Lateral Pulses Research Articles

Société de Biomécanique Young Investigator Award 2019: Upper body behaviour of seated humans in vivo under controlled lateral accelerations

BackgroundA deep understanding of human reactions and stabilization strategies is required to predict their kinematics under external dynamic loadings, such as those that occur in vehicle passengers. Low-level frontal accelerations have been thoroughly investigated; however, the human response to different lateral accelerations is not well understood. The objective of this study is to gain insight regarding the responses of seated humans to lateral perturbations from volunteer experiments in different configurations. MethodsFive volunteers anthropometrically comparable to the 50th-percentile American male, were seated on a sled and submitted to 21 lateral pulses. Seven configurations, each repeated three times, were investigated in this study: a relaxed muscular condition with four pulses, namely, sine and plateau pulses of 0.1 and 0.3 g in a straight spinal posture; a relaxed muscular condition with a plateau pulse of 0.3 g in a sagging spinal posture; and a braced condition with both plateau pulses in a straight spinal posture. Upper body segment kinematics were assessed using inertial measurement units. FindingsThe maximum lateral bending of the head was found to differ significantly among the four acceleration pulses (p < 0.001). Braced muscles significantly reduced lateral bending compared to relaxed muscles (p < 0.001). However, no significant difference was found in lateral bending between straight and sagging spinal postures (p = 0.23). InterpretationThe study shows that not only pulse amplitude but also pulse shape influences human responses to low accelerations, while spinal posture does not influence lateral head bending. These data can be used to evaluate numerical active human body models.

Finite-element simulation of photoinduced strain dynamics in silicon thin plates.

In this paper, we investigate the femtosecond-optical-pulse-induced strain dynamics in relatively thin (100 nm) and thick (10 000 nm) silicon plates based on finite-element simulations. In the thin sample, almost spatially homogeneous excitation by the optical pulse predominantly generates a standing wave of the lowest-order acoustic resonance mode along the out-of-plane direction. At the same time, laterally propagating plate waves are emitted at the sample edge through the open edge deformation. Fourier transformation analysis reveals that the plate waves in the thin sample are mainly composed of two symmetric Lamb waves, reflecting the spatially uniform photoexcitation. In the thick sample, on the other hand, only the near surface region is photo-excited and thus a strain pulse that propagates along the out-of-plane direction is generated, accompanying the laterally propagating pulse-like strain dynamics through the edge deformation. These lateral strain pulses consist of multiple Lamb waves, including asymmetric and higher-order symmetric modes. Our simulations quantitatively demonstrate the out-of-plane and in-plane photoinduced strain dynamics in realistic silicon plates, ranging from the plate wave form to pulse trains, depending on material parameters such as sample thickness, optical penetration depth, and sound velocity.

Residual displacements of RC structures as SDOF systems

SummaryResidual displacements are sensitive to ground motion details, hence more random than peak inelastic displacements. Among the factors with systematic impact on residual displacements, the post‐yield‐stiffness‐ratio has been studied thoroughly; its effects are not investigated further. Concerning another important factor, the hysteresis law, past studies have focused on the bilinear model, which does not represent concrete structures. Residual displacements from nonlinear response‐history analyses of bilinear systems are compared to those from models tuned to concrete structures, conforming to modern codes, deficient or intermediate. Deficient‐type structures, with their narrow, almost self‐centering hysteresis loops, develop markedly smaller residual displacements than those with stable energy‐dissipating behavior. A velocity pulse in the motion increases peak inelastic and residual displacements by about the same proportion. As a fraction of the peak inelastic or spectral displacement, residual displacements are on average almost independent of the period and increase when the lateral strength ratio increases, reaching a limit at a lateral strength ratio of 2 to 5. Peak inelastic displacements are a better basis for estimation of residual displacements than spectral ones: the ratio of the two is almost independent of the period, the lateral strength ratio (beyond values of 2 to 3) and velocity pulses. The spectrum of the ratio of residual displacement to peak inelastic or spectral displacement is considered as a random process of period; its mean and variance functions, marginal probability distributions and autocorrelation functions are given in terms of the lateral strength ratio, the hysteresis model and the presence of a velocity pulse. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Dynamical response of liquid bridges to a step change in the mass force magnitude

We analyze the dynamical response of an isothermal liquid bridge to a step change in the mass force magnitude by numerically solving the three-dimensional Navier-Stokes equations. We study the free surface oscillations caused by both axial and lateral pulses of the mass force. The oscillation amplitude and the dynamical stability limit are calculated for different values of the parameters characterizing the fluid configuration. We examine the stability of one of the liquid bridges to be analyzed in the Japanese and European Research Experiment on Marangoni Instabilities experiment on board of the International Space Station (ISS). We study the response of that liquid bridge to real g-jitter on board of the ISS.

