Improved estimators for dispersion models with dispersion covariates

In this paper we discuss improved estimators for the regression and the dispersion parameters in an extended class of dispersion models (J{\o}rgensen, 1996). This class extends the regular dispersion models by letting the dispersion parameter vary throughout the observations, and contains the dispersion models as particular case. General formulae for the second-order bias are obtained explicitly in dispersion models with dispersion covariates, which generalize previous results by Botter and Cordeiro (1998), Cordeiro and McCullagh (1991), Cordeiro and Vasconcellos (1999), and Paula (1992). The practical use of the formulae is that we can derive closed-form expressions for the second-order biases of the maximum likelihood estimators of the regression and dispersion parameters when the information matrix has a closed-form. Various expressions for the second-order biases are given for special models. The formulae have advantages for numerical purposes because they require only a supplementary weighted linear regression. We also compare these bias-corrected estimators with two different estimators which are also bias-free to the second-order that are based on bootstrap methods. These estimators are compared by simulation

Absolute Calibration of the Radio Astronomy Flux Density Scale at 22 to 43 GHz Using Planck

The Planck mission detected thousands of extragalactic radio sources at frequencies from 28 to 857 GHz. Planck's calibration is absolute (in the sense that it is based on the satellite's annual motion around the Sun and the temperature of the cosmic microwave background), and its beams are well characterized at sub-percent levels. Thus Planck's flux density measurements of compact sources are absolute in the same sense. We have made coordinated VLA and ATCA observations of 65 strong, unresolved Planck sources in order to transfer Planck's calibration to ground-based instruments at 22, 28, and 43 GHz. The results are compared to microwave flux density scales currently based on planetary observations. Despite the scatter introduced by the variability of many of the sources, the flux density scales are determined to 1-2% accuracy. At 28 GHz, the flux density scale used by the VLA runs 3.6% +- 1.0% below Planck values; at 43 GHz, the discrepancy increases to 6.2% +- 1.4% for both ATCA and the VLA.Comment: 16 pages, 4 figures and 4 table

Social work practices and the ecological sustainability of socially vulnerable communities

Environmental problems are also social problems. Social work, as a scientific area, has increasingly assumed the importance of including environmental problems in social intervention. This close linkage to ecological issues is particularly relevant when addressing vulnerable communities. In this article, we analyze the results of a study focused on social work intervention in two Portuguese eco-neighborhoods in the context of ongoing urban regeneration projects, which suggest that social vulnerability accentuates the damage of exposure to environmental threats and amplifies its effects. The analysis of data collected from social workers, through 9 semi-structured interviews and through questionnaires (N = 131), with the residents of the neighborhoods together with non-participant observation, allowed to highlight the difficulties, contradictions, but also the potential of this type intervention. Results appear to support an eco-social model which may help social worker to promote social transformation and change, respecting community rhythms, promoting empowerment of individuals, addressing the challenges of socially vulnerable communities within the complexity of a globalized world.info:eu-repo/semantics/publishedVersio

Students’ perceptions of their experiences with online assessments during the Covid-19 pandemic

Abstract. Assessment is an essential element in teaching and learning, and the outbreak of the Covid-19 pandemic forced teachers and students to adapt this practice to the online modality. Yet, the existence of resources regarding online assessments is still limited. This study aims to explore how students perceived their experiences with online assessment during the pandemic, with a focus on their relationship with feedback, their emotions, and motivation. Qualitative semi-structured interviews were conducted with 10 participants who were within their last four years of basic education in the year 2020, with subsequent content analysis being applied. The results of this study indicate that students did not perceive major changes in the assessment methods applied by teachers. They did, however, perceive new challenges for their learning to emerge, and consequently made adaptations to their studying habits. Moreover, it was revealed that students received less feedback in the online modality, which had an impact on their emotional states and learning practices. Additionally, it was found that the pandemic and online learning contexts imposed new difficulties for students, whose emotions were negatively impacted, and whose motivation toward assessment tasks was significantly decreased. These factors led students to behaviors such as avoiding studying and engaging in dishonest academic practices. In conclusion, this study sheds light on topics relevant to online learning, online assessments, and students’ emotions and motivation regarding assessment, specifically in the context of emergency online learning

On Clifford Subalgebras, Spacetime Splittings and Applications

Z2-gradings of Clifford algebras are reviewed and we shall be concerned with an alpha-grading based on the structure of inner automorphisms, which is closely related to the spacetime splitting, if we consider the standard conjugation map automorphism by an arbitrary, but fixed, splitting vector. After briefly sketching the orthogonal and parallel components of products of differential forms, where we introduce the parallel [orthogonal] part as the space [time] component, we provide a detailed exposition of the Dirac operator splitting and we show how the differential operator parallel and orthogonal components are related to the Lie derivative along the splitting vector and the angular momentum splitting bivector. We also introduce multivectorial-induced alpha-gradings and present the Dirac equation in terms of the spacetime splitting, where the Dirac spinor field is shown to be a direct sum of two quaternions. We point out some possible physical applications of the formalism developed.Comment: 22 pages, accepted for publication in International Journal of Geometric Methods in Modern Physics 3 (8) (2006