The many lives of magnetized neutron stars

The magnetic field strength at birth is arguably one of the most important properties to determine the evolutionary path of a neutron star. Objects with very high fields, collectively known as magnetars, are characterized by high X-ray quiescent luminosities, occurrence of outbursts, and, for some of them, sporadic giant flares. While the magnetic field strength is believed to drive their collective behaviour, however, the diversity of their properties, and, especially, the observation of magnetar-like bursts from “low-field” pulsars, has been a theoretical puzzle. In this review, we discuss results of long-term simulations following the coupled evolution of the X-ray luminosity and the timing properties for a large, homogeneous sample of X-ray emitting isolated neutron stars, accounting for a range of initial magnetic field strengths, envelope compositions, and neutron star masses. In addition, by following the evolution of magnetic stresses within the neutron star crust, we can also relate the observed magnetar phenomenology to the physical properties of neutron stars, and in particular to their age and magnetic field strength and topology. The dichotomy of “high-B” field pulsars versus magnetars is naturally explained, and occasional outbursts from old, low B-field neutron stars are predicted. We conclude by speculating on the fate of old magnetars, and by presenting observational diagnostics of the neutron star crustal field topology.

The X-ray outburst of the Galactic Centre magnetar SGR J1745−2900 during the first 1.5 year

In 2013 April a new magnetar, SGR 1745−2900, was discovered as it entered an outburst, at only 2.4 arcsec angular distance from the supermassive black hole at the centre of the Milky Way, Sagittarius A*. SGR 1745−2900 has a surface dipolar magnetic field of ∼2 × 1014 G, and it is the neutron star closest to a black hole ever observed. The new source was detected both in the radio and X-ray bands, with a peak X-ray luminosity LX ∼ 5 × 1035 erg s−1. Here we report on the long-term Chandra (25 observations) and XMM–Newton (eight observations) X-ray monitoring campaign of SGR 1745−2900 from the onset of the outburst in 2013 April until 2014 September. This unprecedented data set allows us to refine the timing properties of the source, as well as to study the outburst spectral evolution as a function of time and rotational phase. Our timing analysis confirms the increase in the spin period derivative by a factor of ∼2 around 2013 June, and reveals that a further increase occurred between 2013 October 30 and 2014 February 21. We find that the period derivative changed from 6.6 × 10−12 to 3.3 × 10−11 s s−1 in 1.5 yr. On the other hand, this magnetar shows a slow flux decay compared to other magnetars and a rather inefficient surface cooling. In particular, starquake-induced crustal cooling models alone have difficulty in explaining the high luminosity of the source for the first ∼200 d of its outburst, and additional heating of the star surface from currents flowing in a twisted magnetic bundle is probably playing an important role in the outburst evolution.

Modelling of the surface emission of the low magnetic field magnetar SGR 0418+5729

We perform a detailed modelling of the post-outburst surface emission of the low magnetic field magnetar SGR 0418+5729. The dipolar magnetic field of this source, B=6×1012G estimated from its spin-down rate, is in the observed range of magnetic fields for normal pulsars. The source is further characterized by a high pulse fraction and a single-peak profile. Using synthetic temperature distribution profiles, and fully accounting for the general-relativistic effects of light deflection and gravitational redshift, we generate synthetic X-ray spectra and pulse profiles that we fit to the observations. We find that asymmetric and symmetric surface temperature distributions can reproduce equally well the observed pulse profiles and spectra of SGR 0418. None the less, the modelling allows us to place constraints on the system geometry (i.e. the angles ψ and ξ that the rotation axis makes with the line of sight and the dipolar axis, respectively), as well as on the spot size and temperature contrast on the neutron star surface. After performing an analysis iterating between the pulse profile and spectra, as done in similar previous works, we further employed, for the first time in this context, a Markov-Chain Monte Carlo approach to extract constraints on the model parameters from the pulse profiles and spectra, simultaneously. We find that, to reproduce the observed spectrum and flux modulation: (a) the angles must be restricted to 65° ≲ ψ + ξ ≲ 125° or 235° ≲ ψ + ξ ≲ 295°; (b) the temperature contrast between the poles and the equator must be at least a factor of ∼6, and (c) the size of the hottest region ranges between 0.2 and 0.7 km (including uncertainties on the source distance). Lastly, we interpret our findings within the context of internal and external heating models.

