bluuebunny/crossref_metadata_2025 huggingface dataset:
Dry Reforming of Methane (DRM) by Highly Active and Stable Ni Nanoparticles on Renewable Porous Carbons
Authors: Li Yinming , Wang Zhaojia , Zhang Bo , Liu Zhengang , Yang Tianxue
Published: May 2020

In this study, Ni nanoparticles supported on renewable porous carbon were prepared using hydrochar as a carbon precursor via in situ formation and self-reduction. The structure properties of the prepared nanocatalysts were characterized by multiple techniques, including XRD, SEM, and HR-TEM, and the dry reforming of methane (DRM) performance of the nanocatalysts in terms of conversion efficiency and reactivity stability was evaluated. The results revealed that the Ni2+ was uniformly anchored on the surface of the hydrochar, and subsequently the Ni nanoparticles were well dispersed in the composite with a diameter of less than 8 nm and had a narrow particle size distribution at a temperature lower than 800 °C. With an increased temperature from 800 to 900 °C, the significant sintering and agglomeration of nickel particles and the transformation from amorphous carbon to graphitic structure were observed in the composite. The nanocatalysts prepared at a temperature of 700 °C (Ni@C-700) and 800 °C (Ni@C-800) exhibited a high reforming conversion rate and catalytic stability of CH4 by CO2 (around 52% for Ni@C-700 and 70% for Ni@C-800 after 800 min of run-time, respectively). As for the composite obtained at 900 (Ni@C-900), the highly graphitic degree was coupled with the significantly increased nickel particle size, and this resulted in a remarkably decreased conversion efficiency. The present study offers a valuable application of the hydrochar and a facile and green approach to prepare highly active and cost-efficient Ni nanoparticles on porous carbons towards the dry reforming of methane.
Room-Temperature Solid-State Preparation of CoFe2O4@Coal Composites and Their Catalytic Performance in Direct Coal Liquefaction
Authors: Liu Baolin , Li Yizhao , Wu Hao , Ma Fengyun , Cao Yali
Published: May 2020

Iron-based catalysts are promising catalysts in the direct coal liquefaction (DCL) process as they are inexpensive and environmentally friendly. However, most such iron-based catalysts show relatively low activity in coal conversion and oil yield. Common techniques for the synthesis of these catalysts with excellent catalytic performance remain a substantial challenge. We present a simple solid-state synthesis strategy for preparing CoFe2O4 nanoparticles and CoFe2O4 nanoparticles supported on coal (CoFe2O4@coal) composites for DCL. The obtained bimetallic oxide CoFe2O4 nanoparticles show an enhanced catalytic performance in the DCL compared with monometallic components Fe2O3 and Co(OH)2 nanoparticles. The synergistic effect between Co and Fe of CoFe2O4 nanoparticles promotes the catalytic hydrogenation of coal during the DCL process. Moreover, the catalytic performance of CoFe2O4 nanoparticles is further improved when they are loaded on the coal. The conversion, oil yield, liquefaction degree, and gas yield of Dahuangshan lignite are 99.44, 56.01, 82.18 and 19.30 wt %, respectively, with the CoFe2O4@coal composites involved. The smaller particle size and high dispersion of CoFe2O4 supported on coal are of great benefit to full contact between coal and active components. The in-situ solid-state synthesis with coal as support shows great potential to prepare effective iron-based catalysts toward DCL in practice.
Nanosized Cu-SSZ-13 and Its Application in NH3-SCR
Authors: Palčić Ana , Bruzzese Paolo Cleto , Pyra Kamila , Bertmer Marko , Góra-Marek Kinga , Poppitz David , Pöppl Andreas , Gläser Roger , Jabłońska Magdalena
Published: May 2020

Nanosized SSZ-13 was synthesized hydrothermally by applying N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as a structure-directing agent. In the next step, the quantity of TMAdaOH in the initial synthesis mixture of SSZ-13 was reduced by half. Furthermore, we varied the sodium hydroxide concentration. After ion-exchange with copper ions (Cu2+ and Cu+), the Cu-SSZ-13 catalysts were characterized to explore their framework composition (XRD, solid-state NMR, ICP-OES), texture (N2-sorption, SEM) and acid/redox properties (FT-IR, TPR-H2, DR UV-Vis, EPR). Finally, the materials were tested in the selective catalytic reduction of NOx with ammonia (NH3-SCR). The main difference between the Cu-SSZ-13 catalysts was the number of Cu2+ in the double six-membered ring (6MRs). Such copper species contribute to a high NH3-SCR activity. Nevertheless, all materials show comparable activity in NH3-SCR up to 350 °C. Above 350 °C, NO conversion decreased for Cu-SSZ-13(2–4) due to side reaction of NH3 oxidation.
A Coarse Grained Model for Viscoelastic Solids in Discrete Multiphysics Simulations
Authors: Sahputra Iwan H. , Alexiadis Alessio , Adams Michael J.
Published: May 2020

