text: DSpace Collection: http://hdl.handle.net/2381/835 2015-03-31T09:44:58Z 2015-03-31T09:44:58Z The synthesis of travelling ionospheric disturbance (TID) signatures in HF radar observations using ray tracing Stocker, A. J. Arnold, N. F. Jones, T. B. http://hdl.handle.net/2381/31852 2015-03-12T02:02:19Z 2015-03-11T11:23:57Z Title: The synthesis of travelling ionospheric disturbance (TID) signatures in HF radar observations using ray tracing Authors: Stocker, A. J.; Arnold, N. F.; Jones, T. B. Abstract: Characteristic signatures are often observed in HF radar range-time-intensity plots when travelling ionospheric disturbances (TIDs) are present. These signatures, in particular the variation of the F-region skip distance, have been synthesised using a ray tracing model. The magnitude of the skip variation is found to be a function of the peak electron density perturbation associated with the TID and radar frequency. Examination of experimental observations leads to an estimate of the peak electron density perturbation amplitude of around 25% for those TIDs observed by the CUTLASS radar system. The advantage of using the skip variation over the radar return amplitude as an indicator of density perturbation is also discussed. An example of a dual radar frequency experiment has been given. The investigation of the effect of radar frequency on the observations will aid the optimisation of future experiments. 2015-03-11T11:23:57Z The stability of elastically strained nanorings and the formation of quantum dot molecules Gill, Simon P.A. http://hdl.handle.net/2381/31721 2015-02-20T02:01:54Z 2015-02-19T15:53:23Z Title: The stability of elastically strained nanorings and the formation of quantum dot molecules Authors: Gill, Simon P.A. Abstract: Self-assembled nanorings have recently been identified in a number of heteroepitaxially strained material systems. Under some circumstances these rings have been observed to break up into ringshaped quantum dot molecules. A general non-linear model for the elastic strain energy of nonaxisymmetric epitaxially strained nanostructures beyond the small slope assumption is developed. This model is then used to investigate the stability of strained nanorings evolving via surface diffusion subject to perturbations around their circumference. An expression for the fastest growing mode is determined and related to experimental observations. The model predicts a region of stability for rings below a critical radius, and also a region for larger rings which have a proportionally small thickness. The predictions of the model are shown to be consistent with the available results. For the heteroepitaxial InP on In0.5Ga0.5P system investigated by Jevasuwan et al. (2013), the nanorings are found to be stable below a certain critical size. This is in good quantitative agreement with the model predictions. At larger sizes, the rings are unstable. The number of dots in the resulting quantum dot molecule is similar to the mode number for the fastest growing mode. Second order terms show that the number of dots is expected to reduce as the height of the ring increases in proportion to its thickness. The strained In0.4Ga0.6As on GaAs nanorings of Hanke et al (2007) are always stable and this is in accordance with the findings of the analysis. The Au nanorings of Ruffino et al. (2011) are stable as well, even as they expand during annealing. This observation is also shown to be consistent with the proposed model, which is expected to be useful in the design and tailoring of heteroepitaxial systems for the self-organisation of quantum dot molecules. 2015-02-19T15:53:23Z Evolution of frequency composition for Atrial arrhythmias Ahmad, A. Buyamin, S. Tuan, J. H. Ng, G. A. Schlindwein, F. S. http://hdl.handle.net/2381/31669 2015-02-17T02:01:48Z 2015-02-16T12:16:08Z Title: Evolution of frequency composition for Atrial arrhythmias Authors: Ahmad, A.; Buyamin, S.; Tuan, J. H.; Ng, G. A.; Schlindwein, F. S. Abstract: In the United States of America, cardiac arrhythmias remain the leading cause of sudden death with more than 300,000 cases per year [1, 2]. The majority of sustained cardiac arrhythmias are atrial fibrillation and these contribute a major cause of stroke[3-6]. Irregular electrical pulses can be determined inside the atria. Frequency analysis is used to measure changes in the dominant frequency (DF). Welch method is used here to obtain the frequency spectrum of the signals. The 2D frequency strength plotting allows us to identify the evolution of the frequency composition of the signal with time. In physiological studies, we should see a general frequency increase during stimulation. That means the frequency at pre-stimulation should be lower than during stimulation and this should return to pre-stimulation state after simulation stops. The reason is that stimulation of the ganglia is supposed to promote atrial conduction in AF. The initiation and maintenance of AF is significantly enhanced by simultaneous parasympathetic stimulation In physiological studies, we should see a general frequency increase during stimulation. That means the frequency at pre-stimulation should be lower than during stimulation and this should return to pre-stimulation state after simulation stops. The reason is that stimulation of the ganglia is supposed to promote atrial conduction in AF. The initiation and maintenance of AF is significantly enhanced by simultaneous parasympathetic stimulation. © 2014 Penerbit UTM Press. All rights reserved. Description: Embargoed while checking publisher copyright permissions. 2015-02-16T12:16:08Z Distinctive Patterns of Dominant Frequency Trajectory Behavior in Drug-Refractory Persistent Atrial Fibrillation: Preliminary Characterization of Spatiotemporal Instability Salinet, João L. Tuan, Jiun H. Sandilands, Alastair J. Stafford, Peter J. Schlindwein, Fernando S. Ng, Ghulam A. http://hdl.handle.net/2381/31634 2015-02-10T02:01:46Z 2015-02-09T12:18:03Z Title: Distinctive Patterns of Dominant Frequency Trajectory Behavior in Drug-Refractory Persistent Atrial Fibrillation: Preliminary Characterization of Spatiotemporal Instability Authors: Salinet, João L.; Tuan, Jiun H.; Sandilands, Alastair J.; Stafford, Peter J.; Schlindwein, Fernando S.; Ng, Ghulam A. Abstract: The role of substrates in the maintenance of persistent atrial fibrillation (persAF) remains poorly understood. The use of dominant frequency (DF) mapping to guide catheter ablation has been proposed as a potential strategy, but the characteristics of high DF sites have not been extensively studied. This study aimed to assess the DF spatiotemporal stability using high density noncontact mapping (NCM) in persAF. Methods and Results: Eight persAF patients were studied using NCM during AF. Ventricular far-field cancellation was performed followed by the calculation of DF using Fast Fourier Transform. Analysis of DF stability and spatiotemporal behavior were investigated including characteristics of the highest DF areas (HDFAs). A total of 16,384 virtual electrograms (VEGMs) and 232 sequential high density 3-dimensional DF maps were analyzed. The percentage of DF stable points decreased rapidly over time. Repetition or reappearance of DF values were noted in some instances, occurring within 10 seconds in most cases. Tracking the HDFAs' center of gravity revealed 3 types of propagation behavior, namely (i) local, (ii) cyclical, and (iii) chaotic activity, with the former 2 patterns accounting for most of the observed events. Conclusions: DF of individual VEGMs was temporally unstable, although reappearance of DF values occurred at times. Hence, targeting sites of 'peak DF' from a single time frame is unlikely to be a reliable ablation strategy. There appears to be a predominance of local and cyclical activity of HDFAs hinting a potentially nonrandom temporally periodic behavior that provides further mechanistic insights into the maintenance of persAF. 2015-02-09T12:18:03Z Large Eddy Simulation of a Controlled Diffusion Compressor Cascade McMullan, W. Andrew Page, Gary J. http://hdl.handle.net/2381/31519 2015-01-30T02:01:42Z 2015-01-29T16:17:08Z Title: Large Eddy Simulation of a Controlled Diffusion Compressor Cascade Authors: McMullan, W. Andrew; Page, Gary J. Abstract: In this research a Controlled Diffusion (CD) compressor cascade stator blade is simulated at a Reynolds number of ∼700,000, based on inflow velocity and chord length, using Large Eddy Simulation (LES). A wide range of flow inlet angles are computed, including conditions near the design angle, and at high negative and positive incidence. At all inlet angles the surface pressure distributions are well-predicted by the LES. Near the design angle the computed suction side boundary layer thickness agrees well with experimental data, whilst the pressure side boundary layer is poorly predicted due to the inability of LES to capture natural boundary layer transition on the present grid. A good estimation of the loss is computed near the design angle, whilst at both high positive and negative incidences the loss is less well predicted owing to discrepancies between the computed and experimental boundary layer thickness. At incidences above the design angle a laminar separation bubble forms near the leading edge of the suction surface, which undergoes a transition to turbulence. Similar behaviour is noted on the pressure surface at negative incidence. At high negative incidence contra-rotating vortex pairs are found to form around the leading edge in response to an unsteady stagnation line across the span of the blade. Such structures are not apparent in time-averaged statistical data due to their highly-transient nature. 