bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymmetric Hysteresis Modeling Approach Featuring “Inertial System + Shape Function” for Magnetostrictive Actuators
Authors: Si Zhi-Yuan , Bai Xian-Xu ‘Frank’ , Qian Li-Jun
Published: June 2020

Hysteresis of the actuators based on magnetostrictive materials influences the control performance of the application systems. It is of importance and significance to establish an effective hysteresis model for the magnetostrictive actuators for precision engineering. In this paper, based on the analysis of the Duhem model, a first-order inertial system with hysteresis characteristic under harmonic input is used to describe the hysteresis caused by the inertia of the magnetic domains of magnetostrictive materials. Shape function is employed to describe the pinning of domain walls, the interactions of different magnetic domains of magnetostrictive materials, and the saturation properties of the hysteresis. Specifically, under an architecture of “inertial system + shape function” (ISSF-Duhem model), firstly a new hysteresis model is proposed for magnetostrictive actuators. The formulation of the inertial system is constructed based on its general expression, which is capable of describing the hysteresis characteristics of magnetostrictive actuators. Then, the developed models with a Grompertz function-based shape function, a modified hyperbolic tangent function-based shape function employing an exponential function as an offset function, a one-sided dead-zone operator-based shape function are compared with each other, and further compared with the classic modified Prandtl–Ishlinskii model with a one-sided dead-zone operator. Sequentially, feasibility and capability of the proposed hysteresis model are verified and evaluated by describing and predicting the hysteresis characteristics of a commercial magnetostrictive actuator.
Magnetic Nanomaterials as Contrast Agents for MRI
Authors: Caspani Sofia , Magalhães Ricardo , Araújo João Pedro , Sousa Célia Tavares
Published: June 2020

Magnetic Resonance Imaging (MRI) is a powerful, noninvasive and nondestructive technique, capable of providing three-dimensional (3D) images of living organisms. The use of magnetic contrast agents has allowed clinical researchers and analysts to significantly increase the sensitivity and specificity of MRI, since these agents change the intrinsic properties of the tissues within a living organism, increasing the information present in the images. Advances in nanotechnology and materials science, as well as the research of new magnetic effects, have been the driving forces that are propelling forward the use of magnetic nanostructures as promising alternatives to commercial contrast agents used in MRI. This review discusses the principles associated with the use of contrast agents in MRI, as well as the most recent reports focused on nanostructured contrast agents. The potential applications of gadolinium- (Gd) and manganese- (Mn) based nanomaterials and iron oxide nanoparticles in this imaging technique are discussed as well, from their magnetic behavior to the commonly used materials and nanoarchitectures. Additionally, recent efforts to develop new types of contrast agents based on synthetic antiferromagnetic and high aspect ratio nanostructures are also addressed. Furthermore, the application of these materials in theragnosis, either as contrast agents and controlled drug release systems, contrast agents and thermal therapy materials or contrast agents and radiosensitizers, is also presented.
Study on Properties Prediction and Braiding Optimization of Axial Braided Carbon/Carbon Composite
Authors: Wang Chunguang , Cao Peng , Tang Min , Tian Weiping , Liu Ketong , Liu Baorui
Published: June 2020

It is well established that the microstructure has significant effects on the properties of axial braided C/C composites. In this study, a method coupling the homogenization method and finite element method (FEM) was proposed to predict the relationship between the microstructure characteristics and macroscopic properties. Based on the representative volume element (RVE) model, the periodic displacement boundary condition was introduced to predict the equivalent elastic properties of the RVE and component of C/C composite material, and the coefficient of thermal expansion (CTE) of the material was predicted by the energy prediction method. The predicted results were in good agreement with experimental results. By predicting the thermal and mechanical properties of the materials with different braiding spacing and fiber rod diameter, the variation of the properties with braiding spacing and fiber rod diameter was obtained. The research methods and results in this paper could provide important references for the optimization and rational application of composite materials.
A Glance at Processing-Microstructure-Property Relationships for Magnetoelectric Particulate PZT-CFO Composites
Authors: Galizia Pietro , Baldisserri Carlo , Mercadelli Elisa , Capiani Claudio , Galassi Carmen , Algueró Miguel
Published: June 2020

In this work, we investigated the processing-microstructure-property relationships for magnetoelectric (ME) particulate composites consisting of hard ferromagnetic CoFe2O4 (CFO) particles dispersed in a Nb-doped PbZrxTi1-xO3 (PZT) soft ferroelectric matrix. Several preparation steps, namely PZT powder calcination, PZT-CFO mixture milling and composite sintering were tailored and a range of microstructures was obtained. These included open and closed porosities up to full densification, PZT matrices with decreasing grain size across the submicron range down to the nanoscale and well dispersed CFO particles with bimodal size distributions consisting of submicron and micron sized components with varying weights. All samples could be poled under a fixed DC electric field of 4 kV/mm and the dielectric, piezoelectric and elastic coefficients were obtained and are discussed in relation to the microstructure. Remarkably, materials with nanostructured PZT matrices and open porosity showed piezoelectric charge coefficients comparable with fully dense composites with coarsened microstructure and larger voltage coefficients. Besides, the piezoelectric response of dense materials increased with the size of the CFO particles. This suggests a role of the conductive magnetic inclusions in promoting poling. Magnetoelectric coefficients were obtained and are discussed in relation to densification, piezoelectric matrix microstructure and particle size of the magnetic component. The largest magnetoelectric coefficient α33 of 1.37 mV cm−1 Oe−1 was obtained for submicron sized CFO particles, when closed porosity was reached, even if PZT grain size remained in the nanoscale.
Comparison of the Hydration Characteristics of Ultra-High-Performance and Normal Cementitious Materials
Authors: Zhou Haiyun , Zhu Hongbo , Gou Hongxiang , Yang Zhenghong
Published: June 2020