Viscoelastic bonds intended for Discrete Multiphysics (DMP) models are developed to allow the study of viscoelastic particles with arbitrary shape and mechanical inhomogeneity that are relevant to the pharmaceutical sector and that have not been addressed by the Discrete Element Method (DEM). The model is applied to encapsulate particles with a soft outer shell due, for example, to the partial ingress of moisture. This was validated by the simulation of spherical homogeneous linear elastic and viscoelastic particles. The method is based on forming a particle from an assembly of beads connected by springs or springs and dashpots that allow the sub-surface stress fields to be computed, and hence an accurate description of the gross deformation. It is computationally more expensive than DEM, but could be used to define more effective interaction laws.
A Procedure for Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, with Application to 66 Molecules †
Authors: Rablen Paul R.
Published: May 2020

A method is presented for the direct computation of hydrocarbon strain energies using computational group equivalents. Parameters are provided at several high levels of electronic structure theory: W1BD, G-4, CBS-APNO, CBS-QB3, and M062X/6-31+G(2df,p). As an illustration of the procedure, strain energies are computed for 66 hydrocarbons, most of them highly strained.
Review of Growth Defects in Thin Films Prepared by PVD Techniques
Authors: Panjan Peter , Drnovšek Aljaž , Gselman Peter , Čekada Miha , Panjan Matjaž
Published: May 2020

The paper summarizes current knowledge of growth defects in physical vapor deposition (PVD) coatings. A detailed historical overview is followed by a description of the types and evolution of growth defects. Growth defects are microscopic imperfections in the coating microstructure. They are most commonly formed by overgrowing of the topographical imperfections (pits, asperities) on the substrate surface or the foreign particles of different origins (dust, debris, flakes). Such foreign particles are not only those that remain on the substrate surface after wet cleaning procedure, but also the ones that are generated during ion etching and deposition processes. Although the origin of seed particles from external pretreatment of substrate is similar to all PVD coatings, the influence of ion etching and deposition techniques is rather different. Therefore, special emphasis is given on the description of the processes that take place during ion etching of substrates and the deposition of coating. The effect of growth defects on the functional properties of PVD coatings is described in the last section. How defects affect the quality of optical coatings, thin layers for semiconductor devices, as well as wear, corrosion, and oxidation resistant coatings is explained. The effect of growth defects on the permeation and wettability of the coatings is also shortly described.
Fabrication of Hybrid Catalyst ZnO Nanorod/α-Fe2O3 Composites for Hydrogen Evolution Reaction
Authors: Uma Kasimayan , Muniranthinam Elavarasan , Chong Siewhui , Yang Thomas C.-K , Lin Ja-Hon
Published: May 2020

This report presents the synthesis of ZnO nanorod/α-Fe2O3 composites by the hydrothermal method with different weight percentages of α-Fe2O3 nanoparticles. The as-synthesized nanorod composites were characterized by different techniques, such as X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), field emission scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). From our results, it was found that the ZnO/α-Fe2O3 (3 wt%) nanorod composites exhibit a higher hydrogen evolution reaction (HER) activity when compared to other composites. The synergetic effect between ZnO and (3 wt%) of α-Fe2O3 nanocomposites resulted in a low onset potential of −125 mV, which can effectively produce more H2 than pure ZnO. The H2 production rate over the composite of ZnO/α-Fe2O3 (3 wt%) clearly shows a significant improvement in the photocatalytic activity in the heterojunction of the ZnO nanorods and α-Fe2O3 nanoparticles on nickel foam.
Fluorescent Gold Nanoclusters for Biosensor and Bioimaging Application
Authors: Bai Yunlong , Shu Tong , Su Lei , Zhang Xueji
Published: May 2020

With the rapid development of materials technology, fluorescent gold nanoclusters (AuNCs) are emerging as novel functional materials for diagnostic applications including the detection of biomarkers and bioimaging due to the advantages of their ultra-small size, tunable emissions, size-dependent fluorescence and excellent biocompatibility. In this review, we introduced the synthetic methods, and physical and chemical properties of AuNCs. Subsequently, we described the AuNCs-based design strategies for the detection of biomarkers including small molecules, DNA and proteins. The applications of AuNCs for tumor imaging in vitro and in vivo were also presented. Finally, we discussed the challenges and potential solutions of AuNCs-based nanosensors.
Illuminance and Starting Distance of the Far Field of LED-Array Luminaire Operated at Short Working Distance
Authors: Sun Ching-Cherng , Lin Yi-Syuan , Yang Tsung-Hsun , Lin Shih-Kang , Lee Xuan-Hao , Wu Chi-Shou , Yu Yeh-Wei
Published: May 2020

