bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties of Spark Plasma Sintering-Processed Pure Ti and Ti-6Al-4V Alloys: A Comparative Study between Harmonic and Non-Harmonic Microstructures
Authors: Sadat Tarik , Hayashi Kyohei , Haugou Gregory , Morvan Herve , Markiewicz Eric , Dubar Laurent , Bigerelle Maxence , Ameyama Kei , Dirras Guy
Published: May 2021

Microstructure characteristics and compressive property relationships of so-called harmonic (composed by fine and coarse grains) and conventional pure titanium (Ti) and Ti-6Al-4V alloy processed by powder metallurgy route are presented in the present work. Electron backscatter diffraction (EBSD) analysis was performed to characterize the as-processed microstructures. The harmonicity structure of selected samples is described, and relevant EBSD maps are presented. The bulk samples’ hardness is reported, along with compressive responses at quasi-static and intermediate strain rates, ranging from 0.005 s−1 to 16 s−1. The strain rate sensitivity of these metallic samples is discussed, and the benefits in terms of mechanical properties of the harmonic microstructures compared with the non-harmonic conventional ones are highlighted. Finally, a modified Johnson–Cook model was shown to predict fairly the experimental results.
Synthesis, Mass Spectroscopy Detection, and Density Functional Theory Investigations of the Gd Endohedral Complexes of C82 Fullerenols
Authors: Shakirova Anastasia A. , Tomilin Felix N. , Pomogaev Vladimir A. , Vnukova Natalia G. , Churilov Grigory N. , Kudryasheva Nadezhda S. , Tchaikovskaya Olga N. , Ovchinnikov Sergey G. , Avramov Pavel V.
Published: May 2021

Gd endohedral complexes of C82 fullerenols were synthesized and mass spectrometry analysis of their composition was carried out. It was established that the synthesis yields a series of fullerenols Gd@C82Ox(OH)y (x = 0, 3; y = 8, 16, 24, 36, 44). The atomic and electronic structure and properties of the synthesized fullerenols were investigated using the density functional theory calculations. It was shown that the presence of endohedral gadolinium increases the reactivity of fullerenols. It is proposed that the high-spin endohedral fullerenols are promising candidates for application in magnetic resonance imaging.
Synthesis, Crystal Structure, DFT Theoretical Calculationand Physico-Chemical Characterization of a New Complex Material (C6H8Cl2N2)2[Cd3Cl10]·6H2O
Authors: Hermi Sabrine , Althobaiti Mohammed G. , Alotaibi Abdullah A. , Almarri Abdulhadi H. , Fujita Wataru , Lefebvre Frédéric , Ben Nasr Cherif , Mrad Mohamed Habib
Published: May 2021

The chemical preparation, crystal structure, Hirshfeld surface analysis and spectroscopic characterization of the novel cadmium (II) 2,5-dichloro-p-phenylendiaminium decachlorotricadmate(II) hexahydrate complex, (C6H8Cl2N2)2[Cd3Cl10]·6H2O, has been reported. The atomic arrangement can be described as built up by an anionic framework, formed by edge-sharing [CdCl6]2− octahedra in linear polymeric chains spreading along the a-axis, while the organic cations surround these latters. The inspection of the Hirshfeld surface analysis helps to discuss the strength of hydrogen bonds and to quantify the inter-contacts, which reveal that H…Cl/Cl…H (38.9%), H…H (13.9%), and Cd…Cl/Cl…Cd (12.4%) are the main interactions that govern the crystal packing of the studied structure. SEM/EDXwas carried out and the powder XRD confirmed the good crystallinity of the material. FT-IR and the DFT calculation reveal the good correlation between the experimental and the theoretical wavenumbers. The HOMO-LUMO energy gap was used to predict the electric conductivity of the compound. Finally, the thermal TGA/DTA analysis shows stability until 380 K.
The Subterranean Fauna of Križna Jama, Slovenia
Authors: Polak Slavko , Pipan Tanja
Published: May 2021

The karstic cave Križna jama in the South Western part of Slovenia is one of the largest, well known and most beautiful Slovene water caves. The cave consists of more than 8 km of corridors with impressive halls, colossal dripstone formations, a subterranean river and numerous lakes. Considering the subterranean fauna, Križna jama has been identified amongst the richest caves in the world. So far, 60 troglobionts, the obligate subterranean species among them 32 aquatic and 28 terrestrial taxa have been recorded and documented. Križna jama has scientific importance, as well as ten subterranean taxa, which have been described based on specimens from this cave. Despite Križna jama is relatively well-studied, new recent unexpected findings are promising. Thus, further discoveries of specialized subterranean species in the cave are expected.
Peer Mentoring as a Tool for Developing Soft Skills in Clinical Practice: A 3-Year Study
Authors: Lluch Antonio M. , Lluch Clàudia , Arregui María , Jiménez Esther , Giner-Tarrida Luis
Published: May 2021

