DEM modelling of surface indentations caused by granular materials: application to wheel-rail sanding.

The presented surface indentation model is one step towards building a DEM model for wheel-rail sanding. In railways, so-called low-adhesion conditions can cause problems in traction and braking, and sanding is used to overcome this problem. Sand grains are blasted towards wheel-rail contact, fracture repeatedly as they enter the nip and are drawn into the contact and then increase adhesion.

Efficient DEM simulations of railway ballast using simple particle shapes.

For complex shaped materials, computational efficiency and accuracy of DEM models are usually opposing requirements. In the literature, DEM models of railway ballast often use very complex and computationally demanding particle shapes in combination with very simple contact laws. In contrast, this study suggests efficient DEM models for railway ballast using simple particle shapes together with a contact law including more physical effects.

DEM modelling of railway ballast using the Conical Damage Model: a comprehensive parametrisation strategy.

Despite ongoing research, the parametrisation of a DEM model is a challenging task, as it depends strongly on the particle shape representation used, particle-particle contact law and the simulated applications: for railway ballast e.g. lab tests or track conditions.

Search, reuse and sharing of research data in materials science and engineering-A qualitative interview study.

Open research data practices are a relatively new, thus still evolving part of scientific work, and their usage varies strongly within different scientific domains. In the literature, the investigation of open research data practices covers the whole range of big empirical studies covering multiple scientific domains to smaller, in depth studies analysing a single field of research. Despite the richness of literature on this topic, there is still a lack of knowledge on the (open) research data awareness and practices in materials science and engineering.

Shape analysis of railway ballast stones: curvature-based calculation of particle angularity.

Particle shape analysis is conducted, to compare two types of railway ballast: Calcite and Kieselkalk. Focus lies on the characterisation of particle angularity using 3D scanner data. In the literature, angularity is often characterised using 2D data, as these types of data are easier to collect.

Simple particle shapes for DEM simulations of railway ballast: influence of shape descriptors on packing behaviour.

Abstract: In any DEM simulation, the chosen particle shape will greatly influence the simulated material behaviour. For a specific material, e.g.

Micro-mechanical investigation of railway ballast behavior under cyclic loading in a box test using DEM: effects of elastic layers and ballast types.

Abstract: Ballasted tracks are the commonly used railway track systems with constant demands for reducing maintenance cost and improved performance. Elastic layers are increasingly used for improving ballasted tracks. In order to better understand the effects of elastic layers, physical understanding at the ballast particle level is crucial.

Comparison of two different types of railway ballast in compression and direct shear tests: experimental results and DEM model validation.

Railway ballast is an angular and coarse material, which demands careful DEM modelling and validation. Particle shape is often modelled in high accuracy, thus leading to computational expensive DEM models. Whether this effort will increase the DEM model's overall prediction quality will also vitally depend on the used contact law and the validation process.

Parametrisation of a DEM model for railway ballast under different load cases.

The prediction quality of discrete element method (DEM) models for railway ballast can be expected to depend on three points: the geometry representation of the single particles, the used contact models and the parametrisation using principal experiments. This works aims at a balanced approach, where none of the points is addressed with excessive depth. In a first step, a simple geometry representation is chosen and the simplified Hertz-Mindlin contact model is used.

Friction phenomena and their impact on the shear behaviour of granular material.

In the discrete element simulation of granular materials, the modelling of contacts is crucial for the prediction of the macroscopic material behaviour. From the tribological point of view, friction at contacts needs to be modelled carefully, as it depends on several factors, e.g.

Right atrium cholinergic deficit in septic rats.

Heart rate variability (HRV) is mainly determined by the influence of both branches of the Autonomic Nervous System over the sinus node. Low HRV has been associated with a worse prognosis in patients with sepsis. The objective of this study was to explain the reduction in HRV during experimental sepsis in adult rats.

Inhibition of the membrane attack complex of complement for induction of accommodation in the hamster-to-rat heart transplant model.

Background: To induce accommodation in the hamster-to-rat cardiac transplantation model, in addition to cyclosporin A (CSA) to inhibit T-cell-mediated graft rejection, cobra venom factor (CVF) is often used to prevent complement-mediated graft rejection. Although it is generally assumed that CVF makes accommodation possible because it inactivates the complement membrane attack complex (MAC), it is not known which complement components must be inactivated and whether complement activation products generated by CVF are also involved in the induction of accommodation. Therefore, to investigate mechanisms by which CVF contributes to accommodation, we studied induction of accommodation of hamster hearts grafted into rats with complement deficiencies of C6; these rats cannot assemble the MAC but, in contrast to CVF, retain in their native state all complement proteins that precede the MAC.

