Yoshiaki Fukuda
2016-03-01
Full Text Available We report on an experimental investigation of spatial frequency responses of anisotropic transmission refractive index gratings formed in holographic polymer dispersed liquid crystals (HPDLCs. We studied two different types of HPDLC materials employing two different monomer systems: one with acrylate monomer capable of radical mediated chain-growth polymerizations and the other with thiol-ene monomer capable of step-growth polymerizations. It was found that the photopolymerization kinetics of the two HPDLC materials could be well explained by the autocatalytic model. We also measured grating-spacing dependences of anisotropic refractive index gratings at a recording wavelength of 532 nm. It was found that the HPDLC material with the thiol-ene monomer gave higher spatial frequency responses than that with the acrylate monomer. Statistical thermodynamic simulation suggested that such a spatial frequency dependence was attributed primarily to a difference in the size of formed liquid crystal droplets due to different photopolymerization mechanisms.
Polarization-controlled anisotropic coding metamaterials at terahertz frequencies
Liu, Shuo; Xu, Quan; Bao, Di; Du, Liangliang; Wan, Xiang; Tang, Wen Xuan; Ouyang, Chunmei; Zhou, Xiao Yang; Yuan, Hao; Ma, Hui Feng; Jiang, Wei Xiang; Han, Jiaguang; Zhang, Weili; Cheng, Qiang
2015-01-01
Metamaterials based on effective media have achieved a lot of unusual physics (e.g. negative refraction and invisibility cloaking) owing to their abilities to tailor the effective medium parameters that do not exist in nature. Recently, coding metamaterials have been suggested to control electromagnetic waves by designing the coding sequences of digital elements '0' and '1', which possess opposite phase responses. Here, we propose the concept of anisotropic coding metamaterial at terahertz frequencies, in which coding behaviors in different directions are dependent on the polarization status of terahertz waves. We experimentally demonstrate an ultrathin and flexible polarization-controlled anisotropic coding metasurface functioning in the terahertz regime using specially- designed coding elements. By encoding the elements with elaborately-designed digital sequences (in both 1 bit and 2 bits), the x- and y-polarized reflected waves can be deflected or diffused independently in three dimensions. The simulated f...
Eastern Frequency Response Study
Miller, N.W.; Shao, M.; Pajic, S.; D' Aquila, R.
2013-05-01
This study was specifically designed to investigate the frequency response of the Eastern Interconnection that results from large loss-of-generation events of the type targeted by the North American Electric Reliability Corp. Standard BAL-003 Frequency Response and Frequency Bias Setting (NERC 2012a), under possible future system conditions with high levels of wind generation.
Frequency Response Analysis Tool
Etingov, Pavel V.; Kosterev, Dmitry; Dai, T.
2014-12-31
Frequency response has received a lot of attention in recent years at the national level, which culminated in the development and approval of North American Electricity Reliability Corporation (NERC) BAL-003-1 Frequency Response and Frequency Bias Setting Reliability Standard. This report is prepared to describe the details of the work conducted by Pacific Northwest National Laboratory (PNNL) in collaboration with the Bonneville Power Administration and Western Electricity Coordinating Council (WECC) Joint Synchronized Information Subcommittee (JSIS) to develop a frequency response analysis tool (FRAT). The document provides the details on the methodology and main features of the FRAT. The tool manages the database of under-frequency events and calculates the frequency response baseline. Frequency response calculations are consistent with frequency response measure (FRM) in NERC BAL-003-1 for an interconnection and balancing authority. The FRAT can use both phasor measurement unit (PMU) data, where available, and supervisory control and data acquisition (SCADA) data. The tool is also capable of automatically generating NERC Frequency Response Survey (FRS) forms required by BAL-003-1 Standard.
Low frequency noise of anisotropic magnetoresistors in DC and AC-excited metal detectors
Magnetoresistors can replace induction sensors in applications like non-destructive testing and metal detection, where high spatial resolution or low frequency response is required. Using an AC excitation field the magnetic response of eddy currents is detected. Although giant magnetoresistive (GMR) sensors have higher measuring range and sensitivity compared to anisotropic magnetoresistors (AMR), they show also higher hysteresis and noise especially at low frequencies. Therefore AMR sensors are chosen to be evaluated in low noise measurements with combined processing of DC and AC excitation field with respect to the arrangement of processing electronics. Circuit with a commercial AMR sensor HMC1001 and AD8429 preamplifier using flipping technique exhibited 1-Hz noise as low as 125 pT/√Hz. Without flipping, the 1-Hz noise increased to 246 pT/√Hz.
Low frequency eigenmodes of thin anisotropic current sheets and Cluster observations
L. M. Zelenyi
2009-02-01
Full Text Available The eigenmodes of low frequency perturbations of thin anisotropic current sheets with a finite value of the normal magnetic field, are investigated in this paper. It is shown that two possible polarizations of symmetric and asymmetric modes (sausage and kink exist where the growth rate of instabilities is positive. In addition, we demonstrate that a tearing instability might have a positive growth rate in thin anisotropic current sheets. The class of relatively fast wavy flapping oscillations observed by Cluster is described. The main direction of wave motion coincides with the direction of the current and the typical velocity of this motion is comparable with the plasma drift velocity in the current sheet. The comparison of these characteristics with theoretical predictions of the model of anisotropic thin current sheets, demonstrates that, in principle, the theory adequately describes the observations.
Modeling the anisotropic shock response of single-crystal RDX
Luscher, Darby
Explosives initiate under impacts whose energy, if distributed homogeneously throughout the material, translates to temperature increases that are insufficient to drive the rapid chemistry observed. Heterogeneous thermomechanical interactions at the meso-scale (i.e. between single-crystal and macroscale) leads to the formation of localized hot spots. Direct numerical simulations of mesoscale response can contribute to our understanding of hot spots if they include the relevant deformation mechanisms that are essential to the nonlinear thermomechanical response of explosive molecular crystals. We have developed a single-crystal model for the finite deformation thermomechanical response of cyclotrimethylene trinitramine (RDX). Because of the low symmetry of RDX, a complete description of nonlinear thermoelasticity requires a careful decomposition of free energy into components that represent the pressure-volume-temperature (PVT) response and the coupling between isochoric deformation and both deviatoric and hydrostatic stresses. An equation-of-state (EOS) based on Debye theory that defines the PVT response was constructed using experimental data and density functional theory calculations. This EOS replicates the equilibrium states of phase transformation from alpha to gamma polymorphs observed in static high-pressure experiments. Lattice thermoelastic parameters defining the coupled isochoric free energy were obtained from molecular dynamics calculations and previous experimental data. Anisotropic crystal plasticity is modeled using Orowan's expression relating slip rate to dislocation density and velocity. Details of the theory will be presented followed by discussion of simulations of flyer plate impact experiments, including recent experiments diagnosed with in situ X-ray diffraction at the Advanced Photon Source. Impact conditions explored within the experimental effort have spanned shock pressures ranging from 1-10 GPa for several crystallographic orientations
Mateos, I; Lobo, A
2016-01-01
A detailed study about magnetic sensing techniques based on anisotropic magnetoresistive sensors shows that the technology is suitable for low-frequency space applications like the eLISA mission. Low noise magnetic measurements at the sub-millihertz frequencies were taken by using different electronic noise reduction techniques in the signal conditioning circuit. We found that conventional modulation techniques reversing the sensor bridge excitation do not reduce the potential $1/f$ noise of the magnetoresistors, so alternative methods such as flipping and electro-magnetic feedback are necessary. In addition, a low-frequency noise analysis of the signal conditioning circuits has been performed in order to identify and minimize the different main contributions from the overall noise. The results for chip-scale magnetoresistances exhibit similar noise along the eLISA bandwidth ($0.1\\,{\\rm mHz}-1\\,{\\rm Hz}$) to the noise measured by means of the voluminous fluxgate magnetometers used in its precursor mission, kn...
High-frequency interaction-induced rototranslational wings of anisotropic nitrogen spectra
The anisotropic rototranslational scattering spectra of nitrogen gas at high frequency up to 700 cm-1 for several temperatures and from low densities are analyzed in terms of new site-site (M3SV) intermolecular potential and interaction-induced pair polarizability models, using quantum spectral shapes computations. Our theoretical calculations take into account multipole contributions from the mean value and anisotropy of the dipole-dipole polarizability tensor α, two independent components of the dipole-octopole polarizability tensor E and dipole-dipole-quadrupole hyperpolarizability tensor B. The high-frequency wings are discussed in terms of the collision-induced rotational Rayleigh effect and estimates for the dipole-octopole polarizability |E 4| are obtained and checked with recent ab initio theoretical value. Good comparison is found in the frequency range 0-400 cm-1 between the theoretical and experimental spectra. When an exponential contribution [exp(-ν/ν 0)] with ν 0 = 425 cm-1 is considered to model very short-range light scattering mechanisms at room temperature, good agreement is found over the whole frequency range
High-frequency interaction-induced rototranslational wings of anisotropic nitrogen spectra
El-Kader, M.S.A. [Department of Engineering Mathematics and Physics, Faculty of Engineering, Giza, 12211 (Egypt)], E-mail: mohamedsayedabdelkader@yahoo.com; Moustafa, S.I. [Department of Engineering Mathematics and Physics, Faculty of Engineering, Giza, 12211 (Egypt)
2005-11-22
The anisotropic rototranslational scattering spectra of nitrogen gas at high frequency up to 700 cm{sup -1} for several temperatures and from low densities are analyzed in terms of new site-site (M3SV) intermolecular potential and interaction-induced pair polarizability models, using quantum spectral shapes computations. Our theoretical calculations take into account multipole contributions from the mean value and anisotropy of the dipole-dipole polarizability tensor {alpha}, two independent components of the dipole-octopole polarizability tensor E and dipole-dipole-quadrupole hyperpolarizability tensor B. The high-frequency wings are discussed in terms of the collision-induced rotational Rayleigh effect and estimates for the dipole-octopole polarizability |E {sub 4}| are obtained and checked with recent ab initio theoretical value. Good comparison is found in the frequency range 0-400 cm{sup -1} between the theoretical and experimental spectra. When an exponential contribution [exp(-{nu}/{nu} {sub 0})] with {nu} {sub 0} = 425 cm{sup -1} is considered to model very short-range light scattering mechanisms at room temperature, good agreement is found over the whole frequency range.
Guo, Hairun; Zeng, Xianglong; Zhou, Binbin;
2013-01-01
further simulations we demonstrate few-cycle compressed solitons in extremely short crystals, where spectral phenomena, such as blue/red shifting, nonstationary radiation in accordance with the nonlocal phase-matching condition, and dispersive-wave generation are observed and marked, which helps improve......We interpret the purely spectral forward Maxwell equation with up to third-order induced polarizations for pulse propagation and interactions in quadratic nonlinear crystals. The interpreted equation, also named the nonlinear wave equation in the frequency domain, includes quadratic and cubic...... nonlinearities, delayed Raman effects, and anisotropic nonlinearities. The full potential of this wave equation is demonstrated by investigating simulations of solitons generated in the process of ultrafast cascaded second-harmonic generation. We show that a balance in the soliton delay can be achieved due to...
Yang, Chengliang; Wu, Qiang; Xu, Jingjun; Nelson, Keith A; Werley, Christopher A
2010-12-01
Femtosecond optical pulses were used to generate THz-frequency phonon polariton waves in a 50 micrometer lithium niobate slab, which acts as a subwavelength, anisotropic planar waveguide. The spatial and temporal electric field profiles of the THz waves were recorded for different propagation directions using a polarization gating imaging system, and experimental dispersion curves were determined via a two-dimensional Fourier transform. Dispersion relations for an anisotropic slab waveguide were derived via analytical analysis and found to be in excellent agreement with all observed experimental modes. From the dispersion relations, we analyze the propagation-direction-dependent behavior, effective refractive index values, and generation efficiencies for THz-frequency modes in the subwavelength, anisotropic slab waveguide. PMID:21164986
Enhanced high-frequency absorption of anisotropic Fe3O4/graphene nanocomposites
Yin, Yichao; Zeng, Min; Liu, Jue; Tang, Wukui; Dong, Hangrong; Xia, Ruozhou; Yu, Ronghai
2016-05-01
Anisotropic Fe3O4 nanoparticle and a series of its graphene composites have been successfully prepared as high-frequency absorbers. The crystal structure, morphology and magnetic property of the samples were detailed characterized through X-ray diffractometer (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The high-frequency absorbing performance of the composites is evaluated within 2.0–18.0 GHz. Combining reduced graphene oxide (RGO) to Fe3O4 helps to adjust the permittivity and permeability of the composite, balance the dielectric loss and magnetic loss, consequently improve the absorbing performance in view of the impedance matching characteristic. The optimal reflection loss of the pure Fe3O4 sample reaches ‑38.1 dB with a thickness of 1.7 mm, and it increases to ‑65.1 dB for the sample grafted with 3 wt.% RGO. The addition of proper content of RGO both improves the reflection loss and expands the absorbing bandwidth. This work not only opens a new method and an idea for tuning the electromagnetic properties and enhancing the capacity of high-efficient absorbers, but also broadens the application of such kinds of lightweight absorbing materials frameworks.
Enhanced high-frequency absorption of anisotropic Fe3O4/graphene nanocomposites
Yin, Yichao; Zeng, Min; Liu, Jue; Tang, Wukui; Dong, Hangrong; Xia, Ruozhou; Yu, Ronghai
2016-01-01
Anisotropic Fe3O4 nanoparticle and a series of its graphene composites have been successfully prepared as high-frequency absorbers. The crystal structure, morphology and magnetic property of the samples were detailed characterized through X-ray diffractometer (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The high-frequency absorbing performance of the composites is evaluated within 2.0–18.0 GHz. Combining reduced graphene oxide (RGO) to Fe3O4 helps to adjust the permittivity and permeability of the composite, balance the dielectric loss and magnetic loss, consequently improve the absorbing performance in view of the impedance matching characteristic. The optimal reflection loss of the pure Fe3O4 sample reaches −38.1 dB with a thickness of 1.7 mm, and it increases to −65.1 dB for the sample grafted with 3 wt.% RGO. The addition of proper content of RGO both improves the reflection loss and expands the absorbing bandwidth. This work not only opens a new method and an idea for tuning the electromagnetic properties and enhancing the capacity of high-efficient absorbers, but also broadens the application of such kinds of lightweight absorbing materials frameworks. PMID:27142260
Shock Compression of Beryllium Single Crystals: Time-Dependent, Anisotropic Elastic-Plastic Response
Winey, J.; Gupta, Y.
2013-06-01
To gain insight into inelastic deformation mechanisms in shocked Be single crystals, wave propagation simulations were performed for crystals shocked along the c-axis, a-axis, and other crystal directions to peak stresses reaching 7 GPa. The simulations utilized a time-dependent, anisotropic material model that incorporated dislocation dynamics and deformation twinning based descriptions of inelastic deformation. The simulation results showed good qualitative agreement with the measured wave profiles, including features arising from wave mode coupling due to the highly anisotropic inelastic response of Be. The measured wave profiles can be understood in terms of dislocation slip along basal, prismatic, and pyramidal planes, together with deformation twinning. Our results provide insight into the complex nature of inelastic deformation in shocked Be, and are also expected to be valuable for understanding the anisotropic inelastic response of analogous hcp metals subjected to shock compression. Work supported by ARL and DOE/NNSA.
Microwave response of anisotropic high-temperature-superconductor crystals
Gough, C. E.; Exon, N. J.
1994-07-01
Microwave penetration and losses are derived for the anisotropic normal and superconducting states of single crystals in the shape of thin platelets oriented parallel and perpendicular to the oscillating electromagnetic field. For platelet crystals with the microwave field parallel to the major flat faces, the large anisotropy in the normal state can result in dissipation dominated by microwave field penetration through the thin edges rather than across the main faces. The influence of the extreme anisotropy is also considered for the superconducting state and can account for an anomalous peak in microwave loss below Tc sometimes observed in Bi-Sr-Ca-Cu-O crystals. When crystals are mounted with their flat faces perpendicular to the microwave field, the losses in both the normal and superconducting states are shown to be strongly peaked towards the outer perimeter of the crystals. This makes critical demands on the degree of perfection of such regions, if the microwave measurements are not to be complicated by nonintrinsic effects associated with local imperfections.
Tian, Yuan; Han, Yiping, E-mail: yphan@xidian.edu.cn [School of Physics and Optoelectronic Engineering, Xidian University, Xi' an 710071 (China); Ai, Xia [National Key Laboratory of Science and Technology on Test physics and Numerical Mathematical, Beijing 100076 (China); Liu, Xiuxiang [Science and Technology on Space Physics Laboratory, Beijing 100076 (China)
2014-12-15
In this paper, we investigate the propagation of terahertz (THz) electromagnetic wave in an anisotropic magnetized plasma by JE convolution-finite difference time domain method. The anisotropic characteristic of the plasma, which leads to right-hand circularly polarized (RCP) and right-hand circularly polarized (LCP) waves, has been taken into account. The interaction between electromagnetic waves and magnetized plasma is illustrated by reflection and transmission coefficients for both RCP and LCP THz waves. The effects of both the magnetized plasma thickness and the external magnetized field are analyzed and numerical results demonstrate that the two factors could influence the THz wave greatly. It is worthy to note that besides the reflection and transmission coefficients in the frequency domain, the waveform of the electric field in the time domain varying with thicknesses and external magnetic fields for different polarized direction has been studied.
Viscoelastic response of anisotropic biological membranes. Part II: Constitutive models
Lubarda Vlado A.
2014-01-01
Full Text Available In Part I of this series [7] we described the structure of the biopolymer interlayers found in the shell of the mollusk Haliotis rufescens (the red abalone. There we described how the layers can be viewed as a viscoelastic composite reinforced by a network of chitin fibrils arranged in an often nearly unidirectional architecture. Mechanical testing documented the response to tensile testing of layers removed via demineralization. Herein in Part II we describe a general viscoelastic constitutive model for such layers that may be both transversely isotropic or orthotropic as would follow from the network of nearly aligned chitin fibrils described by Bezares et al. in Part I [7]. Part III of this series will be concerned with applying the models to more fully describing the response of these types of biological membranes to mechanical loading.
Stoimenov, Boyko L.; Rossiter, Jonathan M.; Mukai, Toshiharu
2007-01-01
Demands from the fields of bio-medical engineering and biologically-inspired robotics motivate a growing interest in actuators with properties similar to biological muscle, including ionic polymer-metal composites (IPMC), the focus of this study. IPMC actuators consist of an ion-conductive polymer membrane, coated with thin metal electrodes on both sides and bend when voltage is applied. Some of the advantages of IPMC actuators are their softness, lack of moving parts, easy miniaturization, light weight and low actuation voltage. When used in bio-mimetic robotic applications, such as a snake-like swimming robot, locomotion speed can be improved by increasing the bending amplitude. However, it cannot be improved much by increasing the driving voltage, because of water electrolysis. To enhance the bending response of IPMCs we created a "preferred" bending direction by anisotropic surface modification. Introduction of anisotropic roughness with grooves across the length of the actuator improved the bending response by a factor of 2.1. Artificially introduced cracks on the electrodes in direction, in which natural cracks form by bending, improved bending response by a factor of 1.6. Anisotropic surface modification is an effective method to enhance the bending response of IPMC actuators and does not compromise their rigidity under loads perpendicular to the bending plane.
Djebbi, Ramzi
2013-08-19
Anisotropy is an inherent character of the Earth subsurface. It should be considered for modeling and inversion. The acoustic VTI wave equation approximates the wave behavior in anisotropic media, and especially it\\'s kinematic characteristics. To analyze which parts of the model would affect the traveltime for anisotropic traveltime inversion methods, especially for wave equation tomography (WET), we drive the sensitivity kernels for anisotropic media using the VTI acoustic wave equation. A Born scattering approximation is first derived using the Fourier domain acoustic wave equation as a function of perturbations in three anisotropy parameters. Using the instantaneous traveltime, which unwraps the phase, we compute the kernels. These kernels resemble those for isotropic media, with the η kernel directionally dependent. They also have a maximum sensitivity along the geometrical ray, which is more realistic compared to the cross-correlation based kernels. Focusing on diving waves, which is used more often, especially recently in waveform inversion, we show sensitivity kernels in anisotropic media for this case.
Golykh, R. N.
2016-06-01
Progress of technology and medicine dictates the ever-increasing requirements (heat resistance, corrosion resistance, strength properties, impregnating ability, etc.) for non-Newtonian fluids and materials produced on their basis (epoxy resin, coating materials, liquid crystals, etc.). Materials with improved properties obtaining is possible by modification of their physicochemical structure. One of the most promising approaches to the restructuring of non-Newtonian fluids is cavitation generated by high-frequency acoustic vibrations. The efficiency of cavitation in non-Newtonian fluid is determined by dynamics of gaseous bubble. Today, bubble dynamics in isotropic non-Newtonian fluids, in which cavitation bubble shape remains spherical, is most full investigated, because the problem reduces to ordinary differential equation for spherical bubble radius. However, gaseous bubble in anisotropic fluids which are most wide kind of non-Newtonian fluids (due to orientation of macromolecules) deviates from spherical shape due to viscosity dependence on shear rate direction. Therefore, the paper presents the mathematical model of gaseous bubble dynamics in anisotropic non-Newtonian fluids. The model is based on general equations for anisotropic non-Newtonian fluid flow. The equations are solved by asymptotic decomposition of fluid flow parameters. It allowed evaluating bubble size and shape evolution depending on rheological properties of liquid and acoustic field characteristics.
Neutron imaging using the anisotropic response of crystalline organic scintillators
An anisotropy in a scintillator's response to neutron elastic scattering interactions can in principle be used to gather directional information about a neutron source using interactions in a single detector. In crystalline organic scintillators, such as anthracene, both the amplitude and the time structure of the scintillation light pulse vary with the direction of the proton recoil with respect to the crystalline axes. Therefore, we have investigated the exploitation of this effect to enable compact, high-efficiency fast neutron detectors that have directional sensitivity via a precise measurement of the pulse shape. We report measurements of the pulse height and shape dependence on proton recoil angle in anthracene, stilbene, p-terphenyl, diphenyl anthracene (DPA), and tetraphenyl butadiene (TPB). Image reconstruction for simulated neutron sources is demonstrated using maximum likelihood methods for optimal directional sensitivity.
Slot Machine Response Frequency Predicts Pathological Gambling
Linnet, Jakob; Rømer Thomsen, Kristine; Møller, Arne;
2013-01-01
Slot machines are among the most addictive forms of gambling, and pathological gambling slot machine players represent the largest group of treatment seekers, accounting for 35% to 93% of the population. Pathological gambling sufferers have significantly higher response frequency (games / time) on...... slot machines compared with non-problem gamblers, which may suggest increased reinforcement of the gambling behavior in pathological gambling. However, to date it is unknown whether or not the increased response frequency in pathological gambling is associated with symptom severity of the disorder....... This study tested the hypothesis that response frequency is associated with symptom severity in pathological gambling. We tested response frequency among twenty-two pathological gambling sufferers and twenty-one non-problem gamblers on a commercially available slot machine, and screened for...
Frequency response of slow beam extraction process
A servo control system has been incorporated into the practical slow extraction system in order to stabilize the spill structure less than a few kHz. Frequency responses of the components of the servo-spill control system and the open-loop frequency response were measured. The beam transfer function of the slow extraction process was derived from the measured data and approximated using a simple function. This is utilized to improve the performance of the servo-loop. (author)
Humeida, Yousif; Pinfield, Valerie J.; Challis, Richard E.
2013-08-01
Ultrasonic arrays have seen increasing use for the characterisation of composite materials. In this paper, ultrasonic wave propagation in multilayer anisotropic materials has been modelled using plane wave and angular spectrum decomposition techniques. Different matrix techniques, such as the stiffness matrix method and the transfer matrix method, are used to calculate the reflection and transmission coefficients of ultrasonic plane waves in the considered media. Then, an angular decomposition technique is used to derive the bounded beams from finite-width ultrasonic array elements from the plane wave responses calculated earlier. This model is considered to be an analytical exact solution for the problem; hence the diffraction of waves in such composite materials can be calculated for different incident angles for a very wide range of frequencies. This model is validated against experimental measurements using the Full-Matrix Capture (FMC) of array data in both a homogeneous isotropic material, i.e. aluminium, and an inhomogeneous multilayer anisotropic material, i.e. a carbon fibre reinforced composite.
Ultrasonic arrays have seen increasing use for the characterisation of composite materials. In this paper, ultrasonic wave propagation in multilayer anisotropic materials has been modelled using plane wave and angular spectrum decomposition techniques. Different matrix techniques, such as the stiffness matrix method and the transfer matrix method, are used to calculate the reflection and transmission coefficients of ultrasonic plane waves in the considered media. Then, an angular decomposition technique is used to derive the bounded beams from finite-width ultrasonic array elements from the plane wave responses calculated earlier. This model is considered to be an analytical exact solution for the problem; hence the diffraction of waves in such composite materials can be calculated for different incident angles for a very wide range of frequencies. This model is validated against experimental measurements using the Full-Matrix Capture (FMC) of array data in both a homogeneous isotropic material, i.e. aluminium, and an inhomogeneous multilayer anisotropic material, i.e. a carbon fibre reinforced composite
Linjiang, QIN; Changfu, YANG
2016-03-01
The rocks in the crust and the upper mantle of the Earth are believed to exhibit electrical anisotropy to some extent. It is beneficial to further understand and recognize the propagation of the electromagnetic waves in the Earth by investigating the magnetotelluric (which is one of the main geophysical techniques to probe the deep structures in the Earth) responses of the media with anisotropic conductivity structures. In the present study, we examine the magnetotelluric fields over an idealized 2-D model consisting of two segments with axially anisotropic conductivity structures overlying a perfect conductor basement by a quasi-static analytic approach. The resulting analytic solution could not only contribute to the electromagnetic induction theory in the anisotropic Earth but also serve as at least an initial standard solution which could be used to validate the reliability and accuracy of the numerical algorithms developed for modeling the magnetotelluric responses of the 2-D media with much more general anisotropic conductivity.
Qin, Linjiang; Yang, Changfu
2016-06-01
The rocks in the crust and the upper mantle of the Earth are believed to exhibit electrical anisotropy to some extent. It is beneficial to further understand and recognize the propagation of the electromagnetic waves in the Earth by investigating the magnetotelluric (which is one of the main geophysical techniques to probe the deep structures in the Earth) responses of the media with anisotropic conductivity structures. In this study, we examine the magnetotelluric fields over an idealized 2-D model consisting of two segments with axially anisotropic conductivity structures overlying a perfect conductor basement by a quasi-static analytic approach. The resulting analytic solution could not only contribute to the electromagnetic induction theory in the anisotropic Earth but also serve as at least an initial standard solution which could be used to validate the reliability and accuracy of the numerical algorithms developed for modelling the magnetotelluric responses of the 2-D media with much more general anisotropic conductivity.
TRIGA reactor dynamics: Frequency response tests
In this work, the results of frequency response tests conducted on ITU TRIGA Reactor are presented. To conduct the experiments, a special 'micro control rod' and its submersible stepping-motor drive mechanism was designed and constructed. The experiments cover a frequency range of 0.002 - 2 Hz., and 0.02, 4, 200 kW nominal power levels. Zero-power and at-power reactivity to % power transfer functions are presented as gain, and phase shift vs. frequency diagrams. Low power response is in close agreement with the point reactor zero-power transfer function. Response at 200 kW is studied with the help of a Nyquist diagram, and found to be stable. An elaboration on the main features of the feedback mechanism is also given. Power to reactivity feedback was measured to be just about 1.5 cent / % power change. (authors)
Autonomous Demand Response for Primary Frequency Regulation
Donnelly, Matt; Trudnowski, Daniel J.; Mattix, S.; Dagle, Jeffery E.
