Electropolymerization of azure B on a screen-printed carbon electrode and its application to the determination of NADH in a flow injection analysis system

The electrooxidation polymerization of azure B on screen-printed carbon electrodes in neutral phosphate buffer was studied. The poly(azure B) modified electrodes exhibited excellent electrocatalysis and stability for dihydronicotinamide adenine dinucleotide (NADH) oxidation in phosphate buffer (pH 6.9), with an overpotential of more than 400 mV lower than that at the bare electrodes. Different techniques, including cyclic voltammetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy have been employed to characterize the poly (azure B) film. Furthermore, the modified screen-printed carbon electrodes were found to be promising as an amperometric detector for the flow injection analysis (FIA) of NADH, typically with a dynamic range of 0.5 muM to 100 muM.

Copper phthalocyanine organic thin-film transistors with calcium fluoride gate insulator

We report the fabrication of organic thin-film transistors (OTFTs) with copper phthalocyanine (CuPc) as the semiconductor and calcium fluoride (CaF2) as the gate dielectric on the glass substrate. The fabricated transistors show a gate voltage dependent carrier field effect mobility that ranges from 0.001 to 0.5 cm(2) V-1 s(-1). In the devices, the CaF2 dielectric is formed by thermal evaporation; thus OTFTs with a top-gate structure can be fabricated. This provides a convenient way to produce high-performance OTFTs on a large scale and should be useful for the integration of organic displays.

Bottom-contact organic field-effect transistors having low-dielectric layer under source and drain electrodes

An organic thin-film transistor (OTFT) having a low-dielectric polymer layer between gate insulator and source/drain electrodes is investigated. Copper phthalocyanine (CuPc), a well-known organic semiconductor, is used as an active layer to test performance of the device. Compared with bottom-contact devices, leakage current is reduced by roughly one order of magnitude, and on-state current is enhanced by almost one order of magnitude. The performance of the device is almost the same as that of a top-contact device. The low-dielectric polymer may play two roles to improve OTFT performance. One is that this structure influences electric-field distribution between source/drain electrodes and semiconductor and enhances charge injection. The other is that the polymer influences growth behavior of CuPc thin films and enhances physical connection between source/drain electrodes and semiconductor channel. Advantages of the OTFT having bottom-contact structure make it useful for integrated plastic electronic devices.

Preparation of poly(thionine) modified screen-printed carbon electrode and its application to determine NADH in flow injection analysis system

A poly(thionine) modified screen-printed carbon electrode has been prepared by an electrooxidative polymerization of thionine in neutral phosphate buffer. The modified electrodes are found to give stable and reproducible electrocatlytic responses to NADH and exhibit good stability. Several techniques, including cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), have been employed to characterize the poly(thionine) film. Further, the modified screen-printed carbon electrode was found to be promising as an amperometric detector for the flow injection analysis (FIA) of NADH, typically with a dynamic range of 5-100 muM.

Preparation and characteristics of polyimide-TiO2 nanocomposite film

A sol-gel approach has been developed to prepare polyimide-TiO2, hybrid films fi om soluble polyimides and a modified titanium precursor. The rate of the hydrolysis reaction of titanium alkoxide can be controlled by using acetic acid as a modifier. FTIR and XPS indicated that TiO2, particles were well distributed in polyimide matrixes with particle size small per than 60 nm. Polyimide hybrid films having the TiO2, component less than or equal to 10% exhibited high thermal stability, high optical transparency and good mechanical properties and possessed higher dielectric constants than correspondingly polyimides. (C) 2000 Society of Chemical Industry.

Electrocatalytic oxidation of ascorbic acid by norepinephrine embedded in lipid cast film at glassy carbon electrode

A stable lipid cast film was made by casting a lipid in chloroform onto a glassy carbon electrode. We imbedded a new mediator norepinephrine into this lipid cast film, which was considered as a biological membrane model. Through electro catalytic oxidation of ascorbic acid by this system, the anodic overpotential was reduced by about 250 mV compared with that obtained at a bare glassy carbon electrode. The electrochemical behavior of norepinephrine in the cast film was controlled by diffusion. The obtained diffusion coefficient of ascorbic acid was 1.87 x 10(-5) cm 2 s(-1). The catalytic current increased linearly with the concentration of ascorbic acid in the range from 0.5 to 10 mM. Using cyclic voltammetry, we obtained two peaks for ascorbic acid and uric acid in the same solution. The separation between the two peaks is about 147 mV. (C) 2001 Elsevier Science Ltd. All rights reserved.

