Experimental study of hollow rectangular bridge column performance under vertical and cyclically bilateral loads

To investigate the seismic performance of hollow reinforced concrete （RC） bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges （JTG/T B02-01-2008）. The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.

Mechanical and low-cycle fatigue behavior of stainless reinforcing steel for earthquake engineering applications

Use of stainless reinforcing steel （SRS） in reinforced concrete （RC） structures is a promising solution to corrosion issues. However, for SRS to be used in seismic applications, several mechanical properties need to be investigated. These include specified and actual yield strengths, tensile strengths, uniform elongations and low-cycle fatigue behavior. Three types of SRSs （Talley S24100, Talley 316LN and Talley 2205） were tested and the results are reported in this paper. They were compared with the properties of A706 carbon reinforcing steel （RS）, which is typical for seismic applications, and MMFX II, which is a high strength, corrosion resistant RS. Low-cycle fatigue tests of the RS coupons were conducted under strain control with constant amplitude to obtain strain life models of the steels. Test results show that the SRSs have slightly lower moduli of elasticity, higher uniform elongations before necking, and better low-cycle fatigue performance than A706 and MMFX II. All five types of RSs tested satisfy the requirements of the ACI 318 code on the lower limit of the tensile to yield strength ratio. Except Talley 2205, the other four types of RSs investigated meet the ACI 318 requirement that the actual yield strength does not exceed the specified yield strength by more than 18 ksi （124 MPa）. Among the three types of SRSs tested, Talley S24100 possesses the highest uniform elongation before necking, and the best low-cycle fatigue performance.

气波振荡管波系运动与能量传递效率影响机制研究

建立了双开口气波制冷机振荡管三维大涡模拟模型,获得了气波振荡管内波系运动特征。针对高压入射喷嘴与气波振荡管在高速旋转交汇过程引发能量损失的问题,探讨了气波制冷机操作参数和结构参数对能量传递效率的影响机制。数值计算结果表明,在两者切入-覆盖-切出的交汇过程中,伴随着强烈的涡旋和湍流动能耗散。定义瞬时湍流动能损失比R定量评定能量损失程度。研究发现,涡旋中心处R值较大,且随绝压压比增大先增大后减小,当绝压压比为3.61时达到最大值9.0%。R值随转速提高而减小,当转速由1100 r/min提高至2000 r/min时,涡旋中心处R值由10.7%减小至6.0%。远轴壁面和近轴壁面涡旋中心处R值都随着管道宽度增加而减小,近轴壁面涡旋中心处的R值大于远轴壁面涡旋中心处,且两侧差值最大达3.2%。减小入射绝压压比、提高转速和增加气波振荡管宽度有助于减小R值,从而提高气波制冷机能量传递效率,对大流量气波制冷机设计具有指导意义。

Electron donor–acceptor (D-A) tuning to achieve soluble covalent organic polymers for optoelectronic devices

Covalent organic polymers(COPs)have emerged as a unique class of luminescent polymers with pre-designed quasi-ordered architectures.However,their layered stacks and limited solubility preclude further processing for large-scale applications in devices,especially optoelectronic equipment.Herein,a universal strategy to adjust the electron donor–acceptor(D-A)moieties of the building blocks in COPs is proposed,achieved by in situ charge exfoliation of COP blocks into few-layer true solutions in(Lewis)acid and base media.The electron D-A moieties of the building blocks endow the COPs with the ability to accept or donate electrons,by altering the electron cloud distribution as well as the relative energy levels of the frontier molecular orbitals.The resultant soluble COPs can easily be processed into a uniform film by solution processing via the spin-coat method.The obtained COP-N achieves efficient and stable perovskite electroluminescence as a novel hole injection material on indium tin oxide,and the operating lifetime for a perovskite quantum dot light-emitting diodes device exceeds that of a poly(ethylene dioxythiophene):polystyrene sulphonate counterpart.This straightforward electronic regulation strategy provides a new avenue for the rational synthesis of processable reticular molecular polymers for practical electronic devices.

Effect of iron ion configurations on Ni^(2+) removal in electrocoagulation

Electrocoagulation(EC)has been widely used to treat the heavymetal wastewater in industry.A novel process of sinusoidal alternating current electrocoagulation(SACC)is adopted to remove Ni2+in wastewater in this study.The morphology of precipitates and the distribution of the main functional iron configurations were investigated.Ferron timed complex spectroscopy can identify the monomeric iron configurations[Fe(a)],oligomeric iron configurations[Fe(b)]and polymeric iron configurations[Fe(c)].The optimal operating conditions of SACC process were determined through single-factor experiments.The maximum Ni2+removal efficiency[Re(Ni^(2+))]was achieved under the conditions of pH0=7,current density(j)=7 A/m^(2),electrolysis time(t)=25 min,c0(Ni^(2+))=100 mg/L.At pH=7,the proportion of Fe(b)and Fe(c)in the system was 50.4 at.% and 23.1 at.%,respectively.In the SACC process,Fe(b)and Fe(c)are themain iron configurations in solution,while Fe(c)are the vastmajority of the iron configurations in the direct current electrocoagulation(DCC)process.Re(Ni2+)is 99.56% for SACC and 98.75% for DCC under the same optimum conditions,respectively.The precipitates produced by SACC have a high proportion of Fe(b)configurations with sphericalα-FeOOH andγ-FeOOH structures which contain abundant hydroxyl groups.Moreover,it is demonstrated that Fe(b)has better adsorption capacity than Fe(c)through adsorption experiments of methyl orange(MO)dye.Fe(a)configurations in the homogeneous solution had no effect on the removal of nickel.

