Delaminations in composite plates under impact loads

A method is presented for calculating the locations, shapes, and sizes of delaminations which occur in a fiber reinforced composite plate subjected to non-penetrating (low velocity) impact of a solid object. The plate may be simply supported, clamped, or free along its edges. A failure model of the delamination formation was developed. This model was then coupled with a finite element analysis. The model and the finite element analysis were then implemented by a computer code (IMPACT-ST) which can be used to estimate the damage initiation load and the locations, shapes, and sizes of the delaminations. Tests were performed measuring the geometries of the delaminations in graphite-epoxy, graphite-toughened epoxy, and graphite-PEEK plates impacted by a projectile with a spherical tip having masses ranging from 0.355 lbm to 0.963 lbm and velocities from 50 in/sec to 225 in/sec. The data were compared to the results of the model, and good agreements were found between the measured and the calculated delamination lengths and widths

Regression with strongly correlated data

This paper discusses linear regression of strongly correlated data that arises, for example, in magnetohydrodynamic equilibrium reconstructions. We have proved that, generically, the covariance matrix of the estimated regression parameters for fixed sample size goes to zero as the correlations become unity. That is, in this limit the estimated parameters are known with perfect accuracy. Simple examples are shown to illustrate this effect and the nature of the exceptional cases in which the estimate covariance does not go to zero

Delaminations in composite plates caused by non-penetrating impact

A model is presented for estimating the dimensions of delaminations in continuous fiber reinforced composite plates subjected to non-penetrating (low velocity) impact of a solid object. The model is based on dimensional analysis, and results in two simple, closed form expressions, one providing the delamination length, the other the delamination width. Comparisons of delamination lengths and widths calculated by these expressions with experimental data suggest that the model predicts these dimensions with reasonable accuracy

Graviton-photon conversion on spin 0 and 1/2 particles

The differential cross-sections for scattering of gravitons into photons on bosons and fermions are calculated in linearized quantum gravity. They are found to be strongly peaked in the forward direction and become constant at high energies. Numerically, they are very small as expected for such gravitational interactions.Comment: 13 pages, LaTeX with 5 figure

The impact of cattle drinking points on aquatic macroinvertebrates in streams in south-east Ireland

peer-reviewedTeagasc PublicationMeasures that prevent cattle access to watercourses are commonly implemented through agri-environment schemes, in an effort to address the objectives of the Water Framework Directive. Despite the widespread implementation, few studies have assessed the impact of cattle access to streams on aquatic macroinvertebrates. This study assessed the local-scale impact of cattle drinking points on water quality parameters (i.e. macroinvertebrate and water chemistry metrics) on 39 intensively-managed grassland farms in the south-east of Ireland. The results indicate that sites that were more than or equal to good quality upstream of cattle drinking points, were more susceptible to cattle access impacts than sites where upstream water quality was less than good. The European Court of Auditors (2011) recommended that there should be a higher rate of EU contribution for measures with higher environmental potential, in this instance, for cattle exclusion measures targeted to sites where background quality is more than or equal to good. Appropriate efforts should thus be made to incentivise farmers in good to high status sites to adopt cattle exclusion measures

Optimizing Pulsar Timing Arrays to Maximize Gravitational Wave Single Source Detection: a First Cut

Pulsar Timing Arrays (PTAs) use high accuracy timing of a collection of low timing noise pulsars to search for gravitational waves in the microhertz to nanohertz frequency band. The sensitivity of such a PTA depends on (a) the direction of the gravitational wave source, (b) the timing accuracy of the pulsars in the array and (c) how the available observing time is allocated among those pulsars. Here, we present a simple way to calculate the sensitivity of the PTA as a function of direction of a single GW source, based only on the location and root-mean-square residual of the pulsars in the array. We use this calculation to suggest future strategies for the current North American Nanohertz Observatory for Gravitational Waves (NANOGrav) PTA in its goal of detecting single GW sources. We also investigate the affects of an additional pulsar on the array sensitivity, with the goal of suggesting where PTA pulsar searches might be best directed. We demonstrate that, in the case of single GW sources, if we are interested in maximizing the volume of space to which PTAs are sensitive, there exists a slight advantage to finding a new pulsar near where the array is already most sensitive. Further, the study suggests that more observing time should be dedicated to the already low noise pulsars in order to have the greatest positive effect on the PTA sensitivity. We have made a web-based sensitivity mapping tool available at http://gwastro.psu.edu/ptasm.Comment: 14 pages, 3 figures, accepted by Ap

