58 research outputs found
An experimentally driven assessment of the dynamic-on resistance in correlation to other performance indicators in commercial Gallium Nitride power devices
No full textThis work provides an experimentally driven performance comparison of commercial Gallium Nitride on Silicon (GaN-on-Si) power devices rated 600-650V at room and elevated temperatures with the focus being in assessing the on resistance (RON) increase due to hard switching in correlation to other performance indicators. Device technologies evaluated include the Enhancement (E-mode) AlGaN/GaN Hybrid Drain p-GaN layer Gate Injection Transistor (p-GaN HD-GIT), the cascode AlGaN/GaN High Electron Mobility Transistor (cascode HEMT). For the dynamic RON analysis, a special setup was utilized which allows synchronized drain and gate pulses, and the ability to switch from OFF to ON in as little as 20μs. The ability to apply a wide range of voltage levels, stress duration and temperature enabled measurable increase in the dynamic RON in both the cascode HEMT and the p-GaN HD-GIT. Nonetheless, the results highlight a strong difference in their robustness. </p
In-Situ Monitoring of Weld Line Thickness in Continuous Ultrasonic Welding of Thermoplastic Composites
No full textContinuous ultrasonic welding (CUW) is one of the most efficient integration methods of thermoplastic composites. Researchers from our group have already utilized CUW method by using both frame based and robotic welding platforms to achieve sufficient amount of joint strength for aerospace applications [1-3]. On the other hand, the implementation of this method into an industrial manufacturing process still requires the ability of consistent and high-quality welding. It is obvious that a sophisticated monitoring system, which is developed for ensuring the highest-level of weld quality, will play a key role to transform CUW method into a commonly relied on industrial tool. Typically, experimental techniques like micrograph, mechanical testing and fracture surface examination are used to determine the performance of a welded composite joint, which provide the opportunity of correlating the process parameters and other process data with the welded joint performance. Within the context of this study, several experiments are conducted using the welded composite plates by robotic CUW system. It’s seen that the overall weld-line thickness, among other parameters, indicates a remarkable correlation with lap shear strength of welded joints. The results show that for weld line thicknesses above the original energy director thickness, considerable voids can be found in the weld interface. On the other hand, samples with a lower thickness than the original energy director show less voids and improved lap shear performance. After evaluating the aforementioned experimental outcomes, a weld monitoring system is designed for continuous measurement of weld line thickness for in-situ monitoring purposes. Weld monitoring system is built on a frame based continuous ultrasonic welding platform as seen in Figure 1, where the laser sensors are utilized to perform very precise thickness distribution analysis along the weld line during the continuous monitoring applications. A specialized python code is created to analyze the raw sensor data for monitoring purposes. Different monitoring system iterations and python code pairs tested and compared to achieve the most accurate monitoring experience. Results indicate that laser sensor based monitoring system provides very sensitive weld line thickness measurements, which can be related to the weld quality for industrial applications.Aerospace Structures & Computational MechanicsAerospace Manufacturing Technologie
Buckling test of stiffened panels: evaluation of post-buckling and failure by testing and layerwise models
No full textThe present paper deals with the buckling and post-buckling analysis of a multilayered
composite reinforced panel. The panel, designed for aeronautical applications, results in a
complex stacking sequence, and the development of a refined model able to describe its
geometrical nonlinear behavior is mandatory to avoid the usage of highly computational effortrequired 3D finite elements. The proposed approach is a finite element analysis based on the
Carrera Unified Formulation (CUF). Thanks to CUF, a 1D model of the composite panel can be
formulated and complicated stress fields within the structure can be evaluated, so that the
nonlinear behavior is fully described. A refined Equivalent Single Layer (ESL) technique is
employed, making use of Lagrange polynomials for the description of the stacking sequence. The
results clearly demonstrate the reliability of this approach, comparing the linearized buckling and
nonlinear post-buckling solutions with those from Nastran (1D, 2D and 3D) and experiment
Buckling test of stiffened panels: modeling and vibrational correlation testing
