Method and new tabulations for flux-weighted line opacity and radiation line force in supersonic media

In accelerating and supersonic media, the interaction of photons with spectral lines can be of ultimate importance. However, fully accounting for such line forces currently can only be done by specialised codes in 1-D steady-state flows. More general cases and higher dimensions require alternative approaches. We presented a comprehensive and fast method for computing the radiation line-force using tables of spectral line-strength distribution parameters, which can be applied in arbitrary (multi-D, time-dependent) simulations, including those accounting for the line-deshadowing instability, to compute the appropriate opacities. We assumed local thermodynamic equilibrium to compute a flux-weighted line opacity from $>4$ million spectral lines. We derived the spectral line strength and tabulated the corresponding line-distribution parameters for a range of input densities $\rho\in[10^{-20},10^{-10}]gcm^{-3}$ and temperatures $T\in[10^4,10^{4.7}]K$. We found that the variation of the line distribution parameters plays an essential role in setting the wind dynamics in our models. In our benchmark study, we also found a good overall agreement between the O-star mass-loss rates of our models and those derived from steady-state studies using more detailed radiative transfer. Our models reinforce that self-consistent variation of the line-distribution parameters is important for the dynamics of line-driven flows. Within a well-calibrated O-star regime, our results support the proposed methodology. In practice, utilising the provided tables, yielded a factor $>100$ speed-up in computational time compared to specialised 1-D model-atmosphere codes of line-driven winds, which constitutes an important step towards efficient multi-D simulations. We conclude that our method and tables are ready to be exploited in various radiation-hydrodynamic simulations where the line force is important

Empirical mass-loss rates and clumping properties of Galactic early-type O supergiants

International audienceAims. We investigate the impact of optically thick clumping on spectroscopic stellar wind diagnostics in O supergiants and constrain wind parameters associated with porosity in velocity space. This is the first time the effects of optically thick clumping have been investigated for a sample of massive hot stars, using models which include a full optically thick clumping description. Methods. We re-analyse existing spectroscopic observations of a sample of eight O supergiants previously analysed with the non-local-thermodynamic-equilibrium (NLTE) atmosphere code CMFGEN. Using a genetic algorithm wrapper around the NLTE atmosphere code FASTWIND we obtain simultaneous fits to optical and ultraviolet spectra and determine photospheric properties, chemical surface abundances and wind properties. Results. We provide empirical constraints on a number of wind parameters including the clumping factors, mass-loss rates and terminal wind velocities. Additionally, we establish the first systematic empirical constraints on velocity filling factors and interclump densities. These are parameters that describe clump distribution in velocity-space and density of the interclump medium in physical-space, respectively. We observe a mass-loss rate reduction of a factor of 3.6 compared to theoretical predictions from Vink et al. (2000), and mass-loss rates within a factor 1.4 of theoretical predictions from Björklund et al. (2021). Conclusions. We confirm that including optically thick clumping allows simultaneous fitting of optical recombination lines and ultraviolet resonance lines, including the unsaturated ultraviolet phosphorus lines (P v λλ1118-1128), without reducing the phosphorus abundance. We find that, on average, half of the wind velocity field is covered by dense clumps. We also find that these clumps are 25 times denser than the average wind, and that the interclump medium is 3-10 times less dense than the mean wind. The former result agrees well with theoretical predictions, the latter suggests that lateral filling-in of radially compressed gas might be critical for setting the scale of the rarefied interclump matter

Alterações nas reservas de sementes de Dalbergia nigra ((Vell.) Fr. All. ex Benth.) durante a hidratação