Constraining the GRB-Magnetar Model by Means of the Galactic Pulsar Population

A large fraction of Gamma-ray bursts (GRBs) displays an X-ray plateau phase within <105 s from the prompt emission, proposed to be powered by the spin-down energy of a rapidly spinning newly born magnetar. In this work we use the properties of the Galactic neutron star population to constrain the GRB-magnetar scenario. We re-analyze the X-ray plateaus of all Swift GRBs with known redshift, between 2005 January and 2014 August. From the derived initial magnetic field distribution for the possible magnetars left behind by the GRBs, we study the evolution and properties of a simulated GRB-magnetar population using numerical simulations of magnetic field evolution, coupled with Monte Carlo simulations of Pulsar Population Synthesis in our Galaxy. We find that if the GRB X-ray plateaus are powered by the rotational energy of a newly formed magnetar, the current observational properties of the Galactic magnetar population are not compatible with being formed within the GRB scenario (regardless of the GRB type or rate at z = 0). Direct consequences would be that we should allow the existence of magnetars and "super-magnetars" having different progenitors, and that Type Ib/c SNe related to Long GRBs form systematically neutron stars with higher initial magnetic fields. We put an upper limit of ≤16 "super-magnetars" formed by a GRB in our Galaxy in the past Myr (at 99% c.l.). This limit is somewhat smaller than what is roughly expected from Long GRB rates, although the very large uncertainties do not allow us to draw strong conclusion in this respect.

Population synthesis of isolated neutron stars with magneto-rotational evolution – II. From radio-pulsars to magnetars

Population synthesis studies constitute a powerful method to reconstruct the birth distribution of periods and magnetic fields of the pulsar population. When this method is applied to populations in different wavelengths, it can break the degeneracy in the inferred properties of initial distributions that arises from single-band studies. In this context, we extend previous works to include X-ray thermal emitting pulsars within the same evolutionary model as radio-pulsars. We find that the cumulative distribution of the number of X-ray pulsars can be well reproduced by several models that, simultaneously, reproduce the characteristics of the radio-pulsar distribution. However, even considering the most favourable magneto-thermal evolution models with fast field decay, lognormal distributions of the initial magnetic field overpredict the number of visible sources with periods longer than 12 s. We then show that the problem can be solved with different distributions of magnetic field, such as a truncated lognormal distribution, or a binormal distribution with two distinct populations. We use the observational lack of isolated neutron stars (NSs) with spin periods P > 12 s to establish an upper limit to the fraction of magnetars born with B > 1015 G (less than 1 per cent). As future detections keep increasing the magnetar and high-B pulsar statistics, our approach can be used to establish a severe constraint on the maximum magnetic field at birth of NSs.

The outburst decay of the low magnetic field magnetar SWIFT J1822.3−1606: phase-resolved analysis and evidence for a variable cyclotron feature

We study the timing and spectral properties of the low-magnetic field, transient magnetar SWIFT J1822.3−1606 as it approached quiescence. We coherently phase-connect the observations over a time-span of ∼500 d since the discovery of SWIFT J1822.3−1606 following the Swift-Burst Alert Telescope (BAT) trigger on 2011 July 14, and carried out a detailed pulse phase spectroscopy along the outburst decay. We follow the spectral evolution of different pulse phase intervals and find a phase and energy-variable spectral feature, which we interpret as proton cyclotron resonant scattering of soft photon from currents circulating in a strong (≳1014 G) small-scale component of the magnetic field near the neutron star surface, superimposed to the much weaker (∼3 × 1013 G) magnetic field. We discuss also the implications of the pulse-resolved spectral analysis for the emission regions on the surface of the cooling magnetar.

The discovery, monitoring and environment of SGR J1935+2154

We report on the discovery of a new member of the magnetar class, SGR J1935+2154, and on its timing and spectral properties measured by an extensive observational campaign carried out between 2014 July and 2015 March with Chandra and XMM–Newton (11 pointings). We discovered the spin period of SGR J1935+2154 through the detection of coherent pulsations at a period of about 3.24 s. The magnetar is slowing down at a rate of P˙=1.43(1)×10−11 s s−1 and with a decreasing trend due to a negative P¨ of −3.5(7) × 10−19 s s−2. This implies a surface dipolar magnetic field strength of ∼2.2 × 1014 G, a characteristic age of about 3.6 kyr and a spin-down luminosity Lsd ∼1.7 × 1034 erg s−1. The source spectrum is well modelled by a blackbody with temperature of about 500 eV plus a power-law component with photon index of about 2. The source showed a moderate long-term variability, with a flux decay of about 25 per cent during the first four months since its discovery, and a re-brightening of the same amount during the second four months. The X-ray data were also used to study the source environment. In particular, we discovered a diffuse emission extending on spatial scales from about 1 arcsec up to at least 1 arcmin around SGR J1935+2154 both in Chandra and XMM–Newton data. This component is constant in flux (at least within uncertainties) and its spectrum is well modelled by a power-law spectrum steeper than that of the pulsar. Though a scattering halo origin seems to be more probable we cannot exclude that part, or all, of the diffuse emission is due to a pulsar wind nebula.

