Effect Of Gravity Research Articles

Advanced Deep-Plane Rhytidectomy: Advantages for Neck Treatment and Volumization of the Midface.

The aged neck is the most common motivator for patients seeking facial rejuvenation. Unlike the deflated midface, surgical treatment is still the gold standard for optimal outcomes. It is our view that the majority etiology of both the aged neck and deflated midface is gravity's effects on the superficial soft tissue envelope, leading to soft tissue redundancy. It is also our view that the deep-plane rhytidectomy is supported by anatomy, embryology, and clinical evidence as the best methodology to treat soft tissue redundancy without producing the aesthetic and longevity issues associated with superficial musculoaponeurotic system techniques. As one of the early pioneers in deep-plane rhytidectomy, the lead author will define contemporary advances in deep-plane technique such as dissection entry point, flap design, and flap fixation concepts that allow aggressive approach to treating both the aged neck and deflated midface.

Self-assembly of lamellae by elastocapillarity in the presence of gravity: experiments and modeling

Abstract Elastocapillarity describes the self-organization of elastic structures under liquid surface forces, for applications to micro- and nano scale self-assembly. It has recently become evident that precise prediction of elastocapillary self-assembly is challenged by the various phenomena arising due to fluid flow. In this study, we present experiments and a corresponding reduced-order model for the dynamic coalescence of flexible lamellae arrays. Vertical arrays of elastomeric lamellae attached to a substrate at the bottom are fabricated using 3D printed molds. The lamellae have sub-mm thickness and a few millimeters height, a size scale that cannot be achieved by traditional microfabrication. The gaps between the elastic lamellae are filled with liquid while the tips of the lamellae, which are at the top with respect to gravity, are initially fixed, then they are released which leads to their spontaneous bending and coalescence. We study the cluster size as a function of system variables both experimentally and numerically. The solid lamellae are modeled as discrete rigid elements connected by torsional springs to the substrate, while the fluid flow uses lubrication theory and capillarity. Importantly, the model incorporates the gravitational forces to effectively capture the systems' behavior ranging from the microscale with negligible gravity effect to the macroscale where gravity significantly influences the dynamics. We further derive a linearized continuum model from our nonlinear formulation, providing an analytical scaling law for the lamellae cluster size. This work is relevant for new polymorphic fins and lamellae devices, capillary self-folding and origami.

New stellar age estimates using SPInS based on Gaia DR3 photometry and LAMOST DR8 abundances

Reliable stellar age estimates are fundamental for testing several problems in modern astrophysics, in particular since they set the timescales of Galactic dynamical and chemical evolution. In this study, we determine ages using only photometry and parallaxes, in combination with interstellar extinction maps, and spectroscopic metallicities and alpha abundances from the latest data release (DR8) of the LAMOST survey. In contrast with previous age estimates, we do not use spectroscopic effective temperatures or surface gravities, and thus we rely on the excellent precision and accuracy of the Gaia photometry. We use a new version of the publicly available SPInS code with improved features, including the on-the-fly computation of the autocorrelation time and the automatic convergence evaluation. We determine reliable age estimates for 35,096 and 243,768 sub-giant and main-sequence turn-off stars in the LAMOST DR8 low- and medium-resolution surveys with typical uncertainties smaller than 10<!PCT!>. In addition, we successfully test our method on more than 4,000 stars of 14 well-studied open and globular star clusters covering a wide range of ages, confirming the reliability of our age and uncertainty estimates.

Nonlinear waves in a sheared liquid film on a horizontal plane at small Reynolds numbers

The nonlinear waves in a sheared liquid film on a horizontal plate at small Reynolds numbers are examined by theoretical and numerical approaches. The analysis employs the long-wave approximation along with finite difference schemes. The results show that the surface tension can suppress disturbances and prevent the occurrence of singularities. While the film flow is driven by the shear stress on the interface, its instability highly depends on the magnitude and direction of gravity. Specifically, when the direction of gravity is opposite to the wall-normal direction, perturbations are stabilized by gravity. In contrast, when these two directions are the same, the gravitational force is destabilizing, and stationary travelling waves can exist if a balance is reached between the effects of gravity and surface tension. For the steady solitary waves, there are quasi-periodic oscillations occurring between two stationary points, indicating the presence of heteroclinic trajectories. For periodic waves, the evolutions are sensitive to several parameters and initial disturbances, while one steady-state wave exhibits a sine function-like behaviour.

