35 research outputs found
Validation of Large Area Capacitive Sensors for Impact Damage Assessment
No full textImpacts in fiber-reinforced polymer matrix composites can severely inhibit their functionality and prematurely lead to the composite’s failure. This research focuses on determining the efficacy of a novel capacitive sensor, termed as the Soft Elastomeric Capacitor or SEC, to monitor the magnitude of out-of-plane deformations in composites. This work forwards the development of a sensing skin that can be used as an in situ monitoring tool for composites. The capacitive sensor can be made to arbitrary sizes and geometries. The sensor is composed of an elastomer composite that measures strains experienced by the material it is bonded to. The structure of the sensor, fabricated to function as a parallel plate capacitor, responds to impacts by transducing strains into a measurable change in capacitance. In this work, the SECs are deployed on randomly oriented fiberglass-reinforced plates with a polyester resin matrix. The material is impacted at various energy levels until the monitored
composite material reaches its yielding point. The behavior of the sensor in impact detection applications below the proof resilience shows little to no change in the capacitance of the sensor. As the impacts surpass this yielding point, the sensor responds linearly with induced change in the area. The sensor performed within the expectations of the proposed model and demonstrated the efficacy of the proposed large-area sensor as a damage quantification tool in the structural health monitoring of composites.This is an accepted manuscript of an article published as Vereen, Alexander Brennan, Austin Downey, Subramani Sockalingam, and Simon Laflamme. "Validation of Large Area Capacitive Sensors for Impact Damage Assessment." Measurement Science and Technology (2023). doi:https://doi.org/10.1088/1361-6501/ad0954. This Accepted Manuscript is © 2023 The Author(s). This Accepted Manuscript is available for reuse under a CC BY 4.0
Optimally sparse and adaptive far-field sampling and pattern reconstruction: Approach for faster calibration of antenna system using compressed sensing
No full textRadiation pattern measurements is a critical step in characterizing antennas before they are used in any system for a specific application. To identify any defects or to acquire the true radiation characteristics of the antenna under test, densely sampled measurements are desired. However, this results in a time and cost expensive measurement process. Compressed sensing allows accurate reconstruction of radiation patterns using a reduced number of measurements. To ensure exact recovery, it is necessary to select an optimal sampling strategy as well as an effective reconstruction method. In this thesis, the discrete Fourier transform and spherical harmonic expansion of the electric field are used to obtain a sparse representation of radiation patterns. As a variation from the basis pursuit optimization problem which is widely used in compressed sensing for antenna measurements, a sparsity enhancing weighted l1-norm minimization problem is considered. The weights are determined from prior information on antenna from electromagnetic simulations. The proposed method, after investigation with various antennas and comparison with existing benchmark results in a further reduction of number of required measurements. A near-optimal sampling technique is adopted to acquire measurement in an incoherent manner for exact recovery of the pattern. The performance of the method has been evaluated using error metrics specific to important parameters of the radiation pattern such as the gain, peak side lobe level and half power beam width. Radiation patterns with non-idealities and distortions have also been recovered with high accuracy from a small number of measurements using the proposed method.Electrical Engineerin
Goblet cell-intrinsic colonic defense
No full textThe intestine is constantly exposed to billions of commensal microbes as well as
pathogens and opportunistic organisms. Protection of the epithelium depends on the
mucus barrier, produced by goblet cells (GCs), which separates bacteria from host
tissue while maintaining tolerance to the microbiota. Several studies have established
the importance of Muc2 and the inner and outer mucus layers in maintaining intestinal
homeostasis, but multiple key questions remained unresolved in our understanding of
mucus associated protection to bacterial infections. It has been unclear how
specialized GC subsets mature after birth, how pathogens selectively undermine these
protective cells, and how environmental factors such as diet destabilize mucus
integrity to permit disease.
This thesis addresses these gaps by defining the developmental, functional, and
pathological dynamics of distinct GC populations. We show that postnatal maturation
of sentinel goblet cells (senGCs) is driven by microbial colonization, requiring Duox2
signaling to enable rapid, MAMPs-dependent mucus secretion. In parallel,
noncanonical GCs contribute unique proteins to the mucus proteome reinforcing the
structural and antimicrobial properties of the inner mucus layer. Building on this, we
demonstrate that during Citrobacter rodentium infection, the pathogen destabilizes
the inner mucus layer and potentially exploits the type III secretion system effector
EspF to selectively deplete Spdef-dependent intercrypt GCs (icGCs). Loss of these
cells dismantle the intercrypt mucus network, creating niches for bacterial persistence
that cannot be compensated by crypt plume mucus alone. Our study further suggests
that senGCs are important drivers of crypt-specific secondary defense during
infection. They dynamically expand into deep crypts, sustain baseline mucus
secretion, and coordinate Th17 responses. Their absence leads to accelerated GC loss,
sex-specific susceptibility, and early indications of barrier compromise. Finally, we
reveal that short-term exposure to a Western-style diet disrupts jejunal mucus integrity
through increased Tgm2-mediated cross-linking of Muc2, preventing proper mucus
expansion and enabling ectopic colonization of the small intestine by C. rodentium.
