Density functional theory study of the structure and energetics of negatively charged oligopyrroles

First‐principles calculations are used to investigate the electronic properties of negatively charged n‐pyrrole oligomers with n = 2–18. Chains of neutral oligomers are bent, whereas the negatively charged oligomers become almost planar due to accumulation of negative charge at the end monomers. Isomers of short oligomers (n < 6) display negative electron affinity although the corresponding anions are energetically stable. For longer oligomers with n ≥ 6, the electron affinity is small and positive, slowly increasing with oligopyrrole length. Doping of 12‐pyrrole with lithium atoms shows that negative oxidation states are possible due to electron transfer from dopant to oligomer at locations close to dopant. These 12‐pyrrole regions support extra negative charge and exhibit a local structural change from benzenoid to quinoid structure in the C? C backbone conjugation. Comparison between neutral and doped polypyrrole (PPy) indicates that doped polymers displays a substantial depletion of the band gap energy and the appearance of dopant‐based bands in the gap for a 50% per monomer doping level. It is predicted that Li‐doped PPy is not metallic. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Long range energy transfer in conjugated polymer sequential bilayers

Steady-state and time-resolved photoluminescence have been used to investigate the optical properties of bilayer and blend films made from poly(9,9-dioctyl-fluorene-2,7-diyl) (PFO) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH PPV). Energy transfer has been observed in both systems. From steady-state photoluminescence measurements, the energy transfer was characterized by the effective enhancement of the MEH PPV emission intensity after exciting the donor states. Relatively faster decays for the PFO donor emission have been observed in the blends as well as in the bilayer structures, confirming effective energy transfer in both structures. In contrast to the bilayers, the time decay of the acceptor emission in the blends presents a long decay component, which was assigned to the exciplex formation in these samples. For the blends the acceptor emission is in fact a composition of exciplex and MEH PPV emissions, the later being due to Fo?rster energy transfer from PFO. In the bilayers, the exciplex is not observed and temperature dependence photoluminescence measurements show that exciton migration has no significant contribution to the energy transfer. The efficiency and very long range of the energy transfer in the bilayers is explained assuming a surface-surface interaction geometry where the donor/acceptor distances involved are much longer than the common Fo?rster radius.     

Synthesis, structure, and bonding of BaTl4. Size effects on encapsulation of cations in electron-poor metal networks

The synthesis, structure, and bonding of BaTl(4) are described [C2/m, Z = 4, a = 12.408(3), b = 5.351(1), c = 10.383(2) ?, β = 116.00(3)°]. Pairs of edge-sharing Tl pentagons are condensed to generate a network of pentagonal biprisms along b that encapsulate Ba atoms. Alternating levels of prisms along c afford six more bifunctional Tl atoms about the waists of the biprisms, giving Ba a coordination number of 16. Each Tl atom is bonded to five to seven other Tl atoms and to three to five Ba atoms. There is also strong evidence that Hg substitutes preferentially in the shared edges of the Tl biprisms in BaHg(0.80)Tl(3.20) to generate more strongly bound Hg(2) dimers. Cations that are too small relative to the dimensions of the surrounding polyanionic network make this BaTl(4) structure (and for SrIn(4) and perhaps EuIn(4) as well) one stable alternative to tetragonal BaAl(4)-type structures in which cations are bound in larger hexagon-faced nets, as for BaIn(4) and SrGa(4). Characteristic condensation and augmentation of cation-centered prismatic units is common among many relatively cation- and electron-poor, polar derivatives of Zintl phases gain stability. At the other extreme, the large family of Frank-Kasper phases in which the elements exhibit larger numbers of bonded neighbors are sometimes referred to as orbitally rich.     

Synthesis of 2-naphthols via carbonylative Stille coupling reaction of 2-bromobenzyl bromides with tributylallylstannane followed by the Heck reaction

A method for the synthesis of 2-naphthols 4 is described. The carbonylative Stille coupling reactions of 2-bromobenzyl bromides with tributylallylstannane to produce 2-bromobenzyl β,γ-unsaturated ketones 2 in satisfactory to excellent yields has been achieved. The isomerization of 2-bromobenzyl β,γ-unsaturated ketones 2 can readily occur under basic conditions to generate 2-bromobenzyl α,β-unsaturated ketones 3. The 2-bromobenzyl α,β-unsaturated ketones 3 can be transformed into 2-naphthols 4 via intramolecular Heck reaction in satisfactory to good yields.     

