Scientific publications of the Saarland University
Not a member yet
14321 research outputs found
Sort by
A Machine Learning Dataset of Artificial Inner Ring Damage on Cylindrical Roller Bearings Measured Under Varying Cross-Influences
Get PDFIn practical machine learning (ML) applications, covariate shifts and dependencies can significantly impact model robustness and prediction quality, leading to performance degradation under distribution shifts. In industrial settings, it is crucial to account
for covariates during the design of experiments to ensure reliable generalization. The
presented dataset of undamaged and artificially damaged cylindrical roller bearings is
designed to address the lack of data resources for targeting domain and distribution shifts
in this field. The dataset considers multiple key covariates, including mounting position,
load, and rotational speed. Each covariate consists of multiple levels optimized for groupbased cross-validation. This allows the user to exclude specific groups in the training
to validate and test the algorithm. Using this approach, algorithms can be evaluated for
their robustness and the effect on the model caused by distribution shifts, allowing their
generalization capabilities to be studied under realistic conditions
Machine Learning Based Assessment of Inguinal Lymph Node Metastasis in Patients with Squamous Cell Carcinoma of the Vulva
Get PDFBackground/Objectives: Despite great efforts from both clinical and pathological
sides to address the extent of metastatic inguinal lymph node involvement in patients
with vulvar cancer, current research attempts are still mostly aimed at identifying new
imaging parameters or superior tissue diagnostic workflows rather than alternative ways of
statistical data analysis. In the present study, we therefore establish a supervised machine
learning algorithm to predict groin metastasis in patients with squamous cell carcinoma
of the vulva (VSCC) based on classical histomorphological features. Methods: In total,
157 patients with VSCC were included in this retrospective study. After initial exploration
of valuable clinicopathological predictor variables by means of Spearman correlation, a
decision tree was trained and internally validated (5-fold cross-validation) using a training
data set (n = 126) and afterwards externally validated employing a holdout validation
data set (n = 31) using standard metrices such sensitivity, positive predictive value, and
AUROC curve. Results: Our established classifier can predict inguinal lymph node status
with an internal accuracy of 79.4% (AUROC value = 0.64). Reaching similar performances
and an overall accuracy of 83.9% on an unknown data input (external validation set),
our classifier demonstrates robustness. Conclusions: The presented results suggest that
machine learning can predict groin lymph node status in VSCC based on histological
findings of the primary tumor. Such research attempts may be useful in the future for an
additional assessment of inguinal lymph nodes, aiming to maximize oncological safety
when targeting the most accurate diagnosis of lymph node involvement
Bidirectional rotational antagonistic shape memory alloy actuators for high-frequency artificial muscles
Get PDFShape memory alloys (SMA) are commonly utilized in compact actuators due to their high energy
density, meaning possible work output in relation to their weight and volume. Their application area
is limited by their poor dynamic behavior, caused by the thermal activation characteristics of SMA
materials. Typical actuation frequencies of SMA-based actuators range from 1 Hz to 10 Hz. In this work,
we introduce an actuator system architecture, termed bidirectional rotational antagonistic (BIRAN)
SMA actuator, which uses bundles of thin SMA wires to generate repeated rotational movement at
frequencies up to 200 Hz. This marks a new frequency record for electrically activated SMA wire-based
actuator systems. The high frequency reported results from the combination of mechanical design,
electronics, and control strategy. We describe the fabrication techniques and the power electronics
development and demonstrate the system performance through a systematic experimental study. A
bio-inspired robotic wing-flapping joint illustrates the expansion of possible SMA-based application
areas, pushing the dynamic limitations of this actuator technology
Methodik zur Evaluierung von Auswirkungen der geometrischen Komplexität auf die Produktivität additiver Fertigungsverfahren am Beispiel des Selektiven Lasersinterns
