American University of Sharjah
  • Sharjah, United Arab Emirates
Recent publications
Operating proton exchange membrane fuel cells (PEMFCs) at higher temperatures (above the boiling point of water) offer several advantages. It enhances the electrodes' kinetics, allows the recovery of useful heat, and offers better water management due to the formation of water in the vapor phase. There is a crucial need to either, modify the existing perfluorosulfonic acid membranes (i.e. Nafion) or develop a new class of membranes that can withstand higher temperature operation. Heteropolyacids (HPAs) represent a class of inorganic materials that have been investigated as additives in PEMFCs membranes for the purpose of: 1) enhancing the proton conductivity and, 2) reducing the fuel crossover. This review focuses on discussing the recent developments attained upon the introduction of HPAs in proton exchange membranes. The review summarized the various efforts made on either modifying the existing Nafion membranes with HPAs, or by immobilizing them in other polymers such as PBI and SPEEK. Remarkable enhancements in proton conductivities, as well as a significant reduction in fuel crossover, were reported. However, the leaching of HPAs is still a major obstacle. The current review concludes that the successful implementation of HPAs in PEMFCs membranes can be achieved upon developing proper immobilization techniques within the polymers' matrix.
Consumers react negatively to wrongdoings by brands. In this regard, managers often struggle to allocate their recovery resources effectively, as some consumers react more negatively to incidents that affect only themselves while others react more strongly to events that affect many people. In three experiments, we examine how consumers react to negative brand events (NBEs) that only affect themselves (i.e., personal scope) and NBEs that affect many people, including or excluding themselves (i.e., communal scope or external scope). Drawing on self-bias theory, we find that consumers experience stronger feelings of betrayal following an NBE with a personal (vs communal or external) scope, which in turn drives avoidance. We show that this effect may be mitigated if consumers are less self-focused (i.e., score low in grandiose narcissism or egocentric selfishness) or are from a less self-focused culture (i.e., collectivists). This research provides actionable implications for brand managers regarding NBEs.
One of the important aspects of manipulating and controlling liquid transport is the design of membrane surfaces. Janus membranes with opposite wettability characteristics can be manufactured for efficient directional water transfer. In this work, two types of materials were used to fabricate membranes with an asymmetric wettability behavior: copper foam and copper mesh. One side of the membranes was treated by scanning with a femtosecond laser beam, as a result of which it was converted to a superhydrophilic state, while the untreated side remained hydrophobic. Both membranes demonstrated excellent properties of a water diode through which water droplets could easily pass from the hydrophobic side to the hydrophilic side, but not vice versa. This behavior was achieved by finding the optimal laser scanning speed. This type of Janus membrane has found applications in collecting water droplets from fog; therefore, the samples obtained were also tested in terms of harvesting micro-droplets. The Janus mesh-based structure has demonstrated a higher water collection efficiency (3.9 g/cm2 h) compared to the foam-based membrane (2.5 g/cm2 h). Since the fog-water conversion efficiency decreased over time (to 0.5 g/cm2 h in 2 weeks) due to the absorbance of organic pollutants, a coating of titanium oxide was applied to the laser-treated side of the Janus membranes. As a result, the effective function of the systems became distinctly long-lasting and was well maintained for at least 60 days. Moreover, the fabricated systems were protected from further degradation by simply placing them under sunlight for several hours. Our results prove to be useful in developing asymmetric hydrophobic-superhydrophilic membranes, which have potential applications in high-precision drop control and in harvesting water from arid environments.
Azepino[3,4,5‐cd]indole derivatives represent the core scaffold of important natural products and biologically significant compounds. Therefore, the establishment of step‐ and atom‐economic strategies to access this class of compounds is of paramount importance. To this end, complexity‐to‐diversity (CtD) strategy has become one of the most important tools that transforms complex molecules into diverse skeleta. However, many of the reactions that could be employed in CtD are restricted by the functional handles exist in these molecules. This limits the achievement of the desired skeletal diversity. Herein, an efficient and step‐economic strategy to access a diverse collection of azepino‐[3,4,5‐cd]indole architectures via a cascade that unites Pictet‐Spengler with Michael addition, is described. This was achieved by reacting cyclohexadienone acetaldehydes 2a‐2d with indolyl‐4‐ethyl amine 1. Employing a CtD strategy on the developed azepino‐[3,4,5‐cd]indoles, a rapid rearrangement reaction that provided a modular, chemo‐ and diastereoselective access to diverse collection of spiro azepinocarbazole nature‐inspired frameworks, was encountered.
