Efficient Mode-locked and Q-switched Nd∶YVO_4 Laser with Semiconductor Saturable Absorber Mirror

We reported an efficient diode pumped Nd ! YVO, 1 064 nm laser passively mode-locked and Q-switched by a semiconductor saturable absorber mirror(SESAM). At the incident pump power of 7. 5 W, 2. 81 W average output power was obtained during stable CW mode locking with a repetition rate of 111 MHz. The optical conversion efficiency was 37. 5% , and the slope efficiency was 39%. So far as we know, this is the highest optical-optical conversion efficiency with a SESAM at home.

Dependence of ultra-thin gate oxide reliability on surface cleaning approach

In this paper, we investigate the effect of silicon surface cleaning prior to oxidation on the reliability of ultra-thin oxides. It is demonstrated that chemical preoxide grown in H2SO4/H2O2 (SPM) solution prior to oxidation provides better oxide integrity than both HF-based solution dipping and preoxide grown in RCA SC1 or SC2 solutions. It is also found that the oxides with SPM preoxide exhibit better hot-carrier immunity than the RCA cleaned oxides.

Crystallographic and magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

The crystallographic and intrinsic magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) have been investigated. The lattice constants and the unit cell volume of R3Fe29-xTxHy decrease with increasing R atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Regular anisotropic expansions, mainly along the a- and b-axis rather than along the c-axis, are observed for all the compounds upon hydrogenation. Hydrogenation leads to an increase in Curie temperature. First-order magnetization processes (FOMP) occur in magnetic fields of around 1.5 T and 4.0 T at 4.2 K for Nd3Fe24.5Cr4.5H5.0 and Tb(3)Fc(27.0)Cr(2.0)H(2.8), and around 1.4 T at room temperature for Gd3Fe28.0Cr1.0H4.2 Abnormal crystallographic and magnetic properties of Ce3Fe29-xTxHy suggest that the Ce ion is non-triply ionized.

黄河三角洲丹顶鹤生境变化与评价

黄河三角洲丹顶鹤生境变化与评价 摘 要 从水禽角度出发，把影响其生境选择的因素划分为水、食物、隐蔽物和干扰四类。用遥感和地理信息系统软件对黄河三角洲地区3期TM数据进行处理，根据生境要素特征，对生境进行分类，获取该地区1986年、1996年和2001年3个时期各生境要素图。把生境要素图进行叠加，最终得到3个时期的黄河三角洲的水禽生境类型图。 通过对各生境要素图的面积、斑块数变化及转移矩阵的分析，可以看出各生境要素的结构发生了明显的变化，对水禽生境而言，总的结果是干扰加重、积水地区面积增多、植物性食物和适宜隐蔽物范围减小，通过对这种变化进行分析得出：人类有意识的活动（干扰）是引起各生境要素发生变化的主要驱动力。生境要素的变化造成黄河三角洲地区水禽生境质量的下降。 再以黄河三角洲生境分布图为基础，运用遥感和地理信息系统软件得出三个时期丹顶鹤（Grus japonensis）生境分布图。选取一系列的景观指数，通过APACK软件进行计算，结合土地利用动态度的概念对黄河三角洲地区从1986—2001年丹顶鹤生境的动态变化进行量化分析。结果表明：适宜丹顶鹤栖息的总生境面积不断减小，该地区的生境破碎化程度也不断升高；相应的适应丹顶鹤栖息的各生境类型的面积除了轻干扰深积水鱼类苇田（人类活动造成）的面积增加外，其余大多呈减少趋势，总的来说丹顶鹤栖息生境质量呈下降趋势。人类活动是黄河三角洲丹顶鹤生境的变化的主要驱动力。 在利用景观连接度模型进行丹顶鹤生境评价的研究中发现：在黄河三角洲内尚有1062.63 km2适宜丹顶鹤生存的生境，占总面积6021.05 km2的17.65%。其中最适生境面积为205.84km2，占总面积的3.42%；适宜生境面积为142.47 km2，占总面积的2.37%；中等适宜面积为420.27 km2，占总面积的6.98%；勉强适宜面积为294.05 km2，占总面积的4.88%；不太适宜面积为2532.07 km2，占总面积的42.05%；不适宜面积为2426.36 km2，占总面积的40.30%。虽然适宜生境面积还很大，但在空间分布上十分零散，除了几个较大的斑块外，尚有许多较小斑块处于孤立状态，这些斑块将无法为丹顶鹤所利用。 黄河三角洲是我国最大的新生湿地生态系统，优越的生境条件使得该区物种丰富，成为许多水禽迁徙的重要中转站、越冬栖息地和繁殖地。本研究对区域生态保护和物种的生境评价研究有重要的理论和实践意义，为确保东亚鸟类迁飞网络的安全提供了科学的依据，这对黄河三角洲湿地生态系统、湿地鸟类及物种多样性的保护都意义重大。