The transmission of vertical vibration through seats: influence of the characteristics of the human body

The 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

Is the infant car seat challenge useful?:A pilot study in a simulated moving vehicle

Background and objective The American Academy of Pediatrics recommends that preterm infants complete a predischarge 'car seat challenge' observation for cardiorespiratory compromise while in a car seat. This static challenge does not consider the more upright position in a car or the vibration of the seat when the car is moving. This pilot study was designed to assess the cardiorespiratory effects of vibration, mimicking the effect of being in a moving car, on preterm and term infants. Methods A simulator was designed to reproduce vertical vibration similar to that in a rear-facing car seat at 30 mph. 19 healthy newborn term and 21 preterm infants, ready for hospital discharge, underwent cardiorespiratory measurements while lying flat in a cot (baseline), static in the seat (30°), simulator (40°) and during motion (vibration 40°). Results Median test age was 13 days (range 1-65 days) and median weight was 2.5 kg (IQR: 2.1-3.1 kg). Compared with baseline observations, only the total number of desaturations was significantly increased when infants were placed at 30° (p=0.03). At 40°, or with vibration, respiratory and heart rates increased and oxygen saturation decreased significantly. Profound desaturations &lt;85% significantly increased during motion, regardless of gestational age. Conclusions This is the first study to assess the effect of motion on infants seated in a car safety seat. Term and preterm infants showed significant signs of potentially adverse cardiorespiratory effects in the upright position at 40°, particularly with simulated motion, not identified in the standard challenge. A larger study is required to investigate the significance of these results.</p

RA-MAP, molecular immunological landscapes in early rheumatoid arthritis and healthy vaccine recipients

Rheumatoid arthritis (RA) is a chronic inflammatory disorder with poorly defined aetiology characterised by synovial inflammation with variable disease severity and drug responsiveness. To investigate the peripheral blood immune cell landscape of early, drug naive RA, we performed comprehensive clinical and molecular profiling of 267 RA patients and 52 healthy vaccine recipients for up to 18 months to establish a high quality sample biobank including plasma, serum, peripheral blood cells, urine, genomic DNA, RNA from whole blood, lymphocyte and monocyte subsets. We have performed extensive multi-omic immune phenotyping, including genomic, metabolomic, proteomic, transcriptomic and autoantibody profiling. We anticipate that these detailed clinical and molecular data will serve as a fundamental resource offering insights into immune-mediated disease pathogenesis, progression and therapeutic response, ultimately contributing to the development and application of targeted therapies for RA.</p

Factors affecting the dynamic response of the body and the vibration transmitted through seats

The 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

The effect of temperature on railway rolling noise

The stiffness and damping of railpads in a railway track are affected by changes in the temperature of the surrounding environment. This results in the rolling noise radiated by trains increasing as the temperature increases. This paper quantifies this effect for a ballasted track equipped with natural rubber railpads and also studies the behaviour of a cork-reinforced rubber railpad. By means of measurements in a temperature-controlled environment, it is shown that the shear modulus of the natural rubber increases by a factor of six when the temperature is reduced from 40 ℃ to −20 ℃. The loss factor increases from 0.15 at 40 ℃ to 0.65 at −20 ℃. The shear modulus of the cork-reinforced rubber increases by a factor of 10, and the loss factor shows the typical trend of transition between rubbery and glassy regions. The railpad stiffness estimated from decay rate measurements at different temperatures is shown to follow the same trend. Field measurements of the noise from passing trains are performed for temperatures between 0 ℃ and 35 ℃; they show an increase of about 3–4 dB. Similar results are obtained from predictions of noise using the measured dependence of pad stiffness

Direct Photonic Fusion of Vitrified Bonding Materials

The purpose of this study is to show the effects of the direct fusion of raw materials used for vitrified grinding wheels by photonic interactions. The paper describes the construction of a sintering apparatus that employs a pulsed neodymium: yttrium aluminum garnet (Nd:YAG) laser to fuse a combination of raw materials such as ball clay, feldspar, and borax to form a partially-crystalline glass material. The experimental results show that lasers can replace traditional methods of glass frit formation by fusing raw materials used in the manufacture of glass bonds for vitrified grinding wheels. X-ray diffraction data shows that a glass with short range order has formed using the new method. The work described herein provides a new avenue for glass frit formation applied to grinding wheel manufacture

Experimental procedures for testing the performance of rail dampers

Rail dampers work by increasing the attenuation with distance of vibration transmitted along the rail, a quantity known as the track decay rate. Currently, there are no standardized procedures to measure their effectiveness in reducing rolling noise without the need for in-track installation and time-consuming tests. This paper describes and evaluates experimental procedures for assessing rail dampers. Instead of field measurements it is proposed to use laboratory measurements of vertical and lateral decay rates on a free rail equipped with dampers. These are combined with in-situ measurements on an undamped track. The decay rates of a damped track can be approximated by adding the results of the damped free rail to those of the undamped track.Three different methods are studied to measure the decay rates of damped free rails: (i) using a long rail, in the present work 32 m long, from frequency response functions measured at intervals along the rail; (ii) using a short rail, in the present work 6 m long, from the modal properties of the rail; and (iii) directly from the point and transfer frequency response functions at both ends of the short rail. The latter two are complementary: the modal method is more suited to low frequencies while the direct method is more suited to high frequencies. These methods are evaluated theoretically and by comparison with experimental results.Good agreement is found between the various methods, for vibration in both vertical and lateral directions, between 300 Hz and 5 kHz. In practice, the direct short-rail method is likely to be sufficient for most applications. The limitations of the methods are identified and corrections are proposed for the effect of near-field waves in the rai