THEORY OF DIFFUSION OF HEAVY IMPURITIES IN ALKALI-METALS

Interatomic potentials have been developed for heavy atom impurities in alkali metal hosts, and they have been used to calculate characteristic energies for the diffusion of gold in sodium and of silver in lithium. The calculations show that, whilst most impurity atoms should be present substitutionally, the diffusion is dominated by interstitial motion for both Li-Ag and Na-Au. The large difference in observed behaviour stems from the different forms of the interatomic potentials but cannot be described simply in terms of atomic radii or electronegativity arguments. The activation energies predicted are in good quantitative agreement with experiment

The role of artificial intelligence in paediatric cardiovascular magnetic resonance imaging

Artificial intelligence (AI) offers the potential to change many aspects of paediatric cardiac imaging. At present, there are only a few clinically validated examples of AI applications in this field. This review focuses on the use of AI in paediatric cardiovascular MRI, using examples from paediatric cardiovascular MRI, adult cardiovascular MRI and other radiologic experience

Predatory impacts of alien decapod Crustacea are predicted by functional responses and explained by differences in metabolic rate

Alien predators can have large impacts on prey. It is important that we understand, and ideally predict, these impacts. Here, we compare predatory impacts of size-matched decapod crustaceans—invasive alien Eriocheir sinensis and Pacifastacus leniusculus, and native European Austropotamobius pallipes—and use this case study to inform methods for impact prediction. We quantify functional responses (FRs) on three macroinvertebrate prey species, examine switching behaviour, and measure metabolic rates as a possible mechanistic explanation for differences in predation. FRs show a consistent pattern: attack coefficients and maximum feeding rates are ordered E. sinensis ≥ P. leniusculus ≥ A. pallipes for all prey species. Attack coefficients of E. sinensis are up to 6.7 times greater than those of size-matched crayfish and maximum feeding rates up to 3.0 times greater. FR parameters also differ between the invasive and native crayfish, but only up to 2.6 times. We find no evidence of switching behaviour in crayfish but suggestions of negative switching in E. sinensis. Differences in FR parameters are mirrored by differences in routine, but not standard, metabolic rate. Overall, our data predict strong predatory impacts of E. sinensis, even relative to alien P. leniusculus. Strong impacts of P. leniusculus relative to A. pallipes may be driven more by body size or abundance than per capita effect. FRs vary between prey types in line with existing knowledge of impacts, supporting the use of FRs in quantitative, prey-specific impact predictions. MRs could offer a general mechanistic explanation for differences in predatory behaviour and impacts

Size matters: predation of fish eggs and larvae by native and invasive amphipods

Invasive predators can have dramatic impacts on invaded communities. Extreme declines in macroinvertebrate populations often follow killer shrimp (Dikerogammarus villosus) invasions. There are concerns over similar impacts on fish through predation of eggs and larvae, but these remain poorly quantified. We compare the predatory impact of invasive and native amphipods (D. villosus and Gammarus pulex) on fish eggs and larvae (ghost carp Cyprinus carpio and brown trout Salmo trutta) in the laboratory. We use size-matched amphipods, as well as larger D. villosus reflecting natural sizes. We quantify functional responses, and electivity amongst eggs or larvae and alternative food items (invertebrate, plant and decaying leaf). D. villosus, especially large individuals, were more likely than G. pulex to kill trout larvae. However, the magnitude of predation was low (seldom more than one larva killed over 48 hours). Trout eggs were very rarely killed. In contrast, carp eggs and larvae were readily killed and consumed by all amphipod groups. Large D. villosus had maximum feeding rates 1.6 to 2.0 times higher than the smaller amphipods, whose functional responses did not differ. In electivity experiments with carp eggs, large D. villosus consumed the most eggs and the most food in total. However, in experiments with larvae, consumption did not differ between amphipod groups. Overall, our data suggest D. villosus will have a greater predatory impact on fish populations than G. pulex, primarily due to its larger size. Higher invader abundance could amplify this difference. The additional predatory pressure could reduce recruitment into fish populations

