Pollutant flushing with natural displacement ventilation

We examine the time taken to flush pollutants from a naturally ventilated room. A simple theoretical model is developed to predict the time taken for neutrally-buoyant pollutants to be removed from a room by a flow driven by localised heat inputs; both line and point heat sources are considered. We show that the rate of flushing is a function of the room volume, vent areas ( A) and the distribution, number (n) and strength (B) of the heat sources. We also show that the entire problem can be reduced to a single parameter ( μ) that is a measure of the vent areas, and a dimensionless time ( τ) that is a function of B, V and μ. Small-scale salt-bath experiments were conducted to measure the flushing rates in order to validate our modelling assumptions and predictions. The predicted flushing times show good agreement with the experiments over a wide range of μ. We apply our model to a typical open plan office and lecture theatre and discuss some of the implications of our results. © 2005 Elsevier Ltd. All rights reserved.

The mechanism of high temperature aqueous corrosion of steel

A new model is presented which describes the growth of the duplex layers of Fe3O4 on mild steel in high temperature, deoxygenated, neutral or alkaline aqueous solutions. It is shown that the layers grow by the ingress of water along oxide micropores to the metal-oxide interface and by the rate-limiting outward diffusion of Fe ions along oxide grain boundaries. The new model accounts for the observed temperature-dependence and pH-dependence of the corrosion, the morphology of inner and outer layer crystallites, the segregation of alloying elements, and the location of hydrogen evolution. The model can also be generalized to other steels and alloys. © 1989.

The influence of room geometry on the overturning of smoke owing to a floor fire

The present paper explores the influence of room geometry on the overturning of smoke owing to a centrally located floor fire, and examines the implications on smoke filling times. The focus is on presenting practical design guidelines based on the theoretical predictions of the model of Kaye and Hunt. An engineering platform is developed for the prediction of smoke filling times, and a rational basis is provided by way of which smoke behaviour can be specified for simple room designs. The time taken for smoke to fill a room to a given height is critically affected by the room aspect ratio and the characteristic size of the buoyancy source. At large times, taller (small aspect ratio) rooms are shown to fill with smoke at a faster rate than wide (large aspect ratio) rooms owing to large-scale overturning and engulfing of ambient air during the initial transients. Larger area sources of buoyancy also decrease significantly the smoke filling times, with important implications for fire and smoke safety design. Simplified design curves incorporating the main findings have been developed for use as a tool by practising fire-safety engineers.

Electrical properties of LiNbO3 (electrolyte)/Cu (anode) bi-layers

In this work specific film structures of Li-Nb-O/Li/Li-Nb-O are investigated by AC Impedance Spectroscopy measurements at different temperatures. This gives the opportunity to investigate properties of the material itself and, at the same time, to consider the influence of the grain boundaries on the ionic behavior of the polycrystalline Lithium Niobate. On the other hand, LiNbO3/Li/Cu multi-layers are studied as electrolyte/anode bi-layers and potential parts of "Li-free" microbatteries. The Li deficiency in the as deposited Li-Nb-O films is cured by forming a "sandwich" of Li-Nb-O/Li/Li-Nb-O, which after annealing becomes ionic conductor. The electrical behavior of an annealed film depends on two sources. The first is due to properties of the material itself and the second is based on the network of the grain boundaries. The average size of the grains is strongly influenced by the structure of the ohmic-contact/substrate. The electrical behavior of the electrolyte/anode interface of the "Li-free" structure LiNbO3/Li/Cu/Au is very similar to the impedance measurements of the single LiNbO3 single films. The whole multilayer structure, though, presents a third relaxation time which is consistent of a small resistance. This resistance is independent of temperature and it seems that is due to the metallic interface Li/Cu/Au. © 2010 Elsevier B.V. All rights reserved.

Synthesis of high quality n-type CdS nanobelts and their applications in nanodevices

High quality n-type CdS nanobelts (NBs) were synthesized via an in situ indium doping chemical vapor deposition method and fabricated into field effect transistors (FETs). The electron concentrations and mobilities of these CdS NBs are around (1.0x10(16)-3.0x10(17))/cm(3) and 100-350 cm(2)/V s, respectively. An on-off ratio greater than 10(8) and a subthreshold swing as small as 65 mV/decade are obtained at room temperature, which give the best performance of CdS nanowire/nanobelt FETs reported so far. n-type CdS NB/p(+)-Si heterojunction light emitting diodes were fabricated. Their electroluminescence spectra are dominated by an intense sharp band-edge emission and free from deep-level defect emissions. (c) 2006 American Institute of Physics.

