1,794 research outputs found
Electron spectra close to a metal-to-insulator transition
A high-resolution investigation of the electron spectra close to the
metal-to-insulator transition in dynamic mean-field theory is presented. An
all-numerical, consistent confirmation of a smooth transition at zero
temperature is provided. In particular, the separation of energy scales is
verified. Unexpectedly, sharp peaks at the inner Hubbard band edges occur in
the metallic regime. They are signatures of the important interaction between
single-particle excitations and collective modes.Comment: RevTeX 4, 4 pages, 4 eps figures; published versio
Generic susceptibilities of the half-filled Hubbard model in infinite dimensions
Around a metal-to-insulator transition driven by repulsive interaction (Mott
transition) the single particle excitations and the collective excitations are
equally important. Here we present results for the generic susceptibilities at
zero temperature in the half-filled Hubbard model in infinite dimensions.
Profiting from the high resolution of dynamic density-matrix renormalization at
all energies, results for the charge, spin and Cooper-pair susceptibilities in
the metallic and the insulating phase are computed. In the insulating phase, an
almost saturated local magnetic moment appears. In the metallic phase a
pronounced low-energy peak is found in the spin response.Comment: 12 pages, 12 figures; slight changes and one additional figure due to
referees' suggestion
Humanitarianism in the Modern World: The Moral Economy of Famine Relief
This is an innovative new history of famine relief and humanitarianism. The authors apply a moral economy approach to shed new light on the forces and ideas that motivated and shaped humanitarian aid during the Great Irish Famine, the famine of 1921-1922 in Soviet Russia and the Ukraine, and the 1980s Ethiopian famine. They place these episodes within a distinctive periodisation of humanitarianism which emphasises the correlations with politico-economic regimes: the time of elitist laissez-faire liberalism in the nineteenth century as one of ad hoc humanitarianism; that of Taylorism and mass society from c.1900-1970 as one of organised humanitarianism; and the blend of individualised post-material lifestyles and neoliberal public management since 1970 as one of expressive humanitarianism. The book as a whole shifts the focus of the history of humanitarianism from the imperatives of crisis management to the pragmatic mechanisms of fundraising, relief efforts on the ground, and finance
Compositional Performance Modelling with the TIPPtool
Stochastic process algebras have been proposed as compositional specification formalisms for performance models. In this paper, we describe a tool which aims at realising all beneficial aspects of compositional performance modelling, the TIPPtool. It incorporates methods for compositional specification as well as solution, based on state-of-the-art techniques, and wrapped in a user-friendly graphical front end. Apart from highlighting the general benefits of the tool, we also discuss some lessons learned during development and application of the TIPPtool. A non-trivial model of a real life communication system serves as a case study to illustrate benefits and limitations
Asymptotic Symmetries of String Theory on AdS3 X S3 with Ramond-Ramond Fluxes
String theory on AdS3 space-times with boundary conditions that allow for
black hole states has global asymptotic symmetries which include an infinite
dimensional conformal algebra. Using the conformal current algebra for
sigma-models on PSU(1,1|2), we explicitly construct the R-symmetry and Virasoro
charges in the worldsheet theory describing string theory on AdS3 X S3 with
Ramond-Ramond fluxes. We also indicate how to construct the full boundary
superconformal algebra. The boundary superconformal algebra plays an important
role in classifying the full spectrum of string theory on AdS3 with
Ramond-Ramond fluxes, and in the microscopic entropy counting in D1-D5 systems.Comment: 30 page
Poisson-Lie T-dual sigma models on supermanifolds
We investigate Poisson-Lie symmetry for T-dual sigma models on supermanifolds
in general and on Lie supergroups in particular. We show that the integrability
condition on this super Poisson-Lie symmetry is equivalent to the super Jacobi
identities of the Lie super-bialgebras. As examples we consider models related
to four dimensional Lie super-bialgebras and
. Then generally it is shown that for Abelian case (g, I)
the super Poisson-Lie T-duality transforms the role of fermionic (bosonic)
fields in the model to bosonic (fermionic) fields on the dual model and vice
versa.Comment: 13 pages, Revised and accepted for publication in JHE
Long term hard X-ray variability of the anomalous X-ray pulsar 1RXS J170849.0-400910 discovered with INTEGRAL
We report on a multi-band high-energy observing campaign aimed at studying
the long term spectral variability of the Anomalous X-ray Pulsar (AXP) 1RXS
J170849.0-400910, one of the magnetar candidates. We observed 1RXS
J170849.0-400910 in Fall 2006 and Spring 2007 simultaneously with Swift/XRT, in
the 0.1-10 keV energy range, and with INTEGRAL/IBIS, in the 20-200 keV energy
range. Furthermore, we also reanalyzed, using the latest calibration and
software, all the publicly available INTEGRAL data since 2002, and the soft
X-ray data starting from 1999 taken using BeppoSAX, Chandra, XMM, and
Swift/XRT, in order to study the soft and hard X-ray spectral variability of
1RXS J170849.0-400910. We find a long-term variability of the hard X-ray flux,
extending the hardness-intensity correlation proposed for this source over 2
orders of magnitude in energy.Comment: 5 pages, 2 figures, accepted for publication in Astronomy &
Astrophysics main journa
Linking the X-ray timing and spectral properties of the glitching AXP 1RXS J170849-400910
Previous studies of the X-ray flux and spectral properties of 1RXS
J170849-400910 showed hints of a possible correlation with the spin glitches
that occurred in 1999 and 2001. However, due to the sparseness of spectral
measurements and the paucity of detected glitches no firm conclusion could be
drawn. We retrieved and analysed archival XTE pointings of 1RXS J170849-400910
covering the time interval between January 2003 and June 2006 and carried out a
detailed timing analysis by means of phase fitting techniques. We detected two
relatively large glitches Delta nu / nu of 1.2 and 2.1 10^-6 occurred in
January and June 2005. Interestingly, the occurrence times of these glitches
are in agreement with the predictions made in our previous studies. This
finding strongly suggests a connection between the flux, spectral and timing
properties of 1RXS J170849-400910.Comment: Submitted to A&A, 4 pages; results presented at the INT meeting "The
Neutron Star Crust and Surface: Observations and Models" on June 27; referee
comments adde
Single-Particle Dynamics in the Vicinity of the Mott-Hubbard Metal-to-Insulator Transition
The single-particle dynamics close to a metal-to-insulator transition induced
by strong repulsive interaction between the electrons is investigated. The
system is described by a half-filled Hubbard model which is treated by dynamic
mean-field theory evaluated by high-resolution dynamic density-matrix
renormalization. We provide theoretical spectra with momentum resolution which
facilitate the comparison to photoelectron spectroscopy.Comment: 22 pages, 24 figures, comprehensive high-resolution study of single
electron dynamics around a Mott metal-insulator transition, with momentum
resolved spectral densities; slight changes due to referees' suggestion
- âŠ