Mass distribution exponents for growing trees

We investigate the statistics of trees grown from some initial tree by attaching links to preexisting vertices, with attachment probabilities depending only on the valence of these vertices. We consider the asymptotic mass distribution that measures the repartition of the mass of large trees between their different subtrees. This distribution is shown to be a broad distribution and we derive explicit expressions for scaling exponents that characterize its behavior when one subtree is much smaller than the others. We show in particular the existence of various regimes with different values of these mass distribution exponents. Our results are corroborated by a number of exact solutions for particular solvable cases, as well as by numerical simulations

Quantifying Timing Leaks and Cost Optimisation

We develop a new notion of security against timing attacks where the attacker is able to simultaneously observe the execution time of a program and the probability of the values of low variables. We then show how to measure the security of a program with respect to this notion via a computable estimate of the timing leakage and use this estimate for cost optimisation.Comment: 16 pages, 2 figures, 4 tables. A shorter version is included in the proceedings of ICICS'08 - 10th International Conference on Information and Communications Security, 20-22 October, 2008 Birmingham, U

Systems Engineering Solution

The development and realisation of urban infrastructural projects such as bridges is getting increasingly more difficult and complex to manage. The challenge for the actors to develop an effective solution for the project within the traditional dimensions of time, budget and quality is still very present. But society also calls for more sustainable solutions which minimizes an eventual negative impact on the environment and takes into account the interests of stakeholders. The introduction of national and EU regulated procurement methods such as the Most Economically Advantageous Tenders (MEAT), has opened the way towards a more active and balanced involvement of actors and stakeholders in the development and realisation of urban construction projects. In this new environment, the client, consultant, contractor and stakeholders strive to work together in order to realise a sustainable solution. This document describes a methodology for the management of project processes with the aim of achieving a lawful, effective and sustainable construction process. The methodology is based on the principle of Life Cycle Systems Engineering, and facilitates and structures the introduction of sustainability and stakeholders issues in the design and build process. The method uses manly existing guidelines and standards for Life Cycle Systems Engineering

Branched polymers, complex spins and the freezing transition

We show that by coupling complex three-state systems to branched-polymer like ensembles we can obtain models with gamma-string different from one half. It is also possible to study the interpolation between dynamical and crystalline graphs for these models; we find that only when geometry fluctuations are completely forbidden is there a crystalline phase.Comment: 14 pages plain LateX2e, 4 eps figures included using eps

The Effect of Mass Ratio on the Morphology and Time-scales of Disc Galaxy Mergers

The majority of galaxy mergers are expected to be minor mergers. The observational signatures of minor mergers are not well understood, thus there exist few constraints on the minor merger rate. This paper seeks to address this gap in our understanding by determining if and when minor mergers exhibit disturbed morphologies and how they differ from the morphology of major mergers. We simulate a series of unequal-mass moderate gas-fraction disc galaxy mergers. With the resulting g-band images, we determine how the time-scale for identifying galaxy mergers via projected separation and quantitative morphology (the Gini coefficient G, asymmetry A, and the second-order moment of the brightest 20% of the light M20) depends on the merger mass ratio, relative orientations and orbital parameters. We find that G-M20 is as sensitive to 9:1 baryonic mass ratio mergers as 1:1 mergers, with observability time-scales ~ 0.2-0.4 Gyr. In contrast, asymmetry finds mergers with baryonic mass ratios between 4:1 and 1:1 (assuming local disc galaxy gas-fractions). Asymmetry time-scales for moderate gas-fraction major disc mergers are ~ 0.2-0.4 Gyr, and less than 0.06 Gyr for moderate gas-fraction minor mergers. The relative orientations and orbits have little effect on the time-scales for morphological disturbances. Observational studies of close pairs often select major mergers by choosing paired galaxies with similar luminosities and/or stellar masses. Therefore, the various ways of finding galaxy mergers (G-M20, A, close pairs) are sensitive to galaxy mergers of different mass ratios. By comparing the frequency of mergers selected by different techniques, one may place empirical constraints on the major and minor galaxy merger rates.Comment: 16 pages; resubmitted to MNRA

The Effect of Gas Fraction on the Morphology and Time-scales of Disc Galaxy Mergers