2012-02-28
The research documented within this report examines the use of autonomous demand response to provide primary frequency response in an interconnected power grid. The work builds on previous studies in several key areas: it uses a large realistic model (i.e., the interconnection of the western United States and Canada); it establishes a set of metrics that can be used to assess the effectiveness of autonomous demand response; and it independently adjusts various parameters associated with using autonomous demand response to assess effectiveness and to examine possible threats or vulnerabilities associated with the technology.
The Anisotropic Dynamic Response of Ultrafast Shocked Single Crystal PETN and Beta-HMX
Zaug, Joseph; Armstrong, Michael; Crowhurst, Jonathan; Austin, Ryan; Ferranti, Louis; Fried, Laurence; Bastea, Sorin
2015-06-01
We report results from ultrafast shockwave experiments conducted on single crystal high explosives. Experimental results consist of 12 picosecond time-resolved dynamic response wave profile data, (ultrafast time-domain interferometry-TDI), which are used to validate calculations of anisotropic stress-strain behavior of shocked loaded energetic materials. In addition, here we present unreacted equations of state data from PETN and beta-HMX up to higher pressures than previously reported, which are used to extend the predictive confidence of hydrodynamic simulations. Our previous results derived from a 360 ps drive duration yielded anisotropic elastic wave response in single crystal beta-HMX ((110) and (010) impact planes). Here we provide results using a 3x longer drive duration to probe the plastic response regime of these materials. We compare our ultrafast time domain interferometry (TDI) results with previous gun platform results. Ultrafast time scale resolution TDI measurements further guide the development of continuum models aimed to study pore collapse and energy localization in shock-compressed crystals of beta-HMX. This work was performed under the auspices of the U.S. Department of Energy jointly by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Ali, Khuram; Khan, Sohail Aziz; Jafri, Mohd Zubir Mat
2012-10-01
Reduced surface reflectance and enhanced light trapping is required by any high efficiency solar cell. Anisotropic etching was done on silicon (1 0 0) by using tetramethyl ammonium hydroxide TMAH, (CH3)4NOH, solution at 85 °C. Process variables considered were solution concentration and time proposed by response surface methodology (RSM). An effective surface texture was resulted with reflectance less than 8% without antireflection coating. The antireflection mechanism was also co-related with the etch rate of Si. Optimized values predicted by RSM for time and TMAH concentration were 5 min and 3.50% respectively. The technique and optimization of parameters by using response surface methodology (RSM) could be valuable in the texturization process for high-efficiency Si solar cells.
Reyes, E.; Krokhin, A. A.; Roberts, J.
2005-01-01
We calculate the static dielectric tensor of a periodic system of aligned anisotropic dielectric cylinders. Exact analytical formulas for the effective dielectric constants for the E- and H- eigenmodes are obtained for arbitrary 2D Bravais lattice and arbitrary cross-section of anisotropic cylinders. It is shown that depending on the symmetry of the unit cell photonic crystal of anisotropic cylinders behaves in the low-frequency limit like uniaxial or biaxial natural crystal. The developed th...
Step response and frequency response of an air conditioning system
Crommelin, R.D.; Jackman, P.J.
1978-01-01
A system of induction units of an existing air conditioning system has been analyzed with respect to its dynamic properties. Time constants were calculated and measured by analogue models. Comparison with measurements at the installation itself showed a reasonable agreement. Frequency responses were
Regan, John; Wise, John
2015-01-01
The photo-dissociation of H$_2$ by a nearby anisotropic source of radiation is seen as a critical component in creating an environment in which a direct collapse black hole may form. Employing radiative transfer we model the effect of multi-frequency (0.76 eV - 60 eV) radiation on a collapsing halo at high redshift. We vary both the shape of the spectrum which emits the radiation and the distance to the emitting galaxy. We use blackbody spectra with temperatures of $\\rm{T = 10^4\\ K}$ and $\\rm{T = 10^5\\ K}$ and a realistic stellar spectrum. We find that an optimal zone exists between 1 kpc and 4 kpc from the emitting galaxy. If the halo resides too close to the emitting galaxy the photo-ionising radiation creates a large HII region which effectively disrupts the collapsing halo, too far from the source and the radiation flux drops below the level of the expected background and the H$_2$ fraction remains too high. When the emitting galaxy is initially placed between 1 kpc and 2 kpc from the collapsing halo, wit...
Namekata, Daisuke
2016-01-01
We explore the gas dynamics near the dust sublimation radius of active galactic nucleus (AGN). For the purpose, we perform axisymmetric radiation hydrodynamic simulations of a dusty gas disk of radius $\\approx 1\\,\\mathrm{pc}$ around a supermassive black hole of mass $10^{7}\\,\\mathrm{M_{\\odot}}$ taking into account (1) anisotropic radiation of accretion disk, (2) X-ray heating by corona, (3) radiative transfer of infrared (IR) photons reemitted by dust, (4) frequency dependency of direct and IR radiations, and (5) separate temperatures for gas and dust. As a result, we find that for Eddington ratio $\\approx 0.77$, a nearly neutral, dense ($\\approx 10^{6\\operatorname{-}8}\\;\\mathrm{cm^{-3}}$), geometrically-thin ($h/r<0.06$) disk forms with a high velocity ($\\approx 200 \\sim 3000\\;\\mathrm{km/s}$) dusty outflow launched from the disk surface. The disk temperature is determined by the balance between X-ray heating and various cooling, and the disk is almost supported by thermal pressure. Contrary to \\citet{krol...
Graeser, M.; Bente, K.; Neumann, A.; Buzug, T. M.
2016-02-01
In magnetic particle imaging, scanners use different spatial sampling techniques to cover the field of view (FOV). As spatial encoding is realized by a selective low field region (a field-free-point, or field-free-line), this region has to be moved through the FOV on specific sampling trajectories. To achieve these trajectories complex time dependent magnetic fields are necessary. Due to the superposition of the selection field and the homogeneous time dependent fields, particles at different spatial positions experience different field sequences. As a result, the dynamic behaviour of those particles can be strongly spatially dependent. So far, simulation studies that determined the trajectory quality have used the Langevin function to model the particle response. This however, neglects the dynamic relaxation of the particles, which is highly affected by magnetic anisotropy. More sophisticated models based on stochastic differential equations that include these effects were only used for one dimensional excitation. In this work, a model based on stochastic differential equations is applied to two-dimensional trajectory field sequences, and the effects of these field sequences on the particle response are investigated. The results show that the signal of anisotropic particles is not based on particle parameters such as size and shape alone, but is also determined by the field sequence that a particle ensemble experiences at its spatial position. It is concluded, that the particle parameters can be optimized in terms of the used trajectory.
In magnetic particle imaging, scanners use different spatial sampling techniques to cover the field of view (FOV). As spatial encoding is realized by a selective low field region (a field-free-point, or field-free-line), this region has to be moved through the FOV on specific sampling trajectories. To achieve these trajectories complex time dependent magnetic fields are necessary. Due to the superposition of the selection field and the homogeneous time dependent fields, particles at different spatial positions experience different field sequences. As a result, the dynamic behaviour of those particles can be strongly spatially dependent. So far, simulation studies that determined the trajectory quality have used the Langevin function to model the particle response. This however, neglects the dynamic relaxation of the particles, which is highly affected by magnetic anisotropy. More sophisticated models based on stochastic differential equations that include these effects were only used for one dimensional excitation. In this work, a model based on stochastic differential equations is applied to two-dimensional trajectory field sequences, and the effects of these field sequences on the particle response are investigated. The results show that the signal of anisotropic particles is not based on particle parameters such as size and shape alone, but is also determined by the field sequence that a particle ensemble experiences at its spatial position. It is concluded, that the particle parameters can be optimized in terms of the used trajectory. (paper)
Wang, Cheng-Yu; Chen, Chun-Wei; Jau, Hung-Chang; Li, Cheng-Chang; Cheng, Chiao-Yu; Wang, Chun-Ta; Leng, Shi-Ee; Khoo, Iam-Choon; Lin, Tsung-Hsien
2016-08-01
In this paper, we show that anisotropic photosensitive nematic liquid crystals (PNLC) made by incorporating anisotropic absorbing dyes are promising candidates for constructing all-optical elements by virtue of the extraordinarily large optical nonlinearity of the nematic host. In particular, we have demonstrated several room-temperature ‘prototype’ PNLC-based all-optical devices such as optical diode, optical transistor and all primary logic gate operations (OR, AND, NOT) based on such optical transistor. Owing to the anisotropic absorption property and the optical activity of the twist alignment nematic cell, spatially non-reciprocal transmission response can be obtained within a sizeable optical isolation region of ~210 mW. Exploiting the same mechanisms, a tri-terminal configuration as an all-optical analogue of a bipolar junction transistor is fabricated. Its ability to be switched by an optical field enables us to realize an all-optical transistor and demonstrate cascadability, signal fan-out, logic restoration, and various logical gate operations such as OR, AND and NOT. Due to the possibility of synthesizing anisotropic dyes and wide ranging choice of liquid crystals nonlinear optical mechanisms, these all-optical operations can be optimized to have much lower thresholds and faster response speeds. The demonstrated capabilities of these devices have shown great potential in all-optical control system and photonic integrated circuits.
Dynamic Frequency Response of Wind Power Plants
Altin, Müfit
method has less impact of the power system frequency compared to existing control concepts. Another advantage of the proposed inertial response control has the tuning methodology which can be utilized as a generic approach for any power system with high wind power penetration levels. Additionally, an...... maintain sustainable and reliable operation of the power system for these targets, transmission system operators (TSOs) have revised the grid code requirements. Also, the TSOs are planning the future development of the power system with various wind penetration scenarios to integrate more wind power...... according to their grid codes. In these scenarios particularly with high wind power penetration cases, conventional power plants (CPPs) such as old thermal power plants are planned to be replaced with wind power plants (WPPs). Consequently, the power system stability will be affected and the control...
Plant Responses to High Frequency Electromagnetic Fields
Vian, Alain; Davies, Eric; Gendraud, Michel; Bonnet, Pierre
2016-01-01
High frequency nonionizing electromagnetic fields (HF-EMF) that are increasingly present in the environment constitute a genuine environmental stimulus able to evoke specific responses in plants that share many similarities with those observed after a stressful treatment. Plants constitute an outstanding model to study such interactions since their architecture (high surface area to volume ratio) optimizes their interaction with the environment. In the present review, after identifying the main exposure devices (transverse and gigahertz electromagnetic cells, wave guide, and mode stirred reverberating chamber) and general physics laws that govern EMF interactions with plants, we illustrate some of the observed responses after exposure to HF-EMF at the cellular, molecular, and whole plant scale. Indeed, numerous metabolic activities (reactive oxygen species metabolism, α- and β-amylase, Krebs cycle, pentose phosphate pathway, chlorophyll content, terpene emission, etc.) are modified, gene expression altered (calmodulin, calcium-dependent protein kinase, and proteinase inhibitor), and growth reduced (stem elongation and dry weight) after low power (i.e., nonthermal) HF-EMF exposure. These changes occur not only in the tissues directly exposed but also systemically in distant tissues. While the long-term impact of these metabolic changes remains largely unknown, we propose to consider nonionizing HF-EMF radiation as a noninjurious, genuine environmental factor that readily evokes changes in plant metabolism. PMID:26981524
Xu, Qin; Gong, Qin
2014-01-01
Background The present study investigated whether the frequency-following response (FFR) of the auditory brainstem can represent individual frequency-discrimination ability. Method We measured behavioral frequency-difference limens (FDLs) in normal hearing young adults. Then FFRs were evoked by two pure tones, whose frequency difference was no larger than behavioral FDL. Discrimination of FFRs to individual frequencies was conducted as the neural representation of stimulus frequency differenc...
Conductivities in an anisotropic medium
Khimphun, Sunly; Park, Chanyong
2016-01-01
In order to imitate anisotropic medium of a condensed matter system, we take into account an Einstein-Maxwell-dilaton-axion model as a dual gravity theory where the anisotropy is caused by different momentum relaxations. This gravity model allows an anisotropic charged black hole solution. On this background, we investigate how the linear responses of vector modes like electric, thermoelectric, and thermal conductivities rely on the anisotropy. We find that the electric conductivity in low frequency limit shows a Drude peak and that in the intermediate frequency regime it reveals the power law behavior. Especially, when the anisotropy increases the exponent of the power law becomes smaller. In addition, we find that there exist a critical value for the anisotropy at which the DC conductivity reaches to its maximum value.
Terahertz-frequency dielectric response of liquids
Jepsen, Peter Uhd; Møller, Uffe; Cooke, David
-induced dipole moments. In the polar liquid water the fastest relaxational dynamics is found at terahertz frequencies, just below the first intermolecular vibrational and librational modes. In this presentation we will discuss optical terahertz spectroscopic techniques for measurement of the full dielectric...... function of liquids at terahertz frequencies. We will review the current understanding of the high-frequency dielectric spectrum of water, and discuss the relation between the dielectric spectrum and the thermodynamic properties of certain aqueous solutions....
Frequency response function method for evaluation of thermal striping phenomena
A rational analysis method of thermal stress induced by fluid temperature fluctuation is developed, by utilizing frequency response characteristics of structures. High frequency components of temperature fluctuation are attenuated in the transfer process from fluids to structures. Low frequency components hardly induce thermal stress since temperature homogenization in structures. Based on investigations of frequency response mechanism of structures of fluid temperature, a frequency response function of structures was derived, which can predict stress amplitudes on structural surfaces from fluid temperature amplitudes and frequencies. This function is formulated by separation of variables, and is composed of an effective heat transfer function and an effective thermal stress one. The frequency response function method appears to evaluate thermal stress rationally and to give information on damageable frequency range of structures. (author)
Alternative Approaches for Incentivizing the Frequency Responsive Reserve Ancillary Service
Ela, E.; Milligan, M.; Kirby, B.; Tuohy, A.; Brooks, D.
2012-03-01
Frequency responsive reserve is the autonomous response of generators and demand response to deviations of system frequency, usually as a result of the instantaneous outage of a large supplier. Frequency responsive reserve arrests the frequency decline resulting in the stabilization of system frequency, and avoids the triggering of under-frequency load-shedding or the reaching of unstable frequencies that could ultimately lead to system blackouts. It is a crucial service required to maintain a reliable and secure power system. Regions with restructured electricity markets have historically had a lack of incentives for frequency responsive reserve because generators inherently provided the response and on large interconnected systems, more than sufficient response has been available. This may not be the case in future systems due to new technologies and declining response. This paper discusses the issues that can occur without proper incentives and even disincentives, and proposes alternatives to introduce incentives for resources to provide frequency responsive reserve to ensure an efficient and reliable power system.
Leonardo Galvis
Full Text Available In this study, polarized Raman spectroscopy (PRS was used to characterize the anisotropic response of the amide I band of collagen as a basis for evaluating three-dimensional collagen fibril orientation in tissues. Firstly, the response was investigated theoretically by applying classical Raman theory to collagen-like peptide crystal structures. The theoretical methodology was then tested experimentally, by measuring amide I intensity anisotropy in rat tail as a function of the orientation of the incident laser polarization. For the theoretical study, several collagen-like triple-helical peptide crystal structures obtained from the Protein Data Bank were rotated "in plane" and "out of plane" to evaluate the role of molecular orientation on the intensity of the amide I band. Collagen-like peptides exhibit a sinusoidal anisotropic response when rotated "in plane" with respect to the polarized incident laser. Maximal intensity was obtained when the polarization of the incident light is perpendicular to the molecule and minimal when parallel. In the case of "out of plane" rotation of the molecular structure a decreased anisotropic response was observed, becoming completely isotropic when the structure was perpendicular to the plane of observation. The theoretical Raman response of collagen was compared to that of alpha helical protein fragments. In contrast to collagen, alpha helices have a maximal signal when incident light is parallel to the molecule and minimal when perpendicular. For out-of-plane molecular orientations alpha-helix structures display a decreased average intensity. Results obtained from experiments on rat tail tendon are in excellent agreement with the theoretical predictions, thus demonstrating the high potential of PRS for experimental evaluation of the three-dimensional orientation of collagen fibers in biological tissues.
Fractures in anisotropic media
Shao, Siyi
Rocks may be composed of layers and contain fracture sets that cause the hydraulic, mechanical and seismic properties of a rock to be anisotropic. Coexisting fractures and layers in rock give rise to competing mechanisms of anisotropy. For example: (1) at low fracture stiffness, apparent shear-wave anisotropy induced by matrix layering can be masked or enhanced by the presence of a fracture, depending on the fracture orientation with respect to layering, and (2) compressional-wave guided modes generated by parallel fractures can also mask the presence of matrix layerings for particular fracture orientations and fracture specific stiffness. This report focuses on two anisotropic sources that are widely encountered in rock engineering: fractures (mechanical discontinuity) and matrix layering (impedance discontinuity), by investigating: (1) matrix property characterization, i.e., to determine elastic constants in anisotropic solids, (2) interface wave behavior in single-fractured anisotropic media, (3) compressional wave guided modes in parallel-fractured anisotropic media (single fracture orientation) and (4) the elastic response of orthogonal fracture networks. Elastic constants of a medium are required to understand and quantify wave propagation in anisotropic media but are affected by fractures and matrix properties. Experimental observations and analytical analysis demonstrate that behaviors of both fracture interface waves and compressional-wave guided modes for fractures in anisotropic media, are affected by fracture specific stiffness (controlled by external stresses), signal frequency and relative orientation between layerings in the matrix and fractures. A fractured layered medium exhibits: (1) fracture-dominated anisotropy when the fractures are weakly coupled; (2) isotropic behavior when fractures delay waves that are usually fast in a layered medium; and (3) matrix-dominated anisotropy when the fractures are closed and no longer delay the signal. The
Reconfigurable ring filter with controllable frequency response.
Ab Wahab, Norfishah; Mohd Salleh, Mohd Khairul; Ismail Khan, Zuhani; Abd Rashid, Nur Emileen
2014-01-01
Reconfigurable ring filter based on single-side-access ring topology is presented. Using capacitive tuning elements, the electrical length of the ring can be manipulated to shift the nominal center frequency to a desired position. A synthesis is developed to determine the values of the capacitive elements. To show the advantage of the synthesis, it is applied to the reconfigurable filter design using RF lumped capacitors. The concept is further explored by introducing varactor-diodes to continuously tune the center frequency of the ring filter. For demonstration, two prototypes of reconfigurable ring filters are realized using microstrip technology, simulated, and measured to validate the proposed concept. The reconfigured filter using lumped elements is successfully reconfigured from 2 GHz to 984.4 MHz and miniaturized by 71% compared to the filter directly designed at the same reconfigured frequency, while, for the filter using varactor-diodes, the frequency is chosen from 1.10 GHz to 1.38 GHz spreading over 280 MHz frequency range. Both designs are found to be compact with acceptable insertion loss and high selectivity. PMID:25121132
Computer program for network synthesis by frequency response fit
Green, S.
1967-01-01
Computer program synthesizes a passive network by minimizing the difference in desired and actual frequency response. The program solves for the critical points of the error function /weighted least squares fit between calculated and desired frequency response/ by the multivariable Newton-Raphson method with components constrained to an admissible region.
Open-loop frequency response for a chaotic masking system
Huang Xian-Gao; Yu Pei; Huang Wei
2006-01-01
In this paper, a new numerical simulation approach is proposed for the study of open-loop frequency response of a chaotic masking system. Using Chua's circuit and the Lorenz system as illustrative examples, we have shown that one can employ chaos synchronization to separate the feedback network from a chaotic masking system, and then use numerical simulation to obtain the open-loop synchronization response, the phase response, and the amplitude response of a chaotic masking system. Based on the analysis of the frequency response, we have also proved that changing the amplitude of the exciting (input) signal within normal working domain does not influence the frequency response of the chaotic masking system. The new numerical simulation method developed in this paper can be extended to consider the open-loop frequency response of other systems described by differential or difference equations.
Frequency Response of Uncertain Systems: Strong Kharitonov-Like Results
Wang, Long
2002-01-01
In this paper, we study the frequency response of uncertain systems using Kharitonov stability theory on first order complex polynomial set. For an interval transfer function, we show that the minimal real part of the frequency response at any fixed frequency is attained at some prescribed vertex transfer functions. By further geometric and algebraic analysis, we identify an index for strict positive realness of interval transfer functions. Some extensions and applications in positivity verif...
Frequency response of IPMC actuator with palladium electrode
Kobayashi, T.; Omiya, M.
2011-04-01
The present study investigates the frequency response of IPMC actuator. By using the electroless plating method, IPMC actuator with palladium electrode was obtained in 60 minutes, which was shorter than the conventional fabrication time. In the observation of response to step voltages, IPMC actuator with palladium electrode showed larger deformation and slower backward motion than the conventional IPMC actuators with platinum electrode. In the experiments of frequency response, IPMC actuator showed the resonance phenomenon at a specified frequency, and the resonance frequency could be predicted by the simple cantilever beam model. Then, the phase shift increased drastically when the resonance phenomena were observed. Finally, the frequency response of IPMC actuator was modeled by using the transfer function.
Transformation Algorithm of Dielectric Response in Time-Frequency Domain
Ji Liu
2014-01-01
Full Text Available A transformation algorithm of dielectric response from time domain to frequency domain is presented. In order to shorten measuring time of low or ultralow frequency dielectric response characteristics, the transformation algorithm is used in this paper to transform the time domain relaxation current to frequency domain current for calculating the low frequency dielectric dissipation factor. In addition, it is shown from comparing the calculation results with actual test data that there is a coincidence for both results over a wide range of low frequencies. Meanwhile, the time domain test data of depolarization currents in dry and moist pressboards are converted into frequency domain results on the basis of the transformation. The frequency domain curves of complex capacitance and dielectric dissipation factor at the low frequency range are obtained. Test results of polarization and depolarization current (PDC in pressboards are also given at the different voltage and polarization time. It is demonstrated from the experimental results that polarization and depolarization current are affected significantly by moisture contents of the test pressboards, and the transformation algorithm is effective in ultralow frequency of 10−3 Hz. Data analysis and interpretation of the test results conclude that analysis of time-frequency domain dielectric response can be used for assessing insulation system in power transformer.
Modeling a response function to frequency of advertising
Lutoshkin, Igor
2010-01-01
In this paper we study the impact of the frequency of advertising on the product sales We introduce response function and postulate its properties Parametric classes of functions which can serve as response functions are suggested We use real data on advertising impact to estimate response functions and discuss their properties
Effective dielectric response of anisotropic grains of close-packed structure
Klíč, Antonín; Rychetský, Ivan
New Jersey : IEEE - Institute of Electrical and Electronics Engineers, 2012, s. 510-512. ISBN 978-1-4673-2668-1. - (IEEE Conference Publications). [ISAF-ECAPD-PFM 2012. Aveiro (PT), 09.07.2012-13.07.2012] R&D Projects: GA ČR GAP204/12/0232 Institutional research plan: CEZ:AV0Z10100520 Keywords : anisotropic poplycrysta * spectral representation * effective permittivity * 2-component system Subject RIV: BM - Solid Matter Physics ; Magnetism http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6279558
Method of detecting system function by measuring frequency response
Morrison, John L. (Inventor); Morrison, William H. (Inventor); Christophersen, Jon P. (Inventor)
2012-01-01
Real-time battery impedance spectrum is acquired using a one-time record. Fast Summation Transformation (FST) is a parallel method of acquiring a real-time battery impedance spectrum using a one-time record that enables battery diagnostics. An excitation current to a battery is a sum of equal amplitude sine waves of frequencies that are octave harmonics spread over a range of interest. A sample frequency is also octave and harmonically related to all frequencies in the sum. The time profile of this signal has a duration that is a few periods of the lowest frequency. The voltage response of the battery, average deleted, is the impedance of the battery in the time domain. Since the excitation frequencies are known and octave and harmonically related, a simple algorithm, FST, processes the time record by rectifying relative to the sine and cosine of each frequency. Another algorithm yields real and imaginary components for each frequency.
An Exoplanet's Response to Anisotropic Stellar Mass-Loss During Birth and Death
Veras, Dimitri; Tout, Christopher A
2013-01-01
The birth and death of planets may be affected by mass outflows from their parent stars during the T-Tauri or post-main-sequence phases of stellar evolution. These outflows are often modelled to be isotropic, but this assumption is not realistic for fast rotators, bipolar jets and supernovae. Here we derive the general equations of motion for the time evolution of a single planet, brown dwarf, comet or asteroid perturbed by anisotropic mass loss in terms of a complete set of planetary orbital elements, the ejecta velocity, and the parent star's co-latitude and longitude. We restrict our application of these equations to 1) rapidly rotating giant stars, and 2) arbitrarily-directed jet outflows. We conclude that the isotropic mass-loss assumption can safely be used to model planetary motion during giant branch phases of stellar evolution within distances of hundreds of au. In fact, latitudinal mass loss variations anisotropically affect planetary motion only if the mass loss is asymmetric about the stellar equa...
Wu, Jingshi; Deubener, Joachim; Stebbins, Jonathan F.; Grygarova, Lenka; Behrens, Harald; Wondraczek, Lothar; Yue, Yuanzheng
2009-09-01
Aluminoborosilicate melts of E-glass composition have been compressed at pressures up to 500 MPa and subsequently cooled (4-5 K min-1) under pressure from well above the glass transition to room temperature. It is found that increasing uniaxial pressure lead to anisotropic glasses with increasing permanent birefringence, while increasing isostatic pressure resulted in isotropic glasses with increasing density (compaction of 2.1% at 500 MPa). Static and magic-angle spinning nuclear magnetic resonance spectroscopy of B11, N23a, A27l, and S29i were performed to explore pressure-induced changes in the short-range structure of these glasses. NMR experiments readily detected increasing BIV, AVl, and AVIl concentrations with pressure as well as a decrease in the mean distance of sodium to oxygen atoms (0.7% at 500 MPa), but no detectible evidence of short-range structural orientation around these atoms in the birefringent glasses were found. Quantifying the changes in the local boron, aluminum, silicon, and sodium environments revealed that the measured increase of recovered density with pressure in E-glass can only be partly explained by increase in B and Al coordination, and that overall compression of the network and of the network modifier cation volumes must also be important. Structural changes in the intermediate range, which were not detected by NMR, are discussed as a source of birefringence in anisotropic E-glass.
Fuzzy Frequency Response for Stochastic Linear Parameter Varying Dynamic Systems
Ferreia, Carlos Cesar Teixeira; Serra, Ginalber Luiz De Oliveira
2010-01-01
The Fuzzy Frequency Response: Deï¬nition and Analysis for Stochastic Linear Parameter Varying Dynamic Systems is proposed in this chapter. It was shown that the fuzzy frequency response is a region in the frequency domain, deï¬ned by the consequent linear sub-models W i (s), starting from operating regions of the SLPV dynamic system, according to the proposed Theorem 3.1. This formula is very efï¬cient and can be used for robust stability analysis and control design for SLPV dynamic system...
High-frequency response of nanostructured magnetic materials
This paper reports a brief overview on recent developments regarding the high-frequency response in the GHz range of nanostructured magnetic materials. Emphasis is placed on the linear regime in the frequency domain characterized by the dynamic susceptibility spectrum. Some modeling tools and experimental probes allowing determination of the dynamic susceptibility spectrum are first rapidly reviewed and their respective advantages and disadvantages are discussed. Next, some illustrative examples of the high-frequency response of nanopatterned materials based on recent works are presented. The role played by the shape of the element on the characteristics of excitation spectrum is underlined. Lastly, some prospects are proposed and promising trends are highlighted.
