861 research outputs found
Biodynamics of the seated human body with dual-axis excitation: nonlinearity and cross-axis coupling
No full textThe apparent mass of the seated human body and the transmissibility to the upper-body (i.e., the spine and the pelvis) during vertical vibration excitation have been reported to have resonance frequencies around 5 Hz. With fore-and-aft excitation the apparent mass shows a first peak around 1 Hz and second mode around 2 to 3 Hz. Little is known about how the motion of the upper-body during excitation in one direction is affected by the addition of vibration in an orthogonal direction (i.e., the cross-axis coupling). The principal objective of the research reported in this thesis was to identify how the resonances in the apparent mass and transmissibility, and their association, depends on the magnitude of the inline vibration excitation and the addition of an orthogonal vibration excitation. The research was also designed to investigate the characteristics necessary in mathematical models that represent the cross-axis coupling and nonlinearity evident in the biodynamic responses of the human 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 seated male subjects during random vertical vibration excitation (over the range 0.25 to 20 Hz) at three vibration magnitudes (0.25, 0.5 and 1.0 ms-2 r.m.s.) and during fore-and-aft vibration excitation over the same frequency range and at the same three vibration magnitudes. At the highest magnitude of vertical excitation the effect of adding fore-aft excitation (at 0.25, 0.5, and 1.0 ms-2 r.m.s.) was investigated. Similarly, at the highest magnitude of fore-and-aft excitation the effect of adding vertical vibration (at 0.25, 0.5, and 1.0 ms-2 r.m.s.) was investigated. The forces in the fore-and-aft and vertical directions on the seat surface were also measured so as to calculate apparent masses. The subjects adopted a normal upright posture, an erect posture, and a slouched posture. Resonance frequencies in the apparent mass and transmissibility during vertical excitation decreased with increasing magnitude of vertical excitation and with the addition of fore-and-aft excitation. The modulus of the first peak in the apparent mass and transmissibility during fore-and-aft excitation decreased with increasing magnitude of fore-and-aft excitation and with the addition of vertical excitation. Complex vibration modes in the upper-body appear to be responsible for the resonances in both the vertical and the fore-and-aft apparent masses. Compared to the normal upright posture, the erect posture tended to increase the resonance frequency in the apparent mass and transmissibility associated with vertical excitation but decrease the resonance frequency in the apparent mass and transmissibility associated with fore-and-aft excitation. The association between resonances in the transmissibility to the upper body and the resonance in the apparent mass varied with vertical excitation but not with fore-aft excitation.A seven degree-of-freedom multi-body model indicated that the resonance frequency in the vertical apparent mass on the seat and the vertical transmissibility to the upper-body with either vertical or dual-axis excitation is sensitive to the vertical stiffness of tissues beneath the pelvis and closely related to the vertical motion of the upper body. It has also been shown that the first mode of the fore-and-aft apparent mass and the fore-and-aft transmissibility can be attributed to the fore-and-aft movement of the upper-body due to the pelvis pitch, while the second mode can be attributed to the fore-and-aft movement of the upper-body caused by shear deformation of the pelvis tissue. It is suggested that a mathematical model developed with single-axis excitation can represent the biodynamic response with dual-axis excitation by changing these sensitive parameters (e.g., the stiffness of the tissue beneath the pelvis).A finite element human body model with flexible bodies representing the tissue beneath the pelvis and thighs and rigid bodies representing other body segments provided sensible prediction of the first resonance frequencies and the associated modulus in the vertical inline and fore-and-aft cross-axis apparent mass on the seat and the transmissibility to the lumbar spine, as well as the pressure distribution on the seat surface. With the flexible bodies assigned the material properties of nonlinear low density foam, the model was allowed to reflect the softening effect (i.e., a reduce in the resonance frequency of the vertical apparent mass) when the when the magnitude of the vertical excitation was increased
The Author Fluency Task (AFT) as a measure of print exposure for Korean L1 speakers
No full textThe Author Recognition Test (ART) is a proxy measure of quantifying reading experience through estimates of print exposure. The test is simple and quick—participants are given a list of author and non-author names and are instructed to check the names they recognize as authors. However, the ART’s reliability in assessing L2 speakers’ print exposure is of concern. To address this problem, the Author Fluency Task (AFT) has been suggested as an alternative. In the AFT, participants are given 3 minutes to list as many authors as possible, and are assessed based on the number of valid authors provided. In a previous study, the AFT was evaluated in comparison to the ART as a predictor of vocabulary knowledge, in the context of L1 and L2. L1 English speakers (n=60) and L1 French/L2 English speakers (n=60) completed the AFT, ART, and Lexical Test for Advanced Learners of English (LexTALE). Vocabulary was assessed using tests of connectives and collocations knowledge. Results showed that both the AFT and the ART were significant predictors of vocabulary scores, but models for L1 and L2 participants revealed that the preferred predictor in L2 was the AFT. Furthermore, when controlling for English proficiency (LexTALE), only AFT predicted additional variance in L2. These findings suggest that semantic fluency for author names reflects more intentional reading experience compared to the general cultural knowledge indexed by ART, which may be sufficient for assessing L1 speakers. The current study is a replication of the previous study with a different cohort—L1 Korean / L2 English speakers (n=60). Participants will complete the same battery of tasks with the Korean versions of the LexTALE and the ART in place of the French versions. We test whether L1 Korean / L2 English reading experience (as assessed by AFT and ART) is associated with individual differences in knowledge of English connectives and collocations, even when accounting for word recognition in both languages. Analogous findings to the previous study will provide supporting evidence that the AFT is more effective than the ART at gauging print exposure in L2 speakers, even in more distant populations
