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Magnetic Resonance (MR) elastography is a method for measuring tissue elasticity via phase images acquired with an MR scanner. The propagation of periodic mechanical waves through the tissue can be captured by means of a modified phase contrast sequence. These waves are generated with a mechanical oscillator (actuator) and coupled into the tissue through the skin. The actuator must be capable of generating a sinusoidal excitation with excellent phase and amplitude stability, while not disturbing the MR imaging process. In this work, an actuator based on a piezoelectric principle was developed. Based on the imaging evaluation of several material samples, the housing for the piezoelectric ceramic was constructed of aluminum. Smaller parts of the housing were manufactured from brass and titanium to fulfill the mechanical constraints. A lever was used to transfer the oscillation generated by the piezoelectric ceramic to the point of excitation. The lever amplifies the piezoelectric motion, allowing for a more compact design. Three different lever designs were characterized by an acceleration sensor both outside and inside the magnet. It was shown that the rigidity of the lever, as determined by its material and form, was decisive in determining the resonant frequency of the system and therefore the maximum practical frequency of operation. It was also shown that the motion of the oscillator is unaffected by the electromagnetic fields of the MR imager. The final design can be placed directly in the magnet bore within a few centimeters of the tissue volume to be imaged without generating significant artifacts. An amplitude range of 0–1 mm in the frequency range from 0 to over 300 Hz was achieved, sufficient for performing most MR elastography applications. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 239–254, 2002
Men afflicted with hypogonadism have reduced fat-free mass and in some cases a loss in muscle strength. We hypothesize that muscle elasticity of the lower extremities differs between patients with hypogonadism and healthy controls. The shear modulus of the soleus muscle was measured non-invasively using MR elastography (MRE) at 0%, 5%, 10%, 15%, and 20% of the subject’s maximum applied force. The results from this study showed statistical differences between the patients and controls, even though there were no statistical differences in applied force.
Men afflicted with chronic obstructive pulmonary disease (COPD) show signs of muscle dysfunction, such as increased muscle fatigue and acidosis during exercise. We hypothesize that muscle elasticity of the lower extremities differs between patients with COPD and age-related controls. The shear modulus of the soleus muscle was measured non-invasively using MR elastography (MRE) at 0%, 5%, 10%, 15%, and 20% of the subject’s maximum applied force. The results from this study showed statistical differences between the patients and controls, even though there were no statistical differences in the maximum applied force.
The Chylla–Haase polymerization reactor is widely accepted as a benchmark process for the evaluation of control strategies for batch reactors. In this contribution a control concept based on Exact I/O-Linearization is proposed and compared to a conventional cascade control structure. In order to adapt the exact linearization control strategy to various polymerization products and batch conditions, an advanced probabilistic inference algorithm (Sigma-Point Kalman Filter) is applied and investigated. Sigma-Point Kalman Filters have the major improvement of simplified implementation compared to local linearization methods (i.e. Extended Kalman Filter) because no analytical Jacobians are required. Stochastic simulation studies are introduced and show the effectiveness, accuracy and benefit of the control concept. Within several scenarios a satisfying robustness against structural errors in the underlying model equations for the nonlinear control law and the inference algorithm is demonstrated. Furthermore it is pointed out, that with little effort in reassembling the plant design, control performance can be improved significantly.
Stability and cost optimality of power generation and supply systems must not be considered independently from one another. Simple examples show that optimizing cost without considering stability may result in modes of operation that, while economically optimal, are unstable. We demonstrate that stability, robustness, and optimality can be considered systematically and simultaneously by combining bifurcation theory and nonlinear optimization. Essentially, the proposed method enforces a backoff distance between the optimal point of operation and operational or stability boundaries in the space of the optimization variables, where bifurcation theory is used to describe nonlinear stability boundaries.
