High-frequency conductivity of photoionized plasma

Energy Technology Data Exchange (ETDEWEB)

Anakhov, M. V.; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru [National Research Nuclear University “MEPhI,” (Russian Federation)

2016-08-15

The tensor of the high-frequency conductivity of a plasma created via tunnel ionization of atoms in the field of linearly or circularly polarized radiation is derived. It is shown that the real part of the conductivity tensor is highly anisotropic. In the case of a toroidal velocity distribution of photoelectrons, the possibility of amplification of a weak high-frequency field polarized at a sufficiently large angle to the anisotropy axis of the initial nonequilibrium distribution is revealed.

Frequency and voltage dependence dielectric properties, ac electrical conductivity and electric modulus profiles in Al/Co{sub 3}O{sub 4}-PVA/p-Si structures

Energy Technology Data Exchange (ETDEWEB)

Bilkan, Çiğdem, E-mail: cigdembilkan@gmail.com [Department of Physics, Faculty of Sciences, The University of Çankırı Karatekin, 18100 Çankırı (Turkey); Azizian-Kalandaragh, Yashar [Department of Physics, Faculty of Science, The University of Mohaghegh Ardabili, Ardabil (Iran, Islamic Republic of); Altındal, Şemsettin [Department of Physics, Faculty of Sciences, The University of Gazi, 06500 Ankara (Turkey); Shokrani-Havigh, Roya [Department of Physics, Faculty of Science, The University of Mohaghegh Ardabili, Ardabil (Iran, Islamic Republic of)

2016-11-01

In this research a simple microwave-assisted method have been used for preparation of cobalt oxide nanostructures. The as-prepared sample has been investigated by UV–vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM). On the other hand, frequency and voltage dependence of both the real and imaginary parts of dielectric constants (ε′, ε″) and electric modulus (M′ and M″), loss tangent (tanδ), and ac electrical conductivity (σ{sub ac}) values of Al/Co{sub 3}O{sub 4}-PVA/p-Si structures were obtained in the wide range of frequency and voltage using capacitance (C) and conductance (G/ω) data at room temperature. The values of ε′, ε″ and tanδ were found to decrease with increasing frequency almost for each applied bias voltage, but the changes in these parameters become more effective in the depletion region at low frequencies due to the charges at surface states and their relaxation time and polarization effect. While the value of σ is almost constant at low frequency, increases almost as exponentially at high frequency which are corresponding to σ{sub dc} and σ{sub ac}, respectively. The M′ and M″ have low values at low frequencies region and then an increase with frequency due to short-range mobility of charge carriers. While the value of M′ increase with increasing frequency, the value of M″ shows two peak and the peaks positions shifts to higher frequency with increasing applied voltage due to the decrease of the polarization and N{sub ss} effects with increasing frequency.

Frequency dependent polarization in blazars

International Nuclear Information System (INIS)

Bjoernsson, C.I.

1984-10-01

It is argued that the intrinsic frequency dependent polarization in blazars finds its most straightforward explanations in terms of a single rather than a multicomponent sourcemodel. In order to reproduce the observations, under the assumption that the emission mechanism is optically thin synchrotron radiation, both a well ordered magnetic field and an electron distribution with a sharp break or cuttoff are necessary. Non-uniform pitch angle distribution and/or environments where synchrotron losses are important are both conducive to producing strong frequency dependent polarization. Reasons are put forth as to why such conditions ar expected to occur in blazars. Two specific models are discussed in detail and it is shown that they are both able to produce strong frequency dependent polarization, even when the spectral index changes by a small amount only. (orig.)

A study of frequency effects on conductivity measurements

International Nuclear Information System (INIS)

Nurul Ain Ahmad Latif; Mahmood Dollah; Mohd Khidir Kamaron; Suaib Ibrahim

2010-01-01

In eddy current testing (ET), different measurement can be carry out through the selection of the test frequency. In conductivity measurement, the selection of eddy current test frequencies permits to select the specific material properties to be measured. The test frequency selected should be sufficient high that eddy current penetration is limited only to fraction of the test material thickness. This paper describes the effects of test frequency on the conductivity measurement. This experiment done by applying different values of test frequency which is 20 kHz, 100 kHz and 1 MHz. (author)

Modification of Akhieser mechanism in Si nanomembranes and thermal conductivity dependence of the Q-factor of high frequency nanoresonators

International Nuclear Information System (INIS)

Chávez-Ángel, E; Gomis-Bresco, J; Alzina, F; Sotomayor Torres, C M; Zarate, R A

2014-01-01

We present and validate a reformulated Akhieser model that takes into account the reduction of thermal conductivity due to the impact of boundary scattering on the thermal phonons’ lifetime. We consider silicon nanomembranes with mechanical mode frequencies in the GHz range as textbook examples of nanoresonators. The model successfully accounts for the measured shortening of the mechanical mode lifetime. Moreover, the thermal conductivity is extracted from the measured lifetime of the mechanical modes in the high-frequency regime, thereby demonstrating that the Q-factor can be used as an indication of the thermal conductivity and/or diffusivity of a mechanical resonator. (invited article)

Structure, temperature and frequency dependent electrical conductivity of oxidized and reduced electrochemically exfoliated graphite

Science.gov (United States)

Radoń, Adrian; Włodarczyk, Patryk; Łukowiec, Dariusz

2018-05-01

The article presents the influence of reduction by hydrogen in statu nascendi and modification by hydrogen peroxide on the structure and electrical conductivity of electrochemically exfoliated graphite. It was confirmed that the electrochemical exfoliation can be used to produce oxidized nanographite with an average number of 25 graphene layers. The modified electrochemical exfoliated graphite and reduced electrochemical exfoliated graphite were characterized by high thermal stability, what was associated with removing of labile oxygen-containing groups. The presence of oxygen-containing groups was confirmed using Fourier-transform infrared spectroscopy. Influence of chemical modification by hydrogen and hydrogen peroxide on the electrical conductivity was determined in wide frequency (0.1 Hz-10 kHz) and temperature range (-50 °C-100 °C). Material modified by hydrogen peroxide (0.29 mS/cm at 0 °C) had the lowest electrical conductivity. This can be associated with oxidation of unstable functional groups and was also confirmed by analysis of Raman spectra. The removal of oxygen-containing functional groups by hydrogen in statu nascendi resulted in a 1000-fold increase in the electrical conductivity compared to the electrochemical exfoliated graphite.

High-frequency spin-dependent tunnelling in magnetic nanocomposites: Magnetorefractive effect and magnetoimpedance

Energy Technology Data Exchange (ETDEWEB)

Granovsky, Alexander [Faculty of Physics, Lomonosov Moscow State University, Moscow 119992 (Russian Federation)]. E-mail: granov@magn.ru; Kozlov, Andrey [Faculty of Physics, Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Nedukh, Sergey [Institute of Radiophysics and Electronics NAS of Ukraine, Kharkov 61085 (Ukraine); Tarapov, Sergey [Institute of Radiophysics and Electronics NAS of Ukraine, Kharkov 61085 (Ukraine)

2005-07-15

Since the dielectric permittivity is linear with frequency-dependent conductivity, high-frequency properties for any kind of magnetic materials with the high magnetoresistance depend on magnetization. It manifests as magnetorefractive effect (MRE) in the infrared region of spectrum and as magnetoimpedance (MI) in the frequency range between radio and microwaves. The main mechanism of both MRE and MI in nanocomposites with tunnel-type magnetoresistance is high-frequency spin-dependent tunnelling. We report on recent results of theoretical and experimental investigations of MRE and MI in nanocomposites Co{sub 51.5}Al{sub 19.5}O{sub 29}, Co{sub 50.2}Ti{sub 9.1}O{sub 40.7}, Co{sub 52.3}Si{sub 12.2}O{sub 35.5} and (Co{sub 0,4}Fe{sub 0,6}){sub 48}(MgF){sub 52}. Most of the obtained experimental data for MRE and MI are consistent with the theory based on considering the tunnel junction between adjacent granules in percolation cluster as a capacitor.

Engineering frequency-dependent superfluidity in Bose-Fermi mixtures

Science.gov (United States)

Arzamasovs, Maksims; Liu, Bo

2018-04-01

Unconventional superconductivity and superfluidity are among the most exciting and fascinating quantum phenomena in condensed-matter physics. Usually such states are characterized by nontrivial spin or spatial symmetry of the pairing order parameter, such as "spin triplet" or "p wave." However, besides spin and spatial dependence the order parameter may have unconventional frequency dependence which is also permitted by Fermi-Dirac statistics. Odd-frequency fermionic pairing is an exciting paradigm when discussing exotic superfluidity or superconductivity and is yet to be realized in experiments. In this paper we propose a symmetry-based method of controlling frequency dependence of the pairing order parameter via manipulating the inversion symmetry of the system. First, a toy model is introduced to illustrate that frequency dependence of the order parameter can be achieved through our proposed approach. Second, by taking advantage of recent rapid developments in producing spin-orbit-coupled dispersions in ultracold gases, we propose a Bose-Fermi mixture to realize such frequency-dependent superfluid. The key idea is introducing the frequency-dependent attraction between fermions mediated by Bogoliubov phonons with asymmetric dispersion. Our proposal should pave an alternative way for exploring frequency-dependent superfluids with cold atoms.

Measured Temperature Dependence of the cos-phi Conductance in Josephson Tunnel Junctions

DEFF Research Database (Denmark)

Sørensen, O. H.; Mygind, Jesper; Pedersen, Niels Falsig

1977-01-01

The temperature dependence of the cosϕ conductance in Sn-O-Sn Josephson tunnel junctions has been measured just below the critical temperature, Tc. From the resonant microwave response at the junction plasma frequency as the temperature is decreased from Tc it is deduced that the amplitude of the...

Origin of the suppression in low frequency terahertz conductivity in dilute GaAs nitride and bismide alloys

DEFF Research Database (Denmark)

Cocker, Tylor; Lu, Xianfeng; Cooke, David

We have performed time-resolved terahertz spectroscopy on GaAs1-xBix (x=7%) and observed a low-frequency suppression of the real conductivity previously seen only in dilute GaAs nitrides. We have developed a modified Drude model with a frequency-dependent scattering time that provides excellent...

Equilibrium finite-frequency noise of an interacting mesoscopic capacitor studied in time-dependent density functional theory

Science.gov (United States)

Dittmann, Niklas; Splettstoesser, Janine; Helbig, Nicole

2018-03-01

We calculate the frequency-dependent equilibrium noise of a mesoscopic capacitor in time-dependent density functional theory (TDDFT). The capacitor is modeled as a single-level quantum dot with on-site Coulomb interaction and tunnel coupling to a nearby reservoir. The noise spectra are derived from linear-response conductances via the fluctuation-dissipation theorem. Thereby, we analyze the performance of a recently derived exchange-correlation potential with time-nonlocal density dependence in the finite-frequency linear-response regime. We compare our TDDFT noise spectra with real-time perturbation theory and find excellent agreement for noise frequencies below the reservoir temperature.

On conductivity, permittivity, apparent diffusion coefficient, and their usefulness as cancer markers at MRI frequencies.

Science.gov (United States)

Hancu, Ileana; Roberts, Jeannette Christine; Bulumulla, Selaka; Lee, Seung-Kyun

2015-05-01

To investigate the permittivity and conductivity of cancerous and normal tissues, their correlation to the apparent diffusion coefficient (ADC), and the specificity that they could add to cancer detection. Breast and prostate carcinomas were induced in rats. Conductivity and permittivity measurements were performed in the anesthetized animals using a dielectric probe and an impedance analyzer between 50 and 270 MHz. The correlations between ADCs (measured at 128 MHz) and conductivity values were investigated. Frequency-dependent discriminant functions were computed to assess the value that each parameter adds to cancer detection. Tumors exhibited higher permittivity than muscle tissue by 27%/12%/5% at 64/128/270MHz. Frequency independent, 15-20% higher conductivity was also noted in tumors compared to muscle tissue over the same frequency range. Strong negative correlation was observed between tissue conductivity and ADC. Whereas permittivity had the strongest discriminatory power at 64 MHz, it became comparable to ADC at 128 MHz and less important than ADC at 270 MHz. Conductivity measurements offered limited advantages in separating cancer from normal tissue beyond what ADC already provided; conversely, permittivity added separation power when added to the discriminant function. The moderately high cancerous tissue permittivity and conductivity impose strong constraints on the capability of MRI-based tissue electrical property measurements. © 2014 Wiley Periodicals, Inc.

Frequency and Temperature Dependence of Electrical Breakdown at 21, 30, and 39GHz

Science.gov (United States)

Braun, H. H.; Döbert, S.; Wilson, I.; Wuensch, W.

2003-06-01

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 39GHz. 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 and Temperature Dependence of Electrical Breakdown at 21, 30 and 39 GHz

CERN Document Server

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.

Dependence of the optical conductivity on the uniaxial and biaxial strains in black phosphorene

Science.gov (United States)

Yang, C. H.; Zhang, J. Y.; Wang, G. X.; Zhang, C.

2018-06-01

By using the Kubo formula, the optical conductivity of strained black phosphorene was studied. The anisotropic band dispersion gives rise to an orientation dependent optical conductivity. The energy gap can be tuned by the uniaxial and biaxial strains which can be observed from the interband optical conductivity polarized along the armchair (x ) direction. The preferential conducting direction is along the x direction. The dependence of the intraband optical conductivity along the zigzag (y ) direction on the Fermi energy and strain exhibits increasing or decreasing monotonously. However, along the x direction this dependence is complicated which originates from the carriers' inverse-direction movements obtained by two types of the nearest phosphorus atom interactions. The modification of the biaxial strain on the energy structure and optical-absorption property is more effective. The imaginary part of the total optical conductivity (Im σ ) can be negative around the threshold of the interband optical transition by modifying the chemical potential. Away from this frequency region, Im σ exhibits positive value. It can be used in the application of the surface plasmon propagations in multilayer dielectric structures.

Frequency-dependent heat capacity

DEFF Research Database (Denmark)

Behrens, Claus Flensted

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...

Frequency-Dependent Tidal Triggering of Low Frequency Earthquakes Near Parkfield, California

Science.gov (United States)

Xue, L.; Burgmann, R.; Shelly, D. R.

2017-12-01

The effect of small periodic stress perturbations on earthquake generation is not clear, however, the rate of low-frequency earthquakes (LFEs) near Parkfield, California has been found to be strongly correlated with solid earth tides. Laboratory experiments and theoretical analyses show that the period of imposed forcing and source properties affect the sensitivity to triggering and the phase relation of the peak seismicity rate and the periodic stress, but frequency-dependent triggering has not been quantitatively explored in the field. Tidal forcing acts over a wide range of frequencies, therefore the sensitivity to tidal triggering of LFEs provides a good probe to the physical mechanisms affecting earthquake generation. In this study, we consider the tidal triggering of LFEs near Parkfield, California since 2001. We find the LFEs rate is correlated with tidal shear stress, normal stress rate and shear stress rate. The occurrence of LFEs can also be independently modulated by groups of tidal constituents at semi-diurnal, diurnal and fortnightly frequencies. The strength of the response of LFEs to the different tidal constituents varies between LFE families. Each LFE family has an optimal triggering frequency, which does not appear to be depth dependent or systematically related to other known properties. This suggests the period of the applied forcing plays an important role in the triggering process, and the interaction of periods of loading history and source region properties, such as friction, effective normal stress and pore fluid pressure, produces the observed frequency-dependent tidal triggering of LFEs.

Angular-dependent EDMR linewidth for spin-dependent space charge limited conduction in a polycrystalline pentacene

Science.gov (United States)

Fukuda, Kunito; Asakawa, Naoki

2017-08-01

Spin-dependent space charge limited carrier conduction in a Schottky barrier diode using polycrystalline p-type π-conjugated molecular pentacene is explored using multiple-frequency electrically detected magnetic resonance (EDMR) spectroscopy with a variable-angle configuration. The measured EDMR spectra are decomposed into two components derived respectively from mobile and trapped positive polarons. The linewidth of the EDMR signal for the trapped polarons increases with increasing resonance magnetic field for an in-plane configuration where the normal vector of the device substrate is perpendicular to the resonance magnetic field, while it is independent of the field for an out-of-plane configuration. This difference is consistent with the pentacene arrangement on the device substrate, where pentacene molecules exhibit a uniaxial orientation on the out-of-substrate plane. By contrast, the mobile polarons do not show anisotropic behavior with respect to the resonance magnetic field, indicating that the anisotropic effect is averaged out owing to carrier motion. These results suggest that the orientational arrangements of polycrystalline pentacene molecules in a nano thin film play a crucial role in spin-dependent electrical conduction.

Frequency and temperature dependence of the electrical conductivity of KTaO3; Li and PbTiO3; La, Cu: Indication of a low temperature polaron mechanism

International Nuclear Information System (INIS)

Levstik, A.; Filipic, C.; Bidault, O.; Maglione, M.

2008-01-01

Recently, the concept of polarons has again been at the focus of solid-state research, as it can constitute the basis for understanding the high-temperature superconductivity or the colossal magnetoresistance of materials. More than a decade ago there were some indications that polarons play an important role in explaining low temperature maxima in imaginary part of the dielectric constant ε '' (T) in ABO 3 perovskites. In the present work we report the ac electrical conductivities of KTaO 3 ; Li and PbTiO 3 ; La, Cu and their frequency and temperature dependence. The real part of the complex ac conductivity was found to follow the universal dielectric response σ ' ∝ν s . A detailed theoretical analysis of the temperature dependence of the parameter s revealed that, at low temperatures, the tunnelling of small polarons is the dominating charge transport mechanism in ABO 3 perovskites

Studies on frequency dependent electrical and dielectric properties of sintered zinc oxide pellets: effects of Al-doping

Science.gov (United States)

Tewari, S.; Ghosh, A.; Bhattacharjee, A.

2016-11-01

Sintered pellets of zinc oxide (ZnO), both undoped and Al-doped are prepared through a chemical process. Dopant concentration of Aluminium in ZnO [Al/Zn in weight percentage (wt%)] is varied from 0 to 3 wt%. After synthesis structural characterisation of the samples are performed with XRD and SEM-EDAX which confirm that all the samples are of ZnO having polycrystalline nature with particle size from 108.6 to 116 nm. Frequency dependent properties like a.c. conductivity, capacitance, impedance and phase angle are measured in the frequency range 10 Hz to 100 kHz as a function of temperature (in the range 25-150 °C). Nature of a.c. conductivity in these samples indicates hopping type of conduction arising from localised defect states. The frequency and temperature dependent properties under study are found to be as per correlated barrier hoping model. Dielectric and impedance properties studied in the samples indicate distributed relaxation, showing decrease of relaxation time with temperature.

Dynamic conductivity from audio to optical frequencies of semiconducting manganites approaching the metal-insulator transition

Science.gov (United States)

Lunkenheimer, P.; Mayr, F.; Loidl, A.

2006-07-01

We report the frequency-dependent conductivity of the manganite system La1-xSrxMnO3 (x0.2) when approaching the metal-insulator transition from the insulating side. Results from low-frequency dielectric measurements are combined with spectra in the infrared region. For low doping levels the behavior is dominated by hopping transport of localized charge carriers at low frequencies and by phononic and electronic excitations in the infrared region. For the higher Sr contents the approach of the metallic state is accompanied by the successive suppression of the hopping contribution at low frequencies and by the development of polaronic excitations in the infrared region, which finally become superimposed by a strong Drude contribution in the fully metallic state.

Discrete diffusion Monte Carlo for frequency-dependent radiative transfer

International Nuclear Information System (INIS)

Densmore, Jeffery D.; Thompson, Kelly G.; Urbatsch, Todd J.

2011-01-01

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. (author)

Unconventional strain-dependent conductance oscillations in pristine phosphorene.

Science.gov (United States)

Ray, S J; Kamalakar, M Venkata

2018-05-16

Phosphorene is a single elemental, two-dimensional semiconductor that has quickly emerged as a high mobility material for transistors and optoelectronic devices. In addition, being a 2D material it can sustain high levels of strain, enabling sensitive modification of its electronic properties. In this paper, we investigate the strain dependent electronic properties of phosphorene nanocrystals. By performing extensive calculations we determine the electrical conductance as a function of uniaxial, as well as biaxial strain stimuli and uncover a unique zone phase diagram. This enables us to uncover conductance oscillations in pristine phosphorene for the first time, by the simple application of strain. We show that such unconventional current-voltage behaviour is tuneable by the nature of strain, and that an additional gate voltage can modulate the amplitude (peak to valley ratio) of the observed phenomena and its switching efficiency. Furthermore, we show that the switching is highly robust against doping and defects. Our detailed results present new leads for innovation in strain based gauging and high-frequency nanoelectronic switches of phosphorene.

Angular-Dependent EDMR Linewidth for Spin-Dependent Space-Charge-Limited Conduction in a Polycrystalline Pentacene

Directory of Open Access Journals (Sweden)

Kunito Fukuda

2017-08-01

Full Text Available Spin-dependent space-charge-limited carrier conduction in a Schottky barrier diode using polycrystalline p-type π-conjugated molecular pentacene is explored using multiple-frequency electrically detected magnetic resonance (EDMR spectroscopy with a variable-angle configuration. The measured EDMR spectra are decomposed into two components derived, respectively, from mobile and trapped positive polarons. The linewidth of the EDMR signal for the trapped polarons increases with increasing resonance magnetic field for an in-plane configuration where the normal vector of the device substrate is perpendicular to the resonance magnetic field, while it is independent of the field for an out-of-plane configuration. This difference is consistent with the pentacene arrangement on the device substrate, where pentacene molecules exhibit a uniaxial orientation on the out-of-substrate plane. By contrast, the mobile polarons do not show anisotropic behavior with respect to the resonance magnetic field, indicating that the anisotropic effect is averaged out owing to carrier motion. These results suggest that the orientational arrangements of polycrystalline pentacene molecules in a nano thin film play a crucial role in spin-dependent electrical conduction.

Temperature-dependent thermal conductivities of one-dimensional nonlinear Klein-Gordon lattices with a soft on-site potential.

Science.gov (United States)

Yang, Linlin; Li, Nianbei; Li, Baowen

2014-12-01

The temperature-dependent thermal conductivities of one-dimensional nonlinear Klein-Gordon lattices with soft on-site potential (soft-KG) are investigated systematically. Similarly to the previously studied hard-KG lattices, the existence of renormalized phonons is also confirmed in soft-KG lattices. In particular, the temperature dependence of the renormalized phonon frequency predicted by a classical field theory is verified by detailed numerical simulations. However, the thermal conductivities of soft-KG lattices exhibit the opposite trend in temperature dependence in comparison with those of hard-KG lattices. The interesting thing is that the temperature-dependent thermal conductivities of both soft- and hard-KG lattices can be interpreted in the same framework of effective phonon theory. According to the effective phonon theory, the exponents of the power-law dependence of the thermal conductivities as a function of temperature are only determined by the exponents of the soft or hard on-site potentials. These theoretical predictions are consistently verified very well by extensive numerical simulations.

Temperature-dependent thermal conductivities of one-dimensional nonlinear Klein-Gordon lattices with a soft on-site potential

Science.gov (United States)

Yang, Linlin; Li, Nianbei; Li, Baowen

2014-12-01

The temperature-dependent thermal conductivities of one-dimensional nonlinear Klein-Gordon lattices with soft on-site potential (soft-KG) are investigated systematically. Similarly to the previously studied hard-KG lattices, the existence of renormalized phonons is also confirmed in soft-KG lattices. In particular, the temperature dependence of the renormalized phonon frequency predicted by a classical field theory is verified by detailed numerical simulations. However, the thermal conductivities of soft-KG lattices exhibit the opposite trend in temperature dependence in comparison with those of hard-KG lattices. The interesting thing is that the temperature-dependent thermal conductivities of both soft- and hard-KG lattices can be interpreted in the same framework of effective phonon theory. According to the effective phonon theory, the exponents of the power-law dependence of the thermal conductivities as a function of temperature are only determined by the exponents of the soft or hard on-site potentials. These theoretical predictions are consistently verified very well by extensive numerical simulations.

Frequency-dependent transient response of an oscillating electrically actuated droplet

International Nuclear Information System (INIS)

Dash, S; Kumari, N; Garimella, S V

2012-01-01

The transient response of a millimeter-sized sessile droplet under electrical actuation is experimentally investigated. Under dc actuation, the droplet spreading rate increases as the applied voltage is increased due to the higher electrical forces induced. At sufficiently high dc voltages, competition between the electrical actuation force, droplet inertia, the retarding surface tension force and contact line friction leads to droplet oscillation. The timescale for the droplet to attain its maximum wetted diameter during step actuation is analyzed. Systematic experiments are conducted over a frequency range of 5–200 Hz and actuation voltages of 40–80 V rms to determine the dependence of droplet oscillation on these parameters. The response of the droplet to different actuation frequencies and voltages is determined in terms of its contact angle and contact radius variation. The frequency of the driving force (equal to twice the frequency of the applied electrical signal) determines the mode of oscillation of the droplet which, together with its resonance characteristics, governs whether the droplet contact angle and contact radius vary in phase or out of phase with each other. In addition to the primary frequency response at the electrical forcing frequency, the droplet oscillation exhibits sub-harmonic oscillation at half of the forcing frequency that is attributed to the parametric nature of the electrical force acting on the triple contact line of the droplet. (paper)

Dynamic conductivity from audio to optical frequencies of semiconducting manganites approaching the metal-insulator transition

International Nuclear Information System (INIS)

Lunkenheimer, P.; Mayr, F.; Loidl, A.

2006-01-01

We report the frequency-dependent conductivity of the manganite system La 1-x Sr x MnO 3 (x≤0.2) when approaching the metal-insulator transition from the insulating side. Results from low-frequency dielectric measurements are combined with spectra in the infrared region. For low doping levels the behavior is dominated by hopping transport of localized charge carriers at low frequencies and by phononic and electronic excitations in the infrared region. For the higher Sr contents the approach of the metallic state is accompanied by the successive suppression of the hopping contribution at low frequencies and by the development of polaronic excitations in the infrared region, which finally become superimposed by a strong Drude contribution in the fully metallic state. (Abstract Copyright [2006], Wiley Periodicals, Inc.)

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 cutoffs—a collection of two-level systems and a system described by the energy master equation—the 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-difference-dependent stochastic resonance in neural systems

Science.gov (United States)

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.

Temperature dependence of the cosphi conductance in Josephson tunnel junctions determined from plasma resonance experiments

DEFF Research Database (Denmark)

Pedersen, Niels Falsig; Sørensen, O. H.; Mygind, Jesper

1978-01-01

The microwave response at 9 GHz of Sn-O-Sn tunnel-junction current biased at zero dc voltage has been measured just below the critical temperature Tc of the Sn films. The temperature dependence of the cosφ conductance is determined from the resonant response at the junction plasma frequency fp...

Frequency and temperature dependent dielectric properties of TiO2-V2O5 nanocomposites

Science.gov (United States)

Ray, Apurba; Roy, Atanu; De, Sayan; Chatterjee, Souvik; Das, Sachindranath

2018-03-01

In this manuscript, we have reported the crystal structure, dielectric response, and transport phenomenon of TiO2-V2O5 nanocomposites. The nanocomposites were synthesized using a sol-gel technique having different molar ratios of Ti:V (10:10, 10:15, and 10:20). The phase composition and the morphology have been studied using X-ray diffraction and field emission scanning electron microscope, respectively. The impedance spectroscopy studies of the three samples over a wide range of temperature (50 K-300 K) have been extensively described using the internal barrier layer capacitor model. It is based on the contribution of domain and domain boundary, relaxations of the materials, which are the main crucial factors for the enhancement of the dielectric response. The frequency dependent ac conductivity of the ceramics strongly obeys the well-known Jonscher's power law, and it has been clearly explained using the theory of jump relaxation model. The temperature dependent bulk conductivity is fairly recognized to the variable-range hopping of localized polarons. The co-existence of mixed valence state of Ti ions (Ti3+ and Ti4+) in the sample significantly contributes to the change of dielectric property. The overall study of dielectric response explains that the dielectric constant and the dielectric loss are strongly dependent on temperature and frequency and decrease with an increase of frequency as well as temperature.

Pressure dependence of conductivity

International Nuclear Information System (INIS)

Bracewell, B.L.; Hochheimer, H.D.

1993-01-01

The overall objectives of this work were to attempt the following: (1) Measure the pressure dependence of the electrical conductivity of several quasi-one-dimensional, charge-density-wave solids, including measurements along various crystal directions. (2) Measure photocurrents in selected MX solids at ambient and elevated pressures. (3) Measure the resonance Raman spectra for selected MX solids as a function of pressure

Nitric oxide donors enhance the frequency dependence of dopamine release in nucleus accumbens.

Science.gov (United States)

Hartung, Henrike; Threlfell, Sarah; Cragg, Stephanie J

2011-08-01

Dopamine (DA) neurotransmission in the nucleus accumbens (NAc) is critically involved in normal as well as maladaptive motivated behaviors 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 the frequency of presynaptic activation. We detected DA with cyclic voltammetry at carbon-fiber microelectrodes in mouse NAc in slices following stimuli spanning a full range of DA neuron firing frequencies (1-100 Hz). NO donors 3-morpholinosydnonimine hydrochloride (SIN-1) or z-1-[N-(3-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate (PAPA/NONOate) enhanced DA release with increasing stimulus frequency. This NO-mediated enhancement of frequency sensitivity of DA release was not prevented by inhibition of soluble guanylyl cyclase (sGC), DA transporters, or large conductance Ca(2+)-activated K(+) channels, and did not require glutamatergic or GABAergic input. However, experiments to identify whether frequency-dependent NO effects were mediated via changes in powerful acetylcholine-DA interactions revealed multiple components to NO modulation of DA release. In the presence of a nicotinic receptor antagonist (dihydro-β-erythroidine), NO donors increased DA release in a frequency-independent manner. These data suggest that NO in the NAc can modulate DA release through multiple GC-independent neuronal mechanisms whose net outcome varies depending on the activity in DA neurons and accumbal cholinergic interneurons. In the presence of accumbal acetylcholine, NO promotes the sensitivity of DA release to presynaptic activation, but with reduced acetylcholine input, NO will promote DA release in an activity-independent manner through a direct action on dopaminergic terminals.

Frequency-dependent changes in amplitude of low-frequency oscillations in depression: A resting-state fMRI study.

Science.gov (United States)

Wang, Li; Kong, Qingmei; Li, Ke; Su, Yunai; Zeng, Yawei; Zhang, Qinge; Dai, Wenji; Xia, Mingrui; Wang, Gang; Jin, Zhen; Yu, Xin; Si, Tianmei

2016-02-12

We conducted this fMRI study to examine whether the alterations in amplitudes of low-frequency oscillation (LFO) of major depressive disorder (MDD) patients were frequency dependent. The LFO amplitudes (as indexed by amplitude of low-frequency fluctuation [ALFF] and fractional ALFF [fALFF]) within 4 narrowly-defined frequency bands (slow-5: 0.01-0.027Hz, slow-4: 0.027-0.073Hz, slow-3: 0.073-0.198Hz, and slow-2: 0.198-0.25Hz) were computed using resting-state fMRI data of 35 MDD patients and 32 healthy subjects. Repeated-measures analysis of variance (ANOVA) was performed on ALFF and fALFF both within the low frequency bands of slow-4 and slow-5 and within all of the four bands. We observed significant main effects of group and frequency on ALFF and fALFF in widely distributed brain regions. Importantly, significant group and frequency interaction effects were observed in the ventromedial prefrontal cortex, inferior frontal gyrus, precentral gyrus, in a left-sided fashion, the bilateral posterior cingulate and precuneus, during ANOVA both within slow-4 and slow-5 bands and within all the frequency bands. The results suggest that the alterations of LFO amplitudes in specific brain regions in MDD patients could be more sensitively detected in the slow-5 rather than the slow-4 bands. The findings may provide guidance for the frequency choice of future resting-state fMRI studies of MDD. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Numerical Study of Frequency-dependent Seismoelectric Coupling in Partially-saturated Porous Media

Directory of Open Access Journals (Sweden)

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.

Temperature dependent electronic conduction in semiconductors

International Nuclear Information System (INIS)

Roberts, G.G.; Munn, R.W.

1980-01-01

This review describes the temperature dependence of bulk-controlled electronic currents in semiconductors. The scope of the article is wide in that it contrasts conduction mechanisms in inorganic and organic solids and also single crystal and disordered semiconductors. In many experimental situations it is the metal-semiconductor contact or the interface between two dissimilar semiconductors that governs the temperature dependence of the conductivity. However, in order to keep the length of the review within reasonable bounds, these topics have been largely avoided and emphasis is therefore placed on bulk-limited currents. A central feature of electronic conduction in semiconductors is the concentrations of mobile electrons and holes that contribute to the conductivity. Various statistical approaches may be used to calculate these densities which are normally strongly temperature dependent. Section 1 emphasizes the relationship between the position of the Fermi level, the distribution of quantum states, the total number of electrons available and the absolute temperature of the system. The inclusion of experimental data for several materials is designed to assist the experimentalist in his interpretation of activation energy curves. Sections 2 and 3 refer to electronic conduction in disordered solids and molecular crystals, respectively. In these cases alternative approaches to the conventional band theory approach must be considered. For example, the velocities of the charge carriers are usually substantially lower than those in conventional inorganic single crystal semiconductors, thus introducing the possibility of an activated mobility. Some general electronic properties of these materials are given in the introduction to each of these sections and these help to set the conduction mechanisms in context. (orig.)

Velocity form of the Kohn-Sham frequency-dependent polarizability equations

International Nuclear Information System (INIS)

Bartolotti, L.J.

1987-01-01

A single equation is derived for the determination of the first-order correction to the frequency-dependent density, due to the perturbation of a time-varying electric field. This new expression for the first-order correction to the frequency-dependent Kohn-Sham amplitudes depends explicitly upon the velocity form of the dipole-moment operator and the square of the Kohn-Sham Hamiltonian

Inhibition of large conductance calcium-dependent potassium ...

African Journals Online (AJOL)

conductance, calcium and voltage- dependent potassium (BKCa) channels thereby promoting vasoconstriction. Our results show that the Rho-kinase inhibitor, Y-27632, induced concentration-dependent relaxation in rat mesenteric artery.

Frequency-dependent glycinergic inhibition modulates plasticity in hippocampus.

Science.gov (United States)

Keck, Tara; Lillis, Kyle P; Zhou, Yu-Dong; White, John A

2008-07-16

Previous studies have demonstrated the presence of functional glycine receptors (GlyRs) in hippocampus. In this work, we examine the baseline activity and activity-dependent modulation of GlyRs in region CA1. We find that strychnine-sensitive GlyRs are open in the resting CA1 pyramidal cell, creating a state of tonic inhibition that "shunts" the magnitude of EPSPs evoked by electrical stimulation of the Schaffer collateral inputs. This GlyR-mediated shunting conductance is independent of the presynaptic stimulation rate; however, pairs of presynaptic and postsynaptic action potentials, repeated at frequencies above 5 Hz, reduce the GlyR-mediated conductance and increase peak EPSP magnitudes to levels at least 20% larger than those seen with presynaptic stimulation alone. We refer to this phenomenon as rate-dependent efficacy (RDE). Exogenous GlyR agonists (glycine, taurine) block RDE by preventing the closure of postsynaptic GlyRs. The GlyR antagonist strychnine blocks postsynaptic GlyRs under all conditions, occluding RDE. During RDE, GlyRs are less responsive to local glycine application, suggesting that a reduction in the number or sensitivity of membrane-inserted GlyRs underlies RDE. By extending the RDE induction protocol to include 500 paired presynaptic and postsynaptic spikes, we can induce long-term synaptic depression (LTD). Manipulations that lead to reduced functionality of GlyRs, either pharmacologically or through RDE, also lead to increased LTD. This result suggests that RDE contributes to long-term synaptic plasticity in the hippocampus.

Radio frequency self-resonant coil for contactless AC-conductivity in 100 T class ultra-strong pulse magnetic fields

Science.gov (United States)

Nakamura, D.; Altarawneh, M. M.; Takeyama, S.

2018-03-01

A contactless measurement system of electrical conductivity was developed for application under pulsed high magnetic fields over 100 T by using a self-resonant-type, high-frequency circuit. Electromagnetic fields in the circuit were numerically analysed by the finite element method, to show how the resonant power spectra of the circuit depends on the electrical conductivity of a sample set on the probe-coil. The performance was examined using a high-temperature cuprate superconductor, La2-x Sr x CuO4, in magnetic fields up to 102 T with a high frequency of close to 800 MHz. As a result, the upper critical field could be determined with a good signal-to-noise ratio.

Quantitative interpretation of the magnetic susceptibility frequency dependence

Science.gov (United States)

Ustra, Andrea; Mendonça, Carlos A.; Leite, Aruã; Jovane, Luigi; Trindade, Ricardo I. F.

2018-05-01

Low-field mass-specific magnetic susceptibility (MS) measurements using multifrequency alternating fields are commonly used to evaluate concentration of ferrimagnetic particles in the transition of superparamagnetic (SP) to stable single domain (SSD). In classical palaeomagnetic analyses, this measurement serves as a preliminary assessment of rock samples providing rapid, non-destructive, economical and easy information of magnetic properties. The SP-SSD transition is relevant in environmental studies because it has been associated with several geological and biogeochemical processes affecting magnetic mineralogy. MS is a complex function of mineral-type and grain-size distribution, as well as measuring parameters such as external field magnitude and frequency. In this work, we propose a new technique to obtain quantitative information on grain-size variations of magnetic particles in the SP-SSD transition by inverting frequency-dependent susceptibility. We introduce a descriptive parameter named as `limiting frequency effect' that provides an accurate estimation of MS loss with frequency. Numerical simulations show the methodology capability in providing data fitting and model parameters in many practical situations. Real-data applications with magnetite nanoparticles and core samples from sediments of Poggio le Guaine section of Umbria-Marche Basin (Italy) provide additional information not clearly recognized when interpreting cruder MS data. Caution is needed when interpreting frequency dependence in terms of single relaxation processes, which are not universally applicable and depend upon the nature of magnetic mineral in the material. Nevertheless, the proposed technique is a promising tool for SP-SSD content analyses.

Radio frequency and capacitive sensors for dielectric characterization of low-conductivity media

Science.gov (United States)

Sheldon, Robert T.

Low-conductivity media are found in a vast number of applications, for example as electrical insulation or as the matrix polymer in high strength-to-weight ratio structural composites. In some applications, these materials are subjected to extreme environmental, thermal, and mechanical conditions that can affect the material's desired performance. In a more general sense, a medium may be comprised of one or more layers with unknown material properties that may affect the desired performance of the entire structure. It is often, therefore, of great import to be able to characterize the material properties of these media for the purpose of estimating their future performance in a certain application. Low-conductivity media, or dielectrics, are poor electrical conductors and permit electromagnetic waves and static electric fields to pass through with minimal attenuation. The amount of electrical energy that may be stored (and lost) in these fields depends directly upon the material property, permittivity, which is generally complex, frequency-dependent and has a measurable effect on sensors designed to characterize dielectric media. In this work, two different types of dielectric sensors: radio frequency resonant antennas and lower-frequency (work, the capability of characterizing multilayer dielectric structures is studied using a patch antenna, a type of antenna that is primarily designed for data communications in the microwave bands but has application in the field of nondestructive evaluation as well. Each configuration of a patch antenna has a single lowest resonant (dominant mode) frequency that is dependent upon the antenna's substrate material and geometry as well as the permittivity and geometry of exterior materials. Here, an extant forward model is validated using well-characterized microwave samples and a new method of resonant frequency and quality factor determination from measured data is presented. Excellent agreement between calculated and measured

Frequency dependence of polarization phase difference

International Nuclear Information System (INIS)

Rao, K.S.; Rao, Y.S.; Wang, J.R.

1993-09-01

Polarimetric AIRSAR data of July 13, 1990 acquired over Mahatango watershed area was processed for the identification of corn fields an forested areas. Polarization Phase Difference (PPD) values were computed for the corn fields at P-, L- and C- bands and studied as a function of frequency. The results compare well with the model calculations at 24 deg. incidence angle where as the locations of corn fields were computed to be at 35 deg. incidence angle. The discrepancy is attributed to lack of accurate ground truth and the undulating topography of the corn fields. Another study reported here deals with the usefulness of Polarization Index (PI) for the study of vegetation. PI was found to be dependent on frequency for corn fields where as for forest trees no such dependence was noticed. PI HH,HV is more useful parameter compared to PI HH,VV even for the study of corn fields. (author). 19 refs, 7 figs

Influence of frequency of the excitation magnetic field and material's electric conductivity on domain wall dynamics in ferromagnetic materials

International Nuclear Information System (INIS)

Chávez-González, A.F.; Pérez-Benítez, J.A.; Espina-Hernández, J.H.; Grössinger, R.; Hallen, J.M.

2016-01-01

The present work analyzes the influence of electric conductivity on the Magnetic Barkhausen Noise (MBN) signal using a microscopic model which includes the influence of eddy currents. This model is also implemented to explain the dependence of MBN on the frequency of the applied magnetic field. The results presented in this work allow analyzing the influence of eddy currents on MBN signals for different values of the material's electric conductivity and for different frequencies of applied magnetic field. Additionally, the outcomes of this research can be used as a reference to differentiate the influence of eddy currents from that of second phase particles in the MBN signal, which has been reported in previous works. - Highlights: • Electromagnetic simulation of MBN with eddy currents and micro-magnetism. • Influence of applied field frequency on MBN is explained. • Influence of electric conductivity on MBN is analyzed. • Hysteresis losses in ferromagnetic materials is analyzed using the model.

Low frequency ac conduction and dielectric relaxation in poly(N ...

Indian Academy of Sciences (India)

The ac conductivity and dielectric constant of poly(N-methyl pyrrole) thin films have been investigated in the temperature range 77–350 K and in the frequency range 102–106 Hz. The well defined loss peaks have been observed in the temperature region where measured ac conductivity approaches dc conductivity.

Frequency-dependent ultrasound-induced transformation in E. coli.

Science.gov (United States)

Deeks, Jeremy; Windmill, James; Agbeze-Onuma, Maduka; Kalin, Robert M; Argondizza, Peter; Knapp, Charles W

2014-12-01

Ultrasound-enhanced gene transfer (UEGT) is continuing to gain interest across many disciplines; however, very few studies investigate UEGT efficiency across a range of frequencies. Using a variable frequency generator, UEGT was tested in E. coli at six ultrasonic frequencies. Results indicate frequency can significantly influence UEGT efficiency positively and negatively. A frequency of 61 kHz improved UEGT efficiency by ~70 % higher, but 99 kHz impeded UEGT to an extent worse than no ultrasound exposure. The other four frequencies (26, 133, 174, and 190 kHz) enhanced transformation compared to no ultrasound, but efficiencies did not vary. The influence of frequency on UEGT efficiency was observed across a range of operating frequencies. It is plausible that frequency-dependent dynamics of mechanical and chemical energies released during cavitational-bubble collapse (CBC) are responsible for observed UEGT efficiencies.

Action Potential Broadening in Capsaicin-Sensitive DRG Neurons from Frequency-Dependent Reduction of Kv3 Current.

Science.gov (United States)

Liu, Pin W; Blair, Nathaniel T; Bean, Bruce P

2017-10-04

Action potential (AP) shape is a key determinant of cellular electrophysiological behavior. We found that in small-diameter, capsaicin-sensitive dorsal root ganglia neurons corresponding to nociceptors (from rats of either sex), stimulation at frequencies as low as 1 Hz produced progressive broadening of the APs. Stimulation at 10 Hz for 3 s resulted in an increase in AP width by an average of 76 ± 7% at 22°C and by 38 ± 3% at 35°C. AP clamp experiments showed that spike broadening results from frequency-dependent reduction of potassium current during spike repolarization. The major current responsible for frequency-dependent reduction of overall spike-repolarizing potassium current was identified as Kv3 current by its sensitivity to low concentrations of 4-aminopyridine (IC 50 action potentials of small-diameter rat DRG neurons showed spike broadening at frequencies as low as 1 Hz and that spike broadening resulted predominantly from frequency-dependent inactivation of Kv3 channels. Spike width helps to control transmitter release, conduction velocity, and firing patterns and understanding the role of particular potassium channels can help to guide new pharmacological strategies for targeting pain-sensing neurons selectively. Copyright © 2017 the authors 0270-6474/17/379705-10$15.00/0.

Frequency-dependent micromechanics of cellularized biopolymer networks

Science.gov (United States)

Jones, Chris; Kim, Jihan; McIntyre, David; Sun, Bo

Mechanical interactions between cells and the extracellular matrix (ECM) influence many cellular behaviors such as growth, differentiation, and migration. These are dynamic processes in which the cells actively remodel the ECM. Reconstituted collagen gel is a common model ECM for studying cell-ECM interactions in vitro because collagen is the most abundant component of mammalian ECM and gives the ECM its material stiffness. We embed micron-sized particles in collagen and use holographic optical tweezers to apply forces to the particles in multiple directions and over a range of frequencies up to 10 Hz. We calculate the local compliance and show that it is dependent on both the direction and frequency of the applied force. Performing the same measurement on many particles allows us to characterize the spatial inhomogeneity of the mechanical properties and shows that the compliance decreases at higher frequencies. Performing these measurements on cell-populated collagen gels shows that cellular remodeling of the ECM changes the mechanical properties of the collagen and we investigate whether this change is dependent on the local strain and distance from nearby cells.

Conductance of single-atom platinum contacts: Voltage dependence of the conductance histogram

DEFF Research Database (Denmark)

Nielsen, S.K.; Noat, Y.; Brandbyge, Mads

2003-01-01

The conductance of a single-atom contact is sensitive to the coupling of this contact atom to the atoms in the leads. Notably for the transition metals this gives rise to a considerable spread in the observed conductance values. The mean conductance value and spread can be obtained from the first...... peak in conductance histograms recorded from a large set of contact-breaking cycles. In contrast to the monovalent metals, this mean value for Pt depends strongly on the applied voltage bias and other experimental conditions and values ranging from about 1 G(0) to 2.5 G(0) (G(0)=2e(2)/h) have been...... reported. We find that at low bias the first peak in the conductance histogram is centered around 1.5 G(0). However, as the bias increases past 300 mV the peak shifts to 1.8 G(0). Here we show that this bias dependence is due to a geometric effect where monatomic chains are replaced by single-atom contacts...

Frequency-dependent electrodeformation of giant phospholipid vesicles in AC electric field

Science.gov (United States)

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 modeled 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 kilohertz 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 alternating current 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 microliter samples is discussed. PMID:21886342

Comment on “Frequency-dependent dispersion in porous media”

KAUST Repository

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.

Frequency dependence of p-mode frequency shifts induced by magnetic activity in Kepler solar-like stars

Science.gov (United States)

Salabert, D.; Régulo, C.; Pérez Hernández, F.; García, R. A.

2018-04-01

The variations of the frequencies of the low-degree acoustic oscillations in the Sun induced by magnetic activity show a dependence on radial order. The frequency shifts are observed to increase towards higher-order modes to reach a maximum of about 0.8 μHz over the 11-yr solar cycle. A comparable frequency dependence is also measured in two other main sequence solar-like stars, the F-star HD 49933, and the young 1 Gyr-old solar analog KIC 10644253, although with different amplitudes of the shifts of about 2 μHz and 0.5 μHz, respectively. Our objective here is to extend this analysis to stars with different masses, metallicities, and evolutionary stages. From an initial set of 87 Kepler solar-like oscillating stars with known individual p-mode frequencies, we identify five stars showing frequency shifts that can be considered reliable using selection criteria based on Monte Carlo simulations and on the photospheric magnetic activity proxy Sph. The frequency dependence of the frequency shifts of four of these stars could be measured for the l = 0 and l = 1 modes individually. Given the quality of the data, the results could indicate that a physical source of perturbation different from that in the Sun is dominating in this sample of solar-like stars.

Variation in female morph frequencies and mating frequencies : random, frequency-dependent harassment or male mimicry?

NARCIS (Netherlands)

Hammers, Martijn; Van Gossum, Hans

2008-01-01

Female-limited colour polymorphisms occur in a variety of species, where often one female morph (androchrome) resembles the body coloration of the conspecific male, whereas the other (gynochrome) does not. We tested predictions of two frequency-dependent hypotheses that are commonly invoked to

High frequency conductivity of hot electrons in carbon nanotubes

Energy Technology Data Exchange (ETDEWEB)

Amekpewu, M., E-mail: mamek219@gmail.com [Department of Applied Physics, University for Development Studies, Navrongo (Ghana); Mensah, S.Y. [Department of Physics, College of Agriculture and Natural Sciences, U.C.C. (Ghana); Musah, R. [Department of Applied Physics, University for Development Studies, Navrongo (Ghana); Mensah, N.G. [Department of Mathematics, College of Agriculture and Natural Sciences, U.C.C. (Ghana); Abukari, S.S.; Dompreh, K.A. [Department of Physics, College of Agriculture and Natural Sciences, U.C.C. (Ghana)

2016-05-01

High frequency conductivity of hot electrons in undoped single walled achiral Carbon Nanotubes (CNTs) under the influence of ac–dc driven fields was considered. We investigated semi-classically Boltzmann's transport equation with and without the presence of the hot electrons’ source by deriving the current densities in CNTs. Plots of the normalized current density versus frequency of ac-field revealed an increase in both the minimum and maximum peaks of normalized current density at lower frequencies as a result of a strong injection of hot electrons. The applied ac-field plays a twofold role of suppressing the space-charge instability in CNTs and simultaneously pumping an energy for lower frequency generation and amplification of THz radiations. These have enormous promising applications in very different areas of science and technology.

