Aluminothermic reduction of CeO2: mechanism of an economical route to aluminum-cerium alloys.

Cerium oxide is a low-value byproduct of rare-earth mining yet constitutes the largest fraction of the rare earth elements. The reduction of cerium oxide by liquid aluminum is proposed as an energy- and cost-efficient route to produce high-strength Al-Ce alloys. This work investigated the mechanism of a multi-step reduction reaction to facilitate the industrial adaptation of the process. Differential scanning calorimetry in combination with time-resolved synchrotron diffraction data uncovered the rate-limiting reaction step as the origin of the reported temperature dependence of reduction efficiency. This is the first in situ study of a metallothermic reaction mechanism and will serve as guidance for cost- and energy efficient industrial process control.

Laser-Induced Thermal Decomposition of Uranium Coordination Compounds with Non-oxidic Ligands to Produce Nitride and Carbide Materials.

The production of ceramics from uranium coordination compounds can be achieved through thermal processing if an excess amount of the desired atoms (i.e., C or N), or reactive gaseous products (e.g., methane or nitrogen oxide) is made available to the reactive uranium metal core via decomposition/fragmentation of the surrounding ligand groups. Here, computational thermodynamic approaches were utilized to identify the temperatures necessary to produce uranium metal from some starting compounds─UI4(TMEDA)2, UCl4(TMEDA)2, UCl3(pyridine)x, and UI3(pyridine)4. Experimentally, precursors were irradiated by a laser under various gaseous environments (argon, nitrogen, and methane) creating extreme reaction conditions (i.e., fast heating, high temperature profile >2000 °C, and rapid cooling). Despite the fast dynamics associated with laser irradiation, the central uranium atom reacted with the thermal decomposition products of the ligands yielding uranium ceramics. Residual gas analysis identified vaporized products from the laser irradiation, and the final ceramic products were characterized by powder X-ray diffraction. The composition of the uranium precursor as well as the gaseous environment had a direct impact on the production of the final phases.

Unconventional Pathways to Carbide Phase Synthesis via Thermal Decomposition of UI4(1,4-dioxane)2.

UI4(1,4-dioxane)2 was subjected to laser-based heating─a method that enables localized, fast heating (T > 2000 °C) and rapid cooling under controlled conditions (scan rate, power, atmosphere, etc.)─to understand its thermal decomposition. A predictive computational thermodynamic technique estimated the decomposition temperature of UI4(1,4-dioxane)2 to uranium (U) metal to be 2236 °C, a temperature achievable under laser irradiation. Dictated by the presence of reactive, gaseous byproducts, the thermal decomposition of UI4(1,4-dioxane)2 under furnace conditions up to 600 °C revealed the formation of UO2, UIx, and U(C1-xOx)y, while under laser irradiation, UI4(1,4-dioxane)2 decomposed to UO2, U(C1-xOx)y, UC2-zOz, and UC. Despite the fast dynamics associated with laser irradiation, the central uranium atom reacted with the thermal decomposition products of the ligand (1,4-dioxane = C4H8O2) instead of producing pure U metal. The results highlight the potential to co-develop uranium precursors with specific irradiation procedures to advance nuclear materials research by finding new pathways to produce uranium carbide.

Step width variability as a discriminator of age-related gait changes.

BACKGROUND: There is scientific evidence that older adults aged 65 and over walk with increased step width variability which has been associated with risk of falling. However, there are presently no threshold levels that define the optimal reference range of step width variability. Thus, the purpose of our study was to estimate the optimal reference range for identifying older adults with normative and excessive step width variability. METHODS: We searched systematically the BMC, Cochrane Library, EBSCO, Frontiers, IEEE, PubMed, Scopus, SpringerLink, Web of Science, Wiley, and PROQUEST databases until September 2018, and included the studies that measured step width variability in both younger and older adults during walking at self-selected speed. Data were pooled in meta-analysis, and standardized mean differences (SMD) with 95% confidence intervals (CI) were calculated. A single-decision threshold method based on the Youden index, and a two-decision threshold method based on the uncertain interval method were used to identify the optimal threshold levels (PROSPERO registration: CRD42018107079). RESULTS: Ten studies were retrieved (older adults = 304; younger adults = 219). Step width variability was higher in older than in younger adults (SMD = 1.15, 95% CI = 0.60; 1.70; t = 4.72, p = 0.001). The single-decision method set the threshold level for excessive step width variability at 2.14 cm. For the two-decision method, step width variability values above the upper threshold level of 2.50 cm were considered excessive, while step width variability values below the lower threshold level of 1.97 cm were considered within the optimal reference range. CONCLUSION: Step width variability is higher in older adults than in younger adults, with step width variability values above the upper threshold level of 2.50 cm to be considered as excessive. This information could potentially impact rehabilitation technology design for devices targeting lateral stability during walking.

