Role Of Gravity Research Articles

Motor strategies and adiabatic invariants: The case of rhythmic motion in parabolic flights

The role of gravity in human motor control is at the same time obvious and difficult to isolate. It can be assessed by performing experiments in variable gravity. We propose that adiabatic invariant theory may be used to reveal nearly conserved quantities in human voluntary rhythmic motion, an individual being seen as a complex time-dependent dynamical system with bounded motion in phase space. We study an explicit realization of our proposal: An experiment in which we asked participants to perform ∞- shaped motion of their right arm during a parabolic flight, either at self-selected pace or at a metronome's given pace. Gravity varied between 0 and 1.8 g during a parabola. We compute the adiabatic invariants in the participant's frontal plane assuming a separable dynamics. It appears that the adiabatic invariant in vertical direction increases linearly with g, in agreement with our model. Differences between the free and metronome-driven conditions show that participants' adaptation to variable gravity is maximal without constraint. Furthermore, motion in the participant's transverse plane induces trajectories that may be linked to higher-derivative dynamics. Our results show that adiabatic invariants are relevant quantities to show the changes in motor strategy in time-dependent environments.

Between droplets and fluid thread—the role of gravity in meso-scale flow

How gravity affects immiscible liquid co-flow is best illustrated through experiments in inclined conduits. In the macro-domain, gravity leads to flow stratification while in the microscale, the phase distribution is practically insensitive to conduit tilt. The influence of flow orientation in the intermediate scale conventionally known as meso-domain or milli-channel, although noted, has not been discussed earlier. In the present study, flow morphology is experimentally investigated during up, down, and horizontal co-flow of a biphasic liquid mixture in a glass conduit of diameter 2.38 mm. In all orientations, the dispersed phase flows either as droplets/plugs or as a continuous thread. Gravity modulates the process of thread pinch off and regulates the domain of thread/droplet flow. Apart from flow orientation, we also note entry arrangement to influence droplet detachment in horizontal conduit. The experimental observations are explained from a simplified analysis based on momentum and energy considerations; the defining parameters are fluid properties and flow rates, conduit dimension, and flow orientation. The proposed analysis, albeit the approximations, has successfully predicted thread pinch off for the present experiments. Pinch off from the thread tip is noted to be cyclic and comprises several steps, of which inception of necking to its completion is only a part.

Gravity determines the direction of nerve roots sedimentation in the lumbar spinal canal

ObjectivesTo investigate the role of gravity in the sedimentation of lumbar spine nerve roots using magnetic resonance (MR) imaging of various body positions.MethodsA total of 56 patients, who suffered from back pain and underwent conventional supine lumbar spine MR imaging, were selected from sanmen hospital database. All the patients were called back to our hospital to perform MR imaging in prone position or lateral position. Furthermore, the sedimentation sign (SedSign) was determined based on the suspension of the nerve roots in the dural sac on cross-sectional MR images, and 31 cases were rated as positive and another 25 cases were negative.ResultsThe mean age of negative SedSign group was significantly younger than that of positive SedSign group (51.7 ± 8.7 vs 68.4 ± 10.5, P < 0.05). The constitutions of clinical diagnosis were significantly different between patients with a positive SedSign and those with a negative SedSign (P < 0.001). Overall, nerve roots of the vast majority of patients (48/56, 85.7%) subsided to the ventral side of the dural sac on the prone MR images, although that of 8 (14.3%) patients remain stay in the dorsal side of dural sac. Nerve roots of only one patient with negative SedSign did not settle to the ventral dural sac, while this phenomenon occurred in 7 patients in positive SedSign group (4% vs 22.6%, P < 0.001). In addition, the nerve roots of all the five patients subsided to the left side of dural sac on lateral position MR images.ConclusionsThe nerve roots sedimentation followed the direction of gravity. Positive SedSign may be a MR sign of lumbar pathology involved the spinal canal.