Spatial-frequency dependent binocular imbalance in amblyopia.

Science.gov (United States)

Kwon, MiYoung; Wiecek, Emily; Dakin, Steven C; Bex, Peter J

2015-11-25

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 imbalance may be useful for diagnosing amblyopia and as an outcome measure for recovery of binocular vision following therapy.

High frequency characterization of conductive inks embedded within a structural composite

Science.gov (United States)

Pa, Peter; McCauley, Raymond; Larimore, Zachary; Mills, Matthew; Yarlaggada, Shridhar; Mirotznik, Mark S.

2015-06-01

Woven fabric composites provide an attractive platform for integrating electromagnetic functionality—such as conformal load-bearing antennas and frequency selective surfaces—into a structural platform. One practical fabrication method for integrating conductive elements within a woven fabric composite system involves using additive manufacturing systems such as screen printing. While screen printing is an inherently scalable, flexible and cost effective method, little is known about the high frequency electrical properties of its conductive inks when they are embedded within the woven fabric composite. Thus, we have completed numerical and experimental studies to determine the electrical conductivity of screen printable conductive inks that are embedded within this composite. We have also performed mechanical studies to evaluate how printing affects the structural performance of the composite.

Low frequency complex dielectric (conductivity) response of dilute clay suspensions: Modeling and experiments.

Science.gov (United States)

Hou, Chang-Yu; Feng, Ling; Seleznev, Nikita; Freed, Denise E

2018-04-11

In this work, we establish an effective medium model to describe the low-frequency complex dielectric (conductivity) dispersion of dilute clay suspensions. We use previously obtained low-frequency polarization coefficients for a charged oblate spheroidal particle immersed in an electrolyte as the building block for the Maxwell Garnett mixing formula to model the dilute clay suspension. The complex conductivity phase dispersion exhibits a near-resonance peak when the clay grains have a narrow size distribution. The peak frequency is associated with the size distribution as well as the shape of clay grains and is often referred to as the characteristic frequency. In contrast, if the size of the clay grains has a broad distribution, the phase peak is broadened and can disappear into the background of the canonical phase response of the brine. To benchmark our model, the low-frequency dispersion of the complex conductivity of dilute clay suspensions is measured using a four-point impedance measurement, which can be reliably calibrated in the frequency range between 0.1 Hz and 10 kHz. By using a minimal number of fitting parameters when reliable information is available as input for the model and carefully examining the issue of potential over-fitting, we found that our model can be used to fit the measured dispersion of the complex conductivity with reasonable parameters. The good match between the modeled and experimental complex conductivity dispersion allows us to argue that our simplified model captures the essential physics for describing the low-frequency dispersion of the complex conductivity of dilute clay suspensions. Copyright © 2018 Elsevier Inc. All rights reserved.

Temperature-dependent of Nonlinear Optical Conductance of Graphene-based Systems in High-intensity Terahertz Field

Institute of Scientific and Technical Information of China (English)

Jing Lv; Rui-yang Yuan; Hui Yan

2014-01-01

For multi-photon processed with the linear dispersion in the high-intensity terahertz(THz) field,we have systematically investigated the temperature-dependent nonlinear optical response of graphene-based systems, including single layer graphene, graphene superlattice and gapped graphene. In the intrinsic single layer graphene system, it demonstrates that, at low temperature, nonlinear optical conductivities of the thirdand fifth-order are respectively five and ten orders of magnitude larger than the universal conductivity with high-intensity and low frequency THz wave.In the graphene superlattice and gapped graphene systems, the optical responses enhanced because of the anisotropic massless and massive Dirac fermions.

Characterization of frequency-dependent glass transition temperature by Vogel-Fulcher relationship

International Nuclear Information System (INIS)

Bai Yu; Jin Li

2008-01-01

The complex mechanical modulus of polymer and polymer based composite materials showed a frequency-dependent behaviour during glass transition relaxation, which was historically modelled by the Arrhenius equation. However, this might not be true in a broad frequency domain based on the experience from the frequency dependence of the complex dielectric permittivity, which resulted from the same glass transition relaxation as for the complex mechanical modulus. Considering a good correspondence between dielectric and mechanical relaxation during glass transition, the Vogel-Fulcher relationship, previously proposed for the frequency dependence of dielectric permittivity, is introduced for that of the mechanical modulus; and the corresponding static glass transition temperature (T f ) was first determined for polymer and polymer based composite materials. (fast track communication)

High resolution electromagnetic methods and low frequency dispersion of rock conductivity

OpenAIRE

Svetov, B. S.; Ageev, V. V.

1999-01-01

The influence of frequency dispersion of conductivity (induced polarization) of rocks on the results of electromagnetic (EM) sounding was studied on the basis of calculation of electric field of vertical magnetic dipole above horizontally layered polarizable sections. Frequency dispersion was approximated by the Debye formula. Polarizable homogeneous halfspace, two, three and multilayered sections were analyzed in frequency and time domains. The calculations for different values of chargeabil...

Pronounced low-frequency vibrational thermal transport in C60 fullerite realized through pressure-dependent molecular dynamics simulations

Science.gov (United States)

Giri, Ashutosh; Hopkins, Patrick E.

2017-12-01

Fullerene condensed-matter solids can possess thermal conductivities below their minimum glassy limit while theorized to be stiffer than diamond when crystallized under pressure. These seemingly disparate extremes in thermal and mechanical properties raise questions into the pressure dependence on the thermal conductivity of C60 fullerite crystals, and how the spectral contributions to vibrational thermal conductivity changes under applied pressure. To answer these questions, we investigate the effect of strain on the thermal conductivity of C60 fullerite crystals via pressure-dependent molecular dynamics simulations under the Green-Kubo formalism. We show that the thermal conductivity increases rapidly with compressive strain, which demonstrates a power-law relationship similar to their stress-strain relationship for the C60 crystals. Calculations of the density of states for the crystals under compressive strains reveal that the librational modes characteristic in the unstrained case are diminished due to densification of the molecular crystal. Over a large compression range (0-20 GPa), the Leibfried-Schlömann equation is shown to adequately describe the pressure dependence of thermal conductivity, suggesting that low-frequency intermolecular vibrations dictate heat flow in the C60 crystals. A spectral decomposition of the thermal conductivity supports this hypothesis.

Time-domain analysis of frequency dependent inertial wave forces on cylinders

DEFF Research Database (Denmark)

Krenk, Steen

2013-01-01

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......-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...... the reduction of the resonant part of the response for natural structural frequencies above the dominating wave frequency....

Frequency dependence of the active impedance component of silicon thin-film resistors

International Nuclear Information System (INIS)

Belogurov, S.V.; Gostilo, V.V.; Yurov, A.S.

1987-01-01

A high-resistant resistor on the silicon thin-film substrate considerably superior in noise and frequency performance than commercial resistors is described. The frequency dependence of the active impedance component is tested for determining noise and frequency dependences of silicon thin-film resistors. The obtained results permit to calculate the energy equivalent of resistor noise in nuclear radiation detection units at any temperature according to its frequency characteristic at room temperature

Software Toolbox for Low-Frequency Conductivity and Current Density Imaging Using MRI.

Science.gov (United States)

Sajib, Saurav Z K; Katoch, Nitish; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

2017-11-01

Low-frequency conductivity and current density imaging using MRI includes magnetic resonance electrical impedance tomography (MREIT), diffusion tensor MREIT (DT-MREIT), conductivity tensor imaging (CTI), and magnetic resonance current density imaging (MRCDI). MRCDI and MREIT provide current density and isotropic conductivity images, respectively, using current-injection phase MRI techniques. DT-MREIT produces anisotropic conductivity tensor images by incorporating diffusion weighted MRI into MREIT. These current-injection techniques are finding clinical applications in diagnostic imaging and also in transcranial direct current stimulation (tDCS), deep brain stimulation (DBS), and electroporation where treatment currents can function as imaging currents. To avoid adverse effects of nerve and muscle stimulations due to injected currents, conductivity tensor imaging (CTI) utilizes B1 mapping and multi-b diffusion weighted MRI to produce low-frequency anisotropic conductivity tensor images without injecting current. This paper describes numerical implementations of several key mathematical functions for conductivity and current density image reconstructions in MRCDI, MREIT, DT-MREIT, and CTI. To facilitate experimental studies of clinical applications, we developed a software toolbox for these low-frequency conductivity and current density imaging methods. This MR-based conductivity imaging (MRCI) toolbox includes 11 toolbox functions which can be used in the MATLAB environment. The MRCI toolbox is available at http://iirc.khu.ac.kr/software.html . Its functions were tested by using several experimental datasets, which are provided together with the toolbox. Users of the toolbox can focus on experimental designs and interpretations of reconstructed images instead of developing their own image reconstruction softwares. We expect more toolbox functions to be added from future research outcomes. Low-frequency conductivity and current density imaging using MRI includes

Temperature dependence of the resonance frequency of thermogravimetric devices

NARCIS (Netherlands)

Iervolino, E.; Riccio, M.; Van Herwaarden, A.W.; Irace, A.; Breglio, G.; Van der Vlist, W.; Sarro, P.M.

2010-01-01

This paper investigates the temperature dependence of the resonance frequency of thermogravimetric (TG) devices for tip heating over the temperature range of View the MathML source 25–600?C. The resonance frequency of a fabricated TG device shows to be temperature independent for tip heating up to

AC conductivity and dielectric behavior of bulk Furfurylidenemalononitrile

Science.gov (United States)

El-Nahass, M. M.; Ali, H. A. M.

2012-06-01

AC conductivity and dielectric behavior for bulk Furfurylidenemalononitrile have been studied over a temperature range (293-333 K) and frequency range (50-5×106 Hz). The frequency dependence of ac conductivity, σac, has been investigated by the universal power law, σac(ω)=Aωs. The variation of the frequency exponent (s) with temperature was analyzed in terms of different conduction mechanisms, and it was found that the correlated barrier hopping (CBH) model is the predominant conduction mechanism. The temperature dependence of σac(ω) showed a linear increase with the increase in temperature at different frequencies. The ac activation energy was determined at different frequencies. Dielectric data were analyzed using complex permittivity and complex electric modulus for bulk Furfurylidenemalononitrile at various temperatures.

Temperature and frequency response of conductivity in Ag2S doped chalcogenide glassy semiconductor

Science.gov (United States)

Ojha, Swarupa; Das, Anindya Sundar; Roy, Madhab; Bhattacharya, Sanjib

2018-06-01

The electric conductivity of chalcogenide glassy semiconductor xAg2S-(1-x)(0.5S-0.5Te) has been presented here as a function of temperature and frequency. Formation of different nanocrystallites has been confirmed from X-ray diffraction study. It is also noteworthy that average size of nanocrystallites decreases with the increase of dislocation density. Dc conductivity data have been interpreted using Mott's model and Greaves's model in low and high temperature regions respectively. Ac conductivity above the room temperature has been analyzed using Meyer-Neldel (MN) conduction rule. It is interestingly noted that Correlated Barrier Hopping (CBH) model is the most appropriate conduction mechanism for x = 0.35, where pairs of charge carrier are considered to hop over the potential barrier between the sites via thermal activation. To interpret experimental data for x = 0.45, modified non-overlapping small polaron tunnelling (NSPT) model is supposed to be appropriate model due to tunnelling through grain boundary. The conductivity spectra at various temperatures have been analyzed using Almond-West Formalism (power law model). Scaling of conductivity spectra reveals that electrical relaxation process of charge carriers (polaron) is temperature independent but depends upon the composition of the present chalcogenide glassy system.

Influence of frequency of the excitation magnetic field and material's electric conductivity on domain wall dynamics in ferromagnetic materials

Energy Technology Data Exchange (ETDEWEB)

Chávez-González, A.F. [Laboratorio de Evaluación No Destructiva Electromagnética (LENDE), ESIME-SEPI, Edif. Z-4, Instituto Politécnico Nacional, Zacatenco, México D.F., México (Mexico); Pérez-Benítez, J.A., E-mail: benitez_edl@yahoo.es [Laboratorio de Evaluación No Destructiva Electromagnética (LENDE), ESIME-SEPI, Edif. Z-4, Instituto Politécnico Nacional, Zacatenco, México D.F., México (Mexico); Espina-Hernández, J.H. [Laboratorio de Evaluación No Destructiva Electromagnética (LENDE), ESIME-SEPI, Edif. Z-4, Instituto Politécnico Nacional, Zacatenco, México D.F., México (Mexico); Grössinger, R. [Institute of Solid State Physics, Vienna University of Technology, Vienna (Austria); Hallen, J.M. [Departamento de Ingeniería Metalúrgica, ESIQIE, UPALM Edif. 7, Instituto Politécnico Nacional, Zacatenco, C.P. 07738, México D.F., México (Mexico)

2016-03-01

The present work analyzes the influence of electric conductivity on the Magnetic Barkhausen Noise (MBN) signal using a microscopic model which includes the influence of eddy currents. This model is also implemented to explain the dependence of MBN on the frequency of the applied magnetic field. The results presented in this work allow analyzing the influence of eddy currents on MBN signals for different values of the material's electric conductivity and for different frequencies of applied magnetic field. Additionally, the outcomes of this research can be used as a reference to differentiate the influence of eddy currents from that of second phase particles in the MBN signal, which has been reported in previous works. - Highlights: • Electromagnetic simulation of MBN with eddy currents and micro-magnetism. • Influence of applied field frequency on MBN is explained. • Influence of electric conductivity on MBN is analyzed. • Hysteresis losses in ferromagnetic materials is analyzed using the model.

Analytical determination of size-dependent natural frequencies of fully clamped rectangular microplates based on the modified couple stress theory

Energy Technology Data Exchange (ETDEWEB)

Askari, Amir R.; Tahani, Masoud [Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)

2015-05-15

This paper presents an analytical and size-dependent model for vibrational analysis of fully clamped rectangular microplates. Modified couple stress theory (MCST) and the Kirchhoff plate model are considered, and Hamilton's principle is employed to derive the size dependent equation of motion that accounts for the effect of residual stresses. The natural frequencies of the microplate are extracted analytically by extended Kantorovich method. The present findings are validated with the available results in the literature, and an excellent agreement is observed between them. In addition, a parametric study is conducted to demonstrate the significant effects of couple stress components on the natural frequencies of fully clamped microplates. The ratio of MCST natural frequencies to those obtained with classical theory depends only on the Poisson's ratio of the plate and is independent of the aspect ratio of the plate for cases with no residual stresses.

Analytical determination of size-dependent natural frequencies of fully clamped rectangular microplates based on the modified couple stress theory

International Nuclear Information System (INIS)

Askari, Amir R.; Tahani, Masoud

2015-01-01

This paper presents an analytical and size-dependent model for vibrational analysis of fully clamped rectangular microplates. Modified couple stress theory (MCST) and the Kirchhoff plate model are considered, and Hamilton's principle is employed to derive the size dependent equation of motion that accounts for the effect of residual stresses. The natural frequencies of the microplate are extracted analytically by extended Kantorovich method. The present findings are validated with the available results in the literature, and an excellent agreement is observed between them. In addition, a parametric study is conducted to demonstrate the significant effects of couple stress components on the natural frequencies of fully clamped microplates. The ratio of MCST natural frequencies to those obtained with classical theory depends only on the Poisson's ratio of the plate and is independent of the aspect ratio of the plate for cases with no residual stresses.

Reproducibility of frequency-dependent low frequency fluctuations in reaction time over time and across tasks.

Science.gov (United States)

Liu, Zan-Zan; Qu, Hui-Jie; Tian, Zhuo-Ling; Han, Meng-Jian; Fan, Yi; Ge, Lie-Zhong; Zang, Yu-Feng; Zhang, Hang

2017-01-01

Increased levels of reaction time variability (RTV) are characteristics of sustained attention deficits. The clinical significance of RTV has been widely recognized. However, the reliability of RTV measurements has not been widely studied. The present study aimed to assess the test-retest reliability of RTV conventional measurements, e.g., the standard deviation (SD), the coefficient of variation (CV), and a new measurement called the amplitude of low frequency fluctuation (ALFF) of RT. In addition, we aimed to assess differences and similarities of these measurements between different tasks. Thirty-seven healthy college students participated in 2 tasks, i.e., an Eriksen flanker task (EFT) and a simple reaction task (SRT), twice over a mean interval of 56 days. Conventional measurements of RTV including RT-SD and RT-CV were assessed first. Then the RT time series were converted into frequency domains, and RT-ALFF was further calculated for the whole frequency band (0.0023-0.167 Hz) and for a few sub-frequency bands including Slow-6 (frequency bands (Slow-3), but SRT RT-ALFF values showed slightly higher ICC values than EFT values in lower frequency bands (Slow-5 and Slow-4). 2) RT-ALFF magnitudes in each sub-frequency band were greater for the SRT than those for the EFT. 3) The RT-ALFF in the Slow-4 of the EFT was found to be correlated with the RT-ALFF in the Slow-5 of the SRT for both two visits, but no consistently significant correlation was found between the same frequency bands. These findings reveal good test-retest reliability for conventional measurements and for the RT-ALFF of RTV. The RT-ALFF presented frequency-dependent similarities across tasks. All of our results reveal the presence of different frequency structures between the two tasks, and thus the frequency-dependent characteristics of different tasks deserve more attention in future studies.

Microscopic theoretical study of frequency dependent dielectric constant of heavy fermion systems

Science.gov (United States)

Shadangi, Keshab Chandra; Rout, G. C.

2017-05-01

The dielectric polarization and the dielectric constant plays a vital role in the deciding the properties of the Heavy Fermion Systems. In the present communication we consider the periodic Anderson's Model which consists of conduction electron kinetic energy, localized f-electron kinetic energy and the hybridization between the conduction and localized electrons, besides the Coulomb correlation energy. We calculate dielectric polarization which involves two particle Green's functions which are calculated by using Zubarev's Green's function technique. Using the equations of motion of the fermion electron operators. Finally, the temperature and frequency dependent dielectric constant is calculated from the dielectric polarization function. The charge susceptibility and dielectric constant are computed numerically for different physical parameters like the position (Ef) of the f-electron level with respect to fermi level, the strength of the hybridization (V) between the conduction and localized f-electrons, Coulomb correlation potential temperature and optical phonon wave vector (q). The results will be discussed in a reference to the experimental observations of the dielectric constants.

Frequency-dependent Dispersion Measures and Implications for Pulsar Timing

Science.gov (United States)

Cordes, J. M.; Shannon, R. M.; Stinebring, D. R.

2016-01-01

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/frequency2). 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 × 10-5 pc cm-3 for pulsars at ˜1 kpc distance. The corresponding arrival-time variations are a few to hundreds of nanoseconds for DM ≲ 30 pc cm-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.

Staurosporine Inhibits Frequency-Dependent Myofilament Desensitization in Intact Rabbit Cardiac Trabeculae

Directory of Open Access Journals (Sweden)

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.

IDENTIFYING ANTHROPOGENIC METALLIC POLLUTANTS USING FREQUENCY DEPENDENT MAGNETIC SUSCEPTIBILITY MEASUREMENTS IN ABUJA METROPOLIS

Directory of Open Access Journals (Sweden)

Jatto S. Solomon

2017-07-01

Full Text Available Soil formed from lithological and weathering processes of parent rocks generally exhibit paramagnetic properties due to some minerals contained in the rocks and thus have significant value of magnetic susceptibility. This susceptibility arising from the influence of the parent rocks tend to mask anthropogenic grains pollutants released into the environment by human activities. Hence, it becomes difficult to identify the effect of the lithological and anthropogenic magnetic susceptibility in complex soil found in urban areas. The superparamagnetic effect of lithological soil, a single state domain and multi-domain state of anthropogenic grains can easily be investigated by frequency dependent measurements where readings between 0-2.0% indicates the absence of lithological influence, 2.0-8.0% indicates multi-domain grains or mixture of both single stage and multi-domian grains and 8.0-12% indicates the superparamagntic (SP grain from lithological origin. In this work frequency dependent measurements were carried out along 5 selected road networks within the 5 districts of Abuja phase 1. Measurements were also carried out in 379 random points at the surface and depth of 40.0cm to investigate the distribution of anthropogenic grains in Abuja metropolis using the Bartington susceptibility meter. Frequency dependent measurements along the selected road networks indicate0-3.0% immediately after the roads pavement to a distance of about 3.0m from the road, indicating that the magnetic susceptibility arise mostly form anthropogenic influence rather than lithological processes. At the distance of 3.0-8.0m, frequency dependent values of about 3.0-8.0% were recorded, indicating mixture of both superparamagnetic and multi-domain grains. Beyond the distance of 8.0m, the frequency dependent values are mostly above 8.0.0%, indicating virtually all SP grains. The spatial distribution frequency dependent surface map shows the presence of anthropogenic grains in

Low-frequency (0.7-7.4 mHz geomagnetic field fluctuations at high latitude: frequency dependence of the polarization pattern

Directory of Open Access Journals (Sweden)

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.

An asymptotic preserving unified gas kinetic scheme for frequency-dependent radiative transfer equations

Energy Technology Data Exchange (ETDEWEB)

Sun, Wenjun, E-mail: sun_wenjun@iapcm.ac.cn [Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Jiang, Song, E-mail: jiang@iapcm.ac.cn [Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Xu, Kun, E-mail: makxu@ust.hk [Department of Mathematics and Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Hong Kong (China); Li, Shu, E-mail: li_shu@iapcm.ac.cn [Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China)

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

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.

Length-scale dependent ensemble-averaged conductance of a 1D disordered conductor: Conductance minimum

International Nuclear Information System (INIS)

Tit, N.; Kumar, N.; Pradhan, P.

1993-07-01

Exact numerical calculation of ensemble averaged length-scale dependent conductance for the 1D Anderson model is shown to support an earlier conjecture for a conductance minimum. Numerical results can be understood in terms of the Thouless expression for the conductance and the Wigner level-spacing statistics. (author). 8 refs, 2 figs

Electronic transport coefficients in plasmas using an effective energy-dependent electron-ion collision-frequency

Science.gov (United States)

Faussurier, G.; Blancard, C.; Combis, P.; Decoster, A.; Videau, L.

2017-10-01

We present a model to calculate the electrical and thermal electronic conductivities in plasmas using the Chester-Thellung-Kubo-Greenwood approach coupled with the Kramers approximation. The divergence in photon energy at low values is eliminated using a regularization scheme with an effective energy-dependent electron-ion collision-frequency. Doing so, we interpolate smoothly between the Drude-like and the Spitzer-like regularizations. The model still satisfies the well-known sum rule over the electrical conductivity. Such kind of approximation is also naturally extended to the average-atom model. A particular attention is paid to the Lorenz number. Its nondegenerate and degenerate limits are given and the transition towards the Drude-like limit is proved in the Kramers approximation.

Anisotropy of the apparent frequency dependence of backscatter in formalin fixed human myocardium.

Science.gov (United States)

Hall, C S; Verdonk, E D; Wickline, S A; Perez, J E; Miller, J G

1997-01-01

Measurements of the frequency dependence of ultrasonic backscatter are presented for specific angles of insonification for regions of infarcted and noninfarcted human myocardium. A 5-MHz transducer was used to insonify cylindrical cores taken from 7 noninfarcted regions and 12 infarcted regions of the left ventricular free wall of 6 formalin-fixed human hearts explanted because of ischemic cardiomyopathy. The dependence of apparent (uncompensated for diffraction effects and attenuation) backscatter on frequency was approximated by a power-law dependence, magnitude of B(f)2 = afn. Under ideal conditions in a lossless medium, the effect of not compensating for the effects of diffraction and attenuation leads to the value of n to be 2.0 for Rayleigh scatterers while the frequency dependence of the fully compensated backscatter coefficient would be f4. The value of n was determined over the frequency range, 3-7 MHz. Both nonifarcted and infarcted myocardium exhibited anisotropy of the frequency dependence of backscatter, with maxima occurring at angles that were perpendicular to the predominant myofiber direction and minima when parallel to the fibers. Perpendicular insonification yielded results for n of 1.8 +/- 0.1 for noninfarcted myocardium and 1.2 +/- 0.1 for infarcted myocardium while parallel insonification yielded results of 0.4 +/- 0.1 for noninfarcted and 0.0 +/- 0.1 for infarcted myocardium. The functional form of the angle-dependent backscatter is similar for both noninfarcted and infarcted myocardium, although the frequency dependence is clearly different for both tissue states for all angles of insonification. The results of this study indicate that the anisotropy of the frequency dependence of backscatter may play a significant role in ultrasonic imaging and is an important consideration for ultrasonic tissue characterization in myocardium.

Frequency dependence of coherently amplified two-photon emission from hydrogen molecules

Science.gov (United States)

Hara, Hideaki; Miyamoto, Yuki; Hiraki, Takahiro; Masuda, Takahiko; Sasao, Noboru; Uetake, Satoshi; Yoshimi, Akihiro; Yoshimura, Koji; Yoshimura, Motohiko

2017-12-01

We investigate how the efficiency of coherently amplified two-photon emission depends on the frequency of one of the two emitted photons, namely the signal photon. This is done over the wavelength range of 5.048-10.21 μ m by using the vibrational transition of parahydrogen. The efficiency increases with the frequency of the signal photon. Considering experimental errors, our results are consistent with the theoretical prediction for the present experimental conditions. This study is an experimental demonstration of the frequency dependence of coherently amplified two-photon emission, and also presents its potential as a light source.

Low frequency ac conduction and dielectric relaxation in poly(N ...

Indian Academy of Sciences (India)

Unknown

polymer chain in the form of bands analogous to that of a semiconductor and the ... these materials a model has been proposed which suggests the application of two .... values is almost equal to dc conductivity value while in high frequency ...

In Vivo and In Silico Investigation Into Mechanisms of Frequency Dependence of Repolarization Alternans in Human Ventricular Cardiomyocytes.

Science.gov (United States)

Zhou, Xin; Bueno-Orovio, Alfonso; Orini, Michele; Hanson, Ben; Hayward, Martin; Taggart, Peter; Lambiase, Pier D; Burrage, Kevin; Rodriguez, Blanca

2016-01-22

Repolarization alternans (RA) are associated with arrhythmogenesis. Animal studies have revealed potential mechanisms, but human-focused studies are needed. RA generation and frequency dependence may be determined by cell-to-cell variability in protein expression, which is regulated by genetic and external factors. To characterize in vivo RA in human and to investigate in silico using human models, the ionic mechanisms underlying the frequency-dependent differences in RA behavior identified in vivo. In vivo electrograms were acquired at 240 sites covering the epicardium of 41 patients at 6 cycle lengths (600-350 ms). In silico investigations were conducted using a population of biophysically detailed human models incorporating variability in protein expression and calibrated using in vivo recordings. Both in silico and in vivo, 2 types of RA were identified, with Fork- and Eye-type restitution curves, based on RA persistence or disappearance, respectively, at fast pacing rates. In silico simulations show that RA are strongly correlated with fluctuations in sarcoplasmic reticulum calcium, because of strong release and weak reuptake. Large L-type calcium current conductance is responsible for RA disappearance at fast frequencies in Eye-type (30% larger in Eye-type versus Fork-type; Psilico, 2 types of RA are identified, with RA persistence/disappearance as frequency increases. In silico, L-type calcium current and Na(+)/Ca(2+) exchanger current determine RA human cell-to-cell differences through intracellular and sarcoplasmic reticulum calcium regulation. © 2015 The Authors.

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 electrostatic actuation in microfluidic MEMS.

Energy Technology Data Exchange (ETDEWEB)

Zavadil, Kevin Robert; Michalske, Terry A.; Sounart, Thomas L.

2003-09-01

Electrostatic actuators exhibit fast response times and are easily integrated into microsystems because they can be fabricated with standard IC micromachining processes and materials. Although electrostatic actuators have been used extensively in 'dry' MEMS, they have received less attention in microfluidic systems probably because of challenges such as electrolysis, anodization, and electrode polarization. Here we demonstrate that ac drive signals can be used to prevent electrode polarization, and thus enable electrostatic actuation in many liquids, at potentials low enough to avoid electrochemistry. We measure the frequency response of an interdigitated silicon comb-drive actuator in liquids spanning a decade of dielectric permittivities and four decades of conductivity, and present a simple theory that predicts the characteristic actuation frequency. The analysis demonstrates the importance of the native oxide on silicon actuator response, and suggests that the actuation frequency can be shifted by controlling the thickness of the oxide. For native silicon devices, actuation is predicted at frequencies less than 10 MHz, in electrolytes of ionic strength up to 100 mmol/L, and thus electrostatic actuation may be feasible in many bioMEMS and other microfluidic applications.

Identification of temperature-dependent thermal conductivity and experimental verification

International Nuclear Information System (INIS)

Pan, Weizhen; Yi, Fajun; Zhu, Yanwei; Meng, Songhe

2016-01-01

A modified Levenberg–Marquardt method (LMM) for the identification of temperature-dependent thermal conductivity is proposed; the experiment and structure of the specimen for identification are also designed. The temperature-dependent thermal conductivities of copper C10200 and brass C28000 are identified to verify the effectiveness of the proposed identification method. The comparison between identified results and the measured data of laser flash diffusivity apparatus indicates the fine consistency and potential usage of the proposed method. (paper)

A new rate-dependent model for high-frequency tracking performance enhancement of piezoactuator system

Science.gov (United States)

Tian, Lizhi; Xiong, Zhenhua; Wu, Jianhua; Ding, Han

2017-05-01

Feedforward-feedback control is widely used in motion control of piezoactuator systems. Due to the phase lag caused by incomplete dynamics compensation, the performance of the composite controller is greatly limited at high frequency. This paper proposes a new rate-dependent model to improve the high-frequency tracking performance by reducing dynamics compensation error. The rate-dependent model is designed as a function of the input and input variation rate to describe the input-output relationship of the residual system dynamics which mainly performs as phase lag in a wide frequency band. Then the direct inversion of the proposed rate-dependent model is used to compensate the residual system dynamics. Using the proposed rate-dependent model as feedforward term, the open loop performance can be improved significantly at medium-high frequency. Then, combining the with feedback controller, the composite controller can provide enhanced close loop performance from low frequency to high frequency. At the frequency of 1 Hz, the proposed controller presents the same performance as previous methods. However, at the frequency of 900 Hz, the tracking error is reduced to be 30.7% of the decoupled approach.

The vestibular implant: Frequency-dependency of the electrically evoked Vestibulo-Ocular Reflex in humans

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.

Assessing the utility of frequency dependent nudging for reducing biases in biogeochemical models

Science.gov (United States)

Lagman, Karl B.; Fennel, Katja; Thompson, Keith R.; Bianucci, Laura

2014-09-01

Bias errors, resulting from inaccurate boundary and forcing conditions, incorrect model parameterization, etc. are a common problem in environmental models including biogeochemical ocean models. While it is important to correct bias errors wherever possible, it is unlikely that any environmental model will ever be entirely free of such errors. Hence, methods for bias reduction are necessary. A widely used technique for online bias reduction is nudging, where simulated fields are continuously forced toward observations or a climatology. Nudging is robust and easy to implement, but suppresses high-frequency variability and introduces artificial phase shifts. As a solution to this problem Thompson et al. (2006) introduced frequency dependent nudging where nudging occurs only in prescribed frequency bands, typically centered on the mean and the annual cycle. They showed this method to be effective for eddy resolving ocean circulation models. Here we add a stability term to the previous form of frequency dependent nudging which makes the method more robust for non-linear biological models. Then we assess the utility of frequency dependent nudging for biological models by first applying the method to a simple predator-prey model and then to a 1D ocean biogeochemical model. In both cases we only nudge in two frequency bands centered on the mean and the annual cycle, and then assess how well the variability in higher frequency bands is recovered. We evaluate the effectiveness of frequency dependent nudging in comparison to conventional nudging and find significant improvements with the former.

Novel Frequency Swapping Technique for Conducted Electromagnetic Interference Suppression in Power Converter Applications

Directory of Open Access Journals (Sweden)

Ming-Tse Kuo

2016-12-01

Full Text Available Quasi-resonant flyback (QRF converters have been widely applied as the main circuit topology in power converters because of their low cost and high efficiency. Conventional QRF converters tend to generate higher average conducted electromagnetic interference (EMI in the low-frequency domain due to the switching noise generated by power switches, resulting in the fact they can exceed the EMI standards of the European Standard 55022 Class-B emission requirements. The presented paper develops a novel frequency swapping control method that spreads spectral energy to reduce the amplitude of sub-harmonics, thereby lowering average conducted EMI in the low-frequency domain. The proposed method is implemented in a control chip, which requires no extra circuit components and adds zero cost. The proposed control method is verified using a 24 W QRF converter. Experimental results reveals that conducted EMI has been reduced by approximately 13.24 dBμV at 498 kHz compared with a control method without the novel frequency swapping technique. Thus, the proposed method can effectively improve the flyback system to easily meet the CISPR 22/EN55022 standards.

Switched capacitor DC-DC converter with switch conductance modulation and Pesudo-fixed frequency control

DEFF Research Database (Denmark)

Larsen, Dennis Øland; Vinter, Martin; Jørgensen, Ivan Harald Holger

A switched capacitor dc-dc converter with frequency-planned control is presented. By splitting the output stage switches in eight segments the output voltage can be regulated with a combination of switching frequency and switch conductance. This allows for switching at predetermined frequencies, 31...

Evolutionary Graphs with Frequency Dependent Fitness

Science.gov (United States)

Nie, Pu-Yan; Zhang, Pei-Ai

Evolutionary graph theory was recently proposed by Lieberman et al. in 2005. In the previous papers about evolutionary graphs (EGs), the fitness of the residents in the EGs is in general assumed to be unity, and the fitness of a mutant is assumed to be a constant r. We aim to extend EG to general cases in this paper, namely, the fitness of a mutant is heavily dependent upon frequency. The corresponding properties for these new EGs are analyzed, and the fixation probability is obtained for large population.

Radio frequency conductivity of plasma in inhomogeneous magnetic field

International Nuclear Information System (INIS)

Itoh, Sanae; Nishikawa, Kyoji; Fukuyama, Atsushi; Itoh, Kimitaka.

1985-01-01

Nonlocal conductivity tensor is obtained to study the kinetic effects on propagation and absorption of radio frequency (rf) waves in dispersive plasmas. Generalized linear propagator in the presence of the inhomogeneity of magnetic field strength along the field line is calculated. The influence of the inhomogeneity to the rf wave-energy deposition is found to be appreciable. Application to toroidal plasmas is shown. (author)

Large-conductance calcium-dependent potassium channels prevent dendritic excitability in neocortical pyramidal neurons.

Science.gov (United States)

Benhassine, Narimane; Berger, Thomas

2009-03-01

Large-conductance calcium-dependent potassium channels (BK channels) are homogeneously distributed along the somatodendritic axis of layer 5 pyramidal neurons of the rat somatosensory cortex. The relevance of this conductance for dendritic calcium electrogenesis was studied in acute brain slices using somatodendritic patch clamp recordings and calcium imaging. BK channel activation reduces the occurrence of dendritic calcium spikes. This is reflected in an increased critical frequency of somatic spikes necessary to activate the distal initiation zone. Whilst BK channels repolarise the somatic spike, they dampen it only in the distal dendrite. Their activation reduces dendritic calcium influx via glutamate receptors. Furthermore, they prevent dendritic calcium electrogenesis and subsequent somatic burst discharges. However, the time window for coincident somatic action potential and dendritic input to elicit dendritic calcium events is not influenced by BK channels. Thus, BK channel activation in layer 5 pyramidal neurons affects cellular excitability primarily by establishing a high threshold at the distal action potential initiation zone.

Drive frequency dependent phase imaging in piezoresponse force microscopy

International Nuclear Information System (INIS)

Bo Huifeng; Kan Yi; Lu Xiaomei; Liu Yunfei; Peng Song; Wang Xiaofei; Cai Wei; Xue Ruoshi; Zhu Jinsong

2010-01-01

The drive frequency dependent piezoresponse (PR) phase signal in near-stoichiometric lithium niobate crystals is studied by piezoresponse force microscopy. It is clearly shown that the local and nonlocal electrostatic forces have a great contribution to the PR phase signal. The significant PR phase difference of the antiparallel domains are observed at the contact resonances, which is related to the electrostatic dominated electromechanical interactions of the cantilever and tip-sample system. Moreover, the modulation voltage induced frequency shift at higher eigenmodes could be attributed to the change of indention force depending on the modulation amplitude with a piezoelectric origin. The PR phase of the silicon wafer is also measured for comparison. It is certificated that the electrostatic interactions are universal in voltage modulated scanning probe microscopy and could be extended to other phase imaging techniques.

Research of Electrical Conductivity Measurement System for Mine Bursting Water Based on Dual Frequency Method

Directory of Open Access Journals (Sweden)

Zhou Mengran

2016-01-01

Full Text Available This paper presents a double frequency conductivity measurement method for measuring mine bursting water, to solve the capacitance effect of the conductivity sensor itself has the help. The core controller of the system is the single chip microcomputer ATMEGA128. This paper introduces the basic principle of the measurement of the existing problems and the dual frequency measurement method, and then introduces and analyzes the hardware. To test and analyze the collected data, the double frequency method is found to have good stability and accuracy in the measurement of the electrical conductivity of mine inrush water. It is proved that the method and the system design of the hardware circuit can accurately measure the electric conductivity of the mine inrush water source.

High-frequency conductivity of optically excited charge carriers in hydrogenated nanocrystalline silicon investigated by spectroscopic femtosecond pump–probe reflectivity measurements

Energy Technology Data Exchange (ETDEWEB)

He, Wei [University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT (United Kingdom); Yurkevich, Igor V. [Aston University, Nonlinearity and Complexity Research Group, Birmingham B4 7ET (United Kingdom); Zakar, Ammar [University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT (United Kingdom); Kaplan, Andrey, E-mail: a.kaplan.1@bham.ac.uk [University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT (United Kingdom)

2015-10-01

We report an investigation into the high-frequency conductivity of optically excited charge carriers far from equilibrium with the lattice. The investigated samples consist of hydrogenated nanocrystalline silicon films grown on a thin film of silicon oxide on top of a silicon substrate. For the investigation, we used an optical femtosecond pump–probe setup to measure the reflectance change of a probe beam. The pump beam ranged between 580 and 820 nm, whereas the probe wavelength spanned 770 to 810 nm. The pump fluence was fixed at 0.6 mJ/cm{sup 2}. We show that at a fixed delay time of 300 fs, the conductivity of the excited electron–hole plasma is described well by a classical conductivity model of a hot charge carrier gas found at Maxwell–Boltzmann distribution, while Fermi–Dirac statics is not suitable. This is corroborated by values retrieved from pump–probe reflectance measurements of the conductivity and its dependence on the excitation wavelength and carrier temperature. The conductivity decreases monotonically as a function of the excitation wavelength, as expected for a nondegenerate charge carrier gas. - Highlights: • We study high‐frequency conductivity of excited hydrogenated nanocrystalline silicon. • Reflectance change was measured as a function of pump and probe wavelength. • Maxwell–Boltzmann transport theory was used to retrieve the conductivity. • The conductivity decreases monotonically as a function of the pump wavelength.

Conduction gap in graphene strain junctions: direction dependence

International Nuclear Information System (INIS)

Nguyen, M Chung; Nguyen, V Hung; Dollfus, P; Nguyen, Huy-Viet

2014-01-01

It has been shown in a recent study (Nguyen et al 2014 Nanotechnology 25 165201) that unstrained/strained graphene junctions are promising candidates to improve the performance of graphene transistors which is usually hindered by the gapless nature of graphene. Although the energy bandgap of strained graphene still remains zero, the shift of Dirac points in the k-space due to strain-induced deformation of graphene lattice can lead to the appearance of a finite conduction gap of several hundred meV in strained junctions with a strain of only a few per cent. However, since it depends essentially on the magnitude of the Dirac point shift, this conduction gap strongly depends on the direction of applied strain and the transport direction. In this work, a systematic study of conduction-gap properties with respect to these quantities is presented and the results are carefully analyzed. Our study provides useful information for further investigations to exploit graphene-strained junctions in electronic applications and strain sensors. (paper)

Studies of frequency dependent C-V characteristics of neutron irradiated p+-n silicon detectors

International Nuclear Information System (INIS)

Li, Zheng; Kraner, H.W.

1990-10-01

Frequency-dependent capacitance-voltage fluence (C-V) characteristics of neutron irradiated high resistivity silicon p + -n detectors have been observed up to a fluence of 8.0 x 10 12 n/cm 2 . It has been found that frequency dependence of the deviation of the C-V characteristic (from its normal V -1/2 dependence), is strongly dependent on the ratio of the defect density and the effective doping density N t /N' d . As the defect density approaches the effective dopant density, or N t /N' d → 1, the junction capacitance eventually assumes the value of the detector geometry capacitance at high frequencies (f ≤ 10 5 Hz), independent of voltage. A two-trap-level model using the concept of quasi-fermi levels has been developed, which predicts both the effects of C-V frequency dependence and dopant compensation observed in this study

Ballistic heat conduction and mass disorder in one dimension

International Nuclear Information System (INIS)

Ong, Zhun-Yong; Zhang, Gang

2014-01-01

It is well-known that in the disordered harmonic chain, heat conduction is subballistic and the thermal conductivity (κ) scales asymptotically as lim L→∞ κ∝L 0.5 where L is the chain length. However, using the nonequilibrium Green's function (NEGF) method and analytical modelling, we show that there exists a critical crossover length scale (L C ) below which ballistic heat conduction (κ∝L) can coexist with mass disorder. This ballistic-to-subballistic heat conduction crossover is connected to the exponential attenuation of the phonon transmittance function Ξ i.e. Ξ(ω, L) = exp[−L/λ(ω)], where λ is the frequency-dependent attenuation length. The crossover length can be determined from the minimum attenuation length, which depends on the maximum transmitted frequency. We numerically determine the dependence of the transmittance on frequency and mass composition as well as derive a closed form estimate, which agrees closely with the numerical results. For the length-dependent thermal conductance, we also derive a closed form expression which agrees closely with numerical results and reproduces the ballistic to subballistic thermal conduction crossover. This allows us to characterize the crossover in terms of changes in the length, mass composition and temperature dependence, and also to determine the conditions under which heat conduction enters the ballistic regime. We describe how the mass composition can be modified to increase ballistic heat conduction. (paper)

Ballistic heat conduction and mass disorder in one dimension.

Science.gov (United States)

Ong, Zhun-Yong; Zhang, Gang

2014-08-20

It is well-known that in the disordered harmonic chain, heat conduction is subballistic and the thermal conductivity (κ) scales asymptotically as lim(L--> ∞) κ ∝ L(0.5) where L is the chain length. However, using the nonequilibrium Green's function (NEGF) method and analytical modelling, we show that there exists a critical crossover length scale (LC) below which ballistic heat conduction (κ ∝ L) can coexist with mass disorder. This ballistic-to-subballistic heat conduction crossover is connected to the exponential attenuation of the phonon transmittance function Ξ i.e. Ξ(ω, L) = exp[-L/λ(ω)], where λ is the frequency-dependent attenuation length. The crossover length can be determined from the minimum attenuation length, which depends on the maximum transmitted frequency. We numerically determine the dependence of the transmittance on frequency and mass composition as well as derive a closed form estimate, which agrees closely with the numerical results. For the length-dependent thermal conductance, we also derive a closed form expression which agrees closely with numerical results and reproduces the ballistic to subballistic thermal conduction crossover. This allows us to characterize the crossover in terms of changes in the length, mass composition and temperature dependence, and also to determine the conditions under which heat conduction enters the ballistic regime. We describe how the mass composition can be modified to increase ballistic heat conduction.

Structural and frequency dependencies of a.c. and dielectric ...

Indian Academy of Sciences (India)

6Thin Film Laboratory, Department of Physics, Faculty of Education, Ain Shams ... conductivity and its frequency exponents were interpreted in terms of correlated barrier hopping ... cations in high-electron-mobility and heterostructure bipolar.

Effect of Elevated Intracranial Pressure on Amplitudes and Frequency Tuning of Ocular Vestibular Evoked Myogenic Potentials Elicited by Bone-Conducted Vibration.

Science.gov (United States)

Gürkov, Robert; Speierer, Guillaume; Wittwer, Luis; Kalla, Roger

Recently, it could be demonstrated that an increased intracranial pressure causes a modulation of the air conducted sound evoked ocular vestibular evoked myogenic potential (oVEMP). The mechanism for this modulation is not resolved and may depend on a change of either receptor excitability or sound energy transmission. oVEMPs were elicited in 18 healthy subjects with a minishaker delivering 500 and 1000 Hz tone bursts, in supine and tilted positions. The study could confirm the frequency tuning of oVEMP. However, at neither stimulus frequency could a modulating effect of increased intracranial pressure be observed. These data suggest that the observed modulation of the oVEMP response by an increased intracranial pressure is primarily due to the effect of an increased intralabyrinthine pressure onto the stiffness of the inner ear contents and the middle ear-inner ear junction. Future studies on the effect of intracranial pressure on oVEMP should use air-conducted sound and not bone-conducted vibration.

Visuomotor Entrainment and the Frequency-Dependent Response of Walking Balance to Perturbations.

Science.gov (United States)

Franz, Jason R; Francis, Carrie; Allen, Matt; Thelen, Darryl G

2016-08-26

Visuomotor entrainment, or the synchronization of motor responses to visual stimuli, is a naturally emergent phenomenon in human standing. Our purpose was to investigate the prevalence and resolution of visuomotor entrainment in walking and the frequency-dependent response of walking balance to perturbations. We used a virtual reality environment to manipulate optical flow in ten healthy young adults during treadmill walking. A motion capture system recorded trunk, sacrum, and heel marker trajectories during a series of 3-min conditions in which we perturbed a virtual hallway mediolaterally with systematic changes in the driving frequencies of perceived motion. We quantified visuomotor entrainment using spectral analyses and balance deficits using trunk sway, gait variability, and detrended fluctuation analyses (DFA). ML kinematics were highly sensitive to visual perturbations, and instinctively synchronized (i.e., entrained) to a broad range of driving frequencies of perceived ML motion. However, the influence of visual perturbations on metrics of walking balance was frequency-dependent and governed by their proximity to stride frequency. Specifically, we found that a driving frequency nearest to subjects' average stride frequency uniquely compromised trunk sway, gait variability, and step-to-step correlations. We conclude that visuomotor entrainment is a robust and naturally emerging phenomenon during human walking, involving coordinated and frequency-dependent adjustments in trunk sway and foot placement to maintain balance at the whole-body level. These findings provide mechanistic insight into how the visuomotor control of walking balance is disrupted by visual perturbations and important reference values for the emergence of balance deficits due to age, injury, or disease.

Time-domain representation of frequency-dependent foundation impedance functions

Science.gov (United States)

Safak, E.

2006-01-01

Foundation impedance functions provide a simple means to account for soil-structure interaction (SSI) when studying seismic response of structures. Impedance functions represent the dynamic stiffness of the soil media surrounding the foundation. The fact that impedance functions are frequency dependent makes it difficult to incorporate SSI in standard time-history analysis software. This paper introduces a simple method to convert frequency-dependent impedance functions into time-domain filters. The method is based on the least-squares approximation of impedance functions by ratios of two complex polynomials. Such ratios are equivalent, in the time-domain, to discrete-time recursive filters, which are simple finite-difference equations giving the relationship between foundation forces and displacements. These filters can easily be incorporated into standard time-history analysis programs. Three examples are presented to show the applications of the method.

Frequency Dependence of Damping and Compliance in Loudspeaker Suspensions

DEFF Research Database (Denmark)

Thorborg, Knud; Tinggaard, Carsten; Agerkvist, Finn T.

2010-01-01

]. It is an empirical model mathematically describing the effects of visco-elasticity in loudspeaker suspensions. The evaluation is to a high degree based on test loudspeakers with rubber surrounds with a high content of plasticizer combining high compliance and high damping. This is very effective to reduce rim...... 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...... - with the additives normally used to adjust stiffness and damping - neither frequency dependency of compliance nor creep are significant problems. Despite this, experience shows that frequency dependent mechanical damping nevertheless might be present. In this paper some modifications to the LOG-model are proposed...