Parameterized Link Functions in Generalized Linear Random Effect Models: a Case Study on Breast Cancer Treatment

In non-linear random effects some attention has been very recently devoted to the analysis ofsuitable transformation of the response variables separately (Taylor 1996) or not (Oberg and Davidian 2000) from the transformations of the covariates and, as far as we know, no investigation has been carried out on the choice of link function in such models. In our study we consider the use of a random effect model when a parameterized family of links (Aranda-Ordaz 1981, Prentice 1996, Pregibon 1980, Stukel 1988 and Czado 1997) is introduced. We point out the advantages and the drawbacks associated with the choice of this data-driven kind of modeling. Difficulties in the interpretation of regression parameters, and therefore in understanding the influence of covariates, as well as problems related to loss of efficiency of estimates and overfitting, are discussed. A case study on radiotherapy usage in breast cancer treatment is discussed.

O laboratório de ensino de matemática temático centrado nos instrumentos de navegação: uma proposta para o IFRN de Mossoró-RN

This work presents a proposal to build a Mathematics Teaching Laboratory (MTL) whose main theme is the study, construction and use of instruments for navigation and location of mathematical content in an interdisciplinary way approach, and develop a notebook of activities focused on navigational instruments. For this it was necessary a literature review to understand the different conceptions of MTL and its pedagogical implications. The methodology used was literature research, construction and handling of instruments, and pedagogical experimentation. Lorenzato (2006) highlights the importance of an environment and suitable for a professional who can do a good job instruments. The implementation of an LEM can find some obstacles. The lack of support from other teachers or the management, the lack of a suitable place to store the materials produced, the lack of time in the workload of the teacher to prepare the lab activity, etc. Even in unfavorable or adverse conditions, according Lorenzato (2006), its implementation will benefit teachers and students. The lack of teacher training in their initial and continuing education, to use materials, and the lack of manuals with lab activities are also mentioned as factors that keep teachers from MTL. With propóposito assist the teacher of elementary or middle school in building a theme MTL prepared and we are providing a notebook of activities that provides a didactic sequence involving History and Mathematics. The book consists of four accompanied by suggestions for teachers activities, however the teacher has full autonomy to adapt the activities to the reality of your school. Among the instruments of navigation presented in this study chose to build the quadrant due to its simplicity, low cost of material and great teaching potential that this instrument has. But a theme lab is always being built and rebuilt as it is a research environment

A Simultaneous Equation Approach to Estimating HIV Prevalence with Non-Ignorable Missing Responses

Estimates of HIV prevalence are important for policy in order to establish the health status of a country's population and to evaluate the effectiveness of population-based interventions and campaigns. However, participation rates in testing for surveillance conducted as part of household surveys, on which many of these estimates are based, can be low. HIV positive individuals may be less likely to participate because they fear disclosure, in which case estimates obtained using conventional approaches to deal with missing data, such as imputation-based methods, will be biased. We develop a Heckman-type simultaneous equation approach which accounts for non-ignorable selection, but unlike previous implementations, allows for spatial dependence and does not impose a homogeneous selection process on all respondents. In addition, our framework addresses the issue of separation, where for instance some factors are severely unbalanced and highly predictive of the response, which would ordinarily prevent model convergence. Estimation is carried out within a penalized likelihood framework where smoothing is achieved using a parametrization of the smoothing criterion which makes estimation more stable and efficient. We provide the software for straightforward implementation of the proposed approach, and apply our methodology to estimating national and sub-national HIV prevalence in Swaziland, Zimbabwe and Zambia.

La traduzione della canzone d'autore tra l'italiano e il francese: le scelte, la metrica e il suono.

