@article{18010, abstract = {Electronic factors in molecules such as quantum interference and cross-conjugation can lead to dramatic modulation and suppression of conductance in single-molecule junctions. Probing such effects at the single-molecule level requires simultaneous measurements of independent junction properties, as conductance alone cannot provide conclusive evidence of junction formation for molecules with low conductivity. Here, we compare the mechanics of the conducting para-terminated 4,4′-di(methylthio)stilbene and moderately conducting 1,2-bis(4-(methylthio)phenyl)ethane to that of insulating meta-terminated 3,3′-di(methylthio)stilbene single-molecule junctions. We simultaneously measure force and conductance across single-molecule junctions and use force signatures to obtain independent evidence of junction formation and rupture in the meta-linked cross-conjugated molecule even when no clear low-bias conductance is measured. By separately quantifying conductance and mechanics, we identify the formation of atypical 3,3′-di(methylthio)stilbene molecular junctions that are mechanically stable but electronically decoupled. While theoretical studies have envisaged many plausible systems where quantum interference might be observed, our experiments provide the first direct quantitative study of the interplay between contact mechanics and the distinctively quantum mechanical nature of electronic transport in single-molecule junctions.}, author = {Aradhya, Sriharsha V. and Meisner, Jeffrey S. and Krikorian, Markrete and Ahn, Seokhoon and Parameswaran, Radha and Steigerwald, Michael L. and Nuckolls, Colin and Venkataraman, Latha}, issn = {1530-6992}, journal = {Nano Letters}, number = {3}, pages = {1643--1647}, publisher = {American Chemical Society}, title = {{Dissecting contact mechanics from quantum interference in single-molecule junctions of stilbene derivatives}}, doi = {10.1021/nl2045815}, volume = {12}, year = {2012}, } @article{18011, abstract = {We use a modified conducting atomic force microscope to simultaneously probe the conductance of a single-molecule junction and the force required to rupture the junction formed by alkanes terminated with four different chemical link groups which vary in binding strength and mechanism to the gold electrodes. Molecular junctions with amine, methylsulfide, and diphenylphosphine terminated molecules show clear conductance signatures and rupture at a force that is significantly smaller than the measured 1.4 nN force required to rupture the single-atomic gold contact. In contrast, measurements with a thiol terminated alkane which can bind covalently to the gold electrode show conductance and force features unlike those of the other molecules studied. Specifically, the strong Au–S bond can cause structural rearrangements in the electrodes, which are accompanied by substantial conductance changes. Despite the strong Au–S bond and the evidence for disruption of the Au structure, the experiments show that on average these junctions also rupture at a smaller force than that measured for pristine single-atom gold contacts.}, author = {Frei, Michael and Aradhya, Sriharsha V. and Hybertsen, Mark S. and Venkataraman, Latha}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {9}, pages = {4003--4006}, publisher = {American Chemical Society}, title = {{Linker dependent bond rupture force measurements in single-molecule junctions}}, doi = {10.1021/ja211590d}, volume = {134}, year = {2012}, } @article{18013, abstract = {Van der Waals (vdW) interaction, and its subtle interplay with chemically specific interactions and surface roughness at metal/organic interfaces, is critical to the understanding of structure–function relations in diverse areas, including catalysis, molecular electronics and self-assembly1,2,3. However, vdW interactions remain challenging to characterize directly at the fundamental, single-molecule level both in experiments and in first principles calculations with accurate treatment of the non-local, London dispersion interactions. In particular, for metal/organic interfaces, efforts so far have largely focused on model systems consisting of adsorbed molecules on flat metallic surfaces with minimal specific chemical interaction4,5,6,7,8,9. Here we show, through measurements of single-molecule mechanics, that pyridine derivatives10,11 can bind to nanostructured Au electrodes through an additional binding mechanism beyond the chemically specific N–Au donor–acceptor bond. Using density functional theory simulations we show that vdW interactions between the pyridine ring and Au electrodes can play a key role in the junction mechanics. These measurements thus provide a quantitative characterization of vdW interactions at metal/organic interfaces at the single-molecule level.