130,762 research outputs found
Quartieri abusivi di Tirana, Albania. Politiche urbane e interventi di recupero
No full textPeriodico interuniversitario del Centro Studi Urbanistici PVS, Università degli Studi di Roma "La Sapienza", Dipartimento di Pianificazione Territoriale e Urbanistica, Rom
Log Diameter Rounds Algorithms for 2-Vertex and 2-Edge Connectivity
No full textMany modern parallel systems, such as MapReduce, Hadoop and Spark, can be modeled well by the MPC model. The MPC model captures well coarse-grained computation on large data - data is distributed to processors, each of which has a sublinear (in the input data) amount of memory and we alternate between rounds of computation and rounds of communication, where each machine can communicate an amount of data as large as the size of its memory. This model is stronger than the classical PRAM model, and it is an intriguing question to design algorithms whose running time is smaller than in the PRAM model.
In this paper, we study two fundamental problems, 2-edge connectivity and 2-vertex connectivity (biconnectivity). PRAM algorithms which run in O(log n) time have been known for many years. We give algorithms using roughly log diameter rounds in the MPC model. Our main results are, for an n-vertex, m-edge graph of diameter D and bi-diameter D', 1) a O(log D log log_{m/n} n) parallel time 2-edge connectivity algorithm, 2) a O(log D log^2 log_{m/n}n+log D'log log_{m/n}n) parallel time biconnectivity algorithm, where the bi-diameter D' is the largest cycle length over all the vertex pairs in the same biconnected component. Our results are fully scalable, meaning that the memory per processor can be O(n^{delta}) for arbitrary constant delta>0, and the total memory used is linear in the problem size. Our 2-edge connectivity algorithm achieves the same parallel time as the connectivity algorithm of [Andoni et al., 2018]. We also show an Omega(log D') conditional lower bound for the biconnectivity problem
I programmi di Settlement Upgrading in Albania
No full textPlanum The European Journal of Planning, www.planum.net, pubblicato da Planum Association, Roma - Milano, di proprietà dell'Istituto Nazionale di Urbanistica, 19.447 caratteri spazi esclus
In memoriam Andoni Garritz, profesor humanista
No full textAgradezco a la revista Tecné, Episteme y Didaxis la oportunidad de escribir algunas palabras en memoria de Andoni, en este número multitemático, que contiene dife-rentes artículos en educación de ciencia, tecnología y matemáticas, que van desde el uso didáctico de estrategias inductivas, pasa por los modelos y la modelización en la historia de las ciencias, y por la competencia comunicativa del inglés, sigue con el desarrollo de los conocimientos sobre los estudiantes durante las experiencias en el practicum y termina con el conocimiento didáctico del contenido durante la enseñanza de la fuerza eléctrica en bachillerato.Conocí a Andoni hace más de cuarenta años, cuando los dos realizábamos estudios de maestría. Fue entonces cuando reparé en su enorme generosidad. Recuerdo que le pregunté si conocía algún material donde se explicara de manera sencilla el tema de la radiactividad. Al día siguiente, llegó con un documento y me dijo: “Esto te puede servir. Te lo encargo mucho, es la única copia que tengo y está por publicarse”. ¡Me prestaba la única copia que tenía, de un documento que recién había escrito y que aún no se publicaba! Detalles como este, le conocí muchos durante todos estos años en los que tuve la oportunidad de compartir con él diversos proyectos y actividades
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
THE COMPUTATIONAL HARDNESS OF ESTIMATING EDIT DISTANCE
No full textWe prove the first nontrivial communication complexity lower bound for the problem of estimating the edit distance (aka Levenshtein distance) between two strings. To the best of our knowledge, this is the first computational setting in which the complexity of estimating the edit distance is provably larger than that of Hamming distance. Our lower bound exhibits a trade-off between approximation and communication, asserting, for example, that protocols with bits of communication can obtain only approximation , where is the length of the input strings. This case of communication is of particular importance since it captures constant-size sketches as well as embeddings into spaces like and squared-, two prevailing algorithmic approaches for dealing with edit distance. Indeed, the known nontrivial communication upper bounds are all derived from embeddings into . By excluding low-communication protocols for edit distance, we rule out a strictly richer class of algorithms than previous results. Furthermore, our lower bound holds not only for strings over a binary alphabet but also for strings that are permutations (aka the Ulam metric). For this case, our bound nearly matches an upper bound known via embedding the Ulam metric into . Our proof uses a new technique that relies on Fourier analysis in a rather elementary way
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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