• 대한기계학회논문집A
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• 제33권10호
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• pp.1108-1118
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• 2009

A Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source of the order of $950^{\circ}C$ for nuclear hydrogen generation, which can produce hydrogen from water or natural gas. A primary hot gas duct (HGD) as a coaxial double-tube type cross vessel is a key component connecting a reactor pressure vessel and an intermediate heat exchanger in the VHTR. In this study, a structural sizing methodology for the primary HGD of the VHTR is suggested in order to modulate a flow-induced vibration (FIV). And as an example, a structural sizing of the horizontal HGD with a coaxial double-tube structure was carried out using the suggested method. These activities include a decision of the geometric dimensions, a selection of the material, and an evaluation of the strength of the coaxial double-tube type cross vessel components. Also in order to compare the FIV characteristics of the proposed design cases, a fluid-structure interaction (FSI) analysis was carried out using the ADINA code.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권4호
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• pp.1866-1883
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• 2019

As the youngest branch of information hiding, network covert timing channels conceal the existence of secret messages by manipulating the timing information of the overt traffic. The popular model-based framework for constructing covert timing channels always utilizes cumulative distribution function (CDF) of the inter-packet delays (IPDs) to modulate secret messages, whereas discards high-order statistics of the IPDs completely. The consequence is the vulnerability to high-order statistical tests, e.g., entropy test. In this study, a rich security model of covert timing channels is established based on IPD chains, which can be used to measure the distortion of multi-order timing statistics of a covert timing channel. To achieve rich security, we propose two types of covert timing channels based on nested lattices. The CDF of the IPDs is used to construct dot-lattice and interval-lattice for quantization, which can ensure the cell density of the lattice consistent with the joint distribution of the IPDs. Furthermore, compensative quantization and guard band strategy are employed to eliminate the regularity and enhance the robustness, respectively. Experimental results on real traffic show that the proposed schemes are rich-secure, and robust to channel interference, whereas some state-of-the-art covert timing channels cannot evade detection under the rich security model.

• Advances in nano research
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• 제3권1호
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• pp.49-54
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• 2015

The structure represents symmetrical metal electrode (gate 1) - front $SiO_2$ layer - n-Si nanowire FET - buried $SiO_2$ layer - metal electrode (gate 2). At the symmetrical gate voltages high conductive regions near the gate 1 - front $SiO_2$ and gate 2 - buried $SiO_2$ interfaces correspondingly, and low conductive region in the central region of the NW are formed. Possibilities of applications of nanosize FETs at the deep inversion and depletion as a distributed capacitance are demonstrated. Capacity density is an order to ${\sim}{\mu}F/cm^2$. The charge density, it distribution and capacity value in the nanowire can be controlled by a small changes in the gate voltages. at the non-symmetrical gate voltages high conductive regions will move to corresponding interfaces and low conductive region will modulate non-symmetrically. In this case source-drain current of the FET will redistributed and change current way. This gives opportunity to investigate surface and bulk transport processes in the nanosize inversion channel.

• 한국통신학회논문지
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• 제40권11호
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• pp.2121-2130
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• 2015

본 논문에서는 단일 RF 단을 사용하여 다중 스트림을 전송할 수 있는 LM-MIMO (load-modulation multiple-input multiple-output) 시스템에 대하여 알아보고, 이 시스템에서 사용하는 부하변조 (load modulation) 방법이 고차 m-PSK (phase shift keying) 심볼이나 고차 m-QAM (quadrature amplitude modulation) 심볼을 효과적으로 생성할 수 있는지 확인한다. 그리고 부하변조를 사용하는 LM-MIMO 시스템의 성능을 평가한다. LM-MIMO 시스템은 안테나가 확장되어도 단일 RF 단만을 요구하기 때문에 저복잡도, 저전력의 시스템 구성을 할 수 있다. 시뮬레이션의 결과를 살펴보면, T 모델 (model)을 사용하는 부하변조는 고차 m-PSK 변조와 고차 m-QAM 변조를 효과적으로 지원할 수 있다. 또한 부하변조를 사용하는 LM-MIMO 시스템이 기존의 이상적인 m-PSK나 m-QAM 변조를 사용하는 MIMO 시스템과 유사한 성능을 낼 수 있음을 확인하였다. 또한 $4{\times}4$ LM-MIMO 시스템이 기존의 $4{\times}4$ MIMO 시스템과 유사한 성능을 내는 것을 확인하였다.