No full textAls einer der bedeutendsten Vorteile Additiver Fertigungsverfahren wird häufig die Gestaltungsfreiheit genannt. Jedoch bestehen Herausforderungen, da die suggerierte Gestaltungsfreiheit meist ohne Berücksichtigung der verschiedenen Verfahren und Wirkprinzipien dargestellt wird. Dabei zeigt sich im Vergleich unterschiedlicher Verfahren, dass die zu erzeugende Geometrie zum Teil signifikante Auswirkungen auf den Produktionsaufwand in Form von Zeit und Kosten hat. Mit der vorliegenden Arbeit werden diese Problemstellungen aufgegriffen und eine Methodik entwickelt, welche die Evaluierung von Auswirkungen der geometrischen Komplexität auf den additiven Herstellprozess ermöglicht. Demonstriert wird die Methodik am Verfahren des Selektiven Lasersinterns (SLS) für Kunststoffe. Der Fokus liegt dabei auf der Analyse von Zusammenhängen zwischen geometrischen Einflussfaktoren, Prozessparametern sowie resultierenden Produktionsaufwänden. Unter Beibehaltung von Randbedingungen wie dem Bauteilvolumen und der Bauhöhe wird gezeigt, dass sich die Generierdauer durch Steigerung der Komplexität zum Teil mehr als verdreifacht. Mithilfe der entwickelten Methodik können diese Auswirkungen direkt auf das Wechselspiel aus Geometrie und prozessspezifischen Faktoren, wie den Laserscanpfaden zurückgeführt werden. Folglich ist eine quantitative Kategorisierung der Komplexität in Abhängigkeit des Verfahrens möglich, die zusätzlich Rückschlüsse zur Gestaltung von Bauteilen und Bauaufträgen gewährt.Freedom of design is often cited as one of the major advantages of additive manufacturing. However, challenges remain, as the supposed freedom of design is usually presented without considering the various processes and operating principles. The comparison of different processes shows that the geometry to be produced sometimes has a significant impact on production effort in terms of time and costs. In this work, these challenges are addressed and a methodology is developed to assess the impact of geometric complexity on additive manufacturing processes. The methodology is demonstrated using the Selective Laser Sintering (SLS) for plastics. The focus is on the analysis of correlations between geometric influencing factors, process parameters and the resulting production effort. While maintaining boundary conditions such as part volume and build height, the results reveal that the generation time is more than tripled in some cases due to an increase in complexity. By using the developed methodology, these effects can be linked directly to the interaction of geometry and process-specific factors, such as the laser scan paths. Consequently, a quantitative categorization of the complexity in relation to the specific process is possible, which also allows conclusions to be made with regard to the design of parts and build jobs.2022-10 to 2025-05 | Grant
Federal Ministry for Economic Affairs and Climate Action (BMWK) (Berlin, DE
Classification of symplectic birational involutions of manifolds of OG10 type
Get PDFWe give a complete classification of symplectic birational involutions of manifolds of OG10
type. We approach this classification with three techniques—via involutions of the Leech
lattice, via involutions of cubic fourfolds, and finally lattice enumeration via a modified
Kneser’s neighbour algorithm. The classification consists of three involutions with an explicit
geometric realisation via cubic fourfolds, and three exceptional involutions which cannot be
obtained by any known construction
Offener vs. interventioneller Aortenrepair bei Bauchaortenaneurysma: Analyse und Vergleich zweier Verfahren in einem zertifizierten und interdisziplinären Gefäßzentrum
Get PDFHintergrund:
Abdominelle Bauchaortenaneurysmen können heutzutage entweder offen-chirurgisch mit einer Gefäßprothese oder endovaskulär mit einem Stentgraft behandelt werden. In den letzten Jahren hat sich die endovaskuläre Therapie dabei als wichtige Säule neben der operativen Variante etabliert. Durch die Entwicklung neuer Devices und speziell angefertigter endovaskulärer Stentgrafts hat sich auch ihr Einsatzgebiet erheblich erweitert. Diese retrospektive Studie wurde durchgeführt, um einen Vergleich der beiden Verfahren bezüglich ihres Outcomes am zertifizierten Gefäßzentrum der Universitätsklinik in Homburg zu erlangen.
Methoden:
Für die Datenerhebung wurden alle Patienten mit einem abdominellen Aortenaneurysma berücksichtigt, die zwischen dem 01.01.2014 und dem 30.04.2019 im Gefäßzentrum der Universitätsklinik in Homburg durch eine der Therapieformen behandelt wurden. Die Gruppeneinteilung war dabei nicht randomisiert. In jeder Gruppe erfolgte eine weitere Differenzierung zwischen Patienten mit einem rupturierten Aneurysma und
solchen mit einem nicht-rupturierten Aneurysma. Für den direkten Vergleich wurden demografische, aneurysmabezogene, prozedurale und klinische Daten untersucht. Zudem wurde die Länge des gesamtstationären Aufenthalts und des Intensivaufenthalts, die Komplikationsinzidenz und das Komplikationsspektrum sowie die Inzidenz von Reinterventionen/Reoperationen und die primäre Krankenhaussterblichkeit miteinander verglichen.
