• Journal of Astronomy and Space Sciences
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• 제29권3호
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• pp.253-258
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• 2012

We revisit the relation between the peak luminosity $L_{iso}$ and the spectral time lag in the source frame. Since gamma-ray bursts (GRBs) are generally thought to be beamed, it is natural to expect that the collimation-corrected peak luminosity may well correlate with the spectral time lag in the source frame if the lag-luminosity relation in the GRB source frame exists. With 12 long GRBs detected by the Swift satellite, whose redshift and spectral lags in the source frame are known, we computed $L_{0,H}$ and $L_{0,W}$ using bulk Lorentz factors ${\Gamma}_{0,H}$ and ${\Gamma}_{0,W}$ archived in the published literature, where the subscripts H and W represent homogeneous and wind-like circumburst environments, respectively. We have confirmed that the isotropic peak luminosity correlates with the spectral time lag in the source frame. We have also confirmed that there is an anti-correlation between the source-frame spectral lag and the peak energy, $E_{peak}$ (1 + z) in the source frame. We have found that the collimation-corrected luminosity correlates in a similar way with the spectral lag, except that the correlations are somewhat less tight. The correlation in the wind density profile seems to agree with the isotropic peak luminosity case better than in the homogeneous case. Finally we conclude by briefly discussing its implications.

• Structural Engineering and Mechanics
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• 제71권3호
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• pp.291-303
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• 2019

In the paper the analysis of natural vibrations of the transmission line with use of spectral elements and the laboratory experiments is performed. The purpose of the investigation is to analyze the natural vibrations of the transmission line and compare with the results obtained in the numerical simulations. Particular attention is paid to the hysteretic and aerodynamic damping analysis. Sensitivity of the wave number is performed for changing of the tension force, as well as for the different damping parameters. The numerical model is made using the Spectral Element Method. In the spectral model, for various parameters of stiffness, damping and tension force, the system response is checked and compared with the results of the accelerations obtained in the measurements. A frequency response functions (FRF) are calculated. The credibility of the model is assessed through a validation process carried out by comparing graphical plots of FRF and time history analysis and numerical values expressing differences in acceleration amplitude (MSG), phase angle differences (PSG) and differences in acceleration and phase angle total (CSG) values. The next aspect constituting the purpose of this paper is to present the wide possibilities of modelling and simulation of slender conductors using the Spectral Element Method. The obtained results show good accuracy in the range of both experimental measurements as well as simulation analysis. The paper emphasizes the ease with which the sensitivity of the conductor and its response to changes in density of spectral mesh division, tensile strength or material damping can be studied.

• Corrosion Science and Technology
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• 제2권1호
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• pp.18-25
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• 2003

Effects of the precipitation of $\sigma$ phase on the metastable pitting as a precursor of stable pitting corrosion and also on the progress of stale pitting of the 25Cr-7Ni-3Mo-0.25N duplex stainless steel were investigated in chloride solution. Electrochemical potential and current noises of the alloy were measured in 10 % ferric chloride solution ($FeCl_3$) with zero resistance ammeter (ZRA), and then analyzed by power spectral density (PSD) and by corrosion admittance ($A_c$) spectrum. With aging at $850^{\circ}C$, the passive film of the alloy was found to get significantly unstable as represented by power spectral density (PSD) and a transition from metastable pitting state to stable one was observed. In the corrosion admittance spectrum, the number of negative $A_c$ corresponding to the state of localized corrosion increased with aging, suggesting that the precipitation of $\sigma$ phase considerably degraded the passive film by depleting Cr and Mo around it at $\alpha/\sigma$ or $\gamma/\sigma$ phase boundaries, thereby leading to the initiation of the pitting corrosion. However, the Cr and Mo at $\alpha/\sigma$ or $\gamma/\sigma$ phase boundaries which were once depleted due to the precipitation of the $\sigma$ phase were partly replenished by the diffusion of Cr and Mo from the surrounding matrix with aging time longer. The initiation of pitting seems to be associated with the precipitation density of the $\sigma$ phase with an effective size needed to induce the sufficient depletion of Cr and Mo around it.

• 대한의용생체공학회:의공학회지
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• 제30권4호
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• pp.327-332
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• 2009

In this paper, new index was developed to estimate the depth of anesthesia during general anesthesia using EEG. Analysis of the power spectral density(PSD) of EEG was used to develop new parameters because EEG signal tends to have slow wave during anesthesia. Classifier for index creator was developed by using SEF, BDR and BTR parameters, which are calculated by power spectral density. EEG data were obtained from 7 patients (ASA I, II) during general anesthesia with Sevoflurane. The anesthetic depth evaluation indexes ranged from 0 to 100. The average were $86.05{\pm}10.1$, $36.98{\pm}20.2$, $15.33{\pm}13.6$, $50.87{\pm}16.5$ and $87.72{\pm}11.7$ for the states of pre-operation, induction of anesthesia, operation, awaked and post-operation, respectively. The results show that while the depth of anesthesia was evaluated, more accurate information can be provided for anesthetician.

• 설비공학논문집
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• 제10권5호
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• pp.619-629
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• 1998

An experimental work was conducted to investigate a feasibility of simultaneous measurement of gas-liquid two-phase flowrates with double orifice plates using air and water. The tests were carried out under the atmospheric pressure and at the ambient temperature using two different tube sizes. Qualities of an air-water flow in the present study have values less than 0.1 and thus the mixed flow showed bubbly, plug, slug flow regimes. The probability density function (PDF) and the power spectral density function (PSDF) of the instantaneous pressure drop traces for the flow regimes were obtained. It is found that some distinctive features exist in the distribution of these functions, depending upon the two-phase flow pattern. The time-averaged value of the instantaneous pressure drop increases with increasing gas and liquid flowrates, showing a single-valued function for the total mass flowrate and the quality. It is also found that the two-phase discharge coefficient exhibits a consistent trend for variation of dimensionless parameters such as the superficial velocity ratio and the gas Reynolds number. The results indicate that simultaneous measurement of two-phase flowrate may be possible based upon a statistical analysis of the instantaneous pressure drop curves monitored using double orifice plates.

• 천문학회지
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• 제37권5호
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• pp.563-570
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• 2004

Turbulence is a crucial component of dynamics of astrophysical fluids dynamics, including those of ISM, clusters of galaxies and circumstellar regions. Doppler shifted spectral lines provide a unique source of information on turbulent velocities. We discuss Velocity-Channel Analysis (VCA) and its offspring Velocity Coordinate Spectrum (VCS) that are based on the analytical description of the spectral line statistics. Those techniques are well suited for studies of supersonic turbulence. We stress that a great advantage of VCS is that it does not necessary require good spatial resolution. Addressing the studies of mildly supersonic and subsonic turbulence we discuss the criterion that allows to determine whether Velocity Centroids are dominated by density or velocity. We briefly discuss ways of going beyond power spectra by using of higher order correlations as well as genus analysis. We outline the relation between Spectral Correlation Functions and the statistics available through VCA and VCS.

• 대한기계학회논문집
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• 제18권1호
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• pp.166-174
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• 1994

A critical evaluation is made of the spectral bias which occurs in the use of a laser doppler velocimeter(LDV). Two processing algorithms are considered for spectral estimates: the sample and hold interpolation method(SH) and the nonuniform Shannon reconstruction technique(SR). Assessment is made of these for varying data densities $(0.05{\le}d.d.{\le}5)$ and turbulence levels(t.i.=30%, 100%). As an improved version of the spectral estimator, the utility of POCS (the projection onto convex sets) has been tested in the present study. This algorithm is found useful to be in the region when $d.d.{\gep}3.$

• Earthquakes and Structures
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• 제5권4호
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• pp.439-459
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• 2013

Main objective of the present study is to determine the statistical properties and suitable probability distribution functions of spectral displacements from nonlinear static and nonlinear dynamic analysis within the frame work of Monte Carlo simulation for typical low rise and high rise RC framed buildings located in zone III and zone V and designed as per Indian seismic codes. Probabilistic analysis of spectral displacement is useful for strength assessment and loss estimation. To the author's knowledge, no study is reported in literature on comparison of spectral displacement including the uncertainties in capacity and demand in Indian context. In the present study, uncertainties in capacity of the building is modeled by choosing cross sectional dimensions of beams and columns, density and compressive strength of concrete, yield strength and elastic modulus of steel and, live load as random variables. Uncertainty in demand is modeled by choosing peak ground acceleration (PGA) as a random variable. Nonlinear static analysis (NSA) and nonlinear dynamic analysis (NDA) are carried out for typical low rise and high rise reinforced concrete framed buildings using IDARC 2D computer program with the random sample input parameters. Statistical properties are obtained for spectral displacements corresponding to performance point from NSA and maximum absolute roof displacement from NDA and suitable probability distribution functions viz., normal, Weibull, lognormal are examined for goodness-of-fit. From the hypothesis test for goodness-of-fit, lognormal function is found to be suitable to represent the statistical variation of spectral displacement obtained from NSA and NDA.

• ETRI Journal
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• 제36권1호
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• pp.42-50
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• 2014

Orthogonal frequency division multiplexing (OFDM) is a modulation technique that allows the transmission of high data rates over wideband radio channels subject to frequency selective fading by dividing the data into several narrowband and flat fading channels. OFDM has high spectral efficiency and channel robustness. However, a major drawback of OFDM is that the peak-to-average power ratio (PAPR) of the transmitted signals is high, which causes nonlinear distortion in the received data and reduces the efficiency of the high power amplifier in the transmitter. The most straightforward method to solve this problem is to use a nonlinear mapping algorithm to transform the signal into a new signal that has a smaller PAPR. One of the latest nonlinear methods proposed to reduce the PAPR is the $L_2$-by-3 algorithm, which is based on the discrete sliding norm transform. In this paper, a new algorithm based on the $L_2$-by-3 method is proposed. The proposed method is very simple and has a low complexity analysis. Simulation results show that the proposed method performs better, has better power spectral density, and is less sensitive to the modulation type and number of subcarriers than $L_2$-by-3.

• Structural Engineering and Mechanics
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• 제28권4호
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• pp.387-410
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• 2008

The fatigue damage accumulation rates of horizontally curved thin walled box-girder bridge have been estimated from vehicle-induced dynamic stress history using rain flow cycle counting method in the time domain approach. The curved box-girder bridge has been numerically modeled using computationally efficient thin walled box-beam finite elements, which take into account the important structural actions like torsional warping, distortion and distortional warping in addition to the conventional displacement and rotational degrees of freedom. Vehicle model includes heave-pitch-roll degrees of freedom with longitudinal and transverse input to the wheels. The bridge deck unevenness, which is taken as inputs to the vehicle wheels, has been assumed to be a realization of homogeneous random process specified by a power spectral density (PSD) function. The linear damage accumulation theory has been applied to calculate fatigue life. The fatigue life estimated by cycle counting method in time domain has been compared with those found by estimating the PSD of response in frequency domain. The frequency domain method uses an analytical expression involving spectral moment characteristics of stress process. The effects of some of the important parameters on fatigue life of the curved box bridge have been studied.