1,720,988 research outputs found
A power recirculating test rig for ball screws: A new perspective for endurance tests
Full text linkBall screw mechanisms are commonly designed and adopted to work for a high number of cycles, so that one of their most relevant characteristics is mechanical endurance. State-of-art experimental setups designed to characterize these mechanisms under operational load conditions require a layout able to withstand high loads and a relevant power to actuate the ball screw, therefore, being rather complex and expensive. To overcome these issues, this paper proposes an innovative test bench exploiting the recirculating power principle, designed for testing a ball screw under operational loads. It enables (at the same time) a reduction of loads on the test rig frame and a reduction of the mechanical power required to actuate the screw. The concept and the design of the proposed test bench are presented, as well as a simplified model to calculate the motor torque and the forces transmitted at the supports. An experimental setup is then realized and tested under actual loads for endurance tests. The results show that the use of the recirculating principle is promising to realize a test rig for endurance tests on a ball screw, thanks to the effectiveness of the solution and the simplicity of the realization of the system even under heavy loads. Among all the measuring instruments adopted (accelerometers, strain gauges, thermocouples and laser sensors for distance measurement on the test bench), the adoption of accelerometers on the nuts seems to be the most promising for condition monitoring, allowing to detect an incipient fault before a macroscopic failure of the ball screw system occurs
Falls in older adults: Kinematic analyses with a crash test dummy
No full textFalls have always been a frequent and complex problem that might cause fatality, morbidity, loss or damage of body functions and undesired health care needs. The problem is relevant especially for senior citizens and different studies focused on systems for fall detections. This work analyzes the fall kinematics by means of accelerometers placed on head and torso of a crush test dummy used for fall simulations. This configuration reflects the situation in which the subject does not have any voluntary reaction to possible injuries, which is similar to what occurs during elder people fall. Accelerations were measured upon varying the dummy posture; data obtained from accelerometers were compared with those measured with a vision system. The comparison was based on both the peak velocity and on the fall duration. Results showed the compatibility between the data measured with the two methods, outlining the possibility of identifying the peak velocity from videos available on the internet captured, for instance by video surveillance cameras
Automatic fall monitoring using floor vibration
Full text linkThis work investigates the possibility of monitoring the activity and the falls of people in dwellings using three or more accelerometers fixed on the ground. The main difference between the proposed method and existing ones is the use of acceleration to estimate the impact force by using the apparent mass of the floor; the latter is experimentally identified in each room in which the tests were performed using the heel drop test. The study has two parts: 1. the apparent masses of different dwellings' floors have been measured. 2. the ground reaction force is studied using a purposely designed force platform with a surface of approximately 2 m × 1 m. The force platform allowed the measurement of the forces generated by the falls of 21 subjects, of a crash test dummy (falling in front or rear direction from seated and standing position, with or without the interposition of objects on the trajectory), and of common objects (e.g. dishes, water bottles, books). The impact location is estimated by triangulation, using a wavelet algorithm derived from the existent literature. The results show the possibility of identifying the presence of subjects inside the room and the fall of subjects in the majority of dwellings. We conclude that the proposed method allows a clear distinction between the fall of subjects and objects, given that the difference in terms of force (which is estimated from the floor's apparent mass and from the measured acceleration) is at least of one order of magnitude
Analysis of the failure of a tramcar pantograph component through combined experimental approaches
No full textTramcar vehicles collect the required electrical power from the overhead contact line by means of a pantograph that carries a pan head with collector strips in sliding contact with the contact wire. Therefore, any failure of pantograph or of its components has a direct effect on the correct tramcar operation. The paper deals with a case of unexpected failures occurred on a connection element of the articulated frame of the pantograph of tramcars, causing the interruption of the service. No evidence of impact with the overhead line was detected, only it was clear that the immediate cause was the fatigue failure of a pin of the articulated connection between the upper and the lower arms of the frame of the pantograph. To clarify the original cause of the fatigue failure, an approach combining field measurements, laboratory tests and data processing to obtain the stresses acting on the pantograph failed components under service condition was adopted. It was found that the pantograph was subjected to high level of vibrations coming from the vehicle carbody, mainly due to the track irregularity. A comparative failure analysis was carried out and a solution to upgrade the component subjected to failure was proposed and implemented
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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