Formation of the Musca filament: evidence for asymmetries in the accretion flow due to a cloud–cloud collision

Context.Dense molecular filaments are ubiquituous in the interstellar medium, yet their internal physical conditions and the role of gravity, turbulence, the magnetic field, radiation, and the ambient cloud during their evolution remain debated.Aims.We study the kinematics and physical conditions in the Musca filament, the ambient cloud, and the Chamaeleon-Musca complex to constrain the physics of filament formation.Methods.We produced CO(2–1) isotopologue maps with the APEX telescope that cut through the Musca filament. We further study a NANTEN212CO(1–0) map of the full Musca cloud, H Iemission of the Chamaeleon-Musca complex, aPlanckpolarisation map, line radiative transfer models,Gaiadata, and synthetic observations from filament formation simulations.Results.The Musca cloud, with a size of ~3–6 pc, contains multiple velocity components. Radiative transfer modelling of the CO emission indicates that the Musca filament consists of a cold (~10 K), dense (nH2∼ 104cm−3) crest, which is best described with a cylindrical geometry. Connected to the crest, a separate gas component atT~ 15 K andnH2∼ 103cm−3is found, the so-called strands. The velocity-coherent filament crest has an organised transverse velocity gradient that is linked to the kinematics of the nearby ambient cloud. This velocity gradient has an angle ≥30° with respect to the local magnetic field orientation derived fromPlanck, and the magnitude of the velocity gradient is similar to the transonic linewidth of the filament crest. Studying the large scale kinematics, we find coherence of the asymmetric kinematics from the 50 pc H Icloud down to the Musca filament. We also report a strong [C18O]/[13CO] abundance drop by an order of magnitude from the filament crest to the strands over a distance &lt;0.2 pc in a weak ambient far-ultraviolet (FUV) field.Conclusions.The dense Musca filament crest is a long-lived (several crossing times), dynamic structure that can form stars in the near future because of continuous mass accretion replenishing the filament. This mass accretion on the filament appears to be triggered by a H Icloud–cloud collision, which bends the magnetic field around dense filaments. This bending of the magnetic field is then responsible for the observed asymmetric accretion scenario of the Musca filament, which is, for instance, seen as a V-shape in the position–velocity (PV) diagram.

Comparative analysis reveals gravity is involved in the MIZ1-regulated root hydrotropism.

Hydrotropism is the directed growth of roots toward the water found in the soil. However, mechanisms governing interactions between hydrotropism and gravitropism remain largely unclear. In this study, we found that an air system and an agar-sorbitol system induced only oblique water-potential gradients; an agar-glycerol system induced only vertical water-potential gradients; and a sand system established both oblique and vertical water-potential gradients. We employed obliquely oriented and vertically oriented experimental systems to study hydrotropism in Arabidopsis and tomato plants. Comparative analyses using different hydrotropic systems showed that gravity hindered the ability of roots to search for obliquely oriented water, whilst facilitating roots' search for vertically oriented water. We found that the gravitropism-deficient mutant aux1 showed enhanced hydrotropism in the oblique orientation but impaired root elongation towards water in the vertical orientation. The miz1 mutant exhibited deficient hydrotropism in the oblique orientation but normal root elongation towards water in the vertical orientation. Importantly, in contrast to miz1, the miz1/aux1 double mutant exhibited hydrotropic bending in the oblique orientation and attenuated root elongation towards water in the vertical orientation. Our results suggest that gravitropism is required for MIZ1-regulated root hydrotropism in both the oblique orientation and the vertical orientation, providing further insight into the role of gravity in root hydrotropism.

Role of gravity in particle physics: A unified approach

General Relativity (GR) and the Standard Model (SM) of particle physics are two enormously successful frameworks for our understanding the fundamental laws of nature. However, these theoretical schemes are widely disconnected, logically independent and unrelated in scope. Yet, GR and SM at some point must intersect, producing claims about phenomena that should be reconciled. Be it as it may, both schemes share a common basic ground: symmetry under local Lorentz transformations. Here, we will focus on the consequences of assuming this feature from the beginning to combine geometry, matter fields and gauge interactions. We give a rough description of how this could be instrumental for the construction of a unified scheme of gravitation and particle physics.

Metallic Iron in Basalts of the Malyi Yenisei Lava River: Results of Thermomagnetic Study

Thermomagnetic analysis of samples from two sections of lava layers of the Late Cenozoic basalt lava river in the Malyi Yenisei valley is carried out. The main magnetization carrier in the studied basalts is titanomagnetite with the Curie points of 100–120°C which is frequently substantially oxidized both single-phase and heterophase up to magnetite. It is likely that some part of metallic iron in the studied samples has also been oxidized and even disintegrated, which resulted in the significant scatter of iron concentration across the flow against which, however, the increasing trend of iron concentration in the lava flow from the top downwards is observed. The relative magnitude of this increase (iron concentration gradient along the vertical of the lava flow) is almost constant for all flows of the lava sequence probably indicating the decisive role of gravity in iron particle precipitation in the lava. Based on the synthesis of iron particle data from different objects and different regions of the world, this correlation with gravity also follows from the very similar shapes of particle size histograms of iron. This is most clearly seen from the same particle size modes (10–20 μm). Another important finding is that this constant mode of iron particle size does not depend on age and origin of rock as well as on the type of particle source (terrestrial or extraterrestrial).

