Design Principles Guiding Solvent Size Selection in ZIF-Based Type 3 Porous Liquids for Permanent Porosity.

Porous liquids (PLs), which are solvent-based systems that contain permanent porosity due to the incorporation of a solid porous host, are of significant interest for the capture of greenhouse gases, including CO2. Type 3 PLs formed by using metal-organic frameworks (MOFs) as the nanoporous host provide a high degree of chemical turnability for gas capture. However, pore aperture fluctuation, such as gate-opening in zeolitic imidazole framework (ZIF) MOFs, complicates the ability to keep the MOF pores available for gas adsorption. Therefore, an understanding of the solvent molecular size required to ensure exclusion from MOFs in ZIF-based Type 3 PLs is needed. Through a combined computational and experimental approach, the solvent-pore accessibility of exemplar MOF ZIF-8 was examined. Density functional theory (DFT) calculations identified that the lowest-energy solvent-ZIF interaction occurred at the pore aperture. Experimental density measurements of ZIF-8 dispersed in various-sized solvents showed that ZIF-8 adsorbed solvent molecules up to 2 Å larger than the crystallographic pore aperture. Density analysis of ZIF dispersions was further applied to a series of possible ZIF-based PLs, including ZIF-67, -69, -71(RHO), and -71(SOD), to examine the structure-property relationships governing solvent exclusion, which identified eight new ZIF-based Type 3 PL compositions. Solvent exclusion was driven by pore aperture expansion across all ZIFs, and the degree of expansion, as well as water exclusion, was influenced by ligand functionalization. Using these results, a design principle was formulated to guide the formation of future ZIF-based Type 3 PLs that ensures solvent-free pores and availability for gas adsorption.

Sound power and acoustic efficiency of an installed GE F404 jet engine.

Classical jet noise theory indicates that radiated sound power is proportional to the jet velocity raised to the eighth and third powers for subsonic and supersonic jets, respectively. To connect full-scale measurements with classical jet noise theory, this letter presents sound power and acoustic efficiency values for an installed GE-F404 engine. When subsonic, the change in sound power follows the eighth-power law, and the sound power change approximately follows the third-power law at supersonic conditions, with an acoustic efficiency of ∼0.5-0.6%. However, the OAPWL increase from subsonic to supersonic jet velocities is greater than would be predicted.

Identification and Decomposition of Uranium Oxychloride Phases in Oxygen-Exposed UCl3 Salt Compositions.

Complementary X-ray absorption fine structure (XAFS) spectroscopy and Raman spectroscopy studies were conducted on several UCl3 concentrations in several chloride salt compositions. The samples were 5% UCl3 in LiCl (S1), 5% UCl3 in KCl (S2), 5% UCl3 in LiCl-KCl eutectic (S3), 5% UCl3 in LiCl-KCl eutectic (S4), 50% UCl3 in KCl (S5), and 20% UCl3 in KCl (S6) molar concentrations. Sample S3 had UCl3 sourced from Idaho National Laboratory (INL), and all other samples were UCl3 sourced from TerraPower. The initial compositions were prepared in an inert and oxygen-free atmosphere. XAFS measurements were performed in the atmosphere at a beamline, and Raman spectroscopy was conducted inside a glovebox. Raman spectra were able to confirm initial UCl3. XAFS and later Raman spectra measured, however, did not correctly match the literature and computational spectra for the prepared UCl3 salt. Rather, the data shows some complex uranium oxychloride phases at room temperature that transition into uranium oxides upon heating. Oxygen pollution due to failure of the sealing mechanism can result in oxidation of the UCl3 salts. The oxychlorides present may be both a function of the unknown O2 exposure concentration, depending on the source of the leak and the salt composition. Evidence of this oxychloride claim and its subsequent decomposition is justified in this work.

Experimental and Computational Mechanisms that Govern Long-Term Stability of CO2-Adsorbed ZIF-8-Based Porous Liquids.

