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Evidence for suboxic nitrification in recent marine sediments
The classical scheme of biogeochemical zones (BGZ) is known to be an oversimplification
of the microbial processes that occur in organic-rich marine sediments. Results from a coupled
deployment of pore-water gel probes in Loch Duich, Scotland, provide direct evidence for rapid
recycling within the iron reduction (FeR) and sulphate reduction (SR) zones. High resolution porewater
profiles obtained using diffusive equilibrium in thin films (DET) gel probes found a nitrate peak
at the boundary between the FeR and SR zones. This non-steady state feature is consistent with recycling
of reduced N occurring throughout the FeR zone. Both conventional pore-water iron profiles
and results from diffusive gradient in thin films (DGT) probes indicate that iron is solubilised and precipitated
in rapid Fe/S recycling reactions throughout the SR zone. The presence of such complex
recycling reactions confirms the oversimplification of the classical BGZ scheme
Inkjet printing of self-healing polymers for enhanced composite interlaminar properties
Inkjet printing has been used to introduce an organic system that demonstrates thermally activated self-healing in composites. The organic system is composed of monomers that, when polymerised, are capable of thermally activated self-healing through a reversible Diels–Alder mechanism. After being synthesised the monomers were formulated into inks and inkjet printed on to carbon fibre epoxy prepreg. The polymers were co-cured with the prepreg into composite laminates and the effect on the interlaminar properties of the resultant system was investigated. A single ply at the mid-plane of double cantilever beam specimens was shown to increase the initiation (by NL Point) of the interlaminar fracture toughness by 9%. The interlaminar fracture toughness with regards to crack propagation was shown to increase further by up to 27%. Increases in apparent interlaminar shear strength as measured by short beam shear of up to 11% were also observed compared to unprinted controls. After a thermal treatment the short beam shear specimens are retested and the printed specimens are shown to have significantly smaller decreases in properties compared to the control which is consistent with repair in the interlaminar region
Anoxic nitrification in marine sediments
Nitrate peaks are found in pore-water profiles in marine sediments at depths considerably
below the conventional zone of oxic nitrification. These have been interpreted to represent nonsteady-
state effects produced by the activity of nitrifying bacteria, and suggest that nitrification
occurs throughout the anoxic sediment region. In this study, ΣNO3 peaks and molecular analysis of
DNA and RNA extracted from anoxic sediments of Loch Duich, an organic-rich marine fjord, are consistent
with nitrification occurring in the anoxic zone. Analysis of ammonia oxidiser 16S rRNA gene
fragments amplified from sediment DNA indicated the abundance of autotrophic ammonia-oxidising
bacteria throughout the sediment depth sampled (40 cm), while RT-PCR analysis indicated their
potential activity throughout this region. A large non-steady-state pore-water ΣNO3 peak at ~21 cm
correlated with discontinuities in this ammonia-oxidiser community. In addition, a subsurface nitrate
peak at ~8 cm below the oxygen penetration depth, correlated with the depth of a peak in nitrification
rate, assessed by transformation of 15N-labelled ammonia. The source of the oxidant required to
support nitrification within the anoxic region is uncertain. It is suggested that rapid recycling of N is
occurring, based on a coupled reaction involving Mn oxides (or possibly highly labile Fe oxides)
buried during small-scale slumping events. However, to fully investigate this coupling, advances in
the capability of high-resolution pore-water techniques are required
Persistent dynamics in the S = 1/2 quasi-one-dimensional chain compound Rb4Cu(MoO4)3 probed with muon-spin relaxation
We report the results of muon-spin relaxation measurements on the low-dimensional antiferromagnet Rb4Cu(MoO4)3. No long-range magnetic order is observed down to 50 mK implying a ratio TN/J < 0.005 (where J is the principal exchange strength along the spin chains) and an effective ratio of interchain to intrachain exchange of |J⊥/J | < 2 × 10−3, making the material an excellent realization of a one-dimensional quantum Heisenberg antiferromagnet. We probe the persistent spin excitations at low temperatures and find that ballistic spin transport dominates the excitations detected below 0.3 K
Assortative social mixing and sex disparities in tuberculosis burden
