Different Levels Of Gravity Research Articles

Hypogravity modeling of upper extremities: an investigation of manual handling in the workplace.

Experiments on the lower limbs are the only approaches being used to study how hypogravity (HG) (0 < g < 1, e.g., Moon: 1/6g, Mars: 3/8g) affects human movement. The goal of this study was to expand this field experimentally by investigating the effect of HG on the upper extremities during one-handed manual handling tasks in a sitting posture: static weight holding with an outstretched arm, and slow repetitive weight lifting and lowering motions. The hypothesis was that while completing static and dynamic tasks with elements of repetition in HG, the upper body's tilt (angle regarding the vertical axis) would change differently from Earth's gravity. Specifically, upper arm and spine angles, joint torques, and forces were investigated. Twenty-four healthy participants aged 33.6 ± 8.2 years were involved in the trial. Joint angles were examined using vision-based 3D motion analysis. According to this investigation, there is a correlation between a body tilting backward and a gravity level reduction (p < 0.01). Thus, HG causes postural deviation, and this shows that workplace design must be adapted according to the level of gravity to promote comfortable and balanced body alignment, minimizing stress on muscles and joints. To lower the risk of musculoskeletal disorders (MSDs), enhance overall performance, and increase job satisfaction, proper support systems and restrictions for sitting positions should be taken into account, concerning different levels of gravity.

Stick-slip Dynamics in Penetration Experiments on Simulated Regolith

Abstract The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized regolith held weakly to the surface by gravity and contact forces. Understanding the reaction of regolith to an external perturbation will allow for instruments, including sensors and anchoring mechanisms for use on such surfaces, to implement optimized design principles. We analyze the behavior of a flexible probe inserted into loose regolith simulant as a function of probe speed and ambient gravitational acceleration to explore the relevant dynamics. The EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) flew on several parabolic flights. It employs a classic granular physics technique, photoelasticity, to quantify the dynamics of a flexible probe during its insertion into a system of bi-disperse, centimeter-sized model grains. We identify the force chain structure throughout the system during probe insertion at a variety of speeds and for four different levels of gravity: terrestrial, Martian, lunar, and microgravity. We identify discrete, stick-slip failure events that increase in frequency as a function of the gravitational acceleration. In microgravity environments, stick-slip behaviors are negligible, and we find that faster probe insertion can suppress stick-slip behaviors where they are present. We conclude that the mechanical response of regolith on rubble-pile asteroids is likely quite distinct from that found on larger planetary objects, and scaling terrestrial experiments to microgravity conditions may not capture the full physical dynamics.

Bleeding events in COVID-19: the other side of the coin?

We present three cases of patients affected by severe SARS-CoV-2-related pneumonia treated with a low molecular weight heparin for prevention or treatment of pulmonary embolism, who presented a major bleed, in particular an ileopsoas haematoma that caused severe anaemia; in one case it was fatal. In the recent outbreak of novel coronavirus infection, significantly abnormal coagulation parameters in SARS-CoV-2 infection occur very often, but complications in the opposite direction such as bleeding diathesis are very rare. In these cases, there are different levels of gravity: for one patient the major bleed required the anticoagulant therapy to be stopped until bleeding stabilized, one patient needed interventional radiology and one patient died.

Probing regolith-covered surfaces in low gravity

The surfaces of many planetary bodies, including asteroids, moons, and planets, are composed of rubble-like grains held together by varying levels of gravitational attraction and cohesive forces. Future instrumentation for operation on, and interacting with, such surfaces will require efficient and effective design principles and methods of testing. Here we present results from the EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) which flew on several reduced gravity parabolic flights. EMPANADA studies the effects of the insertion of a flexible probe into a granular medium as a function of ambient gravity. This is done for an idealized 2D system as well as a more realistic 3D sample. To quantify the dynamics inside the 2D granular material we employ photoelasticity to identify the grain-scale forces throughout the system, while in 3D experiments we use simulated regolith. Experiments were conducted at three different levels of gravity: martian, lunar, and microgravity. In this work, we demonstrate that the photoelastic technique provides results that complement traditional load cell measurements in the 2D sample, and show that the idealized system exhibits similar behaviour to the more realistic 3D sample. We note that the presence of discrete, stick-slip failure events depends on the gravitational acceleration.

