Curing Simulations of a Fibre-Reinforced Thermoset on a Micro- and Nano-Scale

Die Eigenschaftskombination hoher Steifigkeit und Festigkeit bei gleichzeitig niedriger Massendichte rückt die Materialklasse der faserverstärkten Polymere generell stärker in den Fokus von Mobilitätsanwendungen und bewegten Massen. Nachteilig an der Kombination von steifen Fasern und einer zähen, leichten Polymermatrix erweist sich oft die Verwendung unterschiedlicher Materialtypen. Die in dieser Arbeit verwendete Paarung des glasfaserverstärkten Duromers zeichnet sich speziell durch unterschiedliche thermische Ausdehnungskoeffizienten und die chemische Aushärtereaktion des Duromerharzes aus. Da der Produktionsprozess eines Bauteils aus glasfaserverstärktem Duromer oft bei erhöhter Temperatur stattfinden muss, um entweder die chemische Vernetzungsreaktion zu aktivieren oder zu beschleunigen, erfährt jedes Bauteil thermische Dehnungen und chemischen Schwund. Diese Dehnungen ändern sich nochmals, sobald sich das Bauteil auf Raumtemperatur abkühlt, bleiben aber grundsätzlich aufgrund der Bindung zwischen Fasern und Matrix erhalten. Durch diesen Eigendehnungszustand werden Verzug und lokale Eigenspannungen induziert, wobei sich insbesondere lokale Spannungsspitzen an der Faser-Matrix-Grenzfläche und an den Faserenden ausbilden können. Diese innere Vorbelastung kann eine Vorschädigung des Bauteils in Form von Mikrorissen verursachen, wodurch insgesamt die Bauteileigenschaften und -belastbarkeit herabgesetzt werden. Ein besseres Verständnis der Aushärteprozesse und des Einflusses unterschiedlicher Prozessparameter auf das induzierte Eigendehnungsfeld ist daher unerlässlich, um die effektive und verlässliche Einsetzbarkeit von faserverstärkten Duromeren zu erhöhen. Diese Arbeit beschäftigt sich deshalb mit der Modellierung und Simulation des Aushärteprozesses und der Aushärtereaktion von faserverstärkten Duromeren. Hierbei wird der Fokus skalenübergreifend auf die Mikrostruktur und auf die Molekularebene gelegt, und die Auswirkungen der Aushärtung auf der jeweiligen Skala untersucht. Auf Mikrostrukturebene wird die rechnergestützte Phasenfeldmethode zur Darstellung von Faser-Matrix-Strukturen verwendet, und darauf aufbauend ein Modell zur Beschreibung der mechanischen, thermischen und chemischen Effekte während eines Aushärteprozesses abgeleitet. Weiterhin wird die Rissausbreitung innerhalb faserverstärkter Mikrostrukturen modelliert und ebenfalls mithilfe der Phasenfeldmethode umgesetzt. Hiermit wird ein Beispielprozess simuliert und dessen Verlauf ausgewertet und diskutiert. Die Entwicklung von lokalen Eigendehnungs- und Eigenspannungszuständen bildet hierbei einen Fokus dieser Arbeit. In einem weiteren Schritt wird überprüft, ob diese lokalen Spannungen in eine Mikroriss-Ausbreitung münden. Diese mikroskaligen Betrachtungen werden durch rechnergestützte Molekulardynamiksimulationen auf der Nanoebene begleitet. Die chemische Aushärtereaktion eines Duromers wird hierbei durch Algorithmen zur Herstellung und Auflösung chemischer Bindungen nachgestellt, und so die Aushärtereaktion anhand von Materialkenngrößen wie Volumenschwund nachvollzogen und diskutiert. Die hierdurch erzeugten Polymernetzwerke dienen dann der Berechnung von temperatur- und aushärtegradabhängigen Materialeigenschaften, welche zur Durchführung der Prozesssimulation auf der Mikroebene benötigt werden

Quantitative CT analysis in patients with pulmonary emphysema: is lung function influenced by concomitant unspecific pulmonary fibrosis?

