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Parental Involvement and Children's Development: Can There Be Positive Side Effects?
No full textA growing body of literature indicates that meaningful time spent with parents has a significant influence on early childhood development, a future accumulation of a wide array of cognitive and non-cognitive skills, and the ultimate success of a child. The theoretical model presented in this article features endogenous fertility and labor supply while distinguishing between various types of parental time spent with children. In this model, parents are subsidized for spending publicly verifiable productive time with their children. It is shown that there are low tax-subsidy rates that would allow policymakers to stimulate the labor supply of the primary caretaker in addition to significantly enhancing children's skills. These unique by-products of human capital accumulation can have important implications both in developed countries with an ageing population and in developing countries with low female labor force participation
Public sector expatriation
No full textA public sector expatriate is an employee who is sent abroad by their organization, for an organizational mission, for a precise period of time, and expected to return to their home organization, in their home country, after that time. When the assignment abroad lasts less than 1 year, we usually speak about short-term international assignment
Modeling of Friction Stirring
No full textA Master of Science thesis in Mechanical Engineering by Mohamed Anass Abdalla Badreldin entitled, “Modeling of Friction Stirring”, submitted in November 2018. Thesis advisor is Dr. Mohammad Nazzal and thesis co-advisor is Dr. Basil Darras. Soft and hard copy available.The last two decades have witnessed significant advances in friction stir welding (FSW). This solid-state welding process was originally used for joining Aluminum alloys before being extended to other metallic and non-metallic materials. The high complexity in FSW stems from the complex interactions between highly coupled physical phenomena. As experimental procedures are costly and time-consuming, numerical simulations were used extensively in an effort to develop a comprehensive understanding of the process. This research consists of two parts: one part provides a critical review of the three fundamental components of the numerical simulation of FSW; which are the numerical method, the constitutive model, and the contact model. The second part contains the detailed development of the finite element model to study the FSW process and submerged FSW process (SFSW), with emphasis on the effect of submerging on the temperature profile and thermal history. The finite element model is developed using the Coupled Eulerian-Lagrangian modeling technique and is validated against previous experimental work for the Aluminum 5083 alloy. Temperature profiles for different welding conditions are investigated to validate the model. The developed finite element model is able to predict the temperature profile in both FSW and SFSW processes. It also captures the dissymmetrical temperature distribution around the welding line; and the effect of using the SFSW process on peak temperatures, cooling rates, and size of the heat affected zone. Moreover, flash formation and the material flow patterns are successfully captured. The results show that increasing the rotational speed from 1000 rpm to 1700 rpm for the SFSW of the Aluminum 5083 alloy resulted in an increase in peak temperature by 200%. This temperature rise yields to material softening, improved the material flow, and higher weld quality.College of EngineeringDepartment of Mechanical EngineeringMaster of Science in Mechanical Engineering (MSME
Investigating the Impact of the Flipped Method on Undergraduate and Graduate Students at AUS
No full textA Master of Science thesis in Engineering Systems Management by Raghad Mohd Omar Nihlawi entitled, “Investigating the Impact of the Flipped Method on Undergraduate and Graduate Students at AUS”, submitted in November 2018. Thesis advisor is Dr. Hazim El-Baz and thesis co-advisor is Dr. Cindy Gunn. Soft and hard copy available.The main driver of this research is the continuous high demand of improving the teaching and learning experience in higher education so students are meeting their learning needs, and developing the needed skills for the workforce. Flipped learning is one of the pedagogies that aims to address this improvement where the students review content before the class, while the class time is devoted to activities such as problem solving and discussions. There are few initiatives by some instructors who are applying the flipped methodology at AUS in the College of Engineering and the College of Arts and Sciences at the graduate and undergraduate levels. The objective of this research is to investigate the impact of the flipped method on the students’ perceived learning experience at AUS, in addition to provding a comparison with the lecture-based method regarding both the students’ perceived learning experience and their academic performance. Furthermore, this study looks into the factors contributing mostly to the impact of the flipped method. The research purpose will be addressed by investigating the flipped classes in addition to selected lecture-based ones, adopting the Revised Community of Inquiry framework (RCOI) to assess students’ perceptions of their learning experience, and comparing the students’ academic performance to look for any