Multiplexing of Fiber-Optic Long-Period Grating-Based Interferometric Sensors

Two long-period gratings (LPGs) fabricated in series in an optical fiber form a Mach-Zehnder interferometer, producing a sinusoidal channelled spectrum within the characteristic LPG attenuation bands, which has the appearance of an interference fringe pattern. The phase of the fringes is sensitive to changes in the surrounding environmental parameters, such as refractive index. Fabrication of a number of identical cascaded LPG pairs with different separations produces independent fringe patterns of different frequencies within the attenuation bands. The application of basic Fourier techniques to analyze the transmission spectrum allows the phase of each fringe pattern to be determined independently, facilitating the differentiation of external effects acting on each interferometer.     

通过仿真确保信号完整性设计

PowerPC处理器能帮助实现快速灵活的可编程嵌入式平台设计.Virtex-4 FX平台利用集成于双PowerPC处理器的创新辅助处理器单元(APU)控制器,支持新的硬件加速应用.FX APU控制器又大大改善了软件算法的执行,提高了FPGA资源可用性.本文将介绍使用Xilinx/Ansoft 10Gbps背板设计套件确保互连性能.     

使用基于模型的设计进行虚拟测试

本文分析了系统设计中常用的末期测试可能造成的成本及设计周期的增加,进而提出了基于模型的设计方法,通过在系统设计中并行进行虚拟测试,大大缩短设计周期,降低设计成本.     

A New Family of Proton‐Conducting Electrolytes for Reversible Solid Oxide Cells: BaHfxCe0.8−xY0.1Yb0.1O3−δ

Reversible solid oxide cells based on ceramic proton conductors have potential to be the most efficient system for large‐scale energy storage. The performance and long‐term durability of these systems, however, are often limited by the ionic conductivity or stability of the proton‐conducting electrolyte. Here new family of solid oxide electrolytes, BaHf_xCe_0.8?xY_0.1Yb_0.1O_3?δ (BHCYYb), which demonstrate a superior ionic conductivity to stability trade‐off than the state‐of‐the‐art proton conductors, BaZr_xCe_0.8?xY_0.1Yb_0.1O_3?δ (BZCYYb), at similar Zr/Hf concentrations, as confirmed by thermogravimetric analysis, Raman, and X‐ray diffraction analysis of samples over 500 h of testing are reported. The increase in performance is revealed through thermodynamic arguments and first‐principle calculations. In addition, lab scale full cells are fabricated, demonstrating high peak power densities of 1.1, 1.4, and 1.6 W cm^?2 at 600, 650, and 700 °C, respectively. Round‐trip efficiencies for steam electrolysis at 1 A cm^?2 are 78%, 72%, and 62% at 700, 650, and 600 °C, respectively. Finally, CO₂? H₂O electrolysis is carried out for over 700 h with no degradation.     

Modal Analysis of the Quasi-Optical Performance of Phase Gratings

This paper is concerned with the analysis of phase gratings as passive quasi-optical multiplexing devices. One important application of such components is in the local oscillator injection chain of heterodyne array receivers. Gaussian beam mode analysis can be applied as a powerful tool when modelling the optical performance of phase gratings in a real submillimeter system of finite throughput and bandwidth. In our experimental investigations we have concentrated on the Dammann Grating (DG) which is a binary optical component and thus straightforward to manufacture. A number of quartz gratings were fabricated and carefully tested to evaluate the practical limitations of such quasi-optical components. Because of its convenient refractive index quartz can be used to produce gratings with very low reflection losses. The results presented confirm DGs to be particularly suitable multiplexers for sparse arrays of finite bandwidth.     

Small signal equivalent circuit for Geiger-mode avalanchephotodiodes

The first small signal equivalent circuit for a Geiger-mode avalanche photodiode (GMAP) is presented. The equivalent circuit is derived from a 20 μm-diameter GMAP with 3 μm virtual guard ring overlap; the photodetector has peak responsivity at 600 nm and a calculated electrical bandwidth of 5.97 GHz     

Polymeric Multilayers that Contain Silver Nanoparticles can be Stamped onto Biological Tissues to Provide Antibacterial Activity

The design of polyelectrolyte multilayers (PEMs) that can be prefabricated on an elastomeric stamp and mechanically transferred onto biomedically‐relevant soft materials, including medical‐grade silicone elastomers (E’～450–1500 kPa; E’‐elastic modulus) and the dermis of cadaver skin (E’～200–600 kPa), is reported. Whereas initial attempts to stamp PEMs formed from poly(allylamine hydrochloride) and poly(acrylic acid) resulted in minimal transfer onto soft materials, we report that integration of micrometer‐sized beads into the PEMs (thicknesses of 6–160 nm) led to their quantitative transfer within 30 seconds of contact at a pressure of ～196 kPa. To demonstrate the utility of this approach, PEMs were impregnated with a range of loadings of silver‐nanoparticles and stamped onto the dermis of human cadaver skin (a wound‐simulant) that was subsequently incubated with bacterial cultures. Skin dermis stamped with PEMs that released 0.25 ± 0.01 μg cm^?2 of silver ions caused a 6 log₁₀ reduction in colony forming units of Staphylococcus epidermidis and Pseudomonas aeruginosa within 12 h. Significantly, this level of silver release is below that which is cytotoxic to NIH 3T3 mouse fibroblast cells. Overall, this study describes a general and facile approach for the functionalization of biomaterial surfaces without subjecting them to potentially deleterious processing conditions.     

Performance comparison of local area video streaming systems

The performance of our Quality Oriented Adaptation Scheme (QOAS) for multimedia streaming in local networks is compared with other existing solutions (TFRCP, LDA+, and non-adaptive). This comparison is done in terms of bandwidth utilization, number of concurrent clients, loss rate, and end-user perceived quality. Simulation results show that for the same average end-user quality, our QOAS system can accommodate a significantly higher number of simultaneous clients while also having higher bandwidth utilization. For the same number of clients, the average end-user quality is always higher for QOAS than for the other solutions studied.     

Monitoring hacker activity with a Honeynet

The Honeynet Project was founded by 30 US based security professionals with the intention of researching the techniques, tools, tactics and motives of hackers and the ‘blackhat’ community in general. A Honeynet Project is an all volunteer, non‐profit organization committed to sharing and learning the motives, tools, and tactics of the hacking community. It is comprised of a number of information security professionals dedicated to honeynet research and information security. This paper outlines the technical configuration of a honeynet, presents some of the key attacks on the honeynet to date and provides recommendations for securing networked systems. Copyright © 2005 John Wiley & Sons, Ltd.