Application of neural networks to laser ultrasonic NDE of bonded structures

The purpose of this study is to develop artificial neural networks for the nondestructive evaluation of a bounded structure using laser generated surface waves. The radial basis model is employed and the inputs of the networks are the sampled dispersion curves while the output is the thickness of the bonding layer or unbond ratio. Numerical simulated dispersion curves with noises were used to train and test the neural networks. The dispersion curves of laser ultrasonic experiments acquired by spectral analysis method were also utilized to test the systems. For comparison, simplex inverse method was also introduced. The results demonstrate that neural networks are well suited for on-line evaluation of bonding thickness and unbond ratio of a bonded layered structure.     

Synthesis of a polydimethylsiloxane-block-hydroxyl grafted acrylate prepolymer copolymer to improve the adhesion between silicone rubber and polyurethane by induced surface reconstruction

A new class of hydroxyl-functionalized polydimethylsiloxane-block-hydroxyl graft acrylate prepolymer (PDMS-b-HGAP) copolymers was synthesized. The copolymers were characterized using Fourier transform infrared spectroscopy as well as ¹H and ¹³C nuclear magnetic resonance spectroscopy. The hydroxyl groups of the HGAP were reacted with the chlorine terminal in the PDMS to yield a triblock copolymer consisting of two segments of PDMS linked to a HGAP segment. The induced surface reconstruction of silicone rubber (SR)by blending polysiloxane reactants with bifunctional PDMS-b-HGAP copolymers and curing using mold materials having high critical surface tension such as polyethyleneterephthalate was attempted to improve the adhesion between chemically-inert SR and polyurethane (PU). Surface characterization using Foruier transform infrared-attenuated total reflectance indicated that the surface of the SR was enriched with HGAP. The increased content of surface HGAP was suggested to account for the improved adhesion between SR and PU.     

Laboratory studies of atmospheric corrosion—I. Weight loss and electrochemical measurements

Electrochemical studies have been performed with the atmospheric corrosion monitor (ACM) under thin layers of electrolyte which were drying out at R.H. < 100%. Galvanic couples (Cu/steel, Cu/zinc) and one-metal (steel, zinc) ACMs were used. Measurements were carried out as a function of R.H. and Na₂SO₄ concentration. In addition, weight loss data were collected under identical conditions in thin layer experiments for steel and zinc in 0.01N solutions of NaCl, Na₂SO₄, HCl, H₂SO₄ and distilled H₂O in air, air + 1 ppm SO₂, argon and argon + 1 ppm SO₂. The data obtained in air and air + SO₂ were compared to weight loss results in bulk solutions.The electrochemical technique makes it possible to follow the changes of corrosion rates with time. As observed in outdoor exposure, a large increase of corrosion rates occurs when the electrolyte layers become very thin, shortly before the surface dries out. These findings explain the results of the weight loss data which show for most environments a much larger corrosion rate than in the bulk electrolyte. An accelerating effect of SO₂ was observed for steel at higher R.H. values, while for zinc, no effect occurred in NaCl, Na₂SO₄ and H₂SO₄, but an inhibiting effect was measured in HCl and in distilled H₂O.Since weight loss and electrochemical data were recorded under identical conditions, it is possible to determine how accurately the ACM data reflect the true corrosion rate. It was found for Cu/steel ACMs that the electrochemical data follow the same trends as the weight loss data, but account for only about 20% of the corrosion rate. Due to larger scatter in the weight loss data, a similar efficiency factor could not be determined for Cu/zinc. For steel and zinc ACMs, the true Tafel slopes are not known, which makes a calculation of corrosion rates doubtful. The low cell efficiency is considered to be due to local corrosion of single cell plates and to i.r.-drop effects.Despite the fact that exact corrosion rates cannot, at present, be obtained from ACM data, the technique appears very valuable for following the changes of atmospheric corrosion behaviour and for time-of-wetness measurements.     

Image steganographic scheme based on pixel-value differencing and LSB replacement methods

In order to improve the capacity of the hidden secret data and to provide an imperceptible stego-image quality, a novel steganographic method based on least-significant-bit (LSB) replacement and pixel-value differencing (PVD) method is presented. First, a different value from two consecutive pixels by utilising the PVD method is obtained. A small difference value can be located on a smooth area and the large one is located on an edged area. In the smooth areas, the secret data is hidden into the cover image by LSB method while using the PVD method in the edged areas. Because the range width is variable, and the area in which the secret data is concealed by LSB or PVD method are hard to guess, the security level is the same as that of a single using the PVD method of the proposed method. From the experimental results, compared with the PVD method being used alone, the proposed method can hide a much larger information and maintains a good visual quality of stego-image.     

