Thermophysical properties of warm dense hydrogen

We study the thermophysical properties of warm dense hydrogen using quantum molecular dynamics simulations. New results are presented for the pair distribution functions, the equation of state, the Hugoniot curve, and the reflectivity. We compare with available experimental data and predictions of the chemical picture. Especially, we discuss the nonmetal-to-metal transition which occurs at about 40 GPa in the dense fluid

Thermal evolution of Uranus and Neptune I: adiabatic models

The brightness of Neptune is often found to be in accordance with an adiabatic interior, while the low luminosity of Uranus challenges this assumption. Here we apply revised equation of state data of hydrogen, helium, and water and compute the thermal evolution of Uranus and Neptune assuming an adiabatic interior. For this purpose, we have developed a new planetary model and evolution code. We investigate the influence of albedo, solar energy influx, and equations of state of H and He, and water on the cooling time. Our cooling times of about $\tau_\text{U}=5.1\times 10^9\text{ years}$ for Uranus and $\tau_\text{N}=3.7\times 10^9\text{ years}$ for Neptune bracket the known age of the planets of $4.56\times 10^9\text{ years}$ implying that neither planet's present-day luminosity can be explained by adiabatic cooling. We also find that uncertainties on input parameters such as the level of irradiation matter generally more for Uranus than for Neptune. Our results suggest that in contrast to common assumptions, neither planet is fully adiabatic in the deeper interior.Comment: Accepted for publication in A&A. Reproduced with permission from Astronomy & Astrophysics, \copyright ES

PENGARUH BUDAYA BERWIRAUSAHA DAN PENDIDIKAN KEWIRAUSAHAAN TERHADAP NIAT BERWIRAUSAHA MAHASISWA FAKULTAS BISNIS DAN EKONOMIKA UNIVERSITAS SURABAYA

Penelitian ini bertujuan untuk mengetahui pengaruh variabel budaya berwirausaha (perceived appropriateness, perceived consistence, dan perceived effectiveness) serta pendidikan kewirausahaan sebagai variabel independen terhadap niat berwirausaha sebagai variabel dependen pada mahasiswa Fakultas Bisnis dan Ekonomika Universitas Surabaya. Penelitian kuantitatif ini menggunakan desain survei cross-sectional dengan skala Likert pada aras interval. Kuesioner dalam penelitian ini telah teruji validitas dan reliabilitasnya. Uji hipotesis pada penelitian ini dilakukan dengan menggunakan regresi linier berganda. Jumlah responden dalam penelitian ini adalah 238. Hasil temuan penelitian ini menunjukkan bahwa keempat variabel independen berpengaruh signifikan terhadap variabel dependen. Variabel perceived appropriateness, perceived consistence, dan perceived effectiveness, yang ketiganya merupakan aspek dari budaya berwirausaha, berpengaruh positif secara signifikan terhadap variabel niat berwirausaha; sementara variabel pendidikan kewirausahaan pada penelitian ini memberi pengaruh negatif yang signifikan terhadap variabel niat berwirausaha.&nbsp

Quantum molecular dynamics simulations for the nonmetal-to-metal transition in fluid helium

We have performed quantum molecular dynamics simulations for dense helium to study the nonmetal-to-metal transition at high pressures. We present new results for the equation of state and the Hugoniot curve in the warm dense matter region. The optical conductivity is calculated via the Kubo-Greenwood formula from which the dc conductivity is derived. The nonmetal-to-metal transition is identified at about 1 g/ccm. We compare with experimental results as well as with other theoretical approaches, especially with predictions of chemical models.Comment: 4 pages, 5 figure

Material Properties for the Interiors of Massive Giant Planets and Brown Dwarfs

We present thermodynamic material and transport properties for the extreme conditions prevalent in the interiors of massive giant planets and brown dwarfs. They are obtained from extensive \textit{ab initio} simulations of hydrogen-helium mixtures along the isentropes of three representative objects. In particular, we determine the heat capacities, the thermal expansion coefficient, the isothermal compressibility, and the sound velocity. Important transport properties such as the electrical and thermal conductivity, opacity, and shear viscosity are also calculated. Further results for associated quantities including magnetic and thermal diffusivity, kinematic shear viscosity, as well as the static Love number $k_2$ and the equidistance are presented. In comparison to Jupiter-mass planets, the behavior inside massive giant planets and brown dwarfs is stronger dominated by degenerate matter. We discuss the implications on possible dynamics and magnetic fields of those massive objects. The consistent data set compiled here may serve as starting point to obtain material and transport properties for other substellar H-He objects with masses above one Jovian mass and finally may be used as input for dynamo simulations

Electronic transport coefficients from ab initio simulations and application to dense liquid hydrogen

Using Kubo's linear response theory, we derive expressions for the frequency-dependent electrical conductivity (Kubo-Greenwood formula), thermopower, and thermal conductivity in a strongly correlated electron system. These are evaluated within ab initio molecular dynamics simulations in order to study the thermoelectric transport coefficients in dense liquid hydrogen, especially near the nonmetal-to-metal transition region. We also observe significant deviations from the widely used Wiedemann-Franz law which is strictly valid only for degenerate systems and give an estimate for its valid scope of application towards lower densities

Ab initio equations of state for hydrogen (H-REOS.3) and helium (He-REOS.3) and their implications for the interior of Brown Dwarfs

We present new equations of state (EOS) for hydrogen and helium covering a wide range of temperatures from 60 K to 10$^7$ K and densities from $10^{-10}$ g/cm$^3$ to $10^3$ g/cm$^3$. They include an extended set of ab initio EOS data for the strongly correlated quantum regime with an accurate connection to data derived from other approaches for the neighboring regions. We compare linear-mixing isotherms based on our EOS tables with available real-mixture data. A first important astrophysical application of this new EOS data is the calculation of interior models for Jupiter and the comparison with recent results. Secondly, mass-radius relations are calculated for Brown Dwarfs which we compare with predictions derived from the widely used EOS of Saumon, Chabrier and van Horn. Furthermore, we calculate interior models for typical Brown Dwarfs with different masses, namely Corot-3b, Gliese-229b and Corot-15b, and the Giant Planet KOI-889b. The predictions for the central pressures and densities differ by up to 10$\%$ dependent on the EOS used. Our EOS tables are made available in the supplemental material of this paper.Comment: 14 pages, 19 Figures, accepted at ApJ

Günter Kelbg, the Kelbg potential and its impact on quantum plasma theory

Günter Kelbg did remarkable early work in the field of quantum statistical physics, in particular for dense quantum plasmas. In 2022 we celebrated his 100th birthday. On this occasion, we give a brief overview of his main scientific achievements in the field of quantum plasmas, complemented by some biographical background of his research and teaching environment at Rostock University. Kelbg's main achievement is the derivation of a regularized quantum pair potential. We demonstrate that it is still of high relevance for molecular dynamics and quantum Monte Carlo simulations of dense plasmas.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe