1,721,959 research outputs found
Geographical Load Balancing across green datacenters: A mean field analysis
Full text link"Geographic Load Balancing" is a strategy for reducing the energy cost of data centers spreading across different terrestrial locations. In this paper, we focus on load balancing among micro-datacenters powered by renewable energy sources. We model via a Markov Chain the problem of scheduling jobs by prioritizing datacenters where renewable energy is currently available. Not finding a convenient closed form solution for the resulting chain, we use mean field techniques to derive an asymptotic approximate model which instead is shown to have an extremely simple and intuitive steady state solution. After proving, using both theoretical and discrete event simulation results, that the system performance converges to the asymptotic model for an increasing number of datacenters, we exploit the simple closed form model's solution to investigate relationships and trade-offs among the various system parameters
Lensing cosmic drift
Full text linkAs the Universe expands, the redshift of distant sources changes with time.
Here we discuss gravitational lensing phenomena that are consequence of the
redshift drift between lensed source, gravitational lens, and observer. When
the source is located very close to the drifting caustics, a pair of images
could occur (or disappear) because of the cosmological expansion. Furthermore,
lensing systems act as signal converters of the redshift drift. The angular
position, magnification, distortion, and time delay of already existing
multiple images change. We estimate the expected frequency of these phenomena
and the prospects to observe them in the era of deep and large surveys. The
drift detection in image separation could be within reach of next generation
surveys with arcsec angular resolution.Comment: 6 pages, 2 figures. In press (MNRAS
Modelling the Milky Way halo through adiabatic compression of cold dark matter halo
No full textWe use the adiabatic compression theory to build a physically well-motivated Milky Way mass model in agreement with observational data. The visible mass of the Galaxy is distributed in a spheroidal bulge and a multi-component disc parametrized by three galactic parameters, the Sun distance to the galactic centre, R0, the total bulge mass, , and the local disc surface density, . To model the dark matter component, we adiabatically compress a Navarro, Frenk and White (NFW) halo (with concentration c and total mass ) for fixed values of the spin parameter λ, the fraction of the mass in baryons mb, and the thin disc contribution to total angular momentum jd. An iterative selection procedure is used to explore in detail the wide space of parameters only selecting those combinations of that give rise to a Milky Way model in agreement with observational constraints. This analysis leads us to conclude that only models with kpc, and can be reconciled with the set of observational constraints. As regards the parameters entering the adiabatic compression, we find and , while final estimates of the parameters describing the initial halo profile turn out to be 5 \la c \la 12 and 7 \times 10^{11}~M_{\odot} \la M_{{\rm vir}} \la 17 \times 10^{11}~M_{\odot} (all at 95.7% CL)
Advertisement Delivery and Display in Vehicular Networks
Full text linkThe role of vehicles has been rapidly expanding to become a different kind of utility, no longer just vehicles but nodes of the future Internet. The car producers and the research community are investing considerable time and resources in the design of new protocols and applications that meet customer demand, or that foster new forms of interaction between the moving customers and the rest of the world. Among the variety of new applications and business models, the spreading of advertisements is expected to play a crucial role. Indeed, advertising is already a significant source of revenue and it is currently used over many communication channels, such as the Internet and television. In this paper, we address the targeting of advertisements in vehicular networks, where advertisements are broadcasted by Access Points and then displayed to interested users. In particular, we describe the advertisement dissemination process by means of an optimization model aiming at maximizing the number of advertisements that are displayed to users within the advertisement target area and target time period. We then solve the optimization problem on an urban area, using realistic vehicular traffic traces. Our results highlight the importance of predicting vehicles mobility and the impact of the user interest distribution on the revenue that can be obtained from the advertisement servic
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
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