5,596 research outputs found
Vortex-lattice melting in a one-dimensional optical lattice
We investigate quantum fluctuations of a vortex lattice in a one-dimensional
optical lattice. Our method gives full access to all the modes of the vortex
lattice and we discuss in particular the Bloch bands of the Tkachenko modes.
Because of the small number of particles in the pancake Bose-Einstein
condensates at every site of the optical lattice, finite-size effects become
very important. Therefore, the fluctuations in the vortex positions are
inhomogeneous and the melting of the lattice occurs from the outside inwards.
Tunneling between neighbouring pancakes substantially reduces the inhomogeneity
as well as the size of the fluctuations.Comment: 4 pages, 4 figure
No Spare Parts: Sharing Part Detectors for Image Categorization
This work aims for image categorization using a representation of distinctive
parts. Different from existing part-based work, we argue that parts are
naturally shared between image categories and should be modeled as such. We
motivate our approach with a quantitative and qualitative analysis by
backtracking where selected parts come from. Our analysis shows that in
addition to the category parts defining the class, the parts coming from the
background context and parts from other image categories improve categorization
performance. Part selection should not be done separately for each category,
but instead be shared and optimized over all categories. To incorporate part
sharing between categories, we present an algorithm based on AdaBoost to
jointly optimize part sharing and selection, as well as fusion with the global
image representation. We achieve results competitive to the state-of-the-art on
object, scene, and action categories, further improving over deep convolutional
neural networks
Ultracold Superstrings in atomic boson-fermion mixtures
We propose a setup with ultracold atomic gases that can be used to make a
nonrelativistic superstring in four spacetime dimensions. In particular, we
consider for the creation of the superstring a fermionic atomic gas that is
trapped in the core of a vortex in a Bose-Einstein condensate. We explain the
required tuning of experimental parameters to achieve supersymmetry between the
fermionic atoms and the bosonic modes describing the oscillations in the vortex
position. Furthermore, we discuss the experimental consequences of
supersymmetry.Comment: 4 pages, 4 figures; published versio
Objects2action: Classifying and localizing actions without any video example
The goal of this paper is to recognize actions in video without the need for
examples. Different from traditional zero-shot approaches we do not demand the
design and specification of attribute classifiers and class-to-attribute
mappings to allow for transfer from seen classes to unseen classes. Our key
contribution is objects2action, a semantic word embedding that is spanned by a
skip-gram model of thousands of object categories. Action labels are assigned
to an object encoding of unseen video based on a convex combination of action
and object affinities. Our semantic embedding has three main characteristics to
accommodate for the specifics of actions. First, we propose a mechanism to
exploit multiple-word descriptions of actions and objects. Second, we
incorporate the automated selection of the most responsive objects per action.
And finally, we demonstrate how to extend our zero-shot approach to the
spatio-temporal localization of actions in video. Experiments on four action
datasets demonstrate the potential of our approach
High-level feature detection from video in TRECVid: a 5-year retrospective of achievements
Successful and effective content-based access to digital
video requires fast, accurate and scalable methods to determine the video content automatically. A variety of contemporary approaches to this rely on text taken from speech within the video, or on matching one video frame against others using low-level characteristics like
colour, texture, or shapes, or on determining and matching objects appearing within the video. Possibly the most important technique, however, is one which determines the presence or absence of a high-level or semantic feature, within a video clip or shot. By utilizing dozens, hundreds or even thousands of such semantic features we can support many kinds of content-based video navigation. Critically however, this depends on being able to determine whether each feature is or is not present in a video clip.
The last 5 years have seen much progress in the development of techniques to determine the presence of semantic features within video. This progress can be tracked in the annual TRECVid benchmarking activity where dozens of research groups measure the effectiveness of their techniques on common data and using an open, metrics-based approach. In this chapter we summarise the work
done on the TRECVid high-level feature task, showing the
progress made year-on-year. This provides a fairly comprehensive statement on where the state-of-the-art is regarding this important task, not just for one research group or for one approach, but across the spectrum. We then use this past and on-going work as a basis for highlighting the trends that are emerging in this area, and the questions which remain to be addressed before we can
achieve large-scale, fast and reliable high-level feature detection on video
Antiferromagnetic Order of Strongly Interacting Fermions in a Trap: Real-Space Dynamical Mean-Field Analysis
We apply Dynamical Mean-Field Theory to strongly interacting fermions in an
inhomogeneous environment. With the help of this Real-Space Dynamical
Mean-Field Theory (R-DMFT) we investigate antiferromagnetic states of
repulsively interacting fermions with spin 1/2 in a harmonic potential. Within
R-DMFT, antiferromagnetic order is found to be stable in spatial regions with
total particle density close to one, but persists also in parts of the system
where the local density significantly deviates from half filling. In systems
with spin imbalance, we find that antiferromagnetism is gradually suppressed
and phase separation emerges beyond a critical value of the spin imbalance.Comment: 4 pages 5 figures, published versio
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