Zonal flow generation through four wave interaction in reduced models of fusion plasma turbulence

In tokamaks, turbulence is a key contributor to cross field transport. However, it is also responsible for the spontaneous generation of large scale structures such as zonal ows. These are of relevance to fusion plasmas as they can create transport barriers which aid plasma confinement. The interaction between drift waves and zonal ows can be investigated using reduced models such as the Hasegawa- Mima and Hasegawa-Wakatani equations. A four-wave truncated model is developed for the Extended-Hasegawa-Mima (EHM) equation. This produces a set of four ordinary differential equations (ODEs) that are used to investigate the modulational instability (MI), a mechanism by which drift waves can produce a zonal ow. These equations are linearised to produce a dispersion relation for the MI which is used to produce a set of maps of the linear growth rate of the MI. These show how additional modes become unstable as the gyroradius is increased. The truncated model and dispersion relation are then compared to measurements taken from simulations of the full EHM partial differential equation (PDE) which has been seeded with an appropriate initial condition. Good agreement is found when the pump wave has no component in the direction of the density gradient. A similar truncated model is derived for the Extended-Hasegawa-Wakatani (EHW) equations. As the EHW system has separate equations for density and potential this leads to a set of eight ODEs. The linearisation technique used for the EHM system cannot be applied here. Instead, approximations based on the built in EHW instability are made to calculate a linear growth rate for the zonal ow using the ODEs describing it. These analytical predictions are then compared to a full PDE simulation of the system, which is initialised using random noise. It is found that for particular sets of waves the ODEs provide a good prediction of the linear growth rate. A driving term is added to the EHM equation to reproduce the effect of the built in instability of the EHW equations. This causes a drift wave spectrum to grow when full EHW PDE simulations are seeded with random noise. The four-wave ODE model is updated to include this driving. The ODE model again produces good predictions for the growth rate of the zonal flow

Perinatal aspects on the covid-19 pandemic: a practical resource for perinatal-neonatal specialists.

BackgroundLittle is known about the perinatal aspects of COVID-19.ObjectiveTo summarize available evidence and provide perinatologists/neonatologists with tools for managing their patients.MethodsAnalysis of available literature on COVID-19 using Medline and Google scholar.ResultsFrom scant data: vertical transmission from maternal infection during the third trimester probably does not occur or likely it occurs very rarely. Consequences of COVID-19 infection among women during early pregnancy remain unknown. We cannot conclude if pregnancy is a risk factor for more severe disease in women with COVID-19. Little is known about disease severity in neonates, and from very few samples, the presence of SARS-CoV-2 has not been documented in human milk. Links to websites of organizations with updated COVID-19 information are provided. Infographics summarize an approach to the pregnant woman or neonate with suspected or confirmed COVID-19.ConclusionsAs the pandemic continues, more data will be available that could lead to changes in current knowledge and recommendations

Making It Last: Storage Time and Temperature Have Differential Impacts on Metabolite Profiles of Airway Samples from Cystic Fibrosis Patients.

Metabolites of human or microbial origin have the potential to be important biomarkers of the disease state in cystic fibrosis (CF). Clinical sample collection and storage conditions may impact metabolite abundances with clinical relevance. We measured the change in metabolite composition based on untargeted gas chromatography-mass spectrometry (GC-MS) when CF sputum samples were stored at 4°C, -20°C, or -80°C with one or two freeze-thaw cycles. Daily measurements were taken for 1 week and then weekly for 4 weeks (4°C) and 8 weeks (-20°C). The metabolites in samples stored at -20°C maintained abundances similar to those found at-80°C over the course of 8 weeks (average change in Bray-Curtis distance, 0.06 ± 0.04) and were also stable after one or two freeze-thaw cycles. However, the metabolite profiles of samples stored at 4°C shifted after 1 day and continued to change over the course of 4 weeks (average change in Bray-Curtis distance, 0.31 ± 0.12). The abundances of several amino acids and other metabolites increased with time of storage at 4°C but remained constant at -20°C. Storage temperature was a significant factor driving the metabolite composition (permutational multivariate analysis of variance: r2 = 0.32 to 0.49, P < 0.001). CF sputum samples stored at -20°C at the time of sampling maintain a relatively stable untargeted GC-MS profile. Samples should be frozen on the day of collection, as more than 1 day at 4°C impacts the global composition of the metabolites in the sample. IMPORTANCE Metabolomics has great potential for uncovering biomarkers of the disease state in CF and many other contexts. However, sample storage timing and temperature may alter the abundance of clinically relevant metabolites. To assess whether existing samples are stable and to direct future study design, we conducted untargeted GC-MS metabolomic analysis of CF sputum samples after one or two freeze-thaw cycles and storage at 4°C and -20°C for 4 to 8 weeks. Overall, storage at -20°C and freeze-thaw cycles had little impact on metabolite profiles; however, storage at 4°C shifted metabolite abundances significantly. GC-MS profiling will aid in our understanding of the CF lung, but care should be taken in studies using sputum samples to ensure that samples are properly stored