• 한국정보통신학회논문지
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• 제22권10호
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• pp.1379-1385
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• 2018

기존의 다중사용자 중첩 전송은 순시 채널 전력의 조건에 따라 데이터 심벌의 전력 할당 계수와 사용자별 수신 신호 처리 방법을 결정한다. 그러나 순시 채널 전력의 이용은 시스템의 복잡도를 증가시킬 수 있기 때문에 본 논문에서는 평균 채널 전력을 이용하는 고정적 다중사용자 중첩 전송을 고려한다. 고정적 다중사용자 중첩 전송 기법은 시간에 따라 느리게 변화하는 평균 채널 전력의 조건을 기반으로 데이터 심벌의 전력 할당 계수와 사용자별 수신 신호 처리 방법을 결정하기 때문에 시스템 복잡도를 감소시킬 수 있다. 본 논문에서는 고정적 다중사용자 중첩 전송에 대한 평균 심벌 오차율을 분석한다. 특히, 레일레이 페이딩 채널을 가정하여 M-ary 직교 진폭 변조에 대한 평균 심벌 오차율의 표현식을 유도한다. 또한, 수치적 결과를 통하여 열악한 채널 환경에 있는 사용자에서 고정적 다중사용자 중첩전송과 기존의 다중사용자 중첩 전송의 평균 심벌 오차율 성능이 유사함을 보였다.

• 한국정보통신학회논문지
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• 제12권10호
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• pp.1860-1865
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• 2008

40Gbps로 동작하는 WDM시스템의 성능 최적화를 위해 그 특성을 numerical simulation 을 통해 알아 보았다. 이때 광섬유는 가장 널리 사용되고 있는 표준 단일 모드로 가정하였으며, 변조 방식 역시 가장 간단하면서 널리 사용되고 있는 NRZ 방식을 사용하였다. 이는 40Gbps의 새로운 시스템을 설치하는 경우보다 기존의 시스템에서 각 채널의 전송율을 40Gbps로 증가시킴으로써 최종 전송용량을 향상시킬 경우를 고려하였기 때문이다. 수신단의 필터(optical 및 electrical) 특성을 최적화하고 색분산 보상 및 입력신호 크기의 최적화를 통해 기존에 매설된 단일 모드광섬유로 약 480km (BER < 10-15)까지 전송할 수 있음을 알았다. 또한 시스템의 성능이 EDFA의 ASE 노이즈 특성에 의해 크게 제한 될 때, 수신단의 광 필터는 삽입 손실이 5dB 이상 크지 않다면, Gaussian모양보다는 Flattop 모양의 광 필터가 성능개선에 더 유리함을 알 수 있었다.

• 대한원격탐사학회지
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• 제15권1호
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• pp.61-71
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• 1999

한국 남쪽 해역에서 획득한 SAR 영상들로부터 해양 표면에 나타난 물리 현상등이 관측되었다. 1994년 10월 11일 제주도 남서쪽 연안에서의 ERS-1 SAR 영상에서는 남쪽으로부터의 너울 형태의 파랑이 관측되었으며 변도 전달함수를 적용하여 영상으로부터 파랑 스펙트럼을 구하였다. 1996년 8월 15일 제주도 북쪽 연안의 RADARSAT SAR 영상에서 관측된 내부파는 여름철의 성층화된 해수에서 조류 전류시 조류가 해저 지형과의 상호 작용에 의하여 발생한 것으로 추측되며 솔리톤의 형태를 띠고 있다. 1997년 4월 3일 거제도 부근에서 발생한 유류오염 사고 3일 후에 획득한 RADARSAT SAR 영상에서는 사고 당시 유출된 기름들이 잘 나타났으나 복잡한 해안 지형과 생화학적 요인에 의한 다른 Slicks들도 함께 나타났다.

