Permeation of CO₂ and N₂ through glassy poly(dimethyl phenylene) oxide under steady- and presteady-state conditions

Glassy polymers are often used for gas separations because of their high selectivity. Although the dual‐mode permeation model correctly fits their sorption and permeation isotherms, its physical interpretation is disputed, and it does not describe permeation far from steady state, a condition expected when separations involve intermittent renewable energy sources. To develop a more comprehensive permeation model, we combine experiment, molecular dynamics, and multiscale reaction–diffusion modeling to characterize the time‐dependent permeation of N₂ and CO₂ through a glassy poly(dimethyl phenylene oxide) membrane, a model system. Simulations of experimental time‐dependent permeation data for both gases in the presteady‐state and steady‐state regimes show that both single‐ and dual‐mode reaction–diffusion models reproduce the experimental observations, and that sorbed gas concentrations lag the external pressure rise. The results point to environment‐sensitive diffusion coefficients as a vital characteristic of transport in glassy polymers

Nanocomposites of Tantalum-Based Pyrochlore and Indium Hydroxide Showing High and Stable Photocatalytic Activities for Overall Water Splitting and Carbon Dioxide Reduction

Nanocomposites of tantalum-based pyrochlore nanoparticles and indium hydroxide were prepared by a hydrothermal process for UV-driven photocatalytic reactions including overall water splitting, hydrogen production from photoreforming of methanol, and CO_2 reduction with water to produce CO. The best catalyst was more than 20 times more active than sodium tantalate in overall water splitting and 3 times more active than Degussa P25 TiO_2 in CO_2 reduction. Moreover, the catalyst was very stable while generating stoichiometric products of H_2 (or CO) and O_2 throughout long-term photocatalytic reactions. After the removal of In(OH)_3, the pyrochlore nanoparticles remained highly active for H_2 production from pure water and aqueous methanol solution. Both experimental studies and density functional theory calculations suggest that the pyrochlore nanoparticles catalyzed the water reduction to produce H2, whereas In(OH)_3 was the major active component for water oxidation to produce O_2

Asymmetric Orbifolds and Higher Level Models

I introduce a class of string constructions based on asymmetric orbifolds leading to level two models. In particular, I derive in detail various models with gauge groups $E_6$ and SO(10), including a four generation $E_6$ model with two adjoint representations. The occurrence of multiple adjoint representations is a generic feature of the construction. In the course of describing this approach, I will address the problem of twist phases in higher twisted sectors of asymmetric orbifolds.Comment: 30 pages of LaTe

A de Haas-van Alphen study of the filled skutterudite compounds PrOs4_4As12_{12} and LaOs4_4As12_{12}

Comprehensive magnetic-field-orientation dependent studies of the susceptibility and de Haas-van Alphen effect have been carried out on single crystals of the filled skutterudites PrOs$_4$As$_{12}$ and LaOs$_4$As$_{12}$ using magnetic fields of up to 40~T. Several peaks are observed in the low-field susceptibility of PrOs$_4$As$_{12}$, corresponding to cascades of metamagnetic transitions separating the low-field antiferromagnetic and high-field paramagnetic metal (PMM) phases. The de Haas-van Alphen experiments show that the Fermi-surface topologies of PrOs$_4$As$_{12}$ in its PMM phase and LaOs$_4$As$_{12}$ are very similar. In addition, they are in reasonable agreement with the predictions of bandstructure calculations for LaOs$_4$As$_{12}$ on the PrOs$_4$As$_{12}$ lattice. Both observations suggest that the Pr 4$f$ electrons contribute little to the number of itinerant quasiparticles in the PMM phase. However, whilst the properties of LaOs$_4$As$_{12}$ suggest a conventional nonmagnetic Fermi liquid, the effects of direct exchange and electron correlations are detected in the PMM phase of PrOs$_4$As$_{12}$. For example, the quasiparticle effective masses in PrOs$_4$As$_{12}$ are found to decrease with increasing field, probably reflecting the gradual suppression of magnetic fluctuations associated with proximity to the low-temperature, low-field antiferromagnetic state

Fermi-surface topologies and low-temperature phases of the filled skutterudite compounds CeOs4Sb12 and NdOs4Sb12

MHz conductivity, torque magnetometer and magnetization measurements are reported on single crystals of CeOs4Sb12 and NdOs4Sb12 using temperatures down to 0.5 K and magnetic fields of up to 60 tesla. The field-orientation dependence of the de Haas-van Alphen and Shubnikov-de Haas oscillations is deduced by rotating the samples about the [010] and [0¯11] directions. The results indicate that NdOs4Sb12 has a similar Fermi surface topology to that of the unusual superconductor PrOs4Sb12, but with significantly smaller effective masses, supporting the importance of local phonon modes in contributing to the low-temperature heat capacity of NdOs4Sb12. By contrast, CeOs4Sb12 undergoes a field-induced transition from an unusual semimetal into a high-field, hightemperature state characterized by a single, almost spherical Fermi-surface section. The behavior of the phase boundary and comparisons with models of the bandstructure lead us to propose that the field-induced phase transition in CeOs4Sb12 is similar in origin to the well-known α − γ transition in Ce and its alloys

Mechanism and kinetics for both thermal and electrochemical reduction of N_2 catalysed by Ru(0001) based on quantum mechanics

