Manifold spirals, disc-halo interactions and the secular evolution in N-body models of barred galaxies

The manifold theory of barred-spiral structure provides a dynamical mechanism explaining how spiral arms beyond the ends of galactic bars can be supported by chaotic flows extending beyond the bar's co-rotation zone. We discuss its applicability to N-body simulations of secularly evolving barred galaxies. In these simulations, we observe consecutive `incidents' of spiral activity, leading to a time-varying disc morphology. Besides disc self-excitations, we provide evidence of a newly noted excitation mechanism related to the `off-centering' effect: particles ejected in elongated orbits at major incidents cause the disc center-of-mass to recoil and be set in a wobble-type orbit with respect to the halo center of mass. The time-dependent m=1 perturbation on the disc by the above mechanism correlates with the excitation of new incidents of non-axisymmetric activity beyond the bar. At every new excitation, the manifolds act as dynamical avenues attracting particles which are directed far from corotation along chaotic orbits. The fact that the manifolds evolve morphologically in time, due to varying non-axisymmetric perturbations, allows to reconcile manifolds with the presence of multiple patterns and frequencies in the disc. We find a time-oscillating pattern speed profile $\Omega_p(R)$ at distances R between the bar's corotation, at resonance with the succession of minima and maxima of the non-axisymmetric activity beyond the bar. Finally, we discuss disc thermalization, i.e., the evolution of the disc velocity dispersion profile and its connection with disc responsiveness to manifold spirals.Comment: 20 pages, 22 figures. Accepted for publication in MNRA

Charge Symmetry Breaking in 500 MeV Nucleon-Trinucleon Scattering

Elastic nucleon scattering from the 3He and 3H mirror nuclei is examined as a test of charge symmetry violation. The differential cross-sections are calculated at 500 MeV using a microsopic, momentum-space optical potential including the full coupling of two spin 1/2 particles and an exact treatment of the Coulomb force. The charge-symmetry-breaking effects investigated arise from a violation within the nuclear structure, from the p-nucleus Coulomb force, and from the mass-differences of the charge symmetric states. Measurements likely to reveal reliable information are noted.Comment: 5 page

Alimentación de cerdos con niveles altos de azúcar en dietas de lactancia en combinación con dietas de preiniciación.

Se realizaron dos ensayos en la fase de lactancia de cerdas, en las Estaciones Experimentales de Tibaitatá (2.640 m.s.n.m.) y Palmira (1.000 m.s.n.m.), con el objeto de determinar los niveles más adecuados de sustitución del maíz por azúcar y el sistema de manejo que produjera el mayor rendimiento en peso de hembras y lechones al final de una lactancia. Se utilizaron 2 dietas de lactancia (0 y 60 por ciento de azúcar y 16 por ciento de proteína), 3 dietas de preiniciación (10, 35 y 60 por ciento de azúcar con 18 por ciento de proteína) y 2 sistemas de alimentación de hembras (dentro y fuera del galpón) en un diseño de bloques al azar con arreglo factorial de 2 x 3 x 2, con un total de 60 hembras en Tibaitatá y 24 hembras en Palmira. Los niveles de azúcar de 35 y 60 por ciento en las dietas de preiniciación o al nivel del 60 por ciento en la dieta de la madre, produjeron pesos significativamente mayores al destete. La inclusión de azúcar en dietas de preiniciación y lactancia combinadas, aumentó la producción de cerdos por lactancia y hembra, y la eficiencia de utilización del alimento para producir un kilo de cerdo en el ensayo de Bogotá. En Palmira, no se hizo necesaria la inclusión de azúcar en la dieta de lactancia para obtener la máxima producción, bastando el nivel del 60 por ciento en la dieta de preiniciación. No parece recomendable económicamente la inclusión del 60 por ciento de azúcar en la dieta de lactancia, debido a la mayor cantidad de suplemento protéico requerido para complementar la dieta y al mayor consumo de alimento por las hembras. En las dietas de preiniciación, con el nivel del 35 por ciento se obtuvieron resultados similares al nivel del 60 por ciento, para dietas con 18 por ciento de proteína.PorciculturaMaestría en CienciasMaestrí

Atomic Properties of Lu+^+

Singly ionised Lutetium has recently been suggested as a potential clock candidate. Here we report a joint experimental and theoretical investigation of \ce{Lu^+}. Measurements relevant to practical clock operation are made and compared to atomic structure calculations. Calculations of scalar and tensor polarizabilities for clock states over a range of wavelengths are also given. These results will be useful for future work with this clock candidate.Comment: 12 pages, 5 figure

Accessibility to health care facilities in Montreal Island: an application of relative accessibility indicators from the perspective of senior and non-senior residents

<p>Abstract</p> <p>Background</p> <p>Geographical access to health care facilities is known to influence health services usage. As societies age, accessibility to health care becomes an increasingly acute public health concern. It is known that seniors tend to have lower mobility levels, and it is possible that this may negatively affect their ability to reach facilities and services. Therefore, it becomes important to examine the mobility situation of seniors vis-a-vis the spatial distribution of health care facilities, to identify areas where accessibility is low and interventions may be required.</p> <p>Methods</p> <p>Accessibility is implemented using a cumulative opportunities measure. Instead of assuming a fixed bandwidth (i.e. a distance threshold) for measuring accessibility, in this paper the bandwidth is defined using model-based estimates of average trip length. Average trip length is an all-purpose indicator of individual mobility and geographical reach. Adoption of a spatial modelling approach allows us to tailor these estimates of travel behaviour to specific locations and person profiles. Replacing a fixed bandwidth with these estimates permits us to calculate customized location- and person-based accessibility measures that allow inter-personal as well as geographical comparisons.</p> <p>Data</p> <p>The case study is Montreal Island. Geo-coded travel behaviour data, specifically average trip length, and relevant traveller's attributes are obtained from the Montreal Household Travel Survey. These data are complemented with information from the Census. Health care facilities, also geo-coded, are extracted from a comprehensive business point database. Health care facilities are selected based on Standard Industrial Classification codes 8011-21 (Medical Doctors and Dentists).</p> <p>Results</p> <p>Model-based estimates of average trip length show that travel behaviour varies widely across space. With the exception of seniors in the downtown area, older residents of Montreal Island tend to be significantly less mobile than people of other age cohorts. The combination of average trip length estimates with the spatial distribution of health care facilities indicates that despite being more mobile, suburban residents tend to have lower levels of accessibility compared to central city residents. The effect is more marked for seniors. Furthermore, the results indicate that accessibility calculated using a fixed bandwidth would produce patterns of exposure to health care facilities that would be difficult to achieve for suburban seniors given actual mobility patterns.</p> <p>Conclusions</p> <p>The analysis shows large disparities in accessibility between seniors and non-seniors, between urban and suburban seniors, and between vehicle owning and non-owning seniors. This research was concerned with potential accessibility levels. Follow up research could consider the results reported here to select case studies of actual access and usage of health care facilities, and related health outcomes.</p