Bump磁铁电源控制器的设计

HIRFL—CSR（兰州重离子冷却储存环）是国家 “九五”重大科学工程之一。在磁铁电源的控制系统中需要电源控制器及时准确的提供基准的电压波形，并对输出的波形进行回读监测，以保证加速器正常工作。 论文介绍了电源系统的要求和特点，并根据设计要求给出了设计思想和系统框图，本控制系统主芯片采用TI公司的TMS320C6713芯片，并给出了DSP系统设计的一般流程。文中详细介绍了TMS320C6713芯片的结构和性能指标，以及其外围电路和存储器的扩展情况，指出了在高速电路板设计时应注意的问题。 设计中使用可编程逻辑器件，使设计可灵活配置，电路板设计在有BGA封装器件情况下实现四层板手工布线。 论文完成的Bump磁铁电源控制器的硬件电路设计，为以后的软件编写和测试搭建了坚实的平台

Bump-Surface Multicompartment Micelles from a Linear ABC Triblock Copolymer: A Combination Study by Experiment and Computer Simulation

Novel bump-surface multicompartment micelles formed by a linear amphiphilic ABC triblock copolymer via self-assembly in selective solvent were successfully observed both in simulation and experiment. The results revealed that the block A forms the most inner core, and the blocks B and C form the inner and outer layers, respectively, and the bumps were formed by block A and more likely to be born on curving surfaces. Moreover, the micelle shape could be controlled by changing the solvent selectivity of the blocks A and B. Spherical, cylindrical, and discoidal micelles with bumpy surfaces were obtained both in experiment and simulation.

A thin liquid film and its effects in an atomic force microscopy measurement

Recently, it has been observed that a liquid film spreading on a sample surface will significantly distort atomic force microscopy (AFM) measurements. In order to elaborate on the effect, we establish an equation governing the deformation of liquid film under its interaction with the AFM tip and substrate. A key issue is the critical liquid bump height y(0c) at which the liquid film jumps to contact the AFM tip. It is found that there are three distinct regimes in the variation of y(0c) with film thickness H, depending on Hamaker constants of tip, sample and liquid. Noticeably, there is a characteristic thickness H* physically defining what a thin film is; namely, once the film thickness H is the same order as H* , the effect of film thickness should be taken into account. The value of H* is dependent on Hamaker constants and liquid surface tension as well as tip radius.

Food Consumption by In Situ Pen-Cultured Planktivorous Fishes and Effects on an Algal Bloom in Lake Taihu, China

Silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) were used as a new pen-cultureed biomanipulation technique to control algal blooms in Meiliang Bay of Lake Taihu. In order to evaluate the capacity of these two fishes to decrease algal blooms, diel feeding samplings were carried out in May (without algal blooms) and September (with algal blooms) in 2005. Based on estimated food consumption by the Elliott-Persson model, silver carp increased daily food consumption from 2.07 g dry weight per 100 g wet body weight in May before the outbreak of algal blooms to 4.98 g dry weight per 100 g wet body weight in September during algal blooms outbreak. However, no obvious variation of food consumption was observed in bighead carp during the study period. This species 1.88 and 1.54 g dry weight of plankton per 100 g wet body weight in May and September, respectively. Silver carp had a higher feeding capacity for plankton than bighead carp. Biotic factors (i.e., fish size and conspecific competition with natural species in the lake) may affect the feeding behaviors of both carps as well as seasonal variation of plankton communities in the pen.

Development of solar-blind AlGaN 128x128 ultraviolet focal plane arrays

This paper reports the development of solar-blind aluminum gallium nitride (AlGaN) 128x128 UV Focal Plane Arrays (FPAs). The back-illuminated hybrid FPA architecture consists of an 128x128 back-illuminated AlGaN PIN detector array that is bump-mounted to a matching 128x128 silicon CMOS readout integrated circuit (ROIC) chip. The 128x128 p-i-n photodiode arrays with cuton and cutoff wavelengths of 233 and 258 nm, with a sharp reduction in response to UVB (280-320 nm) light. Several examples of solar-blind images are provided. This solar-blind band FPA has much better application prospect.

热退火对分子束外延生长的高纯GaAs薄膜中深能级的影响

于2010-11-23批量导入

HIRFL-CSRm电子冷却模拟与实验

本论文从理论、模拟和实验三方面研究了HIRFL-CSRm离子束的电子冷却累积过程。 在没有内靶实验装置的电子冷却储存环中，离子束的冷却过程，是离子在电子冷却效应和以束内散射为主的各种加热效应共同作用下，发射度收缩并趋于平衡的过程。其中磁化冷却力的求解是研究电子冷却效应的理论基础，本论文采用Monte-Carlo技术解决了两体碰撞模型下磁化冷却力复杂积分表达式的求解，探讨了影响磁化冷却力的参数。针对离子束内散射过程，论文在B-M模型下束内散射率表达式的基础上，通过应用Carlson第二类椭圆积分形式实现了束内散射导致的束流发射度和动量分散变化的快速计算，分析了其对HIRFL-CSRm冷却累积过程的影响。 由于冷却力是离子-电子相对速度的复杂函数，而且考虑离子在储存环中的横向振荡和纵向运动特性，以及电子束空间电荷效应等情况下，冷却过程中束流发射度和动量分散的时间变化率无法解析计算。本论文采用模型离子跟踪方法，模拟了离子束特征参数在冷却过程中的变化，明确了电子束参数对冷却过程的影响函数，计算了几种典型离子束冷却累积的最佳参数值，并对测量冷却效应的实验方法进行了模拟研究。 对HIRFL-CSRm五种重离子束流（7.07MeV/u12C4+、8.28MeV/u12C5+、7.07MeV/u12C6+、21.6MeV/u36Ar18+、2.93MeV/u129Xe27+）的电子冷却和累积过程进行了初步的实验研究。采用电子束能量调制的方法，测量了12C6+和36Ar18+离子束受到的纵向冷却力随离子-电子相对速度变化的函数，分析了电子束密度、形状及电子束-离子束夹角对36Ar18+离子受到的纵向冷却力大小的影响。通过改变Bump触发的间隔时间研究了12C6+离子的横向冷却效应。实验研究了电子束密度、形状对几种束流的累积效率及储存束流寿命的影响，以及Bump幅度、Bump时间结构、注入间隔时间、绝热展开因子等参数对束流累积效率的影响。实验测量并理论验证了12C6+和36Ar18+强流束的集体效应，探讨了强流离子束的不稳定性。最后，论文展望了在HIRFL-CSR上进一步开展电子冷却实验的方向

