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: 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: The relative importance of economics and environment in debate may soon be reversed due to the influence of three factors. Firstly, in the global economy it is hard to hide the unwanted products of economic processes. Secondly, huge advances in science will reduce the imperfect knowledge of markets, making some monitoring and analyzing tools show the design of sensible and equitable livelihood in communities, which is more important than the motivation of maximising profits for some individuals or firms. Thirdly, China, as the last major player on the planet to take on economic growth, comes from traditions fundamentally different from those economies that have experienced the Industrial Revolution previously. Its challenges with sustainability and environmental conservation predate Western economics by millennia, and it is implementing policies domestically and starting to work on the world stage that acknowledges that the surroundings are the host for any economic and socio-political system.
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 039;information qui peut être obtenue au sujet des directions privilégiées de mouvement des atomes afin d 039;étudier la possibilité de généreré des matrices dynamiques de façon plus efficace et requérant moins de calculs numériques. [Traduit par la Rédaction]
Abstract: We present the results of first-principles computational studies of the dynamical properties of hexagonal ice using both the ab-initio pseudopotential method and the full-potential augmented plane-wave method. Properties obtained using both the generalized gradient approximation (GGA) and the meta-GGA in density-functional theory are compared. The lattice-dynamical properties of the structures are obtained using a finite-difference evaluation of the dynamical matrix and force-constant matrix from atomic forces. Phonon dispersion is evaluated by the direct determination of the force-constant matrix in supercells derived from the primitive molecule unit cells with the assumption that force constants are zero beyond the second molecular nearest neighbors. The k-dependent phonon frequencies are then obtained from the force-constant matrix and dispersion relations, and the Brillouin-zone integrated density of states is evaluated. The importance of phonon dispersion in the various regions of the phonon spectra is then assessed and compared to existing neutron-scattering data. Frozen-phonon calculations are used to compare phonon frequencies evaluated in both the GGA and meta-GGA. PACS Nos.: 61.12Ex, 63.20Dj<P></P>Nous présentons les résultats de calculs fondamentaux des propriétés dynamiques de la glace hexagonale utilisant les deux méthodes du pseudo-potentiel ab initio et de l 039;onde plane augmentée du potentiel complet. Nous comparons les propriétés obtenues, utilisant d 039;une part l 039;approximation du gradient généralisé (GGA) et d 039;autre part du méta-GGA pour la fonctionnelle de densité. Les propriétés dynamiques en réseau des structures sont déterminées en solutionnant par différences finies les matrices dynamiques et les matrices de constantes de force obtenues des forces atomiques. Nous évaluons la dispersion des phonons en déterminant directement la matrice de constantes de force dans les super-cellules dérivées des cellules moléculaires primitives, dans l 039;hypothèse où les constantes de force sont nulles au delà du deuxième plus proche voisin. La dépendance en k de la fréquence des phonons est alors obtenue de la matrice de constantes de force et des relations de dispersion et la densité d 039;états intégrée de la zone de Brillouin est aussi évaluée. L 039;importance de la dispersion des phonons dans les diverses régions du spectre est alors estimée et comparée aux données existantes en diffusion de neutrons. Nous utilisons des calculs sur phonons gelés pour comparer les fréquences de phonon dans les deux approches, GGA et méta-GGA. [Traduit par la Rédaction]
Abstract: First principles calculations are performed on possible structures of silicon monoxide solids. The chemical character of all of the bonding interactions is systematically quantified in real space. It is found that the most stable SiO structure possesses the highest number of inequivalent bond paths. This process reveals a novel metallic Si–Si interaction and provides an explanation for the origin of the unexpectedly high conductivity in thin silicon oxide layers. In this paper a new measure for quantifying metallic character (in direct space) present in a bond has been introduced. Furthermore it has been possible to determine the directional properties of this metallic character in real space using the charge density. This finding is very important for future complementary metal oxide semiconductor technology.
Abstract: We determine the structural data of seven of the polymorphs of ice (ice Ih, ice Ic, ice IX, ice II, ice VI, ice VII and ice VIII) from <I>ab initio</I> calculations. The dynamical properties have been analysed within the harmonic approximation via a finite-difference evaluation of dynamical matrices from atomic forces. Supercells are used to model the various ordered and disordered phases considered. Calculations are done at zero pressure in order to compare directly with neutron scattering studies performed on recovered phases. The normal modes are resolved into projections chosen to display their intra- and inter-molecular character. Further projections are performed for ice VI, ice VII and ice VIII to probe the interactions between sub-lattices. Trends in the dynamical results are discussed in terms of changes in the structural complexity of the various phases considered.
Abstract: The soliton model for motion of the <iopmath latex="$90^{\circ}$">90 176;</iopmath> partial in silicon has provided an explanation for the large reduction in activation energy (1 eV) which occurs under prolonged exposure to an H plasma. Applying the same theoretical model to diamond yields a drop of 1.6 eV and puts dislocation motion into the realm of the possible. Here we examine with the `atoms in molecules' method the bonding in the local energy minima and saddle point structures involved in motion of the <iopmath latex="$90^{\circ}$">90 176;</iopmath> partial. We find bonds with graphite character in the soliton, and, to a greater extent, in its saddle points for motion and kink pair nucleation. The presence of H does not suppress this character in any structure other than the kink pair, in which H is far less compressed. Furthermore we characterize the over-coordination of H in these structures.
