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1
Espey, Brian R. "Empirical Modelling of Public Lighting Emission Functions." Remote Sensing 13, no. 19 (September 24, 2021): 3827. http://dx.doi.org/10.3390/rs13193827.
Повний текст джерелаАнотація:
Study of light at night has increased in recent decades due to the recognition of its impact on the environment, potential health concerns, as well as both the financial and carbon cost of energy waste. The advent of more extensive and improved ground-based measurements together with quantifiable satellite data has revolutionised the field, and provided data to test improved theoretical models. However, “closing the loop” and finding a detailed connection between these measurements requires knowledge of the “city emission function”, the angular distribution of upwelling radiation with zenith distance. Simplified analytical functions have been superseded by more complex models involving statistical approximation of emission sources and obstructions and inversion techniques now permit the estimation of emission functions from the observed sky brightness measurements. In this paper, we present an efficient GIS-based method to model public lighting using real-world photometric data and high-resolution digital elevation maps of obstructions such as buildings and trees at a 1 m scale. We discuss the results of this work for a sample of Irish towns as well as a city area. We also compare our results to previous emission functions as well as to observed asymmetries in emission detected by satellites such as SUOMI VIIRS.
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Salam Azad, Abdus, Mohd Salman, S. C. Kaushik, and Dibakar Rakshit. "Energy saving potential of tubular light pipe system with different colors on internal surfaces." International Journal of Energy Sector Management 14, no. 4 (September 18, 2019): 793–837. http://dx.doi.org/10.1108/ijesm-12-2018-0001.
Повний текст джерелаАнотація:
Purpose Lighting in building sectors (consumes the highest energy in commercial buildings and the second highest in residential buildings in India) has very much potential for energy conservation in buildings. With the use of daylighting system, energy consumption in lighting can be lowered up to 30 to 40 per cent. Design/methodology/approach An experimental effort has been made in this paper to explore the internal wall coloring effect on the performance of tubular light pipe. Trace-pro software has been used and validated. With the help of this software, light pipe has been designed and simulated in a ray tracing mode. Assessment of four globally used prediction models has also been conducted to compare the performances in different seasons for light pipes in the composite climate of New Delhi. Findings It has been conducted based on three statistical indicators as mean bias error, root mean square error and R2. Using regression, an empirical model for average internal illuminance has been developed as a function of light reflectance value (LRV) and solar altitude angle. Trace-pro results confirmed that maximum internal illuminance can be obtained with wall surfaces coated with high LRV color. Finally, by using of a single light pipe system for a test room with the artificial lighting system and applying continuous dimming control, the amount of electrical energy has been saved up to 38.5 per cent per year. Originality/value After going through the literature, it has been identified that there has been no paper published which explores the effect of colors of the internal walls on the performance of the light pipe. Along with this, the comparison between existing empirical performance models and find out which model gives the best result in different seasons has been carried out for New Delhi, India.
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Edwinarto, Dominicus. "Imperfect monitoring, cyclical, and learning model perspectives: Price war in the Indonesian lighting industry." International Journal of Engineering & Technology 7, no. 2.29 (May 22, 2018): 236. http://dx.doi.org/10.14419/ijet.v7i2.29.13323.
Повний текст джерелаАнотація:
In marketing terms, the phenomenon of price war is regarded as the result of over-competition and retaliatory reaction in order to win market share. Based on the available literature, three refined models of price war antecedents has been identified: the imperfect monitoring model, the cyclical model, and the learning model. This article was written as part of a recent empirical observation of four Indonesian lighting companies who consider themselves to be currently engaged in price war. Based on the proposition made earlier by Heil and Helsen (2001), this study was prepared as a qualitative survey using an open-ended questionnaire method. The study found that price war is a result of competitive interaction in periods where demands are declining and induced by intra-brand competition. In conclusion, propositions to manage activities in conditions of price war are presented.
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Li, Jiayi, Yongming Xu, Weiping Cui, Meng Ji, Boyang Su, Yuyang Wu, and Jing Wang. "Investigation of Nighttime Light Pollution in Nanjing, China by Mapping Illuminance from Field Observations and Luojia 1-01 Imagery." Sustainability 12, no. 2 (January 17, 2020): 681. http://dx.doi.org/10.3390/su12020681.
Повний текст джерелаАнотація:
In recent years, the number of artificial light sources has tremendously increased with the development of lighting technology and the economy. Nighttime light pollution has been an increasing environmental problem, resulting in negative impacts on human health and the ecological environment. Detailed knowledge of light pollution is important for the planning and management of urban lighting. In this study, light pollution in Nanjing, China was monitored and analyzed using field observations and a 130-m resolution Luojia 1-01 nighttime light imagery. Combined with in situ observations and satellite imagery, a variety of empirical models were established for estimating ambient illuminance at night. Cross-validation was employed to assess the performance of these models, indicating that the third-degree polynomials model had the best performance (MAE = 5.06 lx, R2 = 0.81). The developed third-degree polynomial model was then applied to the Luojia 1-01 image to map the nighttime illuminance in Nanjing. The nighttime illuminance depicted the spatial pattern of the light environment over Nanjing and also indicated some heavily light-polluted areas. Some lit areas were residential areas, whose high brightness had negative effects on residents and need particular attention. This study provides a quantitative and objective reference for the light pollution management in Nanjing, and also a reference for light pollution survey in other regions.
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Hechfellner, Rudi, Michiel Kruger, Tewe Heemstra, Greg Caswell, Nathan Blattau, and Vikrant More. "A Solder Joint Reliability Model for the Philips Lumileds LUXEON Rebel LED Carrier Using Physics of Failure Methodology." International Symposium on Microelectronics 2013, no. 1 (January 1, 2013): 000887–92. http://dx.doi.org/10.4071/isom-2013-thp44.
