A Novel Absorbing Boundary Condition for the Frequency-DependentFinite-Difference Time-Domain Method
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A new absorbing boundary condition (ABC) for frequency-dependent finite-difference time-domain algorithm for the arbitrary dispersive media is presented. The concepts of the digital systems are introduced to the (FD)2TD method. On the basis of digital filter designing and vector algebra, the absorbing boundary condition under arbitrary angle of incidence are derived. The transient electromagnetic problems in two-dimensions and three-dimensions are calculated and the validity of the ABC is verified.
DEFF Research Database (Denmark)
Christensen, Tage Emil; Behrens, Claus
The frequency dependent specific heat is a significant response function characterizing the glass transition. Contrary to the dielectric response it is not easily measured over many decades. The introduction of the 3-omega method, where the temperature oscillations at a planar oscillatoric heat...... generator is measured, made this possible. The method relied on a 1-d solution to the heat diffusion equation. There have been attempts to invoke the boundary effects to first order. However we present the fully 3-d solution to the problem including these effects. The frequency range can hereby...
DEFF Research Database (Denmark)
Escolano-Carrasco, José; Jacobsen, Finn; López, J.J.
2008-01-01
The finite-difference time-domain (FDTD) method provides a simple and accurate way of solving initial boundary value problems. However, most acoustic problems involve frequency dependent boundary conditions, and it is not easy to include such boundary conditions in an FDTD model. Although solutio...
Kvashnin, A Yu; Yushkanov, A A
2012-01-01
The classical Kramers problem of the kinetic theory is solved. The Kramers problem about isothermal sliding for quantum Fermi gases is considered. Quantum gases with the velocity - dependent collision frequency are considered. Specular - diffusive boundary conditions are applied. Dependence of isothermal sliding on the resulted chemical potential is found out.
[Frequency dependance of compliance].
Gayrard, P
1975-01-01
Resistance of peripheral or "small" airways is only a small part of the total pulmonary resistance (Raw). Even considerable obstruction in these airways will have little effect on total resistance. Conversely this will lead to inequality in the time constants of units in parallel, and dynamic lung compliance (C dyn) shall fall as respiratory frequence increases. C dyn is measured from simultaneous recordings of transpulmonary pressure (esophageal balloon) and volume obtained from a volume displacement plethysmograph. If Raw and static compliance are found to be normal, the frequency dependance of compliance will result from peripheral airway obstruction only. Early stages of chronic airway obstruction can be established by this method. However this appear not suitable for wide-scale studies.
Bursting frequency prediction in turbulent boundary layers
Energy Technology Data Exchange (ETDEWEB)
LIOU,WILLIAM W.; FANG,YICHUNG
2000-02-01
The frequencies of the bursting events associated with the streamwise coherent structures of spatially developing incompressible turbulent boundary layers were predicted using global numerical solution of the Orr-Sommerfeld and the vertical vorticity equations of hydrodynamic stability problems. The structures were modeled as wavelike disturbances associated with the turbulent mean flow. The global method developed here involves the use of second and fourth order accurate finite difference formula for the differential equations as well as the boundary conditions. An automated prediction tool, BURFIT, was developed. The predicted resonance frequencies were found to agree very well with previous results using a local shooting technique and measured data.
Frequency Dependent Attenuation Revisited
Richard, Kowar; Xavier, Bonnefond
2009-01-01
The work is inspired by thermo-and photoacoustic imaging, where recent efforts are devoted to take into account attenuation and varying wave speed parameters. In this paper we study causal equations describing propagation of attenuated pressure waves. We review standard models like frequency power laws and and the thermo-viscous equation. The lack of causality of standard models in the parameter range relevant for photoacoustic imaging requires to derive novel equations. The main ingredients for deriving causal equations are the Kramers-Kronig relation and the mathematical concept of linear system theory. The theoretical results of this work are underpined by numerical experiments.
Brain response to prosodic boundary cues depends on boundary position
Directory of Open Access Journals (Sweden)
Julia eHolzgrefe
2013-07-01
Full Text Available Prosodic information is crucial for spoken language comprehension and especially for syntactic parsing, because prosodic cues guide the hearer’s syntactic analysis. The time course and mechanisms of this interplay of prosody and syntax are not yet well understood. In particular, there is an ongoing debate whether local prosodic cues are taken into account automatically or whether they are processed in relation to the global prosodic context in which they appear. The present study explores whether the perception of a prosodic boundary is affected by its position within an utterance. In an event-related potential (ERP study we tested if the brain response evoked by the prosodic boundary differs when the boundary occurs early in a list of three names connected by conjunctions (i.e., after the first name as compared to later in the utterance (i.e., after the second name. A closure positive shift (CPS — marking the processing of a prosodic phrase boundary — was elicited only for stimuli with a late boundary, but not for stimuli with an early boundary. This result is further evidence for an immediate integration of prosodic information into the parsing of an utterance. In addition, it shows that the processing of prosodic boundary cues depends on the previously processed information from the preceding prosodic context.
State-dependent impulses boundary value problems on compact interval
Rachůnková, Irena
2015-01-01
This book offers the reader a new approach to the solvability of boundary value problems with state-dependent impulses and provides recently obtained existence results for state dependent impulsive problems with general linear boundary conditions. It covers fixed-time impulsive boundary value problems both regular and singular and deals with higher order differential equations or with systems that are subject to general linear boundary conditions. We treat state-dependent impulsive boundary value problems, including a new approach giving effective conditions for the solvability of the Dirichlet problem with one state-dependent impulse condition and we show that the depicted approach can be extended to problems with a finite number of state-dependent impulses. We investigate the Sturm–Liouville boundary value problem for a more general right-hand side of a differential equation. Finally, we offer generalizations to higher order differential equations or differential systems subject to general linear boundary...
Frequency-dependent heat capacity
DEFF Research Database (Denmark)
Behrens, Claus Flensted
and as a thermometer. The aim of the work is to improve and understand this planar heater experiment. I find: • Carbon has advantages as heater material over the traditionally used metal (nickel) heaters. • The thermal coupling to the surrounding temperature bath should not be made through the liquid but through......The frequency–dependent heat capacity of super-cooled glycerol near the glass transition is measured using the 3w detection technique. An electrical conducting thin film with a temperature–dependent electrical resistance is deposited on a substrate. The thin film is used simultaneously as a heater...... the substrate. • Edge effects, as a result of the finite size of the heater, play an important role. The traditionally way of dealing with these effects are not entirely correct. • The Cole–Davidson function with bCD...
Frequency dependence of the subharmonic Shapiro steps.
Tekić, Jasmina; Ivić, Zoran
2011-05-01
Frequency dependence of the subharmonic Shapiro steps has been studied in the ac driven overdamped Frenkel-Kontorova model with deformable substrate potential. As potential gets deformed, in addition to the harmonic steps, subharmonic steps appear in the number and size that increase as the frequency of the external force increases. It was found that size of both harmonic and subharmonic steps strongly depend on the frequency where in the high-amplitude limit oscillatory dependence appears. When expressed as a function of period these oscillations of the step size with frequency have the same form as the oscillations of the step size with amplitude. Deformation of the potential has strong influence on these oscillations, and as in the case of amplitude dependence, with the increase of deformation, the same three distinctive types of behavior have been classified.
Frequency-dependent streaming potentials: a review
Jouniaux, Laurence; 10.1155/2012/648781
2012-01-01
The interpretation of seismoelectric observations involves the dynamic electrokinetic coupling, which is related to the streaming potential coefficient. We describe the different models of the frequency-dependent streaming potential, mainly the Packard's and the Pride's model. We compare the transition frequency separating low-frequency viscous flow and high-frequency inertial flow, for dynamic permeability and dynamic streaming potential. We show that the transition frequency, on a various collection of samples for which both formation factor and permeability are measured, is predicted to depend on the permeability as inversely proportional to the permeability. We review the experimental setups built to be able to perform dynamic measurements. And we present some measurements and calculations of the dynamic streaming potential.
Calculation of multi frequency of Helmholtz boundary integral equation
Institute of Scientific and Technical Information of China (English)
ZHAO Zhigao; HUANG Qibai
2005-01-01
The method using series expansion is presented, and the wavenumber is separated from fundamental solution of Helmholtz boundary element equation, then the system matrices dependent of wavenumber are the matrices series associated with wavenumber, and the astringency of the method is proved. The numerical results show that combined with the CHIEFmethod, the SECHIEF (Series Expansion Combined Helmholtz Integral Equation Formulation) method can not only provide uniqueness of solution and reduce the computational time but also give accurate results under the coarse elements.
Frequency dependent magnetization of superconductor strip
Energy Technology Data Exchange (ETDEWEB)
Thakur, Kailash Prasad [Landcare Research, Palmerston North (New Zealand); Raj, Ashish [Computer Science in Radiology, Weill Medical College, Cornell University, NY (United States); Brandt, Ernst Helmut [Max-Planck-Institut fuer Metallforschung, POB 800665, D-70506 Stuttgart (Germany); Sastry, Pamidi V P S S, E-mail: thakurk@landcareresearch.co.nz, E-mail: asr2004@med.cornell.edu, E-mail: ehb@mf.mpg.de, E-mail: pamidi@caps.fsu.edu [Center for Advanced Power Systems, Florida State University, Tallahassee, FL 32310 (United States)
2011-04-15
The frequency dependence of magnetic ac loss of thin superconductor strip subjected to an ac magnetic field perpendicular to the surface of the strip is investigated by incorporating a flux creep model into the critical state model of Brandt and Indenbom. It is found that the reduced ac loss exhibits a maximum value at a frequency f{sub m}, which is a rapidly varying function of the applied ac magnetic field. At low magnetic field, f{sub m} becomes zero, and ac loss decreases with frequency as a power law ({approx}f{sup -2/n}). Whereas at high magnetic field f{sub m} becomes infinite and ac loss increases with frequency, still following the power law ({approx}f{sup 1/n}). The analytical results are substantiated with experimental data and the results of a 2D finite element simulation.
Frequency dependent changes in NMDAR-dependent synaptic plasticity
Directory of Open Access Journals (Sweden)
Arvind eKumar
2011-09-01
Full Text Available The NMDAR-dependent synaptic plasticity is thought to mediate several forms of learning, and can be induced by spike trains containing a small number of spikes occurring with varying rates and timing, as well as with oscillations. We computed the influence of these variables on the plasticity induced at a single NMDAR containing synapse using a reduced model that was analytically tractable, and these findings were confirmed using detailed, multi-compartment model. In addition to explaining diverse experimental results about the rate and timing dependence of synaptic plasticity, the model made several novel and testable predictions. We found that there was a preferred frequency for inducing long-term potentiation (LTP such that higher frequency stimuli induced lesser LTP, decreasing as 1/f when the number of spikes in the stimulus was kept fixed. Among other things, the preferred frequency for inducing LTP varied as a function of the distance of the synapse from the soma. In fact, same stimulation frequencies could induce LTP or LTD depending on the dendritic location of the synapse. Next, we found that rhythmic stimuli induced greater plasticity then irregular stimuli. Furthermore, brief bursts of spikes significantly expanded the timing dependence of plasticity. Finally, we found that in the ~5-15Hz frequency range both rate- and timing-dependent plasticity mechanisms work synergistically to render the synaptic plasticity most sensitive to spike-timing. These findings provide computational evidence that oscillations can have a profound influence on the plasticity of an NMDAR-dependent synapse, and show a novel role for the dendritic morphology in this process.
Frequency-Dependent Properties of Magnetic Nanoparticle Crystals
Energy Technology Data Exchange (ETDEWEB)
Majetich, Sara [Carnegie Mellon Univ., Pittsburgh, PA (United States)
2016-05-17
In the proposed research program we will investigate the time- and frequency-dependent behavior of ordered nanoparticle assemblies, or nanoparticle crystals. Magnetostatic interactions are long-range and anisotropic, and this leads to complex behavior in nanoparticle assemblies, particularly in the time- and frequency-dependent properties. We hypothesize that the high frequency performance of composite materials has been limited because of the range of relaxation times; if a composite is a dipolar ferromagnet at a particular frequency, it should have the advantages of a single phase material, but without significant eddy current power losses. Arrays of surfactant-coated monodomain magnetic nanoparticles can exhibit long-range magnetic order that is stable over time. The magnetic domain size and location of domain walls is governed not by structural grain boundaries but by the shape of the array, due to the local interaction field. Pores or gaps within an assembly pin domain walls and limit the domain size. Measurements of the magnetic order parameter as a function of temperature showed that domains can exist at high temoerature, and that there is a collective phase transition, just as in an exchange-coupled ferromagnet. Dipolar ferromagnets are not merely of fundamental interest; they provide an interesting alternative to exchange-based ferromagnets. Dipolar ferromagnets made with high moment metallic particles in an insulating matrix could have high permeability without large eddy current losses. Such nanocomposites could someday replace the ferrites now used in phase shifters, isolators, circulators, and filters in microwave communications and radar applications. We will investigate the time- and frequency-dependent behavior of nanoparticle crystals with different magnetic core sizes and different interparticle barrier resistances, and will measure the magnetic and electrical properties in the DC, low frequency (0.1 Hz - 1 kHz), moderate frequency (10 Hz - 500
Frequency Dependent Negative Resistance-A review
Directory of Open Access Journals (Sweden)
D.Susan
2012-08-01
Full Text Available Inductors are bulky and costly but reducing the size of the inductors reduces the quality factor. There is also a fundamental limitation of using inductor that it cannot be suitable for the micro miniature structure and integrated circuits applications. Because of these limitations, inductors cannot be used in most of the analog circuit applications. Hence simulated inductors are used as an alternative. In case the simulated inductor becomes floating some linear transformation is used which results in the formation of a new D element called the Frequency Dependent Negative Resistance (FDNR. This paper presents an overview of the basic circuits of simulating the Frequency Dependent Negative Resistance and its various applications in analog circuits in the place of floating inductor.
Analysis of frequency dependent pump light absorption
Wohlmuth, Matthias; Pflaum, Christoph
2011-03-01
Simulations have to accurately model thermal lensing in order to help improving resonator design of diode pumped solid state lasers. To this end, a precise description of the pump light absorption is an important prerequisite. In this paper, we discuss the frequency dependency of the pump light absorption in the laser crystal and its influence on the simulated laser performance. The results show that the pump light absorption has to include the spectral overlap of the emitting pump source and the absorbing laser material. This information can either be used for a fully frequency dependent absorption model or, at least in the shown examples, to compute an effective value for an exponential Beer-Lambert law of absorption. This is particularly significant at pump wavelengths coinciding with a peak of absorption. Consequences for laser stability and performance are analyzed for different pump wavelengths in a Nd:YAG laser.
Frequency dependent thermal expansion in binary viscoelasticcomposites
Energy Technology Data Exchange (ETDEWEB)
Berryman, James G.
2007-12-01
The effective thermal expansion coefficient beta* of abinary viscoelastic composite is shown to be frequency dependent even ifthe thermal expansion coefficients beta A and beta B of both constituentsare themselves frequency independent. Exact calculations for binaryviscoelastic systems show that beta* is related to constituent valuesbeta A, beta B, volume fractions, and bulk moduli KA, KB, as well as tothe overall bulk modulus K* of the composite system. Then, beta* isdetermined for isotropic systems by first bounding (or measuring) K* andtherefore beta*. For anisotropic systems with hexagonal symmetry, theprincipal values of the thermal expansion beta*perp and beta*para can bedetermined exactly when the constituents form a layered system. In allthe examples studied, it is shown explicitly that the eigenvectors of thethermoviscoelastic system possess non-negative dissipation -- despite thecomplicated analytical behavior of the frequency dependent thermalexpansivities themselves. Methods presented have a variety ofapplications from fluid-fluid mixtures to fluid-solid suspensions, andfrom fluid-saturated porous media to viscoelastic solid-solidcomposites.
Frequency-Dependent Selection at Rough Expanding Fronts
Kuhr, Jan-Timm
2015-01-01
Microbial colonies are experimental model systems for studying the colonization of new territory by biological species through range expansion. We study a generalization of the two-species Eden model, which incorporates local frequency-dependent selection, in order to analyze how social interactions between two species influence surface roughness of growing microbial colonies. The model includes several classical scenarios from game theory. We then concentrate on an expanding public goods game, where either cooperators or defectors take over the front depending on the system parameters. We analyze in detail the critical behavior of the nonequilibrium phase transition between global cooperation and defection and thereby identify a new universality class of phase transitions dealing with absorbing states. At the transition, the number of boundaries separating sectors decays with a novel power law in time and their superdiffusive motion crosses over from Eden scaling to a nearly ballistic regime. In parallel, th...
On the frequency-magnitude distribution of converging boundaries
Marzocchi, W.; Laura, S.; Heuret, A.; Funiciello, F.
2011-12-01
The occurrence of the last mega-thrust earthquake in Japan has clearly remarked the high risk posed to society by such events in terms of social and economic losses even at large spatial scale. The primary component for a balanced and objective mitigation of the impact of these earthquakes is the correct forecast of where such kind of events may occur in the future. To date, there is a wide range of opinions about where mega-thrust earthquakes can occur. Here, we aim at presenting some detailed statistical analysis of a database of worldwide interplate earthquakes occurring at current subduction zones. The database has been recently published in the framework of the EURYI Project 'Convergent margins and seismogenesis: defining the risk of great earthquakes by using statistical data and modelling', and it provides a unique opportunity to explore in detail the seismogenic process in subducting lithosphere. In particular, the statistical analysis of this database allows us to explore many interesting scientific issues such as the existence of different frequency-magnitude distributions across the trenches, the quantitative characterization of subduction zones that are able to produce more likely mega-thrust earthquakes, the prominent features that characterize converging boundaries with different seismic activity and so on. Besides the scientific importance, such issues may lead to improve our mega-thrust earthquake forecasting capability.
DPOAE generation dependence on primary frequencies ratio
Botti, Teresa; Sisto, Renata; Moleti, Arturo; D'Amato, Luisa; Sanjust, Filippo
2015-12-01
Two different mechanisms are responsible for the DPOAE generation. The nonlinear distortion wave-fixed mechanism generates the DPOAE Zero-Latency (ZL) component, as a backward traveling wave from the "overlap" region. Linear reflection of the forward DP wave (IDP) generates the DPOAE Long-Latency (LL) component through a place-fixed mechanism. ZL and LL components add up vectorially to generate the DPOAE recorded in the ear canal. The 2f1 - f2 and 2f2 - f1 DPOAE intensity depends on the stimulus level and on the primary frequency ratio r = f2/f1, where f1 and f2 are the primary stimuli frequencies. Here we study the behavior of the ZL and LL DPOAE components as a function of r by both numerical and laboratory experiments, measuring DPAOEs with an equal primary levels (L1 = L2) paradigm in the range [35, 75] dB SPL, with r ranging in [1.1, 1.45]. Numerical simulations of a nonlocal nonlinear model have been performed without cochlear roughness, to suppress the linear reflection mechanism. In this way the model solution at the base represents the DPOAE ZL component, and the solution at the corresponding DPOAE tonotopic place corresponds to the IDP. This technique has been not effectual to study the 2f2 - f1 DPOAE, as a consequence of its generation mechanism. While the 2f1 - f2 generation place is known to be the tonotopic place x(f2), the 2f2 - f1 DPOAE one has to be assumed basal to its corresponding reflection place. That is because ZL components generated in x(f2) cannot significantly pass through their resonant place. Moreover increasing the ratio r, 2f2 - f1 ZL and LL generation place approach each other, because the overlap region of primary tones decreases. Consequently, the distinction between the two places becomes complicated. DPOAEs have been measured in six young normal-hearing subjects. DPOAE ZL and LL components have been separated by a time-frequency filtering method based on the wavelet transform 1. due to their different phase gradient delay
Frequency dependent polarization analysis of high-frequency seismograms
Park, Jeffrey; Vernon, Frank L., III; Lindberg, Craig R.
1987-11-01
We present a multitaper algorithm to estimate the polarization of particle motion as a function of frequency from three-component seismic data. This algorithm is based on a singular value decomposition of a matrix of eigenspectra at a given frequency. The right complex eigenvector zˆ corresonding to the largest singular value of the matrix has the same direction as the dominant polarization of seismic motion at that frequency. The elements of the polarization vector zˆ specify the relative amplitudes and phases of motion measured along the recorded components within a chosen frequency band. The width of this frequency band is determined by the time-bandwidth product of the prolate spheroidal tapers used in the analysis. We manipulate the components of zˆ to determine the apparent azimuth and angle of incidence of seismic motion as a function of frequency. The orthogonality of the eigentapers allows one to calculate easily uncertainties in the estimated azimuth and angle of incidence. We apply this algorithm to data from the Anza Seismic Telemetered Array in the frequency band 0 ≤ ƒ ≤ 30 Hz. The polarization is not always a smooth function of frequency and can exhibit sharp jumps, suggesting the existence of scattered modes within the crustal waveguide and/or receiver site resonances.
Solving forward and inverse seismic problems by boundary-element method in frequency domain
Energy Technology Data Exchange (ETDEWEB)
Xianxi, J.
1988-01-01
Solving the boundary value problem of wave equation by boundary element method in frequency domain involves these steps: 1. ID Fourier transform of time variable is made to convert the wave equation into Helmholtz equation; 2. this equation is then solved using boundary-element method in frequency domain; 3. the result is returned to time domain by making inverse Fourier transform. Compared with other formulas, the formula in this paper brings higher accuracy but less computation.
The dependency of timbre on fundamental frequency
Marozeau, Jeremy; de Cheveigné, Alain; McAdams, Stephen; Winsberg, Suzanne
2003-11-01
The dependency of the timbre of musical sounds on their fundamental frequency (F0) was examined in three experiments. In experiment I subjects compared the timbres of stimuli produced by a set of 12 musical instruments with equal F0, duration, and loudness. There were three sessions, each at a different F0. In experiment II the same stimuli were rearranged in pairs, each with the same difference in F0, and subjects had to ignore the constant difference in pitch. In experiment III, instruments were paired both with and without an F0 difference within the same session, and subjects had to ignore the variable differences in pitch. Experiment I yielded dissimilarity matrices that were similar at different F0's, suggesting that instruments kept their relative positions within timbre space. Experiment II found that subjects were able to ignore the salient pitch difference while rating timbre dissimilarity. Dissimilarity matrices were symmetrical, suggesting further that the absolute displacement of the set of instruments within timbre space was small. Experiment III extended this result to the case where the pitch difference varied from trial to trial. Multidimensional scaling (MDS) of dissimilarity scores produced solutions (timbre spaces) that varied little across conditions and experiments. MDS solutions were used to test the validity of signal-based predictors of timbre, and in particular their stability as a function of F0. Taken together, the results suggest that timbre differences are perceived independently from differences of pitch, at least for F0 differences smaller than an octave. Timbre differences can be measured between stimuli with different F0's.
Hsieh, T.
1986-10-01
Investigation of downstream boundary effects on the frequency of self-excited oscillations in two-dimensional, separated transonic diffuser flows were conducted numerically by solving the compressible, Reynolds-averaged, thin-layer Navier-Stokes equation with two equation turbulence models. It was found that the flow fields are very sensitive to the location of the downstream boundary. Extension of the diffuser downstream boundary significantly reduces the frequency and amplitude of oscillations for pressure, velocity, and shock. The existence of a suction slot in the experimental setpup obscures the physical downstream boundary and therefore presents a difficulty for quantitative comparisons between computation and experiment.
High-frequency instabilities of stationary crossflow vortices in a hypersonic boundary layer
Li, Fei; Choudhari, Meelan; Paredes, Pedro; Duan, Lian
2016-09-01
Hypersonic boundary layer flows over a circular cone at moderate incidence angle can support strong crossflow instability in between the windward and leeward rays on the plane of symmetry. Due to more efficient excitation of stationary crossflow vortices by surface roughness, such boundary layer flows may transition to turbulence via rapid amplification of the high-frequency secondary instabilities of finite-amplitude stationary crossflow vortices. The amplification characteristics of these secondary instabilities are investigated for crossflow vortices generated by an azimuthally periodic array of roughness elements over a 7° half-angle circular cone in a Mach 6 free stream. The analysis is based on both quasiparallel stability theory in the form of a partial-differential-equation-based eigenvalue analysis and plane marching parabolized stability equations that account for the effects of the nonparallel basic state on the growth of secondary disturbances. Depending on the local amplitude of the stationary crossflow mode, the most unstable high-frequency disturbances either originate from the second (i.e., Mack) mode instabilities of the unperturbed boundary layer or correspond to genuine secondary instabilities that reduce to stable disturbances at sufficiently small amplitudes of the stationary crossflow vortex. The predicted frequencies of the dominant secondary disturbances of either type are similar to those measured during wind tunnel experiments at Purdue University and the Technical University of Braunschweig, Germany. Including transverse surface curvature within the quasiparallel predictions does not alter the topology of the unstable modes; however, the resulting changes in both mode shape and disturbance growth rate are rather significant and curvature can be either stabilizing or destabilizing depending on the disturbance frequency and mode type. Nonparallel effects are shown to be strongly destabilizing for secondary instabilities originating from
Discrete diffusion Monte Carlo for frequency-dependent radiative transfer
Energy Technology Data Exchange (ETDEWEB)
Densmore, Jeffrey D [Los Alamos National Laboratory; Kelly, Thompson G [Los Alamos National Laboratory; Urbatish, Todd J [Los Alamos National Laboratory
2010-11-17
Discrete Diffusion Monte Carlo (DDMC) is a technique for increasing the efficiency of Implicit Monte Carlo radiative-transfer simulations. In this paper, we develop an extension of DDMC for frequency-dependent radiative transfer. We base our new DDMC method on a frequency-integrated diffusion equation for frequencies below a specified threshold. Above this threshold we employ standard Monte Carlo. With a frequency-dependent test problem, we confirm the increased efficiency of our new DDMC technique.
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
Effects of low frequency electromagnetic field on grain boundary segregation in horizontal direct chill (HDC)casting process was investigated experimentally. The grain boundary segregation and microstructures of the ingots,which manufactured by conventional HDC casting and low frequency electromagnetic HDC casting were compared.Results show that low frequency electromagnetic field significantly refines the microstructures and reduces grain boundary segregation. Decreasing electromagnetic frequency or increasing electromagnetic intensity has great effects in reducing grain boundary segregation. Meanwhile, the governing mechanisms were discussed.
Frequency Dependent Losses in Transmission Cable Conductors
DEFF Research Database (Denmark)
Olsen, Rasmus Schmidt; Holbøll, Joachim; Guðmundsdóttir, Unnur Stella
2011-01-01
, such as thermal conditions in and around the cable, as well as the heat generated in conductors, screens, armours etc., taking into account proximity and skin effects. The work performed and presented in this paper is concerned with an improved determination of the losses generated in the conductor, by means...... of better calculation of the AC resistance of transmission cable conductors, in particular regarding higher frequencies. In this way, also losses under harmonics can be covered. Furthermore, the model is suitable for modelling of transient attenuation in high voltage cables. The AC resistance is calculated...
Frequency-Dependent Streaming Potentials: A Review
Directory of Open Access Journals (Sweden)
L. Jouniaux
2012-01-01
which both formation factor and permeability are measured, is predicted to depend on the permeability as inversely proportional to the permeability. We review the experimental setups built to be able to perform dynamic measurements. And we present some measurements and calculations of the dynamic streaming potential.
Frequency Dependent Losses in Transmission Cable Conductors
DEFF Research Database (Denmark)
Olsen, Rasmus Schmidt; Holbøll, Joachim; Guðmundsdóttir, Unnur Stella
2011-01-01
Denmark is taking on the exciting project of undergrounding the electricity transmission grid. In 2009 it was decided by the Danish government to underground large parts of the 400 kV and the entire 132-150 kV transmission network before the end of 2030. For ensuring network stability...... and economical gain, such severe network changes necessitate correct estimation and optimisation of load conditions in the cable grid. Both IEC and IEEE have published standards for rating transmission cables' current carrying capacity. These standards are based on assumptions of a number of parameters...... of better calculation of the AC resistance of transmission cable conductors, in particular regarding higher frequencies. In this way, also losses under harmonics can be covered. Furthermore, the model is suitable for modelling of transient attenuation in high voltage cables. The AC resistance is calculated...
Optimized frequency dependent photothermal beam deflection spectroscopy
Korte, D.; Cabrera, H.; Toro, J.; Grima, P.; Leal, C.; Villabona, A.; Franko, M.
2016-12-01
In the letter the optimization of the experimental setup for photothermal beam deflection spectroscopy is performed by analyzing the influence of its geometrical parameters (detector and sample position, probe beam radius and its waist position etc) on the detected signal. Furthermore, the effects of the fluid’s thermo-optical properties, for optimized geometrical configuration, on the measurement sensitivity and uncertainty determination of sample thermal properties is also studied. The examined sample is a recently developed CuFeInTe3 material. It is seen from the obtained results, that it is a complex problem to choose the proper geometrical configuration as well as sensing fluid to enhance the sensitivity of the method. A signal enhancement is observed at low modulation frequencies by placing the sample in acetonitrile (ACN), while at high modulation frequencies the sensitivity is higher for measurements made in air. For both, detection in air and acetonitrile the determination of CuFeInTe3 thermal properties is performed. The determined values of thermal diffusivity and thermal conductivity are (0.048 ± 0.002) × 10-4 m2 s-1 and 4.6 ± 0.2 W m-1 K-1 and (0.056 ± 0.005) × 10-4 m2 s-1 and 4.8 ± 0.4 W m-1 K-1 for ACN and air, respectively. It is seen, that the determined values agree well within the range of their measurement uncertainties for both cases, although the measurement uncertainty is two times lower for the measurements in ACN providing more accurate results. The analysis is performed by the use of recently developed theoretical description based on the complex geometrical optics. It is also shown, how the presented work fits into the current status of photothermal beam deflection spectroscopy.
Frequency-Dependent Attenuation of Blasting Vibration Waves
Zhou, Junru; Lu, Wenbo; Yan, Peng; Chen, Ming; Wang, Gaohui
2016-10-01
The dominant frequency, in addition to the peak particle velocity, is a critical factor for assessing adverse effects of the blasting vibration on surrounding structures; however, it has not been fully considered in blasting design. Therefore, the dominant frequency-dependent attenuation mechanism of blast-induced vibration is investigated in the present research. Starting with blasting vibration induced by a spherical charge propagating in an infinite viscoelastic medium, a modified expression of the vibration amplitude spectrum was derived to reveal the frequency dependency of attenuation. Then, ground vibration induced by more complex and more commonly used cylindrical charge that propagates in a semi-infinite viscoelastic medium was analyzed by numerical simulation. Results demonstrate that the absorptive property of the medium results in the frequency attenuation versus distance, whereas a rapid drop or fluctuation occurs during the attenuation of ground vibration. Fluctuation usually appears at moderate to far field, and the dominant frequency generally decreases to half the original value when rapid drop occurs. The decay rate discrepancy between different frequency components and the multimodal structure of vibration spectrum lead to the unsmooth frequency-dependent attenuation. The above research is verified by two field experiments. Furthermore, according to frequency-based vibration standards, frequency drop and fluctuation should be considered when evaluating blast safety. An optimized piecewise assessment is proposed for more accurate evaluation: With the frequency drop point as the breakpoint, the assessment is divided into two independent sections along the propagating path.
Institute of Scientific and Technical Information of China (English)
XIE Zhi-nan; LIAO Zhen-peng
2008-01-01
In this paper the explanation of the mechanism of high-frequency oscillation instability resulted from absorbing boundary conditions is further improved. And we analytically prove the proposition that for one dimensional dis- crete model of elastic wave motion, the module of reflection factor will be greater than 1 in high frequency band when artificial wave velocity is greater than 1.5 times the ratio of discrete space step to discrete time step. Based on the proof, the frequency band in which instability occurs is discussed in detail, showing such high-frequency waves are meaningless for the numerical simulation of wave motion.
Task, muscle and frequency dependent vestibular control of posture
Forbes, P.A.; Siegmund, G.P.; Schouten, A.C.; Blouin, J.S.
2015-01-01
The vestibular system is crucial for postural control; however there are considerable differences in the task dependence and frequency response of vestibular reflexes in appendicular and axial muscles. For example, vestibular reflexes are only evoked in appendicular muscles when vestibular
Institute of Scientific and Technical Information of China (English)
Yingqin Luo; Ming Hong; Yuan Liu
2015-01-01
In recent years, as the composite laminated plates are widely used in engineering practice such as aerospace, marine and building engineering, the vibration problem of the composite laminated plates is becoming more and more important. Frequency, especially the fundamental frequency, has been considered as an important factor in vibration problem. In this paper, a calculation method of the fundamental frequency of arbitrary laminated plates under various boundary conditions is proposed. The vibration differential equation of the laminated plates is established at the beginning of this paper and the frequency formulae of specialty orthotropic laminated plates under various boundary conditions and antisymmetric angle-ply laminated plates with simply-supported edges are investigated. They are proved to be correct. Simple algorithm of the fundamental frequency for multilayer antisymmetric and arbitrary laminated plates under various boundary conditions is studied by a series of typical examples. From the perspective of coupling, when the number of laminated plates layersN > 8–10, some coupling influence on the fundamental frequency can be neglected. It is reasonable to use specialty orthotropic laminated plates with the same thickness but less layers to calculate the corresponding fundamental frequency of laminated plates. Several examples are conducted to prove correctness of this conclusion. At the end of this paper, the influence of the selected number of layers of specialty orthotropic laminates on the fundamental frequency is investigated. The accuracy and complexity are determined by the number of layers. It is necessary to use proper number of layers of special orthotropic laminates with the same thickness to simulate the fundamental frequency in different boundary conditions.
Frequency Dependence of Attenuation Constant of Dielectric Materials
Directory of Open Access Journals (Sweden)
A. S. Zadgaonkar
1975-01-01
Full Text Available Different dielectric materials have been studied for frequency dependence of attenuation constant. The sensitive cathode ray oscillograph method has been used to evaluate to the dielectric constant and loss factor, and from these attenuation constants have been calculated. The temperature remaining constant, a regular increase has been observed in attenuation constant, at higher frequencies of electro-magnetic propagating wave.
A molecular explanation of frequency-dependent selection in Drosophila.
Haj-Ahmad, Y; Hickey, D A
1982-09-23
Frequency-dependent selection provides a means for maintaining genetic variability within populations, without incurring a large genetic load. There is a wealth of experimental evidence for the existence of frequency-dependent changes in genotypic fitness among a wide variety of organisms. Examples of traits which have been shown to be subject to frequency-dependent selection include the self-incompatibility alleles of plants, chromosomal rearrangements in Drosophila, visible mutations, enzyme variants and rare-male mating advantage in Drosophila. These experiments have been interpreted in a number of different ways. Principally, frequency dependence of genotype fitness may result from intergenotype facilitation due to the production of biotic residues, or from the differential use of resources by the competing genotypes. However, it has proved extremely difficult to isolate and identify any biotic residue of importance or, alternatively, to understand the manner in which genotypes partition the environment. Thus, the difficulty in the interpretation of experiments which show frequency-dependent selective effects stems largely from our lack of understanding of the exact physiological mechanisms which produce these frequency-dependent effects. The principal aim of this study was to investigate the mechanisms associated with frequency-dependent selection at the amylase locus in Drosophila melanogaster. The excretion of catalytically active amylase enzyme and its effect on food medium composition were correlated with the outcome of intraspecific competition between amylase-deficient and amylase-producing genotypes. Amylase-producing genotypes were shown to excrete enzymatically active amylase protein into the food medium. The excreted amylase causes the external digestion of dietary starch; this accounts for the frequency-dependent increase in the viability of the amylase-deficient mutants in mixed cultures, maintained on a starch-rich diet.
Intermittency and transient chaos from simple frequency-dependent selection.
Gavrilets, S; Hastings, A
1995-08-22
Frequency-dependent selection is an important determinant of the evolution of gametophytic self-incompatibility systems in plants, aposematic (warning) and cryptic coloration, systems of mimicry, competitive interactions among members of a population, mating preferences, predator-prey and host-parasite interactions, aggression and other behavioural traits. Past theoretical studies of frequency-dependent selection have shown it to be a plausible mechanism for the maintenance of genetic variability in natural populations. Here, through an analysis of a simple deterministic model for frequency-dependent selection, we demonstrate that complex dynamic behaviour is possible under a broad range of parameter values. In particular we show that the model exhibits not only cycles and chaos but also, for a more restricted set of parameters, transient chaos and intermittency: alterations between an apparently deterministic behaviour and apparently chaotic fluctuations. This behaviour, which has not been stressed within the population genetics literature, provides an explanation for erratic dynamics of gene frequencies.
On the Casimir Energy of Frequency Dependent Interactions
Graham, N; Weigel, H
2014-01-01
Vacuum polarization (or Casimir) energies can be straightforwardly computed from scattering data for static field configurations whose interactions with the fluctuating field are frequency independent. In effective theories, however,such interactions are typically frequency dependent. As a consequence, the relationship between scattering data and the Green's function is modified, which may or may not induce additional contributions to the vacuum polarization energy. We discuss several examples that naturally include frequency dependent interactions: (i) scalar electrodynamics with a static background potential, (ii) an effective theory that emerges from integrating out a heavy degree of freedom, and (iii) quantum electrodynamics coupled to a frequency dependent dielectric material. In the latter case, we argue that introducing dissipation as required by the Kramers-Kronig relations requires the consideration of the Casimir energy within a statistical mechanics formalism, while in the absence of dissipation we...
Frequency-Dependent Spherical-Wave Reflection in Acoustic Media: Analysis and Inversion
Li, Jingnan; Wang, Shangxu; Wang, Jingbo; Dong, Chunhui; Yuan, Sanyi
2017-02-01
Spherical-wave reflectivity (SWR), which describes the seismic wave reflection in real subsurface media more accurately than plane-wave reflectivity (PWR), recently, again attracts geophysicists' attention. The recent studies mainly focus on the amplitude variation with offset/angle (AVO/AVA) attributes of SWR. For a full understanding of the reflection mechanism of spherical wave, this paper systematically investigates the frequency-dependent characteristics of SWR in a two-layer acoustic medium model with a planar interface. Two methods are used to obtain SWR. The first method is through the calculation of classical Sommerfeld integral. The other is by 3D wave equation numerical modeling. To enhance computation efficiency, we propose to perform wave equation simulation in cylindrical coordinates, wherein we for the first time implement unsplit convolutional perfectly matched layer as the absorbing boundary. Both methods yield the same results, which demonstrate the validity and accuracy of the computation. From both the numerical tests and the theoretical demonstration, we find that the necessary condition when frequency dependence of SWR occurs is that the upper and lower media have different velocities. At the precritical small angle, the SWR exhibits complicated frequency-dependent characteristics for varying medium parameters. Especially when the impedance of upper medium equals that of lower one, the PWR is zero according to geometric seismics. Whereas the SWR is nonzero: the magnitude of SWR decreases with growing frequency, and approaches that of the corresponding PWR at high frequency; the phase of SWR increases with growing frequency, but approaches 90° or -90° at high frequency. At near- and post-critical angles, large difference exists between SWR and PWR, and the difference is particularly great at low frequencies. Finally, we propose a nonlinear inversion method to estimate physical parameters and interface depth of media by utilizing the frequency-dependent
The frequency dependence of scattering imprints on pulsar observations
Geyer, Marisa
2016-01-01
Observations of pulsars across the radio spectrum are revealing a dependence of the characteristic scattering time ($\\tau$) on frequency, which is more complex than the simple power law with a theoretically predicted power law index. In this paper we investigate these effects using simulated pulsar data at frequencies below 300 MHz. We investigate different scattering mechanisms, namely isotropic and anisotropic scattering, by thin screens along the line of sight, and the particular frequency dependent impact on pulsar profiles and scattering time scales of each. We also consider how the screen shape, location and offset along the line of sight lead to specific observable effects. We evaluate how well forward fitting techniques perform in determining $\\tau$. We investigate the systematic errors in $\\tau$ associated with the use of an incorrect fitting method and with the determination of an off-pulse baseline. Our simulations provide examples of average pulse profiles at various frequencies. Using these we co...
Frequency-dependent specific heat from thermal effusion in spherical geometry.
Jakobsen, Bo; Olsen, Niels Boye; Christensen, Tage
2010-06-01
We present a method of measuring the frequency-dependent specific heat at the glass transition applied to 5-polyphenyl-4-ether. The method employs thermal waves effusing radially out from the surface of a spherical thermistor that acts as both a heat generator and a thermometer. It is a merit of the method compared to planar effusion methods that the influence of the mechanical boundary conditions is analytically known. This implies that it is the longitudinal rather than the isobaric specific heat that is measured. As another merit the thermal conductivity and specific heat can be found independently. The method has highest sensitivity at a frequency where the thermal diffusion length is comparable to the radius of the heat generator. This limits in practice the frequency range to 2-3 decades. An account of the 3ω technique used including higher-order terms in the temperature dependence of the thermistor and in the power generated is furthermore given.
Comment on “Frequency-dependent dispersion in porous media”
Davit, Yohan
2012-07-10
In a recent paper, Valdès-Parada and Alvarez-Ramirez used the technique of volume averaging to derive a "frequency-dependent" dispersion tensor, Dγ*, the goal of which is to describe solute transport in porous media undergoing periodic processes. We describe two issues related to this dispersion tensor. First, we demonstrate that the definition of Dγ* is erroneous and derive a corrected version, Dγ*c. With this modification, the approach of Valdès-Parada and Alvarez-Ramirez becomes strictly equivalent to the one devised by Moyne. Second, we show that the term "frequency-dependent dispersion" is misleading because Dγ* and Dγ*c do not depend on the process operating frequency, χ. The study carried out by Valdès-Parada and Alvarez-Ramirez represents a spectral analysis of the relaxation of Dγ* towards its steady-state, independent of any periodic operation or excitation. © 2012 American Physical Society.
Fluctuation-dissipation theorem for frequency-dependent specific heat
DEFF Research Database (Denmark)
Dyre, Jeppe; Nielsen, Johannes K.
1996-01-01
A derivation of the fluctuation-dissipation (FD) theorem for the frequency-dependent specific heat of a system described by a master equation is presented. The FD theorem is illustrated by a number of simple examples, including a system described by a linear Langevin equation, a two-level system......, and a system described by the energy master equation. It is shown that for two quite different models with low-energy cutoffsa collection of two-level systems and a system described by the energy master equationthe frequency-dependent specific heat in dimensionless units becomes universal at low temperatures......, i.e., independent of both energy distribution and temperature. These two models give almost the same universal frequency-dependent specific heat, which compares favorably to experiments on supercooled alcohols....
Frequency-dependent signal transmission and modulation by neuromodulators
Directory of Open Access Journals (Sweden)
Hiroshi T Ito
2008-12-01
Full Text Available The brain uses a strategy of labor division, which may allow it to accomplish more elaborate and complicated tasks, but in turn, imposes a requirement for central control to integrate information among different brain areas. Anatomically, the divergence of long-range neuromodulator projections appears well-suited to coordinate communication between brain areas. Oscillatory brain activity is a prominent feature of neural transmission. Thus, the ability of neuromodulators to modulate signal transmission in a frequency-dependent manner adds an additional level of regulation. Here, we review the significance of frequency-dependent signal modulation in brain function and how a neuronal network can possess such properties. We also describe how a neuromodulator, dopamine, changes frequency-dependent signal transmission, controlling information flow from the entorhinal cortex to the hippocampus.
Frequency-dependent effective hydraulic conductivity of strongly heterogeneous media.
Caspari, E; Gurevich, B; Müller, T M
2013-10-01
The determination of the transport properties of heterogeneous porous rocks, such as an effective hydraulic conductivity, arises in a range of geoscience problems, from groundwater flow analysis to hydrocarbon reservoir modeling. In the presence of formation-scale heterogeneities, nonstationary flows, induced by pumping tests or propagating elastic waves, entail localized pressure diffusion processes with a characteristic frequency depending on the pressure diffusivity and size of the heterogeneity. Then, on a macroscale, a homogeneous equivalent medium exists, which has a frequency-dependent effective conductivity. The frequency dependence of the conductivity can be analyzed with Biot's equations of poroelasticity. In the quasistatic frequency regime of this framework, the slow compressional wave is a proxy for pressure diffusion processes. This slow compressional wave is associated with the out-of-phase motion of the fluid and solid phase, thereby creating a relative fluid-solid displacement vector field. Decoupling of the poroelasticity equations gives a diffusion equation for the fluid-solid displacement field valid in a poroelastic medium with spatial fluctuations in hydraulic conductivity. Then, an effective conductivity is found by a Green's function approach followed by a strong-contrast perturbation theory suggested earlier in the context of random dielectrics. This theory leads to closed-form expressions for the frequency-dependent effective conductivity as a function of the one- and two-point probability functions of the conductivity fluctuations. In one dimension, these expressions are consistent with exact solutions in both low- and high-frequency limits for arbitrary conductivity contrast. In 3D, the low-frequency limit depends on the details of the microstructure. However, the derived approximation for the effective conductivity is consistent with the Hashin-Shtrikman bounds.
Frequency Dependence of Longitudinal Correlation Length in the Yellow Sea
Institute of Scientific and Technical Information of China (English)
LI Feng-Hua; ZHANG Ren-He
2008-01-01
Spatial correlation coefficient is one of the most important parameters for the description of sound propagation in shallow water. Frequency dependence of the longitudinal correlation length is still an open topic. We observe in a shallow water experiment that the longitudinal correlation length in units of wavelength increases with the increase of frequency. This phenomenon has not been seen in the published papers. The theoretical analysis and numerical simulations indicate that the non-linear frequency relationship of the bottom attenuation is the main cause of this phenomenon.
Frequency-difference-dependent stochastic resonance in neural systems
Guo, Daqing; Perc, Matjaž; Zhang, Yangsong; Xu, Peng; Yao, Dezhong
2017-08-01
Biological neurons receive multiple noisy oscillatory signals, and their dynamical response to the superposition of these signals is of fundamental importance for information processing in the brain. Here we study the response of neural systems to the weak envelope modulation signal, which is superimposed by two periodic signals with different frequencies. We show that stochastic resonance occurs at the beat frequency in neural systems at the single-neuron as well as the population level. The performance of this frequency-difference-dependent stochastic resonance is influenced by both the beat frequency and the two forcing frequencies. Compared to a single neuron, a population of neurons is more efficient in detecting the information carried by the weak envelope modulation signal at the beat frequency. Furthermore, an appropriate fine-tuning of the excitation-inhibition balance can further optimize the response of a neural ensemble to the superimposed signal. Our results thus introduce and provide insights into the generation and modulation mechanism of the frequency-difference-dependent stochastic resonance in neural systems.
Dynamical gap generation in graphene with frequency dependent renormalization effects
Carrington, M E; von Smekal, L; Thoma, M H
2016-01-01
We study the frequency dependencies in the renormalization of the fermion Greens function for the $\\pi$-band electrons in graphene and their influence on the dynamical gap generation at sufficiently strong interaction. Adopting the effective QED-like description for the low-energy excitations within the Dirac-cone region we self consistently solve the fermion Dyson-Schwinger equation in various approximations for the photon propagator and the vertex function with special emphasis on frequency dependent Lindhard screening and retardation effects.
Frequency-dependent effects of gravitational lensing within plasma
Rogers, Adam
2015-07-01
The interaction between refraction from a distribution of inhomogeneous plasma and gravitational lensing introduces novel effects to the paths of light rays passing by a massive object. The plasma contributes additional terms to the equations of motion, and the resulting ray trajectories are frequency-dependent. Lensing phenomena and circular orbits are investigated for plasma density distributions N ∝ 1/rh with h ≥ 0 in the Schwarzschild space-time. For rays passing by the mass near the plasma frequency refractive effects can dominate, effectively turning the gravitational lens into a mirror. We obtain the turning points, circular orbit radii and angular momentum for general h. Previous results have shown that light rays behave like massive particles with an effective mass given by the plasma frequency for a constant density h = 0. We study the behaviour for general h and show that when h = 2 the plasma term acts like an additional contribution to the angular momentum of the passing ray. When h = 3 the potential and radii of circular orbits are analogous to those found in studies of massless scalar fields on the Schwarzschild background. As a physically motivated example we study the pulse profiles of a compact object with antipodal hotspots sheathed in a dense plasma, which shows dramatic frequency-dependent shifts from the behaviour in vacuum. Finally, we consider the potential observability and applications of such frequency-dependent plasma effects in general relativity for several types of neutron star.
Frequency dependent Lg attenuation in south-central Alaska
McNamara, D.E.
2000-01-01
The characteristics of seismic energy attenuation are determined using high frequency Lg waves from 27 crustal earthquakes, in south-central Alaska. Lg time-domain amplitudes are measured in five pass-bands and inverted to determine a frequency-dependent quality factor, Q(f), model for south-central Alaska. The inversion in this study yields the frequency-dependent quality factor, in the form of a power law: Q(f) = Q0fη = 220(±30) f0.66(±0.09) (0.75≤f≤12Hz). The results from this study are remarkably consistent with frequency dependent quality factor estimates, using local S-wave coda, in south-central Alaska. The consistency between S-coda Q(f) and Lg Q(f) enables constraints to be placed on the mechanism of crustal attenuation in south-central Alaska. For the range of frequencies considered in this study both scattering and intrinsic attenuation mechanisms likely play an equal role.
Xu, Zhouxiang; Huang, Kaikai; Jiang, Yunfeng; Lu, Xuanhui
2011-12-01
We have realized a long-term frequency stabilization system for external cavity diode laser (ECDL) based on mode boundary detection method. In this system, the saturated absorption spectroscopy was used. The current and the grating of the ECDL were controlled by a computer-based feedback control system. By checking if there are mode boundaries in the spectrum, the control system determined how to adjust current to avoid mode hopping. This procedure was executed periodically to ensure the long-term stabilization of ECDL in the absence of mode hops. This diode laser system with non-antireflection coating had operated in the condition of long-term mode-hop-free stabilization for almost 400 h, which is a significant improvement of ECDL frequency stabilization system.
Task, muscle and frequency dependent vestibular control of posture
Forbes, P.A.; Siegmund, G.P.; Schouten, A.C.; Blouin, J.S.
2015-01-01
The vestibular system is crucial for postural control; however there are considerable differences in the task dependence and frequency response of vestibular reflexes in appendicular and axial muscles. For example, vestibular reflexes are only evoked in appendicular muscles when vestibular informati
Frequency-dependent dynamic effective properties of porous materials
Institute of Scientific and Technical Information of China (English)
Peijun Wei; Zhuping Huang
2005-01-01
The frequency-dependent dynamic effective properties (phase velocity, attenuation and elastic modulus) of porous materials are studied numerically. The coherent plane longitudinal and shear wave equations, which are obtained by averaging on the multiple scattering fields, are used to evaluate the frequency-dependent dynamic effective properties of a porous material. It is found that the prediction of the dynamic effective properties includes the size effects of voids which are not included in most prediction of the traditional static effective properties. The prediction of the dynamic effective elastic modulus at a relatively low frequency range is compared with that of the traditional static effective elastic modulus, and the dynamic effective elastic modulus is found to be very close to the Hashin-Shtrikman upper bound.
Frequency selection mechanisms in the flow of a laminar boundary layer over a shallow cavity
Qadri, Ubaid Ali; Schmid, Peter J.
2017-01-01
We investigate the flow over shallow cavities as a representative configuration for modeling small surface irregularities in wall-bounded shear flows. Due to the globally stable nature of the flow, we perform a frequency response analysis, which shows a significant potential for the amplification of disturbance kinetic energy by harmonic forcing within a certain frequency band. Shorter and more shallow cavities exhibit less amplified responses, while energy from the base flow can be extracted predominantly from forcing that impacts the cavity head on. A structural sensitivity analysis, combined with a componentwise decomposition of the sensitivity tensor, reveals the regions of the flow that act most effectively as amplifiers. We find that the flow inside the cavity plays a negligible role, whereas boundary layer modifications immediately upstream and downstream of the cavity edges contribute significantly to the frequency response. The same regions constitute preferred locations for implementing active or passive control strategies to manipulate the frequency response of the flow.
Influence of the boundary conditions on the natural frequencies of a Francis turbine
Valentín, David; Ramos, David; Bossio, Matías; Presas, Alexandre; Egusquiza, Eduard; Valero, Carme
2016-11-01
Natural frequencies estimation of Francis turbines is of paramount importance in the stage of design in order to avoid vibration and resonance problems especially during transient events. Francis turbine runners are submerged in water and confined with small axial and radial gaps which considerably decrease their natural frequencies in comparison to the same structure in the air. Acoustic-structural FSI simulations have been used to evaluate the influence of these gaps. This model considers an entire prototype of a Francis turbine, including generator, shaft, runner and surrounding water. The radial gap between the runner and the static parts has been changed from the real configuration (about 0.04% the runner diameter) to 1% of the runner diameter to evaluate its influence on the machine natural frequencies. Mode-shapes and natural frequencies of the whole machine are discussed for all the boundary conditions tested.
FREQUENCY-DEPENDENT DISPERSION MEASURES AND IMPLICATIONS FOR PULSAR TIMING
Energy Technology Data Exchange (ETDEWEB)
Cordes, J. M. [Astronomy Department, Cornell University, Ithaca, NY 14853 (United States); Shannon, R. M. [CSIRO Astronomy and Space Science, Box 76, Epping, NSW 1710 (Australia); Stinebring, D. R., E-mail: cordes@astro.cornell.edu, E-mail: ryan.shannon@csiro.au, E-mail: dan.stinebring@oberlin.edu [Department of Physics and Astronomy, Oberlin College, Oberlin, OH 44074 (United States)
2016-01-20
The dispersion measure (DM), the column density of free electrons to a pulsar, is shown to be frequency dependent because of multipath scattering from small-scale electron-density fluctuations. DMs vary between propagation paths whose transverse extent varies strongly with frequency, yielding arrival times that deviate from the high-frequency scaling expected for a cold, uniform, unmagnetized plasma (1/frequency{sup 2}). Scaling laws for thin phase screens are verified with simulations; extended media are also analyzed. The rms DM difference across an octave band near 1.5 GHz is ∼ 4 × 10{sup −5} pc cm{sup −3} for pulsars at ∼1 kpc distance. The corresponding arrival-time variations are a few to hundreds of nanoseconds for DM ≲ 30 pc cm{sup −3} but increase rapidly to microseconds or more for larger DMs and wider frequency ranges. Chromatic DMs introduce correlated noise into timing residuals with a power spectrum of “low pass” form. The correlation time is roughly the geometric mean of the refraction times for the highest and lowest radio frequencies used, ranging from days to years, depending on the pulsar. We discuss implications for methodologies that use large frequency separations or wide bandwidth receivers for timing measurements. Chromatic DMs are partially mitigable by including an additional chromatic term in arrival time models. Without mitigation, an additional term in the noise model for pulsar timing is implied. In combination with measurement errors from radiometer noise, an arbitrarily large increase in total frequency range (or bandwidth) will yield diminishing benefits and may be detrimental to overall timing precision.
On Polarization and Frequency Dependence of Diffuse Indoor Propagation
DEFF Research Database (Denmark)
Nielsen, Jesper Ødum; Andersen, Jørgen Bach; Pedersen, Gert Frølund
2011-01-01
The room electromagnetics (RE) theory describes the radio propagation in a single room assuming diffuse scat- tering. A main characteristic is the exponential power-delay profile (PDP) decaying with the so-called reverberation time (RT) parameter, depending only on the wall area, the volume...... of the room and an absorption coefficient. The PDP is independent on the location in the room, except for the arrival time. Based on measurements in a room with a spherical array of 16 dual- polarized wideband horn antennas, the current work studies how the RE parameters depend on the receiver (Rx) antenna...... polarization and orientation. Also the frequency dependence is investigated, with measurements done at both 2.3 GHz and 5.8 GHz center frequencies. The RE theory was found to fit well to the measurements with a RT in the range 22-25 ns. Only small differences were found due to the polarization and the channel...
Improving Planck calibration by including frequency-dependent relativistic corrections
Quartin, Miguel
2015-01-01
The Planck satellite detectors are calibrated in the 2015 release using the "orbital dipole", which is the time-dependent dipole generated by the Doppler effect due to the motion of the satellite around the Sun. Such an effect has also relativistic time-dependent corrections of relative magnitude 10^(-3), due to coupling with the "solar dipole" (the motion of the Sun compared to the CMB rest frame), which are included in the data calibration by the Planck collaboration. We point out that such corrections are subject to a frequency-dependent multiplicative factor. This factor differs from unity especially at the highest frequencies, relevant for the HFI instrument. Since currently Planck calibration errors are dominated by systematics, to the point that polarization data is currently unreliable at large scales, such a correction can in principle be highly relevant for future data releases.
Improving Planck calibration by including frequency-dependent relativistic corrections
Quartin, Miguel; Notari, Alessio
2015-09-01
The Planck satellite detectors are calibrated in the 2015 release using the "orbital dipole", which is the time-dependent dipole generated by the Doppler effect due to the motion of the satellite around the Sun. Such an effect has also relativistic time-dependent corrections of relative magnitude 10-3, due to coupling with the "solar dipole" (the motion of the Sun compared to the CMB rest frame), which are included in the data calibration by the Planck collaboration. We point out that such corrections are subject to a frequency-dependent multiplicative factor. This factor differs from unity especially at the highest frequencies, relevant for the HFI instrument. Since currently Planck calibration errors are dominated by systematics, to the point that polarization data is currently unreliable at large scales, such a correction can in principle be highly relevant for future data releases.
Frequency- dependent cell responses to an electromagnetic stimulus
Taghian, Toloo; Sheikh, Abdul; Narmoneva, Daria; Kogan, Andrei
2013-03-01
External electric field (EF) acting on cells in the ionic environment can trigger a variety of mechanical and chemical cell responses that regulate cell functions, such as adhesion, migration and cell signaling; thus manipulation of EF can be used in therapeutic applications. To optimize this process, realistic studies of EF interaction with cells are essential. We have developed a combined theoretical-experimental approach to study cell response to the external EF in the native configuration. The cell is modeled as a membrane-enclosed hemisphere which is cultured on a substrate and is surrounded by electrolyte. Maxwell's equations are solved numerically (ANSYS-HFSS) to obtain 3D EF distribution inside and near the cell subjected to an external EF. Theoretical results indicate that the cell response is frequency dependent, where at low frequency EF is excluded from the cell interior while EF penetration into the cell increases for higher frequencies. In both regimes the spatial distribution and strength of induced EF in membrane varies with frequency. Experimental results are consistent with theoretical predictions and show frequency-dependent cell response, including both membrane-initiated and intracellular pathway activation and growth factor release. The authors acknowledge the financial support from the NSF (DMR-1206784 & DMR-0804199 to AK); the NIH (1R21 DK078814-01A1 to DN) and the University of Cincinnati (Interdisciplinary Faculty Research Support Grant to DN and AK).
Institute of Scientific and Technical Information of China (English)
Yu Guo-Liang; Li Yuan-Xun; Zeng Yu-Qin; Li Jie; Zuo Lin; Li Qiang; Zhang Huai-Wu
2013-01-01
The frequency dependence of the magnetoelectric effect in a magnetostrictive-piezoelectric heterostructure is theoretically studied by solving combined magnetic,elastic,and electric equations with boundary conditions.Both the mechanical coupling coefficient and the losses of the magnetostrictive and piezoelectric phases are taken into account.The numerical result indicates that the magnetoelectric coefficient and the resonance frequency are determined by the mechanical coupling coefficient,losses,and geometric parameters.Moreover,at the electromechanical resonance frequency,the module of the magnetoelectric coefficient is mostly contributed by the imaginary part.The relationship between the real and the imaginary parts of the magnetoelectric coefficient fit well to the Cole-Cole circle.The magnetostrictive-piezoelectric heterostructure has a great potential application as miniature and no-secondary coil solid-state transformers.
Spatial-frequency dependent binocular imbalance in amblyopia
Kwon, MiYoung; Wiecek, Emily; Dakin, Steven C.; Bex, Peter J.
2015-01-01
While amblyopia involves both binocular imbalance and deficits in processing high spatial frequency information, little is known about the spatial-frequency dependence of binocular imbalance. Here we examined binocular imbalance as a function of spatial frequency in amblyopia using a novel computer-based method. Binocular imbalance at four spatial frequencies was measured with a novel dichoptic letter chart in individuals with amblyopia, or normal vision. Our dichoptic letter chart was composed of band-pass filtered letters arranged in a layout similar to the ETDRS acuity chart. A different chart was presented to each eye of the observer via stereo-shutter glasses. The relative contrast of the corresponding letter in each eye was adjusted by a computer staircase to determine a binocular Balance Point at which the observer reports the letter presented to either eye with equal probability. Amblyopes showed pronounced binocular imbalance across all spatial frequencies, with greater imbalance at high compared to low spatial frequencies (an average increase of 19%, p amblyopia and as an outcome measure for recovery of binocular vision following therapy. PMID:26603125
Differential Frequency-dependent Delay from the Pulsar Magnetosphere
Hassall, T E; Weltevrede, P; Hessels, J W T; Alexov, A; Coenen, T; Karastergiou, A; Kramer, M; Keane, E F; Kondratiev, V I; van Leeuwen, J; Noutsos, A; Pilia, M; Serylak, M; Sobey, C; Zagkouris, K; Fender, R; Bell, M E; Broderick, J; Eisloffel, J; Falcke, H; Griessmeier, J -M; Kuniyoshi, M; Miller-Jones, J C A; Wise, M W; Wucknitz, O; Zarka, P; Asgekar, A; Batejat, F; Bentum, M J; Bernardi, G; Best, P; Bonafede, A; Breitling, F; Bruggen, M; Butcher, H R; Ciardi, B; de Gasperin, F; de Reijer, J -P; Duscha, S; Fallows, R A; Ferrari, C; Frieswijk, W; Garrett, M A; Gunst, A W; Heald, G; Hoeft, M; Juette, E; Maat, P; McKean, J P; Norden, M J; Pandey-Pommier, M; Pizzo, R; Polatidis, A G; Reich, W; Rottgering, H; Sluman, J; Tang, Y; Tasse, C; Vermeulen, R; van Weeren, R J; Wijnholds, S J; Yatawatta, S
2013-01-01
Some radio pulsars show clear drifting subpulses, in which subpulses are seen to drift in pulse longitude in a systematic pattern. Here we examine how the drifting subpulses of PSR B0809+74 evolve with time and observing frequency. We show that the subpulse period (P3) is constant on timescales of days, months and years, and between 14-5100 MHz. Despite this, the shapes of the driftbands change radically with frequency. Previous studies have concluded that, while the subpulses appear to move through the pulse window approximately linearly at low frequencies ( 820 MHz) near to the peak of the average pulse profile. We use LOFAR, GMRT, GBT, WSRT and Effelsberg 100-m data to explore the frequency-dependence of this phase step. We show that the size of the subpulse phase step increases gradually, and is observable even at low frequencies. We attribute the subpulse phase step to the presence of two separate driftbands, whose relative arrival times vary with frequency - one driftband arriving 30 pulses earlier at 2...
