A Cross-Over in the Enstrophy Decay in Two-Dimensional Turbulence in a Finite Box

The numerical simulation of two-dimensional decaying turbulence in a large but finite box presented in this paper uncovered two physically different regimes of enstrophy decay. During the initial stage, the enstrophy, generated by a random Gaussian initial condition, decays as t^{-gamma} with gamma approximately 0.7-0.8. After that, the flow undergoes a transition to a gas or fluid composed of distinct vortices. Simultaneously, the magnitude of the decay exponent crosses over to gamma approximately 0.4. An exact relation for the total number of vortices, N(t), in terms of the mean circulation of an individual vortex is derived. A theory predicting that N(t) is proportional to t^{-xi} and the magnitudes of exponents gamma=2/5 and xi=4/5 is presented and the possibility of an additional very late-time cross-over to gamma=1/3 and xi=2/3 is also discussed.Comment: 11 pages, 7 figure

Report from an EWRS workshop on modelling weed population dynamics

A three-day workshop on modelling weed population dynamics partially sponsored by the European Weed Research Society (EWRS) was held in October 2006 at Research Centre Flakkebjerg. 24 participants attended the workshop from 8 countries, mainly Europe and USA. The aim of the workshop was to gather some of those active and interested in the field, i.e. most of the participants had either published papers on weed population dynamic models or had a model under development. By gathering these people, it was our hope to learn from each other and possibly benefit by increasing the knowledge and use of each other's work. The EWRS saw the workshop as an opportunity to interconnect some of the work going on in (at least) three working groups: Weed Seed Germination and Early Growth, Crop-Weed Interactions and Physical and Cultural Weed Control. The preparations of the workshop were initiated by the keynote paper on modelling weed population dynamics presented by N. Holst at the EWRS Symposium in Bari, Italy, 2005, which has recently been published in Weed Research. In connection with this, a database with a bibliography of publications on weed population dynamic models was created, and is public online at http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-3180.2007.00534.x. At the workshop, ten weed population dynamics models were presented, and all of these were available on computers for the participants to try. Many of the models are freely available on the Internet, although some must be paid for, and some are still under development. The themes discussed at the workshop were presented under five headings: 1. Using models for understanding weed biology, 2. Modelling tools for understanding the dynamics of weed populations, 3. Using models for prediction purposes and decision support, 4. Understanding basic spatial-temporal dynamics through use of models and 5. Model analysis. A common understanding at the workshop, in respect of the fact that no model can accurately show the complexity of the real world, was that "All models are wrong – but some are useful". Some important discussion points brought up at the workshop were related to application domain and model complexity. Are the models used to explain what actually has happened, or are they used for forecasting. It was decided that some of the participants will collaborate on a common publication on this subject. Another topic was the required level of complexity also phrased as ‘How long do we keep on improving our models?’ Does added complexity make the model more realistic, or does it just add errors? We also discussed how we could make better use of each other's work. In this regard it was decided to make a list of the presented models, including links to the models and where possible open source code, so that parts of generic models could be used by other modellers. In addition, a common database with parameters characterizing different life cycle stages of specific weed species was planned. Since participants agreed that this workshop was a very important opportunity for weed population dynamics modellers to convene, it was suggested that a new workshop should be arranged within 2-3 years, location depending on possibilities for sponsoring

Gender perspectives on views and preferences of older people on exercise to prevent falls: a systematic mixed studies review