Повний текст джерелаАнотація:
Light Emitting Diodes (LEDs) are quickly evolving as the dominant lighting solution for a wide variety of applications. With the elimination of incandescent light bulbs and the toxic limitations of fluorescent bulbs, there has been a dramatic increase in the interest in high-brightness light emitting diodes (HB-LEDs). Getting the light out of the die, with reliable color, while maintaining appropriate thermal control over a long service life is a challenge. These issues must be understood and achieved to meet the needs of unique applications, such as solidstate-lighting, automotive, signage, and medical applications. These applications have requirements for 15–25 years of operation making their reliability of critical importance. The LUXEON Rebel has been accepted as an industry leading LED product, widely used in Mean-Time-Between-Failure (MTBF) sensitive applications. Customers use various mounting platforms, such as FR4 Printed Circuit Board (PCB), FR4 PCB with thermal via's, Aluminum & Copper Metal Core printed Circuit Boards (MCPCB), Super MCPCB, etc. As in other LEDs, when mounting to a platform where a large Coefficient of Thermal Expansion (CTE) exists between the LED & the PCB, Solder fatigue could become an issue that may affect system level lifetime. In this paper we have examined extreme cases and how a solder joint can impact system level reliability. We have modeled the conditions and formed a means to predict system level reliability. We have compared the prediction modeling with empirical tests for validation of the models. It is vital to understand system level reliability factors to build lighting solutions that match the application and customer expectations. It is impractical to test LEDs and other components for 50k hours ~5 years since the device evolution is much faster than that – on average one LED generation every 12–18 month. Hence we need models and prediction methods …..
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Fountas, Grigorios, Adebola Olowosegun, and Socrates Basbas. "Assessing School Travel Safety in Scotland: An Empirical Analysis of Injury Severities for Accidents in the School Commute." Safety 8, no. 2 (April 11, 2022): 29. http://dx.doi.org/10.3390/safety8020029.
Повний текст джерелаАнотація:
School travel has been a significant source of safety concerns for children, parents, and public authorities. It will continue to be a source of concerns as long as severe accidents continue to emerge during pupils’ commute to school. This study provides an empirical analysis of the factors influencing the injury severities of the accidents that occurred on trips to or from school in Scotland. Using 9-year data from the STATS19 public database, random parameter binary logit models with allowances for heterogeneity in the means were estimated in order to investigate injury severities in urban and rural areas. The results suggested that factors such as the road type, lighting conditions, vehicle type, and age of the driver or casualty constitute the common determinants of injury severities in both urban and rural areas. Single carriageways and vehicles running on heavy oil engines were found to induce opposite effects in urban and rural areas, whereas the involvement of a passenger car in the accident decomposed various layers of unobserved heterogeneity for both area types. The findings of this study can inform future policy interventions with a focus on traffic calming in the proximity of schools.
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Mebarki, Chahrazed, Essaid Djakab, Abderrahmane Mejedoub Mokhtari, Youssef Amrane, and Lotfi Derradji. "Improvement of Daylight Factor Model for Window Size Optimization and Energy Efficient Building Envelope Designs." Journal of Daylighting 8, no. 2 (July 29, 2021): 204–21. http://dx.doi.org/10.15627/jd.2021.17.
Повний текст джерелаАнотація:
Based on a new approach for the prediction of the Daylight Factor (DF), using existing empirical models, this research work presents an optimization of window size and daylight provided by the glazed apertures component for a building located in a hot and dry climate. The new approach aims to improve the DF model, considering new parameters for daylight prediction such as the orientation, sky conditions, daytime, and the geographic location of the building to fill in all the missing points that the standard DF, defined for an overcast sky, presents. The enhanced DF model is considered for the optimization of window size based on Non dominated Sorting Genetic Algorithm (NSGA II), for heating and cooling season, taking into account the impact of glazing type, space reflectance and artificial lighting installation. Results of heating and cooling demand are compared to a recommended building model for hot and dry climate with 10% Window to Wall Ratio (WWR) for single glazing. The optimal building model is then validated using a dynamic convective heat transfer simulation. As a result, a reduction of 48% in energy demand and 21.5% in CO2 emissions can be achieved. The present approach provides architects and engineers with a more accurate daylight prediction model considering the effect of several parameters simultaneously. The new proposed approach, via the improved DF model, gives an optimal solution for window design to minimize building energy demand while improving the indoor comfort parameters.
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Neves, Fábio de Oliveira, Henrique Ewbank, José Arnaldo Frutuoso Roveda, Andrea Trianni, Fernando Pinhabel Marafão, and Sandra Regina Monteiro Masalskiene Roveda. "Economic and Production-Related Implications for Industrial Energy Efficiency: A Logistic Regression Analysis on Cross-Cutting Technologies." Energies 15, no. 4 (February 14, 2022): 1382. http://dx.doi.org/10.3390/en15041382.
Повний текст джерелаАнотація:
Increased industrial energy efficiency (EE) has become one of the main environmental actions to mitigate carbon dioxide (CO2) emissions, contributing also to industrial competitiveness, with several implications on the production system and cost management. Unfortunately, literature is currently lacking empirical evidence on the impact of energy efficiency solutions on production. Thus, this work primarily aims at investigating the economic and production-related influence on the reduction in industrial energy consumption, considering the cross-cutting technologies HVAC, motors, lighting systems and air compressor systems. The analysis is performed using data from previous studies that characterized the main EE measures for the cross-cutting technologies. Four logistic models were built to understand how costs and production influence energy efficiency across such cross-cutting technologies. In this way, motivating industries to implement measures to reduce electrical consumption, offering an economic cost–benefit analysis and optimizing industry processes so that the reduction in electricity consumption adds to industrial energy efficiency were the aims of this study. The results of this work show through the adjusted indicators that senior management is mainly responsible for energy savings. The operational measures of each piece of equipment can be oriented in the industry towards a specific maintenance process for each technology, becoming an active procedure in industrial productions to obtain EE. Additionally, maintenance planning and control is essential to the reliability of the reduced energy consumption of cross-cutting technologies. This article concludes with managerial implications and suggestions for future research in this field.
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Martin, Genevieve, Christophe Marty, Robin Bornoff, Andras Poppe, Grigory Onushkin, Marta Rencz, and Joan Yu. "Luminaire Digital Design Flow with Multi-Domain Digital Twins of LEDs." Energies 12, no. 12 (June 21, 2019): 2389. http://dx.doi.org/10.3390/en12122389.
Повний текст джерелаАнотація:
At present, when designing a Light Emitting Diode (LED) luminaire, different strategies of development are followed depending on the size of the company. Since on LED datasheets there is only limited information provided, companies designing LED luminaires spend a lot of effort gathering the required input of LED details to be able to design reliable products. Small and medium size enterprises (SMEs) do not have the bandwidth to gather such input and solely rely on empirical approaches leading to approximated luminaire designs, while larger companies use advanced hardware and software tools to characterize parts, design versions, and finally optimize all design steps. In both cases, considerable time and money is spent on prototyping, sampling, and laboratory testing. Digitalization of the complete product development (also known as Industry 4.0 approach) at all integration levels of the solid state lighting (SSL) supply chain would provide the remedy for these pains. The Delphi4LED European project aimed at developing multi-domain compact models of LED (for a consistent, combined description of electronic, thermal, and optical properties of LEDs) as digital twins of the physical products to support virtual prototyping during the design of luminaires. This paper provides an overview of the Delphi4LED approach aimed at supporting new, completely digital workflows both for SMEs and larger companies (Majors) along with some comparison with the traditional luminaire design. Two demonstration experiments are described: One to show the achievable benefits of the approach and another one to demonstrate the ease of use and ability to be accommodated in a larger scale product design for assessing design choices like e.g., number and type of LEDs versus electrical/thermal conditions and constraints, in a tool agnostic manner.
