Interaction of Lamb Waves with Defects in a Semi-Infinite Plate

Many airplanes, both military and commercial, have exceeded their original design service lives. For such aging structures, the presence of hidden damage can severely limit their performance. It is important to monitor the progress of damage to ensure the safety and integrality of these structures. Typical damage can be several types of corrosion and fatigue cracking. Lap-joints trap moisture and air and are initiation sites for corrosion. These sites are potential locations for wide spread fatigue damage. Generally, corrosion can cause material loss and thickness reduction, which can be detected by non-destructive ultrasonic methods. Conventional methods require point-by-point inspection, which is a time-consuming process. Guided waves, which direct wave energy in the plate, carry information about the material in their path and offer a possible more efficient tool for non-destructive inspection of material loss or thickness reduction. Using a pitch-catch technique, in which one transducer sends a guided wave in a plate structure and a second transducer picks up the signal at a different position, guided waves can be launched and detected to inspect plate-like structures, line by line, thus increasing the inspection efficiency by an order of magnitude. Also, when guided waves pass through a region with material loss, some energy would be reflected back. By studying the characteristics of the reflected waves, information about material loss can be obtained

Assessment of national-level progress towards elements of the Aichi Biodiversity Targets

Progress towards the Aichi Targets adopted through the Convention on Biological Diversity has been measured globally via indicators linked to elements of targets (the 20 targets consist of 54 elements), and nationally based on reporting by parties to the convention in the 5th (2010–2014) and 6th (2014–2018) National Reports. Here we used selected indicators that are readily available for each country to score national level progress (‘moving towards the target’, ‘little or no progress’, or ‘moving away from target’) for 11 elements of eight Aichi Targets (1, 4, 5, 7, 11, 12, 19, 20). Across the selected indicators, elements, and countries for which data were available, in 24.2% of cases countries were moving towards the elements, for 22.3% they were moving away, and for 53.5% there was little or no progress. This overall level of progress is similar to progress to targets as reported in the 5th and 6th National Reports. National progress to three of the 11 elements was positively correlated with progress to targets reported in the 5th National Reports, while progress to none of the elements was correlated with progress reported in the 6th National Reports. Progress to many of the elements considered was positively correlated with better governance, and to a lesser extent GDP per capita, population density and urbanisation. We suggest that post-2020 biodiversity targets should be designed taking greater account of their measurability, and will require improved biodiversity monitoring, both of which would facilitate more effective assessment of progress and enable more insightful policy responses

Tighter Expected Generalization Error Bounds via Convexity of Information Measures

Generalization error bounds are essential to understanding machine learning algorithms. This paper presents novel expected generalization error upper bounds based on the average joint distribution between the output hypothesis and each input training sample. Multiple generalization error upper bounds based on different information measures are provided, including Wasserstein distance, total variation distance, KL divergence, and Jensen-Shannon divergence. Due to the convexity of the information measures, the proposed bounds in terms of Wasserstein distance and total variation distance are shown to be tighter than their counterparts based on individual samples in the literature. An example is provided to demonstrate the tightness of the proposed generalization error bounds

Are changes in breeding habitat responsible for recent population changes of long-distance migrant birds?

Capsule: The direction and magnitude of changes in structure of UK woodlands since the 1980s, are inconsistent with them playing a causative role in the declines of four migrant bird species in upland oak woods. / Aims: To investigate whether changes in woodland structure were a possible cause of population changes of four Afro-Palearctic migrants (Wood Warbler Phylloscopus sibilatrix, Tree Pipit Anthus trivialis, Pied Flycatcher Ficedula hypoleuca and Common Redstart Phoenicurus phoenicurus) in the upland oakwoods of western and northern Britain. / Methods: Bird population estimates and measures of woodland structure were recorded in two time periods 1982–85 and 2003–04 across six regions of the UK. We modelled the effect of habitat change and initial habitat state on population changes between the two time periods. The predicted effects of habitat change on populations were then compared with observed population changes across the different regions. / Results: All four species underwent population declines; there were also significant increases in ground cover and understorey cover. The number of birds in 2003–04 was influenced by habitat structure at this time in addition to showing regional differences. Change in bird numbers varied between regions and was affected by both the initial habitat state and change in habitat structure, with regional variation in the effect of habitat change. There was however no relationship between the predicted effect of change in habitat structure on population size and observed regional population changes. / Conclusions: Changes in woodland structure are unlikely to be the main driver of population change in these four migrant bird species, and large-scale factors affecting demographics in other parts of their breeding range or in their wintering areas are likely reasons for local population declines

Mathematical Modelling of the Rayleigh Wave Reception by the System Whith Elastic Waveguide

Elastic waveguides are often applied in the acoustic nondestructive evaluation systems. Even though elastic waves in the waveguides are studied in the literature rather in detail, the very important problem of the incident wave interaction with the waveguide and its re-emission into the waveguide practically hasn’t been studied

