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In this paper, we numerically study the influence of saturable absorber parameters, namely, modulation depth, recovery time, and saturation energy, on the performance of an ultrafast fiber laser that is mode-locked by a hybrid scheme of a saturation absorber (SA) and a nonlinear polarization rotation (NPR). Maps of mode-locked states related to intracavity wave-plates are created to evaluate the operation of hybrid mode-locking under different modulation depths of the SA. Along with the improvement of modulation depth of the SA, the mode-locked pulse results from a combination effect of the SA and NPR. The numerical analysis reveals that the SA parameters can significantly impact the pulse profile, peak power, and operation state. Moreover, they can also impact the selection of NPR mode-locked points, resulting in variation in stable single pulse output. A higher modulation depth can suppress the unstable multiple pulses' operation and convert them into harmonic mode-locked pulses. The obtained results indicate that the selection of appropriate SA parameters can effectively improve the output characteristics of hybrid mode-locked fiber lasers. [ABSTRACT FROM AUTHOR]

The mode manipulation of Lamb waves plays an important role in damage detection and identification of damage types, location, and size. In this paper, we propose a composite phononic crystal (PC) plate with antisymmetric and symmetric PCs for realizing mode conversion from A0 to S0 mode of Lamb waves. The theoretical analysis, numerical simulations, and experimental validation are introduced and the mode conversion mechanism of the composite PC plate is systematically investigated. The effect of geometrical parameters on band structures of antisymmetric and symmetric PCs is first discussed. Then multi-physics field simulation models are developed and in-plane displacement fields are obtained in numerical simulations, which shows that the mode conversion is enhanced when the period number of the antisymmetric PC decreases and that of symmetric the PC increases. The composite PC plate specimens are fabricated with precision wire cutting technology for experimental measurements and the self-designed polyvinylidene fluoride (PVDF) comb transducer is used to stimulate the Lamb waves. The experimental results are consistent with the numerical simulations, which demonstrate that the proposed composite PC plate can achieve the mode conversion from A0 to S0 mode of Lamb waves. Our proposed structures have applicable values for the mode manipulation of Lamb waves in damage detection. [ABSTRACT FROM AUTHOR]

Locally resonant metamaterial flat panels have proved to potentially exhibit extraordinary sound transmission loss properties when the resonance frequency of the resonators is tuned to the coincidence frequency region. Whether this technique is also effective to address the ring frequency effect for curved panels is investigated in this paper. For this purpose, a cylindrical shell, as a representation of curved panels, is studied from a theoretical and numerical point of view, with a specific focus on the transmission loss behaviour around the ring frequency region when the shell is mounted with local resonators. The influence from the resonators is presented and compared with that for a flat panel. An inverse effect of the resonators is observed on the sound transmission loss between the metamaterial cylindrical shell and the metamaterial flat panel when the resonance frequency of the resonators is tuned to be below or above the ring or coincidence frequency, respectively. Rather than the extraordinary improvement observed for the metamaterial flat panel, tuning such conventional resonators to the ring frequency of curved panels generates two side dips despite a sharp improvement at the ring frequency itself. This phenomenon is explained from an effective impedance point of view developed in this paper. The approach proposed and the conclusions provided may subsequently allow for the design of suitable resonators in order to resolve the ring frequency effect for curved panels. [ABSTRACT FROM AUTHOR]

GaN-based heterostructures have been used in high-power radio frequency applications for a number of years due to the wide bandgap of GaN and high values of spontaneous and piezoelectric polarization, resulting in high breakdown voltages and high 2D carrier concentrations. However, the accurate modeling of low-field electron mobility within such structures remains a topic of interest. This paper presents a comprehensive numerical model for calculating the carrier mobility within a 2D electron gas in Al x Ga 1 − x N/GaN high electron mobility transistors. The model is based on solving the Schrödinger and Poisson equations self-consistently, taking into account the polarization charges at material interfaces and performing semi-classical numerical calculations of low-field electron mobility within the momentum relaxation time approximation, taking into account all relevant scattering mechanisms. Both intra- and inter-subband transitions are considered, and the differences in intra- and inter-subband scattering rates are analyzed for some of the key scattering mechanisms. The importance of including inter-subband transitions in the calculations is demonstrated by comparing the calculated results with experimentally measured mobilities. [ABSTRACT FROM AUTHOR]

In this paper, the stress-induced twin interface nucleation in single-crystalline NiMnGa alloys is studied through theoretical analyses and numerical simulations. First, the mechanical governing system for a single-crystalline NiMnGa sample is formulated, which contains the mechanical field equation and the twin interface movement criteria. To complete the governing system, the nucleations of twin interfaces in the NiMnGa sample under general mechanical loads are investigated. By considering the connection conditions of some physical quantities across a "fictitious" twin interface, the explicit expression of the configurational force on the twin interface is derived. Then, based on the twin interface movement criteria, a practical scheme for predicting the twin interface nucleation is proposed. This scheme can be integrated into the iterative numerical algorithm for solving the mechanical governing system. To demonstrate the efficiency of this scheme, some simulation results are presented for two typical deformations of a NiMnGa sample (i.e., the axial compression and the bending deformation), which show good consistency with the experimental results. By analyzing the evolution properties of the configurational forces on the possible nucleation interfaces, the mechanism responsible for twin interface nucleations under different loading conditions can be revealed. The results obtained in the current work would be helpful for the design of smart devices by utilizing NiMnGa alloys. [ABSTRACT FROM AUTHOR]