Regional frequency response analysis under normal and emergency conditions
Bevrani, Hassan [Department of Electrical and Computer Engineering, University of Kurdistan, Sanandaj, PO Box 416 (Iran); Ledwich, Gerard; Ford, Jason J. [School of Engineering Systems, Queensland University of Technology, Brisbane, Qld 4001 (Australia); Dong, Zhao Yang [Department of Electrical Engineering, The Hong Kong Polytechnic University (China)
2009-05-15
This paper presents a frequency response analysis approach suitable for a power system control area in a wide range of operating conditions. The analytic approach uses the well-known system frequency response model for the turbine-governor and load units to obtain the mathematical representation of the basic concepts. Primary and supplementary frequency controls are properly considered and the effect of emergency control/protection schemes is included. Therefore, the proposed analysis/modeling approach could be grainfully used for the power system operation during the contingency and normal conditions. Time-domain nonlinear simulations with a power system example showed that the results agree with those predicted analytically. (author)
Responses of an isolation system with distinct multiple frequencies
Wu, Ting-shu; Seidensticker, R.W.
1991-01-01
Base isolation systems are generally designed with a single natural frequency. A major concern for these isolation systems is that, if the dominant frequency of a future earthquake is equal or close to the system's natural frequency, the ground motion will be greatly amplified because of resonance,and the superstructure would suffer severe damages. This paper present an isolation system designed with two distinct frequencies. Its responses to different ground motions, including a harmonic motion, show that no excessive amplification will occur. Adoption of this isolation system would greatly enhance the safety of an isolated superstructure against future strong earthquakes. 3 refs., 4 figs., 2 tabs.
Rectennas at optical frequencies: How to analyze the response
Optical rectennas, antenna-coupled diode rectifiers that receive optical-frequency electromagnetic radiation and convert it to DC output, have been proposed for use in harvesting electromagnetic radiation from a blackbody source. The operation of these devices is qualitatively different from that of lower-frequency rectennas, and their design requires a new approach. To that end, we present a method to determine the rectenna response to high frequency illumination. It combines classical circuit analysis with classical and quantum-based photon-assisted tunneling response of a high-speed diode. We demonstrate the method by calculating the rectenna response for low and high frequency monochromatic illumination, and for radiation from a blackbody source. Such a blackbody source can be a hot body generating waste heat, or radiation from the sun
Pan Jin; Wang De-yu
2006-01-01
In this paper, adaptive genetic algorithm (AGA) is applied to topology optimization of truss structure with frequency domain excitations. The optimization constraints include fundamental frequency, displacement responses under force excitations and acceleration responses under foundation acceleration excitations. The roulette wheel selection operator, adaptive crossover and mutation operators are used as genetic operators. Some heuristic strategies are put forward to direct the deletion of the extra bars and nodes on truss structures. Three examples demonstrate that the proposed method can yield the optimum structure form and the lightest weight of the given ground structure while satisfying dynamic response constraints.
Deepak Rajaram Patil
2014-04-01
Full Text Available We report the physical behavior of self-biased multi-functional magneto-mechano-electric (MME laminates simultaneously excited by magnetic and/or mechanical vibrations. The MME laminates composed of Ni and single crystal fiber composite exhibited strong ME coupling under Hdc = 0 Oe at both low frequency and at resonance frequency. Depending on the magnetic field direction with respect to the crystal orientation, the energy harvester showed strong in-plane anisotropy in the output voltage and was found to generate open circuit output voltage of 20 Vpp and power density of 59.78 mW/Oe2 g2 cm3 under weak magnetic field of 1 Oe and mechanical vibration of 30 mg, at frequency of 21 Hz across 1 MΩ resistance.
On the statistical properties of random causal frequency response functions
Langley, R. S.
2016-01-01
In nuclear physics it is known that under broad restrictions a random scattering matrix element H satisfies a condition known as the analyticity-ergodicity (AE) requirement, which states that E [ f (H) ] = f (E [ H ]), where f is some function of H, and E[] represents the ensemble average. A scattering matrix element is directly analogous to a vibrational frequency response function, and it is of significant interest to consider whether the AE requirement is also applicable to random engineering systems. The proof of the AE condition in nuclear physics rests on the assumptions that H is causal and ergodic: causality implies that a Lorentzian frequency average satisfies the AE equation, and ergodicity implies that Lorentzian frequency averages are equal to ensemble averages. In vibrational systems it is readily shown that a typical frequency response function is non-stationary and non-ergodic, so that the Lorentzian and ensemble averages can differ significantly, and this means that the standard proof of the AE requirement breaks down. The question then arises as to whether the AE requirement might nonetheless apply to vibrational systems. It is shown in the present paper that the requirement does apply providing that the random point process representing the system natural frequencies is at least locally stationary (which is a much weaker condition than local stationarity of the frequency response function), and a number of the implications of this result are explored.
Frequency response in surface-potential driven electrohydrodynamics
Ejsing, Louise Wellendorph; Smistrup, Kristian; Pedersen, Christian Møller;
2006-01-01
capacitance where the net flow rate is, in general, zero while harmonic rolls as well as time-averaged vortexlike components may exist depending on the spatial symmetry and extension of the surface potential. In general, the system displays a resonance behavior at a frequency corresponding to the inverse RC...... time of the system. Different surface potentials share the common feature that the resonance frequency is inversely proportional to the characteristic length scale of the surface potential. For the asymptotic frequency dependence above resonance we find a omega(-2) power law for surface potentials...... response the two potentials display different power-law asymptotics with alpha=1 and alpha similar to 2, respectively....
Evaluation of Piloted Inputs for Onboard Frequency Response Estimation
Grauer, Jared A.; Martos, Borja
2013-01-01
Frequency response estimation results are presented using piloted inputs and a real-time estimation method recently developed for multisine inputs. A nonlinear simulation of the F-16 and a Piper Saratoga research aircraft were subjected to different piloted test inputs while the short period stabilator/elevator to pitch rate frequency response was estimated. Results show that the method can produce accurate results using wide-band piloted inputs instead of multisines. A new metric is introduced for evaluating which data points to include in the analysis and recommendations are provided for applying this method with piloted inputs.
Frequency response modeling and control of flexible structures: Computational methods
Bennett, William H.
1989-01-01
The dynamics of vibrations in flexible structures can be conventiently modeled in terms of frequency response models. For structural control such models capture the distributed parameter dynamics of the elastic structural response as an irrational transfer function. For most flexible structures arising in aerospace applications the irrational transfer functions which arise are of a special class of pseudo-meromorphic functions which have only a finite number of right half place poles. Computational algorithms are demonstrated for design of multiloop control laws for such models based on optimal Wiener-Hopf control of the frequency responses. The algorithms employ a sampled-data representation of irrational transfer functions which is particularly attractive for numerical computation. One key algorithm for the solution of the optimal control problem is the spectral factorization of an irrational transfer function. The basis for the spectral factorization algorithm is highlighted together with associated computational issues arising in optimal regulator design. Options for implementation of wide band vibration control for flexible structures based on the sampled-data frequency response models is also highlighted. A simple flexible structure control example is considered to demonstrate the combined frequency response modeling and control algorithms.
Shen Jinsong; Su Benyu; Guo Naichuan
2009-01-01
In fractured reservoirs, the fractures not only provide the storage space for hydrocarbons, but also form the main flow channels which connect the pores of the matrix, so fractures dominate the productivity of reservoirs.However, because of the heterogeneity and randomness of the distribution of fractures, exploration and evaluation of fractured reservoirs is still one of the most difficult problems in the oil industry.In recent years, seismic anisotropy has been applied to the assessment of fractured formations, whereas electrical anisotropy which is more intense in fractured formations than seismic anisotropy has not been studied or used so extensively.In this study, fractured reservoir models which considered multiple sets of fractures with smooth and partly closed, rough surfaces were established based on the fractures and pore network, and the vertical and horizontal electrical resistivities were derived as a function of the matrix and fracture porosities according to Ohm's law.By using the anisotropic resistivity equations, variations of the electrical anisotropy of three types of fractured models under the conditions of free pressure and confining pressure were analyzed through the variations of the exerted pressure, matrix porosity, fracture aperture and formation water resistivity.The differences of the vertical and horizontal resistivities and the anisotropy between the connected and non-connected fractures were also analyzed.It is known from the simulated results that an increase of the confining pressure causes a decrease of electrical anisotropy because of the elasticity of the closed fractures and the decrease of the fracture aperture.For a fixed fracture porosity, the higher the matrix porosity, the weaker the electrical anisotropy in the rock formation.
78 FR 45479 - Frequency Response and Frequency Bias Setting Reliability Standard
2013-07-29
... electronically using word processing software should be filed in native applications or print-to-PDF format and... drafting team sees merit and promise in future research with sample filtering combined with a technique... of frequency response needed for reliable operations for each Balancing Authority within...
Anisotropic Metamaterial Optical Fibers
Pratap, Dheeraj; Pollock, Justin G; Iyer, Ashwin K
2014-01-01
Internal physical structure can drastically modify the properties of waveguides: photonic crystal fibers are able to confine light inside a hollow air core by Bragg scattering from a periodic array of holes, while metamaterial loaded waveguides for microwaves can support propagation at frequencies well below cutoff. Anisotropic metamaterials assembled into cylindrically symmetric geometries constitute light-guiding structures that support new kinds of exotic modes. A microtube of anodized nanoporous alumina, with nanopores radially emanating from the inner wall to the outer surface, is a manifestation of such an anisotropic metamaterial optical fiber. The nanopores, when filled with a plasmonic metal such as silver or gold, greatly increase the electromagnetic anisotropy. The modal solutions in anisotropic circular waveguides can be uncommon Bessel functions with imaginary orders.
Frequency response of a thermocouple wire: Effects of axial conduction
Forney, L. J.; Fralick, G. C.
1990-01-01
Theoretical expressions are derived for the steady-state frequency response of a thermocouple wire. In particular, the effects of axial heat conduction are demonstrated for both a uniform thermocouple wire and a nonuniform wire with unequal material properties and wire diameters across the junction. For the case of a uniform wire, the amplitude ratio and phase angle compare favorably with the series solution of Scadron and Warshawsky (1952) except near the ends of the wire. For the case of a non-uniform wire, the amplitude ratio at low frequency omega yields 0 agrees with the results of Scadron and Warshawsky for a steady-state temperature distribution. Moreover, the frequency response for a non-uniform wire in the limit of infinite length l yields infinity is shown to reduce to a simple expression that is analogous to the classic first order solution for a thermocouple wire with uniform properties.
Modal Identification from Ambient Responses Using Frequency Domain Decomposition
Brincker, Rune; Zhang, Lingmi; Andersen, Palle
2000-01-01
In this paper a new frequency domain technique is introduced for the modal identification from ambient responses, i.e. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical...
Modal Identification from Ambient Responses using Frequency Domain Decomposition
Brincker, Rune; Zhang, L.; Andersen, P.
In this paper a new frequency domain technique is introduced for the modal identification from ambient responses, ie. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical...
Microwire arrays with plasmonic response at microwave frequencies
Maccio, C.; Martin, O. J. F.; Gay-Balmaz, P.
2002-01-01
We study experimentally the response of three-dimensional arrays of microscopic wires. Very good agreement is found with previous theoretical work indicating that such a system can be considered as an effective plasmonic medium with a specific plasma frequency. The sample size threshold where this effective behavior appears is shown to be relatively small. (C) 2002 American Institute of Physics.
Frequency response of Michelson- and Sagnac-based interferometers
Mizuno, J.; Rüdiger, A.; Schilling, R; Winkler, W.; Danzmann, K.
1997-01-01
The frequency response of Michelson- and Sagnac-based interferometers are evaluated and compared, considering the application for gravitational-wave detection. It is shown that Sagnac-based interferometers have some interesting features, but in general do not offer advantages over Michelson-based ones for the detection of gravitational waves.
Fei eTeng
2015-08-01
Full Text Available The demand for ancillary service is expected to increase significantly in the future GB electricity system due to high penetration of wind. In particular, the need for frequency response, required to deal with sudden frequency drops following a loss of generator, will increase because of the limited inertia capability of wind plants. This paper quantifies the requirements for primary frequency response and analyses the benefits of frequency response provision from DSR. The results show dramatic changes in frequency response requirements driven by high penetration of wind. Case studies carried out by using an advanced stochastic generation scheduling model suggest that the provision of frequency response from DSR could greatly reduce the system operation cost, wind curtailment and carbon emissions in the future GB system characterised by high penetration of wind. Furthermore, the results demonstrate that the benefit of DSR shows significant diurnal and seasonal variation, whereas an even more rapid (instant delivery of frequency response from DSR could provide significant additional value. Our studies also indicate that the competing technologies to DSR, namely battery storage and more flexible generation could potentially reduce its value by up to 35%, still leaving significant room to deploy DSR as frequency response provider.
Modeling the frequency response of microwave radiometers with QUCS
Characterization of the frequency response of coherent radiometric receivers is a key element in estimating the flux of astrophysical emissions, since the measured signal depends on the convolution of the source spectral emission with the instrument band shape. Laboratory Radio Frequency (RF) measurements of the instrument bandpass often require complex test setups and are subject to a number of systematic effects driven by thermal issues and impedance matching, particularly if cryogenic operation is involved. In this paper we present an approach to modeling radiometers bandpasses by integrating simulations and RF measurements of individual components. This method is based on QUCS (Quasi Universal Circuit Simulator), an open-source circuit simulator, which gives the flexibility of choosing among the available devices, implementing new analytical software models or using measured S-parameters. Therefore an independent estimate of the instrument bandpass is achieved using standard individual component measurements and validated analytical simulations. In order to automate the process of preparing input data, running simulations and exporting results we developed the Python package python-qucs and released it under GNU Public License. We discuss, as working cases, bandpass response modeling of the COFE and Planck Low Frequency Instrument (LFI) radiometers and compare results obtained with QUCS and with a commercial circuit simulator software. The main purpose of bandpass modeling in COFE is to optimize component matching, while in LFI they represent the best estimation of frequency response, since end-to-end measurements were strongly affected by systematic effects.
Health assessment of bonded composite repairs with frequency response techniques
White, Caleb; Whittingham, Brendan; Li, Henry C. H.; Herszberg, Israel; Mouritz, Adrian P.
2007-01-01
Structural health monitoring (SHM) technology may be applied to composite bonded repairs to enable the continuous through-life assessment of the repair's efficacy. This paper describes an SHM technique for the detection of debonding in composite bonded patches based on frequency response. The external doubler repair, commonly used to patch aircraft structures, is examined in this paper. An experimental investigation was conducted using carbon/epoxy doubler repairs bonded to carbon/epoxy substrates, with piezoelectric devices used to measure variations in the frequency response of the repaired structure due to debonding of the external doubler. Three piezoelectric devices were adhered to the structure; the actuator to the external doubler and two sensors to the parent panel. To simulate real repair design requirements (minimum surface perturbation) piezoelectric devices were installed on 'internal' surfaces. Clearance for the actuator was created by the removal of damaged material. The frequency response signature of the repaired structure with simulated debonds is analysed with respect to the response of fully bonded repairs. Results are discussed with implications for the development of a technique to monitor the integrity of external bonded repairs.
Fractional Modeling of the AC Large-Signal Frequency Response in Magnetoresistive Current Sensors
Sergio Iván Ravelo Arias
2013-12-01
Full Text Available Fractional calculus is considered when derivatives and integrals of non-integer order are applied over a specific function. In the electrical and electronic domain, the transfer function dependence of a fractional filter not only by the filter order n, but additionally, of the fractional order α is an example of a great number of systems where its input-output behavior could be more exactly modeled by a fractional behavior. Following this aim, the present work shows the experimental ac large-signal frequency response of a family of electrical current sensors based in different spintronic conduction mechanisms. Using an ac characterization set-up the sensor transimpedance function is obtained considering it as the relationship between sensor output voltage and input sensing current,[PLEASE CHECK FORMULA IN THE PDF]. The study has been extended to various magnetoresistance sensors based in different technologies like anisotropic magnetoresistance (AMR, giant magnetoresistance (GMR, spin-valve (GMR-SV and tunnel magnetoresistance (TMR. The resulting modeling shows two predominant behaviors, the low-pass and the inverse low-pass with fractional index different from the classical integer response. The TMR technology with internal magnetization offers the best dynamic and sensitivity properties opening the way to develop actual industrial applications.
Fractional modeling of the AC large-signal frequency response in magnetoresistive current sensors.
Ravelo Arias, Sergio Iván; Ramírez Muñoz, Diego; Moreno, Jaime Sánchez; Cardoso, Susana; Ferreira, Ricardo; de Freitas, Paulo Jorge Peixeiro
2013-01-01
Fractional calculus is considered when derivatives and integrals of non-integer order are applied over a specific function. In the electrical and electronic domain, the transfer function dependence of a fractional filter not only by the filter order n, but additionally, of the fractional order α is an example of a great number of systems where its input-output behavior could be more exactly modeled by a fractional behavior. Following this aim, the present work shows the experimental ac large-signal frequency response of a family of electrical current sensors based in different spintronic conduction mechanisms. Using an ac characterization set-up the sensor transimpedance function Z(t)(JF) is obtained considering it as the relationship between sensor output voltage and input sensing current, Z(t)(jf)= V(o, sensor)(jf)/I(sensor)(jf). The study has been extended to various magnetoresistance sensors based in different technologies like anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), spin-valve (GMR-SV) and tunnel magnetoresistance (TMR). The resulting modeling shows two predominant behaviors, the low-pass and the inverse low-pass with fractional index different from the classical integer response. The TMR technology with internal magnetization offers the best dynamic and sensitivity properties opening the way to develop actual industrial applications. PMID:24351648
Detrending moving average algorithm: Frequency response and scaling performances
Carbone, Anna; Kiyono, Ken
2016-06-01
The Detrending Moving Average (DMA) algorithm has been widely used in its several variants for characterizing long-range correlations of random signals and sets (one-dimensional sequences or high-dimensional arrays) over either time or space. In this paper, mainly based on analytical arguments, the scaling performances of the centered DMA, including higher-order ones, are investigated by means of a continuous time approximation and a frequency response approach. Our results are also confirmed by numerical tests. The study is carried out for higher-order DMA operating with moving average polynomials of different degree. In particular, detrending power degree, frequency response, asymptotic scaling, upper limit of the detectable scaling exponent, and finite scale range behavior will be discussed.
Detrending moving average algorithm: Frequency response and scaling performances.
Carbone, Anna; Kiyono, Ken
2016-06-01
The Detrending Moving Average (DMA) algorithm has been widely used in its several variants for characterizing long-range correlations of random signals and sets (one-dimensional sequences or high-dimensional arrays) over either time or space. In this paper, mainly based on analytical arguments, the scaling performances of the centered DMA, including higher-order ones, are investigated by means of a continuous time approximation and a frequency response approach. Our results are also confirmed by numerical tests. The study is carried out for higher-order DMA operating with moving average polynomials of different degree. In particular, detrending power degree, frequency response, asymptotic scaling, upper limit of the detectable scaling exponent, and finite scale range behavior will be discussed. PMID:27415389
Detrending Moving Average Algorithm: Frequency Response and Scaling Performances
Carbone, Anna
2016-01-01
The Detrending Moving Average (DMA) algorithm has been widely used in its several variants for characterizing long-range correlations of random signals and sets (one-dimensional sequences or high-dimensional arrays) either over time or space. In this paper, mainly based on analytical arguments, the scaling performances of the centered DMA, including higher-order ones, are investigated by means of a continuous time approximation and a frequency response approach. Our results are also confirmed by numerical tests. The study is carried out for higher-order DMA operating with moving average polynomials of different degree. In particular, detrending power degree, frequency response, asymptotic scaling, upper limit of the detectable scaling exponent and finite scale range behavior will be discussed.
Frequency-independent response of self-complementary checkerboard screens
Urade, Yoshiro; Nakanishi, Toshihiro; Kitano, Masao
2015-01-01
This research resolves a long-standing problem on the electromagnetic response of self-complementary metallic screens with checkerboard-like geometry. Although Babinet's principle implies that they show a frequency-independent response, this unusual characteristic has not been observed yet due to the singularities of the metallic point contacts in the checkerboard geometry. We overcome this difficulty by replacing the point contacts with resistive sheets. The proposed structure is prepared and characterized by terahertz time-domain spectroscopy. It is experimentally confirmed that the resistive checkerboard structures exhibit a flat transmission spectrum over 0.1--1.1 THz. It is also demonstrated that self-complementarity can eliminate even the frequency-dependent transmission characteristics of resonant metamaterials.
Tunable waveguide bends with graphene-based anisotropic metamaterials
Chen, Zhao-xian
2016-01-15
We design tunable waveguide bends filled with graphene-based anisotropic metamaterials to achieve a nearly perfect bending effect. The anisotropic properties of the metamaterials can be described by the effective medium theory. The nearly perfect bending effect is demonstrated by finite element simulations of various structures with different bending curvatures and shapes. This effect is attributed to zero effective permittivity along the direction of propagation and matched effective impedance at the interfaces between the bending part and the dielectric waveguides. We envisage that the design will be applicable in the far-infrared and terahertz frequency ranges owing to the tunable dielectric responses of graphene.
Schuster, Patricia
2015-01-01
This paper reports a series of measurements that characterize the directional dependence of the scintillation response of crystalline anthracene to incident DT neutrons, DD neutrons, Cs-137 gamma rays, and, for the first time, cosmic ray muons. The neutron measurements give the amplitude and pulse shape dependence on the proton recoil direction over one hemisphere of the crystal, confirming and extending previous results in the literature. In similar measurements using incident gamma rays, no directional effect is evident, and any anisotropy with respect to the electron recoil direction is constrained to have a magnitude of less than a tenth of that present in the proton recoil events. Cosmic muons are measured at two directions, and no anisotropy is observed. This set of observations indicates that high dE/dx is necessary for an anisotropy to be present for a given type of scintillation event, which in turn could be used to discriminate among different hypotheses for the underlying causes of the anisotropy, ...
Frequency response in surface-potential driven electrohydrodynamics
Ejsing, L.; Smistrup, K.; Pedersen, C. M.; Mortensen, N. A.; Bruus, H.
2006-03-01
Using a Fourier approach we offer a general solution to calculations of slip velocity within the circuit description of the electrohydrodynamics in a binary electrolyte confined by a plane surface with a modulated surface potential. We consider the case with a spatially constant intrinsic surface capacitance where the net flow rate is, in general, zero while harmonic rolls as well as time-averaged vortexlike components may exist depending on the spatial symmetry and extension of the surface potential. In general, the system displays a resonance behavior at a frequency corresponding to the inverse RC time of the system. Different surface potentials share the common feature that the resonance frequency is inversely proportional to the characteristic length scale of the surface potential. For the asymptotic frequency dependence above resonance we find a ω-2 power law for surface potentials with either an even or an odd symmetry. Below resonance we also find a power law ωα with α being positive and dependent of the properties of the surface potential. Comparing a tanh potential and a sech potential we qualitatively find the same slip velocity, but for the below-resonance frequency response the two potentials display different power-law asymptotics with α=1 and α˜2 , respectively.
Aircraft Fault Detection Using Real-Time Frequency Response Estimation
Grauer, Jared A.
2016-01-01
A real-time method for estimating time-varying aircraft frequency responses from input and output measurements was demonstrated. The Bat-4 subscale airplane was used with NASA Langley Research Center's AirSTAR unmanned aerial flight test facility to conduct flight tests and collect data for dynamic modeling. Orthogonal phase-optimized multisine inputs, summed with pilot stick and pedal inputs, were used to excite the responses. The aircraft was tested in its normal configuration and with emulated failures, which included a stuck left ruddervator and an increased command path latency. No prior knowledge of a dynamic model was used or available for the estimation. The longitudinal short period dynamics were investigated in this work. Time-varying frequency responses and stability margins were tracked well using a 20 second sliding window of data, as compared to a post-flight analysis using output error parameter estimation and a low-order equivalent system model. This method could be used in a real-time fault detection system, or for other applications of dynamic modeling such as real-time verification of stability margins during envelope expansion tests.
Response of air stagnation frequency to anthropogenically enhanced radiative forcing
Stagnant atmospheric conditions can lead to hazardous air quality by allowing ozone and particulate matter to accumulate and persist in the near-surface environment. By changing atmospheric circulation and precipitation patterns, global warming could alter the meteorological factors that regulate air stagnation frequency. We analyze the response of the National Climatic Data Center (NCDC) air stagnation index (ASI) to anthropogenically enhanced radiative forcing using global climate model projections of late-21st century climate change (SRESA1B scenario). Our results indicate that the atmospheric conditions over the highly populated, highly industrialized regions of the eastern United States, Mediterranean Europe, and eastern China are particularly sensitive to global warming, with the occurrence of stagnant conditions projected to increase by 12–25% relative to late-20th century stagnation frequencies (3–18 + days yr−1). Changes in the position/strength of the polar jet, in the occurrence of light surface winds, and in the number of precipitation-free days all contribute to more frequent late-21st century air mass stagnation over these high-population regions. In addition, we find substantial inter-model spread in the simulated response of stagnation conditions over some regions using either native or bias corrected global climate model simulations, suggesting that changes in the atmospheric circulation and/or the distribution of precipitation represent important sources of uncertainty in the response of air quality to global warming. (letter)
Response of air stagnation frequency to anthropogenically enhanced radiative forcing.
Horton, Daniel E; Harshvardhan; Diffenbaugh, Noah S
2012-01-01
Stagnant atmospheric conditions can lead to hazardous air quality by allowing ozone and particulate matter to accumulate and persist in the near-surface environment. By changing atmospheric circulation and precipitation patterns, global warming could alter the meteorological factors that regulate air stagnation frequency. We analyze the response of the National Climatic Data Center (NCDC) Air Stagnation Index (ASI) to anthropogenically enhanced radiative forcing using global climate model projections of late-21(st) century climate change (SRES A1B scenario). Our results indicate that the atmospheric conditions over the highly populated, highly industrialized regions of the eastern United States, Mediterranean Europe, and eastern China are particularly sensitive to global warming, with the occurrence of stagnant conditions projected to increase 12-to-25% relative to late-20(th) century stagnation frequencies (3-18+ days/year). Changes in the position/strength of the polar jet, in the occurrence of light surface winds, and in the number of precipitation-free days all contribute to more frequent late-21(st) century air mass stagnation over these high-population regions. In addition, we find substantial inter-model spread in the simulated response of stagnation conditions over some regions using either native or bias corrected global climate model simulations, suggesting that changes in the atmospheric circulation and/or the distribution of precipitation represent important sources of uncertainty in the response of air quality to global warming. PMID:23284587
Frequency Response Adaptive Control of a Refrigeration Cycle
Jens G. Balchen
1989-01-01
Full Text Available A technique for the adaptation of controller parameters in a single control loop based upon the estimation of frequency response parameters has been presented in an earlier paper. This paper contains an extension and a generalization of the first method and results in a more versatile solution which is applicable to a wider range of process characteristics. The application of this adaptive control technique is illustrated by a laboratory refrigeration cycle in which the evaporator pressure controls the speed of the compressor.
Superlens from complementary anisotropic metamaterials
Li, G. X.; Tam, H. L.; Wang, F. Y.; Cheah, K. W.
2007-12-01
Metamaterials with isotropic property have been shown to possess novel optical properties such as a negative refractive index that can be used to design a superlens. Recently, it was shown that metamaterials with anisotropic property can translate the high-frequency wave vector k values from evanescence to propagating. However, electromagnetic waves traveling in single-layer anisotropic metamaterial produce diverging waves of different spatial frequency. In this work, it is shown that, using bilayer metamaterials that have complementary anisotropic property, the diverging waves are recombined to produce a subwavelength image, i.e., a superlens device can be designed. The simulation further shows that the design can be achieved using a metal/oxide multilayer, and a resolution of 30 nm can be easily obtained in the optical frequency range.