The hydration mechanism of ultra-high-performance cementitious materials (UHPC) departs considerably from that of normal cementitious materials (NC). In this study, the strength, isothermal calorimetry, chemical shrinkage, X-ray diffraction (XRD), and thermogravimetry (TG) methods are used to determine the hydration characteristics of UHPC and NC that contain silica fume (SF). A simple device was modified to test the chemical shrinkage for long-term growth, and the ultimate chemical shrinkage is obtained by semi-empirical formula fitting. It is found that the degree of hydration of UHPC is significantly lower than that of NC. The hydration kinetics analyzed using the Krstulovic-Dabic model shows that the hydration process of NC is type NG-I-D, which is characterized by gentle and prolonged hydration. However, the hydration of UHPC is type NG-D with the distinguishing features of early sufficiency and later stagnation. The growth of the strength, exothermic evolution, and phase development of UHPC is decelerated as the hydration process proceeds, which confirms the weak development tendency of hydration at the later stage. In addition, the effect of SF on the hydration of UHPC is minor, and the higher content of SF is beneficial to the hydration at the later stage.
Bio-Based Polyethylene Composites with Natural Fiber: Mechanical, Thermal, and Ageing Properties
Authors: Bazan Patrycja , Mierzwiński Dariusz , Bogucki Rafał , Kuciel Stanisław
Published: June 2020

The study evaluated the possibility of using natural fibers as a reinforcement of bio-polyethylene. Flax, coconut, basalt fiber, and wood flour were used in the work. Strength tests like static tensile test, three-point flexural test, or impact strength showed a positive effect of reinforcing bio-polyethylene-based composites. The effect of water and thermal ageing on the mechanical behavior of composites was assessed. In order to analyze the structure, SEM microscope images were taken and the effect of natural fibers on the change in the nature of cracking of composites was presented. Composites with natural fibers at a content of 12% by weight, resulting in increase of strength and rigidity of materials. The greatest strengthening effect for natural fibers was obtained for the composite with basalt fibers.
Effects of Postprocess Hot Isostatic Pressing Treatments on the Mechanical Performance of EBM Fabricated TI-6Al-2Sn-4Zr-2Mo
Authors: Lopez Miguel , Pickett Christina , Arrieta Edel , Murr Lawrence E. , Wicker Ryan B. , Ahlfors Magnus , Godfrey Donald , Medina Francisco
Published: June 2020

An essentially fully acicular alpha-prime martensite within an equiaxed grain structure was produced in an Electron Beam Melting (EBM)-fabricated Ti-6Al-2Sn-4Zr-2Mo (Ti6242) alloy using two different Arcam EBM machines: An A2X system employing tungsten filament thermionic electron emission, and a Q20 system employing LaB6 thermionic electron emission. Post-process Hot Isostatic Pressing (HIP) treatment for 2 h at 850, 950, and 1050 °C resulted in grain refinement and equiaxed grain growth along with alpha-prime martensite decomposition to form an intragranular mixture of acicular martensite and alpha at 850 °C, and acicular alpha phase at 950 and 150 °C, often exhibiting a Widmanstätten (basketweave) structure. The corresponding tensile yield stress and ultimate tensile strength (UTS) associated with the grain growth and acicular alpha evolution decreased from ~1 and ~1.1 GPa, respectively, for the as-fabricated Ti6242 alloy to ~0.8 and 0.9 GPa, respectively, for HIP at 1050 °C. The optimum elongation of ~15–16% occurred for HIP at 850 °C; for both EBM systems. Because of the interactive role played by equiaxed grain growth and the intragrain, acicular alpha microstructures, the hardness varied only by ~7% between 41 and 38 HRC.
Effects of CNC Machining on Surface Roughness in Fused Deposition Modelling (FDM) Products
Authors: Lalegani Dezaki Mohammadreza , Mohd Ariffin Mohd Khairol Anuar , Ismail Mohd Idris Shah
Published: June 2020

Fused deposition modelling (FDM) opens new ways across the industries and helps to produce complex products, yielding a prototype or finished product. However, it should be noted that the final products need high surface quality due to their better mechanical properties. The main purpose of this research was to determine the influence of computer numerical control (CNC) machining on the surface quality and identify the average surface roughness (Ra) and average peak to valley height (Rz) when the specimens were printed and machined in various build orientations. In this study, the study samples were printed and machined to investigate the effects of machining on FDM products and generate a surface comparison between the two processes. In particular, the block and complex specimens were printed in different build orientations, whereby other parameters were kept constant to understand the effects of orientation on surface smoothness. As a result, wide-ranging values of Ra and Rz were found in both processes for each profile due to their different features. The Ra values for the block samples, printed samples, and machined samples were 21, 91, and 52, respectively, whereas the Rz values were identical to Ra values in all samples. These results indicated that the horizontal surface roughness yielded the best quality compared to the perpendicular and vertical specimens. Moreover, machining was found to show a great influence on thermoplastics in which the surfaces became smooth in the machined samples. In brief, this research showed that build orientation had a great effect on the surface texture for both processes.
Fracture Initiation in Notched Specimens Subjected to Compression: Strain Rate Effect
Authors: Bura Elżbieta , Seweryn Andrzej
Published: June 2020

