• The Journal of the Acoustical Society of Korea
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• v.41 no.1
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• pp.38-44
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• 2022

Speech enhancement is performed to improve intelligibility and quality of the noise-corrupted speech. In this paper, speech enhancement performance was compared using different loss functions in time and frequency domains. This study proposes a combination of loss functions to utilize advantage of each domain by considering both the details of spectrum and the speech waveform. In our study, Scale Invariant-Source to Noise Ratio (SI-SNR) is used for the time domain loss function, and Mean Squared Error (MSE) is used for the frequency domain, which is calculated over the complex-valued spectrum and magnitude spectrum. The phase loss is obtained using the sin function. Speech enhancement result is evaluated using Source-to-Distortion Ratio (SDR), Perceptual Evaluation of Speech Quality (PESQ), and Short-Time Objective Intelligibility (STOI). In order to confirm the result of speech enhancement, resulting spectrograms are also compared. The experimental results over the TIMIT database show the highest performance when using combination of SI-SNR and magnitude loss functions.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.6
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• pp.642-653
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• 2008

This study deals with modeling of head-related transfer functions(HRTFs) using principal components analysis(PCA) in the time and frequency domains. Four PCA models based on head-related impulse responses(HRIRs), complex-valued HRTFs, augmented HRTFs, and log-magnitudes of HRTFs are investigated. The objective of this study is to compare modeling performances of the PCA models in the least-squares sense and to show the theoretical relationship between the PCA models. In terms of the number of principal components needed for modeling, the PCA model based on HRIR or augmented HRTFs showed more efficient modeling performance than the PCA model based on complex-valued HRTFs. The PCA model based on HRIRs in the time domain and that based on augmented HRTFs in the frequency domain are shown to be theoretically equivalent. Modeling performance of the PCA model based on log-magnitudes of HRTFs cannot be compared with that of other PCA models because the PCA model deals with log-scaled magnitude components only, whereas the other PCA models consider both magnitude and phase components in linear scale.

• Korean Journal of Applied Biomechanics
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• v.14 no.3
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• pp.83-98
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• 2004

The purpose of this study was to investigate the test-retest of plantar pressures using the F-Scan system over speeds and plantar regions. 6 healthy female subjects in 20's were recruited for the study. Plantar pressure measurements during locomotor activities can provide information concerning foot function, particularly if the timing and magnitude of the loading profile can be related to the location of specific foot structures such as the metatarsal heads. The Tekscan F-Scan system consists of a flexible, 0.18mm thick sole-shape having 1260 pressure sensors, the sensor insole was trimmed to fit the subjects' right. left shoes - sneakers shoes & dress shoes. It was calibrated by the known weight of the test subject standing on one foot. The Tekscan measurements show the insole pressure distribution as a function of the time. This finding has important implications for the development of plantar pressure test protocols where the function of the forefoot is important. According to the result of analysis it is as follows 1) Center of force trajectory in women's dress shoes display direct movement, compare with center of force trajectory in Sneaker shoes displays a little bit curved slow pronation movement. Sneaker shoes in forefoot part display very quick supination movement, therefore, this shoes effects negative effectiveness for ankle's stability Considering center of force trajectory analyzing the more center of force close straight line, the more movement can be quick movement for locomotion. For foot pressure distribution, center of force trajectory in locomotion is better to curved trajectory with pronation movement. So sneaker shoes style is good shoes considering center of pressure distribution trajectory compare with women's dress shoes. 2) Women's dress shoes increased peak pressure in medial, this is effected by high hill's height. The more increased women's dress shoes's height, the more women's peak pressure will increase, pronation can increase compare with before. Supination movement increase, this focused pressure in lateral, also, supination increased more. If the supination movement increased, foot pressure focused in lateral, therefore, it is appeared force distribution in gait direction. This is bad movement in foot's stability. 3) Women's dress shoes in landing phase displayed a long time, this is when women's dress shoes wear, gait movement is unbalance, so, landing phase displayed a long time. For compensation in gait, swing phase quick movement. 4) Women's dress shoes displayed peak pressure distribution in lateral of rearfoot part, Sneakers shoes displayed peak pressure distribution in medial of forefoot part. Its results has good impact absorption compare with women's dress shoes. In forefoot part, sneakers shoes has good propulsive force compare with women's dress shoes.

