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Within a phenomenon-based model of dynamic conductivity of superionic conductors, the contribution of Li+-ionic conductivity to forming the frequency dispersion of non-stoichiometric ceramics Li2O-Fe2O3-Al2O3 at various temperatures has been investigated. There have been determined the predominance of electronic type of conductivity at temperature rate of 295–450 К realised by percolation mechanism. With further temperature rising Li+-cationic conductivity is becoming predominant. With Al+3 ionic content rising in the patterns Li+-ionics conductivity is increasing, but their mobility is decreasing at all temperature rates within the investigation.

The electrical properties of SiO2/p-Si films deposited by ECR-PECVD s were studied at different frequencies (100-1 MHz) and gate voltages (−6–3 V). Results showed a frequency dispersion of C-Vg and G/ω-Vg. With increasing frequency, the capacitance and conductance are strongly decreased. An apparent peak in the depletion regime of the G/ω-Vg plots can be attributed to the existence of density Nss at Si/SiO2. The (Nss)value vary from 1.5 × 1012 to 0.5 × 1011 eV−1 cm−2, it has been determined by High-Low frequency capacitance technic. The Nss- Vg curve presents a peak at about −3 V, suggesting the presence Nss between the (Si)/SiO2 interface. Hill and Coleman method shows that the Nss decreases with increasing frequency which explains the high value of capacitance at low frequency. The Nss and their relaxation time τ by the conductance method ranged from 1.8 × 1013 to 1.37 × 1011 eV−1 cm−2 and 5.17 10−7 to 8 × 10−6 s, in the range (0.189-Ev) and (0.57- Ev) eV, respectively. The Nss was responsible for the non-ideal behavior of C-Vg and G-Vg leading to the breakdown of such device. Comparing the three method results show that parallel conductance is very precise and accurate.

Introduction Atrial Fibrillation (AF) is the most common cardiac arrhythmia, presenting a significant independent risk factor for stroke and thromboembolism. With the emergence of m-Health devices, the importance of automatic detection of AF in an off-clinic setting is growing. This study demonstrates the performance of a bimodal classifier for distinguishing AF from sinus rhythm (SR) that could be used for automated detection of AF episodes. Methods Surface recordings from a hand-held research device and standard electrocardiograms (ECG) were collected and analyzed from 68 subjects. An additional 48 subjects from the MIT-BIH Arrythmia Database were also analyzed. All ECGs were blindly reviewed by physicians independently of the bimodal algorithm analysis. The algorithm selects an artifact-free 6-s ECG segment out of a 20-s long recording and computes a spectral Frequency Dispersion Metric (FDM) and a temporal R-R interval variability (VRR) index. Results Scatter plots of the VRR and FDM indices revealed two distinct clusters. The bimodal scattering of the indices revealed a linear classification boundary that could be employed to differentiate the SR from AF waveforms. The selected classification boundary was able to correctly differentiate all the subjects from both datasets into either SR or AF groups, except for 3 SR subjects from the MIT-BIH dataset. Conclusion Our bimodal classification algorithm was demonstrated to successfully acquire, analyze and interpret ECGs for the presence of AF indicating its potential to support m-Health diagnosis, monitoring, and management of therapy in AF patients.

In this paper, the capacitance frequency dispersion in strong accumulation of capacitance voltage curves has been studied for different high-k dielectric layers in MOS stacks. By studying experimental data at low (77 K) and room temperature (300 K), in oxides with different density of defects, it was possible reflect the spatial distribution of the defects in the capacitance frequency dispersion. The experimental data show that while at room temperature, the capacitance dispersion is dominated by the exchange of carriers from the semiconductor into oxide traps far away from the interface, at low temperature the oxide traps near the Al2O3/InGaAs interface are responsible for the frequency dispersion. The results indicate that the capacitance dispersion in strong accumulation reflect the spatial distribution of traps within the oxide, and that dielectric/semiconductor conduction band offset is a critical parameter for determining the capacitance dispersion for Al2O3/InGaAs based gate stacks. Fil: Palumbo, Félix Roberto Mario. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; Argentina Fil: Aguirre, Fernando Leonel. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina Fil: Pazos, Sebastián Matías. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; Argentina. Comisión Nacional de Energía Atómica; Argentina Fil: Krylov, Igor. Technion - Israel Institute of Technology; Israel Fil: Winter, Roy. Technion - Israel Institute of Technology; Israel Fil: Eizenberg, Moshe. Technion - Israel Institute of Technology; Israel

