Role Of Gravity Research Articles

A Boundary Element Model of Multiple Microcirculatory Bubbles in Cardiovasculature

In order to investigate the role of gravity in a novel cancer treatment strategy called Gas Embolotherapy, we have computationally studied the evolution dynamics of two bubbles sticking to and sliding on the opposite walls of a 2D channel, under gravity-driven flow. We have modeled the moving three-phase contact lines using Tanner laws including contact angle hysteresis and have accounted for the gas-liquid interfacial dynamics in our model. Our model uses a Boundary Element Method (BEM) based moving-interface, multi-domain, iterative method to compute the flows and stresses on the domain boundaries at various instants of time. Since the normal and shear stresses acting on the endothelial layer of blood vessels are a major concern in the development of gas embolotherapy, we have examined the effect of bubble evolution and induced flows on the wall stresses. For a range of initial bubble pressures, we have studied the role of gravity by varying the Bond number and by using two different inclinations of the...

Gravity is an important determinant of oxygenation during one‐lung ventilation

The role of gravity in the redistribution of pulmonary blood flow during one-lung ventilation (OLV) has been questioned recently. To address this controversial but clinically important issue, we used an experimental approach that allowed us to differentiate the effects of gravity from the effects of hypoxic pulmonary vasoconstriction (HPV) on arterial oxygenation during OLV in patients scheduled for thoracic surgery. Forty patients with chronic obstructive pulmonary disease scheduled for right lung tumour resection were randomized to undergo dependent (left) one-lung ventilation (D-OLV; n=20) or non-dependent (right) one-lung ventilation (ND-OLV; n=20) in the supine and left lateral positions. Partial pressure of arterial oxygen (PaO2) was measured as a surrogate for ventilation/perfusion matching. Patients were studied before surgery under closed chest conditions. When compared with bilateral lung ventilation, both D-OLV and ND-OLV caused a significant and equal decrease in PaO(2) in the supine position. However, D-OLV in the lateral position was associated with a higher PaO2 as compared with the supine position [274.2 (77.6) vs. 181.9 (68.3) mmHg, P<0.01, analysis of variance (ANOVA)]. In contrast, in patients undergoing ND-OLV, PaO2 was always lower in the lateral as compared with the supine position [105.3 (63.2) vs. 187 (63.1) mmHg, P<0.01, ANOVA]. The relative position of the ventilated vs. the non-ventilated lung markedly affects arterial oxygenation during OLV. These data suggest that gravity affects ventilation-perfusion matching independent of HPV.

Photoionized gas in hydrostatic equilibrium: the role of gravity

We present a method to include the effects of gravity in the plasma physics code Cloudy. More precisely, a term is added to the desired gas pressure in order to enforce hydrostatic equilibrium, accounting for both the self-gravity of the gas and the presence of an optional external potential. As a test case, a plane-parallel model of the vertical structure of the Milky Way disk near the solar neighbourhood is considered. It is shown that the gravitational force determines the scale height of the disk, and it plays a critical role in setting its overall chemical composition. However, other variables, such as the shape of incident continuum and the intensity of the Galactic magnetic field, strongly affect the predicted structure.

Various Perspectives on Accretionary Wedge Formation and Related Phenomena

The present situation of studies on accretionary wedge formation and related phenomena is briefly summarized from various perspectives, ranging from theories, model experiments, observations on land and submarine, exhumation of high-pressure metamorphic rocks, fluid seepage, stress field, and asperity. Future perspectives are also considered from such recent results with potential areas of study. Gravity acts ubiquitously—everywhere and at all times—on the Earth's materials, so the role of gravity is also accounted for in the wedge development.

