Shapes of clusters and groups of galaxies: Comparison of model predictions with observations

We study the properties of the 3-dimensional and projected shapes of haloes using high resolution numerical simulations and observational data where the latter comes from the 2PIGG (Eke et al. 2004) and SDSS-DR3GC group catalogues (Merchan & Zandivarez 2005). We investigate the dependence of halo shape on characteristics such as mass and number of members. In the 3-dimensional case, we find a significant correlation between the mass and halo shape; massive systems are more prolate than small haloes. We detect a source of strong systematics in estimates of the triaxiality of a halo, which is found to be a strong function of the number of members; LCDM haloes usually characterised by triaxial shapes, slightly bent toward prolate forms, appear more oblate when taking only a small subset of the halo particles. The ellipticities of observed 2PIGG and SDSS-DR3GC groups are found to be strongly dependent on the number of group members, so that poor groups appear more elongated than rich ones. However, this is again an artifact caused by poor statistics and not an intrinsic property of the galaxy groups, nor an effect from observational biases. We interpret these results with the aid of a GALFORM mock 2PIGG catalogue. When comparing the group ellipticities in mock and real catalogues, we find an excellent agreement between the trends of shapes with number of group members. When carefully taking into account the effects of low number statistics, we find that more massive groups are consistent with more elongated shapes. Finally, our studies find no significant correlations between the shape of observed 2PIGG or SDSS-DR3GC groups with the properties of galaxy members such as colour or spectral type index.Comment: 9 pages, 10 figures, submitted to MNRA

Atomic Focusing by Quantum Fields: Entanglement Properties

The coherent manipulation of the atomic matter waves is of great interest both in science and technology. In order to study how an atom optic device alters the coherence of an atomic beam, we consider the quantum lens proposed by Averbukh et al [1] to show the discrete nature of the electromagnetic field. We extend the analysis of this quantum lens to the study of another essentially quantum property present in the focusing process, i.e., the atom-field entanglement, and show how the initial atomic coherence and purity are affected by the entanglement. The dynamics of this process is obtained in closed form. We calculate the beam quality factor and the trace of the square of the reduced density matrix as a function of the average photon number in order to analyze the coherence and purity of the atomic beam during the focusing process.Comment: 10 pages, 4 figure

Cod Year-class Variations and Abundance of Other Commercial Fish in NAFO Divisions 3NO

6 pages, 2 figures, 6 tables.Possible biological relationships of cod (Gadus morhua) with other important commercial fishes are explored. Cod year-class variations are compared with variations of yellowtail flounder and American plaice spawning biomass, mackerel age 1 + group abundance, and redfish densities. The adult fish biomass of these species are considered as an index of their egg and larval abundances. Possible competitive and predator-prey relationships between the 0-age groups and young individuals of cod and these species are examined through correlation analyses. No significant relationships between cod and redfish and yellowtail flounder were found. It seems that mackerel is a predator on cod larvae. A positive high correlation between spawning American plaice biomass and cod year-class strength was found. High American plaice spawning biomass may promote high cod recruitment through a predator-prey interaction. Alternatively, both species may respond similarly to an environmental signal.Peer reviewe

Cod in Div. 3N0I Year-Class Variations and the Abundance of Other Commercial Fish

9 páginas, 8 tablas.-- Scientific Council MeetingPeer reviewe

Cod Stock-Recruitment Relationship in NAFO Divisions 3NO

10 páginas, 5 figuras, 5 tablas.-- Scientific Council MeetingThe cod stock-recruitment relationships in NAFO Div. 3NO were studied by the basic Ricker model and modified Ricker model. Although the models do not adjust to the empirical data, inclusion of the American plaice spawning biomass improves the fit. Adding the mackerel adult biomass also improves the model. Including these two variables in the Ricker model explains almost all variation of the cod stock-recruitment relationship in the area. The confidence level of the parameters in the proposed equation were determined by the bootstrap technique, and its accuracy tested. Was realized a simulation study was performed. The response surfaces show the relations between the four variables studied.Peer reviewe

The non-self-adjointness of the radial momentum operator in n dimensions

The non self-adjointness of the radial momentum operator has been noted before by several authors, but the various proofs are incorrect. We give a rigorous proof that the $n$-dimensional radial momentum operator is not self- adjoint and has no self-adjoint extensions. The main idea of the proof is to show that this operator is unitarily equivalent to the momentum operator on $L^{2}[(0,\infty),dr]$ which is not self-adjoint and has no self-adjoint extensions.Comment: Some text and a reference adde

Dynamics of entanglement in quantum computers with imperfections

The dynamics of the pairwise entanglement in a qubit lattice in the presence of static imperfections exhibits different regimes. We show that there is a transition from a perturbative region, where the entanglement is stable against imperfections, to the ergodic regime, in which a pair of qubits becomes entangled with the rest of the lattice and the pairwise entanglement drops to zero. The transition is almost independent of the size of the quantum computer. We consider both the case of an initial maximally entangled and separable state. In this last case there is a broad crossover region in which the computer imperfections can be used to create a significant amount of pairwise entanglement.Comment: 4 pages, 4 figure