bluuebunny/crossref_metadata_2025 huggingface dataset:
Ag/Ag3PO4 Nanoparticle-Decorated Hydroxyapatite Functionalized Calcium Carbonate: Ultrasound-Assisted Sustainable Synthesis, Characterization, and Antimicrobial Activity
Authors: Di Michele Alessandro , Nocchetti Morena , Pietrella Donatella , Latterini Loredana , Quaglia Giulia , Mattu Ilaria , Padeletti Giuseppina , Kaciulis Saulius , Bolli Eleonora , Ambrogi Valeria
Published: February 2023

Silver nanoparticles are usually prepared by the reduction of silver cations through chemical and non-sustainable procedures that involve the use of reducing chemical agents. Therefore, many efforts have been made in the search for sustainable alternative methods. Among them, an ultrasound-assisted procedure could be a suitable and sustainable method to afford well-dispersed and nanometric silver particles. This paper describes a sustainable, ultrasound-assisted method using citrate as a reducing agent to prepare silver@hydroxyapatite functionalized calcium carbonate composites. For comparison, an ultrasound-assisted reduction was performed in the presence of NaBH4. The composites obtained in the presence of these two different reducing agents were compared in terms of nanoparticle nature, antimicrobial activity, and cytotoxic activity. The nanoparticle nature was investigated by several techniques, including X-ray powder diffraction, field-emission scanning electron microscopy, transmission electron microscopy, UV–Vis spectroscopic measurements, and X-ray photoemission spectroscopy. Nanoparticles with a predominance of Ag or Ag3PO4 were obtained according to the type of reducing agent used. All composites were tested for antimicrobial and antibiofilm activities against Gram-positive and Gram-negative (Staphylococcus aureus and Pseudomonas aeruginosa, respectively) bacteria and for cytotoxicity towards human skin keratinocytes and human fibroblasts. The nature of the nanoparticles, Ag or Ag3PO4, and their predominance seemed to affect the in vitro silver release and the antimicrobial and antibiofilm activities. The composites obtained by the citrate-assisted reduction gave rise to the best results.
Hybrid Fiber Materials according to the Manufacturing Technology Methods and IOT Materials: A Systematic Review
Authors: Han Hye Ree
Published: February 2023

With the development of convergence technology, the Internet of Things (IoT), and artificial intelligence (AI), there has been increasing interest in the materials industry. In recent years, numerous studies have attempted to identify and explore multi-functional cutting-edge hybrid materials. In this paper, the international literature on the materials used in hybrid fibers and manufacturing technologies were investigated and their future utilization in the industry is predicted. Furthermore, a systematic review is also conducted. This includes sputtering, electrospun nanofibers, 3D (three-dimensional) printing, shape memory, and conductive materials. Sputtering technology is an eco-friendly, intelligent material that does not use water and can be applied as an advantageous military stealth material and electromagnetic blocking material, etc. Electrospinning can be applied to breathable fabrics, toxic chemical resistance, fibrous drug delivery systems, and nanoliposomes, etc. 3D printing can be used in various fields, such as core-sheath fibers and artificial organs, etc. Conductive materials include metal nanowires, polypyrrole, polyaniline, and CNT (Carbon Nano Tube), and can be used in actuators and light-emitting devices. When shape-memory materials deform into a temporary shape, they can return to their original shape in response to external stimuli. This study attempted to examine in-depth hybrid fiber materials and manufacturing technologies.
X-ray Tomographic Method to Study the Internal Structure of a TiNi–TiB2 Metal Matrix Composite Obtained by Direct Laser Deposition
Authors: Korobenkov Maxim , Lebedev Mikhail , Promakhov Vladimir , Narikovich Anton
Published: February 2023

The field of additive manufacturing (AM) of various materials is rapidly developing. At the stage of designing and growing products and for the quality control of finished parts, non-destructive methods of analysis, in particular X-ray computed tomography (CT), are in demand. In addition to the advantages of non-destructive imaging of a wide range of materials in three dimensions, modern CT scanners offer a high contrast and high spatial resolution to provide digital information about their three-dimensional geometry and properties. Within the framework of this article, CT was used to follow the structural evolution of a TiNi–TiB2 metal–ceramic composite obtained by direct laser deposition. The relationship has been established between the additive method of production (layered direct laser deposition) and the formed layered structure of the product in the direction of growth. The porosity of the sample was calculated for each scan direction, and the average for the sample was 1.96%. The matrix of the TiNi–TiB2 composite is characterized by the presence of pores of various sizes, shapes and locations. Spherical voids prevail, but keyhole pores are also found. The heterogeneity of the structure was revealed in the form of clearly traced boundaries of the print layers, as well as differences in the density of the inner and outer regions of the composite.
Development of Alkali-Activated Porous Concrete Composition from Slag Waste
Authors: Tamošaitis Gintautas , Vaičiukynienė Danute , Jaskaudas Tomas , Mockiene Jurate , Pupeikis Darius
Published: February 2023