Sin dall’infanzia ho sentito un forte legame con la musica e l’amore per il canto e allo stesso tempo per le lingue straniere, mi ha condotto a frequentare il corso di mediazione linguistica interculturale dell’università di Bologna, che univa e fondeva fino alla radice queste due mie passioni. Nel corso della mia carriera universitaria, “au jour le jour” cercavo di cimentarmi in traduzioni di canzoni ma progredendo nei miei studi, più traducevo e più mi rendevo conto di quante difficoltà possa presentare questo genere di traduzione. Le figure retoriche e le frasi idiomatiche presenti in una canzone non solo sono molto difficili da trasportare nella lingua d’arrivo ma spesso e volentieri devono essere totalmente stravolte per poter mantenere il senso e lo scopo del testo di partenza. Insomma, “se vogliamo che tutto rimanga com’è, bisogna che tutto cambi”. (Giuseppe Tomasi di Lampedusa, 1969:40-41). Troppe volte mi sono imbattuto in canzoni già tradotte il quale senso primario andava disperso nell’oblio. In quanto aspirante traduttore so bene cosa significhi dover tagliare o sconvolgere il testo di partenza quando serve ma ove non ve n’è bisogno, non capisco il perché del doverlo fare. In questa mia tesi di laurea presenterò quattro canzoni d’autore: una canzone in italiano ed una in francese ancora non tradotte ed una canzone in italiano ed un’altra in francese che sono già state tradotte. Nel secondo caso, quello dei testi già tradotti, presenterò una mia versione di traduzione nella quale cercherò di rispettare la metrica, l’equilibrio dei suoni e le figure retoriche.

Auditoría de calidad del servicio al cliente en cadena de restaurantes de comida rapida en el área metropolítana de San Salvador. Caso ilustrativo.

El presente trabajo de grado titulado “Auditoria de calidad del servicio al cliente en cadena de restaurantes de comida rápida en el área metropolitana de San Salvador” caso ilustrativo; tiene como finalidad realizar una auditoría de calidad de servicio al cliente con el fin brindar una herramienta mercadológica y así de esta manera construir una ventaja competitiva y la mejora de la satisfacción del cliente. Con la elaboración de este trabajo de grado se ofrecerá, índices de satisfacción de los clientes en cuanto a la infraestructura, imagen corporativa, aspectos comerciales, productos, procesos internos, recursos humanos además de estrategias encaminadas a la mejora del servicio. Luego se justifica el proyecto de investigación según su practicidad, relevancia y su importancia dentro del mercadeo. Se muestra en el marco teórico, toda la información que contribuya al conocimiento, entendimiento y comprensión del tema en estudio para posteriormente abordar los objetivos que guían la investigación. Dentro de la metodología de investigación se presentan su propósito o finalidad, amplitud y profundidad, tipo de investigación, diseño de la investigación, determinación de la muestra, fuentes de datos, procedimiento para la recolección y procesamiento de datos para realizar posteriormente la propuesta, los instrumentos y técnicas a utilizar, debido a que se recolectará información exacta sobre la satisfacción de los clientes y su percepción hacia las empresas en estudio, los gustos y necesidades de éstos para formar un perfil del consumidor con el fin de que los esfuerzos que se realicen sean orientados para la prestación de un servicio de comida, y de esta manera diferenciarse ante la competencia. En el segundo capítulo trata la investigación de campo relacionada directamente con la auditoria de calidad de servicio al cliente, la cual se mide dentro del área de mercadeo, utilizado los instrumentos con el fin de medir la satisfacción del cliente en el momento de verdad, la investigación se desarrolla en las cadenas de restaurantes de comida rápida ubicadas en el área metropolitana de San Salvador. El contenido de este capítulo está comprendido por planteamiento del problema, su enunciado, la descripción del F.O.D.A. general y por cada cadena de restaurantes, objetivos de la investigación, metodología utilizada para la recolección de información para la cual se utilizó dos herramientas: prueba piloto y la encuesta para ser implementada tanto a los gerentes y empleados de los restaurantes y para medir el momento de verdad a los clientes de éstos restaurantes; posteriormente se muestra la tabulación de la información en donde se refleja los datos para dar a mostrar los resultados de las encuestas a los objetos de estudio; luego se realiza las conclusiones y recomendaciones las cuales son elaboradas conforme a los resultados de los datos obtenidos. En el tercer capítulo contiene el plan de fidelización, donde el objeto es apoyar a la cadena de restaurante de Pollo Campero a contrarrestar el pronunciado y generalizado declive de la lealtad de los clientes; el análisis de las principales causas de esta tendencia indica que el declive de la lealtad se debe, en gran parte, a causas estructurales entre las cuales destaca la dificultad de conseguir una diferenciación verdadera, producida por la competencia de restaurantes de comida rápida en el área metropolitana de San Salvador. El plan de fidelización el cual consiste en establecer vínculos duraderos entre los clientes y la empresa contribuyendo a la creación de una diferenciación en el tiempo a través del desarrollo de los aspectos relacionales CRM; ésta apuesta por un plan de fidelización relacional que esté basada en el análisis de los estudios previos sobre el efecto de la interacción entre los incentivos económicos (como lo son los descuentos) y los aspectos emocionales e instintivos; un plan de fidelización es una estrategia de marketing establecida por las empresas con el propósito de premiar el comportamiento de compra de sus clientes, lo que produce en ellos un sentido de lealtad y fidelidad hacia la empresa; este tipo de programas ofrece acceso a descuentos, premios o cualquier otro tipo de beneficio que logre afirmar su compromiso con la marca. Finalmente se presenta la bibliografía, que comprende los libros de texto, revistas, tesis, páginas web, entre otras, consultadas para el proyecto de investigación. Se incluye una propuesta de los instrumentos a utilizar, es decir, la guía de preguntas para desarrollar las encuestas, la clisa, el cliente incógnito y la observación “in situ” con el objetivo de obtener toda la información pertinente para resolver la problemática en estudio. Las gráficas, tablas y demás elementos visuales que facilitan la comprensión y entendimiento del tema serán abordadas en los anexos.