Kiyono, Ken; Tsujimoto, Yutaka
2016-07-01
We develop a general framework to study the time and frequency domain characteristics of detrending-operation-based scaling analysis methods, such as detrended fluctuation analysis (DFA) and detrending moving average (DMA) analysis. In this framework, using either the time or frequency domain approach, the frequency responses of detrending operations are calculated analytically. Although the frequency domain approach based on conventional linear analysis techniques is only applicable to linear detrending operations, the time domain approach presented here is applicable to both linear and nonlinear detrending operations. Furthermore, using the relationship between the time and frequency domain representations of the frequency responses, the frequency domain characteristics of nonlinear detrending operations can be obtained. Based on the calculated frequency responses, it is possible to establish a direct connection between the root-mean-square deviation of the detrending-operation-based scaling analysis and the power spectrum for linear stochastic processes. Here, by applying our methods to DFA and DMA, including higher-order cases, exact frequency responses are calculated. In addition, we analytically investigate the cutoff frequencies of DFA and DMA detrending operations and show that these frequencies are not optimally adjusted to coincide with the corresponding time scale.
Coupled vibro-acoustic model updating using frequency response functions
Nehete, D. V.; Modak, S. V.; Gupta, K.
2016-03-01
Interior noise in cavities of motorized vehicles is of increasing significance due to the lightweight design of these structures. Accurate coupled vibro-acoustic FE models of such cavities are required so as to allow a reliable design and analysis. It is, however, experienced that the vibro-acoustic predictions using these models do not often correlate acceptably well with the experimental measurements and hence require model updating. Both the structural and the acoustic parameters addressing the stiffness as well as the damping modeling inaccuracies need to be considered simultaneously in the model updating framework in order to obtain an accurate estimate of these parameters. It is also noted that the acoustic absorption properties are generally frequency dependent. This makes use of modal data based methods for updating vibro-acoustic FE models difficult. In view of this, the present paper proposes a method based on vibro-acoustic frequency response functions that allow updating of a coupled FE model by considering simultaneously the parameters associated with both the structural as well as the acoustic model of the cavity. The effectiveness of the proposed method is demonstrated through numerical studies on a 3D rectangular box cavity with a flexible plate. Updating parameters related to the material property, stiffness of joints between the plate and the rectangular cavity and the properties of absorbing surfaces of the acoustic cavity are considered. The robustness of the method under presence of noise is also studied.
[HLA and keloids: antigenic frequency and therapeutic response].
Rossi, A; Bozzi, M
1989-01-01
Twenty keloid subjects were typed for class 1 (HLA-A, B and C) and class 2 (HLA-DR and DQ) histocompatibility antigens. Their frequencies were compared to those found in control populations. Of all the antigens belonging to class 1, B 21 was more prevalent in patients. The findings regarding class 2 antigens were noteworthy: in keloid patients there was a significant prevalence of DR 5 (RR = 3.54 and 7.93 respectively for the two control groups) and DQw 3 (RR = 16.8). The patients typed for HLA-antigens were treated with corticosteroid infiltrations. The responses to the treatments were no related to the histocompatibility antigens. PMID:2628278
Nano-resonator frequency response based on strain gradient theory
This paper aims to explore the dynamic behaviour of a nano-resonator under ac and dc excitation using strain gradient theory. To achieve this goal, the partial differential equation of nano-beam vibration is first converted to an ordinary differential equation by the Galerkin projection method and the lumped model is derived. Lumped parameters of the nano-resonator, such as linear and nonlinear springs and damper coefficients, are compared with those of classical theory and it is demonstrated that beams with smaller thickness display greater deviation from classical parameters. Stable and unstable equilibrium points based on classic and non-classical theories are also compared. The results show that, regarding the applied dc voltage, the dynamic behaviours expected by classical and non-classical theories are significantly different, such that one theory predicts the un-deformed shape as the stable condition, while the other theory predicts that the beam will experience bi-stability. To obtain the frequency response of the nano-resonator, a general equation including cubic and quadratic nonlinearities in addition to parametric electrostatic excitation terms is derived, and the analytical solution is determined using a second-order multiple scales method. Based on frequency response analysis, the softening and hardening effects given by two theories are investigated and compared, and it is observed that neglecting the size effect can lead to two completely different predictions in the dynamic behaviour of the resonators. The findings of this article can be helpful in the design and characterization of the size-dependent dynamic behaviour of resonators on small scales. (paper)
Cropping frequency and area response to climate variability can exceed yield response
Cohn, Avery S.; Vanwey, Leah K.; Spera, Stephanie A.; Mustard, John F.
2016-06-01
The sensitivity of agricultural output to climate change has often been estimated by modelling crop yields under climate change scenarios or with statistical analysis of the impacts of year-to-year climatic variability on crop yields. However, the area of cropland and the number of crops harvested per growing season (cropping frequency) both also affect agricultural output and both also show sensitivity to climate variability and change. We model the change in agricultural output associated with the response of crop yield, crop frequency and crop area to year-to-year climate variability in Mato Grosso (MT), Brazil, a key agricultural region. Roughly 70% of the change in agricultural output caused by climate was determined by changes in frequency and/or changes in area. Hot and wet conditions were associated with the largest losses and cool and dry conditions with the largest gains. All frequency and area effects had the same sign as total effects, but this was not always the case for yield effects. A focus on yields alone may therefore bias assessments of the vulnerability of agriculture to climate change. Efforts to reduce climate impacts to agriculture should seek to limit production losses not only from crop yield, but also from changes in cropland area and cropping frequency.
Study of the Relative Permittivity Response of Metal Nanoantenna at Optical Frequency
Mehnaj Mahbuba; Nafiz Ahmed Chisty
2014-01-01
In this paper the relative permittivity response of some nanometals such as Gold (Au), Silver(Ag), Copper(Cu), Aluminum (Al) and Nickel(Ni) are investigated at optical frequencies. The permittivity response is necessary because the optical response of the metal nanoantenna highly depends on the permittivity of the metals. The surface plasma response largely depends on the permittivity response at optical frequency. This relative permittivity response also playsan ...
Winey, J. M.; Gupta, Y. M.
2014-07-01
Understanding and modeling the response of hcp metals to high stress impulsive loading is challenging because the lower crystal symmetry, compared to cubic metals, results in a significantly more complex material response. To gain insight into the inelastic deformation of hcp metals subjected to high dynamic stresses, shock wave compression of single crystals provides a useful approach because different inelastic deformation mechanisms can be examined selectively by shock compression along different crystal orientations. As a representative example, we report, here, on wave propagation simulations for beryllium (Be) single crystals shocked along the c-axis, a-axis, and several low-symmetry directions to peak stresses reaching 7 GPa. The simulations utilized a time-dependent, anisotropic material model that incorporated dislocation dynamics, deformation twinning, and shear cracking based descriptions of inelastic deformation. The simulation results showed good overall agreement with measured wave profiles for all the different crystal orientations examined [Pope and Johnson, J. Appl. Phys. 46, 720 (1975)], including features arising from wave mode coupling due to the highly anisotropic inelastic response of Be. This good agreement demonstrates that the measured profiles can be understood in terms of dislocation slip along basal, prismatic, and pyramidal planes, together with deformation twinning along { 10 1 ¯ 2 } planes. Our results show that the response of shocked Be single crystals involves the simultaneous operation of multiple, distinct inelastic deformation mechanisms for all orientations except the c-axis. For shocked c-axis Be, the measured wave profiles do not provide good discrimination between pyramidal slip and other inelastic deformation mechanisms, such as shear cracking. The findings presented here provide insight into the complex inelastic deformation response of shocked Be single crystals and are expected to be useful for other hcp crystals. More
Understanding and modeling the response of hcp metals to high stress impulsive loading is challenging because the lower crystal symmetry, compared to cubic metals, results in a significantly more complex material response. To gain insight into the inelastic deformation of hcp metals subjected to high dynamic stresses, shock wave compression of single crystals provides a useful approach because different inelastic deformation mechanisms can be examined selectively by shock compression along different crystal orientations. As a representative example, we report, here, on wave propagation simulations for beryllium (Be) single crystals shocked along the c-axis, a-axis, and several low-symmetry directions to peak stresses reaching 7 GPa. The simulations utilized a time-dependent, anisotropic material model that incorporated dislocation dynamics, deformation twinning, and shear cracking based descriptions of inelastic deformation. The simulation results showed good overall agreement with measured wave profiles for all the different crystal orientations examined [Pope and Johnson, J. Appl. Phys. 46, 720 (1975)], including features arising from wave mode coupling due to the highly anisotropic inelastic response of Be. This good agreement demonstrates that the measured profiles can be understood in terms of dislocation slip along basal, prismatic, and pyramidal planes, together with deformation twinning along (101¯2) planes. Our results show that the response of shocked Be single crystals involves the simultaneous operation of multiple, distinct inelastic deformation mechanisms for all orientations except the c-axis. For shocked c-axis Be, the measured wave profiles do not provide good discrimination between pyramidal slip and other inelastic deformation mechanisms, such as shear cracking. The findings presented here provide insight into the complex inelastic deformation response of shocked Be single crystals and are expected to be useful for other hcp crystals. More
Optics of anisotropic nanostructures
Rokushima, Katsu; Antoš, Roman; Mistrík, Jan; Višňovský, Štefan; Yamaguchi, Tomuo
2006-07-01
The analytical formalism of Rokushima and Yamakita [J. Opt. Soc. Am. 73, 901-908 (1983)] treating the Fraunhofer diffraction in planar multilayered anisotropic gratings proved to be a useful introduction to new fundamental and practical situations encountered in laterally structured periodic (both isotropic and anisotropic) multilayer media. These are employed in the spectroscopic ellipsometry for modeling surface roughness and in-depth profiles, as well as in the design of various frequency-selective elements including photonic crystals. The subject forms the basis for the solution of inverse problems in scatterometry of periodic nanostructures including magnetic and magneto-optic recording media. It has no principal limitations as for the frequencies and period to radiation wavelength ratios and may include matter wave diffraction. The aim of the paper is to make this formalism easily accessible to a broader community of students and non-specialists. Many aspects of traditional electromagnetic optics are covered as special cases from a modern and more general point of view, e.g., plane wave propagation in isotropic media, reflection and refraction at interfaces, Fabry-Perot resonator, optics of thin films and multilayers, slab dielectric waveguides, crystal optics, acousto-, electro-, and magneto-optics, diffraction gratings, etc. The formalism is illustrated on a model simulating the diffraction on a ferromagnetic wire grating.
Study of the Relative Permittivity Response of Metal Nanoantenna at Optical Frequency
Mehnaj Mahbuba
2014-01-01
Full Text Available In this paper the relative permittivity response of some nanometals such as Gold (Au, Silver(Ag, Copper(Cu, Aluminum (Al and Nickel(Ni are investigated at optical frequencies. The permittivity response is necessary because the optical response of the metal nanoantenna highly depends on the permittivity of the metals. The surface plasma response largely depends on the permittivity response at optical frequency. This relative permittivity response also playsan important role in the design process of a nanoantenna. This paper represents the permittivity response at the frequency range of 20-300 THz (the wavelength range of 3-15 µm
Dynamic Response to Pedestrian Loads with Statistical Frequency Distribution
Krenk, Steen
2012-01-01
Pedestrian loads depend on the regularity and frequency of the footfall process. Traditionally, pedestrian loads have been represented by one or more specific harmonic components with a well-defined frequency, and light footbridges have been investigated for resonance vibration generated by the h...
Calzado-Martín, Alicia; Crespo, Lara; Saldaña, Laura; Boré, Alba; Gómez-Barrena, Enrique; Vilaboa, Nuria
2014-09-01
This article reports on the interactions of human bone cells, mesenchymal stem cells (hMSCs) from bone marrow and osteoblasts (hOBs), with a submicron-grooved Ti6Al4V alloy that promotes cell orientation in the direction of the anisotropy. Adhesion sites, actin and tubulin networks and fibronectin extracellular matrix of both cell types align with the direction of the grooves. hMSCs adhere at a higher rate on the patterned substrate than on the polished alloy, while no differences are found in hOBs attachment. Compared to the flat substrate, RhoA activity is higher in hMSCs and hOB cultured on the grooved alloy and treatment with C3 transferase leads to loss of organization of actin and tubulin cytoskeletons. Rho-associated kinase (ROCK) activity of hMSCs is upregulated on the anisotropic samples, but not affected in hOBs. Treatment with hydroxyfasudil disrupts the alignment of adhesion sites in hMSCs but not in hOBs. When cells are cultured in media that support osteogenic maturation, OPN secretion increases in hMSCs on the anisotropic alloy and it remains unaffected in hOBs. Cell layer calcification proceeds to a same extent in hMSCs cultured on the two metallic surfaces but decreases in hOBs cultured on the patterned samples. Taken together, these results indicate that hOBs are less sensitive than hMSCs to the patterned Ti6Al4V alloy. This effect can be attributed to their different stages of cell maturation and may be mediated, at least in part, through ROCK signaling because its activity increases on hMSCs cultured on the patterned alloy, while hOBs fail to upregulate it. PMID:24136907
Frequency-temperature response of a new multiferroic
Nawnit Kumar; Sunanda K. Patri; Ram N.P. Choudhary
2014-01-01
The frequency dependence of the electrical properties of a new complex multiferroic Bi4Pb2Ti3FeNbO18 at different temperatures was investigated by impedance spectroscopy technique. The impedance spectroscopic data were collected at different frequencies (100Hz–1MHz) and temperatures (25–500 °C). This study provides important information about the effect of grain and grain boundary on microstructures of the materials. The data are presented in the Nyquist plots, from which electrical resist...
Application of frequency domain analysis to transient response of nuclear containment structures
A combination of frequency domain and time domain analyses is proposed to obtain the dynamic responses of nuclear power plant containment structures. A soil-structure model of a boiling water reactor containment subjected to an assumed safety relief valve blowdown load is used as illustration. Linear time-invariant systems are analysed using input forcing functions with varying frequency contents. Time domain analysis is performed using a synthesized input forcing function. The system characteristic function is generated in the frequency domain through Fourier transforms of the response time history and the synthesized input time history. The frequency response due to any other forcing function is obtained in frequency domain by using the system characteristic function, and the response time history is obtained by inverse Fourier transforms of the frequency response. The results obtained by the proposed method are in close agreement with the conventional time domain dynamic finite element analysis. (Auth.)
Outer hair cell piezoelectricity: Frequency response enhancement and resonance behavior
Weitzel, Erik K.; Tasker, Ron; Brownell, William E.
2003-09-01
Stretching or compressing an outer hair cell alters its membrane potential and, conversely, changing the electrical potential alters its length. This bi-directional energy conversion takes place in the cell's lateral wall and resembles the direct and converse piezoelectric effects both qualitatively and quantitatively. A piezoelectric model of the lateral wall has been developed that is based on the electrical and material parameters of the lateral wall. An equivalent circuit for the outer hair cell that includes piezoelectricity shows a greater admittance at high frequencies than one containing only membrane resistance and capacitance. The model also predicts resonance at ultrasonic frequencies that is inversely proportional to cell length. These features suggest all mammals use outer hair cell piezoelectricity to support the high-frequency receptor potentials that drive electromotility. It is also possible that members of some mammalian orders use outer hair cell piezoelectric resonance in detecting species-specific vocalizations.
Experimental frequency response for boiling two-phase flow to power variation
This paper presents experimental data on power to void, and power to pressure drop frequency response of boiling two-phase flow in a vertical heated channel with Freon-113 as the working fluid. Experimental frequency response functions are measured with statistical method over a frequency range of 0.02 to 10 Hz. The data cover inlet subcooling of 7.5 and 20 K, mass flux of 500, 1000 and 2000 kg/m2s, and various power levels. Influence of each parameter on the frequency response are described. Finally the data are compared with theoretical value obtained by means of linearization technique. (author)
Makino, Kotaro; Saito, Yuta; Fons, Paul; Kolobov, Alexander V.; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki
2016-01-01
Optical excitation of matter with linearly-polarized femtosecond pulses creates a transient non-equilibrium lattice displacement along a certain direction. Here, the pump and probe pulse polarization dependence of the photo-induced ultrafast lattice dynamics in (GeTe)2/(Sb2Te3)4 interfacial phase change memory material is investigated under obliquely incident conditions. Drastic pump polarization dependence of the coherent phonon amplitude is observed when the probe polarization angle is parallel to the c–axis of the sample, while the pump polarization dependence is negligible when the probe polarization angle is perpendicular to the c–axis. The enhancement of phonon oscillation amplitude due to pump polarization rotation for a specific probe polarization angle is only found in the early time stage (≤2 ps). These results indicate that the origin of the pump and probe polarization dependence is dominantly attributable to the anisotropically-formed photo-excited carriers which cause the directional lattice dynamics. PMID:26805401
Makino, Kotaro; Saito, Yuta; Fons, Paul; Kolobov, Alexander V.; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki
2016-01-01
Optical excitation of matter with linearly-polarized femtosecond pulses creates a transient non-equilibrium lattice displacement along a certain direction. Here, the pump and probe pulse polarization dependence of the photo-induced ultrafast lattice dynamics in (GeTe)2/(Sb2Te3)4 interfacial phase change memory material is investigated under obliquely incident conditions. Drastic pump polarization dependence of the coherent phonon amplitude is observed when the probe polarization angle is parallel to the c-axis of the sample, while the pump polarization dependence is negligible when the probe polarization angle is perpendicular to the c-axis. The enhancement of phonon oscillation amplitude due to pump polarization rotation for a specific probe polarization angle is only found in the early time stage (≤2 ps). These results indicate that the origin of the pump and probe polarization dependence is dominantly attributable to the anisotropically-formed photo-excited carriers which cause the directional lattice dynamics.
Influence of magnetizing and filtering frequencies on Barkhausen noise response
Stupakov, Oleksandr; Melikhov, Y.
2014-01-01
Roč. 50, č. 4 (2014), s. 6100104. ISSN 0018-9464 R&D Projects: GA ČR GA13-18993S Institutional support: RVO:68378271 Keywords : Barkhausen effect * filtering * frequency measurement * magnetic field measurement Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.386, year: 2014
The frequency response measurements of a reactor at low power help in determining the kinetic parameters of a reactor and ultimately in investigating its stability with respect to small perturbations in reactivity. In this report, we present the results of the zero-power frequency response measurements of GHARR-1 by rod method and its analytical analogue. The comparison in calculated and measured values is reasonably good in the frequency range used (author)
Test method of frequency response based on diamond surface acoustic wave devices
CHEN Xi-ming; YANG Bao-he; WU Xiao-guo; WU Yi-zhuo
2011-01-01
In order to reduce the noises affixed to the signals when testing high frequency devices, a single-port test mode (S11) is used to test frequency response of high frequency (GHz) and dual-port surface acoustic wave devices (SAWDs) in this paper.The feasibility of the test is proved by simulating the Fabry-Perot model. The frequency response of the high-frequency dual-port resonant-type diamond SAWD is measured by S11 and the dual-port test mode (S21), respectively. The results show that the quality factor of the device is 51.29 and the 3 dB bandwidth is 27.8 MHz by S11 -mode measurement, which is better than the S21 mode, and is consistent with the frequency response curve by simulation.
DIKEN, H.
2000-06-01
A single-link manipulator consisting of servomotor, elastic shaft and rigid link is chosen to represent an elastic control system. Equations of the torsional elastic system are derived including the servomotor control system parameters. The transfer function of the elastic control system is obtained including not only control system parameters but also the natural frequency and the damping ratio of the torsional vibratory system. Non-dimensional parameters such as the ratio of the structural natural frequency to the substructural natural frequency and the ratio of the substructural natural frequency to the control system frequency are defined. The effects of these parameters on the frequency response of the system are investigated. A simple and effective method using the frequency-response characteristics is proposed to track a cycloidal trajectory precisely.
Efficient 3D frequency response modeling with spectral accuracy by the rapid expansion method
Chu, Chunlei
2012-07-01
Frequency responses of seismic wave propagation can be obtained either by directly solving the frequency domain wave equations or by transforming the time domain wavefields using the Fourier transform. The former approach requires solving systems of linear equations, which becomes progressively difficult to tackle for larger scale models and for higher frequency components. On the contrary, the latter approach can be efficiently implemented using explicit time integration methods in conjunction with running summations as the computation progresses. Commonly used explicit time integration methods correspond to the truncated Taylor series approximations that can cause significant errors for large time steps. The rapid expansion method (REM) uses the Chebyshev expansion and offers an optimal solution to the second-order-in-time wave equations. When applying the Fourier transform to the time domain wavefield solution computed by the REM, we can derive a frequency response modeling formula that has the same form as the original time domain REM equation but with different summation coefficients. In particular, the summation coefficients for the frequency response modeling formula corresponds to the Fourier transform of those for the time domain modeling equation. As a result, we can directly compute frequency responses from the Chebyshev expansion polynomials rather than the time domain wavefield snapshots as do other time domain frequency response modeling methods. When combined with the pseudospectral method in space, this new frequency response modeling method can produce spectrally accurate results with high efficiency. © 2012 Society of Exploration Geophysicists.
Electrodynamic features of anisotropic hard superconductors
Voloshin, I F; Fisher, L M; Aksenov, A V; Yampolskij, V A
2001-01-01
The low-frequency electromagnetic response of the superconducting plates, which are characterized by strong anisotropy of the current-carrying capacity in the sample plane, is experimentally and theoretically studied. The measurements are carried out on the polycrystalline textured plates of the Y-123 system as well as on the monocrystal. It is shown that the form of curves describing the dependence of the q relative losses on the h sub 0 alternate field amplitudes is highly sensitive to the h sub 0 vector orientation in the sample plane. The q(h sub 0) dependence by the h sub 0 orientation along one of the main directions of the current anisotropic critical density symmetry the q(h sub 0) dependence is characterized by the single dimensional maximum. Two dimensional maxima are observed on the q(h sub 0) curve by the h sub 0 significant deviation from the main directions
The effect of feeding frequency on insulin and ghrelin responses in human subjects
Solomon, Thomas; Chambers, Edward S; Jeukendrup, Asker E; Toogood, Andrew A; Blannin, Andrew K
2008-01-01
Recent work shows that increased meal frequency reduces ghrelin responses in sheep. Human research suggests there is an interaction between insulin and ghrelin. The effect of meal frequency on this interaction is unknown. Therefore, we investigated the effect of feeding frequency on insulin and...... ghrelin responses in human subjects. Five healthy male volunteers were recruited from the general population: age 24 (SEM 2)years, body mass 75.7 (SEM 3.2) kg and BMI 23.8 (SEM 0.8) kg/m(2). Volunteers underwent three 8-h feeding regimens: fasting (FAST); low-frequency(two) meal ingestion (LOFREQ......(MEAL)); high-frequency (twelve) meal ingestion (HIFREQ(MEAL)). Meals were equi-energetic within trials,consisting of 64% carbohydrate, 23% fat and 13% protein. Total energy intake was equal between feeding trials. Total area under the curve for serum insulin and plasma ghrelin responses did not differ between...
The optimal control frequency response problem in manual control. [of manned aircraft systems
Harrington, W. W.
1977-01-01
An optimal control frequency response problem is defined within the context of the optimal pilot model. The problem is designed to specify pilot model control frequencies reflective of important aircraft system properties, such as control feel system dynamics, airframe dynamics, and gust environment, as well as man machine properties, such as task and attention allocation. This is accomplished by determining a bounded set of control frequencies which minimize the total control cost. The bounds are given by zero and the neuromuscular control frequency response for each control actuator. This approach is fully adaptive, i.e., does not depend upon user entered estimates. An algorithm is developed to solve this optimal control frequency response problem. The algorithm is then applied to an attitude hold task for a bare airframe fighter aircraft case with interesting dynamic properties.
Claudia Rahmann
2014-09-01
Full Text Available In recent years, only a small number of publications have been presented addressing power system stability with the increased use of large-scale photovoltaic (PV generation around the world. The focus of these publications was on classical stability problems, such as transient and small signal stability, without considering frequency stability. Nevertheless, with increased PV generation, its effects on system frequency response during contingencies can no longer be ignored, especially in the case of weakly interconnected networks or isolated power systems. This paper addresses the impacts of large scale PV generation on the frequency stability of power systems. The positive effects of deloaded PV power plants (PV-PPs able to support system frequency recovery during the initial seconds after major contingencies are also examined. Because this type of frequency support is not covered by current definitions, a new terminology is proposed that includes the frequency response of inertia-less generation units immediately after major power imbalances. We refer to this type of frequency support as fast frequency response (FFR. Finally, a discussion is also presented regarding the applicability and pertinence of frequency-related grid requirements for PV-PPs in the case of real power systems. The investigation is based on the isolated power system of northern Chile. The obtained results indicate that in the case of major power imbalances, no significant effects arise on the system frequency response until PV penetration levels exceed approximately 20%. From a system security perspective, the problems arise for PV penetration levels of approximately 50%, in which case, the frequency response capability in PV-PPs would be justified during certain hours of the year.
Frequency Response of a Gas-filled Tube with Minor Losses
West, Brian M.
2011-01-01
A thesis on the study of the frequency response of a pneumatic system designed to provide pulsed flow for flow control applications is presented. The system consists of a high pressure air source, a high-frequency solenoid valve, a length of tube and a minor loss. The experiment mimics the pneumatic drive for our Coanda-Assisted Spray Manipulation actuator and applies to many flow control applications involving pulsed flow. Square wave signals of various frequency are fed to the solenoid valv...
Palmer, Alan R; Shackleton, Trevor M.; Sumner, Christian J.; Zobay, Oliver; Rees, Adrian
2013-01-01
A differential response to sound frequency is a fundamental property of auditory neurons. Frequency analysis in the cochlea gives rise to V-shaped tuning functions in auditory nerve fibres, but by the level of the inferior colliculus (IC), the midbrain nucleus of the auditory pathway, neuronal receptive fields display diverse shapes that reflect the interplay of excitation and inhibition. The origin and nature of these frequency receptive field types is still open to question. One proposed hy...
High-field response of gated graphene at terahertz frequencies
Razavipour, Hadi; Yang, Wayne; Guermoune, Abdeladim; Hilke, Michael; Cooke, David G.; Al-Naib, Ibraheem; Dignam, Marc M.; Blanchard, François; Hafez, Hassan A.; Chai, Xin; Ferachou, Denis; Ozaki, Tsuneyuki; Lévesque, Pierre L.; Martel, Richard
2015-12-01
We study the Fermi energy level dependence of the nonlinear terahertz (THz) transmission of gated multilayer and single-layer graphene transferred onto sapphire and quartz substrates. The two samples represent two limits of low-field impurity scattering: short-range neutral and long-range charged impurity scattering, respectively. We observe an increase in the transmission as the field amplitude is increased due to intraband absorption bleaching starting at THz fields above 8 kV/cm. This effect arises from a field-induced reduction in THz conductivity that depends strongly on the Fermi energy. We account for intraband absorption using a free carrier Drude model that includes neutral and charged impurity scattering as well as optical phonon scattering. We find that although the Fermi-level dependence in the monolayer and five-layer samples is quite different due to the dominance of long- and short-range momentum scattering, respectively, both exhibit a strong dependence on the field amplitude that cannot be explained on the basis of an increase in the lattice temperature alone. Our results provide a deeper understanding of transport in graphene devices operating at THz frequencies and in modest kV/cm field strengths where nonlinearities exist.
Aeroelastic modal dynamics of wind turbines including anisotropic effects
Fisker Skjoldan, P.
