1,824 research outputs found
Quantitative PET/CT imaging and dosimetry of 89Zr labelled compounds
Lammertsma, A.A. [Promotor]Boellaard, R. [Promotor]Huisman, M.C. [Copromotor
Scattering in and Symmetric Multimode Waveguides: Generalized Conservation Laws and Spontaneous Symmetry Breaking beyond One Dimension
We extend the generalize conservation law of light propagating in a
one-dimensional -symmetric system, i.e., for the
transmittance and the reflectance from the left and right, to a
multimode waveguide with either or symmetry, in which
higher dimensional investigations are necessary. These conservation laws exist
not only in a matrix form for the transmission and reflection matrices; they
also exist in a scalar form for real-valued quantities by defining generalized
transmittance and reflectance. We then discuss, for the first time, how a
multimode -symmetric waveguide can be used to observe spontaneous
symmetry breaking of the scattering matrix, which typically requires tuning the
non-hermiticity of the system (i.e. the strength of gain and loss). Here the
advantage of using a multimode waveguide is the elimination of tuning any
system parameters: the transverse mode order plays the role of the symmetry
breaking parameter, and one observes the symmetry breaking by simply performing
scattering experiment in each waveguide channel at a single frequency and fixed
strength of gain and loss.Comment: 8 pages, 6 figure
Vision-Based Production of Personalized Video
In this paper we present a novel vision-based system for the automated production of personalised video souvenirs for visitors in leisure and cultural heritage venues. Visitors are visually identified and tracked through a camera network. The system produces a personalized DVD souvenir at the end of a visitor’s stay allowing visitors to relive their experiences. We analyze how we identify visitors by fusing facial and body features, how we track visitors, how the tracker recovers from failures due to occlusions, as well as how we annotate and compile the final product. Our experiments demonstrate the feasibility of the proposed approach
Long-lived Giant Number Fluctuations in a Swarming Granular Nematic
Coherently moving flocks of birds, beasts or bacteria are examples of living
matter with spontaneous orientational order. How do these systems differ from
thermal equilibrium systems with such liquid-crystalline order? Working with a
fluidized monolayer of macroscopic rods in the nematic liquid crystalline
phase, we find giant number fluctuations consistent with a standard deviation
growing linearly with the mean, in contrast to any situation where the Central
Limit Theorem applies. These fluctuations are long-lived, decaying only as a
logarithmic function of time. This shows that flocking, coherent motion and
large-scale inhomogeneity can appear in a system in which particles do not
communicate except by contact.Comment: This is the author's version of the work. It is posted here by
permission of the AAAS. The definitive version is to appear in SCIENC
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Dimensional analysis of the earthquake-induced pounding between inelastic structures
In this paper the seismic response of inelastic structures with unilateral contact is revisited with dimensional analysis. All physically realizable contact types are captured via a non-smooth complementarity approach. The implementation of formal dimensional analysis leads to a condensed presentation of the response and unveils remarkable order even though two different types of non-linearity coexist in the response: the boundary non-linearity of unilateral contact and the inelastic behaviour of the structure itself. It is shown that regardless the intensity and frequency content of the excitation, all response spectra become self-similar when expressed in the appropriate dimensionless terms. The proposed approach hinges upon the notion of the energetic length scale of an excitation which measures the persistence of ground shaking to impose deformation demands. Using the concept of persistency which is defined for excitations with or without distinct pulses, the response is scaled via meaningful novel intensity measures: the dimensionless gap and the dimensionless yield displacement. The study confirms that contact may have a different effect on the response displacements of inelastic structures depending on the spectral region. In adjacent inelastic structures, such as colliding buildings or interacting bridge segments, contact is likely to alter drastically the excitation frequencies’ at which the system is most vulnerable. Finally, it is shown that the proposed approach yields maximum response displacements which correlate very well with the persistency of real earthquakes for a bridge system with considerably complex behaviour
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Dimensional analysis of yielding and pounding structures for records without distinct pulses
The seismic response of two fundamental mechanical configurations of earthquake engineering, the elastic–plastic system and the pounding oscillator, is revisited with the aid of dimensional analysis. Starting from the previous work of the authors which focused on pulse-type excitations, the paper offers an alternative, yet physically motivated, way to present the response of yielding and pounding structures under excitations with arbitrary time history. It is shown, that when the appropriate time and length scales are adopted, dimensional analysis can be implemented and remarkable order emerges in the response. Regardless of the acceleration level and frequency content of the excitation, all response spectra become self-similar and when expressed in dimensionless terms, resulting from dimensional analysis, follow a single master curve. The study proposes such scales together with the associated selection criteria among the available in literature strong ground motion parameters and shows that the proposed approach reduces drastically the scatter in the response
Underwater Sound Characteristics of a Ship with Controllable Pitch Propeller
The time-dependent spectral characteristics of underwater sound radiated by an oceanic vessel have complex dependencies on ship machinery, propeller dynamics, and the hydrodynamics of the ship exhaust and motion, as well as onboard activities. Here, the underwater sound radiated by a ship equipped with a controllable pitch propeller (CPP) is analyzed and quantified via its (i) power spectral density for signal energetics, (ii) temporal coherence for machinery tonal sound, and (iii) spectral coherence for propeller amplitude-modulated cavitation noise. Frequency-modulated (FM) tonal signals are also characterized in terms of their frequency variations. These characteristics are compared for different propeller pitch ratios, ranging from 20% to 82% at a fixed number of propeller revolutions per minute (RPM). The efficacy and robustness of ship parameter estimation at different pitches are discussed. Finally, an analysis of one special measurement is provided: propeller pitch and RPM over the duration of the measurement when the ship changes speed. The 50% pitch was found to be a crucial point for this ship, around which the tonal characteristics of its underwater radiated sound attain their peak values while broadband sound and associated spectral coherences are at a minimum. The findings here elucidate the effects of pitch variation on underwater sound radiated by ships with controllable pitch propellers and has applications in ship design and underwater noise mitigation
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