Visuomotor Interactions and Perceptual Judgments in Virtual Reality Simulating Different Levels of Gravity

Visuomotor Interactions and Perceptual Judgments in Virtual Reality Simulating Different Levels of Gravity

Visuomotor Interactions and Perceptual Judgments in Virtual Reality Simulating Different Levels of Gravity.

Virtual reality is used to manipulate sensorimotor interactions in a controlled manner. A critical issue is represented by the extent to which virtual scenarios must conform to physical realism to allow ecological human–machine interactions. Among the physical constraints, Earth gravity is one of the most pervasive and significant for sensorimotor coordination. However, it is still unclear whether visual perception is sensitive to the level of gravity acting on target motion displayed in virtual reality, given the poor visual discrimination of accelerations. To test gravity sensitivity, we asked participants to hit a virtual ball rolling down an incline and falling in air, and to report whether ball motion was perceived as natural or unnatural. We manipulated the gravity level independently for the motion on the incline and for the motion in air. The ball was always visible during rolling, whereas it was visible or occluded during falling before interception. The scene included several cues allowing metric calibration of visual space and motion. We found that the perception rate of natural motion was significantly higher and less variable when ball kinematics was congruent with Earth gravity during both rolling and falling. Moreover, the timing of target interception was accurate only in this condition. Neither naturalness perception nor interception timing depended significantly on whether the target was visible during free-fall. Even when occluded, free-fall under natural gravity was correctly extrapolated from the preceding, visible phase of rolling motion. Naturalness perception depended on motor performance, in addition to the gravity level. In sum, both motor and perceptual responses were guided by an internal model of Earth gravity effects. We suggest that, in order to enhance perceptual sensitivity to physical realism, virtual reality should involve visual backgrounds with metric cues and closed-loop sensorimotor interactions. This suggestion might be especially relevant for the design of rehabilitation protocols.

Failures in sand in reduced gravity environments

The strength of granular materials, specifically sand is important for understanding physical phenomena on other celestial bodies. However, relatively few experiments have been conducted to determine the dependence of strength properties on gravity. In this work, we experimentally investigated relative values of strength (the peak friction angle, the residual friction angle, the angle of repose, and the peak dilatancy angle) in Earth, Martian, Lunar, and near-zero gravity. The various angles were captured in a classical passive Earth pressure experiment conducted on board a reduced gravity flight and analyzed using digital image correlation. The data showed essentially no dependence of the peak friction angle on gravity, a decrease in the residual friction angle between Martian and Lunar gravity, no dependence of the angle of repose on gravity, and an increase in the dilation angle between Martian and Lunar gravity. Additionally, multiple flow surfaces were seen in near-zero gravity. These results highlight the importance of understanding strength and deformation mechanisms of granular materials at different levels of gravity.

Effect of Gravity on Premixed Methane–Air Flames

Premixed flames under different levels of gravity were studied experimentally and numerically. The experiments were carried out in the Bremen Drop tower. The object of investigation were conical premixed rich, lean, and stoichiometric CH4–air flames with wide range of flow regimes, at Reynolds numbers of 600–2000, which were generated on specially designed cone nozzle and premixed cylinder chamber with grids and beads. Planar laser-induced fluorescence OH radicals and high-speed video recording was performed under microgravity, terrestrial conditions, and inverted gravity. All the experiments were performed at atmospheric pressure. Our experiments confirm that gravity has a complex influence on laminar and weakly turbulent premixed flames. Gravity causes flame flickering, while under reduced gravity flames are stable and almost not flicker. Based on the experimental data and numerical simulation, a correlation of flickering frequency with different mixture equivalence ratio and gravity is formed.