2011-03-15
Several methods for aeroelastic modal analysis of a rotating wind turbine are developed and used to analyse the modal dynamics of two simplified models and a complex model in isotropic and anisotropic conditions. The Coleman transformation is used to enable extraction of the modal frequencies, damping, and periodic mode shapes of a rotating wind turbine by describing the rotor degrees of freedom in the inertial frame. This approach is valid only for an isotropic system. Anisotropic systems, e.g., with an unbalanced rotor or operating in wind shear, are treated with the general approaches of Floquet analysis or Hill's method which do not provide a unique reference frame for observing the modal frequency, to which any multiple of the rotor speed can be added. This indeterminacy is resolved by requiring that the periodic mode shape be as constant as possible in the inertial frame. The modal frequency is thus identified as the dominant frequency in the response of a pure excitation of the mode observed in the inertial frame. A modal analysis tool based directly on the complex aeroelastic wind turbine code BHawC is presented. It uses the Coleman approach in isotropic conditions and the computationally efficient implicit Floquet analysis in anisotropic conditions. The tool is validated against system identifications with the partial Floquet method on the nonlinear BHawC model of a 2.3 MW wind turbine. System identification results show that nonlinear effects on the 2.3 MW turbine in most cases are small, but indicate that the controller creates nonlinear damping. In isotropic conditions the periodic mode shape contains up to three harmonic components, but in anisotropic conditions it can contain an infinite number of harmonic components with frequencies that are multiples of the rotor speed. These harmonics appear in calculated frequency responses of the turbine. Extreme wind shear changes the modal damping when the flow is separated due to an interaction between
Study on DFIG wind turbines control strategy for improving frequency response characteristics
Zhao, Dongmei; Wu, Di; Liu, Yanhua; Zhou, Zhiyu
2012-01-01
The active and reactive power decoupling control for the double-fed induction generator wind turbines(DFIG) does not play a positive role to the frequency response ability of power grid because it performs as the hidden inertia for the power grid. If we want to improve the transient frequency stability of the wind turbine when it is integrated with the system, we must ameliorate its frequency response characteristics. The inability of frequency control due to DFIG decoupling control could be overcome through releasing (or absorbing) a part of the kinetic energy stored in the rotor, so as to increase (or decrease) active power injected to the power system when the deviation of power system frequency appears. This paper discusses the mathematical model of the variable speed DFIG, including the aerodynamic model, pitch control system model, shaft model, generator model and inverter control model, and other key components, focusing on the mathematical model of the converters in rotor side and grid side. Based on the existing model of wind generator, the paper attaches the frequency control model on the platform of the simulation software DIgSILENT/PowerFactory. The simulation results show that the proposed control strategy can response quickly to transient frequency deviation and prove that wind farms can participate in the system frequency regulation to a certain extent. Finally, the result verifies the accuracy and plausibility of the inverter control model which attaches the frequency control module.
Unfolded Frequency Response and Model of a Multi-Tap Direct Sampling Mixer
PAN Yun; GE Ning; DONG Zaiwang
2008-01-01
A transform method was used to model a discrete time multi-tap direct sampling mixer. The method transforms the mixed filtering and down.sampling stages to separate cascade filtering and sampling stages to determine the unfolded frequency response which shows the anti-aliasing ability of the mixer. The transformation can also be applied to other mixed signal and multi-rate receiver systems to analyze their unfolded frequency responses. The transformed system architecture was used to calculate the unfolded frequency response of the multi-tap direct sampling mixer and compared with the mixer model without noise in the ad-vanced design system 2005A environment to further evaluate the frequency response. The simulations show that the -3 dB bandwidth is 3.0 MHz and the voltage gain is attenuated by 1.5 dB within a 1-MHz baseband bandwidth.
Arana Aristi, Iván; Holbøll, Joachim; Sørensen, T
2010-01-01
This paper presents the results of several sweep frequency response analysis (SFRA) measurements performed on two identical offshore wind farm transformers. A comparison is made between the transformers based on different recommended measurements and procedures, different measurement systems for...
Arana, Ivan; Soerensen, Troels [DONG Energy (Denmark); Holboell, Joachim [Technical Univ. of Denmark (Denmark)
2010-07-01
This paper presents the results of several sweep frequency response analysis (SFRA) measurements performed on two identical offshore wind farm transformers. A comparison is made between the transformers based on different recommended measurements and procedures, different measurement systems for frequency response analysis (FRA) and different tap changer positions. It was shown how the series impedance and capacitance between windings vary depending on the tap changer position. (orig.)
System-wide contribution to frequency response from variable speed wind turbines
Ruttledge, Lisa; Flynn, Damian
2012-01-01
Due to the differing electromechanical characteristics of modern variable speed wind turbines to conventional generators, the provision of ancillary services from wind generation is likely to change the nature of the frequency response of power systems to contingency events. This paper explores the aggregate contribution from wind turbines to the frequency response of future power systems, considering both emulated inertial and governor controls. In particular, the potential issues that may a...
Low-frequency dielectrophoretic response of a single particle in aqueous suspensions.
Wang, Jingyu; Wei, Ming-Tzo; Ou-Yang, H Daniel
2016-01-01
We use optical tweezers-based dielectrophoresis (DEP) force spectroscopy to investigate the roles of the electrical double layer in the AC dielectric response of an individual colloidal particle in an aqueous medium. Specifically, we measure the DEP crossover frequency as a function of particles size, medium viscosity, and temperature. Experimental results were compared to low frequency relaxation mechanisms predicted by Schwarz, demonstrating the dielectrophoretic responses in the frequency range between 10 kHz and 1 MHz were dominated by counterion diffusion within the electric double layer. PMID:26858820
Rapid estimation of frequency response functions by close-range photogrammetry
Tripp, J. S.
1985-01-01
The accuracy of a rapid method which estimates the frequency response function from stereoscopic dynamic data is computed. It is shown that reversal of the order of the operations of coordinate transformation and Fourier transformation, which provides a significant increase in computational speed, introduces error. A portion of the error, proportional to the perturbation components normal to the camera focal planes, cannot be eliminated. The remaining error may be eliminated by proper scaling of frequency data prior to coordinate transformation. Methods are developed for least squares estimation of the full 3x3 frequency response matrix for a three dimensional structure.
Implementation of Time and Frequency Response Analysis for Web-Based Laboratories
Teyana Sapula
2011-04-01
Full Text Available The University of Dar Es Salaam has developed the web-based laboratory for Time and Frequency Response Analysis. The purpose of this web-based laboratory is the utilization of real data from real experiments, in terms of instrumentation and experimental circuits, rather than simulations. The use of webbased laboratory came after realizing the difficulties imposed by the traditional laboratories. Web-based laboratories allow students and educators to interact with real laboratory equipment located anywhere in the world at anytime. This paper presents the implementation of web-based laboratory of single stage common emitter, resistor capacitor coupled amplifier using National Instruments Educational Laboratory Virtual Instrument Suite platform. Two components are deployed: time response analysis and frequency response analysis. The experiment allows students to carryout time and frequency analysis of the amplifier. The modular can be used to any microelectronic circuits to carry out any time response and frequency response analysis. Both the time response and frequency response analysis results of the amplifier are validated.
Frequency response of slot coating flow to gap disturbances
Lee, Semi; Nam, Jaewook
2016-03-01
Slot coating is a common method of manufacturing films such as optical films, adhesive tapes, etc. It is a pre-metered method: the final wet film thickness is set by the flow rate and the web speed, and independent of other operating parameters and coating liquid properties. Therefore, it is ideal for precise film thickness control. To produce uniform film, the coating flow needs to be steady-state, two-dimensional, and stable. In the slot coating process, however, there are always some small-scale disturbances generated by rotating process units, such as pumps, rolls, etc., and they usually have periodicity. These disturbances cause a non-uniformity of the moving web direction and could spoil the film quality. Therefore, the sensitivity analysis of coating flow under the periodic disturbances is important. Among all disturbances, a change of coating gap, i.e. the distance between the die lip and the moving substrate, is known to the most dangerous disturbance. This type of disturbance is usually called the gap oscillation, and caused by the substrate thickness variations, mechanical vibration of the coating die or roll, and roll run outs. Here, we analyze the effect of fluid properties, operating conditions and die configurations on response of slot coating flow to gap disturbances. In this study, we use Galerkin/finite element method to solve transient Navier-Stokes equation under periodic disturbance. We define the amplification factor as an indicator of film non-uniformity and analyze the effect of different parameters by comparing the factor. In particular, we use Carreau-Yasuda model to describe shear-thinning property of xanthan gum solution and compare with Newtonian fluid.
Non-linear response of an electrode-electrolyte interface impedance with the frequency
Ruiz, G. [Departamento de Bioingenieri' a, UNT/CONICET (Argentina)]. E-mail: gruiz@herrera.unt.edu.ar; Felice, C.J. [Departamento de Bioingenieri' a, UNT/CONICET (Argentina)
2007-01-15
In this paper we analyze the frequency response of a distributed parameters non-linear circuit. This circuit is a fractal model of an electrode-electrolyte interface. The results show that the series equivalent resistance R {sub eq} decreases as the number of fractal levels rises. Its frequency behavior is similar to the results described by other authors that used a constant phase angle element. At low frequency range, the series equivalent reactance X {sub eq} decreases with frequency and R {sub eq} shows a flat response in this range. The model also explains how interface geometry modifies the values of some electrochemical parameters. As roughness increases the Argand diagram shows smaller semicircles. The model behavior is like a single dispersion system with its central frequency increasing with the electrode roughness.
Borgne, H.
2004-12-01
Seismic imaging is an important tool for ail exploration. From the filtered seismic traces and a subsurface velocity model, migration allows to localize the reflectors and to estimate physical properties of these interfaces. The subsurface is split up into a reference medium, corresponding to the low spatial frequencies (a smooth medium), and a perturbation medium, corresponding to the high spatial frequencies. The propagation of elastic waves in the medium of reference is modelled by the ray theory. The association of this theory with a principle of diffraction or reflection allows to take into account the high spatial frequencies: the Kirchhoff approach represents so the medium of perturbations with continuous surfaces, characterized by reflection coefficients. The target of the quantitative migration is to reconstruct this reflection coefficient, notably its behaviour according to the incidence angle. These information will open the way to seismic characterization of the reservoir domain, with. a stratigraphic inversion for instance. In order to improve the qualitative and quantitative migration results, one of the current challenges is to take into account the anisotropy of the subsurface. Taking into account rocks anisotropy in the imaging process of seismic data requires two improvements from the isotropic case. The first one roughly concerns the modelling aspect: an anisotropic propagator should be used to avoid a mis-positioning or bad focusing of the imaged reflectors. The second correction concerns the migration aspect: as anisotropy affects the reflectivity of subsurface, a specific anisotropic imaging formula should be applied in the migration kernel, in order to recover the correct A V A behavior of the subsurface reflectors, If the first correction is DOW made in most so-called anisotropic imaging algorithms, the second one is currently ignored. The first part of my work concerns theoretical aspects. 1 study first the preservation of amplitudes in the
On the quantification of SSVEP frequency responses in human EEG in realistic BCI conditions.
Rafał Kuś
Full Text Available This article concerns one of the most important problems of brain-computer interfaces (BCI based on Steady State Visual Evoked Potentials (SSVEP, that is the selection of the a-priori most suitable frequencies for stimulation. Previous works related to this problem were done either with measuring systems that have little in common with actual BCI systems (e.g., single flashing LED or were presented on a small number of subjects, or the tested frequency range did not cover a broad spectrum. Their results indicate a strong SSVEP response around 10 Hz, in the range 13-25 Hz, and at high frequencies in the band of 40-60 Hz. In the case of BCI interfaces, stimulation with frequencies from various ranges are used. The frequencies are often adapted for each user separately. The selection of these frequencies, however, was not yet justified in quantitative group-level study with proper statistical account for inter-subject variability. The aim of this study is to determine the SSVEP response curve, that is, the magnitude of the evoked signal as a function of frequency. The SSVEP response was induced in conditions as close as possible to the actual BCI system, using a wide range of frequencies (5-30 Hz, in step of 1 Hz. The data were obtained for 10 subjects. SSVEP curves for individual subjects and the population curve was determined. Statistical analysis were conducted both on the level of individual subjects and for the group. The main result of the study is the identification of the optimal range of frequencies, which is 12-18 Hz, for the registration of SSVEP phenomena. The applied criterion of optimality was: to find the largest contiguous range of frequencies yielding the strong and constant-level SSVEP response.
Types, Frequency, and Effectiveness of Responses to Unwanted Pursuit and Stalking
Dutton, Leila B.; Winstead, Barbara A.
2011-01-01
This study investigated the types, frequency, and effectiveness of responses to unwanted pursuit (UP) and stalking after relationship termination. Participants included female and male college students who were either pursued by a former partner or who pursued an ex-partner. Factor analyses of targets' responses to pursuit yielded four factors,…
Sizing of an Energy Storage System for Grid Inertial Response and Primary Frequency Reserve
Knap, Vaclav; Chaudhary, Sanjay Kumar; Stroe, Daniel Loan;
2016-01-01
Large-scale integration of renewable energy sources in power system leads to the replacement of conventional power plants (CPPs) and consequently challenges in power system reliability and security are introduced. This study is focused on improving the grid frequency response after a contingency....... Moreover, it is demonstrated that the ESS can provide the response similar to that provided by the CPPs....
Moth hearing in response to bat echolocation calls manipulated independently in time and frequency.
Jones, G; Waters, D A
2000-08-22
We measured the auditory responses of the noctuid moth Noctua pronuba to bat echolocation calls which were manipulated independently in time and frequency. Such manipulations are important in understanding how insect hearing influences the evolution of echolocation call characteristics. We manipulated the calls of three bat species (Rhinolophus hipposideros, Myotis nattereri and Pipistrellus pipistrellus) that use different echolocation call features by doubling their duration or reducing their frequency, and measured the auditory thresholds from the A1 cells of the moths. Knowing the auditory responses of the moth we tested three predictions. (i) The ranking of the audibility of unmanipulated calls to the moths should be predictable from their temporal and/or frequency structure. This was supported. (ii) Doubling the duration of the calls should increase their audibility by ca. 3 dB for all species. Their audibility did indeed increase by 2.1-3.5 dB. (iii) Reducing the frequency of the calls would increase their audibility for all species. Reducing the frequency had small effects for the two bat species which used short duration (2.7-3.6 ms) calls. However, the relatively long-duration (50 ms), largely constant-frequency calls of R. hipposideros increased in audibility by 21.6 dB when their frequency was halved. Time and frequency changes influence the audibility of calls to tympanate moths in different ways according to call design. Large changes in frequency and time had relatively small changes on the audibility of calls for short, largely broadband calls. Channelling energy into the second harmonic of the call substantially decreased the audibility of calls for bats which use long-duration, constant-frequency components in echolocation calls. We discuss our findings in the contexts of the evolution of both bat echolocation call design and the potential responses of insects which hear ultrasound. PMID:11467425
Alexandre Lehmann
Full Text Available Selective attention is the mechanism that allows focusing one's attention on a particular stimulus while filtering out a range of other stimuli, for instance, on a single conversation in a noisy room. Attending to one sound source rather than another changes activity in the human auditory cortex, but it is unclear whether attention to different acoustic features, such as voice pitch and speaker location, modulates subcortical activity. Studies using a dichotic listening paradigm indicated that auditory brainstem processing may be modulated by the direction of attention. We investigated whether endogenous selective attention to one of two speech signals affects amplitude and phase locking in auditory brainstem responses when the signals were either discriminable by frequency content alone, or by frequency content and spatial location. Frequency-following responses to the speech sounds were significantly modulated in both conditions. The modulation was specific to the task-relevant frequency band. The effect was stronger when both frequency and spatial information were available. Patterns of response were variable between participants, and were correlated with psychophysical discriminability of the stimuli, suggesting that the modulation was biologically relevant. Our results demonstrate that auditory brainstem responses are susceptible to efferent modulation related to behavioral goals. Furthermore they suggest that mechanisms of selective attention actively shape activity at early subcortical processing stages according to task relevance and based on frequency and spatial cues.
Estimation of cochlear response times using lateralization of frequency-mismatched tones
Strelcyk, Olaf; Dau, Torsten
2009-01-01
Behavioral and objective estimates of cochlear response times CRTs and traveling-wave TW velocity were compared for three normal-hearing listeners. Differences between frequency-specific CRTs were estimated via lateralization of pulsed tones that were interaurally mismatched in frequency, similar...... calculated from the obtained CRTs. The correspondence between behavioral and objective estimates of CRT and TW velocity was examined. For frequencies up to 1.5 kHz, the behavioral method yielded reproducible results, which were consistent with the objective estimates. For higher frequencies, CRT differences...... could not be estimated with the behavioral method due to limitations of the lateralization paradigm. The method might be useful for studying the spatiotemporal cochlear response pattern in human listeners....
Zhang Ru, E-mail: zhangruwl@njut.edu.cn [Department of Applied Physics, Nanjing University of Technology, Nanjing 210009 (China); Wu Gaojian; Zhang Li [Department of Applied Physics, Nanjing University of Technology, Nanjing 210009 (China); Li Xin [College of Electronics and Information engineering, Nanjing University of Technology, Nanjing 210009 (China); Zhang Ning [Department of Physics, Nanjing Normal University, Nanjing 210097 (China)
2012-08-15
A theoretical model is presented for frequency dependence of magnetoelectric (ME) effect in piezoelectric-magnetostrictive disk-ring composite structures. Expressions for ME voltage coefficients in piezoelectric-magnetostrictive (PE-MS) disk-ring and MS-PE disk-ring are obtained by solving elastodynamic equations. The calculated resonance frequency and frequency dependence of ME voltage coefficients are in good agreement with the experimental results. This model indicates better mechanical coupling in disk-ring structure than that in traditional layered structure, and this may be responsible for the enhancing ME effect. The analysis suggests the disk-ring composites structures are promising for magnetoelectric applications. - Highlights: Black-Right-Pointing-Pointer Frequency response of ME effect in PE-MS disk-ring composites structures is modeled. Black-Right-Pointing-Pointer The calculated results are in good agreement with the experimental results. Black-Right-Pointing-Pointer This model indicates better mechanical coupling in disk-ring structure.
Oscillating Frequency Response of a Langasite Crystal Microbalance in Liquid Phase
Qi KANG; Huai Jin ZHANG; Xue Yong LIU; Da Zhong SHEN
2005-01-01
The frequency responses of a langasite crystal microbalance (LCM) in liquid phase were investigated. It was shown that the LCM possessed much stronger oscillating ability in liquid phase than that of the commonly used quartz crystal microbalance (QCM). The frequency shifts of the LCM to the changes in mass loading, as well as viscosity and density of the liquid were measured. The LCM was applied to monitor the adsorption process of an ionic liquid film to ethanol vapor.
Frequency response of the vestibulo-ocular reflex /VOR/ in the monkey
Buettner, U. W.; Henn, V.; Young, L. R.
1981-01-01
The frequency response of the vestibulo-ocular reflex has been investigated in the alert monkey during sinusoidal rotation about a vertical axis in a frequency range of 0.001-0.5 Hz. Phase and gain of nystagmus slow phase velocity was determined. In the frequency range above 0.1 Hz, nystagmus slow phase velocity was in phase with (compensated for) head velocity. At lower frequencies, an increasing phase lead was present which could reach more than 90 deg. Gain fell off correspondingly at low frequencies. Calculated time constants were 10-40 s in different monkeys. Animals which had been exposed to numerous previous rotary stimuli in the laboratory showed much shorter time constants than did 'native' monkeys.
Sheath-wave-related resonances in the frequency response of a cylindrical monopole in a plasma
A floating or negatively biased antenna immersed in a plasma is surrounded by an ion sheath. The antenna-sheath-plasma system may support slow surface waves at driving frequencies below the electron plasma frequency. Resonances associated with these so-called sheath waves are observed at certain frequencies in the antenna's response to an applied sinusoidal signal. A detailed experimental study of these resonances is presented here for a short cylindrical monopole in a low-pressure isotropic argon plasma. The effect on the resonance frequencies of a dc bias applied to the antenna and of plasma density and antenna length was investigated. Good agreement was obtained with the theoretical predictions derived from a known dispersion equation for sheath waves. From the experimental data, the relationship between sheath thickness and antenna potential, and the frequency dependence of the antenna admittance could be derived
Calibration Scheme for Large Kinetic Inductance Detector Arrays Based on Readout Frequency Response
Bisigello, L.; Yates, S. J. C.; Murugesan, V.; Baselmans, J. J. A.; Baryshev, A. M.
2016-07-01
Microwave kinetic inductance detector (MKID) provides a way to build large ground-based sub-mm instruments such as NIKA and A-MKID. For such instruments, therefore, it is important to understand and characterize the response to ensure good linearity and calibration over a wide dynamic range. We propose to use the MKID readout frequency response to determine the MKID responsivity to an input optical source power. A signal can be measured in a KID as a change in the phase of the readout signal with respect to the KID resonant circle. Fundamentally, this phase change is due to a shift in the KID resonance frequency, in turn due to a radiation induced change in the quasiparticle number in the superconducting resonator. We show that the shift in resonant frequency can be determined from the phase shift by using KID phase versus frequency dependence using a previously measured resonant frequency. Working in this calculated resonant frequency, we gain near linearity and constant calibration to a constant optical signal applied in a wide range of operating points on the resonance and readout powers. This calibration method has three particular advantages: first, it is fast enough to be used to calibrate large arrays, with pixel counts in the thousands of pixels; second, it is based on data that are already necessary to determine KID positions; third, it can be done without applying any optical source in front of the array.
Generation of artificial time-histories, rich in all frequencies, from given response spectra
In order to apply the time-history method of seismic analysis, it is often desirable to generate a suitable artificial time-history from a given response spectrum. The method described allows the generation of such a time-history that is also rich in all frequencies in the spectrum. This richness is achieved by choosing a large number of closely-spaced frequency points such that the adjacent frequencies have their half-power points overlap. The adjacent frequencies satisfy the condition that the frequency interval Δf near a given frequency f is such that (Δf)/f<2c/csub(c) where c is the damping of the system and csub(c) is the critical damping. In developing an artificial time-history, it is desirable to specify the envelope and duration of the record, very often in such a manner as to reproduce the envelope property of a specific earthquake record, and such an option is available in the method described. Examples are given of the development of typical artificial time-histories from earthquake design response spectra and from floor response spectra
Wahab, M Farooq; Dasgupta, Purnendu K; Kadjo, Akinde F; Armstrong, Daniel W
2016-02-11
With increasingly efficient columns, eluite peaks are increasingly narrower. To take full advantage of this, choice of the detector response time and the data acquisition rate a.k.a. detector sampling frequency, have become increasingly important. In this work, we revisit the concept of data sampling from the theorem variously attributed to Whittaker, Nyquist, Kotelnikov, and Shannon. Focusing on time scales relevant to the current practice of high performance liquid chromatography (HPLC) and optical absorbance detection (the most commonly used method), even for very narrow simulated peaks Fourier transformation shows that theoretical minimum sampling frequency is still relatively low (digital filters. We show that the common wisdom of sampling 20 points per peak can be inadequate for high efficiency columns and that the sampling frequency and response choices do affect the peak shape. If the sampling frequency is too low or response time is too large, the observed peak shapes will not remain as narrow as they really are - this is especially true for high efficiency and high speed separations. It is shown that both sampling frequency and digital filtering affect the retention time, noise amplitude, peak shape and width in a complex fashion. We show how a square-wave driven light emitting diode source can reveal the nature of the embedded filter. We discuss time uncertainties related to the choice of sampling frequency. Finally, we suggest steps to obtain optimum results from a given system. PMID:26803000
Calibration scheme for large Kinetic Inductance Detector Arrays based on Readout Frequency Response
Bisigello, L; Murugesan, V; Baselmans, J J A; Baryshev, A M
2016-01-01
Microwave kinetic inductance detector (MKID) provides a way to build large ground based sub-mm instruments such as NIKA and A-MKID. For such instruments, therefore, it is important to understand and characterize the response to ensure good linearity and calibration over wide dynamic range. We propose to use the MKID readout frequency response to determine the MKID responsivity to an input optical source power. A signal can be measured in a KID as a change in the phase of the readout signal with respect to the KID resonant circle. Fundamentally, this phase change is due to a shift in the KID resonance frequency, in turn due to a radiation induced change in the quasiparticle number in the superconducting resonator. We show that shift in resonant frequency can be determined from the phase shift by using KID phase versus frequency dependence using a previously measured resonant frequency. Working in this calculated resonant frequency, we gain near linearity and constant calibration to a constant optical signal ap...
Anisotropic Stars II Stability
Dev, K; Dev, Krsna; Gleiser, Marcelo
2003-01-01
We investigate the stability of self-gravitating spherically symmetric anisotropic spheres under radial perturbations. We consider both the Newtonian and the full general-relativistic perturbation treatment. In the general-relativistic case, we extend the variational formalism for spheres with isotropic pressure developed by Chandrasekhar. We find that, in general, when the tangential pressure is greater than the radial pressure, the stability of the anisotropic sphere is enhanced when compared to isotropic configurations. In particular, anisotropic spheres are found to be stable for smaller values of the adiabatic index $\\gamma$.
Modelling of ultrasonic nondestructive testing in anisotropic materials - Rectangular crack
Nondestructive testing with ultrasound is a standard procedure in the nuclear power industry when searching for defects, in particular cracks. To develop and qualify testing procedures extensive experimental work on test blocks is usually required. This can take a lot of time and therefore be quite costly. A good mathematical model of the testing situation is therefore of great value as it can reduce the experimental work to a great extent. A good model can be very useful for parametric studies and as a pedagogical tool. A further use of a model is as a tool in the qualification of personnel. In anisotropic materials, e.g. austenitic welds, the propagation of ultrasound becomes much more complicated as compared to isotropic materials. Therefore, modelling is even more useful for anisotropic materials, and it in particular has a greater pedagogical value. The present project has been concerned with a further development of the anisotropic capabilities of the computer program UTDefect, which has so far only contained a strip-like crack as the single defect type for anisotropic materials. To be more specific, the scattering by a rectangular crack in an anisotropic component has been studied and the result is adapted to include transmitting and receiving ultrasonic probes. The component under study is assumed to be anisotropic with arbitrary anisotropy. On the other hand, it is assumed to be homogeneous, and this in particular excludes most welds, where it is seldom an adequate approximation to assume homogeneity. The anisotropy may be arbitrarily oriented and the same is true of the rectangular crack. The crack may also be located near a backside of the component. To solve the scattering problem for the crack an integral equation method is used. The probe model has been developed in an earlier project and to compute the signal response in the receiving probe an electromechanical reciprocity argument is employed. As a rectangle is a truly 3D scatterer the sizes of the
Kasahara, Naoto [Japan Nuclear Cycle Development Inst., Oarai, Ibaraki (Japan). Oarai Engineering Center; Takasho, Hideki [Joyo Industry Co., Ltd., Tokai, Ibaraki (Japan)
2001-09-01
Temperature fluctuation from incomplete fluid mixing induces fatigue damages on structures of nuclear components, which should be prevented. For rational analyses of this phenomenon, the authors have developed a frequency response function of thermal stress induced by one-dimensional temperature gradient across wall thickness. On the other hand, it is pointed out that existence of other stress modes from multi-dimensional structure with complex constraint conditions. This study has extended the frequency response method for adoption to multi-dimensional problems by introducing constraint efficiency factors. Applicability of this function was validated for multi-dimensional problems such as thermal stratification problems and hot/cold spot ones. (author)
The temperature oscillation produced by thermal stratification phenomenon induces thermal fatigue damages on structures of nuclear components, which should be prevented. To evaluate thermal fatigue, the frequency response function was developed. However, this theoretical method does not take particular effects of thermal stratification oscillation into account. To clarify these effects, finite element simulations were conducted with two fluid temperature models. Based on mechanisms of the effects, the frequency response function was improved. Agreement with the results of the finite element simulations confirmed the proposed function. (author)
Frequency response function method with constraint efficiency factors for Hot/Cold spot problems
Temperature fluctuation from incomplete fluid mixing induces typically bending plus peak stress across wall thickness. For this stress mode, author has developed the frequency response function to establish design-by-analysis methodology for this phenomenon. On the other hand, it is pointed out that hot and cold spots appear near T-junctions in piping systems. Those induce other stress modes from three-dimensional temperature distributions. This report describes the extension of the frequency response method to hot and cold spot problems by introducing constraint efficiency factors. Its applicability was validated by application to a hot spot near the T-junction of PHENIX secondary piping system. (author)
Temperature fluctuation from incomplete fluid mixing induces fatigue damages on structures of nuclear components, which should be prevented. For rational analyses of this phenomenon, the authors have developed a frequency response function of thermal stress induced by one-dimensional temperature gradient across wall thickness. On the other hand, it is pointed out that existence of other stress modes from multi-dimensional structure with complex constraint conditions. This study has extended the frequency response method for adoption to multi-dimensional problems by introducing constraint efficiency factors. Applicability of this function was validated for multi-dimensional problems such as thermal stratification problems and hot/cold spot ones. (author)
Infrasound-array-element frequency response: in-situ measurement and modeling
Gabrielson, T.
