Effects Of Gravitational Forces Research Articles

The effect of gravitational force on limbal stem cell growth

AimTo evaluate the effect of gravity on corneal epithelial cell migration in vitro.MethodsFourteen donor peripheral corneoscleral rims were used. Twenty explants were chosen of which 10 were placed vertically and...

High Order Well-Balanced WENO Scheme for the Gas Dynamics Equations Under Gravitational Fields

The gas dynamics equations, coupled with a static gravitational field, admit the hydrostatic balance where the flux produced by the pressure is exactly canceled by the gravitational source term. Many astrophysical problems involve the hydrodynamical evolution in a gravitational field, therefore it is essential to correctly capture the effect of gravitational force in the simulations. Improper treatment of the gravitational force can lead to a solution which either oscillates around the equilibrium, or deviates from the equilibrium after a long time run. In this paper we design high order well-balanced finite difference WENO schemes to this system, which can preserve the hydrostatic balance state exactly and at the same time can maintain genuine high order accuracy. Numerical tests are performed to verify high order accuracy, well-balanced property, and good resolution for smooth and discontinuous solutions. The main purpose of the well-balanced schemes designed in this paper is to well resolve small perturbations of the hydrostatic balance state on coarse meshes. The more difficult issue of convergence towards such hydrostatic balance state from an arbitrary initial condition is not addressed in this paper.

Two-dimensional volume of fluid simulation studies on single bubble formation and dynamics in bubble columns

In this paper, the volume of fluid (VOF) model in conjunction with continuum surface force (CSF) model was used to numerically investigate the single bubble formation and dynamics in the bubble columns on the software platform of Fluent 6.3. A set of transient conservation equations of mass and momentum taking surface tension and gravitational force effects into consideration were solved by pressure implicit splitting operator (PISO) algorithm and a piecewise linear interface calculation (PLIC) was applied to characterize the behavior of gas–liquid interface movement in the VOF method. The simulation results of bubble formation and dynamics compare well with available literature results. The effects of physical properties including surface tension, liquid viscosity and density, gas or liquid operation conditions and orifice size on the single bubble generation, detachment, rising and coaxial bubble coalescence were systematically analyzed, and the effect of superficial liquid velocity on single bubble behavior was especially discussed. It is found that non-zero superficial liquid velocity enhances the bubble detachment, decreases the bubble size, and delays the coaxial bubble coalescence obviously. Increasing superficial liquid velocity largely raises the velocity of the leading bubble and enlarging orifice gas velocity mainly accelerates the second bubble of two coalescence bubbles.

Volume preserving immersed boundary methods for two‐phase fluid flows

SUMMARYIn this article, we propose a simple area‐preserving correction scheme for two‐phase immiscible incompressible flows with an immersed boundary method (IBM). The IBM was originally developed to model blood flow in the heart and has been widely applied to biofluid dynamics problems with complex geometries and immersed elastic membranes. The main idea of the IBM is to use a regular Eulerian computational grid for the fluid mechanics along with a Lagrangian representation of the immersed boundary. Using the discrete Dirac delta function and the indicator function, we can include the surface tension force, variable viscosity and mass density, and gravitational force effects. The principal advantage of the IBM for two‐phase fluid flows is its inherent accuracy due in part to its ability to use a large number of interfacial marker points on the interface. However, because the interface between two fluids is moved in a discrete manner, this can result in a lack of volume conservation. The idea of an area preserving correction scheme is to correct the interface location normally to the interface so that the area remains constant. Various numerical experiments are presented to illustrate the efficiency and accuracy of the proposed conservative IBM for two‐phase fluid flows. Copyright © 2011 John Wiley & Sons, Ltd.