Education currently focuses on improving academic knowledge and clinical skills, but it is also important for students to develop personal and interpersonal skills from the start of their clinical practice. The aim was to evaluate the effect of peer mentoring in third-year students and to gauge the evolution of non-technical skills (NTS) acquisition up to the fifth year. The study groups were selected between September 2015 and May 2018, based on the NTS training they had or had not received: (1) fifth-year students with no training (G1); (2) third-year students mentored in NTS (G2a); and (3) a small group of fifth-year students who became mentors (G2b). A total of 276 students who took part in this study were assessed using a 114-item self-evaluation questionnaire. Data were collected from seven surveys conducted between September 2015 and May 2018, and statistical analysis was performed using one-way ANOVA and Fisher’s post-hoc test. G2a improved their non-technical skill acquisition over three years of clinical training up to their fifth year. This group and G2b showed statistically significant differences compared to non-mentored students (G1). Peer mentoring at the beginning of clinical practice is a valid option for training students in non-technical skills.
DRL-Assisted Resource Allocation for NOMA-MEC Offloading with Hybrid SIC
Authors: Li Haodong , Fang Fang , Ding Zhiguo
Published: May 2021

Multi-access edge computing (MEC) and non-orthogonal multiple access (NOMA) are regarded as promising technologies to improve the computation capability and offloading efficiency of mobile devices in the sixth-generation (6G) mobile system. This paper mainly focused on the hybrid NOMA-MEC system, where multiple users were first grouped into pairs, and users in each pair offloaded their tasks simultaneously by NOMA, then a dedicated time duration was scheduled to the more delay-tolerant user for uploading the remaining data by orthogonal multiple access (OMA). For the conventional NOMA uplink transmission, successive interference cancellation (SIC) was applied to decode the superposed signals successively according to the channel state information (CSI) or the quality of service (QoS) requirement. In this work, we integrated the hybrid SIC scheme, which dynamically adapts the SIC decoding order among all NOMA groups. To solve the user grouping problem, a deep reinforcement learning (DRL)-based algorithm was proposed to obtain a close-to-optimal user grouping policy. Moreover, we optimally minimized the offloading energy consumption by obtaining the closed-form solution to the resource allocation problem. Simulation results showed that the proposed algorithm converged fast, and the NOMA-MEC scheme outperformed the existing orthogonal multiple access (OMA) scheme.
Functional Interdependence in Coupled Dissipative Structures: Physical Foundations of Biological Coordination
Authors: De Bari Benjamin , Paxton Alexandra , Kondepudi Dilip K. , Kay Bruce A. , Dixon James A.
Published: May 2021

Coordination within and between organisms is one of the most complex abilities of living systems, requiring the concerted regulation of many physiological constituents, and this complexity can be particularly difficult to explain by appealing to physics. A valuable framework for understanding biological coordination is the coordinative structure, a self-organized assembly of physiological elements that collectively performs a specific function. Coordinative structures are characterized by three properties: (1) multiple coupled components, (2) soft-assembly, and (3) functional organization. Coordinative structures have been hypothesized to be specific instantiations of dissipative structures, non-equilibrium, self-organized, physical systems exhibiting complex pattern formation in structure and behaviors. We pursued this hypothesis by testing for these three properties of coordinative structures in an electrically-driven dissipative structure. Our system demonstrates dynamic reorganization in response to functional perturbation, a behavior of coordinative structures called reciprocal compensation. Reciprocal compensation is corroborated by a dynamical systems model of the underlying physics. This coordinated activity of the system appears to derive from the system’s intrinsic end-directed behavior to maximize the rate of entropy production. The paper includes three primary components: (1) empirical data on emergent coordinated phenomena in a physical system, (2) computational simulations of this physical system, and (3) theoretical evaluation of the empirical and simulated results in the context of physics and the life sciences. This study reveals similarities between an electrically-driven dissipative structure that exhibits end-directed behavior and the goal-oriented behaviors of more complex living systems.
A Foreground-Aware Framework for Local Face Attribute Transfer
Authors: Fu Yuanbin , Ma Jiayi , Guo Xiaojie
Published: May 2021

In the context of social media, large amounts of headshot photos are taken everyday. Unfortunately, in addition to laborious editing and modification, creating a visually compelling photographic masterpiece for sharing requires advanced professional skills, which are difficult for ordinary Internet users. Though there are many algorithms automatically and globally transferring the style from one image to another, they fail to respect the semantics of the scene and are unable to allow users to merely transfer the attributes of one or two face organs in the foreground region leaving the background region unchanged. To overcome this problem, we developed a novel framework for semantically meaningful local face attribute transfer, which can flexibly transfer the local attribute of a face organ from the reference image to a semantically equivalent organ in the input image, while preserving the background. Our method involves warping the reference photo to match the shape, pose, location, and expression of the input image. The fusion of the warped reference image and input image is then taken as the initialized image for a neural style transfer algorithm. Our method achieves better performance in terms of inception score (3.81) and Fréchet inception distance (80.31), which is about 10% higher than those of competitors, indicating that our framework is capable of producing high-quality and photorealistic attribute transfer results. Both theoretical findings and experimental results are provided to demonstrate the efficacy of the proposed framework, reveal its superiority over other state-of-the-art alternatives.
Diffusion Model of a Non-Integer Order PIγ Controller with TCP/UDP Streams
Authors: Marek Dariusz , Domański Adam , Domańska Joanna , Szyguła Jakub , Czachórski Tadeusz , Klamka Jerzy
Published: May 2021

