Articles

Detecting Point-Like Sources of Unknown Frequency Spectra

Raffaele Solimene et al. — Fri, 26 Apr 2013 06:45:41 PDT

The problem of detecting point-like sources whose frequency spectrum is unknown is addressed. Limitations of single-frequency approaches are identified by analytical as well as numerical arguments. To overcome these limits, different multifrequency approaches which combine frequency data incoherently are compared. In particular, a novel multifrequency MUSIC-like algorithm based on interferometric concepts is proposed. Results show that the algorithm outperforms other methods under comparison.

Simulation Procedure for the Co-Optimization of Photovoltaic Water Pumping Systems.

Brian Norton — Wed, 17 Apr 2013 06:56:58 PDT

Abstract: Photovoltaic (PV)-powered centrifugal water pumping systems have been modelled based on field experience and analysis of long-term measured performance of several installed PV-powered water pumping systems. This paper presents detailed modelling of a PV array, an inverter, a three-phase induction motor, a centrifugal pump, a well, a storage tank, an overflow controller, and an integrated reverse osmosis desalination unit. The component models were validated using both laboratory measurements and long-term monitored data. All system components have been modelled separately, and the system was modelled in TRNSYS. The models are capable of simulating grid-connected, diesel-powered, and PV-powered water pumping systems, and can consider the following design and operational variables: constant voltage tracking, voltage frequency modulation, and maximum power point tracking algorithms; variable inverter frequency with variable motor efficiency, variable inverter frequency with constant motor efficiency, and constant inverter frequency with variable motor efficiency algorithms; and variation in PV temperature.

Proximity Study of a UWB Directional Conformal Antenna on Water Pipe

Domenico Gaetano et al. — Thu, 24 Jan 2013 03:50:34 PST

A preliminary study on the conformal properties of an antipodal exponentially tapered antenna placed on the surface of a flow meter system in the UWB range is presented. It was observed that the water effect can be mitigated by shifting the antenna away from the pipe surface.

Dual-band Omnidirectional Circularly Polarized Antenna

Adam Narbudowicz et al. — Wed, 23 Jan 2013 08:31:13 PST

A dual-band omnidirectional circularly polarized antenna is proposed. The antenna comprises back-to-back microstrip patches fed by a coplanar waveguide. A very low frequency ratio of 1.182 has been achieved, which can be easily tuned by adjusting four lumped capacitors incorporated into the antenna. An analysis of the omnidirectional circular polarization mechanism as well the dual band operation is provided and confirmed by numerical and experimental data. Key parameters to tune the resonant frequencies and the axial ratio have been identified. The prototype antenna provides omnidirectional circular polarization in one plane with cross polar isolation better than 12 dB for both frequency bands.

Optimized Monopole and Dipole Antennas for UWB Asset Tag Location Systems

Antoine Dumoulin et al. — Wed, 23 Jan 2013 05:15:34 PST

Miniaturized monopole and dipole antenna designs are reported with performances optimized for ultrawideband pulsed radio applications. The geometries are created using Bézier spline shapes, which have been refined with a genetic algorithm to simultaneously take account of both frequency- and time-domain criteria. Time-domain measurements of ultra wideband antennas with uniformly distributed energy across the full 3.1-10.6 GHz mask are reported for the first time and validate a new approach to minimization of pulse dispersion effects in the antenna designs.

High Performance ZnO Varistors Prepared From Nanocrystalline Precursors for Miniaturised Electronic Devices

Suresh Pillai et al. — Tue, 15 Jan 2013 03:05:39 PST

An industrially viable solution-based processing route using minimal amounts of solvent has been used to prepare bulk quantity nanopowders (average particle size 15.3 nm) for the fabrication of ZnO varistors. The xerogels, calcined powders and sintered materials were fully characterised. The preparation of varistors from nanopowders has been optimised by studying the effect of temperature on grain growth, densification and breakdown voltage. The varistors are prepared by sintering at 1050 C for 2 hours, a temperature that is significantly lower than that used in the current industrial process. Highly dense varistor discs prepared from the sintered material produce devices, with a breakdown voltage 85% higher than that of commercial varistors, making them suitable for use in miniaturised electronic circuitry. Improved performance of these materials has been attributed to the small grain size and better dispersion of additives on ZnO grains.