CSR特殊磁铁研制

特殊磁铁主要指用于同步加速器束流的注入和引出系统中的各类磁铁，如切割磁铁、BUMP磁铁、KICKER磁铁等。从结构和用途上来看，特殊磁铁基本属于二极偏转磁铁范畴；与常规的二极磁铁相比，只是在运行模式、磁场分布和好场区位置、杂散场分布、磁铁功能以及磁铁结构和材料等方面具有突出的特殊性。如切割磁铁的好场区要紧贴切割边，而切割边外侧的杂散场要降到主场的千分之一以下；BUMP磁铁和KICKER磁铁的磁场值不高，但要以很快的脉冲方式工作，所以就具有大电流、线圈匝数少的特点。各种特殊的性能要求使得特殊磁铁的设计和制造相当复杂。 HIRFL-CSR工程共有四台切割磁铁、四套BUMP磁铁以及两套KICKER磁铁用于加速器束流的注入和引出系统中。论文介绍了特殊磁铁的选型、材料选取、电磁设计、二维及三维磁场计算、电磁参数计算、冷却计算、结构设计以及工艺设计等磁铁设计的全部过程；另外，对磁铁研制的具体细节以及技术要求、加工制造以及测试结果也作了比较全面的介绍。论文将磁铁的二维及三维磁场计算作为设计和论述的重点；因为就目前的技术水平来说，二维及三维磁场的计算是磁铁设计的主要环节，是磁场优化的主要手段，也是其他主要电磁参数计算的基础。特别是三维磁场的计算结果，是磁铁设计的主要技术依据，是一种仿真度极高且经济实用的模拟过程。一些比较成熟的磁场计算软件，如TOSCA、ANSYS、MAFIA等更是具有人机界面简单、建模方便、计算结果直观可靠等优点。特殊磁铁的磁场计算所用的程序是TOSCA；从文中提供的测试结果看，计算结果与实测值的误差只有 1 %，可见其结果是极其可信的。从测试和运行结果来看，各种特殊磁铁的研制是成功的。特殊磁铁的成功研制为HIRFL-CSR的束流注入和引出提供了硬件基础

Methods for physical separation and characterization of soil organic matter fractions

Turnover of soil organic matter (SOM) is coupled to the cycling of nutrients in soil through the activity of soil microorganisms. Biological availability of organic substrate in soil is related to the chemical quality of the organic material and to its degree of physical protection. SOM fractions can provide information on the turnover of organic matter (OM), provided the fractions can be related to functional or structural components in soil. Ultrasonication is commonly used to disrupt the soil structure prior to physical fractionation according to particle size, but may cause redistribution of OM among size fractions. The presence of mineral particles in size fractions can complicate estimations of OM turnover time within the fractions. Densiometric separation allows one to physically separate OM found within a specific size class from the heavier-density mineral particles. Nutrient contents and mineralization potential were determined for discrete size/density OM fractions isolated from within the macroaggregate structure of cultivated grassland soils. Eighteen percent of the total soil C and 25% of the total soil N in no-till soil was associated with fine-silt size particles having a density of 2.07-2.21 g/cm3 isolated from inside macroaggregates (enriched labile fraction or ELF). The amount of C and N sequestered in the ELF fraction decreased as the intensity of tillage increased. The specific rate of mineralization (mug net mineral N/mug total N in the fraction) for macroaggregate-derived ELF was not different for the three tillage treatments but was greater than for intact macroaggregates. The methods described here have improved our ability to quantitatively estimate SOM fractions, which in turn has increased our understanding of SOM dynamics in cultivated grassland systems.

基于随机网络编码的无线广播重传方案及性能分析

针对自动最复重传(ARQ)机制在无线广播系统中吞吐量性能不佳的缺陷,提出一种基于随机网络编码的广播重传方案RNC-ARQ。对于广播节点,采用随机线性码对所有丢失包进行编码组合重传。对于接收节点,当接收的编码包累积到一定数量后可通过解码操作恢复出原始数据。该方案可有效减少重传次数,改善无线广播的吞吐量性能。基于Gilbert-Elliott模型描述的突发错误信道,建立了信道状态和节点接收处理流程合并的多状态马尔可夫模型,并以此为基础推导了RNC-ARQ方案的TQ吐量闭合解。最后,使用NS-2模拟器评估RNC-ARQ方案的性能,结果表明在突发差错信道下,基于随机网络编码重传方案的吞吐量优于传统的选择重传ARQ方案和基于异或编码的重传方案。