}, author = {Aradhya, Sriharsha V. and Frei, Michael and Hybertsen, Mark S. and Venkataraman, Latha}, issn = {1476-4660}, journal = {Nature Materials}, number = {10}, pages = {872--876}, publisher = {Springer Nature}, title = {{Van der Waals interactions at metal/organic interfaces at the single-molecule level}}, doi = {10.1038/nmat3403}, volume = {11}, year = {2012}, } @article{18201, abstract = {Owing to thermal fluctuations, two-dimensional (2D) systems cannot undergo a conventional phase transition associated with the breaking of a continuous symmetry1. Nevertheless they may exhibit a phase transition to a state with quasi-long-range order via the Berezinskii–Kosterlitz–Thouless (BKT) mechanism2. A paradigm example is the 2D Bose fluid, such as a liquid helium film3, which cannot condense at non-zero temperature although it becomes superfluid above a critical phase space density. The quasi-long-range coherence and the microscopic nature of the BKT transition were recently explored with ultracold atomic gases4,5,6. However, a direct observation of superfluidity in terms of frictionless flow is still missing for these systems. Here we probe the superfluidity of a 2D trapped Bose gas using a moving obstacle formed by a micrometre-sized laser beam. We find a dramatic variation of the response of the fluid, depending on its degree of degeneracy at the obstacle location.}, author = {Desbuquois, Rémi and Chomaz, Lauriane and Yefsah, Tarik and Leonard, Julian and Beugnon, Jérôme and Weitenberg, Christof and Dalibard, Jean}, issn = {1745-2481}, journal = {Nature Physics}, number = {9}, pages = {645--648}, publisher = {Springer Nature}, title = {{Superfluid behaviour of a two-dimensional Bose gas}}, doi = {10.1038/nphys2378}, volume = {8}, year = {2012}, } @inbook{18325, abstract = {The computer vision and pattern recognition communities have recently witnessed a surge in feature-based methods for numerous applications including object recognition and image retrieval. Similar concepts and analogous approaches are penetrating the world of 3D shape analysis in a variety of areas including non-rigid shape retrieval and matching. In this chapter, we present both mature concepts and the state-of-the-art of feature-based approaches in 3D shape analysis. In particular, approaches to the detection of interest points and the generation of local shape descriptors are discussed. A wide range of methods is covered including those based on curvature, those based on difference-of-Gaussian scale space, and those that employ recent advances in heat kernel methods.}, author = {Bronstein, Alexander and Bronstein, Michael M. and Ovsjanikov, Maks}, booktitle = {3D Imaging, Analysis and Applications}, editor = {Pears, Nick and Liu, Yonghuai and Bunting, Peter}, isbn = {9781447140627}, pages = {185--219}, publisher = {Springer Nature}, title = {{Feature-Based Methods in 3D Shape Analysis}}, doi = {10.1007/978-1-4471-4063-4_5}, year = {2012}, } @book{18340, abstract = {This book constitutes the thoroughly refereed post-conference proceedings of the Third International Conference on Scale Space Methods and Variational Methods in Computer Vision, SSVM 2011, held in Ein-Gedi, Israel in May/June 2011. The 24 revised full papers presented together with 44 poster papers were carefully reviewed and selected from 78 submissions. The papers are organized in topical sections on denoising and enhancement, segmentation, image representation and invariants, shape analysis, and optical flow. }, editor = {Bruckstein, Alfred M. and ter Haar Romeny, Bart M. and Bronstein, Alexander and Bronstein, Michael M.