In developing countries, the construction industry has been one of the hardest hit by the COVID-19 pandemic. The impact of the pandemic has created a whole new set of risks, causing workforce-related issues, supply chain disruptions, and legal and contractual implications. This research aims to identify and quantitatively analyse COVID-19 emerging risks in the construction industry of Iraq. A mixed method approach was used for data collection and analysis, including a focus group session to identify COVID-19 emerging risks, a survey to rate the identified risks, and the development of a fuzzy-based risk assessment model to analyse the level of riskiness of the identified risks. Results indicate that the most critical COVID-19 risks are (1) contract suspension, (2) contractor bankruptcy, (3) materials price escalation, (4) construction contract claims, (5) inappropriate risk allocation, (6) non-compliance with social distancing guidelines, (7) skills shortage, and (8) poor site and virtual communication. This paper contributes to the body of knowledge by providing academics and industry practitioners with a more comprehensive understanding of the risks arising from the COVID-19 pandemic. Moreover, this paper presents a novel model for analysing risks related to extreme conditions, such as the COVID-19 pandemic and future pandemics.
In this paper, we present a proof-of-concept for a novel temperature sensing approach that combines the thermal expansion and a compliant mechanism. The objective is first to demonstrate its feasibility at the macroscale, develop and validate an FEM model at the macroscale and then scale down the FEM model to verify the possible implementation of the mechanism at the microscale. The sensing approach relies on a mechanical compliant mechanism that amplifies the thermal expansion of a structure. A testing platform equipped with an IR thermometer, thermocouple, a power supply, and laser distance sensors, is implemented to demonstrate the operability of the proposed sensing mechanism. A numerical model of the sensor is developed using the FE software Ansys. The numerical results show a good agreement with their experimental counterparts at the macro scale. The model is then used to numerically investigate several configurations, namely single, double, triple and quadruple compliant mechanisms. The amplification factor is found the highest when using the double compliant mechanism. A temperature sensitivity of 28.5 μm/°C is achieved for this compliant mechanism. The numerical analysis also demonstrated that the performance obtained at the macro scale, can be conserved for microscale devices. However, buckling of some elements is observed for the microscale system which degrades the performance of the sensor when subjected to relatively large displacements. The microscale FEM model shows the possible prevention of buckling issues by slightly modifying the geometry of the compliant mechanisms. The present study is expected to provide baseline and guidance for the implementation of the sensing approach for MEMS devices.
Transition metal carbides/nitrides (MXenes) with eccentric properties are emerging 2D nanomaterials with intriguing applications in the photo and electro-catalytic water splitting (Wsp). MXenes have a regular planer structure with a large specific surface area (SSA), excellent hydrophilicity, metallic conductivity, and a wide range of functionalities and surface termination groups, making them a promising candidate for long-term hydrogen generation (H2, gen). As a result, their use as electro and photo-catalysts in Wsp to solve energy and environmental challenges has increased. MXenes were proposed to overcome major drawbacks of TiO2, the most commonly used photo-catalyst in solar-driven Wsp, such as high band gap and fast recombination of photo-induced charge carriers. MXene has been rigorously investigated based on TiO2 modification (i.e. in-situ derived MXene-TiO2 and MXene/TiO2 nanocomposite) as well as Metal-MXene co-catalyst that provides simple electron channelization to improve overall electro and photo-catalytic activity (CatA)toward Wsp and increase the hydrogen evolution reaction (HER). However, several issues must be resolved before practical applications may be considered, such as weak environmental capabilities and limited intrinsic catalytic activities. Although there have been a few review papers on the synthesis, properties, and applications of Mxenes in various fields, this present work focuses on the most current advances in the synthetic of MXene-derived TiO2 and MXene/TiO2 nanohybrid composites as well as Metals-MXene nanocomposite, clarifying the charge carrier separation mechanism in connection to the formed Schottky junction at MXene- elements interface to attaining high photo-catalytic H2, gen. Furthermore, technical challenges, and enhanced catalytic performance as well as materials design and MXenes derivative with structural features and activity were presented. MXenes' catalytic mechanism is carefully outlined, along with its photocatalytic and electrocatalytic Wsp properties. According to the literature review, Ti3C2 can be combined with a variety of materials to produce electro or photo-catalysis with distinct layered morphology (0D, 1D, 2D, 3D), abundant surface termination groups, and enhanced photo-electrical activities. MXene-derived TiO2 and MXene/TiO2 nanohybrid composites have been proposed as viable electro and photo-catalytic H2, gen alternatives. The photo-catalytic H2, gen rate from Wsp over MXene-derived TiO2 can range from 20 to 50, 000 mol.g-1h−1, with Co-Chl@Ti3C2Tx producing the most.
