1,721,696 research outputs found
Jacobian projection reduced-order models for dynamic systems with contact nonlinearities
No full textIn structural dynamics, the prediction of the response of systems with localized nonlinearities, such as friction dampers, is of particular interest. This task becomes especially cumbersome when high-resolution finite element models are used. While state-of-the-art techniques such as Craig-Bampton component mode synthesis are employed to generate reduced order models, the interface (nonlinear) degrees of freedom must still be solved in-full. For this reason, a new generation of specialized techniques capable of reducing linear and nonlinear degrees of freedom alike is emerging. This paper proposes a new technique that exploits spatial correlations in the dynamics to compute a reduction basis. The basis is composed of a set of vectors obtained using the Jacobian of partial derivatives of the contact forces with respect to nodal displacements. These basis vectors correspond to specifically chosen boundary conditions at the contacts over one cycle of vibration. The technique is shown to be effective in the reduction of several models studied using multiple harmonics with a coupled static solution. In addition, this paper addresses another challenge common to all reduction techniques: it presents and validates a novel a posteriori error estimate capable of evaluating the quality of the reduced-order solution without involving a comparison with the full-order solution
Adaptive microslip projection (AMP) for reduction of frictional and contact non-linearities in shrouded blisks
No full textReduced order models (ROMs) of turbine bladed disks (blisks) are essential to quickly yet accurately characterize vibration characteristics and effectively design for high cycle fatigue. Modeling blisks with contacting shrouds at adjacent blades is especially challenging due to friction damping and localized non-linearities at the contact interfaces which can lead to complex stick-slip behavior. While well-known techniques such as the harmonic balance method and Craig-Bampton component mode synthesis have generally been employed to generate ROMs in the past, they do not reduce degrees of freedom (DoFs) at the interfaces themselves. In this paper we propose a novel method to obtain a set of reduction basis functions for the contact interface DoFs as well as the remaining DoFs called adaptive microslip projection (AMP). The method is based on analyzing a set of linear systems with specifically chosen boundary conditions on the contact interface. Simulated responses of full order baseline models and the novel ROMs under various conditions are studied. Results obtained from the ROMs compare very favorably with the baseline model. The AMP procedure is also easily generalizable to other dynamic systems with Coulomb friction contact
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
Dynamic model order reduction of blisks with nonlinear damping coatings using amplitude dependent mistuning
No full textIn this paper, a reduced order model is developed to simulate the dynamics of a bladed disk or blisk with nonlinear damping coatings adhered to its blades. The nonlinear forces exerted by these coatings on the underlying linear blisk structure are a function of the local strain. It is known that coatings modify the stiffness and damping of each blade depending on its amplitude. Blisks, which are designed as perfectly cyclic symmetric structures with identical blades, never behave as such in practice due to various uncertainties encountered during their manufacturing. This asymmetry in the structure is also referred to as mistuning. Mistuning in the linear blisk structure, which causes different blades to respond with non-identical amplitudes, interacts with the coating nonlinearity to yield a mistuning pattern which depends on the blade amplitudes. Additional stiffness and damping parameters that are dependent on the blade amplitude are introduced into a reduced linear model to formulate the nonlinear reduced order model. It is found that this model captures the nonlinear amplitude dependent mistuning effect and predicts the nonlinear coated blisk responses accurately near isolated blisk mode families in blade-dominated frequency regions where these coating effects are likely to be dominant. Significant reductions in the computational effort are achieved through this reduction
Czy wszystkie archiwalia są niezbędne w pracach biograficznych? (W związku z artykułem Danuty Bogdan i Jerzego Przerackiego).
No full textPolemika Tadeusza Orackiego z artykułem Danuty Bogdan i Jerzego Przerackiego "O przydatności ksiąg metrykalnych dla autorów słowników biograficznych (Na marginesie książki Tadeusza Orackiego)", Komunikaty Mazursko-Warmińskie 2019, nr 3, s. 640–663
G-quadruplex–forming promoter sequences enable transcriptional activation in response to oxidative stress
Full text linkOxidative DNA damage is an implacable consequence of aerobic metabolism and often exacerbated in inflammatory processes that use reactive oxygen species (ROS) both as signaling molecules and as chemical warfare against pathogens. An extensive body of work, recently reviewed in ref. 1, has highlighted the deleterious consequences of oxidative DNA damage, which involves oxidized nucleobases that, if left unrepaired, are either mutagenic or strong replication blockers. Most oxidative DNA damage is efficiently processed by DNA repair pathways, primarily base excision repair (BER), the molecular details of which are generally well understood (2). However, an emerging area of research posits that certain oxidative DNA lesions and their associated repair complexes are intermediates in a signaling transduction cascade that uses ROS as secondary messengers to ultimately effect transcriptional regulation (3⇓⇓⇓–7). In PNAS, Fleming et al. (8) reinforce these notions by describing a compelling mechanism by which 8-oxoguanine (OG), a canonical oxidative DNA damage product, when occurring in guanine-rich, G-quadruplex–forming promoter sequences, directly up-regulates transcription of the downstream gene
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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