bluuebunny/crossref_metadata_2025 huggingface dataset:
A Hierarchical Architecture of Functionalized Polyaniline/Manganese Dioxide Composite with Stable-Enhanced Electrochemical Performance
Authors: Wang Yapeng , Wang Yanxiang , Wang Chengjuan , Wang Yongbo
Published: May 2021

As one of the most outstanding high-efficiency and environmentally friendly energy storage devices, the supercapacitor has received extensive attention across the world. As a member of transition metal oxides widely used in electrode materials, manganese dioxide (MnO2) has a huge development potential due to its excellent theoretical capacitance value and large electrochemical window. In this paper, MnO2 was prepared at different temperatures by a liquid phase precipitation method, and polyaniline/manganese dioxide (PANI/MnO2) composite materials were further prepared in a MnO2 suspension. MnO2 and PANI/MnO2 synthesized at a temperature of 40 °C exhibit the best electrochemical performance. The specific capacitance of the sample MnO2-40 is 254.9 F/g at a scanning speed of 5 mV/s and the specific capacitance is 241.6 F/g at a current density of 1 A/g. The specific capacitance value of the sample PANI/MnO2-40 is 323.7 F/g at a scanning speed of 5 mV/s, and the specific capacitance is 291.7 F/g at a current density of 1 A/g, and both of them are higher than the specific capacitance value of MnO2. This is because the δ-MnO2 synthesized at 40 °C has a layered structure, which has a large specific surface area and can accommodate enough electrolyte ions to participate the electrochemical reaction, thus providing sufficient specific capacitance.
A Review on Mechanical Properties of Natural Fibre Reinforced Polymer Composites under Various Strain Rates
Authors: Khieng Tan Ke , Debnath Sujan , Ting Chaw Liang Ernest , Anwar Mahmood , Pramanik Alokesh , Basak Animesh Kumar
Published: May 2021

With the lightning speed of technological evolution, the demand for high performance yet sustainable natural fibres reinforced polymer composites (NFPCs) are rising. Especially a mechanically competent NFPCs under various loading conditions are growing day by day. However, the polymers mechanical properties are strain-rate dependent due to their viscoelastic nature. Especially for natural fibre reinforced polymer composites (NFPCs) which the involvement of filler has caused rather complex failure mechanisms under different strain rates. Moreover, some uneven micro-sized natural fibres such as bagasse, coir and wood were found often resulting in micro-cracks and voids formation in composites. This paper provides an overview of recent research on the mechanical properties of NFPCs under various loading conditions-different form (tensile, compression, bending) and different strain rates. The literature on characterisation techniques toward different strain rates, composite failure behaviours and current challenges are summarised which have led to the notion of future study trend. The strength of NFPCs is generally found grow proportionally with the strain rate up to a certain degree depending on the fibre-matrix stress-transfer efficiency. The failure modes such as embrittlement and fibre-matrix debonding were often encountered at higher strain rates. The natural filler properties, amount, sizes and polymer matrix types are found to be few key factors affecting the performances of composites under various strain rates whereby optimally adjust these factors could maximise the fibre-matrix stress-transfer efficiency and led to performance increases under various loading strain rates.
Simulation-Based Estimation of the Number of Cameras Required for 3D Reconstruction in a Narrow-Baseline Multi-Camera Setup
Authors: Wachter Andreas , Kost Jan , Nahm Werner
Published: May 2021

Graphical visualization systems are a common clinical tool for displaying digital images and three-dimensional volumetric data. These systems provide a broad spectrum of information to support physicians in their clinical routine. For example, the field of radiology enjoys unrestricted options for interaction with the data, since information is pre-recorded and available entirely in digital form. However, some fields, such as microsurgery, do not benefit from this yet. Microscopes, endoscopes, and laparoscopes show the surgical site as it is. To allow free data manipulation and information fusion, 3D digitization of surgical sites is required. We aimed to find the number of cameras needed to add this functionality to surgical microscopes. For this, we performed in silico simulations of the 3D reconstruction of representative models of microsurgical sites with different numbers of cameras in narrow-baseline setups. Our results show that eight independent camera views are preferable, while at least four are necessary for a digital surgical site. In most cases, eight cameras allow the reconstruction of over 99% of the visible part. With four cameras, still over 95% can be achieved. This answers one of the key questions for the development of a prototype microscope. In future, such a system can provide functionality which is unattainable today.
Stability and Change in Diffusion Model Parameters over Two Years
Authors: von Krause Mischa , Radev Stefan T. , Voss Andreas , Quintus Martin , Egloff Boris , Wrzus Cornelia
Published: May 2021

