5173 research outputs found
Sort by
A state of art review on estimation of solar radiation with various models
No full textSolar radiation is free, and very useful input for most sectors such as heat, health, tourism, agriculture, and energy production, and it plays a critical role in the sustainability of biological, and chemical processes in nature. In this framework, the knowledge of solar radiation data or estimating it as accurately as possible is vital to get the maximum benefit from the sun. From this point of view, many sectors have revised their future investments/plans to enhance their profit margins for sustainable development according to the knowledge/estimation of solar radiation. This case has noteworthy attracted the attention of researchers for the estimation of solar radi-ation with low errors. Accordingly, it is noticed that various types of models have been contin-uously developed in the literature. The present review paper has mainly centered on the solar radiation works estimated by the empirical models, time series, artificial intelligence algorithms, and hybrid models. In general, these models have needed the atmospheric, geographic, climatic, and historical solar radiation data of a given region for the estimation of solar radiation. It is seen from the literature review that each model has its advantages and disadvantages in the estimation of solar radiation, and a model that gives the best results for one region may give the worst results for the other region. Furthermore, it is noticed that an input parameter that strongly improves the performance success of the models for a region may worsen the performance success of another region. In this direction, the estimation of solar radiation has been separately detailed in terms of empirical models, time series, artificial intelligence algorithms, and hybrid algorithms. Accord-ingly, the research gaps, challenges, and future directions for the estimation of solar radiation have been drawn in the present study. In the results, it is well-observed that the hybrid models have exhibited more accurate and reliable results in most studies due to their ability to merge between different models for the benefit of the advantages of each model, but the empirical models have come to the fore in terms of ease of use, and low computational costs
Current practices, potentials, challenges, future opportunities, environmental and economic assumptions for Turkiye's clean and sustainable energy policy: A comprehensive assessment
No full textIn today's world, most countries including Turkiye have met their electricity demand at a dominant rate by burning fossil-based fuels in thermal power plants. However, fossil-fuel reserves have been rapidly depleted, resulting in high volatility in these fuels' markets, as well as alarming environmental, and economic problems for the governments. In recent years, many governments have started to face these problems and have rapidly transitioned to renewable and alternative carbon-free energy sources in their electricity production variety. However, these belated steps have failed to mitigate the increment in global greenhouse gas emissions against the rapid growth of population and energy demand. In recent years, Turkiye has put a noteworthy challenge to mitigate its dominant use of fossil fuels, reducing its energy dependence, sustaining its economic development, and mitigating the carbon footprint. From this point of view, it is witnessed that many power plants have been established, many of them are currently under construction, especially to produce more electricity in a sus-tainable way. Accordingly, the present study aims to comprehensively discuss Turkiye's energy production policy, energy potential and reserves, challenges, future opportunities, and the impacts of the energy sector on the economic and environmental issues for the country. In this framework, it is well-noticed that the country's future energy production policy has been reasonably changed in order to achieve positive economic and envi-ronmental outcomes in the medium and long term
The Impact of Uncertainty on Textile Companies Profitability in the EU 27
No full textRecent studies reveal that uncertainty is a problem for the profitability of companies in various sectors. The purpose of this study was to investigate the impact of uncertainty on the profitability of textile companies in the EU 27. A number of models were performed using the random effects estimator. The results indicate that the uncertainty variable WUI negatively and significantly affects the profitability of the textile industry in all models. In addition, the results show that while equity to total assets and cash flow to operating revenue have a positive effect, capital intensity and operating in Eastern Europe have a negative effect on profitability. Also, size, current ratio, operating revenue to stocks and inflation do not seem to have a significant impact on profitability
Comparative performance analysis of metaheuristic search algorithms in parameter extraction for various solar cell models
No full textIn today's technology, solar energy continues to be one of the leading renewable energy sources in electricity production methods due to its abundance on the Earth's surface and its non-polluting nature. In solar photovoltaic (PV) systems, it is relatively easy to produce electricity from the sun, and their efficiency can be enhanced by accurately estimating the electrical parameters of solar cells. From this point of view, this paper has focused on solar cell design to improve the performance of solar PV systems. To achieve this target, fitness-distance balance-based stochastic fractal search (FDB-SFS), particle swarm optimization (PSO), student psychology-based optimization (SPBO), and adaptive guided differential evolution (AGDE) algorithms are employed. The experimental analysis is performed on single-diode solar cell, double-diode solar cell, and three PV modules. Considering the experimental results, it is observed that the best estimation accuracy is reached by the FDB-SFS algorithm. Accordingly, root mean square error (RMSE) values between measured and estimated data were calculated to be 9.86E-04 for the single-diode solar cell model, 9.84E-04 for the double-diode solar cell model, 2.42E-03 for the Photowatt-PWP201 module, 1.72E-03 for STM6–40/36 module, and 1.67E-02 for STP6–120/36 module. Consequently, the present paper reports that FDB-SFS is an efficient and powerful method for parameter extraction of solar photovoltaic models. © 202
A new numerical algorithm based on Quintic B-Spline and adaptive time integrator for Cou-pled Burger's equation
