Lateral Gravity Research Articles

Mechanisms underlying gait disturbance in Parkinson's disease: a single photon emission computed tomography study.

Single photon emission computed tomography was used to evaluate regional cerebral blood flow changes during gait on a treadmill in 10 patients with Parkinson's disease and 10 age-matched controls. The subjects were injected with [99mTc]hexamethyl-propyleneamine oxime twice: while walking on the treadmill, which moved at a steady speed, and while lying on a bed with their eyes open. On the treadmill, all subjects walked at the same speed with their preferred stride length. The patients showed typical hypokinetic gait with higher cadence and smaller stride length than the controls. In the controls, a gait-induced increase in brain activity was observed in the medial and lateral premotor areas, primary sensorimotor areas, anterior cingulate contex, superior parietal cortex, visual cortex, dorsal brainstem, basal ganglia and cerebellum. The Parkinson's disease patients revealed relative underactivation in the left medial frontal area, right precuneus and left cerebellar hemisphere, whereas they showed relative overactivity in the left temporal cortex, right insula, left cingulate cortex and cerebellar vermis. This is the first experimental study showing that the dorsal brainstem, which corresponds to the brainstem locomotor region in experimental animals, is active during human bipedal gait. The reduced brain activity in the medial frontal motor areas is a basic abnormality in motor performance in Parkinson's disease. The underactivity in the left cerebellar hemisphere, in contrast to the overactivity in the vermis, could be associated with a loss of lateral gravity shift in parkinsonian gait.

Stability of Magnetically Levitated Liquid Bridges of Arbitrary Volume Subjected to Axial and Lateral Gravity

The paramagnetic fluid composed of manganese chloride tetrahydrate dissolved in water was used to form bridges held between two parallel collinear rods. Magnetic levitation was used to control the effective gravity felt by the bridges. Their stability was studied as a function of Bond number and volume of the supported liquid. Data are compared with theoretical predictions for liquid bridges as well as with experimental results, where available.

Effect of a lateral gravitational field on the nonaxisymmetric equilibrium shapes of liquid bridges held between eccentric disks and of volumes equal to those of cylinders

Bifurcation diagrams of nonaxisymmetric cylindrical volume liquid bridges held between nonconcentric circular disks subject to a lateral gravitational force are found by solving the Young-Laplace equation for the interface by a finite difference method. In the absence of lateral gravity, the primary family of liquid bridges that starts with the cylinder when the eccentricity of the disks, e, is zero first loses stability at a subcritical bifurcation point as e increases. Further loss of stability is experienced by the already unstable primary family as a turning point is encountered at yet higher values of the eccentricity. However, the introduction of lateral gravity gl changes entirely the structure of the solutions in that instability always occurs at a turning point with respect to e no matter how small the magnitude of gl. The stability limits calculated are compared with the ones obtained using asymptotic techniques by taking as base solution the cylinder of slenderness Λ=π.

Numerical Simulation of Water Sheet Flow on Pelton Buckets. 1st Report. Discretization of Unsteady Flow Using Animated Cartoon Method.

Since a rotating bucket of Pelton turbines intermittently penetrates into a free water jet, the confined sheet flow with free surface on the bucket is unsteady in space-time. In order to analyze the unsteady flow quasi-steadily, an animated cartoon method is proposed. Assuming the relative inflow to the bucket to be steady within the respective frame of the cartoon, the streak patches of the unsteady flow are computed by integrating the relative flow accelerations due to the constraint, lateral pressure difference and gravity, as well as the apparent centrifugal and Coriolis accelerations, considering the thickness of the water sheet under the atmospheric environment.

Sloshing of cryogenic helium driven by lateral impulse/gravity gradient-dominated/or g-jitter-dominated accelerations and orbital dynamics

The coupling of slosh dynamics within a partially filled rotating dewar of superfluid helium II with spacecraft orbital dynamics is investigated in response to the environmental disturbances of (a) lateral impulses, (b) gravity gradients and (c) g-jitter forces. The purpose of this study is to investigate how the coupling of helium II fluid slosh dynamics driven by three cases of environmental force with spacecraft dynamics can affect the bubble deformations and their associated fluid and spacecraft mass centre fluctuations. The numerical computation of slosh dynamics is based on a rotational frame, while the spacecraft dynamics is associated with a non-rotational frame. Results show that the major contribution of orbital dynamics is driven by coupling with slosh dynamics. Neglecting the effect of slosh dynamics acting on the spacecraft may lead to the wrong results for the development of orbital and attitude control techniques.

