Extension of process models to predict batch screening results under the influence of moisture based on DEM simulations

Screening is a technical simple but still not fully understood process step, which can be used in a wide field of applications to separate bulk materials according to their particle sizes. A severe issue in screening technologies is that particles frequently prevail in moist conditions, due to effects related to the environment, the material or the process. This is often not preventable, although it is not preferred due to attractive forces altering the screening efficiency. For the design of dry screening processes, phenomenological models and detailed particle-based simulation approaches like the discrete element method (DEM) are available. The latter method has recently been extended and validated against experiments to calculate forces caused by liquid bridges formed out between particles or walls close to each other to meet the requirements to tackle real particle systems under moist conditions. In the investigation here, batch screening under the influence of moisture involving different sized glass spheres is investigated numerically with DEM simulations and by using process models. Therein, the related subprocesses stratification and passage as well as the influence of the operating parameters and the liquid amount on the fraction retained per size class are examined. Existing phenomenological process models, which can be applied efficiently for industrial applications due to their short calculation time, are extended to represent batch screening processes under moist conditions for the first time. Therefore, a benchmark is realized in which the fraction retained per size class over time for discontinuous screening under the influence of various amounts of liquid and different mechanical agitations obtained by DEM simulations and process models is compared. In this context, the process models are first adjusted to fit related simulation results and later used in a novel method to predict the outcome of screening with different operating parameters and liquid amounts. Thereby, process models, which consider the subprocesses stratification and passage, predict screening results for process parameters requiring interpolation or extrapolation in the investigated range very well. As a consequence, newly derived process models can function as prototypes to be applied in dynamic process simulation frameworks.DFG, SPP 1679, Dynamische Simulation vernetzter Feststoffprozess

DEM simulations of screening processes under the influence of moisture

In a wide field of applications, screening is required to separate bulk materials according to their particle sizes. Due to environmental, material or process related effects, particles frequently prevail in moist conditions, which is not preferred due to attractive forces altering the screening efficiency, but often not preventable. As for the design of dry screening processes detailed particle-based simulation approaches like the discrete element method (DEM) and phenomenological models are available, a step towards meeting the requirements for real particle systems under moist conditions is made. Therefore, batch screening under the influence of moisture is investigated experimentally and by using DEM simulations involving different sized polyoxymethylene and glass spheres. For this purpose, a DEM code is extended to calculate forces caused by liquid bridges, forming out between particles or walls close to each other under moist conditions. Thereby, the bridge formation and rupture and the liquid distribution are considered. First, the DEM framework is validated against experiments by monitoring the capillary and viscous force acting on two liquid bridge contact partners. Further extensive validations are performed by comparing the fraction retained over time and the final liquid distribution for discontinuous screening under the influence of various amounts of liquid for different mechanical agitations in experiments and simulations. Finally, the detailed liquid distribution over time in the DEM simulations is examined and general conclusions are drawn. The overall aim is to use the framework and the respective data, to extend phenomenological process models for screening under moist conditions in subsequent studies.DFG, SPP 1679, Dynamische Simulation vernetzter Feststoffprozess

Causality and Indeterminism in Human Action. Reflections on Causes and Reasons

When explaining the origin of human action, one of the thematic axes is the study of “causality” and its compatibility with indeterminism. The existence of regularities in the field of social sciences can only be explainable by acknowledging the regularities that underlie human actions. An action is the result of a decision-making process, which has a starting intention. This intentionality is what imposes on the action its regularity and at the same time its singularity. Actions reflect in their structure our rational being, which is therefore free, and also our cultural being: each action is the reflection of historical-cultural conditions that make it predictable. In the analysis of an action, all the elements that lead here to formulate an intention are “causes” of the action; the “causes” no longer exercise as such when, at least, they are dominated intellectually. In this case, the force they exert on the concrete individual decreases, so they are now considered as “reasons”./nWithin the current context of causality, where Woodward has an influential role, this article considers the conception of Tuomela on the formation of the social action, Salmon’s analysis of causality, and Anscombe’s characterization of intention.Para explicar el origen de la acción humana, uno de los ejes temáticos es el estudio de la “causalidad” y su compatibilidad con el indeterminismo. La existencia de regularidades en las Ciencias Sociales solo puede explicarse reconociendo las regularidades que subyacen a las acciones humanas. Una acción es el resultado de un proceso de toma de decisiones, que tiene una intención de partida. Esta intencionalidad es lo que impone a la acción su regularidad y al mismo tiempo su singularidad. Las acciones reflejan en su estructura nuestro ser racional, que es libre, y también nuestro ser cultural: cada acción es el reflejo de las condiciones histórico-culturales que la hacen predecible. Al analizar una acción, los elementos que llevan aquí a formular una intención son “causas” de la acción; las “causas” ya no se ejercen como tales cuando, al menos, están dominadas intelectualmente. Entonces la fuerza que ejercen sobre el individuo concreto disminuye, por lo que ahora se consideran “razones”./nEn el contexto actual de la causalidad, donde Woodward tiene un papel influyente, este artículo considera la concepción de Tuomela sobre la formación de la acción social, el análisis de Salmon sobre la causalidad y la caracterización de intención de Anscombe

A strategy to determine DEM parameters for spherical and non-spherical particles

In Discrete element method (DEM) simulations the choice of appropriate contact parameters is significant to obtain reasonable results. Particularly, for the determination of DEM parameters for non-spherical particles a general straightforward procedure is not available. Therefore, in a first step of the investigation here, methods to obtain the friction and restitution coefficients experimentally for single particles [Polyoxymethylene (POM) spheres and quartz gravel] will be introduced. In the following, these predetermined DEM coefficients are used as initial values for the adjustment of bulk simulations to respective experiments. In the DEM simulations, the quartz gravel particles are represented by non-spherical particles approximated by clustered spheres. The best fit approximation of the non-spherical particles is performed automatically by a genetic algorithm. In order to optimize the sliding and rolling friction coefficients for DEM simulations, the static and dynamic angle of repose are determined from granular piles obtained by slump tests and rotating drum experiments, respectively. Additionally, a vibrating plate is used to obtain the dynamic bed height which is mainly influenced by the coefficient of restitution. The adjustment of the results of the bulk simulations to the experiments is conducted automatically by an optimization tool based on a genetic algorithm. The obtained contact parameters are later used to perform batch-screening DEM simulations and lead to accurate results. This underlines the applicability of the in parts automated strategy to obtain DEM parameters for particulate processes like screening.DFG, SPP 1679, Dynamische Simulation vernetzter Feststoffprozess

Un nuevo análisis del papel de la representación y modelos en la ciencia: Wenceslao J. González (ed.). Bas van Fraassen’s Approach to Representation and Models in Science. Springer, Dordrecht (2014), xiii + 233 pp.

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Why older people refuse to participate in falls prevention trials: A qualitative study

Background/Objectives: Falls are a major public health problem. Older persons are frequently underrepresented in trials, including falls prevention trials. Insight into possible reasons for non-participation could help to improve trial designs and participation rates among this age-group. The aim of this study was to explore reasons why older people refuse to participate in falls prevention trials. Setting: A qualitative study. Participants: Community-dwelling adults aged ≥ 65. years who attended the Emergency Department due to a fall and refused to participate in a falls prevention trial (IMPROveFALL-study). Measurements: A structured interview guide was used, and interview transcripts were subjected to an independent content analysis by two researchers. Results: 15 interviews were conducted. A main reason to refuse trial participation was mobility impairment. In contrast, younger and more "active" and mobile seniors considered themselves "too healthy" to participate. Persons with multiple comorbidities mentioned that they attended a hospital too often, or experienced adequate follow-up by their own physicians already. Transport problems, including distance to the hospital, parking facilities, and travel expenses were another issue. During the interviews it was emphasized by the patients, that they knew the reason for their fall. However, they were not familiar with the positive effects of falls prevention programmes. Conclusions: Older persons reported multiple reasons to refuse participation in a falls prevention study, such as health-related factors, several practical problems, and personal beliefs about the causes and preventability of falls. Anticipation of those issues might contribute to an improvement in participation rates of older fallers, shorter study duration, and a better generalizability of research findings

Cerebral atrophy as outcome measure in short-term phase 2 clinical trials in multiple sclerosis

Cerebral atrophy is a compound measure of the neurodegenerative component of multiple sclerosis (MS) and a conceivable outcome measure for clinical trials monitoring the effect of neuroprotective agents. In this study, we evaluate the rate of cerebral atrophy in a 6-month period, investigate the predictive and explanatory value of other magnetic resonance imaging (MRI) measures in relation to cerebral atrophy, and determine sample sizes for future short-term clinical trials using cerebral atrophy as primary outcome measure

Diagnostic hysteroscopy and saline infusion sonography in the diagnosis of intrauterine abnormalities: an assessment of patient preference

This study was conducted to assess whether women would prefer to undergo saline infusion sonography (SIS) or office hysteroscopy for the investigation of the uterine cavity. In a randomised controlled trial, 100 patients underwent SIS or office hysteroscopy for assessing patients' pain scores. After the investigation, 92 of them were asked to fill out an anonymous questionnaire addressing their preference regarding the method of evaluation and treatment of the uterine cavity. A control group, consisting of 50 women who never underwent SIS or office hysteroscopy, was also asked to complete an identical questionnaire. The questionnaire was completed by 113 women (83.7%). Twenty-four (21.2%) women would opt for SIS, whereas 52 (46.0%) would opt for office hysteroscopy, and 37 (32.7%) had no preference. If therapy would be necessary, 48.7% of the women would opt for an outpatient treatment, whereas 33.0% of the women would prefer treatment under general anaesthesia. Despite the fact that SIS is less painful, the majority of the women prefer office hysteroscopy. Additionally, therapy in an outpatient setting is preferred to a day case setting

Biomarkers of Multiple Sclerosis

The search for an ideal multiple sclerosis biomarker with good diagnostic value, prognostic reference and an impact on clinical outcome has yet to be realized and is still ongoing. The aim of this review is to establish an overview of the frequent biomarkers for multiple sclerosis that exist to date. The review summarizes the results obtained from electronic databases, as well as thorough manual searches. In this review the sources and methods of biomarkers extraction are described; in addition to the description of each biomarker, determination of the prognostic, diagnostic, disease monitoring and treatment response values besides clinical impact they might possess. We divided the biomarkers into three categories according to the achievement method: laboratory markers, genetic-immunogenetic markers and imaging markers. We have found two biomarkers at the time being considered the gold standard for MS diagnostics. Unfortunately, there does not exist a single solitary marker being able to present reliable diagnostic value, prognostic value, high sensitivity and specificity as well as clinical impact. We need more studies to find the best biomarker for MS.publishersversionPeer reviewe