Multiuser OFDM Using Cyclic Time Shift for Wireless Uplink Broadcasting

A combination of orthogonal frequency division multiplexing (OFDM) with frequency-division multiple access (FDMA) called orthogonal frequency-division multiple access (OFDMA) is regarded as a promising solution for improving the performance of interactive wireless broadcasting systems. This paper presents our investigation into reducing the multiple access interference (MAI) introduced by symbol timing misalignment in an OFDMA uplink system. To combat the MAI, we provide a new OFDMA symbol frame employing a simple symbol repetition coupled with a cyclic time shift for typical OFDMA uplink scenarios. Theoretical analysis and computer simulations are used to assess the performance of the proposed OFDMA uplink system. It is found that this scheme can decrease the probability of destroying the orthogonality among the users and provide the MAI-free reception.     

Effect of Conductive Particle Properties on the Reliability of Anisotropic Conductive Film for Chip-on-Glass Applications

This paper describes how the material properties of conductive particles in anisotropic conductive films (ACFs) affect the electrical conductivity and the reliability of ACF interconnections for chip-on-glass (COG) applications. For the conductive particles, Au/Ni-coated polymer particles with a 5-diameter were used. Two different types of conductive particles were characterized with respect to their mechanical and electrical properties, such as ball hardness, recovery behavior, and electrical resistance. In addition, two ACFs were fabricated in the form of a double-layered structure, in which the thickness of the ACF and a nonconductive film (NCF) layer were optimized to have as many conductive particles as possible on the bump after COG bonding. The electrical contact resistance of an ACF interconnection in a COG structure depends mainly on the electrical properties of conductive particles in the ACF. The electrical reliability of an ACF interconnection in a COG structure also depends more on the electrical properties than the mechanical properties of conductive particles under a high-temperature and humid condition. Conductive particles with a lower electrical resistance, higher mechanical hardness, and lower recovery rate show better reliability than conductive particles with a higher electrical resistance, lower mechanical hardness, and higher recovery rate. Cross-sectional scanning electron microscopic (SEM) pictures of a COG interconnection show the deformation of two different conductive particles after the reliability tests. The ACF interconnections in the edge or corner of a driver IC show less reliable joints due to high absorption of moisture.     

Electrospun PEDOT:PSS/PVP nanofibers as the chemiresistor in chemical vapour sensing

Herein, PEDOT:PSS/PVP nanofibers were produced by electrospinning. The presence of PEDOT:PSS in the nanofibers was confirmed by FT-Raman spectroscopy. The applied voltage-dependent diameter of PEDOT:PSS/PVP nanofibers was observed. Also, sensing behaviors of electrospun PEDOT:PSS/PVP nanofibers were explored by measuring its response upon cyclic exposure to organic vapours such as ethanol, methanol, THF, and acetone at room temperature. When PEDOT:PSS/PVP nanofibers were exposed to each solvent, the protic and aprotic solvents resulted in opposite electrical responses. These findings exhibit that electrospun PEDOT:PSS/PVP nanofibers are the promising candidate for the organic vapour sensing material.     

Stereochemical influence on the stability of radio-metal complexes in vivo. Synthesis and evaluation of the four stereoisomers of 2-(p-nitrobenzyl)-trans-CyDTPA

Distinct differences in in vivo stability of the two diastereomeric C-Functionalized CyDTPA chelating agents, (CHX-A DTPA and CHX-B DTPA, both racemates), as recently reported prompted further investigation as to why differences in configuration produced striking effects on the in vivo stability of their yttrium complexes. To this end, the four individual component stereoisomers of CHX-A and CHX-B were synthesized and ability to bind yttrium was investigated both in vitro and in vivo.     

High-frequency SPICE model of anisotropic conductive film flip-chipinterconnections based on a genetic algorithm

This paper firstly reports on the high-frequency SPICE model of the ACF flip-chip interconnections up to 13 GHz. The extraction process is based on an optimization procedure, called a genetic algorithm, which is known as a robust optimization tool. The proposed equivalent circuit model of the ACF interconnection can readily be used in SPICE circuit simulations for signal integrity analysis of high-frequency packages. Two different ACF interconnections were studied using the Au-coated polymer ball and Ni-filled ball. The extracted models of the two ACFs were found strongly dependent on not only size and rigidity of the conducting balls, but also on their magnetic permeability     

Noise in a point-contact dc SQUID

Measurements of five variations of a toroidal point-contact dc superconducting quantum interference device (SQUID) are presented. The energy resolution and other parameters of these SQUIDs are examined and compared with the predictions of the Resistively Shunted Junction model. For these SQUIDs, the measured minimum energy resolution was approximately 2×10^–30 J/Hz. Excess noise in the point contacts was found to limit the energy resolution of the SQUIDs. A comparison between the typical junction parameters and noise obtained for our niobium-niobium point contacts and those of others is given. TheI–V characteristics of the junctions showed the effects of Joule heating. The white voltage noise spectral density was found to have an approximately parabolic dependence on the average voltage for bias currents larger than the critical current. While this parabolic dependence is consistent with heating effects in the junctions, the amplitude of the noise cannot be explained in terms of a heating model. The low-frequency noise of the point contacts has also been investigated.     

Dissolution and reprecipitation of barium at the particulate BaTiO3-aqueous solution interface

The electrokinetic behavior of BaTO₃ particles in an aqueous medium exhibited a hysteresis loop with titration direction. As BaTiO₃ suspension was titrated toward acidic pH, the amount of Ba²⁺ dissolution strongly increased, and in the subsequent titration toward alkaline pH, Ba²⁺ adsorbed and/or reprecipitated on the Ba-depleted BaTiO₃ surface. This dissolution-reprecipitation cycle results in the observed hysteresis behavior. An attempt was made to identify the responsible species of the adsorbed/reprecipitated compound by XPS in conjunction with electrokinetic titrations.     

多孔钢板在双轴受压与边缘剪力荷载共同作用下的极限强度

作为作者系列研究成果[Paik J K．Ultimate strength of perforated steel plates under edge shear loading．Thin-Walled Structures，2007，45：301-6，Paik J K．Ultimate strength of perforated steel plates under axial compressive loading along short edges．Ships Offshore Struct，2007，2（3）：（inpress）]的终结篇，与前期论文在边缘剪力或单轴压力荷载方面进行了对比，目的是研究双轴受压和边缘剪力作用下多孔钢板的极限强度特点，这是船舶和船舶型海洋结构在货物和水压作用下的一个典型受力模式。板的约束考虑为四边简支，中心区域为圆形孔。一系列ANSYS非线性有限元分析中考虑了不同的板尺寸（厚度）。在有限元分析基础上，推导出组合荷载下多孔板的极限强度交互关系公式，可用于可靠性分析或规范中极限强度的预测。