Time-Varying Parameters in Continuous and Discrete Time

We consider models for both deterministic one-time and continuous stochastic parameter change in a continuous time autoregressive model around a deterministic trend function. For the latter we focus on the case where the autoregressive parameter itself follows a first-order autoregression. Exact discrete time analogue models are detailed in each case and compared to corresponding parameter change models adopted in the discrete time literature. The relationships between the parameters in the continuous time models and their discrete time analogues are also explored. For the one- time parameter change model the discrete time models used in the literature can be justified by the corresponding continuous time model, with a only a minor modification needed for the (most likely) case where the changepoint does not coincide with one of the discrete time observation points. For the stochastic parameter change model considered we show that the resulting discrete time model is characterised by an autoregressive parameter the logarithm of which follows an ARMA(1,1) process. We discuss how this relates to models which have been proposed in the discrete time stochastic unit root literature. The implications of our results for a number of extant discrete time models and testing procedures are discussed

Quantification of Maceration Changes using Post Mortem MRI in Fetuses

BACKGROUND: Post mortem imaging is playing an increasingly important role in perinatal autopsy, and correct interpretation of imaging changes is paramount. This is particularly important following intra-uterine fetal death, where there may be fetal maceration. The aim of this study was to investigate whether any changes seen on a whole body fetal post mortem magnetic resonance imaging (PMMR) correspond to maceration at conventional autopsy. METHODS: We performed pre-autopsy PMMR in 75 fetuses using a 1.5 Tesla Siemens Avanto MR scanner (Erlangen, Germany). PMMR images were reported blinded to the clinical history and autopsy data using a numerical severity scale (0 = no maceration changes to 2 = severe maceration changes) for 6 different visceral organs (total 12). The degree of maceration at autopsy was categorized according to severity on a numerical scale (1 = no maceration to 4 = severe maceration). We also generated quantitative maps to measure the liver and lung T2. RESULTS: The mean PMMR maceration score correlated well with the autopsy maceration score (R(2) = 0.93). A PMMR score of ≥4.5 had a sensitivity of 91%, specificity of 64%, for detecting moderate or severe maceration at autopsy. Liver and lung T2 were increased in fetuses with maceration scores of 3-4 in comparison to those with 1-2 (liver p = 0.03, lung p = 0.02). CONCLUSIONS: There was a good correlation between PMMR maceration score and the extent of maceration seen at conventional autopsy. This score may be useful in interpretation of fetal PMMR

The Role of Cardiovascular Magnetic Resonance in Pediatric Congenital Heart Disease

Cardiovascular magnetic resonance (CMR) has expanded its role in the diagnosis and management of congenital heart disease (CHD) and acquired heart disease in pediatric patients. Ongoing technological advancements in both data acquisition and data presentation have enabled CMR to be integrated into clinical practice with increasing understanding of the advantages and limitations of the technique by pediatric cardiologists and congenital heart surgeons. Importantly, the combination of exquisite 3D anatomy with physiological data enables CMR to provide a unique perspective for the management of many patients with CHD. Imaging small children with CHD is challenging, and in this article we will review the technical adjustments, imaging protocols and application of CMR in the pediatric population

Deterministic Parameter Change Models in Continuous and Discrete Time

We consider a model of deterministic one-time parameter change in a continuous time autoregressive model around a deterministic trend function. The exact discrete time analogue model is detailed and compared to corresponding parameter change models adopted in the discrete time literature. The relationships between the parameters in the continuous time model and the discrete time analogue model are also explored. Our results show that the discrete time models used in the literature can be justified by the corresponding continuous time model, with a only a minor modification needed for the (most likely) case where the changepoint does not coincide with one of the discrete time observation points. The implications of our results for a number of extant discrete time models and testing procedures are discussed

Sieve-based inference for infinite-variance linear processes

We extend the available asymptotic theory for autoregressive sieve estimators to cover the case of stationary and invertible linear processes driven by independent identically distributed (i.i.d.) infinite variance (IV) innovations. We show that the ordinary least squares sieve estimates, together with estimates of the impulse responses derived from these, obtained from an autoregression whose order is an increasing function of the sample size, are consistent and exhibit asymptotic properties analogous to those which obtain for a finite-order autoregressive process driven by i.i.d. IV errors. As these limit distributions cannot be directly employed for inference because they either may not exist or, where they do, depend on unknown parameters, a second contribution of the paper is to investigate the usefulness of bootstrap methods in this setting. Focusing on three sieve bootstraps: the wild and permutation bootstraps, and a hybrid of the two, we show that, in contrast to the case of finite variance innovations, the wild bootstrap requires an infeasible correction to be consistent, whereas the other two bootstrap schemes are shown to be consistent (the hybrid for symmetrically distributed innovations) under general conditions