Format and implementation of written assessments

Alle Leistungsnachweise des klinischen Studienabschnittes nach neuer Ärztlicher Approbationsordnung müssen benotet werden; hierzu sind in der Regel schriftliche Prüfungen notwendig. Bisher erprobte Methoden beinhalten die Prüfung passiven Wissens (Einfachauswahlfragen, multiple choice-Fragen, progress test-Fragen) und aktiven Wissens (short essay questions, long essay questions). Vor- und Nachteile dieser Verfahren werden diskutiert, sowie die zur Erstellung, Durchführung und Auswertung schriftlicher Prüfungen notwendigen Ressourcen.According to the new German licensing regulations all clinical certificates have to be graded; mostly this requires written tests. Methods tested to date include tests for passive knowledge (single choice questions, multiple choice questions, progress test) and active knowledge (short essay questions, long essay questions). We discuss advantages and disadvantages of these methods, as well as the resources required for test preparation, testing and grading of student answers

Airway responses and inflammation in subjects with asthma after four days of repeated high-single-dose allergen challenge

Background: Both standard and low-dose allergen provocations are an established tool in asthma research to improve our understanding of the pathophysiological mechanism of allergic asthma. However, clinical symptoms are less likely to be induced. Therefore, we designed a protocol for repetitive high-dose bronchial allergen challenges to generate clinical symptoms and airway inflammation. Methods: A total of 27 patients aged 18 to 40 years with positive skin-prick tests and mild asthma underwent repetitive high-dose allergen challenges with household dust mites for four consecutive days. Pulmonary function and exhaled NO were measured at every visit. Induced sputum was analysed before and after the allergen challenges for cell counts, ECP, IL-5, INF-γ, IL-8, and the transcription factor Foxp3. Results: We found a significant decrease in pulmonary function, an increased use of salbutamol and the development of a late asthmatic response and bronchial hyperresponsiveness, as well as a significant induction of eNO, eosinophils, and Th-2 cytokines. Repeated provocation was feasible in the majority of patients. Two subjects had severe adverse events requiring prednisolone to cope with nocturnal asthma symptoms. Conclusions: Repeated high-dose bronchial allergen challenges resulted in severe asthma symptoms and marked Th-2-mediated allergic airway inflammation. The high-dose challenge model is suitable only in an attenuated form in diseased volunteers for proof-of-concept studies and in clinical settings to reduce the risk of severe asthma exacerbations. Trial registration: ClinicalTrials.govNCT0067720

Implications of carbon, nitrogen and porosity on the γ→α′ martensite phase transformation and resulting hardness in PM-steel Astaloy 85Mo

This study aims at a thorough characterization of the relationship of interstitially solved carbon and nitrogen on the γ → α′ transformation in PM steels, the accompanied volume change and the resulting hardness. Furthermore, the investigations include multiple porosity levels of 6.9, 7.2 and 7.35 g/cm$^{3}$ to characterize porosity effects. Dilatometric samples were carburized and carbonitrided to seven distinct compositions to account for common compositions in the process of thermochemical case hardening heat treatment. The dilatometric samples were rapidly austenitized and quenched and the dilatometric response was evaluated. To fully characterize the martensitic transformation of PM steels, X-ray diffractometry evaluated the amount of retained austenite after quenching. Conclusive results of iterative quenching procedures along with elemental analysis after heat treatment give distinct evidence that PM steels underlie rapid decarburization. This effect ultimately leads to an erroneous evaluation of the martensite transformation kinetics, especially the often proposed effect of porosity on M$_{S}$. However, a distinct effect on the accompanied volume change from austenite to martensite is proposed. To account for an interplay of solved carbon and nitrogen, an effective nitrogen contribution of 25% based on carbon equivalent is proposed. Utilizing the effective content, the impact of nitrogen can be projected on carbon within the range of common carbon and nitrogen contents, and a good predictability of the martensite transformation can be achieved. Regarding the resulting hardness, a dependency solely on carbon is suggested. The overall hardness shows a typical maximum at approximately 0.6–0.7 wt%, irrespective of the solved amount of nitrogen

Concentric Scanning Strategies for Laser Powder Bed Fusion: Porosity Distribution in Practical Geometries

Besides the optimisation of process parameters such as laser power or scan speed, the choice of the scan path represents a possibility to optimise the laser powder bed fusion process even further. The usual hatching strategy creates a homogeneous microstructure but makes it necessary to switch the laser off and on after each scan vector, which can slow down the fabrication. Moreover, the end of each scan vector is a location susceptible to the creation of keyhole pores. In this work, these disadvantages were meant to be avoided by using scan strategies that consist of longer paths and thus less end of track points. To this end, an open-source tool to tailor the LPBF G-code to geometric part features and advanced path configurations was developed and embedded into a co-visualization platform. With this tool, specimens built with four different types of paths were fabricated and the effect of these alternative scan strategies on pore distributions and path neighbourhood was investigated using micro-computed tomography. In the examined example geometry, a spiral scan pattern reduced the distance the laser had to jump between scanning by 78%. However, with the alternative path patterns, the defect architecture was strongly dependant on the part geometry and increased the overall porosity to 0.42%. Respective alleviation approaches are therefore necessary and are discussed in the remainder of this work