Glimmers of a Pre-geometric Perspective

Space-time measurements and gravitational experiments are made by using objects, matter fields or particles and their mutual relationships. As a consequence, any operationally meaningful assertion about space-time is in fact an assertion about the degrees of freedom of the matter (\emph{i.e} non gravitational) fields; those, say for definiteness, of the Standard Model of particle physics. As for any quantum theory, the dynamics of the matter fields can be described in terms of a unitary evolution of a state vector in a Hilbert space. By writing the Hilbert space as a generic tensor product of "subsystems" we analyse the evolution of a state vector on an information theoretical basis and attempt to recover the usual space-time relations from the information exchanges between these subsystems. We consider generic interacting second quantized models with a finite number of fermionic degrees of freedom and characterize on physical grounds the tensor product structure associated with the class of "localized systems" and therefore with "position". We find that in the case of free theories no space-time relation is operationally definable. On the contrary, by applying the same procedure to the simple interacting model of a one-dimensional Heisenberg spin chain we recover the tensor product structure usually associated with "position". Finally, we discuss the possible role of gravity in this framework.

Colloidal and Bacterial Deposition: Role of Gravity

The role of gravitational force on the deposition of 0.5, 1.1, and 1.8 mum carboxylate-modified polystyrene latex (CML) microspheres and bacterium Burkholderia cepacia G4g has been evaluated using a parallel plate flow chamber system. This experimental system utilized an inverted and an upright optical microscope attached with image-capturing devices to directly observe and determine the deposition kinetics onto glass surfaces located at the top and bottom of the flow chamber. Deposition kinetics was quantified at 10 mM KCl under electrostatically unfavorable and favorable attachment conditions and at two flow rates (0.06 and 3 mL/min), simulating the range of flow velocities from groundwater to rapid granular filtration. Comparing the particle deposition kinetics on the top and bottom surfaces under identical flowing exposure time, fluid chemistries, and hydrodynamic conditions, results showed that significant differences were observed between the two surfaces, suggesting that gravity was a significant driving force for the initial stages of deposition of particles that were larger than 1 mum size. Simulation results utilizing a particle trajectory model confirmed these experimental observations. This was further supported by additional deposition experiments with 1.1 mum microspheres suspended in a deuterium oxide (D(2)O)/water mixture (heavy water) where the density of colloid and the suspending heavy water were effectively the same. Under this condition, deposition rates were observed to be identical between the top and bottom surfaces. Results from normal and heavy water solutions indicated that the greater deposition of colloidal particles larger than 1 mum on the bottom in normal water solutions is due to gravity. Finally, the experimental results were compared with deposition studies using smaller 0.5 mum colloids as well as some theoretical calculations of expected rates of particle deposition.

The role of gravity and inertial forces on shoulder during pointing task in children with hemiplegia

The role of gravity and inertial forces on shoulder during pointing task in children with hemiplegia

On the deformation cycle of a strongly coupled plate interface: The triple earthquakes of 16 March 1963, 15 November 2006, and 13 January 2007 along the Kurile subduction zone

The great plate interface Kurile earthquake of 15 November 2006 (Mw = 8.3) was immediately followed by normal aftershocks in the outer rise of the central Kurile subduction zone. Two months later at a distance &lt;50 km from this event the 13 January 2007 (Mw = 8.1) earthquake with a pure normal mechanism occurred in the outer rise of the central Kurile. The 15 November 2006 earthquake ruptured an area of 280 × 150 km2 with maximum slip of almost 7 m, while the 13 January 2007 earthquake ruptured an area of 240 × 40 km2 with a maximum slip of almost 14 m. These two significant events were preceded by a major reverse earthquake on 16 March 1963 (Mw = 7.7) that took place close to the location of the 13 January 2007 earthquake. These very different earthquakes demonstrate the different stages of the deformation cycle along strongly coupled plates at the central Kurile arc and present a rare case of stress regime reversal over a short time span. In order to understand the details of these three earthquakes, we inverted for the source rupture processes of the earthquakes and delineated the location and dimension of asperities. The role of gravity and topography anomalies and their correlation to the asperity distribution as well as the long‐term seismicity is studied in detail. Using trench‐parallel Bouguer anomaly, we have identified the differences in the asperities and the location of larger normal outer rise aftershocks as well as the location of 13 January 2007 earthquake. We also show that the long‐term seismicity of the central Kurile arc is confined to the intraslab and not the plate interface. The static stress transfer for these earthquakes showed that the stress on optimally oriented thrust faults is increased in the northeastern part of the rupture area of the 15 November 2006 earthquake. Absence of major and great earthquakes to the northeastern immediate vicinity of the rupture area of the 15 November 2006 earthquake supports the hypothesis that this area is mature for the next strong earthquake along the Kurile arc.

