Super-orthogonal space-time-frequency trellis coded OFDM

Super-orthogonal space-time trellis codes (SOSTTCs) given in the literature are full rate and provide full spatial diversity with high coding gain in narrowband quasistatic fading channels. The high number of parallel transitions in their trellis structure restricts their performance in wideband channels where the code performance suffers from multipath. Code design criteria are derived and a computer search based method is proposed to design full-rate optimised SOSTTCs exploiting full spatial and multipath diversity for multiple-input multiple-output orthogonal frequency division multiplexing systems. The proposed codes have codewords defined in space, time, and frequency. We evaluate the codeword error rates of the new 16, 32 and 64-state super-orthogonal space-time-frequency trellis codes for quadrature phase shift keying by computer simulation and show that they provide significant error performance improvement compared to their counterparts with equivalent delay length     

Boundary layer equations and stretching sheet solutions for the modified second grade fluid

A modified second grade non-Newtonian fluid model is considered. The model is a combination of power-law and second grade fluids in which the fluid may exhibit normal stresses, shear thinning or shear thickening behaviors. The equations of motion are derived for two dimensional incompressible flows. The boundary layer equations are derived from the equations. Symmetries of the boundary layer equations are calculated using Lie Group theory. For a special power law index of m = −1, the principal Lie algebra extends. Using one of the symmetries, the partial differential system is transferred to an ordinary differential system. The ordinary differential equations are numerically integrated for the stretching sheet boundary conditions. Effects of power-law index and second grade coefficient on the boundary layers are shown and solutions are contrasted with the usual second grade fluid solutions. The shear stress on the boundary is also calculated.     

Data erasure in Fabry–Perot Diode Lasers: effects of facet reflectivity

ABSTRACT

In this study, the effects of facet reflectivity on the data erasure ability of injection-locked Fabry Perot Laser Diode (FPLD), based on a remodulation method in wavelength division multiplexed passive optical network (WDM PON), were investigated. For this purpose, the feasible front facet reflectivity of FPLD was determined as between 0.2% and 7%, depending on the specified injected power interval. Firstly, the system carried out analysis without applying data at the user end to comprehensively demonstrate how much downstream data was completely erased in FPLD. Then, 2.5 Gb/s of non-return-to-zero (NRZ) data was applied and the results compared with the erased downstream signal without data. The results show that upstream transmission improved with an increase in facet reflectivity between 0.2% and 7%.     

Mechanical behaviour of SiC fibre-reinforced titanium/titanium aluminide hybrid composites

The viability of developing an SiC fibre-reinforced titanium/titanium aluminide hybrid matrix composite was explored. The hybrid composites are expected to be used at temperatures beyond those attainable in conventional titanium matrix composites while improving the damage tolerance of the titanium aluminide matrix composites. The room-temperature mechanical characteristics studied were tensile strength, fracture toughness, low-cycle fatigue life and fatigue crack growth rate. The mechanisms of damage initiation and propagation under various loading conditions were also characterized. The directions for developing a satisfactory composite with hybrid titanium/titanium aluminide matrix are also addressed.     

The effect of niobium on the microstructure of ferritic stainless steel

The effect of different amounts of Nb and of homogenization on the ferritic stainless steels containing 17–18 wt.% Cr was investigated with scanning electron microscopy (SEM), optical microscopy, energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential thermal analysis (DTA). It was observed that M₂₃C₆, NbC and sigma phase formed in these steels. In addition, the formation of Nb₂C was observed in the sample containing 3.0 wt.% Nb. While the amount of Nb increased from 0.5 to 3.0 wt.% Nb, the microhardness of the matrix and the amount of M₂₃C₆ decreased and the toughness of the samples increased. After homogenization, the increase in the toughness of the samples containing 1.5–3.0 wt.%Nb was considerable and impressive.     

