High resolution interrogation technique based on linear photodiode array spectrometer for fiber Bragg grating Sensors - art. no. 65952C

A linear photodiode array spectrometer based, high resolution interrogation technique for fiber Bragg grating sensors is demonstrated. Spline interpolation and Polynomial Approximation Algorithm (PAA) are applied to the data points acquired by the spectrometer to improve the original PAA based interrogation method. Thereby fewer pixels are required to achieve the same resolution as original. Theoretical analysis indicates that if the FWHM of a FBG covers more than 3 pixels, the resolution of central wavelength shift will arrive at less than 1 pm. While the number of pixels increases to 6, the nominal resolution will decrease to 0.001 pm. Experimental result shows that Bragg wavelength resolution of similar to 1 pm is obtained for a FBG with FWHM of similar to 0.2 nm using a spectrometer with a pixel resolution of similar to 70 pm.

移动代理数据完整性保护协议分析与实现技术研究

移动代理技术是未来网络计算的一种新模式，特别适合于电子商务领域。其安全性是制约移动代理技术能否广泛应用的重要因素，数据完整性是其中的一个关键问题。 移动代理数据完整性保护协议的设计和安全性分析是移动代理安全性研究的重点和难点。本文从对移动代理环境下的数据完整性属性研究入手，给出了移动代理数据完整性新定义，以此为基础给出了一种分析移动代理协议完整性属性的有效方法，并以典型协议为实例验证了该方法的有效性，针对实例分析中所发现的缺陷，设计了一个可配置移动代理数据完整性保护协议。本文主要创新性工作包括： （1）对移动代理数据完整性进行了重新定义。通过划分安全目标和执行环境，从节点数据完整性和路径完整性两方面对比分析了移动代理数据完整性同传统消息完整性的联系和区别，给出了移动代理数据完整性的新内涵和形式化描述，为此类协议的形式化验证和设计提供了基础。 （2）采用CSP方法建立了典型移动代理数据完整性保护协议的形式化模型。通过对参与者信任程度的划分，建立了此类协议的通用模型结构，用CSP方法描述协议参与者进程和消息集合，建立了此类协议的形式化模型。该模型可以较好地表示协议在多轮次、参与者数量不确定情况下的执行情况。 （3）给出了移动代理路径完整性形式化规约，建立了基于阶函数的路径完整性分析方法。通过路径完整性形式化规约，建立了路径完整性同证据唯一性的关系，通过基于阶函数的路径完整性证明定理，给出了基于阶函数的移动代理路径证据唯一性证明方法，构建了一套移动代理路径完整性分析的形式化方法。 （4）构造了针对典型的移动代理数据完整性保护协议的新型攻击。采用基于阶函数的移动代理完整性分析方法，对PM���议和Cheng-Wei协议进行了分析，发现了协议中存在的路径完整性保护缺陷，并构造了针对该缺陷的概率攻击方案，验证了模型和分析方法的有效性。 （5）给出了移动代理数据完整性保护协议安全限制条件，设计了一个可配置移动代理完整性保护协议。该协议在一定条件下可以防止所发现的新攻击。并给出了该协议在具体条件下的形式化分析结果，证明了该协议在具体条件下能够保证数据的完整性。

