A simple model for the anomalous intrinsic viscosity of dendrimers

The intrinsic viscosity of dendrimers in solution shows several anomalous behaviors that have hitherto not been explained within the existing theoretical frameworks of either Zimm or Rouse. Here we propose a simple two-zone model based on the radial segmental density profile of the dendrimers and combine a non-draining core with a free-draining outer region description, to arrive at a simple formula that captures most of the main features in the intrinsic viscosity data obtained in experiments

Influences of electric pulse on solidification structure of LM-29 Al-Si alloy

The metallographic structure of LM-29 aluminum-silicon alloy modified by electric pulse treatment has been investigated and compared with those untreated. The solidification structure of LM-29 alloy has been analyzed by means of M1AP3 Quantimet image processing and analysis system, and then the solidification process has been analyzed by means of differential scanning calorimetry (DSC). The results indicate that the primary silicon phase was refined remarkably by electric pulse while the tensile strength and elongation properties increased accordingly. Electric pulse treatment can also increase the binding power between silicon clusters and alloy melt matrix, as a result, the precipitation of primary silicon phase is suppressed to meet the demand of supercooling degree for nucleating, correspondingly. The electric pulse modification has great influence on the size of silicon atomic cluster as well as its distribution in the melt, subsequently, leads to the refinement of solidification structure

The C/C++ Integrative Teaching Based on CDIO Education Model

AbstractIn view of the curriculum characteristic of the C/C++ language, a new idea about teaching reform based on CDIO is proposed in this paper. In everyday teaching, the teaching link, which centers on cases and for the purpose of program design skills to improve can effectively improve the ability of students to solve real application problems

Nonlinear Rheological Behaviors in Polymer Melts after Step Shear

Using molecular dynamics simulation, we investigate the evolution of chain conformation, stress relaxation, and fracture for a polymer melt between two walls after step shear. We find that the characteristic overlap time for the reduced relaxation moduli and the time that the stretched primitive chain retracts to its equilibrium length are both much longer than the Rouse time. Importantly, we observe significant fracture-like flow after shear cessation. While there is considerable randomness in the location of the fracture plane and the magnitude of displacement from sample to sample, our analysis suggests that the randomness is not due to thermal noise, but may reflect inherent structural and dynamic heterogeneity in the entangled polymer network