The hydrate saturation is a critical parameter in the evaluation of gas hydrate reservoirs. The complex characteristics of hydrate-bearing sediments pose challenges to the reliability of conventional geophysical techniques for hydrate saturation evaluation. In this paper, we present a study on developing a novel approach to characterize the electrical properties of hydrate-bearing porous media and to evaluate the hydrate saturation quantitatively based on parameters of the complex electrical conductivity. In the laboratory experiments we prepared samples with the tetrahydrofuran hydrate forming in sands to simulate the hydrate-bearing sediments and for measuring the complex conductivity at frequencies from 20 Hz to 100 kHz. The frequency-dispersion characteristics of complex conductivity of the hydrate-bearing samples with different saturations were analyzed, and then three types of hydrate-saturation evaluation models, denoted as the conductance-based, polarization-based and fusion models, were developed based on the in-phase conductivity, frequency-dispersion characteristic parameters of the phase angle and the combination of those two, respectively. A critical frequency (fc = 2 kHz) can be identified, where both the phase angle and imaginary component of the complex conductivity reach their minima. The Archie's formula shows its capability to model the relationship between the in-phase conductivity and hydrate saturation (i.e., conductance-based model), but the frequency higher than fc is preferred because stable Archie parameters can only be obtained in that frequency range. Linear correlations between the hydrate saturation and frequency-dispersion characteristic parameters (i.e., the logarithms of FE (frequency effect) and slope of the relation between FE and FR (frequency ratio) of the phase angle can be obtained, serving as the polarization-based models in the frequency range higher than fc. The fusion model performs the best in the perspective of low errors and high reliability for predicting the hydrate saturation, because more parameters of the complex conductivity and underlying physics of the conductance and polarization have been incorporated. In the frequency range lower than fc in contrast to that of the phase angle, the quadrature conductivity shows remarkable frequency-dispersion characteristics with the variation of the hydrate saturation, showing the great potential for developing new saturation-evaluation models in future.

In this paper we introduce a new reformulation of the Green–Naghdi model in the Camassa–Holm regime for the propagation of internal waves over a flat topography derived by Duchene et al. [18]. These new Green–Naghdi systems are adapted to improve the frequency dispersion of the original model, they share the same order of precision as the standard one but have an appropriate structure which makes them much more suitable for the numerical resolution. We develop a second order splitting scheme where the hyperbolic part of the system is treated with a high-order finite volume scheme and the dispersive part is treated with a finite difference approach. Numerical simulations are then performed to validate the model and the numerical methods.

International audience; The influence of surface distributions on rates of heterogeneous reactions coupled by adsorbed intermediates was studied to determine whether this form of surface heterogeneity can provide a physical explanation for constant-phase-element behavior. Results obtained from finite-element simulations on disk and recessed disk electrodes show that there are two components that give rise to frequency dispersion. Frequency dispersion occurs due to geometry-induced nonuniform current distributions which leads to a complex ohmic impedance. The effects of geometry-induced frequency dispersion may be mitigated by use of small electrodes. Frequency dispersion also occurs due to the potential dependence of the faradaic impedance. The characteristic frequency associated with this form of frequency dispersion is not dependent on disk radius, but the contribution of frequency dispersion associated with reactions coupled by adsorbed intermediates may be reduced with the use of small electrodes.

Y2O3 and Al2O3 were in-situ atomic layer deposited (ALD) on pristine GaAs(001)-46 reconstructed surfaces without surface pretreatments. We have studied the border and interfacial traps in both hetero-structures using the measured electrical responses. On the basis of frequency dispersion analysis of the capacitance-voltage (CV) characteristics, we conclude that Y2O3 has effectively passivated GaAs surface with a much lower interfacial trap density (Dit) than Al2O3 as the gate dielectric. The quasi-static CV and conductance measurements are in agreement with the above conclusion. We have demonstrated an excellent ALD-Y2O3/GaAs interface with low Dit's of (0.52)1012eV1cm2 through the whole GaAs band gap without a mid-gap peak feature. Display Omitted

Molecular beam epitaxy (MBE) HfO2 films ~ 1.5 nm thick were directly deposited on freshly grown GaAs(001)-4 × 6 reconstructed surfaces. The hetero-structure exhibits outstanding thermal stability up to 900 °C with excellent capacitance-voltage (C-V) and leakage current density-electric field (J-E) characteristics. We have extracted low interfacial trap densities (Dit's) with minimum value of 1.3 × 1011 eV− 1 cm− 2 from the measured quasi-static C-V (QSCV) characteristics. The smallest frequency dispersion of the C-Vs for the MBE-HfO2/p-GaAs(001) is ~ 5.2% at frequency range of 500 to 1 MHz and no trap-induced humps were observed in the C-Vs, as measured at 100 °C and 150 °C. Also, the leakage current density remains low of 10− 8(A/cm2) at E

The aim of this work has been the photoelectrochemical (PEC) study of nanostructured photoanodes based on TiO 2 . Highly ordered and well adhered TiO 2 nanotubes (TNTs) of different lengths (∼2–20 μm) were prepared in a two-step process in ethylene glycol solutions containing fluorides, and detailed XPS analysis showed that they have become co-doped with C, N and F. PEC measurements revealed that increasing surface area is not followed by increase in the photoconversion efficiency, but rather that an optimal balance between electroactive surface area (ESA) and charge carrier concentration exists. TNTs of around 10 μm show the optimum incident photon-to-current efficiency (IPCE) of ∼33% and an overall photoconversion efficiency of ∼6.3% under UV illumination of 4 mW cm −2 light intensity. Finally, Mott-Schottky analysis revealed significant frequency dispersion of the estimated space charge layer capacitance, which renders the accurate estimation of the flatband position and charge carrier concentration unreliable. On the other hand, more realistic charge carrier concentrations can be obtained by normalizing the capacitance per ESA.