2015-01-29T16:17:08Z Spark Plasma Sintered bismuth telluride-based thermoelectric materials incorporating dispersed boron carbide Williams, Hugo R. Ambrosi, Richard M. Chen, K. Friedman, U. Ning, H. Reece, M. J. Robbins, M. C. Simpson, K. Stephenson, K. http://hdl.handle.net/2381/31487 2015-01-27T02:01:44Z 2015-01-26T10:32:41Z Title: Spark Plasma Sintered bismuth telluride-based thermoelectric materials incorporating dispersed boron carbide Authors: Williams, Hugo R.; Ambrosi, Richard M.; Chen, K.; Friedman, U.; Ning, H.; Reece, M. J.; Robbins, M. C.; Simpson, K.; Stephenson, K. Abstract: The mechanical properties of bismuth telluride based thermoelectric materials have received much less attention in the literature than their thermoelectric properties. Polycrystalline p-type Bi0.5Sb1.5Te3 materials were produced from powder using spark plasma sintering (SPS). The effects of nano-B4C addition on the thermoelectric performance, Vickers hardness and fracture toughness were measured. Addition of 0.2 vol% B4C was found to have little effect on zT but increased hardness by approximately 27% when compared to polycrystalline material without B4C. The KIC fracture toughness of these compositions was measured as 0.80 MPa m1/2 by Single-Edge V-Notched Beam (SEVNB). The machinability of polycrystalline materials produced by SPS was significantly better than commercially available directionally solidified materials because the latter is limited by cleavage along the crystallographic plane parallel to the direction of solidification. 2015-01-26T10:32:41Z Organised large structure in the post-transition mixing layer. Part 2. Large-eddy simulation McMullan, William A. Gao, S. Coats, Christopher M. http://hdl.handle.net/2381/31436 2015-01-17T02:01:40Z 2015-01-16T15:38:31Z Title: Organised large structure in the post-transition mixing layer. Part 2. Large-eddy simulation Authors: McMullan, William A.; Gao, S.; Coats, Christopher M. Abstract: Three-dimensional large-eddy simulations of two-stream mixing layers developing spatially from laminar boundary layers are presented, replicating wind-tunnel experiments carried out in Part 1 of this study. These simulations have been continued through the mixing transition and into the fully turbulent self-similar flow beyond. In agreement with the experiments, the simulations show that the familiar mechanism of growth by vortex amalgamation is replaced at the mixing transition by a previously unrecognised mechanism in which the spanwise-coherent large structures individually undergo continuous linear growth. In the post-transition flow it is this continuous linear growth of the individual structures that produces the self-similar growth of the mixing-layer thickness, the large-structure interactions occurring as a consequence of the growth, not its cause. New information is also presented on the topography of the organised post-transition flow and on its cyclical evolution through the lifetimes of the individual large structures. The dynamic and kinematic implications of these findings are discussed and shown to define quantitatively the growth rate of the homogeneous post-transition mixing layer in its organised state. Description: The file associated with this record under embargo until 3rd June 2015. 2015-01-16T15:38:31Z Organised large structure in the post-transition mixing layer. Part 1: Experimental evidence Coats, Christopher M. D'Ovidio, A. http://hdl.handle.net/2381/31435 2015-01-30T13:46:27Z 2015-01-16T15:25:52Z Title: Organised large structure in the post-transition mixing layer. Part 1: Experimental evidence Authors: Coats, Christopher M.; D'Ovidio, A. Abstract: New flow-visualization experiments on mixing layers of various velocity and density ratios are reported. It is shown that, in mixing layers developing from laminar initial conditions, the familiar mechanism of growth by vortex amalgamation is replaced at the mixing transition by a previously unrecognized mechanism in which the spanwise-coherent large structures individually undergo continuous linear growth. In the organized post-transition flow it is this continuous linear growth of the individual structures that produces the self-similar growth of the mixing-layer thickness, with the occasional interactions between neighbouring structures occurring as a consequence of their growth, not its cause. It is also observed that periods during which the post-transition mixing layer comprises orderly processions of large structures alternate with periods during which no large-scale organization is apparent downstream of the transition location. These two fully turbulent flow states are characterized by different growth rates, entrainment ratios and orientations of the mixing layer relative to the free streams. The implications of these findings are discussed. 2015-01-16T15:25:52Z Observations of Doppler and delay spreads on HF signals received over polar cap and trough paths at various stages of the solar cycle Stocker, A. J. Warrington, E. Michael Siddle, D. R. http://hdl.handle.net/2381/28985 2014-07-17T15:50:16Z 2014-07-17T15:49:39Z Title: Observations of Doppler and delay spreads on HF signals received over polar cap and trough paths at various stages of the solar cycle Authors: Stocker, A. J.; Warrington, E. Michael; Siddle, D. R. Abstract: Information on delay and Doppler spreading is of importance to designers and operators of digital communication systems within the HF band since modem performance rapidly deteriorates when delay and Doppler spreads exceed system dependent thresholds. The northerly ionosphere is a particularly challenging region in this regard as delay and Doppler spreads often significantly exceed those for similar length paths at midlatitudes. This paper presents results from an extensive set of measurements undertaken over three northerly paths: two subauroral paths aligned along the midlatitude trough (Uppsala to Bruntingthorpe and Nurmijärvi to Bruntingthorpe) and one path (Qaanaaq to Ny-Ålesund) contained entirely within the polar cap. Measurements span the period from the 2009 solar minimum to July 2012, close to solar maximum and 2001, close to the previous solar maximum. 2014-07-17T15:49:39Z Wave scattering by many small bodies and applications Ramm, A. G. Rona, Aldo http://hdl.handle.net/2381/28984 2014-07-18T01:01:21Z 2014-07-17T10:02:27Z Title: Wave scattering by many small bodies and applications Authors: Ramm, A. G.; Rona, Aldo Abstract: Wave scattering problem by many bodies is studied in the case when the bodies are small, ka ≪ 1, where a is the characteristic size of a body. The limiting case when a → 0 and the total number of the small bodies is M = O(a [superscript −(2 − κ)]), where κ ∈ (0, 1) is a number, are studied. Description: The following article appeared in Journal of Mathematical Physics, 2011, 52 (2), pp. 1-8 and may be found at http://scitation.aip.org/content/aip/journal/jmp/52/2/10.1063/1.3555192 2014-07-17T10:02:27Z A novel biomimetic infochemical communication technology: From insects to robots Cole, M Rácz, Z Gardner, JW Pearce, Timothy Charles http://hdl.handle.net/2381/28877 2014-06-23T13:43:10Z 2014-05-28T13:59:34Z Title: A novel biomimetic infochemical communication technology: From insects to robots Authors: Cole, M; Rácz, Z; Gardner, JW; Pearce, Timothy Charles Abstract: In this paper we present the development of a novel, biologically-inspired infochemical communication technology in which mixtures of infochemical ligands (in precisely controlled ratios) are used to encode multiple channels of information. Our research is inspired by infochemical production and information processing within the insect world, more specifically the moth Spodoptera littoralis. We have developed a highly innovative modular chemoemitter-receiver system, capable of information transmission using chemicals alone. The functionality of the combined infochemical communication system has been demonstrated, initially through the development of a proof-of-concept prototype based upon pre-synthesized compounds; and it will ultimately be demonstrated through a coordinated robotteam navigation task. © 2012 IEEE. 2014-05-28T13:59:34Z Biologically inspired computation for chemical sensing Fonollosa, J. Gutierrez-Galvez, A. Lansner, A. Martinez, D. Rospars, J. P. Beccherelli, R. Perera, A. Pearce, Timothy Charles Vershure, P. Persaud, K. http://hdl.handle.net/2381/28859 2014-06-23T13:44:20Z 2014-05-28T13:27:02Z Title: Biologically inspired computation for chemical sensing Authors: Fonollosa, J.; Gutierrez-Galvez, A.; Lansner, A.; Martinez, D.; Rospars, J. P.; Beccherelli, R.; Perera, A.; Pearce, Timothy Charles; Vershure, P.; Persaud, K. Abstract: In this paper, we present how the achievements related to NEUROCHEM project (FP7, Bio-ICT, Grant number 216916) have increased the understanding of the olfactory system and helped to develop novel computing architectures and models for chemical sensing. We present the developed computational models of the olfactory pathway of vertebrates and insects to capture the mechanisms that underlie their chemical information processing abilities. To mimic the biological olfactory epithelium a large scale chemical sensor array has been developed. We also present a robot that demonstrates the chemical search task as a direct application of the computing paradigms extracted. Description: Proceedings of the 2nd European Future Technologies Conference and Exhibition 2011 2014-05-28T13:27:02Z Neuroengineering - a renaissance in brain