significance difference as a possible result of the teaching methodology. The study showed that students’ perceptions for the flipped method were mainly related to the nature of the course and the use of pre-class videos, where students in the technical courses with pre-class videos, and in the conceptual courses in the absence of pre-class videos, had reported significantly higher satisfaction compared to students in the technical courses in the absence of pre-class videos with a p-value ≤ 0.025. Furthermore, students in the technical courses with pre-class videos had outperformed their peers in the lecture-based classes regarding academic performance with a p-value ≤ 0.057 and estimated course grade median deference of 0.3. The outcome of this research helps instructors to decide on future pedagogies to apply in their classes in addition to showing 10 recommendations to be considered in the design of future flipped courses.College of EngineeringDepartment of Industrial EngineeringMaster of Science in Engineering Systems Management (MSESM
Mechanical and phytochemical protection mechanisms of Calligonum comosum in arid deserts
No full textUnlike animals, plants are sessile organisms, lacking circulating antibodies and specialized immune cells and are exposed to various harsh environmental conditions that make them at risk of being attacked by different pathogens and herbivores. Plants produce chemo-signals to respond to the surroundings and be able to distinguish between harmless and harmful signals. In this study, the production of phytochemicals as plant signaling mechanisms and their defensive roles in disease resistance and repelling herbivores are examined in Calligonum comosum. C. comosum is a leafless standalone perennial shrub widespread in sand dunes. The plant has the ability to survive the drastic environmental conditions of the arid/ hyperarid deserts of the Arabia. Structural anatomy and phytochemicals analyses were used to identify both mechanical and chemical defensive mechanisms in C. comosum. Microscopy-based investigations indicated that stems of this species developed hard structures in its outer layers including sclerenchyma and cluster crystals of calcium oxalate (CaOx). Sclerenchyma and CaOx are difficult to be eaten by herbivores and insects and can harm their mouthparts. On the other hand, the plant developed both short-distance (local) and long-distance (systematic over limited sphere) phytochemicals-producing cells located at its outer regions that is surrounding the inner nutrient-rich vascular system (VS). Local chemical was represented by phenolic idioblasts that were released in response to plant cutting. Systematic chemical was represented by toxic volatile oil containing ~50% benzaldehyde derivative (cuminaldehyde). The oil caused strong killing effect on both mammalian cells and microbial pathogens via either direct addition or indirect exposure to its vapor. The plants lost the oil content and allowed fungal growth once cut and dried. The localization of both defensive mechanisms to the outer region of the plant seemed to protect the inner nutrient-rich VS and hence maintained the plant survival. Surprisingly, in relation to traditional folklore use as medicine, local people use only green parts of the plant and only during the winter, where the plant found devoid of volatile oil and phenolic idioblasts. Moreover, it turns into recommendations for local people to avoid any health problems caused by the plant supply
Nonlinear FEA of Soil-Structure-Interaction Effects on RC Shear-Wall Structures
No full textA Master of Science thesis in Civil Engineering by Dina Saadi entitled, “Nonlinear FEA of Soil-Structure-Interaction Effects on RC Shear-Wall Structures”, submitted in May 2018. Thesis advisor is Dr. Mohammad AlHamaydeh and thesis co-advisor is Dr. George Markou. Soft and hard copy available.Considering Soil-Structure-Interaction (SSI) is essential when evaluating the structural system’s response as it can unveil behaviors that are otherwise not accounted for in fixed-base (FB) systems. Nonlinear Finite Element Analysis (NFEA) is performed on a six-story Reinforced Concrete (RC) shear wall structure to investigate SSI effects. The soil medium in consideration represents site class E soil type in accordance to ASCE7-10 standards. The structural elements including the RC wall, slabs, foundation, and soil continuum are modeled using 3D solid hexahedral elements. Additionally, to further enhance accuracy to the modeling, all steel reinforcement including longitudinal and transverse rebars are modeled as embedded bars within the brick elements. The smeared crack approach is utilized for optimal computational efficiency. Four types of RC walls that differ in reinforcement detailing for varying seismicity design levels are explored. The representative structures are loaded with their tributary gravity loads applied to the corresponding slabs. Lateral load effects are imposed onto the structures through displacement-controlled monotonic as well as cyclic pseudo-static protocols. The systems’ responses from the SSI and FB systems are compared through pushover and hysteretic curves (lateral force versus lateral drift), strain/stress contours, as well as interpretive response quantities such as characteristic stiffnesses and energy dissipation. It was found that all SSI models exhibit higher lateral displacements ranging from an additional 34% to 85%, lesser force demands within the superstructure by around 10%, and higher levels of energy dissipation (on an average of 25%) due to soil compressibility. Furthermore, all FB models experienced higher strain concentrations at the bottom region of the shear walls. Thus, it was found that wall shear reinforcement can be reduced by accounting for SSI effects. Lastly, the reinforcement detailing (special versus ordinary) had a noticeable effect on enhancing the system’s performance.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