• 대한통합의학회지
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• 제6권2호
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• pp.17-23
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• 2018

Purpose : The purpose of this study was to investigate whether the respiratory cycle and posture can modulate the autonomic nervous system. Methods : Thirty-two healthy men and women, aged 20-30 years, were enrolled in this study. We conducted 2-second and 6-second respiratory cycle with the subjects in standing, sitting, and supine positions, respectively. Their heart rate variability was measured in each position for both cycle lengths. Results : The low frequency/high frequency (LF/HF) ratio is derived from heart rate variability. In the 2-second respiratory cycles, the LF/HF ratios were highest in standing, sitting, and supine position in descending order. There was a significant difference in heart rate between standing and sitting positions (P<.005). In addition, there was a significant difference in heart rate between standing and supine position (P<.000). In the 6-second respiratory cycles, the LF/HF ratios were again highest in a standing, sitting, and supine position in descending order. However, posture was not found to make a significant difference in this case. Conclusion : Respiratory cycle and posture effectively modulated the autonomic nervous system. Further studies of the clinical application of these results should be conducted.

• 한국통신학회논문지
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• 제28권1C호
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• pp.14-23
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• 2003

본 논문에서는 2 Ms/s의 데이터 rate와 12-비트의 해상도를 갖는 Sigma-delta modulator의 구조를 제안한다. Sigma-delta modulator는 oversampling과 노이즈 shaping의 두 가지 특성으로 인해 낮은 해상도의 A/D 변환기와 결합하여 높은 해상도를 갖는 A/D 변환기의 구현이 가능하다는 장점으로 audio 응용 분야에 널리 사용되어 왔다. 그러나, Sigma-delta modulator를 무선 데이터 통신 등 다양한 응용 분야에서 사용하기 위해서는 좀더 높은 데이터 rate를 갖는 Sigma-delta modulator에 관한 연구가 필요하게 되었다. 본 논문에서 제안한 Sigma-delta modulator 구조는 기존의 64 내지 256의 oversampling비를 16으로 낮추어 sampling을 하여 기존의 수 십에서 수 백 Ks/s정도의 데이터 rate를 1 Ms/s 이상의 높은 데이터 rate에서 동작하도록 하였다. 그리고 두 개의 2차 Sigma-delta modulator를 Cascade 구조로 연결하고, 이득을 최적화하여 4차의 Sigma-delta modulator와 유사한 결과를 얻을 수 있었다. 내부에는 1-비트 A/D, D/A 변환기를 채용하여 부가적인 calibration 회로가 필요 없도록 하였다.

• 한국통신학회논문지
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• 제39A권7호
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• pp.380-388
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• 2014

세계 여러 나라들은 향상된 방송 서비스를 제공하기 위해서 지상파 UHDTV (Ultra High Definition Television) 전송방식에 관한 연구를 진행하고 있으며, 대부분이 다중경로에 강건한 OFDM (Orthogonal Frequency Division Multiplexing) 기반의 다중 반송파 전송방식을 고려하고 있다. 일부 국가에서는 이를 기반으로 하는 DVB-T2 (Digital Video Broadcasting 2nd generation Terrestrial) 표준에 향상된 대용량 데이터 압축기술을 더해 UHDTV 실험 방송을 진행 중이다. 그러나 다중경로에 취약하다고 알려진 단일 반송파 전송방식에서도 수신기에서 주파수 영역에서 채널 등화를 수행하는 SC-FDE (Single Carrier-Frequency Domain Equalizer)를 사용하면 이러한 단점을 보완할 수 있기 때문에, 두 방식 간의 성능 차이가 미미하게 나타난다. 이를 고려해 본 논문에서는 UHDTV 방송을 위해서 고차 신호 성상을 전송하는데 다중 반송파와 단일 반송파 중 어느 방식이 적합한지에 대한 판단 근거를 제공하고자 두 방식의 수신 성능을 비교한다.