Mutations in FOXC2 in Humans (Lymphoedema Distichiasis Syndrome) Cause Lymphatic Dysfunction on Dependency

Background: Human lymphoedema distichiasis syndrome (LDS) results from germline mutations in transcription factor FOXC2. In a mouse model, lack of lymphatic and venous valves is observed plus abnormal smooth muscle cell recruitment to initial lymphatics. We investigated the mechanism of lymphoedema in humans with FOXC2 mutations, specifically the effect of gravitational forces on dermal lymphatic function. Methods: We performed (1) quantitative fluorescence microlymphangiography (FML) on the skin of the forearm (non-swollen region) at heart level, and the foot (swollen region) below heart level (dependent) and then at heart level, and (2) immunohistochemical staining of microlymphatics in forearm and foot skin biopsies, using antibodies to podoplanin, LYVE-1 and smooth muscle actin. Results: FML revealed a marked reduction in fluid uptake by initial lymphatics in the LDS foot during dependency, yet normal uptake (similar to controls) in the same foot at heart level and in LDS forearms. In control subjects, dependency did not impair initial lymphatic filling. Immunohistochemical microlymphatic density in forearm and foot did not differ between LDS and controls. Conclusions:FOXC2 mutations cause a functional failure of dermal initial lymphatics during gravitational stress (dependency), but not hypoplasia. The results reveal a pathophysiological mechanism contributing to swelling in LDS.

Differential findings in post-factum dissections of medieval Korean mummies exhibiting similar preservation patterns on computerized tomography images

In our previous CT and post-factum dissection studies on medieval Korean mummies, well preserved internal organs generally were found to have been displaced to the dorsal side of the body cavity. This movement seems to have been caused by the effect of gravitational force exerted over long burial durations. However, when we recently examined a newly discovered medieval Korean mummy (SN1-2) by CT, most of the mummified organs were found to have remained in their natural positions. Our post-factum dissection of SN1-2 showed that the organs might have undergone expansion by posthumous gas formation, after which they hardened into a stone-like state, which mitigated against their displacement. Similar CT findings were made in the case of a second Korean mummy (KU-1). Since the internal organs within the thoracic cavity were discovered to be in their natural positions, we suspected that they, like those in the case of SN1-2, had also been changed into stony structures. However, the post-factum dissection showed that the internal organs of KU-1 had neither hardened nor been displaced to the back wall of the thoracic cavity, owing possibly to the presence of a pleural adhesion. Overall, our results indicated that CT alone might be inadequate for correct estimation of the preservation status of internal organs in Korean mummies. This calls for further accumulation of dissection data, against which CT diagnoses can be compared and by which they can be improved.

Orientation-Dependent Performance of Portable Proton Exchange Membrane Fuel Cells

The effects of gravitational force on the orientation-dependent performance of portable proton exchange membrane (PEM) fuel cell using serpentine flow channels were investigated by the measurement and analysis of polarization curves. Whether the removal of produced water in the cathode flow channel is resisted or assisted by the gravity depends on the orientation variation, flow direction, and flow channel distribution of a fuel cell. This gravity will then affect the fuel cell performance, especially for fuel cells operating at a high current density. The results show that a fuel cell with perpendicular flow channel distribution and cathode gas flow in vertical direction requires a longer distance of pushing liquid droplets against gravity to remove the produced water, which is difficult to expel the produced water from the flow channels, and the performance reduction is obviously in high current density. A fuel cell operating in a normal position achieves higher performance than one operating in a horizontal position, except the cathode gas flow in vertical direction and feed from lower inlet. Furthermore, for a fuel cell operating in a horizontal position with anode below the membrane, gravitational force transports the water to the anode and blocks the fuel channel in the gas diffusion layer. This leads a fuel cell operating in high current densities with the cathode below the membrane performs better than one with the cathode above the membrane. Therefore, to reduce the effects of gravity on the orientation-dependent performance, a fuel cell with parallel flow channel distribution and feeding the cathode gas from the upper inlet port is recommended in this study.

Nonlinear Disturbance Decoupling for a Mobile Robotic Manipulator over Uneven Terrain

AbstractThis paper considers the nonlinear disturbance decoupling problem for a robotic manipulator that is mounted on a mobile platform. A mobile manipulation system offers a dual advantage of mobility offered by a mobile platform and dexterity offered by the manipulator. In this work, the tracking and nonlinear disturbance decoupling problems are studied with particular focus on disturbances due to uneven terrain. We show that this system possesses the necessary geometric structure for complete disturbance decoupling between the outputs and disturbances. The disturbances are modeled as changes in the effect of gravitational forces on the mobile manipulator due to its motion over a uneven terrain. Simulation results illustrate complete disturbance decoupling even in the presence of significant disturbances using the designed nonlinear controller.

