3 research outputs found
Permeability of layered glass bead samples: Effect of grain size mixing in layer boundaries
No full textGeotechnical projects are successful when there is a lot of knowledge about the soil implemented in safe sustainable solutions. Existing models of hydraulic flow in soils need to be tested and confirmed again and again to make sure it’s trustworthy. With the use of three-layered samples containing 1mm and 3mm glass bead sizes a simplified model of the fining upward (1mm top layer) and coarsening upward (3mm top layer) stratification was made. The top and bottom layers consist of a uniform glass bead size. The middle layer is a binary mixed one with different volumetric percentages to mimic the gradual increase of grain sizes like fining and coarsening upward sediment deposits. A decrease in the permeability was observed as the volume percentage of the smaller glass beads increased. The influence of a possible transition/mixed zone between layers was not clear because of the small ratios of the used glass beads. This is also the case for the effect of the porosity on the permeability. In addition, test samples were prepared to calculate the theoretical harmonic permeability to be able to compare it with the actual measured permeability. This theoretical harmonic permeability seems in the case of the coarsening upward samples smaller than the actual measured permeability as was expected from findings of another research. This study confirms the influence of the relative positioning of the layers with their specific properties on the overall permeability and the deviation from the theoretical harmonic permeability. Future prediction of the permeability’s in layered deposits is a little bit more educated with the findings of this study.Civil Engineerin
The effect of COVID-19 on the academic performance of Zayed University students in the United Arab Emirates
No full textThe outbreak of the coronavirus (COVID-19) pandemic led to significant changes across various sectors, including the field of education. In response to the pandemic, educational institutions worldwide, including Zayed University in the United Arab Emirates (UAE), transitioned to online learning. This study aimed to investigate the impact of COVID-19 on the academic performance of students in the UAE and their satisfaction with remote learning, while also examining gender differences in these variables. This study used a quantitative research design in which a questionnaire was used to collect data. The study employed a snowball sampling method to recruit a total of 1,780 male and female students aged 18 and above from Zayed University in the UAE. The collected data were analyzed using appropriate statistical techniques. This study revealed that students at Zayed University maintained a good level of academic performance (M = 3.34, SD = 0.76) during the COVID-19 pandemic and were satisfied with online learning (M = 3.48, SD = 0.84) during the COVID-19 pandemic. A significant positive correlation was observed between students’ academic performance and their level of satisfaction with online teaching during the COVID-19 pandemic (p \u3c 0.001). Furthermore, no significant differences were found between gender and both academic performance and level of satisfaction with online learning. Finally, we found that more males leaned toward online learning while more females leaned toward face-to-face learning. This study contributes to understanding the impact of COVID-19 on students’ academic performance and satisfaction with remote learning in the UAE context. The findings highlight the significance of student satisfaction for successful online learning and emphasize the need for adequate resources and the maintenance of education quality
MRI-Related Geometric Distortions in Stereotactic Radiotherapy Treatment Planning: Evaluation and Dosimetric Impact
No full textIn view of their superior soft tissue contrast compared to computed tomography, magnetic resonance images are commonly involved in stereotactic radiosurgery/radiotherapy applications for target delineation purposes. It is known, however, that magnetic resonance images are geometrically distorted, thus deteriorating dose delivery accuracy. The present work focuses on the assessment of geometric distortion inherent in magnetic resonance images used in stereotactic radiosurgery/radiotherapy treatment planning and attempts to quantitively evaluate the consequent impact on dose delivery. The geometric distortions for 3 clinical magnetic resonance protocols (at both 1.5 and 3.0 T) used for stereotactic radiosurgery/radiotherapy treatment planning were evaluated using a recently proposed phantom and methodology. Areas of increased distortion were identified at the edges of the imaged volume which was comparable to a brain scan. Although mean absolute distortion did not exceed 0.5 mm on any spatial axis, maximum detected control point disposition reached 2 mm. In an effort to establish what could be considered as acceptable geometric uncertainty, highly conformal plans were utilized to irradiate targets of different diameters (5-50 mm). The targets were mispositioned by 0.5 up to 3 mm, and dose–volume histograms and plan quality indices clinically used for plan evaluation and acceptance were derived and used to investigate the effect of geometrical uncertainty (distortion) on dose delivery accuracy and plan quality. The latter was found to be strongly dependent on target size. For targets less than 20 mm in diameter, a spatial disposition of the order of 1 mm could significantly affect (>5%) plan acceptance/quality indices. For targets with diameter greater than 2 cm, the corresponding disposition was found greater than 1.5 mm. Overall results of this work suggest that efficacy of stereotactic radiosurgery/radiotherapy applications could be compromised in case of very small targets lying distant from the scanner’s isocenter (eg, the periphery of the brain). © The Author(s) 2017
