选择性质子轰击DC-PBH激光器

在普通双沟平面掩埋异质结(DC-PBH)激光器的基础上，采用质子轰击的技术，制作了一种新型的选择性质子轰击DC-PBH激光器。这种新型的激光器结构与以前普遍的DC-PBH结构相比阈值电流降低，傅出功率及量子效率得到提高，尤其是它的调制特性得到明显改善，这种结构激光器的调制带宽由原来的2.0GHz提高到6.0GHz。

中国蔷薇属芹叶组（Rosa Sect. Pimpinellifoliae DC. ex Ser.）的分类学研究

本研究通过我国CDBI、 KUN、PE、SZ等主要标本馆约3, 500份馆藏标本的研究和野外考察相结合，对我国蔷薇属（Rosa L.）芹叶组(Sect. pimpinellifoliae DC. ex Ser.）植物以及相关组的一些种进行了性状特征、形态和微形态的研究，对该组的一些种的形态特征描述进行了补充，同时给出详细的地理和海拔范围分布图。综合花粉以及种子（瘦果）形态的研究结果重新制订了分种检索表，同时，对该组一些形态相近容易混淆的种进行了对比研究，特别对一直存在争议的绢毛复合体（绢毛蔷薇R. sericea Lindl.和峨眉蔷薇R. omeiensis Rolfe）进行了大量宏观形态特征的研究，并用光学显微镜（LM）和扫描电镜(SEM)对二者的花粉及种子形态、微形态进行对比研究和分析，主要研究内容包括： 1. 芹叶组孢粉研究 对芹叶组的10个种及相关的4个组共17个种（18个样品）的植物花粉进行了光镜和扫描电镜观察和比较研究。研究结果表明：蔷薇属植物花粉粒大小为中等偏小，极轴长23.98[21.82(R. graciliflora Rehd. et Wils.)～29.18(R. tsinglingensis Pax. et Hoffm.)] μm，赤道轴长28.65[24.15（R. graciliflora）～34.70(R. davidii Crép.)] μm；花粉属辐射对称等极单花粉，花粉形态赤道面观呈球形到超长球形；极面观为三裂圆形或近圆形,三孔沟，孔缘加厚,具中部突起的桥状盖。花粉外壁纹饰为条纹状，光镜下形态特征相差不大；在电镜下外壁条纹和脊沟内穿孔的形状、大小和频度等特征，常具组至种水平上的可见变异，可作为组至种水平划分的依据。 根据花粉外壁条纹特征及穿孔形状和数目等特征，本研究将这些植物的花粉归为5个类型，并编制了分组检索表。同时，根据条纹状的清晰度，排列方式、条纹形状、穿孔大小及其频度等方面的差异，各有特点，对该组的10个种编制了分种检索表。 2. 芹叶组种子形态研究 应用光学显微镜和扫描电镜对我国蔷薇属芹叶组14个种及相关组5个组共36种植物的种子宏观形态及种皮微形态特征进行了观察研究。结果显示，蔷薇属种子形态多样,形状分别为肾形、卵形或锥形等；种子颜色以淡棕色、褐色以及土黄色为主；种子大小种间相差悬殊，相对体积为（长×宽×厚）36.66（4.79～114.47) mm3。光镜下，种子宏观形态特征具组内一致性，在扫描电镜下种子表面结构特征因种而异，其纹饰以网纹为主，可分为3种类型，即近平滑型、负网纹型和网纹型。研究结果表明，蔷薇属种子表面纹饰与地理分布关系不大,具有组及种内稳定性。其种子形态、大小、表而纹饰类型等特征可作为蔷薇属组及种水平上的分类依据。 结合蔷薇属花粉形态研究结果，得出蔷薇属种皮微形态特征与花粉外壁纹饰特征相吻合，在代表组及种的特征上具相关性的结论。同时根据种子形态、微形态结构特征的组间区别和种间差异编制了分组及芹叶组14个种的分种检索表。 3. 绢毛蔷薇复合体的研究 通过对大量标本的研究、野外观察以及扫描电镜对绢毛蔷薇复合体的花粉形态和种皮表面结构进行研究，通过对小叶、花粉及种子的形态定量分析结果支持Rowley (1959)的观点，将峨眉蔷薇处理为绢毛蔷薇的一个变种。 综上研究结果得出，蔷薇属植物的小叶片数目、花被基数以及花粉及种子形态等性状是较为稳定的，这些特征可很好的作为分类学依据。 The morphology, pollen exine sculpture and seed coat structure of the species of Rosa sect. Pimpinellifoliae and related sections were studied.About 3,500 herbarium specimens at CDBI, KUN, PE, and SZ were examined. Field work in Sichuan and Yunnan were conducted. Revisions of some species were carried out and a new key to species of sect. Pimpinellifoliae was proposed based on morphology, pollen exine sculpture and seed coat structure, Detailed morphological descriptions, geographical distributions and the altitudinal ranges of some taxa are given. The systematics of the species complex, the Rosa sericea complex (R. sericea Lindl. & R. omeiensis Rolfe), was emphasized. This thesis focused on the following three aspects: 1. Pollen morphology of Rosa sect. Pimpinellifoliae The pollen morphology of 18 samples representing 10 species of the Eurasian Rosa sect. Pimpinellifoliae and 7 additional species of related sections was investigated under LM and SEM. The pollen grains are monadic, actinomorphic, equipolar, medium-sized, spheroidal to perprolate in equatorial view, 3-lobed circular or semi-circular in polar view, crassimarginate, pontoperculate, and with striate exine sculpture. The