In this paper, a porous alkali-activated slag concrete was developed that can be used in the construction sector as a sustainable building material and potentially as an alternative to the aerated concrete products currently on the market. Ferrous slag from the metallurgical industry (Finland) and phosphogypsum from a fertilizer plant (Lithuania) were used as precursors in alkali-activated systems. The addition of hydrogen peroxide and phosphogypsum led to positive changes in the final properties of the test material. Porous concrete based on alkali-activated slag was analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) methods. The compressive strength, density, thermal conductivity and porosity of the hardened specimens were evaluated as well. Research is being conducted with the material in question to create a cheap, particularly low-energy demanding building material. This material must have suitable mechanical properties for the structure and, at the same time, suitable thermal conductivity properties. It was determined that this porous concrete had compressive strength in the range of 2.12–7.95 MPa, density from 830 kg/m3 to 1142 kg/m3, and thermal conductivity in the range of 0.0985–0.2618 W/(m·K). The results indicate that the recommended content of phosphogypsum in alkali-activated material is 3–5% due to the optimal distribution of the mechanical and thermal properties and the conductivity. Alkali-activated slag and phosphogypsum material can be used in the manufacture of low-strength insulation blocks and to protect structures from the effects of high temperatures.
Mechanical Behavior of Austenitic Steel under Multi-Axial Cyclic Loading
Authors: Biswas Abhishek , Kurtulan Dzhem , Ngeru Timothy , Azócar Guzmán Abril , Hanke Stefanie , Hartmaier Alexander
Published: February 2023

Low-nickel austenitic steel is subjected to high-pressure torsion fatigue (HPTF) loading, where a constant axial compression is overlaid with a cyclic torsion. The focus of this work lies on investigating whether isotropic J2 plasticity or crystal plasticity can describe the mechanical behavior during HPTF loading, particularly focusing on the axial creep deformation seen in the experiment. The results indicate that a J2 plasticity model with an associated flow rule fails to describe the axial creep behavior. In contrast, a micromechanical model based on an empirical crystal plasticity law with kinematic hardening described by the Ohno–Wang rule can match the HPTF experiments quite accurately. Hence, our results confirm the versatility of crystal plasticity in combination with microstructural models to describe the mechanical behavior of materials under reversing multiaxial loading situations.
Takagi–Sugeno Fuzzy Model-Based Control for Semi-Active Cab Suspension Equipped with an Electromagnetic Damper and an Air Spring
Authors: Zhang Bangji , Liu Minyao , Wang Kunjun , Tan Bohuan , Deng Yuanwang , Qin An , Liu Jingang
Published: February 2023

Variable damping shock absorbers have received extensive attention for their efficient vibration reduction performance, and air springs have also been widely used in high-end commercial vehicles due to their nonlinear stiffness characteristics. This paper presents a novel semi-active cab suspension integrated with an air spring and a variable damping electromagnetic damper (A-EMD). The electromagnetic damper (EMD) prototype was designed, manufactured and tested. Then, due to the interference of nonlinear stiffness characteristics of the air spring with the controller in the subsequent design, the Takagi–Sugeno fuzzy method was adopted to segmentally linearize its nonlinearity, based on which an H∞ state feedback semi-active controller was designed to control the EMD to generate variable damping force. Furthermore, a Luenberger state observer was designed to provide immeasurable state parameters for the controller. Numerical simulations were carried out to validate the effectiveness of the proposed approaches, and the results show that the proposed control strategy can significantly improve the ride comfort of the A-EMD system. The vibration dose value (VDV) acceleration under the bump road and the frequency-weighted acceleration root mean square (FWA-RMS) under the random road decreased by 36.05% and 19.77%, respectively, compared with the passive suspension system.
An Error-Pursuing Adaptive Uncertainty Analysis Method Based on Bayesian Support Vector Regression
Authors: Zhou Sheng-Tong , Jiang Jian , Zhou Jian-Min , Chen Pei-Han , Xiao Qian
Published: February 2023

The Bayesian support vector regression (BSVR) metamodel is widely used in various engineering fields to analyze the uncertainty arising from uncertain parameters. However, the accuracy of the BSVR metamodel based on the traditional one-shot sampling method fails to meet the requirements of the uncertainty analysis of complex systems. To this end, an error-pursing adaptive uncertainty analysis method based on the BSVR metamodel is presented by combining a new adaptive sampling scheme. This new sampling scheme was improved by a new error-pursuing active learning function that is named, herein, adjusted mean square error (AMSE), which guides the adaptive sampling of the BSVR metamodel’s design of experiments (DoE). During the sampling process, AMSE combines mean square error and leave-one-out cross-validation error to estimate the prediction error of the metamodel in the entire design space. Stepwise refinement of the metamodel was achieved by placing the sampled regions at locations with large prediction errors. Six benchmark analytical functions featuring different dimensions were used to validate the proposed method. The effectiveness of the method was then further illustrated by a more realistic application of an overhung rotor system.
Experimental Investigation of Vibration Reduction Effect of High-Pressure Air Compressor Using Composite Damping Base
Authors: Zhao Feng , Li He , Li Hui , Liu Duo
Published: February 2023

