A method to extract the monomer friction coefficient from the linear viscoelastic behavior of linear, entangled polymer melts

The rheological properties of isotactic and atactic polypropylene melts are analyzed in order to obtain the equilibration time, τ e, and monomer friction coefficient, ζ. A procedure is proposed to determine τ e from the zero shear rate viscosity, η 0, using the magnitude of the molecular weight per entanglement, M e, from the literature. This procedure can be applied to both mono- and polydisperse linear, entangled polymer melts. For different polymers this procedure gives very similar results compared to the description of the storage and loss modulus of nearly monodisperse linear, entangled polymer melts by molecular based theories, as well as with values of ζ reported in the literature for linear, non-entangled polymer melts. It is observed that for isotactic and atactic polypropylene M e differs by a factor 1.25 depending on the approach taken. As a consequence, the magnitude of τ e and ζ differ by a factor of about 3.0 and 1.8, respectively. The knowledge of τ e (or ζ) is of importance in order to obtain a better understanding of flow induced crystallization experiments on iP

Vowel Processing in Cluttered Auditory Scenes

Verbeterde herkenning van klinkersProblemen met spraakherkenning zijn te wijten aan een gebrekkige representatie van spraak en aan het toepassen van kennis in een laat stadium van het herkenningsproces. Het eerste doel in het onderzoek van Bea Valkenier was om 'akoestische kenmerksvectoren' te vinden voor de representatie van klinkers waarbij de ruisgevoeligheid verbeterd is ten opzichte van bestaande representaties. Dit deed zij door lokale, energetische karakteristieken te representeren die correleren met de articulatie van spraak.De bruikbaarheid voor automatische spraakherkenning (ASR) kon niet expliciet worden getest met bestaande ASR-systemen omdat het aantal extracties varieert als gevolg van ruis. Valkenier veronderstelt dat mensen, in tegenstelling tot bestaande ASR-systemen, wel kunnen omgaan met een variabele hoeveelheid input features. Daarom heeft zij, als tweede doel, het effect van kennis en verwachting op perceptie bij mensen onderzocht.Het onderzoeksparadigma waarbij spraak in ruis wordt gezien als spraak met extra, irrelevante features biedt nieuwe mogelijkheden voor het begrijpen en modelleren van spraakverwerking. Valkenier heeft twee perceptie-experimenten uitgevoerd. In beide experimenten zijn stimuli aangeboden van gemanipuleerde Nederlands gesproken klinkers, om een situatie te creëren waarin lokale input features missen of juist toegevoegd zijn. Zij concludeert dat het menselijk waarnemingssysteem flexibel kan omgaan met een variërend aantal extracties. Kennis van klanken in een taal leidt bij mensen tot integratie van het deel van de features die samen tot een coherente waarneming leiden.Problems with speech processing are associated with the poor representation of speech and a late use of knowledge to disambiguate the input sounds. The first goal of the current work is to improve acoustical features. We selected the local energetic components from a harmonic complex that correlate to speech articulations. We show that these extractions facilitate noise-robustness. The usefulness for speech recognition could not be explicitly tested with modern ASR techniques because the number of extractions varies which does not fit current systems for ASR.We assume that humans, in contrast to ASR techniques, are able to process a variable number of input features. Therefore, we investigated, as a second goal, the effect of knowledge and expectation on human perception of vowels. The research paradigm where speech in noise can be seen as speech with additional, irrelevant features provides new ways to understanding and modelling speech processing. We performed two perceptual experiments. In two experiments we presented manipulated Dutch spoken vowels. We conclude that the human perceptual system can flexibly handle the varying number of extractions. Knowledge of sounds in a language leads to integration of part of the features that together form a coherent percept

Methylnaltrexone in the treatment of opioid-induced constipation

Constipation is a significant problem related to opioid medications used to manage pain. This review attempts to outline the latest findings related to the therapeutic usefulness of a μ opioid receptor antagonist, methylnaltrexone in the treatment of opioid-induced constipation. The review highlights methylnaltrexone bromide (Relistor™; Progenics/Wyeth) a quaternary derivative of naltrexone, which was recently approved in the United States, Europe and Canada. The Food and Drug Administration in the United States approved a subcutaneous injection for the treatment of opioid bowel dysfunction in patients with advanced illness who are receiving palliative care and when laxative therapy has been insufficient. Methylnaltrexone is a peripherally restricted, μ opioid receptor antagonist that accelerates oral–cecal transit in patients with opioid-induced constipation without reversing the analgesic effects of morphine or inducing symptoms of opioid withdrawal. An analysis of the mechanism of action and the potential benefits of using methylnaltrexone is based on data from published basic research and recent clinical studies

