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     

A Subcarriers Allocation Scheme for Cognitive Radio Systems Based on Multi-Carrier Modulation

Cognitive radio (CR) is a dynamic spectrum access technology as a solution to spectrum under-utilization problem in some licensed bands. Operating over an exceedingly wide spectrum, CR systems usually adopt multi-carrier modulation (MCM) to implement flexible channelization. Consequently, efficient channel allocation scheme becomes extremely important to an MCM based CR (MCM-CR) system. In this paper, a maximum likelihood detection model is developed to detect the presence and locations of licensed users (LUs) signals in the frequency domain. Performance of the detection model, including the optimal detection region, detection probability and false alarm probability, is analyzed. A one-order two-state Markovian chain model is proposed to predict channel status information. In particular, a novel subcarrier allocation scheme for MCM-CR systems is proposed, taking into account the confidence of channel estimation, quality of services (QoS) of rental users (RUs) and throughput. To validate the analytical results, simulations have been conducted to show effectiveness of the proposed scheme.     

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     

A Microfluidic Device to Acquire Gaseous Samples Via Surface Tension Held Gas-Liquid Interface

We present a relatively simple and effective method for acquiring gaseous samples into microfluidic channels. Hydrophobic polymers are photopatterned on hydrophilic substrates. Due to surface tension, aqueous liquid is confined by the hydrophobic polymers, but not completely blocked by a physical wall, thus allowing an interface for gas-liquid interaction. Here, the mechanism is demonstrated by using hydrophobic (poly)iso-bornyl acrylate polymer patterns on hydrophilic glass substrates, and through a Nessler's reagent-ammonia reaction that exhibits changes in color and electrical resistance.     

A mechanistic analysis of the correlation between overall strength and indentation hardness in discontinuously reinforced aluminum

It is well established that the indentation hardness of metallic alloys shows a reasonable correlation with their yield strength or ultimate strength. Experiments illustrate that such a unique correlation is nonexistent for discontinuously reinforced metal matrix composites, even when the indentation size is much greater than the reinforcement size. For aluminum alloys reinforced with silicon carbide particles, the same composite yield strength and tensile strength with different reinforcement fractions do not lead to similar hardness, or vice versa. Finite element analyses are carried out to rationalize the experimental findings. The modeling utilizes a two-dimensional plane-strain formulation. Discrete particles are included in the material model, and the overall stress-strain response and the indentation response are numerically simulated. The results confirm the lack of unique correspondence between the composite hardness and strength. The alteration of local heterogeneity in the composite is found to affect the indentation response. Effects of the geometrical arrangement of particles and thermal residual stresses on the indentation response are also investigated numerically.     

On the relationship between parity space and approaches to fault detection

Parity space approach and H₂ approach are two important fault detection approaches. This paper studies the relationship between these two approaches, which reveals frequency domain characteristics of the optimal solution of the parity space approach on the one side and provides a numerical solution of the H₂-optimal design of residual generators on the other side.     

Photoreactivation of Escherichia coli following medium-pressure ultraviolet disinfection and its control using chloramination.

Ultraviolet (UV) disinfection is becoming increasingly popular as an alternative disinfection technology to chlorination in recent years. In this study, we investigated the photoreactivation of Escherichia coli following medium-pressure (MP) UV disinfection of synthetic water by a bench-scale collimated beam apparatus. The UV doses ranged from 1.6 -19.7 mWs/cm2 and photoreactivation was investigated for 6 hours under fluorescent light. In addition, chloramination was applied after UV disinfection to investigate its ability to control photoreactivation. It was found that photoreactivation occurred for all UV doses tested and the increase in bacteria numbers ranged from 0.04 to 1.35 log10. However, the degree of photoreactivation decreased with increased UV doses. Chloramination experiments revealed that the addition of 0.5 mg/l of monochloramine resulted in suppression of photoreactivation for 1 hour only. An increased monochloramine dose of 1 mg/l was found to prevent photoreactivation for the entire duration of the experiment. The results of this study have shown that photoreactivation occurs even after MP UV disinfection, although it is of a lesser extent at higher UV doses. This study has also established that secondary chloramination can effectively suppress and eliminate photoreactivation with a chloramine dose of 1 mg/l.     

Programmable group-delay module using binary polarization switching

We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system.