关键词： 蒸汽机   内燃机   工业革命  

摘要： 工业革命是促进人类社会进步的主要经济动力。工业革命是一个渐进提升的过程,人类至今经历了多少次工业革命,社会上有多种说法。美国人里夫金的第三次工业革命论,燃起人们对工业革命的新议论。但是,归根结底工业革命还是来源于工业生产动力的创新。

关键词： 螺旋槽   机械密封   数值模拟   开启力   摩擦扭矩   螺旋角  

摘要： 以外侧开槽的螺旋槽机械密封动静环端面间的流体膜为研究对象,建立其三维的有限元周期模型,运用流体力学(CFD)软件Fluent对流场的动力特性进行数值模拟,得到液膜的压力以及开启力的分布规律,并与解析计算得出的结果进行比较,结果表明:模拟值和解析值比较吻合,从而得到合理的液膜数值模拟方法;然后以此模型为基础,数值模拟了工况参数(转速、压差、黏度)和螺旋槽参数(螺旋角、槽深)对液膜流场的泄漏量、摩擦扭矩以及动压特性和开启力的影响规律,研究结果为螺旋槽机械密封的设计提供了有益的参考。

关键词： 有创无创序贯机械通气   慢性阻塞性肺疾病   呼吸衰竭   血流动力学  

摘要： 目的探讨有创无创序贯机械通气对慢性阻塞性肺疾病所致呼吸衰竭患者血流动力学的影响。方法选择2013年5月—2014年5月期间就诊的90例慢性阻塞性肺疾病所致呼吸衰竭患者为研究对象,采用随机数字表法分为观察组和对照组各45例,观察组患者接受有创无创序贯机械通气,对照组接受有创机械通气,比较两组患者的机械通气情况、血流动力学指标。结果观察组患者有创机械通气时间、总机械通气时间、住院总时间、呼吸机相关性肺炎、病死率均明显低于对照组（t/χ^2=5.968-18.484,P〈0.05）;两组SBP、PaO2、PaCO2比较,差异无统计学意义（t=0.781-1.694,P〉0.05）,观察组HR、RR明显低于对照组（t=3.857-9.583,P〈0.05）。结论有创无创序贯机械通气有助于缩短机械通气时间,减少并发症发生,稳定血流动力学指标,是慢性阻塞性肺疾病所致呼吸衰竭患者理想的机械通气模式。

关键词： Advanced oxidation processes   CFD simulation   Degradation kinetics   Henyey-Greenstein function   Scattering phase function   Titanium dioxide  

摘要： A computational fluid dynamic (CFD) model was developed to describe the process performance of a semi-batch annular TiO2-UV photoreactor in an Eulerian framework. The model accounted for the optical behaviour of titanium dioxide (TiO2) suspensions, the flow distribution and the oxalic acid degradation in the reactor. The scattering component of the optical model, explicitly included in the CFD simulations using a TiO2-specific scattering phase function integrated in the radiative transfer equation, was calibrated using an optical goniometer by comparing simulated scattering light profiles against irradiance measurements collected for various TiO2 concentrations and UV wavelengths and subsequently solved by the discrete ordinate (DO) radiation model. Several scattering phase functions were tested against the goniometric measurements confirming that the Henyey-Greenstein (HG) equation was the most appropriate angular distribution function at 254 and 355 nm, irrespective of the TiO2 concentration. Using the calibrated HG function, a new approach for quantifying the absolute values of absorption and scattering coefficients in TiO2 suspensions was proposed. It consists of iteratively solving, using the DO model, the radiative transfer equation for various combinations of absorption and scattering coefficients until the error between observed and predicted angular irradiance measurements is minimized. The accuracy of the optical parameters was verified with independent CFD simulations carried out for an annular photoreactor and already available in the literature. Predicted and simulated irradiance and oxalic acid degradation data were found to be in excellent agreement, confirming the considerable potential of the integrated modelling approach presented in this paper for the design, optimization and scale-up of photocatalytic technologies for water and wastewater treatment applications. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Ozone   N-Heterocycles   Reaction mechanism   Transformation products   Reaction stoichiometry   Reaction kinetics  

