Homogenization of an ensemble of interacting resonant scatterers

We study theoretically the concept of homogenization in optics using an ensemble of randomly distributed resonant stationary atoms with density $\rho$. The ensemble is dense enough for the usual condition for homogenization, viz. $\rho\lambda^3 \gg 1$, to be reached. Introducing the coherent and incoherent scattered powers, we define two criteria to define the homogenization regime. We find that when the excitation field is tuned in a broad frequency range around the resonance, none of the criteria for homogenization is fulfilled, meaning that the condition $\rho\lambda^3\gg 1$ is not sufficient to characterize the homogenized regime around the atomic resonance. We interpret these results as a consequence of the light-induced dipole-dipole interactions between the atoms, which implies a description of scattering in terms of collective modes rather than as a sequence of individual scattering events. Finally, we show that, although homogenization can never be reached for a dense ensemble of randomly positioned laser-cooled atoms around resonance, it becomes possible if one introduces spatial correlations in the positions of the atoms or non-radiative losses, such as would be the case for organic molecules or quantum dots coupled to a phonon bath.Comment: 9 pages, 5 figures. Corrected mistakes in reference

Current ethical issues in synthetic biology: Where should we go from here?

Synthetic Biology (SynBio) is an emerging scientific field which has quickly established momentum and visibility. Although no single definition of SynBio prevails, the field broadly encompasses the application of engineering principles to biology; re-designing biological materials and using them as new substrates to create products and entities not otherwise found in nature. This paper first reviews SynBio, highlighting the novel aspects of this technology. It then synthesises ethical issues highlighted in the literature to date and makes some initial claims that research on the ethical aspects of SynBio should: avoid creating a new sub-type of bioethics, concentrate on novel concepts and problems and be situated within a context of cooperative inter-disciplinary investigation. Keywords: Synthetic biology, ethical issues, regulation, creating life.This article was written by Dr Ainsley Newson during the time of her employment with the University of Bristol, UK (2006-2012). Self-archived in the Sydney eScholarship Repository with permission of Bristol University, Sept 2014

Respiratory tract infection-related healthcare utilisation in children with Down's syndrome

Purpose: Children with Down’s syndrome (DS) are prone to respiratory tract infections (RTIs) due to anatomical variation, immune system immaturity and comorbidities. However, evidence on RTI-related healthcare utilisation, especially in primary care, is incomplete. In this retrospective cohort study, we use routinely collected primary and secondary care data to quantify RTI-related healthcare utilisation in children with DS and matched controls without DS. Methods: Retrospective cohort study of 992 children with DS and 4874 matched controls attending English general practices and hospitals as identified in Clinical disease research using LInked Bespoke studies and Electronic health Records (CALIBER) from 1997 to 2010. Poisson regression was used to calculate consultation, hospitalisation and prescription rates, and rate ratios. Wald test was used to compare risk of admission following consultation. The Wilcoxon rank–sum test was used to compare length of stay by RTI type and time-to-hospitalisation. Results: RTI-related healthcare utilisation is significantly higher in children with DS than in controls in terms of GP consultations (adjusted RR 1.73; 95% CI 1.62–1.84), hospitalisations (adjusted RR 5.70; 95% CI 4.82–6.73), and antibiotic prescribing (adjusted RR 2.34; 95% CI 2.19–2.49). Two percent of children with DS presenting for an RTI-related GP consultation were subsequently admitted for an RTI-related hospitalisation, compared to 0.7% in controls. Conclusions: Children with DS have higher rates of GP consultations, hospitalisations and antibiotic prescribing compared to controls. This poses a significant burden on families. Further research is recommended to characterise healthcare behaviours and clinical decision-making, to optimise care for this at risk group

Effect of antibiotics in preventing hospitalizations from respiratory tract infections in children with Down syndrome

BACKGROUND: Children with Down Syndrome (DS) are at high risk of respiratory tract infections (RTIs) due to anatomical variations, comorbidities and immune system immaturity. Evidence on interventions to reduce this risk is incomplete. This study aims to quantify the effect of antibiotics prescribed for RTIs in primary care on the subsequent risk of RTI-related hospitalisation for children with DS versus controls. METHODS: We conducted a retrospective cohort study of 992 children with DS and 4,874 controls managed by UK National Health Service (NHS) General Practitioners (GPs) and hospitals as identified in CALIBER (Clinical disease research using LInked Bespoke studies and Electronic health Records), 1997-2010. Univariate and multivariate logistic regression were undertaken. RESULTS: In children with DS, the prescription of antibiotics following an RTI-related GP consultation did not significantly reduce the risk of RTI-related hospitalisation in the subsequent 28 days (Risk with antibiotics 1.8%; without 2.5%; Risk Ratio (RR) 0.699, 95% Confidence Interval (CI) 0.471-1.036). Subgroup analyses showed a risk reduction only in infants with DS, after adjustment for covariates. There was no reduction in risk for controls, overall or across subgroups. CONCLUSIONS: In conclusion, whilst prescription of antibiotics following RTI-related GP consultations were effective for infants with DS in reducing subsequent RTI-related hospitalisation, this was not the case for older children with DS. We would encourage further high-quality cohort and randomised controlled trials to interrogate this finding, and to examine the impact of antibiotics on other endpoints, including symptom duration. This article is protected by copyright. All rights reserved

Long-term effect of ventilation tubes for persistent otitis media with effusion in children.

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