bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pulse dynamics in reaction–diffusion equations with strong spatially localized impurities
Authors: Doelman Arjen , van Heijster Peter , Shen Jianhe 
Published: March 2018

In this article, a general geometric singular perturbation framework is developed to study the impact of strong, spatially localized, nonlinear impurities on the existence, stability and bifurcations of localized structures in systems of linear reaction–diffusion equations. By taking advantage of the multiple-scale nature of the problem, we derive algebraic conditions determining the existence and stability of pinned single- and multi-pulse solutions. Our methods enable us to explicitly control the spectrum associated with a (multi-)pulse solution. In the scalar case, we show how eigenvalues may move in and out of the essential spectrum and that Hopf bifurcations cannot occur. By contrast, even a pinned 1-pulse solution can undergo a Hopf bifurcation in a two-component system of linear reaction–diffusion equations with (only) one impurity.
This article is part of the theme issue ‘Stability of nonlinear waves and patterns and related topics’.
Nonlinear modulation near the Lighthill instability threshold in 2+1 Whitham theory
Authors: Bridges Thomas J. , Ratliff Daniel J. 
Published: March 2018

The dispersionless Whitham modulation equations in 2+1 (two space dimensions and time) are reviewed and the instabilities identified. The modulation theory is then reformulated, near the Lighthill instability threshold, with a slow phase, moving frame and different scalings. The resulting nonlinear phase modulation equation near the Lighthill surfaces is a geometric form of the 2+1 two-way Boussinesq equation. This equation is universal in the same sense as Whitham theory. Moreover, it is dispersive, and it has a wide range of interesting multi-periodic, quasi-periodic and multi-pulse localized solutions. For illustration the theory is applied to a complex nonlinear 2+1 Klein–Gordon equation which has two Lighthill surfaces in the manifold of periodic travelling waves.
This article is part of the theme issue ‘Stability of nonlinear waves and patterns and related topics’.
Partial differential systems with non-local nonlinearities: generation and solutions
Authors: Beck Margaret , Doikou Anastasia , Malham Simon J. A. , Stylianidis Ioannis 
Published: March 2018

We develop a method for generating solutions to large classes of evolutionary partial differential systems with non-local nonlinearities. For arbitrary initial data, the solutions are generated from the corresponding linearized equations. The key is a Fredholm integral equation relating the linearized flow to an auxiliary linear flow. It is analogous to the Marchenko integral equation in integrable systems. We show explicitly how this can be achieved through several examples, including reaction–diffusion systems with non-local quadratic nonlinearities and the nonlinear Schrödinger equation with a non-local cubic nonlinearity. In each case, we demonstrate our approach with numerical simulations. We discuss the effectiveness of our approach and how it might be extended.This article is part of the theme issue ‘Stability of nonlinear waves and patterns and related topics’.
The Tactile Receptive Fields of Freely Moving Caenorhabditis elegans Nematodes
Authors: Mazzochette E. A. , Nekimken A. L. , Loizeau F. , Whitworth J. , Huynh B. , Goodman M.B. , Pruitt B.L. 
Published: March 2018

