子午岭人工油松林土壤种子库特征研究

采用野外调查取样和室内观测试验相结合的方法,研究了子午岭人工油松林土壤种子库的物种组成、密度、垂直分布等特征。结果表明:(1)土壤种子库储量密度平均为5711粒/m2,最大密度是9537粒/m2,最小密度是3563粒/m2。(2)土壤种子库的种子的垂直分布主要集中在0—2.5cm,2.5—5cm和5—7.5cm这3个层次,占75.38%～79.32%,枯枝落叶层和7.5—10cm层分布较少,占20.68%～24.62%。(3)土壤种子库物种组成主要为灌木和草本两个种类,无乔木植物,多年生草本在物种数和种子数上占据明显优势。

喷灌分布均匀系数研究

为突出局部灌溉不足或灌溉过量对均匀性的影响程度,提出了基于几何平均数分布均匀系数的概念,将其定义为部分测点水深几何平均值与所有测点算术平均值的比值。并根据部分测点水深数据的提取方法不同,分为1/4低值、1/4高值、1/2低值和1/2高值分布均匀系数。用MATLAB和VC~++语言编制了可以实现上述分布均匀系数计算的软件"SIUEW1.0"。结果初步证明:基于几何平均数的乘法模型要比基于算术平均数的加法模型更加突出了部分低(或高)于平均值的测点水深数据对均匀系数的影响程度,因此更适用于时局部灌溉不足或过量灌溉有严格控制要求地块的灌溉均匀性评价;无论高值和低值,取点数越少,均匀性的评价结果越差。

高性能InGaAs/AlAs共振隧穿二极管的研制与器件模拟分析

在半绝缘的InP衬底上采用分子束外延的方法生长制备了不同势垒厚度的RTD材料样品,室温下测量的最高峰-谷电流比为18.39.通过模拟得到RTD直流特性与势垒厚度、势阱材料及厚度、隔离层厚度以及掺杂浓度间的关系,对结果进行了分析与讨论.

半导体微碟激光器设计原理与工艺制作

用经典量子电动力学理论初步研究了半导体碟型微腔激光器的设计原理，采用光刻、反应离子刻蚀和选择化学腐蚀等现代微加工技术制备出抽运阈值功率很低且品质因数很高的低温光抽运InGaAs/InGaAsP多量子阱微碟激光器。这种激光器制作工艺简单，对有效光子状态密度调制较大，是比较理想的半导体微腔激光器。

Yellow luminescence mechanism and persistent photoconductivity in n-GaN single crystal films grown on alpha-Al2O3(0001) substrates by LP-MOCVD

Unintentionally doped and Si-doped single crystal n-GaN films have been grown on alpha-Al2O3 (0001) substrates by LP-MOCVD. Room temperature photoluminescence measurement showed that besides the bandedges, the spectrum of an undoped sample was a broad deep-level emission band peaking from 2.19 to 2.30eV, whereas the spectrum for a Si-doped sample was composed of a dominant peak of 2.19eV and a shoulder of 2.32eV. At different temperatures, photoconductance buildup and its decay were also observed for both samples.. The likely origins of persistent photoconductivity and yellow luminescence, which might be associated with deep defects inclusive of either Ga vacancy(V-Ga)/Ga vacancy complex induced by impurities or N antisite (N-Ga), will be proposed.

Photocurrent derivative spectra of ZnCdSe-ZnSe double multi-quantum wells

Photocurrent (PC) spectra of ZnCdSe-ZnSe double multi-quantum wells are measured at different temperature. Its corresponding photocurrent derivative (PCD) spectra are obtained by computing, and the PCD spectra have greatly enhanced the sensitivity of the relative weak PC signals. The polarization dependence of the PC spectra shows that the transitions observed in the PC spectra are heavy-hole related, and the transition energy coincide well with the results obtained by envelope function approximation including strain. The temperature dependence of the photocurrent curves indicates that the thermal activation is the dominant transport mechanism of the carriers in our samples. The concept of saturation temperature region is introduced to explain why the PC spectra have different temperature dependence in the samples with different structure parameters. It is found to be very useful in designing photovoltaic devices.

Early effects of carbon-ion irradiation on murine lymphocytes and thymocytes

To estimate the biological risks from space radiation encountered by cosmonauts in outer space, the effects from whole-body exposure to carbon ions or X-rays irradiations at 0, 0.39, 0.55 and 1 Gy at a dose rate of 0.2 Gy/min were investigated in BALB/c mice. The relative thymus and spleen weights were measured at 24 h after exposure, and the cell cycle distribution and percentage of apoptosis of thymocytes and spleen and peripheral blood lymphocytes were determined by flow cytometry. The data showed that exposure to carbon ions delayed cell progression of peripheral blood lymphocytes in S-phase, and delayed thymocytes and spleen lymphocytes in G(0)/G(1)-phase. Apoptosis of thymocytes and peripheral blood lymphocytes induced by carbon ions increased more rapidly with dose than was the case for X-rays. There were some differences between the relative weight loss of the thymus and the spleen with increasing dose of either carbon ions or X-rays. The results obtained provide evidence of dose- and organ-specific differences induced by carbon ions compared to X-rays, with increased apoptosis in peripheral blood lymphocytes and thymocytes, but not spleen lymphocytes. Our data may suggest that further work would be of interest to estimate risk of changes in immune function during particle radiation exposures in space travel. (c) 2007 COSPAR