http://hdl.handle.net/2262/78 Electronic & Electrical Eng Sun, 12 May 2013 21:16:11 GMT 2013-05-12T21:16:11Z http://hdl.handle.net/2262/65807 Title: Use of cognitive radio to improve spectrum usage efficiency and data capacity Author: NOLAN, Keith Description: PUBLISHED Sat, 30 Jun 2012 23:00:00 GMT http://hdl.handle.net/2262/65807 2012-06-30T23:00:00Z http://hdl.handle.net/2262/65806 Title: Cognitive Radio: Ten Years of Experimentation and Development Author: NOLAN, KEITH EDWARD Description: PUBLISHED Tue, 01 Mar 2011 00:00:00 GMT http://hdl.handle.net/2262/65806 2011-03-01T00:00:00Z http://hdl.handle.net/2262/65805 Title: Applications and Opportunities for Cognitive Radio and Networks Author: Nolan, Keith; Doyle, Linda Abstract: we present three aspects of cognitive radio and networks of importance to the research and commercial development community. We firstly outline key emerging application areas for CR/geo-location. Secondly, we look how the concept of whitespaces can be extended beyond the UHF band to other candidate spectrum segments. Thirdly, we examine regulatory policy changes being considered to increase spectrum efficiency and to support future demands for ubiquitous connectivity and capacity Description: PUBLISHED Sat, 30 Jun 2012 23:00:00 GMT http://hdl.handle.net/2262/65805 2012-06-30T23:00:00Z http://hdl.handle.net/2262/63923 Title: Short-range correlations seen in the nematic phase of bent-core liquid crystals by dielectric and electro-optic studies Author: PANOV, VITALY; VIJ, JAGDISH KUMAR; KOCOT, ANTONI; JANG, YUN Abstract: Three bent-core nematic liquid crystals having the same core but with different terminal groups, short (C4) and long (C7,C9) tails, are investigated by dielectric and electro-optic contrast spectroscopic techniques. C4 shows sign reversal in the dielectric anisotropy Δε′ as a function of both temperature and frequency, whereas C9 shows only negative Δε′ in the entire mesophasic region. The behavior of C7 is intermediate of the two. Results of a dielectric study show that both C7 and C9 exhibit strong short-range polar correlations normal to the director. The correlation lengths of these interactions are found to be similar to those from the x-ray scattering. An increased hindered rotation for C9 compared to C4 moves the dielectric dispersion for ε∥′ to much lower frequencies, such that C9 shows only negative Δε′ over the entire temperature range. Description: PUBLISHED Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/2262/63923 2011-01-01T00:00:00Z http://hdl.handle.net/2262/63907 Title: An experimental study of the dynamic properties of nanoparticle colloids with identical magnetization but different particle size Author: FANNIN, PAUL Abstract: Measurements of the frequency dependent complex magnetic susceptibility, χ(ω)=χ′(ω)−iχ″(ω), have been used to determine the dynamic properties of three specially prepared 400 G (0.04 T) magnetic fluids. The samples, denoted by sample 1, sample 2 and sample 3, consisted of magnetite particles of mean diameter 6.4 nm, 7.5 nm and 9 nm respectively and were identical in terms of carrier liquid, surfactant and particle material. From polarised ferromagnetic measurements, the anisotropy field, HA, the Landau-Lifshitz damping parameters, α, and the precessional decay time, τ0 of the particles were determined. The results show that the HA value for sample 3 was almost twice that of sample 1 and 2, thus confirming that the smaller the particle size, the lower the value of HA. The damping parameter, α, was found to be 0.174 (for sample 1), 0.18 (for sample 2) and 0.16 (for sample 3). The values determined for the precessional decay time, τ0 were 1.197×10−9 s, 1.157×10−9 s and 0.789×10−9 s, for samples 1, 2 and 3 respectively. Description: IN_PRESS Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/2262/63907 2012-01-01T00:00:00Z http://hdl.handle.net/2262/63020 Title: Phase space master equations for quantum Brownian motion in a periodic potential: comparison of various kinetic models Author: COFFEY, WILLIAM THOMAS; DOWLING, WILLIAM JOSEPH Abstract: The dynamics of quantum Brownian particles in a cosine periodic potential are studied using the phase space formalism associated with the Wigner representation of quantum mechanics. Various kinetic phase space master equation models describing quantum Brownian motion in a potential are compared by evaluating the dynamic structure factor and escape rate from the differential recurrence relations generated by the models. The numerical solution is accomplished via matrix continued fractions in the manner customarily used for the classical Fokker–Planck equation. The results of numerical calculations of the escape rate from a well of the cosine potential are compared with those given analytically by the quantum-mechanical reaction rate theory solution of the Kramers turnover problem for a periodic potential, given by Georgievskii and Pollak (1994 Phys. Rev. E 49 5098), enabling one to appraise each model. Description: PUBLISHED Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/2262/63020 2011-01-01T00:00:00Z http://hdl.handle.net/2262/62562 Title: Microsecond linear optical response in the unusual nematic phase of achiral bimesogens Author: VIJ, JAGDISH KUMAR; BALACHANDARAN, RESHMA; PANOV, VITALY; NAGARAJ, MAMATHA Abstract: Some hydrocarbon linked mesogenic dimers are known to exhibit an additional nematic phase (N(x)) below a conventional uniaxial nematic (N(u)) phase. Although composed of non-chiral molecules, the N(x) phase is found to exhibit linear (polar) switching under applied electric field. This switching has remarkably low response time of the order of a few microseconds. Two chiral domains with opposite handedness and consequently opposite responses are found in planar cells. Uniformly lying helix, electroclinic, and flexoelectric effects are given as possible causes for this intriguing phenomenon. Description: PUBLISHED Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/2262/62562 2011-01-01T00:00:00Z http://hdl.handle.net/2262/62460 Title: A wavelet-based Bayesian framework for 3D object segmentation in microscopy Author: KOKARAM, ANIL CHRISTOPHER; PAN, KANGYU; RAMASWAMI, MANI; CORRIGAN, DAVID Abstract: In confocal microscopy, target objects are labeled with fluorescent markers in the living specimen, and usually appear with irregular brightness in the observed images. Also, due to the existence of out-of-focus objects in the image, the segmentation of 3-D objects in the stack of image slices captured at different depth levels of the specimen is still heavily relied on manual analysis. In this paper, a novel Bayesian model is proposed for segmenting 3-D synaptic objects from given image stack. In order to solve the irregular brightness and out-offocus problems, the segmentation model employs a likelihood using the luminance-invariant 'wavelet features' of image objects in the dual-tree complex wavelet domain as well as a likelihood based on the vertical intensity profile of the image stack in 3-D. Furthermore, a smoothness 'frame' prior based on the a priori knowledge of the connections of the synapses is introduced to the model for enhancing the connectivity of the synapses. As a result, our model can successfully segment the in-focus target synaptic object from a 3D image stack with irregular brightness. Description: PUBLISHED Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/2262/62460 2012-01-01T00:00:00Z http://hdl.handle.net/2262/62201 Title: The Effect of Local Field Dispersion on the Spectral Characteristics of Nanosized Particles and their Composites Author: PEROVA, TATIANA Editor: G.S. Nicolić Abstract: Infrared (IR) spectroscopy of micro- and nanosized particles and their composites is currently one of the most important enabling technologies in the development of micro- and nanostructures and their application to various areas of science and technology. Decreasing the characteristic size of metallic, dielectric and semiconductor materials results in a dramatic alteration to their optical, electrical and mechanical properties, allowing the fabrication of new materials with unique physical properties (Lamberti, 2008; Cao, 2004). These alterations in the optical properties are related to a quantum confinement effect, as well as to a dielectric, or electrostatic, confinement effect (Cahay et al., 2001; Chemla & Miller, 1986). The effect of quantum confinement is most pronounced in semiconductor materials, where the transition from the bulk state to the microcrystalline state causes a substantial change in the band structure and an enhancement of the non-linear electrooptical properties. Dielectric, or polarisation, confinement has a wider impact, since it influences the frequencies and intensities of absorption bands in the spectra of any condensed matter, including crystalline and amorphous solids, as well as liquids. This is because considerable changes in the polarisation of micro/nanoparticles occur, depending on their form and orientation with respect to the external electromagnetic field and the details of the spatial restriction. Description: PUBLISHED; Rijeka, Croatia Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/2262/62201 2011-01-01T00:00:00Z http://hdl.handle.net/2262/61804 Title: Electrically tunable Fabry-Pérot resonator based on microstrcutured Si containing liquid crystal Author: PEROVA, TATIANA Abstract: We have built Fabry-Pérot resonators based on mi-crostructured silicon and a liquid crystal. The devices exhibit tuning of the resonance peaks over a wide range, with relative spectral shifts of up to ∆λ/λ = 10%. In order to achieve this substantial spectral shift, cavity peaks of high order were used. Under applied voltages of up to 15 V, a variation in the refractive index of the nematic liquid crystal E7 from ∆nLC = 0.12 to ∆nLC = 0.17 was observed. These results may have practical applications in the near-, mid and far-infrared range. Description: PUBLISHED Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/2262/61804 2012-01-01T00:00:00Z