Estableciendo nexos entre Políticas de Ajuste Estructural y su impacto ambiental: una discusión metodológica

Las políticas de Ajuste Estructural han sido la base de la política económica costarricense en los últimos 10 años, por lo cual, han tenido gran incidencia en el análisis de los procesos y relaciones de cualquier sector productivo. En este contexto, los efectos ambientales de los últimos años, están decididamente influenciados por estas políticas, pues aunque, los programas de Ajuste no tienen como propósito direccionar aspectos ambientales, al modificar algunos precios relativos, pueden propiciar un cambio en el patrón de uso de un recurso, y es así como, tienen un efecto directo o indirecto sobre el ambiente

Propuesta de mejora al seguimiento y fidelización del cliente en la empresa Invera a través de los principios de la herramienta CRM

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Metodología para la identificación y evaluación del riesgo que amenaza el negocio en marcha, en empresas donde exista concentración de proveedores.

La auditoría para evaluar la continuidad del negocio en marcha es un trabajo que merece una particular atención por parte de la empresa porque este principio, ayuda a crear acciones futuras en caso que se pueda dar un determinado suceso o condición que ocasione que la entidad no pueda continuar bajo este supuesto, si en dado caso la entidad no cuenta con una evaluación sobre lo apropiado de la continuidad del negocio en marcha. A través de un estudio realizado por Ricardo Monge González y empresa, publicado por la Editorial Tecnológica de Costa Rica, sobre las empresas salvadoreñas y las relaciones que existen con sus proveedores, se determinó que el 73.8% de las empresas mantienen relaciones comerciales con menos de 10 proveedores. Además se observa una importante concentración de las compras que realizan estas empresas en manos de unos pocos proveedores, puesto que el 70.6% de las empresas manifiestan que menos de 4 proveedores suplen el 80% del valor de las compras de su empresa”. Nuestro objetivo general es dar una guía al profesional de contaduría pública que ejerce la auditoria de estados financieros de información histórica, para que pueda identificar y evaluar el riesgo de amenaza de negocio en marcha donde exista una concentración de proveedores. Para poder lograr esto es necesario, que se identifiquen aquellos eventos, que se consideren como riesgo que amenazan el negocio en marcha. El instrumento que se utilizó para recolectar la información de empresas comercializadoras de calzado es la encuesta, a través de la cual se ha conocido la valoración de gerentes generales, contadores y demás personal administrativo de empresas, que se dedican a la venta de calzado. Por otra parte una vez que se recolectaron los datos a través de la encuesta, estos se presentaron y se tabularon en forma conjunta y se elaboraron graficas respectivas donde se reflejaron dichos datos. En la empresa comercializadora de calzado que sirvió como base para realizar el caso práctico se pudo observar que los proveedores en esta empresa representan el 77% de sus pasivos, considerando que solo tienen tres proveedores locales, y un extranjero, lo que significa que hay una concentración de proveedores. Por otra parte cuando se evaluó la capacidad de la empresa para continuar como negocio en marcha, se identificó que no poseen un plan de acción futuro, en caso que un suceso o condición determinada ponga en riesgo la continuidad de negocio en marcha. Es importante que las empresas comercializadoras de zapatos en general tengan un plan de acción futuro en caso que exista un suceso o condición determinado que ponga en riesgo que el negocio pueda seguir funcionando. Además es una medida necesaria que las empresas que se dedican a comercializar calzado, tengan un número de proveedores adecuado de tal manera que no dependan en gran medida de estos suministradores y que tengan opciones inmediatas en caso que alguno deje de funcionar como proveedor de la empresa.