用不对称的P/V操作设计并发算法

多线程并发是提高系统性能的常用手段,文章提出了一种用信号量的不对称P/V操作来设计多线程并发算法的新思路,这种思路适合于设计多线程同步程序以解决某些具有复杂同步语义要求的问题,而这些问题用传统的方法很难得到简洁高效的求解。为了演示这种新思路的特点和优点,笔者对几个常见问题(读写锁、排队锁和记录锁)给出了新的算法设计以及实现。实验数据表明,采用这种思路设计的算法在算法复杂度,读写速度和资源使用方面相对于传统的算法存在较大优势。

P-RBAC:一种门户环境下的访问控制模型

门户能够有效地实现异构信息之间的集成与协作,并为用户提供可定制、统一且遵循规范的访问服务.然而,由于门户所具有的这些不同于普通Web应用的特性,也使得传统访问控制模型无法在门户中直接使用.提出了一种面向门户系统的访问控制模型p-RBAC.P-RBAC扩展了传统的基于角色访问控制模型,并根据行为状态进一步分为静态模型和动态模型.P-RBAC给出了静态模型和动态模型上的行为规则,提出了具体的动态权限指派和角色组织策略,从而有效地解决了门户的访问控制问题.实际的应用案例证明,P-RBAC模型能够适用于门户的访问控制,并较之传统访问控制模型更高效可行.

高分子混合物薄膜表面形态的形成与稳定性

本工作主要从实验上探索了组分的分子量、薄膜厚度、混合物的组成等因素对不相容高分子混合物薄膜表面形态的形成和稳定性的影响规律。在此基础上，利用软印刷的方法对基底表面进行图案化，来控制高分子混合物的相分离行为，以制备规则排列的有序图案。用原子力显微镜（AFM）、偏光显微镜（OM）、X-射线光电子能谱（XPS）等手段，系统研究了PS护MMA混合物薄膜的初始形态及其在退火过程中的形态演变规律。（1）随着PS分子量的增加，研究发现其形态的变化存在一过渡区域并予以合理解释；即：薄膜的初始形态由纳米尺度的相分离向宏观相分离的表面形态过渡；高温下退火时，其形态的演变存在两种过程。（2）对不同厚度的PS／PMMA混合物薄膜，在退火过程中观察到两种能长时间存在的新的表面形态，并阐明其稳定存在的原因；对PS护MMA混合物超薄膜，长时间退火时，在薄膜表面观察到二次相分离。（3）首次提出了利用混合物薄膜的相分离抑制去润湿的方法，即低浓度的PMMA可以抑制PS薄膜的去润湿行为，其稳定机理归结为PMMA优先向基底的表面分离而形成的厚度为少L个纳米的PMMA富相层。（4）研究了PS／P MMA混合物薄膜在OTS图案化基底上的形态变化，结果表明，薄膜的形态演变主要由横向受限和基底的表面自由能决定。通过控制受限程度和退火时间，可得到多种形态。以PS／P 4VP���昆合体系为例，探索了如何利用高分子混合物薄膜的相分离制备具有规则排列的有序结构。研究表明，只有当PS的分子量相对较小时，在SAM图案化的基底表面，才比较容易形成规则排列的相分离图案。该规则排列的相分离图案具有良好的热稳定性。为深刻理解在旋涂过程中高分子聚集结构的变化情况，以SESS为例，用DFM研究了旋涂高分子薄膜的形成过程。当溶液浓度较低时，首次观察到了条状取向结构并提出该结构的形成机理，说明在旋涂过程中其复杂的剪切拉伸场可以引起柔顺性高分子线团或聚集体的取向。

High-Saturation-Power and High-Speed Ge-on-SOI p-i-n Photodetectors

Ge-on-silicon-on-insulator p-i-n photodetectors were fabricated using an ultralow-temperature Ge buffer by ultrahigh-vacuum chemical vapor deposition. For a detector of 70-mu m diameter, the 1-dB small-signal compression power was about 110.5 mW. The 3-dB bandwidth at 3-V reverse bias was 13.4 GHz.

