PURPOSE: To review students' perceived symptom-based computer vision syndrome (CVS) and its determinants and to suggest preventive measures.
METHODS: This cross-sectional survey was conducted in 2021 ...at a university in Central Saudi Arabia. The presence and severity of symptoms related to CVS were investigated. The total CVS symptom score was the outcome variable. The CVS score was correlated to participants' demographics, visual habits when using digital devices, and knowledge about CVS. Due to skewed distribution, a nonparametric method was used for analysis.
RESULTS: Overall, 521 students were surveyed. The prevalence of CVS based on at least one symptom was 96% (95% confidence interval 94.3-97.7). The median score was 8.0 (interquartile range 4.0-12.0). Of the 24 possible CVS scores, 42 students (8%) had scores of 18 or more (severe CVS). Being female (Mann-Whitney MW P < 0.001), being older (Spearman P < 0.001), refractive error (MW P < 0.001), the presence of dry eye (MW P < 0.001), using devices other than a desktop computer (KruskalWallis) P = 0.03), and more than 6 h constantly working with a device (MW P = 0.001) were correlated with a higher CVS score. Older age, female, refractive error, and using digital devices for more than 6 h were the independent and significant predictors of CVS in college students.
CONCLUSION: Most of the students suffered from mild-to-moderate CVS symptoms. Health promotion for prevention and periodic ophthalmic consultations are recommended. Identified predictors should be the focus when implementing strategies to combat CVS in the adolescent Saudi population.
Abstract
Calcium sulfate (CaSO
4
) scale has been identified as one of the most common scales contributing to several serious operating problems in oil and gas wells and water injectors. Removing ...this scale is considered an economically feasible process in most cases as it enhances the productivity of wells and prevents potential severe equipment damage. In this study, a single-step method utilizing potassium carbonate and tetrapotassium ethylenediaminetetraacetate (K4-EDTA) at high temperature (200 °F) has been used to remove CaSO
4
scale. The CaSO
4
scale was converted to calcium carbonate (CaCO
3
) and potassium sulfate (K
2
SO
4
) using a conversion agent, potassium carbonate (K
2
CO
3
), at a high temperature (200 °F) and under various pH conditions. Various parameters were investigated to obtain a dissolver composition at which the optimum dissolution efficiency is achieved including the effect of dissolver pH, soaking time, the concentration of K4-EDTA, the concentration of potassium carbonate (K
2
CO
3
), temperature impact and agitation effect. Fourier transform infrared, X-ray crystallography, ion chromatography, stability tests and corrosion tests were carried out to test the end product of the process and showcase the stability of the dissolver at high temperature conditions. A reaction product (K
2
SO
4
) was obtained in most of the tests with different quantities and was soluble in both water and HCl. It was observed that the dissolver solution was effective at low pH (7) and resulted in a negligible amount of reaction product with 3 wt% CaSO
4
dissolution. The 10.5-pH dissolver was effective in most of the cases and provided highest dissolution efficiency. The reaction product has been characterized and showed it is not corrosive. Both 7-pH and 10.5-pH dissolvers showed high stability at high temperature and minimum corrosion rates. The single step dissolution process showed its effectiveness and could potentially save significant pumping time if implemented in operation.
Drilling issues such as shale hydration, high-temperature tolerance, torque and drag are often resolved by applying an appropriate drilling fluid formulation. Oil-based drilling fluid (OBDF) ...formulations are usually composed of emulsifiers, lime, brine, viscosifier, fluid loss controller and weighting agent. These additives sometimes outperform in extended exposure to high pressure high temperature (HPHT) conditions encountered in deep wells, resulting in weighting material segregation, high fluid loss, poor rheology and poor emulsion stability. In this study, two additives, oil wetter and rheology modifier were incorporated into the OBDF and their performance was investigated by conducting rheology, fluid loss, zeta potential and emulsion stability tests before and after hot rolling at 16 h and 32 h. Extending the hot rolling period beyond what is commonly used in this type of experiment is necessary to ensure the fluid's stability. It was found that HPHT hot rolling affected the properties of drilling fluids by decreasing the rheology parameters and emulsion stability with the increase in the hot rolling time to 32 h. Also, the fluid loss additive's performance degraded as rolling temperature and time increased. Adding oil wetter and rheology modifier additives resulted in a slight loss of rheological profile after 32 h and maintained flat rheology profile. The emulsion stability was slightly decreased and stayed close to the recommended value (400 V). The fluid loss was controlled by optimizing the concentration of fluid loss additive and oil wetter. The presence of oil wetter improved the carrying capacity of drilling fluids and prevented the barite sag problem. The zeta potential test confirmed that the oil wetter converted the surface of barite from water to oil and improved its dispersion in the oil.
This study examines the socio-cultural spaces of the two major groups in Kuwait: the Hadhar and Badu. These groups are not an ethnic classification but are rooted in their historic settlements. The ...Hadhar refer to people who lived in old Kuwait town and were mostly merchants and artisans who made their living from the sea. The Badu on the other hand, most commonly referred to as Bedouins, are nomadic tribes who lived on the outskirts of old Kuwait town or in the Arabian Desert. This study employs cognitive maps to reveal fascinating insights into the lifestyles and cultural differences of these two groups as it relates to their domestic built environment. This study argues that house spatial organization is tightly coupled with a family’s socio-cultural traditions and values; hence, there are major spatial distinctions between the houses of the Hadhar and Badu. These differences are apparent in the houses’ main spaces such as the living hall, male guest reception space or diwaniya, and main entrance. This paper also contends that these differences are rooted historically in the traditional Hadhar mud brick courtyard houses and the traditional Badu Arabian tents. Although the oil boom and consequent impact of globalization transformed Kuwait’s houses into modern villas, on the inside they are still linked to each group’s traditional use of space.