• Smart Structures and Systems
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• 제15권1호
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• pp.135-150
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• 2015

Large concrete structures are prone to cracks and damages over time from human usage, weathers, and other environmental attacks such as flood, earthquakes, and hurricanes. The health of the concrete structures should be monitored regularly to ensure safety. A reliable method of real time communications can facilitate more frequent structural health monitoring (SHM) updates from hard to reach positions, enabling crack detections of embedded concrete structures as they occur to avoid catastrophic failures. By implementing an unconventional mode of communication that utilizes guided stress waves traveling along the concrete structure itself, we may be able to free structural health monitoring from costly (re-)installation of communication wires. In stress-wave communications, piezoelectric transducers can act as actuators and sensors to send and receive modulated signals carrying concrete status information. The new generation of lead zirconate titanate (PZT) based smart aggregates cause multipath propagation in the homogeneous concrete channel, which presents both an opportunity and a challenge for multiple sensors communication. We propose a time reversal based pulse position modulation (TR-PPM) communication for stress wave communication within the concrete structure to combat multipath channel dispersion. Experimental results demonstrate successful transmission and recovery of TR-PPM using stress waves. Compared with PPM, we can achieve higher data rate and longer link distance via TR-PPM. Furthermore, TR-PPM remains effective under low signal-to-noise (SNR) ratio. This work also lays the foundation for implementing multiple-input multiple-output (MIMO) stress wave communication networks in concrete channels.

• Biomolecules & Therapeutics
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• 제30권4호
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• pp.320-327
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• 2022

Neurodevelopmental disorders are complex conditions that pose difficulty in the modulation of proper motor, sensory and cognitive function due to dysregulated neuronal development. Previous studies have reported that an imbalance in the excitation/inhibition (E/I) in the brain regulated by glutamatergic and/or GABAergic neurotransmission can cause neurodevelopmental and neuropsychiatric behavioral deficits such as autism spectrum disorder (ASD). NMDA acts as an agonist at the NMDA receptor and imitates the action of the glutamate on that receptor. NMDA however, unlike glutamate, only binds to and regulates the NMDA receptor subtypes and not the other glutamate receptors. This study seeks to determine whether NMDA administration in mice i.e., over-activation of the NMDA system would result in long-lasting behavioral deficits in the adolescent mice. Both gender mice were treated with NMDA or saline at early postnatal developmental period with significant synaptogenesis and synaptic maturation. On postnatal day 28, various behavioral experiments were conducted to assess and identify behavioral characteristics. NMDA-treated mice show social deficits, and repetitive behavior in both gender mice at adolescent periods. However, only the male mice but not female mice showed increased locomotor activity. This study implies that neonatal exposure to NMDA may illicit behavioral features similar to ASD. This study also confirms the validity of the E/I imbalance theory of ASD and that NMDA injection can be used as a pharmacologic model for ASD. Future studies may explore the mechanism behind the gender difference in locomotor activity as well as the human relevance and therapeutic significance of the present findings.

• 대한방사선기술학회지:방사선기술과학
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• 제45권6호
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• pp.491-502
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• 2022

The purpose of this study was to retrospectively investigate the upper and lower control limits of treatment planning parameters using EBT film based delivery quality assurance (DQA) results and to analyze the results of statistical process control (SPC) in helical tomotherapy (HT). A total of 152 patients who passed or failed DQA results were retrospectively included in this study. Prostate (n = 66), rectal (n = 51), and large-field cancer patients, including lymph nodes (n = 35), were randomly selected. The absolute point dose difference (DD) and global gamma passing rate (GPR) were analyzed for all patients. Control charts were used to evaluate the upper and lower control limits (UCL and LCL) for all the assessed treatment planning parameters. Treatment planning parameters such as gantry period, leaf open time (LOT), pitch, field width, actual and planning modulation factor, treatment time, couch speed, and couch travel were analyzed to provide the optimal range using the DQA results. The classification and regression tree (CART) was used to predict the relative importance of variables in the DQA results from various treatment planning parameters. We confirmed that the proportion of patients with an LOT below 100 ms in the failure group was relatively higher than that in the passing group. SPC can detect QA failure prior to over dosimetric QA tolerance levels. The acceptable tolerance range of each planning parameter may assist in the prediction of DQA failures using the SPC tool in the future.

• 대한청각학회지
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• 제18권3호
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• pp.105-111
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• 2014