替代燃料二甲醚的燃烧特性及其污染物甲醛的生成消耗机理研究

化石燃料的不可再生性决定了其不能长久为全球经济和科技的发展提供能源动力，从可持续发展和能源战略的角度考虑，能够替代石油及其衍生品的清洁替代燃料研究已经成为提高能源供应安全、改善环境污染问题、应对气候变化的重要措施，对替代燃料的研究和应用已经成为各方关注和开发的热点。 二甲醚(DME、CH3OCH3)是一种最简单的醚类，它不含C-C健，可以由天然气、煤、生物质燃料等大量制备，而且具有较高的辛烷值(55-60)，较低的碳氢化合物、CO排放，没有PM���放，因而被认为是一种非常有发展前景的发动机替代燃料，已经受到了广泛的关注。但是，在发动机燃用DME的实验研究表明，在其排气中有非常规污染物甲醛(HCHO)、乙醛(CH3CHO)，甲酸甲酯(HCOOCH3)等排放，这些有机污染物会对环境和人类健康产生严重的危害，在环保要求日益严格的趋势下，这就制约了二甲醚的规模化应用。因此，对二甲醚燃烧性能、氧化中间产物甲醛等的产生和排放机理、相关污染物抑制技术需要进行着重研究，这对二甲醚燃料规模化应用、相关二甲醚燃烧器设计、燃烧性能的优化以及污染物控制技术的研究等都有着重要的理论指导意义和参考价值。 为了充分理解二甲醚燃料的燃烧特性、非常规污染物甲醛的产生和消耗机理，本文以实验和二甲醚化学反应动力学机理为指导，对二甲醚预混燃烧的燃烧特性、相关污染物和甲醛产生和消耗的机理做了详细的研究；并针对二甲醚燃料的不同应用背景，对二甲醚燃料低温下的氧化和甲醛生成特性、DME与LPG掺混燃烧特性和甲醛生成消耗机理进行了深入的研究，具体工作有： 研究了二甲醚预混燃烧特性、火焰中甲醛等污染物的产生特性，建立了火焰中甲醛取样、测量的方法和实验平台。并对当量比和燃料流量对二甲醚预混燃烧的燃烧特性、甲醛生成特性影响进行了考察，实验结果表明二甲醚是一种优良的替代燃料，在二甲醚火焰中甲醛是其重要的中间产物，甲醛浓度分布与当量比和预混气流速密切相关。当量比一定时，随着预混气流速的增加，火焰中甲醛产生的范围变窄，且甲醛浓度峰值逐渐移向燃烧器出口，而甲醛产生的浓度峰值数值上相差不大，甲醛在形成峰值后被快速消耗，其浓度在0.1mm内下降到几乎为零；在二甲醚流量一定时，随着当量比的增加，火焰中产生了更多的甲醛，火焰中甲醛分布的范围也变宽，而且当量比越大，甲醛的消耗也变缓，在当量比为0.8时，甲醛浓度从峰值到被消耗距离变为2mm，远大于当量比0.6和0.7下0.1mm的消耗距离。 对二甲醚预混燃烧进行数值研究和化学动力反应机理分析后发现，在二甲醚燃烧中，二甲醚的氧化反应途径主要是通过脱氢生成CH3OCH2和在高温下的直接裂解反应而进行，其中脱氢反应是低温下二甲醚消耗的主要途径，而在高温反应阶段(T>1000K)，DME的直接裂解和燃料的脱氢反应共同起主导作用；非常规污染物甲醛通过DME脱氢产物CH3OCH2的裂解和外部氧化而生成，在高温时通过DME直接裂解后被氧化产生；甲醛的消耗反应则是通过与H、O、OH和CH3基的氧化反应而完成，其中与O、OH基的反应在燃烧中起主要作用。因此二甲醚燃烧中甲醛的抑制关键在燃烧中甲醛的消耗阶段，采取有效的技术措施，如优化燃烧器结构提高二甲醚燃烧室内的温度、在燃烧区保证充足的氧气供应等措施，加快甲醛的消耗速度以促进其被完全氧化，可以实现二甲醚燃烧中甲醛的零排放。 针对柴油发动机燃用DME燃料时，燃料在燃烧室停留时间过短，造成部分未燃二甲醚随尾气排放，对DME在低温下(<800K)的氧化特性和甲醛生成特性进行了实验研究。结果表明，二甲醚在200℃左右就开始发生氧化反应，在200~400℃温度范围内被氧化而生成大量中间产物甲醛，且在此温度范围内甲醛不易被氧化分解，而发动机尾气温度（一般在200~600℃之间）处于甲醛最易生成的范围，因此未燃二甲醚在尾气中发生低温氧化反应生成的甲醛，是发动机燃用DME而排放高浓度甲醛的重要来源。研究结论为柴油发动机燃用DME抑制非常规污染物甲醛的排放提供了新的参考。 DME作为替代燃料，部分替代及与其他石化系燃料掺混燃烧是目前的重要应用方向，对DME与LPG掺混燃烧特性和甲醛生成特性进行了实验研究，结果表明，在DME与LPG掺混燃烧中，固定当量比和燃料质量流量的条件下，两种燃料存在一个最佳掺混比，在此掺混比例下，混合燃料着火提前，燃料燃烧性能最佳；DME与LPG混合燃料中，二甲醚是燃烧中甲醛产生的主要来源，控制DME的完全氧化和燃烧是抑制DME与LPG掺混燃烧排放甲醛的主要途径，这为更好地应用DME与LPG混合燃料提供了参考。 能否清洁高效燃烧是决定替代燃料DME应用规模和途径中的关键任务，本文对DME燃烧特性、非常规污染物甲醛的生成排放特性、低温下DME的氧化特性、DME与LPG掺混燃烧特性的研究，从不用的应用方向和领域对DME清洁高效燃烧进行了探讨和研究，研究成果可以为清洁高效利用二甲醚、抑制甲醛排放，以及开发相关燃烧技术、燃烧器提供实验依据和理论指导。本文在DME燃烧特性和非常规污染物甲醛的产生与排放方面取得了具有创新性的研究结果。

