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

Viral and host proteins involved in picornavirus life cycle

Picornaviruses cause several diseases, not only in humans but also in various animal hosts. For instance, human enteroviruses can cause hand-foot-and-mouth disease, herpangina, myocarditis, acute flaccid paralysis, acute hemorrhagic conjunctivitis, severe neurological complications, including brainstem encephalitis, meningitis and poliomyelitis, and even death. The interaction between the virus and the host is important for viral replication, virulence and pathogenicity. This article reviews studies of the functions of viral and host factors that are involved in the life cycle of picornavirus. The interactions of viral capsid proteins with host cell receptors is discussed first, and the mechanisms by which the viral and host cell factors are involved in viral replication, viral translation and the switch from translation to RNA replication are then addressed. Understanding how cellular proteins interact with viral RNA or viral proteins, as well as the roles of each in viral infection, will provide insights for the design of novel antiviral agents based on these interactions

Increasing utilization of Internet-based resources following efforts to promote evidence-based medicine: a national study in Taiwan

BACKGROUND: Since the beginning of 2007, the National Health Research Institutes has been promoting the dissemination of evidence-based medicine (EBM). The current study examined longitudinal trends of behaviors in how hospital-based physicians and nurses have searched for medical information during the spread of EBM. METHODS: Cross-sectional postal questionnaire surveys were conducted in nationally representative regional hospitals of Taiwan thrice in 2007, 2009, and 2011. Demographic data were gathered concerning gender, age, working experience, teaching appointment, academic degree, and administrative position. Linear and logistic regression models were used to examine predictors and changes over time. RESULTS: Data from physicians and nurses were collected in 2007 (n = 1156), 2009 (n = 2975), and 2011 (n = 3999). There were significant increases in the use of four Internet-based resources – Web portals, online databases, electronic journals, and electronic books – across the three survey years among physicians and nurses (p < 0.001). Access to textbooks and printed journals, however, did not change over the 4-year study period. In addition, there were significant relationships between the usage of Internet-based resources and users’ characteristics. Age and faculty position were important predictors in relation to the usage among physicians and nurses, while academic degree served as a critical factor among nurses only. CONCLUSIONS: Physicians and nurses used a variety of sources to look for medical information. There was a steady increase in use of Internet-based resources during the diffusion period of EBM. The findings highlight the importance of the Internet as a prominent source of medical information for main healthcare professionals

Effects of Electrolyte Buffer Capacity on Surface Reactant Species and Reaction Rate of CO_2 in Electrochemical CO_2 Reduction

In the aqueous electrochemical reduction of CO_2, the choice of electrolyte is responsible for the catalytic activity and selectivity, although there remains a need for more in-depth understanding of electrolyte effects and mechanisms. In this study, using both experimental and simulation approaches, we report how the buffer capacity of the electrolytes affects the kinetics and equilibrium of surface reactant species and resulting reaction rate of CO_2 with varying partial CO_2 pressure. Electrolytes investigated include KCl (non-buffered), KHCO3 (buffered by bicarbonate), and phosphate buffered electrolytes. Assuming 100% methane production, the simulation successfully explains the experimental trends of maximum CO_2 flux in KCl and KHCO_3, and also highlights the difference between KHCO_3 and phosphate in terms of pKa as well as the impact of buffer capacity. To examine the electrolyte impact on selectivity, the model is run with a constant total current density. Using this model, several factors are elucidated including the importance of local pH, which is not in acid/base equilibrium, the impact of buffer identity and kinetics, and the mass-transport boundary-layer thickness. The gained understanding can help optimize CO_2 reduction in aqueous environments

Effects of Electrolyte Buffer Capacity on Surface Reactant Species and Reaction Rate of CO_2 in Electrochemical CO_2 Reduction

