1,720,978 research outputs found
Transient Stiffness Patterning in Hydrogels Driven by Dissipative Mechanochemical Coupling
Full text linkLiving systems adapt to mechanical forces through a series of biochemical feedback loops and dissipative signal transduction mechanisms across multiple length scales. By contrast, synthetic materials are static, closed systems with minimal interaction with their surroundings and lack the ability to adapt to mechanical deformations. Here, a strategy that enables a hydrogel to adapt to mechanical forces through the temporal modulation of its stiffness properties is reported. It is demonstrated that force-induced bond rupture at the disulfide linkages of the hydrogel, coupled with their chemical reoxidation leads to dissipative, transient stiffness functions. The electrochemical generation of the oxidant as the output of a feedback loop triggered by an externally applied force provides high spatiotemporal control over the dissipative process, enabling the engineering of hydrogels with out-of-equilibrium stiffness patterns. Additionally, dose-controlled, spatiotemporal transient release of model protein payloads from the hydrogel is demonstrated. The proposed concept has the potential to enhance the autonomous and interactive functionalities of hydrogels, advancing their applications in the biomedical field and soft robotics
Ultrathin organic membranes: Can they sustain the quest for mechanically robust device applications?
Full text linkSummary: Ultrathin polymeric films have recently attracted tremendous interest as functional components of coatings, separation membranes, and sensors, with applications spanning from environment-related processes to soft robotics and wearable devices. In order to support the development of robust devices with advanced performances, it is necessary to achieve a deep comprehension of the mechanical properties of ultrathin polymeric films, which can be significantly affected by confinement effects at the nanoscale. In this review paper, we collect the most recent advances in the development of ultrathin organic membranes with emphasis on the relationship between their structure and mechanical properties. We provide the reader with a critical overview of the main approaches for the preparation of ultrathin polymeric films, the methodologies for the investigation of their mechanical properties, and models to understand the primary effects that impact their mechanical response, followed by a discussion on the current trends for designing mechanically robust organic membranes
Design and Finite Element Analysis of an Electrothermally Actuated Microgripper for Biomedical Applications
No full textMicromanipulation devices are becoming fundamental tools to study and understand cell biology and cell mechanics. Indeed, to study the individual cell behaviors and interactions, cell samples need to be grasped and moved to testing devices. In recent years, micromanipulators have been demonstrated as an effective means to provide precise sample manipulation. In this paper, a detailed overview of designing and simulation of a biocompatible electro-thermally actuated microgripper with rotary capacitive position sensor is presented. The microgripper is actuated by a chevron-shaped thermal actuator with thin hinges and a rotary capacitive position sensor is integrated with the links of the microgripper in order to sense the microgripper tweezers position. The microgripper herein reported can manipulate biological samples in the size range between 50 μm to 150 μm. Based on the sensitivity calculation of the rotary capacitive position sensors, the sensitivity of the displacement measurement is 102 fF/μm
A C-shaped hinge for displacement magnification in MEMS rotational structures
No full textThe design, analysis, fabrication, and characterization of two distinct MEMS rotational structures are provided; these structures include a classical symmetrical lancet structure and a novel symmetrical C-shaped structure provided with a tilted arm, and both are actuated by thermal actuators. Our proposed C-shaped structure implemented a curved beam mechanism to enhance the movement delivered by the thermal actuators. The geometrical parameters of our proposed device were optimized using the design of experiment (DOE) method. Furthermore, the analytical modeling based on Castigliano's second theorem and the simulations based on the finite element method (FEM) were used to predict the behavior of the symmetrical C-shaped structure; the results were in good agreement with each other. The MEMS-based rotational structures were fabricated on silicon-on-insulator (SOI) wafers using bulk micromachining technology and deep reactive ion etching (DRIE) processes. The fabricated devices underwent experimental characterization; our results showed that our proposed MEMS rotational structure exhibited a 28% improvement in the delivered displacement compared to the symmetrical lancet structure. Furthermore, the experimental results showed good agreement with those obtained from numerical analysis. Our proposed structures have potential applications in a variety of MEMS devices, including accelerometers, gyroscopes, and resonators, due to their ability to maximize displacement and thus enhance sensitivity
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
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