From Atoms to Colloids: Does the Frenkel Line Exist in Discontinuous Potentials?

The Frenkel line has been proposed as a crossover in the fluid region of phase diagrams between a "non-rigid" and a "rigid" fluid. It is generally described as a crossover in the dynamical properties of a material, and as such has been described theoretically using a very different set of markers from those with which is it investigated experimentally. In this study, we have performed extensive calculations using two simple yet fundamentally different model systems: hard spheres and square well potentials. The former has only hardcore repulsion, while the latter also includes a simple model of attraction. We computed and analysed a series of physical properties used previously in simulations and experimental measurements, and discuss critically their correlations and validity as to being able to uniquely and coherently locate the Frenkel in discontinuous potentials

Squeezing Oil into Water under Pressure: Inverting the Hydrophobic Effect

The molecular structure of dense homogeneous fluid water-methane mixtures has been determined for the first time using high-pressure neutron-scattering techniques at 1.7 and 2.2 GPa. A mixed state with a fully H-bonded water network is revealed. The hydration shell of the methane molecules is, however, revealed to be pressure-dependent with an increase in the water coordination between 1.7 and 2.2 GPa. In parallel, ab initio molecular dynamics simulations have been performed to provide insight into the microscopic mechanisms associated with the phenomenon of mixing. These calculations reproduce the observed phase change from phase separation to mixing with increasing pressure. The calculations also reproduce the experimentally observed structural properties. Unexpectedly, the simulations show mixing is accompanied by a subtle enhancement of the polarization of methane. Our results highlight the key role played by fine electronic effects on miscibility and the need to readjust our fundamental understanding of hydrophobicity to account for these

Pressure-induced Miscibility Increase of CH4 in H2O: A Computational Study Using Classical Potentials

Methane and water demix under normal (ambient) pressure and temperature conditions, due to the polar nature of water and the apolar nature of methane. Recent experimental work has shown, though, that increasing the pressure to values between 1 and 2 GPa (10 to 20 kbar) leads to a marked increase of methane solubility in water, for temperatures which are well below the critical temperature for water. Here we perform molecular dynamics simulations based on classical force fields – which are well-used and have been validated at ambient conditions – for different values of pressure and temperature. We find the expected increase in miscibility for mixtures of methane and supercritical water; however our model fails to reproduce the experimentally observed increase in methane solubility at large pressures and below the critical temperature of water. This points to the need to develop more accurate force fields for methane and methane-water mixtures under pressure

Ammonia Mono Hydrate IV: An Attempted Structure Solution

The mixed homonuclear and heteronuclear hydrogen bonds in ammonia hydrates have been of interest for several decades. In this manuscript, a neutron powder diffraction study is presented to investigate the structure of ammonia monohydrate IV at 170 K at an elevated pressure of 3–5 GPa. The most plausible structure that accounts for all features in the experimental pattern was found in the P21/c space group and has the lattice parameters a=5.487(3) Å, b=19.068(4) Å, c=5.989(3) Å, and β=99.537(16) deg. While the data quality limits discussion to a proton-ordered structure, the structure presented here sheds light on an important part of the ammonia–water phase diagram

From atoms to colloids : does the Frenkel line exist in discontinuous potentials?

The Frenkel line has been proposed as a crossover in the fluid region of phase diagrams between a "non-rigid" and a "rigid" fluid. It is generally described as a crossover in the dynamical properties of a material, and as such has been described theoretically using a very different set of markers from those with which is it investigated experimentally. In this study, we have performed extensive calculations using two simple yet fundamentally different model systems: hard spheres and square well potentials. The former has only hardcore repulsion, while the latter also includes a simple model of attraction. We computed and analysed a series of physical properties used previously in simulations and experimental measurements, and discuss critically their correlations and validity as to being able to uniquely and coherently locate the Frenkel in discontinuous potentials

STUDY REGARDING BIOCHEMICAL CHARACTERIZATION AND SOME PREPARATIONS FROM NETTLE AND WORMWOOD IN ORDER TO CAPITALIZE THEM AS BIOINSECTICIDE / BIOFERTILIZERS IN ORGANIC AGRICULTURE

Plant extracts contain substances that may induce, in treated plant, stimulation of defense mechanism, which will result in increased crop resistance especially against pathogenic microorganisms and pests that are causing the biggest economic losses and propagate the infection risk in time. Plant extracts are topics approached for a long time in support of organic agriculture, but still represents a generous particularly concerning on this essential aspect of a real organic agriculture. This paper is aimed at biochemical characterization of plant extracts of nettle and wormwood in order to capitalize them further as organic bioinsecticide / biofertilizers in organic agriculture. Extracts of nettle and wormwood are repellents and usually used preventative against pests, but also with economic advantages

POSSIBILITIES TO VALORIZE ARTICHOKE UNDER THE CULTIVATION CONDITIONS IN ROMANIA

Generally, in Romania, farmers focused on an agriculture based on large field crops, cereal crops, being less inclined to grow aromatic and medicinal crops that have a newer history in our country. But there are plants that have made history in other countries and that for a while are starting to be valorized in our country in a therapeutic or prophylactic purpose. One of these plants is artichoke (Cynara scolymus), which due to its many uses has become increasingly valuable. In our country is known and used especially in the pharmaceutical and food supplements industry, but food industry and that of cosmetics are making progress in using this wonder plant, with many therapeutic, digestive, hepatic-protective properties. Newly, the problem was posed for its use as an energy plant, by obtaining oil from the seeds. This paper proposes to highlight the possibilities to valorize the artichoke crop in Romania`s conditions, as a source of bioactive raw material for drug products, food supplements, cosmetics and ornaments. The results of experiments can be used by Romanian farmers to draw up plans to valorize all their land, even smaller surfaces

A comparison of different Fourier transform procedures for analysis of diffraction data from noble gas fluids

A comparison is made between the three principal methods for the analysis of neutron and x-ray diffraction data from noble gas fluids by direct Fourier transform. All three methods (standard Fourier transform, Lorch modification, and Soper–Barney modification) are used to analyze four different sets of diffraction data from noble gas fluids. The results are compared to the findings of a full-scale real-space structure determination, namely, Empirical Potential Structure Refinement. Conclusions are drawn on the relative merits of the three Fourier transform methods, what information can be reliably obtained using each method, and which method is most suitable for the analysis of different kinds of diffraction data. The mathematical validity of the Lorch method is critically analyzed