纳米耐油型全硫化热塑性弹性体的制备与形态、结构及性能研究

本文以过氧化物为引发剂，采用反应挤出的方法，制备了甲基丙烯酸缩水甘油酷官能化聚丙烯，采用化学滴定法和红外光谱法均证实了接枝共聚物的存在，并研究了反应条件对PP-g-GMA接枝率、接枝效率和熔体流动速率的影响，结果表明：1．当DCP含量一定时，随着单体含量的增加，接枝产物的接枝率出现了一个峰值。这表明一味地增加单体浓度未必有利于接枝率的提高；2．当GMA单体浓度一定时，PP-g-GMA的接枝率和熔融指数均随着引发剂含量的增加而逐渐增大，这表明引发剂浓度的增加在促进接枝反应的同时也引入了更多的副反应；3．助剂苯乙烯的加入大大地提高了PP-g-GMA的接枝率和接枝效率，且产物的熔融指数与纯聚丙烯相比变化很小，这表明助剂苯乙烯的加入有效地抑制了副反应的发生，且促进了接枝反应的发生。研究了官能化聚丙烯PP-g-GMA的形态、结构与性能，结果表明：1．官能化对聚丙烯的结晶行为有显著的影响，不仅结晶温度和熔融温度有显著的增加，而且结晶度也有一定程度的增加；2．纯聚丙烯的结晶结构为典型的a型结晶，而接枝聚丙烯的结晶则以a型结晶为主，并出现了少量的Y型结晶；3．采用Avrami方程可以很好的描述官能化聚丙烯的初级结晶行为，纯聚丙烯和官能化聚丙烯的 tl几和tmax均随着结晶温度的增加而增加，这表明它们的结晶过程由成核控制；4．采用Jeziornn法研究了官能化聚丙烯的非等温结晶动力学，非等温结晶过程可以分为初级结晶和次级结晶两部分，在次级结晶阶段，曲线偏离了初级结晶部分的直线，表明在次级结晶阶段，官能化聚丙烯的成核与生长方式发生了变化；5．采用DMA研究了官能化聚丙烯的动态热机械行为，官能化后聚丙烯的耐热性提高了，而且随着接枝率的升高，耐热性又有进一步的提高。以官能化聚丙烯作为反应型增容剂，采用反应共棍的方法，制备了耐油型全 硫化CNBR/PP热塑性弹性体，并研究了热塑性弹性体的形态、结构与性能。主要 结果如下：1．采用红外光谱法表征了梭基丁睛粉末橡胶和PP-g-GMA间的反应。 2．透射电子显微镜和原子力显微镜结果表明，当一部分聚丙烯被官能化聚丙烯替代后，体系中橡胶粒子的尺寸明显变小了，分布也更加均一了。在CNBR/PP-g-GMIA 体系中，原位增容反应形成的共聚物位于cNBR和PP-g-GMA两相的界面处。3．加入少量接枝聚丙烯后共混物的力学性能，如拉伸强度、100％定伸强度和断裂伸长 率均有明显的提高，而且，对于CNBR/PPPP-g-GMA共混物，只需少量的界面增 容剂便可以使两相界面达到饱和并达到较好的增容效果。4．动力学和热力学因素 均影响共混物中聚丙烯的结晶行为，在CNBR/PP体系中，动力学因素占主导地位，而CNBR/PP-g-GMA体系中热力学因素占主导作用。另外，采用Avromi方程描述了CNBR/PP和CNBR/PP-g-GMA体系的等温结晶动力学。5．接枝聚丙烯的加入阻碍了接枝聚丙烯与梭基丁睛橡胶两相间的界面层滑移，因此提高了体系的粘度。以官能化聚丙烯作为反应型增容剂，采用反应共混的方法，制备了耐油型全硫化NBR/PP热塑性弹性体，并研究了热塑性弹性体的形态、结构与性能。主要结果如下：1．采用红外光谱法表征了官能化聚丙烯与端氨基液体丁睛橡胶间的反应，但仅从红外光谱的结果很难断定产物的分子结构；2．采用透射电子显微镜观察了NBR/PP共混物的微观形态，结果表明，NBR／PP共混物体系中除了含有直径为几十纳米的小橡胶粒子外，还有直径为几微米甚至几十微米的大橡胶粒子存在，且随着橡胶含量的增加，体系中大橡胶粒子的数量增多了，小橡胶粒子的分布也变得密集了；3．采用差示扫描量热法表征了NB侧PP共混物的受限结晶行为，结果表明，（1）在220℃的高温下，部分丁睛橡胶分子产生了一定的运动，从而限制了聚丙烯分子的运动，使聚丙烯分子产生了受限结晶行为；（2）随着橡胶含量的增加，橡胶粒子间的距离逐渐变小，这使得位于橡胶粒子间隙的聚丙烯分子的运动受到限制，因此聚丙烯表现出受限结晶的行为；（3）受限的聚丙烯分子更倾向于Y型结晶。

