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Electrical Measurements of an AlGaN/GaN High-electron-mobility Transistor Structure Grown on Si
Zhi-Yao Zhang,Shun-Tsung Lo,Li-Hung Lin,Kuang Yao Chen,J. Z. Huang,Zhi-Hao Sun,C.-T. Liang,N. C. Chen,Chin-An Chang,P. H. Chang 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.9
We report on magnetotransport results for an Al<sub>0.15</sub>Ga<sub>0.85</sub>N/GaN high-electron-mobility-transistor structure grown on a p-type Si (111) substrate. Our results show that there exists an approximately temperature (<i>T</i>)-independent point, which could be ascribed to a direct transition from a weak insulator to a high Landau level filling factor quantum Hall state, exists in the longitudinal resistivity ρ<sub>xx</sub>. The Hall resistivity decreases with increasing <i>T</i>, compelling experimental evidence for electron-electron interaction effects in a weakly-disordered two-dimensional (2D) system. We find that electron-electron interaction effects can be estimated and eliminated, giving rise to a corrected nominally temperature-independent Hall slope. By fitting the low-field magnetotransport data to conventional 2D weak localization theory, we find that the dephasing rate 1/τ<sub>φ</sub> is proportional to <i>T</i>. Moreover, 1/τ<sub>φ</sub> is finite as <i>T</i> → 0, evidence for zero-temperature dephasing in our system.
T. Minegishi,Z. Vashaei,G. Fujimoto,H. Suzuki,K. Sumitani,M. Cho,M. Suemitsu,O. Sakata,S. Tokairin,T. Yao,Y. Narita 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.3
We studied ZnO growth on 3C-SiC(001)/Si(001) templates. In-situ reflection high- energy electron diffraction (RHEED) observations implied that ZnO grown on 3C-SiC(001) had a critical thickness (50 nm). From a structural characterization by using X-ray diffraction, we revealed that ZnO films thinner than the critical thickness grown on 3C-SiC(001) had a [10-11] orientation with 4-fold in-plane symmetry. On the other hand, ZnO films thicker than the critical thickness consisted of [10-11] and [0001] orientations. Also, the portion of [0001] oriented ZnO increased with the layer thickness. Possible interface configurations of ZnO(10-11)/3C-SiC(001) and ZnO(0001)/ZnO(10-11) are suggested.
A novel role of dipeptidyl peptidase 9 in epidermal growth factor signaling.
Yao, Tsun-Wen,Kim, Woo-Shin,Yu, Denise M T,Sharbeen, George,McCaughan, Geoffrey W,Choi, Kang-Yell,Xia, Pu,Gorrell, Mark D American Association for Cancer Research 2011 Molecular cancer research Vol.9 No.7
<P>Dipeptidyl peptidase IV (DPP4), DPP8, DPP9, and fibroblast activation protein (FAP), the four proteases of the DPP4 gene family, have unique peptidase and extra-enzymatic activities that have been implicated in various diseases including cancers. We report here a novel role of DPP9 in regulating cell survival and proliferation through modulating molecular signaling cascades. Akt (protein kinase B) activation was significantly inhibited by human DPP9 overexpression in human hepatoma cells (HepG2 and Huh7) and human embryonic kidney cells (HEK293T), whereas extracellular signal-regulated kinases (ERK1/2) activity was unaffected, revealing a pathway-specific effect. Interestingly, the inhibitory effect of DPP9 on Akt pathway activation was growth factor dependent. DPP9 overexpression caused apoptosis and significantly less epidermal growth factor (EGF)-mediated Akt activation in HepG2 cells. However, such inhibitory effect was not observed in cells stimulated with other growth factors, including connective tissue growth factor, hepatic growth factor, insulin or platelet-derived growth factor-BB. The effect of DPP9 on Akt did not occur when DPP9 enzyme activity was ablated by either mutagenesis or inhibition. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is a major downstream effector of Ras. We found that DPP9 and DPP8, but not DPP4 or FAP, associate with H-Ras, a key signal molecule of the EGF receptor signaling pathway. These findings suggest an important signaling role of DPP9 in the regulation of survival and proliferation pathways.</P>
C.Harada,H.Makino,H.Goto,T.Minegishi,T.Suzuki,M.W.Cho,T.Yao 한국물리학회 2004 Current Applied Physics Vol.4 No.6
We report on a surface property of bulk ZnO crystals and an optical method to evaluate it. Bulk ZnO crystals have a damagedsurface layer due to chemomechanical polishing. We prepared the ZnO crystals by etching, and evaluated the improvement of thesurface by high-resolution X-ray diraction (XRD) and photoluminescence (PL). In PL measurements, the relative intensity of therst order longitudinal optical phonon replica of free exciton (FX-1LO) to second order process (FX-2LO) was compared. Therelative intensity becomes weak with increasing etched depth and nally saturates at the etched depth of 5l m. This result agrees wellwith XRD results.
Soft X-ray magnetic circular dichroism of Cr-doped GaN
H.Makino,J.J.Kim,T.Nakamura,T.Muro,K.Kobayashi,T.Yao 한국물리학회 2004 Current Applied Physics Vol.4 No.6
Soft X-ray magnetic circular dichroism (XMCD) have been measured for the Ga0:97Cr0:03N lm grown by NH3-assistedmolecular beam epitaxy. Temperature dependence of the XMCD intensity was well described by the CurieWeiss law. Although thesample showed ferromagnetic behavior at least up to room temperature, the ferromagnetic component could not be detected by the XMCD measurement.