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排序方式: 共有2552条查询结果,搜索用时 15 毫秒
1.
Jared P. Klein Zachary M. Gdowski Richard A. Register 《Journal of polymer science. Part A, Polymer chemistry》2022,60(2):266-275
Though polynorbornene synthesized by ring-opening metathesis polymerization has an intrinsically all-cis configuration of the cyclopentylene backbone rings, a fraction of these rings can be epimerized to the trans configuration during hydrogenation over suitable catalysts. By varying the method of hydrogenation, semicrystalline hydrogenated polynorbornenes (hPNs) with trans levels between 0 and 36% were obtained. With increasing trans content, the glass transition temperature, melting point, and enthalpy of melting decrease modestly. By contrast, the temperature at which the hPN crystal transitions into a rotationally disordered polymorph varies strongly with trans content, ranging from 126 °C (all-cis) to 71 °C at 27% trans; at trans contents of 34% and above, no rotationally-ordered phase is observed at any temperature. The room-temperature Young's modulus shows no dependence on trans content, while the yield stress drops by 20% at 1% trans content and slowly decreases further with additional epimerization. The temperature dependence of the Young's modulus differs for trans-containing versus all-cis polymers, while the temperature dependence of the yield stress is set by the polymorph type (rotationally ordered vs. disordered). 相似文献
2.
In almost every ecological system, growth of various interacting species evolve in different time scales and the implementation of this time scale difference in the corresponding mathematical model exhibits some rich and complex oscillatory dynamics. In this article, we consider a predator–prey model with Beddington–DeAngelis functional response in which the prey reproduction is affected by the predation induced fear and its carry-over effect. Considering the growth of prey species occurs on a faster time scale than that of predator, the proposed system reduces to a ‘slow–fast predator–prey’ system. Using the geometric singular perturbation theory and asymptotic expansion technique, we investigate the system both analytically and numerically, and observe a wide range of rich and complex dynamics such as canard cycles (with or without head) near the singular Hopf-bifurcation threshold and relaxation oscillation cycles. The system experiences a canard explosion through which a rapid transition from small amplitude limit cycle to large amplitude limit cycle occurs in a tiny parametric interval. These types of complex oscillatory dynamics are absent in non slow–fast systems. Furthermore, it is shown that the interplay between fear and its carry-over effect, and the variation of time scale parameter may lead to a regime shift of the oscillatory dynamics. We also study the impact of fear and its carry-over effect on the properties of long transient dynamics. Thus our study provides some valuable biological insights of a slow–fast predator–prey system which will aid in understanding the interplay between fear and its carry-over effect. 相似文献
3.
本文提出了一种新的能够计及尺度效应的微纳米蜂窝等效模量的计算方法。将一种单参数应变梯度理论引入到本构方程当中,并基于能量等效原理推导了蜂窝面内等效模量地计算公式。算例分析表明,本文方法能够有效地计及尺度效应对蜂窝等效模量的影响。尺度效应与胞壁厚度和长度的值都有关,当胞壁厚度较小时,尺度效应显著,本文方法预测的模量会明显高于传统方法;而当胞壁厚度较大时,尺度效应变得微弱乃至可以忽略不计。但如果胞壁的长度/厚度比很大,则面内等效模量会趋近于0,此时是否考虑尺度效应意义不大。 相似文献
4.
Chunhui Liu Dr. Chengyi Xiao Chengcheng Xie Qinglian Zhu Dr. Qiaomei Chen Prof. Wei Ma Prof. Weiwei Li 《Chemphyschem》2022,23(2):e202100725
Adding insulating polymers to conjugated polymers is an efficient strategy to tailor their mechanical properties for flexible organic electronics. In this work, we selected two insulating polymers as additives for high-performance photoactive layers and investigated the mechanical and photovoltaic properties in organic solar cells (OSCs). The insulating polymers were found to reduce the electron mobilities in the photoactive layers, and hence the power conversion efficiencies were significantly decreased. More importantly, we found that the insulating polymers exhibited negative effect on the mechanical properties of the photoactive layers, with reduced Young's modulus and low crack onset strains. Further studies revealed that the insulating polymers had poor miscibility with the photoactive layers, providing large domains and more cavities in blend thin films, which act as negative effect for the tensile test. The studies indicate that rational selection of insulating polymers, especially enhancing the non-covalent interaction with the photoactive layers, will be critically important for the stretchable OSCs. 相似文献
5.
6.
《分析论及其应用》2015,(3):236-243
Let P(z) be a polynomial of degree n and for any complex number α, let D_αP(z) = nP(z)+(α- z) P′(z) denote the polar derivative of the polynomial P(z) with respect to α. In this paper, we obtain inequalities for the polar derivative of a polynomial having all zeros inside a circle. Our results shall generalize and sharpen some well-known results of Turan, Govil, Dewan et al. and others. 相似文献
7.
Vladimir P. Zhdanov 《Physics letters. A》2019,383(8):744-747
Experimental studies of dislocations in nanoparticles are just beginning. The corresponding theoretical models are still lacking. In this context, the author analyzes relaxation of a dislocation in a nanoparticle. Mechanistically, this process is considered to occur primarily via dislocation drift induced by the stress-related image forces. Elementary dislocation displacements include the formation of a kink at one of the sides of the dislocation line, its diffusion along this line, and annihilation at the opposite side. For this mechanism, the dependence of the time of dislocation disappearance on the nanoparticle size has been identified. 相似文献
8.
Tijani A. Apalara 《Journal of Mathematical Analysis and Applications》2019,469(2):457-471
In this work we consider a one-dimensional porous-elastic system with memory effects. It is well-known that porous-elastic system with a single dissipation mechanism lacks exponential decay. In contrary, we prove that the unique dissipation given by the memory term is strong enough to exponentially stabilize the system, depending on the kernel of the memory term and the wave speeds of the system. In fact, we prove a general decay result, for which exponential and polynomial decay results are special cases. Our result is new and improves previous results in the literature. 相似文献
9.
10.
Serife Nur Deveci Tuncer Acar Osman Alagoz 《Mathematical Methods in the Applied Sciences》2020,43(5):2772-2782
In this study, we introduce newly defined Gamma operators which preserve constants and e2μ·, μ>0 functions. In accordance with this purpose, we focus on their approximation properties such as uniform convergence, rate of convergence, asymptotic formula, and saturation results. Superior properties of introduced operators have been tested both theoretically and numerically in certain senses to highlight the performance of the new constructions of Gamma operators. 相似文献