Three phase boost rectifier design

An electric power can be converted from one form to another form by using power electronics devices. The function of power electronics circuits by using semiconductor devices as switch is modifying or controlling a voltage. The goal of power electronics circuits are to convert electrical energy from one form to another, from source to load with highest efficiency, high availability and high reliability with the lowest cost, smallest size and weight. The term rectification refers to the power circuit whose function is to alter the ac characteristic of the line electric power to produce a “rectified”ac power at the load side that contain the dc value In this project, a study has done for the two types of rectifier topology of alternating current to direct current voltage of a three-phase boost rectifier with pulse width modulation (PWM) and a threephase boost rectifier with active power filter (APF). Power factor, shape distortion and voltage can be increased as much as seen through two types of this topology if it is connected to the non-linear loads in power systems. Three phase rectifier with pulsewidth modulation (PWM) is one of controlled rectifier consist six pulses divides into two groups which are top group and bottom group. For top group, IGBT with its collector at the highest potential will conduct at one time. The other two will be reversed. Thus for bottom group, IGBT with the its emitter at the lowest potential will conduct. This project also observes the current, voltage waveform and the harmonics component when the active power filter (AFC) placed in series with non-linear load. Type of rectifier used is uncontrolled rectifier. In this work MATLAB/SIMULINK power system toolbox is used to simulate the system Results of simulations carried out, the advantages and disadvantages, the increase in voltage and waveform distortion for the system under consideration can be show

Amalan pengurusan keselamatan bengkel kemahiran hidup (KHB) Sekolah Menengah Harian Daerah Batu Pahat

Kajian ini dijalankan untuk mengkaji sejauhmanakah persepsi pelajar terhadap amalan pengurusan keselamatan dari aspek keselamatan alatan dan bahan, diri dan rakan serta keselamatan am di bengkel Kemahiran Hidup sekolah menengah harian daerah Batu Pahat. Kajian berbentuk kuantitatif dilaksanakan di empat buah sekolah menengah harian daerah Batu Pahat iaitu SMK Datin Onn Jaafar, SMK Banang Jaya, SMK Dato Onn dan SMK Seri Gading. Sampel kajian terdiri daripada 350 orang pelajar tingkatan dua yang mengambil matapelajaran KHB dan data dikumpul menggunakan instrumen borang soal selidik. Dapatan kajian dianalisis menggunakan perisian Winsteps Version 3.69.1.11 dengan pendekatan Model Pengukuran Rasch sepenuhnya. Data dianalisis menggunakan teknik analisis diskriptif dan analisis inferensi iaitu ujian-t bagi menguji hipotesis kajian. Dapatan kajian menunjukkan bahawa amalan pengurusan keselamatan di bengkel diamalkan secara sederhana bagi ketiga-tiga aspek tersebut. Terdapat perbezaan yang signifikan di antara pelajar di bandar dan luar bandar iaitu t=-4.08 dan p=0.000 di mana nilai min ukuranya pula ialah -.19. Beberapa cadangan telah dikemukakan bagi penambahbaikkan seperti mengadakan kempen kesedaran dan menyediakan sudut standard operasi amalan pengurusan keselamatan agar pelajar sentiasa mematuhi peraturan semasa berada di bengkel Kemahiran Hidup

Review of Race Scholarship and the War on Terror

The 9/11 terrorist attacks and heavy-handed state and popular response to them stimulated increased scholarship on American Muslims. In the social sciences, this work has focused mainly on Arabs and South Asians, and more recently on African Americans. The majority of this scholarship has not engaged race theory in a comprehensive or intersectional manner. The authors provide an overview of the work on Muslims over the past 15 years and argue that the Muslim experience needs to be situated within race scholarship. The authors further show that September 11 did not create racialized Muslims, Arabs, or South Asians. Rather, the authors highlight a preexisting, racializing war on terror and a more complex history of these groups with race both globally and domestically. Islamophobia is a popular term used to talk about Muslim encounters with discrimination, but the concept lacks a clear understanding of race and structural racism. Newer frameworks have emerged situating Muslim experiences within race scholarship. The authors conclude with a call to scholars to embark on studies that fill major gaps in this emerging field of study—such as intersectional approaches that incorporate gender, communities of belonging, black Muslim experiences, class, and sexuality—and to remain conscious of the global dimensions of this racial project

Fieldwork at home: Assumptions, anxieties and fear

This contribution reflects on the experiences of a four month stint of ethnographic fieldwork conducted in Islamabad, Pakistan. It is a case of ‘fieldwork at home’, with serious concerns of positionality, established assumptions, and using a qualitative methodology. Although I had read quite extensively on what to expect, believed I was prepared for the unexpected, it was a jarring experience to see things I had once been used to with a critical ‘researcher’s eye’. Factors like natural gas shortages, blisteringly cold winter days and an environment of anxiety and fear caused by instances of terrorist activities slowed my fieldwork and crept into all my encounters with the participants. Even though I was studying the effects of regional and national processes on local events and individual decision-making, the extent and quality of the effects was unsettling. My assumptions about my city, the people I was working with, and more importantly, their knowledge and assumptions about me, were a constant reminder about the fragility of my position in the field, writes Saher Hasnain

