Impurity diffusion in ion implanted AlN layers on sapphire substrates by thermal annealing

We report on impurity diffusion in ion implanted AlN layers after thermal annealing. Silicon, tin, germanium, and magnesium ions were implanted into single-crystal AlN layers grown on sapphire substrates. By annealing at 1600oC, silicon and magnesium atoms were diffused in the AlN layer, while less change was observed in the distribution of germanium atoms. Silicon implantation introduced vacancy-related defects. By annealing at temperatures over 1300oC, the vacancy-related defects were reduced, while oxygen atoms were diffused from the substrate due to sapphire decomposition. We reproducibly achieved silicon-implanted AlN layers with electrical conductance by controlling the annealing temperature and distribution of silicon and oxygen concentrations.

Clostridioides difficile strain-dependent and strain-independent adaptations to a microaerobic environment

Clostridioides difficile (formerly Clostridium difficile ) colonizes the gastrointestinal tract following disruption of the microbiota and can initiate a spectrum of clinical manifestations ranging from asymptomatic to life-threatening colitis. Following antibiotic treatment, luminal oxygen concentrations increase, exposing gut microbes to potentially toxic reactive oxygen species. Though typically regarded as a strict anaerobe, C. difficile can grow at low oxygen concentrations. How this bacterium adapts to a microaerobic environment and whether those responses to oxygen are conserved amongst strains is not entirely understood. Here, two C. difficile strains (630 and CD196) were cultured in 1.5% oxygen and the transcriptional response to long-term oxygen exposure was evaluated via RNA-sequencing. During growth in a microaerobic environment, several genes predicted to protect against oxidative stress were upregulated, including those for rubrerythrins and rubredoxins. Transcription of genes involved in metal homeostasis was also positively correlated with increased oxygen levels and these genes were amongst the most differentially transcribed. To directly compare the transcriptional landscape between C. difficile strains, a ‘consensus-genome’ was generated. On the basis of the identified conserved genes, basal transcriptional differences as well as variations in the response to oxygen were evaluated. While several responses were similar between the strains, there were significant differences in the abundance of transcripts involved in amino acid and carbohydrate metabolism. Furthermore, intracellular metal concentrations significantly varied both in an oxygen-dependent and oxygen-independent manner. Overall, these results indicate that C. difficile adapts to grow in a low oxygen environment through transcriptional changes, though the specific strategy employed varies between strains.

Thermodynamic modeling of solid fuel gasification in mixtures of oxygen and carbon dioxide

One of the main problems in the use of solid fuels is inevitable formation of significant amounts of carbon dioxide. The prospects for reducing CO2 emissions (carbon capture and storage, CCS) are opening up with the use of new coal technologies, such as thermal power plants with integrated gasification (IGCC) and transition to oxygen-enriched combustion (oxyfuel). In order to study the efficiency of solid fuel conversion processes using carbon dioxide, thermodynamic modeling was carried out. Results show that difference between efficiency of fuel conversion in O2/N2 and O2/CO2 mixtures increases with an increase in the volatile content and a decrease in the carbon content. The effect of using CO2 as a gasification agent depends on the oxygen concentration: at low oxygen concentrations, the process temperature turns out to be low due to dilution; at high oxygen concentrations, the CO2 concentration is not high enough for efficient carbon conversion.

Change in dissolved oxygen concentrations during aeration and mixing using a combined system

Combined mixing and aeration systems are not given priority in the Czech Republic. Still, they are installed at several WWTPs. Their advantage is mixing and aerating at the same time. This article provides data from actual measurements where a combined system was used for drinking water including necessary chemicals. The text below evaluates the course of changes in the concentration of dissolved oxygen in different points in the reactor depending on time.

Mapping manifestations of parametric uncertainty in projected pelagic oxygen concentrations back to contemporary local model fidelity

Pelagic biogeochemical models (BGCMs) have matured into generic components of Earth System Models. BGCMs mimic the effects of marine biota on oceanic nutrient, carbon and oxygen cycles. They rely on parameters that are adjusted to match observed conditions. Such parameters are key to determining the models’ responses to changing environmental conditions. However, many of these parameters are difficult to constrain and constitute a major source of uncertainty in BGCM projections. Here we use, for the first time, variance-based sensitivity analyses to map BGCM parameter uncertainties onto their respective local manifestation in model entities (such as oceanic oxygen concentrations) for both contemporary climate and climate projections. The mapping effectively relates local uncertainties of projections to the uncertainty of specific parameters. Further, it identifies contemporary benchmarking regions, where the uncertainties of specific parameters manifest themselves, thereby facilitating an effective parameter refinement and a reduction of the associated uncertainty. Our results demonstrate that the parameters that are linked to uncertainties in projections may differ from those parameters that facilitate model conformity with present-day observations. In summary, we present a practical approach to the general question of where present-day model fidelity may be indicative for reliable projections.