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Zimmerman, Scott, and Russel J. Reiter. "Melatonin and the Optics of the Human Body." Melatonin Research 2, no. 1 (February 28, 2019): 138–60. http://dx.doi.org/10.32794/mr11250016.
Повний текст джерелаАнотація:
Melatonin is fundamental to the lighting, display, and architectural industries as the primary biomarker used in circadian theory. Billions of dollars are being spent on research, product development, and marketing based on the impact of visible light on melatonin produced by the pineal gland. It has now been shown that the mitochondria produce melatonin in many cells in quantities which are orders of magnitude higher than that produced in the pineal gland. This subcellular melatonin does not necessarily fluctuate with our circadian clock or release into the circulation system, but instead has been proposed to be consumed locally in response to the free radical density within each cell, in particular in response to Near Infrared (NIR) exposure. The main point of this review hypothesizes that the subcellular melatonin is being produced in response to the NIR photons which make up the majority of natural sunlight. Given the number of cells and quantity of subcellular melatonin identified to date, it is reasonable to propose that the body produces and maintains a melatonin reservoir that is separate and apart from the circulatory melatonin generated by the pineal gland. To understand how sunlight may support or stimulate this antioxidant reservoir, it becomes necessary to quantify the free radical density in various parts of the human body. To do this, it is necessary to move away from two-dimensional empirical approaches and develop three-dimensional bio-optical models based on the underlying biological processes at play. Three-dimensional Mechanistic Bio-optical Models (MBM) of the skin, eye, and brain based on non-sequential optical ray tracing and Electron Spin Resonance (ESR) data clearly indicate that the NIR portion of natural sunlight provides the primary stimulus during the day to the majority of the cells in the human body, impacting over 60% of the cells in an adult body and 100% of the cells in the fetus and young children. It is also shown that optically, the human body, under the assumption of natural sunlight, has developed optical mechanisms to gather and localize NIR photons in the most sensitive areas of the human body: blood vessels, retina, brain, skin, and even the fetus. That assumption is no longer valid in modern societies where the majority of our time is spent exposed to visible only lighting and displays, which emit zero NIR photons. Based on an optical and biological review of the literature and the MBM results, it is proposed that the NIR portion of natural sunlight stimulates an excess of antioxidants in each of our healthy cells and that the cumulative effect of this antioxidant reservoir is to enhance the body’s ability to rapidly and locally deal with changing conditions throughout the day. In this approach the role of circulatory melatonin produced by the pineal gland is to provide an efficient method of delivering supplemental melatonin during periods of low cellular activity and solar stimulus to damaged or aging cells in both diurnal and nocturnal animals. While circulatory melatonin may be the “Hormone of Darkness”, subcellular melatonin may be the “Hormone of Daylight”.
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Magi, Brian I. "Global Lightning Parameterization from CMIP5 Climate Model Output." Journal of Atmospheric and Oceanic Technology 32, no. 3 (March 2015): 434–52. http://dx.doi.org/10.1175/jtech-d-13-00261.1.
Повний текст джерелаАнотація:
AbstractLightning is best known as a component of severe weather, but diverse communities of researchers, such as those in atmospheric chemistry and global fire modeling, have long recognized that lightning plays a significant role in many components of the Earth system. Global climate models are unlikely to be able to simulate lightning from first principles, but the same models do simulate many parameters related to convection, including total precipitation rate, convective precipitation rate, and convective mass flux. This study combines satellite observations of lightning and CMIP5 climate model simulations to derive an empirical parameterization of monthly lightning in terms of monthly simulated convective parameters. Convective mass flux best captures the spatiotemporal distribution of observed lightning. Derived lightning seasonality is captured with 95% confidence over 69% of land but only 30% of ocean. Spatially, the correlation of derived lightning and observed lightning is 0.74. Overall, global observations suggest lightning occurs at an annual rate of 47 flashes per second, while lightning from the parameterization occurs at 44 flashes per second. A robust feature of the relationship between lightning and climate model convective parameters is that lightning flash rate increases linearly with increases in convective precipitation rate and in convective mass flux for a significant subset of the total range of those convective parameters. Namely, this linear proportionality is evident when the convective precipitation rate is less than 4–5 mm day−1 and the convective mass flux is less than 15–16 kg m−2 h−1, which account for about 90% of the values simulated by the climate models.
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Pessi, Antti T., and Steven Businger. "The Impact of Lightning Data Assimilation on a Winter Storm Simulation over the North Pacific Ocean." Monthly Weather Review 137, no. 10 (October 1, 2009): 3177–95. http://dx.doi.org/10.1175/2009mwr2765.1.
Повний текст джерелаАнотація:
Abstract In this paper, the potential of lightning data assimilation to improve NWP forecasts over data-sparse oceans is investigated using, for the first time, a continuous, calibrated lightning data stream. The lightning data employed in this study are from the Pacific Lightning Detection Network/Long-Range Lightning Detection Network (PacNet/LLDN), which has been calibrated for detection efficiency and location accuracy. The method utilizes an empirical lightning–convective rainfall relationship, derived specifically from North Pacific winter storms observed by PacNet/LLDN. The assimilation method nudges the model’s latent heating rates according to rainfall estimates derived from PacNet/LLDN lightning observations. The experiment was designed to be employed in an operational setting. To illustrate the promise of the approach, lightning data from a notable extratropical storm that occurred over the northeast Pacific Ocean in late December 2002 were assimilated into the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). The storm exhibited a very electrically active cold front with most of the lightning observed 300–1200 km away from the storm center. The storm deepened rapidly (12 hPa in 12 h) and was poorly forecast by the operational models. The assimilation of lightning data generally improved the pressure and wind forecasts, as the validation of the model results using available surface and satellite data revealed. An analysis is presented to illustrate the impact of assimilation of frontal lightning on the storm development and dynamics. The links among deep convection, thermal wind along the front, and cyclogenesis are explicitly explored.