This paper investigates the asymmetric propagation of acoustic waves in a one-dimensional chain of spherical particles coupled with asymmetric intruders. The chain passes acoustic waves along one direction (forward configuration) whereas partially blocks the acoustic energy propagating along the opposite direction (reverse configuration). A numerical analysis is conducted to investigate this asymmetric propagation by simulating a statically compressed chain of particles interacting via Hertzian contact and subjected to small amplitude periodic displacements at one end. The amount of acoustic energy transmitted through the chain in both configurations is studied and quantified in terms of the acoustic energy transfer ratio, defined as the ratio of the acoustic power at the last particle to the acoustic power at the first particle. The effect of the applied frequency and number of particles in the chain on the transfer ratio is investigated. In addition, a parametric study is performed to evaluate the effects of geometric and material properties on the efficiency of asymmetric acoustic wave propagation in the proposed system. The results show that the proposed design supports asymmetric propagation of low frequency acoustic waves. [ABSTRACT FROM AUTHOR]

In this paper, we observe the dynamic expansion process of positive leader channels under impulses with different rise times in a 1-m air gap using a Mach-Zehnder interferometry and a high-speed video camera. The thermal parameters describing the leader channel under a lightning and switching impulse are obtained through an analysis of interference fringes. The influences of different voltage waveforms on the dynamic expansion of leader channels are obtained. Firstly, the expansion rates of the channel radius are higher for shorter rise times. The average expansion rates are 72.30 ± 9.54, 28.09 ± 5.05, and 14.38 ± 3.02 m/s for the rise times of 1.2, 40, and 100 μs and the crest value of 425 kV for a 0.5-cm-diameter cone electrode; moreover, the temperatures at the centre of the leader channels are 5000–7000 K, 4000–6000 K, and 3000–4500 K, respectively. Secondly, the high-temperature region is larger for the shorter rise times. A numerical model was used to study the expansion of the leader channels, and the simulation results for the leader channel diameters showed good consistency with the experimental measurements. The continuous energy injection results in an over-pressure process in the leader channels and ultimately in their expansion. For a 1.2/50 μs waveform, the vibrational-translational relaxation (QVT) and the thermal dissociation (QD), which dominate the energy flow, are about one order of magnitude greater than that in a 100/2500 μs waveform. The convection loss and the ionization mechanism during the expansion process are also discussed. [ABSTRACT FROM AUTHOR]

Edge illumination (EI) is a promising X-ray phase contrast imaging (XPCI) technique and is expected to translate XPCI into practical applications with laboratory X-ray sources. However, traditional double-mask EI setup requires two acquisitions for extracting phase and absorption information. Although the latest single-mask EI setup allows phase retrieval with single-shot, it requires a nearly ideal detector point spread function (PSF). In this paper, an alternative EI setup is proposed, which remains double-mask but requires only a single-shot. It can implement single-shot XPCI and relax the detector requirements. Numerical calculations are carried out to compare the characteristics of the double- and single-mask EI setup and the proposed setup. The performance of this setup with different illumination conditions is evaluated theoretically. The results suggest that the proposed setup is less affected by the detector PSF compared to the single-mask EI setup and therefore has higher contrast and contrast-to-noise ratio. Phase retrieval can be implemented by this setup with a single-shot, which helps to simplify the operations and eliminate the potential errors in the double-mask EI setup. A narrow illumination width contributes to the contrast but adversely affects the radiation utilization efficiency, and some appropriate trade-offs should be selected according to the practical applications and experimental conditions. On the basis of this setup, the extraction of the quantitative phase and absorption information was also conducted by numerical calculation. [ABSTRACT FROM AUTHOR]

In this paper, the influence of disorder on 1D periodic lattice of resonant scatterers is inspected. These latter have multiple resonance frequencies which produce band gaps in the transmission spectrum. One peculiarity of the presented system is that it is chosen with a nearly perfect overlap between the Bragg and the second hybridization band gaps. In the case of a perfectly ordered lattice, and around this overlap, this produces a narrow transparency band within a large second bandgap. As expected, the effect of the disorder is generally to increase the width of the band gaps. Nevertheless, the transparency band appears to be robust with respect to an increase in the disorder. In this paper, we study this effect by means of experimental investigations and numerical simulations. [ABSTRACT FROM AUTHOR]

The paper numerically studies the contribution of the electric field accompanying the surface acoustic wave to the actuation of the acoustic streaming in microchannels. The finite element method is used. The results obtained as applied to the surface waves on 128° and 64°-rotated Y cuts of LiNbO3 demonstrate that the force created by the electric field is capable of accelerating appreciably the acoustic streaming. In particular, examples are given for the situations where the electric field increases the streaming velocity by a factor of about 2-3 and significantly changes the flow pattern as compared to predictions of computations ignoring the electric field. [ABSTRACT FROM AUTHOR]

