Scientific publications of the Saarland University
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Measuring Lead Userness: Development and Validation of a Hierarchical Scale
Full text linkLead user theory has gained traction in both academia and practice, given that involving lead users (LUs) can yield more innovative and commercially successful products. Yet, measurement inconsistencies have hindered consensus on how to reliably assess lead userness. This paper develops and validates a new 30-item scale that conceptualizes lead userness as a hierarchical construct with two second-order dimensions: ahead of trend (AoT) and high benefit expectation (HBE). Each dimension is further subdivided into three first-order subdimensions, capturing facets such as ideas, information and experience (AoT) or problems, needs and gains (HBE). In multiple studies, the scale demonstrated robust reliability and convergent, discriminant and nomological validity, correlating as expected with key antecedents (e.g., divergent thinking, product knowledge, innate innovativeness and risk aversion) and outcomes (e.g., social innovativeness, opinion leadership, innovation experience and innovation intention). Additionally, a separate predictive and explanatory power study comparing the new scale with seven established measures underscored its superior capacity to account for both past and future user-driven innovation activities. Moreover, a market test across smartphones, e-bikes and refrigerators confirmed that product concepts developed by identified LUs commanded higher willingness to pay than those from regular consumers, reinforcing the scale's practical relevance. Finally, a short-scale variant with six items is introduced as a viable alternative when item minimization is crucial. Taken together, these findings provide a comprehensive inventory for measuring lead userness, laying the foundation for deeper theoretical insights into user-driven innovation and more targeted managerial strategies for collaborating with LUs across diverse product categories
A Bis(germaamidine) through Nitrene Insertion into Ge─Si Bonds
Full text linkAmidines (with two nitrogen atoms around the unsaturated carbon center) are important synthetic building blocks. In particular, phenylene-bridged derivatives are extensively used in the synthesis of cyclic and polymeric structures for pharmaceutical, electrochemical, and materials applications. While various heavier Group 14 congeners of the related imines and guanidines (with one nitrogen less or more, respectively) are known, only one case of an amidine with a SnN bond has been reported. Herein, a bis(germaamidine) with the two germaamidine moieties connected by a silylene-phenylene linking unit is presented. Azide-induced GeGe double bond cleavage in the bridged bis(digermene) precursor results in the concomitant formation of two equivalents of a tetraazagermole by-product. NMR spectroscopic monitoring and the isolation of an intermediately occurring aziridine suggest the initial formation of a bis(germaimine), followed by the insertion of transient nitrene into the GeSi bonds. This is further confirmed by comparative reactions of the Ge(II) centers of the corresponding bis(germylene)-carbene adducts with the azide. Reactions of the bis(germaamidine) with CO2 and MeOH result in additions to the GeN bonds, suggesting significant potential as a bifunctional monomer for the synthesis of poly(germane)s
Adaptive mechanisms in pancreatic islets counteract mitochondrial dysfunction in Barth syndrome
Full text linkAims/hypothesis Barth syndrome is a mitochondrial disorder caused by Tafazzin (TAZ) mutations, which impair cardiolipin
remodelling and contribute to systemic metabolic alterations. While islet dysfunction has been implicated in Barth syndrome,
its underlying mechanisms remain unknown. We aimed to determine how Tafazzin (Taz) deficiency affects mouse pancreatic
islet metabolism and hormone secretion, and whether systemic signals, such as circulating factors, modulate these effects
in vivo. In vivo and in vitro models were used to separate direct islet effects from systemic influences of Taz deficiency.
Methods We used a mouse model of global Taz knockdown (Taz-KD) and combined in vivo and in vitro approaches to assess
pancreatic islet metabolism, morphology and hormone secretion. Islet function was evaluated under basal and glucotoxic
conditions. Transcriptomic profiling was performed to identify gene expression changes in isolated islets from Taz-KD
mice and following in vitro Taz-KD. Additionally, we examined the role of the circulating factor fibroblast growth factor 21
(FGF-21) in modulating islet function.
Results Despite impaired cardiolipin remodelling, pancreatic islets from Taz-KD mice maintained insulin secretion, sup ported by compensatory mechanisms such as increased glucose uptake, expanded mitochondrial volume and increased
metabolic parameters. In addition, alpha cell mass and glucagon secretion were significantly increased in Taz-KD islets.