Measurements of Minute Unsteady Pressure on Three-Dimensional Fan

The present study is a fundamental approach to reveal the minute fluctuating pressures on three-dimensional blade surfaces of a basic propeller fan. Because, among the concerning physical quantities, the unsteady pressures on the rotating blades give us useful information for the fan flow and its sound-noise level. The authors correct the centrifugal-force effect, the gravitational-force effect and the other leading-error effects for accurate measurements of the minute pressures using a measuring technology developed by the authors (Hirata et al., 2009). As a result, we show the Reynolds-number effects and the spatial distributions on the blade of both time-mean pressure and pressure-fluctuation intensity.

The dynamic behavior of magnetic fluid adsorbed to small permanent magnet in alternating magnetic field

The dynamic behavior of a magnetic fluid adsorbed to a small NdFeB permanent magnet subjected to an alternating magnetic field was studied with a high speed video camera system. The directions of alternating magnetic field are parallel and opposite to that of the permanent magnet. It was found that the surface of magnetic fluid responds to the external alternating magnetic field in elongation and contraction with a lot of spikes. Generation of a capillary magnetic fluid jet was observed in the neighbourhood of a specific frequency of alternating field. The effect of gravitational force on surface phenomena of magnetic fluid adsorbed to the permanent magnet was revealed.

3D Calculations of Equilibrium Conditions in Loose-Bed Open Channels with Significant Suspended Sediment Load

The flow, sediment transport, and bathymetry at equilibrium conditions in loose-bed open channels are predicted using a fully three-dimensional (3D) Reynolds-Averaged Navier-Stokes model that was validated for cases in which the bed-load transport is dominant. The paper focuses on two test cases corresponding to laboratory experiments performed in an S-shaped channel in which the suspended sediment load is comparable to the bed load. A modified version of the original model that accounts for gravitational force effects due to the total sediment load is proposed. It is shown that the way bed-slope effects are accounted for plays a major role in improving the predictive capabilities of the model for a case in which the equilibrium bathymetry is characterized by relatively large values and sharp variations of the transverse slope. The model is then used to qualitatively and quantitatively analyze the distributions of several flow variables that are difficult to measure in the laboratory. They include the distributions of the bed-shear stress and of a Chezy-type friction coefficient assumed to be constant by most lower-order (e.g., two-dimensional depth-averaged) models.

Dynamic Pore-Network Simulator for Modeling Buoyancy-Driven Migration During Depressurization of Oil-Saturated Systems

Summary A number of vertically oriented heavy- and light-oil-depletion experiments have been conducted in recent years in an attempt to investigate the effect of gravitational forces on gas evolution during solution-gas drive. Although some experimental results indirectly suggest the occurrence of gas migration during these tests (especially at slow depletion rates), a major limitation of such an interpretation is the difficulty in visualizing the process in reservoir-rock samples. In contrast, experimental observations using transparent glass models have proved invaluable in this context and provide a sound physical basis for modeling gravitational gas migration in gas/oil systems. However, the experimental observations often exhibit somewhat contradictory trends—some studies showing dispersed gas migration, while others describe fingered, channelized flow—and, to date, there appears to have been little systematic effort toward modeling the wide range of behaviors seen in or inferred from laboratory tests. To this end, we present a new pore-network simulator that is capable of modeling the time-dependent migration of growing gas structures. Multiple pore-filling events are modeled dynamically with interface tracking allowing the full range of migratory behaviors to be reproduced, including braided migration (i.e., discontinuous flow of gas through narrow channels) and discontinuous dispersed flow. Simulation results are compared with experiments and are found to be in excellent agreement. Moreover, simulation results clearly show that a number of network and fluid parameters interact in a rather complex manner and, as a consequence, the competition between capillarity and buoyancy produces different gas-evolution patterns during pressure depletion. The implications of evolution regime on recovery from gas/oil systems undergoing depressurization are discussed extensively.

