Populating the Galaxy with low-mass X-ray binaries

We perform binary population synthesis calculations to investigate the incidence of low-mass X-ray binaries and their birth rate in the Galaxy. We use a binary evolution algorithm that models all the relevant processes including tidal circularization and synchronization. Parameters in the evolution algorithm that are uncertain and may affect X-ray binary formation are allowed to vary during the investigation. We agree with previous studies that under standard assumptions of binary evolution the formation rate and number of black-hole low-mass X-ray binaries predicted by the model are more than an order of magnitude less than what is indicated by observations. We find that the common-envelope process cannot be manipulated to produce significant numbers of black-hole low-mass X-ray binaries. However, by simply reducing the mass-loss rate from helium stars adopted in the standard model, to a rate that agrees with the latest data, we produce a good match to the observations. Including low-mass X-ray binaries that evolve from intermediate-mass systems also leads to favourable results. We stress that constraints on the X-ray binary population provided by observations are used here merely as a guide as surveys suffer from incompleteness and much uncertainty is involved in the interpretation of results.Comment: 17 pages and 9 figures; accepted by MNRA

Handling the Past: Using a Specialized Curriculum to Facilitate Narration of Racial Identities

Identity construction takes place where people spend significant amounts of time. For children, those areas include home and school. Evidence exists that Black children are not given opportunities in school to narrate and affirm their racial identities. Racial identity has been shown to affect school success (Carter, 2008; Lea, 2014; Murrell, 2007), political involvement (Diemer and Li, 2011), and psychological well-being (Seaton, Sellers, & Scottham, 2006). Scholars suggest using history, narration, and dialogue to address this problem; however, current research has yet to incorporate these suggestions. I used a critical action research methodology to explore the influence of a specialized curriculum, document student engagement in critical race discourse, and facilitate the racial identity narrations of fourteen Black fifth-grade students. Targeted digital materials containing affirming Black historical portraits were used as springboards to teacher-facilitated conversations about race and subsequent student written reflections. Qualitative analysis was applied to students’ reflections after viewing and discussing the digital materials, students’ answers to direct questions regarding their racial attitudes, researcher observations, and researcher reflections. The findings suggest that students (1) had a severely limited knowledge of Black history and desired to learn more, (2) further developed affirming Black racial identities despite the historical challenges of Black people and despite personal contemporary problems, (3) were nonjudgmental regarding actions that their Black collective group exhibited regarding agency and subsistence, and (4) held exclusionary attitudes toward White people while suggesting the need for various races and cultures to spend time together. Implications for teachers, teacher educators, policy makers, book publishers, and curriculum developers are discussed

A framework for P2P application development

Although Peer-to-Peer (P2P) computing has become increasingly popular over recent years, there still exist only a very small number of application domains that have exploited it on a large scale. This can be attributed to a number of reasons including the rapid evolution of P2P technologies, coupled with their often-complex nature. This paper describes an implemented abstraction framework that seeks to aid developers in building P2P applications. A selection of example P2P applications that have been developed using this framework are also presented