Mossbauer spectra of Fe-57 in a thick film of YBa2(Cu0.97Fe0.03)(3)O7-x irradiated by a large dose of gamma-rays

Mossbauer spectra of Fe-57 in a thick film YBa2(Cu0.97Fe0.03)(3)O7-x irradiated by a large dose of gamma-rays from Co-60 have been measured. The variation of the relative intensities of some subspectra of Fe-57 in the. Mossbauer spectra of the thick film YBa2(Cu0.97Fe0.03)(3)O7-x after irradiation can be observed. This variation indicates that the change of the coordination environment around some Fe atoms in the lattice occurs due to irradiation. The relative intensity of subspectrum D1(Fe) at the Cu(1) site decreases and that of subspectrum D4(Fe) at the Cu(1) site increases. This may be because of the possible oxygen atom hopping between the coordination environments of D1(Fe) and D4(Fe) in the lattice caused by irradiation. The effect of irradiation on the coordination environment around the Fe atom at the Cu(2) site is not appreciable. (C) 1997 Elsevier Science B.V.

ELECTROCATALYSIS AND DETERMINATION OF HYDRAZINE COMPOUNDS IN LIQUID-CHROMATOGRAPHY AT A MIXED-VALENT COBALT OXIDE CYANOCOBALTATE FILM ELECTRODE

A glassy carbon electrode coated with an electrodeposited film of mixed-valent cobalt oxide/cyanocobaltate (Co-O/CN-Co) enabled hydrazine compounds to be catalytically oxidized at the greatly reduced overpotential and in a wide operational pH range (pH 2.0-7.0). Electrocatalytic activity at the Co-O/CN-Co modified electrode was evaluated with respect to solution pH, film thickness, supporting electrolyte ions, potential scan rate, operating potential, concentration dependence and other variables. The Co-O/CN-Co film electrode was completely compatible with a conventional reversed-phase liquid chromatographic (RP-LC) system. Practical RP-LC amperometric detection (RP-LCEC) of hydrazines was performed. A dynamic linear response range over three orders of magnitude and a detection limit at the pmol level were readily obtained. The Co-O/CN-CO film electrode exhibited excellent electrocatalytic stability in the flowing streams.

ELECTROCATALYSIS OF POLYPYRROLE-METHYLENE BLUE FILM MODIFIED ELECTRODE FOR DIRECT REDOX REACTION OF CYTOCHROME-C

The electron transfer process of hemeproteins on the electrode surface is considered a promising subject in the area of bioelectrochemistry. Electrochemists believe that electron transfer between electroactive proteins and electrode surface might be expected to simulate the electron transfer between proteins. This research provides information about the electron transfer mechanism in biological system. Cytochrome c is a typical electron transferring protein,

THIN-LAYER ELECTROCHEMICAL DETECTOR COATED WITH NAFION FILM

Electrochemical detection of the flow system has attracted considerable interest in recent years due to its high sensitivity and selectivity towards electroactive compounds. However, the improvement of sensitivity and selectivity is still a desire for practical application. In this note, a thin-layer electrochemical detector of the

The dynamics of a topological change in a system of soap films

Hutzler, S., Saadatfar, M., van der Net, A., Weaire, D. and Cox, S.J. (2007) The dynamics of a topological change in a system of soap films. Coll. Surf. A, 323:123-131. Sponsorship: This research was supported by the European Space Agency (contracts 14914/02/NL/SH and 14308/00/NL/SH), Science Foundation Ireland. (RFP 05/REP/PHY00/6), and the EU program COST P21 (The Physics of droplets). SJC acknowledges support from EPSRC (EP/D071127/1). MS is supported by the Irish Higher Education Authority (PRTLI-IITAC).

A Cult Film by Proxy: Space is the Place and the Sun Ra Mythos

Sexton, J. (2006). A Cult Film by Proxy: Space is the Place and the Sun Ra Mythos. New Review of Film and Television Studies. 4(3), pp.197-215. RAE2008

Dual-layer frequency-selective grid polarizers on thin-film substrates for THz applications

Dual-layer frequency-selective subwavelength grid polarizers on thin-film dielectric substrates are proposed for THz and sub-THz applications. The dual-layer grids possess enhanced (squared) polarizing efficiency at a sequence of discrete frequencies in reflection and within extended frequency bands in transmission as compared to conventional single grids.

Energy harvesting system design and optimization for wireless sensor networks

Wireless sensor networks (WSN) are becoming widely adopted for many applications including complicated tasks like building energy management. However, one major concern for WSN technologies is the short lifetime and high maintenance cost due to the limited battery energy. One of the solutions is to scavenge ambient energy, which is then rectified to power the WSN. The objective of this thesis was to investigate the feasibility of an ultra-low energy consumption power management system suitable for harvesting sub-mW photovoltaic and thermoelectric energy to power WSNs. To achieve this goal, energy harvesting system architectures have been analyzed. Detailed analysis of energy storage units (ESU) have led to an innovative ESU solution for the target applications. Battery-less, long-lifetime ESU and its associated power management circuitry, including fast-charge circuit, self-start circuit, output voltage regulation circuit and hybrid ESU, using a combination of super-capacitor and thin film battery, were developed to achieve continuous operation of energy harvester. Low start-up voltage DC/DC converters have been developed for 1mW level thermoelectric energy harvesting. The novel method of altering thermoelectric generator (TEG) configuration in order to match impedance has been verified in this work. Novel maximum power point tracking (MPPT) circuits, exploring the fractional open circuit voltage method, were particularly developed to suit the sub-1mW photovoltaic energy harvesting applications. The MPPT energy model has been developed and verified against both SPICE simulation and implemented prototypes. Both indoor light and thermoelectric energy harvesting methods proposed in this thesis have been implemented into prototype devices. The improved indoor light energy harvester prototype demonstrates 81% MPPT conversion efficiency with 0.5mW input power. This important improvement makes light energy harvesting from small energy sources (i.e. credit card size solar panel in 500lux indoor lighting conditions) a feasible approach. The 50mm × 54mm thermoelectric energy harvester prototype generates 0.95mW when placed on a 60oC heat source with 28% conversion efficiency. Both prototypes can be used to continuously power WSN for building energy management applications in typical office building environment. In addition to the hardware development, a comprehensive system energy model has been developed. This system energy model not only can be used to predict the available and consumed energy based on real-world ambient conditions, but also can be employed to optimize the system design and configuration. This energy model has been verified by indoor photovoltaic energy harvesting system prototypes in long-term deployed experiments.