Kinetic Model Study on Enzymatic Hydrolysis of Cellulose Using Artificial Neural Networks

Enzymatic hydrolysis of cellulose was highly complex because of the unclear enzymatic mechanism and many factors that affect the heterogeneous system. Therefore, it is difficult to build a theoretical model to study cellulose hydrolysis by cellulase. Artificial neural network (ANN) was used to simulate and predict this enzymatic reaction and compared with the response surface model (RSM). The independent variables were cellulase amount X-1, substrate concentration X-2, and reaction time X-3, and the response variables were reducing sugar concentration Y-1 and transformation rate of the raw material Y-2. The experimental results showed that ANN was much more suitable for studying the kinetics of the enzymatic hydrolysis than RSM. During the simulation process, relative errors produced by the ANN model were apparently smaller than that by RSM except one and the central experimental points. During the prediction process, values produced by the ANN model were much closer to the experimental values than that produced by RSM. These showed that ANN is a persuasive tool that can be used for studying the kinetics of cellulose hydrolysis catalyzed by cellulase.

Synthesis of biodiesel from waste cooking oil using immobilized lipase in fixed bed reactor

Waste cooking oil (WCO) is the residue from the kitchen, restaurants, food factories and even human and animal waste which not only harm people's health but also causes environmental pollution. The production of biodiesel from waste cooking oil to partially substitute petroleum diesel is one of the measures for solving the twin problems of environment pollution and energy shortage. In this project, synthesis of biodiesel was catalyzed by immobilized Candida lipase in a three-step fixed bed reactor. The reaction solution was a mixture of WCO, water, methanol and solvent (hexane). The main product was biodiesel consisted of fatty acid methyl ester (FAME), of which methyl oleate was the main component. Effects of lipase, solvent, water, and temperature and flow of the reaction mixture on the synthesis of biodiesel were analyzed. The results indicate that a 91.08% of FAME can be achieved in the end product under optimal conditions. Most of the chemical and physical characters of the biodiesel were superior to the standards for 0(#)diesel (GB/T 19147) and biodiesel (DIN V51606 and ASTM D-6751).

Production and characterization of biodiesel from tung oil

The feasibility of biodiesel production from tung oil was investigated. The esterification reaction of the free fatty acids of tung oil was performed using Amberlyst-15. Optimal molar ratio of methanol to oil was determined to be 7.5:1, and Amberlyst-15 was 20.8wt% of oil by response surface methodology. Under these reaction conditions, the acid value of tung oil was reduced to 0.72mg KOH/g. In the range of the molar equivalents of methanol to oil under 5, the esterification was strongly affected by the amount of methanol but not the catalyst. When the molar ratio of methanol to oil was 4.1:1 and Amberlyst-15 was 29.8wt% of the oil, the acid value decreased to 0.85mg KOH/g. After the transesterification reaction of pretreated tung oil, the purity of tung biodiesel was 90.2wt%. The high viscosity of crude tung oil decreased to 9.8mm(2)/s at 40 degrees C. Because of the presence of eleostearic acid, which is a main component of tung oil, the oxidation stability as determined by the Rancimat method was very low, 0.5h, but the cold filter plugging point, -11 degrees C, was good. The distillation process did not improve the fatty acid methyl ester content and the viscosity.

