bluuebunny/crossref_metadata_2025 huggingface dataset:
Corrosion Behavior of Alloyed Cast Iron in Ethylene Glycol-Based Engine Coolants at Elevated Temperature
Authors: Argade Gaurav , Chilukuri Anusha , Perry Justin , Viers Monica , Steenhoek Jacob , Debusk Jacob , Wang Chinpei , Trobaugh Corey
Published: March 2021

For enhanced engine performance, corrosivity of the engine coolants would play a significant role. In this work, corrosion investigation was performed on cast iron material in pre-mixed engine coolant environment to understand the threshold limits of contaminants. The pre-mixed coolant contained combination of organic additives viz. sebacate (SA), 2-ethylhexanoate (2-EH), and tolyltriazole (TTA) with varying concentrations of chloride contaminant. Constant immersion of cast iron samples in engine coolant with different chloride levels at 90 °C was followed by room temperature electrochemical tests. The potentiodynamic polarization tests showed no instability until 100 ppm chloride additions exposed up to 28 days. At lower frequencies in electrochemical impedance spectroscopy (EIS) spectra, inhibition layer characteristics changed from highly capacitive to highly resistive and concurrently a sharp decrease in charge transfer resistance was observed with time for samples exposed to >100 ppm chloride levels. In the longer duration corrosion tests, higher pit depths with increased number density of attacks were observed for cast iron samples exposed to engine coolants containing >100 ppm chloride. For elevated temperature exposures a threshold limit of <200 ppm chloride was established for cast iron samples.
The Physical Properties of Submicron and Nano-Grained La0.7Sr0.3MnO3 and Nd0.7Sr0.3MnO3 Synthesised by Sol–Gel and Solid-State Reaction Methods
Authors: Lau Lik Nguong , Lim Kean Pah , Ishak Amirah Natasha , Awang Kechik Mohd Mustafa , Chen Soo Kien , Ibrahim Noor Baa’yah , Miryala Muralidhar , Murakami Masato , Shaari Abdul Halim
Published: March 2021

La0.7Sr0.3MnO3 (LSMO) and Nd0.7Sr0.3MnO3 (NSMO) possess excellent colossal magnetoresistance (CMR). However, research work on the neodymium-based system is limited to date. A comparative study between LSMO and NSMO prepared by sol–gel and solid-state reaction methods was undertaken to assess their structural, microstructural, magnetic, electrical, and magneto-transport properties. X-ray diffraction and structure refinement showed the formation of a single-phase composition. Sol–gel-synthesised NSMO was revealed to be a sample with single crystallite grains and exhibited intriguing magnetic and electrical transport behaviours. Magnetic characterisation highlighted that Curie temperature (TC) decreases with the grain size. Strong suppression of the metal–insulator transition temperature (TMI) was observed and attributed to the magnetically disordered grain surface and distortion of the MnO6 octahedra. The electrical resistivity in the metallic region was fitted with theoretical models, and the conduction mechanism could be explained by the grain/domain boundary, electron–electron, and electron–magnon scattering process. The increase in the scattering process was ascribed to the morphology changes. Enhancement of low-field magnetoresistance (LFMR) was observed in nano-grained samples. The obtained results show that the grain size and its distribution, as well as the crystallite formation, strongly affect the physical properties of hole-doped manganites.
Isotropic Nature of the Metallic Kagome Ferromagnet Fe3Sn2 at High Temperatures
Authors: Dally Rebecca L. , Phelan Daniel , Bishop Nicholas , Ghimire Nirmal J. , Lynn Jeffrey W.
Published: March 2021

Anisotropy and competing exchange interactions have emerged as two central ingredients needed for centrosymmetric materials to exhibit topological spin textures. Fe3Sn2 is thought to have these ingredients as well, as it has recently been discovered to host room temperature skyrmionic bubbles with an accompanying topological Hall effect. We present small-angle inelastic neutron scattering measurements that unambiguously show that Fe3Sn2 is an isotropic ferromagnet below TC≈660 K to at least 480 K—the lower temperature threshold of our experimental configuration. Fe3Sn2 is known to have competing magnetic exchange interactions, correlated electron behavior, weak magnetocrystalline anisotropy, and lattice (spatial) anisotropy; all of these features are thought to play a role in stabilizing skyrmions in centrosymmetric systems. Our results reveal that at the elevated temperatures measured, there is an absence of significant magnetocrystalline anisotropy and that the system behaves as a nearly ideal isotropic exchange interaction ferromagnet, with a spin stiffness D(T=480 K)=168 meV Å2, which extrapolates to a ground state spin stiffness D(T=0 K)=231 meV Å2.
Transport and Dielectric Properties of Mechanosynthesized La2/3Cu3Ti4O12 Ceramics
Authors: Ahmad Mohamad M. , Kotb Hicham Mahfoz , Joseph Celin , Kumar Shalendra , Alshoaibi Adil
Published: March 2021

