Electrical and Electronic Engineering - Research Publications

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    On the use of switched linear controllers for stabilizability of implicit recursive equations
    Nesic, D (IEEE, 1998-01-01)
    Stabilizability of implicit recursive equations is investigated. These equations arise naturally in the context of output dead-beat control for systems described by NARMAX models. Due to non-uniqueness of the solutions of these equations a special kind of a constrained stabilizability problem is considered. We take a hybrid switching control approach in testing the existence of a locally stabilizing controller. A method for the design of a stabilizing switching controller is also presented.
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    Analysis of minimum phase properties for non-affine nonlinear systems
    Nesic, D ; Skafidas, E ; Mareels, IMY ; Evans, RJ (IEEE, 1997-01-01)
    A system can be termed non-minimum phase according to some definitions available in the literature and yet the same system may exhibit stable zero output constrained dynamics. We show that for non-affine nonlinear systems there may not exist a continuous control law which would keep the output identically equal to zero and for which the zero output constrained dynamics are stable, whereas a discontinuous controller which achieves this exists. We give conditions for existence and present a method for design of discontinuous switching controllers which yield stable zero dynamics. In this sense, the results of this paper enlarge the class of non-affine nonlinear systems that can be termed minimum-phase.
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    Minimum phase properties for input nonaffine nonlinear systems
    Nesic, D ; Skafidas, E ; Mareels, IMY ; Evans, RJ (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 1999-04-01)
    For input nonaffine nonlinear control systems, the minimum phase property of the system in general depends on the control law. Switching or discontinuous controllers may offer advantages in this context. In particular, there may not exist a continuous control law which would keep the output identically equal to zero and for which the zero output constrained dynamics are locally stable, whereas a discontinuous controller which achieves this exists. For single-input/single-output input nonaffine nonlinear systems we give sufficient conditions for existence and present a method for the design of discontinuous switching controllers which yield locally stable zero dynamics.
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    Indoor infrared optical wireless localization system with background light power estimation capability
    Wang, K ; Nirmalathas, A ; Lim, C ; Alameh, K ; Li, H ; Skafidas, E (OPTICAL SOC AMER, 2017-09-18)
    The indoor user localization function is in high demand for high-speed wireless communications, navigations and smart-home applications. The optical wireless technology has been used to localize end users in indoor environments. However, its accuracy is typically very limited, due to the ambient light, which is relatively strong. In this paper, a novel high-localization-accuracy optical wireless based indoor localization system, based on the use of the mechanism that estimates background light intensity, is proposed. Both theoretical studies and demonstration experiments are carried out. Experimental results show that the accuracy of the proposed optical wireless indoor localization system is independent on the localization light strength, and that an average localization error as small as 2.5 cm is attained, which is 80% better than the accuracy of previously reported optical wireless indoor localization systems.
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    Silicon nanowire photodetector enhanced by a bow-tie antenna
    Felic, GK ; Al-Dirini, F ; Hossain, FM ; Thanh, CN ; Skafidas, E (SPRINGER, 2014-05-01)
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    An ab-initio Computational Method to Determine Dielectric Properties of Biological Materials
    Abeyrathne, CD ; Halgamuge, MN ; Farrell, PM ; Skafidas, E (NATURE PUBLISHING GROUP, 2013-05-08)
    Frequency dependent dielectric properties are important for understanding the structure and dynamics of biological materials. These properties can be used to study underlying biological processes such as changes in the concentration of biological materials, and the formation of chemical species. Computer simulations can be used to determine dielectric properties and atomic details inaccessible via experimental methods. In this paper, a unified theory utilizing molecular dynamics and density functional theory is presented that is able to determine the frequency dependent dielectric properties of biological materials in an aqueous solution from their molecular structure alone. The proposed method, which uses reaction field approximations, does not require a prior knowledge of the static dielectric constant of the material. The dielectric properties obtained from our method agree well with experimental values presented in the literature.
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    Predicting the diagnosis of autism spectrum disorder using gene pathway analysis
    Skafidas, E ; Testa, R ; Zantomio, D ; Chana, G ; Everall, IP ; Pantelis, C (NATURE PUBLISHING GROUP, 2014-04-01)
    Autism spectrum disorder (ASD) depends on a clinical interview with no biomarkers to aid diagnosis. The current investigation interrogated single-nucleotide polymorphisms (SNPs) of individuals with ASD from the Autism Genetic Resource Exchange (AGRE) database. SNPs were mapped to Kyoto Encyclopedia of Genes and Genomes (KEGG)-derived pathways to identify affected cellular processes and develop a diagnostic test. This test was then applied to two independent samples from the Simons Foundation Autism Research Initiative (SFARI) and Wellcome Trust 1958 normal birth cohort (WTBC) for validation. Using AGRE SNP data from a Central European (CEU) cohort, we created a genetic diagnostic classifier consisting of 237 SNPs in 146 genes that correctly predicted ASD diagnosis in 85.6% of CEU cases. This classifier also predicted 84.3% of cases in an ethnically related Tuscan cohort; however, prediction was less accurate (56.4%) in a genetically dissimilar Han Chinese cohort (HAN). Eight SNPs in three genes (KCNMB4, GNAO1, GRM5) had the largest effect in the classifier with some acting as vulnerability SNPs, whereas others were protective. Prediction accuracy diminished as the number of SNPs analyzed in the model was decreased. Our diagnostic classifier correctly predicted ASD diagnosis with an accuracy of 71.7% in CEU individuals from the SFARI (ASD) and WTBC (controls) validation data sets. In conclusion, we have developed an accurate diagnostic test for a genetically homogeneous group to aid in early detection of ASD. While SNPs differ across ethnic groups, our pathway approach identified cellular processes common to ASD across ethnicities. Our results have wide implications for detection, intervention and prevention of ASD.