The generalized Gerischer impedance theoretical model for a sinusoidal-shaped electrode has been developed. The impedance is presented as an expansion by the small parameter, which is equal to the ratio of the amplitude to period length of surface roughness. For the case of a weak roughness, we have derived the general expression for the complex roughness function and established its limiting behavior. It is shown that roughness does influence the value of parameters extracted from low − frequency region of an impedance measurement. In anomalous intermediate − frequency region, impedance exhibits frequency dispersion which is caused by the roughness. At high frequencies, the Gerischer impedance acts like the Warburg impedance

Different high-permittivity (high-k) gate dielectric structures of HfO 2 , HfAlO , and HfO 2 /Al 2 O 3 deposited on HF-etched n-GaAs using ALD have been investigated. It has been demonstrated that the stacked structure of HfO 2 /Al 2 O 3 has the lowest interface state density of 8 . 12 × 10 12 eV −1 cm −2 due to the “self-cleaning” reaction process, but the sample of HfAlO shows much better frequency dispersion and much higher dielectric permittivity extracted from the C-V curves. The investigation reveals that the electrical properties of gate dielectrics are improved by introducing alumina into HfO 2 .

This paper describes device simulation studies of surface and buffer trapping effects on static I-V, output-admittance (Y22), and transient characteristics of AlGaN/GaN HEMTs. The TCAD simulation model considering surface donors at EC − 0.5 eV and buffer traps at EC − 0.47 eV have been used to quantitatively reproduce the measured DC, Y22 frequency dispersion, gate-lag (GL) and drain-lag (DL) transients of AlGaN/GaN HEMT with 0.25 µm gate length. Moreover, simulated GL and DL transient responses of AlGaN/GaN HEMT with a longer gate length (0.5 µm) are validated with the reported experimental results. The impact of barrier trap at EC − 0.45 eV on the HEMT properties is also explored. It is shown that by matching simulation results with experimental data, it is possible to identify the trap (surface or buffer) responsible for a particular trapping induced degradation as well as its concentration and capture cross-section.

[EN] We present a framework to solve non-linear eigenvalue problems suitable for a Finite Element discretization. The implementation is based on the open-source finite element software GetDP and the open-source library SLEPc. As template examples, we propose and compare in detail different ways to address the numerical computation of the electromagnetic modes of frequency-dispersive objects. This is a non-linear eigenvalue problem involving a non-Hermitian operator. A classical finite element formulation is derived for five different solutions and solved using algorithms adapted to the large size of the resulting discrete problem. The proposed solutions are applied to the computation of the dispersion relation of a diffraction grating made of a Drude material. The important numerical consequences linked to the presence of sharp corners and sign-changing coefficients are carefully examined. For each method, the convergence of the eigenvalues with respect to the mesh refinement and the shape function order, as well as computation time and memory requirements are investigated. The open-source template model used to obtain the numerical results is provided. Details of the implementation of polynomial and rational eigenvalue problems in GetDP are given in the appendix. Program summary Program title: NonLinearEVP.pro CPC Library link to program files: http://dx.doi.org/10.17632/r57nxxtc62.1 Licensing provisions: GNU General Public License 3 Programming language: Gmsh (http://gmsh.info), GetDP (http://getdp.info) Nature of problem: Computing the eigenvalues and eigenvectors of electromagnetic wave problems involving frequency-dispersive materials. The resulting eigenvalue problem is non-linear and non-hermitian. Solution method: Finite element method coupled to efficient non-linear eigenvalue solvers: Relevant SLEPc solvers were interfaced to the Finite Element software GetDP. Several linearization schemes are benchmarked. (C) 2020 Elsevier B.V. All rights reserved., The work was partly supported by the French National Agency for Research (ANR) under the project "Resonance" (ANR-16-CE240013). The authors acknowledge the members of the project "Resonance'' for fruitful discussions. C. Campos and J. E. Roman were supported by the Spanish Agencia Estatal de Investigacion (AEI) under project SLEPc-HS (TIN2016-75985-P), which includes European Commission ERDF funds. C. Geuzaine was supported by ARC grant for Concerted Research Actions (ARC WAVES 15/19-03), financed by the Wallonia-Brussels Federation of Belgium. The authors thank Christian Engström from Ume¿ Universitet for helpful comments. Maxence Cassier from Institut Fresnel is acknowledged. Finally, the authors address special thanks to Anne-Sophie Bonnet Ben-Dhia and Camille Carvalho from INRIA (POEMS) for their motivating remarks and insights.

In order to accurately predict the variation rule of the effective permittivity and component content of silicon carbide (SiC) composites, the dielectric constants of SiC nano-particulate and its composites have been investigated by experiments and theoretical calculation. Based on the measured relative effective permittivity of samples with different SiC concentration, a calculation method for effective permittivity was established by modifying effective medium formula and Debye model. By the proposed formulas, the intrinsic permittivity of SiC versus frequency was revealed. The effective permittivity of SiC composites as a function of filling content and frequency was also explored. The relative deviation between the theoretical values and the experimental data was less than 5%. The frequency dispersion characteristic of the dielectric parameters of the component as well as the effect of the fillers on the depolarization field of the composite system was fully taken into consideration during the effective permittivity model establishing. Therefore the proposed effective permittivity model should be suitable for both low-filling and high-filling concentration systems.