La2/3Cu3Ti4O12 (LCTO) powder has been synthesized by the mechanochemical milling technique. The pelletized powder was conventionally sintered for 10 h at a temperature range of 975–1025 °C, which is a lower temperature process compared to the standard solid-state reaction. X-ray diffraction analysis revealed a cubic phase for the current LCTO ceramics. The grain size of the sintered ceramics was found to increase from 1.5 ± 0.5 to 2.3 ± 0.5 μm with an increase in sintering temperature from 975 to 1025 °C. The impedance results show that the grain conductivity is more than three orders of magnitude larger than the grain boundary conductivity for LCTO ceramics. All the samples showed a giant dielectric constant (1.7 × 103–3.4 × 103) and dielectric loss (0.09–0.17) at 300 K and 10 kHz. The giant dielectric constant of the current samples was attributed to the effect of internal barrier layer capacitances due to their electrically inhomogeneous structure.
The Influence of Gene Aberrations on Survival in Resected IDH Wildtype Glioblastoma Patients: A Single-Institution Study
Authors: Kalita Ondrej , Sporikova Zuzana , Hajduch Marian , Megova Houdova Magdalena , Slavkovsky Rastislav , Hrabalek Lumir , Halaj Matej , Klementova Yvona , Dolezel Martin , Drabek Jiri , Tuckova Lucie , Ehrmann Jiri , Vrbkova Jana , Trojanec Radek , Vaverka Miroslav
Published: March 2021

This prospective population-based study on a group of 132 resected IDH-wildtype (IDH-wt) glioblastoma (GBM) patients assesses the prognostic and predictive value of selected genetic biomarkers and clinical factors for GBM as well as the dependence of these values on the applied therapeutic modalities. The patients were treated in our hospital between June 2006 and June 2015. Clinical data and tumor samples were analyzed to determine the frequencies of TP53, MDM2, EGFR, RB1, BCR, and CCND1 gene aberrations and the duplication/deletion statuses of the 9p21.3, 1p36.3, 19q13.32, and 10p11.1 chromosome regions. Cut-off values distinguishing low (LCN) and high (HCN) copy number status for each marker were defined. Additionally, MGMT promoter methylation and IDH1/2 mutation status were investigated retrospectively. Young age, female gender, Karnofsky scores (KS) above 80, chemoradiotherapy, TP53 HCN, and CCND1 HCN were identified as positive prognostic factors, and smoking was identified as a negative prognostic factor. Cox proportional regression models of the chemoradiotherapy patient group revealed TP53 HCN and CCND1 HCN to be positive prognostic factors for both progression-free survival and overall survival. These results confirmed the influence of key clinical factors (age, KS, adjuvant oncotherapy, and smoking) on survival in GBM IDH-wt patients and demonstrated the prognostic and/or predictive importance of CCND1, MDM2, and 22q12.2 aberrations.
The Utility of Combined Target and Systematic Prostate Biopsies in the Diagnosis of Clinically Significant Prostate Cancer Using Prostate Imaging Reporting and Data System Version 2 Based on Biparametric Magnetic Resonance Imaging
Authors: Kato Daiki , Ozawa Kaori , Takeuchi Shinichi , Kawase Makoto , Kawase Kota , Nakai Chie , Takai Manabu , Iinuma Koji , Nakane Keita , Kato Hiroki , Matsuo Masayuki , Suzui Natsuko , Miyazaki Tatsuhiko , Koie Takuya
Published: March 2021

This study aimed to determine the predictive value of the Prostate Imaging Reporting and Data System version 2 (PI-RADS v2) based on biparametric magnetic resonance imaging (bpMRI) with combined target biopsy (TBx) and systematic biopsy (SBx) in patients with suspicion of having clinically significant prostate cancer (csPCa). In this retrospective study, we reviewed the clinical and pathological records of 184 consecutive patients who underwent bpMRI before prostate biopsy. We focused on patients with PI-RADS v2 scores ≥ 3. MRI was performed using a 3-Tesla clinical scanner with a 32-channel phased-array receiver coil. PI-RADS v2 was used to describe bpMRI findings based on T2-weighted imaging and diffusion-weighted imaging scores. The primary endpoint was the diagnostic accuracy rate of PI-RADS v2 based on bpMRI for patients with prostate cancer (PCa) who underwent combined TBx and SBx. A total of 104 patients were enrolled in this study. Combined TBx and SBx was significantly superior to either method alone for PCa detection in patients with suspicious lesions according to PI-RADS v2. TBx and SBx detected concordant csPCa in only 24.1% of the patients. In addition, the rate of increase in the Gleason score was similar between SBx (41.5%) and TBx (34.1%). The diagnostic accuracy of bpMRI is comparable to that of standard multiparametric MRI for the detection of csPCa. Moreover, combined TBx and SBx may be optimal for the accurate determination of csPCa diagnosis, the International Society of Urological Pathology grade, and risk classification.
The Role of Denosumab for Surgical Outcomes in Patients with Giant Cell Tumour of Bone: A Systematic Review
Authors: Gupta Abha , Durocher-Allen Lisa , Popovic Snezana , Tozer Richard , Yao Xiaomei , Ghert Michelle
Published: March 2021