Purpose: Quantitative analysis of CT scans has proven to be a reproducible technique, which might help to understand the pathophysiology of chronic obstructive pulmonary disease (COPD) and combined pulmonary fibrosis and emphysema. The aim of this retrospective study was to find out if the lung function of patients with COPD with Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages III or IV and pulmonary emphysema is measurably influenced by high attenuation areas as a correlate of concomitant unspecific fibrotic changes of lung parenchyma. Patients and methods: Eighty-eight patients with COPD GOLD stage III or IV underwent CT and pulmonary function tests. Quantitative CT analysis was performed to determine low attenuation volume (LAV) and high attenuation volume (HAV), which are considered to be equivalents of fibrotic (HAV) and emphysematous (LAV) changes of lung parenchyma. Both parameters were determined for the whole lung, as well as peripheral and central lung areas only. Multivariate regression analysis was used to correlate HAV with different parameters of lung function. Results: Unlike LAV, HAV did not show significant correlation with parameters of lung function. Even in patients with a relatively high HAVof more than 10%, in contrast to HAV (p=0.786) only LAV showed a significantly negative correlation with forced expiratory volume in 1 second (r=−0.309, R2=0.096, p=0.003). A severe decrease of DLCO% was associated with both larger HAV (p=0.045) and larger LAV (p=0.001). Residual volume and FVC were not influenced by LAV or HAV. Conclusion: In patients with COPD GOLD stage III-IV, emphysematous changes of lung parenchyma seem to have such a strong influence on lung function, which is a possible effect of concomitant unspecific fibrosis is overwhelmed

Universal correlations between the fragility and interparticle repulsion of glass-forming liquids

A recently published analytical model, describing and predicting elasticity, viscosity, and fragility of metallic melts, is applied for the analysis of about 30 nonmetallic glassy systems, ranging from oxide network glasses to alcohols, low-molecular-weight liquids, polymers, plastic crystals, and even ionic glass formers. The model is based on the power-law exponent lambda representing the steepness parameter of the repulsive part of the inter-atomic or -molecular potential and the thermal-expansion parameter alpha_T determined by the attractive anharmonic part of the effective interaction. It allows fitting the typical super-Arrhenius temperature variation of the viscosity or dielectric relaxation time for various classes of glass-forming matter, over many decades. We discuss the relation of the model parameters found for all these different glass-forming systems to the fragility parameter m and detect a correlation of lambda and m for the non-metallic glass formers, in accord with the model predictions. Within the framework of this model, thus the fragility of glass formers can be traced back to microscopic model parameters characterizing the intermolecular interactions.Comment: 11 pages, 4 figures + Supplemental Material (9 pages, 11 figures). This article has been accepted by J. Chem. Phys. After it is published, it will be found at https://doi.org/10.1063/5.001445

Validation and Classification of the 9-Item Voice Handicap Index (VHI-9i)

The international nine-item Voice Handicap Index (VHI-9i) is a clinically established short-scale version of the original VHI, quantifying the patients’ self-assessed vocal handicap. However, the current vocal impairment classification is based on percentiles. The main goals of this study were to establish test–retest reliability and a sound statistical basis for VHI-9i severity levels. Between 2009 and 2021, 17,660 consecutive cases were documented. A total of 416 test–retest pairs and 3661 unique cases with complete multidimensional voice diagnostics were statistically analyzed. Classification candidates were the overall self-assessed vocal impairment (VHIs) on a four-point Likert scale, the dysphonia severity index (DSI), the vocal extent measure (VEM), and the auditory–perceptual evaluation (GRB scale). The test–retest correlation of VHI-9i total scores was very high (r = 0.919, p < 0.01). Reliability was excellent regardless of gender or professional voice use, with negligible dependency on age. The VHIs correlated best with the VHI-9i, whereas statistical calculations proved that DSI, VEM, and GRB are unsuitable classification criteria. Based on ROC analysis, we suggest modifying the former VHI-9i severity categories as follows: 0 (healthy): 0 ≤ 7; 1 (mild): 8 ≤ 16; 2 (moderate): 17 ≤ 26; and 3 (severe): 27 ≤ 36

Synthesis and Neurotrophic Activity Studies of Illicium Sesquiterpene Natural Product Analogues

Neurotrophic natural products hold potential as privileged structures for the development of therapeutic agents against neurodegeneration. However, only a few studies have been conducted to investigate a common pharmacophoric motif and structure–activity relationships (SARs). Here, an investigation of structurally more simple analogues of neurotrophic sesquiterpenes of the illicium family is presented. A concise synthetic route enables preparation of the carbon framework of (±)-Merrilactone A and (±)-Anislactone A/B on a gram scale. This has allowed access to a series of structural analogues by modification of the core structure, including variation of oxidation levels and alteration of functional groups. In total, 15 derivatives of the natural products have been synthesized and tested for their neurite outgrowth activities. Our studies indicate that the promising biological activity can be retained by structurally simpler natural product analogues, which are accessible by a straightforward synthetic route

