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

Assessment of plot-scale sediment transport on young moraines in the Swiss Alps using a fluorescent sand tracer

Glacial retreat uncovers large bodies of unconsolidated sediment that are prone to erosion. However, our knowledge of overland flow (OF) generation and sediment transport on moraines that have recently become ice-free is still limited. To investigate how the surface characteristics of young moraines affect OF and sediment transport, we installed five bounded runoff plots on two moraines of different ages in a proglacial area of the Swiss Alps. On each plot we conducted three sprinkling experiments to determine OF characteristics (i.e., total OF and peak OF flow rate) and measured sediment transport (turbidity, sediment concentrations, and total sediment yield). To determine and visualize where sediment transport takes place, we used a fluorescent sand tracer with an afterglow as well as ultraviolet (UV) and light-emitting diode (LED) lamps and a high-resolution camera. The results highlight the ability of this field setup to detect sand movement, even for individual fluorescent sand particles (300–500 µm grain size), and to distinguish between the two main mechanisms of sediment transport: OF-driven erosion and splash erosion. The higher rock cover on the younger moraine resulted in longer sediment transport distances and a higher sediment yield. In contrast, the higher vegetation cover on the older moraine promoted infiltration and reduced the length of the sediment transport pathways. Thus, this study demonstrates the potential of the use of fluorescent sand with an afterglow to determine sediment transport pathways as well as the fact that these observations can help to improve our understanding of OF and sediment transport processes on complex natural hillslopes

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

How well can people observe the flow state of temporary streams?

Even though more than half of the global river network does not have continuous flow, temporary (i.e., non-perennial) streams are poorly represented in traditional monitoring networks. Therefore, new approaches are needed to monitor these streams. Citizen science provides an interesting opportunity as people, equipped with smartphones, can observe the flow state of temporary streams. Such observations can go beyond a simple classification of flow vs. no flow and include ecologically important states, such as standing water, isolated pools, or wet streambeds. However, the quality of citizen science data for temporary streams has so far not been thoroughly assessed. Therefore, we asked more than 1,200 people during 23 field days to visually determine the flow state of eight temporary streams based on six classes ranging from a dry streambed to flowing water. Participants could most clearly distinguish a flowing stream from a non-flowing stream. The overall agreement between participants was 66%; 83% of the selected flow states were within one class of the most frequently selected flow state. The agreement with the expert was lower (56% chose the same class, and 79% chose a state within one class). Inconsistencies between the selected flow state and answers to specific yes-no statements about the temporary stream were largest for the dry streambed and damp/wet streambed states. These discrepancies were partly caused by participants looking at different parts of the stream (i.e., participants considered the flow state for a location further upstream or downstream). To ensure that all participants determine the flow state comparably, we recommend clear definitions of the flow state classes, detailed information on the exact location for which the flow state needs to be determined, as well as more training

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