Spot-like Structures of Neutron Star Surface Magnetic Fields

There is growing evidence, based on both X-ray and radio observations of isolated neutron stars, that besides the large--scale (dipolar) magnetic field, which determines the pulsar spin--down behaviour, small--scale poloidal field components are present, which have surface strengths one to two orders of magnitude larger than the dipolar component. We argue in this paper that the Hall--effect can be an efficient process in producing such small--scale field structures just above the neutron star surface. It is shown that due to a Hall--drift induced instability, poloidal magnetic field structures can be generated from strong subsurface toroidal fields, which are the result of either a dynamo or a thermoelectric instability acting at early times of a neutron star's life. The geometrical structure of these small--scale surface anomalies of the magnetic field resembles that of some types of ``star--spots''. The magnetic field strength and the length--scales are comparable with values that can be derived from various observations.Comment: 4 pages, 2 figures, accepted by Astronomy & Astrophysics Letters; language improved, 2nd para of Sect. 3 change

Spark Model for Pulsar Radiation Modulation Patterns

A non-stationary polar gap model first proposed by Ruderman & Sutherland (1975) is modified and applied to spark-associated pulsar emission at radio wave-lengths. It is argued that under physical and geometrical conditions prevailing above pulsar polar cap, highly non-stationary spark discharges do not occur at random positions. Instead, sparks should tend to operate in well determined preferred regions. At any instant the polar cap is populated as densely as possible with a number of two-dimensional sparks with a characteristic dimension as well as a typical distance between adjacent sparks being about the polar gap height. Our model differs, however, markedly from its original 'hollow cone' version. The key feature is the quasi-central spark driven by pair production process and anchored to the local pole of a sunspot-like surface magnetic field. This fixed spark prevents the motion of other sparks towards the pole, restricting it to slow circumferential drift across the planes of field lines converging at the local pole. We argue that the polar spark constitutes the core pulsar emission, and that the annular rings of drifting sparks contribute to conal components of the pulsar beam. We found that the number of nested cones in the beam of typical pulsar should not excced three; a number also found by Mitra & Deshpande (1999) using a completely different analysis.Comment: 31 pages, 8 figures, accepted by Ap

Recent software developments for special functions in the Santander–Amsterdam project

We give an overview of published algorithms by our group and of current activities and future plans. In particular, we give details on methods for computing special functions and discuss in detail two current lines of research. Firstly, we describe the recent developments for the computation of central and non-central ÷-square cumulative distributions (also called Marcum Q.functions), and we present a new quadrature method for computing them. Secondly, we describe the fourth-order methods for computing zeros of special functions recently developed, and we provide an explicit example for the computation of complex zeros of Bessel functions. We end with an overview of published software by our group for computing special functions

Unraveling the drift behaviour of the remarkable pulsar PSR B0826-34

We present new results from high sensitivity GMRT observations of PSR B0826-34. We provide a model to explain the observed subpulse drift properties of this pulsar, including the apparent reversals of the drift direction. In this model, PSR B0826-34 is close to being an aligned rotator. We solve for the emission geometry of this pulsar and show that the angle between the rotation and the magnetic axes is less than 5 deg. We see evidence for as many as 6 to 7 drifting bands in the main pulse at 318 MHz, which are part of a circulating system of about 15 spark-associated subpulse emission beams. We provide quantitative treatments of the aliasing problem and various effects of geometry. The observed drift rate is an aliased version of the true drift rate, such that a subpulse drifts to the location of the adjacent subpulse (or a multiple thereof) in about one pulsar period. We show that small variations, of the order of 3-8%, in the mean drift rate are then enough to explain the apparent reversals of drift direction. We find the mean circulation time of the drift pattern to be significantly longer than the predictions of the original RS75 model and propose an explanation for this, based on modified models with temperature regulated partial ion flow in the polar vacuum gap. From the variation of the mean subpulse separation across the main pulse window, we show that the spark pattern is not centred around the dipole axis, but around a point much closer (within a degree or so) to the rotation axis -- we discuss the implication of this.Comment: 23 pages (including 9 figure). Submitted to Astronomy and Astrophysics on November 11, 200

Internal inconsistency and risk aversion: Implications on smoking decisions

The main contribution of this paper is an analysis of the nature of the link between internal coherence and risk aversion. Both variables play an important role in individual decisions concerning risk behaviors. We compare the levels of internal consistency and risk aversion among smokers and non-smokers. To measure the individual internal coherence and risk aversion, we use a survey that includes lottery questions. Our results confirm that smokers are consistent in their decisions and they behave as risk averse. These results should be treated with circumspection as lottery questions are based on monetary expectations that depend on socio-economic conditions and they obviate other dimensions such as social recognition. La principal contribución de este artículo es analizar la naturaleza de la asociación entre la coherencia interna y la aversión al riesgo. Ambas variables juegan un papel principal en las decisiones individuales sobre comportamientos de riesgo, tal que como caso particular, comparamos los niveles consistencia interna y aversión al riesgo entre fumadores y no fumadores. Para medir la coherencia interna y la aversión al riesgo individual, recurrimos a una encuesta que incluye preguntas de loterías. Nuestros resultados confirman que los fumadores son consistentes en sus decisiones, y de hecho, se comportan como adversos al riesgo. Estos resultados hay que tomarlos con cautela, pues las preguntas sobre loterías se basan principalmente en expectativas monetarias que dependen de condiciones socio-económicas obviando otras dimensiones como el reconocimiento social

