Peak Frequency Of Spectrum Research Articles

선형발전기가 탑재된 파랑에너지 추출장치 설계 -I. 파력 부이 설계

Design procedure of WEC (wave energy converter) using the heaving motion of a floating cylinder- type buoy coupled with LEG (linear electric generator) system is introduced. It is seen that the maximum power can actually be obtained at the optimal conditions (cPTO=bT, ω = ωN ). Then, based on the developed theory, several design strategies are proposed to further enhance the maximum PTO (power take off), which includes the inten- tional mismatching with the heave natural frequency, which is 15% higher value than the peak frequency of input velocity spectrum. By using the intentional mismatching strategy, the generated power is actually increased and the corresponding draft as well as the required PTO damping value is significantly reduced, which is a big advantage in manufacturing the WEC with practical LEG (linear electric generator) system.

Enhancement of wave-energy-conversion efficiency of a single power buoy with inner dynamic system by intentional mismatching strategy

A PTO (power-take-off) mechanism by using relative heave motions between a floating buoy and its inner mass (magnet or amateur) is suggested. The inner power take-off system is characterized by a mass with linear stiffness and damping. A vertical truncated cylinder is selected as a buoy and a special station-keeping system is proposed to minimize pitch motions while not affecting heave motions. By numerical examples, it is seen that the maximum power can actually be obtained at the optimal spring and damper condition, as predicted by the developed WEC(wave energy converter) theory. Then, based on the developed theory, several design strategies are proposed to further enhance the maximum PTO, which includes the intentional mismatching among heave natural frequency of the buoy, natural frequency of the inner dynamic system, and peak frequency of input wave spectrum. By using the intentional mismatching strategy, the generated power is actually increased and the required damping value is significantly reduced, which is a big advantage in designing the proposed WEC with practical inner LEG (linear electric generator) system.

Theoretical models for electrochemical impedance spectroscopy and local ζ-potential of unfolded proteins in nanopores

Single solid-state nanopores find increasing use for electrical detection and/or manipulation of macromolecules. These applications exploit the changes in signals due to the geometry and electrical properties of the molecular species found within the nanopore. The sensitivity and resolution of such measurements are also influenced by the geometric and electrical properties of the nanopore. This paper continues the development of an analytical theory to predict the electrochemical impedance spectra of nanopores by including the influence of the presence of an unfolded protein using the variable topology finite Warburg impedance model previously published by the authors. The local excluded volume of, and charges present on, the segment of protein sampled by the nanopore are shown to influence the shape and peak frequency of the electrochemical impedance spectrum. An analytical theory is used to relate the capacitive response of the electrical double layer at the surface of the protein to both the charge density at the protein surface and the more commonly measured zeta potential. Illustrative examples show how the theory predicts that the varying sequential regions of surface charge density and excluded volume dictated by the protein primary structure may allow for an impedance-based approach to identifying unfolded proteins.

Multifrequency VLBI Observations of the Broad Absorption Line Quasar J1020 4320: Recently Restarted Jet Activity?

Abstract This paper reports on very-long-baseline interferometry observations of the radio-loud broad absorption line (BAL) quasar J1020$ +$ 4320 at 1.7, 2.3, 6.7, and 8.4 GHz using the Japanese VLBI network (JVN) and European VLBI network (EVN). The radio morphology is compact with a size of $ \sim$ 10 pc. The convex radio spectrum has been stable over the last decade; an observed peak frequency of 3.2 GHz is equivalent to 9.5 GHz in the rest frame, suggesting an age on the order of $ \sim$ 100 years as a radio source, according to an observed correlation between the linear size and the peak frequency of compact steep spectrum (CSS) and giga-hertz peaked spectrum (GPS) radio sources. A low-frequency radio excess suggests a relic of past jet activity. J1020$ +$ 4320 may be one of the quasars with recurrent and short-lived jet activity during a BAL-outflowing phase.

Electrohysterographic evaluation of preterm contractions in a patient with a unicornuate uterus

Women with Müllerian anomalies are at increased risk of preterm labor. The analysis of parameters derived by the electrohysterogram such as its conduction velocity are promising for preterm delivery prediction. However, an electrohysterogram has never been measured in Müllerian anomalies. A multiparous woman with a unicornuate uterus presented at 28 weeks of gestation with preterm contractions. Three electrohysterogram recordings were performed between 28 and 30 weeks of gestation, 4 weeks before delivery. The conduction velocity values were in line with previous literature and differed significantly (p < 0.001) showing an increase between the first and last two recordings. The parameters derived from the electrohysterogram such as conduction velocity and power density spectrum peak frequency are promising ones to follow the evolution of pregnancy towards labor, and to distinguish between productive and unproductive uterine contractions, in the case of a unicornuate uterus as well as one that is normally developed.