An indirect electrochemical impedance spectroscopy method, previously applied to corrosion detection in reinforced concrete structures, was explored as a potential nondestructive method for detecting corrosion of steel in post-tensioned tendons used as reinforcing structural elements in segmental bridge construction. A proof of concept is demonstrated by experiments performed on tendons with passive and corroded strands and through finite-element simulations of the indirect impedance response. The numerical simulations, used to explore the influence of non-uniform current distributions on the indirect impedance response, demonstrate how frequency dispersion influences the impedance measurement. Validation of the model is shown through comparison to experimental measurements.

Display Omitted CV frequency dispersion minima explained for graphene MOS capacitors.Apparent flat-band defined for metal-oxide-graphene structure.Temperature dependent frequency dispersion has been observed and explained.Border trap contribution is suppressed at low T and results in more accurate Cox and Cq estimates.Deducing the doping level of graphene with low temperature CV and the apparent flat-band position. A capacitance-voltage (CV) study on large area CVD single layer graphene MOS capacitors has been carried out. The CV features are carefully examined to reveal the electronic origins of the observed frequency and bias dependence. In this study we investigate the frequency dispersion, propose the definition and extraction of the apparent flat-band Vafb, and finally perform the low temperature CV measurement to deduce the doping level of the graphene MOSCAPs.

Atomic-layer-deposited Al 2 O 3 films were grown on ultrathin-body In 0.53 Ga 0.47 As substrates for III-V compound-semiconductor-based devices. Interface sulfur (S) passivation was performed with wet processing using ammonium sulfide ((NH 4 ) 2 S) solution, and dry processing using post-deposition annealing (PDA) under a H 2 S atmosphere. The PDA under the H 2 S atmosphere resulted in a lower S concentration at the interface and a thicker interfacial layer than the case with (NH 4 ) 2 S wet-treatment. The electrical properties of the device, including the interface property estimated through frequency dispersion in capacitance, were better for (NH 4 ) 2 S wet-treatment than the PDA under a H 2 S atmosphere. They might be improved, however, by optimizing the process conditions of PDA. The PDA under a H 2 S atmosphere following (NH 4 ) 2 S wet-treatment resulted in an increased S concentration at the interface, which improved the electrical properties of the devices.

© 2019 Elsevier B.V. Large landslide-tsunamis are caused by mass movements such as landslides or rock falls impacting into a water body. Research of these phenomena is essentially based on the two idealised water body geometries (i) wave flume (2D, laterally confined wave propagation) and (ii) wave basin (3D, unconfined wave propagation). The wave height in 2D and 3D differs by over one order of magnitude in the far field. Further, the wave characteristics in intermediate geometries are currently not well understood. This article focuses on numerical landslide-tsunami propagation in the far field to quantify the effect of the water body geometry. The hydrodynamic numerical model SWASH, based on the non-hydrostatic non-linear shallow water equations, was used to simulate approximate linear, Stokes, cnoidal and solitary waves in 6 different idealised water body geometries. This includes 2D, 3D as well as intermediate geometries consisting of “channels” with diverging side walls. The wavefront length was found to be an excellent parameter to correlate the wave decay along the slide axis in all these geometries in agreement with Green's law and with diffraction theory in 3D. Semi-theoretical equations to predict the wave magnitude of the idealised waves at any desired point of the water bodies are also presented. Further, simulations of experimental landslide-tsunami time series were performed in 2D to quantify the effect of frequency dispersion. This process may be negligible for solitary- and cnoidal-like waves for initial landslide-tsunami hazard assessment but becomes more important for Stokes-like waves in deeper water. The findings herein significantly improve the reliability of initial landslide-tsunami hazard assessment in water body geometries between 2D and 3D, as demonstrated with the 2014 landslide-tsunami event in Lake Askja.

Ti3SiC2 powders are synthesized via vacuum pressureless sintering method. The dielectric properties of the powders synthesized at different temperature are investigated in the frequency range from 8.2 to 12.4 GHz (X-band), which suggests the remnant TiC has obvious influence on complex permittivity and the pure Ti3SiC2 powders have the highest dielectric loss. The dielectric and microwave absorption properties of Ti3SiC2 powders are studied. Both the real part (e′) and imaginary part (e″) increase with Ti3SiC2 concentration but decrease with increasing frequency, which presents the obvious frequency dispersion effect. Furthermore, the effect of thickness on the microwave absorption property of Ti3SiC2/paraffin mixture is analyzed. The mixture with 70 wt% Ti3SiC2 in 2.0 mm thickness presents the optimum microwave absorption property. The effective absorbing bandwidth (below −10 dB) is almost in the whole frequency range and the lowest reflection loss is −33.83 dB. The results show Ti3SiC2 powders are good microwave absorbents in the X-band frequency range.

