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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]

Sound projection is a method of using highly focused sources to project sound onto reflective surfaces to create the impression of surround sound, which can be realized via beamforming using loudspeaker arrays. Generally, these devices are mounted near a surface with a finite acoustic impedance, such as a TV accent wall. The beamforming performance degrades in this half-space with an impedance boundary when the filters are designed using transfer functions measured in the free field. This paper proposes a model for predicting the beamforming performance in a half-space with an impedance boundary in terms of the transfer functions in the free field. A mathematical model is presented, and the results are compared with practical measurements for a 16-driver line array in real-use environments. The results show that reflections from the boundary lead to "dark bands" in the beam, causing the beam to deviate from the designed direction. Using filters designed with transfer functions calculated by the proposed model yields improved beamforming performance. [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]

This paper presents the synthesis of a non-uniform linear array for two-dimensional Range-Bearing underwater acoustic imaging based on the multiple beam, measurement vectors (MMV) Compressive Sensing (CS) method. This method considers multiple steering directions in the mathematical model and exploits the sparsity of the oversampled linear aperture to obtain a thinned array structure. In this paper, a simulation study to synthesise the sparse linear array (SLA) for a Forward Looking Sonar system considering multiple beams in the field of view (FOV) was conducted. The comparison of the array synthesised using single measurement vector compressive sensing (SMV CS), which considers only the broadside beam in the mathematical model, is also presented. From the imaging point of view, when the SMV CS synthesised SLA is steered in a direction other than broadside, spurious/unwanted lobes appear in the beam pattern (BP). To overcome this problem, the MMV method and demonstrate its performance efficacy with a simulation study are proposed. The design of SLA for 37.5, 75, 150, 300, and 600 kHz with angular resolution 6.4°–0.4° with 11–149 beams in the FOV keeping the aperture fixed are presented, as is a design keeping angular resolution fixed at 1.5° to generalise a design of SLA for the above mentioned interested frequencies. [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]

A common approach when employing discrete mathematical models is to assess the reliability and credibility of the computation of interest through a process known as solution verification. Present-day computed head-related transfer functions (HRTFs) seem to lack robust and reliable assessments of the numerical errors embedded in the results which makes validation of wave-based models difficult. This process requires a good understanding of the involved sources of error which are systematically reviewed here. The current work aims to quantify the pinna-related high-frequency computational errors in the context of HRTFs and wave-based simulations with finite-difference models. As a prerequisite for solution verification, code verification assesses the reliability of the proposed implementation. In this paper, known and manufactured formal solutions are used and tailored for the wave equation and frequency-independent boundary conditions inside a rectangular room of uniform acoustic wall-impedance. Asymptotic estimates for pinna acoustics are predicted in the frequency domain based on regression models and a convergence study on sub-millimeter grids. Results show an increasing uncertainty with frequency and a significant frequency-dependent change among computations on different grids. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate that by using a mathematical physics approach--focusing attention on the physics and using mathematics as a tool--it is possible to visualize the formation of the transverse modes inside a cylindrical waveguide. The opposite (physical mathematics) approach looks at the mathematical problem and then tries to impose a physical interpretation. For cylindrical waveguides, the physical mathematics route leads to the Bessel differential equation, and it is argued that in the core of the waveguide there are only Bessel functions of the first kind in the description of the transverse modes. The Neumann functions are deemed non-physical due to their singularity at the origin and are eliminated from the final description of the solution. In this paper, by combining geometric optics and wave optics concepts, we show that the inclusion of the Neumann function is physically necessary to describe fully and properly the formation of the propagating transverse modes. With this approach, we also show that the field outside a dielectric waveguide arises in a natural way. [ABSTRACT FROM AUTHOR]

