On Third-Order Limiter Functions for Finite Volume Methods

In this article, we propose a finite volume limiter function for a reconstruction on the three-point stencil. Compared to classical limiter functions in the MUSCL framework, which yield $2^{\text{nd}}$-order accuracy, the new limiter is $3^\text{rd}$-order accurate for smooth solutions. In an earlier work, such a $3^\text{rd}$-order limiter function was proposed and showed successful results [2]. However, it came with unspecified parameters. We close this gap by giving information on these parameters.Comment: 8 pages, conference proceeding

Hybrid Entropy Stable HLL-Type Riemann Solvers for Hyperbolic Conservation Laws

It is known that HLL-type schemes are more dissipative than schemes based on characteristic decompositions. However, HLL-type methods offer greater flexibility to large systems of hyperbolic conservation laws because the eigenstructure of the flux Jacobian is not needed. We demonstrate in the present work that several HLL-type Riemann solvers are provably entropy stable. Further, we provide convex combinations of standard dissipation terms to create hybrid HLL-type methods that have less dissipation while retaining entropy stability. The decrease in dissipation is demonstrated for the ideal MHD equations with a numerical example.Comment: 6 page

Third-order Limiting for Hyperbolic Conservation Laws applied to Adaptive Mesh Refinement and Non-Uniform 2D Grids

In this paper we extend the recently developed third-order limiter function $H_{3\text{L}}^{(c)}$ [J. Sci. Comput., (2016), 68(2), pp.~624--652] to make it applicable for more elaborate test cases in the context of finite volume schemes. This work covers the generalization to non-uniform grids in one and two space dimensions, as well as two-dimensional Cartesian grids with adaptive mesh refinement (AMR). The extension to 2D is obtained by the common approach of dimensional splitting. In order to apply this technique without loss of third-order accuracy, the order-fix developed by Buchm\"uller and Helzel [J. Sci. Comput., (2014), 61(2), pp.~343--368] is incorporated into the scheme. Several numerical examples on different grid configurations show that the limiter function $H_{3\text{L}}^{(c)}$ maintains the optimal third-order accuracy on smooth profiles and avoids oscillations in case of discontinuous solutions

Hybrid Riemann Solvers for Large Systems of Conservation Laws

In this paper we present a new family of approximate Riemann solvers for the numerical approximation of solutions of hyperbolic conservation laws. They are approximate, also referred to as incomplete, in the sense that the solvers avoid computing the characteristic decomposition of the flux Jacobian. Instead, they require only an estimate of the globally fastest wave speeds in both directions. Thus, this family of solvers is particularly efficient for large systems of conservation laws, i.e. with many different propagation speeds, and when no explicit expression for the eigensystem is available. Even though only fastest wave speeds are needed as input values, the new family of Riemann solvers reproduces all waves with less dissipation than HLL, which has the same prerequisites, requiring only one additional flux evaluation.Comment: 9 page

Relations between WENO3 and Third-order Limiting in Finite Volume Methods

Weighted essentially non-oscillatory (WENO) and finite volume (FV) methods employ different philosophies in their way to perform limiting. We show that a generalized view on limiter functions, which considers a two-dimensional, rather than a one-dimensional dependence on the slopes in neighboring cells, allows to write WENO3 and $3^\text{rd}$-order FV schemes in the same fashion. Within this framework, it becomes apparent that the classical approach of FV limiters to only consider ratios of the slopes in neighboring cells, is overly restrictive. The hope of this new perspective is to establish new connections between WENO3 and FV limiter functions, which may give rise to improvements for the limiting behavior in both approaches.Comment: 22 page

Nothing more than a pair of curvatures: A common mechanism for the detection of both radial and non-radial frequency patterns.