The features of surface wave modes in the fiber composed of single-negative (SNG) metamaterials have been investigated. The geometric and frequency dispersion of surface wave modes in SNG fibers are considered. The dispersion curves, energy flux and power of lower-order ( m =0,1) surface wave modes are presented. Some interesting properties, such as totally backward or forward wave, zero power, sign-varying energy flux in the core or cladding region, single mode operation, are found.

In this paper, an improved small-signal equivalent model is introduced to eliminate frequency dispersion phenomenon in capacitance–voltage (C–V) measurement, and a new mathematic method is proposed to calculate the amount of bulk defect existing in the GaN buffer layer. Compared with photoluminescence (PL) and high resolution X-ray diffraction (HRXRD) data, it is identified that the main component of the bulk defect concentration is made up of the point defect concentration, rather than the edge dislocation concentration. All these results prove the accuracy of the improved C–V model and feasibility of the mathematic model.

Using the obtained kinetic equations for one-particle f 1 x → 1 , t and two-particle f 2 x → 1 , x → 2 , t distribution functions the frequency dispersion of shear ηS(ω) and bulk ηV(ω) viscosity coefficients of simple liquids are studied. The numerical calculations of the coefficients ηS(ω) and ηV(ω) for liquid Ar, Kr, Xe have been performed for definite potential of intermolecular interaction Φ r → and radial distribution function g r → in broad temperature T, density ρ, and frequency ω ranges. The obtained results of theoretical calculations of viscosity coefficients of these liquids are in good agreements with the existed experimental data.

In this study, we present novel method for improvement of immunity on MeV electron radiation of MOS structures by means of ultra-shallow fluorine implantation from r.f. CF4 plasma. For the purposes of comparison of electrical behavior, MOS capacitors were manufactured. One MeV electron radiation on fabricated MOS devices, was adopted. Obtained results have shown that fluorination of silicon surface results in significant decrease of leakage current as well as uniform distribution of breakdown voltage values. Moreover, capacitance–voltage measurements of MOS structures after fluorine implantation exhibit no frequency dispersion in comparison to reference structures. Presented results demonstrated feasibility of application of ultra-shallow fluorine implantation from r.f. CF4 plasma in technology for radiation-hard silicon devices.

In this paper, a modified leap-frog finite difference (FD) scheme is developed to solve Non linear Shallow Water Equations (NSWE). By adjusting the FD mesh system and modifying the leap-frog algorithm, numerical dispersion is manipulated to mimic physical frequency dispersion for water wave propagation. The resulting numerical scheme is suitable for weakly nonlinear and weakly dispersive waves propagating over a slowly varying water depth. Numerical studies demonstrate that the results of the new numerical scheme agree well with those obtained by directly solving Boussinesq-type models for both long distance propagation, shoaling and re-fraction over a slowly varying bathymetry. Most importantly, the new algorithm is much more computationally efficient than existing Boussinesq-type models, making it an excellent alternative tool for simulating tsunami waves when the frequency dispersion needs to be considered.

We present a depth integrated numerical model for the simulation of the generation and the propagation of tsunamis generated by submerged landslides. The model is able to reproduce at low computational costs the full frequency dispersion of the waves and uses an ad hoc treatment for the incorporation of the effects of the moving seafloor to reproduce the generation of the waves. We also compare the present approach with some simplified techniques used in the past for the generation of these waves in depth integrated models, and we highlight the different behavior of frequency-dispersive and non-dispersive model equations. Reference solutions for comparison and discussion are obtained from the application of a three dimensional solver of the Laplace equation. All the numerical models used in this research are based on linearized model equations and boundary conditions and are therefore expected to provide reliable results for problems involving small amplitude waves and small thickness landslides. The model seems to be useful for rapid and accurate estimation of the properties of landslide generated waves, and can be used to support a tsunami early warning system. (C) 2009 Elsevier Ltd. All rights reserved.

The chopping SiC f /LAS composites were prepared by the hot-pressing method. The effects of hot-pressing time and pressures on the microstructures and the dielectric properties of the composites were researched. Compared with the LAS matrix and the SiC fibre, the results of dielectric constant testing in the range of 8-12 GHz indicate that the dielectric constant real part, imaginary part and dielectric dissipation of all samples increase by 1-3 orders of magnitude, and show obvious frequency dispersion effect. Their real parts increase while their imaginary parts and dielectric dissipations decline with the increase of the hot-pressing time or pressures. The SEM fractographs show that the composite interfacial films between the fibre and the matrix are thickened with the increase of the hot-pressing time or pressures.

A comprehensive model to accurately and simply describe the trapping property and its influence on device frequency characteristics is proposed for SiC MESFET. DC performance is simulated and trap parameters are extracted. Both positive and negative frequency dispersions of transconductance are simulated and analyzed with deep level traps and self-heating effects. Good agreements with reported results are obtained.