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Yang, Jian, Peter J. Weisberg, Thomas E. Dilts, E. Louise Loudermilk, Robert M. Scheller, Alison Stanton, and Carl Skinner. "Predicting wildfire occurrence distribution with spatial point process models and its uncertainty assessment: a case study in the Lake Tahoe Basin, USA." International Journal of Wildland Fire 24, no. 3 (2015): 380. http://dx.doi.org/10.1071/wf14001.
Повний текст джерелаАнотація:
Strategic fire and fuel management planning benefits from detailed understanding of how wildfire occurrences are distributed spatially under current climate, and from predictive models of future wildfire occurrence given climate change scenarios. In this study, we fitted historical wildfire occurrence data from 1986 to 2009 to a suite of spatial point process (SPP) models with a model averaging approach. We then predicted human- and lightning-caused wildfire occurrence over the 2010–2100 period in the Lake Tahoe Basin, a forested watershed in the western US with an extensive wildland–urban interface. The purpose of our research was threefold, including (1) to quantify the influence of biophysical and anthropogenic explanatory variables on spatial patterns of wildfire occurrence, (2) to model current and future spatial distribution of wildfire occurrence under two carbon emission scenarios (A2 and B1), and (3) to assess prediction uncertainty due to model selection. We found that climate variables exerted stronger influences on lightning-caused fires, with climatic water deficit the most important climatic variable for both human- and lightning-caused fires. The recent spatial distribution of wildfire hotspots was mainly constrained by anthropogenic factors because most wildfires were human-caused. The future distribution of hotspots (i.e. places with high fire occurrence density), however, was predicted to shift to higher elevations and ridge tops due to a more rapid increase of lightning-caused fires. Landscape-scale mean fire occurrence density, averaged from our top SPP models with similar empirical support, was predicted to increase by 210% and 70% of the current level under the A2 and B1 scenarios. However, individual top SPP models could lead to substantially different predictions including a small decrease, a moderate increase, and a very large increase, demonstrating the critical need to account for model uncertainty.
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McCaul, Eugene W., Georgios Priftis, Jonathan L. Case, Themis Chronis, Patrick N. Gatlin, Steven J. Goodman, and Fanyou Kong. "Sensitivities of the WRF Lightning Forecasting Algorithm to Parameterized Microphysics and Boundary Layer Schemes." Weather and Forecasting 35, no. 4 (August 1, 2020): 1545–60. http://dx.doi.org/10.1175/waf-d-19-0101.1.
Повний текст джерелаАнотація:
AbstractThe Lightning Forecasting Algorithm (LFA), a simple empirical procedure that transforms kinematic and microphysical fields from explicit-convection numerical models into mapped fields of estimated total lightning flash origin density, has been incorporated into operational forecast models in recent years. While several changes designed to improve LFA accuracy and reliability have been implemented, the basic linear relationship between model proxy amplitudes and diagnosed total lightning flash rate densities remains unchanged. The LFA has also been added to many models configured with microphysics and boundary layer parameterizations different from those used in the original study, suggesting the need for checks of the LFA calibration factors. To assist users, quantitative comparisons of LFA output for some commonly used model physics choices are performed. Results are reported here from a 12-member ensemble that combines four microphysics with three boundary layer schemes, to provide insight into the extent of LFA output variability. Data from spring 2018 in Nepal–Bangladesh–India show that across the ensemble of forecasts in the entire three-month period, the LFA peak flash rate densities all fell within a factor of 1.21 of well-calibrated LFA-equipped codes, with most schemes failing to show differences that are statistically significant. Sensitivities of threat areal coverage are, however, larger, suggesting substantial variation in the amounts of ice species produced in storm anvils by the various microphysics schemes. Current explicit-convection operational models in the United States employ schemes that are among those exhibiting the larger biases. For users seeking optimum performance, we present recommended methods for recalibrating the LFA.
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Arienti, M. Cecilia, Steven G. Cumming, and Stan Boutin. "Empirical models of forest fire initial attack success probabilities: the effects of fuels, anthropogenic linear features, fire weather, and management." Canadian Journal of Forest Research 36, no. 12 (December 1, 2006): 3155–66. http://dx.doi.org/10.1139/x06-188.
Повний текст джерелаАнотація:
Canadian fire managers seek to contain fires below some target size (here 3 ha) by initial attack (IA). Suppression failures occur when fire size at IA exceeds this target (a response failure) or if an initially small fire cannot be contained below it (a containment failure). We examined the effects of cause, season, forest fuels, anthropogenic linear features, weather, and fire management (response time, size at IA) on the probability of these two types of suppression failures, using multiple logistic regression on 1196 fires that occurred within the boreal mixedwood forest of northeastern Alberta during 1995–2002. The frequencies of containment (7%) and response failures (10%) were similar, but the latter accounted for 85% of the area burned. Response failure probability was greater for fires caused by lightning than those caused by humans and increased with longer response times, local abundance of black spruce in summer, and pine fuel under severe fire weather. We found no effect of linear features or other fuel types. Containment failure probability was related to size at IA and fire weather conditions. Our models suggest that a reduction in area burned might be possible if additional fire-specific factors affecting response failure probability could be incorporated into operational decisions.
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Bendakir, Abdelhakim, Abdelhafid Bayadi, and Djalel DIB. "Towards the prospection of an optimal thermal response of ZnO surge arrester in HV power system." International Journal of Electrical and Computer Engineering (IJECE) 11, no. 3 (June 1, 2021): 1865. http://dx.doi.org/10.11591/ijece.v11i3.pp1865-1875.
Повний текст джерелаАнотація:
In order to understand the thermal and electrical properties of surge arrester under standard climatic conditions, it would be useful to evaluate the heating progression in its different elements. These are constituted of heterogeneous materials, which have physical and electrical nonlinear properties along the surge arrester. Temperature predicting solutions for zinc oxide ceramic blocks provide fundamental elements of the electrothermal material characteristics in view of the lifetime estimation. Electrothermal phenomenon analysis of surge arresters is based on empirically-determined parameter models, using finite element method (FEM) simulated on COMSOL Multiphysics software which is a more precise approach compared to the existing models. In this paper, the behavioural model has been developed to study the surge arresters in both cases: the steady state and overvoltage state (lightning). Previous published works validate the first simulation results. This work is therefore extended to consider other operating states, which illustrate the dependence of the type of surge on the amplitudes and durations of electrothermal phenomena.
