Transcritical flow of a stratified fluid: The forced extended Korteweg-de Vries model

Transcritical, or resonant, flow of a stratified fluid over an obstacle is studied using a forced extended Korteweg-de Vries model. This model is particularly relevant for a two-layer fluid when the layer depths are near critical, but can also be useful in other similar circumstances. Both quadratic and cubic nonlinearities are present and they are balanced by third-order dispersion. We consider both possible signs for the cubic nonlinear term but emphasize the less-studied case when the cubic nonlinear term and the dispersion term have the same-signed coefficients. In this case, our numerical computations show that two kinds of solitary waves are found in certain parameter regimes. One kind is similar to those of the well-known forced Korteweg-de Vries model and occurs when the cubic nonlinear term is rather small, while the other kind is irregularly generated waves of variable amplitude, which may continually interact. To explain this phenomenon, we develop a hydraulic theory in which the dispersion term in the model is omitted. This theory can predict the occurence of upstream and downstream undular bores, and these predictions are found to agree quite well with the numerical computations. © 2002 American Institute of Physics.published_or_final_versio

Psychological strategies to resist slowing down or stopping during endurance activity: An expert opinion paper

Within this paper, we provide an expert opinion on five evidence-based psychological strategies that could help endurance participants overcome slowing down and stopping during performance: goal setting, motivational self-talk, relaxation, distraction, and pacing. We argue that these strategies are well-suited for delivery as brief-contact, educational interventions that could be accessible to large numbers of participants who do not have access to a sport and exercise psychologist. These interventions could be delivered using websites, online videos, workshops, or magazine articles. We propose a novel use for implementation intentions (i.e. if-then planning) to develop endurance participants’ conditional knowledge of when to use specific strategies. In addition, although research evidence suggests that these psychological strategies may be efficacious for overcoming thoughts of slowing down or stopping, there are important limitations in the research evidence. In particular, there is a dearth of ecologically valid, field-based effectiveness studies. Finally, we consider situations where attempts to resist slowing down or stopping during endurance activity may not be advisable. Scenarios include when there is an increased likelihood of injury, or when environmental conditions increase the risk of life-threatening event

Structure, Deformations and Gravitational Wave Emission of Magnetars

Neutron stars can have, in some phases of their life, extremely strong magnetic fields, up to 10^15-10^16 G. These objects, named magnetars, could be powerful sources of gravitational waves, since their magnetic field could determine large deformations. We discuss the structure of the magnetic field of magnetars, and the deformation induced by this field. Finally, we discuss the perspective of detection of the gravitational waves emitted by these stars.Comment: 11 pages, 2 figures, prepared for 19th International Conference on General Relativity and Gravitation (GR19), Mexico City, Mexico, July 5-9, 201

Harnessing the health systems strengthening potential of quality improvement using realist evaluation : an example from southern Tanzania

‘Realist evaluation’ begins by establishing an initial programme theory, then identifying opportunities that support skill- and confidence-strengthening for optimising quality improvement (QI) as an implementation research approach. In this paper QI refers to participatory approaches through which stakeholders identify context-specific problems, and create and implement solutions. Local data are collected to determine whether improvements have been made; the entire process is data-driven. The realist evaluation process can generate better understanding about how health systems building blocks may be strengthened through QI processes

KINET: A social marketing programme of treated nets and net treatment for malaria control in Tanzania, with evaluation of child health and long-term survival

We present a large-scale social marketing programme of insecticide-treated nets in 2 rural districts in south-western Tanzania (population 350 000) and describe how the long-term child health and survival impact will be assessed. Formative and market research were conducted in order to understand community perceptions, knowledge, attitudes and practice with respect to the products to be socially marketed. We identified Zuia Mbu (Kiswahili for ‘prevent mosquitoes') as a suitable brand name for both treated nets and single-dose insecticide treatment sachets. A mix of public and private sales outlets is used for distribution. In the first stage of a stepped introduction 31 net agents were appointed and trained in 18 villages: 15 were shop owners, 14 were village leaders, 1 was a parish priest and 1 a health worker. For net treatment 37 young people were appointed in the same villages and trained as agents. Further institutions in both districts such as hospitals, development projects and employers were also involved in distribution. Promotion for both products was intense and used a variety of channels. A total of 22 410 nets and 8072 treatments were sold during the first year: 18 months after launching, 46% of 312 families with children aged under 5 years reported that their children were sleeping under treated nets. A strong evaluation component in over 50 000 people allows assessment of the long-term effects of insecticide-treated nets on child health and survival, anaemia in pregnancy, and the costs of the intervention. This evaluation is based on cross-sectional surveys, and case-control and cohort studie