Dielectric relaxations of Tb 0.91 Yb 1.38 Bi 0.71 Fe 5 O 12 ceramics were investigated. A Debye-type relaxation was observed in the temperature range of 125–620 K with an activation energy of 0.29 eV. This activation energy agreed well with that of carriers hopping between Fe 2+ and Fe 3+ , indicating that this relaxation might be a dipolar-type relaxation associated with the hopping carries. A high relaxorlike dielectric peak with a very strong frequency dispersion in the high temperature range of 400–620 K might be originate from the oxygen vacancies related dielectric relaxation.

Curie temperature, initial permeability and resistivity of MnZn ferrites with Fe-poor composition (less than 50 mol% of Fe2O3) are studied. The experience formula of Curie temperature for MnZn ferrites with Fe-rich composition is modified to calculate the Curie temperature of Fe-poor MnZn ferrites. Tri-segment frequency dispersion model, which consists of domain wall motion, magnetization rotation and gyro-magnetic spin rotation, is used to simulate the permeability spectra of ferrites. The permeability of Fe-poor MnZn ferrites compares with that of Fe-rich MnZn ferrites in low frequency region, and it is still high enough to compare with that of NiZn ferrites in high frequency region. The resistivity of Fe-poor MnZn ferrites is about 103 Ω m, much higher than that of Fe-rich MnZn ferrites.

The present study characterized involuntary movements associated with levodopa-induced dyskinesias (LID) in patients with Parkinson's disease. We used amplitude, proportional energy, frequency dispersion and sample entropy to determine whether LID movement patterns are truly random, as clinical description seems to suggest, or possess some underlying pattern that is not visible to the naked eye. LID was captured using a magnetic tracker system, which provided 3D rendering of whole-body LID. Patients were instructed to maintain a standing position, with arms extended in front of them. We compared the measurements of the dyskinetic PD group (DPD) with 10 patients without dyskinesias (NDPD) and 10 control subjects. In comparison to the other two groups, movement patterns from the DPD group had significantly higher amplitude, confirming the presence of dyskinesias. In addition, higher frequency components in the power spectrum of velocity were detected, suggestive of higher velocity in LID movement. Furthermore, there was a concentration in narrow frequency bands, which suggested stable oscillatory activity. Finally, sample entropy revealed more regularity in the DPD group. Although not statistically significant, we found that the amplitude from the NDPD group had a tendency to be smaller than those of controls. As well, the spectra were often more dispersed for the NDPD group. In conclusion, the present results suggest that LID cannot be considered as purely random movement since they possess some deterministic pattern of motion. This may provide a way for patients to adapt to these involuntary movements while performing voluntary motor acts.

The commonly encountered frequency dispersion and distorted behavior of GaAs and III-V MOS C-V and G-V is clarified by using MOS interface state theory. The relation of the C-V behavior with Fermi-level pinning of III-V MOS is explained. It is shown why it is difficult to quantify the interface state density using the conductance method for III-V MOS. A qualitative distinction of interface state behavior from common frequency dispersion due to series resistance is also put forward and guidelines are given to properly interpret III-V admittance data.

The linear polarizabilities and first hyperpolarizabilities of two geometrical isomers (Z, E) of donor–acceptor azo-enaminones have been calculated, taking into account frequency dispersion effects, through CPHF method. Static results were also obtained at the MP2 level and correlated dynamic values were estimated using the multiplicative correction scheme. Our results show that the diagonal component of the first hypepolarizability of E isomers is enhanced with increasing donor strength. Dispersion effects have a marked influence for the standard frequencies considered here (ω = 0.0239 and 0.0428 a.u), specially for second harmonic generation.

The effects of the external d.c. and a.c. electric field on the dielectric response and relaxor behaviour of lead–barium–zirconate–titanate (PBZT) ceramics of the composition Ba/Zr/Ti 25/70/30 have been studied. The significant influence of the strength of the d.c. bias field and the amplitude of the a.c. field on the dielectric constant maximum and frequency dispersion was determined. The magnitude of the dielectric response strongly decreases under the bias field and increases with the increase of the a.c. field amplitude. All parameters describing the relaxor behaviour of the studied ceramics changed under the external d.c. and a.c. electric field. The experimental results can be explained in terms of existing models of relaxors.

The supersonic complex-velocity versus real-frequency dispersion spectrum of the leaky waves in fluid-loaded anisotropic plates is discussed. Utilizing the sextic plate formalism provides approximate solutions for leaky-wave velocity in a form that reveals their basic features, such as the unique correspondence of the signs of its imaginary part and of the free-plate group velocity, the relation between the leakage and the rate of frequency dispersion, and the principal trends at low, high and near-cutoff frequencies in arbitrary anisotropic plates. A particular thrust of the study is the derivation of closed-form asymptotics for the fundamental leaky-wave velocity branch(es) at low frequency and for the continuum of leaky-wave branches near the fluid-coupled and fluid-uncoupled thickness resonances. Conditions for the asymptotics accuracy are analysed, and a comparison between an analytical approximation and exact numerical curves is presented for various cases.

