• 한국통신학회:학술대회논문집
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• 한국통신학회 2004년도 하계종합학술발표회논문초록집
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• pp.212-212
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• 2004

• 대한기계학회논문집B
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• 제20권4호
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• pp.1501-1509
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• 1996

Differential pressure devices such as an orifice and Venturi are widely used in the measurement of flow rate of fluid mainly due to cost effectiveness and easy installation. In the current study, the viscoelastic effect on discharge and loss coefficients of those flow meters were investigated experimentally. Aqueous solutions of Polyacrylamide (200, 500, and 800 ppm) as viscoelastic fluids were used. Discharge coefficient of an orifice for viscoelastic fluids increased significantly up to approximately 15-20% when compared with that for water, while loss coefficient decreased up to 10-25% depending on the diameter ratio, .betha.. Also, pressure recovery for viscoelastic fluids was extended much longer than that for water. On the other hand, discharge and loss coefficients of Venturi for viscoelastic fluids were found to be strongly dependent on the Reynolds number. In both flow meters, the concentration effect for discharge and loss coefficients was not observed at more over than 200 ppm of aqueous solution. Conclusively, orifice and Venturi flow meters should be calibrated very carefully in the flow rate measurement for viscoelastic fluids.

• 한국통신학회논문지
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• 제23권8호
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• pp.2090-2095
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• 1998

본 논문에서는 한국내 인터넷상의 음성패킷손실을 측정하였고 패킷손실의 변화에 따른 명료도를 분석하였다. RTP를 기반으로 하는 실시간 전송프로토콜과 통화품질 평가법을 고찰하였으며 실험을 위하여 GSM과 RTP/UDP/IP를 이용한 실시간 음성통신 시스템을 구현하였다. 명료도 평가를 위하여 선택된 음절목록은 GSM에 의하여 실시간 코딩 및 압축되었으며 각 패킷은 패킷손실의 복원과 손실률 측정을 위하여 시퀀스번호를 갖고 있다. 한국내 인터넷 상의 7개 라우팅을 거친 전송 실험결과, 트래픽량에 따라 1.6%에서부터 22.5%까지의 패킷손실을 나타내었으며 시퀀스번호 재배열과 FEC 알고리즘을 통한 손실패킷의 복원률은 9%에서 35%까지 나타났고 패킷손실의 변화에 따른 단음절명료도와 2음절 이해도 평가결과는 표 4와 같다.

• Journal of Audiology & Otology
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• 제24권3호
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• pp.127-132
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• 2020

Background and Objectives: In this study, we compared the outcomes of patients with idiopathic sudden sensorineural hearing loss who underwent steroid treatment with or without hyperbaric oxygen (HBO) therapy and were followed-up in our clinic. Subjects and Methods: Patients were divided into two groups according to their treatment regimen. Steroid group received intravenous 1 mg/kg methylprednisolone which was due to be completed in 2-3 weeks with decreasing doses, and five doses of 0.5 mL intratympanic dexamethasone. Steroid+HBO group received the same steroid treatment with the addition of HBO therapy. The audiologic results of both treatment groups were compared after considering the patients' risk factors. Results: There was no significant difference between the steroid and Steroid+HBO groups in terms of hearing gain and degree of recovery, both at all degrees of hearing loss, and in severe and profound hearing loss. Hearing gain was similar when evaluated by audiogram type and admission time in both treatment groups. Conclusions: We found that the addition of HBO therapy to systemic plus intratympanic steroid treatment did not affect hearing gain at all degrees of hearing loss in this study. Furthermore, audiogram type and admission time did not affect hearing gain between the two groups.

• 대한청각학회지
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• 제24권3호
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• pp.127-132
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• 2020

Background and Objectives: In this study, we compared the outcomes of patients with idiopathic sudden sensorineural hearing loss who underwent steroid treatment with or without hyperbaric oxygen (HBO) therapy and were followed-up in our clinic. Subjects and Methods: Patients were divided into two groups according to their treatment regimen. Steroid group received intravenous 1 mg/kg methylprednisolone which was due to be completed in 2-3 weeks with decreasing doses, and five doses of 0.5 mL intratympanic dexamethasone. Steroid+HBO group received the same steroid treatment with the addition of HBO therapy. The audiologic results of both treatment groups were compared after considering the patients' risk factors. Results: There was no significant difference between the steroid and Steroid+HBO groups in terms of hearing gain and degree of recovery, both at all degrees of hearing loss, and in severe and profound hearing loss. Hearing gain was similar when evaluated by audiogram type and admission time in both treatment groups. Conclusions: We found that the addition of HBO therapy to systemic plus intratympanic steroid treatment did not affect hearing gain at all degrees of hearing loss in this study. Furthermore, audiogram type and admission time did not affect hearing gain between the two groups.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권4호
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• pp.1618-1637
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• 2018