AbstractSensory neurons embedded in skin are responsible for the sense of touch. In humans and other mammals, touch sensation depends on thousands of diverse somatosensory neurons. By contrast, Caenorhabditis elegans nematodes have six gentle touch receptor neurons linked to simple behaviors. The classical touch assay uses an eyebrow hair to stimulate freely moving C. elegans, evoking evasive behavioral responses. While this assay has led to the discovery of genes required for touch sensation, it does not provide control over stimulus strength or position. Here, we present an integrated system for performing automated, quantitative touch assays that circumvents these limitations and incorporates automated measurements of behavioral responses. Highly Automated Worm Kicker (HAWK) unites microfabricated silicon force sensors and video analysis with real-time force and position control. Using this system, we stimulated animals along the anterior-posterior axis and compared responses in wild-type and spc-1(dn) transgenic animals, which have a touch defect due to expression of a dominant-negative α spectrin protein fragment. As expected from prior studies, delivering large stimuli anterior to the mid-point of the body evoked a reversal, but such a stimulus applied posterior to the mid-point evoked a speed-up. The probability of evoking a response of either kind depended on stimulus strength and location; once initiated, the magnitude and quality of both reversal and speed-up behavioral responses were uncorrelated with stimulus location, strength, or the absence or presence of the spc-1(dn) transgene. Wild-type animals failed to respond when the stimulus was applied near the mid-point. These results establish that stimulus strength and location govern the activation of a stereotyped motor program and that the C. elegans body surface consists of two receptive fields separated by a gap.
Uncertainpy: A Python toolbox for uncertainty quantification and sensitivity analysis in computational neuroscience
Authors: Tennøe Simen , Halnes Geir , Einevoll Gaute T. 
Published: March 2018

AbstractComputational models in neuroscience typically contain many parameters that are poorly constrained by experimental data. Uncertainty quantification and sensitivity analysis provide rigorous procedures to quantify how the model output depends on this parameter uncertainty. Unfortunately, the application of such methods is not yet standard within the field of neuroscience.Here we present Uncertainpy, an open-source Python toolbox, tailored to perform uncertainty quantification and sensitivity analysis of neuroscience models. Uncertainpy aims to make it easy and quick to get started with uncertainty analysis, without any need for detailed prior knowledge. The toolbox allows uncertainty quantification and sensitivity analysis to be performed on already existing models without needing to modify the model equations or model implementation. Uncertainpy bases its analysis on polynomial chaos expansions, which are more efficient than the more standard Monte-Carlo based approaches.Uncertainpy is tailored for neuroscience applications by its built-in capability for calculating characteristic features in the model output. The toolbox does not merely perform a point-to- point comparison of the “raw” model output (e.g. membrane voltage traces), but can also calculate the uncertainty and sensitivity of salient model response features such as spike timing, action potential width, mean interspike interval, and other features relevant for various neural and neural network models. Uncertainpy comes with several common models and features built in, and including custom models and new features is easy.The aim of the current paper is to present Uncertainpy for the neuroscience community in a user- oriented manner. To demonstrate its broad applicability, we perform an uncertainty quantification and sensitivity analysis on three case studies relevant for neuroscience: the original Hodgkin-Huxley point-neuron model for action potential generation, a multi-compartmental model of a thalamic interneuron implemented in the NEURON simulator, and a sparsely connected recurrent network model implemented in the NEST simulator.SIGNIFICANCE STATEMENTA major challenge in computational neuroscience is to specify the often large number of parameters that define the neuron and neural network models. Many of these parameters have an inherent variability, and some may even be actively regulated and change with time. It is important to know how the uncertainty in model parameters affects the model predictions. To address this need we here present Uncertainpy, an open-source Python toolbox tailored to perform uncertainty quantification and sensitivity analysis of neuroscience models.
A giant amphipathic helix from a perilipin that is adapted for coating lipid droplets
Authors: Čopič Alenka , Antoine-Bally Sandra , Giménez-Andrés Manuel , Torre Garay César La , Antonny Bruno , Manni Marco M. , Pagnotta Sophie , Guihot Jeanne , Jackson Catherine L. 
Published: March 2018