BIODIESEL PRODUCTION FROM DIFFERENT FEEDSTOCKS IN PILOT SCALE SYSTEM

In this study, the preparations of biodiesel from three different feedstocks, including rapeseed oil, high acidified Chinese wood oil and trap grease, were carried out in a pilot scale of 200 t yr(-1) biodiesel production system. The optimum operating conditions for transesterification of rapeseed oil in plug flow reactor were found to be as follows: the catalyst dosage is 1.2 wt%; the retention time is about 17 min; the bed temperature is 65 degrees C; the oil/methanol ratio is 1:6; the content of methyl ester is 96.33% under these conditions. A kind of ion exchange resin, a solid acid catalyst, filled in the fixed bed reactor was used as the esterification catalyst for the pretreating of high acidified oil. The acid value of Chinese wood oil could be reduced from 7 to 0.8 mg KOH.g(-1) after 88 min, the optimum operating conditions were obtained as follow: molar ratio of methanol to oil is about 6:1, the temperature of the fixed bed, 65 degrees C and the retention time, about 88 min. Also a kind of acidified oil, namely trap grease, with the acid value being 114 mg KOH.g(-1) could be equally converted to a good biodiesel product through this system. Generally, the refined biodiesel product generated through this system could meet China #0 Biodiesel Standard, as well as Germany Biodiesel Standard for most indexes. It indicates that the designed process in this system has a good adaptability for different kinds of oil.

A study on the economic efficiency of hydrogen production from biomass residues in China

As part of Pilot Project of KIP of CAS, a feasibility study of hydrogen production system using biomass residues is conducted. This study is based on a process of oxygen-rich air gasification of biomass in a downdraft gasifier plus CO-shift. The capacity of this system is 6.4 t biomass/d. Applying this system, it is expected that an annual production of 480 billion N m(3) H-2 will be generated for domestic supply in China. The capital cost of the plant used in this study is 1328$/(N m(3)/h) H-2 out, and product supply cost is 0.15$/N m(3) H-2. The cost sensitivity analysis on this system tells that electricity and catalyst cost are the two most important factors to influence hydrogen production cost.

Periodic bubble emission and appearance of an ordered bubble sequence (train) during condensation in a single microchannel

Condensation of steam in a single microchannel, silicon test section was investigated visually at low flow rates. The microchannel was rectangular in cross-section with a depth of 30 pm, a width of 800 mu m and a length of 5.0 mm, covered with a Pyrex glass to allow for visualization of the bubble formation process. By varying the cooling rate during condensation of the saturated water vapor, it was possible to control the shape, size and frequency of the bubbles formed. At low cooling rates using only natural air convection from the ambient environment, the flow pattern in the microchannel consisted of a nearly stable elongated bubble attached upstream (near the inlet) that pinched off into a train of elliptical bubbles downstream of the elongated bubble. It was observed that these elliptical bubbles were emitted periodically from the tip of the elongated bubble at a high frequency, with smaller size than the channel width. The shape of the emitted bubbles underwent modifications shortly after their generation until finally becoming a stable vertical ellipse, maintaining its shape and size as it flowed downstream at a constant speed. These periodically emitted elliptical bubbles thus formed an ordered bubble sequence (train). At higher cooling rates using chilled water in a copper heat sink attached to the test section, the bubble formation frequency increased significantly while the bubble size decreased, all the while forming a perfect bubble train flowing downstream of the microchannel. The emitted bubbles in this case immediately formed into a circular shape without any further modification after their separation from the elongated bubble upstream. The present study suggests that a method for controlling the size and generation frequency of microbubbles could be so developed, which may be of interest for microfluidic applications. The breakup of the elongated bubble is caused by the large Weber number at the tip of the elongated bubble induced by the maximum vapor velocity at the centerline of the microchannel inside the elongated bubble and the smaller surface tension force of water at the tip of the elongated bubble.

Bio-syngas production from biomass catalytic gasification

A promising application for biomass is liquid fuel synthesis, such as methanol or dimethyl ether (DME). Previous studies have studied syngas production from biomass-derived char, oil and gas. This study intends to explore the technology of syngas production from direct biomass gasification, which may be more economically viable. The ratio of H-2/CO is an important factor that affects the performance of this process. In this study, the characteristics of biomass gasification gas, such as H-2/CO and tar yield, as well as its potential for liquid fuel synthesis is explored. A fluidized bed gasifier and a downstream fixed bed are employed as the reactors. Two kinds of catalysts: dolomite and nickel based catalyst are applied, and they are used in the fluidized bed and fixed bed, respectively. The gasifying agent used is an air-steam mixture. The main variables studied are temperature and weight hourly space velocity in the fixed bed reactor. Over the ranges of operating conditions examined, the maximum H-2 content reaches 52.47 vol%, while the ratio of H-2/CO varies between 1.87 and 4.45. The results indicate that an appropriate temperature (750 degrees C for the current study) and more catalyst are favorable for getting a higher H-2/CO ratio. Using a simple first order kinetic model for the overall tar removal reaction, the apparent activation energies and pre-exponential factors are obtained for nickel based catalysts. The results indicate that biomass gasification gas has great potential for liquid fuel synthesis after further processing.

