A New Modified Gaussian Approximation Detector for Space-Time Bit-Interleaved Coded Modulation Schemes

To reduce the receiver complexity of the space-time bit-interleaved coded modulation (ST-BICM) scheme, this letter describes a turbo-type iterative structure consisting of a modified Gaussian approximation (MGA) detector and an a posteriori probability (APP) decoder. Utilizing the characteristics of the interleaving and the central limited theoretic, the MGA detector first assumes the superposition of the transmitted signals as a Gaussian random variable. Then, P most significant signal combinations are identified to calculate the log-likelihood ratio of each bit. Without any pre-process on the received signals, the proposed method is free of matrix inverse operation and can be applied in systems with more transmit antennas than receive antennas. Furthermore, the performance of the MGA approaches that of the optimal detection     

Oxygen glow discharge experiment to remove deposited layers and to release trapped hydrogen isotopes in HT-7 superconducting tokamak

An experiment to remove re-deposited layers and to release hydrogen using a glow discharge in oxygen (O-GDC) has been performed in the HT-7 superconducting tokamak. In the absence of magnetic fields, the O-GDC wall conditioning had produced rapid, controlled co-deposit removal. Average removal rates, 5.2 × 10²² H-atoms/h, 5.65 × 10²¹ D-atoms/h and 5.53 × 10²² C-atoms/h, respectively, were obtained during 145 min O-GDC experiment in the pressure range 0.5-1.5 Pa. The corresponding removal rate of co-deposited films was ∼1.19 μm/day (26.5 g/day for carbon) based on an area of 12 m². Compared to thermo-oxidation and O-ICR experiment, high pressure O-GDC wall conditioning promoted the oxidation and improved the C and D atoms removal. In the O-GDC experiment, the removal rates of H-atoms and D-atoms as H₂O, HDO and D₂O were higher than that of H₂ and D₂ by factors of about 20 and 50, respectively. During the 145 min O-GDC experiment, about 14.5% O-atoms were converted into carbon oxides and hydroxides, and about 5.37 × 10²² O-atoms were adsorbed on the walls corresponding to a coverage of 4.5 × 10²¹ O/m² on an wall area of 12 m². In a 100 min helium glow discharge (He-GDC) following the O-GDC experiment, 1.53 × 10²² O-atoms, about 28.5% oxygen retained on the walls, were removed. The removal rate of H-atoms in He-GDC cleaning after O-GDC experiment was lower than that in He-GDC cleaning before O-GDC experiment, which indicates that the O-GDC wall conditioning had effectively reduced hydrogen retention on the walls.     

Scattering from bandlimited fractal fibers

The scattering of electromagnetic or optical waves from tenuous dielectric fibers characterized by bandlimited fractal surfaces is considered. The role of several fractal dimensions is noted, and one suitable for this problem is identified. It is found that in the fractal regime, the Rayleigh-Gans differential scattering cross section as a function of the normalized size parameter exhibits a power-law relation reminiscent of that associated with light scattering from fractal clusters and small-angle X-ray and neutron scattering by porous material. This power-law relation is monotonically related to an appropriate fractal dimension and variance of the fiber surface     

Multirobot-Based Nanoassembly Planning with Automated Path Generation

In this paper, a novel approach of automated multirobot nanoassembly planning is presented. This approach uses an improved self-organizing map to coordinate assembly tasks of nanorobots while generating optimized motion paths at run time with a modified shunting neural network. It is capable of synchronizing multiple nanorobots working simultaneously and efficiently on the assembly of swarms of objects in the presence of obstacles and environmental uncertainty. Operation of the presented approach is demonstrated with experiments at the end of the paper.     

La doping effects on intergrowth Bi2WO6–Bi3TiNbO9 ferroelectrics

La doping effects on intergrowth Bi₂WO₆–Bi₃TiNbO₉ ferroelectric ceramics were studied by X-ray diffraction, electron probe microanalysis and dielectric spectroscopy. It was found that the La³⁺ distribution, ferroelectric phase transition and dielectric relaxation behavior are apparently affected by La doping. With increasing La³⁺ content, the site of dopant ion varies, the grain growth of Bi₅TiNbWO₁₅ is restrained, the Curie temperature is reduced and broadened. Furthermore, two dielectric relaxation loss peaks were observed both in temperature and frequency spectra. The calculated relaxation parameters revealed the oxygen vacancy related to the relaxation process.     

Left-handed transmission lines at millimetre and sub-millimetre wavelengths

Co-planar strip (CPS) transmission lines, aimed at operating up to sub-millimetre wavelengths, were periodically loaded by lumped capacitances and inductances in series and shunt configuration, respectively. Under this condition, propagation on the line is backward with group and phase velocities of opposite signs. The transmission lines were fabricated onto a quartz substrate by e-beam patterning and thin film deposition, silicon nitride and gold layers, on a deep sub-micron scale (~200 nm). A direct evidence of left-handedness between 160 and 380 GHz was achieved via the tracking of phase advance in a differential phase experiment using electro-optic sampling. The comparison between modelling results by electromagnetic full wave circuit analysis and experiment was performed in the time and frequency domains. It shows a good agreement in the dispersion characteristics and ultra-fast variations in the transmitted signals. At last, we took benefit of a lumped element fitting approach in order to discuss of the frequency capability of this non-resonant approach     

Local Structure and Valence State of Mn in Ga1−x Mn x N Epilayers

Mn has been incorporated in epilayers of the large-gap semiconductor GaN grown by molecular beam epitaxy using a nitrogen plasma cell. Detailed extended X-ray absorption fine structure (EXAFS) studies of a Ga_0.98Mn_0.02N epilayer confirm that the Mn atoms substitute the Ga atoms, with an increase by 2.7% of the distance to the nearest nitrogen atoms. Near-edge spectroscopy results tend to indicate that the valence state of Mn is slightly higher than 3+, while EXAFS analysis suggests an electron transfer to the N neighbors.     

Effect of C/Ti ratio on the laser ignited self-propagating high-temperature synthesis reaction of Al-Ti-C system for fabricating TiC/Al composites

TiC/Al composite was successfully synthesized utilizing laser ignited self-propagating high-temperature synthesis (SHS) of Al-C-Ti system with the different C/Ti molar ratio. When the molar ratio of C to Ti is below 1:1 in the starting materials, in addition to fine TiC particulates, a large amount of Al₃Ti phase was found in the composites; however, when the molar ratio of C to Ti is 1:1 in the starting materials, the Al₃Ti phase was almost completely eliminated and the distribution of TiC particulates generally appeared to be more homogeneous throughout the products synthesized.