On the polarimetric variability of bright O-type stars

Polarimetric data associated with multi-parameter observational campaigns of selected bright O-type stars and their variable winds, are analysed in relation to the outcomes of the UV and optical spectroscopic studies. For the stars ξ Per and λ Cep, individual measurement uncertainties are Δρ~±0.0002 with nightly mean uncertainties of Δρ~±0.00007. Although variability is apparent on a night-to-night basis, with differences in δρ~0.0002, no correlations are found between these and the periodic behaviours associated with the stellar Si IV and H α lines. Similar polarimetric variability is seen in the data for the standard star ø Cas used as a reference in this observing campaign. It is suggested that all of these low level fluctuations are not intrinsic to the stars but are engendered by structured instrumental polarization in the diffraction pattern and depolarization effects in combination with inconsistent target acquisition and with variable seeing conditions in the Earth's atmosphere. Reassessment of older data for λ Cep from Hayes (1978) also supports this thesis

A Denotational Semantics for First-Order Logic

In Apt and Bezem [AB99] (see cs.LO/9811017) we provided a computational interpretation of first-order formulas over arbitrary interpretations. Here we complement this work by introducing a denotational semantics for first-order logic. Additionally, by allowing an assignment of a non-ground term to a variable we introduce in this framework logical variables. The semantics combines a number of well-known ideas from the areas of semantics of imperative programming languages and logic programming. In the resulting computational view conjunction corresponds to sequential composition, disjunction to ``don't know'' nondeterminism, existential quantification to declaration of a local variable, and negation to the ``negation as finite failure'' rule. The soundness result shows correctness of the semantics with respect to the notion of truth. The proof resembles in some aspects the proof of the soundness of the SLDNF-resolution.Comment: 17 pages. Invited talk at the Computational Logic Conference (CL 2000). To appear in Springer-Verlag Lecture Notes in Computer Scienc

A design-based approach for research into deaf children’s reading comprehension

Design-based methodologies provide a paradigm for educational research which enables us to see beyond what is or is not working, to develop practices and interventions that ‘work better’ (Kelly et al., 2008, p3). This paper explains the design-based methodology and explores the use of this approach to research deaf children’s reading comprehension in order to make a significant contribution to theory and impact on practice. The research context is presented and current paradigms are reviewed. The issues of researching deafness and reading in a way which takes into account the resources of the individuals and the potential of the context are illustrated and a rationale for using a design-based model is presented. The paper examines and reflects on the use of this methodology for investigating deafness and reading comprehension drawing on a current work in progress into Deafness and Reading for Meaning (DreaM) at the University of Leeds

Structured Text Retrieval Models

Structured text retrieval models provide a formal definition or mathematical framework for querying semistructured textual databases. A textual database contains both content and structure. The content is the text itself, and the structure divides the database into separate textual parts and relates those textual parts by some criterion. Often, textual databases can be represented as marked up text, for instance as XML, where the XML elements define the structure on the text content. Retrieval models for textual databases should comprise three parts: 1) a model of the text, 2) a model of the structure, and 3) a query language [4]: The model of the text defines a tokenization into words or other semantic units, as well as stop words, stemming, synonyms, etc. The model of the structure defines parts of the text, typically a contiguous portion of the text called element, region, or segment, which is defined on top of the text modelâ\u80\u99s word tokens. The query language typically defines a number of operators on content and structure such as set operators and operators like â\u80\u9ccontaining â\u80\u9d and â\u80\u9ccontained-by â\u80\u9d to model relations between content and structure, as well as relations between the structural elements themselves. Using such a query language, the (expert) user can for instance formulate requests like â\u80\u9cI want a paragraph discussing formal models near to a table discussing the differences between databases and information retrievalâ\u80\u9d. Here, â\u80\u9cformal models â\u80\u9d and â\u80\u9cdifferences between databases and information retrieval â\u80\u9d should match the content that needs to be retrieved from the database, whereas â\u80\u9cparagraph â\u80\u9d and â\u80\u9ctable â\u80\u9d refer to structural constraints on the units to retrieve. The features, structuring power, and the expressiveness of the query languages of several models for structured text retrieval are discussed below. HISTORICAL BACKGROUND The STAIRS system (Storage and Information Retrieval System), which was developed at IBM already in the late 1950â\u80\u99s allowed querying both content and structure. Much like todayâ\u80\u99s On-line Public Access Catalogues, it wa