无人机景象匹配视觉导航技术综述

高精度定位与导航是实现无人机自主飞行、高效侦察与精确打击的关键技术之一.景象匹配视觉导航技术因其设备结构简单、被动式、定位精度高等特点,能与惯性系统组合构成自主性很强的高精度导航系统.通过分析当前基于景象匹配的无人机视觉导航技术研究现状,发现国外研究主要集中于单独利用视觉图像信息进行飞机姿态、导航信息提取以及联合IMU等传感器的组合导航系统;国内该领域的研究鲜见报道,但对该技术所涉及的惯性组合导航、视觉/激光测距三维地图重建、视觉导航着陆应用等技术进行了大量研究.本文总结了无人机景象匹配视觉导航技术的特点、分类与研究方法,得出在不同时间、不同视角、不同光照、不同分辨率、不同平台以及不同传感器等条件下,在高精度、强实时、鲁棒、连续视觉导航任务中,无人机景象匹配视觉导航需突破的关键技术.

Reversion of natural ageing and restoration of quick bake-hardening response in Al-Zn-Mg-Cu alloy

The high-strength Al-Zn-Mg-Cu alloy provides much better dent resistance and weight-reduction potential compared to the conventional Al alloys used for the automobile body panels.However,natural ageing(NA)significantly reduces the formability of Al-Zn-Mg-Cu alloy.The reversion of natural ageing has been systematically investigated by hardness test,tensile test,differential scanning calorimetry(DSC)and transmission electron microscopy(TEM).Substantial reversion of natural ageing and thus hardness decrease occurs immediately upon thermal treatment at 120–210℃in an Al-Zn-Mg-Cu alloy.Although the hardness of the most reverted state decreases with increasing temperature,the lowest hardness is still higher than the as-quenched state by 30 HV.As revealed by the complementary DSC and TEM observations,this is ascribed to the synchronization of the dissolution and the re-precipitation of the solutes in the NA clusters during reversion ageing.Reversion at 180–210℃for less than 30 s leads to a hardness decline of 40 HV.The hardening kinetics during NA after reversion is slower than that during first-time NA due to the reduced vacancy concentration.Artificial ageing at 180℃for 30 min after secondary NA of less than 24 h induces intensive precipitation of plate-like pre-ηphases and a giant strength increase of 188–204 MPa.Potential use of high strength Al-Zn-Mg-Cu alloy in automobile body panels could be realized by appropriate reversion treatment improving the formability and the quick bake hardening response.

Performance of CAMS-CSM in Simulating the Shortwave Cloud Radiative Effect over Global Stratus Cloud Regions: Baseline Evaluation and Sensitivity Test

The ability of climate models to correctly reproduce clouds and the radiative effects of clouds is vitally important in climate simulations and projections.In this study,simulations of the shortwave cloud radiative effect(SWCRE)using the Chinese Academy of Meteorological Sciences Climate System Model(CAMS-CSM)are evaluated.The relationships between SWCRE and dynamic–thermodynamic regimes are examined to understand whether the model can simulate realistic processes that are responsible for the generation and maintenance of stratus clouds.Over eastern China,CAMS-CSM well simulates the SWCRE climatological state and stratus cloud distribution.The model captures the strong dependence of SWCRE on the dynamic conditions.Over the marine boundary layer regions,the simulated SWCRE magnitude is weaker than that in the observations due to the lack of low-level stratus clouds in the model.The model fails to simulate the close relationship between SWCRE and local stability over these regions.A sensitivity numerical experiment using a specifically designed parameterization scheme for the stratocumulus cloud cover confirms this assertion.Parameterization schemes that directly depict the relationship between the stratus cloud amount and stability are beneficial for improving the model performance.

Understanding the Performance of an Unstructured-Mesh Global Shallow Water Model on Kinetic Energy Spectra and Nonlinear Vorticity Dynamics

A strategy for evaluating a global shallow water model based on aspects of kinetic energy spectra and nonlinear vorticity dynamics is proposed in this study.The kinetic energy spectra and nonlinear vorticity dynamics of a recently developed global shallow water model on an unstructured mesh are evaluated in comparison with the benchmark solutions from a global high-resolution spectral model.The results show that the kinetic energy spectra,the rotational and divergent components,the stationary and transient components,and the nonlinear spectral fluxes of the developed shallow water model agree well with those generated by the reference model.In addition,the influence of different flux operators for transporting the potential vorticity(PV)is assessed specifically.It is indicated that the second-order flux operator leads to a spurious increase in the kinetic energy at the tail of the spectrum,whereas the upwind third-order flux operator does not support this behavior owing to implicit numerical diffusion.Moreover,the nonlinear vorticity dynamics is studied by using colliding modons.It is found that the grid-point model maintains the symmetrical pattern of vortices,and generates similar kinetic energy spectra and nonlinear spectral fluxes to the reference model.The evaluation provides a reference for assessing the shallow water model in terms of nonlinear dynamics,and the developed global shallow water model presents a good example.