Treatment of Acetonitrile by Catalytic Supercritical Water Oxidation in Compact-Sized Reactor

The objective of this research was to study the treatment of acetonitrile by catalytic supercritical water oxi-dation in a compact-sized tubular reactor, with an internal volume of 4.71 mL. Manganese dioxide was used as the catalyst and H2O2 was used as the oxidant. The oxidation of acetonitrile in supercritical water was studied at 400-500 oC, 25-35 MPa, the flow rate of 2-4 mL/min, the initial concentration of acetonitrile 0.077-0.121 M and the %excess O2 of 50-200%. As a result, the products were mainly N2, CO2 and CO and acetonitrile can be decomposed > 93 % within a very short contact time (1.45-6.19 s). The oxidation process was carried out with respect to the conversion of acetonitrile by 25 factorial design. Regression models were obtained for correlating the conversion of acetonitrile with temperature and flow rate. The complete oxida-tion can be achieved at a condition as moderate as 400 oC, 25 MPa with the flow rate of 2 mL/min.

小型化宽阻带5G半集总混合滤波器设计

面向5G无线通信应用设计了一款微带半集总混合宽阻带带通滤波器。该滤波器阻带可扩展至5G毫米波频段,具有优良的带外抑制、结构紧凑及尺寸小巧的特点。搭建了集总元件的高频电路模型并完成了集总元件的路-场联合仿真,最终实现了由十字加载谐振器混合集总LC并联谐振电路而成的宽阻带滤波器。滤波器的中心频率位于4.08 GHz,通频带覆盖3.96~4.2 GHz,位于目前用于5G室内覆盖的N77频段。滤波器具有极广的阻带抑制特性,且优于20 dB抑制水平的上阻带范围可达22 GHz。滤波器有效电路尺寸仅为5.125mm×7.625 mm,插入损耗水平较低(0.54 dB),具有良好的选择性,适用于高性能5G通信系统应用。

城市紧凑度对城市公共服务设施空间可达性的影响

高品质公共服务设施体系的建设是打造宜居城市的基础性工程,可达性已经成为我国基本公共服务供给侧结构性改革的两大目标取向之一。目前我国城市发展中存在城市紧凑程度恶化与公共服务设施空间可达性状况不佳并存的局面,从城市空间形态这一重要城市整体特性视角研究城市公共服务设施可达性对于优化城市公共服务设施空间布局具有重要意义。以中国地级及以上城市的三类主要公共服务设施为考察对象,量化测度城市公共服务设施空间可达性,在此基础上实证分析城市紧凑度对城市公共服务设施空间可达性的影响,以及对不同类型设施的异质性影响,并检验公共服务设施规模分布和地方财政自主权对上述影响过程的调节效应。实证结果表明,城市紧凑度对城市公共服务设施可达性的影响呈现“U”型,目前多数城市处于U型曲线的上升阶段,高财政自主权强化了紧凑城市建设对于公共服务设施的挤出效应,而设施规模越分散,城市紧凑度对公共服务设施空间可达性的几何正向影响效果越弱。

Novel Compact UWB Band Notch Antenna Design for Body-Centric Communications

This research analyzes and implements an innovative and tiny ultrawideband(UWB)antenna with band-notched features for body-centric communication.The shape of the designed antenna looks like a‘swan’with a slotted patch.Computer Simulation Technology(CST)is used to assess and investigate the performance of this antenna.With a band notch,this antenna can prevent interference from Wireless Local Area Network(WLAN)(5.15–5.825 GHz)and Worldwide Interoperability for Microwave Access(WiMAX)(5.25–5.85 GHz)systems.At first,the performance parameters like return loss response,gain,radiation patterns,and radiation efficiency of this UWB antenna are evaluated.After that,the human body effects on the antenna performance of the antenna are also examined to place the antenna at various distances away from 3-layers of phantom body model at different frequencies.All the on-body performance parameter results are compared and analyzed with free space performance parameter results.Lastly,by changing patch slot length and ground plane length,parametric studies were done for performance comparison.According to this research,it is noticed that the antenna is tiny and new.It shows good performance in body case as well.Hence,the antenna is very suitable for healthcare applications.

