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The use of solar photovoltaic systems has increased in the past years in an effort to move towards cleaner energy sources. Solar panels are however affected by negative factors such as dust deposition which hinder their performance. The negative effects that dust deposition has on solar panels depend on how much dust gets deposited on solar panels and how it spreads on the top surface. The spread of dust on solar panels can be uniform where all the solar panels in a entire solar photovoltaic array have the same amount of dust deposition. This is an ideal case and can be defined as uniform dust deposition. However, in real life operation, the spread of dust deposition can vary with one solar panel having a different quantity of dust deposition from another. This is defined as non-uniform dust deposition. Non-uniform dust deposition negatively affects the performance of solar panels by reducing the irradiance that reaches the solar cells thereby reducing the performance of the solar panels. The negative effects of non-uniform dust deposition are more significant over time and when there is no intervention to remove the dust. In practice, the negative effects of non-uniform dust deposition on photovoltaic modules has been addressed by periodically cleaning their top surfaces. Periodic cleaning can however increase the operational costs in terms of the cleaning frequency, time taken, cost of cleaning resources and effectiveness. In this study, we propose an optimal cleaning strategy for the solar power plants that are prone to the non-uniform dust deposition. To develop the optimal cleaning strategy, we first investigate the dust deposition process and develop a model to describe the relationship between the solar power generation and non-uniform dust deposition patterns. Then we formulate an optimization model to identify the most cost-effective solar panel cleaning plan. In the optimisation, the additional revenue due to cleaning the solar panels is formulated as the objective function. The decision variables are the number of photovoltaic strings cleaned at each cleaning interval. To highlight the effectiveness of the proposed solar panels cleaning strategy, the developed cleaning strategy is applied to a case study where analysis of the performances of other solar panel cleaning strategies, namely “full cleaning”, “no cleaning” and “random cleaning” is done. The results from the study show that the optimal cleaning strategy outperforms all the other cleaning strategies showing its effectiveness. The optimal cleaning strategy developed is useful to solar photovoltaic plants owners whose plants are located in dusty or polluted areas. It first provides them with an understanding of non-uniform dust deposition. It also provides a way of reducing the effects of non-uniform dust deposition through optimized cleaning which is cost effective and that allows the photovoltaic array to continuously give the desired output. / Dissertation (MEng)--University of Pretoria, 2020. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

Low-cost sensors have the potential to create dense air monitoring networks that help enhance our understanding of pollution exposure and variability at the individual and neighborhood-level; however, sensors can be easily influenced by environmental conditions, resulting in performance inconsistencies across monitoring settings. During summer 2020, 20 low-cost particulate sensors were deployed with a reference PM2.5 monitor in Denton, Texas in preparation for calibration. However, from mid to late-summer, dust transported by the Saharan Air Layer moved through the North Texas region periodically, influencing the typical monitoring pattern exhibited between low-cost sensors and reference instruments. Traditional modeling strategies were adapted to develop a new approach to calibrating low-cost particulate sensors. In this study, data collected by sensors was split according to a novel dust filter into dust and non-dust subsets prior to modeling. This approach was compared with building a single model from the data, as is typically done in other studies. Random forest and multiple linear regression algorithms were used to train models for both strategies. The best performing split-model strategy, the multiple linear regression models split according to dust and non-dust subsets (combined R2 = 0.65), outperformed the best performing single-model strategy, a random forest model (R2 = 0.49). The results from this study indicate that low-cost sensor performance can be greatly influenced by the presence of dust, and that adaptive strategies, like the ones presented in this paper, are necessary when calibrating sensors in environments that may experience pollution from inconsistent sources throughout the year.

Silicosis continues to be an important occupational disease in South Africa, particularly in small, poorly regulated industries. A case series is described of six workers who developed silicosis whilst involved in the processing of semi-precious gem stones. They had been employed as stone sculptors in lapidaries where they processed tigers' eye, rose quartz, amethyst, quartz crystal and a variety of other locally occurring semi-precious stones. In five of the cases exposure was in small and poorly regulated lapidaries without specific dust control measures. The sixth was detected during the course of a health and hygiene survey (including dust sampling) that I conducted in one of two lapidaries still operating in the Western Cape. These workers developed serious disease. Progressive massive fibrosis (PMF) was noted in 4 of the 6 cases, three of whom had progression of their disease after cessation of exposure. With the development of PMF the initial restrictive pulmonary function abnormalities were followed by steadily worsening airflow obstruction. Lung biopsies confirmed silicosis in one case and were suggestive in a further two. Tuberculosis was confirmed in two cases and suspected and treated in a third. Workmen's' Compensation was awarded in five cases. The survey confirmed that in semiprecious gem stone processing, the risk of silicosis appears to be confined to stone sculptors. Tried and proven techniques of general and local exhaust ventilation combined with water or oil to control dust at source were capable of effectively reducing dust emission to acceptable levels.

