Influence Of Gravity Research Articles

Toward a pulsed antihydrogen beam for WEP tests in AEgIS

The AEg̅IS collaboration at CERN’s AD produces antihydrogen atoms in the form of a pulsed, isotropic source with a precisely defined formation time. AEg̅IS has recently undergone major upgrades to fully benefit from the increased number of colder antiprotons provided by the new ELENA decelerator and to move toward forming a horizontal beam to directly investigate the influence of gravity on the H̅ atoms, thereby probing the Weak Equivalence Principle for antimatter. This contribution gives an overview of these upgrades as well as subsequent results from the first beam times with ELENA.

Estimating right atrial pressure using upright computed tomography in patients with heart failure

ObjectivesUpright computed tomography (CT) can detect slight changes particularly in the superior vena cava (SVC) volume in healthy volunteers under the influence of gravity. This study aimed to evaluate whether upright CT-based measurements of the SVC area are useful for assessing mean right atrial pressure (mRAP) in patients with heart failure.MethodsWe performed CT in both standing and supine positions to evaluate the SVC (directly below the junction of the bilateral brachiocephalic veins) and inferior vena cava (IVC; at the height of the diaphragm) areas and analyzed their relationship with mRAP, measured by right heart catheterization in 23 patients with heart failure.ResultsThe median age of enrolled patients was 60 (51−72) years, and 69.6% were male. The median mRAP was 3 (1−7) mmHg. The correlations between the standing position SVC and IVC areas and mRAP were stronger than those in the supine position (SVC, ρ = 0.68, p < 0.001 and ρ = 0.43, p = 0.040; IVC, ρ = 0.57, p = 0.005 and ρ = 0.46, p = 0.026; respectively). Furthermore, the SVC area in the standing position was most accurate in identifying patients with higher mRAP (> 5 mmHg) (SVC standing, area under the receiver operating characteristic curve [AUC] = 0.91, 95% confidence interval [CI], 0.77–1.00; SVC supine, AUC = 0.78, 95% CI, 0.59–0.98; IVC standing, AUC = 0.77, 95% CI, 0.55–0.98; IVC supine, AUC = 0.72, 95% CI, 0.49–0.94). The inter- and intraobserver agreements (evaluated by intraclass correlation coefficients) for all CT measurements were 0.962–0.991.ConclusionsUpright CT-based measurement of the SVC area can be useful for non-invasive estimation of mRAP under the influence of gravity in patients with heart failure.Key Points• This study showed that the superior vena cava (SVC) area in the standing position was most accurate in identifying patients with heart failure with higher mean right atrial pressure.• Upright computed tomography-based measurements of the SVC area can be a promising non-invasive method for estimating mean right atrial pressure under the influence of gravity in patients with heart failure.• Clinical management of patients with heart failure based on this non-invasive modality may lead to early assessment of conditional changes and reduced hospitalization for exacerbation of heart failure.

Global bifurcation structure and some properties of steady periodic water waves with vorticity

This paper studies the classical water wave problem with vorticity described by the Euler equations with a free surface under the influence of gravity over a flat bottom. Based on fundamental work [5], we first obtain two continuous bifurcation curves which meet the laminar flow only one time by using the modified analytic bifurcation theorem. They are symmetric waves whose profiles are monotone between each crest and trough. Moreover, we show a connection between the concavity and convexity of wave profile and the monotonicity of the vertical velocity component v along the free surface. As an important application, we make up the missing major aspect on the behavior of v as mentioned in [4, Sect 4.4] for small amplitude waves. In addition, for favorable vorticity, we prove that the vertical displacement of water waves decreases with depth.

Resin infusion in porous preform in the presence of HPM considering complex geometry and gravity: Flow simulation and experimental validation

Present work demonstrates the complete numerical modeling and experimental validation of transient incompressible two-phase flow during vacuum infusion (VI) in the presence and absence of high permeability media (HPM) considering gravity effects. Coupled flow modeling based on continuity equations, Darcy’s law for porous media flow, including gravity effects with level set front tracking algorithm, has been developed on the multiblock-structured grid with higher-order finite-difference framework to predict the spatio-temporal preform saturation during infusion with/without HPM on the complex mold configurations. The model-predicted instantaneous change in pressure, thickness elevation, fill time, flow front positions, and influence of gravity have been validated with experiments for horizontal and vertical flat plates using pressure sensors and digital cameras. For the first time, the complete modeling and experimentation of transient VI in the presence or absence of HPM, including gravity, shows the ability to predict realistic preform saturation during VI in different mold geometry.

