arXiv subjects

Martin Siegert

Publications and source records attributed to Martin Siegert.

5 recordsLinked to original sources

arXiv2021

Dynamic flows create potentially habitable conditions in Antarctic subglacial lakes

Trapped beneath the Antarctic ice sheet lie over 400 subglacial lakes, which are considered to be extreme, isolated, yet viable habitats for microbial life. The physical conditions within subglacial lakes are critical to evaluating how and where life may best exist. Here, we propose that Earth's geothermal flux provides efficient stirring of Antarctic subglacial lake water. We demonstrate that most lakes are in a regime of vigorous turbulent vertical convection, enabling suspension of spherical particulates with diameters up to 36 micrometers. Thus, dynamic conditions support efficient mixing of nutrient- and oxygen-enriched meltwater derived from the overlying ice, which is essential for biome support within the water column. We caution that accreted ice analysis cannot always be used as a proxy for water sampling of lakes beneath a thin (<3.166 kilometers) ice cover, because a stable layer isolates the well-mixed bulk water from the ice-water interface where freezing may occur.

physics.flu-dyn↗

arXiv2021

Relativistic effects for the superheavy reaction Og + 2Ts$_2$ -> Og(Ts)$_4$ : Dramatic relativistic effects for the atomization energy of Oganesson tetratennesside Og(Ts)$_4$ and the prediction of the existence of tetrahedral Og(Ts)$_4$

Our all-electron fully relativistic Dirac-Fock (DF) and nonrelativistic (NR) Hartree-Fock (HF) SCF molecular calculations for the superheavy tetrahedral (T$_d$) oganesson tetratennesside OgT$_4$ predict atomization energy (Ae) of 7.45 and -11.21 eV, respectively. Our DF and NR calculations, however for the square planar (D$_{4h}$)OsTs$_4$ predict atomization energy (Ae) o 6.34 and -8.56 ev, respectively. There are dramatic relativistic effects for the atomization energy of T$_d$ and D$_{4h}$ OgT$_4$ of -18.65 eV and 14.90 eV, respectively. Whereas our DF calculations predict the T$_d$OgT$_4$ to be more stable than the D$_{4h}$ OgT$_4$ by ~1.10 eV, our NR calculations predict the D$_{4h}$ OgT$_4$ to be more stable than the T$_d$ OgT$_4$ by ~2.65eV. Our NR calculations predict both the T$_d$ and D$_{4h}$ OgTs$_4$ to be unbound by 11.21 and 8.56 eV, respectively. However our relativistic DF calculations predict both the T$_d$ and D$_{4h}$ OgT$_4$ to be bound by 7.45 and 6.34 eV respectively and so the relativistic treatment is mandatory for bonding and binding in the pentatomic superheavy system with 586 electrons involving the two heaviest SHE Ts and Og.

physics.chem-ph↗

arXiv2021

Dramatic relativistic and magnetic Breit effects for the superheavy reaction Og + 3Ts$_2$ -> OgTs$_6$: Prediction of atomization energy and the existence of the superheavy octahedral Oganesson hexatennesside OgTs$_6$

Our gargantuan ab initio all-electron fully relativistic Dirac-Fock (DF), nonrelativistic (NR) Hartree-Fock(HF) and Dirac-Fock-Breit-Gaunt(DFBG) molecular SCF calculations for the superheavy octahedral Oganesson hexatenniside OgTs$_6$ predict atomization energy (Ae) of 9.47, -5.54and 9.37 eV, at the optimized Os-Ts bond distances of 3.35, 3.34 and 3.36 angstroms, respectively. There are dramatic effects of relativity for the atomization energy of OgTs$_6$ (with seven superheavy elements and 820 electrons) of ~ 15.0 eV each at both the DF and DFBG levels of theory, respectively. Our calculated energy of reaction for the titled superheavy reaction Og + 3Ts$_2$ -> OgTs$_6$ at the DF, NR and DFBG levels of theory is 6.33, 8.81, and 6.26 eV, respectively. Mulliken analysis as implemented in the DIRAC code for our DF and NR calculations (using the dyall.ev4z basis) yields the charges Og(+0.60) and Og(+0.96), respectively on the central Og atom indicating that our relativistic DF calculations predict octahedral OgTs$_6$ to be less ionic. However, due caution must be used to interpret the results of Mulliken's population analysis, which is highly basis set dependent.

physics.chem-ph↗

arXiv1998

Coarsening Dynamics of Crystalline Thin Films

The formation of pyramid-like structures in thin-film growth on substrates with a quadratic symmetry, e.g., {001} surfaces, is shown to exhibit anisotropic scaling as there exist two length scales with different time dependences. Analytical and numerical results indicate that for most realizations coarsening of mounds is described by an exponent n=0.2357. However, depending on material parameters, n may lie between 0 (logarithmic coarsening) and 1/3. In contrast, growth on substrates with triangular symmetries ({111} surfaces) is dominated by a single length scale and an exponent n=1/3.

cond-mat.stat-mech↗

arXiv1997

Contrasts between coarsening and relaxational dynamics of surfaces

We discuss static and dynamic fluctuations of domain walls separating areas of constant but different slopes in steady-state configurations of crystalline surfaces both by an analytic treatment of the appropriate Langevin equation and by numerical simulations. In contrast to other situations that describe the dynamics in Ising-like systems such as models A and B, we find that the dynamic exponent z=2 that governs the domain wall relaxation function is not equal to the inverse of the exponent n=1/4 that describes the coarsening process that leads to the steady state.

cond-mat↗