On backoff mechanisms for wireless Mobile Ad Hoc Networks

Since their emergence within the past decade, which has seen wireless networks being adapted to enable mobility, wireless networks have become increasingly popular in the world of computer research. A Mobile Ad hoc Network (MANET) is a collection of mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure. MANETs have received significant attention in recent years due to their easiness to setup and to their potential applications in many domains. Such networks can be useful in situations where there is not enough time or resource to configure a wired network. Ad hoc networks are also used in military operations where the units are randomly mobile and a central unit cannot be used for synchronization. The shared media used by wireless networks, grant exclusive rights for a node to transmit a packet. Access to this media is controlled by the Media Access Control (MAC) protocol. The Backoff mechanism is a basic part of a MAC protocol. Since only one transmitting node uses the channel at any given time, the MAC protocol must suspend other nodes while the media is busy. In order to decide the length of node suspension, a backoff mechanism is installed in the MAC protocol. The choice of backoff mechanism should consider generating backoff timers which allow adequate time for current transmissions to finish and, at the same time, avoid unneeded idle time that leads to redundant delay in the network. Moreover, the backoff mechanism used should decide the suitable action to be taken in case of repeated failures of a node to attain the media. Further, the mechanism decides the action needed after a successful transmission since this action affects the next time backoff is needed. The Binary exponential Backoff (BEB) is the backoff mechanisms that MANETs have adopted from Ethernet. Similar to Ethernet, MANETs use a shared media. Therefore, the standard MAC protocol used for MANETs uses the standard BEB backoff algorithms. The first part of this work, presented as Chapter 3 of this thesis, studies the effects of changing the backoff behaviour upon a transmission failure or after a successful transmission. The investigation has revealed that using different behaviours directly affects both network throughput and average packet delay. This result indicates that BEB is not the optimal backoff mechanism for MANETs. Up until this research started, no research activity has focused on studying the major parameters of MANETs. These parameters are the speed at which nodes travel inside the network area, the number of nodes in the network and the data size generated per second. These are referred to as mobility speed, network size and traffic load respectively. The investigation has reported that changes made to these parameters values have a major effect on network performance. Existing research on backoff algorithms for MANETs mainly focuses on using external information, as opposed to information available from within the node, to decide the length of backoff timers. Such information includes network traffic load, transmission failures of other nodes and the total number of nodes in the network. In a mobile network, acquiring such information is not feasible at all times. To address this point, the second part of this thesis proposes new backoff algorithms to use with MANETs. These algorithms use internal information only to make their decisions. This part has revealed that it is possible to achieve higher network throughput and less average packet delay under different values of the parameters mentioned above without the use of any external information. This work proposes two new backoff algorithms. The Optimistic Linear-Exponential Backoff, (OLEB), and the Pessimistic Linear-Exponential Backoff (PLEB). In OLEB, the exponential backoff is combined with linear increment behaviour in order to reduce redundant long backoff times, during which the media is available and the node is still on backoff status, by implementing less dramatic increments in the early backoff stages. PLEB is also a combination of exponential and linear increment behaviours. However, the order in which linear and exponential behaviours are used is the reverse of that in OLEB. The two algorithms have been compared with existing work. Results of this research report that PLEB achieves higher network throughput for large numbers of nodes (e.g. 50 nodes and over). Moreover, PLEB achieves higher network throughput with low mobility speed. As for average packet delay, PLEB significantly improves average packet delay for large network sizes especially when combined with high traffic rate and mobility speed. On the other hand, the measurements of network throughput have revealed that for small networks of 10 nodes, OLEB has higher throughput than existing work at high traffic rates. For a medium network size of 50 nodes, OLEB also achieves higher throughput. Finally, at a large network size of 100 nodes, OLEB reaches higher throughput at low mobility speed. Moreover, OLEB produces lower average packet delay than the existing algorithms at low mobility speed for a network size of 50 nodes. Finally, this work has studied the effect of choosing the behaviour changing point between linear and exponential increments in OLEB and PLEB. Results have shown that increasing the number of times in which the linear increment is used increases network throughput. Moreover, using larger linear increments increase network throughput

The Determinants of Financial Reporting on The Internet: The Case of Companies Listed in The Istanbul Stock Exchange

The objective of this article is to explore the practices of Internet financial reporting by Turkish companies listed on Istanbul Stock Exchange  (ISE). For this purpose, the study investigated the the association between key firm characteristics and the level of internet financial reporting by Turkish companies. The sample which was examined contains 263 publicly traded Turkish companies listed on the Istanbul Stock Exchange. The sample of the study contains companies with web sites as of December 2012. To achieve the purpose of the study descriptive analysis, multicollinearity analysis and regression analysis were employed. The findings of the study show positive relationships between the Internet financial reporting (measured by disclosure index) and the 4 independent variables which are size, leverage, profitability and liquidity. Furthermore,  the findings reveal that the size of the firm and profitability variables are statistically significant at the 5% level while the liquidity and leverage variables appeared to be statistically insignificant at the 5% level. Keywords: Internet, financial reporting, disclosure index

