28,301 research outputs found
The role of dust in "active" and "passive" low-metallicity star formation
We investigate the role of dust in star formation activity of extremely
metal-poor blue compact dwarf galaxies (BCDs). Observations suggest that star
formation in BCDs occurs in two different regimes: "active" and "passive". The
"active" BCDs host super star clusters (SSCs), and are characterised by compact
size, rich H2 content, large dust optical depth, and high dust temperature; the
"passive" BCDs are more diffuse with cooler dust, and lack SSCs and large
amounts of H2. By treating physical processes concerning formation of stars and
dust, we are able to simultaneously reproduce all the above properties of both
modes of star formation (active and passive). We find that the difference
between the two regimes can be understood through the variation of the
"compactness" of the star-forming region: an "active" mode emerges if the
region is compact (with radius \la 50 pc) and dense (with gas number density
\ga 500 cm). The dust, supplied from Type II supernovae in a compact
star-forming region, effectively reprocesses the heating photons into the
infrared and induces a rapid H2 formation over a period of several Myr. This
explains the high infrared luminosity, high dust temperature, and large H2
content of active BCDs. Moreover, the gas in "active" galaxies cools (\la 300
K) on a few dynamical timescales, producing a "run-away" star formation episode
because of the favourable (cool) conditions. The mild extinction and relatively
low molecular content of passive BCDs can also be explained by the same model
if we assume a diffuse region (with radius \ga 100 pc and gas number density
\la 100 cm). We finally discuss primordial star formation in
high-redshift galaxies in the context of the "active" and "passive" star
formation scenario.Comment: Astronomy and Astrophysics, in press, 16 pages, 8 figure
The size--density relation of extragalactic HII regions
We investigate the size--density relation in extragalactic HII regions, with
the aim of understanding the role of dust and different physical conditions in
the ionized medium. First, we compiled several observational data sets for
Galactic and extragalactic HII regions and confirm that extragalactic HII
regions follow the same size (D)--density (n) relation as Galactic ones.
Motivated by the inability of static models to explain this, we then modelled
the evolution of the size--density relation of HII regions by considering their
star formation history, the effects of dust, and pressure-driven expansion. The
results are compared with our sample data whose size and density span roughly
six orders of magnitude. We find that the extragalactic size--density relation
does not result from an evolutionary sequence of HII regions but rather
reflects a sequence with different initial gas densities (``density
hierarchy''). Moreover, the size of many HII regions is limited by dust
absorption of ionizing photons, rather than consumption by ionizing neutral
hydrogen. Dust extinction of ionizing photons is particularly severe over the
entire lifetime of compact HII regions with typical gas densities of greater
than 10^3 cm^{-3}. Hence, as long as the number of ionizing photons is used to
trace massive star formation, much star-formation activity could be missed.
Such compact dense environments, the ones most profoundly obscured by dust,
have properties similar to ``maximum--intensity starbursts''. This implies that
submillimeter and infrared wavelengths may be necessary to accurately assess
star formation in these extreme conditions both locally and at high redshift.Comment: 18 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Positive associations between consumerism and tobacco and alcohol use in early adolescence: cross-sectional study
<p>Background: There is concern about the negative impact of modern consumer culture on young people's mental health, but very few studies have investigated associations with substance use. In those which have, positive associations have been attributed to attempts to satisfy the unmet needs of more materialistic individuals.</p>
<p>Objectives: This study examines associations between different dimensions of consumerism and tobacco and alcohol use among Scottish early adolescents.</p>
<p>Design: Cross-sectional study.</p>
<p>Setting and participants: 2937 (92% of those eligible) secondary school pupils (ages 12–14) completed questionnaires in examination conditions. Analyses were restricted to those with complete data on all relevant variables (N=2736 smoking; N=2737 drinking).</p>
<p>Measures: Dependent variables comprised ever smoking and current drinking. Measures of consumerism comprised number of ‘premium’ (range 0–7) and ‘standard’ (range 0–5) material possessions and three Consumer Involvement subscales, ‘dissatisfaction’, ‘consumer orientation’ and ‘brand awareness’ (each range 3–12). Analyses also included school-year group and family affluence.</p>
<p>Results: Ever smoking and current drinking were both more prevalent among adolescents with more ‘premium’ and ‘standard’ material possessions, greater consumer ‘dissatisfaction’ and ‘brand awareness’ (mutually adjusted analyses including school-year group and family affluence). The strongest relationships occurred for ‘brand awareness’: for each unit increase in ‘brand awareness’ the ORs (95% CI) of ever smoking were 1.17 (1.08 to 1.26) and 1.23 (1.14 to 1.33) in males and females, respectively; and those for drinking were 1.15 (1.08 to 1.23) and 1.21 (1.13 to 1.30). ‘Brand awareness’ had an equal or stronger relationship with both smoking and drinking than did family affluence.</p>