Landslide Stability: Role of Rainfall-Induced, Laterally Propagating, Pore-Pressure Waves

The Johnson Creek Landslide is a translational slide in seaward-dipping Miocene siltstone and sandstone (Astoria Formation) and an overlying Quaternary marine terrace deposit. The basal slide plane slopes sub-parallel to the dip of the Miocene rocks, except beneath the back-tilted toe block, where it slopes inland. Rainfall events raise pore-water pressure in the basal shear zone in the form of pulses of water pressure traveling laterally from the headwall graben down the axis of the slide at rates of 1–6 m/hr. Infiltration of meteoric water and vertical pressure transmission through the unsaturated zone has been measured at ∼50 mm/hr. Infiltration and vertical pressure transmission were too slow to directly raise head at the basal shear zone prior to landslide movement. Only at the headwall graben was the saturated zone shallow enough for rainfall events to trigger lateral pulses of water pressure through the saturated zone. When pressure levels in the basal shear zone exceeded thresholds defined in this paper, the slide began slow, creeping movement as an intact block. As pressures exceeded thresholds for movement in more of the slide mass, movement accelerated, and differential displacement between internal slide blocks became more pronounced. Rainfall-induced pore-pressure waves are probably a common landslide trigger wherever effective hydraulic conductivity is high and the saturated zone is located near the surface in some part of a slide. An ancillary finding is apparently greater accuracy of grouted piezometers relative to those in sand packs for measurement of pore pressures at the installed depth.

Ocular and cervical vestibular evoked myogenic potentials produced by air- and bone-conducted stimuli: Comparative properties and effects of age

Objective To compare amplitudes, latencies, symmetry and the effects of age for both ocular and cervical vestibular evoked myogenic potentials (oVEMPs and cVEMPs) produced by different types of air- (AC) and bone-conducted (BC) stimuli. Methods Sixty-one normal subjects aged 18–80 years participated. Both reflexes were recorded in response to AC clicks, AC and BC 500 Hz tone bursts, forehead taps and lateral mastoid accelerations. Results AC tone bursts, clicks and BC tone bursts evoked oVEMPs in 81%, 59% and 65% of ears, respectively. The AC stimuli had higher thresholds for oVEMPs than for cVEMPs and all three stimuli produced higher asymmetry for the oVEMP than for the cVEMP. Forehead taps and lateral pulses evoked oVEMPs in 96% and 92% of cases. AC click- and BC tone burst-evoked oVEMPs showed a significant decline with age. Conclusions AC stimulation and BC tone bursts delivered to the mastoid are less effective in evoking oVEMPs than in evoking cVEMPs, have high degrees of asymmetry in normals and appear to decline with age. Forehead taps and lateral accelerations produce more symmetrical effects and showed no significant decline with age. Significance Stimulus properties need to be considered when deciding the most appropriate way to investigate vestibular function using oVEMPs.

Maintenance of Lateral Stability During Standing and Walking in the Cat

During free behaviors animals often experience lateral forces, such as collisions with obstacles or interactions with other animals. We studied postural reactions to lateral pulses of force (pushes) in the cat during standing and walking. During standing, a push applied to the hip region caused a lateral deviation of the caudal trunk, followed by a return to the initial position. The corrective hindlimb electromyographic (EMG) pattern included an initial wave of excitation in most extensors of the hindlimb contralateral to push and inhibition of those in the ipsilateral limb. In cats walking on a treadmill with only hindlimbs, application of force also caused lateral deviation of the caudal trunk, with subsequent return to the initial position. The type of corrective movement depended on the pulse timing relative to the step cycle. If the force was applied at the end of the stance phase of one of the limbs or during its swing phase, a lateral component appeared in the swing trajectory of this limb. The corrective step was directed either inward (when the corrective limb was ipsilateral to force application) or outward (when it was contralateral). The EMG pattern in the corrective limb was characterized by considerable modification of the hip abductor and adductor activity in the perturbed step. Thus the basic mechanisms for balance control in these two forms of behavior are different. They perform a redistribution of muscle activity between symmetrical limbs (in standing) and a reconfiguration of the base of support during a corrective lateral step (in walking).