不同压实系数下冻融软土力学特性及孔隙特征研究

季节性冻土地区的路基材料在反复冻融下易发生性能劣化,为了解冻融循环作用下软黏土的力学性质和微观结构特性变化,考虑压实系数、围压、冻融循环次数等因素,对东北地区软黏土进行三轴试验以及核磁共振试验.研究结果表明,不同压实系数的土样的峰值强度与围压呈正相关关系,且强度曲线近似呈线性分布,而峰值强度差值随着围压的增大逐渐减小,当围压增加至300 kPa时,峰值强度增加了约70.8%,而峰值强度差值减小了约44.7%.此外,压实系数对土样弹性模量有着显著的影响,随围压增加土体压实系数与弹性模量呈指数函数变化.同时,围压的增大抑制了由冻胀所产生大孔隙的发育,增强了土体的密实度,进而降低了冻融作用下的土体微观结构的损伤.冻融循环荷载作用下,随着压实系数上升,平均孔径有明显减小趋势,二者呈负相关性.

扬子地块北缘毕机沟岩体下部带堆晶岩结构定量化分析:对层状岩体冷却早期粒间熔体排出机制的约束

层状岩体冷却中—晚期晶粥中粒间熔体的排出被认为与铁钛氧化物的大量结晶关系密切,但在岩体冷却早期铁钛氧化物尚未大量结晶时,粒间熔体能否被有效排出、以及如何排出还需要深入探究。扬子地块北缘毕机沟岩体是我国目前发现的规模最大、分异程度较高且赋存有钒钛磁铁矿矿床的层状岩体。岩体下部带、中部带和上部带分别由斜长橄榄岩、辉长岩和闪长岩组成。本研究以下部斜长橄榄岩相带为对象,通过对斜长石和单斜辉石进行晶体粒度分布(CSDs)和空间展布形式(SDPs)分析,探讨层状岩体冷却早期粒间熔体的排出方式及其控制因素。模拟计算结果表明,样品中封闭粒间熔体比例(FTL)为9%~13%,暗示岩体冷却早期粒间熔体被有效排出。单斜辉石和斜长石的CSD曲线斜率主要为3.36~2.45和2.99~1.87,截距分别为0.45~3.35和1.06~2.83,均具有斜率一致而截距变化较大的特征,与机械压实的CSD曲线一致。单斜辉石和斜长石在SDP图解上均显示负相关关系,也与机械压实趋势一致。因此,毕机沟岩体冷却早期粒间熔体的排出机制为机械压实。在此基础上,我们将毕机沟与全球其他典型层状岩体从岩体规模、粒间熔体和堆晶矿物密度差、晶体堆积速率与压实速率以及晶粥层厚度等方面进行系统对比后发现,在层状岩体冷却早期没有岩浆补给和对流的情况下,当岩体规模相近时,压实受控于堆晶矿物与粒间熔体密度差,密度差越大压实越容易发生;而当岩体规模不同时,规模越大压实越容易发生。

试样尺寸对击实黏土抗拉特性的影响研究

为探究尺寸效应对黏土抗拉特性的影响机制,开展土梁三点弯拉试验,结合数字图像相关(DIC)技术,从宏观和细观角度分析了几何相似和非几何相似(试样高度h、厚度b变化)条件下击实黏土梁的拉裂破坏过程。结果表明:几何相似和非几何相似试样的尺寸增大,均会提升试样的峰值荷载。土体抗拉强度σ_(t)受尺寸效应影响显著,几何相似土梁σ_(t)随试样尺寸增大呈线性递减趋势;仅增大土梁h时,σ_(t)先增长后下降,仅改变土梁b时,σ_(t)随b增大呈先降后增的走势,其中b的变化对σ_(t)的影响更小;引入细观评价指标—局部应变度ε_(a),得出几何相似试样的ε_(a)随尺寸增大而增大,非几何相似试样的ε_(a)随试样h或b的增大呈现先增后降的规律。

