Optimization of Propagation Medium for Enhanced Polyhydroxyalkanoate Production by Pseudomonas oleovorans

Polyhydroxyalkanoates (PHAs) represent a promising alternative to commercially used petroleum-based plastics. Pseudomonas oleovorans is a natural producer of medium-chain-length PHA (mcl-PHA) under cultivation conditions with nitrogen limitation and carbon excess. Two-step cultivation appears to be an efficient but more expensive method of PHA production. Therefore, the aim of this work was to prepare a minimal synthetic medium for maximum biomass yield and to optimize selected independent variables by response surface methodology (RSM). The highest biomass yield (1.71 ± 0.04 g/L) was achieved in the optimized medium containing 8.4 g/L glucose, 5.7 g/L sodium ammonium phosphate and 35.4 mM phosphate buffer. Under these conditions, both carbon and nitrogen sources were completely consumed after 48 h of the cultivation and the biomass yield was 1.7-fold higher than in the conventional medium recommended by the literature. This approach demonstrates the possibility of using two-stage PHA cultivation to obtain the maximum amount of biomass and PHA.

Feasibility of fly ash as fluxing agent in mid- and low-grade phosphate rock carbothermal reduction and its reaction kinetics

The feasibility of industrial waste fly ash as an alternative fluxing agent for silica in carbothermal reduction of medium-low-grade phosphate ore was studied in this paper. With a series of single-factor experiments, the reduction rate of phosphate rock under different reaction temperature, reaction time, particle size, carbon excess coefficient, and silicon–calcium molar ratio was investigated with silica and fly ash as fluxing agents. Higher reduction rates were obtained with fly ash fluxing instead of silica. The optimal conditions were derived as: reaction temperature 1,300°C, reaction time 75 min, particle size 48–75 µm, carbon excess coefficient 1.2, and silicon–calcium molar ratio 1.2. The optimized process condition was verified with other two different phosphate rocks and it was proved universally. The apparent kinetics analyses demonstrated that the activation energy of fly ash fluxing is reduced by 31.57 kJ/mol as compared with that of silica. The mechanism of better fluxing effect by fly ash may be ascribed to the fact that the products formed within fly ash increase the amount of liquid phase in the reaction system and promote reduction reaction. Preliminary feasibility about the recycling of industrial waste fly ash in thermal phosphoric acid industry was elucidated in the paper.

LAMOST J011939.222−012150.45: The most barium-enhanced CEMP-s turnoff star

We have performed chemical abundance analyses for a newly discovered metal-poor turn-off star (Teff = 6276 K, log g = 3.93, [Fe$/$H] = −2.93), LAMOST J011939.222−012150.45, based on high-resolution and high signal-to-noise ratio spectra in both optical and near-UV obtained by Subaru. Abundances have been derived for 20 elements, including 11 light elements such as C, N, Na, Mg, etc., and 9 neutron-capture elements from Sr to Pb. This object is a carbon-enhanced metal-poor star with a large carbon excess of [C$/$Fe] = +2.26. LAMOST J011939.222−012150.45 shows extreme enhancement in s-process elements, especially for Ba, La, and Pb ([Ba$/$Fe] = +3.16 ± 0.18, [La$/$Fe] = +2.29 ± 0.24, [Pb$/$Fe] = +3.38 ± 0.12). A very clear radial velocity variation has also been detected, providing evidence of the existence of a companion. Interestingly, even without any scaling, the observed abundance pattern from light to heavy neutron-capture elements agrees well with predictions of accretion from a companion asymptotic giant branch (AGB) star. Considering the evolutionary status of this object, its surface material is very likely to be completely accreted from its AGB companion and has been preserved until today.

Evidence for an Abrupt Transition between SiO2 and SiC from EELS and Ab Initio Modelling

Electron energy loss spectroscopy (EELS) and ab initio simulations are combined in this study to produce an atomistic interpretation of the interface morphology in lateral 4H-SiC / SiO2 MOSFETs with deposited gate oxides. This allows the question of interface abruptness, and the presence the postulated SiOxCy interlayer to be explored for a subset of devices with deposited oxides. From comparison between EELS and ab initio calculation the interfaces considered are best described as abrupt, but stepped, transitioning without any of the carbon excess or SiOxCy interlayer that have been described for other devices observed.

