Tritium diffusion in the nuclear fusion reactor breeder material Li 2 TiO 3 is a fundamentally important process for the tritium release kinetics. The energy barrier of tritium diffusion in Li 2 TiO 3 was reported with a considerable uncertainty in previous experiments. Here, we perform the systematic density-functional-theory (DFT) studies for the diffusion processes of a positively-charged tritium, which is the most preferable charge state of the tritium interstitial in a single Li 2 TiO 3 crystal. By calculating various local-diffusion minimum-energy paths, we find that the diffusion of the tritium is strongly anisotropic along different crystalline directions. The most favorable diffusion paths appear within a Li 6 atomic single layer of Li 2 TiO 3 and the corresponding DFT diffusion barrier is 0.334 eV, while the diffusion barrier for most favorable diffusion paths crossing a Li 2 Ti 4 atomic layer is 1.006 eV.
Hyaluronic acid (HA) concentration is an important parameter in fermentation process. Currently, carbazole assay is widely used for HA content determination in routine analysis. However, this method is time-consuming, environment polluting and has the risk of microbial contamination, as well as the results lag behind fermentation process. This paper attempted the feasibility to predict the concentration of HA in fermentation broth by using near infrared (NIR) spectroscopy in transmission mode. In this work, a total of 56 samples of fermentation broth from 7 batches were analyzed, which contained HA in the range of 2.35-9.69 g/L. Di®erent data preprocessing methods were applied to construct calibration models. The¯nal optimal model was obtained with¯rst derivative using Savitzky-Golay smoothing (9 points window, second-order polynomial) and partial least squares (PLS) regression with leave-one-block-out cross validation. The correlation coe±cient and Root Mean Square Error of prediction set is 0.98 and 0.43 g/L, respectively, which show the possibility of NIR as a rapid method for microanalysis and to be a promising tool for a rapid assay in HA fermentation.
As efficient and stable nuclear waste forms, singlephase uranium (U 6+ )-incorporated La 2 Zr 2 O 7 nanoparticles were designed and synthesized in an air atmosphere. To obtain a high U loading, divalent magnesium (Mg 2+ ) was introduced to balance the extra charge from the substitution of tetravalent zirconium (Zr 4+ ) by U 6+ with a minimized impact to the lattice. There is a compositiondriven phase transition from order pyrochlore to defect fluorite as the U concentration increases from 10 to 30 mol %, demonstrating both good solubility and stability of the La 2 Zr 2 O 7 host for U and potentially for other actinides. La 2 (U x Mg x Zr 1−2x ) 2 O 7 (x = 0−0.3) nanoparticles showed good dispersity and crystallinity with an average particle size of ∼48 nm. Furthermore, X-ray photoelectron spectroscopy, Raman spectroscopy, and emission spectroscopy revealed that U was stabilized in the hexavalent state in the form of a UO 2 2+ ion. Spectroscopic methods also demonstrated that our samples caused a scintillating response with an orange emission (597 nm) by 230 nm excitation. In addition, density functional theory simulations were employed to investigate the atomic structures and electronic properties of the U-incorporated pyrochlores. The calculated bond lengths, atomic charges, and charge density confirm the existence of UO 2 2+ ions. Supported by both experimental and computational results, a novel geometrical structure was proposed to explain the Mg 2+ −U 6+ substitution. This work demonstrated the successful development of U-incorporated La 2 Zr 2 O 7 nanoparticles and provided an efficient way to immobilize U in these ceramic waste matrixes.
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