Synthesis and properties of soluble polyimides based on isomeric ditrifluoromethyl substituted 1,4-bis(4-aminophenoxy)benzene

A new fluorinated diamine monomer, [1,4-bis(4-amino-3-trifluoromethylphenoxy)benzene (2)], and a known isomeric analog 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (3) were synthesized. A series of organosoluble polyimides Ia-d and IIa were prepared from the diamines (2, 3) and dianhydrides (a-d) by a high-temperature one-step method. The effects of the trifluoromethyl substituents on the properties of polyimides were evaluated through the study of their soluble, thermal, optical, and gas permeability properties. Polyimides (Ia-d) had glass transition temperatures between 229 and 279 degrees C, and the temperatures at 5% weight loss ranged from 510 to 533 degrees C under nitrogen. These polyimides could be cast into flexible and tough membranes from DMAc solutions. The membranes had tensile strengths in the range of 137-169 MPa, tensile modulus in the range of 1.6-2.2 GPa and elongations at break from 11% to 14%. The polyimide la with trifluoromethyl groups ortho to the imide nitrogen exhibited enhanced gas permeability, solubility, transparency, and thermal stability compared with the isomeric polyimide IIa with the CF3 group meta to the imide nitrogen.

Large three-photon absorption cross-section in a novel class of bis-(N-carbazolyl) fluorene derivatives

Two novel symmetrical charge transfer fluorene derivatives (abbreviated as BCZF and BVCZF) with carbazole end-group as the donor moieties have been synthesized. Three-photon absorption cross-sections of these two compounds have been determined by using a Q-switched Nd:YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 140 x 10(-78) and 400 x 10(-78) cm(6) s(2) for BCZF and BVCZF, respectively. The geometries, electronic structures and electronic spectra of these two compounds are systematically studied by AM1 and ZINDO/S methods. On the basis of correct UV-vis spectra, the influence of different molecular structure on three-photon absorption cross-sections is discussed micromechanically. (C) 2005 Elsevier B.V. All rights reserved.

Large three-photon absorption and intramolecular charge transfer of the bis-donor fluorene-based molecules

Three-photon absorption (3PA) of two fluorene-based molecules with D-pi-D structural motifs (abbreviated as BPAF and BCZF) has been determined by using a Q-switched Nd: YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 222 and 140 x 10(-78) cm(6) s(2) for BPAF and BCZF, respectively. AM1 calculations show that attaching different donors changes the charge density distribution of the fluorene skeleton, and it is observed that the 3PA cross-section can be enhanced with increasing intramolecular charge transfer character, measured by the parameter Delta p(1)/Delta p(2)/Delta p(1)'. (c) 2005 Elsevier B.V. All fights reserved.

Identification and molecular cloning of a novel neuromedin U analog from the skin secretions of toad Bombina maxima

Amphibian skin contains rich neuropeptides. In the present study, a novel neuromedin U (NmU) analog was isolated from skin secretions of Chinese red belly Load Bombina maxima. Being 17-amino acids long, its primary structure was established as DSSGIVGRPFFLFRPRN-NH2, in which the C-terminal 8-residue segment (FFLFRPRN) is the same as that of rat NmU, while the N-terminal part DSSGIVGRP shows a great sequence variation compared with those of NmU peptides from different resources. The peptide, named Bm-NmU-17, was found to elicit concentration-dependent contractile effects on smooth muscle of rat uterus horns. The cDNA Structure of the peptide, as obtained by a 3'-RACE strategy and subsequently cloning from a skin cDNA library, was found to contain a coding region of 438 nucleotides. The encoded precursor is composed of 145 amino acids with a single copy of Bm-NmU-17 located towards the C-terminus. The sequence of the peptide is preceded by a dibasic site (Lys-Arg) and followed by the sequence of Gly-Arg-Lys, providing the sites of cleavage and releasing of the mature peptide. (c) 2005 Elsevier B.V. All rights reserved.