science : Tutorial Series from the 3rd Neuro-IT and Neuroengineering Summer School Pearce, Timothy Charles http://hdl.handle.net/2381/28858 2014-06-23T13:50:37Z 2014-05-28T13:21:11Z Title: Neuroengineering - a renaissance in brain science : Tutorial Series from the 3rd Neuro-IT and Neuroengineering Summer School Authors: Pearce, Timothy Charles Editors: Pearce, TC; de Kamps, M; Knoll, A; Orban, G; König, P; Sandini, G; Davide, FA; Engel, AK 2014-05-28T13:21:11Z Why do olfactory neurons have unspecific receptive fields? Sanchez Montanes, M Pearce, Timothy Charles http://hdl.handle.net/2381/28852 2014-05-23T13:26:41Z 2014-05-23T13:24:15Z Title: Why do olfactory neurons have unspecific receptive fields? Authors: Sanchez Montanes, M; Pearce, Timothy Charles Abstract: Biological olfactory neurons are deployed as a population, most responding to a large variety of chemical compounds, that is, they possess unspecific receptive fields. The question of whether this unspecificity results from some physical constraint placed upon chemical transduction, or on the other hand, is beneficial to system performance is unclear. In this paper we employ the notion of Fisher information to address this question by quantifying how both the distribution and the tunings of the receptive fields within olfactory receptor populations affect the optimal estimation performance of the system. Our results show that overlapping sensory neuron tunings that respond to common chemical compounds have better estimation performance than perfectly specific tunings. Our results suggest two phenomena that might represent general principles of organization within biological sensory systems responding to multiple stimuli: maximization of the diversity of tunings and homogeneity in the distribution of these different receptive fields across the stimulus space (independent of the statistics of the input stimuli). Our model predicts that a local randomized mechanism controlling receptor specificities generates optimal multidimensional stimulus estimation, for which there is some experimental evidence from the biology. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above 2014-05-23T13:24:15Z Preface - The neuroinformatics of neural and artificial computation Verschure, PFMJ Pearce, Timothy Charles Konig, P http://hdl.handle.net/2381/28851 2014-05-23T13:26:19Z 2014-05-23T13:20:22Z Title: Preface - The neuroinformatics of neural and artificial computation Authors: Verschure, PFMJ; Pearce, Timothy Charles; Konig, P Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above 2014-05-23T13:20:22Z Neuroengineering --- a renaissance in brain science : Tutorial Series from the 3rd Neuro-IT and Neuroengineering Summer School Pearce, Timothy Charles de Kamps, M. Knoll, A. Orban, G. Konig, P. Sandini, G. Davide, F. A. Engel, A. K. http://hdl.handle.net/2381/28850 2014-05-23T13:25:50Z 2014-05-23T13:17:31Z Title: Neuroengineering --- a renaissance in brain science : Tutorial Series from the 3rd Neuro-IT and Neuroengineering Summer School Authors: Pearce, Timothy Charles; de Kamps, M.; Knoll, A.; Orban, G.; Konig, P.; Sandini, G.; Davide, F. A.; Engel, A. K. Abstract: Editorial Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above 2014-05-23T13:17:31Z Finite element simulation of a biomimetic olfactory microsystem for spatio-temporal signal generation Tan, S. L. Covington, J. A. Gardner, J. W. Pearce, Timothy Charles http://hdl.handle.net/2381/28849 2014-05-23T13:25:28Z 2014-05-23T13:07:58Z Title: Finite element simulation of a biomimetic olfactory microsystem for spatio-temporal signal generation Authors: Tan, S. L.; Covington, J. A.; Gardner, J. W.; Pearce, Timothy Charles Abstract: The sense of smell is a powerful biological tool although it is the least understood. Attempts to mimic this feature over the last two decades have resulted in the creation of the electronic nose. In comparison to the biological system, its ability to distinguish complex odours is poor. This has mainly been attributed to the lack of sensors and their diversity compared to the human in the order of 10[superscript 5] and 10[superscript 2] respectively. In our efforts to improve the performance of the electronic nose, here we have used a different approach using a unique feature of the biological olfactory system. This technique is analogous to a multi-dimensional gas chromatography (MD-GC) technique that is capable in generating spatial and temporal signals to aid odour discrimination. As the physical realisation requires expensive and time consuming micro- nano fabrication processes, finite element method simulations have been used to validate the proposed design and aid optimisation. This paper describes the finite element modelling process and compares these simulation results to that of the well-established analytical model. Preliminary results of the optimised system are also presented; these results are in good agreement to the simulated outputs. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above 2014-05-23T13:07:58Z Design and implementation of a modular biomimetic infochemical communication system Rácz, Z. Cole, M. Gardner, J. W. Chowdhury, M. F. Bula, W. P. Gardeniers, J. G. E. Karout, S. Capurro, A. Pearce, Timothy Charles http://hdl.handle.net/2381/28843 2014-05-22T14:53:10Z 2014-05-22T13:40:15Z Title: Design and implementation of a modular biomimetic infochemical communication system Authors: Rácz, Z.; Cole, M.; Gardner, J. W.; Chowdhury, M. F.; Bula, W. P.; Gardeniers, J. G. E.; Karout, S.; Capurro, A.; Pearce, Timothy Charles Abstract: We describe here the design and implementation of a novel biomimetic infochemical communication system that employs airborne molecules alone to communicate over space and time. The system involves the design and fabrication of a microsystem capable of producing and releasing a precise mix of biosynthetic compounds and a sensor system capable of detecting and decoding the ratiometrically encoded chemical information. The research inspired by biology has been based upon the biosynthetic pathways of infochemical production and information processing within the insect world. In this novel approach, the functional equivalents of the nanoscale biological machinery are implemented by combining the latest advances and convergence of expertise in the fields of biochemistry, molecular biology, neuroscience, micro- and nanofabrication, materials science, and smart sensor and microcircuit design. The biomimetic system comprises a micromachined bio-reactor mimicking the sex gland of the female insect that releases a blend of pheromones in precisely controlled ratios, together with a cell-based biosensor system, mimicking the antennae of the male insect. The signals from the biosensors are classified and ratios decoded using a field-programmable gate array implementation of a neuromorphic model of the antenna lobe of the insect. We believe that this novel, smart infochemical communication system, inspired by the insect's behavior, could eventually be implemented in VLSI technology at low cost and low power with possible application in the fields of automatic identification and data capturing, product labeling, search and rescue, environmental monitoring, and pest control. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above. 2014-05-22T13:40:15Z Time and space are complementary encoding dimensions in the moth antennal lobe Knuesel, P. Carlsson, M. A. Hansson, B. S. Pearce, Timothy Charles Verschure, P. F. M. J. http://hdl.handle.net/2381/28842 2014-05-22T13:29:09Z 2014-05-22T13:29:09Z Title: Time and space are complementary encoding dimensions in the moth antennal lobe Authors: Knuesel, P.; Carlsson, M. A.; Hansson, B. S.; Pearce, Timothy Charles; Verschure, P. F. M. J. Abstract: The contribution of time to the encoding of information by the nervous system is still controversial. The olfactory system is one of the standard preparations where this issue is empirically investigated. For instance, output neurons of the antennal lobe or the olfactory bulb display odor stimulus induced temporal modulations of their firing rate at a scale of hundreds of milliseconds. The role of these temporal patterns in the encoding of odor stimuli, however, is not yet known. Here, we use optical imaging of the projection neurons of the moth antennal lobe to address this question. First, we present a biophysically derived model that provides an accurate description of the calcium response of projection neurons. On the basis of this model, we subsequently show that the calcium response of the projection neurons displays a stimulus specific temporal structure. Finally, we demonstrate that an encoding scheme that includes this temporal information boosts classification performance by 60% as compared to a purely spatial encoding. Although the putative role of combinatorial spatio-temporal encoding strategies has been the subject of debate, our results for the first time establish quantitatively that such an encoding strategy is used by the insect brain. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above. 