In recent years, mathematical models of decision making, such as the diffusion model, have been endorsed in individual differences research. These models can disentangle different components of the decision process, like processing speed, speed–accuracy trade-offs, and duration of non-decisional processes. The diffusion model estimates individual parameters of cognitive process components, thus allowing the study of individual differences. These parameters are often assumed to show trait-like properties, that is, within-person stability across tasks and time. However, the assumption of temporal stability has so far been insufficiently investigated. With this work, we explore stability and change in diffusion model parameters by following over 270 participants across a time period of two years. We analysed four different aspects of stability and change: rank-order stability, mean-level change, individual differences in change, and profile stability. Diffusion model parameters showed strong rank-order stability and mean-level changes in processing speed and speed–accuracy trade-offs that could be attributed to practice effects. At the same time, people differed little in these patterns across time. In addition, profiles of individual diffusion model parameters proved to be stable over time. We discuss implications of these findings for the use of the diffusion model in individual differences research.
Investigation and Validation of Numerical Models for Composite Wind Turbine Blades
Authors: Finnegan William , Jiang Yadong , Dumergue Nicolas , Davies Peter , Goggins Jamie
Published: May 2021

As the world shifts to using renewable sources of energy, wind energy has been established as one of the leading forms of renewable energy. As the requirement for wind energy increases, so too does the size of the turbines themselves, where the latest turbines are 10 MW with a turbine diameter in excess of 190 m. The design and manufacture of the blades for these turbines will be critical if they are to last for the design life, where the accuracy of the numerical models used in the design process is paramount. Therefore, in this paper, three independent numerical models have been created using three available finite element method packages—ABAQUS, ANSYS, and CalculiX—and the results were compiled. Following this, the accuracy of the models has been evaluated and validated against the results from an experimental testing campaign. In order to complete the study, a 13 m full-scale wind turbine blade has been used, which has been subjected to static testing in both the edgewise and flapwise directions. The results from this testing campaign, along with the blade mass and natural frequencies, have been compared to the results from the independent numerical models. The differences in the models, along with other sources of error, have been discussed, which includes recommendations on the development of accurate numerical models.
The Future of Russian Arctic Oil and Gas Projects: Problems of Assessing the Prospects
Authors: Chanysheva Amina , Ilinova Alina
Published: May 2021

The development of Arctic marine resources is currently the focus of the world’s largest oil and gas companies, which is due to the presence of significant hydrocarbon reserves. However, the decision-making process for implementing offshore oil and gas projects in the Arctic is highly uncertain and requires consideration of many factors. This study presents a comprehensive approach to evaluating the prospects of oil production on the Russian Arctic shelf. It is based on a specific methodology which involves expert forecasting methods. We analyze the current conditions and key factors and indicators, focusing on oil prices and quality of technologies that could influence the decision-making in the oil and gas company concerning Arctic offshore fields’ development. We use general scientific methods—analysis, synthesis, classification and systematization—and propose a method for assessing the prospects of Arctic projects which is based on a three-step algorithm. Together with practical tools presented in the article, it will support decision-making on the project initiation and the development of a particular field.
Biocontrol of Aflatoxins Using Non-Aflatoxigenic Aspergillus flavus: A Literature Review
Authors: Khan Rahim , Ghazali Farinazleen Mohamad , Mahyudin Nor Ainy , Samsudin Nik Iskandar Putra
Published: May 2021

Aflatoxins (AFs) are mycotoxins, predominantly produced by Aspergillus flavus, A. parasiticus, A. nomius, and A. pseudotamarii. AFs are carcinogenic compounds causing liver cancer in humans and animals. Physical and biological factors significantly affect AF production during the pre-and post-harvest time. Several methodologies have been developed to control AF contamination, yet; they are usually expensive and unfriendly to the environment. Consequently, interest in using biocontrol agents has increased, as they are convenient, advanced, and friendly to the environment. Using non-aflatoxigenic strains of A. flavus (AF−) as biocontrol agents is the most promising method to control AFs’ contamination in cereal crops. AF− strains cannot produce AFs due to the absence of polyketide synthase genes or genetic mutation. AF− strains competitively exclude the AF+ strains in the field, giving an extra advantage to the stored grains. Several microbiological, molecular, and field-based approaches have been used to select a suitable biocontrol agent. The effectiveness of biocontrol agents in controlling AF contamination could reach up to 99.3%. Optimal inoculum rate and a perfect time of application are critical factors influencing the efficacy of biocontrol agents.
Outcomes and Loop Pattern Analysis of a Road-Map Technique for ERCP with Side-Viewing Duodenoscope in Patients with Billroth II Gastrectomy (with Video)
Authors: Yang Min Jae , Kim Jin Hong , Hwang Jae Chul , Yoo Byung Moo , Li Yu Ji , Kim Soon Sun , Lim Sun Gyo
Published: May 2021