In this article, a way to employ the diffusion approximation to model interplay between TCP and UDP flows is presented. In order to control traffic congestion, an environment of IP routers applying AQM (Active Queue Management) algorithms has been introduced. Furthermore, the impact of the fractional controller PIγ and its parameters on the transport protocols is investigated. The controller has been elaborated in accordance with the control theory. The TCP and UDP flows are transmitted simultaneously and are mutually independent. Only the TCP is controlled by the AQM algorithm. Our diffusion model allows a single TCP or UDP flow to start or end at any time, which distinguishes it from those previously described in the literature.
A Quantum Walk Model for Idea Propagation in Social Network and Group Decision Making
Authors: Zhang Qizi , Busemeyer Jerome
Published: May 2021

We propose a quantum walk model to investigate the propagation of ideas in a network and the formation of agreement in group decision making. In more detail, we consider two different graphs describing the connections of agents in the network: the line graph and the ring graph. Our main interest is to deduce the dynamics for such propagation, and to investigate the influence of compliance of the agents and graph structure on the decision time and the final decision. The methodology is based on the use of control-U gates in quantum computing. The original state of the network is used as controller and its mirrored state is used as target. The state of the quantum walk is the tensor product of the original state and the mirror state. In this way, the proposed quantum walk model is able to describe asymmetric influence between agents.
Fractional Deng Entropy and Extropy and Some Applications
Authors: Kazemi Mohammad Reza , Tahmasebi Saeid , Buono Francesco , Longobardi Maria
Published: May 2021

Deng entropy and extropy are two measures useful in the Dempster–Shafer evidence theory (DST) to study uncertainty, following the idea that extropy is the dual concept of entropy. In this paper, we present their fractional versions named fractional Deng entropy and extropy and compare them to other measures in the framework of DST. Here, we study the maximum for both of them and give several examples. Finally, we analyze a problem of classification in pattern recognition in order to highlight the importance of these new measures.
Teachers’ Expectations and Perceptions of the Relevance of Professional Development MOOCs
Authors: Herranen Jaana Kristiina , Aksela Maija Katariina , Kaul Maya , Lehto Saara
Published: May 2021

Online professional-development courses such as massive open online courses (MOOCs) could bring relevant content to a wider base of teachers who might not otherwise have access to professional development. However, research on the relevance of such online courses is scarce. The main aim of this study is to investigate the relevance (individual, societal, and vocational) of MOOCs (mostly participatory cMOOCs) from the viewpoint of teachers now and in the future. We examined teachers’ expectations and perceptions of 10 courses before (N = 364) and after (N = 177) the courses, using an online questionnaire developed on the basis of relevance theory. According to the results, the studied teachers had positive expectations for the courses in terms of their usefulness for their prospective teaching (especially vocational relevance). Teachers’ expectations related to the usefulness of the course for the future (individual and vocational relevance) were most strongly met. Effort put into the course was connected to, for example, how the course improved the teachers’ interest. The results of this study indicate that MOOCs can serve as relevant courses for teachers’ professional development in science, mathematics, and technology education.
Leveraging Final Degree Projects for Open Source Software Contributions
Authors: Pereira Juanan
Published: May 2021

(1) Background: final year students of computer science engineering degrees must carry out a final degree project (FDP) in order to graduate. Students’ contributions to improve open source software (OSS) through FDPs can offer multiple benefits and challenges, both for the students, the instructors and for the project itself. This work reports on a practical experience developed by four students contributing to mature OSS projects during their FDPs, detailing how they addressed the multiple challenges involved, both from the students and teachers perspective. (2) Methods: we followed the work of four students contributing to two established OSS projects for two academic years and analyzed their work on GitHub and their responses to a survey. (3) Results: we obtained a set of specific recommendations for future practitioners and detailed a list of benefits achieved by steering FDP towards OSS contributions, for students, teachers and the OSS projects. (4) Conclusions: we find out that FDPs oriented towards enhancing OSS projects can introduce students into real-world, practical examples of software engineering principles, give them a boost in their confidence about their technical and communication skills and help them build a portfolio of contributions to daily used worldwide open source applications.
Metamaterial Impedance Matching Network for Ambient RF-Energy Harvesting Operating at 2.4 GHz and 5 GHz
Authors: Coskuner Ertugrul , Garcia-Garcia Joan J.
Published: May 2021

