Showing papers on "Hydrostatic equilibrium published in 2022"

Studying the merging cluster Abell 3266 with eROSITA

Abstract: Abell 3266 is one of the X-ray brightest galaxy clusters in the sky and is a well-known merging system. Using the ability of the eROSITA telescope onboard SRG ( Spectrum Röntgen Gamma ) to observe a wide field with a single pointing, we analysed a new observation of the cluster out to a radius of R 200 . The X-ray images highlight sub-structures present in the cluster, including the north-east-south-west merger seen in previous ASCA, Chandra , and XMM-Newton data, a merging group towards the north-west, and filamentary structures between the core and one or more groups towards the west. We compute spatially resolved spectroscopic maps of the thermodynamic properties of the cluster, including the metallicity. The merging subclusters are seen as low entropy material within the cluster. The filamentary structures could be the rims of a powerful outburst of an active galactic nucleus, or most likely material stripped from the western group(s) as they passed through the cluster core. Seen in two directions is a pressure jump at a radius of 1.1 Mpc, which is consistent with a shock with a Mach number of ~1.5–1.7. The eROSITA data confirm that the cluster is not a simple merging system, but it is made up of several subclusters which are merging or will shortly merge. We computed a hydrostatic mass from the eROSITA data, finding good agreement with a previous XMM-Newton result. With this pointing we detect several extended sources, where we find secure associations between z = 0.36–1.0 for seven of them, that is background galaxy groups and clusters, highlighting the power of eROSITA to find such systems.

Design and characterization of the carbon fiber tube reinforced polymer composite for full ocean depth submersibles

Abstract: The large difference between in-plane and out-of-plane mechanical properties limits the application of traditional composite honeycombs in submersibles. In this work, the carbon fiber tube reinforced polymer composite (CTPC) which have lightweight characteristic and high hydrostatic strength is designed and manufactured. The combination between epoxy resin and carbon fiber tube inhibits the buckling failure and improves the bearing capacity of the tube. Resin binds carbon fiber tubes and forms a stable stress transmission path between them. The hydrostatic response of the CTPC has been investigated by simulation and test. The measured results show good agreement with the simulation. Due to its high hydrostatic bearing capacity and lightweight, the CTPC can be used as a new type of buoyancy material in submersibles.

Dust coagulation during the early stages of star formation: molecular cloud collapse and first hydrostatic core evolution

Abstract: Planet formation in protoplanetary discs requires dust grains to coagulate from the sub-micron sizes that are found in the interstellar medium into much larger objects. For the first time, we study the growth of dust grains during the earliest phases of star formation using three-dimensional hydrodynamical simulations. We begin with a typical interstellar dust grain size distribution and study dust growth during the collapse of a molecular cloud core and the evolution of the first hydrostatic core, prior to the formation of the stellar core. We examine how the dust size distribution evolves both spatially and temporarily. We find that the envelope maintains its initial population of small dust grains with little growth during these phases, except that in the inner few hundreds of au the smallest grains are depleted. However, once the first hydrostatic core forms rapid dust growth to sizes in excess of 100 μm occurs within the core (before stellar core formation). Progressively larger grains are produced at smaller distances from the centre of the core. In rapidly-rotating molecular cloud cores, the ‘first hydrostatic core’ that forms is better described as a pre-stellar disc that may be gravitationally unstable. In such cases, grain growth is more rapid in the spiral density waves leading to the larger grains being preferentially found in the spiral waves even though there is no migration of grains relative to the gas. Thus, the grain size distribution can vary substantially in the first core/pre-stellar disc even at these very early times.

