Effect Of Gravity Research Articles

Effect of Mean Specific Gravity on Combustion Characteristics of Selected High Ash Indian Coal

Effect of Mean Specific Gravity on Combustion Characteristics of Selected High Ash Indian Coal

Quantum gravity effects on dark matter and gravitational waves

We explore how quantum gravity effects, manifested through the breaking of discrete symmetry responsible for both dark matter and domain walls, can have observational effects through cosmic microwave background observations and gravitational waves. To illustrate the idea we consider a simple model with two scalar fields and two Z2 symmetries, one being responsible for dark matter stability, and the other spontaneously broken and responsible for domain walls, where both symmetries are assumed to be explicitly broken by quantum gravity effects. We show the recent gravitational wave spectrum observed by several pulsar timing array projects can help constrain such effects. Published by the American Physical Society 2024

Classification and parameterization of a large Gaia sample of white dwarfs using XP spectra

Context. The latest Gaia data release in July 2022, DR3, in addition to the refinement of the astrometric and photometric parameters from DR2, added a number of important data products to those available in earlier releases, including radial velocity data, information on stellar multiplicity, and XP spectra of a selected sample of stars. Gaia has proved to be an important search tool for white dwarf stars, which are readily identifiable from their absolute G magnitudes as low luminosity objects in the Hertzsprung–Russell (H–R) diagram. Each data release has yielded large catalogs of white dwarfs, containing several hundred thousand objects, far in excess of the numbers known from all previous surveys (∼40 000). While the normal Gaia photometry (G, GBP, and GRP bands) and astrometry can be used to identify white dwarfs with high confidence, it is much more difficult to parameterize the stars and determine the white dwarf spectral type from this information alone. Observing all stars in these catalogs with follow-up spectroscopy and photometry is also a huge logistical challenge with current facilities. Aims. The availability of the XP spectra and synthetic photometry presents an opportunity for a more detailed spectral classification and measurement of the effective temperature and surface gravity of Gaia white dwarfs. Methods. A magnitude limit of G < 17.6 was applied to the routine production of XP spectra for Gaia sources, which would have excluded most white dwarfs. Therefore, we created a catalog of 100 000 high-quality white dwarf identifications for which XP spectra were processed, with a magnitude limit of G < 20.5. Synthetic photometry was computed for all these stars, from the XP spectra, in Johnson, SDSS, and J-PAS, published as the Gaia Synthetic Photometry Catalog – White Dwarfs (GSPC-WD). We took this catalog and applied machine learning techniques to provide a classification of all the stars from the XP spectra. We have then applied an automated spectral fitting program, with χ-squared minimization, to measure their physical parameters (effective temperature and log g) from which we could estimate the white dwarf masses and radii. Results. We present the results of this work, demonstrating the power of being able to classify and parameterize such a large sample of ≈100 000 stars. We describe what we can learn about the white dwarf population from this dataset. We also explored the uncertainties in the process and the limitations of the dataset.

Thermo-Fluidic Analysis of Pulsating Heat Pipes Charged with Water-Based Immiscible Fluid Pairs

Immiscible fluids may provide operational flexibility for pulsating heat pipes (PHPs) due to thermo-hydrodynamic diversity lead by each pure component. In this regard, present paper focuses on the thermo-fluidic analysis of non-uniform pulsating heat pipes charged with water-based immiscible fluid pairs. Research parameters cover gravity effect via the inclination angles (IA) of 0o and 90o, and fluid pair effect via two different water-based immiscible binary fluids as Water (W) – Hexane (H), and Water (W) – Pentane (P). The volumetric mixing ratios are W:H=1:1, 1:4, 4:1, 1:0, 0:1, and W:P=1:1, 1:4, 4:1, 1:0, 0:1; and the non-uniform flat plate type pulsating heat pipe (FP-CLPHP) has alternating-sequence parallel channels. The experiments are performed at the filling ratio of 40% (FR=40%), and flow phenomena is visualized. As some conclusions; at vertical orientation, the FP-CLPHPs having binary fluids of water-pentane show better thermal performance compared to the pure counterparts. Especially, the heat transfer characteristics of W:P=1:1 are the best ones among all the pure and binary fluids. On the other hand, as a conclusion of combination of non-uniform design and suitable thermophysical properties, the FP-CLPHPs charged with pure pentane, pure hexane or binary fluid of W:P=1:4 can work independent from gravitational force.