This paper shows the results of an experimental investigation on fracture in polymethyl methacrylate (PMMA) notched specimens subjected to compression (with unloading) including different strain rates. Three types of notches were used. Flat specimens were weakened by two types of V-notches and U-notches. Additionally, two specimen thicknesses were used (9.7 and 14.5 mm). The load was carried out at the strain rate of 8 × 10−4, 4 × 10−3, and 2 × 10−2 s−1 and the unloading stage was conducted ten times faster, i.e., 8 × 10−3, 4 × 10−2, and 2 × 10−1 s−1, respectively. By using a PHANTOM high-speed camera, fracture initiation moments and locations were indicated. Two types of crack were observed and distinguished as A-type and B-type. The first was formed by the contact stress of the closing notch surfaces, while the latter was formed by the residual stresses during the unloading stage. The type of notch, specimen thickness, and the strain rate have a significant influence on the fracture process. The strain rate has a large impact on the critical load value, which determines the fracture initiation, but does not affect the location and shape of the crack. The strain rate effect usually disappears with increasing specimen thickness.
Pulsed Laser Deposition Derived Bioactive Glass-Ceramic Coatings for Enhancing the Biocompatibility of Scaffolding Materials
Authors: Schitea Ruxandra-Ioana , Nitu Alexandru , Ciobota Andreea-Aurelia , Munteanu Andrei-Lucian , David Irina-Madalina , Miu Dana , Raileanu Mina , Bacalum Mihaela , Busuioc Cristina
Published: June 2020

The purpose of this work was to propose and evaluate a new composition for a bioactive glass-ceramic starting from the well-known 45S5 commercial product. Thus, we developed a modified version, including MgO, an oxide that turned out to induce superior mechanical properties and improved biological response. This had the following molar percentages: 46.1% SiO2, 2.6% P2O5, 16.9% CaO, 10.0% MgO, and 24.4% Na2O. The precursor alkoxides and nitrates were processed by a standard sol-gel technique, resulting in a glass-ceramic target, suitable for laser ablation experiments. Combeite (Na2Ca2Si3O9) was identified as a main crystalline phase within the calcined sol-gel powder, as well as in the case of the target sintered at 900 °C. The thin films were deposited on silicon substrates, at room temperature or 300 °C, being subsequently characterized from the material point of view, as well as in terms of bioactivity in simulated conditions and biocompatibility in relation to human fibroblast BJ cells. The investigations revealed the deposition of nanostructured glassy layers with a low proportion of crystalline domains; it was shown that a higher substrate temperature promoted the formation of surfaces with less irregularities, as a consequence of material arrangement into a shell with better morphological homogeneity. The complex elemental composition of the target was successfully transferred to the coatings, which ensured pronounced mineralization and a stimulating environment for the cell cultures. Thereby, both samples were covered with a thick layer of apatite after immersion in simulated body fluid for 28 days, and the one processed at room temperature was qualified to be the best in relation to the cells.
Attempting AG-Doped Diamond-Like Carbon Film to Improve Seal Performance of Hydraulic Servo-Actuator
Authors: Zhao Zhiyan , Yu Xiang , Zhang Zhiqiang , Shu Wen , Li Jia
Published: June 2020

A hydraulic servo-actuator is a critical aircraft control device whose sealing performance directly affects the sensitivity and accuracy of the aircraft flight attitude. Foreign intrusive particles in hydraulic oil may induce the vulnerable friction pair wear and the seal leak; they may even lead to oil spill accidents. This work attempts to conduct a systematical investigation of Ag-doped diamond-like carbon (Ag-DLC) film to improve the seal performance. The failure of the servo-actuator was analyzed. Then, a series of Ag-DLC films was deposited; the structure and combined tribological performances of the Ag-DLC films were investigated. The results show that the intensity of the Ag (111) crystal face in the films increases with an increase of Ag content. The hardness, intrinsic stress, frictional coefficient, and wear rate of the films tend to decrease with the amount of doping metal. The a:C-Ag10.5% film exhibits optimal combined properties. The Ag doping makes the film toughness improve; both soft Ag particles and a graphitized top layer act as solid lubricants. Our findings may offer a novel approach to make DLC film applicable for improving the seal performance of hydraulic servo-actuator. Based on the experimental data, a mechanism behind the film modification of Ag-DLC film is also revealed.
Improvements to the Sink Strength Theory Used in Multi-Scale Rate Equation Simulations of Defects in Solids
Authors: Ahlgren Tommy , Heinola Kalle
Published: June 2020