Nanomechanical characterization of polymer using atomic force microscopy and nanoindentation

The nanomechanical characteristics of polycarbonate (PC) polymer were investigated by atomic force microscope (AFM) and nanoindentation. Scratching, wear properties, hardness and Young's modulus were obtained. The relationships between scribing feed and speed, surface depth and roughness and applied load were also investigated. The results indicated that as the applied load was increased, the furrow depth and the surface roughness increased. When the scribing feed was increased, the depth and roughness decreased. Increasing the furrow speed also decreased the surface roughness. The applied load is more significant than the scribing speed on the material removal rate. In addition, the Young's modulus and hardness of the polycarbonate material were 1.8 and 0.2 GPa, respectively.     

Phase characterisation of metalenses

Metalenses have emerged as a new optical element or system in recent years, showing superior performance and abundant applications. However, the phase distribut...     

COD: alternative architectures for high speed packet switching

Architectures for packet switches are approaching the limit of electronic switching speed. This raises the question of how best to utilize advances in photonic technology to enable higher speeds. The authors introduce cascaded optical delay line (COD) architectures. The COD architectures utilize an extremely simple distributed electronic control algorithm to configure the states of 2×2 photonic switches and use optical fiber delay lines to temporarily buffer packets if necessary. The simplicity of the architectures may also make them suitable for “lightweight” all-electronic implementations. For optical implementations, the number of 2×2 photonic switches used is a significant factor determining cost. The authors present a “baseline” architecture for a 2×2 buffered packet switch that is work conserving and has the first-in, first-out (FIFO) property. If the arrival processes are independent and without memory, the maximum utilization factor is ρ, and the maximum acceptable packet loss probability is ϵ, then the required number of 2×2 photonic switches is O(log(ϵ)/log(γ)), where γ=ρ²/(ρ²+4-4ρ). If one modifies the baseline architecture by changing the delay line lengths then the system is no longer work conserving and loses the FIFO property, but the required number of 2×2 photonic switches is reduced to O(log[log(ϵ)/log(γ)]). The required number of 2×2 photonic switches is essentially insensitive to the distribution of packet arrivals, but long delay lines are required for bursty traffic     

An indium phosphide MMIC amplifier for 180-205 GHz

This paper describes a high-performance indium phosphide (InP) monolithic microwave integrated circuit (MMIC) amplifier, which has been developed for application in radioastronomy and imaging-array receivers. Implemented using coplanar waveguide, the six-stage amplifier exhibits 15 db gain, 10 dB input and output return loss, and low noise figure over the 180-205 GHz frequency range. Only one design pass was needed to obtain excellent agreement between the predicted and measured characteristics of the circuit, a unique achievement in this frequency band. The circuit is also the first 180-205 GHz amplifier designed for and successfully fabricated using TRW's standard 0.1-μm InP HEMT process     

Functionalization of Graphene Oxide Films with Au and MoOx Nanoparticles as Efficient p‐Contact Electrodes for Inverted Planar Perovskite Solar Cells

A graphene oxide (GO) film is functionalized with metal (Au) and metal‐oxide (MoO_x) nanoparticles (NPs) as a hole‐extraction layer for high‐performance inverted planar‐heterojunction perovskite solar cells (PSCs). These NPs can increase the work function of GO, which is confirmed with X‐ray photoelectron spectra, Kelvin probe force microscopy, and ultraviolet photoelectron spectra measurements. The down‐shifts of work functions lead to a decreased level of potential energy and hence increased V_oc of the PSC devices. Although the GO‐AuNP film shows rapid hole extraction and increased V_oc, a J_sc improvement is not observed because of localization of the extracted holes inside the AuNP that leads to rapid charge recombination, which is confirmed with transient photoelectric measurements. The power conversion efficiency (PCE) of the GO‐AuNP device attains 14.6%, which is comparable with that of the GO‐based device (14.4%). In contrast, the rapid hole extraction from perovskite to the GO‐MoO_x layer does not cause trapping of holes and delocalization of holes in the GO film accelerates rapid charge transfer to the indium tin oxide substrate; charge recombination in the perovskite/GO‐MoO_x interface is hence significantly retarded. The GO‐MoO_x device consequently shows significantly enhanced V_oc and J_sc, for which its device performance attains PCE of 16.7% with great reproducibility and enduring stability.     

大尺寸TFT-LCD电视的彩色和图像增强

最近几年,薄膜晶体管液晶显示器(TFT-LCD)技术取得了快速而显著的进步,其性能超过了PDP、CRT以及投影显示。毫无疑问,TFT-LCD已经成为高清电视应用的最佳实现方案。本文将介绍进一步增强大尺寸LCD电视的彩色和图像性能的技术。