We selected descriptive measures of the centre of pressure (CoP) displacement in quiet standing, by means of a procedure based on principal component analysis, in two groups particularly different in terms of postural behaviours, such as subjects with Parkinson's disease (PD) in the levodopa off and on states. We computed 14 measures of the CoP: 5 measures of CoP trajectory over the support surface, 3 measures that estimated the area covered by the CoP, 1 measure that estimated the principal CoP sway direction, 1 measure that quantified the CoP total power, 1 measure that estimated the variability of CoP frequency content and 3 measures of characteristic CoP frequencies [L. Rocchi, L. Chiari, A. Cappello, Feature selection of stabilometric parameters based on principal component analysis, Med. Biol. Eng. Comput. 42 (2004) 71-79; L. Rocchi, L. Chiari, F.B. Horak, Effects of deep brain stimulation and levodopa on postural sway in Parkinson's disease, J. Neurol. Neurosurg. Psychiatry, 73 (2002) 267-274]. The feature selection, independently applied to the measures obtained in the two groups, resulted in different principal component (PC) subspaces of the 14-dimension original data set (4 PCs in the off and 3 PCs in the on state to account for over 90% of the original variance), but in the same 5 CoP measures (selected features) needed to describe the different postural behaviours: root mean square distance; mean velocity; principal sway direction; centroidal frequency of the power spectrum; frequency dispersion. The five selected features were found to provide insight into the postural control mechanisms and to describe changes in postural strategies in the two groups of PD subjects, off and on levodopa. Thus, the five selected features may be recommended for use in clinical practice and in research, in the direction toward the definition of a standard protocol in quantitative posturography.

We investigated the asymmetry of tremor intensity, frequency and frequency dispersion of Parkinsonian (PT) and essential (ET) tremor using accelerometry. Data of the more and less trembling hands were statistically elaborated. We found that tremor intensity was significantly asymmetric not only in PT but also in ET, while frequency and frequency dispersion were symmetric in ET but asymmetric in PT. We conclude that bilateral assessment of frequency related tremor parameters may be used for differentiation between ET and PT, and provides further details on the central organization of tremor generators.

The structure and dielectric behaviors of compositions near the morphotropic phase boundary (MPB) of (1 − x)Pb(Zn0.2Ni0.8)1/3Nb2/3O3−xPbTiO3 ceramics have been systematically investigated as a function of PbTiO3 (PT) content. XRD experiments demonstrate that compositions with x = 0.26–0.38 lie in the MPB region of this ternary system. Dielectric behaviors of frequency dispersion and diffuse phase transition are gradually weakened with increasing PT content. Composition with x = 0.30 exhibits the maximum dielectric constant of about 24,500 at 1 kHz. Compared with Pb(Ni1/3Nb2/3)O3–PbTiO3 system, the addition of Pb(Zn1/3Nb2/3)O3 in this study brings about the enlargement of the MPB region, the increase in the Curie temperature and the improvement of dielectric properties.

In this paper, static measurements and defect analysis performed on InAlAs/InGaAs/InP HFETs are presented. I d – V ds – T , I d – V gs – T and I g – V gs – T characteristics show anomalies (leakage current, degradation in saturation current, kink effect, distortions on I d – V d characteristics in saturation region after high voltage application, …). Deep defects analysis performed by means of capacitance transient spectroscopy (C-DLTS) and frequency dispersion of the output conductance ( G ds ( f )) prove the presence of deep defects with activation energies ranging from 0.12 to 0.75 eV. The presence of generation–recombination centers, acting like traps, is confirmed by I g – V gs . The localization and the identification of these defects are presented. Finally, the correlation between the anomalies observed on output characteristics and defects is discussed.

The aim of this study was to compare two tests for tremor/fine motor control as regards their sensitivity in relation to effects on tremor of exposure to manganese and cigarette smoke. One hundred manganese-exposed workers were compared with 100 age-matched referents. The subjects were tested with the Klove–Matthews static steadiness test (hole tremormeter) and the DPD TREMOR (accelerometer). The manganese-exposed subjects showed increased postural tremor compared to the referents. The tremor had a larger frequency dispersion among the exposed subjects than among the referents as assessed by the TREMOR 7.0 test system, indicating that the tremor had a pattern where the power was burned at a wider spectre of frequencies among the exposed subjects than among the referents. The two tests differed in their ability to demonstrate tremor, depending of the type of exposure (manganese or cigarette smoke). The static steadiness test was better than the TREMOR at discriminating between manganese-exposed subjects and referents while the TREMOR was better at discriminating between smokers and non-smokers than the static steadiness test. The tests also differed in their ability to demonstrate tremor depending on the frequency of tremor. The Tremor Intensity I was higher for subjects with higher tremor frequency, while no such effect was found for the static steadiness test parameters. When studying the effects of exposures where the quality of the tremor is unknown, it is suggested to include at least two tremor tests, one based on acceleration and the other on displacement.