The application of mean-field rate theory equations have proven to be a versatile method in simulating defect dynamics and temporal changes in the microstructure of materials. The reliability and usefulness of the method, however, depends critically on the defect interaction parameters used. In this study, we show that the main interaction parameter, the sink strength, intrinsically depends on the detrapping, or the dissociation process itself. We present a theory on how to determine the appropriate sink strengths. The correct sink strength required for a detrapping defect, is considerably larger than the values commonly used, and thus should not be neglected.
Special Issue “Advances in Epitaxial Materials”-Editorial Preface
Authors: Leszczynski Mike
Published: June 2020

In this Special Issue, we have 10 excellent papers on epitaxy. In this editorial preface, I will make comments on the following issues: (1) applications of the materials examined, (2) lattice mismatch, (3) epitaxial growth methods used, (4) characterization methods used, (5) material problems: solved and still to be solved. The “Advances in Epitaxial Materials” has a big advantage of having, in one issue, papers on different materials, but in every paper the reader should find interesting information on epitaxial growth and characterization.
Magnetic Behaviour of Mn12-Stearate Single-Molecule Magnets Immobilized on the Surface of 300 nm Spherical Silica Nanoparticles
Authors: Laskowska Magdalena , Pastukh Oleksandr , Konieczny Piotr , Dulski Mateusz , Zalsiński Marcin , Laskowski Lukasz
Published: June 2020

The magnetic behaviour of Mn 12 -stearate single-molecule magnets (SMMs) ([ Mn 12 O 12 ( CH 3 ( CH 2 ) 16 CO 2 ) 16 ] · 2 CH 3 COOH · 4 H 2 O ) on the surface of 300 nm spherical silica nanoparticles were investigated. The SMMs were bonded at the silica surface with the assumed number of anchoring points, which influenced on their degree of freedom and distribution. In order to check the properties of Mn 12 -stearate molecules separated on the silica surface, and check their interactions, the samples containing four different concentration of spacers per single anchoring unit and variously bonded Mn 12 -stearate particles were prepared. The materials have been examined using Raman spectroscopy, transmission electron microscopy, and SQUID magnetometry. The results of magnetic measurements showed a correlation between the way of single-molecule magnets immobilization onto the silica spheres and the magnetic properties of the obtained hybrid materials.
A Review on Alkali-Silica Reaction Evolution in Recycled Aggregate Concrete
Authors: Barreto Santos Miguel , De Brito Jorge , Santos Silva António
Published: June 2020

Alkali-silica reaction (ASR) is one of the major degradation causes of concrete. This highly deleterious reaction has aroused the attention of researchers, in order to develop methodologies for its prevention and mitigation, but despite the efforts made, there is still no efficient cure to control its expansive consequences. The incorporation of recycled aggregates in concrete raises several ASR issues, mainly due to the difficult control of the source concrete reactivity level and the lack of knowledge on ASR’s evolution in new recycled aggregate concrete. This paper reviews several research works on ASR in concrete with recycled aggregates, and the main findings are presented in order to contribute to the knowledge and discussion of ASR in recycled aggregate concrete. It has been observed that age, exposure conditions, crushing and the heterogeneity source can influence the alkalis and reactive silica contents in the recycled aggregates. The use of low contents of highly reactive recycled aggregates as a replacement for natural aggregates can be done without an increase in expansion of concrete. ASR expansion tests and ASR mitigation measures need to be further researched to incorporate a higher content of recycled aggregates.
Ecofriendly Approach for Treatment of Heavy-Metal-Contaminated Water Using Activated Carbon of Kernel Shell of Oil Palm
Authors: Baby Rabia , Hussein Mohd Zobir
Published: June 2020

Heavy metal ion contamination in water poses a significant risk to human health as well as to the environment. Millions of tons of agricultural wastes are produced from oil palm plantations which are challenging to manage. In this study, we converted palm kernel shells (PKS) from a palm oil plantation into activated carbon (AC) having a surface area of 1099 m2/g using phosphoric acid as an activator. The prepared material was characterized using BET, XRD, Raman, FESEM and FTIR analyses. The AC was applied for the treatment of heavy-metal-contaminated water, and different parameters; the pH, adsorbent dosage, contact time and metal ion concentrations were varied to determine the optimal conditions for the metal ion adsorption. Different kinetic models; the zeroth, first-order and second-order, and Freundlich and Langmuir isotherm models were used to determine the mechanism of metal ion adsorption by the AC. Under the optimized conditions, Cr6+ and Pb2+ were removed completely, while Zn2+ and Cd2+ were more than 80% removed. This is a greener approach in which an agricultural waste, PKS is converted into a useful product, activated carbon and subsequently applied for the treatment of heavy metal-contaminated water.
Enhancing the Corrosion Resistance of Al–Cu–Li Alloys through Regulating Precipitation
Authors: Xu Jinjun , Deng Yunlai , Chen Jiqiang
Published: June 2020