Stereospecific synthesis and redox properties of ruthenium(II) carbonyl complexes bearing a redox-active 1,8-naphthyridine unit

Two stereoisomers of cis-[Ru(bpy)(pynp)(CO)Cl]PF₆ (bpy = 2,2′-bipyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine) were selectively prepared. The pyridyl rings of the pynp ligand in [Ru(bpy)(pynp)(CO)Cl]⁺ are situated trans and cis, respectively, to the CO ligand. The corresponding CH₃CN complex ([Ru(bpy)(pynp)(CO)(CH₃CN)]²⁺) was also prepared by replacement reactions of the chlorido ligand in CH₃CN. Using these complexes, ligand-centered redox behavior was studied by electrochemical and spectroelectrochemical techniques. The molecular structures of pynp-containing complexes (two stereoisomers of [Ru(bpy)(pynp)(CO)Cl]PF₆ and [Ru(pynp)₂(CO)Cl]PF₆) were determined by X-ray structure analyses.     

Flow admission control for multi-channel multi-radio wireless networks

Providing Quality of Service (QoS) is a major challenge in wireless networks. In this paper we propose a distributed call admission control protocol (DCAC) to do both bandwidth and delay guaranteed call admission for multihop wireless mesh backbone networks, by exploiting the multi-channel multi-radio (mc-mr) feature. We propose a novel routing metric for route setup, and present an efficient distributed algorithm for link reservation that satisfies the required bandwidth and reduces the delay by a local scheduling that minimizes one hop delay. To the best of our knowledge, this is the first distributed protocol that embeds mc-mr feature in Time Division Medium Access (TDMA) to do QoS call admission in wireless backbone networks. Extensive simulation studies show that our protocol significantly improves network performance on supporting QoS sessions compared with some widely used protocols.     

电励磁同步电机参数辨识方法综述

同步电机数学模型及参数对电力系统分析计算、电机设计、电机运行及控制等都具有重要意义。如何获得精确地同步电机参数已经成为一个重要的研究方向,国内外学者主要从设计计算和测量方法两方面进行研究。频域辨识主要采用同步电机的傅里叶变换形式的数学模型进行分析,而时域辨识的数学模型则采用同步电机瞬态过程的状态方程。本文首先描述了同步...     

A 0.13μm CMOS Δ ∑ fractional-N frequency synthesizer for WLAN transceivers

A fractional-N frequency synthesizer fabricated in a 0.13μm CMOS technology is presented for the application of IEEE 802.11 b/g wireless local area network(WLAN) transceivers.A monolithic LC voltage controlled oscillator(VCO) is implemented with an on-chip symmetric inductor.The fractional-TV frequency divider consists of a pulse swallow frequency divider and a 3rd-order multistage noise shaping(MASH)△Σmodulator with noise-shaped dithering techniques.Measurement results show that in all channels,phase noise of the synthesizer achieves -93 dBc/Hz and -118 dBc/Hz in band and out of band respectively with a phase-frequency detector (PFD) frequency of 20 MHz and a loop bandwidth of 100 kHz.The integrated RMS phase error is no more than 0.8°.The proposed synthesizer consumes 8.4 mW from a 1.2 V supply and occupies an area of 0.86 mm~2.     

多线程同步技术在电感自动测试系统中的应用

多线程同步技术能够更好地开发并行性任务和提高系统性能.为实现高速的仪器测量与低速的机械动作之间的有机协调,提高工作的效率,在研究了Windows线程同步机制和CVI多线程技术中数据保护的基础上,给出了利用事件内核对象和线程安全变量来实现电感自动测试系统的方法,同时给出了工作线程的流程图.实际使用结果表明:该系统对单台测...     

Cobalt oxide nanosheet humidity sensor integrated with circuit on chip

The work studies a micro humidity sensor integrated with a seven-stage ring oscillator circuit-on-a-chip fabricated by the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and a post-process. The structure of the humidity sensor consists of interdigitated electrodes and a sensing film. The sensing film is cobalt oxide nanosheet that is prepared by a precipitation-oxidation method. The sensor, which is a capacitive type, changes in capacitance when the sensing film adsorbs or desorbs water vapor. The ring oscillator circuit is employed to convert the capacitance of the sensor into the oscillation frequency output. The post-process of the sensor includes etching the sacrificial oxide layer and coating the sensing film on the interdigitated electrodes.