Frequency-dependent hydrodynamic interaction between two solid spheres

Science.gov (United States)

Jung, Gerhard; Schmid, Friederike

2017-12-01

Hydrodynamic interactions play an important role in many areas of soft matter science. In simulations with implicit solvent, various techniques such as Brownian or Stokesian dynamics explicitly include hydrodynamic interactions a posteriori by using hydrodynamic diffusion tensors derived from the Stokes equation. However, this equation assumes the interaction to be instantaneous which is an idealized approximation and only valid on long time scales. In the present paper, we go one step further and analyze the time-dependence of hydrodynamic interactions between finite-sized particles in a compressible fluid on the basis of the linearized Navier-Stokes equation. The theoretical results show that at high frequencies, the compressibility of the fluid has a significant impact on the frequency-dependent pair interactions. The predictions of hydrodynamic theory are compared to molecular dynamics simulations of two nanocolloids in a Lennard-Jones fluid. For this system, we reconstruct memory functions by extending the inverse Volterra technique. The simulation data agree very well with the theory, therefore, the theory can be used to implement dynamically consistent hydrodynamic interactions in the increasingly popular field of non-Markovian modeling.

Relaxation dynamics of the conductive processes for PbNb2O6 ferroelectric ceramics in the frequency and time domain

International Nuclear Information System (INIS)

Gonzalez, R L; Leyet, Y; Guerrero, F; Guerra, J de Los S; Venet, M; Eiras, J A

2007-01-01

The relaxation dynamics of the conductive process present in PbNb 2 O 6 piezoelectric ceramics was investigated. A relaxation function in the time domain, Φ(t), was found from the frequency dependence of the dielectric modulus (imaginary component, M'') by using a relaxation function in the frequency domain, F*(ω). The best relaxation function, F*(ω), was found to be a Cole-Cole distribution function, in which relaxation characteristic parameters, such as α and τ CC , are involved. On the other hand, the relaxation function, Φ(t), obtained by the time domain method, was found to be a Kohlrausch-Williams-Watts (KWW) function type. The thermal evolution of the characteristics parameters of the KWW function (β and τ*) was analysed. The values of the activation energy (E a ), obtained in the whole investigated temperature interval, suggest the existence of a relaxation mechanism (a conductive process), which may be interpreted by an ion hopping between neighbouring sites within the crystalline lattice. The results are corroborated with the formalism of the AC conductivity

Mathematical modelling of frequency-dependent hysteresis and energy loss of FeBSiC amorphous alloy

International Nuclear Information System (INIS)

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. - Highlights: • A mathematical model of frequency-dependent hysteresis is proposed. • Dependence of coercivity and energy loss per unit volume on frequency is modelled. • Equivalence between models and relation between model parameters are presented.

Ceramic/Metal Composites with Positive Temperature Dependence of Thermal Conductivity

International Nuclear Information System (INIS)

Li Jianhui; Yu Qi; Sun Wei; Zhang Rui; Wang Ke; Li Jingfeng; Ichigozaki, Daisuke

2013-01-01

Most materials show decreasing thermal conductivity with increasing temperature, but an opposite temperature dependence of thermal conductivity is required for some industrial applications. The present work was conducted with a motivation to develop composite materials with a positive temperature dependence of thermal conductivity. ZrO 2 / stainless steel powders (304L) composite, with 3% stearic acid, was prepared by normal sintering under the protecting of Ar after mixing by mechanical ball milling technique. With the 304L content increasing from 10% to 20%, the thermal conductivity values increased. For all samples, the thermal conductivity in the temperature range of room temperature to 700 °C decreased with temperature below 300 °C, and then began to increase. The increasing thermal conductivity of the composites (within the high temperature range was attributed to the difference of the thermal conductivity and thermal expansion coefficient between ZrO 2 ceramic and 304L stainless steel powders. Two simple models were also used to estimate the thermal conductivity of the composites, which were in good agreement with the experiment results.

Peculiarities of frequency dependence of type 3 solar radio bursts duration

International Nuclear Information System (INIS)

Tsybko, Ya.G.

1989-01-01

From the averaged data of type 3 bursts at the fixed frequencies in the range 12.5-25 MHz and out of this limit it is concluded that there exist two branges of the burst duration dependence on the frequency. This splitting allows to distinguish bursts occurring at the fundamental and the second harmonics of the plasma frequency decreasing with height in the solar corona. The type 3b radiation is characterized by a separate diagram of the mean duration versus frequency of the stria-bursts at the fundamental harmonic

Tuning of Human Modulation Filters Is Carrier-Frequency Dependent

Science.gov (United States)

Simpson, Andrew J. R.; Reiss, Joshua D.; McAlpine, David

2013-01-01

Recent studies employing speech stimuli to investigate ‘cocktail-party’ listening have focused on entrainment of cortical activity to modulations at syllabic (5 Hz) and phonemic (20 Hz) rates. The data suggest that cortical modulation filters (CMFs) are dependent on the sound-frequency channel in which modulations are conveyed, potentially underpinning a strategy for separating speech from background noise. Here, we characterize modulation filters in human listeners using a novel behavioral method. Within an ‘inverted’ adaptive forced-choice increment detection task, listening level was varied whilst contrast was held constant for ramped increments with effective modulation rates between 0.5 and 33 Hz. Our data suggest that modulation filters are tonotopically organized (i.e., vary along the primary, frequency-organized, dimension). This suggests that the human auditory system is optimized to track rapid (phonemic) modulations at high sound-frequencies and slow (prosodic/syllabic) modulations at low frequencies. PMID:24009759

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

Imaging in electrically conductive porous media without frequency encoding.

Science.gov (United States)

Lehmann-Horn, J A; Walbrecker, J O

2012-07-01

Understanding multi-phase fluid flow and transport processes under various pressure, temperature, and salinity conditions is a key feature in many remote monitoring applications, such as long-term storage of carbon dioxide (CO(2)) or nuclear waste in geological formations. We propose a low-field NMR tomographic method to non-invasively image the water-content distribution in electrically conductive formations in relatively large-scale experiments (∼1 m(3) sample volumes). Operating in the weak magnetic field of Earth entails low Larmor frequencies at which electromagnetic fields can penetrate electrically conductive material. The low signal strengths associated with NMR in Earth's field are enhanced by pre-polarization before signal recording. To localize the origin of the NMR signal in the sample region we do not employ magnetic field gradients, as is done in conventional NMR imaging, because they can be difficult to control in the large sample volumes that we are concerned with, and may be biased by magnetic materials in the sample. Instead, we utilize the spatially dependent inhomogeneity of fields generated by surface coils that are installed around the sample volume. This relatively simple setup makes the instrument inexpensive and mobile (it can be potentially installed in remote locations outside of a laboratory), while allowing spatial resolution of the order of 10 cm. We demonstrate the general feasibility of our approach in a simulated CO(2) injection experiment, where we locate and quantify the drop in water content following gas injection into a water-saturated cylindrical sample of 0.45 m radius and 0.9 m height. Our setup comprises four surface coils and an array consisting of three volume coils surrounding the sample. The proposed tomographic NMR methodology provides a more direct estimate of fluid content and properties than can be achieved with acoustic or electromagnetic methods alone. Therefore, we expect that our proposed method is relevant

Conduction mechanism in bismuth silicate glasses containing titanium

International Nuclear Information System (INIS)

Dult, Meenakshi; Kundu, R.S.; Murugavel, S.; Punia, R.; Kishore, N.

2014-01-01

Bismuth silicate glasses mixed with different concentrations of titanium dioxide having compositions xTiO 2 –(60−x)Bi 2 O 3 –40SiO 2 with x=0, 5, 10, 15 and 20 were prepared by the normal melt quench technique. The frequency dependence of the ac electrical conductivity of different compositions of titanium bismuth silicate glasses has been studied in the frequency range 10 −1 Hz to 10 MHz and in the temperature range 623–703 K. The temperature and frequency dependent conductivity is found to obey Jonscher's universal power law for all the compositions of titanium bismuth silicate glass system. The dc conductivity (σ dc ), so called crossover frequency (ω H ), 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 (H f ) and enthalpy of migration (H m ) have also been estimated. The conductivity data have been analyzed in terms of different theoretical models to determine the possible conduction mechanism. Analysis of the conductivity data and the frequency exponent shows that the correlated barrier hopping of electrons between Ti 3+ and Ti 4+ ions in the glasses is the most favorable mechanism for ac conduction. The temperature dependent dc conductivity has been analyzed in the framework of theoretical variable range hopping model (VRH) proposed by Mott which describe the hopping conduction in disordered semiconducting systems. The various polaron hopping parameters have also been deduced. Mott's VRH model is found to be in good agreement with experimental data and the values of inverse localization length of s-like wave function (α) obtained by this model with modifications suggested by Punia et al. are close to the ones reported for a number of oxide glasses

Ionic conductivity of N-alkyl pyridinium halides mesophases

International Nuclear Information System (INIS)

Meftah, Ahmed

1980-01-01

The quasi anhydrous N-alkyl pyridinium halides undergo at a temperature T c a phase transition from a crystalline isolating state to a conducting mesophase (σ = 3.10 -2 Ω -1 cm -1 ). The transition temperature depends on the nature on counter-ion and on the aliphatic chain length. The present study is devoted to the N-alkyl pyridinium chlorides, bromides and iodides varying the number of carbon atoms in the chain from ten to twenty two. The transition temperatures T c were found to increase from 30 deg. C up to 110 deg. C by a step of 10 deg. C for two added carbon atoms in the chain. The electrical measurements have shown that the conductivity of the mesophases which is ionic in origin is due to a large mobility of counter-ions in hydrophilic parts. At high frequencies (F > 10 3 Hz) ionic conductivity predominates in the bulk and does not depend on frequency. At low frequencies (F 3 Hz) the most important are interface phenomena depending on the square root of inverse frequency (ω -1/2 ) and being due to an electronic exchange limited by diffusion velocity of counter-ions. The electrical conductivity depends weekly on the chain length and the mesophases textures. The most conducting mesophase is the optically isotropic. The conductivity increases with increasing water content of the system and decreases with increasing atomic number of counter-ion. The diffusion measurements by radioactive tracers confirm the ionic character of charge carriers although the diffusion factors obtained by this method are largely higher than the calculated ones from the conductivity values. (author) [fr

A hybrid transport-diffusion Monte Carlo method for frequency-dependent radiative-transfer simulations

International Nuclear Information System (INIS)

Densmore, Jeffery D.; Thompson, Kelly G.; Urbatsch, Todd J.

2012-01-01

Discrete Diffusion Monte Carlo (DDMC) is a technique for increasing the efficiency of Implicit Monte Carlo radiative-transfer simulations in optically thick media. In DDMC, particles take discrete steps between spatial cells according to a discretized diffusion equation. Each discrete step replaces many smaller Monte Carlo steps, thus improving the efficiency of the simulation. In this paper, we present 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, as optical thickness is typically a decreasing function of frequency. Above this threshold we employ standard Monte Carlo, which results in a hybrid transport-diffusion scheme. With a set of frequency-dependent test problems, we confirm the accuracy and increased efficiency of our new DDMC method.

Frequency and temperature dependence of ferromagnetic linewidth in exchange biased Permalloy

International Nuclear Information System (INIS)

Lubitz, P.; Rubinstein, M.; Krebs, J. J.; Cheng, S.-F.

2001-01-01

Ferromagnetic resonance linewidths were measured at 9.5 and 35 GHz and in the temperature range from 77 to 350 K for thin Permalloy (Py) films exchange biased by adjacent layers of NiO, CoO, or IrMn. Compared to unoxidized Py alone, for which the linewidth is nearly temperature independent in this range and scales linearly with frequency, exchange biased Py has broader lines with distinctive temperature dependences for each bias material at 9.5 GHz. Different temperature dependences were observed at 35 GHz. Our results are consistent with relaxation related to thermally driven reversal of the antiferromagnetic grains. Intrinsic damping and inhomogeneities also add to the widths. The qualitative features of the temperature and frequency dependences of the linewidths can be described with the usual expression for the slow relaxation linewidth mechanism. The temperature dependence of the relaxation time is taken from Neel's expression for the reversal time using appropriate rate prefactors and activation energies. [copyright] 2001 American Institute of Physics

Concept of frequency separation in life prediction for time-dependent fatigue

International Nuclear Information System (INIS)

Coffin, L.F.

1976-01-01

Two methods are described to improve the predictive capability of the frequency-modified fatigue equations for time-dependent fatigue. These built-on the earlier approach and are applicable to severely unbalanced hysteresis loops. Comparisons made with various wave-shape investigations show favorable results. A new form of hysteresis loop is introduced utilizing frequency separation concepts. 4 tables, 11 fig

The Frequency Spectral Properties of Electrode-Skin Contact Impedance on Human Head and Its Frequency-Dependent Effects on Frequency-Difference EIT in Stroke Detection from 10Hz to 1MHz.

Directory of Open Access Journals (Sweden)

Lin Yang

Full Text Available Frequency-difference electrical impedance tomography (fdEIT reconstructs frequency-dependent changes of a complex impedance distribution. It has a potential application in acute stroke detection because there are significant differences in impedance spectra between stroke lesions and normal brain tissues. However, fdEIT suffers from the influences of electrode-skin contact impedance since contact impedance varies greatly with frequency. When using fdEIT to detect stroke, it is critical to know the degree of measurement errors or image artifacts caused by contact impedance. To our knowledge, no study has systematically investigated the frequency spectral properties of electrode-skin contact impedance on human head and its frequency-dependent effects on fdEIT used in stroke detection within a wide frequency band (10 Hz-1 MHz. In this study, we first measured and analyzed the frequency spectral properties of electrode-skin contact impedance on 47 human subjects' heads within 10 Hz-1 MHz. Then, we quantified the frequency-dependent effects of contact impedance on fdEIT in stroke detection in terms of the current distribution beneath the electrodes and the contact impedance imbalance between two measuring electrodes. The results showed that the contact impedance at high frequencies (>100 kHz significantly changed the current distribution beneath the electrode, leading to nonnegligible errors in boundary voltages and artifacts in reconstructed images. The contact impedance imbalance at low frequencies (<1 kHz also caused significant measurement errors. We conclude that the contact impedance has critical frequency-dependent influences on fdEIT and further studies on reducing such influences are necessary to improve the application of fdEIT in stroke detection.

The Frequency Spectral Properties of Electrode-Skin Contact Impedance on Human Head and Its Frequency-Dependent Effects on Frequency-Difference EIT in Stroke Detection from 10Hz to 1MHz.

Science.gov (United States)

Yang, Lin; Dai, Meng; Xu, Canhua; Zhang, Ge; Li, Weichen; Fu, Feng; Shi, Xuetao; Dong, Xiuzhen

2017-01-01

Frequency-difference electrical impedance tomography (fdEIT) reconstructs frequency-dependent changes of a complex impedance distribution. It has a potential application in acute stroke detection because there are significant differences in impedance spectra between stroke lesions and normal brain tissues. However, fdEIT suffers from the influences of electrode-skin contact impedance since contact impedance varies greatly with frequency. When using fdEIT to detect stroke, it is critical to know the degree of measurement errors or image artifacts caused by contact impedance. To our knowledge, no study has systematically investigated the frequency spectral properties of electrode-skin contact impedance on human head and its frequency-dependent effects on fdEIT used in stroke detection within a wide frequency band (10 Hz-1 MHz). In this study, we first measured and analyzed the frequency spectral properties of electrode-skin contact impedance on 47 human subjects' heads within 10 Hz-1 MHz. Then, we quantified the frequency-dependent effects of contact impedance on fdEIT in stroke detection in terms of the current distribution beneath the electrodes and the contact impedance imbalance between two measuring electrodes. The results showed that the contact impedance at high frequencies (>100 kHz) significantly changed the current distribution beneath the electrode, leading to nonnegligible errors in boundary voltages and artifacts in reconstructed images. The contact impedance imbalance at low frequencies (<1 kHz) also caused significant measurement errors. We conclude that the contact impedance has critical frequency-dependent influences on fdEIT and further studies on reducing such influences are necessary to improve the application of fdEIT in stroke detection.

Frequency dependence of quantum path interference in non-collinear high-order harmonic generation

International Nuclear Information System (INIS)

Zhong Shi-Yang; He Xin-Kui; Teng Hao; Ye Peng; Wang Li-Feng; He Peng; Wei Zhi-Yi

2016-01-01

High-order harmonic generation (HHG) driven by two non-collinear beams including a fundamental and its weak second harmonic is numerically studied. The interference of harmonics from adjacent electron quantum paths is found to be dependent on the relative delay of the driving pulse, and the dependences are different for different harmonic orders. This frequency dependence of the interference is attributed to the spatial frequency chirp in the HHG beam resulting from the harmonic dipole phase, which in turn provides a potential way to gain an insight into the generation of high-order harmonics. As an example, the intensity dependent dipole phase coefficient α is retrieved from the interference fringe. (paper)

Hydrogen-enhanced fatigue crack growth in steels and its frequency dependence.

Science.gov (United States)

Matsunaga, Hisao; Takakuwa, Osamu; Yamabe, Junichiro; Matsuoka, Saburo

2017-07-28

In the context of the fatigue life design of components, particularly those destined for use in hydrogen refuelling stations and fuel cell vehicles, it is important to understand the hydrogen-induced, fatigue crack growth (FCG) acceleration in steels. As such, the mechanisms for acceleration and its influencing factors are reviewed and discussed in this paper, with a special focus on the peculiar frequency dependence of the hydrogen-induced FCG acceleration. Further, this frequency dependence is debated by introducing some potentially responsible elements, along with new experimental data obtained by the authors.This article is part of the themed issue 'The challenges of hydrogen and metals'. © 2017 The Author(s).

Spatial resolution dependence on spectral frequency in human speech cortex electrocorticography

Science.gov (United States)

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

Conductivity-Dependent Strain Response of Carbon Nanotube Treated Bacterial Nanocellulose

Directory of Open Access Journals (Sweden)

S. Farjana

2013-01-01

Full Text Available This paper reports the strain sensitivity of flexible, electrically conductive, and nanostructured cellulose which was prepared by modification of bacterial cellulose with double-walled carbon nanotubes (DWCNTs and multiwalled carbon nanotubes (MWCNTs. The electrical conductivity depends on the modifying agent and its dispersion process. The conductivity of the samples obtained from bacterial cellulose (BNC pellicles modified with DWCNT was in the range from 0.034 S·cm−1 to 0.39 S·cm−1, and for BNC pellicles modified with MWCNTs it was from 0.12 S·cm−1 to 1.6 S·cm−1. The strain-induced electromechanical response, resistance versus strain, was monitored during the application of tensile force in order to study the sensitivity of the modified nanocellulose. A maximum gauge factor of 252 was found from the highest conductive sample treated by MWCNT. It has been observed that the sensitivity of the sample depends on the conductivity of the modified cellulose.

Frequency, moisture content, and temperature dependent dielectric properties of potato starch related to drying with radio-frequency/microwave energy.

Science.gov (United States)

Zhu, Zhuozhuo; Guo, Wenchuan

2017-08-24

To develop advanced drying methods using radio-frequency (RF) or microwave (MW) energy, dielectric properties of potato starch were determined using an open-ended coaxial-line probe and network analyzer at frequencies between 20 and 4,500 MHz, moisture contents between 15.1% and 43.1% wet basis (w.b.), and temperatures between 25 and 75 °C. The results showed that both dielectric constant (ε') and loss factor (ε″) were dependent on frequency, moisture content, and temperature. ε' decreased with increasing frequency at a given moisture content or temperature. At low moisture contents (≤25.4% w.b.) or low temperatures (≤45 °C), ε″ increased with increasing frequency. However, ε″ changed from decrease to increase with increasing frequency at high moisture contents or temperatures. At low temperatures (25-35 °C), both ε' and ε″ increased with increasing moisture content. At low moisture contents (15.1-19.5% w.b.), they increased with increasing temperature. The change trends of ε' and ε″ were different and dependent on temperature and moisture content at their high levels. The penetration depth (d p ) decreased with increasing frequency. RF treatments may provide potential large-scale industrial drying application for potato starch. This research offers useful information on dielectric properties of potato starch related to drying with electromagnetic energy.

Optical conductivity of metal nanoshells

International Nuclear Information System (INIS)

Tomchuk, P.M.; Kulish, V.V.

2004-01-01

The expression for optical conductivity of spherical metal nanoshell as a function of internal and external radii of nanoshell and photon energy - Fermi energy ratio is obtained. Quantization of electron energy in nanoshells is shown to lead to the appearance of an oscillating dependence of optical conductivity on the light frequency. An explicit expression of oscillating addends for optical conductivity is obtained

Comparison of trap characteristics between AlGaN/GaN and AlGaN/InGaN/GaN heterostructure by frequency dependent conductance measurement

International Nuclear Information System (INIS)

Chakraborty, Apurba; Biswas, Dhrubes

2015-01-01

Frequency dependent conductance measurement is carried out to observe the trapping effect in AlGaN/InGaN/GaN double heterostructure and compared that with conventional AlGaN/GaN single heterostructure. It is found that the AlGaN/InGaN/GaN diode structure does not show any trapping effect, whereas single heterostructure AlGaN/GaN diode suffers from two kinds of trap energy states in near depletion to higher negative voltage bias region. This conductance behaviour of AlGaN/InGaN/GaN heterostructure is owing to more Fermi energy level shift from trap energy states at AlGaN/InGaN junction compare to single AlGaN/GaN heterostructure and eliminates the trapping effects. Analysis yielded interface trap energy state in AlGaN/GaN is to be with time constant of (33.8–76.5) μs and trap density of (2.38–0.656) × 10 12  eV −1  cm −2 in −3.2 to −4.8 V bias region, whereas for AlGaN/InGaN/GaN structure no interface energy states are found and the extracted surface trap energy concentrations and time constants are (5.87–4.39) ×10 10  eV −1  cm −2 and (17.8–11.3) μs, respectively, in bias range of −0.8–0.0 V

Contactless measurement of alternating current conductance in quantum Hall structures

Energy Technology Data Exchange (ETDEWEB)

Drichko, I. L.; Diakonov, A. M.; Malysh, V. A.; Smirnov, I. Yu.; Ilyinskaya, N. D.; Usikova, A. A. [A. F. Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Galperin, Y. M. [Department of Physics, University of Oslo, P.O. Box 1048 Blindern, 0316 Oslo (Norway); A. F. Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Kummer, M.; Känel, H. von [Laboratorium für Festkörperphysik ETH Zürich, CH-8093 Zürich (Switzerland)

2014-10-21

We report a procedure to determine the frequency-dependent conductance of quantum Hall structures in a broad frequency domain. The procedure is based on the combination of two known probeless methods—acoustic spectroscopy and microwave spectroscopy. By using the acoustic spectroscopy, we study the low-frequency attenuation and phase shift of a surface acoustic wave in a piezoelectric crystal in the vicinity of the electron (hole) layer. The electronic contribution is resolved using its dependence on a transverse magnetic field. At high frequencies, we study the attenuation of an electromagnetic wave in a coplanar waveguide. To quantitatively calibrate these data, we use the fact that in the quantum-Hall-effect regime the conductance at the maxima of its magnetic field dependence is determined by extended states. Therefore, it should be frequency independent in a broad frequency domain. The procedure is verified by studies of a well-characterized p-SiGe/Ge/SiGe heterostructure.

Frequency-dependent complex modulus of the uterus: preliminary results

Energy Technology Data Exchange (ETDEWEB)

Kiss, Miklos Z [Department of Medical Physics, University of Wisconsin, Madison, WI 53706 (United States); Hobson, Maritza A [Department of Medical Physics, University of Wisconsin, Madison, WI 53706 (United States); Varghese, Tomy [Department of Medical Physics, University of Wisconsin, Madison, WI 53706 (United States); Harter, Josephine [Department of Surgical Pathology, University of Wisconsin, Madison, WI 53706 (United States); Kliewer, Mark A [Department of Radiology, University of Wisconsin, Madison, WI 53706 (United States); Hartenbach, Ellen M [Department of Obstetrics and Gynecology, University of Wisconsin, Madison, WI 53706 (United States); Zagzebski, James A [Department of Medical Physics, University of Wisconsin, Madison, WI 53706 (United States)

2006-08-07

The frequency-dependent complex moduli of human uterine tissue have been characterized. Quantification of the modulus is required for developing uterine ultrasound elastography as a viable imaging modality for diagnosing and monitoring causes for abnormal uterine bleeding and enlargement, as well assessing the integrity of uterine and cervical tissue. The complex modulus was measured in samples from hysterectomies of 24 patients ranging in age from 31 to 79 years. Measurements were done under small compressions of either 1 or 2%, at low pre-compression values (either 1 or 2%), and over a frequency range of 0.1-100 Hz. Modulus values of cervical tissue monotonically increased from approximately 30-90 kPa over the frequency range. Normal uterine tissue possessed modulus values over the same range, while leiomyomas, or uterine fibroids, exhibited values ranging from approximately 60-220 kPa.

Frequency-dependent complex modulus of the uterus: preliminary results

International Nuclear Information System (INIS)

Kiss, Miklos Z; Hobson, Maritza A; Varghese, Tomy; Harter, Josephine; Kliewer, Mark A; Hartenbach, Ellen M; Zagzebski, James A

2006-01-01

The frequency-dependent complex moduli of human uterine tissue have been characterized. Quantification of the modulus is required for developing uterine ultrasound elastography as a viable imaging modality for diagnosing and monitoring causes for abnormal uterine bleeding and enlargement, as well assessing the integrity of uterine and cervical tissue. The complex modulus was measured in samples from hysterectomies of 24 patients ranging in age from 31 to 79 years. Measurements were done under small compressions of either 1 or 2%, at low pre-compression values (either 1 or 2%), and over a frequency range of 0.1-100 Hz. Modulus values of cervical tissue monotonically increased from approximately 30-90 kPa over the frequency range. Normal uterine tissue possessed modulus values over the same range, while leiomyomas, or uterine fibroids, exhibited values ranging from approximately 60-220 kPa

Tuning of gravity-dependent and gravity-independent vertical angular VOR gain changes by frequency of adaptation.

Science.gov (United States)

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.

Range-separated time-dependent density-functional theory with a frequency-dependent second-order Bethe-Salpeter correlation kernel

Energy Technology Data Exchange (ETDEWEB)

Rebolini, Elisa, E-mail: elisa.rebolini@kjemi.uio.no; Toulouse, Julien, E-mail: julien.toulouse@upmc.fr [Laboratoire de Chimie Théorique, Sorbonne Universités, UPMC Univ Paris 06, CNRS, 4 place Jussieu, F-75005 Paris (France)

2016-03-07

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 the He and Be atoms and small molecules (H{sub 2}, N{sub 2}, CO{sub 2}, H{sub 2}CO, and C{sub 2}H{sub 4}). The results suggest that the addition of the long-range second-order Bethe-Salpeter correlation kernel overall slightly improves the excitation energies.

Temperature dependent dielectric relaxation and ac-conductivity of alkali niobate ceramics studied by impedance spectroscopy

Science.gov (United States)

Yadav, Abhinav; Mantry, Snigdha Paramita; Fahad, Mohd.; Sarun, P. M.

2018-05-01

Sodium niobate (NaNbO3) ceramics is prepared by conventional solid state reaction method at sintering temperature 1150 °C for 4 h. The structural information of the material has been investigated by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FE-SEM). The XRD analysis of NaNbO3 ceramics shows an orthorhombic structure. The FE-SEM micrograph of NaNbO3 ceramics exhibit grains with grain sizes ranging between 1 μm to 5 μm. The surface coverage and average grain size of NaNbO3 ceramics are found to be 97.6 % and 2.5 μm, respectively. Frequency dependent electrical properties of NaNbO3 is investigated from room temperature to 500 °C in wide frequency range (100 Hz-5 MHz). Dielectric constant, ac-conductivity, impedance, modulus and Nyquist analysis are performed. The observed dielectric constant (1 kHz) at transition temperature (400 °C) are 975. From conductivity analysis, the estimated activation energy of NaNbO3 ceramics is 0.58 eV at 10 kHz. The result of Nyquist plot shows that the electrical behavior of NaNbO3 ceramics is contributed by grain and grain boundary responses. The impedance and modulus spectrum asserts that the negative temperature coefficient of resistance (NTCR) behavior and non-Debye type relaxation in NaNbO3.

On the flow dependency of the electrical conductivity of blood

NARCIS (Netherlands)

Hoetink, AE; Faes, TJC; Visser, KR; Heethaar, RM

Experiments presented in the literature show that the electrical conductivity of flowing blood depends on flow velocity. The aim of this study is to extend the Maxwell-Fricke theory, developed for a dilute suspension of ellipsoidal particles in an electrolyte, to explain this flow dependency of the

Mutational jackpot events generate effective frequency-dependent selection in adapting populations

Science.gov (United States)

Hallatschek, Oskar

The site-frequency spectrum is one the most easily measurable quantities that characterize the genetic diversity of a population. While most neutral models predict that site frequency spectra should decay with increasing frequency, a high-frequency uptick has been reported in many populations. Anomalies in the high-frequency tail are particularly unsettling because the highest frequencies can be measured with greatest accuracy. Here, we show that an uptick in the spectrum of neutral mutations generally arises when mutant frequencies are dominated by rare jackpot events, mutational events with large descendant numbers. This leads to an effective pattern of frequency-dependent selection (or unstable internal equilibrium at one half frequency) that causes an accumulation of high-frequency polymorphic sites. We reproduce the known uptick occurring for recurrent hitchhiking (genetic draft) as well as rapid adaptation, and (in the future) generalize the shape of the high-frequency tail to other scenarios that are dominated by jackpot events, such as frequent range expansions. We also tackle (in the future) the inverse approach to use the high-frequency uptick for learning about the tail of the offspring number distribution. Positively selected alleles need to surpass, typically, an u NSF Career Award (PoLS), NIH NIGMS R01, Simons Foundation.

Dendritic calcium conductances generate high-frequency oscillation in thalamocortical neurons

OpenAIRE

Pedroarena, Christine; Llinás, Rodolfo

1997-01-01

Cortical-projecting thalamic neurons, in guinea pig brain slices, display high-frequency membrane potential oscillations (20–80 Hz), when their somata are depolarized beyond −45 mV. These oscillations, preferentially located at dendritic sites, are supported by the activation of P/Q type calcium channels, as opposed to the expected persistent sodium conductance responsible for such rhythmic behavior in other central neurons. Short hyperpolarizing pulses reset the phase and transiently increas...

The role of age, gender, mood states and exercise frequency on exercise dependence.

Science.gov (United States)

Costa, Sebastiano; Hausenblas, Heather A; Oliva, Patrizia; Cuzzocrea, Francesca; Larcan, Rosalba

2013-12-01

The purpose of our study was to explore the prevalence, and the role of mood, exercise frequency, age, and gender differences of exercise dependence. Regular exercisers (N = 409) completed a socio-demographic questionnaire, the Exercise Dependence Scale, and the Profile of Mood States. For data analyses, the participants were stratified for sex and age (age ranges = young adults: 18-24 years, adults: 25-44 years, and middle-aged adults: 45-64 years). We found that: (a) 4.4% of the participants were classified as at-risk for exercise dependence; (b) the men and the two younger groups (i.e., young adults and adults) had higher exercise dependence scores; and (c) age, gender, exercise frequency, and mood state were related to exercise dependence. Our results support previous research on the prevalence of exercise dependence and reveal that adulthood may be the critical age for developing exercise dependence. These findings have practical implication for identifying individuals at-risk for exercise dependence symptoms, and may aid in targeting and guiding the implementation of prevention program for adults.

Diameter dependence of the thermal conductivity of InAs nanowires

NARCIS (Netherlands)

Swinkels, M.Y.; van Delft, M.R.; Oliveira, D.S.; Cavalli, A.; Zardo, I.; van der Heijden, R.W.; Bakkers, E.P.A.M.

2015-01-01

The diameter dependence of the thermal conductivity of InAs nanowires in the range of 40–1500 nm has been measured. We demonstrate a reduction in thermal conductivity of 80% for 40 nm nanowires, opening the way for further design strategies for nanoscaled thermoelectric materials. Furthermore, we

Simultaneous reconstruction of permittivity and conductivity using multi-frequency admittance measurement in electrical capacitance tomography

International Nuclear Information System (INIS)

Zhang, Maomao; Soleimani, Manuchehr

2016-01-01

Electrical capacitance tomography (ECT) is an imaging method mainly capable of reconstructing dielectric permittivity. Generally, the reactance part of complex admittance is measured in a selected frequency. This paper presents for the first time an in depth and systematic analysis of complex admittance data for simultaneous reconstruction of both electrical conductivity and dielectric permittivity. A complex-valued forward model, Jacobian matrix and inverse solution are developed in the time harmonic excitation mode to allow for multi-frequency measurements. Realistic noise models are used to evaluate the performance of complex admittance ECT in a range of excitation frequencies. This paper demonstrates far greater potential for ECT as a versatile imaging tool through novel analysis of complex admittance imaging using a dual conductivity permittivity inversion method. The paper demonstrates that various classes of contactless capacitance based measurement devices can be analysed through complex multi-frequency ECT. (paper)

Uncertainties Involved in the Iopospheric Conductivity Estimation

Directory of Open Access Journals (Sweden)

Young-Sil Kwak

2002-12-01

Full Text Available Various uncertainties involved in ionospheric conductivity estimation utilizing the electron density profile obtained from the Sondrestrom incoherent scatter radar are examined. First, we compare the conductivity which is based on raw electron density and the one based on corrected electron density that takes into account the effects of the difference between the electron and ion temperatures and the Debye length. The corrected electron density yields higher Pedersen and Hall conductivities than the raw electron density does. Second, the dependence of collision frequency model on the conductivity estimation is examined. Below 110 km conductivity does not depend significantly on collision frequency models. Above 110 km, however, the collision models affect the conductivity estimation. Third, the influence of the electron and ion temperatures on the conductivity estimation is examined. Electron and ion temperatures carrying an error of about 10% do not seem to affect significantly the conductivity estimation. Fourth, also examined is the effect of the choice of the altitude range of integration in calculating the height-integrated conductivity, conductance. It has been demonstrated that the lower and upper boundaries of the integration are quite sensitive to the estimation of the Hall and Pedersen conductances, respectively.

Human Commercial Models' Eye Colour Shows Negative Frequency-Dependent Selection.

Directory of Open Access Journals (Sweden)

Isabela Rodrigues Nogueira Forti

Full Text Available In this study we investigated the eye colour of human commercial models registered in the UK (400 female and 400 male and Brazil (400 female and 400 male to test the hypothesis that model eye colour frequency was the result of negative frequency-dependent selection. The eye colours of the models were classified as: blue, brown or intermediate. Chi-square analyses of data for countries separated by sex showed that in the United Kingdom brown eyes and intermediate colours were significantly more frequent than expected in comparison to the general United Kingdom population (P<0.001. In Brazil, the most frequent eye colour brown was significantly less frequent than expected in comparison to the general Brazilian population. These results support the hypothesis that model eye colour is the result of negative frequency-dependent selection. This could be the result of people using eye colour as a marker of genetic diversity and finding rarer eye colours more attractive because of the potential advantage more genetically diverse offspring that could result from such a choice. Eye colour may be important because in comparison to many other physical traits (e.g., hair colour it is hard to modify, hide or disguise, and it is highly polymorphic.

The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral Atmosphere

Energy Technology Data Exchange (ETDEWEB)

Prasad, S. Krishna; Jess, D. B. [Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast, BT7 1NN (United Kingdom); Doorsselaere, T. Van [Centre for mathematical Plasma Astrophysics, Mathematics Department, KU Leuven, Celestijnenlaan 200B bus 2400, B-3001 Leuven (Belgium); Verth, G. [School of Mathematics and Statistics, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH (United Kingdom); Morton, R. J. [Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Ellison Building, Newcastle upon Tyne, NE1 8ST (United Kingdom); Fedun, V. [Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield, S1 3JD (United Kingdom); Erdélyi, R. [Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH (United Kingdom); Christian, D. J., E-mail: krishna.prasad@qub.ac.uk [Department of Physics and Astronomy, California State University Northridge, Northridge, CA 91330 (United States)

2017-09-20

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.

Light sensitive memristor with bi-directional and wavelength-dependent conductance control

Energy Technology Data Exchange (ETDEWEB)

Maier, P.; Hartmann, F., E-mail: fabian.hartmann@physik.uni-wuerzburg.de; Emmerling, M.; Schneider, C.; Kamp, M.; Worschech, L. [Technische Physik and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Physikalisches Institut, Universität Würzburg, Am Hubland, D-97074 Würzburg (Germany); Rebello Sousa Dias, M. [Departamento de Fisica, Universidade Federal de São Carlos, 13565-905 São Carlos, São Paulo (Brazil); Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States); Castelano, L. K.; Marques, G. E.; Lopez-Richard, V. [Departamento de Fisica, Universidade Federal de São Carlos, 13565-905 São Carlos, São Paulo (Brazil); Höfling, S. [Technische Physik and Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Physikalisches Institut, Universität Würzburg, Am Hubland, D-97074 Würzburg (Germany); SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS (United Kingdom)

2016-07-11

We report the optical control of localized charge on positioned quantum dots in an electro-photo-sensitive memristor. Interband absorption processes in the quantum dot barrier matrix lead to photo-generated electron-hole-pairs that, depending on the applied bias voltage, charge or discharge the quantum dots and hence decrease or increase the conductance. Wavelength-dependent conductance control is observed by illumination with red and infrared light, which leads to charging via interband and discharging via intraband absorption. The presented memristor enables optical conductance control and may thus be considered for sensory applications in artificial neural networks as light-sensitive synapses or optically tunable memories.

Light sensitive memristor with bi-directional and wavelength-dependent conductance control

International Nuclear Information System (INIS)

Maier, P.; Hartmann, F.; Emmerling, M.; Schneider, C.; Kamp, M.; Worschech, L.; Rebello Sousa Dias, M.; Castelano, L. K.; Marques, G. E.; Lopez-Richard, V.; Höfling, S.

2016-01-01

We report the optical control of localized charge on positioned quantum dots in an electro-photo-sensitive memristor. Interband absorption processes in the quantum dot barrier matrix lead to photo-generated electron-hole-pairs that, depending on the applied bias voltage, charge or discharge the quantum dots and hence decrease or increase the conductance. Wavelength-dependent conductance control is observed by illumination with red and infrared light, which leads to charging via interband and discharging via intraband absorption. The presented memristor enables optical conductance control and may thus be considered for sensory applications in artificial neural networks as light-sensitive synapses or optically tunable memories.

Microstructural, electrical and frequency-dependent properties of Au/p-Cu2ZnSnS4/n-GaN heterojunction.

Science.gov (United States)

Rajagopal Reddy, V; Janardhanam, V; Won, Jonghan; Choi, Chel-Jong

2017-08-01

An Au/Cu 2 ZnSnS 4 (CZTS)/n-GaN heterojunction (HJ) is fabricated with a CZTS interlayer and probed its chemical states, structural, electrical and frequency-dependent characteristics by XPS, TEM, I-V and C-V measurements. XPS and TEM results confirmed that the CZTS films are formed on the n-GaN surface. The band gap of deposited CZTS film is found to be 1.55eV. The electrical properties of HJ correlated with the Au/n-GaN Schottky junction (SJ). The Au/CZTS/n-GaN HJ reveals a good rectification nature with high barrier height (0.82eV) compared to the Au/n-GaN SJ (0.69eV), which suggests the barrier height is influenced by the CZTS interlayer. The barrier height values assessed by I-V, Cheung's and Norde functions are closely matched with one other, thus the methods used here are reliable and valid. The extracted interface state density (N SS ) of Au/CZTS/n-GaN HJ is lower compared to the Au/n-GaN SJ that suggests the CZTS interlayer plays an important role in the reduction of N SS . Moreover, the capacitance-frequency (C-f) and conductance-frequency (G-f) characteristics of SJ and HJ are measured in the range of 1kHz-1MHz, and found that the capacitance and conductance strappingly dependent on frequency. It is found that the N SS estimated from C-f and G-f characteristics is lower compared to those estimated from I-V characteristics. Analysis confirmed that Poole-Frenkel emission dominates the reverse leakage current in both SJ and HJ, probably related to the structural defects and trap levels in the CZTS interlayer. Copyright © 2017 Elsevier Inc. All rights reserved.

Spin-dependent tunnelling at infrared frequencies: magnetorefractive effect in magnetic nanocomposites

International Nuclear Information System (INIS)

Granovsky, A.B.; Inoue, Mitsuteru

2004-01-01

We present a brief review of recent experimental and theoretical results on magnetorefractive effect in magnetic metal-insulator nanogranular alloys with tunnel-type magnetoresistance focusing on its relation with high-frequency spin-dependent tunnelling

Spin-dependent tunnelling at infrared frequencies: magnetorefractive effect in magnetic nanocomposites

Energy Technology Data Exchange (ETDEWEB)

Granovsky, A.B. E-mail: granov@magn.ru; Inoue, Mitsuteru

2004-05-01

We present a brief review of recent experimental and theoretical results on magnetorefractive effect in magnetic metal-insulator nanogranular alloys with tunnel-type magnetoresistance focusing on its relation with high-frequency spin-dependent tunnelling.

Anomalous conductivity of calcium- and cadmium molybdates with colour centers

International Nuclear Information System (INIS)

Reut, E.G.

1983-01-01

Electrical properties of cadmium- and calcium molybdates with colour centers are considered. Electric conductivity and capacitance in the 50 to 100 kHz frequency range at temperature change from 4 to 300 K, are investigated. Temperature- and frequency dependences are described by Debye formulas. The potential distribution over the sample is investigated and a conclusion is drawn that electric characteristics are dependent on the barrier impedance which arises at the crystal-electrode metal interface. Bulk conductivity is determined using a probe technique. The CdMoO 4 electric conductivity is anomalously high and cannot be explained by ion transport CdMoO 4 with colour centers is concluded to be an impurity semiconductor. It has been foUnd that in both crystals bulk conductivity and charge layer relaxation on the contacts depend on the same centers. Center parameters are determined

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....

Frequency and temperature dependence of dielectric properties of chicken meat

Science.gov (United States)

Dielectric properties of chicken breast meat were measured with an open-ended coaxial-line probe between 200 MHz and 20 GHz at temperatures ranging from -20 degree C to +25 degree C. At a given temperature, the frequency dependence of the dielectric constant reveals two relaxations while those of th...

Frequency-dependence of the slow force response.

Science.gov (United States)

von Lewinski, Dirk; Zhu, Danan; Khafaga, Mounir; Kockskamper, Jens; Maier, Lars S; Hasenfuss, Gerd; Pieske, Burkert

2008-05-01

Stretch induces biphasic inotropic effects in mammalian myocardium. A delayed component (slow force response, SFR) has been demonstrated in various species, however, experimental conditions varied and the underlying mechanisms are controversial. The physiological relevance of the SFR is poorly understood. Experiments were performed in ventricular muscle strips from failing human hearts and non-failing rabbit hearts. Upon stretch, twitch force was assessed at basal conditions (1 Hz, 37 degrees C) and after changing stimulation frequency with and without blockade of the Na+/H+-exchanger-1 (NHE1) or reverse-mode Na+/Ca2+-exchange (NCX). Action potential duration (APD) was assessed using floating electrodes. Low stimulation rates (0.2 Hz) potentiated and higher stimulation rates (2 and 3 Hz) reduced the SFR. The extent of SFR inhibition by NHE1 or NCX inhibition was not affected by stimulation rate. APD decreased at 0.2 Hz but was not altered at higher stimulation rates. The data demonstrate frequency-dependence of the SFR with greater positive inotropic effects at lower stimulation rates. Subcellular mechanisms underlying the SFR are not fundamentally affected by stimulation rate. The SFR may have more pronounced physiological effects at lower heart rates.

AC conductivity for a holographic Weyl semimetal

Energy Technology Data Exchange (ETDEWEB)

Grignani, Gianluca; Marini, Andrea; Peña-Benitez, Francisco; Speziali, Stefano [Dipartimento di Fisica e Geologia, Università di Perugia,I.N.F.N. Sezione di Perugia,Via Pascoli, I-06123 Perugia (Italy)

2017-03-23

We study the AC electrical conductivity at zero temperature in a holographic model for a Weyl semimetal. At small frequencies we observe a linear dependence in the frequency. The model shows a quantum phase transition between a topological semimetal (Weyl semimetal phase) with a non vanishing anomalous Hall conductivity and a trivial semimetal. The AC conductivity has an intermediate scaling due to the presence of a quantum critical region in the phase diagram of the system. The phase diagram is reconstructed using the scaling properties of the conductivity. We compare with the experimental data of https://www.doi.org/10.1103/PhysRevB.93.121110 obtaining qualitative agreement.

On Strong Positive Frequency Dependencies of Quality Factors in Local-Earthquake Seismic Studies

Science.gov (United States)

Morozov, Igor B.; Jhajhria, Atul; Deng, Wubing

2018-03-01

Many observations of seismic waves from local earthquakes are interpreted in terms of the frequency-dependent quality factor Q( f ) = Q0 f^{η } , where η is often close to or exceeds one. However, such steep positive frequency dependencies of Q require careful analysis with regard to their physical consistency. In particular, the case of η = 1 corresponds to frequency-independent (elastic) amplitude decays with time and consequently requires no Q-type attenuation mechanisms. For η > 1, several problems with physical meanings of such Q-factors occur. First, contrary to the key premise of seismic attenuation, high-frequency parts of the wavefield are enhanced with increasing propagation times relative to the low-frequency ones. Second, such attenuation cannot be implemented by mechanical models of wave-propagating media. Third, with η > 1, the velocity dispersion associated with such Q(f) occurs over unrealistically short frequency range and has an unexpected oscillatory shape. Cases η = 1 and η > 1 are usually attributed to scattering; however, this scattering must exhibit fortuitous tuning into the observation frequency band, which appears unlikely. The reason for the above problems is that the inferred Q values are affected by the conventional single-station measurement procedure. Both parameters Q 0 and are apparent, i.e., dependent on the selected parameterization and inversion method, and they should not be directly attributed to the subsurface. For η ≈ 1, parameter Q 0 actually describes the frequency-independent amplitude decay in access of some assumed geometric spreading t -α , where α is usually taken equal one. The case η > 1 is not allowed physically and could serve as an indicator of problematic interpretations. Although the case 0 < η < 1 is possible, its parameters Q 0 and may also be biased by the measurement procedure. To avoid such difficulties of Q-based approaches, we recommend measuring and interpreting the amplitude-decay rates

On the role of minority carriers in the frequency dependence of organic magnetoresistance

NARCIS (Netherlands)

Janssen, Paul; Wagemans, W.; Verhoeven, Wouter; van der Heijden, E.H.M.; Kemerink, M.; Koopmans, B.

2011-01-01

In this work we investigate the frequency dependence of organic magnetoresistance (OMAR) both in small molecule-based (Alq3) and polymer (PPV derivative) materials, and investigate its thickness dependence. For all devices, we observed a strong decrease in magnetoconductance (MC) with increasing

Dependence of enhanced asymmetry-induced transport on collision frequency

Science.gov (United States)

Eggleston, D. L.

2014-07-01

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 ϕ1(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 ωR, 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 ≈ vr/ωT, 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.

Dependence of enhanced asymmetry-induced transport on collision frequency

International Nuclear Information System (INIS)

Eggleston, D. L.

2014-01-01

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 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 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 r /ω 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 effects of background noise on subcortical response timing.

Science.gov (United States)

Tierney, A; Parbery-Clark, A; Skoe, E; Kraus, N

2011-12-01

The addition of background noise to an auditory signal delays brainstem response timing. This effect has been extensively documented using manual peak selection. Peak picking, however, is impractical for large-scale studies of spectrotemporally complex stimuli, and leaves open the question of whether noise-induced delays are frequency-dependent or occur across the frequency spectrum. Here we use an automated, objective method to examine phase shifts between auditory brainstem responses to a speech sound (/da/) presented with and without background noise. We predicted that shifts in neural response timing would also be reflected in frequency-specific phase shifts. Our results indicate that the addition of background noise causes phase shifts across the subcortical response spectrum (70-1000 Hz). However, this noise-induced delay is not uniform such that some frequency bands show greater shifts than others: low-frequency phase shifts (300-500 Hz) are largest during the response to the consonant-vowel formant transition (/d/), while high-frequency shifts (720-1000 Hz) predominate during the response to the steady-state vowel (/a/). Most importantly, phase shifts occurring in specific frequency bands correlate strongly with shifts in the latencies of the predominant peaks in the auditory brainstem response, while phase shifts in other frequency bands do not. This finding confirms the validity of phase shift detection as an objective measure of timing differences and reveals that this method detects noise-induced shifts in timing that may not be captured by traditional peak latency measurements. Copyright © 2011 Elsevier B.V. All rights reserved.

The frequency dependence of friction in experiment, theory, and observations of low frequency earthquakes

Science.gov (United States)

Thomas, A.; Beeler, N. M.; Burgmann, R.; Shelly, D. R.

