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This contribution discusses the utilization of RF power in an MRI system with RF mode shimming which enables the superposition of circularly polarized modes of a transmit RF coil array driven by a Butler matrix. Since the required power for the individual modes can vary widely, mode-shimming can result in a significant underutilization of the total available RF power. A variable power combiner (VPC) is proposed to improve the power utilization: it can be realized as a reconfiguration of the MRI transmit system by the inclusion of one additional matrix network which receives the power from all transmit amplifiers at its input ports and provides any desired (combined) power distribution at its output ports by controlling the phase and amplitude of the amplifiers’ input signals. The power distribution at the output ports of the VPC is then fed into the “mode” ports of the coil array Butler matrix in order to superimpose the spatial modes at the highest achievable power utilization. The VPC configuration is compared to the standard configuration of the transmit chain of our MRI system with 8 transmit channels and 16 coils. In realistic scenarios, improved power utilization was achieved from 17% to 60% and from 14% to 55% for an elliptical phantom and a region of interest in the abdomen, respectively, and an increase of the power utilization of 1 dB for a region of interest in the upper leg. In general, it is found that the VPC allows significant improvement in power utilization when the shimming solution demands only a few modes to be energized, while the technique can yield loss in power utilization in cases with many modes required at high power level.
Energieeffizienz und Energiemanagement : ein Überblick heutiger Möglichkeiten und Notwendigkeiten
(2012)
Light-addressable potentiometric sensors (LAPS) are field-effect-based sensors. A modulated light source is used to define the particular measurement spot to perform spatially resolved measurements of chemical species and to generate chemical images. In this work, an organic-LED (OLED) display has been chosen as a light source. This allows high measurement resolution and miniaturisation of the system. A new developed driving method for the OLED display optimised for LAPS-based measurements is demonstrated. The new method enables to define modulation frequencies between 1 kHz and 16 kHz and hence, reduces the measurement time of a chemical image by a factor of 40 compared to the traditional addressing of an OLED display.
The construction of a statistical test is investigated which is based only on “reliability” and “precision” as quality criteria. The reliability of a statistical test is quantifiedin a straightforward way by the probability that the decision of the test is correct. However, the quantification of the precision of a statistical test is not at all evident. Thereforethe paper presents and discusses several approaches. Moreover the distinction of “nullhypothesis” and “alternative hypothesis” is not necessary any longer.
Chemical imaging systems allow the visualisation of the distribution of chemical species on the sensor surface. This work represents a new flexible approach to read out light-addressable potentiometric sensors (LAPS) with the help of a digital light processing (DLP) set-up. The DLP, known well for video projectors, consists of a mirror-array MEMS device, which allows fast and flexible generation of light patterns. With the help of these light patterns, the sensor surface of the LAPS device can be addressed. The DLP approach has several advantages compared to conventional LAPS set-ups, e.g., the spot size and the shape of the light pointer can be changed easily and no mechanical movement is necessary, which reduces the size of the set-up and increases the stability and speed of the measurement. In addition, the modulation frequency and intensity of the light beam are important parameters of the LAPS set-up. Within this work, the authors will discuss two different ways of light modulation by the DLP set-up, investigate the influence of different modulation frequencies and different light intensities as well as demonstrate the scanning capabilities of the new set-up by pH mapping on the sensor surface.
This work describes the novel combination of the light-addressable electrode (LAE) and the light-addressable potentiometric sensor (LAPS) into a microsystem set-up. Both the LAE as well as the LAPS shares the principle of addressing the active spot by means of a light beam. This enables both systems to manipulate resp. to detect an analyte with a high spatial resolution. Hence, combining both principles into a single set-up enables the active stimulation e.g., by means of electrolysis and a simultaneous observation e.g., the response of an entrapped biological cell by detection of extracellular pH changes. The work will describe the principles of both technologies and the necessary steps to integrate them into a single set-up. Furthermore, examples of application and operation of such systems will be presented.
