Biogeography-based optimisation of Cognitive Radio system

Biogeography-based optimisation (BBO) is a novel population-based global optimisation algorithm that is stimulated by the science of biogeography. The mathematical models of biogeography describe how a species arises, migrates from one habitat (Island) to another or gets extinct. BBO searches for the global optimum mainly through two steps: migration and mutation. These steps are controlled by immigration and emigration rates of the species in the habitat which are also used to share information between the habitats. In this paper, BBO has been applied to Cognitive Radio (CR) system for optimising its various transmission parameters to meet the quality of service (QoS) that is defined by the user in terms of minimum transmit power, minimum bit error rate (BER), maximum throughput, minimum interference and maximum spectral efficiency. To confirm the capability of biogeography-based optimisation algorithm, the results obtained by BBO are compared with that obtained by using genetic algorithm (GA) for the various QoS parameters, and it has been observed that BBO outperforms GA in system optimisation.     

Near infrared luminescence of gold nanoclusters affected by the bonding of 1,4-dithiolate durene and monothiolate phenylethanethiolate

The impacts of Au-thiolate bonding on the near infrared (IR) luminescence of Au nanoclusters are studied by designing two types of monolayer reactions. Firstly, 1,4-dithiol durene (durene-DT) is reacted with Au(25) monolayer protected clusters (MPCs) stabilized by phenylethanethiolate (PhC2S) ligands. Upon the addition of durene-DT, the near IR luminescence of Au MPCs intensifies while the well-defined absorbance bands diminish. The optical transition is associated with the ligand exchange process monitored by proton NMR. In the second approach, PhC2S monothiols are reacted with durene-DT stabilized Au nanoclusters (DTCs). The addition of PhC2S to the Au DTCs induces the gradual decrease of the near IR luminescence. Mass spectrometry and NMR analysis reveal similar final products of mixed thiolate Au nanoclusters from both reactions. The results suggest that the 1,4-dithiolate-Au bonding interaction is a promising factor to further enhance the near IR luminescence of Au nanoclusters for biomedical applications.     

Modelling the effects of cutting parameters on residual stresses in hard turning of AISI H11 tool steel

In the present study, an attempt has been made to model the effect of cutting parameters (cutting speed, feed, depth of cut and nose radius) on residual stresses in hard turning of AISI H11 tool steel using ceramic tools. The machining experiments were conducted based on response surface methodology and using the Box–Behnken design of experiments. Residual stresses were determined using the X-ray diffraction technique, and the experimental results were investigated using analysis of variance. The results indicated that the feed and depth of cut are the main influencing factor on residual stresses whereas cutting speed and nose radius are having mild impact on residual stresses. The results show that it is possible to produce tailor-made residual stress levels by controlling the tool geometry and cutting parameters. The aim of this paper is to introduce an original approach for the prediction of residual stresses.     

Band gap engineering in huge-gap semiconductor SrZrO3 for visible-light photocatalysis

Using SrZrO₃ (SZO, the intrinsic band gap being 5.6 eV) as an example, we have investigated the design principles for huge-gap semiconductors with band gap larger than 5 eV for the application of efficient visible-light driven photocatalysts for splitting water into hydrogen. Based on the hybrid density function calculations, the electronic structures of mono-doped and co-doped SZO are investigated to obtain design principles for improving their photocatalytic activity in hydrogen generation. The cationic–anionic co-doping in SZO could reduce the band gap significantly and its electronic band position is excellent for the visible-light photocatalysis. This work reports a new type of candidate material for visible-light driven photocatalysis, i.e., huge-gap semiconductors with band gap larger than 5 eV. Furthermore, based on the present results we have proposed the design principles for band gap engineering that provides general guideline for other huge-gap semiconductors.     

Creating Conductive Copper–Silver Bimetallic Nanostructured Coatings Using a High Temperature Reducing Jet Aerosol Reactor

We report production of bimetallic nanostructured copper– silver coatings by in situ deposition and sintering of metal nanoparticles produced as an aerosol. The metal nanoparticles themselves have potential applications in printed electronics, catalysis, antibacterial coatings, and heat transfer fluids. In many applications, nanoparticles are dispersed in an ink, which is then printed or coated onto a substrate and converted into a nanostructured thin film. Direct deposition from the aerosol allows us to produce nanostructured thin films without first dispersing the particles in a solvent. The high temperature reducing jet process allows formation of these metal nanoparticles from low-cost metal salt precursors in the gas phase. In this method, a fuel-rich hydrogen flame provides a low-cost source of energy to drive nanoparticle formation in a reducing environment. The aqueous precursor solution is delivered into the hot combustion product gases within a converging–diverging nozzle. The high-speed gas flow atomizes the precursor and provides exceptionally rapid mixing of the precursor with the hot gases. Here, particles are formed, then immediately quenched and deposited on a glass substrate. The effect of the silver content of the mixed copper–silver films on their electrical conductivity was studied systematically, revealing an abrupt transition from low conductivity to high conductivity between 30 wt.% and 40 wt.% silver.

