Computersimulation zur Verifizierung und Präsentation eines automatisch gesteuerten Mamma-Biopsiesystems

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Die computerunterstützte Simulations- und Animationstechnik ist ein allgemein anerkanntes Hilfsmittel bei der Planung und Realisierung von technischen Systemen. Der Schwerpunkt des Simulations- und Animationseinsatzes lag ursprünglich nur auf der Planungsabsicherung. Zunehmend wird die Simulation und Animation durchgängig in allen Phasen des Planungs- und Realisierungsprozesses genutzt. In einem Forschungsprojekt wurde eine neuartige automatisch gesteuerte Einrichtung zur präzisen Navigation medizinischer Instrumente innerhalb von MRTomographen, insbesondere zur histologischen Sicherung von Kleintumoren, entwickelt. Die gesamte Einrichtung läßt sich gemeinsam mit einem Patienten im Untersuchungsbereich eines MR-Tomographen positionieren. Mittels einer SD-Simulation wie auch Animation konnte eine Überprüfung und Optimierung des komplexen Gesamtsystems, d.h. der einzelnen Systemkomponenten und deren kinematischen Bewegungsabläufe erfolgen. Desweiteren wurde damit eine Grundlage für die Erstellung einer Präsentationsvorlage realisiert, um der Öffentlichkeit die einzelnen Ablaufvorgänge einfach und plausibel darzustellen und zukünftige Anwender in dieses System schnell einzuweisen

Interplay of shear and bulk viscosity in generating flow in heavy-ion collisions

We perform viscous hydrodynamic calculations in 2+1 dimensions to investigate the influence of bulk viscosity on the viscous suppression of elliptic flow in non-central heavy-ion collisions at RHIC energies. Bulk and shear viscous effects on the evolution of radial and elliptic flow are studied with different model assumptions for the transport coefficients. We find that the temperature dependence of the relaxation time for the bulk viscous pressure, especially its critical slowing down near the quark-hadron phase transition at T_c, partially offsets effects from the strong growth of the bulk viscosity itself near T_c, and that even small values of the specific shear viscosity eta/s of the fireball matter can be extracted without large uncertainties from poorly controlled bulk viscous effects.Comment: 13 pages, 7 figures, 1 table. Submitted to Physical Review C. v2: corrected typos in several entries in Table

Optimal control of number squeezing in trapped Bose-Einstein condensates

We theoretically analyze atom interferometry based on trapped ultracold atoms, and employ optimal control theory in order to optimize number squeezing and condensate trapping. In our simulations, we consider a setup where the confinement potential is transformed from a single to a double well, which allows to split the condensate. To avoid in the ensuing phase-accumulation stage of the interferometer dephasing due to the nonlinear atom-atom interactions, the atom number fluctuations between the two wells should be sufficiently low. We show that low number fluctuations (high number squeezing) can be obtained by optimized splitting protocols. Two types of solutions are found: in the Josephson regime we find an oscillatory tunnel control and a parametric amplification of number squeezing, while in the Fock regime squeezing is obtained solely due to the nonlinear coupling, which is transformed to number squeezing by peaked tunnel pulses. We study splitting and squeezing within the frameworks of a generic two-mode model, which allows us to study the basic physical mechanisms, and the multi-configurational time dependent Hartree for bosons method, which allows for a microscopic modeling of the splitting dynamics in realistic experiments. Both models give similar results, thus highlighting the general nature of these two solution schemes. We finally analyze our results in the context of atom interferometry.Comment: 17 pages, 21 figures, minor correction

Critical systems heuristics

Critical systems heuristics (CSH) is a framework for reflective professional practice organised around the central tool of boundary critique. This paper, written jointly by the original developer, Werner Ulrich, and Martin Reynolds, an experienced practitioner of CSH, offers a systematic introduction to the idea and use of boundary critique. Its core concepts are explained in detail and their use is illustrated by means of two case studies from the domain of environmental planning and management. A particular focus is on working constructively with tensions between opposing perspectives as they arise in many situations of professional intervention. These include tensions such as ‘situation’ versus ‘system’, ‘is’ versus ‘ought’ judgements, concerns of ‘those involved’ versus ‘those affected but not involved’, stakeholders’ ‘stakes’ versus ‘stakeholding issues’, and others. Accordingly, boundary critique is presented as a participatory process of unfolding and questioning boundary judgements rather than as an expert-driven process of boundary setting. The paper concludes with a discussion of some essential skills and considerations regarding the practice of boundary critique. Parts of the account of the NRUA-Botswana study in Section 6.2 of the present paper are reproduced from an earlier publication by one of the authors (Reynolds 2007); we are grateful to the publishers of Edge Press, Point Reyes, CA, for granting us permission to reproduce this material. We do not need the systems concept at all if we are not interested in handling systems boundaries critically

