The Future Is Colorful—An Analysis of the CO2 Bow Wave and Why Green Hydrogen Cannot Do It Alone

In both the private and public sectors, green hydrogen is treated as a promising alternative to fossil energy commodities. However, building up production capacities involves significant carbon production, especially when considering secondary infrastructure, e.g., renewable power sources. The amount of required capacity as well as the carbon production involved is calculated in this article. Using Germany as an example we show that the switch to purely green hydrogen involves significant bow waves in terms of carbon production as well as financial and resource demand. An economic model for an optimal decision is derived and—based on empirical estimates—calibrated. It shows that, even if green hydrogen is a competitive technology in the future, using alternatives like turquoise hydrogen or carbon capture and storage is necessary to significantly reduce or even avoid the mentioned bow waves.

Jet-driven bow waves as electron accelerators in the magnetosheath: Monte Carlo simulations

<p>Magnetosheath jets are fast flows of plasma frequently observed downstream of the Earth's quasi-parallel shock. Previous observations have shown that these jets can exhibit supermagnetosonic speeds relative to the background flow and develop their own bow waves or shocks. Such jets have been observed to be able to accelerate ions and electrons. In our study, we model electron acceleration by jet-driven bow waves in the magnetosheath using test-particle Monte Carlo simulations that include magnetic mirroring and pitch-angle scattering of magnetic irregularities. We compare the simulation results to spacecraft observations of similar events to understand the acceleration mechanisms at play. Our preliminary results suggest that the energy increase of electrons can be explained by shock drift acceleration at the moving bow wave. Our simulations allow us to estimate the efficiency of acceleration as a function of different jet and magnetosheath parameters. The acceleration introduced by jet-driven bow waves amplifies shock acceleration downstream of the Earth’s bow shock and may also be applicable to other shock environments.</p>

Residual Resistance of Displacement Vessels

The hydrodynamics of the residual resistance of ships is formulated for the first time: the residual resistance of vessel displacement is the result of the formation of retaining bow waves, Kelvin wave systems and their interaction—as well as the action of viscosity, which is expressed in the form of a turbulent subsurface boundary layer. Michell’s integral is taken as a basis for calculations of residual resistance. The two corrections take into account the shear layer of wave surface and the shift of the Kelvin bow system by the retaining waves. The correlation of the calculated and experimental curves confirms the validity of the described hydrodynamics of residual resistance. This article is intended for specialists in the field of hydrodynamics of displacement vessels and for designers of the ship hull.

Bow shocks, bow waves, and dust waves – III. Diagnostics

ABSTRACT Stellar bow shocks, bow waves, and dust waves all result from the action of a star’s wind and radiation pressure on a stream of dusty plasma that flows past it. The dust in these bows emits prominently at mid-infrared wavelengths in the range 8 to 60 $\mu$m. We propose a novel diagnostic method, the τ–η diagram, for analysing these bows, which is based on comparing the fractions of stellar radiative energy and stellar radiative momentum that is trapped by the bow shell. This diagram allows the discrimination of wind-supported bow shocks, radiation-supported bow waves, and dust waves in which grains decouple from the gas. For the wind-supported bow shocks, it allows the stellar wind mass-loss rate to be determined. We critically compare our method with a previous method that has been proposed for determining wind mass-loss rates from bow shock observations. This comparison points to ways in which both methods can be improved and suggests a downward revision by a factor of two with respect to previously reported mass-loss rates. From a sample of 23 mid-infrared bow-shaped sources, we identify at least four strong candidates for radiation-supported bow waves, which need to be confirmed by more detailed studies, but no strong candidates for dust waves.