Analog-digital and digital-analog converters using single-electron and MOS transistors

This paper proposes two kinds of novel single-electron analog-digital conversion (ADC) and digital-analog conversion (DAC) circuits that consist of single-electron transistors (SETs) and metal-oxide-semiconductor (MOS) transistors. The SET/MOS hybrid ADC and DAC circuits possess the merits of the SET circuit and the MOS circuit. We obtain the SPICE macro-modeling code of the SET transistor by studying and fitting the characteristics of the SET with SPICE simulation and Monte Carlo simulation methods. The SPICE macro-modeling code is used for the simulation of the SET/MOS hybrid ADC and DAC circuits. We simulate the performances of the SET/MOS hybrid 3-b ADC and 2-b DAC circuits by using the H-SPICE simulator. The simulation results demonstrate that the hybrid circuits can perform analog-digital and digital-analog data conversion well at room temperature. The hybrid ADC and DAC circuits have advantages as-follows: 1) compared with conventional circuits, the architectures of the circuits are simpler; 2) compared with single electron transistor circuits, the circuits have much larger load capability; 3) the power dissipation of the circuits are lower than uW; 4) the data conversion rate of the circuits can exceed 100 MHz; and 5) the resolution of the ADC and DAC circuits can be increased by the pipeline architectures.

Analog computation using quantum-dot cell network

A novel analog-computation system using a quantum-dot cell network is proposed to solve complex problems. Analog computation is a promising method for solving a mathematical problem by using a physical system analogous to the problem. We designed a novel quantum-dot cell consisting of three-stacked. quantum dots and constructed a cell network utilizing the nearest-neighbor interactions between the cells. We then mapped a graph 3-colorability problem onto the network so that the single-electron configuration of the network in the ground state corresponded to one of the solutions. We calculated the ground state of the cell network and found solutions to the problems. The results demonstrate that analog computation is a promising approach for solving complex problems.

酚酞型聚芳醚砜共聚物与共混物－(PP/BiS-T) PES共聚物和(PPS/PES-C)、(PPO/PES-C)共混物的合成、结构与性能研究

本工作旨在通过共聚、共混技术制备酚酞型聚芳醚砜共聚物(PP/BiS-T) PES和共混物(PPS/PES-C)、PPO/PES-C，以便改善酚酞型聚芳醚砜（PES－C）的加工性能（特别是注射加工性能）和耐溶剂性能。通过研究共聚物和共混物的微观结构，聚集态结构与性能的关系，探索改善酚酞型聚芳醚硕性能的有效途径第一部分：(PP/BiS-T) PES共聚物的合成、结构与性能(PP/BiS-T) PES共聚物是以4，4'二氯二苯砜（DCDPS）、酚酞（PP）和4，4'－二羟基二苯硫醚(BiS-T)为单体，采用固体无水K_2CO_3/NMP/TMSO_2 混合溶剂反应体系合成的。共聚反应规律研究表明：在NMP/TMSO_2混合溶剂中，共聚反应可以顺利进行，避免了交联反应的发生，并成功地合成了高分子量的(PP/BiS-T) PES共聚物。DSC分析结果表明(PP/BiS-T) PES系列属于无定形的均相共聚物体系，每一组成比例对应的共聚物只具有一个玻璃化转变温度。且随组成比例的改变呈线性变化，TBA分析结果与DSC基本一致，并证实了(PP/BiS-T) PES属于均相共聚物体系，而不是均聚物的共混物。TG分析表明：共聚物具有良好的耐热氧化稳定性BiS-T链节在分子链中起到了提高自身抗氧性的作用。1R光谱对共聚物的结构进行表征。~(13)C-NMR分析确认共聚物多属于无规共聚物。动态力学试验表明共聚物(PP/BiS-T) PES以及PES－C，在－100 ℃附近和0－100 ℃，存在着次级松驰与转变，并发现水分子的存在对这种转变（次级松驰）有一定的影响。共聚物的熔融流动性试验和溶解性试验表明共聚物(PP/BiS-T) PES具有稍好于PES－C的熔融流动性；溶解性与PES－C类似。力学试验说明共聚物属于强而硬类型的聚合物。第二部分：PPS/PES－C共混物的制备、聚集态结构与性能PPS/PES－C共混物是以联苯/二苯硕混合物为溶剂，采用溶液沉析方法制备的，DSC、WAXD，SEM和1R分析手段对共混物的聚集态结构和微观结构进行了表征。DSC分析认为共混物属于多相体系，PPS的结晶性随着PES－C含量增加而降低。DSC和SEM观察结果表明：相转变发生在PPS占40％左右。PPS占25％时，DSC曲线呈现出界面相玻璃化转变温度。共混物具有良好的耐热氧化稳定性和耐热分解稳定性。微晶大小计算结果：PES－C存在导致了PPS微晶大小降低。WAXD曲线表明PPS占50％，共混物中的PPS具有较好的结晶性。SEM观察发现：随着PES－C含量增加，PES－C由分散相（PES－C50％）变为连续相（PES－C70％）。PPS占50％或低于50％时，共混物体系不仅发生了微观相分离，而且发生了宏观相分离。M.I.指数表明共混物中PPS为连续相时，共混物具有良好的熔融流动性。溶解性试验结果：共混物具有较好的耐溶剂性。第三部分：PPO/PES－C共混物的合成、结构与性能 PPO/PES－C共混物系用溶液－涂膜法，以氯彷为溶剂制备的。讨论了由同一共混物溶液浓度下制备的共混物的互溶性随组成的改变而变化。DSC分析结果：PPO/PES－C属于部分相溶性体系。利用Fox方程推导式计算结果表明PPO在富PES－C相中具有良好的分散性；而PES－C在富PPO相中的分散性较差。共混物(PPO/PES－C)试样经丙酮浸泡后，PPO（>50％）发生了溶剂诱导结晶现象，同时丙酮促使共混物发生完全相分离。结晶溶化热显示共混物中少量的PES－C存在有利于PPO的溶剂诱导结晶。TG分析表明共混物具有良好的耐热分解稳定性和耐热氧化分解稳定性。偏光显微镜下观察到PPO球晶的存在。SEM和FT－1R分别对共混物的形态结构和微观结构进行了表征。WAXD试验证实了丙酮处理的(PPO/PES－C)（70/30），（90/10）共混物中PPO的结晶性。溶解性试验表明：PPO掺入有助于 PES－C的耐溶剂性提高。

