The Causal Boundary of spacetimes revisited

We present a new development of the causal boundary of spacetimes, originally introduced by Geroch, Kronheimer and Penrose. Given a strongly causal spacetime (or, more generally, a chronological set), we reconsider the GKP ideas to construct a family of completions with a chronology and topology extending the original ones. Many of these completions present undesirable features, like those appeared in previous approaches by other authors. However, we show that all these deficiencies are due to the attachment of an ``excessively big'' boundary. In fact, a notion of ``completion with minimal boundary'' is then introduced in our family such that, when we restrict to these minimal completions, which always exist, all previous objections disappear. The optimal character of our construction is illustrated by a number of satisfactory properties and examples.Comment: 37 pages, 10 figures; Definition 6.1 slightly modified; multiple minor changes; one figure added and another replace

Indentation into Polymeric Foams

The effects of the nose shape of rigid indenters on the indentation behaviour of polymethacrylimide(PMI) and polyetherimide(PEI) foams with different densities are investigated. Experimental results show that indentation resistance depends on the geometry of the indenter and the density of the foam. Analytical models based on the deformation mechanisms observed in experiments are developed to predict the indentation resistance. It shows that the analytical predictions are in good agreement with experimental measurements for a range of polymeric foams. This study presents a complete and systematic experimental data on the indentation behaviours of a range of polymeric foams and demonstrates the capability of the analytical model to predict the indentation behaviours of PMI and PEI foams. This record was migrated from the OpenDepot repository service in June, 2017 before shutting down

Effect Of Embryo Thermal Stimulation On The Serum Levels Of Immunoglobulins And Corticosterone, And Organ Histopathology Of 1 Day-old Broilers

Embryo thermal stimulation has been studied as a means to promote epigenetic changes and to improve broiler health and performance. This study aimed at evaluating immunoglobulin (IgM, IgG, and IgA) titers, serum corticosterone levels, and organ integrity of day-old male Cobb (R) and Ross (R) broilers. Embryos were submitted to hot and cold stimuli (thermal stimulation) on days 14-18 of incubation. The thermal manipulation treatments did not affect immunoglobulin titers of 1 day-old Cobb (R) or Ross (R) chicks, and caused severe bursal lesions (scores 3 and 4) in both strains. However, serum corticosterone levels of Cobb (R) chicks were higher when embryos were submitted to hot stimulus (+1.39 degrees C) compared with cold stimulus (+36 degrees C). Serum corticosterone levels of Ross r chicks were not affected by embryo temperature manipulation. The only effect of broiler breeder age was observed on IgM titers of Cobb (R) chicks, which were higher in chicks from 33-wk-old breeders. Further studies are needed to detect the optimal period of embryo thermal stimulation.18717

RNA from LPS-stirnulated macrophages induces the release of tumour necrosis factor-α and interleukin-1 by resident macrophages

The effect of exogenous RNA on many cellular functions has been studied in a variety of eukaryotic cells but there are few reports on macrophages. In the present study, it is demonstrated that cytoplasmatic RNA extracted from rat macrophages stimulated with Escherichia coli lipopolysaccharide (LPS), referred to as L-RNA, induced the release of TNF-α and IL-1 from monolayers of peritoneal resident macrophages. The activity of L-RNA was not altered by polymyxin B but was abolished by ribonuclease (RNase) pretreatment, indicating the absence of LPS contamination and that the integrity of the polynucleotide chain is essential for this activity. Both the poly A(−) and poly A(+) fractions obtained from L-RNA applied to oligo(dT)–cellulose chromatography induced TNF-α and IL-1 release. The L-RNA-induced cytokine release was inhibited by dexamethasone and seemed to be dependent on protein synthesis since this effect was abolished by cycloheximide or actinomycin-D. The LPS-stimulated macrophages, when pre-incubated with [5-3H]-uridine, secreted a trichloroacetic acid (TCA) precipitable material which was sensitive to RNase and KOH hydrolysis, suggesting that the material is RNA. This substance was also released from macrophage monolayers stimulated with IL-1β but not with TNF-α, IL-6 or IL-8. The substance secreted (3H-RNA) sediments in the 4–5S region of a 5–20% sucrose gradient. These results show that L-RNA induces cytokine secretion by macrophage monolayers and support the idea that, during inflammation, stimulated macrophages could release RNA which may further induce the release of cytokines by the resident cell population

Teacher resilience in adverse contexts: issues of professionalism and professional identity

