheme and Nachtsheim-Swigert iteration technique. The obtained numerical results are presented graphically in the form of velocity and temperature. Finally the effects of the relative temperature difference parameter on the skin friction and heat transfer coefficients are also examined.
American International University - Bangladesh (AIUB)
American International University - Bangladesh (AIUB)
American International University - Bangladesh (AIUB)
Due to the popularity of web and enormous amount of information in different formats, it is quite cumbersome to find exact answer of a question. This has led to frustration for users who are not very much familiar with innovative technology and to some extent for expert users as well. To resolve this problem a service is needed to help the users to skim all irrelevant information rapidly. Question answering systems were created to resolve this problem. The main task of question answering system is to retrieve answers to questions rather than full documents. This paper addresses theoretical investigation among question answering techniques as well as performance analysis and evaluation of different approaches. The major approaches of question answering techniques dominated for comparison in this paper. The rationale for comparative analysis will also be discussed. Finally, the direction for future work and the issues raised by the investigation will be explored.