Synthesis of High-Temperature Stable Anatase TiO2 Photocatalyst

Suresh Pillai et al. — Thu, 13 Dec 2012 04:00:35 PST

In the absence of a dopant or precursor odification, anatase to rutile transformation in synthetic TiO2 sually ccurs at a temperature of 600 700 °C. Conventionally, metal oxide dopants (e.g., Al2O3 nd SiO2 are used o tune the anatase to rutile transformation. A simple methodology is reported here to extend the anatase utile transformation by employing various concentrations of urea. XRD and Raman spectroscopy were used uring thermal treatment. A significantly higher anatase phase (97%) as been obtained at 800 C with use of a 1:1 Ti(OPr)4 urea composition and 11% anatase composition is etained even after calcining the powder at 900 . On comparison a sample that has been prepared without rea showed that rutile phases started to form at a temperature as low as 600C. The effect of smaller mounts of urea such as 1:0.25 and 1:0.5 Ti(OPr) urea has also been studied and compared. The investigation oncluded that the stoichiometric modification by urea 1:1 Ti(OPr) urea composition is most effective in

extending the anatase to rutile phase transformation by 200°C compared to the unmodified sample. In addition, ET analysis carried out on samples calcined at 500°C showed that the addition of urea up to 1:1 Ti(OPr4:urea increased the total pore volume (from 0.108 to 0.224 cm3/g) and average pore diameter (11 to 30 nm)compared to the standard sample. Samples prepared with 1:1 Ti(OPr)4:urea composition calcined at 900 °C how significantly higher photocatalytic activity compared to the standard sample prepared under similarconditions. Kinetic analysis shows a marked increase in the photocatalytic degradation of rhodamine 6G on oing from the standard sample (0.27 min, decoloration in 120 min) to the urea-modified sample (0.73min-1, decoloration in 50 min).

A Highly Efficient Ag-ZnO Photocatalyst: Synthesis, Properties, and Mechanism

Suresh Pillai et al. — Thu, 13 Dec 2012 02:45:23 PST

Highly photocatalytically active silver-modified ZnO has been prepared and the effect of silver modification was studied. The structural and optical properties were characterized by X-ray diffraction, Fourier transform IR, differential scanning calorimetry, BET surface area, Raman, UV-vis, and photoluminescence spectroscopy. The photocatalytic activity of these materials was studied by analyzing the degradation of an organic dye, rhodamine 6G (R6G), and it is found that 3 mol % silver-modified ZnO at 400°C shows approximately four times higher rate of degradation than that of unmodified ZnO and a three times higher rate than that of commercial TiO 2 photocatalyst Degussa P-25. It was also noted that the photocatalytic activity for the modified ZnO sample was five times higher than the unmodified sample using sunlight. The effect of silver in enhancing the photocatalytic activity has been studied by analyzing the emission properties of both ZnO and silvermodified ZnO in the presence (emission increases) and absence (emission decreases) of R6G. We attribute these observations to the extent of valence band hole production and the role of silver in trapping the conduction band (CB) electrons in the absence of R6G. In the presence of R6G, the dye preserves the CB electron population in the metal oxide, thus preserving and enhancing emission intensity. The sensitizing property of the dye and electron scavenging ability of silver together constitute to the interfacial charge transfer process in such a way to utilize the photoexcited electrons.

Oxygen Rich Titania: A Dopant Free, A Dopant Free, High Temperature Stable, and Visible-Light Active Anatase Photocatalyst

Vinodkumar Etacheri et al. — Thu, 13 Dec 2012 02:30:38 PST

The simultaneous existence of visible light photocatalytic activity and high temperature anatase phase stability up to 900 ° C in undoped TiO 2 is reported for the fi rst time. These properties are achieved by the in-situ generation of oxygen through the thermal decomposition of peroxo-titania complex (formed by the precursor modifi cation with H 2 O 2 ). Titania containing the highest amount of oxygen (16 H 2 O 2 -TiO 2 )retains 100% anatase phase even at 900 ° C, where as the control sample exists as 100% rutile at this temperature. The same composition exhibits a six-fold and two-fold increase in visible light photocatalytic activities in comparison to the control sample and the standard photocatalyst Degussa P-25 respectively. Among the various para meters affecting the photocatalytic action, such as band gap narrowing, textural properties, crystallite size, and anatase phase stability, band gap narrowing was identifi ed as the major factor responsible for the visible light photocatalytic activity. Increased Ti–O–Ti bond strength and upward shifting of the valence band (VB) maximum, which is responsible for the high temperature stability and visible light activity respectively, are identifi ed from FT–IR, XPS, and photoluminescence (PL) spectroscopic studies. It is therefore proposed that the oxygen excess defects present in these titania samples are responsible for the high temperature stability and enhanced visible light photocatalytic activities.