Together, these findings update our understanding of the intestinal mucus barrier as a
dynamic and adaptable system shaped by microbial signals, dietary factors, and
contributions from specialized GC subsets. By uncovering how senGCs and icGCs
preserve barrier integrity, and how pathogens and diet exploit their vulnerabilities,
this work advances mechanistic understanding of how the intestinal GCs and the
secreted mucus barriers preserve homeostasis and how their functional ablation
creates vulnerabilities during infection
Refractive index engineering of poly (vinyl alcohol)/Li2ZnO2 nanocomposites: Effect of filler content and annealing temperature
No full textDynamic Era of Fijian Writing
No full textIn an article published recently (Fiji Times 04/08/2017) Dr. Joseph Veramu, a policy analyst consultant argues that “apart from the prolific internationally renowned writer Dr. Satendra Nandan, the Fijian writing scene appears dormant”. It might be prudent to imply that the writer is not aware of the number of writers that have emerged in the last few decades. Then again the article is quite contradicting when the author concludes “it appears that a lot of creative works are being produced locally”. In fact, there is a new vigour in Fijian writing as evident from an online publication New Fijian Writing (http://fijianstudies.net/2014-21/) which has significant mix of established and new writers, among them 10 old writers such as Subramani, Teresia Teiawa, Senoa Smiles, Satish Rai, Mohit Prasad, Larry Thomas, Joini Madraiwiwi, Satendra Nandan, Sudesh Mishra, and Brij Lal, with more than 15 new writers such as Bhim Singh, Satvick Dass, Anna Rarasea, Afsana Anzeg, Pauline Reyland, Praveen Chandra, Pranesh Prasad, Sakiusa Viaviaturaga, Seruwaia Vukivou, Anurag Subramani, Izaz Khan, Kelera Tuvou, Shyamendra Shrama and Harish Sharma. The notion of writing in Fiji has always been an ongoing pursuit and there seems to be a thrust in writing as more writers have joined in to continue the legacy
Exploiting tacit knowledge through knowledge management technologies
No full textThe purpose of this paper is to examine the contributions and suitability of the available knowledge management (KM) technologies, including the Web 2.0 for exploiting tacit knowledge. It proposes an integrated framework for extracting tacit knowledge in organisations, which includes Web 2.0 technologies, KM tools, organisational learning (OL) and Community of Practice (CoP). It reviews a comprehensive literature covering overview of KM theories, KM technologies and OL and identifies the current state of knowledge relating to tacit knowledge exploitation. The outcomes of the paper indicate that Internet and Web 2.0 technologies have stunning prospects for creating learning communities where tacit knowledge can be extracted from people. The author recommends that organisations should design procedures and embed them in their Web 2.0 collaborative platforms persuading employees to record their ideas and share them with other members. It is also recommended that no idea should be taken for granted in a learning community where tacit knowledge exploitation is pursued. It is envisaged that future research should adopt empirical approach involving Complex Adaptive Model for Tacit Knowledge Exploitation (CAMTaKE) and the Theory of Deferred Action in examining the effectiveness of KM technologies including Web 2.0 tools for tacit knowledge exploitation
Modeling of the cylinder boring process for prediction of cutting force, temperature and surface error
No full textIn this thesis, models are developed for characterization of the cylinder boring process, a process used for machining cylinder bores in cast engine blocks. The models are used for predicting the lack of cylindricity of machined cylinder bores, also called surface error, which results in poor engine performance and excessive wear of cylinders and pistons. Surface error arises from two causes, namely, the elastic deflection of the bore wall due to cutting forces and the thermal expansion of the cylinder bore during machining. The prediction of cutting forces is achieved through the development of a mechanistic model which accounts for the effect of cutting condition and tool geometry variables on chip load and the magnitude and orientation of cutting forces. Since during machining there is an inherent coupling between the cutting process and the structural vibration of the machining system due to cutting forces, a procedure for computation of process dynamics, using finite element analysis, is developed which invokes this coupling. The predicted cutting forces are used along with an influence coefficient database of the engine block and fixturing to calculate the component of surface error resulting from elastic deflections of the bore wall during machining.The temperature field in the cylinder bore during machining is computed through the development of analytical solutions using the method of integral transforms. In this derivation, the tool-work interface is modeled as a helically moving volumetric heat source. The derived temperature field is used to compute the magnitude of surface error resulting from thermal expansion of the cylinder bore during machining. Experiments have been conducted on a cylinder boring test set-up to study the effect of cutting condition and tool geometry variables on cutting forces, bore temperatures, and surface error. The measured cutting force and temperature data have been used to calibrate and verify the developed models. Comparisons between measured and predicted cutting forces, bore temperatures, and surface error show very good agreement. Simulations performed to study the effect of cutting speed, feed, depth of cut, and tool rake angles on surface error show that feed and depth of cut significantly affect surface error. The use of the developed models for designing the process through sensitivity calculations is discussed.Made available in DSpace on 2011-05-07T13:56:34Z (GMT). No. of bitstreams: 2
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Notched strength and size effect in pseudo-ductile composite laminates
No full textENG- Composite materials are favoured in aviation and automotive industries for their lightweight properties. However, their tendency to brittle failure poses challenges. The advent of thin-ply laminates, with improved fibre alignment and reduced resin-rich zones, offers significant advantages but may also increase brittleness by suppressing sub-critical damage mechanisms. To counter this, introducing pseudo-ductility via hybridisation has been explored to reduce the brittleness of laminated composites.
