Logarithmic Frequency Research Articles

Dielectric Relaxation and Electrical Conduction Properties of La_2NiO_(4+δ) Ceramics

Thermoelectric power, dc conductivity, and the dielectric relaxation properties of are reported in the temperature range of 77 K - 300 K and in a frequency range of 20 Hz - 1 MHz. Thermoelectric power was positive below 300K. The measured thermoelectric power of decreased linearly with temperature. The dc conductivity showed a temperature variation consistent with the variable range hopping mechanism at low temperatures and the adiabatic polaron hopping mechanism at high temperatures. The low temperature dc conductivity mechanism in was analyzed using Mott`s approach. The temperature dependence of thermoelectric power and dc conductivity suggests that the charge carriers responsible for conduction are strongly localized. The relaxation mechanism has been discussed in the frame of the electric modulus and loss spectra. The scaling behavior of the modulus and loss tangent suggests that the relaxation describes the same mechanism at various temperatures. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with activation energy of ~ 0.106eV. At low temperature, variable range hopping and large dielectric relaxation behavior for are consistent with the polaronic nature of the charge carriers.

Time-lapse sonic logs reveal patchy CO2saturation in-situ

[1] Based on time-lapse sonic and neutron porosity logs from the Nagaoka CO2 sequestration experiment, a P-wave velocity-saturation relation at reservoir depth is retrieved. It does not coincide with either of the end-member models of uniform and patchy saturation but falls in between even if realistic error estimates for the host rock properties are considered. Assuming a random distribution of CO2 patches it is shown that the mechanism of wave-induced flow can be evoked to explain this velocity-saturation relation. Characteristic CO2 patch size estimates range from 1 to 5 mm. Such mesoscopic heterogeneity can be responsible for attenuation and dispersion in the well logging frequency band.

Acoustic log simulation in a viscoelastic formation

Abstract It is known that sedimentary rocks demonstrate velocity dispersion in the acoustic log frequency range. In this paper we have calculated the waveforms of sonic log for a borehole located in a viscoelastic medium. The acoustic field in the borehole has been obtained for acoustic multipole sources. To describe the viscoelastic properties of a rock we used the Cole–Cole model. This model describes the dispersion of acoustic wave velocities and quality factors in a wide frequency range. To solve the acoustic log direct problem we have applied the double integral Fourier transform (RAI method). The results obtained have shown the feasibility of S-wave velocity dispersion estimation from acoustic dipole waveform processing.

Very low frequency oscillations in the power spectra of heart rate variability during dry supine immersion and exposure to non-hypoxic hypobaria

The origin of very low frequency (VLF) oscillations in the power spectra of heart rate variability (HRV) is controversial with possible mechanisms involving thermoregulation and/or renin-angiotensin-aldosterone system. Recently, a major contribution from vagal influences has been suggested. The present study investigated the behaviour of VLF (0.004–0.040 Hz) components of HRV power spectra in a group of healthy male volunteers during their exposure to (1) dry, supine, immersion in thermo-neutral water for 6 h (n = 7) and (2) non-hypoxic hypobaria (breathing 40–60% oxygen at 15 000′ simulated in a decompression chamber) for 5 h (n = 15). The two manoeuvres are established to increase vagal outflow. During both the manoeuvres, all the frequency domain indices of HRV exhibited a significant increase. Increase in HRV was much more than that in the R-R interval. At 6 h of immersion, the R-R interval increased by ∼15% but the total power increased ∼fourfold. Similarly, at 5 h of exposure to hypobaria, total power increased ∼twofold with a very modest increase in an R-R of ∼9%. Increase in spectral power was appreciable even after normalization with mean R-R2. Increase in VLF during immersion was more than reported during enalaprilat blockade of angiotensin convertase enzyme. Plasma renin activity did not vary during hypobaria. There was a significant increase in pNN50, an established marker of cardiac vagal activity. Centre frequencies of the spectra and slope (β) of the relation between log(PSD) and log(frequency) did not change. Results were supportive of the notion that the parasympathetic system is pre-potent to influence slower (than respiratory) frequency components in HRV spectrum. Additionally, such an effect was without a change in the time constant of effector responses or pacemaker frequencies of VLF and LF periodicities and HRV was not a simple linear surrogate for cardiac vagal effects. An invariance of spectral exponent (β) ruled out contamination of VLF and LF spectra from fractal power as an alternate explanation.