Synthesis and characterization of novel polyacrylate-clay sol-gel materials

Organo-functional silanes which were able to form chemical bonds with kaolinite and could also have an affinity to the materials of concern here, were studied by the sol-gel process. Polymethacrylate with trialkoxy silyl functional groups were prepared, hydrolysed and co-condensed with kaolinite. The progress of the hydrolysis, which proceeded very slowly, was followed by Karl-Fischer titration. Thermal behavior was investigated by differential thermal analysis. The extent of the reaction leading to network formation was qualitatively followed by Fourier transform-infrared spectroscopy and X-ray diffraction. Free-radical polymerization was carried out ultrasonically in the presence of a catalyst. Trimethoxy silane end-capped silane was found to be covalently bonded to kaolinite. The copolymers, with various amounts of kaolinite, were then hydrolysed and co-condensed in the presence of a catalyst to yield sol-gel materials which have a controllable combination of properties of both the polymer and kaolinite.     

Preparation of chitosan‐coated magnetite nanoparticles and application for immobilization of laccase

In this study, immobilization of laccase (L) enzyme on magnetite (Fe₃O₄) nanoparticles was achieved, so that the immobilized enzyme could be used repeatedly. For this purpose, Fe₃O₄ nanoparticles were coated and functionalized with chitosan (CS) and laccase from Trametes versicolor was immobilized onto chitosan‐coated magnetic nanoparticles (Fe₃O₄‐CS) by adsorption or covalent binding after activating the hydroxyl groups of chitosan with carbodiimide (EDAC) or cyanuric chloride (CC). For chitosan‐coated magnetic nanoparticles, the thickness of CS layer was estimated as 1.0–4.8 nm by TEM, isoelectric point was detected as 6.86 by zeta (ζ)‐potential measurements, and the saturation magnetization was determined as 25.2 emu g^?1 by VSM, indicating that these nanoparticles were almost superparamagnetic. For free laccase and immobilized laccase systems, the optimum pH, temperature, and kinetic parameters were investigated; and the change of the activity against repeated use of the immobilized systems were examined. The results indicated that all immobilized systems retained more than 71% of their initial activity at the end of 30 batch uses. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of Novel Sensors Based on Polyimide Membrane for Sensitive and Selective Determination of Dopamine

Polyimides as dopamine selective membrane were prepared from 4,4′-diaminodicyclohexylmethane and different dianhydrides. The chemical structure and thermal properties of these polyimides were examined. For the voltammetric sensor applications, polyimides exhibited suitable glass transition temperature (T_g), high thermal stability, and good adhesive properties. Moreover, polyimides were coated onto Pt electrode surface for the preparation of dopamine selective electrodes. Electrochemically dopamine responses of polyimide-coated electrodes were examined by differential pulse voltammetry. The sensor characteristics such as sensitivity, linearity, selectivity, response time, and stability of the prepared sensors have been determined. Prepared polyimide-coated electrodes can be used for selective and sensitive dopamine detection.     

Fracture of the ossified Achilles tendon

OBJECTIVE: To analyse the relation between induced abortion and risk of subsequent miscarriage. DESIGN: Case-control study conducted between February 1990 and May 1995. PARTICIPANTS: Case group included 782 women (median age 32 years, range 14-46) admitted for spontaneous abortion (within the 12th week of gestation) to a network of obstetric departments in the greater Milan area. The control group was recruited among women who gave birth at term (> 37 weeks of gestation) to healthy infants on randomly selected days at the hospitals where cases had been identified. A total of 1543 controls (median age 30 years, range 14-45) were interviewed. RESULTS: A total of 102 cases (13%) and 181 controls (12%) reported one or more induced abortions. No clear relation emerged between miscarriage and induced abortions. In comparison with women reporting no induced abortion the odds ratio (OR) for miscarriage were 1.1 (95% CI 0.8-1.4) in women reporting one induced abortion and 0.9 (95% CI 0.4-1.8) in women reporting two or more. Likewise, there was no association between time since last and age at first induced abortion and risk of miscarriage. CONCLUSIONS: This study did not find any strong association between induced and spontaneous abortion.