2011-12-01

Low frequency earthquakes (LFEs) are small amplitude, short duration events composing tectonic tremor, probably generated by shear slip on asperities downdip of the seismogenic zone. In Parkfield, Shelly and Hardebeck [2010] have identified 88 LFE families, or hypocentral locations, that contain over half a million LFEs since 2001 on a 160-km-long section of the San Andreas fault between 16 and 30 km depth. A number of studies have demonstrated the extreme sensitivity of low frequency earthquakes (LFEs) near Parkfield to stress changes ranging from contingent upon the amplitude and frequency content of the applied stress. We attempt to test this framework by comparing observations of LFEs triggered in response to stresses spanning several orders of magnitude in both frequency and amplitude (e.g. tides, teleseismic surface waves, static stress changes, etc.) to the predicted response of a single degree of freedom slider block model with rate and state dependent strength. The sensitivity of failure time in the friction model as developed in previous studies does not distinguish between shear and normal stresses; laboratory experiments show a more complicated sensitivity of failure time to normal stress change than in the published model. Because the shear and normal tidal stresses at Parkfield have different amplitudes and are not in phase, we have modified the model to include the expected sensitivity to normal stress. Our prior investigations of the response of both regular and low frequency earthquakes to tidal stresses [Thomas et al., 2009; Shelly and Johnson, 2011] are qualitatively consistent with the predictions of the friction model , as both the timing and degree (probability) of correlation are in agreement.

Evidence for polaron conduction in nanostructured manganese ferrite

International Nuclear Information System (INIS)

Gopalan, E Veena; Anantharaman, M R; Malini, K A; Saravanan, S; Kumar, D Sakthi; Yoshida, Yasuhiko

2008-01-01

Nanoparticles of manganese ferrite were prepared by the chemical co-precipitation technique. The dielectric parameters, namely, real and imaginary dielectric permittivity (ε' and ε-prime), ac conductivity (σ ac ) and dielectric loss tangent (tanδ), were measured in the frequency range of 100 kHz-8 MHz at different temperatures. The variations of dielectric dispersion (ε') and dielectric absorption (ε-prime) with frequency and temperature were also investigated. The variation of dielectric permittivity with frequency and temperature followed the Maxwell-Wagner model based on interfacial polarization in consonance with Koops phenomenological theory. The dielectric loss tangent and hence ε-prime exhibited a relaxation at certain frequencies and at relatively higher temperatures. The dispersion of dielectric permittivity and broadening of the dielectric absorption suggest the possibility of a distribution of relaxation time and the existence of multiple equilibrium states in manganese ferrite. The activation energy estimated from the dielectric relaxation is found to be high and is characteristic of polaron conduction in the nanosized manganese ferrite. The ac conductivity followed a power law dependence σ ac = Bω n typical of charge transport assisted by a hopping or tunnelling process. The observed minimum in the temperature dependence of the frequency exponent n strongly suggests that tunnelling of the large polarons is the dominant transport process

Effect of frequency on amplitude-dependent internal friction in niobium

International Nuclear Information System (INIS)

Ide, Naoki; Atsumi, Tomohiro; Nishino, Yoichi

2006-01-01

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 -9 was read from the stress-strain curves. It was found that the microplastic flow stress was proportional to the frequency

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.

Magnetic-field dependence of electrothermal conductivity in YBCO

Energy Technology Data Exchange (ETDEWEB)

Marino, A.; Uribe, R. [Universidad del Tolima, Ibague (Colombia); Grupo de Superconductividad y Nuevos Materiales, Universidad Nacional de Colombia, Bogota (Colombia)

2008-11-15

Experimental measurements of the electrothermal conductivity (P) near T{sub c}, as a function of external magnetic field were carried out in undoped YBCO (123) superconducting samples. The electrothermal conductivity which relates electrical and thermal currents, depends on the applied magnetic field in high T{sub c} materials, contrary to conventional low T{sub c} superconductors where P is nearly independent of the magnetic field. The experimental P(B,T) data determined from resistivity and thermopower measurements were analyzed in terms of theoretical models and showed a behavior consistent with an order-parameter symmetry (OPS) of d{sub x{sup 2}-y{sup 2}}-wave type. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Analysis of frequency-dependent series resistance and interface states of In/SiO{sub 2}/p-Si (MIS) structures

Energy Technology Data Exchange (ETDEWEB)

Birkan Selcuk, A. [Department of Nuclear Electronics and Instrumentation, Saraykoey Nuclear Research and Training Center, 06983 Saray, Ankara (Turkey); Tugluoglu, N. [Department of Nuclear Electronics and Instrumentation, Saraykoey Nuclear Research and Training Center, 06983 Saray, Ankara (Turkey)], E-mail: ntuglu@taek.gov.tr; Karadeniz, S.; Bilge Ocak, S. [Department of Nuclear Electronics and Instrumentation, Saraykoey Nuclear Research and Training Center, 06983 Saray, Ankara (Turkey)

2007-11-15

In this work, the investigation of the interface state density and series resistance from capacitance-voltage (C-V) and conductance-voltage (G/{omega}-V) characteristics in In/SiO{sub 2}/p-Si metal-insulator-semiconductor (MIS) structures with thin interfacial insulator layer have been reported. The thickness of SiO{sub 2} film obtained from the measurement of the oxide capacitance corrected for series resistance in the strong accumulation region is 220 A. The forward and reverse bias C-V and G/{omega}-V characteristics of MIS structures have been studied at the frequency range 30 kHz-1 MHz at room temperature. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance (R{sub s}) and interface state density (D{sub it}) values. Both the series resistance R{sub s} and density of interface states D{sub it} are strongly frequency-dependent and decrease with increasing frequency. The distribution profile of R{sub s}-V gives a peak at low frequencies in the depletion region and disappears with increasing frequency. Experimental results show that the interfacial polarization contributes to the improvement of the dielectric properties of In/SiO{sub 2}/p-Si MIS structures. The interface state density value of In/SiO{sub 2}/p-Si MIS diode calculated at strong accumulation region is 1.11x10{sup 12} eV{sup -1} cm{sup -2} at 1 MHz. It is found that the calculated value of D{sub it} ({approx}10{sup 12} eV{sup -1} cm{sup -2}) is not high enough to pin the Fermi level of the Si substrate disrupting the device operation.

Frequency and temperature dependent mobility of a charged carrier and randomly interrupted strand

International Nuclear Information System (INIS)

Kumar, N.; Jayannavar, A.M.

1981-05-01

Randomly interrupted strand model of a one-dimensional conductor is considered. Exact analytical expression is obtained for the temperature dependent as mobility for a finite segment drawn at random, taking into account the reflecting barriers at the two open ends. The real part of mobility shows a broad resonance as a function of both frequency and tempeature, and vanishes quadratically in the dc limit. The frequency (temperature) maximum shifts to higher values for higher temperatures (frequencies). (author)

Unusual polarity-dependent patterns in a bent-core nematic liquid crystal under low-frequency ac field.

Science.gov (United States)

Xiang, Ying; Zhou, Meng-jie; Xu, Ming-Ya; Salamon, Péter; Éber, Nándor; Buka, Ágnes

2015-04-01

Electric-field-induced patterns of diverse morphology have been observed over a wide frequency range in a recently synthesized bent-core nematic (BCN) liquid crystal. At low frequencies (up to ∼25 Hz), the BCN exhibited unusual polarity-dependent patterns. When the amplitude of the ac field was enhanced, these two time-asymmetrical patterns turned into time-symmetrical prewavylike stripes. At ac frequencies in the middle-frequency range (∼50-3000 Hz), zigzag patterns were detected whose obliqueness varied with the frequency. Finally, if the frequency was increased above 3 kHz, the zigzag pattern was replaced by another, prewavylike pattern, whose threshold voltage depended on the frequency; however, the wave vector did not. For a more complete characterization, material parameters such as elastic constants, dielectric permittivities, and the anisotropy of the diamagnetic susceptibility were also determined.

Frequency-Dependent Altered Functional Connections of Default Mode Network in Alzheimer’s Disease

Directory of Open Access Journals (Sweden)

Youjun Li

2017-08-01

Full Text Available Alzheimer’s disease (AD is a neurodegenerative disorder associated with the progressive dysfunction of cognitive ability. Previous research has indicated that the default mode network (DMN is closely related to cognition and is impaired in Alzheimer’s disease. Because recent studies have shown that different frequency bands represent specific physiological functions, DMN functional connectivity studies of the different frequency bands based on resting state fMRI (RS-fMRI data may provide new insight into AD pathophysiology. In this study, we explored the functional connectivity based on well-defined DMN regions of interest (ROIs from the five frequency bands: slow-5 (0.01–0.027 Hz, slow-4 (0.027–0.073 Hz, slow-3 (0.073–0.198 Hz, slow-2 (0.198–0.25 Hzs and standard low-frequency oscillations (LFO (0.01–0.08 Hz. We found that the altered functional connectivity patterns are mainly in the frequency band of slow-5 and slow-4 and that the decreased connections are long distance, but some relatively short connections are increased. In addition, the altered functional connections of the DMN in AD are frequency dependent and differ between the slow-5 and slow-4 bands. Mini-Mental State Examination scores were significantly correlated with the altered functional connectivity patterns in the slow-5 and slow-4 bands. These results indicate that frequency-dependent functional connectivity changes might provide potential biomarkers for AD pathophysiology.

ac Conductivity analysis and dielectric relaxation behaviour of NaNO3-Al2O3 composites

International Nuclear Information System (INIS)

Anantha, P.S.; Hariharan, K.

2005-01-01

The electrical conductivity of NaNO 3 -xAl 2 O 3 composites has been studied over the wide range of temperature and frequency by means of impedance spectroscopy. The real part of the frequency dependent conductivity exhibits a simple power law feature and the dimensionless frequency exponent n has been determined. The conductivity spectra show scaling behaviour when the conductivity spectra are scaled by σ dc T, where T is temperature in Kelvin. The real part of dielectric permittivity shows saturation at higher frequencies and a strong dispersion at lower frequencies. The imaginary part of permittivity varies inversely with frequency, due to the presence of dc conductivity. The frequency dependent plots of M' and Z' show that the conductivity relaxation is non-Debye in nature. The Kohlrausch-Williams-Watts stretched exponential function was used to describe the modulus spectra and the stretching exponent β is found to be temperature independent. The conductivity relaxation time has been estimated from the modulus spectra. The activation energy responsible for relaxation has been evaluated and it was found to be almost same as that of dc conductivity

On the channel width-dependence of the thermal conductivity in ultra-narrow graphene nanoribbons

Energy Technology Data Exchange (ETDEWEB)

Karamitaheri, Hossein [Department of Electrical Engineering, University of Kashan, Kashan 87317-53153 (Iran, Islamic Republic of); Neophytou, Neophytos, E-mail: N.Neophytou@warwick.ac.uk [School of Engineering, University of Warwick, Coventry CV4 7AL (United Kingdom)

2016-08-08

The thermal conductivity of low-dimensional materials and graphene nanoribbons, in particular, is limited by the strength of line-edge-roughness scattering. One way to characterize the roughness strength is the dependency of the thermal conductivity on the channel's width in the form W{sup β}. Although in the case of electronic transport, this dependency is very well studied, resulting in W{sup 6} for nanowires and quantum wells and W{sup 4} for nanoribbons, in the case of phonon transport it is not yet clear what this dependence is. In this work, using lattice dynamics and Non-Equilibrium Green's Function simulations, we examine the width dependence of the thermal conductivity of ultra-narrow graphene nanoribbons under the influence of line edge-roughness. We show that the exponent β is in fact not a single well-defined number, but it is different for different parts of the phonon spectrum depending on whether phonon transport is ballistic, diffusive, or localized. The exponent β takes values β < 1 for semi-ballistic phonon transport, values β ≫ 1 for sub-diffusive or localized phonons, and β = 1 only in the case where the transport is diffusive. The overall W{sup β} dependence of the thermal conductivity is determined by the width-dependence of the dominant phonon modes (usually the acoustic ones). We show that due to the long phonon mean-free-paths, the width-dependence of thermal conductivity becomes a channel length dependent property, because the channel length determines whether transport is ballistic, diffusive, or localized.

Study on Frequency Dependency of ON-Resistance and Pulse-Loss Calculation of MOSFETs for Switch Mode Power Supply

Science.gov (United States)

Yamamura, Hideho; Sato, Ryohei; Iwata, Yoshiharu

Global efforts toward energy conservation, increasing data centers, and the increasing use of IT equipments are leading to a demand in reduced power consumption of equipments, and power efficiency improvement of power supply units is becoming a necessity. MOSFETs are widely used for their low ON-resistances. Power efficiency is designed using time-domain circuit simulators, except for transformer copper-loss, which has frequency dependency which is calculated separately using methods based on skin and proximity effects. As semiconductor technology reduces the ON-resistance of MOSFETs, frequency dependency due to the skin effect or proximity effect is anticipated. In this study, ON-resistance of MOSFETs are measured and frequency dependency is confirmed. Power loss against rectangular current pulse is calculated. The calculation method for transformer copper-loss is expanded to MOSFETs. A frequency function for the resistance model is newly developed and parametric calculation is enabled. Acceleration of calculation is enabled by eliminating summation terms. Using this method, it is shown that the frequency dependent component of the measured MOSFETs increases the dissipation from 11% to 32% at a switching frequency of 100kHz. From above, this paper points out the importance of the frequency dependency of MOSFETs' ON-resistance, provides means of calculating its pulse losses, and improves loss calculation accuracy of SMPSs.

Kubo formula for frequency dispersion of dielectric permittivity and static conductivity of the Coulomb system

International Nuclear Information System (INIS)

Bobrov, V.B.; Trigger, S.A.; Zagorodny, A.G.

2010-01-01

It is proved that the Kubo formula for the conductivity σ(ω) is valid at real frequencies ω. On this basis, an exact relation is derived for the static conductivity σ st of the Coulomb system. It is shown that the static conductivity is determined by the time correlation function in the limit t→∞. It is proved that the permittivity ε(ω) satisfies the Kramers-Kronig relations which take into account a singularity associated with static conductivity.

High resolution electromagnetic methods and low frequency dispersion of rock conductivity

Directory of Open Access Journals (Sweden)

V. V. Ageev

1999-06-01

Full Text Available The influence of frequency dispersion of conductivity (induced polarization of rocks on the results of electromagnetic (EM sounding was studied on the basis of calculation of electric field of vertical magnetic dipole above horizontally layered polarizable sections. Frequency dispersion was approximated by the Debye formula. Polarizable homogeneous halfspace, two, three and multilayered sections were analyzed in frequency and time domains. The calculations for different values of chargeability and time constants of polarization were performed. In the far zone of a source, the IP of rocks led to quasi-wave phenomena. They produced rapid fluctuations of frequency and transient sounding curves (interference phenomena, multireflections in polarizable layers. In the case of transient sounding in the near zone of a source quasistatic distortions prevailed, caused by the counter electromotive force arising in polarizable layers which may lead to strong changes in transient curves. In some cases quasiwave and quasistatic phenomena made EM sounding curves non-interpretable in the class of quasistationary curves over non-dispersive sections. On the other hand, they could increase the resolution and depth of investigation of EM sounding. This was confirmed by an experience of "high-resolution" electroprospecting in Russia. The problem of interpretation of EM sounding data in polarizable sections is nonunique. To achieve uniqueness it is probably necessary to complement them by soundings of other type.

High resolution electromagnetic methods and low frequency dispersion of rock conductivity

International Nuclear Information System (INIS)

Svetov, B.S.; Ageev, V.V.

1999-01-01

The influence of frequency dispersion of conductivity (induced polarization) of rocks on the results of electromagnetic (EM) sounding was studied on the basis of calculation of electric field of vertical magnetic dipole above horizontally layered polarizable sections. Frequency dispersion was approximated by the Debye formula. Polarizable homogeneous half space, two, three and multilayered section were analyzed in frequency and tim domains. The calculations for different values of charge ability and time constants of polarization were performed. In the far zone of a source, the IP of rocks led to quasi-wave phenomena. They produced rapid fluctuations of frequency and transient sounding curves (interference phenomena, multireflections in polarizable layers). In the case of transient sounding in the near zone of a source quasistatic distortions prevailed, caused by the counter electromotive force arising in polarizable layers which may lead to strong change in transient curves. In same case in quasiwave and quasistatic phenomena made EM sounding curves non-interpretable in the class of quasistationary curves over non-dispersive sections. On the other hand, they could increase the resolution and depth of investigation of EM sounding. This was confirmed by an experience of 'high-resolution' electroprospectring in Russia. The problem of interpretation of EM sounding data in polarizable sections is non unique. To achieve uniqueness it is probably to complement them by sounding of other type

High resolution electromagnetic methods and low frequency dispersion of rock conductivity

Energy Technology Data Exchange (ETDEWEB)

Svetov, B.S.; Ageev, V.V. [Geoelectromagnetic Research Institute, Institute of Physics of the Earth, RAS, Moscow (Russian Federation)

1999-08-01

The influence of frequency dispersion of conductivity (induced polarization) of rocks on the results of electromagnetic (EM) sounding was studied on the basis of calculation of electric field of vertical magnetic dipole above horizontally layered polarizable sections. Frequency dispersion was approximated by the Debye formula. Polarizable homogeneous half space, two, three and multilayered section were analyzed in frequency and tim domains. The calculations for different values of charge ability and time constants of polarization were performed. In the far zone of a source, the IP of rocks led to quasi-wave phenomena. They produced rapid fluctuations of frequency and transient sounding curves (interference phenomena, multireflections in polarizable layers). In the case of transient sounding in the near zone of a source quasistatic distortions prevailed, caused by the counter electromotive force arising in polarizable layers which may lead to strong change in transient curves. In same case in quasi wave and quasistatic phenomena made Em sounding curves non-interpretable in the class of quasistationary curves over non-dispersive sections. On the other hand, they could increase the resolution and depth of investigation of Em sounding. This was confirmed by an experience of 'high-resolution' electroprospectring in Russia. The problem of interpretation of EM sounding data in polarizable sections is non unique. To achieve uniqueness it is probably to complement them by sounding of other type.

Stimulus-dependent modulation of spontaneous low-frequency oscillations in the rat visual cortex.

Science.gov (United States)

Huang, Liangming; Liu, Yadong; Gui, Jianjun; Li, Ming; Hu, Dewen

2014-08-06

Research on spontaneous low-frequency oscillations is important to reveal underlying regulatory mechanisms in the brain. The mechanism for the stimulus modulation of low-frequency oscillations is not known. Here, we used the intrinsic optical imaging technique to examine stimulus-modulated low-frequency oscillation signals in the rat visual cortex. The stimulation was presented monocularly as a flashing light with different frequencies and intensities. The phases of low-frequency oscillations in different regions tended to be synchronized and the rhythms typically accelerated within a 30-s period after stimulation. These phenomena were confined to visual stimuli with specific flashing frequencies (12.5-17.5 Hz) and intensities (5-10 mA). The acceleration and synchronization induced by the flashing frequency were more marked than those induced by the intensity. These results show that spontaneous low-frequency oscillations can be modulated by parameter-dependent flashing lights and indicate the potential utility of the visual stimulus paradigm in exploring the origin and function of low-frequency oscillations.

Study on the Effect of Frequency on Conductivity of Underground Strata in Coal Mine Through-the-earth Wireless Communication

Directory of Open Access Journals (Sweden)

Jinyi TAO

2014-09-01

Full Text Available The relationship of conductivity and the frequency, which is of decisive significance in through-the-earth wireless communication in coal mine, is closely related to the options of frequency range in coal mine wireless communication. When through-the-earth wireless communication is applied, the electromagnetic waves need to spread in the semi-conductive medium rocks. The main factors affecting the electromagnetic wave propagation in rocks is the rock strata electromagnetic parameters. These parameters are magnetic permeability m (H/m, dielectric constant e (F/m and electrical conductivity s (S/m. In these parameters, electrical conductivity is not constant. Under the influence of various factors, it will be great changes. This paper, for the specific circumstances of coal mine rock, discuses and conduct dada mining the effect frequency on the electrical conductivity of underground rock in coal mine with through-the-earth wireless communication.

Four-phonon processes in the thermal conductivity of GaSb

International Nuclear Information System (INIS)

Aliev, M.I.; Arasly, D.G.; Guseinov, R.E.

1978-01-01

Phonon thermal conductivity of GaSb in the 300-700 K temperature range is studied by the light pulsed heating which is aimed at estimation of contributions of different polarized branches of acoustic oscillations into lattice thermal conductivity. The role of optico-acoustic interactions and multiphonon processes in phonon-phonon scattering at high temperatures is discussed. It is shown that the X thermal conductivity caused by the current carriers is negligibly small, and the Xsub(ph) phonon conductivity changes depending on temperature according to the Xsub(ph) approximately Tsup(-1.4) law. While calculating Xsub(ph) according to the Holland model taking into account phonon scattering on point defects the phonon thermal conductivity is given as a sum of contributions from longitudinal and transverse low-frequency Xsub(th1) and high-frequency Xsub(th2) acoustic phonons. It is established that at T>500 K Xsub(ph) is caused only by high-frequency transverse phonons and to explain the observed Xsub(ph) dependence on temperature it is necessary to introduce four-phonon process along with the three-phonon processes into intraphonon scattering

Optical conductivity of the Hubbard model

International Nuclear Information System (INIS)

Vicente Alvarez, J.J.; Balseiro, C.A.; Ceccatto, H.A.

1996-07-01

We study the response to a static electric field (charge stiffness) and the frequency-dependent conductivity of the Hubbard model in a resonant-valence-bond-type paramagnetic phase. This phase is described by means of a charge and spin rotational-invariant approach, based on a mixed fermion-boson representation of the original strongly correlated electrons. We found that the Mott transition at half filling is well described by the charge stiffness behaviour, and that the values for this quantity off half filling agree reasonably well with numerical results. Furthermore, for the frequency-dependent conductivity we trace back the origin of the band which appears inside the Hubbard gap to magnetic pair breaking. This points to a magnetic origin of midinfrared band in high-T c compounds, with no relation to superconductivity. (author). 12 refs, 2 tabs

Influence of Gaussian white noise on the frequency-dependent linear polarizability of doped quantum dot

International Nuclear Information System (INIS)

Ganguly, Jayanta; Ghosh, Manas

2014-01-01

Highlights: • Linear polarizability of quantum dot has been studied. • Quantum dot is doped with a repulsive impurity. • The polarizabilities are frequency-dependent. • Influence of Gaussian white noise has been monitored. • Noise exploited is of additive and multiplicative nature. - Abstract: We investigate the profiles of diagonal components of frequency-dependent linear (α xx and α yy ) optical response of repulsive impurity doped quantum dots. The dopant impurity potential chosen assumes Gaussian form. The study principally puts emphasis on investigating the role of noise on the polarizability components. In view of this we have exploited Gaussian white noise containing additive and multiplicative characteristics (in Stratonovich sense). The frequency-dependent polarizabilities are studied by exposing the doped dot to a periodically oscillating external electric field of given intensity. The oscillation frequency, confinement potentials, dopant location, and above all, the noise characteristics tune the linear polarizability components in a subtle manner. Whereas the additive noise fails to have any impact on the polarizabilities, the multiplicative noise influences them delicately and gives rise to additional interesting features

Lattice thermal conductivity of disordered NiPd and NiPt alloys

International Nuclear Information System (INIS)

Alam, Aftab; Mookerjee, Abhijit

2006-01-01

Numerical calculations of lattice thermal conductivity are reported for the binary alloys NiPd and NiPt. The present work is a continuation of an earlier paper by us (Alam and Mookerjee 2005 Phys. Rev. B 72 214207), which developed a theoretical framework for the calculation of configuration-averaged lattice thermal conductivity and thermal diffusivity in disordered alloys. The formulation was based on the augmented space theorem (Mookerjee 1973 J. Phys. C: Solid State Phys. 6 L205) combined with a scattering diagram technique. In this paper we shall show the dependence of the lattice thermal conductivity on a series of variables like phonon frequency, temperature and alloy composition. The temperature dependence of κ(T) and its relation to the measured thermal conductivity is discussed. The concentration dependence of κ appears to justify the notion of a minimum thermal conductivity as discussed by Kittel, Slack and others (Kittel 1948 Phys. Rev. 75 972, Brich and Clark 1940 Am. J. Sci. 238 613; Slack 1979 Solid State Physics vol 34, ed H Ehrenreich, F Seitz and D Turnbull (New York: Academic) p 1). We also study the frequency and composition dependence of the thermal diffusivity averaged over modes. A numerical estimate of this quantity gives an idea about the location of the mobility edge and the fraction of states in the frequency spectrum which is delocalized

Dielectric and conductivity properties of composite polyaniline/polyurethane network

Science.gov (United States)

Liang, C.; Gest, J.; Leroy, G.; Carru, J.-C.

2013-09-01

In this work, we present the dielectric characterization of polyaniline/polyurethane composite. The samples consisting of 0.5%, 1%, and 5% of polyaniline were deposited on glass fiber, and the measurements were performed in a frequency range of 20 Hz to 20 GHz. The results showed a dielectric relaxation strongly dependent on the concentration of polyaniline. This phenomenon is explained by a theoretical model. In this model, we assume that the alternative conductivity of the polymer network systems is due to conducting clusters whose lengths followed a Gaussian distribution. Depending on their size and the frequency of the excitation signal, the clusters showed a resistive or capacitive effect.

The conduction block produced by oxcarbazepine in the isolated rat sciatic nerve: a comparison with lamotrigine.

Science.gov (United States)

Guven, Mustafa; Kahraman, Ibrahim; Koc, Filiz; Bozdemir, Hacer; Sarica, Yakup; Gunay, Ismail

2011-01-01

Oxcarbazepine is an antiepileptic drug widely used for the treatment of neuropathic pain. In the present study, the effects of oxcarbazepine and lamotrigine on conduction properties in the rat sciatic nerves were examined. The experiments were conducted with in vitro sucrose-gap technique on the isolated wistar rat sciatic nerves. The compound action potentials were obtained by tonic (single) and phasic (10, 40, and 100 Hz) stimulation. Oxcarbazepine produced a significant concentration- and frequency-dependent reduction in the compound action potential amplitude. When the two drugs were applied at concentrations that produced equal levels of tonic (i.e., non-frequency-dependent) conduction block, oxcarbazepine produced the greatest phasic (i.e., frequency-dependent) conduction block, followed by lamotrigine. Oxcarbazepine and lamotrigine reduced the 4-aminopyridine-induced amplitude of delayed depolarization; however, oxcarbazepine had a significantly greater effect than lamotrigine. These results suggest that oxcarbazepine produces more potent frequency-dependent conduction block than lamotrigine, and suppresses the delayed depolarization which contributes to sensory signaling and may play a role in neuropathic pain. The findings provide insight into the mechanisms of action of oxcarbazepine and lamotrigine and may help in the development of novel therapies for neuropathic pain.

Effects of aromaticity in cations and their functional groups on the temperature dependence of low-frequency spectrum

Science.gov (United States)

Kakinuma, Shohei; Ramati, Sharon; Wishart, James F.; Shirota, Hideaki

2018-05-01

In this study, we investigate the temperature dependence of low-frequency spectra in the frequency range of 0.3-200 cm-1 for ionic liquids (ILs) whose cations possess two systematically different cyclic groups, using femtosecond Raman-induced Kerr effect spectroscopy. The target ILs are bis(trifluoromethylsulfonyl)amide [NTf2]- salts of 1-cyclohexylmethyl-1-methylpyrrolidinium [CHxmMPyrr]+, 1-cyclohexylmethyl-3-methylimidazolium [CHxmMIm]+, N-cyclohexylmethylpyridinium [CHxmPy]+, 1-benzyl-1-methylpyrrolidinium [BzMPyrr]+, 1-benzyl-3-methylimidazolium [BzMIm]+, and N-benzylpyridinium [BzPy]+ cations. The aim of this study is to better understand the effects of aromaticity in the cations' constituent groups on the temperature-dependent low-frequency spectral features of the ILs. The low-frequency spectra of these ILs are temperature dependent, but the temperature-dependent spectrum of [CHxmMPyrr][NTf2] is different from that of other ILs. While [CHxmMPyrr][NTf2] shows spectral changes with temperature in the low-frequency region below 50 cm-1, the other ILs also show spectral changes in the high-frequency region above 80 cm-1 (above 50 cm-1 in the case of [BzMPyrr][NTf2]). We conclude that the spectral change in the low-frequency region is due to both the cation and anion, while the change in the high-frequency region is attributed to the red shift of the aromatic ring librations. On the basis of the plots of the first moment of the spectra vs. temperature, we found that the first moment of the low-frequency spectrum of the IL whose cation does not have an aromatic ring is less temperature dependent than that of the other ILs. However, the intrinsic first moment, the first moment at 0 K, of the low-frequency spectrum is governed by the absence or presence of a charged aromatic group, while a neutral aromatic group does not have much influence on determining the intrinsic first moment.

Input-dependent frequency modulation of cortical gamma oscillations shapes spatial synchronization and enables phase coding.

Science.gov (United States)

Lowet, Eric; Roberts, Mark; Hadjipapas, Avgis; Peter, Alina; van der Eerden, Jan; De Weerd, Peter

2015-02-01

Fine-scale temporal organization of cortical activity in the gamma range (∼25-80Hz) may play a significant role in information processing, for example by neural grouping ('binding') and phase coding. Recent experimental studies have shown that the precise frequency of gamma oscillations varies with input drive (e.g. visual contrast) and that it can differ among nearby cortical locations. This has challenged theories assuming widespread gamma synchronization at a fixed common frequency. In the present study, we investigated which principles govern gamma synchronization in the presence of input-dependent frequency modulations and whether they are detrimental for meaningful input-dependent gamma-mediated temporal organization. To this aim, we constructed a biophysically realistic excitatory-inhibitory network able to express different oscillation frequencies at nearby spatial locations. Similarly to cortical networks, the model was topographically organized with spatially local connectivity and spatially-varying input drive. We analyzed gamma synchronization with respect to phase-locking, phase-relations and frequency differences, and quantified the stimulus-related information represented by gamma phase and frequency. By stepwise simplification of our models, we found that the gamma-mediated temporal organization could be reduced to basic synchronization principles of weakly coupled oscillators, where input drive determines the intrinsic (natural) frequency of oscillators. The gamma phase-locking, the precise phase relation and the emergent (measurable) frequencies were determined by two principal factors: the detuning (intrinsic frequency difference, i.e. local input difference) and the coupling strength. In addition to frequency coding, gamma phase contained complementary stimulus information. Crucially, the phase code reflected input differences, but not the absolute input level. This property of relative input-to-phase conversion, contrasting with latency codes

Real-time correction of tsunami site effect by frequency-dependent tsunami-amplification factor

Science.gov (United States)

Tsushima, H.

2017-12-01

For tsunami early warning, I developed frequency-dependent tsunami-amplification factor and used it to design a recursive digital filter that can be applicable for real-time correction of tsunami site response. In this study, I assumed that a tsunami waveform at an observing point could be modeled by convolution of source, path and site effects in time domain. Under this assumption, spectral ratio between offshore and the nearby coast can be regarded as site response (i.e. frequency-dependent amplification factor). If the amplification factor can be prepared before tsunamigenic earthquakes, its temporal convolution to offshore tsunami waveform provides tsunami prediction at coast in real time. In this study, tsunami waveforms calculated by tsunami numerical simulations were used to develop frequency-dependent tsunami-amplification factor. Firstly, I performed numerical tsunami simulations based on nonlinear shallow-water theory from many tsuanmigenic earthquake scenarios by varying the seismic magnitudes and locations. The resultant tsunami waveforms at offshore and the nearby coastal observing points were then used in spectral-ratio analysis. An average of the resulted spectral ratios from the tsunamigenic-earthquake scenarios is regarded as frequency-dependent amplification factor. Finally, the estimated amplification factor is used in design of a recursive digital filter that can be applicable in time domain. The above procedure is applied to Miyako bay at the Pacific coast of northeastern Japan. The averaged tsunami-height spectral ratio (i.e. amplification factor) between the location at the center of the bay and the outside show a peak at wave-period of 20 min. A recursive digital filter based on the estimated amplification factor shows good performance in real-time correction of tsunami-height amplification due to the site effect. This study is supported by Japan Society for the Promotion of Science (JSPS) KAKENHI grant 15K16309.

The long-term evolution of multilocus traits under frequency-dependent disruptive selection

NARCIS (Netherlands)

Van Doorn, G. Sander; Dieckmann, Ulf

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

GABAergic activities control spike timing- and frequency-dependent long-term depression at hippocampal excitatory synapses

Directory of Open Access Journals (Sweden)

Makoto Nishiyama

2010-06-01

Full Text Available GABAergic interneuronal network activities in the hippocampus control a variety of neural functions, including learning and memory, by regulating θ and γ oscillations. How these GABAergic activities at pre- and post-synaptic sites of hippocampal CA1 pyramidal cells differentially contribute to synaptic function and plasticity during their repetitive pre- and post-synaptic spiking at θ and γ oscillations is largely unknown. We show here that activities mediated by postsynaptic GABAARs and presynaptic GABABRs determine, respectively, the spike timing- and frequency-dependence of activity-induced synaptic modifications at Schaffer collateral-CA1 excitatory synapses. We demonstrate that both feedforward and feedback GABAAR-mediated inhibition in the postsynaptic cell controls the spike timing-dependent long-term depression of excitatory inputs (“e-LTD” at the θ frequency. We also show that feedback postsynaptic inhibition specifically causes e-LTD of inputs that induce small postsynaptic currents (<70 pA with LTP timing, thus enforcing the requirement of cooperativity for induction of long-term potentiation at excitatory inputs (“e-LTP”. Furthermore, under spike-timing protocols that induce e-LTP and e-LTD at excitatory synapses, we observed parallel induction of LTP and LTD at inhibitory inputs (“i-LTP” and “i-LTD” to the same postsynaptic cells. Finally, we show that presynaptic GABABR-mediated inhibition plays a major role in the induction of frequency-dependent e-LTD at α and β frequencies. These observations demonstrate the critical influence of GABAergic interneuronal network activities in regulating the spike timing and frequency dependences of long-term synaptic modifications in the hippocampus.

Microwave absorptions of ultrathin conductive films and designs of frequency-independent ultrathin absorbers

International Nuclear Information System (INIS)

Li, Sucheng; Anwar, Shahzad; Lu, Weixin; Hang, Zhi Hong; Hou, Bo; Shen, Mingrong; Wang, Chin-Hua

2014-01-01

We study the absorption properties of ultrathin conductive films in the microwave regime, and find a moderate absorption effect which gives rise to maximal absorbance 50% if the sheet (square) resistance of the film meets an impedance matching condition. The maximal absorption exhibits a frequency-independent feature and takes place on an extremely subwavelength scale, the film thickness. As a realistic instance, ∼5 nm thick Au film is predicted to achieve the optimal absorption. In addition, a methodology based on metallic mesh structure is proposed to design the frequency-independent ultrathin absorbers. We perform a design of such absorbers with 50% absorption, which is verified by numerical simulations

Oxygen partial pressure dependence of electrical conductivity in γ'-Bi2MoO6

International Nuclear Information System (INIS)

Vera, C.M.C.; Aragon, R.

2008-01-01

The electrical conductivity of γ'-Bi 2 MoO 6 was surveyed between 450 and 750 deg. C as a function of oxygen partial pressure, in the range 0.01-1 atm. A -1/6 power law dependence, consistent with a Frenkel defect model of doubly ionized oxygen vacancies and interstitials, is evidence for an n-type semiconductive component, with an optical band gap of 2.9 eV. The absence of this dependence is used to map the onset of dominant ionic conduction. - Graphical abstract: Temporal dependence of electrical conductivity at 500 deg. C for γ'-Bi 2 MoO 6 at controlled partial pressures of oxygen

Frequency dependent loss analysis and minimization of system losses in switchmode audio power amplifiers

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...

DETERMINATION OF TEMPERATURE DISTRIBUTION FOR ANNULAR FINS WITH TEMPERATURE DEPENDENT THERMAL CONDUCTIVITY BY HPM

Directory of Open Access Journals (Sweden)

Davood Domairry Ganji

2011-01-01

Full Text Available In this paper, homotopy perturbation method has been used to evaluate the temperature distribution of annular fin with temperature-dependent thermal conductivity and to determine the temperature distribution within the fin. This method is useful and practical for solving the nonlinear heat transfer equation, which is associated with variable thermal conductivity condition. The homotopy perturbation method provides an approximate analytical solution in the form of an infinite power series. The annular fin heat transfer rate with temperature-dependent thermal conductivity has been obtained as a function of thermo-geometric fin parameter and the thermal conductivity parameter describing the variation of the thermal conductivity.

Negative frequency-dependent selection between Pasteuria penetrans and its host Meloidogyne arenaria

Science.gov (United States)

In negative frequency-dependant selection (NFDS), parasite genotypes capable of infecting the numerically dominant host genotype are favored, while host genotypes resistant to the dominant parasite genotype are favored, creating a cyclical pattern of resistant genotypes in the host population and, a...

On the profile of frequency and voltage dependent interface states and series resistance in MIS structures

Energy Technology Data Exchange (ETDEWEB)

Doekme, Ilbilge [Science Education Department, Faculty of Kirsehir Education, Gazi University, Kirsehir (Turkey)]. E-mail: ilbilgedokme@gazi.edu.tr; Altindal, Semsettin [Physics Department, Faculty of Arts and Sciences, Gazi University, 06500, Teknikokullar, Ankara (Turkey)

2007-04-30

The variation in the capacitance-voltage (C-V) and conductance-voltage (G/{omega}-V) characteristics of Au/SiO{sub 2}/n-Si metal-insulator-semiconductor (MIS) structure have been systematically investigated as a function of frequencies in the frequency range 0.5 kHz-10 MHz at room temperature. In addition, the forward and reverse bias current-voltage (I-V) characteristics of this structure were measured at room temperature. The high value of ideality factor was attributed to the high density of interface states localized at Si/SiO{sub 2} interface and interfacial oxide layer. The density of interface states (N{sub ss}) and the series resistance (R{sub ss}) were calculated from I-V and C-V measurements using different methods and the effect of them on C-V and G/{omega}-V characteristics were deeply researched. At the same energy position near the top of valance band, the calculated N{sub ss} values, obtained without taking into account the series resistance of the devices almost one order of magnitude larger than N{sub ss} values obtained by taking into account R{sub ss} values. It is found that the C-V and G/{omega}-V curves exhibit a peak at low frequencies and the peak values of C and G/{omega} decrease with increasing frequency. Also, the plots of R {sub s} as a function of bias give two peaks in the certain voltage range at low frequencies. These observations indicate that at low frequencies, the charges at interface states can easily follow an AC signal and the number of them increases with decreasing frequency. The I-V, C-V and G/{omega}-V characteristics of the MIS structure are affected not only with R {sub s} but also N {sub ss}. Experimental results show that both the R{sub s} and C{sub o} values should be taken into account in determining frequency-dependent electrical characteristics.

ac conductivity of a one-dimensional site-disordered lattice

International Nuclear Information System (INIS)

Albers, R.C.; Gubernatis, J.E.

1978-01-01

We report the results of a numerical study of the ac conductivity for the Anderson model of a one-dimensional, site-disordered system of 400 atoms. For different degrees of disorder, we directly diagonalized the Anderson Hamiltonian, used the Kubo-Greenwood formula to evaluate the conductivity, and then averaged the conductivity over 12 configurations. We found that the dominant frequency dependence of the conductivity consisted of a single peak which shifted to higher frequency and decreased in overall magnitude as the disorder was increased. The joint density of states and the eigenstate localization were also computed and are discussed in connection with our results

Temporary persistence of conduction block after prolonged kilohertz frequency alternating current on rat sciatic nerve

Science.gov (United States)

Bhadra, Narendra; Foldes, Emily; Vrabec, Tina; Kilgore, Kevin; Bhadra, Niloy

2018-02-01

Objective. Application of kilohertz frequency alternating current (KHFAC) waveforms can result in nerve conduction block that is induced in less than a second. Conduction recovers within seconds when KHFAC is applied for about 5-10 min. This study investigated the effect of repeated and prolonged application of KHFAC on rat sciatic nerve with bipolar platinum electrodes. Approach. Varying durations of KHFAC at signal amplitudes for conduction block with intervals of no stimulus were studied. Nerve conduction was monitored by recording peak Gastrocnemius muscle force utilizing stimulation electrodes proximal (PS) and distal (DS) to a blocking electrode. The PS signal traveled through the block zone on the nerve, while the DS went directly to the motor end-plate junction. The PS/DS force ratio provided a measure of conduction patency of the nerve in the block zone. Main results. Conduction recovery times were found to be significantly affected by the cumulative duration of KHFAC application. Peak stimulated muscle force returned to pre-block levels immediately after cessation of KHFAC delivery when it was applied for less than about 15 min. They fell significantly but recovered to near pre-block levels for cumulative stimulus of 50  ±  20 min, for the tested On/Off times and frequencies. Conduction recovered in two phases, an initial fast one (60-80% recovery), followed by a slower phase. No permanent conduction block was seen at the end of the observation period during any experiment. Significance. This carry-over block effect may be exploited to provide continuous conduction block in peripheral nerves without continuous application of KHFAC.

Relaxation oscillations induced by amplitude-dependent frequency in dissipative trapped electron mode turbulence

International Nuclear Information System (INIS)

Terry, P.W.; Ware, A.S.; Newman, D.E.

1994-01-01

A nonlinear frequency shift in dissipative trapped electron mode turbulence is shown to give rise to a relaxation oscillation in the saturated power density spectrum. A simple non-Markovian closure for the coupled evolution of ion momentum and electron density response is developed to describe the oscillations. From solutions of a nonlinear oscillator model based on the closure, it is found that the oscillation is driven by the growth rate, as modified by the amplitude-dependent frequency shift, with inertia provided by the memory of the growth rate of prior amplitudes. This memory arises from time-history integrals common to statistical closures. The memory associated with a finite time of energy transfer between coupled spectrum components does not sustain the oscillation in the simple model. Solutions of the model agree qualitatively with the time-dependent numerical solutions of the original dissipative trapped electron model, yielding oscillations with the proper phase relationship between the fluctuation energy and the frequency shift, the proper evolution of the wave number spectrum shape and particle flux, and a realistic period

Doping dependent tunneling conductance in SDW ordered copper oxide superconductors

International Nuclear Information System (INIS)

Rout, G.C.; Panda, S.K.

2011-01-01

The model calculation reports the co-existences of s-wave superconductivity and spin density wave (SDW) in high-T c cuprates. The doping dependence of the phase diagram explains the experimental observations qualitatively. The calculated tunneling spectra explains the observed multiple peak structures. This calculation provides an alternative to BCS formalism to calculate order parameters from the spectra. It is observed that doping suppresses the long range anti-ferromagnetic order and induces superconducting phase for a suitable doping. In order to study this effect, we present a model study of the doping dependence of the tunneling conductance in high-T c systems. The system is described by the Hamiltonian consisting of spin density wave (SDW) and s-wave type superconducting interaction in presence of varying impurity concentrations. The gap equations are calculated by using Green's functions technique of Zubarev. The gap equations and the chemical potential are solved self-consistently. The imaginary part of the electron Green's functions shows the quasi-particle density of states which represent the tunneling conductance observed by the scanning tunneling microscopy (STM). We investigate the effect of impurity on the gap equations as well as on the tunneling conductance. The results will be discussed based on the experimental observations.

Doping dependent tunneling conductance in SDW ordered copper oxide superconductors

Energy Technology Data Exchange (ETDEWEB)

Rout, G.C., E-mail: gcr@iopb.res.in [Condensed Matter Physics Group, Dept. of Applied Physics and Ballistics, F.M. University, 756 019 Balasore, Orissa (India); Panda, S K [K.D. Science College, Pochilima, Hinjilicut, 761 101 Ganjam, Orissa (India)

2011-07-15

The model calculation reports the co-existences of s-wave superconductivity and spin density wave (SDW) in high-T{sub c} cuprates. The doping dependence of the phase diagram explains the experimental observations qualitatively. The calculated tunneling spectra explains the observed multiple peak structures. This calculation provides an alternative to BCS formalism to calculate order parameters from the spectra. It is observed that doping suppresses the long range anti-ferromagnetic order and induces superconducting phase for a suitable doping. In order to study this effect, we present a model study of the doping dependence of the tunneling conductance in high-T{sub c} systems. The system is described by the Hamiltonian consisting of spin density wave (SDW) and s-wave type superconducting interaction in presence of varying impurity concentrations. The gap equations are calculated by using Green's functions technique of Zubarev. The gap equations and the chemical potential are solved self-consistently. The imaginary part of the electron Green's functions shows the quasi-particle density of states which represent the tunneling conductance observed by the scanning tunneling microscopy (STM). We investigate the effect of impurity on the gap equations as well as on the tunneling conductance. The results will be discussed based on the experimental observations.

Doping dependent tunneling conductance in SDW ordered copper oxide superconductors

Energy Technology Data Exchange (ETDEWEB)

Rout, G.C., E-mail: gcr@iopb.res.in [Condensed Matter Physics Group, Dept. of Applied Physics and Ballistics, F.M. University, 756 019 Balasore, Orissa (India); Panda, S.K. [K.D. Science College, Pochilima, Hinjilicut, 761 101 Ganjam, Orissa (India)

2011-07-15

The model calculation reports the co-existences of s-wave superconductivity and spin density wave (SDW) in high-T{sub c} cuprates. The doping dependence of the phase diagram explains the experimental observations qualitatively. The calculated tunneling spectra explains the observed multiple peak structures. This calculation provides an alternative to BCS formalism to calculate order parameters from the spectra. It is observed that doping suppresses the long range anti-ferromagnetic order and induces superconducting phase for a suitable doping. In order to study this effect, we present a model study of the doping dependence of the tunneling conductance in high-T{sub c} systems. The system is described by the Hamiltonian consisting of spin density wave (SDW) and s-wave type superconducting interaction in presence of varying impurity concentrations. The gap equations are calculated by using Green's functions technique of Zubarev. The gap equations and the chemical potential are solved self-consistently. The imaginary part of the electron Green's functions shows the quasi-particle density of states which represent the tunneling conductance observed by the scanning tunneling microscopy (STM). We investigate the effect of impurity on the gap equations as well as on the tunneling conductance. The results will be discussed based on the experimental observations.

Lead-position dependent regular oscillations and random fluctuations of conductance in graphene quantum dots

International Nuclear Information System (INIS)

Huang Liang; Yang Rui; Lai Yingcheng; Ferry, David K

2013-01-01

Quantum interference causes a wavefunction to have sensitive spatial dependence, and this has a significant effect on quantum transport. For example, in a quantum-dot system, the conductance can depend on the lead positions. We investigate, for graphene quantum dots, the conductance variations with the lead positions. Since for graphene the types of boundaries, e.g., zigzag and armchair, can fundamentally affect the quantum transport characteristics, we focus on rectangular graphene quantum dots, for which the effects of boundaries can be systematically studied. For both zigzag and armchair horizontal boundaries, we find that changing the positions of the leads can induce significant conductance variations. Depending on the Fermi energy, the variations can be either regular oscillations or random conductance fluctuations. We develop a physical theory to elucidate the origin of the conductance oscillation/fluctuation patterns. In particular, quantum interference leads to standing-wave-like-patterns in the quantum dot which, in the absence of leads, are regulated by the energy-band structure of the corresponding vertical graphene ribbon. The observed ‘coexistence’ of regular oscillations and random fluctuations in the conductance can be exploited for the development of graphene-based nanodevices. (paper)

Frequency-dependant homogenized properties of composite using spectral analysis method

International Nuclear Information System (INIS)

Ben Amor, M; Ben Ghozlen, M H; Lanceleur, P

2010-01-01

An inverse procedure is proposed to determine the material constants of multilayered composites using a spectral analysis homogenization method. Recursive process gives interfacial displacement perpendicular to layers in term of deepness. A fast-Fourier transform (FFT) procedure has been used in order to extract the wave numbers propagating in the multilayer. The upper frequency bound of this homogenization domain is estimated. Inside the homogenization domain, we discover a maximum of three planes waves susceptible to propagate in the medium. A consistent algorithm is adopted to develop an inverse procedure for the determination of the materials constants of multidirectional composite. The extracted wave numbers are used as the inputs for the procedure. The outputs are the elastic constants of multidirectional composite. Using this method, the frequency dependent effective elastic constants are obtained and example for [0/90] composites is given.

Estimation of the frequency and magnetic field dependence of the skin depth in Co-rich magnetic microwires from GMI experiments

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.