Viscoelastic electrospun jets: Initial stresses and elongational rheometry

A novel method of characterization of viscoelastic longitudinal stresses in electrospun jets of semi-dilute and concentrated polymer solutions and melts is introduced. The measured longitudinal stresses at the beginning of the thin jet region in the jets of a 6wt% aqueous solution of polyethylene oxide (Mw=400kDa) were of the order of 100kPa, which is two orders of magnitude larger than in any other free viscoelastic jets issued from nozzles and orifices. This is attributed to elongation-driven stretching of polymeric liquids in the transition zone, between the preceding modified Taylor cone zone and the beginning of the thin jet region, where the stretching rates are of the order of 100–1000s−1. The Rouse relaxation times found were in the range of 3–8ms, and the moduli of elasticity were of the order of 100Pa. A novel explanation of the reasons for the formation of the straight sections in the electrospun jets is proposed. The straight sections are stabilized by the high initial longitudinal stresses in the jet generated due to strong electrically driven stretching in the transition zone. The further electrically driven stretching in the jet (after the transition zone) is relatively weak, and viscoelastic Rouse relaxation prevails. The relaxation distance of the longitudinal stresses along the jet increases with the applied voltage (which generates higher initial stresses in the transition zone) and thus the length of straight section of the jet should increase as the applied voltage increases.The results also point at an opportunity to develop an elongational rheometer for concentrated polymeric systems with stretching rates of the order of 100–1000s−1. The proposed rheometer employs excitation of electrically driven jets by single lateral pulses, and observation of the pulse propagation and widening along the jet. This reveals the level of the longitudinal stresses along the jet and allows evaluation of the viscoelastic Rouse relaxation time, modulus of elasticity and the elongational viscosity in the jet.

Do invertebrate communities in floodplains change predictably along a river's length?

Summary1. Invertebrate assemblages were described for nine floodplain sites located on a longitudinal gradient of river discharge in the Altamaha River catchment. The Altamaha River and its tributaries constitute one of the few remaining ‘unregulated’ catchments in the southeastern U.S. We predicted that, as the character of lateral flood pulses into backwater swamps changed along the discharge gradient, so would the structure of invertebrate communities. We also examined the relationship between invertebrate assemblages and physicochemical factors (degree of floodplain inundation, pH, conductivity and nutrient concentrations).2. Cluster analyses of both invertebrate abundance and biomass separated the nine sites into three groups corresponding to their positions in the catchment (upper, mid‐ and lower reach clusters). Non‐metric multidimensional scaling ordinations further corroborated the groupings (with combined axis scores of 92% and 73% for abundance and biomass, respectively) and showed significant correlations with degree of inundation and conductivity (abundance), and conductivity, nitrate and phosphate concentrations (biomass).3. Floodplains in the upper reaches were dominated by terrestrial taxa, such as earthworms, oribatid mites, collembolans and assorted terrestrial fly larvae, and some rapidly developing aquatics (harpacticoid crustaceans and mosquitoes). In the mid‐reach, the dominant taxa were longer lived aquatic organisms such as mayflies and aquatic oligochaetes, although some terrestrial organisms (elaterid beetles and mites) were still common. Invertebrate families dependent on water flow, such as riffle beetles and some mayflies, were common only in mid‐reach floodplain sites. Lower reaches were dominated by lentic aquatic taxa such as dytiscid beetles and asellid isopods, which commonly persist in wetlands after they dry.4. Our study indicates that invertebrate community structure varies predictably among floodplains in the Altamaha catchment, with headwater habitats being dominated by terrestrial and rapidly‐developing aquatic invertebrates, mid‐reaches characterised by an influx of invertebrates from the river and lower reaches being dominated by wetland taxa with desiccation‐resistant stages. This spatial variability should be considered when applying the Flood Pulse Concept.

The Approximate Transient Field of a Horizontal Electric Dipole Excited by a Gaussian Pulse on the Boundary Between a Homogeneous Isotropic Medium and One-Dimensionally Anisotropic Medium

In this letter, we examine the approximate transient field of a horizontal electric dipole excited by a Gaussian pulse on the boundary between a homogeneous isotropic medium and a one-dimensionally anisotropic medium in detail. The final formulas of the transient field are expressed in terms of several fundamental functions. The derivations and computations show that the three time-dependent electric field components consist of two lateral pulses which travel along the boundary with different velocities and different amplitudes. Especially, the Fresnel-integral terms in those formulas do not completely cancel for the three electric field components.

