Avulsion cycles and their stratigraphic signature on an experimental backwater‐controlled delta

River deltas grow in large part through repeated cycles of lobe construction and channel avulsion. Understanding avulsion cycles is important for coastal restoration and ecology, land management, and flood hazard mitigation. Emerging theories suggest that river avulsions on lowland deltas are controlled by backwater hydrodynamics; however, our knowledge of backwater-controlled avulsion cycles is limited. Here, we present results from an experimental delta that evolved under persistent backwater hydrodynamics achieved through variable flood discharges, shallow bed-slopes, and subcritical flows. The experimental avulsion cycles consisted of an initial phase of avulsion setup, an avulsion trigger, selection of a new flow path, and abandonment of the parent channel. Avulsions were triggered during the largest floods (78% of avulsions) after the channel was filled by a fraction (0.3 ± 0.13) of its characteristic flow depth at the avulsion site, which occurred in the upstream part of the backwater zone. The new flow path following avulsion was consistently one of the shortest paths to the shoreline, and channel abandonment occurred through temporal decline in water flow and sediment delivery to the parent channel. Experimental synthetic stratigraphy indicates that the bed thicknesses were maximum at the avulsion sites, consistent with our morphologic measurements of avulsion setup and the idea that there is a record of avulsion locations and thresholds in sedimentary rocks. Finally, we discuss the implications of our findings within the context of sustainable management of deltas, their stratigraphic record, and predicting avulsions on deltas

The macroeconomics of aid: overview

This Special Issue explores macroeconomic effects of aid from various perspectives through a blend of studies, both conceptual and empirical in nature. The overall aim is to enhance the understanding of the macroeconomic dimensions of aid in the policy and research communities, and to inspire further innovative work in this important area. This opening article provides a scene setting summary of five generations of aid research, with a particular focus on how the JDS has contributed to this literature, and ends with an overview of the papers included in this Issue

Subjective estimates of uncertainty during gambling and impulsivity after subthalamic deep brain stimulation for Parkinson\u2019s disease

Subthalamic deep brain stimulation (DBS) for Parkinson\u2019s disease (PD) may modulate chronometric and instrumental aspects of choice behaviour, including motor inhibition, decisional slowing, and value sensitivity. However, it is not well known whether subthalamic DBS affects more complex aspects of decision-making, such as the influence of subjective estimates of uncertainty on choices. In this study, 38 participants with PD played a virtual casino prior to subthalamic DBS (whilst \u2018on\u2019 medication) and again, 3-months postoperatively (whilst \u2018on\u2019 stimulation). At the group level, there was a small but statistically significant decrease in impulsivity postoperatively, as quantified by the Barratt Impulsiveness Scale (BIS). The gambling behaviour of participants (bet increases, slot machine switches and double or nothing gambles) was associated with this self-reported measure of impulsivity. However, there was a large variance in outcome amongst participants, and we were interested in whether individual differences in subjective estimates of uncertainty (specifically, volatility) were related to differences in pre- and postoperative impulsivity. To examine these individual differences, we fit a computational model (the Hierarchical Gaussian Filter, HGF), to choices made during slot machine game play as well as a simpler reinforcement learning model based on the Rescorla-Wagner formalism. The HGF was superior in accounting for the behaviour of our participants, suggesting that participants incorporated beliefs about environmental uncertainty when updating their beliefs about gambling outcome and translating these beliefs into action. A specific aspect of subjective uncertainty, the participant\u2019s estimate of the tendency of the slot machine\u2019s winning probability to change (volatility), increased subsequent to DBS. Additionally, the decision temperature of the response model decreased post-operatively, implying greater stochasticity in the belief-to-choice mapping of participants. Model parameter estimates were significantly associated with impulsivity; specifically, increased uncertainty was related to increased postoperative impulsivity. Moreover, changes in these parameter estimates were significantly associated with the maximum post-operative change in impulsivity over a six month follow up period. Our findings suggest that impulsivity in PD patients may be influenced by subjective estimates of uncertainty (environmental volatility) and implicate a role for the subthalamic nucleus in the modulation of outcome certainty. Furthermore, our work outlines a possible approach to characterising those persons who become more impulsive after subthalamic DBS, an intervention in which non-motor outcomes can be highly variable

