1,354,604 research outputs found
Studio delle pulsars e del loro ambiente attraverso osservazioni gamma alle altissime energie
No full textQuesta Tesi illustra le attività ed i risultati che ho ottenuto durante il mio corso di dottorato presso l’Università degli Studi di Padova. Il mio lavoro si è concentrato principalmente sullo studio di alcune classi di sorgenti Galattiche che emettono nella parte più energetica dello spettro elettromagnetico, le altissime energie VHE (>100 GeV): pulsars, mil- lisecond pulsars e transitional millisecond pulsars.
Le pulsars sono stelle di neutroni estremamente dense (circa 1018 kg/m3) e in rapida rotazione che si formano durante l’esplosione di una stella massiccia ed altamente magnetizzata (107-1015G). Una pulsar standard ha una massa di 1.44 M⊙ e un raggio di circa 10 km. Le pulsars più conosciute emettono nella banda radio ma possono anche produrre pulsazioni ottiche, X e gamma, fino al range delle VHE. Mostrano comportamenti complessi e, ad oggi, il meccanismo con cui emettono non è stato ancora del tutto compreso. Grazie alla loro radiazione coerente emessa sotto forma di fasci collimati uscenti dai due poli magnetici, le pulsar possono essere sfruttate come speciali laboratori per studiare la Fisica fondamentale.
Alcune di queste pulsars ruotano ad una velocità incredibile, alcune centinaia di volte al secondo, diventando così le sor- genti che ruotano più velocemente nell’Universo e che per questo vengono definite pulsars al millisecondo, MSPs. In generale hanno periodi di rotazione di 1−30 ms e dei campi magnetici più deboli rispetto alle pulsars normali (107-1010 G). Sono pulsars “riciclate” che acquistano materia e momento angolare dalla stella compagna. Esiste poi una partico- lare classe di MSP: le tMSPs. Sono sorgenti che periodicamente passano da una fase in cui si comportano come MSP radio a una fase in cui la pulsazione radio si spegne e si comportano come sistemi binari in accrescimento in cui la stella di neutroni inizia a risucchiare materia dalla compagna, cambiando radicalmente la sua fenomenologia. La transizione tra i due stati avviene in tempi brevi, dell’ordine di quache settimana.
Il mio lavoro è principalmente dedicato allo studio dell’emissione VHE e alla ricerca di pulsazione gamma da parte di due sorgenti candidate ad emettere questo tipo di emissione: PSR J0218+4232 (una MSP) e PSR J2229+6114 (una pulsar regolare). Ad oggi sono state rilevate solo tre pulsars nel range delle altissime energie: Crab Pulsar (Aliu et al., 2008), Vela Pulsar (H. E. S. S. Collaboration et al., 2018a) e, molto recentemente, Geminga Pulsar (MAGIC Collabo- ration et al., 2020). In particolare, ho lavorato sui dati raccolti con i telescopi MAGIC situati presso l’Osservatorio di Roque de Los Muchachos nell’isola delle Canarie di La Palma. I dati sono stati presi con il Sum-Trigger-II, un sistema di trigger che, con una soglia di energia di decine di GeV, è in grado di aumentare l’efficienza dei telescopi MAGIC alle più basse energie. Questo sistema è utile per rilevare sorgenti gamma estremamente deboli, come le pulsar. Purtroppo con i telescopi MAGIC non è stato trovato alcun segnale, o emissione pulsata, superiore a 20 GeV, proveniente dalle due sorgenti. Le due sorgenti sono state inoltre osservate e studiate anche utilizzando i dati raccolti dal satellite Fermi-LAT e da quest’analisi risulta che PSR J0218+4232 ha un’emissione pulsata superiore ai 25 GeV, mentre PSR J2229+6114 superiore ai 20 GeV. Una parte del dottorato l’ho dedicata allo studio delle prospettive di emissione delle tMSPs nel range delle altissime energie, in particolare da parte di PSR J1023+0038 e XSS J12270-4859 durante il loro stato di accrescimento. Ho studiato i dati raccolti dal satellite Fermi-LAT considerando diversi modelli spettrali per poi studiare la possibilità di rilevarli con il futuro CTA.This thesis illustrates the activities and the results that I have performed during my PhD course at the University of Padova. My work was mainly focused on the study of some classes of Galactic sources: pulsars, millisecond pulsars and transitional millisecond pulsars in the most energetic part of the electromagnetic spectrum, the Very-High-Energy (VHE), >100 GeV, gamma ray regime.
Pulsars are very dense (about 1018 kg/m3), extremely magnetized (107−1015 G) and rapidly rotating neutron stars, formed after supernova explosions. A standard pulsar has a mass of 1.44 M⊙ and a radius of about 10 km. Most known pulsars are observed in radio but they can also produce detectable optical, X-ray and gamma-ray pulsations, up to the VHE range. Pulsars show complex behaviors and in particular the underlying mechanism by which they emit electromagnetic radiation is still not fully understood. Thanks to their coherent radiation, emitted in the form of collimated beams from the two magnetic poles, they can be exploited as special natural laboratories for fundamental Physics.