Unexpected Course of Nonlinear Cardiac Interbeat Interval Dynamics during Childhood and Adolescence

The fluctuations of the cardiac interbeat series contain rich information because they reflect variations of other functions on different time scales (e.g., respiration or blood pressure control). Nonlinear measures such as complexity and fractal scaling properties derived from 24 h heart rate dynamics of healthy subjects vary from childhood to old age. In this study, the age-related variations during childhood and adolescence were addressed. In particular, the cardiac interbeat interval series was quantified with respect to complexity and fractal scaling properties. The R-R interval series of 409 healthy children and adolescents (age range: 1 to 22 years, 220 females) was analyzed with respect to complexity (Approximate Entropy, ApEn) and fractal scaling properties on three time scales: long-term (slope β of the power spectrum, log power vs. log frequency, in the frequency range 10−4 to 10−2 Hz) intermediate-term (DFA, detrended fluctuation analysis, α2) and short-term (DFA α1). Unexpectedly, during age 7 to 13 years β and ApEn were higher compared to the age <7 years and age >13 years (β: −1.06 vs. −1.21; ApEn: 0.88 vs. 0.74). Hence, the heart rate dynamics were closer to a 1/f power law and most complex between 7 and 13 years. However, DFA α1 and α2 increased with progressing age similar to measures reflecting linear properties. In conclusion, the course of long-term fractal scaling properties and complexity of heart rate dynamics during childhood and adolescence indicates that these measures reflect complex changes possibly linked to hormonal changes during pre-puberty and puberty.

HMM-Based Speaker Emotional Recognition Technology for Speech Signal

In emotion classification of speech signals, the popular features employed are statistics of fundamental frequency, energy contour, duration of silence and voice quality. However, the performance of systems employing these features degrades substantially when more than two categories of emotion are to be classified. In this paper, a text independent method of emotion classification of speech is proposed. The proposed method makes use of short time log frequency power coefficients(LFPC) to represent the speech signals and a discrete Hidden Markov Model (HMM) as the classifier. The category labels used are, the archetypal emotions of anger, joy, sadness and neutral. Results show that the proposed system yields an average accuracy of 82.55%and the best accuracy of 94.4% in the classification of 4 emotions. Results also reveal that LFPC is a better choice as feature parameters for emotion classification than the traditional feature parameters.

Upper Limit on Gravitational Wave Backgrounds at 0.2 Hz with a Torsion-Bar Antenna

We present the first upper limit on gravitational wave (GW) backgrounds at an unexplored frequency of 0.2 Hz using a torsion-bar antenna (TOBA). A TOBA was proposed to search for low-frequency GWs. We have developed a small-scaled TOBA and successfully found Ω(gw)(f)<4.3×10(17) at 0.2 Hz as demonstration of the TOBA's capabilities, where Ω(gw)(f) is the GW energy density per logarithmic frequency interval in units of the closure density. Our result is the first nonintegrated limit to bridge the gap between the LIGO band (around 100 Hz) and the Cassini band (10(-6)-10(-4) Hz).

Discrimination of stimulus variance.

In real-world settings, auditory signals such as speech are highly variable and differ across occurrences and sources. The question addressed is our sensitivity to such differences in global stimulus variability. In a variance discrimination task, the stimuli were sequences of five 100-ms tone pulses separated by 30 ms. The frequency of each tone was sampled independently from a probability distribution that was Gaussian on logarithmic frequency. In the non-signal interval of the 2IFC task, the sampled distribution had a mean frequency Mf and variance Vf. In the signal interval, the variance of the sequence was Vf + ΔVf. The task was to choose the interval with the larger variance; feedback was provided. To restrict the use of decision strategies, Mf was randomly chosen for each presentation(M̄ f=2 kHz). Psychometric functions |P(C) vs ΔVf| were obtained for various values of Vf , and overall performance was poorer than that of an ideal observer. However, like the ideal, Weber’s law behavior was observed: Constant ΔVf / Vf yielded the same performance. Degrading the Ideal with a fixed frequency resolution noise and a multiplicative computational noise provides an excellent account of the real data. [Work supported by NIDCD DC00683.]

