一类平面解析系统强退化奇点的可积性

利用正规型理论研究一类平面解析系统强退化奇点的可积性问题。首先证明,任意一个可微系统,在可微同胚的变量变换以及时间尺度变换下,可积性保持不变。其次,对于二次齐次的微分系统,可以通过仿射变换及时间尺度变换化为4种标准形;针对其中的一种标准形,结合正规型理论,利用主系统是哈密尔顿的,且所对应的哈密尔顿函数的分解式是单因式的形式微分系统可积的充要条件,给出了相应的非线性系统可积的条件。该结果为研究平面系统的相图和局部定性结构提供了理论依据。

二维单向强退化抛物型方程的参数识别反问题

针对矩形区域内两种形式的强退化扩散系数,研究了二维单向强退化抛物型方程中扩散项的参数识别反问题。首先,利用Hölder不等式等证明了扩散项参数识别的唯一性和条件稳定性;然后,给出了数值计算强退化抛物型方程正问题的一种交替方向有限差分隐格式;最后,通过将退化扩散项的参数识别反问题归结为泛函优化问题,提出了基于遗传算法的退化项参数识别方法。计算模拟结果表明,退化项参数能被附加的测量数据有效识别出来,且提出的基于遗传算法的退化项参数识别方法具有很强的鲁棒性。

强退化抛物方程的解

给出强退化抛物方程u/t=ΔA(u)+N∑i=b^i(u)/t^i初边值问题一种边值(BV)弱解的新定义,并通过抛物正则化方法得到解的存在性,利用Kruzkov’s双变量的方法得到解的稳定性.

一类强退化抛物方程弱解的唯一性

研究了如下形式的强退化抛物方程(C(u))/(t)=(2A(u,x,t))/(x2)+(B(u,x,t))/(x),基于Holmgren方法,证明了弱解的唯一性.

一类强退化抛物方程弱解的惟一性

研究了如下形式的强退化抛物方程(C)(u)/(t)=(2A(u,x,t))/(x2)+(B(u,x,t))/(x),基于Holm gren方法,证明了弱解的惟一性.

一类强退化的抛物型方程的双曲特性

MBertsch和R．DalPasso在［1］中研究了方程（其中ψ为严格增函数且为有限数）具有严格增初值的Cauchy问题．讨论了该问题的解与一阶守恒律方程的解的相似性．在[1]中，条件是一个基本假设．本文主要讨论以上方程在退化（即的情况下），相应于特殊初值的Cauchy问题的解仍具有以上双曲现象．

Influence of Device Narrowing on HALO-pMOSFETs' Degradation Under V_g= V_d/2 Stress Mode

The degradation characteristics of both wide and narrow devices under V _g= V _d/2 stress mode is investigated.The width-enhanced device degradation can be seen with devices narrowing.The main degradation mechanism is interface state generation for pMOSFETs with different channel width.The cause of the width-enhanced device degradation is attributed to the combination of width-enhanced threshold voltage and series resistance.

Reliability and sensitivity of bogie frame of high-speed train with strength degradation

High-speed bogie frame is a key mechanical component in a train system. The reliability analysis of the bogie is necessary to the safety of high-speed train. Reliability analysis of a bogie frame was considered. The equivalent load method was employed to account for random repeated loads in structural reliability analysis. Degradation of material strength was regarded as a Gamma process. The probabilistic perturbation method was, then, employed for response moment computation. Example of a high-speed train bogie structure under time-variant load was employed for reliability and sensitivity analyses. Monte-Carlo simulation verifies the accuracy and efficiency of the proposed method in time-variant reliability analysis. The analysis results show that the reliability calculation considering the strength degradation and repeated load is closer to the practicality than the method of considering reliability calculation only. Its decreasing velocity is faster than the traditional reliability. The reliability sensitivity value changes over time. The analysis results provide a variation trend of reliability and sensitivity to design and usage of bogie frame.

Annealing hardening and deformation behavior of layered gradient Zr–Ti composite

To investigate potential strengthening approaches,multi-layered zirconium–titanium(Zr-Ti)composites were fabricated by hot-rolling bonding and annealing.The microstructures of these composites were characterized using scanning electron microscopy with energy dispersive spectroscopy(SEM-EDS)and electron backscatter diffractometry(EBSD).Their mechanical properties were evaluated by uniaxial tension and compression measurements.It was found that the fabricated Zr–Ti composites are composed of alternating Zr/diffusion/Ti layers,and chemical compositions of Zr and Ti showed a gradient distribution in the diffusion layer.Compared with as-rolled samples,annealing can strengthen the layered gradient Zr–Ti composite,and this is mainly caused by solid-solution strengthening and microstructure refinement-induced strengthening.Compared with the raw materials,a synergistic improvement of strength and ductility is achieved in the Zr–Ti composite as a result of the layered gradient microstructure.Tension–compression asymmetry is observed in the Zr–Ti composites,which may be attributed to twinning and microvoids induced by unbalanced diffusion.

