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The accuracy of insulation defect diagnosis based on the dielectric spectrum response is severely influenced by temperature for oil-impregnated paper bushing. The dielectric loss (tan δ) mathematical model with a temperature–frequency factor to restrict the application of the frequency domain dielectric spectrum (FDS) for insulation diagnosis is not clear. In this paper, five temperatures are selected to study the frequency temperature characteristic of the FDS and polarization current for oil-impregnated paper bushing. The experimental results show that the temperature has different effects on the lower frequency (0.001 Hz–1 Hz) and higher frequency (1000 Hz–10 kHz) of FDS. With the increasing temperature, the lower frequency tan δ of 1 mHz–1 Hz shows a better pattern of exponential growth, while the higher frequency tan δ at 1 kHz–10 kHz shows the declining law with the rising temperature. With the increasing temperature, the polarization current shows a better pattern of exponential growth, while resistance obviously shows the declining law of the exponential pattern. The FDS curve of oil-impregnated paper bushings can be amended by the mathematical model of tan δ for the dielectric response on site for accuracy diagnosis. [ABSTRACT FROM AUTHOR]

In order to improve the immunity and speed tracking performance of active inverters in resonant overvoltage flexible suppression under load variation, parameter perturbation, and other uncertainties, a current control strategy of a resonant overvoltage flexible grounding device based on a cascading linear-nonlinear active disturbance rejection controller is proposed in this paper. First, the mathematical model of the flexible device considering load disturbance and parameter mismatch is established. Second, a cascade of linear and nonlinear extended state observers is designed to estimate and compensate the uncertain disturbance of the system in real time. The former linear extended state observer ensures the stability of the system under large disturbance, and the latter nonlinear extended state observer further improves the estimation accuracy of the disturbance by using the nonlinear mechanism. Finally, the flexible grounding system based on PI control and cascaded linear-nonlinear active disturbance rejection control (CL-NLADRC) is simulated and compared. Compared with PI control, NLADRC, and CLADRC, the current drop of the proposed CL-NLADRC during loading is 0.03 kA, which is 81.1%, 85.7%, and 73% of the three, respectively, and the regulation time is 13 ms, which is 82%, 75%, and 18.7% shorter than the three, respectively. The speed increase during load shedding is 93.5%, 80.5%, and 74.3% of the three, and the adjustment time is shortened by 80%, 73%, and 28%, respectively. The superiority of the proposed method is verified. [ABSTRACT FROM AUTHOR]

In this paper, we consider two nonlinear models arising in mathematical physics, namely, the Landau–Ginzburg–Higgs (LGH) equation and the nonlinear dispersive modified Benjamin–Bona (DMBBM) equation. The LGH model describes the exchange between mid-latitude Rossby and equatorial waves, as well as nonlinear waves with long-range and weak scattering interactions between tropical tropospheres and mid-latitude. The DMBBM model explains surface wave propagation estimates in a nonlinear dispersive medium. We employed He's semi-inverse approach in order to solve these models. Specifically, we present hyperbolic wave solutions. The proposed method is straightforward, reliable, and effective, and its potential for use in solving additional partial differential equations in applied research is encouraging. Appropriate values for the parameters are taken into consideration when simulating certain 2D and 3D graphs that correspond to select solutions using Matlab software. [ABSTRACT FROM AUTHOR]

To improve the transmission efficiency and output power of a magnetically coupled resonant wireless energy transmission system, this paper proposes a multi-objective optimization method based on the analytical expression and the improved NSGA-II algorithm. First, the analytical expressions of the electrical and performance parameters in the magnetically coupled resonant mechanism are derived. On this basis, the mathematical model of the multi-objective optimization of the magnetically coupled mechanism is established, with the size, many turns, and wire diameter of the transmitting and receiving coils in the magnetically coupled mechanism as design variables; the resonant frequency of the system, the distance between the coils, and the load size as constraints; and the transmission efficiency and transmission power as optimization objectives. Then the mathematical model is solved by the improved NSGA-II algorithm to obtain the Pareto optimal solution. Finally, the physical system is built to verify the correctness of the simulation experiment and the reliability of the experiment. This study is instructive for optimizing the transmission efficiency and output power of a magnetically coupled resonant wireless energy transmission system. [ABSTRACT FROM AUTHOR]

