Active Ornstein-Uhlenbeck model for self-propelled particles with inertia.

Self-propelled particles, which convert energy into mechanical motion, exhibit inertia if they have a macroscopic size or move inside a gaseous medium, in contrast to micron-sized overdamped particles immersed in a viscous fluid. Here we study an extension of the active Ornstein-Uhlenbeck model, in which self-propulsion is described by colored noise, to access these inertial effects. We summarize and discuss analytical solutions of the particle's mean-squared displacement and velocity autocorrelation function for several settings ranging from a free particle to various external influences, like a linear or harmonic potential and coupling to another particle via a harmonic spring. Taking into account the particular role of the initial particle velocity in a nonstationary setup, we observe all dynamical exponents between zero and four. After the typical inertial time, determined by the particle's mass, the results inherently revert to the behavior of an overdamped particle with the exception of the harmonically confined systems, in which the overall displacement is enhanced by inertia. We further consider an underdamped model for an active particle with a time-dependent mass, which critically affects the displacement in the intermediate time-regime. Most strikingly, for a sufficiently large rate of mass accumulation, the particle's motion is completely governed by inertial effects as it remains superdiffusive for all times.

Increased level of immunogold labeling of epoxy sections by rising the temperature significantly beyond 100 degrees C in the antigen retrieval medium.

The purpose of this study was to compare the level of immunogold labeling of epoxy sections when the sections were subjected to antigen retrieval at different temperatures. Renal swine tissue with glomerular immune complex deposits with reactivity against IgG and C3 was embedded in epoxy resin. Sections from these blocks were exposed to antigen retrieval by heating in citrate solution at temperatures in the range of 25-135 degrees C. Immunogold labeling with anti-IgG and anti-C3 was performed on the heated sections. The level of immunogold labeling increased significantly in the direction of increased heat. Interestingly, the level of immunogold labeling was significantly higher when exposed to heating in the autoclave (121 and 135 degrees C) than at temperatures just below the normal boiling point. Sections stained with anti-C3 turned from almost negative labeling when heated at 95 degrees C to strong positive labeling when heated at 135 degrees C (11 times increased). The intensity of the immunogold labeling with anti-IgG increased almost three times when raising the temperature in the retrieval medium from 95 to 135 degrees C. The practical significance of these results is that antigen retrieval of epoxy sections should be performed by heating in aqueous solutions at 135 degrees C or higher to obtain maximum immunolabeling.