Time-domain harmonic balance method for aerodynamic and aeroelastic simulations of turbomachinery flows

A time-domain Harmonic Balance method is applied to simulate the blade row interactions and vibrations of state- of-the-art industrial turbomachinery configurations. The present harmonic balance approach is a time-integration scheme that turns a periodic or almost-periodic flow problem into the coupled resolution of several steady computations at different time samples of the period of interest. The coupling is performed by a spectral time-derivative operator that appears as a source term of all the steady problems. These are converged simultaneously making the method parallel in time. In this paper, a non-uniform time sampling is used to improve the robustness and accuracy regardless of the considered frequency set. Blade row interactions are studied within a 3.5-stage high-pressure axial compressor representative of the high-pressure core of modern turbofan engines. Comparisons with reference time-accurate computations show that four frequencies allow a fair match of the compressor performance, with a reduction of the computational time up to a factor 30. Finally, an aeroelastic study is performed for a counter-rotating fan stage, where the rear blade is submitted to a prescribed harmonic vibration along its first torsion mode. The aerodynamic damping is analysed, showing possible flutter

A Counterexample to the Quantizability of Modules

Let a Poisson structure on a manifold M be given. If it vanishes at a point m, the evaluation at m defines a one dimensional representation of the Poisson algebra of functions on M. We show that this representation can, in general, not be quantized. Precisely, we give a counterexample for M=R^n, such that: (i) The evaluation map at 0 can not be quantized to a representation of the algebra of functions with product the Kontsevich product associated to the Poisson structure. (ii) For any formal Poisson structure extending the given one and vanishing at zero up to second order in epsilon, (i) still holds. We do not know whether the second claim remains true if one allows the higher order terms in epsilon to attain nonzero values at zero

The effect of metapopulation processes on the spatial scale of adaptation across an environmental gradient

We show that the butterfly Aricia agestis (Lycaenidae) is adapted to its thermal environment in via integer changes in the numbers of generations per year (voltinism): it has two generations per year in warm habitats and one generation per year in cool habitats in north Wales (UK). Voltinism is an “adaptive peak” since individuals having an intermediate number of generations per year would fail to survive the winter, and indeed no populations showed both voltinism types in nature. In spite of this general pattern, 11% of populations apparently possess the “wrong” voltinism for their local environment, and population densities were lower in thermally intermediate habitat patches. Population dynamic data and patterns of genetic differentiation suggest that adaptation occurs at the metapopulation level, with local populations possessing the voltinism type appropriate for the commonest habitat type within each population network. When populations and groups of populations go extinct, they tend to be replaced by colonists from the commonest thermal environment nearby, even if this is the locally incorrect adaptation. Our results illustrate how stochastic population turnover can impose a limit on local adaptation over distances many times larger than predicted on the basis of normal dispersal movements

Resultater fra den strategisk analyse af en fast forbindelse mellem Helsingør og Helsingborg: Artikel

Vejdirektoratet, Trafik-, Bygge- og Boligstyrelsen og Trafikverket afsluttede i januar 2021 en strategisk analyse af en fast forbindelse mellem Helsingør og Helsingborg (HH-forbindelsen). En fast vejforbindelse og en baneforbindelse for persontog kan anlægges som to adskilte, borede tunneller under Øresund. Anlægsomkostningerne vurderes at være mellem 21 og 23 mia. danske kr. for en ren vejforbindelse, mens vej og baneforbindelse samlet vurderes at koste 41-42 mia. danske kr. Forbindelsen forventes at få en vejtrafik på ca. 15.000 køretøjer og ca. 19.000 rejsende med kollektiv trafik pr. hverdagsdøgn i 2040.Samfundsøkonomiske beregninger for hhv. Danmark og Sverige peger på at en ren vejforbindelse er samfundsøkonomisk rentabel og kan finansieres af brugerne af den nye forbindelse. En vej- og baneforbindelse får dog en intern rente på 2,9% og en nettoværdikvote på -0,2 i hhv. Danske og Svenske analyser. Den bliver dermed ikke samfundsøkonomisk rentabel og får behov for væsentlige tilskud til finansieringen ud over bidraget fra brugerfinansieringen

