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Data and scripts for "No Change in the Recent Lunar Impact Flux Required Based on Modeling of Impact Glass Spherule Age Distributions"
No full textData and scripts to reproduce the figures in the manuscript and supporting information
Data and scripts for "No Change in the Recent Lunar Impact Flux Required Based on Modeling of Impact Glass Spherule Age Distributions"
No full textData and scripts to reproduce the figures in the manuscript and supporting information
Principal component analysis of the cross-axis apparent mass nonlinearity during whole-body vibration
No full textDuring whole-body vibration (WBV), dynamic forces measured at the excitation-subject interface in directions other than the excitation axis, i.e. cross-axis response, are analysed using the principal component analysis (PCA) and virtual coherence techniques. The study applied these operations to the inline and cross-axis forces measured with twelve semisupine human subjects exposed to longitudinal horizontal nominally random vibration between 0.25 and 20 Hz at root mean square acceleration levels of 0.125 ms-2 and 1.0 ms-2. The source identification is realised by a reversed path, aiming to identify relative contributions and correlations between the forces in response to a single axis excitation. The inline longitudinal and the cross-axis vertical forces were found to be correlated to each other from a low (e.g. 1 to 3 Hz) to a medium frequency range (e.g. 10 to 15 Hz). Above this range, where the forces were much reduced, the two forces tended to be independent in their contribution to the overall response. The singular vectors and virtual coherences were able to establish the degree of correlation in each of the frequency band identified. A signal processing framework is then proposed to take into account cross-axis responses for human vibration
Mechanism of nonlinear biodynamic response of the human body exposed to whole-body vibration
Full text linkWhen the human body is exposed to mechanical vibration, the resonance frequencies of the
frequency response functions, such as apparent mass and transmissibility, decrease with
increasing magnitude of excitation. For the past two decades, this biodynamic ‘nonlinearity’ has
been reported with vertical and horizontal excitation of the body in a wide variety of static sitting
and standing postures that require activity from muscles to maintain the stability of the body.
There has been speculation, but no experimental evidence, as to the mechanism causing the
non-linearity. A review of the literature suggested that either active muscular activity or passive
thixotropy of soft tissues is the primary cause of the nonlinearity. The principal objective of this
thesis is to identify, and provide experimental evidence of, the primary causal mechanism for
the biodynamic nonlinearity.
With 0.5 to 20 Hz broadband random vertical vibration at 0.25 and 2.0 ms-2 r.m.s., the first
experiment investigated the effect of voluntary periodic upper-body movement and vibration
magnitude on the apparent masses of 14 seated subjects. Some movements of the body, such
as ‘back-abdomen bending’, significantly reduced the difference in resonance frequency at the
two vibration magnitudes compared with the difference during upright static sitting. Without
voluntary periodic movement, the median apparent mass resonance frequency was 5.47 Hz at
the low vibration magnitude and 4.39 Hz at the high vibration magnitude. With voluntary periodic
movement (e.g. back-abdomen bending), the resonance frequency was 4.69 Hz at the low
vibration magnitude and 4.59 Hz at the high vibration magnitude. It was concluded that
voluntary or involuntary muscular activity, or passive thixotropy of soft tissues, or both muscle
activity and thixotropy, could explain the reduction in nonlinearity evident during voluntary
periodic movement.
The effect of shear history and vibration magnitude on the apparent mass was investigated
using 12 subjects in a relaxed semi-supine posture assumed to involve less muscle activity than
static sitting and standing. The semi-supine subjects were exposed to two types of vertical (in
the x-axis of the semi-supine body) and longitudinal horizontal (z-axis) vibration: (i) continuous
random vibration (0.25–20 Hz) at five magnitudes (0.125, 0.25, 0.5, 0.75, and 1.0 ms-2 r.m.s.); (ii)
intermittent random vibration (0.25–20 Hz) alternating between 1.0 and 0.25 ms-2 r.m.s. With
continuous random vibration, the dominant primary resonance frequency in the median
normalised apparent mass decreased from 10.35 to 7.32 Hz as the magnitude of vertical
vibration increased from 0.125 to 1.0 ms-2 r.m.s., and from 3.66 to 2.44 Hz as the magnitude of
horizontal vibration increased from 0.125 to 1.0 ms-2 r.m.s. With the intermittent vibration, the
resonance frequency was higher at the higher magnitude (1.0 ms-2 r.m.s.) and lower at the
lower magnitude (0.25 ms-2 r.m.s.) than during continuous vibration at the same magnitudes.