The Role of Gravity in the Evolution of the Concentration Field in the Electrochemical Membrane Cell

The subject of the study was the osmotic volume transport of aqueous CuSO4 and/or ethanol solutions through a selective cellulose acetate membrane (Nephrophan). The effect of concentration of solution components, concentration polarization of solutions and configuration of the membrane system on the value of the volume osmotic flux ( in a single-membrane system in which the polymer membrane located in the horizontal plane was examined. The investigations were carried out under mechanical stirring conditions of the solutions and after it was turned off. Based on the obtained measurement results , the effects of concentration polarization, convection polarization, asymmetry and amplification of the volume osmotic flux and the thickness of the concentration boundary layers were calculated. Osmotic entropy production was also calculated for solution homogeneity and concentration polarization conditions. Using the thickness of the concentration boundary layers, critical values of the Rayleigh concentration number (), i.e., the switch, were estimated between two states: convective (with higher ) and non-convective (with lower ). The operation of this switch indicates the regulatory role of earthly gravity in relation to membrane transport.

Evaluating a learning progression for the solar system: Progress along gravity and dynamical properties dimensions

AbstractWe previously proposed a hypothetical learning progression around the disciplinary core idea of the Solar System and its formation as a first step in a research program to begin to fill this gap and address questions of student learning in this domain. In this study, we evaluate the effectiveness of two dimensions within the learning progression, dynamical properties and gravity, in describing change in how student reason in the domain across the course of their 14‐week astronomy unit. A sample of sixth‐grade students (N = 24) were interviewed before and after instruction. We compared changes in how students explained the dynamic properties of planets and the role of gravity in the Solar System to their experiences during instruction. Our findings provide evidence for the usefulness of this learning progression in describing how students' explanations may progress, offer insight into how instruction may support that progress, and highlight the challenges in drawing conclusions on how students' explanations may progress when limitations are identified in instructional experiences. We also discuss the connection between these two construct maps but also point out what appears to be a missing element in our original definition of the learning progression: inertia.

Granular dynamics and gravity.

The role of gravity on the dynamics of granular particles is examined via their velocity distributions. Acceleration due to gravity, particle number and the coefficient of restitution have all been varied. Various quantitative relationships governing the relationship between parameters involved in the vertical and horizontal velocity component distributions are derived and applied to the data, and for the horizontal velocity components' distribution in particular remarkably good agreement is obtained.

Role of gravity and capillary waves in the origin of circular hydraulic jumps

A study shows that hydraulic jumps are governed by both gravitational and capillary forces. The jump location results from a competition of supercritical flow with gravity-capillary waves traveling in the upstream direction. Fluid properties, flow conditions, and the state of development scale the respective forces.

A latently quantized force of atomic unification

Given the availability of a force of atomic unification, a sharp interconnection between an antineutrino and a neutron must constitute an antineutrino hydrogen atom. This is one of two atoms that are of crucial value for constructing all of the remaining ones. We discuss a theory in which atomic orbit quantization around a nucleus is carried out with a flavor type dependence. Such an orbit quantized sequence principle leads to the splitting of the spectral lines of atoms in an external field, confirming the availability of a family structure in them. Thereby, it predicts the existence in nature of 63 189 isotope forms of 118 types of atomic systems. We derive the united equations that relate the masses in an atom to the radii of boson, lepton, and antineutrino orbits including the speeds, energies, and revolution periods of their particles. The estimates thus found express, for each of the five forms of uranium and the two types of hydrogen, the idea of an intraatomic force quantized by leptonic families. They unite all of connections necessary for the steadiness and completeness of an atom in a unified whole as a role of gravity in atomic construction. Therefore, a change in both the lifetime and radius of any of the structural particles within an atom originates from the orbit type dependence.