This paper points out the viability of the utilization of metamaterial transmission lines as a multifrequency impedance matching network, improving RF-Energy Harvesting systems operating around 2.4 GHz and 5 GHz. Metamaterial transmission lines introduce additional degrees of freedom in the transmission line design, providing the possibility to match the impedance in multiple bands. The impedance matching structure has been designed and optimized using ADS simulator to match the input impedance of a four-diode-bridge rectifier connected to an energy management system. The proposed Metamaterial Impedance Matching Network (MIMN) has been fabricated using standard PCB technologies and tested in a full operative ambient RF-Energy Harvesting System obtaining a DC output voltage of 1.8 V in a 6.8 mF supercapacitor.
An Experimental Study on Preparation of Reconstituted Tectonic Coal Samples: Optimization of Preparation Conditions
Authors: Geng Jishi , Cao Liwen , Zhong Congyu , Zhang Shuai
Published: May 2021

The uniquely soft and fragile nature of tectonic coal makes it difficult to obtain core samples suitable for laboratory experimentation. Preparation of reconstituted tectonic coal (RTC) samples generally adopts the secondary forming method. Reliable coal samples are needed to obtain credible permeability and mechanical parameters that can guide Coalbed Methane (CBM) extraction and improve mining safety. In this study, the compaction mechanism of coal particles is analyzed based on the Kawakita model, and optimal sample preparation conditions are systemically investigated, particularly particle size and particle size distribution, forming pressure, and moisture content. The density and P-wave velocity of coal samples were used to test whether the RTC samples were realistic. Finally, the mechanical properties and deformation characteristics of the RTC samples were determined. The results indicate that RTC samples prepared for laboratory testing of mechanical properties require (1) the original particle size of the tectonic coal to be retained as much as possible; (2) a forming pressure that compacts the sample similar to the original tectonic coal; and (3) an optimum moisture content.
Multi-Objective Optimization of HVAC Operation for Balancing Energy Use and Occupant Comfort in Educational Buildings
Authors: Franco Alessandro , Bartoli Carlo , Conti Paolo , Miserocchi Lorenzo , Testi Daniele
Published: May 2021

The paper provides a methodology for the optimal control of heating, ventilation, and air conditioning (HVAC) systems used in public buildings, with the purpose of obtaining high comfort and safety standards along with energy efficiency. The combination of the two concurrent objectives of minimizing energy use and guaranteeing high standards of occupant comfort is obtained by means of multi-objective optimization, in which a comfort model is combined along with a dynamic energy model of the building. The use of dynamic setpoints for the HVAC and the inclusion of comfort indicators represent a step forward, compared to the current design and operation procedures suggested by technical standards. The utilization of the proposed methodology is tested with reference to a case study, represented by an academic building used by the University of Pisa for educational purposes, whose extensive and variable occupancy can help to emphasize the importance of comfort in the operation of HVAC systems in different climatic conditions and with different occupancy profiles. We show how this optimization brings interesting results in terms of energy-saving (up to 30%), obtaining an increased comfort level (of more than 25%) compared to the operating conditions suggested by technical standards.
Thermo-Economic Analysis on Integrated CO2, Organic Rankine Cycles, and NaClO Plant Using Liquefied Natural Gas
Authors: Tjahjono Tri , Ehyaei Mehdi Ali , Ahmadi Abolfazl , Hoseinzadeh Siamak , Memon Saim
Published: May 2021

The thermal energy conversion of natural gas (NG) using appropriate configuration cycles represents one of the best nonrenewable energy resources because of its high heating value and low environmental effects. The natural gas can be converted to liquefied natural gas (LNG), via the liquefaction process, which is used as a heat source and sink in various multigeneration cycles. In this paper, a new configuration cycle is proposed using LNG as a heat source and heat sink. This new proposed cycle includes the CO2 cycle, the organic Rankine cycle (ORC), a heater, a cooler, an NaClO plant, and reverse osmosis. This cycle generates electrical power, heating and cooling energy, potable water (PW), hydrogen, and salt all at the same time. For this purpose, one computer program is provided in an engineering equation solver for energy, exergy, and thermo-economic analyses. The results for each subsystem are validated by previous researches in this field. This system produces 10.53 GWh electrical energy, 276.4 GWh cooling energy, 1783 GWh heating energy, 17,280 m3 potable water, 739.56 tons of hydrogen, and 383.78 tons of salt in a year. The proposed system energy efficiency is 54.3%, while the exergy efficiency is equal to 13.1%. The economic evaluation showed that the payback period, the simple payback period, the net present value, and internal rate of return are equal to 7.9 years, 6.9 years, 908.9 million USD, and 0.138, respectively.
Using Thermal Energy Storage to Relieve Wind Generation Curtailment in an Island Microgrid
Authors: Luo Huanhuan , Ge Weichun , Sun Jingzhuo , Jiang Quanyuan , Gong Yuzhong
Published: May 2021

The uncertainty and intermittency of the available wind resource in nature would potentially cause wind generation curtailment when the flexibility of the integrated power grid is limited, especially in small-scale microgrids for islands. In this paper, an optimal configuration method is proposed to use thermal energy storage (TES) to relieve wind generation curtailment in an island microgrid. The thermal network is modeled along with the electrical network to utilize its regulation capability, while TES is introduced as an additional flexibility resource. The detailed cost models of combined heat and power (CHP) units and TES are presented to realize the objective of minimizing the overall operating cost. The performance of TES in improving wind power utilization is firstly validated by using an electrical boiler (EB) as a benchmark and further analyzed under different scenarios considering the growths of wind power capacity, electrical load, and heat load. The effectiveness of the proposed method is validated using real-world data obtained from the practical island microgrid.
Reinforced Demand Side Management for Educational Institution with Incorporation of User’s Comfort
Authors: Tamilarasu Karthick , Sathiasamuel Charles Raja , Joseph Jeslin Drusila Nesamalar , Madurai Elavarasan Rajvikram , Mihet-Popa Lucian
Published: May 2021

