Bubble nucleation in polymer–CO_2 mixtures

We combine density-functional theory with the string method to calculate the minimum free energy path of bubble nucleation in two polymer–CO_2 mixture systems, poly(methyl methacrylate) (PMMA)–CO_2 and polystyrene (PS)–CO_2. Nucleation is initiated by saturating the polymer liquid with high pressure CO_2 and subsequently reducing the pressure to ambient condition. Below a critical temperature (Tc), we find that there is a discontinuous drop in the nucleation barrier as a function of increased initial CO_2 pressure (P0), as a result of an underlying metastable transition from a CO_2-rich-vapor phase to a CO_2-rich-liquid phase. The nucleation barrier is generally higher for PS–CO_2 than for PMMA–CO_2 under the same temperature and pressure conditions, and both higher temperature and higher initial pressure are required to lower the nucleation barrier for PS–CO2 to experimentally relevant ranges. Classical nucleation theory completely fails to capture the structural features of the bubble nucleus and severely underestimates the nucleation barrier

Accurate PpT Data for Methane from (300 to 450) K up to 180 MPa

This paper reports PFT data measured with a high-pressure, single-sinker, magnetic-suspension densimeter (MSD) from (300 to 450) K up to 180 MPa. Our MSD technique yields accurate data, with less than 0.05 % relative uncertainty, over the pressure range of (10 to 200) MPa. The experimental data compare well to the Setzmann and Wagner equation of state as implemented in RefProp 8.0. These methane density data are consistent with the low range of pressure predicted by RefProp 8.0 that has a relative uncertainty of 0.03 % up to 12 MPa and 0.07 % up to 50 MPa. The density predictions of this model agree well with previous data at higher pressures. The equation predicts data with almost the same uncertainty as the experimental data up to 180 MPa. These PFT data also allow reliable determination of both second and third virial coefficients

Global, regional, and national levels and causes of maternal mortality during 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013

The fifth Millennium Development Goal (MDG 5) established the goal of a 75% reduction in the maternal mortality ratio (MMR; number of maternal deaths per 100 000 livebirths) between 1990 and 2015. We aimed to measure levels and track trends in maternal mortality, the key causes contributing to maternal death, and timing of maternal death with respect to delivery

Global, regional, and national incidence and mortality for HIV, tuberculosis, and malaria during 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013

BACKGROUND: The Millennium Declaration in 2000 brought special global attention to HIV, tuberculosis, and malaria through the formulation of Millennium Development Goal (MDG) 6. The Global Burden of Disease 2013 study provides a consistent and comprehensive approach to disease estimation for between 1990 and 2013, and an opportunity to assess whether accelerated progress has occured since the Millennium Declaration. METHODS: To estimate incidence and mortality for HIV, we used the UNAIDS Spectrum model appropriately modified based on a systematic review of available studies of mortality with and without antiretroviral therapy (ART). For concentrated epidemics, we calibrated Spectrum models to fit vital registration data corrected for misclassification of HIV deaths. In generalised epidemics, we minimised a loss function to select epidemic curves most consistent with prevalence data and demographic data for all-cause mortality. We analysed counterfactual scenarios for HIV to assess years of life saved through prevention of mother-to-child transmission (PMTCT) and ART. For tuberculosis, we analysed vital registration and verbal autopsy data to estimate mortality using cause of death ensemble modelling. We analysed data for corrected case-notifications, expert opinions on the case-detection rate, prevalence surveys, and estimated cause-specific mortality using Bayesian meta-regression to generate consistent trends in all parameters. We analysed malaria mortality and incidence using an updated cause of death database, a systematic analysis of verbal autopsy validation studies for malaria, and recent studies (2010-13) of incidence, drug resistance, and coverage of insecticide-treated bednets. FINDINGS: Globally in 2013, there were 1·8 million new HIV infections (95% uncertainty interval 1·7 million to 2·1 million), 29·2 million prevalent HIV cases (28·1 to 31·7), and 1·3 million HIV deaths (1·3 to 1·5). At the peak of the epidemic in 2005, HIV caused 1·7 million deaths (1·6 million to 1·9 million). Concentrated epidemics in Latin America and eastern Europe are substantially smaller than previously estimated. Through interventions including PMTCT and ART, 19·1 million life-years (16·6 million to 21·5 million) have been saved, 70·3% (65·4 to 76·1) in developing countries. From 2000 to 2011, the ratio of development assistance for health for HIV to years of life saved through intervention was US$4498 in developing countries. Including in HIV-positive individuals, all-form tuberculosis incidence was 7·5 million (7·4 million to 7·7 million), prevalence was 11·9 million (11·6 million to 12·2 million), and number of deaths was 1·4 million (1·3 million to 1·5 million) in 2013. In the same year and in only individuals who were HIV-negative, all-form tuberculosis incidence was 7·1 million (6·9 million to 7·3 million), prevalence was 11·2 million (10·8 million to 11·6 million), and number of deaths was 1·3 million (1·2 million to 1·4 million). Annualised rates of change (ARC) for incidence, prevalence, and death became negative after 2000. Tuberculosis in HIV-negative individuals disproportionately occurs in men and boys (versus women and girls); 64·0% of cases (63·6 to 64·3) and 64·7% of deaths (60·8 to 70·3). Globally, malaria cases and deaths grew rapidly from 1990 reaching a peak of 232 million cases (143 million to 387 million) in 2003 and 1·2 million deaths (1·1 million to 1·4 million) in 2004. Since 2004, child deaths from malaria in sub-Saharan Africa have decreased by 31·5% (15·7 to 44·1). Outside of Africa, malaria mortality has been steadily decreasing since 1990. INTERPRETATION: Our estimates of the number of people living with HIV are 18·7% smaller than UNAIDS's estimates in 2012. The number of people living with malaria is larger than estimated by WHO. The number of people living with HIV, tuberculosis, or malaria have all decreased since 2000. At the global level, upward trends for malaria and HIV deaths have been reversed and declines in tuberculosis deaths have accelerated. 101 countries (74 of which are developing) still have increasing HIV incidence. Substantial progress since the Millennium Declaration is an encouraging sign of the effect of global action. FUNDING: Bill & Melinda Gates Foundation