Numerical simulation of triaxial compression test for brittle rock sample using a modified constitutive law considering degradation and dilation behavior

The understanding of the rock deformation and failure process and the development of appropriate constitutive models are the basis for solving problems in rock engineering. In order to investigate progressive failure behavior in brittle rocks, a modified constitutive model was developed which follows the principles of the continuum damage mechanics method. It incorporates non-linear Hoek-Brown failure criterion, confining pressure-dependent strength degradation and volume dilation laws, and is able to represent the nonlinear degradation and dilation behaviors of brittle rocks in the post-failure region. A series of triaxial compression tests were carried out on Eibenstock(Germany) granite samples. Based on a lab data fitting procedure, a consistent parameter set for the modified constitutive model was deduced and implemented into the numerical code FLAC3 D. The good agreement between numerical and laboratory results indicates that the modified constitutive law is well suited to represent the nonlinear mechanical behavior of brittle rock especially in the post-failure region.

Enhanced degradation of carbon tetrachloride by surfactant-modified zero-valent iron

Sorption of carbon tetrachloride （CT） by zero-valent iron （ZVI） is the rate-limiting step in the degradation of CT, so the sorption capacity of ZVl is of great importance. This experiment was aimed at enhancing the sorption of CT by ZVI and the degradation rate of CT by modification of surfactants. This study showed that ZVI modified by cationic surfactants has favorable synergistic effect on the degradation of CT. The CT degradation rate of ZVI modified by cetyl pyridinium bromide （CPB） was higher than that of the unmodified ZVI by 130%, and the CT degradation rate of ZVI modified by cetyl trimethyl ammonium bromide （CTAB） was higher than that of the unmodified ZVI by 81%. This study also showed that the best degradation effect is obtained at the near critical micelle concentrations （CMC） and that high loaded cationic surfactant does not have good synergistic effect on the degradation due to its hydrophilicity and the block in surface reduction sites. Furthermore degradation of CT by ZVI modified by nonionic surfactant has not positive effect on the degradation as the ionic surfactant and the ZVI modified by anionic surfactant has hardly any obvious effects on the degradation.

On the Properties of the Solution of a Strongly Degenerate Parabolic Equation

For a strongly degenerate parabolic equation, we first use the results of Ph. Blanc[1] to get that the Neumann problem may not have a global classical solution. The reason is that the gradients of some local classical solutions blow up in finite time. And under some conditions, we get the global integral solution by the use of semigroup. Then, we give a sufficient condition under which the Neumann problem has a global classical solution. Finally. we study the asymptotic behaviour of the classical solution and prove that the solution converges to the mean of the initial value.

非凸最优化问题可行解序列的有限终止性

Burke与Ferris给出了凸最优化问题可行解序列的有限终止性定理,本文将凸最优化问题中强非退化集与弱强极小集的概念进行了推广,给出了广义强非退化集和广义弱强极小集的定义,并研究了非凸最优化问题的解集在广义强非退化或广义弱强极小的情况下,其可行解序列有限终止性的充要条件,它们是现有最优化问题可行解序列有限终止性充要条件或充分条件的扩展。

Influence of sulfur content in raw materials on oxidized pellets

The influence of sulfur content in raw materials on oxidized pellets was studied. The results show that most sulfur exists in the form of elementary sulfur in pyrite cinder, and over 95% sulfur is removed in producing pyrite cinder oxidized pellets. The compressive strength of fired pellets drops from 3 186 N to 2 405 N when the ratio of pyrite cinder increases from 40% to 70% under the conditions of preheating at 900℃ for 9 min and firing at 1 230 ℃ for 15 min. The porosity and microstructures of fired pellets prove that the higher ratio of pyrite cinder is given, and the more holes and cracks are achieved, leading to the better reducibility index （RI） and reduction swelling index （RSI）, and the lower compressive strength of fired pellets and the worse reduction degradation index （RDI）.

多维拟线性退化抛物方程Cauchy问题解的惟一性

证明了如下形式拟线性退化抛物方程的 Cauchy 问题 BV 解的存在惟一性：(?)u/(?)t=ΔA(u)+sum from i=1 to N ((?)b_i(u))/((?)x_i)，A′(u)≥0，u(x，0)=u_0．

Analysis on degradation behaviors of sisal fibers at various pH conditions

The degradation behaviors(mass loss,tensile strength,crystallinity index,and microstructure)of sisal fibers immersed in sodium hydroxide solution with pH of 13.6,12.9,and 11.9 were investigated via X-ray diffraction and scanning electron microscopy.A three-stage degradation process of natural fibers in an alkaline environment was proposed.The results showed that the sisal fibers exhibited a sharp mass loss over the first 7 d of degradation under all pH conditions,attributable to the rapid hydrolysis of lignin and hemicellulose at the fiber surface.The sisal fibers degraded at pH 12.9 and 13.6 over 1 month exhibited significantly lower tensile strengths(181 and 195 MPa,respectively)than the original fibers(234 MPa)because of the loosely bound structure of the component microfibrils caused by the hydrolysis of the linking lignin and hemicellulose.After 6-month degradation,stripped microfibrils occurred in the fibers,resulting in substantial degradation in tensile strength.The sisal fibers degraded at pH 11.9 largely maintained their integrity and tensile strength,even after 6 months,indicating that reducing the environment pH can effectively mitigate the degradation.