The electrohydrodynamic direct-writing (EDW) technology has been widely used in the integration of micro-/nano-systems. However, the complex model is a critical obstacle for the uniformity and controllability of the EDW fiber. It is difficult to gain an appropriate control strategy for position accuracy and the industrial application of EDW technology. Fuzzy control has a significant effect on objects in which the mathematical models are complex and the dynamic characteristics are difficult to capture. In this paper, the integrated fuzzy control method based on the jet mode and the electrospinning current was designed for the EDW system, and four groups of experiments were set up in different control schemes: the open-loop control, the current control, the jet mode control, and the integrated control. With the integrated control, the volatility percentage of the fiber spacing decreased from 23% to 9.7%, and the volatility percentage of the electrospinning current decreased from 35% to 14%. The fuzzy control shows dramatic effects on the uniformity and the deposition precision of the EDW fibers, which will extend the fields of application of EDW. [ABSTRACT FROM AUTHOR]

The power loss generated by the air cushion belt conveyor when transporting materials mainly depends on the diameter of the orifice, the form of arrangement, and the thickness of the air film. A mathematical model of an air cushion belt conveyor is established through mechanical analysis, and the relationship between load distribution, air film thickness, air film carrying capacity, and power consumption is found. Numerical simulations of orifices of different diameters on the disk groove and the formed air film are carried out, and the loading capacity of the air film was analyzed by observing the stress and deformation of the wire rope core. The results show that the air film formed by the selected type of orifice arrangement in this paper carries the load, which causes the least amount of deformation and stress change in the wire rope core, and the stability of the air film loading capacity is also verified by experiments. [ABSTRACT FROM AUTHOR]

A bearingless flux-switching permanent magnet memory machine (BFSPMMM) is proposed, which demonstrates the advantages of good suspension performance and wide-ranging speed regulation. The bias magnetic field of the radial force generated by the motor is provided by the permanent magnet, which can flexibly decide whether to adopt a single-phase or two-phase mode of conduction according to the needs of radial levitation force in the X- and Y-directions, so as to ensure the tracking of radial levitation forces therein. This paper introduces its structure, which lays a foundation for the subsequent establishment of an accurate mathematical model of a BFSPMMM. [ABSTRACT FROM AUTHOR]

In this paper, a general modeling principle is introduced that was found useful for modeling complex physical systems for engineering applications. The technique is a nonlinear asymptotic method, constructed from simplified physical theories, i.e., physical theories that were developed from particular points of view, that can be used to construct a more global theory. Originally, the technique was envisioned primarily for engineering applications, but its success has led to a more general principle. Four examples are presented to discuss and illustrate this method. [ABSTRACT FROM AUTHOR]

This paper proposes a three-dimensional model to simulate ice accretion on the surface of an aircraft. The model is developed using a prism grid cell, which enables iterations with an unstructured mesh. The model assumes that the impinged water droplets on the surface can form a thin water film, and ice accretion is caused by the flow and solidification of the film. The model is developed by analyzing the conservations of mass, momentum, and energy for the thin water film on the surface. The mass and energy conservation equations of the water film are discretized on the prism grid cell, while the momentum conservation equation, which is simplified using lubrication theory, is integrated along the surface normal direction to obtain an analytical solution for the film velocity. The thicknesses of the water film and ice layer are calculated by iterating the discretized mass and energy conservation equations with the analytical solution of the film velocity. The model is verified by comparing its results with published experimental and numerical data. The results show that the model provides accurate predictions of ice accretion under different conditions, even when using an unstructured grid. [ABSTRACT FROM AUTHOR]

This paper discovers how the surface texture of micro-dimples impacts the tribological performance of the interface between cylinder block and valve plate. For this, a mathematical model which considers the cavitation effect for calculating oil film pressure and oil leakage is established. The radius of the micro dimples is considered for studying the influence of the pressure field and the leakage flow. Then a simulation model is built up according to the mathematical model. Meanwhile, a particular test rig was designed and established to verify the theoretical results. Both simulation and experimental results show that a good designed surface texture of micro-dimples could improve the lubrication performance a lot and the structure parameters could be optimized. The leakage flow of the port plate pair will be greatly decreased by micro dimples and it is positive correlated with the radius of the micro dimples. [ABSTRACT FROM AUTHOR]

