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Evidence has accumulated that irradiated cells affect their unirradiated neighbors, so that they in turn display cellular responses typically associated with direct radiation exposure. These responses are generally known as bystander effects. In this study, cell cycle-related bystander responses were investigated in three strains of human fibroblasts after exposure to densely ionizing radiation. Varying the linear energy transfer (LET) from 11 to 15,000 keV microm(-1) allowed a study of the impact of the complexity of DNA damage in the inducing cells on the responses of bystander cells. Using both broad-beam and microbeam irradiation, transient bystander responses were obtained for the induction of CDKN1A (p21). The latter was also observed when the transmission of bystander signals was limited to soluble factors. Targeted irradiation of single cells in confluent cell monolayers revealed no correlation between the amount of CDKN1A protein in the bystander cells and the radial distance to the targeted cells. In line with the induction of CDKN1A in bystander cells after irradiation with different LETs, a transient delay in the first G1 phase after irradiation of G0/G1 cells was observed. However, the CDKN1A induction revealed no significant effect on premature terminal differentiation considered to underlie fibrosis in irradiated tissue. Thus the unchanged differentiation pattern in bystander cells does not indicate pronounced, long-lasting effects.

In the present paper we experimentally study the effects of a rotating magnetic field (RMF) on the fluid flow in an electrically conducting melt (Gallium), kept in a cylindrical container heated from below (Rayleigh-Bénard configuration). The experimental data are compared to results obtained from three-dimensional, time-dependent numerical calculations. The paper presents the influence of the magnetic induction B, the frequency of the RMF Ω, and the temperature difference ΔT between the hot bottom and cold top of the melt on heat transport and fluid flow, respectively. The results can be summarized in terms of the parameter Nrot, which is defined as the ratio of magnetic Taylor number (∝B2⋅Ω) to Grashof number (∝ΔT). It is shown that for 0.003<Nrot<0.1 large-scale regular thermal waves exist, which travel azimuthally in the same direction as the rotation direction of the RMF. These thermal waves are connected with large-scale temperature fluctuations (amplitude 6%–10% of ΔT). The amplitude decreases with increasing Nrot, whereas the mean frequency increases from 0.001 Hz up to 0.1 Hz for 0.003<Nrot<0.1. For Nrot>0.1 temperature fluctuations with amplitudes smaller than 1%–2% of ΔT and frequencies greater than 0.1 Hz are observed. These oscillations can be attributed to Taylor vortices generated at the vertical cylinder walls. The regions of the different oscillation modes within the parameter space are shown in a stability diagram.

The existing focusing heavy-ion microprobe at the Gesellschaft für Schwerionenforschung in Darmstadt (Germany) has been modified to enable the targeted irradiation of single, selected cells with a defined number of ions. With this setup, ions in the range from helium to uranium with linear energy transfers (LETs) up to approximately 15,000 keV/microm can be positioned with a precision of a few micrometers in the nuclei of single cells that are growing in culture on a thin polypropylene film. To achieve this accuracy, the microbeam traverses a thin vacuum window with minimal scattering. Electron emission from that window is used for particle detection. The cells are kept in a specially designed dish that is mounted directly behind the vacuum window in a setup allowing the precise movement and the imaging of the sample with microscopic methods. The cells are located by an integrated software program that also controls the rapid deflection and switching of the beam. In this paper, the setup is described in detail together with the first experiments showing its performance. We describe the ability of the microprobe to reliably hit randomly positioned etched nuclear tracks in CR-39 with single ions as well as the ability to visualize the ion hits using immunofluorescence staining for 53BP1 as a marker of DNA damage in the targeted cell nuclei.