High-pressure air compressor is one of the most important pieces of equipment for ships, which is one of the main sources of vibration on board. There are a lot of welded plate structures in the installation base of the compressor, which have weak stiffness and low damping and are prone to vibration radiation due to excitation. In this paper, a section of the base is taken as the test object. Through the analysis of the working principle, the vibration characteristics of the air compressor and the corresponding transmission path are mastered. In addition, it is tested and screened by filling different kinds of damping materials. Finally, it is concluded that the super-damping rubber has a better damping effect on the specimen of the base. According to the vibration characteristics of the plate structure, the sandwich structure, which is fixed by a restraint layer with super-damping rubber, is bonded to the plate. When the base is excited, the restraint layer moves in relative slippage, and the damping rubber can consume part of the vibration energy so that the vibration of the plate structure is reduced. Moreover, the technology has the characteristics of small additional mass and a good damping effect. It has been proved that the feet acceleration is reduced by 6 dB or above through experiments.
Two-Dimensional-Based Hybrid Shape Optimisation of a 5-Element Formula 1 Race Car Front Wing under FIA Regulations
Authors: Granados-Ortiz Francisco-Javier , Morales-Higueras Pablo , Ortega-Casanova Joaquín , López-Martínez Alejandro
Published: February 2023

Front wings are a key element in the aerodynamic performance of Formula 1 race cars. Thus, their optimisation makes an important contribution to the performance of cars in races. However, their design is constrained by regulation, which makes it more difficult to find good designs. The present work develops a hybrid shape optimisation approach to obtain an optimal five-element airfoil front wing under the FIA regulations and 17 design parameters. A first baseline design is obtained by parametric optimisation, on which the adjoint method is applied for shape optimisation via Mesh Morphing with Radial Basis Functions. The optimal front wing candidate obtained outperforms the parametric baseline up to a 25% at certain local positions. This shows that the proposed and tested hybrid approach can be a very efficient alternative. Although a direct 3D optimisation approach could be developed, the computational costs would be dramatically increased (possibly unaffordable for such a complex five-element front wing realistic shape with 17 design parameters and regulatory constraints). Thus, the present approach is of strong interest if the computational budget is low and/or a fast new front wing design is desired, which is a frequent scenario in Formula 1 race car design.
Two-Dimensional Analytical Models for Cogging Torque Prediction in Interior Permanent Magnet Machine
Authors: Wang Linwei , Lu Shuai , Chen Yangming
Published: February 2023

Analytical prediction of cogging torque needs accurate flux density and relative permeance closed-form expressions. The accurate two-dimensional (2D) air gap flux density distribution function and the 2D permeance function are currently almost always applied to surface-mounted permanent magnet (SPM) machines, instead of interior permanent magnet (IPM) machines, due to complications from IPMs severe magnetic saturation and leakage flux. To address these issues, this paper proposes a set of new methods to derive the accurate closed-form 2D expressions of IPMs for both flux density and relative permeance. As for the flux density 2D model, a virtual equivalence model for IPM is introduced, so that Laplace’s equation and quasi-Poisson equation can be directly applied to IPM. As for permeance, the same virtual equivalence model also enables 2D models derivation for IPM. Subsequently, the resulting cogging torque analytical expression is obtained with the accurate relative permeance and air gap flux density models. The results from the proposed 2D analytical models showed similar accuracy to the finite element analysis (FEA). In addition, as demonstrated, the proposed 2D analytical models is a highly efficient tool set in the design process of cogging torque optimization, facilitating fast evaluation of different design factors.
Cyber-Physical System for Evaluation of Taekwondo Athletes: An Initial Project Description
Authors: Cunha Pedro , Barbosa Paulo , Ferreira Fábio , Silva Tânia , Martins Nuno , Soares Filomena , Carvalho Vítor
Published: February 2023