染料激光器混合染料体系的研究

分子间的能量转移是当今光化学、光生物学和光物理学中的一个重要课题，长期以来一直受到人们的广泛关注。六十年代染料激光器出现以后，人们很快就将这一原理应用研究染料激光器的工作物质。选择适当的混合染料溶液作为染料激光器的工作物质，可以提高某些染料的激光输出能量或扩展激光波长覆盖范围，这已成为分子间能量转移的一个新的应用领域。本文首先阐述分子间能量转移的基本理论并对混合染料体系的选择及其研究进行了文献综述。另外，对研究过程中，他人工作改采用的实验手段也进行了概述，特别对荧光寿命的测量讨论得较为仔细。实验中我们着重研究了R6G/Red B、R6G/NB两个二元体系和C440/C540/Saf.~(-1)、C440/Fl.Na/Saf.~(-1)以及R6G/Red B/Ox725三个三元混合染料体系。实验方法主要通过测量混合染料溶液的荧光光谱、荧光寿命和激光输出性能。激发源波长始终固定在337.1nm。荧光光谱和荧光寿命多是在英国Applied Photophysics公司生产的SP-70型纳秒荧光分光光度计上测量的。这套仪器的设置从激发、探测以至最后的数据处理（微机处理）都达到较高的灵敏度和精确度。更为主要的是采用了时间相关单光子计数技术这一新的测量方法，真有较高的时间分辨本领，为染料分子的短寿命测量提供了重复性极好的可靠数据。并且由于这套仪器的信噪比大，能够测出高浓度溶液情况下的荧光光谱，而一般地荧光光谱仪却很难探测。激光调谐范围的测量是在QJD-9型染料激光器上进行的，光路结构安排合理，各项技术指标都达到了较高水平。激光强度的测量是采用了通用的光路结构测量混合染料溶液的超辐射模式的激光输出。下面是我们的实验结果。1.R6G/Red B、R6G/NB二元混合染料体系。通过测量R6G/Red B混合染料溶液的荧光光谱，了解到给体R6G有较强的能量转移给受体Red B。又通过荧光寿命的测量，表明溶液浓度达到～10~(-3) mol.L~(-1)时，分子间的能量转移主要是共振转移，且符合Stern-Volmer关系。由此我们进行了一定量讨论，计算了不同浓度溶液中给体与受体分子间的平均距离R。激光性能的测量表明这一体系具有较大的激光强度输出，且通过改变给体、受体浓度可扩展调谐范围。对于R6G/NB，我们做了类似的研究。但与R6G/Red B不同的是，R6G/NB始终是双峰。激光性能测量表明此体系可以扩展调谐范围，且可改善NB的激光输出，降低泵浦阈值。2.C440/C540/Saf.-T、C440/Fl.Na/Saf.-T及R6G/Red B/Ox725三元体系。C440/C540/Saf.-T混合染料溶液的荧光光谱研究表明，三种染料分子之间有较强的能量转移发生，且与溶液浓度配比适当时，可以同时获得三个不同波段处的荧光发射，从而可望扩展波长调谐范围。见图1。对于C440/Fl.Na/Saf.-T混合溶液，我们主要是采用光谱手段，对能量转移过程做了研究。结果表明C440/Fl.Na之间以辐射转移为主要机制，Fl.Na/Saf.-T之间在波度稍大时，发生共振转移的可能性较强。另外对能量转移过程进行了一些定量的讨论。计算求得C440/Fl.Na的临距离R_o = 47.5A，小于Fl.Na/Saf.-T的临界距离R_o = 59.0A，因而后者发生共振转移的可能性较大。R6G/Red B/Ox725体系与前两体系相比是向长波长方向扩展了。激光性能的测量表明，此体系可以作为染料激光器的工作物质。实验结果还表明三种染料混合以后的激光性能比Red B/Ox725二组份混合的效果好得多。R6G/Red B/Ox725的超辐射是图2所示。