The design of cascaded resistors in a new analog switch two-step ADC architecture

In this paper we introduce a new Half-flash analog switch ADC architecture. And we discuss two methods to design the values of the cascaded resistors which generate the reference voltages. Derailed analysis about the effect of analog switches and comparators on reference voltages, and the methods to set the resistor values and correspond;ng voltage errors are given.

An analysis of the performance of a new high-speed single-way analog switch

This paper introduces a new highspeed single-way analog switch which has both highspeed high-resolution mono-direction analog transmission gate function and high-speed digital logic gate function with normal bipolar technology. The analysis of static and transient switching performances as an analog transmission gate is emphasized in the paper. In order to reduce the plug-in effect on high-speed high-resolution systems, an optimum design scheme is also given. This scheme is to achieve accelerated dynamic response with very low bias power dissipation. The analysis of PSPICE simulation as well as the circuit test results confirms the feasibility of the scheme. Now, the circuit has been applied effectively to the designs of novel highspeed A/D and D/A converters.

A one-way MOS analog switch

In this paper, a one-way NMOS analog switch featuring a low plug-in consumption is presented. The performances of analog switch, especially the performances of source follower are simulated under different conditions with PSPICE. Simulation results and factors affecting the deviation between input and output are analyzed, some advice on how to reduce the deviation between input and output is given. Ar the end of the paper, voltage relationship between input and output of the analog switch is obtained. Function of first degree, Vout = kVin + V0, is used to approximate the voltage relationship. The simulation results anti the value achieved from the approximation equation are given as well.

Analog computation using quantum-dot cell network

A novel analog-computation system using a quantum-dot cell network is proposed to solve complex problems. Analog computation is a promising method for solving a mathematical problem by using a physical system analogous to the problem. We designed a novel quantum-dot cell consisting of three-stacked. quantum dots and constructed a cell network utilizing the nearest-neighbor interactions between the cells. We then mapped a graph 3-colorability problem onto the network so that the single-electron configuration of the network in the ground state corresponded to one of the solutions. We calculated the ground state of the cell network and found solutions to the problems. The results demonstrate that analog computation is a promising approach for solving complex problems.