Modellreduktion von redundanten Mehrkörpersystemen

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersEin Grund für die zunehmende Bedeutung der Mehrkörpersimulation (MKS) im virtuellen Entwicklungsprozess ist die Verfügbarkeit automatisierter Modellerzeugungsverfahren. Die so erstellten mathematischen Modelle verwenden redundante Freiheitsgrade und Zwangsbedingungen zur Beschreibung des MKS Modells. Im Vergleich zu einer Minimalkoordinatenbeschreibung ist die Simulationsdauer, bedingt durch die größere Anzahl zu lösender Gleichungen, in der Regel deutlich höher. Ziel der vorliegenden Arbeit ist die Ableitung eines Modellreduktionsverfahrens für die MKS zum Zwecke der Effizienzsteigerung. Aufgrund der geforderten Anwendbarkeit an beliebige Mehrkörpermodelle wurde ein datengestütztes Reduktionsverfahren, basierend auf der „Proper Orthogonal Decomposition“ (POD), ausgewählt. Das Verfahren wurde in folgenden Punkten an die Besonderheiten der MKS adaptiert: (1) Verwendung von Geschwindigkeitsdaten anstatt der üblichen Positionsdaten. (2) Trennung der Koordinaten hinsichtlich ihrer physikalischen Bedeutung (anstatt der üblichen, gemischten Berücksichtigung). (3) Erweiterung der Projektion um ein Residuum, welches die korrekte Abbildung der Anfangsbedingungen sicherstellt. Der durch die adaptierte POD erzeugte Unterraum enthält bereits Informationen über die Zwangsbedingungen des MKS Systems. Aus diesem Grund wird in dieser Dissertation ein Verfahren vorgestellt, welches redundante Zwangsbedingungen im reduzierten Modell erkennt und eliminiert. Im Gegensatz zu den bisherigen Vorschlägen in der Literatur ist das auf diese Weise reduzierte Gleichungssystem immer lösbar und gut konditioniert. Die Effizienz der Methode wird anhand praxisrelevanter Beispiele demonstriert. Unter Einhaltung einer hohen Ergebnisqualität kann die Anzahl der zu lösenden Gleichungen um bis zu 90\% Prozent reduziert werden. Abschließend wird die Methode auch im Rahmen der Parameteridentifikation angewandt. Hierbei wird der aufgespannte Unterraum auch zur Reduktion von adjungierten Gleichungen verwendet.Multibody system (MBS) simulations see an increasing relevance in the field of automated modeling strategies due to several reasons. A redundant set of coordinates in combination with constraint coordination equations are required for such modeling strategies. Consequently, the numerical challenge of solving such models is much higher than it might be if a minimal set of coordinates representation is used. The current dissertation will explain the development of a model order reduction (MOR) technique, which allows to decrease the number of equations, and increase the numerical efficiency of such redundant multibody systems. A databased MOR approach has been chosen since the focus is on a general applicability to arbitrary multibody systems. It is based on the Proper Orthogonal Decomposition (POD), which is adapted to the Special needs of multibody systems by: (1) Using velocity data of the MBS (instead of the commonly used position data). (2) Separate handling of each coordinate type due to its physical meaning (instead of the commonly used mixed coordinate approach). (3) Adding a residual term to the applied projection which ensures the initial conditions to be met. Due to the use of a data-driven reduction approach, the resulting reduction subspace includes constraint information of the original MBS model. Therefore, the present Dissertation introduces a constraint reduction method, which determines and eliminates redundant constraint equations of the reduced order model. In contrast to known literature regarding MBS reduction, the herein derived coordinate and constraint reduced order model is therefore always solvable and illconditioned. The efficiency of the MOR approach is outlined by several practical numerical examples, evolving from automotive tasks. The results underline the efficiency of the novel approach, which ensures high result consistency, while at the same time, the dimension of the mathematical model is reduced up to 90+%. Finally, the approach is also applied to parameter identification tasks in the context of multibody systems. In addition to the previous mentioned reduction, the adjoint equations are reduced as well, by projecting them onto the same subspace as the original MBS model.15

Antenatal depressive symptoms and subjective birth experience in association with postpartum depressive symptoms and acute stress reaction in mothers and fathers: A longitudinal path analysis