Background: The role of denosumab in patients with resectable giant cell tumour of bone remains unclear. We asked the following research question: for patients (aged ≥ 12 years) with resectable giant cell tumour of bone, what are the benefits and harms of denosumab compared with no denosumab in terms of (1) facilitation of surgery (operative time, blood loss), (2) disease recurrence, (3) pain control, (4) disease stability, and (5) adverse effects (e.g., malignant transformation, osteonecrosis of jaw, atypical femur fracture)? One previous systematic review addressed only one outcome—disease recurrence. Therefore, we undertook this new systematic review to address the above five outcomes. Methods: MEDLINE, EMBASE, PubMed, and Cochrane Database of Systematic Reviews databases were searched on June 30, 2020. Results: This systematic review included one previous systematic review and five comparative studies. Due to poor quality, non-randomized studies fraught with selection bias, it is difficult to determine if a significant difference exists in the outcomes for surgical giant cell tumour of bone with perioperative denosumab. There were no reported cases of adverse effects from denosumab. Conclusion: To date, there is insufficient evidence to understand the value of denosumab in the perioperative setting in patients with giant cell tumour of bone.
Fat Composition Measured by Proton Spectroscopy: A Breast Cancer Tumor Marker?
Authors: Bitencourt Almir , Sevilimedu Varadan , Morris Elizabeth A. , Pinker Katja , Thakur Sunitha B.
Published: March 2021

Altered metabolism including lipids is an emerging hallmark of breast cancer. The purpose of this study was to investigate if breast cancers exhibit different magnetic resonance spectroscopy (MRS)-based lipid composition than normal fibroglandular tissue (FGT). MRS spectra, using the stimulated echo acquisition mode sequence, were collected with a 3T scanner from patients with suspicious lesions and contralateral normal tissue. Fat peaks at 1.3 + 1.6 ppm (L13 + L16), 2.1 + 2.3 ppm (L21 + L23), 2.8 ppm (L28), 4.1 + 4.3 ppm (L41 + L43), and 5.2 + 5.3 ppm (L52 + L53) were quantified using LCModel software. The saturation index (SI), number of double bods (NBD), mono and polyunsaturated fatty acids (MUFA and PUFA), and mean chain length (MCL) were also computed. Results showed that mean concentrations of all lipid metabolites and PUFA were significantly lower in tumors compared with that of normal FGT (p ≤ 0.002 and 0.04, respectively). The measure best separating normal and tumor tissues after adjusting with multivariable analysis was L21 + L23, which yielded an area under the curve of 0.87 (95% CI: 0.75–0.98). Similar results were obtained between HER2 positive versus HER2 negative tumors. Hence, MRS-based lipid measurements may serve as independent variables in a multivariate approach to increase the specificity of breast cancer characterization.
The Prognostic and Predictive Role of Somatic BRCA Mutations in Ovarian Cancer: Results from a Multicenter Cohort Study
Authors: Toss Angela , Piombino Claudia , Tenedini Elena , Bologna Alessandra , Gasparini Elisa , Tarantino Vittoria , Filieri Maria Elisabetta , Cottafavi Luca , Giovanardi Filippo , Madrigali Stefano , Civallero Monica , Marcheselli Luigi , Marchi Isabella , Domati Federica , Venturelli Marta , Barbieri Elena , Grandi Giovanni , Tagliafico Enrico , Cortesi Laura
Published: March 2021

Previous research involving epithelial ovarian cancer patients showed that, compared to germline BRCA (gBRCA) mutations, somatic BRCA (sBRCA) mutations present a similar positive impact with regard to overall survival (OS) and platinum and PARP (poly (ADP-ribose) polymerase) inhibitor sensitivity. Nevertheless, molecular testing in these studies did not include copy number variation (CNV) analyses of BRCA genes. The aim of this study was to explore the prognostic and predictive role of sBRCA mutations as compared to gBRCA mutations in patients who were also tested for CNVs. Among the 158 patients included in the study, 17.09% of patients carried a pathogenic or likely pathogenic gBRCA variant and 15.19% of patients presented pathogenetic or likely pathogenic sBRCA variants and/or CNVs. Overall, 81.6% of the patients included in this study were diagnosed with a serous histotype, and 77.2% were in advanced stages. Among women diagnosed in advanced stages, gBRCA patients showed better progression-free survival and OS as compared to sBRCA and wild-type patients, whereas sBRCA patients did not show any advantage in outcome as compared to wild-type patients. In this study, the introduction of CNV analyses increased the detection rate of sBRCA mutations, and the resulting classification among gBRCA, sBRCA and wild-type patients was able to properly stratify the prognosis of OC patients. Particularly, sBRCA mutation patients failed to show any outcome advantage as compared to wild-type patients.
Oral Diagnostic Methods for the Detection of Periodontal Disease
Authors: Ramenzoni Liza L. , Lehner Marc P. , Kaufmann Manuela E. , Wiedemeier Daniel , Attin Thomas , Schmidlin Patrick R.
Published: March 2021