2011-12-01
Most array elements at the infrasound stations of the International Monitoring System use some variant of a multiple-inlet pipe system for wind-noise suppression. These pipe systems have a significant impact on the overall frequency response of the element. The spatial distribution of acoustic inlets introduces a response dependence that is a function of frequency and of vertical and horizontal arrival angle; the system of inlets, pipes, and summing junctions further shapes that response as the signal is ducted to the transducer. In-situ measurements, using a co-located reference microphone, can determine the overall frequency response and diagnose problems with the system. As of July 2011, the in-situ frequency responses for 25 individual elements at 6 operational stations (I10, I53, I55, I56, I57, and I99) have been measured. In support of these measurements, a fully thermo-viscous model for the acoustics of these multiple-inlet pipe systems has been developed. In addition to measurements at operational stations, comparative analyses have been done on experimental systems: a multiple-inlet radial-pipe system with varying inlet hole size; a one-quarter scale model of a 70-meter rosette system; and vertical directionality of a small rosette system using aircraft flyovers. [Funded by the US Army Space and Missile Defense Command
Highlights: • This study proposes a new tool to estimate maximum wind power penetration level. • This tool takes frequency response adequacy into account. • System frequency sensitivity is modelled as a function of inertia and headroom. • A practical power system is investigated as a case study. • Outputs from the proposed tool match with dynamic simulation results. - Abstract: Wind energy is becoming a significant source of generation in many countries because of its zero fuel cost and no air pollution. Due to integration of large-scale wind power in conventional grids, synchronous generators are being economically replaced. Modern wind farms are based on power electronics interface; and unlike synchronous generators, they do not have inherent frequency support capability. So, in a combined synchronous and non-synchronous machine based power system, it has always been a concern for a network operator to maintain system frequency within acceptable limits following a major disturbance. From power system security point of view, wind penetration can be limited by frequency response criteria. Up to now, several methodologies have been proposed to estimate maximum threshold of wind integration. However, none of them recommends how a system operator could be immediately informed about a secured wind penetration limit, as soon as generation profile is known. This paper proposes a new estimation tool of maximum wind penetration level from the frequency response adequacy point of view. Available system information viz. inertia and headroom are used as input parameters in the developed tool. Output of this tool will provide the highest margin of wind power that can be integrated at a particular load condition without violating frequency response constraints. The proposed technique is applied and analysed for a 250 bus, 65 machine Australian electricity network
One-Dimensional Anisotropic Band Gap Structure
无
2000-01-01
The band gap structure of one-dimensional anisotropic photonic crystal has been studied by means of the transfer matrix formalism. From the analytic expressions and numeric calculations we see some general characteristics of the band gap structure of anisotropic photonic crystals, each band separates into two branches and the two branches react to polarization sensitively. In the practical case of oblique incidence, gaps move towards high frequency when the angle of incidence increases. Under some special conditions, the two branches become degenerate again.
A. Mirzajani
2006-07-01
Full Text Available Background/Objective: The brain response to temporal frequencies (TF has been already reported. However, there is no study on different TF with respect to various spatial frequencies (SF. Materials and Methods: Functional magnetic resonance imaging (fMRI was done by a 1.5 T General Electric system for 14 volunteers (9 males and 5 females, aged 19–26 years during square-wave reversal checkerboard visual stimulation with different temporal frequencies of 4, 6, 8 and 10 Hz in 2 states of low SF of 0.4 and high SF of 8 cycles/degree (cpd. All subjects had normal visual acuity of 20/20 based on Snellen’s fraction in each eye with good binocular vision and normal visual field based on confrontation test. The mean luminance of the entire checkerboard was 161.4 cd/m2 and the black and white check contrast was 96%. The activation map was created using the data obtained from the block designed fMRI study. Pixels with a Z score above a threshold of 2.3, at a statistical significance level of 0.05, were considered activated. The average percentage blood oxygenation level dependent (BOLD signal change for all activated pixels within the occipital lobe, multiplied by the total number of activated pixels within the occipital lobe, was used as an index for the magnitude of the fMRI signal at each state of TF&SF. Results: The magnitude of the fMRI signal in response to different TF’s was maximum at 6 Hz for a high SF value of 8 cpd; it was however, maximum at a TF of 8 Hz for a low SF of 0.4 cpd. Conclusion: The results of this study agree with those of animal invasive neurophysiologic studies showing SF and TF selectivity of neurons in visual cortex. These results can be useful for vision therapy and selecting visual tasks in fMRI studies.
David B. Stone; Coffman, Brian A; Juan Bustillo; Cheryl Aine
2014-01-01
Deficits in auditory and visual unisensory responses are well documented in patients with schizophrenia; however, potential abnormalities elicited from multisensory audio-visual stimuli are less understood. Further, schizophrenia patients have shown abnormal patterns in task-related and task-independent oscillatory brain activity, particularly in the gamma frequency band. We examined oscillatory responses to basic unisensory and multisensory stimuli in schizophrenia patients (N = 46) and heal...
The frequency response of dynamic friction: Enhanced rate-and-state models
Cabboi, A.; Putelat, T.; Woodhouse, J.
2016-07-01
The prediction and control of friction-induced vibration requires a sufficiently accurate constitutive law for dynamic friction at the sliding interface: for linearised stability analysis, this requirement takes the form of a frictional frequency response function. Systematic measurements of this frictional frequency response function are presented for small samples of nylon and polycarbonate sliding against a glass disc. Previous efforts to explain such measurements from a theoretical model have failed, but an enhanced rate-and-state model is presented which is shown to match the measurements remarkably well. The tested parameter space covers a range of normal forces (10-50 N), of sliding speeds (1-10 mm/s) and frequencies (100-2000 Hz). The key new ingredient in the model is the inclusion of contact stiffness to take into account elastic deformations near the interface. A systematic methodology is presented to discriminate among possible variants of the model, and then to identify the model parameter values.
Frequency response of forced circulation boiling two-phase flow to inlet flow modulation
This paper presents theoretical analysis and experimental data on the dynamic behavior of two-phase flow in a vertical boiling channel. Continuous, energy and momentum equations are linearized on the basis of small perturbation, and flow to exit void fraction and pressure drop transfer functions are obtained. Experimental frequency response functions are measured with statistical method using Freon-113 as the working fluid over a frequency range of 0.02 to 3 Hz. The data cover mass flux of 450 to 1800 kg/m2s, inlet subcooling of 2 to 300C and various heat flux levels. Influence of flow rate, inlet subcooling and heat flux on frequency response and comparison between experimental and theoretical results are described. (author)
Zhang Yichi
2011-01-01
Full Text Available This study describes an algorithm for determining the fine phase response of equivalent sampling oscilloscopes of a linear time-invariant response function from its magnitude. The Nose-to-Nose (NTN calibration method can give the phase response of the equivalent sampling oscilloscopes, but the phase resolution can only achieve 250 MHz because the limit of the technology. In this study the fine phase response has been reconstructed. Although the truncation of the Kramers-Kronig transform using three basic functions may approximate gives rise to large errors in estimated phase, these errors may be approximated by using three basic functions. This result rests on data obtained by an NTN technique in combination with a swept-sine calibration procedure. The NTN technique yields magnitude and phase information over a broad bandwidth, yet has low frequency resolution. The swept-sine procedure returns only the magnitude of the oscilloscope response function, yet can be made at any frequency at which fundamental microwave power standards are available. As an example, we get the fine phase response of equivalent sampling oscilloscopes Agilent 86100 C from dc to 40 GHz; its frequency resolution achieves 1 MHz. In the process of this analysis, we observe that the true oscilloscope response function as measured by the NTN calibration is indistinguishable from the reconstructed phase response over a very large bandwidth. At last we analyze the phase uncertainty of the phase response, and the uncertainty analysis process is provided. The results show that the algorithm can be used to get the fine phase response of the equivalent sampling oscilloscopes.
Oliveira, Sebastiao E.M. de; Padua Guarini, Antonio de [Centro de Pesquisas de Energia Eletrica (CEPEL), Rio de Janeiro, RJ (Brazil); Souza, Joao A. de; Valgas, Helio M.; Pinto, Roberto del Giudice R. [Companhia Energetica de Minas Gerais (CEMIG), Belo Horizonte, MG (Brazil)
1994-12-31
This work describes the results of the set frequency response tests performed in the generator number 2, 6.9 kV, 25 MVA, of Camargos hydroelectric power plant, CEMIG, and the parameters relatives to determined structures of model. This tests are unpublished in Brazil. (author) 7 refs., 16 figs., 7 tabs.
Estimation of the auto frequency response function at unexcited points using dummy masses
Hosoya, Naoki; Yaginuma, Shinji; Onodera, Hiroshi; Yoshimura, Takuya
2015-02-01
If structures with complex shapes have space limitations, vibration tests using an exciter or impact hammer for the excitation are difficult. Although measuring the auto frequency response function at an unexcited point may not be practical via a vibration test, it can be obtained by assuming that the inertia acting on a dummy mass is an external force on the target structure upon exciting a different excitation point. We propose a method to estimate the auto frequency response functions at unexcited points by attaching a small mass (dummy mass), which is comparable to the accelerometer mass. The validity of the proposed method is demonstrated by comparing the auto frequency response functions estimated at unexcited points in a beam structure to those obtained from numerical simulations. We also consider random measurement errors by finite element analysis and vibration tests, but not bias errors. Additionally, the applicability of the proposed method is demonstrated by applying it to estimate the auto frequency response function of the lower arm in a car suspension.
Trnka, Jan; Pavloušek, P.; Nedomová, Š.; Buchar, J.
2016-01-01
Roč. 47, č. 1 (2016), s. 24-33. ISSN 0022-4901 Institutional support: RVO:61388998 Keywords : berry´s response * dominant frequency * elastic modulus * grape berries Subject RIV: BO - Biophysics Impact factor: 1.367, year: 2014 http://onlinelibrary.wiley.com
Effect of ischemia and cooling on the response to high frequency stimulation in rat tail nerves
Andersen, Henning; Feldbæk Nielsen, Jørgen; Sørensen, Bodil;
2000-01-01
In normal rat tail nerves the effect of temperature and ischemia on the response to long-term high frequency stimulation (HFS) (143 Hz) was studied. The effect of temperature was studied in two consecutive tests at 14 degrees C and 35 degrees C. Prior to the HFS the peak-to-peak amplitude (PP-amp...
Sauvé, Alexandre
2016-01-01
Context: Bolometers are high sensitivity detector commonly used in Infrared astronomy. The HFI instrument of the Planck satellite makes extensive use of them, but after the satellite launch two electronic related problems revealed critical. First an unexpected excess response of detectors at low optical excitation frequency for {\
Lingyu Zhu
Full Text Available The capacitors in high-voltage direct-current (HVDC converter stations radiate a lot of audible noise which can reach higher than 100 dB. The existing noise level prediction methods are not satisfying enough. In this paper, a new noise level prediction method is proposed based on a frequency response function considering both electrical and mechanical characteristics of capacitors. The electro-mechanical frequency response function (EMFRF is defined as the frequency domain quotient of the vibration response and the squared capacitor voltage, and it is obtained from impulse current experiment. Under given excitations, the vibration response of the capacitor tank is the product of EMFRF and the square of the given capacitor voltage in frequency domain, and the radiated audible noise is calculated by structure acoustic coupling formulas. The noise level under the same excitations is also measured in laboratory, and the results are compared with the prediction. The comparison proves that the noise prediction method is effective.
Silva, Walter A.
1993-01-01
A methodology for modeling nonlinear unsteady aerodynamic responses, for subsequent use in aeroservoelastic analysis and design, using the Volterra-Wiener theory of nonlinear systems is presented. The methodology is extended to predict nonlinear unsteady aerodynamic responses of arbitrary frequency. The Volterra-Wiener theory uses multidimensional convolution integrals to predict the response of nonlinear systems to arbitrary inputs. The CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) code is used to generate linear and nonlinear unit impulse responses that correspond to each of the integrals for a rectangular wing with a NACA 0012 section with pitch and plunge degrees of freedom. The computed kernels then are used to predict linear and nonlinear unsteady aerodynamic responses via convolution and compared to responses obtained using the CAP-TSD code directly. The results indicate that the approach can be used to predict linear unsteady aerodynamic responses exactly for any input amplitude or frequency at a significant cost savings. Convolution of the nonlinear terms results in nonlinear unsteady aerodynamic responses that compare reasonably well with those computed using the CAP-TSD code directly but at significant computational cost savings.
David B. Stone
2014-11-01
Full Text Available Deficits in auditory and visual unisensory responses are well documented in patients with schizophrenia; however, potential abnormalities elicited from multisensory audio-visual stimuli are less understood. Further, schizophrenia patients have shown abnormal patterns in task-related and task-independent oscillatory brain activity, particularly in the gamma frequency band. We examined oscillatory responses to basic unisensory and multisensory stimuli in schizophrenia patients (N = 46 and healthy controls (N = 57 using magnetoencephalography (MEG. Time-frequency decomposition was performed to determine regions of significant changes in gamma band power by group in response to unisensory and multisensory stimuli relative to baseline levels. Results showed significant behavioral differences between groups in response to unisensory and multisensory stimuli. In addition, time-frequency analysis revealed significant decreases and increases in gamma-band power in schizophrenia patients relative to healthy controls, which emerged both early and late over both sensory and frontal regions in response to unisensory and multisensory stimuli. Unisensory gamma-band power predicted multisensory gamma-band power differently by group. Furthermore, gamma-band power in these regions predicted performance in select measures of the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS test battery differently by group. These results reveal a unique pattern of task-related gamma-band power in schizophrenia patients relative to controls that may indicate reduced inhibition in combination with impaired oscillatory mechanisms in patients with schizophrenia.
Frequency-response identification of XV-15 tilt-rotor aircraft dynamics
Tischler, Mark B.
1987-01-01
The timely design and development of the next generation of tilt-rotor aircraft (JVX) depend heavily on the in-depth understanding of existing XV-15 dynamics and the availability of fully validated simulation models. Previous studies have considered aircraft and simulation trim characteristics, but analyses of basic flight vehicle dynamics were limited to qualitative pilot evaluation. The present study has the following objectives: documentation and evaluation of XV-15 bare-airframe dynamics; comparison of aircraft and simulation responses; and development of a validated transfer-function description of the XV-15 needed for future studies. A nonparametric frequency-response approach is used which does not depend on assumed model order or structure. Transfer-function representations are subsequently derived which fit the frequency responses in the bandwidth of greatest concern for piloted handling-qualities and control-system applications.
Selective optical transmission in anisotropic multilayers structure
We developed a Green's function method to study theoretically a single-defect photonic crystal composed of anisotropic dielectric materials. This structure can trap light of a given frequency range and filter only a certain frequency light with a very high quality. It is shown that the defect modes appear as peaks in the transmission spectrum. Their intensities and frequency positions depend on the incidence angle and the orientation of the principal axes of layers consisting of the superlattice and the layer defect. Our structure offers a great variety of possibilities for creating and controlling the number and transmitted intensities of defect modes. It can be a good candidate for realizing a selective electromagnetic filter. In addition to this filtration process, the defective anisotropic photonic crystal can be used to switch the modes when appropriate geometry is selected. (author)
Analysis of the frequency-dependent response to wave forcing in the extratropics
A. J. Haklander
2006-02-01
Full Text Available A quasigeostrophic model for the frequency-dependent response of the zonal-mean flow to planetary-wave forcing at Northern Hemisphere (NH midlatitudes is applied to 4-D-Var ECMWF analysis data for six extended winter seasons. The theoretical response is a non-linear function of the frequency of the forcing, the thermal damping time α^{−1}, and a scaling parameter μ which includes the aspect ratio of the meridional to the vertical length scale of the response. Non-linear regression of the calculated response from the analyses onto the theoretical response yields height-dependent estimates for both α^{−1} and μ. The thermal damping time estimated from this dynamical model is about 2 days in the troposphere, 7–10 days in the stratosphere, and 2–4 days in the lower mesosphere. These estimates generally lie within the range of existing estimates, although the values we find for the troposphere are significantly smaller than those calculated in several radiative transfer modeling studies. At most levels, the estimates for μ are significantly lower than can be derived from scaling arguments that apply outside the forcing region. We illustrate with an example how the response of the meridional circulation inside the forcing area can have a higher aspect ratio than the effective response outside the forcing area.
Frequency-domain correction of sensor dynamic error for step response
Yang, Shuang-Long; Xu, Ke-Jun
2012-11-01
To obtain accurate results in dynamic measurements it is required that the sensors should have good dynamic performance. In practice, sensors have non-ideal dynamic characteristics due to their small damp ratios and low natural frequencies. In this case some dynamic error correction methods can be adopted for dealing with the sensor responses to eliminate the effect of their dynamic characteristics. The frequency-domain correction of sensor dynamic error is a common method. Using the existing calculation method, however, the correct frequency-domain correction function (FCF) cannot be obtained according to the step response calibration experimental data. This is because of the leakage error and invalid FCF value caused by the cycle extension of the finite length step input-output intercepting data. In order to solve these problems the data splicing preprocessing and FCF interpolation are put forward, and the FCF calculation steps as well as sensor dynamic error correction procedure by the calculated FCF are presented in this paper. The proposed solution is applied to the dynamic error correction of the bar-shaped wind tunnel strain gauge balance so as to verify its effectiveness. The dynamic error correction results show that the adjust time of the balance step response is shortened to 10 ms (shorter than 1/30 before correction) after frequency-domain correction, and the overshoot is fallen within 5% (less than 1/10 before correction) as well. The dynamic measurement accuracy of the balance is improved significantly.
Casiano, M. J.
2011-01-01
The Common Extensive Cryogenic Engine program demonstrated the operation of a deep throttling engine design. The program, spanning five years from August 2005 to July 2010, funded testing through four separate engine demonstration test series. Along with successful completion of multiple objectives, a discrete response of approximately 4000 Hz was discovered and explored throughout the program. The typical low-amplitude acoustic response was evident in the chamber measurement through almost every operating condition; however, at certain off-nominal operating conditions, the response became discrete with higher amplitude. This paper summarizes the data reduction, characterization, and analysis of the 4,000 Hz response for the entire program duration, using the large amount of data collected. Upon first encountering the response, new objectives and instrumentation were incorporated in future test series to specifically collect 4,000 Hz data. The 4,000 Hz response was identified as being related to the first tangential acoustic mode by means of frequency estimation and spatial decomposition. The latter approach showed that the effective node line of the mode was aligned with the manifold propellant inlets with standing waves and quasi-standing waves present at various times. Contour maps that contain instantaneous frequency and amplitude trackings of the response were generated as a significant improvement to historical manual approaches of data reduction presentation. Signal analysis and dynamic data reduction also uncovered several other features of the response including a stable limit cycle, the progressive engagement of subsequent harmonics, the U-shaped time history, an intermittent response near the test-based neutral stability region, other acoustic modes, and indications of modulation with a separate subsynchronous response. Although no engine damage related to the acoustic mode was noted, the peak-to-peak fluctuating pressure amplitude achieved 12.1% of the
Broadband frequency and angular response of a sinusoidal bull’s eye antenna
Beaskoetxea, U.; Navarro-Cía, M.; Beruete, M.
2016-07-01
A thorough experimental study of the frequency and beaming angle response of a metallic leaky-wave bull’s eye antenna working at 77 GHz with a sinusoidally corrugated profile is presented. The beam scanning property of these antennas as frequency is varied is experimentally demonstrated and corroborated through theoretical and numerical results. From the experimental results the dispersion diagram of the n = ‑1 and n = ‑2 space harmonics is extracted, and the operation at different frequency regimes is identified and discussed. In order to show the contribution of each half of the antenna, numerical examples of the near-field behavior are also displayed. Overall, experimental results are in good qualitative and quantitative agreement with theoretical and numerical calculations. Finally, an analysis of the beamwidth as a function of frequency is performed, showing that it can achieve values below 1.5° in a fractional bandwidth of 4% around the operation frequency, which is an interesting frequency-stable broadside radiation.
Correspondence between phasor transforms and frequency response function in RLC circuits
Abdalla, Hassan Mohamed Abdelalim
2016-01-01
The analysis of RLC circuits is usually made by considering phasor transforms of sinusoidal signals (characterized by constant amplitude, period and phase) that allow the calculation of the AC steady state of RLC circuits by solving simple algebraic equations. In this paper I try to show that phasor representation of RLC circuits is analogue to consider the frequency response function (commonly designated by FRF) of the total impedance of the circuit. In this way I derive accurate expressions for the resonance and anti-resonance frequencies and their corresponding values of impedances of the parallel and series RLC circuits respectively, notwithstanding the presence of damping effects.
Frequency and Phase Synchronization in Neuromagnetic Cortical Responses to Flickering-Color Stimuli
Timashev, S F; Yulmetyev, R M; Demin, S A; Panischev, O Yu; Shimojo, S; Bhattacharya, J
2009-01-01
In our earlier study dealing with the analysis of neuromagnetic responses (magnetoencephalograms - MEG) to flickering-color stimuli for a group of control human subjects (9 volunteers) and a patient with photosensitive epilepsy (a 12-year old girl), it was shown that Flicker-Noise Spectroscopy (FNS) was able to identify specific differences in the responses of each organism. The high specificity of individual MEG responses manifested itself in the values of FNS parameters for both chaotic and resonant components of the original signal. The present study applies the FNS cross-correlation function to the analysis of correlations between the MEG responses simultaneously measured at spatially separated points of the human cortex processing the red-blue flickering color stimulus. It is shown that the cross-correlations for control (healthy) subjects are characterized by frequency and phase synchronization at different points of the cortex, with the dynamics of neuromagnetic responses being determined by the low-fr...
Gransier, Robin; Deprez, Hanne; Hofmann, Michael; Moonen, Marc; van Wieringen, Astrid; Wouters, Jan
2016-05-01
Previous studies have shown that objective measures based on stimulation with low-rate pulse trains fail to predict the threshold levels of cochlear implant (CI) users for high-rate pulse trains, as used in clinical devices. Electrically evoked auditory steady-state responses (EASSRs) can be elicited by modulated high-rate pulse trains, and can potentially be used to objectively determine threshold levels of CI users. The responsiveness of the auditory pathway of profoundly hearing-impaired CI users to modulation frequencies is, however, not known. In the present study we investigated the responsiveness of the auditory pathway of CI users to a monopolar 500 pulses per second (pps) pulse train modulated between 1 and 100 Hz. EASSRs to forty-three modulation frequencies, elicited at the subject's maximum comfort level, were recorded by means of electroencephalography. Stimulation artifacts were removed by a linear interpolation between a pre- and post-stimulus sample (i.e., blanking). The phase delay across modulation frequencies was used to differentiate between the neural response and a possible residual stimulation artifact after blanking. Stimulation artifacts were longer than the inter-pulse interval of the 500pps pulse train for recording electrodes ipsilateral to the CI. As a result the stimulation artifacts could not be removed by artifact removal on the bases of linear interpolation for recording electrodes ipsilateral to the CI. However, artifact-free responses could be obtained in all subjects from recording electrodes contralateral to the CI, when subject specific reference electrodes (Cz or Fpz) were used. EASSRs to modulation frequencies within the 30-50 Hz range resulted in significant responses in all subjects. Only a small number of significant responses could be obtained, during a measurement period of 5 min, that originate from the brain stem (i.e., modulation frequencies in the 80-100 Hz range). This reduced synchronized activity of brain stem
Wang, X.; Zheng, G. T.
2016-02-01
A simple and general Equivalent Dynamic Stiffness Mapping technique is proposed for identifying the parameters or the mathematical model of a nonlinear structural element with steady-state primary harmonic frequency response functions (FRFs). The Equivalent Dynamic Stiffness is defined as the complex ratio between the internal force and the displacement response of unknown element. Obtained with the test data of responses' frequencies and amplitudes, the real and imaginary part of Equivalent Dynamic Stiffness are plotted as discrete points in a three dimensional space over the displacement amplitude and the frequency, which are called the real and the imaginary Equivalent Dynamic Stiffness map, respectively. These points will form a repeatable surface as the Equivalent Dynamic stiffness is only a function of the corresponding data as derived in the paper. The mathematical model of the unknown element can then be obtained by surface-fitting these points with special functions selected by priori knowledge of the nonlinear type or with ordinary polynomials if the type of nonlinearity is not pre-known. An important merit of this technique is its capability of dealing with strong nonlinearities owning complicated frequency response behaviors such as jumps and breaks in resonance curves. In addition, this technique could also greatly simplify the test procedure. Besides there is no need to pre-identify the underlying linear parameters, the method uses the measured data of excitation forces and responses without requiring a strict control of the excitation force during the test. The proposed technique is demonstrated and validated with four classical single-degree-of-freedom (SDOF) numerical examples and one experimental example. An application of this technique for identification of nonlinearity from multiple-degree-of-freedom (MDOF) systems is also illustrated.
Averaging anisotropic cosmologies
We examine the effects of spatial inhomogeneities on irrotational anisotropic cosmologies by looking at the average properties of anisotropic pressure-free models. Adopting the Buchert scheme, we recast the averaged scalar equations in Bianchi-type form and close the standard system by introducing a propagation formula for the average shear magnitude. We then investigate the evolution of anisotropic average vacuum models and those filled with pressureless matter. In the latter case we show that the backreaction effects can modify the familiar Kasner-like singularity and potentially remove Mixmaster-type oscillations. The presence of nonzero average shear in our equations also allows us to examine the constraints that a phase of backreaction-driven accelerated expansion might put on the anisotropy of the averaged domain. We close by assessing the status of these and other attempts to define and calculate 'average' spacetime behaviour in general relativity
Prediction of power system frequency response after generator outages using neural nets
Djukanovic, M.B.; Popovic, D.P. (Electrotechnicki Inst. ' Nikola Tesla' , Belgrade (Yugoslavia)); Sobajic, D.J.; Pao, Y.-H. (Case Western Reserve Univ., Cleveland, OH (United States))
1993-09-01
A new methodology is presented for estimating the frequency behaviour of power systems necessary for an indication of under-frequency load shedding in steady-state security assessment. It is well known that large structural disturbances such as generator tripping or load outages can initiate cascading outages, system separation into islands, and even the complete breakup. The approach provides a fairly accurate method of estimating the system average frequency response without making simplifications or neglecting non-linearities and small time constants in the equations of generating units, voltage regulators and turbines. The efficiency of the new procedure is demonstrated using the New England power system model for a series of characteristic perturbations. The validity of the proposed approach is verified by comparison with the simulation of short-term dynamics including effects of control and automatic devices. (author)
Garcia, J C; Layton, S A; Rubal, B J
1989-05-01
This study compares the frequency response characteristics of catheter-mounted piezoelectric sound transducers with micromanometric transducers. The tip of a 8F catheter with two piezoelectric transducers and two micromanometers was inserted into a water-filled chamber that had a speaker fixed at one end. The speaker was driven by a power amplifier and sine wave generator. The outputs of the transducers were connected to a low-level amplifier. The piezoelectric transducer behaved as a tunable high-pass filter that could be modified by altering the input impedance of the low level amplifier; the frequency response characteristics were examined at five input impedances ranging from 0.96 to 11.8 megohms. The peak-to-peak outputs of the piezoelectric and pressure transducers were recorded at frequency ranges from DC to 1 kHz with a wide-band oscilloscope. The ratio of the outputs from the piezotransducer and micromanometer (Vph/Vpr) was plotted vs. frequency for each input impedance and analyzed to determine the piezotransducer's output resistance and equivalent capacitance; roll-off frequencies were then calculated. The equivalent capacitance of the piezo-element was determined to be 500-700 picofarads. Series capacitance acted with network resistance to produce a predictable frequency-dependent change in signal amplitude and phase angle. The inherent noise of the pressure transducer was found to be approximately 0.2 mm Hg, while the noise of the piezoelectric transducer was immeasurably low. The piezoelectric phonotransducers were superior to micromanometer transducers in their higher gain and lower noise, suggesting that these transducers may prove useful to physiologic and clinical studies for measuring intravascular sound. PMID:2720766
Responses of the ear to low frequency sounds, infrasound and wind turbines.