Postpartum depressive symptoms (PDS) and acute stress reactions (ASR) after childbirth are frequently documented in mothers, but research is scarce in fathers. In a longitudinal path analysis, the interplay of depressive symptoms in pregnancy and the subjective childbirth experience of mothers and fathers are examined with regard to the development of PDS and ASR postpartum.; One hundred eighty nine expectant couples were recruited between August 2006 and September 2009. They completed the Edinburgh Postnatal Depression Scale (EPDS) in the last trimester of pregnancy. In the first week postpartum, they answered the Salmon's Item List (subjective birth experience), and four weeks after birth the EPDS and the Impact of Event Scale - revised (IES-r). The data were evaluated in a longitudinal path analysis.; Compared with fathers, mothers reported more depressive symptoms (pregnancy: p<0.001; postpartum: p<0.001), higher ASR (p<0.001), and lower 'positive birth experience' (p<0.001). The association between depressive symptoms in mothers and fathers was not significant during pregnancy (r=0.107, p>0.10), but moderately correlated four weeks after birth (r=0.387, p<0.001). Depressive symptoms during pregnancy and a negative subjective birth experience were independently predictive of PDS and ASR after childbirth in mothers and fathers controlling for age, mode of delivery, parity, epidural anaesthesia, infant gender and birth weight. Antenatal depressive symptoms were related to subjective childbirth experience only in fathers.; Parental prenatal depressive symptoms and subjective birth experience are important predictors of postnatal psychological adjustment in mothers and fathers

Acute stress reactions in the first 3 weeks postpartum: A study of 219 parturients

OBJECTIVES: There is increasing research on posttraumatic stress (PS) 4-6 weeks and 3 months postpartum, but, there are no data on acute stress reactions (ASR) in the first 3 weeks postpartum, i.e. the potential precursors of PS. However, ASR may have long-term effects, e.g., on a subsequent pregnancy without having manifested as PS in the meantime. We propose: (i) to describe the patterns of ASR after childbirth, (ii) to explore differences between women with normal and traumatogenic ASR, and (iii) to provide data on the early detection of traumatogenic ASR 2 and 3 weeks postpartum. STUDY DESIGN: Intra-event variables (relationship with caregivers, overall birth experience, and dissociative experiences, as well as obstetric variables) were assessed 48-96h. postpartum, as were ASR (by means of the Impact-of-Event Scale IES) in weeks 1, 2, and 3 postpartum. According to research on PS the upper 33%-range of ASR in weeks 2 and 3 was defined as 'traumatogenic'. RESULTS: Normal ASR in week 1 are at a level which in non-obstetric trauma-situations is considered as the upper range of low stress or lower range of medium distress. ASR decline constantly from week 1 to week 3. However, high ASR in week 1 do not drop faster than do low ones, thus indicating a prolonged stress reaction in women with high ASR in week 1. Low ASR (IES-scores 20) in week 1 are highly predictive for normal ASR, and traumatogenic ASR in weeks 2 and 3, respectively. Medium ASR (IES-scores 10-20) in week 1 are of uncertain predictive value for stress reactions in weeks 2 and 3 and have to be re-assessed at that time. CONCLUSIONS: Clinical screening for ASR appears to be helpful in detecting women with a compromised ability to process childbirth-related stress. The association between ASR and long-term development should be further explored

