Wetting Properties of the CO2-Water-Calcite System via Molecular Simulations: Shape and Size Effects

Assessment of the risks and environmental impacts of carbon geosequestration requires knowledge about the wetting behavior of mineral surfaces in the presence of CO₂ and the pore fluids. In this context, the interfacial tension (IFT) between CO₂ and the aqueous fluid and the contact angle, θ, with the pore mineral surfaces are the two key parameters that control the capillary pressure in the pores of the candidate host rock. Knowledge of these two parameters and their dependence on the local conditions of pressure, temperature, and salinity is essential for the correct prediction of structural and residual trapping. We have performed classical molecular dynamics simulations to predict the CO₂-water IFT and the CO₂-water-calcite contact angle. The IFT results are consistent with previous simulations, where simple point charge water models have been shown to underestimate the water surface tension, thus affecting the simulated IFT values. When combined with the EPM2 CO₂ model, the SPC/Fw water model indeed underestimates the IFT in the low-pressure region at all temperatures studied. On the other hand, at high pressure and low temperature, the IFT is overestimated by ∼5 mN/m. Literature data regarding the CO₂/water/calcite contact angle on calcite are contradictory. Using our new set of force field parameters, we performed NVT simulations at 323 K and 20 MPa to calculate the contact angle of a water droplet on the calcite {10.4} surface in a CO₂ atmosphere. We performed simulations for both spherical and cylindrical droplet configurations for different initial radii to study the size dependence of the water contact angle on calcite in the presence of CO₂. Our results suggest that the contact angle of a cylindrical droplet, is independent of droplet size, for droplets with a radius of 50 Å or more. On the contrary, spherical droplets make a contact angle that is strongly influenced by their size. At the largest size explored in this study, both spherical and cylindrical droplets converge to the same contact angle, 38°, indicating that calcite is strongly wetted by water.

The effect of solvation and temperature on the adsorption of small organic molecules on calcite

The effect of multicomponent mixture on small organic molecule adsorption on calcite at nonzero temperature was investigated.

Ab initio calculation of energy levels for phosphorus donors in silicon

The s manifold energy levels for phosphorus donors in silicon are important input parameters for the design and modeling of electronic devices on the nanoscale. In this paper we calculate these energy levels from first principles using density functional theory. The wavefunction of the donor electron's ground state is found to have a form that is similar to an atomic s orbital, with an effective Bohr radius of 1.8 nm. The corresponding binding energy of this state is found to be 41 meV, which is in good agreement with the currently accepted value of 45.59 meV. We also calculate the energies of the excited 1s(T ₂) and 1s(E) states, finding them to be 32 and 31 meV respectively.

Health coping strategies of the people vulnerable to climate change in a resource-poor rural setting in Bangladesh

BACKGROUND

Among the many challenges faced by the people of Bangladesh, the effects of climate change are discernibly threatening, impacting on human settlement, agricultural production, economic development, and human health. Bangladesh is a low-income country with limited resources; its vulnerability to climate change has influenced individuals to seek out health coping strategies. The objectives of the study were to explore the different strategies/measures people employ to cope with climate sensitive diseases and sickness.

METHODS

A cross-sectional study was conducted among 450 households from Rajshahi and Khulna districts of Bangladesh selected through multi-stage sampling techniques, using a semi-structured questionnaire supplemented by 12 focus group discussions and 15 key informant interviews.

RESULTS

Respondents applied 22 types of primary health coping strategies to prevent climate related diseases and sickness. To cope with health problems, 80.8% used personal treatment experiences and 99.3% sought any treatments available at village level. The percentage of respondents that visited unqualified health providers to cope with climate induced health problems was quite high, namely 92.7% visited village doctors, 75.9% drug stores, and 67.3% self-medicated. Ninety per cent of the respondents took treatment from unqualified providers as their first choice. Public health facilities were the first choice of treatment for only 11.0% of respondents. On average, every household spent Bangladesh Currency Taka 9,323 per year for the treatment of climate sensitive diseases and sickness. Only 46% of health expenditure was managed from their savings. The rest, 54% expenditure, was supported by using 24 different sources, such as social capital and the selling of family assets. The rate of out-of-pocket payment was almost 100%.

CONCLUSION

People are concerned about climate induced diseases and sickness and sought preventive as well as curative measures to cope with health problems. The most common and widely used climate health coping strategies among the respondents included self-medicating and seeking the health service of unqualified private health care providers. Per family spending to cope with such health problems is expensive and completely based on out of pocket payment. There is no fund pooling, community funding or health insurance program in rural areas to support the health coping of the people. Policies are needed to reduce out-of-pocket payment, to improve the quality of the unqualified providers and to extend public health services at rural areas and support climate related health coping. Collection of such knowledge on climate related health coping strategies can allow researchers to study any specific issue on health coping, and policy makers to initiate effective climate related health coping strategies for climate vulnerable people.

Ab Initio electronic properties of monolayer phosphorus nanowires in silicon

Epitaxial circuitry offers a revolution in silicon technology, with components that can be fabricated on atomic scales. We perform the first ab initio calculation of atomically thin epitaxial nanowires in silicon, investigating the fundamental electronic properties of wires two P atoms thick, similar to those produced this year by Weber et al. For the first time, we catch a glimpse of disorder-related effects in the wires--a prerequisite for understanding real fabricated systems. Interwire interactions are made negligible by including 40 ML of silicon in the vertical direction (and the equivalent horizontally). Accurate pictures of band splittings and the electronic density are presented, and for the first time the effective masses of electrons in such device components are calculated.

Protein flexibility: multiple molecular dynamics simulations of insulin chain B

Multiple molecular dynamics simulations totaling more than 100 ns were performed on chain B of insulin in explicit solvent at 300 K and 400 K. Despite some individual variations, a comparison of the protein dynamics of each simulation showed similar trends and most structures were consistent with NMR experimental values, even at the elevated temperature. The importance of packing interactions in determining the conformational transitions of the protein was observed, sometimes resulting in conformations induced by localized hydrophobic interactions. The high temperature simulation generated a more diverse range of structures with similar elements of secondary structure and populated conformations to the simulations at room temperature. A broad sampling of the conformational space of insulin chain B illustrated a wide range of conformational states with many transitions at room temperature in addition to the conformational states observed experimentally. The T-state conformation associated with insulin activity was consistently present and a possible mechanism of behavior was suggested.

Effect of external stresses on protein conformation: a computer modelling study

The increasing use of digital technologies such as mobile phones has led to major health concerns about the effects of non-ionizing pulsed radiation exposure. We believe that the health implications of exposure to radiation cannot be fully understood without establishing the molecular mechanisms of biological effects of pulsed microwaves. We aim to establish methods for studying the molecular mechanisms of protein structural and energetic changes occurring due to external stresses related to non-ionizing radiation by using a combination of experimental and theoretical approaches. In this paper, we present the results from our fully atomistic simulation study of chemical and thermal stress response of a prototype protein, insulin. We performed a series of molecular dynamics simulations of insulin in solution under equilibrium conditions, under chemical stress (imitated by reducing the disulfide bonds in the protein molecule), and under short-lived thermal stress (imitated by increasing simulation temperature for up to 2 ns). The resultant protein conformational behaviour was analysed for various properties with the aim of establishing analysis routines for classification of protein unfolding pathways and associated molecular mechanisms.