75,033 research outputs found
Charge excitation dynamics in bosonic fractional Chern insulators
The experimental realization of the Harper-Hofstadter model in ultra-cold
atomic gases has placed fractional states of matter in these systems within
reach---a fractional Chern insulator state (FCI) is expected to emerge for
sufficiently strong interactions when half-filling the lowest band. The
experimental setups naturally allow to probe the dynamics of this topological
state, yet little is known about its out-of-equilibrium properties. We explore,
using density matrix renormalization group (DMRG) simulations, the response of
the FCI state to spatially localized perturbations. After confirming the static
properties of the phase we show that the characteristic, gapless features are
clearly visible in the edge dynamics. We find that a local edge perturbation in
this model propagates chirally independent of the perturbation strength. This
contrasts the behavior of single particle models with counter-propagating edge
states, such as the non-interacting Harper-Hofstadter model, where the
chirality is manifest only for weak perturbations. Additionally, our
simulations show that there is inevitable density leakage from the first row of
sites into the bulk, preventing a naive chiral Luttinger theory interpretation
of the dynamics.Comment: 4+epsilon pages, 4 pages of supplementary material and a total of 8
figures. Published version with updated title, discussion, references, and
supplementary informatio
Detecting shocked intergalactic gas with X-ray and radio observations
Detecting the thermal and non-thermal emission from the shocked cosmic gas
surrounding large-scale structures represents a challenge for observations, as
well as a unique window into the physics of the warm-hot intergalactic medium.
In this work, we present synthetic radio and X-ray surveys of large
cosmological simulations in order to assess the chances of jointly detecting
the cosmic web in both frequency ranges. We then propose best observing
strategies tailored for existing (LOFAR, MWA and XMM) or future instruments
(SKA-LOW and SKA-MID, ATHENA and eROSITA). We find that the most promising
targets are the extreme peripheries of galaxy clusters in an early merging
stage, where the merger causes the fast compression of warm-hot gas onto the
virial region. By taking advantage of a detection in the radio band, future
deep X-ray observations will probe this gas in emission, and help us to study
plasma conditions in the dynamic warm-hot intergalactic medium with
unprecedented detail.Comment: 22 pages, 25 Figures. A\&A accepted, in press. Moderate revision
compared to version 1, with a few new figure
F-formation Detection: Individuating Free-standing Conversational Groups in Images
Detection of groups of interacting people is a very interesting and useful
task in many modern technologies, with application fields spanning from
video-surveillance to social robotics. In this paper we first furnish a
rigorous definition of group considering the background of the social sciences:
this allows us to specify many kinds of group, so far neglected in the Computer
Vision literature. On top of this taxonomy, we present a detailed state of the
art on the group detection algorithms. Then, as a main contribution, we present
a brand new method for the automatic detection of groups in still images, which
is based on a graph-cuts framework for clustering individuals; in particular we
are able to codify in a computational sense the sociological definition of
F-formation, that is very useful to encode a group having only proxemic
information: position and orientation of people. We call the proposed method
Graph-Cuts for F-formation (GCFF). We show how GCFF definitely outperforms all
the state of the art methods in terms of different accuracy measures (some of
them are brand new), demonstrating also a strong robustness to noise and
versatility in recognizing groups of various cardinality.Comment: 32 pages, submitted to PLOS On
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