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Rawat, Shivangana, Akshay L. Chandra, Sai Vikas Desai, Vineeth N. Balasubramanian, Seishi Ninomiya, and Wei Guo. "How Useful Is Image-Based Active Learning for Plant Organ Segmentation?" Plant Phenomics 2022 (February 24, 2022): 1–11. http://dx.doi.org/10.34133/2022/9795275.
Повний текст джерелаАнотація:
Training deep learning models typically requires a huge amount of labeled data which is expensive to acquire, especially in dense prediction tasks such as semantic segmentation. Moreover, plant phenotyping datasets pose additional challenges of heavy occlusion and varied lighting conditions which makes annotations more time-consuming to obtain. Active learning helps in reducing the annotation cost by selecting samples for labeling which are most informative to the model, thus improving model performance with fewer annotations. Active learning for semantic segmentation has been well studied on datasets such as PASCAL VOC and Cityscapes. However, its effectiveness on plant datasets has not received much importance. To bridge this gap, we empirically study and benchmark the effectiveness of four uncertainty-based active learning strategies on three natural plant organ segmentation datasets. We also study their behaviour in response to variations in training configurations in terms of augmentations used, the scale of training images, active learning batch sizes, and train-validation set splits.
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Etminan, Ghazal, Ehsan Vazifeh, and Ardeshir Mahdavi. "The Implications of Assumed Boundary Conditions for the Reliability of Indoor Illuminance Predictions: A Case Study." Applied Mechanics and Materials 861 (December 2016): 501–8. http://dx.doi.org/10.4028/www.scientific.net/amm.861.501.
Повний текст джерелаАнотація:
In order to model daylight availability and distribution in architectural spaces, simulation tools require reliable representations of boundary conditions – typically in terms of sky luminance distribution models. However, the impact of sky model errors on simulation-based indoor illuminance predictions is not well documented. There are different tools and methods to simulate indoor illuminance conditions and related daylight indicators. In the present study, we selected Radiance lighting simulation program. In order to generate sky scene description, Radiance contains two routines, namely, Gendaylit and Gensky. These routines require, as input, information on both direct and diffuse components of solar radiation. To explore the implications of the sky model selection on the fidelity of simulation results, we used Radiance to compute the indoor illuminance in an existing test space on the rooftop of a university building. Thereby, the aforementioned two sky models were considered. A third option (SC) was a sky model generated based on measured values obtained from a sky scanner. Simultaneously, the actual illuminance levels in this room were monitored under different outdoor conditions (clear, intermediate, overcast). The comparison of the measurement results with multiple model prediction results facilitates an empirically based evaluation of the reliability of indoor illuminance predictions in the face of different assumptions pertaining to the prevailing boundary conditions.
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Hnatyshena, Iryna, Inna Khariuk, Inessa Azarova, and Iuliia Ivanytska. "Distance learning of foreign languages for students of economic specialties." Linguistics and Culture Review 5, S4 (November 12, 2021): 780–98. http://dx.doi.org/10.21744/lingcure.v5ns4.1732.
Повний текст джерелаАнотація:
Distance education at lightning-fast speed has become the only possible form of education. Distance learning of a foreign language for students of higher educational institutions has a number of advantages due to the fact that we are talking about pedagogical interaction with the age group of psychologically mature individuals with relatively formed mechanisms of motivation and outlined personal and professional orientation. The purpose of the present research is a comprehensive analysis of the process and results of distance learning of a foreign language (English) for students of economic specialties. The research methods are as follows: the analysis of modern opportunities for organizing distance learning; study of theoretical and methodological papers on the subject matter; method of experimental teaching of foreign languages with an emphasis on tactics of stimulating the personal and motivational sphere of students’ educational activities; development of author’s diagnostic models in order to reveal the dynamics of development of knowledge and practical skills in a foreign language of students of economic profile; qualitative and quantitative analysis of empirical data; statistical and mathematical interpretation of results, their functional analysis; method of generalization and abstraction. According to the data obtained, the hypothesis of the research has been confirmed.
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Hakim, Zainab Q., Scott Archer-Nicholls, Gufran Beig, Gerd A. Folberth, Kengo Sudo, Nathan Luke Abraham, Sachin Ghude, Daven K. Henze, and Alexander T. Archibald. "Evaluation of tropospheric ozone and ozone precursors in simulations from the HTAPII and CCMI model intercomparisons – a focus on the Indian subcontinent." Atmospheric Chemistry and Physics 19, no. 9 (May 16, 2019): 6437–58. http://dx.doi.org/10.5194/acp-19-6437-2019.
Повний текст джерелаАнотація:
Abstract. Here we present results from an evaluation of model simulations from the International Hemispheric Transport of Air Pollution Phase II (HTAPII) and Chemistry Climate Model Initiative (CCMI) model inter-comparison projects against a comprehensive series of ground-based, aircraft and satellite observations of ozone mixing ratios made at various locations across India. The study focuses on the recent past (observations from 2008 to 2013, models from 2009–2010) as this is most pertinent to understanding the health impacts of ozone. To our understanding this is the most comprehensive evaluation of these models' simulations of ozone across the Indian subcontinent to date. This study highlights some significant successes and challenges that the models face in representing the oxidative chemistry of the region. The multi-model range in area-weighted surface ozone over the Indian subcontinent is 37.26–56.11 ppb, whilst the population-weighted range is 41.38–57.5 ppb. When compared against surface observations from the Modelling Atmospheric Pollution and Networking (MAPAN) network of eight semi-urban monitoring sites spread across India, we find that the models tend to simulate higher ozone than that which is observed. However, observations of NOx and CO tend to be much higher than modelled mixing ratios, suggesting that the underlying emissions used in the models do not characterise these regions accurately and/or that the resolution of the models is not adequate to simulate the photo-chemical environment of these surface observations. Empirical orthogonal function (EOF) analysis is used in order to identify the extent to which the models agree with regards to the spatio-temporal distribution of the tropospheric ozone column, derived using OMI-MLS observations. We show that whilst the models agree with the spatial pattern of the first EOF of observed tropospheric ozone column, most of the models simulate a peak in the first EOF seasonal cycle represented by principle component 1, which is later than the observed peak. This suggests a widespread systematic bias in the timing of emissions or some other unknown seasonal process. In addition to evaluating modelled ozone mixing ratios, we explore modelled emissions of NOx, CO, volatile organic compounds (VOCs) and the ozone response to the emissions. We find a high degree of variation in emissions from non-anthropogenic sources (e.g. lightning NOx and biomass burning CO) between models. Total emissions of NOx and CO over India vary more between different models in the same model intercomparison project (MIP) than the same model used in different MIPs, making it impossible to diagnose whether differences in modelled ozone are due to emissions or model processes. We therefore recommend targeted experiments to pinpoint the exact causes of discrepancies between modelled and observed ozone and ozone precursors for this region. To this end, a higher density of long-term monitoring sites measuring not only ozone but also ozone precursors including speciated VOCs, located in more rural regions of the Indian subcontinent, would enable improvements in assessing the biases in models run at the resolution found in HTAPII and CCMI.
