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정환철,이석영 한국물리학회 2023 새물리 Vol.73 No.4
In this study, we investigated the eigenenergy and wave function structures of a mesoscopic rectangular quantum dot on a two-dimensional electron gas using the quantum transport simulation tool KWANT. From adjusting the ratio between the width and height of the quantum dot, we found that the eigenenergy was sensitively influenced by the ratio change and rearranged through the crossing. However, for certain energy states, the crossing was avoided, and anticrossing occurred instead. Further analysis revealed that the wave function became a rotating mode near the anticrossing point but could not evolve continuously through the rotating mode, leading to anticrossing. Our calculations demonstrated the possibility of rearranging the eigenenergy and wavefunctions and forming a rotating mode inside a quantum dot via deformation using nanodevices.
0.7 Anomaly Induced by Fano Resonance in Quantum Point Contact Coupled with Quantum Dot
정환철,정윤철 한국진공학회 2023 Applied Science and Convergence Technology Vol.32 No.1
The conductance through a quantum point contact (QPC) when a quantum dot (QD) is coupled to the side of a QPC channel is studied. It is experimentally demonstrated that a 0.7 conductance plateau can be produced by tuning the Fano resonance between QD and the QPC channel. Numerical simulations show results similar to the experiment. A simple model that adds a Fano resonance peak to the QPC’s quantized conductance curve is introduced. According to the model, the plateau results when the increase in Fano peak conductance compensates for the decrease in QPC conductance when the QPC gate is pinched off. These results suggest that Fano resonance is a possible candidate for the origin of the 0.7 conductance anomaly observed in QPCs.
스마트 센서 응용 프로그램을 테스팅하기 위한 효율적인 방법
정환철 ( Hwan-cheol Joeng ),조장우 ( Jang-wu Jo ) 한국정보처리학회 2013 한국정보처리학회 학술대회논문집 Vol.20 No.1
센서 응용 프로그램을 테스트하는 보편화된 방법은 테스트 보드에 센서를 직접 연결시켜 테스팅 환경의 센서값으로만 응용프로그램을 테스팅 하는 것이다. 본 논문에서는 스마트 센서 응용 프로그램 테스트하기 위해 기존의 방법의 문제점을 소개하였다. 그리고, 문제점을 보완하기 위한 효율적인 테스팅 방법인 센서측정값 생성기를 제안하였다. 센서측정값 생성기는 센서선택, 센서특성화, 출력패턴정의, 통신방식이라는 4단계 과정으로 각 센서의 특성에 맞게 실제와 유사한 테스팅 환경을 제공하고 보다 효율적이고 신뢰성 높은 테스트 결과를 만들어 낼 수 있다.
Cryogenic transimpedance amplifier based on a commercial operational amplifier
양찬욱,최이난,정환철,Park Dongsung T.,Choi Hyung Kook,정윤철 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.7
A transimpedance amplifer working at a temperature around 50 K has been developed. The design of the amplifer is targeted to use specifcally in dry dilution refrigerators for measuring quantum devices. Electrical characteristics such as input noise, bandwidth, and gain of several commercial operational amplifers (op amps) operating at 77 K were evaluated. From a screening process, the op amp OPA827 was chosen for the benchmarking of a cryogenic transimpedance amplifer. The conductance of a quantum point contact (QPC) at 100 mK was measured in a dry dilution refrigerator in order to compare the cryogenic and room temperature performance of transimpedance amplifers built using OPA827. The results were analyzed with a noise model describing the measurement system. We found that it is more advantageous to use a cryogenic transimpedance amplifer when the impedance of the device under test is high as in the case for most quantum devices.
콘크리트용 골재로서 열병합 발전소용 열원 폐재 파쇄물의 활용성에 관한 연구
임남기,김종식,정환철,김효열,허재원 대한건축학회지회연합회 2006 대한건축학회연합논문집 Vol.8 No.4
This study is as a part of the new disposal and recycling plans of heat-resource waste of Daegu dyeing industrial center. We tried to examine applicable possibility of crushed thing(waste aggregate) as aggregates for mortar and concrete. To examine applicable possibility of waste aggregate as a lightweight-aggregate for concrete and mortar, we carried this study by mainly property examination of concrete according to replacement ratio of waste aggregate. We tested out slump, unit weight, compressive strength and test according to replacement ratio of waste aggregate. As the results of that, if we use waste aggregate, lightweight of concrete and mortar will be possible. Specially it shows a strength improvement effect of cement hardening according to using this so it is judged that applicable possibility as aggregate for concrete and mortar is very excellent.