上临界超过程的一类强极限的性质

假设X={X_t, t≥0; P_μ}是局部紧可分距离空间E上的上临界超过程,Ф_0是X的均值半群的生成元的与第一特征值λ_0对应的正特征函数,则M_t:=e^(-λ_0t)<Ф_0, X_t>是非负鞅.令M_∞是M_t的极限,则M_∞是非退化的当且仅当L log L条件成立.当L log L条件不一定成立时,最近, Ren等(2017)证明了存在定义在[0,∞)上的非负函数γ_t及非退化随机变量W使得对任意E上非零Borel有限测度μ,有lim_(t→∞)

Evolution laws of strength parameters of soft rock at the post-peak considering stiffness degradation

To evaluate the strength attenuation law of soft rock in the western mining area of China, we established an evolution model for the strength parameters of soft mudstone at the post-peak stage by employing a tri-linear strain softening model. In the model, a stiffness degradation coefficient co and a softening modulus coefficient a were introduced to take into account the stiff- ness degradation, and the subsequent yield surfaces at post-peak stage were all assumed to meet the Molar-Coulomb yield criterion. Furthermore, attenuation laws of stiffness and strength parameters of soft mudstone were analyzed according to an engineering case. Finally, the model＇s accuracy was verified by comparison of results from numerical calculation and tri-axial compression tests. Results showed that the attenuation of the friction angle was dominated mainly by the instantaneous stress states and damage features, while the attenuation law of cohesion was also related to the plastic behavior. The degradation rates of strength param- eters decreased with increasing confining pressure and the friction angle tended towards its initial value. Residual strengths were also enhanced with increasing confming pressure. The results indicate that the evolution model can accurately describe the strain softening behavior of soft rock.

Effects of Grazing Intensity on Soil Water Regime and Flux in Inner Mongolia Grassland,China

In the past few decades, the increase in grazing intensity has led to soil degradation and desertification in Inner Mongolia grassland, China, due to population growth and shift in the socio-economic system. Two sites with different grazing intensities, continuous grazing site （CG） with 1.2 sheep ha-1 year-1 and heavy grazing site （HG） with 2.0 sheep ha-1 year-1, were investigated at the Inner Mongolia Grassland Ecosystem Research Station （43° 37′ 50″ N, 116° 42′ 18″ E） situated in the northern China to i） characterize the temporal distribution of soil water content along soil profile; and ii） quantify the water fluxes as affected by grazing intensity. Soil water content was monitored by time domain refiectometry （TDR） probes. Soil water retention curves were determined by pressure membrane extractor, furthermore processed by RETC （RETention Curve） software. Soil matric potential, plant available water and water flux were calculated using these data. Both sites showed an identical seasonal soil water dynamics within four defined hydraulic periods： i） wetting transition coincided with a dramatic water increase due to snow and frozen soil thawing from March to April; 2） wet summer, rainfall in accordance with plant growth from May to September; 3） drying transition, a decrease of soil water from October to November due to rainfall limit; and 4） dry winter, freezing from December to next February. Heavy grazing largely reduced soil water content by 43%-48% and plant available water by 46%-61% as compared to the CG site. During growing season net water flux was nearly similar between HG （242 mm） and CG （223 mm） sites between 5 and 20 cm depths. However, between 20 and 40 cm depths, the upward flux was more pronounced at HG site than at CG site, indicating that water was depleted by root uptake at HG site but stored at CG site. In semi-arid grassland ecosystem, grazing intensity can affect soil water regime and flux, particularly in the growing season.

Microstructure and magnetic properties of FeRh thin films with Pt doping

In this paper, the structure and magnetic properties of FeRh alloy thin films with a small amount of Pt doping fabricated onto a glass substrate by sputtering are investigated systematically. XRD results show that the diffraction pattern of as-deposited film exhibits only nonmagnetic y phase. After annealing, the disordered γphase transforms to an ordered α＇ phase. The temperature dependence of saturation magnetization of different annealing times and Pt contents are characterized. The phase transition temperature increases as the Pt component is increased, but the saturation magnetization reduces as the Pt component is in- creased. These results may be caused by the growth of the disordered γ phase.