27 research outputs found
Cylindrical thin-shell wormholes
A general formalism for the dynamics of non rotating cylindrical thin-shell
wormholes is developed. The time evolution of the throat is explicitly obtained
for thin-shell wormholes whose metric has the form associated to local cosmic
strings. It is found that the throat collapses to zero radius, remains static
or expands forever, depending only on the sign of its initial velocity.Comment: 10 page
Morris-Thorne wormholes with a cosmological constant
First, the ideas introduced in the wormhole research field since the work of
Morris and Thorne are briefly reviewed, namely, the issues of energy
conditions, wormhole construction, stability, time machines and astrophysical
signatures. Then, spherically symmetric and static traversable Morris-Thorne
wormholes in the presence of a generic cosmological constant are analyzed. A
matching of an interior solution to the unique exterior vacuum solution is done
using directly the Einstein equations. The structure as well as several
physical properties and characteristics of traversable wormholes due to the
effects of the cosmological term are studied. Interesting equations appear in
the process of matching. For instance, one finds that for asymptotically flat
and anti-de Sitter spacetimes the surface tangential pressure of the
thin-shell, at the boundary of the interior and exterior solutions, is always
strictly positive, whereas for de Sitter spacetime it can take either sign as
one could expect, being negative (tension) for relatively high cosmological
constant and high wormhole radius, positive for relatively high mass and small
wormhole radius, and zero in-between. Finally, some specific solutions with
generic cosmological constant, based on the Morris-Thorne solutions, are
provided.Comment: latex, 49 pages, 8 figures. Expanded version of the paper published
in Physical Review
“Not a good look”: impossible dilemmas for young women negotiating the culture of intoxication in the United Kingdom.
This paper investigates young women's alcohol consumption in the United Kingdom within a widespread culture of intoxication in relation to recent debates about postfeminism and contemporary femininity. Young women are faced with an “impossible dilemma,” arising from the contradiction between a hedonistic discourse of alcohol consumption and postfeminist discourse around attaining and maintaining the “right” form of hypersexual heterosexual femininity. Drawing on a recent interview study with 24 young white working-class and middle-class women in the South-West of England, we explore how young women inhabit the dilemmas of contemporary femininity in youth drinking cultures, striving to achieve the “right” form of hypersexual femininity and an “optimum” level of drunkenness
Benthic macroinvertebrate community structure in a stream of the north-west region of Paraná State, Brazil
Predicting Condom Use: A Comparison of the Theory of Reasoned Action, the Theory of Planned Behavior and an Extended Model of TPB
Rising rural body-mass index is the main driver of the global obesity epidemic in adults
Body-mass index (BMI) has increased steadily in most countries in parallel with a rise in the proportion of the population who live in cities 1,2 . This has led to a widely reported view that urbanization is one of the most important drivers of the global rise in obesity 3�6 . Here we use 2,009 population-based studies, with measurements of height and weight in more than 112 million adults, to report national, regional and global trends in mean BMI segregated by place of residence (a rural or urban area) from 1985 to 2017. We show that, contrary to the dominant paradigm, more than 55 of the global rise in mean BMI from 1985 to 2017�and more than 80 in some low- and middle-income regions�was due to increases in BMI in rural areas. This large contribution stems from the fact that, with the exception of women in sub-Saharan Africa, BMI is increasing at the same rate or faster in rural areas than in cities in low- and middle-income regions. These trends have in turn resulted in a closing�and in some countries reversal�of the gap in BMI between urban and rural areas in low- and middle-income countries, especially for women. In high-income and industrialized countries, we noted a persistently higher rural BMI, especially for women. There is an urgent need for an integrated approach to rural nutrition that enhances financial and physical access to healthy foods, to avoid replacing the rural undernutrition disadvantage in poor countries with a more general malnutrition disadvantage that entails excessive consumption of low-quality calories. © 2019, The Author(s)