Author
Leo Kärkkäinen
Other affiliations: Bell Labs, Aalto University, University of Arizona ...read more
Bio: Leo Kärkkäinen is an academic researcher from Nokia. The author has contributed to research in topics: Quantum chromodynamics & Lattice gauge theory. The author has an hindex of 26, co-authored 125 publications receiving 2190 citations. Previous affiliations of Leo Kärkkäinen include Bell Labs & Aalto University.
Papers published on a yearly basis
Papers
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TL;DR: An electron transport study of lithographically fabricated graphene nanoribbons of various widths and lengths finds that charging effects constitute a significant portion of the activation energy.
Abstract: We report an electron transport study of lithographically fabricated graphene nanoribbons (GNRs) of various widths and lengths. At the charge neutrality point, a length-independent transport gap forms whose size is inversely proportional to the GNR width. In this gap, electrons are localized, and charge transport exhibits a transition between thermally activated behavior at higher temperatures and variable range hopping at lower temperatures. By varying the geometric capacitance, we find that charging effects constitute a significant portion of the activation energy.
434 citations
Patent•
30 Nov 2007TL;DR: In this paper, a method for transferring files stored on a source device to a target device by dragging and dropping the file from the source device touchscreen to the target device touchscreen is described.
Abstract: A method, apparatus, system and computer program product are provided for transferring files stored on a source device to a target device by dragging and dropping the file from the source device touchscreen to the target device touchscreen. When the source device detects that the user has dragged the file to the edge, or other predefined location, of the source device touchscreen, the source device will automatically identify and establish a connection with the target device. Once the connection has been established, an image or icon associated with the file can be transferred to the target device, so that the user of the target device can indicate the location to which the file should be transferred by dragging the icon to that location. Once the target device user drops the icon at the predefined location, the file can be transferred to that location.
135 citations
Proceedings Article•
07 Dec 2015TL;DR: This work proposes two probabilistic interpretations of bidirectional RNNs that can be used to reconstruct missing gaps efficiently and provides results on music data for which the Bayesian inference is computationally infeasible, demonstrating the scalability of the proposed methods.
Abstract: Bidirectional recurrent neural networks (RNN) are trained to predict both in the positive and negative time directions simultaneously. They have not been used commonly in unsupervised tasks, because a probabilistic interpretation of the model has been difficult. Recently, two different frameworks, GSN and NADE, provide a connection between reconstruction and probabilistic modeling, which makes the interpretation possible. As far as we know, neither GSN or NADE have been studied in the context of time series before. As an example of an un-supervised task, we study the problem of filling in gaps in high-dimensional time series with complex dynamics. Although unidirectional RNNs have recently been trained successfully to model such time series, inference in the negative time direction is non-trivial. We propose two probabilistic interpretations of bidirectional RNNs that can be used to reconstruct missing gaps efficiently. Our experiments on text data show that both proposed methods are much more accurate than unidirectional reconstructions, although a bit less accurate than a computationally complex bidirectional Bayesian inference on the unidirectional RNN. We also provide results on music data for which the Bayesian inference is computationally infeasible, demonstrating the scalability of the proposed methods.
99 citations
TL;DR: In this paper, the critical exponents of the three-dimensional Gross-Neveu model with two four-component fermions were measured from the scaling behaviour of observables on lattice sizes 8(3), 12(3, 16(3) and 24(3).
70 citations
Patent•
31 Mar 2010TL;DR: In this article, the authors present an apparatus configured to: receive depth motion signalling associated with depth motion actuation of a physical stylus; and generate image data of a virtual stylus which has a virtual length according to the received depth motion signals.
Abstract: Apparatus, the apparatus configured to: receive depth motion signalling associated with depth motion actuation of a physical stylus; and generate image data of a virtual stylus which has a virtual length according to the received depth motion signalling.
69 citations
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TL;DR: In this paper, a broad review of fundamental electronic properties of two-dimensional graphene with the emphasis on density and temperature dependent carrier transport in doped or gated graphene structures is provided.