The preceding paper in this series [Mantouka, Dogan, White, and Leighton, J. Acoust. Soc. Am. 140, 274-282 (2016)] presented a nonlinear model for acoustic propagation in gassy marine sediments, the baseline for which was established by Leighton [Geo. Res. Lett. 34, L17607 (2007)]. The current paper aims further advancement on those two studies by demonstrating the particular effects of the sediment rheology, the dispersion and dissipation of the first compressional wave, and the higher order re-scattering from other bubbles. Sediment rheology is included through the sediment porosity and the definition of the contact interfaces of bubbles with the solid grains and the pore water. The intrinsic attenuation and the dispersion of the compressional wave are incorporated using the effective fluid density model [Williams, J. Acoust. Soc. Am. 110, 2276-2281 (2001)] for the far field (fully water-saturated sediment). The multiple scattering from other bubbles is included using the method of Kargl [J. Acoust. Soc. Am. 11, 168-173 (2002)]. The overall nonlinear formulation is then reduced to the linear limit in order to compare with the linear theory of Anderson and Hampton [J. Acoust. Soc. Am. 67, 1890-1903 (1980)], and the results for the damping coefficients, the sound speed, and the attenuation are presented. [ABSTRACT FROM AUTHOR]

In this paper, we give a pedagogical introduction to the ideas of quantum thermodynamics and work fluctuations, using only basic concepts from quantum and statistical mechanics. After reviewing the concept of work as usually taught in thermodynamics and statistical mechanics, we discuss the framework of non-equilibrium processes in quantum systems together with some modern developments, such as the Jarzynski equality and its connection to the second law of thermodynamics. We then apply these results to the problem of magnetic resonance, where all calculations can be done exactly. It is shown in detail how to build the statistics of the work, both for a single particle and for a collection of non-interacting particles. We hope that this paper will serve as a tool to bring the new student up to date on the recent developments in non-equilibrium thermodynamics of quantum systems. [ABSTRACT FROM AUTHOR]

This paper presents a study of intentionally induced acoustic mode complexity in rigid-walled ducts of separable geometry and with uniform mean flow. An intermediately located perforated plate conceptualized as an impedance discontinuity is employed to maximize the acoustic mode complexity, in turn producing a unidirectional traveling wave from the source to the impedance discontinuity. The impedance of the perforated plate for realization of a unidirectional traveling wave is derived analytically and is found to be a function of the modal wavenumbers, the Mach number of the mean flow, the position of the perforated plate, and the termination impedance. The conditions derived analytically are verified computationally by finite element analysis. A measure of acoustic mode complexity is defined and also evaluated from the finite element analysis. It is found that the realization of a unidirectional traveling wave is robust at low Mach number mean flows, except at the occurrence of resonances. The method presented in this work provides a strategy to control the transmission of acoustic energy in rigid-walled ducts of separable geometry in the presence of uniform mean flow. [ABSTRACT FROM AUTHOR]

In the field of room acoustics, it is well known that reverberation can be characterized statistically in a particular region of the time-frequency domain (after the transition time and above Schroeder's frequency). Since the 1950s, various formulas have been established, focusing on particular aspects of reverberation: exponential decay over time, correlations between frequencies, correlations between sensors at each frequency, and time-frequency distribution. In this paper, the author introduces a stochastic reverberation model, which permits us to retrieve all these well-known results within a common mathematical framework. To the best of the author's knowledge, this is the first time that such a unification work is presented. The benefits are multiple: several formulas generalizing the classical results are established that jointly characterize the spatial, temporal, and spectral properties of late reverberation. [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]

