Performance and reliability of high radiance InGaAsP/InP DH LED́s operating in the 1.15-1.5 µm wavelength region

The performance and reliability of InGaAsP/InP double heterostructure (DH) light emitting diodes (LED's) have been investigated over a wide range of emission wavelengths1.15-1.5 mum. High radiance performance has been achieved by growing optimized DH structures and adopting a method of coupling a monolithic-lensed LED to a spherical-ended fiber. Interface instability previously encountered in the liquid phase epitaxy (LPE) to grow a DH for 1.5 μm wavelength has been eliminated by a new growth method using a reduced temperature. LED's exhibiting typical output powers of 50, 44, and 21 μW at 100 mA, measured at the end of a 50 μm core 0.20 NA graded-index fiber with a length of 1 m, have been realized, respectively, at wavelengths of 1.15, 1.27, and 1.5 μm. The spectral width, coupled power and its temperature dependence, and the cutoff frequency have been analyzed in terms of the emission wavelength. Operating lives of LED's at three different wavelengths have been estimated from the result of accelerated aging carried out at the ambient temperature of 200°C and at a constant current of 100 mA. It has been found that the degradation rate exhibits no dependence on the wavelength confirming the same value of half-lives in excess of 10⁹h for the 60°C operation.     

Improving performance of AlGaAs/GaAs monolithic laser/FET by GRIN-SCH quantum-well laser

An AlGaAs/GaAs graded-index-waveguide separate-confinement-heterostructure (GRIN-SCH) single-quantum-well (SQW) laser has been monolithically integrated with a couple of field-effect-transistor drivers on a semi-insulating GaAs substrate. The adoption of the GRIN-SCH SQW laser has enabled an improvement in the laser/FET performance, exhibiting a low laser threshold current (12 mA) and a high sensitivity of the output light power to the input gate voltage (7.5 mW/facet/V).     

Use of acid gel electrophoresis in the characterisation of ‘B’ hordein protein in relation to malting quality and mildew resistance of barley

The ‘B’ polypeptides of the storage protein (hordein) of barley were studied in 84 varieties. On the basis of acid gel electrophoresis the varieties were classified into 13 distinct groups. Contrary to the suggestion that varieties preferred for malting tend to show less intensity of staining of the faster moving bands of the ‘B’ fraction of hordein, no consistent association was found in this study. Thus the malting potential of some varieties may be less affected by protein composition than by other factors. The genetic linkage between the Hor-2 locus, specifying the ‘B’ group of polypeptides, and the Mlalocus, determining resistance to powdery mildew (Erysiphe graminis), was illustrated by the similar groupings of varieties carrying the same resistance alleles, but exceptions were observed. Examples of the inheritance of hordein patterns are illustrated and discussed.     

Thermal conductivity of polymer composites with close-packed structure of nano and micro fillers

Thermal conductivity of polymer composites with nano and micro fillers has been investigated numerically and experimentally. The nano fillers used were multi-walled carbon nanotubes (MWNTs) and alumina nanoparticles, and the spherical alumina particles were selected as the micro fillers. A periodic unit cell with a random close-packed structure was created using a packing algorithm that treat the micro filler as spheres. Finite element analyses were also performed to predict the potential of nano fillers to enhance thermal conductivity of the composites and to analyze the effect of microstructure of micro fillers. Additionally, the polymer composites with nano and micro fillers were made and the thermal conductivity of the composites were measured. The results showed that the addition of MWNTs to the matrix lead to a large increase in thermal conductivity of the composites. The proposed thermal model predicted a thermal conductivity in good agreement with experiment.     

Nuclear magnetic relaxation studies of coal

The techniques of both pulsed nuclear magnetic resonance (n.m.r.) and electron spin resonance (e.s.r.) were applied to clarify the nature of coal. The spin-lattice relaxation time (T_1n) and the spin-spin relaxation time (T_2n) for protons were measured. At room temperature T_1n varies with rank of coal and shows a maximum value at about 86% carbon of coal. The values of T_1n for the samples selected increase in the order of extraction residue, parent coal and pyridine extract respectively. The variation of T_1n during solvent treatment reflects the different circumstances of protons in such a heterogeneous system as coal. From spin-spin relaxation time (T_2n) measurements two relaxation regions, that is an immobile region and a relatively free one, are deduced.     