Generalized analysis of a dust collapse in effective loop quantum gravity: Fate of shocks and covariance

Generalized analysis of a dust collapse in effective loop quantum gravity: Fate of shocks and covariance

Optical aspects of Born-Infeld BTZ black holes in massive gravity

We explore the dynamics of thin accretion disks, the radius of black hole shadows, observed intensities, and the visual characteristics of Born-Infeld BTZ black holes in massive gravity. We find out the relations for angular velocity, specific energy, and angular momentum of particles around the black hole. We observe that intense Born-Infeld electromagnetic effects lead to a reduction in the rotational motion of particles within the accretion disk, and the massive gravity slows down the orbital motion of these particles. We reveal that the influence of massive gravity parameter correlates with a reduction in the black hole’s shadow size, which suggests that massive gravity effects intensify the gravitational fields, thereby reducing the angular diameter of the shadows. On the other hand, a higher Born-Infeld parameter enlarges the black hole’s shadow, which manifests a visual relationship between the black hole’s physical dimensions and its gravitational influence. Moreover, we also uncover the optical characteristics of Born-Infeld BTZ black holes, which show that the Born-Infeld parameter greatly influences the electromagnetic field around the black hole, which affects energy distribution in the space. Finally, we observe that massive gravity significantly influences the spacetime structure near black holes, which is crucial for grasping gravitational lensing and the dynamics of accretion disks under such extreme conditions.

Validation of a phase-field approach for contact line hysteresis against a sloshing droplet case

AbstractUnderstanding liquid propellants behavior in microgravity conditions is critical for efficient spacecraft design. For a number of operations, ranging from engine restart to orbital propellant storage and transfer, insight is needed to characterize capillary-dominated flows. In such conditions, surface tension and wetting properties, including contact angle hysteresis, can greatly impact the fluid’s behavior and therefore spacecraft performance. Using experimental data from ESA Propulsion Laboratory, a contact line model for the Cahn–Hilliard phase-field method is validated. The case studied is that of a droplet confined between two oscillating plates, which aims to isolate and observe contact angle-driven physics, limiting the effect of gravity on the flow in a simple and reproducible way on ground. The contact line model allows for the prediction of contact line motion without requiring the computation of dynamic contact angles or contact line velocities, thus simplifying implementation and reducing computational overhead. For the validation, contact line pinning and motion under varying oscillation frequencies is investigated. Specifically, the length between the rear and front contact line edges, as well as the shape of the sloshing droplet are compared. The results show good agreement between simulations and experimental data, confirming the model’s accuracy in predicting contact line behavior and pinning.

A computationally efficient queue-based algorithm for simulating volume-controlled drainage under the influence of gravity on volumetric images of porous materials

Simulating non-wetting fluid invasion in volumetric images of porous materials is of broad interest in applications as diverse as electrochemical devices and CO2 sequestration. Among available methods, image-based algorithms offer much lower computational cost compared to direct numerical simulations. Recent work has extended image-based methods to incorporate more physics such as gravity and volume-controlled invasion. The present work combines these two developments to develop an image-based invasion percolation algorithm that incorporates the effect of gravity. Additionally, the presented algorithm was developed using a priority queue algorithm to drastically reduce the computational cost of the simulation. The priority queue-based method was validated against previous image-based methods both with and without the effect of gravity, showing identical results. It was also shown that the new method provides a speedup of 20X over the previous image-based methods. Finally, comparison with experimental results at three Bond numbers showed that the model can predict the real invasion process with a high accuracy with and without gravitational effects.

