1,721,061 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
A New 3-DOF Spherical Motion Master-Slave Mechanism
No full textAfter a discussion of the basic concepts on which to build a spherical wrist with two and three degrees of freedom (DOFs), with particular reference to telemanipulators for minimally invasive surgery (MIS), a new 3-DOF mechanism with spherical master-slave motion is proposed to be applied in MIS. The proposed tool is manual, mechanical, inexpensive and intuitive to use by the operator and has great potential compared to more complex robotic devices on the market today
Kinematic Synthesis
No full textKinematic synthesis is the procedure through which the type, number, and geometry of kinematic pairs and links of a mechanism are determined to satisfy desired design constraints. Kinematic synthesis has been and still is a beautiful example of a joint process of creativity and rationality, intuition and computation. The scope of synthesis methods is twofold: they are a guide for the designer intuition, but they are also the attempt to capture the schemes of creativity into more and more sophisticated models
The Geometrical Arrangement of Joint Constraints that Makes Natural Motion Possible: Experimental Verification on the Ankle
No full textThe passive motion of a joint, namely the articular motion under no external loads, provides insights into the joint physiology. It represents the baseline motion of an articulation before passive structures are loaded by external loads. Moreover, during natural motion, the strain energy density stored within ligaments and cartilage is minimized, reducing the risk of microdamage and the corresponding metabolic cost for tissue repairing. In a recent paper, we showed that the line of action of resultant forces of all the constraints provided by the passive structures in a joint must intersect the instantaneous helical axis to make the natural motion possible. In other words, the lines of action of all these constraints must cross the same line at each flexion angle to guarantee the natural motion of the joint. This geometrical property was proven theoretically and verified experimentally for the knee. To prove its generality, in this work we will verify the same property on nine ankle specimens
Design and fabrication of personalized knee prostheses by laser-based powder bed fusion: Influence of manufacturing process on geometric accuracy
No full textThe manufacture of metal prostheses by a laser-based powder bed fusion process allows the definition of more effective customized prostheses, increasing the functionality of the operated joint, reducing the risk of implant failure, and increasing the time before revision. For this personalization to be successful, a high accuracy is required when fabricating the prosthesis surfaces. Aiming to understand the performance of this manufacturing process, this article reports the results in terms of geometrical accuracy of a cobalt-chrome alloy knee prosthesis at different process and postprocess conditions. The prosthesis was designed based on experimental data of a real subject. Starting from medical images, a personalized mathematical model of the knee featuring ligament and contact constraints was defined and used to determine the shape of the implant. The process and post-treatment parameters were defined to limit the residual stress of the component after the support removal, in order to minimize geometrical deformations. The optimal process parameters were obtained by experimental tests in combination with a simulation software for the prediction of thermomechanical deformation. The overall manufacturing procedure was validated by comparing the designed and obtained geometry, measured through an optoelectronic system and a laser scanner. Also, the properties of the components in terms of density, hardness, and roughness were verified. The results show that the proposed design procedure is feasible and accurate, reaching an average deviation between the theoretical and obtained surface of -0.02 ± 0.18 mm. The overall procedure also increased the hardness of the prosthesis
A new combined fabrication process to shape small flexure hinges
Get PDFThis paper presents a new combined fabrication method, named 3D-PLAST, aimed at overcoming inherent limitations of conventional additive manufacturing techniques when producing small flexure hinges in compliant mechanisms. Flexure hinges play a crucial role in various applications, offering advantages such as cost reduction, increased precision, and weight reduction. However, traditional additive manufacturing proves challenging in achieving satisfactory mechanical properties when manufacturing small-size hinges. To overcome these limitations, the 3D-PLAST process combines fused filament fabrication with compressive plastic deformation. This hybrid process exploits the advantages of both techniques, i.e., flexibility, low cost, and ease of use. This process enables the fabrication of small-size mechanisms with good dimensional accuracy. Finally, the paper reports experimental tests on two materials comparing flexure hinges manufactured by 3D-PLAST versus 3D printing methods to demonstrate the effectiveness of the proposed process
Variations on the Author
Get PDF“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
Get PDFWe 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
Quantification of the errors associated with marker occlusion in stereophotogrammetric systems and implications on gait analysis
Get PDFOptoelectronic stereophotogrammetric systems (OSSs) represent the standard for gait analysis. Despite widespread, their reported accuracy in nominal working conditions shows a variability of several orders of magnitude, ranging from few microns to several millimetres. No clear explanation for this variability has been provided yet. We hypothesized that this reflects an error affecting OSS outcomes when some of the tracked markers are totally or partially occluded. The aim of this paper is to quantify this error in static and dynamic conditions, also distinguishing between total and partial marker occlusion. A Vicon system featuring 8 cameras is employed in this study. Two camera distributions, one designed to maximize OSS accuracy and another one representative of a typical gait setup, are investigated. For both the setups, static and dynamic tests are performed, evaluating the different impact of partial and total marker occlusions. Marker occlusions significantly affected the system performances. The maximum measure variation reached 1.86 mm and 7.20 mm in static and dynamic conditions, respectively, both obtained in the case of partial occlusion. This systematic source of error is likely to affect gait measures: markers placed on the patient body are often visible only by half of the cameras, with swinging arms and legs providing moving occlusions. The maximum error observed in this study can potentially affect the kinematics outcomes of conventional gait models, particularly on frontal and coronal plane, and consequently the peak muscle forces estimated with musculoskeletal models
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