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Ferrofluids are aqueous or non-aqueous solutions with colloidal particles of iron oxide nanoparticles with high magnetic characteristics. Their magnetic characteristics enable them to be controlled and manipulated when ferrofluids are exposed to magnetic fields. This study aims to inspect the features of unsteady stagnation point flow (SPF) and heat flux from the surface by incorporating ferromagnetic particles through a special kind of second-grade fluid (SGF) across a movable sheet with a nonlinear heat source/sink and magnetic field effect. The mass suction/injection and stretching/shrinking boundary conditions are also inspected to calculate the fine points of the features of multiple solutions.

The leading equations that govern the ferrofluid flow are reduced to a group of ordinary differential equations by applying similarity variables. The converted equations are numerically solved through the bvp4c solver. Afterward, study and discussion are carried out to examine the different physical parameters of the characteristics of nanofluid flow and thermal properties.

Multiple solutions are revealed to happen for situations of unsteadiness, shrinking as well as stretching sheets. Greater suction slows the separation of the boundary layers and causes the critical values to expand. The region where the multiple solutions appear is observed to expand with increasing values of the magnetic, non-Newtonian and suction parameters. Moreover, the fluid velocity significantly uplifts while the temperature declines due to the suction parameter.

The novelty of the work is to deliberate the impact of mass suction/injection on the unsteady SPF through the special second-grade ferrofluids across a movable sheet with an erratic heat source/sink. The confirmed results provide a very good consistency with the accepted papers. Previous studies have not yet fully explored the entire analysis of the proposed model.

The research purpose of this paper is to confirm that internal overvoltages in the push–pull power inverter can be used to improve the discharge ignition in the gliding arc discharge (GAD) plasma reactor.

Investigations are based on the acquisition of voltage changes that occur together with the development of the discharge column and the imaging the GAD with the use of a high-speed camera.

The power supply has the distinctive feature of not having the switching overvoltages completely extinguished, as it is in typical push–pull inverters. The overvoltages still exist but only dangerous peaks are cut off. The remaining ones, of a dumped resonance character (Figure 3), are transferred to the secondary coil of the transformer. Correctly shaped overvoltages are used for ignition improvement in the GAD reactor.

GAD plasma reactors have many applications for pollution control, disinfection and sterilization of surfaces and for plasma deposition, surface functionalization, as well as in agricultural and medical treatment. Investigations prove the push–pull inverter’s advantages in comparison with the transformer-type power supply. Properly configured push–pull inverters have good ignition properties and control options, allowing to generate, desirable for many applications, homogeneous non-thermal plasma.

The idea of using switching overvoltages in transistors of push–pull switching-mode power supplies is new and has not been previously used to improve discharges ignition in a non-thermal plasma reactor.

Large structural objects, primarily concrete bridges, can be reinforced by gluing to their stretched surface tapes of fiber-reinforced polymer (FRP). The condition for this technology to work requires the quality of the bonding of FRP and the concrete to be perfect. Possible defects may arise in the phase of construction but also as a result of long-term fatigue loads. These defects having different forms of voids and discontinuities in the bonding layer are difficult to detect by optical inspection. This paper aims to describe the development of a rapid and nondestructive method for quantitative assessment of the debonding between materials.

The applied technique belongs to the wide class of active infrared (IR) thermography, the principle of which is to heat (or cool) the investigated object, and determine the properties of interest from the recorded, by an IR camera, temperature field. The methodology implemented in this work is to uniformly heat for a few seconds, using a set of halogen lamps, the FRP surface attached to the concrete. The parameter of interest is the thermal resistance of the layer separating the polymer tape and the concrete. The presence of voids and debonding will result in large values of this resistance. Its value is retrieved by solving an inverse transient heat conduction problem. This is accomplished by minimizing, in the sense of least squares, the difference between the recorded and simulated temperatures. The latter is defined as a solution of a 1D transient heat conduction problem with the already mentioned thermal resistance treated as the only decision variable.

A general method has been developed, which detects debonding of the FRP tapes from the concrete. The method is rapid and nondestructive. Owing to a special selection of the compared dimensionless measured and simulated temperatures, the method is not sensitive to the surface quality (roughness and emissivity). Measurements and calculation may be executed within seconds. The efficiency of the technique has been shown at a sample, where the defects have been artificially introduced in a controlled manner.

A quantitative assessment procedure which can be used to determine the extent of the debonding has been developed. The procedure uses inverse technique whose result is the unknown thermal resistance between the member and the FRP strip.

