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Apparent mass of the human body in the vertical direction: Inter-subject variability
No full textThe biodynamic responses of the seated human body to whole-body vibration vary considerably between people, but the reasons for the variability are not well understood. This study was designed to determine how the physical characteristics of people affect their apparent mass and whether inter-subject variability is influenced by the magnitude of vibration and the support of a seat backrest. The vertical apparent masses of 80 seated adults (41 males and 39 females aged 18–65) were measured at frequencies between 0.6 and 20 Hz with four backrest conditions (no backrest, upright rigid backrest, reclined rigid backrest, reclined foam backrest) and with three magnitudes of random vibration (0.5, 1.0 and 1.5 m s-2 rms). Relationships between subject physical characteristics (age, gender, weight, and anthropometry) and subject apparent mass were investigated with multiple regression models. The strongest predictor of the modulus of the vertical apparent mass at 0.6 Hz, at resonance, and at 12 Hz was body weight, with other factors having only a marginal effect. After correction for other variables, the principal resonance frequency was most consistently associated with age and body mass index. As age increased from 18 to 65 years, the resonance frequency increased by up to 1.7 Hz, and when the body mass index was increased from 18 to 34 kg m?2 the resonance frequency decreased by up to 1.7 Hz. These changes were greater than the 0.9-Hz increase in resonance frequency between sitting without a backrest and sitting with a reclined rigid backrest, and greater than the 1.0-Hz reduction in resonance frequency when the magnitude of vibration increased from 0.5 to 1.5 m s?2 rms. It is concluded that the effects of age, body mass index, posture, vibration magnitude, and weight should be taken into account when defining the vertical apparent mass of the seated human body.<br/
Apparent mass of the human body in the vertical direction: Effect of seat backrest
Get PDFThe transmission of vibration through a seat depends on various characteristics of the seat and the dynamic response of the human body. The dynamic response of the body can be represented by its apparent mass, but the effect of the seat on the apparent mass of the body is not well understood. This study was designed to quantify the effect of foam and rigid backrests on the vertical apparent mass of the human measured at the seat surface supporting the body. The apparent masses of 12 subjects were measured during exposure to random vertical vibration (1.0 ms?2 rms from 0.125 to 40 Hz) in a seat with a rigid backrest, in the same rigid seat with three thicknesses of foam backrest (50, 100 and 150 mm), and in the same seat with no backrest. The backrests were inclined at various angles: 0°, 5°, 10°, 15°, 20°, 25° and 30° for the rigid and 100 mm foam backrests, and 0°, 10°, 20° and 30° for the 50 and 150 mm foam backrests. With all vertical backrests (i.e., 0° inclination), there were resonances in the apparent mass of the body around 5 and 10 Hz. With no backrest, the apparent mass was increased at frequencies less than the resonance frequency but decreased at frequencies between 8 and 20 Hz, relative to the apparent mass with the vertical rigid and foam backrests. With the rigid backrest, the primary resonance frequencies in the apparent mass increased with increasing backrest inclination. With the foam backrests, the resonance frequencies decreased with increasing backrest inclination. At frequencies less than the primary resonance, the apparent mass decreased with increasing backrest inclination, particularly with the rigid backrest. Between 8 and 15 Hz, the apparent mass decreased with increasing inclination, most notably with the foam backrests. At inclinations less than 30°, there was little effect of foam thickness on the apparent mass, but at 30° an increase in the thickness of the foam decreased the frequency of the first resonances. Since contact with backrests and the characteristics of backrests influence the vertical apparent mass of the seated body, backrests should be expected to influence the transmission of vertical vibration through a supporting seat cushion
The transmission of vertical vibration through seats: influence of the characteristics of the human body
Get PDFThe transmission of vibration through a seat depends on the impedance of the seat and the apparent mass of the seat occupant. This study was designed to determine how factors affecting the apparent mass of the body (age, gender, physical characteristics, backrest contact, and magnitude of vibration) affect seat transmissibility. The transmission of vertical vibration through a car seat was measured with 80 adults (41 males and 39 females aged 18–65) at frequencies between 0.6 and 20 Hz with two backrest conditions (no backrest and backrest), and with three magnitudes of random vibration (0.5, 1.0, and 1.5 m s-2 rms). Linear regression models were used to study the effects of subject physical characteristics (age, gender, and anthropometry) and features of their apparent mass (resonance frequency, apparent mass at resonance and at 12 Hz) on the measured seat transmissibility. The strongest predictor of both the frequency of the principal resonance in seat transmissibility and the seat transmissibility at resonance was subject age, with other factors having only marginal effects. The transmissibility of the seat at 12 Hz depended on subject age, body mass index, and gender. Although subject weight was strongly associated with apparent mass, weight was not strongly associated with seat transmissibility. The resonance frequency of the seat decreased with increases in the magnitude of the vibration excitation and increased when subjects made contact with the backrest. Inter-subject variability in the resonance frequency and transmissibility at resonance was less with greater vibration excitation, but was largely unaffected by backrest contact. A lumped parameter seat–person model showed that changes in seat transmissibility with age can be predicted from changes in apparent mass with age, and that the dynamic stiffness of the seat appeared to increase with increased loading so as to compensate for increases in subject apparent mass associated with increased sitting weight
Apparent mass of the human body in the vertical direction: Effect of footrest and a steering wheel