Understanding the Stability of Salt-Inclusion Phases for Nuclear Waste-forms through Volume-based Thermodynamics.

Formation enthalpies and Gibbs energies of actinide and rare-earth containing SIMs with silicate and germanate frameworks are reported. Volume-based thermodynamics (VBT) techniques complemented by density functional theory (DFT) were adapted and applied to these complex structures. VBT and DFT results were in closest agreement for the smaller framework silicate structure, whereas DFT in general predicts less negative enthalpies across all SIMs, regardless of framework type. Both methods predict the rare-earth silicates to be the most stable of the comparable structures calculated, with VBT results being in good agreement with the limited experimental values available from drop solution calorimetry.

Versatile Uranyl Germanate Framework Hosting 12 Different Alkali Halide 1D Salt Inclusions.

Single crystals of 13 new uranyl germanate salt-inclusion materials were grown from alkali halide fluxes: [Cs2Cs5F][(UO2)3(Ge2O7)2] (1), [Cs6Ag2Cl2][(UO2)3(Ge2O7)2] (2), [Cs6Ag0.3Na1.7Cl2][(UO2)3(Ge2O7)2] (3), [Cs6Ag0.4Na1.6Cl2][(UO2)3(Ge2O7)2] (4), [Cs6K2Cl2][(UO2)3(Ge2O7)2] (5), [Cs6K1.9Ag0.1Cl2][(UO2)3(Ge2O7)2] (6), [KK6Cl][(UO2)3(Ge2O7)2] (7), [KK6Br0.6F0.4][(UO2)3(Ge2O7)2] (8), [Na0.9Rb6.1F][(UO2)3(Ge2O7)2] (9), [K0.6Na0.4K5CsCl0.5F0.5][(UO2)3(Ge2O7)2] (10), [K0.8Na0.2K4.8Cs1.2Cl0.5F0.5][(UO2)3(Ge2O7)2] (11), [KK1.8Cs4.2F][(UO2)3(Ge2O7)2] (12), and [Cs6Cs0.71Cl0.71][(UO2)3O3(Ge2O7)] (13). Structures 1-12 contain the same [(UO2)3(Ge2O7)2]6- framework whose pores are filled with varied salt species selected by the choice of the specific alkali halide flux used for crystal growth. The size and identity of the salt species also influence whether the [(UO2)3(Ge2O7)2]6- framework adopts a monoclinic or orthorhombic symmetry. The 13th composition, [Cs6Cs0.71Cl0.71][(UO2)3O3(Ge2O7)] (13), crystallizes in a new structure type in the hexagonal crystal system and contains large channels. Optical characterization was performed on [Cs6K1.9Ag0.1Cl2][(UO2)3(Ge2O7)2] (6) and [KK1.8Cs4.2F][(UO2)3(Ge2O7)2] (12), and both exhibit UV-vis absorption and luminescence typical of the uranyl group. The fluorine-containing composition luminesces 10 times as intensely as does the chlorine-containing composition.

A Family of Layered Phosphates Crystallizing in a Rare Geometrical Isomer of the Phosphuranylite Topology: Synthesis, Characterization, and Computational Modeling of A4[(UO2)3O2(PO4)2] (A = Alkali Metal) Exhibiting Intralayer Ion Exchange.