A Low-Frequency and Refinement Stable Impedance Boundary Condition EFIE
Dely, Alexandre; Cools, Kristof
2016-01-01
In this contribution, a discretisation of the IBC EFIE is introduced that (i) yields the correct solution at arbitrarily small frequencies, (ii) requires for its solution a number of matrix vector products bounded as the frequency tends to zero and as the mesh density increases. The low frequency stabilisation is based on a projector-based discrete Helmholtz splitting, rescaling, and recombination that depends on the low frequency behaviour of both the EFIE operator and the surface impedance condition. The dense mesh stabilisation is a modifcation of the Perfect Electric Conductor operator preconditioning approach taking into account the effect on the singular value spectrum of the IBC term.
Singular boundary method using time-dependent fundamental solution for scalar wave equations
Chen, Wen; Li, Junpu; Fu, Zhuojia
2016-11-01
This study makes the first attempt to extend the meshless boundary-discretization singular boundary method (SBM) with time-dependent fundamental solution to two-dimensional and three-dimensional scalar wave equation upon Dirichlet boundary condition. The two empirical formulas are also proposed to determine the source intensity factors. In 2D problems, the fundamental solution integrating along with time is applied. In 3D problems, a time-successive evaluation approach without complicated mathematical transform is proposed. Numerical investigations show that the present SBM methodology produces the accurate results for 2D and 3D time-dependent wave problems with varied velocities c and wave numbers k.
Frequency dependent topological patterns of resting-state brain networks.
Directory of Open Access Journals (Sweden)
Long Qian
Full Text Available The topological organization underlying brain networks has been extensively investigated using resting-state fMRI, focusing on the low frequency band from 0.01 to 0.1 Hz. However, the frequency specificities regarding the corresponding brain networks remain largely unclear. In the current study, a data-driven method named complementary ensemble empirical mode decomposition (CEEMD was introduced to separate the time series of each voxel into several intrinsic oscillation rhythms with distinct frequency bands. Our data indicated that the whole brain BOLD signals could be automatically divided into five specific frequency bands. After applying the CEEMD method, the topological patterns of these five temporally correlated networks were analyzed. The results showed that global topological properties, including the network weighted degree, network efficiency, mean characteristic path length and clustering coefficient, were observed to be most prominent in the ultra-low frequency bands from 0 to 0.015 Hz. Moreover, the saliency of small-world architecture demonstrated frequency-density dependency. Compared to the empirical mode decomposition method (EMD, CEEMD could effectively eliminate the mode-mixing effects. Additionally, the robustness of CEEMD was validated by the similar results derived from a split-half analysis and a conventional frequency division method using the rectangular window band-pass filter. Our findings suggest that CEEMD is a more effective method for extracting the intrinsic oscillation rhythms embedded in the BOLD signals than EMD. The application of CEEMD in fMRI data analysis will provide in-depth insight in investigations of frequency specific topological patterns of the dynamic brain networks.
Compliance boundaries for multiple-frequency base station antennas in three directions.
Thielens, Arno; Vermeeren, Günter; Kurup, Divya; Joseph, Wout; Martens, Luc
2013-09-01
In this article, compliance boundaries and allowed output powers are determined for the front, back, and side of multiple-frequency base station antennas, based on the root-mean-squared electric field, the whole-body averaged specific absorption rate (SAR), and the 10 g averaged SAR in both the limbs and the head and trunk. For this purpose, the basic restrictions and reference levels defined by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for both the general public and occupational exposure are used. The antennas are designed for Global System for Mobile Communications around 900 MHz (GSM900), GSM1800, High Speed Packet Access (HSPA), and Long Term Evolution (LTE), and are operated with output powers at the individual frequencies up to 300 W. The compliance boundaries are estimated using finite-difference time-domain simulations with the Virtual Family Male and have been determined for three directions with respect to the antennas for 800, 900, 1800, and 2600 MHz. The reference levels are not always conservative when the radiating part of the antenna is small compared to the length of the body. Combined compliance distances, which ensure compliance with all reference levels and basic restrictions, have also been determined for each frequency. A method to determine a conservative estimation of compliance boundaries for multiple-frequency (cumulative) exposure is introduced. Using the errors on the estimated allowed powers, an uncertainty analysis is carried out for the compliance distances. Uncertainties on the compliance distances are found to be smaller than 122%.
Doping dependent frequency response of MQW infrared photodetector
Billaha, Md. Aref; Das, Mukul K.; Kumar, S.
2017-04-01
This work is to study the effect of doping concentration in the active layer on the performance of multiple quantum well (MQW) infrared photodetector based on inter sub-band transitions. A theoretical model for the photocurrent and hence, responsivity of the detector in frequency domain is developed considering the effect of doping dependent absorption and carrier capture at the hetero-interfaces. Transit time and capture time limited bandwidth of the detector is computed from the frequency dependent photocurrent. Results show that, besides the usual effect of capture time, doping concentration in the active layer has an important effect on the bandwidth and responsivity of the device particularly for high value of capture time.
Frequency-Dependent Dispersion Measures and Implications for Pulsar Timing
Cordes, J M; Stinebring, D R
2016-01-01
We analyze the frequency dependence of the dispersion measure (DM), the column density of free electrons to a pulsar, caused by multipath scattering from small scale electron-density fluctuations. The DM is slightly different along each propagation path and the transverse spread of paths varies greatly with frequency, yielding time-of-arrival (TOA) perturbations that scale differently than the inverse square of the frequency, the expected dependence for a cold, unmagnetized plasma. We quantify DM and TOA perturbations analytically for thin phase screens and extended media and verify the results with simulations of thin screens. The rms difference between DMs across an octave band near 1.5~GHz $\\sim 4\\times10^{-5}\\,{\\rm pc\\ cm^{-3}}$ for pulsars at $\\sim 1$~kpc distance. TOA errors from chromatic DMs are of order a few to hundreds of nanoseconds for pulsars with DM $\\lesssim 30$~pc~cm$^{-3}$ observed across an octave band but increase rapidly to microseconds or larger for larger DMs and wider frequency ranges....
Task, muscle and frequency dependent vestibular control of posture
Patrick A Forbes; Gunter P Siegmund; Schouten, Alfred C.; Jean-Sébastien eBlouin
2015-01-01
The vestibular system is crucial for postural control; however there are considerable differences in the task dependence and frequency response of vestibular reflexes in appendicular and axial muscles. For example, vestibular reflexes are only evoked in appendicular muscles when vestibular information is relevant to postural control, while in neck muscles they are maintained regardless of the requirement to maintain head on trunk balance. Recent investigations have also shown that the bandwid...
Frequency Dependent Electrical Properties of Ferroelectric Ba0.8Sr0.2TiO3 Thin Film
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Ala’eddin A. SAIF
2011-07-01
Full Text Available The frequency dependent electrical parameters, such as impedance, electric modulus, dielectric constant and AC conductivity for ferroelectric Ba0.8Sr0.2TiO3 thin film have been investigated within the range of 1 Hz and 106 Hz at room temperature. Z* plane shows two regions corresponding to the bulk mechanism and the distribution of the grain boundaries-electrodes process. M" versus frequency plot reveals a relaxation peak, which is not observed in the ε″ plot and it has been found that this peak is a non-Debye-type. The frequency dependent conductivity plot shows three regions of conduction processes, i. e., a low-frequency region due to DC conduction, a mid-frequency region due to translational hopping motions and a high-frequency region due to localized hopping and/or reorientational motion.http://dx.doi.org/10.5755/j01.ms.17.2.490
Frequency-dependent polarizabilities and shielding factors for confined one-electron systems
Montgomery, H. E., Jr.; Pupyshev, Vladimir I.
2017-01-01
Frequency-dependent dipole polarizabilities and shielding factors are calculated for the ground state of spherically symmetric screened one-electron systems embedded in an impenetrable spherical cavity. Coulomb, Yukawa, Hulthén and exponential cosine-screened Coulomb potentials are considered. In contrast to free systems, Dirichlet boundary conditions introduce a contribution to the shielding factor that results from an integral over the surface of the confining boundary. This is a fundamental difference between free and confined systems and results in unexpected modifications to some of the classic relations for free systems. The methods derived also give a simple expression for the polarizability of the confined harmonic oscillator as an example of extending the methods of this work to potentials beyond the four studied.
Improved low frequency room responses by considering finiteness of room boundary surfaces
DEFF Research Database (Denmark)
Jeong, Cheol-Ho
2013-01-01
For room acoustic simulations, the acoustic characteristics of room boundary surfaces are typically calculated under the assumption that the surfaces are sufficiently large. In this study, a reflection coefficient for finite surfaces is suggested and its performance is assessed through case studies...... surface impedance values that are assigned to all the boundary surfaces, the suggested reflection coefficient is found to improve low frequency responses compared to the infinite panel theory; larger improvements are found for a more disproportionate room, more absorptive surfaces, and surfaces having...... larger negative phase angles of the surface impedance. A larger improvement is also found for a nonuniform absorption case than for a uniform absorption setting having a similar equivalent absorption coefficient....
Phase-dependent dual-frequency contrast imaging at sub-harmonic frequency.
Shen, Che-Chou; Cheng, Chih-Hao; Yeh, Chih-Kuang
2011-02-01
Sub-harmonic imaging techniques have been shown to provide a higher contrast-to-tissue ratio (CTR) at the cost of relatively low signal intensity from ultrasound contrast agents (UCAs). In this study, we propose a method of dual-frequency excitation to further enhance the CTR of subharmonic imaging. A dual-frequency excitation pulse is an amplitude-modulated waveform which consists of two sinusoids with frequencies of f₁ (e.g., 9 MHz) and f₂ (e.g., 6 MHz) and the resulting envelope component at (f₁ - f₂) (e.g., 3 MHz) can serve as a driving force to excite the nonlinear response of UCAs. In this study, the f₂, at twice of the resonance frequency of UCAs, is adopted to efficiently generate a sub-harmonic component at half of the f₂ frequency, and f₁ is included to enhance the high-order nonlinear response of UCAs at the sub-harmonic frequency. The second- and third-order nonlinear components resulting from the envelope component would spectrally overlap at the sub-harmonic frequency when f₁ and f₂ are properly selected. We further optimize the generation of the sub-harmonic component by tuning the phase terms between second- and third-order nonlinear components. The results show that, with dual-frequency excitation, the CTR at sub-harmonic frequency improves compared with the conventional tone-burst method. Moreover, the CTR changes periodically with the relative phase of the separate frequency component in the dual-frequency excitation, leading to a difference of as much as 9.1 dB between the maximal and minimal CTR at 300 kPa acoustic pressure. The echo produced from the envelope component appears to be specific for UCAs, and thus the proposed method has the potential to improve both SNR and CTR in sub-harmonic imaging. Nevertheless, the dual-frequency waveform may suffer from frequency-dependent attenuation that degrades the generation of the envelope component. The deviation of the microbubble's resonance characteristics from the selection of
Time-dependent density functional theory with twist-averaged boundary conditions
Schuetrumpf, B; Reinhard, P -G
2016-01-01
Time-dependent density functional theory is widely used to describe excitations of many-fermion systems. In its many applications, 3D coordinate-space representation is used, and infinite-domain calculations are limited to a finite volume represented by a box. For finite quantum systems (atoms, molecules, nuclei), the commonly used periodic or reflecting boundary conditions introduce spurious quantization of the continuum states and artificial reflections from boundary; hence, an incorrect treatment of evaporated particles. These artifacts can be practically cured by introducing absorbing boundary conditions (ABC) through an absorbing potential in a certain boundary region sufficiently far from the described system. But also the calculations of infinite matter (crystal electrons, quantum fluids, neutron star crust) suffer artifacts from a finite computational box. In this regime, twist- averaged boundary conditions (TABC) have been used successfully to diminish the finite-volume effects. In this work, we exte...
Ultra low frequency waves observed by Double Star TC-1 in the plasmasphere boundary layer
Institute of Scientific and Technical Information of China (English)
2008-01-01
The characteristic and properties of ULF waves in the plasmasphere boundary layer during two very quiet periods are present. The ULF waves were detected by Double Star TC-1 when the spacecraft passed through the plasmasphere in an outbound and inbound trajectories, respectively. A clear association between the ULF waves and periodic variations of energetic ions fluxes was observed. The ob-servations showed that the wave frequency was higher inside the plasmasphere than outside. The mechanism generating these ULF waves and possible diagnos-ing of the "classical plasmapause" location with the ULF wave were discussed.
Institute of Scientific and Technical Information of China (English)
蔡袁强; 梁旭; 吴世明
2004-01-01
On the basis of Terzaghi's one-dimensional consolidation theory, the variation of effective stress ratio in layered saturated soils with impeded boundaries under timedependent loading was studied. By the method of Laplace transform, the solution was presented. Influences of different kinds of cyclic loadings and impeded boundaries conditions were discussed. Through numerical inversion of Laplace transform, useful illustrations were given considering several common time-dependent loadings. Pervious or impervious boundary condition is just the special case of the problem considered here. Compared with average index method, the results from the method illustrated are more accurate.
Multiple time-dependent coefficient identification thermal problems with a free boundary
Hussein, MS; Lesnic, D.; Ivanchov, MI; Snitko, HA
2016-01-01
Multiple time-dependent coefficient identification thermal problems with an unknown free boundary are investigated. The difficulty in solving such inverse and ill-posed free boundary problems is amplified by the fact that several quantities of physical interest (conduction, convection/advection and reaction coefficients) have to be simultaneously identified. The additional measurements which render a unique solution are given by the heat moments of various orders together with a Stefan bounda...
Size-Dependent Elastic Modulus and Vibration Frequency of Nanocrystals
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Lihong Liang
2011-01-01
Full Text Available The elastic properties and the vibration characterization are important for the stability of materials and devices, especially for nanomaterials with potential and broad application. Nanomaterials show different properties from the corresponding bulk materials; the valid theoretical model about the size effect of the elastic modulus and the vibration frequency is significant to guide the application of nanomaterials. In this paper, a unified analytical model about the size-dependent elastic modulus and vibration frequency of nanocrystalline metals, ceramics and semiconductors is established based on the inherent lattice strain and the binding energy change of nanocrystals compared with the bulk crystals, and the intrinsic correlation between the elasticity and the vibration properties is discussed. The theoretical predictions for Cu, Ag, Si thin films, nanoparticles, and TiO2 nanoparticles agree with the experimental results, the computational simulations, and the other theoretical models.
Assessment of a PML Boundary Condition for Simulating an MRI Radio Frequency Coil
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Yunsuo Duan
2008-01-01
Full Text Available Computational methods such as the finite difference time domain (FDTD play an important role in simulating radiofrequency (RF coils used in magnetic resonance imaging (MRI. The choice of absorbing boundary conditions affects the final outcome of such studies. We have used FDTD to assess the Berenger's perfectly matched layer (PML as an absorbing boundary condition for computation of the resonance patterns and electromagnetic fields of RF coils. We first experimentally constructed a high-pass birdcage head coil, measured its resonance pattern, and used it to acquire proton (1H phantom MRI images. We then computed the resonance pattern and B1 field of the coil using FDTD with a PML as an absorbing boundary condition. We assessed the accuracy and efficiency of PML by adjusting the parameters of the PML and comparing the calculated results with measured ones. The optimal PML parameters that produce accurate (comparable to the experimental findings FDTD calculations are then provided for the birdcage head coil operating at 127.72 MHz, the Larmor frequency of 1H at 3 Tesla (T.
Dependence of enhanced asymmetry-induced transport on collision frequency
Energy Technology Data Exchange (ETDEWEB)
Eggleston, D. L. [Occidental College, Physics Department, Los Angeles, California 90041 (United States)
2014-07-15
A single-particle code with collisional effects is used to study how asymmetry-induced radial transport in a non-neutral plasma depends on collision frequency. For asymmetries of the form ϕ{sub 1}(r) cos(kz) cos(ωt−lθ), two sources for the transport have been identified: resonant particles and axially trapped particles. The simulation shows that this latter type, which occurs near the radius where ω matches the azimuthal rotation frequency ω{sub R}, is usually dominant at low collision frequency ν but becomes negligible at higher ν. This behavior can be understood by noting that axially trapped particles have a lower trapping frequency than resonant particles. In the low ν (banana) regime, the radial oscillations have amplitude Δr ≈ v{sub r}/ω{sub T}, so axially trapped particles dominate, and the transport may even exceed the resonant particle plateau regime level. As ν increases, collisions start to interrupt the slower axially trapped particle oscillations, while the resonant particles are still in the banana regime, so the axially trapped particle contribution to the transport decreases. At the largest ν values, axially trapped particle transport is negligible and the observed diffusion coefficient matches that given by plateau regime resonant particle theory. Heuristic models based on these considerations give reasonable agreement with the observed scaling laws for the value of the collision frequency where axially trapped particle transport starts to decrease and for the enhancement of the diffusion coefficient produced by axially trapped particles.
Frequency-dependent Drude damping in Casimir force calculations
Energy Technology Data Exchange (ETDEWEB)
Esquivel-Sirvent, R, E-mail: raul@fisica.unam.m [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Apdo. Postal 20-364, Mexico D.F. 01000 (Mexico)
2009-04-01
The Casimir force is calculated between Au thin films that are described by a Drude model with a frequency dependent damping function. The model parameters are obtained from available experimental data for Au thin films. Two cases are considered; annealed and nonannealed films that have a different damping function. Compared with the calculations using a Drude model with a constant damping parameter, we observe changes in the Casimir force of a few percent. This behavior is only observed in films of no more than 300 A thick.
Task, muscle and frequency dependent vestibular control of posture
Directory of Open Access Journals (Sweden)
Patrick A Forbes
2015-01-01
Full Text Available The vestibular system is crucial for postural control; however there are considerable differences in the task dependence and frequency response of vestibular reflexes in appendicular and axial muscles. For example, vestibular reflexes are only evoked in appendicular muscles when vestibular information is relevant to postural control, while in neck muscles they are maintained regardless of the requirement to maintain head on trunk balance. Recent investigations have also shown that the bandwidth of vestibular input on neck muscles is much broader than appendicular muscles (up to a factor of 3. This result challenges the notion that vestibular reflexes only contribute to postural control across the behavioral and physiological frequency range of the vestibular organ (i.e., 0-20 Hz. In this review, we explore and integrate these task-, muscle- and frequency-related differences in the vestibular system’s contribution to posture, and propose that the human nervous system has adapted vestibular signals to match the mechanical properties of the system that each group of muscles controls.
RWM Critical Rotation Frequency and Beta Dependence in NSTX
Sontag, Aaron; Sabbagh, S. A.; Menard, J. E.; Battaglia, D. J.
2005-10-01
The resistive wall mode (RWM) can be stabilized by maintaining the plasma toroidal rotation frequency (φφ) above a critical rotation frequency (φcrit). Recent experiments on NSTX seek to determine φcrit and rotation profile effects through actively braking plasma rotation by the application of external magnetic fields. Results from these experiments indicate that maintaining φφ at the q = 2 surface above φA/4q^2 is a necessary condition for RWM stability where φA is the local Alfven frequency. This result is in agreement with a theoretical model derived from a drift-kinetic energy principle. Similarity experiments with DIII-D are being performed to examine the aspect ratio dependence of the φcrit scaling. When φφ at the q = 2 surface drops below φcrit, the growth of internal kink/ballooning modes can prevent the RWM from terminating the discharge. A small beta collapse which drops φcrit, accompanies this mode growth allowing a recovery of RWM rotational stabilization while maintaining βN> βN^no-wall.
Frequency-dependent effects of gravitational lensing within plasma
Rogers, Adam
2015-01-01
The interaction between refraction from a distribution of inhomogeneous plasma and gravitational lensing introduces novel effects to the paths of light rays passing by a massive object. The plasma contributes additional terms to the equations of motion, and the resulting ray trajectories are frequency-dependent. Lensing phenomena and circular orbits are investigated for plasma density distributions $N \\propto 1/r^h$ with $h \\geq 0$ in the Schwarzschild space-time. For rays passing by the mass near the plasma frequency refractive effects can dominate, effectively turning the gravitational lens into a mirror. We obtain the turning points, circular orbit radii, and angular momentum for general $h$. Previous results have shown that light rays behave like massive particles with an effective mass given by the plasma frequency for a constant density $h=0$. We study the behaviour for general $h$ and show that when $h=2$ the plasma term acts like an additional contribution to the angular momentum of the passing ray. W...
Time and frequency dependent rheology of reactive silica gels.
Wang, Miao; Winter, H Henning; Auernhammer, Günter K
2014-01-01
In a mixture of sodium silicate and low concentrated sulfuric acid, nano-sized silica particles grow and may aggregate to a system spanning gel network. We studied the influence of the finite solubility of silica at high pH on the mechanical properties of the gel with classical and piezo-rheometers. Direct preparation of the gel sample in the rheometer cell avoided any pre-shear of the gel structure during the filling of the rheometer. The storage modulus of the gel grew logarithmically with time with two distinct growth laws. The system passes the gel point very quickly but still shows relaxation at low frequency, typically below 6 rad/s. We attribute this as a sign of structural rearrangements due to the finite solubility of silica at high pH. The reaction equilibrium between bond formation and dissolution maintains a relatively large bond dissolution rate, which leads to a finite life time of the bonds and behavior similar to physical gels. This interpretation is also compatible with the logarithmic time dependence of the storage modulus. The frequency dependence was more pronounced for lower water concentrations, higher temperatures and shorter reaction times. With two relaxation models (the modified Cole-Cole model and the empirical Baumgaertel-Schausberger-Winter model) we deduced characteristic times from the experimental data. Both models approximately described the data and resulted in similar relaxation times.
Directory of Open Access Journals (Sweden)
Michael A. Athanasiou
2015-01-01
Full Text Available In this paper we present results of a comparison between ultra low frequency (ULF electromagnetic (EM radiation, recorded by an electric field instrument onboard the satellite detection of electromagnetic emissions transmitted from earthquake regions in the topside ionosphere, and the seismicity of regions with high and low seismic activity. In particular, we evaluated the energy variations of the ULF Ezelectric field component during a period of four years (2006-2009, in order to examine the possible relation of ULF EM radiation with seismogenic regions located in Central America, Indonesia, the Eastern Mediterranean Basin and Greece. As a tool for evaluating the ULF Ez energy variations we used singular spectrum analysis techniques. The results of our analysis clearly show a significant increase of the ULF EM energy emitted from regions of highest seismic activity at the boundaries tectonic plates. Furthermore, we found that higher electromagnetic radiation was detected in a region above the northern- western Greek Arc (R1 than above the adjacent region including Athens and its urban area. We interpret these results of the present study as suggesting that: i the seismogenic regions at the boundary of tectonic plates radiate ULF EM emissions observed by satellites in the topside ionosphere; and ii that this EM radiation is not only related with the occurrence time of great (M≥5 earthquakes, but it is often present in intermediate times and it appears as a quasi-permanent phenomenon.
Second-order domain derivative of normal-dependent boundary integrals
Balzer, Jonathan
2010-03-17
Numerous reconstruction tasks in (optical) surface metrology allow for a variational formulation. The occurring boundary integrals may be interpreted as shape functions. The paper is concerned with the second-order analysis of such functions. Shape Hessians of boundary integrals are considered difficult to find analytically because they correspond to third-order derivatives of an, in a sense equivalent, domain integral. We complement previous results by considering cost functions depending explicitly on the surface normal. The correctness and practicability of our calculations are verified in the context of a Newton-type shape reconstruction method. © 2010 Birkhäuser / Springer Basel AG.
Directory of Open Access Journals (Sweden)
I. N. Esau
2006-01-01
Full Text Available We consider the resistance law for the planetary boundary layer (PBL from the point of view of the similarity theory. In other words, we select the set of the PBL governing parameters and search for an optimal way to express through these parameters the geostrophic drag coefficient Cg=u* /Ug and the cross isobaric angle α (where u* is the friction velocity and Ug is the geostrophic wind speed. By this example, we demonstrate how to determine the 'parameter space' in the most convenient way, so that make independent the dimensionless numbers representing co-ordinates in the parameter space, and to avoid (or at least minimise artificial self-correlations caused by the appearance of the same factors (such as u* in the examined dimensionless combinations (e.g. in Cg=u* /Ug and in dimensionless numbers composed of the governing parameters. We also discuss the 'completeness' of the parameter space from the point of view of large-eddy simulation (LES modeller creating a database for a specific physical problem. As recognised recently, very large scatter of data in prior empirical dependencies of Cg and α on the surface Rossby number Ro=Ug| fz0|-1 (where z0 is the roughness length and the stratification characterised by µ was to a large extent caused by incompactness of the set of the governing parameters. The most important parameter overlooked in the traditional approach is the typical value of the Brunt-Väisälä frequency N in the free atmosphere (immediately above the PBL, which involves, besides Ro and µ, one more dimensionless number: µN=N/ | f |. Accordingly, we consider Cg and α as dependent on the three (rather then two basic dimensionless numbers (including µN using LES database DATABASE64. By these means we determine the form of the dependencies under consideration in the part of the parameter space representing typical atmospheric PBLs, and provide analytical expressions for Cg and α.
Advanced Reservoir Imaging Using Frequency-Dependent Seismic Attributes
Energy Technology Data Exchange (ETDEWEB)
Fred Hilterman; Tad Patzek; Gennady Goloshubin; Dmitriy Silin; Charlotte Sullivan; Valeri Korneev
2007-12-31
Our report concerning advanced imaging and interpretation technology includes the development of theory, the implementation of laboratory experiments and the verification of results using field data. We investigated a reflectivity model for porous fluid-saturated reservoirs and demonstrated that the frequency-dependent component of the reflection coefficient is asymptotically proportional to the reservoir fluid mobility. We also analyzed seismic data using different azimuths and offsets over physical models of fractures filled with air and water. By comparing our physical model synthetics to numerical data we have identified several diagnostic indicators for quantifying the fractures. Finally, we developed reflectivity transforms for predicting pore fluid and lithology using rock-property statistics from 500 reservoirs in both the shelf and deep-water Gulf of Mexico. With these transforms and seismic AVO gathers across the prospect and its down-dip water-equivalent reservoir, fluid saturation can be estimated without a calibration well that ties the seismic. Our research provides the important additional mechanisms to recognize, delineate, and validate new hydrocarbon reserves and assist in the development of producing fields.
Heppe, Jonas; McGraw, Joshua D.; Bennewitz, Roland; Jacobs, Karin
2015-03-01
In fluid dynamics, the solid/liquid boundary condition can play a major role in the flow behavior of a liquid. For example, in the dewetting of identical polymer films on weak slip or strong slip substrates, large qualitative and quantitative differences are observed. Therefore, when applying an external load to a liquid resting on such substrates, the measured reaction forces and the ensuing flow should also depend on the boundary condition. We present atomic force microscopy measurements in which the reaction force of a cantilever is measured as the tip pierces liquid polymer micron sized droplets and films. These indentations are done on substrates with tuned slip. Accessing the size, depth and rate dependence of the resulting force distance curves, we show an influence of the slip condition on the dissipated energy and adhesion.
Reyes, J. Paxon; Shadwick, B. A.
2015-11-01
Describing a cold-Maxwell fluid system with a spatially-discrete, unbounded Lagrangian is problematic for numerical modeling since boundary conditions must be applied after the variational step. Accurate solutions may still be attained, but do not technically satisfy the derived energy conservation law. The size of the numerical domain, the order accuracy of the discrete approximations used, and the type of boundary conditions applied influence the behavior of the artificially-bounded system. To encode the desired boundary conditions of the equations of motion, we include time-dependent terms into the discrete Lagrangian. Although some foresight is needed to choose these time-dependent terms, this approach provides a mechanism for energy to exit the closed system while allowing the conservation law to account for the energy loss. Results of a spatially-discrete, time-dependent Lagrangian system (with approximations of second-order accuracy in space and fourth order in time) will be presented. The fields and total energy will be compared with models of the same accuracy using a time-independent variational approach as well as a non-variational approach. This work was supported by the U. S. Department of Energy under Contract No. DE-SC0008382 and by the National Science Foundation under Contract No. PHY- 1104683.
Time-Frequency Analysis of Boundary-Layer Instabilites Generated by Freestream Laser Perturbations
Chou, Amanda; Schneider, Steven P.
2015-01-01
A controlled disturbance is generated in the freestream of the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT) by focusing a high-powered Nd:YAG laser to create a laser-induced breakdown plasma. The plasma then cools, creating a freestream thermal disturbance that can be used to study receptivity. The freestream disturbance convects down-stream in the Mach-6 wind tunnel to interact with a flared cone model. The adverse pressure gradient created by the flare of the model is capable of generating second-mode instability waves that grow large and become nonlinear before experiencing natural transition in quiet flow. The freestream laser perturbation generates a wave packet in the boundary layer at the same frequency as the natural second mode, complicating time-independent analyses of the effect of the laser perturbation. The data show that the laser perturbation creates an instability wave packet that is larger than the natural waves on the sharp flared cone. The wave packet is still difficult to distinguish from the natural instabilities on the blunt flared cone.
Predicting pauses in L1 and L2 speech: the effects of utterance boundaries and word frequency
de Jong, N.H.
2016-01-01
This paper compares the distribution of silent and filled pauses in first (L1) and second language (L2) speech. The occurrence of pauses of 52 L2 and 18 L1 Dutch speakers was evaluated with respect to utterance boundaries and word frequency. We found that L2 speakers paused more often than L1
Predicting pauses in L1 and L2 speech: the effects of utterance boundaries and word frequency
de Jong, N.H.
2016-01-01
This paper compares the distribution of silent and filled pauses in first (L1) and second language (L2) speech. The occurrence of pauses of 52 L2 and 18 L1 Dutch speakers was evaluated with respect to utterance boundaries and word frequency. We found that L2 speakers paused more often than L1 speake
Parameter-dependent behaviour of periodic channels in a locus of boundary crisis
Rankin, James; Osinga, Hinke M.
2017-06-01
A boundary crisis occurs when a chaotic attractor outgrows its basin of attraction and suddenly disappears. As previously reported, the locus of a boundary crisis is organised by homo- or heteroclinic tangencies between the stable and unstable manifolds of saddle periodic orbits. In two parameters, such tangencies lead to curves, but the locus of boundary crisis along those curves exhibits gaps or channels, in which other non-chaotic attractors persist. These attractors are stable periodic orbits which themselves can undergo a cascade of period-doubling bifurcations culminating in multi-component chaotic attractors. The canonical diffeomorphic two-dimensional Hénon map exhibits such periodic channels, which are structured in a particular ordered way: each channel is bounded on one side by a saddle-node bifurcation and on the other by a period-doubling cascade to chaos; furthermore, all channels seem to have the same orientation, with the saddle-node bifurcation always on the same side. We investigate the locus of boundary crisis in the Ikeda map, which models the dynamics of energy levels in a laser ring cavity. We find that the Ikeda map features periodic channels with a richer and more general organisation than for the Hénon map. Using numerical continuation, we investigate how the periodic channels depend on a third parameter and characterise how they split into multiple channels with different properties.
A time dependent approach for removing the cell boundary error in elliptic homogenization problems
Arjmand, Doghonay; Runborg, Olof
2016-06-01
This paper concerns the cell-boundary error present in multiscale algorithms for elliptic homogenization problems. Typical multiscale methods have two essential components: a macro and a micro model. The micro model is used to upscale parameter values which are missing in the macro model. To solve the micro model, boundary conditions are required on the boundary of the microscopic domain. Imposing a naive boundary condition leads to O (ε / η) error in the computation, where ε is the size of the microscopic variations in the media and η is the size of the micro-domain. The removal of this error in modern multiscale algorithms still remains an important open problem. In this paper, we present a time-dependent approach which is general in terms of dimension. We provide a theorem which shows that we have arbitrarily high order convergence rates in terms of ε / η in the periodic setting. Additionally, we present numerical evidence showing that the method improves the O (ε / η) error to O (ε) in general non-periodic media.
Ultrasonic Characterization of Tissues via Backscatter Frequency Dependence
DEFF Research Database (Denmark)
Stetson, Paul F.; Sommer, F.G.
1997-01-01
, significantly lower mean frequency of ultrasound backscattered from cirrhotic, compared to normal, liver tissue was noted, Studies of benign and malignant liver tumors (hemangiomas and metastases, respectively) indicated differences in frequency content of these tumors, compared to the adjacent normal liver...
Forati, Ebrahim
2013-01-01
A graphene sheet gated with a ridged ground plane, creating a soft-boundary (SB) graphene nanoribbon, is considered. By adjusting the ridge parameters and bias voltage a channel can be created on the graphene which can guide TM surface plasmon polaritons (SPP). Two types of modes are found; fundemental and higher-order modes with no apparent cutoff frequency and with energy distributed over the created channel, and edge modes with energy concen-trated at the soft-boundary edge. Dispersion curves, electric near-field patterns, and current distributions of these modes are determined. Since the location where energy is concentrated in the edge modes can be easily controlled electronically by the bias voltage and frequency, the edge-mode phenomena is used to propose a novel voltage controlled plasmonic switch and a plasmonic frequency demultiplexer.
Reyes, Jonathan; Shadwick, B. A.
2016-10-01
Modeling the evolution of a short, intense laser pulse propagating through an underdense plasma is of particular interest in the physics of laser-plasma interactions. Numerical models are typically created by first discretizing the equations of motion and then imposing boundary conditions. Using the variational principle of Chen and Sudan, we spatially discretize the Lagrangian density to obtain discrete equations of motion and a discrete energy conservation law which is exactly satisfied regardless of the spatial grid resolution. Modifying the derived equations of motion (e.g., enforcing boundary conditions) generally ruins energy conservation. However, time-dependent terms can be added to the Lagrangian which force the equations of motion to have the desired boundary conditions. Although some foresight is needed to choose these time-dependent terms, this approach provides a mechanism for energy to exit the closed system while allowing the conservation law to account for the loss. An appropriate time discretization scheme is selected based on stability analysis and resolution requirements. We present results using this variational approach in a co-moving coordinate system and compare such results to those using traditional second-order methods. This work was supported by the U. S. Department of Energy under Contract No. DE-SC0008382 and by the National Science Foundation under Contract No. PHY- 1104683.
Phase-dependent audiometry with low-frequency masking revisited.
Rahne, Torsten; Rasinski, Christine; Neumann, Kerstin
2010-05-15
Low-frequency masking is a psychoacoustical phenomenon, describing the modulation of a high-frequency probe tone burst by a low-frequency masker tone. The probe tone threshold is increased, if the probe tone is presented at a low-frequency phases around 90 degrees and 270 degrees . At these phases, the low-frequency masker tone induces a displacement of the basilar membrane of the inner ear which modulates the sensitivity of the inner hair cells. Measuring the modulation depth is partially applied in clinical routine to diagnose the endolymphatic hydrops. Although the modulation depth differs between normal ears and those which reveal an endolymphatic hydrops, the significance of these tests seems debatable. Here, we describe a new experimental setup, completely consisting of commercially available devices. Further, a user interface was developed to enable the application in the clinical routine. The experimental setup was approved with ten normal hearing listeners. All reveal a modulation of the probe stimulus threshold by different phases of the low-frequency masker stimulus. With this experimental setup, custom-made modifications of the essential parameters are feasible. This would be a contribution to solve open questions on the clinical relevance of the low-frequency masking phenomenon.
Indian Academy of Sciences (India)
Arindam Saha; R E Amritkar
2014-12-01
Kuramoto oscillators have been proposed earlier as a model for interacting systems that exhibit synchronization. In this article, we study the difference between networks with symmetric and asymmetric distribution of natural frequencies. We first indicate that synchronization frequency of oscillators in a completely connected network is always equal to the mean of the natural frequency distribution. In particular, shape of the natural frequency distribution does not affect the synchronization frequency in this case. Then, we analyse the case of oscillators in a directed ring network, where asymmetry in the natural frequency distribution is seen to shift the synchronization frequency of the network. We also present an estimate of the shift in the frequencies for slightly asymmetric distributions.
Frequency and Magnetic Field Dependence of the Skin Depth in Co-rich Soft Magnetic Microwires
Directory of Open Access Journals (Sweden)
A. Zhukov
2016-11-01
Full Text Available We studied giant magnetoimpedance (GMI effect in magnetically soft amorphous Co-rich microwires in the extended frequency range. From obtained experimentally dependences of GMI ratio on magnetic field and different frequencies we estimated the penetration depth and its dependence on applied magnetic field and frequency
Phased-Array Antenna Beam Squinting Related to Frequency Dependency of Delay Circuits
Garakoui, S.K.; Klumperink, E.A.M.; Nauta, B.; Vliet, F.E. van
2011-01-01
Practical time delay circuits do not have a perfectly linear phase-frequency characteristic. When these delay circuits are applied in a phased-array system, this frequency dependency shows up as a frequency dependent beam direction (“beam squinting”). This paper quantifies beam squinting for a linea
Modeling frequency dependence of GaAs MESFET characteristics
Conger, Jeff; Peczalski, Andrzej; Shur, Michael S.
1994-01-01
We present a new method of modeling the output conductance dispersion of GaAs MESFET's. High frequency model parameters are extracted and then used to model high frequency output conductance over a wide range of bias conditions. The model is then used to simulate and analyze the effect of output conductance dispersion on the performance of DCFL and SCFL logic gates. Whereas the DCFL performance is not significantly affected by the high frequency effects, the noise margin of SCFL decreases by almost a factor of 30% above 100 kHz, with an associated decrease in the voltage swing and gate delay.
Frequency-Dependent Viscosity of Xenon Near the Critical Point
Berg, Robert F.; Moldover, Michael R.; Zimmerli, Gregory A.
1999-01-01
We used a novel, overdamped oscillator aboard the Space Shuttle to measure the viscosity eta of xenon near its critical density rho(sub c), and temperature T(sub c). In microgravity, useful data were obtained within 0.1 mK of T(sub c), corresponding to a reduced temperature t = (T -T(sub c))/T(sub c) = 3 x 10(exp -7). The data extend two decades closer to T(sub c) than the best ground measurements, and they directly reveal the expected power-law behavior eta proportional to t(sup -(nu)z(sub eta)). Here nu is the correlation length exponent, and our result for the small viscosity exponent is z(sub eta) = 0.0690 +/- 0.0006. (All uncertainties are one standard uncertainty.) Our value for z(sub eta) depends only weakly on the form of the viscosity crossover function, and it agrees with the value 0.067 +/- 0.002 obtained from a recent two-loop perturbation expansion. The measurements spanned the frequency range 2 Hz less than or equal to f less than or equal to 12 Hz and revealed viscoelasticity when t less than or equal to 10(exp -1), further from T(sub c) than predicted. The viscoelasticity scales as Af(tau), where tau is the fluctuation-decay time. The fitted value of the viscoelastic time-scale parameter A is 2.0 +/- 0.3 times the result of a one-loop perturbation calculation. Near T(sub c), the xenon's calculated time constant for thermal diffusion exceeded days. Nevertheless, the viscosity results were independent of the xenon's temperature history, indicating that the density was kept near rho(sub c), by judicious choices of the temperature vs. time program. Deliberately bad choices led to large density inhomogeneities. At t greater than 10(exp -5), the xenon approached equilibrium much faster than expected, suggesting that convection driven by microgravity and by electric fields slowly stirred the sample.
Frequency Dependence of Measured Massive MIMO Channel Properties
DEFF Research Database (Denmark)
Oliveras Martínez, Àlex; Carvalho, Elisabeth De; Nielsen, Jesper Ødum;
2016-01-01
A multi-user massive MIMO measurement campaign is conducted to study the channel propagation characteristics (e.g. user correlation, sum of eigenvalues and condition number), focusing on the stability over frequencies and the impact of the array aperture. We use 3 arrays with 64 antennas (6m linear...... array, 2m linear array and 25cm by 28cm squared 2D array) serving 8 users holding a handset with 2 antennas. The study of the measurements shows that the propagation characteristics of the channel are stable for all the measured frequencies. We also observe that user proximity and user handgrip...... stabilize the studied properties of the channel across the frequencies, and in such case the larger the aperture of the array the more stable the properties. The number of base station antennas improves the propagation characteristics of the channel and stabilizes the properties in the frequency domain....
Frequency-Dependent Blanking with Digital Linear Chirp Waveform Synthesis
Energy Technology Data Exchange (ETDEWEB)
Doerry, Armin Walter [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Andrews, John M. [General Atomics Aeronautical Systems, Inc., San Diego, CA (United States)
2014-07-01
Wideband radar systems, especially those that operate at lower frequencies such as VHF and UHF, are often restricted from transmitting within or across specific frequency bands in order to prevent interference to other spectrum users. Herein we describe techniques for notching the transmitted spectrum of a generated and transmitted radar waveform. The notches are fully programmable as to their location, and techniques are given that control the characteristics of the notches.
Frequency-Dependent Scattering Observed in P- and Surface-Wave Arrivals From South India
Rai, A. K.
2017-03-01
Anomalies in polarization angles of teleseismic waves have been used to understand effect of scattered arrivals from subsurface heterogeneities. Seismological data recorded in southern India show polarization anomalies up to 5° for several stations. These anomalies are most pronounced for earthquakes from western and southern azimuths. Furthermore, stations located near the boundary of Dharwar craton and southern Granulites are more affected by scattered waves. Considering that many of the nearby stations show similar patterns of polarization anomalies, it is likely that the source of scattered energy is located at shallower depths. The non-stationary nature of seismic arrivals warrants determination of frequency-dependent polarization. Result obtained using multi-taper spectral analysis method indicates that data are contaminated at frequencies greater than 2 Hz for most of the stations. Furthermore, surface-wave records also indicate off-azimuth arrivals, and quasi-Love waves indicating heterogeneities or anisotropy in the subsurface. These small-scale heterogeneities that may be located in crust may be important for studies using converted phases and ground motion prediction studies.
Frequency-Dependent Scattering Observed in P- and Surface-Wave Arrivals From South India
Rai, A. K.
2016-12-01
Anomalies in polarization angles of teleseismic waves have been used to understand effect of scattered arrivals from subsurface heterogeneities. Seismological data recorded in southern India show polarization anomalies up to 5° for several stations. These anomalies are most pronounced for earthquakes from western and southern azimuths. Furthermore, stations located near the boundary of Dharwar craton and southern Granulites are more affected by scattered waves. Considering that many of the nearby stations show similar patterns of polarization anomalies, it is likely that the source of scattered energy is located at shallower depths. The non-stationary nature of seismic arrivals warrants determination of frequency-dependent polarization. Result obtained using multi-taper spectral analysis method indicates that data are contaminated at frequencies greater than 2 Hz for most of the stations. Furthermore, surface-wave records also indicate off-azimuth arrivals, and quasi-Love waves indicating heterogeneities or anisotropy in the subsurface. These small-scale heterogeneities that may be located in crust may be important for studies using converted phases and ground motion prediction studies.
Zhou, Yanguang; Zhang, Xiaoliang; Hu, Ming
2017-02-08
By carefully and systematically performing Green-Kubo equilibrium molecular dynamics simulations, we report that the thermal conductivity (κ) of Si nanowires (NWs) does not diverge but converges and increases steeply when NW diameter (D) becomes extremely small (dκ/dD < 0), a long debate of one-dimensional heat conduction in history. The κ of the thinnest possible Si NWs reaches a superhigh level that is as large as more than 1 order of magnitude higher than its bulk counterpart. The abnormality is explained in terms of the dominant normal (N) process (energy and momentum conservation) of low frequency acoustic phonons that induces hydrodynamic phonon flow in the Si NWs without being scattered. With D increasing, the downward shift of optical phonons triggers strong Umklapp (U) scattering with acoustic phonons and attenuates the N process, leading to the regime of phonon boundary scattering (dκ/dD < 0). The two competing mechanisms result in nonmonotonic diameter dependence of κ with minima at critical diameter of 2-3 nm. Our results unambiguously demonstrate the converged κ and the clear trend of κ ∼ D for extremely thin Si NWs by fully elucidating the competition between the hydrodynamic phonon flow and phonon boundary scattering.
Refined Monte Carlo method for simulating angle-dependent partial frequency redistributions
Lee, J.-S.
1982-01-01
A refined algorithm for generating emission frequencies from angle-dependent partial frequency redistribution functions R sub II and R sub III is described. The improved algorithm has as its basis a 'rejection' technique that, for absorption frequencies x less than 5, involves no approximations. The resulting procedure is found to be essential for effective studies of radiative transfer in optically thick or temperature varying media involving angle-dependent partial frequency redistributions.
Nonlinear frequency-dependent synchronization in the developing hippocampus.
Prida, L M; Sanchez-Andres, J V
1999-07-01
Synchronous population activity is present both in normal and pathological conditions such as epilepsy. In the immature hippocampus, synchronous bursting is an electrophysiological conspicuous event. These bursts, known as giant depolarizing potentials (GDPs), are generated by the synchronized activation of interneurons and pyramidal cells via GABAA, N-methyl-D-aspartate, and AMPA receptors. Nevertheless the mechanism leading to this synchronization is still controversial. We have investigated the conditions under which synchronization arises in developing hippocampal networks. By means of simultaneous intracellular recordings, we show that GDPs result from local cooperation of active cells within an integration period prior to their onset. During this time interval, an increase in the number of excitatory postsynaptic potentials (EPSPs) takes place building up full synchronization between cells. These EPSPs are correlated with individual action potentials simultaneously occurring in neighboring cells. We have used EPSP frequency as an indicator of the neuronal activity underlying GDP generation. By comparing EPSP frequency with the occurrence of synchronized GDPs between CA3 and the fascia dentata (FD), we found that GDPs are fired in an all-or-none manner, which is characterized by a specific threshold of EPSP frequency from which synchronous GDPs emerge. In FD, the EPSP frequency-threshold for GDP onset is 17 Hz. GDPs are triggered similarly in CA3 by appropriate periodic stimulation of mossy fibers. The frequency threshold for CA3 GDP onset is 12 Hz. These findings clarify the local mechanism of synchronization underlying bursting in the developing hippocampus, indicating that GDPs are fired when background levels of EPSPs or action potentials have built up full synchronization by firing at specific frequencies (>12 Hz). Our results also demonstrate that spontaneous EPSPs and action potentials are important for the initiation of synchronous bursts in the
DEFF Research Database (Denmark)
Yoon, Gil Ho; Park, Y.K.; Kim, Y.Y.
2007-01-01
A new topology optimization scheme, called the element stacking method, is developed to better handle design optimization involving material-dependent boundary conditions and selection of elements of different types. If these problems are solved by existing standard approaches, complicated finite...... element models or topology optimization reformulation may be necessary. The key idea of the proposed method is to stack multiple elements on the same discretization pixel and select a single or no element. In this method, stacked elements on the same pixel have the same coordinates but may have...
Rupture and frequency-dependent seismic radiation of the 2012 Mw 8.6 Sumatra strike-slip earthquake
Yin, Jiuxun; Yao, Huajian
2016-06-01
On 2012 April 11, a great strike-slip earthquake (moment magnitude of Mw 8.6) occurred off the west coast of northern Sumatra area followed by an Mw 8.2 aftershock 2 hr later. Different geophysical data and methods have been used to investigate the mechanism, faulting, seismic radiation and slip propagation of this event, but frequency-dependent features of its rupture process have not been discussed much. In this study, we use a compressive sensing method based on sparsity inversion in the frequency domain to study the frequency-dependent seismic radiation and rupture process of this event. Our results indicate a very complex rupture process concerning at least three different rupture stages on multiple subfaults with nearly conjugate geometries. The main shock has triggered seismicity on a series of ridge-perpendicular or ridge-parallel conjugate strike-slip faults around the Nighty East Ridge. Obvious frequency-dependent rupture process has been presented and discussed. Combining results from slip inversion based on the finite-fault model, we observe that in the beginning stage of the rupture lower frequency radiation appears to originate from the areas with large slip, while the high-frequency radiation is located at the boundary of large-slip region or rupture front. Some radiation probably originates from the repeating slip on the main faults or triggered events on some nearby faults in the rupture area. The complex frequency-dependent seismic radiation patterns observed in this study provide important information for future investigation of rupture physics of this complex strike-slip event.
Frequency Dependent Harmonic Powers in a Modified Uni-Traveling Carrier (MUTC) Photodetector
2017-01-27
Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/5651--17-9712 Frequency Dependent Harmonic Powers in a Modified Uni-Traveling Carrier...TELEPHONE NUMBER (include area code) b. ABSTRACT c. THIS PAGE 18. NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Frequency Dependent Harmonic Powers in a...N. Hutchinson (202) 767-9549 Fiber optics Analog photonics We use a drift-diffusion model to study frequency dependent harmonic powers in a
Frequency dependence of orthogonal polarisation modes in pulsars
Smits, J.M.; Stappers, B.W.; Edwards, R.T.; Kuijpers, J.; Ramachandran, R.
2006-01-01
We have carried out a study of the orthogonal polarisation mode behaviour as afunction of frequency of 18pulsars, using average pulsar data from the European Pulsar Network(EPN). Assuming that the radiation consists of two100% polarised completely orthogonal superposed modes we separated these
Neuron firing frequency dependence on the static magnetic field intensity
Azanza, M. J.; del Moral, A.
1995-02-01
The effects of static magnetic field (SMF) of B intensity ( B = 0.003-0.72 T) on neurons are studied. The firing frequency f decreases exponentially with B2 and a threshold field B0 (≈ 0.57 T), where f abruptly drops to zero, is observed. A suitable model is developed where SMF's liberate membrane bounded Ca 2+ ions.
Sütterlin, R; Priori, R; Larsson, A; LoMauro, A; Frykholm, P; Aliverti, A
2014-01-01
Superimposed high-frequency jet ventilation (SHFJV) has proved to be safe and effective in clinical practice. However, it is unclear which frequency range optimizes ventilation and gas exchange. The aim of this study was to systematically compare high-frequency jet ventilation (HFJV) with HFJV by assessing chest wall volume variations (ΔEEV(CW)) and gas exchange in relation to variable high frequency. SHFJV or HFJV were used alternatively to ventilate the lungs of 10 anaesthetized pigs (21-25 kg). The low-frequency component was kept at 16 min(-1) in SHFJV. In both modes, high frequencies ranging from 100 to 1000 min(-1) were applied in random order and ventilation was maintained for 5 min in all modalities. Chest wall volume variations were obtained using opto-electronic plethysmography. Airway pressures and arterial blood gases were measured repeatedly. SHFJV increased ΔEEV(CW) compared with HFJV; the difference ranged from 43 to 68 ml. Tidal volume (V(T)) was always >240 ml during SHFJV whereas during HFJV ranged from 92 ml at the ventilation frequency of 100 min(-1) to negligible values at frequencies >300 min(-1). We observed similar patterns for Pa(O₂) and Pa(CO₂). SHFJV provided generally higher, frequency-independent oxygenation (Pa(O₂) at least 32.0 kPa) and CO₂ removal (Pa(CO₂) ∼5.5 kPa), whereas HFJV led to hypoxia and hypercarbia at higher rates (Pa(O₂) 10 kPa at f(HF)>300 min(-1)). In a porcine model, SHFJV was more effective in increasing end-expiratory volume than single-frequency HFJV, but both modes may provide adequate ventilation in the absence of airway obstruction and respiratory disease, except for HFJV at frequencies ≥300 min(-1).
Cue-dependency and Frequency Effects: Evidence from Chinese
Institute of Scientific and Technical Information of China (English)
Gao Dingguo; Yang Zhiliang
2005-01-01
The present study disclosed that a) prime stimuli had a significant effect on the object in implicit tests, but not in the explicit condition, and b) greater priming occurred when the study and test fonts coincided than whey they differeds, Moreover,the performance in implicit memory tests was more impaired by a shift from official to printed fonts than by a shift in the reverse direction. In addition, the results also revealed that low frequency materials produced more priming than did high frequency materials in implicit memory tests, but less effect of this variable on priming in explicit memory tests could be obtained with the same target characters. The above results implied that a transfer appropriate processing approach suggested by Roediger, Weldon and Challis (1989) is more acceptable to interpret the dissociation between implicit and explicit memory. The authors also critically commented on the implicit memory tests of Chinese widely used by researchers.
Frequency Dependence of Damping and Compliance in Loudspeaker Suspensions
DEFF Research Database (Denmark)
Thorborg, Knud; Tinggaard, Carsten; Agerkvist, Finn T.
2010-01-01
textiles used for spiders - have more or less visco-elastic properties; best known is the “creep” effect. This phenomenon in itself is normally of little interest in the audio frequency range. It is mainly a DC phenomenon. As such it manifests itself when a static (DC) force probes the speaker voice coil...... resonances, but less used in high quality loudspeakers today – where “Low Loss Rubber Surround” is currently seen as a marketing feature, as it is expected to have positive impact on sound quality. The plasticized type of surround shows significant creep, followed by compliance and damping increasing towards...... lower frequencies. The LOG-model is found to give good agreement with measurements, also for loudspeakers with low loss surrounds. However, it is not supported by a theory explaining visco-elastic properties in a physical way. Surrounds today are mostly made from SBR rubber for which...
Context specificity of conflict frequency-dependent control.
Vietze, Ina; Wendt, Mike
2009-07-01
Interference in the Eriksen flanker task has been shown to be reduced when the (relative) frequency of conflicting stimuli is increased, a modulation thought to reflect a higher degree of processing selectivity under conditions of frequent conflict (Botvinick, Braver, Barch, Carter, & Cohen, 2001). Previous studies suggest that stimulus location acts as a contextual cue, resulting in location-specific adjustment of processing selectivity when different locations are associated with differential conflict frequencies (Corballis & Gratton, 2003; Wendt, Kluwe, & Vietze, 2008). In the current study we extend these findings by showing that not only stimulus location but also stimulus colour can be used for context-specific adjustments. These findings suggest that processing selectivity is adjusted in parallel with current stimulus processing, potentially serving to resolve a current conflict rather than to prepare for an upcoming new conflict.
Kim, Dong-Hyun; Chauhan, Munish; Kim, Min-Oh; Jeong, Woo Chul; Kim, Hyung Joong; Sersa, Igor; Kwon, Oh In; Woo, Eung Je
2015-02-01
Electrical conductivities of biological tissues show frequency-dependent behaviors, and these values at different frequencies may provide clinically useful diagnostic information. MR-based tissue property mapping techniques such as magnetic resonance electrical impedance tomography (MREIT) and magnetic resonance electrical property tomography (MREPT) are widely used and provide unique conductivity contrast information over different frequency ranges. Recently, a new method for data acquisition and reconstruction for low- and high-frequency conductivity images from a single MR scan was proposed. In this study, we applied this simultaneous dual-frequency range conductivity mapping MR method to evaluate its utility in a designed phantom and two in vivo animal disease models. Magnetic flux density and B(1)(+) phase map for dual-frequency conductivity images were acquired using a modified spin-echo pulse sequence. Low-frequency conductivity was reconstructed from MREIT data by the projected current density method, while high-frequency conductivity was reconstructed from MREPT data by B(1)(+) mapping. Two different conductivity phantoms comprising varying ion concentrations separated by insulating films with or without holes were used to study the contrast mechanism of the frequency-dependent conductivities related to ion concentration and mobility. Canine brain abscess and ischemia were used as in vivo models to evaluate the capability of the proposed method to identify new electrical properties-based contrast at two different frequencies. The simultaneous dual-frequency range conductivity mapping MR method provides unique contrast information related to the concentration and mobility of ions inside tissues. This method has potential to monitor dynamic changes of the state of disease.
Photonic band gap enhancement in frequency-dependent dielectrics.
Toader, Ovidiu; John, Sajeev
2004-10-01
We illustrate a general technique for evaluating photonic band structures in periodic d -dimensional microstructures in which the dielectric constant epsilon (omega) exhibits rapid variations with frequency omega . This technique involves the evaluation of generalized electromagnetic dispersion surfaces omega ( k--> ,epsilon) in a (d+1) -dimensional space consisting of the physical d -dimensional space of wave vectors k--> and an additional dimension defined by the continuous, independent, variable epsilon . The physical band structure for the photonic crystal is obtained by evaluating the intersection of the generalized dispersion surfaces with the "cutting surface" defined by the function epsilon (omega) . We apply this method to evaluate the band structure of both two- and three-dimensional (3D) periodic microstructures. We consider metallic photonic crystals with free carriers described by a simple Drude conductivity and verify the occurrence of electromagnetic pass bands below the plasma frequency of the bulk metal. We also evaluate the shift of the photonic band structure caused by free carrier injection into semiconductor-based photonic crystals. We apply our method to two models in which epsilon (omega) describes a resonant radiation-matter interaction. In the first model, we consider the addition of independent, resonant oscillators to a photonic crystal with an otherwise frequency-independent dielectric constant. We demonstrate that for an inhomogeneously broadened distribution of resonators impregnated within an inverse opal structure, the full 3D photonic band gap (PBG) can be considerably enhanced. In the second model, we consider a coupled resonant oscillator mode in a photonic crystal. When this mode is an optical phonon, there can be a synergetic interplay between the polaritonic resonance and the geometrical scattering resonances of the structured dielectric, leading to PBG enhancement. A similar effect may arise when resonant atoms that are
Frequency-dependent optical steering from subwavelength plasmonic structures.
Djalalian-Assl, A; Gómez, D E; Roberts, A; Davis, T J
2012-10-15
We show theoretically and with numerical simulations that the direction of the in-plane scattering from a subwavelength optical antenna system can be controlled by the frequency of the incident light. This optical steering effect does not rely on propagation phase shifts or diffraction but arises from phase shifts in the localized surface plasmon modes of the antenna. An analytical model is developed to optimize the parameters for the configuration, showing good agreement with a rigorous numerical simulation. The simulation predicts a 25° angular shift in the direction of the light scattered from two gold nanorods for a wavelength change of 12 nm.
Jackson, M B; Konnerth, A; Augustine, G J
1991-01-15
Hormone release from nerve terminals in the neurohypophysis is a sensitive function of action potential frequency. We have investigated the cellular mechanisms responsible for this frequency-dependent facilitation by combining patch clamp and fluorimetric Ca2+ measurements in single neurosecretory terminals in thin slices of the rat posterior pituitary. In these terminals both action potential-induced changes in the intracellular Ca2+ concentration ([Ca2+]i) and action potential duration were enhanced by high-frequency stimuli, all with a frequency dependence similar to that of hormone release. Furthermore, brief voltage clamp pulses inactivated a K+ current with a very similar frequency dependence. These results support a model for frequency-dependent facilitation in which the inactivation of a K+ current broadens action potentials, leading to an enhancement of [Ca2+]i signals. Further experiments tested for a causal relationship between action potential broadening and facilitation of [Ca2+]i changes. First, increasing the duration of depolarization, either by broadening action potentials with the K(+)-channel blocker tetraethylammonium or by applying longer depolarizing voltage clamp steps, increased [Ca2+]i changes. Second, eliminating frequency-dependent changes in duration, by voltage clamping the terminal with constant duration pulses, substantially reduced the frequency-dependent enhancement of [Ca2+]i changes. These results indicate that action potential broadening contributes to frequency-dependent facilitation of [Ca2+]i changes. However, the small residual frequency dependence of [Ca2+]i changes seen with constant duration stimulation suggests that a second process, distinct from action potential broadening, also contributes to facilitation. These two frequency-dependent mechanisms may also contribute to activity-dependent plasticity in synaptic terminals.
Temperature Dependence of Biological Tissues Complex Permitivity at Microwave Frequencies
Directory of Open Access Journals (Sweden)
Dagmar Faktorova
2008-01-01
Full Text Available In the paper an universal overview of polarizing mechanisms with an emphasis on dipolar materials as the investigated tissues are regarded. Experimental apparatus is presented with giving its specificity as well as the method used at calculation of complex permittivity. The experimental part is aimed at temperature dependence of complex permittivity measurement of pig biological tissues with different properties. Experimental results are presented graphically with the commentary for courses of particular tissues.
Temperature Dependence of Biological Tissues Complex Permitivity at Microwave Frequencies
Dagmar Faktorova
2008-01-01
In the paper an universal overview of polarizing mechanisms with an emphasis on dipolar materials as the investigated tissues are regarded. Experimental apparatus is presented with giving its specificity as well as the method used at calculation of complex permittivity. The experimental part is aimed at temperature dependence of complex permittivity measurement of pig biological tissues with different properties. Experimental results are presented graphically with the commentary for courses o...
Temperature dependence of the Raman-active phonon frequencies in indium sulfide
Gasanly, N. M.; Özkan, H.; Aydinli, A.; Yilmaz, İ.
1999-03-01
The temperature dependence of the Raman-active mode frequencies in indium sulfide was measured in the range from 10 to 300 K. The analysis of the temperature dependence of the A g intralayer optical modes show that Raman frequency shift results from the change of harmonic frequency with volume expansion and anharmonic coupling to phonons of other branches. The pure-temperature contribution (phonon-phonon coupling) is due to three- and four-phonon processes.
