• Bulletin of the Korean Chemical Society
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• v.19 no.12
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• pp.1359-1363
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• 1998

The p-fluorobenzyl radical was generated from the p-fluorotoluene and vibronically excited in a corona excited supersonic expansion with inert buffer gases. The vibronic emission spectra of the jet cooled p-fluorobenzyl radical in the D1 → D0 transition have been observed in the visible region. The spectra exhibit several low frequency sequence bands in the vicinity of the every strong vibronic band. The characteristics of the sequence bands have been examined by varying the experimental conditions such as carrier gas and nozzle size to identify the origin of the transition in the spectra.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.12
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• pp.1470-1481
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• 2008

A demand for spectrum resources, especially in the low frequency bands, is ever increasing with the development of mobile telecommunications and so is their economic value as other national resources. Also, development in mobile broadband require more bandwidth with excellent propagation characteristics, such as those frequencies in the 700/800/900 MHz bands. As a way to enhance the economic efficiency of using spectrum resources, many countries including the U.S., the U.K. and Japan, have recently focused on the refarming plan of the low frequency bands according to the transition from analogue to digital TV. By the way, as a result of WRC-07, those parts of the band $698{\sim}960\;MHz$ in Region 2 and the band $790{\sim}960\;MHz$ in Regions 1 and 3 which are allocated to the mobile service on a primary basis are identified for use by administrations wishing to implement International Mobile Telecommunications (IMT). Therefore, after analogue to digital television switchover, some administrations may decide to use all or parts of the band $698{\sim}806/862\;MHz$ for other services to which the band is allocated on a primary basis, in particular the mobile service for the implementation of IMT, while in other countries the broadcasting service will continue to operate in that band. And to conclude, bands already identified for IMT-2000 will also be able to be used for IMT. This work will help establish a policy direction for spectrum refarming in the low frequency bands in Korea(Rep. of).

• Electronics and Telecommunications Trends
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• v.38 no.1
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• pp.55-64
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• 2023

Recently, preparations for 6G have led to the increasing interest in integrated or hybrid communication networks considering low-orbit satellite communication networks with terrestrial mobile communication networks. In addition, the demand for frequency allocation for new mobile services from low-orbit small satellites to provide global internet of things (IoT) services is increasing. The operation of such satellites and terrestrial mobile communication networks may inevitably cause interference in adjacent bands and the same band frequency between satellites and terrestrial systems. Focusing on the results of the recent ITU-R WP4C meeting, this study introduces the current status of frequency sharing and interference issues between satellites and terrestrial systems, and frequency allocation issues for new mobile satellite operations. Coexistence and compatibility studies with terrestrial IMT in L band and 2.6 GHz band, operated by Inmassat and India, respectively, and a new frequency allocation study (WRC-23 AI 1.18) are carried out to reflect satellite IoT demand. For the L band, technical requirements have been developed for emission from IMT devices at 1,492 MHz to 1,518 MHz to bands above 1,518 MHz. Related studies in the 2 GHz and 2.6 GHz bands are not discussed due to lack of contributions at the recent meeting. In particular, concerning the WRC-23 agenda 1.18 study on the new frequency allocation method of narrowband mobile satellite work in the Region 1 candidate band 2,010 MHz to 2,025 MHz, Region 2 candidate bands 1,695 MHz to 1,710 MHz, 3,300 MHz to 3,315 MHz, and 3,385 MHz to 3,400 MHz, ITU-R results show no new frequency allocation to narrow mobile satellite services. Given the expected various collaborations between satellites and the terrestrial component are in the future, interference issues between terrestrial IMT and mobile satellite services are similarly expected to continuously increase. Therefore, participation in related studies at ITU-R WP4C and active response to protect terrestrial IMT are necessary to protect domestic radio resources and secure additional frequencies reflecting satellite service use plans.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.561-564
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• 1998

This paper evaluated autonomic nervous system function in 23 patients with syncope and a positive tilt test result, 21 with a negative test result, and 19 healthy controls. Indexes of heart rate variability were measured during supine resting, immediately afte rtilt-up, standing rsting, immediately before syncope and immediately after tiltdown. There were no significant differences among the groups in any of the indexes of heart rate varability over the 24-hour holter recordings. In patients with a positive tilt result, tilting gaused a decrease in low-frequency (LF) immediately before syncope and incsrease in high-frequency (HF) bands immediately before. In patients with a negative tilt result, tilting caused a decrease in low-frequency (LF) immediately before syncope and decrease in high-frequency (HF) bands immediately before, different from positive tilt results. Our findings showed that patients with vasovagal syncope have no chronic differences from normal subjects in autonomic nervous system activity, but that these patients respond differently to the orthostatic stimulus.

