• Journal of Power Electronics
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• 제15권1호
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• pp.10-17
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• 2015

A quasi-constant on-time controlled buck front end in combined discontinuous conduction mode and boundary conduction mode is proposed to improve power factor (PF).When instantaneous AC input voltage is lower than the output bus voltage per period, the buck converter turns into buck-boost converter with the addition of a level comparator to compare input voltage and output voltage. The gate drive voltage is provided by an additional oscillator during distortion time to eliminate the cross-over distortion of the input current. This high PF comes from the avoidance of the input current distortion, thereby enabling energy to be delivered constantly. This paper presents a series analysis of controlling techniques and efficiency, PF, and total harmonic distortion. A comparison in terms of efficiency and PF between the proposed converter and a previous work is performed. The specifications of the converter include the following: input AC voltage is from 90V to 264V, output DC voltage is 80V, and output power is 94W.This converter can achieve PF of 98.74% and efficiency of 97.21% in 220V AC input voltage process.

• 전력전자학회논문지
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• 제25권3호
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• pp.157-161
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• 2020

High voltage gain converters are essential for distributed power generation systems with renewable energy sources, such as fuel cells and solar cells, because of their low voltage characteristics. This paper introduces a novel nonisolated DC-DC converter topology developed by combining an inverting buck-boost converter and voltage multipliers. In the proposed converter, the input voltage is connected in series with the output, and the majority of the input power is directly delivered to the load. The voltage multipliers are stacked in series to achieve high step-up voltage gain. The voltage stress across all of the switches and capacitors can be significantly reduced. As a result, the switches with low voltage ratings can be used to achieve high efficiency and low cost. To verify the validity of the proposed topology, a 360-W prototype converter is built to obtain the experimental results.

• Nano
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• 제13권11호
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• pp.1850136.1-1850136.12
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• 2018

Three-dimensional (3D) mixed phases NiSe nanoparticles growing on the nickel foam were synthesized via a simple one-step hydrothermal method. A series of experiments were carried out to control the morphology by adjusting the amount of selenium in the synthetic reaction. Meanwhile, the as-prepared novel column-acicular structure NiSe exist three advantages including ideal electrical conductivity, high specific capacity and high cycling stability. It delivered a high capacitance of $10.8F\;cm^{-2}$ at a current density- of $5mA\;cm^{-2}$. An electrochemical capacitor device operating at 1.6 V was then constructed using NiSe/NF and activated carbon (AC) as positive and negative electrodes. Moreover, the device showed high energy density of $31W\;h\;kg^{-1}$ at a power density of $0.81kW\;kg^{-1}$, as well as good cycling stability (77% retention after 1500 cycles).

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.83-85
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• 2019

The use of high voltage gain converters is essential for the distributed power generation systems with renewable energy sources such as the fuel cells and solar cells due to their low voltage characteristics. In this paper, a high voltage gain topology combining cascode Inverting Buck-Boost converter and voltage multiplier structure is introduced. In proposed converter, the input voltage is connected in series at the output, the portion of input power is directly delivered to the load which results in continuous input current. In addition, the voltage multiplier stage stacked in proper manner is not only enhance high step-up voltage gain ratio but also significantly reduce the voltage stress across all semiconductor devices and capacitors. As a result, the high current-low voltage switches can be employed for higher efficiency and lower cost. In order to show the feasibility of the proposed topology, the operation principle is presented and the steady-state characteristic is analyzed in detail. A 380W-40/380V prototype converter was built to validate the effectiveness of proposed converter.

• 한국의학물리학회지:의학물리
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• 제31권3호
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• pp.63-70
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• 2020

Stereotactic radiosurgery is one of the most sophisticated forms of modern advanced radiation therapy. Unlike conventional fractionated radiotherapy, stereotactic radiosurgery uses a high dose of radiation with steep gradient precisely delivered to target lesions. Lars Leksell presented the principle of radiosurgery in 1951. Gamma Knife^® (GK) is the first radiosurgery device used in clinics, and the first patient was treated in the winter of 1967. The first GK unit had 179 cobalt 60 sources distributed on a hemispherical surface. A patient could move only in a single direction. Treatment planning was performed manually and took more than a day. The latest model, Gamma Knife^® Icon^TM, shares the same principle but has many new dazzling characteristics. In this article, first, a brief history of radiosurgery was described. Then, the physical properties of modern radiosurgery machines and physicists' endeavors to assure the quality of radiosurgery were described. Intrinsic characteristics of modern radiosurgery devices such as small fields, steep dose distribution producing sharp penumbra, and multi-directionality of the beam were reviewed together with the techniques to assess the accuracy of these devices. The reference conditions and principles of GK dosimetry given in the most recent international standard protocol, International Atomic Energy Agency TRS 483, were shortly reviewed, and several points needing careful revisions were highlighted. Understanding the principles and physics of radiosurgery will be helpful for modern medical physicists.