The energy class discrimination of low velocity impacts on composite material structure by Bragg grating sensor technique

The low velocity impacts (LVI) often bring damages which cannot be detected from surface of composite material smart structure. In this paper, Bragg grating sensors were used to discriminate energy classes of LVI on composite material smart structure under constant temperature. The energy discrimination was realized by means of this characteristic that the center wave-lengths of Bragg grating sensors on composite structure under LVI are determined by strain. By analyzing the frequency spectrums of LVI signals captured by optic fiber grating demodulator, a threshold for distinguishing energy classes can be figured out after calculating frequency spectrum peak values of all energy classes. The experimental results indicate that Bragg grating sensors can be used for monitoring impacts and discriminate the energy classes of LVI on composite material structure.

Monitoring Low-Cycle Fatigue Material-Degradation by Ultrasonic Methods

Any system consisting of structural material often undergoes fatigue, which is caused by dynamic load cycle. As a structural system, nuclear power plant is very likely to have low-cycle fatigue at many of its components. Taking into account the importance of monitoring low-cycle fatigue on structural components to prevent them from getting failure, the authors have conducted a work to monitor material degradation caused by low-cycle fatigue by using ultrasonic method. An alloy of Cu-40Zn was used as a test specimen. Ultrasonic water immersion procedure was employed in this ultrasonic test. The probe used is a focusing type and has frequency as high as 15 MHz. The specimen area tested is in the middle part divided into 14 points × 23 points. The results, which were frequency spectrums, were analyzed using two parameters: frequency spectrum peak intensity and attenuation function gradient. The analysis indicates that peak intensity increases at the beginning of load cycle and then decreases. Meanwhile, gradient of attenuation function is lower at the beginning of fatigue process, and then consistently gets higher. It concludes that low-fatigue material degradation can be monitored by using ultrasonic method. Received: 20 November 2009; Revised: 31 August 2010; Accepted: 31 August 2010

Dorsal–ventral organization of theta‐like activity intrinsic to entorhinal stellate neurons is mediated by differences in stochastic current fluctuations

The membrane potential dynamics of stellate neurons in layer II of the medial entorhinal cortex are important for neural encoding of location. Previous studies suggest that these neurons generate intrinsic theta-frequency membrane potential oscillations, with a period that depends on neuronal location on the dorsal–ventral axis of themedial entorhinal cortex, and which in behaving animals could support generation of grid-like spatial firing fields. To address the nature and organization of this theta-like activity, we adopt the Lombmethod of least-squares spectral analysis. We demonstrate that peaks in frequency spectra that differ significantly from Gaussian noise do not necessarily imply the existence of a periodic oscillator, but can instead arise from filtered stochastic noise or a stochastic random walk. We show that theta-like membrane potential activity recorded fromstellate neurons in mature brain slices is consistentwith stochastic mechanisms, but not with generation by a periodic oscillator. The dorsal–ventral organization of intrinsic theta-likemembrane potential activity, and themodification of this activity during block of HCN channels, both reflect altered frequency distributions of stochastic spectral peaks, rather than tuning of a periodic oscillator. Our results demonstrate the importance of distinguishing periodic oscillations from stochastic processes.We suggest that dorsal–ventral tuning of theta-like membrane potential activity is due to differences in stochastic current fluctuations resulting from organization of ion channels that also control synaptic integration.

NEW EXPLANATIONS FOR SOME OBSERVATION PHENOMENA OF THE PEAK FREQUENCY OF SOLAR RADIO BURSTS

We present new explanations for some observation phenomena of the peak frequency of solar radio burst spectrum, based on spectrum calculations of gyrosynchrotron radiation in a model of magnetic dipole field. These observation phenomena are: (1) a remarkable constant peak frequency of microwave burst spectrum during their lifetime, (2) a composite CD-type burst with two distinct spectral components respectively peaking in centimeter (cm) and decimeter (dm) ranges, and (3) emission of solar flares in the submillimeter band above 100 GHz (THz) and a new increasing submillimeter spectral component. Our calculation results show that the peak frequency can maintain constant when the energy spectral index d varies only in the range larger than 3, whereas other parameters hold constant. Two distinct spectral components of the dm and cm ranges of the CD-type burst can be produced simultaneously by the energetic electrons with softer energy spectral index (greater than or similar to 6) and lower low-energy cutoff (less than or similar to 30 keV). The THz burst can be generated by energetic electrons with hard spectral index (similar to 3) and high low-energy cutoff (similar to 250 keV) in intense local magnetic fields (mean value (B) over bar = 2100 G) via gyrosynchrotron emission; while a harder spectral index, a higher low-energy cutoff, and higher magnetic field strength are required for the increasing submillimeter spectral component.

