Abstract: Explicit molecular dynamics simulations were applied to a pair of amorphous silica nanoparticles with diameter of 3.2 nm immersed in a background electrolyte. Mean forces acting between the pair of silica nanoparticles were extracted at four different background electrolyte concentrations. The dependence of the interparticle potential of mean force on the separation and the silicon to sodium ratio, as well as on the background electrolyte concentration, are demonstrated. The pH was indirectly accounted for via the ratio of silicon to sodium used in the simulations. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was also investigated. The effect of the sodium double layer on the water ordering was investigated for three Si:Na+ ratios. The number of water molecules trapped inside the nanoparticles was investigated as the Si:Na+ ratio was varied. Differences in this number between the two nanoparticles in the simulations are attributed to differences in the calculated electric dipole moment. The implications of the form of the potentials for aggregation are also discussed.
Abstract: Explicit molecular dynamics simulations were applied to a series of six pairs of amorphous silica nanoparticles in aqueous solution, ranging in diameter from 2.0-4.4 nm and four different background electrolyte concentrations, to extract the mean force acting between pairs of silica nanoparticles. Dependences of the interparticle forces with particle radius, separation and the background electrolyte concentration were demonstrated. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was investigated. In addExplicit molecular dynamics simulations were applied to a series of six pairs of amorphous silica nanoparticles in aqueous solution, ranging in diameter from 2.0-4.4 nm and four different background electrolyte concentrations, to extract the mean force acting between pairs of silica nanoparticles. Dependences of the interparticle forces with particle radius, separation and the background electrolyte concentration were demonstrated. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was investigated. In addition, partial water ordering was observed around the outside of the silica nanoparticle as well as a ’patchy’ double layer of adsorbed sodium counterions. We observed attractive depletion forces between the pairs of silica nanoparticles. Further to this, the varying hydrophilic/hydrophobic nature of silica was indicated from a selection of the mean force-separation plots.ition, partial water ordering was observed around the outside of the silica nanoparticle as well as a ’patchy’ double layer of adsorbed sodium counterions. We observed attractive depletion forces between the pairs of silica nanoparticles. Further to this, the varying hydrophilic/hydrophobic nature of silica was indicated from a selection of the mean force-separation plots.
Abstract: The stability and evolution of the structure of consecutive versions of a series of software architecture graphs are analysed using the theory of complex networks. Brief comparisons are drawn between the scale-free behaviour and second order phase transitions. On this basis a software design metric Icc is proposed. This software metric is used to quantify the evolution of the stability vs. maintainability of the software through various releases. It is demonstrated that the classes in the software graph are acquiring more out-going calls than incoming calls as the software ages. Three examples of software applications where maintainability and continuous refactoring are an inherent part of their development process are presented, in addition to a Sun Java2 framework where growth and backward compatibility are the more important factors for the development. Further to this a projected future evolution of the software structure and maintainability is calculated. Suggestions for future applications to software engineering and the natural sciences are briefly presented.
Abstract: Explicit molecular dynamics simulations were applied to two pairs of amorphous silica nanoparticles in aqueous solution (2.0 and 4.4 nm in diameter) and four different background electrolyte concentrations, to extract the potential of mean force acting between the two pairs of silica nanoparticles. Dependences of the interparticle potential of mean forces with separation and the background electrolyte concentration for the two sizes of particle radius were demonstrated. Radial distribution functions and derived quantities were used to probe the surface environment of the nanoparticles. Direct evidence of the solvation forces is presented in terms of changes of the water ordering at the surfaces of the isolated and double nanoparticles. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was investigated in terms of quantifying the effects of the number of water molecules separately inside the each of the pair of nanoparticles by defining an impermeability measure. Differences in the impermeability between the pairs of nanoparticles are attributed to differences in the calculated dipole moment. A direct correlation was found between impermeability (related to the silica surface ’hairiness’) and the disruption of water ordering.
Abstract: We explore the use of complex networks for understanding of the interaction of computer software applications written in the Java object-oriented language with the "library classes" that they use (those provided by the Java Runtime Environment) as, essentially, a merged network of classes. The dependence of the software on the library is quantified using a recently introduced model that identifies phases close to a second-order phase transition existing in scale-free networks. An example is given of a piece of software whose class network collapses without the presence of the library classes, providing validation of a novel structural coupling measure; Rcoupling. The structural properties of the merged software-Java class networks were found to correlate with the proportion of Java classes contained within the subset delimited by Rcoupling. A mechanism for the preservation of the software class network is also provided for the cases studied where the removal of the library classes does not cause collapse.
Abstract: A new approach to software metrics using concepts from information theory, data compression, complexity theory and analogies with real physical systems is described. A novel application of software obfuscation allows an existing software package to be analysed in terms of the effects of perturbations caused by the obfuscator. Parallels are drawn between the results of the software analysis and the behaviour of physical systems as described by classical thermodynamics.
Abstract: The charge-density distribution in various phases of ice is used to explore the information that can be obtained about the preferred directions of motion of atoms so as to investigate the possibility of the creation of more efficient and computationally cost-effective dynamical matrices. PACS Nos.: 63.20Dj, 31.90+s, 71.10-w<P></P>Nous utilisons la distribution de densité de charge dans différentes phases de glace pour évaluer l'information qui peut être obtenue au sujet des directions privilégiées de mouvement des atomes afin d'étudier la possibilité de généreré des matrices dynamiques de façon plus efficace et requérant moins de calculs numériques. [Traduit par la Rédaction]
