Nanofibers and nanoporous metal oxides for gas sensing applications

Air pollution is one of the greatest problems that the world facing is facing today. The World Health Organization (WHO) has provided air quality guidelines, which represent the most widely agreed and up-to-date assessments of air pollutants on human health, recommending stringent thresholds for air quality. This consequently signifies the need to develop gas sensors with the specifications that meet WHO targets. Additionally, gas sensors are also used in variety of other applications such as in many industrial surveillance and processes, automotive, aviation and food industries, medical analysis and diagnostics as well as homeland security and defense. It has been demonstrated that the key factors for developing efficient semiconducting gas sensors is to make use of selected metal oxides after engineering their morphologies and crystallographies. It is well-known that nanostructured metal oxides are generally superior in performance due to their high specific surface area. Hence, searching for the right nanostructured metal oxides with high specific surface area and controllable structures for effective gas sensing is an important research goal nowadays. Many studies, however, have focused on creating nanofibers and nanopores as these morphologies are recognized to be amongst the most efficient for gas sensing applications. Due to the aforementioned justifications, the author of this PhD thesis became involved in the investigation of three different metal oxide nanofibers and nanopores metal oxides, which are tin oxide (SnO2) nanofibers, niobium oxide (Nb2O5) and tungsten trioxide (WO3) nanopores in both nanoporous and nanofibrious structures. There are many different types of gas sensors including those based on conductometric, Schottky and optical templates. In this research, the PhD candidate explored these three templates and investigated their performances when nanofibers and nanopores SnO2, Nb2O5 and WO3 sensitive layers are incorporated with them. To develop the nanostructured sensing films, the author chose electrospinning and anodization synthesis methods which are the most compatible for forming nanofibrious and nanoporous structures. In the first stage, the PhD candidate demonstrated hydrogen (H2) gas sensors based on hollow and filled well-aligned electrospun SnO2 nanofibers, operating at a low temperature of 150 °C.In the second stage of this research, the PhD candidate developed nanoporous Nb2O5 Schottky diode based ethanol (C2H5OH), H2 and methane (CH4) sensors. The sensing behaviours were studied in terms of the Schottky barrier height variations and properties of the metal catalysts. In the third stage, the PhD candidate focused on developing nanoporous Nb2O5 optical based H2 sensors. The compact nanoporous networks with high active surface areas demonstrated excellent absorbance changes at 100 °C with the response factor of 12.1 %. In the last stage, the PhD candidate explored Schottky diode based C2H5OH and H2 gas sensors fabricated via anodization of tungsten (W) foil to form nanoporous WO3 films. In summary, the PhD candidate believes that the studies carried out in the process of this research provided an in-depth vision regarding the fabrication and performance of nanofibers and nanoporous metal oxide based gas sensors

Substation system simulation models for transformer risk assessment analysis

This paper comprises a study which is carried out to investigate and evaluate the effect of lightning stresses on the 132 kV substation in the way to improve its reliability in the event of active lightning activities. The paper also detailed the modelling parameters of substation for this transient analysis in order to evaluate the performance and to recommend such configuration to optimize its design to be not only to withstand the stresses but to be more cost effective. The modelling and simulation are carried out using one of the most powerful power system simulations tools that is PSCAD-EMTDC and the substation layout design is adapted from 132/11 kV Simpang Renggam -- Ayer Hitam substation, courtesy of TNB. The model is based on single phase line model as it was suggested by the IEEE to be adequate to represent the substation in transient analysis simulation. The outcome of this paper would be the results of lightning stresses in term of voltage level measured at particular points in substation. The results are then compared with the suggested BIL for assessment of transformer failure

The effect of polarity on the lightning breakdown voltages of palm oil and coconut oil under a non-uniform field for transformers application

This paper presents a study of the lightning breakdown voltages of Palm Oil (PO) and Coconut Oil (CO) under a non-uniform field with consideration on the polarity effect at various gap distances. All tests were carried based on a needle-sphere electrode configuration and various gap distances ranging from 2 to 25 mm under positive and negative voltage polarities. Three different testing techniques were used in this study including rising-voltage, up-and-down and multiple-voltage methods. The PO used in this study was Refined, Bleached and Deodorised Palm Oil (RBDPO) Olein. Three different samples of RBDPO and one sample of CO were tested. The Weibull distribution was used as a statistical approach to determine the withstand voltages of all samples at 1% and 50% probabilities for each type of oil. Under positive voltage polarity, it was found that the 50% breakdown voltages of RBDPO and CO were comparable with Mineral Oil (MO) whereby the highest percentage of difference among all gap distances was less than 15%. RBDPO and CO have lower 50% breakdown voltages than MO under a negative lightning impulse for which the highest percentage of difference can be up to 40%