No full textIn this article, the coupled Burger's equation which is one of the known systems of the nonlinear parabolic partial differential equations is studied. The method presented here is based on a combination of the quintic B-spline and a high order time integration scheme known as adaptive Runge-Kutta method. First of all, the application of the new algorithm on the coupled Burger's equation is presented. Then, the convergence of the algorithm is studied in a theorem. Finally, to test the efficiency of the new method, coupled Burger's equations in literature are studied. We observed that the presented method has better accuracy and efficiency compared to the other methods in the literature
Propagation behavior in rectangular metallic waveguide periodically loaded with single negative metamaterial slabs
No full textThis paper focused on propagation characteristics of a single mode supporting waveguide enclosed by metallic sidewalls periodically loaded with lossless single negative (SNG) metamaterial slabs along axial direction. The gap between two successive SNG slabs is filled with a double positive (DPS) material. For the analysis, the periodic structure is assumed having symmetric unit cell (UC) and simplified as a two-port network which is one-half of the symmetric UC. Scattering parameters (S-parameters) are defined by even/odd mode analysis of the symmetric UC, and then the total S-parameters are calculated by solving the cascade connection of N unit cells. Eigenvalue equations are also obtained to explicit the solutions of band edge and pass/stopband diagrams in the microwave regime. Since a SNG can be either epsilon-negative (ENG) or mu-negative (MNG), S-parameters and dispersion behavior are illustrated with numerical examples and discussed for each periodic structure constructed with ENG or MNG slabs
Classification of Resampled Pediatric Epilepsy EEG Data Using Artificial Neural Networks with Discrete Fourier Transforms
No full textEpilepsy is a neurological disorder commonly observed in children. Currently, electroencephalography (EEG) is widely used as the most important diagnostic method for epilepsy in medical practice. The diagnosis of epilepsy in pediatric patients is challenging due to their high level of activity and incomplete brain development. In this study, data sampled at 256 Hz were obtained from patients between the ages of 7-12, collected by Boston Children's Hospital. First, the image intervals that contain seizure waves were identified in the datasets, and the discrete-time Fourier transform (DFT) was applied. The amplitude-frequency features of the frequency spectrum in seizure and nonseizure states were obtained, and patients were classified for seizure detection using a multilayer perceptron (MLP) based on an artificial neural network (ANN) architecture. In the next step, the EEG signals were resampled at low frequencies, and the same analyses were repeated to minimise the disadvantages of limiting factors such as storage space and processing power, resulting in reduced storage space usage and more efficient performance
The effect of burnout levels of cabin crew on their crew resource management skills
No full textLisansüstü Eğitim Enstitüsü, İşletme Ana Bilim DalıTükenmişlik insanlarla yakın ilişkiler içerisinde olunan meslek gruplarında daha sık görülen, hem birey hem de örgüt açısından çok ciddi sonuçları olan psikolojik bir rahatsızlıktır. Bu çalışmada hava yolu taşımacılığında emniyete ve güvenliğe dair önemli görev ve sorumlulukları bulunan kabin ekiplerinin tükenmişlik düzeyleri ile ekip kaynak yönetimi becerileri arasındaki ilişkinin tespit edilmesi amaçlanmıştır. Verilerin elde edilmesi amacıyla Maslach Tükenmişlik Ölçeği ve Kabin Ekip Kaynak Yönetimi Ölçeği kullanılmıştır. Çalışmaya Türkiye'de faaliyet gösteren hava yolu işletmelerinde çalışan toplam 300 kabin ekibi katılmıştır.Burnout is a psychological disorder that is more common in occupational groups with close relationships with people and has very serious consequences for both the individual and the organization. In this study, it is aimed to determine the relationship between the burnout levels and crew resource management skills of cabin crews, who have important duties and responsibilities regarding safety and security in air transportation. Maslach Burnout Scale and Cabin Crew Resource Management Scale were used to obtain data. A total of 300 cabin crew working in airline companies operating in Turkey participated in the study
Energy and exergy analysis of a geothermal energy sourced hot-air drying system
No full textA geothermal energy-sourced drying system was tested for the thin-layer drying process of tomato slices at air temperatures of 40 degrees C, 50 degrees C and 60? and velocities of 0.5 m/s and 1.5 m/s to investigate system performance in terms of the first and second laws of thermodynamics. The energy and the exergy efficiency of the system were found to be 6.6% and 22.31%. The energy utilisation and energy utilisation ratio were calculated in the range of 1.271 kW-5.102 kW and 9.644%-39.56%, respectively. The exergy destruction, exergy efficiency and improvement potential of the drying chamber varied between 0.0198 kW-0.2621 kW, 59.74%-81.95% and 0.00486 kW-0.07396 kW, respectively
CROSS CORRELATIONS BETWEEN MSCI EMERGING MARKETS INDICES AND US STOCK MARKET INDEX: EVIDENCE FROM MODWT
No full textMSCI Emerging Market Indices are developed for international investors to evaluate investment opportunities in developing countries and provide the investor with an opportunity for foresight. Due to the rapid globalization and contagion effects in financial markets, studies on MSCI Emerging Market Indices have attracted great interest in recent years. This study aims to investigate the long-memory characteristics of emerging market volatility and to show the existence of cross-correlations between Emerging Markets and the US stock market. For this purpose, Maximum Overlapping Discrete Wavelet Transform (MODWT), which is widely used in estimations in the field of finance, has been applied. MODWT, which can be used with all the features in the time series, is used in all scale dimensions. In addition, MODWT enables to produce asymptotically more efficient wavelet variance estimators. In the study, MSCI indices of seven emerging markets are used by considering the period between 2 May 2014 and 25 October 2018. The findings show that volatility in all emerging markets is stable and short-memory. There is also evidence of high and time-bound correlations between the US and Emerging Markets