2014-05-22T13:29:09Z Component information is preserved in glomerular responses to binary odor mixtures in the moth Spodoptera littoralis Carlsson, M. A. Chong, K. Y. Daniels, W. Hansson, B. S. Pearce, Timothy Charles http://hdl.handle.net/2381/28841 2014-05-22T13:23:23Z 2014-05-22T13:23:23Z Title: Component information is preserved in glomerular responses to binary odor mixtures in the moth Spodoptera littoralis Authors: Carlsson, M. A.; Chong, K. Y.; Daniels, W.; Hansson, B. S.; Pearce, Timothy Charles Abstract: Natural odors are often complex mixtures of different compounds. These mixtures can be perceived to have qualities that are different from their components. Moreover, components can be difficult to distinguish within a blend, even if those components are identifiable when presented individually. Thus, odor components can interact along the olfactory pathway in a nonlinear fashion such that the mixture is not perceived simply as the sum of its components. Here we investigated odor-evoked changes in Ca2+ concentration to binary blends of plant-related substances in individually identified glomeruli in the moth Spodoptera littoralis. We used a wide range of blend ratios and a range of concentrations below the level at which glomerular responses become saturated. We found no statistically significant cases where the mixture response was greater than both component responses at the same total concentration (synergistic interactions) and no statistically significant cases where the mixture response was less than either component presented individually (suppressive interactions). Therefore, we conclude that, for the plant mixtures studied, information of their components is preserved in the neural representations encoded at the first stage of olfactory processing in this moth species. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above. 2014-05-22T13:23:23Z Towards an artificial olfactory mucosa for improved odour classification Gardner, J. W. Covington, J. A. Tan, S.-L. Pearce, Timothy Charles http://hdl.handle.net/2381/28840 2014-05-22T13:18:14Z 2014-05-22T13:18:14Z Title: Towards an artificial olfactory mucosa for improved odour classification Authors: Gardner, J. W.; Covington, J. A.; Tan, S.-L.; Pearce, Timothy Charles Abstract: Here, we report on a biologically inspired analytical system that represents a new concept in the field of machine olfaction. Specifically, this paper describes the design and fabrication of a novel sensor system, based upon the principle of 'nasal chromatography', which emulates the human olfactory mucosa. Our approach exploits the physical positioning of a series of broadly tuned sensors (equivalent to the olfactory epithelium) along the length of a planar chromatographic channel (analogous to the thin mucus coating of the nasal cavity) from which we extract both spatial (response magnitude) and temporal (retentive delay) sensor signals. Our study demonstrates that this artificial mucosa is capable of generating both spatial and temporal signals which, when combined, create a novel spatio-temporal representation of an odour. We believe that such a system not only offers improved odour discrimination over a sensor array-based electronic nose, but also shorter analysis times than conventional gas chromatographic techniques. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above. 2014-05-22T13:18:14Z Chemical source classification in naturally turbulent plumes Pearce, Timothy Charles Gu, J. Chanie, E. http://hdl.handle.net/2381/28839 2014-05-22T13:08:08Z 2014-05-22T13:08:08Z Title: Chemical source classification in naturally turbulent plumes Authors: Pearce, Timothy Charles; Gu, J.; Chanie, E. Abstract: The spatiotemporal dynamics of chemical plumes in natural environments imposes complex time-varying responses on chemical detectors, challenging the use of conventional chemical analysis instrumentation, which often relies upon precisely controlled sampling of analytes. Insects take a different approach to this problem, typically exposing their diversity of chemical receptors to the full extent of the space-time dynamics inherent to these environments. Here we adopt a similar approach, by exposing differentially tuned chemosensor arrays to analytes dispersed in naturally turbulent chemical plumes from a point source. We propose a novel sensor preprocessing metric for complex time-varying chemosensor responses, termed sensor variation, which after normalization generates a stable array response fingerprint representative of the analyte generating the response, and is invariant over a range of distances from the source and source volumes. When applied to chemosensor array response time series, the resultant fingerprints are demonstrated to reliably support chemical classification of a group of pure analytes advected from a point source. By comparing classification performance to the same analytes at equivalent concentrations in controlled sampling conditions, we show that chemical source classification can be achieved in turbulent chemical plumes with similar accuracy to controlled experimental conditions. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above. 2014-05-22T13:08:08Z Robust ratiometric infochemical communication in a neuromorphic "synthetic moth" Pearce, Timothy Charles Karout, S. Capurro, A. Rácz, Z. Cole, M. Gardner, J. W. http://hdl.handle.net/2381/28838 2014-05-22T14:53:36Z 2014-05-22T12:58:33Z Title: Robust ratiometric infochemical communication in a neuromorphic "synthetic moth" Authors: Pearce, Timothy Charles; Karout, S.; Capurro, A.; Rácz, Z.; Cole, M.; Gardner, J. W. Abstract: An often cited advantage of neuromorphic systems is their robust behavior in the face of operating variability, such as sensor noise and non-stationary stimuli statistics inherent to naturally variable environmental processes. One of the most challenging examples of this is extracting information from advected chemical plumes, which are governed by naturally turbulent unsteady flow, one of the very few remaining macroscopic physical phenomena that cannot be described using deterministic Newtonian mechanics. We describe a "synthetic moth" robotic platform that incorporates a real-time neuromorphic model of early olfactory processing in the moth brain (the macro-glomerular complex) for extracting ratiometric information from chemical plumes. Separate analysis has shown that our neuromorphic model achieves rapid and efficient classification of ratiometrically encoded chemical blends by exploiting early phase chemosensor array transients, with execution times well beyond biological timescales. Here, we test our neuromorphic synthetic moth in a naturally turbulent chemical plume and demonstrate robust ratiometric communication of infochemical information. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above. 2014-05-22T12:58:33Z Wiring the olfactory bulb -- activity - dependent models of axonal targeting in the developing olfactory pathway Gill, D. .S Pearce, Timothy Charles http://hdl.handle.net/2381/28836 2014-05-22T12:47:43Z 2014-05-22T12:47:43Z Title: Wiring the olfactory bulb -- activity - dependent models of axonal targeting in the developing olfactory pathway Authors: Gill, D. .S; Pearce, Timothy Charles Abstract: Two recent experimental studies /20,21/ revealed that odorant-evoked activity-dependent competition is significant in the organisation and maintenance of the olfactory system. In this paper, we investigate the generation of a chemotopic sensory map in the olfactory bulb through three models driven by high-density optical chemosensor arrays which have similar properties to olfactory receptor neurons. By exposing the sensor arrays to various odours, these models were subjected to Hebbian learning to achieve self-organisation, potentially explaining the activity-dependent competition demonstrated by these recent studies. Our final model also predicts a role for periglomerular cells in the formation of the chemotopic sensory map in the olfactory bulb. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above. 2014-05-22T12:47:43Z Temporal features of spike trains in the moth antennal lobe revealed by a comparative time-frequency analysis Capurro, Alberto Baroni, Fabiano Kuebler, Linda S. Kárpáti, Zsolt Dekker, Teun Lei, Hong Hansson, Bill S. Pearce, Timothy C. Olsson, Shannon B. http://hdl.handle.net/2381/28809 2014-05-16T01:01:19Z 2014-05-15T15:42:51Z Title: Temporal features of spike trains in the moth antennal lobe revealed by a comparative time-frequency analysis Authors: Capurro, Alberto; Baroni, Fabiano; Kuebler, Linda S.; Kárpáti, Zsolt; Dekker, Teun; Lei, Hong; Hansson, Bill S.; Pearce, Timothy C.; Olsson, Shannon B. Abstract: The discrimination of complex sensory stimuli in a noisy environment is an immense computational task. Sensory systems often encode stimulus features in a spatiotemporal fashion through the complex firing patterns of individual neurons. To identify these temporal features, we have developed an analysis that allows the comparison of statistically significant features of spike trains localized over multiple scales of time-frequency resolution. Our approach provides an original way to utilize the discrete wavelet transform to process instantaneous rate functions derived from spike trains, and select relevant wavelet coefficients through statistical analysis. Our method uncovered localized features within olfactory projection neuron (PN) responses in the moth antennal lobe coding for the presence of an odor mixture and the concentration of single component odorants, but not for compound identities. We found that odor mixtures evoked earlier responses in biphasic response type PNs compared to single components, which led to differences in the instantaneous firing rate functions with their signal power spread across multiple frequency bands (ranging from 0 to 45.71 Hz) during a time window immediately preceding behavioral response latencies observed in insects. Odor concentrations were coded in excited response type PNs both in low frequency band differences (2.86 to 5.71 Hz) during the stimulus