General properties of the gravitational wave spectrum from phase transitions

In this paper we discuss some general aspects of the gravitational wave background arising from post-inflationary short-lasting cosmological events such as phase transitions. We concentrate on the physics which determines the shape and the peak frequency of the gravitational wave spectrum. We then apply our general findings to the case of bubble collisions during a first order phase transition and compare different results in the recent literature.

The effect of bilateral pelvic neurectomy on uterine and abdominal electrical and pressure activity, as measured by telemetry in conscious, unrestrained pregnant rats

Bilateral pelvic neurectomy (BPN) interferes with delivery in rats. This work measures the effect of BPN on uterine and abdominal electromyography (EMG) and pressure during gestation and delivery. Uterine EMG and intra-uterine pressure (IUP), as well as abdominal muscle EMG and intra-abdominal pressure (IAP), were recorded on days 19-24 in rats. Mean values were determined for the peak frequency of the power density spectrum (PDS) of the uterine and abdominal EMG "bursts," the integral of the abdominal EMG power spectrum (IPS), and the area under the IUP and IAP curves (AUIUP and AUIAP). Uterine EMG power density spectrum peak frequency and AUIUP were low during days 19-21 in all rats, and on days 22-23 increased sharply and significantly in both groups. Before delivery, sham rat recordings showed sudden sharp increases in AUIAP, AUIUP and IPS as "pushing" was observed. Pushing was not observed or recorded in laboring BPN rats and they did not deliver normally. A functional pelvic nerve is required for normal labor and delivery in rats. BPN inhibits abdominal EMG and contractions necessary to expel the fetus.

High-Frequency Organization and Synchrony of Activity in the Purkinje Cell Layer of the Cerebellum

The cerebellum controls complex, coordinated, and rapid movements, a function requiring precise timing abilities. However, the network mechanisms that underlie the temporal organization of activity in the cerebellum are largely unexplored, because in vivo recordings have usually targeted single units. Here, we use tetrode and multisite recordings to demonstrate that Purkinje cell activity is synchronized by a high-frequency (approximately 200 Hz) population oscillation. We combine pharmacological experiments and modeling to show how the recurrent inhibitory connections between Purkinje cells are sufficient to generate these oscillations. A key feature of these oscillations is a fixed population frequency that is independent of the firing rates of the individual cells. Convergence in the deep cerebellar nuclei of Purkinje cell activity, synchronized by these oscillations, likely organizes temporally the cerebellar output.

A comparison of various linear and non-linear signal processing techniques to separate uterine EMG records of term and pre-term delivery groups

Various linear and non-linear signal-processing techniques were applied to three-channel uterine EMG records to separate term and pre-term deliveries. The linear techniques were root mean square value, peak and median frequency of the signal power spectrum and autocorrelation zero crossing; while the selected non-linear techniques were estimation of the maximal Lyapunov exponent, correlation dimension and calculating sample entropy. In total, 300 records were grouped into four groups according to the time of recording (before or after the 26th week of gestation) and according to the total length of gestation (term delivery records--pregnancy duration >or=37 weeks and pre-term delivery records--pregnancy duration <37 weeks). The following preprocessing band-pass Butterworth filters were tested: 0.08-4, 0.3-4, and 0.3-3 Hz. With the 0.3-3 Hz filter, the median frequency indicated a statistical difference between those term and pre-term delivery records recorded before the 26th week (p = 0.03), and between all term and all pre-term delivery records (p = 0.012). With the same filter, the sample entropy indicated statistical differences between those term and pre-term delivery records recorded before the 26th week (p = 0.035), and between all term and all pre-term delivery records (p = 0.011). Both techniques also showed noticeable differences between term delivery records recorded before and after the 26th week (p <or= 0.001).