Eccentricity Evolution in Gaseous Dynamical Friction

Abstract: We analyse how drag forces modify the orbits of objects moving through extended gaseous distributions. We consider how hydrodynamic (surface area) drag forces and dynamical friction (gravitational) drag forces drive the evolution of orbital eccentricity. While hydrodynamic drag forces cause eccentric orbits to become more circular, dynamical friction drag can cause orbits to become more eccentric. We develop a semi-analytic model that accurately predicts these changes by comparing the total work and torque applied to the orbit at periapse and apoapse. We use a toy model of a radial power-law density profile, 𝜌 ∝ 𝑟 − 𝛾 , to determine that there is a critical 𝛾 = 3 power index which separates the eccentricity evolution in dynamical friction: orbits become more eccentric for 𝛾 < 3 and circularize for 𝛾 > 3. We apply these findings to the infall of a Jupiter-like planet into the envelope of its host star. The hydrostatic envelopes of stars are defined by steep density gradients near the limb and shallower gradients in the interior. Under the influence of gaseous dynamical friction, an infalling object’s orbit will first decrease in eccentricity, then increase. The critical separation that delineates these regimes is predicted by the local density slope and is linearly dependent on polytropic index. More broadly, our findings indicate that binary systems may routinely emerge from common envelope phases with non-zero eccentricities that were excited by the dynamical friction forces that drove their orbital tightening.

On Stiffness, Strength, Anisotropy, and Buckling of 30 Strut‐Based Lattices with Cubic Crystal Structures

Abstract: Architected cellular structures are increasingly receiving attention in numerous applications due to advances in additive manufacturing and their promising multi-functional properties. Herein, 30 architected strut-based lattices of cubic crystal symmetry are developed and their stiffness and strength are investigated computationally and experimentally. Finite element simulations are conducted to compute the effective stiffness, yield strength, and buckling strength under uniaxial, shear, and hydrostatic loadings. Also, elastic anisotropy is assessed and bifurcation analysis is performed to estimate the threshold relative density for each lattice. Selected lattices of various relative densities are 3D printed from a polymeric material using selective laser sintering (SLS). The numerical results show that the modes of deformation whether stretching-dominated, bending-dominated, or mixed differ for the various loading conditions. It is observed that by combining different lattice structures in a hybrid approach, a decrease in the anisotropic behavior is obtained, and an overall enhancement of the mechanical properties is achieved. The numerical results show rather good agreement with the experimental findings. The current study can be crucial for using the investigated lattices for enhancing the multi-functional properties of structural systems.

Evaporation of dark matter from celestial bodies

Abstract: Abstract Scatterings of galactic dark matter (DM) particles with the constituents of celestial bodies could result in their accumulation within these objects. Nevertheless, the finite temperature of the medium sets a minimum mass, the evaporation mass, that DM particles must have in order to remain trapped. DM particles below this mass are very likely to scatter to speeds higher than the escape velocity, so they would be kicked out of the capturing object and escape. Here, we compute the DM evaporation mass for all spherical celestial bodies in hydrostatic equilibrium, spanning the mass range [10 -10 - 10 2 ] M ⊙ , for constant scattering cross sections and s -wave annihilations. We illustrate the critical importance of the exponential tail of the evaporation rate, which has not always been appreciated in recent literature, and obtain a robust result: for the geometric value of the scattering cross section and for interactions with nucleons, at the local galactic position, the DM evaporation mass for all spherical celestial bodies in hydrostatic equilibrium is approximately given by E c /T χ ∼ 30, where E c is the escape energy of DM particles at the core of the object and T χ is their temperature. In that case, the minimum value of the DM evaporation mass is obtained for super-Jupiters and brown dwarfs, m evap ≃ 0.7 GeV. For other values of the scattering cross section, the DM evaporation mass only varies by a factor smaller than three within the range 10 -41 cm 2 ≤ σ p ≤ 10 -31 cm 2 , where σ p is the spin-independent DM-nucleon scattering cross section. Its dependence on parameters such as the galactic DM density and velocity, or the scattering and annihilation cross sections is only logarithmic, and details on the density and temperature profiles of celestial bodies have also a small impact.

Post-buckling analysis of GPLs reinforced porous cylindrical shells under axial compression and hydrostatic pressure

Abstract: Research works on post-buckling of cylindrical shells under combined loads are usually presented with insufficient accuracy. It is mainly related to the inherent complexity compared to the case subjected to a single load, particularly when the problem is investigated based on the moderately thick shell theory. In the present study, post-buckling analysis of functionally graded graphene platelets reinforced composite (FG-GPLRC) porous cylindrical shells under the action of axial compression and hydrostatic pressure is performed. The main aim is to obtain reasonably accurate post-buckling characteristic quantities of the problem at hand for a wide range of thicknesses. For this purpose, elaborately constructed boundary conditions, complete post-buckling deformation modes, and a unified shell theory, which is efficient and suitable for extremely thin and moderately thick structures, are carefully taken into account. The solutions based on the symmetric and asymmetric post-buckling modes are established by combining an analytical procedure and the Galerkin’s method. The obtained results from the present solutions agree well with those of existing theoretical and experimentally observed data. The effects of the geometry and the material properties on the post-buckling behavior and knockdown factor (KDF) of the FG-GPLRC porous cylindrical shell are explored. The discrepancies between the results of the classical thin-walled shell theory and those of the moderately thick shell theory are then explained and discussed in detail.