The study aims to determine whether audited organizations experience differences between external audits and official controls.

A survey among 100 organic food producers was conducted to explore differences regarding the usability of external audits and official controls. The survey was conducted in 2020 using the computer-assisted telephone interview (CATI) method supplemented by the computer-assisted web interview (CAWI) method. Organizations processing organic farming products in Poland were chosen for the study.

Three primary benefits associated with external audits and official controls were identified, i.e. (1) enabling and initiating activities related to the improvement of the organization, (2) improving the financial performance of the organization and (3) enhancing credibility. For most organizations, the assessment of these features was at the same level for both external audits and official control. However, if these assessments differed, commercial audits were assessed at a higher level than official controls.

The study is limited to only one specific type of manufacturing organization and one European country.

The literature review shows some conceptual differences between audits and official controls, but the results of this study show that the business environment does not perceive these differences as significant. Thus, the value of the study is reflected in the conclusion that both external audits and official controls are considered useful and credible approaches to monitoring the quality within the organization, which allows us to state that external evaluation is generally seen as an opportunity to improve the performance of the organization.

In this paper, a numerical approach to the topology optimization is proposed to design the permanent magnet excited machines with improved high-speed features. For this purpose the modified multi-level set method (MLSM) was proposed and applied to capture the shape of rotor poles on the fixed mesh using FE analysis. The paper aims to discuss these issues.

This framework is based on theories of topological and shape derivative for the magnetostatic system. During the iterative optimization process, the shape of rotor poles and its evolution is represented by the level sets of a continuous level set function f. The shape optimization of the iron and the magnet rotor poles is provided by the combining continuum design sensitivity analysis with level set method.

To obtain an innovative design of the rotor poles composed of different materials, the modified MLSM is proposed. An essential advantage of the proposed method is its ability to handle a topology change on a fixed mesh by the nucleating a small hole in design domain that leads to more efficient computational scheme then standard level set method.

The proposed numerical approach to the topology design of the 3D model of a PM machine is based on the simplified 2D model under assumption that the eddy currents in both the magnet and iron parts are neglected.

The novel aspect of the proposed method is the incorporation of the Total Variation regularization in the MLSM, which distribution is additionally modified by the gradient derivative information, in order to stabilize the optimization process and penalize oscillations without smoothing edges.

The purpose of this paper is to present the methodology that was used to perform system identification of a dynamically unstable tilt-rotor from flight test data. The method incorporated wavelet transform into the maximum likelihood principle formulation, emphasizing both time and frequency responses. Using wavelets allowed to additionally filter noise in the data, and this increased the estimation quality. This approach did not require measurement and process noise modeling in contrast to the Kalman filter usage for parameter estimation.

In the study, lateral-directional stability and control derivatives of an unstable tiltrotor in hover were estimated. This was performed by applying the maximum likelihood output error method. The estimated model response was decomposed using the Mallat pyramid and matched to wavelet coefficients obtained directly from measurements. In addition, a coherence-based weighting function was used to put more emphasis on the most reliable data. For comparison, the same set of data was used to identify a model with the same structure using the maximum likelihood principle with an incorporated Kalman filter.

It was found that maximum likelihood principle and wavelet transform allowed for estimating aerodynamic coefficients of a dynamically unstable aircraft. The estimation was performed with high accuracy.

The designed method can be used for system identification of unstable aircraft and when additional noise is present (e.g. when noise due to turbulence was observable during the flight test or higher noise levels were present in the sensors data).

The paper presents verification of a wavelet-based maximum likelihood principle output error method using flight test data.

The purpose of this paper is to present the methodology that was used to design a system identification experiment of a generic spinning gasodynamic projectile. For this object, because the high-speed spinning motion, it was not possible to excite the aircraft motion along body axes independently. Moreover, it was not possible to apply simultaneous multi-axes excitations because of the short time in which system identification experiments can be performed (multi-step inputs) or because it is not possible to excite the aircraft with a complex input (multi-sine signals) because of the impulse gasodynamic engines (lateral thrusters) usage.

A linear projectile model was used to obtain information about identifiability regions of stability and control derivatives. On this basis various sets of lateral thrusters’ launching sequences, imitating continuous multi-step inputs were used to excite the nonlinear projectile model. Subsequently, the nonlinear model for each excitation set was identified from frequency responses, and the results were assessed. For comparison, the same approach was used for the same projectile exited with aerodynamic controls.

It was found possible to design launching sequences of lateral thrusters that imitate continuous multi-step input and allow to obtain accurate system identification results in specified frequency range.