Modality-Independent Effect of Gravity in Shaping the Internal Representation of 3D Space for Visual and Haptic Object Perception.

Visual and haptic perceptions of 3D shape are plagued by distortions, which are influenced by nonvisual factors, such as gravitational vestibular signals. Whether gravity acts directly on the visual or haptic systems or at a higher, modality-independent level of information processing remains unknown. To test these hypotheses, we examined visual and haptic 3D shape perception by asking male and female human subjects to perform a "squaring" task in upright and supine postures and in microgravity. Subjects adjusted one edge of a 3D object to match the length of another in each of the three canonical reference planes, and we recorded the matching errors to obtain a characterization of the perceived 3D shape. The results show opposing, body-centered patterns of errors for visual and haptic modalities, whose amplitudes are negatively correlated, suggesting that they arise in distinct, modality-specific representations that are nevertheless linked at some level. On the other hand, weightlessness significantly modulated both visual and haptic perceptual distortions in the same way, indicating a common, modality-independent origin for gravity's effects. Overall, our findings show a link between modality-specific visual and haptic perceptual distortions and demonstrate a role of gravity-related signals on a modality-independent internal representation of the body and peripersonal 3D space used to interpret incoming sensory inputs.

Rounded-corners-induced re-entrant non-occlusion in a horizontal tube

Keeping a tube from being plugged by a fluid is an important process in applications. An interesting re-entrant phenomenon for the capillary state with the occluding state sandwiching the non-occluding state from both the high- and low-Bond-number regions can appear by inserting a rod into a horizontal tube at an eccentric position (Tan et al., J. Fluid Mech, vol. 946, 2022, A7). Containers with rounded corners are very common. We theoretically investigate a situation for a horizontal open tube with rounded corner(s). The results show that a re-entrant non-occlusion at a contact angle can also appear without the insertion of any object. The competition between the rounded corner wetting/non-wetting effect and gravity effect can lead to a re-entrant non-occlusion. The re-entrant non-occlusion is affected by the shape and orientation of the rounded corner(s). For a tube with only one rounded corner, the re-entrant non-occlusion exists when the rounded corner has a not-so-large corner radius and is not in a landscape orientation. For a tube with two (or more) rounded corners, the corner(s) with the strongest corner effect will determine the existence or non-existence of the re-entrant non-occlusion. This paper provides an effective scheme for designing a high-performance capillary with corners that are not easily occluded by a fluid and removing fluid blockage from a capillary in optofluidic/microfluidic applications.

Self-Adaptive Rapid Thermal Conductive Fabrics Based on Hygroscopic Shrinkage Response for Personal Cooling and Drying.

Advanced fabrics with thermal wet management capability as low energy consumption media contribute to personal cooling and drying. Nevertheless, it remains a great challenge to obtain intelligent fabrics with adjustable thermal conductivity (TC) capable of bridging the supply and demand between human body temperature and self-adaptive thermal conduction. Herein, we report hygroscopic-shrinkage nanofiber-based fabrics with excellent moisture sensitivity and significant volume shrinkage, which benefits the construction of high-density thermal conductive pathways by absorbing sweat, with a maximum sweat absorption rate reaching up to 1781%. The TC of the shrunken fabric is significantly increased from the initial 0.102 to 0.731 W·m-1 K-1 with a volume shrinkage rate of 89% due to the synergistic effect of van der Waals force, capillary force, viscous resistance, and gravity. Besides, an enhanced TC of the resulting fabrics facilitates rapid heat transfer to the environments. By capturing the surface temperature variations of the fabric after shrinkage and commercially available cotton/Coolmax, we obtained the fabric that releases the same amount of heat in a shorter period of time (3.3 s). With its exceptional personal thermal and wet management properties, this study paves the way for designing new-generation intelligent fabrics capable of creating more comfortable microclimates.

