Mokken Scale Analysis in R

Mokken scale analysis (MSA) is a scaling procedure for both dichotomous and polytomous items. It consists of an item selection algorithm to partition a set of items into Mokken scales and several methods to check the assumptions of two nonparametric item response theory models: the monotone homogeneity model and the double monotonicity model. First, we present an R package mokken for MSA and explain the procedures. Second, we show how to perform MSA in R using test data obtained with the Adjective Checklist.

Single-leg squats can predict leg alignment in dancers performing ballet movements in turnout

The physical assessments used in dance injury surveillance programs are often adapted from the sports and exercise domain. Bespoke physical assessments may be required for dance, particularly when ballet movements involve “turning out” or external rotation of the legs beyond that typically used in sports. This study evaluated the ability of the traditional single-leg squat to predict the leg alignment of dancers performing ballet movements with turnout. Three-dimensional kinematic data of dancers performing the single-leg squat and five ballet movements were recorded and analyzed. Reduction of the three-dimensional data into a one-dimensional variable incorporating the ankle, knee, and hip joint center positions provided the strongest predictive model between the single-leg squat and the ballet movements. The single-leg squat can predict leg alignment in dancers performing ballet movements, even in “turned out” postures. Clinicians should pay careful attention to observational positioning and rating criteria when assessing dancers performing the single-leg squat

Advances in nonparametric item response theory for scale construction in quality-of-life research

We introduce the special section on nonparametric item response theory (IRT) in Quality of Life Research. Starting from the well-known Rasch model, we provide a brief overview of nonparametric IRT models and discuss the assumptions, the properties, and the investigation of goodness of fit. We provide references to more detailed texts to help readers getting acquainted with nonparametric IRT models. In addition, we show how the rather diverse papers in the special section fit into the nonparametric IRT framework. Finally, we illustrate the application of nonparametric IRT models using data from a questionnaire measuring activity limitations in walking. The real-data example shows the quality of the scale and its constituent items with respect to dimensionality, local independence, monotonicity, and invariant item ordering

On the nature of kink MHD waves in magnetic flux tubes

Magnetohydrodynamic (MHD) waves are often reported in the solar atmosphere and usually classified as slow, fast, or Alfv\'en. The possibility that these waves have mixed properties is often ignored. The goal of this work is to study and determine the nature of MHD kink waves. This is done by calculating the frequency, the damping rate and the eigenfunctions of MHD kink waves for three widely different MHD waves cases: a compressible pressure-less plasma, an incompressible plasma and a compressible plasma with non-zero plasma pressure which allows for MHD radiation. In all three cases the frequency and the damping rate are for practical purposes the same as they differ at most by terms proportional to $(k_z R)^2$. In the magnetic flux tube the kink waves are in all three cases, to a high degree of accuracy incompressible waves with negligible pressure perturbations and with mainly horizontal motions. The main restoring force of kink waves in the magnetised flux tube is the magnetic tension force. The total pressure gradient force cannot be neglected except when the frequency of the kink wave is equal or slightly differs from the local Alfv\'{e}n frequency, i.e. in the resonant layer. Kink waves are very robust and do not care about the details of the MHD wave environment. The adjective fast is not the correct adjective to characterise kink waves. If an adjective is to be used it should be Alfv\'{e}nic. However, it is better to realize that kink waves have mixed properties and cannot be put in one single box

Highly Efficient Biobased Synthesis of Acrylic Acid

Petrochemical based polymers, paints and coatings are cornerstones of modern industry but our future sustainable society demands greener processes and renewable feedstock materials. A challenge is to access platform monomers from biomass resources while integrating the principles of green chemistry in their chemical synthesis. We present a synthesis route starting from biomass-derived furfural towards the commonly used monomers maleic anhydride and acrylic acid, implementing environmentally benign photooxygenation, aerobic oxidation and ethenolysis reactions. Maleic anhydride and acrylic acid, transformed into sodium acrylate, were isolated in yields of 85 % (2 steps) and 81 % (4 steps), respectively. With minimal waste and high atom efficiency, this biobased route provides a viable alternative to access key monomers

Maximum augmented empirical likelihood estimation of categorical marginal models for large sparse contingency tables

