1,720,958 research outputs found
THERMOMECHANICAL CHARACTERIZATION OF ONE-WAY SHAPE MEMORY NITINOL AS AN ACTUATOR FOR ACTIVE SURGICAL NEEDLE
Get PDFNeedle-based intervention insertion is one of the common surgical techniques used in many diagnostic and therapeutic percutaneous procedures. The success of such procedures highly depends on the accuracy of needle placement at target locations. An active needle has the potential to enhance the accuracy of needle placement as well as to improve clinical outcome. Bending forces provided by the attached actuators can assist the maneuverability in order to reach the targets following a desired trajectory. There are three major research parts in the development of active needle project in the Composites Laboratory of Temple University. They are thermomechanical characterization of shape memory alloy (SMA) or Nitinol as an actuator for smart needle, mechanical modeling and design of smart needles, and study of tissue needle interaction. The characterization of SMA is the focus of this dissertation. Unique thermomechanical properties of Nitinol known as shape memory effect and superelasticity make it applicable for different fields such as biomedical, structural and aerospace engineering. These unique behaviors are due to the comparatively large amount of recoverable strain which is being produced in a martensitic phase transformation. However, under certain ranges of stresses and temperatures, Nitinol wires exhibit unrecovered strain (also known as residual strain); which limits their applicability. Therefore, for applications that rely on the strain response in repetitive loading and unloading cycles, it is important to understand the generation of the unrecovered strain in the Nitinol wires. In this study, the unrecovered strain of Nitinol wires with various diameters was investigated, using two experimental approaches: constant stress and uniaxial tensile tests. Moreover, a critical range of stress was found beyond which the unrecovered strain was negligible at temperatures of 70 to 80C depending on the wire diameter. Wire diameters varied from 0.10 to 0.29 mm were tested and different ranges of critical stress were found for different wire diameters. The transformation temperatures of different wire diameters at zero stress have been achieved by performing the Differential Scanning Calorimetry (DSC) test. The actuation force created by Nitinol wire is measured through constant strain experiment. X-Ray Diffraction (XRD) study was also performed to investigate the phase of Nitinol wires under various thermomechanical loading conditions. In summary, the effect of wire diameter on the required critical stresses to avoid the unrecovered strain between first and second cycle of heating and cooling are presented and the results of both mechanical tests are justified by the results obtained from the XRD study.Mechanical Engineerin
MECHANICS AND CONTROL OF BIOINSPIRED SMA-ACTUATED NEEDLE IN SOFT TISSUES
Get PDFThis dissertation presents innovative research on Shape Memory Alloy (SMA)-actuated active steerable needles to address the limitations of conventional bevel tip needles in needle-based medical procedures such as biopsy, brachytherapy, tissue ablation and drug delivery. The active needle design proposed in this study surpasses the limitations of conventional needles by enabling large tip deflection and active control of deflection during needle insertion, thereby achieving accurate needle placement. A needle prototype was developed, demonstrating substantial 50mm and 39mm tip deflections at a 150mm insertion depth in liver and prostate-mimicking gels, respectively. Finite Element Analysis (FEA) accurately predicted the tip deflection in tissue-mimicking gels, with simulation errors measuring only 16.42% and 12.62% in the liver-mimicking gel and prostate-mimicking gel, respectively, validating the effectiveness of the FEA framework developed in this research for predicting tip deflection in soft tissues. Furthermore, a real-time trajectory tracking control system using a Proportional Integral (PI) controller was designed for the SMA-actuated needle, which resulted in minor root mean square errors (RMSE) of 1.42mm and 1.47mm in the two gels, respectively, highlighting the applicability of the needle design. The capabilities of the active needle, including improved tip deflection and trajectory tracking control, enable it to bypass obstacles, maneuver around critical anatomical structures, and increase the accuracy of needle placement, thus enhancing patient safety and procedure success rates.A bioinspired approach was introduced to enhance the functionality of SMA-actuated needles, drawing inspiration from the mosquito proboscis's unique design and skin-piercing technique. By incorporating an innovative cannula design and applying axial vibration to the SMA-actuated needle, a significant reduction in needle-tissue interaction friction was achieved, which resulted in increased needle tip deflection and improved steering accuracy. Including these bioinspired features led to a remarkable decrease in insertion force by up to 26.24% and an increase in tip deflection by 37.11%. Furthermore, the trajectory tracking error was reduced by 48%, and the control effort decreased by 23.25%, underscoring the benefits of the bioinspired enhancements in improving needle insertion mechanics and control.
The findings presented in this dissertation illustrate the potential of SMA-actuated needles and bioinspired features in enhancing needle steering performance during minimally invasive needle-based procedures. Future research will focus on further refining the needle design and control systems, expanding experimental tests to biological tissues, and exploring the application of these advancements on a clinically applicable scale.Mechanical Engineerin
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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