We present a control scheme for a parabolic trough power plant that is equipped with a molten salt thermal energy storage system. We show that the multivariable control problem for the solar field can be decoupled by controlling the three way valve that splits the heat transfer fluid between the storage system and the steam generator. The steam generation cycle is regulated with inlet pressure control. The subsystems of the plant are modeled based on first principles, where we focus on the steam generation cycle. A multi-group extraction turbine with pre- and reheater is considered, which is suitable for solar power plants. We demonstrate the benefits of the proposed control scheme with a day-to-day simulation.
We derive a nonlinear model of the steam cycle of a solar power plant, estimate its unknown parameters with measured data, and design a linear model predictive controller based on the resulting model. Simulations show that the linear model predictive controller is able to regulate the electrical power of the nonlinear steam process of the plant to a given reference trajectory very well. Moreover, it results in very good disturbance rejection.
The synthesis of Nb-doped TiO2 nanoparticles by spray drying: an efficient and scalable method
(2011)
The rock material pentlandite with the composition Fe4.5Ni4.5S8 was synthesized via high temperature synthesis from the elements. The structure and composition of the material was characterized via powder X-ray diffraction (PXRD), Mössbauer spectroscopy (MB), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and energy dispersive X-ray spectroscopy (EDX). Two preparation methods of pentlandite bulk electrodes are presented. In the first approach a piece of synthetic pentlandite rock is directly contacted via a wire ferrule. The second approach utilizes pentlandite pellets, pressed from finely ground powder, which is immobilized in a Teflon casing. Both electrodes, whilst being prepared by an additive-free method, reveal high durability during electrocatalytic conversions in comparison to common drop-coating methods. We herein showcase the striking performance of such electrodes to accomplish the hydrogen evolution reaction (HER) and present a standardized method to evaluate the electrocatalytic performance by electrochemical and gas chromatographic methods. Furthermore, we report stability tests via potentiostatic methods at an overpotential of 0.6 V to explore the material limitations of the electrodes during electrolysis under industrial relevant conditions.
Small and large deformation analysis with the p- and B-spline versions of the Finite Cell Method
(2012)
A new robust design for imperfection sensitive stiffened cylinders used in aerospace engineering
(2015)
Computational models for the personalized analysis of human femurs contain uncertainties in bone material properties and loads, which affect the simulation results. To quantify the influence we developed a probabilistic framework based on polynomial chaos (PC) that propagates stochastic input variables through any computational model. We considered a stochastic E-ρ relationship and a stochastic hip contact force, representing realistic variability of experimental data. Their influence on the prediction of principal strains (ϵ1 and ϵ3) was quantified for one human proximal femur, including sensitivity and reliability analysis. Large variabilities in the principal strain predictions were found in the cortical shell of the femoral neck, with coefficients of variation of ≈40%. Between 60 and 80% of the variance in ϵ1 and ϵ3 are attributable to the uncertainty in the E-ρ relationship, while ≈10% are caused by the load magnitude and 5-30% by the load direction. Principal strain directions were unaffected by material and loading uncertainties. The antero-superior and medial inferior sides of the neck exhibited the largest probabilities for tensile and compression failure, however all were very small (pf<0.001). In summary, uncertainty quantification with PC has been demonstrated to efficiently and accurately describe the influence of very different stochastic inputs, which increases the credibility and explanatory power of personalized analyses of human proximal femurs.
Multi-level hp-finite cell method for embedded interface problems with application in biomechanics
(2018)
This work presents a numerical discretization technique for solving 3-dimensional material interface problems involving complex geometry without conforming mesh generation. The finite cell method (FCM), which is a high-order fictitious domain approach, is used for the numerical approximation of the solution without a boundary-conforming mesh. Weak discontinuities at material interfaces are resolved by using separate FCM meshes for each material sub-domain and weakly enforcing the interface conditions between the different meshes. Additionally, a recently developed hierarchical hp-refinement scheme is used to locally refine the FCM meshes to resolve singularities and local solution features at the interfaces. Thereby, higher convergence rates are achievable for nonsmooth problems. A series of numerical experiments with 2- and 3-dimensional benchmark problems is presented, showing that the proposed hp-refinement scheme in conjunction with the weak enforcement of the interface conditions leads to a significant improvement of the convergence rates, even in the presence of singularities. Finally, the proposed technique is applied to simulate a vertebra-implant model. The application showcases the method's potential as an accurate simulation tool for biomechanical problems involving complex geometry, and it demonstrates its flexibility in dealing with different types of geometric description.