A luminaire with a light-emitting diode (LED) array can provide hotspot illumination in a short range. Therefore, a design of a luminaire with the largest central illuminance (LCI) and a high uniformity is warranted. In this paper, we present a study of illuminance variation with respect to the distance of an illumination target of a luminaire with LED array. The emission property of the luminous intensity is characterized by the cosine power law or the divergent angle of full width at half maximum (FWHM). A real LED module is designed to create the simulation for different luminaire types. The occurrence of the LCI and the far-field region are observed. Our results demonstrate that the LCI distance remains shorter than the starting distance of the far field (SDFF). To simplify the simulation, we propose the replacement of the real LED module with a point or flat-extended source. Such light sources must be equipped with the specific cosine power factor corresponding to the divergent angle of the FWHM of the LED module. These light sources are acceptable for describing illumination characteristics, including the SDFF. Our results may facilitate the design of LED-array luminaires operated at short working distances, such as reading lighting or illumination in microscopes.
Ordering Phase Transition with Symmetry-Breaking from Disorder over Non-Equivalent Sites: Calorimetric and Crystallographic Study of Crystalline d-Sorbose
Authors: Iwagaki Sakiko , Kakuta Hiroki , Yamamura Yasuhisa , Saitoh Hideki , Hishida Mafumi , Fukada Kazuhiro , Saito Kazuya
Published: May 2020

Phase transitions in the crystalline state of chiral sorbose were examined using precise heat capacity calorimetry and X-ray crystallography. The calorimetry established heat capacity below room temperature. Besides the known transition (main transition) at 199.5 K, the calorimetry detected plural thermal anomalies assignable to new phase transitions (around 210 K) and a glass transition (at ca. 120 K). The X-ray diffraction at low temperatures established the crystal structure of the lowest temperature phase. The identification of the broken symmetry upon the main transition solves an apparent contradiction that the structural disorder reported previously does not contribute seemingly to the symmetrization.
Large Area Free-Standing Single Crystalline Films of p-Quinquephenyl: Growth, Structure and Photoluminescence Properties
Authors: Postnikov Valery , Sorokina Nataliya , Lyasnikova Maria , Kulishov Artem , Voloshin Alexey , Borshchev Oleg , Surin Nikolay , Svidchenko Evgeniya , Ponomarenko Sergey
Published: May 2020

Studies of the growth of large-area free-standing single-crystalline films of p-quinquephenyl are presented. High-quality crystals were grown by slow cooling of a hot chlorobenzene solution. Worse quality large-area free-standing single crystals of p-quinquephenyl were also grown by using physical vapor transport and used for comparison. The crystal structure of p-quinquephenyl at 293 K and 85 K was refined by single-crystal X-ray diffraction. The optical absorption and photoluminescence spectra of solutions and crystalline films were obtained and analyzed; a positive solvatochromic effect was detected.
Plasticity through De-Twinning in Twinned BCC Nanowires
Authors: Sainath G. , Goyal Sunil , Nagesha A.
Published: May 2020

The deformation behaviour of twinned FCC nanowires has been extensively investigated in recent years. However, the same is not true for their BCC counterparts. Very few studies exist concerning the deformation behaviour of twinned BCC nanowires. In view of this, molecular dynamics (MD) simulations have been performed to understand the deformation mechanisms in twinned BCC Fe nanowires. The twin boundaries (TBs) were oriented parallel to the loading direction [110] and the number of TBs is varied from one to three. MD simulation results indicate that deformation under the compressive loading of twinned BCC Fe nanowires is dominated by a unique de-twinning mechanism involving the migration of a special twin–twin junction. This de-twinning mechanism results in the complete annihilation of pre-existing TBs along with reorientation of the nanowire. Further, it has been observed that the annihilation of pre-existing TBs has occurred through two different mechanisms, one without any resolved shear stress and other with finite and small resolved shear stress. The present study enhances our understanding of de-twinning in BCC nanowires.
Impact of Phase Structure on Piezoelectric Properties of Textured Lead-Free Ceramics
Authors: Gao Xiaoyi , Dong Nannan , Xia Fangquan , Guo Qinghu , Hao Hua , Liu Hanxing , Zhang Shujun
Published: May 2020

The impact of phase structure on piezoelectric performances of <001> textured Na0.5Bi0.5TiO3 (NBT) based lead-free ceramics was studied, including 0.88NBT-0.08K0.5Bi0.5TiO3-0.04BaTiO3 (88NBT) with morphotropic phase boundary (MPB) composition and 0.90NBT-0.07K0.5Bi0.5TiO3-0.03BaTiO3 (90NBT) with rhombohedral phase. Both textured ceramics exhibit a high Lotgering factor, being on the order of f~96%. The piezoelectric coefficients of the textured 88NBT and 90NBT ceramics are increased by 20% and 60%, respectively, comparing to their randomly oriented ceramics. The piezoelectric enhancement of 90NBT textured ceramic is three times higher than 88NBT, revealing the phase structure plays a significant role in enhancing the piezoelectric performances of textured ceramics. Of particular significance is that the 90NBT textured ceramic exhibits almost hysteresis-free strain behavior. The enhanced piezoelectric property with minimal strain hysteresis is attributed to the <001> poled rhombohedral engineered domain configuration.
Potential of DNA Intercalating Alkaloids and Other Plant Secondary Metabolites against SARS-CoV-2 Causing COVID-19
Authors: Wink Michael
Published: May 2020