Density-Functional Theory for Polymer−Carbon Dioxide Mixtures

We propose a new density-functional theory (DFT) describing inhomogeneous polymer–carbon dioxide (CO2) mixtures. The theory is constructed by combining the bulk Peng–Robinson equation of state (PR-EOS) with the statistical associating fluid theory (SAFT) and the fundamental measure theory (FMT). The weight density functions from FMT are used to extend the bulk excess Helmholtz free energy of PR-EOS to the inhomogeneous case, while the SAFT is used to describe correlations due to polymer chain connectivity and short-range forces due to weakly polar or association interactions. The additional long-range dispersion contributions are included using a mean-field approach. We apply our DFT to the interfacial properties of polystyrene–CO_2 and poly(methyl methacrylate)–CO_2 systems. The calculated interfacial tension values are in good agreement with experimental data at low to intermediate pressures. The inclusion of association energy for CO_2 is shown to have a significant effect. We also point out the limitation of the PR-EOS for describing polymer–CO_2 mixtures at high pressures (P > 35 MPa)

Jump Enhancement of Nucleation in Polymer and Carbon Dioxide Mixtures by Metastable Phase Transition

We combine a newly developed density-functional theory with string method to calculate minimum free energy path of bubble nucleation in compressible poly(methyl methacrylate)-CO_2 mixtures. As increasing initial pressure in the vicinity of a metstable phase transition, the terminal nucleated state jumps from the branch of CO_2- rich-vapor phase to the branch of CO_2 -rich-liquid phase with a jump reduction for free energy barrier and radius of critical nucleus. This result suggests that the nucleation rate is enhanced as a jump discontinuous function of the initial pressure around the boundary of metastable phase transition

Density-Functional Theory for Mixtures of AB Random Copolymer and CO_2

We propose a density-functional theory (DFT) to describe inhomogeneous mixtures of AB random copolymer and carbon dioxide (CO_2). The statistical sequence of monomer in the polymer chain backbone is modeled by a transition matrix in a Markov-step growth process. The parameters of the theory are determined by fitting the bulk experimental data. We apply the DFT to the interfacial properties of binary mixtures of CO_2 with poly(methyl methacrylate co ethyl methacrylate) (P(MMA-co-EMA)), poly(methyl methacrylate co ethyl acrylate) (P(MMA-co-EA) and poly(styrene co ethyl acrylate) (P(S-co-EA)). The dependence of CO_2 solubility and interfacial tension on the copolymer composition and pressure is examined. We find that higher fractions of EA or EMA result in higher solubility of CO_2 at a given pressure, but also results in higher interfacial tension at a fixed CO_2 content in the polymer-rich phase. Using the classical nucleation theory as a rough estimate, we examine the effect of the copolymer composition on the free energy barrier of bubble nucleation in random copolymer–CO_2 mixtures