后张法预应力孔道压浆液初始流动性研究

后张法预应力孔道压浆液的初始流动性是浆液性能的一个极为重要的指标,在一定程度上决定孔道压浆质量的好坏。文中依托南宁外环高速公路中心试验室,根据对那楼河大桥的孔道压浆和试验室条件下的试验结果,分析了原材料及其配合比、温湿度和搅拌机转速对压浆液初始流动度的影响。

聚合条件对聚羧酸减水剂缓释行为的影响

以乙二醇单乙烯基聚乙二醇醚(EPEG)、丙烯酸(AA)、丙烯酸羟乙酯(HEA)为主要合成原料,以3-巯基丙酸为链转移剂,在双氧水/抗坏血酸氧化还原体系下,利用自由基聚合法合成缓释型聚羧酸减水剂,并系统研究了原料配比和溶剂反应条件对聚羧酸减水剂缓释行为的影响。利用傅里叶红外光谱(FT-IR)、核磁共振氢谱(1H NMR)和凝胶渗透色谱(GPC)等对减水剂分子结构进行表征,对掺入不同减水剂的水泥净浆和砂浆进行性能测试。研究表明:在酸醚体积比为3∶1、醇水体积比为1∶2、酸酯体积比为3∶1时,合成的缓释型聚羧酸减水剂具备最佳性能,水泥浆体初始流动度大且具有良好的缓释效果。

早强剂对快速修补材料工作性能的影响

院随着我国基建行业的不断发展,人们对于基础设施的要求越来越高,研究一种快速修补材料对于解决公路路面局部损坏有着非凡的意义。文章通过试验研究,将早强剂分别以0%、5%、10%、15%、20%、25%、30%的掺量等量代替水泥,在不同掺量下检测其对于快速修补材料初始流动度、凝结时间、抗压强度、抗折强度等工作性能的影响。结果发现,不同掺量的早强剂对快速修补材料的初始流动度基本没有影响,但对凝结时间、抗压强度、抗折强度等工作性能影响显著。

Optimal nonlinear excitation of decadal variability of the North Atlantic thermohaline circulation

Nonlinear development of salinity perturbations in the Atlantic thermohaline circulation(THC) is investigated with a three-dimensional ocean circulation model,using the conditional nonlinear optimal perturbation method.The results show two types of optimal initial perturbations of sea surface salinity,one associated with freshwater and the other with salinity.Both types of perturbations excite decadal variability of the THC.Under the same amplitude of initial perturbation,the decadal variation induced by the freshwater perturbation is much stronger than that by the salinity perturbation,suggesting that the THC is more sensitive to freshwater than salinity perturbation.As the amplitude of initial perturbation increases,the decadal variations become stronger for both perturbations.For salinity perturbations,recovery time of the THC to return to steady state gradually saturates with increasing amplitude,whereas this recovery time increases remarkably for freshwater perturbations.A nonlinear(advective) feedback between density and velocity anomalies is proposed to explain these characteristics of decadal variability excitation.The results are consistent with previous ones from simple box models,and highlight the importance of nonlinear feedback in decadal THC variability.

Cauchy-Poisson Problem for a Two-layer Fluid with an Inertial Surface

This paper is concerned with the generation of waves due to initial disturbances at the upper surface of a two-layer fluid, as the upper layer is covered by an inertial surface and the lower layer extends infinitely downwards. The inertial surface is composed of thin but uniform distribution of non-interacting material. In the mathematical analysis, the Fourier and Laplace transform techniques have been utilized to obtain the depressions of the inertial surface and the interface in the form of infinite integrals. For initial disturbances concentrated at a point, the inertial surface depression and the interface depression are evaluated asymptotically for large time and distance by using the method of stationary phase. They are also depicted graphically for two types of initial disturbances and appropriate conclusions are made.

Combustion characteristics of low concentration coal mine methane in divergent porous media burner

Low-concentration methane(LCM) has been one of the biggest difficulties in using coal mine methane.And previous studies found that premixed combustion in porous media is an effective method of low calorific gas utilization. This paper studied the combustion of LCM in a divergent porous medium burner(DPMB) by using computational fluid dynamics(CFD), and investigated the effect of gas initial temperature on combustion characteristic, the distribution of temperature and pollutant at different equivalence ratios in detail. Besides, the comparison of divergent and cylindrical burners was also performed in this paper. The results show that: the peak temperature in DPMB increases as the increasing of equivalence ratio, which is also suitable for the outlet NO discharge; the linear correlation is also discovered between peak temperature and equivalence ratios; NO emission at the initial temperature of 525 K is 5.64 times,larger than NO emission at the initial temperature of 300 K. Thus, it is preferable to balance the effect of thermal efficiency and environment simultaneously when determining the optimal initial temperature range. The working parameter limits of divergent burner are wider than that of cylindrical one which contributes to reducing the influence of LCM concentration and volume fluctuation on combustion.

出口贸易、流动劳动力与工资水平——来自CMDS数据的经验证据

提高流动劳动力工资是我国全面建成小康社会、缩小收入差距的关键。出口贸易具有显著的地区劳动力市场效应,会影响流动劳动力工资水平。结合2011—2017年全国流动人口动态监测(CMDS)数据,系统考察了出口贸易对流动劳动力工资及其内部工资差距的影响。结果发现:第一,出口贸易规模显著正向影响流动劳动力工资水平,且2011—2017年出口贸易对流动劳动力工资的边际效应不断上升。出口贸易对流动劳动力不同分位点影响模式存在差异,且呈现动态变化趋势,从有利于低收入群体逐渐转向有利于高收入群体。第二,出口贸易对流动劳动力内部收入差距的影响从缩小流动劳动力工资收入差距转变为拉大流动劳动力内部工资差距。第三,出口贸易对流动劳动力工资影响随着年龄的增加而逐渐减小,女性流动劳动力、技能劳动力、制造业部门和贸易部门流动劳动力工资受出口贸易影响更大。第四,出口贸易对不同流入时长的流动劳动力工资水平均有正向效应,且随着时长的增加,该效应在不断增加。出口贸易对市内跨县流动劳动力工资效益最大,其次为省内跨市,最后为跨省流动。基于省内流动和跨省流动工资差异分解表明:省内流动和跨省流动劳动力特征差异是其工资差距的主要原因,歧视性因素则是次要原因;出口贸易可以解释省内流动和跨省流动劳动力工资差距缩小。

On the Irrotational Approximation to the 2-Dimensional Isothermal Euler System

The author mainly studies the difference of the weak solutions generated by a wave front tracking algorithm to the steady Euler system and the isothermal Euler system.Under the hypothesis that the initial data are of sufficiently small total variation,it is proved that the difference between the solutions of the steady Euler system and the system of isothermal supersonic flow can be bounded by the cube of the total variation of the initial perturbation.

Nonlinear Saturation Amplitude in Classical Planar Richtmyer–Meshkov Instability

The classical planar Richtmyer–Meshkov instability(RMI) at a fluid interface supported by a constant pressure is investigated by a formal perturbation expansion up to the third order,and then according to definition of nonlinear saturation amplitude(NSA) in Rayleigh–Taylor instability(RTI),the NSA in planar RMI is obtained explicitly.It is found that the NSA in planar RMI is affected by the initial perturbation wavelength and the initial amplitude of the interface,while the effect of the initial amplitude of the interface on the NSA is less than that of the initial perturbation wavelength.Without marginal influence of the initial amplitude,the NSA increases linearly with wavelength.The NSA normalized by the wavelength in planar RMI is about 0.11,larger than that corresponding to RTI.