Single crystals of eight new layered uranyl phosphates were grown from alkali chloride fluxes: Cs1.4K2.6[(UO2)3O2(PO4)2], Cs0.7K3.3[(UO2)3O2(PO4)2], Rb1.4K2.6[(UO2)3O2(PO4)2], K4[(UO2)3O2(PO4)2], K2.9Na0.9Rb0.2[(UO2)3O2(PO4)2], K2.1Na0.7Rb1.2[(UO2)3O2(PO4)2], Cs1.7K4.3[(UO2)5O5(PO4)2], and Rb1.6K4.4[(UO2)5O5(PO4)2]. All structures crystallize in the monoclinic space group, P21/ c and contain uranyl phosphate layers with alkali metals located between the layers for charge balance. Ion exchange experiments on Cs0.7K3.3[(UO2)3O2(PO4)2], Rb1.4K2.6[(UO2)3O2(PO4)2], and K4[(UO2)3O2(PO4)2] demonstrated that Cs and Rb cations cannot be exchanged for K cations; however, K cations can be readily exchanged for Na, Rb, and Cs. Enthalpies of formation were calculated from density functional theory (DFT) and volume-based thermodynamics (VBT) for all six structures. A value for the enthalpy of formation of the phosphuranylite sheet, [(UO2)3O2(PO4)2]4-, was derived using single-ion additive methods coupled with VBT. DFT and VBT calculations were used to justify results of the ion exchange experiments. Cs0.7K3.3[(UO2)3O2(PO4)2], Rb1.4K2.6[(UO2)3O2(PO4)2], and K4[(UO2)3O2(PO4)2] exhibit typical luminescence of the uranyl group.

Observation of an Unusual Uranyl Cation-Cation Interaction in the Strongly Fluorescent Layered Uranyl Phosphates Rb6[(UO2)7O4(PO4)4] and Cs6[(UO2)7O4(PO4)4].

Single crystals of two new uranyl phosphates, A6[(UO2)7O4(PO4)4] (A = Cs, Rb), featuring cation-cation interactions (CCIs) rarely observed in uranium(VI) compounds were synthesized by molten flux methods. This structure crystallizes in the triclinic space group P1̅ with lattice parameters, a = 9.2092(4) Å, b = 9.8405(4) Å, c = 10.1856(5) Å, α = 92.876(2)°, ß = 95.675(2)°, and γ = 93.139(2)° for A = Cs and a = 9.2166(9) Å, b = 9.3771(10) Å, c = 10.1210(11) Å, α = 89.981(4)°, ß = 96.136(4)°, and γ = 92.790(4)° for A = Rb. The optical properties are reported for both compounds and compared to a layered uranyl phosphate, K4[(UO2)3O2(PO4)2], having a similar phosphuranylite-based structure but no CCIs. Partial ion exchange of Cs and Rb cations into the Rb6[(UO2)7O4(PO4)4] and Cs6[(UO2)7O4(PO4)4] structures, respectively, was achieved.

Cocaine and specific cocaine metabolites induce von Willebrand factor release from endothelial cells in a tissue-specific manner.

OBJECTIVE: Cocaine use is associated with arterial thrombosis, including myocardial infarction and stroke. Cocaine use results in increased plasma von Willebrand factor (VWF), accelerated atherosclerosis, and platelet-rich arterial thrombi, suggesting that cocaine activates the endothelium, promoting platelet-VWF interactions. APPROACH AND RESULTS: Human umbilical vein endothelial cells, brain microvasculature endothelial cells, or coronary artery endothelial cells were treated with cocaine or metabolites benzoylecgonine, cocaethylene, norcocaine, or ecgonine methylester. Supernatant VWF concentration and multimer structure were measured, and platelet-VWF strings formed on the endothelial surface under flow were quantified. Cocaine, benzoylecgonine, and cocaethylene induced endothelial VWF release, with the 2 metabolites being more potent than the parent molecule. Brain microvasculature endothelial cells were more sensitive to cocaine and metabolites than were human umbilical vein endothelial cells or coronary artery endothelial cells. Coronary artery endothelial cells released VWF into the supernatant but did not form VWF-platelet strings. Intracellular cAMP concentration was not increased after treatment with cocaine or its metabolites. CONCLUSIONS: Both cocaine and metabolites benzoylecgonine and cocaethylene induced endothelial VWF secretion, possibly explaining thrombotic risk after cocaine ingestion. VWF secretion is likely to vary between vascular beds, with brain endothelial cells being particularly sensitive. These results suggest that clinical management of cocaine-induced ischemia may benefit from therapies aimed at disrupting the VWF-platelet interaction.