Simplified model to consider influence of gravity on impacts on structures: Experimental and numerical validation

Traditionally, the effect of gravitational force has not been considered in the study of impacts on structures, partly due to lack of knowledge. In most cases, it may be reasonable to disregard this effect, but it is not clear where the limit is and, therefore, in which cases its effect should be considered. Is this limit the same regardless of the type of structure? What criterion should be adopted? This paper develops a simplified model that allows, through a simple formulation, the calculation of the displacement and contact force in an impact considering the effect of the force of gravity on the structural response. In this article, the formulation has been validated with experimental impact tests on beams and also with finite element models. In addition, a coefficient is proposed which enables the evaluation, prior to any analysis, of whether the impact will be significantly influenced by the force of gravity, whatever the structure under study.

Numerical investigation to evaluate the effects of gravity and pressure on flame structure and soot formation of turbulent non-premixed methane-air flame

In this study, a turbulent non-premixed (diffusion) methane-air flame has been investigated computationally to analyze the influences of pressure and gravity on flame structure and sooting characteristics between 1 and 10 atm. The simulation has been conducted in a 2-D axisymmetric computational domain using the finite volume-based computational fluid dynamics (CFD) code. The interaction of turbulence and chemistry is modeled by considering the steady laminar flamelet model (SLFM) and the GRI Mech 3.0 chemical mechanism. The radiative heat transfer calculation is carried out by considering the discrete ordinate (DO) method and the weighted sum grey gas model (WSGGM). The semi-empirical Moss-Brookes model is considered to calculate soot. The impact of gravity on flame and sooting characteristics are evaluated by comparing the normal-gravity flames with the zero-gravity flames. The effect of soot and radiation on flame temperature is also examined. The results show a close agreement with the measurement when both soot and radiation are included in the numerical modeling. The rates of soot formation, surface growth, and oxidation increase with increased operating pressure, regardless of gravity. Zero-gravity flames have a higher soot volume fraction, a wider soot-containing zone, a higher CO mass fraction, and a lower flame temperature than normal-gravity flames while maintaining constant pressure. In normal-gravity flames, the CO mass fraction decreases with pressure, whereas it increases with pressure rise in flames of zero gravity. Flames of zero gravity appear taller and broader compared to the flames of normal-gravity for a fixed pressure. An increase in pressure significantly reduces the flame length and width in normal-gravity flames. However, the pressure elevation has little effect on the shape of a zero-gravity flame. The outcomes of the present study will assist in fully understanding the combustion and sooting characteristics of turbulent diffusion flames that will help design and develop high-efficiency, pollutant-free combustion devices and fire suppression systems for space application.

Gravitational scattering of spinning neutrinos by a rotating black hole with a slim magnetized accretion disk

We study neutrinos gravitationally scattered off a rotating supermassive black hole which is surrounded by a thin accretion disk with a realistic magnetic field. Neutrinos are supposed to be Dirac particles having a nonzero magnetic moment. Neutrinos move along arbitrary trajectories, with the incoming flux being parallel to the equatorial plane. We exactly account for the influence of both gravity and the magnetic field on the neutrino motion and its spin evolution. The general statement that the helicity of an ultrarelativistic neutrino is constant in the particle scattering in an arbitrary gravitational field is proven within the quasiclassical approach. We find the measurable fluxes of outgoing neutrinos taking into account the neutrino spin precession in the external field in curved spacetime. These fluxes turn out to be significantly suppressed for some parameters of the system. Finally, we discuss the possibility to observe the predicted phenomena for core-collapsing supernova neutrinos in our Galaxy.

