9,838 research outputs found
Computersimulation zur Verifizierung und PrÀsentation eines automatisch gesteuerten Mamma-Biopsiesystems
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugĂ€nglich.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 computerunterstĂŒtzte Simulations- und Animationstechnik ist ein allgemein anerkanntes Hilfsmittel bei der Planung und Realisierung von technischen Systemen. Der Schwerpunkt des Simulations- und Animationseinsatzes lag ursprĂŒnglich nur auf der Planungsabsicherung. Zunehmend wird die Simulation und Animation durchgĂ€ngig in allen Phasen des Planungs- und Realisierungsprozesses genutzt. In einem Forschungsprojekt wurde eine neuartige automatisch gesteuerte Einrichtung zur prĂ€zisen Navigation medizinischer Instrumente innerhalb von MRTomographen, insbesondere zur histologischen Sicherung von Kleintumoren, entwickelt. Die gesamte Einrichtung lĂ€Ăt sich gemeinsam mit einem Patienten im Untersuchungsbereich eines MR-Tomographen positionieren. Mittels einer SD-Simulation wie auch Animation konnte eine ĂberprĂŒfung und Optimierung des komplexen Gesamtsystems, d.h. der einzelnen Systemkomponenten und deren kinematischen BewegungsablĂ€ufe erfolgen. Desweiteren wurde damit eine Grundlage fĂŒr die Erstellung einer PrĂ€sentationsvorlage realisiert, um der Ăffentlichkeit die einzelnen AblaufvorgĂ€nge einfach und plausibel darzustellen und zukĂŒnftige 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 âsituationâ versus âsystemâ, âisâ versus âoughtâ judgements, concerns of âthose involvedâ versus âthose affected but not involvedâ, stakeholdersâ âstakesâ versus âstakeholding issuesâ, 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
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