and in the odor trace after stimulus offset in low (0 to 2.86 Hz) and high (22.86 to 45.71 Hz) frequency bands. These high frequency differences in both types of PNs could have particular relevance for recruiting cellular activity in higher brain centers such as mushroom body Kenyon cells. In contrast, neurons in the specialized pheromone-responsive area of the moth antennal lobe exhibited few stimulus-dependent differences in temporal response features. These results provide interesting insights on early insect olfactory processing and introduce a novel comparative approach for spike train analysis applicable to a variety of neuronal data sets. 2014-05-15T15:42:51Z Electronic nose for monitoring the flavour of beers Pearce, Timothy C. Gardner, J. W. Friel, S. Bartlett, P. N. Blair, N. http://hdl.handle.net/2381/28808 2014-05-16T01:01:22Z 2014-05-15T15:33:09Z Title: Electronic nose for monitoring the flavour of beers Authors: Pearce, Timothy C.; Gardner, J. W.; Friel, S.; Bartlett, P. N.; Blair, N. Abstract: The flavour of a beer is determined mainly by its taste and smell, which is generated by about 700 key volatile and non-volatile compounds. Beer flavour is traditionally measured through the use of a combination of conventional analytical tools (e.g., gas chromatography) and organoleptic profiling panels. These methods are not only expensive and time-consuming but also inexact due to a lack of either sensitivity or quantitative information. In this paper an electronic instrument is described that has been designed to measure the odour of beers and supplement or even replace existing analytical methods. The instrument consists of an array of up to 12 conducting polymers, each of which has an electrical resistance that has partial sensitivity to the headspace of beer. The signals from the sensor array are then conditioned by suitable interface circuitry and processed using a chemometric or neural classifier. The results of the application of multivariate statistical techniques are given. The instrument, or electronic nose, is capable of discriminating between various commercial beers and, more significantly, between standard and artificially-tainted beers. An industrial version of this instrument is now undergoing trials in a brewery. 2014-05-15T15:33:09Z Rapid processing of chemosensor transients in a neuromorphic implementation of the insect macroglomerular complex. Pearce, Timothy C. Karout, Salah Rácz, Zoltan Capurro, Alberto Gardner, Julian W. Cole, Marina http://hdl.handle.net/2381/28804 2014-05-15T01:01:17Z 2014-05-14T14:53:15Z Title: Rapid processing of chemosensor transients in a neuromorphic implementation of the insect macroglomerular complex. Authors: Pearce, Timothy C.; Karout, Salah; Rácz, Zoltan; Capurro, Alberto; Gardner, Julian W.; Cole, Marina Abstract: We present a biologically-constrained neuromorphic spiking model of the insect antennal lobe macroglomerular complex that encodes concentration ratios of chemical components existing within a blend, implemented using a set of programmable logic neuronal modeling cores. Depending upon the level of inhibition and symmetry in its inhibitory connections, the model exhibits two dynamical regimes: fixed point attractor (winner-takes-all type), and limit cycle attractor (winnerless competition type) dynamics. We show that, when driven by chemosensor input in real-time, the dynamical trajectories of the model's projection neuron population activity accurately encode the concentration ratios of binary odor mixtures in both dynamical regimes. By deploying spike timing-dependent plasticity in a subset of the synapses in the model, we demonstrate that a Hebbian-like associative learning rule is able to organize weights into a stable configuration after exposure to a randomized training set comprising a variety of input ratios. Examining the resulting local interneuron weights in the model shows that each inhibitory neuron competes to represent possible ratios across the population, forming a ratiometric representation via mutual inhibition. After training the resulting dynamical trajectories of the projection neuron population activity show amplification and better separation in their response to inputs of different ratios. Finally, we demonstrate that by using limit cycle attractor dynamics, it is possible to recover and classify blend ratio information from the early transient phases of chemosensor responses in real-time more rapidly and accurately compared to a nearest-neighbor classifier applied to the normalized chemosensor data. Our results demonstrate the potential of biologically-constrained neuromorphic spiking models in achieving rapid and efficient classification of early phase chemosensor array transients with execution times well beyond biological timescales. 2014-05-14T14:53:15Z Timing of single-neuron and local field potential responses in the human medial temporal lobe Rey, Hernan Gonzalo Fried, Itzhak Quian Quiroga, Rodrigo http://hdl.handle.net/2381/28692 2014-03-21T02:01:45Z 2014-03-20T12:01:06Z Title: Timing of single-neuron and local field potential responses in the human medial temporal lobe Authors: Rey, Hernan Gonzalo; Fried, Itzhak; Quian Quiroga, Rodrigo Abstract: The relationship between the firing of single cells and local field potentials (LFPs) has received increasing attention, with studies in animals and humans. Recordings in the human medial temporal lobe (MTL) have demonstrated the existence of neurons with selective and invariant responses, with a relatively late but precise response onset around 300 ms after stimulus presentation and firing only upon conscious recognition of the stimulus. This represents a much later onset than expected from direct projections from inferotemporal cortex. The neural mechanisms underlying this onset remain unclear. To address this issue, we performed a joint analysis of single-cell and LFP responses during a visual recognition task. Single-neuron responses were preceded by a global LFP deflection in the theta range. In addition, there was a local and stimulus-specific increase in the single-trial gamma power. These LFP responses correlated with conscious recognition. The timing of the neurons' firing was phase locked to these LFP responses. We propose that whereas the gamma phase locking reflects the activation of local networks encoding particular recognized stimuli, the theta phase locking reflects a global activation that provides a temporal window for processing consciously perceived stimuli in the MTL. 2014-03-20T12:01:06Z Looking for a face in the crowd : Fixation-related potentials in an eye-movement visual search task Kaunitz, Lisandro N. Kamienkowski, Juan E. Varatharajah, Alexander Sigman, Mariano Quiroga, Rodrigo Quian Ison, Matias J. http://hdl.handle.net/2381/28647 2014-03-11T14:59:02Z 2014-03-11T14:53:49Z Title: Looking for a face in the crowd : Fixation-related potentials in an eye-movement visual search task Authors: Kaunitz, Lisandro N.; Kamienkowski, Juan E.; Varatharajah, Alexander; Sigman, Mariano; Quiroga, Rodrigo Quian; Ison, Matias J. Abstract: Despite the compelling contribution of the study of event related potentials (ERPs) and eye movements to cognitive neuroscience, these two approaches have largely evolved independently. We designed an eye-movement visual search paradigm that allowed us to concurrently record EEG and eye movements while subjects were asked to find a hidden target face in a crowded scene with distractor faces. Fixation event-related potentials (fERPs) to target and distractor stimuli showed the emergence of robust sensory components associated with the perception of stimuli and cognitive components associated with the detection of target faces. We compared those components with the ones obtained in a control task at fixation: qualitative similarities as well as differences in terms of scalp topography and latency emerged between the two. By using single trial analyses, fixations to target and distractors could be decoded from the EEG signals above chance level in 11 out of 12 subjects. Our results show that EEG signatures related to cognitive behavior develop across spatially unconstrained exploration of natural scenes and provide a first step towards understanding the mechanisms of target detection during natural search. 2014-03-11T14:53:49Z Development of thermoacoustic devices for power generation and refrigeration Jaworski, Artur J. Mao, Xiaoan http://hdl.handle.net/2381/28289 2013-10-16T01:02:05Z 2013-10-15T14:34:04Z Title: Development of thermoacoustic devices for power generation and refrigeration Authors: Jaworski, Artur J.; Mao, Xiaoan Abstract: This paper is intended as a technical overview of the research and development work initially undertaken at the University of Manchester and subsequently transferred to the University of Leicester as part of the EPSRC-funded SCORE project (Stove for Cooking, Refrigeration and Electricity supply). The objectives of the work were twofold: Firstly, to develop an early demonstrator of a low-power electricity generator (to deliver approximately 10–20Wof electricity). This was to be based on the concept of using low-cost materials, working fluids and linear alternators suitable for deployment in rural areas of developing countries. The issues of concern here were the development of a suitable thermoacoustic engine topology and control measures; design of suitable heat exchanger configurations from initial use of electrical heaters to heat input through propane combustion; and characterisation of commercial loudspeakers to work as linear alternators and subsequent incorporation of selected models for engine prototyping purposes. These matters will be illustrated by a number of demonstrators and their testing in the laboratory environment. Secondly, to develop a demonstrator of a combustion driven thermoacoustic cooler for storage of vital medical supplies in remote and rural areas where there is no access to electricity grid. To this end, the paper will describe the design, construction and test results of an electrically driven demonstrator of a standing wave thermoacoustic engine coupled to a travelling wave thermoacoustic cooler. The final part of the paper will summarise the achievements to date and outline future work that has spun out from the original SCORE project. This will in particular include the current work on a scaled up version of electricity generator designed to deliver 100W of electricity by using a two-stage engine configuration and the issues of integration of the thermoacoustic electricity generator and thermoacoustic cooler into one system. 