Diketopyrrolopyrrole Organic Thin‐Film Transistors: Impact of Alkyl Substituents and Tolerance of Ethylhexyl Stereoisomers

Bis(thiophen‐2‐yl)‐diketopyrrolopyrrole (DPP) dyes bearing various alkyl substituents at the amide positions (n‐butyl, n‐pentyl, n‐hexyl, n‐heptyl, n‐octyl, 2‐ethylhexyl) and chlorine (Cl), bromine (Br), or cyano (CN) substituents at the thiophene positions have been synthesized and investigated with regard to their molecular and semiconducting properties. Intense absorption, strong fluorescence, and reversible oxidation and reduction processes are common to all of these dyes. Their characterization as organic semiconductors in vacuum‐processed thin‐film transistors reveals p‐channel operation with field‐effect mobilities ranging from 0.01 to 0.7 cm² V^?1 s^?1. The highest mobility is found for the DPP dyes bearing the 2‐ethylhexyl substituents, which is surprising, considering that as a result of the chiral substituents, this material is a mixture of (R,R), (S,S), and (R,S) stereoisomers. The high carrier mobility in the films of the DPPs bearing stereoisomerically inhomogeneous ethylhexyl groups is rationalized here by single‐crystal X‐ray diffraction (XRD) analysis in combination with XRD and atomic force microscopy studies on thin films, which reveal the presence of slightly different 2D layer arrangements for the n‐alkyl and the 2‐ethylhexyl derivatives. For the cyano‐substituted DPPs possessing the lowest LUMO levels, ambipolar transport characteristics are observed.     

3-state BTL closed-loop PWM Class D amplifiers

One of the shortcomings of a number of Class D amplifiers (CDAs) designs is their susceptibility to supply noise, quantified by Power Supply Rejection Ratio (PSRR). Reported investigations thereto to-date remain incomplete/over-simplified, particularly the assumption that the AC ground is noise-less and a simplified fully-differential integrator model. In this paper, the effect of supply noise in the AC ground to PSRR is analytically investigated, and the associated analytical expressions derived. Of specific interest, the analysis is applied to the ubiquitous 3-state Bridge-tied-load (BTL) closed-loop PWM CDA, taking into consideration not only the effect of the non-ideal AC ground, but also the effect of the resistor and capacitor mismatch based on a realistic fully-differential integrator model. Further, the PSRR analysis of 3-state BTL closed-loop CDAs has to date been limited to the single-feedback topology and in this paper, extended to the double-feedback topology. These analyses and derived equations herein are useful as they provide valuable insights to CDA designers into the PSRR mechanisms—for example, the counter-intuitive observation that the CDA with 1st-order integrators provides similar or better PSRR than the CDA with 2nd-order integrators if both CDAs are designed to the same carrier attenuation—including the effect of various circuit parameters, and ensuing trade-offs. The derived analytical expressions are verified by means of HSPICE simulations and on the basis of practical measurements on discretely-realized CDAs.     

EPTR: expected path throughput based routing protocol for wireless mesh network

For effective routing in wireless mesh networks, we proposed a routing metric, expected path throughput (EPT), and a routing protocol, expected path throughput routing protocol (EPTR), to maximize the network throughput. The routing metric EPT is based on the estimated available bandwidth of the routing path, considering the link quality, the inter- and intra-flow interference and the path length. To calculate the EPT of a routing path, we first calculate the expected bandwidth of the link and the clique, and then consider the decay caused by the path length. Based on EPT, a distributed routing protocol EPTR is proposed, aiming to balance the network load and maximize the network throughput. Extensive simulations are conducted to evaluate the performance of the proposed solution. The results show that the proposed EPTR can effectively balance the network load, achieve high network throughput, and out-perform the existing routing protocols with the routing metrics previously proposed for wireless mesh networks.     

偏振模色散及其对光纤通信系统影响的判断

本介绍了偏振模色散（PMD）的产生及其属性，介绍了工程测量仪表方法，结合工程实例，介绍了PMD对光通信系统的影响及其判断。     

用非均匀时频变换提高音频编码器性能

预回声对音频压缩编码器的性能影响很大。人们一般采用窗切换技术来降低其不利影响。窗切换中短窗提高了对暂态信号的时间分辨率,同时降低了对低频稳态信号的频率分辨率。设计了一种非均匀时频变换方法,它在保留了对信号低频平稳分量的频率分辨率的同时提高了对高频暂态分量的时间分辨率。最后用实验验证了方法的可行性和有效性。     

软交换网络中媒体网关控制器的研究与设计

300万像素对于专业摄影来说可能不值一提，但是对于家庭用户而言却已经十分完美了。下面三款数码相机是300万家庭中令人兴奋的新品，它们的价格都在3000元到4000元人民币之间，想想一年前3000万像素的相机要花多少钱？而在测试中它们的表现也的确让人觉得物有所值。     

300脚MSA 10 Gbit/s Transponder模块

分析了开发10Gbit/sTransponder模块的必然性，介绍了10Gbit/sTransponder模块的原理、特点和参数指标。并且用开发出的两只40km300脚10Gbit/sTransponder模块成功地进行了43km的无误码传输试验和测试。     

激光熔覆钴基合金涂层的组织结构

利用5kWCO2连续激光器在16Mn钢表面进行激光熔覆钴基合金涂层，研究了激光覆合金涂层的显微组织形貌，相结构以及显微硬度。激光熔覆涂层可分为三个区域：熔化区（合金层）结合区及基材热影响区。合金涂层由γ-Co枝晶及其间的共晶组织组成，合金涂层的主要组成相为γ-Co和（Cr,Fe)7^C3。     

Diphenylamine‐Substituted Cruciform Oligo(phenylene vinylene): Enhanced One‐ and Two‐Photon Excited Fluorescence in the Solid State

1,4‐di(4′‐N,N‐diphenylaminostyryl)benzene (DPA‐DSB) is a well known compound with a large two‐photon absorption (TPA) section and strong fluorescence in solution. However, the ease with which it crystallizes results in the formation of discontinuous crystalline phases during vacuum deposition processes, thereby greatly limiting its applicability in solid‐state devices. A cruciform dimer of DPA‐DSB, 2,5,2′,5′‐tetra(4′‐N,N‐diphenylaminostyryl)biphenyl (DPA‐TSB) is reported, wherein two DPA‐DSB molecules are linked through a central biphenyl bond. The DPA‐TSB molecules take on a cruciform configuration because of the steric crowding around the central biphenyl core, which has the effect of efficiently suppressing crystalline and intermolecular interactions. The neat DPA‐TSB solid shows strong green–blue fluorescence because of both steady‐state absorption as well as TPA. The DPA‐TSB solid exhibits a photoluminescence (PL) efficiency (η_solid) of 29 % and a solid‐state two‐photon action cross section (δη_solid) of 954 GM (1 GM = 1 × 10^–50 cm⁴ s photon^–1 molecule^–1), which is much greater than for the model compound DPA‐DSB (η_solid = 16 % and δη_solid = 150 GM, where δ is the TPA cross section and η is the fluorescence quantum yield). Based on its high PL efficiency, good film‐forming ability, and strong TPA, DPA‐TSB seems to be a good candidate for applications in solid‐state optical devices.