In this paper, we investigate the stabilization of a one-dimensional piezoelectric (Stretching system) with partial viscous dampings. First, by using Lorenz gauge con- ditions, we reformulate our system to achieve the existence and uniqueness of the solution. Next, by using General criteria of Arendt–Batty, we prove the strong stabil- ity in different cases. Finally, we prove that it is sufficient to control the stretching of the center-line of the beam in x-direction to achieve the exponential stability. Numerical results are also presented to validate our theoretical result.
The de novo assembly of stereochemically and skeletally diverse scaffolds is a powerful tool for the discovery of novel chemotypes. Hence, the development of modular, step- and atom-economic synthetic methods to access stereochemically and skeletally diverse compound collection is particularly important. Herein, we show a metal-free, stereodivergent build/couple/pair strategy that allows access to a unique collection of benzo[5,6][1,4]oxazino[4,3-a]quinazoline, quinolino[1,2-a]quinazoline and benzo[b]benzo [4,5]imidazo[1,2-d][1,4]oxazine scaffolds with complete diastereocontrol and wide distribution of molecular architectures. This metal-free process proceeds via desymmetrization of phenol derivatives. The cascade unites Mannich with aza-Michael addition reactions, providing expeditious entries to diverse classes of molecular shapes in a single operation.
Few researchers have attempted to experimentally evaluate the low-strain shear wave velocity (Vs) of specimens undergoing large strain deformations. They report that the Vs is practically unaffected by the strains, and the reasons behind this behavior are not fully understood. This study presents the continuous measurement of low-strain Vs with bender elements (BE) during monotonic shearing of two sand specimens in a triaxial device. The results are analyzed using a micro-mechanical model based on contact theory. The results of this study confirm that the Vs values from BE measurements are unaffected by an increase in axial strains that are induced by a separate mechanism. The micro-mechanical model predictions of Vs agree well with the results of this study and with the results of previous studies. They show that the mean effective stress and increase in inter-particle stiffness controls the low-strain stiffness despite a global increase in strains during monotonic loading.
This work presents recent developments of algal bioreactors used for CO2 removal and the factors affecting the reactor performance. The main focus of the study is on light intensity and photoperiods. The role of algae in CO2 removal, types of algal species used in bioreactors and conventional types of bioreactors including tubular bioreactor, vertical airlift reactor, bubble column reactor, flat panel or plate reactor, stirred tank reactor and specific type bioreactors such as hollow fibre membrane and disk photobioreactors etc. are discussed in details with respect to utilization of light. The effects of light intensity, light incident, photoinhibition, light provision arrangements and photoperiod on the performance of algal bioreactors for CO2 removal are also discussed. Efficient operation of algal photobioreactors cannot be achieved without the improvement in the utilization of incident light intensity and photoperiods. The readers may find this article has a much broader significance as algae is not only limited to removal or sequestration of CO2 but also it is used in a number of commercial applications including in energy (biofuel), nutritional and food sectors.
Airborne laser scanning sensors are impressive in their ability to collect a large number of topographic points in three dimensions in a very short time thus providing a high-resolution depiction of complex objects in the scanned areas. The quality of any final product naturally depends on the original data and the methods of generating it. Thus, the quality of the data should be evaluated before assessing any of its products. In this research, a detailed evaluation of a LIDAR system is presented, and the quality of the LIDAR data is quantified. This area has been under-emphasized in much of the published work on the applications of airborne laser scanning data. The evaluation is done by field surveying. The results address both the planimetric and the height accuracy of the LIDAR data. The average discrepancy of the LIDAR elevations from the surveyed study area is 0.12 m. In general, the RMSE of the horizontal offsets is approximately 0.50 m. Both relative and absolute height discrepancies of the LIDAR data have two components of variation. The first component is a random short-period variation while the second component has a less significant frequency and depends on the biases in the geo-positioning system.