Porous liquids (PLs) based on the zeolitic imidazole framework ZIF-8 are attractive systems for carbon capture since the hydrophobic ZIF framework can be solvated in aqueous solvent systems without porous host degradation. However, solid ZIF-8 is known to degrade when exposed to CO2 in wet environments, and therefore the long-term stability of ZIF-8-based PLs is unknown. Through aging experiments, the long-term stability of a ZIF-8 PL formed using the water, ethylene glycol, and 2-methylimidazole solvent system was systematically examined, and the mechanisms of degradation were elucidated. The PL was found to be stable for several weeks, with no ZIF framework degradation observed after aging in N2 or air. However, for PLs aged in a CO2 atmosphere, formation of a secondary phase occurred within 1 day from the degradation of the ZIF-8 framework. From the computational and structural evaluation of the effects of CO2 on the PL solvent mixture, it was identified that the basic environment of the PL caused ethylene glycol to react with CO2 forming carbonate species. These carbonate species further react within the PL to degrade ZIF-8. The mechanisms governing this process involves a multistep pathway for PL degradation and lays out a long-term evaluation strategy of PLs for carbon capture. Additionally, it clearly demonstrates the need to examine the reactivity and aging properties of all components in these complex PL systems in order to fully assess their stabilities and lifetimes.

Can a Computer-based Force Feedback Hip Fracture Skills Simulator Improve Clinical Task Performance? A Cadaveric Validation Study.

BACKGROUND: This cadaveric study seeks to determine whether skills acquired on the simulator translate to improved performance of the clinical task. We hypothesized that completion of simulator training modules would improve performance of percutaneous hip pinning. METHODS: Eighteen right-handed medical students from two academic institutions were randomized: trained (n = 9) and untrained (n = 9). The trained group completed nine simulator-based modules of increasing difficulty, designed to teach techniques of placing wires in an inverted triangle construct in a valgus-impacted femoral neck fracture. The untrained group had a brief simulator introduction but did not complete the modules. Both groups received a hip fracture lecture, an explanation and pictorial reference of an inverted triangle construct, and instruction on using the wire driver. Participants then placed three 3.2 mm guidewires in cadaveric hips in an inverted triangle construct under fluoroscopy. Wire placement was evaluated with CT at 0.5 mm sections. RESULTS: The trained group significantly outperformed the untrained group in most parameters (P ≤ 0.05). CONCLUSIONS: The results suggest that a force feedback simulation platform with simulated fluoroscopic imaging using an established, increasingly difficult series of motor skills training modules has potential to improve clinical performance and might offer an important adjunct to traditional orthopaedic training.

Effect of Linker Structure and Functionalization on Secondary Gas Formation in Metal-Organic Frameworks.

Rare-earth terephthalic acid (BDC)-based metal-organic frameworks (MOFs) are promising candidate materials for acid gas separation and adsorption from flue gas streams. However, previous simulations have shown that acid gases (H2O, NO2, and SO2) react with the hydroxyl on the BDC linkers to form protonated acid gases as a potential degradation mechanism. Herein, gas-phase computational approaches were used to identify the formation energies of these secondary protonated acid gases across multiple BDC linker molecules. Formation energies for secondary protonated acid gases were evaluated using both density functional theory (DFT) and correlated wave function methods for varying BDC-gas reaction mechanisms. Upon validation of DFT to reproduce wave function calculation results, rotated conformational linkers and chemically functionalized BDC linkers with -OH, -NH2, and -SH were investigated. The calculations show that the rotational conformation affects the molecule stability. Double-functionalized BDC linkers, where two functional groups are substituted onto BDC, showed varied reaction energies depending on whether the functional groups donate or withdraw electrons from the aromatic system. Based on these results, BDC linker design must balance adsorption performance with degradation via linker dehydrogenation for the design of stable MOFs for acid gas separations.

Dramatic Enhancement of Rare-Earth Metal-Organic Framework Stability Via Metal Cluster Fluorination.