Regardless of the type of sport, coaches must perform the difficult task of evaluating the performance of athletes. In some cases, this task is aided using technology which provides tools for this purpose. When the sport considered is taekwondo this scenario does not apply as the athlete evaluation methods used are mostly manual. Thus, the project presented in this paper has the main objective to develop a system that can be used as a tool to evaluate the performance of taekwondo athletes in real time, with special attention to the low cost of implementation and ease of use. With the intention of meeting these requirements, the developed system comprises a 3D camera with a depth sensor (Orbbec Astra), Inertial Measurement Units (IMUs) with accelerometer and gyroscope, a computer and specific software developed for this purpose. This system allows the collection of data from the athletes’ movements necessary for the creation of a dataset that is then analyzed and interpretated. The system permits the user to obtain real-time information about the speed, acceleration, and strength of the athlete’s limbs during training as well as the identification of some movements and their accounting. To achieve this functionality, deep-learning architecture models were used, more specifically long short-term memory (LSTM). The intention is to provide a new training methodology through faster feedback, so that a faster evolution of the athlete’s performance is possible, contributing to the technological development of the assessment practices used in taekwondo.
Novel Feature Extraction and Locomotion Mode Classification Using Intelligent Lower-Limb Prosthesis
Authors: Liu Yi , An Honglei , Ma Hongxu , Wei Qing
Published: February 2023

Intelligent lower-limb prosthesis appears in the public view due to its attractive and potential functions, which can help amputees restore mobility and return to normal life. To realize the natural transition of locomotion modes, locomotion mode classification is the top priority. There are mainly five steady-state and periodic motions, including LW (level walking), SA (stair ascent), SD (stair descent), RA (ramp ascent), and RD (ramp descent), while ST (standing) can also be regarded as one locomotion mode (at the start or end of walking). This paper mainly proposes four novel features, including TPDS (thigh phase diagram shape), KAT (knee angle trajectory), CPO (center position offset) and GRFPV (ground reaction force peak value) and designs ST classifier and artificial neural network (ANN) classifier by using a user-dependent dataset to classify six locomotion modes. Gaussian distributions are applied in those features to simulate the uncertainty and change of human gaits. An angular velocity threshold and GRFPV feature are used in the ST classifier, and the artificial neural network (ANN) classifier explores the mapping relation between our features and the locomotion modes. The results show that the proposed method can reach a high accuracy of 99.16% ± 0.38%. The proposed method can provide accurate motion intent of amputees to the controller and greatly improve the safety performance of intelligent lower-limb prostheses. The simple structure of ANN applied in this paper makes adaptive online learning algorithms possible in the future.
Shock Absorption for Legged Locomotion through Magnetorheological Leg-Stiffness Control
Authors: Christie Matthew Daniel , Sun Shuaishuai , Deng Lei , Du Haiping , Zhang Shiwu , Li Weihua
Published: February 2023

The objective of this study was to evaluate the performance of a magnetorheological-fluid-based variable stiffness actuator leg under high impact forces through optimal tuning and control of stiffness and damping properties. To achieve this, drop testing experiments were conducted with the leg at various drop heights and payload masses. The results showed that while lower stiffness and higher damping can lead to lower impact forces and greater energy dissipation, respectively, optimal control can also protect the leg from deflecting beyond its functional range. Comparison with a rigid leg with higher damping showed a 57.5% reduction in impact force, while a more compliant leg with lower damping results in a 61.4% reduction. These findings demonstrate the importance of considering both stiffness and damping in the design of legged robots for high impact force resistance. This simultaneously highlights the efficacy of the proposed magnetorheological-fluid-based leg design for this purpose.
Nonlinear Dynamics and Vibration Localization of Shrouded Blisk with Contact and Friction Effects
Authors: Yuan Gaofei , Wang Yuefang
Published: February 2023

Shrouds have been widely used to reduce the level of excessive vibration of blisks. However, complicated nonlinear motion can be induced by the contact and friction between shrouds. Even worse, harmful localization of vibration can be encountered due to nonsmooth behaviour at the shroud contact interfaces in the tuned disk. In this paper, the nonlinear dynamics and localization of vibration of a shrouded blisk are studied considering the spin softening. The continuous parametric model of a shrouded blisk is established, and the transition boundaries between different status (i.e., stick, slip and separation) of shrouds are determined based on the Coulomb friction model. The steady-state responses of the blisk are analysed using variable rotation speed, and the primary resonance, beat and quasi-periodic vibration are presented in connection with the non-smooth behaviour of contact. A particular type of vibration localization initiated by the contact and friction effect of the shrouds in the form of asymmetric vibration in the tuned blisk is discovered. It is found that the blades-disk coupling has strong influences on the level of the localization. The effects of the contact stiffness and localization on the blade vibration are demonstrated through the change in the powers of the blade motions.
Effect of the Bionic Transverse Stripe on Wear Resistance and Crushing Performance of Cement Grinding Roller
Authors: Chen Tingkun , Wang Lin , Xu Jin , Qin Xiuzhang , Dong Xinju , Wang Qingbo , Qi Yingchun , Jin Jingfu , Cong Qian , Liu Chaozong
Published: February 2023