Origin of the lateral return error in a five-axis ultraprecision machine tool and its influence on ball-end milling surface roughness

Abstract: Precision ball-end milling is widely used in the manufacture of complex microstructures. The purpose of this paper is to explore the origin of the lateral return error in an ultraprecision five-axis machine tool and its influence on a precision ball-end milling surface. First, the origin of the lateral return error of the linear axis is analyzed. Theoretical analysis and experimental results show that the root of the lateral return error is the gap variation between the slider and the guide, which is decided by the eccentric force moment acting on the hydrostatic guideway. The eccentric force moment relies on the external force and motor eccentricity. In general, the larger the eccentric force moment, the more the gap variation, and resultantly the greater the lateral return error. In addition, the lateral return error is inversely proportional to the oil supply pressure. Because the cutting forces are small enough, the cutting parameters, such as feed speed, cutting depth and cutting stepover, have little effect on the error. Secondly, the lateral return error has an important impact on the yield surface roughness, which will significantly increase the surface roughness and reduce the surface quality. Finally, the lateral return error of the hydrostatic guideway can be suppressed by compensating the machining program. The experimental results show that the surface quality of the compensated surface is significantly improved.

Pressure-induced coupled structural–electronic transition in SnS2 under different hydrostatic environments up to 39.7 GPa

Abstract: A series of in situ high-pressure Raman spectroscopy and electrical conductivity experiments have been performed to investigate the vibrational and electrical transport properties of SnS2 under non-hydrostatic and hydrostatic environments. Upon compression, an coupled structural–electronic transition in SnS2 occurred at 30.2 GPa under non-hydrostatic conditions, which was evidenced by the splitting of the Eg mode and the discontinuities in Raman shifts, Raman full width at half maximum (FWHM) and electrical conductivity. However, the coupled structural–electronic transition took place at a higher pressure of 33.4 GPa under hydrostatic conditions, which may be due to the influence of the pressure medium. Furthermore, our first-principles theoretical calculations results revealed that the bandgap energy of SnS2 decreased slowly with increasing pressure and it closed in the pressure range of 30–40 GPa, which agreed well with our Raman spectroscopy and electrical conductivity results. Upon decompression, the recoverable Raman peaks and electrical conductivity indicated that the coupled structural–electronic transition was reversible, which was further confirmed by our HRTEM observations.

ASUCA: The JMA Operational Non-hydrostatic Model

Abstract: The non-hydrostatic numerical weather prediction (NWP) model ASUCA developed by the Japan Meteorological Agency (JMA) was launched into operation as 2 and 5 km-resolution regional models in 2015 and 2017, respectively. This paper outlines specifications of ASUCA with focus on the dynamical core and its configuration/accuracy as an operational model. ASUCA is designed for high computational stability and efficiency, mass conservation and forecast accuracy. High computational stability is achieved via a time-split integration scheme to compute acoustic terms and an advection scheme with a flux-limiter function to avoid numerical oscillation. In addition, vertical advection and sedimentation are calculated together with another exclusive time-splitting technique. ASUCA adopts hybrid parallelization using Message Passing Interface (MPI) and Open Multi Processing (OpenMP) for high computational efficiency on massive parallel scalar computers. The three-dimensional arrays are allocated such that the vertical direction is the stride-one innermost dimension to make effective use of cache and multi-thread parallelization. This is particularly advantageous for physical processes evaluated in a vertical column. To ensure mass conservation, density rather than pressure is integrated as a prognostic variable in flux-form fully compressible governing equations. ASUCA exhibited better performance than the previous operational model in idealized and NWP tests.