Rare-earth polynuclear metal-organic frameworks (RE-MOFs) have demonstrated high durability for caustic acid gas adsorption and separation based on gas adsorption to the metal clusters. The metal clusters in the RE-MOFs traditionally contain RE metals bound by µ3-OH groups connected via organic linkers. Recent studies have suggested that these hydroxyl groups could be replaced by fluorine atoms during synthesis that includes a fluorine-containing modulator. Here, a combined modeling and experimental study was undertaken to elucidate the role of metal cluster fluorination on the thermodynamic stability, structure, and gas adsorption properties of RE-MOFs. Through systematic density-functional theory calculations, fluorinated clusters were found to be thermodynamically more stable than hydroxylated clusters by up to 8-16 kJ/mol per atom for 100% fluorination. The extent of fluorination in the metal clusters was validated through a 19F NMR characterization of 2,5-dihydroxyterepthalic acid (Y-DOBDC) MOF synthesized with a fluorine-containing modulator. 19F magic-angle spinning NMR identified two primary peaks in the isotropic chemical shift (δiso) spectra located at -64.2 and -69.6 ppm, matching calculated 19F NMR δiso peaks at -63.0 and -70.0 ppm for fluorinated systems. Calculations also indicate that fluorination of the Y-DOBDC MOF had negligible effects on the acid gas (SO2, NO2, H2O) binding energies, which decreased by only ∼4 kJ/mol for the 100% fluorinated structure relative to the hydroxylated structure. Additionally, fluorination did not change the relative gas binding strengths (SO2 > H2O > NO2). Therefore, for the first time the presence of fluorine in the metal clusters was found to significantly stabilize RE-MOFs without changing their acid-gas adsorption properties.

Discovery of Complex Binding and Reaction Mechanisms from Ternary Gases in Rare Earth Metal-Organic Frameworks.

Understanding the selectivity of metal-organic frameworks (MOFs) to complex acid gas streams will enable their use in industrial applications. Herein, ab initio molecular dynamic simulations (AIMD) were used to simulate ternary gas mixtures (H2 O-NO2 -SO2 ) in rare earth 2,5-dihydroxyterephthalic acid (RE-DOBDC) MOFs. Stronger H2 O gas-metal binding arose from thermal vibrations in the MOF sterically hindering access of SO2 and NO2 molecules to the metal sites. Gas-gas and gas-linker interactions within the MOF framework resulted in the formation of multiple secondary gas species including HONO, HNO2 , NOSO, and HNO3 - . Four gas adsorption sites were identified along with a new de-protonation reaction mechanism not observable through experiment. This study not only provides valuable information on competitive gas binding energies in the MOF, it also provides important chemical insights into transient chemical reactions and mechanisms.

In Situ Determination of Speciation and Local Structure of NaCl-SrCl2 and LiF-ZrF4 Molten Salts.

Understanding the local environment of the metal atoms in salt melts is important for modeling the properties of melts and predicting their behavior and thus helping enable the development of technologies such as molten salt reactors and solar-thermal power systems and new approaches to recycling rare-earth metals. Toward that end, we have developed an in situ approach for measuring the coordination of metals in molten salt coupling X-ray absorption spectroscopy (XAS) and Raman spectroscopy. Our approach was demonstrated for two salt mixtures (1.9 and 5 mol % SrCl2 in NaCl, 0.8 and 5 mol % ZrF4 in LiF) at up to 1100 °C. Near-edge (X-ray absorption near-edge structure, XANES) and extended X-ray absorption fine structure (EXAFS) spectra were measured. The EXAFS response was modeled using ab initio FEFF calculations. Strontium's first shell is observed to be coordinated with chlorine (Sr2+-Cl-) and zirconium's first shell is coordinated by fluorine (Zr4+-F-), both having coordination numbers that decrease with increasing temperature. Multiple zirconium complexes are believed to be present in the melt, which may interfere and distort the EXAFS spectra and result in an anomalously low zirconium first shell coordination number. The use of boron nitride (BN) powder as a salt diluent for XAFS measurements was found to not interfere with measurements and thus can be used for investigations of such systems.

