18,115 research outputs found
Grasping unknown objects in clutter by superquadric representation
© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper, a quick and efficient method is presented for grasping unknown objects in clutter. The grasping method relies on real-time superquadric (SQ) representation of partial view objects and incomplete object modelling, well suited for unknown symmetric objects in cluttered scenarios which is followed by optimized antipodal grasping. The incomplete object models are processed through a mirroring algorithm that assumes symmetry to first create an approximate complete model and then fit for SQ representation. The grasping algorithm is designed for maximum force balance and stability, taking advantage of the quick retrieval of dimension and surface curvature information from the SQ parameters. The pose of the SQs with respect to the direction of gravity is calculated and used together with the parameters of the SQs and specification of the gripper, to select the best direction of approach and contact points. The SQ fitting method has been tested on custom datasets containing objects in isolation as well as in clutter. The grasping algorithm is evaluated on a PR2 robot and real time results are presented. Initial results indicate that though the method is based on simplistic shape information, it outperforms other learning based grasping algorithms that also work in clutter in terms of time-efficiency and accuracy.Peer ReviewedPostprint (author's final draft
Facial Asymmetry Analysis Based on 3-D Dynamic Scans
Facial dysfunction is a fundamental symptom which often relates to many neurological illnesses, such as stroke, Bell’s palsy, Parkinson’s disease, etc. The current methods for detecting and assessing facial dysfunctions mainly rely on the trained practitioners which have significant limitations as they are often subjective. This paper presents a computer-based methodology of facial asymmetry analysis which aims for automatically detecting facial dysfunctions. The method is based on dynamic 3-D scans of human faces. The preliminary evaluation results testing on facial sequences from Hi4D-ADSIP database suggest that the proposed method is able to assist in the quantification and diagnosis of facial dysfunctions for neurological patients
A Framework for Symmetric Part Detection in Cluttered Scenes
The role of symmetry in computer vision has waxed and waned in importance
during the evolution of the field from its earliest days. At first figuring
prominently in support of bottom-up indexing, it fell out of favor as shape
gave way to appearance and recognition gave way to detection. With a strong
prior in the form of a target object, the role of the weaker priors offered by
perceptual grouping was greatly diminished. However, as the field returns to
the problem of recognition from a large database, the bottom-up recovery of the
parts that make up the objects in a cluttered scene is critical for their
recognition. The medial axis community has long exploited the ubiquitous
regularity of symmetry as a basis for the decomposition of a closed contour
into medial parts. However, today's recognition systems are faced with
cluttered scenes, and the assumption that a closed contour exists, i.e. that
figure-ground segmentation has been solved, renders much of the medial axis
community's work inapplicable. In this article, we review a computational
framework, previously reported in Lee et al. (2013), Levinshtein et al. (2009,
2013), that bridges the representation power of the medial axis and the need to
recover and group an object's parts in a cluttered scene. Our framework is
rooted in the idea that a maximally inscribed disc, the building block of a
medial axis, can be modeled as a compact superpixel in the image. We evaluate
the method on images of cluttered scenes.Comment: 10 pages, 8 figure
Hyperfine characterization and coherence lifetime extension in Pr3+:La2(WO4)3
Rare-earth ions in dielectric crystals are interesting candidates for storing
quantum states of photons. A limiting factor on the optical density and thus
the conversion efficiency is the distortion introduced in the crystal by doping
elements of one type into a crystal matrix of another type. Here, we
investigate the system Pr3+:La2(WO4)3, where the similarity of the ionic radii
of Pr and La minimizes distortions due to doping. We characterize the
praseodymium hyperfine interaction of the ground state (3H4) and one excited
state (1D2) and determine the spin Hamiltonian parameters by numerical analysis
of Raman-heterodyne spectra, which were collected for a range of static
external magnetic field strengths and orientations. On the basis of a crystal
field analysis, we discuss the physical origin of the experimentally determined
quadrupole and Zeeman tensor characteristics. We show the potential for quantum
memory applications by measuring the spin coherence lifetime in a magnetic
field that is chosen such that additional magnetic fields do not shift the
transition frequency in first order. Experimental results demonstrate a spin
coherence lifetime of 158 ms - almost three orders of magnitude longer than in
zero field.Comment: 14 pages, 6 figure
Phase diagram and spin Hamiltonian of weakly-coupled anisotropic S=1/2 chains in CuCl2*2((CD3)2SO)
Field-dependent specific heat and neutron scattering measurements were used
to explore the antiferromagnetic S=1/2 chain compound CuCl2 * 2((CD3)2SO). At
zero field the system acquires magnetic long-range order below TN=0.93K with an
ordered moment of 0.44muB. An external field along the b-axis strengthens the
zero-field magnetic order, while fields along the a- and c-axes lead to a
collapse of the exchange stabilized order at mu0 Hc=6T and mu0 Hc=3.5T,
respectively (for T=0.65K) and the formation of an energy gap in the excitation
spectrum. We relate the field-induced gap to the presence of a staggered
g-tensor and Dzyaloshinskii-Moriya interactions, which lead to effective
staggered fields for magnetic fields applied along the a- and c-axes.
Competition between anisotropy, inter-chain interactions and staggered fields
leads to a succession of three phases as a function of field applied along the
c-axis. For fields greater than mu0 Hc, we find a magnetic structure that
reflects the symmetry of the staggered fields. The critical exponent, beta, of
the temperature driven phase transitions are indistinguishable from those of
the three-dimensional Heisenberg magnet, while measurements for transitions
driven by quantum fluctuations produce larger values of beta.Comment: revtex 12 pages, 11 figure
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