An Integrated Optical Pressure Sensor in the GaAs/AlGaAs Ternary System

The principal concerns of this thesis are the design, fabrication and demonstration of an optical pressure sensor in the aluminium gallium arsenide (AlGaAs) ternary epitaxial layer system. The device is based on a ridge optical waveguide traversing a section of GaAs wafer which has been wet-chemically etched, in a well-defined area, from the wafer base, through the substrate (approximately 400um thick) to within approximately 10um of the top surface of the wafer. A deflection of the membrane from equilibrium by a pressure differential across its thin dimension results in a stress-induced change in the refractive index of the membrane material. A guided wave on the top surface of the membrane experiences a change of phase as it passes through the stress field produced by the membrane deformation. A mathematical theory of photoelasticity is developed to model the deflection and stress-induced refractive index changes of a membrane of material in the zinc-blende cubic crystal class (43m), of which GaAs is a member. The theoretical model was firstly tested by measuring the deflection of membranes under pressure by observing them in a microscope equipped with a Tolansky interferometer. Using the experimental apparatus described in this thesis, membrane deflection was achieved by evacuating one side of the membranes. This resulted in the pressure being limited to one atmosphere across a membrane (or limited by the evacuating capability of the vacuum pump). Two types of device are investigated -the first uses only straight waveguides and is here referred to as a birefringent pressure sensor while the second incorporates a Mach-Zehnder waveguide structure. (1) The birefringent pressure sensing device was fabricated and tested. It consisted of a number of straight waveguides crossing a membrane and was placed in an external Mach-Zehnder interferometer in order to measure the phase-shift of light in the waveguide when a uniform pressure was applied to one surface of the membrane. The theoretical model indicates that the change in phase for TE and TM polarisations is different i. e there is stress-induced birefringence. Thus linearly polarised light launched into a straight waveguide (equally exciting the TE and TM polarisations) experiences a change of polarisation with pressure. The polarisation of the light output by the device could be monitored without placing the device in an external interferometer -hence the name 'birefringent pressure sensor'. This sensor was studied using both the techniques described above. (2) The design considerations for a waveguide Mach-Zehnder interferometric pressure sensor are based on both the photoelasticity model developed in this thesis and the results obtained from the birefringent pressure sensor. The device parameters were chosen to allow at least 2pi phase-shift (i. e one cycle) within the one atmosphere pressure limit in this thesis. The arm separation of the Mach-Zehnder structure is 300um and the total device length is about 17mm. The Y-junctions are symmetric and are formed by two intersecting S-bends of radius of curvature 40mm. The arm separation and S-bend radii are limited by the losses of the device. Theoretical calculations indicate that considerably smaller radii for the S-bends would be acceptable with only a small reduction in optical transmission. In order to estimate the losses, the transmission of the Mach-Zehnder waveguides was compared to those for straight waveguides of the same overall length. The Y-junction structures forming the Mach-Zehnder waveguide configurations were also fabricated individually in order to assess the losses relative to straight guides. The results have been compared to theoretical models of the losses in S-bends and Y-junctions. The fabrication methods for waveguides and membranes are described. Straight waveguides, Y-junction and Mach-Zehnder waveguide structures were fabricated by both Reactive Ion Etching and wet-chemical etching and a comparison of the propagation characteristics is given. Dry etching was not used for membrane fabrication mainly due to the extensive etching depths required to form membrane structures (several hundred microns). In addition wet-chemical etching was more readily available and better developed for selective etching which allowed greater control over the thickness of the membranes

Selective Strong Screenability

Screenability and strong screenability were both introduced some sixty years ago by R.H. Bing in his paper Metrization of Topological Spaces. Since then, much work has been done in exploring selective screenability (the selective version of screenability). However, the corresponding selective version of strong screenability has been virtually ignored. In this paper we seek to remedy this oversight. It is found that a great deal of the proofs about selective screenability readily carry over to proofs for the analogous version for selective strong screenability. We give some examples of selective strongly screenable spaces with the primary example being Pol\u27s space. We go on to explore a natural weakening of selective strong screenability in topological groups. We conclude with an exploration of the difficulty in extending discrete families of sets as well as giving several directions one might go in when continuing the exploration of selective strong screenability

Dimensions of Organisational Culture in Quantity Surveying Firms in Nigeria

The functionalist paradigm of organisational culture (OC) views culture as a variable subject to conscious manipulation and control in order to solve organisational challenges. Therefore, this paper provides information on how OC is a solution to the challenges in Quantity Surveying firms (QSFs).  This was achieved by eliciting the dimensions of OC in forty two QSFs in Lagos, Nigeria, which are the business, people and external environment dimensions. The paper concludes that OC is a relevant solution to the identity and management related challenges in QSFs. Specifically, the paper informs on the implications of business and people dimensions of OC as a solution to the identity challenges, as well as on the implication of the external environment dimension of OC to the management challenges. Based on the findings, practical implications and recommendations were directed at the management and employees QSs in QSFs and Quantity Surveying researchers