The aim of this
study was to investigate the effect of Shoulder versus Chamfer margin design on the marginal adaptation of zirconia (Zr) copings.
40 extracted molar teeth were mounted in resin and ...prepared for zirconia crowns with two margin preparation designs (20=Shoulder and 20=Chamfer). The copings were manufactured by Cercon® (DeguDent GmbH, Germany) using the CAD/CAM system for each tooth. They were tried on each tooth, cemented, thermocycled, re-embedded in resin and were subsequently cross sectioned centrally into two equal mesial and distal halves. They were examined under electron microscope at 200 X magnification and the measurements were recorded at 5 predetermined points in micrometers (µm).
The
verall mean marginal gap for the two groups was found to be 206.98+42.78µm with Shoulder margin design (Marginal Gap=199.50+40.72µm) having better adaptation compared to Chamfer (Marginal Gap=214.46+44.85µm). The independent-samples t-test showed a statistically non-significant difference (p=.113) between the means of marginal gap for Shoulder and Chamfer margin designs and the measurements were recorded at 5 predetermined points for the two groups.
The Chamfer margin design appeared to offer the same adaptation results as the Shoulder margin design.
This paper presents a case study where wellbore organic deposits were cleaned out using an emulsified system. The organic scale deposits exist in a well that was drilled and completed to inject water ...to maintain the oil reservoir pressure. The water injector well completion was located above a tar formation. The organic deposits in the wellbore affected the injectivity of water and restricted the water injection operations. Samples were collected from the downhole from the water injector well, and these samples were analyzed in the laboratory using IRS (infrared spectroscopy) and extraction by solvents. Laboratory analysis showed that the downhole sample consists of maltene in the form of resins, saturates, and aromatics. The sample contains some asphaltene as well. Extensive solubility experiments were carried out at the downhole temperature using different solvents. Solvents such as aromatics and xylene in diesel were used to dissolve the organic deposits. The optimum formulation in terms of cost, solubility, required time, and chemicals hazards was selected for further field treatment. The emulsified system that was selected for the field treatment consists of freshwater, emulsifier,
n
-methyl pyrrolidone, and solvent (aromatic). The emulsified solvent system was able to dissolve wellbore organic deposits of Well-X during field treatment, and the well injectivity was restored after the treatment.
A reservoir’s static bottom-hole pressures (SBHPs) are an integral component of many reservoir evaluation disciplines. The SBHP is normally acquired through gauge measurements; however, this method ...has disadvantages such as cost and risk. Accordingly, the ability to accurately estimate the SBHP would provide a cost-effective and safe alternative to well intervention. In this work, a new calculation method is introduced to predict the SBHP of a natural gas well. This method differs from existing methods by utilizing the apparent molecular weight profiling concept. Based on the inputs of pressure and temperature gradient data, an iterative calculation scheme is applied to produce a well-specific molecular weight profile. This profile is used along with a modified form of the equation of state to perform top node pressure calculations and ultimately predict the SBHP for gas wells. The top node method was tested rigorously using 75 case studies from five different fields and reservoirs and the prediction results were compared with actual field measurements. Also, the prediction performance of the top node method was compared with those of four previous methods (Rawlins and Schellhardt, Rzasa and Katz, Sukkar and Cornell, and Cullender and Smith). The results of this work showed that the top node calculation method was accurate in predicting the SBHP and has outperformed the four previous methods.
In this article, the piezoelectric coverage area of a shear deformable cantilever beam is optimized for maximum modal electromechanical coupling coefficient. A discrete layer finite element model ...with piezoelectric capability is implemented to solve the free vibration problem under open-circuit and short-circuit electric boundary conditions. A binary-coded genetic algorithm was used to carry out the optimization. The piezoelectric coverage locations are found to be dependent upon the mode of vibration, which is primarily due to charge cancelation at higher modes. Optimal distribution tends to cover part of the beam experiencing maximum bending. It is shown that the type of base beam material has negligible effect on the optimum locations of the piezoelectric material. Furthermore, an optimum ratio of piezoelectric-to-beam thickness exists for the first three modes.
During hydrocarbon drilling operations, the presence of hydrogen sulfide (H2S) gas could cause serious health and safety issues. Scavenging this gas and eliminating its impact are essential ...requirements for a safe drilling operation. This study investigated the impact of three H2S scavenger additives (copper nitrate, iron gluconate, and potassium permanganate) on water-based drilling fluids (WBDFs). The additives were tested on two actual field drilling mud samples that differ mainly in their weight. The scavengers’ impact on drilling muds was investigated by measuring their scavenging capacity and their effect on rheology, fluid loss, and pH. Potassium permanganate outperformed the other scavengers when added to the lighter (lower density) WBDF. However, it did not impact the scavenging capacity of the heavier mud system. Copper nitrate outperformed the other scavengers in the heavier drilling mud system. Also, the addition of copper nitrate in the lighter mud system increased its H2S-scavenging capacity greatly, while for iron gluconate, it did not perform very well. Overall, all the scavenger-containing drilling muds did not have any significant harmful impact on the plastic viscosity or the fluid loss properties of the drilling muds. Furthermore, all the tested drilling mud samples showed an excellent ability to clean wellbores and suspend drill cuttings evident by the high carrying capacity with the exception of iron gluconate or potassium permanganate with the heavy mud system.
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