Logarithmic growth dynamics in software networks

In a recent paper, Krapivsky and Redner (Phys. Rev. E, 71 (2005) 036118) proposed a new growing network model with new nodes being attached to a randomly selected node, as well to all ancestors of the target node. The model leads to a sparse graph with an average degree growing logarithmically with the system size. Here we present compeling evidence for software networks being the result of a similar class of growing dynamics. The predicted pattern of network growth, as well as the stationary in- and out-degree distributions are consistent with the model. Our results confirm the view of large-scale software topology being generated through duplication-rewiring mechanisms. Implications of these findings are outlined.Comment: 7 pages, 3 figures, published in Europhysics Letters (2005

Sustainable growth in complex networks

Based on the empirical analysis of the dependency network in 18 Java projects, we develop a novel model of network growth which considers both: an attachment mechanism and the addition of new nodes with a heterogeneous distribution of their initial degree, $k_0$. Empirically we find that the cumulative degree distributions of initial degrees and of the final network, follow power-law behaviors: $P(k_{0}) \propto k_{0}^{1-\alpha}$, and $P(k)\propto k^{1-\gamma}$, respectively. For the total number of links as a function of the network size, we find empirically $K(N)\propto N^{\beta}$, where $\beta$ is (at the beginning of the network evolution) between 1.25 and 2, while converging to $\sim 1$ for large $N$. This indicates a transition from a growth regime with increasing network density towards a sustainable regime, which revents a collapse because of ever increasing dependencies. Our theoretical framework is able to predict relations between the exponents $\alpha$, $\beta$, $\gamma$, which also link issues of software engineering and developer activity. These relations are verified by means of computer simulations and empirical investigations. They indicate that the growth of real Open Source Software networks occurs on the edge between two regimes, which are either dominated by the initial degree distribution of added nodes, or by the preferential attachment mechanism. Hence, the heterogeneous degree distribution of newly added nodes, found empirically, is essential to describe the laws of sustainable growth in networks.Comment: 5 pages, 2 figures, 1 tabl

Activity ageing in growing networks

We present a model for growing information networks where the ageing of a node depends on the time at which it entered the network and on the last time it was cited. The model is shown to undergo a transition from a small-world to large-world network. The degree distribution may exhibit very different shapes depending on the model parameters, e.g. delta-peaked, exponential or power-law tailed distributions.Comment: 9 pages, 2 figure

Sema as Zikr: The Language of the Whirling Dance

This paper explores the parallels found in the dance of the whirling dervishes and Rumi’s poetry. The dance, or sema, is a remembrance of God, zikr, which Rumi beautifully describes in his poetry. It is an honoring and mirroring of the revolutions, cycles, circles, centers, and turnings of life. This poetry in motion, done in the silence of the dervish, brings us to the sema, as a pronounced capacity topresence, because it is both poetry and thing. As poetry, it affords us to undergo an experience with language and the silence that bring us nearer to our center. There is much that is said in the sema even if nothing is spoken. What is said is heard in the silence cultivated by sema. The dance of the whirling dervishes is zikr, a remembrance of God.

Micro-eukaryotic diversity in hypolithons from Miers Valley, Antarctica

The discovery of extensive and complex hypolithic communities in both cold and hot deserts has raised many questions regarding their ecology, biodiversity and relevance in terms of regional productivity. However, most hypolithic research has focused on the bacterial elements of the community. This study represents the first investigation of micro-eukaryotic communities in all three hypolith types. Here we show that Antarctic hypoliths support extensive populations of novel uncharacterized bryophyta, fungi and protists and suggest that well known producer-decomposer-predator interactions may create the necessary conditions for hypolithic productivity in Antarctic deserts

Production of Two Pions Induced by Neutrinos

We study the threshold production of two pions induced by neutrinos in nucleon targets. The contribution of nucleon pole, pion and contact terms is calculated using a chiral Lagrangian. The contribution of the Roper resonance, neglected in earlier studies, has also been taken into account.Comment: Contribution to the proceedings of Chiral07, RCNP, Osaka, Japan. Corrected version because of problems on some pdf viewer

The role of interchange fees in two-sided markets: An empirical investigation on payment cards

We study the impact of reductions in interchange fees on payment card services. We find that consumer and merchant acceptance and transaction volumes increased when interchange fees were reduced. Our results suggest that a 10 percent reduction in the rate of decline per quarter in the average interchange fee by an acquirer resulted in a rate of increase in merchant acceptance per quarter of up to 1.4 percent. Additionally, a 10 percent increase in the rate of interaction of merchant acceptance and the total number of cards increased the rate of quarterly issuer transaction volumes up to 1.7 percent