Brassica rapa L. seed development in hypergravity

AbstractPrevious experiments had shown that microgravity adversely affected seed development in Brassica rapa L. We tested the hypothesis that gravity controls seed development via modulation of gases around the developing seeds, by studying how hypergravity affects the silique microenvironment and seed development. Using an in vitro silique maturation system, we sampled internal silique gases for 16 d late in the seed maturation sequence at 4 g or 1 g. The carbon dioxide level was significantly higher inside the 4-g siliques, and the immature seeds became heavier than those maturing at 1 g. Pollination and early embryo development were also studied by growing whole plants at 2 g or 4 g for 16 d inside chambers mounted on a large-diameter centrifuge. Each day the rotor was briefly stopped to permit manual pollination of flowers, thereby producing cohorts of same-aged siliques for comparison with stationary control material. The loss of starch and soluble carbohydrates during seed development was accelerated in hypergravity, with seeds developing at 4 g more advanced by 2 d than those at 1 g. Seeds produced at 4 g contained more lipid than those at 1 g. Taken together, these results indicate that hypergravity enhances gas availability to the developing embryos. Gravity's role in seed development is of importance to the space programme because of the plan to use plants for food production and habitat regeneration in extraterrestrial settings. These results are significant because they underscore the tight co-regulation of Brassica seed development and the atmosphere maintained inside the siliques.

Regenerative capacity of the planarian Girardia tigrina and the snail Helix lucorum exposed to microgravity during an orbital flight on board the international space station

244 A better understanding of the role of gravity in various processes vitally important for terrestrial organisms is a paradigm of space biology. In particular, regeneration of injured or lost organs and tissues is studied under the conditions of a spaceflight. The available experimental data on regenerative morphogenesis under microgravity are scarce and contradictory. As reported in [1‐3], amputated limbs, tails, retina, and crystalline lens of tritons Pleurodeles waltlii regenerated rapidly under microgravity. Other authors [4] have reported that regeneration of triton stumps under microgravity is noticeably delayed as compared to the terrestrial control (the regenerated bones have atypical lamellar structure). It should be emphasized that, in these experiments conducted on board spacecrafts Bion and Photon, the orbital flight lasted for about 16 days, whereas regeneration was studied a long time after the return to Earth. In another experiment, two Wistar rats that remained under microgravity for two weeks displayed a delayed posttraumatic regeneration: the size of the callus was reduced, and a lower strength of bone fragment consolidation was observed after the surgical fracture of the fibula (diaphysis) made two days before launching of a biosatellite (a terrestrial group of animals served as a control) [5]. Regeneration of the freshwater planarian Girardia tigrina , both whole animals and fragments, as well as regeneration of eye tentacles in the snail Helix lucorum , was studied during the orbital flight of the International Space Station (ISS). G. tigrina is an asexual race: when an animal reaches a certain body size, the hind part of the body is gradually constricted to break away from the fore part. During several days, two new planarians

Starmaker Exhibits Properties of an Intrinsically Disordered Protein

Fish otoliths composed of calcium carbonate and an organic matrix play a primary role in gravity sensing and the perception of sound. Starmaker (Stm) was the first protein found to be capable of influencing the process of biomineralization of otoliths. Stm dictates the shape, size, and selection of calcium carbonate polymorphs in a concentration-dependent manner. To facilitate exploration of the molecular basis of Stm function, we have developed and optimized a protocol for efficient expression and purification of the homogeneous nontagged Stm. The homogeneous nontagged Stm corresponds to its functional form, which is devoid of a signal peptide. A comprehensive biochemical and biophysical analysis of recombinant Stm, along with in silico examinations, indicate for the first time that Stm exhibits the properties of intrinsically disordered proteins. The functional significance of Stm having intrinsically disordered protein properties and its possible role in controlling the formation of otoliths is discussed.