The addition of hollow aluminium oxide bubbles to the 7075 aluminium matrix results in a lightweight syntactic foam with a reduced density and an increased peak compression strength. The presence of ceramic bubbles also aids in a reduced coefficient of thermal expansion and thermal conductivity in comparison to aluminium alloys. In spite of their enhanced material properties, the inclusion of hollow aluminium oxide bubbles presents the challenge of poor machinability. In order to elucidate the problem of poor surface machinability, an attempt has been made to develop a thermo-mechanical finite element machining model using AdvantEdgeTM software with which surface quality and machined syntactic foam material can be analyzed. If the novel model developed is combined with virtual reality technology, CNC technicians can observe the machining results to evaluate and optimize the machining program. The main novelty behind this software is that the material foam is assumed as a homogeneous material model for simplifying the material model as a complex heterogeneous material system. The input parameters used in this study are cutting speed, feed, average size and volume fraction of hollow aluminium oxide bubbles, and coolant. For the output parameters, the numerical analysis showed a 6.24% increase in peak tensile machining induced stress as well as a 51.49% increase in peak cutting temperature as cutting speed (25 m/min to 100 m/min) and uncut chip thickness (0.07 mm to 0.2 mm) were increased. The average size and volume fraction of hollow aluminium oxide bubbles showed a significant impact on the magnitude of cutting forces and the depth of tensile induced stress distribution. It was observed on the machined surface that, as the average size of hollow aluminium oxide bubbles became coarser, the peak machining induced tensile stress on the cut surface reduced by 4.47%. It was also noted that an increase in the volume fraction of hollow aluminium oxide bubbles led to an increase in both the peak machining induced tensile stress and the peak cutting temperature by 29.36% and 20.11%, respectively. This study also showed the influence of the ceramic hollow bubbles on plastic deformation behavior in 7075 aluminium matrix; the machining conditions for obtaining a favorable stress distribution in the machined surface and sub-surface of 7075 closed cell syntactic foam are also presented.
Rural–urban immigration, regional wars, refugees, and natural disasters all bring to prominence the importance of studying urban growth. Increased urban growth rates are becoming a global phenomenon creating stress on agricultural land, spreading pollution, accelerating global warming, and increasing water run-off, which adds exponentially to pressure on natural resources and impacts climate change. Based on the integration of machine learning (ML) and geographic information system (GIS), we employed a framework to delineate future urban boundaries for future expansion and urban agglomerations. We developed it based on a Time Delay Neural Network (TDNN) that depends on equal time intervals of urban growth. Such an approach is used for the first time in urban growth as a predictive tool and is coupled with Land Suitability Analysis, which incorporates both qualitative and quantitative data to propose evaluated urban growth in the Greater Irbid Municipality, Jordan. The results show the recommended future spatial expansion and proposed results for the year 2025. The results show that urban growth is more prevalent in the eastern, northern, and southern areas and less in the west. The urban growth boundary map illustrates that the continuation of urban growth in these areas will slowly further encroach upon and diminish agricultural land. By means of suitability analysis, the results showed that 51% of the region is unsuitable for growth, 43% is moderately suitable and only 6% is suitable for growth. Based on TDNN methodology, which is an ML framework that is dependent on the growth of urban boundaries, we can track and predict the trend of urban spatial expansion and thus develop policies for protecting ecological and agricultural lands and optimizing and directing urban growth.
Low-cost desktop-sized fused deposition modeling (FDM) printers have been widely embraced by small to large-scale institutions and individuals. To further enhance their utility and increase the range of materials that they can process, this work proposes a low-cost solution that adapts to low-cost desktop-sized extruders and enables them to fabricate filaments comprising a wide range of nonorganic reinforcing particles. This solution will fill a gap in the field, as low-cost fabrication techniques for reinforced filaments have been lacking. In the proposed solution, particles are heated and deposited on thermoplastic pellets to form a coating. Coated pellets are subsequently extruded using a low-cost desktop single-screw extruder. The effectiveness of the process is demonstrated by fabricating polylactic acid (PLA) filaments reinforced with two types of reinforcements, namely, dune sand and silicon carbide. Filaments’ stiffness and strength were measured, and their microstructure along their lateral and longitudinal directions were investigated. Improvements in tensile strength (up to 8%) and stiffness (up to 4.5%) were observed, but at low reinforcement levels (less than 2 wt%). Results showed that the proposed process could be used to fabricate filaments with multiple types of particles. The produced filaments were successfully used to fabricate 3D parts using a commercial desktop FDM printer.
Herein, experimental and numerical validation studies were conducted on internal channel cooling in which seven jets impinging inside a rotating semi-cylindrical channel. These studies were conducted by considering a Reynolds number of 7,500 for a jet at five rotation speeds (ranging from 0 to 200 rpm). Numerical analysis was performed using the shear stress transport (SST) k–ω turbulence model with a properly analyzed fine mesh containing eight million nodes. A test setup with required instrumentation was developed inhouse for this study. Two temperature measurement techniques, namely thermochromic liquid crystals (TLCs) and thermocouples, were adopted. Further, the target surface temperature contours were precisely analyzed by comparing the TLC temperature measurements with the numerical temperature results. The captured temperature contours indicated points of minimum-temperature regions, which corresponded to the jet impingement regions. By examining the temperature distribution along the axial centerline, a good agreement was established between the numerical results and the experimental measurements. For Reynolds number of 7,500, increasing ration speed from 0 to 250 rpm has reduced the variation in temperature between different jets. The size of inlet port to feeding duct has a strong imapact on jet formation, which led to different mass flow rate across jets. Furthermore, a small deviation between numerical and experimental data can be observed near the end side of the channel owing to the radial and lateral heat transfer losses and outlet flow restriction.