}, isbn = {9783642247842}, issn = {1611-3349}, pages = {XIV, 798}, publisher = {Springer Nature}, title = {{Scale Space and Variational Methods in Computer Vision}}, doi = {10.1007/978-3-642-24785-9}, volume = {6667}, year = {2012}, } @inproceedings{18341, abstract = {Similarity and correspondence are two fundamental archetype problems in shape analysis, encountered in numerous application in computer vision and pattern recognition. Many methods for shape similarity and correspondence boil down to the minimum-distortion correspondence problem, in which two shapes are endowed with certain structure, and one attempts to find the matching with smallest structure distortion between them. Defining structures invariant to some class of shape transformations results in an invariant minimum-distortion correspondence or similarity. In this paper, we model shapes using local and global structures, formulate the invariant correspondence problem as binary graph labeling, and show how different choice of structure results in invariance under various classes of deformations.}, author = {Wang, Chaohui and Bronstein, Michael M. and Bronstein, Alexander and Paragios, Nikos}, booktitle = {3rd International Conference on Scale Space and Variational Methods in Computer Vision}, isbn = {9783642247842}, issn = {1611-3349}, location = {Ein-Gedi, Israel}, pages = {580 -- 591}, publisher = {Springer Nature}, title = {{Discrete minimum distortion correspondence problems for non-rigid shape matching}}, doi = {10.1007/978-3-642-24785-9_49}, volume = {6667}, year = {2012}, } @inproceedings{18342, abstract = {Finding a match between partially available deformable shapes is a challenging problem with numerous applications. The problem is usually approached by computing local descriptors on a pair of shapes and then establishing a point-wise correspondence between the two. In this paper, we introduce an alternative correspondence-less approach to matching fragments to an entire shape undergoing a non-rigid deformation. We use diffusion geometric descriptors and optimize over the integration domains on which the integral descriptors of the two parts match. The problem is regularized using the Mumford-Shah functional. We show an efficient discretization based on the Ambrosio-Tortorelli approximation generalized to triangular meshes. Experiments demonstrating the success of the proposed method are presented.}, author = {Pokrass, Jonathan and Bronstein, Alexander and Bronstein, Michael M.}, booktitle = {3rd International Conference on Scale Space and Variational Methods in Computer Vision}, isbn = {9783642247842}, issn = {1611-3349}, location = {Ein-Gedi, Israel}, pages = {592 -- 603}, publisher = {Springer Nature}, title = {{A correspondence-less approach to matching of deformable shapes}}, doi = {10.1007/978-3-642-24785-9_50}, volume = {6667}, year = {2012}, } @inproceedings{18343, abstract = {In this paper, we explore the use of the diffusion geometry framework for the fusion of geometric and photometric information in local heat kernel signature shape descriptors. Our construction is based on the definition of a diffusion process on the shape manifold embedded into a high-dimensional space where the embedding coordinates represent the photometric information. Experimental results show that such data fusion is useful in coping with different challenges of shape analysis where pure geometric and pure photometric methods fail.}, author = {Kovnatsky, Artiom and Bronstein, Michael M. and Bronstein, Alexander and Kimmel, Ron}, booktitle = {3rd International Conference on Scale Space and Variational Methods in Computer Vision}, isbn = {9783642247842}, issn = {1611-3349}, location = {Ein-Gedi, Israel}, pages = {616--627}, publisher = {Springer Nature}, title = {{Photometric heat kernel signatures}}, doi = {10.1007/978-3-642-24785-9_52}, volume = {6667}, year = {2012}, } @inproceedings{18344, abstract = {Analysis of intrinsic symmetries of non-rigid and articulated shapes is an important problem in pattern recognition with numerous applications ranging from medicine to computational aesthetics. Considering articulated planar shapes as closed curves, we show how to represent their extrinsic and intrinsic symmetries as self-similarities of local descriptor sequences, which in turn have simple interpretation in the frequency domain. The problem of symmetry detection and analysis thus boils down to analysis of descriptor sequence patterns. For that purpose, we show two efficient computational methods: one based on Fourier analysis, and another on dynamic programming.}, author = {Hooda, Amit and Bronstein, Michael M. and Bronstein, Alexander and Horaud, Radu P.