Deep centers investigations of P-HEMT functional materials of ultra-high-speed microstructures grown by MBE

The deep centers of high electron mobility transistor (HEMT) and pseudomorphic-HEMT (P-HEMT) functional materials of ultra-high-speed microstructures grown by MBE are investigated using deep level transient spectroscopy (DLTS) technique. DLTS spectra demonstrate that midgap states, having larger concentrations and capture cross sections, are measured in n-AlGaAs layers of HEMT and P-HEMT structures. These states may correlate strongly with oxygen content of n-AlGaAs layer. At the same time, one can observe that the movement of DX center is related to silicon impurity that is induced by the strain in AlGaAs layer of the mismatched AlGaAs/InGaAs/GaAs system of P-HEMT structure. The experimental results also show that DLTS technique may be a tool of optimization design of the practical devices.

Investigation on the origin of wurtzite domains in thick cubic GaN using reactive ion etching

We measured the depth profiling of photoluminescence (PL) in cubic GaN films. The depth-resolved PL of normal grown GaN layers showed that the near-band-edge luminescence intensities of both cubic and wurtzite domains remained constant only until an etching depth of up to 2.7 mu m, but their ratio remained unchanged at all etching depths. Moreover, when a thin In0.1Ga0.9N layer was sandwiched between two GaN layers, the content of the wurtzite domains increased, and its distribution showed a dependence on thickness. As the reactive ion etching depth increased, the PL intensity ratio of cubic GaN to wurtzite domains increased. Based on the distribution, the strain relaxation, instead of the instability of cubic GaN at high temperature, was attributed to the origin of wurtzite domains. (C) 2000 Elsevier Science S.A. All rights reserved.

Uniformity enhancement of the self-organized InAs quantum dots

Growth interruption was introduced after the deposition of GaAs cap layer, which is thinner than the height of quantum dots. Uniformity of quantum dots has been enhanced because the full-width of half-maximum of photoluminescence decrease from 80 to 27 meV in these samples as the interruption time is increased. Meanwhile, we have observed that the peak position of photoluminescence is a function of interruption time, which can be used to modulate energy level of quantum dots. All of the phenomenon mentioned above can be attributed to the diffusion of In atoms from the tops of InAs islands to the top of GaAs cap layer caused by the difference between the surface energies of InAs and GaAs. (C) 1999 Elsevier Science B.V. All rights reserved.

cryptanalysis of the end-to-end security protocol for mobile communications with end-user identification/authentication

IEEE Computer Society

黄土高原沟壑区通量数据空间代表性研究

利用FSAM(Flux Source Area Model)模型,对中国科学院长武黄土高原农业生态试验站2004—2005年冬小麦生育期内的通量数据空间代表性进行了研究。结果发现,在90%贡献率水平下,整个冬小麦各生育期内通量源区范围动态变化明显,通量贡献最大点在距离观测点7.7~36.2m范围内变化。在盛行风向上,通量源区离观测点最近点为3.3 m,最远点可达172.8 m;在侧风向上,通量源区在38.1~128.4 m范围内变化。不同观测高度的对比研究表明,观测高度从1.86 m增加到12.17 m,盛行风向上源区距观测点最远距离从172.8 m增加到1 555.2 m;在侧风向上则从123.2 m增加到665.8 m,通量源区范围随高度的增加而增大。大气稳定度对通量贡献源区影响很大,在大气稳定状态下,通量源区面积最大,距观测点最远距离达到135.3 m;中性条件下次之,为101.7 m;在不稳定条件下面积最小,为36.3 m。同一日内,夜晚源区面积较白天大。在日和季尺度上,大气稳定度是影响通量源区范围的一个重要因素。