Organon: A Symbolic Constraint Framework & Solver

Organon is an open source system for expressing and solving complex symbolic constraints between generic entities. Our design avoids restricting the programmer s ability to phrase constraints; Organon acts purely as a framework that defines and holds together the key concepts of forms, constraints, and solvers. It has three main components: (1) Forms: Abstract representations of the entities to be constrained. (2) Constraints: Functions that symbolically express requirements on the relationships between forms as well as provide information a solver can use to improve the constraint s satisfaction. (3) Solvers: Functions which inspect instantiations of forms and manipulate them in an attempt to satisfy a set of objective constraints

Technical Efficiency in Rice Production Among Smallholder Farmers in Central Liberia: A Stochastic Production Frontier Analysis

Demand for rice remains high in Liberia with low farm-level productivity (1.2 t/ha). The ability of smallholder rice farmers to improve output levels and attain sustainable production depends on efficient farm practices, hence technical efficiency. A stochastic frontier production function was applied to examine the technical efficiency of rice production. A two stage random sampling with stratification was used to collect data from 400 rice farmers in Bein Garr and Panta Districts, Central Liberia. The study has revealed that technical efficiency among farmers range from 14% to 88%, with the mean of 55%; indicating that on average, the actual output can be increased by 45% in the study area with the available technology and resources.  The determinants explaining efficiency variation in the study area were education, farming experience, household size, credit access, group membership and the type of seed used. The study recommends policies that target on increasing and improving farmers’ access to credit so as to enable the farmers get the needed production inputs such as improved seeds and fertilizer on time. Furthermore, farmers should be encouraged to organize themselves into associations/cooperatives around major rice producing and processing hubs. Keywords: smallholder farmers, rice, technical efficiency, stochastic frontier, Liberi

Synthesis of Sialic Acid Derivative for Modifying Cell Surface Sialylation

The exterior of cell surfaces express a dense layer of glycans which are often terminated by sialic acid (SA). SA is an acidic monosaccharide whose presence is found on the terminal ends of glycans of either glycoproteins or glycolipids. Due to its hydrophilic and electronegative nature, SA is often involved in both physiological and pathological processes, such as in regulating cellular interactions with ligands, microbes and neighboring cells. In addition to these functions, SA is also implicated in controlling cellular activation, differentiation, transformation and migration. Cell surface glycometabolic engineering provides a useful tool to remodel cell surface SA. In this study, a di-methyl amide derivative of SA, which lacks anionic character, was designed and synthesized for modulation of cell surface SA application. By treating cells with this amide derivative of SA, it is possible to modify the native SA expressed on the cell surface (sialylation status) and study the functions of cell surface SA. The di-methyl amide derivative of SA is synthesized from free SA via benzyl-O-sialoside, amidation and hydrogenation in 6 steps. We hope that the di-methyl amide derivative of SA will provide information regarding the specific mechanisms that are involved in SA biosynthesis and binding events as well as possible cellular consequence due to SA derivation. Eventually, by modifying the cell surface sialylation status, it may be possible to modify cellular functions.https://engagedscholarship.csuohio.edu/u_poster_2018/1030/thumbnail.jp

Assessment of Pre-Service Teacher Dispositions

Measurement of pre-service teacher dispositions is an important part of teacher preparation programs. A strong correlation exists between dispositions of teachers and the quality of their student’s learning. Teachers, in addition to sharing content knowledge, are responsible for demonstrating and sharing core values relating to virtues such as honesty, justice, fairness, care, empathy, integrity, courage, respect, and responsibility, and these values must guide their own conduct and interpersonal relations. As teachers serve pupils who are minors, their conduct and potential to serve effectively and ethically in the profession must be evaluated. However, a thorough faculty-led instrument to assess pre-service teacher candidates’ disposition does not currently exist. The purpose of this research was to develop an assessment of pre-service teachers’ dispositions for use in teacher education programs. A 25-item instrument was created through assessment of teacher education program needs and review of best practices on building teacher evaluation instruments, national professional teaching standards, and existing assessment tools. Teacher education faculty completed the instrument assessing roughly 600 students in a masters-level teacher education program. Results indicate that this instrument is a valid and reliable tool that will allow teacher education faculty and administrators to assess teacher candidate professional skills and conduct

Child Work, Child Schooling And Educational Achievement: An Empirical Evidence For Nigeria

As a result of the growing international concern about child labour, child work and the effects on the welfare and future of these children, the practices are now being questioned in Nigeria. The recent perception of child labour and child work as a problem stems from the belief, and finding on investigations that involvement of children in economic activities outside the home is injurious to the children’s intellectual and physical growth. According to Oloko (1996) working is believed to expose children to physical danger, sexual abuse and other forms of harassment. It is also believed that work prevents children from doing well in school with the resultant risk of condemning them to low wage income in the future (Falayajo, Makoju, Okebukola, Onuga & Olubodun, 1997 and Ray, 2000). An International Labour Organisation (ILO) study quoted by Beguile and Boyden (1988) even went further to suggest that child labour may contribute to adult unemployment. This may be so since children could become substitute workers at cheaper wage rates