Energy Technology Data Exchange (ETDEWEB)
Hebner, Gregory A [Sandia National Laboratories, Albuquerque NM 87185-1423 (United States); Barnat, Edward V [Sandia National Laboratories, Albuquerque NM 87185-1423 (United States); Miller, Paul A [Sandia National Laboratories, Albuquerque NM 87185-1423 (United States); Paterson, Alex M [Applied Materials, 974 Arques Avenue, Sunnyvale CA, 94086 (United States); Holland, John P [Applied Materials, 974 Arques Avenue, Sunnyvale CA, 94086 (United States)
2006-11-01
Argon plasma characteristics in a dual-frequency, capacitively coupled, 300 mm-wafer plasma processing system were investigated for rf drive frequencies between 10 and 190 MHz. We report spatial and frequency dependent changes in plasma parameters such as line-integrated electron density, ion saturation current, optical emission and argon metastable density. For the conditions investigated, the line-integrated electron density was a nonlinear function of drive frequency at constant rf power. In addition, the spatial distribution of the positive ions changed from uniform to peaked in the centre as the frequency was increased. Spatially resolved optical emission increased with frequency and the relative optical emission at several spectral lines depended on frequency. Argon metastable density and spatial distribution were not a strong function of drive frequency. Metastable temperature was approximately 400 K.
Maassen, Jesse; Lundstrom, Mark
2016-03-01
Understanding ballistic phonon transport effects in transient thermoreflectance experiments and explaining the observed deviations from classical theory remains a challenge. Diffusion equations are simple and computationally efficient but are widely believed to break down when the characteristic length scale is similar or less than the phonon mean-free-path. Building on our prior work, we demonstrate how well-known diffusion equations, namely, the hyperbolic heat equation and the Cattaneo equation, can be used to model ballistic phonon effects in frequency-dependent periodic steady-state thermal transport. Our analytical solutions are found to compare excellently to rigorous numerical results of the phonon Boltzmann transport equation. The correct physical boundary conditions can be different from those traditionally used and are paramount for accurately capturing ballistic effects. To illustrate the technique, we consider a simple model problem using two different, commonly used heating conditions. We demonstrate how this framework can easily handle detailed material properties, by considering the case of bulk silicon using a full phonon dispersion and mean-free-path distribution. This physically transparent approach provides clear insights into the nonequilibrium physics of quasi-ballistic phonon transport and its impact on thermal transport properties.
Directory of Open Access Journals (Sweden)
Xiao eLin
2015-09-01
Full Text Available Neuroimaging studies have revealed that the task-related functional brain activities are impaired in Internet gaming disorder (IGD subjects. However, little is known about the alternations in spontaneous brain activities about them. Recent studies have proposed that the brain activities of different frequency ranges are generated by different nervous activities and have different physiological and psychological functions. Thus, in this study, we set to explore the spontaneous brain activities in IGD subjects by measuring the fractional amplitude of low-frequency fluctuation (fALFF, to investigate band-specific changes of resting-state fALFF. We subdivided the frequency range into five bands based on literatures. Comparing to healthy controls, the IGD group showed decreased fALFF values in the cerebellum posterior lobe and increased fALFF values in superior temporal gyrus. Significant interactions between frequency bands and groups were found in the cerebellum, the anterior cingulate, the lingual gyrus, the middle temporal gyrus and the middle frontal gyrus. Those brain regions are proved related to the executive function and decision-making. These results revealed the changed spontaneous brain activity of IGD, which contributed to understanding the underlying pathophysiology of IGD.
Zhan, Yihong; Cao, Zhenning; Bao, Ning; Li, Jianbo; Wang, Jun; Geng, Tao; Lin, Hao; Lu, Chang
2012-06-28
Conventional electroporation has been conducted by employing short direct current (dc) pulses for delivery of macromolecules such as DNA into cells. The use of alternating current (ac) field for electroporation has mostly been explored in the frequency range of 10kHz-1MHz. Based on Schwan equation, it was thought that with low ac frequencies (10Hz-10kHz), the transmembrane potential does not vary with the frequency. In this report, we utilized a flow-through electroporation technique that employed continuous 10Hz-10kHz ac field (based on either sine waves or square waves) for electroporation of cells with defined duration and intensity. Our results reveal that electropermeabilization becomes weaker with increased frequency in this range. In contrast, transfection efficiency with DNA reaches its maximum at medium frequencies (100-1000Hz) in the range. We postulate that the relationship between the transfection efficiency and the ac frequency is determined by combined effects from electrophoretic movement of DNA in the ac field, dependence of the DNA/membrane interaction on the ac frequency, and variation of transfection under different electropermeabilization intensities. The fact that ac electroporation in this frequency range yields high efficiency for transfection (up to ~71% for Chinese hamster ovary cells) and permeabilization suggests its potential for gene delivery.
Boundary-Dependent Chaotic Regions for a Bose-Einstein Condensate Interacting with Laser Field
Institute of Scientific and Technical Information of China (English)
ZHU Qian-Quan; HAI Wen-Hua; DENG Hai-Ming
2007-01-01
Spatial chaos of a Bose-Einstein condensate perturbed by a weak laser standing wave and a weak laser S pulse is studied. By using the perturbed chaotic solution we investigate the new type of Melnikov chaotic regions, which depend on an integration constant CQ determined by the boundary conditions. It is shown that when the |c0| values are small, the chaotic region corresponds to small values of laser wave vector k, and the chaotic region for the larger k values is related to the large |c0| values. The result is confirmed numerically by finding the chaotic and regular orbits on the Poincaré section for the two different parameter regions. Thus, for a fixed c0 the adjustment of k from a small value to large value can transform the chaotic region into the regular one or on the contrary, which suggests a feasible method for eliminating or generating Melnikov chaos.
Strings on a Violin: Location Dependence of Frequency Tuning in Active Dendrites
Das, Anindita; Rathour, Rahul K.; Narayanan, Rishikesh
2017-01-01
Strings on a violin are tuned to generate distinct sound frequencies in a manner that is firmly dependent on finger location along the fingerboard. Sound frequencies emerging from different violins could be very different based on their architecture, the nature of strings and their tuning. Analogously, active neuronal dendrites, dendrites endowed with active channel conductances, are tuned to distinct input frequencies in a manner that is dependent on the dendritic location of the synaptic inputs. Further, disparate channel expression profiles and differences in morphological characteristics could result in dendrites on different neurons of the same subtype tuned to distinct frequency ranges. Alternately, similar location-dependence along dendritic structures could be achieved through disparate combinations of channel profiles and morphological characteristics, leading to degeneracy in active dendritic spectral tuning. Akin to strings on a violin being tuned to different frequencies than those on a viola or a cello, different neuronal subtypes exhibit distinct channel profiles and disparate morphological characteristics endowing each neuronal subtype with unique location-dependent frequency selectivity. Finally, similar to the tunability of musical instruments to elicit distinct location-dependent sounds, neuronal frequency selectivity and its location-dependence are tunable through activity-dependent plasticity of ion channels and morphology. In this morceau, we explore the origins of neuronal frequency selectivity, and survey the literature on the mechanisms behind the emergence of location-dependence in distinct forms of frequency tuning. As a coda to this composition, we present some future directions for this exciting convergence of biophysical mechanisms that endow a neuron with frequency multiplexing capabilities.
Di Lillo, Luigi; Bergamini, Andrea; Albino Carnelli, Dario; Ermanni, Paolo
2012-07-01
A physical model for the frequency-dependent dielectric response of multilayered structures is reported. Two frequency regimes defined by the relative permittivities and volume resistivities of the layers have been analytically identified and experimentally investigated on a structure consisting of polyimide and poly(vinilydenefluoride) layers. The relative permittivity follows an effective medium model at high frequency while showing a dependence on the volume resistivity at low frequency. In this regime, relative permittivities exceeding those expected from effective medium model are recorded. These findings provide insights into inhomogeneous dielectrics behavior for the development of high energy density dielectric films.
Methylammonium lead iodide grain boundaries exhibit depth-dependent electrical properties
Energy Technology Data Exchange (ETDEWEB)
MacDonald, Gordon A.; Yang, Mengjin; Berweger, Samuel; Killgore, Jason P.; Kabos, Pavel; Berry, Joseph J.; Zhu, Kai; DelRio, Frank W.
2016-01-01
In this communication, the nanoscale through-film and lateral photo-response and conductivity of large-grained methylammonium lead iodide (MAPbI3) thin films are studied. In perovskite solar cells (PSC), these films result in efficiencies >17%. The grain boundaries (GBs) show high resistance at the top surface of the film, and act as an impediment to photocurrent collection. However, lower resistance pathways between grains exist below the top surface of the film, indicating that there exists a depth-dependent resistance of GBs (RGB(z)). Furthermore, lateral conductivity measurements indicate that RGB(z) exhibits GB-to-GB heterogeneity. These results indicate that increased photocurrent collection along GBs is not a prerequisite for high-efficiency PSCs. Rather, better control of depth-dependent GB electrical properties, and an improvement in the homogeneity of the GB-to-GB electrical properties, must be managed to enable further improvements in PSC efficiency. Finally, these results refute the implicit assumption seen in the literature that the electrical properties of GBs, as measured at the top surface of the perovskite film, necessarily reflect the electrical properties of GBs within the thickness of the film.
Vacuum Energy and Casimir Force in a Presence of Skin-depth Dependent Boundary Condition
Lebedev, S L
2001-01-01
The vacuum energy-momentum tensor (EMT) and the vacuum energy corresponding to massive scalar field on $\\Re_{t}\\times [0,l] \\times \\Re^{D-2}$ space-time with boundary condition involving a dimensional parameter ($\\delta$) are found. The dependent on the cavity size $l$ Casimir energy $\\wt E_{C}$ is a uniquely determinable function of mass $m$, size $l$ and "skin-depth" $\\delta$. This energy includes the "bulk" and the surface (potential energy) contributions. The latter dominates when $l \\sim \\delta$. Taking the surface potential energy into account is crucial for the coincidence between the derivative $-\\d \\wt E_{C}/\\d l$ and the $ll$-component of the vacuum EMT. Casimir energy $\\wt E_C$ and the bulk contribution to it are interconnected through Legendre transformation, in which the quantity $\\delta^{-1}$ is conjugate to the vacuum surface energy multiplied by $\\delta$. The surface singularities of the vacuum EMT do not depend on $l$ and, for even $D$, $\\delta =0$ or $\\infty$, possess finite interpretation. ...
Martirosyan, Varsik; Baghdasaryan, Naira; Ayrapetyan, Sinerik
2013-09-01
In the present work, the frequency-dependent effects of extremely low-frequency electromagnetic field (ELF EMF) on Escherichia coli K-12 growth have been studied. The frequency-dependent effects of ELF EMF have shown that it can either stimulate or inhibit the growth of microbes. However, the mechanism by which the ELF EMF affects the bacterial cells is not clear yet. It was suggested that the aqua medium can serve as a target through which the biological effect of ELF EMF on microbes may be realized. To check this hypothesis, the frequency-dependent effects (2, 4, 6, 8, 10 Hz, B = 0.4 mT, 30 min) of ELF EMF on the bacterial growth were studied in both cases where the microbes were in the culture media during the exposure and where culture media was preliminarily exposed to the ELF EMF before the addition of bacteria. For investigating the cell proliferation, the radioactive [(3)H]-thymidine assay was carried out. It has been shown that EMF at 4 Hz exposure has pronounced stimulation while at 8 Hz it has inhibited cell proliferation.
Zhang, Jun-Hua; Li, Jun; Xiao, Wen; Tan, Ming-You; Zhang, Yun-Ying; Cui, Shi-Ling; Qu, Zhi-Peng
2016-06-01
The phase velocity of seismic waves varies with the propagation frequency, and thus frequency-dependent phenomena appear when CO2 gas is injected into a reservoir. By dynamically considering these phenomena with reservoir conditions it is thus feasible to extract the frequency-dependent velocity factor with the aim of monitoring changes in the reservoir both before and after CO2 injection. In the paper, we derive a quantitative expression for the frequency-dependent factor based on the Robinson seismic convolution model. In addition, an inversion equation with a frequency-dependent velocity factor is constructed, and a procedure is implemented using the following four processing steps: decomposition of the spectrum by generalized S transform, wavelet extraction of cross-well seismic traces, spectrum equalization processing, and an extraction method for frequency-dependent velocity factor based on the damped least-square algorithm. An attenuation layered model is then established based on changes in the Q value of the viscoelastic medium, and spectra of migration profiles from forward modeling are obtained and analyzed. Frequency-dependent factors are extracted and compared, and the effectiveness of the method is then verified using a synthetic data. The frequency-dependent velocity factor is finally applied to target processing and oil displacement monitoring based on real seismic data obtained before and after CO2 injection in the G89 well block within Shengli oilfield. Profiles and slices of the frequency-dependent factor determine its ability to indicate differences in CO2 flooding, and the predicting results are highly consistent with those of practical investigations within the well block.
Tracey, Brian; Williams, Michael
2011-06-01
Standard bioelectric field models assume that the tissue is purely resistive and frequency independent, and that capacitance, induction, and propagation effects can be neglected. However, real tissue properties are frequency dependent, and tissue capacitance can be important for problems involving short stimulation pulses. A straightforward interpolation scheme is introduced here that can account for frequency-dependent effects, while reducing runtime over a direct computation by several orders of magnitude. The exact Helmholtz solution is compared to several approximate field solutions and is used to study neural stimulation. Results show that frequency-independent tissue capacitance always acts to attenuate the stimulation pulse, thereby increasing firing thresholds, while the dispersion effects introduced by frequency-dependent capacitance may decrease firing thresholds.
Stoeckel, Solenn; Klein, Etienne K; Oddou-Muratorio, Sylvie; Musch, Brigitte; Mariette, Stéphanie
2012-02-01
Negative frequency dependent selection (NFDS) is supposed to be the main force controlling allele evolution at the gametophytic self-incompatibility locus (S-locus) in strictly outcrossing species. Genetic drift also influences S-allele evolution. In perennial sessile organisms, evolution of allelic frequencies over two generations is mainly shaped by individual fecundities and spatial processes. Using wild cherry populations between two successive generations, we tested whether S-alleles evolved following NFDS qualitative and quantitative predictions. We showed that allelic variation was negatively correlated with parental allelic frequency as expected under NFDS. However, NFDS predictions in finite population failed to predict more than half S-allele quantitative evolution. We developed a spatially explicit mating model that included the S-locus. We studied the effects of self-incompatibility and local drift within populations due to pollen dispersal in spatially distributed individuals, and variation in male fecundity on male mating success and allelic frequency evolution. Male mating success was negatively related to male allelic frequency as expected under NFDS. Spatial genetic structure combined with self-incompatibility resulted in higher effective pollen dispersal. Limited pollen dispersal in structured distributions of individuals and genotypes and unequal pollen production significantly contributed to S-allele frequency evolution by creating local drift effects strong enough to counteract the NFDS effect on some alleles.
Caplan, R M
2011-01-01
An easy to implement modulus-squared Dirichlet (MSD) boundary condition is formulated for numerical simulations of time-dependent complex partial differential equations in multidimensional settings. The MSD boundary condition approximates a constant modulus-square value of the solution at the boundaries. Application of the MSD boundary condition to the nonlinear Schr\\"odinger equation is shown, and numerical simulations are performed to demonstrate its usefulness and advantages over other simple boundary conditions.
Sun, Wenjun; Jiang, Song; Xu, Kun; Li, Shu
2015-12-01
This paper presents an extension of previous work (Sun et al., 2015 [22]) of the unified gas kinetic scheme (UGKS) for the gray radiative transfer equations to the frequency-dependent (multi-group) radiative transfer system. Different from the gray radiative transfer equations, where the optical opacity is only a function of local material temperature, the simulation of frequency-dependent radiative transfer is associated with additional difficulties from the frequency-dependent opacity. For the multiple frequency radiation, the opacity depends on both the spatial location and the frequency. For example, the opacity is typically a decreasing function of frequency. At the same spatial region the transport physics can be optically thick for the low frequency photons, and optically thin for high frequency ones. Therefore, the optical thickness is not a simple function of space location. In this paper, the UGKS for frequency-dependent radiative system is developed. The UGKS is a finite volume method and the transport physics is modeled according to the ratio of the cell size to the photon's frequency-dependent mean free path. When the cell size is much larger than the photon's mean free path, a diffusion solution for such a frequency radiation will be obtained. On the other hand, when the cell size is much smaller than the photon's mean free path, a free transport mechanism will be recovered. In the regime between the above two limits, with the variation of the ratio between the local cell size and photon's mean free path, the UGKS provides a smooth transition in the physical and frequency space to capture the corresponding transport physics accurately. The seemingly straightforward extension of the UGKS from the gray to multiple frequency radiation system is due to its intrinsic consistent multiple scale transport modeling, but it still involves lots of work to properly discretize the multiple groups in order to design an asymptotic preserving (AP) scheme in all
Boundary implications for frequency response of interval FIR and IIR filters
Bose, N. K.; Kim, K. D.
1991-01-01
It is shown that vertex implication results in parameter space apply to interval trigonometric polynomials. Subsequently, it is shown that the frequency responses of both interval FIR and IIR filters are bounded by the frequency responses of certain extreme filters. The results apply directly in the evaluation of properties of designed filters, especially because it is more realistic to bound the filter coefficients from above and below instead of determining those with infinite precision because of finite arithmetic effects. Illustrative examples are provided to show how the extreme filters might be easily derived in any specific interval FIR or IIR filter design problem.
The long-term evolution of multilocus traits under frequency-dependent disruptive selection
Van Doorn, G. Sander; Dieckmann, Ulf
2006-01-01
Frequency-dependent disruptive selection is widely recognized as an important source of genetic variation. Its evolutionary consequences have been extensively studied using phenotypic evolutionary models, based on quantitative genetics, game theory, or adaptive dynamics. However, the genetic
Smalø, Hans S.; Åstrand, Per-Olof; Mayer, Alexandre
2013-07-01
A molecular mechanics model for the frequency-dependent polarisability is presented. It is a combination of a recent model for the frequency dependence in a charge-dipole model [Nanotechnology 19, 025203, 2008] and a nonmetallic modification of the electronegativity equalisation model rephrased as atom-atom charge-transfer terms [J. Chem. Phys. 131, 044101, 2009]. An accurate model for the frequency-dependent polarisability requires a more accurate partitioning into charge and dipole contributions than the static polarisability, which has resulted in several modifications of the charge-transfer model. Results are presented for hydrocarbons, including among others, alkanes, polyenes and aromatic systems. Although their responses to an electric field are quite different in terms of the importance of charge-transfer contributions, it is demonstrated that their frequency-dependent polarisabilities can be described with the same model and the same set of atom-type parameters.
Strongly Frequency-dependent Photoinduced Magnetic Disaccommodation in YIG: 0.001 Ca
Institute of Scientific and Technical Information of China (English)
2000-01-01
By measuring frequency dependence of photoinduced double peaks of disaccommodation, DA as a function of temperature was observed at very Iow frequency: 0.07～0.30 kHz, in a single crystal of yttrium iron garnet, YIG with small amounts of Ca: 0.001, while only single peak existed at the higher frequency 0.5 kHz. The behavior is explained based on theoretical approach on a domain wall dynamics.
Energy Technology Data Exchange (ETDEWEB)
Liu, Han-Chun; Ye, Tianyu; Mani, R. G. [Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States); Wegscheider, W. [Laboratorium für Festkörperphysik, ETH Zürich, CH-8093 Zürich (Switzerland)
2015-02-14
Linear polarization angle, θ, dependent measurements of the microwave radiation-induced oscillatory magnetoresistance, R{sub xx}, in high mobility GaAs/AlGaAs 2D electron devices have shown a θ dependence in the oscillatory amplitude along with magnetic field, frequency, and extrema-dependent phase shifts, θ{sub 0}. Here, we suggest a microwave frequency dependence of θ{sub 0}(f) using an analysis that averages over other smaller contributions, when those contributions are smaller than estimates of the experimental uncertainty.
Frequency-dependent moment release of very low frequency earthquakes in the Cascadia subduction zone
Takeo, A.; Houston, H.
2014-12-01
Episodic tremor and slip (ETS) has been observed in Cascadia subduction zone at two different time scales: tremor at a high-frequency range of 2-8 Hz and slow slip events at a geodetic time-scale of days-months. The intermediate time scale is needed to understand the source spectrum of slow earthquakes. Ghosh et al. (2014, IRIS abs) recently reported the presence of very low frequency earthquakes (VLFEs) in Cascadia. In southwest Japan, VLFEs are usually observed at a period range around 20-50 s, and coincide with tremors (e.g., Ito et al. 2007). In this study, we analyzed VLFEs in and around the Olympic Peninsula to confirm their presence and estimate their moment release. We first detected VLFE events by using broadband seismograms with a band-pass filter of 20-50 s. The preliminary result shows that there are at least 16 VLFE events with moment magnitudes of 3.2-3.7 during the M6.8 2010 ETS. The focal mechanisms are consistent with the thrust earthquakes at the subducting plate interface. To detect signals of VLFEs below noise level, we further stacked long-period waveforms at the peak timings of tremor amplitudes for tremors within a 10-15 km radius by using tremor catalogs in 2006-2010, and estimated the focal mechanisms for each tremor source region as done in southwest Japan (Takeo et al. 2010 GRL). As a result, VLFEs could be detected for almost the entire tremor source region at a period range of 20-50 s with average moment magnitudes in each 5-min tremor window of 2.4-2.8. Although the region is limited, we could also detect VLFEs at a period range of 50-100 s with average moment magnitudes of 3.0-3.2. The moment release at 50-100 s is 4-8 times larger than that at 20-50 s, roughly consistent with an omega-squared spectral model. Further study including tremor, slow slip events and characteristic activities, such as rapid tremor reversal and tremor streaks, will reveal the source spectrum of slow earthquakes in a broader time scale from 0.1 s to days.
A trapped ion with time-dependent frequency interaction with a laser field
Energy Technology Data Exchange (ETDEWEB)
MartInez, J M Vargas; Moya-Cessa, H [INAOE, Apartado Postal 51 y 216, 72000 Puebla (Mexico)
2004-06-01
We analyse the problem of a trapped ion with time-dependent frequency interacting with a laser field. By using a set of unitary time-dependent transformations we show that this system is equivalent to the interaction between a quantized field and a double level with time-dependent interaction parameters. In passing, we show that in the on-resonance case different vibrational transitions may be achieved by using time-dependent parameters.
DEFF Research Database (Denmark)
Cardoso, J. F.; Delabrouille, J.; Ganga, K.;
2015-01-01
Planck has mapped the intensity and polarization of the sky at microwave frequencies with unprecedented sensitivity. We use these data to characterize the frequency dependence of dust emission. We make use of the Planck 353 GHz I, Q, and U Stokes maps as dust templates, and cross-correlate them w...
Directory of Open Access Journals (Sweden)
Raymond eVan De Berg
2015-01-01
Full Text Available The Vestibulo-Ocular Reflex (VOR shows frequency-dependent behavior. This study investigated whether the characteristics of the electrically evoked VOR (eVOR elicited by a vestibular implant, showed the same frequency-dependency.Twelve vestibular electrodes implanted in 7 patients with bilateral vestibular hypofunction were tested. Stimuli consisted of amplitude-modulated electrical stimulation with a sinusoidal profile at frequencies of 0.5Hz, 1Hz, and 2Hz. The main characteristics of the eVOR were evaluated and compared to the natural VOR characteristics measured in a group of age-matched healthy volunteers who were subjected to horizontal whole body rotations with equivalent sinusoidal velocity profiles at the same frequencies.A strong and significant effect of frequency was observed in the total peak eye velocity of the eVOR. This effect was similar to that observed in the natural VOR. Other characteristics of the (eVOR (angle, habituation-index, and asymmetry showed no significant frequency-dependent effect. In conclusion, this study demonstrates that, at least at the specific (limited frequency range tested, responses elicited by a vestibular implant closely mimic the frequency-dependency of the normal vestibular system.
van de Berg, Raymond; Guinand, Nils; Nguyen, T A Khoa; Ranieri, Maurizio; Cavuscens, Samuel; Guyot, Jean-Philippe; Stokroos, Robert; Kingma, Herman; Perez-Fornos, Angelica
2014-01-01
The vestibulo-ocular reflex (VOR) shows frequency-dependent behavior. This study investigated whether the characteristics of the electrically evoked VOR (eVOR) elicited by a vestibular implant, showed the same frequency-dependency. Twelve vestibular electrodes implanted in seven patients with bilateral vestibular hypofunction (BVH) were tested. Stimuli consisted of amplitude-modulated electrical stimulation with a sinusoidal profile at frequencies of 0.5, 1, and 2 Hz. The main characteristics of the eVOR were evaluated and compared to the "natural" VOR characteristics measured in a group of age-matched healthy volunteers who were subjected to horizontal whole body rotations with equivalent sinusoidal velocity profiles at the same frequencies. A strong and significant effect of frequency was observed in the total peak eye velocity of the eVOR. This effect was similar to that observed in the "natural" VOR. Other characteristics of the (e)VOR (angle, habituation-index, and asymmetry) showed no significant frequency-dependent effect. In conclusion, this study demonstrates that, at least at the specific (limited) frequency range tested, responses elicited by a vestibular implant closely mimic the frequency-dependency of the "normal" vestibular system.
DEFF Research Database (Denmark)
Cardoso, J. F.; Delabrouille, J.; Ganga, K.
2015-01-01
Planck has mapped the intensity and polarization of the sky at microwave frequencies with unprecedented sensitivity. We use these data to characterize the frequency dependence of dust emission. We make use of the Planck 353 GHz I, Q, and U Stokes maps as dust templates, and cross-correlate them...
Frequency dependence of the pump-to-signal RIN transfer in fiber optical parametric amplifiers
DEFF Research Database (Denmark)
Pakarzadeh Dezfuli Nezhad, Hassan; Rottwitt, Karsten; Zakery, A.
2009-01-01
Using a numerical model, the frequency dependence of the pump-to-signal RIN transfer in FOPAs has been investigated. The model includes fiber loss, pump depletion as well as difference in group velocity among interacting beams.......Using a numerical model, the frequency dependence of the pump-to-signal RIN transfer in FOPAs has been investigated. The model includes fiber loss, pump depletion as well as difference in group velocity among interacting beams....
Smith, E. F.; Macdonald, F. A.; Schrag, D. P.; Laakso, T.
2014-12-01
The GSSP Precambrian-Cambrian boundary in Newfoundland is defined by the first appearance datum (FAD) of Treptichnus pedum, which is considered to be roughly coincident with the FAD of small shelly fossils (SSFs) and a large negative carbon isotope excursion. An association between the FAD of T. pedum and a negative carbon isotope excursion has previously been documented in Northwest Canada (Narbonne et al., 1994) and Death Valley (Corsetti and Hagadorn, 2000), and since then has been used as an chronostratigraphic marker of the boundary, particularly in siliciclastic poor sections that do not preserve T. pedum. Here we present new high-resolution carbon isotope (δ13C ) chemostratigraphy from multiple sections in western Mongolia and the western United States that span the Ediacaran-Cambrian transition. High-resolution sampling (0.2-1 m) reveals that instead of one large negative excursion, there are multiple, high-frequency negative excursions with an overall negative trend during the latest Ediacaran. These data help to more precisely calibrate changes in the carbon cycle across the boundary as well as to highlight the potential problem of identifying the boundary with just a few negative δ13C values. We then use a simple carbon isotope box model to explore relationships between phosphorous delivery to the ocean, oxygenation, alkalinity, and turnovers in carbonate secreting organisms. Corsetti, F.A., and Hagadorn, J.W., 2000, Precambrian-Cambrian transition: Death Valley, United States: Geology, v. 28, no. 4, p. 299-302. Narbonne, G.M., Kaufman, A.J., and Knoll, A.H., 1994, Integrated chemostratigraphy and biostratigraphy of the Windermere Supergroup, northwestern Canada: Implications for Neoproterozoic correlations and the early evolution of animals: Geological Society of America Bulletin, v. 106, no. 10, p. 1281-1292.
Fujisaki, Jun; Furuya, Atsushi; Uehara, Yuji; Shimizu, Koichi; Ataka, Tadashi; Tanaka, Tomohiro; Oshima, Hirotaka; Ohkubo, Tadakatsu; Hirosawa, Satoshi; Hono, Kazuhiro
2016-05-01
This paper is focused on the micromagnetic simulation study about the orientation dependence of grain boundary properties on the coercivity of polycrystalline Nd-Fe-B sintered magnets. A multigrain object with a large number of meshes is introduced to analyze such anisotropic grain boundaries and the simulation is performed by combining the finite element method and the parallel computing. When the grain boundary phase parallel to the c-plane is less ferromagnetic the process of the magnetization reversal changes and the coercivity of the multigrain object increases. The simulations with various magnetic properties of the grain boundary phases are executed to search for the way to enhance the coercivity of polycrystalline Nd-Fe-B sintered magnets.
Sinex, Donal G
2013-04-01
Binary time-frequency (TF) masks can be applied to separate speech from noise. Previous studies have shown that with appropriate parameters, ideal TF masks can extract highly intelligible speech even at very low speech-to-noise ratios (SNRs). Two psychophysical experiments provided additional information about the dependence of intelligibility on the frequency resolution and threshold criteria that define the ideal TF mask. Listeners identified AzBio Sentences in noise, before and after application of TF masks. Masks generated with 8 or 16 frequency bands per octave supported nearly-perfect identification. Word recognition accuracy was slightly lower and more variable with 4 bands per octave. When TF masks were generated with a local threshold criterion of 0 dB SNR, the mean speech reception threshold was -9.5 dB SNR, compared to -5.7 dB for unprocessed sentences in noise. Speech reception thresholds decreased by about 1 dB per dB of additional decrease in the local threshold criterion. Information reported here about the dependence of speech intelligibility on frequency and level parameters has relevance for the development of non-ideal TF masks for clinical applications such as speech processing for hearing aids.
P300 ERP Component Depends on Both Spatial Frequency and Contrast
Directory of Open Access Journals (Sweden)
Li-Ting Tsai
2011-05-01
Full Text Available Contrast perception depends on not only the early visual responses, but also top-down modulations. We measured how does P300, a well-documented event-related potential (ERP index for top-down influence, change with both spatial frequency and contrast. ERP were acquired from 10 participants, aged 18–50 years, when they were performing a visual oddball task. The target was a Gabor patch whose spatial frequency was either 4 or 8 cy/degree and contrasts 90% or 30%. The probability of target presence in a trial was 30%. All target stimuli produced a reliable P300 component. At the low spatial frequency, the amplitude of P300 was larger and the latency was shorter for the low contrast patterns than for the higher contrast ones for all electrodes. Such difference was not observed in high spatial frequency patterns. The latency was slightly longer for high spatial frequency patterns than the low spatial frequency ones. Our results showed an interaction between spatial frequency and contrast in P300. The characteristics of P300 at low spatial frequency correlated with task difficulty, but not at high spatial frequency. This suggests that the top-down influence on contrast perception may be spatial frequency depended.
Stone, Emily; Haario, Heikki; Lawrence, J Josh
2014-12-01
In this paper we use a simple model of presynaptic neuromodulation of GABA signaling to decipher paired whole-cell recordings of frequency dependent cholinergic neuromodulation at CA1 parvalbumin-containing basket cell (PV BC)-pyramidal cell synapses. Variance-mean analysis is employed to normalize the data, which is then used to estimate parameters in the mathematical model. Various parameterizations and hidden parameter dependencies are investigated using Markov Chain Monte Carlo (MCMC) parameter estimation techniques. This analysis reveals that frequency dependence of cholinergic modulation requires both calcium-dependent recovery from depression and mAChR-induced inhibition of presynaptic calcium entry. A reduction in calcium entry into the presynaptic terminal in the kinetic model accounted for the frequency-dependent effects of mAChR activation.
Directory of Open Access Journals (Sweden)
Dongyuan Liu
2015-01-01
Full Text Available We consider the following state dependent boundary-value problem D0+αy(t-pD0+βg(t,y(σ(t+f(t,y(τ(t=0, 0
Valent, Tullio
1988-01-01
In this book I present, in a systematic form, some local theorems on existence, uniqueness, and analytic dependence on the load, which I have recently obtained for some types of boundary value problems of finite elasticity. Actually, these results concern an n-dimensional (n ~ 1) formal generalization of three-dimensional elasticity. Such a generalization, be sides being quite spontaneous, allows us to consider a great many inter esting mathematical situations, and sometimes allows us to clarify certain aspects of the three-dimensional case. Part of the matter presented is unpublished; other arguments have been only partially published and in lesser generality. Note that I concentrate on simultaneous local existence and uniqueness; thus, I do not deal with the more general theory of exis tence. Moreover, I restrict my discussion to compressible elastic bodies and I do not treat unilateral problems. The clever use of the inverse function theorem in finite elasticity made by STOPPELLI [1954, 1957a, 1957b]...
Shear-coupled grain-boundary migration dependence on normal strain/stress
Combe, N.; Mompiou, F.; Legros, M.
2017-08-01
In specific conditions, grain-boundary (GB) migration occurs in polycrystalline materials as an alternative vector of plasticity compared to the usual dislocation activity. The shear-coupled GB migration, the expected most efficient GB based mechanism, couples the GB motion to an applied shear stress. Stresses on GB in polycrystalline materials seldom have, however, a unique pure shear component. This work investigates the influence of a normal strain on the shear coupled migration of a Σ 13 (320 )[001 ] GB in a copper bicrystal using atomistic simulations. We show that the yield shear stress inducing the GB migration strongly depends on the applied normal stress. Beyond, the application of a normal stress on this GB qualitatively modifies the GB migration: while the Σ 13 (320 )[001 ] GB shear couples following the 〈110 〉 migration mode without normal stress, we report the observation of the 〈010 〉 mode under a sufficiently high tensile normal stress. Using the nudge elastic band method, we uncover the atomistic mechanism of this 〈010 〉 migration mode and energetically characterize it.
Energy Technology Data Exchange (ETDEWEB)
Florinski, V.; Roux, J. A. le [Department of Space Sciences, University of Alabama in Huntsville, Huntsville, AL 35899 (United States); Stone, E. C.; Cummings, A. C. [Space Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125 (United States)
2015-04-10
In the preceding paper, we showed that large second-order anisotropies of heliospheric ions measured by the Voyager 1 space probe during the August 2012 boundary crossing event could be explained by a magnetic shear across the heliopause preventing particles streaming along the magnetic field from escaping the inner heliosheath. According to Stone et al., the penetration distance of heliospheric ions into the outer heliosheath had a strong dependence on the particle’s Larmor radius. By comparing hydrogen, helium, and oxygen ions with the same energy per nucleon, these authors argued that this effect must be attributed to larger cyclotron radii of heavier species rather than differences in velocity. We propose that gradient drift in a nonuniform magnetic field was the cause of both the large second-order anisotropies and the spatial differentiation based on the ion’s rigidity. A latitudinal gradient of magnetic field strength of about 10% per AU between 2012.7 and 2012.9 could have provided drift motion sufficient to match both LECP and CRS Voyager 1 observations. We explain the transient intensity dropout observed prior to the heliocliff using flux tube structures embedded in the heliosheath and magnetically connected to interstellar space. Finally, this paper reports a new indirect measurement of the plasma radial velocity at the heliopause on the basis of the time difference between two cosmic-ray telescopes measuring the same intensity dropout.
Time-domain analysis of frequency dependent inertial wave forces on cylinders
DEFF Research Database (Denmark)
Krenk, Steen
2013-01-01
-number, and the relevant range of waves shorter than about six times the diameter typically corresponds to deep water waves. This permits a universal non-dimensional frequency representation, that is converted to rational form to provide the relevant filter equation. Simple time-domain simulations demonstrate...... a simple time-domain procedure for the inertial force, in which the frequency dependence is represented via a simple explicit time filter on the wave particle acceleration or velocity. The frequency dependence of the inertia coefficient is known analytically as a function of the wave...
On the temperature dependence of amide I frequencies of peptides in solution.
Amunson, Krista E; Kubelka, Jan
2007-08-23
The temperature dependence of the amide I vibrational frequencies of peptides in solution was investigated. In D2O, the amide I' bands of both an alpha-helical oligopeptide, the random-coil poly(L-lysine), and the simplest amide, N-methyl acetamide (NMA), exhibit linear frequency shifts of approximately 0.07 cm(-1)/degrees C with increasing temperature. Similar amide I frequency shifts are also observed for NMA in both polar (acetonitrile and DMSO) and nonpolar (1,4-dioxane) organic solvents, thus ruling out hydrogen-bonding strength as the cause of these effects. The experimental NMA amide I frequencies in the organic solvents can be accurately described by a simple theory based on the Onsager reaction field with temperature-dependent solvent dielectric properties and a solute molecular cavity. DFT-level calculations (BPW91/cc-pVDZ) for NMA with an Onsager reaction field confirm the significant contribution of the molecular cavity to the predicted amide I frequencies. Comparison of the computations to experimental data shows that the frequency-dependent response of the reaction field, taken into account by the index of refraction, is crucial for describing the amide I frequencies in polar solvents. The poor predictions of the model for the NMA amide I band in D2O might be due, in part, to the unknown temperature dependence of the refractive index of D2O in the mid-IR range, which was approximated by the available values in the visible region.
Xin, Fu-Long; Bai, Xian-Xu; Qian, Li-Jun
2016-10-01
Magnetorheological elastomers (MREs), a smart composite, exhibit dual characteristics of both MR materials and particle reinforced composites, i.e., the viscoelasticity of MREs depends on external magnetic field as well as strain amplitude and excitation frequency. In this article, the principle of a frequency-, amplitude-, and magneto-dependent linear dynamic viscoelastic model for isotropic MREs is proposed and investigated. The viscoelasticity of MREs is divided into frequency- and amplitude-dependent mechanical viscoelasticity and frequency-, amplitude-, and magneto-dependent magnetic viscoelasticity. Based on the microstructures of ferrous particles and matrix, the relationships between mechanical shear modulus corresponding to the mechanical viscoelasticity and strain amplitude and excitation frequency are obtained. The relationships between magnetic shear modulus corresponding to the magnetic viscoelasticity with strain amplitude, excitation frequency, and further external magnetic field are derived using the magneto-elastic theory. The influence of magnetic saturation on the MR effect is also considered. The dynamic characteristics of a fabricated isotropic MRE sample under different strain amplitudes, excitation frequencies and external magnetic fields are tested. The parameters of the proposed model are identified with the experimental data and the theoretical expressions of shear storage modulus and shear loss modulus of the MRE sample are obtained. In the light of the theoretical expressions, the loss factors of the MRE sample under different loading conditions are analyzed and compared with the test results to evaluate the effectiveness of the proposed model.
Analytical solution for beam with time-dependent boundary conditions versus response spectrum
Energy Technology Data Exchange (ETDEWEB)
Gou, P.F.; Panahi, K.K. [GE Nuclear Energy, San Jose, CA (United States)
2001-07-01
This paper studies the responses of a uniform simple beam for which the supports are subjected to time-dependent conditions. Analytical solution in terms of series was presented for two cases: (1) Two supports of a simple beam are subjected to a harmonic motion, and (2) One of the two supports is stationary while the other is subjected to a harmonic motion. The results of the analytical solution were investigated and compared with the results of conventional response spectrum method using the beam finite element model. One of the applications of the results presented in this paper can be used to assess the adequacy and accuracy of the engineering approaches such as response spectra methods. It has been found that, when the excitation frequency equals the fundamental frequency of the beam, the results from response spectrum method are in good agreement with the exact calculation. The effects of initial conditions on the responses are also examined. It seems that the non-zero initial velocity has pronounced effects on the displacement time histories but it has no effect on the maximum accelerations. (author)
Negative frequency-dependent preferences and variation in male facial hair.
Janif, Zinnia J; Brooks, Robert C; Dixson, Barnaby J
2014-01-01
Negative frequency-dependent sexual selection maintains striking polymorphisms in secondary sexual traits in several animal species. Here, we test whether frequency of beardedness modulates perceived attractiveness of men's facial hair, a secondary sexual trait subject to considerable cultural variation. We first showed participants a suite of faces, within which we manipulated the frequency of beard thicknesses and then measured preferences for four standard levels of beardedness. Women and men judged heavy stubble and full beards more attractive when presented in treatments where beards were rare than when they were common, with intermediate preferences when intermediate frequencies of beardedness were presented. Likewise, clean-shaven faces were least attractive when clean-shaven faces were most common and more attractive when rare. This pattern in preferences is consistent with negative frequency-dependent selection.
DEFF Research Database (Denmark)
Escolano-Carrasco, José; Jacobsen, Finn
2007-01-01
Digital waveguide mesh (DWM) is a popular method for time domain modelling of sound fields. DWM consists of a recursive digital filter structure where a D'Alembert solution of the wave equation is propagated. One of the attractive characteristics of this method is related to the simplicity of inc...
Directory of Open Access Journals (Sweden)
Baoqiang Yan
2006-07-01
Full Text Available In this paper, Krasnoselskii's theorem and the fixed point theorem of cone expansion and compression are improved. Using the results obtained, we establish the existence of multiple positive solutions for the singular second-order boundary-value problems with derivative dependance on finite and infinite intervals.
Bennewitz, John William
This research investigation encompasses experimental tests demonstrating the control of a high-frequency combustion instability by acoustically modulating the propellant flow. A model rocket combustor burned gaseous oxygen and methane using a single-element, pentad-style injector. Flow conditions were established that spontaneously excited a 2430 Hz first longitudinal combustion oscillation at an amplitude up to p'/pc ≈ 6%. An acoustic speaker was placed at the base of the oxidizer supply to modulate the flow and alter the oscillatory behavior of the combustor. Two speaker modulation approaches were investigated: (1) Bands of white noise and (2) Pure sinusoidal tones. The first approach adjusted 500 Hz bands of white noise ranging from 0-500 Hz to 2000-2500 Hz, while the second implemented single-frequency signals with arbitrary phase swept from 500-2500 Hz. The results showed that above a modulation signal amplitude threshold, both approaches suppressed 95+% of the spontaneous combustion oscillation. By increasing the applied signal amplitude, a wider frequency range of instability suppression became present for these two acoustic modulation approaches. Complimentary to these experiments, a linear modal analysis was undertaken to investigate the effects of acoustic modulation at the inlet boundary on the longitudinal instability modes of a dump combustor. The modal analysis employed acoustically consistent matching conditions with a specific impedance boundary condition at the inlet to represent the acoustic modulation. From the modal analysis, a naturally unstable first longitudinal mode was predicted in the absence of acoustic modulation, consistent with the spontaneously excited 2430 Hz instability observed experimentally. Subsequently, a detailed investigation involving variation of the modulation signal from 0-2500 Hz and mean combustor temperature from 1248-1685 K demonstrated the unstable to stable transition of a 2300-2500 Hz first longitudinal mode. The
Hlubek, M D; Cobbett, P
2000-09-15
Recordings were made from magnocellular neuroendocrine cells dissociated from the supraoptic nucleus of the adult guinea pig to determine the role of voltage gated K(+) channels in controlling the duration of action potentials and in mediating frequency-dependent action potential broadening exhibited by these neurons. The K(+) channel blockers charybdotoxin (ChTx), tetraethylammonium (TEA), and 4-aminopyridine (4-AP) increased the duration of individual action potentials indicating that multiple types of K(+) channel are important in controlling action potential duration. The effect of these K(+) channel blockers was almost completely reversed by simultaneous blockade of voltage gated Ca(2+) channels with Cd(2+). Frequency-dependent action potential broadening was exhibited by these neurons during trains of action potentials elicited by membrane depolarizing current pulses presented at 10 Hz but not at 1 Hz. 4-AP but not ChTx or TEA inhibited frequency-dependent action potential broadening indicating that frequency-dependent action potential broadening is dependent on increasing steady-state inactivation of A-type K(+) channels (which are blocked by 4-AP). A model of differential contributions of voltage gated K(+) channels and voltage gated Ca(2+) channels to frequency-dependent action potential broadening, in which an increase of Ca(2+) current during each successive action potential is permitted as a result of the increasing steady-state inactivation of A-type K(+) channels, is presented.
Through the Looking Glass: AdS-FT with time dependent boundary conditions and black hole formation
Copsey, K
2004-01-01
I solve for the behavior of scalars in Lorentzian AdS with time dependent boundary conditions, focusing in particular on the dilaton. This corresponds, via the AdS-CFT correspondence, to considering a gauge theory with a time dependent coupling. Changes which keep the gauge coupling nonzero result in finite but physically interesting states in the bulk, including black holes, while sending the gauge coupling to zero appears to produce a cosmological singularity in the bulk.
The Frequency Dependence of the Added Mass of Quartz Tuning Fork Immersed in He II
Gritsenko, I.; Klokol, K.; Sokolov, S.; Sheshin, G.
2016-11-01
We measured the dependences of the resonance frequency of tuning forks immersed in liquid helium at T = 0.365 K in the pressure interval from saturated vapor pressure to 24.8 atm. The quartz tuning forks have been studied with different resonance frequencies of 6.65, 8.46, 12.1, 25.0 and 33.6 kHz in vacuum. The measurements were taken in the laminar flow regime. The experimental data allow us to determine the added mass of a quartz tuning fork in He II. It was found that the added mass per unit length of the prong fork is frequency dependent. Some possible qualitative explanations for such dependence are proposed. In addition, we observed, at T = 0.365 K, the changes in added mass with pressure according to the pressure dependence of He II density.
Ramstad, Robin; Barabash, Stas; Futaana, Yoshifumi; Holmstrom, Mats
2016-10-01
The long operational life (2003-) of Mars Express (MEX) has allowed the spacecraft to make plasma measurements in the Martian environment over a wide range of upstream conditions. We have analyzed ~5000 MEX orbits, covering three orders of magnitude in solar wind dynamic pressure, with data from the on-board Analyzer of Space Plasmas and Energetic Particles (ASPERA-3) package, mapping the locations where MEX crosses the main plasma boundaries; induced magnetosphere boundary (IMB), ionosphere boundary (IB) and bow shock (BS). A coincidence scheme was employed, where data from the Ion Mass Analyzer (IMA) and the Electron Spectrometer (ELS) had to agree for a positive boundary identification, which resulted in crossings from 882 orbit segments that were used to create dynamic 2-parameter (solar wind density, nsw, and velocity vsw dependent global dynamic models for the IMB, IB and BS. The modeled response is found to be individual to each boundary; the BS is stationary for all but extremely thin and slow solar wind, the IMB scales solely dependent on dynamic pressure and the IB changes morphology with different trends for nsw and vsw. We find no significant trend in IMB location with changing EUV intensities when the upstream solar wind is constrained to nominal conditions. Finally, the IMB model is used to extrapolate the solar wind stand-off distance in the ancient (0.7 Ga old) solar wind.
Martin, Raleigh L; Chamecki, Marcelo
2016-01-01
The wind-blown transport of sand is driven by turbulent winds that fluctuate over a broad range of temporal and spatial scales. Increasingly sophisticated models and wind tunnel experiments have attempted to capture these dynamics of aeolian saltation, yet model predictions often diverge substantially from field observations. To help fill this knowledge gap, we collected comprehensive high-frequency field measurements to characterize the dynamics of aeolian saltation under natural conditions. Here, we provide detailed description of our field deployments, including information about sites, instruments, and data processing methods. We then demonstrate how our field measurements can help to improve understanding of the mechanics of aeolian processes. We also describe the limitations of our measurement techniques and the needs for future work.
Boundary conditions for multistep finite-difference methods for time-dependent equations
Gottlieb, D.; Turkel, E.
1978-01-01
The stability and accuracy of various boundary treatments are analyzed for the two-step Richtmyer and MacCormack methods. Special attention is paid to ways of imposing the extra boundary conditions after the first step of the two-step process. The theory of Kreiss is used to study stability properties for both scalar and vector equations. The theory of Skollermo is used to compare accuracies of the various methods. Computations were also performed on both wavelike equations and on systems that approach a steady state. Several suggestions are given for more reliable boundary treatments.
Dependence of the ray transference of model eyes on the frequency of light
Directory of Open Access Journals (Sweden)
Tanya Evans
2016-03-01
Full Text Available The transference defines the first-order character of an optical system; almost all the system’s optical properties can be calculated from it. It is useful, therefore, to have some idea of how it depends on the frequency of light. We examine the dependence for two Gaussian eyes. It turns out to be nearly linear for all four fundamental properties. The result is an equation for the dependence of the transference on frequency which is almost symplectic. We also transform the transference into Hamiltonian space, obtain equations for the least-squares straight line for the three independent transformed properties and map them back to the group of transferences. The result is an equation for the dependence of the transference on frequency which is exactly symplectic and therefore representative of an optical system. The results may approximate those of real eyes and give estimates of the dependence of almost all optical properties on frequency.Keywords: ray transference; frequency; symplecticity
Directory of Open Access Journals (Sweden)
Emran Tohidi
2016-01-01
Full Text Available This article contributes a matrix approach by using Taylor approximation to obtain the numerical solution of one-dimensional time-dependent parabolic partial differential equations (PDEs subject to nonlocal boundary integral conditions. We first impose the initial and boundary conditions to the main problems and then reach to the associated integro-PDEs. By using operational matrices and also the completeness of the monomials basis, the obtained integro-PDEs will be reduced to the generalized Sylvester equations. For solving these algebraic systems, we apply a famous technique in Krylov subspace iterative methods. A numerical example is considered to show the efficiency of the proposed idea.
National Research Council Canada - National Science Library
El Khoury, George K; Schlatter, Philipp; Brethouwer, Geert; Johansson, Arne V
2014-01-01
Direct numerical simulation data of fully developed turbulent pipe flow are extensively compared with those of turbulent channel flow and zero-pressure-gradient boundary layer flow for Re-tau up to 1 000...
Frequency and Temperature Dependence of Electrical Breakdown at 21, 30 and 39 GHz
Braun, Hans Heinrich; Wilson, Ian H; Wuensch, Walter
2003-01-01
A TeV-range e+e- linear collider has emerged as one of the most promising candidates to extend the high energy frontier of experimental elementary particle physics. A high accelerating gradient for such a collider is desirable to limit its overall length. Accelerating gradient is mainly limited by electrical breakdown, and it has been generally assumed that this limit increases with increasing frequency for normal-conducting accelerating structures. Since the choice of frequency has a profound influence on the design of a linear collider, the frequency dependence of breakdown has been measured using six exactly scaled single-cell cavities at 21, 30, and 39 GHz. The influence of temperature on breakdown behavior was also investigated. The maximum obtainable surface fields were found to be in the range of 300 to 400 MV/m for copper, with no significant dependence on either frequency or temperature.
Frequency, pressure, and strain dependence of nonlinear elasticity in Berea Sandstone
Rivière, Jacques; Pimienta, Lucas; Scuderi, Marco; Candela, Thibault; Shokouhi, Parisa; Fortin, Jérôme; Schubnel, Alexandre; Marone, Chris; Johnson, Paul A.
2016-04-01
Acoustoelasticity measurements in a sample of room dry Berea sandstone are conducted at various loading frequencies to explore the transition between the quasi-static (f→0) and dynamic (few kilohertz) nonlinear elastic response. We carry out these measurements at multiple confining pressures and perform a multivariate regression analysis to quantify the dependence of the harmonic content on strain amplitude, frequency, and pressure. The modulus softening (equivalent to the harmonic at 0f) increases by a factor 2-3 over 3 orders of magnitude increase in frequency. Harmonics at 2f, 4f, and 6f exhibit similar behaviors. In contrast, the harmonic at 1f appears frequency independent. This result corroborates previous studies showing that the nonlinear elasticity of rocks can be described with a minimum of two physical mechanisms. This study provides quantitative data that describes the rate dependency of nonlinear elasticity. These findings can be used to improve theories relating the macroscopic elastic response to microstructural features.
Energy Technology Data Exchange (ETDEWEB)
Li, Faqi; Zeng, Deping; He, Min; Wang, Zhibiao, E-mail: dzhang@nju.edu.cn, E-mail: wangzhibiao@haifu.com.cn [State Key Laboratory of Ultrasound Engineering in Medicine Co-founded by Chongqing and the Ministry of Science and Technology, College of Biomedical Engineering, Chongqing Medical University, Chongqing 401121 (China); Song, Dan; Lei, Guangrong [National Engineering Research Center of Ultrasound Medicine, Chongqing 401121 (China); Lin, Zhou; Zhang, Dong, E-mail: dzhang@nju.edu.cn, E-mail: wangzhibiao@haifu.com.cn [Institute of Acoustics, Key Laboratory of Modern Acoustics, MOE, Nanjing University, Nanjing 210093 (China); Wu, Junru [Department of Physics, University of Vermont, Burlington, VT 05405 (United States)
2015-12-15
Resolution of high intensity focused ultrasound (HIFU) focusing is limited by the wave diffraction. We have developed a spherical cavity transducer with two open ends to improve the focusing precision without sacrificing the acoustic intensity (App Phys Lett 2013; 102: 204102). This work aims to theoretically and experimentally investigate the frequency dependence of the acoustic field generated from the spherical cavity transducer with two open ends. The device emits high intensity ultrasound at the frequency ranging from 420 to 470 kHz, and the acoustic field is measured by a fiber optic probe hydrophone. The measured results shows that the spherical cavity transducer provides high acoustic intensity for HIFU treatment only in its resonant modes, and a series of resonant frequencies can be choosen. Furthermore, a finite element model is developed to discuss the frequency dependence of the acoustic field. The numerical simulations coincide well with the measured results.
Jackson, M B; Konnerth, A.; Augustine, G.J.
1991-01-01
Hormone release from nerve terminals in the neurohypophysis is a sensitive function of action potential frequency. We have investigated the cellular mechanisms responsible for this frequency-dependent facilitation by combining patch clamp and fluorimetric Ca2+ measurements in single neurosecretory terminals in thin slices of the rat posterior pituitary. In these terminals both action potential-induced changes in the intracellular Ca2+ concentration ([Ca2+]i) and action potential duration were...
Webster, M. J.; Easter, B.; Hornsby, J. S.
1990-02-01
A three element frequency dependent equivalent circuit which characterizes a symmetric step microstrip discontinuity is determined using the method of lines. This method was applied so as to exploit to the full the processing capabilities of the available Cyber 205 computer, and to obtain results with the highest possible accuracy at frequencies in the range 4-16 GHz. Numerical values of scattering parameters are given for three geometries.
DEFF Research Database (Denmark)
Silva, Filipe Miguel Faria da
2016-01-01
analyses the simulation errors of different Bergeron models to a reference frequency-dependent model for a 150kV cable. The simulations consider flat and trefoil installation, both-ends bonding and cross-bonding, ideal voltage source and modelling of the area around the cable. The Bergeron model...... the modelling of the area around the cable being energised, the Bergeron model has a small error if tuned for the right frequency....
Bradshaw-Hajek, B H; Miklavcic, S J; White, L R
2008-05-06
This paper outlines the application of a self-consistent cell-model theory of electrokinetics to the problem of determining the electrical conductivity of a dense suspension of spherical colloidal particles. Numerical solutions of the standard electrokinetic equations, subject to self-consistent boundary conditions, are implemented in formulas for the electrical conductivity appropriate to the particle-averaged cell model of the suspension. Results of calculations as a function of frequency, zeta potential, volume fraction, and electrolyte composition, are presented and discussed.
Thorvaldsen, Andreas J.; Ruud, Kenneth; Rizzo, Antonio; Coriani, Sonia
2008-10-01
We present the first gauge-origin-independent, frequency-dependent calculations of the hypermagnetizability anisotropy, which determines the temperature-independent contribution to magnetic-field-induced linear birefringence, the so-called Cotton-Mouton effect. A density-matrix-based scheme for analytical calculations of frequency-dependent molecular properties for self-consistent field models has recently been developed, which is also valid with frequency- and field-dependent basis sets. Applying this scheme to Hartree-Fock wave functions and using London atomic orbitals in order to obtain gauge-origin-independent results, we have calculated the hypermagnetizability anisotropy. Our results show that the use of London orbitals leads to somewhat better basis-set convergence for the hypermagnetizability compared to conventional basis sets and that London orbitals are mandatory in order to obtain reliable magnetizability anisotropies.
A new algorithm for frequency-dependent shear-wave splitting parameters extraction
Zhang, Jian-li; Wang, Yun; Lu, Jun
2013-10-01
In the exploration of a fractured reservoir, it is very important for reservoir engineers to get information about fracture sizes, because macro-scale fractures are more significant to the control of reservoir storability and fluid flow even though both micro-scale cracks and macro-scale fractures contribute to the dominant anisotropy. Recently, a poroelastic equivalent medium model was proposed by Chapman, which describes the frequency-dependent anisotropy effect with the fracture size being one of the key parameters. Based on this model, geophysicists have done work to measure fracture sizes from seismic data. However, it is necessary to extract frequency-dependent anisotropy before inverting for fracture size. In this paper, a new algorithm is developed for extracting frequency-dependent anisotropic parameters from surface multi-component seismic data, especially from a common-receiver-gather. Compared with the conventional method of extracting the splitting parameters only for different frequency bands, it is possible to extract splitting parameters for each frequency with the new algorithm. To check the reliability of the algorithm, a common-receiver-all-azimuth-gather is synthesized by the vector convolution method, involving the splitting parameters dependent on frequency. Test results show that the frequency-dependent splitting parameters will be extracted accurately with a general level of noise (the signal to noise ratio, SNR for shot, equals 3). More importantly, under the joint constraints of multi-azimuth data, a satisfactory result will be obtained even if the noise is significant (SNR equals 1). The good performance of the algorithm in a model test indicates its potential for field applications.
Martin, Christopher H
2016-06-01
The adaptive landscape provides the foundational bridge between micro- and macroevolution. One well-known caveat to this perspective is that fitness surfaces depend on ecological context, including competitor frequency, traits measured, and resource abundance. However, this view is based largely on intraspecific studies. It is still unknown how context-dependence affects the larger features of peaks and valleys on the landscape which ultimately drive speciation and adaptive radiation. Here, I explore this question using one of the most complex fitness landscapes measured in the wild in a sympatric pupfish radiation endemic to San Salvador Island, Bahamas by tracking survival and growth of laboratory-reared F2 hybrids. I present new analyses of the effects of competitor frequency, dietary isotopes, and trait subsets on this fitness landscape. Contrary to expectations, decreasing competitor frequency increased survival only among very common phenotypes, whereas less common phenotypes rarely survived despite few competitors, suggesting that performance, not competitor frequency, shapes large-scale features of the fitness landscape. Dietary isotopes were weakly correlated with phenotype and growth, but did not explain additional survival variation. Nonlinear fitness surfaces varied substantially among trait subsets, revealing one-, two-, and three-peak landscapes, demonstrating the complexity of selection in the wild, even among similar functional traits. © 2016 The Author(s). Evolution © 2016 The Society for the Study of Evolution.
Sérazin, Guillaume; Penduff, Thierry; Terray, Laurent; Grégorio, Sandy; Barnier, Bernard; Molines, Jean-Marc
2015-04-01
Ocean-atmosphere heat fluxes are particularly strong in Western Boundary Current (WBC) regions where SST front variations influence basin-scale climate variability. Observed low-frequency fluctuations in latitude and strength of these oceanic jets are classically thought to be essentially atmospherically-driven by wind stress curl variability via the oceanic Rossby wave adjustment. Yet academic eddy-resolving process-oriented models with double-gyre configurations have revealed that an idealized WBC may exhibit low-frequency intrinsic fluctuations without low-frequency external forcing (e.g. Berloff et al., 2007, Dijkstra and Ghil, 2005, etc). Experiments with eddying Ocean General Circulation Models (OGCMs) have also shown that the amount of low-frequency Sea Level Anomaly (SLA) variability is largely intrinsic in WBCs (Penduff et al. 2011; Sérazin et al 2014) and that the frontal-scale (<10°) pattern of the Kuroshio Extension (KE) variability is similar to intrinsic modes (Taguchi et al. 2010). Based on a pair of atmospherically-forced 1/12° OGCM experiments that simulate with accuracy either the intrinsic variability (seasonally-forced) or the observed total variability (forced with the full range of atmospheric timescales), Empirical Orthogonal Function analysis is performed on zonally-averaged SLA fields of four main WBCs (e.g. Gulf Stream, Kuroshio Extension, Agulhas Current and East Australian Current). The first two modes of the KE and GS exhibit a similar spatial structure that is shaped by oceanic intrinsic processes. The frequency content is however different between the intrinsic and total Principal Components, the former containing a wide range of timescales similar to a red noise and the latter being more autocorrelated at interannual-to-decadal timescales. These modes are compared with those obtained from the 20 years of altimetry observation and relationships with low-frequency westward propagative features in the respective oceanic basin are
Vortex precession frequency and its amplitude-dependent shift in cylindrical nanomagnets
Energy Technology Data Exchange (ETDEWEB)
Metlov, Konstantin L., E-mail: metlov@fti.dn.ua [Donetsk Institute for Physics and Technology NAS, Donetsk 83114 (Ukraine)
2013-12-14
Frequency of free magnetic vortex precession in circular soft ferromagnetic nano-cylinders (magnetic dots) of various sizes is an important parameter, used in design of spintronic devices (such as spin-torque microwave nano-oscillators) and characterization of magnetic nanostructures. Here, using a recently developed collective-variable approach to non-linear dynamics of magnetic textures in planar nano-magnets, this frequency and its amplitude-dependent shift are computed analytically and plotted for the full range of cylinder geometries. The frequency shift is positive in large planar dots, but becomes negative in smaller and more elongated ones. At certain dot dimensions, a zero frequency shift is realized, which can be important for enhancing frequency stability of magnetic nano-oscillators.
Maraghechi, Borna; Hasani, Mojtaba H; Kolios, Michael C; Tavakkoli, Jahan
2016-05-01
Ultrasound-based thermometry requires a temperature-sensitive acoustic parameter that can be used to estimate the temperature by tracking changes in that parameter during heating. The objective of this study is to investigate the temperature dependence of acoustic harmonics generated by nonlinear ultrasound wave propagation in water at various pulse transmit frequencies from 1 to 20 MHz. Simulations were conducted using an expanded form of the Khokhlov-Zabolotskaya-Kuznetsov nonlinear acoustic wave propagation model in which temperature dependence of the medium parameters was included. Measurements were performed using single-element transducers at two different transmit frequencies of 3.3 and 13 MHz which are within the range of frequencies simulated. The acoustic pressure signals were measured by a calibrated needle hydrophone along the axes of the transducers. The water temperature was uniformly increased from 26 °C to 46 °C in increments of 5 °C. The results show that the temperature dependence of the harmonic generation is different at various frequencies which is due to the interplay between the mechanisms of absorption, nonlinearity, and focusing gain. At the transmit frequencies of 1 and 3.3 MHz, the harmonic amplitudes decrease with increasing the temperature, while the opposite temperature dependence is observed at 13 and 20 MHz.