In this paper, the transition mechanisms between symmetric and asymmetric discharges in atmospheric helium dielectric barrier discharges (DBDs) are investigated via a one-dimensional fluid model. By gradually increasing the gap width, a complete evolution trajectory of the discharge states (i.e. from symmetric single period discharge (SP1) to asymmetric single-period (AP1) discharge, finally returns back to SP1 discharge) is observed. Unlike the previous reports which emphasize the dominant role of residual positive column, this work demonstrates that the transitions between SP1 and AP1 discharges could also be induced by the electron backflow effect. It is the residual electron backflow region that provides extra seed electrons to the subsequent discharge, restraining the development of electric field in the breakdown process, thus weakening the next discharge pulse. Upon the impairment of one discharge pulse, due to the reduction of charge generation and the impairment of electron backflow effect in the relevant discharge phase, its subsequent discharge would be strengthened. Those mechanisms function in different current pulses at different gap widths, inducing the mode transition. In addition, our simulation result reveals that the "residual positive column" referred in previous publications is essentially a special form of the "electron backflow region", which is typically more remarkable in large gap widths. As a consequence, the dynamics of electron backflow provides more insights regarding the transition of nonlinear states in DBDs with controlling parameters varying. [ABSTRACT FROM AUTHOR]

This paper aimed to present the thermoluminescence (TL) characteristics of phosphorus pentoxide (P2O5) nanopowders as a glass former, modified with barium oxide (BaO) glass, the mixture was activated with titanium oxide (TiO2), and then co-activated with magnesium oxide (MgO) and sodium oxide (NaO). The glass was arranged into five different samples depending on the activator concentration and co-activator with the glass matrix 40 P2O5 - 50 BaO. The sample glass 40P2O5 – 50BaO - 2.5Na2O – 2.5MgO - 5TiO2 confirmed and proved the following properties: simple, reasonable, modest way of synthesis, losing nearly about 18.57% from its TL information in 10 days, apparent glow curve shape, linear response, less fading, and high Zeff value. Thus, this new formed kind of glass might play a crucial role especially in the field of high radiation environmental dosimetry. [ABSTRACT FROM AUTHOR]

Wavefront manipulation is of great importance in the development of science and technology, and the generation of vortex beam is one of the most effective methods to improve the channel capacity and communication accuracy. However, current available vortex beam generators suffer from complex structure, large size, especially narrow bandwidth. To solve these issues, we propose a general strategy to enhance the bandwidth of the vortex beam generator by using double-layered reflective metasurface. The well-optimized double-layered reflective element possesses dual resonance, which realizes complete phase coverage (larger than 360 degrees) and a flat slope of the reflection phase, resulting in a broad bandwidth (8.5-11.5GHz). A compact and low-profile vortex-beam generator is proposed by combining the parabolic phase and the spiral phase plate phase. Both near field and far field experiments are performed to demonstrate the predesigned effects. A pure vortex beam is observed clearly with a topological charge of m=1 in a wide frequency window of 3 GHz (8.5-11.5GHz). More importantly, the working efficiency of the vortex beam is better than 90% at center frequency 10 GHz. The findings in this paper motivate the realization of high-performance reflective metasurfaces and other functional metadevices. [ABSTRACT FROM AUTHOR]

In this paper we propose four kinds of two-dimensional square beam-like zigzag lattice structures and study their bandgaps and directional propagation of elastic waves. The band structures are calculated by using the finite element method. Both the in-plane and out-of-plane waves are investigated simultaneously via the three-dimensional Euler beam elements. The mechanism of the bandgap generation is analyzed by studying the vibration modes at the bandgap edges. The effects of the geometry parameters of the xy- and z-zigzag lattices on the bandgaps are investigated and discussed. Multiple complete bandgaps are found owing to the separation of the degeneracy by introducing bending arms. The bandgaps are sensitive to the geometry parameters of the periodic systems. The deformed displacement fields of the harmonic responses of a finite lattice structure subjected to harmonic loads at different positions are illustrated to show the directional wave propagation. An extension of the proposed concept to the hexagonal lattices is also presented. The research work in this paper is relevant to the practical design of cellular structures with enhanced vibro-acoustics performance. [ABSTRACT FROM AUTHOR]

