Discussion of "Sequential Quasi-Monte Carlo" by Mathieu Gerber and Nicolas Chopin

A discussion on the possibility of reducing the variance of quasi-Monte Carlo estimators in applications. Further details are provided in the accompanying paper "Variance Reduction for Quasi-Monte Carlo"

Weight loss maintenance: An agenda for health psychology

This is the peer reviewed version of the editorial, which has been published in final form at doi:10.1111/bjhp.12107. This editorial may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for self-archiving.n/a (Editorial)NIHR'Fuse' (British Heart Foundation, Cancer Research UK, ESRC, MRC

Significance of buoyancy in turbulence closure for computational fluid dynamics modelling of ultraviolet disinfection in maturation ponds

Buoyancy-driven turbulent dispersion in a maturation pond is studied by a combination of field measurements and computational fluid dynamics. Modelling flow in maturation ponds requires turbulent closure models because of the large physical size and the need to model on diurnal time scales. Simulation results are shown to be more sensitive to the inclusion of a buoyancy production term appearing in the turbulent transport equations than to the model choice. Comparisons with experimental thermal profiles show that without this term, thermal mixing is over predicted. When including the term, stratification occurs but thermal mixing is under-predicted in the lower water column. In terms of pond performance, the effect of this term is to cause increased surface die-off of Escherichia coli during sunlight hours due to the generation of stratification. It is recommended that future modelling consider and implement this term

Spatial variations in snowpack chemistry, isotopic composition of NO3− and nitrogen deposition from the ice sheet margin to the coast of western Greenland

The relative roles of anthropogenic nitrogen (N) deposition and climate change in causing ecological change in remote Arctic ecosystems, especially lakes, have been the subject of debate over the last decade. Some palaeoecological studies have cited isotopic signals (δ(15N)) preserved in lake sediments as evidence linking N deposition with ecological change, but a key limitation has been the lack of co-located data on both deposition input fluxes and isotopic composition of deposited nitrate (NO3−). In Arctic lakes, including those in western Greenland, previous palaeolimnological studies have indicated a spatial variation in δ(15N) trends in lake sediments but data are lacking for deposition chemistry, input fluxes and stable isotope composition of NO3−. In the present study, snowpack chemistry, NO3− stable isotopes and net deposition fluxes for the largest ice-free region in Greenland were investigated to determine whether there are spatial gradients from the ice sheet margin to the coast linked to a gradient in precipitation. Late-season snowpack was sampled in March 2011 at eight locations within three lake catchments in each of three regions (ice sheet margin in the east, the central area near Kelly Ville and the coastal zone to the west). At the coast, snowpack accumulation averaged 181 mm snow water equivalent (SWE) compared with 36 mm SWE by the ice sheet. Coastal snowpack showed significantly greater concentrations of marine salts (Na+, Cl−, other major cations), ammonium (NH4+; regional means 1.4–2.7 µmol L−1), total and non-sea-salt sulfate (SO42−; total 1.8–7.7, non-sea-salt 1.0–1.8 µmol L−1) than the two inland regions. Nitrate (1.5–2.4 µmol L−1) showed significantly lower concentrations at the coast. Despite lower concentrations, higher precipitation at the coast results in greater net deposition for NO3− as well as NH4+ and non-sea-salt sulfate (nss-SO42−) relative to the inland regions (lowest at Kelly Ville 6, 4 and 3; highest at coast 9, 17 and 11 mol ha−1 a−1 of NO3−, NH4+ and nss-SO42− respectively). The δ(15N) of snowpack NO3− shows a significant decrease from inland regions (−5.7 ‰ at Kelly Ville) to the coast (−11.3 ‰). We attribute the spatial patterns of δ(15N) in western Greenland to post-depositional processing rather than differing sources because of (1) spatial relationships with precipitation and sublimation, (2) within-catchment isotopic differences between terrestrial snowpack and lake ice snowpack, and (3) similarities between fresh snow (rather than accumulated snowpack) at Kelly Ville and the coast. Hence the δ(15N) of coastal snowpack is most representative of snowfall in western Greenland, but after deposition the effects of photolysis, volatilization and sublimation lead to enrichment of the remaining snowpack with the greatest effect in inland areas of low precipitation and high sublimation losses

First birth following spindle transfer for mitochondrial replacement therapy: hope and trepidation

