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Evaluation of 3D Concrete Printing in the United Arab Emirates
No full textA Master of Science thesis in Civil Engineering by Aktham S. Alchaar entitled, “Evaluation of 3D Concrete Printing in the United Arab Emirates”, submitted in February 2020. Thesis advisor is Adil Al-Tamimi. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).3D concrete printing has been recently studied as a new scheme of construction. The automated nature of such technique allows for reductions in waste generation, less manpower requirements, and fabrication of complex geometries. However, the use of concrete for this application is challenging. The material shall be flowable for ease of extrusion. Printed layers shall preserve their shape and rapidly attain strength to bear their own weight and the subsequent layers. However, there is a lack of guidance on the design of 3D printing concrete mixes. In addition, the change in performance of 3D printing concrete under different environmental conditions is still generic. The aim of this research is to develop a concrete mix using local materials, and to evaluate it in two environmental conditions: ambient and site conditions. The experimental program addressed fresh state properties through flow table, open time, extrudability, and shape stability. Compressive strength, flexural strength, and interlayer bond shear strength have been evaluated as mechanical properties in this research by testing a total of 61 specimens. A novel test setup was designed for bond strength evaluation at different printing time intervals. 19 trial mixes were performed, and one mix was chosen as the optimum based on extrudability and shape stability/quality. It was observed that inclusion of fibers enhances shape stability, but higher dosages of superplasticizer become required. It was found that flow table and open time of site conditions decreased by 9% and 16% respectively, compared to ambient flow table (86%) and open time (7.2 minutes) on average. This was owing to accelerated loss of flowability. Shape retention index (ambient) was 0.94-0.96 for different lengths and number of layers, and dropped by 2-8.5% under site conditions. Compressive strength was evaluated to be 47 MPa in control cubes. Results from compression and bond tests indicated accelerated water evaporation and surface dehydration in site conditions, and that the presence of joints in printed parts is detrimental to such strength parameters. Finally, flexural strength was increased in site conditions compared to control and ambient specimens by 21% and 18% respectively. Flexural strength results demonstrated that fibers are better oriented through print process, and can be further improved in hot mixes due to lower viscosities.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
Towards Monitoring of Nutrient Pollution in Coastal Lake Using Remote Sensing and Regression Analysis
No full textThe last few decades have witnessed a tremendous increase in nutrient levels (phosphorus and nitrogen) in coastal water leading to excessive algal growth (Eutrophication). The presence of large amounts of algae turns the water’s color into green or red, in the case of algal blooms. Chlorophyll-a is often used as an indicator of algal biomass. Due to increased human activities surrounding Dubai creek, there have been eutrophication concerns given the levels of nutrients in that creek. This study aims to map chlorophyll-a in Dubai Creek from WorldView-2 imagery and explore the relationship between chlorophyll-a and other eutrophication indicators. A geometrically and atmospherically-corrected WorldView-2 image and in-situ data have been utilized to map chlorophyll-a in the creek. A spectral model, developed from theWorldView-2 multispectral image to monitor Chlorophyll-a concentration, yielded 0.82 R² with interpolated in-situ chlorophyll-a data. To address the time lag between the in-situ data and the image, L and sat 7 Enhanced Thematic Mapper Plus (ETM+) images were used to demonstrate the accuracy of the WorldView-2 model. The images, acquired on 20 May and 23 July 2012, were processed to extract chlorophyll-a band ratios (Band 4/Band 3) following the standard approach. Based on the availability, the 20 May image acquisition date is the closest to the middle of Quarter 2 (Q2) of the in-situ data (15 May). The 23 July 2012 image acquisition date is the closest to theWorldView-2 image date (24 July). Another model developed to highlight the relationship between spectral chlorophyll-a levels, and total nitrogen and orthophosphate levels, yielded 0.97 R², which indicates high agreement. Furthermore, the generated models were found to be useful in mapping chlorophyll-a, total nitrogen, and orthophosphate, without the need for costly in-situ data acquisition efforts.American University of Sharja
Parametric Study of a Single Effect Lithium Bromide-Water Absorption Chiller Powered by a Renewable Heat Source
No full textThis work investigates the performance of a single-effect absorption chiller utilizing an aqueous lithium bromide solution as the working fluid and driven by hot fluid rejected from either a geothermal power plant or the outlet of a thermal solar collector.