This paper proposes a physics-based model of flat-band capacitance Cfb for metal oxide thin-film transistors, in which the influences of free carriers and electrons trapped in deep/tail states are taken into account. Hereinto, a parameter Ls is introduced to characterize the screening length in the metal oxide semiconductor, which is similar to the extrinsic Debye length (Ld) for conventional MOS structure. Based on the proposed model, the flat-band voltage Vfb can be consequently determined as the gate voltage corresponding to Cgs equal to Cfb. It is shown that the value of Vfb determined by the proposed model is consistent with that extracted from experimental data of I-V and C-V or the simulated results of 2D device simulator ATLAS. Moreover, we investigate the effect of the parameters of density of states on the flat band capacitance and Cgs-Vgs characteristics of metal oxide TFTs by ATLAS in details. It is found that both tail states and deep states should be simultaneously taken into account for determining the flat band capacitance and flat band voltage of metal oxide TFTs. The proposed model for the flat band capacitance of metal oxide TFTs is expected to be useful for device characterization since it is analytical and physically meaningful. [ABSTRACT FROM AUTHOR]

In this paper, we consider a delayed smoking model in which the potential smokers are assumed to satisfy the logistic equation. We discuss the dynamical behavior of our proposed model in the form of Delayed Differential Equations (DDEs) and show conditions for asymptotic stability of the model in steady state. We also discuss the Hopf bifurcation analysis of considered model. Finally, we use the nonstandard finite difference (NSFD) scheme to show the results graphically with help of MATLAB. [ABSTRACT FROM AUTHOR]

This paper provides an effective numerical technique for obtaining the approximate solution of mixed Volterra-Fredholm Integral Equations (VFIEs) of second kind. The VFIEs arise from parabolic boundary value problems, mathematical modelling of the spatio-temporal development of an epidemic, and from various physical and Engineering models. The proposed method is based on the discretization of VFIEs by Bernstein’s approximation. Some results on convergence are also established which suggests that the technique converges to a smooth approximate solution. Its remarkable accuracy properties are finally demonstrated by several examples with graphical representation. [ABSTRACT FROM AUTHOR]

Thermal harvesting devices based on transformation optics, which can manipulate the heat flux concentration significantly through rational arrangements of the conductivities, have attracted considerable interest owing to several great potential applications of the technique for high-efficiency thermal conversion and collection. However, quantitative studies on the geometrical effects, particularly wedge angles, on the harvesting behaviors are rare. In this paper, we adopt wedge structure-based thermal harvesting schemes, and focus on the effects of the geometrical parameters including the radii ratios and wedge angles on the harvesting performance. The temperature deformations at the boundaries of the compressional region and temperature gradients for the different schemes with varying design parameters are investigated. Moreover, a concept for temperature stabilization was derived to evaluate the fluctuation in the energy distributions. In addition, the effects of interface thermal resistances have been investigated. Considering the changes in the radii ratios and wedge angles, we proposed a modification of the harvesting efficiency to quantitatively assess the concentration performance, which was verified through random tests and previously fabricated devices. In general, this study indicates that a smaller radii ratio contributes to a better harvesting behavior, but causes larger perturbations in the thermal profiles owing to a larger heat loss. We also find that a smaller wedge angle is beneficial to ensuring a higher concentration efficiency with less energy perturbations. These findings can be used to guide the improvement of a thermal concentrator with a high efficiency in reference to its potential applications as novel heat storage, thermal sensors, solar cells, and thermoelectric devices. [ABSTRACT FROM AUTHOR]

In this paper, the transformation characteristics of current sensor under pulsating DC leakage current is investigated. The mathematical model of current sensor is proposed to accurately describe the secondary side current and excitation current. The transformation process of current sensor is illustrated in details and the transformation error is analyzed from multi aspects. A simulation model is built and a sensor prototype is designed to conduct comparative evaluation, and both simulation and experimental results are presented to verify the correctness of theoretical analysis. [ABSTRACT FROM AUTHOR]

Skin factor is often regarded as a constant in most of the mathematical model for well test analysis in oilfields, but this is only a kind of simplified treatment with the actual skin factor changeable. This paper defined the average permeability of a damaged area as a function of time by using the definition of skin factor. Therefore a relationship between a variable skin factor and time was established. The variable skin factor derived was introduced into existing traditional models rather than using a constant skin factor, then, this newly derived mathematical model for well test analysis considering variable skin factor was solved by Laplace transform. The dimensionless wellbore pressure and its derivative changed with dimensionless time were plotted with double logarithm and these plots can be used for type curve fitting. The effects of all the parameters in the expression of variable skin factor were analyzed based on the dimensionless wellbore pressure and its derivative. Finally, actual well testing data were used to fit the type curves developed which validates the applicability of the mathematical model from Sheng-2 Block, Shengli Oilfield, China. [ABSTRACT FROM AUTHOR]