The designed experiment can be used during polygonal shooting to obtain a true projectile aerodynamic model.

The paper proposes a novel approach to gasodynamic projectiles system identification and can be easily applied for similar cases.

The recent advancements in smartphone technology and social media platforms have increased the popularity of artificial intelligence (AI) color cosmetics. Meanwhile, China is a lucrative market for various foreign beauty products and technological innovations. This research aims to investigate the adoption of AI color cosmetics applications and their electronic word-of-mouth (e-WOM) intention among Chinese social media influencers. Several key concepts have been proposed in this research, namely body esteem, price sensitivity, social media addiction and actual purchase.

An online questionnaire design was used in this research. A combination of purposive sampling and snowball sampling of AI color cosmetics users who are also social media influencers in China yields 221 respondents. To analyze the data, this research employs Structural Equation Modelling (SEM) method via SPSS and AMOS software. A 2-step approach, Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA), is implemented to prove the hypotheses and generate the results.

1) Social media addiction is a positive predictor of AI color cosmetics usage, (2) AI color cosmetics usage is a positive predictor of actual purchase, (3) actual purchase is a positive predictor of e-WOM intention and lastly, (4) there is a full mediation effect of actual purchase.

This research draws on the uses and gratification (U&G) theory to investigate how specific user characteristics affect Chinese social media influencers' adoption of AI color cosmetics, as well as how this may affect their decision to purchase branded color cosmetics and their e-WOM.

The purpose of this paper was to investigate the influence of non-uniform temperature distribution inside a box furnace during the firing process on electrical properties of the low-temperature co-fired ceramic (LTCC) materials used in radio frequency (RF)/microwave applications.

The authors studied the change in dielectric constant of two popular LTCC materials (DP 951 and DP 9K7) depending on the position of their samples inside the box furnace. Before firing of the samples, temperature distribution inside the box furnace was determined. The dielectric constant was measured using the method of two microstrip lines.

The findings showed that non-uniform temperature distribution with spatial difference of 6°C can result in 3-4 per cent change of the dielectric constant. It was also found that dielectric constant of the two tested materials shows disparate behavior under the same temperature distribution inside the box furnace.

The dielectric constant of the substrate materials is crucial for RF/microwave applications. Therefore, it was shown that 3-4 per cent deviation in dielectric constant can result in considerable detuning of microwave circuits and antennas.

To the best of the authors’ knowledge, the quantitative description of the impact of temperature distribution inside a box furnace on electrical properties of the LTCC materials has never been published in the open literature. The findings should be helpful when optimizing production process for high yield of reliable LTCC components like filters, baluns and chip antennas.

The optimality objectives are the structure weight and embodied energy as well as calculating the cost and embodied carbon of the resulting optimum options. Three optimality algorithms developed in MATLAB, namely, genetic algorithms (GA), particle swarm optimisation (PSO) and harmony search algorithm (HSA), were used for structural optimisation to compare the effectiveness of the algorithms. Two life-cycle stages were considered, production and construction stages, which include three boundaries: materials, transportation and erection. In the formulation of the optimum design problem, 107 universal steel beams (UKB) and 64 columns (UKC) sections were considered for the discrete design variables. The imposed behavioural constraints in the optimum design process were set according to the provision of Eurocode 3 (EC3). The study aims to find the optimum solution of 2D steel frames whilst considering weight and embodied energy, investigate the performance of the analysis integrated with MATLAB and provide three examples to which all these are applied to.

Undoubtedly, in structural engineering, the best design of any structure aims at the most economical and environmental option, without impairing the functional and its structural integrity. In the paper, multi-objective stochastic search methods are proposed for optimum design of three two-dimensional multi-story frames.

Results showed that the optimised designs obtained by HSA are better than those found by the GA and PSO with an average difference of 16% from GA and PSO, where this difference increases at larger frame structures. It was, therefore, concluded that the integration of the analysis, design and optimisation methods employed in MATLAB can be effective in obtaining prompt optimum results during the decision-making stage.

There may be some possible limitations in the study. Due to the time constraints, only three meta-heuristic approaches were investigated, where more methods should be investigated to fully understand their effectiveness in multi-objective problems.

Investigating the performance of three optimisation methods in multi-objective problems developed in MATLAB. More importantly, developing optimisation models for evaluation of embodied energy, embodied carbon and cost for steel structures to assist designers, during the initial stages, to evaluate design decisions against their energy consumption and carbon impacts.