This paper introduces the concept of
entropic value-at-risk
(EVaR), a new coherent risk measure that corresponds to the tightest possible upper bound obtained from the Chernoff inequality for the
...value-at-risk
(VaR) as well as the
conditional value-at-risk
(CVaR). We show that a broad class of stochastic optimization problems that are computationally intractable with the CVaR is efficiently solvable when the EVaR is incorporated. We also prove that if two distributions have the same EVaR at all confidence levels, then they are identical at all points. The dual representation of the EVaR is closely related to the Kullback-Leibler divergence, also known as the relative entropy. Inspired by this dual representation, we define a large class of coherent risk measures, called
g-entropic
risk measures. The new class includes both the CVaR and the EVaR.
•Energy, exergy, economic, advanced/extended exergy analyses for wind turbines.•Case study of advanced exergy analysis in Tehran and Manjil.•Case study of extended exergy analysis in Tehran and ...Manjil.
Energy, exergy, economic, advanced exergy, and extended exergy analyses are reported of a Bergey Excel-S wind turbine with nominal power of 10 kW in two cities: Tehran (medium wind potential) and Manjil (high wind potential). The results show that the energy efficiency of the wind turbine is higher in Manjil (3.33%) than Tehran (1.08%). The exergy efficiency in these areas is lower. This means that the exergy efficiency in Manjil is 10.8% but in Tehran is 6.43%. The cost of electricity generated by the wind turbine in Tehran is 0.23US$kWh. This cost is reduced to 0.73US$kWh in Manjil. The advanced exergy analysis demonstrates that the avoidable exergy destruction percentage of the wind turbine increases with wind speed. The extended exergy analysis shows that, in windy areas, the highest exergy percentage is exhibited by the system’s input and output exergy flows and power production (88.7%), while, in areas with medium wind speed potential, the exergy is equal to is the equivalent extended exergy content of the influx of capital cost (58.9%).
Metal-oxide-semiconductor (MOS) structures are essential for a wide range of semiconductor devices. This study reviews the development of MOS Schottky diode, which offers enhanced performance when ...compared with conventional metal-semiconductor Schottky diode structures because of the presence of the oxide layer. This layer increases Schottky barrier heights and reduced leakage currents. It also compared the MOS and metal-semiconductor structures. Recent advances in the development of MOS Schottky diodes are then discussed, with a focus on aspects such as insulating materials development, doping effects, and manufacturing technologies, along with potential device applications ranging from hydrogen gas sensors to photodetectors. Device structures, including oxide semiconductor thin film-based devices, p-type and n-type oxide semiconductor materials, and the optical and electrical properties of these materials are then discussed with a view toward optoelectronic applications. Finally, potential future development directions are outlined, including the use of thin-film nanostructures and high-k dielectric materials, and the application of graphene as a Schottky barrier material.
Hydrogen, as a clean fuel, can provide all the requirements and characteristics of a clean and reliable energy carrier in the long term as a suitable alternative to fossil fuels. In this paper, a ...power generation system using hydrogen storage has been investigated. For this purpose, 64 photovoltaic modules with area of 2.16 m2 for each module and 329 PW and 5.5 kW PEM fuel cell and electrolyzer were used in this hybrid system. The day product of hydrogen day has been calculated as 158 kg. The system has been subjected to exergy analysis and, hence the efficiency and destruction of exergy components have been calculated. The annual average electrical production by photovoltaic system is 4850 W. The average annual exergy efficiency of each component including compressor, electrolyzer, fuel cell, and photovoltaic cell has been calculated as 75.9%, 11.2%, 32.8%, and 10.8%, respectively. The energy and exergy efficiencies of the system have been calculated for different days and its average annual values have been obtained 20.4% and 21.8%, respectively. Cost of electricity is 0.127 $/kWh, which is compatible with solar thermal and wind turbine offshore electricity costs. Finally, according to the advanced exergy analysis in all equipment’s except the photovoltaic cell, the highest exergy destruction has been related to exogenous unavoidable.
