Synthesis of Well‐Defined Figure‐of‐Eight‐Shaped Polymers by a Combination of ATRP and Click Chemistry

Well‐defined figure‐of‐eight‐shaped (8‐shaped) polystyrene (PS) with controlled molecular weight and narrow polydispersities has been prepared by the combination of atom transfer radical polymerization (ATRP) and click chemistry. The synthesis involves two steps: 1) Preparation of a linear tetrafunctional PS with two azido groups, one at each end of the polymer chain, and two acetylene groups at the middle of the chain. 2) Intramolecular cyclization of the linear tetrafunctional PS at a very low concentration by a click reaction to produce the 8‐shaped polystyrenes. The resulting intermediates and the target polymers were characterized by ¹H NMR and FT‐IR spectroscopy, and gel permeation chromatography. The glass transition temperatures (T_gs) were determined by differential scanning calorimetry and it was found that the decrease in chain mobility by cyclization resulted in higher T_gs for 8‐shaped polystyrenes as compared to their corresponding precursors.

     

Bifurcations of limit cycles from quintic Hamiltonian systems with a double figure eight loop

This paper deals with Liénard equations of the form , , with P and Q polynomials of degree 5 and 4 respectively. Attention goes to perturbations of the Hamiltonian vector fields with an elliptic Hamiltonian of degree six, exhibiting a double figure eight loop. The number of limit cycles and their distributions are given by using the methods of bifurcation theory and qualitative analysis.     

先天学关于太阳系定位原理

天上星星，繁而不乱。根据《易》“太极”2^k序列编出一个三角数表，可描测太阳系已知与未知行星的轨道参数。其中排行第七的一颗“女帛星”(合理存在)，按开普勒第三定律计算出公转速度与周期后，发现太阳系十大行星的动态组合就是一个“先天八卦模型”，进而可以解读太阳系平衡态运动的数学机理及其结构特征。     

集成结构振动主动控制和抑制

采用一种新的压电板单元,建立了含有分布压电传感元件和执行元件的集成结构的有限元动力模型。研究了这种集成结构在常增益负速度反馈控制规律作用下,振动的主动控制与抑制的问题,并提出了集成结构振动主动控制和抑制的一般方法。最后,提供了数值示例,说明本文提出方法的有效性。     

Design of novel morphing structures based on bistable composites with piezoceramic actuators

Instead of attempts to avoid the large out-of-plane deformations of multilayered fiber-reinforced composites caused by residual stresses, these deformations can be advantageously used for technical applications such as novel morphing structures, where only a discontinuous energy impulse of an actuator is necessary to change the configuration of the structure. For the design of such innovative morphing structures with piezoelectric actuators, novel nonlinear semi-analytical and numerical simulation models have been developed and verified experimentally. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 4, pp. 475–494, July–August, 2006.     

Field‐induced bending deformation of various rubber films

The field‐induced bending deformation of various rubber films was measured. The deformation tended to increase with the increase in the conductivity of the films. In addition, the effect of doping with tetracyanoethylene (TCNE) was also studied. This doping significantly enhanced the bending deformation and conductivity when the film was made of acrylonitrile‐butadiene rubber. The tip of the film (5 × 30 mm², 0.28 mm thick) moved by 3 mm due to the bending deformation induced by the applied voltage (140 V). Such a rubber film may find applications as a polymer actuator. Copyright © 2007 John Wiley & Sons, Ltd.     

Electromagnetic Activation of Shape Memory Polymer Networks Containing Magnetic Nanoparticles

Summary: By incorporation of surface‐modified superparamagnetic nanoparticles into shape memory polymer matrices, remote actuation of complex shape transitions by electromagnetic fields is possible. The composite thermosets of oligo(ε‐caprolactone)dimethacrylate/butyl acrylate contain between 2 and 12 wt.‐% magnetite nanoparticles serving as nanoantennas for magnetic heating. It is shown that the particles are dispersed homogenously within the matrix and that the basic thermal and mechanical properties of the polymer matrix are maintained. The specific loss power of the particles is determined to be 30 W · g⁻¹ at 300 kHz and 5.0 W. During the shape transition at 43 °C, no further temperature increase is observed.

     

Monitoring surface breaking defects with piezoelectric active systems

This paper is concerned with an experimental study and a numerical study of the application of two active techniques to monitor the growth of fatigue cracks and simulated defects in beams using piezoelectric sensors and actuators. The first technique is a transfer function method that consists of exciting the structure with piezoelectric actuators, while recording the electromechanical response of sensors placed close to the defect. Results have shown that the choice of adequate parameters, such as sensor size and its distance to the defect edge, allows the detection of small changes in defect depth. Finite-element simulations were also performed to determine a correlation between sensor response and defect depth. The second method is an impedance technique where a single piezoelectric element is used to excite and to monitor the growth of the defect. This technique was evaluated through experiments where a machined slot of increasing depth was monitored by measuring the electrical admittance of the piezoelectric sensor.     

Small but Smart: Sensitive Microgel Capsules

Microgel capsules are micrometer‐sized particles that consist of a cross‐linked and swollen polymer network complexed with additives. These capsules can be actuated by external stimulation if they are formed from sensitive or supramolecular polymer networks. To make this truly useful, it is crucial to control the microgel size, shape, and loading; this can be achieved by droplet‐based microfluidic templating.