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3차원 탄도-확산 방정식을 통한 다중 제약 영역에서의 포논 수송 계산
김창호(Changho Kim),설재훈(Jae Hun Seol) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
According to the correlation between the size of micro/nanodevices and phonon mean free path, the phonon transport exhibits ballistic and diffusive behavior. Boltzmann transport equation (BTE) is a method that can accurately calculate the phonon transport in micro/nanodevices. On the other hand, ballistic-diffusive equation (BDE) overcomes the significant computational cost of BTE by modeling the ballistic and diffusive parts, separately. In this paper, three-dimensional approach of BDE is proposed to analyze the heat transfer in multi-constrained domain. The calculations were performed using commercial finite element analysis software (COMSOL Multiphysics). In order to validate the results based on BDE, the results of BTE were compared to the results. Also, the obtained results show the effect of ballistic phonons such as temperature jumps at the boundaries. Therefore, it is clear that the calculation is a promising analytical method for elucidating the heat transfer in multi-constrained structures.
그래핀 채널 내 블러프 바디에 따른 포논 와류 거동 연구
김창호(Changho Kim),설재훈(Jae Hun Seol) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11
We study phonon vortex dynamics with bluff bodies in graphene channels by solving the phonon Boltzmann transport equation under Callaway’s dual relaxation model and measurements with suspended micro-devices. In order to accurate calculations, the phonon scattering rates in graphene are obtained from the ab initio calculations. The phonon vortex can be observed in a hydrodynamic phonon transport regime, where phonon transports like a viscous fluid. Such phonon vortex strongly depends on the temperature, size, isotope as well as shape of bluff bodies. Here, we introduce rectangular, circular, and crescent shapes of bluff bodies to make a difference in generated phonon vortex and analyze the contribution of the vortex to phonon transport by comparing each other. This work provides a physical understanding of phonon vortex with respect to the shape of bluff bodies.
공공조직 리더십이 구성원의 조직몰입에 미치는 영향: 조직구조의 조절효과를 중심으로
황창호 ( Changho Hwang ),김정숙 ( Jungsook Kim ),최정인 ( Jungin Choe ),문명재 ( M. Jae Moon ) 중앙대학교 국가정책연구소 2019 국가정책연구 Vol.33 No.1
기업가정신은 기업의 혁신을 주도하는 정신이나 가치관이며, 기업가정신이 발현하기 위해서는 조직의 리더가 기업가적 리더십을 갖출 것이 요구된다. 본 논문은 공공 부문의 혁신을 위하여 강조되는 기업가적 리더십이 조직몰입에 어떠한 영향을 미치고 있으며, 어떠한 조직구조 하에서 조직 몰입을 높일 수 있는지를 실증적으로 규명고자 하였다. 이를 위해 기업가적 리더십이 조직 몰입에 주는 영향과 함께 공식화, 집권화, 공식화의 조절효과를 살펴보았다. 본 연구에서는 정부기관과 공공기관 종사자들을 대상으로 하여 설문조사를 실시하여 자료를 수집하고, 분석방법으로 조절회귀분석을 활용하였다. 분석 결과, 기업가적 리더십은 조직몰입에 영향을 미치고 조직구조의 세 가지 특성 중 집권화가 기업가적 리더십과 조직몰입을 조절하는 효과를 갖는 것으로 나타났다. 이같은 결과는 통제의 권한이 집중된 집권화된 조직에서는 기업가적 행동과 리더십의 발현이 조직구성원들의 조직몰입에 긍정적인 영향력으로 작용할 수 있다는 점을 시사한다. This study examines the effects of entrepreneurial leadershipon organizational commitment in a context where the importance of innovation for the public sector is increasing. The authors further explores how the entrepreneurial leadership and organizational commitment relationship changes depending on the organizational structure types. The results of this study demonstrate that entrepreneurial leadership have impacts on organizational commitment and centralization, one of organizational structure types, has a moderating effect.