Spectroscopic Distance, Mass, and Age Estimations for APOGEE DR17

We derive distances and masses of stars from the Sloan Digital Sky Survey (SDSS) Apache Point Observatory Galactic Evolution Experiment Data Release 17 using simple neural networks. Training data for distances comes from Gaia EDR3, supplemented by literature distances for star clusters. For masses, the network is trained using asteroseismic masses for evolved stars and isochrone masses for main-sequence stars. The models are trained on effective temperature, surface gravity, metallicity, and carbon and nitrogen abundances. We found that our distance predictions have median fractional errors that range from ≈20% at low log g and ≈10% at higher log g with a standard deviation of ≈11%. The mass predictions have a standard deviation of ±12%. Using the masses, we derive ages for evolved stars based on the correspondence between mass and age for giant stars given by isochrones. The results are compiled into a Value Added Catalog called DistMass that contains distances and masses for 733,901 independent spectra, plus ages for 396,548 evolved stars.

Peculiar properties in quasinormal spectra from loop quantum gravity effect

Peculiar properties in quasinormal spectra from loop quantum gravity effect

A possible solution to the Hubble tension from quantum gravity

We investigate the relevance of quantum gravity during inflation to address the Hubble tension that arises from Planck 2018 and supernova H0 for the equation of state data sets. We show that the effect of quantum gravity during inflation can increase the rate of change of H0 , thereby accounting for a wide range of observed H0 . Further, we show that due to the quantum gravity effect on inflation, the temperature at the onset of reheating can be lower than the standard case, causing delays in the reheating process. The role of quantum gravity is inevitable in settling the Hubble tension. The results of the present study may find use in resolving the Hubble tension, in validating inflationary model and quantum gravity.

Radio resource management Satellite Communication Networks MCDM Method

A communications satellite would be an artificial satellite that creates a channel here for the transmission of a communication through a transponder between a sender and a recipient located at various locations on Earth. Communications via satellite are used in telecommunications, radio, broadcast, computer, and military applications. Satellites offer three different kinds of communication services: data communication, broadcasting, and telephone. Lower Geostationary satellite, Networks for Low-Earth-orbiting (LEO) and Medium Eccentricity Orbit (MEO) are the three different types of satellite networks. A satellite system or a portion of a satellite system with only one satellite in it and a working ground station is known as a satellite network. Models 1, 2, and 3. A satellite network is a system that uses satellite technology to transmit media services to recipients. The two main components of communication systems are the ground component, which consists of stationary or mobility transmissions, receptions, and ancillary equipment, and indeed the space component, which primarily consists of the satellite. In addition to offering in-flight communications, satellites are frequently the primary voice communication method in rural areas and places where telephone connections have been disrupted during a catastrophe. Satellites are also a major source of time for cell phones and pagers. With nine operating communications satellites in geo-stationary orbit, one of the largest domestic satellite communications networks in the Asia-Pacific region is the Indian National Television (INSAT) system. Radio and cable television are provided to us. They allow us to use our mobile phones to make long distance calls. So that we can find ourselves and get directions, they offer us the Global Positioning System (GPS) our destinations. Satellites offer data on Earth's atmosphere, seas, land, and clouds. They can also see smoke, volcanoes, and forest fires. All of this data aids in weather and climate prediction. Farmers benefit from knowing what crops to plant. PROMETHEE (Priority Ranking System Method for Enrichment Assessments) About PROMETHEE methods and usage to uncover current research to classify and explain A classification scheme and a comprehensive literature review is presented. Alternative is Laser communication, optical networks, satellite optical communication, vibrations and satellite network. Evaluation parameters are Solar Radiation Pressure, Thermal Bending, Micro Meteorite impacts, Solar and Lunar Gravity and Earth oblations effects. Vibrations are got the first rank whereas is the Optical networks are having the Lowest rank. Satellite Communication Networks for using the analysis of PROMETHEE Method. Vibrations is got the first rank whereas is the Optical networks is having the Lowest rank.

