Surface viscoelasticity in model polymer multilayers: From planar interfaces to rising bubbles

International audienceIn the present work a polymeric transient viscoelastic network is used as a model system to investigate several fundamentals of interfacial viscoelasticity and non-linear behavior, in simple shear, compression and for simple mixed deformations. A supramolecular polymer bilayer, characterized by long but finite relaxation times, is created at the water-air interface using a layer-by-layer assembly method. The possibility of studying the individual layers starting from an unstrained reference state enabled the independent quantification of the equilibrium ther-modynamic properties, and the viscoelastic response of the bilayer could be studied separately for shear and compressional deformations. Time-and frequency-dependent material functions of the layer were determined in simple shear and uniform compression. Moreover, a quasi linear neo-Hookean model for elastic interfaces was adapted to describe step strain experiments on a viscoelastic system by allowing the material properties to be time-dependent. The use of this model made it possible to calculate the response of the system to step deformations. Within the linear response regime, both stress-strain proportionality and the superposition principle were investigated. Furthermore, the onset of non-linear behavior of the extra stresses was characterized in shear and for the first time in pure compression. We conclude by investigating the multilayer system in a rising bubble setup and show that the neo-Hookean model is able to predict the extra and deviatoric surface stresses well, up to moderate deformations

In utero exposure to malaria is associated with metabolic traits in adolescence: The Agogo 2000 birth cohort study.

OBJECTIVES: Malaria in pregnancy (MiP) contributes to fetal undernutrition and adverse birth outcomes, and may constitute a developmental origin of metabolic diseases in the offspring. In a Ghanaian birth cohort, we examined the relationships between MiP-exposure and metabolic traits in adolescence. METHODS: MiP at delivery was assessed in 155 mother-child pairs. Among the now teenaged children (mean age, 14.8 years; 53% male), we measured fasting plasma glucose (FPG), body mass index (BMI), and systolic and diastolic blood pressure (BP). Associations of MiP with the adolescents' FPG, BMI, and BP were examined by linear regression. RESULTS: At delivery, 45% were MiP-exposed, which increased FPG in adolescence, adjusted for mother's age at delivery, parity and familial socio-economic status (infected vs. uninfected: mean ΔFPG = 0.20 mmol/L; 95% confidence interval (CI): 0.01, 0.39; p = 0.049). As a trend,this was discernible for BP, particularly for microscopic infections (mean Δsystolic BP = 5.43 mmHg; 95% CI: 0.00, 10.88; p = 0.050; mean Δdiastolic BP = 3.67 mmHg; 95% CI: -0.81, 8.14; p = 0.107). These associations were largely independent of birth weight, gestational age and teenage BMI. Adolescent BMI was not related to MiP. CONCLUSIONS: In rural Ghana, exposure to malaria during fetal development contributes to metabolic conditions in young adulthood

Changes in the relationship between self-reference and emotional valence as a function of dysphoria

The self-positivity bias is found to be an aspect of normal cognitive function. Changes in this bias are usually associated with changes in emotional states, such as dysphoria or depression. The aim of the present study was to clarify the role of emotional valence within self-referential processing. By asking non-dysphoric and dysphoric individuals to rate separately the emotional and self-referential content of a set of 240 words, it was possible to identify the differences in the relationship between self-reference and emotional valence, which are associated with dysphoria. The results support the existence of the self-positivity bias in non-dysphoric individuals. More interestingly, dysphoric individuals were able to accurately identify the emotional content of the word stimuli. They failed, however, to associate this emotional valence with self-reference. These findings are discussed in terms of attributional self-biases and their consequences for cognition

Accidental Outcomes Guide Punishment in a “Trembling Hand” Game

How do people respond to others' accidental behaviors? Reward and punishment for an accident might depend on the actor's intentions, or instead on the unintended outcomes she brings about. Yet, existing paradigms in experimental economics do not include the possibility of accidental monetary allocations. We explore the balance of outcomes and intentions in a two-player economic game where monetary allocations are made with a “trembling hand”: that is, intentions and outcomes are sometimes mismatched. Player 1 allocates $10 between herself and Player 2 by rolling one of three dice. One die has a high probability of a selfish outcome, another has a high probability of a fair outcome, and the third has a high probability of a generous outcome. Based on Player 1's choice of die, Player 2 can infer her intentions. However, any of the three die can yield any of the three possible outcomes. Player 2 is given the opportunity to respond to Player 1's allocation by adding to or subtracting from Player 1's payoff. We find that Player 2's responses are influenced substantially by the accidental outcome of Player 1's roll of the die. Comparison to control conditions suggests that in contexts where the allocation is at least partially under the control of Player 1, Player 2 will punish Player 1 accountable for unintentional negative outcomes. In addition, Player 2's responses are influenced by Player 1's intention. However, Player 2 tends to modulate his responses substantially more for selfish intentions than for generous intentions. This novel economic game provides new insight into the psychological mechanisms underlying social preferences for fairness and retribution