Current balance factor (CBF) value, the ratio of the recombination current density and the total current density of a device, has an important function in fluorescence-based organic light-emitting diodes (OLEDs), as well as in the performance of the organic electrophosphorescent devices. This paper investigates the influence of the applied voltage of a device on the CBF value of single layer OLED based on the numerical model of a bipolar single layer OLED with organic layer trap free and without doping. Results show that the largest CBF value can be achieved when the electron injection barrier (ϕn) is equal to the hole injection barrier (ϕp) in the lower voltage region at any instance. The largest CBF in the higher voltage region can be achieved in the case of ϕn >ϕp under the condition of electron mobility (μ0n) > hole mobility (μ0p), whereas the result for the case of μ0n <μ0p, is opposite. The largest CBF when μ0n =μ0p can be achieved in the case of ϕn =ϕp in the entire region of the applied voltage. In addition, the CBF value of the device increases with increasing applied voltage. The results obtained in this paper can present an in-depth understanding of the OLED working mechanism and help in the future fabrication of high efficiency OLEDs. [ABSTRACT FROM AUTHOR]

In this paper, the critical state Bean model is employed to estimate the effect of the electromagnetic force on the fracture behavior of the superconductor slab. The superconductor slab with an inclined crack is subjected to an applied field. Based on the finite element method, the stress intensity factors are computed for two activation processes, zero field cooling and field cooling. Numerical results obtained show that the crack length and the inclined angle have significant effects on the fracture behavior. Generally, maximum of mode-I stress intensity factor is larger than that of mode-II stress intensity factor. The stress intensity factors analyzed in the paper are useful to learn fracture behavior and mechanical failure of superconductors. [ABSTRACT FROM AUTHOR]

The enhancement of the efficiency in free-electron lasers (FELs) through the use of a tapered wiggler is well known. The physics of the tapered wiggler interaction has been studied in theory and simulation, and large efficiency enhancements have been observed in the laboratory in oscillators and seeded amplifiers. In this paper, we study the differences in the tapered wiggler interaction between seeded amplifiers and in FELs that start up from noise and grow to saturation in a single pass through the wiggler. This configuration is commonly referred to as self-amplified spontaneous emission (SASE). In comparison with seeded amplifiers, SASE FELs exhibit shot-to-shot fluctuations due to random phase noise in the electron bunches, and our purpose in this paper is to determine the effect of this phase noise on the tapered wiggler interaction. To this end, we study the interaction numerically using the MEDUSA simulation code for seeded and SASE FELs operating in the infrared regime. The results of the simulations indicate that the overall efficiencies of the seeded and SASE FELs are comparable for a uniform wiggler but that the output spectrum for the SASE FEL is much broader than for the seeded case. For a tapered wiggler, the efficiency enhancement in the SASE FEL is less than that found in the seeded example due to the broader excited spectrum that detunes the tapered wiggler interaction. [ABSTRACT FROM AUTHOR]

Polymer composites reinforced by carbon nanofibers (CNFs) in the form of paper sheet show significant vibration and acoustic damping improvement when compared to pure matrix materials. Without looking into the microscopic energy dissipation mechanisms, this paper analyzes the wave propagation in the composites from a macroscopic point of view. The CNF nanocomposites in this study were treated as stacking of alternating layers of pure polymer and CNF reinforced polymer. Analyses of acoustic wave propagation focused on revealing the effects of acoustic impedance discontinuity at the interfaces of the layered structure. Plane wave transmission coefficient has been calculated as a function of the number of the layer repeats and thickness at different wave frequencies. Oscillations in the transmission coefficient have been observed when the acoustic wavelength is on the same order of the bilayer thickness, indicating the possibility of designing the nanocomposite structure to optimize noise reduction characteristics. The numerical analysis converges with effective media theory when acoustic wavelength is much larger than the layer thickness. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the radiative heat transport in layered structures. The analysis is based on our prior description of the spectrum of thermally excited waves in systems with a heat flux. The developed method correctly predicts results for all known special cases for both large and closing gaps. Numerical examples demonstrate the applicability of our approach to the calculation of the radiative heat transport coefficient across various layered structures. [ABSTRACT FROM AUTHOR]

A generalized enthalpy based equation of state, which includes thermal electron excitations explicitly, is formulated from simple considerations. Its application to obtain Hugoniot of materials needs simultaneous evaluation of pressure-volume curve and temperature, the latter requiring solution of a differential equation. The errors involved in two recent papers [Huayun et al., J. Appl. Phys. 92, 5917 (2002); 92, 5924 (2002)], which employed this approach, are brought out and discussed. In addition to developing the correct set of equations, the present work also provides a numerical method to implement this approach. Constant pressure specific heat of ions and electrons and ionic enthalpy parameter, needed for applications, are calculated using a three component equation of state. The method is applied to porous Cu with different initial porosities. Comparison of results with experimental data shows good agreement. It is found that temperatures along the Hugoniot of porous materials are significantly modified due to electronic effects. [ABSTRACT FROM AUTHOR]

This paper proposes a double-vibrator three-component pillared phononic crystal plate and theoretically studies the properties of vibration band gaps of this plate. The band structures and the displacement fields of the eigenmodes are calculated by the finite element method. Comparing the transmission power spectrums of the vibrations in the plate, the flexural vibration gap is proved more useful than the longitudinal vibration gap. The influence of the lattice constant, the height, and diameter of the pillars on the flexural vibration gaps are investigated. A supercell composed of the uni-vibrator and the double-vibrator unit cells is also investigated, and the analysis shows that the starting frequencies of the gaps in this supercell structure depend on the features of its pillars. This research can be used in the low frequency vibration insulation of plate structures. [ABSTRACT FROM AUTHOR]