• KIEAE Journal
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• v.1 no.2
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• pp.47-54
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• 2001

Single sound absorbers such as porous materials, panels, and Helmholts resonators have limited performance with some extents of frequency region. For example, porous materials do not attenuate low frequency sounds, while panels do not absorb high frequency sounds. Composite absorption structure with coverings, porous materials, and air gaps are an alternative for wide band sound absorption. Slits, panels, perforated panels are those materials for coverings, glass wool, mineral wool, polyester, and polyurethane are frequently used porous materials. Air gap between the porous material and background surface is one of major factors which governs the absorption characteristics of composite absorption structures, especially in the low frequency area. Calculations and measurements show that the absorption coefficients of composite absorption structure, in mid and low frequency bands, are getting higher with increased air gaps. Perforated panels rather than slits and panels are good coverings with higher number as far as absorption coefficient is concerned. Perforated panels with porous materials and 37 cm of air gaps in background have high absorption coefficients for all frequency bands, above 0.7 to 1.0. All measurements are performed in reverberation chamber, Mokpo National University, according to ISO 354 and ISO 3382.

• Journal of Sensor Science and Technology
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• v.31 no.2
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• pp.120-124
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• 2022

With advancements in underwater stealth technology for naval vessels, new sensor configurations for detecting targets have been attracting increased attention. Latest underwater mines adopt multiple sensor configurations that include electric field sensors to detect targets and to help acquire accurate ignition time. An underwater electric field sensor consists of a pair of electrodes, signal processing unit, and preamplifier. For detecting underwater electric fields, the preamplifier requires low-noise amplification at ultra-low frequency bands. In this paper, the specific requirements for low-noise preamplifiers are discussed along with the experimental results of various setups of matched transistors and chopper stabilized operational amplifiers. The results showed that noise characteristics at ultra-low frequency bands were affected significantly by the voltage noise density of the chopper amplifier and the number of matched transistors used for differential amplification. The fabricated preamplifier was operated within normal design parameters, which was verified by testing its gain, phase, and linearity.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.2059-2064
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• 2004

Texture analysis is an important role for automatic visual insfection. This paper presents an application of wavelet extension and Gray level co-occurrence matrix (GLCM) for detection of defect encountered in textured images. Texture characteristic in low quality images is not to easy task to perform caused by noise, low frequency and small dimension. In order to solve this problem, we have developed a procedure called wavelet image extension. Wavelet extension procedure is used to determine the frequency bands carrying the most information about the texture by decomposing images into multiple frequency bands and to form an image approximation with higher resolution. Thus, wavelet extension procedure offers the ability to robust feature extraction in images. Then the features are extracted from the co-occurrence matrices computed from the sub-bands which performed by partitioning the texture image into sub-window. In the detection part, Mahalanobis distance classifier is used to decide whether the test image is defective or non defective.

• 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.

• Geosciences Journal
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• v.22 no.6
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• pp.1027-1039
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• 2018

Seismic attributes are often used to identify lithology and evaluate reservoir properties. However, interpretation based only on structural attributes and without knowledge of the Vp/Vs ratio can limit the ability to evaluate changes in heavy oil reservoirs. These limitations are often due to less obvious impedance differences. In order to investigate pieces of evidence of a heavy-oil shaly-sand reservoir from seismic data, besides geochemistry, we studied seismic attributes and characterized the reservoir using seismic stack data and well logging data. The study area was the Muglad rift basin in South Sudan. We conducted a seismic complex analysis to evaluate the target reservoir. To delineate the frequency responses of the different lithological units, we applied the spectral decomposition method to the target reservoir. The most unexpected result was continuous bands of strong seismic reflectors in the target reservoir, which extended across the borehole. Spectral decomposition analysis showed that the low-frequency zone of 25 Hz dominant frequency was consistent with instantaneous attributes. This approach can identify lithology, reveal frequency anomalies, and filter the stacked section into low- and high-frequency bands. The heavy-oil reservoir zones exhibited velocity attenuation and the amplitude was strongly frequency dependent.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.65-71
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• 2001

Absorbers such as porous materials and panels have limited absorption characteristics to some frequency bands. There is a need for absorbers with high absorption coefficients in a wide frequency ranges to make good response of room acoustics. This is almost impossible for a single absorption material. Composite absorption structure with cover, porous material. and air gap is known to have those wide frequency characteristics. In this basis. various composite absorption structures are measured and investigated as wide range absorption structures. Measurements are performed according to an international standard, ISO 354. Various surface types such as wooden slits, wood/steel perforated panels are selected as surface covers, and also various porous materials such as polyurethanes, polyesters, and glasswools are used inside the covers. Result shows that the area of void parts of surface materials is critical to high frequency absorptions, and thickness of air gaps are critical factor of the peak absorptions of low frequency bands.