The instability derived from the cochlear model is a phenomenon used to characterize its active processing, which is one of the fundamentals of hearing. This processing relates to the activities of outer hair cells (OHCs) lining in the cochlea. The decline of this processing function is accounted for by the spatially irregular activities of OHCs. Current cochlear models show excessive instability when cochlea containing the irregular activity of the OHCs is simulated. To explain this phenomenon, there are two possibilities. First, excessive instability may be essential to the model. Second, discretized errors may affect the instability of the model in numerical calculation. To investigate these possibilities, a state space model of two-dimensional cochlear mechanics is developed and applied to a high-accuracy scheme of numerical calculation. As a result of this simulation, the basilar membrane responses include the discretization error, which depends on the modeling accuracy. Furthermore, the transfer function and the temporal response show more instability with higher modeling accuracy, with the irregularity of the feedback gain corresponding to the activities of the OHCs. Therefore, when the discretization error is large, the instability is weakened. Consequently, this paper concludes that excessive instability is an essential feature of the cochlear model. [ABSTRACT FROM AUTHOR]

The usage of time-reversal in underwater communications relies on array channel matched-filtering, coherent channel replica alignment and summation. Traditionally, replicas are channel responses to probe signals received at a previous time. These are noisy and subject to distortion due to channel variability. This paper offers an alternative where noisy and potentially distorted channel replicas are replaced by noise-free and time-updated replicas generated by a numerical model constrained on previously data-identified environmental parameters. The method is applied on real data, where a quadrature phase shift key modulated signal on a 25.6 kHz carrier at 4 kbit/s was transmitted in a shallow water area over a distance of approximately 900 m. Sustained analysis without supervision shows that the proposed method may attain a mean square error gain up to 5.4 dB when compared to traditional time-reversal. [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]

This work develops the mathematical model for a steerable binaural system that determines the instantaneous direction of a sound source in space. The model combines system angular speed and interaural time delays (ITDs) in a differential equation, which allows monitoring the change of source position in the binaural reference frame and therefore resolves the confusion about azimuth and elevation. The work includes the analysis of error propagation and presents results from a realtime application that was performed on a digital signal processing device. Theory and experiments demonstrate that the azimuthal angle to the sound source is accurately yielded in the case of horizontal rotations, whereas the elevation angle is estimated with large uncertainty. This paper also proves the equivalence of the ITD derivative and the Doppler shift appearing between the binau-rally captured audio signals. The equation of this Doppler shift is applicable for any kind of motion. It shows that weak binaural pitch differences may represent an additional cue in localization of sound. Finally, the paper develops practical applications from this relationship, such as the synthesizing of binaural images of pure and complex tones emitted by a moving source, and the generation of multiple frequency images for binaural beat experiments. [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]

This short paper describes a useful teaching tool, ideal for demonstration purposes within the classroom or lab setting. It is based on the simple dynamic response of flexible cantilevers and evolves naturally from the underlying principles of a vibrating reed tachometer. Utilizing a 3D-printer, these ideas conveniently encompass the phenomenon of resonance in which all the cantilevers of a similar length respond in harmony when just one of their number is plucked. [ABSTRACT FROM AUTHOR]

Wolf notes are generally undesirable sounds that occur in string instruments, particularly in cellos. State-of-the-art passive wolf note eliminators affect the whole cello sound and can become ineffective when environmental conditions and, therefore, the cello's structural properties change. In this paper, an approach is presented that uses smart materials to eliminate the wolf note with little effects to the cello's sound. Based on preliminary measurements, a mathematical model of the cello for generating the wolf note and for developing a wolf note elimination controller is set up. The controller consists of a wolf detection criterion that triggers a velocity feedback controller to actively induce damping into the cello's body whenever a wolf note is detected. The controller setup is experimentally validated by an implementation on a test cello. The velocity feedback to induce the active damping is implemented by means of a piezoelectric patch actuator attached to the cello's body. Both the results of the mathematical model and the results of the experimental investigation show a good performance in eliminating the wolf note on a cello. [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]

The scattering of sound by a membrane-covered cavity in a duct with shear flow is calculated with a linear model based on the multimodal method. The model is verified by comparison against the previous experiments focused on sound suppression of a stable system with high-tension membranes and a low-speed flow. It is shown in this paper that such a situation is drastically changed when the flow velocity is larger than the in vacuo flexural wave speed of the membrane. One of the neutral hydrodynamic modes can be destabilized under certain conditions, and this flexural instability can lead to sound amplification. For a given flow profile, the axial growth rate of the instability increases with the mean flow velocity but saturates at high velocities. For a given mean flow velocity, there is an optimum boundary layer thickness for the instability. Increasing the structural damping tends to stabilize the instability and thus inhibit the sound amplification. [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]