Physical Parameters and Properties of 20 Cold Brown Dwarfs in JWST

We present a comprehensive analysis of 20 T and Y dwarfs using spectroscopy from the Near-Infrared Spectrograph (NIRSpec) CLEAR/PRISM and Mid-Infrared Instrument (MIRI) low-resolution spectrometer instruments on the James Webb Space Telescope. To characterize the atmospheric parameters, we utilize two atmospheric model grids: the Sonora Elf Owl and ATMO2020++. The effective temperatures derived from the two models are relatively consistent, and metallicities are both close to solar values. However, significant discrepancies are found in other parameters, particularly in surface gravity, with the values obtained from the Sonora Elf Owl models typically being about 1 dex lower than those from the ATMO2020++ models. Further comparisons using the ATMO2020 models highlight that the adiabatic convective process introduced in the ATMO2020++ models has a significant impact on the determination of surface gravity. Using the fitted effective temperatures and absolute parallaxes from the literature, we derive radii for the brown dwarfs, which range from approximately 0.8–1.2 R Jup. The estimated masses and ages, derived using evolutionary tracks, indicate that most brown dwarfs in our sample have masses below 30 M Jup and are younger than 6 Gyr. Specifically, Y dwarfs have masses ranging from 2 to 20 M Jup and ages between 0.1 and 6.7 Gyr. In addition, we discuss the determination of atmospheric parameters using only NIRSpec or MIRI spectra. Comparisons with results from the combined spectra show that the effective temperatures and surface gravities derived solely from NIRSpec spectra are largely consistent with those obtained from the combined spectra.

Gaia/GSP-spec spectroscopic properties of γ Doradus pulsators

Context. The third Data Release of the ESA Gaia mission has provided a large sample of new gravity-mode pulsators, among which more than 11 600 are γ Dor stars. Aims. The goal of the present work is to present the spectroscopic parameters of these γ Dor pulsators estimated by the GSP-Spec module that analysed millions of Gaia spectra. Such a parametrisation could help confirm their γ Dor nature and provide their chemo-physical properties. Methods. The Galactic positions, kinematics, and orbital properties of these new Gaia pulsators were examined in order to define a sub-sample belonging to the Milky Way thin disc, in which these young stars should preferentially be found. The stellar luminosities, radii, and astrometric surface gravities were estimated without adopting any priors from uncertain stellar evolution models. These parameters, combined with the GSP-Spec effective temperatures, spectroscopic gravities, and metallicities were then validated by comparison with recent literature studies. Results. Most stars are found to belong to the Galactic thin disc, as expected. It is also found that the derived luminosities, radii, and astrometric surface gravities are high quality and have values typical of genuine γ Dor pulsators. Moreover, we show that Teff and [M/H] of pulsators with high enough S/N spectra or slow to moderate rotation rates are robust. This allowed to define a sub-sample of genuine slow-rotating Gaiaγ Dor pulsators. Their Teff were found to be between ∼6500 and ∼7800 K, log(g) is around 4.2, and the luminosities and stellar radii peak at ∼5 L⊙ and ∼1.7 R⊙, The median metallicity is close to the Solar value, although γ Dor with higher and lower metallicities by about ±0.5 dex were also identified. The [α/Fe] content is fully consistent with the chemical properties of the Galactic disc. Conclusions.Gaia/DR3 spectroscopic properties of γ Dor stars therefore confirm the nature of these pulsators and allow to chemo-physically parametrise a new large sample of such stars. Moreover, future Gaia data releases should drastically increase the number of γ Dor stars with parameters spectroscopically derived with good precision.