2013-10-15T14:34:04Z Theoretical analysis of the evanescent wave absorption coefficient for multimode fibre-optic evanescent wave absorption sensors Xu, Yu Jones, N. Barrie Fothergill, John C. Hanning, Chris D. http://hdl.handle.net/2381/28276 2013-10-09T12:23:57Z 2013-10-09T12:23:13Z Title: Theoretical analysis of the evanescent wave absorption coefficient for multimode fibre-optic evanescent wave absorption sensors Authors: Xu, Yu; Jones, N. Barrie; Fothergill, John C.; Hanning, Chris D. Abstract: In an optical fibre of circular cross section, leaky skew rays transmit power in a different way from trapped and meridional rays. In this paper, a theoretical analysis of the evanescent wave absorption coefficient for leaky skew rays in multimode optical fibre evanescent wave absorption sensors is presented. Further, a comprehensive expression for the effective evanescent wave absorption coefficient is obtained. Some numerical results are given to illustrate this theoretical analysis. This work could be applied to optimize the design of fibre-optic evanescent wave absorption sensors. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above. 2013-10-09T12:23:13Z Improvement of PEA signal analysis using simulations for complex geometry samples Holé, Stéphane Griseri, Virginie Dissado, Leonard A. Fothergill, John C. http://hdl.handle.net/2381/28275 2013-10-09T12:04:45Z 2013-10-09T12:03:10Z Title: Improvement of PEA signal analysis using simulations for complex geometry samples Authors: Holé, Stéphane; Griseri, Virginie; Dissado, Leonard A.; Fothergill, John C. Abstract: Complex geometry structures, such as produced by imperfections, cause the electric field to reach a very high local value even at low applied voltages. These are often the initiators of breakdown. Though direct measurement methods for space charge and electric field can be used only for planar or coaxial geometry, the authors propose to apply the pulsed-electro-acoustic (PEA) method to such complex geometry structures by using a simulation technique. The physical background of the simulation is presented. Comparisons between simulated and experimental signals are shown to be in good agreement meaning that simulations can be used as a tool for signal analysis. Description: Full text of this item is not currently available on the LRA. The final published version may be available through the links above. 2013-10-09T12:03:10Z A novel surface electrocardiogram-based marker of ventricular arrhythmia risk in patients with ischemic cardiomyopathy. Nicolson, William B. McCann, Gerry P. Brown, Peter D. Sandilands, Alastair J. Stafford, Peter J. Schlindwein, Fernando Soares Samani, Nilesh J. Ng, G. André http://hdl.handle.net/2381/27870 2013-10-23T15:08:32Z 2013-04-22T15:53:50Z Title: A novel surface electrocardiogram-based marker of ventricular arrhythmia risk in patients with ischemic cardiomyopathy. Authors: Nicolson, William B.; McCann, Gerry P.; Brown, Peter D.; Sandilands, Alastair J.; Stafford, Peter J.; Schlindwein, Fernando Soares; Samani, Nilesh J.; Ng, G. André Abstract: Background: Better sudden cardiac death risk markers are needed in ischemic cardiomyopathy (ICM). Increased heterogeneity of electrical restitution is an important mechanism underlying the risk of ventricular arrhythmia (VA). Our aim was to develop and test a novel quantitative surface electrocardiogram–based measure of VA risk in patients with ICM: the Regional Restitution Instability Index (R2I2). Methods and Results: R2I2, the mean of the standard deviation of residuals from the mean gradient for each ECG lead at a range of diastolic intervals, was measured retrospectively from high-resolution 12-lead ECGs recorded during an electrophysiology study. Patient groups were as follows: Study group, 26 patients with ICM being assessed for implantable defibrillator; Control group, 29 patients with supraventricular tachycardia undergoing electrophysiology study; and Replication group, 40 further patients with ICM. R2I2 was significantly higher in the Study patients than in Controls (mean ± standard error of the mean: 1.09±0.06 versus 0.63±0.04, P<0.001). Over a median follow-up period of 23 months, 6 of 26 Study group patients had VA or death. R2I2 predicted VA or death independently of demographic factors, electrophysiology study result, left ventricular ejection fraction, or QRS duration (Cox model, P=0.029). R2I2 correlated with peri-infarct zone as assessed by cardiac magnetic resonance imaging (r=0.51, P=0.024). The findings were replicated in the Replication group: R2I2 was significantly higher in 11 of 40 Replication patients experiencing VA (1.18±0.10 versus 0.92±0.05, P=0.019). In combined analysis of ICM cohorts, R2I2 ≥1.03 identified subjects with significantly higher risk of VA or death (43%) compared with R2I2 <1.03 (11%) (P=0.004). Conclusions: In this pilot study, we have developed a novel VA risk marker, R2I2, and have shown that it correlated with a structural measure of arrhythmic risk and predicted risk of VA or death in patients with ICM. R2I2 may improve risk stratification and merits further evaluation. 2013-04-22T15:53:50Z Models of bipolar charge transport in polyethylene Boufayed, F. Teyssèdre, G. Laurent, C. Le Roy, S. Dissado, Len A. Ségur, P. Montanari, G.C. http://hdl.handle.net/2381/27863 2013-04-17T01:02:02Z 2013-04-16T15:42:53Z Title: Models of bipolar charge transport in polyethylene Authors: Boufayed, F.; Teyssèdre, G.; Laurent, C.; Le Roy, S.; Dissado, Len A.; Ségur, P.; Montanari, G.C. Abstract: We introduce and develop two bipolar transport models which are based on appreciably different physical assumptions regarding the distribution function in the energy levels of trap states. In the first model, conduction is described by an effective mobility of the carriers and the accumulation of stored space charge is taken into account through a single trapping level. In the second model the hypothesis of an exponential distribution function of trap depth is made, with conduction taking place via a hopping process from site to site. The results of simulations of the two models are compared with experimental data for the external current and the space-time evolution of the electrical space charge distribution. The two descriptions are evaluated in a critical way, and the prospects for these models to adequately describe real systems are given. 2013-04-16T15:42:53Z Fast soliton-like charge pulses in insulating polymers Dissado, Len A. Montanari, G.C. Fabiani, D. http://hdl.handle.net/2381/27860 2013-04-17T01:02:03Z 2013-04-16T14:28:38Z Title: Fast soliton-like charge pulses in insulating polymers Authors: Dissado, Len A.; Montanari, G.C.; Fabiani, D. Abstract: A previously unknown mode of conduction is identified in insulating polymers at moderate fields (40-50 MV/m). This takes the form of coherent charged pulses with a mobility (similar to 10(-10) m(2)V(-1)s(-1)) several orders of magnitude larger than that traditionally associated with independent charge carriers (similar to 10(-14) m(2)V(-1)s(-1)). It is shown that this phenomenon is consistent with a mechanism in which a charged compression boundary is formed electro-mechanically during injection and thereafter travels as a coherent solitary wave (soliton) through the polymer. 2013-04-16T14:28:38Z Distinctive Patterns of Dominant Frequency Trajectory Behaviour in Persistent Atrial Fibrillation: Characterisation of Spatio-Temporal Instability Salinet, João L., Jr. Tuan, Jiun H. Sandilands, Alistair J. Stafford, Peter J. Schlindwein, Fernando Soares Ng, G. André http://hdl.handle.net/2381/27856 2013-05-01T12:38:34Z 2013-04-15T13:25:00Z Title: Distinctive Patterns of Dominant Frequency Trajectory Behaviour in Persistent Atrial Fibrillation: Characterisation of Spatio-Temporal Instability Authors: Salinet, João L., Jr.; Tuan, Jiun H.; Sandilands, Alistair J.; Stafford, Peter J.; Schlindwein, Fernando Soares; Ng, G. André Abstract: Background: Substrates for maintenance of persistent atrial fibrillation (persAF) remain poorly understood. The use of dominant frequency (DF) mapping to guide catheter ablation has been proposed as a potential strategy, but the characteristics of high DF sites have not been extensively studied. Methods and Results: We assessed the temporal stability of DF using both contact and non-contact mapping of persAF. A total of 18 patients were included in the study. Group 1 consisted of 8 patients with contact and non-contact mapping and group 2 consisted of 10 patients who had contact mapping only. The percentage of stable DF points from both AF contact and virtual electrograms decreased rapidly over time in an exponential fashion. Sites with highest DF did not remain spatially stable and periodic DF behaviour was noted, occurring within 10 s in most cases. Tracking of the centre of gravity of highest DF areas revealed 3 types of propagation characteristics, namely i) local, ii) cyclical and iii) chaotic activity, with the former 2 patterns accounting for most of the observed events. Conclusions: DF of AF electrograms are not spatiotemporally stable and targeting sites of peak DF alone is unlikely to be a reliable ablation strategy. There appears to be a predominance of local and cyclical activity when centre of gravity of highest DF areas are tracked, which provides further mechanistic insights into maintenance of persAF. Description: Embargo length currently unknown. The article is still in press and the full text will be made available once it has been published. 