砂介质渗透性影响因素的试验研究

达西试验是砂介质渗透性能的主要确定方法。但是受到砂介质粒度与压实度、水的溶解性总固体(TDS)与水头差、试验温度等多种因素的影响,获得的达西试验结果存在巨大差异,给实际应用造成很大的不确定性。为探究不同条件下达西试验产生的不同结果,在常温常压环境下,选择不同砂介质,开展不同温度、TDS、供排水水头差等情况下的试验。结果表明:(1)水温增高,渗透系数增大,渗透性越好的介质,受温度的影响越显著;(2)TDS增高,渗透系数减小,渗透性好的介质,渗透性随TDS呈对数函数或指数函数变化,即水在低TDS变化时引起的介质的渗透性变化剧烈,反之亦然,而渗透性差的介质,渗透性随着TDS增高近似呈线性减小;(3)供排水水头差增加到一定值时,渗透系数不再恒定,临界雷诺数细砂为0.4,中砂为3.3;(4)压实度越高,渗透系数越小;(5)孔隙度相同时,粒径越大则渗透系数越大。本试验结果将为今后渗透系数的获取、应用提供借鉴,为地下水评价、地质灾害防治等水文地质参数选取提供依据。

粒径尺寸对红黏土持水曲线及孔径分布影响研究

为探究粒径尺寸对红黏土的持水特性及孔径分布的影响,用轴平移技术和蒸汽平衡技术对不同粒径尺寸制备的红黏土压实样开展广吸力范围内的持水特性试验和压汞试验,基于不同粒径尺寸试样的持水曲线和孔径分布曲线,揭示粒径尺寸影响土体持水特性的细观机理。具体结论如下:(1)粒径尺寸只对压实样在低吸力范围的持水曲线产生影响,表现为粒径尺寸越小,制备试样进气值则越大。(2)不同粒径制备的饱和压实样均为单峰型孔径结构,且粒径尺寸越小,制备试样的集中孔径分布的峰值越高,分布的范围也越小,表明粒径越小的试样的孔径分布越均匀。(3)预测和实测持水曲线的比较结果显示,由于无法考虑土体干化路径下的孔隙比减小,孔径分布曲线可用于预测土体在对应吸力下的含水率,而预测饱和度低于实测的饱和度。

辉长岩骨料全级配碾压混凝土力学特性研究

辉长岩坚硬致密,具有高强度、高弹模特性,但将辉长岩骨料应用于大型水电工程在国内外尚无先例,缺乏可借鉴的工程实践经验,且湿筛碾压混凝土试件的力学性能无法真实反映全级配碾压混凝土的力学特性。对辉长岩骨料最大粒径为80 mm的全级配碾压混凝土的力学特性演化规律开展了系统研究,包括抗压强度、劈拉强度、轴压性能、轴拉性能、抗剪性能等,对比分析了全级配碾压混凝土抗压、劈拉强度及其湿筛试件的尺寸效应,并将试验结果与国内典型工程所用碾压混凝土的力学性能发展规律进行对比分析,此外还建立了辉长岩骨料全级配碾压混凝土抗压强度、劈拉强度、轴压性能、轴拉性能等力学性能-养护龄期演化函数模型。结果表明:辉长岩骨料全级配碾压混凝土的抗压强度、劈拉强度、抗剪等力学性能随龄期的发展规律符合国内同类工程碾压混凝土力学性能发展的一般规律;C_(90)20W8F100辉长岩全级配碾压混凝土试件与其湿筛试件抗压强度平均尺寸效应系数为0.80、劈拉强度平均尺寸效应系数为0.66;相关力学性能演化模型相关性高(R^(2)=0.9643~0.9992)。可见辉长岩骨料用于大型水电工程碾压混凝土坝建设具有可行性。

大中型泵站施工中自密实混凝土运用分析

自密实混凝土能够满足以泵站为代表的水利水电工程建设发展的要求。基于新时期水利工程建设发展的背景,以水泵工程为主要研究对象,在简单介绍自密实混凝土施工技术应用内容的基础上,结合实际的大中型泵站项目案例,探讨其中应用的自密实混凝土施工技术,明确在实际施工中需要重点关注的内容,旨在为相关工程的施工建设提供借鉴的经验和思路。