Soaring energy demand and the establishment of various trends in the energy market have paved the way for developing demand-side management (DSM) from the consumer side. This paper proposes a reinforced DSM (RDSM) approach that uses an enhanced binary gray wolf optimization algorithm (EBGWO) that benefits the consumer premises with load scheduling, and peak demand reduction. To date, DSM research has been carried out for residential, commercial and industrial loads, whereas DSM approaches for educational loads have been less studied. The institution load also consumes much utility energy during peak hours, making institutional consumers pay a high amount of cost for energy consumption during peak hours. The proposed objective is to reduce the total electricity cost and to improve the operating efficiency of the entire load profile at an educational institution. The proposed architecture integrates the solar PV (SPV) generation that supplies the user-comfort loads during peak operating hours. User comfort is determined with a metric termed the user comfort index (UCI). The novelty of the proposed work is highlighted by modeling a separate class of loads for temperature-controlled air conditioners (AC), supplying the user comfort loads from SPV generation and determining user comfort with percentage UCI. The improved transfer function used in the proposed EBGWO algorithm performs faster in optimizing nonlinear objective problems. The electricity price in the peak hours is high compared to the off-peak hours. The proposed EBGWO algorithm shift and schedules the loads from the peak hours to off-peak hours, and incorporating SPV in satisfying the user comfort loads aids in reducing the power consumption from the utility during peak hours. Thus, the proposed EBGWO algorithm greatly helps the consumer side decrease the peak-to-average ratio (PAR), improve user comfort significantly, reduce the peak demand, and save the institution’s electricity cost by USD 653.046.
Long-Run Dynamics of Gas Emissions, Economic Growth, and Low-Carbon Energy in the European Union: The Fostering Effect of FDI and Trade
Authors: Horobet Alexandra , Popovici Oana Cristina , Zlatea Emanuela , Belascu Lucian , Dumitrescu Dan Gabriel , Curea Stefania Cristina
Published: May 2021

The European Union’s environmental goal by 2050 is to become the first climate-neutral continent in the world. This means specific efforts for diversifying the energy mix and investing in low-carbon energy. Our study investigates the nexus among carbon emissions, energy consumption and mix, and economic growth in a modified framework that includes the contribution of inward foreign direct investments and international trade to lowering air pollution. We have used a two-step approach to explore in more detail the links between these variables in 24 EU countries over the period 1995–2018, followed by a panel VECM analysis. Our results indicate that there is a unidirectional link between economic growth and CO2 emissions, which should imply a decoupling of environmental improvement measures from the pace of economic growth. We also find bidirectional causal relationships between low-carbon energy shares in consumption and CO2 emissions, as well as between low-carbon energy share in consumption and GDP per capita, which confirms both pollution haven and the halo effect hypotheses for FDI on gas emissions. However, in the long term, FDI, exports, and imports have positively impacted the reduction in CO2 emissions; therefore, stronger EU investment and trade integration should be promoted to improve the quality of the environment.
Long-Range Integrated Development Analysis: The Cuban Isla de la Juventud Study Case
Authors: Alberto Alvarez Ernesto , Korkeakoski Mika , Santos Fuentefría Ariel , Lourdes Filgueiras Sainz de Rozas Miriam , Arcila Padura Ramsés , Luukkanen Jyrki
Published: May 2021

The use of renewable energy sources (RES) has increased exponentially worldwide, as an alternative to the indiscriminate use of fossil fuels and to mitigate their effects on the environment. Cuba is not lagging behind in this development since the government’s plan until 2030 includes the contribution of renewable sources as a fundamental component in the national energy mix. This paper models possible scenarios based on 2019 statistics for achieving a 25% and 100% penetration of renewable sources by 2030 in the Isla de la Juventud’s (an island south of the main island of Cuba) electrical power system (EPS). This modeling is carried out utilizing and open source Excel-based accounting framework Long-range Integrated Development Analysis (LINDA). For this purpose, international and national trends in the use and development of renewable energy sources and the influence of the characteristics of each renewable source (wind, solar, biodiesel, battery storage) were analyzed. The analysis of Isla de la Juventud’s electrical power system was based on the characteristics of its energy mix, the possibilities of renewable energy penetration and the current and future energy demand by sector. Based on the analysis, two probable scenarios were modeled with LINDA model: a 25% renewable energy-based scenario (RENES) and a 100% renewables-based scenario (MAXRES). Results from RENES and MAXRES scenarios show high penetration of renewable energy sources in electricity generation is theoretically possible with the abundance of renewable energy resources, and thus it is possible for Cuba to move towards 100% renewable energy mix. However, the choices regarding the best fit energy mix need to be carefully analyzed in order to design a least cost system that answers the needs of the future demand.
Cost-Effective Increase of Photovoltaic Electricity Feed-In on Congested Transmission Lines: A Case Study of The Netherlands
Authors: Braat Maaike , Tsafarakis Odysseas , Lampropoulos Ioannis , Besseling Joris , van Sark Wilfried G. J. H. M.
Published: May 2021

