Determination of tensile forces to enhance the supply stability of reinforced fiber

The manufacturing process of long fiber thermoplastic is initiated by supplying reinforced fiber wound in a spool dispenser. If problems such as tangling or kinking occur in the apparatus used for supplying the reinforced fiber in the long-fiber thermoplastic direct process, the productivity of the long-fiber thermoplastic decreases. Therefore, it is important to enhance the supply stability of reinforced fiber. In general, the increase in supply stability can be achieved by maintaining a steady balloon shape that is controlled by the unwinding velocity or tensile force of the reinforced fiber. In this research, the range of suitable tensile force was determined under the assumption that the unwinding velocity remained constant. The reinforced fiber was assumed to be inextensible, homogeneous, and isotropic and to have uniform density. The transient-state unwinding equation of motion to analyze the unwinding motion of reinforced fiber can be derived by using Hamilton’s principle for an open system in which mass can change within a control volume. In the process of solving the transient-state unwinding equation of motion, the exact two-point boundary conditions are adopted for each time step.     

Analysis of unbound materials in carbon‐black‐filled NR vulcanizates

Extraction of unbound materials from carbon‐black‐filled natural rubber (NR) vulcanizates with different cure systems was studied using various solvents with different dielectric constants of n‐hexane, toluene, THF, acetone, and acetonitrile. The extraction was performed at room temperature and 40°C for 2 days and in the boiling solvent for 8 h. Amounts of extracted materials from the NR vulcanizates increase by increasing the temperature. Amounts of extracted materials from the NR vulcanizates with n‐hexane, toluene, and THF are more than those with acetone and acetonitrile. Amounts of extracted materials from the NR vulcanizate with a high crosslink density are less than those from the NR vulcanizate with a low one. Thermogravimetric analysis of the NR vulcanizates before and after the extraction were carried out to investigate components of the extracted materials. It was found that there were polymer components and metal complexes, as well as organic matters with a low molecular weight in the extracted materials. Abilities of the solvents to extract unbound materials from the NR vulcanizates were discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1995–2005, 1999     

The synthesis of new chiral salen complexes immobilized on MCM‐41 by grafting and their catalytic activity in the asymmetric borohydride reduction of ketones

The new chiral salen complexes were synthesized and supported on mesoporous MCM‐41 through the condensation of 3‐aminopropyltrimethoxysilane and 2,6‐diformyl‐4‐tert‐butylphenol by the multi‐grafting method. The immobilized optically active Co(II) salen complexes showed a very high enantioselectivity in the asymmetric borohydride reduction of aromatic ketones. The chiral salen Co(II) complexes immobilized over MCM‐41 were stable during the reaction and exhibited a relatively high enantioselectivity for the reduction of ketones as compared with the homogeneous salen catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Removal of N-Nitrosamines and Their Precursors by Nanofiltration and Reverse Osmosis Membranes

Rejection of selected N-nitrosamines, a group of probable human carcinogens, and their precursors by nanofiltration (NF) and brackish water reverse osmosis (BWRO) membranes was evaluated using a bench-scale cross-flow filtration apparatus. The tested nitrosamines included N-nitrosodimethylamine, N-nitrosomethylethylamine, N-nitrosopyrrolidine, N-nitrosodiethylamine, N-nitrosodi-n-propylamine, and N-nitrosodi-n-butylamine. The target nitrosamine precursors included secondary amines such as dimethylamine, methylethylamine, diethylamine, and dipropylamine. Rejection of nitrosamines varied greatly depending on the tested membranes (9–75% for NF membranes and 54–97% for BWRO membranes) and the molecular weight of nitrosamines. Experimental data obtained with the BWRO membranes matched well with an irreversible thermodynamic model coupled with film theory. The model further suggested that effective diffusion of nitrosamines through the BWRO membranes is responsible for the relatively low rejections observed experimentally, and the aqueous diffusivity of nitrosamines could be used as an accurate measure of nitrosamine permeability through these membranes. The steady-state rejection of all the tested nitrosamine precursors reached over 98%. This study suggests that a strategy for membrane-based water treatment processes to reduce nitrosamines should consider the removal of precursors before nitrosamines are formed during subsequent disinfection and water distribution.     

Probability-Based Optimization of Inter-Sensing Duration and Power Control in Cognitive Radio

Probability-based strategies are proposed in this letter to determine the optimal inter-sensing duration and power control for cognitive radio (CR). With utilization of the statistics of licensed band occupancy, appropriate inter-sensing duration is determined to capture the recurrence of spectrum opportunity in time when the licensed signal is detected, or to achieve the maximum spectrum efficiency under a certain level of interference with licensed communication when the licensed signal is declared absent. Transmit power is varied dynamically according to the non-interfering probability at each sample so as to increase the transmission rate and decrease the interference power.     

Fracture Mechanics of Solder Bumps During Ball Shear Testing: Effect of Bump Size

This paper examines the mechanics of ball shear testing with the objective of understanding the mechanism by which the maximum shear force and the rate of crack growth is dependent on the solder bump size. For this, Pb-Sn solder bumps with diameters between 460 μm and 760 μm are soldered to 400 μm-diameter Cu pads and subjected to ball shear testing. In spite of the constant interface area, the bump size significantly impacts the measured shear fracture force and the crack growth rate. Both the fracture force and the crack growth rate increase with bump size, and in the case of the fracture force, the increase is almost linear. Our analysis finds that the linear increase in the fracture force is a result of the bump deformation force, which increases with bump size. A simple model that accounts for the deformation force component is developed and used to extract the true interface fracture force. The estimated true interface fracture force is found to vary little with bump size, tightly converging to the 40 MPa to 48 MPa range. On the other hand, the dependence of crack growth rate on bump size is found to result from the higher degree of rotational moment associated with larger bumps.     

Nanogap Array Fabrication Using Doubly Clamped Freestanding Silicon Nanowires and Angle Evaporations

We present a simple semiconductor process to fabricate nanogap arrays for application in molecular electronics and nano‐bio electronics using a combination of freestanding silicon nanowires and angle evaporation. The gap distance is modulated using the height of the silicon dioxide, the width of the Si nanowires, and the evaporation angle. In addition, we fabricate and apply the nanogap arrays in single‐electron transistors using DNA‐linked Au nanoparticles for the detection of DNA hybridization.     

Surface Modification of Sericite Using TiO2 Powders Prepared by Alkoxide Hydrolysis: Whiteness and SPF Indices of TiO2-Adsorbed Sericite

Titania (TiO₂) powders have been prepared from the 0.025-M titanium isopropoxide/ethanol solution and the 0.5-M distilled water/ethanol solution. The prepared TiO₂ powders showed an anatase phase and a rutile phase after heat treatment at 500°C for 2 h and 1000°C for 2 h, respectively. The heterocoagulation adsorption between TiO₂ powder and sericite surface in water was achieved in the range of pH 3.63.7 (where this pH range shows a maximum Zeta-potential difference for two powders). On the other hand, an anomalous transformation behavior appeared in the TiO₂-adsorbed sericite after heat treatment at 1000°C. The surface modification of sericite through the TiO₂-adsorption improved the whiteness as well as the SPF (Sun Protection Factor) indices.