Far-field scattering microscopy applied to analysis of slow light, power enhancement, and delay times in uniform Bragg waveguide gratings

A novel method is presented for determining the group index, intensity enhancement and delay times for waveguide gratings, based on (Rayleigh) scattering observations. This far-field scattering microscopy (FScM) method is compared with the phase shift method and a method that uses the transmission spectrum to quantify the slow wave properties. We find a minimum group velocity of 0.04c and a maximum intensity enhancement of ~14.5 for a 1000-period grating and a maximum group delay of ~80 ps for a 2000-period grating. Furthermore, we show that the FScM method can be used for both displaying the intensity distribution of the Bloch resonances and for investigating out of plane losses. Finally, an application is discussed for the slow-wave grating as index sensor able to detect a minimum cladding index change of $10^{-8}$, assuming a transmission detection limit of $10^{-4}$

Optical conductivity of wet DNA

Motivated by recent experiments we have studied the optical conductivity of DNA in its natural environment containing water molecules and counter ions. Our density functional theory calculations (using SIESTA) for four base pair B-DNA with order 250 surrounding water molecules suggest a thermally activated doping of the DNA by water states which generically leads to an electronic contribution to low-frequency absorption. The main contributions to the doping result from water near DNA ends, breaks, or nicks and are thus potentially associated with temporal or structural defects in the DNA.Comment: 4 pages, 4 figures included, final version, accepted for publication in Phys. Rev. Let

Antidepressant use in late gestation and risk of postpartum haemorrhage: a retrospective cohort study

Objective: To investigate the association between antidepressant use in late gestation and postpartum haemorrhage (PPH). Design: Retrospective cohort study. Tertiary teaching hospital in Adelaide, Australia. Population: A total of 30 198 women delivering between 2002 and 2008. Methods: Relative risks adjusted for maternal sociodemographics and comorbidities (aRRs) were calculated for PPH, comparing women with late-gestation exposure to antidepressants (n = 558), women with a psychiatric illness but no antidepressant use (n = 1292), and women with neither antenatal exposures (n = 28 348). Additional sensitivity analyses were undertaken, examining associations with severe PPH and postpartum anaemia. Main Outcome Measures: The primary outcome was PPH, defined as a recorded blood loss of ≥500 mL for vaginal deliveries and ≥1000 mL for caesarean sections. Secondary outcomes included severe PPH (≥1000 mL blood loss, irrespective of method of delivery), and the presence of postpartum anaemia (identified from hospital medical records). Results: Compared with unexposed controls, women exposed to antidepressants had an increased risk of PPH (aRR 1.53; 95% confidence interval, 95% CI 1.25-1.86), whereas no increased risk was observed for women with a psychiatric illness but no antidepressant use (aRR 1.04; 95% CI 0.89-1.23). In sensitivity analyses, late gestation antidepressant exposure was associated with an increased risk of severe PPH (aRR 1.84; 95% CI 1.39-2.44), as well as postpartum anaemia (aRR 1.80; 95% CI 1.46-2.22). Conclusions: Exposure to antidepressants in late gestation was associated with a significantly increased risk of PPH. Although potential confounding by unmeasured factors cannot be ruled out, these findings suggest a direct effect of antidepressant exposure on PPH.LE Grzeskowiak, R McBain, GA Dekker, VL Clifto

Models for local ohmic quantum dissipation

We construct model master equations for local quantum dissipation. The master equations are in the form of Lindblad generators, with imposed constraints that the dissipations be strictly linear (i.e. ohmic), isotropic and translationally invariant. A particular form for is chosen to satisfy the constraints. The resulting master equations are given in both the Schr\"odinger and Heisenberg forms. We obtain fluctuation-dissipation relations, and discuss the relaxation of average kinetic energy to effective thermal equilibrium values. We compare our results to the Dekker and the Caldeira-Leggett master equations. These master equations allow a more general approach to quantum dissipation and the dynamics of quantum coherence to account for the nontrivial system-environment coupling in a local environment.Comment: 19 pages, REVTEX, PSU/TH/12