Exclusão e abandono em uma liga de futebol infantil e juvenil na Argentina

Resumen: Introducción: El fútbol infantil y juvenil es un fenómeno cultural y social de gran importancia en Argentina. Objetivo: Este trabajo tiene como objetivo dar cuenta de aspectos fundamentales de la estructura organizativa del fútbol infantil y juvenil en la liga de Mar del Plata, una de las ciudades más importantes del país. Métodos: El análisis de datos cuantitativos básicos permite dar cuenta de los aspectos fundamentales de la estructura organizativa del fútbol infantil y juvenil en esta liga. Este análisis elemental de cuantitativo se combina con una interpretación de informes basada tanto en un análisis discursivo como etnográfico. Resultados y discusión: Existe un severo proceso de exclusión y abandono en la liga de fútbol de Mar del Plata (LMF). No sólo ocurre que el número de jugadoras mujeres es extremadamente bajo en comparación con el número de jugadores varones, sino que también ocurre que más de mil varones son abandonados año tras año por la LMF. El complejo proceso de abandono y exclusión también está fuertemente ligado a una serie de fenómenos diversos, como el sexismo, la ausencia de personas con discapacidad, la imitación de prácticas de fútbol profesional y el uso de etiquetas y estereotipos. Conclusiones: Dado que promueve sistemáticamente la exclusión y el abandono, el LMF no puede cumplir una función educativa o inclusiva, y ni siquiera puede ayudar a formar jugadores profesionales de alto nivel. En su estado actual, la estructura organizativa de la LMF debería implementar algunas transformaciones radicales pero plausibles.Abstract: Introduction: Children’s and youth football is a cultural and social phenomenon of huge importance in Argentina. Aim: This work aims at accounting for fundamental aspects of the organizational structure of children’s and youth football in the league of Mar del Plata, one of the most important cities in the country. Methods: The analysis of basic quantitative data enables us to account for the fundamental aspects of the organizational structure of children’s and youth football in the league of Mar del Plata. This elementary quantitative analysis is combined with an interpretation of reports based both on a discursive and an ethnographic analysis. Results & discussion: There is a severe process of exclusion and abandonment in the Mar del Plata football league (MFL). Not only it is the case that the number of female players is extremely low compared to the number of male players, but it is also the case that more than a thousand male players are abandoned year after year by the MFL. The complex process of abandonment and exclusion is also strongly connected with a series of diverse phenomena, like sexism, the absence of people with disabilities, the imitation of professional football practices, and the use of labels and stereotypes. Conclusions: Since it systematically promotes exclusion and abandonment, the MFL cannot fulfill an educational or inclusive function, and cannot even help to form high-level professional players. In its current state, the organizational structure of the MFL should apply some radical but plausible transformations.Resumo: Introdução: O futebol infantil e juvenil é um fenômeno cultural e social de grande importância na Argentina. Objetivo: Este trabalho visa dar conta dos aspectos fundamentais da estrutura organizacional do futebol infanto-juvenil da liga de Mar del Plata, uma das cidades mais importantes do país. Métodos: A análise de dados quantitativos básicos permite dar conta dos aspectos fundamentais da estrutura organizacional do futebol infanto-juvenil desta liga. Esta análise quantitativa elementar é combinada com uma interpretação de relatórios com base na análise discursiva e etnográfica. Resultados e discussão: Há um severo processo de exclusão e abandono no campeonato de futebol de Mar del Plata (LMF). Não só o número de jogadoras femininas é extremamente baixo em comparação com o número de jogadores masculinos, mas também acontece que mais de mil jogadores masculinos são abandonados ano após ano pela LMF. O complexo processo de abandono e exclusão também está fortemente ligado a uma série de fenômenos diversos, como o sexismo, a ausência de pessoas com deficiência, a imitação de práticas profissionais do futebol e o uso de rótulos e estereótipos. Conclusões: Por promover sistematicamente a exclusão e o abandono, o LMF não pode cumprir uma função educativa ou inclusiva e nem mesmo pode ajudar na formação de jogadores profissionais de alto nível. Em seu estado atual, a estrutura organizacional do MFL deve aplicar algumas transformações radicais, mas plausíveis