Periodontitis is a common immune-inflammatory oral disease. Early detection plays an important role in its prevention and progression. Saliva is a reliable medium that mirrors periodontal health and is easily obtainable for identifying periodontal biomarkers in point-of-care diagnostics. The aim of this study is to evaluate the effectiveness of diagnostic salivary tests to determine periodontal status. Whole saliva (stimulated/unstimulated) from twenty healthy and twenty stage III grade B generalized periodontitis patients was tested for lactoferrin, alkaline phosphatase, calcium, density, osmolarity, pH, phosphate, buffer capacity, salivary flow rate and dynamic viscosity. A semi-quantitative urinary strip test was used to evaluate markers of inflammation in saliva (erythrocytes, leukocytes, urobilinogen, nitrite, glucose, bilirubin, and ketones), clinical periodontal parameters and pathogenic bacteria. Concentrations of lactoferrin, hemoglobin, and leukocytes were found to be significantly higher in the stimulated and unstimulated saliva in periodontitis patients compared to healthy patients, whereas alkaline phosphatase levels were higher in unstimulated saliva of periodontitis patients (p < 0.05). Periodontal biomarker analysis using test strips may be considered rapid and easy tool for distinguishing between periodontitis and healthy patients. The increase in lactoferrin, hemoglobin, and leucocytes—determined by strip tests—may provide a non-invasive method of periodontal diagnosis.
Myocardial Work: Methodology and Clinical Applications
Authors: Papadopoulos Konstantinos , Özden Tok Özge , Mitrousi Konstantina , Ikonomidis Ignatios
Published: March 2021

A precise and accurate assessment of left ventricular (LV) contractility is of utmost importance in terms of prognosis in most cardiac pathologies. Given the limitations of ejection fraction (EF) and global longitudinal strain (GLS) due to their load dependency, a novel imaging tool called myocardial work (MW) has emerged as a promising method for LV performance evaluation. MW is a novel, less load-dependent method based on computation of myocardial strain–arterial blood pressure curves. This method provides a more detailed assessment of segmental and global LV function incorporating the patient’s LV pressure and is derived by brachial artery pressure utilizing an empiric reference curve adjusted to the duration of the isovolumic and ejection phases as determined by echocardiography. The clinical implications of this unique method have been expanding in the last few years, which attest to the robust additive role of MW in routine practice.
Stirling Refrigerating Machine Modeling Using Schmidt and Finite Physical Dimensions Thermodynamic Models: A Comparison with Experiments
Authors: Dobre Cătălina , Grosu Lavinia , Dobrovicescu Alexandru , Chişiu Georgiana , Constantin Mihaela
Published: March 2021

The purpose of the study is to show that two simple models that take into account only the irreversibility due to temperature difference in the heat exchangers and imperfect regeneration are able to indicate refrigerating machine behavior. In the present paper, the finite physical dimensions thermodynamics (FPDT) method and 0-D modeling using the Schmidt model with imperfect regeneration were applied in the study of a β type Stirling refrigeration machine.The 0-D modeling is improved by including the irreversibility caused by imperfect regeneration and the finite temperature difference between the gas and the heat exchangers wall. A flowchart of the Stirling refrigerator exergy balance is presented to show the internal and external irreversibilities. It is found that the irreversibility at the regenerator level is more important than that at the heat exchangers level. The energies exchanged by the working gas are expressed according to the practical parameters, necessary for the engineer during the entire project. The results of the two thermodynamic models are presented in comparison with the experimental results, which leads to validation of the proposed FPDT model for the functional and constructive parameters of the studied refrigerating machine.
Spectral Ranking of Causal Influence in Complex Systems
Authors: Zalmijn Errol , Heskes Tom , Claassen Tom
Published: March 2021

Similar to natural complex systems, such as the Earth’s climate or a living cell, semiconductor lithography systems are characterized by nonlinear dynamics across more than a dozen orders of magnitude in space and time. Thousands of sensors measure relevant process variables at appropriate sampling rates, to provide time series as primary sources for system diagnostics. However, high-dimensionality, non-linearity and non-stationarity of the data are major challenges to efficiently, yet accurately, diagnose rare or new system issues by merely using model-based approaches. To reliably narrow down the causal search space, we validate a ranking algorithm that applies transfer entropy for bivariate interaction analysis of a system’s multivariate time series to obtain a weighted directed graph, and graph eigenvector centrality to identify the system’s most important sources of original information or causal influence. The results suggest that this approach robustly identifies the true drivers or causes of a complex system’s deviant behavior, even when its reconstructed information transfer network includes redundant edges.
Demonstration of Three True Random Number Generator Circuits Using Memristor Created Entropy and Commercial Off-the-Shelf Components
Authors: Stoller Scott , Campbell Kristy A.
Published: March 2021

In this work, we build and test three memristor-based true random number generator (TRNG) circuits: two previously presented in the literature and one which is our own design. The functionality of each circuit is assessed using the National Institute of Standards and Technology (NIST) Statistical Test Suite (STS). The TRNG circuits were built using commercially available off-the-shelf parts, including the memristor. The results of this work confirm the usefulness of memristors for successful implementation of TRNG circuits, as well as the ease with which a TRNG can be built using simple circuit designs and off-the-shelf breadboard circuit components.
Vector Arithmetic in the Triangular Grid
Authors: Abuhmaidan Khaled , Aldwairi Monther , Nagy Benedek
Published: March 2021

