Mechanical and electrical characterization of /spl beta/-Ga/sub 2/O/sub 3/ nanostructures for sensing applications

Single crystalline /spl beta/-Ga/sub 2/O/sub 3/ nanowire and nanoribbon materials were synthesized, and electrical and mechanical properties were studied for sensing applications. The structural analysis showed that the Ga/sub 2/O/sub 3/ nanomaterials were stoichiometric and had the same crystal lattice structure as the /spl beta/ phase Ga/sub 2/O/sub 3/ crystal. The mechanical study on individual Ga/sub 2/O/sub 3/ nanowires and nanoribbons showed that they had a bending modulus of around 300 GPa, are flexible (in bending and twisting), and are easy to be cleaved along their crystal lattice. The current-voltage electrical characterization through the thickness of nanoribbon and along the length of nanowire confirmed their semiconducting characteristic. A two-terminal device fabricated with an individual Ga/sub 2/O/sub 3/ nanowire showed good sensing response to ethanol gas at low-operating temperature, which revealed the potential of using such nanostructures for effective sensing applications.     

Coherent l1‐SVD method for DOA estimation of wideband signals

The l₁‐SVD is an efficient method for spatial sparsity based direction of arrival (DOA) estimation of narrowband signals. We propose a coherent strategy for extension of the l₁‐SVD method to wideband signals. In this method, focusing matrices are used for transferring different frequency bins data to the reference bin, and then the transformed data are combined. Finally the l₁‐SVD is applied for the combined data. The proposed method outperforms the non‐coherent strategy with a lower computational burden. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Blind downlink channel estimation for TDD‐based multiuser massive MIMO in the presence of nonlinear HPA

In time division duplex (TDD)‐based multiuser massive multiple input multiple output (MIMO) systems, the uplink channel is estimated and the results are used in downlink for signal detection. Owing to noisy uplink channel estimation, the downlink channel should also be estimated for accurate signal detection. Therefore, recently, a blind method was developed, which assumes the use of a linear high‐power amplifier (HPA) in the base station (BS). In this study, we extend this method to a scenario with a nonlinear HPA in the BS, where the Bussgang decomposition is used for HPA modeling. In the proposed method, the average power of the received signal for each user is a function of channel gain, large‐scale fading, and nonlinear distortion variance. Therefore, the channel gain is estimated, which is required for signal detection. The performance of the proposed method is analyzed theoretically. The simulation results show superior performance of the proposed method compared to that of the other methods in the literature.     

CPM modulation index estimation using LS and BLUE methods

In this paper, we propose two methods for blind estimation of modulation index of full‐response binary continuous phase modulation (CPM) scheme. Most of previous works assume that there is a single sample for each symbol; thus, they cannot improve their performance when sampling rate is bigger than symbol rate. In our proposed methods, modulation index is estimated using samples of autocorrelation function of the received signal, which is a nonlinear function of modulation index. We propose Taylor expansion for approximating this nonlinear function by a linear function. Then, by choosing some samples of the autocorrelation function, we estimate the modulation index with the least square (LS) estimator. For decreasing estimation errors, in the second proposed method, we apply the statistical properties of the autocorrelation function estimation errors, to design the best linear unbiased estimation (BLUE) estimator. The numerical performance analysis in terms of mean‐squared error (MSE) and bit error rate (BER) shows that the proposed methods outperform the reference methods in accurate estimation of the modulation index.     

Carbon nanotube network-based biomolecule detection

In this paper, we describe a single-wall carbon nanotube (SWNT) based biological sensor for the detection of biomolecules like Streptavidin and IgG. SWNTs have been employed for two types of sensing mechanisms. First, the changes in the electrical conductance of the carbon nanotube (CNT) matrix on noncovalent binding of the biomolecules to the side walls of the CNT and, second, quantification of mass uptake of the matrix on biomolecule incubation are presented. Both sensing mechanisms exhibited consistent and highly sensitive responses. Biomolecular immobilization on the CNT surface was monitored by atomic force microscopy.     

Efficient and stable HER electrocatalyst using Pt-nanoparticles@poly(3,4–ethylene dioxythiophene) modified sulfonated graphene nanocomposite

The green production of hydrogen by electrochemical water splitting has been recently paid attention. It is more focused to research about the preparation of efficient electrocatalysts, which catalyze hydrogen evolution reaction (HER) in acidic media at low overpotential. Platinum is known as an ideal option, but its rarity and high-cost limit its application in practical industrial plants. Hence, minimizing the level of it can be a solution. It can be achieved by the decoration of platinum nanoparticles (PtNPs) on the different composites such as poly(3,4–ethylene dioxythiophene, PEDOT) and sulfonated graphene nanosheets (SG) in this work. Accordingly, the successful preparation and HER electrocatalytic manner of this nanocomposite were main objectives in the present report. The related characterization and performance were monitored using various analytical and electrochemical techniques. The low charge transfer resistance (around 50 Ω), low overpotential (?0.040 V vs. RHE), and stable manner (until 500 cycles) resulted in this HER electrocatalyst. It was controlled by Tafel reaction with electrochemical adsorption-desorption because of kinetic factors including Tafel slope (28.4 mV dec^?1), charge-transfer coefficient of 2.0, and exchange current of 7.27 mA cm^?2.     