Innovative thinking opens up new growth prospects in mechanical and plant engineering. Mechanical and plant engineering has been traditionally very important to the industrial location of Germany [1]. With an export share of 70%, it has a considerable direct influence on economic structure and job market. In addition, mechanical engineering is the “innovation engine” for other core industries in Germany – as supplier of production equipment for industries such as the car manufacture, plastics processing and electrical engineering sectors. Only through this production equipment can innovative products reach production readiness in the first place, and can “Made in Germany” continue to enjoy an excellent reputation all over the world.
Documents are supporting pillars of information and communication within and between companies. An electronically supported document management, which fulfils the company requirements, makes it possible to quickly and efficiently collect the required information objects and to reliably find them again. Document management serves as a core, from which the knowledge management of a company can be developed continuously.
Archimedes sollte herausfinden, ob die Krone von Hieron II tatsächlich aus Gold sei. Das spezifische Gewicht von Gold war ihm bekannt, aber für die Bestimmung des Goldgehalts musste er das Volumen der Krone berechnen. Er dachte mehrere Tage darüber nach. Doch erst als er ein Bad nahm und beobachtete, wie sein Körper das Wasser verdrängte, erkannte er, dass er das Volumen der Krone über ihre Wasserverdrängung bestimmen konnte. Er rief: Heureka! ? Ich hab´s gefunden! Archimedes ist damit zum Sinnbild für plötzliche Geistesblitze geworden. Doch warum ist er nicht sofort auf die Lösung gekommen?
Vitaler Wissensaustausch
(2008)
Schätzungen zufolge besitzen ein Viertel bis ein Drittel der Mitarbeiter eines Unternehmens unverzichtbares Experten-Know-how. Keine Organisation kann es sich heutzutage leisten, dieses Wissen nicht oder auch nur unvollständig zu nutzen. Darüber hinaus führt der demografische Wandel in Deutschland dazu, dass dieses Wissen den Unternehmen zunehmend verloren geht, wenn sie keinen vitalen Wissensaustausch betreiben.
Die Hauptaufgabe des Unternehmers ist es, das operative Tagesgeschäft und die strategische Ausrichtung des Unternehmens unter einen Hut zu bekommen. Selbst wenn ein Unternehmen das beste Produkt hat, wird es nur dann langfristig erfolgreich sein, wenn es auch eine tragfähige Strategie besitzt, welche die Richtung für die Zukunft vorgibt.
Der österreichische Psychotherapeut Paul Watzlawick hat einmal in einem Interview gesagt, dass Menschen in beratenden Berufen - seien es nun Psychotherapeuten oder Unternehmensberater - in Bezug auf ihre Klienten vor einer paradoxen Anforderung stünden. Die Anforderung lautet: "Ändere mich, ohne mich zu ändern". Das heißt, der Klient würde zwar gerne sein Problem lösen, aber nicht auf Kosten einer Veränderung des Status quo. Vor einer ähnlich paradoxen Anforderung stehen Innovatoren im Unternehmen. Die Anforderung, die dort gestellt wird, lautet: "Betreibe Innovation, ohne zu erneuern". Das bedeutet, dass Unternehmen sich gerne Innovationen wünschen, aber wiederum nicht auf Kosten einer Veränderung des status quo.