Transconductance frequency dispersion measurements were performed on fully implanted MESFETs made on bulk semi-insulating 4H-SiC to observe bulk, as well as surface, traps in the channel region. A 30% reduction in the transconductance was observed by increasing the frequencies from 0.1 Hz to 10 MHz. Five traps were recorded in this study. Bulk traps observed at 0.52 and 0.65 eV in the gated channel region, which were also seen in the capacitance-DLTS study, are believed to be due to the nitrogen implant-defect complex and vanadium deep donor dopant, respectively. Surface traps of the ungated channel region between the source and gate and gate and drain were observed at 0.18, 0.3 and 0.4 eV. The trap at 0.4 eV has shown an upward transconductance dispersion behavior with increasing frequency, whereas all the remaining four traps have shown a downward frequency dispersion behavior. The origins of the surface traps are not known at this time.

The effects of DC bias fields on the dielectric properties of Ba(Ti1−xZrx)O3 (BTZ) ceramics were investigated. BTZ ceramics exhibited fine DC bias properties. Frequency dispersion and diffusion phase transition were found in BTZ ceramics, whereas the temperature Tm which corresponding to the maximum dielectric constant showed little dependence on the testing frequency. The dielectric constant increased at first and then decreased with the increase of DC bias at the temperature Tm. At temperatures far from Tm the dielectric constant showed a continuous decreasing tendency. The dielectric loss of the ceramics was small and decreased with increasing DC bias at room temperature. The related mechanism was also discussed.

Phase transition and dielectric properties of La-doped Pb(Zr,Sn,Ti)O3 antiferroelectric ceramics under hydrostatic pressure have been studied, and effects of temperature on the pressure-induced phase transition and the dielectric property dependence on the applied hydrostatic pressure have been investigated. The ferroelectric–antiferroelectric phase transition pressure is decreased with increasing temperature, these phenomena are helpful for understanding of the behaviors of pressure-induced dielectric frequency dispersion and diffuse phase transition.

Oxygen ion implantation has been employed, for the first time, to form the high-resistance layer in the surface of GaAs MESFETs. Comparable DC and RF performance were achieved for MESFETs with and without oxygen ion implantation; however, MESFETs with the extra surface oxygen ion implantation demonstrated good breakdown performance, less frequency dispersion of drain current, and good time dependence of drain current at 150 °C in air. This enhancement is a result of the lower surface trapping effects resulting form a high-resistance layer by oxygen ion implantation. This approach relaxes the surface passivation problem in a standard GaAs MESFET.

An ab initio calculation has been performed to study the hyperpolarizabilities of substituted octupolar triazines in the frame of a tensorial formalism. Electron correlation, solvent effect and frequency dispersion have also been explored. It is found that the impact of electron correlation is very important on the hyperpolarizabilities. Solvent effects on the β values are significant and about the same at various approximation (HF, MP2, MP3, and MP4) levels. Dispersion effects are also important on the hyperpolarizabilities. Considered these effects, the calculated values are in agreement with the experimental results.

The propagation of electromagnetic waves through a spherical multilayered stack is numerically studied. We assume that layers in the stack have an essential frequency dispersion of the dielectric permittivity. Our calculations show that in such a structure the electromagnetic field is almost completely confined to the layered spherical substrate.

The Lagrange approach to the theory of thermal hydrodynamic fluctuations is developed. The rotational motion of a Lagrange particle is studied in detail. The apparent expression for the angular velocity autocorrelation function (AVACF) at arbitrary times is derived. The obtained results are used to explain the specificity of the behaviour of the AVACF for a molecule. The collective contribution to the rotational self-diffusion coefficient as well as the manifestation of collective effects in the frequency dispersion of the dielectric permittivity are discussed. The peculiarities of the AVACF for two-dimensional liquids are considered.

A new lead-free relaxor ceramic FeNbTiO6 was first synthesized following a multicalcination procedure. The ferroelectric relaxor behavior and dielectric properties of FeNbTiO6 sample were systemically investigated. XRD patterns show that the material exhibits a single-phase with tetragonal rutile structure. Diffuse phase transition and frequency dispersion of the dielectric constant, which are two typical characteristics for relaxor ferroelectrics, are observed in FeNbTiO6 ceramic. Dielectric relaxor behavior obeys a modified the Curie–Weiss law. A remarkably good fit to the Vogel–Fulcher relation further supports such a relaxor nature. The results show that the FeNbTiO6 ceramic is one of the promising lead-free candidate relaxor ferroelectrics for high-temperature applications.

Frequency dispersion of second hyperpolarizability of furan homologues is calculated by the time-dependent Hartree–Fock (TDHF) method. Using the calculated results, the most reliable theoretical values for the second hyperpolarizability are estimated including both effects of electron correlation and frequency dispersion with the comparison of several approximation methods. The estimated values are compared with the observed values measured by the optical Kerr effect (OKE) method. It is found that by inclusion of the effect of frequency dispersion the calculated results approach more closely to the observed values especially for the molecules with heavier hetero atoms like thiophene, selenophene or tellurophene.

Due to very weak screening in nanowires, their conductivity is very sensitive to contact geometry and any wire inhomogeneities. For different geometry of Ohmic contacts, the current–voltage characteristics and frequency dispersion of wire conductivity are calculated for uniform wires and wires with different kinds of inhomogeneities. The effects of Coulomb blockade in nanowires are also discussed.