摘要： Piperidine, piperazine and morpholine as archetypes for secondary heterocyclic amines, a structural unit that is often present in pharmaceuticals (e.g., ritalin, cetirizine, timolol, ciprofloxacin) were investigated in their reaction with ozone. In principle the investigated compounds can be degraded with ozone in a reasonable time, based on their high reaction rate constants with respect to ozone (1.9 x 10(4) -2.4 x 10(5) M-1 s(-1)). However, transformation is insufficient (13-16%), most likely due to a chain reaction, which decomposes ozone. This conclusion is based on (OH)-O-center dot scavenging experiments, leading to increased compound transformation (18-27%). The investigated target compounds are similar in their kinetic and stoichiometric characteristics. However, the mechanistic considerations based on product formation indicate various reaction pathways. Piperidine reacts with ozone via a nonradical addition reaction to N-hydroxypiperidine (yield: 92% with and 94% without scavenging, with respect to compound transformation). However, piperazine degradation with ozone does not lead to N-hydroxypiperazine. In the morpholine/ozone reaction, N-hydroxymorpholine was identified. Additional oxidation pathways in all cases involved the formation of (OH)-O-center dot with high yields. One important pathway of piperazine and morpholine by zonation could be the formation of C-centered radicals after ozone or OH radical attack. Subsequently, O-2 addition forms unstable peroxyl radicals, which in one pathway loose superoxide radicals by generating a carbon-centered cation. Subsequent hydrolysis of the carbon-centered cation leads to formaldehyde, whereby ozonation of the N-hydroxy products can proceed in the same way and in addition give rise to hydroxylamine. A second pathway of the short-lived peroxyl radicals could be a dimerization to form short-lived tetraoxides, which cleave by forming hydrogen peroxide. All three products have been found. (C) 2015 Published by E

关键词： 混合动力技术   工程机械   应用   混合动力系统   发电机组   发动机   技术控制   驱动系统  

摘要： 作为一种新型技术控制下的工程机械,混合动力工程机械在近期得到了广泛利用。该项课题的研究,将会更好地提升混合动力技术的应用水平,从而更好地保证工程机械的实际运用效果。本文从介绍混合动力系统着手本课题的研究。一、油电混合动力系统1.串联式油电混合动力系统发动机、发电机、电动机和外载四大基本构成采用＂串联＂方式组成驱动系统。发动机输出动力全部通过发电机发电,实际上发动机和发电机组合可看作是一个电能供应装置,发动机不直接驱动外载。

关键词： Dental adhesive   Silane   Co-initiator   Fourier transform infrared   Dynamic mechanical analysis   Polymerization kinetic  

摘要： Objectives. The purpose of this study was to evaluate the polymerization behavior of a model dentin adhesive with tris(trimethylsilyl)silane (TTMSS) as a co-initiator, and to investigate the polymerization kinetics and mechanical properties of copolymers in dry and wet conditions. Methods. A co-monomer mixture based on HEMA/BisGMA (45/55, w/w) was used as a model dentin adhesive. The photoinitiator system included camphorquinone (CQ) as the photo sensitizer and the co-initiator was ethyl-4-(dimethylamino) benzoate (EDMAB) or TTMSS. Iodonium salt, diphenyliodonium hexafluorophosphate (DPIHP) serving as a catalyst, was selectively added into the adhesive formulations. The control and the experimental formulations were characterized with regard to the degree of conversion (DC) and dynamic mechanical properties under dry and wet conditions. Results. In two-component photoinitiator system (CQ/TTMSS), with an increase of TTMSS concentration, the polymerization rate and DC of C=C double bond increased, and showed a dependence on the irradiation time and curing light intensity. The copolymers that contained the three-component photoinitiator system (CQ/TTMSS/DPIHP) showed similar dynamic mechanical properties, under both dry and wet conditions, to the EDMAB-containing system. Significance. The DC of formulations using TTMSS as co-initiator showed a strong dependence on irradiation time. With the addition of TTMSS, the maximum polymerization rate can be adjusted and the network structure became more homogenous. The results indicated that the TTMSS could be used as a substitute for amine-type co-initiator in visible-light induced free radical polymerization of methacrylate-based dentin adhesives. (C) 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

