Approximating incremental combinatorial optimization problems

We consider incremental combinatorial optimization problems, in which a solution is constructed incrementally over time, and the goal is to optimize not the value of the final solution but the average value over all timesteps. We consider a natural algorithm of moving towards a global optimum solution as quickly as possible. We show that this algorithm provides an approximation guarantee of (9 + √21)/15 > 0.9 for a large class of incremental combinatorial optimization problems defined axiomatically, which includes (bipartite and non-bipartite) matchings, matroid intersections, and stable sets in claw-free graphs. Furthermore, our analysis is tight

An aerospace requirements setting model to improve system design

Decisions at an early conceptual stage of the product lifecycle, are made with relatively low confidence, but such decisions greatly influence the overall product and service development. It is, therefore, critical to define the risks involved in order to help designers to make informed decisions. This research project investigates the risk and uncertainties in delivering products to meet top-level business requirements. The aim is to improve the existing process of setting business requirements and the current design approaches to achieve an optimised system design. This project also examines different approaches in assessing the risk of product and service delivery. To achieve that, a dedicated software tool, based on Weibull distribution function reliability model, has been created. An example of Rolls-Royce Civil Large Engine (CLE) gas turbine design process is used in this research as the case study. An analysis of the gap between the current design achievements and the targeted business requirements of a new product is performed at whole engine, module and component level. Further comparison of the new product business requirements, the novelty in the design and the historical reliability data is used to define and assess the risk of new product delivery

Improved and Robust Controversy Detection in General Web Pages Using Semantic Approaches under Large Scale Conditions

Detecting controversy in general web pages is a daunting task, but increasingly essential to efficiently moderate discussions and effectively filter problematic content. Unfortunately, controversies occur across many topics and domains, with great changes over time. This paper investigates neural classifiers as a more robust methodology for controversy detection in general web pages. Current models have often cast controversy detection on general web pages as Wikipedia linking, or exact lexical matching tasks. The diverse and changing nature of controversies suggest that semantic approaches are better able to detect controversy. We train neural networks that can capture semantic information from texts using weak signal data. By leveraging the semantic properties of word embeddings we robustly improve on existing controversy detection methods. To evaluate model stability over time and to unseen topics, we asses model performance under varying training conditions to test cross-temporal, cross-topic, cross-domain performance and annotator congruence. In doing so, we demonstrate that weak-signal based neural approaches are closer to human estimates of controversy and are more robust to the inherent variability of controversies

A note on the convergence of parametrised non-resonant invariant manifolds

Truncated Taylor series representations of invariant manifolds are abundant in numerical computations. We present an aposteriori method to compute the convergence radii and error estimates of analytic parametrisations of non-resonant local invariant manifolds of a saddle of an analytic vector field, from such a truncated series. This enables us to obtain local enclosures, as well as existence results, for the invariant manifolds

Sex and age effects on monk parakeet home-range variation in the urban habitat

Home-range size is a key aspect of space-use, and variation in home-range size and structure may have profound consequences for the potential impact of damage and control strategies for invasive species. However, knowledge on home-range structure of naturalized parrot species is very limited. The aim of this study was to quantify patterns of home-range variation according to sex and age of the monk parakeet Myiopsitta monachus, an invasive parakeet in Europe. Mean kernel home-range size was 12.4 ± 1.22 ha (range 1.7–74.1 ha; N = 73 birds). Juveniles had a larger home-range size than adults, but sexes did not differ in kernel home-range size. The mean maximum distance moved by monk parakeets was 727 ± 37.0 m (range: 150–1581 m), and it was not dependent on either the sex or age of the birds. Having a small home range is one of the conditions for the feasible eradication of an invasive species; hence, the small home range of urban monk parakeets that we report here is good news for pest managers. However, this small home-range size can limit the effectiveness of culling operations with traps or feeders with contraceptives or poison, and other alternatives, such as funnel nets or traps, should be used

Initial evaluation of nighttime restlessness in a naturally occurring canine model of osteoarthritis pain

