Electromagnetic Dissociation and Space Radiation

Relativistic nucleus-nucleus reactions occur mainly through the Strong or Electromagnetic (EM) interactions. Transport codes often neglect the latter. This work shows the importance of including EM interactions for space radiation applications.Comment: 11 page

Nucleon emission via electromagnetic excitation in relativistic nucleus-nucleus collisions: Re-analysis of the Weizsacker-Williams method

Previous analyses of the comparison of Weizsacker-Williams (WW) theory to experiment for nucleon emission via electromagnetic (EM) excitations in nucleus-nucleus collisions were not definitive because of different assumptions concerning the value of the minimum impact parameter. This situation is corrected by providing criteria that allows definitive statements to be made concerning agreement or disagreement between WW theory and experiment

Electric quadrupole excitations in the interactions of Y-89 with relativistic nuclei

The first complete calculations of electric quadrupole excitations in relativistic nucleus-nucleus collisions are presented herein. Neutron emission from Y-89 is studied and quadrupole effects are found to be a significant fraction of the cross section

Investigations into a plankton population model: Mortality and its importance in climate change scenarios

The potential for marine plankton ecosystems to influence climate by the production of dimethylsulphide (DMS) has been an important topic of recent research into climate change. Several General Circulation Models, used to predict climate change, have or are being modified to include interactions of ecosystems with climate. Climate change necessitates that parameters within ecosystem models must change during long-term simulations, especially mortality parameters that increase as organisms are pushed toward the boundaries of their thermal tolerance. Changing mortality parameters can have profound influences on ecosystem model dynamics. There is therefore a pressing need to understand the influence of varying mortality parameters on the long-term behaviour of ecosystem models. This work examines the sensitivity of a model of DMS production by marine ecosystems to variations in three linear mortality coefficients. Significant differences in behaviour are observed, and we note the importance of these results in formulating ecosystem models for application in simulations of climate change

Electromagnetic interactions of cosmic rays with nuclei

Parameterizations of single nucleon emission from the electromagnetic interactions of cosmic rays with nuclei are presented. These parameterizations are based upon the most accurate theoretical calculations available today. When coupled with Strong interaction parameterizations, they should be very suitable for use in cosmic ray propagation through intersteller space, the Earth's atmosphere, lunar samples, meteorites and spacecraft walls

Simulating the impacts of climate change on ecosystems: the importance of mortality

Griffith Sciences, Griffith School of EnvironmentNo Full Tex

Variational problems with singular perturbation

In this paper, we construct the local minimum of a certain variational problem which we take in the form $\mathrm{inf}\int_\Omega\left\{\frac{\epsilon}{2}kg^2|\nabla w|^2+\frac{1}{4\epsilon}f^2g^4(1-w^2)^2\right\}\,\mathrm{d}x$, where $\epsilon$ is a small positive parameter and $\Omega\subset\mathbb{R}^n$ is a convex bounded domain with smooth boundary. Here $f,g,k\in C^3(\Omega)$ are strictly positive functions in the closure of the domain $\bar{\Omega}$. If we take the inf over all functions $H^1(\Omega)$, we obtain the (unique) positive solution of the partial differential equation with Neumann boundary conditions (respectively Dirichlet boundary conditions). We wish to restrict the inf to the local (not global) minimum so that we consider solutions of this Neumann problem which take both signs in $\Omega$ and which vanish on $(n-1)$ dimensional hypersurfaces $\Gamma_\epsilon\subset\Omega$. By using a $\Gamma$-convergence method, we find the structure of the limit solutions as $\epsilon\to0$ in terms of the weighted geodesics of the domain $\Omega$

Long-term coexistence for a competitive system of spatially varying gradient reaction-diffusion equations

Spatial distribution of interacting chemical or biological species is usually described by a system of reaction-diffusion equations. In this work we consider a system of two reaction diffusion equations with spatially varying diffusion coefficients which are different for different species and with forcing terms which are the gradient of a spatially varying potential. Such a system describes two competing biological species. We are interested in the possibility of long-term coexistence of the species in a bounded domain. Such long-term coexistence may be associated either with a periodic in time solution (usually associated with a Hopf bifurcation), or with time-independent solutions. We prove that no periodic solution exists for the system. We also consider some steady-states (the time-independent solutions) and examine their stability and bifurcations