A review of three-dimensional viscoelastic models with an application to viscoelasticity characterization using nanoindentation

This work reviewed different three-dimensional viscoelastic models, including Hooke, Newton, Maxwell, Voigt, Boltzmann, Zener, Tsay, Burgers, Weichert, and Kelvin models. The relaxation moduli and creep compliances are derived and related via the viscoelastic parameters. Physical meanings of viscoelastic parameters are also explained for each model. The formulae of relaxation test, creep test, and dynamic loading test for each viscoelastic models are formulated. Relaxation moduli and creep compliances are drawn for visualizing and comparing. The less discussed time-dependent Poisson’s ratios are also emphasized and compared in this work. All viscoelastic functions can be represented as the relaxation-creep duality representation. The instantaneous and permanent moduli and compliances as well as the fractions of exponential and complementary exponential pairs with different characteristic times can be immediately understood via the relaxation-creep duality representation. The three-dimensional Burgers model is selected to describe the viscoelastic behavior of PMMA with nanoindentation test. The two-step curve fitting method is introduced to fit the P–t curve and h–t curve separately. The fitting results are better than the direct fitting of P–h curve in the literature. The relaxation moduli and creep compliances can then be used to understand the viscoelastic behavior of PMMA.     

Image super-resolution by textural context constrained visual vocabulary

Example-based super-resolution (SR) approach hallucinates the missing high-resolution (HR) details by learning the example image patches. This approach implicitly assumes that the similarity of the low-resolution (LR) patches can infer the similarity of the corresponding HR patches. However, this similarity preserving assumption may not be held in practice. Thus the example-based super-resolved image inevitably contains artifacts not close to the ground truth. In this paper, we propose a novel single-image SR method by integrating an enforced similarity preserving process by using visual vocabulary into example-based SR approach. By jointly learning the HR and LR visual vocabularies, we can obtain a geometric co-occurrence prior to make the geometric similarity preserved within each visual word. We further propose a two-step framework for SR. The first step estimates the optimum visual word using textural context cue while the second step enforces the visual word subspace constraint and reconstruction constraint for estimating the final result. Experiments demonstrate the effectiveness of our method for recovering the missing HR details, especially texture.     

Investigation of Laser-Assisted Microcrystalline SiGe Films Deposited at Low Temperature

SiGe films deposited by conventional plasma-enhanced chemical vapor deposition (PECVD) were compared with microcrystalline SiGe (μc-SiGe) films deposited at a low temperature using a laser-assisted plasma-enhanced chemical vapor deposition (LAPECVD). In the LAPECVD system, a CO₂ laser was used to assist the pyrolytic decomposition of SiH₄ and GeH₄ reactant gases. The μc-SiGe structure was identified using electron diffraction patterns from high-resolution transmission electron microscopy images. Microcrystalline SiGe films were analyzed using various measurements.     

A study of the backup reprovisioning problem for FIPP p-cycles on WDM networks

As networks grow in size and complexity, both the probability and the impact of failures increase. The pre-allocated backup bandwidth cannot provide 100% protection guarantee when multiple failures occur in a network. In this article, we focus on how to recover the protecting capabilities of FIPP (Failure-independent path-protecting) p-cycles against the subsequent links failure on WDM networks, after recovering the working paths affected by the failure of link. Two recovering policies are designed to recover the protecting capabilities of the FIPP p-cycles if possible, unless there is no sufficient network resource. They are Cycle Recovery Policy and Path Recovery Policy. In addition, a Cycle Adjust algorithm is proposed and used to recover the affected cycles. The simulation results of the proposed methods are also given.     

基于BACnet/6Lo WPAN协议的无线传感器网络设计与实现

提出一种基于BACnet/6LowPAN协议的无线传感器网络设计方案,并对网络中的硬件与软件平台以及网络拓扑进行了详细的论述,设计并实现了与用户交互及监控整个网络工作状态的平台。系统测试表明,该无线网络工作正常,达到预期目的。     