Conductivity and dielectric behaviour of indium substituted zinc ferrites prepared by coprecipitation method

International Nuclear Information System (INIS)

Cvejić, Željka; Rakić, Srđan; Jankov, Stevan; Skuban, Sonja; Rapajić, Sanja; Srdić, Vladimir V

2015-01-01

This paper presents the results concerning dielectric behavior and conductivity of the nanosized Zn 1−x In x Fe 2 O 4 powders (x = 0, 0.15, 0.2, and 0.3), obtained by coprecipitation method. The frequency dependence of dielectric permittivity and conductivity of the samples is determined in the frequency range of 1–10 5 Hz, at temperatures from 300–350 K, while the temperature dependence of conductivity was recorded at 100 Hz, 10 kHz and 100 kHz. The ac conductivity was found to follow universal dielectric response, which is typical for charge transport by hopping or tunneling processes. Analyzing the variation of the parameter n (as a measure of the degree of correlation between conductivity and frequency), with the temperatures we discuss the possible conduction mechanism in investigated samples. Qualitatively, non-overlapping small polarons (NSPT) are usually associated with increase in n with increasing temperature, while correlated barrier hopping (CBH) shows a decrease in n with increasing T. (paper)

Monitoring voltage-dependent charge displacement of Shaker B-IR K+ ion channels using radio frequency interrogation.

Directory of Open Access Journals (Sweden)

Sameera Dharia

2011-02-01

Full Text Available Here we introduce a new technique that probes voltage-dependent charge displacements of excitable membrane-bound proteins using extracellularly applied radio frequency (RF, 500 kHz electric fields. Xenopus oocytes were used as a model cell for these experiments, and were injected with cRNA encoding Shaker B-IR (ShB-IR K(+ ion channels to express large densities of this protein in the oocyte membranes. Two-electrode voltage clamp (TEVC was applied to command whole-cell membrane potential and to measure channel-dependent membrane currents. Simultaneously, RF electric fields were applied to perturb the membrane potential about the TEVC level and to measure voltage-dependent RF displacement currents. ShB-IR expressing oocytes showed significantly larger changes in RF displacement currents upon membrane depolarization than control oocytes. Voltage-dependent changes in RF displacement currents further increased in ShB-IR expressing oocytes after ∼120 µM Cu(2+ addition to the external bath. Cu(2+ is known to bind to the ShB-IR ion channel and inhibit Shaker K(+ conductance, indicating that changes in the RF displacement current reported here were associated with RF vibration of the Cu(2+-linked mobile domain of the ShB-IR protein. Results demonstrate the use of extracellular RF electrodes to interrogate voltage-dependent movement of charged mobile protein domains--capabilities that might enable detection of small changes in charge distribution associated with integral membrane protein conformation and/or drug-protein interactions.

Monitoring voltage-dependent charge displacement of Shaker B-IR K+ ion channels using radio frequency interrogation.

Science.gov (United States)

Dharia, Sameera; Rabbitt, Richard D

2011-02-28

Here we introduce a new technique that probes voltage-dependent charge displacements of excitable membrane-bound proteins using extracellularly applied radio frequency (RF, 500 kHz) electric fields. Xenopus oocytes were used as a model cell for these experiments, and were injected with cRNA encoding Shaker B-IR (ShB-IR) K(+) ion channels to express large densities of this protein in the oocyte membranes. Two-electrode voltage clamp (TEVC) was applied to command whole-cell membrane potential and to measure channel-dependent membrane currents. Simultaneously, RF electric fields were applied to perturb the membrane potential about the TEVC level and to measure voltage-dependent RF displacement currents. ShB-IR expressing oocytes showed significantly larger changes in RF displacement currents upon membrane depolarization than control oocytes. Voltage-dependent changes in RF displacement currents further increased in ShB-IR expressing oocytes after ∼120 µM Cu(2+) addition to the external bath. Cu(2+) is known to bind to the ShB-IR ion channel and inhibit Shaker K(+) conductance, indicating that changes in the RF displacement current reported here were associated with RF vibration of the Cu(2+)-linked mobile domain of the ShB-IR protein. Results demonstrate the use of extracellular RF electrodes to interrogate voltage-dependent movement of charged mobile protein domains--capabilities that might enable detection of small changes in charge distribution associated with integral membrane protein conformation and/or drug-protein interactions.

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.

Analysis of the conduction mechanism and dielectric properties of N, N', N" tris(4-methylphenyl)phosphoric triamide

Science.gov (United States)

Ali, H. A. M.

2016-03-01

The structure for the powder of N,N', N"-tris(4-methylphenyl)phosphoric triamide, TMP-TA, was characterized using X-ray diffraction (XRD) and differential thermal analysis (DTA) techniques. The ac conductivity and dielectric properties were measured in the frequency range of 42-105 Hz for the bulk TMP-TA in a pellet form at different temperatures. The frequency dependence of ac conductivity was expressed by a Jonscher's universal power law. The frequency exponent (s) was determined from the fitting of experimental data of ac conductivity. The correlated barrier hopping (CBH) model was found to be responsible for the ac conduction mechanism in TMP-TA. The activation energy was calculated from the temperature dependence of ac conductivity. The values of the density of states at the Fermi level were determined for different frequencies. The components of the electric modulus (M' and M") were calculated and used to estimate the relaxation time.

Frequency-dependent changes in the amplitude of low-frequency fluctuations in patients with Wilson's disease: a resting-state fMRI study.

Science.gov (United States)

Hu, Xiaopeng; Chen, Siyi; Huang, Chang-Bing; Qian, Yinfeng; Yu, Yongqiang

2017-06-01

To investigate the frequency-dependent changes in the amplitude of low-frequency fluctuations (ALFF) in patients with Wilson's disease (WD). Resting-state function magnetic resonance imaging (R-fMRI) were employed to measure the amplitude of ALFF in 28 patients with WD and 27 matched normal controls. Slow-5 (0.01-0.027 Hz) and slow-4 (0.027-0.073 Hz) frequency bands were analyzed. Apart from the observation of atrophy in the cerebellum, basal ganglia, occipital gyrus, frontal gyrus, precentral gyrus, and paracentral lobule, we also found widespread differences in ALFF of the two bands in the medial frontal gyrus, inferior temporal gyrus, insula, basal ganglia, hippocampus/parahippocampal gyrus, and thalamus bilaterally. Compared to normal controls, WD patients had increased ALFF in the posterior lobe of the cerebellum, inferior temporal gyrus, brain stem, basal ganglia, and decreased ALFF in the anterior lobe of the cerebellum and medial frontal gyrus. Specifically, we observed that the ALFF abnormalities in the cerebellum and middle frontal gyrus were greater in the slow-5 than in the slow-4 band. Correlation analysis showed consistently positive correlations between urinary copper excretion (Cu), serum ceruloplasmin (CP) and ALFFs in the cerebellum. Our study suggests the accumulation of copper profoundly impaired intrinsic brain activity and the impairments seem to be frequency-dependent. These results provide further insights into the understanding of the pathophysiology of WD.

Non-Arrhenius conductivity in the fast ionic conductor Li0.5La0.5TiO3: Reconciling spin-lattice and electrical-conductivity relaxations

International Nuclear Information System (INIS)

Leon, C.; Santamaria, J.; Paris, M.A.; Sanz, J.; Ibarra, J.; Torres, L.M.

1997-01-01

Nuclear magnetic resonance and electrical conductivity measurements are conducted to study the dynamics of the ionic diffusion process in the crystalline ionic conductor Li 0.5 La 0.5 TiO 3 . dc conductivity shows a non-Arrhenius temperature dependence, similar to the one recently reported for some ionic conducting glasses. Spin-lattice and conductivity relaxations are analyzed in the same frequency and temperature range in terms of the non-Arrhenius dependence of the correlation time. Both relaxations are then described using a single correlation function of the form f(t)=exp(-(t/τ) β ), with β=0.4 over the whole temperature range. copyright 1997 The American Physical Society

Complete FDTD analysis of microwave heating processes in frequency-dependent and temperature dependent media

Energy Technology Data Exchange (ETDEWEB)

Torres, F.; Jecko, B. [Univ. de Limoges (France). Inst. de Recherche en Communications Optiques et Microondes

1997-01-01

It is well known that the temperature rise in a material modifies its physical properties and, particularly, its dielectric permittivity. The dissipated electromagnetic power involved in microwave heating processes depending on {var_epsilon}({omega}), the electrical characteristics of the heated media must vary with the temperature to achieve realistic simulations. In this paper, the authors present a fast and accurate algorithm allowing, through a combined electromagnetic and thermal procedure, to take into account the influence of the temperature on the electrical properties of materials. First, the temperature dependence of the complex permittivity ruled by a Debye relaxation equation is investigated, and a realistic model is proposed and validated. Then, a frequency-dependent finite-differences time-domain ((FD){sup 2}TD) method is used to assess the instantaneous electromagnetic power lost by dielectric hysteresis. Within the same iteration, a time-scaled form of the heat transfer equation allows one to calculate the temperature distribution in the heated medium and then to correct the dielectric properties of the material using the proposed model. These new characteristics will be taken into account by the EM solver at the next iteration. This combined algorithm allows a significant reduction of computation time. An application to a microwave oven is proposed.

INTERLAYER OPTICAL CONDUCTIVITY OF A SUPERCONDUCTING BILAYER

NARCIS (Netherlands)

GARTSTEIN, YN; RICE, MJ; VANDERMAREL, D

1994-01-01

We employ the Bardeen-Cooper-Schrieffer theory to calculate the frequency-dependent interlayer conductivity of a superconducting bilayer, the two layers of which are coupled by weak single-particle tunneling. The effect of the superconducting transition on the normal-state absorption band is to

Influence of Gaussian white noise on the frequency-dependent first nonlinear polarizability of doped quantum dot

Energy Technology Data Exchange (ETDEWEB)

Ganguly, Jayanta [Department of Chemistry, Brahmankhanda Basapara High School, Basapara, Birbhum 731215, West Bengal (India); Ghosh, Manas, E-mail: pcmg77@rediffmail.com [Department of Chemistry, Physical Chemistry Section, Visva Bharati University, Santiniketan, Birbhum 731 235, West Bengal (India)

2014-05-07

We investigate the profiles of diagonal components of frequency-dependent first nonlinear (β{sub xxx} and β{sub yyy}) optical response of repulsive impurity doped quantum dots. We have assumed a Gaussian function to represent the dopant impurity potential. This study primarily addresses the role of noise on the polarizability components. We have invoked Gaussian white noise consisting of additive and multiplicative characteristics (in Stratonovich sense). The doped system has been subjected to an oscillating electric field of given intensity, and the frequency-dependent first nonlinear polarizabilities are computed. The noise characteristics are manifested in an interesting way in the nonlinear polarizability components. In case of additive noise, the noise strength remains practically ineffective in influencing the optical responses. The situation completely changes with the replacement of additive noise by its multiplicative analog. The replacement enhances the nonlinear optical response dramatically and also causes their maximization at some typical value of noise strength that depends on oscillation frequency.

Frequency-Modulated Wave Dielectrophoresis of Vesicles And Cells: Periodic U-Turns at the Crossover Frequency

Science.gov (United States)

Frusawa, Hiroshi

2018-06-01

We have formulated the dielectrophoretic force exerted on micro/nanoparticles upon the application of frequency-modulated (FM) electric fields. By adjusting the frequency range of an FM wave to cover the crossover frequency f X in the real part of the Clausius-Mossotti factor, our theory predicts the reversal of the dielectrophoretic force each time the instantaneous frequency periodically traverses f X . In fact, we observed periodic U-turns of vesicles, leukemia cells, and red blood cells that undergo FM wave dielectrophoresis (FM-DEP). It is also suggested by our theory that the video tracking of the U-turns due to FM-DEP is available for the agile and accurate measurement of f X . The FM-DEP method requires a short duration, less than 30 s, while applying the FM wave to observe several U-turns, and the agility in measuring f X is of much use for not only salty cell suspensions but also nanoparticles because the electric-field-induced solvent flow is suppressed as much as possible. The accuracy of f X has been verified using two types of experiment. First, we measured the attractive force exerted on a single vesicle experiencing alternating-current dielectrophoresis (AC-DEP) at various frequencies of sinusoidal electric fields. The frequency dependence of the dielectrophoretic force yields f X as a characteristic frequency at which the force vanishes. Comparing the AC-DEP result of f X with that obtained from the FM-DEP method, both results of f X were found to coincide with each other. Second, we investigated the conductivity dependencies of f X for three kinds of cell by changing the surrounding electrolytes. From the experimental results, we evaluated simultaneously both of the cytoplasmic conductivities and the membrane capacitances using an elaborate theory on the single-shell model of biological cells. While the cytoplasmic conductivities, similar for these cells, were slightly lower than the range of previous reports, the membrane capacitances obtained

Study on the Effect of Frequency on Conductivity of Underground Strata in Coal Mine Through-the-earth Wireless Communication

OpenAIRE

Jinyi TAO; Yuchen ZHANG

2014-01-01

The relationship of conductivity and the frequency, which is of decisive significance in through-the-earth wireless communication in coal mine, is closely related to the options of frequency range in coal mine wireless communication. When through-the-earth wireless communication is applied, the electromagnetic waves need to spread in the semi-conductive medium rocks. The main factors affecting the electromagnetic wave propagation in rocks is the rock strata electromagnetic parameters. These p...

Deposition of a conductive near-infrared cutoff filter by radio-frequency magnetron sputtering

International Nuclear Information System (INIS)

Lee, Jang-Hoon; Lee, Seung-Hyu; Yoo, Kwang-Lim; Kim, Nam-Young; Hwangbo, Chang Kwon

2002-01-01

We have designed a conductive near-infrared (NIR) cutoff filter for display application, i.e., a modified low-emissivity filter based on the three periods of the basic design of [TiO2|Ti|Ag| TiO2] upon a glass substrate and investigated the optical, structural, chemical, and electrical properties of the conductive NIR cutoff filter prepared by a radio frequency magnetron sputtering system. The results show that the average transmittance is 61.1% in the visible, that the transmittance in the NIR is less than 6.6%, and that the sheet resistance and emissivity are 0.9 Ω/□ (where □ stands for a square film) and 0.012, respectively, suggesting that the conductive NIR cutoff filter can be employed as a shield against the hazard of electromagnetic waves as well as to cut off the NIR

Frequency Dependencies of the Exchange Spin Wave Reflection Coefficient on a One-Dimensional Magnon Crystal with Complex Interfaces

Directory of Open Access Journals (Sweden)

Serhii O. Reshetniak

2017-09-01

Conclusions. It is shown that the frequency dependencies are periodic, points of full transmission and areas, full of reflection. Decreasing exchange parameter value in interface causes the increase of reflectance coefficient. Changing the material parameters we get the necessary intensity value of the reflection coefficient depending on the frequency at a constant value of the external magnetic field.

Similarity of dependences of thermal conductivity and density of uranium and tungsten hexafluorides on desublimation conditions

International Nuclear Information System (INIS)

Barkov, V.A.

1989-01-01

Consideration is given to results of investigations of the dependence of thermal conductivity and density of UF 6 and WF 6 desublimates on volume content of hexafluoride in initial gaseous mixture. Similarity of these dependences, as well as the dependences of thermal conductivity of desublimates on their density was revealed. Generalized expressions, relating thermal conductivity and density of desublimates among each ofter and with volume content of hexafluoride in gaseous mixture were derived. Possibility of applying the generalized relations for calculation of thermal conductivity and density of other compounds of MeF 6 type under prescribed desublimation conclitions is shown. 15 refs.; 6 figs

Evolution of frequency-dependent mate choice: keeping up with fashion trends.

Science.gov (United States)

Kokko, Hanna; Jennions, Michael D; Houde, Anne

2007-05-22

The diversity of sexual traits favoured by females is enormous and, curiously, includes preferences for males with rare or novel phenotypes. We modelled the evolution of a preference for rarity that yielded two surprising results. First, a Fisherian 'sexy son' effect can boost female preferences to a frequency well above that predicted by mutation-selection balance, even if there are significant mortality costs for females. Preferences do not reach fixation, however, as they are subject to frequency-dependent selection: if choosy females are too common, then rare genotypes in one generation become common, and thus unattractive, in the offspring generation. Nevertheless, even at relatively low frequency, preferences maintain polymorphism in male traits. The second unexpected result is that the preferences can evolve to much higher frequencies if choice is hindered, such that females cannot always express their preferences. Our results emphasize the need to consider feedback where preferences determine the dynamics of male genotypes and vice versa. They also highlight the similarity between the arbitrariness of behavioural norms in models of social evolution with punishment (the so-called 'folk theorem') and the diversity of sexual traits that can be preferred simply because deviating from the norm produces unattractive offspring and is, in this sense, 'punished'.

Frequency-dependent springs in the seismic analysis of structures

International Nuclear Information System (INIS)

Tyapin, A.G.

2005-01-01

This paper presents a two-step algorithm for the seismic analysis of structure resting on the rigid embedded basement. Frequency-domain analysis of SSI is carried out on the second step for a platform model with special 'soil spring' which is complex, frequency-dependent, wave-dependent and non-balanced. Theory is presented to obtain the parameters of the soil spring on the first step of the analysis, performed without structure (only geometry of the basement is used) using well-known SASSI code (Lysmer et al, 1981) or in some other ways. On the second step in the SASSI analysis the soil spring is included in the model as a special finite element. Thus, the first step enables to save the computer resources on structure, the second step-to save resources on soil. Soil spring is the most general form for a SSI linear analysis: conventional springs and dashpots can be easily represented in such a format. Thus, the presented approach enables to study the impact of various factors (such as the embedment depth and soil-structure separation, the off-diagonal stiffness, various formulas for stiffness and damping, etc.) on the soil spring parameters. These parameters can be studied separately from the structure itself. As an example, the study of the horizontal soil mesh size is presented. Lumped soil spring may be used on the second step to obtain structural response spectra. To get stresses complex stiffness may be distributed over the basement slab and embedded walls. The proposed approach may be considered to be the alternative to the impedance method (see ASCE4-98). (authors)

DPOAE generation dependence on primary frequencies ratio

Science.gov (United States)

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

Modeling of frequency-dependent negative differential capacitance in InGaAs/InP photodiode

Science.gov (United States)

Wang, Yidong; Chen, Jun; Xu, Jintong; Li, Xiangyang

2018-03-01

The negative differential capacitance (NDC) of p-i-n InGaAs/InP photodetector has been clearly observed, and the small signal model of frequency-dependent NDC is established, based on the accumulation and emission of electrons at the p-InP/i-InGaAs interface. The NDC phenomenon is contributed by the additional capacitance (CT), which is caused by the charging-discharging process in the p-InP/i-InGaAs interface. It is found that the NDC becomes more obvious with decreasing frequency, which is consistent with the conclusion of the experiment. It is proved that the probability of electron capture/escape in the p-i interface is affected by frequency. Therefore, the smaller frequency applied, the higher additional capacitance is obtained.

Conductivity-Dependent Flow Field-Flow Fractionation of Fulvic and Humic Acid Aggregates

Directory of Open Access Journals (Sweden)

Martha J. M. Wells

2015-09-01

Full Text Available Fulvic (FAs and humic acids (HAs are chemically fascinating. In water, they have a strong propensity to aggregate, but this research reveals that tendency is regulated by ionic strength. In the environment, conductivity extremes occur naturally—freshwater to seawater—warranting consideration at low and high values. The flow field flow fractionation (flow FFF of FAs and HAs is observed to be concentration dependent in low ionic strength solutions whereas the corresponding flow FFF fractograms in high ionic strength solutions are concentration independent. Dynamic light scattering (DLS also reveals insight into the conductivity-dependent behavior of humic substances (HSs. Four particle size ranges for FAs and humic acid aggregates are examined: (1 <10 nm; (2 10 nm–6 µm; (3 6–100 µm; and (4 >100 µm. Representative components of the different size ranges are observed to dynamically coexist in solution. The character of the various aggregates observed—such as random-extended-coiled macromolecules, hydrogels, supramolecular, and micellar—as influenced by electrolytic conductivity, is discussed. The disaggregation/aggregation of HSs is proposed to be a dynamic equilibrium process for which the rate of aggregate formation is controlled by the electrolytic conductivity of the solution.

Electrical conductivity studies of Bi2O3–Li2O–ZnO–B2O3 glasses

International Nuclear Information System (INIS)

Bale, Shashidhar; Rahman, Syed

2012-01-01

Highlights: ► Ac conductivity measurements and its analysis has been performed on Bi 2 O 3 –Li 2 O–ZnO–B 2 O 3 glasses in the temperature range 30–300 °C and a frequency range of 100 Hz to 1 MHz. ► The dc conductivity increased and the activation energy decreased with lithium content. ► The frequency dependent conductivity has been analyzed employing conductivity and modulus formalisms. ► The onset of conductivity relaxation shifts towards higher frequencies with temperature. ► The Almond–West conductivity formalism is used to explain the scaling behavior, and the relaxation mechanism is independent of temperature. -- Abstract: Ac conductivity measurements and its analysis has been performed on xBi 2 O 3 –(65−x)Li 2 O–20ZnO–15B 2 O 3 (0 ≤ x ≤ 20) glasses in the temperature range 30–300 °C and a frequency range of 100 Hz to 1 MHz. The dc conductivity increased and the activation energy decreased with lithium content. The frequency dependent conductivity has been analyzed employing conductivity and modulus formalisms. The onset of conductivity relaxation shifts towards higher frequencies with temperature. The Almond–West conductivity formalism is used to explain the scaling behavior, and the relaxation mechanism is independent of temperature.

A DTI-based model for TMS using the independent impedance method with frequency-dependent tissue parameters

Science.gov (United States)

De Geeter, N.; Crevecoeur, G.; Dupré, L.; Van Hecke, W.; Leemans, A.

2012-04-01

Accurate simulations on detailed realistic head models are necessary to gain a better understanding of the response to transcranial magnetic stimulation (TMS). Hitherto, head models with simplified geometries and constant isotropic material properties are often used, whereas some biological tissues have anisotropic characteristics which vary naturally with frequency. Moreover, most computational methods do not take the tissue permittivity into account. Therefore, we calculate the electromagnetic behaviour due to TMS in a head model with realistic geometry and where realistic dispersive anisotropic tissue properties are incorporated, based on T1-weighted and diffusion-weighted magnetic resonance images. This paper studies the impact of tissue anisotropy, permittivity and frequency dependence, using the anisotropic independent impedance method. The results show that anisotropy yields differences up to 32% and 19% of the maximum induced currents and electric field, respectively. Neglecting the permittivity values leads to a decrease of about 72% and 24% of the maximum currents and field, respectively. Implementing the dispersive effects of biological tissues results in a difference of 6% of the maximum currents. The cerebral voxels show limited sensitivity of the induced electric field to changes in conductivity and permittivity, whereas the field varies approximately linearly with frequency. These findings illustrate the importance of including each of the above parameters in the model and confirm the need for accuracy in the applied patient-specific method, which can be used in computer-assisted TMS.

Complexity of low-frequency blood oxygen level-dependent fluctuations covaries with local connectivity.

Science.gov (United States)

Anderson, Jeffrey S; Zielinski, Brandon A; Nielsen, Jared A; Ferguson, Michael A

2014-04-01

Very low-frequency blood oxygen level-dependent (BOLD) fluctuations have emerged as a valuable tool for describing brain anatomy, neuropathology, and development. Such fluctuations exhibit power law frequency dynamics, with largest amplitude at lowest frequencies. The biophysical mechanisms generating such fluctuations are poorly understood. Using publicly available data from 1,019 subjects of age 7-30, we show that BOLD fluctuations exhibit temporal complexity that is linearly related to local connectivity (regional homogeneity), consistently and significantly covarying across subjects and across gray matter regions. This relationship persisted independently of covariance with gray matter density or standard deviation of BOLD signal. During late neurodevelopment, BOLD fluctuations were unchanged with age in association cortex while becoming more random throughout the rest of the brain. These data suggest that local interconnectivity may play a key role in establishing the complexity of low-frequency BOLD fluctuations underlying functional magnetic resonance imaging connectivity. Stable low-frequency power dynamics may emerge through segmentation and integration of connectivity during development of distributed large-scale brain networks. Copyright © 2013 Wiley Periodicals, Inc.

Contact area affects frequency-dependent responses to vibration in the peripheral vascular and sensorineural systems.

Science.gov (United States)

Krajnak, Kristine; Miller, G R; Waugh, Stacey

2018-01-01

Repetitive exposure to hand-transmitted vibration is associated with development of peripheral vascular and sensorineural dysfunctions. These disorders and symptoms associated with it are referred to as hand-arm vibration syndrome (HAVS). Although the symptoms of the disorder have been well characterized, the etiology and contribution of various exposure factors to development of the dysfunctions are not well understood. Previous studies performed using a rat-tail model of vibration demonstrated that vascular and peripheral nervous system adverse effects of vibration are frequency-dependent, with vibration frequencies at or near the resonant frequency producing the most severe injury. However, in these investigations, the amplitude of the exposed tissue was greater than amplitude typically noted in human fingers. To determine how contact with vibrating source and amplitude of the biodynamic response of the tissue affects the risk of injury occurring, this study compared the influence of frequency using different levels of restraint to assess how maintaining contact of the tail with vibrating source affects the transmission of vibration. Data demonstrated that for the most part, increasing the contact of the tail with the platform by restraining it with additional straps resulted in an enhancement in transmission of vibration signal and elevation in factors associated with vascular and peripheral nerve injury. In addition, there were also frequency-dependent effects, with exposure at 250 Hz generating greater effects than vibration at 62.5 Hz. These observations are consistent with studies in humans demonstrating that greater contact and exposure to frequencies near the resonant frequency pose the highest risk for generating peripheral vascular and sensorineural dysfunction.

Extended exergy concept to facilitate designing and optimization of frequency-dependent direct energy conversion systems

International Nuclear Information System (INIS)

Wijewardane, S.; Goswami, Yogi

2014-01-01

Highlights: • Proved exergy method is not adequate to optimize frequency-dependent energy conversion. • Exergy concept is modified to facilitate the thermoeconomic optimization of photocell. • The exergy of arbitrary radiation is used for a practical purpose. • The utility of the concept is illustrated using pragmatic examples. - Abstract: Providing the radiation within the acceptable (responsive) frequency range(s) is a common method to increase the efficiency of the frequency-dependent energy conversion systems, such as photovoltaic and nano-scale rectenna. Appropriately designed auxiliary items such as spectrally selective thermal emitters, optical filters, and lenses are used for this purpose. However any energy conversion method that utilizes auxiliary components to increase the efficiency of a system has to justify the potential cost incurred by those auxiliary components through the economic gain emerging from the increased system efficiency. Therefore much effort should be devoted to design innovative systems, effectively integrating the auxiliary items and to optimize the system with economic considerations. Exergy is the widely used method to design and optimize conventional energy conversion systems. Although the exergy concept is used to analyze photovoltaic systems, it has not been used effectively to design and optimize such systems. In this manuscript, we present a modified exergy method in order to effectively design and economically optimize frequency-dependent energy conversion systems. Also, we illustrate the utility of this concept using examples of thermophotovoltaic, Photovoltaic/Thermal and concentrated solar photovoltaic

AC electrical conductivity in amorphous indium selenide thin films

International Nuclear Information System (INIS)

Di Giulio, H.; Rella, R.; Tepore, A.

1987-01-01

In order to obtain additional information about the nature of the conduction mechanism in amorphous InSe films results of an experimental study concerning the frequency and temperature dependence of the ac conductivity are reported. The measurements were performed on specimens of different thickness and different electrode contact areas. The results can be explained assuming that conduction occurs by phonon-assisted hopping between localized states near the Fermi level

Complex conductivity of organic-rich shales

Science.gov (United States)

Woodruff, W. F.; Revil, A.; Torres-Verdin, C.

2013-12-01

We can accurately determine the intrinsic anisotropy and material properties in the laboratory, providing empirical evidence of transverse isotropy and the polarization of the organic and metallic fractions in saturated and unsaturated shales. We develop two distinct approaches to obtain the complex conductivity tensor from spectral induced polarization (SIP) measurements. Experimental results indicate clear anisotropy, and characterize the effects of thermal maturation, TOC, and pyrite, aiding in the calibration and interpretation of geophysical data. SIP is a non-intrusive measurement, sensitive to the surface conductance of mineral grains, frequency-dependent polarization of the electrical double layer, and bulk conductivity of the pore water. The in-phase and quadrature components depend upon parameters of principal importance in unconventional shale formation evaluation (e.g., the distribution of pore throat sizes, formation factor, permeability, salinity and cation exchange capacity (CEC), fluid saturation and wettability). In addition to the contribution of the electrical double layer of non-conducting minerals to surface conductivity, we have observed a clear relaxation associated with kerogen pyrolysis, pyrite distribution, and evidence that the CEC of the kerogen fraction may also contribute, depending on thermal maturation history. We utilize a recent model for anisotropic complex conductivity, and rigorous experimental protocols to quantify the role of kerogen and pyrolysis on surface and quadrature conductivity in mudrocks. The complex conductivity tensor σ* describes the directional dependence of electrical conduction in a porous medium, and accounts for both conduction and polarization. The complex-valued tensor components are given as σ*ij , where σ'ij represents in-phase and σ"ij denotes quadrature conductivities. The directional dependence of the complex conductivity tensor is relegated to the textural properties of the material. The

Electrical conductivity and dielectric properties of TlInS2 single crystals

Science.gov (United States)

El-Nahass, M. M.; Youssef, S. B.; Ali, H. A. M.; Hassan, A.

2011-07-01

TlInS2 single crystals were grown by using Bridgman-Stockbauer technique. Measurements of DC conductivity were carried out in parallel (σ//) and perpendicular (σ⊥) directions to the c-axis over a temperature range from 303 to 463 K. The anisotropic behaviour of the electrical conductivity was also detected. AC conductivity and dielectric measurements were studied as a function of both frequency (102-106 Hz) and temperature (297-375 K). The frequency dependence of the AC conductivity revealed that σac(ω) obeys the universal law: σac(ω) = Aωs. The mechanism of the ac charge transport across the layers of TlInS2 single crystals was referred to the hopping over localized states near the Fermi level in the frequency range >3.5 × 103 Hz. The temperature dependence of σac(ω) for TlInS2 showed that σac is thermally activated process. Both of ɛ1 and ɛ2 decrease by increasing frequency and increase by increasing temperature. Some parameters were calculated as: the density of localized states near the Fermi level NF = 1.5 × 1020 eV-1 cm-3, the average time of charge carrier hoping between localized states τ = 3.79 μs and the average hopping distance R = 6.07 nm.

Experimental Investigation of Electrical Conductivity and Permittivity of SC-TiO 2 -EG Nanofluids

Science.gov (United States)

Fal, Jacek; Barylyak, Adriana; Besaha, Khrystyna; Bobitski, Yaroslav V.; Cholewa, Marian; Zawlik, Izabela; Szmuc, Kamil; Cebulski, Józef; żyła, Gaweł

2016-08-01

The paper presents experimental studies of dielectric properties of nanofluids based on ethylene glycol and SC-TiO2 nanoparticles with average size of 15-40 nm with various mass concentrations. The dielectric permittivity both real part and imaginary part as a function of temperature and frequency were measured. Also, dependence ac conductivity on frequency, temperature, and mass concentration were investigated. Based on the curves of ac conductivity, dc conductivity was calculated, and 400 % enhancement in dc conductivity was exposed.

Frequency dependence of magnetic ac loss in a Roebel cable made of YBCO on a Ni-W substrate

Science.gov (United States)

Lakshmi, L. S.; Staines, M. P.; Badcock, R. A.; Long, N. J.; Majoros, M.; Collings, E. W.; Sumption, M. D.

2010-08-01

We have investigated the frequency dependent contributions to the magnetic ac loss in a 10 strand Roebel cable with 2 mm wide non-insulated strands and a transposition length of 90 mm. This cable is made from 40 mm wide YBCO coated conductor tape manufactured by AMSC and stabilized by electroplating 25 µm thick copper on either side prior to the mechanical punching of the cable strands. The measurements were carried out in both perpendicular and parallel field orientation, at frequencies in the range of 30-200 Hz. While the loss in the perpendicular orientation is predominantly hysteretic in nature, we observe some frequency dependence of the loss when the cable approaches full flux penetration at high field amplitudes. The magnitude is consistent with eddy current losses in the copper stabilization layer. This supports the fact that the inter-strand coupling loss is not significant in this frequency range. In the parallel field orientation, the hysteresis loss in the Ni-W alloy substrate dominates, but we see an unusually strong frequency dependent contribution to the loss which we attribute to intra-strand current loops.

How to include frequency dependent complex permeability Into SPICE models to improve EMI filters design?

Science.gov (United States)

Sixdenier, Fabien; Yade, Ousseynou; Martin, Christian; Bréard, Arnaud; Vollaire, Christian

2018-05-01

Electromagnetic interference (EMI) filters design is a rather difficult task where engineers have to choose adequate magnetic materials, design the magnetic circuit and choose the size and number of turns. The final design must achieve the attenuation requirements (constraints) and has to be as compact as possible (goal). Alternating current (AC) analysis is a powerful tool to predict global impedance or attenuation of any filter. However, AC analysis are generally performed without taking into account the frequency-dependent complex permeability behaviour of soft magnetic materials. That's why, we developed two frequency-dependent complex permeability models able to be included into SPICE models. After an identification process, the performances of each model are compared to measurements made on a realistic EMI filter prototype in common mode (CM) and differential mode (DM) to see the benefit of the approach. Simulation results are in good agreement with the measured ones especially in the middle frequency range.

Capacitance measurements and AC conductivity of Nickel Phthalocyanine films

International Nuclear Information System (INIS)

Darwish, S.

2005-01-01

A C dark Current measurements of nickel phthalocyanine thin films using ohmic gold electrodes are investigated in the frequency range 30-10 Hz and within the temperature range 295-385 K. The A C conductivity as D Ac is found to vary as within the index s < 1, indicating a dominant hopping process at low temperatures. From the temperature dependence of A C conductivity, free carrier conduction with mean activation energy of 0.31 eV is observed at higher temperatures. Capacitance and loss tangent are found to be decreased with increasing frequency and increase with increasing temperature. Such characteristics are found to be in good qualitative agreement with existing equivalent circuit model assuming ohmic contacts

Flow of chemically reactive magneto Cross nanoliquid with temperature-dependent conductivity

Science.gov (United States)

Hayat, Tasawar; Ullah, Ikram; Waqas, Muhammad; Alsaedi, Ahmed

2018-05-01

Influence of temperature-dependent thermal conductivity on MHD flow of Cross nanoliquid bounded by a stretched sheet is explored. The combined feature of Brownian motion and thermophoresis in nanoliquid modeling is retained. In addition, the attributes of zero mass flux at sheet are imposed. First-order chemical reaction is retained. The resulting problems are numerically computed. Plots and tabulated values are presented and examined. It is figured out that larger thermophoretic diffusion and thermal conductivity significantly rise the thermal field, whereas opposite situation is seen for heat transfer rate.

Frequency-Dependent Amplitude Panning for the Stereophonic Image Enhancement of Audio Recorded Using Two Closely Spaced Microphones

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.

Frequency dependence of magnetic shielding performance of HTS plates in mixed states

International Nuclear Information System (INIS)

Kamitani, Atsushi; Yokono, Takafumi; Yokono, Takafumi

2000-01-01

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 ω. The results of computations show that the HTS plate has a possibility of shielding the high-frequency magnetic field with ω > or approx. 1 kHz. (author)

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)

Conductivity and dielectric studies on (Na0·4Ag0·6)2PbP2O7 ...

Indian Academy of Sciences (India)

Temperature dependence of d.c. and a.c. conductivity indicates that electrical conduction in the material is a ther- mally activated process. The frequency dependence of the a.c. conduction activation energy was found to obey a mathematical formula. Keywords. Impedance spectroscopy; scaling; a.c. conductivity; modulus ...

Frequency dependence of anomalous transport in field theory and holography⋆,⋆⋆

Directory of Open Access Journals (Sweden)

Megías Eugenio

2014-01-01

Full Text Available We study the frequency dependence of anomalous transport coefficients for a relativistic gas of free chiral fermions and for a strongly coupled conformal field theory with holographic dual. We perform the computation by using the Kubo formulae for- malism, and compare with a hydrodynamic calculation of two point functions. Some implications for heavy ion physics are discussed.

Resolution of effects in multi-frequency eddy current data for reliable diagnostics of conductive materials

DEFF Research Database (Denmark)

Egorov, Alexander; Kucheryavskiy, Sergey V.; Polyakov, Viktor

2017-01-01

The effect of eddy currents is widely used for diagnostics of conductive materials. It allows to create very simple and inexpensive systems for non-destructive measurements. However, the results of the measurements depend on many factors, including first of all, a conductivity of material...

Frequency dependence and passive drains in fish-eye lenses

Science.gov (United States)

Quevedo-Teruel, O.; Mitchell-Thomas, R. C.; Hao, Y.

2012-11-01

The Maxwell fish eye lens has previously been reported as being capable of the much sought after phenomenon of subwavelength imaging. The inclusion of a drain in this system is considered crucial to the imaging ability, although its role is the topic of much debate. This paper provides a numerical investigation into a practical implementation of a drain in such systems, and analyzes the strong frequency dependence of both the Maxwell fish eye lens and an alternative, the Miñano lens. The imaging capability of these types of lens is questioned, and it is supported by simulations involving various configurations of drain arrays. Finally, a discussion of the near-field and evanescent wave contribution is given.

On the frequency dependence of the otoacoustic emission latency in hypoacoustic and normal ears

Science.gov (United States)

Sisto, R.; Moleti, A.

2002-01-01

Experimental measurements of the otoacoustic emission (OAE) latency of adult subjects have been obtained, as a function of frequency, by means of wavelet time-frequency analysis based on the iterative application of filter banks. The results are in agreement with previous OAE latency measurements by Tognola et al. [Hear. Res. 106, 112-122 (1997)], as regards both the latency values and the frequency dependence, and seem to be incompatible with the steep 1/f law that is predicted by scale-invariant full cochlear models. The latency-frequency relationship has been best fitted to a linear function of the cochlear physical distance, using the Greenwood map, and to an exponential function of the cochlear distance, for comparison with derived band ABR latency measurements. Two sets of ears [94 audiometrically normal and 42 impaired with high-frequency (f>3 kHz) hearing loss] have been separately analyzed. Significantly larger average latencies were found in the impaired ears in the mid-frequency range. Theoretical implications of these findings on the transmission of the traveling wave are discussed.

Soil permittivity response to bulk electrical conductivity for selected soil water sensors

Science.gov (United States)

Bulk electrical conductivity can dominate the low frequency dielectric loss spectrum in soils, masking changes in the real permittivity and causing errors in estimated water content. We examined the dependence of measured apparent permittivity (Ka) on bulk electrical conductivity in contrasting soil...

38 CFR 3.30 - Frequency of payment of improved pension and parents' dependency and indemnity compensation (DIC).

Science.gov (United States)

2010-07-01

... improved pension and parents' dependency and indemnity compensation (DIC). 3.30 Section 3.30 Pensions... Dependency and Indemnity Compensation General § 3.30 Frequency of payment of improved pension and parents' dependency and indemnity compensation (DIC). Payment shall be made as shown in paragraphs (a), (b), (c), (d...

Interaural multiple frequency tympanometry measures: clinical utility for unilateral conductive hearing loss.

Science.gov (United States)

Norrix, Linda W; Burgan, Briana; Ramirez, Nicholas; Velenovsky, David S

2013-03-01

Tympanometry is a routine clinical measurement of the acoustic immittance of the ear as a function of ear canal air pressure. The 226 Hz tympanogram can provide clinical evidence for conditions such as a tympanic membrane perforation, Eustachian tube dysfunction, middle ear fluid, and ossicular discontinuity. Multiple frequency tympanometry using a range of probe tone frequencies from low to high has been shown to be more sensitive than a single probe tone tympanogram in distinguishing between mass- and stiffness-related middle ear pathologies (Colletti, 1975; Funasaka et al, 1984; Van Camp et al, 1986). In this study we obtained normative measures of middle ear resonance by using multiple probe tone frequency tympanometry. Ninety percent ranges for middle ear resonance and for interaural differences were calculated. In a mixed design, normative data were collected from both ears of male and female adults. Twelve male and 12 female adults with normal hearing and normal middle ear function participated in the study. Multiple frequency tympanograms were recorded with a commercially available immittance instrument (GSI Tympstar) to obtain estimates of middle ear resonant frequency (RF) using ΔB, positive tail, and negative tail methods. Data were analyzed using three-way mixed analyses of variance with gender as a between-subject variable and ear and method as within-subject variables. T-tests were performed, using the Bonferroni adjustment, to determine significant differences between means. Using the positive and negative tail methods, a wide range of approximately 500 Hz was found for middle ear resonance in adults with normal hearing and normal middle ear function. The difference in RF between an individual's ears is small with 90% ranges of approximately ±200 Hz, indicating that the right ear RF should be either 200 Hz higher or lower in frequency compared to the left ear. This was true for both negative and positive tail methods. Ninety percent ranges were

Dependence of the colored frequency noise in spin torque oscillators on current and magnetic field

Science.gov (United States)

Eklund, Anders; Bonetti, Stefano; Sani, Sohrab R.; Majid Mohseni, S.; Persson, Johan; Chung, Sunjae; Amir Hossein Banuazizi, S.; Iacocca, Ezio; Östling, Mikael; Åkerman, Johan; Gunnar Malm, B.

2014-03-01

The nano-scale spin torque oscillator (STO) is a compelling device for on-chip, highly tunable microwave frequency signal generation. Currently, one of the most important challenges for the STO is to increase its longer-time frequency stability by decreasing the 1/f frequency noise, but its high level makes even its measurement impossible using the phase noise mode of spectrum analyzers. Here, we present a custom made time-domain measurement system with 150 MHz measurement bandwidth making possible the investigation of the variation of the 1/f as well as the white frequency noise in a STO over a large set of operating points covering 18-25 GHz. The 1/f level is found to be highly dependent on the oscillation amplitude-frequency non-linearity and the vicinity of unexcited oscillation modes. These findings elucidate the need for a quantitative theoretical treatment of the low-frequency, colored frequency noise in STOs. Based on the results, we suggest that the 1/f frequency noise possibly can be decreased by improving the microstructural quality of the metallic thin films.

Dependence of the colored frequency noise in spin torque oscillators on current and magnetic field

International Nuclear Information System (INIS)

Eklund, Anders; Sani, Sohrab R.; Chung, Sunjae; Amir Hossein Banuazizi, S.; Östling, Mikael; Gunnar Malm, B.; Bonetti, Stefano; Majid Mohseni, S.; Persson, Johan; Iacocca, Ezio; Åkerman, Johan

2014-01-01

The nano-scale spin torque oscillator (STO) is a compelling device for on-chip, highly tunable microwave frequency signal generation. Currently, one of the most important challenges for the STO is to increase its longer-time frequency stability by decreasing the 1/f frequency noise, but its high level makes even its measurement impossible using the phase noise mode of spectrum analyzers. Here, we present a custom made time-domain measurement system with 150 MHz measurement bandwidth making possible the investigation of the variation of the 1/f as well as the white frequency noise in a STO over a large set of operating points covering 18–25 GHz. The 1/f level is found to be highly dependent on the oscillation amplitude-frequency non-linearity and the vicinity of unexcited oscillation modes. These findings elucidate the need for a quantitative theoretical treatment of the low-frequency, colored frequency noise in STOs. Based on the results, we suggest that the 1/f frequency noise possibly can be decreased by improving the microstructural quality of the metallic thin films

Frequency dependent power fluctuations: a feature of the ESR system or physical?

Directory of Open Access Journals (Sweden)

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

Frequency dependent power fluctuations: a feature of the ESR system or physical?

Directory of Open Access Journals (Sweden)

Y. Ogawa

2000-09-01

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

Autobiographical Memory Performance in Alzheimer's Disease Depends on Retrieval Frequency.

Science.gov (United States)

Müller, Stephan; Mychajliw, Christian; Reichert, Carolin; Melcher, Tobias; Leyhe, Thomas

2016-04-18

Alzheimer's disease (AD) is characterized by memory disturbances primarily caused by pathogenic mechanisms affecting medial temporal lobe structures. As proposed by current theories of memory formation, this decrease is mediated by the age of the acquired knowledge. However, they cannot fully explain specific patterns of retrograde amnesia in AD. In the current study we examined an alternative approach and investigated whether the extent and severity of retrograde amnesia in AD is mediated by the frequency of memory retrieval or whether it depends on the mere age of knowledge. We compared recall of autobiographical incidents from three life periods in patients with amnestic mild cognitive impairment (aMCI), patients with early dementia of Alzheimer type (eDAT), and healthy control (HC) individuals using the Autobiographical Memory Interview. Retrieval frequency was operationalized by a paired comparison analysis. In contrast to HC individuals, recall of autobiographical incidents was impaired in patients with aMCI and eDAT following Ribot's gradient, with a reduced memory loss for remote compared to more recent life events. However, there was a strong effect of retrieval frequency on memory performance with frequently retrieved incidents memorized in more detail than less frequently retrieved episodes. Remote memories were recalled more often than recent ones. These findings suggest that more frequently retrieved autobiographical memories generally become more independent of the hippocampal complex and might thus be better protected against early hippocampal damage related to AD. Hence, the extent of retrograde amnesia in AD appears mainly mediated by the frequency of memory retrieval, which could plausibly explain why cognitive activity can effectively delay the onset of memory decline in AD.

Temperature dependence of the cosphi conductance in Josephson tunnel junctions determined from plasma resonance experiments

International Nuclear Information System (INIS)

Pedersen, N.F.; Soerensen, O.H.; Mygind, J.

1978-01-01

The microwave response at 9 GHz of Sn-O-Sn tunnel-junction current biased at zero dc voltage has been measured just below the critical temperature T/sub c/ of the Sn films. The temperature dependence of the cosphi conductance is determined from the resonant response at the junction plasma frequency f/sub p/ as the temperature is decreased from T/sub c/. We used three different schemes for observation of the plasma oscillations: (a) second-harmonic generation (excitation at approx. 4.5 GHz, f/sub p/ approx. 4.5 GHz); (b) mixing (excitations at approx. 9 and approx. 18 GHz, f/sub p/ approx. 9 GHz); (c) parametric half-harmonic oscillation (excitation at approx. 18 GHz, f/sub p/ approx. 9 GHz). Measurements were possible in two temperature intervals; 0.994 or = T/T/sub c/ > or = 0.930, with the result that as the temperature was decreased the cosphi amplitude first increased from about zero to positive values and then at lower temperatures decreased approaching -1 at the lowest temperatures of the experiment

GENERAL APROACH TO MODELING NONLINEAR AMPLITUDE AND FREQUENCY DEPENDENT HYSTERESIS EFFECTS BASED ON EXPERIMENTAL RESULTS

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.

Thermal conductivity profile determination in proton-irradiated ZrC by spatial and frequency scanning thermal wave methods

International Nuclear Information System (INIS)

Jensen, C.; Chirtoc, M.; Horny, N.; Antoniow, J. S.; Pron, H.; Ban, H.

2013-01-01

Using complementary thermal wave methods, the irradiation damaged region of zirconium carbide (ZrC) is characterized by quantifiably profiling the thermophysical property degradation. The ZrC sample was irradiated by a 2.6 MeV proton beam at 600 °C to a dose of 1.75 displacements per atom. Spatial scanning techniques including scanning thermal microscopy (SThM), lock-in infrared thermography (lock-in IRT), and photothermal radiometry (PTR) were used to directly map the in-depth profile of thermal conductivity on a cross section of the ZrC sample. The advantages and limitations of each system are discussed and compared, finding consistent results from all techniques. SThM provides the best resolution finding a very uniform thermal conductivity envelope in the damaged region measuring ∼52 ± 2 μm deep. Frequency-based scanning PTR provides quantification of the thermal parameters of the sample using the SThM measured profile to provide validation of a heating model. Measured irradiated and virgin thermal conductivities are found to be 11.9 ± 0.5 W m −1 K −1 and 26.7 ±1 W m −1 K −1 , respectively. A thermal resistance evidenced in the frequency spectra of the PTR results was calculated to be (1.58 ± 0.1) × 10 −6 m 2 K W −1 . The measured thermal conductivity values compare well with the thermal conductivity extracted from the SThM calibrated signal and the spatially scanned PTR. Combined spatial and frequency scanning techniques are shown to provide a valuable, complementary combination for thermal property characterization of proton-irradiated ZrC. Such methodology could be useful for other studies of ion-irradiated materials

Filter frequency response of time dependent signal using Laplace transform

Energy Technology Data Exchange (ETDEWEB)

Shestakov, Aleksei I. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2018-01-16

We analyze the effect a filter has on a time dependent signal x(t). If X(s) is the Laplace transform of x and H (s) is the filter Transfer function, the response in frequency space is X (s) H (s). Consequently, in real space, the response is the convolution (x*h) (t), where hi is the Laplace inverse of H. Effects are analyzed and analytically for functions such as (t/t_c)² e^-t/t$_c$, where t_c = const. We consider lowpass, highpass and bandpass filters.

Frequency-Dependent Disease Transmission and the Dynamics of the Silene-Ustilago Host-Pathogen System

NARCIS (Netherlands)

Thrall, P.H.; Biere, A.; Uyenoyama, M.K.