Features of anisotropic compact stars in rastall teleparallel gravity via linear equation of state

This paper aims to discuss the model of compact stars based on spherically symmetric spacetime, with a focus on the gravitational effects of Rastall teleparallel gravity, where T represents torsion and λ represents the Rastall parameter. In this study, we evaluate the spherically symmetric spacetime component e a(r) in terms of e b(r) using the linear equation of state p r = β ρ + γ, while the other component e b(r) is assumed from the literature. The paper delves into a detailed analysis of various properties of compact stars such as energy density profile, pressure components, gradients profiles, anisotropic conduct, energy limits, equation of state profiles, velocities of sound profiles, TOV equation profiles, and compactification profile. We use the well-known junction conditions to facilitate the evaluation of the unknown parameters, taking the standard Schwarzschild metric as the outer spacetime. Through detailed analysis in graphical form, we demonstrate that the model showing the anisotropic conduct of stellar objects is viably legitimate, regular, and stable. Overall, the paper provides a comprehensive analysis of the properties of compact stars, which will undoubtedly contribute to our understanding of these astrophysical phenomena.

Effect of cryogenic feed line thermal mass distribution and orientation on chill-down performance

Chilldown performance of cryogenic systems is highly influenced by parameters like feed line orientation, thermal mass of the feed system and its distribution, mass flux of the cryogen and heat in-leak. In this work, the impact of feed line orientation and mass flux of cryogen on chilldown is evaluated through a parameter defined as Chilldown Performance Index. A set of experimental data generated with Liquid Nitrogen employing a test section insulated with poly-isocynurate foam is used for this study. Chilldown Performance Index is found to be lower with downward inclination upto 60° downward orientation of test section as compared to that of horizontal orientation. Beyond this, at 90° downward orientation, it is seen to be better as compared to 60° orientation. Chilldown performance improves significantly with upward inclination of test section. Chilldown time is found to be highly sensitive to mass flux, whereas effect on Chilldown Performance Index is not so significant. Experiments also show that chilldown performance is significantly influenced by the distribution of feed line thermal mass. Chilldown is faster in experiments with higher thermal mass distributed near to the inlet to the test section as compared to the case wherein they are distributed near to the exit of the test section. Flow visualisation studies are also conducted employing a vacuum jacketed view glass made of borosilicate material to capture the flow structure prevailing in experiments with different upward and downward orientation and to assess its influence on chilldown. Flow structure is observed to be significantly different in experiments with upward inclination, compared to those with horizontal and downward orientation. Observations made with upward inclination, show the existence of plug or slug flow in the test section, leading to faster chilldown. Flow pattern observed in experiments with 30° and 45° downward orientation is also different compared to other orientations, as liquid flow is mostly confined to the core of the test section, due to gravity effects.

Performance evaluation of PSO-PID and PSO-FLC for continuum robot’s developed modeling and control

Continuum robots are complex structures that require sophisticated modeling and control methods to achieve accurate position and motion tracking along desired trajectories. They are highly coupled, nonlinear systems with multiple degrees of freedom that pose a significant challenge for conventional approaches. In this paper, we propose a system dynamic model based on the Euler–Lagrange formulation with the assumption of piecewise constant curvature (PCC), where we accounts for the elasticity and gravity effects of the continuum robot. We also develop and apply a particle swarm optimization (PSO) algorithm to optimize the parameters of our developed controllers: an inverse dynamic proportional integral derivative (PID) controller and an inverse dynamic fuzzy logic controller (FLC), where we use the integral time of absolute error (ITAE) as the objective function for the PSO algorithm. We validate our proposed model and optimized controllers through different designed trajectories, simulated using our developed unique animated MATLAB simulation. The results show that the PSO-PID controller improves the rise time, overshoot percentage, and settling time by 16.3%, 31.1%, and 64.9%, respectively, compared to the PID controller without PSO. The PSO-FLC controller shows the best performance among all controllers, with a settling time of 0.7 s and a rise time of 0.4 s, leading to the highest level of precision in trajectory tracking. The ITAE error for the PSO-FLC controller is 11.4% and 29.9% lower than that of the PSO-PID and FLC controllers, respectively.