Ergebnisse:
Von insgesamt 185 Patienten wurden 115 endovaskulär therapiert. Die restlichen 70 Patienten wurden durch eine offen-chirurgische Therapie behandelt. Im Durchschnitt verbrachten die operativ therapierten Patienten 3 Tage länger auf der Intensivstation (p<0,001) und wurden durchschnittlich 4 Tage später aus dem Krankenhaus entlassen (p<0,001). Prozedurassoziierte Komplikationen und Re-Eingriffe traten während der Primärhospitalisation jeweils häufiger in der endovaskulären Gruppe auf (Komplikationen: EVAR: 75,7%; OP: 34,3%; p<0,001 // Re-Eingriffe: EVAR: 33,9%; OP: 27,1%; p=0,336). Die häufigste endovaskuläre Komplikation, die dabei erfasst werden konnte, war das Auftreten eines Endoleaks (68/115 Patienten; 59,1%) (über 85 Prozent Grad I der Clavien-Dindo-Klassifikation). Operativ kam es am häufigsten zu Darmischämien (11/70 Patienten; 15,7%) und abdominellen Kompartmentsyndromen (6/70 Patienten; 8,6%) (Grad IIIB bis Grad V der Clavien-Dindo-Klassifikation). Auch nach der Entlassung kamen prozedurassoziierte Komplikationen und Re-Eingriffe
häufiger in der endovaskulären Gruppe vor (Komplikationen: EVAR: 19,1%; OP: 11,4%; p=0,218 // Re-Eingriffe: EVAR: 16,5%; OP: 10%; p=0,216). Die führende endvaskuläre Komplikation war abermals das Auftreten eines Endoleaks (8/115 Patienten; 7,0%) (vorallem Grad IIIA der Clavien-Dindo-Klassifikation). Im Langzeitverlauf traten jedoch auch schwerwiegendere Komplikationen wie sekundäre Rupturen und Stentgraftinfektionen
auf (Grad IIIB bis Grad IVB der Clavien-Dindo-Klassifikation). In der operativen Gruppe kam es nach der Entlassung am häufigsten zu Narbenhernien (6/70 Patienten; 8,6%) (Grad IIIB der Clavien-Dindo-Klassifikation). Bezüglich der Mortalität zeigte sich während der Primärhospitalisation eine signifikant
niedrigere Mortalitätsrate in der endovaskulären Gruppe (EVAR: 3,5%; OP: 20%; p=0,001). Zu beachten ist hierbei allerdings eine ungleiche Gruppenverteilung rupturierter Aneurysmen, die mit einem erhöhten Mortalitätsrisiko einhergehen. Die Rate rupturierter Aneurysmen betrug in der operativen Gruppe 27,1 Prozent und in der endovaskulären Gruppe 7,8 Prozent.
Schlussfolgerung:
Die EVAR-Gruppe wies eine signifikant niedrigere Krankenhaussterblichkeit und einen signifikant kürzeren Krankenhausaufenthalt auf. Allerdings verzeichnete sie auch eine deutlich niedrigere Rate rupturierter Aneurysmen. Re-Eingriffe und prozedurassoziierte Komplikationen traten häufiger in der endovaskulären Gruppe auf. Ein früher endovaskulärer Vorteil durch risikoarme Komplikationen wurde im Langzeitverlauf durch risikoreiche Komplikationen wie sekundäre Rupturen und Stentgraftinfektionen aufgehoben. Background:
Abdominal aortic aneurysms can nowadays be treated either by open surgery with a vascular prosthesis or endovascularly with a stent graft. In recent years, endovascular therapy has established itself as an important pillar alongside the surgical variant. The development of new devices and specially manufactured endovascular stent grafts has also considerably expanded their field of application. This retrospective study was conducted to compare the two procedures in terms of their outcome at the certified vascular centre of the University Hospital in Homburg.