When a depolarizing event occurs across a cell membrane there is a remarkable change in its electrical properties. A complete depolarization event produces a considerably rapid increase in voltage that propagates longitudinally along the axon and is accompanied by changes in axial conductance. A dynamically changing magnetic field is associated with the passage of the action potential down the axon. Over 75 years of research has gone into the quantification of this phenomenon. To date, no unified model exist that resolves transmembrane polarization in a closed-form description. Here, a simple but formative description of propagated signaling phenomena in the membrane of an axon is presented in closed-form. The focus is on using both biophysics and mathematical methods for elucidating the fundamental mechanisms governing transmembrane polarization. The results presented demonstrate how to resolve electromagnetic and thermodynamic factors that govern transmembrane potential. Computational results are supported by well-established quantitative descriptions of propagated signaling phenomena in the membrane of an axon. The findings demonstrate how intracellular conductance, the thermodynamics of magnetization, and current modulation function together in generating an action potential in a unified closed-form description. The work presented in this paper provides compelling evidence that three basic factors contribute to the propagated signaling in the membrane of an axon. It is anticipated this work will compel those in biophysics, physical biology, and in the computational neurosciences to probe deeper into the classical and quantum features of membrane magnetization and signaling. It is hoped that subsequent investigations of this sort will be advanced by the computational features of this model without having to resort to numerical methods of analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a low-cost double rotor axial flux motor (DRAFM) with low cost soft magnetic composite (SMC) core and ferrite permanent magnets (PMs). The topology and operating principle of DRAFM and design considerations for best use of magnetic materials are presented. A 905W 4800 rpm DRAFM is designed for replacing the high cost NdFeB permanent magnet synchronous motor (PMSM) in a refrigerator compressor. By using the finite element method, the electromagnetic parameters and performance of the DRAFM operated under the field oriented control scheme are calculated. Through the analysis, it is shown that that the SMC and ferrite PM materials can be good candidates for low-cost electric motor applications. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the heat transport by acoustic waves in arbitrary layered structures that may include several vacuum layers. The analysis is based on our prior description of the spectrum of thermally excited waves in systems with a heat flux, and on the new approach to the coupling between acoustic fields in separated bodies as well as a description of the interference of thermally excited waves. The developed method correctly predicts results for all known special cases for both large and closing gaps, it agrees with the available experimental measurements, and it explains the phenomena of interface thermal resistance as well as thermal rectification (asymmetry of thermal transport). Numerical examples demonstrate the applicability of our approach to the calculation of the heat transport coefficient across nanoscale gaps due to acoustic waves. [ABSTRACT FROM AUTHOR]

In this paper, we present a study of the effects of different superlattice structural parameters on the bandgap and on both the vertical and in-plane mobility of electrons in InAs/GaSb type-II superlattices using a fully numerical finite difference method. The analysis of our results clearly indicates the significance of interface roughness scattering and, in particular, that the influence of interface roughness correlation length and height is considerable. A comparison of our calculated results with published experimental data is shown to be in good agreement. [ABSTRACT FROM AUTHOR]

In this paper, a new structure of two-dimensional phononic crystals consisting of one or more rows of parallel rectangular rods placed periodically in a homogenous slab, in which the rods are not connected directly but linked through neck structures with the slab, is proposed, and the Lamb wave propagation in this structure is investigated with numerical analysis. The dispersion relations and the power transmission spectra are studied using the finite-element method. In contrast to the phononic crystals where the rods and the slab are completely in contact, the proposed structure with necks are proved to display band gaps at much lower frequencies. The displacement fields of the eigenmodes of the band edges are computed and analyzed to clarify the mechanism for the generation of the low-frequency band gaps. It is found that the low-frequency band gaps are attributed to the interaction between the local resonance of the rod inclusion connected with the neck and the Lamb modes of the four plates which are formed by the introduction of the neck. Furthermore, the influences of the geometry parameters of the neck on the band gaps are discussed. Numerical results show that band gaps are significantly dependent upon the width and the position of the necks while insensitive to the neck length. These properties of Lamb waves can potentially be applied to optimize band gaps, generate filters, and design acoustic devices. [ABSTRACT FROM AUTHOR]

In the paper, we investigate the miniband structure of one-dimensional quantum dash array and its dependence on geometrical parameters by using a newly developed and efficient numerical method. We show that miniband energy significantly depends on the dash height and width, while the miniband width depends on the array period and the dash width. The excited minibands may exhibit the effect of zero miniband gap and the multiple anticrossings, which are followed by the swapping of the character of adjacent minibands top and bottom. The wetting layer allows formation of a miniband cluster in the vicinity of the well top, which essentially represents the barrier continuum embedded into the well of array. [ABSTRACT FROM AUTHOR]