2013-04-15T13:25:00Z Visualizing Intracardiac Atrial Fibrillation Electrograms Using Spectral Analysis Salinet, João Loures, Jr. Oliveira, Guilherme N. Vanheusden, Frederique Jos Comba, João Luiz Dihl Ng, G. André Schlindwein, Fernando Soares http://hdl.handle.net/2381/27854 2013-04-15T14:27:10Z 2013-04-10T14:44:35Z Title: Visualizing Intracardiac Atrial Fibrillation Electrograms Using Spectral Analysis Authors: Salinet, João Loures, Jr.; Oliveira, Guilherme N.; Vanheusden, Frederique Jos; Comba, João Luiz Dihl; Ng, G. André; Schlindwein, Fernando Soares Abstract: Atrial fibrillation is the most common cardiac arrhythmia, and it is associated with increased risk of stroke, heart failure, and mortality. This work describes spectral analysis techniques that are being used in conjunction with visualization algorithms to help guide catheter ablation procedures that aim at treating patients with arrhythmia. 2013-04-10T14:44:35Z Analysis of QRS-T Subtraction in Unipolar Atrial Fibrillation Electrograms Salinet Jr., J.L. Madeiro, João P.V. Cortez, Paulo C. Stafford, Peter J. Ng, G. André Schlindwein, Fernando Soares http://hdl.handle.net/2381/27853 2014-04-07T01:45:04Z 2013-04-10T14:10:36Z Title: Analysis of QRS-T Subtraction in Unipolar Atrial Fibrillation Electrograms Authors: Salinet Jr., J.L.; Madeiro, João P.V.; Cortez, Paulo C.; Stafford, Peter J.; Ng, G. André; Schlindwein, Fernando Soares Abstract: This paper presents a QRS-T subtraction approach for atrial fibrillation (AF) intracardiac atrial electrograms (AEG). It also presents a comparison between the proposed method and two alternative ventricular subtraction techniques: average beat subtraction (ABS) using a fixed length window and an approach based on flat interpolation for QRS cancellation. Areas of the atrium close to the mitral valve showed stronger ventricular influence on the AEGs when compared with the remaining atrial regions. Ventricular influence affects the spectral power distribution of the AEG and can also affect the estimation of the dominant frequency unless the whole ventricular activity influence (QRS-T) is removed. The average power after QRS-T subtraction is significantly reduced for frequencies above 10 Hz (mostly associated with QRS complexes), as well as for frequencies between 3 and 5.5 Hz, (mostly related to T waves). The results indicate that the proposed approach removes ventricular influence on the AF AEGs better than the QRS cancellation method. Spectral analysis showed that both the ABS and the proposed method do well and no method should be preferred to the other. In the time domain, the proposed approach is matched to the lengths and timings of onset and offset for individual QRS-T segments while the ABS approach uses an arbitrary length around the QRS for the pattern used for QRS-T removal. 2013-04-10T14:10:36Z Heart Rate Variability in Low Birth Weight Growth Restricted Children During Sleep and Wake Stages Aziz, Wajid Biala, Taher Ali Said Habib, Nazneen Abbasi, Muhammad S. Wailoo, Michael P. Schlindwein, Fernando Soares http://hdl.handle.net/2381/27852 2013-04-22T14:49:41Z 2013-04-10T13:36:54Z Title: Heart Rate Variability in Low Birth Weight Growth Restricted Children During Sleep and Wake Stages Authors: Aziz, Wajid; Biala, Taher Ali Said; Habib, Nazneen; Abbasi, Muhammad S.; Wailoo, Michael P.; Schlindwein, Fernando Soares Abstract: Poor fetal growth may alter the regularity mechanism of cardiac autonomic system that is involved in the development of these diseases. The malfunctioning of the cardiac autonomic system assessed by decrease in heart rate variability (HRV) is associated with negative cardiovascular outcomes. This study is aimed at investigating the risk of development of coronary heart disease in IUGR children in later life. For that purpose HRV analysis of normal and growth restricted children was performed during sleep and wake stages. The study group consisted of 9 to 10 years old, 32 normal, 20 low birth weight IUGR children. The standard time domain HRV metrics (mean RR, SDNN, RMSSD, NN50 and pNN50) and Poincaré indices (SD1 and SD2) were used to analyse and compare the RR-interval time series of these groups. The IUGR children showed lower HRV as compared with normal children during both sleep and wake stages. The significantly decreased HRV during sleep provide an evidence of autonomic derangement that may be associated with higher risk of lethal arrhythmias in the IUGR children in later life. 2013-04-10T13:36:54Z New Approach for T-Wave Peak Detection and T-Wave End Location in 12-lead Paced ECG Signals based on a Mathematical Model Madeiro, João P.V. Nicolson, William B. Cortez, Paulo C. Marques, João A.L. Vázquez-Seisdedos, Carlos R. Elangovan, Narmadha Ng, G. André Schlindwein, Fernando Soares http://hdl.handle.net/2381/27851 2013-04-15T14:26:27Z 2013-04-09T15:53:19Z Title: New Approach for T-Wave Peak Detection and T-Wave End Location in 12-lead Paced ECG Signals based on a Mathematical Model Authors: Madeiro, João P.V.; Nicolson, William B.; Cortez, Paulo C.; Marques, João A.L.; Vázquez-Seisdedos, Carlos R.; Elangovan, Narmadha; Ng, G. André; Schlindwein, Fernando Soares Abstract: This paper presents an innovative approach for T-wave peak detection and subsequent T-wave end location in 12-lead paced ECG signals based on a mathematical model of a skewed Gaussian function. Following the stage of QRS segmentation, we establish search windows using a number of the earliest intervals between each QRS offset and subsequent QRS onset. Then, we compute a template based on a Gaussian-function, modified by a mathematical procedure to insert asymmetry, which models the T-wave. Cross-correlation and an approach based on the computation of Trapezium's area are used to locate, respectively, the peak and end point of each T-wave throughout the whole raw ECG signal. For evaluating purposes, we used a database of high resolution 12-lead paced ECG signals, recorded from patients with ischaemic cardiomyopathy (ICM) in the University Hospitals of Leicester NHS Trust, UK, and the well-known QT database. The average T-wave detection rates, sensitivity and positive predictivity, were both equal to 99.12%, for the first database, and, respectively, equal to 99.32% and 99.47%, for QT database. The average time errors computed for T-wave peak and T-wave end locations were, respectively, −0.38 ± 7.12 ms and −3.70 ± 15.46 ms, for the first database, and 1.40 ± 8.99 ms and 2.83 ± 15.27 ms, for QT database. The results demonstrate the accuracy, consistency and robustness of the proposed method for a wide variety of T-wave morphologies studied. 2013-04-09T15:53:19Z Heart rate variability: Linear and non-linear analysis of pre-awake period for normal and intrauterine growth restricted children at 10 year Biala, Taher Ali Said Aziz, Wajid Wailoo, Michael P. Schlindwein, Fernando Soares http://hdl.handle.net/2381/27850 2013-04-15T14:33:16Z 2013-04-09T15:15:56Z Title: Heart rate variability: Linear and non-linear analysis of pre-awake period for normal and intrauterine growth restricted children at 10 year Authors: Biala, Taher Ali Said; Aziz, Wajid; Wailoo, Michael P.; Schlindwein, Fernando Soares Abstract: Non-optimal fetal growth has been associated with an increased risk of coronary heart diseases in later life. Heart rate variability (HRV) is a non-invasive method reflecting autonomic cardiac function and decreased heart rate variability has been associated with arrhythmic complications in humans. This study compares the result of linear and nonlinear HRV measures performed in long term (24 h) versus short term (15 min before awakening) interbeat interval time series data of normal and growth restricted children who were 9-10 years old. The aim of the study was to investigate which HRV measures obtained from short term recording reliably reflect information provided by long term recording. The comparability of HRV parameters derived from long term and short term recordings showed that low birth weight growth restricted children (IUGR) have low HRV. The findings indicated that low birth weight in growth retarded may be associated with negative cardiovascular outcome. 