Isolated Single-stage Power Electronic Building Blocks Using Medium Voltage Series-stacked Wide-bandgap Switches

The demand for efficient power conversion systems that can process the energy at high power and voltage levels is increasing every day. These systems are to be used in microgrid applications. Wide-bandgap semiconductor devices (i.e. Silicon Carbide (SiC) and Gallium Nitride (GaN) devices) are very promising candidates due to their lower conduction and switching losses compared to the state-of-the-art Silicon (Si) devices. The main challenge for these devices is that their breakdown voltages are relatively lower compared to their Si counterpart. In addition, the high frequency operation of the wide-bandgap devices are impeded in many cases by the magnetic core losses of the magnetic coupling components (i.e. coupled inductors and/or high frequency transformers) utilized in the power converter circuit. Six new dc-dc converter topologies are propose. The converters have reduced voltage stresses on the switches. Three of them are unidirectional step-up converters with universal input voltage which make them excellent candidates for photovoltaic and fuel cell applications. The other three converters are bidirectional dc-dc converters with wide voltage conversion ratios. These converters are very good candidates for the applications that require bidirectional power flow capability. In addition, the wide voltage conversion ratios of these converters can be utilized for applications such as energy storage systems with wide voltage swings

Assessment for the Environmental Impacts of Chemical Constituents’ Percentage Variation for Ceramic Manufacturing

Ceramic tile manufacturing process is energy intensive since within several stages the product is subject to thermal treatment. The source of thermal energy used is by combustion of natural gas. Unfortunately, the oxidation of this fossil fuel produces greenhouse gases. The impact severity on environment and humans is influenced by the chemical composition of ceramic. Hence the objective of this research is to study the effect of changing the percentage of seven samples with the most effective composition of ceramic used in many countries.  The selected impact categories for the study were global warming, Climate change, acidification, eutrophication, and human toxicity. The constituents’ percentages of ceramic manufacturing have been evaluated using GABI vs OpenLCA. It was found that lowering the percentage of Silicon dioxide in the mixture from 51.01% to 87.8 leads to an overall emission reduction of 28% and the differences between the results were close for both software

Modeling Online Student Engagement Using Social Cognitive Theory

This study applied social cognitive theory to investigates the influence of personal and environmental factors on student engagement (concerning the behavioral, emotional, and cognitive engagement dimensions) and, in turn, perceived learning and student satisfaction (as outcomes) in the online learning environment. The study explored the perceptions of Egypt’s higher education students with regard to their engagement, learning, and satisfaction with their online learning experience

Effect of self-curing admixture on concrete properties in hot climate conditions

Hot climates prevail in many regions of the globe. The average summer temperature of hot arid areas is in the range of 40-50°C with temperatures exceeding these values under direct solar radiation. Curing concrete in these regions may be challenging due to limited availability of suitable water for curing and/or rapid loss of curing water by evaporation. For many years self-curing admixtures were recommended as an alternative to water curing, however, limited studies have been conducted on their performance in hot weather conditions. In this investigation, the effects of a hot climate on the fresh and hardened properties of self-curing (SC) concrete and normal conventional concrete (NC) in hot weather were studied. A water- soluble polymer self-curing agent, polyethylene glycol (PEG 400), was added to the SC mixes. The testing parametersOwere concrete dry materials (25 or 50OC) and/or mix water temperatures (5, 20 or 35 C) at the time of mixing. NC samples were continuously water cured at 25 or 50 OC, whereas the SC ones were air cured at the same temperatures. The tested properties were workability, compressive strength, splitting tensile strength, and flexural strength. It was found that SC outperformed NC under varying conditions. The results could not be simply attributed to the retention of mix water by the self-curing admixture. A more comprehensive explanation for the observations is proposed

Influence of blended powders on properties of ultra-high strength fibre reinforced self compacting concrete subjected to elevated temperatures

Ultra-High Strength Fibre Reinforced Self Compacting Concrete (UHSFRSCC) is in great demand for use in construction projects around the globe. Unless fillers are utilized in this concrete, its production will come at an excessive environmental cost due to the high Carbon footprint of Portland cement. A gap in the published literature was identified, where quaternary mixes, containing Portland cement with three fillers, incorporating fibres, and achieving ultra high strength, were not cited. In this study ternary and quaternary mixes were designed and produced, satisfying the European Guidelines for SCC, with compressive strengths exceeding 115 MPa. Some mixes had compressive strengths between 125 – 150 MPa, which were not previously reported in the literature. The mixes contained Silica Fume (SF), Metakaolin (MK), Limestone powder (LS) as partial Portland cement replacement and quartz powder (QP) as partial sand replacement. Basalt Fibres were added to reinforce the matrix. Compressive & tensile strength of the mixes along with UPV, sorptivity, absorption and SEM Micro-structure features were studied at ambient temperature and after the samples were exposed to either 200 or 300 oC; since the behavior of HSC at elevated temperature is always a cause for concern. The active and inert fillers exhibited a synergic behavior at all temperature conditions. The mix containing: 15% SF, 5% MK, 20% LS and 34% QP achieved the best performance. Compressive and splitting tensile strength improve by 10% and 17% while sorptivity and absorption decline by 40% and 29% respectively at ambient temperature. Residual compressive strength improved by 10% and 19% while, residual splitting tensile strength significantly increases by 21% and 28% after exposure to elevated temperatures 200°C and 300°C respectively. Meanwhile, residual sorptivity decreases by 39% and 38% after exposure to these elevated temperatures. Microstructure properties supported and agreed with the mechanical and permeation characteristics results. The results will contribute to the development of UHSFRSCC in hot weather countries