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Anderson, Daniel C., Bryan N. Duncan, Arlene M. Fiore, Colleen B. Baublitz, Melanie B. Follette-Cook, Julie M. Nicely, and Glenn M. Wolfe. "Spatial and temporal variability in the hydroxyl (OH) radical: understanding the role of large-scale climate features and their influence on OH through its dynamical and photochemical drivers." Atmospheric Chemistry and Physics 21, no. 8 (April 30, 2021): 6481–508. http://dx.doi.org/10.5194/acp-21-6481-2021.
Повний текст джерелаАнотація:
Abstract. The hydroxyl radical (OH) is the primary atmospheric oxidant responsible for removing many important trace gases, including methane, from the atmosphere. Although robust relationships between OH drivers and modes of climate variability have been shown, the underlying mechanisms between OH and these climate modes, such as the El Niño–Southern Oscillation (ENSO), have not been thoroughly investigated. Here, we use a chemical transport model to perform a 38 year simulation of atmospheric chemistry, in conjunction with satellite observations, to understand the relationship between tropospheric OH and ENSO, Northern Hemispheric modes of variability, the Indian Ocean Dipole, and monsoons. Empirical orthogonal function (EOF) and regression analyses show that ENSO is the dominant mode of global OH variability in the tropospheric column and upper troposphere, responsible for approximately 30 % of the total variance in boreal winter. Reductions in OH due to El Niño are centered over the tropical Pacific and Australia and can be as high as 10 %–15 % in the tropospheric column. The relationship between ENSO and OH is driven by changes in nitrogen oxides in the upper troposphere and changes in water vapor and O1D in the lower troposphere. While the correlations between monsoons or other modes of variability and OH span smaller spatial scales than for ENSO, regional changes in OH can be significantly larger than those caused by ENSO. Similar relationships occur in multiple models that participated in the Chemistry–Climate Model Initiative (CCMI), suggesting that the dependence of OH interannual variability on these well-known modes of climate variability is robust. Finally, the spatial pattern and r2 values of correlation between ENSO and modeled OH drivers – such as carbon monoxide, water vapor, lightning, and, to a lesser extent, NO2 – closely agree with satellite observations. The ability of satellite products to capture the relationship between OH drivers and ENSO provides an avenue to an indirect OH observation strategy and new constraints on OH variability.
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Schoennagel, Tania, and Monica Turner. "The Effects of Climatically Altered Fire Regimes on Initial Successional Responses in Yellowstone National Park." UW National Parks Service Research Station Annual Reports 24 (January 1, 2000): 165–68. http://dx.doi.org/10.13001/uwnpsrc.2000.3441.
Повний текст джерелаАнотація:
Many scientists predict that due to the quick response of fire regimes to changes in climate (Flannigan et al. 1998; Stocks et al. 1998), the most rapid and extensive effects of climate change will be mediated by altered disturbance regimes (Davis and Botkin 1985; Franklin et al. 1992; Graham et al. 1990; Weber and Flannigan 1997). Under climate scenarios expected for C02 doubling, Price and Rind (1994) predict a 44% increase in lightning-caused fires and a 78% increase in total area burned for the U.S. Although regional climate scenarios are still subject to a fairly high degree of uncertainty, regional predictions for Yellowstone National Park (YNP) estimate an increase in aridity (Balling et al. 1992) and mean July temperatures (Bartlein et al. 1997), suggesting that fire frequencies could significantly increase in YNP over the next century. While several models have simulated the response of western coniferous forests to altered fire regimes (Baker et al. 1991; Gardner et al. 1996; Keane et al. 1990; Keane et al. 1995; Romme and Turner 1991), little empirical work on the successional responses to different intervals of standÂreplacing fire has been incorporated, and remains a critical element in predicting the effects of climatically altered disturbance regimes in forested landscapes. Previous work in Yellowstone has considered the effects of fire severity, fire size and level of serotiny in explaining initial pathways of postfrre succession across the Yellowstone landscape (Turner et al. 1994; Turner et al. 1997). The effects of the third component of the disturbance regime, fire interval, remains largely unexplored, and represents a fundamental link in predicting potential effects of climate change on the Yellowstone landscape. The specific objectives of our research, therefore, were to assess: Are there a significantly different successional responses following different intervals of stand-replacing fire in Yellowstone National Park? Because serotiny exerts a strong influence on initial post-fire succession in Yellowstone (characterized by variation in lodgepole pine densities), we also sought to track stand-level changes in serotiny over time. In order to flesh out a possible mechanism for why postfrre succession may vary depending upon the age at which the stand burns we asked: What is the temporal variation in lodgepole pine serotiny within the park?
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Patil, K. N., S. C. Kaushik, and S. N. Garg. "Performance Prediction and Assessment of Energy Conservation Potential for a Light Pipe System in Indian Composite Climate of New Delhi." Journal of Solar Energy Engineering 140, no. 5 (June 18, 2018). http://dx.doi.org/10.1115/1.4039656.
Повний текст джерелаАнотація:
Light pipes are popularly used for transporting outdoor sunlight into deep spaces of the building, and hence, use of artificial lighting could be substantially reduced. Performance prediction of a light pipe is an essential step before its use in buildings, so that energy saving potential of the light pipe could be quantified. This paper deals with experimental validation of three existing semi-empirical models for light pipes with different aspect ratios, installed on a windowless test room, at IIT Delhi, New Delhi. Two new semi-empirical models based on the existing correlations are developed. The new model found to perform better with mean bias error (MBE) and root-mean-squared error (MSE) of 0.076 and 0.01, respectively. The better performing new model is used for the evaluation of hourly internal illuminance by the light pipe in a typical meteorological year (TMY) in New Delhi. From hourly internal illuminance in a typical meteorological year, the energy saving potential and CO2 mitigation potential of light pipe system for the test room are evaluated. Monthly average energy saving potentials of the light pipe-fluorescent tube light system are found to be 50% for continuous dimming control and 38% for three-step on–off control. Results show that the light pipe-fluorescent tube light system, with different lighting controls, could reduce CO2 emissions to 15–50%.