Chronic pain due to osteoarthritis (OA) can lead to significant disruption of sleep and increased restlessness. Our objective was to assess whether naturally occurring canine OA is associated with nighttime restlessness and so has potential as a model of OA-associated sleep disturbance. The study was designed as a two-part prospective masked, placebo-controlled study using client-owned dogs (Part A n = 60; Part B n = 19). Inclusion criteria consisted of OA-associated joint pain and mobility impairment. The primary outcome measure for both parts was nighttime accelerometry. In Part B, quality of sleep was assessed using a clinical metrology instrument (Sleep and Night Time Restlessness Evaluation Score, SNoRE). Part A included dogs receiving two weeks of non-steroidal anti-inflammatory drug (NSAID) preceded with two weeks of no treatment. Part B was a crossover study, with NSAID/placebo administered for two weeks followed by a washout period of one week and another two weeks of NSAID/placebo. Repeated measures analysis of variance was used to assess differences between baseline and treatment. There were no significant changes in accelerometry-measured nighttime activity as a result of NSAID administration. SNoRE measures indicated significant improvements in aspects of the quality of nighttime sleep that did not involve obvious movement. These results reflect the few similar studies in human OA patients. Although accelerometry does not appear to be useful, this model has potential to model the human pain-related nighttime sleep disturbance, and other outcome measures should be explored in this model

High-resolution state-selected ion-molecule reaction studies using pulsed field ionization photoelectron-secondary ion coincidence method

We have developed an octopole-quadrupole photoionization apparatus at the Advanced Light Source for absolute integral cross-section measurements of rovibrational-state-selected ion-molecule reactions. This apparatus consists of a high-resolution photoionization ion source, a wired ion gate lens, a dual radio-frequency (rf) octopole ion guide reaction gas cell, and a quadrupole mass spectrometer for reactant and product ion detection. The unique feature of this apparatus is the implementation of the high-resolution pulsed field ionization-photoelectron (PFI-PE)-photoion coincidence (PFI-PEPICO) technique, which has allowed the rotational-state selection of diatomic ions for ion-molecule reaction studies. The novel application of the wired ion gate lens for the rejection of false coincidence background ions is described. This application, along with the differential-ion-gate scheme, has made possible the measurements of rovibrational-state-selected absolute integral reaction cross sections for ion-molecule collisions using the PFI-PE-secondary ion coincidence PFI-PESICO method. The successful measurement of absolute state-selected cross sections for H2 + (X,v+,N+)+Ar(Ne) with v+ up to 17 [the third to the last vibrational state of H2+(X)] demonstrates the high sensitivity of this differential-ion-gate PFI-PESICO method. In order to gain a detailed understanding and to obtain optimal performance of the wired ion gate lens for PFI-PESICO measurements, we have carried out ion trajectory calculations of reactant ions between the photoionization region and the rf-octopole ion guide. On the basis of these calculations, possible future improvements for the application of this differential-ion-gate PFI-PESICO scheme are discussed

Multi-Timescale Perceptual History Resolves Visual Ambiguity

When visual input is inconclusive, does previous experience aid the visual system in attaining an accurate perceptual interpretation? Prolonged viewing of a visually ambiguous stimulus causes perception to alternate between conflicting interpretations. When viewed intermittently, however, ambiguous stimuli tend to evoke the same percept on many consecutive presentations. This perceptual stabilization has been suggested to reflect persistence of the most recent percept throughout the blank that separates two presentations. Here we show that the memory trace that causes stabilization reflects not just the latest percept, but perception during a much longer period. That is, the choice between competing percepts at stimulus reappearance is determined by an elaborate history of prior perception. Specifically, we demonstrate a seconds-long influence of the latest percept, as well as a more persistent influence based on the relative proportion of dominance during a preceding period of at least one minute. In case short-term perceptual history and long-term perceptual history are opposed (because perception has recently switched after prolonged stabilization), the long-term influence recovers after the effect of the latest percept has worn off, indicating independence between time scales. We accommodate these results by adding two positive adaptation terms, one with a short time constant and one with a long time constant, to a standard model of perceptual switching

Shot noise in normal metal-d-wave superconducting junctions

We present theoretical calculations and predictions for the shot noise in voltage biased junctions of $d_{x^2-y^2}$ superconductors and normal metal counter-electrodes. In the clean limit for the d-wave superconductor the shot noise vanishes at zero voltage because of resonant Andreev reflection by zero-energy surface bound states. We examine the sensitivity of this resonance to impurity scattering. We report theoretical results for the magnetic field dependence of the shot noise, as well the fingerprints of subdominant $s$- and $d_{xy}$ pairing channels.Comment: 15 pages, 8 figures and 3 tables embedde