Optical and electrical characterization of carbon nanoparticles produced in laminar premixed flames

Optical and electrical properties of carbonaceous particles produced in laboratory scale, premixed ethylene/air flames are obtained. Light absorption and Raman spectroscopy show that the change in particle nanostructure follows a graphitization trajectory as the flame richness increases. The optical band gap decreases and the size of the aromatic network in the particle increases, while the interlayer spacing between parallel layers decreases. The electrical conductivity of the materials increases by increasing flame richness in agreement to the graphitization trajectory. A non-ohmic behavior has been found and explained in terms of electron tunneling in a percolative network. Our results show that the electrical properties of flame formed carbon nanoparticles are strongly dependent on their nanostructure, and hence they have to be used carefully for the determination of particle concentration with conductometric sensors. Moreover, the dependence of the electrical properties of combustion formed particles might be useful for the development of cheap sensors for the selective detection of different classes of combustion aerosols.     

不同临床情况患者床旁心脏超声检查的必要性及其对诊治的影响

目的　探讨不同临床情况患者申请床旁心脏超声检查的必要性及其对患者诊断和治疗的影响。方法　连续入组2013年7月1日至30日北京协和医院申请并完成床旁心脏超声检查的所有患者，分析其临床情况，评价床旁超声检查申请的必要性，并比较不同临床情况患者完成心脏超声检查后对诊治的影响。结果　共入组患者58例（男性33例，56.9%），平均年龄（56.4±19.9）岁。急诊科申请37例（63.8%），各重症监护室16例（27.6%），其他科室5例（8.6%）。床旁超声的申请目的中，符合美国心脏超声学会和急诊医师学会共识建议的36例（62.1%）。完成床旁心脏超声检查后达到申请目的者53例（91.4%），根据结果明确了诊断或者对原有诊断作出修正的患者13例（22.4%），对原有诊断更有信心患者40例（69.0%），对诊断没有帮助者5例（8.6%）；床旁心脏超声检查后，需根据心脏情况调整原有治疗方案者16例（27.6%）。完成检查后，经心内科医生判断确实需要进行床旁超声检查者23例（39.7%），不需要进行床旁超声检查者35例（60.3%）。符合共识建议的申请，获得对于诊断有价值信息的可能性显著高于其他申请（P=0.01），且倾向于更能影响患者的治疗方案（P=0.06）；申请符合共识建议检查的必要性显著高于其他申请（P＜0.01）。结论目前床旁心脏超声申请需更为严格把握指征；严格按照相关共识的建议申请床旁心脏超声，更有可能获得对诊断和治疗有价值的信息，从而更为合理有效地利用有限的医疗资源。     

充填采煤液压支架充填特性理论研究及工程实践

固体充填采煤液压支架既具有传统支架掩护采煤所需要的基本功能,又具有掩护充填所需要的特殊功能,是实现采充一体化的关键设备。针对其掩护充填的特殊功能,提出充填特性的概念,并分别从支护强度、后顶梁支护强度、运动特性、夯实力、夯实离顶距以及地质条件适应性6方面具体阐述了充填特性的基本内涵。架型结构、地质条件、充填工艺是影响充填特性的主要因素,其中架型结构直接决定充填支架的充填特性;煤层厚度、煤层顶底板、煤层倾角、煤层埋深等地质条件影响充填特性的发挥;充填工艺则通过改变离顶距及夯实力大小、改善对不同地质条件的适应性3方面影响充填性能的保障。具体工程实践中则通过工作面布置优化、结构设计优化、充填工艺优化、实时在线监测等措施保障充填性能的发挥。济三矿ZZC10000/20/40型六柱正四连杆充填采煤液压支架的工程应用验证了本文的研究成果。     

Four different configurations of a 5 kW class shell-and-tube methane steam reformer with a low-temperature heat source

The methane steam reforming reaction is an extremely high endothermic reaction that needs a high temperature heat source. Various fuel cell hybrid systems have been developed to improve the thermal efficiency of the entire system. This paper presents a low temperature steam reformer for those hybrid systems to maximize the utilization of energy from a low temperature waste heat source. In this study, the steam reformer has a shell and tube configuration that is divided into the following zones: the inlet heat exchanging zone, the reforming zone and the exit heat exchanging zone. Four different configurations for methane steam reformers are developed to examine the effect of heat transfer on the methane conversion performance of the low temperature steam reformer. The experimental results show that the overall heat transfer area is a critical parameter in achieving a high methane conversion rate. When the heat transfer area increases about 30%, the results showed elevated dry mole fractions of hydrogen about 3% with about 30 °C rise of reformer outlet temperature.     

Multi-scale characteristics of magnesium potassium phosphate cement modified by metakaolin

Workability and early-ages mechanical properties are important indicators of magnesium potassium phosphate cement (MKPC) as a repair material. The effect of metakaolin (MK) on the setting time, fluidity and early-ages strength of MKPC paste was studied, and its influence mechanism was analyzed through pore structure, microstructure and nanomechanical properties. The results show that 10% and 20% of MK prolong the setting time of MKPC paste, but excessive MK shortens the setting time of MKPC paste. Meanwhile, incorporating MK reduces the fluidity of MKPC paste, and the early-ages strength of MKPC specimens increases when the substitution ratio of MK is 10%. When 10% of MK is incorporated to the MKPC paste, the 30-d shrinkage of the sample is only 69% of the control group. Meanwhile, a proper amount of MK can improve the pore structure of the MKPC specimen and make its microstructure denser by generating amorphous aluminosilicate phosphate gel. It is observed from the nano-scale characteristics that incorporating 10% MK can reduce the content of pore phase and unreacted MgO phase, and increase the volume fraction of hydration products.     

Design of Synchronous Drive Mechanism of Opposed-Piston Hydraulic-Output Engine

In order to improve the thermal power conversion capacity of the internal combustion engine,combined with existing opposed-piston two-stroke engine(OP2S) and hydraulic free piston engine (HFPE),the integral structure for a new type of opposed-piston hydraulic-output (OPHO) engine has been designed,an operating principle has been introduced,the composition of its synchronous drive mechanism has been carefully analyzed,and a mathematical model has been built.In addition,the kinematics models of both the mechanism and the conventional crank-link mechanism have been established by utilizing MATLAB,and the movement rules of the pivotal moving components have been obtained.According to the simulation results,the piston movement of this new type of opposed-piston hydraulic-output engine reveals a prominent asymmetry compared to the conventional crank-link engine.Under a fixed engine revolving speed,the compression time of the opposedpiston hydraulic-output engine is shortened while the expanding time is lengthened,thus the gas turbulence intensity is strengthened around the top dead center (TDC) position.Meanwhile,the piston obtains a longer isometric process compared to conventional engines,which could be benefitial to enhance the combustion efficiency.     

构件动态热作用计算分析

叙述了构件动态传热的原理;介绍了ISO 13786国际标准对构件动态热作用的计算方法,对动态传热系数等参数的定义和计算公式给予了详细的描述;并通过6种典型墙体热工参数的计算,与我国目前构件动态热作用计算方法的分析对比,可以看出当选定构件动态传热系数小于0.5 W/(m2·K)作为隔热设计标准时,可以满足GB 50176给出的房间自然通风条件下构件的隔热要求;提出应参考ISO 13786的方法,改进我国构件动态热特性计算体系及评价方式。