青海湖的理化性質和生物学特性

<正> 青海省青海湖是我国最大的內陆湖,湖水的化学性貭,过去仅有俄国科学院的Schmidt以在1872年和1880年先后在青海湖南部采得的水样进行过分析,測定湖水中总盐量为11.1463—13.5937％,其中含氯量为4.2889—5.4029％。作者等于1956年8月間在青海湖調查时,曾进行了湖的东、南、西三部分湖水的理化性貭观察和分析,其結果如表所列。青海湖面积将近4,000平方公里,湖床平坦,湖水平均深度在25米以上,最深处有31.4米。湖水在

Driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status

1. We studied driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status, the oligotrophic deep Lake Fuxian and the eutrophic shallow Lake Xingyun. 2. Phytoplankton samples were taken monthly for a year and phytoplankton species were sorted into the main taxonomic groups and associations proposed by Reynolds. A canonical correspondence analysis (CCA) was used to test the occurrence of these classification schemes and to determine their discriminatory power. 3. The results suggest that the major driving forces in Lake Fuxian were physical variables, and particularly the underwater light climate, whereas, nutrients were the important driving force in Lake Xingyun. 4. Top-down control through zooplankton grazing in Lake Fuxian was hardly ever a significant determinant itself, because of the scarcity of zooplankton and their low grazing efficiency of predation while a dominance of inedible cyanobacteria throughout the year rendered top-down controls ineffective failing in Lake Xingyun. Hence phytoplankton communities in both lakes appear to be regulated primarily by bottom-up controls.

Redescription of Camallanus hypophthalmichthys Dogel and Akhmerov, 1959 (Nematoda : Camallanidae) and its first record from fishes in China

The nematode Camallanus hypophthalmichthys Dogel and Akhmerov, 1959 is redescribed from specimens collected from the intestine of the bighead carp Aristichthys nobilis, from Liangzihu Lake (Yangtze River basin), Hubei Province, central China. The light and scanning electron microscopical examination made it possible to study in detail the morphology of this so far little-known species and to confirm its validity. The main specific features of C. hypophthalmichthys distinguishing it from the most similar Camallanus spp. is the presence of 3 small caudal processes on the male tail tip, 13-16 longitudinal ridges on the inner surface of the valve of the buccal capsule, and the arrangement of preanal and postanal genital papillae in the male. This finding represents a new host record, the first record of this parasite in the Yangtze River basin, and the first documented record of C. hypophthalmichthys from China. Camallanus hypophthalmichthys is considered a specific intestinal parasite of fishes of the cyprinid Hypophthalmichthyinae.

Optical microwave generation using two parallel DFB lasers integrated with Y-branch waveguide coupler

A new device of two parallel distributed feedback (DFB) lasers integrated monolithically with Y-branch waveguide coupler was fabricated by means of quantum well intermixing. Optical microwave signal was generated in the Y-branch waveguide coupler through frequency beating of the two laser modes coming from two DFB laser in parallel, which had a small difference in frequency. Continuous rapid tuning of optical microwave signal from 13 to 42 GHz were realized by adjusting independently the driving currents injected into the two DFB lasers.

Occupation modulation of higher subbands in a three-barrier tunnelling structure with a magnetic field

We verify that the magnetic suppression of intersubband LO or LA phonon scattering can give rise to a noticeable nonthermal occupation in higher-lying subbands. This is clearly determined by the relative intensity ratio of the interband photoluminescence spectra for the E-2 - HH1 and E-1 - HH1 transitions. The observed phenomenon may provide an effective method to control the intersubband scattering rate, which is a key factor of the so-called quantum cascade lasers. This is helpful for the population inversion between both the subbands in quantum wells.

求和生成器的相关性分析

J.Dj,Golic运用线性序列电路逼进的方法来分析具有任意个输入的求和生成器,他猜想可以通过这种方法来获得所有具有最大相关系数的输入和输出线性函数对,但是他未给出证明。利用Walsh变换技术证明了当n是偶数的时候这个猜想成立。另外,还研究了求和生成器的相关系数总和,发现它与带1比特组合器的相关系数总和非常类似。

用注入锁模法改善DFB激光器的频率响应

验证了通过注入锁模方法，分布反馈（DFB）半导体激光器的频率响应可以得到明显的改善．实验中通过一个环形器，将主激光器的输出光注入到从激光器．测量了从激光器在有注入光和没有注入光时的光谱和频率响应．发现在不同的注入光强度和波长下，激光器的调制带宽和弛豫振荡峰频率会发生变化．通过适当选择注入光的强度和波长，频率响应可以得到改善．激光器频率响应的改善可以用两个模式的拍频来解释，一个模式是从激光器的主模，另一个是主激光器的模式，该模式与从激光器的边带重合．该理论与实验结果符合得很好。

氧化限制型垂直腔面发射激光器串联电阻分

含氧化限制孔的VCSEL具有低的阈值电流,但氧化孔的存在也会加大串联电阻.本文采用理论模型,详细计算了氧化限制型VCSEL的串联电阻.把串联电阻分解为垂直方向电阻和横向电阻,分析了串联电阻与氧化孔半径的关系,提出了降低VCSEL串联电阻的具体方法.

单节拍浮点运算神经元的组合逻辑设计

介绍了通用神经计算机CASSANDRA-Ⅱ中单节拍浮点运算神经元的硬件设计方法.基于通用超曲面神经元模型,以组合电路与EPROM查表分别实现浮点数加法、乘法及p次幂运算,从而实现了单节拍内完成浮点运算|W(X-Y)|p的神经元组合逻辑设计.该设计使通用神经计算机硬件具有更强的适应能力和更好的网络性能.