Vector arithmetic is a base of (coordinate) geometry, physics and various other disciplines. The usual method is based on Cartesian coordinate-system which fits both to continuous plane/space and digital rectangular-grids. The triangular grid is also regular, but it is not a point lattice: it is not closed under vector-addition, which gives a challenge. The points of the triangular grid are represented by zero-sum and one-sum coordinate-triplets keeping the symmetry of the grid and reflecting the orientations of the triangles. This system is expanded to the plane using restrictions like, at least one of the coordinates is an integer and the sum of the three coordinates is in the interval [−1,1]. However, the vector arithmetic is still not straightforward; by purely adding two such vectors the result may not fulfill the above conditions. On the other hand, for various applications of digital grids, e.g., in image processing, cartography and physical simulations, one needs to do vector arithmetic. In this paper, we provide formulae that give the sum, difference and scalar product of vectors of the continuous coordinate system. Our work is essential for applications, e.g., to compute discrete rotations or interpolations of images on the triangular grid.
Industry 4.0 Quantum Strategic Organizational Design Configurations. The Case of 3 Qubits: One Reports to Two
Authors: Villalba-Diez Javier , Losada Juan Carlos , Benito Rosa María , González-Marcos Ana
Published: March 2021

In this work we explore how the relationship between one subordinate reporting to two leaders influences the alignment of the latter with the company’s strategic objectives in an Industry 4.0 environment. We do this through the implementation of quantum circuits that represent decision networks. This is done for two cases: One in which the leaders do not communicate with each other, and one in which they do. Through the quantum simulation of strategic organizational design configurations (QSOD) through 500 quantum circuit simulations, we conclude that in the first case both leaders are not simultaneously in alignment, and in the second case that both reporting nodes need to have an alignment probability higher than 90% to support the leader node.
Dissemination of Social Accounting Information: A Bibliometric Review
Authors: Rodrigues Margarida , do Céu Alves Maria , Oliveira Cidália , Vale Vera , Vale José , Silva Rui
Published: March 2021

The discussion in recent decades about sustainable development issues has given rise to a new accounting dimension: social accounting. Currently, this issue remains an emerging theme. Although there are some studies and literature reviews, none include disclosure of social accounting information or the analysis of research paradigms. This article reviews the research on social accounting disclosure and tries to answer the following research questions: What research streams have been followed? Which theories and research paradigms have been used? The search for articles to be included in the literature review was performed through the Web of Science. The 126 articles obtained were later analyzed using Bibliometrix software. Results expose the growing interest in this theme and identify three distinct research lines (three clusters): Cluster 1—Social accounting disclosures, Cluster 2—Legitimacy vs. disclosure of social accounting, and Cluster 3—Motivations for disclosure of social accounting. The main contribute of this article resides, on the one hand, in the fact that no literature review articles have been found that include the theme of the disclosure of information on social accounting and, on the other hand, the treatment of data has been done with innovative software, an R package for bibliometric and co-citation analysis called Bibliometrix. As well as mapping the literature, another theoretical contribution of this study was identifying the main research approaches used in the studies. Within the paradigmatic plurality of social accounting research, the results suggest that social accounting research can also be critically addressed when addressing the sustainability challenges posed by climate change or carbon emissions, among many other aspects. This study is, to our knowledge, the first bibliometric review done about social accounting information disclosure.
Continuous Automotive Software Updates through Container Image Layers
Authors: Ayres Nicholas , Deka Lipika , Paluszczyszyn Daniel
Published: March 2021

The vehicle-embedded system also known as the electronic control unit (ECU) has transformed the humble motorcar, making it more efficient, environmentally friendly, and safer, but has led to a system which is highly dependent on software. As new technologies and features are included with each new vehicle model, the increased reliance on software will no doubt continue. It is an undeniable fact that all software contains bugs, errors, and potential vulnerabilities, which when discovered must be addressed in a timely manner, primarily through patching and updates, to preserve vehicle and occupant safety and integrity. However, current automotive software updating practices are ad hoc at best and often follow the same inefficient fix mechanisms associated with a physical component failure of return or recall. Increasing vehicle connectivity heralds the potential for over the air (OtA) software updates, but rigid ECU hardware design does not often facilitate or enable OtA updating. To address the associated issues regarding automotive ECU-based software updates, a new approach in how automotive software is deployed to the ECU is required. This paper presents how lightweight virtualisation technologies known as containers can promote efficient automotive ECU software updates. ECU functional software can be deployed to a container built from an associated image. Container images promote efficiency in download size and times through layer sharing, similar to ECU difference or delta flashing. Through containers, connectivity and OtA future software updates can be completed without inconveniences to the consumer or incurring expense to the manufacturer.
Real-Time Implementation of the Predictive-Based Control with Bacterial Foraging Optimization Technique for Power Management in Standalone Microgrid Application
Authors: Dubuisson Félix , Rezkallah Miloud , Ibrahim Hussein , Chandra Ambrish
Published: March 2021