In this paper the smallest or optimal dimensions of a Halbach cylinder of a finite length for a given sample volume and desired flux density are determined using numerical modeling and parameter variation. A sample volume that is centered in and shaped as the Halbach cylinder bore but with a possible shorter length is considered. The external radius and the length of the Halbach cylinder with the smallest possible dimensions are found as a function of a desired internal radius, length of the sample volume and mean flux density. It is shown that the optimal ratio between the outer and inner radius of the Halbach cylinder does not depend on the length of the sample volume. Finally, the efficiency of a finite length Halbach cylinder is considered and compared with the case of a cylinder of infinite length. The most efficient dimensions for a Halbach cylinder are found and it is shown that the efficiency increases slowly with the length of the cylinder. [ABSTRACT FROM AUTHOR]

Considering electro-osmotic flow in axisymmetric microducts is of both fundamental interest and practical significance. In this paper, an axisymmetric lattice Boltzmann model which solves the complete nonlinear Poisson-Boltzmann equation is presented to obtain the electric potential distribution in the electrolytes, and another axisymmetric lattice Boltzmann model is employed to solve the velocity field. First, the lattice Boltzmann model is validated by the electric potential distribution in the electrolyte with analytical solutions and finite volume method. Second, velocity distributions in circular tubes at various conditions are discussed. Then, we extend the lattice Boltzmann model for steady and pulsating electro-osmotic flow through annular microducts and the influences of inner to outer radius ratio, inner to outer zeta potential ratio and oscillating frequency are investigated. In addition, a numerical study of electro-osmotic flow in circular and annular microducts considering the non-Newtonian fluid behavior is also conducted for the first time. The results show that the microannular electro-osmotic flow exhibits much difference from the planar flow and the non-Newtonian rheology has significant effect on the flow behavior as well. [ABSTRACT FROM AUTHOR]

Results of multiparticle Monte Carlo simulations of midinfrared quantum cascade lasers structure initially fabricated by Page et al. are presented. The main aim of this paper is to discuss in details how electric current flows through the structure and which subbands are involved in this process. Monte Carlo method allows to predict the electron population inversion between the lasing levels and gives microscopic insight into processes leading to such behavior. Importance of a subband belonging to the laser injector region, with energy slightly below the upper lasing level, is demonstrated. The electron-electron Coulomb interactions influence the shapes of electron distribution functions; the values of average electron energies and effective subbands' temperatures are calculated. [ABSTRACT FROM AUTHOR]

This paper attempts to quantify the effects of contaminants on electrical contact resistance. Based on an idealized model, simple and explicit scaling laws for the electrical contact resistance with dissimilar materials are constructed. The model assumes arbitrary resistivity ratios and aspect ratios in the current channels and their contact region, for both Cartesian and cylindrical geometries. The scaling laws have been favorably tested in several limits, and in sample calculations using a numerical simulation code. From the scaling laws and a survey of the huge parameter space, some general conclusions are drawn on the parametric dependence of the contact resistance on the geometry and on the electrical resistivity in different regions. [ABSTRACT FROM AUTHOR]

The paper presents a comprehensive numerical analysis of x-ray and neutron scattering from finite-conducting rough surfaces which is performed in the frame of the boundary integral equation method in a rigorous formulation for high ratios of characteristic dimension to wavelength. The single integral equation obtained involves boundary integrals of the single and double layer potentials. A more general treatment of the energy conservation law applicable to absorption gratings and rough mirrors is considered. In order to compute the scattering intensity of rough surfaces using the forward electromagnetic solver, Monte Carlo simulation is employed to average the deterministic diffraction grating efficiency due to individual surfaces over an ensemble of realizations. Some rules appropriate for numerical implementation of the theory at small wavelength-to-period ratios are presented. The difference between the rigorous approach and approximations can be clearly seen in specular reflectances of Au mirrors with different roughness parameters at wavelengths where grazing incidence occurs at close to or larger than the critical angle. This difference may give rise to wrong estimates of rms roughness and correlation length if they are obtained by comparing experimental data with calculations. Besides, the rigorous approach permits taking into account any known roughness statistics and allows exact computation of diffuse scattering. [ABSTRACT FROM AUTHOR]

Electromagnetic forming (EMF) is a forming process that relies on the inductive electromagnetic force to deform metallic workpiece at high speed. Calculation of the electromagnetic force is essential to understand the EMF process. However, accurate calculation requires complex numerical solution, in which the coupling between the electromagnetic process and the deformation of workpiece needs be considered. In this paper, an appropriate formula has been developed to calculate the electromagnetic force in metal work-piece in the sheet EMF process. The effects of the geometric size of coil, the material properties, and the parameters of discharge circuit on electromagnetic force are taken into consideration. Through the formula, the electromagnetic force at different time and in different positions of the workpiece can be predicted. The calculated electromagnetic force and magnetic field are in good agreement with the numerical and experimental results. The accurate prediction of the electromagnetic force provides an insight into the physical process of the EMF and a powerful tool to design optimum EMF systems. [ABSTRACT FROM AUTHOR]

