arXiv subjects

Julian Hofmann

Publications and source records attributed to Julian Hofmann.

4 recordsLinked to original sources

arXiv2020

Leidenfrost temperature in sprays: role of the substrate and liquid properties

In this study the Leidenfrost temperature during spray cooling of very hot substrates is experimentally measured. The spray parameters, i.e. the drop diameters and velocities and the mass flux, are very accurately measured. Astonishingly, the measured Leidenfrost temperature is independent of any of the spray impact parameters, but is determined exclusively by the materials of the liquid and the substrate. The mechanism of film boiling is explained by the formation of a fast propagating vaporizing front, when the inertial forces in the associated liquid flow are comparable with the viscous stresses. This leads to a theoretical prediction for the Leidenfrost temperature which agrees well with the experimental data.

physics.flu-dyn↗

arXiv2019

Characteristics-based Simulink implementation of first-order quasilinear partial differential equations

The paper deals with solving first-order quasilinear partial differential equations in an online simulation environment, such as Simulink, utilizing the well-known and well-recommended method of characteristics. Compared to the commonly applied space discretization methods on static grids, the characteristics-based approach provides better numerical stability. Simulink subsystem implementing the method of characteristics is developed. It employs Simulink's built-in solver and its zero-crossing detection algorithm to perform simultaneous integration of a pool of characteristics as well as to create new characteristics dynamically and discard the old ones. Numerical accuracy of the solution thus obtained is established. The subsystem has been tested on a full-state feedback example and produced better results than the space discretization-based "method of lines". The implementation is available for download and can be used in a wide range of models.

cs.MS↗

arXiv2010

Highly-efficient state-selective sub-microsecond photoionization detection of single atoms

We experimentally demonstrate a detection scheme suitable for state analysis of single optically trapped atoms in less than 1 μs with an overall detection efficiency η exceeding 98%. The method is based on hyperfine-state-selective photoionization and subsequent registration of the correlated photoion-electron pairs by coincidence counting via two opposing channel electron multipliers. The scheme enables the calibration of absolute detection efficiencies and might be a key ingredient for future quantum information applications or precision spectroscopy of ultracold atoms.

quant-ph↗

arXiv2005

Coupled-channel study of baryon resonances with charm

Identifying a zero-range exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a rich spectrum of molecules is formed. We argue that chiral symmetry and large-$N_c$ considerations determine that part of the interaction which generates the spectrum. A bound state with exotic quantum numbers is predicted at mass 2.78 GeV. It couples strongly to the $(\bar D_s N),(\bar D Λ),(\bar D Σ)$ channels. A further charm minus-one system is predicted at mass 2.84 GeV as a result of $(\bar D_s Λ), (\bar D Ξ)$ interactions. The two so far observed s-wave baryons with charm one are recovered. We argue that the $Λ_c(2880)$ is not a s-wave state. In addition to those states we predict the existence of about ten narrow s-wave baryon states with masses below 3 GeV. A triplet of crypto-exotic states decaying dominantly into channels with an $η'$ is obtained with masses 4.24 GeV and 4.44 GeV.

nucl-th↗