1995-01-01

Models incorporating density-dependent disease transmission functions generally provide a good fit for airborne and directly transmitted bacterial or viral diseases. However, the transmission dynamics of sexually transmitted and vector-borne diseases are likely to be frequency- rather than density-

Phonon thermal conductance of disordered graphene strips with armchair edges

International Nuclear Information System (INIS)

Shi Lipeng; Xiong Shijie

2009-01-01

Based on the model of lattice dynamics together with the transfer matrix technique, we investigate the thermal conductances of phonons in quasi-one-dimensional disordered graphene strips with armchair edges using Landauer formalism for thermal transport. It is found that the contributions to thermal conductance from the phonon transport near von Hove singularities is significantly suppressed by the presence of disorder, on the contrary to the effect of disorder on phonon modes in other frequency regions. Besides the magnitude, for different widths of the strips, the thermal conductance also shows different temperature dependence. At low temperatures, the thermal conductance displays quantized features of both pure and disordered graphene strips implying that the transmission of phonon modes at low frequencies are almost unaffected by the disorder

Thermal conduction by dark matter with velocity and momentum-dependent cross-sections

OpenAIRE

Vincent, Aaron C.; Scott, Pat

2013-01-01

We use the formalism of Gould and Raffelt to compute the dimensionless thermal conduction coefficients for scattering of dark matter particles with standard model nucleons via cross-sections that depend on the relative velocity or momentum exchanged between particles. Motivated by models invoked to reconcile various recent results in direct detection, we explicitly compute the conduction coefficients $\\alpha$ and $\\kappa$ for cross-sections that go as $v_{\\rm rel}^2$, $v_{\\rm rel}^4$, $v_{\\rm...

Frequency-dependent squeeze-amplitude attenuation and squeeze-angle rotation by electromagnetically induced transparency for gravitational-wave interferometers

International Nuclear Information System (INIS)

Mikhailov, Eugeniy E.; Goda, Keisuke; Corbitt, Thomas; Mavalvala, Nergis

2006-01-01

We study the effects of frequency-dependent squeeze-amplitude attenuation and squeeze-angle rotation by electromagnetically induced transparency (EIT) on gravitational-wave (GW) interferometers. We propose the use of low-pass, bandpass, and high-pass EIT filters, an S-shaped EIT filter, and an intracavity EIT filter to generate frequency-dependent squeezing for injection into the antisymmetric port of GW interferometers. We find that the EIT filters have several advantages over the previous filter designs with regard to optical losses, compactness, and the tunability of the filter linewidth

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

Monitoring cure of composite resins using frequency dependent electromagnetic sensing techniques

Science.gov (United States)

Kranbuehl, D. E.; Hoff, M. S.; Loos, A. C.; Freeman, W. T., Jr.; Eichinger, D. A.

1988-01-01

A nondestructive in situ measurement technique has been developed for monitoring and measuring the cure processing properties of composite resins. Frequency dependent electromagnetic sensors (FDEMS) were used to directly measure resin viscosity during cure. The effects of the cure cycle and resin aging on the viscosity during cure were investigated using the sensor. Viscosity measurements obtained using the sensor are compared with the viscosities calculated by the Loos-Springer cure process model. Good overall agreement was obtained except for the aged resin samples.

Thermal Conductivity and High-Frequency Dielectric Properties of Pressureless Sintered SiC-AlN Multiphase Ceramics

Directory of Open Access Journals (Sweden)

Jialin Gu

2018-06-01

Full Text Available SiC-AlN multiphase ceramics with 10 wt. %Y2O3-BaO-SiO2 additives were fabricated by pressureless sintering in a nitrogen atmosphere. The effects of SiC contents and sintering temperatures on the sinterability, microstructure, thermal conductivity and high-frequency dielectric properties were characterized. In addition to 6H-SiC and AlN, the samples also contained Y3Al5O12 and Y4Al2O9. SiC-AlN ceramics sintered with 50 wt. % SiC at 2173 K exhibited the best thermal diffusivity and thermal conductivity (26.21 mm2·s−1 and 61.02 W·m−1·K−1, respectively. The dielectric constant and dielectric loss of the sample sintered with 50 wt. % SiC and 2123 K were 33–37 and 0.4–0.5 at 12.4–18 GHz. The dielectric constant and dielectric loss of the samples decreased as the frequency of electromagnetic waves increased from 12.4–18 GHz. The dielectric thermal conductivity properties of the SiC-AlN samples are discussed.

Probing the Jet Turnover Frequency Dependence on Mass and Mass Accretion Rate

Science.gov (United States)

Hammerstein, Erica; Gültekin, Kayhan; King, Ashley

2018-01-01

We have examined a sample of 15 sub-Eddington supermassive black holes (SMBHs) in a variety of galaxy classifications to further understand the proposed fundamental plane of black hole activity and scaling relations between black hole masses and their radio and X-ray luminosities. This plane describes black holes from stellar-mass to supermassive. The physics probed by these sub-Eddington systems is thought to be a radiatively inefficient, jet-dominated accretion flow. By studying black holes in this regime, we can learn important information on the disk-jet connection for accreting black holes.A key factor in studying the fundamental plane is the turnover frequency — the frequency at which emission transitions from optically thick at lower frequencies to optically thin at higher frequencies. This turnover point can be measured by observing the source in both radio and X-ray. Our project aims to test the dependence of the turnover frequency on mass and mass accretion rate.Radio observations of the sample were obtained using the Karl G. Jansky Very Large Array (VLA) in the range of 5-40 GHz across four different frequency bands in A configuration to give the highest spatial resolution to focus on the core emission. Our carefully chosen sample of SMBHs with dynamically measured masses consists of two sub-samples: those with approximately constant mass accretion rate (LX/LEdd ~ 10‑7) and those with approximately constant mass (MBH ~ 108 Msun). X-ray data were obtained from archival Chandra observations. To find the turnover frequency, we used Markov Chain Monte Carlo methods to fit two power laws to the radio data and the archival X-ray data. The intersection of the radio and X-ray fits is the turnover frequency.We present the results for both subsamples of SMBHs and their relationship between the turnover frequency and X-ray luminosity, which we take to scale with mass accretion rate, and jet power derived from both radio and X-ray properties.

Investigations on electrical conductivity and dielectric properties of Na doped ZnO synthesized from sol gel method

Energy Technology Data Exchange (ETDEWEB)

Tabib, Asma; Sdiri, Nasr [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B.P. 95 Hammam-Lif, 2050 (Tunisia); Elhouichet, Habib, E-mail: habib.elhouichet@fst.rnu.tn [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B.P. 95 Hammam-Lif, 2050 (Tunisia); Département de Physique, Faculté des Sciences de Tunis, University Tunis El Manar, Tunis 2092 (Tunisia); Férid, Mokhtar [Laboratoire de Physico-Chimie des Matériaux Minéraux et leurs Applications, Centre National de Recherches en Sciences des Matériaux, B.P. 95 Hammam-Lif, 2050 (Tunisia)

2015-02-15

Highlights: • ZnO nanoparticles doped with Na were prepared from sol-gel method. • Electric conductivity and dielectric properties were investigated. • The ZnO conductivity is estimated to be of p-type for critical Na doping of 1.5% at. - Abstract: Na doped ZnO nanoparticles (NPs) were elaborated by sol gel technique. The X-ray diffraction patterns show that the peaks are indexed to the hexagonal structure without any trace of an extra phase. Electric and dielectric properties were investigated using complex impedance spectroscopy. The impedance spectra were analyzed in terms of equivalent circuits involving resistors, capacitors and constant phase elements (CPE). The contribution of grain boundary resistance to the total resistance of the system is remarkable. The AC conductivity increases with temperature following the Arrhenius law, with single apparent activation energy for conduction process. The frequency dependence of the electric conductivity follows a simple power law behavior, in according to relation σ{sub AC}(ω) = σ(0) + A ω{sup s}, where s is smaller than 1. The analysis of dc conductivity indicates that the conduction is ionic in nature. The study of its variation, at fixed temperature, with Na content shows sharp decrease which is explained by the formation of Na{sub Zn} acceptor. It was found that the dc conductivity reaches its minimum value for critical Na concentration of 1.5% at which the conductivity is estimated to be of p-type. Impedance and modulus study reveals the temperature dependent non-Debye type relaxation phenomenon. Dielectric studies revealed a promising dielectric properties (relatively high ε′ at low frequencies and low loss at high frequencies). In the low-frequency region, the values of M′ tends to zero suggesting negligible or absent electrode polarization phenomenon. The frequency dependent maxima in the imaginary modulus are found to obey to Arrhenius law.

Study of dielectric relaxation and AC conductivity of InP:S single crystal

Science.gov (United States)

El-Nahass, M. M.; Ali, H. A. M.; El-Shazly, E. A.

2012-07-01

The dielectric relaxation and AC conductivity of InP:S single crystal were studied in the frequency range from 100 to 5.25 × 105 Hz and in the temperature range from 296 to 455 K. The dependence of the dielectric constant (ɛ1) and the dielectric loss (ɛ2) on both frequency and temperature was investigated. Since no peak was observed on the dielectric loss, we used a method based on the electric modulus to evaluate the activation energy of the dielectric relaxation. Scaling of the electric modulus spectra showed that the charge transport dynamics is independent of temperature. The AC conductivity (σAC) was found to obey the power law: Aωs. Analysis of the AC conductivity data and the frequency exponent showed that the correlated barrier hopping (CBH) model is the dominant mechanism for the AC conduction. The variation of AC conductivity with temperature at different frequencies showed that σAC is a thermally activated process.

Self-inductance of chiral conducting nanotubes

International Nuclear Information System (INIS)

Miyamoto, Yoshiyuki; Rubio, Angel; Louie, Steven G.; Cohen, Marvin L.

1998-01-01

Chiral conductivity in nanotubes has recently been predicted theoretically. The realization and application of chiral conducting nanotubes can be of great interest from both fundamental and technological viewpoints. These chiral currents, if they are realized, can be detected by measuring the self-inductance. We have treated Maxwell's equations for chiral conducting nanotubes (nanocoils) and find that the self-inductance and the resistivity of nanocoils should depend on the frequency of the alternating current even when the capacitance of the nanocoils is not taken into account. This is in contrast to elementary treatment of ordinary coils. This fact is useful to distinguish nanocoils by electrical measurements

Similar patterns of frequency-dependent selection on animal personalities emerge in three species of social spiders.

Science.gov (United States)

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.

A thermal conductivity model for nanofluids including effect of the temperature-dependent interfacial layer

International Nuclear Information System (INIS)

Sitprasert, Chatcharin; Dechaumphai, Pramote; Juntasaro, Varangrat

2009-01-01

The interfacial layer of nanoparticles has been recently shown to have an effect on the thermal conductivity of nanofluids. There is, however, still no thermal conductivity model that includes the effects of temperature and nanoparticle size variations on the thickness and consequently on the thermal conductivity of the interfacial layer. In the present work, the stationary model developed by Leong et al. (J Nanopart Res 8:245-254, 2006) is initially modified to include the thermal dispersion effect due to the Brownian motion of nanoparticles. This model is called the 'Leong et al.'s dynamic model'. However, the Leong et al.'s dynamic model over-predicts the thermal conductivity of nanofluids in the case of the flowing fluid. This suggests that the enhancement in the thermal conductivity of the flowing nanofluids due to the increase in temperature does not come from the thermal dispersion effect. It is more likely that the enhancement in heat transfer of the flowing nanofluids comes from the temperature-dependent interfacial layer effect. Therefore, the Leong et al.'s stationary model is again modified to include the effect of temperature variation on the thermal conductivity of the interfacial layer for different sizes of nanoparticles. This present model is then evaluated and compared with the other thermal conductivity models for the turbulent convective heat transfer in nanofluids along a uniformly heated tube. The results show that the present model is more general than the other models in the sense that it can predict both the temperature and the volume fraction dependence of the thermal conductivity of nanofluids for both non-flowing and flowing fluids. Also, it is found to be more accurate than the other models due to the inclusion of the effect of the temperature-dependent interfacial layer. In conclusion, the present model can accurately predict the changes in thermal conductivity of nanofluids due to the changes in volume fraction and temperature for

Parametric electroconvection in a weakly conducting fluid in a horizontal parallel-plate capacitor

International Nuclear Information System (INIS)

Kartavykh, N. N.; Smorodin, B. L.; Il’in, V. A.

2015-01-01

We study the flows of a nonuniformly heated weakly conducting fluid in an ac electric field of a horizontal parallel-plate capacitor. Analysis is carried out for fluids in which the charge formation is governed by electroconductive mechanism associated with the temperature dependence of the electrical conductivity of the medium. Periodic and chaotic regimes of fluid flow are investigated in the limiting case of instantaneous charge relaxation and for a finite relaxation time. Bifurcation diagrams and electroconvective regimes charts are constructed. The regions where fluid oscillations synchronize with the frequency of the external field are determined. Hysteretic transitions between electroconvection regimes are studied. The scenarios of transition to chaotic oscillations are analyzed. Depending on the natural frequency of electroconvective system and the external field frequency, the transition from periodic to chaotic oscillations can occur via quasiperiodicity, a subharmonic cascade, or intermittence

Parametric electroconvection in a weakly conducting fluid in a horizontal parallel-plate capacitor

Energy Technology Data Exchange (ETDEWEB)

Kartavykh, N. N.; Smorodin, B. L., E-mail: bsmorodin@yandex.ru; Il’in, V. A. [Perm State National Research University (Russian Federation)

2015-07-15

We study the flows of a nonuniformly heated weakly conducting fluid in an ac electric field of a horizontal parallel-plate capacitor. Analysis is carried out for fluids in which the charge formation is governed by electroconductive mechanism associated with the temperature dependence of the electrical conductivity of the medium. Periodic and chaotic regimes of fluid flow are investigated in the limiting case of instantaneous charge relaxation and for a finite relaxation time. Bifurcation diagrams and electroconvective regimes charts are constructed. The regions where fluid oscillations synchronize with the frequency of the external field are determined. Hysteretic transitions between electroconvection regimes are studied. The scenarios of transition to chaotic oscillations are analyzed. Depending on the natural frequency of electroconvective system and the external field frequency, the transition from periodic to chaotic oscillations can occur via quasiperiodicity, a subharmonic cascade, or intermittence.

On the frequency dependence of the magnetic permeability of FeHfO thin films

NARCIS (Netherlands)

Bloemen, P.J.H.; Rulkens, B.

1998-01-01

The frequency dependence of the magnetic permeability as well as of the electrical impedance have been investigated for soft-magnetic granular FeHfO thin films. The impedance measurements indicate that capacitive effects resulting from the inhomogeneous structure of the layers are of no importance

Concentration-dependent ionic conductivity and thermal stability of magnetron-sputtered nanocrystalline scandia-stabilized zirconia

DEFF Research Database (Denmark)

Sillassen, M.; Eklund, P.; Pryds, Nini

2010-01-01

grain size, yielding a grain size of 6 nm and a microstrain of 2.5% at -200 V and -250 V with additional incorporation of argon. Temperature-dependent impedance spectroscopy of the SSZ films showed that the in-plane ionic conductivity had a maximum close to 10.7 mol% and decreased almost an order...... of magnitude as the scandia - content was increased to 15.9 mol%. The activation energy for oxygen ion migration was determined to be between 1.30 - 1.43 eV. In addition, no dependence on grain size was observed. The above observations suggest a bulk mechanism for ionic conduction....

Electrical conductivity and modulus formulation in zinc modified bismuth boro-tellurite glasses

Science.gov (United States)

Dhankhar, Sunil; Kundu, R. S.; Dult, Meenakshi; Murugavel, S.; Punia, R.; Kishore, N.

2016-09-01

The ac conductivity of zinc modified tellurium based quaternary glasses having composition 60 TeO2-10 B2O3-(30 - x) Bi2O3-x ZnO; x = 10, 15, 20, 25 and 30 has been investigated in the frequency range 10-1-105 Hz and in temperature range 483-593 K. Frequency and temperature dependent ac conductivity found to obey Jonscher power law modified by Almond-West. DC conductivity, crossover frequency and frequency exponent have been estimated from the fitting of the experimental data of conductivity with Jonscher power law modified by Almond-West. The ac conductivity and its frequency exponent have been analyzed by various theoretical models. In presently studied glasses ac conduction takes place via tunneling of overlapping large polaron tunneling. Activation energy is found to be increased with increase in zinc content and dc conduction takes place via variable range hopping proposed by Mott with some modification suggested by Punia et al. The value of the stretched exponent ( β) obtained by fitting of M^' ' }} reveals the presence of non-Debye type relaxation. Scaling spectra of ac conductivity and electric modulus collapse into a single master curve for all compositions and temperatures, reveals the presence of composition and temperature independent conduction and relaxation process in these glasses. Activation energy of conduction ( W) and electric modulus ( E R ) are nearly equal, indicating that polaron have to overcome the same energy barrier during conduction as well as relaxation processes.

Temperature dependent charge transport in poly(3-hexylthiophene) diodes

Science.gov (United States)

Rahaman, Abdulla Bin; Sarkar, Atri; Banerjee, Debamalya

2018-04-01

In this work, we present charge transport properties of poly(3-hexylthiophene) (P3HT) diodes under dark conditions. Temperature dependent current-voltage (J-V) characteristics shows that charge transport represents a transition from ohomic to trap limited current. The forward current density obeys a power law J˜Vm, m>2 represents the space charge limited current region in presence of traps within the band gap. Frequency dependent conductivity has been studied in a temperature range 150K-473K. The dc conductivity values show Arrhenius like behavior and it gives conductivity activation energy 223 meV. Temperature dependent conductivity indicates a thermodynamic transition of our system.

Effect of asymmetrical double-pockets and gate-drain underlap on Schottky barrier tunneling FET: Ambipolar conduction vs. high frequency performance

Science.gov (United States)

Shaker, Ahmed; Ossaimee, Mahmoud; Zekry, A.

2016-08-01

In this paper, a proposed structure based on asymmetrical double pockets SB-TFET with gate-drain underlap is presented. 2D extensive modeling and simulation, using Silvaco TCAD, were carried out to study the effect of both underlap length and pockets' doping on the transistor performance. It was found that the underlap from the drain side suppresses the ambipolar conduction and doesn't enhance the high-frequency characteristics. The enhancement of the high-frequency characteristics could be realized by increasing the doping of the drain pocket over the doping of the source pocket. An optimum choice was found which gives the conditions of minimum ambipolar conduction, maximum ON current and maximum cut-off frequency. These enhancements render the device more competitive as a nanometer transistor.

Frequency-dependent local field factors in dielectric liquids by a polarizable force field and molecular dynamics simulations

International Nuclear Information System (INIS)

Davari, Nazanin; Haghdani, Shokouh; Åstrand, Per-Olof

2015-01-01

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

Frequency-dependent tACS modulation of BOLD signal during rhythmic visual stimulation.

Science.gov (United States)

Chai, Yuhui; Sheng, Jingwei; Bandettini, Peter A; Gao, Jia-Hong

2018-05-01

Transcranial alternating current stimulation (tACS) has emerged as a promising tool for modulating cortical oscillations. In previous electroencephalogram (EEG) studies, tACS has been found to modulate brain oscillatory activity in a frequency-specific manner. However, the spatial distribution and hemodynamic response for this modulation remains poorly understood. Functional magnetic resonance imaging (fMRI) has the advantage of measuring neuronal activity in regions not only below the tACS electrodes but also across the whole brain with high spatial resolution. Here, we measured fMRI signal while applying tACS to modulate rhythmic visual activity. During fMRI acquisition, tACS at different frequencies (4, 8, 16, and 32 Hz) was applied along with visual flicker stimulation at 8 and 16 Hz. We analyzed the blood-oxygen-level-dependent (BOLD) signal difference between tACS-ON vs tACS-OFF, and different frequency combinations (e.g., 4 Hz tACS, 8 Hz flicker vs 8 Hz tACS, 8 Hz flicker). We observed significant tACS modulation effects on BOLD responses when the tACS frequency matched the visual flicker frequency or the second harmonic frequency. The main effects were predominantly seen in regions that were activated by the visual task and targeted by the tACS current distribution. These findings bridge different scientific domains of tACS research and demonstrate that fMRI could localize the tACS effect on stimulus-induced brain rhythms, which could lead to a new approach for understanding the high-level cognitive process shaped by the ongoing oscillatory signal. © 2018 Wiley Periodicals, Inc.

Empowering Malaysian dentists to tobacco dependence treatment conduct.

Science.gov (United States)

Nordin, Amer Siddiq Amer; Kadir, Rahimah Abdul; Yahya, Nurul Asyikin; Zakaria, Hazli; Rashid, Rusdi Abdul; Habil, Mohamed Hussain

2014-08-01

As a signatory to the World Health Organisation 2003 Framework Convention on Tobacco Control, Malaysia has policies in place and funded 300 public Quit clinics. Unfortunately, government dentists are not included to run tobacco dependence treatment. A cross-sectional exploratory survey was carried out to seek Malaysian dentists' opinion on their knowledge, perception and willingness to conduct tobacco dependence treatment. Participation was voluntary from those who attended a specially designed one-day, four-module workshop on tobacco cessation intervention. Data were collected using the Audience-Response-System equipment which tracked immediate responses covering four domains namely: smoking as a public health problem, smoking as an addiction, the role of dentists in the programme and confidence in conducting smoking cessation in the clinic. Sample comprised more female dentists (73.5%), mean age 33.6 (SD 8.99) years and with more than 3 years working experience. Findings indicated that the majority agreed Malaysia has a rising problem in the prevalence of smoking (71.6%) and predicted that it will affect mostly the young (81.9%). Only half of the dentists surveyed (58.9%) routinely recorded their patients' smoking habits. The majority (71.6%) believed that dentists are effective in helping their patient to stop smoking and 76.3% agreed that dentists should discuss the smoking habit with their patients; however, 60% agreed that doing so is too time consuming. In addition, only 24.7% knew of more ways to treat a smoking habit. The majority felt comfortable giving advice to patients about changing their habits (76.5%) or discussing treatment options (60.5%): 75% would opt for a combined programme of counselling and use of medication if they have to do, 15% would choose to go on counselling only, while 8% did not want to treat. In conclusion, the findings suggest that dentists have a strong potential to contribute significantly to providing smoking cessation

Age dependence of dielectric properties of bovine brain and ocular tissues in the frequency range of 400 MHz to 18 GHz

International Nuclear Information System (INIS)

Schmid, Gernot; Ueberbacher, Richard

2005-01-01

In order to identify possible age-dependent dielectric properties of brain and eye tissues in the frequency range of 400 MHz to 18 GHz, measurements on bovine grey and white matter as well as on cornea, lens (cortical) and the vitreous body were performed using a commercially available open-ended coaxial probe and a computer-controlled vector network analyser. Freshly excised tissues of 52 animals of two age groups (42 adult animals, i.e. 16-24 month old and 10 young animals, i.e. 4-6 month old calves) were examined within 8 min (brain tissue) and 15 min (eye tissue), respectively, of the animals' death. Tissue temperatures for the measurements were 32 ± 1 0 C and 25 ± 1 0 C for brain and eye tissues, respectively. Statistical analysis of the measured data revealed significant differences in the dielectric properties of white matter and cortical lens tissue between the adult and the young group. In the case of white matter the mean values of conductivity and permittivity of young tissue were 15%-22% and 12%-15%, respectively, higher compared to the adult tissue in the considered frequency range. Similarly, young cortical lens tissue was 25%-76% higher in conductivity and 27%-39% higher in permittivity than adult cortical lens tissue

Temperature dependence of frequency dispersion in III–V metal-oxide-semiconductor C-V and the capture/emission process of border traps

Energy Technology Data Exchange (ETDEWEB)

Vais, Abhitosh, E-mail: Abhitosh.Vais@imec.be; Martens, Koen; DeMeyer, Kristin [Department of Electrical Engineering, KU Leuven, B-3000 Leuven (Belgium); IMEC, Kapeldreef 75, B-3001 Leuven (Belgium); Lin, Han-Chung; Ivanov, Tsvetan; Collaert, Nadine; Thean, Aaron [IMEC, Kapeldreef 75, B-3001 Leuven (Belgium); Dou, Chunmeng [Frontier Research Center, Tokyo Institute of Technology, Yokohama 226-8502 (Japan); Xie, Qi; Maes, Jan [ASM International, B-3001 Leuven (Belgium); Tang, Fu; Givens, Michael [ASM International, Phoenix, Arizona 85034-7200 (United States); Raskin, Jean-Pierre [Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Universiteé Catholique de Louvain, B-1348 Louvain-la-Neuve (Belgium)

2015-08-03

This paper presents a detailed investigation of the temperature dependence of frequency dispersion observed in capacitance-voltage (C-V) measurements of III-V metal-oxide-semiconductor (MOS) devices. The dispersion in the accumulation region of the capacitance data is found to change from 4%–9% (per decade frequency) to ∼0% when the temperature is reduced from 300 K to 4 K in a wide range of MOS capacitors with different gate dielectrics and III-V substrates. We show that such significant temperature dependence of C-V frequency dispersion cannot be due to the temperature dependence of channel electrostatics, i.e., carrier density and surface potential. We also show that the temperature dependence of frequency dispersion, and hence, the capture/emission process of border traps can be modeled by a combination of tunneling and a “temperature-activated” process described by a non-radiative multi-phonon model, instead of a widely believed single-step elastic tunneling process.

High-frequency response and the possibilities of frequency-tunable narrow-band terahertz amplification in resonant tunneling nanostructures

International Nuclear Information System (INIS)

Kapaev, V. V.; Kopaev, Yu. V.; Savinov, S. A.; Murzin, V. N.

2013-01-01

The characteristics of the high-frequency response of single- and double-well resonant tunneling structures in a dc electric field are investigated on the basis of the numerical solution of a time-dependent Schrödinger equation with open boundary conditions. The frequency dependence of the real part of high frequency conductivity (high-frequency response) in In 0.53 Ga 0.47 As/AlAs/InP structures is analyzed in detail for various values of the dc voltage V dc in the negative differential resistance (NDR) region. It is shown that double-well three-barrier structures are promising for the design of terahertz-band oscillators. The presence of two resonant states with close energies in such structures leads to a resonant (in frequency) response whose frequency is determined by the energy difference between these levels and can be controlled by varying the parameters of the structure. It is shown that, in principle, such structures admit narrow-band amplification, tuning of the amplification frequency, and a fine control of the amplification (oscillation) frequency in a wide range of terahertz frequencies by varying a dc electric voltage applied to the structure. Starting from a certain width of the central intermediate barrier in double-well structures, one can observe a collapse of resonances, where the structure behaves like a single-well system. This phenomenon imposes a lower limit on the oscillation frequency in three-barrier resonant tunneling structures.

GENERAL APROACH TO MODELING NONLINEAR AMPLITUDE AND FREQUENCY DEPENDENT HYSTERESIS EFFECTS BASED ON EXPERIMENTAL RESULTS

OpenAIRE

Christopher Heine; Markus Plagemann

2014-01-01

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 u...

Predictive Accuracy of Sweep Frequency Impedance Technology in Identifying Conductive Conditions in Newborns.

Science.gov (United States)

Aithal, Venkatesh; Kei, Joseph; Driscoll, Carlie; Murakoshi, Michio; Wada, Hiroshi

2018-02-01

Diagnosing conductive conditions in newborns is challenging for both audiologists and otolaryngologists. Although high-frequency tympanometry (HFT), acoustic stapedial reflex tests, and wideband absorbance measures are useful diagnostic tools, there is performance measure variability in their detection of middle ear conditions. Additional diagnostic sensitivity and specificity measures gained through new technology such as sweep frequency impedance (SFI) measures may assist in the diagnosis of middle ear dysfunction in newborns. The purpose of this study was to determine the test performance of SFI to predict the status of the outer and middle ear in newborns against commonly used reference standards. Automated auditory brainstem response (AABR), HFT (1000 Hz), transient evoked otoacoustic emission (TEOAE), distortion product otoacoustic emission (DPOAE), and SFI tests were administered to the study sample. A total of 188 neonates (98 males and 90 females) with a mean gestational age of 39.4 weeks were included in the sample. Mean age at the time of testing was 44.4 hr. Diagnostic accuracy of SFI was assessed in terms of its ability to identify conductive conditions in neonates when compared with nine different reference standards (including four single tests [AABR, HFT, TEOAE, and DPOAE] and five test batteries [HFT + DPOAE, HFT + TEOAE, DPOAE + TEOAE, DPOAE + AABR, and TEOAE + AABR]), using receiver operating characteristic (ROC) analysis and traditional test performance measures such as sensitivity and specificity. The test performance of SFI against the test battery reference standard of HFT + DPOAE and single reference standard of HFT was high with an area under the ROC curve (AROC) of 0.87 and 0.82, respectively. Although the HFT + DPOAE test battery reference standard performed better than the HFT reference standard in predicting middle ear conductive conditions in neonates, the difference in AROC was not significant. Further analysis revealed that the

Thermal Conductance and High-Frequency Properties of Cryogenic Normal or Superconducting Semi-rigid Coaxial Cables in the Temperature Range of 1-8 K

Science.gov (United States)

Kushino, A.; Kasai, S.; Ukibe, M.; Ohkubo, M.

2018-04-01

In this study, the characteristics of thin semi-rigid cables composed of different conductors and with outer diameters ranging from 0.86 to 1.19 mm were investigated at low temperatures. The thermal conductance was measured between approximately 1 and 8 K, and the frequency dependence of the attenuation in the cables was obtained at 3 K. The electrical conductors used in the cables were alloys: beryllium copper, brass, stainless steel (SUS304), phosphor bronze, cupronickel (CuNi), and niobium-titanium (NbTi). The thermal conductance of a commercial miniature coaxial cable with braided wires forming the outer electrical conductor was also examined for reference. The measured thermal conductance was compared to published data and that generated from material libraries and databases. Among the measured cables using normal metals, the semi-rigid cable composed of SUS304 conductors and a polytetrafluoroethylene insulator showed the lowest thermal conductance. The transmission performance of the semi-rigid cables using SUS304 or CuNi was improved by plating the central conductors with a silver coating of approximately 3 μm thickness, and their thermal conductance with the plating increased by approximately one order of magnitude. The superconducting NbTi semi-rigid cable exhibited the lowest thermal conductance of all the cables considered in the present study along with very small attenuation up to above 5 GHz.

Interplay of activation kinetics and the derivative conductance determines resonance properties of neurons

Science.gov (United States)

Pena, Rodrigo F. O.; Ceballos, Cesar C.; Lima, Vinicius; Roque, Antonio C.

2018-04-01

In a neuron with hyperpolarization activated current (Ih), the correct input frequency leads to an enhancement of the output response. This behavior is known as resonance and is well described by the neuronal impedance. In a simple neuron model we derive equations for the neuron's resonance and we link its frequency and existence with the biophysical properties of Ih. For a small voltage change, the component of the ratio of current change to voltage change (d I /d V ) due to the voltage-dependent conductance change (d g /d V ) is known as derivative conductance (GhDer). We show that both GhDer and the current activation kinetics (characterized by the activation time constant τh) are mainly responsible for controlling the frequency and existence of resonance. The increment of both factors (GhDer and τh) greatly contributes to the appearance of resonance. We also demonstrate that resonance is voltage dependent due to the voltage dependence of GhDer. Our results have important implications and can be used to predict and explain resonance properties of neurons with the Ih current.

Broad-band conductivity and dielectric spectroscopy of composites of multiwalled carbon nanotubes and poly(ethylene terephthalate) around their low percolation threshold

Science.gov (United States)

Nuzhnyy, D.; Savinov, M.; Bovtun, V.; Kempa, M.; Petzelt, J.; Mayoral, B.; McNally, T.

2013-02-01

Composites of multiwalled carbon nanotubes with poly(ethylene terephthalate) (PET-MWCNT) with up to 3 vol% MWCNTs were prepared and characterized by broad-band AC conductivity and dielectric spectroscopy up to the infrared range using several techniques. A very low electrical percolation threshold of 0.07 vol% MWCNTs was revealed from the low-frequency conductivity plateau as well as from DC conductivity, whose values show the same critical power dependence on MWCNT concentration with the exponent t = 4.3. Above the plateau, the AC conductivity increases with frequency up to the THz range, where it becomes overlapped with the absorption of vibrational modes. The temperature dependence down to ˜5 K has shown semiconductor behaviour with a concentration-independent but weakly temperature-dependent small activation energy of ˜3 meV. The behaviour is compatible with the previously suggested fluctuation-induced tunnelling conductivity model through a thin (˜1 nm) polymer contact layer among the adjacent MWCNTs within percolated clusters. At higher frequencies, deviations from the simple universal conductivity behaviour are observed, indicating some distribution of energy barriers for an electron hopping mechanism.

Explanation for the temperature dependence of plasma frequencies in SrTiO3 using mixed-polaron theory

International Nuclear Information System (INIS)

Eagles, D.M.; Georgiev, M.; Petrova, P.C.

1996-01-01

A theory of mixed polarons is used to interpret the published experimental results of Gervais et al. on temperature-dependent plasma frequencies in Nb-doped SrTiO 3 . For given polaron masses before mixing, the appropriate average mixed-polaron mass at any temperature T depends on two quantities, δ and b, which are measures of the separation between the bottoms of large and nearly small polaron bands before mixing and of a mixing matrix element; δ and b are assumed to have arbitrary linear dependences on T, probably related to a T dependence of the bare mass, and a term quadratic in T is included in δ, determined from the T dependence of large-polaron binding energies. Including a constraint on the ratio δ/|b| at low T from known masses from specific-heat data, satisfactory agreement is obtained with masses determined from plasma frequencies. This gives further support for the theory of mixed polarons in SrTiO 3 in addition to that already published. copyright 1996 The American Physical Society

A time-dependent model to determine the thermal conductivity of a nanofluid

Energy Technology Data Exchange (ETDEWEB)

Myers, T. G., E-mail: tmyers@crm.cat; MacDevette, M. M., E-mail: mmacdevette@crm.cat; Ribera, H. [Centre de Recerca Matematica (Spain)

2013-07-15

In this paper, we analyse the time-dependent heat equations over a finite domain to determine expressions for the thermal diffusivity and conductivity of a nanofluid (where a nanofluid is a fluid containing nanoparticles with average size below 100 nm). Due to the complexity of the standard mathematical analysis of this problem, we employ a well-known approximate solution technique known as the heat balance integral method. This allows us to derive simple analytical expressions for the thermal properties, which appear to depend primarily on the volume fraction and liquid properties. The model is shown to compare well with experimental data taken from the literature even up to relatively high concentrations and predicts significantly higher values than the Maxwell model for volume fractions approximately >1 %. The results suggest that the difficulty in reproducing the high values of conductivity observed experimentally may stem from the use of a static heat flow model applied over an infinite domain rather than applying a dynamic model over a finite domain.

Frequency-dependent viscoelastic parameters of mouse brain tissue estimated by MR elastography

Energy Technology Data Exchange (ETDEWEB)

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.

Anisotropy of heat conduction in Mo/Si multilayers

International Nuclear Information System (INIS)

Medvedev, V. V.; Yakshin, A. E.; Kruijs, R. W. E. van de; Bijkerk, F.; Yang, J.; Schmidt, A. J.; Zoethout, E.

2015-01-01

This paper reports on the studies of anisotropic heat conduction phenomena in Mo/Si multilayers with individual layer thicknesses selected to be smaller than the mean free path of heat carriers. We applied the frequency-domain thermoreflectance technique to characterize the thermal conductivity tensor. While the mechanisms of the cross-plane heat conduction were studied in detail previously, here we focus on the in-plane heat conduction. To analyze the relative contribution of electron transport to the in-plane heat conduction, we applied sheet-resistance measurements. Results of Mo/Si multilayers with variable thickness of the Mo layers indicate that the net in-plane thermal conductivity depends on the microstructure of the Mo layers

Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

International Nuclear Information System (INIS)

Mamand, S.M.; Omar, M.S.; Muhammad, A.J.

2012-01-01

Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: ► A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. ► A direct method is used to calculate phonon group velocity for these nanowires. ► 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. ► Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2–300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10 14 m −2 the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10 14 m −2 , lattice thermal conductivity would be independent of that.

Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

Energy Technology Data Exchange (ETDEWEB)

Mamand, S.M., E-mail: soran.mamand@univsul.net [Department of Physics, College of Science, University of Sulaimani, Sulaimanyah, Iraqi Kurdistan (Iraq); Omar, M.S. [Department of Physics, College of Science, University of Salahaddin, Arbil, Iraqi Kurdistan (Iraq); Muhammad, A.J. [Department of Physics, College of Science, University of Kirkuk, Kirkuk (Iraq)

2012-05-15

Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: Black-Right-Pointing-Pointer A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. Black-Right-Pointing-Pointer A direct method is used to calculate phonon group velocity for these nanowires. Black-Right-Pointing-Pointer 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. Black-Right-Pointing-Pointer Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2-300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10{sup 14} m{sup -2} the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10{sup 14} m{sup -2}, lattice thermal conductivity would be independent of that.

Pulse frequency dependency of photobiomodulation on the bioenergetic functions of human dental pulp stem cells.

Science.gov (United States)

Kim, Hong Bae; Baik, Ku Youn; Choung, Pill-Hoon; Chung, Jong Hoon

2017-11-21

Photobiomodulation (PBM) therapy contributes to pain relief, wound healing, and tissue regeneration. The pulsed wave (PW) mode has been reported to be more effective than the continuous wave (CW) mode when applying PBM to many biological systems. However, the reason for the higher effectiveness of PW-PBM is poorly understood. Herein, we suggest using delayed luminescence (DL) as a reporter of mitochondrial activity after PBM treatment. DL originates mainly from mitochondrial electron transport chain systems, which produce reactive oxygen species (ROS) and adenosine triphosphate (ATP). The decay time of DL depends on the pulse frequencies of applied light, which correlate with the biological responses of human dental pulp stem cells (hDPSCs). Using a low-power light whose wavelength is 810 nm and energy density is 38 mJ/cm 2 , we find that a 300-Hz pulse frequency prolonged the DL pattern and enhanced alkaline phosphatase activity. In addition, we analyze mitochondrial morphological changes and their volume density and find evidence supporting mitochondrial physiological changes from PBM treatment. Our data suggest a new methodology for determining the effectiveness of PBM and the specific pulse frequency dependency of PBM in the differentiation of hDPSCs.

Conductivity of the electron-impurity system

International Nuclear Information System (INIS)

Goettig, S.

1983-09-01

The free-carrier absorption of electromagnetic radiation due to the presence of static scatterers is examined taking into account the electron-electron interaction, the plasma-phonon polar coupling and the plasma anisotropy. For the case of strong coupling in the isotropic plasma the absorption due to the collective-mode excitation processes is, for frequencies just above the plasmon-like collective mode frequency, shown to be dominant over the absorption due to single-particle excitations. The expression for the frequency-dependent absorptive part of the conductivity due to the long-wavelength collective-mode excitations is derived for the case of multicomponent anisotropic degenerate plasma (e.g. lead chalcogenides). The results are discussed in detail and compared with available experimental data for n-PbSe. The comparison with the previous theories is also given. (author)

Dependence of synchronization frequency of Kuramoto oscillators ...

Indian Academy of Sciences (India)

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 ...

Conductivity of oriented bis-azo polymer films

DEFF Research Database (Denmark)

Apitz, D.; Bertram, R.P.; Benter, N.

2006-01-01

The conductivity properties of electro-optic photoaddressable, dense bis-ozo chromophore polymer films are investigated by using samples corona poled at various temperatures. A dielectric spectrometer is applied to measure the frequency dependence of the conductivity at different temperatures...... before and after heating the material to above the glass transition temperature. The results show that the orientation of the chromophores changes the charge-carrier mobility. Ionic conductivity dominates in a more disordered configuration of the material, while the competing process of hole hopping...... takes over as a transition to a liquid-crystalline phase occurs when the material is heated to much higher than the gloss transition temperature. Such micro-crystallization strongly enhances the conductivity....

Study of temperature-dependent charge conduction in silicon-nanocrystal/SiO{sub 2} multilayers

Energy Technology Data Exchange (ETDEWEB)

Mavilla, Narasimha Rao; Chavan, Vinayak [National Centre for Photovoltaic Research and Education (NCPRE), Powai, Mumbai 400 076 (India); Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076 (India); Solanki, Chetan Singh [National Centre for Photovoltaic Research and Education (NCPRE), Powai, Mumbai 400 076 (India); Department of Energy Science and Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076 (India); Vasi, Juzer [National Centre for Photovoltaic Research and Education (NCPRE), Powai, Mumbai 400 076 (India); Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076 (India)

2016-08-01

Silicon-nanocrystals (Si-NCs) realized by SiO{sub x} {sub <} {sub 2}/SiO{sub 2} multilayer (ML) approach have shown promise for realizing tightly-controlled dimensions, thus efficiently exploiting the size-dependent quantum effects for device applications. Unfortunately, the confining insulating barriers (SiO{sub 2} sublayers), instrumental for realizing quantum size effects in Si-NC MLs, can also hinder the charge conduction which is crucial for device applications including Si-NC based tandem solar cells and multi-exciton solar cells. Owing to this, a comprehensive study of conduction mechanisms has been carried out using a thorough analysis of temperature-dependent dark I-V measurements of SiO{sub 2} thin film and Si-NC multilayer samples fabricated by Inductively Coupled Plasma CVD (ICPCVD). As the ML samples consisted of interleaved SiO{sub 2} sublayers, current in SiO{sub 2} thin film has initially been studied to understand the conduction properties of bulk ICPCVD SiO{sub 2}. For 21 nm thick SiO{sub 2} film, conduction is observed to be dominated by Fowler–Nordheim (FN) tunneling for higher electric fields (> 8 MV/cm; independent of temperature), while for lower electric fields (5–8 MV/cm) at higher temperatures, the trap-related Generalized Poole–Frenkel (GPF) is dominant. This signified the role of traps in modifying the conduction in bulk ICPCVD SiO{sub 2} films. We then present the conduction in ML samples. For multilayer samples with SiO{sub 2} sublayer thickness of 1.5 nm and 2.5 nm, Direct Tunneling (DT) is observed to be dominant, while for SiO{sub 2} sublayer thickness of 3.5 nm, Space Charge Limited Conduction (SCLC) with exponential trap distribution is found to be the dominant conduction mechanism. This signifies the role of traps in modifying the conduction in Si-NC multilayer samples and SiO{sub 2} sublayer thickness dependence. - Highlights: • Electrical conduction in SiO{sub 2} film & Si-nanocrystal layers (Si-NCs) is reported. • Si

Binder-free highly conductive graphene laminate for low cost printed radio frequency applications

Energy Technology Data Exchange (ETDEWEB)

Huang, Xianjun; Leng, Ting; Zhang, Xiao; Hu, Zhirun, E-mail: Z.Hu@manchester.ac.uk [School of Electrical and Electronic Engineering, University of Manchester, Manchester (United Kingdom); Chen, Jia Cing; Chang, Kuo Hsin [BGT Materials Limited, Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Geim, Andre K. [Manchester Centre for Mesoscience and Nanotechnology, University of Manchester, Manchester (United Kingdom); Novoselov, Kostya S. [School of Physics and Astronomy, University of Manchester, Manchester (United Kingdom)

2015-05-18

In this paper, we demonstrate realization of printable radio frequency identification (RFID) antenna by low temperature processing of graphene ink. The required ultra-low resistance is achieved by rolling compression of binder-free graphene laminate. With compression, the conductivity of graphene laminate is increased by more than 50 times compared to that of as-deposited one. Graphene laminate with conductivity of 4.3 × 10{sup 4 }S/m and sheet resistance of 3.8 Ω/sq (with thickness of 6 μm) is presented. Moreover, the formation of graphene laminate from graphene ink reported here is simple and can be carried out in low temperature (100 °C), significantly reducing the fabrication costs. A dipole antenna based on the highly conductive graphene laminate is further patterned and printed on a normal paper to investigate its RF properties. The performance of the graphene laminate antenna is experimentally measured. The measurement results reveal that graphene laminate antenna can provide practically acceptable return loss, gain, bandwidth, and radiation patterns, making it ideal for low cost printed RF applications, such as RFID tags and wearable wireless sensor networks.

Binder-free highly conductive graphene laminate for low cost printed radio frequency applications

International Nuclear Information System (INIS)

Huang, Xianjun; Leng, Ting; Zhang, Xiao; Hu, Zhirun; Chen, Jia Cing; Chang, Kuo Hsin; Geim, Andre K.; Novoselov, Kostya S.

2015-01-01

In this paper, we demonstrate realization of printable radio frequency identification (RFID) antenna by low temperature processing of graphene ink. The required ultra-low resistance is achieved by rolling compression of binder-free graphene laminate. With compression, the conductivity of graphene laminate is increased by more than 50 times compared to that of as-deposited one. Graphene laminate with conductivity of 4.3 × 10 4  S/m and sheet resistance of 3.8 Ω/sq (with thickness of 6 μm) is presented. Moreover, the formation of graphene laminate from graphene ink reported here is simple and can be carried out in low temperature (100 °C), significantly reducing the fabrication costs. A dipole antenna based on the highly conductive graphene laminate is further patterned and printed on a normal paper to investigate its RF properties. The performance of the graphene laminate antenna is experimentally measured. The measurement results reveal that graphene laminate antenna can provide practically acceptable return loss, gain, bandwidth, and radiation patterns, making it ideal for low cost printed RF applications, such as RFID tags and wearable wireless sensor networks

Cellular elements for seeing in the dark: voltage-dependent conductances in cockroach photoreceptors

Directory of Open Access Journals (Sweden)

Salmela Iikka

2012-08-01

Full Text Available Abstract Background The importance of voltage-dependent conductances in sensory information processing is well-established in insect photoreceptors. Here we present the characterization of electrical properties in photoreceptors of the cockroach (Periplaneta americana, a nocturnal insect with a visual system adapted for dim light. Results Whole-cell patch-clamped photoreceptors had high capacitances and input resistances, indicating large photosensitive rhabdomeres suitable for efficient photon capture and amplification of small photocurrents at low light levels. Two voltage-dependent potassium conductances were found in the photoreceptors: a delayed rectifier type (KDR and a fast transient inactivating type (KA. Activation of KDR occurred during physiological voltage responses induced by light stimulation, whereas KA was nearly fully inactivated already at the dark resting potential. In addition, hyperpolarization of photoreceptors activated a small-amplitude inward-rectifying (IR current mediated at least partially by chloride. Computer simulations showed that KDR shapes light responses by opposing the light-induced depolarization and speeding up the membrane time constant, whereas KA and IR have a negligible role in the majority of cells. However, larger KA conductances were found in smaller and rapidly adapting photoreceptors, where KA could have a functional role. Conclusions The relative expression of KA and KDR in cockroach photoreceptors was opposite to the previously hypothesized framework for dark-active insects, necessitating further comparative work on the conductances. In general, the varying deployment of stereotypical K+ conductances in insect photoreceptors highlights their functional flexibility in neural coding.

Structural, dielectric and AC conductivity study of Sb2O3 thin film ...

Indian Academy of Sciences (India)

52

However, to date, no reports have appeared on impedance spectroscopy, modulus behavior, electrical conductivity, dielectric relaxation and dielectric properties of crystalline Sb2O3 thin films. This paper deals for the first time with the frequency and temperature dependence of AC conductivity and complex electric modulus ...

Frequency Dependence of Helioseismic Measurements of the Center-to-Limb Effect and Flow-induced Travel-time Shifts

Science.gov (United States)

Chen, Ruizhu; Zhao, Junwei

2018-02-01

Time–distance helioseismology measures acoustic travel times to infer the structure and flow field of the solar interior; however, both the mean travel times and the travel-time shifts suffer systematic center-to-limb variations, which complicate the interpretation and inversions of the time–distance measurements. In particular, the center-to-limb variation in travel-time shifts (CtoL effect) has a significant impact on the inference of the Sun’s meridional circulation, and needs to be removed from the helioseismic measurements, although the observational properties and the physical cause of the CtoL effect have yet to be investigated. In this study, we measure the CtoL effect in the frequency domain using Doppler-velocity data from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, and study its properties as a function of disk-centric distance, travel distance, and frequency of acoustic waves. It is found that the CtoL effect has a significant frequency dependence—it reverses sign at a frequency around 5.4 mHz and reaches maximum at around 4.0 mHz before the sign reversal. The tendency of frequency dependence varies with disk-centric distance in a way that both the sign-reversal frequency and the maximum-value frequency decrease closer to the limb. The variation tendency does not change with travel distance, but the variation magnitude is approximately proportional to travel distance. For comparison, the flow-induced travel-time shifts show little frequency dependence. These observational properties provide more clues on the nature of the CtoL effect, and also possibly lead to new ways of effect-removal for a more robust determination of the deep meridional flow.