Background: To offer fall prevention exercise programs that attract older people of both sexes there is a need to understand both womens and mens views and preferences regarding these programs. This paper aims to systematically review the literature to explore any underlying gender perspectives or gender interpretations on older peoples views or preferences regarding uptake and adherence to exercise to prevent falls. Methods: A review of the literature was carried out using a convergent qualitative design based on systematic searches of seven electronic databases (PubMed, CINAHL, Amed, PsycINFO, Scopus, PEDro, and OTseeker). Two investigators identified eligible studies. Each included article was read by at least two authors independently to extract data into tables. Views and preferences reported were coded and summarized in themes of facilitators and barriers using a thematic analysis approach. Results: Nine hundred and nine unique studies were identified. Twenty five studies met the criteria for inclusion. Only five of these contained a gender analysis of mens and womens views on fall prevention exercises. The results suggests that both women and men see women as more receptive to and in more need of fall prevention messages. The synthesis from all 25 studies identified six themes illustrating facilitators and six themes describing barriers for older people either starting or adhering to fall prevention exercise. The facilitators were: support from professionals or family; social interaction; perceived benefits; a supportive exercise context; feelings of commitment; and having fun. Barriers were: practical issues; concerns about exercise; unawareness; reduced health status; lack of support; and lack of interest. Considerably more women than men were included in the studies. Conclusion: Although there is plenty of information on the facilitators and barriers to falls prevention exercise in older people, there is a distinct lack of studies investigating differences or similarities in older womens and mens views regarding fall prevention exercise. In order to ensure that fall prevention exercise is appealing to both sexes and that the inclusion of both men and women are encouraged, more research is needed to find out whether gender differences exists and whether practitioners need to offer a range of opportunities and support strategies to attract both women and men to falls prevention exercise.Funding Agencies|Swedish Research Council [2015-03481]; Strategic Research Programme in Care Sciences, Umea University; Karolinska Institute, Sweden; Umea University</p

Antibiotic use among 8-month-old children in Malmö, Sweden – in relation to child characteristics and parental sociodemographic, psychosocial and lifestyle factors

In the county of Scania, Sweden, antibiotic use among small children is among the highest in the country. The aim of this study was to investigate the associations between antibiotic use among 8-month-old children in Malmö and characteristics of the child as well as parental sociodemographic characteristics, lifestyle factors, and psychosocial support. The study was a population-based cross-sectional survey. The study population consisted of children who visited the Child Health Care (CHC) centres in Malmö for their 8-month health checkup during 2003–2006 and whose parents answered a self-administered questionnaire (n = 7266 children). The questionnaire was distributed to parents of children registered with the CHC and invited for an 8-month checkup during the study period. The odds of using antibiotics increased as parental educational level decreased. Using high educational level as a reference group, low maternal educational level was associated with an increased antibiotic use for the child, odds ratio (OR) = 1.61 (95% CI: 1.34–1.93). Furthermore, children whose parents were born outside Sweden showed higher antibiotic use, OR = 1.43 (95% CI: 1.24–1.65), in comparison with children whose parents were born in Sweden. Exposure to environmental smoking, parental experience of economic stress, and a low level of emotional support increased the odds for antibiotic use. Boys had higher odds of use of antibiotics than girls, OR = 1.40 (95% CI: 1.25–1.57). Having a low birth weight, having an allergy and having siblings also increased the odds for early antibiotic use, while breastfeeding seemed to have a protective role. Conclusion There were clear associations between parental factors such as sociodemographic, psychosocial and lifestyle factors and antibiotic use at this early stage of life. Several characteristics of the child also affected the use of antibiotics

The Mre11-Rad50-Nbs1 complex mediates activation of TopBP1 by ATM

The activation of ATR-ATRIP in response to double-stranded DNA breaks (DSBs) depends upon ATM in human cells and Xenopus egg extracts. One important aspect of this dependency involves regulation of TopBP1 by ATM. In Xenopus egg extracts, ATM associates with TopBP1 and thereupon phosphorylates it on S1131. This phosphorylation enhances the capacity of TopBP1 to activate the ATR-ATRIP complex. We show that TopBP1 also interacts with the Mre11-Rad50-Nbs1 (MRN) complex in egg extracts in a checkpoint-regulated manner. This interaction involves the Nbs1 subunit of the complex. ATM can no longer interact with TopBP1 in Nbs1-depleted egg extracts, which suggests that the MRN complex helps to bridge ATM and TopBP1 together. The association between TopBP1 and Nbs1 involves the first pair of BRCT repeats in TopBP1. In addition, the two tandem BRCT repeats of Nbs1 are required for this binding. Functional studies with mutated forms of TopBP1 and Nbs1 suggested that the BRCT-dependent association of these proteins is critical for a normal checkpoint response to DSBs. These findings suggest that the MRN complex is a crucial mediator in the process whereby ATM promotes the TopBP1-dependent activation of ATR-ATRIP in response to DSBs