This paper presents an improved theoretical description of the mode-mismatched thermal lens effect using models that account for heat transport both within the sample and out to the surrounding coupling medium. Analytical and numerical finite element analysis (FEA) solutions are compared and subsequently used to model the thermal lens effect that would be observed using continuous laser excitation. FEA model results were found to be in excellent agreement with the analytical solutions. The model results show that heat transfer to the air coupling medium introduces only a minor effect when compared with the solution obtained without considering axial air-sample heat flux for practical examples. On the other hand, the thermal lens created in the air coupling fluid has a relatively more significant effect on the time-dependent photothermal lens signals. [ABSTRACT FROM AUTHOR]

In this paper, a circuit model to predict the microwave response of a shunt-connected capacitive microelectromechanical coplanar switch is proposed. The numerical values of the lumped elements composing the equivalent circuit are computed by means of a fully analytic approach. In particular, the contribution of resistive and inductive parasitic elements has been evaluated by using closed-form expressions. Configurations characterized by different technological solutions have been obtained and modeled. Simulations performed with the proposed approach correlate very well with actual measurements. [ABSTRACT FROM AUTHOR]

Recent progress in sensor array technology has boosted the use of beamforming (BF) in a number of applications. The same progress has generated interest in other imaging modalities such as diffraction tomography (DT). This paper demonstrates the existence of a linear mapping between BF and DT, which is represented by a linear filter in the spatial frequency domain. The filter is used to study and compare the information content of images obtained with the two imaging modalities. In particular, it is demonstrated that a BF image is a distorted version of the corresponding DT image. Moreover, the analytical expression of the filter is derived leading to an algorithm for DT which, in contrast to currently available algorithms, does not require the use of data interpolation techniques. [ABSTRACT FROM AUTHOR]

We present a detailed numerical simulation study of the effects caused by the magnetodipolar interaction between ferromagnetic (FM) layers of a trilayer magnetic nanoelement on its magnetization dynamics. As an example, we use a Co/Cu/Ni80Fe20 element with a square lateral shape where the magnetization of FM layers forms a closed Landau-like domain pattern. First, we show that when the thickness of the nonmagnetic (NM) spacer is in the technology relevant region h∼10 nm, magnetodipolar interaction between 90° Neel domain walls in FM layers qualitatively changes the equilibrium magnetization state of these layers. In the main part of the paper, we compare the magnetization dynamics induced by a sub-nsec field pulse in a single-layer Ni80Fe20 (Py) element and in the Co/Cu/Py trilayer element. Here, we show that (i) due to the spontaneous symmetry breaking of the Landau state in the FM/NM/FM trilayer, its domains and domain walls oscillate with different frequencies and have different spatial oscillation patterns; (ii) magnetization oscillations of the trilayer domains are strongly suppressed due to different oscillation frequencies of domains in Co and Py; (iii) magnetization dynamics qualitatively depends on the relative rotation sense of magnetization states in Co and Py layers and on the magnetocrystalline anisotropy kind of Co crystallites. Finally, we discuss the relation of our findings with experimental observations of magnetization dynamics in magnetic trilayers, performed using the element-specific time-resolved x-ray microscopy. [ABSTRACT FROM AUTHOR]

A numerical study based on finite element simulations reveals the experimentally indicated fact [N. F. Declercq et al., J. Appl. Phys. 96, 5836 (2004)] that leaky Rayleigh waves propagating along the horizontal surface of a thick fluid-loaded solid plate are transmitted around the corner of the solid plate. The mentioned experiments are based on the so-called Schoch effect, accompanied by the presence of a null strip in the reflected part of the beam, and phenomena occurring when the incident beam, generating the effect, approaches the edge of the solid plate. The referred experiments indicate that leaky Rayleigh waves are generated around the corner of the plate, but the experimental evidence is not fully conclusive whether the effect is caused merely by incident Rayleigh waves on the upper surface or by scattering effects when the incident beam interacts with the corner. The current study first confirms the reported experiments by means of the finite element method and then proofs that the assumption made in the referred paper about Rayleigh waves, being primarily stimulated by the edge of an incident bounded beam rather than the middle, is correct. Ultimately the model is applied to study leaky Rayleigh waves separately from the incident and reflected bounded beams. It is shown that the Rayleigh waves themselves are the physical origin of the transmission of Rayleigh waves rather than scattering effects caused by the incident bounded beam. [ABSTRACT FROM AUTHOR]

This paper provides a full numerical tool set for modeling and predicting an effective apparent dielectric constant of multiphase microporous media, which includes a multiparameter random generation-growth algorithm for generating microstructures of multiphase porous media and a lattice Boltzmann solver for the electric potential transport equations through porous structures. After being validated by the theoretical solutions for simple geometries, the present methods are used to investigate the phase distribution effects on the effective dielectric constant of multiphase microporous media, including the effects of particle size, structure anisotropy, and phase aggregation caused by wetting characteristics between phases for multiphase cases. The resultant predictions at the end agree well with the existing experimental data for both two-phase and three-phase cases. [ABSTRACT FROM AUTHOR]

Magnetic fluid dynamic behaviors during resistance spot welding have important influences on weld nugget formation. In this paper, a coupled multiphysics finite element model, which realizes the coupling of mass conservation, momentum conservation, energy conservation, and the Maxwell system of equations, is proposed to systematically investigate the fluid flow and heat transfer behaviors in a spot weld nugget. It is found that the flow field in the spot weld nugget evolves through five consecutive stages: incubation, fluctuation, rapid growth, rapid attenuation, and termination. Molten metal in the nugget makes regular rotational flow in four symmetrical loops, which changes the temperature gradient in weld nugget during heating and holding, and also yields significant effects on the shape and thickness of weld nugget. [ABSTRACT FROM AUTHOR]

