1,720,996 research outputs found
Driving bifurcating parametrized nonlinear PDEs by optimal control strategies: Application to Navier-Stokes equations with model order reduction
Full text linkThis work deals with optimal control problems as a strategy to drive bifurcating solution of nonlinear parametrized partial differential equations towards a desired branch. Indeed, for these governing equations, multiple solution configurations can arise from the same parametric instance. We thus aim at describing how optimal control allows to change the solution profile and the stability of state solution branches. First of all, a general framework for nonlinear optimal control problem is presented in order to reconstruct each branch of optimal solutions, discussing in detail the stability properties of the obtained controlled solutions. Then, we apply the proposed framework to several optimal control problems governed by bifurcating Navier-Stokes equations in a sudden-expansion channel, describing the qualitative and quantitative effect of the control over a pitchfork bifurcation, and commenting in detail the stability eigenvalue analysis of the controlled state. Finally, we propose reduced order modeling as a tool to efficiently and reliably solve parametric stability analysis of such optimal control systems, which can be challenging to perform with standard discretization techniques such as Finite Element Method
Model order reduction for bifurcating phenomena in fluid-structure interaction problems
No full textThis work explores the development and the analysis of an efficient reduced order model for the study of a bifurcating phenomenon, known as the Coandă effect, in a multi-physics setting involving fluid and solid media. Taking into consideration a fluid-structure interaction problem, we aim at generalizing previous works towards a more reliable description of the physics involved. In particular, we provide several insights on how the introduction of an elastic structure influences the bifurcating behavior. We have addressed the computational burden by developing a reduced order branch-wise algorithm based on a monolithic proper orthogonal decomposition. We compared different constitutive relations for the solid, and we observed that a nonlinear hyper-elastic law delays the bifurcation w.r.t. the standard model, while the same effect is even magnified when considering linear elastic solid
Efficient computation of bifurcation diagrams with a deflated approach to reduced basis spectral element method
Full text linkThe majority of the most common physical phenomena can be described using
partial differential equations (PDEs). However, they are very often
characterized by strong nonlinearities. Such features lead to the coexistence
of multiple solutions studied by the bifurcation theory. Unfortunately, in
practical scenarios, one has to exploit numerical methods to compute the
solutions of systems of PDEs, even if the classical techniques are usually able
to compute only a single solution for any value of a parameter when more
branches exist. In this work we implemented an elaborated deflated continuation
method, that relies on the spectral element method (SEM) and on the reduced
basis (RB) one, to efficiently compute bifurcation diagrams with more
parameters and more bifurcation points. The deflated continuation method can be
obtained combining the classical continuation method and the deflation one: the
former is used to entirely track each known branch of the diagram, while the
latter is exploited to discover the new ones. Finally, when more than one
parameter is considered, the efficiency of the computation is ensured by the
fact that the diagrams can be computed during the online phase while, during
the offline one, one only has to compute one-dimensional diagrams. In this
work, after a more detailed description of the method, we will show the results
that can be obtained using it to compute a bifurcation diagram associated with
a problem governed by the Navier-Stokes equations.Comment: 26 pages, 30 figure
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
Combination therapy with dexamethasone intravitreal implant and macular grid laser in patients with branch retinal vein occlusion.
No full textPURPOSE: To test a combination of dexamethasone intravitreal
implant with macular grid laser formacular edema in
patients with branch retinal vein occlusion (BRVO).
DESIGN: Prospective interventional, randomized, multicenter
study.
METHODS: Patients with macular edema secondary to
BRVO underwent an Ozurdex intravitreal implant at
baseline. After 1 month, patients were randomly assigned
to 2 study groups. Patients in Group 1 were followed up
monthly and retreated with Ozurdex implant whenever
there was a recurrence of macular edema or a decrease
in best-corrected visual acuity (BCVA). In Group 2
patients macular grid laser was performed between weeks
6 and 8. After that, patients were followed up and
retreated as for Group 1.
RESULTS: In Group 1 at 4 months, mean BCVA was
0.49 ± 0.35 logMAR and central retinal thickness (CRT)
was 391±172mm; both improved significantly at 6months,
to 0.32 ± 0.29 logMAR and 322 ± 160mm, respectively. In
Group 2, CRT was reduced significantly to 291 ± 76 mmat
4months, andBCVAimproved to0.25±0.20logMAR.At
the final visit, BCVA was 0.18 ± 0.14 logMAR and mean
CRT was 271 ± 44 mm. The number of Ozurdex implants
at 4 months was 12 of 25 (48%) in Group 1 patients vs 3 of
25 (12%) inGroup 2 patients (P[.012). At 6months 3 of
25 patients (12%) in Group 1 vs 0 of 25 (0%) in Group 2
(P [ .23) were retreated.
CONCLUSIONS: The combination of Ozurdex implant
and macular grid laser is synergistic in increasing BCVA
and lengthening the time between injections
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
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