Many plants produce secondary metabolites (PSMs) with antiviral activities. Among the antiviral PSMs, lipophilic terpenoids in essential oils can disturb the lipid envelope of viruses. Phenols and polyphenols (flavonoids, rosmarinic acid and tannins) attack viral proteins present in the viral membrane or inside the virus particle. Both phenolics and essential oils are active against free viral particles but not—or to a lesser degree—after a virus has entered a host cell. Another group of PSMs is directed against DNA or RNA. These are DNA intercalators such as sanguinarine, berberine, emetine and other isoquinoline alkaloids, ß-carboline, and quinoline alkaloids such as quinine, cinchonine, dictamine and skimmianine. The DNA intercalators stabilize double-stranded nucleic acids and inhibit the replication, transcription, and translation of genetic material. These alkaloids can inhibit viral development and viral replication in cells, as shown for SARS-CoV-1 and other viruses. Since chloroquine (which is also a DNA intercalator and a chemical derivative of the alkaloid quinine) is apparently clinically helpful against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, it is assumed that intercalating alkaloids, or the medicinal plants producing them, may be interesting candidates for the development of new antiviral drugs for the treatment of coronavirus disease 2019 (COVID-19).
Vulnerable Forests of the Pink Sea Fan Eunicella verrucosa in the Mediterranean Sea
Authors: Chimienti Giovanni
Published: May 2020

The pink sea fan Eunicella verrucosa (Cnidaria, Anthozoa, Alcyonacea) can form coral forests at mesophotic depths in the Mediterranean Sea. Despite the recognized importance of these habitats, they have been scantly studied and their distribution is mostly unknown. This study reports the new finding of E. verrucosa forests in the Mediterranean Sea, and the updated distribution of this species that has been considered rare in the basin. In particular, one site off Sanremo (Ligurian Sea) was characterized by a monospecific population of E. verrucosa with 2.3 ± 0.2 colonies m−2. By combining new records, literature, and citizen science data, the species is believed to be widespread in the basin with few or isolated colonies, and 19 E. verrucosa forests were identified. The overall associated community showed how these coral forests are essential for species of conservation interest, as well as for species of high commercial value. For this reason, proper protection and management strategies are necessary.
Factors Affecting the Detection of an Imperiled and Cryptic Species
Authors: Crawford John A. , Dreslik Michael J. , Baker Sarah J. , Phillips Christopher A. , Peterman William E.
Published: May 2020

Population surveying and monitoring are important for identifying conservation needs and tracking trends in populations, communities, and ecosystems over time and laying the groundwork for conservation management and policy decisions. If species or populations go undetected because of inadequate effort or sampling design, protection and management cannot be properly provided. Due to the widespread loss of populations, the Eastern Massasauga (a rattlesnake) was recently listed as a federally threatened species in the United States; it is also listed as threatened in Canada. Given its current conservation status, there is considerable interest at state and federal levels in determining how to best survey for Eastern Massasaugas to aid in management decisions. Using a 16-year dataset, we examined the relationships among environmental, temporal, area, management, and search effort factors on the detection probability of Eastern Massasaugas. We found that four abiotic parameters (solar irradiance, shaded air temperature, three-day maximum air temperature, and humidity) and three search parameters (effort per researcher, search area, and search time of day) influenced detection of Eastern Massasaugas. As the current biodiversity crisis continues, the cost-effective use of resources and scientific expertise will continue to increase in importance. We hope our results stimulate similar analyses in other taxa, which will be critical for designing and implementing regional survey and monitoring programs.
New Insights into the Distribution, Physiology and Life Histories of South American Galaxiid Fishes, and Potential Threats to This Unique Fauna
Authors: Cussac Víctor Enrique , Barrantes María Eugenia , Boy Claudia Clementina , Górski Konrad , Habit Evelyn , Lattuca María Eugenia , Rojo Javier Hernán
Published: May 2020

South American galaxiids occupy both Patagonia and the ichthyogeographic Chilean Province, encompassing glacial Andean deep lakes, shallow plateau lakes, reservoirs, short Pacific rivers and long Atlantic rivers. The total fish fauna includes 29 species, comprising Neotropical fishes (siluriforms and characids), galaxiids, percichthyids, atherinopsids and mugilids, two lamprey species, and several exotic fishes (salmonids, Gambusia spp. and common carp). The family Galaxiidae shares a common ancestry with the Gondwanan temperate fish fauna, played a major role in the post-glacial colonization of Andean lakes and streams, and contributes key species to the food webs. Galaxiid species occupy an enormous latitudinal gradient, show a wide variety of life history patterns and are the southernmost native freshwater fishes of the world. Knowledge of South American galaxiids has improved notably, but new challenges arise due to climate change, biological invasions, damming, aquaculture and contamination. In this changing environment, the future of South American galaxiids should be carefully considered as a legacy of the old Gondwana and a unique attribute of the freshwaters of southern South America.
An Optimum Tea Fermentation Detection Model Based on Deep Convolutional Neural Networks
Authors: Kimutai Gibson , Ngenzi Alexander , Said Rutabayiro Ngoga , Kiprop Ambrose , Förster Anna
Published: May 2020