Natural course of subjects with elevated liver tests and normal liver histology

BACKGROUND & AIMS: Liver biopsy (LB) is performed if non-invasive work-up of liver disease is inconclusive. The examination of liver tissue occasionally reveals normal histology. Long-term follow-up of such patients has not been performed. METHODS: We identified a total 70 subjects from our LB database with elevated liver tests and normal liver histology after a mean of 90.5 ± 52.3 (range 15-216) months and conducted reassessment of medical history, physical examination, laboratory testing, ultrasound, transient elastography and LB if indicated. RESULTS: At follow-up examination, 15 (7 females (f)/8 males (m); 21.4%) subjects had normal liver tests and no further evidence of liver disease. A subset of 37 (29 f/8 m; 52.9%) subjects had persistently elevated liver tests without evidence indicating progressive liver disease but the cause thereof remained unexplained also at the follow-up visit. Three (0 f/3 m; 4.3%) subjects had consumed excessive alcohol with indicators of alcoholic liver disease. Eleven subjects (4 f/7 m; 15.7%) had developed steatosis on ultrasound examination along with weight gain and/or biochemical features of the metabolic syndrome. In addition, three (2 f/1 m) patients developed autoimmune hepatitis, one female presented with primary biliary cirrhosis. One male was diagnosed with cholangiocellular carcinoma 3 months after the initial evaluation. CONCLUSION: The clinical course of most patients was benign, but in approximately 20% of the subjects a liver disease developed. Particular attention should be given to autoimmune liver diseases in subjects with positive autoantibodies. In addition, lifestyle factors such as weight gain and alcohol consumption were associated with the manifestation of liver diseases

Maternal mental health in the first three weeks postpartum : The impact of caregiver support and the subjective experience of childbirth: a longitudinal path model

Acute stress reactions (ASR) and postpartum depressive symptoms (PDS) are frequent after childbirth. The present study addresses the change and overlap of ASR and PDS from the 1- to 3-week postpartum and examines the interplay of caregiver support and subjective birth experience with regard to the development of ASR/PDS within a longitudinal path model

Experimental Insights Into Space Weathering of Phobos : Laboratory Investigation of Sputtering by Atomic and Molecular Planetary Ions

Investigating the space weathering of the Martian moon Phobos represents an important step toward understanding the development from its origin to its present-day appearance. Depending on Phobos' orbital position, its surface is continuously sputtered by the solar wind and planetary ions that originate in the Martian atmosphere. Based on Mars Atmosphere and Volatile Evolution measurements, it has been proposed that sputtering by planetary O+ and O-2(+) ions dominates in the Martian tail region, where the planet mostly shadows Phobos from the solar wind. In these models, uncertainties for sputtering yield inputs still exist due to the lack of sufficient analog experiments. Therefore, sputtering measurements with O+, O-2(+), C+, and CO2+ ions between 1 and 5 keV were performed using augite samples as Phobos analogs. The experimental results for O+ irradiations show smaller mass changes than predicted by SDTrimSP simulations, which probably can be attributed to O implantation enabled by the Fe content of the target. Sputtering with O-2(+) and CO2+ in the low keV range shows no deviations in the sputtering yields attributable to molecular effects. Therefore, CO2+ ions will most likely be negligible for the sputtering of Phobos according to the current understanding of ion fluxes on the Martian moon. Ultimately, our experiments suggest that the sputtering contribution on Phobos by O ions is about 50% smaller than previously assumed. This does not change the qualitative outcome from previous modeling stating that planetary O ions are by far the dominant sputtering contribution on Phobos in the Martian tail region

Solar wind sputtering of wollastonite as a lunar analogue material – Comparisons between experiments and simulations

sputtering of wollastonite (CaSiO 3 ) by solar wind-relevant ions has been investigated experimentally and the results are compared to the binary collision approximation (BCA) codes SDTrimSP and SRIM-2013. Absolute sputtering yields are presented for Ar projectiles as a function of ion impact energy, charge state and impact angle as well as for solar wind H projectiles as a function of impact angle. Erosion of wollastonite by singly charged Ar ions is dominated by kinetic sputtering. The absolute magnitude of the sputtering yield and its dependence on the projectile impact angle can be well described by SDTrimSP as long as the actual sample composition is used in the simulation. SRIM-2013 largely overestimates the yield especially at grazing impact angles. For higher Ar charge states, the measured yield is strongly enhanced due to potential sputtering. Sputtering yields under solar wind-relevant H + bombardment are smaller by two orders of magnitude compared to Ar. Our experimental yields also show a less pronounced angular dependence than predicted by both BCA programs, probably due to H implantation in the sample. Based on our experimental findings and extrapolations to other solar wind ions by using SDTrimSP, we present a model for the complete solar wind sputtering of a flat wollastonite surface as a function of projectile ion impact angle, which predicts a sputtering yield of 1.29 atomic mass units per solar wind ion for normal impact. We find that mostly He and some heavier ions increase the sputtering yield by more than a factor of two as compared to bombardment with only H + Ions