1,602 research outputs found
A Parallel Decomposition Scheme for Solving Long-Horizon Optimal Control Problems
We present a temporal decomposition scheme for solving long-horizon optimal
control problems. In the proposed scheme, the time domain is decomposed into a
set of subdomains with partially overlapping regions. Subproblems associated
with the subdomains are solved in parallel to obtain local primal-dual
trajectories that are assembled to obtain the global trajectories. We provide a
sufficient condition that guarantees convergence of the proposed scheme. This
condition states that the effect of perturbations on the boundary conditions
(i.e., initial state and terminal dual/adjoint variable) should decay
asymptotically as one moves away from the boundaries. This condition also
reveals that the scheme converges if the size of the overlap is sufficiently
large and that the convergence rate improves with the size of the overlap. We
prove that linear quadratic problems satisfy the asymptotic decay condition,
and we discuss numerical strategies to determine if the condition holds in more
general cases. We draw upon a non-convex optimal control problem to illustrate
the performance of the proposed scheme
Aby Warburg: His Aims and Methods
In this issue of Engramma: Giulia Zanonâs "Zooming Mnemosyne" deals with the use of details in Warburgâs Bilderatlas, Monica Centanniâs "Collateral effects of the âvisibile parlareâ (Dante, Pg. X, v. 95)" reconstructs the hypothesis of a visual model for the legend of Trajanâs Justice, according to Warburg intuition about it; this contribution is connected of the paper by Filippo Perfettiâs "Dante, Botticelli, and Trajan. An Open Note" where the author investigates how Botticelli could have come to know that the bas-relief of the Arch of Constantine liberatori urbis was related to an episode in Trajan's lifeâ. The focus of this issue is then extended to Warburg's cultural environment. Matilde Sergioâs "Aby Warburg, Walter Benjaming, and the Memory of Images" investigates the influence of Warburg's essay about Luther, on Benjamin's thought, while Dorothee Gelhardâs "Gertrud Bingâs Scientific Beginnings" reconstructs the intellectual history of Bing's doctoral thesis and its influences on Warburgian work. The theme of Warburgâs Denkraum is the focal point of Salvatore Settisâ "Anselm Kiefer's Logic of Inversion": a fundamental overview of Kiefer's Questi scritti, quando verranno bruciati, daranno finalmente un poâ di luce (Andrea Emo) on display at Sala dello Scrutinio in Palazzo Ducale, Venezia from March to October 2022. The third section of the issue is dedicated to new publications and exhibitions. Echoing Settisâ reflection on Denkraum, we present Clio Nicastroâs "La Dialettica del Denkraum in Aby Warburg", published this year for Palermo University Press; an introduction to "Cultural Memories": a series published by Peter Lang and edited by Katia Pizzi. Giacomo Calandra di Roccolino with "Mary Hertz Warburg: Free and Unconventional" reviews the exhibition of the artist Mary Hertz Warburg. The issue closes with the important "Choral Reading of "Il metodo di Aby Warburg" by Kurt W. Forster. Lâantico dei gesti. Il futuro della memoria", where Barbara Baert, Victoria Cirlot, Georges Didi-Huberman, Michael Diers, Andrea Pinotti and Ianick Takaes offer us their personal reading of Warburgâs life and thought as they are presented by Forsterâs newly translated book, edited by Ronzani editore
CFD modelling of wind turbine airfoil aerodynamics
This paper reports the first findings of an ongoing research programme on wind turbine computational aerodynamics at the
University of Glasgow. Several modeling aspects of wind turbine airfoil aerodynamics based on the solution of the Reynoldsaveraged
Navier-Stokes (RANS) equations are addressed.
One of these is the effect of an a priori method for structured grid adaptation aimed at improving the wake resolution.
