Reflections on the Analysis of Interfaces and Grain Boundaries by Atom Probe Tomography.

Interfaces play critical roles in materials and are usually both structurally and compositionally complex microstructural features. The precise characterization of their nature in three-dimensions at the atomic scale is one of the grand challenges for microscopy and microanalysis, as this information is crucial to establish structure-property relationships. Atom probe tomography is well suited to analyzing the chemistry of interfaces at the nanoscale. However, optimizing such microanalysis of interfaces requires great care in the implementation across all aspects of the technique from specimen preparation to data analysis and ultimately the interpretation of this information. This article provides critical perspectives on key aspects pertaining to spatial resolution limits and the issues with the compositional analysis that can limit the quantification of interface measurements. Here, we use the example of grain boundaries in steels; however, the results are applicable for the characterization of grain boundaries and transformation interfaces in a very wide range of industrially relevant engineering materials.

Long-term trends in child maltreatment in England and Wales, 1858-2016: an observational, time-series analysis.

BACKGROUND: It is unclear whether child maltreatment is increasing or decreasing in England and Wales. More evidence is needed, from multiple sources and over longer periods of time, to explore trends in child maltreatment. We investigated whether the annual incidence of child maltreatment has changed over time, using official record data and time-series methods to establish long-term trends. METHODS: In this observational time-series analysis, we used six data sources (Government records for child mortality, police-recorded child homicides, crimes against children, child protection, and children in care; and NSPCC data) to estimate the incidence of child maltreatment in England and Wales and examine long-term trends. We included nationally representative data that could estimate the incidence of child maltreatment for more than 25 years. Our primary outcomes were the number of victims (age <20 years) or perpetrators (age >16 years) of child maltreatment per 12-month period in England, including or excluding Wales. We fitted Poisson regression models with year as the exposure and the number of victims or perpetrators of child maltreatment as the outcome (adjusted for population age-structure and size). When a linear trend was not appropriate, we fitted generalised additive models with penalised splines to visualise trends. FINDINGS: The incidence of child mortality by homicide or assault decreased by 90% (2·7 per 100 000 children) between 1858 and 2016 and the incidence of people guilty of child cruelty or neglect decreased by 83% (6·7 per 100 000 adults) between 1893 and 2016, whereas child protection registrations increased by 182% (328·7 per 100 000 children) between 1988 and 2016. Crimes against children and children entering care increased between 2000 and 2016. In 2016, 40 children died by homicide, with twice as many adolescent (15-19 years) deaths than infant (age <1 year) deaths. In 2016, 67 700 children were placed on the child protection register and neglect and emotional abuse were the most common reasons. INTERPRETATION: Although long-term trends have decreased, child maltreatment remains a major public health problem in England and Wales. Further research is needed to establish whether adolescents are a particularly vulnerable age group and whether neglect and emotional abuse are increasing. Future child protection policies and practices should respond to these areas of growing need. FUNDING: Andrew W Mellon Foundation and Clarendon through The Oxford Research Centre in the Humanities, Oxford.

CONVERGENCE PROPERTIES OF ADAPTIVE SYSTEMS AND THE DEFINITION OF EXPONENTIAL STABILITY.

The convergence properties of adaptive systems in terms of excitation conditions on the regressor vector are well known. With persistent excitation of the regressor vector in model reference adaptive control the state error and the adaptation error are globally exponentially stable or, equivalently, exponentially stable in the large. When the excitation condition, however, is imposed on the reference input or the reference model state, it is often incorrectly concluded that the persistent excitation in those signals also implies exponential stability in the large. The definition of persistent excitation is revisited so as to address some possible confusion in the adaptive control literature. It is then shown that persistent excitation of the reference model only implies local persistent excitation (weak persistent excitation). Weak persistent excitation of the regressor is still sufficient for uniform asymptotic stability in the large, but not exponential stability in the large. We show that there exists an infinite region in the state-space of adaptive systems where the state rate is bounded. This infinite region with finite rate of convergence is shown to exist not only in classic open-loop reference model adaptive systems but also in a new class of closed-loop reference model adaptive systems.