Effects of epidemic threshold definition on disease spread statistics

We study the statistical properties of the SIR epidemics in heterogeneous networks, when an epidemic is defined as only those SIR propagations that reach or exceed a minimum size s_c. Using percolation theory to calculate the average fractional size of an epidemic, we find that the strength of the spanning link percolation cluster $P_{\infty}$ is an upper bound to . For small values of s_c, $P_{\infty}$ is no longer a good approximation, and the average fractional size has to be computed directly. The value of s_c for which $P_{\infty}$ is a good approximation is found to depend on the transmissibility T of the SIR. We also study Q, the probability that an SIR propagation reaches the epidemic mass s_c, and find that it is well characterized by percolation theory. We apply our results to real networks (DIMES and Tracerouter) to measure the consequences of the choice s_c on predictions of average outcome sizes of computer failure epidemics.Comment: 12 pages, 8 figure

The Large Magellanic Cloud and the Distance Scale

The Magellanic Clouds, especially the Large Magellanic Cloud, are places where multiple distance indicators can be compared with each other in a straight-forward manner at considerable precision. We here review the distances derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing Binaries, and show that the results from these distance indicators generally agree to within their errors, and the distance modulus to the Large Magellanic Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science. From a presentation at the conference The Fundamental Cosmic Distance Scale: State of the Art and the Gaia Perspective, Naples, May 201

Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events

The $B^0$-$\bar B^0$ oscillation frequency has been measured with a sample of 23 million \B\bar B pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we select events in which both B mesons decay semileptonically and use the charge of the leptons to identify the flavor of each B meson. A simultaneous fit to the decay time difference distributions for opposite- and same-sign dilepton events gives $\Delta m_d = 0.493 \pm 0.012{(stat)}\pm 0.009{(syst)}$ ps$^{-1}$.Comment: 7 pages, 1 figure, submitted to Physical Review Letter

Allan Sandage and the Cosmic Expansion

This is an account of Allan Sandage's work on (1) The character of the expansion field. For many years he has been the strongest defender of an expanding Universe. He later explained the CMB dipole by a local velocity of 220 +/- 50 km/s toward the Virgo cluster and by a bulk motion of the Local supercluster (extending out to ~3500 km/s) of 450-500 km/s toward an apex at l=275, b=12. Allowing for these streaming velocities he found linear expansion to hold down to local scales (~300 km/s). (2) The calibration of the Hubble constant. Probing different methods he finally adopted - from Cepheid-calibrated SNe Ia and from independent RR Lyr-calibrated TRGBs - H_0 = 62.3 +/- 1.3 +/- 5.0 km/s/Mpc.Comment: 12 pages, 11 figures, 1 table, Submitted to Astrophysics and Space Science, Special Issue on the Fundamental Cosmic Distance Scale in the Gaia Er

Measurement of the CP-Violating Asymmetry Amplitude sin2β\beta

We present results on time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurements use a data sample of about 88 million Y(4S) --> B Bbar decays collected between 1999 and 2002 with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We study events in which one neutral B meson is fully reconstructed in a final state containing a charmonium meson and the other B meson is determined to be either a B0 or B0bar from its decay products. The amplitude of the CP-violating asymmetry, which in the Standard Model is proportional to sin2beta, is derived from the decay-time distributions in such events. We measure sin2beta = 0.741 +/- 0.067 (stat) +/- 0.033 (syst) and |lambda| = 0.948 +/- 0.051 (stat) +/- 0.017 (syst). The magnitude of lambda is consistent with unity, in agreement with the Standard Model expectation of no direct CP violation in these modes

Measurement of the electron energy spectrum and its moments in inclusive B -> Xe nu decays

We report a measurement of the inclusive electron energy spectrum for semileptonic decays of B mesons in a data sample of 52 million Y(4S)-->B(B) over bar decays collected with the BABAR detector at the PEP-II asymmetric-energy B-meson factory at SLAC. We determine the branching fraction, first, second, and third moments of the spectrum for lower cutoffs on the electron energy between 0.6 and 1.5 GeV. We measure the partial branching fraction to be B(B-->Xenu,E-e>0.6 GeV)=[10.36+/-0.06(stat.)+/-0.23(sys.)]%

Projectile focusing near the recoil-ion threshold

The post-collisional interactions in ion-atom ionization collisions are studied around the electron capture to the continuum (ECC) process. For this purpose, a suitable double differential cross section is introduced, involving the longitudinal recoil-ion momentum and the projectile transverse momentum transfer. Using the fact that the ECC process is closely related to the threshold in the longitudinal momentum distribution, we study this distribution as a function of the projectile scattering angle. Using the CDW-EIS approximation we theoretically find a focusing (defocusing) effect as we get closer to the distribution threshold for proton (antiproton) impact on He atoms. © 2007 IOP Publishing Ltd

Ionization of helium by fast and highly charged ions

We present CDW-EIS theoretical calculations for the projectile deflection in single ionization of Helium by heavy-ion impact as a function of ionized electron energies. These calculations account for the projectile-residual target ion interaction through a first order static potential and a second order polarization potential. The results are compared with recent experimental data by impact of 3.6 MeV/amu Au53+. A good agreement is found. © 2007 IOP Publishing Ltd