Methods:
All patients with an abdominal aortic aneurysm who were treated with one of the forms of therapy at the Vascular Centre of the University Hospital in Homburg between 1 January 2014 and 30 April 2019 were included in the data collection. The group allocation was not randomised. Within each group, a further distinction was made between patients with ruptured and non-ruptured aneurysms. Demographic, aneurysm-related, procedural and clinical data were analysed for the direct comparison. In addition, the length of the overall inpatient stay and intensive care stay, the incidence of complications and the range of complications as well as the incidence of reinterventions/reoperations and the primary hospital mortality were compared.
Results:
Of a total of 185 patients, 115 underwent endovascular therapy. The remaining 70 patients were treated by open surgery. On average, the surgically treated patients spent 3 days longer in the intensive care unit (p<0.001) and were discharged from hospital an average of 4 days later (p<0.001). Procedure-associated complications and reinterventions occurred more frequently in the endovascular group during primary hospitalisation (complications: EVAR: 75.7%; OP: 34.3%; p<0.001 // reinterventions: EVAR: 33.9%; OP: 27.1%; p=0.336). The most common endovascular complication observed in this case was the occurrence of an
endoleak (68/115 patients; 59.1%) (over 85 per cent grade I of the Clavien-Dindo classification). Intestinal ischaemia (11/70 patients; 15.7%) and abdominal compartment syndromes (6/70 patients; 8.6%) were the most common surgical complications (grade IIIB to grade V of the Clavien-Dindo classification). Even after discharge procedure-associated complications and reinterventions were detected more frequently in the endovascular group (complications: EVAR: 19.1%; OP: 11.4%; p=0.218 // reinterventions: EVAR: 16.5%; OP: 10%; p=0.216). The leading endovascular complication was again the occurrence of an endoleak (8/115 patients; 7.0%) (mainly grade IIIA of the Clavien-Dindo classification). However, more serious complications such as secondary ruptures and stent graft infections also occurred in the long-term course (grade IIIB to grade IVB of the Clavien-Dindo classification). In the surgical group, incisional hernias were the most common complication after inpatient discharge (6/70 patients; 8.6%) (grade IIIB of the Clavien-Dindo classification). With regard to mortality during primary hospitalisation, the mortality rate was significantly lower in the endovascular group (EVAR: 3.5%; OP: 20%; p=0.001). However, an uneven group distribution of ruptured aneurysms, which are associated with an increased mortality risk, should be noted. The rate of ruptured aneurysms was 27.1 percent in the surgical group and 7.8 percent in the endovascular group.
Conclusions:
The EVAR group had a significantly lower hospital mortality rate and a significantly shorter hospital stay. However, it also recorded a significantly lower rate of ruptured aneurysms. Reinterventions and procedure-associated occurred more frequently in the endovascular group. An early endovascular advantage due to low-risk complications was cancelled out in the long-term course by high-risk complications such as secondary
ruptures and stent graft infections.Abstract
Open versus interventional aortic repair for abdominal aortic aneurysm:
Analysis and comparison of two procedures in a certified and interdisciplinary
vascular centre
Background:
Abdominal aortic aneurysms can nowadays be treated either by open surgery with a
vascular prosthesis or endovascularly with a stent graft. In recent years, endovascular
therapy has established itself as an important pillar alongside the surgical variant. The
development of new devices and specially manufactured endovascular stent grafts has
also considerably expanded their field of application. This retrospective study was
conducted to compare the two procedures in terms of their outcome at the certified
vascular centre of the University Hospital in Homburg.
Methods:
All patients with an abdominal aortic aneurysm who were treated with one of the forms
of therapy at the Vascular Centre of the University Hospital in Homburg between 1
January 2014 and 30 April 2019 were included in the data collection. The group allocation
was not randomised. Within each group, a further distinction was made between
patients with ruptured and non-ruptured aneurysms. Demographic, aneurysm-related,
procedural and clinical data were analysed for the direct comparison. In addition, the
length of the overall inpatient stay and intensive care stay, the incidence of complications
and the range of complications as well as the incidence of reinterventions/reoperations
and the primary hospital mortality were compared.
Results:
Of a total of 185 patients, 115 underwent endovascular therapy. The remaining 70 patients
were treated by open surgery. On average, the surgically treated patients spent
3 days longer in the intensive care unit (p<0.001) and were discharged from hospital
an average of 4 days later (p<0.001).