Frequency-dependent gating of synaptic transmission and plasticity by dopamine
Directory of Open Access Journals (Sweden)
Hiroshi T Ito
2007-11-01
Full Text Available The neurotransmitter dopamine (DA plays an important role in learning by enhancing the saliency of behaviorally relevant stimuli. How this stimulus selection is achieved on the cellular level, however, is not known. Here, in recordings from hippocampal slices, we show that DA acts specifically at the direct cortical input to hippocampal area CA1 (the temporoammonic (TA pathway to filter the excitatory drive onto pyramidal neurons based on the input frequency. During low-frequency patterns of stimulation, DA depressed excitatory TA inputs to both CA1 pyramidal neurons and local inhibitory GABAergic interneurons via presynaptic inhibition. In contrast, during high-frequency patterns of stimulation, DA potently facilitated the TA excitatory drive onto CA1 pyramidal neurons, owing to diminished feedforward inhibition. Analysis of DA's effects over a broad range of stimulus frequencies indicates that it acts as a high-pass filter, augmenting the response to high-frequency inputs while diminishing the impact of low-frequency inputs. These modulatory effects of DA exert a profound influence on activity-dependent forms of synaptic plasticity at both TA-CA1 and Schaffer-collateral (SC-CA1 synapses. Taken together, our data demonstrate that DA acts as a gate on the direct cortical input to the hippocampus, modulating information flow and synaptic plasticity in a frequency-dependent manner.
The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral Atmosphere
Krishna Prasad, S.; Jess, D. B.; Van Doorsselaere, T.; Verth, G.; Morton, R. J.; Fedun, V.; Erdélyi, R.; Christian, D. J.
2017-09-01
High spatial and temporal resolution images of a sunspot, obtained simultaneously in multiple optical and UV wavelengths, are employed to study the propagation and damping characteristics of slow magnetoacoustic waves up to transition region heights. Power spectra are generated from intensity oscillations in sunspot umbra, across multiple atmospheric heights, for frequencies up to a few hundred mHz. It is observed that the power spectra display a power-law dependence over the entire frequency range, with a significant enhancement around 5.5 mHz found for the chromospheric channels. The phase difference spectra reveal a cutoff frequency near 3 mHz, up to which the oscillations are evanescent, while those with higher frequencies propagate upward. The power-law index appears to increase with atmospheric height. Also, shorter damping lengths are observed for oscillations with higher frequencies suggesting frequency-dependent damping. Using the relative amplitudes of the 5.5 mHz (3 minute) oscillations, we estimate the energy flux at different heights, which seems to decay gradually from the photosphere, in agreement with recent numerical simulations. Furthermore, a comparison of power spectra across the umbral radius highlights an enhancement of high-frequency waves near the umbral center, which does not seem to be related to magnetic field inclination angle effects.
Dynamical gap generation in graphene with frequency-dependent renormalization effects
Carrington, M. E.; Fischer, C. S.; von Smekal, L.; Thoma, M. H.
2016-09-01
We study the frequency dependencies in the renormalization of the fermion Green's function for the π -band electrons in graphene and their influence on the dynamical gap generation at sufficiently strong interaction. Adopting the effective QED-like description for the low-energy excitations within the Dirac-cone region, we self-consistently solve the fermion Dyson-Schwinger equation in various approximations for the photon propagator and the vertex function with special emphasis on frequency-dependent Lindhard screening and retardation effects.
An angular frequency dependence on the Aharonov–Casher geometric phase
Energy Technology Data Exchange (ETDEWEB)
Barboza, P.M.T.; Bakke, K., E-mail: kbakke@fisica.ufpb.br
2015-10-15
A quantum effect characterized by a dependence of the angular frequency associated with the confinement of a neutral particle to a quantum ring on the quantum numbers of the system and the Aharonov–Casher geometric phase is discussed. Then, it is shown that persistent spin currents can arise in a two-dimensional quantum ring in the presence of a Coulomb-type potential. A particular contribution to the persistent spin currents arises from the dependence of the angular frequency on the geometric quantum phase.
DEFF Research Database (Denmark)
Yamauchi, Akira; Knott, Arnold; Jørgensen, Ivan Harald Holger
2014-01-01
In this paper, frequency dependent losses in switch-mode audio power amplifiers are analyzed and a loss model is improved by taking the voltage dependence of the parasitic capacitance of MOSFETs into account. The estimated power losses are compared to the measurement and great accuracy is achieved....... By choosing the optimal switching frequency based on the proposed analysis, the experimental results show that system power losses of the reference design are minimized and an efficiency improvement of 8 % in maximum is achieved without compromising audio performances....
Frequency-dependent signal processing in apical dendrites of hippocampal CA1 pyramidal cells.
Watanabe, H; Tsubokawa, H; Tsukada, M; Aihara, T
2014-10-10
Depending on an animal's behavioral state, hippocampal CA1 pyramidal cells receive distinct patterns of excitatory and inhibitory synaptic inputs. The time-dependent changes in the frequencies of these inputs and the nonuniform distribution of voltage-gated channels lead to dynamic fluctuations in membrane conductance. In this study, using a whole-cell patch-clamp method, we attempted to record and analyze the frequency dependencies of membrane responsiveness in Wistar rat hippocampal CA1 pyramidal cells following noise current injection directly into dendrites and somata under pharmacological blockade of all synaptic inputs. To estimate the frequency-dependent properties of membrane potential, membrane impedance was determined from the voltage response divided by the input current in the frequency domain. The cell membrane of most neurons showed low-pass filtering properties in all regions. In particular, the properties were strongly expressed in the somata or proximal dendrites. Moreover, the data revealed nonuniform distribution of dendritic impedance, which was high in the intermediate segment of the apical dendritic shaft (∼220-260μm from the soma). The low-pass filtering properties in the apical dendrites were more enhanced by membrane depolarization than those in the somata. Coherence spectral analysis revealed high coherence between the input signal and the output voltage response in the theta-gamma frequency range, and large lags emerged in the distal dendrites in the gamma frequency range. Our results suggest that apical dendrites of hippocampal CA1 pyramidal cells integrate synaptic inputs according to the frequency components of the input signal along the dendritic segments receiving the inputs.
Dependence structure of the Korean stock market in high frequency data
Kim, Min Jae; Kwak, Young Bin; Kim, Soo Yong
2011-03-01
This paper analyzes the evolution of the dependence structure for various time window intervals, known as Epps effect, using the Trade and Quote data of 663 actively traded stocks in Korean stock market. It is found that the random matrix theory analysis could not represent the dependence structure of the stock market in the microstructure regime. The Cook-Johnson copula is introduced as a parsimonious alternative method to handle this problem, and the existence of the Epps effect is confirmed for the 663 stocks using high frequency data. It was also found that large capitalization companies tend to have a stronger dependence structure, except for the largest capitalization group, since the phenomenon of price level resistance leads to the weak dependence structure in the largest capitalization group. In addition, grouping the industry as a sub-portfolio is an appropriate approach for hour interval traders, whereas this approach is not a strategy recommended for high frequency traders.
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Te-Wen Tu
2015-01-01
Full Text Available An analytical solution for the heat transfer in hollow cylinders with time-dependent boundary condition and time-dependent heat transfer coefficient at different surfaces is developed for the first time. The methodology is an extension of the shifting function method. By dividing the Biot function into a constant plus a function and introducing two specially chosen shifting functions, the system is transformed into a partial differential equation with homogenous boundary conditions only. The transformed system is thus solved by series expansion theorem. Limiting cases of the solution are studied and numerical results are compared with those in the literature. The convergence rate of the present solution is fast and the analytical solution is simple and accurate. Also, the influence of physical parameters on the temperature distribution of a hollow cylinder along the radial direction is investigated.
Galagusz, Ryan; Nave, Jean-Christophe
2015-01-01
We present a high order, Fourier penalty method for the Maxwell's equations in the vicinity of perfect electric conductor boundary conditions. The approach relies on extending the irregular non-periodic domain of the equations to a regular periodic domain by removing the exact boundary conditions and introducing an analytic forcing term in the extended domain. The forcing, or penalty term is chosen to systematically enforce the boundary conditions to high order in the penalty parameter, which then allows for higher order numerical methods. We present an efficient numerical method for constructing the penalty term, and discretize the resulting equations using a Fourier spectral method. We demonstrate convergence orders of up to 3.5 for the one dimensional Maxwell's equations, and show that the numerical method does not suffer from dispersion (or pollution) errors. We also illustrate the approach in two dimensions and demonstrate convergence orders of 2.5 for transverse magnetic modes and 1.5 for the transverse...
Numerical Study of Frequency-dependent Seismoelectric Coupling in Partially-saturated Porous Media
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Djuraev Ulugbek
2017-01-01
Full Text Available The seismoelectric phenomenon associated with propagation of seismic waves in fluid-saturated porous media has been studied for many decades. The method has a great potential to monitor subsurface fluid saturation changes associated with production of hydrocarbons. Frequency of the seismic source has a significant impact on measurement of the seismoelectric effects. In this paper, the effects of seismic wave frequency and water saturation on the seismoelectric response of a partially-saturated porous media is studied numerically. The conversion of seismic wave to electromagnetic wave was modelled by extending the theoretically developed seismoelectric coupling coefficient equation. We assumed constant values of pore radius and zeta-potential of 80 micrometers and 48 microvolts, respectively. Our calculations of the coupling coefficient were conducted at various water saturation values in the frequency range of 10 kHz to 150 kHz. The results show that the seismoelectric coupling is frequency-dependent and decreases exponentially when frequency increases. Similar trend is seen when water saturation is varied at different frequencies. However, when water saturation is less than about 0.6, the effect of frequency is significant. On the other hand, when the water saturation is greater than 0.6, the coupling coefficient shows monotonous trend when water saturation is increased at constant frequency.
Self-consistent modeling of terahertz waveguide and cavity with frequency-dependent conductivity
Huang, Y. J.; Chu, K. R.; Thumm, M.
2015-01-01
The surface resistance of metals, and hence the Ohmic dissipation per unit area, scales with the square root of the frequency of an incident electromagnetic wave. As is well recognized, this can lead to excessive wall losses at terahertz (THz) frequencies. On the other hand, high-frequency oscillatory motion of conduction electrons tends to mitigate the collisional damping. As a result, the classical theory predicts that metals behave more like a transparent medium at frequencies above the ultraviolet. Such a behavior difference is inherent in the AC conductivity, a frequency-dependent complex quantity commonly used to treat electromagnetics of metals at optical frequencies. The THz region falls in the gap between microwave and optical frequencies. However, metals are still commonly modeled by the DC conductivity in currently active vacuum electronics research aimed at the development of high-power THz sources (notably the gyrotron), although a small reduction of the DC conductivity due to surface roughness is sometimes included. In this study, we present a self-consistent modeling of the gyrotron interaction structures (a metallic waveguide or cavity) with the AC conductivity. The resulting waveguide attenuation constants and cavity quality factors are compared with those of the DC-conductivity model. The reduction in Ohmic losses under the AC-conductivity model is shown to be increasingly significant as the frequency reaches deeper into the THz region. Such effects are of considerable importance to THz gyrotrons for which the minimization of Ohmic losses constitutes a major design consideration.
Spatial resolution dependence on spectral frequency in human speech cortex electrocorticography
Muller, Leah; Hamilton, Liberty S.; Edwards, Erik; Bouchard, Kristofer E.; Chang, Edward F.
2016-10-01
Objective. Electrocorticography (ECoG) has become an important tool in human neuroscience and has tremendous potential for emerging applications in neural interface technology. Electrode array design parameters are outstanding issues for both research and clinical applications, and these parameters depend critically on the nature of the neural signals to be recorded. Here, we investigate the functional spatial resolution of neural signals recorded at the human cortical surface. We empirically derive spatial spread functions to quantify the shared neural activity for each frequency band of the electrocorticogram. Approach. Five subjects with high-density (4 mm center-to-center spacing) ECoG grid implants participated in speech perception and production tasks while neural activity was recorded from the speech cortex, including superior temporal gyrus, precentral gyrus, and postcentral gyrus. The cortical surface field potential was decomposed into traditional EEG frequency bands. Signal similarity between electrode pairs for each frequency band was quantified using a Pearson correlation coefficient. Main results. The correlation of neural activity between electrode pairs was inversely related to the distance between the electrodes; this relationship was used to quantify spatial falloff functions for cortical subdomains. As expected, lower frequencies remained correlated over larger distances than higher frequencies. However, both the envelope and phase of gamma and high gamma frequencies (30-150 Hz) are largely uncorrelated (<90%) at 4 mm, the smallest spacing of the high-density arrays. Thus, ECoG arrays smaller than 4 mm have significant promise for increasing signal resolution at high frequencies, whereas less additional gain is achieved for lower frequencies. Significance. Our findings quantitatively demonstrate the dependence of ECoG spatial resolution on the neural frequency of interest. We demonstrate that this relationship is consistent across patients and
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L. Cafarella
2001-06-01
Full Text Available A statistical analysis of the polarization pattern of low-frequency geomagnetic field fluctuations (0.7-7.4 mHz covering the entire 24-h interval was performed at the Antarctic station Terra Nova Bay (80.0°S geomagnetic latitude throughout 1997 and 1998. The results show that the polarization pattern exhibits a frequency dependence, as can be expected from the frequency dependence of the latitude where the coupling between the magnetospheric compressional mode and the field line resonance takes place. The polarization analysis of single pulsation events shows that wave packets with different polarization sense, depending on frequency, can be simultaneously observed.
Energy Technology Data Exchange (ETDEWEB)
Lepidi, S.; Cafarella, L. [Istituto Nazionale di Geofisica e Vulcanologia, L' Aquila (Italy); Francia, P. [L' Aquila Univ., L' Aquila (Italy). Dipt. di Fisica
2001-06-01
A statistical analysis of the polarization pattern of low-frequency geomagnetic field fluctuations (0.7-7.4 m Hz) covering the entire 24-h interval was performed at the Antarctic station Terra Nova Bay (80.0{sup 0}S geomagnetic latitude) throughout 1997 and 1998. The results show that the polarization pattern exhibits a frequency dependence, as can be expected from the frequency dependence of the latitude where the coupling between the magnetospheric compressional mode and the field line resonance takes place. The polarization analysis of single pulsation events shows that wave packets with different polarization sense, depending on frequency, can be simultaneously observed.
Frequency dependent attenuation of seismic waves for Delhi and surrounding area, India
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Babita Sharma
2015-06-01
Full Text Available The attenuation properties of Delhi & surrounding region have been investigated using 62 local earthquakes recorded at nine stations. The frequency dependent quality factors Qa (using P-waves and Qb (using S-waves have been determined using the coda normalization method. Quality factor of coda-waves (Qc has been estimated using the single backscattering model in the frequency range from 1.5 Hz to 9 Hz. Wennerberg formulation has been used to estimate Qi (intrinsic attenuation parameter and Qs (scattering attenuation parameter for the region. The values Qa, Qb, Qc, Qi and Qs estimated are frequency dependent in the range of 1.5Hz-9Hz. Frequency dependent relations are estimated as Qa=52f1.03, Qb=98f1.07 and Qc=158f0.97. Qc estimates lie in between the values of Qi and Qs but closer to Qi at all central frequencies. Comparison between Qi and Qs shows that intrinsic absorption is predominant over scattering for Delhi and surrounding region.
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Evgenia Sitnikova
2014-01-01
Full Text Available The risk of neurological diseases increases with age. In WAG/Rij rat model of absence epilepsy, the incidence of epileptic spike-wave discharges is known to be elevated with age. Considering close relationship between epileptic spike-wave discharges and physiologic sleep spindles, it was assumed that age-dependent increase of epileptic activity may affect time-frequency characteristics of sleep spindles. In order to examine this hypothesis, electroencephalograms (EEG were recorded in WAG/Rij rats successively at the ages 5, 7, and 9 months. Spike-wave discharges and sleep spindles were detected in frontal EEG channel. Sleep spindles were identified automatically using wavelet-based algorithm. Instantaneous (localized in time frequency of sleep spindles was determined using continuous wavelet transform of EEG signal, and intraspindle frequency dynamics were further examined. It was found that in 5-months-old rats epileptic activity has not fully developed (preclinical stage and sleep spindles demonstrated an increase of instantaneous frequency from beginning to the end. At the age of 7 and 9 months, when animals developed matured and longer epileptic discharges (symptomatic stage, their sleep spindles did not display changes of intrinsic frequency. The present data suggest that age-dependent increase of epileptic activity in WAG/Rij rats affects intrinsic dynamics of sleep spindle frequency.
Dynamic Acousto-Elasticity: Pressure and Frequency Dependences in Berea Sandstone.
Riviere, J. V.; Pimienta, L.; Latour, S.; Fortin, J.; Schubnel, A.; Johnson, P. A.
2014-12-01
Nonlinear elasticity is studied at the laboratory scale with the goal of understanding observations at earth scales, for instance during strong ground motion, tidal forcing and earthquake slip processes. Here we report frequency and pressure dependences on elasticity when applying dynamic acousto-elasticity (DAE) of rock samples, analogous to quasi-static acousto-elasticity. DAE allows one to obtain the elastic behavior over the entire dynamic cycle, detailing the full nonlinear behavior under tension and compression, including hysteresis and memory effects. We perform DAE on a sample of Berea sandstone subject to 0.5MPa uniaxial load, with sinusoidal oscillating strain amplitudes ranging from 10-6 to 10-5 and at frequencies from 0.1 to 260Hz. In addition, the confining pressure is increased stepwise from 0 to 30MPa. We compare results to previous measurements made at lower (mHz) and higher (kHz) frequencies. Nonlinear elastic parameters corresponding to conditioning effects, third order elastic constants and fourth order elastic constants are quantitatively compared over the pressure and frequency ranges. We observe that the decrease in modulus due to conditioning increases with frequency, suggesting a frequency and/or strain-rate dependence that should be included in nonlinear elastic models of rocks. In agreement with previous measurements, nonlinear elastic effects also decrease with confining pressure, suggesting that nonlinear elastic sources such as micro-cracks, soft bonds and dislocations are turned off as the pressure increases.
Frequency-dependent modulation of KCNQ1 and HERG1 potassium channels
DEFF Research Database (Denmark)
Diness, Thomas Goldin; Hansen, Rie Schultz; Olesen, Søren-Peter
2006-01-01
of the beta-subunits KCNE1 and KCNE2. In addition, the functional role of HERG1 in native guinea pig cardiac myocytes was demonstrated at different pacing frequencies by application of 10microM of the new HERG1 activator, NS1643. In conclusion, we have demonstrated that HERG1 and hKCNQ1 channels are inversely......To obtain information about a possible frequency-dependent modulation of HERG1 and hKCNQ1 channels, we performed heterologous expression in Xenopus laevis oocytes. Channel activation was obtained by voltage protocols roughly imitating cardiac action potentials at frequencies of 1, 3, 5.8, and 8.3Hz....... The activity of HERG1 channels was inhibited down to 65% at high frequencies. In contrast, hKCNQ1 channel activity was increased up to 525% at high frequencies. The general frequency-dependent modulation of the channels was unaffected by both co-expression of hKCNQ1 and HERG1 channels, and by the presence...
An exponential ESS model and its application to frequency-dependent selection.
Li, J; Liu, L
1989-10-01
A nonlinear ESS model is put forward, that is, a nonnegative exponential ESS model. For a simple case, we discuss the existence, uniqueness, and stability of an ESS. As an application of the model, we give a quantitative analysis of frequency-dependent selection in population genetics when the rare type has an advantage.
Susan E. Meyer; David L. Nelson; Suzette Clement; Alisa Ramakrishnan
2010-01-01
Evolutionary processes that maintain genetic diversity in plants are likely to include selection imposed by pathogens. Negative frequency-dependent selection is a mechanism for maintenance of resistance polymorphism in plant - pathogen interactions. We explored whether such selection operates in the Bromus tectorum - Ustilago bullata pathosystem. Gene-for-gene...
Frequency-Dependent Social Dominance in a Color Polymorphic Cichlid Fish
Dijkstra, Peter; Lindström, Jan; Metcalfe, Neil B.; Hemelrijk, Charlotte K.; Brendel, Mischa; Seehausen, Ole; Groothuis, Ton G.G.
2010-01-01
A mechanism commonly suggested to explain the persistence of color polymorphisms in animals is negative frequency-dependent selection. It could result from a social dominance advantage to rare morphs. We tested for this in males of red and blue color morphs of the Lake Victoria cichlid, Pundamilia.
Temperature Dependence of the Radio-Frequency Dielectric Properties of Chicken Meat
Dielectric properties of chicken breast meat were measured with an open-ended coaxial-line probe between 200 MHz and 20 GHz at temperature ranging from -20 oC to +25 oC. At a given frequency, the temperature dependence reveals a sharp increase of the dielectric constant and dielectric loss factor a...
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Bloom Clifford O.
1996-01-01
Full Text Available The asymptotic behavior as λ → ∞ of the function U ( x , λ that satisfies the reduced wave equation L λ [ U ] = ∇ ⋅ ( E ( x ∇ U + λ 2 N 2 ( x U = 0 on an infinite 3-dimensional region, a Dirichlet condition on ∂ V , and an outgoing radiation condition is investigated. A function U N ( x , λ is constructed that is a global approximate solution as λ → ∞ of the problem satisfied by U ( x , λ . An estimate for W N ( x , λ = U ( x , λ − U N ( x , λ on V is obtained, which implies that U N ( x , λ is a uniform asymptotic approximation of U ( x , λ as λ → ∞ , with an error that tends to zero as rapidly as λ − N ( N = 1 , 2 , 3 , ... . This is done by applying a priori estimates of the function W N ( x , λ in terms of its boundary values, and the L 2 norm of r L λ [ W N ( x , λ ] on V . It is assumed that E ( x , N ( x , ∂ V and the boundary data are smooth, that E ( x − I and N ( x − 1 tend to zero algebraically fast as r → ∞ , and finally that E ( x and N ( x are slowly varying; ∂ V may be finite or infinite. The solution U ( x , λ can be interpreted as a scalar potential of a high frequency acoustic or electromagnetic field radiating from the boundary of an impenetrable object of general shape. The energy of the field propagates through an inhomogeneous, anisotropic medium; the rays along which it propagates may form caustics. The approximate solution (potential derived in this paper is defined on and in a neighborhood of any such caustic, and can be used to connect local “geometrical optics” type approximate solutions that hold on caustic free subsets of V .The result of this paper generalizes previous work of Bloom and Kazarinoff [C. O. BLOOM and N. D. KAZARINOFF, Short Wave Radiation Problems in Inhomogeneous Media: Asymptotic Solutions, SPRINGER VERLAG, NEW YORK, NY, 1976].
Audio-Band Frequency-Dependent Squeezing for Gravitational-Wave Detectors.
Oelker, Eric; Isogai, Tomoki; Miller, John; Tse, Maggie; Barsotti, Lisa; Mavalvala, Nergis; Evans, Matthew
2016-01-29
Quantum vacuum fluctuations impose strict limits on precision displacement measurements, those of interferometric gravitational-wave detectors among them. Introducing squeezed states into an interferometer's readout port can improve the sensitivity of the instrument, leading to richer astrophysical observations. However, optomechanical interactions dictate that the vacuum's squeezed quadrature must rotate by 90° around 50 Hz. Here we use a 2-m-long, high-finesse optical resonator to produce frequency-dependent rotation around 1.2 kHz. This demonstration of audio-band frequency-dependent squeezing uses technology and methods that are scalable to the required rotation frequency and validates previously developed theoretical models, heralding application of the technique in future gravitational-wave detectors.
Grain orientation dependence of extended planar dislocation boundaries in rolled aluminium
DEFF Research Database (Denmark)
Lin, F.X.; Godfrey, A.; Winther, Grethe
2009-01-01
The dislocation boundary alignment in 124 grains in cold-rolled aluminium has been investigated by a combination of backscattered electron channelling contrast and electron backscatter diffraction. The asymmetric slip geometry of the Copper and S orientations together with the existence of differ...
Richardson, H.; Basu, S.; Holtslag, A.A.M.
2013-01-01
For many decades, attempts have been made to find the universal value of the critical bulk Richardson number (Ri Bc ; defined over the entire stable boundary layer). By analyzing an extensive large-eddy simulation database and various published wind-tunnel data, we show that Ri Bc is not a constant,
Boundary Element Method Solution in the Time Domain For a Moving Time-Dependent Force
DEFF Research Database (Denmark)
Nielsen, Søren R.K.; Kirkegaard, Poul Henning; Rasmussen, K. M.
2001-01-01
satisfy the radiation conditions exactly. In this paper a model based on the BEM is formulated for the solution of the mentioned problem. A numerical solution is obtained for the 2D plane strain case, and comparison is made with the results obtained from a corresponding FEM solution with an impedance...... absorbing boundary condition....
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J.-S. Chen
2011-04-01
Full Text Available This study presents a generalized analytical solution for one-dimensional solute transport in finite spatial domain subject to arbitrary time-dependent inlet boundary condition. The governing equation includes terms accounting for advection, hydrodynamic dispersion, linear equilibrium sorption and first order decay processes. The generalized analytical solution is derived by using the Laplace transform with respect to time and the generalized integral transform technique with respect to the spatial coordinate. Several special cases are presented and compared to illustrate the robustness of the derived generalized analytical solution. Result shows an excellent agreement. The analytical solutions of the special cases derived in this study have practical applications. Moreover, the derived generalized solution which consists an integral representation is evaluated by the numerical integration to extend its usage. The developed generalized solution offers a convenient tool for further development of analytical solution of specified time-dependent inlet boundary conditions or numerical evaluation of the concentration field for arbitrary time-dependent inlet boundary problem.
Frequency dependence of signal power and spatial reach of the local field potential.
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Szymon Łęski
Full Text Available Despite its century-old use, the interpretation of local field potentials (LFPs, the low-frequency part of electrical signals recorded in the brain, is still debated. In cortex the LFP appears to mainly stem from transmembrane neuronal currents following synaptic input, and obvious questions regarding the 'locality' of the LFP are: What is the size of the signal-generating region, i.e., the spatial reach, around a recording contact? How far does the LFP signal extend outside a synaptically activated neuronal population? And how do the answers depend on the temporal frequency of the LFP signal? Experimental inquiries have given conflicting results, and we here pursue a modeling approach based on a well-established biophysical forward-modeling scheme incorporating detailed reconstructed neuronal morphologies in precise calculations of population LFPs including thousands of neurons. The two key factors determining the frequency dependence of LFP are the spatial decay of the single-neuron LFP contribution and the conversion of synaptic input correlations into correlations between single-neuron LFP contributions. Both factors are seen to give low-pass filtering of the LFP signal power. For uncorrelated input only the first factor is relevant, and here a modest reduction (100 Hz compared to the near-DC ([Formula: see text] value of about [Formula: see text]. Much larger frequency-dependent effects are seen when populations of pyramidal neurons receive correlated and spatially asymmetric inputs: the low-frequency ([Formula: see text] LFP power can here be an order of magnitude or more larger than at 60 Hz. Moreover, the low-frequency LFP components have larger spatial reach and extend further outside the active population than high-frequency components. Further, the spatial LFP profiles for such populations typically span the full vertical extent of the dendrites of neurons in the population. Our numerical findings are backed up by an intuitive
Kumar, Sushil; Singh, Priyamvada; Singh, Pitam; Biswal, Shubhasmita; Parija, Mahesh Prasad
2016-03-01
Digital seismogram data of 82 earthquakes from the Northwestern Himalayan (India) region recorded at different stations during 2004-2006 were analyzed to study the seismic coda wave attenuation characteristics in this region. We used 132 seismic observations from local earthquakes with a hypocentral distance India) by the Wadia institute of Himalayan Geology, Dehradun. The QC values were estimated at 10 central frequencies: 1.5, 3, 5, 7, 9, 12, 16, 20, 24, and 28 Hz using starting lapse-times of 10, 20, 30, 40, 50, and 60 s and coda window-lengths of 10, 20, 30, 40, and 50 s. The QC fits the frequency dependent power-law, QC =Q0fn . For a 10 s lapse time with a 10-s coda window length QC = 47.42f1.012 and for a 50 s lapse time with a 50 s coda window length, QC = 204.1f0.934 . Q0 (QC at 1 Hz) varied from ∼47 for a 10 s lapse time and a 10 s window length, to ∼204 for a 50 s lapse time and a 50 s window length. An average frequency dependent power law fit for the study region may be given as QC = 116.716f0.9943 . The exponent of the frequency dependence law n ranged from 1.08 to 0.9, which correlates well with values obtained in other seismically and tectonically active and heterogeneous regions of the world. In our study region, QC increases both with respect to lapse time and frequency, i.e., the attenuation decreases as the quality factor is inversely proportional to attenuation. The low QC values or high attenuation at lower frequencies and high QC values or low attenuation at higher frequencies suggest that the heterogeneity decreases with increasing depth in our study region.
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Kenneth D. Varian
2012-01-01
Full Text Available Myofilament calcium sensitivity decreases with frequency in intact healthy rabbit trabeculae and associates with Troponin I and Myosin light chain-2 phosphorylation. We here tested whether serine-threonine kinase activity is primarily responsible for this frequency-dependent modulations of myofilament calcium sensitivity. Right ventricular trabeculae were isolated from New Zealand White rabbit hearts and iontophoretically loaded with bis-fura-2. Twitch force-calcium relationships and steady state force-calcium relationships were measured at frequencies of 1 and 4 Hz at 37 °C. Staurosporine (100 nM, a nonspecific serine-threonine kinase inhibitor, or vehicle (DMSO was included in the superfusion solution before and during the contractures. Staurosporine had no frequency-dependent effect on force development, kinetics, calcium transient amplitude, or rate of calcium transient decline. The shift in the pCa50 of the force-calcium relationship was significant from 6.05±0.04 at 1 Hz versus 5.88±0.06 at 4 Hz under control conditions (vehicle, P<0.001 but not in presence of staurosporine (5.89±0.08 at 1 Hz versus 5.94±0.07 at 4 Hz, P=NS. Phosphoprotein analysis (Pro-Q Diamond stain confirmed that staurosporine significantly blunted the frequency-dependent phosphorylation at Troponin I and Myosin light chain-2. We conclude that frequency-dependent modulation of calcium sensitivity is mediated through a kinase-specific effect involving phosphorylation of myofilament proteins.
Frequency-dependent critical current and transport ac loss of superconductor strip and Roebel cable
Energy Technology Data Exchange (ETDEWEB)
Thakur, Kailash Prasad [Landcare Research, Palmerston North 4442 (New Zealand); Raj, Ashish [Computer Science in Radiology, Weill Medical College, Cornell University, NY 10022 (United States); Brandt, Ernst Helmut [Max-Planck-Institut fuer Metallforschung, PO B 800665, D-70506 Stuttgart (Germany); Kvitkovic, Jozef; Pamidi, Sastry V, E-mail: thakurk@landcareresearch.co.nz, E-mail: asr2004@med.cornell.edu, E-mail: ehb@mf.mpg.de, E-mail: kvitkovic@caps.fsu.edu, E-mail: pamidi@caps.fsu.edu [Center for Advanced Power System, Florida State University, Tallahassee, FL 32310 (United States)
2011-06-15
The frequency-dependent critical current of a superconductor strip and Roebel cable has been studied using a 2D finite element simulation. It is shown that the critical current of the superconductor increases with frequency as f{sup 1/n}, where n is the exponent of the power law flux creep model. Transport ac loss in a superconductor strip decreases with frequency as f{sup -2/n} when the amplitude of the applied ac current is far less than its critical current. However, when the applied current is large and becomes comparable to the critical current, the transport ac loss decreases with frequency as 1/f. The analytical results are substantiated with available experimental data and the results of a 2D finite element simulation.
Frequency-dependent amplification of stretch-evoked excitatory input in spinal motoneurons.
Powers, Randall K; Nardelli, Paul; Cope, T C
2012-08-01
Voltage-dependent calcium and sodium channels mediating persistent inward currents (PICs) amplify the effects of synaptic inputs on the membrane potential and firing rate of motoneurons. CaPIC channels are thought to be relatively slow, whereas the NaPIC channels have fast kinetics. These different characteristics influence how synaptic inputs with different frequency content are amplified; the slow kinetics of Ca channels suggest that they can only contribute to amplification of low frequency inputs (EPSPs), we measured the averaged stretch-evoked EPSPs in cat medial gastrocnemius motoneurons in decerebrate cats at different subthreshold levels of membrane potential. EPSPs were produced by muscle spindle afferents activated by stretching the homonymous and synergist muscles at frequencies of 5-50 Hz. We adjusted the stretch amplitudes at different frequencies to produce approximately the same peak-to-peak EPSP amplitude and quantified the amount of amplification by expressing the EPSP integral at different levels of depolarization as a percentage of that measured with the membrane hyperpolarized. Amplification was observed at all stretch frequencies but generally decreased with increasing stretch frequency. However, in many cells the amount of amplification was greater at 10 Hz than at 5 Hz. Fast amplification was generally reduced or absent when the lidocaine derivative QX-314 was included in the electrode solution, supporting a strong contribution from Na channels. These results suggest that NaPICs can combine with CaPICs to enhance motoneuron responses to modulations of synaptic drive over a physiologically significant range of frequencies.
Institute of Scientific and Technical Information of China (English)
Zhang An; Zhao xiao-Ru; Duan Li-Bing; Liu Jin-Ming; Zhao Jian-Lin
2011-01-01
The dependence of transistor characteristics on grain boundary (GB) position in short-channel ZnO thin film transistors (TFTs) has been investigated using two-dimensional numerical simulations. To simulate the device accurately,both tail states and deep-level states are taken into consideration. It is shown that both the transfer and output characteristics of ZnO TFTs change dramatically with varying GB position, which is different from polycrystalline Si (poly-Si)TFTs. By analysing the mechanism of the carrier transportation in the device, it is revealed that the dependence is derived from the degrees of carrier concentration descent and mobility variation with GB position.
Directory of Open Access Journals (Sweden)
Christopher Heine
2014-08-01
Full Text Available A detailed description of the rubber parts’ properties is gaining in importance in the current simulation models of multi-body simulation. One application example is a multi-body simulation of the washing machine movement. Inside the washing machine, there are different force transmission elements, which consist completely or partly of rubber. Rubber parts or, generally, elastomers usually have amplitude-dependant and frequency-dependent force transmission properties. Rheological models are used to describe these properties. A method for characterization of the amplitude and frequency dependence of such a rheological model is presented within this paper. Within this method, the used rheological model can be reduced or expanded in order to illustrate various non-linear effects. An original result is given with the automated parameter identification. It is fully implemented in Matlab. Such identified rheological models are intended for subsequent implementation in a multi-body model. This allows a significant enhancement of the overall model quality.
P and S Wave Finite-frequency Imaging of the Cordillera-craton Boundary Zone in Western Canada
Gu, Y. J.; Chen, Y.; Hung, S. H.
2016-12-01
The Western Canada Sedimentary Basin (WCSB) marks a boundary zone and a strong seismic lateral velocity gradient in the upper mantle between the Precambrian North American craton and the Phanerozoic Cordillera. While much of the tectonic imprints are buried below thick sediments, seismic data coverage in this region has been greatly improved to unravel the underlying structure, owing to a growing number of regional broadband arrays. In this study we conduct a high-resolution survey of the mantle P- and S-wave velocities in the WCSB using a multi-scale parameterization and the finite-frequency theory. Our models suggest respective increases of 4% and 6% of Vp and Vs velocities across the Cordilleran Deformation Front (CDF) toward the craton interior. This sharp gradient resides to the west of the CDF, which may imply the over-thrusting of the crustal terranes of the Cordillera onto the craton edge. Significant along-strike variation in the lithospheric basal geometry and dip could reflect secular tectonic modifications such as episodic shortening/extension and convective erosion. The results of our finite-frequency tomography indicate vertically continuous high velocities at least down to 200 km beneath the crustal domains of the Precambrian Buffalo Head Terrane (BHT), Hearne craton and Medicine Hat Block (MHB). The lithosphere beneath the southern Hearne province could extend down to 280 km, nearly 70 km deeper than those of its neighboring cratons of similar ages. The velocity anomalies and their intricate variations/reversals within the mantle lithosphere may be evidence for a multi-stage formation of western Laurentia during Precambrian plate convergence. On the other hand, destruction processes since formation, e.g., convective removal and thermomagmatic erosion, may also have played key roles in shaping the mantle lithosphere beneath the western margin of the North American craton.
Nemnes, G. A.; Palici, Alexandra; Manolescu, A.
2016-11-01
Transparent boundary conditions for the time-dependent Schrödinger equation are implemented using the R-matrix method. The employed scattering formalism is suitable for describing open quantum systems and provides the framework for the time-dependent coherent transport. Transmission and reflection of wave functions at the edges of a finite quantum system are essential for an accurate and efficient description of the time-dependent processes on large time scales. We detail the computational method and point out the numerical advantages stemming from the open system approach based on the R-matrix formalism. The approach is used here to describe time-dependent transport across nanostructured interfaces relevant for photovoltaic applications.
On the dependence of the reflection operator on boundary conditions for biharmonic functions
Savina, Tatiana
2010-01-01
The biharmonic equation arises in areas of continuum mechanics including linear elasticity theory and the Stokes flows, as well as in a radar imaging problem. We discuss the reflection formulas for the biharmonic functions $u(x,y)\\in\\mathbb{R}^2$ subject to different boundary conditions on a real-analytic curve in the plane. The obtained formulas, generalizing the celebrated Schwarz symmetry principle for harmonic functions, have different structures. In particular, in the special case of the boundary, $\\Gamma_0 :=\\{y=0\\}$, reflections are point to point when the given on $\\Gamma_0$ conditions are $u=\\partial_nu=0$, $u=\\Delta u=0$ or $\\partial_nu=\\partial n\\Delta u=0$, and point to a continuous set when $u=\\partial_n\\Delta u=0$ or $\\partial_nu=\\Delta u=0$ on $\\Gamma_0$.
Spatial and frequency dependence of plasma currents in a 300 mm capacitively coupled plasma reactor
Energy Technology Data Exchange (ETDEWEB)
Miller, Paul A [Sandia National Laboratories, MS 1423, PO Box 5800, Albuquerque, NM 87185-1423 (United States); Barnat, Edward V [Sandia National Laboratories, MS 1423, PO Box 5800, Albuquerque, NM 87185-1423 (United States); Hebner, Gregory A [Sandia National Laboratories, MS 1423, PO Box 5800, Albuquerque, NM 87185-1423 (United States); Paterson, Alex M [Applied Materials, Inc., 974 Arques Avenue, Sunnyvale, CA 94086 (United States); Holland, John P [Applied Materials, Inc., 974 Arques Avenue, Sunnyvale, CA 94086 (United States)
2006-11-01
There is much interest in scaling rf-excited capacitively coupled plasma reactors to larger sizes and to higher frequencies. As the size approaches operating wavelength, concerns arise about non-uniformity across the work piece, particularly in light of the well-documented slow-surface-wave phenomenon. We present measurements and calculations of spatial and frequency dependence of rf magnetic fields inside argon plasma in an industrially relevant, 300 mm plasma-processing chamber. The results show distinct differences in the spatial distributions and harmonic content of rf fields in the plasma at the three frequencies studied (13.56, 60 and 176 MHz). Evidence of a slow-wave structure was not apparent. The results suggest that interaction between the plasma and the rf excitation circuit may strongly influence the structures of these magnetic fields and that this interaction is frequency dependent. At the higher frequencies, wave propagation becomes extremely complex; it is controlled by the strong electrical nonlinearity of the sheath and is not explained simply by previous models.
Mechanism of frequency-dependent broadening of molluscan neurone soma spikes.
Aldrich, R W; Getting, P A; Thompson, S H
1979-06-01
1. Action potentials recorded from isolated dorid neurone somata increase in duration, i.e. broaden, during low frequency repetitive firing. Spike broadening is substantially reduced by external Co ions and implicates an inward Ca current. 2. During repetitive voltage clamp steps at frequencies slower than 1 Hz, in 100 mM-tetraethyl ammonium ions (TEA) inward Ca currents do not increase in amplitude. 3. Repetitive action potentials result in inactivation of delayed outward current. Likewise, repetitive voltage clamp steps which cause inactivation of delayed outward current also result in longer duration action potentials. 4. The frequency dependence of spike broadening and inactivation of the voltage dependent component (IK) of delayed outward current are similar. 5. Inactivation of IK is observed in all cells, however, only cells with relative large inward Ca currents show significant spike broadening. Spike broadening apparently results from the frequency dependent inactivation of IK which increases the expression of inward Ca current as a prominent shoulder on the repolarizing phase of the action potential. In addition, the presence of a prolonged Ca current increases the duration of the first action potential thereby allowing sufficient time for inactivation of IK.
Energy Technology Data Exchange (ETDEWEB)
Vdovin, V.; Watari, T.; Fukuyama, A.
1996-12-01
We develop the theory for the wave excitation, propagation and absorption in 3-dimensional (3D) stellarator equilibrium high beta plasma in ion cyclotron frequency range (ICRF). This theory forms a basis for a 3D code creation, urgently needed for the ICRF heating scenarios development for the constructed LHD and projected W7-X stellarators and for the stellarators being at operation (like CHS, W7-AS, etc.). The theory solves the 3D Maxwell-Vlasov antenna-plasma-conducting shell boundary value problem in the non - orthogonal flux coordinates ({psi}, {theta}, {phi}), {psi} being magnetic flux function, {theta} and {phi} being the poloidal and toroidal angles, respectively. All basic physics, like wave refraction, reflection and diffraction are firstly self consistently included, along with the fundamental ion and ion minority cyclotron resonances, two ion hybrid resonance, electron Landau and TTMP absorption. Antenna reactive impedance and loading resistance are also calculated and urgently needed for an antenna -generator matching. This is accomplished in a real confining magnetic field being varying in a plasma major radius direction, in toroidal and poloidal directions, through making use of the hot dense plasma dielectric kinetic tensor. The theory is developed in a manner that includes tokamaks and magnetic mirrors as the particular cases through general metric tensor (provided by an equilibrium solver) treatment of the wave equations. We describe the structure of newly developed stellarator ICRF 3D full wave code STELION, based on theory described in this report. (J.P.N.)
Chiu, Bernard; Krasinski, Adam; Spence, J David; Parraga, Grace; Fenster, Aaron
2010-01-01
Quantitative measurements of the progression (or regression) of carotid plaque burden are important in monitoring patients and evaluating new treatment options. We previously developed a quantitative metric to analyze changes in carotid plaque morphology from 3-D ultrasound (US) on a point-by-point basis. This method requires multiple segmentations of the arterial wall and lumen boundaries to obtain the local standard deviation (SD) of vessel-wall-plus-plaque thickness (VWT) so that t-tests could be used to determine whether a change in VWT is statistically significant. However, the requirement for multiple segmentations makes clinical trials laborious and time-consuming. Therefore, this study was designed to establish the relationship between local segmentation SD and local signal difference on the arterial wall and lumen boundaries. We propose metrics to quantify segmentation SD and signal difference on a point-by-point basis, and studied whether the signal difference at arterial wall or lumen boundaries could be used to predict local segmentation SD. The ability to predict the local segmentation SD could eliminate the need of repeated segmentations of a 2-D transverse image to obtain the local segmentation standard deviation, thereby making clinical trials less laborious and saving time. Six subjects involved in this study were associated with different degrees of atherosclerosis: three carotid stenosis subjects with mean plaque area >3 cm(2) and >60% carotid stenosis were involved in a clinical study evaluating the effect of atorvastatin, a cholesterol-lowering and plaque-stabilizing drug; and three subjects with carotid plaque area >0.5 cm(2) were subjects with moderate atherosclerosis. Our results suggest that when local signal difference is higher than 8 greyscale value (GSV), the local segmentation SD stabilizes at 0.05 mm and is thus predictable. This information provides a target value of local signal difference on the arterial boundaries that should be
Energy Technology Data Exchange (ETDEWEB)
Huseynov, E.; Garibli, A., E-mail: elchin.huse@yahoo.com [National Nuclear Research Center, Department of Nanotechnology and Radiation Material Science, 1073, Inshaatchilar pr. 4, Baku (Azerbaijan)
2016-11-01
It has been reviewed the frequency dependencies of electrical conductivity of nanoparticles affected by neutron flux at different times and initial state, at various constant temperatures such as 100, 200, 300 and 400 K. Measurements have been carried out at each temperature at the different 97 values of frequency in the 1 Hz - 1 MHz range. From interdependence between real and imaginary parts of electrical conductivity it has been determined the type of conductivity. Moreover, in the work it is given the mechanism of electrical conductivity according to the obtained results. (Author)
Derkachova, A
2008-01-01
Multipolar plasmon oscillation frequencies and corresponding damping rates for nanospheres formed of the simplest free-electron metals are studied. The possibility of controlling plasmon features by choosing the size and dielectric properties of the sphere surroundings is discussed. Optical properties of the studied metals are described within the Drude-Sommerfeld model of the dielectric function with effective parameters acounting for the contribution of conduction electrons and of interband transitions. No approximation is made in respect of the size of a particle; plasmon size characteristics are described rigorously. The results of our experiment on sodium nanodroplets [1] are compared with the oscillation frequency size dependence of dipole and quadrupole plasmon.
Energy Technology Data Exchange (ETDEWEB)
Oliveira, Diego F.M., E-mail: diegofregolente@gmail.co [Departamento de Fisica, Instituto de Geociencias e Ciencias Exatas, Universidade Estadual Paulista, Av. 24A, 1515 Bela Vista, CEP, 13506-900 Rio Claro, SP (Brazil); Leonel, Edson D., E-mail: edleonel@rc.unesp.b [Departamento de Estatistica, Matematica Aplicada e Computacao, Instituto de Geociencias e Ciencias Exatas, Universidade Estadual Paulista, Av. 24A, 1515 Bela Vista, CEP, 13506-900 Rio Claro, SP (Brazil)
2010-07-05
Some dynamical properties for a dissipative time-dependent oval-shaped billiard are studied. The system is described in terms of a four-dimensional nonlinear mapping. Dissipation is introduced via inelastic collisions of the particle with the boundary, thus implying that the particle has a fractional loss of energy upon collision. The dissipation causes profound modifications in the dynamics of the particle as well as in the phase space of the non-dissipative system. In particular, inelastic collisions can be assumed as an efficient mechanism to suppress Fermi acceleration of the particle. The dissipation also creates attractors in the system, including chaotic. We show that a slightly modification of the intensity of the damping coefficient yields a drastic and sudden destruction of the chaotic attractor, thus leading the system to experience a boundary crisis. We have characterized such a boundary crisis via a collision of the chaotic attractor with its own basin of attraction and confirmed that inelastic collisions do indeed suppress Fermi acceleration in two-dimensional time-dependent billiards.
Kamens, Helen M; Corley, Robin P; Richmond, Phillip A; Darlington, Todd M; Dowell, Robin; Hopfer, Christian J; Stallings, Michael C; Hewitt, John K; Brown, Sandra A; Ehringer, Marissa A
2016-09-01
Common SNPs in nicotinic acetylcholine receptor genes (CHRN genes) have been associated with drug behaviors and personality traits, but the influence of rare genetic variants is not well characterized. The goal of this project was to identify novel rare variants in CHRN genes in the Center for Antisocial Drug Dependence (CADD) and Genetics of Antisocial Drug Dependence (GADD) samples and to determine if low frequency variants are associated with antisocial drug dependence. Two samples of 114 and 200 individuals were selected using a case/control design including the tails of the phenotypic distribution of antisocial drug dependence. The capture, sequencing, and analysis of all variants in 16 CHRN genes (CHRNA1-7, 9, 10, CHRNB1-4, CHRND, CHRNG, CHRNE) were performed independently for each subject in each sample. Sequencing reads were aligned to the human reference sequence using BWA prior to variant calling with the Genome Analysis ToolKit (GATK). Low frequency variants (minor allele frequency antisocial drug behaviors.
Role of acoustic phonons in frequency dependent electronic thermal conductivity of graphene
Bhalla, Pankaj
2017-03-01
We study the effect of the electron-phonon interaction on the finite frequency dependent electronic thermal conductivity of two dimensional graphene. We calculate it for various acoustic phonons present in graphene and characterized by different dispersion relations using the memory function approach. It is found that the electronic thermal conductivity κe (T) in the zero frequency limit follows different power law for the longitudinal/transverse and the flexural acoustic phonons. For the longitudinal/transverse phonons, κe (T) ∼T-1 at the low temperature and saturates at the high temperature. These signatures qualitatively agree with the results calculated by solving the Boltzmann equation analytically and numerically. Similarly, for the flexural phonons, we find that κe (T) shows T 1 / 2 law at the low temperature and then saturates at the high temperature. In the finite frequency regime, we observe that the real part of the electronic thermal conductivity, Re [κe (ω , T) ] follows ω-2 behavior at the low frequency and becomes frequency independent at the high frequency.
Energy Technology Data Exchange (ETDEWEB)
Randelia, R.R.; Sahai, V.
1987-01-01
A numerical analysis of a two-phase, laminar boundary layer is carried out using the Keller Box method. The two phases are assumed to be immiscible. The problem considered involves the boundary layer flow of a compressible gas with variable properties over a flat surface in the presence of a thin liquid film with power law temperature dependent viscosity. Both zero and nonzero pressure gradients are considered. The main purpose of the study was to investigate the effect of the presence of the liquid layer on the velocity and temperature distributions. A limited set of results are presented in terms of varying liquid Prandtl numbers, film thickness, and viscosity exponents on these distributions as well as the shear stress and heat transfer parameters at the wall and at the interface between the two fluids.
Ito, Hidetaka
2014-01-01
Interaction between vehicles and pedestrians is seen in many areas such as crosswalks and intersections. In this paper, we study a totally asymmetric simple exclusion process with a bottleneck at a boundary caused by an interaction. Due to the time-dependent effect originating from the speed of pedestrians, the flow of the model varies even if the average hopping probability at the last site is the same. We analyze the phenomenon by using two types of approximations: (2+1)-cluster approximation and isolated rarefaction wave approximation. The approximate results capture intriguing features of the model. Moreover, we discuss the situation where vehicles turn right at the intersection by adding a traffic light at the boundary condition. The result suggests that pedestrian scrambles are valid to eliminate traffic congestion in the right turn lane.
The origin of the frequency-dependent behaviour of pulsar radio profiles
Dyks, J
2014-01-01
We present further development of a pulsar emission model based on multiple streams diverging away from the magnetic dipole axis, and forming azimuthally-structured fan-shaped beams. It is shown that this geometry, successfully tested on profiles with bifurcated features, naturally solves several classical pulsar problems and avoids some difficulties of the traditional nested cone/core model. This is best visible for profiles with several components, such as those of class T, Q and M, because they most clearly exhibit a range of effects previously interpreted within the conal model. In particular, with no reference to the flaring boundary of the polar magnetic flux tube, the stream model explains the apparent radius-to-frequency mapping (RFM), including its reduced strength for the inner pair of components. The lag of the central component (apparent `core') with respect to the centroids of the flanking (`conal') components can also be naturally explained with no reference to emission rings located at disparat...
Global Discrete Artificial Boundary Conditions for Time-Dependent Wave Propagation
Ryaben'kii, V. S.; Tsynkov, S. V.; Turchaninov, V. I.
2001-12-01
We construct global artificial boundary conditions (ABCs) for the numerical simulation of wave processes on unbounded domains using a special nondeteriorating algorithm that has been developed previously for the long-term computation of wave-radiation solutions. The ABCs are obtained directly for the discrete formulation of the problem; in so doing, neither a rational approximation of “nonreflecting kernels” nor discretization of the continuous boundary conditions is required. The extent of temporal nonlocality of the new ABCs appears fixed and limited; in addition, the ABCs can handle artificial boundaries of irregular shape on regular grids with no fitting/adaptation needed and no accuracy loss induced. The nondeteriorating algorithm, which is the core of the new ABCs, is inherently three-dimensional, it guarantees temporally uniform grid convergence of the solution driven by a continuously operating source on arbitrarily long time intervals and provides unimprovable linear computational complexity with respect to the grid dimension. The algorithm is based on the presence of lacunae, i.e., aft fronts of the waves, in wave-type solutions in odd-dimensional spaces. It can, in fact, be built as a modification on top of any consistent and stable finite-difference scheme, making its grid convergence uniform in time and at the same time keeping the rate of convergence the same as that of the unmodified scheme. In this paper, we delineate the construction of the global lacunae-based ABCs in the framework of a discretized wave equation. The ABCs are obtained for the most general formulation of the problem that involves radiation of waves by moving sources (e.g., radiation of acoustic waves by a maneuvering aircraft). We also present systematic numerical results that corroborate the theoretical design properties of the ABC algorithm.
Smith, Tristan L
2016-01-01
We calculate the sensitivity to a circular polarization of an isotropic stochastic gravitational wave background (ISGWB) as a function of frequency for ground- and space-based interferometers and observations of the cosmic microwave background. The origin of a circularly polarized ISGWB may be due to exotic primordial physics (i.e., parity violation in the early universe) and may be strongly frequency dependent. We present calculations within a coherent framework which clarifies the basic requirements for sensitivity to circular polarization, in distinction from previous work which focused on each of these techniques separately. We find that the addition of an interferometer with the sensitivity of the Einstein Telescope in the southern hemisphere improves the sensitivity of the ground-based network to circular polarization by about a factor of two. The sensitivity curves presented in this paper make clear that the wide range in frequencies of current and planned observations ($10^{-18}\\ {\\rm Hz} \\lesssim f \\...
Frequency dependence of junction capacitance of BPW34 and BPW41 p-i-n photodiodes
Indian Academy of Sciences (India)
Habibe Bayhan; Şadan Özden
2007-04-01
This article investigates the frequency dependence of small-signal capacitance of silicon BPW34 and BPW41 (Vishay) p-i-n photodiodes. We show that the capacitance-frequency characteristics of these photodiodes are well-described by the Schibli and Milnes model. The activation energy and the concentration of the dominant trap levels detected in BPW34 and BPW41 are 280{330 meV and 1.1 × 1012 - 1.2 × 1012 cm-3, respectively. According to the high-frequency - measurements, the impurity concentrations are determined to be about 5.3 × 1012 and 1.9 × 1013 cm-3 in BPW41 and BPW34, respectively using the method of / (-2) vs. .
A Polarization-Dependent Frequency-Selective Metamaterial Absorber with Multiple Absorption Peaks
Directory of Open Access Journals (Sweden)
Guangsheng Deng
2017-06-01
Full Text Available A polarization-dependent, frequency-selective metamaterial (MM absorber based on a single-layer patterned resonant structure intended for F frequency band is proposed. The design, fabrication, and measurement for the proposed absorber are presented. The absorber’s absorption properties at resonant frequencies have unique characteristics of a single-band, dual-band, or triple-band absorption for different polarization of the incident wave. The calculated surface current distributions and power loss distribution provide further understanding of physical mechanism of resonance absorption. Moreover, a high absorption for a wide range of TE-polarized oblique incidence was achieved. Hence, the MM structure realized on a highly flexible polyimide film, makingthe absorber suitable for conformal geometry applications. The proposed absorber has great potential in the development of polarization detectors and polarizers.
A study of frequency dependent electrical and dielectric properties of NiO nanoparticles
Usha, V.; Kalyanaraman, S.; Vettumperumal, R.; Thangavel, R.
2017-01-01
Nickel oxide nanoparticles were synthesized using low cost sol-gel method. The structure of as prepared NiO nanoparticles has been confirmed from X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray (SEM and EDX) spectroscopic analysis. The electrical and dielectric properties were characterized by complex impedance spectroscopy as a function of frequency at different temperatures. To study the dielectric behavior of the nanoparticles different plots like Nyquist plot, modulus plot and Bode plot were used. Also the frequency dependent ac conductivity is analyzed and the activation energy is calculated. The dielectric constant and dielectric loss as a function of frequency at various temperatures are also studied.
Constraints on frequency-dependent violations of Shapiro delay from GW150914
Directory of Open Access Journals (Sweden)
Emre O. Kahya
2016-05-01
Full Text Available On 14th September 2015, a transient gravitational wave (GW150914 was detected by the two LIGO detectors at Hanford and Livingston from the coalescence of a binary black hole system located at a distance of about 400 Mpc. We point out that GW150914 experienced a Shapiro delay due to the gravitational potential of the mass distribution along the line of sight of about 1800 days. Also, the near-simultaneous arrival of gravitons over a frequency range of about 200 Hz within a 0.2 s window allows us to constrain any violations of Shapiro delay and Einstein's equivalence principle between the gravitons at different frequencies. From the calculated Shapiro delay and the observed duration of the signal, frequency-dependent violations of the equivalence principle for gravitons are constrained to an accuracy of O(10−9.
Frequency-dependent dielectric function of semiconductors with application to physisorption
Zheng, Fan; Tao, Jianmin; Rappe, Andrew M.
2017-01-01
The dielectric function is one of the most important quantities that describes the electrical and optical properties of solids. Accurate modeling of the frequency-dependent dielectric function has great significance in the study of the long-range van der Waals (vdW) interaction for solids and adsorption. In this work we calculate the frequency-dependent dielectric functions of semiconductors and insulators using the G W method with and without exciton effects, as well as efficient semilocal density functional theory (DFT), and compare these calculations with a model frequency-dependent dielectric function. We find that for semiconductors with moderate band gaps, the model dielectric functions, G W values, and DFT calculations all agree well with each other. However, for insulators with strong exciton effects, the model dielectric functions have a better agreement with accurate G W values than the DFT calculations, particularly in high-frequency region. To understand this, we repeat the DFT calculations with scissors correction, by shifting the DFT Kohn-Sham energy levels to match the experimental band gap. We find that scissors correction only moderately improves the DFT dielectric function in the low-frequency region. Based on the dielectric functions calculated with different methods, we make a comparative study by applying these dielectric functions to calculate the vdW coefficients (C3 and C5) for adsorption of rare-gas atoms on a variety of surfaces. We find that the vdW coefficients obtained with the nearly free electron gas-based model dielectric function agree quite well with those obtained from the G W dielectric function, in particular for adsorption on semiconductors, leading to an overall error of less than 7% for C3 and 5% for C5. This demonstrates the reliability of the model dielectric function for the study of physisorption.
Jordi, Claudio; Schmelzbach, Cedric; Greenhalgh, Stewart
2016-08-01
Frequency-dependent traveltime tomography does not rely on the high frequency assumption made in classical ray-based tomography. By incorporating the effects of velocity structures in the first Fresnel volume around the central ray, it offers a more realistic and accurate representation of the actual physics of seismic wave propagation and thus, enhanced imaging of near-surface structures is expected. The objective of this work was to apply frequency-dependent first arrival traveltime tomography to surface seismic data that were acquired for exploration scale and near-surface seismic imaging. We adapted a fat ray tomography algorithm from global-earth seismology that calculates the Fresnel volumes based on source and receiver (adjoint source) traveltime fields. The fat ray tomography algorithm was tested on synthetic model data that mimics the dimensions of two field data sets. The field data sets are presented as two case studies where fat ray tomography was applied for near-surface seismic imaging. The data set of the first case study was recorded for high-resolution near-surface imaging of a Quaternary valley (profile length 10 km). All results of fat ray tomography are compared against the results of classical ray-based tomography. We show that fat ray tomography can provide enhanced tomograms and that it is possible to recover more information on the subsurface when compared to ray tomography. However, model assessment based on the column sum of the Jacobian matrix revealed that especially the deep parts of the structure in the fat ray tomograms might not be adequately covered by fat rays. Furthermore, the performance of the fat ray tomography depends on the chosen input frequency in relation to the scale of the seismic survey. Synthetic data testing revealed that the best results were obtained when the frequency was chosen to correspond to an approximate wavelength-to-target depth ratio of 0.1.
Lobato, L.; Lizana, A.; Márquez, A.; Moreno, I.; Iemmi, C.; Campos, J.; Yzuel, M. J.
2011-04-01
The diffractive efficiency of Liquid Crystal on Silicon (LCoS) displays can be greatly diminished by the appearance of temporal phase fluctuations in the reflected beam, depolarization effects and also because of phase modulation depths smaller than 2π. In order to maximize the efficiency of the Diffractive Optical Elements (DOEs) implemented in the LCoS device, the Minimum Euclidean Distance principle can be applied. However, not all the diffractive elements can be corrected in the same way due to the anamorphic and frequency dependent phenomenon, which is related to the LCoS response, largely dependending on the period and the spatial orientation of the generated DOE. Experimental evidence for the anamorphic and frequency dependent phenomenon is provided in this paper, as well as a comparative study between the efficiency obtained for binary gratings of different periods
Temperature-Dependence of the Amide-I Frequency Map for Peptides and Proteins
Institute of Scientific and Technical Information of China (English)
Chen Han; Jian-ping Wang
2011-01-01
In our recent work [Phys.Chem.Chem.Phys.11,9149 (2009)],a molecular-mechanics force field-based amide-I vibration frequency map (MM-map) for peptides and proteins was constructed.In this work,the temperature dependence of the MM-map is examined based on high-temperature molecular dynamics simulations and infrared (IR) experiments.It is shown that the 298-K map works for up to 500-K molecular dynamics trajectories,which reasonably reproduces the 88 ℃ experimental IR results.Linear IR spectra are also simulated for two tripeptides containing natural and unnatural amino acid residues,and the results are in reasonable agreement with experiment.The results suggest the MM-map can be used to obtain the temperature-dependent amide-I local mode frequencies and their distributions for peptide oligomers,which is useful in particular for understanding the IR signatures of the thermally unfolded species.
Frequency-dependent response of a pinned charge-density wave
Vinokur, Valerii; Fogler, Michael
2003-03-01
Recent theoretical advances in the theory of collective pinning [M. M. Fogler, Phys. Rev. Lett. 88, 186402 (2002)] enable us to go beyond the usual phenomenology in the theory of a finite-frequency response of a pinned charge-density wave (CDW) and to calculate ω and T dependences of the complex dielectric function without additional assumptions. According to our estimates, in typical electrical experiments on CDW, the dominant process is a thermal activation over atypically shallow barriers. It gives rise to a novel T^3/4-dependence of the linear response, in agreement with the experiment. A close analogy with acoustic attenuation in glassy dielectrics is noted.
Directory of Open Access Journals (Sweden)
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.
Nitric oxide donors enhance the frequency-dependence of dopamine release in nucleus accumbens
Hartung, Henrike; Threlfell, Sarah; Cragg, Stephanie J
2011-01-01
Abstract Dopamine (DA) neurotransmission in the nucleus accumbens (NAc) is critically involved in normal as well as maladaptive motivated behaviours including drug addiction. Whether the striatal neuromodulator nitric oxide (NO) influences DA release in NAc is unknown. We investigated whether exogenous NO modulates DA transmission in NAc core and how this interaction varies depending on frequency of presynaptic activation. We detected DA with cyclic voltammetry at carbon-fiber micr...
Correction of Frequency-Dependent Nonlinear Errors in Direct-Conversion Transceivers
2016-03-31
University of Oklahoma Norman , Oklahoma, USA, 73019 pyraminxrox@ou.edu, fulton@ou.edu Abstract: Correction of nonlinear and frequency dependent...behavior of low -cost integrated transceivers, especially in the area of phased arrays, where many transceivers will be used to comprise the system as...analog RF portion of the receive chain of the low -cost, direct-conversion radar system initially presented in [2]. The spectral distortion seen here
Zhang, Shi-Jiang; Pan, Hui; Wang, Hai-Long
2017-04-01
An effective quantum field theory (EQFT) graphene sheet with arbitrary one dimensional strain field is derived from a microscopic effective low energy Hamiltonian. The geometric meaning of the strain-induced complex gauge field is clarified. The optical conductivity is also investigated, and a frequency dependent optical conductivity is obtained. The actual value of interband optical conductivity along the deformed direction is C0 + C1/ω2 in spite of the particular strain fields at T=0.
Frequency dependence and viral diversity imply chaos in an HIV model
Iwami, Shingo; Nakaoka, Shinji; Takeuchi, Yasuhiro
2006-11-01
In this paper, we consider the effect of viral diversity on the human immune system with frequency dependent rate of proliferation of CTLs (cytotoxic T-lymphocytes) and rate of elimination of infected cells by CTLs. We show that the interior equilibrium of our model can become unstable without viral diversity and we observe stable periodic orbits. Furthermore, our mathematical models suggest that viral diversity produces strange attractors.
Zhang, Lange; Kou, Yu; Zhao, Yunlong; Fu, Xinyuan
2016-08-01
Previous studies have found that when low-status group members are aware that their in-group is stereotyped as dependent by a specific out-group (i.e. a dependency meta-stereotype is salient), they are reluctant to seek help from the high-status out-group to avoid confirming the negative meta-stereotype. However, it is unclear whether low-status group members would seek more help in the context of a salient dependency meta-stereotype when there is low (vs. high) group boundary permeability. Therefore, we conducted two experiments to examine the moderating effect of permeability on meta-stereotype confirmation with a real group. In study 1, we manipulated the salience of the dependency meta-stereotype, measured participants' perceived permeability and examined their help-seeking behaviour in a real-world task. Participants who perceived low permeability sought more help when the meta-stereotype was salient (vs. not salient), whereas participants who perceived high permeability sought the same amount of help across conditions. In study 2, we manipulated the permeability levels and measured the dependency meta-stereotype. Participants who endorsed a high-dependency meta-stereotype sought more help than participants who endorsed a low-dependency meta-stereotype; this effect was particularly strong in the low-permeability condition. The implications of these results for social mobility and intergroup helping are discussed.
Absorbing boundary conditions for scalar waves in anisotropic media. Part 2: Time-dependent modeling
Savadatti, Siddharth; Guddati, Murthy N.
2010-09-01
With the ultimate goal of devising effective absorbing boundary conditions (ABCs) for general anisotropic media, we investigate the well-posedness and accuracy aspects of local ABCs designed for the transient modeling of the scalar anisotropic wave equation. The ABC analyzed in this paper is the perfectly matched discrete layers (PMDL), a simple variant of perfectly matched layers (PML) that is also equivalent to rational approximation based ABCs. Specifically, we derive the necessary and sufficient condition for the well-posedness of the initial boundary value problem (IBVP) obtained by coupling an interior and a PMDL ABC. The derivation of the reflection coefficient presented in a companion paper (S. Savadatti, M.N. Guddati, J. Comput. Phys., 2010, doi:10.1016/j.jcp.2010.05.018) has shown that PMDL can correctly identify and accurately absorb outgoing waves with opposing signs of group and phase velocities provided the PMDL layer lengths satisfy a certain bound. Utilizing the well-posedness theory developed by Kreiss for general hyperbolic IBVPs, and the well-posedness conditions for ABCs derived by Trefethen and Halpern for isotropic acoustics, we show that this bound on layer lengths also ensures well-posedness. The time discretized form of PMDL is also shown to be theoretically stable and some instability related to finite precision arithmetic is discussed.
Chabrol, H; Duconge, E; Roura, C; Casas, C
2004-01-01
The aims of this paper is to study the relations between anxious, depressive and borderline symptomatology and cannabis use and dependence in adolescents and young adults. A convenient sample of 212 subjects composed of high-school and college students from Toulouse, France (85 boys, 127 girls; mean age=18.3 1.8 Years) completed questionnaires assessing the patterns of cannabis use, age of first use, the symptoms of dependence using a questionnaire derived from the Mini International Neuropsychiatric Interview, and the anxious, depressive and borderline symptomatology using the STAI-YA (State-Trait Anxiety Inventory; Spielberger et al., 1970), the CES-D (Center for Epidemiological Studies-Depression scale; Radloff, 1977) and the BPI (Borderline Personality Inventory; Leichsenring, 1999), respectively; 54% of subjects reported having used cannabis once during the last 6 Months (45.3% of girls and 66.6% of boys, p=0.002). Frequency of use was higher in boys: eg, 61% of boys used cannabis at least almost daily versus 31% of girls (pcannabis dependence (p=0.003). BPI, CES-D and STAI-YA scores were compared between non-users and users and between non-dependent and dependent users: the only significant differences were that BPI scores were higher in users versus non-users and in dependent users versus non-dependent users; CES-D and STAI-YA scores did not distinguished users from non-users and dependent users from non-dependent users. BPI and CES-D scores were correlated with the length of cannabis use (Pearson r=0.19 and r=0.19, respectively, pcannabis use, we entered age, sex, CES-D, STAI-YA and BPI scores. This model accounted for 23% of the variance of the frequency of use (F5,206=14.4, pcannabis use given the high proportion of daily users. The consequence may be that responses to mood questionnaire express both the acute effect of cannabis consumption and the chronic effect that might be different: the acute euphoriant effect of cannabis may mask a chronic
Frequency-dependent selection by wild birds promotes polymorphism in model salamanders
Directory of Open Access Journals (Sweden)
Shook Kim
2009-05-01
Full Text Available Abstract Background Co-occurrence of distinct colour forms is a classic paradox in evolutionary ecology because both selection and drift tend to remove variation from populations. Apostatic selection, the primary hypothesis for maintenance of colour polymorphism in cryptic animals, proposes that visual predators focus on common forms of prey, resulting in higher survival of rare forms. Empirical tests of this frequency-dependent foraging hypothesis are rare, and the link between predator behaviour and maintenance of variation in prey has been difficult to confirm. Here, we show that predatory birds can act as agents of frequency-dependent selection on terrestrial salamanders. Polymorphism for presence/absence of a dorsal stripe is widespread in many salamander species and its maintenance is a long-standing mystery. Results We used realistic food-bearing model salamanders to test whether selection by wild birds maintains a stripe/no-stripe polymorphism. In experimental manipulations, whichever form was most common was most likely to be attacked by ground-foraging birds, resulting in a survival advantage for the rare form. Conclusion This experiment demonstrates that frequency-dependent foraging by wild birds can maintain colour polymorphism in cryptic prey.
Real-time seismic intensity prediction using frequency-dependent site amplification factors
Ogiso, Masashi; Aoki, Shigeki; Hoshiba, Mitsuyuki
2016-05-01
A promising approach for the next generation of earthquake early warning system is based on predicting ground motion directly from observed ground motion, without any information of hypocenter. In this study, we predicted seismic intensity at the target stations from the observed ground motion at adjacent stations, employing two different methods of correction for site amplification factors. The first method was frequency-dependent correction prediction, in which we used a digital causal filter to correct the site amplification for the observed waveform in the time domain. The second method was scalar correction, in which we used average differences in seismic intensity between two stations for the site amplification correction. Results from thousands of station pairs that covered almost all of Japan showed that seismic intensity prediction with frequency-dependent correction prediction was more accurate than prediction with scalar correction. Frequency-dependent correction for site amplification in the time domain may lead to more accurate prediction of ground motion in real time.
Directory of Open Access Journals (Sweden)
Kazumasa Uehara
Full Text Available Failure to suppress antagonist muscles can lead to movement dysfunction, such as the abnormal muscle synergies often seen in the upper limb after stroke. A neurophysiological surrogate of upper limb synergies, the selectivity ratio (SR, can be determined from the ratio of biceps brachii (BB motor evoked potentials to transcranial magnetic stimulation prior to forearm pronation versus elbow flexion. Surprisingly, cathodal transcranial direct current stimulation (c-TDCS over ipsilateral primary motor cortex (M1 reduces (i.e. improves the SR in healthy adults, and chronic stroke patients. The ability to suppress antagonist muscles may be exacerbated at high movement rates. The aim of the present study was to investigate whether the selective muscle activation of the biceps brachii (BB is dependent on altering frequency demands, and whether the c-tDCS improvement of SR is dependent on task frequency. Seventeen healthy participants performed repetitive isometric elbow flexion and forearm pronation at three rates, before and after c-tDCS or sham delivered to ipsilateral left M1. Ipsilateral c-tDCS improved the SR in a frequency dependent manner by selectively suppressing BB antagonist excitability. Our findings confirm that c-tDCS is an effective tool for improving selective muscle activation, and provide novel evidence for its efficacy at rates of movement where it is most likely to benefit task performance.
FORWARD MODELING OF PROPAGATING SLOW WAVES IN CORONAL LOOPS AND THEIR FREQUENCY-DEPENDENT DAMPING
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Mandal, Sudip; Banerjee, Dipankar [Indian Institute of Astrophysics, Koramangala, Bangalore 560034 (India); Magyar, Norbert; Yuan, Ding; Doorsselaere, Tom Van, E-mail: sudip@iiap.res.in [Center for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, bus 2400, B-3001, Leuven (Belgium)
2016-03-20
Propagating slow waves in coronal loops exhibit a damping that depends upon the frequency of the waves. In this study we aim to investigate the relationship of the damping length (L{sub d}) with the frequency of the propagating wave. We present a 3D coronal loop model with uniform density and temperature and investigate the frequency-dependent damping mechanism for the four chosen wave periods. We include the thermal conduction to damp the waves as they propagate through the loop. The numerical model output has been forward modeled to generate synthetic images of SDO/AIA 171 and 193 Å channels. The use of forward modeling, which incorporates the atomic emission properties into the intensity images, allows us to directly compare our results with the real observations. The results show that the damping lengths vary linearly with the periods. We also measure the contributions of the emission properties on the damping lengths by using density values from the simulation. In addition to that we have also calculated the theoretical dependence of L{sub d} with wave periods and showed that it is consistent with the results we obtained from the numerical modeling and earlier observations.
Energy Technology Data Exchange (ETDEWEB)
Barış, Behzad, E-mail: behzadbaris@gmail.com
2013-10-01
Al/rubrene/p-Si Schottky diode has been fabricated by forming a rubrene layer on p type Si by using the spin coating method. The frequency dependent capacitance–voltage (C–V–f) and conductance–voltage (G–V–f) characteristics of Al/rubrene/p-Si Schottky diyotes has been investigated in the frequency range of 5 kHz–500 kHz at room temperature. The C–V plots show a peak for each frequency. The capacitance of the device decreased with increasing frequency. The decrease in capacitance results from the presence of interface states. The plots of series resistance–voltage (R{sub s}−V) gave a peak in the depletion region at all frequencies. The density of interface states (N{sub ss}) and relaxation time (τ) distribution profiles as a function of applied voltage bias have been determined from the C–V and G–V measurements. The values of the N{sub ss} and τ have been calculated in the ranges of 8.37×10{sup 11}–4.85×10{sup 11} eV{sup −1} cm{sup −2} and 5.17×10{sup −6}–1.02×10{sup −5} s, respectively.
Richter, Tom; Wegler, Ulrich
2015-04-01
Modeling of peak ground velocity caused by induced earthquakes requires detailed knowledge about seismic attenuation properties of the subsurface. Especially shear wave attenuation is important, because shear waves usually show the largest amplitude in high frequency seismograms. We report intrinsic and scattering attenuation coefficients of shear waves near three geothermal reservoirs in Germany for frequencies between 2 Hz and 50 Hz. The geothermal plants are located in the sedimentary basins of the upper Rhine graben (Insheim and Landau) and the Molasse basin (Unterhaching). The method optimizes the fit between Green's functions for the acoustic, isotropic radiative transfer theory and observed energy densities of induced earthquakes. The inversion allows the determination of scattering and intrinsic attenuation, site corrections, and spectral source energies for the investigated frequency bands. We performed the inversion at the three sites for events with a magnitude between 0.7 and 2. We determined a transport mean free path of 70 km for Unterhaching. For Landau and Insheim the transport mean free path depends on frequency. It ranges from 2 km (at 2 Hz) to 30 km (at 40 Hz) for Landau and from 9 km to 50 km for Insheim. The quality factor for intrinsic attenuation is constant for frequencies smaller than 10 Hz at all three sites. It is around 100 for Unterhaching and 200 for Landau and Insheim with higher values above 10 Hz.
Frequency dependent electrical properties of nano-CdS/Ag junctions
Mohanta, D.; Choudhury, A.
2005-05-01
Polymer embedded cadmium sulfide nanoparticles/quantum dots were synthesized by a chemical route using polyvinyl alcohol (lmw) as the desired matrix. In an attempt to measure the electrical properties of nano-CdS/Ag samples, we propose that contribution from surface traps are mainly responsible in determining the I˜ V and C˜ V characteristics in high frequency ranges. To be specific, beyond 1.2 MHz, the carrier injection from the trap centers of the embedded quantum dots is ensured by large current establishment even at negative biasing condition of the junction. The unexpected nonlinear signature of C˜ V response is believed to be due to the fact that while trying to follow very high signal frequency (at least 10-3 of recombination frequency), there is complete abruptness in carrier trapping (charging) or/and detrapping (decay) in a given CdS nanoparticle assembly. The frequency dependent unique role of the trap carriers certainly find application in nanoelectronic devices at a desirable frequency of operation.
Grunskaya, L V; Isakevich, D V; Sushkova, L T
2016-01-01
Signal eigenvectors and components analyser (RF Utility model patent 116242) was used to explore the time-series of the electric field vertical component Ez in the Earth atmosphere boundary layer. There have been detected non-coherent complex-periodic components localized at the frequencies of gravity-wave impact of binary stars and at the frequency of axion-photon interaction. These components cannot be detected by means of quadrature scheme of spectral analysis and have RMS values from 0.05 V/m to 0.5 V/m at binary stars gravity-wave impact frequencies and from 0.7 V/m to 2.7 V/m at axion-photon interaction frequency. It was also demonstrated that the axion-photon interaction frequency modulates the amplitude
Park, K.; Bayram, C.
2016-10-01
Here, we investigate the effects of thermal boundary resistance (TBR) and temperature-dependent thermal conductivity on the thermal resistance of GaN/substrate stacks. A combination of parameters such as substrates {diamond, silicon carbide, silicon, and sapphire}, thermal boundary resistance {10-60 m2K/GW}, heat source lengths {10 nm-20 μm}, and power dissipation levels {1-8 W} are studied by using technology computer-aided design (TCAD) software Synopsys. Among diamond, silicon carbide, silicon, and sapphire substrates, the diamond provides the lowest thermal resistance due to its superior thermal conductivity. We report that due to non-zero thermal boundary resistance and localized heating in GaN-based high electron mobility transistors, an optimum separation between the heat source and substrate exists. For high power (i.e., 8 W) heat dissipation on high thermal conductive substrates (i.e., diamond), the optimum separation between the heat source and substrate becomes submicron thick (i.e., 500 nm), which reduces the hotspot temperature as much as 50 °C compared to conventional multi-micron thick case (i.e., 4 μm). This is attributed to the thermal conductivity drop in GaN near the heat source. Improving the TBR between GaN and diamond increases temperature reduction by our further approach. Overall, we provide thermal management design guidelines for GaN-based devices.
KARAT-LAMBDA - frequency dependent ray-traced troposphere delays for space applications
Hobiger, Thomas; Baron, Philippe
2014-05-01
Space-geodetic microwave techniques work under the assumption that the only dispersive, i.e. frequency dependent delay contribution is caused by the ionosphere. In general, the refractivity, even for the troposphere, is a complex quantity which can be denoted as N = N0 + (N'(f) + i N''(f)) where N0 is a frequency independent term, and N'(f) and N''(f) represent the complex frequency dependence. Thereby, the imaginary part can be used to derive the loss of energy (absorption) and the real part can be assigned to the changes in the propagation velocity (refraction) and thus describes the delay of an electromagnetic wave which propagates through that medium. Although the frequency dependent delay contribution appears to be of small order, one has to consider that signals are propagating through few kilometers of troposphere at high elevations to hundredths of kilometers at low elevations. Therefore, the Kashima Ray-Tracing package (Hobiger et al., 2008) has been modified (and named KARAT-LAMBDA) to enable the consideration of a frequency dependent refractivity. By using this tool, it was studied if and to which extent future space geodetic instruments are affected from dispersive troposphere delays. Moreover, a semi-empirical correction model for the microwave link of the Atomic Clock Ensemble in Space (ACES) has been developed, based on ray-tracing calculations with KARAT-LAMBDA. The proposed model (Hobiger et al., 2013) has been tested with simulated ISS overflights at different potential ACES ground station sites and it could be demonstrated that this model is capable to remove biases and elevation dependent features caused by the dispersive troposphere delay difference between the up-link and down-link. References: T. Hobiger, R. Ichikawa, T. Kondo, and Y. Koyama (2008), Fast and accurate ray-tracing algorithms for real-time space geodetic applications using numerical weather models, Journal of Geophysical Research, vol. 113, iss. D203027, pp. 1-14. T. Hobiger, D
The Frequency-Dependent Neuronal Length Constant in Transcranial Magnetic Stimulation
Ilmoniemi, Risto J.; Mäki, Hanna; Saari, Jukka; Salvador, Ricardo; Miranda, Pedro C.
2016-01-01
Background: The behavior of the dendritic or axonal membrane voltage due to transcranial magnetic stimulation (TMS) is often modeled with the one-dimensional cable equation. For the cable equation, a length constant λ0 is defined; λ0 describes the axial decay of the membrane voltage in the case of constant applied electric field. In TMS, however, the induced electric field waveform is typically a segment of a sinusoidal wave, with characteristic frequencies of the order of several kHz. Objective: To show that the high frequency content of the stimulation pulse causes deviations in the spatial profile of the membrane voltage as compared to the steady state. Methods: We derive the cable equation in complex form utilizing the complex frequency-dependent representation of the membrane conductivity. In addition, we define an effective length constant λeff, which governs the spatial decay of the membrane voltage. We model the behavior of a dendrite in an applied electric field oscillating at 3.9 kHz with the complex cable equation and by solving the traditional cable equation numerically. Results: The effective length constant decreases as a function of frequency. For a model dendrite or axon, for which λ0 = 1.5 mm, the effective length constant at 3.9 kHz is decreased by a factor 10 to 0.13 mm. Conclusion: The frequency dependency of the neuronal length constant has to be taken into account when predicting the spatial behavior of the membrane voltage as a response to TMS. PMID:27555808
Dependence of the transference of a reduced eye on frequency of light*
Directory of Open Access Journals (Sweden)
T. Evans
2011-12-01
Full Text Available In Gaussian optics the transference is a matrix that is a complete representation of the effects of the system on a ray traversing it. Almost all of the familiar optical properties of the system, such asrefractive error and power of the system, can be calculated from the transference. Because of the central importance of the transference it is useful to have some idea of how it depends on the frequencyof light. This paper examines the simplest model eye, the reduced eye. The dependence of the transference is calculated in terms of both frequency andwavelength of light and both dependencies are displayed graphically. The principal matrix logarithms are also calculated and displayed graphically. Chromatic difference in refractive compensation, power and ametropia are obtained for the reduced eye from the transferences. (S Afr Optom 2011 70(4 149-155
Yakushin, Sergei B
2012-06-01
The gain of the vertical angular vestibulo-ocular reflex (aVOR) was adaptively increased and decreased in a side-down head orientation for 4 h in two cynomolgus monkeys. Adaptation was performed at 0.25, 1, 2, or 4 Hz. The gravity-dependent and -independent gain changes were determined over a range of head orientations from left-side-down to right-side-down at frequencies from 0.25 to 10 Hz, before and after adaptation. Gain changes vs. frequency data were fit with a Gaussian to determine the frequency at which the peak gain change occurred, as well as the tuning width. The frequency at which the peak gravity-dependent gain change occurred was approximately equal to the frequency of adaptation, and the width increased monotonically with increases in the frequency of adaptation. The gravity-independent component was tuned to the adaptive frequency of 0.25 Hz but was uniformly distributed over all frequencies when the adaptation frequency was 1-4 Hz. The amplitude of the gravity-independent gain changes was larger after the aVOR gain decrease than after the gain increase across all tested frequencies. For the aVOR gain decrease, the phase lagged about 4° for frequencies below the adaptation frequency and led for frequencies above the adaptation frequency. For gain increases, the phase relationship as a function of frequency was inverted. This study demonstrates that the previously described dependence of aVOR gain adaptation on frequency is a property of the gravity-dependent component of the aVOR only. The gravity-independent component of the aVOR had a substantial tuning curve only at an adaptation frequency of 0.25 Hz.
Alves, I. P.; Degrazia, G. A.; Buske, D.; Vilhena, M. T.; Moraes, O. L. L.; Acevedo, O. C.
2012-12-01
In this study an integral and an algebraic formulation for the eddy diffusivities in a shear driven planetary boundary layer are derived for pollutant dispersion applications. The expressions depend on the turbulence properties and on the distance from the source. They are based on the turbulent kinetic energy spectra, Taylor’s statistical diffusion theory and measured turbulent characteristics during intense wind events. The good agreement between the algebraic and the integral formulation for the eddy diffusivities corroborate the hypothesis that using an algebraic formulation as a surrogate for the eddy diffusivities in the neutral planetary boundary layer is valid. As a consequence, the vertical eddy diffusivity provided by the algebraic formulation and its asymptotic limit for large time (diffusion time much larger than the Lagrangian integral time scale), were introduced into an analytical air pollution model and validated against data from the classic Prairie Grass project. A statistical analysis, employing specific indices shows that the results are in good agreement with the observations. Furthermore, this study suggests that the inclusion of the memory effect, which is important in regions near to a continuous point source, improves the description of the turbulent transport process of atmospheric contaminants. Therefore, the major finding of this paper is the necessity of including the downwind distance-dependent eddy diffusivity for low continuous point sources in air quality modeling studies.
Gall, Clarence A.
1999-05-01
When an electromagnetic radiation (EMR) source is in uniform motion with respect to an observer, a spectral (Doppler) shift in frequency is seen (blue as it approaches, red as it recedes). Since special relativity is limited to coordinate systems in uniform relative motion, this theory should be subject to this condition. On the other hand, the gravitational red shift (Einstein; Relativity: The Special and the General Theory, Crown,(1961), p.129) claims that EMR frequency decreases as the gravitational field, where the source is located, increases. As a gravitational effect, one would expect its derivation from a solution of the general relativistic field equations (R_μσ=0). Up to now, it has only been possible to derive it indirectly, by comparing the gravitational field to a (centrifugal) field produced by coordinate systems in relative rotational motion as an approximation of special relativity. Since rotation implies acceleration, it does not meet the conditions of special relativity so this is unsatisfactory. This work shows that the problem lies in the Schwarzschild metric which is independent of EMR frequency. By contrast it is easy to deduce the gravitational red shift from the frequency dependent Gall metric (Gall in AIP Conference Proceedings 308, The Evolution of X-Ray Binaries,(1993), p. 87).
FREQUENCY DEPENDENCE OF POLARIZATION OF ZEBRA PATTERN IN TYPE-IV SOLAR RADIO BURSTS
Energy Technology Data Exchange (ETDEWEB)
Kaneda, Kazutaka; Misawa, H.; Tsuchiya, F.; Obara, T. [Planetary Plasma and Atmospheric Research Center, Tohoku University, Sendai, Miyagi 980-8578 (Japan); Iwai, K., E-mail: k.kaneda@pparc.gp.tohoku.ac.jp [National Institute of Information and Communications Technology, 4-2-1, Nukui-Kitamachi, Koganei, Tokyo 184-8795 (Japan)
2015-08-01
We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZPs. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time. The degree of circular polarization was 50%–70% right-handed and it varied little as a function of frequency. Cross-correlation analysis determined that the left-handed circularly polarized component was delayed by 50–70 ms relative to the right-handed component over the entire frequency range of the ZP and this delay increased with the frequency. We examined the obtained polarization characteristics by using pre-existing ZP models and concluded that the ZP was generated by the double-plasma-resonance process. Our results suggest that the ZP emission was originally generated in a completely polarized state in the O-mode and was partly converted into the X-mode near the source. Subsequently, the difference between the group velocities of the O-mode and X-mode caused the temporal delay.
Mierau, Andreas; Klimesch, Wolfgang; Lefebvre, Jérémie
2017-09-30
Neural populations produce complex oscillatory patterns thought to implement brain function. The dominant rhythm in the healthy adult human brain is formed by alpha oscillations with a typical power peak most commonly found between 8 and 12Hz. This alpha peak frequency has been repeatedly discussed as a highly heritable and stable neurophysiological "trait" marker reflecting anatomical properties of the brain, and individuals' general cognitive capacity. However, growing evidence suggests that the alpha peak frequency is highly volatile at shorter time scales, dependent on the individuals' "state". Based on the converging experimental and theoretical results from numerous recent studies, here we propose that alpha frequency variability forms the basis of an adaptive mechanism mirroring the activation level of neural populations which has important functional implications. We here integrate experimental and computational perspectives to shed new light on the potential role played by shifts in alpha peak frequency and discuss resulting implications. We further propose a potential mechanism by which alpha oscillations are regulated in a noisy network of spiking neurons in presence of delayed feedback. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.
Frequency-dependent viscoelastic parameters of mouse brain tissue estimated by MR elastography
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Clayton, E H; Bayly, P V [Department of Mechanical Engineering and Materials Science, Washington University in St Louis, 1 Brookings Drive, Campus Box 1185, Saint Louis, MO 63130 (United States); Garbow, J R, E-mail: clayton@wustl.edu, E-mail: garbow@wustl.edu, E-mail: pvb@wustl.edu [Biomedical Magnetic Resonance Laboratory, Department of Radiology, Washington University in St Louis, 4525 Scott Avenue, Campus Box 8227, Saint Louis, MO 63110 (United States)
2011-04-21
Viscoelastic properties of mouse brain tissue were estimated non-invasively, in vivo, using magnetic resonance elastography (MRE) at 4.7 T to measure the dispersive properties of induced shear waves. Key features of this study include (i) the development and application of a novel MR-compatible actuation system which transmits vibratory motion into the brain through an incisor bar, and (ii) the investigation of the mechanical properties of brain tissue over a 1200 Hz bandwidth from 600-1800 Hz. Displacement fields due to propagating shear waves were measured during continuous, harmonic excitation of the skull. This protocol enabled characterization of the true steady-state patterns of shear wave propagation. Analysis of displacement fields obtained at different frequencies indicates that the viscoelastic properties of mouse brain tissue depend strongly on frequency. The average storage modulus (G') increased from approximately 1.6 to 8 kPa over this range; average loss modulus (G'') increased from approximately 1 to 3 kPa. Both moduli were well approximated by a power-law relationship over this frequency range. MRE may be a valuable addition to studies of disease in murine models, and to pre-clinical evaluations of therapies. Quantitative measurements of the viscoelastic parameters of brain tissue at high frequencies are also valuable for modeling and simulation of traumatic brain injury.
Frequency Dependence of Polarization of Zebra Pattern in Type-IV Solar Radio Bursts
Kaneda, Kazutaka; Iwai, Kazumasa; Tsuchiya, Fuminori; Obara, Takahiro
2015-01-01
We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZP. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time. The degree of circular polarization was 50-70 percent right-handed and it varied little as a function of frequency. Cross-correlation analysis determined that the left-handed circularly polarized component was delayed by 50-70 ms relative to the right-handed component over the entire frequency range of the ZP and this delay increased with the frequency. We examined the obtained polarization characteristics by using pre-existing ZP models and concluded that the ZP was generated by the double plasma resonance process. Our results suggest that the ZP emission was originally generated in a completely polarized state in...
Zhang, Zhibo; Platnick, Steven E.; Ackerman, Andrew S.; Cho, Hyoun-Myoung
2014-01-01
Low-level warm marine boundary layer (MBL) clouds cover large regions of Earth's surface. They have a significant role in Earth's radiative energy balance and hydrological cycle. Despite the fundamental role of low-level warm water clouds in climate, our understanding of these clouds is still limited. In particular, connections between their properties (e.g. cloud fraction, cloud water path, and cloud droplet size) and environmental factors such as aerosol loading and meteorological conditions continue to be uncertain or unknown. Modeling these clouds in climate models remains a challenging problem. As a result, the influence of aerosols on these clouds in the past and future, and the potential impacts of these clouds on global warming remain open questions leading to substantial uncertainty in climate projections. To improve our understanding of these clouds, we need continuous observations of cloud properties on both a global scale and over a long enough timescale for climate studies. At present, satellite-based remote sensing is the only means of providing such observations.
El Khoury, George K.; Schlatter, Philipp; Brethouwer, Geert; Johansson, Arne V.
2014-04-01
Direct numerical simulation data of fully developed turbulent pipe flow are extensively compared with those of turbulent channel flow and zero-pressure-gradient boundary layer flow for Reτ up to 1000. In the near-wall region, a high degree of similarity is observed in the three flow cases in terms of one-point statistics, probability density functions of the wall-shear stress and pressure, spectra, Reynolds stress budgets and advection velocity of the turbulent structures. This supports the notion that the near-wall region is universal for pipe and channel flow. Probability density functions of the wall shear stress, streamwise turbulence intensities, one-dimensional spanwise/azimuthal spectra of the streamwise velocity and Reynolds-stress budgets are very similar near the wall in the three flow cases, suggesting that the three canonical wall-bounded flows share many features. In the wake region, the mean streamwise velocity and Reynolds stress budgets show some expected differences.
Mosgaard, Lars D; Heimburg, Thomas
2013-01-01
Membranes are two-dimensional structures embedded in a three-dimensional heat reservoir. At constant temperature, the heat capacity is proportional to the enthalpy fluctuations. However, when the membrane is embedded in a finite aqueous reservoir, the enthalpy and temperature fluctuations of the reservoir are intimately coupled to the enthalpy fluctuations of the membrane. Employing Monte Carlo simulations, we show that membranes embedded in water reservoirs of various sizes display different enthalpy fluctuations and fluctuation time scales. In particular, larger water reservoirs result in a larger enthalpy fluctuations of the membrane and in slower fluctuation time scales (relaxation times). In periodic processes such as sound propagation in membranes, the membrane has only a finite time available to exchange heat with the medium. A larger frequency therefore reduces the accessible volume of the reservoir. We discuss the relevance of these considerations for the frequency dependence of the compressibility a...
Effect of frequency on amplitude-dependent internal friction in niobium
Energy Technology Data Exchange (ETDEWEB)
Ide, Naoki [Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)]. E-mail: ide@nitech.ac.jp; Atsumi, Tomohiro [Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Nishino, Yoichi [Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan)
2006-12-20
Amplitude-dependent internal friction (ADIF) was measured in a polycrystalline niobium using four modes of flexural vibration from the fundamental to the third-order resonance at room temperature. The ADIF was detected in each vibration mode. The internal-friction versus strain-amplitude curve of the ADIF shifted to a larger strain-amplitude range as frequency increased. The stress-strain curves were derived from the ADIF data, and the microplastic flow stress defined as the stress required to produce a plastic strain of 1 x 10{sup -9} was read from the stress-strain curves. It was found that the microplastic flow stress was proportional to the frequency.
Directory of Open Access Journals (Sweden)
J. Vrba
2013-12-01
Full Text Available In this article, a known concept and measurement probe geometry for the estimation of the dielectric properties of oils have been adapted. The new probe enables the~measurement in the frequency range of 1 to 3000 MHz. Additionally, the measurement probe has been equipped with a~heat exchanger, which has enabled us to measure the dielectric properties of sunflower and olive oil as well as of two commercial emulsion concentrates. Subsequently, corresponding linear empirical temperature and frequency dependent models of the dielectric properties of the above mentioned oils and concentrates have been created. The dielectric properties measured here as well as the values obtained based on the empirical models created here match the data published in professional literature very well.
Dependence of exponents on text length versus finite-size scaling for word-frequency distributions
Corral, Álvaro; Font-Clos, Francesc
2017-08-01
Some authors have recently argued that a finite-size scaling law for the text-length dependence of word-frequency distributions cannot be conceptually valid. Here we give solid quantitative evidence for the validity of this scaling law, using both careful statistical tests and analytical arguments based on the generalized central-limit theorem applied to the moments of the distribution (and obtaining a novel derivation of Heaps' law as a by-product). We also find that the picture of word-frequency distributions with power-law exponents that decrease with text length [X. Yan and P. Minnhagen, Physica A 444, 828 (2016), 10.1016/j.physa.2015.10.082] does not stand with rigorous statistical analysis. Instead, we show that the distributions are perfectly described by power-law tails with stable exponents, whose values are close to 2, in agreement with the classical Zipf's law. Some misconceptions about scaling are also clarified.
Temperature dependence of low-frequency optical phonons in TlInS{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Paucar, Raul; Wakita, Kazuki [Electronics and Computer Engineering, Chiba Institute of Technology, Chiba (Japan); Shim, YongGu [Graduate School of Engineering, Osaka Prefecture University, Osaka (Japan); Alekperov, Oktay; Mamedov, Nazim [Institute of Physics, Azerbaijan National Academy of Sciences, Baku (Azerbaijan)
2015-06-15
The unpolarized Stocks component of the Raman spectra of the layered ternary thallium dichalcogenide, TlInS{sub 2} was studied with the aid of a Raman confocal microscope system in the low-frequency region of 35-150 cm{sup -1} over the temperature range that embraced the region of the successive phase transitions in this crystal. The observed spectra were deconvoluted into Lorentzian peaks to single-out the contribution of each Raman mode. The temperature dependence of the Raman frequency and broadening associated with each mode was then obtained. The irregular temperature behaviour of most modes was disclosed in the proximity of phase transitions. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Frequency dependence of magnetic shielding performance of HTS plates in mixed states
Energy Technology Data Exchange (ETDEWEB)
Kamitani, Atsushi; Yokono, Takafumi [Yamagata Univ., Yonezawa (Japan). Faculty of Engineering; Yokono, Takafumi [Tsukuba Univ., Ibaraki (Japan). Inst. of Information Sciences and Electronics
2000-06-01
The magnetic shielding performance of the high-Tc superconducting (HTS) plate is investigated numerically. The behavior of the shielding current density in the HTS plate is expressed as the integral-differential equation with a normal component of the current vector potential as a dependent variable. The numerical code for solving the equation has been developed by using the combination of the Newton-Raphson method and the successive substitution method and, by use of the code, damping coefficients and shielding factors are evaluated for the various values of the frequency {omega}. The results of computations show that the HTS plate has a possibility of shielding the high-frequency magnetic field with {omega} > or approx. 1 kHz. (author)
State-dependent bulk-boundary maps and black hole complementarity
Papadodimas, Kyriakos; Raju, Suvrat
2014-01-01
We provide a simple and explicit construction of local bulk operators that describe the interior of a black hole in the AdS/CFT correspondence. The existence of these operators is predicated on the assumption that the mapping of CFT operators to local bulk operators depends on the state of the CFT.
Symmetries and invariants of the oscillator and envelope equations with time-dependent frequency
Directory of Open Access Journals (Sweden)
Hong Qin
2006-05-01
Full Text Available The single-particle dynamics in a time-dependent focusing field is examined. The existence of the Courant-Snyder invariant, a fundamental concept in accelerator physics, is fundamentally a result of the corresponding symmetry admitted by the harmonic oscillator equation with linear time-dependent frequency. It is demonstrated that the Lie algebra of the symmetry group for the oscillator equation with time-dependent frequency is eight dimensional, and is composed of four independent subalgebras. A detailed analysis of the admitted symmetries reveals a deeper connection between the nonlinear envelope equation and the oscillator equation. A general theorem regarding the symmetries and invariants of the envelope equation, which includes the existence of the Courant-Snyder invariant as a special case, is demonstrated. As an application to accelerator physics, the symmetries of the envelope equation enable a fast numerical algorithm for finding matched solutions without using the conventional iterative Newton’s method, where the envelope equation needs to be numerically integrated once for every iteration, and the Jacobi matrix needs to be calculated for the envelope perturbation.
Jensen, Lasse; van Duijnen, Piet Th.; Snijders, Jaap G.
2003-12-01
We present a discrete solvent reaction field (DRF) model for the calculation of frequency-dependent hyperpolarizabilities of molecules in solution. In this model the solute is described using density functional theory (DFT) and the discrete solvent molecules are described with a classical polarizable model. The first hyperpolarizability is obtained in an efficient way using time-dependent DFT and the (2n+1) rule. The method was tested for liquid water using a model in which a water molecule is embedded in a cluster of 127 classical water molecules. The frequency-dependent first and second hyperpolarizabilities related to the electric field induced second harmonic generation (EFISH) experiment, were calculated both in the gas phase and in the liquid phase. For water in the gas phase, results are obtained in good agreement with correlated wave function methods and experiments by using the so-called shape-corrected exchange correlation (xc)-potentials. In the liquid phase the effect of using asymptotically correct functionals is discussed. The model reproduced the experimentally observed sign change in the first hyperpolarizaibility when going from the gas phase to the liquid phase. Furthermore, it is shown that the first hyperpolarizability is more sensitive to damping of the solvent-solute interactions at short range than the second hyperpolarizability.
Gasem, Zuhair Mattoug
The need to predict the fatigue performance of aging aerospace structures has focused interest on environmentally assisted cracking in thick-section damage-tolerant aluminum alloys (AA). The objective of this research is to characterize and understand the time-dependent processes that govern environmental fatigue crack propagation (EFCP) in 7XXX series aluminum alloys exposed to an aggressive environment. Results are utilized to identify the rate-controlling step in growth enhancement in order to develop a mechanistic model describing the time dependency of EFCP. Aluminum alloy 7075, tested in the sensitive (SL) orientation and exposed to aqueous chloride solution, is studied. Da/dNcrit for different D K levels depends on 1/√fcrit, as predicted by process zone hydrogen-diffusion-limited crack growth modeling. A model based on hydrogen diffusion controlled growth is modified to include a stress-dependent critical hydrogen concentration normalized with the crack tip hydrogen concentration (Ccrit/CS). It is proposed that da/dNcrit for a given D K and R corresponds to the distance ahead of the crack tip where the local tensile stress associated with Kmax is maximum. The reversed plasticity estimate of this location equals da/dNcrit for two aging conditions of 7075 (SL)/NaCl at R = 0.1. The EFCP dependencies on alloy microstructure (T6 vs. T7), crack orientation (SL vs. LT), and stress ratio are measured and interpreted based on their effect on da/dN crit and fcrit as well as environmental closure. Chromate addition to the chloride solution eliminates the environmental acceleration of crack growth and reduces corrosion-product induced closure. In chromate-inhibited solution, the frequency dependence of EFCP in 7075 (SL) is unique. Da/dN is reduced at moderate and low frequencies to a value similar to crack growth rate in moist air, probably due to formation of a passive film which inhibits hydrogen uptake. Inhibition is mitigated by increasing frequency or increasing
National Aeronautics and Space Administration — Large amplitude, unsteady heating loads and steep flow gradients produced in regions of shock-wave/turbulent boundary-layer interaction (SWTBLI) pose a serious and...
National Aeronautics and Space Administration — Large amplitude, unsteady heating loads and steep flow gradients produced in regions of shock-wave/turbulent boundary-layer interaction (SWTBLI) pose a serious and...
Frequency dependence of CA3 spike phase response arising from h-current properties
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Melodie eBorel
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.
Punia, R.; Kundu, R. S.; Dult, Meenakshi; Murugavel, S.; Kishore, N.
2012-10-01
The ac conductivity of bismuth zinc vanadate glasses with compositions 50V2O5. xBi2O3. (50-x) ZnO has been studied in the frequency range 10-1 Hz to 2 MHz and in temperature range 333.16 K to 533.16 K. The temperature and frequency dependent conductivity is found to obey Jonscher's universal power law for all the compositions of bismuth zinc vanadate glass system. The dc conductivity (σdc), crossover frequency (ωH), and frequency exponent (s) have been estimated from the fitting of experimental data of ac conductivity with Jonscher's universal power law. Enthalpy to dissociate the cation from its original site next to a charge compensating center (Hf) and enthalpy of migration (Hm) have also been estimated. It has been observed that mobility of charge carriers and ac conductivity in case of zinc vanadate glass system increases with increase in Bi2O3 content. In order to determine the conduction mechanism, the ac conductivity and its frequency exponent have been analyzed in the frame work of various theoretical models based on classical hopping over barriers and quantum mechanical tunneling. The ac conduction takes place via tunneling of overlapping large polarons in all the compositions of presently studied vanadate glasses. The fitting of experimental data of ac conductivity with overlapping large polarons tunneling model has also been done. The parameters; density of states at Fermi level (N(EF)), activation energy associated with charge transfer between the overlapping sites (WHO), inverse localization length (α) and polaron radius (rp) obtained from fitting of this model with experimental data are reasonable.
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Clinton B McCracken
Full Text Available High-frequency electrical stimulation of specific brain structures, known as deep brain stimulation (DBS, is an effective treatment for movement disorders, but mechanisms of action remain unclear. We examined the time-dependent effects of DBS applied to the entopeduncular nucleus (EP, the rat homolog of the internal globus pallidus, a target used for treatment of both dystonia and Parkinson's disease (PD. We performed simultaneous multi-site local field potential (LFP recordings in urethane-anesthetized rats to assess the effects of high-frequency (HF, 130 Hz; clinically effective, low-frequency (LF, 15 Hz; ineffective and sham DBS delivered to EP. LFP activity was recorded from dorsal striatum (STR, ventroanterior thalamus (VA, primary motor cortex (M1, and the stimulation site in EP. Spontaneous and acute stimulation-induced LFP oscillation power and functional connectivity were assessed at baseline, and after 30, 60, and 90 minutes of stimulation. HF EP DBS produced widespread alterations in spontaneous and stimulus-induced LFP oscillations, with some effects similar across regions and others occurring in a region- and frequency band-specific manner. Many of these changes evolved over time. HF EP DBS produced an initial transient reduction in power in the low beta band in M1 and STR; however, phase synchronization between these regions in the low beta band was markedly suppressed at all time points. DBS also enhanced low gamma synchronization throughout the circuit. With sustained stimulation, there were significant reductions in low beta synchronization between M1-VA and STR-VA, and increases in power within regions in the faster frequency bands. HF DBS also suppressed the ability of acute EP stimulation to induce beta oscillations in all regions along the circuit. This dynamic pattern of synchronizing and desynchronizing effects of EP DBS suggests a complex modulation of activity along cortico-BG-thalamic circuits underlying the therapeutic
Frequency-dependent action potential prolongation in Aplysia pleural sensory neurones.
Edstrom, J P; Lukowiak, K D
1985-10-01
The effects of repetitive activity on action-potential shape in Aplysia californica pleural sensory cells are described. Action potentials were evoked by intracellular current injection at frequencies between 7.41 and 0.2 Hz. In contrast to other molluscan neurons having brief action potentials, it was found that at these firing rates the normally brief action potential develops a prominent shoulder or plateau during the repolarization phase. Higher stimulus rates broaden the action potential more rapidly and to a greater extent than lower stimulus rates. Inactivation is slow relative to activation; effects of 3-s 6-Hz trains are detectable after 1 min rest. The amplitude of the plateau voltage reaches a maximum of 50-70 mV at the highest stimulus rates tested. Frequency-dependent increases in action-potential duration measured at half-amplitude normally range between 6 and 15 ms. Cadmium, at concentrations between 0.05 and 0.5 mM, antagonizes frequency-dependent broadening. The increases in duration induced by repetitive activity are more sensitive to cadmium than are the increases in plateau amplitude. Tetraethylammonium, at concentrations between 0.5 and 10 mM, slightly increases the duration and amplitude of single action potentials. During repetitive activity at high stimulus rates the maximum duration and rate of broadening are both increased but the amplitude of the plateau potential is not affected by these tetraethylammonium concentrations. Above 10 mM, tetraethylammonium greatly increases the duration and amplitude of single action potentials as well as the rates of action-potential duration and amplitude increase during repetitive activity. These high tetraethylammonium concentrations also cause the normally smoothly increasing duration and amplitude to reach a maximum value early in a train and then decline slowly during the remainder of the train. The consequences of frequency-dependent spike broadening in these neurons have not yet been investigated
Resolution theory and static- and frequency dependent cross-talk in piezoresponse force microscopy
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Jesse, Stephen [ORNL; Guo, Senli [ORNL; Kumar, Amit [ORNL; Rodriguez, Brian [University College, Dublin; Proksch, Roger [Asylum Research, Santa Barbara, CA; Kalinin, Sergei V [ORNL
2010-01-01
Probing materials functionality locally by scanning probe microscopy requires reliable framework for identifying the target signal and separating it from the effects of surface morphology and instrument non-idealities, i.e. instrumental and topographical cross-talk. Here we develop the linear resolution theory framework to describe the cross-talk effects, and apply it for elucidation of frequency dependent cross-talk mechanisms in the Piezoresponse Force Microscopy. The use of band excitation method allows electromechanical/electrical and mechanical/topographic signals to be unambiguously separated. The applicability of functional fit approach and multivariate statistical analysis methods for data identification in band excitation SPM is explored.
Modelling the energy dependencies of high-frequency QPO in black hole X-ray binaries
Zycki, P. T.; A. Niedzwiecki(University of Lodz, Poland); Sobolewska, M. A.
2007-01-01
We model energy dependencies of the quasi periodic oscillations (QPO) in the model of disc epicyclic motions, with X-ray modulation caused by varying relativistic effects. The model was proposed to explain the high frequency QPO observed in X-ray binaries. We consider two specific scenarios for the geometry of accretion flow and spectral formation. Firstly, a standard cold accretion disc with an active X-ray emitting corona is assumed to oscillate. Secondly, only a hot X-ray emitting accretio...
Investigating the frequency dependence of mantle Q by stacking P and PP spectra
Warren, Linda M.; Shearer, Peter M.
2000-11-01
Using seismograms from globally distributed, shallow earthquakes between 1988 and 1998, we compute spectra for P arrivals from epicentral distances of 40° to 80° and PP arrivals from 80° to 160°. Selecting records with estimated signal-to-noise ratios greater than 2, we find 17,836 P and 14,721 PP spectra. We correct each spectrum for the known instrument response and for an ω-2 source model that accounts for varying event sizes. Next, we stack the logarithms of the P and PP spectra in bins of similar source-receiver range. The stacked log spectra, denoted as log(DP') and log(DPP'), appear stable between about 0.16 and 0.86 Hz, with noise and/or bias affecting the results at higher frequencies. Assuming that source spectral differences are randomly distributed, then for shallow events, when the PP range is twice the P range, the average residual source spectrum may be estimated as 2 log(DP')-log(DPP'), and the average P wave attenuation spectrum may be estimated as log(DPP') - log(DP'). The residual source spectral estimates exhibit a smooth additional falloff as ω-0.15±0.05 between 0.16 and 0.86 Hz, indicating that ω-2.15±0.05 is an appropriate average source model for shallow events. The attenuation spectra show little distance dependence over this band and have a P wave t¯* value of ˜0.5 s. We use t¯* measurements from individual P and PP spectra to invert for a frequency-independent Q model and find that the upper mantle is nearly 5 times as attenuating as the lower mantle. Frequency dependence in Qα is difficult to resolve directly in these data but, as previous researchers have noted, is required to reconcile these values with long-period Q estimates. Using Q model QL6 [Durek and Ekström, 1996] as a long-period constraint, we experiment with fitting our stacked log spectra with an absorption band model. We find that the upper corner frequency f2 in the absorption band must be depth-dependent to account for the lack of a strong distance
van Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J.
1998-12-01
In this paper we present time-dependent density functional calculations on frequency-dependent first (β) and second (γ) hyperpolarizabilities for the set of small molecules, N2, CO2, CS2, C2H4, NH3, CO, HF, H2O, and CH4, and compare them to Hartree-Fock and correlated ab initio calculations, as well as to experimental results. Both the static hyperpolarizabilities and the frequency dispersion are studied. Three approximations to the exchange-correlation (xc) potential are used: the widely used Local Density Approximation (LDA), the Becke-Lee-Yang-Parr (BLYP) Generalized Gradient Approximation (GGA), as well as the asymptotically correct Van Leeuwen-Baerends (LB94) potential. For the functional derivatives of the xc potential the Adiabatic Local Density Approximation (ALDA) is used. We have attempted to estimate the intrinsic quality of these methods by using large basis sets, augmented with several diffuse functions, yielding good agreement with recent numerical static LDA results. Contrary to claims which have appeared in the literature on the basis of smaller studies involving basis sets of lesser quality, we find that the static LDA results for β and γ are severely overestimated, and do not improve upon the (underestimated) Hartree-Fock results. No improvement is provided by the BLYP potential which suffers from the same incorrect asymptotic behavior as the LDA potential. The results are however clearly improved upon by the LB94 potential, which leads to underestimated results, slightly improving the Hartree-Fock results. The LDA and BLYP potentials overestimate the frequency dependence as well, which is once again improved by the LB94 potential. Future improvements are expected to come from improved models for asymptotically correct exchange-correlation potentials. Apart from the LB94 potential used in this work, several other asymptotically correct potentials have recently been suggested in the literature and can also be expected to improve considerably
On the value of frequency-dependent traveltime tomography for surface-seismic data
Jordi, Claudio; Schmelzbach, Cedric; Greenhalgh, Stewart
2015-04-01
Frequency-dependent traveltime tomography does not rely on the high-frequency assumption made in classical (asymptotic ray-theory based) tomography. By incorporating the influence of velocity structures in a nearby region (called the first Fresnel volume) around the central ray, it offers a more realistic and accurate representation of the actual physics of seismic wave propagation and thus, improved imaging of the subsurface is expected. Improvements in seismic imaging include the recovery of additional information on the subsurface model, enhanced (model) resolution and better detection and delineation of low velocity zones. It has been argued that finite-frequency effects on traveltimes may be more pronounced in near-surface imaging considering the typical seismic wavelengths and dimensions of heterogeneities compared to global-scale traveltime tomography. To account for the finite frequency characteristics of seismic data, a so-called fat-ray tomography algorithm was developed. The algorithm forms the sum of source and receiver (adjoint) traveltime fields, calculated by finite-difference modeling of the eikonal equation, to determine the necessary Fresnel volumes and sensitivity kernels for the tomographic inversion. Using different scale surface-seismic synthetic data examples, the imaging capabilities of the fat-ray tomography algorithm were investigated and compared to the results of classical ray tomography. The velocity fields used to generate the synthetic data were chosen to emulate two real field data sets, to which the fat-ray tomography was also applied. The first real data example is a large-scale data set (profile length > 10 km) acquired for hydrocarbon search; the second data set was recorded for high-resolution near-surface imaging of a Quaternary valley (profile length < 1 km). Resolution of the tomograms was assessed on the basis of checkerboard tests and a column sum of the sensitivity matrix. For the synthetic data examples as well as for the
Bards, poets, and cliques: frequency-dependent selection and the evolution of language genes.
Cartwright, Reed A
2011-09-01
The ability of humans to communicate via language is a complex, adapted phenotype, which undoubtedly has a recently evolved genetic component. However, the evolutionary dynamics of language-associated alleles are poorly understood. To improve our knowledge of such systems, a population-genetics model for language-associated genes is developed. (The model is general and applicable to social interactions other than communication.) When an allele arises that potentially improves the ability of individuals to communicate, it will experience positive frequency-dependent selection because its fitness will depend on how many other individuals communicate the same way. Consequently, new and rare alleles are selected against, posing a problem for the evolutionary origin of language. However, the model shows that if individuals form language-based cliques, then novel language-associated alleles can sweep through a population. Thus, the origin of language ability can be sufficiently explained by Darwinian processes operating on genetic diversity in a finite population of human ancestors.
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Bruno, R.; Trenchi, L., E-mail: roberto.bruno@iaps.inaf.it [INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, 00133 Roma (Italy)
2014-06-01
We investigate the radial dependence of the spectral break separating the inertial from the dissipation range in power density spectra of interplanetary magnetic field fluctuations, between 0.42 and 5.3 AU, during radial alignments between MESSENGER and WIND for the inner heliosphere and between WIND and ULYSSES for the outer heliosphere. We found that the spectral break moves to higher and higher frequencies as the heliocentric distance decreases. The radial dependence of the corresponding wavenumber is of the kind κ {sub b} ∼ R {sup –1.08}, in good agreement with that of the wavenumber derived from the linear resonance condition for proton cyclotron damping. These results support conclusions from previous studies which suggest that a cyclotron-resonant dissipation mechanism must participate in the spectral cascade together with other possible kinetic noncyclotron-resonant mechanisms.
The influence of frequency-dependent radiative transfer on the structures of radiative shocks
Vaytet, N; Audit, E; Chabrier, G
2013-01-01
Radiative shocks are shocks in a gas where the radiative energy and flux coming from the very hot post-shock material are non-negligible in the shock's total energy budget, and are often large enough to heat the material ahead of the shock. Many simulations of radiative shocks, both in the contexts of astrophysics and laboratory experiments, use a grey treatment of radiative transfer coupled to the hydrodynamics. However, the opacities of the gas show large variations as a function of frequency and this needs to be taken into account if one wishes to reproduce the relevant physics. We have performed radiation hydrodynamics simulations of radiative shocks in Ar using multigroup (frequency dependent) radiative transfer with the HERACLES code. The opacities were taken from the ODALISC database. We show the influence of the number of frequency groups used on the dynamics and morphologies of subcritical and supercritical radiative shocks in Ar gas, and in particular on the extent of the radiative precursor. We fin...
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P. W. J. Glover
2012-01-01
Full Text Available Frequency-dependent streaming potential coefficient measurements have been made upon Ottawa sand and glass bead packs using a new apparatus that is based on an electromagnetic drive. The apparatus operates in the range 1 Hz to 1 kHz with samples of 25.4 mm diameter up to 150 mm long. The results have been analysed using theoretical models that are either (i based upon vibrational mechanics, (ii treat the geological material as a bundle of capillary tubes, or (iii treat the material as a porous medium. The best fit was provided by the Pride model and its simplification, which is satisfying as this model was conceived for porous media rather than capillary tube bundles. Values for the transition frequency were derived from each of the models for each sample and were found to be in good agreement with those expected from the independently measured effective pore radius of each material. The fit to the Pride model for all four samples was also found to be consistent with the independently measured steady-state permeability, while the value of the streaming potential coefficient in the low-frequency limit was found to be in good agreement with other steady-state streaming potential coefficient data.
Frequency-dependent electrodeformation of giant phospholipid vesicles in AC electric field
Peterlin, Primoz
2010-01-01
A model of vesicle electrodeformation is described which obtains a parametrized vesicle shape by minimizing the sum of the membrane bending energy and the energy due to the electric field. Both the vesicle membrane and the aqueous media inside and outside the vesicle are treated as leaky dielectrics, and the vesicle itself is modelled as a nearly spherical shape enclosed within a thin membrane. It is demonstrated (a) that the model achieves a good quantitative agreement with the experimentally determined prolate-to-oblate transition frequencies in the kHz range, and (b) that the model can explain a phase diagram of shapes of giant phospholipid vesicles with respect to two parameters: the frequency of the applied AC electric field and the ratio of the electrical conductivities of the aqueous media inside and outside the vesicle, explored in a recent paper (S. Aranda et al., Biophys. J. 95:L19--L21, 2008). A possible use of the frequency-dependent shape transitions of phospholipid vesicles in conductometry of m...
Botti, Teresa; Sisto, Renata; Sanjust, Filippo; Moleti, Arturo; D'Amato, Luisa
2016-02-01
In this study, a systematic analysis of the dependence on stimulus level and primary frequency ratio r of the different components of human distortion product otoacoustic emissions has been performed, to check the validity of theoretical models of their generation, as regards the localization of the sources and the relative weight of distortion and reflection generation mechanisms. 2f1 - f2 and 2f2 - f1 distortion product otoacoustic emissions of 12 normal hearing ears from six human subjects have been measured at four different levels, in the range [35, 65] dB sound pressure level, at eight different ratios, in the range [1.1, 1.45]. Time-frequency filtering was used to separate distortion and reflection components. Numerical simulations have also been performed using an active nonlinear cochlear model. Both in the experiment and in the simulations, the behavior of the 2f1 - f2 distortion and reflection components was in agreement with previous measurements and with the predictions of the two-source model. The 2f2 - f1 response showed a rotating-phase component only, whose behavior was in general agreement with that predicted for a component generated and reflected within a region basal to the characteristic place of frequency 2f2 - f1, although alternative interpretations, which are also discussed, cannot be ruled out.
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P. W. J. Glover
2012-01-01
Full Text Available Electrokinetic phenomena link fluid flow and electrical flow in porous and fractured media such that a hydraulic flow will generate an electrical current and vice versa. Such a link is likely to be extremely useful, especially in the development of the electroseismic method. However, surprisingly few experimental measurements have been carried out, particularly as a function of frequency because of their difficulty. Here we have considered six different approaches to make laboratory determinations of the frequency-dependent streaming potential coefficient. In each case, we have analyzed the mechanical, electrical, and other technical difficulties involved in each method. We conclude that the electromagnetic drive is currently the only approach that is practicable, while the piezoelectric drive may be useful for low permeability samples and at specified high frequencies. We have used the electro-magnetic drive approach to design, build, and test an apparatus for measuring the streaming potential coefficient of unconsolidated and disaggregated samples such as sands, gravels, and soils with a diameter of 25.4 mm and lengths between 50 mm and 300 mm.
Efroimsky, M.
2012-09-01
It was demonstrated back in 2001 that fitting of the LLR data results in the quality factor Q of the Moon scaling as the frequency ξ to a negative power [8]: Q ˜ ξp , where p = -0.19 . (1) At the same time, numerous measurements by various seismological teams agree on the exponent being positive, not negative [4]. The positive sign of the exponent stems also from geodetic measurements [1], and it finds its explanation within the theory of friction in minerals [5]. On all these grounds, the aforementioned finding by the LLR team appears to be implausible and to disagree with the conventional wisdom of solid state mechanics and seismology. A later reexamination in [9] rendered a less upsetting value, p = -0.09 , which was still negative and still seemed to contradict our knowledge of microphysical processes in solids. The authors later wrote [10]: "There is a weak dependence of tidal specific dissipation Q on period. The Q increases from ˜ 30 at a month to ˜ 35 at one year. Q for rock is expected to have a weak dependence on tidal period, but it is expected to decrease with period rather than increase. The frequency dependence of Q deserves further attention and should be improved." A possible explanation of this paradox comes from the observation that the LLR measurements provided information on the tidal and not seismic dissipation. The difference between these two processes comes from self-gravitation of the celestial body. To address the problem accurately, one has to calculate the tidal factors kl sin ɛl showing up in the Darwin-Kaula expansion for the tidal torque or force. Here kl is the degree-l Love number, while ɛl is the appropriate tidal lag. Sometimes sin ɛl is denoted with 1/Q , which is not recommended, because this notation does not distinguish between the tidal reaction appropriate to harmonics of different degree. This notation also puts one at risk of confusing the tidal damping with the seismic damping, two process that have much in common
Frequency dependent power fluctuations: a feature of the ESR system or physical?
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Y. Ogawa
Full Text Available The k-dependence of the received power in high signal-to-noise ratio (SNR conditions, occurring for naturally enhanced ion-acoustic lines (NEIALs and for real satellites, is investigated by using the EISCAT Svalbard Radar (ESR, where the data are recorded in eight separate channels using different frequencies. For the real satellites we find large variations of the relative powers from event to event, which is probably due to a different number of pulses catching the satellite over the integration period. However, the large power difference remains unexpected in one case. Over short time scale (< 10 s the relative power difference seems to be highly stable. For most NEIAL events the differences between channels are within noise level. In a few cases variations of the relative power well above both the estimated and expected 1-sigma level occur over a signal preintegrated profile. We thus suggest that the frequency dependence of the power in NEIAL events has its origin in the scattering medium itself as the most plausible explanation.
Key words: Ionosphere (auroral ionosphere; plasma waves and instabilities; instruments and techniques
Analysis of the frequency-dependent response to wave forcing in the extratropics
Directory of Open Access Journals (Sweden)
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.
Modelling the energy dependencies of high-frequency QPO in black hole X-ray binaries
Zycki, P T; Sobolewska, M A
2007-01-01
We model energy dependencies of the quasi periodic oscillations (QPO) in the model of disc epicyclic motions, with X-ray modulation caused by varying relativistic effects. The model was proposed to explain the high frequency QPO observed in X-ray binaries. We consider two specific scenarios for the geometry of accretion flow and spectral formation. Firstly, a standard cold accretion disc with an active X-ray emitting corona is assumed to oscillate. Secondly, only a hot X-ray emitting accretion flow oscillates, while the cold disc is absent at the QPO radius. We find that the QPO spectra are generally similar to the spectrum of radiation emitted at the QPO radius, and they are broadened by the relativistic effects. In particular, the QPO spectrum contains the disc component in the oscillating disc with a corona scenario. We also review the available data on energy dependencies of high frequency QPO, and we point out that they appear to lack the disc component in their energy spectra. This would suggest the hot...