The Gaia-ESO survey: New spectroscopic binaries in the Milky Way

The survey (GES) is a large public spectroscopic survey that acquired spectra for more than stars across all major components of the Milky Way. In addition to atmospheric parameters and stellar abundances that have been derived in previous papers of this series, the GES spectra allow us to detect spectroscopic binaries with one (SB1), two (SB2), or more (SB$n 3$) components. The present paper discusses the statistics of GES SB$n 2$ after analysing GIRAFFE HR10 and HR21 spectra, amounting to unique Milky Way field targets. Cross-correlation functions (CCFs) have been re-computed thanks to a dozen spectral masks probing a range of effective temperatures ($ kelvin < T_ eff kelvin $), surface gravities ($1.0 < g < 4.7$), and metallicities ($-2.6 < Fe H < 0.3$). By optimising the mask choice for a given spectrum, the newly computed, so-called (NArrow CRoss-correlation Experiment) CCFs are narrower and allow more stellar components to be unblended than standard masks. The (Detection Of Extrema) extremum-finding code then selects the individual components and provides their radial velocities. From the sample of HR10 and HR21 spectra corresponding to objects the present study leads to the detection of SB2, ten SB3 (three of them being tentative), and two tentative SB4. In particular, compared to our previous study, the CCFs allowed us to multiply the number of SB2 candidates by $ The colour-magnitude diagram reveals, as expected, the shifted location of the SB2 main sequence. A comparison between the SB identified in DR3 and the ones detected in the present work was performed and the complementarity of the two censuses is discussed. An application to the mass-ratio determination is presented, and the mass-ratio distribution of the GES SB2 is discussed. When accounting for the SB2 detection rate, an SB2 frequency of $ percent $ is derived within the present stellar sample of mainly FGK-type stars. As primary outliers identified within the GES data, SB$n$ spectra produce a wealth of information and useful constraints for the binary population synthesis studies.

Construction of a ballistic model of the motion of uncontrolled cargo during its autonomous high-precision drop from a fixed-wing unmanned aerial vehicle

The object of this study is the process related to the fall of an uncontrolled cargo from a height of 400–600 meters relative to sea level in an air environment under the influence of gravity, air drag, and wind in the presence of an initial air speed of about 20 m/s. The study solves the task to build a ballistic model of the movement of an unguided cargo during autonomous high-precision dropping from an unmanned aerial vehicle of aircraft type. A system of equations was derived that explicitly describes the dependence of the cargo's travel speed and coordinates on time and takes into account the effect of gravity, air drag, and the influence of wind. The scope of application of the equations corresponds to drop heights of up to 400 m relative to the surface of the earth and the initial horizontal speed of the cargo up to 20 m/s. The resulting equations were analyzed using an example of a spherical load weighing 10 kg and the largest cross-sectional area of 7.1·10-2 m2 when it falls from heights of 200, 300, and 400 m relative to the earth's surface. In the absence of wind, the horizontal component of the load's speed at the moment of falling is ≈(13–15) m/s, and the vertical component is ≈(50–60) m/s. At the same time, the horizontal displacement of the load under the conditions of a weak crosswind can reach ≈(150–220) m. With a vertical wind speed profile, the equivalent constant wind speed can be determined, resulting in the same effect on the load as a variable speed wind. An algorithm for determining the point of unloading the cargo has been proposed. The cargo delivery error has been evaluated. The most important parameters are the flight time of the cargo and the drop height. In order to achieve a hit accuracy of ±5 m, an error in determining the time of the fall of the load is not more than ≈0.16 s, and an error in determining the height of the drop is not more than ±8 m

Steady and periodical heat-mass transfer behavior of mixed convection nanofluid with reduced gravity, radiation and activation energy effects

Significance of this study is to explore Arrhenius activation energy, microgravity, chemical reaction and porous medium effects on Darcy nanofluid over a stretching sheet with nonlinear thermal radiations. Purpose of this study is to enhance the lubrication efficiency, excessive heat reduction, surface roughness and tool wear in drilling, milling, grinding and cutting tools of machining procedures. Use of Brownian and thermophoretic nanoparticles in base liquid is very effective to reduce friction in tool-chip and tool-work interfaces, tool life ability and cooling ability through nanofluid minimum quantity lubrication in machining operations. A refined mathematical model is solved using dimensionless variables; oscillatory stokes conditions and primitive variables. The implicit form of finite difference method is applied for numerical results using Gaussian elimination approach. The numerical and physical outputs are secured using Gaussian elimination methodology in FORTRAN tool and TecPlot-360. Graphs are displayed by using numerical data in Tecplot-360 program. Impact of activation energy (AE), solar radiation (Rd), microgravity (RG), porosity (Ω), thermophoresis (NT), chemical reaction (Kr), Prandtl (Pr) and Schmidt factor (Sc) on oscillating frequency of heat and mass transport is depicted. Amplitude in fluid velocity, surface temperature and volume of concentration is enhanced as radiation, microgravity and activation energy increases. It is noted that the increasing amplitude in fluid velocity, temperature and fluid concentration is found with activation energy, radiation and buoyancy force effects. Steady behavior of skin friction and mass transport decreases as Darcy porous medium and reaction rate decreases. Frequency of oscillating skin friction and oscillating heat transfer increases as Schmidt and Prandtl coefficient increases. Fluctuations and amplitude in the frequency of heat and mass transport enhances as thermophoretic nanoparticle enhances.