Endoscopic retrograde cholangiopancreatography (ERCP) in patients who have undergone a Billroth II gastrectomy is a major challenge. This study aimed to evaluate the outcomes of the road-map technique for duodenal intubation using a side-viewing duodenoscope for ERCP in Billroth II gastrectomy patients with naïve papilla, and to analyze the formation and release patterns of common bowel loops that occur when the duodenoscope navigates the afferent limb. The duodenoscopy approach success rate was 85.8% (97/113). In successful duodenoscopy approach patients, there were five bowel looping patterns that occurred when the preceding catheter-connected duodenoscope was advanced into the duodenum: (1) reverse ɣ-loop (29.9%), (2) fixed reverse ɣ-loop (5.2%), (3) simple U-loop (22.7%), (4) N-loop (28.9%), and (5) reverse alpha loop (13.4%). The duodenoscopy cannulation and duodenoscopy therapeutic success rates were 81.4% (92/113) and 80.5% (91/113), respectively, while the overall cannulation and therapeutic success rates were 92.0% (104/113) and 87.6% (99/113), respectively. Bowel perforation occurred in three patients (2.7%). The road-map technique may benefit duodenoscope-based ERCP in Billroth II gastrectomy patients by minimizing the tangential axis alignment between the duodenoscopic tip and driving of the afferent limb, and by predicting and counteracting bowel loops that occur when the duodenoscope navigates the afferent limb.
Prescription Pattern of Antidepressants and the Potential for Personalized Medicine in the Qatari Population
Authors: Bastaki Kholoud , El Anbari Mohammed , Ghuloum Suhaila , Jithesh Puthen Veettil
Published: May 2021

Studying the prescription pattern of medications will help in understanding potential unnecessary prescriptions, due to the trial-and-error method of prescribing, and the need for personalized medicine in a population. Therefore, in this study, our aim was to explore the prescribing pattern and off-label use of antidepressants in the Qatari population. We conducted a retrospective study of Qatari patients who received prescriptions for antidepressants from the major healthcare providers in Qatar, for a period of 24 months between June 2018 and May 2020. The number of patients, prescriptions, and diagnostic indications were analyzed. The chi-square test was used for identifying statistically significant association of the number of individuals prescribed with age category or gender. Of the 14,601 Qatari patients who were prescribed antidepressants, the majority were female (61%, p < 2.2 × 10−16), and were at or above 60 years of age (27%, p < 2.2 × 10−16). More numbers of selective serotonin reuptake inhibitors (SSRIs) (22,085 out of 48,031; 46%), were dispensed than other classes of antidepressants, with escitalopram (26%) at the top of the list. Preponderance of prescription of antidepressants for non-mental health diseases was observed. Population-level prescription trends, as we reported here, when combined with patient genetic variability and outcome data, will have the power to predict the potential for treatment failures and adverse effects of these medications in the population. We also recommend educating non-mental health prescribers about the adherence to evidence and guidelines to ensure patient safety while prescribing antidepressants.
Recommendations for a Combined Laparoscopic and Transanal Approach in Treating Deep Endometriosis of the Lower Rectum—The Rouen Technique
Authors: Nastasia Şerban , Simionescu Anca Angela , Tuech Jean Jacques , Roman Horace
Published: May 2021

The complete excision of low rectovaginal deep endometriosis is a demanding surgery associated with an increased risk of intra- and postoperative complications, which can impact the quality of life. Given the choices of optimal surgery procedures available, we would like to emphasize that a minimally invasive approach with plasma medicine and a transanal disc excision could significantly improve surgery for deep endometriosis, avoiding the lateral thermal damage of vascular and parasympathetic fibers of roots S2–S5 in the pelvic plexus. The management of low rectal deep endometriosis is distinct from other gastrointestinal-tract endometriosis nodules. Suggestions and explanations are presented for this minimal approach. These contribute to individualized medical care for deep endometriosis. In brief, a laparoscopic transanal disc excision (LTADE; Rouen technique) was performed through a laparoscopic deep rectal dissection, combined with plasma energy shaving, and followed by a transanal disc excision of the low and mid-rectal deep endometriotic nodules, with the use of a semi-circular stapler. LTADE is indicated as the first-line surgical treatment for low and mid-rectal deep endometriotic nodule excisions, because it can preserve rectal length and innervation. This technique requires a multidisciplinary team with surgical colorectal training.
Online User Review Analysis for Product Evaluation and Improvement
Authors: Yang Cheng , Wu Lingang , Tan Kun , Yu Chunyang , Zhou Yuliang , Tao Ye , Song Yu
Published: May 2021

Traditional user research methods are challenged for the decision-making in product design and improvement with the updating speed becoming faster, considering limited survey scopes, insufficient samples, and time-consuming processes. This paper proposes a novel approach to acquire useful online reviews from E-commerce platforms, build a product evaluation indicator system, and put forward improvement strategies for the product with opinion mining and sentiment analysis with online reviews. The effectiveness of the method is validated by a large number of user reviews for smartphones wherein, with the evaluation indicator system, we can accurately predict the bad review rate for the product with only 9.9% error. And improvement strategies are proposed after processing the whole approach in the case study. The approach can be applied for product evaluation and improvement, especially for the products with needs for iterative design and sailed online with plenty of user reviews.
Stream Temperature and Environment Relationships in a Semiarid Riparian Corridor
Authors: Durfee Nicole , Ochoa Carlos G. , Jones Gerrad
Published: May 2021

