Anisotropic united-atoms (AUA) potential for alcohols

An anisotropic united-atom (AUA4) intermolecular potential has been derived for the family of alkanols by first optimizing a set of charges to reproduce the electrostatic potential of the isolated molecules of methanol and ethanol and then by adjusting the parameters of the OH group to fit selected equilibrium properties. In particular, the proposed potential includes additional extra-atomic charges in order to improve the matching to the electrostatic field. Gibbs ensemble Monte Carlo simulations were performed to determine the phase equilibria, while the critical region was explored by means of grand canonical Monte Carlo simulations combined with histogram reweighting techniques. In order to increase the transferability of the model, only the parameters of the Lennard-Jones OH group have been fitted, the parameters of the other AUA groups are taken from previous works. Nevertheless, a good level of agreement was obtained for all compounds considered in this work. In particular, excellent results were obtained for the Henry constants calculation of different gases in alkanols.     

Structure modification in hen egg yolk low density lipoproteins layers between 30 and 45 mN/m observed by AFM

We have studied the structure of films made by low density lipoproteins (LDL) from hen egg yolk, which are composed of apoproteins, neutral lipids and phospholipids. These LDL have been deposited on air–water interface to form a monolayer which has been compressed to measure an isotherm using Langmuir balance. This isotherm presented three transitions (neutral lipid (surface pressure, π = 19 mN/m), apoprotein–lipid (π = 41 mN/m) and phospholipid (π = 51 mN/m) transitions). We have studied only the apoprotein–lipid transition. In order to observe the LDL film structure before (π = 30 mN/m) and after (π = 45 mN/m) the apoprotein–lipid transition, the formed films were transferred and visualised by atomic force microscopy (AFM). Our results have shown that the structures observed in the LDL film were different depending on the surface pressure. The apoproteins and neutral lipids appeared to be miscible up to the apoprotein–lipid transition, when demixing occured. The structures observed after the apoprotein–lipid transition should be due to the demixing between apoproteins and neutral lipids. On the other hand, apoproteins and phospholipids seemed miscible whatever the surface pressure. Hence, the first transition (π = 19 mN/m) should be attributed to the free neutral lipid collapse; the second transition (π = 41 mN/m) should be attributed to the demixing of apoprotein–neutral lipid complexes; and the last transition (π = 51 mN/m) should be attributed to phospholipid collapse or to demixing of apoprotein–phospholipid complexes.     

An anisotropic united atoms (AUA) potential for thiophenes

The optimization of the parameters of the Lennard-Jones (LJ) 12-6 potential of the sulfur atom in thiophene has allowed the AUA 4 potential to be successfully extended to alkyl and polythiophenes. Monte Carlo Gibbs ensemble and grand canonical simulations combined with histogram reweighting techniques have been performed to investigate the resulting phase equilibrium and the critical region of different molecules of this family in order to test the proposed potential. Excellent agreement with experimental densities, enthalpies of vaporization, and saturation pressures has been obtained in most of the cases. In particular, the critical point of our model for thiophene has been located with a statistical precision of less than 0.1% and is within 1% of the experimental value. The calculation of the critical points has been made through a recently implemented methodology based on the calculation of a fourth order cumulant (Binder parameter) combined with the use of finite size scaling methods, allowing the critical points to be located in a straightforward and accurate way.     

An equilibrium ab initio atomistic thermodynamics study of chlorine adsorption on the Cu(001) surface

The effect of chlorine (Cl) chemisorption on the energetics and atomic structure of the Cu(001) surface over a wide range of chlorine pressures and temperatures has been studied using equilibrium ab initio atomistic thermodynamics to elucidate the formation of cuprous chloride (CuCl) as part of the Deacon reaction on copper metal. The calculated surface free energies show that the 1/2 monolayer (ML) c(2 × 2)-Cl phase with chlorine atoms adsorbed at the hollow sites is the most stable structure for a wide range of Cl chemical potential, in agreement with experimental observations. It is also found that at very low pressure and exposure, but elevated temperature, the 1/9 ML and 1/4 ML phases become the most stable. By contrast, a high coverage of Cl does not lead to thermodynamically stable geometries. The subsurface adsorption of Cl atoms, however, dramatically increases the stability of the 1 ML and 2 ML adsorption configurations providing a possible pathway for the formation of the bulk-chloride surface phases in the kinetic regime.     

Performance of a motorway noise barrier at Heston

This paper reports on the performance and costs of a 300 m long experimental noise barrier erected alongside an elevated section of the M4 motorway to protect existing two-storey housing which is as close as 20 m to the motorway. Measured reductions in L₁₀ values, at the façades of these dwellings, were around 8 dB(A) at first floor windows and around 4 dB(A) at ground floor windows. These measured reductions were based on the levels with no barrier but with some screening due to the elevation of the road.A wooden fence in the barrier position at the start of the experiment gave reductions of about 3 dB(A) at the façades of the nearby houses. The subjective impressions of the occupants showed a markedly favourable overall reaction to the change from the wooden fence to the experimental noise barrier.A reduction in the variability of the received noise levels from the partially screened situation without a barrier to the screened situation was found. There was no significant increase in noise levels for positions on the opposite side of the motorway.