Spanning Trees with a Bounded Number of Branch Vertices in a Claw-Free Graph

Let k be a non-negative integer. A branch vertex of a tree is a vertex of degree at least three. We show two sufficient conditions for a connected claw-free graph to have a spanning tree with a bounded number of branch vertices: (i) A connected claw-free graph has a spanning tree with at most k branch vertices if its independence number is at most 2k + 2. (ii) A connected claw-free graph of order n has a spanning tree with at most one branch vertex if the degree sum of any five independent vertices is at least n ? 2. These conditions are best possible. A related conjecture also is proposed.     

NMR-based characterization of a novel yellow chlorophyll catabolite, Ed-YCC,isolated from Egeria densa

A novel yellow chlorophyll catabolite, Ed-YCC, was isolated from leaves detached from Egeria densa shoots, in which chlorophyll degradation and anthocyanin synthesis were induced in 0.1 M fructose solution under light illumination as a plant senescence process, a model of autumnal leaf coloration. Structure elucidation was accomplished by various NMR techniques including 2D-INADEQUATE.     

Magnetoresistance and interlayer exchange coupling in perovskite manganite junctions

We study magnetoresistance (MR) and interlayer exchange coupling (IEC) in perovskite manganite junctions. We show that in La_2/3Sr_1/3MnO₃/SrTiO₃/La_2/3Sr_1/3MnO₃ tunneling junctions, the MR ratio remains finite up to high temperatures near T_C of bulk manganites. In the case of La_2/3Ba_1/3MnO₃/LaNiO₃/La_2/3Ba_1/3MnO₃ metallic trilayers, we predict that the oscillation period of the IEC constant is dramatically changed by hole doping into the LaNiO₃ spacer, while the MR ratio is relatively unaffected.     

Generation of 10 GHz similariton pulse trains from 1.2 km-long erbium-doped fibre amplifier for application to multi-wavelength pulse sources

A 10 GHz similariton pulse train is generated from a 1.2 km-long erbium-doped fibre amplifier and applied to a multi-wavelength pulse source. Slicing the spectrum of the similariton pulse train, a 10 Gbit/s transmitter was constructed, which has excellent Q-factors of over 25.3 dB in the entire bandwidth. Such uniform characteristics of the sliced pulse train originate from the high spectral flatness of the similariton.     

Interfacial approach tod-dimensional ±J Ising models in the neighborhood of the ferromagnetic phase boundary

Two- and three-dimensional ±J Ising models in the neighborhood of the ferromagnetic phase (FP) boundary in the concentration-temperature (p-T) plane are studied, investigating the size dependence of interfacial free energies calculated by a transfer matrix method. Thep andT dependences of two stiffness exponents relevant to the FP and the nonferromagnetic ordered phase lead to the following results in two dimensions, giving a unified view. It is confirmed that the random antiphase state (RAS) exists in contact with the vertical FP boundary. Spatial fluctuations are dominant near the vertical boundary, which is separated by the Nishimori line from the remaining FP boundary governed by thermal fluctuations. The RAS is a kind of Mattis spin glass such that it changes to the FP smoothly with nonsingular physical connectivity, but with a percolation singularity of its ferromagnetic part. Universal finite-size critical amplitudes are consistent with them. Results in three dimensions give only suggestions which are similar to the two-dimensional results. These results suggest important insight into spin-glass properties in higher dimensions.     

New two-mode bistability in an asymmetric absorptive multisectionlaser diode: theoretical analysis

A novel two-mode bistable laser diode (TMBLD) with an asymmetric cavity configuration is proposed and analyzed. It consists of a gain region, a saturable absorber region, and a set of mode-selective mirrors (or filters). These elements are arranged such that the saturable absorber acts as an intracavity loss for one mode and a bleachable absorber external to the cavity of the other mode. Both modes share the same gain medium and compete for the same gain. Bleaching of the absorber leads to a switching of the modes and possible bistability. This two-mode bistability results from the complementary processes of mode competition in the gain section and the mode-dependent effective cross section of the saturable absorber. A rate equation analysis of the device indicates that a switching time less than 200 ps and a modulation rate over 3 Gb/s should be obtainable     

Measurements of 220 GHz atmospheric opacity on Mt. Fuji with a radiometer/radome system

We measured atmospheric opacity at 220 GHz at the summit of Mt. Fuji (alt. 3776 m) about one year in order to explore a feasibility of submillimeter-wave astronomical observations. For this purpose, a 220 GHz radiometer system enclosed in a radome (51×51×62 cm³) has been developed. The 220 GHz opacity was lower than 0.06 for a significant fraction (～ 45 %) of time from November 1994 to March 1995. Diurnal variation of the opacity at the summit of Mt. Fuji is so small that continuous observation at submillimeter-wave is possible through day and night. Yearly variation of the opacity is studied from water vapor pressure data measured at the weather station for the past 3 years. To prevent accumulation of ice and snow on the Gore-Tex membrane in the radome, the outer membrane was supplied with a thermal flux of 0.63 kW m^?2 and the adjacent metal radome surfaces were supplied with a flux of ～0.9 kW m^?2. We evaluate from the 220 GHz transmission data that this heat flux is sufficient to keep the membrane on the radome free of ice and snow during 83 % of the time in 5 winter months. The summit of Mt. Fuji appears to be a promising site for submillimeter-wave observations.     

Properties of High-Frequency Conducted Noise from Automotive Electrical Accessories

This paper describes generation mechanisms and electrical characteristics of high-frequency conducted noise from electrical contacts and accessory drive/control motors, which may cause logic errors in automotive electronic devices. High-frequency conducted noise due to contacts in both horn sounding and lighting circuits results from spark discharge initiated by breakdown across the contacts; and a showering arc which sustains spark discharge for hundreds of microseconds was observed at contacts in lighting circuits. High-frequency conducted noise due to accessory drive/control motors was caused by reactance voltage fluctuations and commutator sparks. To analyze electrical characteristics of high-frequency conducted noise, a measuring system for amplitude distributions in both the time domain and the frequency domain was developed, and an attempt was made to fit a distribution pattern to observed data in each domain. In the time domain, the noise voltages due to contact breaking were distributed between 360 and 530 V. The distribution pattern in the time domain fitted closely to the normal distribution curve, while the pattern in the frequency domain fitted to the lognormal distribution curve.     

Influence of pinning trap in Ti/4H–SiC Schottky barrier diode

Ti/4H–SiC Schottky barrier diode without any intentional edge termination is fabricated. The obtained properties, low on-resistance of 3 mΩ cm² and low leakage current of 10⁻⁴ A/cm² at 1000 V, are evaluated by device simulation considering pinning at metal/semiconductor interface. The breakdown voltage is explained by minimization of electric field enhancement at the Schottky electrode edge due to pinning. The leakage current corresponds to Schottky barrier tunneling current depending on drift layer doping and Schottky barrier height.