• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.4
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• pp.406-412
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• 2009

In this work, a new method to obtain the effective ground conductivity value in the middle frequency band where the informations of soil characteristics are insufficient was proposed. The proposed method obtained the effective ground conductivity values with the measured field strength from sea reference stations and general attenuation model in the middle frequency band. In addition, the proposed method used statistical method to minimize the error between the measurements and the predictions. Then, the effective ground conductivity in Korea peninsular was obtained by using the proposed method. Finally, it was verified that the effective ground conductivity using the proposed method is useful to predict electric field strength in the middle frequency band.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.4
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• pp.598-603
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• 2003

This paper presents a sub-band feature extraction approach in which the feature extraction method in the individual frequency sub-bands is determined in terms of speech recognition accuracy. As in the multi-band paradigm, features are extracted independently in frequency sub-regions of the speech signal. Since the spectral shape is well structured in the low frequency region, the all pole model is effective for feature extraction. But, in the high frequency region, the nonparametric transform, discrete cosine transform is effective for the extraction of cepstrum. Using the sub-band specific feature extraction method, the linguistic information in the individual frequency sub-bands can be extracted effectively for automatic speech recognition. The validity of the proposed method is shown by comparing the results of speech recognition experiments for our method with those obtained using a full-band feature extraction method.

• The Journal of Korean Physical Therapy
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• v.27 no.3
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• pp.129-134
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• 2015

Purpose: The purpose of this study was to determine the influence of WBV exercise on CMJ and quadriceps muscle activation according to different frequency of vibration in soccer player and also to find effective frequency for leading appropriate treatment reaction. Methods: Thirty three subjects were randomly divided into three groups: the three groups are WBV group using 20 Hz frequency, WBV group using 30 Hz frequency and squat exercise group according to training method. The exercise program was conducted for six weeks. Subjects were measured on CMJ and quadriceps muscle activation. Results: Significant difference in CMJ was observed in the group I, II compared with the group III (p<0.05). Results of post-hoc, showed a significant difference in CMJ in on group I, II compared with the group III, but no a statistically significant difference between group I and II. Significant difference in quadriceps muscle activation was observed in the group I, II compared with the group III (p<0.05, p<0.01). Results of post-hoc, significant difference in quadriceps muscle activation in on group I, II compared with the group III and significant difference between group I and group II. Conclusion: This research intervened WBV for soccer players and compared the differences of CMJ and quadriceps muscle activation; as a result of the effective frequency for improving performance, there is a significant difference in CMJ and quadriceps muscle activation of WBV group with comparison of control group; and it was proved that WBV is effective using 30 Hz frequency for improving quadriceps muscle activation.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.13-16
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• 2000

This paper introduces a more effective usage of the limited OVSF cod in compressed mode which is used during inter-frequency/inter-system handover in UTRA(Universal mobile telecommunications system) Terrestrial Radio Access). The usager is to use dynamic common channel which is shared by several users during the compressed mode.

• Journal of Industrial Technology
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• v.22 no.B
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• pp.169-173
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• 2002

In this paper, we discussed an effective VDSL frequency plan for symmetric 10MDSL service. The frequency plan 998 and plan 997 for asymmetric VDSL services have been not optimally designed for 10MDSL services. To obtain the reaches and data rates of 10MDSL, we proposed two frequency allocation schemes : Static method and dynamic method. We can select frequency bands with their fixed boundaries in static method while with their variable boundaries in dynamic method. To show the effectiveness of our proposed methods, we performed some simulations about plan 997 and plan 998, new static method, and new dynamic method. According to the simulation results, the proposed dynamic method can provide the best data rates and reaches for 10 Mbps symmetric VDSL services.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.824-829
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• 1994

High-frequency and complex vibration ultrasonic wire bonding systems are propsed and their welding characteristic are studied. Ultrasonic wire bonding is used widely for joining thin connecting wire of various electronic devices including IC or LSI. Conventional bonding systems use vibration frequency of 40 or 60 kHz and linear vibration welding tips. Complex vibration welding tip which vibrates in elliptical to circular or rectangular to square in the same or different frequency is effective to join welding specimens in shorter welding time and under smaller vibration amplitude, and furthermore high-frequency systems such as 90, 120, 190 kHz are also significantly effective. High-frequency and complex vibration welding system of 90, 120 and 190 kHz are designed. Welding characteristics of these systems are found very superior than a conventional system. Welding specimens of aluminum wire of 0.1mm diameter are successfully.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.395-398
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• 1999

In ac PDP(plasma Display Panel), the discharge characteristics is very important to display clear images. In this paper, we have studied the measurement of voltage transfer curves which show the discharge characteristics in AC PDP. The change of the effective wall capacitance during a discharge is also studied. These depend on lateral spreading of charge distribution and the strength of the discharge. As a parameter of the frequency, we observed the effects of the frequency in voltage transfer curves and in effective wall capacitance changes. As frequency increases, minimum sustain voltage and firing voltage decrease. In upper region of gap voltage the chance of the effective wall capacitance is independent of frequency.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.5
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• pp.207-214
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• 2004

This paper presents the characteristics of transient and effective impulse impedances for deeply driven grounding electrodes used in soil with high resistivity or in downtown areas. The laboratory test associated with the time domain performance of grounding piles subjected to a lightning stroke current has been carried out using an actual-sized model grounding system. The ground impedances of the deeply driven ground rods and grounding pile under impulse currents showed inductive characteristics, and the effective impulse ground impedance owing to the inductive component is higher than the power frequency ground impedance. Both power frequency ground impedance and effective impulse ground impedance decrease upon increasing the length of the model grounding electrodes. Furthermore, the effective impulse ground impedances of the deeply driven grounding electrodes are significantly amplified in impulse currents with a rapid rise time. The reduction of the power frequency ground impedance is decisive to improve the impulse impedance characteristics of grounding systems.

• Journal of Communications and Networks
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• v.18 no.5
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• pp.773-783
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• 2016

Both coordinated multi-point transmission and frequency reuse are effective approaches to mitigate inter-cell interference and improve network coverage. The motivation of this work is to explore the manner to effectively utilize the spectrum resource by reasonably combining cooperation and frequency reuse. The $Mat{\acute{e}}rn$ cluster process, which is appropriate to model networks with hot spots, is used to model the spatial distribution of base stations. Two cooperative mechanisms, coherent and non-coherent joint transmission (JT), are analyzed and compared. We also evaluate the effect of multiple antennas and imperfect channel state information. The simulation reveals that the proposed approach to combine cooperation and frequency reuse is effective to improve the network coverage for users located at both the center and the boundary of the cooperative region.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1376-1385
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• 2017

This paper proposes a method for estimating the expected frequency of voltage swells caused by asymmetrical faults in a power system. Although voltage swell is less common than voltage sag, repeated swells can have severe destructive impact on sensitive equipment. It is essential to understand system performance related to voltage swells for finding optimal countermeasures. An expected swell frequency at a sensitive load terminal can be estimated based on the concept of an area of vulnerability (AOV) and long-term system fault data. This paper describes an effective method for calculating an AOV to voltage swells. Interval estimation for an expected swell frequency is also presented for effective understanding of system performance. The proposed method provides long-term performance evaluation of the frequency and degree of voltage swell occurrences.