To improve the wear resistance and mineral crushing performance of grinding rollers in cement, mining, and other engineering fields, a striped groove morphology was designed on the normal grinding roller surface in this study. The wear resistance of grinding rollers with different striped groove parameters and the crushing performance of quartz sand were tested with a purposely designed device. The depth and number of striped grooves were used as the structural parameters of the striped grooves, and the test protocol was designed with the experimental design method. The results showed that the wear resistance and crushing performance of the grinding roller with striped grooves were better than those of the smooth grinding roller for quartz sand. For example, the wear of the 3# bionic grinding roller was reduced by 53.58% compared with the average wear amount of a normal grinding roller, and the crushing effect of the quartz sand was also improved. The regression equation between the stripe depth, number of stripes, and wear amount of the grinding roller was constructed on the basis of the multiple orthogonal regression method. It was found that the influence of the striped groove depth on the wear amount of the grinding roller was greater than that of the distribution number of the striped grooves. According to the results and the analysis the striped grooves distributed on the grinding roller’s surface caused the friction state between the quartz sand and the grinding roller to be in a state of sliding friction, and the wear amount was reduced. Striped grooves on the grinding roller surface might also change the stress state of the quartz sand in the crushing process. Additionally, the performance of the bionic grinding roller in crushing quartz sand was improved, and the wear amount of the bionic grinding roller was also reduced compared with that of the normal grinding roller.
Characteristic, C-Characteristic and Positive Cones in Hyperfields
Authors: Kędzierski Dawid Edmund , Linzi Alessandro , Stojałowska Hanna
Published: February 2023

We study the notions of the positive cone, characteristic and C-characteristic in (Krasner) hyperfields. We demonstrate how these interact in order to produce interesting results in the theory of hyperfields. For instance, we provide a criterion for deciding whether certain hyperfields cannot be obtained via Krasner’s quotient construction. We prove that any positive integer (larger than 1) can be realized as the characteristic of some infinite hyperfield and an analogous result for the C-characteristic. Finally, we study the (directed) graph associated with the strict partial order induced by a positive cone in a hyperfield in various examples.
Numerical Simulation of Heat Transfer and Spread of Virus Particles in the Car Interior
Authors: Panfilov Ivan , Beskopylny Alexey , Meskhi Besarion
Published: February 2023

The epidemic caused by the coronavirus infection SARS-CoV-2 at the beginning of 2022 affected approximately 500 million people in all countries. The source of infection is the particles of the virus, which, when breathing, talking, and coughing, are released with the respiratory droplets and aerosol dust of an infected person. Actions aimed at combating and minimizing the consequences of coronavirus infection led to taking measures in scientific areas to investigate the processes of the spread of viral particles in the air, in ventilation, and air conditioning systems of premises and transport, filtration through masks, the effect of partitions, face shields, etc. The article presents a mathematical model of the spread of viral particles in technological transport. Air intake diverters and the operator’s respiratory tract are the sources of the virus. The Euler–Lagrange approach was used to simulate liquid droplets in a flow. Here, the liquid phase is considered as a continuous medium using Navier–Stokes equations, the continuity equation, the energy equation, and the diffusion equation. Accounting for diffusion makes it possible to explicitly model air humidity and is necessary to consider the evaporation of droplets (changes in the mass and size of particles containing the virus). Liquid droplets are modeled using the discrete-phase model (DPM), in which each particle is tracked in a Lagrange coordinate system. The DPM method is effective, since the volume fraction of particles is small relative to the total volume of the medium, and the interaction of particles with each other can be neglected. In this case, the discrete and continuous phases are interconnected through the source terms in the equations. The averaged RANS equations are solved numerically using the k-ω turbulence model in the Ansys Fluent package. The task was solved in a static form and in the time domain. For a non-stationary problem, the stabilization time of the variables is found. The simulation results are obtained in the form of fields of pressures, velocities, temperatures and air densities, and the field of propagation of particles containing the virus. Various regimes were studied at various free flow rates and initial velocities of droplets with viral particles. The results of trajectories and velocities of particles, and particle concentrations depending on time, size, and on the evaporability of particles are obtained.
Multi-Layer Decomposition and Synthesis of HDR Images to Improve High-Saturation Boundaries
Authors: Kwon Hyuk-Ju , Lee Sung-Hak
Published: February 2023

Recently, high dynamic range (HDR) imaging has been used in many fields such as display, computer graphics, and digital cameras. Various tone mapping operators (TMOs) are used for effective HDR imaging. TMOs aim to express HDR images without loss of information and natural images on existing display equipment. In this paper, to improve the color distortion that occurs during tone mapping, multi-layer decomposition-based color compensation and global color enhancement of the boundary region are proposed. Multi-layer decomposition is used to preserve the color information of the input image and to find the area where color distortion occurs. Color compensation and enhancement are especially used to improve the color saturation of the border area, which is degraded due to color distortion and tone processing. Color compensation and enhancement are processed in IPT color space with excellent hue linearity to improve effective performance by reducing interference between luminance and chrominance components. The performance of the proposed method was compared to the existing methods using naturalness, distortion, and tone-mapped image quality metrics. The results show that the proposed method is superior to the existing methods.
Exploring the Predictors of Co-Nationals’ Preference over Immigrants in Accessing Jobs—Evidence from World Values Survey
Authors: Homocianu Daniel
Published: February 2023