Ultra-narrow dual-channel filter based on symmetrical sampled fibre Bragg grating

A kind of ultra-narrow dual-channel filter is proposed in principle and demonstrated experimentally. This filter is designed by means of two sampled fibre Bragg gratings (SFBGs), where one is periodic 0-pi sampling and the other is symmetrical spatial sampling. The former can create two stopbands in the transmission spectra and the latter can produce two ultra-riarrow passbands. Our filter has the 3-dB bandwidth of about 1 pm, whose value is two orders of magnitude less than the bandwidth of the traditional SFBG filters. The proposed filter has a merit that the channel spacing remains unchanged when tuning the filter.

Theoretical design or single-polarization single-mode microstructured polymer optical fibres

Using the full-vector plane-wave expansion method, a kind of PMMA-based polarization-maintaining microstructured optical fibre (PM-mPOF) is theoretically studied. Dependence of the cutoff wavelengths of the two orthogonal polarization states (polarized along the two principal axes of PM-mPOF) on the structure parameters of the fibre is investigated in detail. A single-polarization single-mode (SPSM) PM-mPOF working in the visible region is designed and optimized with the result of the maximum SPSM bandwidth of 140 nm.

A novel dual-wavelength DFB fiber laser based on symmetrical FBG structure

A novel grating structure is proposed and demonstrated to obtain stable dual-wavelength (DW) distributed-feedback (DFB) fiber lasers at room temperature. The proposed grating is based on a symmetrical structure, where one half is periodically sampled by "0"-to-"pi" period and the other half is done by "pi"-to-"0" period. This structure can create two separated resonance cavities and hence achieve the stable DW lasing operation. By fabricating the proposed grating on a piece of Er: Yb-codoped fiber, we experimentally obtain a stable DW-DFB fiber laser with wavelength spacing of similar to 440 pm at room temperature.

黄土高原旱地小麦氮磷钾与有机肥优化配施试验

试验研究了不同施肥处理对小麦产量及肥料、水分利用率的影响。结果表明:氮磷配施对产量的贡献率最高,产量达5 099.8 kg/hm2,增产率达21.5%,较氮、磷肥单施产量分别增产14.0%和18.4%,具有正交互效应;单施有机肥较NM、PM���NPM���产率分别达到6.63%、4.12%、11.3%。化肥配施可显著提高旱地小麦的肥料利用率和水分利用效率,氮磷有机肥配施肥料氮、磷肥的利用率分别较氮、磷肥单施提高1.71和12.55个百分点;氮磷配施可同时提高氮肥、磷肥肥效,此时氮贡献率为15.53%,磷贡献率达12.26%,且水分利用率提高了24.1%,耗水系数降低了17.57%。

黄土旱塬长期施肥条件下小麦钾素营养和肥料利用率的研究

为了给黄土旱地经济合理施肥、粮食增产提供科学依据。[方法]在长期定位试验的基础上,研究了不同施肥对小麦产量、各生育期钾素营养和肥料利用率的影响。[结果]不同施肥小麦增产效果差异显著。单施氮肥小麦增产75.3%,单施磷肥小麦产量则降低24.7%,NM、PM���NPM���施小麦增产75.9%~92.9%;小麦钾素的吸收主要集中在生长发育前期,孕穗期以后因泌钾现象多表现为负吸收,施用有机肥,特别是无机肥与有机肥配施,促进小麦吸钾作用明显,小麦植株各器官含钾量明显提高;单施N肥、NP配施小麦钾素的吸收量、吸收速率较高,单施有机肥及有机无机肥配合施用小麦钾素吸收量和吸收速率比对照也有明显提高;单施N肥小麦氮肥利用率较高为76.73%,单施P肥小麦磷肥利用率较低仅为14.20%,NP配施与单施P肥相比,吸磷量、吸钾量分别增加112.53%和79.36%。施用有机肥可以显著提高作物氮、磷、钾吸收量,但肥料利用率却不高。[结论]施用有机肥以及有机无机肥配合施用,可以明显促进小麦对氮、磷、钾养分的吸收,提高小麦产量。