In this issue, Zhang et al. (2017) report the birth of a healthy boy after mitochondrial replacement therapy (MRT) by spindle transfer to prevent transmission of mitochondrial disease from mother to child. The case was first publicized in the lay press (Hamzelou, 2016; see also editorial by Johnson, 2016) and then presented during the 2016 Annual Meeting of the American Society for Assisted Reproduction (ASRM) in October 2016 (Zhang et al., 2016a). It followed an earlier report of an unsuccessful attempt at MRT by pronuclear transfer by the same group (Zhang et al., 2016b). This world-first birth represents an achievement and a steppingstone, and it has played a role in encouraging the Human Fertilization and Embryology Authority (HFEA) in the UK to issue a final recommendation that the technique ‘be approved for cautious use in specific circumstances’. (http://www.hfea.gov.uk/10559.html) We, the editors, were unanimous in deciding that this paper should be published in RBMO, based on our conviction that the scientific community must be informed of the details of the work in full in order to evaluate it critically and discuss it openly. We decided this despite the fact that the work has weaknesses and limitations in a number of areas. Moreover, although we were able to encourage the authors to include more details of their work in the submission, some uncertainties concerning methodologies and results still remain. Here we outline our concerns regarding the approach and the treatment process described by Zhang and colleagues

Squirrelpox virus: assessing prevalence, transmission and environmental degradation

Red squirrels (Sciurus vulgaris) declined in Great Britain and Ireland during the last century, due to habitat loss and the introduction of grey squirrels (Sciurus carolinensis), which competitively exclude the red squirrel and act as a reservoir for squirrelpox virus (SQPV). The disease is generally fatal to red squirrels and their ecological replacement by grey squirrels is up to 25 times faster where the virus is present. We aimed to determine: (1) the seropositivity and prevalence of SQPV DNA in the invasive and native species at a regional scale; (2) possible SQPV transmission routes; and, (3) virus degradation rates under differing environmental conditions. Grey (n = 208) and red (n = 40) squirrel blood and tissues were sampled. Enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qPCR) techniques established seropositivity and viral DNA presence, respectively. Overall 8% of squirrels sampled (both species combined) had evidence of SQPV DNA in their tissues and 22% were in possession of antibodies. SQPV prevalence in sampled red squirrels was 2.5%. Viral loads were typically low in grey squirrels by comparison to red squirrels. There was a trend for a greater number of positive samples in spring and summer than in winter. Possible transmission routes were identified through the presence of viral DNA in faeces (red squirrels only), urine and ectoparasites (both species). Virus degradation analyses suggested that, after 30 days of exposure to six combinations of environments, there were more intact virus particles in scabs kept in warm (25°C) and dry conditions than in cooler (5 and 15°C) or wet conditions. We conclude that SQPV is present at low prevalence in invasive grey squirrel populations with a lower prevalence in native red squirrels. Virus transmission could occur through urine especially during warm dry summer conditions but, more notably, via ectoparasites, which are shared by both species

Amplifier spurious input current components in electrode-electrolyte interface impedance measurements

BACKGROUND: In Impedance Microbiology, the time during which the measuring equipment is connected to the bipolar cells is rather long, usually between 6 to 24 hrs for microorganisms with duplication times in the order of less than one hour and concentrations ranging from 10(1 )to 10(7 )[CFU/ml]. Under these conditions, the electrode-electrolyte interface impedance may show a slow drift of about 2%/hr. By and large, growth curves superimposed on such drift do not stabilize, are less reproducible, and keep on distorting all over the measurement of the temporal reactive or resistive records due to interface changes, in turn originated in bacterial activity. This problem has been found when growth curves were obtained by means of impedance analyzers or with impedance bridges using different types of operational amplifiers. METHODS: Suspecting that the input circuitry was the culprit of the deleterious effect, we used for that matter (a) ultra-low bias current amplifiers, (b) isolating relays for the selection of cells, and (c) a shorter connection time, so that the relays were maintained opened after the readings, to bring down such spurious drift to a negligible value. Bacterial growth curves were obtained in order to test their quality. RESULTS: It was demonstrated that the drift decreases ten fold when the circuit remained connected to the cell for a short time between measurements, so that the distortion became truly negligible. Improvement due to better-input amplifiers was not as good as by reducing the connection time. Moreover, temperature effects were insignificant with a regulation of ± 0.2 [°C]. Frequency did not influence either. CONCLUSION: The drift originated either at the dc input bias offset current (I(os)) of the integrated circuits, or in discrete transistors connected directly to the electrodes immersed in the cells, depending on the particular circuit arrangement. Reduction of the connection time was the best countermeasure