Numerical Simulation of Phase Transitions in Porous Media with Three-Phase Flows Considering Steam Injection into the Oil Reservoir

This study focuses on the analysis of an approach to the simulation of the phase transition in porous media when hot steam is injected into the oil reservoir. The reservoir is assumed to consist of a porous medium with homogeneous thermal properties. Its porous space is filled with a three-phase mixture of steam, water, and oil. The problem is considered in a non-stationary and non-isothermal formulation. Each phase is considered to be incompressible, with constant thermal properties, except for the dynamic viscosity of oil, which depends on the temperature. The 1D mathematical model of filtration, taking into account the phase transition, consists of continuity, Darcy, and energy equations. Steam injection and oil production in the model are conducted via vertical or horizontal wells. In the case of horizontal wells, the influence of gravity is also taken into account. The Lee model is used to simulate the phase transition between steam and water. The convective terms in the balance equations are calculated without accounting for artificial diffusion. Spatial discretization of the 1D domain is carried out using the finite volume method, and time discretization is implemented using the inverse (implicit) Euler scheme. The proposed model is analyzed in terms of the accuracy of the phase transition simulation for various sets of independent phases and combinations of continuity equations. In addition, we study the sensitivity of the model to the selected independent phases, to the time step and spatial mesh parameters, and to the intensity of the phase transition. The obtained results allow us to formulate recommendations for simulations of the phase transition using the Lee model.

Interface Dynamics and the Influence of Gravity on Droplet Generation in a Y-microchannel.

The present experimental investigation is focused on the influence of gravity upon water-droplet formation in a Y-microchannel filled with oil. The flows are in the Stokes regime, with very small capillary numbers and Ohnesorge numbers less than one. The study was performed in a square-cross-section channel, with a = 1.0 mm as the characteristic dimension and a flow rate ratio κ in a range between 0.55 and 1.8. The interface dynamics in the vicinity of breakup and the transitory plug flow regime after the detachment of the droplet were analysed. The dependence of droplet length L was correlated with the channel position against the gravity and κ parameters. The results of the work prove that, for κ=1, the droplet length L is independent of channel orientation.

Granular piston-probing in microgravity: powder compression, from densification to jamming

The macroscopic response of granular solids is determined by the microscopic fabric of force chains, which, in turn, is intimately linked to the history of the solid. To query the influence of gravity on powder flow behavior, a granular material is subjected to compression by a piston in a closed container, on-ground and in microgravity (on parabolic flights). Results show that piston-probing densifies the packing, eventually leading to jamming of the material compressed by the piston, regardless of the gravitational environment. The onset of jamming is found to appear at lower packing fraction in microgravity ({varphi }_{J}^{mu -{{{rm{g}}}}}=0.567pm 0.014) than on-ground ({varphi }_{J}^{{{{rm{gnd}}}}}=0.579pm 0.014). We interpret these findings as the manifestation of a granular fabric altered by the gravitational force field: in absence of a secondary load (due to gravitational acceleration) to stimulate reorganization in a different direction to the major compression stress, the particles’ configuration becomes stable at lower density, as the particles have no external drive to promote reorganization into a denser packing. This is coupled with a change in interparticular force balance which takes place under low gravity, as cohesive interactions become predominant. We propose a combination of microscopic and continuum arguments to rationalize our results.

Gravi-Sensitivity of Mosses and Their Gravity-Dependent Ontogenetic Adaptations.

Gravi-morphoses affect the variability of plants and are the morphogenetic adaptation to different environmental conditions. Gravity-dependent phenotypic plasticity of gametophytes as well as gravi-sensitivity of moss protonemata in microgravity and simulated microgravity conditions are discussed. The moss protonema, a filamentous multicellular system, representing a juvenile stage of moss development, develops as a result of the elongation and division of the apical cell. This apical cell of the protonema is a unique object for research on moss gravi-sensitivity, as graviperception and gravitropic growth occur within the same single cell. Attention is focused on the influence of gravity on bryophyte ontogenesis, including the gravitropic reactivity of moss protonemata, gravi-sensitivity at the stage of leafy shoot development and sporogonium formation, gravity-influenced morphogenesis of apical cell budding, and gravity-dependent spiral growth patterns. The role of gravireceptors in the growth processes of mosses at the cellular level under microgravity conditions are being discussed, as well as the involvement of auxin transport, Ca2+-induced gravitropism and the cytoskeleton in gravitropic reactions.