Comparison of distinctive models for calculating an interlobar emphysema heterogeneity index in patients prior to endoscopic lung volume reduction

Background: The degree of interlobar emphysema heterogeneity is thought to play an important role in the outcome of endoscopic lung volume reduction (ELVR) therapy of patients with advanced COPD. There are multiple ways one could possibly define interlobar emphysema heterogeneity, and there is no standardized definition. Purpose: The aim of this study was to derive a formula for calculating an interlobar emphysema heterogeneity index (HI) when evaluating a patient for ELVR. Furthermore, an attempt was made to identify a threshold for relevant interlobar emphysema heterogeneity with regard to ELVR. Patients and methods: We retrospectively analyzed 50 patients who had undergone technically successful ELVR with placement of one-way valves at our institution and had received lung function tests and computed tomography scans before and after treatment. Predictive accuracy of the different methods for HI calculation was assessed with receiver-operating characteristic curve analysis, assuming a minimum difference in forced expiratory volume in 1 second of 100 mL to indicate a clinically important change. Results: The HI defined as emphysema score of the targeted lobe (TL) minus emphysema score of the ipsilateral nontargeted lobe disregarding the middle lobe yielded the best predicative accuracy (AUC =0.73, P=0.008). The HI defined as emphysema score of the TL minus emphysema score of the lung without the TL showed a similarly good predictive accuracy (AUC =0.72, P=0.009). Subgroup analysis suggests that the impact of interlobar emphysema heterogeneity is of greater importance in patients with upper lobe predominant emphysema than in patients with lower lobe predominant emphysema. Conclusion: This study reveals the most appropriate ways of calculating an interlobar emphysema heterogeneity with regard to ELVR

Dynamic Virtualized Deployment of Particle Physics Environments on a High Performance Computing Cluster

The NEMO High Performance Computing Cluster at the University of Freiburg has been made available to researchers of the ATLAS and CMS experiments. Users access the cluster from external machines connected to the World-wide LHC Computing Grid (WLCG). This paper describes how the full software environment of the WLCG is provided in a virtual machine image. The interplay between the schedulers for NEMO and for the external clusters is coordinated through the ROCED service. A cloud computing infrastructure is deployed at NEMO to orchestrate the simultaneous usage by bare metal and virtualized jobs. Through the setup, resources are provided to users in a transparent, automatized, and on-demand way. The performance of the virtualized environment has been evaluated for particle physics applications

Deoxyguanosine kinase mutation F180S is associated with a lean phenotype in mice

Background: Deoxyguanosine kinase (DGUOK) deficiency is one of the genetic causes of mitochondrial DNA depletion syndrome (MDDS) in humans, leading to the hepatocerebral or the isolated hepatic form of MDDS. Mouse models are helpful tools for the improvement of understanding of the pathophysiology of diseases and offer the opportunity to examine new therapeutic options. Methods: Herein, we describe the generation and metabolic characterization of a mouse line carrying a homozygous DguokF180S/F180S mutation derived from an N-ethyl-N-nitrosourea-mutagenesis screen. Energy expenditure (EE), oxygen consumption (VO2) and carbon dioxide production (VCO2) were assessed in metabolic cages. LC-MS/MS was used to quantify plasma adrenal steroids. Plasma insulin and leptin levels were quantified with commercially available assay kits. Results: Mutant animals displayed significantly lower body weights and reduced inguinal fat pad mass, in comparison to unaffected littermates. Biochemically, they were characterized by significantly lower blood glucose levels, accompanied by significantly lower insulin, total cholesterol, high density lipoprotein and triglyceride levels. They also displayed an almost 2-fold increase in transaminases. Moreover, absolute EE was comparable in mutant and control mice, but EE in mutants was uncoupled from their body weights. Histological examination of inguinal white adipose tissue (WAT) revealed adipocytes with multilocular fat droplets reminiscent of WAT browning. In addition, mRNA and protein expression of Ucp1 was increased. Mutant mice also presented differing mitochondrial DNA content in various tissues and altered metabolic activity in mitochondria, but no further phenotypical or behavioral abnormalities. Preliminary data imply normal survival of DguokF180S/F180S mutant animals. Conclusion: Taken together, DGUOK mutation F180S leads to a lean phenotype, with lower glucose, insulin, and lipid levels rendering this mouse model not only useful for the study of MDDS forms but also for deciphering mechanisms resulting in a lean phenotyp