Aggregation of Red Blood Cells: From Rouleaux to Clot Formation

Red blood cells are known to form aggregates in the form of rouleaux. This aggregation process is believed to be reversible, but there is still no full understanding on the binding mechanism. There are at least two competing models, based either on bridging or on depletion. We review recent experimental results on the single cell level and theoretical analyses of the depletion model and of the influence of the cell shape on the binding strength. Another important aggregation mechanism is caused by activation of platelets. This leads to clot formation which is life saving in the case of wound healing but also a major cause of death in the case of a thrombus induced stroke. We review historical and recent results on the participation of red blood cells in clot formation

A Comprehensive Manual for Science Education

This paper introduces a novel analytical framework for dissecting and visualizing the fine-grained structure of scientific explanations through Element Maps. It delves into the methodological principles that transition from grammatical surface structures to deeper sense-making layers, such as propositions and individual elements. The manual outlines a two-part process designed to deconstruct written text into evaluable propositions which can then be refined into a granular elementary structure. This approach is illustrated through the analysis of an explanation for the day-night cycle, demonstrating the utility of Element Maps in capturing features like the complexity, coherence, and appropriateness of explanations as well as use of key terms. By representing the elementary structure in a network visualization, the study highlights how Element Maps can serve as a useful tool for educators and researchers in understanding the structure of an explanation which can be used to help learners write better scientific explanations. Beyond the analysis of explanations, the application of this method on scientific arguments is discussed. Examples and a glossary of grammatical terms support support science educators in using the presented approach

Station Location - Complexity and Approximation

We consider a geometric set covering problem. In its original form it consists of adding stations to an existing geometric transportation network so that each of a given set of settlements is not too far from a station. The problem is known to be NP-hard in general. However, special cases with certain properties have been shown to be efficiently solvable in theory and in practice, especially if the covering matrix has (almost) consecutive ones property. In this paper we are narrowing the gap between intractable and efficiently solvable cases of the problem. We also present an approximation algorithm for cases with almost consecutive ones property

Assessing the quality of scientific explanations with networks

This article introduces a network approach to describe the quality of written scientific explanations. Existing approaches evaluate explanations mainly on the level of sentences or as a whole but not on the elementary level of single terms. Moreover, evaluation of explanations is often based on highly inferential scoring techniques. We addressed both issues by converting the elementary structure of terms in explanations into networks (so-called element maps) and analysing these with mathematical measures, thus extracting the size and complexity of an explanation, adequacy, coherence, and use of key terms. A total of 65 explanations of experts and students were analysed quantitatively and qualitatively. Differences between expert and student maps’ measures can be interpreted meaningfully against the background of existing research findings. Thus, we argue that our approach using network analysis provides a precise, fine-grained, and low-inferential tool that complements and refines existing approaches. Element maps have the potential to improve teaching and research by precisely revealing the strengths and weaknesses of explanations.Peer Reviewe

Thermal expansion of water in the science lab-advantages and disadvantages of different experimental setups

When the thermal expansion of water is discussed in school or university lessons, functional relationships are often inferred without considering measurement uncertainties. Moreover, in some learning materials, the goal of experimentation and the experimental setup do not match. This creates the wrong picture of scientific practice. In this article we compare five experimental setups with different complexity to investigate the relationship between heat and volume change of water. We take different goals of experimentation into account, as well as measurement uncertainties. We compare the different experimental setups, show advantages and limitations, and give advises for their implementation in the classroom. By doing so, we demonstrate that thermal expansion can be very well adopted for applying scientific practice in school. It is shown that the more complex the experimental setup, the more precise the quantitative significance of the functional relationship.Peer Reviewe

Recharge variability and sensitivity to climate: The example of Gidabo River Basin, Main Ethiopian Rift

AbstractStudy regionGidabo River Basin, located in the south eastern Main Ethiopian Rift (MER).Study focusThe focus is to characterize the spatial and temporal variability of groundwater recharge, identify the drivers that govern its distribution, and to improve the understanding of its sensitivity to precipitation and temperature in the MER by applying the semi-distributed hydrological model, Soil and Water Assessment Tool (SWAT).New hydrological insights for the regionThe average annual recharge for 1998–2010 reveals a remarkable decrease from the highland (410mm/year) towards the rift floor (25mm/year). Both the spatial and temporal recharge variability is mainly controlled by the climate. In the rift floor, recharge is found to occur only when annual precipitation exceeds a threshold of approximately 800mm. A sensitivity analysis reveals that annual recharge is very sensitive to variations in precipitation and moderately sensitive to temperature changes. The relative sensitivity increases from the highland to the rift floor across the watershed. Increases in both precipitation and temperature, as suggested by climate change projections for Ethiopia, appear to have an overall positive impact on recharge in the majority of the catchment. These findings have implications also for other catchments where recharge is spatially nonuniform and provide a basis for further investigations into the assessment of groundwater resources and their vulnerability to climate change at the watershed and sub-watershed scale