A Comparison of Volunteers and Dummy Upper Torso Kinematics with and Without Shoulder Belt Slack in a Low Speed Side/Pre-Roll Environment

Objective. The objective of this study was to compare the occupant and dummy kinematics in a low-speed lateral environment with and without shoulder belt slack. Methods. A buck of a small European car was mounted on a side impact sled. The parameters evaluated were pulses, sitting location, and belt slack. A total of 24 tests were carried out. Three 50th-percentile male volunteers and one Hybrid III 50th-percentile male were tested. The pulses consisted of Pulse 1:+/- 0.7 g's pulse and Pulse 2: a -0.9 g pulse to simulate low-speed pre-roll/side events. Both pulses had a duration of 500 msec. Results. The peak lateral head excursion was higher in the far-side occupants than in the near-side occupants. Furthermore, for the far-side volunteers, lateral head displacements were lower in the no-slack condition than in the slack condition, at 388 ± 64 mm and 455 ± 84 mm respectively for Pulse 1 and at 138 ± 2 mm and 207 ± 70 mm for Pulse 2. The timing required to reach peak lateral displacement was higher in Pulse 1 than in Pulse 2. In comparison to the volunteers, the Hybrid III dummy lateral motion was lower. The peak lateral displacement in Pulse 1 was 231 mm with slack and 194 mm without and 98 mm and 107 mm for Pulse 2, respectively. Conclusions. The results obtained in this study indicate that removing seatbelt slack would be more beneficial for far-sided occupants than near-sided. They also point to the lack of biofidelity of the Hybrid III dummy in low g lateral pulses.

Far-Side Occupant Kinematics in Low Speed Lateral Sled

Objective. The objective of this study was to evaluate the far-side occupant kinematics in low-speed lateral pulses with and without a seatbelt system. Methods. The kinematics responses of three volunteers and a Hybrid III were compared in three low-to-moderate lateral pulses. The parameters evaluated were pulses and belt usage. A total of 24 tests were carried out in a side-impact sled. The subjects consisted of two 50th-percentile males (Vol 1 & 2), one 5th-percentile female (Vol 3), and a Hybrid III 50th-percentile male (ATD). All subjects were seated in a far-side impact. Three low speed pulses were used: Pulse 1: a 4 g at 6 km/h, Pulse 2: 4 g/8 kph followed by a -2.5 g pulse to simulate a low curb impact, and Pulse 3: a 4 g's pulse at 10 km/h. In addition, the kinematics result from Pulse 2 was used to assess the performance of a human model. The human model was developed by TNO. Results. For all three pulses, the peak head lateral displacement was greater with the 5th female (Vol 3) than the male volunteers. The ATD results in the 6 and 10 km/h pulses were comparable to the volunteers. However, in Pulse 2, the ATD motion was higher than the volunteers. Conclusion. The results obtained in this study suggest the Hybrid III is a somewhat conservative device for an evaluation of occupant kinematics in low-speed lateral pulses. The human model also seemed to be representative of volunteer kinematics.

Approximate formulas for lateral electromagnetic pulses from a horizontal electric dipole on the surface of one-dimensionally anisotropic medium

In this paper, approximate formulas are derived for the electromagnetic pulse due to a delta-function current in a horizontal electric dipole on the planar boundary between a homogeneous isotropic medium and one-dimensionally anisotropic medium. The components of the electric field consist of two delta-function lateral pulses which decrease with the amplitude factor /spl rho//sup -2/ and travel along the boundary with different velocities and different amplitudes. Also, it is noted that the formulas for the time-dependent magnetic field components obtained by Fourier transforms from the approximate formulas in the frequency domain are not adequate.

Volunteer and Dummy Head Kinematics in Low-Speed Lateral Sled Tests

Understanding human head kinematics prior to the safety countermeasure activation is important to help minimize potential for injury in side impact and rollover situations. The objective of this study was to compare three volunteers and the Hybrid III responses in three low-to-moderate lateral crash pulses. The parameters evaluated were lateral pulses and belt usage. A total of 24 tests were carried out in a side impact sled. The subjects consisted of two 50th percentile males (Volunteers 1 and 2), one 5th percentile female (Volunteer 3) and a Hybrid III 50th percentile male. All subjects were in near-side impacts. The pulses consisted of two 4 g pulses (6 and 8 kph) and a 4 g/8 kph followed by a m 2.5 g pulse to simulate a low curb impact. In the 6 and 8 kph pulses, the antropometric test devices' head trajectory is somewhat similar to the volunteers'. For near-sided/belted occupants, the peak lateral excursion was 327 - 53 mm for the volunteers, and 269 mm for the Hybrid III in the 6 kph pulse, while it was 321 - 35 mm respectively in the 8 kph pulse. It was also observed that, in the first phase of the motion, the Hybrid III vertical displacement remained positive while the volunteers' vertical displacement was initially negative. This is probably due to the rigidity of the Hybrid III spine and the lack of flexibility in its torso compared to humans. In the 4 g/8 kph followed by a m 2.5 g pulse, the lateral head excursion was higher with a Hybrid III than with volunteers. For near-sided/belted occupants, the lateral excursion was 155 - 10 mm for the volunteers and 291 mm for the Hybrid III. The results suggest that the Hybrid III is a useful tool to evaluate head kinematics in slow-speed lateral impacts at 6 and 8 kph. For the 4 g/8 kph pulse followed by a m 2.5 g pulse acceleration, a better correlation between the Hybrid III and volunteer head excursion may be needed to improve the biofidelity of the Hybrid III kinematics.