Radial frequency (RF) patterns, which are sinusoidal modulations of a radius in polar coordinates, are commonly used to study shape perception. Previous studies have argued that the detection of RF patterns is either achieved globally by a specialized global shape mechanism, or locally using as cue the maximum tangent orientation difference between the RF pattern and the circle. Here we challenge both ideas and suggest instead a model that accounts not only for the detection of RF patterns but also for line frequency patterns (LF), i.e. contours sinusoidally modulated around a straight line. The model has two features. The first is that the detection of both RF and LF patterns is based on curvature differences along the contour. The second is that this curvature metric is subject to what we term the Curve Frequency Sensitivity Function, or CFSF, which is characterized by a flat followed by declining response to curvature as a function of modulation frequency, analogous to the modulation transfer function of the eye. The evidence that curvature forms the basis for detection is that at very low modulation frequencies (1-3 cycles for the RF pattern) there is a dramatic difference in thresholds between the RF and LF patterns, a difference however that disappears at medium and high modulation frequencies. The CFSF feature on the other hand explains why thresholds, rather than continuously declining with modulation frequency, asymptote at medium and high modulation frequencies. In summary, our analysis suggests that the detection of shape modulations is processed by a common curvature-sensitive mechanism that is subject to a shape-frequency-dependent transfer function. This mechanism is independent of whether the modulation is applied to a circle or a straight line

Imagining circles: empirical data and a perceptual model for the arc-size illusion

An essential part of visual object recognition is the evaluation of the curvature of both an object's outline as well as the contours on its surface. We studied a striking illusion of visual curvature--the arc-size illusion (ASI)--to gain insight into the visual coding of curvature. In the ASI, short arcs are perceived as flatter (less curved) compared to longer arcs of the same radius. We investigated if and how the ASI depends on (i) the physical size of the stimulus and (ii) on the length of the arc. Our results show that perceived curvature monotonically increases with arc length up to an arc angle of about 60°, thereafter remaining constant and equal to the perceived curvature of a full circle. We investigated if the misjudgment of curvature in the ASI translates into predictable biases for three other perceptual tasks: (i) judging the position of the centre of circular arcs; (ii) judging if two circular arcs fall on the circumference of the same (invisible) circle and (iii) interpolating the position of a point on the circumference of a circle defined by two circular arcs. We found that the biases in all the above tasks were reliably predicted by the same bias mediating the ASI. We present a simple model, based on the central angle subtended by an arc, that captures the data for all tasks. Importantly, we argue that the ASI and related biases are a consequence of the fact that an object's curvature is perceived as constant with viewing distance, in other words is perceptually scale invariant

Hoitotyöntekijöiden valmiudet näyttöön perustuvassa hoitotyössä : kirjallisuuskatsaus