In this paper, the predictive-based control with bacterial foraging optimization technique for power management in a standalone microgrid is studied and implemented. The heuristic optimization method based on the social foraging behavior of Escherichia coli bacteria is employed to determine the power references from the non-renewable energy sources and loads of the proposed configuration, which consists of a fixed speed diesel generator and battery storage system (BES). The two-stage configuration is controlled to maintain the DC-link voltage constant, regulate the AC voltage and frequency, and improve the power quality, simultaneously. For these tasks, on the AC side, the obtained power references are used as input signals to the predictive-based control. With the help of the system parameters, the predictive-based control computes all possible states of the system on the next sampling time and compares them with the estimated power references obtained using the bacterial foraging optimization (BFO) technique to get the inverter current reference. For the DC side, the same concept based on the predictive approach is employed to control the DC-DC buck-boost converter by regulating the DC-link voltage using the forward Euler method to generate the discrete-time model to predict in real-time the BES current. The proposed control strategies are evaluated using simulation results obtained with Matlab/Simulink in presence of different types of loads, as well as experimental results obtained with a small-scale microgrid.
Passive Model Predictive Control on a Two-Body Self-Referenced Point Absorber Wave Energy Converter
Authors: Montoya Dan , Tedeschi Elisabetta , Castellini Luca , Martins Tiago
Published: March 2021

Wave energy is nowadays one of the most promising renewable energy sources; however, wave energy technology has not reached the fully-commercial stage, yet. One key aspect to achieve this goal is to identify an effective control strategy for each selected Wave Energy Converter (WEC), in order to extract the maximum energy from the waves, while respecting the physical constraints of the device. Model Predictive Control (MPC) can inherently satisfy these requirements. Generally, MPC is formulated as a quadratic programming problem with linear constraints (e.g., on position, speed and Power Take-Off (PTO) force). Since, in the most general case, this control technique requires bidirectional power flow between the PTO system and the grid, it has similar characteristics as reactive control. This means that, under some operating conditions, the energy losses may be equivalent, or even larger, than the energy yielded. As many WECs are designed to only allow unidirectional power flow, it is necessary to set nonlinear constraints. This makes the optimization problem significantly more expensive in terms of computational time. This work proposes two MPC control strategies applied to a two-body point absorber that address this issue from two different perspectives: (a) adapting the MPC formulation to passive loading strategy; and (b) adapting linear constraints in the MPC in order to only allow an unidirectional power flow. The results show that the two alternative proposals have similar performance in terms of computational time compared to the regular MPC and obtain considerably more power than the linear passive control, thus proving to be a good option for unidirectional PTO systems.
Experimental Study on the Performance of a Novel Compact Electrostatic Coalescer with Helical Electrodes
Authors: Shi Yi , Chen Jiaqing , Pan Zehao
Published: March 2021

As most of the light and easy oil fields have been produced or are nearing their end-life, the emulsion stability is enhanced and water cut is increasing in produced fluid which have brought challenges to oil–water separation in onshore and offshore production trains. The conventional solution to these challenges includes a combination of higher chemical dosages, larger vessels and more separation stages, which often demands increased energy consumption, higher operating costs and larger space for the production facility. It is not always feasible to address the issues by conventional means, especially for the separation process on offshore platforms. Electrostatic coalescence is an effective method to achieve demulsification and accelerate the oil–water separation process. In this paper, a novel compact electrostatic coalescer with helical electrodes was developed and its performance on treatment of water-in-oil emulsions was investigated by experiments. Focused beam reflectance measurement (FBRM) was used to make real-time online measurements of water droplet sizes in the emulsion. The average water droplet diameters and number of droplets within a certain size range are set as indicators for evaluating the effect of coalescence. We investigated the effect of electric field strength, frequency, water content and fluid velocity on the performance of coalescence. The experimental results showed that increasing the electric field strength could obviously contribute to the growth of small water droplets and coalescence. The extreme value of electric field strength achieved in the high-frequency electric field was much higher than that in the power-frequency (50 Hz) electric field, which can better promote the growth of water droplets. The initial average diameters of water droplets increase with higher water content. The rate of increment in the electric field was also increased. Its performance was compared with that of the plate electrodes to further verify the advantages of enhancing electrostatic coalescence and demulsification with helical electrodes. The research results can provide guidance for the optimization and performance improvement of a compact electrocoalescer.
Predicting the Performance of Undeveloped Multi-Fractured Marcellus Gas Wells Using an Analytical Flow-Cell Model (FCM)
Authors: Waters David , Weijermars Ruud
Published: March 2021