This paper presents a simple and affordable experiment on the thermal lens effect, suitable for an undergraduate educational laboratory or as a tabletop demonstration in a lecture on nonlinear optics. Such an experiment exploits the formation of a lens in an absorbing medium illuminated by a laser beam with a Gaussian intensity profile. As an absorber, we use a commercial soy sauce, which exhibits a strong thermal lensing effect. Additionally, we show how to measure the radius of a Gaussian beam using the knife-edge method, and how to estimate the focal length of the induced thermal lens. [ABSTRACT FROM AUTHOR]

When a chain flows up over the edge of a container and then falls to the ground below, it is observed that the top of the chain rises up above the container's edge. This is called a "chain fountain," and is an entertaining and counterintuitive phenomenon. In this paper, the steady-state motion of the fountain is analyzed experimentally and theoretically. Measurements are given for the speeds and heights for three different chains and three different distances from the container to the floor. It is shown that the distance the chain rises above the container is proportional to the force from the container on the chain. A simple model is developed for how the chain interacts with the container, and shows that a link lifts-off from the container after rotating by a relatively small angle. The model's predictions agree very well with the measurements for the two ball-chains. [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]

An extension to the angular spectrum approach for modelling pressure fields of a cylindrically curved array transducer is described in this paper. The proposed technique is based on representing the curved transducer surface as a set of planar elements whose contributions are combined at a selected intermediate plane from which the field is further propagated using the conventional angular spectrum approach. The accuracy of the proposed technique is validated through comparison with Field II simulations. [ABSTRACT FROM AUTHOR]

The coherence factor (CF) and Wiener postfilter methods have been proposed as effective approaches for reducing the output noise of the delay-and-sum (DAS) beamformer in ultrasound imaging. The theoretical framework between them was also established. However, past researches about the CF and Wiener postfilter methods mainly focused on the summation of an array signal. This paper analyzes the CF and Wiener postfilter in the synthetic aperture (SA) imaging mode, where two-dimensional echo data are recorded. Different CF definitions in the SA imaging are first given and the corresponding Wiener postfilter methods are then proposed, including a Wiener postfilter especially for the SA imaging, named as WienerSA. The performances of different CF and Wiener postfilter methods were evaluated on both simulated and experimental SA data. Results showed that the proposed WienerSA outperformed the other Wiener postfilters in reducing the sidelobe noise level. It obtained the highest contrast ratio among the Wiener postfilter methods, which was even higher than some of the CF methods. Meanwhile it could benefit a much higher contrast-to-noise ratio than those CF methods with further suppression of incoherent noises. Consequently, the WienerSA is believed to be a promising approach in enhancing the SA image quality. [ABSTRACT FROM AUTHOR]

Most musical instruments consist of dynamical subsystems connected at a number of constraining points through which energy flows. For physical sound synthesis, one important difficulty deals with enforcing these coupling constraints. While standard techniques include the use of Lagrange multipliers or penalty methods, in this paper, a different approach is explored, the Udwadia-Kalaba (U-K) formulation, which is rooted on analytical dynamics but avoids the use of Lagrange multipliers. This general and elegant formulation has been nearly exclusively used for conceptual systems of discrete masses or articulated rigid bodies, namely, in robotics. However its natural extension to deal with continuous flexible systems is surprisingly absent from the literature. Here, such a modeling strategy is developed and the potential of combining the U-K equation for constrained systems with the modal description is shown, in particular, to simulate musical instruments. Objectives are twofold: (1) Develop the U-K equation for constrained flexible systems with subsystems modelled through unconstrained modes; and (2) apply this framework to compute string/body coupled dynamics. This example complements previous work [Debut, Antunes, Marques, and Carvalho, Appl. Acoust. 108, 3–18 (2016)] on guitar modeling using penalty methods. Simulations show that the proposed technique provides similar results with a significant improvement in computational efficiency. [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]

