14,529 research outputs found
Past, Present, and Future of Simultaneous Localization And Mapping: Towards the Robust-Perception Age
Simultaneous Localization and Mapping (SLAM)consists in the concurrent
construction of a model of the environment (the map), and the estimation of the
state of the robot moving within it. The SLAM community has made astonishing
progress over the last 30 years, enabling large-scale real-world applications,
and witnessing a steady transition of this technology to industry. We survey
the current state of SLAM. We start by presenting what is now the de-facto
standard formulation for SLAM. We then review related work, covering a broad
set of topics including robustness and scalability in long-term mapping, metric
and semantic representations for mapping, theoretical performance guarantees,
active SLAM and exploration, and other new frontiers. This paper simultaneously
serves as a position paper and tutorial to those who are users of SLAM. By
looking at the published research with a critical eye, we delineate open
challenges and new research issues, that still deserve careful scientific
investigation. The paper also contains the authors' take on two questions that
often animate discussions during robotics conferences: Do robots need SLAM? and
Is SLAM solved
String Phenomenology: Past, Present and Future Perspectives
The observation of a scalar resonance at the LHC, compatible with
perturbative electroweak symmetry breaking, reinforces the Standard Model
parameterisation of all subatomic data. The logarithmic evolution of the SM
gauge and matter parameters suggests that this parameterisation remains viable
up to the Planck scale, where gravitational effects are of comparable strength.
String theory provides a perturbatively consistent scheme to explore how the
parameters of the Standard Model may be determined from a theory of quantum
gravity. The free fermionic heterotic string models provide concrete examples
of exact string solutions that reproduce the spectrum of the Minimal
Supersymmetric Standard Model. Contemporary studies entail the development of
methods to classify large classes of models. This led to the discovery of
exophobic heterotic-string vacua and the observation of spinor-vector duality,
which provides an insight to the global structure of the space of (2,0)
heterotic-string vacua. Future directions entail the study of the role of the
massive string states in these models and their incorporation in cosmological
scenarios. A complementary direction is the formulation of quantum gravity from
the principle of manifest phase space duality and the equivalence postulate of
quantum mechanics, which suggest that space is compact. The compactness of
space, which implies intrinsic regularisation, may be tightly related to the
intrinsic finite length scale, implied by string phenomenology.Comment: 35 pages. No figures. To appear in the special volume edited by
Gerald Cleaver on "Particle Physics and Quantum Gravity Implications for
Cosmology". Based on talk presented at the 2012 CERN Summer Institute on
String Phenomenolog
A PARTAN-Accelerated Frank-Wolfe Algorithm for Large-Scale SVM Classification
Frank-Wolfe algorithms have recently regained the attention of the Machine
Learning community. Their solid theoretical properties and sparsity guarantees
make them a suitable choice for a wide range of problems in this field. In
addition, several variants of the basic procedure exist that improve its
theoretical properties and practical performance. In this paper, we investigate
the application of some of these techniques to Machine Learning, focusing in
particular on a Parallel Tangent (PARTAN) variant of the FW algorithm that has
not been previously suggested or studied for this type of problems. We provide
experiments both in a standard setting and using a stochastic speed-up
technique, showing that the considered algorithms obtain promising results on
several medium and large-scale benchmark datasets for SVM classification
T-duality of NSR superstring: The worldsheet perspective
We formulate target space duality symmetry of NSR superstring from the
perspectives of worldsheet. The worldsheet action is presented in the
superspace formalism in the presence of massless backgrounds. We start from a
-dimensional target space worldsheet action and compactify the theory
on a d-dimensional torus, . It is assumed that the backgrounds are
independent of compact (super)coordinates. We adopt the formalism of our
earlier work to introduce dual supercoordinates along compact directions and
introduce the corresponding dual backgrounds. It is demonstrated that combined
equations of motion of the two sets of coordinates can be expressed in a
manifestly covariant form analogous to the equations of motions for
closed bosonic string derived by us. Furthermore, we show that the vertex
operators associated with excited massive levels of NSR string can be expressed
in an invariant form generalizing earlier result for closed bosonic
string.Comment: 21 page
Quantum Fluctuations and the Unruh Effect in Strongly-Coupled Conformal Field Theories
Through the AdS/CFT correspondence, we study a uniformly accelerated quark in
the vacuum of strongly-coupled conformal field theories in various dimensions,
and determine the resulting stochastic fluctuations of the quark trajectory.
