11,670 research outputs found
Defects in Jackiw-Teitelboim Quantum Gravity
We classify and study defects in 2d Jackiw-Teitelboim gravity. We show these
are holographically described by a deformation of the Schwarzian theory where
the reparametrization mode is integrated over different coadjoint orbits of the
Virasoro group. We show that the quantization of each coadjoint orbit is
connected to 2d Liouville CFT between branes with insertions of Verlinde loop
operators. We also propose an interpretation for the exceptional orbits. We use
this perspective to solve these deformations of the Schwarzian theory,
computing their partition function and correlators. In the process, we define
two geometric observables: the horizon area operator and the geodesic
length operator . We show this procedure is structurally related to
the deformation of the particle-on-a-group quantum mechanics by the addition of
a chemical potential. As an example, we solve the low-energy theory of complex
SYK with a U(1) symmetry and generalize to the non-abelian case.Comment: 66 pages, v4: clarifications added, typos corrected, matches
published versio
Effect of Our Galaxy's Motion on Weak Lensing Measurements of Shear and Convergence
In this work we investigate the effect on weak-lensing shear and convergence
measurements due to distortions from the Lorentz boost induced by our Galaxy's
motion. While no ellipticity is induced in an image from the Lorentz boost to
first order in beta = v/c, the image is magnified. This affects the inferred
convergence at a 10 per cent level, and is most notable for low multipoles in
the convergence power spectrum C {\kappa}{\kappa} and for surveys with large
sky coverage like LSST and DES. Experiments which image only small fractions of
the sky and convergence power spectrum determinations at l > 5 can safely
neglect the boost effect to first order in beta.Comment: 4 pages, replaced to reflect changes made for publication to MNRA
De economische en sociale toestand van de opstandelingen uit het Brugse Vrije, wier goederen na de slag bij Cassel (1328) verbeurd verklaard werden
Computer-supported laboratory for production-oriented electrotechnical systems
At the electrical engineering department of the K.U.Leuven an education research project was started in October 1997. The target is to develop a powerful environment to teach students to solve practice-oriented problems as they will encounter them in industry furtheron in their career. In order to give a wide use to the developed environment, a close collaboration has been established with three polytechnical engineering institutes. Self-dependence has to be stimulated by creating possibilities for real “hands-on experience”. Such an educational environment implicates time-problems, high investment costs and last but not least safety restrictions. The project contributes to the solution of these problems by using simulation- and softwareenvironments, without loosing the real hands-on feeling
Image reconstruction from photon sparse data
We report an algorithm for reconstructing images when the average number of photons recorded per pixel is of order unity, i.e. photon-sparse data. The image optimisation algorithm minimises a cost function incorporating both a Poissonian log-likelihood term based on the deviation of the reconstructed image from the measured data and a regularization-term based upon the sum of the moduli of the second spatial derivatives of the reconstructed image pixel intensities. The balance between these two terms is set by a bootstrapping technique where the target value of the log-likelihood term is deduced from a smoothed version of the original data. When compared to the original data, the processed images exhibit lower residuals with respect to the true object. We use photon-sparse data from two different experimental systems, one system based on a single-photon, avalanche photo-diode array and the other system on a time-gated, intensified camera. However, this same processing technique could most likely be applied to any low photon-number image irrespective of how the data is collected
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