The conversion of N_(2(g)) to NH_(3(g)) is an important industrial process that plays a vital role in sustaining the current human population. This chemical transformation relies heavily on the Haber–Bosch process (N2 thermal reduction, N_2TR), which requires enormous quantities of energy (2% of the world supply) and extreme conditions (200 atm and 500 °C). Alternatively, N_(2(g)) can be reduced to NH_(3(g)) through electrochemical means (N_2ER), which may be a less energy intensive and lower-capital approach since the H atoms come from H_2O not H_2. However, N_2ER efficiency is far from satisfactory. In order to provide the basis for developing a new generation of energy efficient processes, we report the detailed atomistic mechanism and kinetics for N_2ER on Ru(0001) along with a comparison to N2TR. We obtained these results using a new electrochemical model for quantum mechanics (QM) calculations to obtain free energy surfaces for all plausible reaction pathways for N_2ER under a constant electrode potential of 0.0 V_(SHE). For both processes, the elementary steps involve several steps of breaking of the NN bonds, hydrogenation of surface N_2H_X or NH_X, and NH_3 release. We find similar energetics for the NN cleavage steps for both systems. However, the hydrogenation steps are very different, leading to much lower free energy barriers for N_2ER compared to N_2TR. Thus, N_2ER favors an associative route where successive hydrogen atoms are added to N_2 prior to breaking the NN bonds rather than the dissociative route preferred by N_2TR, where the NN bonds are broken first followed by the addition of Hs. Our QM results provide the detailed free energy surfaces for N_2ER and N_2TR, suggesting a strategy for improving the efficiency of N_2ER

Mechanism and kinetics for both thermal and electrochemical reduction of N_2 catalysed by Ru(0001) based on quantum mechanics

The conversion of N_(2(g)) to NH_(3(g)) is an important industrial process that plays a vital role in sustaining the current human population. This chemical transformation relies heavily on the Haber–Bosch process (N2 thermal reduction, N_2TR), which requires enormous quantities of energy (2% of the world supply) and extreme conditions (200 atm and 500 °C). Alternatively, N_(2(g)) can be reduced to NH_(3(g)) through electrochemical means (N_2ER), which may be a less energy intensive and lower-capital approach since the H atoms come from H_2O not H_2. However, N_2ER efficiency is far from satisfactory. In order to provide the basis for developing a new generation of energy efficient processes, we report the detailed atomistic mechanism and kinetics for N_2ER on Ru(0001) along with a comparison to N2TR. We obtained these results using a new electrochemical model for quantum mechanics (QM) calculations to obtain free energy surfaces for all plausible reaction pathways for N_2ER under a constant electrode potential of 0.0 V_(SHE). For both processes, the elementary steps involve several steps of breaking of the NN bonds, hydrogenation of surface N_2H_X or NH_X, and NH_3 release. We find similar energetics for the NN cleavage steps for both systems. However, the hydrogenation steps are very different, leading to much lower free energy barriers for N_2ER compared to N_2TR. Thus, N_2ER favors an associative route where successive hydrogen atoms are added to N_2 prior to breaking the NN bonds rather than the dissociative route preferred by N_2TR, where the NN bonds are broken first followed by the addition of Hs. Our QM results provide the detailed free energy surfaces for N_2ER and N_2TR, suggesting a strategy for improving the efficiency of N_2ER

Backbone and side-chain 1H, 13C and 15N assignments of the ubiquitin-associated domain of human X-linked inhibitor of apoptosis protein

X-linked inhibitor of apoptosis protein (XIAP), a leading member of the family of inhibitor of apoptosis (IAP) proteins, is considered as the most potent and versatile inhibitor of caspases and apoptosis. It has been reported that XIAP is frequently overexpressed in cancer and its expression level is implicated in contributing to tumorigenesis, disease progression, chemoresistance and poor patient-survival. Therefore, XIAP is one of the leading targets in drug development for cancer therapy. Recently, based on bioinformatics study, a previously unrecognized but evolutionarily conserved ubiquitin-associated (UBA) domain in IAPs was identified. The UBA domain is found to be essential for the oncogenic potential of IAP, to maintain endothelial cell survival and to protect cells from TNF-α-induced apoptosis. Moreover, the UBA domain is required for XIAP to activate NF-κB. In the present study, we report the near complete resonance assignments of the UBA domain-containing region of human XIAP protein. Secondary structure prediction based on chemical shift index (CSI) analysis reveals that the protein is predominately α-helical, which is consistent with the structures of known UBA proteins

Expression of human ficolin-2 in hepatocytes confers resistance to infection by diverse hepatotropic viruses

The liver-expressed pattern recognition receptors (PRRs) mannose binding lectin (MBL), ficolin-2 and ficolin-3 contribute to the innate immune response by activating complement. Binding of soluble ficolin-2 to viral pathogens can directly neutralize virus entry. We observed that the human hepatoma cell line HuH7.5, which is routinely used for the study of hepatotropic viruses, is deficient in expression of MBL, ficolin-2 and ficolin-3. We generated a cell line that expressed and secreted ficolin-2. This cell line (HuH7.5 [FCN2]) was more resistant to infection with hepatitis C virus (HCV), ebolavirus (EBOV) and vesicular stomatitis virus (VSV), but surprisingly was more susceptible to infection with rabies virus (RABV). Cell-to-cell spread of HCV was also inhibited in ficolin-2 expressing cells. This illustrates that ficolin-2 expression in hepatocytes contributes to innate resistance to virus infection, but some viruses might utilise ficolin-2 to facilitate entry