Thermo-Economic Evaluation of Maisotsenko-Desiccant Cooling Systems for Gas Turbine Power Plants
No full textA Master of Science thesis in Mechanical Engineering by Waleed Moustafa El-Damaty entitled, “Thermo-Economic Evaluation of Maisotsenko-Desiccant Cooling Systems for Gas Turbine Power Plants”, submitted in October 2018. Thesis advisor is Dr. Mohamed Gadalla. Soft and hard copy available.With the everlasting increase in population, a huge surge in the electricity consumption has been recorded. Thus, power plants manufacturers and utility companies need to augment the plants performance to cope with these rising of energy demands. Turbine blade cooling is a vital procedure in gas turbine power plants due to the high turbine inlet temperatures achieved. The main objective of the thesis is to cool down the air bled from the compressor for turbine blade cooling, using Maisotesnko-desiccant cooling systems. This will reduce the amount of bled air and improve the efficiency. In this research, the performance of 50 MWe gas turbine power plants with three different configurations; a simple gas turbine, a gas turbine with an air bottoming cycle (GTABC) and intercooled, reheated and recuperated (IcRhRc) gas turbine integrated with the proposed cooling systems are investigated. Research results indicated that the GTABC yielded an increase in the overall efficiency from 42.57 % without cooling to 43.27%, to 43.54% and to 43.83% for the triple stage Maisotsenko-desiccant (TS-MD), triple stage precooling Maisotsenko-desiccant (TS-PMD) and triple stage extra cooling Maisotsenko-desiccant (TS-EMD), respectively. Furthermore, a maximum reduction in the fuel mass flow rate was observed from 2.713 kg/s to 2.653 kg/s in the TS-EMD system leading to a decrease in the carbon foot print which agrees with recent United Nations sustainability reports. The exergoeconomic results of the IcRhRc gas turbine exhibited a reduction in the exergy destruction rate from 44.86 MW without cooling to 43.34 MW after integrating TS-EMD cooling system. Consequently, the exergy efficiency has increased from 50.92% to 51.43%, to 51.63% and to 51.86% after incorporating TS-MD, TS-PMD and TS-EMD, respectively. Subsequently, the cost rate of exergy destruction has decreased from 924.2/hr after implementing the TS-EMD cooling system. Moreover, the investment cost flow rate has decreased from 101/hr after integrating the TS-EMD cooling system. The exergoeconomic factor and relative cost difference were also evaluated to assess each component for further performance improvement.College of EngineeringDepartment of Mechanical EngineeringMaster of Science in Mechanical Engineering (MSME
Optimization of Energy Consumption in Cloud Computing Datacenters
No full textA Master of Science thesis in Computer Engineering by Ahmed Osman Osman entitled, “Optimization of Energy Consumption in Cloud Computing Datacenters”, submitted in June 2018. Thesis advisor is Dr. Assim Sagahyroon and thesis co-advisors are Dr. Fadi Aloul and Dr. Raafat Aburukba. Soft and hard copy available.In recent years, cloud computing has emerged as a practical paradigm for providing IT resources, infrastructure and services. This has led to the establishment of large scale datacenters that have substantial energy demands for their operation. These centers are estimated to have the fastest growing carbon foot print among all information and communication technology sector. This work investigates the optimization of the energy consumption in cloud datacenters by using energy efficient allocation of tasks to resources. The work seeks to develop formal optimization models that minimize the energy consumption of computational resources and evaluates the use of existing optimization solvers in testing these models. Energy consumption of cloud computing datacenters is mainly disbursed by the CPU, memory, disk storage, and network, with the CPU consuming the major portion. Hence, as tasks arrive for processing, these tasks must be scheduled efficiently by the cloud resource allocation mechanism. Here, the scheduling problem is modeled using the Integer Linear Programming (ILP) techniques, where models are formulated with the objective of minimizing the total power consumed by the active and idle cores of the servers’ CPUs while meeting a set of constraints. Next, we use these models to carry out a detailed performance comparison between a selected set of Generic ILP and 0-1 Boolean Satisfiability based solvers in solving the ILP formulations. Simulation work is carried out using datacenters configured following industry-standard servers specifications. Results indicate that the developed models have saved up to 37.9% in energy consumption when compared to common techniques such as Round Robin. Furthermore, results also showed that from our selected set of solvers, generic ILP solvers had superior performance when compared to SAT-based ILP solvers especially as the number of tasks and resources grow in size.College of EngineeringDepartment of Computer Science and EngineeringMaster of Science in Computer Engineering (MSCoE
Effect of Construction Void Defects on Flexural and Axial Load Capacity of Reinforced Concrete Members