The launching of cosmic ray-driven outflows

Abstract: Cosmic rays (CRs) are thought to be an important feedback mechanism in star-forming galaxies. They can provide an important source of pressure support and possibly drive outflows. We perform multidimensional CR-magnetohydrodynamic simulations including transport by streaming and diffusion to investigate wind launching from an initially hydrostatic atmosphere by CRs. We estimate a characteristic Eddington limit on the CR flux for which the CR force exceeds gravity and compare it to simulated systems. Scaling our results to conditions in star-forming galaxies, we find that CRs are likely to contribute to driving outflows for a broad range of star formation environments. We quantify the momentum and energy transfer between CRs and gas, along with the associated mass outflow rates under different assumptions about the relative importance of streaming and diffusion for transport. In simulations with streaming, we observe the growth and saturation of the CR acoustic instability, but the CRs and gas remain well coupled, with CR momentum transferred efficiently to the gas even when this instability is present. Higher CR fluxes transferr more energy to the gas and drive stronger outflows. When streaming is present, most of the transferred energy takes the form of Alfv\'{e}n wave heating of the gas, raising its pressure and internal energy, with a lower fractional contribution to the kinetic energy of the outflow. We also consider runs with radiative cooling, which modifies gas temperature and pressure profiles but does not seem to have a large impact on the mass outflow for super-Eddington CR fluxes.

A disturbing FABLE of mergers, feedback, turbulence, and mass biases in simulated galaxy clusters

Abstract: The use of galaxy clusters as cosmological probes often relies on understanding the properties and evolution of the intracluster medium (ICM). However, the ICM is a complex plasma, regularly stirred by mergers and feedback, with non-negligible bulk and turbulent motions and a non-thermal pressure component, making it difficult to construct a coherent and comprehensive picture. To this end, we use the FABLE simulations to investigate how the hydrostatic mass bias is affected by mergers, turbulence, and feedback. Following in detail a single, massive cluster we find the bias varies significantly over cosmic time, rarely staying at the average value found at a particular epoch. Variations of the bias at a given radius are contemporaneous with periods where outflows dominate the mass flux, either due to mergers or interestingly, at high redshift, AGN feedback. The $z=0$ ensemble median mass bias in FABLE is $\sim\!13$ per cent at $R_\mathrm{500}$ and $\sim\!15$ per cent at $R_\mathrm{200}$, but with a large scatter in individual values. In halo central regions, we see an increase in temperature and a decrease in non-thermal pressure support with cosmic time as turbulence thermalises, leading to a reduction in the mass bias within $\sim\!0.2 \, R_\mathrm{200}$. When using a fitted pressure profile, instead of the simulation data, to estimate the bias, we find there can be significant differences, particularly at larger radii and higher redshift. We therefore caution over the use of such fits in future work when comparing with the next generation of X-ray and SZ observations.

A 3D printed hydrostatic skeleton for an earthworm-inspired soft burrowing robot.

Abstract: Moving through soil is challenging for robots, particularly for soft robots. Herein, we propose a support structure, based on the hydrostatic skeleton of earthworms, to overcome this problem. To create extremely flexible, thin-walled, worm-sized deformed segments, a specialized 3D printer for low-hardness rubber was utilized. To obtain large radial deformation, we investigated the properties of the soft materials for 3D printing and the geometry of the segments. Notably, segments are deformed with multiply-wound shape memory alloy wires. We constructed an earthworm robot by connecting shape memory alloy-driven segments in series and experimentally demonstrated that this robot could propel in the soil. The proposed robot is unique in that it has a small diameter of 10 mm and exhibits a peristaltic motion in soil.

A robust method for quantification of surface elasticity in soft solids

Abstract: We propose an approach to measure surface elastic constants of soft solids. Generally, this requires one to probe interfacial mechanics at around the elastocapillary length scale, which is typically microscopic. Deformations of microscopic droplets embedded in soft solids are particularly attractive, because they avoid intrinsic nonlinearities associated with previous experiments such as the equilibrium of contact lines and the relaxation of patterned surfaces. We derive analytical solutions for the shape of droplets under uniaxial deformation and for the radius of droplets upon hydrostatic inflation. We couple mechanical deformations to the dissolution of droplets to assess experimental sensitivities. Combined with experimental data from both modes of deformation, one should be able to reliably extract the complete set of isotropic surface material parameters following a specific minimization procedure.