Pebble bed: reflector treatment and pressure\ud velocity coupling

In this report, we describe some models and numerical methods used to simulate the flow and temperature in a pebble bed modular nuclear reactor. The reactor core is filled with around 450000 spheres containing low enriched uranium and helium is forced through these hot pebbles to cool the system down. The group first investigated the flow model in the pebbles. Numerical aspects were then considered to tackle difficulties encountered with the flow simulation and the temperature inside the pebbles. Numerical schemes are presented that can significantly improve the accuracy of the computed results

Electrical Characterization of 1.8 MeV Proton-Bombarded ZnO

We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects that are responsible for carrier compensation

The Curious Case of the “Heartworm” Nebula

© 2022. The Author(s). Published by the American Astronomical Society. This work is licensed under the terms of the Creative Commons Attribution 4.0 licence. https://creativecommons.org/licenses/by/4.0/The curious Galactic features near G357.2−0.2 were observed with the MeerKAT radio interferometer array in the UHF and L bands (0.56–1.68 GHz). There are two possibly related features: a newly identified faint heart-shaped partial shell (the “heart”), and a series of previously known but now much better imaged narrow, curved features (the “worm”) interior to the heart. Polarized emission suggests that much of the emission is nonthermal and is embedded in a dense plasma. The filaments of the worm appear to be magnetic structures powered by embedded knots that are sites of particle acceleration. The morphology of the worm broadly resembles some known pulsar wind nebulae (PWNe) but there is no known pulsar or PWN which could be powering this structure. We also present eROSITA observations of the field; no part of the nebula is detected in X-rays, but the current limits do not preclude the existence of a pulsar/PWN of intermediate spin-down luminosity.Peer reviewe

Electrical characterization of 1.8 MeV proton-bombarded ZnO

We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects that are responsible for carrier compensation

Comparative study of the electrical properties of Pd/ZnO Schottky contacts fabricated using electron beam deposition and resistive/thermal evaporation techniques

A systematic investigation to check the quality of Pd Schottky contacts deposited on ZnO has been performed on electron beam (e-beam) deposited and resistively/thermally evaporated samples using current-voltage, IV, and conventional deep level transient spectroscopy (DLTS) measurements. Room temperature IV measurements reveal the dominance of pure thermionic emission on the resistively evaporated contacts, while the e-beam deposited contacts show the dominance of generation recombination at low voltages,<0.30 V, and the dominance of pure thermionic emission at high voltages, greater than 0.30 V. The resistively evaporated contacts have very low reverse currents of the order of 10 10 A at a reverse voltage of 1.0 V whereas the e-beam deposited contacts have reverse currents of the order of 10 6 A at 1.0 V. Average ideality factors have been determined as (1.4360.01) and (1.6660.02) for the resistively evaporated contacts and e-beam deposited contacts, respectively. The IV barrier heights have been calculated as (0.72160.002) eV and (0.62460.005) eV for the resistively evaporated and e-beam deposited contacts, respectively. Conventional DLTS measurements reveal the presence of three prominent defects in both the resistive and e-beam contacts. Two extra peaks with energy levels of 0.60 and 0.81 eV below the conduction band minimum have been observed in the e-beam deposited contacts. These have been explained as contributing to the generation recombination current that dominates at low voltages and high leakage currents. Based on the reverse current at 1.0 V, the degree of rectification, the dominant current transport mechanism and the observed defects, we conclude that the resistive evaporation technique yields better quality Schottky contacts for use in solar cells and ultraviolet detectors compared to the e-beam deposition technique. The 0.60 eV has been identified as possibly related to the unoccupied level for the doubly charged oxygen vacancy, Vо2+.The National Research Foundation of South Africahttp://dx.doi.org/10.1063/1.3658027nf201

Investigating atmospheric corrosion behavior of carbon steel in coastal regions of Mauritius using Raman Spectroscopy

Low carbon steel was exposed at two sites in Mauritius, namely Port Louis and Belle Mare. The site at Port Louis is basically an industrial marine one whereas the one at Belle Mare is a purely marine site. Though the corrosion loss trend at both sites follow the power law, the corrosion loss at Port Louis was found to be higher than that at Belle Mare. This study has been performed to investigate the surface characteristics of the rust layers of the samples exposed at the two sites, through Raman spectroscopy and SEM, so as to get a better insight into the mechanism of the atmospheric corrosion process. For Port Louis, it was observed that there was not much change in the corrosion products in the rust layer over the 3 years period. The structure was less compact than that at Belle Mare with the presence of lepidocrocite and akaganeite as commonly observed corrosion products. The corrosion rate at Port Louis is, therefore, expected to follow the same trend over the long term. For Belle Mare, the corrosion products changed significantly after 3 years of exposure. Though lepidocrocite and akaganeite were observed on the surface after 0.2 years of exposure, magnetite was the most probable corrosion product in the more compact rust layer after 3 years of exposure. This compactness of the rust layer is expected to have reduced the corrosion rate as compared to that of Port Louis. Significant changes in the corrosion rate at Belle Mare are, therefore, expected over the medium and the long term

MIGHTEE-H i: possible interactions with the galaxy NGC 895

The transformation and evolution of a galaxy is strongly influenced by interactions with its environment. Neutral hydrogen (H i) is an excellent way to trace these interactions. Here, we present H i observations of the spiral galaxy NGC 895, which was previously thought to be isolated. High-sensitivity H i observations from the MeerKAT large survey project MIGHTEE reveal possible interaction features, such as extended spiral arms and the two newly discovered H i companions, that drive us to change the narrative that it is an isolated galaxy. We combine these observations with deep optical images from the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and its companions. We do find an excess of light in the outer parts of the companion galaxy MGTH_J022138.1-052631, which could be an indication of external perturbation and thus possible sign of interactions. Our analysis shows that NGC 895 is an actively star-forming galaxy with a SFR of 1.75 ± 0.09[M⊙/yr], a value typical for high-stellar mass galaxies on the star-forming main sequence. It is reasonable to state that different mechanisms may have contributed to the observed features in NGC 895, and this emphasizes the need to revisit the target with more detailed observations. Our work shows the high potential and synergy of using state-of-the-art data in both H i and optical to reveal a more complete picture of galaxy environments

Electrical Characterization of Vapor-Phase-Grown Single-Crystal ZnO

Gold Schottky-barrier diodes (SBDs) were fabricated on vapor-phase-grown single-crystal ZnO. Deep-level transient spectroscopy, using these SBDs, revealed the presence of four electron traps, the major two having levels at 0.12 eV and 0.57 below the conduction band. Comparison with temperature-dependent Hall measurements suggests that the 0.12 eV level has a temperature activated capture cross section with a capture barrier of about 0.06 eV and that it may significantly contribute to the free-carrier density. Based on the concentrations of defects other than this shallow donor, we conclude that the quality of the vapor-phase-grown ZnO studied here supercedes that of other single-crystal ZnO reported up to now

Alelula Lentsu lagi Morena

Sepedi church music workshop recording, unaccompanied. Response after the readings