Photovoltaic (PV) panels are similar in many aspects to the leaves of trees, both are standing in the Sun to capture the sunlight, however, PV panels get soiled especially in desert areas, while the leaves remain clean to a very good extent. The question is, why leaves remain clean while PV panels get soiled quite easily? The leaves are hanging on the stem of trees and these stems are flexible to motion, such that if the wind blows in any direction over the stem it vibrates allowing any deposited particle to fall off the surface. The objective of this research is to develop a fixation method for PV panels similar to the stems of trees, such that the panel can vibrate as the wind blows in order to minimize dust accumulation. Different fixation methods for the PV panel are designed, and the air flow around the panel is simulated using the CFD package Ansys Fluent. It has been found that a PV panel pivoted at its lower edge, such that it can revolve around the lower edge, together with a vertical wind shield attached to its upper edge and a spring attached at the middle of its backside has the largest vibration amplitude due to the applied wind compared to the other designs. Experiments have been done to infer the influence of the new fixation method of the PV panel on dust accumulation over the panel. After 6 weeks of operation, it has been found that the efficiency of the PV panel that is flexibly fixed has dropped by only 5%, while the efficiency of the panel that is rigidly fixed has dropped by 25%. It can be concluded that a PV panel operating a light post should be fixed on a flexible base that allows the panel to vibrate as the wind blows over it in order to mitigate dust.

The photovoltaic modules are mostly installed outdoors, exposing them to different conditions. These conditions significantly affect their performance. One of the most influential factors on photovoltaic modules is the soiling phenomenon from dust deposition. Dust deposition on the surface of the modules causes transmittance loss. Some studies in different parts of the world have tried to find mathematical correlations between particulate deposition and transmittance. These correlations are a function of dust characteristics and environmental factors. This study proposes a new methodology to mathematically combine the photovoltaic model and transmittance loss correlations. The proposed model could examine and predict the effect of soiling on photovoltaic modules\' performance. Three photovoltaic modules with different capacities are selected. Using the proposed model, they are modeled by assuming clean and dirty photovoltaic surfaces depending on the installation conditions. This study is based on actual data from the center of Tehran, located at 35° 41\' north latitude and 51° 23\' east longitude for 12 months in the year 2020. The module\'s performance was investigated in the presence of dust. The presented results are validated by comparing them with other studies. The results show that the soiling effect is not dependent on the modules\' capacity.

A comprehensive model of indoor particle deposition onto surfaces of historic interiors was developed. The model takes into account the most important deposition processes observed in historic buildings: Brownian and turbulent diffusion, gravitational settling, turbophoresis, and thermophoresis. The developed model is expressed as a function of important parameters characterizing historic interiors: the friction velocity - capturing the effect of the indoor airflow intensity, the difference between the temperature of the air and the surface, and surface roughness. In particular, a new form of the thermophoretic term was proposed to account for an important mechanism of surface soiling driven by frequent large temperature differences between indoor air and surfaces in historic buildings. The form adopted allowed the temperature gradients to be calculated down to low distances from the surfaces and showed insignificant dependence of the temperature gradient on the diameter of particles, which yielded a meaningful physical description of the process. The predictions of the developed model agreed with the outcome of the previous models, in turn correctly interpreting the experimental data. The model was used in simulating the total deposition velocity in a small-size church taken as an example of a historic building, heated in the cold period. The model adequately predicted the deposition processes and proved to be able to map magnitudes of deposition velocities for specific surface orientations. The crucial effect of the surface roughness on the deposition paths was documented.