This paper presents the results of an exploration of the most resilient influences determining the attitude regarding prioritizing co-nationals over immigrants for access to employment. The source data were from the World Values Survey. After many selection and testing steps, a set of the seven most significant determinants was produced (a fair-to-good model as prediction accuracy). These seven determinants (a hepta-core model) correspond to some features, beliefs, and attitudes regarding emancipative values, gender discrimination, immigrant policy, trust in people of another nationality, inverse devoutness or making parents proud as a life goal, attitude towards work, the post-materialist index, and job preferences as more inclined towards self rather than community benefits. Additional controls revealed the significant influence of some socio-demographic variables. They correspond to gender, the number of children, the highest education level attained, employment status, income scale positioning, settlement size, and the interview year. All selection and testing steps considered many principles, methods, and techniques (e.g., triangulation via adaptive boosting (in the Rattle library of R), and pairwise correlation-based data mining—PCDM, LASSO, OLS, binary and ordered logistic regressions (LOGIT, OLOGIT), prediction nomograms, together with tools for reporting default and custom model evaluation metrics, such as ESTOUT and MEM in Stata). Cross-validations relied on random subsamples (CVLASSO) and well-established ones (mixed-effects). In addition, overfitting removal (RLASSO), reverse causality, and collinearity checks succeeded under full conditions for replicating the results. The prediction nomogram corresponding to the most resistant predictors identified in this paper is also a powerful tool for identifying risks. Therefore, it can provide strong support for decision makers in matters related to immigration and access to employment. The paper’s novelty also results from the many robust supporting techniques that allow randomly, and non-randomly cross-validated and fully reproducible results based on a large amount and variety of source data. The findings also represent a step forward in migration and access-to-job research.
Adaptive Output Feedback Control for Constrained Switched Systems with Input Quantization
Authors: Qi Shuyan , Zhao Jun , Tang Li
Published: February 2023

This paper investigates adaptive output feedback control problem for switched uncertain nonlinear systems with input quantization, unmeasured system states and state constraints. Firstly, fuzzy logic systems are introduced to identify system uncertainties, then the fuzzy based observer is constructed to estimate unavailable states. Secondly, combing the backstepping technique and the barrier Lyapunov function method, an adaptive fuzzy output feedback control law is designed, which guarantees that all signals in the closed-loop system are bounded, the system output tracks the reference signal, and system states satisfy their corresponding constraint conditions. Finally, simulation results further show the good performances of the proposed control scheme.
Fault-Tolerant Terminal Sliding Mode Control with Disturbance Observer for Vibration Suppression in Non-Local Strain Gradient Nano-Beams
Authors: Alsubaie Hajid , Yousefpour Amin , Alotaibi Ahmed , Alotaibi Naif D. , Jahanshahi Hadi
Published: February 2023

This research investigates the stabilization and control of an uncertain Euler–Bernoulli nano-beam with fixed ends. The governing partial differential equations of motion for the nano-beam are derived using Hamilton’s principle and the non-local strain gradient theory. The Galerkin method is then applied to transform the resulting dimensionless partial differential equation into a nonlinear ordinary differential equation. A novel fault-tolerant terminal sliding mode control technique is proposed to address the uncertainties inherent in micro/nano-systems and the potential for faults and failures in control actuators. The proposed controller includes a finite time estimator, the stability of which and the convergence of the error dynamics are established using the Lyapunov theorem. The significance of this study lies in its application to the field of micro/nano-mechanics, where the precise control and stabilization of small-scale systems is crucial for the development of advanced technologies such as nano-robotics and micro-electromechanical systems (MEMS). The proposed control technique addresses the inherent uncertainties and potential for faults in these systems, making it a valuable choice for practical applications. The simulation results are presented to demonstrate the effectiveness of the proposed control scheme and the high accuracy of the estimation algorithm.
Continuous Selections and Extremally Disconnected Spaces
Authors: Pimienta Adolfo , Sanchis Manuel
Published: February 2023

This paper deals with extremally disconnected spaces and extremally disconnected P-spaces. A space X is said to be extremally disconnected if, for every open subset V of X, the closure of V in X is also an open set. P-spaces are spaces in which the intersection of countably many open sets is an open set. The authors present a new characterization of extremally disconnected spaces, and the extremally disconnected P-spaces, by means of selection theory. If X is either an extremally disconnected space or an extremally disconnected P-space, then the usual theorems of extension of real-valued continuous functions for a dense subset S of X can be deduced from our results. A corollary of our outcomes is that every nondiscrete space X of nonmeasurable cardinality has a dense subset S such that S is not C-embedded in X.
Adaptive Controller for Bus Voltage Regulation on a DC Microgrid Using a Sepic/Zeta Battery Charger/Discharger
Authors: Montenegro-Oviedo Jhoan Alejandro , Ramos-Paja Carlos Andres , Orozco-Gutierrez Martha Lucia , Franco-Mejía Edinson , Serna-Garcés Sergio Ignacio
Published: February 2023