4
Abstract
Procedure-associated complications and reinterventions occurred more frequently in
the endovascular group during primary hospitalisation (complications: EVAR: 75.7%;
OP: 34.3%; p<0.001 // reinterventions: EVAR: 33.9%; OP: 27.1%; p=0.336). The most
common endovascular complication observed in this case was the occurrence of an
endoleak (68/115 patients; 59.1%) (over 85 per cent grade I of the Clavien-Dindo classification).
Intestinal ischaemia (11/70 patients; 15.7%) and abdominal compartment
syndromes (6/70 patients; 8.6%) were the most common surgical complications (grade
IIIB to grade V of the Clavien-Dindo classification).
Even after discharge procedure-associated complications and reinterventions were detected
more frequently in the endovascular group (complications: EVAR: 19.1%; OP:
11.4%; p=0.218 // reinterventions: EVAR: 16.5%; OP: 10%; p=0.216). The leading endovascular
complication was again the occurrence of an endoleak (8/115 patients;
7.0%) (mainly grade IIIA of the Clavien-Dindo classification). However, more serious
complications such as secondary ruptures and stent graft infections also occurred in
the long-term course (grade IIIB to grade IVB of the Clavien-Dindo classification). In
the surgical group, incisional hernias were the most common complication after inpatient
discharge (6/70 patients; 8.6%) (grade IIIB of the Clavien-Dindo classification).
With regard to mortality during primary hospitalisation, the mortality rate was significantly
lower in the endovascular group (EVAR: 3.5%; OP: 20%; p=0.001). However, an
uneven group distribution of ruptured aneurysms, which are associated with an increased
mortality risk, should be noted. The rate of ruptured aneurysms was 27.1 percent
in the surgical group and 7.8 percent in the endovascular group.
Conclusions:
The EVAR group had a significantly lower hospital mortality rate and a significantly
shorter hospital stay. However, it also recorded a significantly lower rate of ruptured
aneurysms. Reinterventions and procedure-associated occurred more frequently in the
endovascular group. An early endovascular advantage due to low-risk complications
was cancelled out in the long-term course by high-risk complications such as secondary
ruptures and stent graft infections
Liquid-like versus stress-driven dynamics in a metallic glass former observed by temperature scanning X-ray photon correlation spectroscopy
Get PDFSince several decades, the dynamics and vitrification kinetics of supercooled
liquids are the subject of active research in science and engineering. Profiting
from modern detector technology and highly brilliant fourth-generation syn chrotron radiation, we apply temperature scanning X-ray photon correlation
spectroscopy (XPCS) to probe the dynamics of a Pt-based metallic glass former
in the glass, glass transition region, and supercooled liquid, covering up to six
orders of magnitude in timescales. Our data demonstrates that the structural
α-relaxation process is still observable in the glass, although it is partially
masked by a faster source of decorrelation observed at atomic scale. We
present an approach that interprets these findings as the superposition of
heterogeneous liquid-like and stress-driven ballistic-like atomic motions. This
work not only extends the dynamical range probed by standard isothermal
XPCS but also adds a different view on the α-relaxation across the glass tran sition and provides insights into the anomalous, compressed temporal decay
of the density-density correlation functions observed in metallic glasses and
many out-of-equilibrium soft materials
Lifetime Variations of Prolactin Receptor Isoforms mRNA in the Hippocampus and Dentate Gyrus of the Rat—Effects of Aging
Get PDFProlactin is a hormone for which actions on the central nervous system such as
neurogenesis and neuroprotection have been described by acting on specific receptors. The
presence of prolactin receptors in the brain, including the hippocampus, is well documented;
however, it is unknown whether these receptors change with age and whether they are
related to sex. For this reason, a study of the expression of prolactin receptors, in the short
and long isoforms, in the hippocampus of male and female rats has been carried out by
qPCR and in situ hybridization, with a densitometric analysis in the following life stages:
prepubertal, postpubertal, young adult, adult, and old. The results revealed the greater
expression of the long isoform than of the short isoform in males, but not in females, with
significant differences between males and females and in the different life stages studied.
With significant differences, the highest expression of both isoforms appeared in male rats
in the postpubertal stage, and the lowest expression was observed in adult and old animals.