This study examined the relationship between stream temperature and environmental variables in a semiarid riparian corridor in northcentral Oregon, USA. The relationships between riparian vegetation cover, subsurface flow temperature, and stream temperature were characterized along an 800 m reach. Multiple stream temperature sensors were located along the reach, in open and closed canopy areas, with riparian vegetation cover ranging from 4% to 95%. A support vector regression (SVR) model was developed to assess the relationship between environmental characteristics and stream temperature at the larger valley scale. At the reach scale, results show that air temperature was highly correlated with stream temperature (Pearson’s r = 0.97), and no significant (p < 0.05) differences in stream temperature levels were found among sensor locations, irrespective of percent vegetation cover. Channel subsurface temperature levels from an intermittent flow tributary were generally cooler than those in the perennial stream in the summer and warmer during winter months, indicating that the tributary may have a localized moderating effect on stream temperature. At the valley scale, results from the SVR model showed that air temperature, followed by streamflow, was the strongest variable influencing stream temperature. Also, riparian area land cover showed little effect on stream temperature along the entire riparian corridor. This research indicates that air temperature, subsurface flow, and streamflow are important variables affecting the stream temperature variability observed in the study area.
Relative Contribution of the Xiaolangdi Dam to Runoff Changes in the Lower Yellow River
Authors: Zhao Qinghe , Ding Shengyan , Ji Xiaoyu , Hong Zhendong , Lu Mengwen , Wang Peng
Published: May 2021

Human activities are increasingly recognized as having a critical influence on hydrological processes under the warming of the climate, particularly for dam-regulated rivers. To ensure the sustainable management of water resources, it is important to evaluate how dam construction may affect surface runoff. In this study, using Mann–Kendall tests, the double mass curve method, and the Budyko-based elasticity method, the effects of climate change and human activities on annual and seasonal runoff were quantified for the Yellow River basin from 1961–2018; additionally, effects on runoff were assessed after the construction of the Xiaolangdi Dam (XLD, started operation in 2001) on the Yellow River. Both annual and seasonal runoff decreased over time (p < 0.01), due to the combined effects of climate change and human activities. Abrupt changes in annual, flood season, and non-flood season runoff occurred in 1986, 1989, and 1986, respectively. However, no abrupt changes were seen after the construction of the XLD. Human activities accounted for much of the reduction in runoff, approximately 75–72% annually, 81–86% for the flood season, and 86–90% for the non-flood season. Climate change approximately accounted for the remainder: 18–25% (annually), 14–19% (flood season), and 10–14% (non-flood season). The XLD construction mitigated runoff increases induced by heightened precipitation and reduced potential evapotranspiration during the post-dam period; the XLD accounted for approximately 52% of the runoff reduction both annually and in the non-flood season, and accounted for approximately −32% of the runoff increase in the flood season. In conclusion, this study provides a basic understanding of how dam construction contributes to runoff changes in the context of climate change; this information will be beneficial for the sustainable management of water resources in regulated rivers.
Oscillatory Behaviour of Ni Supported on ZrO2 in the Catalytic Partial Oxidation of Methane as Determined by Activation Procedure
Authors: Pietrogiacomi Daniela , Campa Maria Cristina , Pettiti Ida , Tuti Simonetta , Luccisano Giulia , Ardemani Leandro , Luisetto Igor , Gazzoli Delia
Published: May 2021

Ni/ZrO2 catalysts, active and selective for the catalytic partial oxidation of methane to syngas (CH4-CPO), were prepared by the dry impregnation of zirconium oxyhydroxide (Zhy) or monoclinic ZrO2 (Zm), calcination at 1173 K and activation by different procedures: oxidation-reduction (ox-red) or direct reduction (red). The characterization included XRD, FESEM, in situ FTIR and Raman spectroscopies, TPR, and specific surface area measurements. Catalytic activity experiments were carried out in a flow apparatus with a mixture of CH4:O2 = 2:1 in a short contact time. Compared to Zm, Zhy favoured the formation of smaller NiO particles, implying a higher number of Ni sites strongly interacting with the support. In all the activated Ni/ZrO2 catalysts, the Ni–ZrO2 interaction was strong enough to limit Ni aggregation during the catalytic runs. The catalytic activity depended on the activation procedures; the ox-red treatment yielded very active and stable catalysts, whereas the red treatment yielded catalysts with oscillating activity, ascribed to the formation of Niδ+ carbide-like species. The results suggested that Ni dispersion was not the main factor affecting the activity, and that active sites for CH4-CPO could be Ni species at the boundary of the metal particles in a specific configuration and nuclearity.
Solution Processed PVB/Mica Flake Coatings for the Encapsulation of Organic Solar Cells
Authors: Channa Iftikhar Ahmed , Chandio Ali Dad , Rizwan Muhammad , Shah Aqeel Ahmed , Bhatti Jahanzeb , Shah Abdul Karim , Hussain Fayaz , Shar Muhammad Ali , AlHazaa Abdulaziz
Published: May 2021