纳帕海黑颈鹤(Grus nigricollis)越冬行为生态研究

2006年10月～2007年5月，我们采用固定路线调查、瞬时扫描行为取样法对云南纳帕海越冬黑颈鹤的行为时间分配、鹤群结构、栖息地利用等方面作了研究。 黑颈鹤越冬期日间行为主要以觅食和警戒为主，分别为76.81±9.1％和11.84±5.6％，两种行为共占了黑颈鹤日间行为时间分配比例的88.65％；其它几种行为除理羽（5.18±4.2％）、走动（3.37±2.25％）和休息（1.32±1.7％）外，其所占比例均在1％以下，它们分别为：飞行0.59±0.89 ％、鸣叫0.41±0.63％、争斗0.22±0.30％和其它0.22±47％。越冬期中黑颈鹤日间行为具有明显节律性，觅食行为呈早晚双峰型节律，且傍晚的觅食高峰较高。黑颈鹤在纳帕海越冬期间从数量变化上可分为4个时期：1 早期的越冬集散期；2 中期的越冬稳定期；3 晚期的迁飞集散期；4 末期的幼鹤滞留期。鹤群结构及行为在不同的时期之间有着显著的变化。在越冬期中期，黑颈鹤特别是带有幼鹤的繁殖家庭更偏向于选择以家庭为单位的活动形式活动。集群鹤和领域鹤间在行为的时间分配上存在显著差异，集群活动有着集体警戒的优势使得集群鹤有了更多的时间用于觅食，但集群中的繁殖家庭并不能有效的利用这种优势，集群密集活动中高的争斗比例给集群中的幼鹤带更多的威胁，增加了繁殖家庭中成鹤的负担。家庭鹤为了维护领域不受侵犯，付出了更高的警戒时间，而减少了觅食的时间分配，但稳定的环境给幼鹤的稳定成长提供了更可靠的保证。鹤群结构组成的研究表明，繁殖家庭倾向于选择在一定的家庭领域中单独活动，非繁殖成鹤则更多的选择活动在集群中。集群中的幼鹤跟家庭中的幼鹤在觅食、警戒、理羽、走动、休息、争斗等主要行为上并无差异，但集群中的幼鹤的躲避攻击的行为要显著高于家庭活动中的幼鹤，说明了家庭活动对幼鹤有着更好的保护作用，集群中的高争斗行为对幼鹤产生了一定的不利影响。幼鹤和成鹤间行为存在明显差异：幼鹤的觅食比例比较高，略高于集群中的成鹤而显著高于家庭中的成鹤，走动和休息两种行为高于成鹤，相反鸣叫、争斗行为低于成鹤。这说明，幼鹤在活动中的警戒作用很少，更多时间是用于觅食和休息中，家庭中的幼鹤也并不更多的承担警戒和维护家庭领域的任务，而同样以觅食和休息为主。 越冬鹤群白天栖息地主要有浅水沼泽、农地、草地、猪拱地和开阔水域5种，其中猪拱地与草甸裸地为浅水沼泽和草地的次生生境。5种栖息地中以浅水沼泽利用比例最大为32.26％，其次是猪拱地（31.49％），然后农地（18.01％）和草地（10.91％）；开阔水域最小，只5.55％（图11）。这5种栖息地中，农地和猪拱地中鹤群的觅食比例最大分别为：78.85％和76.61％，是黑颈鹤越冬季觅食的重要地点之一。草地中鹤群的觅食行为比例（61.63％）相对其它4种栖息地中的觅食比例中最低，相反，移动和休整行为比例最高，是鹤群休息和转换觅食地的场所。鹤群对浅水沼泽的利用率最大，但浅水沼泽中鹤群的觅食比例并不是最高（71.22％），略低于农地和猪拱地中鹤群的觅食比例，这可能是因为沼泽中食物营养比较高，鹤群可以在不高的觅食时间中获取足够的能量造成的。猪拱地和裸泥地的利用率及鹤群在此种栖息地中的觅食比例均较高，仅次于浅水沼泽和农地两种最主要的栖息地类型，说明家畜的影响在一定程度上为越冬鹤群增加了新的觅食地，有利于黑颈鹤的越冬。 纳帕海越冬黑颈鹤春季迁徙时间从3月底开始持续至4月中下旬，2007年春季迁徙共持续时间22天。天气条件和日时间对鹤群的迁徙有着明显的影响，鹤群迁徙主要出现在晴天或多云天气的10:00-12:00段。晴朗的天气有利于形成上升气流，10:00-12:00时间段上升气流最强、最为稳定，能为鹤群迁徙节省最多的能量，有利于鹤群的迁徙。

珊瑚骨骼生长研究评述

珊瑚骨骼生长有年、月、日周期,能够当作古生物钟来记录地质历史。块状珊瑚

Mechanisms of optical confinement in phase-locked laser arrays

The nature of optical confinement in phase-locked laser arrays (PLLAs) with a mesa-stripe structure (MSS) has been studied. Two main mechanisms are distinguished, which are based on the variation of the waveguide effective refractive index due to MSS formation and on the refractive index modulation induced by the heating of the structure. Stable operation was achieved when either weak or strong optical coupling was realized in the PLLA. A phase-locked regime of radiation was obtained only for laser diodes with strong optical coupling. In the latter case the angle divergency was not greater than 2 degrees for the antisymmetric supermode emission from the PLLA.

Quantum interference effect in GaAs/AlGaAs double quantum wells

Quantum interference properties of GaAs/AlGaAs symmetric double quantum wells were investigated in a magnetic field parallel to heterointerfaces at 1.9 K. For two types of samples used in our experiments, two GaAs quantum wells with the same width of 60 Angstrom are separated by an AlGaAs barrier layer of 120 Angstrom and 20 degrees thick, respectively. The channels with the length of 2 mu m are defined by alloyed ohmic contacts. The conductance oscillation as a function of the magnetic flux Phi(= B/s) was observed and oscillation period is approximately equal to h/e. The results are in agreement with the theoretical expectation of the Aharonov-Bohm effect. Conductance oscillations are apparent slightly in the samples with a thinner AlGaAs barrier.