L’électromyogramme utérin : principes et intérêt pour le diagnostic de travail prématuré

Preterm labour diagnosis rely on clinical arguments exhibiting low positive predictive values. Discrimination between uterine contractions leading to preterm delivery and physiologic uterine activity increase throughout pregnancy and remains difficult. Uterine electrical activity can be recorded non-invasively from the abdominal wall and could help in the diagnosis of preterm labour. Electrical signal characteristics are reflecting myometrial cells electrical properties which are varying throughout pregnancy and labour. During pregnancy, uterine electrical activity is very low. During term and preterm labour, uterine electrical activity increases as well as mechanical activity. Bursts become regular with high amplitude. Spectral analysis demonstrates an increase in the frequency content, as represented by the shift of the burst power density spectrum peak frequency from low to high frequencies. Consequently, the electromyogram signal reflects myometrial excitability and allows differentiating powerful uterine contractions leading to delivery from uterine physiologic activity. Moreover, electromyogram signal modifications occur before any increase in mechanical activity in the pregnant rats, allowing identification of preterm labour earlier than uterine mechanical activity measured by intrauterine pressure. Two studies performed in women present with preterm contractions are supporting the potential interest of the uterine electromyogram recording to help in the diagnosis of preterm labour; but further investigations are necessary.

A Study of the Peak Frequency of the Geosynchronous Spectrum in a Nonuniform Source

This paper investigates in detail the peak frequency of gyrosynchrotron radiation spectrum with self and gyroresonance absorption for a model of nonuniform magnetic field. It is found that the peak frequency shifts from lower frequency to higher frequency with increases in the low-energy cutoff, number density, input depth of energetic electrons, magnetic field strength and viewing angle. When the number density and temperature of thermal electrons increase, the peak frequency also shifts to a slightly higher frequency. However, the peak frequency is independent of the energy spectral index, high-energy cutoff of energetic electrons and the height of the radio source’s upper boundary. It is also found for the first time that there is a good linear correlation between the logarithms of the peak frequency and the low-energy cutoff, number density, input depth of energetic electrons, magnetic field strength, and viewing angle, respectively. Their correlation coefficients are higher than 0.95 and the standard errors are less than 0.06.

Linear Correlations between Peak Frequency of Gyrosynchrotron Spectrum and Photosphere Magnetic Fields

The gyrosynchrotron spectra are computed in a nonuniform magnetic field case, taking into account the self- and gyroresonance absorption. It is found that the peak frequency νp of the gyrosynchrotron spectrum systematically increases with the increasing photosphere magnetic field strength B0 and increasing viewing angle θ. It is also found for the first time that there are good positive linear correlations between νp and B0, and between log νp and log θ, with linear correlation coefficient 0.99 between νp and B0 and 0.95 between log νp and log θ. We apply the correlations to analyze two burst events observed with OVSA and find that the evolution tendencies of the photosphere magnetic field strength B0 estimated from the above expression are comparable with the observational results of SOHO/MDI. We also give a comparison of the diagnostic results of coronal magnetic field strength in both uniform and nonuniform source models.

A Comparison Of Frequency And Time Domain Analyses Of Motor Unit Rate Coding

Frequency domain analysis of the modulation of motor unit firing rate (rate coding) during sinusoidal force modulation tasks described dominant periodic components in the rate code, but were insensitive to instances of very high discharge rates. These discharge behaviors may have a relatively large impact on the gradation of muscular force. The PURPOSE was to compare the information from simultaneous time (TD) and frequency domain (FD) analyses of motor unit rate coding. METHODS: Motor unit spike trains were recorded from 9 subjects as they performed sinusoidal isometric index finger abduction force matching tasks at .3, .6 and .9-Hz task frequencies. These oscillations were centered at 20% of each subjects' maximum voluntary contraction (MVC) force and had amplitude of+/−3% MVC. Motor unit action potentials were recorded from first dorsal interosseous (FDI) muscle using fine-wire electrodes. Firing rate time series were created from individual motor unit spike trains. In the FD, the amplitude of rate coding was estimated from peaks in frequency spectra. In the TD, maxima, minima and mean firing rates were measured from individual cycles within each trial. Amplitude of rate coding in TD was computed as difference between the minima and maxima firing rates. RESULTS: The average (+/−SE) amplitude of firing rate modulation was greater when described using TD measures [TD: 26.6 (1.02) pps, FD: 2.1(.12) pps]. The relationship between the TD and FD measures of rate coding amplitude was r=0.53 (Pearson correlation). When the effect of task frequency was tested using each measure, the TD measure revealed significant decreases in rate coding amplitude with increases in task frequency (p<05). Despite a parallel trend, FD measures were not supported statistically. The TD measures indicated that significant changes in the amplitude of rate coding were due to changes in the firing rate maxima while the mean and minima firing rates remained stable. CONCLUSION: These results support combined use of time and frequency domain measures for a complete description of rate coding mechanism. While spectral techniques provide a good descriptor of prevailing behavior, averages of cycle-by-cycle time domain measures of discharge rates describe in greater detail the variety in motor unit discharge behavior.

