1,722,483 research outputs found
A seat-occupant model for the prediction of backrest transmissibility in the fore-and-aft direction
No full textCross-axis apparent mass of the seated human body during single-axis and dual-axis vibration
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Transmission of roll, pitch and yaw vibration to the backrest of a seat supported on a non-rigid car floor
No full textThe transmission of roll, pitch and yaw vibration from the floor of a small car to the seat backrest has been investigated with three road conditions. At the seat base, there were distinctive differences between roll vibration at the front and rear of the seat base and between pitch vibration at the left- and right-hand side of the seat base. The yaw motion was generally small relative to the roll and pitch motion. At high frequencies, the yaw motion calculated from the difference between fore-aft vibration at the left- and right-hand side of the seat base was less than the yaw motion calculated from the differences between lateral vibration at the front and back of the seat base. Furthermore, yaw motion calculated from the difference in lateral vibration at the right-hand side of the seat was greater than that at the left-hand side, due to differences between the two lateral accelerations at the two right corners of the seat base. The measurements indicated that the seat base was not a rigid structure in either roll, pitch or yaw.The transmission of rotational vibration from the non-rigid seat base to fore-and-aft, lateral and vertical vibration at the seat backrest was investigated using single- and multi-input models. It was found that pitch and roll vibration, together with translational vibration at the seat base, made significant contributions to seat backrest vibration. For predicting seat transmissibility in the fore-aft and vertical directions, a translational model comprising all the least-correlated fore-aft and vertical inputs, and a combined rotational and translational model consisting of the pitch vibration input and part of the least-correlated fore-aft and vertical inputs appeared equally good. Low coherency in the transmission of vibration to the lateral direction of the seat backrest observed when considering only translational vibration at the seat base was resolved after taking into account the effect of the roll vibration at the seat base
Transmission of vibration to the backrest of a car seat evaluated with multi-input models
No full textThe transmission of vibration to the occupant of a car seat has been studied using the multiple vibration inputs to the seat. Twelve input signals at the seat base (tri-axial vibration at the four corners) and six output signals (tri-axial vibration at the backrest and seat pan) were measured while driving. The results showed that vibration inputs to the seat varied between the four positions at the seat base. The two fore-aft input accelerations at the left-hand side of the seat base and the two fore-aft input accelerations at the right-hand side of the seat base were highly correlated with each other. There was also a high correlation between the two pairs of lateral acceleration inputs at the front and rear of the seat base. A computer program for studying seat vibration transmission via multi-input channels was developed to allow the calculation of seat transmissibility with up to 12 different inputs. The transmission of multi-axis seat base vibration to fore-aft seat backrest vibration was investigated using single-input, two-input, six-input and eight-input models. Results showed that the fore-aft vibration and the vertical vibration, but not lateral vibration, at the four corners of the seat base contributed to fore-aft vibration of the backrest. The primary peak of the fore-aft backrest transmissibility occurred around 4–5 Hz. The coherency was improved when using the multi-input models, although the characteristics of the transmissibility remained similar. The transmission of lateral vibration at the seat base to lateral vibration at the backrest was studied using single-input and two-input models. With single-input models, the transmission of lateral acceleration at the seat base to lateral acceleration at the backrest was amplified between 18 and 35 Hz, with a peak at 26 Hz. Coherency was greater at frequencies above 20 Hz than at lower frequencies. The coherency at low frequencies was increased with a two-input model. The transmission of vertical vibration to vertical vibration at the backrest was investigated using single-input, four-input and six-input models. The results showed that vertical acceleration at the four corners of the seat base was highly correlated with vertical acceleration at the backrest. The results are consistent with previous findings that a single-input model is not sufficient to study the transmission of vibration to the seat back in the horizontal directions, while for the transmission of vertical vibration a single-input model is probably sufficient, especially when low frequencies are of main concern
Serum ACTH and Cortisol Level is Associated with the Acute Gastrointestinal Injury Grade in ICU Patients [Erratum]
No full textXu W, Qiu Y, Qiu H, Zhong M, Li L. Int J Gen Med. 2024;17:127–134.
