8,328 research outputs found
Zusammensetzung rezyklierter (Th, U) O-Brennelemente mit mitterem U-Anreicherungsgrad und ihre Auswirkung auf den Kernbrennstoffkreislauf
The MEU-HTR fuel element is proposed in order to use lower enriched U and to preserve the potential of the HTR as converter and as process heat source. If the final storage of nuclear fuel is not licensed in the Federal Republic of Germany, a complete fuel cycle must be available for the spent nuclear fuel management of this type of fuel. Therefore, the composition of spent mixed oxide MEU-HTR fuel was calculated in this study, considering various recycling strategies. The following conclusions may be drawn from the resulting data. [...
Experimental Investigation of Temperature Feedback Control Systems Applicable to Turbojet-engine Control
Temperature - fuel-flow and temperature-area feedback control systems were investigated as means of controlling tailpipe gas temperature of a turbojet engine during transient operation in the high-speed region. Proportional-plus-integral control was used in both systems, but in the temperature-area control system it was necessary to add nonlinear components to the basic proportional-plus-integral control to provide satisfactory transient response to a desired step increase in temperature. Time integral of temperature-error functions were used as criteria for determining optimum transient response. A description of engine dynamics was obtained from frequency-response data
Experimental Comparison of Speed : Fuel-flow and Speed-area Controls on a Turbojet Engine for Small Step Disturbances
Optimum proportional-plus-integral control settings for speed - fuel-flow control, determined by minimization of integral criteria, correlated well with analytically predicted optimum settings. Engine response data are given for a range of control settings around the optimum. An inherent nonlinearity in the speed-area loop necessitated the use of nonlinear controls. Response data for two such nonlinear control schemes are presented
Neutral description and exchange of design computational workflows
Proposed in this paper is a neutral representation of design computational workflows which allows
their exchange and sharing between different project partners and across design stages. This is
achieved by the de-coupling of configuration and execution logic. Thus, the same underlying
workflow can be executed with different (fidelity) models and different software tools as long as the
inputs and outputs of the constituent process are kept the same. To this purpose, an object model is
proposed to define different simulation objects, their scope, and hierarchy in the simulation process.
An XML based computer readable representation of workflows based on the proposed object model, is
also suggested. The application of the proposed representation is demonstrated via a case study
involving the exchange of workflows between two design partners. The case study also demonstrates
how the same workflow can be executed using different execution tools and involving different
fidelity models
Block-Spin Approach to Electron Correlations
We consider an expansion of the ground state wavefunction of quantum lattice
many-body systems in a basis whose states are tensor products of block-spin
wavefunctions. We demonstrate by applying the method to the antiferromagnetic
spin-1/2 chain that by selecting the most important many-body states the
technique affords a severe truncation of the Hilbert space while maintaining
high accuracy.Comment: 17 pages, 3 Postscript figure
LIFECYCLE MANAGEMENT, MONITORING AND ASSESSMENT FOR SAFE LARGE-SCALE INFRASTRUCTURES: CHALLENGES AND NEEDS
Many European infrastructures dating back to ’50 and ’60 of the last century like bridges and viaducts are approaching the end of their design lifetime. In most European countries costs related to maintenance of infrastructures reach a quite high percentage of the construction budget and additional costs in terms of traffic delay are due to downtime related to the inspection and maintenance interventions. In the last 30 years, the rate of deterioration of these infrastructures has increased due to increased traffic loads, climate change related events and man-made hazards. A sustainable approach to infrastructures management over their lifecycle plays a key role in reducing the impact of mobility on safety (over 50 000 fatalities in EU per year) and the impact of greenhouse gases emission related to fossil fuels. The events related to the recent collapse of the Morandi bridge in Italy tragically highlighted the sheer need to improve resilience of aging transport infrastructures, in order to increase the safety for people and goods and to reduce losses of functionality and the related consequences. In this focus Structural Health Monitoring (SHM) is one of the key strategies with a great potential to provide a new approach to performance assessment and maintenance over the life cycle for an efficient, safe, resilient and sustainable management of the infrastructures. In this paper research efforts, needs and challenges in terms of performance monitoring, assessment and standardization are described and discussed.The networking support of COST Action TU1402 on ‘Quantifying the Value of Structural Health Monitoring’ and of COST Action TU1406 on ‘Quality specifications for roadway bridges, standardization at a European level (BridgeSpec)
Designable electron transport features in one-dimensional arrays of metallic nanoparticles: Monte Carlo study of the relation between shape and transport
We study the current and shot noise in a linear array of metallic
nanoparticles taking explicitly into consideration their discrete electronic
spectra. Phonon assisted tunneling and dissipative effects on single
nanoparticles are incorporated as well. The capacitance matrix which determines
the classical Coulomb interaction within the capacitance model is calculated
numerically from a realistic geometry. A Monte Carlo algorithm which
self-adapts to the size of the system allows us to simulate the single-electron
transport properties within a semiclassical framework. We present several
effects that are related to the geometry and the one-electron level spacing
like e.g. a negative differential conductance (NDC) effect. Consequently these
effects are designable by the choice of the size and arrangement of the
nanoparticles.Comment: 13 pages, 12 figure
Emergence of chaotic scattering in ultracold Er and Dy
We show that for ultracold magnetic lanthanide atoms chaotic scattering
emerges due to a combination of anisotropic interaction potentials and Zeeman
coupling under an external magnetic field. This scattering is studied in a
collaborative experimental and theoretical effort for both dysprosium and
erbium. We present extensive atom-loss measurements of their dense magnetic
Feshbach resonance spectra, analyze their statistical properties, and compare
to predictions from a random-matrix-theory inspired model. Furthermore,
theoretical coupled-channels simulations of the anisotropic molecular
Hamiltonian at zero magnetic field show that weakly-bound, near threshold
diatomic levels form overlapping, uncoupled chaotic series that when combined
are randomly distributed. The Zeeman interaction shifts and couples these
levels, leading to a Feshbach spectrum of zero-energy bound states with
nearest-neighbor spacings that changes from randomly to chaotically distributed
for increasing magnetic field. Finally, we show that the extreme temperature
sensitivity of a small, but sizeable fraction of the resonances in the Dy and
Er atom-loss spectra is due to resonant non-zero partial-wave collisions. Our
threshold analysis for these resonances indicates a large collision-energy
dependence of the three-body recombination rate
Interaction induced collapse of a section of the Fermi sea in in the zig-zag Hubbard ladder
Using the next-nearest neighbor (zig-zag) Hubbard chain as an one
dimemensional model, we investigate the influence of interactions on the
position of the Fermi wavevectors with the density-matrix renormalization-group
technique (DMRG). For suitable choices of the hopping parameters we observe
that electron-electron correlations induce very different renormalizations for
the two different Fermi wavevectors, which ultimately lead to a complete
destruction of one section of the Fermi sea in a quantum critical point
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