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排序方式: 共有3491条查询结果,搜索用时 15 毫秒
31.
32.
考虑混合H2/H∞控制问题的降阶控制器的设计问题.基于线性矩阵不等式(LMI),分别‘给出了连续和离散情形下混合H2/H∞问题的降阶控制器的设计. 相似文献
33.
从一个新的角度讨论常微分方程中解的存在唯一性定理在偏微分方程数值解法中的重要应用。给出一类伪双曲型偏微分方程的新的分裂混合有限元数值格式,将该格式转化成常微分方程系统,利用解的存在唯一性定理证明该系统是存在唯一解的。通过简短的讨论、概述明确解的存在唯一定理在偏微分方程数值解中的应用方法.并希望能够在教学科研未来的发展中有新的观念。 相似文献
34.
This article reports reversible changes in surface morphology and surface wettability of mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes with PS Mn slightly lower than that of PMMA in response to combined selective solvent treatments and thermal annealing. The mixed brushes were synthesized from asymmetric difunctional initiator-terminated monolayers by controlled radical polymerizations. Two sets of experiments were performed. The first set involved treating the samples with glacial acetic acid (AA), a selective solvent for PMMA, followed by treatment with cyclohexane, a selective solvent for PS, or thermal annealing. The surfaces were rough and composed of relatively ordered nanodomains after AA treatment. Subsequent cyclohexane treatment or thermal annealing made the surfaces flattened and surface analysis indicated that the outermost layers were occupied by PS. The second set of experiments involved treating the samples with cyclohexane or thermal annealing, followed by AA treatment. The surfaces were smooth after cyclohexane treatment or thermal annealing and became very rough in the subsequent AA treatment. The nanodomains formed in AA treatment were speculated to be micelles with PS forming the core shielded by PMMA chains. 相似文献
35.
《矿业科学技术学报(英文版)》2016,26(6):1065-1071
Near-surface deposits that extend to considerable depths are often amenable to both open pit mining and/or underground mining. This paper investigates the strategy of mining options for an orebody using a Mixed Integer Linear Programming(MILP) optimization framework. The MILP formulation maximizes the Net Present Value(NPV) of the reserve when extracted with(i) open pit mining,(ii) underground mining, and(iii) concurrent open pit and underground mining. Comparatively, implementing open pit mining generates a higher NPV than underground mining. However considering the investment required for these mining options, underground mining generates a better return on investment than open pit mining. Also, in the concurrent open pit and underground mining scenario, the optimizer prefers extracting blocks using open pit mining. Although the underground mine could access ore sooner, the mining cost differential for open pit mining is more than compensated for by the discounting benefits associated with earlier underground mining. 相似文献
36.
Weixin Guan Xiaochen Yang Chenyuan Dong Xiaoming Yan Wenji Zheng Yuan Xi Xuehua Ruan Yan Dai Gaohong He 《应用聚合物科学杂志》2021,138(8):49895
The packing pattern of two-dimensional (2D) sheet-like fillers in membranes is relatively random, leading to the unfavorable permeability from tortuous diffusion pathway. A new strategy that using prestructured materials with uniform channels as fillers was proposed. In this work, Ti3AlC2 is etched to prepare multilayered MXene (m-MXene), the channels aggregate as a whole unit, ensure the impossibility of ineffective packing compared with traditional individual sheets, largely facilitating the selective permeation. Then, the m-MXene/Poly (amide-6-b-ethylene oxide) (Pebax) MMMs are synthesized. SEM images demonstrate the accordion shaped structure of filler, which is the multi-channels laminates. Furthermore, the results of gas permeation test exhibit enhanced performance of m-MXene/Pebax MMMs. MMM with 0.5 wt.% m-MXene behaved best, CO2 permeability of 86.22 Barrer as well as CO2/N2 selectivity of 104.85, transcending the Robeson upper bound (2008). Having distinct enhancement for CO2 separation, the m-MXene/Pebax MMMs in this work offer prospective practical applications. 相似文献
37.
《Journal of the European Ceramic Society》2021,41(16):256-265
Functionally graded materials (FGMs) play an essential role in tissue engineering because of their satisfactory histocompatibility and excellent mechanical performance. While traditional manufacturing methods allow production of simple FGMs, precise control of composition and customized property at transition between the dissimilar materials is still a challenge. Here, an extrusion-based functionally graded additive manufacturing (FGAM) platform was developed to generate smooth graded parts by thrusting out monolithic cylindrical filaments with high viscosity. Furthermore, the rheological properties, hydrodynamic behavior, and mixed homogeneity of the non-Newtonian fluids were studied. Therefore, the appropriate solid contents, alternative energy-efficient mixers, and optimized printing parameters were proved to be beneficial for an outstanding deposition effect of the suspension. Ultimately, an object with smooth gradient was successfully manufactured. The validity of this strategy was verified via optical microscopy combined with an image processing method to gauge homogeneity and a scanning electron microscope to investigate graded composition and microstructure. 相似文献
38.
添加含碳熔剂细化镁合金晶粒的方法 总被引:22,自引:4,他引:22
提出了镁合金用粉末状晶粒细化剂加入的新方式-子母球混合粉压块加入法,以常用镁合金AZ31为基,将采用普通方式加入细化剂和采用子母球混合粉压块加入细化剂的镁合金微观组织进行了定量比较,并对熔炼时碳粉在熔体中的分散方式进行了简单的模拟,最后采用纯镁对该加入方式的有效性进行了进一步的验证,试验证明,该加入方式对以改善碳粉对镁及其合金的细化效果,并且操作简单易行。 相似文献
39.
针对传统蚁群算法因初期信息素分布不均导致算法初期路径选择概率随机性大、搜索速度慢等缺陷,设计一种使用混合参数的蚁群改进算法。在算法开始阶段引入遗传算法,对遗传算法的适应度函数进行改进;设置一个评价点使遗传算法在合适的时机进入蚁群算法,并对算法的信息素挥发因子p采用一种自适应调整方式;对遗传算法的交叉率和变异率以及蚁群算法的信息因子和期望因子采用变异的混合参数,发挥4个参数因子在算法中的优点;在蚁群算法后面设置一个路径进化率的评价点判定是否再次进行遗传变异操作,目的是使蚁群算法跳出局部最优;算法最后引入B样条曲线光滑机制。实验结果表明:改进算法在简单和复杂的环境里找到的路径长度和路径拐点数明显减少,有比其他3种算法更快更准的寻找全局最优能力。 相似文献
40.
Significant progress has already been achieved in green manufacturing including dry and hard, often high-speed, machining technologies. For instance, the demand for higher productivity has resulted in the wider application of ceramic and PCBN tools with special multi-radii (wiper) geometry. This paper reports some important characteristics of the surface roughness produced in the turning of a hardened low-chromium alloy steel using mixed alumina–titanium carbon (TiC) ceramic cutting tools equipped with both conventional and wiper inserts. The characteristic geometrical features of surfaces obtained in both these turning operations have been assessed by means of representative two-dimensional (2D) surface roughness parameters, and some 3D visualizations, which allowed more complete characterization of the surface topography and prediction of its service properties. Results show that keeping equivalent feed rates, i.e. 0.1 mm/rev for conventional and 0.2 mm/rev for wiper tools, the surfaces obtained have similar 3D height roughness parameters, and comparable values of skew and kurtosis. At defined cutting parameters, surfaces produced by wiper tools contain blunt peaks with distinctly smaller slopes resulting in better bearing properties. Only marginal changes of Ra parameter were recorded during 15 min machining trials. 相似文献