Tämän opinnäytetyön tarkoituksena on kuvata hoitotyöntekijöiden valmiuksia toteuttaa näyttöön perustuvaa hoitotyötä. Tutkimustehtävänä oli selvittää 1) Millaiset ovat hoitotyöntekijöiden asenteet näyttöön perustuvaa hoitotyötä kohtaan ja 2) Millainen on hoitotyöntekijöiden tietoperusta näyttöön perustuvassa hoitotyössä sekä 3) Millaiset ovat hoitotyöntekijöiden taidot toteuttaa näyttöön perustuvaa hoitotyötä. Tämä opinnäytetyö on osa suurempaa kehittämisprojektia Näyttöön perustuvan hoitotyön osaamisen vahvistaminen työelämässä, joka toteutetaan Metropolia Ammattikorkeakoulun ja Helsingin kaupungin terveyskeskuksen akuuttisairaalaosastojen sekä Bournemouthin yliopiston yhteistyönä. Kirjallisuuskatsauksen aineisto muodostui 16 hoitotieteellisestä artikkelista. Aineisto analysoitiin deduktiivisella sisällönanalyysillä. Tulosten mukaan hoitohenkilökunta pitää mahdollisuutena kehittyä paremmaksi näyttöön perustuvassa hoitotyössä. Näyttöön perustuvan hoitotyön projekteihin osallistuneen henkilökunnan asenne muuttui positiivisemmaksi tutkittua tietoa kohtaan ja kehitti heidän taitojaan tutkitun tiedon käytöön. Esteenä näyttöön perustuvalle hoitotyölle on osaavien hoitajien puute ja vastustus sekä haluton asenne tutkimustietoa ja sen hyödyntämistä kohtaan. Myös ajan puute, rahoitus, internetyhteydet, työn kuormittavuus, yhteistyön puute ja henkisen tuen puute koettiin esteiksi. Hoitajat arvioivat itsensä aloittelijoiksi tutkimustiedon löytämisessä ja tarkastelussa. Näyttöön perustuvat tiedon lähteet tunnettiin huonosti ja hoitotieteellisiä tutkimuksia käytettiin vähän. Koulutus vaikutti tietolähteiden käyttöön positiivisesti. Edistävinä tekijöinä tutkimustiedon hyödyntämiselle mainittiin tutkimuksen esittely ja tutkimuksen lukemisen opetus sekä tutkimuksesta saatava hyöty käytäntöön. Osa hoitajista hyödynsi hyvin tutkimustietoa hoitotoimien hallinnassa ja potilaiden hoidossa. Kokeneemmat hoitajat olivat varmempia käyttämään tutkimusnäyttöä ja kokemus toi varmuutta soveltaa lukemaansa hoitotyöhön. Näyttöön perustuvan hoitotyön esteenä oli tutkimustiedon vieraskielisyys. Tutkimusraporteilta odotettiin tulosten sovellettavuuden selvittämistä, helpompaa saatavuutta ja parempaa tarjontaa sekä raportin tulisi olla omalla kielellä.The Purpose of this study was to describe nurses’ readiness to practice evidence-based nursing. The aim was to clarify nurses’ attitudes, knowledge and skills concerning evidence-based nursing. This study forms a part of a larger development project called Development of Competence in Evidence-based Nursing Practice which is carried out as a joint venture with Helsinki Metropolia University of Applied Sciences, the acute wards of Helsinki Health Centre and Bournemouth University. The data for this study was collected from nursing science publications. The total number of articles was 16. The method used in the analysis of the data was deductive content analysis. According to the results, the nursing staff see themselves capable of improving in evidence-based nursing. The evidence-based nursing projects changed the attitudes of the staff towards research knowledge in a more positive direction. The projects also developed the skills of the staff in using research knowledge. Obstacles for evidence-based nursing are the on deficiency and resistance of skillful nurses and also a reluctant attitude towards research knowledge and its exploitation. Also, the lack of time, funding, internet connections, cooperation and mental support as well as high work load were seen as barriers. Nurses evaluated themselves as beginners in finding and reviewing the research knowledge. The sources of knowledge on evidence-based nursing were poorly known and studies in nursing were hardly ever used. Education affected the use of knowledge sources in a positive way. Introduction of a study, teaching how to read it and practical benefits of it were mentioned as promoting factors in using knowledge sources. Some of the nurses used the knowledge sources well in mastering the nursing chores and patient care. The more experienced nurses were more confident in using evidence-based nursing and in applying their knowledge to the work. What hindered the evidence-based nursing was research knowledge written in a foreign language. It was expected that the research reports should explain how the findings could be applied into practice, they should also be more easily accessible and there should be a better supply of them. The reports were also expected to be in one’s own native language

Modeling probability and additive summation for detection across multiple mechanisms under the assumptions of signal detection theory.

Many studies have investigated how multiple stimuli combine to reach threshold. There are broadly speaking two ways this can occur: additive summation (AS) where inputs from the different stimuli add together in a single mechanism, or probability summation (PS) where different stimuli are detected independently by separate mechanisms. PS is traditionally modeled under high threshold theory (HTT); however, tests have shown that HTT is incorrect and that signal detection theory (SDT) is the better framework for modeling summation. Modeling the equivalent of PS under SDT is, however, relatively complicated, leading many investigators to use Monte Carlo simulations for the predictions. We derive formulas that employ numerical integration to predict the proportion correct for detecting multiple stimuli assuming PS under SDT, for the situations in which stimuli are either equal or unequal in strength. Both formulas are general purpose, calculating performance for forced-choice tasks with M alternatives, n stimuli, in Q monitored mechanisms, each subject to a non-linear transducer with exponent τ. We show how the probability (and additive) summation formulas can be used to simulate psychometric functions, which when fitted with Weibull functions make signature predictions for how thresholds and psychometric function slopes vary as a function of τ, n, and Q. We also show how one can fit the formulas directly to real psychometric functions using data from a binocular summation experiment, and show how one can obtain estimates of τ and test whether binocular summation conforms more to PS or AS. The methods described here can be readily applied using software functions newly added to the Palamedes toolbox