From the perspective of an inertial observer, these are quantum fluctuations
induced by the gluonic radiation emitted by the accelerated quark. From the
point of view of the quark itself, they originate from the thermal medium
predicted by the Unruh effect. We scrutinize the relation between these two
descriptions in the gravity side of the correspondence, and show in particular
that upon transforming the conformal field theory from Rindler space to the
open Einstein universe, the acceleration horizon disappears from the boundary
theory but is preserved in the bulk. This transformation allows us to directly
connect our calculation of radiation-induced fluctuations in vacuum with the
analysis by de Boer et al. of the Brownian motion of a quark that is on average
static within a thermal medium. Combining this same bulk transformation with
previous results of Emparan, we are also able to compute the stress-energy
tensor of the Unruh thermal medium.Comment: 1+31 pages; v2: reference adde
Strong Coupling Fixed Points of Current Interactions and Disordered Fermions in 2D
The all-orders beta function is used to study disordered Dirac fermions in
2D. The generic strong coupling fixed `points' of anisotropic current-current
interactions at large distances are actually isotropic manifolds corresponding
to subalgebras of the maximal current algebra at short distances. The IR
theories are argued to be current algebra cosets. We illustrate this with the
simple example of anisotropic su(2), which is the physics of
Kosterlitz-Thouless transitions. We work out the phase diagram for the
Chalker-Coddington network model which is in the universality class of the
integer Quantum Hall transition. One massless phase is in the universality
class of dense polymers.Comment: published version (Phys. Rev. B
Recurrence networks - A novel paradigm for nonlinear time series analysis
This paper presents a new approach for analysing structural properties of
time series from complex systems. Starting from the concept of recurrences in
phase space, the recurrence matrix of a time series is interpreted as the
adjacency matrix of an associated complex network which links different points
in time if the evolution of the considered states is very similar. A critical
comparison of these recurrence networks with similar existing techniques is
presented, revealing strong conceptual benefits of the new approach which can
be considered as a unifying framework for transforming time series into complex
networks that also includes other methods as special cases.
It is demonstrated that there are fundamental relationships between the
topological properties of recurrence networks and the statistical properties of
the phase space density of the underlying dynamical system. Hence, the network
description yields new quantitative characteristics of the dynamical complexity
of a time series, which substantially complement existing measures of
recurrence quantification analysis
Optical Flow Guided Feature: A Fast and Robust Motion Representation for Video Action Recognition
Motion representation plays a vital role in human action recognition in
videos. In this study, we introduce a novel compact motion representation for
video action recognition, named Optical Flow guided Feature (OFF), which
enables the network to distill temporal information through a fast and robust
approach. The OFF is derived from the definition of optical flow and is
orthogonal to the optical flow. The derivation also provides theoretical
support for using the difference between two frames. By directly calculating
pixel-wise spatiotemporal gradients of the deep feature maps, the OFF could be
embedded in any existing CNN based video action recognition framework with only
a slight additional cost. It enables the CNN to extract spatiotemporal
information, especially the temporal information between frames simultaneously.
This simple but powerful idea is validated by experimental results. The network
with OFF fed only by RGB inputs achieves a competitive accuracy of 93.3% on
UCF-101, which is comparable with the result obtained by two streams (RGB and
optical flow), but is 15 times faster in speed. Experimental results also show
that OFF is complementary to other motion modalities such as optical flow. When
the proposed method is plugged into the state-of-the-art video action
recognition framework, it has 96:0% and 74:2% accuracy on UCF-101 and HMDB-51
respectively. The code for this project is available at
https://github.com/kevin-ssy/Optical-Flow-Guided-Feature.Comment: CVPR 2018. code available at
https://github.com/kevin-ssy/Optical-Flow-Guided-Featur
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