Open Science Research Excellence

N Aziz

Publications

9

Publications

9
2209
Implementation and Simulation of Half-Bridge Series Resonant Inverter in Zero Voltage Switching
Abstract:
In switch mode power inverters, small sized inverters can be obtained by increasing the switching frequency. Switching frequency increment causes high driver losses. Also, high dt di and dt dv produced by the switching action creates high Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI). In this paper, a series half bridge series resonant inverter circuit is simulated and evaluated practically to demonstrate the turn-on and turn-off conditions during zero or close to zero voltage switching. Also, the reverse recovery current effects of the body diode of the MOSFETs were investigated by operating above and below resonant frequency.
Keywords:
Driver losses, Half Bridge series resonant inverter,Zero Voltage Switching
8
9645
Unsteady Aerodynamics of Multiple Airfoils in Configuration
Abstract:
A potential flow model is used to study the unsteady flow past two airfoils in configuration, each of which is suddenly set into motion. The airfoil bound vortices are modeled using lumped vortex elements and the wake behind the airfoil is modeled by discrete vortices. This consists of solving a steady state flow problem at each time-step where unsteadiness is incorporated through the “zero normal flow on a solid surface" boundary condition at every time instant. Additionally, along with the “zero normal flow on a solid surface" boundary condition Kelvin-s condition is used to compute the strength of the latest wake vortex shed from the trailing edge of the airfoil. Location of the wake vortices is updated at each time-step to get the wake shape at each time instant. Results are presented to show the effect of airfoil-airfoil interaction and airfoil-wake interaction on the aerodynamic characteristics of each airfoil.
Keywords:
Aerodynamics, Airfoils, Configuration, Unsteady.
7
12789
Impact of the Amendments of Malaysian Code of Corporate Governance (2007) on Governance of GLCs and Performance
Abstract:
The study aims to investigate the impact on board and audit committee characteristics and firm performance before and after the revision of MCCG (2007) on GLCs over the period 2005-2010. We used Return on Assets (ROA) as a proxy for firm performance. The data consists of two groups; data collected before and after the amendments of MCCG (2007). Findings show that boards of directors with accounting / finance qualifications (BEXP) are statistically significant with performance for period before the amendments. As for audit committee members with accounting or finance qualifications (ACEXP), correlation results indicate a negative association and non-significant results for the years before amendments. However, the years after the amendments show positive relationship with highly significant correlations (1%) to ROA. This indicates that the amendments of MCCG 2007 on the audit committee members- literacy in accounting have impacted the governance structures and performance of GLCs.
Keywords:
BOD and Audit Committees, firm performance, GLCs.
6
14436
Gauss-Seidel Iterative Methods for Rank Deficient Least Squares Problems
Abstract:
We study the semiconvergence of Gauss-Seidel iterative methods for the least squares solution of minimal norm of rank deficient linear systems of equations. Necessary and sufficient conditions for the semiconvergence of the Gauss-Seidel iterative method are given. We also show that if the linear system of equations is consistent, then the proposed methods with a zero vector as an initial guess converge in one iteration. Some numerical results are given to illustrate the theoretical results.
Keywords:
rank deficient least squares problems, AOR iterativemethod, Gauss-Seidel iterative method, semiconvergence.
5
9996655
Breaking of Charge Independence of Nucleon-Nucleon Interaction Using Phase Shift Calculations
Abstract:

Using calculated phase- shift values, for pp, nn, and np elastic scattering in the energy range 1MeV to 350MeV, the charge independence breaking of nucleon-nucleon interaction is investigated. We have used Darboux transformation to calculate phase-shift for the first three values of

Keywords:
Phase-shift, charge independence breaking, Darboux transformation.
4
10006260
Development of Prediction Models of Day-Ahead Hourly Building Electricity Consumption and Peak Power Demand Using the Machine Learning Method
Abstract:

To encourage building owners to purchase electricity at the wholesale market and reduce building peak demand, this study aims to develop models that predict day-ahead hourly electricity consumption and demand using artificial neural network (ANN) and support vector machine (SVM). All prediction models are built in Python, with tool Scikit-learn and Pybrain. The input data for both consumption and demand prediction are time stamp, outdoor dry bulb temperature, relative humidity, air handling unit (AHU), supply air temperature and solar radiation. Solar radiation, which is unavailable a day-ahead, is predicted at first, and then this estimation is used as an input to predict consumption and demand. Models to predict consumption and demand are trained in both SVM and ANN, and depend on cooling or heating, weekdays or weekends. The results show that ANN is the better option for both consumption and demand prediction. It can achieve 15.50% to 20.03% coefficient of variance of root mean square error (CVRMSE) for consumption prediction and 22.89% to 32.42% CVRMSE for demand prediction, respectively. To conclude, the presented models have potential to help building owners to purchase electricity at the wholesale market, but they are not robust when used in demand response control.

Keywords:
Building energy prediction, data mining, demand response, electricity market.
3
10006814
Factors Affecting Current Ratings for Underground and Air Cables
Abstract:

The aim of this paper is to present a parametric study to determine the major factors that influence the calculations of current rating for both air and underground cables. The current carrying capability of the power cables rely largely on the installation conditions and material properties. In this work, the influences on ampacity of conductor size, soil thermal resistivity and ambient soil temperature for underground installations are shown. The influences on the current-carrying capacity of solar heating (time of day effects and intensity of solar radiation), ambient air temperature and cable size for cables air are also presented. IEC and IEEE standards are taken as reference.

Keywords:
Cable ampacity, underground cable, IEC standard, air cables.
2
10007789
Improvement of Antibacterial Activity for Ceftazidime by Partially Purified Tannase from Penicillium expansum
Abstract:

Tannase has wide applications in food, beverage, brewing, cosmetics and chemical industries and one of the major applications of tannase is the production of gallic acid. Gallic acid is used for manufacturing of trimethoprim. In the present study, a local fungal strain of Penicillium expansum A4 isolated from spoilt apple samples gave the highest production level of tannase. Tannase was partially purified with a recovery yield of 92.52% and 6.32 fold of purification by precipitation using ammonium sulfate at 50% saturation. Tannase led to increased antimicrobial activity of ceftazidime against Pseudomonas aeruginosa and S. aureus and had a synergism effect at low concentrations of ceftazidime, and thus, tannase may be a useful adjuvant agent for the treatment of many bacterial infections in combination with ceftazidime.

Keywords:
Ceftazidime, Penicillium expansum, tannase, antimicrobial activity.
1
10010071
Received Signal Strength Indicator Based Localization of Bluetooth Devices Using Trilateration: An Improved Method for the Visually Impaired People
Abstract:

The instantaneous and spatial localization for visually impaired people in dynamically changing environments with unexpected hazards and obstacles, is the most demanding and challenging issue faced by the navigation systems today. Since Bluetooth cannot utilize techniques like Time Difference of Arrival (TDOA) and Time of Arrival (TOA), it uses received signal strength indicator (RSSI) to measure Receive Signal Strength (RSS). The measurements using RSSI can be improved significantly by improving the existing methodologies related to RSSI. Therefore, the current paper focuses on proposing an improved method using trilateration for localization of Bluetooth devices for visually impaired people. To validate the method, class 2 Bluetooth devices were used along with the development of a software. Experiments were then conducted to obtain surface plots that showed the signal interferences and other environmental effects. Finally, the results obtained show the surface plots for all Bluetooth modules used along with the strong and weak points depicted as per the color codes in red, yellow and blue. It was concluded that the suggested improved method of measuring RSS using trilateration helped to not only measure signal strength affectively but also highlighted how the signal strength can be influenced by atmospheric conditions such as noise, reflections, etc.

Keywords:
Bluetooth, indoor/outdoor localization, received signal strength indicator, visually impaired.