Trace-Driven Simulation for Energy Consumption in High Throughput Computing Systems

High Throughput Computing (HTC) is a powerful paradigm allowing vast quantities of independent work to be performed simultaneously. However, until recently little evaluation has been performed on the energy impact of HTC. Many organisations now seek to minimise energy consumption across their IT infrastructure though it is unclear how this will affect the usability of HTC systems. We present here HTC-Sim, a simulation system which allows the evaluation of different energy reduction policies across an HTC system comprising a collection of computational resources dedicated to HTC work and resources provided through cycle scavenging -- a Desktop Grid. We demonstrate that our simulation software scales linearly with increasing HTC workload

de-Broglie Wave-Front Engineering

We propose a simple method for the deterministic generation of an arbitrary continuous quantum state of the center-of-mass of an atom. The method's spatial resolution gradually increases with the interaction time with no apparent fundamental limitations. Such de-Broglie Wave-Front Engineering of the atomic density can find applications in Atom Lithography, and we discuss possible implementations of our scheme in atomic beam experiments.Comment: The figures' quality was improved, the text remains intact. 5 pages, 3 figures; submitted to PR

Shubnikov–de Haas effect in multiband quasi-two-dimensional metals

We analyze the behavior of the longitudinal conductivity zz in a field perpendicular to the highly conducting plane of a quasi-two-dimensional multiband metal in the case of a closed system where chemical potential oscillations may be observed compared with the case of an open system for various forms of scattering. In all but one case, we find that there are mixing frequencies present. However, they exhibit different qualitative behaviors, as befits their different origins, and in the case of interband scattering in an open system, may in fact be absent in the de Haas–van Alphen oscillations of that system

Determination of the neutrino mass hierarchy in the regime of small matter effect

We point out a synergy between T-conjugated oscillation channels in the determination of the neutrino mass hierarchy with oscillation experiments with relatively short baselines (L < 700 km), where the matter effect is small. If information from all four oscillation channels $\nu_\mu\to\nu_e$, $\bar\nu_\mu\to\bar\nu_e$, $\nu_e\to\nu_\mu$ and $\bar\nu_e\to\bar\nu_\mu$ is available, a matter effect of few percent suffices to break the sign-degeneracy and allows to determine the neutrino mass hierarchy. The effect is discussed by analytical considerations of the relevant oscillation probabilities, and illustrated with numerical simulations of realistic experimental setups. Possible configurations where this method could be applied are the combination of a super beam experiment with a beta beam or a neutrino factory, or a (low energy) neutrino factory using a detector with muon and electron charge identification.Comment: 13 pages, 3 figure

Superconductivity in a Hubbard-Frohlich model and in cuprates

Using the variational Monte Carlo method, we find that a relatively weak long-range electron-phonon interaction induces a d-wave superconducting state in doped Mott-Hubbard insulators and/or strongly correlated metals with a condensation energy significantly larger than can be obtained with Coulomb repulsion only. Moreover, the superconductivity is shown to exist for infinite on-site Coulomb repulsion without the need for additional mechanisms such as spin fluctuations to mediate d-wave superconductivity. We argue that our superconducting state is robust with respect to a more intricate choice of the trial-wave function and that a possible origin of high-temperature superconductivity lies in a proper combination of strong electron-electron correlations with poorly screened Fröhlich electron-phonon interaction

Regularized zero-range model and an application to the triton and the hypertriton

We examine the regularized zero-range model in an application to three-fermion systems -- the triton and the hypertriton. We consider bound states and low-energy neutron-deuteron and lambda-deuteron scattering. The model is shown to provide an adequate quantitative description of these system on a par with finite-range potential models. The well known correlation between the doublet $nd$ scattering length and the triton binding energy (Phillips line) finds a natural explanation within the model.Comment: 20 pages, 7 figure