Search results for " graph"

Superfluid weight and Berezinskii-Kosterlitz-Thouless transition temperature of twisted bilayer graphene

2019

We study superconductivity of twisted bilayer graphene with local and non-local attractive interactions. We obtain the superfluid weight and Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for microscopic tight-binding and low-energy continuum models. We predict qualitative differences between local and non-local interaction schemes which could be distinguished experimentally. In the flat band limit where the pair potential exceeds the band width we show that the superfluid weight and BKT temperature are determined by multiband processes and quantum geometry of the band.

Electron-phonon interaction in flat-band superconductivity

2017

Parhaiten tunnettu suprajohtavuuden syntymekanismi perustuu fononien välittämään vetovoimaan elektronien välillä. Tässä tutkielmassa tutkin fononien välittämää suprajohtavuutta systeemeissä, jossa elektronivyöt ovat tasomaisia. Tasovyöllä elektronien dispersio on erittäin heikko, jolloin tilatiheys on tavanomaista suurempi. Tämän takia suprajohtavuus tasovyöllä on tavanomaista voimakkaampi silloin kun elektronien välinen vetovoima on heikko. Eliashbergin teoria on elektroni–fononi-suprajohtavuuden teoria, joka ottaa luonnollisella tavalla fononien äärellisen nopeuden huomioon elektronien välisessä vuorovaikutuksessa. Pohjustuksena tasovyösuprajohtavuuteen perehdyn Eliashbergin teoriaan ensi…

Sensors for the monitoring of analytes in the sweat

In the last decade, can be found an exceptional growth in research activity relating to the development of wearable devices, capable of continuously monitoring the health conditions of the wearer by analyzing body fluids such as blood, urine, saliva, tears and sweat. Among the body fluids available, sweat is a biofluid of particular interest, as it allows a non-invasive, continuous and comfortable collection. Human sweat contains useful information on the health of an individual and therefore is an excellent biofluid for the detection of specific analytes. The most abundant ions in the sweat are Na+ and Cl- (10 - 100 mM), and their monitoring is useful in patients with cystic fibrosis. Othe…

Hadronic light-by-light contribution to $(g-2)_\mu$ from lattice QCD with SU(3) flavor symmetry

2020

We perform a lattice QCD calculation of the hadronic light-by-light contribution to $(g-2)_\mu$ at the SU(3) flavor-symmetric point $m_\pi=m_K\simeq 420\,$MeV. The representation used is based on coordinate-space perturbation theory, with all QED elements of the relevant Feynman diagrams implemented in continuum, infinite Euclidean space. As a consequence, the effect of using finite lattices to evaluate the QCD four-point function of the electromagnetic current is exponentially suppressed. Thanks to the SU(3)-flavor symmetry, only two topologies of diagrams contribute, the fully connected and the leading disconnected. We show the equivalence in the continuum limit of two methods of computin…

A Repository for Multirelational Dynamic Networks

2012

Nowadays, WWW contains a number of social media sites, which are growing rapidly. One of the main features of social media sites is to allow to its users creation and modification of contents of the site utilizing the offered WWW interfaces. Such contents are referred to as user generated contents and their type varies from site to site. Social media sites can be modeled as constantly evolving multirelational directed graphs. In this paper we discuss persistent data structures for such graphs, and present and analyze queries performed against the structures. We also estimate the space requirements of the proposed data structures, and compare them with the naive "store each complete snapshot…

Interface Detection Using a Quenched-Noise Version of the Edwards-Wilkinson Equation

2015

We report here a multipurpose dynamic-interface-based segmentation tool, suitable for segmenting planar, cylindrical, and spherical surfaces in 3D. The method is fast enough to be used conveniently even for large images. Its implementation is straightforward and can be easily realized in many environments. Its memory consumption is low, and the set of parameters is small and easy to understand. The method is based on the Edwards-Wilkinson equation, which is traditionally used to model the equilibrium fluctuations of a propagating interface under the influence of temporally and spatially varying noise. We report here an adaptation of this equation into multidimensional image segmentation, an…

User session level diverse reranking of search results

2018

Most Web search diversity approaches can be categorized as Document Level Diversification (DocLD), Topic Level Diversification (TopicLD) or Term Level Diversification (TermLD). DocLD selects the relevant documents with minimal content overlap to each other. It does not take the coverage of query subtopics into account. TopicLD solves this by modeling query subtopics explicitly. However, the automatic mining of query subtopics is difficult. TermLD tries to cover as many query topic terms as possible, which reduces the task of finding a query's subtopics into finding a set of representative topic terms. In this paper, we propose a novel User Session Level Diversification (UserLD) approach bas…

Designing browsing for in-car music player

2012

User interface features of a touch based mobile music player and their comparative impact on driver distraction when searching music albums were investigated. In a driving simulator experiment (N=18) three scrolling methods buttons, swipe and kinetic were compared, whereat the number of music tracks presented in a list-style format varied between three, five and seven items per page. Half of the participants used the music player in a portrait mode and half of them in a landscape mode. It was expected that swipe supports less severe distraction effects than kinetic or button due to systematic page-by-page scrolling and low levels of pointing accuracy required for browsing. Three items shoul…

Automatic dynamic texture segmentation using local descriptors and optical flow

2012

A dynamic texture (DT) is an extension of the texture to the temporal domain. How to segment a DT is a challenging problem. In this paper, we address the problem of segmenting a DT into disjoint regions. A DT might be different from its spatial mode (i.e., appearance) and/or temporal mode (i.e., motion field). To this end, we develop a framework based on the appearance and motion modes. For the appearance mode, we use a new local spatial texture descriptor to describe the spatial mode of the DT; for the motion mode, we use the optical flow and the local temporal texture descriptor to represent the temporal variations of the DT. In addition, for the optical flow, we use the histogram of orie…

Biased graph walks for RDF graph embeddings

2017

Knowledge Graphs have been recognized as a valuable source for background information in many data mining, information retrieval, natural language processing, and knowledge extraction tasks. However, obtaining a suitable feature vector representation from RDF graphs is a challenging task. In this paper, we extend the RDF2Vec approach, which leverages language modeling techniques for unsupervised feature extraction from sequences of entities. We generate sequences by exploiting local information from graph substructures, harvested by graph walks, and learn latent numerical representations of entities in RDF graphs. We extend the way we compute feature vector representations by comparing twel…