Understanding the internet topology evolution dynamics

The internet structure is extremely complex. The Positive-Feedback Preference (PFP) model is a recently introduced internet topology generator. The model uses two generic algorithms to replicate the evolution dynamics observed on the internet historic data. The phenomenological model was originally designed to match only two topology properties of the internet, i.e. the rich-club connectivity and the exact form of degree distribution. Whereas numerical evaluation has shown that the PFP model accurately reproduces a large set of other nontrivial characteristics as well. This paper aims to investigate why and how this generative model captures so many diverse properties of the internet. Based on comprehensive simulation results, the paper presents a detailed analysis on the exact origin of each of the topology properties produced by the model. This work reveals how network evolution mechanisms control the obtained topology properties and it also provides insights on correlations between various structural characteristics of complex networks.Comment: 15 figure

Degree and connectivity of the Internet's scale-free topology

In this paper we theoretically and empirically study the degree and connectivity of the Internet's scale-free topology at the autonomous system (AS) level. The basic features of the scale-free network have influence on the normalization constant of the degree distribution p(k). We develop a mathematics model of the Internet's scale-free topology. On this model we theoretically get the formulas of the average degree, the ratios of the kmin-degree (minimum degree) nodes and the kmax-degree (maximum degree) nodes, the fraction of the degrees (or links) in the hands of the richer (top best-connected) nodes. We find the average degree is larger for smaller power-law exponent {\lambda} and larger minimum or maximum degree. The ratio of the kmin-degree nodes is larger for larger {\lambda} and smaller kmin or kmax. The ratio of the kmax-degree ones is larger for smaller {\lambda} and kmax or larger kmin. The richer nodes hold most of the total degrees of the AS-level Internet topology. In addition, we reveal the ratio of the kmin-degree nodes or the rate of the increase of the average degree has power-law decay with the increase of the kmin. The ratio of the kmax-degree nodes has power-law decay with the increase of the kmax, and the fraction of the degrees in the hands of the richer 27% nodes is about 73% (the '73/27 rule'). At last, we empirically calculate, based on empirical data extracted from BGP, the average degree and the ratio and fraction using our method and other methods, and find that our method is rigorous and effective for the AS-level Internet topology.Comment: 22 pages, 8 figure

Halophyte–Endophyte Interactions: Linking Microbiome Community Distribution and Functionality to Salinity

Many plants are unable to adapt to rapid environmental changes (e.g., salinity, drought, or limited nutrients) and may acquire assistance from microbes that have the capacity to increase tolerance of host-plants in stress conditions. By having the right microbes, the plants are more resilient! Such microbes include endophytes that inhabit inner tissues of the plant without causing symptoms of disease in their host. However, this plant–endophytic association exists only when chemical equilibrium is maintained between both, therefore making this mutualistic interaction even more unique. Therefore it is interesting to decode the endophytic community composition in halophytes specifically in the most salt-tolerant halophyte species Salicornia europaea, and further determine the factors that could affect this association. Moreover, understanding the endophytes potential plant growth-promoting activities in association with host (S. europaea) and non-host plant (non-halophytes) are the focus of this chapter

Measuring productivity and efficiency: a Kalman filter approach

In the Kalman filter setting, one can model the inefficiency term of the standard stochastic frontier composed error as an unobserved state. In this study a panel data version of the local level model is used for estimating time-varying efficiencies of firms. We apply the Kalman filter to estimate average efficiencies of U.S. airlines and find that the technical efficiency of these carriers did not improve during the period 1999-2009. During this period the industry incurred substantial losses, and the efficiency gains from reorganized networks, code-sharing arrangements, and other best business practices apparently had already been realized