Fast blind channel estimation for space–time block coded MIMO–OFDM systems

Fast blind subspace channel estimation using circular property of the channel matrix is investigated for space–time block coded (STBC) multiple-input multiple-output orthogonal frequency division multiplexing (MIMO–OFDM) systems in this paper. The noise subspace computed from the correlation matrix of received signals requires a large number of symbols to converge in the subspace channel estimation. Using the circular property of the channel matrix, we propose both the cyclic repetition method (CRM) and the forward–backward method (FBM) to generate N times of equivalent signals for each STBC–OFDM symbol, respectively, where N is the size of FFT operation. With these equivalent symbols, the proposed CRM, FBM and CRM–FBM (CFBM) channel estimations can perform very well within a few OFDM symbols. The CRM, FBM and CFBM schemes are applicable to the CP-OFDM, ZP-OFDM and VC-OFDM systems, respectively. The identifiability of the subspace channel estimation is investigated that the channel matrix is determined up to two ambiguity matrices. Computer simulations demonstrate that the CRM-based, FBM-based and CFBM-based channel estimations have better performances than the conventional ones.     

A review of industrial wireless networks in the context of Industry 4.0

There have been many recent advances in wireless communication technologies, particularly in the area of wireless sensor networks, which have undergone rapid development and been successfully applied in the consumer electronics market. Therefore, wireless networks (WNs) have been attracting more attention from academic communities and other domains. From an industrial perspective, WNs present many advantages including flexibility, low cost, easy deployment and so on. Therefore, WNs can play a vital role in the Industry 4.0 framework, and can be used for smart factories and intelligent manufacturing systems. In this paper, we present an overview of industrial WNs (IWNs), discuss IWN features and related techniques, and then provide a new architecture based on quality of service and quality of data for IWNs. We also propose some applications for IWNs and IWN standards. Then, we will use a case from our previous achievements to explain how to design an IWN under Industry 4.0. Finally, we highlight some of the design challenges and open issues that still need to be addressed to make IWNs truly ubiquitous for a wide range of applications.     

Study of wetting reaction between eutectic AuSn and Au foil

Wetting reactions between eutectic AuSn solder and Au foil have been studied. During the reflow process, Au foil dissolution occurred at the interface of AuSn/Au, which increases with temperature and time. The activation energy for Au dissolution in molten AuSn solder is determined to be 41.7 kJ/mol. Au₅Sn is the dominant interfacial compound phase formed at the interface. The activation energy for the growth of interfacial Au₅Sn phase layer is obtained to be 54.3 kJ/mol over the temperature range 360–440°C. The best wettability of molten AuSn solder balls on Au foils occurred at 390°C (wetting angle is about 25°). Above 390°C, the higher solder oxidation rate retarded the wetting of the molten AuSn solder.     

Nanotribological Characteristics of Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript>, Cu<Subscript>3</Subscript>Sn,and Ni<Subscript>3</Subscript>Sn<Subscript>4</Subscript> Intermetallic Compounds

Nanotribological characteristics, including the coefficient of friction, wear coefficient, and wear resistance, of Cu₆Sn₅, Cu₃Sn, and Ni₃Sn₄ intermetallic compounds developed by the annealing of Sn–Cu or Sn–Ni diffusion couples were investigated in this work. The scratch test conditions combined a constant normal load of 10 mN, 20 mN, or 30 mN and a scratch rate of 0.1 μm/s, 1 μm/s, or 10 μm/s. Experimental results indicated that, as the normal load increases, the pile-up grows taller and the scratch deepens, leading to a greater coefficient of friction and wear coefficient, and reduced wear resistance. Moreover, the scratch rate does not have a significant effect on the nanotribological characteristics except for those of Cu₆Sn₅ and Cu₃Sn under a normal load of 10 mN. Though the hardness of Cu₆Sn₅, Cu₃Sn, and Ni₃Sn₄ is similar, Ni₃Sn₄ appears to be more prone to wear damage.     

Suppressing Growth of the Cu<Subscript>5</Subscript>Zn<Subscript>8</Subscript> Intermetallic Layer in Sn-Zn-Ag-Al-Ga/Cu Solder Joints

Cu₅Zn₈ normally forms between Sn-Zn solder and Cu metallization. In this study, the growth of the intermetallic compound (IMC) layer is slowed by increasing the silver content in the Sn-8.5Zn-Ag-Al-Ga/Cu system. Experimental results showed that the total thickness of the IMC layers formed with 1.5 wt.% silver content was about half that without silver. The reduction might be due to the formation of the intermetallic compound (Ag,Cu)-Zn at the interface in addition to silver.