Diabetes is sweeping the world as a silent epidemic, posing a growing threat to public health. Modeling diabetes is an effective method to monitor the increasing prevalence of diabetes and develop cost-effective strategies that control the incidence of diabetes and its complications. This paper focuses on a mathematical model known as the diabetes complication (DC) model. The DC model is analyzed using different numerical methods to monitor the diabetic population over time. This is by analyzing the model using five different numerical methods. Furthermore, the effect of the time step size and the various parameters affecting the diabetic situation is examined. The DC model is dependent on some parameters whose values play a vital role in the convergence of the model. Thus, parametric analysis was implemented and later discussed in this paper. Essentially, the Runge-Kutta (RK) method provides the highest accuracy. Moreover, Adam-Moulton's method also provides good results. Ultimately, a comprehensive understanding of the development of diabetes complications after diagnosis is provided in this paper. The results can be used to understand how to improve the overall public health of a country, as governments ought to develop effective strategic initiatives for the screening and treatment of diabetes.
Reinforced Concrete (RC) structures deteriorate over years due to many reasons including corrosion of reinforcing steel, carbonation of concrete, overload on structural members, among others. This may result in flexural or shear deficiency in RC beams. The failure of shear-deficient RC beams is usually brittle, sudden and with little warning, if any. Diagonal shear cracks will form due to load increase that may result in complete fracture of the RC beam. Therefore, deteriorated and shear-deficient RC beams need to be strengthened to avoid such undesirable shear failure. This paper investigates shear strengthening of RC T-Beams using carbon fiber reinforced polymer (CFRP) laminates anchored with spike anchors. The beams have been strengthened in flexure to avoid flexural failure and then strengthened in shear using CFRP sheets that were anchored with CFRP spikes. Six beams were strengthened with CFRP laminates at 45o and at 90o inclination angles and anchored with embedded CFRP spikes with different depths (50 mm and 75 mm) and different diameters (10 mm and 12 mm). Wrapping (U-Wrapped) was also used for anchoring the flexural CFRP laminates. The beams are tested to failure and their capacity were compared with that of an unstrengthen control beam. It is observed that the capacity of the strengthened beams is increased up to 45% compared to that of the control beam. Anchoring with U-wraps enhanced the beam capacity further. The inclination of the CFRP sheets, dowel diameter, and the embedment depth of the spike anchors influenced shear and deformation capacity of the tested RC T-Beams.
In recent years recycled aggregates, from construction demolition waste, has been used as a replacement to normal (natural) aggregates in concrete. This is to preserve the depletion of natural resources and to further reduce carbon footprints in terms of energy depletion and waste disposition. Mechanical properties, such as compressive and tensile strengths, of recycled aggregates concrete (RAC) have been investigated by several researchers and were compared with that of normal aggregate concrete (NAC). In this investigation, the shear strengths and modes of failure of RAC and NAC beams have been investigated. In addition, the behavior of RAC and NAC beams strengthened with carbon-fiber-reinforced-polymer (CFRP) U-wrapped laminates have been examined. Four RAC and NAC shear-deficient rectangular beams were cast, two of which were strengthened in shear with CFRP U-wraps. The beams were tested to failure under four-point bending. The test results indicate that the shear capacity of all specimens strengthened with CFRP composites increased significantly compared to the control beam specimens. The performance of the RAC and NAC beams before and after strengthening were compared. It was observed that the RAC specimens provided similar shear strength as that of the NAC beams. The percentage increase in the shear capacity of RAC beams reached almost 60% of the control beam for the beams with U-wraps. The ACI 318-19 and ACI440.2R-17 codes are also used to predict the shear strength of the tested RAC and NAC beams and it was observed that the predicted capacities were close to the experimentally measured ones.
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3,380 members
Rodrigo Basco
  • Department of Management
Zayid Abdulhadi
  • Department of Mathematics and Statistics
M Sajid Khan
  • Department of Marketing
Mehmet Egilmez
  • Department of Physics
Information
Address
Sharjah, United Arab Emirates
Head of institution
Dr. Bjorn Kjerfve, Chancellor
Website
www.aus.edu
Phone
+971 6 515 5555