Gas-rich galaxy mergers are more easily identified by their disturbed morphologies than mergers with less gas. Because the typical gas fraction of galaxy mergers is expected to increase with redshift, the under-counting of low gas-fraction mergers may bias morphological estimates of the evolution of galaxy merger rate. To understand the magnitude of this bias, we explore the effect of gas fraction on the morphologies of a series of simulated disc galaxy mergers. With the resulting g-band images, we determine how the time-scale for identifying major and minor galaxy mergers via close projected pairs and quantitative morphology (the Gini coefficient G, the second-order moment of the brightest 20% of the light M20, and asymmetry A) depends on baryonic gas fraction f(gas). Strong asymmetries last significantly longer in high gas-fraction mergers of all mass ratios, with time-scales ranging from >= 300 Myr for f(gas) ~ 20% to >= 1 Gyr for f(gas) ~ 50%. Therefore the strong evolution with redshift observed in the fraction of asymmetric galaxies may reflect evolution in the gas properties of galaxies rather than the global galaxy merger rate. On the other hand, the time-scale for identifying a galaxy merger via G-M20 is weakly dependent on gas-fraction (~ 200-400 Myr), consistent with the weak evolution observed for G-M20 mergers.Comment: 15 pages; resubmitted to MNRA

Lowest-energy structures of 13-atom binary clusters: Do icosahedral clusters exist in binary liquid alloys?

Although the existence of 13-atom icosahedral clusters in one-component close-packed undercooled liquids was predicted more than half a century ago by Frank, the existence of such icosahedral clusters is less clear in liquid alloys. We study the lowest-energy structures of 13-atom AxB13-x Lennard-Jones binary clusters using the modified space-fixed genetic algorithm and the artificial Lennard-Jones potential designed by Kob and Andersen. Curiously, the lowest-energy structures are non-icosahedral for almost all compositions. The role played by the icosahedral cluster in a binary glass is questionable.Comment: 10 pages, 3 figure (conference paper of LAM12) to be published in J. Non-Crystalline Solid

Micro-class mobility: social reproduction in four countries

In the sociological literature on social mobility, the long-standing convention has been to assume that intergenerational reproduction takes one of two forms, either a categorical form that has parents passing on a big-class position to their children, or a gradational form that has parents passing on their socioeconomic standing to their children. These conventional approaches ignore in their own ways the important role that occupations play in transferring advantage and disadvantage from one generation to the next. In log-linear analyses of nationally representative data from the United States, Sweden, Germany, and Japan, we show that (a) occupations are an important conduit for reproduction, (b) the most extreme rigidities in the mobility regime are only revealed when analyses are carried out at the detailed occupational level, and (c) much of what shows up as big-class reproduction in conventional mobility analyses is in fact occupational reproduction in disguise. Although the four countries studied here differ in the extent to which the occupational form has been institutionalized, we show that it is too prominent to ignore in any of these countries. Even in Japan, which has long been regarded as distinctively 'deoccupationalized,' we find evidence of extreme occupational rigidities. These results suggest that an occupational mechanism for reproduction may be a fundamental feature of all contemporary mobility regimes. [author's abstract

Cluster model of glass transition in simple liquids

On the basis of microscopic statistical mechanics of simple liquids the orientational interaction between clusters consisting of a particle and its nearest neighbors is estimated. It is shown that there are ranges of density and temperature where the interaction changes sign as a function of a radius of a cluster. The model of interacting cubic and icosahedral clusters is proposed and solved in mean-field replica symmetric approximation. It is shown that the glass order parameter grows smoothly upon cooling, the transition temperature being identified with the temperature of the replica symmetry breaking. It is shown that upon cooling a Lennard-Jones system, cubic clusters freeze first. The transition temperature for icosahedral clusters is about ten per cent lower. So the local structure of Lennard-Jones glass in the vicinity of glass transition should be most probably cubic.Comment: 4 pages, 3 figure

The Formation of High Redshift Submillimeter Galaxies

We describe a model for the formation of \zsim 2 Submillimeter Galaxies (SMGs) which simultaneously accounts for both average and bright SMGs while providing a reasonable match to their mean observed spectral energy distributions (SEDs). By coupling hydrodynamic simulations of galaxy mergers with the high resolution 3D polychromatic radiative transfer code Sunrise, we find that a mass sequence of merger models which use observational constraints as physical input naturally yield objects which exhibit black hole, bulge, and H2 gas masses similar to those observed in SMGs. The dominant drivers behind the 850 micron flux are the masses of the merging galaxies and the stellar birthcloud covering fraction. The most luminous (S850 ~ 15 mJy) sources are recovered by ~10^13 Msun 1:1 major mergers with a birthcloud covering fraction close to unity, whereas more average SMGs ~5-7 mJy) may be formed in lower mass halos ~5x10^12 Msun. These models demonstrate the need for high spatial resolution hydrodynamic and radiative transfer simulations in matching both the most luminous sources as well as the full SEDs of SMGs. While these models suggest a natural formation mechanism for SMGs, they do not attempt to match cosmological statistics of galaxy populations; future efforts along this line will help ascertain the robustness of these models.Comment: MNRAS Accepted; Revised version includes expanded discussion of simulated radio properties of SMG