Effect of Charge Density on Energy‐Transfer Properties of Cationic Conjugated Polymers

Cationic conjugated polymers (CCPs) with different charge densities are synthesized via Suzuki polymerization. The CCPs show similar optical properties in aqueous solutions but obvious difference in fluorescence resonance energy transfer (FRET) to Texas Red‐labeled single‐stranded DNA (ssDNA‐TR). Both CCP and TR fluorescence quenching are revealed to influence the energy‐transfer process. The difference in quantum yields of CCP/ssDNA complexes highlights the importance of polymer side‐chain structures and charge density. A CCP with a high charge density and ethylene oxide as the side chain provides the highest quantum yield for CCP/ssDNA complexes, which favors FRET. TR quenching within the CCP/ssDNA complexes is predominantly determined by the CCP charge density. In contrast to the other two polymers, the CCP with low charge density provides the most‐intense polymer‐sensitized TR emission, which is due to the collective response of more optically active polymer units around TR and the minimized TR self‐quenching within the CCP/ssDNA‐TR complexes. These studies provide a new guideline for improving the signal amplification of conjugated‐polymer‐based optical sensors.     

High-power long-wavelength room-temperature MOVPE-grown quantum cascade lasers with air-semiconductor waveguide

Quantum cascade lasers grown by metal organic vapour phase epitaxy (MOVPE) with high peak output power of 1.3 W at 300 K emitting a wavelength of 9.8 mum are reported. The devices are processed in wide ridge waveguide structures with an air-semiconductor interface to confine the laser optical mode. This design increases the optical overlap factor and reduces waveguide losses.     

The effect of RF-driven gate current on DC/RF performance in GaAs pHEMT MMIC power amplifiers

This paper describes RF-driven gate current effects on the dc/RF performance of 0.15-/spl mu/m (gate length) 2-mil (substrate thickness) GaAs pseudomorphic high-electron mobility transistor (pHEMT) monolithic microwave integrated circuit power amplifiers (PAs). High gate current is generated in PAs under RF drive at room temperature. A long-term lifetest of PAs with various gate currents induced by RF drive was performed to investigate the effect of RF-driven gate current on dc/RF performance in GaAs pHEMT PAs. Accordingly, an empirical model was developed to predict the dc/RF performance of V-band PA modules by the end of life (EOL). This information is crucial for system engineers in order to budget sufficient output power so that the system can still maintain performance capability by EOL.     

C12A7-Mg催化剂水蒸汽重整生物油、石脑油和CH4制氢

利用自制的C12A7-Mg催化剂,研究了催化水蒸汽重整生物油、石脑油和CH4制备氧气的性能,以及催化剂寿命,并用X射线光电子能谱对催化剂进行了表征．温度测试范围为250-850℃．对于催化水蒸汽重整生物油反应,在750℃时,氢气产率最大达到80％,碳的转化率接近95％．在相同的反应温度下,催化水蒸汽重整石脑油和CH4的氢气产率和碳的转化率要低于重整生物油反应．催化剂的失活主要是由于重整过程中的积碳．     

Immunolocalization of MAP-2 in routinely formalin-fixed, paraffin-embedded guinea pig brain sections using microwave irradiation: a comparison of different combinations of antibody clones and antigen retrieval buffer solutions.

The present study was designed to evaluate the efficacy of different microwave pretreatment methods to retrieve microtubule-associated protein 2 (MAP-2) immunoreactivity in formalin-fixed, paraffin-embedded guinea pig brain sections. Brain sections, microwave pretreated in boiling sodium citrate, citric acid, Tris hydrochloride, and EDTA buffers of pH 4, 6, and 8, were labeled with four different clones of MAP-2 monoclonal antibodies. No MAP-2 immunoreactivity was observed in control sections processed without microwave pretreatment. Optimal MAP-2 immunoreactivity was observed only when MAP-2 antibody clone AP18 was used in conjunction with citric acid buffer of pH 6.0. Using this combination, brain sections from nerve agent soman-exposed guinea pigs were found to exhibit marked reduction in MAP-2 immunostaining in the hippocampus. These observations suggest that the clone of the antibody in addition to the type and pH of antigen retrieval (AR) solution are important variables to be considered for establishing an optimal AR technique. When studying counterpart antigens of species other than that to which the antibodies were originally raised, different antibody clones must be tested in combination with different microwave-assisted AR (MAR) methods. This MAR method makes it possible to conduct retrospective studies on archival guinea pig brain paraffin blocks to evaluate changes in neuronal MAP-2 expression as a consequence of chemical warfare nerve agent toxicity.     