Fuzzy control of an electrodynamic shaker for automotive and aerospace vibration testing

A fuzzy logic based digital time domain sinusoidal acceleration waveform amplitude controller for an electrodynamic shaker is presented. The purpose of Fuzzy Logic Control (FLC) is to reproduce a pre-defined sinusoidal acceleration amplitude profile (in amplitude, frequency and time) at the shaker table. Sinusoidal vibration profiles (sine and logarithmic sine sweep) are considered for a controlled vibration generation in typical automotive and aerospace testing. The difficulty in sine sweep testing is that the non-rigid load dynamics are unknown and it can severely modify the shaker’s performance during sweep test. Since a logarithmic frequency sweep is normally used, a controller needs to be robust to un-modeled dynamics and also fast enough to hold the desired acceleration amplitude within predefined limits throughout the sweep test. The controller structure is developed based on the usual power amplifier technology. The control action is implemented on a waveform-by-waveform basis and a FLC is developed in the LabVIEW environment on a PXI platform for real time control of the shaker. To attenuate the shaker suspension mode resonance a compensator based on electromechanical model of the shaker is designed and cascaded to FLC. The shaker model, suspension mode compensator design, FLC synthesis and experimental implementation results are presented in this paper.

Using Benfords Law To Detect Fraud In The Insurance Industry

Benford's Law is the mathematical phenomena that states that the first digits or left most digits in a list of numbers will occur with an expected logarithmic frequency. While this method has been used in industries such as oil and gas and manufacturing to identify fraudulent activity, it has not been applied to the health insurance industry. Since health insurance companies process a large number of claims each year and these claims are susceptible to fraud, the use of this method in this industry is appropriate. This paper examines the application of Benford's Law to four health insurance companies located in the Midwest. For each company, analysis was performed on the first digit distribution, the first two-digit distribution, and providers with high volumes of claims. The results show that the populations are similar to the frequencies predicted by Benfords Law. The findings also suggested possible fraudulent activity by specific providers, however, the com-panies determined that these results occurred due to abnormal billing practices and were not frau-dulent. The insurance companies that participated in this study will continue to use this method to further detect fraudulent claims.

Logarithmic Frequency Scale Parallel Filter Design With Complex and Magnitude-Only Specifications

Recently, the fixed-pole design of second-order parallel filters has been introduced to accomplish arbitrary (e.g., logarithmic) frequency resolution for transfer function modeling and equalization. The frequency resolution is set by the pole frequencies, and the resulting filter response corresponds to the smoothed (moving-average filtered) version of the target frequency response. This letter presents the frequency-domain version of the design algorithm for complex and real filter coefficients. The proposed frequency-domain design, besides its computational benefits, allows the use of frequency weighting. In addition, a magnitude-only variation of the algorithm is proposed. Examples of loudspeaker-room modeling and equalization are presented.

Viscoelastic properties of the intervertebral disc and the effect of nucleus pulposus removal

The viscoelastic properties of 12 ovine lumbar discs attached to the adjacent vertebrae were investigated using dynamic mechanical analysis. Each specimen was subjected to a sinusoidally varying compressive force of between 36 and 44 N at frequencies in the range 0.1–10 Hz. Storage stiffness, loss stiffness, and phase angle were calculated. The nucleus pulposus was then removed and the dynamic mechanical analysis was repeated for the denucleated specimen. During the testing the intact and denucleated discs were viscoelastic. Storage stiffness for the intact and denucleated discs increased linearly with log frequency. After removal of the nucleus pulposus the storage stiffness can increase or decrease. The experimental procedure may be useful for investigating whether nucleus replacement implants can restore the viscoelastic properties of an intact disc.

Dielectric Analysis of Response Time in Electrorheological Fluids Developed for Medical Devices

Three electrorheological fluids (ERFs) of recently synthesized Polyaniline.HCl and Cellulose fluids as well as a commercial product from Fludicon® (Germany), were evaluated with a two-electrode probe unit and by Dielectric Analysis (DEA). The study was a part of an ongoing medical device development project. The dielectric response times were calculated using the critical peak frequency in a corresponding Debye plot of Tan Delta (loss factor/permittivity) vs. log frequency. The DEA revealed the response times (tau, τ) in ms. The Fludicon® ERF was DEA durable (repeat cycles produced same results) and the τ was temperature dependent: 16 ms at 25°C and 0.16 ms at 80°C. The Cellulose ERF was somewhat DEA durable and the τ was 5.5 ms at 25°C and 0.21 ms at 80°C. The response times were logarithmic with the temperature (°C) with a correlation coefficient of >0.98 for the Cellulose and Fludicon® ERFs. The Polyaniline ERF had a τ of 53 ms at 25°C in the 1st DEA run and there was no indication of a τ for the remaining DEA tests.