Characterization of metal contacts for two-dimensional MoS2 nanoflakes

While layered materials are increasingly investigated for their potential in nanoelectronics, their functionality and efficiency depend on charge injection into the materials via metallic contacts.This work explores the characteristics of different metals (aluminium, tungsten, gold, and platinum) deposited on to nanostructured thin films made of two-dimensional (2D) MoS2 flakes. Metals are chosen based on their work functions relative to the electron affinity of MoS2. It is observed, and analytically verified that lower work functions of the contact metals lead to smaller Schottky barrier heights and consequently higher charge carrier injection through the contact

Evaluation of Fuzzy Logic Subsets Effects on Maximum Power Point Tracking for Photovoltaic System

Photovoltaic system (PV) has nonlinear characteristics which are affected by changing the climate conditions and, in these characteristics, there is an operating point in which the maximum available power of PV is obtained. Fuzzy logic controller (FLC) is the artificial intelligent based maximum power point tracking (MPPT) method for obtaining the maximum power point (MPP). In this method, defining the logical rule and specific range of membership function has the significant effect on achieving the best and desirable results. This paper presents a detailed comparative survey of five general and main fuzzy logic subsets used for FLC technique in DC-DC boost converter. These rules and specific range of membership functions are implemented in the same system and the best fuzzy subset is obtained from the simulation results carried out in MATLAB. The proposed subset is able to track the maximum power point in minimum time with small oscillations and the highest system efficiency (95.7%). This investigation provides valuable results for all users who want to implement the reliable fuzzy logic subset for their works

Evaluation and assessment of transformer failure on 132kV substation

Insulation coordination models are an essential part of power system studies and are used to determine the expected overhead line back-flashover rate. A study is carried out to investigate and evaluate the effect of lightning stresses on the 132 kV substation in the way to improve its reliability in the event of active lightning activities. This paper also presents the modeling guidelines on substation for this transient analysis in order to evaluate the performance and to recommend such configuration to optimize its design to be not only to withstand the stresses but to be more cost effective. The modeling and simulation are carried out using one of the most powerful power system simulations tools that is PSCAD-EMTDC and the substation layout design is adapted from 132/11 kV Simpang Renggam-Ayer Hitam substation, courtesy of Tenaga Nasional Berhad, Malaysia (TNB). The model is based on single phase line model as it is suggested by the IEEE to be adequate to represent the substation in transient analysis simulation. The outcome of this paper will be the results of lightning stresses in term of voltage level measured at particular points in substation. The results are then compared with the suggested basic lightning insulation level (BIL) for assessment of transformer failure

Improvement in energy conversion for unmanned aerial vehicle charging pad

An efficient charging station is a necessity for Unmanned Aerial Vehicle (UAV) systems. However, if that implementation adds more complexity and onboard weight, then that exercise becomes a burden rather than a benefit since UAV's engineers aim to improve efficiency by reducing the energy consumed by the software and hardware of the complete aeronautical system. This article recommends a fully automatic contact charging station for UAVs, which can charge UAVs and thus resolve flight endurance restrictions of the UAV. The ground station consists of square copper plates that are positively and negatively polarized successively in a chessboard with particular sizes to guarantee electric contact at the landing. The design methodology used with the loading station takes into account the differences in UAV orientation once the platform has landed. In addition, this innovation uses independent charging after touchdown. Thus, this technology relaxes common flight times and help to enhance general mission times. This paper presents a unique charging platform in a “chessboard” configuration, which is devised as an interconnecting interface to facilitate the charging process and overcome inaccuracies with the landing. The solution devised in this research requires few components and presents two power source options (solar & mains power). Additionally, this work presents, to the best of our knowledge, a uniquely innovative recharging landing platform, which incidentally requires no additional software or changes to the UAV’s onboard software settings

Clinimetric evaluation of active range of motion measures in patients with non-specific neck pain: a systematic review

The study is to provide a critical analysis of the research literature on clinimetric properties of instruments that can be used in daily practice to measure active cervical range of motion (ACROM) in patients with non-specific neck pain. A computerized literature search was performed in Medline, Cinahl and Embase from 1982 to January 2007. Two reviewers independently assessed the clinimetric properties of identified instruments using a criteria list. The search identified a total of 33 studies, investigating three different types of measurement instruments to determine ACROM. These instruments were: (1) different types of goniometers/inclinometers, (2) visual estimation, and (3) tape measurements. Intra- and inter-observer reliability was demonstrated for the cervical range of motion instrument (CROM), Cybex electronic digital instrument (EDI-320) and a single inclinometer. The presence of agreement was assessed for the EDI-320 and a single inclinometer. The CROM received a positive rating for construct validity. When clinical acceptability is taken into account both the CROM and the single inclinometer can be considered appropriate instruments for measuring the active range of motion in patients with non-specific neck pain in daily practice. Reliability is the aspect most frequently evaluated. Agreement, validity and responsiveness are documented less frequently