Organic photovoltaics (OPVs) die due to their interactions with environmental gases, i.e., moisture and oxygen, the latter being the most dangerous, especially under illumination, due to the fact that most of the active layers used in OPVs are extremely sensitive to oxygen. In this work we demonstrate solution-based effective barrier coatings based on composite of poly(vinyl butyral) (PVB) and mica flakes for the protection of poly (3-hexylthiophene) (P3HT)-based organic solar cells (OSCs) against photobleaching under illumination conditions. In the first step we developed a protective layer with cost effective and environmentally friendly methods and optimized its properties in terms of transparency, barrier improvement factor, and bendability. The developed protective layer maintained a high transparency in the visible region and improved oxygen and moisture barrier quality by the factor of ~7. The resultant protective layers showed ultra-flexibility, as no significant degradation in protective characteristics were observed after 10 K bending cycles. In the second step, a PVB/mica composite layer was applied on top of the P3HT film and subjected to photo-degradation. The P3HT films coated with PVB/mica composite showed improved stability under constant light irradiation and exhibited a loss of <20% of the initial optical density over the period of 150 h. Finally, optimized barrier layers were used as encapsulation for organic solar cell (OSC) devices. The lifetime results confirmed that the stability of the OSCs was extended from few hours to over 240 h in a sun test (65 °C, ambient RH%) which corresponds to an enhanced lifetime by a factor of 9 compared to devices encapsulated with pristine PVB.
Cardiovascular Stents: A Review of Past, Current, and Emerging Devices
Authors: Scafa Udriște Alexandru , Niculescu Adelina-Gabriela , Grumezescu Alexandru Mihai , Bădilă Elisabeta
Published: May 2021

One of the leading causes of morbidity and mortality worldwide is coronary artery disease, a condition characterized by the narrowing of the artery due to plaque deposits. The standard of care for treating this disease is the introduction of a stent at the lesion site. This life-saving tubular device ensures vessel support, keeping the blood-flow path open so that the cardiac muscle receives its vital nutrients and oxygen supply. Several generations of stents have been iteratively developed towards improving patient outcomes and diminishing adverse side effects following the implanting procedure. Moving from bare-metal stents to drug-eluting stents, and recently reaching bioresorbable stents, this research field is under continuous development. To keep up with how stent technology has advanced in the past few decades, this paper reviews the evolution of these devices, focusing on how they can be further optimized towards creating an ideal vascular scaffold.
Investigation of the Powder Aerosol Deposition Method Using Shadowgraph Imaging
Authors: Glosse Philipp , Denneler Stefan , Stier Oliver , Moos Ralf
Published: May 2021

The powder aerosol deposition method (PAD) is a vacuum-based spray coating technology. It allows for production of highly dense coatings at room temperature, especially of brittle-breaking materials. This yields new options for coating substrate materials that even melt at low temperatures. The film formation mechanism is called room temperature impact consolidation (RTIC). The occurrence of this mechanism is strongly linked to the gas jet used in the process. The velocity and direction of the particles in the gas jet forming between the nozzle orifice and the substrate are the main factors influencing the quality of the coating. This dependency aimed to be elaborated with a measurement setup and coating experiments and is shown in this work. We investigated the gas jet formation using a shadow optical imaging system. Regions of different gas density are visualized by this technique. Several parameter sets, in particular gas flow rates and chamber pressures, were investigated. In addition, coatings were produced on glass substrates with the same parameters. As a coating material, the superconducting ceramic-like magnesium diboride (MgB2) was chosen. A correlation between shadow images and thickness profiles of the coatings shows how the gas jet formation affects the uniformity of thickness. Shadow optical images provide valuable information on the flight direction of the particles and allow validation of simulation results.
A Parallel Coupled Lattice Boltzmann-Volume of Fluid Framework for Modeling Porous Media Evolution
Authors: Alihussein Hussein , Geier Martin , Krafczyk Manfred
Published: May 2021

In this paper, we present a framework for the modeling and simulation of a subset of physical/chemical processes occurring on different spatial and temporal scales in porous materials. In order to improve our understanding of such processes on multiple spatio-temporal scales, small-scale simulations of transport and reaction are of vital importance. Due to the geometric complexity of the pore space and the need to consider a representative elementary volume, such simulations require substantial numerical resolutions, leading to potentially huge computation times. An efficient parallelization of such numerical methods is thus vital to obtain results in acceptable wall-clock time. The goal of this paper was to improve available approaches based on lattice Boltzmann methods (LBMs) to reliably and accurately predict the combined effects of mass transport and reaction in porous media. To this end, we relied on the factorized central moment LBM as a second-order accurate approach for modeling transport. In order to include morphological changes due to the dissolution of the solid phase, the volume of fluid method with the piece-wise linear interface construction algorithm was employed. These developments are being integrated into the LBM research code VirtualFluids. After the validation of the analytic test cases, we present an application of diffusion-controlled dissolution for a pore space obtained from computer tomography (CT) scans.
Comparison of Latest and Innovative Silica-Based Consolidants for Volcanic Stones
Authors: Colella Abner , Capasso Ilaria , Iucolano Fabio
Published: May 2021

