American International University-Bangladesh (AIUB)
Kitami Institute of Technology, Japan
Kitami Institute of Technology, Japan
In this paper, an adaptive parameter identification system is designed to
estimate the stator resistance, rotor resistance and core-loss resistance of an
induction motor (IM) taking core-loss into account. The designed procedure of
the identification technique is based on the model reference adaptive system (MRAS)
theory. In order to design the MRAS, an adjustable model (AD), which is a
mathematical model of IM, should be designed. Since the mathematical expression
of an IM behaves like a bilinear system, a bilinear model of IM is considered in
AD. A bilinear observer is also designed to estimate the unmeasured state
quantities of IM. By means of Lyapunov stability criterion, the gain of bilinear
observer and the updating law of parameters can be found by choosing an
appropriate reference model. The magnetizing current and rotor flux are
estimated from the terminal measured values by using adaptive bilinear observer.
The performance of observer and proposed identification technique are verified
by simulation results, which are carried out by Matlab/Simulink software. The
simulation results are found to have excellent performance for estimation of
unmeasured state quantities and changeable parameters of IM taking core loss
into account.
American International University-Bangladesh (AIUB)
Bangladesh University of Engineering and Technology (BUET)
In this work, an optimization method for obtaining improved modulation performance of a near-infrared 980nm VCSEL has been presented. Optimum values of relative intensity noise (RIN) and frequency modulation (FM) noise of the VCSEL have been obtained by optimizing differential gain, injection current, number of quantum wells (QWs) and active radius. After a number of trials the optimum values of the above mentioned parameters have been obtained where, the noise level has been found as low during modulation. The optimum value of RIN of -160.86 dB/Hz and the FM noise of 107.68 dB have been obtained for the optimum value of the differential gain of 10x10-16 cm2, the injection current of 7.4mA, the number of QW of 3 and the active radius of 4µm. A maximum modulation bandwidth of 24 GHz of the VCSEL is obtained by reducing the noise during modulation. The results thus obtained show improved performance over some recent works.
American International University-Bangladesh (AIUB)
Bangladesh University of Engineering and Technology (BUET)
RC frame structures are used for the building construction and these frames
are usually in-filled with masonry walls for aesthetic reasons, water proofing,
heat and sound insulation and better security. The infill also contributes
lateral stiffness to columns. Structural response to an earthquake significantly
depends on the building height, infill condition and structural irregularity.
Normally the Equivalent Static Force method is considered in structural
analysis. Since static and linear dynamic analyses do not properly reflect the
effect of soft story, non-linear time-history analysis is needed when
deformation increases gradually. In this study column size, column stiffness and
wall stiffness are determined for different number of building stories.
Responses of structures are simulated and analyzed by time-history analysis for
different ground motions, considering both linear and non-linear cases for
different infill conditions. Finally, responses of these structures are
compared. In elastic analysis, it is observed that frames with infill always
perform better. In addition, maximum inter story drift of frames without infill
become larger than soft story with increasing story height. But in inelastic
analysis, frames with soft story are more vulnerable. Thus vulnerability of soft
story structures can be better understood with inelastic analysis.
American International University-Bangladesh (AIUB)
Bangladesh University of Engineering and Technology (BUET)
Bangladesh University of Engineering and Technology (BUET)
In this work, a 1250nm IR bottom emitting VCSEL has been designed using MQWs with a superior quaternary compound Ga0.88In0.12N0.01As0.99 as the well material and the binary compound GaAs as the barrier material, AlAs/GaAs top DBR system and AlAs/GaAs bottom DBR system with Ti/Pt/Au as the p-side contact and Ni/Ge/Au as the n –side contact. In the active region, three quantum wells and two barrier layers using the materials mentioned above have been used. Two SCH layers of GaAs (same as the barrier), a p-cladding layer made of Al0.4Ga0.6As (doped with Si) and an n-cladding layer made of Al0.4Ga0.6As (doped with Be) have been used. The optical cavity length has been adjusted to 1.5 wavelengths. The VCSEL is designed for fabrication on a one micron GaAs substrate with 20 pairs of AlAs/GaAs bottom DBR system grown epitaxially. On top of the bottom DBR the active region is to be grown. The top DBR consists of 32 pairs of AlAs/GaAs to be grown epitaxially. The computed reflectivity of the bottom DBR at the operating wavelength is 99.5% and the same of the top DBR is 99.99%. The top of the top DBR system is HR coated and the bottom of the substrate is to be AR coated since the VCSEL is a bottom emitting one. The cavity diameter has been restricted to 10micron by using two oxide layers on top and bottom of the SCH regions. Intracavity structure has been used in the design of the VCSEL to reduce unnecessary heating in the DBR layers due to the injection current. Starting from the substrate up to the end of the top DBR the entire VCSEL is lattice matched and designed for epitaxial growth.
