École Polytechnique Fédérale de Lausanne
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The union of congruent cubes in three dimensions
No full textDCGProfessor Pach's number: [161]. Also in: 17th ACM Symposium on Computational Geometry, ACM Press, 2001, 19-28
A history of rational homotopy theory
No full textRational homotopy theory is the study of topological spaces “modulo torsion”. When rational homotopy theorists calculate algebraic invariants of a topological space, such as its homotopy or homology groups, they retain only the nontorsion information. Algebraic models of topological spaces are the most important tools of the rational homotopy theorist.UPHES
Distributed Similarity Search in High Dimensions Using Locality Sensitive Hashing
No full textIn this paper we consider distributed K-Nearest Neighbor (KNN) search and range query processing in high dimensional data. Our approach is based on Locality Sensitive Hashing (LSH) which has proven very efficient in answering KNN queries in centralized settings. We consider mappings from the multi-dimensional LSH bucket space to the linearly ordered set of peers that jointly maintain the indexed data and derive requirements to achieve high quality search results and limit the number of network accesses. We put forward two such mappings that come with these salient properties: being locality preserving so that buckets likely to hold similar data are stored on the same or neighboring peers and having a predictable output distribution to ensure fair load balancing. We show how to leverage the linearly aligned data for efficient KNN search and how to efficiently process range queries which is, to the best of our knowledge, not possible in existing LSH schemes. We show by comprehensive performance evaluations using real world data that our approach brings major performance and accuracy gains compared to state-of-the-art.LSI
A Stochastic Perturbative Approach to Design a Defect-Aware Thresholder in the Sense Amplifier of Crossbar Memories
Get PDFThe use of nanowire crossbars to build devices with large storage capabilities is a very promising architectural paradigm for forthcoming nanoscale memory devices. However, this new type of memory devices raises questions regarding how to test their correct operation. In particular, the variability affecting the decoder is expected to make very complex the test of these new devices. In this paper we present a method to simplify the test of these new devices by using a current thresholder to detect badly addressed nanowires. In the proposed method, the thresholder design is based on a stochastic and perturbative model of the current through the nanowires. Thus, the calculated thresholder parameters are robust against technology variation. As our experimental results indicate, the thresholder error probability is initially only ∼ 10−4, which can be also reduced further (up to ~60×) by trading-off only ~35% area overhead in the memory.LSMLSI1ES
Points surrounding the origin
Get PDFSuppose d > 2, n > d+1, and we have a set P of n points in d-dimensional Euclidean space. Then P contains a subset Q of d points such that for any p ∈ P, the convex hull of Q∪{p} does not contain the origin in its interior.
We also show that for non-empty, finite point sets A1, ..., Ad+1 in ℝd, if the origin is contained in the convex hull of Ai ∪ Aj for all 1≤i<j≤d+1, then there is a simplex S containing the origin such that |S∩Ai|=1 for every 1≤i≤d+1. This is a generalization of Bárány’s colored Carathéodory theorem, and in a dual version, it gives a spherical version of Lovász’ colored Helly theorem.DCGProfessor Pach's number: [216
Role of Inner- and Outer-Sphere Bonding in the Sensitization of EuIII-Luminescence Deciphered by Combined Analysis of Experimental Electron Density Distribution Function and Photophysical Data
No full textA series of lanthanide adducts with different amounts of 1,10-phenanthroline, chloride ions, and water molecules in the inner and outer coordination spheres are investigated with the aim of relating the chemical bonding pattern in the crystals to the luminescence properties of the Eu ion: [LnCl1Phen2(H2O)3]Cl2(H2O) (Ln ) Eu, 1Eu; Gd, 1Gd; Tb, 1Tb), [EuCl2Phen2(H2O)2]Cl1(H2O) (2), and [EuCl2Phen1(H2O)4]Cl1(H2O) (3). The influence of inner- versus outersphere ligands on the Ln-X bond lengths and angles in the structure is examined. A detailed topological analysis of the electron density function derived from the X-ray diffraction data for 1Gd is performed within the frame of the “atoms in molecule” theory for the first time for a lanthanide complex. The chemical bonding pattern is interpreted in terms of net atomic charges, bond energies, and electron transfers from the ligands to the metal ion. A noteworthy finding is that the energy of extended noncovalent interactions occurring in the second coordination sphere (Hbonding and π-stacking interactions) is comparable to that of Ln-ligand bonds. The luminescence properties of the three Eu adducts are interpreted with the results of electron density distribution function topology. An intraligand charge transfer state is identified, and its contribution in the ligand-to-europium energy transfer process is analyzed. The outcome of this study is that specific interionic interactions which are usually not considered in theoretical calculations or in the interpretation of luminescence properties play an important role in the sensitization of the Eu luminescence.LCS