}, booktitle = {Scale Space and Variational Methods in Computer Vision}, isbn = {9783642247842}, issn = {1611-3349}, location = {Ein-Gedi, Israel}, pages = {665–676}, publisher = {Springer Nature}, title = {{Shape palindromes: Analysis of intrinsic symmetries in 2D articulated shapes}}, doi = {10.1007/978-3-642-24785-9_56}, volume = {6667}, year = {2012}, } @inproceedings{18345, abstract = {In classical signal processing, it is common to analyze and process signals in the frequency domain, by representing the signal in the Fourier basis, and filtering it by applying a transfer function on the Fourier coefficients. In some applications, it is possible to design an optimal filter. A classical example is the Wiener filter that achieves a minimum mean squared error estimate for signal denoising. Here, we adopt similar concepts to construct optimal diffusion geometric shape descriptors. The analogy of Fourier basis are the eigenfunctions of the Laplace-Beltrami operator, in which many geometric constructions such as diffusion metrics, can be represented. By designing a filter of the Laplace-Beltrami eigenvalues, it is theoretically possible to achieve invariance to different shape transformations, like scaling. Given a set of shape classes with different transformations, we learn the optimal filter by minimizing the ratio between knowingly similar and knowingly dissimilar diffusion distances it induces. The output of the proposed framework is a filter that is optimally tuned to handle transformations that characterize the training set.}, author = {Aflalo, Yonathan and Bronstein, Alexander and Bronstein, Michael M. and Kimmel, Ron}, booktitle = {3rd International Conference on Scale Space and Variational Methods in Computer Vision}, isbn = {9783642247842}, issn = {1611-3349}, location = {Ein-Gedi, Israel}, pages = {689--700}, publisher = {Springer Nature}, title = {{Deformable shape retrieval by learning diffusion kernels}}, doi = {10.1007/978-3-642-24785-9_58}, volume = {6667}, year = {2012}, } @inproceedings{18346, abstract = {Understanding of articulated shape motion plays an important role in many applications in the mechanical engineering, movie industry, graphics, and vision communities. In this paper, we study motion-based segmentation of articulated 3D shapes into rigid parts. We pose the problem as finding a group-valued map between the shapes describing the motion, forcing it to favor piecewise rigid motions. Our computation follows the spirit of the Ambrosio-Tortorelli scheme for Mumford-Shah segmentation, with a diffusion component suited for the group nature of the motion model. Experimental results demonstrate the effectiveness of the proposed method in non-rigid motion segmentation.}, author = {Rosman, Guy and Bronstein, Michael M. and Bronstein, Alexander and Wolf, Alon and Kimmel, Ron}, booktitle = {3rd International Conference on Scale Space and Variational Methods in Computer Vision}, isbn = {9783642247842}, issn = {1611-3349}, location = {Ein-Gedi, Israel}, pages = {725--736}, publisher = {Springer Nature}, title = {{Group-valued regularization framework for motion segmentation of dynamic non-rigid shapes}}, doi = {10.1007/978-3-642-24785-9_61}, volume = {6667}, year = {2012}, } @inproceedings{18347, abstract = {Multi-part shape matching is an important class of problems, arising in many fields such as computational archaeology, biology, geometry processing, computer graphics and vision. In this paper, we address the problem of simultaneous matching and segmentation of multiple shapes. We assume to be given a reference shape and multiple parts partially matching the reference. Each of these parts can have additional clutter, have overlap with other parts, or there might be missing parts. We show experimental results of efficient and accurate assembly of fractured synthetic and real objects.}, author = {Litany, Or and Bronstein, Alexander and Bronstein, Michael M.}, booktitle = {Computer Vision, ECCV 2012 - Workshops and Demonstrations}, isbn = {9783642338625}, issn = {1611-3349}, location = {Florence, Italy}, number = {Part 1}, pages = {1--11}, publisher = {Springer Nature}, title = {{Putting the pieces together: Regularized multi-part shape matching}}, doi = {10.1007/978-3-642-33863-2_1}, volume = {7583}, year = {2012}, } @inproceedings{18348, abstract = {We present a novel method for estimation of articulated motion in depth scans. The method is based on a framework for regularization of vector- and matrix- valued functions on parametric surfaces. We extend augmented-Lagrangian total variation regularization to smooth rigid motion cues on the scanned 3D surface obtained from a range scanner. We demonstrate the resulting smoothed motion maps to be a powerful tool in articulated scene understanding, providing a basis for rigid parts segmentation, with little prior assumptions on the scene, despite the noisy depth measurements that often appear in commodity depth scanners.