Vibration effect on the Soret-induced convection of ternary mixture in a rectangular cavity heated from below

This paper presents the results of numerical simulation of the Soret-induced convection of ternary mixture in the rectangular cavity elongated in horizontal direction in gravity field. The cavity has rigid impermeable boundaries. It is heated from the bellow and undergoes translational linearly polarized vibrations of finite amplitude and frequency in the horizontal direction. The problem is solved by finite difference method in the framework of full unsteady non-linear approach. The procedure of diagonalization of the molecular diffusion coefficient matrix is applied, allowing to eliminate cross-diffusion components in the equations and to reduce the number of the governing parameters. The calculations are performed for model ternary mixture with positive separation ratios of the components. The data on the vibration effect on temporal evolution of instantaneous and average fields and integral characteristics of the flow and heat and mass transfer at different levels of gravity are obtained.

Onset of Convection in a Ternary Mixture in a Square Cavity Heated from Above at Various Gravity Levels

The influence of a static gravity level on Soret-driven convection of a ternary mixture in a square cavity heated from above is investigated. The problem is solved by the finite difference method using the equations of thermosolutal convection in multicomponent mixtures. These equation are transformed to a set of equations to eliminate the cross-diffusion effects and to reduce the number of governing parameters. Calculations are performed to study a ternary mixture with the components having different signs of the separation ratios at different levels of gravity. Due to the thermodiffusion effect, the component with a negative separation ratio moves to the upper (hot) wall. This leads to the development of instability accompanied by a sharp increase in the flow intensity and a sharp decrease in the concentration difference between the upper and lower boundaries. Numerical data on the time evolution of integral characteristics of flow and heat and mass transfer, and data on the structure fields of stream function and concentration at different times for different values of the Rayleigh number (different levels of gravity) are obtained.

Quench cooling under reduced gravity

We report quench cooling experiments performed with liquid O(2) under different levels of gravity, simulated with magnetic gravity compensation. A copper disk is quenched from 300 to 90 K. It is found that the cooling time in microgravity is very long in comparison with any other gravity level. This phenomenon is explained by the insulating effect of the gas surrounding the disk. A weak gas pressurization (which results in subcooling of the liquid with respect to the saturation temperature) is shown to drastically improve the heat exchange, thus reducing the cooling time (about 20 times). The effect of subcooling on the heat transfer is analyzed at different gravity levels. It is shown that this type of experiment cannot be used for the analysis of the critical heat flux of the boiling crisis. The film boiling heat transfer and the minimum heat flux of boiling are analyzed as functions of gravity and subcooling.

Pressure drop and void fraction during flow boiling in rectangular minichannels in weightlessness

An experimental investigation has been carried out on flow boiling in a minichannel to explain heat transfer enhancement observed experimentally under the conditions of weightlessness. The analysis is based on the local void fraction and frictional pressure loss measurements. Frictional pressure loss in two-phase flows in minichannels under terrestrial gravity is described by several well-known correlations. In weightlessness, however, few experimental results are available on the void fraction and the frictional pressure loss. The experiments for this study have been performed at constant heat flux supplied to the minichannel with inlet liquid mass velocity ranging between 30 and 248 kg s−1 m−2. The influence of hypergravity (gravity level of 1.8g) and microgravity (gravity level of ±0.05g) on the frictional pressure loss is observed and explained using the flow patterns visualization and experimental void fraction determination through image treatment. Pressure drops for two-phase flow in microgravity are found to be significantly higher than for single-phase flow under similar conditions; possible explanations for the difference are discussed. The experimental thermal measurements have been previously analyzed using inverse techniques which led to evaluation of the local heat transfer coefficient. The heat transfer enhancement observed during weightlessness is explained in the present work by investigating the differences in flow patterns and void fraction under different levels of gravity.

Dynamics of a finite-width liquid film in a co-current microchannel gas flow

The velocity fields and the parameters of a finite-width liquid film moving along the bottom of a mini- and a microchannel under the action of a gas flow are calculated. The investigations are performed for different levels of gravity. It is found that the thin liquid film distorts the velocity field in the gaseous phase. In contrast to the minichannel flow, in the microchannel the film surface is not leveled with increase in the gravity force.