No full textThe apparent mass of the seated human body influences the vibration transmitted through a car seat. The apparent mass of the body is known to be influenced by sitting posture but the influence of the position of the hands and the feet is not well understood. This study was designed to quantify the influence of steering wheel location and the position of a footrest on the vertical apparent mass of the human body. The influences of the forces applied by the hands to a steering wheel and by the feet to a footrest were also investigated. Twelve subjects were exposed to whole-body vertical random vibration (1.0 m s?2 rms over the frequency range 0.13–40.0 Hz) while supported by a rigid seat with a backrest reclined to 15°. The apparent mass of the body was measured with five horizontal positions and three vertical positions of a steering wheel and also with hands in the lap, and with five horizontal positions of a footrest. The influence of five forward forces (0, 50, 100, 150, 200 N) applied separately to the ‘steering wheel’ and the footrest were also investigated as well as a ‘no backrest’ condition. With their hands in their laps, subjects exhibited a resonance around 6.7 Hz, compared to 4.8 Hz when sitting upright with no backrest. In the same posture holding a steering wheel, the mass supported on the seat surface decreased and there was an additional resonance at 4 Hz. Moving the steering wheel away from the body reduced the apparent mass at the primary resonance frequency and increased the apparent mass around the 4 Hz resonance. As the feet moved forward, the mass supported on the seat surface decreased, indicating that the backrest and footrest supported a greater proportion of the subject weight. Applying force to either the steering wheel or the footrest reduced the apparent mass at resonance and decreased the mass supported on the seat surface. It is concluded that the positions and contact conditions of the hands and the feet affect the biodynamic response of the body in a car driving posture. As the biodynamic response influences the vibration transmitted through seats, these factors should be considered in dynamic models of vehicle seating.<br/
Factors affecting the dynamic response of the body and the vibration transmitted through seats
No full textThe vibration transmitted through a seat is influenced by the dynamics of the seat and thedynamics of the occupant. The principal objective of this thesis is to understand how the dynamicsof the body and factors affecting the dynamics of the body influence the vibration transmittedthrough seats. Previous studies have shown that the apparent mass of the body and seattransmissibility are affected by the seating environment (e.g. vibration input spectra, backrest,hands position, foot position) and variability between people (i.e. physical characteristics), butthese effects have not previously been systematically explored for realistic seating conditions.The apparent masses of 12 subjects were measured during exposure to random vertical vibration(from 0.125 to 40 Hz) to investigate the effects of the seat backrest, the footrest and steeringwheel, and input spectra. In a rigid seat with no backrest, there were resonances in the apparentmass of the body around 5 and 10 Hz (with 1.0 ms-2 r.m.s broadband vibration). In the same seatwith a rigid backrest, the median resonance frequency in the apparent mass increased from 5.47 to6.35 Hz as the backrest was reclined to 30 degrees in 5 degrees increments; with a 100-mm foambackrest, the median resonance frequency decreased from 5.18 to 4.49 Hz as the backrest wasreclined to 30 degrees. When subjects held a steering wheel, the mass supported on the seatsurface decreased and there was an additional resonance at 4 Hz in the apparent mass. Movingthe steering wheel away from the body reduced the apparent mass at resonance and increased theapparent mass around the 4 Hz resonance. As the feet moved forward, the mass supported on theseat surface increased, indicating that the backrest and footrest supported a lesser proportion ofthe subject weight. Applying force (0, 50, 100, 150, 200 N) to either the steering wheel or thefootrest reduced the apparent mass at resonance and decreased the mass supported on the seatsurface. Narrowband inputs at ½-octave intervals (from 1 to 16 Hz) presented at five magnitudes(0.25, 0.4, 0.63, 1.0 and 1.6 ms-2 r.m.s.) showed that the extent of nonlinearity previously observedwith broadband vibration was frequency-dependent: the magnitude of vibration at frequencies lessthan 4 Hz had the greatest effect on the apparent mass at resonance, while vibration atfrequencies less than 8 Hz had the greatest effect on the resonance frequency.A simple lumped parameter model was used to demonstrate that changes in the apparent masswith backrest contact, backrest inclination, hand position, foot position and vibration magnitudecould be closely represented by changing the parameters in the model. Trends in modelparameters, the damping ratios, and the damped natural frequencies were identified as a functionof the model variables.A study was designed to determine how the physical characteristics of 80 seated adults (41 malesand 39 females aged 18 to 65) affected their apparent mass and the transmission of vibrationthrough a seat. Multiple regression models showed that while the strongest predictor of the verticalapparent mass at 0.6 Hz, at resonance, and at 12 Hz was bodyweight, weight was not stronglyassociated with seat transmissibility. A lumped parameter seat-person model was used to showthat the dynamic stiffness of the seat increased with increased loading so as to compensate forincreases in apparent mass associated with increased sitting weight. As age increased from 18 to65 years, the apparent mass resonance frequency increased by up to 1.7 Hz. This change wasgreater than the 0.9-Hz increase in resonance frequency between sitting without a backrest andsitting with a backrest reclined to 15° and greater than the 1.0-Hz reduction in resonance frequencywhen the magnitude of vibration increased from 0.5 to 1.5 ms-2 r.m.s. Subject age was much thestrongest predictor of the seat transmissibility resonance frequency and the transmissibility atresonance. The model was used to show that changes in the seat transmissibility with age could bepredicted from changes in the apparent mass with age
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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