FEM-calculations on the frequency dependence of hysteretic losses in coated conductors
Energy Technology Data Exchange (ETDEWEB)
Sander, M; Grilli, F, E-mail: michael.sander@kit.ed [Karlsruhe Institute of Technology, Institute for Technical Physics (ITEP), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)
2010-06-01
Calculations based on two different finite-element models have been carried out to investigate the flux flow behaviour of High Temperature Superconductors (HTS), in particular of Coated Conductors (CC) based on 123-HTS. The models allow the simulation of the response of the CC to various experimental operating conditions: e.g. a fast ramping of the transport current typically done in measurements of the critical current I{sub c} or sinusoidal changes of an external magnetic field typically used in AC loss measurements. The models also allow calculating the response to arbitrary combinations of current and field changes. The superconductor is modelled by using either a simple power-law E(J) characteristic or one which also accounts for field and temperature dependences. The obtained results go beyond Bean's approximation, which is mostly employed for interpreting such flux penetration effects. One consequence is that hysteretic losses, which in Bean's model are frequency independent, show a dependence on the time scales of current or field changes. The field and frequency ranges where such deviations from Bean's model should be taken into account are discussed.
Chamakuri, Nagaiah; Engwer, Christian; Kunisch, Karl
2014-09-01
Optimal control for cardiac electrophysiology based on the bidomain equations in conjunction with the Fenton-Karma ionic model is considered. This generic ventricular model approximates well the restitution properties and spiral wave behavior of more complex ionic models of cardiac action potentials. However, it is challenging due to the appearance of state-dependent discontinuities in the source terms. A computational framework for the numerical realization of optimal control problems is presented. Essential ingredients are a shape calculus based treatment of the sensitivities of the discontinuous source terms and a marching cubes algorithm to track iso-surface of excitation wavefronts. Numerical results exhibit successful defibrillation by applying an optimally controlled extracellular stimulus.
The evolution of social learning rules: payoff-biased and frequency-dependent biased transmission.
Kendal, Jeremy; Giraldeau, Luc-Alain; Laland, Kevin
2009-09-21
Humans and other animals do not use social learning indiscriminately, rather, natural selection has favoured the evolution of social learning rules that make selective use of social learning to acquire relevant information in a changing environment. We present a gene-culture coevolutionary analysis of a small selection of such rules (unbiased social learning, payoff-biased social learning and frequency-dependent biased social learning, including conformism and anti-conformism) in a population of asocial learners where the environment is subject to a constant probability of change to a novel state. We define conditions under which each rule evolves to a genetically polymorphic equilibrium. We find that payoff-biased social learning may evolve under high levels of environmental variation if the fitness benefit associated with the acquired behaviour is either high or low but not of intermediate value. In contrast, both conformist and anti-conformist biases can become fixed when environment variation is low, whereupon the mean fitness in the population is higher than for a population of asocial learners. Our examination of the population dynamics reveals stable limit cycles under conformist and anti-conformist biases and some highly complex dynamics including chaos. Anti-conformists can out-compete conformists when conditions favour a low equilibrium frequency of the learned behaviour. We conclude that evolution, punctuated by the repeated successful invasion of different social learning rules, should continuously favour a reduction in the equilibrium frequency of asocial learning, and propose that, among competing social learning rules, the dominant rule will be the one that can persist with the lowest frequency of asocial learning.
Method of frequency dependent correlations: investigating the variability of total solar irradiance
Pelt, J.; Käpylä, M. J.; Olspert, N.
2017-03-01
Context. This paper contributes to the field of modeling and hindcasting of the total solar irradiance (TSI) based on different proxy data that extend further back in time than the TSI that is measured from satellites. Aims: We introduce a simple method to analyze persistent frequency-dependent correlations (FDCs) between the time series and use these correlations to hindcast missing historical TSI values. We try to avoid arbitrary choices of the free parameters of the model by computing them using an optimization procedure. The method can be regarded as a general tool for pairs of data sets, where correlating and anticorrelating components can be separated into non-overlapping regions in frequency domain. Methods: Our method is based on low-pass and band-pass filtering with a Gaussian transfer function combined with de-trending and computation of envelope curves. Results: We find a major controversy between the historical proxies and satellite-measured targets: a large variance is detected between the low-frequency parts of targets, while the low-frequency proxy behavior of different measurement series is consistent with high precision. We also show that even though the rotational signal is not strongly manifested in the targets and proxies, it becomes clearly visible in FDC spectrum. A significant part of the variability can be explained by a very simple model consisting of two components: the original proxy describing blanketing by sunspots, and the low-pass-filtered curve describing the overall activity level. The models with the full library of the different building blocks can be applied to hindcasting with a high level of confidence, Rc ≈ 0.90. The usefulness of these models is limited by the major target controversy. Conclusions: The application of the new method to solar data allows us to obtain important insights into the different TSI modeling procedures and their capabilities for hindcasting based on the directly observed time intervals.
Frequency and amplitude dependences of molding accuracy in ultrasonic nanoimprint technology
Mekaru, Harutaka; Takahashi, Masaharu
2009-12-01
We use neither a heater nor ultraviolet lights, and are researching and developing an ultrasonic nanoimprint as a new nano-patterning technology. In our ultrasonic nanoimprint technology, ultrasonic vibration is not used as a heat generator instead of the heater. A mold is connected with an ultrasonic generator, and mold patterns are pushed down and pulled up at a high speed into a thermoplastic. Frictional heat is generated by ultrasonic vibration between mold patterns and thermoplastic patterns formed by an initial contact force. However, because frictional heat occurs locally, the whole mold is not heated. Therefore, a molding material can be comprehensively processed at room temperature. A magnetostriction actuator was built into our ultrasonic nanoimprint system as an ultrasonic generator, and the frequency and amplitude can be changed between dc-10 kHz and 0-4 µm, respectively. First, the ultrasonic nanoimprint was experimented by using this system on polyethylene terephthalate (PET, Tg = 69 °C), whose the glass transition temperature (Tg) is comparatively low in engineering plastics, and it was ascertained that the most suitable elastic material for this technique was an ethyl urethane rubber. In addition, we used a changeable frequency of the magnetostriction actuator, and nano-patterns in an electroformed-Ni mold were transferred to a 0.5 mm thick sheet of PET, polymethylmethacrylate (PMMA) and polycarbonate (PC), which are typical engineering plastics, under variable molding conditions. The frequency and amplitude dependence of ultrasonic vibration to the molding accuracy were investigated by measuring depth and width of imprinted patterns. As a result, regardless of the molding material, the imprinted depth was changed drastically when the frequency exceeded 5 kHz. On the other hand, when the amplitude of ultrasonic vibration grew, the imprinted depth gradually deepened. Influence of the frequency and amplitude of ultrasonic vibration was not observed
Ivanisenko, P V
2012-01-01
The Kramers problem for quantum fermi-gases with specular - diffuse boundary conditions of the kinetic theory is considered. On an example of Kramers problem the new generalised method of a source of the decision of the boundary problems from the kinetic theory is developed. The method allows to receive the decision with any degree of accuracy. At the basis of a method lays the idea of representation of a boundary condition on distribution function in the form of a source in the kinetic equation. By means of integrals Fourier the kinetic equation with a source is reduced to the integral equation of Fredholm type of the second kind. The decision is received in the form of Neumann's series.
Bedrikova, E A
2012-01-01
The Kramers problem for quantum Bose-gases with specular-diffuse boundary conditions of the kinetic theory is considered. On an example of Kramers' problem the new generalized method of a source of the decision of the boundary problems from the kinetic theory is developed. The method allows to receive the decision with any degree of accuracy. At the basis of a method lays the idea of representation of a boundary condition on distribution function in the form of a source in the kinetic equation. By means of integrals Fourier the kinetic equation with a source is reduced to the integral equation of Fredholm type of the second kind. The decision is received in the form of Neumann's series.
Frequency and Field Dependences of Giant Magneto-Impedance Effect in Sandwiched FeCuCrVSiB Films
Institute of Scientific and Technical Information of China (English)
DAI You-Yong; XIAO Shu-Qin; LIU Yi-Hua; ZHANG Lin; WU Hou-Zheng; ZHANG Yan-Zhong
2001-01-01
The giant magneto-impedance (GMI) effect has been investigated in sandwiched FeCuCrVSiB films annealed at 300 ℃ for 1.5 h. The frequency and field dependences of the GMI have been observed in the frequency range from 50 kHz to 13 MHz. The GMI ratio increases at first with increasing frequency, and reaches its maximum value of 136% at a very low characteristic frequency of about 4 MHz, and then decreases with further increasing frequency. These superior properties are related to the special structure of the sandwiched films.
van Roekeghem, Ambroise; Vaugier, Loïg; Jiang, Hong; Biermann, Silke
2016-09-01
We calculate the strength of the frequency-dependent on-site electronic interactions in the iron pnictides LaFeAsO, BaFe2As2 , BaRu2As2 , and LiFeAs and the chalcogenide FeSe from first principles within the constrained random phase approximation. We discuss the accuracy of an atomiclike parametrization of the two-index density-density interaction matrices based on the calculation of an optimal set of three independent Slater integrals, assuming that the angular part of the Fe d localized orbitals can be described within spherical harmonics as for isolated Fe atoms. We show that its quality depends on the ligand-metal bonding character rather than on the dimensionality of the lattice: it is excellent for ionic-like Fe-Se (FeSe) chalcogenides and a more severe approximation for more covalent Fe-As (LaFeAsO, BaFe2As2 ) pnictides. We furthermore analyze the relative importance of different screening channels, with similar conclusions for the different pnictides but a somewhat different picture for the benchmark oxide SrVO3: the ligand channel does not appear to be dominant in the pnictides, while oxygen screening is the most important process in the oxide. Finally, we analyze the frequency dependence of the interaction. In contrast to simple oxides, in iron pnictides its functional form cannot be simply modeled by a single plasmon, and the actual density of modes enters the construction of an effective Hamiltonian determining the low-energy properties.
Turbulent structures dependent on tidal currents in the bottom boundary layer of the Venice Lagoon
Energy Technology Data Exchange (ETDEWEB)
Cavazzoni, S.; Crosera, F.
The time series of horizontal and vertical turbulent velocity fluctuations u', w' have been recorded by means of an electromagnetic currentmeter in proximity of the bottom of a channel feeding the Venetian Lagoon. Simultaneous surface gradients have been recorded at two tide gauge stations, one upstream and the other downstream of the chosen test site. The time series of u', w' and u'w' values have been analysed using standard digital methods and, for each record, spectra, cross-spectra, co-spectra, quadrature spectra, phase and coherence of u' and w' have been computed. This analysis allows us to determine temporal and spatial dimensions of turbulent structures that give the greatest contribution to Reynolds stress (- rhoanti u'anti w', where rho is the water density). These structures that seem to be dependent on longitudinal surface gradients are primarily responsible for vertical momentum transport and, consequently, for the lift-up and transport of sediments. Statistic distributions of u', w' and u'w' values indicate that the greatest turbulent structures are those with u'w'<0 and with u'<0 predominating.
EFFECTS OF LOW-FREQUENCY ELECTROACUPUNCTURE ON THE IMMUNOLOGIC FUNCTION IN MORPHINE DEPENDENCE RATS
Institute of Scientific and Technical Information of China (English)
韩肖华; 吴绪平; 刘又香; 章敏; 王亚文
2003-01-01
Objective: To observe the effect of low-frequency electroacupuncture (EA) on the immunologic tunc-tion in morphine dependence rats. Methods: Forty SD rats were used in this study. Morphine-dependence model wasestablished by intraperitoneal injection of morphine hydrochloride continuously for 5 days and hastened by administra-tion (i. p) of Naloxone. These rats were randomly divided into control, model, EA and auto-demorphinization groupswith 10 cases being in each group. In EA group, "Guanyuan"(CV 4),"Mingmen"(GV 4), etc. were punctured andstimulated electrically. Positive T lymphocyte subgroups, CD+4 and CD8+ in the peripheral blood were detected with flu-orescence immuno-assay. Results: In model group, sertrn percentage of CD+4 and CD+4/CD+8 decreased considerablyin comparison with those of control group (P＜ 0.01 ); while in EA group, CD+4 level and CD+4/CD+8 increased signifi-cantly compared with those of model group ( P ＜ 0.01); and no significant differences were found between auto-demor-phinization group and model group and between EA and control groups in these two indexes. Conclusion: Low-frequen-cy EA can promote the restoration of the immune function of morphine dependence rats.
Kobayashi, Tatsuya; Itoh, Kimitaka; Ida, Katsumi; Inagaki, Sigeru; Itoh, Sanae-I.
2017-07-01
In this paper we propose a new set of formulae for estimating the harmonic frequency dependence of the diffusion coefficient and the convective velocity in the heat pulse propagation experiment in order to investigate the transport hysteresis. The assumptions that are used to derive the formulae can result in dummy frequency dependences of the transport coefficients. It is shown that these dummy frequency dependences of the transport coefficients can be distinguished from the true frequency dependence due to the transport hysteresis by using a bidirectional heat pulse propagation manner, in which both the outward propagating heat pulse and the inward propagating heat pulse are analyzed. The validity of the new formulae are examined in a simple numerical calculation.
Han, Kai-Feng; Zeng, Xin-Wu
2011-06-01
Based on the dual source cumulative rotation technique in the time-domain proposed by Zeng and MacBeth (1993), a new algebraic processing technique for extracting shear-wave splitting parameters from multi-component VSP data in frequency-dependent medium has been developed. By using this dual source cumulative rotation technique in the frequency-domain (DCTF), anisotropic parameters, including polarization direction of the shear-waves and timedelay between the fast and slow shear-waves, can be estimated for each frequency component in the frequency domain. It avoids the possible error which comes from using a narrow-band filter in the current commonly used method. By using synthetic seismograms, the feasibility and validity of the technique was tested and a comparison with the currently used method was also given. The results demonstrate that the shear-wave splitting parameters frequency dependence can be extracted directly from four-component seismic data using the DCTF. In the presence of larger scale fractures, substantial frequency dependence would be found in the seismic frequency range, which implies that dispersion would occur at seismic frequencies. Our study shows that shear-wave anisotropy decreases as frequency increases.
Resolution theory, and static and frequency-dependent cross-talk in piezoresponse force microscopy
Energy Technology Data Exchange (ETDEWEB)
Jesse, S; Guo, S; Kumar, A; Kalinin, S V [The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Rodriguez, B J [Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4 (Ireland); Proksch, R [Asylum Research, Santa Barbara, CA 93117 (United States)
2010-10-08
Probing the functionality of materials locally by means of scanning probe microscopy (SPM) requires a reliable framework for identifying the target signal and separating it from the effects of surface morphology and instrument non-idealities, e.g. instrumental and topographical cross-talk. Here we develop a linear resolution theory framework in order to describe the cross-talk effects, and apply it for elucidation of frequency-dependent cross-talk mechanisms in piezoresponse force microscopy. The use of a band excitation method allows electromechanical/electrical and mechanical/topographic signals to be unambiguously separated. The applicability of a functional fit approach and multivariate statistical analysis methods for identification of data in band excitation SPM is explored.
Picosecond laser-induced breakdown at 5321 and 5347 A - Observation of frequency-dependent behavior
Smith, W. L.; Bechtel, J. H.; Bloembergen, N.
1977-01-01
A study is presented of picosecond laser-induced breakdown at 3547 and 5321 A of several materials. The thresholds obtained for breakdown at 5321 A are compared to previous results obtained at 1.064 microns using the same laser system. This comparison illustrates the transition of bulk laser-induced breakdown as it becomes increasingly frequency dependent. UV picosecond pulses are obtained by mixing 5321 A and 1.064 micron pulses in a KH2PO4 crystal. Upper and lower bounds on the 3547 A breakdown threshold are defined, although some effects of walk-off distortion and self-focusing are observed. The results are discussed with reference to models for the intrinsic processes involved in the breakdown, i.e., avalanche and multiphoton ionization.
Roberts, D. A.; Goldstein, M. L.; Klein, L. W.
1990-01-01
A study is presented of the heliocentric distance, frequency, and stream structure dependence of the amplitudes of interplanetary fluctuations in the velocity and magnetic field from 0.3 to nearly 20 AU and for spacecraft-frame periods of 10 days to a few hours. Evidence is presented that, at a given heliocentric distance, the amplitude of the magnetic field fluctuations is proportional to the magnitude of the field, nearly independently of the solar wind speed. The radial evolution of magnetic fluctuations is shown to be nearly consistent with WKB expectations except at smaller scales in the inner heliosphere and at the largest scales in the outer heliosphere. While the large-scale velocity fluctuations are kinetic energy-dominated in the inner heliosphere due to the presence of streams, the magnetic fluctuation energy eventually comes to be slightly dominant over the kinetic energy at all scales. The theoretical implications of the results are considered.
Energy Technology Data Exchange (ETDEWEB)
Gould, A.; Huang, M.; Bhagat, S.M. (Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (USA) Center for Superconductivity Research, University of Maryland, College Park, Maryland 20742-4111 (USA)); Tyagi, S. (Department of Physics and Atmospheric Science, Drexel University, Philadelphia, Pennsylvania 11004 (USA))
1991-04-15
Hysteresis in the microwave-power absorption of HTSC powders was studied as a function of temperature ({ital T}), field-sweep amplitude ({ital H}{sub max}), and orientation between the dc field ({bold H}{sub dc}) and the wave vector of the microwaves ({bold k}). It was found that (i) the sizable low-temperature hysteresis effects occur only if {bold H}{sub dc}{parallel}{bold k}, (ii) the temperature and frequency dependence of the hysteresis is strongly affected by {ital H}{sub max}, (iii) the high- and low-temperature virgin curves are quite different, and (iv) the minimum of the absorption signal increases with {ital H}{sub max} and {ital T}. The low-temperature hysteresis loops were found to be similar to loops obtained from nonlinear equations describing cusp catastrophes.
Beraha, N.; Soba, A.; Carusela, M. F.
2016-12-01
Following the nonequilibrium Green's function formalism we study the thermal transport in a composite chain subject to a time-dependent perturbation. The system is formed by two finite linear asymmetric harmonic chains subject to an on-site potential connected together by a time-modulated coupling. The ends of the chains are coupled to two phononic reservoirs at different temperatures. We present the relevant equations used to calculate the heat current along each segment. We find that the system presents different transport regimes according the driving frequency and temperature gradients. One of the regimes corresponds to a heat pump against thermal gradient, thus a characterization of the cooling performance of the device is presented.
Iijima, Yukina; Kudo, Nobuki
2017-07-01
Acoustic fields of a short-pulsed ultrasound propagating through a transparent medium with ultrasound attenuation were visualized by the focused shadowgraph technique. A brightness waveform and its spatial integrations were derived from a visualized field image and compared with a pressure waveform measured by a membrane hydrophone. The experimental results showed that first-order integration of the brightness wave has good agreement with the pressure waveforms. Frequency-dependent attenuation of the pulse propagating through castor oil was derived from brightness and pressure waveforms, and attenuation coefficients determined from focused shadowgraphy and hydrophone techniques showed good agreement. The results suggest the usefulness of the shadowgraph technique not only for the visualization of ultrasound fields but also for noncontact estimation of rough pressure waveforms and correct ultrasound attenuation.
Wear, Keith A.
2002-05-01
Measurements of ultrasonic properties of calcaneus (heel bone) have been shown to be effective for the diagnosis of osteoporosis. However, the mechanisms underlying the interaction between ultrasound and bone are currently not well understood. A model that predicts backscatter from trabecular bone has been developed. Scattering is assumed to originate from the surfaces of trabeculae, which are modeled as long, thin, elastic cylinders with radii small compared with the ultrasonic wavelength. Experimental measurements of backscatter using broadband ultrasound centered at 500 kHz from 43 trabecular bone samples (from human calcaneus) in vitro have been performed. Microcomputed tomography has been performed on all 43 samples in order to measure microarchitectural features. The theory correctly predicts the measured dependences of backscatter on ultrasonic frequency and trabecular thickness. [Funding from the FDA Office of Womens Health is gratefully acknowledged.
Chau, Ying; Suen, Wai Leung Langston; Tse, Ho Yan; Wong, Hoi Sang
2017-03-30
We previously employed ultrasound as a needleless approach to deliver macromolecules via the transscleral route to the back of the eye in live animals (Suen et al., 2013). Here, we investigated the nature of the ultrasound-enhanced transport through sclera, the outermost barrier in the transscleral route. Thus, the possible role of cavitation from ultrasound was explored; its effect during and after sonication on scleral penetration was measured; and the dependence on the size of macromolecules was determined. We applied ultrasound frequency from 40kHz to 3MHz at ISATA (spatial-average-temporal-average intensity) of 0.05W/cm(2) to fresh rabbit sclera ex vivo. Fluorescent dextran of size 20kDa to 150kDa was used as macromolecular probes. We measured the distance of penetration of the probes through the sclera over 30s during sonication and over 15min after sonication from cryosectioned tissue images. Deeper penetration in the sclera was observed with decreasing frequency. The presence of stable cavitation was further verified by passive acoustic detection. The effect during sonication increased penetration distance up to 20 fold and was limited to macromolecular probes ≤70kDa. The effect post sonication increased penetration distance up to 3 fold and attributed to the improved intrasscleral transport of macromolecules ≥70kDa. Post-sonication enhancement diminished gradually in 3h. As the extent of cavitation increased with decreasing frequency, the trend observed supports the contribution of (stable) cavitation to enhancing transport through sclera. Effect during sonication was attributed to flow associated with acoustic microstreaming. Effect post sonication was attributed to the temporary increase in scleral permeability. Flow-associated effect was more pronounced but only applied to smaller macromolecules. Copyright © 2017. Published by Elsevier B.V.
Li, Bai-Yan; Feng, Bin; Tsu, Hwa Y; Schild, John H
2007-06-21
Sensory information arising from visceral organ systems is encoded into action potential trains that propagate along afferent fibers to target nuclei in the central nervous system. These information streams range from tight patterns of action potentials that are well synchronized with the sensory transduction event to irregular, patternless discharge with no clear correlation to the sensory input. In general terms these afferent pathways can be divided into unmyelinated and myelinated fiber types. Our laboratory has a long standing interest in the functional differences between these two types of afferents in terms of the preprocessing of sensory information into action potential trains (synchrony, frequency, duration, etc.), the reflexogenic consequences of this sensory input to the central nervous system and the ionic channels that give rise to the electrophysiological properties of these unique cell types. The aim of this study was to determine whether there were any functional differences in the somatic action potential characteristics of unmyelinated and myelinated vagal afferents in response to different rates of sensory nerve stimulation. Our results showed that activity and frequency-dependent widening of the somatic action potential was quite prominent in unmyelinated but not myelinated vagal afferents. Spike broadening often leads to increased influx of Ca(2+) ions that has been associated with a diverse range of modulatory mechanisms both at the cell body and central synaptic terminations (e.g. increased neurotransmitter release.) We conclude that our observations are indicative of fundamentally different mechanisms for neural integration of sensory information arising from unmyelinated and myelinated vagal afferents.
Energy Technology Data Exchange (ETDEWEB)
Brill, J. W.; Shahi, Maryam; Yao, Y. [Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055 (United States); Payne, Marcia M.; Anthony, J. E. [Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055 (United States); Edberg, Jesper; Crispin, Xavier [Department of Science and Technology, Organic Electronics, Linköping University, SE-601 74 Norrköping (Sweden)
2015-12-21
We have used a photothermal technique, in which chopped light heats the front surface of a small (∼1 mm{sup 2}) sample and the chopping frequency dependence of thermal radiation from the back surface is measured with a liquid-nitrogen-cooled infrared detector. In our system, the sample is placed directly in front of the detector within its dewar. Because the detector is also sensitive to some of the incident light, which leaks around or through the sample, measurements are made for the detector signal that is in quadrature with the chopped light. Results are presented for layered crystals of semiconducting 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pn) and for papers of cellulose nanofibrils coated with semiconducting poly(3,4-ethylene-dioxythiophene):poly(styrene-sulfonate) (NFC-PEDOT). For NFC-PEDOT, we have found that the transverse diffusivity, smaller than the in-plane value, varies inversely with thickness, suggesting that texturing of the papers varies with thickness. For TIPS-pn, we have found that the interlayer diffusivity is an order of magnitude larger than the in-plane value, consistent with previous estimates, suggesting that low-frequency optical phonons, presumably associated with librations in the TIPS side groups, carry most of the heat.
Lakowicz, Joseph R.; Gryczynski, Ignacy; Szmacinski, Henryk; Nowaczyk, Kazimierz; Johnson, Michael L.
1992-02-01
During the past seven years, there have been remarkable advances in the frequency-domain method for measurement of time-resolved emission or light scattering. In this presentation we describe the recent extension of the frequency range to 10 GHz using a specially designed microchannel plate PMT. Experimental data will be shown for measurement of picosecond rotational diffusion and for sub-picosecond resolution of time delays. The resolution of ps to ns timescale processes is not obtained at the expense of sensitivity or is it shown by measurements on the intrinsic tryptophan emission from hemoglobin. We also describe a time- resolved reflectance imaging experiment on a scattering medium containing an absorbing object. Time-resolved imaging of the back-scattered light is realized by means of a RF-phase- sensitive camera, synchronized to the laser pulses. By processing the stored images, a final image can be created, the contrast of which is based only on time differences of the back- scattered photons. This image reveals the presence and position of the absorber within the scattering medium. And finally, we describe a new methodology, fluorescence lifetime imaging (FLIM), in which the contrast depends on the fluorescence lifetime at each point in a two-dimensional image, and not the local concentration and/or intensity of the fluorophore. We used FLIM to create lifetime images of NADH when free in solution and when bound to malate dehydrogenase. FLIM has numerous potential applications in cell biology and imaging.
Frequency dependent steering with backward leaky waves via photonic crystal interface layer.
Colak, Evrim; Caglayan, Humeyra; Cakmak, Atilla O; Villa, Alessandro D; Capolino, Filippo; Ozbay, Ekmel
2009-06-08
A Photonic Crystal (PC) with a surface defect layer (made of dimers) is studied in the microwave regime. The dispersion diagram is obtained with the Plane Wave Expansion Method. The dispersion diagram reveals that the dimer-layer supports a surface mode with negative slope. Two facts are noted: First, a guided (bounded) wave is present, propagating along the surface of the dimer-layer. Second, above the light line, the fast traveling mode couple to the propagating spectra and as a result a directive (narrow beam) radiation with backward characteristics is observed and measured. In this leaky mode regime, symmetrical radiation patterns with respect to the normal to the PC surface are attained. Beam steering is observed and measured in a 70 degrees angular range when frequency ranges in the 11.88-13.69 GHz interval. Thus, a PC based surface wave structure that acts as a frequency dependent leaky wave antenna is presented. Angular radiation pattern measurements are in agreement with those obtained via numerical simulations that employ the Finite Difference Time Domain Method (FDTD). Finally, the backward radiation characteristics that in turn suggest the existence of a backward leaky mode in the dimer-layer are experimentally verified using a halved dimer-layer structure.
Long range dependence in the high frequency USD/INR exchange rate
Kumar, Dilip
2014-02-01
Using high frequency data, this paper examines the long memory property in the unconditional and conditional volatility of the USD/INR exchange rate at different time scales using the Local Whittle (LW), the Exact Local Whittle (ELW) and the FIAPARCH models. Results indicate that the long memory property remains quite stable across different time scales for both unconditional and conditional volatility measures. Results from the non-overlapping moving window approach indicate that the extreme events (such as the subprime crisis and the European debt crisis) resulted in highly persistent behavior of the USD/INR exchange rate and thus lead to market inefficiency. This paper also examines the long memory property in the realized volatility based on different time scale data. Results indicate that the realized volatility measures based on different scales of the high frequency data exhibit a consistent and stable long memory property. However, the realized volatility measures based on daily data exhibit lower degree of long-range dependence. This study has implications for traders and investors (with different trading horizons) and can be helpful in predicting expected future volatility and in designing and implementing trading strategies at different time scales.
Directory of Open Access Journals (Sweden)
Hamed Hooshangnejad
2016-06-01
Full Text Available The main purpose of this study is to build a Computational model based on ModelFest dataset which is able to predict contrast sensitivity while it benefits from simplicity, efficiency and accuracy, which makes it suitable for hardware implementation, practical uses, online tests, real-time processes, an improved Standard Observer and retina prostheses. It encompasses several components, and in particular, frequency dependent aperture effect (FDAE which is used for the first time on this dataset, which made the model more accurate and closer to reality. Shortcomings of previous models and the necessity of existence of FDAE for more accuracy led us to develop a new model based on Wavelet Transform that gives us the advantage of speed and the capability to process each frequency channels output. Considering our goal for building an efficient model, we introduce a new formula for modeling contrast sensitivity function, which generates lower RMS error and better timing performance. Eventually, this new model leads to having as yet lowest RMS error and solving the problem of long execution time of prior models and reduces them by almost a factor of twenty.
Singh, Kamakhya Prasad
1995-01-01
A new methodology is developed to simulate unsteady flows about prescribed and aerodynamically determined moving boundary problems. The method couples the fluid dynamics and rigid-body dynamics equations to capture the time-dependent interference between stationary and moving boundaries. The unsteady, compressible, inviscid (Euler) equations are solved on dynamic, unstructured grids by an explicit, finite-volume, upwind method. For efficiency, the grid adaptation is performed within a window around the moving object. The Eulerian equations of the rigid-body dynamics are solved by a Runge-Kutta method in a non-inertial frame of reference. The two-dimensional flow solver is validated by computing the flow past a sinusoidally-pitching airfoil and comparing these results with the experimental data. The overall methodology is used for two two-dimensional examples: the flow past an airfoil which is performing a three-degrees-of-freedom motion in a transonic freestream, and the free-fall of a store after separation from a wing-section. Then the unstructured mesh methodology is extended to three-dimensions to simulate unsteady flow past bodies in relative motion, where the trajectory is determined from the instantaneous aerodynamics. The flow solver and the adaptation scheme in three dimensions are validated by simulating the transonic, unsteady flow around a wing undergoing a forced, periodic, pitching motion, and comparing the results with the experimental data. To validate the trajectory code, the six-degrees-of-freedom motion of a store separating from a wing was computed using the experimentally determined force and moment fields, then comparing with an independently generated trajectory. Finally, the overall methodology was demonstrated by simulating the unsteady flowfield and the trajectory of a store dropped from a wing. The methodology, its computational cost notwithstanding, has proven to be accurate, automated, easy for dynamic gridding, and relatively efficient
Frequency-dependent effect of nitric oxide donor nitroglycerin on bone.
Wimalawansa, S; Chapa, T; Fang, L; Yallampalli, C; Simmons, D; Wimalawansa, S
2000-06-01
Recently, we showed that supplementation with nitric oxide (NO) via donor nitroglycerin (NG) alleviated the ovariectomy and corticosteroid-induced bone loss in rats. In humans, high doses or frequent applications of NG (i.e., for angina) lead to rapid loss of its efficacy in relieving angina. To examine whether there is a similar effect on the loss of efficacy of NG on bone, we examined the frequency-dependent effects of NG on bone mineral density (BMD), bone mass, trabecular bone volumes (BV/TV), and blood pressure in rats. Thirty 7-month-old female Brown Norway rats underwent ovariectomy, and an additional six rats were sham-operated. The ovariectomized rats were treated either with vehicle (ovariectomized control), 17beta-estradiol (E2; positive control), or 0.2 mg NG (via dermal application) once, twice, or three times a day. Before and at the end of the 10-week treatment period, BMD of the lumbar spine was measured by dual-energy X-ray absorptiometric (DXA) scanning and expressed as a percentage change. BMD in ovariectomized rats was significantly lower (-2.5 +/- 2.0%) compared with the sham-operated rats (+6.3 +/- 5.3%; p < 0.01). Estrogen therapy completely abolished the ovariectomy-induced potential bone loss (+5.9 +/- 3.4%). Application of NG once daily also completely prevented (+6.2 +/- 2.8%; p < 0.01) the ovariectomy-induced bone loss (i.e., it was as effective as estrogen). However, the beneficial effects of NG on BMD were significantly reduced with increased frequency of application of NG (+1.9 +/- 2.1%, twice a day and -0.2 +/- 3.3% three times a day). Estrogen or once daily administration of NG preserved femur weights, BV/TV, and decreased urinary deoxypyridinoline levels as expected. However, a higher level of serum osteocalcin and bone-specific alkaline phosphatase levels were maintained only with once daily administration of NG. There were no adverse effects of these doses of NG on blood pressure, but a tendency to lower blood pressure was
Dependence of Brillouin frequency shift on water absorption ratio in polymer optical fibers
Minakawa, Kazunari; Koike, Kotaro; Hayashi, Neisei; Koike, Yasuhiro; Mizuno, Yosuke; Nakamura, Kentaro
2016-06-01
We studied the dependence of the Brillouin frequency shift (BFS) on the water-absorption ratio in poly(methyl methacrylate)-based polymer optical fibers (POFs) to clarify the effect of the humidity on POF-based Brillouin sensors. The BFS, deduced indirectly using an ultrasonic pulse-echo technique, decreased monotonically as the water absorption ratio increased, mainly because of the decrease in the Young's modulus. For the same water absorption ratio, the BFS change was larger at a higher temperature. The maximal BFS changes (absolute values) at 40, 60, and 80 °C were 158, 285, and 510 MHz, respectively (corresponding to the temperature changes of ˜9 °C, ˜16 °C, and ˜30 °C). Thus, some countermeasure against the humidity is indispensable in implementing strain/temperature sensors based on Brillouin scattering in POFs, especially at a higher temperature. On the other hand, Brillouin-based distributed humidity sensors might be developed by exploiting the BFS dependence on water absorption in POFs.
Directory of Open Access Journals (Sweden)
Oliver Pabst
2013-03-01
Full Text Available Reasoned by its dynamical behavior, the memristor enables a lot of new applications in analog circuit design. Since some realizations have been shown (e.g. 2007 by Hewlett Packard, the development of applications with memristors becomes more and more interesting. Besides applications in neural networks and storage devices, analog memristive circuits also promise further applications. Therefore, this article proposes a frequency dependent rectifier memristor bridge for different purposes, for example, using as a programmable synaptic membrane voltage generator for Spike-Time-Dependent-Plasticity and describes the circuit theory. In this context it is shown that the Picard Iteration is one possibility to analytically solve the system of nonlinear state equations of memristor circuits. An intuitive picture of how a memristor works in a network in general is given as well and in this context some research on the dynamical behavior of a HP memristor should be done. After all it is suggested to use the memristor bridge as a neuron.
Isakevich, V V; Isakevich, D V
2016-01-01
Using the signal eigenvectors and components analyser (Grunskaya L.V., Isakevich V.V., Isakevich D.V. the RF Utility Model Patent 116242 of 30.09.2011) made it possible to detect non-coherent complex-period components localized at lunar tide frequencies in the time-series of the electric field vertical component of the Earth atmosphere boundary layer. The detected components are unobservable by means of spectral analysis quadrature scheme. The probability of the detected effects being pseudo-estimates is not more than 0.00025
Dependence of Boiling Histotripsy Treatment Efficiency on HIFU Frequency and Focal Pressure Levels.
Khokhlova, Tatiana D; Haider, Yasser A; Maxwell, Adam D; Kreider, Wayne; Bailey, Michael R; Khokhlova, Vera A
2017-09-01
Boiling histotripsy (BH) is a high-intensity focused ultrasound (HIFU)-based method of mechanical tissue fractionation that utilizes millisecond-long bursts of HIFU shock waves to cause boiling at the focus in milliseconds. The subsequent interaction of the incoming shocks with the vapor bubble mechanically lyses surrounding tissue and cells. The acoustic parameter space for BH has been investigated previously and an inverse dependence between the HIFU frequency and the dimensions of a BH lesion has been observed. The primary goal of the present study was to investigate in more detail the ablation rate and reliability of BH in the frequency range relevant to treatment of deep abdominal tissue targets (1-2 MHz). The second goal was to investigate the effect of focal peak pressure levels and shock amplitude on BH lesion formation, given a constant duty factor, a constant ratio of the pulse duration to the time to reach boiling and a constant number of BH pulses. A custom-built 12-element sector array HIFU transducer with F-number = 1.05 was used in all experiments. BH pulses at 5 different frequencies (1, 1.2, 1.5, 1.7 and 1.9 MHz) were delivered to optically transparent polyacrylamide gel phantoms and ex vivo bovine liver and myocardium tissue to observe cavitation and boiling bubble activity with high-speed photography and B-mode ultrasound imaging, correspondingly. In gel phantoms, a cavitation bubble cloud was shown to form prefocally and to shield the focus in all exposures at 1 and 1.2 MHz and in the highest amplitude exposures at 1.5-1.7 MHz; shielding was not observed at 1.9 MHz. In ex vivo tissue, this shielding effect was observed in 25% of exposures when peak negative in situ pressure exceeded 10.2 MPa at 1 MHz and 14.5 MPa at 1.5 MHz. When shielding occurred, the exposures resulted in mild tissue disruption in the prefocal region, but not liquefaction. The dimensions of liquefied lesions followed the inverse proportionality trend with
Hajdok, G; Battista, J J; Cunningham, I A
2008-07-01
A frequency-dependent x-ray Swank factor based on the "x-ray interaction" modulation transfer function and normalized noise power spectrum is determined from a Monte Carlo analysis. This factor was calculated in four converter materials: amorphous silicon (a-Si), amorphous selenium (a-Se), cesium iodide (CsI), and lead iodide (PbI2) for incident photon energies between 10 and 150 keV and various converter thicknesses. When scaled by the quantum efficiency, the x-ray Swank factor describes the best possible detective quantum efficiency (DQE) a detector can have. As such, this x-ray interaction DQE provides a target performance benchmark. It is expressed as a function of (Fourier-based) spatial frequency and takes into consideration signal and noise correlations introduced by reabsorption of Compton scatter and photoelectric characteristic emissions. It is shown that the x-ray Swank factor is largely insensitive to converter thickness for quantum efficiency values greater than 0.5. Thus, while most of the tabulated values correspond to thick converters with a quantum efficiency of 0.99, they are appropriate to use for many detectors in current use. A simple expression for the x-ray interaction DQE of digital detectors (including noise aliasing) is derived in terms of the quantum efficiency, x-ray Swank factor, detector element size, and fill factor. Good agreement is shown with DQE curves published by other investigators for each converter material, and the conditions required to achieve this ideal performance are discussed. For high-resolution imaging applications, the x-ray Swank factor indicates: (i) a-Si should only be used at low-energy (e.g., mammography); (ii) a-Se has the most promise for any application below 100 keV; and (iii) while quantum efficiency may be increased at energies just above the K edge in CsI and PbI2, this benefit is offset by a substantial drop in the x-ray Swank factor, particularly at high spatial frequencies.
Spatial heterogeneity, frequency-dependent selection and polymorphism in host-parasite interactions
Directory of Open Access Journals (Sweden)
Tellier Aurélien
2011-11-01
Full Text Available Abstract Background Genomic and pathology analysis has revealed enormous diversity in genes involved in disease, including those encoding host resistance and parasite effectors (also known in plant pathology as avirulence genes. It has been proposed that such variation may persist when an organism exists in a spatially structured metapopulation, following the geographic mosaic of coevolution. Here, we study gene-for-gene relationships governing the outcome of plant-parasite interactions in a spatially structured system and, in particular, investigate the population genetic processes which maintain balanced polymorphism in both species. Results Following previous theory on the effect of heterogeneous environments on maintenance of polymorphism, we analysed a model with two demes in which the demes have different environments and are coupled by gene flow. Environmental variation is manifested by different coefficients of natural selection, the costs to the host of resistance and to the parasite of virulence, the cost to the host of being diseased and the cost to an avirulent parasite of unsuccessfully attacking a resistant host. We show that migration generates negative direct frequency-dependent selection, a condition for maintenance of stable polymorphism in each deme. Balanced polymorphism occurs preferentially if there is heterogeneity for costs of resistance and virulence alleles among populations and to a lesser extent if there is variation in the cost to the host of being diseased. We show that the four fitness costs control the natural frequency of oscillation of host resistance and parasite avirulence alleles. If demes have different costs, their frequencies of oscillation differ and when coupled by gene flow, there is amplitude death of the oscillations in each deme. Numerical simulations show that for a multiple deme island model, costs of resistance and virulence need not to be present in each deme for stable polymorphism to occur
Babiarz, Joshua E.; Halley, Jeffrey E.; Rine, Jasper
2006-01-01
SWR1-Com, which is responsible for depositing H2A.Z into chromatin, shares four subunits with the NuA4 histone acetyltransferase complex. This overlap in composition led us to test whether H2A.Z was a substrate of NuA4 in vitro and in vivo. The N-terminal tail of H2A.Z was acetylated in vivo at multiple sites by a combination of NuA4 and SAGA. H2A.Z acetylation was also dependent on SWR1-Com, causing H2A.Z to be efficiently acetylated only when incorporated in chromatin. Unacetylatable H2A.Z mutants were, like wild-type H2A.Z, enriched at heterochromatin boundaries, but were unable to block spreading of heterochromatin. A mutant version of H2A.Z that could not be acetylated, in combination with a mutation in a nonessential gene in the NuA4 complex, caused a pronounced decrease in growth rate. This H2A.Z mutation was lethal in combination with a mutant version of histone H4 that could not be acetylated by NuA4. Taken together, these results show a role for H2A.Z acetylation in restricting silent chromatin, and reveal that acetylation of H2A.Z and H4 can contribute to a common function essential to life. PMID:16543222
Mathematical modelling of frequency-dependent hysteresis and energy loss of FeBSiC amorphous alloy
Koprivica, Branko; Milovanovic, Alenka; Mitrovic, Nebojsa
2017-01-01
The aim of this paper is to present a novel mathematical model of frequency-dependent magnetic hysteresis. The major hysteresis loop in this model is represented by the ascending and descending curve over an arctangent function. The parameters of the hysteresis model have been calculated from a measured hysteresis loop of the FeBSiC amorphous alloy sample. A number of measurements have been performed with this sample at different frequencies of the sinusoidal excitation magnetic field. A variation of the coercive magnetic field with the frequency has been observed and used in the modelling of frequency-dependent hysteresis with the proposed model. A comparison between measured and modelled hysteresis loops has been presented. Additionally, the areas of the obtained hysteresis loops, representing the energy loss per unit volume, have been calculated and the dependence of the energy loss on the frequency is shown. Furthermore, two models of the frequency dependence of the coercivity and two models of the energy loss separation have been used for fitting the experimental and simulation results. The relations between these models and their parameters have been observed and analysed. Also, the relations between parameters of the hysteresis model and the parameters of the energy loss separation models have been analysed and discussed.
Directory of Open Access Journals (Sweden)
Mohd. Manjur Alam
2014-12-01
Full Text Available Speaker identification is a biometric technique. The objective of automatic speaker recognition is to extract, characterize and recognize the information about speaker identity. Speaker Recognition technology has recently been used in large number of commercial areas successfully such as in voice based biometrics; voice controlled appliances, security control for confidential information, remote access to computers and many more interesting areas. A speaker identification system has two phases which are the training phase and the testing phase. Feature extraction is the first step for each phase in speaker recognition. Many algorithms are suggested by the researchers for feature extraction. In this work, the Mel Frequency Cepstrum Coefficient (MFCC feature has been used for designing a text dependent speaker identification system. While, in the identification phase, the existing reference templates are compared with the unknown voice input. In this thesis, a Bayesian network is used as the training/recognition algorithm which makes the final decision about the specification of the speaker by comparing unknown features to all models in the database and selecting the best matching model. i, e. the highest scored model. The speaker who obtains the highest score is selected as the target speaker.
The Protective Effect of Conditioning on Noise-Induced Hearing Loss Is Frequency-Dependent
Directory of Open Access Journals (Sweden)
Akram Pourbakht
2012-10-01
Full Text Available We compared the extent of temporary threshold shift (TTS and hair cell loss following high level 4 kHz noise exposure with those preconditioned with moderate level 1 and 4 kHz octave band noise. Fifteen Male albino guinea pigs (300- 350 g in weight were randomly allocated into three groups: those exposed to 4 kHz octave band noise at 102 dB SPL (group 1, n=5; those conditioned with 1 kHz octave band noise at 85 dB SPL, 6 hours per day for 5 days, then exposed to noise (group 2, n=5; those conditioned with 4 kHz octave band noise at 85 dB SPL, then exposed to noise (group 3, n=5. An hour and one week after noise exposure, threshold shifts were evaluated by auditory-evoked brainstem response (ABR and then animals were euthanized for histological evaluation. We found that TTS and cochlear damage caused by noise exposure were significantly reduced by 1 kHz and 4 kHz conditioning (P<0.001. We also showed that 4 kHz protocol attenuates noise- induced TTS but no significant TTS reduction occurred by 1 kHz conditioning. Both protocol protected noise-induced cochlear damage. We concluded that lower tone conditioning could not protect against higher tone temporary noise-induced hearing loss, thus conditioning is a local acting and frequency-dependent phenomenon.
Chung, Y Anny; Rudgers, Jennifer A
2016-07-27
Understanding the mechanisms of species coexistence is key to predicting patterns of species diversity. Historically, the ecological paradigm has been that species coexist by partitioning resources: as a species increases in abundance, self-limitation kicks in, because species-specific resources decline. However, determining coexistence mechanisms has been a particular puzzle for sedentary organisms with high overlap in their resource requirements, such as plants. Recent evidence suggests that plant-associated microbes could generate the stabilizing self-limitation (negative frequency dependence) that is required for species coexistence. Here, we test the key assumption that plant-microbe feedbacks cause such self-limitation. We used competition experiments and modelling to evaluate how two common groups of soil microbes (rhizospheric microbes and biological soil crusts) influenced the self-limitation of two competing desert grass species. Negative feedbacks between the dominant plant competitor and its rhizospheric microbes magnified self-limitation, whereas beneficial interactions between both plant species and biological soil crusts partly counteracted this stabilizing effect. Plant-microbe interactions have received relatively little attention as drivers of vegetation dynamics in dry land ecosystems. Our results suggest that microbial mechanisms can contribute to patterns of plant coexistence in arid grasslands.
Evolution of learned strategy choice in a frequency-dependent game.
Katsnelson, Edith; Motro, Uzi; Feldman, Marcus W; Lotem, Arnon
2012-03-22
In frequency-dependent games, strategy choice may be innate or learned. While experimental evidence in the producer-scrounger game suggests that learned strategy choice may be common, a recent theoretical analysis demonstrated that learning by only some individuals prevents learning from evolving in others. Here, however, we model learning explicitly, and demonstrate that learning can easily evolve in the whole population. We used an agent-based evolutionary simulation of the producer-scrounger game to test the success of two general learning rules for strategy choice. We found that learning was eventually acquired by all individuals under a sufficient degree of environmental fluctuation, and when players were phenotypically asymmetric. In the absence of sufficient environmental change or phenotypic asymmetries, the correct target for learning seems to be confounded by game dynamics, and innate strategy choice is likely to be fixed in the population. The results demonstrate that under biologically plausible conditions, learning can easily evolve in the whole population and that phenotypic asymmetry is important for the evolution of learned strategy choice, especially in a stable or mildly changing environment.
Park, Hyekyoung; Delayen, Jean
2017-01-01
A theory of surface resistance of superconductor was rigorously formulated by Bardeen, Cooper, Schrieffer more than 50 years ago. Since then the accelerator community has been used the theory as a guideline to improve the surface resistance of the superconducting cavity. It has been observed that the surface resistance is dependent on frequency, temperature and rf field strength, and surface preparation. To verify these dependences, a well-controlled study is required. Although many different types of cavities have been tested, the typical superconducting cavities are built for specific frequencies of their application. They do not provide data other than at its own frequency. A superconducting half wave cavity is a cavity that enables us to collect the surface resistance data across frequencies of interest for particle accelerators and evaluate preparation techniques. This paper will present the design of the half wave cavity, its electromagnetic mode characteristics and experimental results. Research supported by NSF Award PHY-1416051.
Bland, S. R.
1982-01-01
Finite difference methods for unsteady transonic flow frequency use simplified equations in which certain of the time dependent terms are omitted from the governing equations. Kernel functions are derived for two dimensional subsonic flow, and provide accurate solutions of the linearized potential equation with the same time dependent terms omitted. These solutions make possible a direct evaluation of the finite difference codes for the linear problem. Calculations with two of these low frequency kernel functions verify the accuracy of the LTRAN2 and HYTRAN2 finite difference codes. Comparisons of the low frequency kernel function results with the Possio kernel function solution of the complete linear equations indicate the adequacy of the HYTRAN approximation for frequencies in the range of interest for flutter calculations.
Indian Academy of Sciences (India)
A ASHERY; A H ZAKI; M HUSSIEN MOURAD; A M AZAB; A A M FARAG
2016-08-01
In this work, heterojunction of InSb/InP was grown by liquid phase epitaxy (LPE). Surface morphology and crystalline structure of the heterojunction were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The frequency and temperature dependences of a.c. conductivity and dielectric properties of the heterojunctions were investigated in the ranges of 100 kHz–5 MHz and 298–628 K, respectively. The a.c. conductivity and its frequency exponents were interpreted in terms of correlated barrier hopping model (CBH), as the dominant conduction mechanism for charge carrier transport. The calculated activation energy, from the Arrhenius plot, was found to decrease with increasing frequency. Experimental results of both dielectric constant $\\epsilon_1$ and dielectric loss $\\epsilon_2$ showed a remarkable dependence of both frequency and temperature.
Frequency dependent capacitance studies of the CdS/Cu2S thin-film solar cell
Hmurcik, L. V.; Serway, R. A.
1982-05-01
The dark capacitance of CdS cells has been measured as a function of both bias voltage and operating signal frequency. Results indicate a frequency dependence of the dark current capacitance which can be attributed to deep trapping states in the bulk CdS and at the interface; these states can be characterized by a time constant in the simple relaxation model. Photocapacitance measurements indicate that hole trapping takes place in a narrow region of the i layer near the Cu2S/CdS junction. The results are interpreted in terms of a frequency-dependent model proposed by Schibli and Milnes (1968). It is shown that the simple planar junction model commonly used to describe the CdS cell is accurate at high frequencies.
DEFF Research Database (Denmark)
Christensen, Anders Tornvig; Ordoñez, Rodrigo Pizarro; Hammershøi, Dorte
2014-01-01
Active amplifiers within the cochlea generate, as a by-product of their function, distortion-product otoacoustic emissions (DPOAEs) in response to carefully chosen two-tone stimuli. Focus has been on invoking emissions in a mid-frequency range from 500 to 4000 Hz. Below 500 Hz, physiological noise...... audiometrically normal hearing for inclusion in our experiment. DPOAEs were measured with pure-tone stimuli in four configurations: f2 fixed around a mid-frequency (2050-2180 Hz), f2 fixed around a low frequency (512-545 Hz), fdp fixed at a mid-frequency (1231 Hz) and fdp low frequency (246 Hz). Eight stimulus...
Dependence of microwave-excitation signal parameters on frequency stability of caesium atomic clock
Petrov, A. A.; Davydov, V. V.; Vologdin, V. A.; Zalyotov, D. V.
2015-11-01
New scheme of the microwave - excitation signal for the caesium atomic clock is based on method of direct digital synthesis. The theoretical calculations and experimental research showed decrease step frequency tuning by several orders and improvement the spectral characteristics of the output signal of frequency synthesizer. A range of generated output frequencies is expanded, and the possibility of detuning the frequency of the neighboring resonance of spectral line that makes it possible to adjust the C-field in quantum frequency standard is implemented. Experimental research of the metrological characteristics of the quantum frequency standard on the atoms of caesium - 133 with new design scheme of the microwave - excitation signal showed improvement in daily frequency stability on 1.2*10-14.
DEFF Research Database (Denmark)
Jeong, Cheol-Ho
2016-01-01
characteristics of their own configurations. This study aims to predict the absorption coefficient for various mounting conditions from a single measurement of an arbitrary mounting condition by extracting the air flow resistivity of the test specimen and the frequency-dependent effect of the chamber......Fibrous absorbers can be installed with various air backing conditions to fulfil a given low frequency acoustic requirement. Since absorber manufacturers cannot provide the absorption coefficients for all possible mounting conditions, acousticians have difficulties knowing the absorption...
Borah, Manjit; Mohanta, Dambarudhar
2016-05-01
We report the effect of Tb-doping on the structural and high frequency impedance response of the nanoscale BaTiO3 (BT) systems. While exhibiting a mixed phase crystal structure, the nano-BT systems are found to evolve with edges, and facets. The interplanar spacing of crystal lattice fringes is ~0.25 nm. The Cole-Cole plots, in the impedance formalism, have demonstrated semicircles which are the characteristic feature of grain boundary resistance of several MΩ. A lowering of ac conductivity with doping was believed to be due to the manifestation of oxygen vacancies and vacancy ordering.
Magnetic field dependence of piezoelectric resonance frequency in CoFe2O4-BaTiO3 composites
Kagomiya, Isao; Hayashi, Yusuke; Kakimoto, Ken-ichi; Kobayashi, Kazuyoshi
2012-08-01
The particulate and the multilayer CoFe2O4(CFO)-BaTiO3(BT) composites were prepared by the conventional solid state reaction method and the tape casting method, respectively. Both the prepared composites were simultaneously ferroelectric and ferromagnetic at room temperature. For the multilayer composite sample, a piezoelectric resonance frequency remarkably depended on the applied DC magnetic field, while no remarkable magnetic field dependence was observed for the particulate composite samples. An uniform magnetostriction of the CFO phase in the multilayer composite contributes to piezoelectric effect of the BT phases, resulting in the modulation of the piezoelectric resonance frequency.
Rebolini, Elisa
2015-01-01
We present a range-separated linear-response time-dependent density-functional theory (TDDFT) which combines a density-functional approximation for the short-range response kernel and a frequency-dependent second-order Bethe-Salpeter approximation for the long-range response kernel. This approach goes beyond the adiabatic approximation usually used in linear-response TDDFT and aims at improving the accuracy of calculations of electronic excitation energies of molecular systems. A detailed derivation of the frequency-dependent second-order Bethe-Salpeter correlation kernel is given using many-body Green-function theory. Preliminary tests of this range-separated TDDFT method are presented for the calculation of excitation energies of four small molecules: N2, CO2, H2CO, and C2H4. The results suggest that the addition of the long-range second-order Bethe-Salpeter correlation kernel overall slightly improves the excitation energies.
Institute of Scientific and Technical Information of China (English)
M.L.Sánchez; V.M.Prida; B.Hernando; G.V.Kurlyandskaya; J.D.Santos; M.Tejedor; M.Vázquez
2002-01-01
The magnetoimpedance effect and changes of the relaxation frequency fx are studied in CoFeSiB and CoFeMoSiB amorphous and FeCuNbSiB nanocrystalline ribbons. The evolution of the magnetostriction constant λs and relaxation frequency is analysed for the states with different magnetic anisotropies induced in the same ribbons.A monotonic decrease of the relaxation frequency is observed for shifting of λs towards positive values.
Frequency-dependent changes in sensorimotor and pain affective systems induced by empathy for pain
Motoyama, Yoshimasa; Ogata, Katsuya; Hoka, Sumio; Tobimatsu, Shozo
2017-01-01
Background Empathy for pain helps us to understand the pain of others indirectly. To better comprehend the processing of empathic pain, we report the frequency-dependent modulation of cortical oscillations induced by watching movies depicting pain using high-density electroencephalography (EEG), magnetoencephalography (MEG), and motor evoked potentials (MEP). Methods Event-related desynchronization of EEG and MEG was assessed while participants viewed videos of painful (needle) or neutral (cotton swab) situations. The amplitudes of MEPs were also compared between the needle and cotton swab conditions. Results The degree of suppression in α/β band power was significantly increased, whereas that of γ band power was significantly decreased, in the needle condition compared with the cotton swab condition. EEG revealed that significant differences in α/β band were distributed in the right frontocentral and left parietooccipital regions, whereas significant γ band differences were distributed predominantly over the right hemisphere, which were confirmed by source estimation using MEG. There was a significant positive correlation between the difference in γ power of the two conditions and the visual analog scale subjective rating of aversion, but not in the α/β band. The amplitude of MEPs decreased in the needle condition, which confirmed the inhibition of the primary motor cortex. Conclusion MEP suppression supports that modulation of cortical oscillations by viewing movies depicting pain involves sensorimotor processing. Our results suggest that α/β oscillations underlie the sensory qualities of others’ pain, whereas the γ band reflects the cognitive aspect. Therefore, α/β and γ band oscillations are differentially involved in empathic pain processing under the condition of motor cortical suppression. PMID:28615963
Power dependence of terahertz carrier frequency in a plasma-based two-color generation process
Zhao, Ji; Zhang, Liang-Liang; Luo, Yi-Man; Wu, Tong; Zhang, Cun-Lin; Zhao, Yue-Jin
2014-12-01
We conduct a frequency spectrum experiment to investigate terahertz (THz) emissions from laser-induced air plasma under different laser incident powers. The frequency spectra are measured using both air-biased-coherent detection and a Michelson interferometer. The red-shift of the THz pulse carrier frequency is observed as a response to increased pump power. These phenomena are related to plasma collisions and can be explained by the plasma collision model. Based on these findings, it is apparent that the tuning of the THz carrier frequency can be achieved through regulation of the pump beam.
Requirements on Needed Frequency Bandwidth Depending on Pulse Waveforms and Their Allowed Distortion
Sigmund, Milan; Brancik, Lubomir
2016-12-01
This paper deals with pulse signals influenced by loss of energy in high frequency band. Five types of pulses were tested and evaluated under various conditions. Achieved results can be helpful for some specific tasks in signal transmission. An example presents highest frequency of periodic pulse signals processed on printed circuit board.
Energy Technology Data Exchange (ETDEWEB)
Lofland, S.; Huang, M.X.; Bhagat, S.M. (Dept. of Physics and Center for Superconductivity Research, Univ. of Maryland, College Park (United States))
1992-12-10
The intergranular AC susceptibility loss peak in high-Tc superconductors is measured as a function of frequency and field amplitude. The variation of peak temperature with frequency is strongly influenced by the grain size. For large grains, the maximum loss increases with field amplitude. This is ascribed to a non-zero intergranular lower critical field H[sub cl]. (orig.).
Dai, Shaoyang; Xia, Wei; Zhang, Yin; Zhao, Jianye; Zhou, Dawei; Wang, Qing; Yu, Qi; Li, Kunqian; Qi, Xianghui; Chen, Xuzong
2016-11-01
The femtosecond fiber-based optical frequency combs have been proved to be powerful tools for investigating the energy levels of atoms and molecules. In this paper, an Er-doped fiber femtosecond optical frequency comb has been implemented for studying the polarization dependence of 5S-5D two-photon transitions in thermal gas of atomic rubidium 87 using an entirely symmetrical optical configuration. By changing the polarization states of the counter-propagating light beams, the polarization dependence of direct two photon transition spectrum is demonstrated, and a dramatic variation (up to 5.5 times) of the two-photon transitions strength has been observed. The theory for the polarization dependence of two photon transition based on the second-order perturbation was established, which is in good agreement with the experimental results. The measurement results indicate that the polarization state manipulation with the existing frequency comb is used for femtosecond optical frequency comb based two photon transition spectroscopic purposes, which will improve the precision measurement of the absolute transition frequency and related applications.
2010-07-01
... 38 Pensions, Bonuses, and Veterans' Relief 1 2010-07-01 2010-07-01 false Frequency of payment of improved pension and parents' dependency and indemnity compensation (DIC). 3.30 Section 3.30 Pensions, Bonuses, and Veterans' Relief DEPARTMENT OF VETERANS AFFAIRS ADJUDICATION Pension, Compensation, and...
DEFF Research Database (Denmark)
van Driel, A. F.; Allan, G.; Delerue, C.;
2005-01-01
We studied the rate of spontaneous emission from colloidal CdSe and CdTe nanocrystals at room temperature. The decay rate, obtained from luminescence decay curves, increases with the emission frequency in a supralinear way. This dependence is explained by the thermal occupation of dark exciton...
Adams, T. N. G.; Leonard, K. M.; Minerick, A. R.
2013-01-01
Alternating current (AC) dielectrophoresis (DEP) experiments for biological particles in microdevices are typically done at a fixed frequency. Reconstructing the DEP response curve from static frequency experiments is laborious, but essential to ascertain differences in dielectric properties of biological particles. Our lab explored the concept of sweeping the frequency as a function of time to rapidly determine the DEP response curve from fewer experiments. For the purpose of determining an ideal sweep rate, homogeneous 6.08 μm polystyrene (PS) beads were used as a model system. Translatability of the sweep rate approach to ∼7 μm red blood cells (RBC) was then verified. An Au/Ti quadrapole electrode microfluidic device was used to separately subject particles and cells to 10Vpp AC electric fields at frequencies ranging from 0.010 to 2.0 MHz over sweep rates from 0.00080 to 0.17 MHz/s. PS beads exhibited negative DEP assembly over the frequencies explored due to Maxwell-Wagner interfacial polarizations. Results demonstrate that frequency sweep rates must be slower than particle polarization timescales to achieve reliable incremental polarizations; sweep rates near 0.00080 MHz/s yielded DEP behaviors very consistent with static frequency DEP responses for both PS beads and RBCs. PMID:24396548
Directory of Open Access Journals (Sweden)
Arcady Zhukov
2016-09-01
Full Text Available We studied giant magnetoimpedance (GMI effect in magnetically soft amorphous Co-rich microwires in the extended frequency range. From obtained experimentally dependences of the GMI ratio on magnetic field at different frequencies we estimated the penetration depth and its dependence on applied magnetic field and frequency.
Frequency dependent capacitance studies of the CdS/Cu/sub 2/S thin-film solar cell
Energy Technology Data Exchange (ETDEWEB)
Hmurcik, L.V.; Serway, R.A.