Globally, men have higher tuberculosis (TB) burden but the mechanisms underlying this sex disparity are not fully understood. Recent surveys of social mixing patterns have established moderate preferential within-sex mixing in many settings. This assortative mixing could amplify differences from other causes. We explored the impact of assortative mixing and factors differentially affecting disease progression and detection using a sex-stratified deterministic TB transmission model. We explored the influence of assortativity at disease-free and endemic equilibria, finding stronger effects during invasion and on increasing male:female prevalence (M:F) ratios than overall prevalence. Variance-based sensitivity analysis of endemic equilibria identified differential progression as the most important driver of M:F ratio uncertainty. We fitted our model to prevalence and notification data in exemplar settings within a fully Bayesian framework. For our high M:F setting, random mixing reduced equilibrium M:F ratios by 12% (95% CrI 0–30%). Equalizing male case detection there led to a 20% (95% CrI 11–31%) reduction in M:F ratio over 10 years—insufficient to eliminate sex disparities. However, this potentially achievable improvement was associated with a meaningful 8% (95% CrI 4–14%) reduction in total TB prevalence over this time frame
Knowledge engineering with image data in real-world settings
We report on experiences in adding ML-trained visual recognition modules to a human-oriented image semantic annotation tool which creates RDF descriptions of images and scene contents. We conclude that ML cannot replace expert humans but can aid them in various ways, some unexpected. Semantic markup systems can be to designed to align human and machine blind spots. Finally, we briefly outline directions for future work
Electronic properties of shallow level defects in ZnO grown by pulsed laser deposition
We have used deep level transient spectroscopy (DLTS) to characterise four defects
with shallow levels in ZnO grown by pulsed laser deposition (PLD). These defects all have
DLTS peaks below 100 K. From DLTS measurements and Arrhenius plots we have calculated
the energy levels of these defects as 31 meV, 64 meV, 100 meV and 140 meV, respectively,
below the conduction band. The 100 meV defect displayed metastable behaviour: Annealing
under reverse bias at temperatures of above 130 K introduced it while annealing under zero
bias above 110 K removed it. The 64 meV and 140 meV defects exhibited a strong electric
field assisted emission, indicating that they may be donors
Electronic properties of shallow level defects in ZnO grown by pulsed laser deposition
We have used deep level transient spectroscopy (DLTS) to characterise four defects
with shallow levels in ZnO grown by pulsed laser deposition (PLD). These defects all have
DLTS peaks below 100 K. From DLTS measurements and Arrhenius plots we have calculated
the energy levels of these defects as 31 meV, 64 meV, 100 meV and 140 meV, respectively,
below the conduction band. The 100 meV defect displayed metastable behaviour: Annealing
under reverse bias at temperatures of above 130 K introduced it while annealing under zero
bias above 110 K removed it. The 64 meV and 140 meV defects exhibited a strong electric
field assisted emission, indicating that they may be donors
A scalable quantum computer with an ultranarrow optical transition of ultracold neutral atoms in an optical lattice
We propose a new quantum-computing scheme using ultracold neutral ytterbium
atoms in an optical lattice. The nuclear Zeeman sublevels define a qubit. This
choice avoids the natural phase evolution due to the magnetic dipole
interaction between qubits. The Zeeman sublevels with large magnetic moments in
the long-lived metastable state are also exploited to address individual atoms
and to construct a controlled-multiqubit gate. Estimated parameters required
for this scheme show that this proposal is scalable and experimentally
feasible.Comment: 6 pages, 6 figure
Transmission modeling to infer tuberculosis incidence prevalence and mortality in settings with generalized HIV epidemics
Tuberculosis (TB) killed more people globally than any other single pathogen over the past decade. Where surveillance is weak, estimating TB burden estimates uses modeling. In many African countries, increases in HIV prevalence and antiretroviral therapy have driven dynamic TB epidemics, complicating estimation of burden, trends, and potential intervention impact. We therefore develop a novel age-structured TB transmission model incorporating evolving demographic, HIV and antiretroviral therapy effects, and calibrate to TB prevalence and notification data from 12 African countries. We use Bayesian methods to include uncertainty for all TB model parameters, and estimate age-specific annual risks of TB infection, finding up to 16.0%/year in adults, and the proportion of TB incidence from recent (re)infection, finding a mean across countries of 34%. Rapid reduction of the unacceptably high burden of TB in high HIV prevalence settings will require interventions addressing progression as well as transmission
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