This relatively low enthalpy return fluid, which will otherwise be reinjected back into the earth, will be utilized as the thermal energy source of the chiller. Although such chillers are considered low-grade energy refrigeration cycles, the one proposed here has an advantage in terms of economy and efficiency. A parametric analysis is performed using Engineering Equation Solver software and is used to highlight the effect of the heat exchanger size on the coefficient of performance of the chiller. The analysis proved that the proposed device can operate with excellent cooling capacity, reaching 16 kW, and a relatively high coefficient of performance (~ 0.7) while being driven by the low-grade energy. The heat source temperature, solution heat exchanger effectiveness and the size of the absorber were shown to be key parameters for the design and operation of absorption chillers. Moreover, increasing the heat source mass flow rate has a significant impact on both cooling capacity and coefficient of performance at low values ( 10 kg/s)
Behavioral Modeling of GaN Doherty Power Amplifiers Using Memoryless Polar Domain Functions and Deep Neural Networks
No full textIn this paper, novel Doherty Power Amplifier (DPA) models are presented. The motivation behind the proposed models is to accurately predict static nonlinearities in the compression regions of the carrier and peaking amplifiers. DPAs suffer from a nonlinearity that originates from the carrier amplifier, and a second more pronounced nonlinearity generated at the full compression region following the turn-on of the peaking amplifier. Moreover, these distortions are often observed at different input power levels depending on whether the AM-AM or the AM-PM characteristic is considered. Therefore, the proposed static model is based on independent modeling of the memoryless gain in the polar domain. The static model of the memoryless AM-AM and AM-PM characteristics is augmented with either memory polynomials or deep neural network functions for memory effects modeling. The methodology of building the proposed models and the achieved results are discussed in this paper. The MP based proposed model achieves an NMSE as low as - 45:3dB with only 78 model parameters, while the DNN based model achieves an NMSE as low as - 46:1dB with only 156 model parameters. However, the DNN based model achieves the best model resilience to changes in the identification data.American University of Sharja
Optical Flow Based Extraction of Breathing Signal from Cone-Beam CT Projections
No full textA Master of Science thesis in Biomedical Engineering by Shafiya Sabah entitled, “Optical Flow Based Extraction of Breathing Signal from Cone-Beam CT Projections”, submitted in May 2020. Thesis advisor is Dr. Salam Dhou. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).Lung cancer continues to be the most common type of cancer worldwide. Radiotherapy is used to break tumor cells by application of radiation beams during cancer treatment. Adapting radiotherapy to respiratory movements has always been a major concern in thoracic and upper-abdomen radiotherapy. Thus, estimating the respiration induced organ motion has been widely studied. Respiratory motion can be estimated using external equipment that trace the chest motion during breathing or tracking of radio-opaque markers implanted surgically in the lungs. However, these techniques are either invasive or require external equipment. The objective of this thesis is to propose an image-based method to estimate the respiratory motion without the involvement of any external equipment or implanted markers. To achieve this objective optical flow was implemented to acquire dense motion vectors from sequence of cone beam CT projection images. Principal component analysis was then performed on the motion vectors to project data to a lower dimension while preserving the dataset motion trends. Extracted signal was sorted into phase bins followed by 4D-reconstruction using a single phase to eliminate the effect of breathing motion. Several experiments were conducted to gauge the feasibility of this study. The dataset comprised of three computer simulations of cone beam CT projections as well as three real datasets acquired under clinical settings. The computer simulated phantom datasets were generated to include different scenarios such as fast breathing, slow breathing and irregular breathing patterns. The average phase shift error for phantom dataset under fast breathing motion was 0.6 ± 0.66 projections, 0.4 ± 0.5 under slow breathing and 0.53 ± 0.51 under irregular breathing. For clinical datasets the average phase shift for patient 1 was observed to be 1.936 ± 0.734, 1.185 ± 0.781 for patient 2 and 1.537 ± 0.93 for patient 3. Four-dimensional CBCT reconstruction was performed for one phantom dataset. Reconstructed image had a peak signal to noise ratio of 45.75.College of EngineeringMultidisciplinary ProgramsMaster of Science in Biomedical Engineering (MSBME
Sesamum indicum (sesame) enhances NK anti-cancer activity, modulates Th1/Th2 balance, and suppresses macrophage inflammatory response