Copyright 2013 American Association for Aerosol Research     

Experimental Investigation for the Hardness of Castings Produced by Using ZCast Process

ZCast direct metal casting process is one of the important techniques of additive manufacturing which is used for printing the shell moulds for casting of non-ferrous materials. In the present work, an attempt was made to experimentally investigate the effect of different control factors on the hardness of castings produced using this ZCast process. Taguchi’s design of experimental method was used to perform the experimentation. Aluminium, brass and copper alloy castings were obtained in three different sizes using 3D printed shell moulds of different wall thicknesses. The obtained results were analysed using signal-to-noise ratio and analysis-of-variance. Analysis showed that the hardness depended on the casting material and 3D printed shell mould wall thickness. Cooling curve analysis and microstructure analysis of casting obtained with mould of different thickness were also performed. Paper revealed the potential suitability of copper, brass and aluminium for producing casting using ZCast process. The present research could provide valuable data of hardness of rapid castings of different material and might confirm the effectiveness and applicability of ZCast process in foundry industry.     

Assessment of a nanoparticle bridge platform for molecular electronics measurements

A combination of electron beam lithography, photolithography and focused ion beam milling was used to create a nanogap platform, which was bridged by gold nanoparticles in order to make electrical measurements and assess the platform under ambient conditions. Non-functionalized electrodes were tested to determine the intrinsic response of the platform and it was found that creating devices in ambient conditions requires careful cleaning and awareness of the contributions contaminants may make to measurements. The platform was then used to make measurements on octanethiol (OT) and biphenyldithiol (BPDT) molecules by functionalizing the nanoelectrodes with the molecules prior to bridging the nanogap with nanoparticles. Measurements on OT show that it is possible to make measurements on relatively small numbers of molecules, but that a large variation in response can be expected when one of the metal-molecule junctions is physisorbed, which was partially explained by attachment of OT molecules to different sites on the surface of the Au electrode using a density functional theory calculation. On the other hand, when dealing with BPDT, high yields for device creation are very difficult to achieve under ambient conditions. Significant hysteresis in the I-V curves of BPDT was also observed, which was attributed primarily to voltage induced changes at the interface between the molecule and the metal.     

Expanding the Scope of Biocatalysis: Oxidative Biotransformations on Solid‐Supported Substrates

Oxidative biocatalytic reactions were performed on solid‐supported substrates, thus expanding the repertoire of biotransformations that can be carried out on the solid phase. Various phenylacetic and benzoic acid analogues were attached to controlled pore glass beads via an enzyme‐cleavable linker. Reactions catalyzed by peroxidases (soybean and chloro), tyrosinase, and alcohol oxidase/dehydrogenase gave a range of products, including oligophenols, halogenated aromatics, catechols, and aryl aldehydes. The resulting products were recovered following cleavage from the beads using α‐chymotrypsin to selectively hydrolyze a chemically non‐labile amide linkage. Controlled pore glass (CPG) modified with a polyethylene glycol (PEG) linker afforded substantially higher product yields than non‐PEGylated CPG or non‐swellable polymeric resins. This work represents the first attempt to combine solid‐phase oxidative biotransformations with subsequent protease‐catalyzed cleavage, and serves to further expand the use of biocatalysis in synthetic and medicinal chemistry.     

An in vitro model of a retinal prosthesis

Epiretinal prostheses are being developed to bypass a degenerated photoreceptor layer and excite surviving ganglion and inner retinal cells. We used custom microfabricated multielectrode arrays with 200-microm-diameter stimulating electrodes and 10-microm-diameter recording electrodes to stimulate and record neural responses in isolated tiger salamander retina. Pharmacological agents were used to isolate direct excitation of ganglion cells from excitation of other inner retinal cells. Strength-duration data suggest that, if amplitude will be used for the coding of brightness or gray level in retinal prostheses, shorter pulses (200 micros) will allow for a smaller region in the area of the electrode to be excited over a larger dynamic range compared with longer pulses (1 ms). Both electrophysiological results and electrostatic finite-element modeling show that electrode-electrode interactions can lead to increased thresholds for sites half way between simultaneously stimulated electrodes (29.4 +/- 6.6 nC) compared with monopolar stimulation (13.3 +/- 1.7 nC, p < 0.02). Presynaptic stimulation of the same ganglion cell with both 200- and 10-microm-diameter electrodes yielded threshold charge densities of 12 +/- 6 and 7.66 +/- 1.30 nC/cm2, respectively, while the required charge was 12.5 +/- 6.2 and 19 +/- 3.3 nC.