Tea is one of the most popular beverages in the world, and its processing involves a number of steps which includes fermentation. Tea fermentation is the most important step in determining the quality of tea. Currently, optimum fermentation of tea is detected by tasters using any of the following methods: monitoring change in color of tea as fermentation progresses and tasting and smelling the tea as fermentation progresses. These manual methods are not accurate. Consequently, they lead to a compromise in the quality of tea. This study proposes a deep learning model dubbed TeaNet based on Convolution Neural Networks (CNN). The input data to TeaNet are images from the tea Fermentation and Labelme datasets. We compared the performance of TeaNet with other standard machine learning techniques: Random Forest (RF), K-Nearest Neighbor (KNN), Decision Tree (DT), Support Vector Machine (SVM), Linear Discriminant Analysis (LDA), and Naive Bayes (NB). TeaNet was more superior in the classification tasks compared to the other machine learning techniques. However, we will confirm the stability of TeaNet in the classification tasks in our future studies when we deploy it in a tea factory in Kenya. The research also released a tea fermentation dataset that is available for use by the community.
Open-Loop Single-Phase Space State Model and Equivalent Circuit of a Non-Conventional Three-Phase Inverter
Authors: Melo Vinícius , Melo Alexandre , Santos Walbermark , Fardin Jussara , Encarnação Lucas
Published: May 2020

Recently, many non-conventional three-phase inverters, topologies for green energy source grid-connection systems, and electric drives have been proposed. Simplifying the inverter circuit is crucial to analyze and solve their models in order to design them. The main goal of the study is centered on obtaining a single-phase equivalent circuit and space state model from non-conventional three-phase inverters based on bidirectional direct current–direct current (DC–DC) Buck-Boost topology using isolated gate bipolar transistors (IGBT). From just one phase of the three-phase inverter, the single-phase equivalent circuit was obtained by means of Kirchhoff’s laws. The equivalent circuit operation steps were presented in order to obtain the space state model. Finally, the equivalent circuit was simulated, and experimental results with a 200 W three-phase inverter feeding a resistive, inductive, and capacitive loads were performed to confirm the theoretical and simulation analyses. The results show the state space dynamic behavior variables of single-phase and three-phase models are quite similar. Therefore, it can be concluded that the proposed circuit can be used with property to represent equivalent single-phase models of non-conventional three-phase inverters.
Recent Developments and Challenges on AC Microgrids Fault Detection and Protection Systems–A Review
Authors: Hussain Noor , Nasir Mashood , Vasquez Juan Carlos , Guerrero Josep M.
Published: May 2020

The protection of AC microgrids (MGs) is an issue of paramount importance to ensure their reliable and safe operation. Designing reliable protection mechanism, however, is not a trivial task, as many practical issues need to be considered. The operation mode of MGs, which can be grid-connected or islanded, employed control strategy and practical limitations of the power electronic converters that are utilized to interface renewable energy sources and the grid, are some of the practical constraints that make fault detection, classification, and coordination in MGs different from legacy grid protection. This article aims to present the state-of-the-art of the latest research and developments, including the challenges and issues in the field of AC MG protection. A broad overview of the available fault detection, fault classification, and fault location techniques for AC MG protection and coordination are presented. Moreover, the available methods are classified, and their advantages and disadvantages are discussed.
Resource Assessment and Numerical Modeling of CBM Extraction in the Upper Silesian Coal Basin, Poland
Authors: Chećko Jarosław , Urych Tomasz , Magdziarczyk Małgorzata , Smoliński Adam
Published: May 2020

The paper presents the assessment of the resources of methane considered as the main mineral in the most prospective selected areas of the Upper Silesian Coal Basin, Poland in the region of undeveloped deposits. The methane resources were estimated by means of a volumetric method at three depth levels, 1000, 1250, and 1500 m. A part of the Studzienice deposit comprising three coal seams, 333, 336, and 337, located in a methane zone was chosen for the numerical modeling of simulated methane production. The presented static 3D model has been developed using Petrel Schlumberger software. The total resources of methane in the area amount to approximately 446.5 million of Nm3. Numerical simulations of methane production from the selected coal seams with hydraulic fracturing were conducted by means of Schlumberger ECLIPSE reservoir simulator. Based on the simulations, it was concluded that, in the first six months of the simulations, water is produced from the seams, which is connected with the decrease in the rock mass pressure. The process prompts methane desorption from the coal matrix, which in turn results in a total methane production of 76.2 million of Nm3 within the five-year period of the simulations, which constitutes about 17% of total methane resources (GIP). The paper also presents a detailed analysis of Polish legislation concerning the activities aimed at prospecting, exploring, and extracting the deposits of hydrocarbons.
A Super Twisting Fractional Order Terminal Sliding Mode Control for DFIG-Based Wind Energy Conversion System
Authors: Sami Irfan , Ullah Shafaat , Ali Zahoor , Ullah Nasim , Ro Jong-Suk
Published: May 2020