Influence of Upstream Conditions and Gravity on Highly Inertial Thin-Film Flow

Steady two-dimensional thin-film flow of a Newtonian fluid is examined in this theoretical study. The influence of exit conditions and gravity is examined in detail. The considered flow is of moderately high inertia. The flow is dictated by the thin-film equations of boundary layer type, which are solved by expanding the flow field in orthonormal modes in the transverse direction and using Galerkin projection method, combined with integration along the flow direction. Three types of exit conditions are investigated, namely, parabolic, semiparabolic, and uniform flow. It is found that the type of exit conditions has a significant effect on the development of the free surface and flow field near the exit. While for the parabolic velocity profile at the exit, the free surface exhibits a local depression, for semiparabolic and uniform velocity profiles, the height of the film increases monotonically with streamwise position. In order to examine the influence of gravity, the flow is studied down a vertical wall as well as over a horizontal wall. The role of gravity is different for the two types of wall orientation. It is found that for the horizontal wall, a hydraulic-jump-like structure is formed and the flow further downstream exhibits a shock. The influence of exit conditions on shock formation is examined in detail.

Hydrogen atom in Palatini theories of gravity

We study the effects that the gravitational interaction of $f(R)$ theories of gravity in Palatini formalism has on the stationary states of the hydrogen atom. We show that the role of gravity in this system is very important for Lagrangians $f(R)$ with terms that grow at low curvatures, which have been proposed to explain the accelerated expansion rate of the universe. In fact, new gravitationally induced terms in the atomic Hamiltonian generate a strong backreaction that is incompatible with the very existence of bound states. In fact, in the $1/R$ model, hydrogen disintegrates in less than two hours. The universe that we observe is, therefore, incompatible with that kind of gravitational interaction. Lagrangians with high curvature corrections do not lead to such instabilities.

Core Mass Function: The Role of Gravity

We analyze the mass distribution of cores formed in an isothermal, magnetized, turbulent, and self-gravitating nearly critical molecular cloud model. Cores are identified at two density threshold levels. Our main results are that the presence of self-gravity modifies the slopes of the core mass function (CMF) at the high-mass end. At low thresholds, the slope is shallower than the one predicted by pure turbulent fragmentation. The shallowness of the slope is due to the effects of core coalescence and gas accretion. Most importantly, the slope of the CMF at the high-mass end steepens when cores are selected at higher density thresholds, or alternatively, if the CMF is fitted with a lognormal function, the width of the lognormal distribution decreases with increasing threshold. This is due to the fact that gravity plays a more important role in denser structures selected at higher density threshold and leads to the conclusion that the role of gravity is essential in generating a CMF that bears more resemblance to the IMF when cores are selected with an increasing density threshold in the observations.

Einstein–Yang–Mills solitons: The role of gravity

The canonical Bartnik–McKinnon solitons are regular solutions of the coupled Einstein–Yang–Mills system in which gravity may balance the repulsive nature of the Yang–Mills field. We examine the role played by gravity in balancing the system and determine its strength. In particular, we obtain an analytic lower bound on the fundamental mass-to-radius ratio, maxr{2m(r)/r}>2/3, which is a necessary condition for the existence of globally regular Einstein–Yang–Mills solitons. Our analytical results are in accord with numerical calculations.

A numerical study of the dynamics of the surface grain in a granular chain and the role of gravity

We revisit the dynamical behavior of particles in a chain of spherical elastic grains, where the system is assumed to be placed in such a way that the grains suffer progressive loading as function of depth due to the presence of the gravitational acceleration g . Here we address, for the first time, the dynamics of the surface grain in this rather well studied problem (see [R.S. Sinkovits, S. Sen, Phys. Rev. Lett. 74 (1995) 2686; J. Hong, J.Y. Ji, H. Kim, Phys. Rev. Lett. 82 (1999) 3058]) and make predictions that may be verified experimentally by monitoring the dynamics of a single edge grain. When g → 0 , the surface grain dynamics can be associated with the problem of propagation of solitary waves in the chain. When g > 0 , the dynamics of the surface grain turns out to be dramatically different, reflective of the very different dynamics exhibited by the grains in a gravitationally loaded chain. As we shall see, these studies provide a necessary first step towards developing an understanding of a difficult but important problem in physics and engineering — namely, the dynamics of the surface grains of a gravitationally loaded close-packed granular bed.

