997 research outputs found
ClassCut for Unsupervised Class Segmentation
Abstract. We propose a novel method for unsupervised class segmentation on a set of images. It alternates between segmenting object instances and learning a class model. The method is based on a segmentation energy defined over all images at the same time, which can be optimized efficiently by techniques used before in interactive segmentation. Over iterations, our method progressively learns a class model by integrating observations over all images. In addition to appearance, this model captures the location and shape of the class with respect to an automatically determined coordinate frame common across images. This frame allows us to build stronger shape and location models, similar to those used in object class detection. Our method is inspired by interactive segmentation methods [1], but it is fully automatic and learns models characteristic for the object class rather than specific to one particular object/image. We experimentally demonstrate on the Caltech4, Caltech101, and Weizmann horses datasets that our method (a) transfers class knowledge across images and this improves results compared to segmenting every image independently; (b) outperforms Grabcut [1] for the task of unsupervised segmentation; (c) offers competitive performance compared to the state-of-the-art in unsupervised segmentation and in particular it outperforms the topic model [2].
Nonequilibrium effects due to charge fluctuations in intrinsic Josephson systems
Nonequilibrium effects in layered superconductors forming a stack of
intrinsic Josephson junctions are investigated. We discuss two basic
nonequilibrium effects caused by charge fluctuations on the superconducting
layers: a) the shift of the chemical potential of the condensate and b) charge
imbalance of quasi-particles, and study their influence on IV-curves and the
position of Shapiro steps.Comment: 17 pages, 2 figures, revised version slightly shortene
Charge-imbalance effects in intrinsic Josephson systems
We report on two types of experiments with intrinsic Josephson systems made
from layered superconductors which show clear evidence of nonequilibrium
effects: 1. In 2-point measurements of IV-curves in the presence of high-
frequency radiation a shift of the voltage of Shapiro steps from the canonical
value hf/(2e) has been observed. 2. In the IV-curves of double-mesa structures
an influence of the current through one mesa on the voltage measured on the
other mesa is detected. Both effects can be explained by charge-imbalance on
the superconducting layers produced by the quasi-particle current, and can be
described successfully by a recently developed theory of nonequilibrium effects
in intrinsic Josephson systems.Comment: 8pages, 9figures, submitted to Phys. Rev.
Image Co-localization by Mimicking a Good Detector's Confidence Score Distribution
Given a set of images containing objects from the same category, the task of
image co-localization is to identify and localize each instance. This paper
shows that this problem can be solved by a simple but intriguing idea, that is,
a common object detector can be learnt by making its detection confidence
scores distributed like those of a strongly supervised detector. More
specifically, we observe that given a set of object proposals extracted from an
image that contains the object of interest, an accurate strongly supervised
object detector should give high scores to only a small minority of proposals,
and low scores to most of them. Thus, we devise an entropy-based objective
function to enforce the above property when learning the common object
detector. Once the detector is learnt, we resort to a segmentation approach to
refine the localization. We show that despite its simplicity, our approach
outperforms state-of-the-art methods.Comment: Accepted to Proc. European Conf. Computer Vision 201
Keep it SMPL: Automatic Estimation of 3D Human Pose and Shape from a Single Image
We describe the first method to automatically estimate the 3D pose of the
human body as well as its 3D shape from a single unconstrained image. We
estimate a full 3D mesh and show that 2D joints alone carry a surprising amount
of information about body shape. The problem is challenging because of the
complexity of the human body, articulation, occlusion, clothing, lighting, and
the inherent ambiguity in inferring 3D from 2D. To solve this, we first use a
recently published CNN-based method, DeepCut, to predict (bottom-up) the 2D
body joint locations. We then fit (top-down) a recently published statistical
body shape model, called SMPL, to the 2D joints. We do so by minimizing an
objective function that penalizes the error between the projected 3D model
joints and detected 2D joints. Because SMPL captures correlations in human
shape across the population, we are able to robustly fit it to very little
data. We further leverage the 3D model to prevent solutions that cause
interpenetration. We evaluate our method, SMPLify, on the Leeds Sports,
HumanEva, and Human3.6M datasets, showing superior pose accuracy with respect
to the state of the art.Comment: To appear in ECCV 201
A Comparative Study of Energy Minimization Methods for Markov Random Fields with Smoothness-Based Priors
Tomonaga-Luttinger model with an impurity for a weak two-body interaction
The Tomonaga-Luttinger model with impurity is studied by means of flow
equations for Hamiltonians. The system is formulated within collective density
fluctuations but no use of the bosonization formula is made. The truncation
scheme includes operators consisting of up to four fermion operators and is
valid for small electron-electron interactions. In this regime, the exact
expression for the anomalous dimension is recovered. Furthermore, we verify the
phase diagram of Kane and Fisher also for intermediate impurity strength. The
approach can be extended to more general one-body potentials.Comment: 10 pages, 1 figur
Observation of isotonic symmetry for enhanced quadrupole collectivity in neutron-rich 62,64,66Fe isotopes at N=40
The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied
using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb
excitation reactions. The deduced E2 strengths illustrate the enhanced
collectivity of the neutron-rich Fe isotopes up to N=40. The results are
interpreted by the generalized concept of valence proton symmetry which
describes the evolution of nuclear structure around N=40 as governed by the
number of valence protons with respect to Z~30. The deformation suggested by
the experimental data is reproduced by state-of-the-art shell calculations with
a new effective interaction developed for the fpgd valence space.Comment: 4 pages, 2 figure
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