The Invincible (1758) site: an integrated geophysical assessment

Chirp sub-bottom profiler and repeat sidescan sonar imaging of the Invincible wreck site (1758) in the Solent (U.K.), interpretation, and implications for management of the site

A Symplectic Integrator for Hill's Equations

Hill's equations are an approximation that is useful in a number of areas of astrophysics including planetary rings and planetesimal disks. We derive a symplectic method for integrating Hill's equations based on a generalized leapfrog. This method is implemented in the parallel N-body code, PKDGRAV and tested on some simple orbits. The method demonstrates a lack of secular changes in orbital elements, making it a very useful technique for integrating Hill's equations over many dynamical times. Furthermore, the method allows for efficient collision searching using linear extrapolation of particle positions.Comment: 15 pages, 2 figures; minor revisions; accepted for publication in the Astronomical Journa

Teacher Sense-making and Policy Implementation: A Qualitative Case Study of a School District's Reading Initiative in Science

In response to No Child Left Behind federal legislation and Maryland's Bridge to Excellence Act, a school district created a strategic plan that included a program initiative for improving reading in secondary schools. The initiative involved the implementation of Reading Apprenticeship, a program that required content teachers to infuse reading instruction into their practice by modeling reading behaviors and utilizing tools designed to promote metacognitive conversations with their students. This qualitative case study used a cognitive perspective to explore the sense-making of a team of middle school science teachers who received training and sought to implement the program in their instructional practice during the 2004-2005 school year. The findings revealed that policy implementation varied for the different members of the team and was adversely affect by other policies and resistance by students. At the same time, policy implementation was enhanced by teacher participation in the communities of practice associated with the initiative. Implications from the study advocate that school districts actively engage in sense-giving activities and support the communities of practice that are established when new policy measures are introduced. The study calls for further research on how students respond to policy initiatives and how they shape their teachers' sense-making. This study contributed to the sparse body of literature in this new field of education policy implementation research

The (In)Stability of Planetary Systems

We present results of numerical simulations which examine the dynamical stability of known planetary systems, a star with two or more planets. First we vary the initial conditions of each system based on observational data. We then determine regions of phase space which produce stable planetary configurations. For each system we perform 1000 ~1 million year integrations. We examine upsilon And, HD83443, GJ876, HD82943, 47UMa, HD168443, and the solar system (SS). We find that the resonant systems, 2 planets in a first order mean motion resonance, (HD82943 and GJ876) have very narrow zones of stability. The interacting systems, not in first order resonance, but able to perturb each other (upsilon And, 47UMa, and SS) have broad regions of stability. The separated systems, 2 planets beyond 10:1 resonance, (we only examine HD83443 and HD168443) are fully stable. Furthermore we find that the best fits to the interacting and resonant systems place them very close to unstable regions. The boundary in phase space between stability and instability depends strongly on the eccentricities, and (if applicable) the proximity of the system to perfect resonance. In addition to million year integrations, we also examined stability on ~100 million year timescales. For each system we ran ~10 long term simulations, and find that the Keplerian fits to these systems all contain configurations which may be regular on this timescale.Comment: 37 pages, 49 figures, 13 tables, submitted to Ap

Wreck Sites as Systems Disrupted by Trawling

This chapter examines the effects of bottom trawling on shipwreck sites, conceptualising them as process-response systems that achieve a quasi-equilibrium state over time. Disruptions to this state by bottom-contact fishing gear are analysed through examples from recent geophysical surveys in the Irish, Baltic, and North Seas. The study highlights the capabilities and limitations of modern geophysical methods in detecting changes at underwater archaeological sites caused by bottom trawling. Specifically, it addresses the challenges of identifying evidence of disturbance on dynamic seabeds and suggests that detailed analysis of wreck distribution might provide indirect proxies of structural damage due to trawling activities. Furthermore, it emphasises the potential of these disturbances to mobilise hazardous materials, such as unexploded ordnance and fuel from modern shipwrecks, posing an added environmental risk. Acknowledging existing knowledge gaps in the understanding of trawling impacts on underwater cultural heritage and the marine environment, the authors call for more case study research

N-Body Simulations of Growth from 1 km Planetesimals at 0.4 AU

We present N-body simulations of planetary accretion beginning with 1 km radius planetesimals in orbit about a 1 solar mass star at 0.4 AU. The initial disk of planetesimals contains too many bodies for any current N-body code to integrate; therefore, we model a sample patch of the disk. Although this greatly reduces the number of bodies, we still track in excess of 10^5 particles. We consider three initial velocity distributions and monitor the growth of the planetesimals. The masses of some particles increase by more than a factor of 100. Additionally, the escape speed of the largest particle grows considerably faster than the velocity dispersion of the particles, suggesting impending runaway growth, although no particle grows large enough to detach itself from the power law size-frequency distribution. These results are in general agreement with previous statistical and analytical results. We compute rotation rates by assuming conservation of angular momentum around the center of mass at impact and that merged planetesimals relax to spherical shapes. At the end of our simulations, the majority of bodies that have undergone at least one merger are rotating faster than the breakup frequency. This implies that the assumption of completely inelastic collisions (perfect accretion), which is made in most simulations of planetary growth at sizes 1 km and above, is inappropriate. Our simulations reveal that, subsequent to the number of particles in the patch having been decreased by mergers to half its initial value, the presence of larger bodies in neighboring regions of the disk may limit the validity of simulations employing the patch approximation.Comment: 19 pages, 32 figures, 5 tables, accepted to Icaru

Accurate Mental Maps as an Aspect of Local Ecological Knowledge (LEK): A Case Study from Lough Neagh, Northern Ireland

A mental map of the substrate of Lough Neagh, Northern Ireland, compiled from interviews with local fishermen, is compared with maps produced by science-based techniques. The comparison reveals that the mental map is highly accurate. This finding contrasts with the spatial distortion characteristic of the classic mental map. The accuracy of the Lough Neagh map is attributed to the fact that it is a compendium of the knowledge of several generations, rather than an individual perception. Individual distortions are filtered out, and accuracy is promoted by economic self-interest. High accuracy may be characteristic of the mental maps held by artisanal exploiters of natural resources