• Parasites, Hosts and Diseases
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• 제54권2호
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• pp.201-204
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• 2016

Toxoplasma gondii is an intracellular protozoan that can modulate the environment of the infected host. An unfavorable environment modulated by T. gondii in the brain includes tumor microenvironment. Literature has suggested that T. gondii infection is associated with development of brain tumors. However, in Korea, epidemiological data regarding this correlation have been scarce. In this study, in order to investigate the relationship between T. gondii infection and brain tumor development, we investigated the seroprevalence of T. gondii among 93 confirmed brain tumor patients (various histological types, including meningioma and astrocytoma) in Korea using ELISA. The results revealed that T. gondii seropositivity among brain tumor patients (18.3%) was significantly (P<0.05) higher compared with that of healthy controls (8.6%). The seropositivity of brain tumor patients showed a significant age-tendency, i.e., higher in younger age group, compared with age-matched healthy controls (P<0.05). In conclusion, this study supports the close relationship between T. gondii infection and incidence of brain tumors.

• Nutrition Research and Practice
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• 제9권5호
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• pp.489-495
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• 2015

BACKGROUND/OBJECTIVES: The present study was conducted to investigate the effects of dried Momordica charantia aqueous extracts (MCA) and ethanol extracts (MCE) on obesity and lipid profiles in mice fed a high-fat diet. MATERIALS/METHODS: Forty two ICR mice were randomly divided into six groups. The normal group was fed a basal diet, and other groups were fed a 45% high-fat diet (HFD) for 7 weeks. The normal and HFD groups were also orally administered distilled water each day for 7 weeks. The remaining groups received Momordica charantia extract (0.5 or 1.0 g/kg/day MCA, and 0.5 or 1.0 g/kg/day MCE). In order to measure the anti-obesity and lipid profile improvement effects, body and visceral tissue weight, lipid profiles, plasma insulin levels, hepatic malondialdehyde (MDA) levels and superoxide dismutase (SOD) activity were measured. RESULTS: Both MCA and MCE significantly decreased body and visceral tissue weight relative to those of the HFD group (P < 0.05). Additionally high doses of MCE and MCA significantly reduced the plasmatic insulin levels compared to the HFD groups (P < 0.05) to concentrations comparable to those found in the normal group. MCA and MCE supplementation also significantly modulated the lipid profiles in plasma, liver, and feces compared to mice fed the HFD (P < 0.05). Furthermore MCA and MCE significantly increased hepatic SOD activity, and reduced MDA generation in the liver of the HFD mice (P < 0.05). CONCLUSIONS: Results from the present study suggest that Momordica charantia extracts have anti-obesity effects and the ability to modulate lipid prolife of mice fed a HFD by suppressing body weight gain, visceral tissue weight, plasma and hepatic lipid concentrations, and lipid peroxidation along with increasing lipid metabolism.

• 한국식품영양학회지
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• 제22권3호
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• pp.456-462
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• 2009

Adlay, barley and rice bran were extracted using various concentrations of methanol(10% and 80%) and chloroform : methanol(2 : 1) to examine the biological activities of these raw grains. Extraction with 80% methanol resulted in high Vitamin C Equivalent Antioxidant Capacity(VCEAC), in the order of barley > rice bran > adlay, as determined by DPPH and ABTS assays. In addition, the extracts of adlay and rice bran showed high cellular antioxidant activity in HepG2 cells possibly due to the presence of polyphenol glycosides in these grains. We examined the expression of glucose/fatty acid metabolizing genes in differentiated 3T3-L1 adipocyte cells. Glut1 was downregulated after treatment with rice bran and no changes in the expression of Glut4 was observed. In contrast, genes involved in fatty acid metabolism, CD36 and aP2, were upregulated. Since these physiological changes were matched with peroxisome proliferator activating receptor $\gamma$(PPAR $\gamma$) agonism, we suggest that the extracts from adlay, barley and rice bran may play preventive roles against aging and diabetes via antioxidant activity and increased uptake of fatty acids by adipocytes.