In the aqueous electrochemical reduction of CO_2, the choice of electrolyte is responsible for the catalytic activity and selectivity, although there remains a need for more in-depth understanding of electrolyte effects and mechanisms. In this study, using both experimental and simulation approaches, we report how the buffer capacity of the electrolytes affects the kinetics and equilibrium of surface reactant species and resulting reaction rate of CO_2 with varying partial CO_2 pressure. Electrolytes investigated include KCl (non-buffered), KHCO3 (buffered by bicarbonate), and phosphate buffered electrolytes. Assuming 100% methane production, the simulation successfully explains the experimental trends of maximum CO_2 flux in KCl and KHCO_3, and also highlights the difference between KHCO_3 and phosphate in terms of pKa as well as the impact of buffer capacity. To examine the electrolyte impact on selectivity, the model is run with a constant total current density. Using this model, several factors are elucidated including the importance of local pH, which is not in acid/base equilibrium, the impact of buffer identity and kinetics, and the mass-transport boundary-layer thickness. The gained understanding can help optimize CO_2 reduction in aqueous environments

Modeling Vapor-fed Electrolyzers for CO2 Reduction

The electrochemical reduction of CO2 (CO2R) to value-added products is an attractive route for tackling the rising atmospheric CO2 levels and storing intermittent renewable energy. Fundamental understanding of CO2R has progressed significantly in recent years and is critical in the development of industrial-scale CO2 electrolyzers. However, most of our understanding has been drawn from experiments optimized for aqueous-phase CO2R systems. These systems are limited by mass transfer at low current densities (in the order of 10 mA/cm2) due to unfavorable CO2 solubility and transport in aqueous media, whereas technoeconomic analysis emphasizes the need to operate CO2R at current densities above 100 mA/cm2 for industrial viability. To achieve commercially-relevant CO2R rates, gas-diffusion electrodes (GDEs) play a critical role as they can decrease the diffusion length of CO2 from 100 µm seen in aqueous systems to as small as 10 nm, and increase the local concentration of CO2. These architectures enable current densities that are almost two orders of magnitude greater than what is achievable with planar electrodes in an aqueous electrolyte at the same applied cathode overpotential. The thin diffusion layer in GDEs allows access to higher CO2R current densities, as well as environments with higher OH concentrations. The addition of porous cathode layers, however, introduces several parameters that require tuning in order to optimize GDE cell performance. Because the structure of GDEs is complex and CO2R in such systems involves the simultaneous occurrence of many physical processes, it is very hard, if not impossible, to assess the impact of a particular change in the composition and structure of the GDE without a detailed model that accounts for the convoluted chemistry and physics interrelationships. An overview of such model is presented in Chapter 2, and the complex interplays are probed through the model in Chapter 3 and used to shed light on the optimization of GDEs. With the order-of-magnitude increase in current density obtained by GDEs, conventional cell designs for planar electrodes become severely limited by the ohmic drop across the cell, making membrane-electrode assemblies (MEAs) an attractive alternative. MEAs have smaller cell resistances as they do not have aqueous electrolyte compartments and can greatly reduce the distance between the two electrodes. These MEA designs are investigated through a complete electrochemical cell model in Chapter 4 and Chapter 5; cell design considerations such as the distribution of the applied voltage, water management, and CO2 utilization efficiencies are explored. Chapter 4 uses silver-based MEAs (Ag-MEAs) as a model system and studies the performance and limitations of two MEA designs: one with gaseous feeds at both the anode and cathode, and the other with an aqueous anode feed (KHCO¬3 or KOH exchange solution, or liquid H2O) and a gaseous cathode feed. Copper-based MEAs (Cu-MEAs) are examined in Chapter 5. Copper has been shown to be the most effective CO2R catalyst to yield high selectivity towards hydrocarbons and alcohols; Cu-MEAs hold promise for increasing the energy efficiency for electrochemical reduction of CO2 to C2+ products while maintaining high current densities. However, fundamental understanding of Cu-MEAs is still limited compared to the wealth of knowledge available for aqueous electrolyte Cu systems. Sensitivity analysis shows that catalyst layer properties can be optimized to increase the energy efficiencies of C2+ products. Issues associated with water management and tradeoffs associated with elevated operating temperatures are also discussed to guide the optimization of Cu-MEAs. Finally, Chapter 6 summarizes the finding in relation to the field and proposes future directions to progress the development of practical CO2 electrolyzers. Overall, this dissertation demonstrates how physics-based modeling can assist in the transfer of knowledge from aqueous to vapor-fed systems by deconvoluting the impacts of the multiple physical processes occurring in the device