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    All-Graphene Planar Self-Switching MISFEDs, Metal-Insulator-Semiconductor Field-Effect Diodes
    Al-Dirini, F ; Hossain, FM ; Nirmalathas, A ; Skafidas, E (NATURE PUBLISHING GROUP, 2014-02-05)
    Graphene normally behaves as a semimetal because it lacks a bandgap, but when it is patterned into nanoribbons a bandgap can be introduced. By varying the width of these nanoribbons this band gap can be tuned from semiconducting to metallic. This property allows metallic and semiconducting regions within a single Graphene monolayer, which can be used in realising two-dimensional (2D) planar Metal-Insulator-Semiconductor field effect devices. Based on this concept, we present a new class of nano-scale planar devices named Graphene Self-Switching MISFEDs (Metal-Insulator-Semiconductor Field-Effect Diodes), in which Graphene is used as the metal and the semiconductor concurrently. The presented devices exhibit excellent current-voltage characteristics while occupying an ultra-small area with sub-10 nm dimensions and an ultimate thinness of a single atom. Quantum mechanical simulation results, based on the Extended Huckel method and Nonequilibrium Green's Function Formalism, show that a Graphene Self-Switching MISFED with a channel as short as 5 nm can achieve forward-to-reverse current rectification ratios exceeding 5000.
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    A Label-Free, Quantitative Fecal Hemoglobin Detection Platform for Colorectal Cancer Screening
    Soraya, GV ; Nguyen, TC ; Abeyrathne, CD ; Huynh, DH ; Chan, J ; Nguyen, PD ; Nasr, B ; Chana, G ; Kwan, P ; Skafidas, E (MDPI, 2017-06-01)
    The early detection of colorectal cancer is vital for disease management and patient survival. Fecal hemoglobin detection is a widely-adopted method for screening and early diagnosis. Fecal Immunochemical Test (FIT) is favored over the older generation chemical based Fecal Occult Blood Test (FOBT) as it does not require dietary or drug restrictions, and is specific to human blood from the lower digestive tract. To date, no quantitative FIT platforms are available for use in the point-of-care setting. Here, we report proof of principle data of a novel low cost quantitative fecal immunochemical-based biosensor platform that may be further developed into a point-of-care test in low-resource settings. The label-free prototype has a lower limit of detection (LOD) of 10 µg hemoglobin per gram (Hb/g) of feces, comparable to that of conventional laboratory based quantitative FIT diagnostic systems.
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    Pathway-wide association study identifies five shared pathways associated with schizophrenia in three ancestral distinct populations
    Liu, C ; Bousman, CA ; Pantelis, C ; Skafidas, E ; Zhang, D ; Yue, W ; Everall, IP (SPRINGERNATURE, 2017-02-21)
    Genome-wide association studies have confirmed the polygenic nature of schizophrenia and suggest that there are hundreds or thousands of alleles associated with increased liability for the disorder. However, the generalizability of any one allelic marker of liability is remarkably low and has bred the notion that schizophrenia may be better conceptualized as a pathway(s) disorder. Here, we empirically tested this notion by conducting a pathway-wide association study (PWAS) encompassing 255 experimentally validated Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways among 5033 individuals diagnosed with schizophrenia and 5332 unrelated healthy controls across three distinct ethnic populations; European-American (EA), African-American (AA) and Han Chinese (CH). We identified 103, 74 and 87 pathways associated with schizophrenia liability in the EA, CH and AA populations, respectively. About half of these pathways were uniquely associated with schizophrenia liability in each of the three populations. Five pathways (serotonergic synapse, ubiquitin mediated proteolysis, hedgehog signaling, adipocytokine signaling and renin secretion) were shared across all three populations and the single-nucleotide polymorphism sets representing these five pathways were enriched for single-nucleotide polymorphisms with regulatory function. Our findings provide empirical support for schizophrenia as a pathway disorder and suggest schizophrenia is not only a polygenic but likely also a poly-pathway disorder characterized by both genetic and pathway heterogeneity.