Investigation of Metastable Low Dimensional Halometallates.

The solvothermal synthesis, structure determination and optical characterization of five new metastable halometallate compounds, [1,10-phenH][Pb3.5I8] (1), [1,10-phenH2][Pb5I12]·(H2O) (2), [1,10-phen][Pb2I4] (3), [1,10-phen]2[Pb5Br10] (4) and [1,10-phenH][SbI4]·(H2O) (5), are reported. The materials exhibit rich structural diversity and exhibit structural dimensionalities that include 1D chains, 2D sheets and 3D frameworks. The optical spectra of these materials are consistent with bandgaps ranging from 2.70 to 3.44 eV. We show that the optical behavior depends on the structural dimensionality of the reported materials, which are potential candidates for semiconductor applications.

Correlational Approach to Predict the Enthalpy of Mixing for Chloride Melt Systems.

A methodology to estimate the heat of mixing (Δmix H) for salt liquids in unexplored AkCl-AnCl x /LnCl x (Ak = alkali, An = actinide, Ln = lanthanide) systems is developed. It improves upon previous empirical approaches by eliminating the need for arbitrarily choosing the required composition at maximum short-range ordering, the minimum Δmix H prior to performing the estimation, which avoids the intrinsic ambiguity of that approach. This semiempirical method has computationally reproduced the behavior of NaCl-UCl3 and KCl-UCl3 systems, providing Δmix H values that agree well with the reported measurements within a propagated two standard deviations (2σ). The capability of the approach is demonstrated in its application to the entirety of the AkCl-UCl3 and AkCl-PuCl3 systems, the results from which have facilitated the accurate thermodynamic modeling of these and other AkCl-AnCl3/LnCl3 systems. The resultant assessed Gibbs energy functions and models have been incorporated in the Molten Salt Thermal Properties Database-Thermochemical (MSTDB-TC).

The Hallux Metatarsophalangeal Capsule: An Anatomic Study With Respect to Percutaneous Hallux Valgus Correction.

BACKGROUND: Minimally invasive surgery for the treatment of hallux valgus deformities has become increasingly popular. Knowledge of the location of the hallux metatarsophalangeal (MTP) proximal capsular origin on the metatarsal neck is essential for surgeons in planning and executing extracapsular corrective osteotomies. A cadaveric study was undertaken to further study this anatomic relationship. METHODS: Ten nonpaired fresh-frozen frozen cadaveric specimens were used for this study. Careful dissection was performed, and the capsular origin of the hallux MTP joint was measured from the central portion of the metatarsal head in the medial, lateral, dorsal, plantarmedial, and plantarlateral dimensions. RESULTS: The ten specimens had a mean age of 77 years, with 5 female and 5 male. The mean distances from the central hallux metatarsal head to the MTP capsular origin were 15.2 mm dorsally, 8.4 mm medially, 9.6 mm laterally, 19.3 mm plantarmedially, and 21.0 mm plantarlaterally. CONCLUSION: The MTP capsular origin at the hallux metatarsal varies at different anatomic positions. Knowledge of this capsular anatomy is critical for orthopaedic surgeons when planning and performing minimally invasive distal metatarsal osteotomies for the correction of hallux valgus. TYPE OF STUDY: Cadaveric Study.

Current surgical practice for septic arthritis of the knee in the United States.

For septic arthritis of the knee, we attempted to determine: the preferred surgical technique in the United-States (US), the believed "gold-standard" treatment among others. This was performed by an electronic-survey distributed to all academic orthopaedic faculty throughout the US. The preferred method was arthroscopy (69.8%). Arthroscopy is believed to be the gold-standard in 27.0%, arthrotomy in 29.4%, while 43.5% believe no gold-standard exists. In conclusion the majority of surgeons prefer arthroscopy when managing a native, septic knee in an adult patient. However, there is no national consensus on a gold-standard treatment or the role of synovectomy.

