电动钢轨打磨车恒力磨削控制方法的研究

电气驱动的钢轨打磨装置在磨削过程中钢轨不平顺、振动等强干扰因素的影响下会产生磨削力的波动，导致打磨精度的下降。为了有效抑制打磨压力的波动，本文基于矢量控制原理设计了用于稳定打磨电机转速的电机调速系统；基于干扰估计器（负载转矩估计器）和系统在线逼近模型（小波神经网络“无延迟负载——电流”模型）设计了控制磨削力稳定的Smith预估控制器。仿真结果表明：相比PID控制，本文设计的控制器能够实现阶跃输入的无超调、无振荡的快速跟踪响应；另外，控制器对外界强干扰的抑制作用明显，整个控制过程中反映磨削力波动情况的打磨电机主轴电流的波动幅度很小。     

Numerical treatment of a quasilinear initial value problem with boundary layer

The paper deals with the singularly perturbed quasilinear initial value problem exhibiting initial layer. First the nature of solution of differential problem before presenting method for its numerical solution is discussed. The numerical solution of the problem is performed with the use of a finite-fitted difference scheme on an appropriate piecewise uniform mesh (Shishkin-type mesh). An error analysis shows that the method is first-order convergent except for a logarithmic factor, in the discrete maximum norm, independently of the perturbation parameter. Finally, numerical results supporting the theory are presented.     

Preparation,optimization, characterization and in vivo pharmacokinetic study of asiatic acid tromethamine salt-loaded solid lipid nanoparticles

Purpose: To enhance the oral bioavailability of asiatic acid tromethamine salt (AAS) by encapsulation in solid lipid nanoparticles (SLN).

Methods: The AAS-loaded SLN (AASLN) was prepared by the modified solvent injection method with glycerin monostearate (GMS) as lipid and poloxamer 188 as surfactant. A Box–Behnken design was used to optimize the formulations. Physicochemical characterization was carried out by using dynamic light scattering, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Stabilities at 4?°C and pH 1.2 were investigated by particle size or/and entrapment efficiency (EE%). The in vivo pharmacokinetics was evaluated by HPLC-MS/MS.

Results: The optimal formulation of AASLN had an average size of 237?nm with zeta potential of ?35.9?mV, and EE% of 64.4%. SEM showed that the AASLN had spherical shape with smooth surface. Furthermore, DSC and X-ray analyses indicated that AAS was amorphous state and the crystal degree of GMS was significantly decreased in the formulation. AASLN showed excellent stability at 4?°C for 1 month and no coacervation at pH 1.2. The bioavailability of AAS in SLN was found to be 2.5-fold higher than that of AAS alone after a single oral administration in rats.

Conclusions: This study reveals that SLN is developed as a promising oral delivery system of AAS with significantly enhanced bioavailability and good storage stability.     

Interpolation-tuned salient region detection

Image salient region detection is very useful in many multimedia applications,such as image retrieval,adaptive content delivery,and adaptive compression.Most existing methods are based on centersurround diferences,usually detecting the diferences around region boundaries,so these methods emphasize the high-contrast edges instead of detecting the regions.Diferent from traditional methods,our method smoothly propagates salient region information to the whole image by performing color interpolation and produces such saliency maps that uniformly highlight the whole salient regions and have high contrast between salient regions and backgrounds.We compare our method with five state-of-the-art salient region detection methods on a large public data set.The proposed method not only generates visually reasonable results but also achieves higher precision and better recall rates.     

Study of plasma-based stable and ultra-wideband electromagnetic wave absorption for stealth application

A plasma-based stable,ultra-wideband electromagnetic (EM) wave absorber structure is studied in this paper for stealth applications.The stability is maintained by a multi-layer structure with several plasma layers and dielectric layers distributed alternately.The plasma in each plasma layer is designed to be uniform,whereas it has a discrete nonuniform distribution from the overall view of the structure.The nonuniform distribution of the plasma is the key to obtaining ultra-wideband wave absorption.A discrete Epstein distribution model is put forward to constrain the nonuniform electron density of the plasma layers,by which the wave absorption range is extended to the ultra-wideband.Then,the scattering matrix method (SMM) is employed to analyze the electromagnetic reflection and absorption of the absorber structure.In the simulation,the validation of the proposed structure and model in ultra-wideband EM wave absorption is first illustrated by comparing the nonuniform plasma model with the uniform case.Then,the influence of various parameters on the EM wave reflection of the plasma are simulated and analyzed in detail,verifying the EM wave absorption performance of the absorber.The proposed structure and model are expected to be superior in some realistic applications,such as supersonic aircraft.     