Numerical study of the effects of gravity on soot formation in laminar coflow methane/air diffusion flames under different air stream velocities

Numerical simulations of laminar coflow methane/air diffusion flames at atmospheric pressure and different gravity levels were conducted to gain a better understanding of the effects of gravity on soot formation by using relatively detailed gas-phase chemistry and complex thermal and transport properties coupled with a semi-empirical two-equation soot model. Thermal radiation was calculated using the discrete-ordinates method coupled with a non-grey model for the radiative properties of CO, CO2, H2O, and soot. Calculations were conducted for three coflow air velocities of 77.6, 30, and 5 cm/s to investigate how the coflowing air velocity affects the flame structure and soot formation at different levels of gravity. The coflow air velocity has a rather significant effect on the streamwise velocity and the fluid parcel residence time, especially at reduced gravity levels. The flame height and the visible flame height in general increase with decreasing the gravity level. The peak flame temperature decreases with decreasing either the coflow air stream velocity or the gravity level. The peak soot volume fraction of the flame at microgravity can either be greater or less than that of its normal gravity counterpart, depending on the coflow air velocity. At sufficiently high coflow air velocity, the peak soot volume fraction increases with decreasing the gravity level. When the coflow air velocity is low enough, soot formation is greatly suppressed at microgravity and extinguishment occurs in the upper portion of the flame with soot emission from the tip of the flame owing to incomplete oxidation. The numerical results provide further insights into the intimate coupling between flame size, residence time, thermal radiation, and soot formation at reduced gravity level. The importance of thermal radiation heat transfer and coflow air velocity to the flame structure and soot formation at microgravity is demonstrated for the first time.

The effect of altered gravity states on the perception of orientation

We measured the effect of the orientation of the visual background on the perceptual upright (PU) under different levels of gravity. Brief periods of micro- and hypergravity conditions were created using two series of parabolic flights. Control measures were taken in the laboratory under normal gravity with subjects upright, right side down and supine. Participants viewed a polarized, natural scene presented at various orientations on a laptop viewed through a hood which occluded all other visual cues. Superimposed on the screen was a character the identity of which depended on its orientation. The orientations at which the character was maximally ambiguous were measured and the perceptual upright was defined as half way between these orientations. The visual background affected the orientation of the PU less when in microgravity than when upright in normal gravity and more when supine than when upright in normal gravity. A weighted vector sum model was used to quantify the relative influence of the orientations of gravity, vision and the body in determining the perceptual upright.

Environmental Security: A Geographic Information System Analysis Approach—The Case of Kenya

Studies into the relationships between environmental factors and violence or conflicts constitute a very debated research field called environmental security. Several authors think that environmental scarcity, which is scarcity of renewable resources, can contribute to generate violence or social unrest, particularly within states scarcely endowed with technical know-how and social structures, such as developing countries. In this work, we referred to the theoretical model developed by the Environmental Change and Acute Conflict Project. Our goal was to use easily available spatial databases to map the various sources of environmental scarcity through geographic information systems, in order to locate the areas apparently most at risk of suffering negative social effects and their consequences in terms of internal security. The analysis was carried out at a subnational level and applied to the case of Kenya. A first phase of the work included a careful selection of databases relative to renewable resources. Spatial operations among these data allowed us to obtain new information on the availability of renewable resources (cropland, forests, water), on the present and foreseen demographic pressure, as well as on the social and technical ingenuity. The results made it possible to identify areas suffering from scarcity of one or more renewable resources, indicating different levels of gravity. Accounts from Kenya seem to confirm our results, reporting clashes between tribal groups over the access to scarce resources in areas that our work showed to be at high risk.

Indicadores microbiológicos de contaminación de las fuentes de agua.

El crecimiento de la población a nivel mundial ha incrementado los niveles de contaminación. Esta contaminación está relacionada con el vertido de agua de desecho de origen doméstico e industrial a los cuerpos de agua. En el caso de los residuos de origen doméstico, la carga contaminante está representada por altos porcentajes de materia orgánica y microorganismos de origen fecal. El control de la calidad microbiológica del agua de consumo y de desecho, requiere de análisis dirigidos a determinar la presencia de microorganismos patógenos; los agentes involucrados en la transmisión hídrica son las bacterias, virus y protozoos, que pueden causar enfermedades con diferentes niveles de gravedad, desde gastroenteritis simple hasta casos fatales de diarrea, disentería, hepatitis o fiebre tifoidea. El diagnóstico de estos microorganismos, requiere laboratorios especializados y representa varios días de análisis y costos elevados. Como alternativa a estos inconvenientes, se ha propuesto el uso de indicadores microbianos que se puedan identificar mediante el uso de métodos sencillos, rápidos y económicos.El diagnóstico y posterior recuperación de las fuentes de agua naturales contaminadas, debe hacerse además, teniendo en cuenta las implicaciones que en términos ecológicos y sanitarios representa la degradación del recurso. En este sentido, las microalgas perifiticas se constituyen como buenos indicadores del estado trófico de los ecosistemas y responden a los disturbios ocurridos modificando su estructura en cuanto a composición y abundancia se refiere. Este trabajo hace una revisión de los principales bioindicadores de contaminación y su significado en la evaluación de la calidad del agua.

