1,721,481 research outputs found
A Dyson sphere around a black hole
Full text linkThe search for extraterrestrial intelligence (SETI) has been conducted for nearly 60 yr. A Dyson sphere, a spherical structure that surrounds a star and transports its radiative energy outwards as an energy source for an advanced civilization, is one of the main targets of SETI. In this study, we discuss whether building a Dyson sphere around a black hole is effective. We consider six energy sources: (i) the cosmic microwave background, (ii) the Hawking radiation, (iii) an accretion disc, (iv) Bondi accretion, (v) a corona, and (vi) relativistic jets. To develop future civilizations (for example, a Type II civilization), 4×1026W(1L⊙) is expected to be needed. Among (iii) to (vi), the largest luminosity can be collected from an accretion disc, reaching 105L⊙, enough to maintain a Type II civilization. Moreover, if a Dyson sphere collects not only the electromagnetic radiation but also other types of energy (e.g. kinetic energy) from the jets, the total collected energy would be approximately 5 times larger. Considering the emission from a Dyson sphere, our results show that the Dyson sphere around a stellar-mass black hole in the Milky Way (10kpc away from us) is detectable in the ultraviolet (10−400nm), optical (400−760nm), near-infrared (760nm−5μm), and mid-infrared (5−40μm) wavelengths via the waste heat radiation using current telescopes such as Galaxy Evolution Explorer Ultraviolet Sky Surveys. Performing model fitting to observed spectral energy distributions and measuring the variability of radial velocity may help us to identify these possible artificial structures
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Nitric oxide metabolism and hypoxic vasodilation
No full textINTRODUCTION. When arterial O2 content is reduced, reflex increases in blood flow occur
in an attempt to restore local O2 supply. This "hypoxic vasodilation" involves excess levels of nitric oxide (NO). However, controversy persists as to whether this is due to increased NO production by NO synthase, increased NO generation from nitrite (by nitrite reductase), or
through decreased NO metabolism by mitochondria.
OBJECTIVES. To confirm that vasodilation is a NO-mediated response to tissue hypoxia,
and to clarify mechanisms underlying this reflex.
METHODS. Under isoflurane anaesthesia, spontaneously-breathing fluid-resuscitated male Wistar rats (250–350 g) underwent intravascular cannulation for blood pressure (ABP) monitoring, blood gas analysis, and fluid/drug administration. Tissue PO2 (tPO2) was determined using a luminescence probe placed in thigh muscle. Animals were allowed to stabilize for 300 after surgery and were then randomized to receive either room air or a hypoxic mixture (FiO2 0.125). In separate experiments both groups received, alone or in combination, a 100 continuous infusion of the non-selective NOS-inhibitor SEITU (1.5 mg/kg/min), the nitritedonor
NaNO2 (0.25 mg/kg/min), or vehicle. Data shown as mean ± SD. Statistics were
performed using 2-way repeated-measurement ANOVA and post-hoc Tukey’s test.
RESULTS. Hypoxia significantly reduced PaO2 from a baseline level of 10.8 ± 1.1 to
6.2 ± 2.8 kPa (p\0.001); tPO2 dropped from 6.1 ± 0.8 to 3.0 ± 0.4 kPa (p\0.001). None
of the interventions modified PaO2 or tPO2 levels.CONCLUSIONS. Hypoxic vasodilation is, at least in part, an NO-mediated process: hypoxia reduced ABP and tPO2, blunted the hypertensive effect of SEITU and accentuated the hypotensive effect of nitrite. We argue that, in hypoxia, NO derives only partially from NOS synthesis. Further insights into NO metabolism in hypoxia may help to better understanding mechanisms underlying haemodynamic adaptations.
REFERENCES. 1. Blitzer ML, et al. Am J Physiol (Heart Circ Physiol) 1996;271:H1182–5.
2. Allen JD, et al. Br J Pharmacol 2009;158:1653–4.
GRANT ACKNOWLEDGMENT. MU was supported by a Physiology Award of the Accademia
Nazionale dei Lincei (Roma)/Royal Society (London)
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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