The doubly fed induction generator (DFIG)-based wind energy conversion systems (WECSs) are prone to certain uncertainties, nonlinearities, and external disturbances. The maximum power transfer from WECS to the utility grid system requires a high-performance control system in the presence of such nonlinearities and disturbances. This paper presents a nonlinear robust chattering free super twisting fractional order terminal sliding mode control (ST-FOTSMC) strategy for both the grid side and rotor side converters of 2 MW DFIG-WECS. The Lyapunov stability theory was used to ensure the stability of the proposed closed-loop control system. The performance of the proposed control paradigm is validated using extensive numerical simulations carried out in MATLAB/Simulink environment. A detailed comparative analysis of the proposed strategy is presented with the benchmark sliding mode control (SMC) and fractional order terminal sliding mode control (FOTSMC) strategies. The proposed control scheme was found to exhibit superior performance to both the stated strategies under normal mode of operation as well as under lumped parametric uncertainties.
Microwave-Assisted Noncatalytic Esterification of Fatty Acid for Biodiesel Production: A Kinetic Study
Authors: Nguyen Hoang Chinh , Wang Fu-Ming , Dinh Kim Khue , Pham Thanh Truc , Juan Horng-Yi , Nguyen Nguyen Phuong , Ong Hwai Chyuan , Su Chia-Hung
Published: May 2020

This study developed a microwave-mediated noncatalytic esterification of oleic acid for producing ethyl biodiesel. The microwave irradiation process outperformed conventional heating methods for the reaction. A highest reaction conversion, 97.62%, was achieved by performing esterification with microwave irradiation at a microwave power of 150 W, 2:1 ethanol:oleic acid molar ratio, reaction time of 6 h, and temperature of 473 K. A second-order reaction model (R2 of up to 0.997) was established to describe esterification. The reaction rate constants were promoted with increasing microwave power and temperature. A strong linear relation of microwave power to pre-exponential factors was also established, and microwave power greatly influenced the reaction due to nonthermal effects. This study suggested that microwave-assisted noncatalytic esterification is an efficient approach for biodiesel synthesis.
Energy Distribution of Optical Radiation Emitted by Electrical Discharges in Insulating Liquids
Authors: Kozioł Michał
Published: May 2020

This article presents the results of the analysis of energy distribution of optical radiation emitted by electrical discharges in insulating liquids, such as synthetic ester, natural ester, and mineral oil. The measurements of optical radiation were carried out on a system of needle–needle type electrodes and on a system for surface discharges, which were immersed in brand new insulating liquids. Optical radiation was recorded using optical spectrophotometry method. On the basis of the obtained results, potential possibilities of using the analysis of the energy distribution of optical radiation as an additional descriptor for the recognition of individual sources of electric discharges were indicated. The results can also be used in the design of various types of detectors, as well as high-voltage diagnostic systems and arc protection systems.
Predicting the Structural Reliability of LNG Processing Plate-Fin Heat Exchanger for Energy Conservation
Authors: Saggu Mustansar Hayat , Sheikh Nadeem Ahmed , Niazi Usama Muhammad , Irfan Muhammad , Glowacz Adam
Published: May 2020

Liquefied natural gas (LNG) is one of the hydrocarbon fuels with the least carbon footprint having a rapidly rising global share in the prime energy market. LNG processing for transportation at longer distances works under cryogenic conditions, especially when used for liquefaction and gasification applications. The supply chain of the eco-environmental friendly hydrocarbon is heavily dependent on the processing plant used for liquefaction and subsequent re-gasification of the natural gas. Plate-fin heat exchangers are extensively used in the LNG industry for both re-gasification as well as liquefaction processes. The exchange of heat during the process of natural gas phase change involves plate-fin heat exchangers working under cryogenic low-temperature conditions. The heat exchangers are designed to have brazed joints that are most vulnerable to failure under these temperature conditions. One failure of such a joint can not only hinder the supply chain but also may result in fire and life hazards. In almost all earlier studies, analytical and numerical methods were used to analyze these braze joints using finite element method methods and examining the stresses while keeping them at or near to ambient conditions. In this research, the plate-fin heat exchanger is investigated for its structural stability of brazed fins for three different fin configurations: plain, wavy and compound having different joint geometries. In addition, the analyses are carried out using experimentally measured brazed joint strength which is measured to be on average 22% lower than the base material strength owing to brazing process and resultant heat-affected zone (HAZ). Therefore, the reliability is assessed for these joints in terms of factor of safety (FOS) while keeping in view the actual yield criteria. It was found that the structural stability of compound fins configuration is weakest amongst all considered fin configurations. The failure of the compound fin brazed joint is expected to be along the horizontal path of the joint due to yielding. The study also predicts the life of the fin brazed joints in different joining directions with different topologies of fins commonly recommended in the literature. It is observed that the commonly recommended safe fin geometries are predicted to be susceptible to failure if a reduction in the brazed joint is considered. The analysis and recommendation in this paper shall provide a reliable and safe design approach for plate-fin exchangers for different operating conditions especially in low to cryogenic temperature applications.
Long-Term Cycling Behavior of Electrospun Separators for Lithium-Ion Batteries: A Comparison with Conventional Separators
Authors: Makhov Semen V. , Ivanishchev Aleksandr V.
Published: May 2020