Model Predictive Lateral Pulse Jet Control of an Atmospheric Rocket

Uncontrolled direct fire atmospheric rockets exhibit high impact point dispersion, even at relatively short range, and, as such, have been employed as area weapons on the battlefield. To reduce the dispersion of a direct fire rocket, the use of a small number of short-duration lateral pulses acting as a control mechanism is investigated. A unique control law is reported that combines model predictive control and linear projectile theory for lateral pulse jet control of an atmospheric rocket. The impact point in the target plane is directly controlled. Through simulation, this model predictive flight control law is shown to efficiently reduce direct fire rocket dispersion. A parametric trade study on an example rocket configuration is reported that details the effect of the number and amplitude of individual pulse jets, as well as the effect of the flight control system computation cycle time.

Lateral olfactory tract input to dentate gyrus is depressed by prior noradrenergic activation using nucleus paragigantocellularis stimulation

Nucleus paragigantocellularis stimulation potentiates the medial perforant path population spike in the dentate gyrus via β-receptor activation. In this study, the same paragigantocellularis stimulation preceding lateral olfactory tract pulses depressed the lateral perforant path mediated synaptic potential in dentate gyrus. Depression of the lateral olfactory tract input was blocked by a β-antagonist. These in vivo results confirm in vitro reports that norepinephrine induces potentiation of medial perforant path input and depression of lateral perforant path input to dentate gyrus.

Lateral electromagnetic waves and pulses on open microstrip

The propagation of lateral electromagnetic waves and pulses on microstrip is investigated. Interference patterns generated by the superposition of the lateral and direct waves along the air-substrate surface are shown. The field generated by the pulse excitation of a horizontal dipole on the air-substrate boundary is shown to consist of a lateral-wave pulse and a slower direct-wave pulse. Their differences in shape and decay rate are clarified. It is shown that the shape of a Gaussian pulse propagating along an open microstrip transmission line is closely related to the shape of the lateral electric-field pulse generated by a Gaussian current pulse in a dipole on the air-substrate boundary. >

Lateral Electromagnetic Pulses Generated on a Plane Boundary between Dielectrics by Vertical and Horizontal Dipole Sources with Gaussian Pulse Excitation

The exact lateral electromagnetic pulse generated by a vertical dipole excited by a Gaussian pulse is derived. A comparison with the previously derived approximate formula shows that the latter gives the correct field at all radial distances except for the nonappearance of the relatively small second pulse. Corresponding approximate formulas are derived for the electric field of a horizontal dipole. These should give the correct field except for the nonappearance of the small second pulse in some components.

Lateral Electromagnetic Pulses Generated by a Vertical Dipole on a Plane Boundary Between Dielectrics

Approximate, quite simple formulas are derived for the transient field generated by a vertical electric dipole on the boundary between two dielectric half-spaces when the permittivity of one of these is much greater than that of the other. The three components of the field are determined for both delta-function and Gaussian-pulse excitation. The field of the former is compared with the corresponding exact expressions with generally good agreement and some interesting, readily explained differences.

Lateral electromagnetic pulses generated by a vertical dipole on the boundary between two dielectrics

An exact solution in terms of elementary functions is obtained in the time domain for the vertical electric field Ez(ρ,t) and the transverse magnetic field Bφ(ρ,t) of a dipole located on the plane boundary z=0 between air (region 2, z&amp;lt;0) and a perfect dielectric (region 1, z&amp;gt;0) when the dipole is excited by a single delta-function current pulse. The vertical electric field on the boundary consists of a delta-function pulse that travels in the air with the velocity c, an oppositely directed delta-function pulse that travels in the dielectric with the smaller velocity c/ε1/2, an amplitude structure that varies in time between the two pulses, and a final static electric field due to the charges left on the dipole. The horizontal magnetic field is similar. For comparison, the vertical electric field in the equatorial plane of the same dipole in a homogeneous dielectric is also derived. The comparison indicates that the field along the boundary is a surface-wave or lateral pulse.