Footwear impression evidence in dust is often difficult to locate in ambient light and is a fragile medium that both collection and enhancement techniques can destroy or distort. The collection of footwear impression evidence always begins with non-destructive photographic techniques; however, current methods are limited to oblique lighting of the impression followed by an attempt to photograph in situ12,15,17. For the vast majority of footwear impressions, an interactive collection method, and thus a potentially destructive procedure, is subsequently carried out to gather the evidence18. Therefore, alternative non-destructive means for the preservation and enhancement of footwear impressions in dust merits further attention. Previous research performed with reflected ultraviolet (UV) photography and reflected ultraviolet imaging systems (RUVIS) has shown that there are additional non-destructive methodologies that can be applied to the search for and documentation of footwear impressions in dust34,36,37. Unfortunately, these prior studies did not include robust comparisons to traditional oblique white light, instead choosing to focus on different UV wavelengths. This study, however, seeks to evaluate the use of a RUVIS device paired with a 254 nanometer (nm) UV light source to locate 2-D footwear impressions in dust on multiple substrates against standard oblique white light techniques and assess the visibility of the impression and amount of background interference present. The optimal angle of incident UV light for each substrate was also investigated. Finally, this study applied an image enhancement technique in order to evaluate its usefulness when looking at the visibility of a footwear impression and the amount of background interference present for enhanced white light and RUVIS pictures of footwear impressions in dust. A collection of eight different substrate types was gathered for investigation, including vinyl composition tile (VCT), ceramic tile, marble tile, magazine paper, steel sheet metal, vinyl flooring, wood flooring, and carpet. Heel impressions were applied to the various substrates utilizing vacuum collected dust and normal walking pressure. Each substrate was then explored and photographed in ambient fluorescent light, oblique white light at 0, 15, 30, and 0 with the light source below the surface plane of the substrate, and 254 nm UV light at 0, 15, 30, 45, 60, 75, 90 and 0 with the light source below the surface plane of the substrate. All pictures were evaluated for clarity and visible detail of the footwear impression and the amount of background interference present, selecting for the best images within a lighting condition group. Additional intra- and intergroup comparisons were carried out to explore differences created by the various lighting conditions. Enhanced images were then created with the best scored pictures and evaluated for additional modifications in impression visibility and background interference. Photographs of footwear impressions in dust illuminated with ambient fluorescent light proved to be the most difficult conditions under which a footwear impression could be visualized. However, both oblique white light and 254 nm UV light lighting conditions showed improvements in either visualization or background dropout, or both, over ambient light conditions. An assessment of the white light and 254 nm UV light RUVIS images also demonstrated that the best angles for the light source for all substrates were oblique 0 and oblique 0 below the surface plane of the substrate lighting. It was found that white light photographs generally provided higher visibility ratings, while RUVIS 254 nm UV light photographs provided better grades for reducing background interference. Enhanced images of white light conditions provided generally poorer quality and quantity of details, while enhanced RUVIS images seemed to improve upon these areas. The use of a RUVIS to capture photographs of footwear impression evidence in dust was found to be a successful secondary non-destructive technique that can be paired with traditional oblique white light procedures. Additionally, the use of below the surface plane of the substrate lighting techniques were found to improve either visibility or background dropout, or both, over standard 0 oblique lighting, depending on the light source, and should be employed, when applicable. Finally, further investigation into digital photo-editing enhancement techniques for footwear impression evidence in dust is needed.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18805号 / 理博第4063号 / 新制||理||1584(附属図書館) / 31756 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 土`山 明, 准教授 三宅 亮, 准教授 伊藤 正一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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The Wide-field Infrared Survey Explorer (WISE) mission surveyed the sky in four infrared wavelength bands (3.4, 4.6, 12 and 22 μm) between January 2010 and February 2011. During the mission, WISE serendipitously observed 160 comets, including 21 newly discovered objects. About 89 of the comets observed by WISE displayed a significant dust tail in the 12 and 22 μm (thermal emission) bands, showing a wide range of activity levels and dust morphology. Since the observed objects are a mix of both long-period comets (LPCs) and short-period comets (SPCs), differences in their activity can be used to better understand the thermal evolution that each of these populations has undergone. For the comets that displayed a significant dust tail, we have estimated the sizes and ages of the particles using dynamical models based on the Finson-Probstein method [Finson and Probstein, 1968]. For a selection of 40 comets, we have then compared these models to the data using a novel tail-fitting method that allows the best-fit model to be chosen analytically rather than subjectively. For comets that were observed multiple times by WISE, the particle properties were estimated separately, and then compared. We find that the dust tails of both LPCs and SPCs are primarily comprised of ~mm-cm sized particles, which were the result of emission that occurred several months to several years prior to the observations. The LPCs nearly all have strong emission close to the comet*s perihelion distance, and the SPCs mostly have strong emission close to perihelion, but some have strong emission well before perihelion.

