基于猜谜机制的增强权证防御技术

权证机制能有效地防御DoS攻击,但其新引起的拒绝权证攻击则严重地制约了其防御效果,因此针对此类攻击,提出基于猜谜的增强权证请求机制,如果一旦请求信道带宽被耗尽,权证路由器将实施拥塞猜谜策略,向请求权证的所有源主机发送谜题,要求其必须首先解谜,并将答案附于增强请求包中,经路由器验证后才予转发．仿真试验证明：该机制具有较好的防御效果,即使在恶意权证请求严重泛滥的情况下也能保证合法用户高效地获得权证．     

Geometrical frustration in 2D optical patterns

In the case of 2D optical patterns, frustration comes from the interplay between the physical constraints (light-matter interaction) and the geometrical constraints (cavity length and structure). Depending on the dynamical parameters, we are able to single out two distinct behaviors. For small diffusion and close to threshold, the system is forced to fulfill the geometrical constraints giving rise to a phase dynamics of quasicrystals. For larger diffusion, the system fragmentates into spatial domains giving rise to a competition between different patterns. By means of a geometrical argument, we show that the spatial distribution of domains is related to the symmetry imposed by the geometrical constraint and that the domain borders are disinclination defects. These defects being the nucleation centers of spatial domains, they trigger the onset of pattern competition. Received 27 December 1999 and Received in final form 29 March 2000     

A Dual-Responsive Liquid Crystal Elastomer for Multi-Level Encryption and Transient Information Display

Information security has gained increasing attention in the past decade, leading to the development of advanced materials for anti-counterfeiting, encryption and instantaneous information display. However, it remains challenging to achieve high information security with simple encryption procedures and low-energy stimuli. Herein, a series of strain/temperature-responsive liquid crystal elastomers (LCEs) are developed to achieve dual-modal, multi-level information encryption and real-time, rewritable transient information display. The as-prepared polydomain LCEs can change from an opaque state to a transparent state under strain or temperature stimuli, with the transition strains or temperatures highly dependent on the concentration of long-chain flexible spacers. Information encrypted by different LCE inks can be decrypted under specific strains or temperatures, leading to multi-level protection of information security. Furthermore, with the combination of the phase transition of polydomain LCEs and the photothermal effect of multi-walled carbon nanotubes (MWCNTs), we achieved a repeatable transient information display by using near-infrared (NIR) light as a pen for writing. This study provides new insight into the development of advanced encryption materials with versatility and high security for broad applications.     

Plasma Characteristics and Antenna Electrical Characteristics of an Internal Linear Inductively Coupled Plasma Source with a Multi-Polar Magnetic Field

The development of a large-area plasma source with high density plasmas is desired for a variety of plasma processes from microelectronics fabrication to flat panel display device fabrication. In this study, a novel internal-type linear inductive antenna referred to as “double comb-type antenna” was used for a large-area plasma source with the substrate area of 880 mm × 660 mm and the effect of plasma confinement by applying multi-polar magnetic field was investigated. High density plasmas on the order of 3.2 × 10¹¹ cm^?3 which is 50% higher than that obtained for the source without the magnetic field could be obtained at the pressure of 15 mTorr Ar and at the inductive power of 5,000 W with good plasma stability. The plasma uniformity <3% could be also obtained within the substrate area. When SiO₂ film was etched using the double comb-type antenna, the average etch rate of about 2,100 Å/min could be obtained with the etch uniformity of 5.4% on the substrate area using 15 mTorr SF₆, 5,000 W of rf power, and ?34 V of dc-bias voltage. The higher plasma density with an excellent uniformity and a lower rf antenna voltage obtained by the application of the magnetic field are related to the electron confinement in a direction normal to the antenna line.     

Effects of nano nickel powders addition on flash pyrolysis of poly(ethylene glycol)

Pure PEG and the mixture of PEG and nano nickel powders (PEG/n-Ni) were pyrolyzed at 500 °C for 5 min in N₂ atmosphere. GC/MS and FTIR were employed to detect the volatile products. Some important regularity in the mass spectra of the PEG pyrolysis products was discovered, and 11 series of PEG pyrolysis products were identified. The experimental results show that the nano Ni powders evidently change the relative contents of each products series. The statistical results of the ratio of C-O cleavage to C-C cleavage, as well as the ratio of hydrogenation to dehydrogenation, indicate that nano Ni powders have remarkable effects on the bonds cleavage and free radicals annihilation. The process of hydrogenolysis and hydrogenation were propounded to explain the effects of nano Ni addition on PEG flash pyrolysis.     

基于翻转课堂-PBL的混合式“金课”教学*——以“药物分析”为例

以创新应用能力及岗位需求重构课程标准,更新教学方法和教学手段,从教学设计、教学实施、教学评价、教学效果等4个方面系统地探索了基于翻转课堂-PBL教学的药物分析课程教学模式建设与应用,旨在形成多元化、多层次的药物分析教学新体系,将“以教师教为主”的教学模式转变为“以学生学为主”,让学生化“被动”为“主动”学习,锻炼学生自主学习能力,增强学生团队协作及分析解决问题的能力,启发学生创新应用能力。     

Minimizing permeability of PET substrates using Oxygen plasma treatment

Surface plasma treatment in a reactive ion etching system is used to observe a considerable decrease in permeability of polyethylene terephthalate to gases. The effects of oxygen plasma on the surface properties and morphology of PET polymers are investigated by scanning electron microscopy (SEM), x-ray photo-electron spectroscopy (XPS) and atomic force microscopy (AFM). In addition, the optical transmission properties of the treated samples have been investigated corroborating the findings of SEM and AFM analyses. Moreover, the penetration of air through the treated substrates was investigated using a vacuum test. The treated PET substrates can be used to realize flexible plasma display panels.     

种电热驱动法布里 珀罗光调制器

提出了一种用于显示基于微机电系统的电热驱动法布里 珀罗光调制器.利用多光束干涉理论分析了该调制器的原理及光学特性.分析表明:当腔长为(2k+1)λ/4时,反射光强取极大值|当腔长为2kλ/4时,反射光强取极小值|通过改变腔长可以实现显示.光源谱宽越窄,衬比度越高|干涉级次越低,衬比度越高|衬比度随反射率的增加而减小.借助Ansys软件仿真分析了调制器的驱动特性.加工了器件并搭建实验装置进行了动态响应特性测试实验.结果表明,该调制器具有驱动电压低至3.2 V,响应速度约为5 kHz的良好驱动特性.实验结果初步验证了该结构的可行性.