This paper considered the electrochemical behavior of new electrospun separators for lithium-ion batteries on the basis of nano- and microfibers of polyvinylidene fluoride (PVDF) and its polymer composition, with polytetrafluoroethylene (PTFE) having advanced electroconductive properties over conventionally used separators based on polypropylene (PP) and glass-fibers (GF). Such advancement is associated with the low density of electrospun material leading to lower mechanical strengths. However, its use in the electrochemical systems with middle-voltage anode materials where dendrite growth is excluded is very prospective. The performance at the operation of the separators were investigated in the three-electrode-containing laboratory half-cells having Li4Ti5O12 as the electrode under investigation. Galvanostatic charge and discharge tests of cells were conducted under variation of the experimental conditions: the current varied in the range 0.1 C–1 C, and 1C cycling was conducted over 100 cycles. The working electrode and separator characteristics at cycling were monitored by the electrochemical impedance spectroscopy (EIS) method. The gradual decrease of Li4Ti5O12 transport characteristics at cycling was noticed for all the types of separators. However, the least degradation rate was associated with the PVDF and the PTFE-based separator. This fact is explained by the better conductivity of an electrospun separator compared to others, with therefore a better current distribution on the electrode surface and a lower concentration perturbation in the electrode.
Operation of a PV Power Plant during Overpower Events Caused by the Cloud Enhancement Phenomenon
Authors: Järvelä Markku , Valkealahti Seppo
Published: May 2020

Partly cloudy days possess two characteristics that can significantly increase the photovoltaic (PV) generator power: the operating temperature of the PV panels can cool down during the shade periods, and the irradiance can be enhanced due to the cloud enhancement phenomenon. If an overirradiance event is preceded by a long shade period, the maximum power of a PV generator can occasionally be much higher than the nominal nameplate power. During the overpower events, the inverter is operating in power-limiting mode whereby the operating voltage is increased to decrease the power of the PV generator. We created a simulation model of a 31.9 kW PV generator and used 12 months of irradiance and PV panel temperature measurement data to analyze its operation. We analyzed the PV generator power during the overirradiance events and applied various static power limits to calculate the operating voltage ranges in case of power curtailment. During the observation period, the maximum power produced by the PV generator was 1.42 times its nominal power. The duration of the overpower events was up to several minutes, but the typical duration was only some tens of seconds. The strongest overpower events occur seldom and their duration is only some seconds. Due to the overpower events, the operating voltage may receive high values, especially if the DC-to-AC power ratio is large.
The effects of Microalgae Biomass Co-Substrate on Biogas Production from the Common Agricultural Biogas Plants Feedstock
Authors: Dębowski Marcin , Kisielewska Marta , Kazimierowicz Joanna , Rudnicka Aleksandra , Dudek Magda , Romanowska-Duda Zdzisława , Zieliński Marcin
Published: May 2020

The aim of this study was to determine the effects on methane production of the addition of microalgae biomass of Arthrospira platensis and Platymonas subcordiformis to the common feedstock used in agricultural biogas plants (cattle manure, maize silage). Anaerobic biodegradability tests were carried out using respirometric reactors operated at an initial organic loading rate of 5.0 kg volatile solids (VS)/m3, temperature of 35°C, and a retention time of 20 days. A systematic increase in the biogas production efficiency was found, where the ratio of microalgae biomass in the feedstock increased from 0% to 40% (%VS). Higher microalgae biomass ratio did not have a significant impact on improving the efficiency of biogas production, and the biogas production remained at a level comparable with 40% share of microalgae biomass in the feedstock. This was probably related to the carbon to nitrogen (C/N) ratio decrease in the mixture of substrates. The use of Platymonas subcordiformis ensured higher biogas production, with the maximum value of 1058.8 ± 25.2 L/kg VS. The highest content of methane, at an average concentration of 65.6% in the biogas produced, was observed in setups with Arthrospira plantensis biomass added at a concentration of between 20%–40% to the feedstock mixture.
A Review of Microgrid-Based Approach to Rural Electrification in South Africa: Architecture and Policy Framework
Authors: Motjoadi Vinny , Bokoro Pitshou N. , Onibonoje Moses O.
Published: May 2020

Access to electricity for every South African citizen, including rural dwellers, is a human right issue guaranteed by the government’s laws and policies. However, many remote rural areas still suffer from a lack of this very important amenity, due to the expensive prospect of connecting them to the central national grid. The feasible approach to connecting the rural communities to electricity supply is suggestively through the use of microgrid solutions. The microgrid technology is a very recent and viable option for the energy revolution. Microgrids result from the incorporation of energy storage systems, distributed generators, and localized loads. The application of this technology requires deliberate and extensive work on the operational architecture and the policy framework to be adopted. The energy storage devices form an integral part of the microgrid configuration or architecture to make sure more maintainable and constant operation is attained. This paper presents a review of the architectures of the existing microgrid systems, as well as the policy framework for implementable solutions. The various architectures display the peculiarity of the systems based on the increased grid performance, stability, quality of electricity, and other comparative advantages. The microgrid architectures are fundamentally recognized according to their AC, DC, or hybrid distribution buses and the complexity inherent to them. In the Policy And Development Section, the problems are treated as ‘a search for the truth’—a truth being revealed by close and objective examination. The core of the problem to be solved is revealed clearly, thereby giving the basis for simplifying and solving it. The policies encourage the accomplishment of a zero-carbon dioxide (CO 2 ) emissions, energy security attainment, the meeting of the electricity demand, and, lastly, the promotion of access to electricity in rural areas. It is established that the returns through charges of the consumers are very insignificant. Although returns on investment always come in conflict with the human right demands of the local indigenes, the policy framework would be explicit on the mode of returns for the government, private partners, and the communities—a return that can be short, medium, or long term. Policymakers would be keen on the exhaustive analysis of issues, leading to optimal decision making.
Case of Study of the Electrification of a Tractor: Electric Motor Performance Requirements and Design
Authors: Troncon Diego , Alberti Luigi
Published: May 2020