Charm Quark Contribution to K+ -> pi+ nu anti-nu at Next-to-Next-to-Leading Order

We calculate the complete NNLO QCD corrections to the charm contribution of the rare decay K+ -> pi+ nu nu-bar. We encounter several new features, which were absent in lower orders. We discuss them in detail and present the results for the 2-loop matching conditions of the Wilson coefficients, the 3-loop anomalous dimensions, and the 2-loop matrix elements of the relevant operators that enter the NNLO renormalization group analysis of the Z-penguin and the electroweak box contribution. The inclusion of the NNLO QCD corrections leads to a significant reduction of the theoretical uncertainty from 9.8% down to 2.4% in the relevant parameter Pc, implying the leftover scale uncertainties in BR(K+ -> pi+ nu nu-bar) and in the determination of |V_td|, sin(2 beta), and gamma from the K -> pi nu nu system to be 1.3%, 1.0%, 0.006, and 1.2 degrees, respectively. For the charm quark MSbar mass mc=(1.30+-0.05) GeV and |V_us|= 0.2248 the NLO value Pc=0.37+-0.06 is modified to Pc=0.38+-0.04 at the NNLO level with the latter error fully dominated by the uncertainty in mc. We present tables for Pc as a function of mc and alphas(MZ) and a very accurate analytic formula that summarizes these two dependences as well as the dominant theoretical uncertainties. Adding the recently calculated long-distance contributions we find BR(K+ -> pi+ nu nu-bar)=(8.0+-1.1)*10^-11 with the present uncertainties in mc and the Cabibbo-Kobayashi-Maskawa elements being the dominant individual sources in the quoted error. We also emphasize that improved calculations of the long-distance contributions to K+ -> pi+ nu nu-bar and of the isospin breaking corrections in the evaluation of the weak current matrix elements from K+ -> pi0 e+ nu would be valuable in order to increase the potential of the two golden K -> pi nu nu decays in the search for new physics.Comment: 74 pages, 28 figures. Erratum added: We correct the treatment of anomalous triangle diagrams. The associated numerical correction is below a permille; v3: Typographical mistakes in (108), (111) and (112) corrected. Thanks to Xu Feng for pointing them out. Numerical results unchange

Force-extension relation of cross-linked anisotropic polymer networks

Cross-linked polymer networks with orientational order constitute a wide class of soft materials and are relevant to biological systems (e.g., F-actin bundles). We analytically study the nonlinear force-extension relation of an array of parallel-aligned, strongly stretched semiflexible polymers with random cross-links. In the strong stretching limit, the effect of the cross-links is purely entropic, independent of the bending rigidity of the chains. Cross-links enhance the differential stretching stiffness of the bundle. For hard cross-links, the cross-link contribution to the force-extension relation scales inversely proportional to the force. Its dependence on the cross-link density, close to the gelation transition, is the same as that of the shear modulus. The qualitative behavior is captured by a toy model of two chains with a single cross-link in the middle.Comment: 7 pages, 4 figure

Blown-up p-Branes and the Cosmological Constant

We consider a blown-up 3-brane, with the resulting geometry R^(3,1) \times S^(N-1), in an infinite-volume bulk with N > 2 extra dimensions. The action on the brane includes both an Einstein term and a cosmological constant. Similar setups have been proposed both to reproduce 4-d gravity on the brane, and to solve the cosmological constant problem. Here we obtain a singularity-free solution to Einstein's equations everywhere in the bulk and on the brane, which allows us to address these question explicitely. One finds, however, that the proper volume of S^(N-1) and the cosmological constant on the brane have to be fine-tuned relatively to each other, thus the cosmological constant problem is not solved. Moreover the scalar propagator on the brane behaves 4-dimensionally over a phenomenologically acceptable range only if the warp factor on the brane is huge, which aggravates the Weak Scale - Planck Scale hierarchy problem.Comment: 21 pages, no figure