Morphology,electro-optical and dielectric properties of polymer network liquid crystals in visible wavelengths

The correlations among electrical, optical properties and polymer morphologies of polymer network liquid crystals (PNLCs) constructed with various curing parameters are investigated. The experimental results indicate that high UV curing intensity, low curing temperature and high monomer-dopant concentration reduce the sizes of liquid crystal (LC) domains, thereby decreasing field-off response time and light scattering and increasing phase retardation of the PNLC cells. Photoinitiator concentration affects the LC domain size as well. For instance, increase in photoinitiator concentration results in the acceleration of polymerisation and thus decreases LC domain size. This effect increases driving voltages of the PNLC cells. Notably, excessive amounts of photoinitiator increases the LC domain size of the PNLC cell. Furthermore, dielectric measurement reveals that decrease in the LC domain size generally increases the dielectric relaxation frequency of the PNLC cells. When the LC domain size is small enough, the dielectric relaxation frequency of the PNLC cell is further dominated by the monomer concentration owing to the increased densities of polymer networks that facilitate the alignment of LC molecules.     

Robust fabric defect detection and classification using multiple adaptive wavelets

The wavelet transform has been widely used for defect detection and classification in fabric images. The detection and classification performance of the wavelet transform approach is closely related to the selection of the wavelet. Instead of predetermining a wavelet, a method of designing a wavelet to adapt to the detection or classification of fabric defects has been developed. For further improvement of the performance, the paper extends the adaptive wavelet-based methodology from the use of a single adaptive wavelet to multiple adaptive wavelets. For each class of fabric defect, a defect-specific adaptive wavelet was designed to enhance the defect region at one channel of the wavelet transform, where the defect region can be detected by using a simple threshold classifier. Corresponding to the multiple defect-specific adaptive wavelets, the multiscale edge responses to defect regions have been shown to be more efficient in characterising defects, which leads to a new approach to the classification of defects. In comparison with the single adaptive wavelet approach, the use of multiple adaptive wavelets yields better performance on defect detection and classification, especially for defects that are poorly detected by the single adaptive wavelet approach. The proposed method has been evaluated on the inspection of 56 images containing eight classes of fabric defects, and 64 images without defects. In defect detection, 98.2% detection rate and 1.5% false alarm rate were achieved, and in defect classification, 97.5% accuracy was achieved.     

Improvement on the noise performance of InAs-based HEMTs with gate sinking technology

Improvement on the RF and noise performance for 80 nm InAs/In_0.7Ga_0.3As high-electron mobility transistor (HEMT) through gate sinking technology is presented. After gate sinking at 250 °C for 3 min, the device exhibited a high transconductance of 1900 mS/mm at a drain bias of 0.5 V with 1066 mA/mm drain-source saturation current. A current-gain cutoff frequency (f_T) of 113 GHz and a maximum oscillation frequency (f_max) of 110 GHz were achieved at extremely low drain bias of 0.1 V. The 0.08 × 40 μm² device with gate sinking demonstrated 0.82 dB minimum noise figure and 14 dB associated gain at 17 GHz with only 1.14 mW DC power consumption. Significant improvement in RF and noise performance was mainly attributed to the reduction of gate-to-channel distance together with the parasitic source resistance through gate sinking technology.     

Critical comments on “On the constancy of the velocity of light”

A new theory of four-dimensional symmetry introduced by Hsu has been criticized as logically inconsistent. We answer the criticisms that have been raised and show that in fact this theory is not logically inconsistent.Supported in part by the U.S. ERDA, NASA and NRC.     

Large signal characteristics of stimulated Brillouin scattering andGaussian beam phase conjugation

Stimulated Brillouin scattering has an inherent threshold. The characteristics above this threshold must be analyzed in terms of a large signal backward traveling-wave parametric interaction. The conventional treatment is valid only below the threshold of stimulated scattering and is limited to small signals. Here, the large signal theory is applied to Gaussian beam phase conjugation. The results agree in all aspects with recent experimental measurements. It is found that, for phase conjugation mirror applications, the threshold can be eliminated by incorporating an auxiliary end mirror     

Gold Stud Bumps Flip-Chip Bonded onto Copper Electrodes with Titanium and Silver Layers

The purpose of this study was to develop the thermosonic flip-chip bonding process for gold stud bumps bonded onto copper electrodes on an alumina substrate. Copper electrodes were deposited with silver as the bonding layer and with titanium as the diffusion barrier layer. Deposition of these layers on copper electrodes improves the bonding quality between the gold stud bumps and copper electrodes. With appropriate bonding parameters, 100% bondability was achieved. Bonding strength between the gold stud bumps and copper electrodes was much higher than the value converted from the standards of the Joint Electron Device Engineering Council (JEDEC). The effects of process parameters, including bonding force, ultrasonic power, and bonding time, on bonding strength were also investigated. Experimental results indicate that bonding strength increased as bonding force and ultrasonic power increased and did not deteriorate after prolonged storage at elevated temperatures. Thus, the reliability of the high-temperature storage (HTS) test for gold stud bumps flip-chip bonded onto a silver bonding layer and titanium diffusion barrier layer is not a concern. Deposition of these two layers on copper electrodes is an effective and direct method for thermosonic flip-chip bonding of gold stud bumps to a substrate, and ensures excellent bond quality. Applications such as flip-chip bonding of chips with low pin counts or light-emitting diode (LED) packaging are appropriate.     

Analysis of fragmentation data and molecular orbital calculations of small argon ion clusters

Distributions of argon clusters (Ar _n ⁺ wheren=1–27) obtained in a molecular beam/time-of-flight system were analyzed in order to assess the influence of fragmentation. The results from rudimentary pseudopotential molecular calculations were calculated to predict the most stable structures and stabilities for the smaller argon ion sized clusters (Ar _n ⁺ wheren=3−9).