The influences of aging treatments on microstructures and the corrosion properties of an Al–Cu–Li alloy were investigated through an immersion test in intergranular corrosion (IGC) solutions, a potentiodynamic polarization test, and electrochemical impedance spectra (EIS), combined with scanning and transmission electron microscopy. The results demonstrated that the Al–Cu–Li alloy displayed outstanding comprehensive mechanical properties and IGC resistance after treating with pre-strain deformation and a double aging process (PDA). Both the PDA and pre-strain followed by creep aging (PCA) treatments significantly increased the number densities of T1 and θ’ precipitates in the grain interior. The increase in precipitates in the grain interior greatly reduced the Cu-rich precipitates on the grain boundaries and inhibited the formation of a precipitate-free zone (PFZ). The electrochemical characteristics of the Al–Cu–Li alloy were influenced by the precipitates in the grain interior and grain boundaries. The studied alloy gained high IGC resistance due to the refinement of its microstructure, and the main corrosion mode was intra-granular pitting corrosion; thus, the corrosion diffusion rate was slowed down.
Electrospun Composite Nanofibrous Materials Based on (Poly)-Phenol-Polysaccharide Formulations for Potential Wound Treatment
Authors: Fras Zemljič Lidija , Maver Uroš , Kraševac Glaser Tjaša , Bren Urban , Knez Hrnčič Maša , Petek Gabrijela , Peršin Zdenka
Published: June 2020

In this paper, we focus on the preparation of electrospun composite nanofibrous materials based on (poly)-phenol-polysaccharide formulation. The prepared composite nanofibres are ideally suited as a controlled drug delivery system, especially for local treatment of different wounds, owing to their high surface and volume porosity and small fibre diameter. To evaluate the formulations, catechin and resveratrol were used as antioxidants. Both substances were embedded into chitosan particles, and further subjected to electrospinning. Formulations were characterized by determination of the particle size, encapsulation efficiency, as well as antioxidant and antimicrobial properties. The electrospinning process was optimised through fine-tuning of the electrospinning solution and the electrospinning parameters. Scanning electron microscopy was used to evaluate the (nano)fibrous structure, while the successful incorporation of bio substances was assessed by X-ray Photoelectron Spectroscopy and Fourier transform infrared spectroscopy. The bioactive properties of the formed nanofibre -mats were evaluated by measuring the antioxidative efficiency and antimicrobial properties, followed by in vitro substance release tests. The prepared materials are bioactive, have antimicrobial and antioxidative properties and at the same time allow the release of the incorporated substances, which assures a promising use in medical applications, especially in wound care.
The Effect of Lightweight Concrete Cores on the Thermal Performance of Vacuum Insulation Panels
Authors: Chung Sang-Yeop , Sikora Pawel , Stephan Dietmar , Abd Elrahman Mohamed
Published: June 2020

The performance of vacuum insulation panels (VIPs) is strongly affected by several factors, such as panel thickness, design, quality of vacuum, and material type. In particular, the core materials inside VIPs significantly influence their overall performance. Despite their superior insulation performance, VIPs are limited in their widespread use as structural materials, because of their low material strength and the relatively expensive core materials. As an alternative core material that can compensate these limitations, foamed concrete, a type of lightweight concrete with very low density, can be used. In this study, two different types of foamed concrete were used as VIP core materials, with their effects on the thermal behavior of the VIPs having been evaluated using experimental and numerical methods. To confirm and generate numerical models for VIP analysis, micro-computed tomography (micro-CT) was utilized. The obtained results show that insulation effects increase effectively when panels with lightweight concrete are in a vacuum, and both foamed concrete types can be effectively used as VIP core materials.
Adsorption and Release of Growth Factors from Four Different Porcine-Derived Collagen Matrices
Authors: Nica Cristina , Lin Zhikai , Sculean Anton , Asparuhova Maria B.
Published: June 2020

Xenogeneic acellular collagen matrices represent a safe alternative to autologous soft tissue transplants in periodontology and implant dentistry. Here, we aimed to investigate the adsorption and release of growth factors from four porcine-derived collagen matrices using enzyme-linked immunosorbent assay. Non-crosslinked collagen matrix (NCM), crosslinked collagen matrix (CCM), dried acellular dermal matrix (DADM), and hydrated acellular dermal matrix (HADM) adsorbed each of the following growth factors, TGF-β1, FGF-2, PDGF-BB, GDF-5 and BMP-2, with an efficiency close to 100%. Growth factor release for a 13-day period was in the range of 10–50% of the adsorbed protein, except for the BMP-2 release that was in the range of 5–7%. Generally, protein release occurred in two phases. Phase I was arbitrary defined by the highest release from the matrices, usually within 24 h. Phase II, spanning the period immediately after the peak release until day 13, corresponded to the delayed release of the growth factors from the deeper layers of the matrices. HADM showed significantly (P < 0.001) higher TGF-β1, FGF-2, and PDGF-BB release in phase II, compared to the rest of the matrices. NCM exhibited significantly (P < 0.001) higher FGF-2 release in phase II, compared to CCM and DADM as well as a characteristic second peak in PDGF-BB release towards the middle of the tested period. In contrast to NCM and HADM, CCM and DADM showed a gradual and significantly higher release of GDF-5 in the second phase. Several burst releases of BMP-2 were characteristic for all matrices. The efficient adsorption and sustained protein release in the first 13 days, and the kinetics seen for HADM, with a burst release within hours and high amount of released growth factor within a secondary phase, may be beneficial for the long-term tissue regeneration following reconstructive periodontal surgery.
Effects of Preparation Methods on the Thermoelectric Performance of SWCNT/Bi2Te3 Bulk Composites
Authors: Liu Yuqi , Du Yong , Meng Qiufeng , Xu Jiayue , Shen Shirley Z.
Published: June 2020

