• Progress in Superconductivity
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• v.14 no.1
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• pp.1-10
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• 2012

We fabricated a closed coils by using resistive-joint method and the joint resistance of the coils were estimated by field decay technique in liquid nitrogen. We used the Runge-kutta method for the numerical analysis to calculate the decay properties. The closed coil was wound by $(Bi,Pb)_2Sr_2Ca_2Cu_3O_x$/Ag tape. Both ends the tape were overlapped and soldered to each other. The current was induced in a closed coils by external magnetic flux density. Its decay characteristic was observed by means of measuring the magnetic flux density generated by induced current at the center of the closed coil with hall sensor. The joint resistance was calculated as the ratio of the inductance of the loop to the time constants. The joint resistances were evaluated as a function of critical current of loop, contact length, sweep time, and external magnetic flux density in a contact length of 7 cm. It was observed that joint resistance was dependent on contact length of a closed coil, but independent of critical current, sweep time, and external magnetic flux density. The joint resistance was measured to be higher for a standard four-probe method, compared with that for the field decay technique. This implies that noise of measurement in a standard four-probe method is larger than that of field decay technique. It was estimated that joint resistance was $8.0{\times}10^{-9}{\Omega}$ to $11.4{\times}10^{-9}{\Omega}$ for coils of contact length for 7 cm. It was found that 40Pb/60Sn solder are unsuitable for persistent mode.

• Journal of Electrical Engineering and Technology
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• v.11 no.2
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• pp.529-536
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• 2016

In this paper we proposed an unsupervised algorithm to estimate the reverberation time (RT) directly from the reverberant speech signal. For estimation process we use maximum likelihood estimation (MLE) which is a very well-known and state of the art method for estimation in the field of signal processing. All existing RT estimation methods are based on the decay rate distribution. The decay rate can be obtained either from the energy envelop decay curve analysis of noise source when it is switch off or from decay curve of impulse response of an enclosure. The analysis of a pre-existing method of reverberation time estimation is the foundation of the proposed method. In one of the state of the art method, the reverberation decay is modeled as a Laplacian distribution. In this paper, the proposed method models the reverberation decay as a Gamma distribution along with the unification of an effective technique for spotting free decay in reverberant speech. Maximum likelihood estimation technique is then used to estimate the RT from the free decays. The method was motivated by our observation that the RT of a reverberant signal when falls in specific range, then the decay rate of the signal follows Gamma distribution. Experiments are carried out on different reverberant speech signal to measure the accuracy of the suggested method. The experimental results reveal that the proposed method performs better and the accuracy is high in comparison to the state of the art method.

• Progress in Superconductivity and Cryogenics
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• v.22 no.3
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• pp.13-19
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• 2020

This study presents the experiment and simulation results on the magnetic field response and electrical stability behaviors of no-insulation (NI) and metal insulation with stainless steel tape (MI-SS) which wound in form of racetrack type coils. First of all, the structural design of the racetrack type bobbin was shown along with its parameters. Then, the current-voltage tests were carried out to measure the critical current of both test coils. Also, the sudden discharging and charging tests were performed in the steady state to estimate the decay field time and magnetic field response, respectively. Finally, the overcurrent tests were conducted in the transient state to investigate the electrical stability of these test coils. Based on the experimental results, the contact surface resistances were calculated and applied to the field coils (FCs) of 10-MW-class second generation high temperature superconducting generator (2G HTSG) used in wind offshore environment. The charging delay time and electrical stability for NI and MI-SS HTS FCs of 10-MW-class 2G HTSG are analyzed by the equivalent circuit model and the key parameters which were obtained from the electromagnetic finite element analysis results.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.47.1-47.1
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• 2013

Supersonic turbulence is believed to decay rapidly within a flow crossing time irrespective of the degree of magnetization. However, this consensus of decaying magnetohydrodynamic (MHD) turbulence relies on local isothermal simulations, which are unable to investigate the role of global magnetic fields and structures. Utilizing three-dimensional MHD simulations including interstellar cooling and heating, we investigate decaying MHD turbulence within cold neutral medium sheets embedded in warm neutral medium. Early evolution is consistent with previous studies characterized rapid decay of turbulence with the decaying time shorter than a flow crossing time and power-law temporal decay of turbulent kinetic energy with slope of -1. If initial magnetic fields are strong and perpendicular to the sheet, however long term evolutions of kinetic energy shows that a significant amount of turbulent energy still remains even after ten flow crossing times, and decaying rate is reduced as field strengths increase. We analyse power spectra of remaining turbulence to show that incompressible, in-plane motions dominate.

• Ocean and Polar Research
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• v.25 no.1
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• pp.63-74
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• 2003

The build-up of the heat field in shallow coastal water due to a point source has been investigated using an analytical solution of a time-integral form derived by extending the solutions by Holley(1969) and also presented in Harleman (1971). The uniform water depth is assumed with non-isotropic turbulent dispersion. The alongshore-flow is assumed to be uni-directional, spatially uniform and oscillatory. Due to the presence of the oscillatory alongshore-flow, the heat build-up occurs in an oscillatory manner, and the excess temperature thereby fluctuates in that course and even in the quasi-steady state. A series of calculations reveal that proper choices of the decay coefficient as well as dispersion coefficients are critical to the reliable prediction of the excess temperature field. The dispersion coefficients determine the absolute values of the excess temperature and characterize the shoreline profile, particularly within the tidal excursion distance, while the decay coefficient determines the absolute value of the excess temperature and the convergence rate to that of the quasi-steady state. Within the e-folding time scale $1/k_d$ (where $k_d$ is the heat decay coefficient), heat build-up occurs more than 90% of the quasi-steady state values in a region within a tidal excursion distance (L), while occurs increasingly less the farther we go to the downstream direction (about 80% at 1.25L, and 70% at 1.5L). Calculations with onshore and offshore discharges indicate that thermal spreading in the direction of the shoreline is reduced as the shoreline constraint which controls the lateral mixing is reduced. The importance of collecting long-term records of in situ meteorological conditions and clarifying the definition of the heat loss coefficient is addressed. Interactive use of analytical and numerical modeling is recommended as a desirable way to obtain a reliable estimate of the far-field excess temperature along with extensive field measurements.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.05a
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• pp.68-71
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• 1993

In this study, decay time and frquency response characteristics of Self-Integrating Magnetic Sensor were investigated, decay time is 4.4[ms], frequency band that could be measuring is from 40[Hz] to 1[kHz]. The magnetic field components produced by operation of electric machines is measured and analyzed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.11
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• pp.1309-1317
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• 2007

In this paper, the Induced voltage on transmission line by lightning was calculated using FDTD method and the lightning parameters such as peak voltage, rise time, and decay time for the lightning location and line length were analyzed. To verify the results, lightning induced voltage was measured in the field using real telecommunication line. Results from the collected data were compared with the calculated results. It was found that the rise time and the decay time were increased as the line length and the distance between the line and lightning location were increased. Also, the peak voltage was affected more by the overhead line length than by the total line length, while the rise time and the decay time were more affected by the total line length.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.291-293
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• 2002

In this paper, we fabricated a persistent current mode magnet using Bi-2223 HTS tapes. The coil system consists of double pancake magnet and a persistent current switch and jointed them with solder. Persistent current mode operation of the system was measured experimentally by the decay behavior of the current. We found that resistive component of the system including flux flow resistance lead the exponentially field decay with time.

• Journal of the Korean Society of Tobacco Science
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• v.18 no.2
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• pp.170-176
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• 1996

This paper describes the generation and decay phenomena of gas, vapor and particulate phase components of environmental tobacco smoke in 18 m3 controlled experimental atmosphere chamber. Real time-weighted average concentration ratios of markers were determinated at no ventilation rates and sampling durations of starting to smoking 45 min. Average concentration of major ETS markers was no significant on the mainstream smoke contents of commercial cigarette and decay ratios were dependent on first order kinetic. RSP/nicotine, solanesol and 3-EP were good predictors of ETS concentration in the public indoor field. The concentration ratio of vapor phase and particulate phase components is highly variable to assessment of indoor air quality with ETS. Key words : ETS, chamber study, ETS markers.

• Progress in Superconductivity
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• v.12 no.2
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• pp.82-87
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• 2011

We studied the trapped field properties of bulk Y-Ba-Cu-O superconductors by applying 3 T of the permanent or $Nb_3Ti$ superconducting magnet. The 28 mm circular type of YBCO bulk superconductor was prepared and then hole at the center of bulk, parallel to the c-axis, was mechanically drilled. Typical size of hole in YBCO bulk was 10 mm in diameter. In order to examine the trapped field variation in terms of different impregnated materials, a hole in YBCO bulk was filled with resin and indium respectively. The trapped field decay due to flux flow was determined in terms of time. Our preliminary result indicates the trapped field value measured on the YBCO without hole after 30 minute by applying 3 T, was 6,500 G, which is much higher than that, 4,500 G, measured on YBCO with hole. Also, we confirmed that the tendency of a trapped field decrement with time was almost the same regardless of the impregnated materials in YBCO.