In this paper an effective meshless method is proposed to solve time-harmonic acoustic problems defined on unbounded domains. To this end, the near field is discretized by a set of nodes and the far field effect is taken into account by considering radiative boundary conditions. The approximation within the near field is performed using a set of local residual-free basis functions defined on a series of finite clouds. For considering the far field effect, a series of infinite clouds are defined on which another set of residual-free bases, satisfying the radiation conditions, are considered for the approximation. Validation of the results is performed through solving some acoustic problems. [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]

The quantum mechanical behavior of a particle in a double well defies our intuition based on classical reasoning. Not surprisingly, an asymmetry in the double well will restore results more consistent with the classical picture. What is surprising, however, is how a very small asymmetry can lead to essentially classical behavior. In this paper, we use the simplest version of a double-well potential to demonstrate these statements. We also show how this system accurately maps onto a two-state system, which we refer to as a "toy model." [ABSTRACT FROM AUTHOR]

A model, combining acoustical radiosity and the image source method, including phase shifts on reflection, has been developed. The model is denoted Phased Acoustical Radiosity and Image Source Method (PARISM), and it has been developed in order to be able to model both specular and diffuse reflections with complex-valued and angle-dependent boundary conditions. This paper mainly describes the combination of the two models and the implementation of the angle-dependent boundary conditions. It furthermore describes how a pressure impulse response is obtained from the energy-based acoustical radiosity by regarding the model as being stochastic. Three methods of implementation are proposed and investigated, and finally, recommendations are made for their use. Validation of the image source method is done by comparison with finite element simulations of a rectangular room with a porous absorber ceiling. Results from the full model are compared with results from other simulation tools and with measurements. The comparisons of the full model are done for real-valued and angle-independent surface properties. The proposed model agrees well with both the measured results and the alternative theories, and furthermore shows a more realistic spatial variation than energy-based methods due to the fact that interference is considered. [ABSTRACT FROM AUTHOR]

Sound transmission through a single leaf panel has mostly been discussed and explained by using the approaching wave concept, from which the well-known mass law can be derived. In this paper, the modal behavior in sound transmission coefficients is explored, and it is shown that the mutual modal radiation impedances in modal sound transmission coefficients may not be ignored even for a panel immersed in a light fluid. By introducing the equivalent modal impedance which incorporates the inter-modal coupling effect, an analytical expression for the modal sound transmission coefficient is derived, and the overall sound transmission coefficient is simply a modal superposition of modal sound transmission coefficients. A good correlation is obtained between analytical calculation and boundary element method. In addition, it is found that inter-modal coupling has noticeable effects in modal sound transmission coefficients in the subsonic region but may be ignored as modes become supersonic. It is also shown that the well-known mass law performance is attributed to all the supersonic modes. [ABSTRACT FROM AUTHOR]

The feasibility of representing the excitation source characteristics in expressive voice signals by an aperiodic sequence of impulses in the time domain is examined in this paper. In particular, the aperiodic components of excitation of expressive voices, like the Noh voice, are examined in some detail. The aperiodic component is extracted from the speech signal using a modified zero-frequency filtering method, and it is represented using a sequence of impulses with amplitudes corresponding to the relative strength of excitation around each impulse. The spectral characteristics of the aperiodic sequence show subharmonics and harmonics of the fundamental frequency corresponding to pitch. The effects of aperiodicity are examined using spectrograms and saliency plots of synthetic amplitude and duration (i.e., frequency) modulation of sequences of impulses. [ABSTRACT FROM AUTHOR]