In many areas in the world, the high voltage (HV) electricity grid is saturated, which makes it difficult to accommodate additional solar photovoltaic (PV) systems connection requests. In this paper, different scenarios to increase the installed PV capacity in a saturated grid are assessed on the basis of the net present value (NPV). The developed scenarios compare an increase of grid capacity, PV system azimuth variation, curtailment, and battery storage. For each scenario the net present value (NPV) is assessed using an optimization model as a function of the overbuild capacity factor, which is defined as the relative amount of PV capacity added beyond the available capacity. The scenarios are applied on a case study of the Netherlands, and the analysis shows that, by optimising curtailment, a PV system’s capacity can be increased to 120% overbuild capacity. For larger overbuild capacity investments in the electricity-grid are preferred when these costs are taken into account. However, the optimum NPV lies at 40% overbuild, thus the societal and NPV optimum are not always aligned. Furthermore, the use of a battery system as an alternative to an infrastructure upgrade was not found to be a cost-effective solution. Thus, applying curtailment could be cost-efficient to a certain extent to allow for additional PV capacity to be connected to a saturated grid. Furthermore, the inverter size compared to the installed PV capacity should be significantly reduced. For a connection request that exceeds 120% overbuild increasing network capacity should be considered.
Structural, Optical, and Magnetic Properties of Cobalt-Doped ZnAl2O4 Nanosheets Prepared by Hydrothermal Synthesis
Authors: Gurugubelli Thirumala Rao , Babu Bathula , Yoo Kisoo
Published: May 2021

Nanomaterials with collective optical and magnetic properties are called smart or functional materials and have promising applications in many fields of science and technology. Undoped and Co-doped ZnAl2O4 were prepared using a co-precipitation-assisted hydrothermal method. A systematic investigation was carried out to understand the effects of the Co concentration on the crystalline phase, morphology, and optical and magnetic properties of Co-doped ZnAl2O4. X-ray diffraction confirmed the cubic spinel structure with the Fd3m space group, and there was no impurity phase. X-ray photoelectron spectroscopy of Co-doped ZnAl2O4 confirmed the existence of Zn, Al and O, and the Co in the optimized sample of ZAO-Co-3 confirmed the oxidation state of cobalt as Co2+. Transmission electron microscopy of pure and Co-doped ZnAl2O4 revealed micro-hexagons and nanosheets, respectively. The optical absorption results showed that the bandgap of ZnAl2O4 decreased with increasing Co concentration. The hysteresis loop of Co-doped ZnAl2O4 revealed clear ferromagnetic behavior at room temperature. The as-prepared materials are suitable for energy storage applications, such as in supercapacitors and fuel cells. This work aims to focus on the effect of cobalt ions in different concentrations on structural, optical and magnetic properties.
Open Dual Cycle with Composition Change and Limited Pressure for Prediction of Miller Engines Performance and Its Turbine Temperature
Authors: Lecuona Antonio , Nogueira José I. , Famiglietti Antonio
Published: May 2021

An improved thermodynamic open Dual cycle is proposed to simulate the working of internal combustion engines. It covers both spark ignition and Diesel types through a sequential heat release. This study proposes a procedure that includes (i) the composition change caused by internal combustion, (ii) the temperature excursions, (iii) the combustion efficiency, (iv) heat and pressure losses, and (v) the intake valve timing, following well-established methodologies. The result leads to simple analytical expressions, valid for portable models, optimization studies, engine transformations, and teaching. The proposed simplified model also provides the working gas properties and the amount of trapped mass in the cylinder resulting from the exhaust and intake processes. This allows us to yield explicit equations for cycle work and efficiency, as well as exhaust temperature for turbocharging. The model covers Atkinson and Miller cycles as particular cases and can include irreversibilities in compression, expansion, intake, and exhaust. Results are consistent with the real influence of the fuel-air ratio, overcoming limitations of standard air cycles without the complex calculation of fuel-air cycles. It includes Exhaust Gas Recirculation, EGR, external irreversibilities, and contemporary high-efficiency and low-polluting technologies. Correlations for heat ratio γ are given, including renewable fuels.
The Influence of Engine Downsizing in Hybrid Powertrains on the Energy Flow Indicators under Actual Traffic Conditions
Authors: Szałek Andrzej , Pielecha Ireneusz
Published: May 2021