Single-walled carbon nanotube (SWCNT)/Bi2Te3 composite powders were fabricated via a one-step in situ reductive method, and their corresponding bulk composites were prepared by a cold-pressing combing pressureless sintering process or a hot-pressing process. The influences of the preparation methods on the thermoelectric properties of the SWCNT/Bi2Te3 bulk composites were investigated. All the bulk composites showed negative Seebeck coefficients, indicating n-type conduction. A maximum power factor of 891.6 μWm−1K−2 at 340 K was achieved for the SWCNT/Bi2Te3 bulk composites with 0.5 wt % SWCNTs prepared by a hot-pressing process, which was ~5 times higher than that of the bulk composites (167.7 μWm−1K−2 at 300 K) prepared by a cold-pressing combing pressureless sintering process, and ~23 times higher than that of the bulk composites (38.6 μWm−1K−2 at 300 K) prepared by a cold-pressing process, mainly due to the enhanced density of the hot-pressed bulk composites.
An Analytical Method for Generating Determined Torque Ripple in Synchronous Machines with Surface Magnets by Harmonic Current Injection
Authors: Vollat Matthias , Hartmann Daniel , Gauterin Frank
Published: June 2020

In this paper, we present a new analytical method to calculate the required amplitudes and phase angles of the injected harmonic currents, to generate a determined torque ripple for synchronous machines with surface-mounted permanent magnets. First, we described the machine equations as a function of the phase current and the back electromotive force. We then introduced a new asymmetrical power system. After combining the equations, we established a linear system of equations. The solution of the equation system yielded the amplitudes and phase angles of the harmonic currents to be injected. Finally, we validated the method with several finite element method simulations. With this method, a previously defined torque ripple could be generated very accurately for synchronous machines with surface magnets.
Spin Cross-Over (SCO) Anionic Fe(II) Complexes Based on the Tripodal Ligand Tris(2-pyridyl)ethoxymethane
Authors: Cuza Emmelyne , Benmansour Samia , Cosquer Nathalie , Conan Françoise , Pillet Sébastien , Gómez-García Carlos J. , Triki Smail
Published: June 2020

Reactions of Fe(II) with the tripodal chelating ligand 1,1,1-tris(2-pyridyl)ethoxymethane (py3C-OEt) and (NCE)− co-ligands (E = S, Se, BH3) give a series of mononuclear complexes formulated as [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1) and BH3 (2). These compounds are the first Fe(II) spin cross-over (SCO) complexes based on the tripodal ligand tris(2-pyridyl)ethoxymethane and on the versatile co-ligands (NCS)− and (NCBH3)−. The crystal structure reveals discrete monomeric isomorph structures formed by a cationic [Fe(py3C-OEt)2]2+ complex and by two equivalent anionic [Fe(py3C-OEt)(NCE)3]− complexes. In the cations the Fe(II) is facially coordinated by two py3C-OEt tripodal ligands whereas in the anion the three nitrogen atoms of the tripodal ligand are facially coordinated and the N-donor atoms of the three (NCE)− co-ligands occupy the remaining three positions to complete the distorted octahedral environment of the Fe(II) centre. The magnetic studies show the presence of gradual SCO for both complexes: A one-step transition around 205 K for 1 and a two-step transition for compound 2, centered around 245 K and 380 K.
Digital Topological Properties of an Alignment of Fixed Point Sets
Authors: Han Sang-Eon
Published: June 2020

The present paper investigates digital topological properties of an alignment of fixed point sets which can play an important role in fixed point theory from the viewpoints of computational or digital topology. In digital topology-based fixed point theory, for a digital image ( X , k ) , let F ( X ) be the set of cardinalities of the fixed point sets of all k-continuous self-maps of ( X , k ) (see Definition 4). In this paper we call it an alignment of fixed point sets of ( X , k ) . Then we have the following unsolved problem. How many components are there in F ( X ) up to 2-connectedness? In particular, let C k n , l be a simple closed k-curve with l elements in Z n and X : = C k n , l 1 ∨ C k n , l 2 be a digital wedge of C k n , l 1 and C k n , l 2 in Z n . Then we need to explore both the number of components of F ( X ) up to digital 2-connectivity (see Definition 4) and perfectness of F ( X ) (see Definition 5). The present paper addresses these issues and, furthermore, solves several problems related to the main issues. Indeed, it turns out that the three models C 2 n n , 4 , C 3 n − 1 n , 4 , and C k n , 6 play important roles in studying these topics because the digital fundamental groups of them have strong relationships with alignments of fixed point sets of them. Moreover, we correct some errors stated by Boxer et al. in their recent work and improve them (see Remark 3). This approach can facilitate the studies of pure and applied topologies, digital geometry, mathematical morphology, and image processing and image classification in computer science. The present paper only deals with k-connected spaces in DTC. Moreover, we will mainly deal with a set X such that X ♯ ≥ 2 .
A Numerical Algorithm for the Solutions of ABC Singular Lane–Emden Type Models Arising in Astrophysics Using Reproducing Kernel Discretization Method
Authors: Arqub Omar Abu , Osman Mohamed S. , Abdel-Aty Abdel-Haleem , Mohamed Abdel-Baset A. , Momani Shaher
Published: June 2020