• The korean journal of orthodontics
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• v.26 no.3
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• pp.291-299
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• 1996

Orthodontic force is a mechanical stress controlling both of tooth movement and skeletal growth. The mechanical stress stimulate bone cells that may exert some influence on bone remodeling. The purpose of this study was to evaluate the difference in cellular activity depending on mechanical stresses such as compressive and tensile force by determining the alkaline phosphatase(ALP) activity. A clonal osteogenic cell line MC3T3-E1 was seeded into a 24-well plate($2{\times}10^4/well$). At the confluent phase, a continuous compressive hydrostatic pressure($25g/cm^2$, $300g/cm^2$) and continuous tensile hydrostatic pressure($-25g/cm^2$, $-300g/cm^2$) were applied for 4, 6, 10, 14, 18, 20 days respectively by a diaphgragm pump. At the end of the stimulation period, cell layers were prepared for ALP activity assay. The ALP activity of the compressive group increased more than that of the tensile group at same force magnitude, whereas the cells responded to a similar pattern regardless of the type of mechanical stress The ALP activity of the compressive and tensile group turned into the level of the control group as the length of time increased. These results indicated that a mechanical stress may be more effective on cellular activity during active cellular proliferation and differentiation periods. The time to achieve maximum ALP activity was delayed as the mechanical stress increased in both the compressive and the tensile group. Accordingly, the magnitude of the stress rather than the type of mechanical stress may have more influence on cellular activity.

• Korean Journal of Applied Biomechanics
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• v.34 no.2
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• pp.81-92
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• 2024

Objective: The purpose of this study was to analyze the impact acceleration, shock attenuation and biomechanical variables at various running speed. Method: 20 subjects (height: 176.15 ± 0.63 cm, weight: 70.95 ± 9.77 kg, age: 27.00 ± 4.65 yrs.) participated in this study. The subjects ran at four different speeds (2.5 m/s, 3.0 m/s, 3.5 m/s, 4.0 m/s). Three-dimensional accelerometers were attached to the distal tibia, sternum and head. Gait parameters, biomechanical variables (lower extremity joint angle, moment, power and ground reaction force) and acceleration variables (impact acceleration, shock attenuation) were calculated during the stance phase of the running. Repeated measures ANOVA was used with an alpha level of .05. Results: In gait parameters, decreased stance time, increasing stride length and stride frequency with increasing running speed. And at swing time 2.5 m/s and 4.0 m/s was decreased compared to 3.0 m/s and 3.5 m/s. Biomechanical variables statistically increased with increasing running speed except knee joint ROM, maximum ankle dorsiflexion moment, and maximum hip flexion moment. In acceleration variables as the running speed increased (2.5 m/s to 4.0 m/s), the impact acceleration on the distal tibia increased by more than twice, while the sternum and head increased by approximately 1.1 and 1.2 times, respectively. And shock attenuation (tibia to head) increased as the running speed increased. Conclusion: When running speed increases, the magnitude and increasing rate of sternum and head acceleration are lower compared to the proximal tibia, while shock attenuation increases. This suggests that limiting trunk movement and increasing lower limb movement effectively reduce impact from increased shock. However, to fully understand the body's mechanism for reducing shock, further studies are needed with accelerometers attached to more segments to examine their relationship with kinematic variables.

• Korean Journal of Radiology
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• v.24 no.6
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• pp.564-573
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• 2023

Objective: To investigate the feasibility of assessing the viscoelastic properties of the brain using magnetic resonance elastography (MRE) and a novel MRE transducer to determine the relationship between the viscoelastic properties and glymphatic function in neurologically normal individuals. Materials and Methods: This prospective study included 47 neurologically normal individuals aged 23-74 years (male-to-female ratio, 21:26). The MRE was acquired using a gravitational transducer based on a rotational eccentric mass as the driving system. The magnitude of the complex shear modulus |G^*| and the phase angle 𝛗 were measured in the centrum semiovale area. To evaluate glymphatic function, the Diffusion Tensor Image Analysis Along the Perivascular Space (DTI-ALPS) method was utilized and the ALPS index was calculated. Univariable and multivariable (variables with P < 0.2 from the univariable analysis) linear regression analyses were performed for |G^*| and 𝛗 and included sex, age, normalized white matter hyperintensity (WMH) volume, brain parenchymal volume, and ALPS index as covariates. Results: In the univariable analysis for |G^*|, age (P = 0.005), brain parenchymal volume (P = 0.152), normalized WMH volume (P = 0.011), and ALPS index (P = 0.005) were identified as candidates with P < 0.2. In the multivariable analysis, only the ALPS index was independently associated with |G^*|, showing a positive relationship (β = 0.300, P = 0.029). For 𝛗, normalized WMH volume (P = 0.128) and ALPS index (P = 0.015) were identified as candidates for multivariable analysis, and only the ALPS index was independently associated with 𝛗 (β = 0.057, P = 0.039). Conclusion: Brain MRE using a gravitational transducer is feasible in neurologically normal individuals over a wide age range. The significant correlation between the viscoelastic properties of the brain and glymphatic function suggests that a more organized or preserved microenvironment of the brain parenchyma is associated with a more unimpeded glymphatic fluid flow.

