Filtering performance improvement in V-doped ZnO/diamond surface acoustic wave filters

High-frequency surface acoustic wave (SAW) filters using undoped and V-doped ZnO films were fabricated on diamond. Compared with their counterparts, the SAW filters using V-doped ZnO films have higher electromechanical coupling coefficient of ∼2.9% and lower insertion loss. The filtering performance improvement is considered to be due to the ferroelectricity in V-doped ZnO films and the resultant high piezoresponse (∼110 pm/V), which is one order of magnitude larger than that of undoped ZnO films. In addition, more perfect (0 0 2) preferred orientation, better uniform grains and smoother surface of V-doped ZnO films also contribute to the filtering performance improvement.     

Effects of the transducer dynamics in underwater acoustic communication

The inter-carrier interference (ICI) of Orthogonal Frequency Division Multiplexing (OFDM) symbols, which is caused by the transducer’s dynamics, has been analysed and simulated in this paper. The small Cyclic Prefix (CP) method is proposed to overcome the ICI caused by the transducer in order to maintain the orthogonality between sub-carriers without much loss of the energy and the bandwidth efficiency. The simulation results show that the small CP whose length is longer than the transient response of the transducer can eliminate the ICI problem.     

The Influence of Charge Transport and Recombination on the Performance of Dye‐Sensitized Solar Cells

Electrochemical impedance spectroscopy (EIS) and transient voltage decay measurements are applied to compare the performance of dye sensitized solar cells (DSCs) using organic electrolytes, ionic liquids and organic‐hole conductors as hole transport materials (HTM). Nano‐crystalline titania films sensitized by the same heteroleptic ruthenium complex NaRu(4‐carboxylic acid‐4′‐carboxylate) (4,4′‐dinonyl‐2,2′‐bipyridyl)(NCS)₂ , coded Z‐907Na are employed as working electrodes. The influence of the nature of the HTM on the photovoltaic figures of merit, that is, the open circuit voltage, short circuit photocurrent and fill factor is evaluated. In order to derive the electron lifetime, as well as the electron diffusion coefficient and charge collection efficiency, EIS measurements are performed in the dark and under illumination corresponding to realistic photovoltaic operating conditions of these mesoscopic solar cells. A theoretical model is established to interpret the frequency response off the impedance under open circuit conditions, which is conceptually similar to photovoltage transient decay measurements. Important information on factors that govern the dynamics of electron transport within the nanocrystalline TiO₂ film and charge recombination across the dye sensitized heterojunction is obtained.     

Immunochemical characterisation of structure and allergenicity of peanut 2S albumins using different formats of immunoassays

Proteins of the 2S albumin family, such as Ara h2 and Ara h6, are most frequently involved in peanut allergy. We have developed a reverse enzyme allergo-sorbent test (EAST) in which total serum IgE antibodies are first captured by immobilised anti-human IgE monoclonal antibodies, and then the binding of the anti-Ara h2 and anti-Ara h6 specific IgE to the corresponding labelled allergens is measured. This reverse immunoassay was used either as a direct EAST or as an EAST inhibition assay to study the interactions of whole peanut protein extract and purified Ara h2 and Ara h6 with IgE antibodies from peanut-allergic patients. Finally, we identified some IgE-binding epitopes on Ara h6 using a format of EAST in which the protein is immobilised in a particular, well defined, manner through interactions with specific monoclonal antibodies (mAbs) coated on the micro-plates. The fine specificity of those mAbs has been characterised at the epitope level, and their binding to the allergen thus masks a known particular epitope and makes it unavailable for recognition by IgE antibodies. The reverse EAST increased the ratio specific signal/background. It avoids interferences with competitors such as anti-peanut protein IgG antibodies and allows the study of the specificity and/or affinity of the interactions between IgE antibodies and Ara h2 or Ara h6 with a higher sensitivity and accuracy than the conventional EAST. The EAST results obtained when the allergens are presented by specific mAbs suggest that the homologous molecular domain(s) in peanut 2S albumins encompass major IgE epitope(s) and are strongly involved in peanut allergenicity.     

Mixed Measures of Convex Cylinders and Quermass Densities of Boolean Models

Translative integral formulas for curvature measures of convex bodies were obtained by Schneider and Weil by introducing mixed measures of convex bodies. These results can be extended to arbitrary closed convex sets since mixed measures are locally defined. Furthermore, iterated versions of these formulas due to Weil were used by Fallert to introduce quermass densities for (non-stationary and non-isotropic) Poisson processes of convex bodies and respective Boolean models. In the present paper, we first compute the special form of mixed measures of convex cylinders and prove a translative integral formula for them. After adapting some results for mixed measures of convex bodies to this setting we then use this integral formula to obtain quermass densities for (non-stationary and non-isotropic) Poisson processes of convex cylinders. Furthermore, quermass densities of Boolean models of convex cylinders are expressed in terms of mixed densities of the underlying Poisson process generalizing classical formulas by Davy and recent results by Spiess and Spodarev.      