SummaryHow proteins are targeted to lipid droplets (LDs) and distinguish the LD surface from the surfaces of other organelles is poorly understood, but many contain predicted amphipathic helices (AHs) that are involved in targeting. We have focused on human perilipin 4 (Plin4), which contains an AH that is exceptional in terms of length and repetitiveness. Using model cellular systems, we show that AH length, hydrophobicity, and charge are important for AH targeting to LDs and that these properties can compensate for one another, albeit at a loss of targeting specificity. Using synthetic lipids, we show that purified Plin4 AH binds poorly to lipid bilayers but strongly interacts with pure triglycerides, acting as a coat and forming small oil droplets. Because Plin4 overexpression alleviates LD instability under conditions where their coverage by phospholipids is limiting, we propose that the Plin4 AH replaces the LD lipid monolayer, for example during LD growth.
Disentangling genetically confounded polygenic associations between Attention-Deficit/Hyperactivity Disorder, literacy and language
Authors: Verhoef Ellen , Demontis Ditte , Burgess Stephen , Shapland Chin Yang , Dale Philip S. , Okbay Aysu , Neale Benjamin M. , Faraone Stephen V. ,   iPSYCH-Broad-PGC ADHD Consortium, Stergiakouli Evie , Smith George Davey , Fisher Simon E. , Børglum Anders D. , St Pourcain Beate 
Published: March 2018

AbstractInterpreting polygenic overlap between ADHD and both literacy- and language-related impairments is challenging as genetic confounding can bias associations. Here, we investigate evidence for links between polygenic ADHD risk and multiple literacy- and language-related abilities (LRAs), assessed in UK children (N≤5,919), conditional on genetic effects shared with educational attainment (EA). Genome-wide summary statistics on clinical ADHD and years-of-schooling were obtained from large consortia (N≤326,041). ADHD-polygenic scores (ADHD-PGS) were inversely associated with LRAs in ALSPAC, most consistently with reading-related abilities, and explained ≤1.6% phenotypic variation. Polygenic links were then dissected into both genetic effects shared with and independent of EA using multivariable regressions (MVR), analogous to Mendelian Randomization approaches accounting for mediating effects. Conditional on EA, polygenic ADHD risk remained associated with multiple literacy-related skills, phonemic awareness and verbal intelligence, but not language-related skills such as listening comprehension and non-word repetition. Pooled reading performance showed the strongest overlap with ADHD independent of EA. Using conservative ADHD-instruments (P-threshold<5×10−8) this corresponded to a 0.35 decrease in Z-scores per log-odds in ADHD-liability (P=9.2×10−5). Using subthreshold ADHD-instruments (P-threshold<0.0015), these associations had lower magnitude, but higher predictive accuracy, with a 0.03 decrease in Z-scores (P=1.4×10−6). Polygenic ADHD-effects shared with EA were of equal strength and at least equal magnitude compared to those independent of EA, for all LRAs studied, and only detectable using subthreshold instruments. Thus, ADHD-related polygenic links are highly susceptible to genetic confounding, concealing an ADHD-specific association profile that primarily involves reading-related impairments, but few language-related problems.
Evolutionary inferences about quantitative traits are affected by underlying genealogical discordance
Authors: Mendes Fábio K. , Fuentes-González Jesualdo A. , Schraiber Joshua G. , Hahn Matthew W. 
Published: March 2018

AbstractModern phylogenetic methods used to study how traits evolve often require a single species tree as input, and do not take underlying gene tree discordance into account. Such approaches may lead to errors in phylogenetic inference because of hemiplasy — the process by which single changes on discordant trees appear to be homoplastic when analyzed on a fixed species tree. Hemiplasy has been shown to affect inferences about discrete traits, but it is still unclear whether complications arise when quantitative traits are analyzed. In order to address this question and to characterize the effect of hemiplasy on traits controlled by a large number of loci, we present a multispecies coalescent model for quantitative traits evolving along a species tree. We demonstrate theoretically and through simulations that hemiplasy decreases the expected covariances in trait values between more closely related species relative to the covariances between more distantly related species. This effect leads to an overestimation of a trait’s evolutionary rate parameter, to a decrease of the trait’s phylogenetic signal, and to increased false positive rates in comparative methods such as the phylogenetic ANOVA. We also show that hemiplasy affects discrete, threshold traits that have an underlying continuous liability, leading to false inferences of convergent evolution. The number of loci controlling a quantitative trait appears to be irrelevant to the trends reported, for all analyses. Our results demonstrate that gene tree discordance and hemiplasy are a problem for all types of traits, across a wide range of methods. Our analyses also point to the conditions under which hemiplasy is most likely to be a factor, and suggest future approaches that may mitigate its effects.
Voxel-wise T2 relaxometry of Normal Pediatric Brain Development in 326 healthy infants and toddlers
Authors: Fonov Vladimir S. , Leppert Ilana R. , Pike G. Bruce , Collins D. Louis ,   Brain Development Cooperative Group
Published: March 2018

