Order-of-magnitude physics of neutron stars

We use basic physics and simple mathematics accessible to advanced undergraduate students to estimate the main properties of neutron stars. We set the stage and introduce relevant concepts by discussing the properties of "everyday" matter on Earth, degenerate Fermi gases, white dwarfs, and scaling relations of stellar properties with polytropic equations of state. Then, we discuss various physical ingredients relevant for neutron stars and how they can be combined in order to obtain a couple of different simple estimates of their maximum mass, beyond which they would collapse, turning into black holes. Finally, we use the basic structural parameters of neutron stars to briefly discuss their rotational and electromagnetic properties.Comment: 13 pages, 3 figures, accepted for publication in European Physical Journal

Catalizadores heterogéneos utilizados para la obtención de biodiesel

El ahorro energético y el cuidado medioambiental son de gran importancia en todos los países, debido a estos aspectos se ha desarrollado la búsqueda de combustibles alternos para sustituir los provenientes defuentes fósiles. En este artículo se presenta información relacionada con los diferentes catalizadores utilizados para la producción de biodiesel, mencionando su clasificación química y física, también se citan las propiedades químicas y las características morfológicas que los hacen ser una opción apropiada para utilizarlos en la reacción de transesterificación, la cual está implicada en la producción de biodiesel. Además, se resalta la importancia de los catalizadores heterogéneos por sus características de baja contaminación al medio ambiente, su capacidad de ser reutilizados y porque pueden separarse fácilmente del producto

Single Muscle Fibre Contractile Function With Ageing

Ageing is accompanied by decrements in the size and function of skeletal muscle that compromise independence and quality of life in older adults. Developing therapeutic strategies to ameliorate these changes is critical but requires an in-depth mechanistic understanding of the underlying physiology. Over the past 25 years, studies on the contractile mechanics of isolated human muscle fibres have been instrumental in facilitating our understanding of the cellular mechanisms contributing to age-related skeletal muscle dysfunction. The purpose of this review is to characterize the changes that occur in single muscle fibre size and contractile function with ageing and identify key areas for future research. Surprisingly, most studies observe that the size and contractile function of fibres expressing slow myosin heavy chain (MHC) I are well-preserved with ageing. In contrast, there are profound age-related decrements in the size and contractile function of the fibres expressing the MHC II isoforms. Notably, lifelong aerobic exercise training is unable to prevent most of the decrements in fast fibre contractile function, which have been implicated as a primary mechanism for the age-related loss in whole-muscle power output. These findings reveal a critical need to investigate the effectiveness of other nutritional, pharmaceutical or exercise strategies, such as lifelong resistance training, to preserve fast fibre size and function with ageing. Moreover, integrating single fibre contractile mechanics with the molecular profile and other parameters important to contractile function (e.g. phosphorylation of regulatory proteins, innervation status, mitochondrial function, fibre economy) is necessary to comprehensively understand the ageing skeletal muscle phenotype

Impact of caries and dental fluorosis on oral health-related quality of life: a cross-sectional study in schoolchildren receiving water naturally fluoridated at above-optimal levels

Purpose The purpose of this study was to evaluate the impact of caries and fluorosis on oral health-related quality of life (OHRQoL) among schoolchildren living in areas with high concentrations of fluoride in water. Methods Five hundred and twenty-four schoolchildren (8–12 year olds) residing in rural communities in central Mexico were examined for oral hygiene, caries (International Caries Detection and Assessment System, ICDAS II), and fluorosis (Thylstrup and Fejerskov Index, TFI). OHRQoL was evaluated with the Child Perceptions Questionnaire for two age groups (CPQ8–10 and CPQ11–14). Generalized structural equation models were constructed for data analysis. Results Overall prevalence of caries was 88.5% and fluorosis 46.9%. In the group of 8–10 year olds, 48% of the children had advanced carious lesions in primary or permanent teeth (ICDAS ≥4), 22.6% had moderate/severe fluorosis, and 59.9% of children had an impact on OHRQoL. Schoolchildren with ICDAS ≥4 were more likely [OR = 1.75, (95% CI 1.34–2.28)] to suffer a negative impact on OHRQoL. In the group of 11–12 year olds, 19.9% of children had advanced carious lesions and 23.2% showed moderate/severe fluorosis; 67.3% of children reported had an impact on OHRQoL. Children 11–12 year olds with fluorosis (TFI ≥4) [OR = 2.39 (95% CI 2.12–2.69)], caries (ICDAS ≥4) [OR = 2.18 (95% CI 2.13–2.24)], and low brushing frequency [OR = 2.04 (95% CI 1.21–3.44)] were more likely to have deterioration on OHRQoL. Conclusion A negative impact on OHRQoL was observed in children with caries and fluorosis

One is Not Enough: Multiple Exemplars Facilitate Infants' Generalizations of Novel Properties

Across three experiments, we examined 9- and 11-month-olds’ mappings of novel sound properties to novel animal categories. Infants were familiarized with novel animal–novel sound pairings (e.g., Animal A [red]–Sound 1) and then tested on: (1) their acquisition of the original pairing and (2) their gen- eralization of the sound property to a new member of a familiarized cate- gory (e.g., Animal A [blue]–Sound 1). When familiarized with a single exemplar of a category, 11-month-olds showed no evidence of acquiring or generalizing the animal–sound pairings. In contrast, 11-month-olds learnt the original animal–sound mappings and generalized the sound property to a novel member of that category when familiarized with multiple exemplars of a category. Finally, when familiarized with multiple exemplars, 9-month- old infants learnt the original animal–sound pairing, but did not extend the novel sound property. The results of these experiments provide evidence for developmental differences in the facilitative role of multiple exemplars in promoting the learning and generalization of information

Water politics in El Salvador : power, water and social change in poor communities of San José Villanueva

This dissertation explores how social power relations affect poor, vulnerable people’s access to clean and sustainable water in El Salvador. It does so using an in-depth case study of people living in seven socially deprived rural communities of San José Villanueva, province of La Libertad, southern El Salvador. Drawing on several strands of social and political theory, the research conceptualises ‘power’ along three axes: on local/global, material/ideational and structure/agency lines. Using El Salvador’s neoliberal transition as its sociohistorical backdrop, the research explores the power dynamics shown by water actor groups in positions of hegemony, counter-hegemony and social exclusion. The study shows how these water actors use strategies, tactics and actions along the three power axes. The thesis assembles empirical evidence from academic research; policy documents, media outlets and civil society sources; interviews with policy makers; and poor people’s narratives. The research argues that the current state of unequal power relations in water governance constitutes the main factor shaping poor people’s water access outcomes today. Five key knowledge contributions emerge from this enquiry. First, the thesis handles the concept of ‘power’ as a tool to enrich the traditionally depoliticised approaches regarding water access today in El Salvador. Second, the research builds an innovative conceptual synthesis on power, an ‘axes of power approach’. Third, the thesis provides new empirical evidence using an in-depth case study. Fourth, the study fills an existing gap in country-specific water politics knowledge. Finally, the research offers relevant knowledge in a key water governance period for El Salvador as policy-makers negotiate the country’s first General Water Law in its history

One Step Non SUSY Unification

We show that it is possible to achieve one step gauge coupling unification in a general class of non supersymmetric models which at low energies have only the standard particle content and extra Higgs fields doublets. The constraints are the experimental values of $\alpha_{em}$, $\alpha_s$ and $\sin^2\theta_W$ at $10^2 GeVs$, and the lower bounds for FCNC and proton decay rates. Specific example are pointed out.Comment: 10 pages, Latex file,, uses epsf style, Two Postscript figures included. To appear in Europhysics Letter