Teacher resilience is a construct that is relative, developmental and dynamic; it is socially constructed and depends on personal and professional dispositions. Issues of commitment, professionalism, and professional identity, for instance, need to be taken into account if teacher resilience is to be fully understood. In this chapter I draw upon a larger piece of research aimed at investigating teachers’ work and lives in challenging circumstances. Data were collected through a national survey (n=2702 teachers), focus group (n=99 teachers) and interviews to 11 school principals. Findings suggest the connection between teacher commitment and resilience which are associated with issues of school culture and leadership, a sense of vocation, and teachers’ beliefs and professional values. Factors and sources of teacher motivation and resilience are also identified within a context marked by teacher intensification, lack of trust, worsening of teaching conditions, lower social and economic status and legislative “tsunami”. The chapter ends with the discussion of the importance of relationships in the teaching profession and issues of motivation and professionalism which entails given ways of being and feeling as a teacher.Financial Support by CIEC (Research Centre on Child Studies, IE, UMinho; FCT R&D unit 317, Portugal) by the Strategic Project UID/CED/00317/2013, with financial support of National Funds through the FCT (Foundation for Science and Technology) and co-financed by European Regional Development Funds (FEDER) through the COMPETE 2020 - Competitiveness and Internationalization Operational Program (POCI) with the reference POCI-01-0145-FEDER-00756

Prevalence of acute dizziness and vertigo in cortical stroke

BACKGROUND: In posterior circulation stroke, vertigo can be a presenting feature. However, whether isolated hemispheric strokes present with vertigo is less clear, despite a few single case-reports in the literature. Here we, a) explored the prevalence of vertigo/dizziness in acute stroke and, b) considered the cortical distribution of these lesions in relation to both the known vestibular cortex and evolution of these symptoms. METHODS: We conducted structured interviews in 173 consecutive unselected patients admitted to the hyperacute stroke unit at the University College London Hospitals. The interview was used to evaluate whether the patient was suffering from dizziness and/or vertigo before the onset of the stroke and at the time of the stroke (acute dizziness/vertigo), and the nature of these symptoms. RESULTS: 112 patients had subcortical lesions and 53 patients had cortical infarcts, of which 21 patients reported acute dizziness. Out of these 21, five patients reported rotational vertigo. 17 of the total 53 patients had lesions in known vestibular cortical areas distributed within the insular and parietal opercular cortices. CONCLUSIONS: The prevalence of vertigo in acute cortical strokes was 9%, with no single locus of lesion overlap. There is growing evidence supporting a lateralised vestibular cortex, with speculation that cortical strokes affecting the right hemisphere, are more likely to cause vestibular symptoms than left-hemispheric strokes. We observed a trend for this association, with the right hemisphere affected in four of five patients who reported spinning vertigo at the onset of the stroke

Nematic fluctuations and phase transitions in LaFeAsO: A Raman scattering study

Raman scattering experiments on LaFeAsO with distinct antiferromagnetic (TAFM=140 K) and tetragonal-orthorhombic (TS=155 K) transitions show a quasielastic peak (QEP) in B2g symmetry (2 Fe tetragonal cell) that fades away below ∼TAFM and is ascribed to electronic nematic fluctuations. A scaling of the reported shear modulus with the T dependence of the QEP height rather than the QEP area indicates that magnetic degrees of freedom drive the structural transition. The large separation between TS and TAFM in LaFeAsO compared to BaFe2As2 manifests itself in slower dynamics of nematic fluctuations in the former

Evidence for SU(3) symmetry breaking from hyperon production

We examine the SU(3) symmetry breaking in hyperon semileptonic decays (HSD) by considering two typical sets of quark contributions to the spin content of the octet baryons: Set-1 with SU(3) flavor symmetry and Set-2 with SU(3) flavor symmetry breaking in HSD. The quark distributions of the octet baryons are calculated with a successful statistical model. Using an approximate relation between the quark fragmentation functions and the quark distributions, we predict polarizations of the octet baryons produced in $e^+e^-$ annihilation and semi-inclusive deeply lepton-nucleon scattering in order to reveal the SU(3) symmetry breaking effect on the spin structure of the octet baryons. We find that the SU(3) symmetry breaking significantly affects the hyperon polarization. The available experimental data on the $\Lambda$ polarization seem to favor the theoretical predictions with SU(3) symmetry breaking. We conclude that there is a possibility to get a collateral evidence for SU(3) symmetry breaking from hyperon production. The theoretical errors for our predictions are discussed.Comment: 3 tables, 14 figure