AbstractQuantitative T2 data from an NIH-sponsored multi-center study of Normal Brain Development was used to perform automatic voxel-wise analysis of the changes in T2 evolution in the brain in healthy children within the age range from birth to 5 years. All data were non-linearly registered into a common coordinate space. The T2 parameters were estimated by 2 point fitting from the PD-weighted and T2-weighted image data, or by least-squares fitting of 4 data points when addition intermediate weighting images were available. The main result of this study is voxel-level map of monoexponential evolution of T2 in this age range indicating the delay (in months) and the rate (in 1/months) of development. The automatic maps are compared to manual region-of-interest based estimates of T2 evolution.
Enabling entrepreneurial behaviour in a land-based university
Authors: Manning Louise 
Published: March 2018

PurposeThe purpose of this paper is to develop a conceptual framework along with a set of hypotheses that reflects the dynamic relationships that operate within an entrepreneurial land-based university in order to then undertake empirical research.Design/methodology/approachThis paper, through reflection on existing literature, critiques the interactions between student, academic, educational institution and industry in order to conceptualise the entrepreneurial modus operandi of a land-based university.FindingsSpecialist universities, such as those that serve the land-based sector, need to demonstrate multiple excellences not only in terms of the education they provide for students, but also in terms of consistently meeting or exceeding government, research community, employers and societies expectations. An institutional framework must be in place to facilitate and enhance the quadruple interface of academic, institutional, industry and student entrepreneurial behaviour. The social and economic factors that mediate the dynamics within this framework first underpin student development supporting them to reach their potential, second inform teaching excellence and research practice and finally, lead to outcomes that contribute to the global, national and regional economy.Originality/valueThis paper is of value for those working in the educational sector as the model outlined can be used to critically reflect on current principles and practice and derive options for action to embed entrepreneurship more deeply within the organisational culture of a university.
A review of entrepreneurship education research
Authors: Henry Colette , Lewis Kate 
Published: March 2018

Purpose
The purpose of this paper is to review recent published research on entrepreneurship education (EE) specifically within the special issue collections of the journal Education +Training, and to assess the overall contribution to the field. The research questions focus on: What topics are explored by these SI papers? What trends can be observed in relation to country context and methodological approach? How is EE defined in these papers, and how do the papers contribute to the wider entrepreneurship research agenda?

Design/methodology/approach
The paper uses an adapted version of the systematic literature review approach, focusing on the discrete special issues on entrepreneurship/enterprise education published in the journal Education + Training since 2010. A comprehensive reading guide was used to review the papers, with completed data compiled into a single excel spreadsheet to facilitate analysis. A total of 66 papers were reviewed.

Findings
A considerable range of themes, geographical contexts and methodological approaches were used in the papers reviewed. A mix of qualitative and quantitative approaches were also found. The papers were characterised by a strong international and applied dimension, with the core collective contribution of the SI papers laying in their direct relevance to practice.

Research limitations/implications
The paper is limited by its deliberate focus on a discrete set of special issue papers; however, the total of 66 papers included in the review is noteworthy.

Practical implications
The paper demonstrates the considerable learning that can be garnered from the Education + Training special issue collection for EE practitioners.