The influence of head rotation on human upright posture during balanced bilateral vibration

During a balanced bilateral vibration of tensor fasciae latae muscles evoking no evident postural changes in a standing human the slow head turns resulted in a pronounced lateral common gravity centre displacements to the 'occipital' side. Neck influences were most prominent at intermediate tonic background and were lacking both during very weak and strong vibratory stimulation in contrast to usual tonic vibratory reflex which becomes stronger with the increase of frequency. Body sway was induced not only by actual head turns but also by illusory ones evoked by neck muscle vibration. The neck influences on standing posture are therefore present in healthy adults, but they require a definite level of tonic readiness for their manifestation and are incorporated in the whole system of body scheme mechanisms.

The influence of head rotation on human upright posture during balanced bilateral vibration

During a balanced bilateral vibration of tensor fasciae latae muscles evoking no evident postural changes in a standing human the slow head turns resulted in a pronounced lateral common gravity centre displacements to the 'occipital' side. Neck influences were most prominent at intermediate tonic background and were lacking both during very weak and strong vibratory stimulation in contrast to usual tonic vibratory reflex which becomes stronger with the increase of frequency. Body sway was induced not only by actual head turns but also by illusory ones evoked by neck muscle vibration. The neck influences on standing posture are therefore present in healthy adults, but they require a definite level of tonic readiness for their manifestation and are incorporated in the whole system of body scheme mechanisms.

Sedimentation from gravity currents generated by turbulent plumes

ABSTRACTSedimentation from radially spreading gravity currents generated at the top of ascending sediment‐laden plumes is described by a model which assumes that sediment is dispersed homogeneously by turbulence in the gravity current, resulting in an exponential decrease in the concentration of sediment with time as particles settle out of the lower boundary of the current. For radial spreading this model predicts a Gaussian distribution of sediment accumulation away from the source with an exponential constant, B, which depends on flow rate, Q, and particle settling velocity, v (B=nv/Q). In the experiments described, sedimentation occurs from gravity currents generated by ascent of buoyant, particle‐laden plumes of fresh water in a tank of salty water. The sediment accumulation shows close agreement with the theoretical model, and the Gaussian decay constant, B, can be determined from a maximum in the accumulated mass of sediment per unit distance and from the slope of the line In(S/S0) = ‐Br2, where r is the radial distance, S is the sediment mass flux per unit area and S0 is the value of S at r=0. Data from the dispersal of volcanic ejecta from a large (c. 24 km high) plinian eruption column in the Azores also show good agreement with the theory, confirming that it is general and independent of scale and the nature of the fluid. The experimental data also show a change in sedimentation behaviour at distances from the source corresponding to the corner of the plume where it diverts into a lateral gravity current and there is an abrupt decrease in vertical velocity. Sedimentation of coarse grain sizes, between the source and the corner, occurs from the inclined plume margins and does not behave as predicted by the theoretical model.

Morne Patates volcano, southern Dominica, Lesser Antilles

AbstractMornes Patates is the youngest volcano in Dominica occupying a depression on the southwestern flank of a larger stratovolcano, Morne Plat Pays. Within the depression an arcuate ridge, apparently of acid andesite lavas, has been cored and largely buried by the explosive emplacement of two acid andesite domes and their associated pyroclastic deposits, mainly block-and-ash flow deposits. A basaltic scoria horizon, exposed on the northern side of the depression, has a14C age of 28450 ± 1500 years B.P. and is not seen on the volcano itself, which suggests that the domes and pyroclastic rocks are younger than this. A14C age of 450 ± 90 years B.P. from a block-and-ash flow deposit from the Morne Patates dome apparently confirms this and the youthful morphology also suggests a young age. The angular shape of the depression and the steep submarine slopes are consistent with an origin as a lateral gravity slide rather than a caldera collapse. Vigorous fumarolic activity and swarms of local earthquakes suggest that magma exists at depth (several kilometres) beneath the Morne Patates–Morne Plat Pays area.

Buckling of Open Cylindrical Shells under Lateral Load

A technique for obtaining the buckling load of open cylindrical shells with simply supported ends and free longitudinal edges, subjected to lateral gravity loading, is presented. General equations based on the large deflection theory are developed and a set of nonlinear finite difference equations is obtained and solved by the Newton-Raphson method. Using the linear terms only, deflections and stresses based on relatively coarse nets compared favorably with existing analytical solutions. The lowest nonlinear buckling load was found to be associated with a deflection pattern symmetric about the transverse centerline, but asymmetric about the longitudinal centerline. In an example, equilibrium paths and deflection patterns were obtained for a shell subjected to uniform load, and to uniform load with a small additional antisymmetric load. The lowest buckling under uniform load was obtained by reducing this additional load to zero. For the example examined, the buckling load was about 1/2 of the classical linear buckling pressure of a full cylinder.