Salt, Alec N; Hullar, Timothy E
2010-09-01
Infrasonic sounds are generated internally in the body (by respiration, heartbeat, coughing, etc) and by external sources, such as air conditioning systems, inside vehicles, some industrial processes and, now becoming increasingly prevalent, wind turbines. It is widely assumed that infrasound presented at an amplitude below what is audible has no influence on the ear. In this review, we consider possible ways that low frequency sounds, at levels that may or may not be heard, could influence the function of the ear. The inner ear has elaborate mechanisms to attenuate low frequency sound components before they are transmitted to the brain. The auditory portion of the ear, the cochlea, has two types of sensory cells, inner hair cells (IHC) and outer hair cells (OHC), of which the IHC are coupled to the afferent fibers that transmit "hearing" to the brain. The sensory stereocilia ("hairs") on the IHC are "fluid coupled" to mechanical stimuli, so their responses depend on stimulus velocity and their sensitivity decreases as sound frequency is lowered. In contrast, the OHC are directly coupled to mechanical stimuli, so their input remains greater than for IHC at low frequencies. At very low frequencies the OHC are stimulated by sounds at levels below those that are heard. Although the hair cells in other sensory structures such as the saccule may be tuned to infrasonic frequencies, auditory stimulus coupling to these structures is inefficient so that they are unlikely to be influenced by airborne infrasound. Structures that are involved in endolymph volume regulation are also known to be influenced by infrasound, but their sensitivity is also thought to be low. There are, however, abnormal states in which the ear becomes hypersensitive to infrasound. In most cases, the inner ear's responses to infrasound can be considered normal, but they could be associated with unfamiliar sensations or subtle changes in physiology. This raises the possibility that exposure to the
Hwu, Chyanbin
2010-01-01
As structural elements, anisotropic elastic plates find wide applications in modern technology. The plates here are considered to be subjected to not only in plane load but also transverse load. In other words, both plane and plate bending problems as well as the stretching-bending coupling problems are all explained in this book. In addition to the introduction of the theory of anisotropic elasticity, several important subjects have are discussed in this book such as interfaces, cracks, holes, inclusions, contact problems, piezoelectric materials, thermoelastic problems and boundary element a
Pérez-Nadal, Guillem
2016-01-01
We consider a non-relativistic free scalar field theory with a type of anisotropic scale invariance in which the number of coordinates "scaling like time" is generically greater than one. We propose the Cartesian product of two curved spaces, with the metric of each space parameterized by the other space, as a notion of curved background to which the theory can be extended. We study this type of geometries, and find a family of extensions of the theory to curved backgrounds in which the anisotropic scale invariance is promoted to a local, Weyl-type symmetry.
Cortisol response and subjective sleep disturbance after low-frequency noise exposure
Persson Waye, K.; Agge, A.; Clow, A.; Hucklebridge, F.
2004-10-01
A previous experimental study showed that the cortisol response upon awakening was reduced following nights with low-frequency noise exposure. This study comprised a larger number of subjects and an extended period of acclimatisation nights. In total, 26 male subjects slept during five consecutive nights in a sleep laboratory. Half of the subjects were exposed to low-frequency noise (40 dBA) on the 4th night and had their reference night (24 dBA) on the 5th night, while the reverse conditions were present for the other half of the group. Subjective sleep disturbances were recorded by questionnaires and cortisol response upon awakening was measured in saliva. The results showed that subjects were more tired and felt less socially orientated in the morning after nights with low-frequency noise. Mood was negatively affected in the evening after nights with low-frequency noise. No effect of noise condition was found on the cortisol secretion. There was a significant effect of group and weekday, indicating that further methodological developments are necessary before saliva cortisol secretion can be reliably used as an indicator of noise-disturbed sleep.
Declercq, Frédéric; Meganck, Reitske; Deheegher, J; Van Hoorde, H
2011-02-01
In this study, the authors compared the respective contribution of an individual's subjective response and the frequency of exposure to critical incidents to the development of symptoms of posttraumatic stress disorder (PTSD) in a sample of 136 nurses and ambulance personnel working in military facilities. They found no relationship between the frequency of encountered critical incidents and the occurrence of PTSD symptoms. The subjective response to a stressor contributed to the development of PTSD symptoms and was most strongly associated with intrusion, partial eta squared =.23, and hyperarousal symptoms, partial eta squared =.16. Stressors that elicited the most intense affects within this population were those involving children and those where workers encountered limitations in supplies and resources. PMID:21351174
Robust controller design for the nuclear reactor power by extended frequency response method
In this study, a controller for a nuclear power is designed. The reactor is modeled using the three dimensional reactor design code MASTER. From the relationship of the input and output of the reactor code, a reactor dynamic model is derived by the system identification method. This model is more realistic than the one based on mathematical theories. With this model, a robust controller is designed by the extended frequency response method. As this method has the same theoretical background as the classical method, all of the existing design techniques of the classical method can be used directly. Furthermore, by introducing the real part of a Laplacian operator into the frequency response, the control design specification can be considered at the initial stage of design. The designed controller is simple, and gives a sufficient robustness with good performance
Frequency-response-based analysis of respiratory sensor measuring capacitance built across skin
Terasawa, Makie; Kumagai, Shinya; Sasaki, Minoru
2016-04-01
A capacitive respiratory sensor is studied by attaching the electrodes to the skin. The signal characteristics related to the electrode position and body motion are examined. The frequency response indicates the nearly pure capacitance characteristics. The sensing mechanism model based on the equivalent skin thickness change generated by the body volume change accompanying respiration is reasonably consistent with the experimental results. The sensing method is examined by measuring the frequency response under some different conditions including the grounding issue. The electrode attached to the concave site tends to show a smaller signal difference between inhalation and exhalation. The convex site stabilizes the measurement. The bellyband combined with the electrode realizes stable sensing with comfortable fit on the skin.
Open Photoacoustic Cell for Blood Sugar Measurement: Numerical Calculation of Frequency Response
Baumann, Bernd; Teschner, Mark
2015-01-01
A new approach for continuous and non-invasive monitoring of the glucose concentration in human epidermis has been suggested recently. This method is based on photoacoustic (PA) analysis of human interstitial fluid. The measurement can be performed in vitro and in vivo and, therefore, may form the basis for a non-invasive monitoring of the blood sugar level for diabetes patients. It requires a windowless PA cell with an additional opening that is pressed onto the human skin. Since signals are weak, advantage is taken of acoustic resonances of the cell. Recently, a numerical approach based on the Finite Element (FE) Method has been successfully used for the calculation of the frequency response function of closed PA cells. This method has now been adapted to obtain the frequency response of the open cell. Despite the fact that loss due to sound radiation at the opening is not included, fairly good accordance with measurement is achieved.
Marijn Van Dongen
2015-03-01
These findings are subsequently verified using in vitro experiments in which the response of a Purkinje cell is measured due to a stimulation signal in the molecular layer of the cerebellum of a mouse. For this purpose a stimulator circuit is developed that is able to produce a monophasic high frequency switched-mode stimulation signal. The results confirm the modeling by showing that switched-mode stimulation is able to induce similar responses in the Purkinje cell as classical stimulation using a constant current source. This conclusion opens up possibilities for novel stimulation designs that can improve the performance of the stimulator circuitry. Care has to be taken to avoid losses in the system due to the higher operating frequency.
Recent measurements at the LIGO Hanford Observatory have confirmed the predicted high-frequency dynamic response of km scale Fabry-Perot cavities to length and laser frequency variations. The dynamic response functions have been exploited to determine a number of cavity parameters including the cavity length and the resonance width. A new technique based on a variation of these measurements has been utilized to measure the interferometer arm cavity lengths with a precision of 80 μm. We present an overview of these measurements and discuss how the dynamic field responses could be used to measure the cavity g factors which are related to the mirror radii of curvature
Optimization of a space spectrograph main frame and frequency response analysis of the frame
Zhang, Xin-yu; Chen, Zhi-yuan; Yang, Shi-mo
2009-07-01
A space spectrograph main structure is optimized and examined in order to satisfy the space operational needs. The space spectrograph will be transported into its operational orbit by the launch vehicle and it will undergo dynamic environment in the spacecraft injection period. The unexpected shocks may cause declination of observation accuracy and even equipment damages. The main frame is one of the most important parts because its mechanical performance has great influence on the operational life of the spectrograph, accuracy of observation, etc. For the reason of cost reduction and stability confirming, lower weight and higher structure stiffness of the frame are simultaneously required. Structure optimization was conducted considering the initial design modal analysis results. The base modal frequency raised 10.34% while the whole weight lowered 8.63% compared to the initial design. The purpose of this study is to analyze the new design of main frame mechanical properties and verify whether it can satisfy strict optical demands under the dynamic impact during spacecraft injection. For realizing and forecasting the frequency response characteristics of the main structure in mechanical environment experiment, dynamic analysis of the structure should be performed simulating impulse loads from the bottom base. Therefore, frequency response analysis (FRA) of the frame was then performed using the FEA software MSC.PATRAN/NASTRAN. Results of shock response spectrum (SRS) responses from the base excitations were given. Stress and acceleration dynamic responses of essential positions in the spacecraft injection course were also calculated and spectrometer structure design was examined considering stiffness / strength demands. In this simulation, maximum stresses of Cesic material in two acceleration application cases are 45.1 and 74.1 MPa, respectively. They are all less than yield strengths. As is demonstrated from the simulation, strength reservation of the frame is
De Ruiter, Stacy Lynn; Southall, Brandon L.; Calambokidis, John; Zimmer, Walter M X; Sadykova, Dinara; Falcone, Erin A.; Friedlaender, Ari S.; John E. Joseph; Moretti, David; Schorr, Gregory S.; Thomas, Len; Tyack, Peter Lloyd
2013-01-01
Most marine mammal strandings coincident with naval sonar exercises have involved Cuvier's beaked whales (Ziphius cavirostris). We recorded animal movement and acoustic data on two tagged Ziphius and obtained the first direct measurements of behavioural responses of this species to mid-frequency active (MFA) sonar signals. Each recording included a 30-min playback (one 1.6-s simulated MFA sonar signal repeated every 25 s); one whale was also incidentally exposed to MFA sonar from distant nav...
Frequency Response Of Series And Parallel Combination Of Two Single Feedback Class D Amplifier
R. Sivarajan; K. R. Padmavathy; A.kasthoory; N. Santha; S. Subashri
2015-01-01
Amplifier is generally used to increase the amplitude of the signal. Consider the audio signal, if the amplitude of the audio signal is increased, then automatically loudness of the signal is increased. Class D Amplifier (CDA) consists of integrator, PWM modulator and output stage. This system can be defined as a open loop CDA system. The main factor to be considered for any amplifier circuit is the gain which is obtained by frequency response. To improve the gain of the amplifier, ...
A Posteriori Error Analysis of Component Mode Synthesis for the Frequency Response Problem
Jakobsson, Håkan; Larson, Mats G.
2012-01-01
We consider the frequency response problem and derive a posteriori error estimates for the discrete error in a reduced finite element model obtained using the component mode synthesis (CMS) method. We provide estimates in a linear quantity of interest and the energy norm. The estimates reflect to what degree each CMS subspace influence the overall error in the reduced solution. This enables automatic error control through adaptive algorithms that determine suitable dimensions of each subspace...
Real-time open-loop frequency response analysis of flight test data
Bosworth, J. T.; West, J. C.
1986-01-01
A technique has been developed to compare the open-loop frequency response of a flight test aircraft real time with linear analysis predictions. The result is direct feedback to the flight control systems engineer on the validity of predictions and adds confidence for proceeding with envelope expansion. Further, gain and phase margins can be tracked for trends in a manner similar to the techniques used by structural dynamics engineers in tracking structural modal damping.
Moth hearing in response to bat echolocation calls manipulated independently in time and frequency.
Jones, G.; Waters, D A
2000-01-01
We measured the auditory responses of the noctuid moth Noctua pronuba to bat echolocation calls which were manipulated independently in time and frequency. Such manipulations are important in understanding how insect hearing influences the evolution of echolocation call characteristics. We manipulated the calls of three bat species (Rhinolophus hipposideros, Myotis nattereri and Pipistrellus pipistrellus) that use different echolocation call features by doubling their duration or reducing the...
A Practical Method for Measuring the Spatial Frequency Response of Light Field Cameras
Firmenich, Damien; Süsstrunk, Sabine; Baboulaz, Loïc
2014-01-01
The spatial frequency response (SFR) is one of the most important and unbiased image quality measures of a digital camera. It evaluates to which extent a lens/sensor combination can resolve scene details. In this paper, we propose a simple and practical method to measure the SFR of microlens-based light field cameras. The particularity of such cameras resides in their ability to capture both spatial and angular information of the incoming light field thanks to an array of microlenses located ...
Hall, G; Hantos, Z.; Wildhaber, J; Petak, F; Sly, P
2001-01-01
BACKGROUND—The contribution of the pulmonary tissues to the mechanical behaviour of the respiratory system is well recognised. This study was undertaken to detect airway and lung tissue responses to inhaled methacholine (Mch) using the low frequency forced oscillation technique (LFOT). METHODS—The respiratory system impedance (Zrs, 0.5-20 Hz) was determined in 17 asymptomatic infants. A model containing airway resistance (Raw) and inertance (Iaw) and a constant phase tissue ...
Individual Differences in the Frequency-Following Response: Relation to Pitch Perception.
Emily B J Coffey
Full Text Available The scalp-recorded frequency-following response (FFR is a measure of the auditory nervous system's representation of periodic sound, and may serve as a marker of training-related enhancements, behavioural deficits, and clinical conditions. However, FFRs of healthy normal subjects show considerable variability that remains unexplained. We investigated whether the FFR representation of the frequency content of a complex tone is related to the perception of the pitch of the fundamental frequency. The strength of the fundamental frequency in the FFR of 39 people with normal hearing was assessed when they listened to complex tones that either included or lacked energy at the fundamental frequency. We found that the strength of the fundamental representation of the missing fundamental tone complex correlated significantly with people's general tendency to perceive the pitch of the tone as either matching the frequency of the spectral components that were present, or that of the missing fundamental. Although at a group level the fundamental representation in the FFR did not appear to be affected by the presence or absence of energy at the same frequency in the stimulus, the two conditions were statistically distinguishable for some subjects individually, indicating that the neural representation is not linearly dependent on the stimulus content. In a second experiment using a within-subjects paradigm, we showed that subjects can learn to reversibly select between either fundamental or spectral perception, and that this is accompanied both by changes to the fundamental representation in the FFR and to cortical-based gamma activity. These results suggest that both fundamental and spectral representations coexist, and are available for later auditory processing stages, the requirements of which may also influence their relative strength and thus modulate FFR variability. The data also highlight voluntary mode perception as a new paradigm with which to
It is shown that some common machine structural failures can be identified on-line by monitoring in some chosen characteristic frequency response functions. The response signatures are shown to be insensitive to variations in machine loading and, by suitable location of vibration monitoring points, can be used to accurately locate and identify the cause of failure. The method is used to identify faults such as shaft misalignment and bearing failures on a high speed motor-pump assembly and to detect and predict fatigue failures in shafts subjected to torsional loads. (author)
Analysis of the frequency-dependent response to wave forcing in the extratropics
A. J. Haklander
2006-01-01
Full Text Available A quasigeostrophic model for the frequency-dependent response of the zonal-mean flow to planetary-wave forcing at Northern Hemisphere (NH midlatitudes is applied to 4-D-Var ECMWF analysis data for six extended winter seasons. The theoretical response is a non-linear function of the frequency of the forcing, the thermal damping time α−1, and a scaling parameter µ which includes the aspect ratio of the meridional to the vertical length scale of the response. Regression of the calculated response from the analyses onto the theoretical response yields height-dependent estimates for both α−1 and µ. The thermal damping time estimated from this dynamical model is about 2 days in the troposphere, 7–10 days in the stratosphere, and 2–4 days in the lower mesosphere. For the stratosphere and lower mesosphere, the estimates lie within the range of existing radiative damping time estimates, but for the troposphere they are significantly smaller.
Responses of Waveform-Selective Absorbing Metasurfaces to Oblique Waves at the Same Frequency
Wakatsuchi, Hiroki; Gao, Fei; Yagitani, Satoshi; Sievenpiper, Daniel F.
2016-01-01
Conventional materials vary their electromagnetic properties in response to the frequency of an incoming wave, but these responses generally remain unchanged at the same frequency unless nonlinearity is involved. Waveform-selective metasurfaces, recently developed by integrating several circuit elements with planar subwavelength periodic structures, allowed us to distinguish different waves even at the same frequency depending on how long the waves continued, namely, on their pulse widths. These materials were thus expected to give us an additional degree of freedom to control electromagnetic waves. However, all the past studies were demonstrated with waves at a normal angle only, although in reality electromagnetic waves scatter from various structures or boundaries and therefore illuminate the metasurfaces at oblique angles. Here we study angular dependences of waveform-selective metasurfaces both numerically and experimentally. We demonstrate that, if designed properly, capacitor-based waveform-selective metasurfaces more effectively absorb short pulses than continuous waves (CWs) for a wide range of the incident angle, while inductor-based metasurfaces absorb CWs more strongly. Our study is expected to be usefully exploited for applying the concept of waveform selectivity to a wide range of existing microwave devices to expand their functionalities or performances in response to pulse width as a new capability. PMID:27516346
Research on the iterative method for model updating based on the frequency response function
Wei-Ming Li; Jia-Zhen Hong
2012-01-01
Model reduction technique is usually employed in model updating process,In this paper,a new model updating method named as cross-model cross-frequency response function (CMCF) method is proposed and a new iterative method associating the model updating method with the model reduction technique is investigated.The new model updating method utilizes the frequency response function to avoid the modal analysis process and it does not need to pair or scale the measured and the analytical frequency response function,which could greatly increase the number of the equations and the updating parameters.Based on the traditional iterative method,a correction term related to the errors resulting from the replacement of the reduction matrix of the experimental model with that of the finite element model is added in the new iterative method.Comparisons between the traditional iterative method and the proposed iterative method are shown by model updating examples of solar panels,and both of these two iterative methods combine the CMCF method and the succession-level approximate reduction technique.Results show the effectiveness of the CMCF method and the proposed iterative method.
Wu, Tsung-Tsong; Tang, He-Tai; Chen, Yung-Yu
2005-08-01
Focused interdigital transducers (FIDTs) based on concentric wave surfaces can excite surface acoustic wave (SAW) with high intensity, high beamwidth compression ratio and small localized area. In this paper, we developed a model to analyse the frequency response of a SAW device with FIDTs based on concentric wave surfaces. First, we constructed a focused SAW device by adopting a pair of FIDTs shaped as the concentric wave surface. To calculate its frequency response, a simulation model was established based on the 2D SAW filter model, effective permittivity approach and perturbation theory. Further, the focused SAW devices were designed and fabricated via the microelectromechanical system process technique. A good agreement between the simulated and measured results was found. Finally, the frequency responses of focused SAW devices based on concentric wave surfaces were discussed and some attractive features were found, such as less ripples of pass-band and high stop-band rejection. In addition, in comparison with the conventional SAW devices with uniform interdigital transducers, the focused SAW devices are more sensitive to variations in the focal area, instead of the whole delayline region. Accordingly, they are suitable to be applied to detect or manipulate some localized variations, such as acousto-optic or acousto-electric effects.
Optimizing the frequency response of a steering mirror mount for interferometry applications
Penado, F. Ernesto; Clark, James H., III
2009-08-01
The Navy Prototype Optical Interferometer (NPOI) in Flagstaff, Arizona, makes use of separate smaller telescopes spaced along a Y-array and used simultaneously to simulate an equivalent single large telescope. The performance of the NPOI can be improved by increasing the steering response of the 8-in. diameter Narrow Angle Tracker (NAT). The mirrors of the NAT correct the image position for atmospherically induced motion. The current tracker has a slow response due to the low fundamental frequency of the mount and limits the quality of the data. A higher frequency will allow a faster servo feedback to the steering mirror, which will enhance the tracking performance on stellar objects resulting in final fringe data of higher quality. Also, additional and fainter objects could be observed with a faster response system, and the interferometer as a whole would be less sensitive to fluctuations in atmospheric quality. Improvements in the NAT performance over the current cast aluminum frame and glass mirror were achieved by the use of advanced composite materials in the design of the frame and mirror. Various design possibilities were evaluated using finite element analysis. It was found that the natural frequency of the NAT can be increased from 68 to 217 Hz, and the corresponding weight decreased by a factor of 5.6, by using a composite mount with a composite mirror.
Responses of Waveform-Selective Absorbing Metasurfaces to Oblique Waves at the Same Frequency.
Wakatsuchi, Hiroki; Gao, Fei; Yagitani, Satoshi; Sievenpiper, Daniel F
2016-01-01
Conventional materials vary their electromagnetic properties in response to the frequency of an incoming wave, but these responses generally remain unchanged at the same frequency unless nonlinearity is involved. Waveform-selective metasurfaces, recently developed by integrating several circuit elements with planar subwavelength periodic structures, allowed us to distinguish different waves even at the same frequency depending on how long the waves continued, namely, on their pulse widths. These materials were thus expected to give us an additional degree of freedom to control electromagnetic waves. However, all the past studies were demonstrated with waves at a normal angle only, although in reality electromagnetic waves scatter from various structures or boundaries and therefore illuminate the metasurfaces at oblique angles. Here we study angular dependences of waveform-selective metasurfaces both numerically and experimentally. We demonstrate that, if designed properly, capacitor-based waveform-selective metasurfaces more effectively absorb short pulses than continuous waves (CWs) for a wide range of the incident angle, while inductor-based metasurfaces absorb CWs more strongly. Our study is expected to be usefully exploited for applying the concept of waveform selectivity to a wide range of existing microwave devices to expand their functionalities or performances in response to pulse width as a new capability. PMID:27516346
Frequency dependence of CA3 spike phase response arising from h-current properties
Hyun Jae Jang
2013-12-01
Full Text Available The phase of firing of hippocampal neurons during theta oscillations encodes spatial information. Moreover, the spike phase response to synaptic inputs in individual cells depends on the expression of the hyperpolarisation-activated mixed cation current (Ih, which differs between CA3 and CA1 pyramidal neurons. Here, we compared the phase response of these two cell types, as well as their intrinsic membrane properties. We found that both CA3 and CA1 pyramidal neurons show a voltage sag in response to negative current steps but that this voltage sag is significantly smaller in CA3 cells. Moreover, CA3 pyramidal neurons have less prominent resonance properties compared to CA1 pyramidal neurons. This is consistent with differential expression of Ih by the two cell types. Despite their distinct intrinsic membrane properties, both CA3 and CA1 pyramidal neurons displayed bidirectional spike phase control by excitatory conductance inputs during theta oscillations. In particular, excitatory inputs delivered at the descending phase of a dynamic clamp-induced membrane potential oscillation delayed the subsequent spike by nearly 50 mrad. The effect was shown to be mediated by Ih and was counteracted by increasing inhibitory conductance driving the membrane potential oscillation. Using our experimental data to feed a computational model, we showed that differences in Ih between CA3 and CA1 pyramidal neurons could predict frequency-dependent differences in phase response properties between these cell types. We confirmed experimentally such frequency-dependent spike phase control in CA3 neurons. Therefore, a decrease in theta frequency, which is observed in intact animals during novelty, might switch the CA3 spike phase response from unidirectional to bidirectional and thereby promote encoding of the new context.
On the Newtonian anisotropic configurations
Shojai, F. [University of Tehran, Department of Physics, Tehran (Iran, Islamic Republic of); Institute for Research in Fundamental Sciences (IPM), Foundations of Physics Group, School of Physics, Tehran (Iran, Islamic Republic of); Fazel, M.R.; Stepanian, A. [University of Tehran, Department of Physics, Tehran (Iran, Islamic Republic of); Kohandel, M. [Alzahra University, Department of Sciences, Tehran (Iran, Islamic Republic of)
2015-06-15
In this paper we are concerned with the effects of an anisotropic pressure on the boundary conditions of the anisotropic Lane-Emden equation and the homology theorem. Some new exact solutions of this equation are derived. Then some of the theorems governing the Newtonian perfect fluid star are extended, taking the anisotropic pressure into account. (orig.)
B B Bhowmik; A Rajput
2004-06-01
Anisotropic Bianchi Type-I cosmological models have been studied on the basis of Lyra's geometry. Two types of models, one with constant deceleration parameter and the other with variable deceleration parameter have been derived by considering a time-dependent displacement field.
Anisotropic Ambient Volume Shading.
Ament, Marco; Dachsbacher, Carsten
2016-01-01
We present a novel method to compute anisotropic shading for direct volume rendering to improve the perception of the orientation and shape of surface-like structures. We determine the scale-aware anisotropy of a shading point by analyzing its ambient region. We sample adjacent points with similar scalar values to perform a principal component analysis by computing the eigenvectors and eigenvalues of the covariance matrix. In particular, we estimate the tangent directions, which serve as the tangent frame for anisotropic bidirectional reflectance distribution functions. Moreover, we exploit the ratio of the eigenvalues to measure the magnitude of the anisotropy at each shading point. Altogether, this allows us to model a data-driven, smooth transition from isotropic to strongly anisotropic volume shading. In this way, the shape of volumetric features can be enhanced significantly by aligning specular highlights along the principal direction of anisotropy. Our algorithm is independent of the transfer function, which allows us to compute all shading parameters once and store them with the data set. We integrated our method in a GPU-based volume renderer, which offers interactive control of the transfer function, light source positions, and viewpoint. Our results demonstrate the benefit of anisotropic shading for visualization to achieve data-driven local illumination for improved perception compared to isotropic shading. PMID:26529745
Dynamics of Anisotropic Universes
Pérez, J
2006-01-01
We present a general study of the dynamical properties of Anisotropic Bianchi Universes in the context of Einstein General Relativity. Integrability results using Kovalevskaya exponents are reported and connected to general knowledge about Bianchi dynamics. Finally, dynamics toward singularity in Bianchi type VIII and IX universes are showed to be equivalent in some precise sence.
Multi-frequency response of a cylinder subjected to vortex shedding and support motions
Vikestad, Kyrre
1998-12-31
This thesis deals with an experimental investigation of vortex induced vibrations of a circular cylinder. The purpose of the experiment was to identify the influence from a controlled disturbance of the cylinder motions on the response caused by vortex shedding. The cylinder investigated is 2 m long and the diameter is 10 cm. The cylinder is elastically mounted in an apparatus using springs, where the foundation of one of the springs can have a harmonic motion. The apparatus is placed on a carriage in a 25 m long towing tank. Towing velocities are varied between 0.140 m/s and 0.655 m/s corresponding to reduced velocity range from 2.8 to 13.2. The still water natural frequency is 0.497 Hz, and the natural frequency in air is 0.634 Hz. The cylinder is only able to oscillate in the cross-flow direction. The support motion frequency was varied between 0.26 Hz and 1.01 Hz, and the force motion amplitude was varied using 2, 4 and 6 cm support amplitudes. Three sets of experiments were carried out: (1) Still water oscillations due to harmonic support motion excitation, support amplitude and frequencies varied, (2) Towing tests with no support motion, the velocity is varied, (3) Combined excitation: Towing tests with support motion. All possible combinations of experiments (1) and (2) are carried out. The two first experiments provide reference values for the combined excitation experiments and for verification purposes. The results reveal the ability of the external disturbance to influence the vortex shedding process both regarding frequency and the resulting response amplitudes. Results for added mass, in-line drag and damping are also obtained. The work may be of use in deep water floating petroleum production. 81 refs., 73 figs., 6 tabs.