Role of gravity in condensation flow of R1234ze(E) inside horizontal mini/macro-channels

The condensation patterns of R1234ze(E) inside horizontal mini/macro-channels were numerically investigated under normal-gravity and zero-gravity conditions. The gravity effects on condensation heat transfer coefficients, liquid film thickness, film distribution, cross-sectional stream-traces, and liquid-phase velocity were analyzed detailedly. The influence of surface tension on condensation flow was also discussed. The gravity effect on condensation heat transfer coefficients was negligible in mini-channels with D = 1 mm, while was important for D = 2 mm and D = 4.57 mm. The gravity effect can either enhance or weaken the condensation heat transfer coefficient, which was dependent on the tube diameter and vapor quality. The enhancement on heat transfer caused by the gravity was more pronounced at lower vapor quality and mass fluxes with a larger diameter tube. The gravity affected the condensation heat performance through changing the vapor-liquid distribution, rather than the film thickness. The gravity has a great influence on the condensation flow field in both circumferential and axial direction. The surface tension played an important role in heat transfer under zero-gravity condition.

Responses of Bioconvection of Tetrahymena thermophila to Partial Gravity Created by Aircraft Flight.

Bioconvection is a form of collective pattern formation driven by negative gravitaxis of swimming microorganisms. In bioconvection, the interaction between individual swimmers results in self-organization leading to the development of a macroscopic structure typically 100-1000 times greater than an individual microorganism. To gain insight into the role of gravity in this self-organization phenomenon, we investigated the bioconvective behavior of the ciliate Tetrahymena thermophila under short-term partial gravity, i.e., gravitational acceleration < 1 g, achieved by quasiparabolic flight maneuvers of an aircraft. The bioconvective responses of T. thermophila were assessed by observing the collective motion simultaneously in two separate scales, which we call macroscale and microscale, using a newly designed "dual-objective" device with two different magnifications. Microscale analysis revealed that the magnitude of gravikinesis, i.e., active regulation of the propulsive thrust, decreased almost linearly with changes in gravitational acceleration, while gravitactic characteristics, assessed by the distribution of the swimming direction, did not change significantly during partial gravity. Macroscale analysis demonstrated that downward plumes of convection pattern gradually shortened from the lower end, and disappeared under partial gravity. The sustained time of the plumes decreased almost linearly with changes in gravitational acceleration. The response of downward plumes to partial gravity may be attributable to the accumulation of cells into blobs in downward migration, which increases the rate of downward migration enough to exceed the rate of upward movement, which is enhanced due to gravikinesis. This suggests that gravity may act on cells involved in collective pattern formation differently than on free-swimming cells.

Tests of General Relativity and Fundamental Physics with Space-based Gravitational Wave Detectors

Low-frequency gravitational-wave astronomy can perform precision tests of general relativity and probe fundamental physics in a regime previously inaccessible. A space-based detector will be a formidable tool to explore gravity's role in the cosmos, potentially telling us if and where Einstein's theory fails and providing clues about some of the greatest mysteries in physics and astronomy, such as dark matter and the origin of the Universe.

The effect of rough vs. smooth aggregate surfaces on the characteristics of the interfacial transition zone

Due to its higher porosity, the interfacial transition zone (ITZ) between cement paste and aggregates in cementitious composites is often viewed as a weak link in the microstructure. Sectional plane analysis based on back-scattered electron scanning electron microscope (SEM-BSE) images is used to quantify the ITZ porosity gradient, yet not much research has focused on the effect of aggregate surface morphology on the ITZ composition. In this paper, a model concrete specimen with a single spherical ceramic particle acting as an aggregate is used to study the properties of the ITZ and its uneven distribution around the aggregate based on quantitative analysis of SEM-BSE images. A careful treatment of the statistics of the ITZ was employed. The average porosity of the ITZ at a smooth part of the aggregate surface was smaller than that found at a rough part of the aggregate surface. A method is proposed to describe the local surface roughness (SR) at the pixel level and relate this quantity to other ITZ properties. The relationship between the surface roughness and the ITZ porosity gradient within 30 μm of the aggregate surface was analyzed with the “K-means” clustering method. The role of gravity was seen, since more porous ITZ regions tended to form underneath the aggregate than above the aggregate, with intermediate results at the aggregate sides.