The assessment of the right ventricle (RV) is a challenge in today's cardiology, but of growing clinical impact regarding patient prognosis in different cardiac diseases. The detection and differentiation of small wall motion abnormalities may help to enhance the differentiation of cardiomyopathies including Arrhythmogenic Rightventricular Cardiomyopathy. Cardiovascular magnetic resonance (CMR) at 1.5T is the accepted gold standard for RV quantification. The higher spatial resolution achievable at ultrahigh field strength (UHF) offers the potential to gain new insights into the structure and function of the RV. To approach this goal accurate RV chamber quantification at 7T has to be proven. Consequently this study examines the feasibility of assessment of RV dimensions and function at 7T using improved spatial resolution enabled by the intrinsic sensitivity gain of UHF CMR. For this purpose, a dedicated 16 channel TX/RX RF coil array is used together with 2D CINE fast gradient echo (FGRE) imaging. For comparison RV chamber quantification is conducted at 1.5T using a SSFP based state of the art clinical protocol.
The interest in PET detectors with monolithic block scintillators is growing. In order to obtain high spatial resolutions dedicated positioning algorithms are required. But even an ideal algorithm can only deliver information which is provided by the detector. In this simulation study we investigated the light distribution on one surface of cuboid LSO scintillators of different size. Scintillators with a large aspect ratio (small footprint and large height) showed significant position information only for a minimum interaction depth of the gamma particle. The results allow a quantitative estimate for a useful aspect ratio.
In the introduction to their book "What is philosophy?" Gilles Deleuze and Felix Guattari deplore the inflationary and trivialised use of the term concept: "Finally, the most shameful moment came when computer science, marketing, design and advertising, all the disciplines of communication, seized hold of the word concept itself and said: 'This is our concern, we are the creative ones, we are the ideas men! We are the friends of the concept, we put in our computers.' " This doctoral thesis shares the concern of Gilles Deleuze and Felix Guattari, but still, it is a thesis in architecture and thus collocated within the field of the representatives of the "ideas men". It engages in architectural design theory, and refers in particular to the investigation of methodological approaches within the design process. Therefore, the thesis will not contribute to the philosophical dimension of the term, but intends to overcome its imprecise use within the architectural discourse, in compliance with Eugène Viollet-le-Duc's admonition relative to vague definitions: "Dans les arts, et dans l'architecture en particulier, les définitions vagues ont causé bien des erreurs, ont laissé germer bien des préjugés, enraciner bien des idées fausses. On met un mot en avant, chacun y attache un sens différent." The term concept in architecture is very often used as pure marketing collateral, it serves to sell an idea, a product, a design. Its functional applicability is reduced to a special manner of illustration, produced as one of the various design presentation documents at the end of the design process. In contrast, the original contribution of this thesis aims to give a precise, instrumental dimension to the term concept: the concept is the expression of a specific logic, capable to guide the decisional sequences of the process and thus to improve the quality of the designed projects. The motivation to define a specific instrumentality of the concept is closely connected to the issue of interdisciplinarity in the architects’ profession. The interdisciplinary character of the architectural field is widely accepted and discussed as such, but the thesis intends to give a more precise definition of the various kinds of competences involved by classifying them into either the internal or the external group. The traditional notion of interdisciplinarity, predominantly seen as collaboration between architects and technical experts, and, most notably, the historical, sometimes contentious, relationship between architects and engineers is described. Referring to recent developments, the transformation of the architect’s role within the professional sphere, marked by an increasing importance of diverse influences and linked to a growing risk of marginalisation, is illustrated. The thesis describes different ways to adapt to this specific kind of interdisciplinarity, which generally requires the architect’s ability to connect and to integrate various contents, different points of view and diverse scales. On the other hand, the big potential which is implicit in the interdisciplinary field is exposed: architects can inform their core competence, the design, by extracting contents of different disciplinary competences, pertaining or not pertaining to their own professional field. They have the possibility to cross fields of external competences in a selective way and by doing so they can build up a corpus of knowledge capable to generate and communicate guidelines and systematic methodologies for their design. At the end, the analysis of these two aspects allows the definition of a more specific professional profile of the architect as specialist of interdisciplinarity. The thesis is concerned with the theories around the design process. The design process is seen as open to inspection and critical evaluation, with major focus on the decisional sequences which characterise it. It concentrates on the process’ descriptiveness and the degree of self-conscious approaches applied within it. The importance of regulative, strategic mechanisms is illustrated by testimonies taken from a series of design researches and leads to the functional definition of the figure of the concept as representation of a coherent set of ideas, as generator of a project-specific system of rules and as communicator of decisional strategies. The concept's function is furthermore defined as communicative interface which generates and transmits the system of rules authoritative for all the disciplinary competences involved in the design process, a communicative interface which constitutes a basis of shared convictions capable to increase the efficiency of collaboration. Furthermore, the concept's capacity to explore and elaborate the contents of external disciplines is identified as a possible methodological approach to innovative design thinking. The approach to a specific functional definition of the concept is continued by the description of a series of instruments that are simultaneously generating and communicating it. It is outlined to which degree the concept itself is already the result of an ideational process, collocated within the initial phase of the design proceedings, serving as a guideline to them, but still continuously evolving and adapting in its progression. In addition, it is illustrated how all the diverse instruments of the concept are operational media through which the knowledge transition between different disciplines can occur. The considerations about the concept as operational instrument of design are elaborated with regard to a number of examples of didactical applications that are particularly involved in the development and teaching of specific design methods. These examples illustrate the interrelations between design theory and design education. They are derived from very different schools of architecture and diverse mindsets, but all of them transmit models of conceptual design thinking.
