From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca-Au-Al: In Situ Variable-Temperature Transformation.

The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu4.39Al1.61 to its cubic 2/1 crystalline approximant (CA) Ca13Au56.31(3)Al21.69 (CaAu4.33(1)Al1.67, Pa3̅ (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at ∼570 °C and complete by ∼650 °C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au59.86(2)Al17.14□3.00] and an icosahedral shell of only Al [Al10.5□1.5]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au-Al nearest neighbor contacts over homoatomic Al-Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. According to electronic structure calculations, a cubic 1/1 CA, "Ca24Au88Al64" (CaAu3.67Al2.67) is proposed.

Outcomes of Patients with a Mechanical Heart Valve and Poor Anticoagulation Control on Warfarin.

BACKGROUND: Patients with a mechanical heart valve (MHV) require oral anticoagulation. Poor anticoagulation control is thought to be associated with adverse outcomes, but data are limited. OBJECTIVE: To assess the risks of clinical outcomes in patients with a MHV and poor anticoagulation control on warfarin. METHODS: We conducted a retrospective study of consecutive patients undergoing MHV implantation at a tertiary care center (2010-2019). Primary outcome was a composite of ischemic stroke, systemic embolism, or prosthetic valve thrombosis. Major bleeding and death were key secondary outcomes. We constructed multivariable regression models to assess the association between time in therapeutic range (TTR) on warfarin beyond 90 days after surgery with outcomes. RESULTS: We included 671 patients with a MHV (80.6% in aortic, 14.6% in mitral position; mean age 61 years, 30.3% female). Median follow-up was 4.9 years, mean TTR was 62.5% (14.5% TTR <40%, 24.6% TTR 40-60%, and 61.0% TTR >60%). Overall rates of the primary outcome, major bleeding, and death were 0.73, 1.41, and 1.44 per 100 patient-years. Corresponding rates for patients with TTR <40% were 1.31, 2.77, and 3.22 per 100 patient-years. In adjusted analyses, every 10% decrement in TTR was associated with a 31% increase in hazard for the primary outcome (hazard ratio [HR]: 1.31, 95% confidence interval [CI]: 1.13-1.52), 34% increase in major bleeding (HR: 1.34, 95% CI: 1.17-1.52), and 32% increase in death (HR: 1.32, 95% CI: 1.11-1.57). CONCLUSION: In contemporary patients with a MHV, poor anticoagulation control on warfarin was associated with increased risks of thrombotic events, bleeding, and death.

Characterization and 2D self-assembly of CdSe quantum dots at the air-water interface.

Langmuir film properties, UV-vis spectroscopy, epifluorescence microscopy, and transmission electron microscopy were used to study CdSe quantum dots (QDs) in 2D. By combining these results, it was possible to determine the molar absorptivity, limiting nanoparticle area, luminescence property, and arrangement of the QDs in the monolayer films at the air-water interface. Either trioctylphosphine oxide (TOPO) or 1-octadecanethiol (ODT) stabilized the QDs. The data collected reveal that TOPO forms close-packed monolayers on the surface of the QDs and that ODT-stabilized QDs undergo alkyl chains interdigitation. It was also found that varying the nanoparticle size, nature of surfactant, surface pressure, and mixed monolayers could help engineer the 2D self-assembly of the QDs at the air-water interface. Of practical importance is the transfer of these monolayer films onto hydrophilic or hydrophobic solid substrates, which could be successfully accomplished via the Langmuir-Blodgett film deposition technique.