}, author = {Rosman, Guy and Bronstein, Alexander and Bronstein, Michael M. and Tai, Xue-Cheng and Kimmel, Ron}, booktitle = {Computer Vision, ECCV 2012 - Workshops and Demonstrations}, isbn = {9783642338625}, issn = {1611-3349}, location = {Florence, Italy}, number = {Part 1}, pages = {52--62}, publisher = {Springer Nature}, title = {{Group-valued regularization for analysis of articulated motion}}, doi = {10.1007/978-3-642-33863-2_6}, volume = {7583}, year = {2012}, } @inproceedings{18349, abstract = {The rapid development of 3D acquisition technology has brought with itself the need to perform standard signal processing operations such as filters on 3D data. It has been shown that the eigenfunctions of the Laplace-Beltrami operator (manifold harmonics) of a surface play the role of the Fourier basis in the Euclidean space; it is thus possible to formulate signal analysis and synthesis in the manifold harmonics basis. In particular, geometry filtering can be carried out in the manifold harmonics domain by decomposing the embedding coordinates of the shape in this basis. However, since the basis functions depend on the shape itself, such filtering is valid only for weak (near all-pass) filters, and produces severe artifacts otherwise. In this paper, we analyze this problem and propose the fractional filtering approach, wherein we apply iteratively weak fractional powers of the filter, followed by the update of the basis functions. Experimental results show that such a process produces more plausible and meaningful results.}, author = {Kovnatsky, Artiom and Bronstein, Michael M. and Bronstein, Alexander}, booktitle = {Computer Vision, ECCV 2012 - Workshops and Demonstrations}, isbn = {9783642338625}, issn = {0302-9743}, location = {Florence, Italy}, number = {Part 1}, pages = {83--91}, publisher = {Springer Nature}, title = {{Stable Spectral Mesh Filtering}}, doi = {10.1007/978-3-642-33863-2_9}, volume = {7583}, year = {2012}, } @inproceedings{18350, abstract = {We introduce an (equi-)affine invariant geometric structure by which surfaces that go through squeeze and shear transformations can still be properly analyzed. The definition of an affine invariant metric enables us to evaluate a new form of geodesic distances and to construct an invariant Laplacian from which local and global diffusion geometry is constructed. Applications of the proposed framework demonstrate its power in generalizing and enriching the existing set of tools for shape analysis.}, author = {Raviv, Dan and Bronstein, Alexander and Bronstein, Michael M. and Kimmel, Ron and Sochen, Nir}, booktitle = {15th International Workshop on Theoretical Foundations of Computer Vision}, isbn = {9783642340901}, issn = {1611-3349}, location = {Dagstuhl, Germany}, pages = {177--190}, publisher = {Springer Nature}, title = {{Equi-affine invariant geometries of articulated objects}}, doi = {10.1007/978-3-642-34091-8_8}, volume = {7474}, year = {2012}, } @article{18364, abstract = {Region feature detectors and descriptors have become a successful and popular alternative to point descriptors in image analysis due to their high robustness and repeatability, leading to a significant interest in the shape analysis community in finding analogous approaches in the 3D world. Recent works have successfully extended the maximally stable extremal region (MSER) detection algorithm to surfaces. In many applications, however, a volumetric shape model is more appropriate, and modeling shape deformations as approximate isometries of the volume of an object, rather than its boundary, better captures natural behavior of non-rigid deformations. In this paper, we formulate a diffusion-geometric framework for volumetric stable component detection and description in deformable shapes. An evaluation of our method on the SHREC'11 feature detection benchmark and SCAPE human body scans shows its potential as a source of high-quality features. Examples demonstrating the drawbacks of surface stable components and the advantage of their volumetric counterparts are also presented.