Watkins, B. J.; Fallen, C. T.; Secan, J. A.
2013-12-01
We present new results from O-mode ionospheric heating experiments at the HAARP facility in Alaska to demonstrate that the magnitude of artificial ionization production is critically dependent on the choice of HF frequency near gyro-harmonics. For O-mode heating in the lower F-region ionosphere, typically about 200 km altitude, artificial ionization enhancements are observed in the lower ionosphere (about 150 - 220 km) and also in the topside ionosphere above about 500 km. Lower ionosphere density enhancements are inferred from HF-enhanced ion and plasma-line signals observed with UHF radar. Upper ionospheric density enhancements have been observed with TEC (total electron content) experiments by monitoring satellite radio beacons where signal paths traverse the HF-modified ionosphere. Both density enhancements and corresponding upward plasma fluxes have also been observed in the upper ionosphere via in-situ satellite observations. The data presented focus mainly on observations near the third and fourth gyro-harmonics. The specific values of the height-dependent gyro-harmonics have been computed from a magnetic model of the field line through the HF heated volume. Experiments with several closely spaced HF frequencies around the gyro-harmonic frequency region show that the magnitude of the lower-ionosphere artificial ionization production maximizes for HF frequencies about 1.0 - 1.5 MHz above the gyro-harmonic frequency. The response is progressively larger as the HF frequency is increased in the frequency region near the gyro-harmonics. For HF frequencies that are initially greater than the gyro-harmonic value the UHF radar scattering cross-section is relatively small, and non-existent or very weak signals are observed; as the signal returns drop in altitude due to density enhancements the HF interaction region passes through lower altitudes where the HF frequency is less than the gyro-harmonic value, for these conditions the radar scattering cross-section is
Oda, Hitoshi
2016-06-01
The aspherical structure of the Earth is described in terms of lateral heterogeneity and anisotropy of the P- and S-wave velocities, density heterogeneity, ellipticity and rotation of the Earth and undulation of the discontinuity interfaces of the seismic wave velocities. Its structure significantly influences the normal mode spectra of the Earth's free oscillation in the form of cross-coupling between toroidal and spheroidal multiplets and self-coupling between the singlets forming them. Thus, the aspherical structure must be conversely estimated from the free oscillation spectra influenced by the cross-coupling and self-coupling. In the present study, we improve a spectral fitting inversion algorithm which was developed in a previous study to retrieve the global structures of the isotropic and anisotropic velocities of the P and S waves from the free oscillation spectra. The main improvement is that the geographical distribution of the intensity of the S-wave azimuthal anisotropy is represented by a nonlinear combination of structure coefficients for the anisotropic velocity structure, whereas in the previous study it was expanded into a generalized spherical harmonic series. Consequently, the improved inversion algorithm reduces the number of unknown parameters that must be determined compared to the previous inversion algorithm and employs a one-step inversion method by which the structure coefficients for the isotropic and anisotropic velocities are directly estimated from the fee oscillation spectra. The applicability of the improved inversion is examined by several numerical experiments using synthetic spectral data, which are produced by supposing a variety of isotropic and anisotropic velocity structures, earthquake source parameters and station-event pairs. Furthermore, the robustness of the inversion algorithm is investigated with respect to the back-ground noise contaminating the spectral data as well as truncating the series expansions by finite terms
Within the framework of a sequential quantum mechanical model, the response and the power of a coherent generation have been obtained numerically in a resonant-tunneling diode in a wide range of frequencies with the electron-electron interaction. The quantum regime of generation is shown to be sustained under the electron-electron interaction. Thus, a high-power generation is probable under frequencies exceeding the width of the resonant level
Gamma-beam propagation in the anisotropic medium
V.A. Maisheev
1997-01-01
Propagation of gamma-beam in the anisotropic medium is considered. The simpliest example of such a medium of the general type is a combination of the two linearly polarized monochromatic laser waves with different frequencies (dichromatic wave). The optical properties of this combination are described with the use of the permittivity tensor. The refractive indices and polarization characteristics of normal electromagnetic waves propagating in the anisotropic medium are found. The relations, d...
Aeroelastic modal dynamics of wind turbines including anisotropic effects
Skjoldan, Peter Fisker; Hansen, Morten Hartvig; Rubak, Rune; Thomsen, Kenneth
2011-01-01
Several methods for aeroelastic modal analysis of a rotating wind turbine are developed and used to analyse the modal dynamics of two simplified models and a complex model in isotropic and anisotropic conditions. The Coleman transformation is used to enable extraction of the modal frequencies, damping, and periodic mode shapes of a rotating wind turbine by describing the rotor degrees of freedom in the inertial frame. This approach is valid only for an isotropic system. Anisotropic systems, e...
Dual-band frequency selective surface with quasi-elliptic bandpass response
Based on the substrate integrated waveguide technology, we present a dual-band frequency selective surface (FSS) with a quasi-elliptic bandpass response. The characteristics of the quasi-elliptic bandpass response are realized by shunting two substrate integrated waveguide cavities of different sizes, with the same slots on both sides of the metal surfaces. Four cavities of different sizes and two slots of different sizes are used to design the novel FSS. Every bandpass response with sharp sidebands is induced by two transmission nulls that are generated by the coupling between the slot aperture resonance and the cavity resonance. The simulation results show that such dual-band FSS has the advantages of high selectivity and stable performance at different oblique incident angles. Moreover, it is easy to fabricate. (general)
Time-frequency analysis of railway bridge response in forced vibration
Cantero, Daniel; Ülker-Kaustell, Mahir; Karoumi, Raid
2016-08-01
This paper suggests the use of the Continuous Wavelet Transform in combination with the Modified Littlewood-Paley basis to analyse bridge responses exited by traversing trains. The analysis provides an energy distribution map in the time-frequency domain that offers a better resolution compared to previous published studies. This is demonstrated with recorded responses of the Skidträsk Bridge, a 36 m long composite bridge located in Sweden. It is shown to be particularly useful to understand the evolution of the energy content during a vehicle crossing event. With this information it is possible to distinguish the effect of several of the governing factors involved in the dynamic response including vehicle's speed and axle configuration as well as non-linear behaviour of the structure.
Dual-band frequency selective surface with quasi-elliptic bandpass response
Zhou Hang; Qu Shao-Bo; Peng Wei-Dong; Wang Jia-Fu; Ma Hua; Zhang Jie-Qiu; Bai Peng; Xu Zhuo
2012-01-01
Based on the substrate integrated waveguide technology,we present a dual-band frequency selective surface (FSS) with a quasi-elliptic bandpass response. The characteristics of the quasi-elliptic bandpass response are realized by shunting two substrate integrated waveguide cavities of different sizes,with the same slots on both sides of the metal surfaces.Four cavities of different sizes and two slots of different sizes are used to design the novel FSS.Every bandpass response with sharp sidebands is induced by two transmission nulls that are generated by the coupling between the slot aperture resonance and the cavity resonance.The simulation results show that such dual-band FSS has the advantages of high selectivity and stable performance at different oblique incident angles.Moreover,it is easy to fabricate.
Frequency dependent gamma-ray irradiation response of Sm2O3 MOS capacitors
The frequency dependent irradiation influences on Sm2O3 MOS capacitors have been investigated and possible use of Sm2O3 in MOS-based radiation sensor was discussed in this study. To examine their gamma irradiation response over a range of doses, the fabricated MOS capacitors were irradiated up to 30 grays. Capacitance–Voltage (C–V) measurements were recorded for various doses and the influences of irradiation were determined from the mid-gap and flat-band voltage shifts. In addition, the degradations of irradiation have been studied by impedance based leakage current–voltage (J–V) characteristics. The results demonstrate that J–V characteristics have not been significantly change by irradiation and implying that the excited traps have a minor effect on current for given dose ranges. However, the frequency of applied voltage during the C–V measurements affects the irradiation response of devices, significantly. The variations on the electrical characteristics may be attributed to the different time dependency of acceptor and donor-like interface states. In spite of the variations on the device characteristics, low frequency measurements indicate that Sm2O3 is a potential candidate to be used as a dielectric layer in MOS based irradiation sensors
Huge low-frequency dielectric response of (Nb,In)-doped TiO2 ceramics
Wu, Y. Q.; Zhao, X.; Zhang, J. L.; Su, W. B.; Liu, J.
2015-12-01
The (Nb,In)-doped TiO2 ceramics have drawn considerable attention as a type of promising giant-permittivity dielectric materials in recent years. However, a significant controversy concerning the giant dielectric mechanism currently exists, and clarifying it is vitally important from both scientific and technological viewpoints. This letter reports the results of a systematical comparison study, where two kinds of (Nb,In)-doped TiO2 ceramics with a substantial difference in dielectric loss are used. Dielectric properties and complex impedance are investigated over a broad frequency band of 3 mHz-110 MHz. A huge low-frequency dielectric response in addition to the giant dielectric relaxation appearing above 1 MHz is observed for both kinds of (Nb,In)-doped TiO2 ceramics in dielectric dispersion. The huge dielectric response observed in the low frequency range can be ascribed to a non-ohmic electrode-contact, and the dielectric relaxation appearing above 1 MHz can be attributed to an internal barrier layer capacitance effect. An electrical equivalent circuit model suggested can well describe the observed dielectric properties and electrical behaviors.
Ruhnau, Philipp; Keitel, Christian; Lithari, Chrysa; Weisz, Nathan; Neuling, Toralf
2016-01-01
We tested a novel combination of two neuro-stimulation techniques, transcranial alternating current stimulation (tACS) and frequency tagging, that promises powerful paradigms to study the causal role of rhythmic brain activity in perception and cognition. Participants viewed a stimulus flickering at 7 or 11 Hz that elicited periodic brain activity, termed steady-state responses (SSRs), at the same temporal frequency and its higher order harmonics. Further, they received simultaneous tACS at 7 or 11 Hz that either matched or differed from the flicker frequency. Sham tACS served as a control condition. Recent advances in reconstructing cortical sources of oscillatory activity allowed us to measure SSRs during concurrent tACS, which is known to impose strong artifacts in magnetoencephalographic (MEG) recordings. For the first time, we were thus able to demonstrate immediate effects of tACS on SSR-indexed early visual processing. Our data suggest that tACS effects are largely frequency-specific and reveal a characteristic pattern of differential influences on the harmonic constituents of SSRs. PMID:27199707
Differential responses to high-frequency electrical stimulation in ON and OFF retinal ganglion cells
Twyford, Perry; Cai, Changsi; Fried, Shelley
2014-04-01
Objective. The field of retinal prosthetics for artificial vision has advanced considerably in recent years, however clinical outcomes remain inconsistent. The performance of retinal prostheses is likely limited by the inability of electrical stimuli to preferentially activate different types of retinal ganglion cell (RGC). Approach. Here we examine the response of rabbit RGCs to high-frequency stimulation, using biphasic pulses applied at 2000 pulses per second. Responses were recorded using cell-attached patch clamp methods, and stimulation was applied epiretinally via a small cone electrode. Main results. When prolonged stimulus trains were applied to OFF-brisk transient (BT) RGCs, the cells exhibited a non-monotonic relationship between response strength and stimulus amplitude; this response pattern was different from those elicited previously by other electrical stimuli. When the amplitude of the stimulus was modulated transiently from a non-zero baseline amplitude, ON-BT and OFF-BT cells exhibited different activity patterns: ON cells showed an increase in activity while OFF cells exhibited a decrease in activity. Using a different envelope to modulate the amplitude of the stimulus, we observed the opposite effect: ON cells exhibited a decrease in activity while OFF cells show an increase in activity. Significance. As ON and OFF RGCs often exhibit opposing activity patterns in response to light stimulation, this work suggests that high-frequency electrical stimulation of RGCs may be able to elicit responses that are more physiological than traditional pulsatile stimuli. Additionally, the prospect of an electrical stimulus capable of cell-type specific selective activation has broad applications throughout the fields of neural stimulation and neuroprostheses.
Ruediger eGeis
2013-01-01
Full Text Available Frequency modulations occur in many natural sounds, including vocalizations. The neuronal response to frequency modulated (FM stimuli has been studied extensively in different brain areas, with an emphasis on the auditory cortex and the central nucleus of the inferior colliculus. Here, we measured the responses to FM sweeps in whole-cell recordings from neurons in the dorsal cortex of the mouse inferior colliculus. Both up- and downward logarithmic FM sweeps were presented at two different speeds to both the ipsi- and the contralateral ear. Based on the number of action potentials that were fired, between 10-24% of cells were selective for rate or direction of the FM sweeps. A somewhat lower percentage of cells, 6-21%, showed selectivity based on EPSP size. To study the mechanisms underlying the generation of FM selectivity, we compared FM responses with responses to simple tones in the same cells. We found that if pairs of neurons responded in a similar way to simple tones, they generally also responded in a similar way to FM sweeps. Further evidence that FM selectivity can be generated within the dorsal cortex was obtained by reconstructing FM sweeps from the response to simple tones using three different models. In about half of the direction selective neurons the selectivity was generated by spectrally asymmetric synaptic inhibition. In addition, evidence for direction selectivity based on the timing of excitatory responses was also obtained in some cells. No clear evidence for the local generation of rate selectivity was obtained. We conclude that FM direction selectivity can be generated within the dorsal cortex of the mouse inferior colliculus by multiple mechanisms.
Hu, L; Zhang, Z G; Mouraux, A; Iannetti, G D
2015-05-01
oscillations, obtaining single-trial estimate of response latency, frequency, and magnitude. This permits within-subject statistical comparisons, correlation with pre-stimulus features, and integration of simultaneously-recorded EEG and fMRI. PMID:25665966
Visser, P. J. de, E-mail: p.j.devisser@tudelft.nl [Kavli Institute of NanoScience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft (Netherlands); Yates, S. J. C. [SRON Netherlands Institute for Space Research, Landleven 12, 9747AD Groningen (Netherlands); Guruswamy, T.; Goldie, D. J.; Withington, S. [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Neto, A.; Llombart, N. [Faculty of Electrical Engineering, Mathematics and Computer Science, Terahertz Sensing Group, Delft University of Technology, Mekelweg 4, 2628 CD Delft (Netherlands); Baryshev, A. M. [SRON Netherlands Institute for Space Research, Landleven 12, 9747AD Groningen (Netherlands); Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen (Netherlands); Klapwijk, T. M. [Kavli Institute of NanoScience, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft (Netherlands); Physics Department, Moscow State Pedagogical University, Moscow 119991 (Russian Federation); Baselmans, J. J. A. [SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht (Netherlands); Faculty of Electrical Engineering, Mathematics and Computer Science, Terahertz Sensing Group, Delft University of Technology, Mekelweg 4, 2628 CD Delft (Netherlands)
2015-06-22
We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on, the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice, this is a measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.
We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on, the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice, this is a measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements
Spears, D. L.
1980-01-01
Near ideal optical heterodyne performance was obtained at GHz IF frequencies in the 10 micrometer wavelength region with liquid nitrogen cooled HgCdTe photodiodes. Heterodyne NEP's as low as 2.7 x 10 to the minus 20th power W/Hz at 100MHz, 5.4 x 10 to the minus 20th power W/Hz at 1.5 GHz, and 9.4 x 19 to the minus 20th power W/Hz at 3 GHz were achieved. Various physical phenomena which occur within a photodiode and affect heterodyne operation were examined in order to assess the feasibility of extending the operating temperature, wavelength, and frequency response of these HgCdTe photomixers.
Cortical contributions to the auditory frequency-following response revealed by MEG.
Coffey, Emily B J; Herholz, Sibylle C; Chepesiuk, Alexander M P; Baillet, Sylvain; Zatorre, Robert J
2016-01-01
The auditory frequency-following response (FFR) to complex periodic sounds is used to study the subcortical auditory system, and has been proposed as a biomarker for disorders that feature abnormal sound processing. Despite its value in fundamental and clinical research, the neural origins of the FFR are unclear. Using magnetoencephalography, we observe a strong, right-asymmetric contribution to the FFR from the human auditory cortex at the fundamental frequency of the stimulus, in addition to signal from cochlear nucleus, inferior colliculus and medial geniculate. This finding is highly relevant for our understanding of plasticity and pathology in the auditory system, as well as higher-level cognition such as speech and music processing. It suggests that previous interpretations of the FFR may need re-examination using methods that allow for source separation. PMID:27009409
Frequency Response Analysis of an Actively Lubricated Rotor/Tilting-Pad Bearing System
Nicoletti, Rodrigo; Santos, Ilmar
In the present paper, the dynamic response of a rotor supported by an active lubricated tilting-pad bearing is investigated in the frequency domain. The theoretical part of the investigation is based on a mathematical model obtained by means of rigid body dynamics. The oil film forces are inserted...... into the model by using two different approaches: (a) linearized active oil film forces and the assumption that the hydrodynamic forces and the active hydraulic forces can be decoupled; (b) equivalent dynamic coefficients of the active oil film and the solution of the modified Reynolds' equation for...... the active lubrication. The second approach based on the equivalent dynamic coefficients leads to more accurate results since it includes the frequency dependence of the active hydraulic forces. Theoretical and experimental results reveal the feasibility of reducing resonance peaks by using the active...
Low-noise extended-frequency response with cooled silicon photodiodes
Neiswander, R. S.; Plews, G. S.
1975-01-01
It is shown that a substantial reduction in internal noise generated by the photodiode and the preamplifier can be produced by a modest cooling of the components and by optimization of preamplifier design. With this reduction the silicon detectors can, in the SNR range of 5 or greater, produce better performance than photon-noise-limited photomultipliers. The circuit noise and frequency response model suggested by Goranson and Skipper (1974) is expanded to include the effects of frequency dependent FET voltage noise and FET load resistance noise. The modeling of the photodiode and preamplifier is described and the noise characteristics of a 0.01 Hz to 100 kHz bandwidth detector/amplifier channel are evaluated.
Qiu, Q.; Fang, Z. P.; Wan, H. C.; Zheng, L.
2013-07-01
Based on the Donnell assumptions and linear visco-elastic theory, the constitutive equations of the cylindrical shell with multilayer Passive Constrained Layer Damping (PCLD) treatments are described. The motion equations and boundary conditions are derived by Hamilton principle. After trigonometric series expansion and Laplace transform, the state vector is introduced and the dynamic equations in state space are established. The transfer function method is used to solve the state equation. The dynamic performance including the natural frequency, the loss factor and the frequency response of clamped-clamped multi-layer PCLD cylindrical shell is obtained. The results show that multi-layer PCLD cylindrical shell is more effective than the traditional three-layer PCLD cylindrical shell in suppressing vibration and noise if the same amount of material is applied. It demonstrates a potential application of multi-layer PCLD treatments in many critical structures such as cabins of aircrafts, hulls of submarines and bodies of rockets and missiles.
Based on the Donnell assumptions and linear visco-elastic theory, the constitutive equations of the cylindrical shell with multilayer Passive Constrained Layer Damping (PCLD) treatments are described. The motion equations and boundary conditions are derived by Hamilton principle. After trigonometric series expansion and Laplace transform, the state vector is introduced and the dynamic equations in state space are established. The transfer function method is used to solve the state equation. The dynamic performance including the natural frequency, the loss factor and the frequency response of clamped-clamped multi-layer PCLD cylindrical shell is obtained. The results show that multi-layer PCLD cylindrical shell is more effective than the traditional three-layer PCLD cylindrical shell in suppressing vibration and noise if the same amount of material is applied. It demonstrates a potential application of multi-layer PCLD treatments in many critical structures such as cabins of aircrafts, hulls of submarines and bodies of rockets and missiles
Dynamic Response Calculation of Spatial Elastic Multibody Systems with High-Frequency Excitation
The objective of this paper is to establish a computational scheme for dynamic response calculations of a three-dimensional multibody mechanical system with impulsive forces, which give rise to high-frequency excitations. The finite-element method is employed to represent the local deformations of three-dimensional beam-like elastic components by either a finite set of nodal coordinates or a truncated set of modal coordinates. A reduced-order model is obtained by invoking a modal transformation. Both planar and complex modal reduction schemes are established. The developed formulation is implemented into a multibody simulation program that assembles the equations of motion and proceeds with its solution. The computational scheme permits a change in the basis of the modal space in order to regulate the admittance of higher frequencies and to accommodate any change in the kinematic configuration. Numerical examples are presented to demonstrate the applicability of the developed computational scheme
Response of a Hodgkin-Huxley neuron to a high-frequency input.
Borkowski, L S
2009-11-01
We study the response of a Hodgkin-Huxley neuron stimulated by a periodic sequence of conductance pulses arriving through the synapse in the high-frequency regime. In addition to the usual excitation threshold there is a smooth crossover from the firing to the silent regime for increasing pulse amplitude gsyn. The amplitude of the voltage spikes decreases approximately linearly with gsyn. In some regions of parameter space the response is irregular, probably chaotic. In the chaotic regime between the mode-locked regions 3:1 and 2:1 near the lower excitation threshold, the output interspike interval histogram (ISIH) undergoes a sharp transition. If the driving period is below the critical value, TT* even multiples of Ti also appear in the histogram, starting from the largest values. Near T* the ISIH scales logarithmically on both sides of the transition. The coefficient of variation of ISIH has a cusp singularity at T*. The average response period has a maximum slightly above T*. Near the excitation threshold in the chaotic regime the average firing rate rises sublinearly from frequencies of order 1 Hz. PMID:20365013
The oscillation of a thermal stratification layer can induce thermal fatigue damage on structures with nuclear components. To evaluate the thermal stress induced by thermal stratification oscillation, a frequency response function was developed in our previous research. However, this function does not consider the thickness of the stratified layer. Thus, it is difficult to evaluate the stress generated by actual thermal stratified layers having finite thicknesses with sufficient accuracy. To clarify the effects of layer thickness on induced thermal stress, finite element simulations were conducted under various fluid conditions. As a result, it was clarified that the non-dimensional layer thickness Ht*, which is the ratio of layer thickness to layer oscillation length, can explain the thermal stress response mechanism with layer thickness. Based on the clarified mechanisms, the frequency response function was improved. Applicability of the proposed function to a closed branch pipe of a Light Water Reactor (LWR) and the upper plenum of a pressure vessel of a Fast Breeder Reactor (FBR) was validated through comparison with finite element simulations. (author)
Frequency response of laminated composite plates and shells with matrix cracks type of damage mode
Emam, Aly A.
The present study has been designed to tackle a new set of problems for structural composites, as these materials are finding new applications in civil engineering field. An attempt has been made to study the frequency response of laminated polymer composite plates and shallow shells containing matrix cracks type of damage with arbitrary support conditions and free vibratory motions. The shell governing equations are derived using a simplified shallow shell theory based on a first order shear deformation field. The continuum damage mechanics approach has been used to model the matrix cracks in a damaged region within the plates and shallow shells. In such approach, the damage is accounted for in the laminate constitutive equations by using a set of second order tensor internal state variables which are strain-like quantities. The simplified damage model was then used to study the changes in frequency response of laminated composite plates and shallow cylindrical shells. The Ritz method and a finite element method have been proposed and developed as approximate solution procedures to quantify the change in the free vibration frequencies due to matrix cracks type of damage under both material as well as geometrical variables such as size, shape and extent of damage, degree of curvature, ratio of orthotropy, thickness ratio as well as support conditions. The analysis of various plates and shells with a centrally located damaged-zone depicts a typical trend of reduction in the vibration frequencies. This reduction is more pronounced for higher frequency modes and it shows greater sensitivity toward the size of the damaged region and density of cracks. The results also show that the changes in the frequency, especially for the fundamental mode, appear to be less sensitive to the shell boundary conditions as well as small values of curvature. The investigation of various undamaged plates and shallow shells demonstrates the importance of a first-order shear deformation
Power-law models of totally anisotropic scattering
Tuntsov, Artem V; Walker, Mark A; 10.1093/mnras/sts527
2012-01-01
The interstellar scattering responsible for pulsar parabolic arcs, and for intra-day variability of compact radio quasars, is highly anisotropic in some cases. We numerically simulate these observed phenomena using totally anisotropic, power-law models for the electron density fluctuations which cause the scattering. By comparing our results to the scattered image of PSR B0834+06 and, independently, to dual-frequency light curves of the quasar PKS1257-326, we constrain the nature of the scattering media on these lines of sight. We find that models with spectral indices slightly below \\beta=3, including the one-dimensional Kolmogorov model, are broadly consistent with both data sets. We confirm that a single physical model suffices for both sources, with the scattering medium simply being more distant in the case of B0834+06. This reinforces the idea that intra-day variability and parabolic arcs have a common cause in a type of interstellar structure which, though obscure, is commonplace. However, the implied ...
Anisotropic progressive photon mapping
Liu, XiaoDan; Zheng, ChangWen
2014-01-01
Progressive photon mapping solves the memory limitation problem of traditional photon mapping. It gives the correct radiance with a large passes, but it converges slowly. We propose an anisotropic progressive photon mapping method to generate high quality images with a few passes. During the rendering process, different from standard progressive photon mapping, we store the photons on the surfaces. At the end of each pass, an anisotropic method is employed to compute the radiance of each eye ray based on the stored photons. Before move to a new pass, the photons in the scene are cleared. The experiments show that our method generates better results than the standard progressive photon mapping in both numerical and visual qualities.
Frequency Response Analysis of an Actively Lubricated Rotor/Tilting-Pad Bearing System
Nicoletti, Rodrigo; Santos, Ilmar
2004-01-01
In the present paper, the dynamic response of a rotor supported by an active lubricated tilting-pad bearing is investigated in the frequency domain. The theoretical part of the investigation is based on a mathematical model obtained by means of rigid body dynamics. The oil film forces are inserted...... lubricated tilting-pad bearing. By applying a simple proportional controller, it is possible to reach 30% reduction of the resonance peak associated with the first rigid body mode shape of the system. One of the most important consequences of such a vibration reduction in rotating machines is the feasibility...
Frequency Response Analysis of an Actively Lubricated Rotor/Tilting-Pad Bearing System
Nicoletti, Rodrigo; Santos, Ilmar
2005-01-01
In the present paper the dynamic response of a rotor supported by an active lubricated tilting-pad bearing is investigated in the frequency domain. The theoretical part of the investigation is based on a mathematical model obtained by means of rigid body dynamics. The oil film forces are inserted...... active lubricated tilting-pad bearing. By applying a simple proportional controller it is possible to reach 30% reduction of the resonance peak associated with the first rigid body mode shape of the system. One of the most important consequences of such a vibration reduction in rotating machines is the...
Activation of the SOS response increases the frequency of small colony variants
Vestergaard, Martin; Paulander, Wilhelm Erik Axel; Ingmer, Hanne
2015-01-01
different mechanism of action influence the formation of SCVs that are resistant to otherwise lethal concentrations of the aminoglycoside, gentamicin. We found that exposure of S. aureus to fluoroquinolones and mitomycin C increased the frequency of gentamicin resistant SCVs, while other antibiotic classes...... failed to do so. The higher proportion of SCVs in cultures exposed to fluoroquinolones and mitomycin C compared to un-exposed cultures correlate with an increased mutation rate monitored by rifampicin resistance and followed induction of the SOS DNA damage response. CONCLUSION: Our observations suggest...
Effects of low-spatial-frequency response of phase plates on TEM imaging
Edgcombe, C. J.
2015-10-01
Images of simple objects produced by a perfect lens and a phase plate have been calculated by use of Abbe theory for Foucault, Hilbert and Zernike phase plates. The results show that with a Zernike plate, white outlines and ringing like those observed previously can be caused by the beam hole, which limits the low-spatial-frequency response of the system even when the lens behaves perfectly. When the change of phase added by the phase plate is distributed over a range of radius rather than a simple step, the unwanted effects are substantially reduced.