• International Journal of Computer Science & Network Security
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• 제23권4호
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• pp.156-165
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• 2023

IEEE 802.15.4e-TSCH is recognized as a wireless industrial sensor network standard used in IoT systems. To ensure both power savings and reliable communications, the TSCH standard uses techniques including channel hopping and bandwidth reserve. In TSCH mode, scheduling is crucial because it allows sensor nodes to select when data should be delivered or received. Because a wide range of applications may necessitate energy economy and transmission dependability, we present a distributed approach that uses a cluster tree topology to forecast scheduling requirements for the following slotframe, concentrating on the Poisson model. The proposed Optimized Minimal Scheduling Function (OMSF) is interested in the details of the scheduling time intervals, something that was not supported by the Minimal Scheduling Function (MSF) proposed by the 6TSCH group. Our contribution helps to deduce the number of cells needed in the following slotframe by reducing the number of negotiation operations between the pairs of nodes in each cluster to settle on a schedule. As a result, the cluster tree network's error rate, traffic load, latency, and queue size have all decreased.

• 방사성폐기물학회지
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• 제22권2호
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• pp.117-128
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• 2024

The 300 concrete silo systems installed and operated at the site of Wolsong nuclear power plant (NPP) have been storing CANDU spent nuclear fuel (SNF) under dry conditions since 1992. The dry storage system must be operated safely until SNF is delivered to an interim storage facility or final repository located outside the NPP in accordance with the SNF management policy of the country. The silo dry storage system consists of a concrete structure, liner steel plate in the inner cavity, and fuel basket. Because the components of the silo system are exposed to high energy radiation owing to the high radioactivity of SNF inside, the effects of irradiation during long-term storage must be analyzed. To this end, material specimens of each component were manufactured and subjected to irradiation and strength tests, and mechanical characteristics before and after irradiation were examined. Notably, the mechanical characteristics of the main components of the silo system were affected by irradiation during the storage of spent fuel. The test results will be used to evaluate the long-term behavior of silo systems in the future.

• Nuclear Engineering and Technology
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• 제56권8호
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• pp.3268-3275
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• 2024

Isotopes are an important aspect of modern medical and scientific research and cyclotron-based isotope production is of particular interest. Cooling devices are required to manage the heat generated by high-energy particle beams to ensure that they can be delivered securely. However, there is considerable scope for further advancements in the design of cooling systems. Therefore, this study uses simulations to investigate the design of innovative cooling systems. Various designs and materials are considered using a variable four-sector collimator and various particle-beam conditions. Thus, new design principles and material and structural optimization strategies are proposed, which can be used to improve the stability and efficiency of isotope production. The results provide insight into technical challenges and may contribute toward advances in medical diagnostics, radiotherapy, and fundamental scientific research. In particular, they can guide the development of isotopebased technologies in nuclear medicine.

• 전기화학회지
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• 제19권4호
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• pp.123-128
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• 2016

본 연구에서는 poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP)를 나노 크기의 $Al_2O_3$ 세라믹입자와 혼합하여 전기방사법으로 복합 겔 고분자 전해질을 제조하였다. $Al_2O_3$ 세라믹입자를 혼합한 복합 겔 고분자 전해질의 이온전도도는 $9.5{\times}10^{-2}Scm^{-1}$로, 순수한 PVdF-HFP 겔 고분자 전해질보다 높은 이온전도도를 나타내며 전기화학적 안정성도 5.2 V까지 개선하였다. 전기화학적 성능을 분석하기 위해서 $LiNi_{1/3}Mn_{1/3}Co_{1/3}O_2$ (NMC)양극과 함께 전지로 제작되었으며 순수 겔 고분자 전해질과 복합 겔 고분자 전해질 셀은 0.1C-rate에서 각각 $168.2mAh\;g^{-1}$과 $189.6mAh\;g^{-1}$의 방전 용량을 가지며 우수한 수명 특성을 보여 주었다. 따라서 고유전율 세라믹 입자의 복합화는 리튬 이온 겔 고분자 전지의 안정성과 전기화학적 특성을 향상시키는 좋은 대안이 될 것으로 판단된다.

• 한국방사선학회논문지
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• 제12권3호
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• pp.289-295
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• 2018

대부분의 진단용 방사선 장치는 엑스선을 사용하며, 엑스선은 다양한 에너지를 갖는 스펙트럼을 갖는다. 진단 영상에서 엑스선의 정량적 및 정성적 분석은 선량을 줄이면서 영상 화질을 유지하는데 필수적이다. 본 연구의 목적은 진단 영상에 사용되는 엑스선 스펙트럼을 몬테칼로 시뮬레이션으로 측정하는 것이다. 다양한 엑스선 에너지 스펙트럼이 몬테칼로 시뮬레이션으로 측정되었다. 이 스펙트럼들은 다항식을 보간 한 양극 텅스텐 모델에 의해 계산된 결과와 비교하였다. 엑스선 관전압은 50, 60, 80, 100, 110 kV 였다. 검출기로는 카드뮴 텔루라이드와 비정질 셀레늄 물질을 사용하였다. 엑스선 에너지 스펙트럼의 시뮬레이션 결과는 참조 결과와 일치하였고, NRMSD 값은 최소 1.1%에서 최대 5.7%를 보였다. 시뮬레이션 결과에 의하면 진단 영상을 획득할 때 적절한 관전압의 선택을 가능하게 할 것이다. 또한, 영상 획득 전 환자에 전달되는 선량을 예측하는데 기여할 것이다.