Evaporation kinetics of wettability-moderated capillary bridges and squeezed droplets

We experimentally and theoretically probe the evaporation kinetics of liquid capillary bridges and squeezed droplets for different heights and wettability conditions. Water droplets of uniform volume were squeezed between hydrophilic and superhydrophobic (SH) flat substrates, and the relative spacing between them is varied to understand the role of bridge height on its evaporation behavior. The transient evolution of bridge profile during the evaporation is monitored using optical imaging technique, with thermal imaging aid. Our observations reveal augmented evaporation rate for smaller relative spacing between the hydrophilic surfaces due to increased curvature of the liquid–vapor interface. For SH surfaces, the vapor entrapment phenomenon plays a significant role in addition to interfacial curvature, especially for small relative spacing. For mixed wettability bridge, the shape of the bridge exhibits a transition in curvature, which governs its temporal evaporation rate. We show that the bridge stability and contact line dynamics during evaporation is strongly dictated by the capillary pressure and the geometry of the liquid–vapor interface. For smaller relative spacing, the contact line de-pins at early stages and the liquid bridge remains stable for a longer duration. Whereas, bridges pinch off at early stages for higher spacing conditions via rapid evaporation of the neck. To model the evaporative mass loss rate, the transient bridge interfacial profile under influence of gravity is quantified using the principal of energy minimization, and the curvature driven evaporative flux is summed up over this interface to obtain the evaporation rate. The model predictions conform well to the experimental observations.

Unexpected Slow Kinetics of Poly(Methacrylic Acid) Phase Separation in the Semi-Dilute Regime.

Poly (methacrylic acid) (PMAA) solutions are known to exhibit a lower critical solution temperature (LCST). A temperature-composition phase diagram of PMAA has been constructed by standard cloud point determination through transmittance measurements, and also by studying the steady states reached under phase separation. This allows us to reconstruct the binodal curve describing the phase behavior of PMAA for both low and high concentration regimes, and to determine accurately the LCST temperature. In a second step, the structures formed following a temperature jump above the cloud point and their evolution in time have been investigated at the nanoscale using small angle neutron scattering (SANS). This approach shows that the formation of phase-separated nanostructures is a slow process, requiring more than 12 h. The formed structures are then shown to depend on the amplitude of the temperature jump above the cloud point. An original mechanism of phase separation is identified in the semi-dilute regime. The growth of micrometric-size droplets with an inner structure displaying the rheological properties of a gel leads to the formation of a percolating network which hinders the influence of gravity. Such a result can explain the slow kinetics of the PMAA LCST transition.

Multi-criticality and related bifurcation in accretion discs around non-rotating black holes: an analytical study

Low angular momentum, general relativistic, axially symmetric accretion of hydrodynamic fluid onto Schwarzschild black holes may undergo more than one critical transition. To obtain the stationary integral solutions corresponding to such multi-critical accretion flow, one needs to employ numerical solutions of the corresponding fluid dynamics equations. In the present work, we develop a completely analytical solution scheme which may be used to find several trans-critical flow behaviours of aforementioned accretion, without explicitly solving the flow equations numerically. We study all possible geometric configurations of the flow profile, governed by all possible thermodynamic equations of state. We use Sturm’s chain algorithm to find out how many physically acceptable critical points the accretion flow can have, and discuss the transition from the mono to the multi-critical flow profile, and related bifurcation phenomena. We thus illustrate, completely analytically, the application of certain aspects of the dynamical systems theory in the field of large-scale astrophysical flow under the influence of strong gravity. Our work may possibly be generalized to calculate the maximal number of equilibrium points certain autonomous dynamical systems can have in general.

On the velocity, size, and temperature of gaseous dendritic flames

Dendritic combustion in Hele–Shaw cells is investigated qualitatively using a simplified one-dimensional thermo-diffusive model. Formulas for the velocity, size, and temperature of the flamelets are derived. The temperature and velocity of the flames increase for small radii to allow for their survival regardless of the activation energy. In addition, the results obtained with very large activation energy were compared with experimental results, finding that additional tests are required due to the strong influence of gravity on the velocity and size estimations. Conditions for the existence of this anomalous propagation are investigated, confirming analytically that it can only happen for low Lewis numbers.

Influence of various application systems on the amount of extruded irrigant in simulated immature teeth with regard to gravity: An ex-vivo study.