关键词： Magnesium matrix composites   mechanical properties   molecular dynamics simulation   nickel-coated carbon nanotube  

摘要： As the interfacial structure and bonding strength play an important role in determining the mechanical performance of carbon nanotube reinforced metal matrix composite, investigating the interfacial mechanical properties of surface modified carbon nanotube reinforced metal matrix composite becomes one of the key factors for the improvement. The mechanical behaviors of nickel-coated single-walled carbon nanotube reinforced magnesium matrix composites were investigated using molecular dynamics simulation method. The results show that the Young's modulus of the nickel-coated single-walled carbon nanotube/Mg composite is obviously larger than that of the uncoated single-walled carbon nanotube/Mg composite. The results also show that the interfacial bonding of single-walled carbon nanotube/Mg composite can be drastically increased by addition of nickel coating to improve the wettability of the nanotube surface and Mg matrix. Furthermore, the influences of nickel coating number on the interfacial bonding characteristics of single-walled carbon nanotube/Mg composites also were studied. For three types of nickel coating number, i.e. without nickel coating, with one layer of nickel and two layers of nickel, the final pullout interfacial bonding strength of the nickel-coated single-walled carbon nanotube from Mg matrix about are 3.9 and 11.9 times larger, respectively, than that of the uncoated single-walled carbon nanotube. The simulation results have proved that such interfaces can effectively transfer load between the nanotube and magnesium matrix in the carbon nanotube/Mg composite, and this will provide the theoretical and experimental basis for the interface mechanics design of the carbon nanotube reinforced composites.

关键词： Optomechanics   Driven system   Stability   Lyapunov exponent   Survival probability  

摘要： Theoretical analysis of a suspended nano-mechanical membrane subject to an optical driving field in an optomechanical cavity is presented, which is confirmed through numerical simulations. In the presence of an optical field between its mirrors, the high-finesse optomechanical resonator acts as an oscillator driven by a radiation pressure force. The periodic nature of the radiation pressure force makes the nano-mechanical membrane in the optomechanical system as a kicked harmonic oscillator. Mathematically the physical system displays a stochastic web map that helps to understand several properties of the kicked membrane in classical phase space. We find that our web map is area preserving and displays quasiperiodic symmetrical structures in phase space which we express as q-fold symmetry. It is shown that under appropriate control of certain parameters, namely the frequency ratio and the kicking strength, the dynamics of kicked membrane exhibits chaotic dynamics. We provide the stability analysis by means of Lyapunov exponent and survival probability.

关键词： Laminates   Damage tolerance   Fracture   Damage mechanics   Finite element analysis (PEA)  

摘要： Split Hopkinson pressure bar (SHPB) is one of the most important and recognized apparatus used for characterizing the dynamic behavior of materials. In the first part of this study, the results from a series of SHPB tests on the woven composites are presented in this paper. The compressive material properties are determined by testing the [0 degrees/90 degrees](26) laminate systems from low to high strain rates. Samples of cubic geometry are tested in in-plane and out-of-plane direction. Preliminary compressive stress-strain vs. strain rates data obtained show that the dynamic material strength increases with increasing strain rates. The tests show a strong material sensitivity to dynamic loading. For in-plane tests, there is a transitional strain rate, reflecting the dependencies on strain rate observed in experiments. The results indicate that the stress-strain curves, maximum compressive stresses and strains evolve as strain rate changes. During the experiments, a high speed camera was used to determine the kinetics of damage. The specimens are mainly damaged in a crushing and shear failure mode under out-of-plane loading, as for in-plane test, the failure was dominated by fiber buckling and delamination. In the second part of this study, numerical models without damage are developed to investigate the validity of assumptions of compression Split-Hopkinson Pressure Bar technique. Abaqus software was used for the numerical simulation. The results obtained by numerical investigation of SHPB are compared with the in-plane and out-of-plane compression test of a woven composite. A good correlation was noted between the experimental and numerical results, which allows validate the numerical approach. (C) 2015 Elsevier Ltd. All rights reserved.