These islet-specific adaptations occurred alongside improved whole-body glucose tolerance, elevated circulating FGF-21
levels and enhanced glucose uptake in brown adipose tissue. In contrast, in vitro Taz-KD led to impaired islet function and
reduced insulin secretion. Transcriptomic analysis revealed distinct gene expression patterns between in vivo and in vitro
Taz-KD models. While in vivo upregulation of genes related to N-acetylglucosamine biosynthesis and O-GlcNAcylation
were related to compensatory mechanisms, in vitro Taz-KD affected, among others, the MAPK pathway, contributing to islet
dysfunction. Notably, islet incubation with FGF-21 was able to restore insulin secretion after in vitro Taz-KD.
Conclusions/interpretation Our findings demonstrate that while Taz and cardiolipin remodelling are essential for beta
cell physiology, systemic and islet-specific compensatory mechanisms preserve insulin secretion in vivo in Taz-KD mice,
alongside increased glucagon secretion. These adaptations probably contribute to the altered metabolic phenotype observed
in Barth syndrome and highlight a potential role for hormones and circulating factors such as FGF-21 in maintaining islet
function and glucose homeostasis
Tuning guidelines for model-free control
Full text linkThe control of complex systems without the need of deriving a detailed physics-based mathematical model of the system, which is a necessity for most of the common control approaches, is a desirable goal. Considering the fact that the complexity of modern systems is ever increasing, the need for a universal control solution is also growing. Fliess and Join (2009, 2013) have proposed a signal-based control approach that neither requires a physically-motivated model of the system considered nor relies on time-consuming and data-intensive training. However, the systematic tuning of these so-called model-free controllers is still a challenging task. In this thesis, the sampling of the control parameter set for a proportional valve and a magnetically supported plate lay the foundation for a systematic tuning approach of the proposed control method. It is shown that the stability of the closed loop can be analysed using the generalised Hermite-Biehler theorem. Theoretical bounds for the controller parameters are calculated for a DC motor as a basic example and validated by various experiments. Additionally, the parametrisation of the algebraic differentiators used to estimate the unknown quantities required for the implementation of the control law is investigated. With these new findings, guidelines can be formulated leading to a systematic tuning of the model-free control law.Die Regelung komplexer Systeme ohne Kenntnis eines detaillierten physikalisch-mathematischen Modells, wie es die meisten gängigen Ansätze erfordern, ist ein erstrebenswertes Ziel. In Anbetracht der Tatsache, dass die Komplexität moderner Systeme ständig zunimmt, wächst der Bedarf an einer universellen Regelungsstrategie. Fliess und Join (2009, 2013) haben einen signalbasierten Ansatz vorgeschlagen, der weder ein physikalisch motiviertes Modell des Systems benötigt noch auf zeitaufwändiges und datenintensives Training angewiesen ist. Die systematische Auslegung dieser so genannten modellfreien Regler stellt jedoch weiterhin eine anspruchsvolle Aufgabe dar. In dieser Arbeit wird mit dem Abtasten des Parameterraums für ein Proportionalventil und eine magnetisch gelagerte Platte die Grundlage für eine systematische Auslegung des betrachteten Reglers gelegt. Es wird gezeigt, dass die Stabilität des geschlossenen Regelkreises mit Hilfe des verallgemeinerten Hermite-Biehler-Theorems analysiert werden kann. Theoretische Grenzen für die Reglerparameter werden am Beispiel eines Gleichstrommotors berechnet und durch diverse Experimente validiert. Zusätzlich wird die Parametrierung der algebraischen Ableitungsschätzer untersucht, die zur Schätzung der unbekannten Größen sowie für die Implementierung des Regelgesetzes verwendet werden. Mit diesen neuen Erkenntnissen werden Leitlinien abgeleitet, die zu einer systematischen Parametrierung des modellfreien Reglers führen
Interfacing TRNSYS with MATLAB for Building Energy System Optimization
Full text linkThis contribution investigates whether the use of the MATLAB Optimization
Toolbox on a parameter identification problem for a TRNSYS model provides better performance in iteration time. It presents the development of a framework connecting the
MATLAB Optimization Toolbox with TRNSYS on the one hand and coordinating the optimization process of a TRNSYS model by GenOpt through MATLAB on the other hand.
A benchmark framework in MATLAB was created to link TRNSYS and MATLAB and to
configure the optimization process of GenOpt and the MATLAB Optimization Toolbox.
