Strain specific motility patterns and surface adhesion of virulent and probiotic Escherichia coli.

Bacterial motility provides the ability for bacterial dissemination and surface exploration, apart from a choice between surface colonisation and further motion. In this study, we characterised the movement trajectories of pathogenic and probiotic Escherichia coli strains (ATCC43890 and M17, respectively) at the landing stage (i.e., leaving the bulk and approaching the surface) and its correlation with adhesion patterns and efficiency. A poorly motile strain JM109 was used as a control. Using specially designed and manufactured microfluidic chambers, we found that the motion behaviour near surfaces drastically varied between the strains, correlating with adhesion patterns. We consider two bacterial strategies for effective surface colonisation: horizontal and vertical, based on the obtained results. The horizontal strategy demonstrated by the M17 strain is characterised by collective directed movements within the horizontal layer during a relatively long period and non-uniform adhesion patterns, suggesting co-dependence of bacteria in the course of adhesion. The vertical strategy demonstrated by the pathogenic ATCC43890 strain implies the individual movement of bacteria mainly in the vertical direction, a faster transition from bulk to near-surface swimming, and independent bacterial behaviour during adhesion, providing a uniform distribution over the surface.

Concentration dependence of droplet deformation in a phase separation process under an electric field.

We show how deformation of droplets, arising in a phase separation process of a two-phase dielectric or conducting liquid composite material under a low frequency electric field, depends on their volume fraction. The electric interactions between distorted particles is taken into account in a self-consistent way based on the effective medium approach. It follows from our model that the main physical mechanism responsible for the dependence of droplets' deformation on the volume fraction is the formation of an effective anisotropic medium. A two-parameter condition of the droplet instability was derived as a function of the dielectric permittivity or conductivity mismatch between the two phases and the volume fraction of the inclusions.

Contribution of photoinduced densification to refractive-index modulation in Bragg gratings written in Ge-doped silica fibers.

We have computed the contribution of UV-light-induced densification to the refractive-index modulation of fiber Bragg gratings. Our results confirm that, for strong gratings written in Ge-doped silica fibers with 248-nm UV light, density changes account for a major part of the photosensitivity effect.

Analysis of photoinduced stress distribution in fiber Bragg gratings.

We discuss the analytical expressions that describe the displacement field resulting from the inscription of a Bragg grating in a Ge-doped optical fiber. The equations stem from a phenomenological approach and allow calculation of the induced stresses. Our model provides an efficient tool to analyze the effects of radiation-induced density variations on the properties of fiber Bragg gratings.

Radiation-induced wave-front aberrations: a new approach.

We present experimental evidence that the action of gamma radiation on an optical system can result in significant wave-front aberrations. To quantify such aberrations with sufficient accuracy for diffraction-limited optical systems, we have used a phenomenological approach based on the concept of dose coefficients. We have measured the dose coefficients for LaK9 and LaK9G15 glasses. Our results confirm this approach and indicate that radiation-induced wave-front aberrations cannot necessarily be neglected for space optical systems that use radiation-hardened glasses.