American International University-Bangladesh (AIUB)
The Increase in demand of mobile multimedia services contributes to the increase in energy consumption of mobile communications. High data with minimal transmission bit energy is one of the significant issues that need considerable attention to reduce overall energy consumption by mobile communications. In this paper, we address this issue using femtocells in the coverage of the macrocell in Long Term Evolution-Advanced (LTE-Advanced) systems. The energy efficiency performance of conventional schedulers such as Round Robin, Max-Min, and Proportional Fair schedulers are carried out in the system level simulation scenario under varying user density. The quality of service performance of all schedulers in terms of fair resource allocation among users is also carried out under the energy efficiency constraint. An extensive system level simulation is performed to evaluate the energy efficiency performance of all these schedulers. The simulation results show that irrespective of the user density and type, the presence of femtocells reduces the average energy per bit transmission requirement of all schedulers. Because of optimal tradeoff between average energy per bit transmission and fairness performances, we propose Proportional Fair scheduler with femtocells to improve downlink transmission energy efficiency in LTE-Advanced systems.
American International University-Bangladesh (AIUB)
Bangladesh University of Engineering and Technology (BUET)
Bangladesh University of Engineering and Technology (BUET)
In this work, a top emitting 459.5 nm Blue VCSEL has been designed for room
temperature operation using In0.22Ga0.78N/ In0.12Ga0.88N multi-quantum well in
the active region, SiO2/ TiO2 in the top DBR, AlInN/ GaN in the bottom DBR. In
this design, the active region of the VCSEL has been formed using five
In0.22Ga0.78N quantum wells, four barrier layers using In0.12Ga0.88N, two SCH
layers using the same ternary compound semiconductor In0.12Ga0.88N. Mg doped
Al0.01Ga0.99N has been used as the p-cladding material and Si doped
Al0.01Ga0.99N has been used as the n-cladding material. The VCSEL has been
designed for fabrication on a Si doped GaN layer grown on a c-plane Sapphire
substrate. Starting from the substrate upto the p-cladding material the layers
are lattice matched and can be fabricated using modern epitaxial growth
techniques. An indium tin oxide (ITO) layer is grown on top of the p-cladding
material. The top DBR layers are to be formed separately and then have to be
wafer bonded with the ITO layer as the top DBR system is made of dielectric
material to have the desired reflectivity of 99.5% with minimum number of pairs.
The bottom DBR system has been designed for providing 99.99% reflectivity. Intra
cavity structure has been chosen to avoid current flow through the top as well
as the bottom DBR mirror systems. Computations show an acceptable performance
characteristic of the designed VCSEL.
Bangladesh University of Engineering and Technology (BUET)
Bangladesh University of Engineering and Technology (BUET)
In this work, a top emitting 1330 nm Ga0.6 In0.4As/Ga0.2In0.8P MQW vertical cavity surface emitting laser (VCSEL) has been designed for optical pumping through its bottom by an electrically pumped 980 nm Ga0.87In0.13As/Al0.03Ga0.97As VCSEL. The electrically pumped 980 nm VCSEL is first fabricated on a GaAs substrate and then the 1330nm nm VCSEL is fabricated on top of it by first wafer bonding the bottom most DBR layer of the 1330 nm VCSEL on top of the top most DBR layer of the 980nm VCSEL to take care of the slight lattice mismatch of these two layers. However, in each of the two VCSELs the layers are almost lattice matched which makes the device attractive for epitaxial growth. The two VCSELs are thus vertically integrated in one device. In this design, the active region of the intracavity structure 980 nm VCSEL consists of 3 quantum wells (QWs) using Ga0.87In0.13As, 2 barriers using Al0.03Ga0.97As and 2 separate confinement hetero-structures (SCH) using same material as the barrier. Si doped GaInP has been chosen as the p-cladding layer and C doped GaInP has been chosen as the n-cladding layer for the laser. Both the top distributed bragg reflector (DBR) and bottom DBR mirrors hve been formed using the same AlAs/GaAs pairs materials for the 980nm VCSEL. The active region of the top emitting 1330 nm VCSEL consists of 3 QWs using Ga0.6 In0.4As, 2 barriers using Ga0.2In0.8P and 2 SCH using same material as the barrier. Si doped AlInAs has been chosen as the p-cladding layer and C doped AlInAs has been chosen as the n-cladding layer for the laser. Both the top DBR and bottom DBR mirrors have been formed using the same Al0.26Ga0.21In0.53As/InP pairs of materials for the 1330nm VCSEL. This integrated VCSEL is expected to work well after fabrication because of it’s simple structure and the widely used materials chosen for the active as well as the DBR layers.
