On the rms-radius of the proton

We study the world data on elastic electron-proton scattering in order to determine the proton charge rms-radius. After accounting for the Coulomb distortion and using a parameterization that allows to deal properly with the higher moments we find a radius of 0.895+-0.018 fm, which is significantly larger than the radii used in the past.Comment: 9 pages, 2 figures, submitted to Phys.Lett.

Planetary embryos and planetesimals residing in thin debris disks

We consider constraints on the planetesimal population residing in the disks of AU Microscopii, Beta Pictoris and Fomalhaut taking into account their observed thicknesses and normal disk opacities. We estimate that bodies of radius 5, 180 and 70 km are responsible for initiating the collisional cascade accounting for the dust production for AU-Mic, Beta-Pic and Fomalhaut's disks, respectively, at break radii from the star where their surface brightness profiles change slope. Larger bodies, of radius 1000km and with surface density of order 0.01 g/cm^2, are required to explain the thickness of these disks assuming that they are heated by gravitational stirring. A comparison between the densities of the two sizes suggests the size distribution in the largest bodies is flatter than that observed in the Kuiper belt. AU Mic's disk requires the shallowest size distribution for bodies with radius greater than 10km suggesting that the disk contains planetary embryos experiencing a stage of runaway growth.Comment: submitted to MNRA

Post-yield characterisation of metals with significant pile-up through spherical indentations

Finite element simulations of spherical indentations accounting for frictional contact provide validated load–indentation output for assessing and improving existing methods used to determine the stress–strain curve of materials with significant pile-up. The importance of friction to the proper assessment of the pile-up effect is established. Weaknesses in current characterisation relations and procedures are also identified. Existing correction formulae accounting for pile-up are modified so that the contact area radius is more accurately determined. This modification is implemented in the context of a characterisation process that relies on analysing unloading portions of load–indentation curves. Post-yield material behaviour predictions from such analysis are found to be in very good agreement with the initial finite element material input

Second-order matter perturbations in a LambdaCDM cosmology and non-Gaussianity

We obtain exact expressions for the effect of primordial non-Gaussianity on the matter density perturbation up to second order in a LambdaCDM cosmology, fully accounting for the general relativistic corrections arising on scales comparable with the Hubble radius. We present our results both in the Poisson gauge and in the comoving and synchronous gauge, which are relevant for comparison to different cosmological observables.Comment: 15 pages. LaTeX file. Invited article for CQG issue on non-linear cosmolog

Electrostatics of Vortices in Type II Superconductors

In a type II superconductor the gap variation in the core of a vortex line induces a local charge modulation. Accounting for metallic screening, we determine the line charge of individual vortices and calculate the electric field distribution in the half space above a field penetrated superconductor. The resulting field is that of an atomic size dipole ${\bf d} \sim e a_{{\rm B}} {\bf {\hat z}}$, $a_{{\rm B}} = \hbar^2/m e^2$ is the Bohr radius, acting on a force microscope in the pico to femto Newton range.Comment: 9 pages, late

The Cosmology of Massless String Modes

We consider the spacetime dynamics of a gas of closed strings in the context of General Relativity in a background of arbitrary spatial dimensions. Our motivation is primarily late time String Gas Cosmology, where such a spacetime picture has to emerge after the dilaton has stabilized. We find that after accounting for the thermodynamics of a gas of strings, only string modes which are massless at the self-dual radius are relevant, and that they lead to a dynamics which is qualitatively different from that induced by the modes usually considered in the literature. In the context of an ansatz with three large spatial dimensions and an arbitrary number of small extra dimensions, we obtain isotropic stabilization of these extra dimensions at the self-dual radius. This stabilization occurs for fixed dilaton, and is induced by the special string states we focus on. The three large dimensions undergo a regular Friedmann-Robertson-Walker expansion. We also show that this framework for late-time cosmology is consistent with observational bounds.Comment: 15 pages, no figures, references added (again