Conjugated polyelectrolyte with pendant carboxylate groups: Synthesis,photophysics, and pH responses in the presence of surfactants

This article reports the synthesis, optical properties, and pH responses of a water‐soluble poly(phenylene ethynylene) with pendant carboxylate groups. This conjugated polyelectrolyte, PPE‐OBS, was prepared via a facile synthetic route, using 1,4‐di(ethyl 4‐oxy‐butyrate)‐2,5‐diiodo‐benzene as polymeric monomer and followed by the alkali induced saponification. PPE‐OBS absorbs strongly in the blue region and emits a moderately intense fluorescence. However, it subjects to unstable emission in neutral aqueous media, which is believed to arise because the polymer tends to become more hydrophobic via protonation and to form much heavier aggregates (clusters). Subsequent studies on the interaction and stabilization of PPE‐OBS with various surfactants indicate that its fluorescence stability can be largely improved in the presence of a small amount of surfactant. More interestingly, even at low pH, the surfactant‐stabilized polyelectrolyte with its pendant groups being ? COOH rather than ? COO^? remains water‐soluble and emits efficiently, which is expected of great significance for the covalent linkage to bio‐molecules. In addition, the sensitive pH response in emission spectrum of PPE‐OBS/surfactant complex over a relatively wide range suggests surely a potential access to the fluorescent sensing of pH variation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3056–3065, 2009     

Surface cleaning of germanium nanodot ionization substrate for surface‐assisted laser desorption/ionization mass spectrometry

In surface‐assisted laser desorption/ionization mass spectrometry (SALDI‐MS), a chemical background signal, arising from organic contaminants such as plasticizers, is frequently observed mainly under m/z ca. 600, which impairs the advantages of the matrix‐free approach. Silver salts, which are used for the cationization of aromatic compounds, are also difficult to remove completely after the measurements. In this study, surface cleaning techniques used in semiconductor processing were used to clean our developed silicon‐based SALDI substrate on which self‐assembled germanium nanodots (GeNDs) had been deposited (termed a GeND chip). An immersion cleaning method using acetone with sonication, and a sulfuric‐peroxide mixture (SPM) cleaning method using a mixture of H₂SO₄/H₂O₂/deionized water, were examined for their effectiveness in removing organic compounds and residual silver salts. Removal of both types of contaminants was successfully performed by SPM cleaning. The limit of detection for glutathione was improved from ca. 5 pmol without cleaning to ca. 50 fmol after the SPM cleaning. Since GeND chips can tolerate acidic cleaning and sonication due to their chemical inertness and rigid nanodot structures, they appear to be an ideal reusable SALDI substrate. Copyright © 2009 John Wiley & Sons, Ltd.     

基于粗糙集的经济预警规则发现

应用粗糙集的理论和方法对经济预警有关数据进行分析,挖掘其中隐含的有用信息,提取规则并对规则进行约简,从而求取表达经济预警信息的最小决策规则,为经济预警有用信息的获取提供一种有效的方法.     

Highly enantioselective addition of methyl propiolate to aldehydes catalyzed by a titanium(IV) complex of a β-hydroxy amide

Three chiral β-hydroxy amide ligands were prepared by the reaction of benzyl chloride with amino alcohols derived from l-tyrosine. The titanium(IV) complex of chiral ligand 4a was found to be an effective catalyst for the asymmetric addition of methyl propiolate to aliphatic and aromatic aldehydes. The γ-hydroxy-α,β-acetylenic esters were obtained in excellent enantiomeric excesses (up to 94% ee) under optimized conditions.     

Anode spot plasma deposition of insulating layers on aluminum

The deposition of an insulating layer upon an aluminum plate in an argon plasma is described. The process is effected in a low-power DC discharge to which a small amount of sulfur hexafluoride (SF₆) has been added, causing the formation of anode spots at sharp metallic surfaces. The insulator is deposited in the region beneath the spot     

Lamb wave sensors array for nonviscous liquid sensing

The interdigital transducer (IDT) can excite Lamb wave in a piezoelectric plate loading with a liquid layer, and the phase velocity of Lamb wave is associated with the properties of the liquid layer. In this paper, the concept of effective permittivity is introduced to study the Lamb wave’s potential application in liquid sensing. Considering the measuring of ideal nonviscous liquid, the sensors array is designed to sense the density and the dielectric constant of the liquid layer simultaneously. Using LiNbO₃ as piezoelectric material, in order to improve the sensors array sensitivity and the electro-mechanical coupling coefficient, the optimized results including plate thicknesses and cut orientations are presented by numerical simulation. These studies show that the Lamb wave sensors array can be potential in liquid sensing.     

基于可控提前期和服务水平约束的(Q,r)库存问题

本文研究了存在顾客流失情况下，基于可控提前期和服务水平约束的连续盘点（Q，r）库存管理同题。当市场需求分布未知时采用MiniMax方法建立年总成本函数表达式，修正以往研究中对安全系数取值范围错误判断，推导出合理的安全系数取值范围，并给出最优解的计算方法。     

Two-stage autoignition and combustion mode evolution in boundary layer flows above a cold flat plate

Boundary layers are omnipresent in fundamental kinetic experimental facilities and practical combustion engines, which can cause ambiguity and misleading results in kinetic target acquisition and even abnormal engine combustion. In this paper, using n-heptane as a representative large hydrocarbon fuel exhibiting pronounced low-temperature chemistry (LTC), two-dimensional numerical simulation is conducted to resolve the transient autoignition phenomena affected by a boundary layer. We focus on the ignition characteristics and the subsequent combustion mode evolution of a hot combustible mixture flowing over a colder flat plate in an isobaric environment. For cases with autoignition occurring within the boundary layer, similarity is observed in the first-stage ignition as manifested by a constant temperature at all locations. The first-stage ignition is found to be rarely affected by heat and radical loss within the boundary layer. While for the main ignition event, an obvious dependence of ignition process on boundary layer thickness is identified, where the thermal-chemical process exhibits similarity at locations with similar boundary layer thickness, and the main ignition tends to first occur within the boundary layer at the domain end and generates a C-shape reaction front. It is found that sequential spontaneous autoignition is the dominant subsequent combustion mode at high-pressure conditions. At low to intermediate pressures, auto-ignition assisted flame propagation is nevertheless the dominant mode for combustion evolution. This research identifies novel features of autoignition and the subsequent combustion mode evolution affected by a cold, fully developed boundary layer, and provides useful guidance to the interpretation of abnormal combustion and combustion mode evolution in boundary layer flows.     

纳秒脉冲等离子体合成射流激励器的流场特性分析

采用一台高重频、快上升沿纳秒脉冲电源作为激励源,对典型的双电极合成射流激励器进行放电,通过粒子图像测速法（particle image velocimetry,PIV）测量放电实验中激励器稳定流场特性以及发展速度.分析实验结果发现,随着重复频率的提高,合成射流的平均发展速度也随之增大,1 kHz时的平均速度最高达到28.28 m/s,并在单脉冲能量远低于微秒脉冲的情况下,实现了更快的稳态流场控制,表明高重复频率下,更多次数的脉冲放电可提高激励总能量,有效地弥补纳秒脉冲单脉冲输出能量不足的缺点.而且频率越高,流场发展速度越快,说明高重频工作模式会对输出总能量有补偿作用.