The focus of this paper is the potential electrification of specialized agricultural tractors involved in vineyards and orchards. This category of machinery has not received research attention to date; however, regulations are encouraging lower emissions and higher efficiency, requiring the adoption of new technologies. Traction makes up only a limited part of this application, and the working cycle is not trivial; therefore, the design of the system is not straightforward. This study takes advantage of experimental measurements carried out under real operating conditions on a traditional specialized tractor, which was chosen as performance target. The performance requirements of the hybrid powertrain components are investigated, with particular focus placed on the electric motor. According to the dimension constraints, the design of the electric motor is carried out considering the requirements in terms of its thermal-equivalent torque and overload capability. The results are validated through a detailed thermal simulation under real duty cycles.
Benchmarking of Industrial Energy Efficiency. Outcomes of an Energy Audit Policy Program
Authors: Locmelis Kristaps , Blumberga Dagnija , Blumberga Andra , Kubule Anna
Published: May 2020

Latvia’s industrial energy efficiency policy imposes the implementation of mandatory energy audits and energy management systems in large industrial enterprises and large industrial electricity consumers to improve industrial competitiveness, to move towards a carbon-neutral economy and to increase the security of supply. Companies affected by this energy efficiency policy are obliged to report to the national energy efficiency monitoring system on energy efficiency measures indicated in energy audits or energy management systems with the highest savings or economical potential. The purpose of this study was to assess the initial outcomes of the first industrial energy efficiency program in Latvia, using data from the national energy efficiency monitoring system, including an analysis of individual energy audit reports, and benchmarking it with findings from a similar program, thereby revealing untapped energy efficiency and CO2 emission reduction potential. Although the national monitoring system made it possible to ascertain results of the energy efficiency program, the statistical analysis of the data did not allow for a robust conclusion on the technical or economic industrial energy efficiency potential. This study suggests that Latvia’s energy efficient policy should continue its course in implementation and provides recommendations for improvements on the national energy efficiency monitoring system.
Energy Consumption Reduction of a Chiller Plant by Adding Evaporative Pads to Decrease Condensation Temperature
Authors: Rey Martínez Francisco J. , San José Alonso Julio F. , Velasco Gómez Eloy , Tejero González Ana , Esquivias Paula M , Rey Hernández Javier M.
Published: May 2020

The high energy consumption of cooling systems justifies the need for strategies to increase the efficiency of the facilities, in order to reduce the related CO2 emissions. This study aims to improve the performance and reduce the energy consumption of an 8.6 MW air cooled chiller. This installed capacity is biased due to the screw compressors, of 2.98 Energy Efficiency Ratio (EER) at full load (characteristics provided by the manufacturer). The chiller unit has been modified by placing evaporating cooling pads before the condensing coils. The chiller has been monitored for three months, recording over 544,322 measurements (5 min-step data), with and without the evaporative cooling pads, to assess the performance. Data comparison has been done by selecting two days (with and without evaporative panels) with the same health care load and temperatures. Implementing the proposed strategy yields an improvement in the European Seasonal Energy Efficiency Ratio (ESEER) from 3.69 to 4.83, while the Total Equivalent Warming Impact (TEWI) decreases about 1000 tCO2. Energy savings of up to 32.6 MWh result into a payback period lower than 2 years.
A GIS-Based Methodology for Speedy Energy Efficiency Mapping: A Case Study in Bologna
Authors: Gaspari Jacopo , De Giglio Michaela , Antonini Ernesto , Vodola Vincenzo
Published: May 2020

The paper reports a methodology developed to map energy consumption of the building stock at the urban scale on a GIS environment. Energy consumption has been investigated, focusing on the shift from the individual building scale to the district one with the purpose of identifying larger homogenous energy use areas for addressing policies and plans to improve the quality and the performance levels at the city scale. The urban planning zoning concept was extended to the energy issue to include the energy behavior of each zone that depends on the performance of its individual buildings. The methodology generates GIS maps providing a district scale visualization of energy consumption according to shared criteria. A case study in Bologna city (Italy) is provided. In the specific case, the last update of Emilia-Romagna regional urban planning regulation required a mapping action regarding energy efficiency of homogeneous urban portions defined by the General Urban Plan. The main achieved results are (a) a methodology to identify homogeneous areas for analyzing energy consumption; (b) an updated energy map of Bologna Municipality.