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Ammar, Mohsen Ben, Rim Ben Ammar, and Abdelmajid Oualha. "Photovoltaic Power Prediction for Solar Car Park Lighting Office Energy Management." Journal of Energy Resources Technology 143, no. 3 (August 27, 2020). http://dx.doi.org/10.1115/1.4048060.
Повний текст джерелаАнотація:
Abstract The photovoltaic energy is widely used in modern power network due to its environmental and economic benefits. Solar car park is one of the solar photovoltaic system applications. The photovoltaic energy has disadvantages of intermittence and weather's variation. Thus, photovoltaic power prediction is very necessary to guarantee a balance between the produced energy and the solar car park requirements. The prediction of the photovoltaic energy is related to solar irradiation and ambient temperature forecasting. The aim of this study was to evaluate various methodologies for weather data estimation, namely, the empirical models, the multilayer perceptron neural network (MLPNN), and the adaptive neuro-fuzzy inference system (ANFIS). The simulation results show that the ANFIS model can be successfully used to forecast the photovoltaic power. The forecasted photovoltaic energy was used for the solar car park lighting office management algorithm.
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Lagemann, Christian, Kai Lagemann, Sach Mukherjee, and Wolfgang Schroeder. "Generalization of deep recurrent optical flow estimation for particle-image velocimetry data." Measurement Science and Technology, May 26, 2022. http://dx.doi.org/10.1088/1361-6501/ac73db.
Повний текст джерелаАнотація:
Abstract Particle-Image Velocimetry (PIV) is one of the key techniques in modern experimental fluid mechanics to determine the velocity components of flow fields in a wide range of complex engineering problems. Current PIV processing tools are mainly handcrafted models based on cross-correlations computed across interrogation windows. Although widely used, these existing tools have a number of well-known shortcomings, including limited spatial output resolution and peak-locking biases. Recently, new approaches for PIV processing leveraging a novel neural network architecture for optical flow estimation called Recurrent All-Pairs Field Transforms (RAFT) have been developed. These have matched or exceeded the performance of classical, handcrafted models. While the RAFT-PIV method is a promising approach, it is important for the broader fluids community to more completely understand its empirical behavior and performance. To this end, in this study, we thoroughly investigate the performance of RAFT-PIV under varying image and lighting conditions. We consider applications spanning synthetic and experimental data, with a breadth and depth going far beyond currently available empirical results. The results for the wide variation of experiments shed new light on the capabilities of deep learning for PIV processing.
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Eugenio, Teresa, Pedro Carreira, Nina Miettinen, and Isabel Maria Estima Costa Lourenço. "Understanding students' future intention to engage in sustainability accounting: the case of Malaysia and the Philippines." Journal of Accounting in Emerging Economies, December 28, 2021. http://dx.doi.org/10.1108/jaee-10-2020-0277.
Повний текст джерелаАнотація:
Purpose The study investigates whether the level of sustainability concerns of Higher Education Institutions (HEIs) in Malaysia and the Philippines is positively associated with accounting students' intentions to engage in sustainability accounting through its effect on students' attitude, subjective norm and perceived behavioural control regarding environmental sustainability practices. Design/methodology/approach This empirical study relies on a structural equation model computed using data collected through a questionnaire and data collected from the HEIs websites. Findings The findings show that the willingness to engage in sustainability accounting is determined by students' subjective norm and perceived behavioural control, but it is not determined by attitude regarding environmental sustainability practices. The authors also found that the greater the concern with sustainability of the HEI in which a student is enrolled, the greater his/her attitude, subjective norm and perceived behavioural control towards environmental sustainability, and, indirectly, the greater his/her intention to engage in sustainability accounting. Originality/value These findings add to the literature on higher education and sustainability accounting by high-lighting the importance of the HEIs sector in promoting sustainability policies and practices, in acting as role models regarding sustainability issues, and in preparing students for building a sustainable society.
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Huang, Rong, Xuan Zhao, Yufei Yuan, Qiang Yu, and Winnie Daamen. "Open Experimental Data-Sets to Reveal Behavioural Insights of High-Deck Coach Evacuations." Fire Technology, May 5, 2022. http://dx.doi.org/10.1007/s10694-022-01253-y.
Повний текст джерелаАнотація:
AbstractNumerous evacuation performance data for the utilization in evacuation modelling and simulations have been established for the conventional/widely studied scenarios, such as building evacuation scenarios. However, such data are typically scarce for a new scenario in literature — evacuation from high-deck coaches. This paper fulfills this gap by presenting empirical high-deck coach evacuation data-sets that can be used for model configuration and validation. To this end, firstly, five essential and commonly used performance metrics, i.e., evacuation time, flow rate, alighting time gap, velocity on stairways and exit choice, were collected and derived from two series of controlled experiments with 7 and 22 runs that involved 44 and 96 participants respectively. Then, all these datasets were structured in the distribution form, based on which three critical behavioural insights are revealed regardless of the evacuation conditions (the types of high-deck coaches, lighting conditions, and age groups). First, the evacuation behaviour in normal (experimental) conditions conforms to a multi-stage pattern (a modified four-stage pattern, i.e., reaction, acceleration, fluctuation and saturation stages). Second, the instantaneous flow rate can be well captured by the Burr, Loglogistic and Lognormal distributions, and the alighting time gap can be represented by the Burr distribution. Third, more than 50% of passengers evacuate through the rear door in the front-and-rear-door evacuations. The frequency of choosing the front door is found to shift towards the direction of the rear door compared to the ideal results (based on the shortest distance calculation) with a magnitude of approximately 1.95 seat rows. The presented data-sets are valuable resources for the development of high-deck coach evacuation models. The empirical findings promote the understanding upon the evacuation behaviour of high-deck coach passengers.
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Koranteng, Christian, Barbara Simons, and Kwabena Abrokwa Gyimah. "Potential measures towards the reduction of cooling loads of office buildings in Ghana." Frontiers in Engineering and Built Environment ahead-of-print, ahead-of-print (August 10, 2021). http://dx.doi.org/10.1108/febe-03-2021-0016.