PySSED: an automated method of collating and fitting stellar spectral energy distributions

Abstract Stellar atmosphere modelling predicts the luminosity and temperature of a star, together with parameters such as the effective gravity and the metallicity, by reproducing the observed spectral energy distribution. Most observational data come from photometric surveys, using a variety of passbands. We herein present the Python Stellar Spectral Energy Distribution (PySSED) routine, designed to combine photometry from disparate catalogues, fit the luminosity and temperature of stars, and determine departures from stellar atmosphere models such as infrared or ultraviolet excess. We detail the routine’s operation, and present use-cases on both individual stars, stellar populations, and wider regions of the sky. PySSED benefits from fully automated processing, allowing fitting of arbitrarily large data sets at the rate of a few seconds per star.

Adaptive linear inversion of Moho topography in the Tibetan Plateau by combining gravity and seismic data

The Tibetan Plateau is a region where the Indian and Asian-European plates collide. A high-precision Moho topography model is important for the study of plate motion and internal tectonics of the Tibetan Plateau. However, previous gravity-based models failed in representing adequately the Moho topography because crustal effects and biases in the inversion parameters were not fully considered. To address these issues, we extracted the gravity effect caused by the crust using wavelet multi-scale analysis, and used an adaptive linear inversion method with available gravity and seismic data to estimate more accurate inversion parameters. With these two improvements, we inverted for a high-precision Moho topography model of the Tibetan Plateau. The results show that the majority of the Tibetan Plateau has a Moho depth of 60–70 km. The Moho depth in the center of the Qaidam Basin is about 50 km, and the Moho topography between the east and west of the basin has obvious undulations. The Moho depth of the Tarim Basin ranges from 38–50 km. While the undulation of Moho is limited in the center of the basin, obvious uplifts are shown in northern and southern basin. The plate driving force between the Tibetan Plateau and the Tarim Basin may be the primary cause of this phenomenon. By comparing the difference with the seismic data, we found that the RMS of our model is 2.8 km smaller than that of the CRUST 1.0 model, which shows that our model is more accurate.

Effects of altered gravity on growth and morphology in Wolffia globosa implications for bioregenerative life support systems and space-based agriculture

Understanding the response of plants to varied gravitational conditions is vital for developing effective food production in space bioregenerative life support systems. This study examines the impact of altered gravity conditions on the growth and morphological responses of Wolffia globosa (commonly known as “water lentils” or “duckweed”), assessing its potential as a space crop. Although an experiment testing the effect of simulated microgravity on Wolffia globosa has been previously conducted, for the first time, we investigated the effect of multiple gravity levels on the growth and morphological traits of Wolffia globosa plants. The plant responses to simulated microgravity, simulated partial gravity (Moon), and hypergravity environments were evaluated using random positioning machines and the large-diameter centrifuge. As hypothesized, we observed a slight reaction to different gravitational levels in the growth and morphological traits of Wolffia globosa. The relative growth rates (RGR) of plants subjected to simulated microgravity and partial gravity were reduced when compared to those in other gravity levels. The morphological analysis revealed differences in plant dimensions and frond length-to-width ratios under diverse gravity conditions. Our findings showed that Wolffia globosa is responsive to gravitational changes, with its growth and morphological adaptations being slightly influenced by varying gravitational environments. As for other crop species, growth was reduced by the microgravity conditions; however, RGR remained substantial at 0.33 a day. In conclusion, this study underscores the potential of Wolffia globosa as a space crop and its adaptability to diverse gravitational conditions, contributing to the development of sustainable food production and bioregenerative life support systems for future space exploration missions.

Experimental investigation on parameter optimization of liquid spectral beam splitter for continuous photocatalytic hydrogen production accompanied with photovoltaic power generation under solar full spectrum