This research explores the new perspectives in conservation and protection of two macroporous tuff stones, widely employed in the architectural heritage of Campania region, characterized by highly heterogeneous rock fabric and texture and a variable mineralogical composition that represent crucial factors responsible for their weak durability. The consolidation treatments were performed with a recently and widely used suspension of nano-silica crystals in water and with a lithium silicate solution that has received up to now scarce attention as a consolidant agent. Physical investigations (open porosity, Hg porosimetry, water absorption), morphological observations (SEM analyses) and visual appearance test (colorimetric measurements), along with assessments of performance indicators such as ultrasonic pulse velocity, surface cohesion test (peeling test) and durability test (salt crystallization), were carried out to investigate the consolidation effectiveness. Overall, lithium silicate consolidant showed a better behavior in terms of superficial cohesion, a most successful strengthening action and a considerable enhancement of salt resistance.
Influence of Tool Holder Types on Vibration in Rough Milling of AZ91D Magnesium Alloy
Authors: Zagórski Ireneusz , Korpysa Jarosław , Weremczuk Andrzej
Published: May 2021

The article presents the results of an analysis of the influence of the technological parameters related to tool holder types on the vibrations occurring during the milling of AZ91D magnesium alloy. Magnesium alloys are very low-density materials and, therefore, are increasingly being considered as replacement materials for the more commonly used aluminium alloys. The tool used in the study was a carbide end mill with TiAlN coating, clamped in three different types of tool holder: ER collet, heat shrink, and Tendo E hydraulic. The milling tests used straight toolpaths at varied cutting speeds and feed per tooth values. Based on the vibration displacement and acceleration signals recorded during the machining tests, the following were analysed: maximum value, amplitude, and root mean square (RMS) value of the vibrations. As part of the study, composite multiscale entropy (CMSE) analysis was also performed, describing the level of disorderliness of the obtained vibration signals. The increase in machining parameters caused an increase in the values characterising the displacement and acceleration of the vibrations. It was noted that multiscale entropy might be an important parameter describing the vibration signal (both displacement and acceleration).
Determination of Optimal Flat-End Head Geometries for Pressure Vessels Based on Numerical and Experimental Approaches
Authors: Romanowicz Paweł J. , Szybiński Bogdan
Published: May 2021

The experimental and numerical analyses of the pressure vessels with different flat ends are presented and discussed in the paper. The main aim of the study is to propose the optimal flat head end geometry. The analyses are focused on the comparison of standardized geometries and with the proposed elliptical cut-out. The experimental tests with the application of strain-gauge measurements and numerical modeling of the pressure vessel are conducted. The behavior under low and high pressures and the influence of the residual welding stresses, material properties, and geometrical tolerances on the level of the plastic deformation in the flat end is discussed. It is presented that the rules given in the recent standard are not sufficient for optimal selection of the optimal geometry. It is observed that in certain geometries the deviations of the pipe thickness may lead to a significant increase of the equivalent stresses. The residual welding stresses have a significant influence on the stress and strain level—particularly in the stress relief groove (SRG). The performed study and comparison of the different geometries allow for the proposal of the optimal shape of the flat end. It appeared that the pressure vessels with SRG are the most optimal choice, particularly when elliptic shapes are in use. In some cases (i.e., pipe with wall-thickness equal to 40 mm and the flat end with circular SRG), the optimal configuration is reached for dimensions beyond the admissible by code range.
Study on Fabrication and Properties of Graphite/Al Composites by Hot Isostatic Pressing-Rolling Process
Authors: Jia Hao , Fan Jianzhong , Liu Yanqiang , Zhao Yuehong , Nie Junhui , Wei Shaohua
Published: May 2021

Graphite/Al composites have attracted much attrition due to their excellent thermal properties. However, the improvement of thermal conductivity (TC) is limited by the difficulty in controlling the orientation of graphite and the poor wettability between graphite and aluminum. In this study, a novel process for fabricating the Graphite/Al composites is proposed, which involves fabricating graphite film and aluminum foil into laminate material. Then, taking a rolling method, the fractured and well oriented graphite film can help the composite achieve high TC while maintaining a certain strength. The result reveals that both single and total reduction have a significant influence on the diameter and orientation of the graphite, and by adjusting the process parameters, composites with high TC can be acquired at a relatively low reinforcement volume. This near-net-forming process can directly meet the thickness requirements for electronic packaging and avoids the exposure of graphite to the surface during secondary processing, which is promising to promote the application for high TC Graphite/Al composites in thermal management.
Determining Adsorption Parameters of Potentially Contaminant-Releasing Materials Using Batch Tests with Differing Liquid-Solid Ratios
Authors: Sakanakura Hirofumi , Ito Kenichi , Tang Jiajie , Nakagawa Mikako , Ishimori Hiroyuki
Published: May 2021