}, author = {Litman, R. and Bronstein, Alexander and Bronstein, M.M.}, issn = {0097-8493}, journal = {Computers & Graphics}, number = {5}, pages = {569--576}, publisher = {Elsevier}, title = {{Stable volumetric features in deformable shapes}}, doi = {10.1016/j.cag.2012.03.034}, volume = {36}, year = {2012}, } @inproceedings{18378, abstract = {In this work, we present intrinsic shape context (ISC) descriptors for 3D shapes. We generalize to surfaces the polar sampling of the image domain used in shape contexts: for this purpose, we chart the surface by shooting geodesic outwards from the point being analyzed; `angle' is treated as tantamount to geodesic shooting direction, and radius as geodesic distance. To deal with orientation ambiguity, we exploit properties of the Fourier transform. Our charting method is intrinsic, i.e., invariant to isometric shape transformations. The resulting descriptor is a meta-descriptor that can be applied to any photometric or geometric property field defined on the shape, in particular, we can leverage recent developments in intrinsic shape analysis and construct ISC based on state-of-the-art dense shape descriptors such as heat kernel signatures. Our experiments demonstrate a notable improvement in shape matching on standard benchmarks.}, author = {Kokkinos, I. and Bronstein, M. M. and Litman, R. and Bronstein, Alexander}, booktitle = {2012 IEEE Conference on Computer Vision and Pattern Recognition}, isbn = {9781467312264}, issn = {1063-6919}, location = {Providence, RI, United States}, publisher = {IEEE}, title = {{Intrinsic shape context descriptors for deformable shapes}}, doi = {10.1109/cvpr.2012.6247671}, year = {2012}, } @inproceedings{18379, abstract = {We consider the problem of minimum distortion intrinsic correspondence between deformable shapes, many useful formulations of which give rise to the NP-hard quadratic assignment problem (QAP). Previous attempts to use the spectral relaxation have had limited success due to the lack of sparsity of the obtained “fuzzy” solution. In this paper, we adopt the recently introduced alternative L 1 relaxation of the QAP based on the principles of game theory. We relate it to the Gromov and Lipschitz metrics between metric spaces and demonstrate on state-of-the-art benchmarks that the proposed approach is capable of finding very accurate sparse correspondences between deformable shapes.}, author = {Rodola, E. and Bronstein, Alexander and Albarelli, A. and Bergamasco, F. and Torsello, A.}, booktitle = {2012 IEEE Conference on Computer Vision and Pattern Recognition}, isbn = {978-1-4673-1226-4}, issn = {1063-6919}, location = {Providence, RI, United States}, publisher = {IEEE}, title = {{A game-theoretic approach to deformable shape matching}}, doi = {10.1109/cvpr.2012.6247674}, year = {2012}, } @article{18412, abstract = {SIFT-like local feature descriptors are ubiquitously employed in computer vision applications such as content-based retrieval, video analysis, copy detection, object recognition, photo tourism, and 3D reconstruction. Feature descriptors can be designed to be invariant to certain classes of photometric and geometric transformations, in particular, affine and intensity scale transformations. However, real transformations that an image can undergo can only be approximately modeled in this way, and thus most descriptors are only approximately invariant in practice. Second, descriptors are usually high dimensional (e.g., SIFT is represented as a 128--dimensional vector). In large-scale retrieval and matching problems, this can pose challenges in storing and retrieving descriptor data. We map the descriptor vectors into the Hamming space in which the Hamming metric is used to compare the resulting representations. This way, we reduce the size of the descriptors by representing them as short binary strings and learn descriptor invariance from examples. We show extensive experimental validation, demonstrating the advantage of the proposed approach.}, author = {Strecha, C. and Bronstein, Alexander and Bronstein, M. M. and Fua, P.}, issn = {2160-9292}, journal = {IEEE Transactions on Pattern Analysis and Machine Intelligence}, number = {1}, pages = {66--78}, publisher = {Institute of Electrical and Electronics Engineers}, title = {{LDAHash: Improved matching with smaller descriptors}}, doi = {10.1109/tpami.2011.103}, volume = {34}, year = {2012}, }