Indirect Measurements of Acceleration Atelectasis and the Role of Inspired Oxygen Concentrations

BACKGROUND: A growing number of symptom reports suggestive of acceleration atelectasis in fast jet aircrew have raised the question as to whether traditional guidelines on inspired gas composition remain valid. The aim of this study was to assess the effects of inspired O2 concentration on the development of acceleration atelectasis when wearing modern anti-G garments. METHODS: There were 14 nonaircrew subjects who completed 5 centrifuge exposures to +5 Gz lasting 90 s. During exposures subjects breathed a gas mixture containing 21, 35, 45, 60, or 75% O2. To assess the extent of atelectasis post-Gz, forced inspiratory vital capacity (FIVC), regional FIVC (EITFIVC), shunt, respiratory resistance, reactance, and compliance and peripheral O2 saturation during a hypoxic exposure were measured. RESULTS: Compared with baseline, FIVC was not statistically significantly altered. EITFIVC was 14.4% lower after the 75% O2 exposure only with a greater symptom reporting with higher FIO2 in some individuals. A significantly greater shunt (3>6%) followed the 60 and 75% O2 exposures. O2 concentration during Gz had no effect on respiratory resistance, reactance, compliance, or hypoxemia. DISCUSSION: There is evidence of mild acceleration atelectasis present when breathing 60% O2, particularly in susceptible individuals, with 75% O2 causing more obvious physiological compromise. An inspired oxygen concentration of <60% will prevent the majority of individuals from developing acceleration atelectasis. Pollock RD, Gates SD, Radcliffe JJ, Stevenson AT. Indirect measurements of acceleration atelectasis and the role of inspired oxygen concentrations. Aerosp Med Hum Perform. 2021; 92(10):780785.

Tracer and observationally-derived constraints on diapycnal diffusivities in an ocean state estimate

Use of an ocean parameter and state estimation framework–such as the Estimating the Circulation &amp; Climate of the Ocean (ECCO) framework–could provide an opportunity to learn about the spatial distribution of the diapycnal diffusivity parameter (κρ) that observations alone cannot due to gaps in coverage. However, we show that the assimilation of existing in situ temperature, salinity, and pressure observations is not sufficient to constrain κρ estimated with ECCO, as κρ from ECCO does not agree closely with observations–specifically, κρ inferred from microstructure measurements. We investigate whether there are observations with more global coverage and well-understood measurement uncertainties that can be assimilated by ECCO to improve its representation of κρ. Argo-derived κρ using a strain-based parameterization of finescale hydrographic structure is one potential source of information. Argo-derived κρ agrees well with microstructure. However, because Argo- derived κρ has both measurement and structural uncertainties, we propose dissolved oxygen concentrations as a candidate for future data assimilation with ECCO. We perform sensitivity analyses with ECCO to test whether oxygen concentrations provide information about κρ. We compare two adjoint sensitivity calculations: one that uses misfits to Argo-derived κρ and the other uses misfits to dissolved oxygen concentrations. We show that adjoint sensitivities of dissolved oxygen concentration misfits to the state estimate's control space typically direct κρ to improve relative to the Argo-derived and microstructure-inferred values. However, assimilation of dissolved oxygen concentrations would likely not serve as a substitute for assimilating accurately measured κρ.

High-Sustained Concentrations of Organisms at Very low Oxygen Concentration Indicated by Acoustic Profiles in the Oxygen Deficit Region Off Peru

The oxygen deficient mesopelagic layer (ODL) off Peru has concentrations below 5 μmol O2 kg–1 and is delimited by a shallow upper oxycline with strong vertical gradient and a more gradual lower oxycline (lOx). Some regions show a narrow band of slightly increased oxygen concentrations within the ODL, an intermediate oxygen layer (iO2). CTD, oxygen and lowered Acoustic Doppler Current Profiler (LADCP, 300 kHz) profiles were taken on the shelf edge and outside down to mostly 2000 m. We evaluate here the acoustic volume backscatter strength of the LADCP signal representing organisms of about 5 mm size. Dominant features of the backscatter profiles were a minimum backscatter strength within the ODL, and just below the lOx a marked backscatter increase reaching a maximum at less than 3.0 μmol O2 kg–1. Below this maximum, the acoustic backscatter strength gradually decreased down to 1000 m below the lOx. The backscatter strength also increased at the iO2 in parallel to the oxygen concentration perturbations marking the iO2. These stable backscatter features were independent of the time of day and the organisms represented by the backscatter had to be adapted to live in this microaerobic environment. During daylight, these stable structures were overlapped by migrating backscatter peaks. Outstanding features of the stable backscatter were that at very low oxygen concentrations, the volume backscatter was linearly related to the oxygen concentration, reaching half peak maximum at less than 2.0 μmol O2 kg–1 below the lOx, and the depth-integrated backscatter of the peak below the lOx was higher than the integral above the Ox. Both features suggest that sufficient organic material produced at the surface reaches to below the ODL to sustain the major fraction of the volume backscatter-producing organisms in the water column. These organisms are adapted to the microaerobic environment so they can position themselves close to the lower oxycline to take advantage of the organic particles sinking out of the ODL.