Bereits Joseph Alois Schumpeter – der von einem seiner Biografen auch der „Prophet of Innovation“ genannt wird – nennt in seinem 1912 erschienenen Buch „Theorie der wirtschaftlichen Entwicklung“, einem seiner Hauptwerke, neben der reinen Produktinnovation folgende weitere Möglichkeiten zur Innovation: neue Produktionsmethoden, neue Absatzmärkte, neue Beschaffungsmärkte und neue Organisationen.
In Zeiten zunehmender Marktdynamik und kürzer werdender Innovationszyklen fragen sich viele Unternehmen: Wie können wir das kreative Potenzial unserer eigenen Mitarbeiter besser nutzen? Denn es gibt sie in jeder Organisation: Leute, die das radikal Neue nicht nur denken, sondern auch umsetzen wollen.
Bisher findet man in der Literatur nur vereinzelt Ansätze, wie Nachhaltigkeit in eine Supply Chain implementiert werden kann. Dieser Artikel skizziert ein theoretisches Grundgerüst einer nachhaltigen Supply Chain, um darauf aufbauend ein ‚Green Logistics Framework ' zu entwickeln, in dem mögliche Maßnahmen aufgezeigt werden, die hin zum Lieferanten-und Kundenmarkt eine optimale Steuerung der Supply Chain im Sinne des 6-Märkte-Modells unterstützen. Entschei-dungsträgern wird eine umfassende Toolbox an die Hand gegeben, um ein nachhaltiges Logis-tigkonzept im Sinne der unternehmerischen Zielsetzung umsetzen zu können. Stellschrau-ben finden sich im Bereich des nachhaltigen Transportmanagements, des nachhaltigen Lagerhausmanagements sowie des nachhaltigen Verpackungsmanagements. Im Rahmen des nachhaltigen Transportmanagements gilt es u. a. Transporte zu vermeiden , Transportmengen zu vermindern oder Transportschädlichkeit zu verringern. Welcher Ressourcenverbrauch und welche Aspekte der Umweltverträglichkeiten in den einzelnen Teilbereichen zu berücksichtigen sind und wie man negativen ökologischen Auswirkungen begegnet, steht im Fokus dieses Beitrags.
eFood in Deutschland
(2015)
Im Vergleich zu „Pionierbranchen“ wie Mode oder Medien steht der Online-Handel mit Lebensmitteln erst am Anfang. Dabei kann dieser zu einem Wettbewerbsvorteil werden – wenn der Handel es richtig angeht. Auf der anderen Seite steht das Risiko einer strategischen Falle, d.h. es wird unter Umständen aufgrund der Widerstände beim Verbraucher nur ein Nischenmarkt bedient, der eine geringe Profitabilität aufweist. Im Spannungsfeld „Marktpotenzial auf Handelsseite“ vs. „Zurückhaltung beim Verbraucher“ rücken dabei Fragen der Kommunikationspolitik im Online-Lebensmittelhandel in den Fokus. Für eine erfolgreiche Umsetzung stellt eine eindeutige Typologie eine notwendige Basis dar, um die konkreten Bedürfnisse potenzieller Konsumenten anzusprechen. Ein Engagement im eFood-Bereich ist daher als Investition in die zukünftige Entwicklung der Märkte und ihrer Zielgruppen zu betrachten. Although online trading in the food sector is still in early stages, it may become a competitive edge – if retailers go about it the right way. On the other hand, due to consumer resistance, there is the risk of serving only a niche market, which cannot be maintained in terms of profitability. Therefore, a stronger focus on communication policies is needed. Engaging in the eFood sector finally has to be seen as an important investment into future markets and their target groups. Keywords: online lebensmittelhandel, lieferfenster, informationszeitalter, face to the customer
Die Definition der individuellen Kreativität basiert auf einem fundamentalen Spannungsverhältnis zwischen Neuartigkeit und Originalität auf der einen Seite sowie Nützlichkeit und Angemessenheit auf der anderen Seite. Man kann in Anlehnung an den Welle-Teilchen-Dualismus des Lichtes auch von einem Originalitäts-Effektivitäts-Dualismus der Kreativität sprechen. Diese zweiteilige Serie betrachtet die Auswirkungen dieses Spannungsverhältnisses auf den kreativen Prozess und die Komponenten der Kreativität. In diesem ersten Teil wird das Spannungsverhältnis des kreativen Prozesses aus Handeln und Geschehen-Lassen betrachtet. In der nächsten Ausgabe folgt ein Beitrag über die Spannungsfelder der Komponenten der Kreativität nach Amabile: Expertise, kreative Denkfertigkeiten und Motivation. Zur Darstellung dieser Sachverhalte wird das Wertequadrat nach Helwig (1967) und Schulz von Thun (1998) verwendet, in dem ein Wert ins Verhältnis mit seinem positiven Gegenwert gesetzt wird. Dadurch können bzgl. des kreativen Prozesses die negativen Auswirkungen operativer Hektik in Form einer „Culture of Looking Busy“ und Implikationen für das individuelle Zeitmanagement abgeleitet werden.
