Integrated Calendar

Genetically identical microbial cells often display diverse phenotypes. Stochasticity at the single-cell level contributes significantly to this phenotypic variability, and cells utilize a variety of mechanisms to regulate noise. In turn, these control mechanisms lead to correlations in various cellular traits across the lineage tree. I will present recent models we developed for understanding cellular homeostasis, with special focus on protein levels and cell size. These models allow us to characterize single-cell variability, including the emerging correlations and distributions. I will discuss the implications of stochasticity on the population growth. In contrast to the dogma, we find that variability may be detrimental to the population growth, suggesting that evolution would tend to suppress it.

Halide Perovskites (HaPs) have remarkable electronic and optical characteristics, but much is still unknown regarding the connection between their physical and chemical properties. Cation or anion substitution can change the optical absorption edge, with or without change of structure. In this work I explored the halide exchange reaction in methylammonium lead tri-halides single crystals (SCs) in order to understand the process of exchange and the stability of the product(s). I demonstrate halide exchange in mm-sized SCs, achieved by diffusion. Using the Boltzmann-Matano method and diffusion profiles obtained by electron dispersive spectroscopy it is possible to evaluate the halide diffusion coefficients, which are not constant and depend on the mixture of halides. For all permutations, the change in composition as result of the diffusion, strongly affects the optical and electrical properties and especially the band gap of the semiconducting crystals, as seen in cathodoluminescence measurements in the scanning electron microscope. While these gradients cause a lattice parameter change and may cause a symmetry change, X-ray diffraction measurements show that if the interchanged halide pair is such that their sizes are relatively similar (e.g., and , and but not and ) the resulting material remains surprisingly single crystalline. These findings are valid, no matter which one of the two halides is being exchanged. These results suggest that for these similar-sized halide pairs, this exchange occurs through a solid-state chemical reaction such that the resulting crystal orientation is determined by that of the initial crystal.

Emerging and re-emerging virus infections pose a threat to global health. Viruses mutate to inevitably evade the effects of pathogen-specific antivirals, and the time required to develop a vaccine specific for an outbreak virus leaves populations unprotected for months. Our strategy is to focus on broad spectrum antivirals for diverse acute virus infections: interferons (IFNs)-. IFNs- exert both direct antiviral effects in infected cells and modulate host immune responses to clear virus. Data will be presented providing evidence for the antiviral effects of IFNs-against influenza A viruses H5N1 and pandemic H1N1, the SARS coronavirus and ebola virus, in vitro and in clinical studies during outbreaks. The mechanisms whereby IFNs-exert their antiviral effects and override the inhibitory effects of viruses will be described.

According to the synaptic trace theory of memory, activity-induced changes in the pattern of synaptic connections underlie the storage of information for long periods. In this framework, the stability of memory critically depends on the stability of the underlying synaptic connections. Surprisingly however, the excitatory synaptic connections, which constitute most of the synapses in the cortex, are highly volatile in the living brain, which poses a fundamental challenge to the synaptic trace theory. We show that in the balanced cortex, patterns of neural activity are primarily determined by the inhibitory connectivity, despite the fact that most synapses and neurons are excitatory. Similarly, we show that the inhibitory network is more effective in storing memory patterns than the excitatory one. As a result, network activity is robust to ongoing volatility of excitatory synapses, as long as this volatility does not disrupt the balance between excitation and inhibition. We thus hypothesize that inhibitory connectivity, rather than excitatory, controls the maintenance and loss of information over long periods of time in the volatile cortex.