Integrated Calendar

Driven by recent technological advancements, behavior and brain activity can now be measured at an unprecedented resolution and scale. This “big-data” revolution is akin to a similar revolution in biology. In biology, the wealth of data allowed systems-biologists to uncover the underlying design principles that are shared among biological systems. In my studies, I apply design principles from systems-biology to cognitive phenomena. In my talk I will demonstrate this approach in regard to creative search. Using a novel paradigm, I discovered that people’s search exhibits exploration and exploitation durations that were highly correlated along a line between quick-to-discover/quick-to-drop and slow-to-discover/slow-to-drop strategies. To explain this behavior, I focused on the property of scale invariance, which allows sensory systems to adapt to environmental signals spanning orders of magnitude. For example, bacteria search for nutrients, by responding to relative changes in nutrient concentration rather than absolute levels, via a sensory mechanism termed fold change detection (FCD). Scale invariance is prevalent in cognition, yet the specific mechanisms are mostly unknown. I found that an FCD model best describes creative search dynamics and further predicts robustness to variations in meaning perception, in agreement with behavioral data. These findings suggest FCD as a specific mechanism for scale invariant search, connecting sensory processes of cells and cognitive processes in human. I will end with a broader perspective and outline the benefits of the search for computational design principles of cognition.

Mixing semi-dilute solutions of oppositely charged polyelectrolytes generally yields compositions spanning complexes (solid) to coacervates (elastic liquid) to dissolved solutions with increasing salt concentration. In this work we show how to form a strong network of oppositely charged polyelectrolytes by using an interplay of hydrogen, hydrophobic, and electrostatic interactions.

3D halide perovskites have emerged as a new class of semiconductors, but some basic optoelectronic properties of 3D bulk halide perovskites are still shrouded in mystery. The talk will start from a simplified representation of the halide perovskite lattice allowing to progressively account for various advanced topics.

Halide (hybrid) perovskites (HaP) have emerged as a new class of semiconductors that truly encompass all the desired physical properties for building optoelectronic and quantum devices such as large tunable band-gaps, large absorption coefficients, long diffusion lengths, low effective mass, good mobility and long radiative lifetimes. In addition, HaPs are solution processed or low-temperature vapor grown semiconductors and are made from earth abundant materials thus making them technologically relevant in terms of cost/performance. As a result, proof-of-concept high efficiency optoelectronic devices such as photovoltaics and LEDs have been fabricated. In fact, photovoltaic efficiencies have sky rocketed to 23% merely in the past five years and are nearly on-par with mono-crystalline Si based solar cells. Such unprecedented progress has attracted tremendous interest among researchers to investigate the structure-function relationship and understand as to what makes Halide hybrid perovskites special?
In my talk, I will attempt to answer some of the key questions and in doing so share the results from our work on HaPs over the past four years in understanding structure induced properties of HaPs. I will also highlight fundamental bottlenecks that exist going forward which present opportunities to create platforms to understand the interplay between light, fields and structure on the properties of perovskite-based materials.

Protein design—i.e., the construction of entirely new protein sequences that fold into prescribed structures—has come of age: it is possible now to generate a wide variety stable protein folds from scratch using rational and/or computational approaches. A challenge for the field is to move from what have been largely in vitro exercises to protein design in living cells and, in so doing, to augment biology. This talk will illustrate what is currently possible in this nascent field using de novo -helical coiled-coil peptides as building blocks.1

Coiled coils are bundles of 2 or more  helices that wrap around each other to form rope-like structures. They are one of the dominant structures that direct natural protein-protein interactions. Our understanding of coiled coils provides a strong basis for building new proteins from the bottom up. The first part of this talk will survey this understanding,1 our design methods,2,3 and our current “toolkit” of de novo coiled coils.4-6

Next, I will describe how the toolkit can be used to direct protein-protein interactions and build complex protein assemblies in bacterial cells. First, in collaboration with the Savery lab (Bristol), we have used homo- and hetero-oligomeric coiled coils as modules in engineered and de novo transcriptional activators and repressors.7 Secondly, with the Warren (Kent) and the Verkade (Bristol) labs, we have engineered hybrids of a de novo heterodimer and a natural component of bacterial microcompartments to form a “cytoscaffold” that permeates E. coli cells.8 This can be used to support the co-localisation of functional enzymes.

Due to the immense complexity of the human brain, the study of its development, function, and dysfunction during health and disease has proven to be challenging. The advent of patient-derived human induced pluripotent stem cells, and subsequently their self-organization into three-dimensional (3D) brain organoids, which mimics the complexity of the brain's architecture and function, offers an unprecedented opportunity to model human brain development and disease in new ways. However, there is still a pressing need to develop new technologies that recapitulate the long-term developmental trajectories and the complex in vivo cellular environment of the brain. To address this need, we have developed a human brain organoid-based approach to generate a chimeric human/animal brain system that facilitates long-term ana! tomical integration, differentiation, and vascularization in vivo. We also demonstrated the development of functional neuronal networks within the brain organoid and synaptic-cross interaction between the organoid axonal projections and the host brain. This approach set the stage for investigating human brain development and mental disorders in vivo, and run therapeutic studies under physiological conditions.

The trion, a three-body charge-exciton bound state, offers unique opportunities to simultaneously manipulate charge, spin and excitation in one-dimensional single-walled carbon nanotubes (SWNTs) at room temperature. Effective exploitation of trion quasiparticles requires fundamental insight into their creation and decay dynamics. Such knowledge, however, remains elusive for SWNT trion states, due to the electronic and morphological heterogeneity of commonly interrogated SWNT samples, and the fact that transient spectroscopic signals uniquely associated with the trion state have not been identified. Here length-sorted SWNTs and precisely controlled charge carrier-doping densities are used to determine trion dynamics using femtosecond pump-probe spectroscopy. Identification of the trion transient absorptive hallmark enables us to demonstrate that trions (i) derive from a precursor excitonic state, (ii) are produced via migration of excitons to stationary hole-polaron sites, and (iii) decay in a first-order manner. Importantly, under appropriate carrier-doping densities, exciton-to-trion conversion in SWNTs can approach 100% at ambient temperature. We further show that ultrafast pump-probe spectroscopy, coupled with these fundamental insights into trion formation and decay dynamics, enables a straightforward approach for quantitatively evaluating the extent of optically-driven free carrier generation (FCG) in SWNTs: this work provides fundamental new insights into how quantum yields for optically-driven FCG [Φ(Enn → h+ + e−)] in SWNTs may be modulated as functions of the optical excitation energy and medium dielectric strength. Collectively, these findings open up new possibilities for exploiting trions in SWNT optoelectronics, ranging from photovoltaics, photodetectors, to spintronics.