Effective utilization of solar energy is of great significance for a sustainable future. Herein, we report a cascade system for hydrogen-electricity co-production (PH-PV) utilizing solar full spectrum. The output performance of the system can be precisely adjusted by controlling certain parameters of liquid spectral beam splitter (LSBS) which contains TiO2 nanoparticle suspension simultaneously generating hydrogen via a photocatalytic reaction process. Typically, the thickness of LSBS, the loading amount of TiO2, the flowrate of suspension and the light intensity have been investigated in detail. It is found that LSBS is necessary in our system as it could ensure the safe operation of PV while the light intensities larger than 8 suns. With the decrease of the thickness or loading amount of photocatalyst, more electricity could be produced by PV module but less hydrogen from PH module. Further increase of above two parameters simultaneously could lead to aggregation and settlement of particle suspension in LSBS, which is detrimental to the optical absorbance of the system. Besides, changing the flowrate will diversify the surface features of particles by shear-induced effect. At optimal flowrate, the particles in LSBS could exhibit oscillation characteristics under synergistic effect of shear force and gravity, which would lead to excellent light absorption and transmittance. Furthermore, an obvious gain for both hydrogen and electricity output and system efficiency could be obtained through increasing light intensity appropriately. Finally, the improved merit function (MF) was employed to evaluate the performance of hybrid system and more obvious effect of flowrate on MF value than other parameters was found. The optimal MF value of 3.07 was reached when flowrate was 60 mL/min. Our work is expected to provide important guidance for the optimization of PH-PV cascade system driven by outdoor direct solar energy.

Immediate effect of upright position on lumbar disc using multiposture MRI: Preliminary results.

Gravity loading on lumbar intervertebral discs (IVDs) is affected by body position. Although the long-term effects of gravity on IVDs have been reported, the immediate effects of gravity on IVDs remain unclear. We considered that changes in IVD structure in the upright and supine positions provided new diagnostic information. Therefore, we compared the apparent diffusion coefficient (ADC), transverse relaxation time (T2), and morphology of the lumbar spine between the quickly changing upright and supine positions using an original magnetic resonance imaging (MRI) system that can obtain images in any position (multiposture MRI). On a 0.4-T multiposture MRI, diffusion-weighted images of the lumbar spine in seven healthy volunteers were obtained using single-shot diffusion echo-planar imaging (b = 0 and 600 s/mm2) in quickly changing upright and supine positions. Moreover, spin-echo images with multiple echo times (echo time = 30, 60, 90, and 120 ms) were obtained in each position. We calculated the ADC and T2 of each IVD (L1 and S1) without any disc degeneration. In addition, the lumbar lordosis angle and length of the lumbar spine were measured to evaluate the morphology of the lumbar spine. The T2 of the IVD between L4 and L5 in the upright position was significantly lower than that in the supine position (P < 0.05). No significant differences were observed in the ADC. The morphology of the lumbar spine did not differ significantly between the two positions. The T2 of the IVD between L4 and L5 was likely decreased by the effect of gravity due to the postural change from supine to upright.

Mixed convection analysis in a dual-driven cavity with a stable vertical temperature gradient using the lattice Boltzmann method

The complex dynamics of mixed convection circumstances, concentrating on two examples. In the first case, mixed convection was investigated in a single-sided lid-driven cavity with a top and bottom walls arrangement and the second scenario explores parallel and anti-parallel topologies, focusing on mixed convection in a double-sided lid-driven cavity. The main parameters in this study are the Reynolds, Rayleigh, Prandtl, Grashof, and Richardson numbers. Calculation of numerical solutions to the Navier-Stokes equations over wide ranges in parameters, 0 ? Gr ? 106, 0 ? Re ? 3000, Pr~O(1), and an aspect ratio approximately O(1). The study analyzes these results systematically to understand the relative importance of natural convection and forced convection. As a result of this study, a two-dimensional cavity with specific boundary conditions was created. In a square domain with adiabatic side walls, a top wall is maintained at a higher temperature than the bottom wall. The flow characteristics approach those of a typical driven-cavity of a non-stratified fluid when Gr/Re2 ? 1. There are low fluctuations in temperature and well-mixed fluids throughout the majority of the interior. Much of the inner cavity?s middle and bottom are stationary when Gr/Re2?1. Temperature patterns in these areas are vertically linear and isotherms are nearly horizontal. Lattice Boltzmann method considers the effect of gravity on mixed convection by adjusting the y-velocity using a temperature-dependent forcing factor. The calculation of the Nusselt number at the top wall reveals enhanced heat transfer, with the results suggesting increased intensity when Gr/Re2?1.