EXISTENCE OF POSITIVE SOLUTIONS TO A THREE-POINT BOUNDARY VALUE PROBLEM FOR SECOND ORDER DYNAMIC EQUATIONS WITH DERIVATIVE ON TIME SCALES

In this paper, we consider the existence of positive solutions to a three-point boundary value problem for second order dynamic equations with derivative on time scales.Applying Leggett-Williams fixed point theorem, we obtain at least three positive solutions to the problem. An example is also presented to illustrate the applications of the results obtained.     

Tubular structured bacterial cellulose-based nitrite sensor: preparation and environmental application

Journal of Solid State Electrochemistry - Bacterial cellulose (BC) is a polysaccharide with tubular structure and can be produced by various species of bacteria particularly Acetobacter xylinum. It...     

Design synthesis and photocatalytic activity of a novel lilac-like silver-vanadate hybrid solid based on dicyclic rings of [V4O12]4- with {Ag7}7+ cluster

An unusual two-dimensional bicyclic [V(4)O(12)](4-)-based coordination polymer with a novel maximum {Ag(7)}(7+) cluster and containing five crystallographically-independent silver atoms was obtained and showed good photocatalytic activity for the degradation of methylene blue.     

Global dynamics of a population model from river ecology

In this paper, we investigate the population dynamics of a two-species Lotka-Volterra competition system arising in river ecology. An interesting feature of this modeling system lies in the boundary conditions at the downstream end, where the populations may be exposed to differing magnitudes of loss of individuals. By applying the theory of principal eigenvalue and monotone dynamical systems, we obtain a complete understanding on the global dynamics, which suggests that slower dispersal is selected for. Our results can be seen as a further development of a recent work by Tang and Chen (J. Differential Equations, 2020, 2020(269), 1465--1483).     

Cryogenic Exfoliation of Non‐layered Magnesium into Two‐Dimensional Crystals

Physical exfoliation of layered precursors is one of the most prevailing techniques to prepare two‐dimensional (2D) crystals, which, however, is considered to be intrinsically inapplicable to non‐layered bulks. Now, plane cleavage differentiation is identified in metallic magnesium at cryogenic temperature (CT), and a cryogenic exfoliation strategy of non‐layered magnesium into 2D crystals is developed. The cleavage anisotropy of the Mg lattice in response to the external mechanical stress originates from the CT‐induced specific inactivation of basal slip, which results in the basal cleavage perpendicular to c axis. The exfoliated novel 2D Mg crystals exhibit remarkable localized surface plasmon resonances, holding great promise for the applications in harvesting and converting solar energy. Beyond creating a new member for the burgeoning 2D family, this study may provide a useful tool for the physical exfoliations of various non‐layered materials.     

Probing the Contraction and Association of Polystyrene Chains in Semidilute Solution by Non‐Radiative Energy Transfer

The interchain contraction and association of polystyrene in semidilute solution near the Θ temperature are studies using NET. The results reveal that during a drop of temperature, polystyrene chains pass through different states: a smooth change of conformation at temperatures above the Θ temperature, an accelerated contraction and association, aggregation of polymer chains, and then further continuous contraction below the Θ temperature. A pronounced hysteresis is observed during repeated heating. A viscosity study of the same solution was compared with the NET results. It indicates that NET can effectively be used to study conformational changes like contraction and association of polymer chains in a semidilute solution.

     

广义有限元方法研究进展

广义有限元方法是常规有限元方法在思想上的延伸,它基于单位分解方法,通过在结点处引入广义自由度,对结点自由度进行再次插值,从而提高有限元方法的逼近精度,或满足对特定问题的特殊逼近要求.基于广义有限元方法对单元形状函数构造理论的深入研究,具有任意内部特征(空洞、夹杂、裂纹等)及外部特征(凹角、角点、棱边等)的复杂问题,都将在简单、且与区域无关的有限元网格上加以求解.本文主要介绍广义有限元方法的基本思想、主要特征及对重要细节的处理策略,包括线性相关性的处理、局部逼近函数的获取、区域上的数值积分技术以及边界条件的处理.与扩展有限元方法和有限覆盖方法比较,分析它们各自的特点.综述广义有限元方法的研究现状、应用,展望广义有限元方法的未来发展.     

Novel adamantane-based periodic mesoporous organosilica film with ultralow dielectric constant and high mechanical strength

Journal of Sol-Gel Science and Technology - In this work, a novel bridged organosilane precursor, adamantane-bridged organosilane (ADBO), was synthesized successfully which was employed to prepare...     

Hydrolysis of Methylal Catalyzed by Ion Exchange Resins in Aqueous Media

In the present work, the chemical equilibrium and kinetics of methylal (PODE₁) hydrolysis catalyzed by ion–exchange resin in aqueous solutions were investigated. The study covers temperatures between 333.15 and 363.15 K at various starting compositions covering (PODE₁ + MeOH)/water molar ratio ranges from 0.5 to 1.5 in a time scale. On the basis of the experimental results, a mole fraction-based model of the chemical equilibrium and a pseudohomogeneous model are proposed to fit data based on true amount of monomeric formaldehyde. It has been demonstrated that the hydrolysis of PODE1 is slightly endothermic with the enthalpy 8.19 kJ/mol and the rate determining step. Finally, a feed–forward artificial neural networks (ANN) model is developed to model the concentration change of methanol in aqueous solutions. The results showed that the predicted data from designed ANN model were in good agreement with the experimental data with the coefficient (R²) of 0.98. Designed ANN provides a reliable method for modeling the hydrolysis reaction of methylal (PODE1).