In forensic casework it is often necessary to obtain genetic profiles from crime scene samples that contain increasingly smaller amounts of genetic material, called Low Template DNA (LTDNA). Two examples of LTDNA sources are touch DNA evidence and dust bunnies. Touch DNA refers to DNA that is left behind through casual contact of a donor with an object or another person. Touch DNA can be used to prove a suspect was present at a crime scene. Dust bunnies, or dust conglomerates, typically contain trapped shed skin cells of anyone in the vicinity along with fibers, dirt, hair, and other trace materials. Dust specimens are a potential source of forensic evidence that has been widely underutilized in the forensic community. This is unfortunate because a dust bunny could not only be used to associate a person or crime scene – through trace materials such as fibers – but also to positively identify – through a DNA profile. For example, if a dust specimen is found on a piece of evidence suspected of being moved from its original location, for instance as a body that is too heavy to carry and therefore collects dust while being dragged, then it could be used to link a suspect to a crime scene. Standard methods for obtaining and analyzing touch DNA have been established, but the techniques are not ideal. First, by nature, the 'blind-swabbing' technique, which involves cotton swabs or adhesive tape being applied to an area of interest, can artificially create mixtures of biological material that was originally spatially separated. Second, because the amount of DNA present is typically very low, standard analysis methods may not be sensitive enough to produce probative profiles. In the case of mixtures, the minor component's DNA may go undetected. Dust specimens contain degraded genetic material that has been accumulating for an unknown amount of time. Additionally, dust is usually a conglomeration of genetic material from multiple donors so a mixed profile, if any, is likely to be recovered if standard analysis methods are used. In order to overcome these obstacles presented by LTDNA, a micro-manipulation and combined cell lysis/direct PCR amplification technique has been developed that is sensitive enough to obtain full or probative STR profiles from single or clumped bio-particles collected from touch DNA and dust evidence. Sources of touch DNA evidence such as worn clothing items, touched objects, and skin/skin mixtures are easily sampled using an adhesive material on a microscope slide. Dust specimens can be dispersed onto an adhesive material as well. Targeted bio-particles are then "picked" with a water-soluble adhesive on a tungsten needle and deposited into a micro-volume STR amplification mix. Individual selection and analysis of isolated bio-particles reduces the chance of mixed profile recovery. To aid in the release of genetic material present in the bio-particles, a lysis mix containing a thermostable proteinase is then added to the sample. Samples are then analyzed using standard capillary electrophoresis (CE) methods. In addition to identifying the donor source of these LTDNA sources, it would be beneficial to a criminal investigation to identify the tissue source of the biological material as well. While it is widely speculated that the material originates from shed skin cells, there is little confirmatory evidence proving this assertion. Knowledge of the nature of the evidence could be vital to prevent its misinterpretation during the investigation and prosecution of a crime. Here tissue specific mRNA biomarkers have been evaluated for their use in tissue source determination using a highly sensitive High Resolution Melt (HRM) temperature assay that detects the selectively amplified targets based on their melt temperatures. Using the enhanced genetic analysis technique described above, DNA profile recovery has been markedly enhanced in sources of Touch DNA evidence and dust specimens compared to standard methods. Additionally, the molecular-based characterization method could potentially provide a better understanding of the meaningfulness of the recovered DNA profiles. This optimized strategy provides a method for recovering highly probative data from biological material in low template samples in an efficient and cost effect manner.