Abstract: Dislocations in semiconductors can be strongly affected by a hydrogen plasma; core states may be passivated and mobility changed. For example, in silicon the activation barrier for dislocation motion drops by 1.0 eV upon exposure to H plasma for one hour at 470-540 176;C. If such an effect were to be found in diamond, a simple scaling argument would yield an activation energy of 1.9 eV. Here, density functional calculations have been applied to the 90 176; partial dislocation in diamond which confirm this prediction. They also show that, energetically, the soliton model for motion of the 90 176; partial is as viable as the strained-bond model.
Abstract: Density functional calculations accurately reproduce the known bond lengths for C60F18, shown recently (single crystal X-ray structure) to possess a fully aromatic hexagonal ring, and they correctly predict the planarity of this ring. Isostructural C60H18 is also calculated to have an aromatic benzenoid hexagonal ring, and to be marginally less planar. The four benzenoid hexagonal rings of T symmetry C60H36 and C60F36, and the three benzenoid rings of C3 symmetry C60H36 and C60F36 are predicted to be aromatic, with both the T symmetry and the fluorinated species again having the slightly shorter bond lengths and the greater planarity; by these measures T-C60F36 is as aromatic as C60F18. In another C3v isomer of C60H18, which had been predicted (AM1) to be thermodynamically more stable than the known isomer, density functional calculations show the central benzenoid ring to have slightly greater bond alternation, greater bond lengths, to be less planar and the molecule to be overall less stable than the known isomer; this is attributed to the greater strain in the three adjacent pentagonal rings. Sites for ether formation are conjectured based on the recent finding that oxygen inserts into long FC?CF bonds of fluorofullerenes.
Abstract: We have determined the normal modes of ice VIII, a 16-molecule supercell, using <I>ab initio</I> calculations. The dynamical matrices so obtained are diagonalized and the eigenvectors projected on to the stretching, bending and libration modes of each water molecule in turn. We can therefore accurately correlate the symmetry assignments of the zone centre modes and the corresponding frequencies of these dynamical results with Raman, infrared and neutron scattering data. In particular, using neutron scattering data, we obtain excellent agreement with the frequencies of the <IMG SRC="common/upsilon.gif" ALT="upsilon" ALIGN="TOP"/> <SUB><I>R<SUB>y</SUB> </I> </SUB> B<SUB>1<I>u</I> </SUB> phonon mode which is inactive in Raman or infrared spectroscopy.
Abstract: Using the theory of atoms in molecules (AIM), the intermolecular interactions, including hydrogen bonds (HBs) and the new intermolecular bonds (O?O) found recently in ice IX, ice II, ice VI, ice VII and ice VIII, can be described and classified by the topological properties of the charge density ?(rb) at the (3, ?1) bond critical points (BCPs) where the gradient of ?(r) vanishes. For 27 representative HBs and 27 representative O?O interactions, we show that the kinetic energy density G(rb) and the potential energy density V(rb) at the BCP depend exponentially on the HB and O?O distances, respectively. We also show and quantify the long-suspected result that HBs in ice Ih have some degree of covalent character, and moreover that this covalent character of the HBs persists for all of the HBs in all of the studied phases except ice VIII.
Abstract: We present studies of the vibrational properties of a number of ice structures as evaluated by ?first principles? lattice dynamics. Calculations are performed within the generalized gradient approximation to density functional theory using the ?ab initio? pseudopotential method. Dynamical properties are determined within the harmonic approximation by finite difference evaluation of the dynamical matrix from atomic forces. The resulting normal modes of vibration are analyzed in detail by projection onto pure intra- and inter-molecular modes. The importance of configurational disorder is assessed by comparison of results from different water molecule orientations in similar supercells. All structures considered here comprise of tetrahedral hydrogen-bonded networks and include low-pressure hexagonal and cubic structures and high-pressure cubic structures. Calculated vibrational density of states are compared with results from quasielastic neutron scattering and the microscopic origin of various features in the spectra discussed.
Abstract: Abstract: The many different intermolecular bonding interactions present in seven of the phases of water ice representing a large portion of the phase diagram are systematically examined using the theory of "atoms in molecules" (AIM), we obtain the total charge density distributions calculated using the generalized gradient approximation (GGA) and norm-conserving pseudopotentials. With this approach, we follow the changing properties of the intermolecular bonding from the low- to high-pressure phases of ice, examining ice Ic, ice Ih, ice IX, ice II, ice VI, ice VII, and ice VIII and various proton orderings within these phases. We quantify and characterize not only the familiar hydrogen bonds but also some novel intermolecular O--O bonding interactions, enhancing the understanding of bonding in ice and allowing a more complete explanation of the unusually high number of distinct phases of ice. We also quantify the relative compressibility of the structural features and the bond path rigidity in these ice phases, which have consequences for the mechanisms involved in phase transformations.
Abstract: Abstract: We present a detailed study of the structural and dynamical properties of ice Ih. Methods used include the ab-initio pseudopotential and molecular orbital techniques. In order to simulate the proton disorder present in ice Ih supercells are constructed with the orientation of water molecules determined in such a way that all possible nearest neighbor orientations are included while still obeying the Bernal-Fowler ice rules. For structures considered all structural parameters are relaxed. The dependence of bond length on the orientation of surrounding molecules in both the dimer and fully coordinated system is discussed. All local dimer orientations are accounted for in the supercell of ice Ih considered. The dynamical properties of a 16-molecule supercell model of ice Ih are then investigated via direct determination of the zone center dynamical matrix. Here the dynamical matrix is calculated directly from atomic forces obtained when each atom is shifted away from its equilibrium position. The vibrational modes are then calculated, and the mode frequency as a function of microscopic deformation is discussed.