Split-Capacitance and Conductance-Frequency Characteristics of SOI Wafers in Pseudo-MOSFET Configuration

KAUST Repository

Pirro, Luca

2015-09-01

Recent experimental results have demonstrated the possibility of characterizing silicon-on-insulator (SOI) wafers through split C-V measurements in the pseudo-MOSFET configuration. This paper analyzes the capacitance and conductance versus frequency characteristics. We discuss the conditions under which it is possible to extract interface trap density in bare SOI wafers. The results indicate, through both measurements and simulations, that the signature due to interface trap density is present in small-area samples, but is masked by the RC response of the channel in regular, large-area ones, making the extraction in standard samples problematic. © 1963-2012 IEEE.

Split-Capacitance and Conductance-Frequency Characteristics of SOI Wafers in Pseudo-MOSFET Configuration

KAUST Repository

Pirro, Luca; Diab, Amer El Hajj; Ionica, Irina; Ghibaudo, Gerard; Faraone, Lorenzo; Cristoloveanu, Sorin

2015-01-01

Recent experimental results have demonstrated the possibility of characterizing silicon-on-insulator (SOI) wafers through split C-V measurements in the pseudo-MOSFET configuration. This paper analyzes the capacitance and conductance versus frequency characteristics. We discuss the conditions under which it is possible to extract interface trap density in bare SOI wafers. The results indicate, through both measurements and simulations, that the signature due to interface trap density is present in small-area samples, but is masked by the RC response of the channel in regular, large-area ones, making the extraction in standard samples problematic. © 1963-2012 IEEE.

The Temperature Condition of the Plate with Temperature-Dependent Thermal Conductivity and Energy Release

Directory of Open Access Journals (Sweden)

V. S. Zarubin

2016-01-01

Full Text Available The temperature state of a solid body, in addition to the conditions of its heat exchange with the environment, can greatly depend on the heat release (or heat absorption processes within the body volume. Among the possible causes of these processes should be noted such as a power release in the fuel elements of nuclear reactors, exothermic or endothermic chemical reactions in the solid body material, which respectively involve heat release or absorbtion, heat transfer of a part of the electric power in the current-carrying conductors (so-called Joule’s heat or the energy radiation penetrating into the body of a semitransparent material, etc. The volume power release characterizes an intensity of these processes.The extensive list of references to the theory of heat conductivity of solids offers solutions to problems to determine a stationary (steady over time and non-stationary temperature state of the solids (as a rule, of the canonical form, which act as the sources of volume power release. Thus, in general case, a possibility for changing power release according to the body volume and in solving the nonstationary problems also a possible dependence of this value on the time are taken into consideration.However, in real conditions the volume power release often also depends on the local temperature, and such dependence can be nonlinear. For example, with chemical reactions the intensity of heat release or absorption is in proportion to their rate, which, in turn, is sensitive to the temperature value, and a dependence on the temperature is exponential. A further factor that in such cases makes the analysis of the solid temperature state complicated, is dependence on the temperature and the thermal conductivity of this body material, especially when temperature distribution therein  is significantly non-uniform. Taking into account the influence of these factors requires the mathematical modeling methods, which allow us to build an adequate

Evaluation of ac conductivity behaviour of graphite filled

Indian Academy of Sciences (India)

Composites of epoxy resin having different amounts of graphite particles have been prepared by solution casting method. Temperature dependence of dielectric constant, tan and a.c. conductivity was measured in the frequency range, 1–20 kHz, temperature range, 40–180°C for 0.99, 1.96 and 2.91 wt% graphite filled ...

Frequency Dependent Nudging of Hydrographic Data Into a Numerical Model of the North Atlantic

Science.gov (United States)

Thompson, K. R.; Wright, D. G.

2002-12-01

Nudging is one of the simplest ways of assimilating data into ocean models and it has been used for many years in studies of large-scale ocean circulation. One of its drawbacks is the suppression of eddies when nudging an eddy-permitting ocean model strongly toward an observed seasonal climatology. We propose a straightforward extension of nudging in which the model's climatology, rather than its instantaneous state, is nudged toward the observed seasonal climatology. In effect we propose nudging in specific frequency bands that are centered on the discrete frequencies evident in the observed climatology (e.g. 0, 1/12 and 1/6 cycles per month). This extension of conventional nudging allows the difference between the observed and modeled climatologies arbitrarily to be made small while allowing variations outside the selected frequency bands to evolve freely. We show how the method can be implemented efficiently in complex models using a Kalman filter and also discuss the benefits of spatially smoothing the nudges. We conclude with a demonstration of frequency dependent nudging using a 1/3 degree model of the North Atlantic.

Frequency and amplitude dependences of molding accuracy in ultrasonic nanoimprint technology

International Nuclear Information System (INIS)

Mekaru, Harutaka; Takahashi, Masaharu

2009-01-01

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, T g = 69 °C), whose the glass transition temperature (T g ) 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

Calculation and applications of the frequency dependent neutron detector response functions

International Nuclear Information System (INIS)

Van Dam, H.; Van Hagen, T.H.J.J. der; Hoogenboom, J.E.; Keijzer, J.

1994-01-01

The theoretical basis is presented for the evaluation of the frequency dependent function that enables to calculate the response of a neutron detector to parametric fluctuations ('noise') or oscillations in reactor core. This function describes the 'field view' of a detector and can be calculated with a static transport code under certain conditions which are discussed. Two applications are presented: the response of an ex-core detector to void fraction fluctuations in a BWR and of both in and ex-core detectors to a rotating neutron absorber near or inside a research reactor core. (authors). 7 refs., 4 figs

The functional dependence of canopy conductance on water vapor pressure deficit revisited

Science.gov (United States)

Fuchs, Marcel; Stanghellini, Cecilia

2018-03-01

Current research seeking to relate between ambient water vapor deficit (D) and foliage conductance (g F ) derives a canopy conductance (g W ) from measured transpiration by inverting the coupled transpiration model to yield g W = m - n ln(D) where m and n are fitting parameters. In contrast, this paper demonstrates that the relation between coupled g W and D is g W = AP/D + B, where P is the barometric pressure, A is the radiative term, and B is the convective term coefficient of the Penman-Monteith equation. A and B are functions of g F and of meteorological parameters but are mathematically independent of D. Keeping A and B constant implies constancy of g F . With these premises, the derived g W is a hyperbolic function of D resembling the logarithmic expression, in contradiction with the pre-set constancy of g F . Calculations with random inputs that ensure independence between g F and D reproduce published experimental scatter plots that display a dependence between g W and D in contradiction with the premises. For this reason, the dependence of g W on D is a computational artifact unrelated to any real effect of ambient humidity on stomatal aperture and closure. Data collected in a maize field confirm the inadequacy of the logarithmic function to quantify the relation between canopy conductance and vapor pressure deficit.

AC-conductance and capacitance measurements for ethanol vapor detection using carbon nanotube-polyvinyl alcohol composite based devices.

Science.gov (United States)

Greenshields, Márcia W C C; Meruvia, Michelle S; Hümmelgen, Ivo A; Coville, Neil J; Mhlanga, Sabelo D; Ceragioli, Helder J; Quispe, Jose C Rojas; Baranauskas, Vitor

2011-03-01

We report the preparation of inexpensive ethanol sensor devices using multiwalled carbon nanotube-polyvinyl alcohol composite films deposited onto interdigitated electrodes patterned on phenolite substrates. We investigate the frequency dependent response of the device conductance and capacitance showing that higher sensitivity is obtained at higher frequency if the conductance is used as sensing parameter. In the case of capacitance measurements, higher sensitivity is obtained at low frequency. Ethanol detection at a concentration of 300 ppm in air is demonstrated. More than 80% of the sensor conductance and capacitance variation response occurs in less than 20 s.

Nanoscale Electromechanics To Measure Thermal Conductivity, Expansion, and Interfacial Losses.

Science.gov (United States)

Mathew, John P; Patel, Raj; Borah, Abhinandan; Maliakkal, Carina B; Abhilash, T S; Deshmukh, Mandar M

2015-11-11

We study the effect of localized Joule heating on the mechanical properties of doubly clamped nanowires under tensile stress. Local heating results in systematic variation of the resonant frequency; these frequency changes result from thermal stresses that depend on temperature dependent thermal conductivity and expansion coefficient. The change in sign of the linear expansion coefficient of InAs is reflected in the resonant response of the system near a bath temperature of 20 K. Using finite element simulations to model the experimentally observed frequency shifts, we show that the thermal conductivity of a nanowire can be approximated in the 10-60 K temperature range by the empirical form κ = bT W/mK, where the value of b for a nanowire was found to be b = 0.035 W/mK(2), significantly lower than bulk values. Also, local heating allows us to independently vary the temperature of the nanowire relative to the clamping points pinned to the bath temperature. We suggest a loss mechanism (dissipation ~10(-4)-10(-5)) originating from the interfacial clamping losses between the metal and the semiconductor nanostructure.

An analysis of boundary-effects in obtaining the frequency dependent specific heat by effusivity measurements

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 g...

Electrical conduction and dielectric relaxation in p-type PVA/CuI polymer composite

Directory of Open Access Journals (Sweden)

M.H. Makled

2013-11-01

Full Text Available PVA/CuI polymer composite samples have been prepared and subjected to characterizations using FT-IR spectroscopy, DSC analysis, ac spectroscopy and dc conduction. The FT-IR spectral analysis shows remarkable variation of the absorption peak positions whereas DSC illustrates a little decrease of both glass transition temperature, Tg, and crystallization fraction, χ, with increasing CuI concentration. An increase of dc conductivity for PVA/CuI nano composite by increasing CuI concentration is recoded up to 15 wt%, besides it obeys Arhenuis plot with an activation energy in the range 0.54–1.32 eV. The frequency dependence of ac conductivity showed power law with an exponent 0.33 < s < 0.69 which predicts hopping conduction mechanism. The frequency dependence of both dielectric permittivity and dielectric loss obeys Debye dispersion relations in wide range of temperatures and frequency. Significant values of dipole relaxation time obtained which are thermally activated with activation energies in the range 0.33–0.87 eV. A significant value of hopping distance in the range 3.4–1.2 nm is estimated in agreement with the value of Bohr radius of the exciton.

Conductivity in alkali doped CoO-B2O3 glasses

International Nuclear Information System (INIS)

Nagaraja, N; Sankarappa, T; Santoshkumar; Sadashivaiah, P J; Yenkayya

2009-01-01

Two series of cobalt-borate glasses doped with Li 2 O and K 2 O in single and mixed proportions have been synthesized by melt quenching method and investigated for ac conductivity in the frequency range of 50Hz to 5MHz and temperature range of 310K to 610K. From the measured total conductivity, the pure ac component and its frequency exponent, s were determined. In the single alkali doped glasses, for all the frequencies, the conductivity increased with increase of Li 2 O up to 0.4 mole fractions and decreased for further increase of Li 2 O. The temperature dependence of conductivity has been analyzed using Mott's small polaron hopping model and activation energy for ac conduction has been determined. Based on conductivity and activation behaviors, in single alkali glasses, a change over of conduction mechanism predominantly from ionic to electronic has been predicted. In mixed alkali doped glasses, the conductivity passed through minimum and activation energy passed through maximum for second alkali (K 2 O) content of 0.2 mole fractions. This result revealed the mixed alkali effect to be occurring at 0.2 mole fractions of K 2 O. The frequency exponent, s, was compared with theoretical models such as Quantum Mechanical Tunneling and Correlated Barrier Hopping models and found them to be inadequate to explain the experimental observations. Time-temperature superposition principle has been verified in both the sets of glasses.

Frequency Dependence of C-V Characteristics of MOS Capacitors Containing Nanosized High-κ Ta2O5 Dielectrics

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Nenad Novkovski

2017-01-01

Full Text Available Capacitance of metal–insulator–Si structures containing high permittivity dielectric exhibits complicated behaviour when voltage and frequency dependencies are studied. From our study on metal (Al, Au, W–Ta2O5/SiO2–Si structures, we identify serial C-R measurement mode to be more convenient for use than the parallel one usually used in characterization of similar structures. Strong frequency dependence that is not due to real variations in the dielectric permittivity of the layers is observed. Very high capacitance at low frequencies is due to the leakage in Ta2O5 layer. We found that the above observation is mainly due to different leakage current mechanisms in the two different layers composing the stack. The effect is highly dependent on the applied voltage, since the leakage currents are strongly nonlinear functions of the electric field in the layers. Additionally, at low frequencies, transition currents influence the measured value of the capacitance. From the capacitance measurements several parameters are extracted, such as capacitance in accumulation, effective dielectric constant, and oxide charges. Extracting parameters of the studied structures by standard methods in the case of high-κ/interfacial layer stacks can lead to substantial errors. Some cases demonstrating these deficiencies of the methods are presented and solutions for obtaining better results are proposed.

Weak ferromagnetism and temperature dependent dielectric properties of Zn{sub 0.9}Ni{sub 0.1}O diluted magnetic semiconductor

Energy Technology Data Exchange (ETDEWEB)

Ahmed, Raju [Department of Electrical and Electronic Engineering, Shahjalal University of Science and Technology, Sylhet 3114 (Bangladesh); Department of Applied Physics, Electronics and Communication Engineering, University of Dhaka, Dhaka 1000 (Bangladesh); Moslehuddin, A.S.M.; Mahmood, Zahid Hasan [Department of Applied Physics, Electronics and Communication Engineering, University of Dhaka, Dhaka 1000 (Bangladesh); Hossain, A.K.M. Akther, E-mail: akmhossain@phy.buet.ac.bd [Department of Physics, Bangladesh University of Engineering and Technology, Dhaka 1000 (Bangladesh)

2015-03-15

Highlights: • Single phase wurtzite structure was confirmed from XRD analysis. • Weak ferromagnetic behaviour at room temperature. • Pure semiconducting properties confirmed from temperature dependent conductivity. • Smaller dielectric properties at higher frequency. • Possible potential application in high frequency spintronic devices. - Abstract: In this study the room temperature ferromagnetic behaviour and dielectric properties of ZnO based diluted magnetic semiconductor (DMS) have been investigated using nominal chemical composition Zn{sub 0.9}Ni{sub 0.1}O. The X-ray diffraction analysis confirmed formation of single phase hexagonal wurtzite structure. An increase in grain size with increasing sintering temperature was observed from scanning electron microscopy. Field dependent DC magnetization values indicated dominant paramagnetic ordering along with a slight ferromagnetic behaviour at room temperature. Frequency dependent complex initial permeability showed some positive values around 12 at room temperature. In dielectric measurement, an increasing trend of complex permittivity, loss tangent and ac conductivity with increasing temperature were observed. The temperature dependent dispersion curves of dielectric properties revealed clear relaxation at higher temperature. Frequency dependent ac conductivity was found to increase with frequency whereas complex permittivity and loss tangent showed an opposite trend.

Dependence of conductivity on thickness within the variable-range hopping regime for Coulomb glasses

Directory of Open Access Journals (Sweden)

M. Caravaca

Full Text Available In this paper, we provide some computational evidence concerning the dependence of conductivity on the system thickness for Coulomb glasses. We also verify the Efros–Shklovskii law and deal with the calculation of its characteristic parameter as a function of the thickness. Our results strengthen the link between theoretical and experimental fields. Keywords: Coulomb glass, Conductivity, Density of states, Efros–Shklovskii law

Temperature dependence of low-frequency polarized Raman scattering spectra 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; Mimura, Kojiro [Graduate School of Engineering, Osaka Prefecture University, Osaka (Japan); Alekperov, Oktay; Mamedov, Nazim [Institute of Physics, Azerbaijan National Academy of Sciences, Baku (Azerbaijan)

2017-06-15

In this work, we examined phase transitions in the layered ternary thallium chalcogenide TlInS{sub 2} by studying the temperature dependence of polarized Raman spectra with the aid of the Raman confocal microscope system. The Raman spectra were measured over the temperature range of 77-320 K (which includes the range of successive phase transitions) in the low-frequency region of 35-180 cm{sup -1}. The optical phonons that showed strong temperature dependence were identified as interlayer vibrations related to phase transitions, while the phonons that showed weak temperature dependence were identified as intralayer vibrations. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Nature of Dielectric Properties, Electric Modulus and AC Electrical Conductivity of Nanocrystalline ZnIn2Se4 Thin Films

Science.gov (United States)

El-Nahass, M. M.; Attia, A. A.; Ali, H. A. M.; Salem, G. F.; Ismail, M. I.

2018-02-01

The structural characteristics of thermally deposited ZnIn2Se4 thin films were indexed utilizing x-ray diffraction as well as scanning electron microscopy techniques. Dielectric properties, electric modulus and AC electrical conductivity of ZnIn2Se4 thin films were examined in the frequency range from 42 Hz to 106 Hz. The capacitance, conductance and impedance were measured at different temperatures. The dielectric constant and dielectric loss decrease with an increase in frequency. The maximum barrier height was determined from the analysis of the dielectric loss depending on the Giuntini model. The real part of the electric modulus revealed a constant maximum value at higher frequencies and the imaginary part of the electric modulus was characterized by the appearance of dielectric relaxation peaks. The AC electrical conductivity obeyed the Jonscher universal power law. Correlated barrier hopping model was the appropriate mechanism for AC conduction in ZnIn2Se4 thin films. Estimation of the density of states at the Fermi level and activation energy, for AC conduction, was carried out based on the temperature dependence of AC electrical conductivity.

Mitigating artifacts in back-projection source imaging with implications for frequency-dependent properties of the Tohoku-Oki earthquake

Science.gov (United States)

Meng, Lingsen; Ampuero, Jean-Paul; Luo, Yingdi; Wu, Wenbo; Ni, Sidao

2012-12-01

Comparing teleseismic array back-projection source images of the 2011 Tohoku-Oki earthquake with results from static and kinematic finite source inversions has revealed little overlap between the regions of high- and low-frequency slip. Motivated by this interesting observation, back-projection studies extended to intermediate frequencies, down to about 0.1 Hz, have suggested that a progressive transition of rupture properties as a function of frequency is observable. Here, by adapting the concept of array response function to non-stationary signals, we demonstrate that the "swimming artifact", a systematic drift resulting from signal non-stationarity, induces significant bias on beamforming back-projection at low frequencies. We introduce a "reference window strategy" into the multitaper-MUSIC back-projection technique and significantly mitigate the "swimming artifact" at high frequencies (1 s to 4 s). At lower frequencies, this modification yields notable, but significantly smaller, artifacts than time-domain stacking. We perform extensive synthetic tests that include a 3D regional velocity model for Japan. We analyze the recordings of the Tohoku-Oki earthquake at the USArray and at the European array at periods from 1 s to 16 s. The migration of the source location as a function of period, regardless of the back-projection methods, has characteristics that are consistent with the expected effect of the "swimming artifact". In particular, the apparent up-dip migration as a function of frequency obtained with the USArray can be explained by the "swimming artifact". This indicates that the most substantial frequency-dependence of the Tohoku-Oki earthquake source occurs at periods longer than 16 s. Thus, low-frequency back-projection needs to be further tested and validated in order to contribute to the characterization of frequency-dependent rupture properties.

Reflecting and Polarizing Properties of Conductive Fabrics in Ultra-High Frequency Range

Directory of Open Access Journals (Sweden)

Oleg Kiprijanovič

2015-09-01

Full Text Available The system based on ultra-wide band (UWB signals was employed for qualitative estimation of attenuating, reflecting and polarizing properties of conductive fabrics, capable to prevent local static charge accumulation. Pulsed excitation of triangle monopole antenna of 6.5 cm height by rectangular electric pulses induced radiation of UWB signals with spectral density of power having maximum in ultra-high frequency (UHF range. The same antenna was used for the radiated signal receiving. Filters and amplifiers of different passband were employed to divide UHF range into subranges of 0.3-0.55 GHz, 0.55-1 GHz, 1-2 GHz and 2-4 GHz bands. The free space method, when conductive fabric samples of 50x50 cm2 were placed between transmitting and receiving antennas, was used to imitate a practical application. Received wideband signals corresponding to the defined range were detected by unbiased detectors. The fabrics made of two types of warps, containing different threads with conductive yarns, were investigated. It was estimated attenuation and reflective properties of the fabrics when electric field is collinear or perpendicular to thread direction. In the UHF range it was revealed good reflecting properties of the fabrics containing metallic component in the threads. The system has advantages but not without a certain shortcoming. Adapting it for specific tasks should lead to more effective usage, including yet unused properties of the UWB signals.

Modeling the frequency-dependent detective quantum efficiency of photon-counting x-ray detectors.

Science.gov (United States)

Stierstorfer, Karl

2018-01-01

To find a simple model for the frequency-dependent detective quantum efficiency (DQE) of photon-counting detectors in the low flux limit. Formula for the spatial cross-talk, the noise power spectrum and the DQE of a photon-counting detector working at a given threshold are derived. Parameters are probabilities for types of events like single counts in the central pixel, double counts in the central pixel and a neighboring pixel or single count in a neighboring pixel only. These probabilities can be derived in a simple model by extensive use of Monte Carlo techniques: The Monte Carlo x-ray propagation program MOCASSIM is used to simulate the energy deposition from the x-rays in the detector material. A simple charge cloud model using Gaussian clouds of fixed width is used for the propagation of the electric charge generated by the primary interactions. Both stages are combined in a Monte Carlo simulation randomizing the location of impact which finally produces the required probabilities. The parameters of the charge cloud model are fitted to the spectral response to a polychromatic spectrum measured with our prototype detector. Based on the Monte Carlo model, the DQE of photon-counting detectors as a function of spatial frequency is calculated for various pixel sizes, photon energies, and thresholds. The frequency-dependent DQE of a photon-counting detector in the low flux limit can be described with an equation containing only a small set of probabilities as input. Estimates for the probabilities can be derived from a simple model of the detector physics. © 2017 American Association of Physicists in Medicine.

Feedforward and feedback frequency-dependent interactions in a large-scale laminar network of the primate cortex.

Science.gov (United States)

Mejias, Jorge F; Murray, John D; Kennedy, Henry; Wang, Xiao-Jing

2016-11-01

Interactions between top-down and bottom-up processes in the cerebral cortex hold the key to understanding attentional processes, predictive coding, executive control, and a gamut of other brain functions. However, the underlying circuit mechanism remains poorly understood and represents a major challenge in neuroscience. We approached this problem using a large-scale computational model of the primate cortex constrained by new directed and weighted connectivity data. In our model, the interplay between feedforward and feedback signaling depends on the cortical laminar structure and involves complex dynamics across multiple (intralaminar, interlaminar, interareal, and whole cortex) scales. The model was tested by reproducing, as well as providing insights into, a wide range of neurophysiological findings about frequency-dependent interactions between visual cortical areas, including the observation that feedforward pathways are associated with enhanced gamma (30 to 70 Hz) oscillations, whereas feedback projections selectively modulate alpha/low-beta (8 to 15 Hz) oscillations. Furthermore, the model reproduces a functional hierarchy based on frequency-dependent Granger causality analysis of interareal signaling, as reported in recent monkey and human experiments, and suggests a mechanism for the observed context-dependent hierarchy dynamics. Together, this work highlights the necessity of multiscale approaches and provides a modeling platform for studies of large-scale brain circuit dynamics and functions.

Dependence of synchronization frequency of Kuramoto oscillators on symmetry of intrinsic frequency in ring network

Science.gov (United States)

Saha, Arindam; Amritkar, R. E.

2014-12-01

Kuramoto oscillators have been proposed earlier as a model for interacting systems that exhibit synchronisation. In this article we study the difference between networks with symmetric and asymmetric distribution of natural frequencies. We first indicate that the synchronisation frequency of the oscillators is independent of the natural frequency distribution for a completely connected network. Further we analyse the case of oscillators in a directed ring-network where asymmetry in the natural frequency distribution is seen to shift the synchronisation frequency of the network. We also present an estimate of the shift in the frequencies for slightly asymmetric distributions.

Circularly polarized harmonic generation by intense bicircular laser pulses: electron recollision dynamics and frequency dependent helicity

Science.gov (United States)

Bandrauk, André D.; Mauger, François; Yuan, Kai-Jun

2016-12-01

Numerical solutions of time-dependent Schrödinger equations for one and two electron cyclic molecules {{{H}}}nq+ exposed to intense bichromatic circularly polarized laser pulses of frequencies {ω }1 and {ω }2, such that {ω }1/{ω }2={n}1/{n}2 (integer) produce circularly polarized high order harmonics with a cut-off recollision maximum energy at and greater than the linear polarization law (in atomic units) {N}m{ω }1={I}p+3.17{U}p, where I p is the ionization potential and {U}p={(2{E}0)}2/4{ω }2 is the ponderomotive energy defined by the field E 0 (intensity I={{cE}}02/8π ) from each pulse and mean frequency ω =({ω }1+{ω }2)/2 . An electron recollision model in a rotating frame at rotating frequency {{Δ }}ω =({ω }1-{ω }2)/2 predicts this simple result as a result of recollision dynamics in a combination of bichromatic circularly polarized pulses. The harmonic helicities and their intensities are shown to depend on compatible symmetries of the net pulse electric fields with that of the molecules.

a.c. conductance study of polycrystal C60

International Nuclear Information System (INIS)

Yan Feng; Wang Yening; Huang Yineng; Gu Min; Zhang Qingming; Shen Huimin

1995-01-01

The a.c. (1 60 polycrystal (grain size 30 nm) has been studied from 100 to 350 K. Below 150 K, the a.c. conductance is nearly proportional to the temperature and frequency. This is proposed to be due to the hopping of localized states around the Fermi level. Above 200 K, the a.c. conductance exhibits a rapid increase with temperature, and shows a thermally activated behaviour with an activation energy of 0.389 eV below a certain temperature and 0.104 eV above it. A frequency dependent conductance at a fixed temperature is also obtained with a power law σ similar ω s (s∼0.8). For a sample of normal grain size, we have measured a peak near 250 K and a much smaller conductance. These results indicate that the defective na ture of our sample (small grain size, disorder or impurities) plays an important role for the transport properties. The existence of nanocrystals in the sample may give rise to localized states and improve its a.c. conductance. The two activation energies can be attributed to the coexistence of the crystalline and amorphous phases of C 60 . ((orig.))

Frequency-dependent failure mechanisms of nanocrystalline gold interconnect lines under general alternating current

Science.gov (United States)

Luo, X. M.; Zhang, B.; Zhang, G. P.

2014-09-01

Thermal fatigue failure of metallization interconnect lines subjected to alternating currents (AC) is becoming a severe threat to the long-term reliability of micro/nanodevices with increasing electrical current density/power. Here, thermal fatigue failure behaviors and damage mechanisms of nanocrystalline Au interconnect lines on the silicon glass substrate have been investigated by applying general alternating currents (the pure alternating current coupled with a direct current (DC) component) with different frequencies ranging from 0.05 Hz to 5 kHz. We observed both thermal fatigue damages caused by Joule heating-induced cyclic strain/stress and electromigration (EM) damages caused by the DC component. Besides, the damage formation showed a strong electrically-thermally-mechanically coupled effect and frequency dependence. At lower frequencies, thermal fatigue damages were dominant and the main damage forms were grain coarsening with grain boundary (GB) cracking/voiding and grain thinning. At higher frequencies, EM damages took over and the main damage forms were GB cracking/voiding of smaller grains and hillocks. Furthermore, the healing effect of the reversing current was considered to elucidate damage mechanisms of the nanocrystalline Au lines generated by the general AC. Lastly, a modified model was proposed to predict the lifetime of the nanocrystalline metal interconnect lines, i.e., that was a competing drift velocity-based approach based on the threshold time required for reverse diffusion/healing to occur.

Determination of head conductivity frequency response in vivo with optimized EIT-EEG.

Science.gov (United States)

Dabek, Juhani; Kalogianni, Konstantina; Rotgans, Edwin; van der Helm, Frans C T; Kwakkel, Gert; van Wegen, Erwin E H; Daffertshofer, Andreas; de Munck, Jan C

2016-02-15

Electroencephalography (EEG) benefits from accurate head models. Dipole source modelling errors can be reduced from over 1cm to a few millimetres by replacing generic head geometry and conductivity with tailored ones. When adequate head geometry is available, electrical impedance tomography (EIT) can be used to infer the conductivities of head tissues. In this study, the boundary element method (BEM) is applied with three-compartment (scalp, skull and brain) subject-specific head models. The optimal injection of small currents to the head with a modular EIT current injector, and voltage measurement by an EEG amplifier is first sought by simulations. The measurement with a 64-electrode EEG layout is studied with respect to three noise sources affecting EIT: background EEG, deviations from the fitting assumption of equal scalp and brain conductivities, and smooth model geometry deviations from the true head geometry. The noise source effects were investigated depending on the positioning of the injection and extraction electrode and the number of their combinations used sequentially. The deviation from equal scalp and brain conductivities produces rather deterministic errors in the three conductivities irrespective of the current injection locations. With a realistic measurement of around 2 min and around 8 distant distinct current injection pairs, the error from the other noise sources is reduced to around 10% or less in the skull conductivity. The analysis of subsequent real measurements, however, suggests that there could be subject-specific local thinnings in the skull, which could amplify the conductivity fitting errors. With proper analysis of multiplexed sinusoidal EIT current injections, the measurements on average yielded conductivities of 340 mS/m (scalp and brain) and 6.6 mS/m (skull) at 2 Hz. From 11 to 127 Hz, the conductivities increased by 1.6% (scalp and brain) and 6.7% (skull) on the average. The proper analysis was ensured by using recombination of

Implementation of the frequency dependent line model in a real-time power system simulator

Directory of Open Access Journals (Sweden)

Reynaldo Iracheta-Cortez

2017-09-01

Full Text Available In this paper is described the implementation of the frequency-dependent line model (FD-Line in a real-time digital power system simulator. The main goal with such development is to describe a general procedure to incorporate new realistic models of power system components in modern real-time simulators based on the Electromagnetic Transients Program (EMTP. In this procedure are described, firstly, the steps to obtain the time domain solution of the differential equations that models the electromagnetic behavior in multi-phase transmission lines with frequency dependent parameters. After, the algorithmic solution of the FD-Line model is implemented in Simulink environment, through an S-function programmed in C language, for running off-line simulations of electromagnetic transients. This implementation allows the free assembling of the FD Line model with any element of the Power System Blockset library and also, it can be used to build any network topology. The main advantage of having a power network built in Simulink is that can be executed in real-time by means of the commercial eMEGAsim simulator. Finally, several simulation cases are presented to validate the accuracy and the real-time performance of the FD-Line model.

Optimizing electrical conductivity and optical transparency of IZO thin film deposited by radio frequency (RF) magnetron sputtering

Science.gov (United States)

Zhang, Lei

Transparent conducting oxide (TCO) thin films of In2O3, SnO2, ZnO, and their mixtures have been extensively used in optoelectronic applications such as transparent electrodes in solar photovoltaic devices. In this project I deposited amorphous indium-zinc oxide (IZO) thin films by radio frequency (RF) magnetron sputtering from a In2O3-10 wt.% ZnO sintered ceramic target to optimize the RF power, argon gas flowing rate, and the thickness of film to reach the maximum conductivity and transparency in visible spectrum. The results indicated optimized conductivity and transparency of IZO thin film is closer to ITO's conductivity and transparency, and is even better when the film was deposited with one specific tilted angle. National Science Foundation (NSF) MRSEC program at University of Nebraska Lincoln, and was hosted by Professor Jeff Shields lab.

THE ENERGY DEPENDENCE OF THE CENTROID FREQUENCY AND PHASE LAG OF THE QUASI-PERIODIC OSCILLATIONS IN GRS 1915+105

International Nuclear Information System (INIS)

Qu, J. L.; Lu, F. J.; Lu, Y.; Song, L. M.; Zhang, S.; Wang, J. M.; Ding, G. Q.

2010-01-01

We present a study of the centroid frequencies and phase lags of quasi-periodic oscillations (QPOs) as functions of photon energy for GRS 1915+105. It is found that the centroid frequencies of the 0.5-10 Hz QPOs and their phase lags are both energy dependent, and there exists an anticorrelation between the QPO frequency and phase lag. These new results challenge the popular QPO models, because none of them can fully explain the observed properties. We suggest that the observed QPO phase lags are partially due to the variation of the QPO frequency with energy, especially for those with frequency higher than 3.5 Hz.

Direction of information flow in large-scale resting-state networks is frequency-dependent.

Science.gov (United States)

Hillebrand, Arjan; Tewarie, Prejaas; van Dellen, Edwin; Yu, Meichen; Carbo, Ellen W S; Douw, Linda; Gouw, Alida A; van Straaten, Elisabeth C W; Stam, Cornelis J

2016-04-05

Normal brain function requires interactions between spatially separated, and functionally specialized, macroscopic regions, yet the directionality of these interactions in large-scale functional networks is unknown. Magnetoencephalography was used to determine the directionality of these interactions, where directionality was inferred from time series of beamformer-reconstructed estimates of neuronal activation, using a recently proposed measure of phase transfer entropy. We observed well-organized posterior-to-anterior patterns of information flow in the higher-frequency bands (alpha1, alpha2, and beta band), dominated by regions in the visual cortex and posterior default mode network. Opposite patterns of anterior-to-posterior flow were found in the theta band, involving mainly regions in the frontal lobe that were sending information to a more distributed network. Many strong information senders in the theta band were also frequent receivers in the alpha2 band, and vice versa. Our results provide evidence that large-scale resting-state patterns of information flow in the human brain form frequency-dependent reentry loops that are dominated by flow from parieto-occipital cortex to integrative frontal areas in the higher-frequency bands, which is mirrored by a theta band anterior-to-posterior flow.

Interstitial pressure dependence of the thermal conductivity of some rare earth oxide powders

International Nuclear Information System (INIS)

Pradeep, P.

1997-01-01

Thermal transport properties of powdered materials depend upon interstitial gas pressure. The present study reports the experimental results for the effective thermal conductivity of three rare earth oxide powders viz. yttrium oxide, samarium oxide, and gadolinium oxide, at various interstitial pressures by using transient plane source (TPS) method. A theoretical model is also proposed for the interpretation of the variation of the effective thermal conductivity with interstitial gas pressure. Its validity is found to be good in low pressure range of 45 mm Hg to normal pressure when compared with the experimental results. Also an attempt has been made to calculate the variation of thermal conductivity with interstitial pressure in the high pressure range up to 2 kbar using the proposed model. (author)

Heat conduction in a plate-type fuel element with time-dependent boundary conditions

International Nuclear Information System (INIS)

Faya, A.J.G.; Maiorino, J.R.

1981-01-01

A method for the solution of boundary-value problems with variable boundary conditions is applied to solve a heat conduction problem in a plate-type fuel element with time dependent film coefficient. The numerical results show the feasibility of the method in the solution of this class of problems. (Author) [pt

Model of electrical conductivity of skeletal muscle based on tissue structure

NARCIS (Netherlands)

Gielen, F.L.H.; Cruts, H.E.P.; Alberts, B.A.; Boon, K.L.; Wallinga, W.; Boom, H.B.K.

1986-01-01

Recent experiments carried out in our laboratory with the four-electrode method showed that the electrical conductivity of skeletal muscle tissue depends on the frequency of the injected current and the distance between the current electrodes. A model is proposed in order to study these effects. The

Rolling estimations of long range dependence volatility for high frequency S&P500 index

Science.gov (United States)

Cheong, Chin Wen; Pei, Tan Pei

2015-10-01

This study evaluates the time-varying long range dependence behaviors of the S&P500 volatility index using the modified rescaled adjusted range (R/S) statistic. For better computational result, a high frequency rolling bipower variation realized volatility estimates are used to avoid possible abrupt jump. The empirical analysis findings allow us to understand better the informationally market efficiency before and after the subprime mortgage crisis.

Capacitance and conductance characterization of nano-ZnGa{sub 2}Te{sub 4}/n-Si diode

Energy Technology Data Exchange (ETDEWEB)

Fouad, S.S. [Thin Film Laboratory, Department of Physics, Faculty of Education, Ain Shams University, Roxy, Cairo (Egypt); Sakr, G.B. [Nano-Science Laboratory, Physics Department, Faculty of Education, Ain Shams University, Roxy, Cairo (Egypt); Yahia, I.S., E-mail: isyahia@gmail.com [Nano-Science Laboratory, Physics Department, Faculty of Education, Ain Shams University, Roxy, Cairo (Egypt); Semiconductor Laboratory, Physics Department, Faculty of Education, Ain Shams University, Roxy, Cairo (Egypt); Department of Physics, Faculty of Science, King Khalid University, P.O. Box 9004, Abha (Saudi Arabia); Abdel-Basset, D.M. [Nano-Science Laboratory, Physics Department, Faculty of Education, Ain Shams University, Roxy, Cairo (Egypt); Yakuphanoglu, F. [Department of Physics, Faculty of Science, Firat University, Elazig (Turkey)

2014-01-01

Graphical abstract: - Highlights: • XRD and DTA micrographs were used to study the structure of ZnGa{sub 2}Te{sub 4}. • C–V, G–V and R{sub s}–V of the diode characteristics have been analyzed for the first time. • Dielectric constant, dielectric loss, loss tangent and ac conductivity were determined. • The interfaces states were determined using conductance–voltage technique. • ZnGa{sub 2}Te{sub 4} is a good candidate for electronic device applications. - Abstract: Capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of p-ZnGa{sub 2}Te{sub 4}/n-Si HJD were studied over a wide frequency and temperature. Both the interface states density N{sub ss} and series resistance R{sub s} were strongly frequency and temperature dependent. The interface states density N{sub ss} is decreased with increasing frequency and increase with increasing temperature. The values of the built-in potential (V{sub bi}) were calculated and found to increase with increasing temperature and frequency. The values of capacitance C, conductance G, series resistance R{sub s}, corrected capacitance C{sub ADJ}, corrected conductance G{sub ADJ}, dielectric constant (ε′), dielectric loss (ε″), loss tangent (tan δ) and the AC conductivity (σ{sub ac}) are strongly dependent on the applied frequency, voltage and temperature. The obtained results show that the locations of N{sub ss} and R{sub s} have a significant effect on the electrical characteristics of the studied diode.

Development of a new medium frequency EM device: Mapping soil water content variations using electrical conductivity and dielectric permittivity

Science.gov (United States)

Kessouri, P.; Buvat, S.; Tabbagh, A.

2012-12-01

Both electrical conductivity and dielectric permittivity of soil are influenced by its water content. Dielectric permittivity is usually measured in the high frequency range, using GPR or TDR, where the sensitivity to water content is high. However, its evaluation is limited by a low investigation depth, especially for clay rich soils. Electrical conductivity is closely related not only to soil water content, but also to clay content and soil structure. A simultaneous estimation of these electrical parameters can allow the mapping of soil water content variations for an investigation depth close to 1m. In order to estimate simultaneously both soil electrical conductivity and dielectric permittivity, an electromagnetic device working in the medium frequency range (between 100 kHz and 10 MHz) has been designed. We adopted Slingram geometry for the EM prototype: its PERP configuration (vertical transmission loop Tx and horizontal measuring loop Rx) was defined using 1D ground models. As the required investigation depth is around 1m, the coil spacing was fixed to 1.2m. This prototype works in a frequency range between 1 and 5 MHz. After calibration, we tested the response of prototype to objects with known properties. The first in situ measurements were led on experimental sites with different types of soils and different water content variations (artificially created or natural): sandy alluvium on a plot of INRA (French National Institute for Agricultural Research) in Orléans (Centre, France), a clay-loam soil on an experimental site in Estrée-Mons (Picardie, France) and fractured limestone at the vicinity of Grand (Vosges, France). In the case of the sandy alluvium, the values of dielectric permittivity measured are close to those of HF permittivity and allow the use of existing theoretical models to determine the soil water content. For soils containing higher amount of clay, the coupled information brought by the electrical conductivity and the dielectric

Frequency and temperature dependence of high damping elastomers

International Nuclear Information System (INIS)

Kulak, R.F.; Hughes, T.H.

1993-01-01

High damping steel-laminated elastomeric seismic isolation bearings are one of the preferred devices for isolating large buildings and structures. In the US, the current reference design for the Advanced Liquid Metal Reactor (ALMR) uses laminated bearings for seismic isolation. These bearings are constructed from alternating layers of high damping rubber and steel plates. They are typically designed for shear strains between 50 and 100% and are expected to sustain two to three times these levels for beyond design basis loading conditions. Elastomeric bearings are currently designed to provide a system frequency between 0.4 and 0.8 Hz and expected to operate between -20 and 40 degrees Centigrade. To assure proper performance of isolation bearings, it is necessary to characterize the elastomer's response under expected variations of frequency and temperature. The dynamic response of the elastomer must be characterized within the frequency range that spans the bearing acceptance test frequency, which may be as low as 0.005 Hz, and the design frequency. Similarly, the variation in mechanical characteristics of the elastomer must be determined over the design temperature range, which is between -20 and 40 degrees Centigrade. This paper reports on (1) the capabilities of a testing facility at ANL for testing candidate elastomers, (2) the variation with frequency and temperature of the stiffness and damping of one candidate elastomer, and (3) the effect of these variations on bearing acceptance testing criteria and on the choice of bearing design values for stiffness and damping

Effect of pH on the electrical properties and conducting mechanism of SnO_2 nanoparticles

International Nuclear Information System (INIS)

Periathai, R.Sudha; Abarna, S.; Hirankumar, G.; Jeyakumaran, N.; Prithivikumaran, N.

2017-01-01

Semiconductor nanoparticles have attracted more interests because of their size-dependent optical and electrical properties.SnO_2 is an oxygen-deficient n-type semiconductor with a wide band gap of 3.6 eV (300 K). It has many remarkable applications as sensors, catalysts, transparent conducting electrodes, anode material for rechargeable Li- ion batteries and optoelectronic devices. In the present work, the role of pH in determining the electrical and dielectric properties of SnO_2 nanoparticles has been studied as a function of temperature ranging from Room temperature (RT) to 114 °C in the frequency range of 7 MHz to 50 mHz using impedance spectroscopic technique. The non linear behavior observed in the thermal dependence of the conductance of SnO_2 nanoparticles is explained by means of the surface property of SnO_2 nanoparticles where proton hopping mechanism is dealt with. Jonscher's power law has been fitted for the conductance spectra and the frequency exponent (“s” value) gives an insight about the ac conducting mechanism. The temperature dependence of electrical relaxation phenomenon in the material has been observed. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation.

Cross correlation measurement of low frequency conductivity noise

Science.gov (United States)

Jain, Aditya Kumar; Nigudkar, Himanshu; Chakraborti, Himadri; Udupa, Aditi; Gupta, Kantimay Das

2018-04-01

In order to study the low frequency noise(1/f noise)an experimental technique based on cross correlation of two channels is presented. In this method the device under test (DUT)is connected to the two independently powered preamplifiers in parallel. The amplified signals from the two preamplifiers are fed to two channels of a digitizer. Subsequent data processing largelyeliminates the uncorrelated noise of the two channels. This method is tested for various commercial carbon/metal film resistors by measuring equilibrium thermal noise (4kBTR). The method is then modified to study the non-equilibrium low frequency noise of heterostructure samples using fiveprobe configuration. Five contact probes allow two parts of the sample to become two arms of a balanced bridge. This configuration helps in suppressing the effect of power supply fluctuations, bath temperature fluctuations and contact resistances.

Electrical actuation of electrically conducting and insulating droplets using ac and dc voltages

International Nuclear Information System (INIS)

Kumari, N; Bahadur, V; Garimella, S V

2008-01-01

Electrical actuation of liquid droplets at the microscale offers promising applications in the fields of microfluidics and lab-on-chip devices. Much prior research has targeted the electrical actuation of electrically conducting liquid droplets using dc voltages (classical electrowetting). Electrical actuation of conducting droplets using ac voltages and the actuation of insulating droplets (using dc or ac voltages) has remained relatively unexplored. This paper utilizes an energy-minimization-based analytical framework to study the electrical actuation of a liquid droplet (electrically conducting or insulating) under ac actuation. It is shown that the electromechanical regimes of classical electrowetting, electrowetting under ac actuation and insulating droplet actuation can be extracted from the generic electromechanical actuation framework, depending on the electrical properties of the droplet, the underlying dielectric layer and the frequency of the actuation voltage. This paper also presents experiments which quantify the influence of the ac frequency and the electrical properties of the droplet on its velocity under electrical actuation. The velocities of droplets moving between two parallel plates under ac actuation are experimentally measured; these velocities are then related to the actuation force on the droplet which is predicted by the electromechanical model developed in this work. It is seen that the droplet velocities are strongly dependent on the frequency of the ac actuation voltage; the cut-off ac frequency, above which the droplet fails to actuate, is experimentally determined and related to the electrical conductivity of the liquid. This paper then analyzes and directly compares the various electromechanical regimes for the actuation of droplets in microfluidic applications

Low frequency dielectric relaxation processes and ionic conductivity of montmorillonite clay nanoparticles colloidal suspension in poly(vinyl pyrrolidone−ethylene glycol blends

Directory of Open Access Journals (Sweden)

2008-11-01

Full Text Available The dielectric dispersion behaviour of montmorillonite (MMT clay nanoparticles colloidal suspension in poly(vinyl pyrrolidone-ethylene glycol (PVP-EG blends were investigated over the frequency range 20 Hz to 1 MHz at 30°C. The 0, 1, 2, 3, 5 and 10 wt% MMT clay concentration of the weight of total solute (MMT+PVP were prepared in PVP-EG blends using EG as solvent. The complex relative dielectric function, alternating current (ac electrical conductivity, electric modulus and impedance spectra of these materials show the relaxation processes corresponding to the micro-Brownian motion of PVP chain, ion conduction and electrode polarization phenomena. The real part of ac conductivity spectra of these materials obeys Jonscher power law σ′(ω =σdc + Aωn in upper frequency end of the measurement, whereas dispersion in lower frequency end confirms the presence of electrode polarization effect. It was observed that the increase of clay concentration in the PVP-EG blends significantly increases the ac conductivity values, and simultaneously reduces the ionic conductivity relaxation time and electric double layer relaxation time, which suggests that PVP segmental dynamics and ionic motion are strongly coupled. The intercalation of EG structures in clay galleries and exfoliation of clay sheets by adsorption of PVP-EG structures on clay surfaces are discussed by considering the hydrogen bonding interactions between the hydroxyl group (–OH of EG molecules, carbonyl group (C=O of PVP monomer units, and the hydroxylated aluminate surfaces of the MMT clay particles. Results suggest that the colloidal suspension of MMT clay nano particles in the PVP-EG blends provide a convenient way to obtain an electrolyte solution with tailored electrical conduction properties.

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...

Determination of acoustic properties of thin polymer films utilizing the frequency dependence of the reflection coefficient of ultrasound.

Science.gov (United States)

Tohmyoh, Hironori; Sakamoto, Yuhei

2015-11-01

This paper reports on a technique to measure the acoustic properties of a thin polymer film utilizing the frequency dependence of the reflection coefficient of ultrasound reflected back from a system comprising a reflection plate, the film, and a material that covers the film. The frequency components of the echo reflected from the back of the plate, where the film is attached, take their minimum values at the resonant frequency, and from these frequency characteristics, the acoustic impedance, sound velocity, and the density of the film can be determined. We applied this technique to characterize an ion exchange membrane, which has high water absorbability, and successfully determined the acoustic properties of the membrane without getting it wet.

A least squares method for a longitudinal fin with temperature dependent internal heat generation and thermal conductivity

International Nuclear Information System (INIS)

Aziz, A.; Bouaziz, M.N.

2011-01-01

Highlights: → Analytical solutions for a rectangular fin with temperature dependent heat generation and thermal conductivity. → Graphs give temperature distributions and fin efficiency. → Comparison of analytical and numerical solutions. → Method of least squares used for the analytical solutions. - Abstract: Approximate but highly accurate solutions for the temperature distribution, fin efficiency, and optimum fin parameter for a constant area longitudinal fin with temperature dependent internal heat generation and thermal conductivity are derived analytically. The method of least squares recently used by the authors is applied to treat the two nonlinearities, one associated with the temperature dependent internal heat generation and the other due to temperature dependent thermal conductivity. The solution is built from the classical solution for a fin with uniform internal heat generation and constant thermal conductivity. The results are presented graphically and compared with the direct numerical solutions. The analytical solutions retain their accuracy (within 1% of the numerical solution) even when there is a 60% increase in thermal conductivity and internal heat generation at the base temperature from their corresponding values at the sink temperature. The present solution is simple (involves hyperbolic functions only) compared with the fairly complex approximate solutions based on the homotopy perturbation method, variational iteration method, and the double series regular perturbation method and offers high accuracy. The simple analytical expressions for the temperature distribution, the fin efficiency and the optimum fin parameter are convenient for use by engineers dealing with the design and analysis of heat generating fins operating with a large temperature difference between the base and the environment.

Sounding of Groundwater Through Conductive Media in Mars Analog Environments Using Transient Electromagnetics and Low Frequency GPR.

Science.gov (United States)

Jernsletten, J. A.; Heggy, E.

