4,228 research outputs found
Quadratic deformation of Minkowski space
We present a deformation of the Minkowski space as embedded into the
conformal space (in the formalism of twistors) based in the quantum versions of
the corresponding kinematic groups. We compute explicitly the star product,
whose Poisson bracket is quadratic. We show that the star product although
defined on the polynomials can be extended differentiably. Finally we compute
the Eucliden and Minkowskian real forms of the deformation.Comment: Presented at XVII European Workshop on String Theory 2011. Padova
(Italy) September 05-09; Fortschr. Phys. 1-7 (2012
Explosive synchronization in weighted complex networks
The emergence of dynamical abrupt transitions in the macroscopic state of a
system is currently a subject of the utmost interest. Given a set of phase
oscillators networking with a generic wiring of connections and displaying a
generic frequency distribution, we show how combining dynamical local
information on frequency mismatches and global information on the graph
topology suggests a judicious and yet practical weighting procedure which is
able to induce and enhance explosive, irreversible, transitions to
synchronization. We report extensive numerical and analytical evidence of the
validity and scalability of such a procedure for different initial frequency
distributions, for both homogeneous and heterogeneous networks, as well as for
both linear and non linear weighting functions. We furthermore report on the
possibility of parametrically controlling the width and extent of the
hysteretic region of coexistence of the unsynchronized and synchronized states
Revisiting the usurer: the portrayal of Shylock as an affectionate father in Howard Jacobson''s Shylock is my name
This article aims to re-interpret the figure of Shylock in William Shakespeare's The Merchant of Venice by exploring how its novel rewriting by Howard Jacobson provides a more positive portrayal of the Jewish usurer. I attempt to argue that Jacobson's Shylock Is My Name contributes to re-reading Shylock as a thoughtful father who truly loves his daughter Jessica. Indeed, this 21st-century retelling revolves around the connection between Shylock and Simon Strulovitch, a Jewish philanthropist who has also been neglected by his daughter. The novel presents Shylock as a trustworthy character that is determined to help his friend create an emotional bond with his daughter. Moreover, Jacobson succeeds in empowering Shakespeare's Shylock to such an extent that he evolves from being an underdog in Venice to being widely respected by English society. As regards methodology, I have used the rhizomatic model proposed by Douglas Lanier with the purpose of exploring the enriching dialogue between the source text and this rewriting
From historical map to online 3D recreation: the 1861 cadastral map of Horta (Barcelona)
The recent study and classification of over 200 cadastral maps created in the nineteenth century in Catalonia have provided a valuable source of information about the agricultural landscape country’s past, but by linking them with data recorded in tax books known as amillaramientos, it is possible to gain a better knowledge of the past. By applying this method to the 1861 cadastral map of Horta and its corresponding amillaramiento, a planimetric map showing the land use distribution in the town was created. The resulting land use map was subsequently overlaid on top of a digital elevation model to create 3D visualizations which show the altitudinal distribution of crops and other features. Finally, the article explores a way of distributing the results online, making them accessible to the public and increasing the research impact of future findings. Therefore, the method described in this article allows the systematic recreation and distribution of past landscapes by using Catalan cadastral maps of the nineteenth century, something which can help enrich the scientific knowledge of many disciplines
Stability of the replica symmetric solution for the information conveyed by by a neural network
The information that a pattern of firing in the output layer of a feedforward
network of threshold-linear neurons conveys about the network's inputs is
considered. A replica-symmetric solution is found to be stable for all but
small amounts of noise. The region of instability depends on the contribution
of the threshold and the sparseness: for distributed pattern distributions, the
unstable region extends to higher noise variances than for very sparse
distributions, for which it is almost nonexistant.Comment: 19 pages, LaTeX, 5 figures. Also available at
http://www.mrc-bbc.ox.ac.uk/~schultz/papers.html . Submitted to Phys. Rev. E
Minor change
Rigorous Bounds to Retarded Learning
We show that the lower bound to the critical fraction of data needed to infer
(learn) the orientation of the anisotropy axis of a probability distribution,
determined by Herschkowitz and Opper [Phys.Rev.Lett. 86, 2174 (2001)], is not
always valid. If there is some structure in the data along the anisotropy axis,
their analysis is incorrect, and learning is possible with much less data
points.Comment: 1 page, 1 figure. Comment accepted for publication in Physical Review
Letter
Precision radial velocities of double-lined spectroscopic binaries with an iodine absorption cell
A spectroscopic technique employing an iodine absorption cell (I_2) to
superimpose a reference spectrum onto a stellar spectrum is currently the most
widely adopted approach to obtain precision radial velocities of solar-type
stars. It has been used to detect ~80 extrasolar planets out of ~130 know. Yet
in its original version, it only allows us to measure precise radial velocities
of single stars. In this paper, we present a novel method employing an I_2
absorption cell that enables us to accurately determine radial velocities of
both components of double-lined binaries. Our preliminary results based on the
data from the Keck I telescope and HIRES spectrograph demonstrate that 20-30
m/s radial velocity precision can be routinely obtained for "early" type
binaries (F3-F8). For later type binaries, the precision reaches ~10 m/s. We
discuss applications of the technique to stellar astronomy and searches for
extrasolar planets in binary systems. In particular, we combine the
interferometric data collected with the Palomar Testbed Interferometer with our
preliminary precision velocities of the spectroscopic double-lined binary HD
4676 to demonstrate that with such a combination one can routinely obtain
masses of the binary components accurate at least at the level of 1.0%.Comment: Accepted for publication in The Astrophysical Journa
Higher Order Analogues of Tracy-Widom Distributions via the Lax Method
We study the distribution of the largest eigenvalue in formal Hermitian
one-matrix models at multicriticality, where the spectral density acquires an
extra number of k-1 zeros at the edge. The distributions are directly expressed
through the norms of orthogonal polynomials on a semi-infinite interval, as an
alternative to using Fredholm determinants. They satisfy non-linear recurrence
relations which we show form a Lax pair, making contact to the string
literature in the early 1990's. The technique of pseudo-differential operators
allows us to give compact expressions for the logarithm of the gap probability
in terms of the Painleve XXXIV hierarchy. These are the higher order analogues
of the Tracy-Widom distribution which has k=1. Using known Backlund
transformations we show how to simplify earlier equivalent results that are
derived from Fredholm determinant theory, valid for even k in terms of the
Painleve II hierarchy.Comment: 24 pages. Improved discussion of Backlund transformations, in
addition to other minor improvements in text. Typos corrected. Matches
published versio
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