striate sculpture varies among sections and species. The equatorial axis ranges from 17.97 μm (R. sikangensis) to 29.18 μm (R. tsinglingensis) with an average of 23.98 μm in length, while polar axis varies from 24.15 μm (R. gracilifolra) to 34.70 μm (R. davidii) with an average of 28.65 μm in length. The pollens can be divided into five types based on striate sculpture and a key to the sections sampled was proposed accordingly. The pollen morphology of species of sect. Pimpinellifoliae is more homogeneous and different from other sections sampled and did not support the two-series subdivisions in sect. Pimpinellifoliae. A key is also provided based on characers of pollen morphology among species in sect. Pimpinellifoliae. 2. Seed coat structure of Rosa sect. Pimpinellifoliae The seed coat structure of 39 samples representing 14 species of Rosa sect. Pimpinellifoliae and 12 additional species of related sections was investigated under LE and SEM. The seed relative volume (Length × width × thickness) ranges from 4.79 to 114.47 mm3 with an average of 36.66. mm3. The seeds are reniform, ovate or oblong in shape, with orange-brown, light brown or deep brown color. Seed coat sculpture was reticulate or striate-like reticulate. There was no difference in sculpture character of various speices under LM, while three types of seed coat sculpture were identified under SEM and a key to species based on the seed coat sculpture was provided. The three types of seed coat sculpture were nearly smooth, areolate and reticulate. The study of the seed coat sculpture of same species sampled from different populations showed that characters on the seed coat are stable, and thus the size, shape and seed coat sculpture can be used in species level identification. Interestingly, characters in the seed coat sculpture and the pollen morphology in sect. Pimpinellifoliae are consistent at in specific or sectional levels. A key to the 14 species sampled was given based on seed coat sculpture. 3. The study on Rosa sericea complex The Rosa sericea complex contains R. omeiensis and R. sericea. They are morphologically similar to one another and the systematic status of R. omeiensis has been controversial. In this study we examined large numbers of herbarium specimens of R. omeiensis and R. sericea and conducted field observations in the Hengduan Mts.. We also performed SEM study of pollen morphology and seed coat structure of R. omeiensis and R. sericea. We further carried out intensive morphometric study on the leaflet, pollen, and seed morphology. Our results showed that R. omeiensis should be sunk to be a variety of R. sericea, just as Rowley’s treatment in 1959. In conclusion, the features in the number of leaflet and petal, and the morphological character on pollen and seed are relatively stable. Therefore these characters are very useful in taxon delimition.