Rapid Microwave Synthesis of Mesoporous TiO2 for Electrochromic Displays

Suresh Pillai et al. — Thu, 13 Dec 2012 02:10:31 PST

Silver Doped Titanium Dioxide Nanomaterials for Enhanced Visible Light Photocatalysis

Michael Seery et al. — Thu, 13 Dec 2012 01:05:30 PST

This paper presents a systematic study on two different preparation methods for titanium dioxide with silver. The silver can be incorporated by irradiating the reaction mixture during preparation to reduce silver ion to silver metal or by direct calcination of the sol–gel material to decompose silver nitrate to silver. Of the two methods, we found the latter produces a more effective photocatalytic material (6–50% improvement in catalytic efficiency), which is attributed to the fact that the silver is homogeneously dispersed throughout the material. The efficiency of the materials were examined using a Q-Sun solar simulator (visible light) and in Dublin summer sunlight (latitude 54◦N). In both cases, the addition of increasing amounts of silver, for both batches of samples, significantly increases the rate of degradation of a model dye, rhodamine 6G (R6G), increasing the rate of degradation from 0.06 min

−1 for TiO2 to 0.34 min−1 for 5 mol% Ag–TiO2

. This is attributed to the increasing visible absorption capacity due to the presence of silver nanoparticles

Application of response surface methodology for studying the influence of hydrothermal processing on the phytochemical constituents of Irish edible brown seaweed

Sabrina Cox — Fri, 07 Dec 2012 06:45:32 PST

We used response surface methodology to investigate the
effect of time and temperature of hydrothermal processing
(blanching) on the phytochemical content, texture and colour
of a semi-dried brown seaweed ( Himanthalia elongata ). A
central composite design was employed with a hydrothermal
processing time of 10 – 30 min and temperature of 60 – 90 ° C.
Predicted models were found to be signifi cant for total phenolic
content, 2,2-diphenyl-1-picrylhydrazyl radical scavenging
activity, total fl avonoids, total condensed tannins, texture and
colour. The predicted values for each of the responses were
in good agreement with experimental values. Processing time
had the most signifi cant effect on phytochemical constituents
of H. elongata . An acceptable edible texture and colour of
seaweed was also achieved during the blanching procedure.
Thus, central composite design and response surface methodology
can be used to model phytochemical content, texture
and colour of H. elongata while minimising the number of
experiments required. Multiple response optimisation demonstrated
that the phytochemical content of H. elongata may
be maximised by blanching for 20.4 min at 80.5 ° C.

The Generalised Zakharov-Shabat System and the Gauge Group Action

Georgi Grahovski — Mon, 15 Oct 2012 02:45:30 PDT

The generalized Zakharov-Shabat systems with complex-valued non-regular Cartan elements and the systems studied by Caudrey, Beals and Coifman (CBC systems) and their gauge equivalent are studied. This study includes: the properties of fundamental analytical solutions (FAS) for the gauge-equivalent to CBC systems and the minimal set of scattering data; the description of the class of nonlinear evolutionary equations, solvable by the inverse scattering method, and the recursion operator, related to such systems; the hierarchies of Hamiltonian structures. The results are illustrated on the example of the multi-component nonlinear Schrodinger (MNLS) equations and the corresponding gauge-equivalent multi-component Heisenberg ferromagnetic (MHF) type models, related to so(5;C) algebra.

Omnidirectional Circularly Polarised Microstrip Patch Antenna

Max Ammann et al. — Fri, 10 Aug 2012 05:05:18 PDT

An omnidirectional circularly-polarised patch antenna is proposed. The antenna radiates right-handed circular-polarisation with an average axial ratio of 2.3 dB over a full 360° . A shallow diagonal CPW inset-feed was used to achieve good matching to the back-to-back coupled patches, providing a measured S11 < -15 dB at the centre frequency. The measured cross-polar performance is better than 13 dB and the realised gain variation is ~3 dB in the plane normal to the substrate.

