Doctor of Philosophy

dissertationRefractive errors of vision are very common in all human beings, namely myopia, hyperopia, presbyopia, and astigmatism. Worldwide, over 1 billion people were estimated to suffer from presbyopia with around 410 million of them suffering from near vision loss. The result of refractive errors is blurred vision, affecting our ability to focus on near or far objects. The utilization of conventional fixed, uniform, or graded power eyeglasses is generally unsatisfactory as fixed power eyepieces cannot provide any accommodation restoration. In this dissertation, we demonstrate compact tunable-focus liquid lenses suitable for ophthalmic adaptive eyeglasses. These lightweight, low footprint tunable-focus lenses augment the accommodation range of vision, thus restoring normal vision function. First, a tunable-focus large aperture liquid lens is constructed using shape memory alloy (SMA) springs as actuators. The lens mainly consists of a shallow liquid-filled cylindrical cavity bound by a thin compressible annular rim and encapsulated by a flexible circular membrane on the top of the rim and a rigid circular plate at the rim bottom. The lens optical power is adjusted by a controlled compression of the annular rim in vertical direction via actuation of the three shape memory alloy (SMA) springs. Second, we report a compact tunable-focus liquid lens with large aperture actuated by piezo-electric bimorph actuators. The lens consists of a rigid annular sealing rim encapsulated by two membranes forming a sealed chamber with a fixed volume of high index optical fluid filled in it. When a normal force is applied to the bottom piston via piezo-electric bimorph actuators, the shape of the top membrane is changed, causing the change of focal length. We did the simulation using Python to improve the lens optical quality, and lens parameters were determined from the simulation. While simulation and fabrication of the tunable-focus liquid lens using piezo-electric bimorph actuators, we noticed the effect of tension over lens membrane to determine lens optical power and optical quality. This gave us the idea of implementing tunable-focus liquid lens by changing the tension of the membrane. The theory, simulation, fabrication, and experimentation for these three different lenses are discussed in this dissertation

Optimization and Control of Lumped Transmitting Coil-Based In-Motion Wireless Power Transfer Systems

Wireless inductive power transfer systems are the only viable option for transferring energy to a moving vehicle. In recent years, there has been a great deal of interest in in-motion vehicle charging. The dominant technology thus far for in motion charging is elongated tracks, creating a constant eld for the moving vehicle. This technology suers from high volt ampere ratings and lower efficiency of 70%. On the other hand, stationary charging systems can demonstrate efficiency up to 95%. This thesis proposes lumped coils, similar to stationary charging coils for in-motion electric vehicle charging application. This novel primary coil architecture introduces new challenges in optimization and control. Traditional design of wireless inductive power transfer systems require designer experience, use of time consuming 3D FEM algorithms and lacks the comprehensive nature required for these systems. This thesis proposes two new optimization algorithms for the design problem which are comprehensive, based on only analytical formulations and do not need designer experience. There are challenges in the control of power transfer as well. Higher efficiency comparable to stationary systems can only be realized with proper synchronization of primary voltage with the vehicle position. Vehicle position detection and communication introduce significant cost and convenience issues. This thesis proposes a novel control algorithm which eliminates the need for vehicle position sensing and yet transfers the required percentage of energy. Both the optimization and control algorithms are verified with hardware setup

Multi-objective Optimization: A Case Study

The aim of this literature is to illustrate the application of multi-objective optimization routines through a case study of face milling operation. For this purpose, the face milling operation is designed as a multi-objective optimization problem and then solved to obtain optimum values for the machining parameters - cutting speed (Vc), feed rate (fz) and depth of cut (t) using the optimization routines. The formulated problem of face milling operation includes two conflicting objectives - to maximize Material Removal Rate (MRR) and to minimize surface roughness (Ra). Among various multi-objective optimization routines, five of them namely Global Criterion Method, Lexicographic Method, Weighted Sum Method, Epsilon Constraint Method and Genetic Algorithm are used in this literature. The outcomes of these multi-objective optimization routines are then compared to reflect their relative attractiveness.Comment: MSc course project report presenting five multi-objective optimization routines - Global Criterion Method, Lexicographic Method, Weighted Sum Method, Epsilon Constraint Method, and Genetic Algorithm for a sample example proble

Grain Dust and Health: A Competing Risk Analysis for the Grain Workers in Saskatchewan