For the film/substrate bimaterial system, some considerable efforts have been made to predict the stress distribution in the film. However, only the normal stress in the film at the position away from the edge is usually considered. Moreover, the stress gradient through the thickness in the film and the stress in the substrate are often ignored. In this paper, an analytical model is developed to analyze the edge effects on the stress gradients in the film and the substrate. In order to obtain the closed-form solutions for the stresses in the film and the substrate, the shear lag model in the planar geometry is used to solve the stress transfer problem. By comparing the results from the present model with those from the existing analytical models, finite element analysis, and the experimental measurements, it can be concluded that the present analytical model is very rigorous. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study single electron charging of a floating gate composed of nanocrystals in a metal-oxide-semiconductor transistor. We present a three-dimensional model of electron tunneling into quantum islands that are spherical in shape. This model can be numerically solved through a two-dimensional finite element approach. In this way, extensive and accurate numerical experimentations can be carried out due to the reduced computer time cost. The curves of tunneling time versus bias voltage exhibit complex serrated shapes, related to both the energy subbands of the channel and the energy states of the nanocrystal. The results are discussed for different channel doping densities. [ABSTRACT FROM AUTHOR]

This paper examines in detail the characteristics of a leaky Lamb wave propagating in a piezoelectric plate immersed in a dielectric or conductive fluid. The analysis is based on the partial wave analysis and its numerical calculations. Some corrections have been made so that both the changes in phase velocity and the wave attenuation of leaky Lamb waves caused by fluid’s mechanical, dielectric, and conductive loadings are determined accurately. Influences of each material property of the loading fluid such as mass density, wave speed, permittivity, and conductivity on the leaky Lamb wave have been quantitatively characterized. Particular emphasis is placed on the velocity variations and excessive attenuation caused by the fluid’s conductivity. The results are important in designing piezoelectric acoustic wave sensors working in liquid phase. [ABSTRACT FROM AUTHOR]

Raman spectroscopy finds applications in many research fields to monitor stress on a micrometric scale. Unfortunately, the interpretation of Raman maps is always complicated by the tensorial nature of stress and by averaging effects due to the finite spatial resolution of the technique. Usually, the interpretation is either purely qualitative or based on thorough simplifications. In this paper we present an approach that compares the experimental data with a virtual experiment using a finite-element model. The method is applied to the study of the stress generated in a microelectronic device during the manufacturing process. The results are used both as a feedback and a validation for the modeling and also for the interpretation of the Raman data. [ABSTRACT FROM AUTHOR]

This paper presents the results of the numerical finite-difference time-domain analysis of a strongly localized antisymmetric plasmon, coupled across a nanogap between two identical metal wedges. Dispersion, dissipation, field structure, and existence conditions of such coupled wedge plasmons are determined and investigated on an example of the fundamental coupled mode. It is shown that in the general case there exist three critical wedge angles and a critical gap width (separation between the wedge tips). If the gap width is larger than the critical separation, then the antisymmetric wedge plasmons can exist only in the ranges between the first and the second critical angles, and between the third critical angle and 180°. If the gap width is smaller or equal to the critical separation, then the third and the second critical angles merge, leaving only one interval of wedge angles within which the antisymmetric coupled wedge plasmons can exist. The effect of rounded wedge tips is also investigated and is shown to be similar to that of different wedge angles. Feasibility of using these plasmons for the design of efficient subwavelength waveguides is discussed. [ABSTRACT FROM AUTHOR]

The nonparametric estimation of the distribution of relaxation-time approach is not as frequently used in the analysis of dispersed response of dielectric or conductive materials as are other immittance data analysis methods based on parametric curve fitting techniques. Nevertheless, such distributions can yield important information about the physical processes present in measured material. In this paper, we apply two quite different numerical inversion methods to estimate the distribution of relaxation times for glassy Li0.5La0.5TiO3 dielectric frequency-response data at 225 K. Both methods yield unique distributions that agree very closely with the actual exact one accurately calculated from the corrected bulk-dispersion Kohlrausch model established independently by means of parametric data fit using the corrected modulus formalism method. The obtained distributions are also greatly superior to those estimated using approximate function equations given in the literature. [ABSTRACT FROM AUTHOR]

Stoney's equation and subsequent modifications and some approximations are widely used to evaluate the macrostress within a film on a substrate, though some of these solutions are only applicable for thin films. The purpose of this paper is to review the considerable efforts devoted to the analysis of residual stresses in a single-layer film in the last century and recent years and to estimate the errors involved in using these formulas. The following are some of the important results that can be obtained. (1) The exact solution for the residual stress can be expressed in terms of Stoney's equation [Proc. R. Soc. London A82, 172 (1909)] and a correction factor, (1+Ση3)/(1+η), where Σ,η are the ratios of the elastic modulus and the thickness of the film to those of the substrate, respectively. (2) When the thickness ratio of the film and the substrate is less than 0.1, Stoney's equation and Röll's approximation [J. Appl. Phys. 47, 3224 (1976)] do not cause serious errors. (3) The approximation proposed by Vilms and Kerps [J. Appl. Phys. 53, 1536 (1982)] is an improved modification for Stoney's equation and can be applicable when η≤0.3. (4) The approximations proposed by Brenner and Senderoff [J. Res. Natl. Bur. Stand. 42, 105 (1949)] and Teixeira [Thin Solid Films 392, 276 (2001)] can lead to serious errors and should be avoided. (5) The approximation based on the assumption of constant elastic modulus is only applicable for a ratio of η≤0.01 and can be very misleading. [ABSTRACT FROM AUTHOR]

