Interacting quintessence from a variational approach. I. Algebraic couplings

We present a new approach to build models of quintessence interacting with dark or baryonic matter. We use a variational approach for relativistic fluids to realize an effective description of matter fields at the Lagrangian level. The coupling is introduced directly in the action by considering a single function mixing the dynamical degrees of freedom of the theory. The resulting gravitational field equations are derived by variations with respect to the independent variables. New interesting phenomenology can be obtained at both small scales, where new screening mechanisms for scalar fields can be realized, and large scales, where one finds an original and rich class of interacting quintessence models. The background cosmology of two of these models is studied in detail using dynamical system techniques. We find a variety of interesting results: for instance, these models contain dark energy dominated late-time attractors and scaling solutions, both with early-time matter dominated epochs and a possible inflationary origin. In general this new approach provides the starting point for future in-depth studies on new interacting quintessence models

Interacting quintessence from a variational approach. II. Derivative couplings

We consider an original variational approach for building new models of quintessence interacting with dark or baryonic matter. The coupling is introduced at the Lagrangian level using a variational formulation for relativistic fluids, where the interacting term generally depends on both the dynamical degrees of freedom of the theory and their spacetime derivatives. After deriving the field equations from the action, we consider applications in the context of cosmology. Two simple models are studied using dynamical system techniques showing the interesting phenomenology arising in this framework. We find that these models contain dark energy dominated late-time attractors with early-time matter dominated epochs and also obtain a possible dynamical crossing of the phantom barrier. The formulation and results presented here complete and expand the analysis exposed in the first part of this work, where only algebraic couplings, without spacetime derivatives, were considered

Einstein static universe in scalar-fluid theories

A new Lagrangian framework has recently been proposed to describe interactions between relativistic perfect fluids and scalar fields. In this paper we investigate the Einstein static universe in this new class of theories, which have been named scalar-fluid theories. The stability of the static solutions to both homogeneous and inhomogeneous perturbations is analyzed deriving the relevant cosmological perturbation equations at the linear order. We can find several configurations corresponding to an Einstein static universes which are stable against inhomogeneous perturbations, but unstable against homogeneous perturbations. This shows the possible applications of scalar-fluid theories to the inflationary emergent universe scenario

What can polysemy tell us about theories of explanation?

Philosophical accounts of scientific explanation are broadly divided into ontic and epistemic views. This paper explores the idea that the lexical ambiguity of the verb to explain and its nominalisation supports an ontic conception of explanation. I analyse one argument which challenges this strategy by criticising the claim that explanatory talk is lexically ambiguous, 375–394, 2012). I propose that the linguistic mechanism of transfer of meaning, 109–132, 1995) provides a better account of the lexical alternations that figure in the systematic polysemy of explanatory talk, and evaluate the implications of this proposal for the debate between ontic and epistemic conceptions of scientific explanation

Strong oviposition preference for Bt over non-Bt maize in Spodoptera frugiperda and its implications for the evolution of resistance

BACKGROUND: Transgenic crops expressing Bt toxins have substantial benefits for growers in terms of reduced synthetic insecticide inputs, area-wide pest management and yield. This valuable technology depends upon delaying the evolution of resistance. The ‘high dose/refuge strategy’, in which a refuge of non-Bt plants is planted in close proximity to the Bt crop, is the foundation of most existing resistance management. Most theoretical analyses of the high dose/refuge strategy assume random oviposition across refugia and Bt crops. RESULTS: In this study we examined oviposition and survival of Spodoptera frugiperda across conventional and Bt maize and explored the impact of oviposition behavior on the evolution of resistance in simulation models. Over six growing seasons oviposition rates per plant were higher in Bt crops than in refugia. The Cry1F Bt maize variety retained largely undamaged leaves, and oviposition preference was correlated with the level of feeding damage in the refuge. In simulation models, damage-avoiding oviposition accelerated the evolution of resistance and either led to requirements for larger refugia or undermined resistance management altogether. Since larval densities affected oviposition preferences, pest population dynamics affected resistance evolution: larger refugia were weakly beneficial for resistance management if they increased pest population sizes and the concomitant degree of leaf damage. CONCLUSIONS: Damaged host plants have reduced attractiveness to many insect pests, and crops expressing Bt toxins are generally less damaged than conventional counterparts. Resistance management strategies should take account of this behavior, as it has the potential to undermine the effectiveness of existing practice, especially in the tropics where many pests are polyvoltinous. Efforts to bring down total pest population sizes and/or increase the attractiveness of damaged conventional plants will have substantial benefits for slowing the evolution of resistance

