Signal extraction with frequency arrangement (SEFA) andsuperimposed subcarrier modulation (SSM) schemes in fiber-orientedwireless access systems

This paper describes technologies for the improvement of the noise and nonlinearity characteristics of wireless access systems based on subcarrier optical transmission. First, the superimposed subcarrier modulation (SSM) technique is proposed to reduce the reflection noise induced by fiber connectors. We experimentally confirmed that the proposed method reduces this noise, and we found the optimum frequency and power of the superimposed subcarrier, SSM design methodology is also presented, taking both noise and nonlinearity into account. Second, signal extraction with frequency arrangement (SEFA) is proposed for increasing the optical modulation index, because the third-order intermodulation distortion (IM3) produced by the optical devices can be ignored. Simulation results show that SEFA greatly improves the transmission performance in terms of both the ratio of desired-to-undesired signal and the receiver sensitivity under Rayleigh fading. Combining the SSM and SEFA is also considered, for use with FP-LDs or DFB-LDs. These technologies will enable cheaper FP-LD implementation in fiber-oriented wireless access systems     

Eddy current testing by upgraded microloop magnetic sensor array

A micro-eddy current testing (ECT) probe, which consists of a planar microloop inductive magnetic sensor array and a pancake-type exciting coil, was developed to upgrade the ECT technology, especially as it is used for inspecting steam generator tubing in a pressurized nuclear power plant (PWR). Eddy currents and resultant magnetic fields are perturbed due to a flaw in a conductor. The flaw is detected via perturbation of the electromotive force (EMF) and phase from the array. Flaws manufactured by electric discharge machining in INCONEL 600 planar specimens, the thickness of which was 1.25 mm, were detected and reconstructed by using stacked database and simplified algorithm. Even an outer-edged 10 percent flaw could be detected. Measured EMF and phase signals were compared with numerical results obtained by using a three-dimensional eddy current and field analysis code and then verified. The experiment confirmed that the spatial resolution of detection of the micro-ECT probe is superior to that of the conventional pancake-type ECT probe. Finally, it was demonstrated that it is possible to establish the same measurement speed using the micro-ECT probe as it is by using the pancake-type ECT probe.     

Wide-frequency fiber-optic phase modulator using piezoelectricpolymer coating

The highly sensitive response of a fiber-optic phase modulator that is coated with 80-90-μm-thick vinylidene fluoride/trifluoroethylene copolymer on an 80-μm-diameter single-mode fiber and made piezoactive by radial poling is demonstrated over a wide frequency range, from 500 Hz to 50 MHz. In the range of 10 kHz up to 2 MHz, a relatively flat response is measured, whereas at high frequencies between 6 and 50 MHz, the phase modulation exhibits multiple peaks dominated by radial resonances of the fiber-jacket composite. Theoretical considerations on the phase shift and experimental results are given     

A 68-ns 4-Mbit CMOS EPROM with high-noise-immunity design

In a VLSI memory, noise generated by its own operation is a serious problem. The noise disturbs data sensing, especially in EPROMs which have a single-ended sensing scheme. To develop high-density and high-speed EPROMs, it is necessary to solve the noise problems. Incorrect EPROM functions due to the noise are discussed. High-noise-immunity circuit techniques for stable data sensing and high-speed access time are proposed. These are divided bit-line layout, reference line with dummy bit lines, and a chip-enable transition detector. Using these circuit techniques and 0.8-μm n-well CMOS technology, a 512 K×8-b CMOS EPROM was developed. A 68-ns access time was achieved. The die size is 5.62 mm×15.30 mm, and it is assembled in a 600-mil cerdip package     

Comparison of the effects of thyroxine and triiodothyronine on protein turnover and apoptosis in primary chick muscle cell cultures

Primary chick muscle cells were treated with physiological level of thyroxine (T4) or triiodothyronine (T3) to examine the effects of the hormones on growth, protein turnover, and apoptosis of the cells. Creatine kinase activity, as an index of differentiation, was increased by both T4 and T3. Even when the conversion from T4 to T3 was blocked by iopanoic acid, T4 increased creatine kinase activity. The rate of protein degradation estimated from [3H] tyrosine release was increased by T3 but not by T4. DNA cleavage and fragmentation, as indices of apoptosis, were induced by T3 but not by T4. These results show that T4 stimulates cell differentiation but not protein degradation and apoptosis in primary chick muscle cells, while all events are stimulated by T3.     

Separate or simultaneous immobilization of glucose oxidase and peroxidase on latex particles and their function

Glucose oxidase and peroxidase were immobilized individually or simultaneously on aminated latex particles by using sodium meta-periodide and borohydride. The amount of immobilized enzymes and their activity depended on the surface potential of particles and the surface density of their own, respectively. In the simultaneous immobilization of two enzymes, the predominant immobilization of peroxidase is attributed to higher carbohydrate content in peroxidase compared with that in glucose oxidase. Simultaneously immobilized enzymes worked better in the determination of glucose than the mixture of separately immobilized ones because of the close proximity of the two enzymes.     

Modification of primary structures of hairpin ribozymes for probing active conformations

Hairpin ribozymes consist of two stem-loop domains, and these domains are assumed to interact with each other to produce the self-cleavage activity. We have studied the relationship of the tertiary structure of the hairpin ribozyme and the cleavage activity by dividing and re-joining the domains. A hairpin ribozyme (E50) was divided at the hinge region, and the main part was joined to a substrate (S1) using tri- or penta-cytidylates. These ribozymes retained the cleavage activity in the presence of the rest of the molecule, indicating that the active conformation could be maintained if the two domains interacted with each other. Based on the these results, we designed a new type of hairpin ribozyme by replacing one of the domains. To maintain the interaction of the domains, oligocytidylates were inserted at a junction. These reversely jointed ribozyme complexes showed cleavage activity that was dependent on the linker lengths. These modifications in the primary structure of the hairpin ribozyme confirm the structural requirement for the catalytic reaction and provide information for the correlation of the tertiary structure with the cleavage of the hairpin ribozyme.     

Successful enhancement of lifetime for SiO/sub 2/ on 4H-SiC by N/sub 2/O anneal

Time-dependent dielectric breakdown (TDDB) measurement by constant current stress has been performed to investigate the oxide (SiO/sub 2/) reliability grown on n-type 4H-SiC. At 300K, the intrinsic injected charge to breakdown (Q/sub BD/) of thermally grown SiO/sub 2/ in wet O/sub 2/ ambience is about 0.1 C/cm/sup 2/, whereas N/sub 2/O anneal after the thermal oxidation results in the drastic improvement of the reliability. The intrinsic Q/sub BD/ of N/sub 2/O annealed SiO/sub 2/ is found to be 10 C/cm/sup 2/, which is two orders of magnitude larger than that of the oxide without N/sub 2/O anneal, suggesting that the quality of SiO/sub 2/ and/or SiO/sub 2//SiC interface is improved. TDDB measurement has been also performed at high temperatures up to 423 K. The activation energy of oxide lifetime estimated from time to failure of 80% is 0.35 and 0.10 eV for the oxide with and without N/sub 2/O anneal, respectively.