Ultrasound elasticity of diamond at gigapascal pressures

Diamond is the hardest known material in nature and features a wide spectrum of industrial and scientific applications. The key to diamond's outstanding properties is its elasticity, which is associated with its exceptional hardness, shear strength, and incompressibility. Despite many theoretical works, direct measurements of elastic properties are limited to only ∼1.4 kilobar (kb) pressure. Here, we report ultrasonic interferometry measurements of elasticity of void-free diamond powder in a multianvil press from 1 atmosphere up to 12.1 gigapascal (GPa). We obtained high-accuracy bulk modulus of diamond as K0 = 439.2(9) GPa, K0′ = 3.6(1), and shear modulus as G0 = 533(3) GPa, G0′ = 2.3(3), which are consistent with our first-principles simulation. In contrast to the previous experiment of isothermal equation of state, the K0′ obtained in this work is evidently greater, indicating that the diamond is not fully described by the “n-m” Mie–Grüneisen model. The structural and elastic properties measured in this work may provide a robust primary pressure scale in extensive pressure ranges.

Larson–Penston Self-similar Gravitational Collapse

Using numerical integration, in 1969 Penston (Mon Not R Astr Soc 144:425–448, 1969) and Larson (Mon Not R Astr Soc 145:271–295, 1969) independently discovered a self-similar solution describing the collapse of a self-gravitating asymptotically flat fluid with the isothermal equation of state $$p=k\varrho $$ p = k ϱ , $$k>0$$ k > 0 , and subject to Newtonian gravity. We rigorously prove the existence of such a Larson–Penston solution.

Thermodynamic processes in dusty plasma

Here, we propose a thermodynamic model for dusty plasma, where the dust is confined in a small volume within a large plasma background by external fields. In this model, the parameters of dust, e.g. Helmholtz energy, pressure, entropy and enthalpy, etc. can be calculated for given dust density and temperature. The model is solved analytically in the mean field (gaseous) limit and various processes associated with the gaseous phase of dust, e.g. adiabatic/isothermal/constant internal energy expansion/compression, specific heat, free expansion within the plasma background, and the dispersion of novel acoustic waves are studied. Some predictions of the model, e.g. electrostatic pressure of the dust and the isothermal equation of state, have been earlier verified in experiments and numerical simulations. The model is compared with an earlier thermodynamic model of dusty plasma proposed by Hamaguchi and Farouki.

Importance of radiative effects in gap opening by planets in protoplanetary disks

Recent ALMA observations revealed concentric annular structures in several young class-II objects. In an attempt to produce the rings and gaps in some of these systems, they have been modeled numerically with a single embedded planet assuming a locally isothermal equation of state. This is often justified by observations targeting the irradiation-dominated outer regions of disks (approximately 100 au). We test this assumption by conducting hydrodynamics simulations of embedded planets in thin locally isothermal and radiative disks that mimic the systems HD 163296 and AS 209 in order to examine the effect of including the energy equation in a seemingly locally isothermal environment as far as planet–disk interaction is concerned. We find that modeling such disks with an ideal equation of state makes a difference in terms of the number of produced rings and the spiral arm contrast in the disk. Locally isothermal disks produce sharper annular or azimuthal features and overestimate a single planet’s gap-opening capabilities by producing multiple gaps. In contrast, planets in radiative disks carve a single gap for typical disk parameters. Consequently, for accurate modeling of planets with semimajor axes up to about 100 au, radiative effects should be taken into account even in seemingly locally isothermal disks. In addition, for the case of AS 209, we find that the primary gap is significantly different between locally isothermal and radiative models. Our results suggest that multiple planets are required to explain the ring-rich structures in such systems.

Quasi-hydrostatic equation of state of silicon up to 1 megabar at ambient temperature

The isothermal equation of state of silicon has been determined by synchrotron x-ray diffraction experiments up to 105.2 GPa at room temperature using diamond anvil cells. A He-pressure medium was used to minimize the effect of uniaxial stress on the sample volume and ruby, gold and tungsten pressure gauges were used. Seven different phases of silicon have been observed along the experimental conditions covered in the present study.

Adsorption Capacity and Selectivity of Molecularly Imprinted Polymers towards β-Sitosterol

Molecularly imprinted polymers (MIP) as an adsorbent has been synthesized using β-sitosterol as molecule template on free radical polymerization reaction. The capacity and selectivity of the adsorption from MIP to β-sitosterol was studied in this study. The β-sitosterol concentration in the adsorption-desorption test and the MIP selectivity test were analyzed by UV-visible and HPLC. The MIP obtained from the synthesis results in a high adsorption capacity. Based on the Freundlich adsorption isothermal equation, the adsorption capacity (k) was found to be 1.24 mg/g. The MIP can adsorb 100 % β-sitosterol while cholesterol was only 3 %. The MIP is most selective to β-sitosterol, therefore, has high potential to apply as adsorbent at solid phase extraction method to isolate β-sitosterol from sample extract.

Magnetohydrodynamics in a cylindrical shearing box

ABSTRACT We develop a framework for magnetohydrodynamical (MHD) simulations in a local cylindrical shearing box by extending the formulation of the Cartesian shearing box. We construct shearing-periodic conditions at the radial boundaries of a simulation box from the conservation relations of the basic MHD equations, taking into account the explicit radial dependence of physical quantities. We demonstrate quasi-steady mass accretion, which cannot be handled by the standard Cartesian shearing box model, with an ideal MHD simulation in a vertically unstratified cylindrical shearing box for up to 200 rotations. In this demonstrative run we set up (i) net vertical magnetic flux, (ii) a locally isothermal equation of state, and (iii) a sub-Keplerian equilibrium rotation, whereas the sound velocity and the initial Alfvén velocity have the same radial dependence as that of the Keplerian velocity. Inward mass accretion is induced to balance the outward angular momentum flux of the MHD turbulence triggered by the magnetorotational instability in a self-consistent manner. We discuss detailed physical properties of the saturated magnetic field, in comparison to the results of a Cartesian shearing box simulation.

The possible hierarchical scales of observed clumps in high-redshift disc galaxies

ABSTRACTGiant clumps on ∼kpc scales and with masses of $10^8\rm {-}10^9 \, \mathrm{M_{\odot }}$ are ubiquitous in observed high-redshift disc galaxies. Recent simulations and observations with high spatial resolution indicate the existence of substructure within these clumps. We perform high-resolution simulations of a massive galaxy to study the substructure formation within the framework of gravitational disc instability. We focus on an isolated and pure gas disc with an isothermal equation of state with T = 104 K that allows capturing the effects of self-gravity and hydrodynamics robustly. The main mass of the galaxy resides in rotationally supported clumps which grow by merging to a maximum clump mass of $10^8 \, \mathrm{M_{\odot }}$ with diameter ∼120 pc for the dense gas. They group to clump clusters (CCs) within relatively short times ($\ll 50 \, \mathrm{Myr}$), which are present over the whole simulation time. We identify several mass and size scales on which the clusters appear as single objects at the corresponding observational resolution between ${\sim } 10^8 \,\rm{and}\, 10^9 \, \mathrm{M_{\odot }}$. Most of the clusters emerge as dense groups and for larger beams they are more likely to be open structures represented by a single object. In the high-resolution runs higher densities can be reached, and the initial structures can collapse further and fragment to many clumps smaller than the initial Toomre length. In our low-resolution runs, the clumps directly form on larger scales 0.3–1 kpc with $10^8\rm {-}10^9 \, \mathrm{M_{\odot }}$. Here, the artificial pressure floor which is typically used to prevent spurious fragmentation strongly influences the initial formation of clumps and their properties at very low densities.