土石混合物击实特性的颗粒尺寸效应研究

土石混合物击实特性存在颗粒尺寸效应,因此针对黄土、块石混合物开展了固定含石率、不同最大粒径和含水率条件下室内击实试验,获得了不同粒径土石混合物试样最佳含水率和最大干密度,并分析了颗粒尺寸效应对土石混合物击实效果的影响。研究结果表明,随着含水率的增大,试样从最开始脱模时产生塌落逐渐转变为完整状态,干密度逐渐增大。含水率超过最佳含水率后,水分子起到了润滑作用,将周边土体挤出,使整体体积不再减小,并呈软塑流动状,试样从完整脱模状态转变为脱模时产生较大变形。随着石料的加入,混合物最大干密度得到了明显提升,如在含石率为70%的条件下,最大粒径20、30、40 mm试样最大干密度的增长率分别为24.9%、28.1%、29.7%,且最大粒径越大,干密度提升效果越明显;最佳含水率随着最大粒径的增加而降低,在最大粒径20~40 mm的情况下,对应的最佳含水率为5.2%~5.9%,且随着最大粒径的增大,最佳含水率的变化量分别为0.2%、0.5%。因此可以看出,在70%含石率下,最大粒径20~40 mm范围内,随着最大粒径的增大,土石混合物最佳含水率的降低速率呈增大趋势。

Densification simulation of compacted Al powders using multi-particle finite element method

The powder compaction simulations were performed to demonstrate deformation behavior of particles and estimate the effect of different punch speeds and particle diameters on the relative density of powder by a multi-particle finite element model(MPFEM). Individual particle discretized with a finite element mesh allows for a full description of the contact mechanics. In order to verify the reliability of compaction simulation by MPFEM, the compaction tests of porous aluminum with average particle size of 20 μm and 3 μm were performed at different ram speeds of 5, 15, 30 and 60 mm/min by MTS servo-hydraulic tester. The results show that the slow ram speed is of great advantage for powder densification in low compaction force due to sufficient particle rearrangement and compaction force increases with decrease in average particle size of aluminum.

ANALYSIS OF SIZE EFFECT,SHEAR DEFORMATION AND DILATION IN DIRECT SHEAR TEST BASED ON GRADIENT- DEPENDENT PLASTICITY

The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band,and based on gradient-dependent plasticity,an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen,the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain,the dilation and compaction within shear band are analyzed. Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.

Size structure of urban agglomerations in China:rationality evaluation,patterns, and implications

This paper establishes a diagnostic model for assessing the rationality of size structure of urban agglomerations(UAs) in China. The model is designed to determine from a three-dimensional index including size distribution index(SDI), size compactness index(SCI), and size efficiency index(SEI). The spatio-temporal pattern of size structure involving the studied 19 UAs and its implications are explored. The results indicate that size structure of China's UAs advanced from a low rationality development stage to a moderate rationality development stage in 1995-2015.Among them, the SDI and SEI were reasonably high, and the SCI was relatively low. Spatially, the high rationality UAs were distributed across eastern China, while the low rationality UAs were located in western China. UAs with positive size structure possessed typically a dual-or multicenter urban structure, while UAs with negative size structure usually presented as a single-center structure. The evolutionary trajectories of rationality of size structure of UAs can be summarized as four different stages. Our findings suggest that, in addition to consolidating the status of national-level UAs, the development of regional-level UAs should be promoted. Also, the fostering focus and direction should be oriented toward an UA with dual-or multicenter spatial structure.