No full textTo evaluate the potential immunomodulatory effects of an aqueous extract of Sesamum indicum seeds with regard to splenocyte proliferation, Th1/Th2 balance, macrophage function, and the cytotoxic activity of natural killer (NK) cells. Methods: Splenocyte proliferation was measured by [3H]- thymidine incorporation. Griess assay was performed to evaluate the production of nitric oxide by macrophages. The levels of cytokines secreted by splenocytes and macrophages were measured by ELISA. JAM assay was performed to examine the cytotoxic activity of NK cells against YAC-1 tumor cells. Results: Sesamum indicum significantly enhanced splenocyte proliferation in a dose-dependent manner. Sesamum indicum also increased and suppressed the secretion of Th1 and Th2 cytokines, respectively, by splenocytes. The secretion of key pro-inflammatory mediators (IL-6, TNFα, and nitric oxide) by primary macrophages was significantly inhibited by Sesamum indicum. Moreover, Sesamum indicum increased the cytotoxic activity of NK cells against YAC-1 tumor cells. Conclusions: Sesamum indicum shows potent immunomodulatory, anti-inflammatory, and anti-cancer effects. Constituents of Sesamum indicum may be used as effective therapeutic agents in regulating immune reactions implicated in various infectious and non- infectious conditions including cancer
Microplastic Pollution Detection in Coastal Waters of Dubai
No full textA Master of Science thesis in Civil Engineering by Batoul Mohsen entitled, “Microplastic Pollution Detection in Coastal Waters of Dubai”, submitted in November 2020. Thesis advisor is Dr. Md. Maruf Mortula and thesis co-advisor is Dr. Tarig Ali. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
The Recruitment, Selection and Preparation of Expatriates
No full textFor organisations and for individuals, effective recruitment, selection and preparation of new employees or employees in new circumstances are always important. This issue is exacerbated in the case of international assignments, where issues of cross-national adjustment complicate the picture. The objective of this chapter is to examine and summarise the extant research on expatriate recruitment, selection and preparation. The chapter is structured as follow. First, we discuss expatriate recruitment sources, methods, and the expatriates' motivations to work abroad. Second, we examine expatriate selection criteria, methods, and how expatriates are selected in practice. Third, we present the variety of expatriate preparation methods, discuss expatriate training effectiveness and expatriate preparation in practice. We conclude by considering future avenues of research. Overall, there is good material for researchers to build on and a growing understanding of the key issues. Nevertheless, there remains here a rich field for exciting research in the future
A Micromorphic Beam Theory for Beams with Elongated Microstructures
No full textA novel micromorphic beam theory that considers the exact shape and size of the beam’s microstructure is developed. The new theory complements the beam theories that are based on the classical mechanics by modeling the shape and size of the beam’s microstructure. This theory models the beam with a microstructure that has shape and size and exhibits microstrains that are independent of the beam’s macroscopic strains. This theory postulates six independent degrees of freedom to describe the axial and transverse displacements and the axial and shear microstrains of the beam. The detailed variational formulation of the beam theory is provided based on the reduced micromorphic model. For the first time, the displacement and microstrain fields of beams with elongated microstructures are developed. In addition, six material constants are defined to fully describe the beam’s microscopic and macroscopic stiffnesses, and two length scale parameters are used to capture the beam size effect. A case study of clamped-clamped beams is analytically solved to show the influence of the beam’s microstructural stiffness and size on its mechanical deformation. The developed micromorphic beam theory would find many important applications including the mechanics of advanced beams such as meta-, phononic, and photonic beams.Abu Dhabi Universit
Construction Disputes in the UAE: Causes and Resolution Methods
No full textClaims and disputes occur frequently in the construction industry between different contracting parties, mainly the owner, the designer and the contractor. Consequently, valuable time and a significant amount of money are lost. The United Arab Emirates (UAE) construction industry, one of the most vibrant sectors globally, is experiencing a high level of construction disputes and claims. This paper aims to identify and assess the major causes of disputes in the UAE and weigh the effectiveness of the methods used for their avoidance and resolution. The sources of disputes, and their avoidance/resolution methods, were identified through a comprehensive literature review. A survey was then developed and sent to 150 construction professionals. Fifty-four responses were received and analyzed. The results show that the top five sources of disputes in the UAE are variations initiated by the owner, obtaining permit/approval from the municipality and other governmental authorities, material change and approval during the construction phase, the slowness of the owner in decision-making, and the short time available during the design phase. As for the avoidance and the resolution method, the most effective method was found to be negotiation.American University of Sharja