1,720,970 research outputs found
Le scienziate dimenticate: Margaret Hamilton, le missioni sulla Luna, matematica e programmazione
Full text linkGuerra fredda, 1961: l’Unione Sovietica ha dato un terribile smacco agli Stati Uniti, mandando il primo uomo nello spazio. Il presidente Kennedy decide di tentare la carta della missione di conquista della Luna, difficilissima ma di grandissimo impatto mediatico.
La giovane matematica Margaret Hamilton si trova quasi per caso a essere un personaggio chiave della missione: assunta come programmatrice quando la sua esperienza era minima, diventa in breve tempo tanto esperta da essere messa a capo del gruppo NASA responsabile del software del computer di guida dell’Apollo 11. Inventa nuovi metodi di coordinamento e controllo del software che diventeranno importantissimi nell’immediato futuro, pioniera del software engineering, disciplina a cui lei stessa dà il nome.
La complessità del programma Apollo 11 è enorme sia dal punto di vista ingegneristico che matematico e informatico, coinvolge centinaia di persone, può fallire in mille modi diversi, ma grazie anche alla scrupolosità di Margaret ha il successo che sappiamo. Il suo importantissimo contributo è premiato dal presidente Obama nel 2017.Cold War, 1961: the Soviet Union gave the United States a terrible blow by sending the first man into space. President Kennedy decides to try the road of the mission to conquer the Moon, very difficult but of great media impact. The young mathematician Margaret Hamilton finds herself almost by accident to be a key figure in the mission: hired as a programmer when her experience was minimal, she quickly becomes expert enough to be put in charge of the NASA team responsible for the software of the guidance computer of the Apollo 11. She invents new methods of software coordination and control that will become very important in the near future, she was a pioneer of software engineering, a discipline to which she herself gives her name. The complexity of the Apollo program is enormous both from an engineering, mathematical and computer science point of view, it involves hundreds of people, it can fail in a thousand different ways, but thanks to Margaret's scrupulousness it has the success we know. Her very important contribution is rewarded by President Obama
From the Earth to the Moon: Two Stories of Women and Mathematics
No full textWe will tell two stories with a common denominator: in both cases we talk about extraordinary women and challenges, successful thanks to a lot of mathematics and computer science. The first story is well rooted on the ground: it speaks of Eniac, the first general purpose computer, built as part of a secret project of the US Defense during World War II. Six young women mathematicians designed its software, while programming languages, or even manuals and operating systems, were not available; without knowing the exact top secret architecture of the new computer, they became familiar with it and they performed complicated calculations of ballistic trajectories, founding this way the modern programming. The second story takes us to the Moon, where the protagonist made Apollo 11 land: it is the story of Margaret Hamilton’s adventure the head of the project of the Apollo Guidance Computer software project, the on-board computer of the command and the lunar module. Two stories that, twenty years far from each other, present (fortunately) significant differences, but also surprisingly similar and curious experiences, starting from the methods with which the selection for hiring took place..
Testing and reconfiguration of VLSI linear arrays
No full textAbstractAchieving fault tolerance through incorporation of redundancy and reconfiguration is quite common. In this paper we study the fault tolerance of linear arrays of N processors with k bypass links whose maximum length is g. We consider both arrays with bidirectional links and unidirectional links.We first consider the problem of testing whether a set of n faulty processors is catastrophic, i.e., precludes reconfiguration. We provide new testing algorithms which improve and generalize known testing algorithms. For bidirectional arrays we provide an O(kn) time testing algorithm and for unidirectional arrays we provide an O(n) time algorithm for the case k = 1, and an O(kn log k) time algorithm, for the case k 1.When the fault pattern is not catastrophic we study the problem of finding an optimal reconfiguration of the array. We consider optimality with respect to two parameters: the size of the reconfigured array and the number of redundant links to activate. Considering optimality with respect to the size of the reconfigured array, we prove that the problem is NP-hard in the strong sense if the bypass links are bidirectional, while it can be solved in O(kng) time if the bypass links are unidirectional. Considering optimality with respect to the number of bypass links to activate, we prove that the problem can be solved in O(kn) time if the bypass links are bidirectional, and in O(kng) time if the bypass links are unidirectional
Compacting and grouping mobile agents on dynamic rings
No full textWe consider computations by a distributed team of autonomous mobile agents that move on an unoriented dynamic ring network. In particular, we consider 1-interval connected dynamic rings (i.e. at any time, at most one of the edges might be missing). The agents move according to a Look-Compute-Move life cycle, under a synchronous scheduler. The agents may be homogenous (thus identical and monochromatic) or they may be heterogenous (distinct agents have distinct colors from a set of c≥1 colors). For monochromatic agents starting from any dispersed configuration we want the agents to form a compact segment, where agents occupy a continuous part of the ring and no two agents are on the same node – we call this the Compact Configuration Problem. In the case of multiple colors (c>1), agents of the same color are required to occupy continuous segments, such that agents having the same color are all grouped together, while agents of distinct colors are separated. These formation problems are different from the classical and well studied problem of Gathering all agents at a node, since unlike the gathering problem, we do not allow collisions (each node may host at most one agent of a color). We study these two problems and determine the necessary conditions for solving the problems. For all solvable cases, we provide algorithms for both the monochromatic and the colored version of the compact configuration problem, allowing for at most one intersection between the colored segments (which cannot be avoided in a dynamic ring). All our algorithms work even for the simplest model where agents have no persistent memory, no communication capabilities and do not agree on a common orientation. To the best of our knowledge this is the first work on the compaction problem in any type of dynamic network
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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