Connecting planet formation and astrochemistry

Combining a time-dependent astrochemical model with a model of planet formation and migration, we compute the carbon-to-oxygen ratio (C/O) of a range of planetary embryos starting their formation in the inner solar system (1–3 AU). Most of the embryos result in hot Jupiters (M ≥ MJ, orbital radius <0.1 AU) while the others result in super-Earths at wider orbital radii. The volatile and ice abundance of relevant carbon and oxygen bearing molecular species are determined through a complex chemical kinetic code that includes both gas and grain surface chemistry. This is combined with a model for the abundance of the refractory dust grains to compute the total carbon and oxygen abundance in the protoplanetary disk available for incorporation into a planetary atmosphere. We include the effects of the refractory carbon depletion that has been observed in our solar system, and posit two models that would put this missing carbon back into the gas phase. This excess gaseous carbon then becomes important in determining the final planetary C/O because the gas disk now becomes more carbon rich relative to oxygen (high gaseous C/O). One model, where the carbon excess is maintained throughout the lifetime of the disk results in hot Jupiters that have super-stellar C/O. The other model deposits the excess carbon early in the disk life and allows it to advect with the bulk gas. In this model the excess carbon disappears into the host star within 0.8 Myr, returning the gas disk to its original (substellar) C/O, so the hot Jupiters all exclusively have substellar C/O. This shows that while the solids tend to be oxygen rich, hot Jupiters can have super-stellar C/O if a carbon excess can be maintained by some chemical processing of the dust grains. The atmospheric C/O of the super-Earths at larger radii are determined by the chemical interactions between the gas and ice phases of volatile species rather than the refractory carbon model. Whether the carbon and oxygen content of the atmosphere was accreted primarily by gas or solid accretion is heavily dependent on the mass of the atmosphere and where in the disk the growing planet accreted.

Carbon star wind models at solar and sub-solar metallicities: a comparative study

Context. The heavy mass loss observed in evolved stars on the asymptotic giant branch (AGB) is usually attributed to dust-driven winds, but it is still an open question how much AGB stars contribute to the dust production in the interstellar medium, especially at lower metallicities. In the case of C-type AGB stars, where the wind is thought to be driven by radiation pressure on amorphous carbon grains, there should be significant dust production even in metal-poor environments. Carbon stars can manufacture the building blocks needed to form the wind-driving dust species themselves, irrespective of the chemical composition they have, by dredging up carbon from the stellar interior during thermal pulses. Aims. We investigate how the mass loss in carbon stars is affected by a low-metallicity environment, similar to the Large and Small Magellanic Clouds (LMC and SMC). Methods. The atmospheres and winds of C-type AGB stars are modeled with the 1D spherically symmetric radiation-hydrodynamical code Dynamic Atmosphere and Radiation-driven Wind models based on Implicit Numerics (DARWIN). The models include a time-dependent description for nucleation, growth, and evaporation of amorphous carbon grains directly out of the gas phase. To explore the metallicity-dependence of mass loss we calculate model grids at three different chemical abundances (solar, LMC, and SMC). Since carbon may be dredged up during the thermal pulses as AGB stars evolve, we keep the carbon abundance as a free parameter. The models in these three different grids all have a current mass of one solar mass; effective temperatures of 2600, 2800, 3000, or 3200 K; and stellar luminosities equal to logL*∕L⊙ = 3.70, 3.85, or 4.00. Results. The DARWIN models show that mass loss in carbon stars is facilitated by high luminosities, low effective temperatures, and a high carbon excess (C–O) at both solar and subsolar metallicities. Similar combinations of effective temperature, luminosity, and carbon excess produce outflows at both solar and subsolar metallicities. There are no large systematic differences in the mass-loss rates and wind velocities produced by these wind models with respect to metallicity, nor any systematic difference concerning the distribution of grain sizes or how much carbon is condensed into dust. DARWIN models at subsolar metallicity have approximately 15% lower mass-loss rates compared to DARWIN models at solar metallicity with the same stellar parameters and carbon excess. For both solar and subsolar environments typical grain sizes range between 0.1 and 0.5 μm, the degree of condensed carbon varies between 5 and 40%, and the gas-to-dust ratios between 500 and 10 000. Conclusions. C-type AGB stars can contribute to the dust production at subsolar metallicities (down to at least [Fe∕H] = −1) as long as they dredge up sufficient amounts of carbon from the stellar interior. Furthermore, stellar evolution models can use the mass-loss rates calculated from DARWIN models at solar metallicity when modeling the AGB phase at subsolar metallicities if carbon excess is used as the critical abundance parameter instead of the C/O ratio.

Synthesis and Magnetic Characterization of Graphite-Coated Iron Nanoparticles

Graphite-coated iron nanoparticles were prepared from magnetite nanoparticles by chemical vapour deposition (CVD) under methane and hydrogen atmosphere. After being purified from carbon excess, graphite-coated iron nanoparticles were tested for morphological and magnetic properties. It was found that, during the thermal process, magnetite nanoparticles 6 nm in size coalesce and transform into graphite-coated iron 200 nm in size, as revealed by scanning electron microscopy (SEM). Raman characterization assessed that high-quality graphite coats the iron core. Magnetic measurements revealed the phase change (magnetite to iron) as an increase in the saturation magnetization from 50 to 165 emu/g after the CVD process.