Measurement of the t-channel single top quark production cross section

The D0 collaboration reports direct evidence for electroweak production of single top quarks through the t-channel exchange of a virtual W boson. This is the first analysis to isolate an individual single top quark production channel. We select events containing an isolated electron or muon, missing transverse energy, and two, three or four jets from 2.3 fb^-1 of ppbar collisions at the Fermilab Tevatron Collider. One or two of the jets are identified as containing a b hadron. We combine three multivariate techniques optimized for the t-channel process to measure the t- and s-channel cross sections simultaneously. We measure cross sections of 3.14 +0.94 -0.80 pb for the t-channel and 1.05 +-0.81 pb for the s-channel. The measured t-channel result is found to have a significance of 4.8 standard deviations and is consistent with the standard model prediction.Comment: 7 pages, 6 figure

Measurements of differential cross sections of Z/gamma*+jets+X events in proton anti-proton collisions at sqrt{s}=1.96 TeV

We present cross section measurements for Z/gamma*+jets+X production, differential in the transverse momenta of the three leading jets. The data sample was collected with the D0 detector at the Fermilab Tevatron proton anti-proton collider at a center-of-mass energy of 1.96 TeV and corresponds to an integrated luminosity of 1 fb-1. Leading and next-to-leading order perturbative QCD predictions are compared with the measurements, and agreement is found within the theoretical and experimental uncertainties. We also make comparisons with the predictions of four event generators. Two parton-shower-based generators show significant shape and normalization differences with respect to the data. In contrast, two generators combining tree-level matrix elements with a parton shower give a reasonable description of the the shapes observed in data, but the predicted normalizations show significant differences with respect to the data, reflecting large scale uncertainties. For specific choices of scales, the normalizations for either generator can be made to agree with the measurements.Comment: Published in PLB. 11 pages, 3 figure

Measurement of Leptonic Asymmetries and Top Quark Polarization in ttbar Production

We present measurements of lepton (l) angular distributions in ttbar -> W+ b W- b -> l+ nu b l- nubar bbar decays produced in ppbar collisions at a center-of-mass energy of sqrt(s)=1.96TeV, where l is an electron or muon. Using data corresponding to an integrated luminosity of 5.4fb^-1, collected with the D0 detector at the Fermilab Collider, we find that the angular distributions of l- relative to anti-protons and l+ relative to protons are in agreement with each other. Combining the two distributions and correcting for detector acceptance we obtain the forward-backward asymmetry A^l_FB = (5.8 +- 5.1(stat) +- 1.3(syst))%, compared to the standard model prediction of A^l_FB (predicted) = (4.7 +- 0.1)%. This result is further combined with the measurement based on the analysis of the l+jets final state to obtain A^l_FB = (11.8 +- 3.2)%. Furthermore, we present a first study of the top-quark polarization.Comment: submitted versio

Measurement of trilinear gauge boson couplings from WW + WZ to lnu jj events in pp-bar collisions at sqrt{s}=1.96 TeV

We present a direct measurement of trilinear gauge boson couplings at gammaWW and ZWW vertices in WW and WZ events produced in pp-bar collisions at sqrt{s}=1.96 TeV. We consider events with one electron or muon, missing transverse energy, and at least two jets. The data were collected using the D0 detector and correspond to 1.1/fb of integrated luminosity. Considering two different relations between the couplings at the gammaWW and ZWW vertices, we measure these couplings at 68% C.L. to be kappa_{gamma}=1.07^{+0.26}_{-0.29}, lambda =0.00^{+0.06}_{-0.06} and g_{1}^{Z}=1.04^{+0.09}_{-0.09} in a scenario respecting SU(2)_L x U(1)_Y gauge symmetry and kappa =1.04^{+0.11}_{-0.11} and lambda=0.00^{+0.06}_{-0.06} in an "equal couplings" scenario.Comment: 14 pages, 7 figures, published in Phys. Rev. D, updated to published versio

Measurement of the W boson mass

We present a measurement of the W boson mass in W -> ev decays using 1 fb^-1 of data collected with the D0 detector during Run II of the Fermilab Tevatron collider. With a sample of 499830 W -> ev candidate events, we measure M_W = 80.401 +- 0.043 GeV. This is the most precise measurement from a single experiment.Comment: As published in PR