In a DC microgrid that involves a battery storage system, the primary energy management is performed by a battery charger/discharger based on a dc/dc power converter. Moreover, the battery charger/discharger is also used to regulate the voltage of the dc bus. One of the challenges at the control level is to regulate the DC bus voltage under battery charge and discharge conditions but also under different relations between the battery and bus voltages. For this reason, this paper proposes a battery charger/discharger based on the Sepic/Zeta converter and an adaptive controller, which provides bidirectional current flow, stable bus voltage, and satisfactory electrical characteristics. The main advantage of the proposed control system is the capability to adapt the controller parameters to any operation condition, which provides a general solution to interface any battery to any bus voltage. This study is focused on the design procedure of both the power converter and the controller, where a detailed mathematical analysis is performed to ensure the system performance and stability. Finally, the proposed solution is validated using an experimental prototype and a practical application case.
Survival and Duration Analysis of MSMEs in Chiang Mai, Thailand: Evidence from the Post-COVID-19 Recovery
Authors: Yamaka Woraphon , Maneejuk Paravee , Phadkantha Rungrapee , Puntoon Wiranya , Tarkhamtham Payap , Sudtasan Tatcha
Published: February 2023

This study attempts to reveal the consequences of coronavirus disease 2019 (COVID-19) on micro, small, and medium enterprises (MSMEs) in Chiang Mai, Thailand. A total of 786 MSMEs were surveyed during May and August 2022, corresponding to the period when the recovery of businesses and livelihoods from the ongoing COVID-19 crisis became more perceptible. The perceptions of COVID-19’s impact on MSMEs and their survivability are explored and investigated. To achieve this goal, a copula-based sample selection survival model is introduced. This idea of the model is extended from the concept of the Cox proportional hazards model and copula-based sample selection model, enabling us to construct simultaneous equations—namely, the probability-of-failure equation (selection equation) and the duration-of-survival equation (time-to-event or outcome equation). Several copula functions with different dependence patterns are considered to join the failure equation and the duration-of-survival equation. By comparing the Akaike and Bayesian information criteria values of the candidate copulas, we find that Farlie–Gumbel–Morgenstern (FGM) copula performs the best-fit joint function in our analysis. Empirically, the results from this best-fit model reveal that the survival probability of MSMEs in the next year is around 80%. However, some MSMEs may not survive more than three months after the interview. Finally, our results also reveal that the tourism MSMEs have a lower chance of survival than the commercial and manufacturing MSMEs. Notably, the business size and the support schemes from the government—such as the debt restructuring process, the tax payment deadline extension, and the reduced social security contributions—exhibited a role in lengthening the survival duration of the non-surviving MSMEs.
Dynamics of a Four-Dimensional Economic Model
Authors: Moza Gheorghe , Brandibur Oana , Găină Ariana
Published: February 2023

The interdependency between interest rates, investment demands and inflation rates in a given economy has a continuous dynamics. We propose a four-dimensional model which describes these interactions by imposing a control law on the interest rate. By a qualitative analysis based on tools from dynamical systems theory, we obtain in the new model that the three economic indicators can be stabilized to three equilibrium states.
MRBERT: Pre-Training of Melody and Rhythm for Automatic Music Generation
Authors: Li Shuyu , Sung Yunsick
Published: February 2023

Deep learning technology has been extensively studied for its potential in music, notably for creative music generation research. Traditional music generation approaches based on recurrent neural networks cannot provide satisfactory long-distance dependencies. These approaches are typically designed for specific tasks, such as melody and chord generation, and cannot generate diverse music simultaneously. Pre-training is used in natural language processing to accomplish various tasks and overcome the limitation of long-distance dependencies. However, pre-training is not yet widely used in automatic music generation. Because of the differences in the attributes of language and music, traditional pre-trained models utilized in language modeling cannot be directly applied to music fields. This paper proposes a pre-trained model, MRBERT, for multitask-based music generation to learn melody and rhythm representation. The pre-trained model can be applied to music generation applications such as web-based music composers that includes the functions of melody and rhythm generation, modification, completion, and chord matching after being fine-tuned. The results of ablation experiments performed on the proposed model revealed that under the evaluation metrics of HITS@k, the pre-trained MRBERT considerably improved the performance of the generation tasks by 0.09–13.10% and 0.02–7.37%, compared to the usage of RNNs and the original BERT, respectively.
Flexible Metamaterial-Based Frequency Selective Surface with Square and Circular Split Ring Resonators Combinations for X-Band Applications
Authors: Prasad Nagandla , Pardhasaradhi Pokkunuri , Madhav Boddapati Taraka Phani , Das Sudipta , Awan Wahaj Abbas , Hussain Niamat
Published: February 2023