Changes of the neurotransmitter serotonin but not of hormones during short time music perception.

We studied the impact of the perception of pleasant and unpleasant music, as rated by healthy subjects with a psychometric scale, on the hormones prolactin and ACTH. In addition, the neurotransmitter serotonin (5-HT) was studied using the platelet model for central neurotransmission of 5-HT. We did not observe any significant changes of prolactin and ACTH during the perception of different kinds of music.

The impact of HIV infection on primary headache. Unexpected findings from retrospective, cross-sectional, and prospective analyses.

Headache is one of the most important factors influencing the quality of life in patients infected with the human immunodeficiency virus type 1 (HIV). However, only symptomatic headache but not changes or primary headache types during HIV infection have been studied to date. Therefore, we aimed to determine the impact of an HIV infection on frequency and semiology of different primary headache types.

A retrospective long-term analysis of the epidemiology and features of drug-induced headache.

Drug-induced headache is well known to result from the abuse of compounds taken for the treatment of primary headache. The features of drug-induced headache depend on various features including the availability of drugs, the regional health system, and psychogenic factors of the patients. We performed a retrospective study on a series of 257 consecutive German patients presenting with drug-induced headache during the period 1983-1996.

Sumatriptan and ergotamine overuse and drug-induced headache: a clinicoepidemiologic study.

Drug-induced headache, particularly ergotamine-induced headache, is a common problem in migraine treatment. Some case reports suggest that even the new serotonergic antimigraine drugs such as sumatriptan can lead to overuse and subsequent drug-induced headache. We performed a controlled study to identify the rate of sumatriptan overuse and sumatriptan-induced headache and compared it to the rate of ergotamine overuse and ergotamine-induced headache.

Cognitive processing is involved in cluster headache but not in chronic paroxysmal hemicrania.

Background: Cognitive processing in migraine is characterized by a loss of habituation during the interval and increased latencies in an attack. No studies are available on event-related potentials (ERPs) in cluster headache or chronic paroxysmal hemicrania.

Objective: To determine the involvement of cognitive processing in cluster headache and chronic paroxysmal hemicrania as measured by ERPs.

Dynamic changes of cognitive habituation and serotonin metabolism during the migraine interval.

Migraine patients show a specific cognitive processing with a loss of habituation in the interval and a normal habituation in the attack as measured by event-related potentials (ERPs). It is unknown whether the loss of habituation changes during the migraine interval or is a stable state. Serotonin (5HT) metabolism is involved in the pathophysiology of migraine and also in the generation of ERPs.

Drug-induced headache: long-term results of stationary versus ambulatory withdrawal therapy.

Drug-induced headache is a well-known complication of the treatment of primary headache disorders, and its successful management is only possible by withdrawal therapy. However, it is unknown whether ambulatory or stationary withdrawal is the therapy preferred. We conducted a prospective study on the outcome of stationary versus ambulatory withdrawal therapy in patients with drug-induced headache according to the International Headache Society criteria.

Long-term follow-up of living kidney donors: quality of life after donation.

The University of Minnesota has been a strong advocate of living donor kidney transplants. The benefits for living donor recipients have been well documented. The relative low risk of physical complications during donation has also been well documented.

Influence of end-stage renal failure and hemodialysis on event-related potentials.

Chronic renal failure frequently causes uremic encephalopathy with impairment of different cognitive functions, but the pathophysiology of uremic encephalopathy is still unknown. We measured visually evoked event-related potentials (ERPs) in 33 neurologically asymptomatic patients before and after they underwent hemodialysis and compared their data with those of a strictly age-matched healthy control group. Before hemodialysis, the patients' P3 latency was significantly increased and P3 amplitude was significantly decreased as compared with that of the healthy control group.

Cognitive processing in primary headache: a study on event-related potentials.

Background: There is experimental evidence for loss of cognitive habituation in migraine but not in other types of headache and not by visual event-related potentials (ERP).

Objective: Determining the latencies (msec) and amplitudes (microV) of ERP components and the differences of these values in a two-trial analysis representing the amount of cognitive habituation.

Participants: Two hundred thirty-three patients with a headache diagnosis according to the criteria of the International Headache Society: migraine without aura (N = 77); migraine with aura (N = 31); cluster headache during period (N = 26); cluster headache during interval (N = 11); chronic paroxysmal hemicrania (N = 8); episodic tension-type headache (N = 33); ergotamine-induced headache (N = 47).