An Empirical Investigation of Corporate Dividend Payout Policy in an Emerging Market: Evidence from Palestine Securities Exchange

This manuscript aims at investigating factors that affect corporate dividend policy of the listed companies on Palestine Securities Exchange. For this purpose, the study considers the impact of six explanatory determinants namely, firm’s size, profitability, risk, leverage, liquidity and growth opportunities by using balanced panel dataset of Palestinian listed firms between the years 2009 and 2013. The sample which was investigated is composed of 24 listed and traded companies as of December 2013. Descriptive analysis, multicollinearity analysis and multiple regression analysis were used to test the model of the study. Empirical findings show that that growth, risk, and profitability explanatory variables have positive and statistically significant association with dividends payout ratio. Furthermore, the results indicate that the firm size and leverage ratio factors  were found to have statistically no significant relationship with dividends payout ratio. Liquidity appeared to have a negative association with dividends payout but not statistically significant. Keywords: Dividend Payout Policy, Palestine Securities Exchang

An Analysis of Prepositional Errors Committed by Undergraduate ESL Learners of Pakistan

Second Language Acquisition (SLA) phenomena are very important for social, practical and academic reasons. About 6000 languages are spoken in the world and almost all of them have been learned by second languages by some portion of their speaker. There are four most commonly-used languages and English is one of them that is acquired as L1 by 427 million people and as L2 by 950 million speakers. In Pakistan, English has become most important language for communication and also a symbol of prestige in the society. It has turned into a great asset for Pakistani students; they learn it as their second language from basic to advance level. Moreover, English enjoys the status of official language in Pakistan. However, Pakistani learners face many difficulties and problems in using English in their writings and during speaking. Committing errors in the use of prepositions is one of such difficulties. This research examines the misuse of English prepositions by Pakistani undergraduate ESL learners. The purpose of the study is to find out whether male learners commit more prepositional errors or female. Other than this, following study also focuses on the types of prepositional errors found in tests of MCQs and word deletion. For this purpose, thirty (30) students of Government college university of Faisalabad (fifteen participants from each gender) were selected randomly for quantitative research. The data was collected through two tests; first test was based on gap filling exercise and second was based on MCQs. These tests were then analyzed through tables and graphics by using Microsoft excel software. Researcher used Hot Potatoes as a tool for making test and used statistical methods to find the frequencies and percentage of errors. The study found out various types of prepositional errors in both type of tests. Resultantly, the ratio of errors committed by female ESL learners was higher than male ESL learners. Keywords: Prepositions, gender analysis, error analysis, influence of L1 on L2 DOI: 10.7176/JLLL/53-0

Experimental and numerical investigation of mechanical effect of externally weak layers in thick hybrid composites

There is a growing interest in the use of thick hybrid composite laminates in the structural elements of aerospace and hydrospace structures. As amount of composite materials used in aircraft structures has now exceeded 50% by weight, it is more crucial than ever to study their mechanical properties and failure behaviors. In the present work, the influence of weak external layers of carbon and glass fibers on the flexural behavior of thick carbon/glass fiber reinforced hybrid composite laminates was examined to monitor their failure mechanisms. In the first part, four types of symmetric laminate structures were designed by tailoring the stacking sequence of glass (G) and carbon (C) fiber reinforced prepregs. Hot Press Curing (HPC) technique was utilized for manufacturing of the laminates. In each composite structure, 48 prepreg plies were used; and their configurations were adjusted to (C8/G8/G8)s, (G8/C8/G8)s, (G8/G8/C8)s, and (C8/G8/C8)s. Flexural tests showed that the highest flexural strength (1260 MPa) was exhibited by the laminate with the configuration of (G8/C8/G8)s, and the highest flexural modulus (79.64 GPa) was shown by the laminate with configuration of (C8/G8/C8). In addition, Digital Image Correlation (DIC) technique was used for the full-field in-plane strain and displacement registration, and for the study of failure mode development during the bending tests. The results indicated that the type of fiber placed along the horizontal midplane of the laminate controlled the failure mode, and the type of fiber available on the faces governed the behavior of stress strain curve. The fracture surface characterization performed by optical and scanning electron microscopy techniques indicated that the compressive failures in the form of kink band formation and shear-driven interlaminar delamination were the two most prevalent forms of failure in thick hybrid laminates. In parallel to the experimental study, numerical study was carried out by Finite Element Method (FEM) to investigate the displacement values in the direction parallel and transverse to the loading axis, and for obtaining the longitudinal and shear strain values. Both experimental and numerical studies emphasized the importance of using stacking sequence of a thick hybrid laminate as a practical approach in controlling the flexural properties of the composites. To conclude, this work provides a new insight into the design and fabrication of thick-section hybrid laminates by the adjustment of their stacking sequenc