2013-04-09T15:15:56Z Computerized Cardiotocography Analysis System based on Hilbert Transform Marques, João A.L. Cortez, Paulo C. Madeiro, João P.V. Schlindwein, Fernando Soares http://hdl.handle.net/2381/27848 2013-04-10T01:02:02Z 2013-04-09T13:53:05Z Title: Computerized Cardiotocography Analysis System based on Hilbert Transform Authors: Marques, João A.L.; Cortez, Paulo C.; Madeiro, João P.V.; Schlindwein, Fernando Soares Abstract: The visual analysis of Cardiotocographic (CTG) examinations is a very subjective process. The accurate detection and segmentation of the fetal heart rate (FHR) features and their time correlation with the uterine contractions (UC) allow a better diagnostic and the possibility of anticipation of many problems related to fetal distress. This paper presents a diagnostic aid system based on digital signal processing techniques to detect and segment changes in the FHR and the uterine tone signals automatically. The FHR baseline detection is proposed after pre-processing filtering. The detection line is an auxiliary signal based on the Baseline and a moving average. The Hilbert Transform is then used with adaptive thresholding techniques for identifying fiducial points on the signals. For an antepartum validation database, i.e., exams collected before labor, the positive predictivity value (PPV) found is 96.80% for the FHR decelerations, and 96.18% for the FHR accelerations. For an intrapartum validation database, the PPV found was 91.31% for the uterine contractions, 94.01% for the FHR decelerations, and 100% for the FHR accelerations. For the whole set of exams, PPV and SE were both 100% for the identification of FHR DIP II and prolonged decelerations. 2013-04-09T13:53:05Z Determination of the shape and indium distribution of low-growth-rate InAs quantum dots by cross-sectional scanning tunneling microscopy Bruls, D.M. Vugs, J.W.A.M. Koenraad, P.M. Salemink, H.W.M. Wolter, J.H. Hopkinson, M. Skolnick, M.S. Long, Fei Gill, Simon P.A. http://hdl.handle.net/2381/27845 2013-04-09T01:01:52Z 2013-04-08T14:33:30Z Title: Determination of the shape and indium distribution of low-growth-rate InAs quantum dots by cross-sectional scanning tunneling microscopy Authors: Bruls, D.M.; Vugs, J.W.A.M.; Koenraad, P.M.; Salemink, H.W.M.; Wolter, J.H.; Hopkinson, M.; Skolnick, M.S.; Long, Fei; Gill, Simon P.A. Abstract: We present a cross-sectional scanning-tunneling microscopy investigation of the shape, size, and composition of InAs quantum dots in a GaAs matrix, grown by molecular beam epitaxy at low growth rate. From the dimensional analysis we conclude that the investigated quantum dots have an average height of 5 nm, a square base of 18 nm oriented along [010] and [100] and the shape of a truncated pyramid. From outward relaxation and lattice constant profiles we conclude that the dots consist of an InGaAs alloy and that the indium concentration increases linearly in the growth direction. Our results justify the predictions obtained from previous photocurrent measurements on similar structures and the used theoretical model. 2013-04-08T14:33:30Z Percolation model for electrical breakdown in insulating polymers Wu, Kai Dissado, Len A. Okamoto, Tatsuki http://hdl.handle.net/2381/27843 2013-04-09T01:01:49Z 2013-04-08T13:27:31Z Title: Percolation model for electrical breakdown in insulating polymers Authors: Wu, Kai; Dissado, Len A.; Okamoto, Tatsuki Abstract: It is suggested that an electric field above a given value eliminates the barriers to the transport of trapped charge carriers so as to produce an extended state in the form of a percolation cluster, and that the consequent current multiplication results in electrical breakdown. This model provides an estimated value of intrinsic breakdown strength close to the actual value. By considering the interactions between trap barrier potentials, the effect of electrical aging can be explained in terms of an increase in trap density. Many phenomena, such as the effect of weak points and the change of breakdown strength with the content of co-monomers or additives, can also be explained using this model. 2013-04-08T13:27:31Z Erratum: 'Percolation model for electrical breakdown in insulating polymers' (vol 85, pg 4454, 2004) Wu, Kai Okamoto, Tatsuki Dissado, Len A. http://hdl.handle.net/2381/27835 2013-04-08T13:35:37Z 2013-03-27T16:18:20Z Title: Erratum: 'Percolation model for electrical breakdown in insulating polymers' (vol 85, pg 4454, 2004) Authors: Wu, Kai; Okamoto, Tatsuki; Dissado, Len A. 2013-03-27T16:18:20Z Enhanced elastic interactions between conical quantum dots Gill, Simon P.A. http://hdl.handle.net/2381/27834 2013-03-28T02:02:15Z 2013-03-27T15:54:17Z Title: Enhanced elastic interactions between conical quantum dots Authors: Gill, Simon P.A. Abstract: An analytical model for the elastic energy of a system of conical heteroepitaxial quantum dots of finite slope is presented. An expression for the surface tractions at the dot-substrate interface is proposed. This includes a singularity in the stress field at the perimeter of the dot. The strength of this singularity increases as the slope of the dot increases. This dramatically enhances the elastic interaction between dots and the metastability of a quantum dot array. This could help explain the stability of bimodal island size distributions observed in some quantum dot systems. 2013-03-27T15:54:17Z An analytical model for the growth of quantum dots on ultrathin substrates Gill, Simon P.A. http://hdl.handle.net/2381/27832 2013-03-28T02:01:54Z 2013-03-27T14:46:45Z Title: An analytical model for the growth of quantum dots on ultrathin substrates Authors: Gill, Simon P.A. Abstract: The self-assembly of heteroepitaxial quantum dots on ultrathin substrates is analyzed within the context of small perturbation theory. Analytical expressions are derived for the dependence of the quantum dot separation on the substrate thickness. It is shown that the substrate thickness is critical in determining this separation when it is below the intrinsic material length scale of the system. The model is extended to simultaneous dot growth on both sides of the substrate. It is shown that vertically anticorrelated structures are preferred with an increase in the dot separation of 15% above that found in the one-sided case. 2013-03-27T14:46:45Z Encounters with vortices in a turbine nozzle passage Gostelow, J. Paul Mahallati, A. Carscallen, W.E. Rona, Aldo http://hdl.handle.net/2381/27749 2014-02-28T13:30:44Z 2013-02-11T15:46:02Z Title: Encounters with vortices in a turbine nozzle passage Authors: Gostelow, J. Paul; Mahallati, A.; Carscallen, W.E.; Rona, Aldo Abstract: Experiments were conducted on the flow through a transonic turbine cascade. Secondary flows and a wide range of vortex types were encountered, including horseshoe vortices, shock-induced passage vortices, and streamwise vortices on the suction surface. In the separation region on the suction surface, a large rollup of passage vorticity occurred. The blunt leading edge gave rise to strong horseshoe vortices and secondary flows. The suction surface had a strong convex curvature over the forward portion and was quite flat further downstream. Surface flow visualization was performed and this convex surface displayed coherent streamwise vorticity. At subsonic speeds, strong von Kármán vortex shedding resulted in a substantial base pressure deficit. For these conditions, time-resolved measurements were made of the Eckert-Weise energy separation in the blade wake. At transonic speeds, exotic shedding modes were observed. These phenomena all occurred in experiments on the flow around one particular turbine nozzle vane in a linear cascade. 2013-02-11T15:46:02Z Mechanisms contributing to central excitability changes during hearing loss. Pilati, N Ison, MJ Barker, M Mulheran, M Large, CH Forsythe, ID Matthias, J Hamann, M http://hdl.handle.net/2381/27091 2012-10-24T09:22:56Z 2012-10-24T09:22:55Z Title: Mechanisms contributing to central excitability changes during hearing loss. Authors: Pilati, N; Ison, MJ; Barker, M; Mulheran, M; Large, CH; Forsythe, ID; Matthias, J; Hamann, M Abstract: Exposure to loud sound causes cochlear damage resulting in hearing loss and tinnitus. Tinnitus has been related to hyperactivity in the central auditory pathway occurring weeks after loud sound exposure. However, central excitability changes concomitant to hearing loss and preceding those periods of hyperactivity, remain poorly explored. Here we investigate mechanisms contributing to excitability changes in the dorsal cochlear nucleus (DCN) shortly after exposure to loud sound that produces hearing loss. We show that acoustic overexposure alters synaptic transmission originating from the auditory and the multisensory pathway within the DCN in different ways. A reduction in the number of myelinated auditory nerve fibers leads to a reduced maximal firing rate of DCN principal cells, which cannot be restored by increasing auditory nerve fiber recruitment. In contrast, a decreased membrane resistance of DCN granule cells (multisensory inputs) leads to a reduced maximal firing rate of DCN principal cells that is overcome when additional multisensory fibers are recruited. Furthermore, gain modulation by inhibitory synaptic transmission is disabled in both auditory and multisensory pathways. These cellular mechanisms that contribute to decreased cellular excitability in the central auditory pathway are likely to represent early neurobiological markers of hearing loss and may suggest interventions to delay or stop the development of hyperactivity that has been associated with tinnitus. 2012-10-24T09:22:55Z Dielectric ageing: Materials, measurements and modelling of nano- to meso-scale processes Vaughan, AS Chen, G Lewin, PL Dodd, SJ Swingler, SG Vaughan, AS http://hdl.handle.net/2381/22194 2012-10-24T09:11:14Z 2012-10-24T09:11:14Z Title: Dielectric ageing: Materials, measurements and modelling of nano- to meso-scale processes Authors: Vaughan, AS; Chen, G; Lewin, PL; Dodd, SJ; Swingler, SG; Vaughan, AS 2012-10-24T09:11:14Z