Interplay between London Dispersion, Hubbard U, and Metastable States for Uranium Compounds.

High-throughput computational studies of lanthanide and actinide chemistry with density-functional theory are complicated by the need for Hubbard U corrections, which ensure localization of the f-electrons, but can lead to metastable states. This work presents a systematic investigation of the effects of both Hubbard U value and metastable states on the predicted structural and thermodynamic properties of four uranium compounds central to the field of nuclear fuels: UC, UN, UO2, and UCl3. We also assess the impact of the exchange-hole dipole moment (XDM) dispersion correction on the computed properties. Overall, the choice of Hubbard U value and inclusion of a dispersion correction cause larger variations in the computed geometric properties than result from metastable states. The weak dependence of structure optimization on metastable states should simplify future high-throughput calculations on actinides. Conversely, addition of the dispersion correction is found to offset the repulsion introduced by the Hubbard U term and provides greatly improved agreement with experiment for both cell volumes and heats of formation. The XDM dispersion correction is largely invariant to the chosen U value, making it a robust dispersion correction for actinide systems.

Flux Growth of Uranyl Titanates: Rare Examples of TiO4 Tetrahedra and TiO5 Square Bipyramids.

Single crystals of four new uranyl titanates have been grown via the flux growth method using mixed alkali halide fluxes. Na2(UO2)(TiO)O3 and KNa(UO2)(TiO)O3 have analogous layered structures containing titanyl (TiO2+) units coordinated into TiO5 square pyramids. Cs2(UO2)TiO4 crystallizes in the Cs2USiO6 structure type and is a rare example of a structure containing TiO4 tetrahedra. Cs2(UO2)Ti2O6 crystallizes in a new tunnel structure and contains the also rare TiO5 trigonal bipyramids. DFT studies were performed to understand the bonding in the observed titanate polyhedra. Furthermore, the luminescence properties of the compounds are reported, and leaching studies are reported for Cs2(UO2)Ti2O6.

Targeting complex plutonium oxides by combining crystal chemical reasoning with density-functional theory calculations: the quaternary plutonium oxide Cs2PuSi6O15.

The stability of the novel Pu(iv) silicate, Cs2PuSi6O15, was predicted from a combination of crystal chemical reasoning and DFT calculations and confirmed by its synthesis via flux crystal growth. Formation enthalpies of the A2MSi6O15 (A = Na-Cs; M = Ce, Th, U-Pu) compositional family were calculated and indicated the Cs-containing phases should preferentially form in the Cmc21 structure type, consistent with previous experimental findings and the novel phases produced in this work, Cs2PuSi6O15 and Cs2CeSi6O15. The formation enthalpies of a second set of compositions, A2MSi3O9, were also calculated and a comparison between the two compositional families correctly predicted A2MSi6O15 to be on average more stable than A2MSi3O9.

Effect of Training Modules on Hip Fracture Surgical Skills Simulation Performance: Early Validation of the AAOS/OTA Simulator.