Electromagnetic coupling reduction in dual-band microstrip antenna array using ultra-compact single-negative electric metamaterials for MIMO application

In this paper, an ultra-compact single negative（SNG） electric waveguided metamaterial（WG-MTM） is first investigated and used to reduce the mutual coupling in E ＆ H planes of a dual-band microstrip antenna array. The proposed SNG electric WG-MTM unit cell is designed by etching two different symmetrical spiral lines on the ground, and has two stopbands operating at 1.86 GHz and 2.40 GHz. The circuit size is very compact, which is only λ_0/33.6 ×λ_0/15.1（where λ_0 is the wavelength at 1.86 GHz in free space）. Taking advantage of the dual-stopband property of the proposed SNG electric WG-MTM, a dual-band microstrip antenna array operating at 1.86 GHz and 2.40 GHz with very low mutual coupling is designed by embedding a cross shaped array of the proposed SNG electric WG-MTM. The measured and simulated results of the designed dual-band antenna array are in good agreement with each other, indicating that the mutual coupling of the fabricated dual-band antenna array realizes 9.8/11.1 d B reductions in the H plane, 8.5/7.9 d B reductions in the E plane at1.86 GHz and 2.40 GHz, respectively. Besides, the distance of the antenna elements in the array is only 0.35 λ_0（where λ_0 is the wavelength at 1.86 GHz in free space）. The proposed strategy is used for the first time to reduce the mutual coupling in E ＆ H planes of the dual-band microstrip antenna array by using ultra-compact SNG electric WG-MTM.

实变量Compact-2D-FDTD方法与电磁特性中的应用

探讨了电大尺寸目标中电磁波传输特性分析方法问题,提出了实变量Compact-2D-FDTD方法与MPI-Open MP并行FDTD方法,并推导了实变量Compact-2D-FDTD方法基本公式。实验表明,实变量Compact-2D-FDTD方法和MPI-Open MP并行FDTD方法与传统FDTD方法计算结果相吻合,且计算时间明显减少,因此,有效地解决了电大尺寸目标仿真时的计算时间长和内存需求大的问题。

Numerical Simulation and Experimental Research on Microstructural Evolution During Compact Hot Extrusion of Heavy Caliber Thick-Wall Pipe

Compact hot extrusion(CHE) process of heavy caliber thick-wall pipe is a new material-saving production process. In order to reveal the optimum hot extrusion parameters in CHE process, the e ects of the extrusion parameters on the microstructural evolution are investigated systematically. The metadynamic recrystallization(MDRX) kinetic models and grain size models of as-cast P91 steel are established for the first time according to the hot compression tests performed on the Gleeble-3500 thermal-simulation machine. Then a thermal-mechanical and micro-macro coupled hot extrusion finite element(FE) model is established and further developed in DEFORM software. The results indicated that the grain size of the extruded pipe increases with the increasing of initial temperature and extrusion speed, decreases when extrusion ratio increases. Moreover, the grain size is more sensitive to the initial temperature and the extrusion ratio. The optimum hot extrusion parameters are including that, the initial extrusion temperature of 1250 °C, the extrusion ratio of 9 and the extrusion speed of 50 mm/s. Furthermore, in order to verify the simulation precisions, hot extrusion experiment verification on the heavy caliber thick-wall pipe is carried out on the 500 MN vertical hot extrusion equipment. The load–displacement curve of the extrusion process and the grain sizes of the middle part extruded pipe are in good accuracy with the simulation results, which confirms that the hot extrusion FE models of as-cast P91 steel could estimate the hot extrusion behaviors. The proposed hot extrusion FE model can be used to guide the industrial production research of CHE process.

粗颗粒土缩尺方法及缩尺效应研究进展

粗颗粒土作为土石坝的主要填筑材料,最大颗粒尺寸达到米级,室内试验试样只能进行缩尺。如何缩尺保证室内试验成果反映大坝实际填料的力学特性,一直是土石坝研究的难题。近年来大量学者就粗粒土的缩尺方法及缩尺效应开展了一系列卓有成效的研究工作,但在某些方面仍存在分歧。对现有粗颗粒土缩尺方法、试样试验边界效应、缩尺效应规律研究进行了系统总结和分析。最后,为解决粗颗粒土缩尺方法难题,介绍了长江科学院提出的一种粗颗粒土缩尺方法“旁压模量当量密度法”,阐明了“旁压模量相等”与“力学性质一致”的关系,诠释了“旁压模量当量密度法”的理论基础,为深入研究粗颗粒土缩尺方法提供了技术支撑。