The response was typical of thixotropy being the primary cause of the nonlinearity.
Harmonic distortions in the dynamic force of semi-supine subjects exposed to sinusoidal
excitation showed similar dependence on the frequency and magnitude of vibration as
previously reported for seated subjects, again suggesting thixotropy as a primary cause of the
nonlinearity.
In a group of 12 subjects, the apparent mass and transmissibility to the sternum, upper
abdomen, and lower abdomen were measured in three supine postures (relaxed semi-supine,
lying flat, and constrained semi-supine) during vertical random vibration (0.25 to 20 Hz) at
seven vibration magnitudes (nominally 0.0313, 0.0625, 0.125, 0.25, 0.5, 0.75 and 1.0 ms-2
r.m.s.). The motion transmission path that included more soft tissues exhibited a greater
nonlinear response. The substantial nonlinearities found in transmissibilities to both the sternum
and the abdomen of supine subjects, and previously reported for the transmissibilities of seated
and standing subjects, imply that soft tissues at the excitation-subject interface contribute to the
nonlinearity.
It is concluded that the thixotropy of soft tissues, rather than voluntary or involuntary muscular
activity, is the primary cause of the biodynamic nonlinearity seen with varying magnitudes of
excitation
Construction and disillusionment of the cultural Utopia of Huang Ya
Full text linkAfter the World War II, the civil war broke out between the Chinese Nationalist Party
(Kuomintang) and the Communist Party of China （ CPC). Subsequently, a great
number of intellectuals who supported Kuomintang and the Third Force decided to
leave Hong Kong in the hope of rebuilding the traditional culture which was destroyed
by the Communist Party of China. Some of them worked in Hong Kong press
company to promote the Chinese culture, some engaged in media printing and
publishing of student and youth magazines with financial support from the United
States Information Agency (USIA). Thereafter, Union Press in Hong Kong set up
branches in Singapore to publish the Chao Foon and Student Weekly literary
magazines, with the intention to develop Chinese traditional culture and provide the
youth in Malaya and Singapore with different kinds of reading materials. In the 50s
(1959), Huang Ya arrived Malaya after Shen Qing, Yao Tuo, Fang Tian and Huang
Sicheng. He worked as an editor for Chao Foon and Student Weekly in Kuala Lumpur.
Huang Ya was born in Xiamen, China. Due to the changes in mainland political
situation, he exiled to Hong Kong in 1950 and worked in Union Press. During the first
10 years in Malaya (1959 – 1969), he showed a great interest in the development of
Mahua literary and cultural activities, and also actively advocated the writing of
modernist literature among the youth writers. In the early 60s, besides putting effort in
publishing youth magazines, such as Hai Tian, Huang Yuan and Xin Chao in peninsula
of Malaya, Huang Ya took a great initiative to promote the development of Malaysian
Chinese Literature. Moreover, his dedication in establishing literary groups and
publishers shows his great ambition of building up an Utopia of culture. In this thesis,
I try to study the various cultural activities promoted by Huang Ya while constructing
Utopia culture in Malaya , from beginning until the end , and how does it influence the
generation of Chinese youth writers in Malaya, and affirm his contribution to Mahua
Literary
Nonlinearity in apparent mass and transmissibility of the supine human body during vertical whole-body vibration
No full textResonance frequencies evident in the apparent mass and the transmissibility of the human body decrease with increasing vibration magnitude, but the mechanisms responsible for this nonlinearity have not been established. This experiment was designed to explore the effects of body location on the nonlinearity of the body in supine postures. In a group of 12 male subjects, the apparent mass and transmissibility to the sternum, upper abdomen, and lower abdomen were measured in three postures (relaxed semi-supine, flat supine and constrained semi-supine) with vertical random vibration (0.25–20 Hz) at seven vibration magnitudes (nominally 0.0313, 0.0625, 0.125, 0.25, 0.5, 0.75, and 1.0 ms?2 rms). In all three postures, the apparent mass resonance frequencies and the primary peak frequencies in the transmissibilities to the upper and lower abdomen decreased with increases in vibration magnitude from 0.25 to 1.0 ms?2 rms. Nonlinearity generally apparent in transmissibility to the abdomen was less evident in transmissibility to the sternum and less evident in transmissibilities to the abdomen at vibration magnitudes less than 0.125 ms?2 rms. The nonlinearity was more apparent in the flat supine posture than in the semi-supine postures. The findings are consistent with the nonlinearity being associated with the response of soft tissues, more likely a consequence of passive thixotropy than muscle activit