Grain dust industry workers are exposed to a number of work-related hazards, including high levels of endotoxin, microorganisms and dust. Multiple studies have reported immunological, toxicological and clinical effects of occupational exposure to grain dust contaminants. The study aims to determine the effects of various prognostic and demographic factors on health-related outcomes among the grain industry workers in Saskatchewan. Statistical analyses of the grain dust data can be carried out in a competing risk framework. In this context, competing risk is defined when an individual has a chance of getting one or more events to emulate with event of interest (e.g. death, time to relapse, time o disease type etc.). The competing risk analysis involves fitting the Cox PH model separately for each event type, treating the other (competing) event types as censored in addition to those who are censored from loss to follow-up or withdrawal. One of the assumptions of competing risk analysis is that censoring is independent of events regardless of the different ways that censoring can occur, including failure from competing risks other than the event-type of interest. We define three competing events for the grain dust industry workers in Saskatchewan: chronic cough or phlegm, shortness of breath and allergy. Each worker can experience any of these events over the follow-up period from 1978 to 2005. We then consider seven covariates to assess their effects on the hazards of each of these three events: age, history of health problem (yes/no), history of asthma (yes/no), body mass index (BMI), forced expiratory volume in one second (FEV1), FEV1/FVC ratio which is the proportion of the amount of air exhaled in the first second (FEV1) to all of the air exhaled during a maximal exhalation (FVC) and smoking. Our competing risk analyses reveal that FEV1/FVC ratio and smoking are highly significant to the risk of developing chronic cough or phlegm (p-value = 0.0238 and 0.0009 respectively). For shortness of breath, history of asthma and smoking are found significant, with p-values 0.0481 and 0.024, respectively. Results also indicate a high impact of age and FEV1 on allergy. Our analyses are based on a relatively small sample (n = 226), and therefore caution should be applied to generalize our findings. Nevertheless, our findings could be useful for policy makers to make the environment of grain industries safe and secure for the workers with respect to standards and guidelines. Results could also be useful for human awareness

Cathode Interface Engineering for High Performance Planar Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have already improved their power conversion efficiency (PCE) from 3.9% to ~22.1% at present. This demonstrated that PSCs can be a promising alternative to conventional silicon solar cells. PSCs have been marked as one of the most favorable next-generation solar cells due to their high extinction coefficient, broad light absorption range and ambipolar charge transport properties, low production cost, and simple fabrication processing. Various device architectures have been designed and investigated for constructing high performance PSCs consisting of different electron transport layers (ETL) and hole transport layers (HTL). In general, PSCs are fabricated in two structures: mesoporous scaffold n-i-p and planar heterojunction p-i-n PSCs. Although mesoscopic PSCs have obtained an impressive PCE, it requires high temperature process (\u3e 450oC) for forming compact TiO2 and mesoporous TiO2 that hinders their applications that require mechanical flexibility. On the other hand, planar p-i-n PSCs have drawn attention due to low temperature processing, mechanical flexible devices. The goal of this work is to introduce a non-conjugated polymer material Polyvinylpyrrolidone (PVP) as cathode buffer layer (CBL) and understand interfacial engineering in planar p-i-n PSCs. PVP was used for the first time as a CBL in PSCs. The ETL and HTL are highly responsible to increase carrier separation, improve charge collection and reduce recombination. Additionally, the buffer layer between ETL and metal cathode (like Ca, Al, Ag) electrode in PSCs plays a crucial role in energy-level alignment, trap state passivation and PSCs film morphology. A comparative study on PSCs without and with CBL was investigated where rhodamine as CBL was considered for control device. The thickness of PVP CBL was analyzed by changing spin speed from 1000 rpm to 5000 rpm at an interval of 2000 rpm. The optimal spin speed was found at 3000 rpm, which achieved an average efficiency of 15.30%. The concentrations of PVP dissolved in isopropanol was optimized from 0.5 mg/ml to 2.0 mg/ml. There was simultaneous enhancement of short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), and overall power conversion efficiency (PCE) due to incorporation of PVP. The best device achieved a PCE of 16.35%. Various device characterizations such as atomic force microscopy (AFM), scanning electron microscopy (SEM) etc. were performed to interpret the enhancement of device performance

Online Content Popularity in the Twitterverse: A Case Study of Online News

With the advancement of internet technology, online news content has become very popular. People can now get live updates of the world's news through online news sites. Social networking sites are also very popular among Internet users, for sharing pictures, videos, news links and other online content. Twitter is one of the most popular social networking and microblogging sites. With Twitter's URL shortening service, a news link can be included in a tweet with only a small number of characters, allowing the rest of the tweet to be used for expressing views on the news story. Social links can be unidirectional in Twitter, allowing people to follow any person or organization and get their tweet updates, and share those updates with their own followers if desired. Through Twitter thousands of news links are tweeted every day. Whenever there is a popular new story, different news sites will publish identical or nearly identical versions (``clones'') of that story. Though these clones have the same or very similar content, the level of popularity they achieve may be quite different due to content agnostic factors such as influential tweeters, time of publication and the popularities of the news sites. It is very important for the content provider site to know about which factor plays a important role to make their news link popular. In this thesis research, a data set is collected containing the tweets made for the 218 members of 25 distinct sets of news story clones. The collected data is analyzed with respect to basic popularity characteristics concerning number of tweets of various types, relative publication times of clone set members, tweet timing and number of tweeter followers. Then, several other factors are investigated to see their impact in making some news story clones more popular than others. It is found that multiple content-agnostic factors i.e. maximum number of followers, self promotional tweets plays an impact on news site's stories overall popularity, and a first step is taken at quantifying their relative importance