Abstract: We provide a broad review of fundamental electronic properties of two-dimensional graphene with the emphasis on density and temperature dependent carrier transport in doped or gated graphene structures. A salient feature of our review is a critical comparison between carrier transport in graphene and in two-dimensional semiconductor systems (e.g. heterostructures, quantum wells, inversion layers) so that the unique features of graphene electronic properties arising from its gap- less, massless, chiral Dirac spectrum are highlighted. Experiment and theory as well as quantum and semi-classical transport are discussed in a synergistic manner in order to provide a unified and comprehensive perspective. Although the emphasis of the review is on those aspects of graphene transport where reasonable consensus exists in the literature, open questions are discussed as well. Various physical mechanisms controlling transport are described in depth including long- range charged impurity scattering, screening, short-range defect scattering, phonon scattering, many-body effects, Klein tunneling, minimum conductivity at the Dirac point, electron-hole puddle formation, p-n junctions, localization, percolation, quantum-classical crossover, midgap states, quantum Hall effects, and other phenomena.
2,930 citations
University of Cambridge1, Istituto Italiano di Tecnologia2, Lancaster University3, University of Manchester4, Catalan Institution for Research and Advanced Studies5, Technical University of Denmark6, Nokia7, University of Trento8, Queen Mary University of London9, fondazione bruno kessler10, Technische Universität München11, Polytechnic University of Milan12, Centre national de la recherche scientifique13, University of Trieste14, University of Ioannina15, University of Geneva16, Trinity College, Dublin17, Texas Instruments18, University of Paris19, Spanish National Research Council20, Leiden University21, Delft University of Technology22, University of Patras23, École Normale Supérieure24, Radboud University Nijmegen25, Nest Labs26, Airbus UK27, Seoul National University28, Yonsei University29, University of Oxford30, Chalmers University of Technology31, University of Groningen32, STMicroelectronics33, Chemnitz University of Technology34, Max Planck Society35, Aalto University36
TL;DR: An overview of the key aspects of graphene and related materials, ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries are provided.
Abstract: We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.
2,560 citations
TL;DR: In this article, the main results obtained by the BRAHMS Collaboration on the properties of hot and dense hadronic and partonic matter produced in ultrarelativistic heavy ion collisions at RHIC are reviewed.
1,860 citations
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TL;DR: In this article, the authors review the theory and phenomenology of instantons in quantum chromodynamics (QCD) and provide a pedagogical introduction to semiclassical methods in quantum mechanics and field theory.
Abstract: The authors review the theory and phenomenology of instantons in quantum chromodynamics (QCD). After a general overview, they provide a pedagogical introduction to semiclassical methods in quantum mechanics and field theory. The main part of the review summarizes our understanding of the instanton liquid in QCD and the role of instantons in generating the spectrum of light hadrons. The authors also discuss properties of instantons at finite temperature and how instantons can provide a mechanism for the chiral phase transition. They give an overview of the role of instantons in some other models, in particular low-dimensional sigma models, electroweak theory, and supersymmetric QCD.
1,089 citations
Patent•
13 Jun 2015
TL;DR: In this article, the authors provide methods and systems for creating virtual and augmented reality experiences to users, which include an image capturing device to capture one or more images and a processor communicatively coupled to the image-capturing device to extract a set of map points from the set of images.
Abstract: To provide methods and systems for creating virtual and augmented reality.SOLUTION: Configurations are disclosed for presenting virtual reality and augmented reality experiences to users. The systems may comprise an image capturing device to capture one or more images, the one or more images corresponding to a field of view of a user of a head-mounted augmented reality device, and a processor communicatively coupled to the image capturing device to extract a set of map points from the set of images, to identify a set of sparse points and a set of dense points from the extracted set of map points, and to perform normalization on the set of map points.SELECTED DRAWING: Figure 1
995 citations