The objective of the present study is to predict how changes in the fracture treatment design parameters will affect the production performance of new gas wells in a target zone of the Marcellus shale. A recently developed analytical flow-cell model can estimate future production for new wells with different completion designs. The flow-cell model predictions were benchmarked using historic data of 11 wells and 6 different completion designs. First, a type well was generated and used with the flow-cell model to predict the performance of the later infill wells—with variable completion designs—based off the performance of earlier wells. The flow-cell model takes into account known hyperbolic forecast parameters (qi, Di, and b-factor) and fracture parameters (height, half-length, and spacing) of a type well. Next, the flow-cell model generates the hyperbolic decline parameters for an offset well based on the selected changes in the fracture treatment design parameters. Using a numerical simulator, the flow-cell model was verified as an accurate modeling technique for forecasting the production performance of horizontal, multi-fractured, gas wells.
Transient Stability Analysis of Grid-Connected Converter Driven by Imbalance Power under Non-Severe Remote Voltage Sag
Authors: Quan Xuli , Lin Xinchun , Zheng Yun , Kang Yong
Published: March 2021

In the transient process of the grid-connected converter (GCC), the existing research mainly focuses on the impact of the control loops. Little attention is paid to the transient stability issues driven by the imbalance between the input power and output power of GCC. This paper shows that the transient stability issues will still exist even if ignoring the dynamics of phase-locked loop (PLL) and current loop. In this paper, the models of the AC grid and the GCC are built under the assumption that the dynamics of the PLL and current loop are ignored. Then, by analyzing the transient process of GCC under non-severe remote voltage sag, the effects of the imbalance power on the transient stability of GCC are discussed. Moreover, for the GCC to operate stably after the transient process, there should be a maximum input power limit (MIPL) for GCC, and the imbalance power equation is applied in this paper to determine the transient stability of GCC. Furthermore, the effects of the current limitation on the transient stability of the GCC are also discussed. Finally, the theoretical analysis has been verified by means of simulations.
Insulation Life Span of Low-Voltage Electric Motors—A Survey
Authors: Höpner Vanessa Neves , Wilhelm Volmir Eugênio
Published: March 2021

The use of static frequency converters, which have a high switching frequency, generates voltage pulses with a high rate of change over time. In combination with cable and motor impedance, this generates repetitive overvoltage at the motor terminals, influencing the occurrence of partial discharges between conductors, causing degradation of the insulation of electric motors. Understanding the effects resulting from the frequency converter–electric motor interaction is essential for developing and implementing insulation systems with characteristics that support the most diverse applications, have an operating life under economically viable conditions, and promote energy efficiency. With this objective, a search was carried out in three recognized databases. Duplicate articles were eliminated, resulting in 1069 articles, which were systematically categorized and reviewed, resulting in 481 articles discussing the causes of degradation in the insulation of electric motors powered by frequency converters. A bibliographic portfolio was built and evaluated, with 230 articles that present results on the factors that can be used in estimating the life span of electric motor insulation. In this structure, the historical evolution of the collected information, the authors who conducted the most research on the theme, and the relevance of the knowledge presented in the works were considered.
Measurement of Static Frequency Characteristics of Home Appliances in Smart Grid Systems
Authors: Beláň Anton , Cintula Boris , Cenký Matej , Janiga Peter , Bendík Jozef , Eleschová Žaneta , Šimurka Adam
Published: March 2021

The current transformation of power systems is aiming towards distributed source integration and general decentralization. Renewable energy sources and support of local energy supply create conditions for widespread use of new technologies and smart grids. As the electrical grids become more electrically independent, the importance of frequency control will rise. Stability of the system in such cases is no longer only relying on rotating inertia of generators as in the centralized grid. This known scenario has already been analyzed by many with computational models for optimal safety precautions of the grid. This paper aims to update the common home appliance frequency characteristics through measurements and compare them to those currently used. These devices were divided into two groups: general categorization and light sources. Subsequently, the frequency sensitivity coefficients were evaluated and analyzed home appliances were sorted into three categories according to the size of their frequency sensitivity coefficient values: positive, negative, and no effect. The results were compared with studies aimed at evaluating the static load characteristics. A simplified simulation of the frequency control, presented in the discussion section, was carried out to determine the consequences of the newly measured characteristics and concludes the paper.
A Matrix FMEA Analysis of Variable Delivery Vane Pumps
Authors: Fabis-Domagala Joanna , Domagala Mariusz , Momeni Hassan
Published: March 2021

Hydraulic systems are widely used in the aeronautic, machinery, and energy industries. The functions that these systems perform require high reliability, which can be achieved by examining the causes of possible defects and failures and by taking appropriate preventative measures. One of the most popular methods used to achieve this goal is FMEA (Failure Modes and Effects Analysis), the foundations of which were developed and implemented in the early 1950s. It was systematized in the following years and practically implemented. It has also been standardized and implemented as one of the methods of the International Organization for Standardization (ISO) 9000 series standards on quality assurance and management. Apart from wide application, FMEA has a number of weaknesses, which undoubtedly include risk analysis based on the RPN (Risk Priority Number), which is evaluated as a product of severity, occurrence, and detection. In recent years, the risk analysis has been very often replaced by fuzzy logic. This study proposes the use of matrix analysis and statistical methods for performing simplified RCA (Root Cause Analysis) and for classification potential failures for a variable delivery vane pump. The presented methodology is an extension of matrix FMEA and allows for prioritizing potential failures and their causes in relation to functions performed by pump components, the end effects, and the defined symptoms of failure of the vane pump.
Why We Continue to Need Energy Efficiency Programmes—A Critical Review Based on Experiences in Switzerland and Elsewhere
Authors: Patel Martin K. , Broc Jean-Sébastien , Cho Haein , Cabrera Daniel , Eberle Armin , Federici Alessandro , Freyre Alisa , Jeanneret Cédric , Narula Kapil , Oikonomou Vlasios , Yilmaz Selin
Published: March 2021