Seed imbibitions is the first stage of the germination process and is characterized by the hydration of tissues and cells and the activation and/or induction of the enzymes responsible for mobilizing reserves for respiration and the construction of new cell structures. The objective of this study was to investigate the alterations in reserve substances during slow hydration of Bahia Rosewood (Dalbergia nigra) seeds in water. Seeds from two different lots (Lot I and II) were placed in saturated desiccators (95-99% RH) to hydrate at 15 and 25 °C until water contents of 10, 15, 20 and 25% were reached. At each level of hydration, changes in lipid reserves, soluble carbohydrates, starch and soluble proteins were evaluated. The mobilization of reserves was similarly assessed in both lots, with no differences being observed between the two hydration temperatures. Lipid contents showed little variation during hydration, while the contents of soluble carbohydrates and starch decreased after the 15% water content level. Soluble proteins showed a gradual tendency to decrease between the control (dry seeds) up to 25% water content

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Quantitative near infra-red spectroscopy of massive stars

Interest in near infra-red spectroscopy of massive stars has increased dramatically over the last decades, as it offers the possibility to analyze stars embedded in dusty star forming regions and near the Galactic center. We present an analysis of both high resolution optical and, separately, high resolution VLT/CRIRES near-IR spectra in the J, H, K and L-band of nearby dwarf O-type stars. Applying a genetic fitting algorithm approach using state-of-the-art FASTWIND non-LTE atmospheres, we present a comparison of the stellar and wind properties as derived from these two spectral regimes. In this approach we retrieve the effective temperature to within a sub-type and the surface gravity to within 0.2 dex, but find a discrepancy in the mass-loss rates of 0.2 up to 1.0 dex. We find that He II 1012 nm and Brackett-α lines do not yield consistent mass-loss estimates, the former producing much lower values than Hα, while Brackett-α and Hα are consistent

Effect of green gold nanoparticles synthesized with plant on the flexural strength of heat-polymerized acrylic resin

Purpose: The aim of this study was to investigate the effect of gold nanoparticle on the flexural strength of polymethyl methacrylate (PMMA).Materials and Methods: PMMA specimens (65 mm × 10 mm × 3.3 mm) containing different sizes (45 nm, 55 nm, and 65 nm) and concentrations (0.05% and 0.2%) of gold nanoparticles were prepared, along with a control group containing no added nanoparticles. Flexural strength of all specimens was measured, and one‑way ANOVA and Tukey–Kramer post hoc multiple comparisons tests were performed to identify statistical differences between groups.Results: The addition of gold nanoparticles increased the flexural strength of acrylic resin. Significantly greater increases were obtained with lower concentrations (0.05%) when compared to higher concentrations (0.20%).Conclusion: Differences in concentrations of gold nanoparticles added to PMMA have significantly different effects on PMMA flexural strength, whereas differences in sizes of gold nanoparticles added to PMMA do not significantly affect its flexural strength. Accordingly, adding gold nanoparticles to PMMA may enhance the mechanical properties of denture bases used in clinical practice.Keywords: Flexural strength, gold, nanoparticles, polymethyl methacrylat

Method and new tabulations for flux-weighted line opacity and radiation line force in supersonic media

Context. In accelerating and supersonic media, understanding the interaction of photons with spectral lines can be of utmost importance, especially in an accelerating flow. However, fully accounting for such line forces is computationally expensive and challenging, as it involves complicated solutions of the radiative transfer problem for millions of contributing lines. This currently can only be done by specialised codes in 1D steady-state flows. More general cases and higher dimensions require alternative approaches. Aims. We present a comprehensive and fast method for computing the radiation line force using tables of spectral-line-strength distribution parameters, which can be applied in arbitrary (multi-D, time-dependent) simulations, including those that account for the line-deshadowing instability, to compute the appropriate opacities. Methods. We assume local thermodynamic equilibrium to compute a flux-weighted line opacity from ~4 million spectral lines. We fit the opacity computed from the line list with an analytic result derived for an assumed distribution of the spectral line strength and found the corresponding line-distribution parameters, which we tabulate here for a range of assumed input densities ρ ∈- [10-20, 10-10] g cm-3 and temperatures T ∈- [104, 1047] K. Results. We find that the variation in the line-distribution parameters plays an essential role in setting the wind dynamics in our models. In our benchmark study, we also find a good overall agreement between the O-star mass-loss rates of our models and those derived from steady-state studies that use a more detailed radiative transfer. Conclusions. Our models reinforce the idea that self-consistent variation in the line-distribution parameters is important for the dynamics of line-driven flows. Within a well-calibrated O-star regime, our results support the proposed methodology. In practice, utilising the provided tables, yielded a factor >100 speed-up in computational time compared to specialised 1D model-atmosphere codes of line-driven winds, which constitutes an important step towards efficient multi-dimensional simulations. We conclude that our method and tables are ready to be exploited in various radiation-hydrodynamic simulations where the line force is important