2004-05-01

INTRODUCTION: This study compares the use of (diffusive) Transient Electromagnetics (TEM) for sounding of subsurface water in conductive Mars analog environments to the use of (propagative) Ground-Penetrating Radar (GPR) for the same purpose. We show data from three field studies: 1) Radar sounding data (GPR) from the Nubian aquifer, Bahria Oasis, Egypt; 2) Diffusive sounding data (TEM) from Pima County, Arizona; and 3) Shallower sounding data using the Fast-Turnoff TEM method from Peña de Hierro in the Rio Tinto area, Spain. The latter is data from work conducted under the auspices of the Mars Analog Research and Technology Experiment (MARTE). POTENTIAL OF TEM: A TEM survey was carried out in Pima County, Arizona, in January 2003. Data was collected using 100 m Tx loops, a ferrite-cored magnetic coil Rx antenna, and a sounding frequency of 16 Hz. The dataset has ~500 m depth of investigation, shows a ~120 m depth to the water table (confirmed by several USGS test wells in the area), and a conductive (~20-40 Ω m) clay-rich soil above the water table. The Rio Tinto Fast-Turnoff TEM data was collected using 40 m Tx loops, 10 m Rx loops, and a 32 Hz sounding frequency. Note ~200 m depth of investigation and a conductive high at ~80 m depth (interpreted as water table). Data was also collected using 20 m Tx loops (10 m Rx loops) in other parts of the area. Note ~50 m depth of investigation and a conductive high at ~15 m depth (interpreted as subsurface water flow under mine tailings matching surface flows seen coming out from under the tailings, and shown on maps). Both of these interpretations were roughly confirmed by preliminary results from the MARTE ground truth drilling campaign carried out in September and October 2003. POTENTIAL OF GPR: A GPR experiment was carried out in February 2003 in the Bahria Oasis in the western Egyptian desert, using a 2 MHz monostatic GPR, mapping the Nubian Aquifer at depths of 100-900 m, beneath a thick layer of homogenous marine

Viscoelastic characterization of compacted pharmaceutical excipient materials by analysis of frequency-dependent mechanical relaxation processes

Science.gov (United States)

Welch, K.; Mousavi, S.; Lundberg, B.; Strømme, M.

2005-09-01

A newly developed method for determining the frequency-dependent complex Young's modulus was employed to analyze the mechanical response of compacted microcrystalline cellulose, sorbitol, ethyl cellulose and starch for frequencies up to 20 kHz. A Debye-like relaxation was observed in all the studied pharmaceutical excipient materials and a comparison with corresponding dielectric spectroscopy data was made. The location in frequency of the relaxation peak was shown to correlate to the measured tensile strength of the tablets, and the relaxation was interpreted as the vibrational response of the interparticle hydrogen and van der Waals bindings in the tablets. Further, the measured relaxation strength, holding information about the energy loss involved in the relaxation processes, showed that the weakest material in terms of tensile strength, starch, is the material among the four tested ones that is able to absorb the most energy within its structure when exposed to external perturbations inducing vibrations in the studied frequency range. The results indicate that mechanical relaxation analysis performed over relatively broad frequency ranges should be useful for predicting material properties of importance for the functionality of a material in applications such as, e.g., drug delivery, drug storage and handling, and also for clarifying the origin of hitherto unexplained molecular processes.

Two models of the sound-signal frequency dependence on the animal body size as exemplified by the ground squirrels of Eurasia (mammalia, rodentia).

Science.gov (United States)

Nikol'skii, A A

2017-11-01

Dependence of the sound-signal frequency on the animal body length was studied in 14 ground squirrel species (genus Spermophilus) of Eurasia. Regression analysis of the total sample yielded a low determination coefficient (R 2 = 26%), because the total sample proved to be heterogeneous in terms of signal frequency within the dimension classes of animals. When the total sample was divided into two groups according to signal frequency, two statistically significant models (regression equations) were obtained in which signal frequency depended on the body size at high determination coefficients (R 2 = 73 and 94% versus 26% for the total sample). Thus, the problem of correlation between animal body size and the frequency of their vocal signals does not have a unique solution.

Leading temperature dependence of the conductance in Kondo-correlated quantum dots

Science.gov (United States)

Aligia, A. A.

2018-04-01

Using renormalized perturbation theory in the Coulomb repulsion, we derive an analytical expression for the leading term in the temperature dependence of the conductance through a quantum dot described by the impurity Anderson model, in terms of the renormalized parameters of the model. Taking these parameters from the literature, we compare the results with published ones calculated using the numerical renormalization group obtaining a very good agreement. The approach is superior to alternative perturbative treatments. We compare in particular to the results of a simple interpolative perturbation approach.

Frequency-Dependent Streaming Potential of Porous Media—Part 1: Experimental Approaches and Apparatus Design

Directory of Open Access Journals (Sweden)

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.

Frequency dependence of the magnetostrictive phenomenon in Metglas® 2605SA1 ribbon: A minor-loop case

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.

Frequency dependence and frequency control of microbubble streaming flows

Science.gov (United States)

Wang, Cheng; Rallabandi, Bhargav; Hilgenfeldt, Sascha

2013-02-01

Steady streaming from oscillating microbubbles is a powerful actuating mechanism in microfluidics, enjoying increased use due to its simplicity of manufacture, ease of integration, low heat generation, and unprecedented control over the flow field and particle transport. As the streaming flow patterns are caused by oscillations of microbubbles in contact with walls of the set-up, an understanding of the bubble dynamics is crucial. Here we experimentally characterize the oscillation modes and the frequency response spectrum of such cylindrical bubbles, driven by a pressure variation resulting from ultrasound in the range of 1 kHz raisebox {-.9ex{stackrel{textstyle <}{˜ }} }f raisebox {-.9ex{stackrel{textstyle <}{˜ }} } 100 kHz. We find that (i) the appearance of 2D streaming flow patterns is governed by the relative amplitudes of bubble azimuthal surface modes (normalized by the volume response), (ii) distinct, robust resonance patterns occur independent of details of the set-up, and (iii) the position and width of the resonance peaks can be understood using an asymptotic theory approach. This theory describes, for the first time, the shape oscillations of a pinned cylindrical bubble at a wall and gives insight into necessary mode couplings that shape the response spectrum. Having thus correlated relative mode strengths and observed flow patterns, we demonstrate that the performance of a bubble micromixer can be optimized by making use of such flow variations when modulating the driving frequency.

Investigating the Inter-Tube Conduction Mechanism in Polycarbonate Nanocomposites Prepared with Conductive Polymer-Coated Carbon Nanotubes

KAUST Repository

Ventura, Isaac Aguilar

2015-12-16

A well-known strategy to improve the electrical conductivity of polymers is to dope them with high-aspect-ratio and conductive nanoparticles such as carbon nanotubes (CNTs). However, these nanocomposites also exhibit undesirable properties such as damage-sensitive and history-dependent conductivity because their macroscopic electrical conductivity is largely determined by the tunneling effect at the tube/tube interface. To reduce these issues, new nanocomposites have been developed with CNTs that have been coated with a conductive layer of poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT/PSS). It has been posited that the insulating region between the CNTs is replaced by a conductive polymer bridge; this has not been proven up to now. We propose here to investigate in-depth how the macroscopic conductivity of these materials is changing when (1) varying the frequency of the electrical loading (impedance spectroscopy), (2) varying the mechanical hydrostatic pressure, and (3) varying the voltage of the electrical loading. The response is systematically compared to the one of conventional carbon nanotube/polycarbonate (CNT/PC) nanocomposites so we can clarify how efficiently the tunneling effect is suppressed from these composites. The objective is to elucidate further the mechanism for conduction in such material formulations.

Temperature dependence of the thermal conductivity in chiral carbon nanotubes

Energy Technology Data Exchange (ETDEWEB)

Mensah, N.G. [Department of Mathematics, University of Cape Coast, Cape Coast (Ghana); Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Nkrumah, G. [Department of Physics, University of Ghana, Legon, Accra (Ghana) and Abdus Salam International Centre for Theoretical Physics, Trieste (Italy)]. E-mail: geon@ug.edu.gh; Mensah, S.Y. [Department of Physics, Laser and Fibre Optics Centre, University of Cape Coast, Cape Coast (Ghana); Allotey, F.K.A. [Institute of Mathematical Sciences, Accra (Ghana)

2004-08-30

The thermal conductivity of a chiral carbon nanotube (CCNT) is calculated using a tractable analytical approach. This is based on solving the Boltzmann kinetic equation with energy dispersion relation obtained in the tight binding approximation. The results obtained are numerically analysed. Unusually high electron thermal conductivity {chi}{sub ez} is observed along the tubular axis. The dependence of {chi}{sub ez} against temperature T was plotted for varying {delta}{sub z} and a given {delta}{sub s} ({delta}{sub z} and {delta}{sub s} are the overlapping integrals (exchange energy) for the jumps along the tubular axis and the base helix, respectively). It is noted that {chi}{sub ez} shows a peaking behaviour before falling off at higher temperature. As {delta}{sub z} varies from 0.010 eV to 0.048 eV for a given {delta}{sub s}=0.0150 eV, the peak values of {chi}{sub ez} shift from 40000 W/m K at 100 K to 55000 W/m K at about 300 K. Interestingly our results at 104 K which is 41000 W/m K and occurred at {delta}{sub z}=0.023 eV compares very well with that reported for a 99.9% isotopically enriched {sup 12}C diamond crystal. Another interesting result obtained is the fact that the circumferential electron thermal conductivity {chi}{sub ec} appears to be very small. The ratio of {chi}{sub ez} to {chi}{sub ec} is of the order of 2.

Mixed conductivity studies in silver oxide based barium vanado-tellurite glasses

International Nuclear Information System (INIS)

Pant, Meenakshi; Kanchan, D.K.; Sharma, Poonam; Jayswal, Manish S.

2008-01-01

The dc conductivity and frequency dependent ac conductivity of the quaternary glass system x(BaO:1.5 Ag 2 O)-(95 - x)V 2 O 5 -5TeO 2 , are reported in the frequency range 1 Hz to 32 MHz in the temperature range from room temperature to 433 K. The dc conductivity measured in high temperature range increased with transition metal oxide content while the activation range decreased. The conductivity arises mainly from polaron hopping between V 4+ and V 5+ ions. High temperature conductivity data satisfy Mott's small polaron hopping model. It is found that a mechanism of non-adiabatic hopping is the most appropriate conduction model for these glasses. A power law behavior σ(ω) = σ dc + Aω n (with 0 < n < 1) is well exhibited by the ac conductivity data of the glasses. The activation energy calculated from both the relaxation time and dc conductivity is found to be nearly same in both the cases. A scaling of the conductivity spectra with respect to temperature and composition is attempted and it is observed that the relaxation dynamics of charge carriers in the present glasses is independent of temperature and composition

Measurements of temperature characteristics and estimation of terahertz negative differential conductance in resonant-tunneling-diode oscillators

Directory of Open Access Journals (Sweden)

M. Asada

2017-11-01

Full Text Available The temperature dependences of output power, oscillation frequency, and current-voltage curve are measured for resonant-tunneling-diode terahertz (THz oscillators. The output power largely changes with temperature owing to the change in Ohmic loss. In contrast to the output power, the oscillation frequency and current-voltage curve are almost insensitive to temperature. The measured temperature dependence of output power is compared with the theoretical calculation including the negative differential conductance (NDC as a fitting parameter assumed to be independent of temperature. Very good agreement was obtained between the measurement and calculation, and the NDC in the THz frequency region is estimated. The results show that the absolute values of NDC in the THz region significantly decrease relative to that at DC, and increases with increasing frequency in the measured frequency range.

Application of the parametric proper generalized decomposition to the frequency-dependent calculation of the impedance of an AC line with rectangular conductors

Directory of Open Access Journals (Sweden)

Sancarlos-González Abel

2017-12-01

Full Text Available AC lines of industrial busbar systems are usually built using conductors with rectangular cross sections, where each phase can have several parallel conductors to carry high currents. The current density in a rectangular conductor, under sinusoidal conditions, is not uniform. It depends on the frequency, on the conductor shape, and on the distance between conductors, due to the skin effect and to proximity effects. Contrary to circular conductors, there are not closed analytical formulas for obtaining the frequency-dependent impedance of conductors with rectangular cross-section. It is necessary to resort to numerical simulations to obtain the resistance and the inductance of the phases, one for each desired frequency and also for each distance between the phases’ conductors. On the contrary, the use of the parametric proper generalized decomposition (PGD allows to obtain the frequency-dependent impedance of an AC line for a wide range of frequencies and distances between the phases’ conductors by solving a single simulation in a 4D domain (spatial coordinates x and y, the frequency and the separation between conductors. In this way, a general “virtual chart” solution is obtained, which contains the solution for any frequency and for any separation of the conductors, and stores it in a compact separated representations form, which can be easily embedded on a more general software for the design of electrical installations. The approach presented in this work for rectangular conductors can be easily extended to conductors with an arbitrary shape.

Application of the parametric proper generalized decomposition to the frequency-dependent calculation of the impedance of an AC line with rectangular conductors

Science.gov (United States)

Sancarlos-González, Abel; Pineda-Sanchez, Manuel; Puche-Panadero, Ruben; Sapena-Bano, Angel; Riera-Guasp, Martin; Martinez-Roman, Javier; Perez-Cruz, Juan; Roger-Folch, Jose

2017-12-01

AC lines of industrial busbar systems are usually built using conductors with rectangular cross sections, where each phase can have several parallel conductors to carry high currents. The current density in a rectangular conductor, under sinusoidal conditions, is not uniform. It depends on the frequency, on the conductor shape, and on the distance between conductors, due to the skin effect and to proximity effects. Contrary to circular conductors, there are not closed analytical formulas for obtaining the frequency-dependent impedance of conductors with rectangular cross-section. It is necessary to resort to numerical simulations to obtain the resistance and the inductance of the phases, one for each desired frequency and also for each distance between the phases' conductors. On the contrary, the use of the parametric proper generalized decomposition (PGD) allows to obtain the frequency-dependent impedance of an AC line for a wide range of frequencies and distances between the phases' conductors by solving a single simulation in a 4D domain (spatial coordinates x and y, the frequency and the separation between conductors). In this way, a general "virtual chart" solution is obtained, which contains the solution for any frequency and for any separation of the conductors, and stores it in a compact separated representations form, which can be easily embedded on a more general software for the design of electrical installations. The approach presented in this work for rectangular conductors can be easily extended to conductors with an arbitrary shape.

Thermal conductivity model for nanoporous thin films

Science.gov (United States)

Huang, Congliang; Zhao, Xinpeng; Regner, Keith; Yang, Ronggui

2018-03-01

Nanoporous thin films have attracted great interest because of their extremely low thermal conductivity and potential applications in thin thermal insulators and thermoelectrics. Although there are some numerical and experimental studies about the thermal conductivity of nanoporous thin films, a simplified model is still needed to provide a straightforward prediction. In this paper, by including the phonon scattering lifetimes due to film thickness boundary scattering, nanopore scattering and the frequency-dependent intrinsic phonon-phonon scattering, a fitting-parameter-free model based on the kinetic theory of phonon transport is developed to predict both the in-plane and the cross-plane thermal conductivities of nanoporous thin films. With input parameters such as the lattice constants, thermal conductivity, and the group velocity of acoustic phonons of bulk silicon, our model shows a good agreement with available experimental and numerical results of nanoporous silicon thin films. It illustrates that the size effect of film thickness boundary scattering not only depends on the film thickness but also on the size of nanopores, and a larger nanopore leads to a stronger size effect of the film thickness. Our model also reveals that there are different optimal structures for getting the lowest in-plane and cross-plane thermal conductivities.

Design Dependent Cutoff Frequency of Nanotransistors Near the Ultimate Performance Limit

Science.gov (United States)

Kordrostami, Zoheir; Sheikhi, M. Hossein; Zarifkar, Abbas

2012-12-01

We have studied the effect of different structural designs of double gate MOSFETs (DG-MOSFETs) and carbon nanotube field effect transistors (CNTFETs) on the cutoff frequency (fT). The effects of metallic contacts with Schottky barriers, gate work function, dual material gate (DMG), halo doped channel and lightly doped drain and source (LDDS) architectures on the fT have been investigated for DG-MOSFETs and CNTFETs and the design dependent fT for both types of transistors has been studied for the first time. The simulations are based on the Schrödinger-Poisson solvers developed for each nanotransistor separately. The ballistic limit has been studied as the ultimate performance limit of the DG-MOSFETs and CNTFETs. The results of this paper, for the first time, show how some designations used for modification of short channel effects or current-voltage characteristics affect the fT. The results revealed that the cutoff frequencies of both types of the transistors exhibit the same behavior with changing design parameters. We have shown that the Schottky barriers, parasitic capacitances and halo doping reduce the fT and have proposed the DMG and LDDS artchitectures as ways to increase the fT for DG-MOSFETs and CNTFETs for the first time.

Frequency-dependent photothermal measurement of transverse thermal diffusivity of organic semiconductors

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.

Ecological genetics of the Bromus tectorum (Poaceae) - Ustilago Bullata (Ustilaginaceae): A role for frequency dependent selection?

Science.gov (United States)

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...

Effect of pH on the electrical properties and conducting mechanism of SnO{sub 2} nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Periathai, R.Sudha [Department of Physics, Standard Fireworks Rajaratnam College for Women, Sivakasi 626123 (India); Abarna, S.; Hirankumar, G. [Centre for Scientific and Applied Research, PSN College of Engineering and Technology, Tirunelveli 627152 (India); Jeyakumaran, N. [Department of Physics, V.H.N. Senthikumara Nadar College, Virudhunagar 626001 (India); Prithivikumaran, N., E-mail: janavi_p@yahoo.com [Department of Physics, V.H.N. Senthikumara Nadar College, Virudhunagar 626001 (India)

2017-03-15

Semiconductor nanoparticles have attracted more interests because of their size-dependent optical and electrical properties.SnO{sub 2} is an oxygen-deficient n-type semiconductor with a wide band gap of 3.6 eV (300 K). It has many remarkable applications as sensors, catalysts, transparent conducting electrodes, anode material for rechargeable Li- ion batteries and optoelectronic devices. In the present work, the role of pH in determining the electrical and dielectric properties of SnO{sub 2} nanoparticles has been studied as a function of temperature ranging from Room temperature (RT) to 114 °C in the frequency range of 7 MHz to 50 mHz using impedance spectroscopic technique. The non linear behavior observed in the thermal dependence of the conductance of SnO{sub 2} nanoparticles is explained by means of the surface property of SnO{sub 2} nanoparticles where proton hopping mechanism is dealt with. Jonscher's power law has been fitted for the conductance spectra and the frequency exponent (“s” value) gives an insight about the ac conducting mechanism. The temperature dependence of electrical relaxation phenomenon in the material has been observed. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation.

Correlation of carrier localization with relaxation time distribution and electrical conductivity relaxation in silver-nanoparticle-embedded moderately doped polypyrrole nanostructures

Science.gov (United States)

Biswas, Swarup; Dutta, Bula; Bhattacharya, Subhratanu

2014-02-01

The electrical conductivity relaxation in moderately doped polypyrrole and its nanocomposites reinforced with different proportion of silver nanoparticles was investigated in both frequency and time domain. An analytical distribution function of relaxation times is constructed from the results obtained in the frequency domain formalism and is used to evaluate the Kohlrausch-Williams-Watts (KWW) type decay function in the time domain. The thermal evolution of different relaxation parameters was analyzed. The temperature-dependent dc electrical conductivity, estimated from the average conductivity relaxation time is observed to depend strongly on the nanoparticle loading and follows Mott three-dimensional variable range hopping (VRH) conduction mechanism. The extent of charge carrier localization calculated from the VRH mechanism is well correlated to the evidences obtained from the structural characterizations of different nanostructured samples.

Water-assisted and thermally-enhanced protonic conduction in HZSM-5, effect of gamma-irradiation on the electric properties. [Zeolites

Energy Technology Data Exchange (ETDEWEB)

Higazy, A.A.; Kassem, M.E. (Qatar Univ. (Qatar). Physics Dept.); Sayed, M.B. (Qatar Univ. (Qatar). Chemistry Dept.)

1992-01-01

Analysis of the a.c. conductivity of the zeolite HZSM-5, in the 0.1-100 kHz frequency region and the 300-700 K temperature range, reveals semiconducting features based predominantly on an ionic mechanism. This is reflected in a low-frequency Cole-Cole dependence of the Z''(Z') impedance and in a linear dependence of the {epsilon}''(''epsilon''') dielectric constant throughout the temperature range. The zeolite Broensted sites are the active centers responsible for the ionic conduction. As the conductivity drops to 373 K, sorbed water seems to participate in the conduction as a vehicle assisting the proton mobility. Above 373 K, the conductivity continues to rise as an indication of critical transition into a thermally enhanced ionic conduction. Both low-temperature sorbed water and high-temperature thermal motion are necessary to ensure a firm contact at the aggregate surfaces, where conduction takes place. Gamma-irradiation also participates in the conduction by creating new sites sensitive to the same parameters governing the conduction mechanism. (author).

Bias-dependent amino-acid-induced conductance changes in short semi-metallic carbon nanotubes

International Nuclear Information System (INIS)

Abadir, G B; Walus, K; Pulfrey, D L

2010-01-01

We study the interaction between short semi-metallic carbon nanotubes and different amino acids using molecular dynamics and ab initio (density functional theory/non-equilibrium Green's function) simulations. We identify two different mechanisms of nanotube conductance change upon adsorption of amino acids: one due to the change of the coordinates of the nanotube arising from van der Waals forces of interaction with the adsorbed amino acid; and one due to electrostatic interactions, which appear only in the case of charged amino acids. We also find that the transport mechanism and the changes in the conductance of the tube upon amino acid adsorption are bias dependent.

Advancement in the Understanding of the Field and Frequency Dependent Microwave Surface Resistance of Niobium

Energy Technology Data Exchange (ETDEWEB)

Martinello, M. [Fermilab; Aderhold, S. [Fermilab; Chandrasekaran, S. K. [Fermilab; Checchin, M. [Fermilab; Grassellino, A. [Fermilab; Melnychuk, O. [Fermilab; Posen, S. [Fermilab; Romanenko, A. [Fermilab; Sergatskov, D. A. [Fermilab

2017-07-24

The radio-frequency surface resistance of niobium resonators is incredibly reduced when nitrogen impurities are dissolved as interstitial in the material, conferring ultra-high Q-factors at medium values of accelerating field. This effect has been observed in both high and low temperature nitrogen treatments. As a matter of fact, the peculiar anti Q-slope observed in nitrogen doped cavities, i.e. the decreasing of the Q-factor with the increasing of the radio-frequency field, come from the decreasing of the BCS surface resistance component as a function of the field. Such peculiar behavior has been considered consequence of the interstitial nitrogen present in the niobium lattice after the doping treatment. The study here presented show the field dependence of the BCS surface resistance of cavities with different resonant frequencies, such as: 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 GHz, and processed with different state-of-the-art surface treatments. These findings show for the first time that the anti Q-slope might be seen at high frequency even for clean Niobium cavities, revealing useful suggestion on the physics underneath the anti Q-slope effect.

Frequency dependent characteristics of solar impulsive radio bursts

International Nuclear Information System (INIS)

Das, T.K.; Das Gupta, M.K.

1983-01-01

An investigation was made of the impulsive radio bursts observed in the frequency range 0.245 to 35 GHz. Important results obtained are: (i) Simple type 1 bursts with intensities 0 to 10 f.u. and simple type 2 bursts with intensities 10 to 500 f.u. are predominant in the frequency ranges 1.415 to 4.995 GHz and 4.995 to 8.8 GHz, respectively; (ii) With maxima around 2.7 GHz and 4 GHz for the first and second types respectively, the durations of the radio bursts decrease gradually both towards lower and higher frequencies; (iii) As regards occurrences, the first type dominates in the southern solar hemisphere peaking around 8.8 GHz, whereas the second type favours the north with no well-defined maximum in any frequency; (iv) Both types prefer the eastern hemisphere, the peak occurrences being around 8.8 GHz and 5 GHz for the two successive types, respectively; (c) The spectra of impulsive radio bursts are generally of the inverted U-type with the maximum emission intensity between 5 and 15 GHz. (author)

Moderate temperature-dependent surface and volume resistivity and low-frequency dielectric constant measurements of pure and multi-walled carbon nanotube (MWCNT) doped polyvinyl alcohol thin films

Science.gov (United States)

Edwards, Matthew; Guggilla, Padmaja; Reedy, Angela; Ijaz, Quratulann; Janen, Afef; Uba, Samuel; Curley, Michael

2017-08-01

Previously, we have reported measurements of temperature-dependent surface resistivity of pure and multi-walled carbon nanotube (MWNCT) doped amorphous Polyvinyl Alcohol (PVA) thin films. In the temperature range from 22 °C to 40 °C with humidity-controlled environment, we found the surface resistivity to decrease initially, but to rise steadily as the temperature continued to increase. Moreover, electric surface current density (Js) was measured on the surface of pure and MWCNT doped PVA thin films. In this regard, the surface current density and electric field relationship follow Ohm's law at low electric fields. Unlike Ohmic conduction in metals where free electrons exist, selected captive electrons are freed or provided from impurities and dopants to become conduction electrons from increased thermal vibration of constituent atoms in amorphous thin films. Additionally, a mechanism exists that seemingly decreases the surface resistivity at higher temperatures, suggesting a blocking effect for conducting electrons. Volume resistivity measurements also follow Ohm's law at low voltages (low electric fields), and they continue to decrease as temperatures increase in this temperature range, differing from surface resistivity behavior. Moreover, we report measurements of dielectric constant and dielectric loss as a function of temperature and frequency. Both the dielectric constant and dielectric loss were observed to be highest for MWCNT doped PVA compared to pure PVA and commercial paper, and with frequency and temperature for all samples.

ac conductivity and dielectric properties of amorphous Se80Te20-xGex chalcogenide glass film compositions

International Nuclear Information System (INIS)

Hegab, N.A.; Afifi, M.A.; Atyia, H.E.; Farid, A.S.

2009-01-01

Thin films of the prepared Se 80 Te 20-x Ge x (x = 5, 7 and 10 at.%) were prepared by thermal evaporation technique. X-ray diffraction patterns showed that the films were in amorphous state. The ac conductivity and dielectric properties of the investigated film compositions were studied in the frequency range 0.1-100 kHz and in temperature range (303-373 K). The experimental results indicated that the ac conductivity and the dielectric properties depended on the temperature and frequency. The ac conductivity is found to obey the ω s law, in accordance with the hopping model, s is found to be temperature dependent (s 1 and dielectric loss ε 2 were found to decrease with frequency and increase with temperature. The maximum barrier height W m , calculated from dielectric measurements according to Guintini equation, agrees with that proposed by the theory of hopping over potential barrier as suggested by Elliott in case of chalcogenide glasses. The density of localized states was estimated for the studied film compositions. The variation of the studied properties with Ge content was also investigated.

Frequency Dependent Electrical and Dielectric Properties of Au/P3HT:PCBM:F4-TCNQ/n-Si Schottky Barrier Diode

Science.gov (United States)

Taşçıoğlu, İ.; Tüzün Özmen, Ö.; Şağban, H. M.; Yağlıoğlu, E.; Altındal, Ş.

2017-04-01

In this study, poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester: 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (P3HT:PCBM:F4-TCNQ) organic film was deposited on n-type silicon (n-Si) substrate by spin coating method. The electrical and dielectric analysis of Au/P3HT:PCBM:F4-TCNQ/n-Si Schottky barrier diode was conducted by means of capacitance-voltage ( C- V) and conductance-voltage ( G/ ω- V) measurements in the frequency range of 10 kHz-2 MHz. The C- V- f plots exhibit fairly large frequency dispersion due to excess capacitance caused by the presence of interface states ( N ss). The values of N ss located in semiconductor bandgap at the organic film/semiconductor interface were calculated by Hill-Coleman method. Experimental results show that dielectric constant ( ɛ') and dielectric loss ( ɛ″) decrease with increasing frequency, whereas loss tangent (tan δ) remains nearly the same. The decrease in ɛ' and ɛ″ was interpreted by the theory of dielectric relaxation due to interfacial polarization. It is also observed that ac electrical conductivity ( σ ac) and electric modulus ( M' and M″) increase with increasing frequency.

Heat conduction in graphene: experimental study and theoretical interpretation

International Nuclear Information System (INIS)

Ghosh, S; Nika, D L; Pokatilov, E P; Balandin, A A

2009-01-01

We review the results of our experimental investigation of heat conduction in suspended graphene and offer a theoretical interpretation of its extremely high thermal conductivity. The direct measurements of the thermal conductivity of graphene were performed using a non-contact optical technique and special calibration procedure with bulk graphite. The measured values were in the range of ∼3000-5300 W mK -1 near room temperature and depended on the lateral dimensions of graphene flakes. We explain the enhanced thermal conductivity of graphene as compared to that of bulk graphite basal planes by the two-dimensional nature of heat conduction in graphene over the whole range of phonon frequencies. Our calculations show that the intrinsic Umklapp-limited thermal conductivity of graphene grows with the increasing dimensions of graphene flakes and can exceed that of bulk graphite when the flake size is on the order of a few micrometers. The detailed theory, which includes the phonon-mode-dependent Gruneisen parameter and takes into account phonon scattering on graphene edges and point defects, gives numerical results that are in excellent agreement with the measurements for suspended graphene. Superior thermal properties of graphene are beneficial for all proposed graphene device applications.

Electrical Conduction of Ba(Ti0.99Fe0.01)O3-δ Ceramic at High Temperatures

Science.gov (United States)

Yu, Zi-De; Chen, Xiao-Ming

2018-03-01

BaTiO3 and Ba(Ti0.99Fe0.01)O3-δ ceramics with dense microstructure have been synthesized by a solid-state reaction method, and their electrical conduction investigated by broadband electrical impedance spectroscopy at frequencies from 0.05 Hz to 3 × 106 Hz and temperatures from 200°C to 400°C. Compared with BaTiO3, the real part of the permittivity and the phase-transition temperature of Ba(Ti0.99Fe0.01)O3-δ decreased. Relaxation peaks appeared in the curves of the imaginary part of the permittivity as a function of frequency. With increase in frequency, the peaks gradually shifted towards higher frequency and their height increased. Conductivity was closely related to frequency and temperature. Frequency-dependent conductivity was analyzed using the Jonscher double power law. Compared with BaTO3, Ba(Ti0.99Fe0.01)O3-δ exhibited high impedance at given frequency and temperature. Impedance Cole-Cole plots displayed two semicircles, which could be well fit using two parallel RC equivalent circuit models. The conductivity activation energy was found to be around 1 eV. For Ba(Ti0.99Fe0.01)O3-δ , the electrical modulus curve versus frequency displayed two peaks.

Study of temperature-dependent charge conduction in silicon-nanocrystal/SiO_2 multilayers

International Nuclear Information System (INIS)

Mavilla, Narasimha Rao; Chavan, Vinayak; Solanki, Chetan Singh; Vasi, Juzer

2016-01-01

Silicon-nanocrystals (Si-NCs) realized by SiO_x _ 8 MV/cm; independent of temperature), while for lower electric fields (5–8 MV/cm) at higher temperatures, the trap-related Generalized Poole–Frenkel (GPF) is dominant. This signified the role of traps in modifying the conduction in bulk ICPCVD SiO_2 films. We then present the conduction in ML samples. For multilayer samples with SiO_2 sublayer thickness of 1.5 nm and 2.5 nm, Direct Tunneling (DT) is observed to be dominant, while for SiO_2 sublayer thickness of 3.5 nm, Space Charge Limited Conduction (SCLC) with exponential trap distribution is found to be the dominant conduction mechanism. This signifies the role of traps in modifying the conduction in Si-NC multilayer samples and SiO_2 sublayer thickness dependence. - Highlights: • Electrical conduction in SiO_2 film & Si-nanocrystal layers (Si-NCs) is reported. • SiO_2/SiO_x multilayer based Si-NCs were realized by Inductively Coupled plasma CVD. • For SiO_2 film, Fowler–Nordheim tunneling & Generalized Poole–Frenkel are observed. • For Si-NCs with thin SiO_2 sublayers (< 2.5 nm) Direct Tunneling is dominant. • For Si-NCs with 3.5 nm SiO_2 sublayers Space Charge Limited Conduction is dominant.

The evolution of social learning rules: payoff-biased and frequency-dependent biased transmission.

Science.gov (United States)

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.

a.c. conductance study of polycrystal C{sub 60}

Energy Technology Data Exchange (ETDEWEB)

Yan Feng [Nanjing Univ. (China). Nat. Lab. of Solid State Microstructure; Wang Yening [Nanjing Univ. (China). Nat. Lab. of Solid State Microstructure; Huang Yineng [Nanjing Univ. (China). Nat. Lab. of Solid State Microstructure; Gu Min [Nanjing Univ. (China). Nat. Lab. of Solid State Microstructure; Zhang Qingming [Nanjing Univ. (China). Nat. Lab. of Solid State Microstructure; Shen Huimin [Nanjing Univ. (China). Nat. Lab. of Solid State Microstructure

1995-06-05

The a.c. (1conductance of a C{sub 60} polycrystal (grain size 30 nm) has been studied from 100 to 350 K. Below 150 K, the a.c. conductance is nearly proportional to the temperature and frequency. This is proposed to be due to the hopping of localized states around the Fermi level. Above 200 K, the a.c. conductance exhibits a rapid increase with temperature, and shows a thermally activated behaviour with an activation energy of 0.389 eV below a certain temperature and 0.104 eV above it. A frequency dependent conductance at a fixed temperature is also obtained with a power law {sigma} similar {omega}{sup s} (s{approx}0.8). For a sample of normal grain size, we have measured a peak near 250 K and a much smaller conductance. These results indicate that the defective na ture of our sample (small grain size, disorder or impurities) plays an important role for the transport properties. The existence of nanocrystals in the sample may give rise to localized states and improve its a.c. conductance. The two activation energies can be attributed to the coexistence of the crystalline and amorphous phases of C{sub 60}. ((orig.)).

Heavy carriers, non-drude optical conductivity and transfer of spectral weight in MnSi

International Nuclear Information System (INIS)

Mena, F.P.; Damascelli, A.; Marel, D. van der; Fath, M.; Menovsky, A.A.; Mydosh, J.A.

2004-01-01

The optical properties of the weak magnetic metal MnSi were determined using reflectance at 80 deg. (2-800 meV) and ellipsometry (0.8-4.5 eV). At low frequencies in the magnetic phase we observe a departure of the optical conductivity from Drude behavior: m*(ω)/m is strongly frequency dependent and 1/τ(ω) is approximately linear in frequency. In fact, we show that σ(ω)/σ(0)=(1+iω/Γ) -0.5 . Moreover, in the magnetic phase, the plasma frequency shifts to the red indicating that spectral weight is transferred to high frequencies. This is opposite to the effect recently seen in other magnetic compounds

Membrane voltage fluctuations reduce spike frequency adaptation and preserve output gain in CA1 pyramidal neurons in a high conductance state

Science.gov (United States)

Fernandez, Fernando R.; Broicher, Tilman; Truong, Alan; White, John A.

2011-01-01

Modulating the gain of the input-output function of neurons is critical for processing of stimuli and network dynamics. Previous gain control mechanisms have suggested that voltage fluctuations play a key role in determining neuronal gain in vivo. Here we show that, under increased membrane conductance, voltage fluctuations restore Na+ current and reduce spike frequency adaptation in rat hippocampal CA1 pyramidal neurons in vitro. As a consequence, membrane voltage fluctuations produce a leftward shift in the f-I relationship without a change in gain, relative to an increase in conductance alone. Furthermore, we show that these changes have important implications for the integration of inhibitory inputs. Due to the ability to restore Na+ current, hyperpolarizing membrane voltage fluctuations mediated by GABAA-like inputs can increase firing rate in a high conductance state. Finally, our data show that the effects on gain and synaptic integration are mediated by voltage fluctuations within a physiologically relevant range of frequencies (10–40 Hz). PMID:21389243

Energy drink consumption and increased risk for alcohol dependence.

Science.gov (United States)

Arria, Amelia M; Caldeira, Kimberly M; Kasperski, Sarah J; Vincent, Kathryn B; Griffiths, Roland R; O'Grady, Kevin E

2011-02-01

Energy drinks are highly caffeinated beverages that are increasingly consumed by young adults. Prior research has established associations between energy drink use and heavier drinking and alcohol-related problems among college students. This study investigated the extent to which energy drink use might pose additional risk for alcohol dependence over and above that from known risk factors. Data were collected via personal interview from 1,097 fourth-year college students sampled from 1 large public university as part of an ongoing longitudinal study. Alcohol dependence was assessed according to DSM-IV criteria. After adjustment for the sampling design, 51.3%(wt) of students were classified as "low-frequency" energy drink users (1 to 51 days in the past year) and 10.1%(wt) as "high-frequency" users (≥52 days). Typical caffeine consumption varied widely depending on the brand consumed. Compared to the low-frequency group, high-frequency users drank alcohol more frequently (141.6 vs. 103.1 days) and in higher quantities (6.15 vs. 4.64 drinks/typical drinking day). High-frequency users were at significantly greater risk for alcohol dependence relative to both nonusers (AOR = 2.40, 95% CI = 1.27 to 4.56, p = 0.007) and low-frequency users (AOR = 1.86, 95% CI = 1.10, 3.14, p = 0.020), even after holding constant demographics, typical alcohol consumption, fraternity/sorority involvement, depressive symptoms, parental history of alcohol/drug problems, and childhood conduct problems. Low-frequency energy drink users did not differ from nonusers on their risk for alcohol dependence. Weekly or daily energy drink consumption is strongly associated with alcohol dependence. Further research is warranted to understand the possible mechanisms underlying this association. College students who frequently consume energy drinks represent an important target population for alcohol prevention. Copyright © 2010 by the Research Society on Alcoholism.

Ac conductivity and relaxation mechanism in Ba0.9Sr0.1TiO3

International Nuclear Information System (INIS)

Singh, A.K.; Barik, Subrat K.; Choudhary, R.N.P.; Mahapatra, P.K.

2009-01-01

The ac conductivity and relaxation mechanism in Ba 0.9 Sr 0.1 TiO 3 ceramics have been investigated systematically. A high-temperature solid-state reaction technique was used to synthesize the compound. The formation of the compound was checked by an X-ray diffraction (XRD) technique. The dielectric permittivity and the loss tangent of the sample were measured in a frequency range from 1 kHz to 1 MHz at different temperatures (30-500 deg. C). A study on dielectric properties reveals the electrical relaxation phenomenon occurs in the material. The activation energy was calculated from the temperature variation of dc conductivity. Studies of frequency and temperature dependence of ac conductivity of the compound suggest that conduction process in the material is thermally activated.

Increased excitability of spinal pain reflexes and altered frequency-dependent modulation in the dopamine D3-receptor knockout mouse.

Science.gov (United States)

Keeler, Benjamin E; Baran, Christine A; Brewer, Kori L; Clemens, Stefan

2012-12-01

Frequency-dependent modulation and dopamine (DA) receptors strongly modulate neural circuits in the spinal cord. Of the five known DA receptor subtypes, the D3 receptor has the highest affinity to DA, and D3-mediated actions are mainly inhibitory. Using an animal model of spinal sensorimotor dysfunction, the D3 receptor knockout mouse (D3KO), we investigated the physiological consequences of D3 receptor dysfunction on pain-associated signaling pathways in the spinal cord, the initial integration site for the processing of pain signaling. In the D3KO spinal cord, inhibitory actions of DA on the proprioceptive monosynaptic stretch reflex are converted from depression to facilitation, but its effects on longer-latency and pain-associated reflex responses and the effects of FM have not been studied. Using behavioral approaches in vivo, we found that D3KO animals exhibit reduced paw withdrawal latencies to thermal pain stimulation (Hargreaves' test) over wild type (WT) controls. Electrophysiological and pharmacological approaches in the isolated spinal cord in vitro showed that constant current stimulation of dorsal roots at a pain-associated frequency was associated with a significant reduction in the frequency-dependent modulation of longer-latency reflex (LLRs) responses but not monosynaptic stretch reflexes (MSRs) in D3KO. Application of the D1 and D2 receptor agonists and the voltage-gated calcium-channel ligand, pregabalin, but not DA, was able to restore the frequency-dependent modulation of the LLR in D3KO to WT levels. Thus we demonstrate that nociception-associated LLRs and proprioceptive MSRs are differentially modulated by frequency, dopaminergics and the Ca(2+) channel ligand, pregabalin. Our data suggest a role for the DA D3 receptor in pain modulation and identify the D3KO as a possible model for increased nociception. Copyright © 2012 Elsevier Inc. All rights reserved.

Advances on Frequency Diverse Array Radar and Its Applications

Directory of Open Access Journals (Sweden)

Wang Wenqin

2018-04-01

Full Text Available Unlike the conventional phased array that provides only angle-dependent transmit beampattern, Frequency Diverse Array (FDA employs a small frequency increment across its array elements to produce automatic beam scanning without requiring phase shifters or mechanical steering. FDA can produce both rangedependent and time-variant transmit beampatterns, which overcomes the disadvantages of conventional phased arrays that produce only angle-dependent beampattern. Thus, FDA has many promising applications. Based on a previous study conducted by the author, “Frequency Diverse Array Radar: Concept, Principle and Application” (Journal of Electronics & Information Technology, 2016, 38(4: 1000–1011, the current study introduces basic FDA radar concepts, principles, and application characteristics and reviews recent advances on FDA radar and its applications. In addition, several new promising applications of FDA technology are discussed, such as radar electronic warfare and radar-communications, as well as open technical challenges such as beampattern variance, effective receiver design, adaptive signal detection and estimation, and the implementation of practical FDA radar demos.

Is the colour dimorphism in Dactylorhiza sambucina maintained by differential seed viability instead of frequency-dependent selection?

Czech Academy of Sciences Publication Activity Database

Jersáková, Jana; Kindlmann, Pavel; Renner, S.S.

2006-01-01

Roč. 41, - (2006), s. 61-76 ISSN 0015-5551 R&D Projects: GA AV ČR(CZ) KJB6141302 Keywords : Dactylorhiza * flower colour polymorphism * frequency-dependent selection * pollinator discrimination * rewardless flowers * seed viability Subject RIV: EF - Botanics Impact factor: 1.033, year: 2005

Size dependent polaronic conduction in hematite

International Nuclear Information System (INIS)

Sharma, Monika; Banday, Azeem; Murugavel, Sevi

2016-01-01

Lithium Ion Batteries have been attracted as the major renewable energy source for all portable electronic devices because of its advantages like superior energy density, high theoretical capacity, high specific energy, stable cycling and less memory effects. Recently, α-Fe_2O_3 has been considered as a potential anode material due to high specific capacity, low cost, high abundance and environmental benignity. We have synthesized α-Fe_2O_3 with various sizes by using the ball milling and sol-gel procedure. Here, we report the dc conductivity measurement for the crystallite size ranging from 15 nm to 50 nm. It has been observed that the enhancement in the polaronic conductivity nearly two orders in magnitude while reducing the crystallite size from bulk into nano scale level. The enhancement in the conductivity is due to the augmented to compressive strain developed in the material which leads to pronounced decrease in the hopping length of polarons. Thus, nanocrystaline α-Fe_2O_3 may be a better alternative anode material for lithium ion batteries than earlier reported systems.

A study of the electromagnetic shielding mechanisms in the GHz frequency range of graphene based composite layers

Energy Technology Data Exchange (ETDEWEB)

Drakakis, E. [Electrical Engineering Department, School of Engineering, Technological Educational Institute of Crete, Heraklion (Greece); Kymakis, E. [Electrical Engineering Department, School of Engineering, Technological Educational Institute of Crete, Heraklion (Greece); Center of Materials Technology and Photonics, School of Engineering, Technological Educational Institute of Crete, Heraklion (Greece); Tzagkarakis, G.; Louloudakis, D.; Katharakis, M. [Center of Materials Technology and Photonics, School of Engineering, Technological Educational Institute of Crete, Heraklion (Greece); Kenanakis, G. [Institute of Electronic Structure & Laser (IESL), Foundation for Research and Technology (FORTH) Hellas, Heraklion (Greece); Suchea, M.; Tudose, V. [Center of Materials Technology and Photonics, School of Engineering, Technological Educational Institute of Crete, Heraklion (Greece); Chemistry Faculty, “Al.I.Cuza” University of Iasi, Iasi (Romania); Koudoumas, E., E-mail: koudoumas@staff.teicrete.gr [Electrical Engineering Department, School of Engineering, Technological Educational Institute of Crete, Heraklion (Greece); Center of Materials Technology and Photonics, School of Engineering, Technological Educational Institute of Crete, Heraklion (Greece)

2017-03-15

Highlights: • Optimum paint contents should be chosen so that homogeneous and uniform nanocomposite layers exist exhibiting effective electromagnetic shielding. • The electromagnetic shielding in the frequency range studied comes mainly from absorption and increases with frequency. • Reflection reduces with increasing frequency, the decrease rate being smaller than that of the increase in absorption. • The shielding efficiency depends on both conductivity and thickness, the first dependence being more pronounced. - Abstract: We report on the mechanisms of the electromagnetic interference shielding effect of graphene based paint like composite layers. In particular, we studied the absorption and reflection of electromagnetic radiation in the 4–20 GHz frequency of various dispersions employing different amounts of graphene nanoplatelets, polyaniline, and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), special attention given on the relative contribution of each process in the shielding effect. Moreover, the influence of the composition, the thickness and the conductivity of the composite layers on the electromagnetic shielding was also examined.

A study of the electromagnetic shielding mechanisms in the GHz frequency range of graphene based composite layers

International Nuclear Information System (INIS)

Drakakis, E.; Kymakis, E.; Tzagkarakis, G.; Louloudakis, D.; Katharakis, M.; Kenanakis, G.; Suchea, M.; Tudose, V.; Koudoumas, E.

2017-01-01

Highlights: • Optimum paint contents should be chosen so that homogeneous and uniform nanocomposite layers exist exhibiting effective electromagnetic shielding. • The electromagnetic shielding in the frequency range studied comes mainly from absorption and increases with frequency. • Reflection reduces with increasing frequency, the decrease rate being smaller than that of the increase in absorption. • The shielding efficiency depends on both conductivity and thickness, the first dependence being more pronounced. - Abstract: We report on the mechanisms of the electromagnetic interference shielding effect of graphene based paint like composite layers. In particular, we studied the absorption and reflection of electromagnetic radiation in the 4–20 GHz frequency of various dispersions employing different amounts of graphene nanoplatelets, polyaniline, and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), special attention given on the relative contribution of each process in the shielding effect. Moreover, the influence of the composition, the thickness and the conductivity of the composite layers on the electromagnetic shielding was also examined.

Effect of paramagnetic manganese ions doping on frequency and high temperature dependence dielectric response of layered Na1.9Li0.1Ti3O7 ceramics

International Nuclear Information System (INIS)

Pal, Dharmendra; Pandey, J.L.

2010-01-01

The manganese doped layered ceramic samples (Na 1.9 Li 0.1 )Ti 3 O 7 : XMn (0.01 ≤ X ≤ 0.1) have been prepared using high temperature solid state reaction. The room temperature electron paramagnetic resonance (EPR) investigations exhibit that at lower percentage of doping the substitution of manganese ions occur as Mn 3+ at Ti 4+ sites, whereas for higher percentage of doping Mn 2+ ions occupy the two different interlayer sodium/lithium sites. In both cases, the charge compensation mechanism should operate to maintain the overall charge neutrality of the lattice. The manganese doped derivatives of layered Na 1.9 Li 0. 1Ti 3 O 7 (SLT) ceramics have been investigated through frequency dependence dielectric spectroscopy in this work. The results indicate that the dielectric losses in these ceramics are the collective contribution of electric conduction, dipole orientation and space charge polarization. Smeared peaks in temperature dependence of permittivity plots suggest diffuse nature of high temperature ferroelectric phase transition. The light manganese doping in SLT enhances the dielectric constant. However, manganese doping decreases dielectric loss due to inhibition of domain wall motion, enhances electron-hopping conduction, and impedes the interlayer ionic conduction as well. Manganese doping also gives rise to contraction of interlayer space. (author)

Temperature dependence of conductivity in high mobility MIS structures on a base of (001) silicon

International Nuclear Information System (INIS)

Vyrodov, E.A.; Dolgopolov, V.T.; Dorozhkin, C.I.; Zhitenev, N.B.

1988-01-01

Measurements of the temperature dependence of the conductivity of two-dimensional electrons in silicon MIS structures were carried out. It is shown that the observed dependence is well described by the equation σ(T) = σ(0)(1-Q(kT var-epsilon F )-P(kT/var-epsilon F )3/2 + O[(kT/var-epsilon F ) 2 ]). The variation of the coefficient Q with the density N S of the two-dimensional electrons is determined, and it is shown that the observed trend of the Q(s) curve is described by consideration of the temperature dependence of the dielectric function of a two-dimensional electron gas

Dipolar Excitation of a Perfectly Electrically Conducting Spheroid in a Lossless Medium at the Low-Frequency Regime

Directory of Open Access Journals (Sweden)

Panayiotis Vafeas

2018-01-01