Originality/value
To the authors’ knowledge, this is the first time this discrete collection of special issue papers has been reviewed.
Towards a multi-level servitization framework
Authors: Lenka Sambit , Parida Vinit , Sjödin David Rönnberg , Wincent Joakim 
Published: March 2018

PurposeThe dominant-view within servitization literature presupposes a progressive transition from product to service orientation. In reality, however, many manufacturing firms maintain both product and service orientations throughout their servitization journey. Using the theoretical lens of organizational ambivalence, the purpose of this paper is to explore the triggers, manifestation and consequences of these conflicting orientations.Design/methodology/approachA multiple case study method was used to analyze five large manufacturing firms that were engaged in servitization. Semi-structured interviews were conducted with 35 respondents across different functions within these firms.FindingsServitizing firms experience organizational ambivalence during servitization because of co-existing product and service orientations. This paper provides a framework that identifies the triggers of this ambivalence, its multi-level manifestation and its consequences. These provide implications for explaining why firms struggle to implement servitization strategies due to co-existing product and services orientations. Understanding organizational ambivalence, provides opportunity to manage related challenges and can be vital to successful servitization.Originality/valueConsidering the theoretical concept of ambivalence could advance the understanding of the effects and implications of conflicting orientations during servitization in manufacturing firms.
Six Sigma in healthcare: a systematic review of the literature
Authors: Antony Jiju , Palsuk Pruksathorn , Gupta Sandeep , Mishra Deepa , Barach Paul 
Published: March 2018

Purpose
The purpose of this paper is to illustrate the systematic role played by Six Sigma methodology in improving the quality of healthcare. The literature review identifies the relevant opportunities for successful introduction and development of Six Sigma approach in healthcare sector.

Design/methodology/approach
A systematic methodology to identifying literature on Six Sigma in healthcare is presented. Web of Science, Medline, Emerald Insight, ASQ and ProQuest databases (1998-2016) were searched, and 68 papers of fair methodological quality were identified.

Findings
The findings of the systematic review reveal a growing interest in research on Six Sigma adoption in healthcare. The findings indicate that Six Sigma applications in healthcare have been focused on the entire hospital with no real focus on a particular department or function. The key findings on benefits, success factors, challenges and common tools of Six Sigma from the existing literature are also presented in the paper.

Research limitations/implications
The papers included in the systematic review were peer-reviewed papers available in English. Due to these limitations, relevant papers may have been excluded. Moreover, the authors have excluded all conference and white papers for their inclusion in this study.

Originality/value
This paper can serve as a guide on how Six Sigma approach can be applied to improve the quality of healthcare. The authors also believe that this is possibly the most comprehensive systematic literature review on the topic and will set the foundation for various research avenues based on the key findings of this study.
Understanding and detecting data fabrication in large-scale assessments
Authors: Yamamoto Kentaro , Lennon Mary Louise 
Published: March 2018

PurposeFabricated data jeopardize the reliability of large-scale population surveys and reduce the comparability of such efforts by destroying the linkage between data and measurement constructs. Such data result in the loss of comparability across participating countries and, in the case of cyclical surveys, between past and present surveys. This paper aims to describe how data fabrication can be understood in the context of the complex processes involved in the collection, handling, submission and analysis of large-scale assessment data. The actors involved in those processes, and their possible motivations for data fabrication, are also elaborated.Design/methodology/approachComputer-based assessments produce new types of information that enable us to detect the possibility of data fabrication, and therefore the need for further investigation and analysis. The paper presents three examples that illustrate how data fabrication was identified and documented in the Programme for the International Assessment of Adult Competencies (PIAAC) and the Programme for International Student Assessment (PISA) and discusses the resulting remediation efforts.FindingsFor two countries that participated in the first round of PIAAC, the data showed a subset of interviewers who handled many more cases than others. In Case 1, the average proficiency for respondents in those interviewers’ caseloads was much higher than expected and included many duplicate response patterns. In Case 2, anomalous response patterns were identified. Case 3 presents findings based on data analyses for one PISA country, where results for human-coded responses were shown to be highly inflated compared to past results.Originality/valueThis paper shows how new sources of data, such as timing information collected in computer-based assessments, can be combined with other traditional sources to detect fabrication.