Dynamics of two interacting particles in classical billiards

The problem of two interacting particles moving in a d-dimensional billiard is considered here. A suitable coordinate transformation leads to the problem of a particle in an unconventional hyperbilliard. A dynamical map can be readily constructed for this general system, which greatly simplifies calculations. As a particular example, we consider two identical particles interacting through a screened Coulomb potential in a one-dimensional billiard. We find that the screening plays an important role in the dynamical behavior of the system and only in the limit of vanishing screening length can the particles be considered as bouncing balls. For more general screening and energy values, the system presents strong non-integrability with resonant islands of stability.Comment: REVTEX manuscript, 4 figures (1 ps + 3 gif, Postscript versions available upon request). Also available at http://www.phy.ohiou.edu/~ulloa/ulloa.htm

Local governance under austerity : hybrid organisations and hybrid officers

Using the case of Cardiff, Wales, we argue that the hybridisation of local governance forms is exacerbated by the downscaling and offloading of austerity politics. Conceptualising hybridity as a process which operates across governmental scales, at the organisational and at the individual level helps understand the growing complexities of local governance under austerity and the tensions which arise in seeking to assemble locally appropriate ideas and practices. Conceptualising hybridity as practice, we consider how 'hybrid officers' at the frontline experience austerity, their situated agency, and the implications for higher levels of governance

Interaction-induced chaos in a two-electron quantum-dot system

A quasi-one-dimensional quantum dot containing two interacting electrons is analyzed in search of signatures of chaos. The two-electron energy spectrum is obtained by diagonalization of the Hamiltonian including the exact Coulomb interaction. We find that the level-spacing fluctuations follow closely a Wigner-Dyson distribution, which indicates the emergence of quantum signatures of chaos due to the Coulomb interaction in an otherwise non-chaotic system. In general, the Poincar\'e maps of a classical analog of this quantum mechanical problem can exhibit a mixed classical dynamics. However, for the range of energies involved in the present system, the dynamics is strongly chaotic, aside from small regular regions. The system we study models a realistic semiconductor nanostructure, with electronic parameters typical of gallium arsenide.Comment: 4 pages, 3ps figure

Probing Yukawian gravitational potential by numerical simulations. I. Changing N-body codes

In the weak field limit general relativity reduces, as is well known, to the Newtonian gravitation. Alternative theories of gravity, however, do not necessarily reduce to Newtonian gravitation; some of them, for example, reduce to Yukawa-like potentials instead of the Newtonian potential. Since the Newtonian gravitation is largely used to model with success the structures of the universe, such as for example galaxies and clusters of galaxies, a way to probe and constrain alternative theories, in the weak field limit, is to apply them to model the structures of the universe. In the present study, we consider how to probe Yukawa-like potentials using N-body numerical simulations.Comment: 17 pages, 11 figures. To appear in General Relativity and Gravitatio

Evolution of the Mass-Metallicity relations in passive and star-forming galaxies from SPH-cosmological simulations

We present results from SPH-cosmological simulations, including self-consistent modelling of SN feedback and chemical evolution, of galaxies belonging to two clusters and twelve groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star-forming activity, as parametrized by their sSFR, across a redshift range up to z=2. Its slope shows irrelevant evolution in the passive sample, being steeper in groups than in clusters. However, the sub-sample of high-mass passive galaxies only is characterized by a steep increase of the slope with redshift, from which it can be inferred that the bulk of the slope evolution of the ZM relation is driven by the more massive passive objects. (...ABRIDGED...) The ZM relation for the star-forming sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The star-forming galaxies make up a tight sequence in the SFR-M_* plane at high redshift, whose scatter increases with time alongside with the consolidation of the passive sequence. We also confirm the anti-correlation between sSFR and stellar mass, pointing at a key role of the former in determining the galaxy downsizing, as the most significant means of diagnostics of the star formation efficiency. Likewise, an anti-correlation between sSFR and metallicity can be established for the star-forming galaxies, while on the contrary more active galaxies in terms of simple SFR are also metal-richer. We discuss these results in terms of the mechanisms driving the evolution within the high- and low-mass regimes at different epochs: mergers, feedback-driven outflows and the intrinsic variation of the star formation efficiency.Comment: Emended list of author

A semiquantal approach to finite systems of interacting particles

A novel approach is suggested for the statistical description of quantum systems of interacting particles. The key point of this approach is that a typical eigenstate in the energy representation (shape of eigenstates, SE) has a well defined classical analog which can be easily obtained from the classical equations of motion. Therefore, the occupation numbers for single-particle states can be represented as a convolution of the classical SE with the quantum occupation number operator for non-interacting particles. The latter takes into account the wavefunctions symmetry and depends on the unperturbed energy spectrum only. As a result, the distribution of occupation numbers $n_s$ can be numerically found for a very large number of interacting particles. Using the model of interacting spins we demonstrate that this approach gives a correct description of $n_s$ even in a deep quantum region with few single-particle orbitals.Comment: 4 pages, 2 figure

Contracting for Social Cohesion: Can Local Area Agreements Make a Difference?

Summary. Under the Labour government, Local Strategic Partnerships (LSPs) in England were responsible for the delivery of Local Area Agreements (LAAs) – agreed targets between central and local government. This paper uses statistical techniques and local authority case studies to explore the impact of LAAs on LSPs’ efforts to promote social cohesion. The results suggest that LSPs with an LAA for social cohesion experienced a better rate of improvement in community cohesiveness than those without, and that tougher targets resulted in stronger improvement. The impact of changes in LSPs approaches to promoting social cohesion appears to be responsible for this finding

Probing Yukawian Gravitational Potential by Numerical Simulations. II. Elliptical Galaxies

Since the Newtonian gravitation is largely used to model with success the structures of the universe, such as galaxies and clusters of galaxies, for example, a way to probe and constrain alternative theories, in the weak field limit, is to apply them to model the structures of the universe. We then modified the well known Gadget-2 code to probe alternative theories of gravitation through galactic dynamics. In particular, we modified the Gadget-2 code to probe alternatives theories whose weak field limits have a Yukawa-like gravitational potential. As a first application of this modified Gadget-2 code we simulate the evolution of elliptical galaxies. These simulations show that galactic dynamics can be used to constrain the parameters associated with alternative theories of gravitation.Comment: 6 pages, 5 figures - To appear in General Relativity and Gravitatio

Effect of heuristics on serendipity in path-based storytelling with linked data

Path-based storytelling with Linked Data on the Web provides users the ability to discover concepts in an entertaining and educational way. Given a query context, many state-of-the-art pathfinding approaches aim at telling a story that coincides with the user's expectations by investigating paths over Linked Data on the Web. By taking into account serendipity in storytelling, we aim at improving and tailoring existing approaches towards better fitting user expectations so that users are able to discover interesting knowledge without feeling unsure or even lost in the story facts. To this end, we propose to optimize the link estimation between - and the selection of facts in a story by increasing the consistency and relevancy of links between facts through additional domain delineation and refinement steps. In order to address multiple aspects of serendipity, we propose and investigate combinations of weights and heuristics in paths forming the essential building blocks for each story. Our experimental findings with stories based on DBpedia indicate the improvements when applying the optimized algorithm