驻波教学中的初相问题

从推导驻波方程的一般形式出发,讨论了入射波和反射波的初相在驻波形成中的作用和关系.     

Superresolution imaging of DNA tetrahedral nanostructures in cells by STED method with continuous wave lasers

DNA tetrahedral nanostructures are considered to be uew nanocarriers because they can be precisely controlled and hold excellent penetration ability to the cellular membrane. Although the DNA tetrahedral nanostructure is extensively studied in biology and medicine, its behavior in the cells with nanoscale resolution is not understood clearly. In this letter, we demonstrate superrcsolution fluorescence imaging of the distribution of DNA tetrahedral nanostructures in the cell with a simulated emission depletion （STED） microscope, which is built based on a conventional eonfocal microscope and can t）rovide a resolution of 70 nm.     

Kinetic and thermodynamic modeling of Portland cement hydration at low temperatures

Portland cement have to hydrate in cold climates in some particular conditions. Therefore, a better understanding of cement hydration under low temperatures would benefit the cement-based composites application. In this study, Portland cement was, therefore, kinetically and thermodynamically simulated based on a simple kinetics model and minimization of Gibbs free energy. The results of an evaluation indicate that Portland cement hydration impact factors include the water–cement ratio (w/c), temperature, and specific surface area, with the latter being an especially remarkable factor. Therefore, increasing the specific surface area to an appropriate level may be a solution to speed the delayed hydration due to low temperatures. Meanwhile, the w/c ratio is believed to be controlled under cold climates with consideration of durability. The thermodynamic calculation results suggest that low-temperature influences can be divided into three levels: irrevocable effects (<0 °C), recoverable effects (0–10 °C), and insignificant effects (10–20 °C). Portland cement was additionally measured via X-ray diffraction, thermal gravity analysis, and low-temperature nitrogen adsorption test in a laboratory and comparisons were drawn that validate the simulation result.     

NONLINEAR DYNAMICS AND SYNCHRONIZATION OF TWO COUPLED PIPES CONVEYING PULSATING FLUID

In this paper, the nonlinear dynamical behavior of two coupled pipes conveying pulsating fluid is studied. The connection between the two pipes is considered as a distributed linear spring. Based on this consideration, the equations of motion of the coupled two-pipe system are obtained. The two coupled nonlinear partial differential equations, discretized using the fourth- order Galerkin method, are solved by a fourth-order Runge-Kutta integration algorithm. Results show that the connection stiffness has a significant effect on the dynamical behavior of the coupled system. It is found that for some parameter values the motion types of the two pipes might be synchronous.     

Synthesis of polymer with defined fluorescent end groups via reversible addition fragmentation transfer polymerization for characterizing the conformations of polymer chains in solutions

A new type of chain transfer agent used in reversible addition fragmentation chain transfer (RAFT) polymerization named 9‐anthracenylmethyl (4‐cyano‐4‐(N‐carbazylcarbodithioate) pentanoate) (ACCP) was synthesized with a total yield over 75% by the incorporation of both fluorescent donor and acceptor chromophores. Polymerization of heterotelechelic α,ω end‐labeled dye‐functionalized polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(n‐butyl methacrylate) (PBMA) with adjustable molecular weights and narrow polydispersity could be conducted by a one‐pot procedure through RAFT polymerization with this bischromophore chain transfer agent. The polymerizations demonstrated “living” controlled characteristics. By taking advantage of the characteristic fluorescence resonance energy transfer (FRET) response between the polymer chain terminals, the variation of chain dimensions in solution from the dilute region to the semidilute region can be monitored by changes in the ratio of the fluorescence intensities of the carbazolyl group to the anthryl group, which lends itself to potential applications in characterizing chain dimensions in solutions for thermodynamic or dynamic studies. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2413–2420     

Environmentally Stable Polymer Gels with Super Deformability and High Recoverability Enhanced by Sub‐5 nm Particles in the Nonvolatile Solvent

It remains challenging to satisfy the combined performances for hydrogels with excellent mechanical behavior, high deformability, and super recoverability under harsh environmental conditions. In this study, we first established a strong polymer network via the crosslinking of polymer chains on the surfaces of sub‐5‐nm calcium hydroxide nanospherulites in ethylene glycol solvent. The organic gel expressed excellent mechanical properties such as a recoverable compressive engineering stress of 249 MPa and an elongation stress of 402 KPa, which was attributed to the uniform nanosized crosslinking structure as characterized by SEM. Moreover, the nonvolatile solvent remained in the gel, meaning that the sample can resist a wide temperature range of ?56 to 100 °C without losing the elastic properties. This novel organic gel could provide promising routes to develop the ideal elastic carriers for wearable devices, smart skin sensors, and damping materials. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 713–721     

A research study on the spallation strength of LY12 aluminum under the pre-compression condition

Science China Physics, Mechanics & Astronomy - To pre-compress the disk-shaped LY12 samples along the radial direction can be done with the aid of overstress assembly by heating or by...