This paper deals with the numerical solutions and convergence analysis for general singular Lane–Emden type models of fractional order, with appropriate constraint initial conditions. A modified reproducing kernel discretization technique is used for dealing with the fractional Atangana–Baleanu–Caputo operator. In this tendency, novel operational algorithms are built and discussed for covering such singular models in spite of the operator optimality used. Several numerical applications using the well-known fractional Lane–Emden type models are examined, to expound the feasibility and suitability of the approach. From a numerical viewpoint, the obtained results indicate that the method is intelligent and has several features stability for dealing with many fractional models emerging in physics and mathematics, using the new presented derivative.
Longer-Term Forecasting of Excess Stock Returns—The Five-Year Case
Authors: Kyriakou Ioannis , Mousavi Parastoo , Nielsen Jens Perch , Scholz Michael
Published: June 2020

Long-term return expectations or predictions play an important role in planning purposes and guidance of long-term investors. Five-year stock returns are less volatile around their geometric mean than returns of higher frequency, such as one-year returns. One would, therefore, expect models using the latter to better reduce the noise and beat the simple historical mean than models based on the former. However, this paper shows that the general tendency is surprisingly the opposite: long-term forecasts over five years have a similar or even better predictive power when compared to the one-year case. We consider a long list of economic predictors and benchmarks relevant for the long-term investor. Our predictive approach consists of adopting and implementing a fully nonparametric smoother with the covariates and the smoothing parameters chosen by cross-validation. We consistently find that long-term forecasting performs well and recommend drawing more attention to it when designing investment strategies for long-term investors. Furthermore, our preferred predictive model did stand the test of Covid-19 providing a relatively optimistic outlook in March 2020 when uncertainty was all around us with lockdown and facing an unknown new pandemic.
Location of Multiple Damage Types in a Truss-Type Structure Using Multiple Signal Classification Method and Vibration Signals
Authors: Perez-Ramirez Carlos A. , Machorro-Lopez Jose M. , Valtierra-Rodriguez Martin , Amezquita-Sanchez Juan P. , Garcia-Perez Arturo , Camarena-Martinez David , Romero-Troncoso Rene de J.
Published: June 2020

A new multiple signal classification (MUSIC)-based methodology is presented for detecting and locating multiple damage types in a truss-type structure subjected to dynamic excitations. The methodology is based mainly on two steps: in step 1, the MUSIC method is employed to obtain the pseudo-spectra of vibration signatures, healthy and damaged, to be used for damage detection. In step 2, a new damage index, based on the obtained pseudo-spectra, is proposed to measure the structure condition. Furthermore, the damage location is estimated according to the variation in the amplitudes of the estimated pseudo-spectra. The presented results show that the proposed methodology can make an accurate and reliable estimation of the condition and location of three specific damage conditions, i.e., loosened bolts, internal corrosion, and external corrosion.
The Role of Gender Diversity in Downside Risk: Empirical Evidence from Vietnamese Listed Firms
Authors: Tran Cong-Duc , Phung Minh-Tuan , Yang Fu-Ju , Wang Yi-Hsien
Published: June 2020

Corporate governance has been marked as an important component of the fast-growing pace of the Vietnam economy recently. Aligning with the concern that gender plays a critical role in corporate management, this study aims to reveal the entire benefits of the appearance of women on board to reduce downside risk in the frontier countries. By using a unique dataset from Vietnamese listed firms and appropriate econometric methods, we present tight results that the presentation of women at firm management level is more likely to lessen the downside risk. In particular, female non-senior reduces all risk attributes, whereas the presence of women in executive board decrease firm risk only. Furthermore, the decreasing of individual and systemic risk are additionally driven by female Chief Executive Officer (CEO) and chairman. We found strong evidence that female leadership may decrease risk-taking in the low-risk firms at all managerial levels but not in the case of a female CEO. In summary, by examining data from specific frontier areas such as Vietnam, we confirm that the role of female leadership in terms of reducing the downside risk depend on their power managerial levels and the firm-risk behavior.
A Competitive Memory Paradigm for Multimodal Optimization Driven by Clustering and Chaos
Authors: Gálvez Jorge , Cuevas Erik , Gopal Dhal Krishna
Published: June 2020

Evolutionary Computation Methods (ECMs) are proposed as stochastic search methods to solve complex optimization problems where classical optimization methods are not suitable. Most of the proposed ECMs aim to find the global optimum for a given function. However, from a practical point of view, in engineering, finding the global optimum may not always be useful, since it may represent solutions that are not physically, mechanically or even structurally realizable. Commonly, the evolutionary operators of ECMs are not designed to efficiently register multiple optima by executing them a single run. Under such circumstances, there is a need to incorporate certain mechanisms to allow ECMs to maintain and register multiple optima at each generation executed in a single run. On the other hand, the concept of dominance found in animal behavior indicates the level of social interaction among two animals in terms of aggressiveness. Such aggressiveness keeps two or more individuals as distant as possible from one another, where the most dominant individual prevails as the other withdraws. In this paper, the concept of dominance is computationally abstracted in terms of a data structure called “competitive memory” to incorporate multimodal capabilities into the evolutionary operators of the recently proposed Cluster-Chaotic-Optimization (CCO). Under CCO, the competitive memory is implemented as a memory mechanism to efficiently register and maintain all possible optimal values within a single execution of the algorithm. The performance of the proposed method is numerically compared against several multimodal schemes over a set of benchmark functions. The experimental study suggests that the proposed approach outperforms its competitors in terms of robustness, quality, and precision.
Establishing New Criteria for Oscillation of Odd-Order Nonlinear Differential Equations
Authors: Moaaz Osama , Awrejcewicz Jan , Muhib Ali
Published: June 2020