SU-GG-T-77: Effect of Mobile Seed Components on Dosimetry of Theragenic Model 200 Pd-103 Seed Source

Purpose: To investigate the influence of mobile internal source components of Theragenic Model 200 seed source on its dose rate distribution and TG‐43 parameters. Method and Materials : By using BrachyDose Monte Carlo code, the geometry of Theragenic Model 200 seed source was modeled in five different configurations. In each configuration, internal components are located at different positions in order to take into account the effect of gravitational force on the seed geometry. Physical dimensions of seed components are identical in all seed models. Air kerma strenghts and dose per unit activitiy were determined separately for each seed design on a plane which is in a direction where dose variations are expected to be maximum. Calculated data were used to produce TG‐43 parameters. Results: Comparison of TG‐43 dosimetric parameters for each seed configuation showed that dose rate constant varies up to 11% due to the position of internal source elements. For radial dose fuction, there are significant differences increasing up to 40% at distances 0.1≤ r 0.5 discrepancies are negligible (i.e. about 1–2%). Anisotropy functions were calculated at radial distances of 0.25, 0.5, 1.0 and 5.0 cm. It is observed that anisotropy function changes adruptly (up to 40%) for polar angels θ 165° at all radial distances. Differences are less than 5% for all other angles and decreases with increasing radial distance. Conclusions: The geometry variation effects investigated in this study are ignored in the TG‐43 formalism. This work indicates that these effects may change absorbed dose values significantly at some points around the Theragenic Model 200 seed source. This investigation was supported by Celal Bayar University (Project number: 2009/138) and ULAKBIM High Performance and Grid Computing Center (TR‐grid)

Measurements of Minute Unsteady Pressure on Three-Dimensional Fan with Arbitrary Axis Direction

The present study is a fundamental approach to develop the measuring technology for minute fluctuating pressures on the three-dimensional blade surfaces of the fan which rotates with an arbitrary rotation-axis direction. In this situation, we are required to correct the centrifugal-force effect, the gravitational-force effect and the other leading-error effects for accurate measurements of the minute pressures. The working fluid is air. A pressure transducer rotating with an arbitrary attitude is closely sealed by a twofold shroud system. The rotational motion with an arbitrary attitude is produced by fixing the pressure transducer to the cantilever which is connected to a motor-driven disc of 500mm in diameter and 5mm in thickness. As a result, we have quantitatively determined main governing effects upon the non-effective component of the pressure-transducer signal.

Study of large-scale deformation induced by gravity on the La Clapière landslide (Saint-Etienne de Tinée, France) using numerical and geophysical approaches

Abstract The large-scale deformation of high mountain slopes finds its origin in many phenomena with very different time-constants. Gravitational effect, tectonic forces, and water infiltration are generally the principal causes. However, it is always very difficult to distinguish which cause is dominant and which are their respective effects. A two-dimensional numerical experiment coupled with geophysical approach was carried out to determine (1) the effect of gravitational force on the mechanical behaviour of the “la Clapiere” area, (2) a 2D-depth structure of this landslide. The results show that gravitational instability is possible and leads to destabilisation of the massif by a regressive evolution of the landslide from the bottom at 1100 m up to a height of 1800 m, which is actually the top of the La Clapiere landslide. This deformation progression only concerns a depth of around 150 ± 50 m, which can be correlated to the sliding surface, as suggested by our electrical data obtained by resistivity investigations and previous studies. Our numerical results suggest that changes of the slope topography “drive” the diffusion of the plastic deformation in the mass, possibly through a channel which could be then the privileged zone along which the fracture is initiated.

Measurements of Minute Unsteady Pressure on Three-Dimensional Fan

The present study is a fundamental approach to reveal the minute fluctuating pressures on three-dimensional blade surfaces of a basic propeller fan. Because, among the concerning physical quantities, the unsteady pressures on the rotating blades give us useful information for the fan flow and its sound-noise level. The authors correct the centrifugal-force effect, the gravitational-force effect and the other leading-error effects for accurate measurements of the minute pressures using a measuring technology developed by the authors (Hirata et al., 2009). As a result, we show the Reynolds-number effects and the spatial distributions on the blade of both time-mean pressure and pressure-fluctuation intensity.

Is Bone's Response to Mechanical Signals Dominated by Muscle Forces?