Investigation and Development of a Fully 3D Tilt Capable Hybrid SPECT - CT System for Dedicated Breast Imaging

X-ray mammography has been the gold standard for breast imaging for decades, despite the significant limitations posed by the two dimensional (2D) image acquisitions. Difficulty in diagnosing lesions close to the chest wall and axilla, high amount of structural overlap and patient discomfort due to compression are only some of these limitations. To overcome these drawbacks, three dimensional (3D) breast imaging modalities have been developed including dual modality single photon emission computed tomography (SPECT) and computed tomography (CT) systems. This thesis focuses on the development and integration of the next generation of such a device for dedicated breast imaging. The goals of this dissertation work are to: [1] understand and characterize any effects of fully 3-D trajectories on reconstructed image scatter correction, absorbed dose and Hounsifeld Unit accuracy, and [2] design, develop and implement the fully flexible, third generation hybrid SPECT-CT system capable of traversing complex 3D orbits about a pendant breast volume, without interference from the other. Such a system would overcome artifacts resulting from incompletely sampled divergent cone beam imaging schemes and allow imaging closer to the chest wall, which other systems currently under research and development elsewhere cannot achieve.

The dependence of x-ray scatter radiation on object shape, size, material composition and the CT acquisition trajectory, was investigated with a well-established beam stop array (BSA) scatter correction method. While the 2D scatter to primary ratio (SPR) was the main metric used to characterize total system scatter, a new metric called ‘normalized scatter contribution’ was developed to compare the results of scatter correction on 3D reconstructed volumes. Scatter estimation studies were undertaken with a sinusoidal saddle (±15° polar tilt) orbit and a traditional circular (AZOR) orbit. Clinical studies to acquire data for scatter correction were used to evaluate the 2D SPR on a small set of patients scanned with the AZOR orbit. Clinical SPR results showed clear dependence of scatter on breast composition and glandular tissue distribution, otherwise consistent with the overall phantom-based size and density measurements. Additionally, SPR dependence was also observed on the acquisition trajectory where 2D scatter increased with an increase in the polar tilt angle of the system.

The dose delivered by any imaging system is of primary importance from the patient’s point of view, and therefore trajectory related differences in the dose distribution in a target volume were evaluated. Monte Carlo simulations as well as physical measurements using radiochromic film were undertaken using saddle and AZOR orbits. Results illustrated that both orbits deliver comparable dose to the target volume, and only slightly differ in distribution within the volume. Simulations and measurements showed similar results, and all measured dose values were within the standard screening mammography-specific, 6 mGy dose limit, which is used as a benchmark for dose comparisons.

Hounsfield Units (HU) are used clinically in differentiating tissue types in a reconstructed CT image, and therefore the HU accuracy of a system is very important, especially when using non-traditional trajectories. Uniform phantoms filled with various uniform density fluids were used to investigate differences in HU accuracy between saddle and AZOR orbits. Results illustrate the considerably better performance of the saddle orbit, especially close to the chest and nipple region of what would clinically be a pedant breast volume. The AZOR orbit causes shading artifacts near the nipple, due to insufficient sampling, rendering a major portion of the scanned phantom unusable, whereas the saddle orbit performs exceptionally well and provides a tighter distribution of HU values in reconstructed volumes.

Finally, the third generation, fully-suspended SPECT-CT system was designed in and developed in our lab. A novel mechanical method using a linear motor was developed for tilting the CT system. A new x-ray source and a custom made 40 x 30 cm2 detector were integrated on to this system. The SPECT system was nested, in the center of the gantry, orthogonal to the CT source-detector pair. The SPECT system tilts on a goniometer, and the newly developed CT tilting mechanism allows ±15° maximum polar tilting of the CT system. The entire gantry is mounted on a rotation stage, allowing complex arbitrary trajectories for each system, without interference from the other, while having a common field of view. This hybrid system shows potential to be used clinically as a diagnostic tool for dedicated breast imaging.