Harmonics Temporal Profile in High-Voltage Networks: Case Study

This chapter presents a case study about harmonics measurements in high-voltage networks. Measurements were conducted at two locations in the main interconnected system (MIS) of Oman. Voltage and current THDs were recorded for a period of 1 week. The power quality analyzer was set to record required data for a period of 1 week, and the observation period for each recorded value is 10 minutes. At the first location, the grid station (132/33) is feeding industrial as well as other customers. The second grid station (220/132/33 kV) is dedicated to large industrial customers including arc furnaces and rolling mills. The power quality analyzer was installed at the 132 kV side of power transformers at both locations. Recorded data are analyzed, and temporal harmonics profiles are studied. A clear temporal variation of harmonics similar to that of aggregate load and local voltage profiles was observed at the grid station feeding mixed residential and industrial loads. However, this correlation between system load and harmonics profile diminishes at the grid station dedicated for heavy industrial loads

Experimental Study on the Effect of Dust Deposition on a Car Park Photovoltaic System with Different Cleaning Cycles

For a decade, investments in solar photovoltaic (PV) systems have been increasing exponentially in the Middle East. Broadly speaking, these investments have been facing tremendous challenges due to the harsh weather in this particular part of the world. Dust accumulation is one the challenges that negatively affects the performance of solar PV systems. The overall goal of this paper is to thoroughly investigate the effect of dust accumulation on the energy yield of car park PV systems. With this aim in mind, the paper presents scientific values for further research and opens the horizon for attracting further investments in solar PV systems. This study is based on a real PV system in the Sultanate of Oman and considers different cleaning cycles for 16 months (from 29 July 2018 to 10 November 2019). Furthermore, four different PV groups were assessed, and the system was monitored under different cleaning frequencies. In general, it was found that dust accumulation has a significant impact; under 29-day, 32-day, 72-day, and 98-day cleaning cycles, the average percentages of energy loss due to soiling were 9.5%, 18.2%, 31.13%, and 45.6%, respectively. In addition, the dust effect has a seasonal variation. The study revealed that dust accumulation has a more negative impact during summer than during winter. During summer, the energy losses due to soiling were 8.7% higher than those during winter. The difference was attributed to different environmental conditions, with high humidity and low wind speed being the main factors that worsen the impact of dust during summer. Based on the findings of this research, a monthly cleaning program is highly recommended in the city of Muscat

Liver fibrosis‑4 score predicts mortality in critically ill patients with coronavirus disease 2019

Background: Emerging evidence suggests that liver dysfunction in the course of coronavirus disease 2019 (COVID‑19) illness is a critical prognostic factor for mortality in COVID‑19 patients, and the Fibrosis‑4 (FIB‑4) score, developed to reflect level of hepatic fibrosis, has been associated with adverse outcomes in hospitalized COVID‑19 patients. This study aimed to investigate intensive care unit (ICU) admitted patients, a high‑risk subpopulation, research on which is lacking. Materials and Methods: This retrospective cohort study examined FIB‑4 scores and clinical endpoints including death, acute cardiac injury (ACI), acute kidney injury, and need for mechanical ventilation in critically ill COVID‑19 patients, without prior hepatic disease, throughout ICU stay. Results: Of 60 patients enrolled, 35% had ICU admission FIB‑4 >2.67. Among nonsurvivors FIB‑4 was significantly higher at admission (median 3.19 vs. 1.44; P < 0.001) and only a minority normalized <1.45 (36.0%). Each one‑unit increment in admission FIB‑4 was associated with 67.4% increased odds of death (95% confidence interval [CI], 9.8%–162.6%; P = 0.017). FIB‑4 >2.67 was associated with a median survival time of 18 days from ICU admission versus 40 days with FIB‑4 <2.67 (P = 0.016). Admission FIB‑4 was also higher in patients developing ACI (median 4.99 vs. 1.76; P < 0.001). FIB‑4 correlated with age (r = 0.449; P < 0.001), and aspartate transaminase with alanine transaminase (r = 0.674; P < 0.001) and lactate dehydrogenase (r = 0.618; P < 0.001). Conclusion: High ICU admission FIB‑4 is associated with mortality in critically ill COVID‑19 patients, with failure to normalize at time of death, however, the high score is likely a result of generalized cytotoxicity rather than advanced hepatic fibrosis

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population