Abstract from the paper: "SPH simulations of gas flow in barred galaxies. Effect of hydrodynamical and numerical parameters" by Patsis and Athanassoula (2000) (Astron. Astrophys. 358, 45)

We use SPH to calculate the gas response in a potential representing a strongly barred galaxy. We examine the dependence of the morphology and of the inflow rate of this response on hydrodynamical and numerical parameters used in the simulations. In particular we study the effects of the sound speed, the rate of growth of the bar and the number of particles 10⁴ < N < 10⁵ used in our models. We also investigate the appropriate value of the artificial viscosity to be used in the models, delimiting a region of values within which the flow is correctly described. We conclude that models with number of particles have similar overall morphology, although their inflow rates may differ. The existence of straight-line "dust-lane'' shocks is not affected by any of the above mentioned parameters. They do, however, influence the location, the strength, the width and the longevity of these shocks. At sound speed Cs=20 km/s we find the longer lasting (for about 10 rotational periods of the bar) sharply described shocks. The ``x2'' region morphology changes slightly during the evolution of the models. The sound speed influences both this rate of change and the inflow rate of he gas. Finally introducing the bar abruptly from the beginning gives a response morphology which is different from what is obtained if the bar is introduced slowly over two pattern rotations; this also influences the inflow rate.

Abstract from te paper "Interarm features in gaseous models of spiral galaxies" by Patsis et al. (1997, A&A...323..762)

We study the response of gaseous disks, under the influence of spiral perturbations. In particular we compare the morphology of spiral arms and interarm regions in SPH models, with Population I features observed on B images of normal, grand design spiral galaxies. We place the 4/1 resonance at the end of the strong symmetric spiral arms of these galaxies. This basic hypothesis, leads to the appearance of features in the models similar to those observed, while other assumptions for the spiral pattern speed did not show the same good agreement. The "4/1" models, especially when a weak m=1 component is included in the imposed spiral potential, reproduce many morphological aspects of these galaxies. The main result is that the 4/1 resonance generates a clear signature in galaxies, namely a bifurcation of the arms typical for the morphology of normal, late-type, grand design spirals. This bifurcation also gives rise to the main interarm features.

• Patsis, P. A.; Athanassoula, E. SPH simulations of gas flow in barred galaxies. Effect of hydrodynamical and numerical parameters 2000 A&A...358...45
• Patsis, P. A.; Grosbol, P.; Hiotelis, N. Interarm features in gaseous models of spiral galaxies. 1997 A&A...323..762
• Patsis, P. A.; Athanassoula, E. SPH Gas Response to Barred Perturbations
  in The Interplay Between Massive Star Formation, the ISM and Galaxy Evolution. Proceedings of the 11th IAP Astrophysics Meeting, Institut d'Astrophysique, Paris, July 3-8, 1995, Gif-sur-Yvette: Editions Frontieres. Edited by Daniel Kunth, B. Guiderdoni, M. Heydari-Malayeri, and Trinh Xu Thuan, 1996., p.545
• Patsis, P. A. The Relation between existing Resonances and observed Morphology
  in Disk Galaxies 2nd Hellenic astronomical conference : proceedings / Edited by Michael E. Contadakis, John D. Hadjidemetriou, Lyssinmachos N. Mavridis, and John H. Seiradakis. Greece : Hellenic Astronomical Society, c1996., p.346
• Patsis, P. A.; Hiotelis, N.; Contopoulos, G.; Grosbol, P. Hydrodynamic simulations of open normal spiral galaxies: OLR, corotation and 4/1 models, 1994 A&A...286...46
• Patsis, P. A.; Hiotelis, N. Interarm Features in Normal Spiral Galaxies: SPH Models, 1994 MmSAI..65.1055
• Patsis, P. A.; Hiotelis, N. SPH Simulations of the Gas Flow in Normal Spiral Galaxies, 1994 LNP...430..261