Towards a rheological classification of flow induced crystallization experiments of polymer melts

Departing from molecular based rheology and rubber theory, four different flow regimes are identified associated to (1) the equilibrium configuration of the chains, (2) orientation of the contour path, (3) stretching of the contour path, and (4) rotational isomerization and a deviation from the Gaussian configuration of the polymer chain under strong stretching conditions. The influence of the ordering of the polymer chains on the enhanced point nucleation, from which spherulites grow, and on fibrous nucleation, from which the shish-kebab structure develops, is discussed in terms of kinetic and thermodynamic processes. The transitions between the different flow regimes, and the associated physical processes governing the flow induced crystallization process, are defined by Deborah numbers based on the reptation and stretching time of the chain, respectively, as well as a critical chain stretch. An evaluation of flow induced crystallization experiments reported in the literature performed in shear, uniaxial and planar elongational flows quantitatively illustrates that the transition from an enhanced nucleation rate of spherulites towards the development of the shish-kebab structure correlates with the transition from the orientation of the chain segments to the rotational isomerization of the high molecular weight chains in the melt. For one particular case this correlation is quantified by coupling the wide angle X-ray diffraction and birefringence measurements of the crystallization process to numerical simulations of the chain stretch of the high molecular weight chains using the extended Pom-Pom model in a cross-slot flo

Analytical solution of compression, free swelling and electrical loading of saturated charged porous media

Analytical solutions are derived for one-dimensional consolidation, free swelling and electrical loading of a saturated charged porous medium. The governing equations describe infinitesimal deformations of linear elastic isotropic charged porous media saturated with a mono-valent ionic solution. From the governing equations a coupled diffusion equation in state space notation is derived for the electro-chemical potentials, which is decoupled introducing a set of normal parameters, being a linear combination of the eigenvectors of the diffusivity matrix. The magnitude of the eigenvalues of the diffusivity matrix correspond to the time scales for Darcy flow, diffusion of ionic constituents and diffusion of electrical potential

Self-guided smartphone excursions in university teaching—experiences from exploring “Water in the City”

Like many other university teachers, we were faced with an unprecedented situation in spring 2020, when we had to cancel on-site teaching and excursions due to the Covid-19 pandemic. However, we were in the fortunate position that we had already started to develop a smartphone-based self-guided excursion on the topic of “Water in the City”. We accelerated this development and used it to replace the traditional group excursion in our Bachelor level introductory course in Hydrology and Climatology. The excursion of this course is visited by around 150 students each year. Because the student feedback was overall very positive, we used the self-guided excursion again in 2021 and plan to continue to use it in the coming years. In this paper, we describe the excursion, discuss the experiences of the students and ourselves, and present recommendations and ideas that could be useful for similar excursions at other universities

Citizen science approaches for water quality measurements

Citizen science has become a widely used approach in water quality studies. Although there are literature reviews about citizen science and water quality assessments, an overview of the most commonly used methods and their strengths and weaknesses is still lacking. Therefore, we reviewed the scientific literature on citizen science for surface water quality assessments and examined the methods and strategies used by the 72 studies that fulfilled our search criteria. Special attention was given to the parameters monitored, the monitoring tools, and the spatial and temporal resolution of the data collected in these studies. In addition, we discuss the advantages and disadvantages of the different approaches used in water quality assessments and their potential to complement traditional hydrological monitoring and research

The CrowdWater game: A playful way to improve the accuracy of crowdsourced water level class data

Data quality control is important for any data collection program, especially in citizen science projects, where it is more likely that errors occur due to the human factor. Ideally, data quality control in citizen science projects is also crowdsourced so that it can handle large amounts of data. Here we present the CrowdWater game as a gamified method to check crowdsourced water level class data that are submitted by citizen scientists through the CrowdWater app. The app uses a virtual staff gauge approach, which means that a digital scale is added to the first picture taken at a site and this scale is used for water level class observations at different times. In the game, participants classify water levels based on the comparison of the new picture with the picture containing the virtual staff gauge. By March 2019, 153 people had played the CrowdWater game and 841 pictures were classified. The average water level for the game votes for the classified pictures was compared to the water level class submitted through the app to determine whether the game can improve the quality of the data submitted through the app. For about 70% of the classified pictures, the water level class was the same for the CrowdWater app and game. For a quarter of the classified pictures, there was disagreement between the value submitted through the app and the average game vote. Expert judgement suggests that for three quarters of these cases, the game based average value was correct. The initial results indicate that the CrowdWater game helps to identify erroneous water level class observations from the CrowdWater app and provides a useful approach for crowdsourced data quality control. This study thus demonstrates the potential of gamified approaches for data quality control in citizen science projects