The role of gravity in the asymmetry of flames in narrow combustion chambers

The symmetry breaking of a fuel lean premixed laminar methane/air flame, propagating in a horizontal narrow tube of internal diameter ℓi=5 mm, is investigated experimentally and numerically. The methane/air flame numerical simulations performed include complex molecular transport and chemistry, and the fully coupled solving of heat transfer at and within the wall. In place of a symmetric flame, experiments show the stability of a slanted flame with a preferential anchoring at the top. This is observed for both flames freely propagating along isothermal walls (T = 300 K), and flames stabilised by the incoming flow and thermally coupled with heat transfer inside the walls. Numerical simulations with and without gravity demonstrate its preponderant contribution in the symmetry breaking. The slight flow stratification is sufficient to break the symmetry, with a dominant role of the baroclinic torque, leading to a specific deviation of the incoming streamlines observed both experimentally and numerically.

What Height System Should be Used in Geomatics

The contribution is going to introduce first the idea of a height system as a conglomerate of the reference surface, a.k.a. a datum and properly defined heights. Then the kinds of height systems used in practice are going to be discussed. These are three: the Geodetic system consisting of the reference ellipsoid as a datum and Geodetic heights (also incorrectly often called “ellipsoidal heights”), the Classical system that consists of the geoid as a datum and Orthometric heights (above the sea level), and the Molodenskij system composed of the quasigeoid as a datum and Normal heights (referred to the quasi-geoid). The Geodetic system is used when heights are being determined by satellites, Classical system has been used throughout the world since individual nations introduced their national height systems and Molodenskij’s system is now being used in Russia and several European countries. Further, the question of realization of a height system in practice will be discussed. This discussion is going to deal with mean sea level (MSL), sea surface topography (SST), the way observed heights and height differences are transformed into proper heights and height differences and the role of gravity in these transformations, the role of potential numbers and dynamic heights. Next, the properties of height systems that make them appropriate for practice will be shown: first and utmost, the system must be congruent, i.e., the datum and heights taken together must give us, as closely as possible, the Geodetic heights, the heights must be holonomic to allow us to adjust loops of height differences and the system must be useful in practice.

The role of gravity in the prediction of the circular hydraulic jump radius for high-viscosity liquids

The free-surface flow formed by a circular jet impinging on a stationary disk is analysed theoretically. We develop a simple and coherent model to predict the location and height of the jump for high-viscosity liquids. The study explores the effect of gravity in the supercritical flow. The formulation reduces to a problem, involving only one parameter: $\unicode[STIX]{x1D6FC}=Re^{1/3}Fr^{2}$, where $Re$ and $Fr$ are the Reynolds and Froude numbers based on the flow rate and the jet radius. We show that the jump location coincides with the singularity in the thin-film equation when gravity is included, suggesting that the jump location can be determined without the knowledge of downstream flow conditions such as the jump height, the radius of the disk, which corroborates earlier observations in the case of type I circular hydraulic jumps. Consequently, there is no need for a boundary condition downstream to determine the jump radius. Our results corroborate well existing measurements and numerical simulation. Our predictions also confirm the constancy of the Froude number $Fr_{J}$ based on the jump radius and height as suggested by the measurements of Duchesne et al. (Europhys. Lett., vol. 107, 2014, 54002). We establish theoretically the conditions for $Fr_{J}$ to remain independent of the flow rate. The subcritical flow and the height of the hydraulic jump are sought subject to the thickness at the edge of the disk, comprising contributions based on the capillary length and minimum flow energy. The thickness at the edge of the disk appears to be negligibly small for high-viscosity liquids.

The Role of Gravity in Producing Power-law Mass Functions

Abstract Numerical simulations of star formation have found that a power-law mass function can develop at high masses. In a previous paper, we employed isothermal simulations that created large numbers of sinks over a large range in masses to show that the power-law exponent of the mass function, , asymptotically and accurately approaches Γ = −1. Simple analytic models show that such a power law can develop if the mass accretion rate , as in Bondi–Hoyle accretion; however, the sink mass accretion rates in the simulations show significant departures from this relation. In this paper, we show that the expected accretion rate dependence is more closely realized provided the gravitating mass is taken to be the sum of the sink mass and the mass in the near environment. This reconciles the observed mass functions with the accretion rate dependencies, and demonstrates that power-law upper mass functions are essentially the result of gravitational focusing, a mechanism present in, for example, the competitive accretion model.