82,568 research outputs found
A New Equation of State for CCS Pipeline Transport: Calibration of Mixing Rules for Binary Mixtures of CO2 with N2, O2 and H2
One of the aspects currently holding back commercial scale deployment of
carbon capture and storage (CCS) is an accurate understanding of the
thermodynamic behaviour of carbon dioxide and relevant impurities during the
pipeline transport stage. In this article we develop a general framework for
deriving pressure-explicit EoS for impure CO2. This flexible framework
facilitates ongoing development of custom EoS in response to new data and
computational applications. We use our method to generalise a recent EoS for
pure CO2 [Demetriades et al. Proc IMechE Part E, 227 (2013) pp. 117] to binary
mixtures with N2, O2 and H2, obtaining model parameters by fitting to
experiments made under conditions relevant to CCS-pipeline transport. Our model
pertains to pressures up to 16MPa and temperatures between 273K and the
critical temperature of pure CO2. In this region, we achieve close agreement
with experimental data. When compared to the GERG EoS, our EoS has a comparable
level of agreement with CO2 -N2 VLE experiments and demonstrably superior
agreement with the O2 and H2 VLE data. Finally, we discuss future options to
improve the calibration of EoS and to deal with the sparsity of data for some
impurities
Noncariogenic Sweeteners: Sugar Substitutes for Caries Control
The evidence is clear that the incidence of dental caries is related to the frequency of eating sugar. The use of sugar substitutes is a suggested way of reducing sugar intake. A variety of noncariogenic sweeteners exists, but most have no practical value for caries control because of their technical or safety problems, taste, or cost. Urinary bladder tumorigenic effects have been reported in experimental animals treated with saccharin and cyclamates. Because of concerns for human safety, cyclamates were banned in the U.S., and saccharin use was permitted only by special legislation. The polyalcohols sorbitol and xylitol are important sugar substitutes since they are not efficient substrates for plaque bacteria and therefore produce only minimal plaque pH drop.
Aspartame, with its sugar-like taste, is an excellent low-calorie sweetener now used in over 100 products under the name NutraSweet. Consumption of aspartame by normal humans is safe and does not promote tooth decay. Individuals with a need to control their phenylalanine intake should handle aspartame like any other source of phenylalanine
The prospects for mathematical logic in the twenty-first century
The four authors present their speculations about the future developments of
mathematical logic in the twenty-first century. The areas of recursion theory,
proof theory and logic for computer science, model theory, and set theory are
discussed independently.Comment: Association for Symbolic Logi
Inferring HIV escape rates from multi-locus genotype data
Cytotoxic T-lymphocytes (CTLs) recognize viral protein fragments displayed by
major histocompatibility complex (MHC) molecules on the surface of virally
infected cells and generate an anti-viral response that can kill the infected
cells. Virus variants whose protein fragments are not efficiently presented on
infected cells or whose fragments are presented but not recognized by CTLs
therefore have a competitive advantage and spread rapidly through the
population. We present a method that allows a more robust estimation of these
escape rates from serially sampled sequence data. The proposed method accounts
for competition between multiple escapes by explicitly modeling the
accumulation of escape mutations and the stochastic effects of rare multiple
mutants. Applying our method to serially sampled HIV sequence data, we estimate
rates of HIV escape that are substantially larger than those previously
reported. The method can be extended to complex escapes that require
compensatory mutations. We expect our method to be applicable in other contexts
such as cancer evolution where time series data is also available
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Multiple environmental controls explain global patterns in soil animal communities
Soil animals play important roles in ecosystem functioning and stability, but the environmental controls on their communities are not fully understood. In this study, we compiled a dataset of soil animal communities for which the abundance and body mass of multiple soil animal groups were recorded. The mass–abundance scaling relationships were then used to investigate multiple environmental controls on soil animal community composition. The data reveal latitudinal shifts from high abundances of small soil animals at high latitudes to greater relative abundances of large soil animals at low latitudes. A hierarchical linear mixed effects model was applied to reveal the environmental variables shaping these latitudinal trends. The final hierarchical model identified mean annual temperature, soil pH and soil organic carbon content as key environmental controls explaining global mass–abundance scaling relationships in soil animal communities (R2c = 0.828, Ngroup = 117). Such relationships between soil biota with climate and edaphic conditions have been previously identified for soil microbial, but not soil animal, communities at a global scale. More comprehensive global soil community datasets are needed to better understand the generality of these relationships over a broader range of global ecosystems and soil animal groups
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