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利用主成分分析和分层聚类分析方法研究了具有抗肺炎克雷伯氏菌的氟诺喹酮类药物分子的结构活性关系.主成分分析方法表明变量ELUMO、ΔEHL、μ、Q3、Q5、QA、lgP、MP、MR能够有效地对抗肺炎克雷伯氏菌的氟诺喹酮类药物进行分类.分层聚类方法和主成分分析方法的结果一致.这表明两种方法都能够对新的具有抗肺炎克雷伯氏菌的氟诺喹酮类药物的分类提供一个可信的规律.利用主成分分析法和分层聚类分析法对其他4个氟诺喹酮类药物分子进行分析,结果都表明有三个药物分子具有较强的抗肺炎克雷伯氏菌活性,此结果和临床结果相吻合. 相似文献
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Growth of Semi-Insulating GaN Using N2 as Nucleation Layer Carrier Gas Combining with an Optimized Annealing Time 下载免费PDF全文
Semi-insulating (SI) GaN is grown using N2 as the nucleation layer (NL) carrier gas combined with an optimized annealing time by metalorganic chemical vapour deposition. Influence of using 1-12 and N2 as the NL carrier gas is investigated in our experiment. It is found that the sheet resistance of unintentionally doped GaN can be increased from 10^4 Ω/sq to 10^10 Ω/sq by changing the NL carrier gas from 1-12 to N2 while keeping the other growth parameters to be constant, however crystal quality and roughness of the tilm are degraded unambiguously. This situation can be improved by optimizing the NL annealing time. The high resistance of GaN grown on NL using N2 as the carrier gas is due to higher density of threading dislocations caused by the higher density of nucleation islands and small statistic diameter grain compared to the one using 1-12 as carrier gas. Annealing the NL for an optimized annealing time can decrease the density of threading dislocation and improve the tilm roughness and interface of AlGaN/GaN without degrading the sheet resistance of as-grown GaN signiticantly. High-quality SI GaN is grown after optimizing the annealing time, and AlGaN/GaN high electron mobility transistors are also prepared. 相似文献
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Growth and Characterization of A1GaN/A1N/GaN HEMT Structures with a Compositionally Step-Graded A1GaN Barrier Layer 下载免费PDF全文
A new A1GaN/A1N/GaN high electron mobility transistor (HEMT) structure using a compositionally step-graded A1GaN barrier layer is grown on sapphire by metalorganic chemical vapour deposition (MOCVD). The structure demonstrates significant enhancement of two-dimensional electron gas (2DEG) mobility and smooth surface morphology compared with the conventional HEMT structure with high A1 composition A1GaN barrier. The high 2DEG mobility of 1806 cm2/Vs at room temperature and low rms surface roughness of 0.220 nm for a scan area of 5μm×5 μm are attributed to the improvement of interracial and crystal quality by employing the stepgraded barrier to accommodate the large lattice mismatch stress. The 2DEG sheet density is independent of the measurement temperature, showing the excellent 2DEG confinement of the step-graded structure. A low average sheet resistance of 314.5Ω/square, with a good resistance uniformity of 0.68%, is also obtained across the 50 mm epilayer wafer. HEMT devices are successfully fabricated using this material structure, which exhibits a maximum extrinsic transconductance of 218 mS/ram and a maximum drain current density of 800 mA/mm. 相似文献
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We report a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) with atomic layer deposited (ALD) Al2O3 gate dielectric. Based on the previous work [Appl. Phys. Lett. 86 (2005) 063501] of Ye et al. by decreasing the thickness of the gate oxide to 3.5nm and optimizing the device fabrication process, the device with maximum transconductance of 150mS/mm is produced and discussed in comparison with the result of lOOmS/mm of Ye et al. The corresponding drain current density in the 0.8-μm-gate-length MOS-HEMT is 800mA/mm at the gate bias of 3.0 V. The gate leakage is two orders of magnitude lower than that of the conventional A1GaN/GaN HEMT. The excellent characteristics of this novel MOS-HEMT device structure with ALD Al2O3 gate dielectric are presented. 相似文献
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Electrical Characterization of Metal-Insulator-Metal Capacitors with Atomic-Layer-Deposited HfO2 Dielectrics for Radio Frequency Integrated Circuit Application 下载免费PDF全文
Metal-insulator-metal (MIM) capacitors with atomic-layer-deposited HfO2 dielectric and TaN electrodes are investigated for rf integrated circuit applications. For 12nm HfO2, the fabricated capacitor exhibits a high capacitance density of 15.5fF/μm2 at 100kHz, a small leakage current density of 6.4 × 10^-9 A/cm^2 at 1.8V and 125℃, a breakdown electric field of 2.6 MV//cm as well as voltage coefficients of capacitance (VCCs) of 2110ppm/V^2 and -824 ppm/V at 100kHz. Further, it is deduced that the conduction mechanism in the high field range is dominated by the Poole-Frenkel emission, and the conduction mechanism in the low field range is possibly related to trap-assisted tunnelling. Finally, comparison of various HfO2 MIM capacitors is present, suggesting that the present MIM capacitor is a promising candidate for future rf integrated circuit application. 相似文献
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新一轮课程改革的总体目标是要构建符合素质教育的课程新体系,既要为高一级学校输送合格人材,又要为社会输送合格劳动者,是面向全体学生的教学理念.新课程提出的新理念对教师的教育观念和教学实践提出了挑战.要求物理教师既要领会新课程的精神、把握新课程的标准、吃透新教材的内容.还要深化自身的知识结构、扩展自身的能力结构. 相似文献
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