Method and new tabulations for flux-weighted line opacity and radiation line force in supersonic media

Context. In accelerating and supersonic media, understanding the interaction of photons with spectral lines can be of utmost importance, especially in an accelerating flow. However, fully accounting for such line forces is computationally expensive and challenging, as it involves complicated solutions of the radiative transfer problem for millions of contributing lines. This currently can only be done by specialised codes in 1D steady-state flows. More general cases and higher dimensions require alternative approaches. Aims. We present a comprehensive and fast method for computing the radiation line force using tables of spectral-line-strength distribution parameters, which can be applied in arbitrary (multi-D, time-dependent) simulations, including those that account for the line-deshadowing instability, to compute the appropriate opacities. Methods. We assume local thermodynamic equilibrium to compute a flux-weighted line opacity from ~4 million spectral lines. We fit the opacity computed from the line list with an analytic result derived for an assumed distribution of the spectral line strength and found the corresponding line-distribution parameters, which we tabulate here for a range of assumed input densities ρ ∈- [10-20, 10-10] g cm-3 and temperatures T ∈- [104, 1047] K. Results. We find that the variation in the line-distribution parameters plays an essential role in setting the wind dynamics in our models. In our benchmark study, we also find a good overall agreement between the O-star mass-loss rates of our models and those derived from steady-state studies that use a more detailed radiative transfer. Conclusions. Our models reinforce the idea that self-consistent variation in the line-distribution parameters is important for the dynamics of line-driven flows. Within a well-calibrated O-star regime, our results support the proposed methodology. In practice, utilising the provided tables, yielded a factor >100 speed-up in computational time compared to specialised 1D model-atmosphere codes of line-driven winds, which constitutes an important step towards efficient multi-dimensional simulations. We conclude that our method and tables are ready to be exploited in various radiation-hydrodynamic simulations where the line force is important

The R136 star cluster dissected with Hubble Space Telescope/STIS III. The most massive stars and their clumped winds

Context. The star cluster R136 inside the Large Magellanic Cloud hosts a rich population of massive stars, including the most massive stars known. The strong stellar winds of these very luminous stars impact their evolution and the surrounding environment. We currently lack detailed knowledge of the wind structure that is needed to quantify this impact. Aims. Our goal is to observationally constrain the stellar and wind properties of the massive stars in R136, in particular the wind-structure parameters related to wind clumping. Methods. We simultaneously analyse optical and ultraviolet spectroscopy of 53 O-type and three WNh-stars using the FASTWIND model atmosphere code and a genetic algorithm. The models account for optically thick clumps and effects related to porosity and velocity-porosity, as well as a non-void interclump medium. Results. We obtain stellar parameters, surface abundances, mass-loss rates, terminal velocities, and clumping characteristics and compare them to theoretical predictions and evolutionary models. The clumping properties include the density of the interclump medium and the velocity-porosity of the wind. For the first time, these characteristics are systematically measured for a wide range of effective temperatures and luminosities. Conclusions. We confirm a cluster age of 1.0–2.5 Myr and derived an initial stellar mass of ≥250 M⊙ for the most massive star in our sample, R136a1. The winds of our sample stars are highly clumped, with an average clumping factor of fcl = 29 ± 15. We find tentative trends in the wind-structure parameters as a function of the mass-loss rate, suggesting that the winds of stars with higher mass-loss rates are less clumped. We compare several theoretical predictions to the observed mass-loss rates and terminal velocities and find that none satisfactorily reproduce both quantities. The prescription of Krtička & Kubát (2018) matches the observed mass-loss rates best