Skeletal loading in vertebrates controls modeling drifts, modulated remodeling rates, and affects growth trajectories. It is unclear whether the majority of the mechanical stimulus detected by bone cells originates from muscle contraction forces or from gravitational forces associated with substrate impact. Several clinical and basic science reports indicate that muscle forces play a dominant role in generating the mechanical stimulus in exercise-induced bone gain. Although it is, in most cases, difficult to separate the effects of gravitational forces acting on body mass from muscle contractions, several well-conceived experiments offer considerable insight into the propensity of muscle-derived forces per se to drive the adaptive response in bone. Load-induced osteogenesis requires that mechanical signals come packaged with particular characteristics, all of which can be generated from either gravitational or muscle forces. Neither of these two sources have been demonstrated empirically to be the source of bone's adaptive response, but a convincing body of data suggests that muscle contractions are present, significant, and capable of accounting for most of the adaptive responses.

Motions of gently sloping ground during earthquakes

During past earthquakes, gently sloping ground surfaces have been observed to shift laterally over areas as large as a few square kilometers. These permanent downward motions have been attributed to temporary and partial reductions in shear strength of soil deposits (e.g., liquefaction), static gravity forces, and transient earthquake shakings. These motions, the amplitudes of which remain challenging to predict, have been frequently modeled using Newmark sliding blocks for ground that is statically stable and occasionally partially or completely loses its shear strength during earthquakes. This paper investigates in more details the deformations of gently sloping ground that becomes temporarily unstable under the combined effects of gravitational forces and earthquake shakings. Using a physical model, we propose two definitions of earthquake contributions to the displacement of gently sloping ground, which may include or not the effects of initial velocity. In both cases, Monte Carlo simulations reveal that motions of gently sloping ground are influenced by pulses of earthquake ground velocity for a wide range of reduction in soil shear strength, even for very severe loss of shear strength. For practical purposes, when large soil deposits become unstable during earthquakes, the analysis concludes that the motions of gently sloping ground are likely influenced by earthquake ground velocity.

Rock fabric, pore geometry and mineralogy effects on water transport in fractured dolostones

The combined influence of rock fabric, pore geometry and mineralogy (petrological parameters) on transport properties in complex and heterogeneous naturally fractured rocks was studied experimentally. As fissure geometry quantification has rarely been addressed in most theoretical studies of transport properties, emphasis was placed on the effects of fissure geometry on both non-saturated media (capillary rise) and saturated media (permeability). We proved that prediction of transport properties in complex rocks is not guaranteed by the estimation of the classic micro-structural variables considered in the literature and that accurate prediction can only be attained when petrological parameters are first quantified in depth, and then combined. Principal component analysis and the regression models proposed here clearly demonstrated on the one hand that, a meaningful porous network in non-saturated media must be modelled with a combination of different geometrical capillary tubes representing the matrix (cylindrical) and the fissure (rectangular prism) and on the other hand, that in saturated media a well-in-deep fissure size quantification enabled a more accurate prediction of permeability to be made. The experimental data confirm that transport properties and its anisotropy are closely dependent on fissure typology, textural characteristics, mineralogy and spatial distribution of the whole rock fabric elements. Enlarged-fissures weakly exert capillary suction due to the retarding effect of gravitational forces, but they are vital in controlling permeability. Cracklebreccias with small clasts, high dolomite cement content and high inter-clast fissure density exhibit strong capillary suction. However, high calcite cement produces abnormally low rates of capillary rise, due to possible pore surface contamination, together with a high contact angle effect. Good agreement between permeability and geometric factors provided a suitable basis for identifying preferred permeable directions. Additionally, we found a critical fissure density which defined the isotropic matrix permeability. We also present a new practical and simple linear model relating permeability to capillarity with meaningfully and easily estimated petrological parameters. Results obtained in the present study demonstrated the correct identification and use of more directly related petrological variables for modelling transport properties. Moreover, the analysis of these results using multivariate analysis is considerably more demanding compared to the conventional approaches.

Effect of gravitational force upon traffic flow with gradients

We study the effect of gravitational force upon traffic flow on a highway with sag, uphill, and downhill. We extend the optimal velocity model to take into account the gravitational force which acts on vehicles as an external force. We study the traffic states and jamming transitions induced by the slope of highway. We derive the fundamental diagrams (flow-density diagrams) for the traffic flow on the sag, the uphill, and downhill by using the extended optimal velocity model. We clarify where and when traffic jams occur on a highway with gradients. We show the relationship between densities before and after the jam. We derive the dependence of the fundamental diagram on the slope of gradients.