Novel surface acoustic wave-interdigitated array electrode gas sensor for dissolved ammonia

 A novel surface acoustic wave-interdigitated array electrode (SAW-IDA) ammonia gas sensor is proposed. A gas-permeable membrane is employed to separate the buffer solution in the inner cell of the gas-sensing probe from the sample solution in the detection cell. The response of the IDA conductive electrodes is based on the impedance change of the buffer solution during ammonia adsorption. Therefore, this gas sensor overcomes the influence of water vapour in the conventional film-coated SAW gas sensor and can be used for the detection of gases in aqueous solutions. The ammonia sensor exhibits a favourable frequency response to 5×10^-7–1×10^-3 mol/l ammonia. The optimal buffer composition and probe parameters have been determined. Dynamic range, response time, selectivity, and temperature drift are discussed. The ammonia sensor was also applied to the determination of serum ammonia. Results were in good agreement with those from the conventional enzymatic-spectrophotometric method. Received: 1 December 1995/Revised: 9 April 1996/Accepted: 14 April 1996     

Determination of lipase activity in porcine pancreas and clinical analysis of lipase in human serum with surface acoustic wave enzyme sensor system

A new kind of surface acoustic wave (SAW) enzyme sensor system has been applied to the assay of extracted lipase activity based on triacetin solution as substrate. A linear relationship between the frequency change and the enzyme activity up to 500 U/L has been obtained, and the detection limit has been evaluated to 0.3 U/L. Kinetic parameters of the extracted lipase as well as that of the standard enzyme have been estimated. The effects of temperature, pH value and surfactants have been investigated. A comparison between SAW sensor system and the conductometric method has been carried out. The technique has been applied to the determination of lipase activity in serum samples. Received: 17 January 1995 / Revised: 9 March 1995 / Accepted: 16 March 1995 Correspondence to: Shouzhuo Yao     

XeCl与XeBr激光同时振荡的时间特性

本文首次报道了ＸｅＣｌ与ＸｅＢｒ两激光在双振荡过程中的时间关系，给出了影响这一时间关系的因素。并就其中的动力学过程作了定性的讨论。     

构建可运营、可管理、电信级的光以太网

本对构建可运营可管理电信级光以太网所涉及到的封装技术、用户管理、QoS保证等相关问题进行探讨。     

Orthonormal minimal structure for n-dimensional denominator-separable digital filters for multiprocessor implementation

A new structure for n-dimensional-separable digital filters is derived based on an orthonormal expansion. The new structure processes well behaved filter parameters that are easily calculated, needs the minimum number of delays and has only lossless and passive substructures that are free from overflow oscillations and have low sensitivity and low roundoff noise. It can be mapped into a systolic multiprocessor array in a straightforward manner.<>     

Inorganic–organic hybrids involving poly(ε‐caprolactone) and silica network: Hydrogen‐bonding interactions and isothermal crystallization kinetics

Inorganic–organic hybrids mediated by hydrogen‐bonding interactions involving silicon oxide network and poly(ε‐caprolactone) (PCL) were prepared via an in situ sol–gel process of tetraethoxysilane in the presence of PCL. Fourier transform infrared spectroscopy indicated that there were hydrogen‐bonding interactions between carbonyls of PCL and silanol hydroxyls that were formed by incomplete polycondensation in the sol–gel process. In terms of the frequency shift of the hydroxyl stretching vibration bands, it is concluded that the strength of the interassociation between PCL and silicon oxide networks is weaker than that of the self‐association in the control silica network. The phenomenon of equilibrium melting point depression was observed for the PCL/silica system. The hybridization of PCL with silica network causes a considerable increase in the overall crystallization rate and dramatically influences the mechanism of nucleation and growth of the PCL crystallization. The analysis of isothermal crystallization kinetic data according to the Hoffman‐Lauritzen theory shows that with increasing silica content in the hybrids, the surface energy of extremity surfaces increases dramatically for the hybrids. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2594–2603, 2005     