Monopole Acoustic Transmitter Comprising A Plurality Of Piezoelectric Discs

A monopole acoustic transmitter with at least one disc assembly with a plurality of piezoelectric discs configured to optimized acoustic pressure output within a desired frequency range while meeting physical restrictions of LWD and MWD logging systems. The transmitter is disposed in a recess or “slot” in the perimeter of a logging tool housing to reduce acoustic pressure waves transmitted directly along the tool housing and to optimize acoustic energy transmission into the borehole environs. In order to increase acoustic pressure output at a desired logging frequency range, the plurality of piezoelectric discs in each of at least one disc assembly are connected electrically in parallel and fired simultaneously. The polarity of the discs and the wiring arrangement are such that each disc expands or contracts in a common direction during simultaneous firing by an applied voltage. The desired output frequency is obtained by selectively polarizing and dimensioning the discs within the one or more disc assemblies. Each disc assembly is preferably disposed within an oil filled pressure housing that is pressure and temperature compensated. The axis of the at least one disc assembly can be parallel or perpendicular to the major axis of the logging tool.

Lake metabolism and the diel oxygen technique: State of the science

Significant improvements have been made in estimating gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) from diel, “free‐water” changes in dissolved oxygen (DO). Here we evaluate some of the assumptions and uncertainties that are still embedded in the technique and provide guidelines on how to estimate reliable metabolic rates from high‐frequency sonde data. True whole‐system estimates are often not obtained because measurements reflect an unknown zone of influence which varies over space and time. A minimum logging frequency of 30 min was sufficient to capture metabolism at the daily time scale. Higher sampling frequencies capture additional pattern in the DO data, primarily related to physical mixing. Causes behind the often large daily variability are discussed and evaluated for an oligotrophic and a eutrophic lake. Despite a 3‐fold higher day‐to‐day variability in absolute GPP rates in the eutrophic lake, both lakes required at least 3 sonde days per week for GPP estimates to be within 20% of the weekly average. A sensitivity analysis evaluated uncertainties associated with DO measurements, piston velocity (k), and the assumption that daytime R equals nighttime R. In low productivity lakes, uncertainty in DO measurements and piston velocity strongly impacts R but has no effect on GPP or NEP. Lack of accounting for higher R during the day underestimates R and GPP but has no effect on NEP. We finally provide suggestions for future research to improve the technique.

AC conductivity and dielectric relaxation in Ba(Sm 1/2Nb 1/2)O 3 ceramic

The complex perovskite oxide a barium samarium niobate (BSN) synthesized by solid-state reaction technique has single phase with cubic structure. The scanning electron micrograph of the sample shows the average grain size of BSN∼1.22 μm. The field dependence of dielectric response and loss tangent were measured in the temperature range from 323 to 463 K and in the frequency range from 50 Hz to 1 MHz. The complex plane impedance plots show the grain boundary contribution for higher value of dielectric constant in the low frequency region. An analysis of the dielectric constant ( ε′) and loss tangent (tan δ) with frequency was performed assuming a distribution of relaxation times as confirmed by the scaling behaviour of electric modulus spectra. The low frequency dielectric dispersion corresponds to DC conductivity. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with an activation energy of 0.71 eV. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behaviour of imaginary part of electric modulus M″ and dielectric loss spectra suggest that the relaxation describes the same mechanism at various temperatures in BSN. All the observations indicate the polydispersive relaxation in BSN.

Temperature-dependent dielectric properties of honey associated with dielectric heating

Dielectric properties of pure yellow-locust and jujube honey and their water solutions at seven final water content levels from 17.4% to 42.6% were measured with an open-ended coaxial-line probe from 10 to 4500 MHz at 20–80 °C. The results showed that the dielectric constants of pure honey increased with increasing temperature when frequency was above 40 MHz. For honey solutions, the dielectric constant decreased with increasing temperature at the lower frequencies, but increased at the higher frequencies. At any given water content, the relaxation frequency shifted to a higher frequency with increasing temperature, while the loss factor peaks showed little change. There was a strong negative linear correlation between penetration depth and frequency in log–log plot for pure honey at 20–80 °C. The research will be helpful in developing effective honey pasteurization processes with radio-frequency and microwave dielectric heating.

A real experiment is a factorial experiment?