Global modeling of tropospheric iodine aerosol

Natural aerosols play a central role in the Earth system. The conversion of dimethyl sulfide to sulfuric acid is the dominant source of oceanic secondary aerosol. Ocean emitted iodine can also produce aerosol. Using a GEOS-Chem model, we present a simulation of iodine aerosol. The simulation compares well with the limited observational data set. Iodine aerosol concentrations are highest in the tropical marine boundary layer (MBL) averaging 5.2 ng (I) m −3 with monthly maximum concentrations of 90 ng (I) m −3. These masses are small compared to sulfate (0.75% of MBL burden, up to 11% regionally) but are more significant compared to dimethyl sulfide sourced sulfate (3% of the MBL burden, up to 101% regionally). In the preindustrial, iodine aerosol makes up 0.88% of the MBL burden sulfate mass and regionally up to 21%. Iodine aerosol may be an important regional mechanism for ocean-atmosphere interaction

A nocturnal atmospheric loss of CH2I2 in the remote marine boundary layer.

Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH2I2) and chloro-iodomethane (CH2ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH2I2 and CH2ICl in air and of CH2I2 in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH2I2 was lower in amplitude than that of CH2ICl, despite its faster photolysis rate. We speculate that night-time loss of CH2I2 occurs due to reaction with NO3 radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k CH2I2+NO3 of ≤4 × 10-13 cm3 molecule-1 s-1; a previous kinetic study carried out at ≤100 Torr found k CH2I2+NO3 of 4 × 10-13 cm3 molecule-1 s-1. Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/- 0.8 nmol m-2 d-1 for CH2I2 and 3.7 +/- 0.8 nmol m-2 d-1 for CH2ICl), we show that the model overestimates night-time CH2I2 by >60 % but reaches good agreement with the measurements when the CH2I2 + NO3 reaction is included at 2-4 × 10-13 cm3 molecule-1 s-1. We conclude that the reaction has a significant effect on CH2I2 and helps reconcile observed and modeled concentrations. We recommend further direct measurements of this reaction under atmospheric conditions, including of product branching ratios.LJC acknowledges NERC (NE/J00619X/1) and the National Centre for Atmospheric Science (NCAS) for funding. The laboratory work was supported by the NERC React-SCI (NE/K005448/1) and RONOCO (NE/F005466/1) grants.This is the final version of the article. It was first available from Springer via http://dx.doi.org/10.1007/s10874-015-9320-

Adolescent health in rural Ghana: A cross-sectional study on the co-occurrence of infectious diseases, malnutrition and cardio-metabolic risk factors.

In sub-Saharan Africa, infectious diseases and malnutrition constitute the main health problems in children, while adolescents and adults are increasingly facing cardio-metabolic conditions. Among adolescents as the largest population group in this region, we investigated the co-occurrence of infectious diseases, malnutrition and cardio-metabolic risk factors (CRFs), and evaluated demographic, socio-economic and medical risk factors for these entities. In a cross-sectional study among 188 adolescents in rural Ghana, malarial infection, common infectious diseases and Body Mass Index were assessed. We measured ferritin, C-reactive protein, retinol, fasting glucose and blood pressure. Socio-demographic data were documented. We analyzed the proportions (95% confidence interval, CI) and the co-occurrence of infectious diseases (malaria, other common diseases), malnutrition (underweight, stunting, iron deficiency, vitamin A deficiency [VAD]), and CRFs (overweight, obesity, impaired fasting glucose, hypertension). In logistic regression, odds ratios (OR) and 95% CIs were calculated for the associations with socio-demographic factors. In this Ghanaian population (age range, 14.4-15.5 years; males, 50%), the proportions were for infectious diseases 45% (95% CI: 38-52%), for malnutrition 50% (43-57%) and for CRFs 16% (11-21%). Infectious diseases and malnutrition frequently co-existed (28%; 21-34%). Specifically, VAD increased the odds of non-malarial infectious diseases 3-fold (95% CI: 1.03, 10.19). Overlap of CRFs with infectious diseases (6%; 2-9%) or with malnutrition (7%; 3-11%) was also present. Male gender and low socio-economic status increased the odds of infectious diseases and malnutrition, respectively. Malarial infection, chronic malnutrition and VAD remain the predominant health problems among these Ghanaian adolescents. Investigating the relationships with evolving CRFs is warranted