A mathematical model is presented for three-dimensional unsteady boundary layer slip flow of Newtonian nanofluids containing gyrotactic microorganisms over a stretching cylinder. Both hydrodynamic and thermal slips are included. By applying suitable similarity transformations, the governing equations are transformed into a set of nonlinear ordinary differential equations with appropriate boundary conditions. The transformed nonlinear ordinary differential boundary value problem is then solved using the Runge-Kutta-Fehlberg fourth-fifth order numerical method in Maple 18 symbolic software. The effects of the controlling parameters on the dimension- less velocity, temperature, nanoparticle volume fractions and microorganism motile density functions have been illustrated graphically. Comparisons of the present paper with the existing published results indicate good agreement and supports the validity and the accuracy of our numerical computations. Increasing bioconvection Schmidt number is observed to depress motile micro-organism density function. Increasing thermal slip parameter leads to a decrease in temperature. Thermal slip also exerts a strong influence on nano-particle concentration. The flow is accelerated with positive unsteadiness parameter (accelerating cylinder) and temperature and micro-organism density function are also increased. However nano-particle concentration is reduced with positive unsteadiness parameter. Increasing hydrodynamic slip is observed to boost temperatures and micro-organism density whereas it decelerates the flow and reduces nano-particle concentrations. The study is relevant to nano-biopolymer manufacturing processes. [ABSTRACT FROM AUTHOR]

This paper presents a simple treatment of elastic wave scattering at periodically structured surfaces and interfaces of solids, and the existence and nature of surface acoustic waves (SAW) and interfacial (IW) waves at such structures. Our treatment is embodied in phenomenological models in which the periodicity resides in the boundary conditions. These yield zone folding and band gaps at the boundary of, and within the Brillouin zone. Above the transverse bulk wave threshold, there occur leaky or pseudo-SAW and pseudo-IW, which are attenuated via radiation into the bulk wave continuum. These have a pronounced effect on the transmission and reflection of bulk waves. We provide examples of pseudo-SAW and pseudo-IW for which the coupling to the bulk wave continuum vanishes at isloated points in the dispersion relation. These supersonic guided waves correspond to embedded discrete eigenvalues within a radiation continuum. We stress the generality of the phenomena that are exhibited at widely different scales of length and frequency, and their relevance to situations as diverse as the guiding of seismic waves in mine stopes, the metrology of periodic metal interconnect structures in the semiconductor industry, and elastic wave scattering by an array of coplanar cracks in a solid. [ABSTRACT FROM AUTHOR]

Presently there is quite few analytical studies in traffic flows due to the non-linearity of the governing equations. In the present paper we introduce travelling wave solutions for the homogeneous one-dimensional FREFLO model, which are expressed in the form of series and describe the procedure that vehicles/pedestrians move with a negative velocity and decelerate until rest, then accelerate inversely to positive velocities. This method is expect to be extended to more complex situations in the future. [ABSTRACT FROM AUTHOR]

The plasma sheath-surrounded hypersonic vehicle is a dynamic and time-varying medium and it is almost impossible to calculate time-varying physical parameters directly. The in-fight detection of the time-varying degree is important to understand the dynamic nature of the physical parameters and their effect on re-entry communication. In this paper, a constant envelope zero autocorrelation (CAZAC) sequence based on time-varying frequency detection and channel sounding method is proposed to detect the plasma sheath electronic density time-varying property and wireless channel characteristic. The proposed method utilizes the CAZAC sequence, which has excellent autocorrelation and spread gain characteristics, to realize dynamic time-varying detection/channel sounding under low signal-to-noise ratio in the plasma sheath environment. Theoretical simulation under a typical time-varying radio channel shows that the proposed method is capable of detecting time-variation frequency up to 200 kHz and can trace the channel amplitude and phase in the time domain well under –10 dB. Experimental results conducted in the RF modulation discharge plasma device verified the time variation detection ability in practical dynamic plasma sheath. Meanwhile, nonlinear phenomenon of dynamic plasma sheath on communication signal is observed thorough channel sounding result. [ABSTRACT FROM AUTHOR]