Degradation behavior of shape memory polymer due to water and diesel fuel

Shape memory polymers (SMP) are smart materials, which have the ability to memorize the original or permanent shape. Owing to this characteristic SMP can be used as a sensor, a transplant, as well as structural materials in wide range of applications. Despite its importance, its degradation behavior is still not completely known; and only a limited amount of work has been reported in the literature. In this thesis, the experiments have been carried out to evaluate the degradation behavior of Veriflex- SMP (industry supplied SMP samples) upon exposure to two different types of liquids; water and diesel fuel separately. It has been found that the “glass transition temperature, Tg” decreases due to immersion in water and diesel fuel. The immersion of Veriflex- SMP in water and diesel fuel facilitates the breakage of existing bonds and the formation of new bonds, thereby increasing the mobility of polymeric chains. In addition, water and diesel fuel are found to be effectively plasticize the SMPs, by reducing the storage modulus; and thus decreasing the structural integrity of the SMP. It is also observed that upon exposure to diesel fuel for a couple of weeks, the Tg of Veriflex- SMP goes below the room temperature. As a result, Veriflex- SMP goes back to the original shape without the application of external energy. The stress relaxation tests are also conducted to determine the changes in physical properties of SMP. The decay of the stress is found much faster and eventually to a much lower value in the degraded samples, in comparison to the untreated samples, tested under the similar conditions. It is also found that the stress decay is increased with the increase of immersion time in water and in the diesel fuel. From Fourier Transform Infrared (FTIR) tests it has been found that the formation of hydrogen bonding between the SMP and the solvents (water and diesel fuel) is the main reason for the degradation of SMP; although the hydrogen has a minor effect on the structure of SMP, but it has an obvious influence on the glass transition temperature, Tg

Excess molar enthalpies of binary and ternary systems involving hydrocarbons and ethers

In modern separation design, an important part of many phase-equilibrium calculations is the mathematical representation of pure-component and mixture enthalpies. Mixture enthalpy data are important not only for determination of heat loads, but also for the design of distillation units. Further, mixture enthalpy data, when available, are useful for extending vapor-liquid equilibria to higher (or lower) temperatures, through the use of the Gibbs-Helmholtz equation. In this connection excess molar enthalpies for several binary and ternary mixtures involving ethers and hydrocarbons have been measured at the temperature 298.15 K and atmospheric pressure, over the whole mole fraction range. Values of the excess molar enthalpies were measured by means of a modified flow microcalorimeter (LKB 10700-1) and the systems show endothermic behavior. The Redlich-Kister equation has been used to correlate experimental excess molar enthalpy data of binary mixtures. Smooth representations of the excess molar enthalpy values of ternary mixtures are accomplished by means of the Tsao-Smith equation with an added ternary contribution term and are used to construct excess enthalpy contours on Roozeboom diagrams. The values of the standard deviations indicate good agreement between experimental results and those calculated from the smoothing equations. The experimental excess enthalpy data are also correlated and predicted by means of solution theories (Flory theory and Liebermann-Fried model) for binary and ternary mixtures, respectively. These solution theories correlate the binary heats of mixing data with reasonable accuracy. The prediction of ternary excess molar enthalpy by means of the solution theories are also presented on Roozeboom diagrams. The predictions of ternary excess enthalpy data by means of these theories are reasonably reliable

Factors Affecting Employee Engagement: A Study on Private Organizations in Bangladesh

Employee engagement is essential for a company to maintain positive and productive work environment. Employee engagement and motivation at work are key factors in the success of teams and the entire organization. It improves productivity, reduces turnover rates, and fosters a positive work culture. This study explores the various ways in which organizations can increase employee engagement and motivation. The study also highlights the importance of leaders and managers in promoting a supportive work culture. Employee engagement is used to describe a worker's emotional and intellectual attachment to their organization, which expresses as dedication, enthusiasm, excitement, focused work, and enthusiasm. Engaged workers typically feel better about their jobs. Companies with engaged employees also typically generate higher profit. The study discusses the importance of work independency, equitable pay structure, professional growth, work-life balance, and cooperation of supervisor co-worker. This study identifies the most influential drivers that motivate employees to engage their job psychologically and physically. This study also determine the factor that policy maker should consider in order to increase employee engagement. Keywords: Employee engagement, work independency, work-life balance, Professional growth DOI: 10.7176/EJBM/15-16-03 Publication date:September 30th 2023