Amide–acid functional SiO2 nanocomposites based on new semi‐crystalline poly(ether‐sulfone‐amide): thermal,combustion and mechanical studies

New amide–acid functional SiO₂ nanoparticle (FSNP)‐reinforced semi‐crystalline aliphatic–aromatic poly(ether‐sulfone‐amide) (PESA) was synthesized using a solution method in dimethylformamide. The surfaces of SiO₂ nanoparticles were functionalized with phthalic anhydride, and subsequently PESA was synthesized using direct polymerization with good yield and desired molar mass. PESA / SiO₂ nanocomposites (PSNCs) were prepared with three different contents of FSNP and the morphology and mechanical, thermal and combustion properties of the PSNCs were studied. The results of X‐ray diffraction, field‐emission scanning electron microscopy and transmission electron microscopy showed a uniform dispersion for FSNP in the PESA matrix. According to the results of mechanical tests, the tensile strength and the Young's modulus of PESA were enhanced by FSNP loading. Thermogravimetric analysis and derivative thermogravimetry results showed a substantial improvement in thermal properties of PESA. The temperature at 5% mass loss was increased from 371.7 to 395.8 °C for the PSNC containing 8 mass% of FSNP, as well as the char yield being enhanced greatly, which was about 30% higher than that of neat PESA. Significant improvements in combustion properties were observed for PSNCs from microscale combustion calorimetry. The peak heat release rate showed an obvious improvement and decreased by about 57% compared to that of neat PESA on 8 mass% loading of FSNP. © 2016 Society of Chemical Industry     

Life prediction of stainless steels by cyclic and stable hysteresis curves

Abstract

This study develops an analytical expression to describe the cyclic stress‐strain curve obtained from a series of fully‐reversed fatigue tests. A set of stress‐strain relationships is proposed to simulate the tensile branch of the stable hysteresis loop. The complete shape of the stable hysteresis loop is then constructed and the associated theoretical plastic work calculated by integrating the area within the enclosed curve. The theoretical plastic work is employed to predict the fatigue lives of the investigated materials on the basis of their respective stable plastic work per cyclelife curves. In this paper, the current mathematical derivations are based upon the endochronic theory of plasticity. The accuracy of the proposed set of stress‐strain relationships is verified by conducting fully‐reversed constant strain amplitude fatigue tests on AISI 316 and AISI 304 stainless steels. The experimental and simulation results are found to be in good agreement, hence confirming the accuracy of the proposed analytical stress‐strain relationships. Again, comparing the obverted and predicted fatigue lives, a good agreement is found between the two sets of results.     

Coded source neutron imaging with a MURA mask

In coded source neutron imaging the single aperture commonly used in neutron radiography is replaced with a coded mask. Using a coded source can improve the neutron flux at the sample plane when a very high L/D ratio is needed. The coded source imaging is a possible way to reduce the exposure time to get a neutron image with very high L/D ratio. A 17×17 modified uniformly redundant array coded source was tested in this work. There are 144 holes of 0.8 mm diameter on the coded source. The neutron flux from the coded source is as high as from a single 9.6 mm aperture, while its effective L/D is the same as in the case of a 0.8 mm aperture. The Richardson-Lucy maximum likelihood algorithm was used for image reconstruction. Compared to an in-line phase contrast neutron image taken with a 1 mm aperture, it takes much less time for the coded source to get an image of similar quality.     

石武客运专线某现浇箱梁高支撑碗扣式模架施工技术

石武客运专线工程某现浇箱梁施工中,结合现场条件,设计了碗扣式钢管支架体系并对其受力进行验算,严格按支架体系的设计和施工要点组织施工,未发生安全及质量事故。经实际观测,满堂支架的设计符合要求。