A new method to find the potential center of N-body systems

We present a new and fast method to nd the potential center of an N-body distribution. The method uses an iterative algorithm which exploits the fact that the gradient of the potential is null at its center: it uses a smoothing radius to avoid getting trapped in secondary minima. We have tested this method on several random realizations of King models (in which the numerical computation of this center is rather dicult, due to the constant density within their cores), and com- pared its performance and accuracy against a more straightforward, but computer intensive method, based on cartesian meshes of increasing spatial resolution. In all cases, both methods converged to the same center, within the mesh resolution, but the new method is two orders of magnitude faster. We have also tested the method with one astronomical problem: the evolu- tion of a 105 particle King model orbiting around a xed potential that represents our Galaxy. We used a spherical harmonics expansion N-body code, in which the potential center determination is crucial for the correct force computation. We compared this simulation with another one in which a method previously used to determine the expansion center is employed (White 1983). Our routine gives better results in energy conservation and mass loss.Fil: Aguilar, L. A.. Universidad Nacional Autonoma de Mexico. Instituto de Astronomia; MéxicoFil: Cruz, F.. Universidad Nacional Autonoma de Mexico. Instituto de Astronomia; MéxicoFil: Carpintero, Daniel Diego. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

Challenging the status quo: women's experiences of opting for a home birth in Andalucia, Spain

Objective To explore the perceptions, beliefs and attitudes of women who opted for a home birth in Andalusia (Spain). Background Home birth is currently an unusual choice among Spanish women. It is not an option covered by the Spanish National Health Service and women who opt for a home birth have to pay for an independent midwife. Design A qualitative study with a phenomenological approach was adopted. All participants who took part in this study had chosen to have a home birth and given written consent to take part in the study. Methods Data collection was conducted in 2015–16. Face-to-face, semi-structured interviews were undertaken with women who chose a home birth in the last 5 years. Findings The sample consisted of thirteen women. Seven themes were created through analysis: 1. Getting informed about home birth; 2. Home birth as a choice, despite feeling unsupported; 3. The best way to have a personalized and a physiological birth; 4. Seeking a healing and empowering experience 5. The need for emotional safety, establishing a relationship and trusting the midwife; 6. Preparing for birth and working on fears; 7. Inequality of access (because of financial implications). Conclusions Women opted to plan birth at home because they wanted a personalised birth and control over their decision-making in labour, which they felt would not have been afforded to them in hospital settings. Andalusian maternity care leaders should strive to ensure that all pregnant women receive respectful and high-quality personalised care, by appropriately trained staff, both in the hospital and in the community

Measure of the size of CP violation in extended models

In this letter we introduce a possible measure of the size of CP violation in the Standard Model and its extensions, based on quantities invariant under the change of weak quark basis. We also introduce a measure of the ``average size'' of CP violation in a model, which can be used to compare the size of CP violation in models involving extra sequential or vector-like quarks, or left-right symmetry.Comment: LaTeX, 7 pages, no figure

A new method to find the potential center of <i>N</i>-body systems

We present a new and fast method to nd the potential center of an N-body distribution. The method uses an iterative algorithm which exploits the fact that the gradient of the potential is null at its center: it uses a smoothing radius to avoid getting trapped in secondary minima. We have tested this method on several random realizations of King models (in which the numerical computation of this center is rather dicult, due to the constant density within their cores), and compared its performance and accuracy against a more straightforward, but computer intensive method, based on cartesian meshes of increasing spatial resolution. In all cases, both methods converged to the same center, within the mesh resolution, but the new method is two orders of magnitude faster. We have also tested the method with one astronomical problem: the evolution of a 105 particle King model orbiting around a xed potential that represents our Galaxy. We used a spherical harmonics expansion N-body code, in which the potential center determination is crucial for the correct force computation. We compared this simulation with another one in which a method previously used to determine the expansion center is employed (White 1983). Our routine gives better results in energy conservation and mass loss.Se presenta un método rápido para encontrar el centro del potencial de una distribución de N-cuerpos. El método usa un algoritmo iterativo que aprovecha el hecho de que el gradiente del potencial es nulo en su centro; emplea asimismo un radio de suavizado para evitar quedar atrapado en mínimos locales. Se ha probado el método con modelos de King (cuyos núcleos, de densidad relativamente constante, hacen particularmente difícil la determinación numérica de este centro), y se ha comparado su eficiencia y precisión con un método más directo, aunque de cálculo intensivo, basado en mallas cartesianas de resolución espacial creciente. En todos los casos, ambos métodos convergen al mismo centro dentro de la resolución de la malla, aunque el método iterativo es dos órdenes de magnitud más rápido. Utilizamos este método en un problema astronómico: la evolución de un modelo de King de 105 partículas, en órbita alrededor de un potencial fijo representativo de nuestra Galaxia. Se utilizó un código de N-cuerpos con expansión en armónicos esféricos, en el que la determinación del centro del potencial es esencial para un cálculo correcto de las fuerzas. Se comparó esta simulación con el mismo código pero con un método empleado anteriormente para determinar el centro de expansión (White 1983). Con nuestra rutina se obtienen mejores resultados en la conservación de energía y de la masa.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

A new method to find the potential center of <i>N</i>-body systems

We present a new and fast method to nd the potential center of an N-body distribution. The method uses an iterative algorithm which exploits the fact that the gradient of the potential is null at its center: it uses a smoothing radius to avoid getting trapped in secondary minima. We have tested this method on several random realizations of King models (in which the numerical computation of this center is rather dicult, due to the constant density within their cores), and compared its performance and accuracy against a more straightforward, but computer intensive method, based on cartesian meshes of increasing spatial resolution. In all cases, both methods converged to the same center, within the mesh resolution, but the new method is two orders of magnitude faster. We have also tested the method with one astronomical problem: the evolution of a 105 particle King model orbiting around a xed potential that represents our Galaxy. We used a spherical harmonics expansion N-body code, in which the potential center determination is crucial for the correct force computation. We compared this simulation with another one in which a method previously used to determine the expansion center is employed (White 1983). Our routine gives better results in energy conservation and mass loss.Se presenta un método rápido para encontrar el centro del potencial de una distribución de N-cuerpos. El método usa un algoritmo iterativo que aprovecha el hecho de que el gradiente del potencial es nulo en su centro; emplea asimismo un radio de suavizado para evitar quedar atrapado en mínimos locales. Se ha probado el método con modelos de King (cuyos núcleos, de densidad relativamente constante, hacen particularmente difícil la determinación numérica de este centro), y se ha comparado su eficiencia y precisión con un método más directo, aunque de cálculo intensivo, basado en mallas cartesianas de resolución espacial creciente. En todos los casos, ambos métodos convergen al mismo centro dentro de la resolución de la malla, aunque el método iterativo es dos órdenes de magnitud más rápido. Utilizamos este método en un problema astronómico: la evolución de un modelo de King de 105 partículas, en órbita alrededor de un potencial fijo representativo de nuestra Galaxia. Se utilizó un código de N-cuerpos con expansión en armónicos esféricos, en el que la determinación del centro del potencial es esencial para un cálculo correcto de las fuerzas. Se comparó esta simulación con el mismo código pero con un método empleado anteriormente para determinar el centro de expansión (White 1983). Con nuestra rutina se obtienen mejores resultados en la conservación de energía y de la masa.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

A new method to find the potential center of <i>N</i>-body systems

We present a new and fast method to nd the potential center of an N-body distribution. The method uses an iterative algorithm which exploits the fact that the gradient of the potential is null at its center: it uses a smoothing radius to avoid getting trapped in secondary minima. We have tested this method on several random realizations of King models (in which the numerical computation of this center is rather dicult, due to the constant density within their cores), and compared its performance and accuracy against a more straightforward, but computer intensive method, based on cartesian meshes of increasing spatial resolution. In all cases, both methods converged to the same center, within the mesh resolution, but the new method is two orders of magnitude faster. We have also tested the method with one astronomical problem: the evolution of a 105 particle King model orbiting around a xed potential that represents our Galaxy. We used a spherical harmonics expansion N-body code, in which the potential center determination is crucial for the correct force computation. We compared this simulation with another one in which a method previously used to determine the expansion center is employed (White 1983). Our routine gives better results in energy conservation and mass loss.Se presenta un método rápido para encontrar el centro del potencial de una distribución de N-cuerpos. El método usa un algoritmo iterativo que aprovecha el hecho de que el gradiente del potencial es nulo en su centro; emplea asimismo un radio de suavizado para evitar quedar atrapado en mínimos locales. Se ha probado el método con modelos de King (cuyos núcleos, de densidad relativamente constante, hacen particularmente difícil la determinación numérica de este centro), y se ha comparado su eficiencia y precisión con un método más directo, aunque de cálculo intensivo, basado en mallas cartesianas de resolución espacial creciente. En todos los casos, ambos métodos convergen al mismo centro dentro de la resolución de la malla, aunque el método iterativo es dos órdenes de magnitud más rápido. Utilizamos este método en un problema astronómico: la evolución de un modelo de King de 105 partículas, en órbita alrededor de un potencial fijo representativo de nuestra Galaxia. Se utilizó un código de N-cuerpos con expansión en armónicos esféricos, en el que la determinación del centro del potencial es esencial para un cálculo correcto de las fuerzas. Se comparó esta simulación con el mismo código pero con un método empleado anteriormente para determinar el centro de expansión (White 1983). Con nuestra rutina se obtienen mejores resultados en la conservación de energía y de la masa.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Complex Scaled Spectrum Completeness for Coupled Channels

The Complex Scaling Method (CSM) provides scattering wave functions which regularize resonances and suggest a resolution of the identity in terms of such resonances, completed by the bound states and a smoothed continuum. But, in the case of inelastic scattering with many channels, the existence of such a resolution under complex scaling is still debated. Taking advantage of results obtained earlier for the two channel case, this paper proposes a representation in which the convergence of a resolution of the identity can be more easily tested. The representation is valid for any finite number of coupled channels for inelastic scattering without rearrangement.Comment: Latex file, 13 pages, 4 eps-figure

Cerenkov angle and charge reconstruction with the RICH detector of the AMS experiment

The Alpha Magnetic Spectrometer (AMS) experiment to be installed on the International Space Station (ISS) will be equipped with a proximity focusing Ring Imaging Cerenkov (RICH) detector, for measurements of particle electric charge and velocity. In this note, two possible methods for reconstructing the Cerenkov angle and the electric charge with the RICH, are discussed. A Likelihood method for the Cerenkov angle reconstruction was applied leading to a velocity determination for protons with a resolution of around 0.1%. The existence of a large fraction of background photons which can vary from event to event, implied a charge reconstruction method based on an overall efficiency estimation on an event-by-event basis.Comment: Proceedings submitted to RICH 2002 (Pylos-Greece