Complex Absorbing Potential Method for Dirac Operators. Clusters of Resonances

Jimmy Kungsman et al. — Mon, 18 Jun 2012 06:23:37 PDT

For both nonrelativistic and relativistic Hamiltonians, the Complex Absorbing Potential (CAP) method has been applied extensively to calculate resonances in Physics and Chemistry. We study clusters of resonances for the perturbed Dirac operator near the real axis and, in the semiclassical limit, we establish the CAP method rigorously by showing that resonances are perturbed eigenvalues of the nonselfadjoint CAP Hamiltonian, and vice versa.

Abstract Criteria for Multiple Solutions to Nonlinear Coupled Equations Involving Magnetic Schrodinger Operators

Mattias Enstedt et al. — Mon, 18 Jun 2012 06:05:39 PDT

We consider a system of nonlinear coupled equations involving magnetic Schrodinger

operators and general potentials. We provide a criteria for the existence of multiple

solutions to these equations. As special cases we get the classical results on

existence of innitely many distinct solutions within Hartree and Hartree-Fock

theory of atoms and molecules subject to an external magnetic fields. We also

extend recent results within this theory, including Coulomb system with a constant

magnetic field, a decreasing magnetic field and a "physically measurable" magnetic field.

Monofilar Spiral Slot Antenna for Dual-Frequency Dual-Sense Circular Polarization

Xiulong Bao et al. — Mon, 16 Apr 2012 09:00:42 PDT

A dual-band antenna with right-hand circular polarization for the first frequency and the counter polarization at the second frequency is realized with compact printed spiral slots. The coupled spiral slots are fed by a 50 Ω microstrip line. Dual-sense circularly-polarized performance is achieved by realizing oppositely-directed current rotation for the two frequency bands. A parametric study shows that the additional slot significantly improves the bandwidth for both frequency bands. Measured results show that the fractional impedance bandwidth is greater than 18% for both bands. The 3 dB axial-ratio bandwidths are 4.5% and 3.5% for the RHCP and LHCP bands, respectively.

Wideband Dual-Frequency Dual-Polarized Dipole-Like Antenna

Xiulong Bao et al. — Mon, 16 Apr 2012 09:00:40 PDT

A wideband dual-frequency dual-polarized printed antenna is proposed for LTE, WLAN, and UWB systems. The dual-band antenna provides wide impedance bandwidths of 74% with respect to the center frequency of 2.725 GHz, and 39% with respect to the center frequency of 7.15 GHz. An open slot in the ground plane between the feed arms provides an orthogonal path to realize an embedded circularly polarized band at 2.35 GHz with an axial-ratio bandwidth of 16%. Dual-band characteristics are achieved by an asymmetrical dipole-like element and the coupling configuration between the T-shaped feed line and the wide ground-plane slot.

Wideband Printed Monopole Design Using a Genetic Algorithm

Matthias John et al. — Mon, 26 Mar 2012 04:03:26 PDT

A method for the design and optimisation of wide-band printed planar monopoles using a genetic algorithm is presented. This novel technique employs overlapping sub-patches which ensures electrical contact in such constellations where two sub-patches are touching only at the corner, hence re-ducing losses. The method was usd optimisation of wide-band printed planar monopoles using a genetic algorithm is presented. This novel technique employs overlapping sub-patches which ensures electrical contact in such constellations where two sub-patches are touching only at the corner, hence re-ducing losses. The method was used to design a wideband monopole antenna with application in higher cellular, WLAN and UWB. Furthermore, the technique is modified for multi-goal optimisation to achieve multiple bands and reduce the lower edge frequencyed to design a wideband monopole antenna with application in higher cellular, WLAN and UWB. Furthermore, the technique is modified for multi-goal optimisation to achieve multiple bands and reduce the lower edge frequency. The best solutions were prototyped and a full experimental evaluation was made.

Printed Circularly-Polarized Antenna with Ultra-Wide Axial-Ratio Bandwidth

Xiulong Bao et al. — Fri, 04 Nov 2011 11:00:19 PDT

A circularly polarised printed dipole-like antenna employing asymmetrical arms and an orthogonal slit in the ground plane is presented. It is fed by a stepped microstrip line which connects to the shorter arm. By utilising surface currents on the asymmetrical arms and the orthogonal feedline structure, circular polarisation is realised. Experimental and numerical data are in agreement and the measured results show a fractional impedance bandwidth of 41.3% (1.77–2.69 GHz) and a wide axial-ratio bandwidth of 38.4% (1.81–2.67 GHz).