Characterizing and Understanding the Generalization Error of Transfer Learning with Gibbs Algorithm

We provide an information-theoretic analysis of the generalization ability of Gibbs-based transfer learning algorithms by focusing on two popular transfer learning approaches, $\alpha$-weighted-ERM and two-stage-ERM. Our key result is an exact characterization of the generalization behaviour using the conditional symmetrized KL information between the output hypothesis and the target training samples given the source samples. Our results can also be applied to provide novel distribution-free generalization error upper bounds on these two aforementioned Gibbs algorithms. Our approach is versatile, as it also characterizes the generalization errors and excess risks of these two Gibbs algorithms in the asymptotic regime, where they converge to the $\alpha$-weighted-ERM and two-stage-ERM, respectively. Based on our theoretical results, we show that the benefits of transfer learning can be viewed as a bias-variance trade-off, with the bias induced by the source distribution and the variance induced by the lack of target samples. We believe this viewpoint can guide the choice of transfer learning algorithms in practice

Information-Theoretic Characterizations of Generalization Error for the Gibbs Algorithm

Various approaches have been developed to upper bound the generalization error of a supervised learning algorithm. However, existing bounds are often loose and even vacuous when evaluated in practice. As a result, they may fail to characterize the exact generalization ability of a learning algorithm. Our main contributions are exact characterizations of the expected generalization error of the well-known Gibbs algorithm (a.k.a. Gibbs posterior) using different information measures, in particular, the symmetrized KL information between the input training samples and the output hypothesis. Our result can be applied to tighten existing expected generalization errors and PAC-Bayesian bounds. Our information-theoretic approach is versatile, as it also characterizes the generalization error of the Gibbs algorithm with a data-dependent regularizer and that of the Gibbs algorithm in the asymptotic regime, where it converges to the standard empirical risk minimization algorithm. Of particular relevance, our results highlight the role the symmetrized KL information plays in controlling the generalization error of the Gibbs algorithm

Relating characteristics of global biodiversity targets to reported progress

To inform governmental discussions on the nature of a revised Strategic Plan for Biodiversity of the Convention on Biological Diversity (CBD), we reviewed the relevant literature and assessed the framing of the 20 Aichi Biodiversity Targets in the current strategic plan. We asked international experts from nongovernmental organizations, academia, government agencies, international organizations, research institutes, and the CBD to score the Aichi Targets and their constituent elements against a set of specific, measurable, ambitious, realistic, unambiguous, scalable, and comprehensive criteria (SMART based, excluding time bound because all targets are bound to 2015 or 2020). We then investigated the relationship between these expert scores and reported progress toward the target elements by using the findings from 2 global progress assessments (Global Biodiversity Outlook and the Intergovernmental Science‐Policy Platform on Biodiversity and Ecosystem Services). We analyzed the data with ordinal logistic regressions. We found significant positive relationships (p < 0.05) between progress and the extent to which the target elements were perceived to be measurable, realistic, unambiguous, and scalable. There was some evidence of a relationship between progress and specificity of the target elements, but no relationship between progress and ambition. We are the first to show associations between progress and the extent to which the Aichi Targets meet certain SMART criteria. As negotiations around the post‐2020 biodiversity framework proceed, decision makers should strive to ensure that new or revised targets are effectively structured and clearly worded to allow the translation of targets into actionable policies that can be successfully implemented nationally, regionally, and globally

A Niche-Based Framework to Assess Current Monitoring of European Forest Birds and Guide Indicator Species' Selection

Concern that European forest biodiversity is depleted and declining has provoked widespread efforts to improve management practices. To gauge the success of these actions, appropriate monitoring of forest ecosystems is paramount. Multi-species indicators are frequently used to assess the state of biodiversity and its response to implemented management, but generally applicable and objective methodologies for species' selection are lacking. Here we use a niche-based approach, underpinned by coarse quantification of species' resource use, to objectively select species for inclusion in a pan-European forest bird indicator. We identify both the minimum number of species required to deliver full resource coverage and the most sensitive species' combination, and explore the trade-off between two key characteristics, sensitivity and redundancy, associated with indicators comprising different numbers of species. We compare our indicator to an existing forest bird indicator selected on the basis of expert opinion and show it is more representative of the wider community. We also present alternative indicators for regional and forest type specific monitoring and show that species' choice can have a significant impact on the indicator and consequent projections about the state of the biodiversity it represents. Furthermore, by comparing indicator sets drawn from currently monitored species and the full forest bird community, we identify gaps in the coverage of the current monitoring scheme. We believe that adopting this niche-based framework for species' selection supports the objective development of multi-species indicators and that it has good potential to be extended to a range of habitats and taxa