Impedance measurements at thin polyaniline films – the influence of film morphology

AC impedance measurements of thin 100-nm polyaniline films electrosynthesized in various acidic electrolyte solutions known to support different film morphologies are reported. By carefully defining experimental parameters obtained data could be satisfactorily explained invoking a simple equivalent circuit assuming a double layer capacity assigned to the polymer/solution interface, a pseudocapacity related to the internal _redox capacity of the film, a film and a solution resistance and could be related to film morphologies. The data can be related to structural/morphological features of PANI films in close agreement with generally accepted changes of PANI films as a function of the degree of oxidation and type of anion present during electropolymerization.     

Effect of sparse basis selection on ultrasonic signal representation

Recently, adaptive sparse representations of ultrasonic signals have been utilized to improve the performance of scanning acoustic microscopy (SAM), a common nondestructive tool for failure analysis of microelectronic packages. The adaptive sparse representation of an ultrasonic signal is generated by decomposing it in a learned overcomplete dictionary using a sparse basis selection algorithm. Detection and location of ultrasonic echoes are then performed on the basis of the resulting redundant representation. This paper investigates the effect of sparse basis selection algorithms on ultrasonic signal representation. The overcomplete independent component analysis, focal underdetermined system solver (FOCUSS), and sparse Bayesian learning algorithms are examined. Numerical simulations are performed to quantitatively analyze the efficiency of ultrasonic signal representations. Experiments with ultrasonic A-scans acquired from flip-chip packages are also carried out in the study. The efficiency of ultrasonic signal representations are evaluated in terms of the different criteria that can be used to measure its performance for different SAM applications, such as waveform estimation, echo detection, echo location and C-scan imaging. The results show that the FOCUSS algorithm performs best overall.     

High frequency SAW devices based on third harmonic generation

We demonstrate the third harmonic generation in a ZnO/Si layered structure to obtain high frequency SAW devices. This configuration eliminates the need of high lithography resolution and allows easy integration of such devices and electronics on the same wafer. A theoretical study was carried out for the determination of the phase velocity and the electromechanical coupling coefficient (K²) dispersion curves of the surface acoustic waves. These results are also in agreement with those measured on a SAW filter designed for the third harmonic generation and the operating frequency is up to 2468 MHz.     

Investigation of structural, morphological, luminescent and thermal properties of combusted aluminium-based iron oxide

Nanocomposites of aluminium integrated hematite α-Fe₂O₃ are synthesized by combustion route using aqueous solutions of AR grade ferric trichloride and aluminium nitrate as precursors. The influence of aluminium incorporation on to the morphology, XPS, photoluminescence and thermal properties has been investigated. The FESEM and AFM micrographs depict that the samples are compact and have homogeneously distributed grains of varying sizes (∼20-60 nm). Chemical composition and valence states of constituent elements in hematite are analyzed by XPS. In room temperature photoluminescence (PL) study, we observed strong violet emission around 436 nm without any deep-level emission and a small PL FWHM indicating that the concentrations of defects are responsible for deep-level emissions. The specific heat and thermal conductivity study shows the phonon conduction behavior is dominant. We studied interparticle interactions using complex impedance spectroscopy. We report a new potential candidate for its possible applications in optoelectronics and magnetic devices.     

Durability of aluminum cooling system in electric power plants

The final step in gas turbine electric power production plants is the cooling of water after the turbine expansion. In some thermal plants, the temperature reduction of the recycling fluid is partially obtained by heat exchanging with the atmosphere by passing the fluid through huge aluminum heat exchangers. From the corrosion point of view, most critical is the starting step of the power plant, when the aluminum cooling system comes in contact with water for the first time and reaches a surface condition in dynamic equilibrium with the liquid. This paper describes a systematic study of aluminum surface evolution in the cooling system of an electric power plant during the first weeks of operation. Some aluminum samples were placed inside the cooling system in significant locations and removed after scheduled times. The surface conditions of the samples were characterized using surface analyses, electrochemical techniques and microscopic observations. At the same time, the chemical conditions of the recycling fluids were monitored. The obtained results describe the corrosion resistance of the aluminum surface as a function of the conditioning time, proving the growth of a partially protective layer able to produce corrosion decrease during the service time of the energy production plant. Copyright © 2009 John Wiley & Sons, Ltd.