Adsorption parameters such as the distribution coefficient are required to predict the release behavior of contaminants using advection-dispersion models. However, for potentially contaminant-releasing materials (PCMs) such as dredged sludge and coal ash, these parameters cannot be obtained by conventional adsorption tests. This study developed a method to determine adsorption parameters for PCMs from a set of batch tests conducted in parallel as a function of the liquid-solid ratio (LS-parallel test). This LS-parallel test was performed on sandy soil derived from marine sediment using liquid-solid ratios from 1 to 300 L/kg. The water-contact time was also changed from 10 min to 28 d to elucidate the kinetics or equilibrium of contaminants released from the sample. Adsorption parameters were successfully obtained if the substance was under adsorption control. A column percolation test was performed to confirm the effectiveness of the obtained parameters. Good agreements were observed for SO42− and B, but discrepancies remained for other substances such as F− and As suggesting that improvements are necessary in both the LS-parallel test procedure and the advection-dispersion model.
Synthesis and Characterization of Electrospun Composite Scaffolds Based on Chitosan-Carboxylated Graphene Oxide with Potential Biomedical Applications
Authors: Cojocaru Elena , Ghitman Jana , Biru Elena Iuliana , Pircalabioru Gratiela Gradisteanu , Vasile Eugeniu , Iovu Horia
Published: May 2021

This research study reports the development of chitosan/carboxylated graphene oxide (CS/GO-COOH) composite scaffolds with nanofibrous architecture using the electrospinning method. The concept of designed composite fibrous material is based on bringing together the biological properties of CS, mechanical, electrical, and biological characteristics of GO-COOH with the versatility and efficiency of ultra-modern electrospinning techniques. Three different concentrations of GO-COOH were added into a chitosan (CS)-poly(ethylene oxide) (PEO) solution (the ratio between CS/PEO was 3/7 (w/w)) and were used in the synthesis process of composite scaffolds. The effect of GO-COOH concentration on the spinnability, morphological and mechanical features, wettability, and biological properties of engineered fibrous scaffolds was thoroughly investigated. FTIR results revealed the non-covalent and covalent interactions that could take place between the system’s components. The SEM micrographs highlighted the nanofibrous architecture of scaffolds, and the presence of GO-COOH sheets along the composite CS/GO-COOH nanofibers. The size distribution graphs showed a decreasing trend in the mean diameter of composite nanofibers with the increase in GO-COOH content, from 141.40 nm for CS/PG 0.1% to 119.88 nm for CS/PG 0.5%. The dispersion of GO-COOH led to composite scaffolds with increased elasticity; the Young’s modulus of CS/PG 0.5% (84 ± 4.71 MPa) was 7.5-fold lower as compared to CS/PEO (662 ± 15.18 MPa, p < 0.0001). Contact angle measurements showed that both GO-COOH content and crosslinking step influenced the surface wettability of scaffolds, leading to materials with ~1.25-fold higher hydrophobicity. The in vitro cytocompatibility assessment showed that the designed nanofibrous scaffolds showed a reasonable cellular proliferation level after 72 h of contact with the fibroblast cells.
Mathematical Modelling of the Impact of Non-Pharmacological Strategies to Control the COVID-19 Epidemic in Portugal
Authors: Caetano Constantino , Morgado Maria Luísa , Patrício Paula , Pereira João F. , Nunes Baltazar
Published: May 2021

In this paper, we present an age-structured SEIR model that uses contact patterns to reflect the physical distance measures implemented in Portugal to control the COVID-19 pandemic. By using these matrices and proper estimates for the parameters in the model, we were able to ascertain the impact of mitigation strategies employed in the past. Results show that the March 2020 lockdown had an impact on disease transmission, bringing the effective reproduction number (R(t)) below 1. We estimate that there was an increase in the transmission after the initial lift of the measures on 6 May 2020 that resulted in a second wave that was curbed by the October and November measures. December 2020 saw an increase in the transmission reaching an R(t) = 1.45 in early January 2021. Simulations indicate that the lockdown imposed on the 15 January 2021 might reduce the intensive care unit (ICU) demand to below 200 cases in early April if it lasts at least 2 months. As it stands, the model was capable of projecting the number of individuals in each infection phase for each age group and moment in time.
Orbit Entropy and Symmetry Index Revisited
Authors: Jalali-Rad Maryam , Ghorbani Modjtaba , Dehmer Matthias , Emmert-Streib Frank
Published: May 2021

The size of the orbits or similar vertices of a network provides important information regarding each individual component of the network. In this paper, we investigate the entropy or information content and the symmetry index for several classes of graphs and compare the values of this measure with that of the symmetry index of certain graphs.
Linear Operators That Preserve Arctic Ranks of Boolean Matrices
Authors: Kang Kyung-Tae , Song Seok-Zun
Published: May 2021

We study some properties of arctic rank of Boolean matrices. We compare the arctic rank with Boolean rank and term rank of a given Boolean matrix. Furthermore, we obtain some characterizations of linear operators that preserve arctic rank on Boolean matrix space.
A Sampling-Based Sensitivity Analysis Method Considering the Uncertainties of Input Variables and Their Distribution Parameters
Authors: Peng Xiang , Xu Xiaoqing , Li Jiquan , Jiang Shaofei
Published: May 2021

