Optimization of the shape memory effect in shape memory polymers

In this article, we show that given a thermoresponsive shape memory polymer, it is possible to alter a number of its properties, such as the recovery temperature, shape fixity ratio, maximum recovery stress, and final recovery stress (and even a right combination of some of them, e.g., the maximum recovery stress and final recovery stress), simply by means of selecting the programming temperature to achieve optimized performance. Some concerns for the implementation in real engineering practice are also discussed. Although the focus is on the case of a fixed maximum strain in programming, alternative programming approaches can be investigated in a similar way for optimized performance as well. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

冰蓄冷低温送风空调系统风管管路分析研究

研究得出冰蓄冷低温送风空调系统较常规空调系统在风管管路阻力及风管截面积的优越性。依据管路阻力计算公式利用VB语言编写风管比摩阻的计算程序,并利用该计算程序对相同工况下的典型的低温送风温度与常规送风温度的比摩阻进行计算,进而得到风管管路阻力,同时计算得出各送风温度下的风管截面积,并进行对比分析。相同计算条件下,冰蓄冷低温送风空调系统的风管沿程阻力是常规送风系统的40%—70%;采用8℃低温送风方式时,其风管截面积较常规空调可减少20%—30%。与常规空调系统相比,采用冰蓄冷低温送风空调系统可明显减小风管的沿程阻力和截面积,大大降低了风机耗能和建筑层高,节省了运行及建材费用。     

质子交换膜燃料电池阴极电化学反应路径分析

质子交换膜燃料电池阴极电化学反应对其性能有至关重要的影响。论文基于二电子反应机理,模拟了质子交换膜燃料电池阴极氧和质子电化学反应路径,分析了电化学反应过程中各个步骤能量变化规律和氢氧键形成机制。研究发现,氧分子还原过程中,4个质子逐个接近氧分子,形成氢氧键,最终生成2个水分子;第一个质子采用和氧分子氢氧键102°夹角的方向接近其中一个氧原子,形成第一个氢氧键;当第二个质子和另一个氧原子构成氢氧键时,需要很大的活化能,这是氧还原反应的控制步骤,生成中间产物过氧化氢。研究结果为理解质子交换膜燃料电池电化学反应原理,推动质子交换膜燃料电池的应用具有重要意义。     

Investigation on bistable resistance switching characteristics of an organic donor–acceptor material for high density data storage

In this paper, organic thin films of a donor-acceptor material N,N′-bis[4-(1,1-dicyanovinyl)phenyl]N,N′-bis(4-fluorophenyl)benzidine (TPD-FCN) were prepared by a vacuum vapor deposition method. The N,N,N′,N′-tetraphenylbenzidine moiety can be served as an excellent nonplanar electron donor and the 1,1-dicyanovinyl group is an excellent electron acceptor. The typical macroscopic I–V curves of the device based on TPD-FCN thin film exhibit a bistable resistive switching characteristics for memory application. Furthermore, stable nanoscale electrical information storage was achieved on the TPD-FCN thin film by scanning tunneling microscopy. The average size of the recorded marks is about 10 nm. Local I–V characteristics suggest that the formation of the recording dots is due to the local change of electrical property of the thin film, and the intermolecular charge transfer induced by an electric field is proposed as the reason for the information dot formation. The results indicate that TPD-FCN is a promising candidate for nanoscale recording materials.     

On the finite integral transform method for exact bending solutions of fully clamped orthotropic rectangular thin plates

Exact bending solutions of fully clamped orthotropic rectangular thin plates subjected to arbitrary loads are derived using the finite integral transform method. In the proposed mathematical method one does not need to predetermine the deformation function because only the basic governing equations of the classical plate theory for orthotropic plates are used in the procedure. Therefore, unlike conventional semi-inverse methods, it serves as a completely rational and accurate model in plate bending analysis. The applicability of the method is extensive, and it can handle plates with different loadings in a uniform procedure, which is simpler than previous methods. Numerical results are presented to demonstrate the validity and accuracy of the approach as compared with those previously reported in the bibliography.     

Acoustic model of ceramic angular contact ball bearing based on multi-sound source method

This study focuses on the radiation noise of ceramic angular contact ball bearings for motorised spindles. The differential equations of the vibrations for each bearing component are established, and the characteristics of various sound sources are analysed. Then, a multi-sound source method for calculating the radiation noise of a ceramic angular contact ball bearing is developed. The accuracy and validity of the proposed method are verified through numerical calculations and a corresponding experiment. Subsequently, the frequency spectrum characteristics of the radiation noise of the bearing components are discussed in detail according to the multi-sound source method. The radiation noise of each bearing component varies nonlinearly with the rotation speed, and the variation is consistent with the total radiation noise of the bearing. The eigenfrequency noise of each component appears clearly in the noise frequency spectrum. The results show that the proposed method can well predict the radiation noise of a ceramic angular contact ball bearing and provide a theoretical reference for the study of silent ceramic angular contact ball bearings for motorised spindles.     

Monitoring minor over-heating/cooling temperature based on the temperature memory effect in shape memory materials via DSC

Journal of Thermal Analysis and Calorimetry - The temperature memory effect (TME) has been reported as another interesting feature of many shape memory materials (SMMs). In this paper, we briefly...     

自组装非接触测距仪

介绍一种非接触测距仪的制作和设计理念,并对仪器的使用特点和测量精度进行了分析。     

介电体围绕下绳束状碳纳米管的场发射特性(英文)

在周边环绕玻璃薄片介电体的作用下,绳束状碳纳米管宏观体的场发射电流发生异常跃迁,同时伴随有场发射电子光斑的横向扩展,导致跃迁后的场发射电流明显高于正常情况。所有观察到的现象均与介电体存在下的电场重新分布和电子轨迹偏离有关。理论分析及随后的场发射测试检验了介电体几何尺寸、间距、介电常数等因素对场发射I-V性能的影响。研究结果提供了一种控制Spindt型场发射体电子发射性能的新的可行途径。     

Queueing network model for a single-operator machine interference problem with external operations

Machine interference is a significant problem in many manufacturing systems. Prior research shows that machine interference may be as high as 10% of machine time. This paper proposes a queueing network model for a single-operator, machine interference problem with external operations, i.e., those tasks that can be completed while the machine is running. The interactions for part/machine and machine/operator are modeled as an open and a closed queueing network, respectively. In the open network, part inter-arrival time follows an exponential distribution. In both networks, service times follow a general distribution that is characterized by their first two moments. An iterative procedure is developed to solve the proposed model. Solution quality is justified by an industry-based case study. Data were collected from the integrated circuit (IC) ink-marking machines of a leading IC packaging company in Taiwan that allowed the construction of an experimental design for computational tests that encompassed a wide range of production scenarios. Empirical results show promise for the proposed methodology in helping to solve industrial problems. Model limitations as well as future research opportunities are discussed.