Gravity impact has been mainly evaluated in mature teeth related to debris extrusion, even though it may affect the amount of apically extruded irrigant. In the literature the influence of gravity on the amount of apically extruded irrigant in immature teeth has been studied by a 45o inclined plate to mimic the position of the maxillary teeth and 90o for the mandibular teeth. However, patients are positioned horizontally in the dental chair while treatment. There is no study in the literature testing the horizontal position to mimic the clinical settings realistically. The aim of this study was to evaluate the influence of various irrigation systems on the amount of extruded irrigant in simulated immature maxillary and mandibular teeth irrigated in vertical and horizontal positions. Twenty-five maxillary central incisors with an apical opening of 1.3 mm in diameter were included. Irrigation procedures were performed with EndoVac, closed-ended, and open-ended needles using a VATEA peristaltic pump. The amount of apically extruded irrigant was determined using a microbalance. Statistical analysis was performed using the Kruskal-Wallis test. The EndoVac system caused almost no irrigant extrusion in all tested positions (P > 0.05); however, closed-ended and open-ended needles extruded more irrigant in a mandibular vertical position compared to maxillary vertical (P < 0.05) and maxillary horizontal positions (P < 0.05). Open-ended needles extruded the highest amount of irrigant. The EndoVac macrocannula is a more reliable and safer irrigation system as it prevents irrigant extrusion independent of the position of the tooth.

Numerical Assessment of Symmetric Wedge Water-entry Impact Using OpenFOAM

The hydrodynamic problem of a two-dimensional symmetric wedge vertically entering the water, initially flat, with a deadrise angle of 30° is considered. This numerical study assesses turbulence, gravity, viscosity, and surface tension during the early stage of penetration. The OpenFOAM software package has been used to simulate the water entry of the wedge at a constant speed of 3 m/s. The governing equations have been numerically built in the solver called overInterDyMFoam. The method has also been used to model the turbulence effect. The effects of turbulent and laminar flow assumptions and for the laminar flow, viscosity, gravity, and surface tension influence on pressure distributions along the wedge's walls have been investigated. It is illustrated that turbulence, viscosity, and surface tension have negligible effects on the pressure distribution in the primary water entry process. However, the pressure distribution is found to be significantly influenced by gravity.

Numerical Assessment of Gravity for Sloshing in Tank Using OpenFOAM

We numerically study gravity’s effect on sloshing in a two-dimensional tank which is highly filled by water (95% water and 5% air). Both fluids are considered to be incompressible and inviscid. The surface tension and phase change are neglected. OpenFOAM software is used for the simulation. A standing wave of water impacting the lid of the tank at its center and a symmetric wetted region starts to advance along the lid. The simulation carried out (only on the right-half side of the tank due to symmetric geometry of the impact) with and without gravity to investigate the influence of gravity on this impact. The numerical results are validated by comparing to published data. The effect of gravity on the size of the wetted region, free-surface elevation and on the pressure distribution has been analyzed. It is shown that gravity is affecting the free-surface elevation and consequently the size of the wetted region. These effects growth as time goes. Pressure distribution along the wetted region of the lid is also influenced by gravity.

Cooling characteristics of hot rolled seamless steel tube by jet impingement

The flow and temperature field variation of hot rolled seamless steel tube with outer diameter of 140 mm and wall thickness of 10 mm were studied by experiment and numerical simulation. The finite element model of circular jet impinging cooling steel tube was established, and the steel tube was divided into different regions in circumferential direction. It was found that the uniformly arranged multiple jets have non-uniform cooling characteristics under the influence of gravity and hollow characteristic. Under the condition of 12 jets, the average heat transfer coefficient in circumferential direction of −15 ∼ −45° region is 8385 W/(m2K), and the fluctuation of the average heat transfer coefficient in different regions reaches 3222 W/(m2K). According to statistical average cooling rate of the experiment, the average cooling rate increases by 34% when 2 jets are increased to 4 jets. When the number of jets exceeds 8, increasing the number of jets has a limited effect on improving average cooling rate. Through reasonable configuration of jet velocity of different nozzle positions, a way to realize uniform cooling was proposed and preliminarily verified. The improved average heat transfer coefficient fluctuation of circumferential was limited to 1000 W/(m2K), which significantly improved the uniformity of jet cooling.

Influence of gravity on the freezing dynamics of drops on a solid surface

The influence of gravity on water droplet freezing on a cold solid surface has been investigated in this study. Experimental results over a range of Bond numbers, for both pendent and sessile droplets, show that gravity can significantly influence the freezing processes via shaping the initial droplet. Despite the significant difference in the initial droplet shape, some remarkable similarities have been found for pendent and sessile droplets at small and large Bond numbers. The final height of a frozen droplet is found to be proportional to its initial height.