To meet the demand for modern communication technology, the development of satellite communications has been consistently investigated. In this article, a rectangle-type SRR is attached to circular-type SRR for obtaining two frequencies in X-band operation. The designed structure exhibits negative metamaterial properties (Epsilon, mu and refractive index are negative) and the design was fabricated on a polyimide dielectric material with a 10 × 10 mm2 size. The polyimide dielectric material is chosen with a thickness of 0.1 mm and a dielectric constant of 0.0027. The proposed unit cell is designed and simulated by using one of the numerical simulation tools, CSTMW studio, in which the frequency limit is chosen from 7 to 12 GHz. From the results, we can observe that the proposed design resonates at two X-band frequencies at 9.84 GHz and 11.46 GHz and the measurement results of the proposed design resonate at 9.81 GHz and 11.61 GHz. It is worth noting that the simulation and measurement findings both obtain the same X-band frequencies, with only a minor difference in the frequency values. Thus, the recommended design is very much useful for X-band applications.
Interfacial Stresses for a Coated Irregularly Shaped Hole Embedded in an Infinite Solid under Point Heat Singularity
Authors: Liao Yi-Lun , Tseng Shao-Chen , Chao Ching-Kong
Published: February 2023

Particle-reinforced metals are being developed for advanced heat dissipation applications. However, an irregularly shaped void develops during eutectic solidification and enhances interfacial stress induced by visco-plastic deformation in temperature gradient conditions. An analytical solution to an irregularly shaped coated hole embedded in an infinite substrate under an arbitrarily located heat source or sink is presented. For a coated polygonal hole with any number of edges, a rapidly convergent series solution of the temperature and stress functions is expressed in an elegant form using conformal mapping, the analytic continuation theorem, and the alternation method. The iterations of the trial-and-error method are utilized to obtain the solution for the correction terms. First, temperature contours are obtained to provide an optimal suggestion that a larger thermal conductivity of the coating layer exhibits better heat absorption capacity. Furthermore, interfacial stresses between a coating layer and substrate increase if the strength of a point thermal singularity and thermal mismatch increases. This study provides a detailed explanation for the growth of an irregular void at an ambient temperature gradient.
The Sense of Cooperation on Interdependent Networks Inspired by Influence-Based Self-Organization
Authors: Li Xiaopeng , Wang Zhonglin , Liu Jiuqiang , Yu Guihai
Published: February 2023

Influence, as an inherently special attribute, is bound to profoundly affect a player’s behavior. Meanwhile, a growing body of studies suggests that interactions among networks may be more important than isolated ones. Thus, we try our best to research whether such a setup can stimulate the sense of cooperation in spatial prisoner’s dilemma games through the co-evolution of strategy imitation and interdependence networks structures. To be specific, once a player’s influence exceeds the critical threshold τ, they will be permitted to build a connection with the corresponding partner on another network in a self-organized way, thus gaining additional payoff. However, a player’s influence changes dynamically with the spread of strategy, resulting in time-varying connections between networks. Our results show that influence-based self-organization can facilitate cooperation, even under quite poor conditions, where cooperation cannot flourish in a single network. Furthermore, there is an optimal threshold τ to optimize the evolution of cooperation. Through microcosmic statistical analysis, we are surprised to find that the spontaneous emergence of connections between interdependence networks, especially those between cooperators, plays a key role in alleviating social dilemmas. Finally, we uncover that if the corresponding links between interdependence networks are adjusted to random ones, the evolution of cooperation will be blocked, but it is still better than relying on simple spatial reciprocity on an isolated lattice.
Some Functionals and Approximation Operators Associated with a Family of Discrete Probability Distributions
Authors: Acu Ana Maria , Raşa Ioan , Srivastava Hari M.
Published: February 2023

A certain discrete probability distribution was considered in [“A discrete probability distribution and some applications”, Mediterr. J. Math., 2023]. Its basic properties were investigated and some applications were presented. We now embed this distribution into a family of discrete distributions depending on two parameters and investigate the properties of the new distributions.
Relative Controllability and Ulam–Hyers Stability of the Second-Order Linear Time-Delay Systems
Authors: Abuasbeh Kinda , Mahmudov Nazim I. , Awadalla Muath
Published: February 2023

We introduce the delayed sine/cosine-type matrix function and use the Laplace transform method to obtain a closed form solution to IVP for a second-order time-delayed linear system with noncommutative matrices A and Ω. We also introduce a delay Gramian matrix and examine a relative controllability linear/semi-linear time delay system. We have obtained the necessary and sufficient condition for the relative controllability of the linear time-delayed second-order system. In addition, we have obtained sufficient conditions for the relative controllability of the semi-linear second-order time-delay system. Finally, we investigate the Ulam–Hyers stability of a second-order semi-linear time-delayed system.