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김호경,김문영 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.2
The TCUD method (Kim and Lee, 2001) can provides the reasonable initial shape of cable-supported bridges under full dead load by including the unstrained lengths of the cable members as unknowns and introducing additional constraint conditions equal to the total number of the cable members. However, the axial deformations in the girder and main tower members are not avoidable which result in some difference from a target configuration when long-span cable-supported bridges are considered. In this study, an effective method to be able to eliminate those axial deformations as well as to preserve merits of the TCUD method is newly proposed. For this purpose, the TCUD method and the initial force method with successive substitution are reviewed based on an elastic catenary cable element, respectively, and a new algorithm combining two methods efficiently is presented. In addition, a truss-cable element for modeling hangers and a beam-column element for the girder and main tower members are supplementarily developed, respectively. The proposed method is applied for two suspension bridges and a cable-stayed bridge to demonstrate its accuracy and effectiveness.
Schottky Contacts to Polar and Nonpolar n-type GaN
김호경,박수현,Keun-Man Song,김동욱 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.1
Using the current-voltage measurements, we observed the barrier heights of c-plane GaN in Pt and Au Schottky contacts to be higher than those of a-plane GaN. However, the barrier height of c-plane GaN was lower than that of a-plane GaN in the Ti Schottky contacts. The N/Ga ratio calculated by integrating the X-ray photoelectron spectroscopy (XPS) spectra of Ga 3d and N 1s core levels showed that c-plane GaN induced more Ga vacancies near the interface than a-plane GaN in the Ti Schottky contacts, reducing the effective barrier height through an enhancement of the tunneling probability.
Barrier Inhomogeneity in Ag Schottky Contacts to Bulk ZnO Grown by Different Methods
김호경,손아름,김동욱 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.3
The electrical properties of Ag Schottky contacts to differently grown bulk ZnO single crystals were comparatively investigated. Schottky contacts to O-polar ZnO revealed higher barrier heights and lower ideality factors than those to Zn-polar ZnO. A higher degree of oxidation at the Ag-ZnO interface might occur for the O-polar ZnO, increasing the barrier heights. Compared to the current values measured under vacuum, those measured in an air ambient were decreased, suggesting that compensation of the surface conductive layer by acceptor-like adsorbates such as O2 and H2O plays an important role in the current transport of Ag/ZnO contacts.