Physically enhanced training for modeling rate-independent plasticity with feedforward neural networks

In recent years, a lot of progress has been made in the field of material modeling with artificial neural networks (ANNs). However, the following drawbacks persist to this day: ANNs need a large amount of data for the training process. This is not realistic, if real world experiments are intended to be used as data basis. Additionally, the application of ANN material models in finite element (FE) calculations is challenging because local material instabilities can lead to divergence within the solution algorithm. In this paper, we extend the approach of constrained neural network training from [28] to elasto-plastic material behavior, modeled by an incrementally defined feedforward neural network. Purely stress and strain dependent equality and inequality constraints are introduced, including material stability, stationarity, normalization, symmetry and the prevention of energy production. In the Appendices, we provide a comprehensive framework on how to implement these constraints in a gradient based optimization algorithm. We show, that ANN material models with training enhanced by physical constraints leads to a broader capture of the material behavior that underlies the given training data. This is especially the case, if a limited amount of data is available, which is important for a practical application. Furthermore, we show that these ANN models are superior to classically trained ANNs in FE computations when it comes to convergence behavior, stability, and physical interpretation of the results

Erklärung physikalischer Phänomene mit Modellen

Ziel dieser Arbeit ist es, die Verwendung von Modellen in schriftlichen Erklärungen optischer Phänomene vor dem Hintergrund eines praxisorientierten Modellbegriffs zu analysieren. Dafür wird ausgehend von einer bereits existierenden Charakterisierung von Modellen ein praxisrelevanter Modellbegriff entwickelt und dargelegt, wie Erklärungen in Bezug auf diesen Begriff zu verstehen sind. Als wesentliches Merkmal von Modellen stellt sich dabei ihre Position als funktionale Vermittler zwischen Ausschnitten von Phänomenen und Theorien heraus. Sprachliche Erklärungen sind demnach sprachliche Darstellungen von Modellen. Zur Untersuchung der Schwierigkeiten Physiklernender in schriftlichen Erklärungen wird ein geeignetes Verfahren zur Analyse der Modellstruktur in den Erklärungen entwickelt. Als geeignete Darstellung dieser Struktur erweisen sich Concept Maps, die hier jedoch noch um eine Kategorienstruktur erweitert werden. Das Verfahren zum Erstellen von kategorienorientierten Concept Maps kann in einer Vorstudie als reliabel und valide gekennzeichnet werden. In einer qualitativen Untersuchung von 64 Erklärungen Physikstudierender und Experten zu Phänomenen der optischen Hebung wird das Verfahren angewendet. Dabei können verschiedene Schwierigkeiten präzise benannt werden. Studierende führen das Phänomen teilweise einzig auf den Begriff der Brechung von Licht zurück, ohne diesen Zusammenhang präzise darzulegen. In einigen Erklärungen werden Begriffe aus nicht relevanten optischen Konzepten eingebunden, es fehlen zentrale Elemente oder Erklärungen zerfallen in Fragmente. Vor allem die Schnittstelle zwischen Phänomen und Theorie zeigt sich besonders fehleranfällig. Kategorienorientierte Concept Maps eignen sich auch, um auf Basis der fehlerbehafteten Erklärungen Vorschläge für konstruktive Interventionen zu entwickeln, die zu einer fachlich angemessenen Erklärung führen. Die Ergebnisse belegen die Notwendigkeit und Fruchtbarkeit eines praxisorientierten Modellbegriffs.Goal of this thesis is to analyze the use of models in written explanations of optics phenomena, based on a practice-orientated framework on models. Starting from an already existing framework, an authentic model conception will be developed and the notion ‘explanation’ will be integrated in the conception. The position of models as functional mediators between relevant aspects of phenomena and theory turns out to be their core characteristic. Written explanations are linguistic presentations of models. A procedure will be developed directly from the given description of models in order to visualize the structure of written explanations. The result is a modified network visualization based on concept maps with inherent categories. This visualization is called ‘categorized concept map’. In a preliminary study, the procedure can be described as reliable and valid. In a following qualitative investigation of 64 explanations of optics phenomena (‘apparent depth’) by means of light rays, given by university physics students and experts, categorized concept maps are used to identify difficulties in giving appropriate explanations. Students trace back the observed phenomena only to the term of ‘refraction’, instead of precisely describing the interrelation between ray optics and those phenomena. Furthermore, elements of other conceptions (waves, particles) appear in some of the explanations, whereas central elements of ray optics (i.e., the image concept) are missed. The cut point between theory and the real world turns out to be the most fragile part in students models. Categorized concept maps show their strength in making a variety of difficulties visible and also in subsequently giving the opportunity to develop an appropriate explanation. The results show both, the need and the fruitfulness of an authentic model conception