Evaluation of theories of complex movement planning in different levels of gravity

Due to high redundancy of degrees of freedom in the human body, we can perform any movement, from the simplest to the most complex, in many different ways. Several studies are still trying to identify the motor strategies that master this redundancy and generate the movements whose characteristics are highly stereotyped. The aim of this work is to build a simulator that is able to evaluate different motor planning hypotheses. The most interesting applications of this tool occur in studies of the motor strategy in microgravity conditions. The comparison between simulated movements and kinematics data recorded both on Earth, and during a 5-month mission on board the Mir station shows that for a complex whole-body movement (such as trunk bending) a single planning criterion cannot explain all movement aspects. However, the simulator allows an understanding of the motor planning adaptation of astronauts. In space, the lack of equilibrium constraint (which on Earth brings about the center of mass control) leads to a new motor strategy that minimizes dynamic interactions with the floor.

Simulation of particle agglomeration and fragmentation in a low gravity environment

We are developing simulation tools to design aerosol experiments in a space environment. The simulations will be used to assess trade-offs among the level of gravity, active experimental volume, particle density and primary particle size. In our previous work [1] we simulated the formation of particle clusters in a low gravity environment using a modified version of the CONTAIN code [2]. The model did not include the effect of cluster fragmentation on the particle size distribution and deposition on the cell walls. Before implementing complex modifications to the CONTAIN code we have investigated the effects of fragmentation using the Monte Carlo (MC) method to simulate aerosol dynamics. The constant-N Monte Carlo method developed by the Matsoukas group [3–5] was used. In this method the number of particles in the system is kept constant and the mean cluster volume is increased or decreased depending on the event (fragmentation, agglomeration,…). We are particularly interested in measuring the average volume of clusters and probability, Pk, of finding a cluster containing k primary particles. Both quantities are measurable in a low microgravity experiment. Results are presented for different levels of gravity, particle density and fragmentation kernel. The results demonstrate the potential benefits of a full simulation of the planned experiments.

Effects of Gravity on Output of Humidity Sensors with Different Detection Mechanisms at Constant Humidity.

The effects of gravity on output of sensors with different detection mechanisms under constant humidity were investigated to screen humidity sensors for small plant growth chambers under microgravity. Different levels of gravity were established by parabolic flight using aircraft in which air pressure and temperature were maintained almost constant (the variations were within 0.6kPa and 0.2°C, respectively). Four types of polymer sensors, a thermistor sensor and an electrolytic sensor were used for the experiment. Air with relative humilities of 75% and 58% was prepared using saturated salt solutions of NaCl and NaBr, respectively. Six types of sensors were fixed either in a vessel (1L) or independently in small vessels (10mL) including the solution absorbed by polymer film. When the sensors were placed in a vessel, only the output signal of the thermistor sensor varied with gravity level. It was lowest under 2G and highest under low gravity under both relative humidity conditions. This variation was observed in both cases when air in the vessel was and was not stirred. This might be due to a filter protecting the sensor surface to cancel the effect of wind velocity on sensor. Air diffusion inside the filter in both cases seemed to be governed by natural convection of which the strength was affected by gravity level. The same tendency in thermistor sensor output was observed in the small vessels in which each sensor was independently fixed, indicating that an interaction between sensors placed in one vessel is negligible. Thus the change in air diffusion with gravity seemed to be the reason why the output signal of thermistor sensor changed with gravity level.