• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1825-1834
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• 2022

Performing high-fidelity computational fluid dynamics (HF-CFD) to predict the flow and heat transfer state of the coolant in the reactor core is expensive, especially in scenarios that require extensive parameter search, such as uncertainty analysis and design optimization. This work investigated the performance of utilizing a multi-fidelity reduced-order model (MF-ROM) in PWR rod bundles simulation. Firstly, basis vectors and basis vector coefficients of high-fidelity and low-fidelity CFD results are extracted separately by the proper orthogonal decomposition (POD) approach. Secondly, a surrogate model is trained to map the relationship between the extracted coefficients from different fidelity results. In the prediction stage, the coefficients of the low-fidelity data under the new operating conditions are extracted by using the obtained POD basis vectors. Then, the trained surrogate model uses the low-fidelity coefficients to regress the high-fidelity coefficients. The predicted high-fidelity data is reconstructed from the product of extracted basis vectors and the regression coefficients. The effectiveness of the MF-ROM is evaluated on a flow and heat transfer problem in PWR fuel rod bundles. Two data-driven algorithms, the Kriging and artificial neural network (ANN), are trained as surrogate models for the MF-ROM to reconstruct the complex flow and heat transfer field downstream of the mixing vanes. The results show good agreements between the data reconstructed with the trained MF-ROM and the high-fidelity CFD simulation result, while the former only requires to taken the computational burden of low-fidelity simulation. The results also show that the performance of the ANN model is slightly better than the Kriging model when using a high number of POD basis vectors for regression. Moreover, the result presented in this paper demonstrates the suitability of the proposed MF-ROM for high-fidelity fixed value initialization to accelerate complex simulation.

• 한국전문물리치료학회지
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• 제29권1호
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• pp.48-53
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• 2022

Background: The gastrocnemius tightness can easily occur. Gastrocnemius tightness results in gait disturbance. Thus, various interventions have been used to release a tight gastrocnemius muscle and improve gait performance. Moreover, focal muscle vibration (FMV) has recently been extensively researched in terms of tight muscle release and muscle performance. However, no study has investigated the effects of FMV application on medial gastrocnemius architectural changes. Objects: In this study, we aimed to investigate the effects of FMV on medial gastrocnemius architecture in persons with limited ankle dorsiflexion. Methods: Thirty one persons with <10° of passive ankle dorsiflexion participated in this study. We excluded persons with acute ankle injury within six months prior to study onset, a history of ankle fracture, leg length discrepancy greater than 2 cm, no history of neurological dysfunction, or trauma affecting the lower limb. The specifications of the FMV motor were as follows: a fixed frequency (fast wave: 150 Hz) and low amplitude (0.3-0.5 mm peak to peak) of vibration; the motor was used to release the medial gastrocnemius for 15 minutes. Each participant completed three trials for 10 days; a 30-second rest period was provided between each trial. Medial gastrocnemius architectural parameters [muscle thickness (MT), fiber bundle length (FBL), and pennation angle (PA)] were measured via ultrasonography. Results: MT significantly decreased after FMV application (p < 0.05). FBL significantly increased from its baseline value after FMV application (p < 0.05). PA significantly decreased from its baseline value after FMV application (p < 0.05). Conclusion: FMV application may be advantageous in reducing medial gastrocnemius excitability following a decrease in the amount of contractile tissue. Furthermore, FMV application can be used as a stretching method to alter medial gastrocnemius architecture.

• 대한정형외과학회지
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• 제55권4호
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• pp.311-317
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• 2020

전방십자인대 재건술에 있어서 최근 가장 각광받고 있는 개념은 해부학적 전방십자인대 재건술이다. 경경골 술식을 이용한 고전적인 방법에 비하여 해부학적 재건술을 위해서 경골터널은 이전보다 전방으로 이동하며 대퇴터널은 낮고 비스듬한 방향으로 만들게 된다. 따라서 낮고 비스듬한 해부학적인 위치의 대퇴터널을 만들기 위하여 전내측 도달법을 통한 술식(anteromedial portal technique), outside-in 술식, 그리고 변형된 경경골 술식(modified transtibial technique) 등이 시행되고 있다. 각각의 방법은 장단점이 있어 술자의 선호도, 경험, 사용 가능한 기구 및 이식건의 선택 등에 따라 선택된다.