Assistive listening devices (ALDs) refer to various types of amplification equipment designed to improve the communication of individuals with hard of hearing to enhance the accessibility to speech signal when individual hearing instruments are not sufficient. There are many types of ALDs to overcome a triangle of speech to noise ratio (SNR) problems, noise, distance, and reverberation. ALDs vary in their internal electronic mechanisms ranging from simple hard-wire microphone-amplifier units to more sophisticated broadcasting systems. They usually use microphones to capture an audio source and broadcast it wirelessly over a frequency modulation (FM), infra-red, induction loop, or other transmission techniques. The seven types of ALDs are introduced including hardwire devices, FM sound system, infra-red sound system, induction loop system, telephone listening devices, television, and alert/alarm system. Further development of digital wireless technology in hearing instruments will make possible direct communication with ALDs without any accessories in the near future. There are two technology solutions for digital wireless hearing instruments improving SNR and convenience. One is near-field magnetic induction combined with Bluetooth radio frequency (RF) transmission or proprietary RF transmission and the other is proprietary RF transmission alone. Recently launched digital wireless hearing aid applying this new technology can communicate from the hearing instrument to personal computer, phones, Wi-Fi, alert systems, and ALDs via iPhone, iPad, and iPod. However, it comes with its own iOS application offering a range of features but there is no option for Android users as of this moment.

• 한국축산식품학회지
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• 제43권4호
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• pp.659-673
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• 2023

Compared to infant formula, breast milk is the best source of nutrition for infants; it not only improves the neonatal intestinal function, but also regulates the immune system and gut microbiota composition. However, probiotic-fortified infant formula may further enhance the infant gut environment by overcoming the limitations of traditional infant formula. We investigated the probiotic formula administration for one month by comparing 118 Korean infants into the following three groups: infants in each group fed with breast milk (50), probiotic formula (35), or placebo formula-fed group (33). Probiotic formula improved stool consistency and defecation frequency compared to placebo formula-fed group. The probiotic formula helped maintaining the level of secretory immunoglobulin A (sIgA), which had remarkably decreased over time in placebo formula-fed infants (compared to weeks 0 and 4). Moreover, probiotic formula decreased the acidity of stool and considerably increased the butyrate concentration. Furthermore, the fecal microbiota of each group was evaluated at weeks 0 and 4. The microbial composition was distinct between each groups, and the abundance of health-promoting bacteria increased in the probiotic formula compared to the placebo formula-fed group. In summary, supplementation of probiotic infant formula can help optimize the infant gut environment, microbial composition, and metabolic activity of the microbiota, mimicking those of breast milk.

• 한국전기전자재료학회논문지
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• 제37권4호
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• pp.400-406
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• 2024

Next-generation wide-bandgap semiconductors such as SiC, GaN, and Ga2O3 are being considered as potential replacements for current silicon-based power devices due to their high mobility, larger size, and production of high-quality wafers at a moderate cost. In this study, we investigate the gradual modulation of chemical composition in multi-stacked metal oxide semiconductor thin films to enhance the performance and bias stability of thin-film transistors (TFTs). It demonstrates that adjusting the Ga ratio in the indium gallium oxide (IGO) semiconductor allows for precise control over the threshold voltage and enhances device stability. Moreover, employing multiple deposition techniques addresses the inherent limitations of solution-processed amorphous oxide semiconductor TFTs by mitigating porosity induced by solvent evaporation. It is anticipated that solution-processed indium gallium oxide (IGO) semiconductors, with a Ga ratio exceeding 50%, can be utilized in the production of oxide semiconductors with wide band gaps. These materials hold promise for power electronic applications necessitating high voltage and current capabilities.

• 한국의학물리학회지:의학물리
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• 제34권4호
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• pp.48-54
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• 2023

Purpose: In this study, the dosimetric characteristics of lung stereotactic body radiotherapy (SBRT) plans using the new Halcyon system were analyzed to assess its suitability. Methods: We compared the key dosimetric parameters calculated for the Halcyon SBRT plans with those of a conventional C-arm linear accelerator (LINAC) equipped with a high-definition multileaf collimator (HD-MLC)-Trilogy Tx. A total of 10 patients with non-small-cell lung cancer were selected, and all SBRT plans were generated using the RapidArc technique. Results: Trilogy Tx exhibited significant superiority over Halcyon in terms of target dose coverage (conformity index, homogeneity index, D_{0.1 cc}, and D_95%) and dose spillage (gradient). Trilogy Tx was more efficient than Halcyon in the lung SBRT beam delivery process in terms of the total number of monitor units, modulation factor, and beam-on time. However, it was feasible to achieve a dose distribution that met SBRT plan requirements using Halcyon, with no significant differences in satisfying organs at risk dose constraints between both plans. Conclusions: Results confirm that Halcyon is a viable alternative for performing lung SBRT in the absence of a LINAC equipped with HD-MLC. However, extra consideration should be taken in determining whether to use Halcyon when the planning target volume setting is enormous, as in the case of significant tumor motions.