OBJECTIVE: To evaluate outcomes of adopting the Swenson-like technique in transanal pull-through for Hirschsprung disease (HD) at a children\'s institution in Southeast Asia.
METHODS: A retrospective chart review was performed over 42 months at a safety-net pediatric hospital in Vietnam.
RESULTS: From January 2019 to June 2022, the Swenson-like technique was implemented and performed on 139 patients (115 male, 24 female, mean age 6.4 ± 11.96 months). There were 123 transanal-only resections, 5 transanal plus laparoscopic, and 11 transanal plus laparotomy. The mean operative time was 70.9 ± 43.6 min. The average length of the resected specimen was 18.8 ± 10.9 cm. No urethral or vaginal injuries occurred. Postoperative complications included 1 anastomotic leak (0.7%), 4 anastomotic stenoses (2.8%), and 2 perianal abscesses in the setting of recurrent enterocolitis (1.4%). With a mean follow-up of 26 ± 11.9 months (range 3-48 months), there were 25 enterocolitis cases (17.9%), 45 patients with constipation (32.3%), 1 episode of fecal incontinence lasting longer than 6 months (0.7%), and 1 rectal-vestibular fistula noted one year postoperatively (0.7%). There were no deaths.
CONCLUSIONS: The Swenson-like technique in transanal pull-through for Hirschsprung\'s disease was safely adopted at our institution. The results show that applying this technique uniformly in a single institution led to excellent outcomes.

BACKGROUND: In patients with Hirschsprung disease (HSCR), soiling may be related to anal sphincter damage following the initial pull-through. No optimal treatment has been developed for such patients, although enemas (rectal or antegrade) have been applied with some success. We present the one-year outcomes of a new technique for anal sphincter reconstruction.
METHODS: All patients with HSCR referred from other institutions for post pull-through soiling were studied. Seven patients with patulous sphincters underwent sphincter reconstruction. Six had a full preoperative evaluation and were included in the study. Their 12-month outcomes were assessed.
RESULTS: All six patients had soiling without voluntary bowel movements (VBMs). One patient was clean on Malone flushes when referred. Three underwent pre- and post-reconstruction non-sedated three-dimensional anorectal manometry, and objectively were able to close their sphincters following the reconstruction. All patients without Down syndrome (4 of 6) showed improvement in the abbreviated Baylor Continence Scale (4.5 vs. 0.75). One patient has achieved total bowel control without antegrade flushes, three now have VBMs which they did not have before but have occasional accidents and use antegrade flushes intermittently. They reported higher productivity, the ability to participate in sports and be away from home with confidence in their regimen. Two of 6 patients have Down syndrome and required a redo pull-through for other indications and underwent empiric sphincter reconstruction. For these two patients we do not have an outcomes assessment.
CONCLUSIONS: A new technique for sphincter reconstruction shows promising results in improvement of bowel control at one year.
METHODS: IV.

In this paper we conducted an experimental study to evaluate the impact of soiling on the temperature and electricity production of two photovoltaic technologies (Poly-Si and CdTe) under a hot semi-arid climate of Morocco. For this purpose, two modules -from each technology-were exposed for one year where one is cleaned every day and the other is left to accumulate soiling on its surface. In parallel, the electrical parameters, the weather data and the modules temperature were monitored using high precision instruments. Results show that the Poly-Si technology is highly affected by soiling in comparison to the CdTe where the measured daily Soiling ratio (SR) can reach 0.70 and 0.73 respectively. This values lead to a drop on the energy production of 15% for the Poly-Si and 13%. Regarding the modules temperature (Tm) results show that soiling has an impact on increasing the temperature for both technologies, but the Poly-Si module is more affected than the CdTe one, where the daily average temperature difference between the clean and the soiled modules is around 1.5 °C and 1.3 °C for both technologies, respectively.

In this work, an image analysis technique combining a new generation optical microscope (Leica DM6 M) and Cleanliness Expert image acquisition and processing software is proposed for the study of dirt particles on PV modules in three different regions: Souss-Massa region, Drâa-Tafilalet region, and Rabat-Salé-Kénitra region. This method offers the possibility of providing an appropriate assessment of the particle size distribution. The analyzed glass samples were installed in these three different regions, on wooden holders tiled 15°, 30°, and 45° and for a period ranging from 64 to 75 days. The studies carried out to evaluate the soiling phenomenon based on image processing are very limited and do not take into account the total scanning of the analyzed surface. They are generally limited to a single (one) or a few images taken at different locations of the sample and are then extrapolated over the entire surface. This observation raises the question of the representativeness of the results obtained with respect to the result on the entire surface of the sample. In this context, we thought of carrying out this experimental study, which aims to answer this question and evaluate the particle size of the dirt samples on the PV modules. The results obtained in this study have shown that three images will be enough to represent the whole area of the sample. In addition, the dominant particle diameters by number are in the range of 1-5 µm.