Using this framework, a comprehensive comparison of the optimization solvers in GenOpt
and the MATLAB Optimization Toolbox for the identification of the overall heat transfer
coefficient of a TRNSYS heat exchanger model regarding the optimization time and number
of iterations is presented as a use case. The results for the given problem show that GenOpt
gives slightly better results in optimization time, whereas MATLAB has more potential
and flexibility
Insights from lipidomics into the terminal maturation of circulating human reticulocytes
Full text linkIn the age of “omics”, lipidomics of erythropoiesis is still missing. How reticulocytes mature in the circulation into functional
erythrocytes is also largely unknown. We have isolated here two populations of human circulating reticulocytes at different levels of
maturation, and three subpopulations of erythrocytes of different age, and characterized the evolution of their lipidome.
(Sphingomyelin+cholesterol) and partly phosphatidylethanolamine increase relative to total lipids, whereas phosphatidylcholine
and phosphatidylserine decrease from immature reticulocytes to mature erythrocytes, at the same time as the surface area per cell
decreases. The relative amounts of more than 70 phospholipid subclasses, based on the number of carbon atoms (12–24) and of
double bonds (0–6) in the fatty acids linked to the phospholipid, also change in the process. As reticulocytes and erythrocytes
cannot perform de-novo phospholipid synthesis, lipid remodeling likely requires selective removal of phospholipids from the
membrane or their exchange with plasma or both, with the possible involvement of lipid transfer proteins such as VPS13A, which is
expressed in reticulocytes and erythrocytes. These findings not only shed light on fundamental aspects of red blood cell physiology
and erythropoiesis but also raise intriguing questions surrounding protein-lipid interactions, membrane architecture, and lipid
trafficking mechanisms
Towards a Comprehensive Framework for Made-to-Measure Alginate Scaffolds for Tissue Engineering Using Numerical Simulation
Full text linkAlginate hydrogels are integral to many cell-based models in tissue engineering
and regenerative medicine. As a natural biomaterial, the properties of alginates can vary
and be widely adjusted through the gelation process, making them versatile additives or
bulk materials for scaffolds, microcarriers or encapsulation matrices in tissue engineering
and regenerative medicine. The requirements for alginates used in biomedical applications
differ significantly from those for technical applications. Particularly, the generation of
novel niches for stem cells requires reliable and predictable properties of the resulting
hydrogel. Ultra-high viscosity (UHV) alginates possess alginates with special physicochemical properties, and thus far, numerical simulations for the gelation process are currently
lacking but highly relevant for future designs of stem cell niches and cell-based models.
In this article, the gelation of UHV alginates is studied using a microscopic approach for
disc- and sphere-shaped hydrogels. Based on the collected data, a multiphase continuum
model was implemented to describe the cross-linking process of UHV alginate polysaccharides. The model utilizes four coupled kinetic equations based on mixture theory, which
are solved using finite element software. A good agreement between simulation results
and experimental data was found, establishing a foundation for future refinements in the
development of an interactive tool for cell biologists and material scientists
Contributions to boundary control of distributed-parameter systems
Full text linkEine neuartige Entwurfsmethodik wird für die Regelung von linearen hyperbolischen oder parabolischen partiellen Differentialgleichungen (PDEs) vorgestellt, welche an einem Rand aktuiert und am anderen Rand mit nichtlinearen gewöhnlichen Differentialgleichungen (ODEs) gekoppelt sind. In Anlehnung an die wohlbekannte Backstepping-Methode für lineare Systeme wird eine nichtlineare Zustandstransformation herangezogen, um das System in eine für den Reglerentwurf besonders geeignete Form zu bringen. Das zentrale Ergebnis der vorliegenden Arbeit ist die Konstruktion dieser Zustandstransformation mithilfe der Lösung eines angemessen formulierten Cauchy-Problems. Die Verwendung einer flachheitsbasierten Parametrierung der entsprechenden PDE-Teilsysteme erleichtert diesen Entwurfsschritt. Zudem gestattet die Kombination von Backstepping und flachheitsbasierten Parametrierungen, auf bekannte Ergebnisse aus der bestehenden Literatur aufzubauen. Des Weiteren wird für den Spezialfall linearer Systeme gezeigt, dass der vorgestellte Ansatz sowohl für hyperbolische als auch für parabolische PDE-ODE-Systeme äquivalent zur Backstepping-Methode ist. Die in dieser Arbeit für den Reglerentwurf präsentierte Vorgehensweise bewältigt zuvor ungelöste Probleme und lässt sich aufgrund ihrer Systematik auf eine breitere Systemklasse