Die Definition der individuellen Kreativität basiert auf einem fundamentalen Spannungsverhältnis zwischen Neuartigkeit und Originalität auf der einen Seite sowie Nützlichkeit und Angemessenheit auf der anderen Seite. Man kann in Anlehnung an den Welle-Teilchen-Dualismus des Lichtes auch von einem Originalitäts-Effektivitäts-Dualismus der Kreativität sprechen. Diese zweiteilige Serie betrachtet die Auswirkungen dieses Spannungsverhältnisses auf den kreativen Prozess und die Komponenten der Kreativität. Im ersten Teil wurde bereits das Spannungsverhältnis des kreativen Prozesses aus Handeln und Geschehen-Lassen betrachtet. In diesem Beitrag werden die Spannungsfelder der Komponenten der Kreativität nach Amabile behandelt: Expertise, kreatives Denken und Motivation. Zur Darstellung dieser Sachverhalte wird das Wertequadrat nach Helwig und Schulz von Thun verwendet, in dem ein Wert ins Verhältnis mit seinem positiven Gegenwert gesetzt wird. Dadurch können bzgl. der Komponenten der Kreativität Verbesserungsmaßnahmen abgeleitet und ein morphologischer Kasten der Kreativität aufgestellt werden.
A central question for managers in charge of innovation is to what extent creativity and inno-vation can be controlled and supervised, or whether they just have to be set free and allowed to take shape. In assessing this dilemma the authors conclude that there is a contradiction of action versus inaction on the personal level as well as a contradiction of control versus loss of control on the organizational level. What European innovators can learn from philosophical Daoism is an attitude that allows a process to just develop “naturally” and refrains from prem-ature interference with the intention to permanently be in control. In business structures that judge everything according to its usefulness, i.e. profitability for the company, a look at the laid-back attitude of Daoism where usefulness and uselessness are relative qualities might relief the pressure on people to perform in a premeditated way. Innovation can be supported, but creativity cannot be forced. It can only be allowed to happen when control, interference, and action are balanced out with non-interference, and go-with-the-flow. This attitude in not an excuse for stressed-out managers to neglect their duty, but a time honoured worldview of one of the oldest civilizations in the world that can give them the sovereignty to “get out of the way” and let innovation happen.
The standard definition of individual creativity is based on a tension between originality on the one side and effectiveness (usefulness and appropriateness) on the other side. In this article this tension is called the originality-effectiveness duality of creativity. The article explores how this duality pervades the componential theories of creativity. To analyze the components of creativity with regard to their tensions, the so called value square (“Wertequadrat”) developed by Helwig (1967) and Schulz von Thun (1998) is used. The value square explains each component as a dynamic equilibrium and shows how a positive value is balanced with its positive countervalue. Tensions of mindfulness, precision and ambiguity, as well as immersion and detachment are identified permeating the components of creativity. This article explores the implications these tensions have for creativity research and for businesses in a creative economy.