A simulation tool for better management of retinal services

Background: Advances in the management of retinal diseases have been fast-paced as new treatments become available, resulting in increasing numbers of patients receiving treatment in hospital retinal services. These patients require frequent and long-term follow-up and repeated treatments, resulting in increased pressure on clinical workloads. Due to limited clinic capacity, many National Health Service (NHS) clinics are failing to maintain recommended follow-up intervals for patients receiving care. As such, clear and robust, long term retinal service models are required to assess and respond to the needs of local populations, both currently and in the future. Methods: A discrete event simulation (DES) tool was developed to facilitate the improvement of retinal services by identifying efficiencies and cost savings within the pathway of care. For a mid-size hospital in England serving a population of over 500,000, we used 36 months of patient level data in conjunction with statistical forecasting and simulation to predict the impact of making changes within the service. Results: A simulation of increased demand and a potential solution of the 'Treat and Extend' (T&E) regimen which is reported to result in better outcomes, in combination with virtual clinics which improve quality, effectiveness and productivity and thus increase capacity is presented. Without the virtual clinic, where T&E is implemented along with the current service, we notice a sharp increase in the number of follow-ups, number of Anti-VEGF injections, and utilisation of resources. In the case of combining T&E with virtual clinics, there is a negligible (almost 0%) impact on utilisation of resources. Conclusions: Expansion of services to accommodate increasing number of patients seen and treated in retinal services is feasible with service re-organisation. It is inevitable that some form of initial investment is required to implement service expansion through T&E and virtual clinics. However, modelling with DES indicates that such investment is outweighed by cost reductions in the long term as more patients receive optimal treatment and retain vision with better outcomes. The model also shows that the service will experience an average of 10% increase in surplus capacity.Peer reviewedFinal Published versio

Isolated colostomy site recurrence in rectal cancer-two cases with review of literature

<p>Abstract</p> <p>Background</p> <p>Colostomy site carcinomas are rare with only eight cases reported in the world literature. Various etiological factors like adenoma-cancer sequence, bile acids, recurrent and persistent physical damage at the colostomy site by faecal matter due to associated stomal stenosis have been considered responsible. Two such cases are being reported and in both cases there was no evidence of any local recurrence in the pelvis or liver and distant metastasis. Both patients had received adjuvant chemotherapy following surgery.</p> <p>Case presentation</p> <p>First case was a 30-year-old male that had reported with large bowel obstruction due to an obstructing ulcero-proliferative growth (poorly differentiated adenocarcinoma) at the colostomy site after abdomino-perineal resection, performed for low rectal cancer six years previously. Wide local excision with microscopically free margins was performed with a satisfactory outcome. Four years later he presented with massive malignant ascites, cachexia and multiple liver metastasis and succumbed to his disease.</p> <p>Second case was a 47-year-old male that presented with acute large bowel obstruction due to an annular growth (well differentiated adenocarcinoma) in the upper rectum. He was managed by Hartmann's operation and the sigmoid colostomy was closed six months later. Five years following closure of colostomy, he presented with two parietal masses at the previous colostomy site scar, which, on fine needle aspiration cytology were found to be well-differentiated adenocarcinomas of colorectal type. Surgery in the form of wide local resection with free margins was performed. He presented again after five years with recurrence along the previous surgery scar and an incisional hernia and was managed by wide local excision along with hernioplasty. Follow-up of nine years following first surgery is satisfactory.</p> <p>Conclusion</p> <p>Colostomy site/scar recurrence of rectal carcinoma is rare and could be due to various etiological factors, although the exact causative mechanism is not known. Surgery with microscopically free margins is recommended in the absence of metastatic disease. Stenosis of the stoma is considered as one of the most important contributory factors and should be followed carefully.</p

A systematic review of biomarkers for disease progression in Parkinson's disease

Peer reviewedPublisher PD

Which circulating antioxidant vitamins are confounded by socioeconomic deprivation? The MIDSPAN family study

&lt;p&gt;&lt;b&gt;Background:&lt;/b&gt; Antioxidant vitamins are often described as having “independent” associations with risk of cancer, cardiovascular disease (CVD) and mortality. We aimed to compare to what extent a range of antioxidant vitamins and carotenoids are associated with adulthood and childhood markers of socioeconomic deprivation and to adverse lifestyle factors.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Methods and Findings:&lt;/b&gt; Socioeconomic and lifestyle measures were available in 1040 men and 1298 women from the MIDSPAN Family Study (30–59 years at baseline) together with circulating levels of vitamins A, C, E, and carotenoids (α-carotene, β-carotene, lutein and lycopene). Markers of socioeconomic deprivation in adulthood were consistently as strongly associated with lower vitamin C and carotenoid levels as markers of adverse lifestyle; the inverse association with overcrowding was particularly consistent (vitamin C and carotenoids range from 19.1% [95% CI 30.3–6.0] to 38.8% [49.9–25.3] lower among those in overcrowded residencies). These associations were consistent after adjusting for month, classical CVD risk factors, body mass index, physical activity, vitamin supplements, dietary fat and fibre intake. Similar, but weaker, associations were seen for childhood markers of deprivation. The association of vitamin A or E were strikingly different; several adult adverse lifestyle factors associated with higher levels of vitamin A and E, including high alcohol intake for vitamin A (9.5% [5.7–13.5]) and waist hip ratio for vitamin E (9.5% [4.8–14.4]), with the latter associations partially explained by classical risk factors, particularly cholesterol levels.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Conclusions:&lt;/b&gt; Plasma vitamin C and carotenoids have strong inverse associations with adulthood markers of social deprivation, whereas vitamin A and E appear positively related to specific adverse lifestyle factors. These findings should help researchers better contextualize blood antioxidant vitamin levels by illustrating the potential limitations associated with making causal inferences without consideration of social deprivation.&lt;/p&gt