By means of compressive sensing (CS) technique, this paper considers the collection of sensor data with spatiotemporal correlations in wireless sensor networks (WSNs). In energy-constrained WSNs, one-dimensional CS methods need a lot of data transmissions since they are less applicable in fully exploiting the spatiotemporal correlations, while the Kronecker CS (KCS) methods suffer performance degradations when the signal dimension increases. In this paper, an appropriate sensing matrix as well as an efficient sensing method is proposed to further reduce the data transmissions without the loss of the recovery performance. Different matrices for the temporal signal of each sensor node are separately designed. The corresponding energy-efficient data gathering method is presented, which only transmitting a subset of sensor readings to recover data of the entire WSN. Theoretical analysis indicates that the sensing structure could have the relatively small mutual coherence according to the selection of matrix. Compared with the existing spatiotemporal CS (CS-ST) method, the simulation results show that the proposed efficient measurement method could reduce data transmissions by about 25% with the similar recovery performance. In addition, compared with the conventional KCS method, for 95% successful recovery, the proposed sensing structure could improve the recovery performance by about 20%.

• Biotechnology and Bioprocess Engineering:BBE
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• 제2권2호
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• pp.117-121
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• 1997

Glutamic acid can be crystallized inside cation exchange column when displacer NaOH concentration is high enough to concentrate displaced glutamic acid beyond its solubility limit. Resulting crystal layer of glutamic acid was moved with liquid phase through the column, and thus could be eluted from the column and recovered in fraction collector. For the purpose of enhancing crystal recovery, effects of operating parameters on the crystal formation were investigated. The increase in the degree of crosslinking of resin favored crystal recovery because of its low degree of swelling. Higher concentration of displacer NaOH was advantageous. If NaOH concentration is too high, however, crystal recovery was lowered due to the solubility-enhancing effects of high pH and ionic strength. The decrease of mobile phase flow rate enhanced crystal recovery because enough time to attain local equilibrium could be provided, but film diffusion would control the overall crystal formation with extremely low flow rate. Lower temperature reduced solubility of glutamic acid and thus favored crystal formation unless the rate of ion exchange was severely reduced. The ion exchange operated by displacement mode coupled with crystallization was advantageous in reducing the burden of further purification steps and in preventing purity-loss resulted from overlapping between adjacent bands.

• Journal of Power Electronics
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• 제11권1호
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• pp.97-104
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• 2011

This paper proposes a new alternating current driving method for highly capacitive loads such as plasma display panels or piezoelectric actuators, etc. In the proposed scheme, a current balance transformer, which has two windings with the same turn-ratio, provides not only a resonance inductance for energy recovery but also a current balance among all of the switching devices of the driver for current stress reduction. The smaller conduction loss than conventional circuits occurs due to the dual conduction paths which are parallel each other in the current balance transformer. Also, the leakage inductances of the transformer are utilized as resonant inductors for energy recovery by the series resonance to the capacitive load. Furthermore, the resonance contributes to the small switching losses of the switching devices by soft-switching operation. To confirm the validity of the proposed circuit, prototype hardware with a 12-inch mercury-free flat fluorescent lamp is implemented. The experimental results are compared with a conventional energy-recovery circuit from the perspective of luminance performances.

• Journal of Korean Society for Atmospheric Environment
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• 제18권E4호
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• pp.181-190
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• 2002

A novel portable device for the direct measurement of alveolar breath carbon monoxide (CO) was developed. The major components of the device include a mouthpiece, non-rebreathing two-way valve, Teflon tube, and CO dosimeter. An alveolar CO measurement can be completed within 1.5 min when using the proposed device and measurement protocol. Measurements could be read to the nearest 0.1 ppm. Humidity did not influence the CO measurements taken by the CO dosimeter, plus there were no problems associated with the recovery and carryover of CO through the device. The criterion for significance in statistical analyses was p< 0.05. The average recovery was 103 and 99% for recovery and carryover experiments, respectively. Test results using the proposed alveolar CO measurement system reflected a good reproducibility. This reproducibility was also supported by the finding that the relative standard deviations (RSDs) of the data sets were less than 7％ for the loss experiment and less than 8% for the carryover experiment. Consequently, it would appear that the proposed device can be effectively applied to measure CO levels found in breath, thereby overcoming several disadvantages associated with the conventional bag and adsorbent tube sampling methods.

• 설비공학논문집
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• 제17권10호
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• pp.956-964
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• 2005

In order to control indoor air quality and save energy, it is needed to install a suitable ventilation system equipped with heat exchanger for heat recovery The purpose of this research is to find the factors affecting the performance of paper heat exchanger for exhaust heat recovery, which can be applied directly to the conventional ventilation unit, air-purifier, and air-conditioning system. In this study, thermal performance and pressure loss of the paper heat exchanger are measured and compared at various operating conditions. The effectiveness of sensible, latent and total heat at the face velocity of 0.75 m/s are $77\%,\;47\%\;and\;57\%$ in the cooling condition and $77\%,\;59\%,\;and\;\%$ in the heating condition, respectively. The effectiveness for sensible heat is only affected by velocity. On the other hand, the effectiveness for latent heat is affected. by temperature and relative humidity.