1,721,202 research outputs found
Dual-gated WTe2/MoSe2 van der Waals tandem solar cells
No full textWe propose and numerically investigate, through a multiscale approach, a tandem solar cell based on a van der Waals heterostructure comprising of two monolayers of transition-metal dichalcogenides. The electronic connection between the two subcells is obtained via tunneling through the van der Waals heterojunction, which is electrostatically controlled by means of a dual gate. Furthermore, by adjusting the dual-gate voltages, the photocurrents in the two subcells can be matched and the tandem cell performances can be optimized. Assuming an optimal absorptance, as expected in light-trapping systems, we predict that a power conversion efficiency of 30.7%, largely exceeding that of the single subcells, can be achieved. The proposed design being suitable for other van der Waals heterojunctions shows that it represents a viable option for future high-efficiency photovoltaic system
Countdown Slack: A Run-Time Library to Reduce Energy Footprint in Large-Scale MPI Applications
Full text linkThe power consumption of supercomputers is a major chal-
lenge for system owners, users, and society. It limits the capacity of
system installations, it requires large cooling infrastructures, and it is the
cause of a large carbon footprint. Reducing power during application
execution without changing the application source code or increasing
time-to-completion is highly desirable in real-life high-performance com-
puting scenarios.
The power management run-time frameworks proposed in the last
decade are based on the assumption that the duration of communication
and application phases in an MPI application can be predicted and used
at run-time to trade-off communication slack with power consumption.
In this manuscript, we first show that this assumption is too general and
leads to mispredictions, slowing down applications, thereby jeopardizing
the claimed benefits. We then propose a new approach based on (i) the
separation of communication phases and slack during MPI calls and
(ii) a timeout algorithm to cope with the hardware power management
latency, which jointly makes it possible to achieve performance-neutral
power saving in MPI applications without requiring labor-intensive and
risky application source code modifications. We validate our approach
in a tier-1 production environment with widely adopted scientific appli-
cations. Our approach has a time-to-completion overhead lower than
1% , while it successfully exploits slack in communication phases to
achieve an average energy saving of 10% . If we focus on a large-
scale application runs, the proposed approach achieves 22% energy
saving with an overhead of only 0.4% . With respect to state-of-the-art
approaches, COUNTDOWN Slack is the only that always leads to an
energy saving with negligible overhead ( < 3% )
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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