多相同步DC-DC PWM控制器LTC1629

LTC1629是Linear公司专门为低压大电流的DC-DC变换电路设计的PWM控制电路,应用该公司的PolyPhaseTM~(TM)技术,有效地减少了输入输出纹波电流,同时提高了变换器的效率。本文介绍它的基本组成部分的功能和简单应用电路。

LT码的性能分析与研究

LT码(Luby Transform Codes)属于数字喷泉码,是一类新型前向纠错编码算法,适用于基于包通信的删除信道环境。本文概述了LT码的编译码原理及实现方法,对LT码的理想孤子度分布算法和鲁棒孤子度分布算法进行了仿真验证,分析了LT码在包删除信道下的性能,讨论了实际应用中的参数优化规则,研究结果对提高实时纠删应用的性能具有重要的实用价值。

OBSERVATION OF MOSSBAUER-EFFECT IN THE HIGH-TEMPERATURE SUPERCONDUCTOR EUBA2CU3O7-X WITH DC ELECTRIC-CURRENT

The difference between the Mossbauer parameters for EuBa2Cu3O7-x with dc electric current and those without dc electric current at 83 K has been observed. The change in isomer shift, electric quadrupole splitting and the asymmetry parameter of the electric field gradient at the Eu-151 nucleus may be caused by the movement of a mass of conduction electrons along a certain direction in the EuBa2Cu3O7-x crystal with a layered structure.

Effective response of nonlinear composite under external AC and DC electric field

A perturbation method is used to study effective response of nonlinear Kerr composites, which are subject to the constitutive relation of electric displacement and electric field, D-alpha = epsilon(alpha)E + chi(alpha)vertical bar E vertical bar(2)E. Under the external AC and DC electric field E-app = E-a (1 + sinwt), the effective nonlinear responses and local potentials are induced by the cubic nonlinearity of Kerr materials at all harmonics. As an example in three dimensions, we have investigated this kind of nonlinear composites with spherical inclusions embedded in a host. At all harmonic frequencies, the potentials in inclusion and host regions are derived. Furthermore, the formulae of the effective linear and nonlinear responses are given in the dilute limit.

Effective dielectric response of nonlinear composites with external ac and dc electric field

The perturbation method is developed to investigate the effective nonlinear dielectric response of Kerr composites when the external ac and dc electric field is applied. Under the external ac and dc electric field E-app=E-a(1+sin omegat), the effective coupling nonlinear response can be induced by the cubic nonlinearity of Kerr nonlinear materials at the zero frequency, the finite basic frequency omega, the second and the third harmonics, 2omega and 3omega, and so on. As an example, we have investigated the cylindrical inclusions randomly embedded in a host and derived the formulas of the effective nonlinear dielectric response at harmonics in dilute limit. For a higher concentration of inclusions, we have proposed a nonlinear effective-medium approximation by introducing the general effective nonlinear response. With the relationships between the effective nonlinear response at harmonics and the general effective nonlinear response, we have derived a set of formulas of the effective nonlinear dielectric responses at harmonics for a larger volume fraction. (C) 2004 American Institute of Physics.

Effective AC and DC responses of nonlinear composites at higher concentration

For higher concentration of inclusions, an effective medium approximation (EMA) method is used to investigate the bulk effective response of weakly nonlinear composites, which are subject to the constitutive relation of electric displacement and electric field, D-alpha = epsilon E-alpha + chi(alpha)|E|(2) E. As an example of three dimensions, under the external AC and DC electric fields E-app = E-a (1 + sin omega t), we have derived the general effective nonlinear response of composites by the EMA method for higher concentration of spherical inclusions. Furthermore, the effective nonlinear responses at harmonics are predicted.