Effect of gravity on the growth of vertical single-walled carbon nanotubes in a chemical vapor deposition process

Vertically aligned single-walled carbon nanotubes (SWCNTs) can be fabricated on the Co∕Si(100) substrate in a gravity assisted chemical vapor deposition process. The Co∕Si(100) substrate is tilted such that its surface normal points downwards in the chemical vapor deposition process. All the SWCNTs are lined up with the direction of gravity. The length of SWCNTs increases with growth time. A modified vapor-liquid-solid mechanism is proposed to explain the role of gravity in the precipitation of SWCNTs and in the lineup behavior of SWCNTs.

The role of gravity in the motion of plasma arcs inside ‘Plasma Balls’: An investigation in the NASA reduced gravity student flight opportunities program

We present results of an investigation performed by undergraduates as part of the NASA Reduced Gravity Student Flight Opportunities Program. The goal was to determine the importance of buoyancy-driven convection on the motion of plasma streamers in commercially available ‘plasma balls.’ The motion of the plasma streamers was studied as a function of acceleration level provided by drop experiments and parabolic flights on NASA’s KC-135. We determined that there were more than two contributing factors to the motion of plasma arcs: buoyancy-driven convection and magnetic fields from the Tesla coil that generated the high voltage in the plasma ball. When the plasma ball was isolated from the Tesla coil, the streamer velocities were higher. The velocities were nonzero at zero acceleration level and increased with increasing acceleration level. The nonzero velocity at zero acceleration could be the result of residual acceleration in the KC-135 or more likely an intrinsic aspect of this system.

The effects of microgravity on the development of surface righting in rats.

The active interaction of neonatal animals with their environment has been shown to be a decisive factor in the postnatal development of sensory systems, which demonstrates a critical period in their maturation. The direct demonstration of such a dependence on the rearing environment has not been demonstrated for motor system function. Nor has the role of gravity in mammalian motor system development been investigated. Here we report the results of two space flight missions examining the effect of removing gravity on the development of surface righting. Since the essential stimulus that drives this synergy, gravitation, was missing, righting did not occur while the animals were in the microgravity environment. We hypothesize that this absence of contextual motor experience arrested the maturation of the motor tactics for surface righting. Such effects were permanent in rats spending 16 days (from postnatal day (P), P14 to P30), but were transient in animals spending nine days (from P15 to P24) in microgravity. Thus, active, contextual interaction with the environment during a critical period of development is necessary for the postnatal maturation of motor tactics as exemplified by surface righting, and such events must occur within a particular time period. Further, Earth's gravitational field is not assumed by the developing motor system. Rather, postnatal motor system development is appropriate to the gravitational field in which the animal is reared.

The Role of Gravity in Adaptation of the Vertical Angular Vestibulo‐Ocular Reflex

The gain of the vertical angular vestibulo-ocular reflex (aVOR) was adapted in side-down and prone positions in two monkeys and tested in four planes: left-/right-side down; forward/backward; and two intermediate planes that lie approximately in the planes of the vertical semicircular canal pairs, left anterior/right posterior (LA/RP) and right anterior/left posterior (RA/LP). Gain changes, expressed as a percent of preadapted values, were plotted as a function of head orientation in the planes of tilt, and fitted with sinusoids to obtain the gravity-dependent (amplitude) and gravity-independent (bias) components of adaptation. Gravity-dependent gain changes were always maximal when tested in a plane that included the head orientation in which the aVOR gain had been adapted. Changes were minimal when the head was tilted in a plane orthogonal to the plane of adaptation, and were smaller but still significant when tested in the two intermediate planes. Gravity-independent VOR gain changes were uniform over all planes of head tilt. Thus, the gravity-dependent and gravity-independent components could be separated experimentally. The aVOR gain changes from the head tilts in different directions were utilized to reconstruct the gain changes in three dimensions. They formed a continuous surface, which peaked in and around the position of adaptation. These studies support the postulate that gain adaptation has both gravity-independent and gravity-dependent components, and further show that these gain changes have a three-dimensional structure. These results are similar to those in humans, indicating that the gravity-dependent adaptation of the aVOR is likely to be a common phenomenon across species.