PASSIVATION OF COPPER BY LITHIUM IN P-TYPE GAAS

We report the passivation of two deep copper-related acceptor levels in Cu-diffused p-type GaAs by the group-I element lithium. The deep-level-transient-spectroscopy (DLTS) signals of the well-known Cu-related levels with apparent activation energies 0.15 eV and 0.40 eV disappear in Cu-diffused samples when they are diffused with Li, but can be reactivated by annealing. Photoluminescence measurements show a corresponding disappearance and reappearance of the copper-related luminescence at 1.36 eV. Also we observe with DLT'S an energy level at E(V) + 0.32 eV in the Cu-Li-diff-used samples. The level is neither present in the Cu-diffused samples before Li diffusion nor in Cu-Li-diffused samples after annealing. As the level is not observed in starting materials or solely Li-diffused samples we suggest that it is related to a Cu-Li complex.

RADIATIVE RECOMBINATION IN N-TYPE AND P-TYPE GAAS COMPENSATED WITH LI

We report fundamental changes of the radiative recombination in a wide range of n-type and p-type GaAs after diffusion with the group-I element Li. These optical properties are found to be a bulk property and closely related to the electrical conductivity of the samples. In the Li-doped samples the radiative recombination is characterized by emissions with excitation-dependent peak positions which shift to lower energies with increasing degree of compensation and concentration of Li. These properties are shown to be in qualitative agreement with fluctuations of the electrostatic potential in strongly compensated systems. For Li-diffusion temperatures above 700-800-degrees-C semi-insulating conditions with electrical resistivity exceeding 10(7) OMEGA cm are obtained for all conducting starting materials. In this heavy Li-doping regime, the simple model of fluctuating potentials is shown to be inadequate for explaining the. experimental observations unless the number of charged impurities is reduced through complexing with Li. For samples doped with low concentrations of Li, on the other hand, the photoluminescence properties are found to be characteristic of impurity-related emissions.

LITHIUM PASSIVATION OF ZN AND CD ACCEPTORS IN P-TYPE GAAS

We report lithium passivation of the shallow acceptors Zn and Cd in p-type GaAs which we attribute to the formation of neutral Li-Zn and Li-Cd complexes. Similar to hydrogen, another group-I element, lithium strongly reduces the concentration of free holes when introduced into p-type GaAs. The passivation is inferred from an increase of both the hole mobility and the resisitivity throughout the bulk of the sample. It is observed most clearly for Li concentrations comparable to the shallow-acceptor concentration. In addition, compensation of shallow acceptors by randomly distributed donors is present in varying degree in the Li-diffused samples. Unlike hydrogenation of n-type GaAs, Li doping shows no evidence of neutralizing shallow donors in GaAs.

PHOTOEMISSION-STUDY ON THE SNO2/P A-SICX-H INTERFACE

Ultraviolet and X-ray photoemission spectroscopies (UPS and XPS) have been employed to SnO2 and its interface with P-type a-SiCx:H. The HeI valence band spectra of SnO2 show that the valence band maximum (VBM) shifts from 4.7 eV to 3.6 eV below the Fermi level (E(F)), and the valence band tail (VBT) extends up to the E(F), as a consequence of H-plasma treatments. The work function difference between SnO2 and P a-SiCx:H is found to decrease from 0.98 eV to 0.15 eV, owing to the increase of the work function of the treated SnO2. The reduction of SnO2 to metallic Sn is also observed by XPS profiling, and it is found that this leads to a wider interfacial region between the treated SnO2 and the successive growth of P a-SiCx:H.

A NEW RESULT IN TRANSIENT CURRENT EXPERIMENT ON A-SI-H P/I/N AND N/I/N DEVICES

The transient current response of a-Si:H in both p/i/n and n/i/n structures has been measured as a function of pulse intermittence and pulse amplitude. The results are consistent with the picture that in p/i/n samples the peculiar current response is caused by the competing contributions of electrons and holes which show themselves in different time scales.