Nuclear magnetic proton relaxation studies of oxidized coals

Coals of NCB rank 301 a (coking), 502 (caking) and 802 (very weakly caking) are oxidized in air at 373 K or 383 K for up to 42 days. Spin-lattice and spin-spin relaxation times, T₁ and T₂ respectively, of oxidized coals are measured using a Bruker SXP 4–100 and FT spectrometer. Free radical concentrations in the coals are obtained using a JES PE e.s.r. spectrometer. Infrared spectra of oxidized coals are obtained and optical textures of cokes from fresh and oxidized coals are assessed by optical microscopy. For two coking coals, decreasing values of T₁, and increasing concentration of free radicals occurred with oxidation at 383 K to 16 and 28 days. Thereupon values of T₁, increased and free radical concentrations decreased with further progressive oxidation. At the point of inflexion in properties, resultant cokes from the coals ceased to shown any anisotropy in their optical textures and became isotropic resembling cokes from low-rank coals. For the caking coals, T₁ increased at all stages of oxidation to 42 days with decreasing concentrations of free radicals. Two values of T₂ were found in each coal corresponding to a rigid and mobile component ((T₂)_r < (T₂)_m). The rigid component (T₂)_r was not affected by oxidation but values of (T₂)_m decreased with increasing duration of oxidation. It is considered that coking and caking coals exhibit different effects of oxidation with perhaps phenols and quinones in caking coals acting as inhibitors to the growth of stable free radicals. Oxidized coking coal may behave like fresh caking coal.     

Examination and Linearization of Torque Control System for Direct Torque Controlled IPMSM

This paper examines the torque response based on direct torque control (DTC) for an interior permanent magnet synchronous motor. DTC with a PI controller for torque control is used in this paper. The relationship between the gains of the PI controller and the torque response is derived based on the transfer function of the torque control loop. In addition, this paper discusses the influence of the nonlinearity of the torque control loop on the torque response. It also proposes a linearization method for the torque control loop based on gain scheduling, and improvement of torque response is achieved. The effectiveness of the proposed method is verified by both simulation and experimental results.      

Performance Analysis of OFDM Repeater Networks with Spatial Fading Correlation

This paper analyzes the performance of the OFDM diversity systems with the spatial fading correlation when the network includes an RF repeater. In case of OFDM transmission, since the combining scheme is usually employed in the frequency domain, the correlation between different subchannels should be considered. In a multipath channel, correlation varies over subchannels depending on the channel delay profile and the spatial correlation between each individual delayed paths. In this study, a multipath channel is constructed by the repeated signal instead of natural multipath due to cluttered environments and the system performance with spatial correlation per subcarrier is evaluated. Previously, it is reported that the effect of correlation can be reduced by the Time Shifted Sampling (TSS) technique which relies on the multipath diversity. Numerical results indicate that the TSS technique is also effective in reducing the effect of correlation for the multipath channels constructed by the repeaters.     

Adjacent Channel Interference Cancellation Using Orthogonal Precoding for Fractional Sampling OFDM Receiver

To achieve diversity with a single antenna, fractional sampling has been proposed. The imaging component of a desired signal must be transmitted by increasing the baseband filter bandwidth. This paper proposes and evaluates a system in which the imaging component is transmitted on the adjacent channel to the desired signal. The adjacent channel interference is cancelled by the precoding generated based on the basis of the channel state information of all the terminals. In this paper, the performance with perfect feedback and limited feedback is evaluated. Numerical results obtained through computer simulation show that the proposed scheme with a 6 bit random codebook for QPSK modulation improves the performance compared with that with the conventional scheme in the low $E_b/N_0$ region.