BACKGROUND: A preliminary validation study on a computer-based force-feedback simulation platform demonstrated the ability of the simulator to distinguish between novice and experienced users during a simulated hip-pinning procedure. The purpose of the present study was to further investigate whether the simulator and associated training modules are effective for improving user performance during simulated percutaneous hip-pinning procedures. METHODS: With institutional review board approval, 24 medical students at our institution were randomized to "Trained" and "Untrained" groups. After a basic introduction, the Untrained group placed 3 guidewires in a valgus-impacted femoral neck fracture with use of the simulator. The Trained group completed 9 simulator-based training modules before performing the same task. Measured outcomes included an overall performance score and the distance from the pin to various ideals on the femoral neck, femoral head articular surface, and lateral cortex. Performance parameters were compared between groups with the Mann-Whitney U test. RESULTS: The Trained group achieved a significantly higher overall score (median, 29) compared with the Untrained group (median, 6) (p < 0.01), outperformed the Untrained group in 4 specific performance metrics, and trended toward improvement over the Untrained group in 4 pin placement measures (p < 0.2). CONCLUSIONS: Completion of novel training modules for percutaneous hip pinning on this fluoroscopic surgery simulator improves skill performance on simulator-based objective measurements and a simulated orthopaedic procedure compared with non-simulator-trained surgically inexperienced users. Improvement in the overall score and on 4 of 13 specific performance parameters implies that the training modules more effectively teach only certain motor and 3-dimensional spatial skills. CLINICAL RELEVANCE: A valid platform such as the one described here has the potential to improve surgical education in orthopaedic trauma.

A Web-Based Atlas Combining MRI and Histology of the Squirrel Monkey Brain.

The squirrel monkey (Saimiri sciureus) is a commonly-used surrogate for humans in biomedical research. In the neuroimaging community, MRI and histological atlases serve as valuable resources for anatomical, physiological, and functional studies of the brain; however, no digital MRI/histology atlas is currently available for the squirrel monkey. This paper describes the construction of a web-based multi-modal atlas of the squirrel monkey brain. The MRI-derived information includes anatomical MRI contrast (i.e., T2-weighted and proton-density-weighted) and diffusion MRI metrics (i.e., fractional anisotropy and mean diffusivity) from data acquired both in vivo and ex vivo on a 9.4 Tesla scanner. The histological images include Nissl and myelin stains, co-registered to the corresponding MRI, allowing identification of cyto- and myelo-architecture. In addition, a bidirectional neuronal tracer, biotinylated dextran amine (BDA) was injected into the primary motor cortex, enabling highly specific identification of regions connected to the injection location. The atlas integrates the results of common image analysis methods including diffusion tensor imaging glyphs, labels of 57 white-matter tracts identified using DTI-tractography, and 18 cortical regions of interest identified from Nissl-revealed cyto-architecture. All data are presented in a common space, and all image types are accessible through a web-based atlas viewer, which allows visualization and interaction of user-selectable contrasts and varying resolutions. By providing an easy to use reference system of anatomical information, our web-accessible multi-contrast atlas forms a rich and convenient resource for comparisons of brain findings across subjects or modalities. The atlas is called the Combined Histology-MRI Integrated Atlas of the Squirrel Monkey (CHIASM). All images are accessible through our web-based viewer ( https://chiasm.vuse.vanderbilt.edu /), and data are available for download at ( https://www.nitrc.org/projects/smatlas/ ).

Construct Validation of a Novel Hip Fracture Fixation Surgical Simulator.

INTRODUCTION: A surgical simulation platform has been developed to simulate fluoroscopically guided surgical procedures by coupling computer modeling with a force-feedback device as a training tool for orthopaedic resident education in an effort to enhance motor skills and potentially minimize radiation exposure. The objective of this study was to determine whether the simulation platform can distinguish between novice and experienced practitioners of percutaneous pinning of hip fractures. METHODS: Medical students, orthopaedic residents, orthopaedic trauma fellows, and attending surgeons completed in situ hip-pinning simulation that recorded performance measures related to surgical accuracy, time, and use of fluoroscopy. Linear regression models were used to compare the association between performance and practitioner experience. RESULTS: Notable associations were shown between performance and practitioner experience in 10 of the 15 overall measures (P < 0.05) and 9 of 11 surgical accuracy parameters (P < 0.05). CONCLUSION: This novel simulation platform can distinguish between novice and experienced practitioners and defines a performance curve for completion of simulated in situ hip pinning. This important first step lays the groundwork for subsequent validation studies, which will seek to demonstrate the efficacy of this simulator in improving clinical performance by trainees completing a sequence of skills-training modules.