The development of internal combustion engines is currently based around the ideas of downsizing and rightsizing. These trends, however, are not very widespread in vehicles with hybrid drive systems. Nevertheless, the authors analyzed the performance indicators of hybrid drives in downsized vehicles. Two generations of a vehicle model, equipped with hybrid drive systems, were used in the analysis in which not only the design of the internal combustion engine was changed, but also other hybrid drive systems (including the transmission, electric motors and high-voltage batteries). The paper analyzes the energy flow in two hybrid vehicles of different generations during tests in real road driving conditions in accordance with the requirements of the RDE (real driving emissions) tests. The authors have confirmed that newer vehicle designs extend the vehicle range by 38% in the electric mode under the conditions of road traffic (68% in the urban conditions). The application of a combustion engine with better operating indexes did not result in its greater load, but led to limitation of the maximum pressure-volume (PV) diagram. The change of the battery to Li-ion, despite its lower electric and energy capacity, led to an increase in vehicle’s working parameters (power and regenerative braking).
State-of-the-Art Review of Effervescent-Swirl Atomizers
Authors: Czernek Krystian , Hyrycz Michał , Krupińska Andżelika , Matuszak Magdalena , Ochowiak Marek , Witczak Stanisław , Włodarczak Sylwia
Published: May 2021

This paper presents issues in the field of theory, construction, calculations, as well as the design of effervescent-swirl atomizers. The results of experimental studies of spraying liquids with different physico-chemical properties for this type of atomizers are discussed. Effervescent-swirl atomization is a complex process and its mechanism is not fully understood. Therefore, the purpose of the manuscript is the complexity of the atomization process and its mechanism as well as the influence of individual parameters on its efficiency were thoroughly analyzed. The analyzed parameters include: atomizer design, outlet shape, gas and liquid flow rate, injection pressure, physicochemical properties of the atomized liquid, pressure drop, outflow coefficient, spray angle, quantitative droplet distributions, and average droplet diameter. Moreover, in the work, on the basis of the literature review, the results of the research related to, inter alia, the phenomenon of air core formation and the influence of a number of parameters on the efficiency of the atomization process are analyzed. The literature review included in the work makes it possible to better understand the atomization process carried out in effervescent-swirl atomizers, and also provides better design criteria and analysis of the efficiency of the tested devices. The article presents correlation equations covering the basic features of the atomization process, which relate a large number of parameters influencing the efficiency of this process and the character of the sprayed liquid, which may be useful in design practice.
Initial Study into the Possible Use of Digital Sound Processing for the Development of Automatic Longwall Shearer Operation
Authors: Kiljan Piotr , Moczulski Wojciech , Kalinowski Krzysztof
Published: May 2021

Competition on the local and global market forces enterprises to implement modern solutions and adapt to technological changes. Applying modern solutions allows an increase in the quality of the product and reduces production costs. The acoustic sensor, as a relatively cheap solution, allows signals to be obtained which, after appropriate processing, can be used to develop an automatic control of the longwall shearer, together with the recognition of the type of shale. This paper presents an introductory research, the goal of which has been to check whether acoustic signals carry useful information on what kind of material–shale or coal–is being cut by the cutting head of a longwall shearer. For this purpose, the fast Fourier transform and short-time Fourier transform functions implemented in MatLab were used. The results of the analysis are presented in the form of three-dimensional graphs and spectrograms. To sum up, the research carried out so far justifies the need for continuation in the form of systematic experiments, the results of which could be incorporated into the control system of an unmanned combine.
Optimal Design on Fossil-to-Renewable Energy Transition of Regional Integrated Energy Systems under CO2 Emission Abatement Control: A Case Study in Dalian, China
Authors: Liu Xinxin , Li Nan , Liu Feng , Mu Hailin , Li Longxi , Liu Xiaoyu
Published: May 2021

Optimal design of regional integrated energy systems (RIES) offers great potential for better managing energy sources, lower costs and reducing environmental impact. To capture the transition process from fossil fuel to renewable energy, a flexible RIES, including the traditional energy system (TES) based on the coal and biomass based distributed energy system (BDES), was designed to meet a regional multiple energy demand. In this paper, we analyze multiple scenarios based on a new rural community in Dalian (China) to capture the relationship among the energy supply cost, increased share of biomass, system configuration transformation, and renewable subsidy according to regional CO2 emission abatement control targets. A mixed integer linear programming (MILP) model was developed to find the optimal solutions. The results indicated that a 40.58% increase in the share of biomass in the RIES was the most cost-effective way as compared to the separate TES and BDES. Based on the RIES with minimal cost, by setting a CO2 emission reduction control within 40%, the RIES could ensure a competitive total annual cost as compared to the TES. In addition, when the reduction control exceeds 40%, a subsidy of 53.83 to 261.26 RMB/t of biomass would be needed to cover the extra cost to further increase the share of biomass resource and decrease the CO2 emission.
Boundary Conditions for Transient and Robust Performance of a Reduced-Order Model-Based State Feedback Controller with PI Observer
Authors: Amare Nebiyeleul Daniel , Kim Doe Hun , Yang Sun Jick , Son Young Ik
Published: May 2021

