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571.
Rodolfo G. Pereyra Marcelo A. Carignano 《Journal of Polymer Science.Polymer Physics》2019,57(19):1343-1350
Using molecular dynamics, we study the formation of chemical gels from an initial solution of reactive polymers that undergo a crosslinking reaction. We study the effect of the polymer persistence length and different densities of crosslinkers along the chains. As the reaction progresses, different structural features are identified in the system leading to the development of a percolated cluster. These features are (a) single strands, (b) double strands, and (c) bridges. We found that the total numbers of these three kinds of features are roughly independent of the persistence length; however, the average lengths of single and double strands grow with this variable. The average length of double strands strongly increases with increasing crosslinker density and the amount of single strands sharply falls as crosslinker density grows. We also found that general structural features of polymer networks are highly dependent on chain persistence length and crosslinker density. Fully flexible chains with high density of crosslinkers result in inhomogeneous network structures with large voids. In contrast, precursor chains with high rigidity and scarce number of crosslinkers result in homogeneous networks having small cavities. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1343–1350 相似文献
572.
We introduce simplicial persistence, a measure of time evolution of motifs in networks obtained from correlation filtering. We observe long memory in the evolution of structures, with a two power law decay regimes in the number of persistent simplicial complexes. Null models of the underlying time series are tested to investigate properties of the generative process and its evolutional constraints. Networks are generated with both a topological embedding network filtering technique called TMFG and by thresholding, showing that the TMFG method identifies high order structures throughout the market sample, where thresholding methods fail. The decay exponents of these long memory processes are used to characterise financial markets based on their efficiency and liquidity. We find that more liquid markets tend to have a slower persistence decay. This appears to be in contrast with the common understanding that efficient markets are more random. We argue that they are indeed less predictable for what concerns the dynamics of each single variable but they are more predictable for what concerns the collective evolution of the variables. This could imply higher fragility to systemic shocks. 相似文献
573.
We consider a reaction–diffusion population model with predator–prey-dependent functional response. Firstly, we discuss the conditions which ensure the model has a unique positive constant solution. Secondly, we investigate the dynamical properties of the model, including the large time behaviors of the nonconstant solutions and the local and the global asymptotic stability of the positive constant solution. 相似文献
574.
新媒体环境下新闻摄影教学的变革与坚守 总被引：1，自引：0，他引：1
冯菊香 《玉林师范学院学报》2010,31(4)
在新媒体环境下进行新闻摄影教学改革是新闻摄影教学当前关注的焦点。环境的改变促使我们在新闻教育过程中既要跟上传播技术的发展,又要重视对学生的社会责任感和人文关怀精神的培养,从而加强我们对新闻摄影教学的变革与坚守进行的理性思考。 相似文献
575.
Na Zhang Birong Tian Zhaofeng Wang Andrew T. Smith Zhidong Ma Zhonghua Xue Luyi Sun 《Advanced Optical Materials》2021,9(13):2100137
The distinctive crystal characteristics of undoped LiGa5O8 allow the production of abundant defects and traps in the structure, contributing to attractive luminescent properties. In this work, the mechanoluminescent pathways of LiGa5O8 are demonstrated in terms of the defect induced localized energy levels and trap levels, which are further optimized by adjusting the synthesis atmosphere. The results suggest that the LiGa5O8 synthesized under a reducing atmosphere exhibits an extremely intense mechanoluminescence, which is even better than that of commercial ZnS:Cu. Because of the existence of shallow trap with the spontaneous transfer activity at room temperature, the mechanoluminescence of LiGa5O8 can also exhibit a persistent behavior, overcoming the transient emitting problem in most of the previous mechanoluminescent materials. In addition, the mechanoluminescence of LiGa5O8 can be easily and quickly recovered by refilling the energy in traps. As a result, the undoped LiGa5O8 is confirmed to be an efficient material with intense, persistent, and recoverable mechanoluminescence, which is promising to substitute the doped ones for various applications. 相似文献
576.
Yuenan Kang;Linfei Nie; 《Mathematical Methods in the Applied Sciences》2024,47(12):9669-9702
The diversity of transmission modes and the heterogeneity of populations in the transmission of infectious diseases are issues that have to be faced in the current disease protection. In this paper, an infectious disease model incorporating age structure and horizontal and environmental spread, along with asymptomatic infection, is proposed to describe diversification of disease transmission routes and population heterogeneity. The expression of the basic reproduction number is derived by a linear approximation method, and it is concluded that if , the disease-free steady state is globally asymptotically stable; if , the model has a unique endemic steady state which is locally asymptotically stable under certain conditions. Further, the uniform persistence of disease is proved using the persistence theory of the infinite-dimensional dynamical system when . In additional, the issue of optimal control problem according to this model is investigated, and the representation of optimal control with respect to state variables and adjoint variables is obtained which also imply the existence and uniqueness of optimal control. Finally, numerical simulations are carried out to interpret the theoretical results and to discuss the impact of age and control measures in disease transmission. 相似文献
577.
Shahemi Nur Hidayah;Ahmad Ruzaidi Dania Adila;Ab Rahim Sharaniza;Amir Muhammad Abid;Mahat Mohd Muzamir; 《先进技术聚合物》2024,35(8):e6546
Biodegradable polymers are pivotal in tissue engineering, facilitating long-term tissue reintegration and reducing the necessity for surgery. However, collagen, a crucial component of the extracellular matrix, encountered challenges due to its limited mechanical strength and rapid in-vivo degradation. This study addresses these issues through crosslinking and functionalizing collagen with synthetic 4-arm amine-terminated polyethylene glycol (PEG) in a semi-interpenetrating network (IPN) hydrogel. The first goal is to enhance resistance to hydrolysis, thus extending the biodegradation rate. Then, to explore its electrical conductivity properties for certain applications like neural tissue regeneration. The hydrogels were fabricated using sequential IPN formation synthesis where their structural stability and type of degradation by-products were confirmed using Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR). Next, its mechanical and degradation properties investigations exhibit a 92% enhancement in hardness and a 90% retainment of its initial mass over time under physiological conditions. Additionally, the introduction of polypyrrole (PPy) via in-situ polymerization increases its electrical conductivity, achieving a remarkable 104-fold increase at a 0.75 M concentration, attributed to the interconnectivity of PPy chain networks within the three-dimensional structure of IPN collagen/PEG hydrogel. The increased PPy concentration improves conductivity and reduces energy requirements for redox reactions, ensuring electrochemical stability as revealed by cyclic voltammetry analysis. The demonstrated structural and electrochemical stability of the semi-IPN collagen/PEG/PPy hydrogel within a physiological environment through a facile sequential crosslinking method underscores its promising practical applications in enhancing clinical effectiveness. 相似文献
578.
研究了一类多时滞的离散捕食系统,运用差分方程的比较原理,得到了保证系统种群持续生存的充分条件,并对定理条件可实现性进行了实例数值验证. 相似文献
579.
卓相来 《北华大学学报(自然科学版)》2010,11(6):481-486
建立了一类具有连续控制的有关传染性害虫的数学模型,研究了模型正平衡点的全局渐近稳定性,并得到了控制变量的最小上界. 相似文献
580.
In this paper, we consider an immunotherapy model for breast cancer with stochastic perturbations and pulsed chemotherapy. By using stochastic Lyapunov analysis and the strong law of large numbers, we first prove the existence, uniqueness and the stochastic ultimate boundedness of the global positive solution for the model. Then we obtain sufficient conditions for the extinction of tumor cells and the persistence of all three kinds of cells for this model. Finally, we use numerical simulations to verify the theoretical results which are obtained in the paper. 相似文献