Thermodynamic stability, configurational motions and internal forces of haemoglobin (Hb) of three endotherms (platypus, Ornithorhynchus anatinus; domestic chicken, Gallus gallus domesticus and human, Homo sapiens) and an ectotherm (salt water crocodile, Crocodylus porosus) were investigated using circular dichroism, incoherent elastic neutron scattering and coarse-grained Brownian dynamics simulations. The experimental results from Hb solutions revealed a direct correlation between protein resilience, melting temperature and average body temperature of the different species on the 0.1 ns time scale. Molecular forces appeared to be adapted to permit conformational fluctuations with a root mean square displacement close to 1.2 Å at the corresponding average body temperature of the endotherms. Strong forces within crocodile Hb maintain the amplitudes of motion within a narrow limit over the entire temperature range in which the animal lives. In fully hydrated powder samples of human and chicken, Hb mean square displacements and effective force constants on the 1 ns time scale showed no differences over the whole temperature range from 10 to 300 K, in contrast to the solution case. A complementary result of the study, therefore, is that one hydration layer is not sufficient to activate all conformational fluctuations of Hb in the pico- to nanosecond time scale which might be relevant for biological function. Coarse-grained Brownian dynamics simulations permitted to explore residue-specific effects. They indicated that temperature sensing of human and chicken Hb occurs mainly at residues lining internal cavities in the β-subunits.
Upper and lower bound theorems of limit analyses have been presented in part I of the paper. Part II starts with the finite element discretization of these theorems and demonstrates how both can be combined in a primal–dual optimization problem. This recently proposed numerical method is used to guide the development of a new class of closed-form limit loads for circumferential defects, which show that only large defects contribute to plastic collapse with a rapid loss of strength with increasing crack sizes. The formulae are compared with primal–dual FEM limit analyses and with burst tests. Even closer predictions are obtained with iterative limit load solutions for the von Mises yield function and for the Tresca yield function. Pressure loading of the faces of interior cracks in thick pipes reduces the collapse load of circumferential defects more than for axial flaws. Axial defects have been treated in part I of the paper.
Suburethral slings as well as different meshes are widely used treating stress urinary incontinence and prolaps in women. With the development of MiniSlings and special meshes using less alloplastic material anchorage systems become more important to keep devices in place and to put some tension especially on the MiniSlings. To date, there are many different systems of MiniSlings of different companies on the market which differ in the structure of the used meshes and anchors. A new objective measurement method to compare different properties of MiniSling systems (mesh and anchor) is presented in this article. Ballistic gelatine acts as soft tissue surrogate. Significant differences in parameters like pull-out strength of anchors or shrinkage of meshes under loading conditions have been determined. The form and size of the anchors as well as the structural stability of the meshes are decisive for a proper integration. The tested anchorings sytems showed markedly different mechanical function at their respective load bearing capacity. As the stable fixation of the device in tissue is a prerequisite for a permanet reinforcement, the proposed test system permits further optimisation of anchor and mesh devices to improve the success of the surgical treatment