Areas with abundant sunlight, such as the Middle East and North Africa (MENA), are optimal for photovoltaic (PV) power generation. However, the average power loss of photovoltaic modules caused by dust accumulation is extreme and may reach 1%/day, necessitating frequent cleaning which adds to the cost of operations and maintenance. One of the solutions to the problem of PV soiling is to develop anti-soil coatings, where hydrophilic or hydrophobic coatings with spectral characteristics suitable for PV applications are added to the outer layer of PV glass. However, the effectiveness of such coatings depends extensively on climatic conditions and geographical locations. Since coatings add to the cost of solar panels, it is imperative that they are first tested for suitability at the intended location and/or in similar weather conditions prior to their large-scale deployment. This critical review focuses on various anti-dust technologies employed to mitigate the PV soiling issue. The in-depth comparison of the various developed techniques and materials aims at providing a relevant input in adapting the right technology based on particles\' accumulation mechanism, weather conditions, and geographical location. Though the mechanical cleaning process is the most used solution to date, development of thin film anti-dust coating could be a better alternative-when it is relevant-due to its abrasion-free capability, large deployment, economic viability, and durability. This review aims at serving as a reference in this topic, thereby paving the way to adapting efficient anti-dust coatings, especially in the MENA region and/or desert environment at large, where it is the most relevant.

Several soiling mitigation solutions and cleaning techniques have been developed to maintain high efficiency of photovoltaic (PV) panels. First of its kind, the investigation of the adaptability of the cleaning systems to solar trackers has been performed. The majority of these systems are dedicated to fixed installations whereas only few systems that can be adapted to solar trackers are presented in the updated cleaning systems background. For this reason, this paper presents an innovative approach which consists of combining trackers with an integrated cleaning system that has been designed. Based on the conducted experimental study, a maximum of 7% in soiling losses has been found for the PV generator of 4 kWp equipped with a dual-axis tracker installed in Rabat-Morocco over almost 1 year. Consequently, a reduced cleaning prototype has been realized and tested to evaluate the energy recovery based on the performed cleaning. The automatic cleaning has presented a similar efficiency with the manual cleaning with a slight difference of 0.95 pp and an increase of energy of 11.5% in the arid region. Through the economic analysis carried out taking into account the gain in energy production, the automatic cleaning cost was 0.14 USD/kWh. It has been found that the cleaning technique based on the telescopic arm would be more effective if the tracker is installed in an arid region where soiling is higher than Rabat. In this case, the payback time of the cleaning solution is faster (8 to 9 years), hence its profitability.

The present work aims at the characterization of the dust particles in South India through an image analysis of glass samples inclined at a tilt of 0° and 13° for four different exposure periods (approximately 30 to 40 days/exposure period). It aims as well at the study of the different factors influencing the accuracy of the image analysis of dust particles. The analysis of the shape factor reveals that the dust particles on tilted surface (13°) have regular shapes, and irregular shapes are more observed in horizontal surfaces. The size analysis of the dust particles with magnification of 20 × has revealed that the size distribution is in the range of 0-4 µm but more concentrated in the range of 0-1 µm. However, with 10 × magnification, larger particles are more detected. Furthermore, average results from three sample images seem to be more precise and representative than results from two images. The fractional coverage area of the dust particles on the sample has been calculated and compared with the transmittance losses. These two variables are found to be proportional with an R2 of 53%. Nevertheless, the comparison showed again that three images give better results with an R2 of 75% against 11% for two images. The results obtained in this study are very useful for the development of high precision soiling sensors that are based on image analysis and outdoor soiling microscopes, which are the main components for an efficient and economic cleaning of solar PV modules.