手机媒介的现代性影响

数字技术的发展,推动手机大众传播特性的突显。手机人性化的传播方式,深得中国人的偏爱,并且在社会转型的过程中,参与了现代性的建构。社会现代性出现了新的向度,亦即与传统中国社会颇多相似的现代性受到重视。手机在中国的广泛应用,正是应了这种趋势,并且将在某种程度上推动中国现代性的复苏。     

Strong quantum-confined Stark effect in germanium quantum-well structures on silicon

Silicon is the dominant semiconductor for electronics, but there is now a growing need to integrate such components with optoelectronics for telecommunications and computer interconnections. Silicon-based optical modulators have recently been successfully demonstrated; but because the light modulation mechanisms in silicon are relatively weak, long (for example, several millimetres) devices or sophisticated high-quality-factor resonators have been necessary. Thin quantum-well structures made from III-V semiconductors such as GaAs, InP and their alloys exhibit the much stronger quantum-confined Stark effect (QCSE) mechanism, which allows modulator structures with only micrometres of optical path length. Such III-V materials are unfortunately difficult to integrate with silicon electronic devices. Germanium is routinely integrated with silicon in electronics, but previous silicon-germanium structures have also not shown strong modulation effects. Here we report the discovery of the QCSE, at room temperature, in thin germanium quantum-well structures grown on silicon. The QCSE here has strengths comparable to that in III-V materials. Its clarity and strength are particularly surprising because germanium is an indirect gap semiconductor; such semiconductors often display much weaker optical effects than direct gap materials (such as the III-V materials typically used for optoelectronics). This discovery is very promising for small, high-speed, low-power optical output devices fully compatible with silicon electronics manufacture.     

Evolutionary gain of highly divergent tRNA specificities by two isoforms of human histidyl-tRNA synthetase

The discriminator base N73 is a key identity element of tRNA^His. In eukaryotes, N73 is an “A” in cytoplasmic tRNA^His and a “C” in mitochondrial tRNA^His. We present evidence herein that yeast histidyl-tRNA synthetase (HisRS) recognizes both A73 and C73, but somewhat prefers A73 even within the context of mitochondrial tRNA^His. In contrast, humans possess two distinct yet closely related HisRS homologues, with one encoding the cytoplasmic form (with an extra N-terminal WHEP domain) and the other encoding its mitochondrial counterpart (with an extra N-terminal mitochondrial targeting signal). Despite these two isoforms sharing high sequence similarities (81% identity), they strongly preferred different discriminator bases (A73 or C73). Moreover, only the mitochondrial form recognized the anticodon as a strong identity element. Most intriguingly, swapping the discriminator base between the cytoplasmic and mitochondrial tRNA^His isoacceptors conveniently switched their enzyme preferences. Similarly, swapping seven residues in the active site between the two isoforms readily switched their N73 preferences. This study suggests that the human HisRS genes, while descending from a common ancestor with dual function for both types of tRNA^His, have acquired highly specialized tRNA recognition properties through evolution.     

Matched glass-to-Kovar seals in N2 and Ar atmospheres

The oxidation of Kovar alloy was investigated, the wetting and spreading behavior of hard and soft glasses on Kovar alloy were studed by using the sessile drop method, and the quality and the seal strength of glass-Kovar seals were tested. The experimental results indicated that the preoxidation of Kovar alloy for approximately 10 min at 700°C in air resulted in excellent adherence in glass-Kovar seals. The wetting and spreading behavior of glass on preoxidized Kovar alloy were superior to that on nonoxidized Kovar alloy. The wetting ability of ASF110 glass, at 950°C and 980°C in Ar and N₂ atmospheres, was significantly superior to that of ASF200R and ASF700 glasses. The seal quality of the glass-preoxidized Kovar seal was superior to that of the glass-nonoxidized Kovar seal. The shear strength of the ASF110 glass-preoxidized Kovar seal, which was prepared at 980°C for 20 min in an Ar atmosphere, was approximately 3.9 MPa.     

Dependence of 6β-acetoxy-7α-hydroxyroyleanone block of Kv1.2 channels on C-type inactivation

Voltage-gated K⁺ (Kv) channels exhibit slow or C-type inactivation during continuous depolarization. A selective pharmacological agent targeting C-type inactivation is hitherto lacking. Here, we report that 6β-acetoxy-7α-hydroxyroyleanone (AHR), a diterpenoid compound isolated from Taiwania cryptomerioides, can selectively modify C-type inactivation of Kv1.2 channels. Extracellular, but not intracellular, AHR (50 μM) dramatically accelerated the slow decay of Kv currents and left-shifted the steady-state inactivation curve. AHR blocked Kv currents with an IC₅₀ of 17.7 μM. AHR did not affect the kinetics and voltage-dependence of Kv1.2 channel activation. Channel block by AHR was independent of intracellular K⁺ concentration. In addition, effect of AHR was much attenuated in a Kv1.2 V370G mutant defective in C-type inactivation. Therefore, block of Kv1.2 channels by AHR did not appear to involve direct occlusion of the outer pore but depended on C-type inactivation. AHR could thus be a probe targeting Kv channel C-type inactivation gate.     

耐磨型复合纤维在无石棉摩擦材料中的研究

为了提高目前无石棉摩擦材料的综合性能，尤其是降低材料的热衰退性以及磨损率，通过对摩擦材料原料的分析以及大量的试验研究，研制了一种耐磨型复合纤维，将其应用于无石棉摩擦材料中．通过对添加了耐磨型复合纤维的无石棉摩擦材料的测试，表明该无石棉摩擦材料具有安全、环保、抗热衰退性好、耐磨等独特的性能优点，是一种较为理想的无石棉摩擦材料．     

非破坏性检测地下LNAPL污染技术研究

采用非破坏性透地雷达,对台湾嘉义市水上乡地下污染情况施测,参考实地钻探报告,对污染范围进行描绘,经比对施测结果与钻探报告,透地雷达检测比水轻非水相液体(LNAPL)污染结果准确,污染范围判定吻合.     

对称屏蔽带状线内TE模的数值研究

采用有限差分法对对称屏蔽带状线内TE模进行了数值研究,得出了在不同导体带宽度情况下两个最低TE模的色散曲线以及前四个TE模的纵向磁场分量在横截面上的分布图.结果表明:随着导体带宽度的增加,使得其最低阶TE模的截止频率下降,而次低阶TE模的截止频率基本不变.     

重子五夸克态波函数及能谱的研究

基于手征SU(3)夸克模型,研究了一类包含1个反夸克的五夸克系统(q4-q).采用Jacobi坐标,利用五体理论方法,推导建立了四夸克子系统的波函数,并和反夸克耦合后得到了五夸克系统波函数,在雅可比坐标系下分别计算了夸克-夸克及夸克-反夸克的各个相互作用势.通过T-M变换得到同一Jacobi坐标下五夸克态系统Diamond结构(q4-q)20个态的能量.