Developing an optimized strategy achieving design flexibility in small-area units: Case study of Egyptian economic housing

Some countries, especially Egypt, have sought to use small housing units as a solution for housing financial problems. Unfortunately, householders faced various problems with units’ design which obliged them to either leave their units, modify them to meet their needs, or live in their poorly designed units. The current work aims at obtaining an optimized design strategy through applying the “design flexibility” concept on economic housing units. The achieved strategy was investigated on a selected case study in Egypt, namely: Mubarak housing for youth. This strategy led to area optimized utilization. Hence, involving design flexibility makes the units more suitable and affordable for individuals, Fundable for the economy and friendly for the environment (reduce wasted material and energy). Therefore, design flexibility matches the sustainability principles (social, economic and environmental). Keywords: Optimization strategy, Design flexibility, Sustainable design, Housing problems, Economic housin

Impact of Phase Change Materials on Cooling Demand of an Educational Facility in Cairo, Egypt

Heat gains and losses via building envelopes are impacted by varied characteristics such as geometry, orientation, properties of the building materials, and the type of construction and its interface with the exterior environment. Current studies are investigating the use of phase change materials (PCMs) characterized by high latent heat and low thermal conductivity that may cause temperature time lag and reduce amounts of heat transferred through building envelopes. The prime objectives of this research are evaluating zones’ energy consumption by type for an educational facility in a dry arid climate, examining the effects of a PCM (RT28HC) and polyurethane insulating material, comparing these effects to the existing situation with respect to cooling energy savings and CO2 emissions, and studying the effect of varying PCM thicknesses. The working methodology depended on gathering the real status and actual material of the building, constructing models of the building using Design Builder (DB) simulation software, and comparing the insulation effect of incorporating polyurethane and phase change insulating materials. A parametric study evaluated various PCM thicknesses (6, 12, 18, 24, 30, and 36 mm). Validation was performed primarily for a selected year’s energy usage; simulation results complied with field measurements. The results revealed that an 18 mm PCM had a high efficiency regarding thermal comfort attributes, which reduced cooling energy by 17.5% and CO2 emissions by 12.4%. Consequently, this study has shown the significant potential of PCM regarding improved energy utilization in buildings

Evaluation of the effects of dexmedetomidine infusion on oxygenation and lung mechanics in morbidly obese patients with restrictive lung disease

Abstract Background Dexmedetomidine infusion improves oxygenation and lung mechanics in patients with chronic obstructive lung disease; however, its effect in patients with restrictive lung disease has not been thoroughly investigated yet. The aim of this work was to evaluate the effects of dexmedetomidine infusion on oxygenation and lung mechanics in morbidly obese patients with restrictive lung disease. Methods Forty-two morbidly obese patients scheduled for bariatric surgery were included in the study. Patients were randomized to receive either dexmedetomidine infusion at a bolus dose of 1mcg/Kg followed by infusion at 1 mcg/Kg/hour for 90 min (Dexmedetomidine group), or normal saline infusion (Control group). Both groups were compared with regard to: oxygenation {P/F ratio: PaO2/fraction of inspired oxygen (FiO2)}, lung compliance, dead space, plateau pressure, blood pressure, and heart rate. Results Dexmedetomidine group showed significant improvement of the PaO2/FiO2 ratio, and higher lung compliance compared to control group by the end of drug infusion. Dexmedetomidine group demonstrated decreased dead space, plateau pressure, blood pressure, and heart rate compared to control group by the end of drug infusion. Conclusion A 90-min dexmedetomidine infusion resulted in moderate improvement in oxygenation and lung mechanics in morbidly obese patients with restrictive lung disease. Trial registration clinicaltrials.gov: NCT02843698 on 20 July 2016

Hemodynamic effects of lateral tilt before and after spinal anesthesia during cesarean delivery: an observational study

Abstract Background Post-spinal hypotension is a common maternal complication during cesarean delivery. Aortocaval compression by the gravid uterus has been assumed as a precipitating factor for post-spinal hypotension. The role of left lateral tilting position in improving maternal cardiac output after subarachnoid block (SAB) is unclear. The aim of this work is to investigate the effect of left lateral tilting on maternal hemodynamics after SAB. Methods A prospective observational study was conducted including 105 full term pregnant women scheduled for cesarean delivery. Mean arterial pressure, heart rate, cardiac output (measured by electrical cardiometry), stroke volume, and systemic vascular resistance were recorded in three positions (supine, 150, and 300 left lateral positions) before SAB, after SAB, and after delivery of the fetus. Results Before SAB, no significant hemodynamic changes were reported with left lateral tilting. A significant decrease was reported in mean arterial pressure, cardiac output, stroke volume, and systemic vascular resistance after SAB (in supine position). When performing left lateral tilting, there was an increase in cardiac output, heart rate, and mean arterial pressure. No difference was reported between the two tilt angles (150 and 300). Conclusions Changing position of full term pregnant woman after SAB from supine to left lateral tilted position results increased cardiac output and mean arterial pressure. There is no difference between the two tilt angles (150 and 300). Trial registration clinicaltrials.gov ( NCT02828176 ) retrospectively registered