No full textA Master of Science thesis in Civil Engineering by Mohammad Mustafa Al Moukdad entitled, “Effect of Construction Void Defects on Flexural and Axial Load Capacity of Reinforced Concrete Members”, submitted in May 2018. Thesis advisor is Dr. Sami W. Tabsh. Soft and hard copy available.A common construction defect in reinforced concrete is honeycombing, which consists of loosely connected coarse aggregates with little mortar in-between them over a small volume located within a structural member. Such a void defect has a detrimental effect on the structural behavior because it creates weak localized regions within the member. This study is concerned with the effect of such voids on the structural behavior and capacity of reinforced concrete members under the effect of flexure and axial compression. In order to know more about the causes, characteristics, and repair methods of void defects in concrete structures, practicing structural and construction engineers in the country were surveyed. Using the 54 received responses, a research plan was developed consisting of experimental and theoretical phases. The experimental part consisted of testing 20 intact and defective scaled beams under the effect of bending moment, and columns under the effect of pure axial compression. The flexural specimens were 2-m long with a 150 mm x 300 mm cross-section, whereas the axial compression specimens were 1-m height with a 200 mm square cross-section. The experimental program considered the size (5%-20% of the intact cross-section), shape (square and rectangular), and length (100-200 mm) of the void within the member. It addressed two different concrete compressive strengths (30 and 50 MPa) and two steel reinforcement ratios (1% and 2%). The experimental tests were complemented with theoretical analyses involving the software Response 2000 and SPColumn. The load-deflection relationships from the tests generally confirmed that the presence of a void decreases the stiffness of the member, ductility, and strength, and the decrease depends on the size of the defect. Voids that occupy 20% of the cross-sectional area of a beam can reduce its flexural capacity by 30-40%, depending on the concrete compressive strength, reinforcement ratio, and shape of the void. The corresponding decrease in the compressive capacity of a defective column is in the range of 19-22%. Theoretical predictions of the flexural capacity of beams and axial capacity of columns based on the ACI 318 code can be reasonable if the void is less than 5% of the intact section; however, this can lead to over-estimation of the actual capacity if the void is greater than 5%. Accounting for the eccentricity of the load from the plastic centroid of a voided column in the analysis can lead to conservative results.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
Strengthening of Shear Deficient Beams with CFRP Laminates with Different Types of Anchorage Systems
No full textA Master of Science thesis in Civil Engineering by Khalid Mustafa Elradi Mohamed entitled, “Strengthening of Shear Deficient Beams with CFRP Laminates with Different Types of Anchorage Systems”, submitted in March 2018. Thesis advisor is Dr. Jamal Abdalla and thesis co-advisor is Dr. Rami Hawileh. Soft and hard copy available.Retrofitting and repairing deteriorating structures have been achieved using several techniques. Strengthening of Reinforced Concrete (RC) members in shear with externally bonded fiber reinforced polymer (FRP) plates and sheets has been commonly accepted. FRP de-bonding from the concrete substrate is one of the most common types of failure in shear strengthening of RC beams. Many shear strengthening methods have used different anchorage systems to solve the problem of the de-bonding of FRP laminates. The most common types of anchorage in use include full wrapping, U-wrapping, FRP-spikes, in addition to other types of mechanical anchorages. This study explores the use of groove-epoxy and bore-epoxy anchorages. In this investigation, 15 shear deficient rectangular RC beams were strengthened with carbon (CFRP) sheets and plates bonded by groove-epoxy anchorages of different widths and bore-epoxy anchorages of different depths and spacing. The beams were tested under four-point bending. The aim of this study is to investigate the feasibility of using epoxy-anchorages, specifically groove-epoxy and bore-epoxy to reduce or eliminate FRP de-bonding failure and increase the FRP strength that will lead to an increase in shear strength of aging beams. Both methods have shown an increase in the shear capacity when compared with the control beams and with the externally bonded reinforcement (EBR) strengthening method without anchorage. In the groove-epoxy anchorage method, the two medium grooves of 10 mm width showed the best performance among the groove widths while in bore-epoxy anchorage method, the large bores of 30 mm diameter showed the best performance among the bore diameters. Groove-epoxy anchors have increased the shear capacity by 112 % over the control beam and 52 % over the EBR strengthened beam. Bore-epoxy anchors have increased the shear capacity up to 68 % over the control beam and 20 % over the EBR strengthened beam. The shear strength of three specimens were predicted using the relevant codes of practice (ACI-440.2R-08, CAN/CSA-S806-02, FIB 14 and TR55). The prediction showed that CAN/CSA-S806-02 is the most accurate when compared with the other codes.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE