• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.4
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• pp.178-187
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• 2003

In this study, ventilation flow rate and pressure rise through a tunnel are simulated numerically using computational fluid dynamics (CFD) for various conditions such as roughness height of the surface of tunnel, swirl angle and hub/tip ratio of jet fan, and entrance and exit effects. By using a modified wall function, friction factor can be predicted with respect to the Moody chart within 10% of error for the circular pipe flow and 15% for the present tunnel. For more accurate design, the effect of the swirl angle and hub/tip ratio of jet fan, which is not included in the theoretical equation of pressure rise by jet fan needs to be considered.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.12
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• pp.4099-4113
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• 2022

In this paper, we propose improved maximum access delay time, noise variance, and power delay profile (PDP) estimation schemes for orthogonal frequency division multiplexing (OFDM) system in multipath fading channels. To this end, we adopt the approximate maximum likelihood (ML) estimation strategy. For the first step, the log-likelihood function (LLF) of the received OFDM symbols is derived by utilizing only the cyclic redundancy induced by cyclic prefix (CP) without additional information. Then, the set of the initial path powers is sub-optimally obtained to maximize the derived LLF. In the second step, we can select a subset of the initial path power set, i.e. the maximum access delay time, so as to maximize the modified LLF. Through numerical simulations, the benefit of the proposed method is verified by comparison with the existing methods in terms of normalized mean square error, erroneous detection, and good detection probabilities.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.5 no.1
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• pp.33-44
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• 2012

A class of recurrent neural networks is proposed and proven to be capable of identifying any discrete-time dynamical system. The applications of the proposed network are addressed in the encoding, identification, and extraction of finite state automata. Simulation results show that the identification of finite state automata using the proposed network, trained by the hybrid greedy simulated annealing with a modified error function in the learning stage, exhibits generally better performance than other conventional identification schemes.

• The Journal of Korean Physical Therapy
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• v.21 no.1
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• pp.41-48
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• 2009

Purpose: The examine the Reliability and Validity of the modified Emory Functional Ambulation Profile (mEFAP), Tinetti. Gait (TG), Timed Up & Go Tes t (TUG), Comfortable Gait Speed (CGS), Berg Balance Scale (BBS) in assessing gait function and balance in elderly person. Methods: The 45 community-dwelling subjects were participated in this study. Reliability was determined by intra-class correlation coefficient (ICC$_{3,1}$), Bland and Altman method (Standard Error of Measurement (SEM), Smallest Real Difference (SRD)). Results: Validity was examined by correlation the mEFAP, TG, TUG, CGS, BBS. The intra-rater reliability were High (ICC$_{3,1}$ : mEFAP=0.95, TG=0.96, TUG=0.94, CGS=0.96, BBS=0.92) and Absolute reliability were excellent (SEM: mEFAP=1.90, TG=0.21, TUG=0.28 CGS=0.25, BBS=0.52), (SRD: mEFAP=5.26, TG=0.58, TUG=0.77, CGS=0.69, BBS=1.44). There were significant correlations between assessment tool (r=.0.58$\sim$0.78, p<0.01) indicating good validity. Our results provide strong evidence that the assessment tool has good reliability, validity for assessing elderly person undergoing rehabilitation. Conclusion: The gait assessment tool is a useful scale for measuring walking function and recovery in elderly person.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.195-200
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• 2006

Laboratory creep experiments show that compaction of unconsolidated shale is an irrecoverable process caused by viscous time-dependent deformation. Using Perzyna's viscoplasticity framework combined with the modified Cam-clay theory, we found the constitutive equation expressed in the form of strain rate as a power law function of the ratio between the sizes of dynamic and static yield surfaces. We derived the volumetric creep strain at a constant hydrostatic pressure level as a logarithmic function of time, which is in good agreement with experimental results. The determined material constants indicate that the yield stress of the shale increases by 6% as strain rate rises by an order of magnitude. This demonstrates that the laboratory-based prediction of yield stress (and porosity) may result in a significant error in estimating the properties in situ.

• Journal of Institute of Control, Robotics and Systems
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• v.16 no.5
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• pp.415-419
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• 2010

A variety of methods for sound source localization have been developed and applied to several applications such as noise detection system, surveillance system, teleconference system, robot auditory system and so on. In the previous work, we proposed the sound source localization using the spatially mapped GCC functions based on TDOA for robot auditory system. Performance of the proposed one for the noise effect and estimation resolution was verified with the real environmental experiment under the single source assumption. However, since multi-talker case is general in human-robot interaction, multiple source localization approaches are necessary. In this paper, the proposed localization method under the single source assumption is modified to be suitable for multiple source localization. When there are two sources which are correlated, the spatially mapped GCC function for localization has three peaks at the real source locations and imaginary source location. However if two sources are uncorrelated, that has only two peaks at the real source positions. Using these characteristics, we modify the proposed localization method for the multiple source cases. Experiments with human speeches in the real environment are carried out to evaluate the performance of the proposed method for multiple source localization. In the experiments, mean value of estimation error is about $1.4^{\circ}$ and percentage of multiple source localization is about 62% on average.

• Journal of Power Electronics
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• v.6 no.3
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• pp.235-244
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• 2006

Recently, speed sensorless vector control for synchronous reluctance motors (SYRMs) has deserved attention because of its advantages. Although rotor angle calculation using flux estimation is a straightforward approach, the DC offset can cause an increasing pure integrator error in this estimator. In addition, this method is affected by parameter fluctuation. In this paper, to control the motor at the low speed region, a modified programmable cascaded low pass filter (MPCPLF) with sensorless online parameter identification based on a block pulse function is proposed. The use of the MPCLPF is suggested because in programmable, cascade low pass filters (PCLPF), which previously have been applied to induction motors, the drift increases vastly wl)en motor speed decreases. Parameter identification is also used because it does not depend on estimation accuracy and can solve parameter fluctuation effects. Thus, sensorless speed control in the low speed region is possible. The experimental system includes a PC-based control with real time Linux and an ALTERA Complex Programmable Logic Device (CPLD), to acquire data from sensors and to send commands to the system. The experimental results show the proposed method performs well, speed and angle estimation are correct. Also, parameter identification and sensorless vector control are achieved at low speed, as well as, as at high speed.

• Current Optics and Photonics
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• v.6 no.3
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• pp.244-251
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• 2022

We introduce a spectral reconstruction method to enhance the spectral resolution in a static modulated Fourier-transform spectrometer. The optical-path difference and the interferogram in the focal plane, as well as the relationship of the interferogram and the spectrum, are discussed. Additionally, for better spectral reconstruction, applications of phase-error correction and apodization are considered. As a result, the transfer function of the spectrometer is calculated, and then the spectrum is reconstructed based on the relationship between the transfer function and the interferogram. The spectrometer comprises a modified Sagnac interferometer. The spectral reconstruction is conducted with a source with central wave number of 6,451 cm^-1 and spectral width of 337 cm^-1. In a conventional Fourier-transform method the best spectral resolution is 27 cm^-1, but by means of the spectral reconstruction method the spectral resolution improved to 8.7 cm^-1, without changing the interferometric structure. Compared to a conventional Fourier-transform method, the spectral width in the reconstructed spectrum is narrower by 20 cm^-1, and closer to the reference spectrum. The proposed method allows high performance for static modulated Fourier-transform spectrometers.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.2
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• pp.22-28
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• 2007

High PAPR (peak-to-average power ratio) is a major drawback of OFDM (orthogonal frequency division multiplexing) signals. In this paper, a modified SLM (selective mapping) technique that uses erasure decoding of RS (Reed-Solomon) codes is presented. At the transmitter a set of phase sequences are multiplied such that some portions of check symbols in RS-coded OFDM data blocks are phase-rotated. At the receiver, RS decoding is performed with the phase-rotated check symbols being treated as erasures. Hence, there is no need to send side information about the phase sequence selected to transmit for the lowest PAPR. In addition, the estimation process for the selected phase sequence is no longer needed at the receiver, leading to improvement in terms of complexity and performance. To evaluate the performance of this technique, the CCDF (complementary cumulative distribution function) of PAPR, the BER (bit error rate) and the decoding failure probability are compared with those of the previous SLM techniques.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.6
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• pp.563-571
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• 2010

The GPS satellite has three or four atomic clocks that consist of cesiums and rubidiums and the NANU messages can be used to identify the kind of the onboard atomic clock because they classify the clock type on a daily basis. In this study, for long-term analysis of the GPS satellite clock behavior, we extracted satellite clock errors for every PRN from years 2001 through 2009 using the SP3 files that are provided by the IGS. As a result, the cesium clock offsets usually have a linear trend of drifting. On the other hand, rubidium offsets show curvilinear variations in general, even though they cannot be represented as anyone specific polynomial function. For short-term analysis, we extracted satellite clock errors for each PRN for a week-long period using the CLK files that are also provided by the IGS and curve-fitted them with first-order and second-order polynomial functions. In cases of cesium clock errors, they were well-represented by first-order polynomial functions and rubidium clock errors were similar with second-order polynomials. However, some of rubidium clock errors could not be represented as any polynomial fitting function. To analyze the characteristic of GPS satellite by each block and atomic clock, we applied Modified Allan Deviation criterion to the dataset from years 2007 and 2010. We found that the Modified Allan Deviation characteristics changed significantly according the block and atomic clock type.