Integrated Calendar

Direction selective retinal ganglion cells encode motion in the visual field. They respond strongly to an object moving in one direction, called the preferred direction, and weakly to an object moving in the opposite direction. This response is thought to arise by asymmetric wiring of inhibitory neurons onto the direction selective cells. I will demonstrate that adaptation with short visual stimulation of a direction selective ganglion cell using drifting gratings can reverse this cell’s directional preference by 180 degrees. This reversal is robust, long-lasting, and independent of the animal’s age. My findings indicate that, even within circuits that are hardwired, the computation of direction can be altered by dynamic circuit mechanisms that are guided by visual stimulation.

The diffraction limit, mathematically formulated by Ernst Abbe nearly 150 years ago, has shaped optical microscopy for over a century. In the last 20 years various methods have been used to break the diffraction limit in fluorescence microscopy, all relying on intricate properties of the (organic) fluorophores used, and where resolution is strongly linked with fluorophore stability. Inorganic fluorophores, such as colloidal semiconductor quantum dots, which exhibit superior stability thus
potentially offer dramatic improvements in resolution, but their photophysical properties are incompatible with current sub diffraction limited imaging techniques. Recently developed chemical synthesis methods now enable intricate band-gap engineering of semiconductor nanocrystal heterostructures, opening pathways towards adaptation of these inorganic fluorophores for such advanced imaging applications. Our recent work on systems such as colloidal double quantum dots exhibiting unique optical phenomena including two-color antibunching and incoherent luminescence upconversion will be discussed, along with a new quantum-optics based scheme for breaking the classical diffraction barrier.

Understanding the dynamics of a complex fluid on a macro scale requires thorough understanding of the dynamics of its constituents on a micro scale. The latter consists of studying the individual dynamics of a single soft micro-object in an external flow and its back-reaction on the flow field, as well as interactions with other micro-objects in the flow.
Using a novel experimental method we were able to conduct long time observation of one or more vesicles subject to an external linear flow field. This allowed us to investigate the role of thermal noise in vesicle dynamics and to confront the experimental results with theoretical/numerical predictions regarding a vesicle dynamical state called trembling. We have shown that the thermal noise is significantly amplified due to coupling with the complex dynamics of the vesicle in trembling state, and causes excitation of higher order odd modes and concavities in the vesicle shape, similar to those, observed in wrinkling type instability. Our main conclusion was that the existing theoretical/numerical models without thermal noise are inappropriate for the description of the trembling state as it is observed in the experiments.