Nonlinear dual-axis biodynamic response of the semi-supine human body during longitudinal horizontal whole-body vibration
No full textThe resonance frequencies in frequency response functions of the human body (e.g. apparent mass and transmissibility) decrease with increasing vibration magnitude. This nonlinear biodynamic response is found with various sitting and standing postures requiring postural control. The present study measured the apparent mass of the body in a relaxed semi-supine posture with two types of longitudinal horizontal vibration (in the z-axis of the semi-supine body): (i) continuous random excitation (0.25–20 Hz) at five magnitudes (0.125, 0.25, 0.5, 0.75 and 1.0 ms?2 rms); (ii) intermittent random excitation (0.25–20 Hz) alternately at 0.25 and 1.0 ms?2 rms. With continuous random vibration, the dominant primary resonance frequency in the median normalised apparent mass decreased from 3.7 to 2.4 Hz as the vibration magnitude increased from 0.125 to 1.0 ms?2 rms. A nonlinear response was apparent in both the horizontal (z-axis) apparent mass and the vertical (x-axis) cross-axis apparent mass. With intermittent random vibration, as the vibration magnitude increased from 0.25 to 1.0 ms?2 rms, the median resonance frequency of the apparent mass decreased from 3.2 to 2.5 Hz whereas, with continuous random vibration over the same range of magnitudes, the resonance frequency decreased from 3.4 to 2.4 Hz. The median change in the resonance frequency (between 0.25 and 1.0 ms?2 rms) was 0.6 Hz with the intermittent random vibration and 0.9 Hz with the continuous random vibration. With intermittent vibration, the resonance frequency was higher at the high magnitude and lower at the low magnitude than with continuous vibration at the same magnitudes. The responses were consistent with passive thixotropy being a primary cause of nonlinear biodynamic responses to whole-body vibration, although reflex activity of the muscles may also have an influence
Identification of biomechanical nonlinearity in whole-body vibration using a reverse path multi-input-single-output method
Full text linkThe study implements a classic signal analysis technique, typically applied to structural dynamics, to examine the nonlinear characteristics seen in the apparent mass of a recumbent person during whole-body horizontal random vibration. The nonlinearity in the present context refers to the amount of ‘output’ that is not correlated or coherent to the ‘input’, usually indicated by values of the coherence function that are less than unity. The analysis is based on the longitudinal horizontal inline and vertical cross-axis apparent mass of twelve human subjects exposed to 0.25–20 Hz random acceleration vibration at 0.125 and 1.0 ms-2 r.m.s. The conditioned reverse path frequency response functions (FRF) reveal that the uncorrelated ‘linear’ relationship between physical input (acceleration) and outputs (inline and cross-axis forces) has much greater variation around the primary resonance frequency between 0.5 and 5 Hz. By reversing the input and outputs of the physical system, it is possible to assemble additional mathematical inputs from the physical output forces and mathematical constructs (e.g. square root of inline force). Depending on the specific construct, this can improve the summed multiple coherence at frequencies where the response magnitude is low. In the present case this is between 6 and 20 Hz. The statistical measures of the response force time histories of each of the twelve subjects indicate that there are potential anatomical ‘end-stops’ for the sprung mass in the inline axis. No previous study has applied this reverse path multi-input-single-output approach to human vibration kinematic and kinetic data before. The implementation demonstrated in the present study will allow new and existing data to be examined using this different analytical tool
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