One common technique employed in control system design to minimize system model complexity is model order reduction. However, controllers designed by using a reduced-order model have the potential to cause the closed-loop system to become unstable when applied to the original full-order system. Additionally, system performance improvement techniques such as disturbance observers produce unpredictable outcomes when augmented with reduced-order model-based controllers. In particular, the closed-loop system stability is compromised when a large value of observer gain is employed. In this paper, a boundary condition for the controller and observer design parameters in which the closed-loop system stability is maintained is proposed for a reduced-order proportional-integral observer compensated reduced-order model-based controller. The boundary condition was obtained by performing the stability analysis of the closed-loop system using the root locus method and the Routh-Hurwitz criterion. Both the observer and the state feedback controller were designed using a reduced-order system model based on the singular perturbation theory. The result of the theoretical analysis is validated through computer simulations using a DC (direct current) motor position control problem.
A Comprehensive Study on the Recent Progress and Trends in Development of Small Hydropower Projects
Authors: Kishore Teegala Srinivasa , Patro Epari Ritesh , Harish V. S. K. V. , Haghighi Ali Torabi
Published: May 2021

In terms of fuel resource, hydropower possesses a prominent advantage over any other large power plants which burn fossil fuels to generate electricity. Moreover, due to the abundance in resource availability (as a domestic source in small streams and rivers), small hydropower (SHP) plants are showing prominence all over the world. SHP plants have led to improved access to electricity usage in under-developed and developing nations, thereby contributing to sustainable development goals and social empowerment. SHP, as a technology, is regarded as the largest density renewable resource with high adaptability, and low investment costs. The primary objective of the paper is to study and analyze recent developments in SHP technologies with reporting statistical figures in terms of installed capacity and MW potential in several parts of the world. Methodologies adopted by researchers to conduct techno-economic analysis of SHP projects are reviewed. Various costs involved in conducting pre-feasibility studies—such as constructing, maintaining, and sustainably operating SHP projects—are studied. The results of the study indicate cost and regulatory issues are the major factors affecting the growth of the small hydropower sector in many nations. Major impediments to construction, development and deployment of SHP projects, mutually existing among the nations worldwide, are also reported. Technical hindrances include non-availability of the grid and very limited accessibility to SHP sites, emissions due to storage of water, disruptive technologies with limited manpower and non-technical hindrances include discouragement from local bodies and groups, lack of suitable and precise pathways to accomplish SHP goals of a nation, lack of incentives for encouraging private players to invest in SHP projects, complex approval processes, and many more.
Theoretical Deduction of the Optimum Tilt Angles for Small-Scale Linear Fresnel Reflectors
Authors: Barbón Arsenio , Bayón-Cueli Covadonga , Fernández Rubiera José A. , Bayón Luis
Published: May 2021

A theoretical justification and computation of the optimum values of the two longitudinal tilt angles of a small-scale linear Fresnel reflector is provided. The optimum angle of the mobile structure is proved to be half the latitude of the geographic location, while the optimum angle of the secondary reflector system is proved to be equal to that latitude. Brute-force verification is carried out for five EU cities, each in one of the five European climate zones.
Uncertainty Cost Functions in Climate-Dependent Controllable Loads in Commercial Environments
Authors: Losada Daniel , Al-Sumaiti Ameena , Rivera Sergio
Published: May 2021

This article presents the development, simulation and validation of the uncertainty cost functions for a commercial building with climate-dependent controllable loads, located in Florida, USA. For its development, statistical data on the energy consumption of the building in 2016 were used, along with the deployment of kernel density estimator to characterize its probabilistic behavior. For validation of the uncertainty cost functions, the Monte-Carlo simulation method was used to make comparisons between the analytical results and the results obtained by the method. The cost functions found differential errors of less than 1%, compared to the Monte-Carlo simulation method. With this, there is an analytical approach to the uncertainty costs of the building that can be used in the development of optimal energy dispatches, as well as a complementary method for the probabilistic characterization of the stochastic behavior of agents in the electricity sector.
Experimental Study of Thermal Properties and Dynamic Viscosity of Graphene Oxide/Oil Nano-Lubricant
Authors: Ranjbarzadeh Ramin , Chaabane Raoudha
Published: May 2021

This experimental study was carried out based on the nanotechnology approach to enhance the efficacy of engine oil. Atomic and surface structures of graphene oxide (GO) nanoparticles were investigated by using a field emission scanning electron microscope and X-ray diffraction. The nano lubricant was produced by using a two-step method. The stability of nano lubricant was analyzed through dynamic light scattering. Various properties such as thermal conductivity, dynamic viscosity, flash point, cloud point and freezing point were investigated and the results were compared with the base oil (Oil- SAE-50). The results show that the thermal conductivity of nano lubricant was improved compared to the base fluid. This increase was correlated with progressing temperature. The dynamic viscosity was increased by variations in the volume fraction and reached its highest value of 36% compared to the base oil. The cloud point and freezing point are critical factors for oils, especially in cold seasons, so the efficacy of nano lubricant was improved maximally by 13.3% and 12.9%, respectively, compared to the base oil. The flash point was enhanced by 8%, which remarkably enhances the usability of the oil. It is ultimately assumed that this nano lubricant to be applied as an efficient alternative in industrial systems.