EFFECTS OF SOG ON DPP-RECEPTOR BINDING

Concentration gradients of morphogens are known to be instrumental in cell signaling and tissue patterning. Of interest here is how the presence of a competitor of BMP ligands affects cell signaling. The effects of Sog on the binding of Dpp with cell receptors are analyzed for dorsal-ventral morphogen gradient formation in vertebrate and Drosophila embryos. This prototype system includes diffusing ligands, degradation of morphogens, and cleavage of Dpp-Sog complexes by Tolloid to free up Dpp. Simple and biologically meaningful necessary and sufficient conditions for the existence of a steady state gradient configuration are established, and existence theorems are proved. For high Sog production rates (relative to the Dpp production rate), it is found that the steady state configuration exhibits a more intense Dpp-receptor concentration near the dorsal midline. Numerical simulations of the evolution of the system show that, beyond some threshold Sog production rate, the transient Dpp-receptor concentration at the dorsal midline would become more intense than that of the steady state, before subsiding and approaching a nonuniform steady state of lower magnitude. The magnitude of the transient concentration has been found to increase by several fold with increasing Sog production rate. The highly intense Dpp activity at and around the dorsal midline is consistent with available experimental observations and other analytical studies.     

Magnetic nanoparticles used in headspace extraction coupled with DSI-GC-IT/MS for analysis of VOCs in dry Traditional Chinese Medicine

A novel magnetic method using polystyrene modified magnetic nanoparticles to perform thermoheadspace extraction was successfully developed for extraction and preconcentration of volatile organic components in dry Traditional Chinese Medicine(TCM) based on gas chromatography-ion trap/mass spectrometry with a Chromato Probe direct sample introduction device. The dried fruit of Amomum testaceum Ridl. was used as the object TCM. The optimum parameters of headspace magnetic solid-phase extraction were investigated, in which desorption solvent ethyl acetate played a key role in this method,and the headspace extraction temperature of 90℃ and the headspace extraction time of 15 min finally decided. Headspace solid-phase microextraction method was also used to analyze volatile compounds in the TCM to compare with the proposed method. The results show that 60 components were identified totally by two methods; most of the low boiling point chemical compounds are isolated by this new method. In this work, an environmental-friendly and cheap analytical method was established, and a new approach to analyze volatile compounds in dry Traditional Chinese Medicine was also provided.     

运载火箭结构动特性分析工具的设计与实现

运载火箭的结构模型复杂,只有通过开发专用的仿真分析软件,才能高效、便捷的对其开展动力学特性分析。为保证工具建设的实用性,该软件基于航天领域应用广泛的Patran/Nastran软件进行二次开发。针对仿真分析流程,设计实现了运载火箭结构动特性分析工具,涵盖了建模与计算模块、结果后处理模块、模态筛选模块与模型修正模块,并提炼了其中的关键技术。经工程实践表明,工具可提升设计效率,且计算结果准确、通用性与扩展性强,在工程中具备良好的应用价值。     

Minimizing the hydrodynamic size of quantum dots with multifunctional multidentate polymer ligands

We report a new strategy to minimize the hydrodynamic size of quantum dots (QDs) and to overcome their colloidal stability and photobleaching problems based on the use of multifunctional and multidentate polymer ligands. A novel finding is that a balanced composition of thiol (-SH) and amine (-NH 2) coordinating groups grafted to a linear polymer chain leads to highly compact nanocrystals with exceptional colloidal stability, a strong resistance to photobleaching, and high fluorescence quantum yields. In contrast to the standing brushlike conformation of PEGylated dihydrolipoic acid molecules, mutlidentate polymer ligands can wrap around the QDs in a closed "loops-and-trains" conformation. This structure is highly stable thermodynamically and is responsible for the excellent colloidal and optical properties. We have optimized this process for the preparation of ultrastable CdTe nanocrystals and have found the strategy to be broadly applicable to a wide range of nanocrystalline materials and heterostructures. This work has led to a new generation of bright and stable QDs with small hydrodynamic diameters between 5.6 and 9.7 nm with tunable fluorescence emission from the visible (515 nm) to the near-infrared (720 nm). These QDs are well suited for molecular and cellular imaging applications in which the nanoparticle hydrodynamic size must be minimized.