In situ hybridization showed differences in the localization of PRLR mRNA expression in
CA1, CA3, and DG depending on the age and sex of the rats. The results obtained suggest
that hippocampal aging is related to a decrease in prolactin receptors, which helps to better
understand brain aging
Energieverbrauchsvorhersage in Kraftfahrzeugbordnetzen unter Verwendung hochdimensionaler Netzwerkkommunikationsdaten – ein Ansatz aus dem Maschinellen Lernen
Get PDFThe dissertation addresses a data-driven approach to analyze and predict the energy consumption of auxiliary components within the low-voltage electrical system of electric vehicles. A scalable data-processing pipeline was developed to preprocess measurement data for machine-learning models using state-of-the-art feature engineering methods. An appropriate regression algorithm is selected and validated to accurately forecast energy consumption. To improve interpretability and enable root-cause analysis, explainable AI techniques were integrated into the pipeline. The developed methods provide deeper insights into influencing factors of energy consumption, helping engineers optimize vehicle architectures and operational strategies in a data-driven manner, ultimately enhancing the accuracy of range estimation already during the development phase.Die Elektrifizierung des Individualverkehrs sowie regulatorische Vorgaben zur Emissionsreduktion erfordern eine Maximierung der Energieeffizienz von Elektrofahrzeugen. Neben der Erhöhung der Batteriekapazität ist die Optimierung des Gesamtenergieverbrauchs essenziell. Insbesondere das Niederspannungsbordnetz, das zahlreiche Nebenverbraucher versorgt, stellt einen bislang unterschätzten Einflussfaktor dar. Diese Arbeit verfolgt einen datengetriebenen Ansatz zur Analyse und Prognose des Energieverbrauchs von Steuergeräten und deren Peripherie. Hierzu wird eine skalierbare Datenverarbeitungspipeline entwickelt, die Messdaten importiert, auswählt, verarbeitet und für Machine-Learning-Modelle gemäß neuester Feature Engineering Methoden aufbereitet. Zur Verbrauchsvorhersage erfolgt die Auswahl und Validierung eines geeigneten Regressionsalgorithmus. Zur Erhöhung der Transparenz und der Ursachen des Energieverbrauchs wird Explainable AI in die Pipeline integriert. Dies ermöglicht eine detaillierte Analyse der Einflussgrößen auf den Verbrauch und erleichtert die Interpretation der Modellentscheidungen durch die Anwender. Dadurch erhalten Ingenieure fundierte Einblicke zur Optimierung der Bordnetzarchitektur und Betriebsstrategien der Komponenten. Die entwickelten Methoden leisten einen Beitrag zur datengetriebenen Effizienzsteigerung elektrischer Fahrzeugplattformen und ermöglichen schlussendlich eine präzisere Reichweitenprognose bereits in der Entwicklungsphase
TRPC6 in Human Peripheral Nerves—An Investigation Using Immunohistochemistry
Get PDFSince its discovery, TRPC6 has been associated with a variety of physiological
and pathophysiological processes in different tissues. It functions as a non-selective cation
channel and belongs to the group of TRP channels. Its importance in the development
of pain hypersensitivity is becoming increasingly apparent. This condition has already
been associated with increased expression of TRPC6 in dorsal root ganglia. Apart from
the fact that most of the evidence has been obtained from samples of animal origin, it
remains unclear whether the channel is also expressed in peripheral nerves outside the
dorsal root ganglia. The aim of this work was therefore to examine peripheral nerves from
human samples for TRPC6. For this purpose, samples of both the sciatic and ulnar nerves
were taken from a total of eight body donors and analyzed by immunohistochemistry.
Both longitudinal and transverse sections were obtained from the samples and stained. In
total, 43 of 48 histological sections showed a positive immunosignal. There were no major
differences between the sciatic and ulnar nerves with regard to staining. There was a slight
difference in the staining intensity of transverse and longitudinal sections. The longitudinal
sections of both nerves were consistently colored slightly more intensely. However, the
inter-individual differences between the donors were more pronounced. Interestingly, the
samples of a donor who suffered from chronic pain syndrome during his lifetime were
particularly strongly stained. This is consistent with the knowledge gained to date, largely
from animal experiments, that the channel shows increased expression in pain conditions
in dorsal root ganglia. In the future, TRPC6 could therefore be a target in pain therapy