Development and implementation of a simulated microgravity setup for edible cyanobacteria

Regenerative life support systems for space crews recycle waste into water, food, and oxygen using different organisms. The European Space Agency’s MELiSSA program uses the cyanobacterium Limnospira indica PCC8005 for air revitalization and food production. Before space use, components’ compatibility with reduced gravity was tested. This study introduced a ground analog for microgravity experiments with oxygenic cyanobacteria under continuous illumination, using a random positioning machine (RPM) setup. L. indica PCC8005 grew slower under low-shear simulated microgravity, with proteome analysis revealing downregulation of ribosomal proteins, glutamine synthase, and nitrate uptake transporters, and upregulation of gas vesicle, photosystem I and II, and carboxysome proteins. Results suggested inhibition due to high oxygen partial pressure, causing carbon limitation when cultivated in low-shear simulated microgravity. A thicker stagnant fluid boundary layer reducing oxygen release in simulated microgravity was observed. These findings validate this RPM setup for testing the effects of non-terrestrial gravity on photosynthetic microorganisms.

Inertial effects on free surface pumping with an undulating surface

Free surface flows driven by boundary undulations are observed in many biological phenomena, including the feeding and locomotion of water snails. To simulate the feeding strategy of apple snails, we develop a centimetric robotic undulator that drives a thin viscous film of liquid with the wave speed $V_w$ . Our experimental results demonstrate that the behaviour of the net fluid flux $Q$ strongly depends on the Reynolds number $Re$ . Specifically, in the limit of vanishing $Re$ , we observe that $Q$ varies non-monotonically with $V_w$ , which has been successfully rationalised by Pandey et al. (Nat. Commun., vol. 14, no. 1, 2023, p. 7735) with the lubrication model. By contrast, in the regime of finite inertia ( ${Re} \sim O(1)$ ), the fluid flux continues to increase with $V_w$ and completely deviates from the prediction of lubrication theory. To explain the inertia-enhanced pumping rate, we build a thin-film, two-dimensional model via the asymptotic expansion in which we linearise the effects of inertia. Our model results match the experimental data with no fitting parameters and also show the connection to the corresponding free surface shapes $h_2$ . Going beyond the experimental data, we derive analytical expressions of $Q$ and $h_2$ , which allow us to decouple the effects of inertia, gravity, viscosity and surface tension on free surface pumping over a wide range of parameter space.

Well-posedness and stability for the two-phase periodic quasistationary Stokes flow

The two-phase horizontally periodic quasistationary Stokes flow in \mathbb{R}^{2} , describing the motion of two immiscible fluids with equal viscosities that are separated by a sharp interface, parameterized as the graph of a function f=f(t) , is considered in the general case when both gravity and surface tension effects are included. Using potential theory, the moving boundary problem is formulated as a fully nonlinear and nonlocal parabolic problem for the function f . Based on abstract parabolic theory, it is shown that the problem is well-posed in all subcritical spaces \mathrm{H}^{r}(\mathbb{S}) , with r\in(3/2,2) . Moreover, the stability properties of the flat equilibria are analyzed in dependence on the physical properties of the fluids.

Quantum gravity phenomenology and the blackbody radiation

Abstract We analyze the blackbody radiation problem in the presence of quantum gravity effects encoded in modified dispersion relations. The spectral radiance and the generalized Stefan-Boltzmann law are studied in this context. Furthermore, the regime of low temperatures is also contemplated, where features related to the blackbody thermal laws and the thermodynamic quantities such as energy, pressure, entropy, and specific heat are obtained. Possible implications in compact objects such as neutron stars are also discussed.