Investigation on the cross sensitivity of NO2 sensors based on In2O3 thin films prepared by sol-gel and vacuum thermal evaporation

In₂O₃ thin films have been prepared from commercially available pure In₂O₃ powders by high vacuum thermal evaporation (HVTE) and from indium iso-propoxide solutions by sol-gel techniques (SG). The films have been deposited on sapphire substrates provided with platinum interdigital sputtered electrodes. The as-deposited HVTE and SG films have been annealed at 500°C for 24 and 1 h, respectively. The film morphology, crystalline phase and chemical composition have been characterised by SEM, glancing angle XRD and XPS techniques. After annealing at 500°C the films’ microstructure turns from amorphous to crystalline with the development of highly crystalline cubic In₂O_3−x (JCPDS card 6-0416). XPS characterisation has revealed the formation of stoichiometric In₂O₃ (HVTE) and nearly stoichiometric In₂O_3−x (SG) after annealing. SEM characterisation has highlighted substantial morphological differences between the SG (highly porous microstructure) and HVTE (denser) films. All the films show the highest sensitivity to NO₂ gas (0.7–7 ppm concentration range), at 250°C working temperature. At this temperature and 0.7 ppm NO₂ the calculated sensitivities (S=R_g/R_a) yield S=10 and S=7 for SG and HVTE, respectively. No cross sensitivity have been found by exposing the In₂O₃ films to CO and CH₄. Negligible H₂O cross has resulted in the 40–80% relative humidity range, as well as to 1 ppm Cl₂ and 10 ppm NO. Only 1000 ppm C₂H₅OH has resulted to have a significant cross to the NO₂ response.     

Modelling and optimisation of biomass supply chains: a review

A growing number of researchers are attracted by the domain of bioenergies, due to the problems induced by greenhouse gas emissions and increasing energy demand. One possible way of producing biofuels in a renewable way is to use biomass, however the economic viability of a biorefinery system depends critically on the cost of its supplies. As biomass is not very expensive, logistics is responsible of an important fraction of this cost. Models and methods to optimise biomass supply chains are surveyed in this article, after introducing some technical terms and describing the main activities in these chains. This review aims to give a comprehensive overview of the research in this field with a focus on optimisation modelling issues and solution approaches. Recent advances in the current research and possible new directions are sketched.     

Room-temperature hydrogen sensor based on palladium nanowires

Palladium (Pd) nanowires, synthesized by template-nanomanufacturing techniques, has been studied for hydrogen gas-sensing applications at room temperature. In this study, parallel arrays of Pd nanowires were fabricated by electrodeposition from an aqueous plating solution onto the surface of highly oriented pyrolytic graphite (HOPG). The nanowires were then transferred onto a polystyrene film and silver electrical contact pads were fabricated by shadow masking. The morphology of the nanowires was analyzed using atomic force microscope (AFM) in noncontact mode and the diameter of the observed nanowires was measured to be approximately 250 nm. Scanning electron microscope (SEM) images revealed that the nanowires fabricated by this procedure were parallel and continuous. Electrodes were patterned by shadow masking and the I-V characteristics of the nanowires were studied. Experimental results indicated that the sensors are highly sensitive to hydrogen, showing a two-order change in conductance. The morphology of the nanowires was analyzed using SEM and AFM in order to understand the properties responsible for the high sensitivity of the nanowires. SEM images showed that the nanowires contain nanogaps in absence of H/sub 2/. Upon exposure to H/sub 2/, the Pd absorbed hydrogen, resulting in the expansion of Pd grains. This expansion results in the closing of the nanogaps. The expansion occurred due to the phase transition from /spl alpha/ to /spl beta/ and the Pd lattice expansion.     

Unitary coherent strategy for spatial sparsity‐based DOA estimation of wideband signals

The coherent l₁‐singular value decomposition (l₁‐SVD) uses a non‐unitary coherent strategy for transferring different frequency bin data to a reference bin, which decreases the signal‐to‐error ratio (SER) in transferring, thereby leading to a decrease in accuracy in the direction of arrival (DOA) estimation. To cope with this problem, in this paper we propose a unitary coherent strategy that uses unitary focusing matrices for transferring data. Simulation results show that the proposed method outperforms the coherent l₁‐SVD method in accurate DOA estimation. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.