No full textRepresentative stiffened panels are optimized such that multiple buckling modes and failure (using open hole allowables) occur within a range of 10% of the lowest buckling load. This implies the panels cannot be loaded up to the buckling load without risking failure, hence vibrational correlation testing was used to estimate the buckling loads and modes. At the same time, a finite element model was created using the Carrera Unified Formulation. This model was validated using the tests and a good correlation between both was observed. Three panels were manufactured and each panel was put in place for testing twice. Each time a panel was put in place, the test was repeated three times. This allowed us to get a ballpark estimate for the variation due to replicas of the panel, the test set-up and repeating the tests.Aerospace Structures & Computational Mechanic
A braidoid equivalence for spherical knotoids
No full textBraidoids form a counterpart theory to the theory of planar knotoids, just as braids do for three-dimensional links. As such, planar knotoid diagrams represent the same knotoid in if and only if they can be presented as the closure of two labeled braidoid diagrams related by an equivalence relation, named -equivalence. In this paper, we refine the notion of -equivalence of braidoid diagrams in order to obtain an equivalence theorem for (multi)-knotoid diagrams in when represented as the closure of labeled braidoid diagrams.25 pages, 23 figures. arXiv admin note: substantial text overlap with arXiv:1908.06053 by other author
On the Static Performance of Commercial GaN-on-Si Devices at Elevated Temperatures
No full textThis work provides an experimentally driven comparison between commercialized Gallium Nitride on Silicon (GaN-on-Si) and Silicon (Si) Super Junction (S-J) power devices at elevated temperatures. Elevated temperature experiments were performed to analyze the static performance of the Panasonic PGA26C09DV Enhancement (E-mode) p-GaN layer Gate Injected Transistor (GIT), the Transphorm TPH3206LD, TPH3206PD cascode GaN High Electron Mobility Transistors (HEMTs) and the Infineon SPA15N60C3 Silicon S-J. The Device Under Tests (DUTs) were characterized in a thermal chamber using the B1505A Power Device Analyzer. The elevated temperature measurements were taken; analyzed and compared. The performance of the GaN-on-Si indicated a strong robustness in thermally challenging environments and demonstrated superior performances at higher temperatures in comparison to traditional Si S-J technology.</p
Greek Education in Australia
No full textThis article provides readers with a well-researched portrait of the Greek experience in Australia. The author describes the various waves of immigration ‘down under’ and how the education system struggled to keep up with the demand. Problems of immigration and identity have forged the Australian Greek community into a stong, well-established group. Nevertheless, the current Australian situation resembles that of Canada and the United States in that second- and third-generation parents and children must adjust to maintain the Greek language and culture as the clientele for Greek education has changed dramatically. The author describes both student and teacher needs within the contemporary context as well as the importance of the Paideia Omogenon Program.This article provides readers with a well-researched portrait of the Greek experience in Australia. The author describes the various waves of immigration ‘down under’ and how the education system struggled to keep up with the demand. Problems of immigration and identity have forged the Australian Greek community into a stong, well-established group. Nevertheless, the current Australian situation resembles that of Canada and the United States in that second- and third-generation parents and children must adjust to maintain the Greek language and culture as the clientele for Greek education has changed dramatically. The author describes both student and teacher needs within the contemporary context as well as the importance of the Paideia Omogenon Program.Cet article présente un portrait de la communauté grecque d`Australie et de son évolution a travers les différentes vagues d’immigration vers ce pays. La question de l’éducation hellénophone est abordée à travers les changements survenus au sein de la communauté, en particulier avec l’apparition de la deuxième et de la troisième génération de Grecs, dont la conception en cette matière n’est pas nécessairement la même à celle de leurs parents. En ce sens les problèmes de cette éducation ressemblent, en partie du moins, à ceux auxquels font face les communautés grecques du Canada et même des États-Unis. L’auteur présente les besoins tant des enseignants que des élèves dans ce nouveau contexte et souligne l’importance du programme Paideia Omogenon pour les combler
Development of a cost-effectiveness model for optimisation of the screening interval in diabetic retinopathy screening
No full textBACKGROUND:
The English NHS Diabetic Eye Screening Programme was established in 2003. Eligible people are invited annually for digital retinal photography screening. Those found to have potentially sight-threatening diabetic retinopathy (STDR) are referred to surveillance clinics or to Hospital Eye Services.