Kim Changho,Yeo In Hwan,Kim Jong Kun,Cho Yeonjoo,Lee Mi Jin,Jung Haewon,Cho Jae Wan,Ham Ji Yeon,Lee Suk Hee,Chung Han Sol,Mun You Ho,Lee Sang Hun,Kim Yang Hun 대한감염학회 2020 Infection and Chemotherapy Vol.52 No.4
Background: There is currently a lack of evidence-based postresuscitation or postmortem guidelines for patients with out-of-hospital cardiac arrest (OHCA) in the setting of an emerging infectious disease. This study aimed to develop and validate a multimodal screening tool that aids in predicting the disease confirmation in emergency situations and patients with OHCA during a coronavirus disease 2019 (COVID-19) outbreak. Materials and Methods: We conducted a retrospective, multicenter observational study of adult patients with OHCA in Daegu, Korea. To identify the potential predictors that could be used in screening tools in the emergency department, we applied logistic regression to data collected from March 1 to March 14. The prediction performance of the screening variables was then assessed and validated on the data of patients with OHCA who were treated between February 19 and March 31, 2020. General patient characteristics and hematological findings of the COVID-19-negative and COVID-19-positive groups were compared. We also evaluated confirmation test criteria as predictors for COVID-19 positivity in patients with OHCA. Results: Advanced age, body temperature, and abnormal chest X-ray (CXR) revealed significant predictive ability in the derivation cohort. Of the 184 adult patients with OHCA identified in the validation cohort, 80 patients were included in the analysis. Notably, 9 patients were positive and 71 were negative on the COVID-19 reverse transcription polymerase chain reaction test. Five patients (55.6%) in the COVID-19-positive group had a fever before OHCA, and 12 (16.9%) of the COVID-19-negative group had a fever before OHCA (P = 0.018). Eight patients (88.9%) in the COVID-19-positive group had a CXR indicating pneumonic infiltration. Of the criteria for predicting COVID-19, fever or an abnormal CXR had a sensitivity of 100% (95% confidence interval [CI]: 65.4 – 100) and a specificity of 22.5% (95% CI: 13.5 – 34.0). Conclusion: The screening tools that combined fever or abnormal CXR had a good discriminatory ability for COVID-19 infection in adult patients with OHCA. Therefore, during the COVID-19 outbreak period, it is recommended to suspect COVID-19 infection and perform COVID-19 test if patients present with a history of fever or show abnormal findings in postmortem CXR.
그래핀 채널 내 블러프 바디에 따른 포논 와류 거동 연구
김창호(Changho Kim),설재훈(Jae Hun Seol) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11
We study phonon vortex dynamics with bluff bodies in graphene channels by solving the phonon Boltzmann transport equation under Callaway’s dual relaxation model and measurements with suspended micro-devices. In order to accurate calculations, the phonon scattering rates in graphene are obtained from the ab initio calculations. The phonon vortex can be observed in a hydrodynamic phonon transport regime, where phonon transports like a viscous fluid. Such phonon vortex strongly depends on the temperature, size, isotope as well as shape of bluff bodies. Here, we introduce rectangular, circular, and crescent shapes of bluff bodies to make a difference in generated phonon vortex and analyze the contribution of the vortex to phonon transport by comparing each other. This work provides a physical understanding of phonon vortex with respect to the shape of bluff bodies.
The Micro Pirani Gauge with Low Noise CDS-CTIA for In-Situ Vacuum Monitoring
Gyungtae Kim,Changho Seok,Taehyun Kim,Jae Hong Park,Heeyeoun Kim,Hyoungho Ko 대한전자공학회 2014 Journal of semiconductor technology and science Vol.14 No.6
A resistive micro Pirani gauge using amorphous silicon (a-Si) thin membrane is proposed. The proposed Pirani gauge can be easily integrated with the other process-compatible membrane-type sensors, and can be applicable for in-situ vacuum monitoring inside the vacuum package without an additional process. The vacuum level is measured by the resistance changes of the membrane using the low noise correlated double sampling (CDS) capacitive trans-impedance amplifier (CTIA). The measured vacuum range of the Pirani gauge is 0.1 to 10 Torr. The sensitivity and non-linearity are measured to be 78 ㎷ / Torr and 0.5% in the pressure range of 0.1 to 10 Torr. The output noise level is measured to be 268 μVrms in 0.5 ㎐ to 50 ㎐, which is 41.2% smaller than conventional CTIA.