•Feasibility study of hybrid system for power and hydrogen production.•Energy, exergy, advanced exergy and economic analyses are presented.•Electricity cost is 0.127 $/kWh.•The highest hydrogen production is obtained 1420 kg/month in June.•The highest exergetic efficiency are calculated as 8.2% in June.
The nearby open cluster NGC 752 presents a rare opportunity to study stellar properties at ages >1 Gyr. However, constructing a membership catalog for it is challenging; most surveys have been ...limited to identifying its giants and dwarf members earlier than mid-K. We supplement past membership catalogs with candidates selected with updated photometric and proper-motion criteria, generating a list of 258 members, a >50% increase over previous catalogs. Using a Bayesian framework to fit MESA Isochrones & Stellar Tracks evolutionary models to literature photometry and the Tycho-Gaia Astrometric Solution data available for 59 cluster members, we infer the age of and distance to NGC 752: 1.34 0.06 Gyr and pc. We also report the results of our optical monitoring of the cluster using the Palomar Transient Factory. We obtain rotation periods for 12 K and M cluster members, the first periods measured for such low-mass stars with a well-constrained age >1 Gyr. We compare these new periods to data from the younger clusters Praesepe and NGC 6811, and to a theoretical model for angular momentum loss, to examine stellar spin-down for low-mass stars over their first 1.3 Gyr. While on average NGC 752 stars are rotating more slowly than their younger counterparts, the difference is not significant. Finally, we use our spectroscopic observations to measure H for cluster stars, finding that members earlier than M2 are magnetically inactive, as expected at this age. Forthcoming Gaia data should solidify and extend the membership of NGC 752 to lower masses, thereby increasing its importance for studies of low-mass stars.
•Viscosity regularization is assessed in predicting transient flows.•Natural convection of Bingham fluid in a square cavity is studied.•Common error evaluation methods significantly overestimate the ...accuracy of results.•Complete loss of accuracy is observed in the proximity of the motionless state.•A counterexample is presented to disprove convergence of yield surfaces.
We present an assessment of viscosity regularization (VR) in predicting transient flows of viscoplastic fluids (VPF). Although VR has been the most popular approach for computational studies of VPF in the last decade, the understanding of its effects on the predicted flow behaviour has remained largely qualitative. To reveal the effects of VR, we present a systematic quantitative comparison of the solutions of the regularized and exact (i.e. not regularized) problems. We consider free convection of a Bingham fluid in a two-dimensional square cavity with differentially heated sidewalls. We use bi-viscosity as a representative VR model and use augmented Lagrangian (AL) method to solve the exact problem. We show that common methods of assessing the solution error can hugely overestimate the accuracy of the results of VR. In particular, complete loss of accuracy is observed when flow conditions approach the motionless state, rendering the lower computational cost and algorithmic simplicity of VR irrelevant. Furthermore, we quantify the accuracy of bi-viscosity regularization in predicting the unyielded regions. This analysis disproves by counterexample that using yield stress contours produces convergent numerical estimates of the unyielded regions.