American International University-Bangladesh (AIUB)
American International University-Bangladesh (AIUB)
American International University-Bangladesh (AIUB)
Thermal environment of urban spaces plays a great role on the quality of life
in a city. It directly affects people’s behaviour and usage of outdoor spaces.
Therefore, an environmentally conscious urban design solution should give high
priority to the thermal comfort implications of urban microclimate.
Deterioration of urban microclimate due to unplanned construction of built forms
which is largely the outcome of uncontrolled urbanization is a major concern in
Dhaka. Regarding the context of Bangladesh where climate change is a crucial
issue, a proper arrangement of urban blocks with comfortable outdoor spaces can
positively contribute to mitigate the harmful impacts of urban climate. The
study of urban thermal environment and outdoor comfort demands an urgent thought
specially due to the introduction the new building construction rule 2008. The
rule encourages a high density urban development through a relaxed building
height and plot coverage rules and regulations. Building height, distance
between buildings and street widths are important design features which need to
be considered at the design stage of urban outdoor spaces. The impact of the
rule is being reflected in the recent high-rise characters in city’s residential
and commercial areas. The commercial areas in particular are being hastily
filled up with high-rise structures under fast urban expansion. It is becoming
increasingly difficult to ignore the unfavourable impact of built forms on urban
micro-climate. These high rise buildings built to achieve the highest commercial
benefits with least consideration for climatic issues are a large contributor of
urban heat islands. Uncomfortable urban microclimate not only affects urban life
on outdoor spaces but also increases energy demand of buildings. This study
attempts to examine the role of physical configuration of urban canyons in
controlling the microclimate. For this study, an existing urban canyon in Dhaka
city have been chosen which is generated by two rows of high-rise structures
with high H/W ratio. It will observe the air temperature, humidity, mutual
shading, sky view factor and wind speed which represent the microclimatic
characteristics of the canyons. Finally, the aim of this study is to explore the
role of urban planning and urban design in creating favourable urban
micro-climate so that the experts are aware of its consequences at the early
design stage. Integration of climatic considerations into city planning and
design can thus contribute to sustainable urban development as well as
mitigation of the adverse impacts of climate change.
American International University-Bangladesh (AIUB)
The issue of desirable urban form that is capable of feeding contemporary needs without disturbing a city’s intrinsic character is the prime focus of this research. The debate over an ideal or desirable urban form is an issue that is investigated over a long period all over the world. However, despite the intention of achieving a livable urban form, in practice we hardly see success achieved by learning from the past, through the careful study of morphogenetic process. The research claims that if it is possible to reconcile the civic ideals that have been evolved through ages of human efforts will ensure the overall sustainability by expanding the longevity of urban layout and form. For this purpose, a comprehensive morphological study (based on both archival and empirical data) is conducted in Melbourne CBD to investigate the degree of continuity of urban form and its impact on the quality of living condition. The morphological investigation illustrates how the proposition of continuity influences sustainability. This phenomena of urban continuity as a tool of sustainability helps to form the hypothesis of this research.
University of Asia Pacific, Bangladesh
American International University-Bangladesh (AIUB)
A digital society is an Information and Communication Technology (ICT) driven
knowledge-based society where information and services will be readily available
on line. To achieve this, we need such a communication infrastructure which
supports expansion of broadband and introduction of Triple play (Voice +Data
+Video) over fixed and mobile line. Next Generation Network (NGN) is a packet
based network which is able to provide triple play services on line. A major
challenge is in the transmission access network. In this paper, first the
present communication network infrastructure of Bangladesh and its limitations
to tackle the future challenges has been presented. Then the possible options to
meet the ever-growing demand of high-speed and high bandwidth of new generation
services with quality of service (QoS) have been explored and their performance
has been compared. Finally, an All-IP NGN model for Bangladesh has been proposed
and its implementation with possible options has been discussed with QoS and
cost analysis.
American International University-Bangladesh (AIUB)
American International University-Bangladesh (AIUB)
American International University-Bangladesh (AIUB)
American International University-Bangladesh (AIUB)
Student’s satisfaction plays a vital role in success of an educational institute. Hence, many educational institutes continuously improve their service to produce a supportive learning environment to satisfy the student need. For this reason, Educational institutions collect student satisfaction data to make decision about institutional quality, but till now it cannot be determined because student satisfaction is a complex matter which is influenced by variety of characteristics of students and institutions. There are many studies have been performed to inspect student satisfaction in the form of college services, programs, student’s accommodation, student– faculty interaction, consulting hours etc. So, still we cannot have a standard method to know what is going on about satisfaction in the case of a core course. In this research we determined the attributes that heavily affect student satisfaction in a core course of computer science and the current status of other attributes as well.