Research on the Mechanism of Femtosecond Laser Ablation Concave-Convex Microstructure Transformation.

The phenomenon of femtosecond laser ablation of convex structures from the bottom to the top is interesting. In this study, AZ31B magnesium alloy was used as the substrate to analyze the impact of the laser pulse energy and scanning speed on the morphology of concave-convex microstructures. Subsequently, a unified two-dimensional numerical model incorporating solid, liquid, and gas phases was established, and combined with experimental data, the mechanism and formation process of concave-convex transformation in magnesium alloy under laser ablation were revealed. The results indicate that the transition from concave to convex structures is significantly influenced by the laser scanning speed, whereas the laser pulse energy primarily affects the shape and size of the convex structures. During the ablation process, molten material is expelled and gradually accumulates on both sides of the ablation groove under the action of the recoil pressure. During cooling, the molten material at both ends of the groove merges to form protrusions under the combined effects of internal negative pressure, gravity, and Marangoni forces. Moreover, this method of femtosecond laser ablation for generating convex structures deviates from the traditional single-texture approach to concave structures, potentially broadening the application of laser composite processing surfaces.

Effect of surface roughness on the liquid bridge between two rigid spheres

We aimed to investigate the impact of surface roughness on liquid bridges between spherical particles. Sandblasting was used to control the particle size and produce glass beads and plates with different surface roughness. First, by measuring the advancing and receding contact angles of droplets on different rough surfaces, we analyzed the effects of surface roughness on wettability and hysteresis. Next, we used a custom-made liquid-bridge stretching device to measure the capillary forces of the liquid bridges between spherical particles with different surface roughness values. A charge-coupled device camera acquisition system was set up to capture the morphological changes of the liquid bridge during stretching, and Image View software was used to extract the morphological parameters of the liquid bridge. Theoretically, we reasonably simplified and solved the differential equations for the liquid bridge morphology and used the Young–Laplace equation to calculate the theoretical capillary force of the liquid bridge, providing an in-depth analysis of the influence of surface roughness on the capillary force. Finally, we studied the impact of surface roughness on the volume ratio of the liquid bridge during static stretching and the residual liquid remaining after the liquid bridge breaks. Experimental results indicated that, as the surface roughness increased, the hydrophobicity and wettability hysteresis of the solid surface also increased. The increased hydrophobicity of the surface reduces the solid-liquid contact area of the liquid bridges between the particles, making it easier to form “columnar” or “convex” liquid bridges. Additionally, the enhanced wettability hysteresis causes the solid-liquid contact boundary to lag during the stretching of the liquid bridge, resulting in a decrease in the solid-liquid contact angle. These factors directly alter the geometric shape of liquid bridges during static stretching, thereby affecting capillary forces. Meanwhile, the increase in surface roughness weakens the effect of gravity on the morphology of the liquid bridge, resulting in less liquid mass remaining on the lower sphere after the liquid bridge breaks as the surface becomes rougher.

Gravity-guided snapping sequence in 3D modular multistable metamaterials

The snapping sequence of multistable metamaterials is critical for their applications in elastic wave control and energy release. Despite being a fundamental property, the effect of gravity on the snapping sequence has never been studied. This paper investigates the mechanical mechanism how structural gravity affects the snapping sequence of multistable metamaterials to construct deterministic static and dynamic snapping sequences. A biaxial snap-through availability three-dimensional (3D) modular multistable metamaterial (MMM) is developed. The 3D MMM is assembled from unit cells consisting of a dismountable middle bar (M-bar) and a fixed frame containing two bistable curved beams. Except experimental tests and numerical simulations, analytical analyses are also conducted to verify the snapping sequence induced by gravity in the 3D MMM. In addition, given that the M-bar is dismountable, the effects of its length on the mechanical properties and the impact resistance of the 3D MMM are discussed in detail. It is found that gravity can guide both static and dynamic deterministic snapping sequences of the 3D MMM to optimize the process of elastic wave propagation and energy release, and the proposed 3D MMM can enhance structural impact resistance through elastic deformations.