Binary inspiral, gravitational radiation, and cosmology

Observations of binary inspiral in a single interferometric gravitational wave detector can be cataloged according to signal-to-noise ratio $\rho$ and chirp mass $\cal M$. The distribution of events in a catalog composed of observations with $\rho$ greater than a threshold $\rho_0$ depends on the Hubble expansion, deceleration parameter, and cosmological constant, as well as the distribution of component masses in binary systems and evolutionary effects. In this paper I find general expressions, valid in any homogeneous and isotropic cosmological model, for the distribution with $\rho$ and $\cal M$ of cataloged events; I also evaluate these distributions explicitly for relevant matter-dominated Friedmann-Robertson-Walker models and simple models of the neutron star mass distribution. In matter dominated Friedmann-Robertson-Walker cosmological models advanced LIGO detectors will observe binary neutron star inspiral events with $\rho>8$ from distances not exceeding approximately $2\,\text{Gpc}$, corresponding to redshifts of $0.48$ (0.26) for $h=0.8$ ($0.5$), at an estimated rate of 1 per week. As the binary system mass increases so does the distance it can be seen, up to a limit: in a matter dominated Einstein-deSitter cosmological model with $h=0.8$ ($0.5$) that limit is approximately $z=2.7$ (1.7) for binaries consisting of two $10\,\text{M}_\odot$ black holes. Cosmological tests based on catalogs of the kind discussed here depend on the distribution of cataloged events with $\rho$ and $\cal M$. The distributions found here will play a pivotal role in testing cosmological models against our own universe and in constructing templates for the detection of cosmological inspiraling binary neutron stars and black holes.Comment: REVTeX, 38 pages, 9 (encapsulated) postscript figures, uses epsf.st

The Cosmological Constant and Advanced Gravitational Wave Detectors

Interferometric gravitational wave detectors could measure the frequency sweep of a binary inspiral [characterized by its chirp mass] to high accuracy. The observed chirp mass is the intrinsic chirp mass of the binary source multiplied by $(1+z)$, where $z$ is the redshift of the source. Assuming a non-zero cosmological constant, we compute the expected redshift distribution of observed events for an advanced LIGO detector. We find that the redshift distribution has a robust and sizable dependence on the cosmological constant; the data from advanced LIGO detectors could provide an independent measurement of the cosmological constant.Comment: 13 pages plus 5 figure, LaTeX. Revised and final version, to appear in Phys. Rev.

Higher order corrections to the Newtonian potential in the Randall-Sundrum model

The general formalism for calculating the Newtonian potential in fine-tuned or critical Randall-Sundrum braneworlds is outlined. It is based on using the full tensor structure of the graviton propagator. This approach avoids the brane-bending effect arising from calculating the potential for a point source. For a single brane, this gives a clear understanding of the disputed overall factor 4/3 entering the correction. The result can be written on a compact form which is evaluated to high accuracy for both short and large distances.Comment: 12 pages, LaTeX2e with RevTeX4, 3 postscript figures; Minor corrections, references update

Rotochemical Heating of Neutron Stars: Rigorous Formalism with Electrostatic Potential Perturbations

The electrostatic potential that keeps approximate charge neutrality in neutron star matter is self-consistently introduced into the formalism for rotochemical heating presented in a previous paper by Fernandez and Reisenegger. Although the new formalism is more rigorous, we show that its observable consequences are indistinguishable from those of the previous one, leaving the conclusions of the previous paper unchanged.Comment: 14 pages, including 4 eps figures. Accepted for publication in The Astrophysical Journa