Presented results emphasize that the proposed adaptation strategy greatly improves the wake resolution in the far-field,
whereas the wake is completely diffused by the non-adapted grid with the same number and distribution of grid nodes. A grid
refinement analysis carried out with the adapted grid shows that the improvements of flow resolution thus achieved are of a
smaller magnitude with respect to those accomplished by adapting the grid keeping constant the number of nodes. The
proposed adaptation approach can be easily included in the structured generation process of both commercial and in-house
structured mesh generators systems.
The study also aims at quantifying the solution inaccuracy arising from not modeling the laminar-to-turbulent transition. It
is found that the drag forces obtained by considering the flow as transitional or fully turbulent may differ by 50 %.
The impact of various turbulence models on the predicted aerodynamic forces is also analyzed.
All these issues are investigated using a special-purpose hyperbolic grid generator and a multi-block structured finitevolume
RANS code. The numerical experiments consider the flow field past a wind turbine airfoil for which an exhaustive
campaign of steady and unsteady experimental measurements was conducted. The predictive capabilities of the CFD solver
are validated by comparing experimental data and numerical predictions for selected flow regimes. The incompressible
analysis and design code XFOIL is also used to support the findings of the comparative analysis of numerical RANS-based
results and experimental data
Planar Gravitational Corrections For Supersymmetric Gauge Theories
In this paper we discuss the contribution of planar diagrams to gravitational
F-terms for N=1 supersymmetric gauge theories admitting a large N description.
We show how the planar diagrams lead to a universal contribution at the
extremum of the glueball superpotential, leaving only the genus one
contributions, as was previously conjectured. We also discuss the physical
meaning of gravitational F-terms.Comment: 20 pages, 4 figure
Composite pulses in Hyper-Ramsey spectroscopy for the next generation of atomic clocks
The next generation of atomic frequency standards based on an ensemble of
neutral atoms or a single-ion will provide very stringent tests in metrology,
applied and fundamental physics requiring a new step in very precise control of
external systematic corrections. In the proceedings of the 8th Symposium on
Frequency Standards and Metrology, we present a generalization of the recent
Hyper-Ramsey spectroscopy with separated oscillating fields using composites
pulses in order to suppress field frequency shifts induced by the interrogation
laser itself. Sequences of laser pulses including specific selection of phases,
frequency detunings and durations are elaborated to generate spectroscopic
signals with a strong reduction of the light-shift perturbation by off resonant
states. New optical clocks based on weakly allowed or completely forbidden
transitions in atoms, ions, molecules and nuclei will benefit from these
generalized Ramsey schemes to reach relative accuracies well below the
10 level.Comment: accepted as proceedings of the 8th Symposium on Frequency Standards
and Metrology (Potsdam Germany, 12-16 october 2015
Synthetic Frequency Protocol in the Ramsey Spectroscopy of Clock Transitions
We develop an universal method to significantly suppress probe-induced shifts
in any types of atomic clocks using the Ramsey spectroscopy. Our approach is
based on adaptation of the synthetic frequency concept [V. I. Yudin, et al.,
Phys. Rev. Lett. 107, 030801 (2011)] (previously developed for BBR shift
suppression) to the Ramsey spectroscopy with the use of interrogations for
different dark time intervals. Universality of the method consists in
arbitrariness of the possible Ramsey schemes. However, most extremal results
are obtained in combination with so-called hyper-Ramsey spectroscopy [V. I.
Yudin, et al., Phys. Rev. A 82, 011804(R) (2010)]. In the latter case, the
probe-induced frequency shifts can be suppressed considerably below a
fractional level of 10 practically for any optical atomic clocks, where
this shift previously was metrologically significant. The main advantage of our
method in comparison with other radical hyper-Ramsey approaches [R. Hobson, et
al., Phys. Rev. A 93, 010501(R) (2016); T. Zanon-Willette, et al., Phys. Rev. A
93, 042506 (2016)] consist in much greater efficiency and resistibility in the
presence of decoherentization.Comment: 9 pages, 7 figure
- âŠ