基于支持向量机的Internet流量分类研究

准确的网络流量分类是众多网络研究工作的基础,也一直是网络测量领域的研究热点.近年来,利用机器学习方法处理流量分类问题成为了该领域一个新兴的研究方向.在目前研究中应用较多的是朴素贝叶斯(nave Bayes,NB)及其改进算法.这些方法具有实现简单、分类高效的特点.但该方法过分依赖于样本空间的分布,具有内在的不稳定性.因此,提出一种基于支持向量机(support vector machine,SVM)的流量分类方法.该方法利用非线性变换和结构风险最小化(structural risk minimization,SRM)原则将流量分类问题转化为二次寻优问题,具有良好的分类准确率和稳定性.在理论分析的基础上,通过在实际网络流集合上与朴素贝叶斯算法的对比实验,可以看出使用支持向量机方法处理流量分类问题,具有以下3个优势:1)网络流属性不必满足条件独立假设,无须进行属性过滤;2)能够在先验知识相对不足的情况下,仍保持较高的分类准确率;3)不依赖于样本空间的分布,具有较好的分类稳定性.

Investigation of high cycle and Very-High-Cycle Fatigue behaviors for a structural steel with smooth and notched specimens

The high cycle and Very-High-Cycle Fatigue (VHCF) properties of a structural steel with smooth and notched specimens were studied by employing a rotary bending machine with frequency of 52.5 Hz. For smooth specimens, VHCF failure did occur at fatigue cycles of 7.1 x 10(8) with the related S-N curve of stepwise tendency. Scanning Electron Microscopy (SEM) was used for the observations of the fracture surfaces It shows that for smooth specimens the crack origination is surface mode in the failure regime of less than 10(7) cycles While at VHCF regime, the material failed from the nonmetallic inclusion lies in the interior of material, leading to the formation of fisheye pattern. The dimensions of crack initiation region were measured and discussed with respect to the number of cycles to failure. The mechanism analysis by means of low temperature fracture technique shows that the nonmetallic inclusion in the interior of specimen tends to debond from surrounding matrix and form a crack. The crack propagates and results to the final failure. The stress intensity factor and fatigue strength were calculated to investigate the crack initiation properties. VHCF study on the notched specimens shows that the obtained S-N curve decreases continuously. SEM analysis reveals that multiple crack origins are dominant on specimen surface and that fatigue crack tends to initiate from the surface of the specimen. Based on the fatigue tests and observations, a model of crack initiation was used to describe the transition of fatigue initiation site from subsurface to surface for smooth and notched specimens. The model reveals the influences of load, grain size, inclusion size and surface notch on the crack initiation transition. (C) 2010 Elsevier Ltd. All rights reserved

Extracting nanobelt mechanical properties from nanoindentation

A three-spring-in-series model is proposed for the nanobelt (NB) indentation test. Compared with the previous two-spring-in-series model, which considers the bending stiffness of atomic force microscope cantilever and the indenter/NB contact stiffness, this model adds a third spring of the NB/substrate contact stiffness. NB is highly flexural due to its large aspect ratio of length to thickness. The bending and lift-off of NB form a localized contact with substrate, which makes the Oliver-Pharr method [W. C. Oliver and G. M. Pharr, J. Mater. Res. 7, 1564 (1992)] and Sneddon method [I. N. Sneddon, Int. J. Eng. Sci. 3, 47 (1965)] inappropriate for NB indentation test. Because the NB/substrate deformation may have significant impact on the force-indentation depth data obtained in experiment, the two-spring-in-series model can lead to erroneous predictions on the NB mechanical properties. NB in indentation test can be susceptible to the adhesion influence because of its large surface area to volume ratio. NB/substrate contact and adhesion can have direct and significant impact on the interpretation of experimental data. Through the three-spring-in-series model, the influence of NB/substrate contact and adhesion is analyzed and methods of reducing such influence are also suggested. (C) 2010 American Institute of Physics. [doi:10.1063/1.3432748]

Fabrication of nano-sized grains by pulsed laser surface melting

In this work, the formation and characterization of nano-sized grains on the modified surfaces of GCr15 and H13 steels have been investigated. The material was processed by pulsed laser surface melting (LSM) under different depths of de-ionized water. The microstructures and phases of the melted zones were examined by x-ray diffraction, environmental field emission scanning electron microscopy and high resolution transmission electron microscopy. The results indicate that LSM under water can successfully fabricate nano-scaled grains on the surfaces of steel, due to the rapid solidification and crystallization by heterogeneous nucleation. The elemental segregation of chromium and activated heterogeneous nucleation mechanism of austenite in liquid metal play a key role in the formation of nano-sized grains at high cooling rates. This one-step technique provides us a new way to prepare uniform nano-scaled grains, and is of great importance for further understanding the growth of nano-materials under extreme conditions.