Intravenous contrast agent-enhanced magnetic resonance imaging of the endolymphatic space (ELS) of the inner ear permits direct, in-vivo, non-invasive visualization of labyrinthine structures and ...thus verification of endolymphatic hydrops (ELH). However, current volumetric assessment approaches lack normalization. The aim of this study was to develop a probabilistic atlas of the inner ear’s bony labyrinth as a first step towards an automated and reproducible volume-based quantification of the ELS. The study included three different datasets: a source dataset (D1) to build the probabilistic atlas and two testing sets (D2, D3). D1 included 24 right-handed patients (12 females; mean age 51.5 ± 3.9 years) and D2 5 patients (3 female; mean age 48.8 ± 5.01 years) with vestibular migraine without ELH or any measurable vestibular deficits. D3 consisted of five patients (one female; mean age 46 ± 5.2 years) suffering from unilateral Menière’s disease and ELH. Data processing comprised three steps: preprocessing using an affine and deformable fusion registration pipeline, computation of an atlas for the left and right inner ear using a label-assisted approach, and validation of the atlas based on localizing and segmenting previously unseen ears. The three-dimensional probabilistic atlas of the inner ear’s bony labyrinth consisted of the internal acoustic meatus and inner ears (including cochlea, otoliths, and semicircular canals) for both sides separately. The analyses showed a high level of agreement between the atlas-based segmentation and the manual gold standard with an overlap of 89% for the right ear and 86% for the left ear (measured by dice scores). This probabilistic in vivo atlas of the human inner ear’s bony labyrinth and thus of the inner ear’s total fluid space for both ears represents a necessary step towards a normalized, easily reproducible and reliable volumetric quantification of the perilymphatic and endolymphatic space in view of MR volumetric assessment of ELH. The proposed atlas lays the groundwork for state-of-the-art approaches (e.g., deep learning) and will be provided to the scientific community.
The conventional digital hardware computational blocks with different structures are designed to compute the precise results of the assigned calculations. The main contribution of our proposed ...Bio-inspired Imprecise Computational blocks (BICs) is that they are designed to provide an applicable estimation of the result instead of its precise value at a lower cost. These novel structures are more efficient in terms of area, speed, and power consumption with respect to their precise rivals. Complete descriptions of sample BIC adder and multiplier structures as well as their error behaviors and synthesis results are introduced in this paper. It is then shown that these BIC structures can be exploited to efficiently implement a three-layer face recognition neural network and the hardware defuzzification block of a fuzzy processor.
► In this study we present a binary particle swarm optimization (BPSO) for the optimal placement of phasor measurement units (PMUs). ► Flow measurements and injection measurements are considered as ...conventional measurements. ► This study shows the Effect of maximization measurement redundancy on the test system. ► We conclude that the whole system can be observable with installing PMUs on less than 25% of system buses.
This study presents a binary particle swarm optimization (BPSO) based methodology for the optimal placement of phasor measurement units (PMUs) when using a mixed measurement set. The optimal PMU placement problem is formulated to minimize the number of PMUs installation subject to full network observability and to maximize the measurement redundancy at the power system buses. In order to ensure full network observability in an electric power network the topology-based algorithm is used and Several factors considered; such as the available data from existing conventional measurements, the number and location of zero injection buses, the number and location of installed PMUs and of course, the system topology. The efficiency of the proposed method is verified by the simulation results of IEEE 14-bus, 30-bus, 57-bus-118 bus systems, respectively. The results show that the whole system can be observable with installing PMUs on less than 25% of system buses. For verification of our proposed method, the results are compared with some newly reported methods which show the method as a novel solution to obtain redundant measurement system with the least number of phasor measurement units.
The availability of reliable electricity and heat sources for community guarantees a better living environment in terms of education, healthcare and economy. Two main parameters should be considered ...in heat production which are the cost of this production and the performance of the devices used to produce this heat. In this work, a thermodynamic analysis based on energy and exergy analyses as well as economic analysis are presented to analyze the performance of parabolic trough solar collector (PTC). A multiobjective swarm optimization (MOPSO) technique is used to find out the maximum exergy efficiency and the minimum heat production cost of PTC. The optimum results show that the exergy efficiency, energy efficiency and heat cost are 29.22%, 35.55% and 0.0142 $/kWh. The effect of PTC geometrical parameters such as length, focal length, width and internal absorber diameter on the performance of PTC and heat production cost are investigated. Energy efficiencies of the system at different times during the day are calculated and they are in good agreement with the experimental results available in literature. The proposed system of PTC is located in Tehran, Iran.
•Energy, exergy and economic analyses in optimization of PTC.•Optimization of a PTC with MOPSO algorithm.•Selection the best geometric specification and working fluid mass flow rate.•Sensitivity analysis of optimized parameters.•Optimization of a PTC with multi-objective shuffled frog-leaping algorithm.
PDF