Energy efficiency programmes (EEPs) are schemes operated by utilities or other bodies in order to incentivize energy efficiency improvement, in particular by adoption of energy-efficient products and typically by means of an economic reward. Ample experience has been gained, especially in the U.S., where EEPs have been in use for decades, with the rationale of avoiding additional energy supply by improving energy efficiency. More recently, EEPs have been implemented in Europe and in Switzerland. This review paper presents insights from the U.S., the EU and especially from Switzerland, with a focus on levelised programme cost of saved energy (LPC) as a key performance indicator. These LPC values, which take the perspective of the programme operator, are typically low to very low compared to the cost of electricity supply, thereby representing an important argument in favour of their use. The country examples show that EEPs are being effectively and successfully put into practice, for example, in Switzerland both as (i) a national tender-based scheme (called ProKilowatt) and in the form of a (ii) utility-operated obligation-based scheme (in Geneva). EEPs not only call for diligent implementation but also for suitable legal settings, e.g., in the form of mandatory energy efficiency savings targets (as realised for energy efficiency obligations, EEOs) in combination with programme cost recovery. The main criticism of EEPs is the free-rider effect, which needs to be minimised. On the other hand, EEPs are accompanied by significant co-benefits (environmental, health-related and social) and spillover effects. In their currently prevalent form, EEPs allow one to effectively save energy at a (very) low cost (“low-hanging fruit”). They can hence play an important role in fostering the energy transition; however, they should be implemented as part of a policy portfolio, in combination with other policy instruments.
A Single-Well Gas-Assisted Gravity Drainage Enhanced Oil Recovery Process for U.S. Deepwater Gulf of Mexico Operations
Authors: Saikia Bikash D. , Rao Dandina N.
Published: March 2021

The U.S. Deepwater Gulf of Mexico (DGOM) area that has some of the most prolific oil reservoirs is still awaiting the development of a viable enhanced oil recovery (EOR) process. Without it, DGOM will remain severely untapped. Exorbitant well costs, in excess of $200 million, preclude having extensive injection patterns, commonly used in EOR design frameworks. Aside from injection patterns, even operationally waterflooding has met with significant challenges because of injectivity issues in these over pressurized turbidities. The gas-assisted gravity drainage (GAGD) EOR process, that holds promise for deepwater environments because of lesser injectivity issues, among others, has been adapted in this work to overcome these limitations. A novel design in the form of a single well—gas assisted gravity drainage (SW-GAGD) process, has been demonstrated to emulate the benefits of a GAGD process in a cost-effective manner. Unlike conventional GAGD processes, which need multiple injectors and separate horizontal production wells, the SW-GAGD process just uses a single well for injection and well production. The performance of the process has been established using partially scaled visual glass models based on dimensional analyses for scale up of the process. The recovery factor has been shown to be in the range of 65–80% in the immiscible mode alone, and the process is orders of magnitude faster than natural gravity drainage. A toe-to-heel configuration of the SW-GAGD process has also been tested and for the configuration to be immune from reservoir layering, the toe of the well should ideally end at the top of the payzone. Better sweep of the payzone and consequent high recovery factor of 80% OOIP was observed, if the heel part of the bottom lateral is located in a lower permeability zone.
A Quadratically Constrained Optimization Problem for Determining the Optimal Nominal Power of a PV System in Net-Metering Model: A Case Study for Croatia
Authors: Budin Luka , Grdenić Goran , Delimar Marko
Published: March 2021

The world’s demand for electrical energy is increasing rapidly while the use of fossil fuels is getting limited more and more by energy policies and the need for reducing the impact of climate change. New sources of energy are required to fulfill the world’s demand for electricity and they are currently found in renewable sources of energy, especially in solar and wind power. Choosing the optimal PV nominal power minimizes the unnecessary surplus of electrical energy that is exported to the grid and thus is not making any impact on the grid more than necessary. Oversizing the PV system according to the Croatian net-metering model results in switching the calculation of the costs to the prosumer model which results in a decrease of the project’s net present value (NPV) and an increase in the payback period (PP). This paper focuses on formulating and solving the optimization problem for determining the optimal nominal power of a grid-connected PV system with a case study for Croatia using multiple scenarios in the variability of electricity production and consumption. In this paper, PV systems are simulated in the power range that corresponds to a typical annual high-tariff consumption in Croatian households. Choosing the optimal power of the PV system maximizes the investor’s NPV of the project as well as savings on the electricity costs. The PP is also minimized and is determined by the PV production, household consumption, discount rate, and geographic location. The optimization problem is classified as a quadratically constrained discrete optimization problem, where the value of the optimal PV power is not a continuous variable because the PV power changes with a step of one PV panel power. Modeling and simulations are implemented in Python using the Gurobi optimization solver.