Some pulsars rotate at an incredible rate of a few hundred times per second, making them the fastest-spinning stars known in the Universe. They are the so-called Millisecond Pulsars (MSPs). Generally, they have spin-periods of 1−30 ms and lower magnetic fields than standard pulsars (107 −1010 G). They are “recycled” pulsars that accrete matter and angular momentum from a companion star. In particular, there is a class of MSPs which belong to binary systems: the Transitional MSPs (tMSPs). They are neutron stars rotating at a period of a few milliseconds which undergo transi- tions between two states: a bright X-ray pulsar regime powered by the accretion onto the neutron star surface of matter transferred by the companion star and a radio (and possibly gamma-ray) pulsar regime powered by the energy loss due to the fast rotation of the neutron star magnetic field. The transitions between the two regimes take place on short time-scales of less than a few weeks.
My research is mainly focused on studying the VHE emission and gamma-ray pulsation from two of the best pulsars candidates for VHE gamma-ray emission: PSR J0218+4232 (a MSP) and PSR J2229+6114 (a regular pulsar). Up to now, only three pulsars have been detected at VHE: the Crab Pulsar (Aliu et al., 2008), the Vela Pulsar (H. E. S. S. Collaboration et al., 2018a) and, very recently, the Geminga Pulsar (MAGIC Collaboration et al., 2020). In particular I used data taken with the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes located at the Observatory of the Roque de Los Muchachos in the Canary Island of La Palma. The data were taken with the Sum- Trigger-II system which has an energy threshold of about tens of GeV, in order to increase the detection efficiency at the lowest energies reached by MAGIC. This system is extremely useful to detect soft gamma-ray sources, such as pulsars. In the search for pulsed emission from both sources, PSR J0218+4232 and PSR J2229+6114, no signal or pulsed emis- sion above 20 GeV was found with the MAGIC telescopes. The sources were also studied using Fermi-LAT and PSR J0218+4232 shows high energy pulsed emission above 25 GeV and PSR J2229+6114 above 20 GeV.
During my PhD I dedicated a part of the time also to the study of the prospects for VHE gamma-ray emission from tMSPs, in particular from the two systems PSR J1023+0038 and XSS J12270-4859, during their accretion disk state. I studied their Fermi-LAT emission considering different spectral models and then I investigated the feasibility to detect them with the future Cherenkov Telescope Array (CTA) and the prospect for studying them
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
Variations on the Author
No full text“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
No full textWe 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
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
Timing analysis and pulse profile of the Vela pulsar in the optical band from Iqueye observations
No full textThe Vela pulsar is among a number of pulsars which show detectable optical pulsations. We
performed optical observations of this pulsar in 2009 January and December with the Iqueye
instrument mounted at the ESO 3.5 m New Technology Telescope. Our aim was to perform
phase fitting of the Iqueye data, and to measure the optical pulse profile of the Vela pulsar at
high time resolution, its absolute phase, and rotational period. We calculated for the first time
an independent optical timing solution and obtained the most detailed optical pulse profile
available to date. Iqueye detected a distinct narrow component on the top of one of the two
main optical peaks, which was not resolved in previous observations, and a third statistically
significant optical peak not aligned with the radio one. The quality of the Iqueye data allowed
us to determine the relative time of arrival of the radio-optical-gamma-ray peaks with an
accuracy of a fraction of a millisecond.We compare the shape of the Iqueye pulse profile with
that observed in other energy bands and discuss its complex multiwavelength structure
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
No full textThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
The Thursday Murder Club: Launching a megabrand author - a publishing case study
No full textIn 2020, the Christmas book charts in the UK made headlines: Barack Obama’s eagerly awaited autobiography, The Promised Land, was beaten to the top spot by The Thursday Murder Club by Richard Osman, a debut cosy crime novel set in a retirement village. Not only did Osman’s book beat the former US president’s expected bestseller, it also broke records, becoming the fastest-selling debut crime novel of all time. Although Osman has a certain level of fame in the UK from his TV appearances on shows such as Pointless, his celebrity status does not entirely explain the novel’s huge sales. This article tracks the acquisition, publication, and promotion journey of The Thursday Murder Club in order to understand the industry and cultural context of its success and to interrogate the role of celebrity in the creation of author brands. The findings suggest that the unexpected scale of the success of the book owed to a number of factors, including in-depth editing by the novel’s agent, editor, and author to tighten up the plot, an extensive and strategic promotional campaign, the pandemic (which drove interest in the book’s genre and themes), and the quality of the writing. We find that the book’s success was accentuated by Osman’s celebrity status rather than being entirely reliant on it. This research adds to the growing scholarship on celebrity authorship by means of an in-depth case study and provides insight into the processes behind publishing a ‘celebrity’ book and launching a megabrand author
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
The vanishing author in computer-generated works: a critical analysis of recent Australian case law
No full textAbstract
The use of software is ubiquitous in the creation of many copyright works, yet the requirement in copyright law that every work have a human author who engages in independent intellectual effort means that its use may prevent copyright subsistence. Several recent Australian cases have refocused attention on authorship as an essential criterion of copyright subsistence, and these cases suggest that much computer-produced output may be authorless and thus lack copyright protection. This article, the first in a two-part series, analyses how each case deals with the question of authorship of computer-produced works and why the use of software diminishes copyright protection for a significant number of computer-generated works. The article critiques the application of conventional notions of human authorship developed in the pre-computer age to modern productions and suggests alternative approaches to authorship that satisfy both the major objectives of copyright policy and the need to adapt to the computer age. The article argues that, without a broader judicial approach to authorship of computer-generated works, Parliament must remedy the lacuna in protection for these ‘authorless’ works. Possible solutions for reform are suggested. In a forthcoming article, the author comprehensively examines those reform proposals
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