A local method is developed for estimating the effective conductivity for materials with varying deterministic or random conductivity on domains with mixed boundary conditions. The effective conductivity is the conductivity of a virtual homogeneous material which behaves globally as the original heterogeneous material. It is shown that the effective conductivity can be calculated from the values of the potential at a relatively small number of points in the specimen. A method is developed for calculating the potential at an arbitrary point in the specimen directly, rather than extracting its value from a field solution. The method is based on some technical concepts related to properties of diffusion processes and an extension of Itô’s formula for continuous semimartingales to the case of reflected diffusion processes. However, the application of the method is intuitive and uses elementary Monte Carlo simulation algorithms. The paper presents essential facts proving the validity of the proposed method and two numerical examples illustrating the calculation of the effective conductivity for specimens with deterministic and random conductivity fields. [ABSTRACT FROM AUTHOR]

In this paper, we studied the intervalley interactions between the orbital functions associated with multivalley of silicon (Si) quantum dots. Numerical calculations show that the intervalley coupling between orbital functions increases rapidly with an applied electric field. We also considered the potential applications to quantum bit operation utilizing controlled intervalley interactions. Quantum bits are the multivalley symmetric and antisymmetric orbitals. Evolution of these orbitals would be controlled by an external electric field which turns on and off the intervalley interactions. Estimates of the decoherence time are made for the longitudinal-acoustic-phonon process. Elementary single- and two-qubit gates are also proposed. [ABSTRACT FROM AUTHOR]

In this paper we revisit the absorption and thermal emission of electromagnetic radiation by a rough surface. We use a numerical simulation of the absorptivity of a grating to explore the validity of the ray tracing approach. We show that it often predicts correctly the absorptivity and emissivity of a surface with characteristic lengths on the order of a wavelength. Recent advances in the understanding of the microscopic mechanism of thermal emission in the near field are used to discuss the data and to explain this surprising result. We also identify three different regimes depending on the ratio of the period to the wavelength: the homogenization regime, the resonance regime, and the geometrical optics regime. [ABSTRACT FROM AUTHOR]

With the rapid development of automation techniques, the claw-poled stepping motors are widely used, especially in optical scanners. Most research on stepping motors has concentrated on electrical properties, but a few papers have reported on the performance in relation to the magnetic-field distribution. The purpose of this study is to analyze the effect of the shape of the stator tooth and to search for the optimal parameters using a magnetic-circuit simulation technique. Through numerical calculations, the optimal performance conditions can be obtained by varying the ratio between the two bases of the trapezoid teeth between 1/5 and 1/3, and varying the ratio between the heights of individual teeth in relation to the separation between the two yokes from 11/15 to 13/15. [ABSTRACT FROM AUTHOR]

This paper describes a large-scale and highly accurate magnetostatic field analysis targeting a magnetic shield. The hybrid finite element–boundary element method and the magnetic moment method do not require mesh division for the free space and can easily treat the nonlinearity of magnetic property. Therefore, these methods are considered very effective for the analysis of a magnetic shield which has a high aspect ratio of the size scale to the thickness. However, large memory and computational time have been required due to the dense matrices generated by those integral-based formulations. To overcome the difficulties, we introduce the fast multipole method into the hybrid method and the magnetic moment method. Furthermore, to achieve more reduction of CPU time, we propose an effective preconditioning technique suitable for the hybrid method. Some numerical results that demonstrate the effectiveness of these approaches are also presented. [ABSTRACT FROM AUTHOR]

This paper deals with the numerical analysis of soft magnetic materials with hysteresis in dynamic axial symmetric problems. We present a procedure based on a 1D Finite Difference Time Domain (FDTD) algorithm where there are implemented magnetization dependent Preisach based models. Experimental measurements of the virgin curve and the major loop are used to identify the models. The numerical scheme in the time domain proposed is discussed and a probe of its intrinsic stability is given. Numerical codes based on the above algorithm are used to show some of the possibilities of this numerical tool for the dynamic magnetic analysis. [ABSTRACT FROM AUTHOR]

This paper describes calculations and comparisons of eddy current losses in a cylindrical linear oscillatory actuator with a Halbach array permanent magnet mover for different voltage source waveforms. Using the magnetic vector potential and a two-dimensional cylindrical coordinate system, the paper presents an analytical procedure and obtains solutions for the eddy current losses using the Poynting theorem. To verify the proposed method, the eddy current losses obtained from the analytical solutions are compared with the results of a non-linear finite element method. Moreover, this paper shows that the eddy current losses are more significant when the actuator is driven by a square voltage waveform than when it is driven by a sinusoidal voltage waveform. [ABSTRACT FROM AUTHOR]