• International Journal of Computer Science & Network Security
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• 제23권5호
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• pp.172-178
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• 2023

In this paper, performance of autoencoder based OFDM communication systems is compared with IEEE 802.11a Wireless Lan System (Wi-Fi). The proposed autoencoder based OFDM system is composed of the following steps. First, one sub-carrier's transmitter - channel - receiver system is created by autoencoder. Then learning process of the one sub-carrier autoencoder generates constellation map. Secondly, using the plural sub-carrier autoencoder systems, parallel bundle is configured with inserting IFFT and FFT before and after the channel to configure OFDM system. Finally, the receiver part of the OFDM communication system was updated by re-learning process for adapting channel condition such as multipath channel. For performance comparison, IEEE802.11a and the proposed autoencoder based OFDM system are compared. For channel estimation, Wi-Fi uses initial long preamble to measure channel condition. but Autoencoder needs re-learning process to create an equalizer which compensate a distortion caused by the transmission channel. Therefore, this autoencoder based system has basic advantage to the Wi-Fi system. For the comparison of the system, additive random noise and 2-wave and 4-wave multipaths are assumed in the transmission path with no inter-symbol interference. A simulation was performed to compare the conventional type and the autoencoder. As a result of the simulation, the autoencoder properly generated automatic constellations with QPSK, 16QAM, and 64QAM. In the previous simulation, the received data was relearned, thus the performance was poor, but the performance improved by making the initial value of reception a random number. A function equivalent to an equalizer for multipath channels has been realized in OFDM systems. As a future task, there is not include error correction at this time, we plan to make further improvements by incorporating error correction in the future.

• Journal of the Korean Wood Science and Technology
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• 제51권4호
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• pp.309-319
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• 2023

Bamboo culm is in the form of a tube/pipe, composed of internodes which are bounded by a partition/diaphragm (node). Anatomically, bamboo is composed of vascular bundles and parenchyma ground tissue. One of the constituents of vascular bundles is fibers that are grouped to form a fiber sheath. The anatomical structure of the nodes and internodes is thought to influence the strength of bamboo strips, including tensile strength. This study aimed to determine the characteristics of vascular bundles (distribution and fiber percentage) and their effects on the density and tensile strength of Gigantochloa apus bamboo strips with and without nodes. The bamboo culms were divided into three parts (outer, middle, and inner) along the radial direction. The results showed that the distribution of vascular bundles and percentage of fiber sheaths decreased significantly from the outer to the inner layer. This also had a significantly decreased density and tensile strength. Furthermore, the number of vascular bundles (in the transverse plane) was greater in the internodes than in the nodes. Anatomically, the orientation of the vascular bundles at irregular nodes is observed in the radial and tangential planes, where the direction is not only in the axial direction, but also in the radial and tangential directions. This caused the tensile strength of the G. apus bamboo strips to be lower at the nodes than at the internodes.

• 항공우주시스템공학회지
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• 제17권6호
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• pp.35-45
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• 2023

본 논문에서는 항공기용 차폐 케이블의 구조에 따른 간접낙뢰의 영향성을 분석하고, 차폐력 향상을 위한 차폐 케이블 구조를 분석하였다. 항공기에서 케이블은 부품 중에 가장 많은 비중을 차지하고 있고, 항공기 프레임과 전자기기들이 연결되어 있어 영향을 많이 줄 수 있다. 특히, 간접낙뢰 노이즈는 항공 전자기기 오동작 및 손상을 발생시킬 수 있어, 차폐 케이블을 활용하여 간접낙뢰 노이즈로 인한 피해를 줄일 수 있다. 항공기용 차폐 케이블의 차폐층 유무, 내심, 절연체 등의 케이블 구조에 따른 간접낙뢰 영향성 분석을 진행하였다. 또한, 간접낙뢰 공인 규격인 RTCA DO-160G Sec. 22를 적용하여 시뮬레이션 및 실험하여 검증하였다.

