לוח שנה משולב

We constrain the dominant optical selection e ffects biasing the Gamma-Ray Burst
(GRB) redshift distribution using Swift triggered redshifts acquired from the optical
afterglow. Models for the Malmquist, redshift desert, and dust extinction biases
are used to show how the "true" GRB redshift distribution is distorted to its presently
observed biased distribution. The statistically optimal model shows
that GRB host galaxy dust extinction could account for up to 17% of missing redshifts.
The model also requires an increasing mean optical afterglow luminosity with redshift. This could be explained by a decrease
in dust obscuration in GRB hosts at high-z. Alternatively, the optimal model can also
be obtained without optical afterglow brightness evolution, but requires a source rate
evolution four times higher than the star formation rate at z = 10 compared to z = 0.

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.