1982-05-01
Measurements of the dark capacitance of CdS cells as a function of the frequency of the applied signal voltage have shown that the capacitance varies with frequency according to the relation C-C/sub infinity/ = (C/sub 0/-C/sub infinity/)/(1+..omega../sup 2/tau/sup 2/), where tau is the time constant associated with interfacial and deep bulk states. Photocapacitance studies show that the CdS cell can be treated according to the frequency dependent model of Schibli and Milnes. Under the influence of light, Capprox.1/(..omega..)/sup 1/2/. Further work demonstrates that the simple planar junction model most often used to describe the CdS cell is accurate at high frequencies.
Dependence of in-situ Bose condensate size on final frequency of RF-field in evaporative cooling
Mishra, S. R.; Ram, S. P.; Tiwari, S. K.; Rawat, H. S.
2017-04-01
We report the results of in-situ characterization of 87Rb atom cloud in a quadrupole Ioffe configuration (QUIC) magnetic trap after a radio-frequency (RF) evaporative cooling of the trapped atom cloud. The in-situ absorption images of the atom cloud have shown clear bimodal optical density (OD) profiles which indicate the Bose-Einstein condensation (BEC) phase transition in the trapped gas. Also, we report here, for the first time, the measured variation in the sizes of the condensate and thermal clouds with the final frequency selected in the frequency scan of the RF-field for evaporative cooling. These results on frequency-dependent sizes of the clouds are consistent with the theoretical understanding of the BEC phenomenon in the trap.
Indian Academy of Sciences (India)
S R MISHRA; S P RAM; S K TIWARI; H S RAWAT
2017-04-01
We report the results of $\\it{in-situ}$ characterization of $^{87}$Rb atom cloud in a quadrupole Ioffe configuration (QUIC) magnetic trap after a radio-frequency (RF) evaporative cooling of the trapped atom cloud. The $\\it{in-situ}$ absorption images of the atom cloud have shown clear bimodal optical density (OD) profiles which indicate the Bose–Einstein condensation (BEC) phase transition in the trapped gas. Also, we report here, for the first time, the measured variation in the sizes of the condensate and thermal clouds with the final frequency selected in the frequency scan of the RF-field for evaporative cooling. These results on frequency-dependent sizes of the clouds are consistent with the theoretical understanding of the BEC phenomenon in the trap.
Frequency-dependent changes in sensorimotor and pain affective systems induced by empathy for pain
Directory of Open Access Journals (Sweden)
Motoyama Y
2017-05-01
Full Text Available Yoshimasa Motoyama,1,2,* Katsuya Ogata,1,* Sumio Hoka,2 Shozo Tobimatsu1 1Department of Clinical Neurophysiology, Neurological Institute, 2Department of Anesthesiology and Critical Care Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan *These authors contributed equally to this work Background: Empathy for pain helps us to understand the pain of others indirectly. To better comprehend the processing of empathic pain, we report the frequency-dependent modulation of cortical oscillations induced by watching movies depicting pain using high-density electroencephalography (EEG, magnetoencephalography (MEG, and motor evoked potentials (MEP. Methods: Event-related desynchronization of EEG and MEG was assessed while participants viewed videos of painful (needle or neutral (cotton swab situations. The amplitudes of MEPs were also compared between the needle and cotton swab conditions.Results: The degree of suppression in α/β band power was significantly increased, whereas that of γ band power was significantly decreased, in the needle condition compared with the cotton swab condition. EEG revealed that significant differences in α/β band were distributed in the right frontocentral and left parietooccipital regions, whereas significant γ band differences were distributed predominantly over the right hemisphere, which were confirmed by source estimation using MEG. There was a significant positive correlation between the difference in γ power of the two conditions and the visual analog scale subjective rating of aversion, but not in the α/β band. The amplitude of MEPs decreased in the needle condition, which confirmed the inhibition of the primary motor cortex.Conclusion: MEP suppression supports that modulation of cortical oscillations by viewing movies depicting pain involves sensorimotor processing. Our results suggest that α/β oscillations underlie the sensory qualities of others’ pain, whereas the γ band
Field dependence of the complex resistivity of YBa_2Cu_3O_7-δ thin films at high frequencies
Wu, Dong Ho; Booth, James C.; Anlage, Steven M.
1996-03-01
We have measured the complex resistivity ρ_1(H,ω) + i ρ_2(H,ω) of YBa_2Cu_3O_7-δ thin films with field variation at various fixed frequencies from 45 MHz through 50 GHz.footnote[1]Dong Ho Wu, James C. Booth and Steven M. Anlage, Phys. Rev. Lett. 75 , 525 (1995) Experiments indicate that the real part of the resistivity follows a power law (ρ_1(H) ~ H^n with n>=4) field dependence at frequencies below a characteristic frequency. In contrast, ρ_1(H) follows a single particle model at frequencies above the characteristic frequency, exhibiting a magnetic field crossover at a characteristic field. For all frequencies, the imaginary part of the resistivity shows a peak at a field denoted as H_peak. Analysis suggests that the H_peak discretely decreases with increasing measurement frequency ω for T < T_c. Analysis and interpretation on these behaviors of the complex resistivity will be presented.
Li, Yinfeng; Lin, Qianling; Cui, Daxiang
2017-02-01
Graphene annulus possesses special wrinkling phenomenon with wide range of potential applications. Using molecular dynamics simulation, this study concerns the effect of boundary on the mechanical properties of circular and elliptical graphene annuli under circular shearing at inner edge. Both the wrinkle characteristic and torque capacity of annular graphene can be effectively tuned by outer boundary radius and aspect ratio. For circular annulus with fixed inner radius, the critical angle of rotation can be increased by several times without sacrificing its torque capacity by increasing outer boundary radius. The wrinkle characteristic of graphene annulus with elliptical outer boundary differs markedly with that of circular annulus. Torque capacity anomalously decreases with the increase of aspect ratio, and a coupled effect of the boundary aspect ratio and the ratio of minor axis to inner radius on wrinkling are revealed. By studying the stress distribution and wrinkle characteristics, we find the decay of torque capacity is the result of circular stress concentration around the minor axis, while the nonuniform stress distribution is anomalously caused by the change of wrinkle profiles near the major axis. The specific mechanism of out-of-plane deformation on in-plane strength provides a straightforward means to develop novel graphene-based devices.
Li, Yinfeng; Lin, Qianling; Cui, Daxiang
2017-01-01
Graphene annulus possesses special wrinkling phenomenon with wide range of potential applications. Using molecular dynamics simulation, this study concerns the effect of boundary on the mechanical properties of circular and elliptical graphene annuli under circular shearing at inner edge. Both the wrinkle characteristic and torque capacity of annular graphene can be effectively tuned by outer boundary radius and aspect ratio. For circular annulus with fixed inner radius, the critical angle of rotation can be increased by several times without sacrificing its torque capacity by increasing outer boundary radius. The wrinkle characteristic of graphene annulus with elliptical outer boundary differs markedly with that of circular annulus. Torque capacity anomalously decreases with the increase of aspect ratio, and a coupled effect of the boundary aspect ratio and the ratio of minor axis to inner radius on wrinkling are revealed. By studying the stress distribution and wrinkle characteristics, we find the decay of torque capacity is the result of circular stress concentration around the minor axis, while the nonuniform stress distribution is anomalously caused by the change of wrinkle profiles near the major axis. The specific mechanism of out-of-plane deformation on in-plane strength provides a straightforward means to develop novel graphene-based devices. PMID:28198805
Time and frequency dependence of disposable ECG electrode-skin impedance.
Olson, W H; Schmincke, D R; Henley, B L
1979-01-01
The magnitude and phase of disposable electrode-skin impedance were studied as functions of time, 0-48 hours, and frequency, 1 Hz-1 kHz. For both unabraded and mildly abraded skin, the impedance decreased as a function of time steadily or exponentially with time constants of several hours. Impedance decreased as a function of frequency by factors of 2 to 20 with greatest change at low frequencies. For heavily abraded skin, the impedance decreased slightly and then increased as a function of time especially at low frequencies. Impedance imbalance between pairs of identical electrodes applied in a like manner to the forearm were often greater than k omega, nearly equal to individual electrode-skin impedances, and decreased with time. Electrode impedance imbalance is particularly important because it affects noise levels in ECG recordings.
Moya-Díaz, José; Álvarez, Yanina D.; Montenegro, Mauricio; Bayonés, Lucas; Belingheri, Ana V.; González-Jamett, Arlek M.; Cárdenas, Ana M.; Marengo, Fernando D.
2016-01-01
Under basal conditions the action potential firing rate of adrenal chromaffin cells is lower than 0.5 Hz. The maintenance of the secretory response at such frequencies requires a continuous replenishment of releasable vesicles. However, the mechanism that allows such vesicle replenishment remains unclear. Here, using membrane capacitance measurements on mouse chromaffin cells, we studied the mechanism of replenishment of a group of vesicles released by a single action potential-like stimulus (APls). The exocytosis triggered by APls (ETAP) represents a fraction (40%) of the immediately releasable pool, a group of vesicles highly coupled to voltage dependent calcium channels. ETAP was replenished with a time constant of 0.73 ± 0.11 s, fast enough to maintain synchronous exocytosis at 0.2–0.5 Hz stimulation. Regarding the mechanism involved in rapid ETAP replenishment, we found that it depends on the ready releasable pool; indeed depletion of this vesicle pool significantly delays ETAP replenishment. On the other hand, ETAP replenishment also correlates with a dynamin-dependent fast endocytosis process (τ = 0.53 ± 0.01 s). In this regard, disruption of dynamin function markedly inhibits the fast endocytosis and delays ETAP replenishment, but also significantly decreases the synchronous exocytosis during repetitive APls stimulation at low frequencies (0.2 and 0.5 Hz). Considering these findings, we propose a model in where both the transfer of vesicles from ready releasable pool and fast endocytosis allow rapid ETAP replenishment during low stimulation frequencies. PMID:27507935
Directory of Open Access Journals (Sweden)
José Moya-Díaz
2016-07-01
Full Text Available Under basal conditions the action potential firing rate of adrenal chromaffin cells is lower than 0.5 Hz. The maintenance of the secretory response at such frequencies requires a continuous replenishment of releasable vesicles. However, the mechanism that allows such vesicle replenishment remains unclear. Here, using membrane capacitance measurements on mouse chromaffin cells, we studied the mechanism of replenishment of a group of vesicles released by a single action potential-like stimulus (APls. The exocytosis triggered by APls (ETAP represents a fraction (40% of the immediately releasable pool, a group of vesicles highly coupled to voltage dependent calcium channels. ETAP was replenished with a time constant of 0.73 +/- 0.11 s, fast enough to maintain synchronous exocytosis at 0.2-0.5 Hz stimulation. Regarding the mechanism involved in rapid ETAP replenishment, we found that it depends on the ready releasable pool; indeed depletion of this vesicle pool significantly delays ETAP replenishment. On the other hand, ETAP replenishment also correlates with a dynamin-dependent fast endocytosis process (τ=0.53±0.01 s. In this regard, disruption of dynamin function markedly inhibits the fast endocytosis and delays ETAP replenishment, but also significantly decreases the synchronous exocytosis during repetitive APls stimulation at low frequencies (0.2 and 0.5 Hz. Considering these findings, we propose a model in where both the transfer of vesicles from ready releasable pool and fast endocytosis allow rapid ETAP replenishment during low stimulation frequencies.
Nomura, M.; Shimada, T.; Tamura, F.; Yamamoto, M.; Hara, K.; Hasegawa, K.; Ohmori, C.; Takata, K.; Toda, M.; Yoshii, M.; Schnase, A.
2014-06-01
We employ Magnetic Alloy (MA) core loaded RF cavities for the J-PARC synchrotrons to achieve a high field gradient. The MA core has a laminated structure of 18 μm thick ribbon layers. We have been developing high shunt impedance MA cores to prepare for an increase of beam power. At low frequencies, it is well known that the eddy current loss in the ribbon is proportional to the square of the ribbon thickness. The MA core shunt impedance can be increased by using thinner ribbons. On the other hand, at high frequencies, the MA core magnetic characteristics are largely different from low frequencies. Using thinner ribbons might be effective to increase the MA core shunt impedance in the accelerating frequency region of the J-PARC synchrotrons. We reviewed the theoretical calculations of the ribbon thickness dependence of the MA core magnetic characteristics and we derived the ribbon thickness dependence from measured data. The measured data show that the MA core shunt impedance is inversely proportional to the ribbon thickness in the accelerating frequency region of the J-PARC synchrotrons, which is consistent with our calculations.
Energy Technology Data Exchange (ETDEWEB)
Carter, Hamilton, E-mail: hcarter3@nmsu.edu [Department of Physics, New Mexico State University, Las Cruces, NM 88003 (United States); Pate, Stephen, E-mail: pate@nmsu.edu [Department of Physics, New Mexico State University, Las Cruces, NM 88003 (United States); Goedecke, George, E-mail: ggoedeck@nmsu.edu [Department of Physics, New Mexico State University, Las Cruces, NM 88003 (United States)
2013-02-14
Highlights: ► AC magnetic field strength required for levitation is independent of frequency. ► RMS magnetic field strength is in good agreement with DC magnetic field strength. ► Dependence of YBCO levitation force on AC magnetic field frequency is investigated. -- Abstract: The dependence of the magnetic field strength required for levitation of a melt textured, single domain YBCO superconductor disk on the frequency of the current generating the levitating magnetic field has been investigated. The magnetic field strength is found to be independent of frequency between 10 and 300 Hz. This required field strength is found to be in good experimental and theoretical agreement with the field strength required to levitate the same superconductor with a non-oscillating magnetic field. Hysteretic losses within the superconductor predicted by Bean’s critical-state model were also calculated. The measured data rules out any significant Bean’s model effects on the required levitation field strength within the measured frequency range.
Directory of Open Access Journals (Sweden)
Chan Jun Chun
2016-02-01
Full Text Available In this paper, we propose a new frequency-dependent amplitude panning method for stereophonic image enhancement applied to a sound source recorded using two closely spaced omni-directional microphones. The ability to detect the direction of such a sound source is limited due to weak spatial information, such as the inter-channel time difference (ICTD and inter-channel level difference (ICLD. Moreover, when sound sources are recorded in a convolutive or a real room environment, the detection of sources is affected by reverberation effects. Thus, the proposed method first tries to estimate the source direction depending on the frequency using azimuth-frequency analysis. Then, a frequency-dependent amplitude panning technique is proposed to enhance the stereophonic image by modifying the stereophonic law of sines. To demonstrate the effectiveness of the proposed method, we compare its performance with that of a conventional method based on the beamforming technique in terms of directivity pattern, perceived direction, and quality degradation under three different recording conditions (anechoic, convolutive, and real reverberant. The comparison shows that the proposed method gives us better stereophonic images in a stereo loudspeaker reproduction than the conventional method without any annoying effects.
Lichtenstein, J L L; Pruitt, J N
2015-06-01
Frequency-dependent selection is thought to be a major contributor to the maintenance of phenotypic variation. We tested for frequency-dependent selection on contrasting behavioural strategies, termed here 'personalities', in three species of social spiders, each thought to represent an independent evolutionary origin of sociality. The evolution of sociality in the spider genus Anelosimus is consistently met with the emergence of two temporally stable discrete personality types: an 'aggressive' or 'docile' form. We assessed how the foraging success of each phenotype changes as a function of its representation within a colony. We did this by creating experimental colonies of various compositions (six aggressives, three aggressives and three dociles, one aggressive and five dociles, six dociles), maintaining them in a common garden for 3 weeks, and tracking the mass gained by individuals of either phenotype. We found that both the docile and aggressive phenotypes experienced their greatest mass gain in mixed colonies of mostly docile individuals. However, the performance of both phenotypes decreased as the frequency of the aggressive phenotype increased. Nearly identical patterns of phenotype-specific frequency dependence were recovered in all three species. Naturally occurring colonies of these spiders exhibit mixtures dominated by the docile phenotype, suggesting that these spiders may have evolved mechanisms to maintain the compositions that maximize the success of the colony without compromising the expected reproductive output of either phenotype. © 2015 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2015 European Society For Evolutionary Biology.
Lucas del Pozo, Irene; Michelena, M D; de Manuel, V; Duch, M; Esteve, J; Plaza, J A
2010-01-01
The dynamic properties of membranes have been object of many researches since they can be used as sensor heads in different devices. Some methods have been proposed to solve the problem of determining the resonance frequencies and their dependence on the stress caused by forces applied on the membrane surface. The problem of the vibrating rectangular membrane under a stress caused by a uniform in-plane force is well known. However, the resonance frequency behaviour when the force is out-of-plane instead of in-plane, is not so well understood and documented. A gradiometer which uses a silicon square membrane with a magnet fixed on it as a sensor head has been developed in a previous work. This device reports a quadratic dependence of the frequency on the out-of-plane magnetic force. In this work, simulations to obtain the dependence of the frequency of the fundamental flexural mode on the stress have been performed. It has been studied the influence of in-plane and out-of-plane forces applied to the membrane. ...
Directory of Open Access Journals (Sweden)
Araújo Denise Sardinha Mendes Soares de
2003-01-01
Full Text Available OBJECTIVE: To evaluate the level of satisfaction with body weight and the self-perception of the weight/height ratio and to verify the influence of the frequency of present and past physical activity on these variables. METHODS: Using questionnaires or interviews, we obtained height data, reported and desired weight, self-perception of the weight/height ratio, and the frequency of current physical activity in 844 adults (489 women. Of these, evaluated the frequency of physical activity during high school of 193 individuals,and we measured their height and weight. RESULTS: Less than 2/3 of the individuals had body mass index between 20 and 24.9 kg/m2. A tendency existed to overestimate height by less than 1 cm and to underestimate weight by less than 1kg. Desired weight was less than that reported (p<0.001, and only 20% were satisfied with their current weight. Only 42% of men and 25% of women exercised regularly. No association was found between the frequency of physical activity and the variables height, weight, and body mass index, and the level of satisfaction with current weight. CONCLUSION: Height and weight reported seem to be valid for epidemological studies, and great dissatisfaction with body weight and a distorted self-perception of height/weight ratio exists, especially in women, regardless of the frequency of physical activity.
DEFF Research Database (Denmark)
Bukh, K. R.; Jacobsen, Claus Schelde; Hansen, Jørn Bindslev
2000-01-01
The characteristics of the magnetic flux noise in high temperature superconducting thin-films of yttrium-barium-copper-oxide (YBa2Cu3O7) in the vicinity of artificial grain boundaries have been studied by means of a low critical temperature superconducting quantum interference device (SQUID...
Di Bernardo, A; Diesch, S; Gu, Y; Linder, J; Divitini, G; Ducati, C; Scheer, E; Blamire, M G; Robinson, J W A
2015-01-01
The theory of superconductivity developed by Bardeen, Cooper and Schrieffer (BCS) explains the stabilization of electron pairs into a spin-singlet, even frequency, state by the formation of an energy gap within which the density of states is zero. At a superconductor interface with an inhomogeneous ferromagnet, a gapless odd frequency superconducting state is predicted, in which the Cooper pairs are in a spin-triplet state. Although indirect evidence for such a state has been obtained, the gap structure and pairing symmetry have not so far been determined. Here we report scanning tunnelling spectroscopy of Nb superconducting films proximity coupled to epitaxial Ho. These measurements reveal pronounced changes to the Nb subgap superconducting density of states on driving the Ho through a metamagnetic transition from a helical antiferromagnetic to a homogeneous ferromagnetic state for which a BCS-like gap is recovered. The results prove odd frequency spin-triplet superconductivity at superconductor/inhomogeneous magnet interfaces.
Kawamura, Hironao; Kozuka, Masahiro; Itamoto, Naoki; Shinjo, Kazuo; Ishii, Masaru
Lightning faults on transmission lines often cause instantaneous voltage drops in power systems. Influences of instantaneous voltage drops become increasingly serious in high technology industries etc. As countermeasures of instantaneous voltage drops, uninterruptible power supplies (UPS) are employed. On the other hand, line surge arresters are installed on transmission lines increasingly as one of the effective countermeasures of double-circuit faults caused by lightning strokes. Additionally, the arresters are effective as one of the reduction methods for the frequency of instantaneous voltage drops. In this paper, the frequency of instantaneous voltage drops reduced by installation of line surge arresters on transmission lines is estimated by employing EMTP analysis. Also, the accuracy of the method in estimating the frequency of instantaneous voltage drops in power systems is evaluated through comparison with experience.
Dmitriev, Alexander L
2011-01-01
Results of measurements of free falling acceleration of a closed container with a rotor of a mechanical gyroscope placed inside it on the frequency of the rotor rotation are briefly described. Time of separate accelerations measurements is 40 ms, the period of sampling is from 0.5 up to 1.0 minute. In rotation's frequencies range of 20-400 Hz, the negative changes of free falling container acceleration prevail. On individual frequencies the "resonant" maxima and minima of acceleration are observed. The obtained data apparently contradict the equivalence principle of inertial and gravitating masses. The expediency of development of ballistic gravimetry of high time resolution with use of rotating or oscillating test bodies is noted.
Rosenbaum, Robert; Rubin, Jonathan; Doiron, Brent
2012-01-01
Depletion of synaptic neurotransmitter vesicles induces a form of short term depression in synapses throughout the nervous system. This plasticity affects how synapses filter presynaptic spike trains. The filtering properties of short term depression are often studied using a deterministic synapse model that predicts the mean synaptic response to a presynaptic spike train, but ignores variability introduced by the probabilistic nature of vesicle release and stochasticity in synaptic recovery time. We show that this additional variability has important consequences for the synaptic filtering of presynaptic information. In particular, a synapse model with stochastic vesicle dynamics suppresses information encoded at lower frequencies more than information encoded at higher frequencies, while a model that ignores this stochasticity transfers information encoded at any frequency equally well. This distinction between the two models persists even when large numbers of synaptic contacts are considered. Our study provides strong evidence that the stochastic nature neurotransmitter vesicle dynamics must be considered when analyzing the information flow across a synapse.
Mandal, Swapan
2017-03-01
The classical harmonic oscillator with time dependent mass and frequency is investigated to obtain a closed form exact analytical solution. It is found that the closed form analytical solutions are indeed possible if the time dependent mass of the oscillator is inversely proportional to the time dependent frequency. The scaled wronskian obtained from the linearly independent solutions of the equation of motion of the classical oscillator is used to obtain the solution corresponding to its quantum mechanical counterpart. The analytical solution of the present oscillator is used to obtain the squeezing effects of the input coherent light. In addition to the possibilities of getting the squeezed states, the present solution will be of use for investigating various quantum statistical properties of the radiation fields. As an example, we investigate the antibunching of the input thermal (chaotic) light coupled to the oscillator. Therefore, the appearance of the photon antibunching does not warrant the squeezing and vice-versa. The exact solution is obtained at the cost of the stringent condition where the product of time dependent mass and frequency of the oscillator is time invariant.
Analysis of Age Dependent Effects of Heat Stress on EEG Frequency Components in Rats
Institute of Scientific and Technical Information of China (English)
RAKESH KUMAR SINHA
2009-01-01
Objective To demonstrate changes in different frequencies of cerebral electrical activity or electroencephalogram (EEG) following exposure to high environmental heat in three different age groups of freely moving rats. Methods Rats were divided into three groups (i) acute heat stress - subjected to a single exposure for four hours at 38 ℃; (ii) chronic heat stress -exposed for 21 days daily for one hour at 38 ℃, and (iii) handling control groups. The digital polygraphic sleep-EEG recordings were performed just after the heat exposure from acute stressed rats and on 22nd day from chronic stressed rats by simultaneous recording of cortical EEG EOG (electrooculogram), and EMG (electromyogram). Further, power spectrum analyses were performed to analyze the effects of heat stress. Results The frequency analysis of EEG signals following exposure to high environmental heat revealed that in all three age groups of rats, changes in higher frequency components (β2) were significant in all sleep-wake states following both acute and chronic heat stress conditions. After exposure to acute heat, significant changes in EEG frequencies with respect to their control groups were observed, which were reversed partly or fully in four hours of EEG recording. On the other hand, due to repetitive chronic exposure to hot environment, adaptive and long-term changes in EEG frequency patterns were observed. Conclusion The present study has exhibited that the cortical EEG is sensitive to environmental heat and alterations in EEG frequencies in different sleep-wake states due to heat stress can be differentiated efficiently by EEG power spectrum analysis.
Maxworth, A. S.; Golkowski, M.; Cohen, M.; Moore, R. C.
2014-12-01
Generation of Extremely Low Frequency (ELF) and Very Low Frequency (VLF) signals through ionospheric modification has been practiced for many years. Heating the lower ionosphere with high power HF waves allows for modulation of natural current systems. Our experiments were carried out at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska, USA. In this experiment, the ionosphere was heated with a vertical amplitude modulating signal and the modulation frequency was changed sequentially within an array of 40 frequencies followed by a frequency ramp. The observed magnetic field amplitude and polarization of the generated ELF/VLF signals were analyzed for multiple sites and as a function of modulation frequency. Our three observation sites: Chistochina, Paxson and Paradise are located within 36km (azimuth 47.7°), 50.2km (azimuth -20°) and 99km (azimuth 80.3°) respectively. We show that the peak amplitudes observed as a function of frequency result from vertical resonance in the Earth-ionosphere waveguide and can be used to diagnose the D-region profile. Polarization analysis showed that out of the three sites Paxson shows the highest circularity in the magnetic field polarization, compared to Chistochina and Paradise which show highly linear polarizations. The experimental results were compared with a theoretical simulation model results and it was clear that in both cases, the modulated Hall current dominates the observed signals at Chistochina and Paradise sites and at Paxson there is an equal contribution from Hall and Pedersen currents. The Chistochina site shows the highest magnetic field amplitudes in both experimental and simulation environments. Depending upon the experimental and simulation observations at the three sites, a radiation pattern for the HAARP ionospheric heater can be mapped
Ethyl benzene-induced ototoxicity in rats : a dose-dependent mild-frequency hearing loss
Cappaert, N.L.M.; Klis, S.F.L.; Baretta, A.B.; Muijser, H.; Smoorenburg, G.F.
2000-01-01
Rats were exposed to ethyl benzene at 0, 300, 400 and 550 ppm for 8 hours/day for 5 consecutive days. Three to six weeks after the exposure, auditory function was tested by measuring compound action potentials (CAP) in the frequency range of 1-24 kHz and 2f1-f2 distortion product otoacoustic
Can the frequency-dependent specific heat be measured by thermal effusion methods?
Christensen, Tage; Olsen, Niels Boye; Dyre, Jeppe C.
2007-01-01
It has recently been shown that plane-plate heat effusion methods devised for wide-frequency specific-heat spectroscopy do not give the isobaric specific heat, but rather the so-called longitudinal specific heat. Here it is shown that heat effusion in a spherical symmetric geometry also involves the longitudinal specific heat.
Sokalski, Krzysztof Z
2015-01-01
Recently introduced model of magnetic hysteresis was extended into set of the following features: frequency, pick of induction and temperature of specimen. Group theoretical classification of hysteresis loops' sets is presented. An effect analogous to the Zeeman splitting has been revealed in the set of the all hysteresis loops.
Happel, Max F. K.; Ohl, Frank W.
2017-01-01
Robust perception of auditory objects over a large range of sound intensities is a fundamental feature of the auditory system. However, firing characteristics of single neurons across the entire auditory system, like the frequency tuning, can change significantly with stimulus intensity. Physiological correlates of level-constancy of auditory representations hence should be manifested on the level of larger neuronal assemblies or population patterns. In this study we have investigated how information of frequency and sound level is integrated on the circuit-level in the primary auditory cortex (AI) of the Mongolian gerbil. We used a combination of pharmacological silencing of corticocortically relayed activity and laminar current source density (CSD) analysis. Our data demonstrate that with increasing stimulus intensities progressively lower frequencies lead to the maximal impulse response within cortical input layers at a given cortical site inherited from thalamocortical synaptic inputs. We further identified a temporally precise intercolumnar synaptic convergence of early thalamocortical and horizontal corticocortical inputs. Later tone-evoked activity in upper layers showed a preservation of broad tonotopic tuning across sound levels without shifts towards lower frequencies. Synaptic integration within corticocortical circuits may hence contribute to a level-robust representation of auditory information on a neuronal population level in the auditory cortex. PMID:28046062
The Frequency-Predictability Interaction in Reading: It Depends Where You're Coming from
Hand, Christopher J.; Miellet, Sebastien; O'Donnell, Patrick J.; Sereno, Sara C.
2010-01-01
A word's frequency of occurrence and its predictability from a prior context are key factors determining how long the eyes remain on that word in normal reading. Past reaction-time and eye movement research can be distinguished by whether these variables, when combined, produce interactive or additive results, respectively. Our study addressed…
Ethyl benzene-induced ototoxicity in rats : a dose-dependent mild-frequency hearing loss
Cappaert, N.L.M.; Klis, S.F.L.; Baretta, A.B.; Muijser, H.; Smoorenburg, G.F.
2000-01-01
Rats were exposed to ethyl benzene at 0, 300, 400 and 550 ppm for 8 hours/day for 5 consecutive days. Three to six weeks after the exposure, auditory function was tested by measuring compound action potentials (CAP) in the frequency range of 1-24 kHz and 2f1-f2 distortion product otoacoustic emissio
Simplified frequency-dependent formulae for series-impedance matrices of single-core HVAC cables
DEFF Research Database (Denmark)
Silva, Filipe Miguel Faria da
2015-01-01
The installation of HVAC underground cables became more common in recent years, a trend expected to continue in the future. Underground cables are more complex than overhead lines and the calculation of their resistance and reactance can be challenging and time consuming for frequencies that are ...
Temperature and frequency dependent dielectric properties of Ni–Mg–Zn–Co ferrites
Energy Technology Data Exchange (ETDEWEB)
Patil, S.B., E-mail: sarjeraopatil97@gmail.com [Krantisinh Nana Patil College, Walwa, Sangli 416313, Maharashtra (India); Patil, R.P. [Department of Chemistry, M.H. Shinde Mahavidyalaya, Tisangi 416206, Maharashtra (India); Ghodake, J.S. [Department of Physics, Padmabhushan Dr. Vasantraodada Patil College, Tasgaon, Sangli 416312, Maharashtra (India); Chougule, B.K. [Materials Research Laboratory, Department of Physics, Shivaji University, Kolhapur 416004, Maharashtra (India)
2014-01-15
The ferrites having general formula Ni{sub 0.5−x}Mg{sub x−0.01}Zn{sub 0.5−y}Co{sub y+0.01}Fe{sub 2}O{sub 4} (x=0.1, 0.2, 0.3, 0.4 and y=0.1, 0.2, 0.3, 0.4) were prepared by ceramic method. The X-ray diffraction studies of compositions reveal formation of single-phase cubic spinal structure. Dielectric properties such as dielectric constant ε′, dielectric loss tangent (tan δ), and ac resistivity were measured at room temperature as a function of frequency in the range from 1 kHz to 1 MHz. The plots of dielectric constant ε′ vs frequency show a normal dielectric behavior of spinel ferrites. The variation of loss tangent (tan δ) as a function of frequency shows a decreasing trend for all the samples except for the composition with x=0.3 and y=0.1, and y=0.2. The variation of ac resistivity with frequency of all the samples shows a decreasing trend with increase in frequency, a normal behavior of ferrites. All the variations are explained on the basis of Fe{sup 2+}/Fe{sup 3+} ion concentration on octahedral sites as well as the electronic hopping between Fe{sup 2+}↔Fe{sup 3+} ions. - Highlights: • Ni{sub 0.5−x}Mg{sub x−0.01}Zn{sub 0.5−y}Co{sub y+0.01}Fe{sub 2}O{sub 4} were prepared by ceramic method. • Single-phase cubic spinal structure. • Normal dielectric behavior.
Zhou, Jianqin; Shen, Jun; Neill, W. Stuart
2016-07-01
A method of frequency analysis for the measurement of the temperature coefficient of refractive index (dn/dT) using a Fabry-Perot interferometer was developed and tested against ethanol and water. The temperature-dependent interferometric signal described by Airy's formula was analyzed in both the temperature and frequency domains. By fast Fourier transform, a low-pass filter was designed and employed to eliminate the noise superimposed on the signal. dn/dT was determined accurately from the noise-removed signal by peak analysis. Furthermore, the signal frequency parameters may be utilized for the material thermophysical property characterization. This method lays the foundation for an online dn/dT instrument for monitoring chemical processes.
Carter, Hamilton; Pate, Stephen; Goedecke, George
2013-02-01
The dependence of the magnetic field strength required for levitation of a melt textured, single domain YBCO superconductor disk on the frequency of the current generating the levitating magnetic field has been investigated. The magnetic field strength is found to be independent of frequency between 10 and 300 Hz. This required field strength is found to be in good experimental and theoretical agreement with the field strength required to levitate the same superconductor with a non-oscillating magnetic field. Hysteretic losses within the superconductor predicted by Bean’s critical-state model were also calculated. The measured data rules out any significant Bean’s model effects on the required levitation field strength within the measured frequency range.
Lin, C S; Lim, H S; Wang, Z K; Ng, S C; Kuok, M H; Adeyeye, A O
2011-03-01
An understanding of the spin dynamics of nanoscale magnetic elements is important for their applications in magnetic sensing and storage. Inhomogeneity of the demagnetizing field in a non-ellipsoidal magnetic element results in localization of spin waves near the edge of the element. However, relative little work has been carried out to investigate the effect of the applied magnetic fields on the nature of such localized modes. In this study, micromagnetic simulations are performed on an equilateral triangular nanomagnet to investigate the magnetic field dependence of the mode profiles of the lowest-frequency spin wave. Our findings reveal that the lowest-frequency mode is localized at the base edge of the equilateral triangle. The characteristics of its mode profile change with the ground state magnetization configuration of the nanotriangle, which, in turn, depends on the magnitude of the in-plane applied magnetic field.
Directory of Open Access Journals (Sweden)
Faten eMina
2013-07-01
Full Text Available A number of studies showed that deep brain stimulation (DBS can modulate the activity in the epileptic brain and that a decrease of seizures can be achieved in responding patients. In most of these studies, the choice of stimulation parameters is critical to obtain desired clinical effects. In particular, the stimulation frequency is a key parameter that is difficult to tune. A reason is that our knowledge about the frequency-dependant mechanisms according to which DBS indirectly impacts the dynamics of pathological neuronal systems located in the neocortex is still limited. We address this issue using both computational modeling and intracerebral EEG (iEEG data.We developed a macroscopic (neural mass model of the thalamocortical network. In line with already-existing models, it includes interconnected neocortical pyramidal cells and interneurons, thalamocortical cells and reticular neurons. The novelty was to introduce, in the thalamic compartment, the biophysical effects of direct stimulation. Regarding clinical data, we used a quite unique data set recorded in a patient (drug-resistant epilepsy with a focal cortical dysplasia (FCD. In this patient, DBS strongly reduced the sustained epileptic activity of the FCD for low-frequency (LFS, < 2 Hz and high-frequency stimulation (HFS, > 70 Hz while intermediate-frequency stimulation (IFS, around 50 Hz had no effect.Signal processing, clustering and optimization techniques allowed us to identify the necessary conditions for reproducing, in the model, the observed frequency-dependent stimulation effects. Key elements which explain the suppression of epileptic activity in the FCD include a feed-forward inhibition and synaptic short-term depression of thalamocortical connections at LFS, and b inhibition of the thalamic output at HFS. Conversely, modeling results indicate that IFS favors thalamic oscillations and entrains epileptic dynamics.
Directory of Open Access Journals (Sweden)
S. U. Jen
2014-12-01
Full Text Available Frequency dependence of magnetostrictive phenomenon of as-cast 2605SA1 ribbon was studied. We applied a sinusoidal sweeping field (H, with a fixed frequency (f, along length (L of the ribbon, and simultaneously recorded the longitudinal magnetostriction (λ∥ and the transverse magnetostriction (λ⊥ as a function of time (t, respectively. f was varied from 0.07 to 122 Hz. In the low-f case (f =0.07 Hz, we observed the frequency-doubling (FD feature in λ∥(t and λ⊥(t curves; i.e., only even harmonic magnetostrictive signals showed up. In the high-f case (f = 122 Hz, we observed the no-frequency-doubling (NFD feature; i.e., both odd and even harmonic magnetostrictive signals showed up. A theory, based on the balance among various torques acting on magnetization, is developed to explain the f dependence of the magnetostriction phenomenon observed. From this theory, we conclude that only when the reflection symmetry of the system is reserved, i.e., when the equivalent easy axis (EEA is perpendicular to L, will λ∥(t and λ⊥(t have the true-frequency-doubling (TFD feature. However, for the as-cast 2605SA1 ribbon, EEA is not perpendicular to L. Thus, strictly speaking, we should observe the NFD feature only. Nevertheless, in the low-f limit, we can show that the FD feature is somewhat allowed under the condition, b/α being close to 1, where b and α are the two parameters used in the theory. From experimental data, this condition is met for as-cast 2605SA1. To make a distinction from TFD, this low-f feature is called close-frequency-doubling (CFD in this paper. In general, the theory explains all the experimental results fairly well.
The neural code for auditory space depends on sound frequency and head size in an optimal manner.
Directory of Open Access Journals (Sweden)
Nicol S Harper
Full Text Available A major cue to the location of a sound source is the interaural time difference (ITD-the difference in sound arrival time at the two ears. The neural representation of this auditory cue is unresolved. The classic model of ITD coding, dominant for a half-century, posits that the distribution of best ITDs (the ITD evoking a neuron's maximal response is unimodal and largely within the range of ITDs permitted by head-size. This is often interpreted as a place code for source location. An alternative model, based on neurophysiology in small mammals, posits a bimodal distribution of best ITDs with exquisite sensitivity to ITDs generated by means of relative firing rates between the distributions. Recently, an optimal-coding model was proposed, unifying the disparate features of these two models under the framework of efficient coding by neural populations. The optimal-coding model predicts that distributions of best ITDs depend on head size and sound frequency: for high frequencies and large heads it resembles the classic model, for low frequencies and small head sizes it resembles the bimodal model. The optimal-coding model makes key, yet unobserved, predictions: for many species, including humans, both forms of neural representation are employed, depending on sound frequency. Furthermore, novel representations are predicted for intermediate frequencies. Here, we examine these predictions in neurophysiological data from five mammalian species: macaque, guinea pig, cat, gerbil and kangaroo rat. We present the first evidence supporting these untested predictions, and demonstrate that different representations appear to be employed at different sound frequencies in the same species.
The neural code for auditory space depends on sound frequency and head size in an optimal manner.
Harper, Nicol S; Scott, Brian H; Semple, Malcolm N; McAlpine, David
2014-01-01
A major cue to the location of a sound source is the interaural time difference (ITD)-the difference in sound arrival time at the two ears. The neural representation of this auditory cue is unresolved. The classic model of ITD coding, dominant for a half-century, posits that the distribution of best ITDs (the ITD evoking a neuron's maximal response) is unimodal and largely within the range of ITDs permitted by head-size. This is often interpreted as a place code for source location. An alternative model, based on neurophysiology in small mammals, posits a bimodal distribution of best ITDs with exquisite sensitivity to ITDs generated by means of relative firing rates between the distributions. Recently, an optimal-coding model was proposed, unifying the disparate features of these two models under the framework of efficient coding by neural populations. The optimal-coding model predicts that distributions of best ITDs depend on head size and sound frequency: for high frequencies and large heads it resembles the classic model, for low frequencies and small head sizes it resembles the bimodal model. The optimal-coding model makes key, yet unobserved, predictions: for many species, including humans, both forms of neural representation are employed, depending on sound frequency. Furthermore, novel representations are predicted for intermediate frequencies. Here, we examine these predictions in neurophysiological data from five mammalian species: macaque, guinea pig, cat, gerbil and kangaroo rat. We present the first evidence supporting these untested predictions, and demonstrate that different representations appear to be employed at different sound frequencies in the same species.
Picht, Eckard; DeSantiago, Jaime; Huke, Sabine; Kaetzel, Marcia A.; Dedman, John R.; Bers, Donald M.
2006-01-01
Cardiac Ca2+/calmodulin-dependent protein kinase II (CaMKII) in heart has been implicated in Ca2+ current (ICa) facilitation, enhanced sarcoplasmic reticulum (SR) Ca2+ release and frequency dependent acceleration of relaxation (FDAR) via enhanced SR Ca2+ uptake. However, questions remain about how CaMKII may work in these three processes. Here we tested the role of CaM-KII in these processes using transgenic mice (SR-AIP) that express four concatenated repeats of the CaMKII inhibitory peptide...
Delfino, Federico; Procopio, Renato; Rossi, Mansueto; Rachidi, Farhad
2009-06-01
This paper is aimed at analyzing the influence of the frequency-dependent behavior of the ground electrical parameters (conductivity and ground permittivity) on the electromagnetic field radiated by a cloud-to-ground lightning return stroke. Both radiation in air (over the conducting ground plane) and underground are considered in the analysis. The adopted method is based on the classical Sommerfeld's theory and takes advantage of an efficient ad hoc numerical procedure to face with the slow converging Sommerfeld's integrals. This feature allows the electromagnetic field to be computed without any sort of mathematical approximation and, since it is carried out in the frequency domain, can be used either if the ground permittivity and conductivity are considered constant or if they vary with the working frequency with any functional law. Simulations have been performed to identify the cases in which the approximation of constant ground permittivity and conductivity leads to satisfactory results. It is shown that for soils with water contents of 2% to 10% (ground conductivities in the order of 0.001 to 0.01 S/m), the assumption of constant electrical parameters appears to be reasonable. However, for either very poorly conducting soils (10-4 S/m or so) or highly conducting soils (10-1 S/m), the electromagnetic field components appear to be significantly affected by the frequency dependence of the ground electrical parameters.
Tsai, David; Morley, John W.; Suaning, Gregg J.; Lovell, Nigel H.
2011-10-01
The ability to elicit visual percepts through electrical stimulation of the retina has prompted numerous investigations examining the feasibility of restoring sight to the blind with retinal implants. The therapeutic efficacy of these devices will be strongly influenced by their ability to elicit neural responses that approximate those of normal vision. Retinal ganglion cells (RGCs) can fire spikes at frequencies greater than 200 Hz when driven by light. However, several studies using isolated retinas have found a decline in RGC spiking response rate when these cells were stimulated at greater than 50 Hz. It is possible that the mechanism responsible for this decline also contributes to the frequency-dependent 'fading' of electrically evoked percepts recently reported in human patients. Using whole-cell patch clamp recordings of rabbit RGCs, we investigated the causes for the spiking response depression during direct subretinal stimulation of these cells at 50-200 Hz. The response depression was not caused by inhibition arising from the retinal network but, instead, by a stimulus-frequency-dependent decline of RGC voltage-gated sodium current. Under identical experimental conditions, however, RGCs were able to spike at high frequency when driven by light stimuli and intracellular depolarization. Based on these observations, we demonstrated a technique to prevent the spiking response depression.
Przyklenk, A.; Hördt, A.; Radić, T.
2016-05-01
Capacitively-Coupled Resistivity (CCR) is conventionally used to emulate DC resistivity measurements and may provide important information about the ice content of material in periglacial areas. The application of CCR theoretically enables the determination of both electrical parameters, i.e. the resistivity and the electrical permittivity, by analyzing magnitude and phase shift spectra. The electrical permittivity may dominate the impedance, especially in periglacial areas or regions of hydrogeological interest. However, previous theoretical work suggested that the phase shift may strongly depend on electrode height above ground, implying that electrode height must be known with great accuracy to determine electrical permittivity. Here, we demonstrate with laboratory test measurements, theoretical modelling and by analysing the Jacobian matrix of the inversion, that the sensitivity towards electrode height is drastically reduced if the electrical permittivity is frequency dependent in a way that is typical for ice. For the fist time, we used a novel broadband CCR device "Chameleon" for a field test located in one of the ridge galleries beneath the crest of Mount Zugspitze. A permanently ice covered bottom of a tunnel was examined. For the inversion of the measured spectra, the frequency dependance of the electrical parameters was parameterized in 3 different ways. A Debye Model for pure ices, a Cole-Cole Model for pure ices and a dual Cole-Cole Model including interfacial water additionally. The frequency-dependent resistivity and permittivity spectra obtained from the inversion, including low and high frequency limits, agree reasonably well with laboratory and field measurements reported in the literature.
Energy Technology Data Exchange (ETDEWEB)
Davari, Nazanin; Haghdani, Shokouh; Åstrand, Per-Olof [Department of Chemistry, Norwegian University of Science and Technology (NTNU), Trondheim (Norway)
2015-12-31
A force field model for calculating local field factors, i.e. the linear response of the local electric field for example at a nucleus in a molecule with respect to an applied electric field, is discussed. It is based on a combined charge-transfer and point-dipole interaction model for the polarizability, and thereby it includes two physically distinct terms for describing electronic polarization: changes in atomic charges arising from transfer of charge between the atoms and atomic induced dipole moments. A time dependence is included both for the atomic charges and the atomic dipole moments and if they are assumed to oscillate with the same frequency as the applied electric field, a model for frequency-dependent properties are obtained. Furthermore, if a life-time of excited states are included, a model for the complex frequency-dependent polariability is obtained including also information about excited states and the absorption spectrum. We thus present a model for the frequency-dependent local field factors through the first molecular excitation energy. It is combined with molecular dynamics simulations of liquids where a large set of configurations are sampled and for which local field factors are calculated. We are normally not interested in the average of the local field factor but rather in configurations where it is as high as possible. In electrical insulation, we would like to avoid high local field factors to reduce the risk for electrical breakdown, whereas for example in surface-enhanced Raman spectroscopy, high local field factors are desired to give dramatically increased intensities.
Furukawa, Yukio
2000-03-01
The modulation-frequency dependencies of the intensity and the phase delay of photoinduced infrared absorption from poly(p-phenylene) have been observed and simulated numerically on the basis of a model based on second-order kinetics involving a neutralization recombination process between the positive and negative charge carriers (polarons) that are formed from a photogenerated polaron pair (interchain charge-transfer exciton). The rate constant of the bimolecular recombination has been obtained.
Chan, Calvin; Ohta, Taisuke; Kellogg, Gary; Mansfield, Lorelle; Noufi, Rommel
2014-03-01
Chalcopyrite Cu(In1-xGax)Se2 (CIGS) is an interesting photovoltaic material because it holds the laboratory record for thin-film solar power conversion efficiency (η > 20 %) despite its disordered microcrystalline structure. However, commercialization of this technology has been limited by structural and chemical variations in CIGS films. Many microscopic and spectroscopic studies have shown built-in electric potentials (Φbi) at CIGS grain boundaries. This may assist with electron-hole separation, but the reported magnitude and statistical distribution of Φbi remains inconsistent between studies. In this work, photoemission and low-energy electron microscopies (PEEM and LEEM) were used to reconcile these reported differences. Highly surface sensitive PEEM measurements showed Φbi ~ 0 . 5 V, which was consistent with most other reports. However, more bulk sensitive LEEM measurements showed Φbi ~ 1 . 5 V, which strongly suggests p- to n-type inversion at CIGS grain boundaries. This formation of pn junctions at CIGS grain boundaries is likely responsible for the high performance of CIGS photovoltaics. Sandia is managed by Sandia Corp., a subsidiary of Lockheed Martin, for the U.S. DOE NNSA (DE-AC04-94AL85000). Work was supported by an U.S. DOE EERE SunShot Bridging Research Interactions through collaborative Development Grants in Energy (BRIDGE).
Amplitude and frequency dependence of hysteresis loss in a magnet-superconductor levitation system
Yang, Z. J.; Hull, J. R.; Mulcahy, T. M.; Rossing, T. D.
1995-08-01
Using an electromagnetically controlled mechanical pendulum, we measured the energy loss for different amplitudes in a magnetic levitation system that contained high temperature superconductors (HTSs). Two procedures were followed to measure losses at 77 K for frequencies of 93.8 mHz to 80 Hz. In the first procedure, the distance between the permanent magnet and the HTS levitator was the same as that during (field) cooling. In the second procedure, the magnet was lowered (after cooling) closer to the HTS levitator before the measurements were performed. The experimental data show that these two procedures give essentially the same results at the same distance despite different cooling (and magnetization) histories for melt-textured YBaCuO levitators, and the frequency-independent energy loss is a power-law function of amplitude. We attribute the energy loss to magnetic hysteresis in the superconductor.
Comment on "Orientation dependence of the optical spectra in graphene at high frequencies"
Nguyen, Huy-Viet; Nguyen, V. Hung
2016-09-01
Zhang et al. [Phys. Rev. B 77, 241402(R) (2008), 10.1103/PhysRevB.77.241402] reported a theoretical study of the optical spectra of monolayer graphene employing the Kubo formula within a tight-binding model. Their calculations predicted that at high frequencies the optical conductivity of graphene becomes strongly anisotropic. In particular, at frequencies comparable to the energy separation of the upper and lower bands at the Γ point, the optical conductivity is strongly suppressed if the field polarization is along the zigzag direction whereas it is significantly high for the armchair one. We find that, unfortunately, this result is just a consequence of the incorrect determination of the current operator in k space. Here, we present a standard scheme to obtain this operator correctly. As a result, we show that the optical conductivity of monolayer graphene is indeed isotropic, which is consistent with the results of other (both theoretical and experimental) studies in the literature.
Analysis of frequency- and temperature-dependent interface states in PtSi/p-Si Schottky diodes
Energy Technology Data Exchange (ETDEWEB)
Sellai, A. [Physics Department, P.O. Box 36, Sultan Qaboos University 123, Muscat (Oman)], E-mail: asellai@squ.edu.om; Ouennoughi, Z. [Laboratoire Optoelectronique et Composants, Departement de Physique UFAS Setif Algerie (Algeria)
2008-12-05
To yield quantitative information about their interface states, PtSi/p-Si Schottky structures have been studied using conductance and capacitance measurements over a wide range of frequencies (1 kHz to 1 MHz) and at several temperatures (80-140 K). The increase in capacitance at lower frequencies is seen as a signature of interface states, the densities of which are evaluated to be of the order of {approx}10{sup 12} eV{sup -1} cm{sup -2}. The presence of interface states is also evidenced as a peak in the conductance-frequency characteristics that increases in magnitude with decreasing temperatures. The variations of interface conductance are best described by an analytical equation derived assuming an energy-dependent cross-section of these interface states. The conductance data is subsequently used to extract the relaxation times of interface states and their energy distribution with respect to the top of the valence band. Relaxation times, in particular, while temperature dependent with an average value of {approx}4 {mu}s, show a noticeably weak dependence on bias.
2008-01-01
Multipolar plasmon oscillation frequencies and corresponding damping rates for nanospheres formed of the simplest free-electron metals are studied. The possibility of controlling plasmon features by choosing the size and dielectric properties of the sphere surroundings is discussed. Optical properties of the studied metals are described within the Drude-Sommerfeld model of the dielectric function with effective parameters acounting for the contribution of conduction electrons and of interband...
Time-domain representation of frequency dependent inertial forces on offshore structures
DEFF Research Database (Denmark)
Krenk, Steen
2013-01-01
The inertial wave force on a vertical cylinder decreases with decreasing wave length, when the wave length is less than about six times the diameter of the diameter of the cylinder. In structures with a largediameter component like mono-towers the resonance frequency of the structure is typically...... section are uncoupled, and they are easily integrated with e.g. a central difference scheme for the state-space variables. © 2013 Taylor & Francis Group, London....
Directory of Open Access Journals (Sweden)
Juan C. Torres
2014-05-01
Full Text Available A series of polymer dispersed liquid crystal devices using glass substrates have been fabricated and investigated focusing on their electrical properties. The devices have been studied in terms of impedance as a function of frequency. An electric equivalent circuit has been proposed, including the influence of the temperature on the elements into it. In addition, a relevant effect of temperature on electrical measurements has been observed.
Ansari, S.; P. Voosogh S. Moshtaghian
2008-01-01
Life-long red blood transfusion remains the main treatment for severe thalassemia. The development of hemolytic alloantibodies and erythrocyte autoantibodies complicated transfusion therapy in thalassemia patients. The frequency causes and prevention of this phenomenon among 80 transfused thalassemia patients were evaluated in Ali Asghar Children's Hospital during 1998-2004 in a cross-sectional study. In our study the mean age at the initiation of transfusion was 1.7 years (SD = 1.94) an...
Frequency dependence of the superparamagnetic transition in a Finemet-type nanocrystalline alloy
Energy Technology Data Exchange (ETDEWEB)
Franco, V.; Blazquez, J.S.; Conde, C.F.; Conde, A. [Dpto. Fisica de la Materia Condensada. ICMSE-CSIC, Universidad de Sevilla, P.O. Box 1065, 41080-Sevilla (Spain); Kiss, L.F.; Kemeny, T. [Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences. P.O. Box 49, 1525-Budapest (Hungary); Hillier, A.D. [ISIS Facility, CCLRC, Rutherford Appleton Laboratory, Chilton, OX11 0QX (United Kingdom)
2004-12-01
The transition to superparamagnetism in a Cr-containing Finemet alloy has been studied by means of ac susceptibility and muon spin relaxation experiments. The influence of bias field and measuring frequency has been analyzed. The transition temperature is controlled by the interaction between the particles. These results are consistent with previous static magnetic measurements. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Wu, Yue-Chao; Zhao, Bin; Lee, Soo-Y.
2016-02-01
Femtosecond stimulated Raman spectroscopy (FSRS) on the Stokes side arises from a third order polarization, P(3)(t), which is given by an overlap of a first order wave packet, |" separators=" Ψ2 ( 1 ) ( p u , t ) > , prepared by a narrow band (ps) Raman pump pulse, Epu(t), on the upper electronic e2 potential energy surface (PES), with a second order wave packet, resembles the zeroth order wave packet |" separators=" Ψ1 ( 0 ) ( t ) > on the lower PES spatially, but with a force on |" separators=" Ψ2 ( 1 ) ( p u , t ) > along the coordinates of the reporter modes due to displacements in the equilibrium position, so that . The observable FSRS Raman gain is related to the imaginary part of P(3)(ω). The imaginary and real parts of P(3)(ω) are related by the Kramers-Kronig relation. Hence, from the FSRS Raman gain, we can obtain the complex P(3)(ω), whose Fourier transform then gives us the complex P(3)(t) to analyze for ω ¯ j ( t ) . We apply the theory, first, to a two-dimensional model system with one conformational mode of low frequency and one reporter vibrational mode of higher frequency with good results, and then we apply it to the time-resolved FSRS spectra of the cis-trans isomerization of retinal in rhodopsin [P. Kukura et al., Science 310, 1006 (2005)]. We obtain the vibrational frequency up-shift time constants for the C12-H wagging mode at 216 fs and for the C10-H wagging mode at 161 fs which are larger than for the C11-H wagging mode at 127 fs, i.e., the C11-H wagging mode arrives at its final frequency while the C12-H and C10-H wagging modes are still up-shifting to their final values, agreeing with the findings of Yan et al. [Biochemistry 43, 10867 (2004)].
Chen, Zhangguo; Viboolsittiseri, Sawanee S; O'Connor, Brian P; Wang, Jing H
2012-10-15
Activation-induced deaminase (AID) catalyses class switch recombination (CSR) and somatic hypermutation (SHM) in B lymphocytes to enhance Ab diversity. CSR involves breaking and rejoining highly repetitive switch (S) regions in the IgH (Igh) locus. S regions appear to be preferential targets of AID. To determine whether S region sequence per se, independent of Igh cis regulatory elements, can influence AID targeting efficiency and mutation frequency, we established a knock-in mouse model by inserting a core Sγ1 region into the first intron of proto-oncogene Bcl6, which is a non-Ig target of SHM. We found that the mutation frequency of the inserted Sγ1 region was dramatically higher than that of the adjacent Bcl6 endogenous sequence. Mechanistically, S region-enhanced SHM was associated with increased recruitment of AID and RNA polymerase II, together with Spt5, albeit to a lesser extent. Our studies demonstrate that target DNA sequences influence mutation frequency via regulating AID recruitment. We propose that the nucleotide sequence preference may serve as an additional layer of AID regulation by restricting its mutagenic activity to specific sequences despite the observation that AID has the potential to access the genome widely.
Dependence of a frequency bandwidth on a spill structure in the RF-knockout extraction
Nakanishi, Tetsuya
2010-09-01
A spill structure in the RF-knockout extraction was studied on colored noise of the RF-knockout, in order to investigate the diffusion process of particles inside the separatrix. It is found that frequency bands solely around the resonances ( n+1/3 and n+2/3) contribute to the diffusion and the uniform spill, or equivalently uniform diffusion requires to include many bands around the resonances. A particle density distribution inside the separatrix would be modulated in the process of diffusion even if a frequency band covers the single betatron tune spread. With a spectrum of RF knockout including many bands around the resonances, the superposition of modulations by each band would make the unevenness of distribution small. The colored noise with multi-bands is proposed to reduce the power of amplifier, since frequency bands outside around the resonances do not contribute to the extraction. The simulation using the multi-bands spectrum shows the same uniform spill with a wide bandwidth.
Dependence of a frequency bandwidth on a spill structure in the RF-knockout extraction
Energy Technology Data Exchange (ETDEWEB)
Nakanishi, Tetsuya, E-mail: nakanishi.tetsuya@nihon-u.ac.j [College of Industrial Technology, Nihon University, 1-2-1 Izumicho, Narashino, Chiba 275-8575 (Japan)
2010-09-21
A spill structure in the RF-knockout extraction was studied on colored noise of the RF-knockout, in order to investigate the diffusion process of particles inside the separatrix. It is found that frequency bands solely around the resonances (n+1/3 and n+2/3) contribute to the diffusion and the uniform spill, or equivalently uniform diffusion requires to include many bands around the resonances. A particle density distribution inside the separatrix would be modulated in the process of diffusion even if a frequency band covers the single betatron tune spread. With a spectrum of RF knockout including many bands around the resonances, the superposition of modulations by each band would make the unevenness of distribution small. The colored noise with multi-bands is proposed to reduce the power of amplifier, since frequency bands outside around the resonances do not contribute to the extraction. The simulation using the multi-bands spectrum shows the same uniform spill with a wide bandwidth.
Reymbaut, A.; Gagnon, A.-M.; Bergeron, D.; Tremblay, A.-M. S.
2017-03-01
The computation of transport coefficients, even in linear response, is a major challenge for theoretical methods that rely on analytic continuation of correlation functions obtained numerically in Matsubara space. While maximum entropy methods can be used for certain correlation functions, this is not possible in general, important examples being the Seebeck, Hall, Nernst, and Reggi-Leduc coefficients. Indeed, positivity of the spectral weight on the positive real-frequency axis is not guaranteed in these cases. The spectral weight can even be complex in the presence of broken time-reversal symmetry. Various workarounds, such as the neglect of vertex corrections or the study of the infinite frequency or Kelvin limits, have been proposed. Here, we show that one can define auxiliary response functions that allow one to extract the desired real-frequency susceptibilities from maximum entropy methods in the most general multiorbital cases with no particular symmetry. As a benchmark case, we study the longitudinal thermoelectric response and corresponding Onsager coefficient in the single-band two-dimensional Hubbard model treated with dynamical mean-field theory and continuous-time quantum Monte Carlo. We thereby extend the maximum entropy analytic continuation with auxiliary functions (MaxEntAux method), developed for the study of the superconducting pairing dynamics of correlated materials, to transport coefficients.
Directory of Open Access Journals (Sweden)
Robert Rosenbaum
Full Text Available Depletion of synaptic neurotransmitter vesicles induces a form of short term depression in synapses throughout the nervous system. This plasticity affects how synapses filter presynaptic spike trains. The filtering properties of short term depression are often studied using a deterministic synapse model that predicts the mean synaptic response to a presynaptic spike train, but ignores variability introduced by the probabilistic nature of vesicle release and stochasticity in synaptic recovery time. We show that this additional variability has important consequences for the synaptic filtering of presynaptic information. In particular, a synapse model with stochastic vesicle dynamics suppresses information encoded at lower frequencies more than information encoded at higher frequencies, while a model that ignores this stochasticity transfers information encoded at any frequency equally well. This distinction between the two models persists even when large numbers of synaptic contacts are considered. Our study provides strong evidence that the stochastic nature neurotransmitter vesicle dynamics must be considered when analyzing the information flow across a synapse.
Frequency-dependent, cell type-divergent signaling in the hippocamposeptal projection.
Mattis, Joanna; Brill, Julia; Evans, Suzanne; Lerner, Talia N; Davidson, Thomas J; Hyun, Minsuk; Ramakrishnan, Charu; Deisseroth, Karl; Huguenard, John R
2014-08-27
Hippocampal oscillations are critical for information processing, and are strongly influenced by inputs from the medial septum. Hippocamposeptal neurons provide direct inhibitory feedback from the hippocampus onto septal cells, and are therefore likely to also play an important role in the circuit; these neurons fire at either low or high frequency, reflecting hippocampal network activity during theta oscillations or ripple events, respectively. Here, we optogenetically target the long-range GABAergic projection from the hippocampus to the medial septum in rats, and thereby simulate hippocampal input onto downstream septal cells in an acute slice preparation. In response to optogenetic activation of hippocamposeptal fibers at theta and ripple frequencies, we elicit postsynaptic GABAergic responses in a subset (24%) of septal cells, most predominantly in fast-spiking cells. In addition, in another subset of septal cells (19%) corresponding primarily to cholinergic cells, we observe a slow hyperpolarization of the resting membrane potential and a decrease in input resistance, particularly in response to prolonged high-frequency (ripple range) stimulation. This slow response is partially sensitive to GIRK channel and D2 dopamine receptor block. Our results suggest that two independent populations of septal cells distinctly encode hippocampal feedback, enabling the septum to monitor ongoing patterns of activity in the hippocampus.
Khanday, M. A.; Hussain, Fida
2015-07-01
To predict the behaviour of thermal physiology of a finite biological tissue in severe cold climatic conditions, a mathematical model has been established based on Pennes' bio-heat transfer equation with oscillatory boundary condition and time dependent heat source term. Crank-Nicholson scheme has been employed to obtain the solution of the boundary value problem to understand the change in stable temperature profiles at the peripheral tissues of human body subjected to forced convection due to cold. Thermal stress at these regions with respect to different input parameters has been computed under extreme environmental conditions using MATLAB Software. The results have shown a relative significance and provide a reasonable outcome in terms of variable metabolic heat generation and oscillatory heat source. The oscillations of the temperature profiles from the mean temperatures were computed in relation with tissue medium and other physiological parameters.