erweitern. Allerdings sind im Rahmen dessen auch eine Vielzahl an Herausforderungen und interessanten Fragestellungen für weiterführende Untersuchungen entstanden.A novel framework is presented for the late-lumping boundary control of linear hyperbolic or parabolic partial differential equations (PDEs) that are interconnected with nonlinear ordinary differential equations (ODEs) at the unactuated boundary. Inspired by the well-established backstepping method for linear systems, a nonlinear state transformation is utilized to map the plant into a desired target system. The central result of this thesis is the construction of the state transformation through the solution of an appropriately formulated Cauchy problem. This is facilitated by the use of flatness-based parameterizations of the corresponding PDE subsystems. In fact, the combination of backstepping and flatness-based parameterizations allows this work to build upon a substantial body of existing literature. Furthermore, for the special case of linear systems, the approach is shown to be equivalent to the backstepping method for both hyperbolic and parabolic PDE-ODE systems. Although the presented control strategy overcomes previously unsolved problems and enables the systematic development of advanced designs for a broader system class, it has also given rise to numerous challenges and interesting problems for future research
A Novel Virtual Planned-Orthodontic-Surgical Approach for Proportional Condylectomy in Condylar Hyperplasia
Full text linkBackground/Objectives: Condylectomy is a delicate and intricate procedure
commonly employed in the management of temporomandibular joint (TMJ) disorders,
osteochondromas, condylar hyperplasia, hemimandibular hyperplasia, and other pathologies affecting the condylar region. The advent of surgical cutting guides has introduced
a new dimension to condylectomy procedures as they enable surgeons to plan and execute precise cuts with a heightened level of accuracy. In the literature already exists
cases of cutting guide-based condylectomy, but they only depend on the mere mirroring
procedure in virtual planning, which has accuracy limitations because it does not consider
asymmetry of peri-condylar structures at the level of the ramus, body, and mandibular
angle. Methods: CAD-CAM orthodontic preparation through the NEMOFAB Software
was performed to correct the canting of the occlusal plane, following the “orthodontic first”
technique. The same software was used for VSP of the surgical cutting guide to perform
the condylectomy, basing not to the mere mirroring of the opposite side but considering
the whole condylar-TMJ-glenoid fossa structure. Results: At 6 months follow-up, the
patient showed good occlusion and an almost totally recovered lower third symmetry as
median-upper and lower interincisive lines coincide with each other and with the chin
median. A good occlusal and masticatory outcome was obtained. The joint structure
was preserved with remodeling of the glenoid cavity caused by the presence of the joint
disc, which was preserved during surgery. Conclusions: The goal of this study is to
propose a method of therapeutic management of condylar hyperplasia that benefits from
accurate pre-operative orthodontic treatment (orthodontics first) to maximize the results
of proportional condylectomy, reducing post-operative orthodontic care as well as any
need for any adjuvant orthognathic surgery. A new virtual surgical planning method is
also proposed for creating a cutting guide that not only takes advantage of the mirroring
technique to accurately calculate the amount of condyle to be cut but also considers the
entire condyle–TMJ complex to perform a condylectomy that is more precise
A 14-year-old child with a benign osteoma tumor in the external ear canal: a rare case report
Full text linkIntroduction: A benign osteoma is a non-cancerous bone tumor in the external ear canal that can cause hearing loss. Treatment may require surgery if symptoms arise. Case presentation: A 14-year-old child severed right ear pain, thick discharge, and hearing loss for a week after unsuccessful treatment elsewhere. Examination showed swollen ear canal and purulent discharge. After antibiotic treatment, thick debris remained. The osteoma was excised through its pedicle to minimize the risk of recurrence. Clinical discussion: Osteomas are benign ear growths that can cause hearing loss and blockage. Severe symptoms may require surgery, with the endoscopic transcanal method being effective for osteomas. Blockage can also occur from wax buildup or foreign bodies, potentially leading to cholesteatoma. Osteomas are typically asymptomatic and identified through CT scans, predominantly located in the external auditory canal (EAC). Surgery is advised for symptomatic cases, while regular check-ups are recommended for asymptomatic patients. Conclusion: Additional research is necessary to fully comprehend the causes and optimal treatment strategies for benign osteoma in the EAC