Categorical marginal models (CMMs) are flexible tools for modelling dependent or clustered categorical data, when the dependencies themselves are not of interest. A major limitation of maximum likelihood (ML) estimation of CMMs is that the size of the contingency table increases exponentially with the number of variables, so even for a moderate number of variables, say between 10 and 20, ML estimation can become computationally infeasible. An alternative method, which retains the optimal asymptotic efficiency of ML, is maximum empirical likelihood (MEL) estimation. However, we show that MEL tends to break down for large, sparse contingency tables. As a solution, we propose a new method, which we call maximum augmented empirical likelihood (MAEL) estimation and which involves augmentation of the empirical likelihood support with a number of well-chosen cells. Simulation results show good finite sample performance for very large contingency tables

Nonlinear Instability of kink oscillations due to shear motions

First results from a high-resolution three-dimensional nonlinear numerical study of the kink oscillation are presented. We show in detail the development of a shear instability in an untwisted line-tied magnetic flux tube. The instability produces significant deformations of the tube boundary. An extended transition layer may naturally evolve as a result of the shear instability at a sharp transition between the flux tube and the external medium. We also discuss the possible effects of the instability on the process of resonant absorption when an inhomogeneous layer is included in the model. One of the implications of these results is that the azimuthal component of the magnetic field of a stable flux tube in the solar corona, needed to prevent the shear instability, is probably constrained to be in a very specific range

Calvyn se vierde diens, die doktore-amp, en artikel 18 van die kerkorde van Dordrecht 1618 en 1619: ’n Kritiese refleksie

Die artikel fokus op Calvyn se besondere rol in die formulering van artikels 2 en 18 van die kerkorde van Dordrecht 1618 en 1619. Hierdie kerkorde word steeds deur ’n groot aantal gereformeerde kerke in die wêreld aanvaar en gebruik. Onderwerpe en probleme wat aangeraak word, sluit vrae in soos die volgende: Wie is verantwoordelik vir die onderrig van Teologie? Is die tradisie geldig dat daar naas die drie dienste van Woordbedienaar, ouderling en diaken ook ’n vierde diens bestaan, naamlik dié van doktor in die Teologie? Kan hierdie tradisie, wat hoofsaaklik op die standpunte van Bucer en Calvyn berus, met die gegewens in die Bybel versoen word? Besondere aandag word aan die volgende aspekte gegee: • Historiese gegewens oor doktor in die Teologie met besondere verwysing na die standpunte en invloed van Calvyn. • ’n Kritiese evaluering van die begronding van die vierde diens op die Bybel. • Die verhouding tussen teologiese opleiding in die konteks van die kerk en/of ’n universiteit. • Besondere aandag word gegee aan die situasie in die Gereformeerde Kerke in Suid-Afrika ten opsigte van die funksionering van hierdie vierde diens. Van die belangrikste konklusies wat gemaak word, is die volgende: die kerk het deur die eeue ’n besondere waardering en respek gehad vir die taak en funksie van die doktore in die Teologie. Dit het inderdaad tot groot seën van die kerke gedien. Calvyn se standpunte het dikwels tot verwarring aanleiding gegee, maar andersyds ook bygedra tot die erkenning van die belangrike funksie of taak wat hierdie vierde diens kerklik verrig. Net so vervul die doktore in die Teologie ’n besondere wetenskaplike rol aan teologiese fakulteite van universiteite. Calvin’s fourth office, the doctor ministry, and article 18 of the church order of Dordrecht 1618 and 1619: A critical reflection. This article focuses on Calvin’s special role in the ecclesiastical formulation of articles 2 and 18 in the church order of Dordrecht 1618 and 1619, which is still retained in a large number of reformed church orders in the reformed fellowship of churches. Topics and issues which are addressed include questions such as: Who is responsible for the teaching of Theology? Is the tradition valid that the doctorial or professorial office in theology exists as a fourth office beside that of ministers, elders and deacons? Is this tradition, which mainly rests on the views of Bucer and Calvin, correct in terms of the Bible? Particular attention to the following aspects is given: • Historical data on the doctor ecclesiae focusing on the views and influence of Calvin. • A critical evaluation of the foundation of the fourth office on the Bible. • The relationship between theological training in the context of a church and/or a university. • A special investigation of the situation within the Reformed Churches in South Africa in this regard. Important conclusions are made, for example that the church through the ages had a very high esteem and respect for the office of the doctor in Theology; that this fourth office is still retained in many reformed churches, with great blessing. Calvin’s views did cause some confusion on the one hand, but on the other hand it contributed to the acknowledgement of the important function the doctors in Theology have on behalf of the church and in the faculties of Theology at universities