Повний текст джерелаАнотація:
PurposeGiven the climatic context and economic challenge of Ghana in its developmental strides, energy use of office buildings continues to be a task on the economy. Therefore, the study was about finding measures that could reduce cooling loads in 10 office buildings. The paper presents the outcome of a long-term study of the thermal conditions in a selected number of office buildings in Accra and Kumasi, Ghana.Design/methodology/approachThrough long-term monitoring of environmental data, the buildings were consequently modelled in a simulation application. Thereafter, a validation of the simulation models (using regression coefficients, r2 of 0.53–0.90) was undertaken towards finding measures to reduce cooling loads.FindingsThe results showed various potentials of efficient lighting, thermal mass, night ventilation, insulation to attic floors, efficient glazing, blind deployments, etc. in reducing cooling loads in the range of 2–17.5%. By combining the potential measures to study their synergistic effects on the loads, 35, 39 and 38% improvements were achieved for the low-rise, multi-storey and fully glazed office buildings.Originality/valueThese potential measures ought to be incorporated in the design, specification, construction and operation of Ghanaian office buildings to reduce the burden on the economy and the environment. Now more than ever, there is the need for climatic regions to come up with empirical data that could help relieve the world's economies from the post-pandemic stress.
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Montt, Cecilia, Juan Carlos Castro, Alejandra Valencia, Astrid Oddershede, and Luis Quezada. "Artificial Neural Network and a Nonlinear Regression Model for Predicting Electrical Pole Crash." INTERNATIONAL JOURNAL OF COMPUTERS COMMUNICATIONS & CONTROL 15, no. 5 (August 30, 2020). http://dx.doi.org/10.15837/ijccc.2020.5.3879.
Повний текст джерелаАнотація:
This paper presents the investigation about a problem situation that Electric Distributor Companies are facing in Chile resulting from transit accidents. The number of vehicle crashes to power distribution poles and street lighting has grown. This situation causes discomfort to citizen and mainly to the neighbors due to power cuts and even on occasion , losses of human lives because of the accident that have occurred. Based on previous research, the accidents are not random nor chance dependent, but the majority of transit accident follow parameters or variables from the scenery where it occurs. In order to analyze the variables and the degree this variables affect the accidents, a model of Perceptron and Multipercetron Artificial Neural Networks and a Multiple Nonlinear Regression model are proposed. An empirical study was made; collecting data from a distributor company and from Chilean National Traffic Safety Commission, where the more frequent variables involved in accidents were determined to develop the mentioned models. These variables were investigated and also their influence on the occurrence of vehicle crashes to power distribution poles could be confirmed. With this data, the prediction of post crashes was developed, where through the application of the neural network and multiple nonlinear regression, revealed 95.7% of acceptable predictions. This study will bring benefits to power distribution companies considering a risk index in the streets, based on the number of crashes of poles per street; this will allow optimal decisions in future electrical distribution projects avoiding critical areas.
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Stolz, Douglas C., Kelsey R. Bilsback, Jeffrey R. Pierce, and Steven A. Rutledge. "Evaluating Empirical Lightning Parameterizations in Global Atmospheric Models." Journal of Geophysical Research: Atmospheres 126, no. 4 (February 12, 2021). http://dx.doi.org/10.1029/2020jd033695.
Повний текст джерела
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Kinkead, Joyce. "An Empirical Research Project in English and Writing Studies." Prompt: A Journal of Academic Writing Assignments 3, no. 2 (August 6, 2019). http://dx.doi.org/10.31719/pjaw.v3i2.40.
Повний текст джерелаАнотація:
English majors generally are adept at literary criticism but tend to have less experience in conducting empirical research that draws on both qualitative and quantitative methods and engages human participants. To introduce those methods to students and to satisfy a university requirement for quantitative instruction applied to the discipline, I developed a course called Approaches to Research in English Studies. The students complete individual IRB-approved projects that result in a research report, a poster, and a lightning talk. Before undertaking the individual projects, the students engage in a whole-class research project that models the process, and this latter assignment is described here in this essay.
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Meyer, Hans Kristian Hygen, Frank Mauseth, Martine Husøy, and Atle Pedersen. "Breakdown in short rod-plane air gaps under positive lightning impulse stress." Proceedings of the Nordic Insulation Symposium, no. 25 (October 5, 2017). http://dx.doi.org/10.5324/nordis.v0i25.2366.
Повний текст джерелаАнотація:
<p>Prediction of withstand voltages in air-insulated systems are made on the basis of empirical models that are not sufficiently accurate for complex geometries. Better understanding of the spatiotemporal development of electrical discharges is necessary to improve the present models. Discharges in lightning impulse stressed 20–100mm rod-plane gaps are examined using a highspeed camera, photo-multiplier tubes (PMTs) and a highbandwidth current measurement system. The images and measurements of gaps larger than 20mm show a fast initial streamer discharge with a current rise time of some tens of ns, followed by a dark period of a few μs and a propagation of a slower leader-type channel leading to breakdown. The breakdown mechanisms in the shortest gaps are faster and geometry dependent, probably occuring by heating of initial streamer channels. Different light filters used with the PMTs indicate that all parts of the leader-type discharge development emit light over a spectrum from UV to IR. The initial discharges emit low amounts of warm light and IR compared to the leader-type channel. Finally, it is suggested that empirical breakdown voltage prediction models should be interpreted in light of the leader-type breakdown mechanism.</p>
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Meyer, Hans Kristian Hygen, Frank Mauseth, Martine Husøy, and Atle Pedersen. "Breakdown in short rod-plane air gaps under positive lightning impulse stress." Proceedings of the Nordic Insulation Symposium, no. 25 (October 3, 2017). http://dx.doi.org/10.5324/nordis.v0i25.2377.
Повний текст джерелаАнотація:
<p>Prediction of withstand voltages in air-insulated systems are made on the basis of empirical models that are not sufficiently accurate for complex geometries. Better understanding of the spatiotemporal development of electrical discharges is necessary to improve the present models. Discharges in lightning impulse stressed 20–100 mm rod-plane gaps are examined using a highspeed camera, photo-multiplier tubes (PMTs) and a highbandwidth current measurement system. The images and measurements of gaps larger than 20mm show a fast initial streamer discharge with a current rise time of some tens of ns, followed by a dark period of a few μs and a propagation of a slower leader-type channel leading to breakdown. The breakdown mechanisms in the shortest gaps are faster and geometry dependent, probably occuring by heating of initial streamer channels. Different light filters used with the PMTs indicate that all parts of the leader-type discharge development emit light over a spectrum from UV to IR. The initial discharges emit low amounts of warm light and IR compared to the leader-type channel. Finally, it is suggested that empirical breakdown voltage prediction models should be interpreted in light of the leader-type breakdown mechanism.</p>