Frequency Dependant P Wave Structure of D" Beneath Central America Imaged by Kirchhoff Migration
Hutko, A. R.; Lay, T.; Revenaugh, J.
2006-12-01
We use thousands of seismograms from South and Central American earthquakes recorded by western North American seismic networks to image the lowermost mantle beneath Central America using a 3D Kirchhoff migration scheme. P wave studies of the deep mantle often rely on some form of stacking of many records in order to enhance the signal-to-noise ratio of weak phases generated by deep structure, such as reflections off of the D" discontinuity. These methods, however, often assume one-dimensional structure, which is at odds with the evidence for significant heterogeneity. Kirchhoff migration is a three-dimensional stacking method that allows interactions with structure off of the source-receiver plane, thus imaging a much larger volume and avoiding false projections of scattered arrivals onto specular reflectors. The D" discontinuity beneath Central America has been readily observed in S wave studies and may be the result of the shear wave velocity increase associated with the recently discovered perovskite to post-perovskite phase transition. This phase transition is expected to have weaker effects on P wave velocities than on S wave velocities and the sharpness of this transition is unknown. We observe structures consistent with a discontinuity about 200 km above the core-mantle boundary (CMB). The fact that this is seen at all in short period data suggests that its boundary must be less than 10 to 20 km thick, while observation with broadband data exclude the possibility of it being a thin layer or lamella. Whether the discontinuity is co-located for both P and S waves is difficult to resolve given uncertainties in the long-scale velocity heterogeneity. In addition, both broadband and short period P wave data sets reveal a sharp out-of-plane scatterer, which may be located close to the CMB. The short period data also indicate reflectivity about 400 km above the CMB, well above the aforementioned D" discontinuity, and similar reflectivity is observed under the
Directory of Open Access Journals (Sweden)
Baele Guy
2010-08-01
Full Text Available Abstract Background Recent approaches for context-dependent evolutionary modelling assume that the evolution of a given site depends upon its ancestor and that ancestor's immediate flanking sites. Because such dependency pattern cannot be imposed on the root sequence, we consider the use of different orders of Markov chains to model dependence at the ancestral root sequence. Root distributions which are coupled to the context-dependent model across the underlying phylogenetic tree are deemed more realistic than decoupled Markov chains models, as the evolutionary process is responsible for shaping the composition of the ancestral root sequence. Results We find strong support, in terms of Bayes Factors, for using a second-order Markov chain at the ancestral root sequence along with a context-dependent model throughout the remainder of the phylogenetic tree in an ancestral repeats dataset, and for using a first-order Markov chain at the ancestral root sequence in a pseudogene dataset. Relaxing the assumption of a single context-independent set of independent model frequencies as presented in previous work, yields a further drastic increase in model fit. We show that the substitution rates associated with the CpG-methylation-deamination process can be modelled through context-dependent model frequencies and that their accuracy depends on the (order of the Markov chain imposed at the ancestral root sequence. In addition, we provide evidence that this approach (which assumes that root distribution and evolutionary model are decoupled outperforms an approach inspired by the work of Arndt et al., where the root distribution is coupled to the evolutionary model. We show that the continuous-time approximation of Hwang and Green has stronger support in terms of Bayes Factors, but the parameter estimates show minimal differences. Conclusions We show that the combination of a dependency scheme at the ancestral root sequence and a context-dependent
Mina, Faten; Benquet, Pascal; Pasnicu, Anca; Biraben, Arnaud; Wendling, Fabrice
2013-01-01
A number of studies showed that deep brain stimulation (DBS) can modulate the activity in the epileptic brain and that a decrease of seizures can be achieved in "responding" patients. In most of these studies, the choice of stimulation parameters is critical to obtain desired clinical effects. In particular, the stimulation frequency is a key parameter that is difficult to tune. A reason is that our knowledge about the frequency-dependant mechanisms according to which DBS indirectly impacts the dynamics of pathological neuronal systems located in the neocortex is still limited. We address this issue using both computational modeling and intracerebral EEG (iEEG) data. We developed a macroscopic (neural mass) model of the thalamocortical network. In line with already-existing models, it includes interconnected neocortical pyramidal cells and interneurons, thalamocortical cells and reticular neurons. The novelty was to introduce, in the thalamic compartment, the biophysical effects of direct stimulation. Regarding clinical data, we used a quite unique data set recorded in a patient (drug-resistant epilepsy) with a focal cortical dysplasia (FCD). In this patient, DBS strongly reduced the sustained epileptic activity of the FCD for low-frequency (LFS, 70 Hz) while intermediate-frequency stimulation (IFS, around 50 Hz) had no effect. Signal processing, clustering, and optimization techniques allowed us to identify the necessary conditions for reproducing, in the model, the observed frequency-dependent stimulation effects. Key elements which explain the suppression of epileptic activity in the FCD include: (a) feed-forward inhibition and synaptic short-term depression of thalamocortical connections at LFS, and (b) inhibition of the thalamic output at HFS. Conversely, modeling results indicate that IFS favors thalamic oscillations and entrains epileptic dynamics.
Butcher, Michael T; Bertram, John E A; Syme, Douglas A; Hermanson, John W; Chase, P Bryant
2014-10-01
The digital flexors of horses must produce high force to support the body weight during running, and a need for these muscles to generate power is likely limited during locomotion over level ground. Measurements of power output from horse muscle fibers close to physiological temperatures, and when cyclic strain is imposed, will help to better understand the in vivo performance of the muscles as power absorbers and generators. Skinned fibers from the deep (DDF) and superficial (SDF) digital flexors, and the soleus (SOL) underwent sinusoidal oscillations in length over a range of frequencies (0.5-16 Hz) and strain amplitudes (0.01-0.06) under maximum activation (pCa 5) at 30°C. Results were analyzed using both workloop and Nyquist plot analyses to determine the ability of the fibers to absorb or generate power and the frequency dependence of those abilities. Power absorption was dominant at most cycling frequencies and strain amplitudes in fibers from all three muscles. However, small amounts of power were generated (0.002-0.05 Wkg(-1)) at 0.01 strain by all three muscles at relatively slow cycling frequencies: DDF (4-7 Hz), SDF (4-5 Hz) and SOL (0.5-1 Hz). Nyquist analysis, reflecting the influence of cross-bridge kinetics on power generation, corroborated these results. The similar capacity for power generation by DDF and SDF versus lower for SOL, and the faster frequency at which this power was realized in DDF and SDF fibers, are largely explained by the fast myosin heavy chain isoform content in each muscle. Contractile function of DDF and SDF as power absorbers and generators, respectively, during locomotion may therefore be more dependent on their fiber architectural arrangement than on the physiological properties of their muscle fibers. © 2014 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.
Frequency dependence of hysteretic magnetoimpedance in CoFeMoSiB amorphous ribbons
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Tejedor, M.; Hernando, B. E-mail: grande@pinon.ccu.uniovi.es; Sanchez, M.L.; Prida, V.M.; Kurlyandskaya, G.V.; Garcia, D.; Vazquez, M
2000-06-02
The hysteretic behaviour of the resistive and reactive components of the complex impedance at different frequencies in Co-based ribbons is presented. Sensitivities of the order of 1.2%/Am{sup -1} at 70 kHz for the reactive component of the MI and 0.63%/Am{sup -1} at 500 kHz for the resistive one were attained in the field range of 80-560 Am{sup -1}. The maximum relative ratio of MI was reached at 120 kHz with a sensitivity of 0.41%/Am{sup -1}.
Reineman, B. D.; Lenain, L.; Melville, W. K.
2014-12-01
We present measurements obtained during the October 2012 EquatorMix experiment (0N, 140W), in which we deployed ship-launched and recovered Boeing-Insitu ScanEagle unmanned aerial vehicles (UAVs) to measure momentum and energy fluxes, ocean surface processes, and the marine atmospheric boundary layer (MABL). The UAV dataset is complemented by measurements from a suite of ship-based instrumentation, including a foremast MABL eddy covariance system, scanning and point lidar altimeters, a laser Doppler wind profiler, and a digitized X-band radar system (WaMoS). The combination of the unmanned aircraft and the ship instrumentation provides a novel and valuable dataset of many air-sea interaction phenomena, extending from 100s of meters below the surface to 1500 m above. Ocean surface displacements observed with the UAV lidar altimeter (coupled with a GPS/IMU) give evidence of high-frequency equatorial internal waves, with measurements consistent and coherent with those from ship-based X-band radar, the Hydrographic Doppler Sonar System (HDSS), and a theoretical model. UAV-based flux measurements at low altitudes (down to 30 meters) are consistent with ship-based eddy covariance measurements, but reveal differences between along- and crosswind sampling flight legs associated with longitudinal roll structures that are not captured by the ship measurements from tracks mainly in the upwind-downwind directions.
Resistance to Change and Frequency of Response-Dependent Stimuli Uncorrelated with Reinforcement
Podlesnik, Christopher A.; Jimenez-Gomez, Corina; Ward, Ryan D.; Shahan, Timothy A.
2009-01-01
Stimuli uncorrelated with reinforcement have been shown to enhance response rates and resistance to disruption; however, the effects of different rates of stimulus presentations have not been assessed. In two experiments, we assessed the effects of adding different rates of response-dependent brief stimuli uncorrelated with primary reinforcement…
Directory of Open Access Journals (Sweden)
Baoqiang Yan
2008-10-01
Full Text Available Using the fixed point theorem in cones, this paper shows the existence of multiple positive solutions for the singular $m$-point boundary-value problem $$displaylines{ x''(t+a(tf(t,x(t,x'(t=0,quad 0
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Nelson Hwynn
2011-01-01
Full Text Available Background. Nonmotor symptoms (NMS of Parkinson's disease (PD may be more debilitating than motor symptoms. The purpose of this study was to determine the frequency and corecognition of NMS among our advanced PD cohort (patients considered for deep brain stimulation (DBS and caregivers. Methods. NMS-Questionnaire (NMS-Q, a self-administered screening questionnaire, and NMS Assessment-Scale (NMS-S, a clinician-administered scale, were administered to PD patients and caregivers. Results. We enrolled 33 PD patients (23 males, 10 females and caregivers. The most frequent NMS among patients using NMS-Q were gastrointestinal (87.9%, sleep (84.9%, and urinary (72.7%, while the most frequent symptoms using NMS-S were sleep (90.9%, gastrointestinal (75.8%, and mood (75.8%. Patient/caregiver scoring correlations for NMS-Q and NMS-S were 0.670 (<0.0001 and 0.527 (=0.0016, respectively. Conclusion The frequency of NMS among advanced PD patients and correlation between patients and caregivers varied with the instrument used. The overall correlation between patient and caregiver was greater with NMS-Q than NMS-S.
Frequency-dependent performance analysis of a parallel DSP-based computer system
Christou, Ch. S.
2014-11-01
The performance of a shared-memory low-cost high-performance DSP-Based multiprocessor system [3] is investigated, by varying the frequency of the core processor from 200MHz to 1GHZ, in steps of 200 MHZ, and keeping constant parameters such as the shared-memory-access-time and the prefetching-workload-size. The innovation of this Parallel DSP-Based computer system is the introduction of two small programmable small fast memories (Twins) between the processor and the shared bus interconnect. While one memory (Twin) transfers data from/to the shared memory, the other Twin supplies the core DSP-processor with data. Results indicate an increase of the shared-bus bottleneck as the core DSP processors' clock-rate increases. Workload of the Twins is processed faster thus greater the demand of the shared-bus. Results show an effectively supported robust parallel shared-memory system where fewer but faster (clocked with higher frequency) processors produce the same execution times as a greater number of slower processors, with most system configurations achieving perfect speedups, mainly due to the twin-prefetching mechanism.
Frequency-dependent stability of CNT Joule heaters in ionizable media and desalination processes
Dudchenko, Alexander V.; Chen, Chuxiao; Cardenas, Alexis; Rolf, Julianne; Jassby, David
2017-07-01
Water shortages and brine waste management are increasing challenges for coastal and inland regions, with high-salinity brines presenting a particularly challenging problem. These high-salinity waters require the use of thermally driven treatment processes, such as membrane distillation, which suffer from high complexity and cost. Here, we demonstrate how controlling the frequency of an applied alternating current at high potentials (20 Vpp) to a porous thin-film carbon nanotube (CNT)/polymer composite Joule heating element can prevent CNT degradation in ionizable environments such as high-salinity brines. By operating at sufficiently high frequencies, these porous thin-films can be directly immersed in highly ionizable environments and used as flow-through heating elements. We demonstrate that porous CNT/polymer composites can be used as self-heating membranes to directly heat high-salinity brines at the water/vapour interface of the membrane distillation element, achieving high single-pass recoveries that approach 100%, far exceeding standard membrane distillation recovery limits.
Ade, P A R; Aniano, G; Armitage-Caplan, C; Arnaud, M; Atrio-Barandela, F; Aumont, J; Baccigalupi, C; Banday, A J; Barreiro, R B; Battaner, E; Benabed, K; Benoit-Lévy, A; Bernard, J -P; Bersanelli, M; Bielewicz, P; Bock, J J; Bond, J R; Borrill, J; Bouchet, F R; Boulanger, F; Burigana, C; Cardoso, J -F; Catalano, A; Chamballu, A; Chiang, H C; Colombo, L P L; Combet, C; Couchot, F; Coulais, A; Crill, B P; Curto, A; Cuttaia, F; Danese, L; Davies, R D; Davis, R J; de Bernardis, P; de Zotti, G; Delabrouille, J; Désert, F -X; Dickinson, C; Diego, J M; Donzelli, S; Doré, O; Douspis, M; Dunkley, J; Dupac, X; Enßlin, T A; Eriksen, H K; Falgarone, E; Fanciullo, L; Finelli, F; Forni, O; Frailis, M; Fraisse, A A; Franceschi, E; Galeotta, S; Ganga, K; Ghosh, T; Giard, M; González-Nuevo, J; Górski, K M; Gregorio, A; Gruppuso, A; Guillet, V; Hansen, F K; Harrison, D L; Helou, G; Hernández-Monteagudo, C; Hildebrandt, S R; Hivon, E; Hobson, M; Holmes, W A; Hornstrup, A; Jaffe, A H; Jaffe, T R; Jones, W C; Keihänen, E; Keskitalo, R; Kisner, T S; Kneissl, R; Knoche, J; Kunz, M; Kurki-Suonio, H; Lagache, G; Lamarre, J -M; Lasenby, A; Lawrence, C R; Leahy, J P; Leonardi, R; Levrier, F; Liguori, M; Lilje, P B; Linden-Vørnle, M; López-Caniego, M; Lubin, P M; Macías-Pérez, J F; Maffei, B; Magalhães, A M; Maino, D; Mandolesi, N; Maris, M; Marshall, D J; Martin, P G; Martínez-González, E; Masi, S; Matarrese, S; Mazzotta, P; Melchiorri, A; Mendes, L; Mennella, A; Migliaccio, M; Miville-Deschênes, M -A; Moneti, A; Montier, L; Morgante, G; Mortlock, D; Munshi, D; Murphy, J A; Naselsky, P; Nati, F; Natoli, P; Netterfield, C B; Noviello, F; Novikov, D; Novikov, I; Oppermann, N; Oxborrow, C A; Pagano, L; Pajot, F; Paoletti, D; Pasian, F; Perdereau, O; Perotto, L; Perrotta, F; Piacentini, F; Pietrobon, D; Plaszczynski, S; Pointecouteau, E; Polenta, G; Popa, L; Pratt, G W; Rachen, J P; Reach, W T; Reinecke, M; Remazeilles, M; Renault, C; Ricciardi, S; Riller, T; Ristorcelli, I; Rocha, G; Rosset, C; Roudier, G; Rubiño-Martín, J A; Rusholme, B; Salerno, E; Sandri, M; Savini, G; Scott, D; Spencer, L D; Stolyarov, V; Stompor, R; Sudiwala, R; Sutton, D; Suur-Uski, A -S; Sygnet, J -F; Tauber, J A; Terenzi, L; Toffolatti, L; Tomasi, M; Tristram, M; Tucci, M; Valenziano, L; Valiviita, J; Van Tent, B; Vielva, P; Villa, F; Wandelt, B D; Zacchei, A; Zonca, A
2014-01-01
Planck has mapped the intensity and polarization of the sky at microwave frequencies with unprecedented sensitivity. We make use of the Planck 353 GHz I, Q, and U Stokes maps as dust templates, and cross-correlate them with the Planck and WMAP data at 12 frequencies from 23 to 353 GHz, over circular patches with 10 degree radius. The cross-correlation analysis is performed for both intensity and polarization data in a consistent manner. We use a mask that focuses our analysis on the diffuse interstellar medium at intermediate Galactic latitudes. We determine the spectral indices of dust emission in intensity and polarization between 100 and 353 GHz, for each sky-patch. The mean values, $1.63\\pm0.03$ for polarization and $1.52\\pm0.02$ for intensity, for a mean dust temperature of 18.7 K, are close, but significantly different. We determine the mean spectral energy distribution (SED) of the microwave emission, correlated with the 353 GHz dust templates, by averaging the results of the correlation over all sky-p...
Synchronization to metrical levels in music depends on low-frequency spectral components and tempo.
Burger, Birgitta; London, Justin; Thompson, Marc R; Toiviainen, Petri
2017-07-15
Previous studies have found relationships between music-induced movement and musical characteristics on more general levels, such as tempo or pulse clarity. This study focused on synchronization abilities to music of finely-varying tempi and varying degrees of low-frequency spectral change/flux. Excerpts from six classic Motown/R&B songs at three different tempos (105, 115, and 130 BPM) were used as stimuli in this experiment. Each was then time-stretched by a factor of 5% with regard to the original tempo, yielding a total of 12 stimuli that were presented to 30 participants. Participants were asked to move along with the stimuli while being recorded with an optical motion capture system. Synchronization analysis was performed relative to the beat and the bar level of the music and four body parts. Results suggest that participants synchronized different body parts to specific metrical levels; in particular, vertical movements of hip and feet were synchronized to the beat level when the music contained large amounts of low-frequency spectral flux and had a slower tempo, while synchronization of head and hands was more tightly coupled to the weak flux stimuli at the bar level. Synchronization was generally more tightly coupled to the slower versions of the same stimuli, while synchronization showed an inverted u-shape effect at the bar level as tempo increased. These results indicate complex relationships between musical characteristics, in particular regarding metrical and temporal structure, and our ability to synchronize and entrain to such musical stimuli.
Braunstein, D.; Page, J. H.; Strybulevych, A.; Peressini, D.; Scanlon, M. G.
2012-12-01
Technological performance of wheat flour varies among different wheat varieties. Gluten plays a key role within the solid phase of dough in the formation and the retention of gas bubbles during breadmaking. Rheological tests are usually performed to predict breadmaking potential. The aim here was to investigate the ability of ultrasound to discriminate wheat doughs based on breadmaking qualities. The ultimate goal is the development of an online quality control system currently unavailable in the baked goods industry, rendering this work innovative. Samples were prepared from a strong wheat flour, with one control sample and one added with inulin and distilled monoglycerides, producing doughs of distinct breadmaking quality. Doughs were subjected to density determination, elongation tests, and ultrasound analysis. The ultrasound tests were performed in the frequency range of 300 kHz - 6 MHz. Ultrasonic phase velocity increased with increasing frequency to about 2 MHz, becoming constant and then decreasing from 3 MHz for the control sample. Distinct differences in attenuation coefficient between the fibre-enriched and control doughs were observed. Ultrasound can potentially add to a better understanding of dough quality and can discriminate between doughs of contrasting properties.
Teichrieb, Claudio A.; Acevedo, Otávio C.; Degrazia, Gervásio A.; Moraes, Osvaldo L. L.; Roberti, Débora R.; Zimermann, Hans R.; Santos, Daniel M.; Alves, Rita C. M.
2013-03-01
The study presents an analysis of two-point correlations between time series of nocturnal atmospheric wind, obtained from two micrometeorological towers, 45 m horizontally apart, each equipped with two sonic anemometers, 2.5 m vertically apart. It focuses on the scale dependence of the two-point correlations obtained from sensors vertically and horizontally separated. In particular, the role of low-frequency non-turbulent processes in the correlations is assessed, and compared to that of the turbulent scales of motion. The vertical correlations of the streamwise and vertical wind components show little dependence on the turbulence intensity, but those of the spanwise component decrease appreciably as it gets more turbulent. Multiresolution decomposition shows that the two-point correlations become increasingly dominated by low-frequency scales as it gets less turbulent, and that such large-scale processes are largely reduced in fully turbulent conditions. It is also shown that the vertical correlations of the spanwise wind component is negative for very small time scales. Horizontal two-point correlations obtained at the 45 m separation distance between the towers are almost entirely dominated by low-frequency motions, regardless of the turbulence intensity, but the magnitude of such correlations decreases with increasing turbulence intensity for any wind components. A comparison between the horizontal two-point correlations and autocorrelations taken with a time lag given by the ratio of the horizontal separation to the mean wind component in the direction that connects the two towers leads to the conclusion that the statistical properties of turbulence are often preserved over the horizontal distance, despite the lack of turbulence correlations for that separation.
Dutt, G. B.; Sachdeva, A.
2003-05-01
Rotational relaxation of three organic solutes, coumarin 6 (C6), 2,5-dimethyl-1, 4-dioxo3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP), and nile red (NR), that are similar in size but distinct in shape has been studied in a nonpolar solvent, squalane as a function of temperature to find out how the mechanical friction experienced by the solute molecule is influenced by its shape. It has been observed that C6 rotates slowest followed by NR and DMDPP. The results are analyzed using Stokes-Einstein-Debye (SED) hydrodynamic theory and also quasihydrodynamic theories of Gierer and Wirtz, and Dote, Kivelson, and Schwartz. Analysis of the data using the SED theory reveals that the measured reorientation times of C6 and DMDPP follow subslip behavior whereas those of NR are found to match slip predictions. While no single model could mimic the observed trend even in a qualitative manner, the reorientation times of C6 and DMDPP when normalized by their respective shape factors and boundary-condition parameters can be scaled on a common curve over the entire range of temperature studied. The probable reasons for the distinctive rotational behavior of NR as compared to C6 and DMDPP are explained in terms of its molecular shape and how this in turn influences the boundary-condition parameter are discussed.
Kubelka, Jan
2013-10-15
Changes in the amide I' IR band with temperature are widely used for elucidation of peptide and protein conformational transitions and folding equilibria. Since amide I' exhibits inherent temperature dependent frequency shifts, standard mixture analysis methods are not applicable. To reliably extract the true thermodynamic states, frequency shifts of the component spectra must be explicitly taken into account. For this purpose, new methods termed shifted multivariate spectra analysis (SMSA) and parametric SMSA (pSMSA) are developed and tested on sets of synthetic data as well as real experimental amide I' spectra for thermal unfolding of an α-helical peptide. SMSA uses no specific functional form for the transition (soft modeling), while the parametric variant (pSMSA) assumes a thermodynamic model (hard modeling). The implementation is optimized specifically for amide I' IR in that it takes advantage of known, linear dependence of the frequencies as well as intensities on temperature. The synthetic data tests demonstrate the robustness of the methods; the initial test parameters are recovered with a high degree of reliability, although the nonparameteric SMSA is subject to the rotational ambiguity. Application to the peptide experimental amide I' data illustrates additional complications encountered with the analysis of real systems, such as correction for the side-chain spectra and interference of spectral shape changes. Nevertheless, the results are in excellent agreement with the independent control using circular dichroism (CD) data. The general applicability and limitations of the methods are discussed along with potential extensions.
Fu, W.; El Abbassi, M.; Hasler, T.; M. Jung; M. Steinacher; Calame, M.; Schönenberger,C.; Puebla-Hellmann, G.; Hellmüller, S.; T. Ihn; Wallraff, A.
2014-01-01
We performed radiofrequency (RF) reflectometry measurements at 2.4 GHz on electrolyte-gated graphene field-effect transistors (GFETs) utilizing a tunable stub-matching circuit for impedance matching. We demonstrate that the gate voltage dependent RF resistivity of graphene can be deduced even in the presence of the electrolyte which is in direct contact with the graphene layer. The RF resistivity is found to be consistent with its DC counterpart in the full gate voltage range. Furthermore, in...
DEFF Research Database (Denmark)
Gacitua, Guisella; Uribe, José Andrés; Tamstorf, Mikkel Peter
2011-01-01
Ground penetrating radar (GPR) was used to detect internal features and conditions in the active layer of Zackenberg valley in North-East Greenland. For about 16 years there has been a monitoring programme that registers the physical and biological processes in the ecosystem.We aim to improve...... the monitoring accuracy of the active layer development and estimated soil water content. We used two different GPR frequencies to study their performance in High-Arctic cryoturbated soils. Here we present the analysis of the signal received by quantifying the power of the signal that is reflected from the top...... are suitable to measure thickness and to detect features in the active layer, the 400 MHz gives a better impression of the influence of the dielectric contrast effect from top of the permafrost zone which can be used to quantify the soil water content....
Directory of Open Access Journals (Sweden)
S. Ansari
2008-05-01
Full Text Available Life-long red blood transfusion remains the main treatment for severe thalassemia. The development of hemolytic alloantibodies and erythrocyte autoantibodies complicated transfusion therapy in thalassemia patients. The frequency causes and prevention of this phenomenon among 80 transfused thalassemia patients were evaluated in Ali Asghar Children's Hospital during 1998-2004 in a cross-sectional study. In our study the mean age at the initiation of transfusion was 1.7 years (SD = 1.94 and mean interval of transfusion 33.73 day (SD = 20.74. Autoimmunization in 15 patients was positive and 8 patients had hemolytic reaction in transfusion. Our data show that alloimmunization to minor erythrocyte antigens and erythrocyte autoimmunization of significant clinical variables, are frequent findings in transfused thalassemia patients. However data suggest that prevalence of immunization in our patients is less than other Asian countries.
Frequency dependence of complex moduli of brain tissue using a fractional Zener model
Energy Technology Data Exchange (ETDEWEB)
Kohandel, M [Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada); Sivaloganathan, S [Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada); Tenti, G [Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada); Darvish, K [Center for Applied Biomechanics, University of Virginia, Charlottesville, VA (United States)
2005-06-21
Brain tissue exhibits viscoelastic behaviour. If loading times are substantially short, static tests are not sufficient to determine the complete viscoelastic behaviour of the material, and dynamic test methods are more appropriate. The concept of complex modulus of elasticity is a powerful tool for characterizing the frequency domain behaviour of viscoelastic materials. On the other hand, it is well known that classical viscoelastic models can be generalized by means of fractional calculus to describe more complex viscoelastic behaviour of materials. In this paper, the fractional Zener model is investigated in order to describe the dynamic behaviour of brain tissue. The model is fitted to experimental data of oscillatory shear tests of bovine brain tissue to verify its behaviour and to obtain the material parameters.
Pressureless mechanical induction of stem cell differentiation is dose and frequency dependent.
Directory of Open Access Journals (Sweden)
Roland Fuhrer
Full Text Available Movement is a key characteristic of higher organisms. During mammalian embryogenesis fetal movements have been found critical to normal tissue development. On the single cell level, however, our current understanding of stem cell differentiation concentrates on inducing factors through cytokine mediated biochemical signaling. In this study, human mesenchymal stem cells and chondrogenesis were investigated as representative examples. We show that pressureless, soft mechanical stimulation precipitated by the cyclic deformation of soft, magnetic hydrogel scaffolds with an external magnetic field, can induce chondrogenesis in mesenchymal stem cells without any additional chondrogenesis transcription factors (TGF-β1 and dexamethasone. A systematic study on the role of movement frequency revealed a classical dose-response relationship for human mesenchymal stem cells differentiation towards cartilage using mere mechanical stimulation. This effect could even be synergistically amplified when exogenous chondrogenic factors and movement were combined.
Energy Technology Data Exchange (ETDEWEB)
Hernando, B. E-mail: grande@pinon.ccu.uniovi.es; Prida, V.M.; Sanchez, M.L.; Tejedor, M.; Vazquez, M.; Feng, L.-Y
2003-01-01
Amorphous ferromagnetic wire with a highly positive saturation magnetostriction coefficient, made of Fe{sub 73.5}Si{sub 13.5}B{sub 9}Nb{sub 3}Cu{sub 1}, was simultaneously submitted to both, an AC current passing through it and a torsional stress, in order to induce a helical magnetic anisotropy in the wire that modifies its domain structure and therefore the magnetic response of the sample. The aim of this work is to study the reactive, resistive and impedance behaviour in this Fe-rich wire, submitted to different applied torsional stresses, and for several values of the AC current amplitude through the wire (5-20 mA{sub rms}), in the low frequency range, f
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Amit Banerjee
2012-09-01
Full Text Available Metallic nanocantilevers of gold are fabricated from self-supporting polycrystalline thin film (100 nm by focused ion beam assisted milling and ion induced manipulation processes. The surfactant assisted growth of the thin film leads to self-organized dendrite like morphology. This self-organized dendrite like morphology of the gold film imposes a new characteristic length scale corresponding to the mean size of gold grains present within the branches of the dendrite pattern in the film. The resonance characteristic investigated on cantilevers having different widths shows a significant drop in energy dissipation and hence an enhancement in the resonance amplitude at a characteristic width. At this width the resonance frequency of a vibrating cantilever approaches the theoretically expected value anticipated from an ideal cantilever treated like an elastic continuum.
Frequency-dependent viscous flow in channels with fractal rough surfaces
Energy Technology Data Exchange (ETDEWEB)
Cortis, A.; Berryman, J.G.
2010-05-01
The viscous dynamic permeability of some fractal-like channels is studied. For our particular class of geometries, the ratio of the pore surface area-to-volume tends to {infinity} (but has a finite cutoff), and the universal scaling of the dynamic permeability, k({omega}), needs modification. We performed accurate numerical computations of k({omega}) for channels characterized by deterministic fractal wall surfaces, for a broad range of fractal dimensions. The pertinent scaling model for k({omega}) introduces explicitly the fractal dimension of the wall surface for a range of frequencies across the transition between viscous and inertia dominated regimes. The new model provides excellent agreement with our numerical simulations.
Widyaparaga, Adhika; Koshimizu, Takao; Noda, Eiji; Sakoda, Naoya; Kohno, Masamichi; Takata, Yasuyuki
2011-10-01
We have constructed and tested two travelling wave thermoacoustic heat pumps using a coaxial configuration with the regenerator positioned in the annulus. We discovered a frequency dependent positional reversal of the cold section and hot section of the regenerator within the test frequency range. By decomposing the measured pressure wave within the annulus, we obtained the positive ( w+) and negative ( w-) propagating travelling waves. It has been revealed the change of frequency is accompanied by a change in magnitudes of w+ and w- which is in part influenced by the presence of travelling wave attenuation through the regenerator. The resulting change of dominant travelling wave on a given end of the regenerator will then change the direction of thermoacoustic heat pumping at that end. This will alter the regenerator temperature distribution and may reverse the cold and hot sections of the regenerator. As the reversal does not require additional moving parts, merely a change in frequency, this feature in coaxial travelling wave devices has tremendous potential for applications which require both heating and cooling operation.
Sabaeian, Mohammad
2012-10-20
The problem of finding analytical solutions for time-dependent or time-independent heat equations, especially for solid-state laser media, has required a lot of work in the field of thermal effects. However, to calculate the temperature distributions analytically, researchers often have to make some approximations or employ complex methods. In this work, we present full analytical solutions for anisotropic time-dependent heat equations in the Cartesian coordinates with various source terms corresponding to various pumping schemes. Moreover, the most general boundary condition of Robin (or impedance boundary condition), corresponding to the convection cooling mechanism, was applied. This general condition can be easily switched to constant temperature and thermal insulation as special cases. To this end, we first proposed a general approach to solving time-dependent heat equations with an arbitrary heat source. We then applied our approach to explore the temperature distribution for three cases: steady-state pumping or long transient, single-shot pumping or short transient, and repetitively pulsed pumping. Our results show the possibility of an easier and more accurate approach to analytical calculations of the thermal dispersion, thermal stresses (strains), thermal bending, thermal phase shift, and other thermal effects.
Li, Jin; Xiong, Bing; Sun, Changzheng; Miao, Di; Luo, Yi
2015-08-24
A back-illuminated mesa-structure InGaAs/InP modified uni-traveling-carrier photodiode (MUTC-PD) is fabricated and its frequency response is investigated. A bandwidth of 40 GHz and a saturation photocurrent up to 33 mA are demonstrated. A photocurrent-dependent equivalent circuit model is proposed to analyze the frequency response of the high power MUTC-PDs. The influences of the space-charge screening, self-induced electric field and over-shoot effects are discussed in detail based on the model. Fitted curves obtained from the simple equivalent circuit model are found to be in good agreement with the data measured under different bias voltages and photocurrents.
Li, Haipeng; Xu, Hu; Shen, Xiaopeng; Han, Kui; Bi, Zetong; Xu, Runfeng
2016-06-01
We investigated the electronic properties and second hyperpolarizabilities of hydrogenated silicon nanoclusters (H-SiNCs) by using the density functional theory method. The effects of cluster size, external electric field and incident frequency on the second hyperpolarizability were also examined, respectively. We found that small H-SiNCs exhibit large second hyperpolarizability. With the increase of the number of silicon atoms in H-SiNCs, the frontier molecular orbital energy gap decreases, attributed to the enhancement of the second hyperpolarizability. Interestingly, we also found the electric-field-induced gigantic enhancement of the second hyperpolarizability for H-SiNCs due to the change of electron density distributions. In addition, our results demonstrate a significant dependence on the frequency of incident light.
Li, Haipeng; Xu, Hu; Shen, Xiaopeng; Han, Kui; Bi, Zetong; Xu, Runfeng
2016-06-16
We investigated the electronic properties and second hyperpolarizabilities of hydrogenated silicon nanoclusters (H-SiNCs) by using the density functional theory method. The effects of cluster size, external electric field and incident frequency on the second hyperpolarizability were also examined, respectively. We found that small H-SiNCs exhibit large second hyperpolarizability. With the increase of the number of silicon atoms in H-SiNCs, the frontier molecular orbital energy gap decreases, attributed to the enhancement of the second hyperpolarizability. Interestingly, we also found the electric-field-induced gigantic enhancement of the second hyperpolarizability for H-SiNCs due to the change of electron density distributions. In addition, our results demonstrate a significant dependence on the frequency of incident light.
Garofalo, Fabio; Bruus, Henrik
2016-01-01
The mechanical and electrical response of acoustophoretic microfluidic devices attached to an ac-voltage-driven piezoelectric transducer is studied by means of numerical simulations. The governing equations are formulated in a variational framework that, introducing Lagrangian and Hamiltonian densities, is used to derive the weak form for the finite element discretization of the equations and to characterize the device response in terms of frequency-dependent figures of merit or indicators. The effectiveness of the device in focusing microparticles is quantified by two mechanical indicators: the average direction of the pressure gradient and the amount of acoustic energy localized in the microchannel. Further, we derive the relations between the Lagrangian, the Hamiltonian and three electrical indicators: the resonance Q-value, the impedance and the electric power. The frequency response of the hard-to-measure mechanical indicators is correlated to that of the easy-to-measure electrical indicators, and by int...
Li, Haipeng; Xu, Hu; Shen, Xiaopeng; Han, Kui; Bi, Zetong; Xu, Runfeng
2016-01-01
We investigated the electronic properties and second hyperpolarizabilities of hydrogenated silicon nanoclusters (H-SiNCs) by using the density functional theory method. The effects of cluster size, external electric field and incident frequency on the second hyperpolarizability were also examined, respectively. We found that small H-SiNCs exhibit large second hyperpolarizability. With the increase of the number of silicon atoms in H-SiNCs, the frontier molecular orbital energy gap decreases, attributed to the enhancement of the second hyperpolarizability. Interestingly, we also found the electric-field-induced gigantic enhancement of the second hyperpolarizability for H-SiNCs due to the change of electron density distributions. In addition, our results demonstrate a significant dependence on the frequency of incident light. PMID:27305957
Dineshkumar, Sengottuvelu; Muthusamy, Athianna; Chandrasekaran, J.
2017-01-01
Three azomethine diol monomers were synthesized by condensing with methanolic solution of aromatic aldehydes with ethylenediamine. These monomers were oxidatively polymerized using NaOCl as an oxidant. The structures of the monomers and polymers were confirmed by various spectroscopic techniques. Spectral results showed that the repeating units are linked by Csbnd C and Csbnd Osbnd C couplings. The polyazomethines have fluorescent property with high stokes shift. Solid state electrical conductivity of polymers both in I2 doped and undoped states, temperature and frequency dependent dielectric measurements were made by two probe method. The electrical conductivities of polyazomethines were compared based on the charge densities on imine nitrogens obtained from Huckel calculation. The conductivity of polymers increases with increase in iodine vapour contact time. Among the synthesized polymers PHNAE has shown high dielectric constant at low applied frequency of 50 Hz at 393 K due the presence of bulky naphthalene unit in polymer chain.
Archer, Elizabeth K; Bennett, Nigel C; Faulkes, Chris G; Lutermann, Heike
2016-02-01
Due to the density-dependent nature of parasite transmission parasites are generally assumed to constrain the evolution of sociality. However, evidence for a correlation between group size and parasite burden is equivocal, particularly for mammals. Host contact rates may be modified by mobility of the host and parasite as well as social barriers. In the current study, we used the common mole-rat (Cryptomys hottentotus hottentotus), a social subterranean rodent, as a model system to investigate the effect of host density and frequency of contact rates on ectoparasite burdens. To address these factors we used a study species that naturally varies in population densities and intergroup contact rates across its geographic range. We found that ectoparasite prevalence, abundance and species richness decreased with increasing host density at a regional scale. At the same time, measures of parasite burden increased with intergroup contact rates. Ectoparasite burdens decreased with colony size at the group level possibly as a result of increased grooming rates. Equating group size with population density might be too simplistic an approach when assessing parasite distributions in social mammals. Our data suggest that frequency-dependent mechanisms may play a much greater role at a population level than density-dependent mechanisms in determining parasite distributions in social species. We suggest that future studies should explicitly consider behavioural mechanisms that may affect parasite distribution.
Zhang, Yanqiu; Jiang, Shuyong; Zhu, Xiaoming; Sun, Dong
2016-11-01
Molecular dynamics simulation was performed in order to investigate the dependence of void growth on crystallographic orientation at the triple junction of grain boundaries in nanoscale tricrystal nickel film subjected to uniaxial tensile loading. The nucleation, the emission and the transmission of Shockley partial dislocations play a predominant role in the growth of void at the triple junction of grain boundaries. The orientation factors of various slip systems are calculated according to Schmid law. The slip systems activated in a grain of tricrystal nickel film basically conform to Schmid law which is completely suitable for a single crystal. The activated slip systems play an important role in plastic deformation of nanoscale tricrystal nickel film subjected to uniaxial tensile loading. The slip directions exhibit great difference among the activated slip systems such that the void is caused to be subjected to various stress conditions, which further leads to the difference in void growth among the tricrystal nickel films with different orientation distributions. It can be concluded that the grain orientation distribution has a significant influence on void growth at the triple junction of grain boundaries.
Frequency doubling in LiNbO3 using temperature dependent QPM
DEFF Research Database (Denmark)
Belmonte, Michele; Skettrup, Torben; Pedersen, Christian
1999-01-01
We report the application of temperature-dependent quasi-phase matching (QPM) for second harmonic generation of green light using periodically field poled LiNbO3. In contrast to the usual QPM devices, here the fundamental and second harmonic waves are polarized orthogonally so that the second...... efficiency. However, the use of QPM in our geometry with orthogonally polarized waves results in a greatly enhanced temperature tunability, which increases the versatility of the devices. Moreover, the domain inversion grating period required in this geometry for first-order QPM at the Nd laser wavelength...
Konstantinidis, T; Wagner, P K
1978-08-01
In a attempt to prove the dependence of duodenitis upon the morphological status of the gastric mucosa, a biopsy of the corpus, antrum, and duodenal canal had been made of 354 patients. In 56 cases, a superficial duodenitis was histologically verified; however, this infection had not contaminated the Brunner' glands. A duodenitis was found to be more often associated with surface gastritis of the corpus and antrum than it was with atropic gastritis. A duodenitis was discovered by a biopsy in 16 patients possessing a normal antrum mucosa and in 25 patients having a normal corpus mucosa, thus proving the possibility of isolated duodenitis.
Stepped Frequency GPR for Utility Line Detection using Polarization Dependent Scattering
DEFF Research Database (Denmark)
Jensen, Ole Kiel; Gregersen, Ole
2000-01-01
A GPR for detection of buried cables and pipes is developed by Ekko Dome Production in cooperation with Aalborg University. The appearance is a "lawn mower" model including antennas, electronics and on-line data processing. A successful result is obtained by combining dedicated hardware and signal...... processing. The inherent signal to clutter ratio is bad, but making measurements at many polarization angles and subsequent signal processing improves the ratio. A simple model of the polarization dependence of the scattering from the target is used. The method is improved by combining the polarization...
Modulation of Cortical Oscillations by Low-Frequency Direct Cortical Stimulation Is State-Dependent.
Directory of Open Access Journals (Sweden)
Sankaraleengam Alagapan
2016-03-01
Full Text Available Cortical oscillations play a fundamental role in organizing large-scale functional brain networks. Noninvasive brain stimulation with temporally patterned waveforms such as repetitive transcranial magnetic stimulation (rTMS and transcranial alternating current stimulation (tACS have been proposed to modulate these oscillations. Thus, these stimulation modalities represent promising new approaches for the treatment of psychiatric illnesses in which these oscillations are impaired. However, the mechanism by which periodic brain stimulation alters endogenous oscillation dynamics is debated and appears to depend on brain state. Here, we demonstrate with a static model and a neural oscillator model that recurrent excitation in the thalamo-cortical circuit, together with recruitment of cortico-cortical connections, can explain the enhancement of oscillations by brain stimulation as a function of brain state. We then performed concurrent invasive recording and stimulation of the human cortical surface to elucidate the response of cortical oscillations to periodic stimulation and support the findings from the computational models. We found that (1 stimulation enhanced the targeted oscillation power, (2 this enhancement outlasted stimulation, and (3 the effect of stimulation depended on behavioral state. Together, our results show successful target engagement of oscillations by periodic brain stimulation and highlight the role of nonlinear interaction between endogenous network oscillations and stimulation. These mechanistic insights will contribute to the design of adaptive, more targeted stimulation paradigms.
Resistance to change and frequency of response-dependent stimuli uncorrelated with reinforcement.
Podlesnik, Christopher A; Jimenez-Gomez, Corina; Ward, Ryan D; Shahan, Timothy A
2009-09-01
Stimuli uncorrelated with reinforcement have been shown to enhance response rates and resistance to disruption; however, the effects of different rates of stimulus presentations have not been assessed. In two experiments, we assessed the effects of adding different rates of response-dependent brief stimuli uncorrelated with primary reinforcement on relative response rates and resistance to change. In both experiments, pigeons responded on variable-interval 60-s schedules of food reinforcement in two components of a multiple schedule, and brief response-dependent keylight-color changes were added to one or both components. Although relative response rates were not systematically affected in either experiment, relative resistance to presession feeding and extinction were. In Experiment 1, adding stimuli on a variable-interval schedule to one component of a multiple schedule either at a low rate (1 per min) for one group or at a high rate (4 per min) for another group similarly increased resistance to disruption in the components with added stimuli. When high and low rates of stimuli were presented across components (i.e., within subjects) in Experiment 2, however, relative resistance to disruption was greater in the component presenting stimuli at a lower rate. These results suggest that stimuli uncorrelated with food reinforcement do not strengthen responding in the same way as primary reinforcers.
van Berkum, Susanne; Dee, Joris T; Philipse, Albert P; Erné, Ben H
2013-05-14
Chemically responsive hydrogels with embedded magnetic nanoparticles are of interest for biosensors that magnetically detect chemical changes. A crucial point is the irreversible linkage of nanoparticles to the hydrogel network, preventing loss of nanoparticles upon repeated swelling and shrinking of the gel. Here, acrylic acid monomers are adsorbed onto ferrite nanoparticles, which subsequently participate in polymerization during synthesis of poly(acrylic acid)-based hydrogels (PAA). To demonstrate the fixation of the nanoparticles to the polymer, our original approach is to measure low-field AC magnetic susceptibility spectra in the 0.1 Hz to 1 MHz range. In the hydrogel, the magnetization dynamics of small iron oxide nanoparticles are comparable to those of the particles dispersed in a liquid, due to fast Néel relaxation inside the particles; this renders the ferrogel useful for chemical sensing at frequencies of several kHz. However, ferrogels holding thermally blocked iron oxide or cobalt ferrite nanoparticles show significant decrease of the magnetic susceptibility resulting from a frozen magnetic structure. This confirms that the nanoparticles are unable to rotate thermally inside the hydrogel, in agreement with their irreversible fixation to the polymer network.
Directory of Open Access Journals (Sweden)
Ben H. Erné
2013-05-01
Full Text Available Chemically responsive hydrogels with embedded magnetic nanoparticles are of interest for biosensors that magnetically detect chemical changes. A crucial point is the irreversible linkage of nanoparticles to the hydrogel network, preventing loss of nanoparticles upon repeated swelling and shrinking of the gel. Here, acrylic acid monomers are adsorbed onto ferrite nanoparticles, which subsequently participate in polymerization during synthesis of poly(acrylic acid-based hydrogels (PAA. To demonstrate the fixation of the nanoparticles to the polymer, our original approach is to measure low-field AC magnetic susceptibility spectra in the 0.1 Hz to 1 MHz range. In the hydrogel, the magnetization dynamics of small iron oxide nanoparticles are comparable to those of the particles dispersed in a liquid, due to fast Néel relaxation inside the particles; this renders the ferrogel useful for chemical sensing at frequencies of several kHz. However, ferrogels holding thermally blocked iron oxide or cobalt ferrite nanoparticles show significant decrease of the magnetic susceptibility resulting from a frozen magnetic structure. This confirms that the nanoparticles are unable to rotate thermally inside the hydrogel, in agreement with their irreversible fixation to the polymer network.
van Berkum, Susanne; Dee, Joris T.; Philipse, Albert P.; Erné, Ben H.
2013-01-01
Chemically responsive hydrogels with embedded magnetic nanoparticles are of interest for biosensors that magnetically detect chemical changes. A crucial point is the irreversible linkage of nanoparticles to the hydrogel network, preventing loss of nanoparticles upon repeated swelling and shrinking of the gel. Here, acrylic acid monomers are adsorbed onto ferrite nanoparticles, which subsequently participate in polymerization during synthesis of poly(acrylic acid)-based hydrogels (PAA). To demonstrate the fixation of the nanoparticles to the polymer, our original approach is to measure low-field AC magnetic susceptibility spectra in the 0.1 Hz to 1 MHz range. In the hydrogel, the magnetization dynamics of small iron oxide nanoparticles are comparable to those of the particles dispersed in a liquid, due to fast Néel relaxation inside the particles; this renders the ferrogel useful for chemical sensing at frequencies of several kHz. However, ferrogels holding thermally blocked iron oxide or cobalt ferrite nanoparticles show significant decrease of the magnetic susceptibility resulting from a frozen magnetic structure. This confirms that the nanoparticles are unable to rotate thermally inside the hydrogel, in agreement with their irreversible fixation to the polymer network. PMID:23673482
Cell Type-Dependent RNA Recombination Frequency in the Japanese Encephalitis Virus
Directory of Open Access Journals (Sweden)
Wei-Wei Chiang
2014-01-01
Full Text Available Japanese encephalitis virus (JEV is one of approximately 70 flaviviruses, frequently causing symptoms involving the central nervous system. Mutations of its genomic RNA frequently occur during viral replication, which is believed to be a force contributing to viral evolution. Nevertheless, accumulating evidences show that some JEV strains may have actually arisen from RNA recombination between genetically different populations of the virus. We have demonstrated that RNA recombination in JEV occurs unequally in different cell types. In the present study, viral RNA fragments transfected into as well as viral RNAs synthesized in mosquito cells were shown not to be stable, especially in the early phase of infection possibly via cleavage by exoribonuclease. Such cleaved small RNA fragments may be further degraded through an RNA interference pathway triggered by viral double-stranded RNA during replication in mosquito cells, resulting in a lower frequency of RNA recombination in mosquito cells compared to that which occurs in mammalian cells. In fact, adjustment of viral RNA to an appropriately lower level in mosquito cells prevents overgrowth of the virus and is beneficial for cells to survive the infection. Our findings may also account for the slower evolution of arboviruses as reported previously.
Cell type-dependent RNA recombination frequency in the Japanese encephalitis virus.
Chiang, Wei-Wei; Chuang, Ching-Kai; Chao, Mei; Chen, Wei-June
2014-01-01
Japanese encephalitis virus (JEV) is one of approximately 70 flaviviruses, frequently causing symptoms involving the central nervous system. Mutations of its genomic RNA frequently occur during viral replication, which is believed to be a force contributing to viral evolution. Nevertheless, accumulating evidences show that some JEV strains may have actually arisen from RNA recombination between genetically different populations of the virus. We have demonstrated that RNA recombination in JEV occurs unequally in different cell types. In the present study, viral RNA fragments transfected into as well as viral RNAs synthesized in mosquito cells were shown not to be stable, especially in the early phase of infection possibly via cleavage by exoribonuclease. Such cleaved small RNA fragments may be further degraded through an RNA interference pathway triggered by viral double-stranded RNA during replication in mosquito cells, resulting in a lower frequency of RNA recombination in mosquito cells compared to that which occurs in mammalian cells. In fact, adjustment of viral RNA to an appropriately lower level in mosquito cells prevents overgrowth of the virus and is beneficial for cells to survive the infection. Our findings may also account for the slower evolution of arboviruses as reported previously.
Directory of Open Access Journals (Sweden)
Hofmann Frank
2009-09-01
Full Text Available Abstract Background The magnitude and longevity of synaptic activity-induced changes in synaptic efficacy is quantified by measuring evoked responses whose potentiation requires gene transcription to persist for more than 2-3 hours. While miniature EPSCs (mEPSCs are also increased in amplitude and/or frequency during long-term potentiation (LTP, it is not known how long such changes persist or whether gene transcription is required. Results We use whole-cell patch clamp recordings from dissociated hippocampal cultures to characterise for the first time the persistence and transcription dependency of mEPSC upregulation during synaptic potentiation. The persistence of recurrent action potential bursting in these cultures is transcription-, translation- and NMDA receptor-dependent thus providing an accessible model for long-lasting plasticity. Blockade of GABAA-receptors with bicuculline for 15 minutes induced action potential bursting in all neurons and was maintained in 50-60% of neurons for more than 6 hours. Throughout this period, the frequency but neither the amplitude of mEPSCs nor whole-cell AMPA currents was markedly increased. The transcription blocker actinomycin D abrogated, within 2 hours of burst induction, both action potential bursting and the increase in mEPSCs. Reversible blockade of action potentials during, but not after this 2 hour transcription period suppressed the increase in mEPSC frequency and the recovery of burst activity at a time point 6 hours after induction. Conclusion These results indicate that increased mEPSC frequency persists well beyond the 2 hour transcription-independent phase of plasticity in this model. This long-lasting mEPSC upregulation is transcription-dependent and requires ongoing action potential activity during the initial 2 hour period but not thereafter. Thus mEPSC upregulation may underlie the long term, transcription-dependent persistence of action potential bursting. This provides mechanistic
Dependence of Small Planet Frequency on Stellar Metallicity Hidden by Their Prevalence
Zhu, Wei; Wang, Ji; Huang, Chelsea
2016-12-01
The dependence of gas giant planet occurrence rate on stellar metallicity has been firmly established. We extend this so-called planet-metallicity correlation to broader ranges of metallicities and planet masses/radii. In particular, we assume that the planet-metallicity correlation is a power law below some critical saturation threshold, and that the probability of hosting at least one planet is unity for stars with metallicity above the threshold. We then are able to explain the discrepancy between the tentative detection and null detection in previous studies regarding the planet-metallicity correlation for small planets. In particular, we find that the null detection of this correlation can be attributed to the combination of high planet occurrence rate and low detection efficiency. Therefore, a planet-metallicity correlation for small planets cannot be ruled out. We propose that stars with metallicities lower than the solar value are better targets for testing the planet-metallicity correlation for small planets.
Dependence of Small Planet Frequency on Stellar Metallicity Hidden by Their Prevalence
Zhu, Wei; Huang, Chelsea
2016-01-01
The dependence of gas giant planet occurrence rate on stellar metallicity has been firmly established. We extend this so-called planet-metallicity correlation to broader ranges of metallicities and planet masses/radii. In particular, we assume that the planet-metallicity correlation is a power law below some critical saturation threshold, and that the probability of hosting at least one planet is unity for stars with metallicity above the threshold. We then are able to explain the discrepancy between the tentative detection and null detection in previous studies regarding the planet-metallicity correlation for small planets. In particular, we find that the null detection of this correlation can be attributed to the combination of high planet occurrence rate and low detection efficiency. Therefore, a planet-metallicity correlation for small planets cannot be ruled out. We propose that stars with metallicities lower than the Solar value are better targets for testing the planet-metallicity correlation for small...
Energy Technology Data Exchange (ETDEWEB)
Di Gioacchino, D.; Celani, F.; Tripodi, P. [Istituto Nazionale di Fisica Nucleare, Frascati, RM (Italy). Laboratori Nazionali di Frascati; Testa, A.M. [Consiglio Nazionale per le Ricerche, Monterotondo, RM, (Italy). Istituto di Chimica dei Materiali; Pace, S. [INFM, Univ. Salerno, Salerno (Italy). Dept. of Physics
1999-07-01
The paper is organized as follows. In Sec. 2 the non-linear diffusion problem is formulated in terms of a partial differential equation, together with the parallel resistor model for the 1-5 characteristics. To study in some detail the effects of thermally activated processes in different cases, we have chosen different temperature functional dependencies for the pinning potential, U{sub p}(T), and the critical current density, J{sub c}(T), related to particular pinning models. Local magnetic field profiles, magnetization cycles and {chi}n (T) are discussed in Sec. 3. Moreover, a comparison of numerical results with available experimental data and analytical approximated predictions is also presented. Finally, Sec. 4 is devoted to summary and conclusions.
Kasting, James F; Kopparapu, Ravikumar; Ramirez, Ramses M; Harman, Chester E
2014-09-02
The habitable zone (HZ) around a star is typically defined as the region where a rocky planet can maintain liquid water on its surface. That definition is appropriate, because this allows for the possibility that carbon-based, photosynthetic life exists on the planet in sufficient abundance to modify the planet's atmosphere in a way that might be remotely detected. Exactly what conditions are needed, however, to maintain liquid water remains a topic for debate. In the past, modelers have restricted themselves to water-rich planets with CO2 and H2O as the only important greenhouse gases. More recently, some researchers have suggested broadening the definition to include arid, "Dune" planets on the inner edge and planets with captured H2 atmospheres on the outer edge, thereby greatly increasing the HZ width. Such planets could exist, but we demonstrate that an inner edge limit of 0.59 AU or less is physically unrealistic. We further argue that conservative HZ definitions should be used for designing future space-based telescopes, but that optimistic definitions may be useful in interpreting the data from such missions. In terms of effective solar flux, S(eff), the recently recalculated HZ boundaries are: recent Venus--1.78; runaway greenhouse--1.04; moist greenhouse--1.01; maximum greenhouse--0.35; and early Mars--0.32. Based on a combination of different HZ definitions, the frequency of potentially Earth-like planets around late K and M stars observed by Kepler is in the range of 0.4-0.5.
Kasting, James F.; Kopparapu, Ravikumar; Ramirez, Ramses M.; Harman, Chester E.
2014-09-01
The habitable zone (HZ) around a star is typically defined as the region where a rocky planet can maintain liquid water on its surface. That definition is appropriate, because this allows for the possibility that carbon-based, photosynthetic life exists on the planet in sufficient abundance to modify the planet's atmosphere in a way that might be remotely detected. Exactly what conditions are needed, however, to maintain liquid water remains a topic for debate. In the past, modelers have restricted themselves to water-rich planets with CO2 and H2O as the only important greenhouse gases. More recently, some researchers have suggested broadening the definition to include arid, "Dune" planets on the inner edge and planets with captured H2 atmospheres on the outer edge, thereby greatly increasing the HZ width. Such planets could exist, but we demonstrate that an inner edge limit of 0.59 AU or less is physically unrealistic. We further argue that conservative HZ definitions should be used for designing future space-based telescopes, but that optimistic definitions may be useful in interpreting the data from such missions. In terms of effective solar flux, Seff, the recently recalculated HZ boundaries are: recent Venus-1.78; runaway greenhouse-1.04; moist greenhouse-1.01; maximum greenhouse-0.35; and early Mars-0.32. Based on a combination of different HZ definitions, the frequency of potentially Earth-like planets around late K and M stars observed by Kepler is in the range of 0.4-0.5.
Laaser, Jennifer E; Zanni, Martin T
2013-07-25
We present ways in which pulse sequences and polarizations can be used to extract structural information from one- and two-dimensional vibrational sum frequency generation (2D SFG) spectra. We derive analytic expressions for the polarization dependence of systems containing coupled vibrational modes, and we present simulated spectra to identify the features of different molecular geometries. We discuss several useful polarization combinations for suppressing strong diagonal peaks and emphasizing weaker cross-peaks. We investigate unique capabilities of 2D SFG spectra for obtaining structural information about SFG-inactive modes and for identifying coupled achiral chromophores. This work builds on techniques that have been developed for extracting structural information from 2D IR spectra. This paper discusses how to utilize these concepts in 2D SFG experiments to probe multioscillator systems at interfaces. The sample code for calculating polarization dependence of 1D and 2D SFG spectra is provided in the Supporting Information .
Frequency-dependent associative long-term potentiation at the hippocampal mossy fiber-CA3 synapse.
Derrick, B E; Martinez, J L
1994-10-25
The mossy fiber-CA3 synapse displays an N-methyl-D-aspartate-receptor-independent mu-opioid-receptor-dependent form of long-term potentiation (LTP) that is thought not to display cooperativity or associativity with coactive afferents. However, because mossy fiber LTP requires repetitive synaptic activity for its induction, we reevaluated cooperativity and associativity at this synapse by using trains of mossy fiber stimulation. Moderate-, but not low-, intensity trains induced mossy fiber LTP, indicating cooperativity. Low-intensity mossy fiber trains that were normally ineffective in inducing LTP could induce mossy fiber LTP when delivered in conjunction with trains delivered to commissural-CA3 afferents. Associative mossy fiber LTP also could be induced with single mossy fiber pulses when delivered with commissural trains in the presence of a mu-opioid-receptor agonist. Our findings suggest a frequency-dependent variation of Hebbian associative LTP induction that is regulated by the release of endogenous opioid peptides.
Gaifullin; Matsuda; Chikumoto; Shimoyama; Kishio
2000-03-27
We report the first detailed and quantitative study of the Josephson coupling energy in the vortex liquid, Bragg glass, and vortex glass phases of Bi(2)Sr(2)CaCu(2)O(8+delta) by the Josephson plasma resonance. The measurements revealed distinct features in the T and H dependencies of the plasma frequency omega(pl) for each of these three vortex phases. When going across either the Bragg-to-vortex glass or the Bragg-to-liquid transition line, omega(pl) shows a dramatic change. We provide a quantitative discussion on the properties of these phase transitions, including the first order nature of the Bragg-to-vortex glass transition.
Zhao, Xu-yan; Liu, Yu-qi; Fu, Yi-cheng; Xu, Bin; Gao, Jin-liao; Zheng, Xiao-qin; Lin, Min; Chen, Mei-yan; Li, Yang
2012-03-01
The rapidly activating delayed rectifier potassium current (I(Kr)), whose pore-forming alpha subunit is encoded by the human ether-a-go-go-related gene (hERG), is a key contributor to the third phase of action potential repolarization. The aim of this study was to investigate the effect and mechanism of arecoline hydrobromide induced inhibition of hERG K(+) current (I(hERG)). Transient transfection of hERG channel cDNA plasmid pcDNA3.1 into the cultured HEK293 cells was performed using Lipofectamine. A standard whole-cell patch-clamp technique was used to record the I(hERG) before and after the exposure to arecoline. Arecoline decreased the amplitude and the density of the I(hERG) in a concentration-dependent manner (IC(50) = 9.55 mmol/L). At test potential of +60 mV, the magnitude of I(hERG) tail at test pulse of -40 mV was reduced from (151.7 ± 6.2) pA/pF to (84.4 ± 7.6) pA/pF (P arecoline in the open and inactivated state was significant in a state-dependent manner. The maximal blockade was achieved in the inactivated state. Studies of gating mechanism showed that the steady-state activation curve of I(hERG) was significantly negatively shifted by arecoline. Time constants of activation were shortened. Steady-state inactivation curve and time constants of fast inactivation were not significantly affected by arecoline. Furthermore, the inhibition of I(hERG) by arecoline was characterized markedly by a frequency-dependent manner from 0.03 to 1.00 Hz pulse. Arecoline could potently block I(hERG) in both frequency and state-dependent manner.
The effects of frequency-dependent quasar evolution on the celestial reference frame
Shabala, Stanislav; McCallum, Jamie; Titov, Oleg; Blanchard, Jay; Lovell, Jim; Watson, Christopher
2013-01-01
We examine the relationship between source position stability and astrophysical properties of radio-loud quasars making up the International Celestial Reference Frame. We construct light curves for 95 most frequently observed ICRF2 quasars at both the geodetic VLBI observing bands. Because the appearance of new quasar components corresponds to an increase in quasar flux density, these light curves allow us to probe source structure on sub-100 microarcsecond scales, much smaller than conventional VLBI imaging. Flux density monitoring also allows us to trace the evolution of quasar structure. We test how source position stability depends on three astrophysical parameters: (1) Flux density variability at X-band; (2) Time lag between S and X-band light curves; (3) Spectral index rms, defined as the variability in the ratio between S and X-band flux densities. We find that small (<0.15 years) time lags between S and X-band light curves and low (<0.10) spectral index variability are excellent indicators of po...
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.