Facile formation of acenaphtho[1,2-a]pyrene structures by thermal isomerization of bis(8-ethynyl-1-naphthyl)ethynes

The title 1,8-naphthylene-ethynylene compounds underwent thermal isomerization into acenaphtho[1,2-a]pyrene derivatives, and the structure of the new polycyclic aromatic system was established by X-ray analysis. The mechanism of the isomerization is explained in terms of sequential cyclization reactions via biradical intermediates followed by hydrogen migration.     

Independently driven DG MOSFETs for mixed-signal circuits: part II-applications on cross-coupled feedback and harmonics generation

Circuit applications utilizing the tight quasi-static and nonquasi-static channel coupling in independently driven double-gate (IDDG) MOSFETs are presented. The performances of cross-coupled differential amplifiers and mixers with IDDG are compared with those of the SDDG counterparts. The quasi-static coupling in IDDG increases output voltage swing and improves voltage waveform symmetry in the cross-coupled differential amplifier. The nonquasi-static coupling in IDDG provides fast feedback in the differential amplifiers, and allows higher frequencies in the input signals for harmonic generation in mixers. We have identified plausible advantages in IDDG that cannot be readily implemented by SDDG, which justifies the fabrication cost and parasitic capacitance penalty of IDDG.     

Noninvasive detection of inhomogeneities in turbid media with time-resolved log-slope analysis

Detecting foreign objects embedded in turbid media using noninvasive optical tomography techniques is of great importance in many practical applications, such as in biomedical imaging and diagnosis, safety inspection on aircrafts and submarines, and LIDAR techniques. In this paper we develop a novel optical tomography approach based on slope analysis of time-resolved back-scattered signals collected at the medium boundaries where the light source is an ultrafast, short-pulse laser. As the optical field induced by the laser-pulse propagates, the detected temporal signals are influenced by the optical properties of the medium traversed. The detected temporal signatures therefore contain information that can indicate the presence of an inhomogeneity as well as its size and location relative to the laser source and detection systems. The log-slope analysis of the time-resolved back-scattered intensity is shown to be an effective method for extracting the information contained in the signal. The technique is validated by experimental results and by Monte Carlo simulations.     

Effects of alkali post‐treatment on the particle morphology of soap‐free poly(methyl methacrylate‐ethyl acrylate‐acrylic acid) latices

Poly(methyl methacrylate‐ethyl acrylate‐acrylic acid) P(MMA‐EA‐AA) latices with narrow particle size distribution and “clean” particle surface were first synthesized by batch soap‐free emulsion polymerization, and the latex particles with anomalous morphology were obtained by alkali post‐treatment. Effects of treatment temperature and time, initial pH value, as well as 2‐butanone amount, on the morphology of latex particles were investigated. Results showed that anomalous structure of the dried latex particles could be easily identified using transmission electron microscopy (TEM) observation under the conditions of temperature >60°C, initial pH > 10.5 and 4.0–7.0 ml of 2‐butanone used. The higher the pH value is, the earlier the anomalous structure will occur. The volume expansion (ΔV) of the particle increased with the increase in treatment temperature and 2‐butanone amount. However, with the increase of initial pH value and treatment time, ΔV increased first and then decreased, and different maximum of ΔV values were observed based on different conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

面向MANET环境的动态自适应副本放置算法研究

移动自组网环境给数据复制技术带来了新的挑战。本文提出了一种分布式动态自适应副本放置算法,算法以数据访问的通信开销作为目标函数,每个副本节点从其邻居节点收集读写请求的局部信息,动态地调整副本放置方案以适应访问请求和网络拓扑的变化。本文还提出了基于稳定邻居的副本放置算法以减小由于节点移动给副本放置带来的振荡。模拟实验表明,在移动自组网环境中,本文提出的算法有效地减少了数据访问的通信开销,提高了数据访问的效率。