Most studies addressing lexical processing make use of factorial designs. For many researchers in this field of inquiry, a real experiment is a factorial experiment. Methods such as regression and factor analysis would not allow for hypothesis testing and would not contribute substantially to the advancement of scientific knowledge. Their use would be restricted to exploratory studies at best. This paper is an apology coming to the defense of regression designs for experiments including lexical distributional variables as predictors. In studies of the mental lexicon, we often are dealing with two kinds of predictors, to which I will refer as treatments and covariates. Stimulus-onset asynchrony (soa) is an example of a treatment. If we want to study the effect of a long versus a short soa, it makes sense to choose sensible values, say 200 ms versus 50 ms, and to run experiments with these two settings. If the researcher knows that the effect of soa is linear, and that it can be administered independently of the intrinsic properties of the items, then the optimal design testing for an effect of soa is factorial. One would loose power by using a regression design testing for an effect at a sequence of SOA intervals, say 50, 60, 70, . . . , 200 ms. This advantage of sampling at the extremes is well-known (see, e.g., Crawley, 2002, p. 67): the further apart the values of soa are, the larger the corresponding sum of squares, and the smaller the standard error for the slope. The advantage of designs with maximal contrasts for treatment predictors is often assumed to carry over to the study of lexical covariates such as frequency, length, neighborhood density, etc. In order to test for an effect of frequency, the traditional wisdom advises us to create a data set with very high-frequency words on the one hand, and very low-frequency words on the other hand. The problem that one runs into very quickly is that the set of highfrequency words will comprise short words with many neighbors, and that the low-frequency words will be long words with few neighbors. The massive correlations characterizing lexical properties create the problem that an effect of frequency could just as well be an effect of length or an effect of neighborhood density, or any combination of these variables. The traditional solution is to create a factorial contrast for frequency, while matching for the other predictors. This can be done by hand, or with the help of Maarten van Casteren’s mix program (Van Casteren and Davis, 2006). The aim of this contribution is to illustrate, by means of some simple simulations, that this matching process leads to a severe loss of power (following up on, e.g., Cohen, 1983; MacCallum et al., 2002). In all the simulations to follow, the dependent variable (RT) is a function of two numerical predictors, X1 (this could be log frequency, or the word’s imageability) and X2 (this could be number of orthographic neighbors, or word length), which both follow a standard normal

Josephson admittance spectroscopy application for frequency analysis of broadband THz antennas

Application of Josephson admittance spectroscopy for the spectral analysis of a broad-band log-periodic superconducting antenna was demonstrated at the frequency range from 50 to 700 GHz. The [001]-tilt YBa2Cu3O7−x bicrystal Josephson junctions, integrated with sinuous log-periodic YBa2Cu3O7−x antennas, were fabricated on NdGaO3 bicrystal substrates. A real part of the antenna admittance ReY(f) as a function of the frequency f was reconstructed from the modification of the dc current-voltage characteristic of the junction, induced by the antenna. Resonance features were observed in the recovered ReY(f)-spectra with a periodicity in the logarithmic frequency scale, corresponding to log-periodic geometry of the antenna. The ReY(f)-spectra, recovered by Josephson spectroscopy, were compared with the ReY(f)-spectra, obtained by CAD simulation, and both spectra were shown to be similar in their main features. A value of 23 was obtained for an effective permittivity of the NdGaO3 bicrystal substrates by fitting simulated data to those obtained from Josephson spectroscopy.

Viscoelastic properties of phonosurgical biomaterials at phonatory frequencies

The purpose of this study was to examine the functional biomechanical properties of several injectable biomaterials currently or potentially used for vocal fold augmentation. Rheometric investigation of phonosurgical materials in vitro. Linear viscoelastic shear properties of 3% bovine collagen (atelocollagen), micronized AlloDerm (Cymetra; LifeCell Corp., Branchburg, NJ), calcium hydroxylapatite (CaHA) (Radiesse; BioForm Medical, San Mateo, CA), and 2.4% cross-linked hyaluronic acid (HA) gel (Juvéderm; Allergan, Inc., Irvine, CA) were quantified as functions of frequency covering the phonatory range, and compared to those of the human vocal fold cover. Measurements of elastic shear modulus (G') and dynamic viscosity (eta') were made at up to 250 Hz with a controlled-strain simple-shear rheometer. Linear least-squares regression was conducted to curve-fit log G' and log eta' versus log frequency, and statistical analysis was performed with one-way analysis of variance. Radiesse and Cymetra were found to be the stiffest and the most viscous materials, followed by Juvéderm and atelocollagen. There were significant differences in the magnitudes of G' and eta' among the phonosurgical materials and the normal human vocal fold cover (p < .001), whereas there was no significant difference in the frequency dependence of G' and eta' among the materials. Post hoc Tukey tests revealed significant differences (p < .05) in pairwise comparisons of the magnitudes of G' and eta' among all materials and the vocal fold cover. These findings suggested that although these biomaterials may be injected lateral to the lamina propria for the treatment of glottic insufficiency, none of them are rheologically optimal for the functional reconstruction of the vocal fold lamina propria.