1,721,100 research outputs found
Experimental Analysis of the Crankshaft Natural Frequencies by Means Electrical Input Impedance Measurement
No full textA Model for the Theoretical Characterization of Thin Piezoceramic Rings
No full textThis work describes a matrix model of the radial mode of a thin piezoceramic ring capable of predicting the dynamic behavior when the two main surfaces are stress free, while the lateral, inner, and outer are loaded by an external medium. The ring is modeled as a three-port system with two mechanical ports and one electrical port. With this approach it is easy to compute the resonance frequency spectrum, the radial displacement, and the electric impedance of a thin ring. Good agreement between the computed and the measured electric impedance is found. The resonance frequency spectrum is computed as a function of the inner-to-outer radius ratio G: when the inner radius vanishes, the resonances of the ring coincide with those of a disk, while, increasing G up to one, the first-mode frequencies decrease approaching the value obtained with a lumped mode model. The frequencies of the higher-order modes, on the other hand, increase to infinity, justifying the lumped mode approximation. The spatial distribution of the displacement in the radial direction is also computed; it has a Bessel function shape which, as expected, becomes linear by increasing the inner radius. Finally, the behavior of the effective coupling factor k/sub eff/ with G is examined. It is shown that, when G/spl rarr/1, k/sub eff/ approaches the material coupling factor k/sub 31/, while when G/spl rarr/0, k/sub eff/ is proportional to the planar coupling factor k/sub p/. Further it is shown that for G>0.6, the approximation of the ring to a lumped mode system is quite acceptable
An Approximated 3–D Model of Cylinder–Shaped Piezoceramic Elements for Transducer Design
No full textIn this paper an approximated 3-D model of cylinder shaped piezoceramics is described. In the hypothesis of axial symmetry, the element vibration in the extensional and radial directions is described by two coupled differential wave equations. The model is obtained choosing, as solution of these equations, two orthogonal wave functions, each depending only on one axis, corresponding to the propagation direction. The mechanical boundary conditions are applied imposing continuity between the stresses and the external forces on the surfaces of the element in an integral way, while, as far as the electrical boundary condition is concerned, two possibilities are explored: to neglect the piezoelectric constant in the transverse direction and to impose an integral condition also for the electric field. Comparisons with experimental results show this last approach to give better results. The model predicts with sufficient accuracy only the first radial and the first thickness modes of the cylinder-shaped piezoceramic element of arbitrary aspect ratio; but, for these modes, it is able to compute all the relations between the input applied voltage and the output forces and velocities on every external surface. Because only these two modes are of relevance in the practical applications of piezoceramic elements as ultrasonic transducers, the model can be used as a simple and useful tool in transducer design and optimization. Experimental validations of the model are also shown in the work
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
A Matrix Model of the Axle Vibration of a Piezoelectric Motor
No full textIn this work, a matrix model of the axle vibration of a piezoelectric motor is proposed. The stator of this motor is composed of a thin piezoelectric membrane and a steel axle fitted at the center of the membrane. The rotor consists of a cylinder-shaped permanent magnet, pressed in contact with the other end of the axle by means of the magnetic forces. A travelling wave is excited in the membrane by using four electrodes and four, properly delayed, driving signals. The rotating flexural displacement of the membrane produces a wide precessional motion of the axle. In this way, a continuous slipping takes place between the axle and the rotor, and therefore, a torque is transmitted to the rotor. In this paper, the precessional motion of the axle is modeled as the composition of two transverse vibrations belonging to two perpendicular planes passing through the axle. The axle, vibrating in its transverse mode, is modeled as a two-port system: the input is the bending moment supplied by the membrane, and the output is the transverse force at the terminal end of the axle. With this model, we have computed the trasmission transfer function as a function of frequency, and the transversal displacement along the axle at its resonance frequency. The computed results are in reasonable agreement with experimental interferometric measurements carried out on a prototype
L’esercizio fisico nella malattia renale cronica: una vecchia storia da raccontare o un efficace intervento da attuare? [Physical exercise in chronic kidney disease: an empty narrative or an effective intervention?]
No full textChronic kidney disease (CKD) is growing worldwide, with increasing numbers of patients facing end-stage renal disease, high cardiovascular risk, disability and mortality. Early recognition of CKD and improvements in lifestyle are crucial for maintaining or recovering both physical function and quality of life. It is well known that reducing sedentariness, increasing physical activity and initiating exercise programs counteract cardiovascular risk and frailty, limit deconditioning and sarcopenia, and improve mobility, without side-effects. However, these interventions, often requested by CKD patients themselves, are scarcely available. Indeed, it is necessary to identify and train specialists on exercise in CKD and to sensitize doctors and health personnel, so that they can direct patients towards an active lifestyle. On the other hand, effective and sustainable interventions, capable of overcoming patients' barriers to exercise, remain unexplored. Scientific societies, international research teams and administrators need to work together to avoid that exercise in nephrology remains an empty narrative, a niche interest without any translations into clinical practice, with no benefit to the physical and mental health of CKD patients
Defining and reporting exercise intensity in interventions for older adults: a modified Delphi process
No full textBackground: Many exercise studies, including older adults, do not report all relevant exercise characteristics. Especially the description of exercise intensity is missing and mostly not controlled. This leads to difficulties in interpreting study results and summarizing the evidence in systematic reviews or meta-analyses. Therefore, the aim of the present Delphi study was to gain recommendations about the categorization of exercise intensity and for the conducting and reporting of characteristics in future intervention studies with older adults by experts in exercise science and physiology. Methods: Two hundred ninety-seven international interdisciplinary participants from an EU COST action were invited to participate in three rounds of online questionnaires in April/May 2023. Up to N = 93 experts participated in each round. Round 1 included open-ended questions to solicit possible recommendations and categorizations for light, moderate, vigorous, and high intensity. In round 2, the experts rated their agreement using Likert scales (1–10) on the revealed categories and recommendations. Clusters with a higher average rating of M = 8.0 were summarized into round 3. In the final round, the results were presented for a final rating of agreement (based on a simple majority > 50%). Results: In round 1 a total of 416 qualitative statements were provided from thirteen questions. From round 1 to round 3, a total of 38 items were excluded, with 205 items retained for the final consensus. In round three 37 participants completed the whole questionnaire. The experts showed overall agreement on the final categorizations with 6.7 to 8.8 out of 10 points on the Likert scale. They also showed broad consensus on the relevance of reporting exercise intensity and the recommendations for future conducting and reporting of study results. However, exercise types such as yoga, balance, and coordination training led to conflicting results for categorization into light or moderate. Discussion and implications: The results of the current survey can be used to classify the intensity of exercise and suggest a practical approach that can be adopted by the scientific community and applied when conducting systematic reviews and meta-analysis articles when vital and objective information regarding exercise intensity is lacking from the original article
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