819 research outputs found
Modeling and simulation of bulk gallium nitride power semiconductor devices
Bulk gallium nitride (GaN) power semiconductor devices are gaining significant interest in recent years, creating the need for technology computer aided design (TCAD) simulation to accurately model and optimize these devices. This paper comprehensively reviews and compares different GaN physical models and model parameters in the literature, and discusses the appropriate selection of these models and parameters for TCAD simulation. 2-D drift-diffusion semi-classical simulation is carried out for 2.6 kV and 3.7 kV bulk GaN vertical PN diodes. The simulated forward current-voltage and reverse breakdown characteristics are in good agreement with the measurement data even over a wide temperature range
The future of automated fare collection systems : a perspective from the eThekwini municipality
Papers presented virtually at the 41st International Southern African Transport Conference on 10-13 July 2023.In 2009, the National Department of Transport (NDoT) legislated, as per the National Land
Transport Act (NLTA), 2009 (Act No.5 of 2009), that fare payments must be made through
any bank-issued fare payment system and be interoperable through all participating banks.
Commuters with participating bank accounts should be able to use bank cards and
commuters without bank accounts should be able to use prepaid cards. NDoT defined an
Automated Fare Collection (AFC) data structure that must be loaded onto all the Smart
Cards and stipulated that the Europay, Mastercard, Visa (EMV) card is the standard of
card technology that must be used to enable the hosting of the NDoT data structure.
The eThekwini Municipality (herein after referred to as βthe Cityβ) went out to tender in
2010 for an AFC system that was compliant with the requirements of the Act and the
system was successfully implemented in 2012 and is still in use today.
The system did not meet all the objectives that it was originally intended to. There were
aspects of the system that worked well but there were also several challenges that were
experienced. One of the major issues with the system was related to the inoperability of
the banks with the EMV/NDoT pre-paid cards. This issue only surfaced once the City had
already implemented the first compliant system and was in the process of implementing a
new system. The technical constraints were identified with NDoT and the participating
banks at the time, but there was a lack of capacity by the banks to co-operate to resolve
the issue. In addition the system was costly and complex to manage requiring
cumbersome reconciliation processes and technical constraints imposed by the restriction
to utilise the EMV/NDoT compliant card.
The lessons learned from the AFC implementations conducted by the City to-date has
informed the Cityβs procurement approach for future AFC systems. Research has been
conducted through various literature and discussion with colleagues in the sector to
establish the latest trends globally for AFC systems, exploring changes that have been
made to the technology and implementation approach that is being adopted to cater for the
future needs of Public Transport in the City. The findings show that the future of AFCβs
should first and foremost take into consideration the needs of the commuters by providing
convenience, ease of use and cater for seamless travel between multiple modes of
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41st Southern African Transport Conference
ISBN: 978-0-6397-8659-9
Produced by: www.betaproducts.co.za
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10-13 July 2023
Pretoria, South Africa
Conference Proceedings
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41st Southern African Transport Conference
ISBN: 978-0-6397-8659-9
Produced by: www.betaproducts.co.za
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10-13 July 2023
Pretoria, South Africa
Conference Proceedings
transport. Consideration also needs to be given to the overall operating costs for the City
and sustainability in terms of the ratio of AFC system implementation costs to fare
revenue.
The NDoT is in the process of legislating the South African National Roads Agencyβs
(SANRAL) Account Based Ticketing (ABT) system as the AFC solution to be adopted for
all Public Transport in the South Africa (herein after referred to as βthe countryβ). The City
has engaged with other Cities regarding the benefits, pitfalls and views on the
recommended approach with regards to AFC systems for use in Public Transport across
the Country. Considering global trends, current limitations, and unique challenges within
the context of the country, the collective view is that AFC systems should not be restricted
to a βone-size-fits-allβ approach and the objectives of customer centricity and minimising
operating costs are paramount
Diffusion of hydrogen in crystalline silicon
The coefficient of diffusion of hydrogen in crystalline silicon is calculated
using tight-binding molecular dynamics. Our results are in good quantitative
agreement with an earlier study by Panzarini and Colombo [Phys. Rev. Lett. 73,
1636 (1994)]. However, while our calculations indicate that long jumps dominate
over single hops at high temperatures, no abrupt change in the diffusion
coefficient can be observed with decreasing temperature. The (classical)
Arrhenius diffusion parameters, as a consequence, should extrapolate to low
temperatures.Comment: 4 pages, including 5 postscript figures; submitted to Phys. Rev. B
Brief Repor
Proprotein convertase expression and localization in epidermis: evidence for multiple roles and substrates