<p>Conclusions: These results suggest aassociations between consumerism and both smoking and drinking might arise because adolescent identities incorporate both consumerism and substance use, or be the result of promotion (indirectly in the case of tobacco) linking consumerist or aspirational lifestyles with these behaviours.</p>
Orientation of \u3ci\u3eHylobius Pales\u3c/i\u3e and \u3ci\u3ePachylobius Picivorus\u3c/i\u3e (Coleoptera: Curculionidae) to Visual Cues
Pitfall traps with above-ground silhouettes of various colors and diameters were used in field tests to evaluate the role of vision in host orientation by adult pales weevils, Hylobius pales, and pitch-eating weevils, Pachylobius picivorus. White traps (11 em outer diameter) baited with ethanol and turpentine caught significantly more weevils than similarly baited black or green traps (11 cm outer diameter). Trap diameter (range of 6-22 cm outer diameter) did not affect trap catch. Pitfall traps can be used to monitor root weevil populations in young pine plantations and Christmas tree farms, where they are major pests. These results demonstrate that visual and chemical cues can be integrated to improve trap efficiency
Managing multiple morbidity in mid-life: a qualitative study of attitudes to drug use
OBJECTIVE: To examine attitudes towards drug use among middle aged respondents with high levels of chronic morbidity. DESIGN: Qualitative study with detailed interviews. SETTING: West of Scotland. PARTICIPANTS: 23 men and women aged about 50 years with four or more chronic illnesses. MAIN OUTCOME MEASURE: Participants' feelings about long term use of drugs to manage chronic multiple morbidity. RESULTS: Drugs occupied a central place in the way people managed their comorbidities. Respondents expressed an aversion to taking drugs, despite acknowledging that they depended on drugs to live as "normal" a life as possible. Respondents expressed ambivalence to their drugs in various ways. Firstly, they adopted both regular and more flexible regimens and might adhere to a regular regimen in treating one condition (such as hypertension) while adopting a flexible regimen in relation to others, in response to their experience of symptoms or varying demands of their daily life. Secondly, they expressed reluctance to take drugs, but an inability to be free of them. Thirdly, drugs both facilitated performance of social roles and served as evidence of an inability to perform such roles. CONCLUSIONS: Insight into the considerable tension experienced by people managing complex drug regimens to manage multiple chronic illness may help medical carers to support self care practices among patients and to optimise concordance in their use of prescribed drugs
Consumerism and well-being in early adolescence
It has been suggested that consumerism is negatively related to well-being in children and adolescents, as well as adults. Few studies have explored whether certain aspects of consumerism have stronger associations with well-being than others, or between-group differences in associations. This article uses data from a sample of early adolescents to examine: levels of consumerism; relationships between different aspects of consumerism and well-being; and differences according to gender, school year group and family affluence. Data were obtained in 2010 via secondary school pupil surveys (N=2934). Consumerism measures comprised number of ‘standard’ and ‘premium’ possessions and four dimensions of consumer involvement; well-being measures comprised self-esteem, psychological distress and anger. There was evidence of high penetration of consumerist values. There were positive associations between number of possessions and anger, and between ‘dissatisfaction’ and poorer well-being, regardless of how measured. ‘Brand awareness’ was associated with positive male well-being, but negative female well-being. Many relationships between consumerism and well-being were stronger than those between family affluence and well-being. These results suggest only certain aspects of consumerism are associated with poorer adolescent well-being. Although, for some sub-groups, other aspects might be associated with better well-being, there was no evidence that modern consumer goods promote happiness
Network Synchronization in a Noisy Environment with Time Delays: Fundamental Limits and Trade-Offs
We study the effects of nonzero time delays in stochastic synchronization
problems with linear couplings in an arbitrary network. Using the known exact
threshold value from the theory of differential equations with delays, we
provide the synchronizability threshold for an arbitrary network. Further, by
constructing the scaling theory of the underlying fluctuations, we establish
the absolute limit of synchronization efficiency in a noisy environment with
uniform time delays, i.e., the minimum attainable value of the width of the
synchronization landscape. Our results have also strong implications for
optimization and trade-offs in network synchronization with delays.Comment: 3 figure
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