Hydrogen and muonium in diamond: A path-integral molecular dynamics simulation

Isolated hydrogen, deuterium, and muonium in diamond have been studied by path-integral molecular dynamics simulations in the canonical ensemble. Finite-temperature properties of these point defects were analyzed in the range from 100 to 800 K. Interatomic interactions were modeled by a tight-binding potential fitted to density-functional calculations. The most stable position for these hydrogenic impurities is found at the C-C bond center. Vibrational frequencies have been obtained from a linear-response approach, based on correlations of atom displacements at finite temperatures. The results show a large anharmonic effect in impurity vibrations at the bond center site, which hardens the vibrational modes with respect to a harmonic approximation. Zero-point motion causes an appreciable shift of the defect level in the electronic gap, as a consequence of electron-phonon interaction. This defect level goes down by 70 meV when replacing hydrogen by muonium.Comment: 11 pages, 8 figure

Nonlinear properties of AlGaAs waveguides in continuous wave operation regime

Aluminum Gallium Arsenide (AlGaAs) is an attractive platform for the development of integrated optical circuits for all-optical signal processing thanks to its large nonlinear coefficients in the 1.55-μm telecommunication spectral region. In this paper we discuss the results of the nonlinear continuous-wave optical characterization of AlGaAs waveguides at a wavelength of 1.55 μm. We also report the highest value ever reported in the literature for the real part of the nonlinear coefficient in this material (Re(γ) ≈521 W<sup>−1</sup>m<sup>−1</sup>)

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 “the City”) 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 City’s 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 AFC’s 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 ——————————————————————————————— 41st Southern African Transport Conference ISBN: 978-0-6397-8659-9 Produced by: www.betaproducts.co.za ——————————————————————————————— 10-13 July 2023 Pretoria, South Africa Conference Proceedings ——————————————————————————————— 41st Southern African Transport Conference ISBN: 978-0-6397-8659-9 Produced by: www.betaproducts.co.za ——————————————————————————————— 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 Agency’s (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 “the country”). 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 “one-size-fits-all” approach and the objectives of customer centricity and minimising operating costs are paramount

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

Mechanical properties of ZnO epitaxial layers grown on a- and c-axis sapphire

The mechanical properties of zinc oxide epitaxial layers grown on a- and c-axis sapphire have been studied by spherical nanoindentation and cross-sectional transmission electron microscopy. As-grown threading dislocations, which are characteristic of epitaxialmaterial, combined with the presence of the much harder, underlying substrate are found to have a significant effect on the mechanical behavior of ZnO epilayers as compared to bulk material. Epilayer material is found to be significantly harder than its bulk counterpart. For a-axis epilayers, analysis of load–unload data yields a hardness of 6.6±1.2GPa, and 5.75±0.8GPa for c-axis layers. We attribute this increased hardness to strain compensation via the presence of as-grown defects. These defects inhibit the slip mechanism responsible for relative softness of bulk single crystals. The absence of pop-in events from analyzed continuous-load nanoindentation data is further evidence for strain compensation by native defects within the epilayers. Large variations in the spread of collected data are indicative of inhomegenity in the epilayers.The University of Sydney, for constructive comments and support. The work at UF is partially supported by the AFOSR under Grant Nos. F49620-03-1-0370 sT.S.d and NSF DMR 0400416

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

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