Searching for planet-driven dust spirals in ALMA visibilities

Atacama Large Millimetre/submillimetre Array (ALMA) observations of the thermal emission from protoplanetary disc dust have revealed a wealth of substructures that could evidence embedded planets, but planet-driven spirals, one of the more compelling lines of evidence, remain relatively rare. Existing works have focused on detecting these spirals using methods that operate in image space. Here, we explore the planet detection capabilities of fitting planet-driven spirals to disc observations directly in visibility space. We test our method on synthetic ALMA observations of planet-containing model discs for a range of disc/observational parameters, finding it significantly outperforms image residuals in identifying spirals in these observations and is able to identify spirals in regions of the parameter space in which no gaps are detected. These tests suggest that a visibility-space fitting approach warrants further investigation and may be able to find planet-driven spirals in observations that have not yet been found with existing approaches. We also test our method on six discs in the Taurus molecular cloud observed with ALMA at 1.33 mm, but find no evidence for planet-driven spirals. We find that the minimum planet masses necessary to drive detectable spirals range from ≈0.03 to 0.5 MJup over orbital radii of 10–100 au, with planet masses below these thresholds potentially hiding in such disc observations. Conversely, we suggest that planets ≳0.5–1 MJup can likely be ruled out over orbital radii of ≈20–60 au on the grounds that we would have detected them if they were present

Strain balancing of MOVPE InAs/GaAs quantum dots using GaAs0.8P0.2

MOVPE growth of stacked InAs/ GaAs QDs with and without GaAs 0.8 P 0.2 strain balancing layers has been studied. The GaAsP layers reduce the accumulated strain whilst maintaining the electrical characteristics. This should enable closer stacking of QD layers leading to higher gain and improved laser performance

The efficiency of dust trapping in ringed protoplanetary discs

Interstellar matter and star formatio

Superresolution trends in the ALMA Taurus survey: structured inner discs and compact discs

Stars and planetary system

Bereavement care for ethnic minority communities : a systematic review of access to, models of, outcomes from, and satisfaction with, service provision

Objectives To review and synthesize the existing evidence on bereavement care, within the United Kingdom (UK), for ethnic minority communities in terms of barriers and facilitators to access; models of care; outcomes from, and satisfaction with, service provision. Design A systematic review adopting a framework synthesis approach was conducted. An electronic search of the literature was undertaken in MEDLINE, Embase, PsycINFO, Social Work Abstract and CINAHL via EBSCO, Global Health, Cochrane library, the Trip database and ProQuest between 1995 and 2020. Search terms included bereavement care, ethnic minority populations and the UK setting. Results From 3,185 initial records, following screening for eligibility, and full-text review of 164 articles, seven studies were identified. There was no research literature outlining the role of family, friends and existing networks; and a real absence of evidence about outcomes and levels of satisfaction for those from an ethnic minority background who receive bereavement care. From the limited literature, the overarching theme for barriers to bereavement care was ‘unfamiliarity and irregularities’. Four identified subthemes were ‘lack of awareness’; ‘variability in support’; ‘type and format of support’; and ‘culturally specific beliefs’. The overarching theme for facilitators for bereavement care was ‘accessibility’ with the two subthemes being ‘readily available information’ and ‘inclusive approaches’. Three studies reported on examples of different models of care provision. Conclusions This review reveals a stark lack of evidence about bereavement care for ethnic minority populations. In particular, understanding more about the role of family, friends and existing support systems, alongside outcomes and satisfaction will begin to develop the evidence base underpinning current provision. Direct user-representation through proactive engagement and co-design approaches may begin to determine the most appropriate models and format of bereavement care for ethnic minority communities to inform service design and delivery