arXiv subjects

J. Horn

Publications and source records attributed to J. Horn.

3 recordsLinked to original sources

arXiv2020

Modelling pathogen spread in a healthcare network: indirect patient movements

A hybrid network--deterministic model for simulation of multiresistant pathogen spread in a healthcare system is presented. The model accounts for two paths of pathogen transmission between the healthcare facilities: inter-hospital patient transfers (direct transfers) and readmission of colonized patients (indirect transfers). In the latter case, the patients may be readmitted to the same facility or to a different one. Intra-hospital pathogen transmission is governed by a SIS model expressed by a system of ordinary differential equations. Using a network model created for a Lower Saxony region (Germany), we showed that the proposed model reproduces the basic properties of healthcare-associated pathogen spread. Moreover, it shows the important contribution of the readmission of colonized patients on the prevalence of individual hospitals as well as of overall healthcare system: it can increase the overall prevalence by the factor of 4 as compared to inter-hospital transfers only. The final prevalence in individual healthcare facilities was shown to depend on average length of stay by a non-linear concave function. Finally, we demonstrated that the network parameters of the model may be derived from administrative admission/discharge records. In particular, they are sufficient to obtain inter-hospital transfer probabilities, and to express the patients' transfer as a Markov process.

q-bio.PE↗

arXiv2019

A variational formulation for steady surface water waves on a Beltrami flow

This paper considers steady surface waves `riding' a Beltrami flow (a three-dimensional flow with parallel velocity and vorticity fields). It is demonstrated that the hydrodynamic problem can be formulated as two equations for two scalar functions of the horizontal spatial coordinates, namely the elevation $η$ of the free surface and the potential $Φ$ defining the gradient part (in the sense of the Hodge-Weyl decomposition) of the horizontal component of the tangential fluid velocity there. These equations are written in terms of a nonlocal operator $H(η)$ mapping $Φ$ to the normal fluid velocity at the free surface, and are shown to arise from a variational principle. In the irrotational limit the equations reduce to the Zakharov-Craig-Sulem formulation of the classical three-dimensional steady water-wave problem, while $H(η)$ reduces to the familiar Dirichlet-Neumann operator.

math.AP↗

arXiv2001

H2 and CO emission from disks around TTauri and HerbigAe pre-main-sequence stars and from debris disks around young stars: warm and cold circumstellar gas

We present ISO-SWS observations of H2 pure-rotational line emission from the disks around low and intermediate mass pre-main-sequence stars as well as from young stars thought to be surrounded by debris disks. We detect `warm' (T ~ 100-200 K) H2 gas around many sources, including tentatively the debris-disk objects. The mass of this warm gas ranges from ~1E-4 Solar mass up to 8E-3 Solar mass, and can constitute a non-negligible fraction of the total disk mass. Complementary single-dish 12CO 3-2, 13CO 3-2 and 12CO 6-5 observations have been obtained as well. These transitions probe cooler gas at T ~ 20-80 K. Most objects show a double-peaked CO emission profile characteristic of a disk in Keplerian rotation, consistent with interferometer data on the lower-J lines. The ratios of the 12CO 3-2/ 13CO 3-2 integrated fluxes indicate that 12CO 3-2 is optically thick but that 13CO 3-2 is optically thin or at most moderately thick. The 13CO 3-2 lines have been used to estimate the cold gas mass. If a H2/CO conversion factor of 1E4 is adopted, the derived cold gas masses are factors of 10-200 lower than those deduced from 1.3 millimeter dust emission assuming a gas/dust ratio of 100,in accordance with previous studies. The warm gas is typically 1-10 % of the total mass deduced from millimeter continuum emission, but can increase up to 100% or more for the debris-disk objects. Thus, residual molecular gas may persist into the debris-disk phase. No significant evolution in the H2, CO or dust masses is found for stars with ages in the range of 1E6-1E7 years, although a decrease is found for the older debris-disk star beta Pictoris. Existing models fail to explain the amount of warm gas quantitatively.

astro-ph↗