• 한국지반환경공학회 논문집
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• 제25권6호
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• pp.13-17
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• 2024

현재 국내외적으로 토사사면의 사면안정을 위해 사용하고 있는 일반 Soil Nailing은 지반을 천공 후 단일 철근을 활용, 그라우팅하여 일종의 중력식 옹벽을 형성하여 사면의 안정을 도모하고 있다. 이러한 공법을 공사비 절감과 시공의 용이성, 상대적인 강도와 변위면에서 우수한 효율을 낼 수 있는 공법이다. 동일한 공종으로 진행하되 단일 철근을 다발철근으로 변경하여 활용할 경우 항복 인발력에 대한 그라우팅과 철근의 부착력 차이, 동일한 인발저항 대비 변형량의 차이를 현장시험을 통해 분석하여 공학적 우수성을 규명하고 공사비 측면에서 강도정수가 동일한 지반에 대하여 저항력이 동일하게 적용할 경우, 천공수의 차이와 재료비 등 전체 공사비에 미치는 영향분석을 통해 절감효과의 비교를 분석하여 평가하였다.

• 한국경제지리학회지
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• 제26권4호
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• pp.421-442
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• 2023

본 연구는 비수도권 청년층의 이주유형 특성이 지역별로 상이하게 나타난다는 점에 주목하여 이주유형별 결정요인의 차이를 비교 분석하는 데 주요 목적을 두었다. 먼저 비수도권 청년층의 이주 실태 및 특성을 탐색적으로 분석한 후 위계로짓모형을 활용하여 이주유형별 결정요인을 각각 추정하였다. 분석 결과 이주유형별 특성이 지역별로 상이하게 관찰되었고, 각각의 이주유형별 결정요인 또한 서로 다른 변수(개인 및 지역수준)들의 묶음(bundle)으로 구성되어 있음을 확인할 수 있었다. 향후 비수도권의 청년인력 확보 정책은 다양한 이주선택의 결정요인을 충분히 고려하고 지역적 맥락이 반영될 때 정책의 효과를 배가시킬 수 있을 것이다.

• 한국환경복원기술학회지
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• 제26권6호
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• pp.97-115
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• 2023

Ecosystem services (ES) are the benefits that people obtain from ecosystems. Traditional ES assessment methods have focused on the supply of ES, using biophysical data. However, these methods often fail to capture the full value of ES, which is also determined by social and cultural factors. This study proposes a new approach to ES assessment that incorporates socio-cultural perspectives. The study was conducted in Seoul, South Korea. A survey was conducted of 1,805 residents of Seoul to assess their satisfaction with ecosystem services. Exploratory factor analysis was used to identify bundles of ES that were perceived as important by residents. A revised importance-satisfaction analysis was used to calculate the urgency level of each bundle. The results of the study showed that the 21 ES that were considered in the survey could be grouped into three bundles: urban green area-based, biodiversity-based, and resilience-based. The urgency level analysis showed that some bundles were more important than others, and that some bundles were more urgent than others. The findings of this study have several implications. First, they suggest that a socio-cultural approach to ES assessment can provide a more comprehensive and accurate assessment of ES. Second, they show that this approach can be used to identify areas where ES management is most needed. Third, they suggest that this approach could be used to inform ES management and policy decisions.

• 대한수의학회지
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• 제64권2호
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• pp.14.1-14.6
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• 2024

In human, ultrasonography is used to measure the pennation angle in various muscles to identify muscle functions such as force production, and to study alterations of the pennation angle during muscle contraction, hypertrophy, and atrophy. However, assessments of the pennation angle have not yet been conducted in dogs. This study aims to assess the normal pennation angle of the tibialis cranialis muscle in dogs using ultrasound and to detect changes in this angle in dogs with muscular atrophy. Sixty-eight healthy dogs were examined to establish normal values, while 12 ataxic and 12 lame dogs with suspected hindlimb muscle atrophy were also included. The pennation angle was measured using ultrasound at the midpoint between the proximal end of the tibia and the malleolus, measuring the angle between the muscle bundle and the deep aponeurosis. To confirm the significance between the 5 breeds and to identify a difference between normal and atrophied muscles, statistical analysis was conducted. The study found no significant difference in pennation angle between breeds, with mean values (± standard deviation) of 4.97° (± 1.88) in neutral, 7.25° (± 2.68) in flexion, and 3.31° (± 1.33) in extension positions. Decrease of the pennation angle was identified in muscle atrophy and the flexion position was determined to be the most appropriate for pennation angle measurement of tibialis cranialis muscle. We recommend considering the pennation angle as a valuable indicator of muscle health in dogs, as it demonstrates significant potential for diagnosing and monitoring muscular conditions.