• Investigative Magnetic Resonance Imaging
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• v.22 no.4
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• pp.218-228
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• 2018

Purpose: The objective of this study is to determine the effect of physical changes on MR temperature imaging at 7.0T and to examine proton-resonance-frequency related changes of MR phase images and T1 related changes of MR magnitude images, which are obtained for MR thermometry at various magnetic field strengths. Materials and Methods: An MR-compatible capacitive-coupled radio-frequency hyperthermia system was implemented for heating a phantom and swine muscle tissue, which can be used for both 7.0T and 3.0T MRI. To determine the effect of flip angle correction on T1-based MR thermometry, proton resonance frequency, apparent T1, actual flip angle, and T1 images were obtained. For this purpose, three types of imaging sequences are used, namely, T1-weighted fast field echo with variable flip angle method, dual repetition time method, and variable flip angle method with radio-frequency field nonuniformity correction. Results: Signal-to-noise ratio of the proton resonance frequency shift-based temperature images obtained at 7.0T was five-fold higher than that at 3.0T. The T1 value increases with increasing temperature at both 3.0T and 7.0T. However, temperature measurement using apparent T1-based MR thermometry results in bias and error because B1 varies with temperature. After correcting for the effect of B1 changes, our experimental results confirmed that the calculated T1 increases with increasing temperature both at 3.0T and 7.0T. Conclusion: This study suggests that the temperature-induced flip angle variations need to be considered for accurate temperature measurements in T1-based MR thermometry.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.6
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• pp.490-494
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• 2020

Sulphur hexafluoride (SF₆) is mostly used as a current-insulating medium in gas-insulated switchgears (GIS), owing to its excellent dielectric strength and arc-extinguishing performance. The global warming potential (GWP) of SF₆, however, is 23,900 times that of CO₂, and its life time in the atmosphere is 3,200 years. For these reasons, new eco-friendly gases to replace SF₆ are required. In this study, the partial discharge (PD) characteristics of green gas for grid (g³) and dry air (N₂/O₂) were analyzed to compare with those of SF₆. A PD electrode system was designed to simulate the protrusion defect in GISs and fabricated for experimentation. To compare the PD characteristics of each gas, the discharge inception voltage (DIV), discharge extinction voltage (DEV), discharge magnitude, discharge pulse number, and phase pattern were analyzed. Results from this study are expected to provide fundamental materials for the design of eco-friendly GISs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.4
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• pp.319-324
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• 2011

This paper dealt with a partial discharge (PD) detection method for insulation diagnosis in cast-resin transformers. To detect PD pulse, a planar-capacitive probe was designed and fabricated. The probe has no insulation problem and can be installed on cast-resin transformers even in operation since it does not connect with high voltage conductor. The PD measurement system consists of the capacitive probe, a coupling network of 100 [kHz] low-cutoff frequency, and an amplifier with a gain of 40 [dB] and a frequency bandwidth of 500 [Hz]~45 [MHz]. A plane-needle and a plane-plane electrode system were fabricated to simulate insulation defects in a cast-resin transformer. Sensitivity of the PD measurement system, which is evaluated by a standard calibrator was 0.35 [mV/pC] for positive and 0.45 [mV/pC] for negative, respectively. The PD detection by the capacitive probe was less sensitive than that by a coupling capacitor according to IEC 60270, but we could analyze the magnitude and the phase distribution of PD pulse.

• Korean Journal of Applied Biomechanics
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• v.24 no.2
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• pp.95-101
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• 2014

The purpose of this study was to investigate the training and detraining effects of a 8-week water exercise on lower extremities coordination during obstacle gait in the female elderly. Eight elderly participants (age: $76.58{\pm}4.97$ yrs, height: $148.88{\pm}7.19$ cm, body mass: $56.62{\pm}6.82$ kg, and leg length: $82.36{\pm}2.98$ cm), who stayed at the Seoul K welfare center, were recruited for this study. All participants had no history of orthopedic abnormality within the past 1 year and completed the aquatic exercise program which lasted for 8 weeks. To identify the training and detraining effect of 8 weeks of water exercise, a 3-D motion analysis with 7 infrared cameras and one force plate sampling frequency set at 100 Hz and 1,000 Hz, respectively, was performed. A two-way ANOVA was performed to find training and detraining effects among diferent obstacle heights. In this study significant level was set at .05. Significant training effects of LTS (lead foot thigh and shank) coordination in all obstacle height were found (p<.05). It is also found that the training effect of LTS remained 37%, 58%, and 25% in obstacle height of 30%, 40%, and 50%, respectively. Lead foot showed the greater detraining effect of coordination compared with trail foot, and SF (shank and foot) coordination revealed better detraining effects of coordination compare with TS (thigh and shank) in both feet. Based on the findings, a 8 week water exercise give an positive effects to the elderly in terms of segment cooperation which potentially helps reducing their accident falls. The magnitude of detraining may also help the elderly to find the retraining moment.