Parameter optimization and mechanical properties of 42CrMo4 manufactured by laser powder bed fusion

To study the manufacturability and mechanical properties of a low alloy heat treatable medium carbon steel by additive manufacturing, 42CrMo4 (AISI4140) specimens were manufactured by laser powder bed fusion. Influences of processing parameters on relative density and crack density were investigated. Moreover, Charpy impact tests, microhardness, and tensile tests for specimens with and without preheating were also studied. Results showed that the primary defects in the microstructure of additively manufactured samples were the lack of fusion pores and microcracks. The variation of processing parameters influences the porosity and microcracks prominently. The impact toughness of specimens with preheating is around three times higher than specimens without preheating. However, post heat treatment for as-built specimens, such as tempering at different temperature ranges, did not improve the impact toughness further. The detailed fracture mechanism for the massive difference in the impact toughness was investigated

Integrated collinear refractive index sensor with Ge PIN photodiodes

Refractive index sensing is a highly sensitive and label-free detection method for molecular binding events. Commercial implementations of biosensing concepts based on plasmon resonances typically require significant external instrumentation such as microscopes and spectrometers. Few concepts exist that are based on direct integration of plasmonic nanostructures with optoelectronic devices for on-chip integration. Here, we present a CMOS-compatible refractive index sensor consisting of a Ge heterostructure PIN diode in combination with a plasmonic nanohole array structured directly into the diode Al contact metallization. In our devices, the photocurrent can be used to detect surface refractive index changes under simple top illumination and without the aid of signal amplification circuitry. Our devices exhibit large sensitivities > 1000 nm per refractive index unit in bulk refractive index sensing and could serve as prototypes to leverage the cost-effectiveness of the CMOS platform for ultra-compact, low-cost biosensors.Comment: 21 pages, 6 figures, supporting information with 11 pages and 11 figures attache

Problems of Nonidentifiability and Alternative Solutions

The bifactor model is a widely applied model to analyze general and specific abilities. Extensions of bifactor models additionally include criterion variables. In such extended bifactor models, the general and specific factors can be correlated with criterion variables. Moreover, the influence of general and specific factors on criterion variables can be scrutinized in latent multiple regression models that are built on bifactor measurement models. This study employs an extended bifactor model to predict mathematics and English grades by three facets of intelligence (number series, verbal analogies, and unfolding). We show that, if the observed variables do not differ in their loadings, extended bifactor models are not identified and not applicable. Moreover, we reveal that standard errors of regression weights in extended bifactor models can be very large and, thus, lead to invalid conclusions. A formal proof of the nonidentification is presented. Subsequently, we suggest alternative approaches for predicting criterion variables by general and specific factors. In particular, we illustrate how (1) composite ability factors can be defined in extended first-order factor models and (2) how bifactor(S-1) models can be applied. The differences between first-order factor models and bifactor(S-1) models for predicting criterion variables are discussed in detail and illustrated with the empirical example

Improving the inner surface state of thick-walled tubes by heat treatments with internal quenching considering a simulation based optimization

Internal Quenching is an innovative heat treatment method for difficult to access component sections. Especially, the microstructure, as well as the residual stress state at inner surfaces, of thick-walled tubes can be adjusted with the presented flexible heat treatment process. Based on multiphysical FE-models of two different steels, a simulative optimization study, considering different internal quenching strategies, was performed in order to find the optimal cooling conditions. The focus hereby was on the adjustment of a martensitic inner surface with high compressive residual stresses. The simulatively determined optimal cooling strategies were carried out experimentally and analyzed. A good agreement of the resulting hardness and residual stresses was achieved, validating the presented Fe-model of the Internal Quenching process. The shown results also indicate that the arising inner surface state is very sensitive to the transformation behavior of the used steel. Furthermore, the presented study shows that a preliminary simulative consideration of the heat treatment process helps to evaluate significant effects, reducing the experimental effort and time

libNMF -- A Library for Nonnegative Matrix Factorization

We present libNMF -- a computationally efficient high performance library for computing nonnegative matrix factorizations (NMF) written in C. Various algorithms and algorithmic variants for computing NMF are supported. libNMF is based on external routines from BLAS (Basic Linear Algebra Subprograms), LAPack (Linear Algebra package) and ARPack, which provide efficient building blocks for performing central vector and matrix operations. Since modern BLAS implementations support multi-threading, libNMF can exploit the potential of multi-core architectures. In this paper, the basic NMF algorithms contained in libNMF and existing implementations found in the literature are briefly reviewed. Then, libNMF is evaluated in terms of computational efficiency and numerical accuracy and compared with the best existing codes available. libNMF is publicly available at http://rlcta.univie.ac.at/software