The health potential of neighborhoods:A population-wide study in the Netherlands

Background: While differences in population health across neighborhoods with different socioeconomic characteristics are well documented, health disparities across neighborhoods with similar socioeconomic characteristics are less well understood. We aimed to estimate population health inequalities, both within and between neighborhoods with similar socioeconomic status, and assessed the association of neighborhood characteristics and socioeconomic spillover effects from adjacent neighborhoods. Methods: Based on Dutch whole-population data we determined the percentage of inhabitants with good or very good self-assessed health (SAH) and the percentage of inhabitants with at least one chronic disease (CD) in 11,504 neighborhoods. Neighborhoods were classified by quintiles of a composite neighborhoods socioeconomic status score (NSES). A set of spatial models was estimated accounting for spatial effects in the dependent, independent, and error components of the model. Results: Substantial population health disparities in SAH and CD both within and between neighborhoods NSES quintiles were observed, with the largest SAH variance in the lowest NSES group. Neighborhoods adjacent to higher SES neighborhoods showed a higher SAH and a lower prevalence of CD. Projected impacts from the spatial regressions indicate how modest changes in NSES among the lowest socioeconomic neighborhoods can contribute to population health in both low- and high-SES neighborhoods. Conclusion: Population health differs substantially among neighborhoods with similar socioeconomic characteristics, which can partially be explained by a spatial socio-economic spillover effect

High-Field Electrical Transport in Single-Wall Carbon Nanotubes

Using low-resistance electrical contacts, we have measured the intrinsic high-field transport properties of metallic single-wall carbon nanotubes. Individual nanotubes appear to be able to carry currents with a density exceeding 10^9 A/cm^2. As the bias voltage is increased, the conductance drops dramatically due to scattering of electrons. We show that the current-voltage characteristics can be explained by considering optical or zone-boundary phonon emission as the dominant scattering mechanism at high field.Comment: 4 pages, 3 eps figure

Completely Positive Quantum Dissipation

A completely positive master equation describing quantum dissipation for a Brownian particle is derived starting from microphysical collisions, exploiting a recently introduced approach to subdynamics of a macrosystem. The obtained equation can be cast into Lindblad form with a single generator for each Cartesian direction. Temperature dependent friction and diffusion coefficients for both position and momentum are expressed in terms of the collision cross-section.Comment: 8 pages, revtex, no figure

Exploration and confirmation of factors associated with uncomplicated pregnancy in nulliparous women: prospective cohort study

Objective: To identify factors at 15 and 20 weeks’ gestation associated with a subsequent uncomplicated pregnancy. Design: Prospective international multicentre observational cohort study. Setting: Auckland, New Zealand and Adelaide, Australia (exploration and local replication dataset) and Manchester, Leeds, and London, United Kingdom, and Cork, Republic of Ireland (external confirmation dataset). Participants: 5628 healthy nulliparous women with a singleton pregnancy. Main outcome measure: Uncomplicated pregnancy, defined as a normotensive pregnancy delivered at >37 weeks’ gestation, resulting in a liveborn baby not small for gestational age, and the absence of any other significant pregnancy complications. In a stepwise logistic regression the comparison group was women with a complicated pregnancy. Results: Of the 5628 women, 3452 (61.3%) had an uncomplicated pregnancy. Factors that reduced the likelihood of an uncomplicated pregnancy included increased body mass index (relative risk 0.74, 95% confidence intervals 0.65 to 0.84), misuse of drugs in the first trimester (0.90, 0.84 to 0.97), mean diastolic blood pressure (for each 5 mm Hg increase 0.92, 0.91 to 0.94), and mean systolic blood pressure (for each 5 mm Hg increase 0.95, 0.94 to 0.96). Beneficial factors were prepregnancy fruit intake at least three times daily (1.09, 1.01 to 1.18) and being in paid employment (per eight hours’ increase 1.02, 1.01 to 1.04). Detrimental factors not amenable to alteration were a history of hypertension while using oral contraception, socioeconomic index, family history of any hypertensive complications in pregnancy, vaginal bleeding during pregnancy, and increasing uterine artery resistance index. Smoking in pregnancy was noted to be a detrimental factor in the initial two datasets but did not remain in the final model. Conclusions: This study identified factors associated with normal pregnancy through adoption of a novel hypothesis generating approach, which has shifted the emphasis away from adverse outcomes towards uncomplicated pregnancies. Although confirmation in other cohorts is necessary, this study implies that individually targeted lifestyle interventions (normalising maternal weight, increasing prepregnancy fruit intake, reducing blood pressure, stopping misuse of drugs) may increase the likelihood of normal pregnancy outcomes.Lucy C Chappell, Paul T Seed, Jenny Myers, Rennae S Taylor, Louise C Kenny, Gustaaf A Dekker, James J Walker, Lesley M E McCowan, Robyn A North, Lucilla Posto