For engineering products with uncertain input variables and distribution parameters, a sampling-based sensitivity analysis methodology was investigated to efficiently determine the influences of these uncertainties. In the calculation of the sensitivity indices, the nonlinear degrees of the performance function in the subintervals were greatly reduced by using the integral whole domain segmentation method, while the mean and variance of the performance function were calculated using the unscented transformation method. Compared with the traditional Monte Carlo simulation method, the loop number and sampling number in every loop were decreased by using the multiplication approximation and Gaussian integration methods. The proposed algorithm also reduced the calculation complexity by reusing the sample points in the calculation of two sensitivity indices to measure the influence of input variables and their distribution parameters. The accuracy and efficiency of the proposed algorithm were verified with three numerical examples and one engineering example.
Mindlin-Reissner Analytical Model with Curvature for Tunnel Ventilation Shafts Analysis
Authors: Álvarez-Pérez José , Peña Fernando
Published: May 2021

The formulation and analytic solution of a new mathematical model with constitutive curvature for analysis of tunnel ventilation shaft wall is proposed. Based on the Mindlin–Reissner theory for thick shells, this model also takes into account the shell constitutive curvature and considers an expression of the shear correction factor variable (αn) in terms of the thickness (h) and the radius of curvature (R). The main advantage of the proposed model is that it has the possibility to analyze thin, medium and thick tunnel ventilation shafts. As a result, two comparisons were made: the first one, between the new model and the Mindlin–Reissner model without constitutive curvature with the shear correction factor αn=5/6 as a constant, and the other, between the new model and the tridimensional numerical models (solids and shells) obtained by finite element method for different slenderness ratios (h/R). The limitation of the proposed model is that it is to be formulated for a general linear-elastic and axial-symmetrical state with continuous distribution of the mass.
Data Interpolation by Near-Optimal Splines with Free Knots Using Linear Programming
Authors: Thakur Lakshman S. , Bragin Mikhail A.
Published: May 2021

The problem of obtaining an optimal spline with free knots is tantamount to minimizing derivatives of a nonlinear differentiable function over a Banach space on a compact set. While the problem of data interpolation by quadratic splines has been accomplished, interpolation by splines of higher orders is far more challenging. In this paper, to overcome difficulties associated with the complexity of the interpolation problem, the interval over which data points are defined is discretized and continuous derivatives are replaced by their discrete counterparts. The l∞-norm used for maximum rth order curvature (a derivative of order r) is then linearized, and the problem to obtain a near-optimal spline becomes a linear programming (LP) problem, which is solved in polynomial time by using LP methods, e.g., by using the Simplex method implemented in modern software such as CPLEX. It is shown that, as the mesh of the discretization approaches zero, a resulting near-optimal spline approaches an optimal spline. Splines with the desired accuracy can be obtained by choosing an appropriately fine mesh of the discretization. By using cubic splines as an example, numerical results demonstrate that the linear programming (LP) formulation, resulting from the discretization of the interpolation problem, can be solved by linear solvers with high computational efficiency and the resulting spline provides a good approximation to the sought-for optimal spline.
Zero-Inflated Generalized Linear Mixed Models: A Better Way to Understand Data Relationships
Authors: Fávero Luiz Paulo , Hair Joseph F. , Souza Rafael de Freitas , Albergaria Matheus , Brugni Talles V.
Published: May 2021

Our article explores an underused mathematical analytical methodology in the social sciences. In addition to describing the method and its advantages, we extend a previously reported application of mixed models in a well-known database about corruption in 149 countries. The dataset in the mentioned study included a reasonable amount of zeros (13.19%) in the outcome variable, which is typical of this type of research, as well as quite a bit of social sciences research. In our paper, present detailed guidelines regarding the estimation of models where the data for the outcome variable includes an excess number of zeros, and the dataset has a natural nested structure. We believe our research is not likely to reject the hypothesis favoring the adoption of mixed modeling and the inflation of zeros over the original simpler framework. Instead, our results demonstrate the importance of considering random effects at country levels and the zero-inflated nature of the outcome variable.
A Fourth Order Symplectic and Conjugate-Symplectic Extension of the Midpoint and Trapezoidal Methods
Authors: Iavernaro Felice , Mazzia Francesca
Published: May 2021

The paper presents fourth order Runge–Kutta methods derived from symmetric Hermite–Obreshkov schemes by suitably approximating the involved higher derivatives. In particular, starting from the multi-derivative extension of the midpoint method we have obtained a new symmetric implicit Runge–Kutta method of order four, for the numerical solution of first-order differential equations. The new method is symplectic and is suitable for the solution of both initial and boundary value Hamiltonian problems. Moreover, starting from the conjugate class of multi-derivative trapezoidal schemes, we have derived a new method that is conjugate to the new symplectic method.
Modified Tseng’s Method with Inertial Viscosity Type for Solving Inclusion Problems and Its Application to Image Restoration Problems
Authors: Kaewyong Nattakarn , Sitthithakerngkiet Kanokwan
Published: May 2021

In this paper, we study a monotone inclusion problem in the framework of Hilbert spaces. (1) We introduce a new modified Tseng’s method that combines inertial and viscosity techniques. Our aim is to obtain an algorithm with better performance that can be applied to a broader class of mappings. (2) We prove a strong convergence theorem to approximate a solution to the monotone inclusion problem under some mild conditions. (3) We present a modified version of the proposed iterative scheme for solving convex minimization problems. (4) We present numerical examples that satisfy the image restoration problem and illustrate our proposed algorithm’s computational performance.