OBJECTIVES:
To determine whether personalised screening intervals are cost-effective.
DESIGN:
Risk factors were identified in Gloucestershire, UK using survival modelling. A probabilistic decision hidden (unobserved) Markov model with a misgrading matrix was developed. This informed estimation of lifetime costs and quality-adjusted life-years (QALYs) in patients without STDR. Two personalised risk stratification models were employed: two screening episodes (SEs) (low, medium or high risk) or one SE with clinical information (low, medium-low, medium-high or high risk). The risk factor models were validated in other populations.
SETTING:
Gloucestershire, Nottinghamshire, South London and East Anglia (all UK).
PARTICIPANTS:
People with diabetes in Gloucestershire with risk stratification model validation using data from Nottinghamshire, South London and East Anglia.
MAIN OUTCOME MEASURES:
Personalised risk-based algorithm for screening interval; cost-effectiveness of different screening intervals.
RESULTS:
Data were obtained in Gloucestershire from 12,790 people with diabetes with known risk factors to derive the risk estimation models, from 15,877 people to inform the uptake of screening and from 17,043 people to inform the health-care resource-usage costs. Two stratification models were developed: one using only results from previous screening events and one using previous screening and some commonly available GP data. Both models were capable of differentiating groups at low and high risk of development of STDR. The rate of progression to STDR was 5 per 1000 person-years (PYs) in the lowest decile of risk and 75 per 1000 PYs in the highest decile. In the absence of personalised risk stratification, the most cost-effective screening interval was to screen all patients every 3 years, with a 46% probability of this being cost-effective at a £30,000 per QALY threshold. Using either risk stratification models, screening patients at low risk every 5 years was the most cost-effective option, with a probability of 99-100% at a £30,000 per QALY threshold. For the medium-risk groups screening every 3 years had a probability of 43-48% while screening high-risk groups every 2 years was cost-effective with a probability of 55-59%.
CONCLUSIONS:
The study found that annual screening of all patients for STDR was not cost-effective. Screening this entire cohort every 3 years was most likely to be cost-effective. When personalised intervals are applied, screening those in our low-risk groups every 5 years was found to be cost-effective. Screening high-risk groups every 2 years further improved the cost-effectiveness of the programme. There was considerable uncertainty in the estimated incremental costs and in the incremental QALYs, particularly with regard to implications of an increasing proportion of maculopathy cases receiving intravitreal injection rather than laser treatment. Future work should focus on improving the understanding of risk, validating in further populations and investigating quality issues in imaging and assessment including the potential for automated image grading
Experimental and physics based study of the Schottky Barrier Height inhomogeneity and associated traps affecting 3C-SiC-on-Si Schottky Barrier Diodes
No full textThe ability of cubic phase (3C-) Silicon Carbide (SiC) to grow heteroepitaxially on Silicon (Si) substrates (3C-SiC-on-Si) is an enabling feature for cost-effective Wide Bandgap devices and homogeneous integration with Si devices. In this paper, the authors evaluated 3C-SiC-on-Si Schottky Barrier Contacts by fabricating and testing non-freestanding lateral Schottky Barrier Diodes (LSBD). To gain a deep physical insight of the complex carrier transport phenomena that take place in this material, advanced Technology Computer Aided Design (TCAD) models were developed which allowed accurately matching of measurements with simulations. The models incorporate the device geometry, an accurate representation of the bulk material properties, and complex trapping/de-trapping and tunnelling phenomena which appear to affect the device performance. The observed non-uniformities of the Schottky Barrier Height (SBH) were successfully modelled through the incorporation of interfacial traps. The combination of TCAD with fabrication and measurements enabled the identification of trap profiles and pin their influence on the electrical performance of 3C-SiC-on-Si LSBD. The effect of temperature was studied by engaging the identified trap profiles and calculating the occupation distribution of electrons in 3C-SiC at elevated temperature. The investigation constitutes an imperative knowledge step towards the development of devices that take advantage of 3C-SiC material properties
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