On page 127, the third author’s name should read from “Hongping Qiu” to “Hongping Qu”.
This error was introduced by the Editorial staff during the publication process
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
Biodynamic response of the seated human body to single-axis and dual-axis vibration: effect of backrest and non-linearity
No full textThe biodynamic responses to the human body give an understanding of why human responses to vibration (changes in health, comfort, and performance) vary with the frequency and direction of vibration. Studies have shown that biodynamic responses also vary with the magnitude of vibration and that the backrests of seats influence the transmission of vibration to the seated human body. There has been little study of the nonlinearity in the biodynamic responses of the body to dual-axis excitation and no study of the influence of backrests during dual-axis excitation. This study investigated the apparent mass and cross-axis apparent mass of the human body exposed to random vibration (0.2 to 20 Hz) in all 15 possible combinations of four magnitudes (0, 0.25, 0.5 and 1.0 ms(-2) r.m.s.) of fore-and-aft vibration and the same four magnitudes of vertical vibration. Nonlinearity was evident, with the body softening with increasing magnitude of vibration when using a fixed magnitude of vibration in one direction and varying the magnitude of vibration in the other direction. The fore-and-aft apparent mass on the seat was greater without a backrest at the lower frequencies but greater with a backrest at the higher frequencies. The vertical apparent mass on the seat was decreased by the backrest at low frequencies. Cross-axis coupling was evident, with excitation in one axis producing a response in the other axis. It is concluded that the nonlinearity of the body evident during single-axis and multi-axis vibration, and the influence of backrests, should be taken into account when determining frequency weightings for predicting human responses to vibration and when optimising the dynamics of seating to minimise exposure to vibration
Vertical and dual-axis vibration of the seated human body: nonlinearity, cross-axis coupling, and associations between resonances in transmissibility and apparent mass
No full textThe vertical apparent mass of the human body exhibits nonlinearity, with the principal resonance frequency reducing as the vibration magnitude increases. Measures of the transmission of vibration to the spine and the pelvis have suggested complex modes are responsible for the dominant resonance during vertical excitation, but the modes present with dual-axis excitation have not been investigated. This study was designed to examine how the apparent mass and transmissibility of the human body depend on the magnitude of vertical excitation and the addition of fore-and-aft excitation, and the relation between the apparent mass and the transmissibility of the body. The movement of the body (over the first, fifth and twelfth thoracic vertebrae, the third lumbar vertebra, and the pelvis) in the fore-and-aft and vertical directions (and in pitch at the pelvis) was measured in 12 male subjects sitting with their hands on their laps during random vertical vibration excitation (over the range 0.25–20 Hz) at three vibration magnitudes (0.25, 0.5 and 1.0 m s?2 rms). At the highest magnitude of vertical excitation (1.0 m s?2 rms) the effect of adding fore-aft vibration (at 0.25, 0.5, and 1.0 m s?2 rms) was investigated. The forces in the vertical and fore-and-aft directions on the seat surface were also measured so as to calculate apparent masses. Resonances in the apparent mass and transmissibility to the spine and pelvis in the fore-and-aft and vertical directions, and pitch transmissibility to the pelvis, shifted to lower frequencies as the magnitude of vertical excitation increased and as the magnitude of the additional fore-and-aft excitation increased. The nonlinear resonant behaviour of the apparent mass and transmissibility during dual-axis vibration excitation suggests coupling between the principal mode associated with vertical excitation and the cross-axis influence of fore-and-aft excitation. The transmissibility measures are consistent with complex modes contributing to motion of the body at the principal resonance: pitch motions of the upper thoracic and lumbar spine, and vertical and fore-aft motion of the pelvis and spine. The mode varies with the magnitude of vertical and fore-and-aft excitation.<br/
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