Analysis of interfacial shrinkage stresses in patch repairs

This paper presents simple analytical expressions that predict the interfacial shrinkage stresses in a repair patch over time. Four repair materials (L2, L3, L4 and G1) were applied by spraying (gunite) to unpropped compression members of two highway structures, and their performance was monitored to approximately six months' age. The elastic moduli of all the repair materials, E rm , were greater than the elastic moduli of the substrate concrete, E sub . The mechanics of patch repair interaction with the substrate were established, and analytical models, based on an analogy of the bimetallic strip undergoing a drop in temperature, were developed. Basic properties of the repair material (elastic modulus, shrinkage and tensile creep) and substrate concrete (elastic modulus), and geometrical details of the repair patch, are required to analyse the interfacial stresses in the repair patch. Verification of the analytical procedures is based on the field data, and the results show a satisfactory correlation between the actual and predicted stress redistribution.</p

Intrinsically narrowband pair photon generation in microstructured fibres

In this paper we study the tailoring of photon spectral properties generated by four-wave mixing in a birefringent photonic crystal fibre (PCF). The aim is to produce intrinsically narrow-band photons and hence to achieve high non-classical interference visibility and generate high fidelity entanglement without any requirement for spectral filtering, leading to high effective detection efficiencies. We show unfiltered Hong-Ou-Mandel interference visibilities of 77% between photons from the same PCF, and 80% between separate sources. We compare results from modelling the PCF to these experiments and analyse photon purities.Comment: 23 pages, 17 figures, Comments Welcom

Measuring health inequality among children in developing countries: does the choice of the indicator of economic status matter?

Background Currently, poor-rich inequalities in health in developing countries receive a lot of attention from both researchers and policy makers. Since measuring economic status in developing countries is often problematic, different indicators of wealth are used in different studies. Until now, there is a lack of evidence on the extent to which the use of different measures of economic status affects the observed magnitude of health inequalities. Methods This paper provides this empirical evidence for 10 developing countries, using the Demographic and Health Surveys data-set. We compared the World Bank asset index to three alternative wealth indices, all based on household assets. Under-5 mortality and measles immunisation coverage were the health outcomes studied. Poor-rich inequalities in under-5 mortality and measles immunisation coverage were measured using the Relative Index of Inequality. Results Comparing the World Bank index to the alternative indices, we found that (1) the relative position of households in the national wealth hierarchy varied to an important extent with the asset index used, (2) observed poor-rich inequalities in under-5 mortality and immunisation coverage often changed, in some cases to an important extent, and that (3) the size and direction of this change varied per country, index, and health indicator. Conclusion Researchers and policy makers should be aware that the choice of the measure of economic status influences the observed magnitude of health inequalities, and that differences in health inequalities between countries or time periods, may be an artefact of different wealth measures used

Colossal terahertz magnetoresistance at room temperature in epitaxial La0.7Sr0.3MnO3 nanocomposites and single-phase thin films

Colossal magnetoresistance (CMR) is demonstrated at terahertz (THz) frequencies by using terahertz time-domain magnetospectroscopy to examine vertically-aligned nanocomposites (VANs) and planar thin films of La_0.7Sr_0.3MnO_3. At the Curie temperature (room temperature) the THz conductivity of the VAN was dramatically enhanced by over 2 orders of magnitude under the application of a magnetic field, with a non-Drude THz conductivity that increased with frequency. The dc CMR of the VAN is controlled by extrinsic magnetotransport mechanisms such as spin-polarized tunneling between nano-grains. In contrast, we find that THz CMR is dominated by intrinsic, intragrain transport: the mean free path was smaller than the nanocolumn size, and the planar thin-film exhibited similar THz CMR to the VAN. Surprisingly, the observed colossal THz magnetoresistance suggests that the magnetoresistance can be large for ac motion on nanometre length scales, even when the magnetoresistance is negligible on the macroscopic length scales probed by dc transport. This suggests that colossal magnetoresistance at THz frequencies may find use in nanoelectronics and in THz optical components controlled by magnetic fields. The VAN can be scaled in thickness while retaining a high structural quality, and offers a larger THz CMR at room temperature than the planar film