Identification of Human Term and Preterm Labor using Artificial Neural Networks on Uterine Electromyography Data

To use artificial neural networks (ANNs) on uterine electromyography (EMG) data to classify term/preterm labor/non-labor pregnant patients. A total of 134 term and 51 preterm women (all ultimately delivered spontaneously) were included. Uterine EMG was measured trans-abdominally using surface electrodes. "Bursts" of elevated uterine EMG, corresponding to uterine contractions, were quantified by finding the means and/or standard deviations of the power spectrum (PS) peak frequency, burst duration, number of bursts per unit time, and total burst activity. Measurement-to-delivery (MTD) time was noted for each patient. Term and preterm patient groups were sub-divided, resulting in the following categories: [term-laboring (TL): n = 75; preterm-laboring (PTL): n = 13] and [term-non-laboring (TN): n = 59; preterm-non-laboring (PTN): n = 38], with labor assessed using clinical determinations. ANN was then used on the calculated uterine EMG data to algorithmically and objectively classify patients into labor and non-labor. The percent of correctly categorized patients was found. Comparison between ANN-sorted groups was then performed using Student's t test (with p < 0.05 significant). In total, 59/75 (79%) of TL patients, 12/13 (92%) of PTL patients, 51/59 (86%) of TN patients, and 27/38 (71%) of PTN patients were correctly classified. ANNs, used with uterine EMG data, can effectively classify term/preterm labor/non-labor patients.

Real-time terahertz imaging over a standoff distance (&amp;gt;25meters)

The authors demonstrate the use of a terahertz quantum cascade laser (QCL) for real-time imaging in transmission mode at a standoff distance of 25meters. Lasing frequency was selected for optimum transmission within an atmospheric window at ∼4.9THz. Coarse frequency selection was made by design of the QCL gain medium. Finer selection (to within 0.1THz) was made by judicious choice of laser cavity length to adjust facet losses and therefore lasing threshold bias, in order to overlap the peak frequency of the Stark-shifted gain spectrum with the atmospheric window. Images are shown using an uncooled 320×240 microbolometer camera.

Nonlinear amplitude–frequency characteristics of attenuation in rock under pressure

Laboratory experiments have been carried out to investigate the influence of change in strain amplitude on the frequency dependence of attenuation in samples of sandstone, smoky quartz and duralumin. The measurements were performed using the reflection method on pulse frequency of 1 MHz in the strain range ~(0.3–2.0) × 10−6 under a confining pressure of 20 MPa. The attenuation in rocks is nonlinearly dependent on frequency and strain amplitude. In sandstone for P-waves and in smoky quartz for P- and S-waves, the dependences Q−1p(f) and Q−1s(f) have the attenuation peak. With increasing amplitude, the peak frequency can shift towards both the lower and the higher frequencies. It depends on the location of the frequency of an incident (input) pulse with respect to the peak frequency on the frequency axis. For sandstone the peak frequency of P-waves shifts towards the higher frequencies. For smoky quartz the shift of peak frequency is absent in P-waves, and S-waves shift towards the lower frequencies. The attenuation at the incident frequency always monotonically decreases with amplitude, and the other frequency components have complex or monotonic characters depending on the location of the incident frequency in the relaxation spectrum. Q−1p(f) in duralumin has monotonic character, i.e. a relaxation peak in the measurement frequency band is absent. Attenuation strongly decreases with increasing frequency and weakly depends on strain amplitude. The curve Q−1s(f) has an attenuation peak, and its character essentially depends on strain amplitude. With increasing amplitude, the peak frequency shifts towards the lower frequencies. The unusual increase of peak frequency of the P-wave spectrum in the bottom reflection in comparison with peak frequency in spectrum of the initial reflection is detected. The unusual behaviour of attenuation is explained by features of the joint action of viscoelastic and microplastic mechanisms. These results can be used for improving methods of geological interpretation of seismic data.