Specific proteolysis plays an important role in the terminal differentiation of keratinocytes in the epidermis and several types of proteases have been implicated in this process. The proprotein convertases (PCs) are a family of Ca 2+ -dependent serine proteases involved in processing and activation of several types of substrates. In this study we examined the expression and some potential substrates of PCs in epidermis. Four PCs are expressed in epidermis: furin, PACE4, PC5/6 and PC7/8. Furin is detected in two forms, either with or without the transmembrane domain, suggesting occurrence of post-translational cleavage to produce a soluble enzyme. In addition the furin active site has differential accessibility in the granular layer of the epidermis relative to the basal layer, whereas antibodies to the transmembrane domain stain both layers. These findings suggest that furin has access to different types of substrates in granular cells as opposed to basal cells. PC7/8, in contrast, is detected throughout the epidermis with antibodies to both the transmembrane and active site and no soluble form observed. A peptide PC inhibitor (dec-RVKR-CMK) inhibits cleavage of Notch-1, a receptor important in cell fate determination that is found throughout the epidermis. Profilaggrin, found in the granular layer, is specifically cleaved by furin and PACE4 in vitro at a site between the amino terminus and the first filaggrin repeat. This work suggests that the PCs play multiple roles during epidermal differentiation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75749/1/j.1600-0625.2001.010003193.x.pd
Carrier-mediated ferromagnetic ordering in Mn ion-implanted p+GaAs:C
Highly p-type GaAs:C was ion-implanted with Mn at differing doses to produce
Mn concentrations in the 1 - 5 at.% range. In comparison to LT-GaAs and
n+GaAs:Si samples implanted under the same conditions, transport and magnetic
properties show marked differences. Transport measurements show anomalies,
consistent with observed magnetic properties and with epi- LT-(Ga,Mn)As, as
well as the extraordinary Hall Effect up to the observed magnetic ordering
temperature (T_C). Mn ion-implanted p+GaAs:C with as-grown carrier
concentrations > 10^20 cm^-3 show remanent magnetization up to 280 K
Using data smartly ? moving towards a smart city
The eThekwini Transport Authority (ETA) is currently developing and pursuing smart city strategies and interventions to make eThekwini more caring and liveable. A key component of smart cities is to use data smartly. This includes measuring, monitoring and evaluating the effectiveness of current projects and programmes. To this end a GIS based tool comprising databases from various sectors has been developed to allow the ETA to research and evaluate the effectiveness of past and current management, maintenance and sector specific strategies.Paper presented at the 35th Annual Southern African Transport Conference 4-7 July 2016 "Transport ? a catalyst for socio-economic
growth and development opportunities to improve quality of life", CSIR International Convention Centre, Pretoria, South Africa.The Minister of Transport, South AfricaTransportation Research Board of the US
Ferromagnetism in Fe-substituted spinel semiconductor ZnGaO
Motivated by the recent experimental observation of long range ferromagnetic
order at a relatively high temperature of 200K in the Fe-doped ZnGaO
semiconducting spinel, we propose a possible mechanism for the observed
ferromagnetism in this system. We show, supported by band structure
calculations, how a model similar to the double exchange model can be written
down for this system and calculate the ground state phase diagram for the two
cases where Fe is doped either at the tetrahedral position or at the octahedral
position. We find that in both cases such a model can account for a stable
ferromagnetic phase in a wide range of parameter space. We also argue that in
the limit of high Fe concentration at the tetrahedral positions a
description in terms of a two band model is essential. The two orbitals
and the hopping between them play a crucial role in stabilizing the
ferromagnetic phase in this limit. The case when Fe is doped simultaneously at
both the tetrahedral and the octahedral position is also discussed.Comment: 10 pages, 9 figures, added text, J. Phys. Cond. Mat. (to appear
Tailoring ferromagnetic chalcopyrites
If magnetic semiconductors are ever to find wide application in real
spintronic devices, their magnetic and electronic properties will require
tailoring in much the same way that band gaps are engineered in conventional
semiconductors. Unfortunately, no systematic understanding yet exists of how,
or even whether, properties such as Curie temperatures and band gaps are
related in magnetic semiconductors. Here we explore theoretically these and
other relationships within 64 members of a single materials class, the Mn-doped
II-IV-V2 chalcopyrites, three of which are already known experimentally to be
ferromagnetic semiconductors. Our first-principles results reveal a variation
of magnetic properties across different materials that cannot be explained by
either of the two dominant models of ferromagnetism in semiconductors. Based on
our results for structural, electronic, and magnetic properties, we identify a
small number of new stable chalcopyrites with excellent prospects for
ferromagnetism.Comment: 6 pages with 4 figures, plus 3 supplementary figures; to appear in
Nature Material
MgZnO/AlGaN heterostructure light-emitting diodes
We report on p-n junction light-emitting diodes fabricated from MgZnO/ZnO/AlGaN/GaN triple heterostructures. Energy band diagrams of the light-emitting diode structure incorporating piezoelectric and spontaneous polarization fields were simulated, revealing a strong hole confinement near the n-ZnO/p-AlGaN interface with a hole sheet density as large as 1.82x10(13) cm(-2) for strained structures. The measured current-voltage (IV) characteristics of the triple heterostructure p-n junctions have rectifying characteristics with a turn-on voltage of similar to3.2 V. Electron-beam-induced current measurements confirmed the presence of a p-n junction located at the n-ZnO/p-AlGaN interface. Strong optical emission was observed at similar to390 nm as expected for excitonic optical transitions in these structures. Experimental spectral dependence of the photocurrent confirmed the excitonic origin of the optical transition at 390 nm. Light emission was measured up to 650 K, providing additional confirmation of the excitonic nature of the optical transitions in the devices
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