Nitrate respiration and diel migration patterns of diatoms are linked in sediments underneath a microbial mat

Diatoms are among the few eukaryotes known to store nitrate (NO3−) and to use it as an electron acceptor for respiration in the absence of light and O2. Using microscopy and 15N stable isotope incubations, we studied the relationship between dissimilatory nitrate/nitrite reduction to ammonium (DNRA) and diel vertical migration of diatoms in phototrophic microbial mats and the underlying sediment of a sinkhole in Lake Huron (USA). We found that the diatoms rapidly accumulated NO3− at the mat-water interface in the afternoon and 40% of the population migrated deep into the sediment, where they were exposed to dark and anoxic conditions for ~75% of the day. The vertical distribution of DNRA rates and diatom abundance maxima coincided, suggesting that DNRA was the main energy generating metabolism of the diatom population. We conclude that the illuminated redox-dynamic ecosystem selects for migratory diatoms that can store nitrate for respiration in the absence of light. A major implication of this study is that the dominance of DNRA over denitrification is not explained by kinetics or thermodynamics. Rather, the dynamic conditions select for migratory diatoms that perform DNRA and can outcompete sessile denitrifiers

Quantitative predictions on auxin-induced polar distribution of PIN proteins during vein formation in leaves

The dynamic patterning of the plant hormone auxin and its efflux facilitator the PIN protein are the key regulator for the spatial and temporal organization of plant development. In particular auxin induces the polar localization of its own efflux facilitator. Due to this positive feedback auxin flow is directed and patterns of auxin and PIN arise. During the earliest stage of vein initiation in leaves auxin accumulates in a single cell in a rim of epidermal cells from which it flows into the ground meristem tissue of the leaf blade. There the localized auxin supply yields the successive polarization of PIN distribution along a strand of cells. We model the auxin and PIN dynamics within cells with a minimal canalization model. Solving the model analytically we uncover an excitable polarization front that triggers a polar distribution of PIN proteins in cells. As polarization fronts may extend to opposing directions from their initiation site we suggest a possible resolution to the puzzling occurrence of bipolar cells, such we offer an explanation for the development of closed, looped veins. Employing non-linear analysis we identify the role of the contributing microscopic processes during polarization. Furthermore, we deduce quantitative predictions on polarization fronts establishing a route to determine the up to now largely unknown kinetic rates of auxin and PIN dynamics.Comment: 9 pages, 4 figures, supplemental information included, accepted for publication in Eur. Phys. J.

Study protocol : improving newborn survival in rural southern Tanzania : a cluster-randomised trial to evaluate the impact of a scaleable package of interventions at community level with health system strengthening

Child mortality has declined substantially in many countries including Tanzania, but newborn mortality remains high and around 3 million babies die every year in the first 28 days of life. Community-based approaches with home visits in the first week of life have shown great potential to reduce newborn mortality. INSIST aimed1 to develop, implement and evaluate an integrated, two-part strategy that combines interventions at community level with health system strengthening in rural Southern Tanzania to reduce newborn mortality. The community intervention focused around interpersonal communication through home visits in pregnancy and the early neonatal period by a village-based "agent of change". Key messages focused on hygiene during delivery, immediate and exclusive breastfeeding, and identification and extra care for babies born small because of low birth weight or prematurity. Extra care for babies born small included skin-to-skin care for small babies and referral to hospital for very small babies. The community intervention was implemented in six poor rural districts in Southern Tanzania, with 65 of the 132 wards within these districts randomized to receive the community intervention. In addition, a health system quality-improvement package was implemented in all health facilities of one district. Data collection for the evaluation included i) a baseline household survey in 2007 of all 243,000 households in 5 of the 6 study districts to estimate baseline mortality and prevalence of newborn care behaviours, ii) an adequacy survey in 2011 in a representative sample of 5,000 households to estimate coverage of home visits and prevalence of newborn care behaviours, and iii) an endline household survey in 2013 in a representative sample of 200,000 households to estimate newborn and maternal mortality and prevalence of newborn care behaviours. The final analysis was based on "intention to treat", comparing newbor