Accurate prediction of the acoustics of fluid-structure interaction is important in devising quieting designs for engineering systems equipped with extensive flow duct networks where the thin duct wall panels are in contact with the flowing fluid. The flow unsteadiness generates acoustic waves that propagate back to the source region to modify the flow process generating them. Meanwhile the unsteady flow pressure excites the thin panels to vibrate, which in turn modifies the flow processes. Evidently a strong coupling between the fluid aeroacoustics and the panel structural dynamics exists. Such coupled physical processes have to be thoroughly understood; otherwise, effective quieting design is never achieved. This paper reports an analysis, using a time-domain numerical methodology the authors have recently developed, of the nonlinear aeroacoustic-structural interaction experienced by a flexible panel in a duct carrying a uniform mean flow. With no mean flow, the numerical results agree well with existing theories and reveal the physics of duct transmission loss. Four regimes of aeroacoustic-structural interaction are identified when the duct flow velocity increases from low subsonic to low supersonic values. Insight in the underlying physics of duct transmission loss at different velocities are highlighted and discussed. [ABSTRACT FROM AUTHOR]

While audiovisual interactions in speech perception have long been considered as automatic, recent data suggest that this is not the case. In a previous study, Nahorna et al. [(2012). J. Acoust. Soc. Am. 132, 1061-1077] showed that the McGurk effect is reduced by a previous incoherent audiovisual context. This was interpreted as showing the existence of an audiovisual binding stage controlling the fusion process. Incoherence would produce unbinding and decrease the weight of the visual input in fusion. The present paper explores the audiovisual binding system to characterize its dynamics. A first experiment assesses the dynamics of unbinding, and shows that it is rapid: An incoherent context less than 0.5 s long (typically one syllable) suffices to produce a maximal reduction in the McGurk effect. A second experiment tests the rebinding process, by presenting a short period of either coherent material or silence after the incoherent unbinding context. Coherence provides rebinding, with a recovery of the McGurk effect, while silence provides no rebinding and hence freezes the unbinding process. These experiments are interpreted in the framework of an audiovisual speech scene analysis process assessing the perceptual organization of an audiovisual speech input before decision takes place at a higher processing stage. [ABSTRACT FROM AUTHOR]

This paper studies the acoustical properties of hard-backed porous layers with periodically embedded air filled Helmholtz resonators. It is demonstrated that some enhancements in the acoustic absorption coefficient can be achieved in the viscous and inertial regimes at wavelengths much larger than the layer thickness. This enhancement is attributed to the excitation of two specific modes: Helmholtz resonance in the viscous regime and a trapped mode in the inertial regime. The enhancement in the absorption that is attributed to the Helmholtz resonance can be further improved when a small amount of porous material is removed from the resonator necks. In this way the frequency range in which these porous materials exhibit high values of the absorption coefficient can be extended by using Helmholtz resonators with a range of carefully tuned neck lengths. [ABSTRACT FROM AUTHOR]

This paper presents an elastodynamic analysis of two-dimensional time-harmonic elastic wave propagation in periodically multilayered elastic composites, which are also frequently referred to as one-dimensional phononic crystals, with a periodic array of strip-like interior or interface cracks. The transfer matrix method and the boundary integral equation method in conjunction with the Bloch-Floquet theorem are applied to compute the elastic wave fields in the layered periodic composites. The effects of the crack size, spacing, and location, as well as the incidence angle and the type of incident elastic waves on the wave propagation characteristics in the composite structure are investigated in details. In particular, the band-gaps, the localization and the resonances of elastic waves are revealed by numerical examples. In order to understand better the wave propagation phenomena in layered phononic crystals with distributed cracks, the energy flow vector of Umov and the corresponding energy streamlines are visualized and analyzed. The numerical results demonstrate that large energy vortices obstruct elastic wave propagation in layered phononic crystals at resonance frequencies. They occur before the cracks reflecting most of the energy transmitted by the incoming wave and disappear when the problem parameters are shifted from the resonant ones. [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]