Bone reposition device, method and system
No full textInventor name used in this publication: 顾国强, Koo Terry K.Inventor name used in this publication: 麦福达, Mak Arthur F.Inventor name used in this publication: 赵以甦, Chao Edmund Y.Title in Traditional Chinese: 骨定位裝置和系統ChinaVersion of Recor
Aerodynamic flight control to provide flight control augmentation for aft cg future launch vehicles
No full textThis document reports on the past six years of the extensive and comprehensive flight mechanics — stability and control, special research project conducted at the NASA Marshall Space Flight Center where the author was the designated Principal Investigator and only investigator. The author has proposed, designed, wind-tunnel tested, and analyzed the static and dynamic stability and control characteristics of both forward and aft located, all-movable, blunt-trailing-edge, flight control augmentors (FCA\u27s) for futm-e aft-cg large Saturn-class launch vehicles (LV\u27s) that would not be controllable with engine gimbaling alone. To the author\u27s knowledge, all-movable FCA\u27s have never been used on a large Saturn-class LV. A review of our national heritage of LV\u27s that have used aerodynamic surfaces (V-2, Pershing, Redstone, Saturn I, Saturn IB, Saturn V, X-15) and current usage of these surfaces by other nations has been conducted. Stability derivatives and control derivatives have been calculated from both wind tunnel test programs data and the U.S. Air Force DATCOM computer code. The enhanced static and dynamic flight stability of the aft-cg experimental LV, when treated with the author-designed FCA\u27s, has been assessed and quantified using static margin and short-period damping as criteria. The increased control effectiveness of the blunt-trailing-edge FCA design was found to provide the maximum flight control augmentation. A titanium matrix composite was selected as the FCA material and a design review was held at the manufacturer, Textron Specialty Materials Company. The change in aeroelastic effects of the aft-cg LV were considered. From the NASTRAN generated modal data, significant mode shapes and response spectra have been analyzed and presented for both the original and aft-cg experimental LV
Conservation and Ecotourism in Brazil and Mexico: The Development Impact
No full textConservation projects alter local productive modes and have an impact on livelihoods. For example, sea turtle conservation projects affect fishing communities through hunting restrictions. It is not painless for communities to improve fishing technology in order to prevent the accidental capture of sea turtles. The inability to adapt to environmental requirements forces fishermen to abandon traditional livelihoods. A combination of environmental conservation and ecotourism development can provide the solution. (...)Conservation and Ecotourism in Brazil and Mexico: The Development Impact
Flow over partially liquid filled cavity
No full textExperiments have been carried out to investigate the effect of liquid cavity filling on the behavior of the gas flow over a flat plate cavity. PIV measurements in the gas phase reveal that cavity filling can affect vortex shedding in the cavity mouth. Shear layer vortices can break-up into smaller vortices, thereby losing their periodic interaction with the aft wall and, hence, their sound producing potential. Expected is that this is one of the mechanisms causing sound mitigation in corrugated pipes with liquid addition, observed in literature
An ultrasound indentation system for biomechanical properties assessment of soft tissues in-vivo
No full textRehabilitation Engineering CentreVersion of RecordPublishedVoR allowe
Portable ultrasonic palpation system
No full textInventor name used in this publication: Fuk Tat MakInventor name used in this publication: Yong Ping ZhengUS6494840; US6494840 B1; US6494840B1; US6,494,840; US 6,494,840 B1; 6494840; Appl. No. 09/629,901USVersion of Recor
Development of a simple approach to modify the supporting properties of seating ham for pressure relief
No full textVersion of RecordPublishedPublisher permissio
An “Author Fluency Task”: Semantic fluency as predictor of L2 vocabulary knowledge
No full textReading experience provides critical input for language learning. This is typically quantified via estimates of print exposure, such as the Author Recognition Test (ART), although it may be unreliable in L2. This study introduces the Author Fluency Task (AFT) as an alternative measure, comparing with ART for assessing knowledge of English discourse connectives and collocations among 60 bilingual French/English speakers, and a comparison sample of 60 L1 English speakers. Participants completed AFT, ART, and LexTALE in both languages. Analysis of L2 measures showed AFT more accurately predicted L2 vocabulary knowledge than ART, even when controlling for proficiency (LexTALE). Conversely, ART was more effective for L1 speakers, showing a striking dissociation between the measures across language groups. Additionally, data showed limited contributions from L1 proficiency and print exposure on L2 vocabulary. These findings recommend AFT as a valuable tool for quantifying the role of L2 print exposure for language learning
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