Introducing pseudo-ductility in composites promotes sub-critical damage mechanisms, such as fibre or ply fragmentation, to produce a metal-like non-linear stress-strain response. While pseudo-ductility has been experimentally demonstrated in various instances, most studies examining its impact on notched laminates have been experimental, limited only to the realised pseudo-ductility levels. Factors like interlaminar toughness or ply strength ratios may limit these pseudo-ductility levels. Further, research on the size effect (relationship between the notched strength and specimen size) in pseudo-ductile laminates remains sparse and lacks definitive conclusions. Furthermore, the inevitable increase in ply thickness in the orientation-blocked sub-laminate approach, a typical method to attain pseudo-ductility, complicates the attribution of improvements solely to pseudo-ductility due to several interdependencies. This highlights the necessity for a numerically based approach to explore the complex relationships between material parameters defining pseudo-ductility and the laminate or semi-structural characteristics such as translaminar toughness, stress concentration factors, and notched strength/size-effect behaviour. This thesis aims to identify the optimal pseudo-ductile material properties at the laminate level for notched applicationsCAT- Els materials compostos són molt utilitzats en les indústries de l'aviació i l'automoció per les seves propietats lleugeres. No obstant això, la seva tendència a la ruptura fràgil planteja reptes. L'aparició de laminats de capa fina, amb una millor alineació de fibres i reducció de zones riques en resina, ofereix avantatges significatius, però també pot augmentar la seva fragilitat en suprimir mecanismes subcrítics de dany. Per contrarestar això, s'ha explorat la introducció de pseudo-ductilitat mitjançant hibridació per reduir la fragilitat dels compostos laminats.
Introduir pseudo-ductilitat en els compostos promou mecanismes de dany subcrític, com la fragmentació de fibres o capes, per produir una resposta de tensió-deformació no lineal semblant a la dels metalls. Encara que la pseudo-ductilitat ha estat demostrada experimentalment en diverses ocasions, la majoria dels estudis que examinen el seu impacte en laminats amb entalledures han estat experimentals, limitats només als nivells de pseudo-ductilitat realitzats. Factors com la tenacitat interlaminar o les proporcions de resistència de les capes poden limitar aquests nivells de pseudo-ductilitat. A més, la investigació sobre l'efecte de la mida (relació entre la resistència amb entalladures i la mida de la mostra) en laminats pseudo-dúctils és escassa i no presenta conclusions definitives. L'augment inevitable del gruix de capa en els sublaminats formats per capes d'igual orientació, un mètode típic per assolir la pseudo-ductilitat, complica l'atribució de millores únicament a la pseudo-ductilitat a causa de diverses interdependències. Això destaca la necessitat d'un enfocament basat en models numèrics per explorar les complexes relacions entre els paràmetres del material que defineixen la pseudo-ductilitat i les característiques del laminat o semi-estructurals com la tenacitat translaminar, els factors de concentració de tensions i el comportament de resistència vs. efecte de mida amb entalladures. Aquesta tesi té com a objectiu identificar les propietats pseudo-dúctils del material òptimes a nivell de laminat per a aplicacions amb entalladuresThe work contained in this Ph.D. thesis was conducted at the AMADE research group (Department of Mechanical Engineering and Industrial Construction, University of Girona, Spain). The thesis was carried out with the financial support from the PDI grant (INV309/2019) and the predoctoral grant IFUdG2020 from the University of Girona and Santander Universidades. The author also acknowledges the financial supports from the Spanish Ministerio de Ciencia, Innovación y Universidades through the projects TOUGHCOMP (RTI2018-097880-B-I00) and SUBHYCO (PID2021-126989OB-I00).
A part of the thesis is dedicated to the TOUGHCOMP project from Ministerio de Ciencia, Innovación y Universidades for the project Mejora de la tenacidad translaminar de materiales compuestos mediante nuevas estrategias de hibridación en (TOUGHCOMP) - (RTI2018-097880-B-I00). Part of the research presented in this thesis was developed during the Ph.D. candidate's research stay at the Institute COMATEC in Haute Ecole d’Ingénierie et de Gestion du canton de Vaud (HEIG-VD) with the financial support from the mobility grant MOB21 from the University of GironaPrograma de Doctorat en Tecnologia
Author response image 1. Overexpression of MgtA D373-BFP, and MgtA D373N-GFP in E. coli analysed by Western blotting.
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