By establishing new conditions for the non-existence of so-called Kneser solutions, we can generate sufficient conditions to ensure that all solutions of odd-order equations are oscillatory. Our results improve and expand the previous results in the literature.
Functional Location-Scale Model to Forecast Bivariate Pollution Episodes
Authors: Oviedo-de La Fuente Manuel , Ordóñez Celestino , Roca-Pardiñas Javier
Published: June 2020

Predicting anomalous emission of pollutants into the atmosphere well in advance is crucial for industries emitting such elements, since it allows them to take corrective measures aimed to avoid such emissions and their consequences. In this work, we propose a functional location-scale model to predict in advance pollution episodes where two pollutants are involved. Functional generalized additive models (FGAMs) are used to estimate the means and variances of the model, as well as the correlation between both pollutants. The method not only forecasts the concentrations of both pollutants, it also estimates an uncertainty region where the concentrations of both pollutants should be located, given a specific level of uncertainty. The performance of the model was evaluated using real data of SO 2 and NO x emissions from a coal-fired power station, obtaining good results.
Markov-Switching Stochastic Processes in an Active Trading Algorithm in the Main Latin-American Stock Markets
Authors: De la Torre-Torres Oscar V. , Galeana-Figueroa Evaristo , Álvarez-García José
Published: June 2020

In the present paper, we review the use of two-state, Generalized Auto Regressive Conditionally Heteroskedastic Markovian stochastic processes (MS-GARCH). These show the quantitative model of an active stock trading algorithm in the three main Latin-American stock markets (Brazil, Chile, and Mexico). By backtesting the performance of a U.S. dollar based investor, we found that the use of the Gaussian MS-GARCH leads, in the Brazilian market, to a better performance against a buy and hold strategy (BH). In addition, we found that the use of t-Student MS-ARCH models is preferable in the Chilean market. Lastly, in the Mexican case, we found that is better to use Gaussian time-fixed variance MS models. Their use leads to the best overall performance than the BH portfolio. Our results are of use for practitioners by the fact that MS-GARCH models could be part of quantitative and computer algorithms for active trading in these three stock markets.
Fuzzy Multicriteria Modelling of Decision Making in the Renewal of Healthcare Technologies
Authors: Domínguez Sergio , Carnero María Carmen
Published: June 2020

In the current literature, there are a clear lack of systems to assist in making decisions about the renewal of technology for healthcare equipment, which means that the limited capacity to invest in new equipment cannot usually be appropriately applied as determined by the care requirements of a community. This may have important repercussions for patients, such as the inability to offer treatment or diagnosis, having to delay treatment or diagnosis, increase the risk of patients and care staff of using obsolete equipment, and preventing early, accurate, and reliable diagnosis, all of which have effects on the quality of care to a community. This study therefore describes the first multicriteria model in a fuzzy environment to assist in decision making related to the renewal of healthcare equipment. The fuzzy analytic hierarchy process (FAHP), which allows for ambiguities, uncertainties, and doubts inherent in real-world decision processes to be taken into account, was used to do this. The model produces a plan with actions to be taken depending on the obtained results. The model includes a novel methodology that consists of modifying the top–down technique to allow for the levels of priority for renewing healthcare equipment to be determined from judgements given by three experts. The model was validated by applying it to a set of medical devices, and we show the results for a surgical C-arm, an X-ray CT room, a neonatal ventilator, a defibrillator, and a video-colonoscope. A program was also created using the NI Labview software to process the model so that it could be applied with a user interface that acts quickly, simply, and intuitively.
Porous Three-Dimensional Scaffold Generation for 3D Printing
Authors: Lee Chaeyoung , Jeong Darae , Yoon Sungha , Kim Junseok
Published: June 2020

In this paper, we present an efficient numerical method for arbitrary shaped porous structure generation for 3D printing. A phase-field model is employed for modeling phase separation phenomena of diblock copolymers based on the three-dimensional nonlocal Cahn–Hilliard (CH) equation. The nonlocal CH equation is a fourth-order nonlinear partial differential equation. To efficiently solve the governing equation, an unconditionally gradient stable convex splitting method for temporal discretization with a Fourier spectral method for the spatial discretization is adopted. The standard fast Fourier transform is used to speed up the computation. A new local average concentration function is introduced to the original nonlocal CH equation so that we can locally control the morphology of the structure. The proposed algorithm is simple to implement and complex shaped structures can also be implemented with corresponding signed distance fields. Various numerical tests are performed on simple and complex structures. The computational results demonstrate that the proposed method is efficient to generate irregular porous structures for 3D printing.